Biochemistry and cell biology Research Papers

GAZİ ÜNİVERSİTESİ, EĞİTİM FAKÜLTESİ ÖĞRENCİLERİNİN ÜNİVERSİTE YAŞAMINA UYUM DURUMLARI

2005, Gazi Üniversitesi Kastamonu …

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Python: a programming language for software integration and development

1999, J Mol Graph Model

Over the last decade we have witnessed the emergence of technologies such as libraries, Object Orientation, software architecture and visual programming. The common goal of these technologies is to achieve software reuse. Even though,... more

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LAPORAN PRAKTIKUM BIOLOGI

by Q. D.

2015

Sebuah buku laporan hasil praktikum mata kuliah Biologi

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Effects of creatine supplementation on the performance and body composition of competitive swimmers

by Renata Mendes

2004, Journal of Nutritional Biochemistry

The objective of this study was to determine the effect of creatine supplementation on performance and body composition of swimmers. Eighteen swimmers were evaluated in terms of post-performance lactate accumulation, body composition,... more

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Standard methods for the examination of water and wastewater

by Chalbi Marie Fernandez

1912

Y ellowstone National Park Water Quality Monitoring Greater Y ellowstone Inventory and Monitoring Network

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Green Energy and Technology

by Dimitrios Vlachos and

The integration of Renewable Energy Sources (RES) within the contextual framework of existing thermal energy production systems has emerged as a promising and sustainable policy towards addressing the growing global energy demand.... more

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Quantification of histochemical staining by color deconvolution

by Arnout Ruifrok

2001, Analytical and quantitative cytology and histology / the International Academy of Cytology [and] American Society of Cytology

To develop a flexible method of separation and quantification of immunohistochemical staining by means of color image analysis. An algorithm was developed to deconvolve the color information acquired with red-green-blue (RGB) cameras and... more

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Thermodynamics of Fuel Cells

by William Rivera

2011, Green Energy and Technology

The basic element of a photovoltaic system (PV) is solar cells which convert the sunlight energy directly to direct current. A typical solar cell consists of a PN junction formed in a semi-conductor material similar to a diode. Semi-conductor material most widely used in solar cells is silicon. Each material gives different efficiency and has different cost. There are several types of solar material cells:

Fig. 1.4 Market share of crystalline silicon 4. Dye-sensitized solar cell (DSC) is formed by a photo-sensitized anode and an electrolyte. Its efficiency is around 11.1%.

Fig. 1.2, Monocrystalline silicon cell [2]

Fig. 1.7 Efficiency of different material cells in laboratory [2]

The MPP is reached when The left member of Eq. 1.7 is the incremental internal resistance of the PV generator (the minus sign is due to the choice for that device of the generator reference directions). The right member is the apparent resistance of the load. Thus, one can consider Eq. 1.7 as the equation defining the resistance adaptation of the load the internal resistance of the PV generator.

Fig. 1.10 Current versus voltage Ipv—Vpv characteristic for a solar cell

Fig. 1.12 Temperature effect on electrical characteristic [31] Fig. 1.11 Irradiance effect on electrical characteristic

Fig. 1.14 Stand-alone PV system with battery storage powering DC and AC loads Figure 1.14 shows a diagram of a typical stand-alone PV system powering DC and AC loads [7].

Thus, if the conductor is perfect, we have:

1.4.1 Estimating the Size of a Photovoltaic System

1.5 Maintenance of Photovoltaic Systems Fig. 1.19 Flowchart of estimating the size of a PV [11] We have to calculate the sunshine available for the panels on an average day during the worst month of the year. It is called the insolation value.

LS eS OS eee Ole ee lee eee Figure 2.7 shows the corresponding radiance as a function of the zenith angle. We can see that this second order approximation is not realistic since it leads to 1egative values of the radiance. In fact, the function /,(t’,) thus obtained is a smooth function unable to correctly describe the directional properties of radiance near the ground level, because at that boundary the sky and soil radiances do not 1ave the same form. 2.1.3.8 Enhanced Approximation for Hemispherical Radiance

In literature, there are several mathematical models that describe the operation and behavior of the photovoltaic generator. For example, Borowy and Salameh [29] have given a simplified model, with which the maximum power output can be calculated for a module once photovoltaic solar irradiance on the photovoltaic module and the temperature is found, and Jones and Underwood [30] also intro- duced a simplified model of the maximum power output which has a reciprocal relationship with the temperature module and logarithmic relationship with the solar radiation absorbed by the photovoltaic module. In addition, Jones and Underwood have given the thermal model of the temperature module photovoltaic through the evaluation of many factors. These models differ in the calculation procedure, accuracy and the number of parameters involved in the calculation of the current-voltage characteristic.

We have with [,, (A) is the photocurrent that is equal to short-circuit current, Ig (A) is the reverse saturation current of the diode, q is the electron charge (1.602 x 10-'° ©), K Botzman’s constant (1.381 x 10~*° J/K), A is diode ideality factor, Tj is junction temperature of the panels (°K), /g is the current shunted through the intrinsic diode, V,, is the voltage across the PV cell. The simplified equivalent circuit of a solar cell consists of a diode and a current source connected in parallel (Fig. 2.9). The current source produces the photo- current Ipn, which is directly proportional to solar irradiance G. The two key parameters often used to characterize a PV cell are its short-circuit current and its open-circuit voltage which are provided by the manufacturer’s data sheet. The equation of the current voltage J,,-V,, simplified equivalent circuit is derived from Kirchhoff’s law. MUKTW Le...

We can determine the reverse saturation current Jp by setting J,,=0 (case when 0 output current).

Thus we obtain, taking into account the fact that, with this model, the photo- current is equal to the short-circuit current:

Fig. 2.13 Bloc diagram of model with ohmic losses

Fig. 2.14 PV subsystem bloc diagram of model with ohmic losses [195] Fig. 2.15 Simplified equivalent circuit of solar cell

The first model studied in this section is defined, as one of these Sects. 2.2.1 and 2.2.2, by an equivalent circuit. This one consists of a single diode for the phe- nomena of cell polarization and two resistors (series and shunt) for the losses (Fig. 2.15). It can thus be named “one diode model”. This model is used by manufacturers by giving the technical characteristics of their solar cells (data sheets).

We can then find the cell parameters at the operating temperature of cells and solar irradiance from: The other parameters are calculated by the following equations:

Fig. 2.16 Flowchart of resolution with parameters P;

Fig. 2.20 Characteristics [py = f (Vpy) and Ppy = f (Vpy) in STC conditions

Fig. 2.21 Effects of solar irradiance changing

Fig. 2.22 Effects of temperature changing

Fig. 2.26 PV subsystem (Model No. 2) [195]

Fig. 2.25 Bloc diagram of Model No. 2 [195] The simple relationship of power for a photovoltaic module is

Fig. 2.27 Characteristics J,, = f(Vpy) and Pp, = f(Vpy) under the STC conditions (Model No. 2)

Fig. 2.29 Effect of temperature changing (model No. 2)

Fig. 2.31 Bloc diagram of Model No. 3 [195]

Fig. 2.33 Effects of solar irradiance changing (Model No. 3) [195

Fig. 2.35 Characteristics [,, = f (Vpy) and Ppy = f (Vpy) (Model No. 3) [195]

Fig. 2.34 Effects of temperature changing (Model No. 3) [195]

The expression of Vince, can have the following form:

Fig. 2.37 Block diagram of two diode model [195]

Fig. 2.38 Characteristics [,, = f (Vpy) and Ppy = f (Vpy) simulation results (two diode model) [195]

Fig. 2.40 Variations of power for different days of the year (Model No. 1) [9]

2.2.4 General Remarks on PV Arrays Models That additional equation allows determining one more parameter using the nom- inal values of a photovoltaic cell or module.

connected to the AC mains). According to the power rating of a converter, the switching frequency may range from several kHz for high to medium power converters to more than 1 MHz for very low power converters. The use of a high switching frequency makes easier the filtering of the current and voltage ripples generated at the switching frequency at the input and output of the converter. Moreover, as the energy which has to be stored inside the passive components is lower when the internal frequency is high, the frequency increase allows reducing the size and the cost of the passive components. Unfortunately, an increase of the switching frequency increases the commu- tation losses, so the choice of this frequency results from a compromise which is mainly ruled by the switching speed of the semiconductors. As the commutation losses are lower when the components can commute faster, the optimal switching frequencies grow more and more as the semiconductor performances are imnronved

input and output current and voltage, the sizing is governed by the product of the bigger voltage by the bigger current. A big value of the ratio k leads to oversized converter, and then lower efficiency. For that reason, the output voltage is not too large and one can admit that, occasionally, the optimum PV voltage becomes higher than the output voltage. When that case occurs, the converter reduces to direct connection (Fig. 3.4) but it remains possible to short-circuit the PV if necessary by keeping the transistor “on”. The fact that the inductor is in series with input is interesting because it

3.2.2.3 Example of Application of DC-DC Converter with Photovoltaic: a Battery Charger It is the simplest system where only one converter exists that loads the battery. Then the battery is directly connected to the load (Fig. 3.10).

battery bank. We consider as example the circuit of Fig. 3.6 (buck converter). To model the battery charger, we use the equivalent circuit of Fig. 3.11. As long as the battery is not fully charged, the control circuit act on the switches of DC/DC converter in order to maximize the battery current. However, it can estimate the charge of the battery using measurements of battery voltage, current and often temperature and current integral. It can thus limit the battery current if its value is too large considering the battery state of charge. Often, the control circuit can also acts on a relay in order to disconnect the load when the battery is too discharged. In theory, a model of the battery is needed in order to estimate the battery state of charge. Several control circuits include a fuzzy logic controlle1 which can determinate implicitly such a model after some cycles of charge.

commercially “solar inverter” often includes several power electronic converters. As a first example, we can have a dual-stage inverter (Fig. 3.15). This topology consists of a DC—DC converter which is used for the MPPT, and a DC-AC inverter. The control signals applied to the power switches of the final stage can then be 180 or 120° conduction at the grid frequency (50 or 60 Hz). Then, commutation losses of the inverter are very low. This is possible without strong oversize output filter if the output from the DC—DC converter is modulated to follow a rectified sine wave. Another example of double stage inverter is given in Fig. 3.16. In the Fig. 3.16, the DC link between the DC—DC converter which carries out

Fig. 3.19 Example of complex “solar inverter” topology

Fig. 3.21 Example of complex “solar inverter” with several independent inputs In that case, we can use several stages of the conversion: only the first stage is own to each subarray and subsequent stages are common. So, we can use at first stage a simple circuit such as a transformerless boost (Fig. 3.5) in order to keep a good efficiency in spite of the reduced power. Figure 3.21 shows a circuit made of several boosts, a common fixed duty factor push—pull converter in order to adapt the voltage level and to provide galvanic insulation, a storage capacitor and finally an inverter.

nigh power quality in compliance with the standards. At the limit case, it is possible to associate a DC/AC converter with each module, which can then be called AC-modules (Fig. 3.24). This solution has the advantage of being totally modular. It is an interesting solution when the photo- voltaic array is subject to complex shadows, since each module can always be used at its optimal power. However, the DC/AC converters are complex since there is a large difference in the input and output voltage levels, and their nominal power is low since each of them controls only one module. Their efficiency is thus relatively low.

3.3 Empirical Modeling of the Converters

Unfortunately, manufacturer data are usually insufficient in order to determine all the coefficients of (Eq. 3.14). When manufacturer gives values of efficiency for several input voltages, it is generally for different configurations of the converter obtained by changing the turn numbers of transformer windings, so obtaining several and different values of the nominal input voltage. Then, there are as many different expressions of losses as different configurations, but often the data for each configuration describe the losses only for the nominal input voltage of that conficuration.

3.6.4 Control Systems for Inverters Most distributed energy resources are not suitable for direct power transfer to the electrical grid due to the characteristics of the energy produced. Therefore, power electronic interfaces (inverter or converter) and their control systems are required for interfacing the distributed energy resources with the electric grid. The importance of the inverter is increased because its role has two important aspects. First, it extracts and manages the maximum power from the source. Second, it conditions the input power in order to deliver clean and compliant power to the grid.

nominal efficiency could be observed [73]. PV arrays must be installed so that they maximize the amount of direct exposure to the sun. That usually means placement in an area clear of shading, in a southward direction and at an angle equal to the latitude of the location. The power provided by the PV array varies with solar irradiance and temperature, since these parameters influence the I-V characteris- tics of solar cells. In order to optimize the energy transfer from the PV array to the load, it is necessary to force the working point to be at the maximum power point (MPP) [31, 63].

Table 4.1 Control action for different operating points of the power—voltage characteristic of a photovoltaic generator

Fig. 4.3. MPPT control scheme and voltage regulation of Vpy

This control places the system at maximum operating point (Vopt, Lop). The first system with MPPT was introduced in 1968 for a space system [65]. Over the years, several MPPT algorithms have been developed and widely adapted to determine the maximum power point [31, 66, 67]. The control technique the most used consist to act on the duty cycle automatically to place the generator at its optimal value whatever the variations of the metrological conditions or sudden changes in loads which can occur at any time. The main components of the MPPT circuit are its power stage and the controller. The two configurations of MPPT scheme are represented in Figs. 4.5 and 4.6. In Fio 485 the nower ctace innit voaltace Vand ecirrent 7 are need hv the parameter « is continuously turned until the PV array is loaded at its MPP. Many methods have been developed to determine the maximum power point (MPP). In Ref. [68], to track MPP, a look-up table on a microcomputer is employed. It is based on the use of a database that includes parameters and data such as typical curves of the PV generator for different irradiances and tempera- tures. In Ref. [69], curve-fitting method is used, where the nonlinear characteristic of PV generator is modeled using mathematical equations or numerical approxi- mations. These two algorithms have as disadvantage that they may require a large

Fig. 4.4 [,,(Vpy) and Ppy(Vpy) characteristics [9]

memory capacity, for calculation of the mathematical formulations and for storage of the data. Open-circuit voltage photovoltaic generator method is employed in Ref. [70], it approximates linearly the voltage of PV generator at the MPP to its open-circuit voltage and a linear dependency between the current at the MPP and the short-circuit current for the short-circuit photovoltaic generator method pre- sented in Ref. [71]. These methods are apparently simple and economical, but they are not able to adapt to changeable environmental conditions. Santos et al. present perturb and observe (P&O) method which is based on iterative algorithms to track continuously the MPP through the current and voltage measurement of the PV module. Most control schemes use the P&O technique because it is easy to implement [73-76] but the oscillation problem is unavoidable. Conductance incremental method presented in Ref. [76] requires complex control circuit. The two last strategies have some disadvantages such as high cost, difficulty, com- plexity and instability. Intelligent based control schemes MPPT have been introduced (fuzzy logic,

Fig. 4.7 Block diagram of Perturb and Observe method

Fig. 4.8 Flowchart of Perturb and Observe method

In turn, Eqs. 4.6 and 4.7 are used to determine the direction in which a perturbation must occur to shift the operating point toward the MPP, and the perturbation is repeated until Eq. 4.5 is satisfied. Once the MPP is reached, the MPPT continues to operate at this point until a change in current is measured which will correlate to a change in irradiance on the array Fig. 4.13. The relationship between voltage and current, for the one-exponential model, is siven by the following equation: Equation 4.4 explains that the operating voltage is below the voltage at the maximum power point if the conductance is larger than the incremental conduc- tance, and vice versa. Thus, the task of this algorithm is to track the voltage operating point at which conductance is equal to incremental conductance. Hence,

Fig. 4.15 Flowchart of the incremental conductance method

The block diagram of Incremental Conductance method is the same as that of Perturb & Observe method Fig. 4.14. Ficure 4.15 shows the flowchart of this method.

Incremental Conductance (INC) method is simple and easy to implement and its tracking efficiency is very high. It is able to tell whether the current working point is at the MPP or not, in case of ideal conditions. But in the measurements, the operating point could oscillate around the MPP. In the modified INC method, we added the part which monitors the maximum and minimum values of the power oscillations on the PV side. These values can be used to find out how close the current operating point is to the MPP, thereby slowing down the increment of the reference, in order not to cross the MPP [113].

4.2.6 MPPT Controls Based on Relations of Proportionality These methods are based on proportional relationships between parameters of optimal maximum power point (op, Vopt) and the characteristic parameters of the panel (/,., Voc). 4.2.6.1 Constant Reference Voltage Algorithm

Fig. 4.18 Power—voltage characteristic P,(Vpy) of PV generator a-Variable irradiance, constant temperature b-Variable temperature, constant irradiance Fig. 4.19 Block diagram of open circuit voltage method [9]

Fig. 4.21 Block diagram of Short circuit current method [9]

where the control saturate if xg + k,o is out of range, where k, is a positive scaling constant Fig. 4.24.

The power variation (APpy,) is either in the positive direction or in the negative me. The value of AP,, can also be small or on the contrary large. This control ullows the research of the optimum point while being based on the expert observations. From these judgments, the reference photovoltaic voltage Vpy ser 1S ncreased or decreased in a small or large way in the direction which makes it dossible to increase the power Ppy. TOL. ....,%*...... # ge dQ QT a, ee ey en ee Se ee

Fig. 4.26 Structure of MPPT fuzzy controller

Fig. 4.27 Membership functions of AP,,, AVpy and of AVpy, re pv?

Fig. 4.28 Membership function plots in Matlab [9]

<Fig. 4.30 Simulation results of fuzzy logic controller versus theoretical PV array characteristic, temperature 7; is changed from 10 to 50°C at constant irradiance (1000 Wim’). (a): Pov(Vpy), (b):Ppy Upy), (€):Ipv (Vpy) a. Power-voltage characteristic of a PV module for different temperatures. b. Power-current characteristic of a PV module for different temperatures. c. Current-voltage characteristic of a PV module for different temperatures [31] Fig. 4.33 Architecture of the PBA algorithm

Fig. 4.36 Photovoltaic system with MPPT control by neuro-fuzzy networks

Fig. 4.37 Block diagram of a PV system based on Genetic algorithm [110]

Fig. 4.38 Efficiency comparison of different MPPT methods

Fig. 5.8 Modified Thevenin model 5.1.3.5 Thevenin Battery Model

Fig. 6.31 Simulation diagram of the electromagnetic torque control

out in order to vary the parameters, such as state of charge, current density and temperature.

Fig. 5.12 Modified Thevenin equivalent battery model

Fig. 5.13. Model from a series experimental test [137]

5.1.5.7 Practical Identification of Battery Impedance In practice, the determination of batteries impedances is often made on stationary batteries. The basic principle is to impose on the battery an excitation in voltage or current [31]. Measurement at weak frequency gives more information on elec- trochemical operation because the internal kinetics of the battery has thus the time

Fig. 5.31 Circuit measurement of battery impedances

Fig. 5.32 Measured signals S; current and S, voltage

Fig. 6.1 General configuration of a photovoltaic pumping system [62]

DC motor and a centrifugal pump. There are two configurations of PV pumping systems based on DC motor. In the first system (Fig. 6.2), the motor could be connected directly to the PV generator. For allowing operation of the pumping system at maximum power, the motor controller has to be able to perform the tracking of the MPP. eee — =e eae “ s a

Fig. 6.3 Photovoltaic system loaded by DC motor via DC—DC buck-boost converter Fig. 6.4 Equivalent circuit of DC Shunt motor

The dynamical model of DC shunt motor can be written as

The nonlinear dynamical mathematical model is given by:

6.2 PV Pumping Systems Based on AC Motor

Fig. 6.10 RMSE and MBE results for the centrifugal pumps C, [62]

Fig. 6.11 RMSE and MBE results for the centrifugal pumps C, [62]

We obtain the following mathematical model:

with L,, as the magnetizing inductance of the motor and L, and L, are the stator and rotor inductances and

Fig. 6.16 RMSE and MBE results for the centrifugal pumps D, [62]

Fig. 6.18 Subsystem of an IM fed by an MLI inverter

The undesirable harmonics of a square wave can be eliminated and the funda- mental voltage component can be controlled as well by what is known as the harmonic elimination method. In this method, notches are created in the square wave at predetermined angles (Fig. 6.19). It can be shown that the notch angles can be controlled to eliminate certain harmonic components and control the fun- damental voltage [158].

Fig. 6.20 Angles notches for different harmonic ranks

Then, the following system of transcendental equations is obtained: In a quarter-cycle symmetrical waveform, only the sine odd harmonics exist. Therefore, the coefficients are given by:

minimization PWM technique. In this method, the total harmonic voltage distor- tion factor (THD) is minimized. The minimization of this quantity and the control of the fundamental are achieved by an appropriate positioning of the switching angles. Considering that higher harmonics are easier to filter, we take into account harmonics until nth with a weigh decreasing with frequency. The THD perfor- mance factor is then defined as:

X» = , L, the magnetizing reactance (Q), w, the angular frequency of the supply (rd/s), @-ac the motor speed (rd/s) and ea eee es lr eee Assuming thatR,, is infinite, the stator current 7, and the rotor current J, in the elements X, and R,/g are related by the phasorial expression

Fig. 6.22 Induction motor equivalent circuit

Fig. 6.26 Vector control of the PV pumping system based on induction machine

Power converted in mechanical power, stator current and stator power will be:

6.2.4 Vector Control of the PV System Based on Induction Machine

Fig. 6.33 Evolution of the torque, speed, stator current and stator flux with a speed reference 6.2.5.4 DTC of IM Fed by a PV Generator

Fig. 6.27 Block diagram of the conventional direct torque control of induction motor drives Table 6.2 Switching table for the conventional DTC A configuration of the DTC scheme is represented in Fig. 6.27. In this system the instantaneous values of flux and torque can be calculated from stator variables and mechanical speed or using only stator variables. Stator flux and torque can be controlled directly and independently by properly selecting the inverter switching configurations. With a three-phase voltage source inverter, six non-zero voltage vectors and two zero-voltage vectors can be applied to the machine terminals. The stator flux can be estimated using measured current and voltage vectors

Fig. 6.30 Simulation diagram of stator flux control

Fig. 6.34 Simulation of direct torque control of the induction generator fed by PV generator

Fig. 6.36 Simulation results obtained from the PV generator according to the variation in irradiance

Fig. 6.37 Maximum power point tracking with DC motor

Fig. 6.38 Maximum Power Point Tracking with AC motor

Fig. 6.39 Working parameters of three-pumps with a total head of 20 m [62]

Fig. 6.45 Water produced by 1000 pumps of type C. with an average working time of 5 h, an input power of 950 W at different heads

Fig. 7.3. Configuration of the hybrid system with DC and AC buses

Fig. 7.4 Block diagram of the hybrid photovoltaic/diesel generator system

fig. 7.5 Centralized AC bus architecture

Fig. 7.7 Centralized DC bus architecture The mechanical speed evolution is determined from the total torque Tyec applied to the electrical generator rotor

Induction machines are largely used in the field of wind energy conversion. Fo! standalone operations, the squirrel induction machine is preferred because it is robust, needs little maintenance and does not need an auxiliary supply for mag. netizing it. The simplest way to use it as an autonomous generator consists ir connecting its stator windings to a capacitor bank in parallel to the load. The remaining magnetic flux, added to the magnetizing current through the capacito: bank yields the built up of the electromotive force and its increase to a usefu value. This approach is very cheap and is well adapted to convert the wind energy into an electrical one for isolated areas or areas faraway from the distribution gric

Fig. 7.14 Hybrid wind/photovoltaic system

Fig. 7.17 Areas of photovoltaic panels and wind turbines

Fig. 7.18 Number of photovoltaic panels and wind turbines as a function of the fraction of the load

Fig. 7.19 Characteristic Ipy(Vpy) panel with photovoltaic power Reference P,.¢ , produced [9]

Fig. 7.21 Characteristic Pw(@) with photovoltaic power Reference Pref py produced (Case 3)

7.3.3.4 Application of the Control of Hybrid Photovoltaic/Wind System

7.3.4 Hybrid Photovoltaic/Wind//Hydro/Diesel System

Fig. 7.25 Photovoltaic power output, maximum (Ppy max) and reference power (Prefs). a Summer day. b Winter day

Fig. 7.26 Wind power output, maximum (Py max) and its reference (Prep w). a Summer day. b Winter day

Fig. 7.29 Total power required, power output (Pw + Ps) and power supplied by batteries. a Summer day. b Winter day Fig. 7.28 Power supplied by batteries. a Summer day. b Winter day

Fig. 7.30 Description of hybrid photovoltaic/wind//hydro/diesel system

Fig. 7.32 Description of a hybrid photovoltaic-Electrolyzer-fuel cell System [193]

Fig. 7.34 Description of a hybrid photovoltaic-Electrolyzer-fuel cell system with DC indirect coupling Fig. 7.33 Description of a hybrid photovoltaic-Electrolyzer-fuel cell system with DC direct coupling

Fig. 7.35 Description of a hybrid photovoltaic-Electrolyzer-fuel cell system with AC coupled 1193]

with Py = Patm as the initial condition. Fig. 7.38 Cathode model

Fig. 7.48 Solar-wind-hydrogen energy cycle

Table 5.1 Zebra battery properties [122] 5.1.1.7 Sodium-Metal Chloride Batteries Sodium-Metal Chloride Battery is also known as ZEBRA (zero emission battery research activity) battery and it is a system operating at around 270-350°C [119, 120]. The chemical reaction in the battery converts sodium chloride and nickel to nickel chloride and sodium during the charging phase. During discharge, the reaction is reversed. Each cell is enclosed in a robust steel case. A ZEBRA battery is designed for a 2 h discharge with peak power capability as required [119-122]. The normal operation can be written as:

Table 5.2 Comparison of different Li-ion batteries [114]

Table 5.3 Comparison of different batteries [118]

Table 5.4 Peukert constant e Rate of charge/discharge e Environmental temperature e Age/Shelf life 5.1.2.1 Electrochemical Battery Models 5.1.2.2 Peukert Equation

Table 7.1 Classification of hybrid systems by power range [194]

Fig. 7.11 Supervisor of hybrid wind/photovoltaic/ diesel generator system

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A Study of the Trend of Smartphone and its Usage Behavior in Malaysia

by Zainal Sanusi

The purpose of this exploratory study is to better understand the current dynamics of the Malaysian market for smartphone and the usage behaviors of consumers. This paper presents the result of a survey on the trend of smartphone from the... more

Fig. 2. Familiarity Crosstab by Gender Fig. 2 has pointed out that male consumers tend to have higher familiarity towards smartphone compared to their female counterparts. It implies that smartphones as a kind of information and communication technologies do inherit the nature of general technology in which male users are speculated to have higher interest and skills in technology [17]. 5.3 Brands and Service Providers

Fig. 1. Familiarity of Respondents towards Smartpohone nternational Journal on New Computer Architectures and Their Applications (IINCAA) 2(1): 275-! The Society of Digital Information and Wireless Communications, 2012 (ISSN: 2220-9085)

Fig. 3. Crosstab Analysis of Design by Age Fig. 3 shows the percentage of respondents who agreed that design is an important factor, categorized by age groups. The result demonstrates that design of smartphone is less important to the older consumers, compared to their younger counterparts. With regard to the operating perceive operating platform as an important criterion to be taken into account, than their female counterparts. This assertion is supported by the result that demonstrates the respondents who agreed that operating platform is important constitute 70% male respondents, whereas only 30% are female.

Fig. 4. Corsstab Analysis of Computing Power by Age According to Table 4, the most common usage of smartphone is still related to its core functionalities which are to make phone call, and SMS. Interestingly, the 40 % of the respondents have reported that they use smartphone for instant messaging daily. This would imply that consumers no longer solely depend on computer to send instant messages, but smartphone is another important platform for the consumers to interact with others through _ instant messaging. As sending instant message is commonly free of charge, whereas sending ordinary SMS will incur communication fee

Fig. 6: Frequency of Blogging via Smartphone blogging have become a widely accepted communication means in the context of nternet usage. With regard to this, it is interesting to find out the acceptance of blogging using smartphone. The finding as shown in Fig. 6 indicates that blogging through smartphone is yet a common practice for users. About half (47%) of the respondents have not tried to blog by using their smartphones, whereas only 21 percent of respondents do so on regular basis. The considerably low acceptance of this practice may be due to inconvenience and inefficiency in utilizing smartphone to write a blog. Blogging can be done faster and easier by using a computer. Previous study has found that ease-of-use and usefulness are the main factors that affect the utilization of certain technologies [21, 22]. This study extends the finding to the context of smartphone application software.

Fig. 5. Frequency of Accessing Website via Mobile

Fig. 7 Frequency of playing game via Mobile 6. DISCUSSION

For instance, 35.6% of the total 1814 respondents reported that the trend in community is an important criterion that influences smartphone purchasing decision. The next most important determinants are the needs for the smartphone, software preferences, cost of plan, and hardware. Signal reception seems to be the weakest determinants for the consumers to acquire smartphone. A point worth to be emphasized is that about 30% of the respondents agreed that cost of plan is an important factor to be considered in the purchase decision process. Nowadays it is common that cellular providers offer attractive package where consumers can purchase the mobile phone with discounted price, with the condition that they will be bonded with the cellular operator for a specified period. The finding in this study indicates that these attractive offers have become one of the important determinants for the consumers in Malaysia in buying a smartphone. As a main interest of this study, the determinants of smartphone purchasing decision have been identified and discussed. Table 2 shows the percentage of total respondents that have chosen a particular determinant.

Table 3. Importance of Device Specifications Surprisingly, only 30.2% of the total respondents reported that price factor is a consideration in purchasing decision. This phenomenon could due to the fact that smartphone is considered as _ durable merchandise, which can be used for years. Hence, the consumer might perceive the design, features, and overall quality would outweigh the price difference in the long run. Previous study has also found that consumer price sensitivity tends to be lower towards other durable items [20]. age of According to the statistics, built-in Wi- Fi adapter is the second most common specification that is important to consumers, and this is followed by computing power. Crosstab analysis on the Wi-Fi adapter by suggests that about 40% of the consumers from all age groups equally perceive Wi-Fi adapter as important to them, with exception of only ap who perceive that Wi- of t Ma pro call his phenomenon could hat the consumers above aysia are generally proximately 19% he consumers older than 57 years old Fi capability is pertinent to them. The plausible explanation be due to the fact 57 years old in poor in English ficiency and not computer literate. Thus, hese situations have become obstacles to Internet browsing. Their usage of mobile phone is most probably limited to the fundamental functions such as making voice

Table 4. Usage Patterns of Smartphone According to the data analysis, entertainment is another major type of smartphone usage. Entertainment refers to the usage of music playing, movies, and games. Hence, the finding suggests that other than as a means of communication, smartphone is perceived by consumers as a source of entertainment or media.

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Biotransformari Celulare si Fiziologice 2006 - 2017 Editie Adaugita

by Cristian Muresanu

2017, Biotransformari_Celulare_Si_Fiziologice_Complexe_2006_-_2017_Editie_Adaugita.

Lucrare interdisciplinară cu conţinut ştiinţific pe probleme de biologie, sănătate, dietă şi psihologie, redactată sub formă de naraţiune cu nuanţe umoristice, în anumite capitole, care dezvăluie evoluţia personalităţii autorului, de la... more

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Molecular and cellular aspects of planarian regeneration

by Kiyokazu Agata

1999, Seminars in Cell & Developmental Biology

Neoblasts, which are classically defined as prospective totipotent stem cells, supporting planarian regeneration, now have been identified by expression of the DjvlgA gene coding for a vasa-type ATP-dependent RNA helicase. DjvlgA-positive... more

Figure 1. The structure of the chromatoid body and expression pattern of DjulgA. (A) The chromatoid bodies are derived from the nucleus. nu, nucleus; cb, chromatoid body; mt mitochondoria. Arrows indicate the chromatoid bodies passing through nuclear pore (modifiec from ref. 20). (B) DjvigA-expressing cells are located in the mesenchymal space. (C) Accumulatior of DjvigA-expressing cells are observed in the blastema and in the regenerating pharynx in planaria regenerating from a head piece. (D) Expression of DjvigA decreased drastically 10 day: after X-ray irradiation. Modified from ref 4. brates, it has been clearly demonstrated by cell cul- ture and molecular markers that differentiated cells can participate in regeneration through dedifferen- tiation events,!°"!” and see Gardiner et ai,'® this issue. Even in planarian regeneration, it has been suggested based on electron-microscopic observations, that the pharynx-lumen epithelium may form by transdiffer- entiation from intestinal epithelial cells. However, we could not find any evidence indicating a contribution from differentiated cells to planarian regeneration, even though we have extensively analyzed the regen- eration process using molecular markers and chimeric analysis.'” On the contrary, our observa- tions clearly indicate that the cells participating in regeneration appear in the mesenchymal space where the stem cells are distributed.*!? In the case of phar- ynx regeneration, DjMHC-A (a_pharynx-muscle- specific gene; MHC, myosin heavy chain) expressing cells appear in the mesenchymal space surrounding the prospective pharynx forming region before for- mation of a pharynx rudiment.'? These observations suggest that the cells participating in planarian re- generation may be mainly derived from the undif- What type of cells participate in planarian regenera- tion? Classical observations and experiments sug- gested that totipotent stem cells, so called ‘neoblasts’, may exist in the mesenchymal space through the entire body of the worm and differentiate to supply appropriate cells for regeneration.'*'* However, the evidence supporting this idea is still scarce. On the other hand, in the case of regeneration in the verte-

Figure 2. Cells participating in regeneration appear in the mesenchymal space in a position-dependent manner, be- fore migrating to the organ rudiments or blastema. (A) Whole mount in situ hybridization of head pieces at 3 days of regeneration. Neck-forming (middle piece) and pharynx-muscle-forming cells (right piece) appear in the mesenchymal space surrounding the brain (left piece) at 3 days after amputation. (B) Saggital section at 3.5 days of regeneration of head piece. Arrowheads indicate that DjMHC-A-expressing cells appear in the mesenchymal space in the stump, not in the blastema, and participate in pharynx-muscle formation through the base of the pharynx rudiment. Modified from ref 19.

Figures 3, 4 & 5. Legends on facing page.

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The antimicrobial activities of methanolic extracts of Eucalyptus camaldulensis and Terminalia catappa against some pathogenic microorganisms

by Joseph Okogun and

2004

Methanolic extracts of leaves of Eucalyptus camaldulensis and Terminalia catappa were studied for in vitro microbial activities by agar dilution method. The phytochemical analysis of the crude extracts of the medicinal plants revealed the... more

Table 1. Phytochemical components of the crude extracts

Table2: Antimicrobial activities of the crude extracts on pathogenic microorganisms at 2000 pg/ml concentration Table2: Antimicrobial activities of the crude extracts on pathogenic microorganisms at 2000 pg/ml concentration Antimicrobial activity of the crude extracts

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A simplification of the protein assay method of Lowry et al. which is more generally applicable

by Al An

1977, Analytical Biochemistry

Some recent modifications of the protein assay by the method of Lowry, Rosebrough, Farr, and Randall (1951, .I. Biol. Chem. 193, 265-275) have been reexamined and altered to provide a consolidated method which is simple, rapid, objective,... more

Fic. 1. Standard curve for the microassay using brine shrimp membrane protein calibrated against BSA. Open circles are samples processed through the DOC-TCA precipitation step prior to color reaction. Closed circles are samples processed directly for color reaction with- out prior precipitation.

Fic. 2. Log—log plot of the standard curve for 10-200 yg of BSA using the standard assay volume.

EFFECTIVENESS OF THE DOC~TCA PRECIPITATION STEP ON RECOVERY OF BRINE SHRIMP MEMBRANE PROTEINS (50 yg) IN THE PRESENCE OF DIFFERENT AMOUNTS OF INTERFERING LUBROL WX AND SUCROSE?

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The impact of climate change on human health: some international implications

by kulbhooshan saini

1993, Cellular and Molecular Life Sciences

Figure 1. Relationship between maximum temperature and mortality: Shanghai; 1980-89. Reviews

Figure 2. Relationship between maximum temperature and mortality: Guangzhou: 1980-1989.

Figure 3. Relationship between maximum temperature and mortality: Cairo, Egypt: 1982.

Study periods for each country are as follows: *1964—1966, 1972- 1978, 1980; ©1958-1988; ©1980-1989; 41981-1985. Table 1. Cities evaluated in the study Reviews sizable amount of information was missing from many records, and those years were not utilized in this study). Ten Canadian cities were examined between the years 1958 and 1988. For both the United States and Canada, daily mortality sums for the summer (June, July, Au- gust) and winter (December, January, February) were grouped by age (less than one year, greater than or equal to 65 years, all ages) and cause of death (a weather-related group, including all respiratory causes, influenza, injury, stroke/cerebrovascular and, for sum- mer, heat stroke/heat stress; and a total death group). There is conflicting evidence in the literature about the validity of evaluating specifically weather-related causes of death. Many researchers continue to utilize total mortality figures in their analyses, as deaths from a surprisingly large number of causes appear to escalate with more extreme weather':°. In an attempt to circum- vent this apparent disagreement among researchers, weather-related and all causes categories were evaluated separately in this study. ri Ps, a , ( , cn , fr on « . cn nL.

Table 2. Weather variables used in the mortality study *LST — Local standard time. Values represent cloud cover and wind speed measured at 1400 hrs (2 pm LST).

Table 3. GISS doubled CO, scenarios for selected cities 'Location given in latitude and longitude coordinates.

*Research indicates little chance of acclimatization in the Chinese and Egyptian cities!!. Table 4. Present-day and future estimates of total summer mor- tality

*Total suspended particulates in micrograms per cubic meter. >Positive and negative mortality values reflect variation around < baseline of zero. Total suspended particulates/mortality means for maximum tem- perature below threshold (31 °C) in Philadelphia Canadian mortality

Total suspended particulates/mortality means for maximum tem- perature above threshold (31 °C) in Philadelphia

Ozone/mortality means for maximum temperature below threshold (31 °C) in Philadelphia @Ozone in parts per million. >Ppositive and negative mortality values reflect variation around a baseline of zero.

Ozone/mortality means for maximum temperature above threshold (31 °C) in Philadelphia

Table 8. Offensive air masses in summer for Shanghai

*Actual deaths/death rate per 100,000 population. >The difference between the computed number of deaths by the regression on days above the threshold and the average of the regular days. Table 7. Summer mortality analysis: Shanghai and Guangzhou

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Image analysis and machine learning applied to breast cancer diagnosis and prognosis

by Nick Street

Analytical and quantitative cytology and histology / the International Academy of Cytology [and] American Society of Cytology

Fine needle aspiration (FNA) accuracy is limited by, among other factors, the subjective interpretation of the aspirate. We have increased breast FNA accuracy by coupling digital image analysis methods with machine learning techniques.

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Gay Language: Defying THE Structural Limits OF English Language

by Norberto Casabal

2008, kritika kultura

published in newspapers. To illustrate: and interviews, from blog sites mainly designed for gayspeak fora, and from various articles

and names will be classified according to the following categories: To analyze these words, expressions, and names according to the grammatical structure o

be categorized according to the following:

A. PROPER NOUNS REFERING TO NAMES OF PERSONS

B. OTHER PROPER NOUNS (television shows, brands, etc.

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The signal peptide

by Gunnar von Heijne

1990, Journal of Membrane Biology

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VETERINARY HISTOLOGY MODULE

by Sultan A Neja

There is shortage of references in higher teaching institutions especially in newly opened institutions engaged in training of various Veterinary professionals in the country. Hence, some of the strategies that are used to skirt these... more

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Memory

by Jonathan Levenson

2006, Cellular and Molecular Life Sciences

In this review we address the idea that conservation of epigenetic mechanisms for information storage represents a unifying model in biology, with epigenetic mechanisms being utilized for cellular memory at levels from behavioral memory... more

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Veterinary Cytology Dog, Cat, Horse & Cow Self-Assessment (2007)

by Mohammad Rifky

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Oxidative stress and cancer: An overview

by Matilde Lleonart and

2013, Ageing Research Reviews

Reactive species, which mainly include reactive oxygen species (ROS), are products generated as a consequence of metabolic reactions in the mitochondria of eukaryotic cells. In normal cells, low-level concentrations of these compounds are... more

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Biological activities of Schottenol and Spinasterol, two natural phytosterols present in argan oil and in cactus pear seed oil, on murine miroglial BV2 cells

by Pierre Andreoletti and

2014, Biochemical and Biophysical Research Communications

The objective of this study was to evaluate the biological activities of the major phytosterols present in argan oil (AO) and in cactus seed oil (CSO) in BV2 microglial cells. Accordingly, we first determined the sterol composition of AO... more

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Micropropagation of Rubus and Ribes spp

by Ewa Dziedzic

2012, Methods in Molecular Biology

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A quantitative starch–iodine method for measuring alpha-amylase and glucoamylase activities

by Reginald Storms

2006, Analytical Biochemistry

Alpha-amylase (EC 3.2.1.1), which cleaves internal -1,4glycosidic linkages in starch to produce glucose, maltose, or dextrins, and glucoamylase (EC 3.2.1.3), which cuts -1,4and -1,6-glycosidic linkages to release glucose from the... more

Alpha-amylase (EC 3.2.1.1), which cleaves internal -1,4glycosidic linkages in starch to produce glucose, maltose, or dextrins, and glucoamylase (EC 3.2.1.3), which cuts -1,4and -1,6-glycosidic linkages to release glucose from the nonreducing ends of starch, are widely used in the industrial conversion of starch into sugars. The characterization of -amylases and glucoamylases generally needs to use diVerent chromatography techniques such as paper chromatography [1,2], high-performance liquid chromatography , and thin-layer chromatography . There are mainly two types of assays that are used to determine the activity of -amylase and glucoamylase. One is based on measuring the amount of reducing sugars by the dinitrosalicylic acid (DNS) 2 assay or the Nelson-Somogyi method, whereas the other is based on the decreased staining value of blue starch-iodine complexes . The second method, which was developed by Fuwa and is widely used , is based on color development that results from iodine binding to starch polymers. However, the starch-iodine assays reported by diVerent researchers are quite diverse with iodine concentrations ranging from 3 M [12] to 0.25 mM and with the wavelength used to measure color development varying from 550 nm [15] to 700 nm . Moreover, -amylase activity is calculated as relative activity according to the following equation. Dextrinizing activity D (D 0 -D) ¥ D 0 £ 100 ¥ 10, where D is the absorbance of the enzyme sample and D 0 is the absorbance of the amylose control without the addition of enzyme . Dextrinizing activity calculated using this formula is therefore not expressed in units that are related to the amount of substrate consumed. In addition, since the assay has a Wnal volume of 20-200 ml, it is not suitable for screening a large number of samples. In this paper, we describe a microplate-based starch-iodine assay that measures the amount of starch degraded to determine the activity of -amylase and glucoamylase. We also propose a new strategy to distinguish between -amylase and glucoamylase enzymes by comparing the results obtained from the DNS and starch-iodine assays.

Fig. 1. Absorbance of the starch-iodine complexes. (A) Absorbance spec- tra of the starch—-iodine complexes; (B) standard curve for the microplate- based starch-iodine assay.

Activity of a-amylase and glucoamylase as determined with the microplate-based starch-iodine assay and the DNS assay All data are averages of triplicate determinations. * One unit (U) of activity as determined by the DNS assay is defined as an average of 1 mg of glucose equivalents released per min in the assay reactior > One unit (U) for the microplate-based starch—iodine assay is defined as the disappearance of an average of | mg of iodine binding starch material pe min in the assay reaction. U/ml was calculated using the formula: U/ml = (Aggy control —A5g) sample) + A5g9/mg starch + 30 min + 0.04 ml, where As, control is the absorbance obtained from the starch without the addition of enzyme, A;g) sample is the absorbance for the starch digested with enzym« Asgo/mg starch is the absorbance for 1 mg of starch as derived from the standard curve in Fig. 1B, 30 min is the assay incubation time, and 0.04 ml is th volume of the enzyme used in the assay. +2 Enzyme assays were performed in the presence of 250 mM maltose. © The calculated ¢ value for glucoamylase is 1.61, below the critical t value of 2.14 at p= 0.05, df= 14, when we compare the activity determined by th DNS assay with that by the starch-iodine assay. 4 The calculated F values of the microplate-based starch—iodine assay to the DNS assay for both enzymes are below the critical F value of 3.79 at 95° neanidaanre lasel«aHth At 7 7

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(2013) Advanced Dairy Chemistry - Vol 1A.pdf

by Mohammad Rifky

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Imbalance of RANK, RANKL and OPG expression during tibial fracture repair in diabetic rats

by Fernanda Amorim

2008, Journal of Molecular Histology

To clarify the mechanisms of altered bone repair in the diabetic state, we investigated RANK, RANKL and OPG expression by immunohistochemistry and RT-PCR in the fracture sites of rats that were either healthy or made diabetic by alloxan.... more

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Antioxidant activity and phenolic compounds of 112 traditional Chinese medicinal plants associated with anticancer

by Harold Corke

2004, Life sciences

Cancer prevention and treatment using traditional Chinese medicines have attracted increasing interest. This study characterizes antioxidant activity and phenolic compounds of traditional Chinese medicinal plants associated with... more

Fig. 1. Distribution (percentage) of 112 medicinal herbs associated with anticancer among different ranges of antioxidant activity (TEAC value). A: < 100.0 umol TEAC/100 g DW; B: 100.1 — 500.0 jrmol/100 g; C: 500.1 — 1,000.0 umol/100 g; and D: >1,000.1 umol/100 g (TEAC value of methanol extracts). were used for COMparison. A total of 112 medicinal plant species from 50 families were collected, extracted, and tes ed. Thei TEAC values (Table 1) indicated extremely large variation in antioxidant activity. Total antioxidar capacity of the aqueous extracts ranged from 43.9 to 17,674 umol Trolox equivalents per 1 weight (umol TEAC/100 g DW), and the averaged TEAC value was 787.9 umol/100 g DW. T 00 g dr he TEAC values for the methanolic extracts ranged from 46.7 to 17,323 mol/100 g DW, and the mean value wa 941.1 umol/100 g DW. Chinese Galls from Rhus chinensis/R. potaninii contained the highest antioxidan concentration (aqueous/methanolic: 17,674/17,323 umol TEAC/100 g), followed by dried extract (Catechu) from branches and stems of Acacia catechu (aqueous/methanolic: 10,049/11,197 umol TEAC 100 g). Of the 112 medicinal herb species, it was found that 18 species (16.1%) contained more tha 1,000.1 mol TEAC/100 g, and 21 species (18.7%) were below 100 umol TEAC/100 g, while th majority (65.2%) had medium amounts of antioxidants, i.e., 49 species (43.8%) between 100.1 and 50! umol TEAC/100 g and 24 species (21.4%) between 500.1 and 1,000.0 umol TEAC/100 g (Fig. 1). It was also found that the total phenolic content of 112 medicinal herbs had significant variatior

Fig. 2. Relationship between total antioxidant capacity (umol TEAC/100 g DW) and total phenolic content (g gallic acid equivalents/100 g DW) of methanolic (A, B) and aqueous (C, D) extracts from 112/110 medicinal herbs associated with anticancer.

Fig. 3. Typical HPLC chromatogram of parts of phenolic standards at 280 nm analyzed with the improved method. Peaks: 1, gallic acid; 2, catechin; 3, vanillic acid; 4, caffeic acid; 5, cyanidin-3-O-glucoside; 6, ferulic acid; 7, coumarin; 8, resveratrol; 9, myricitrin; 10, rutin; 11, quercitrin; 12, diosmin; 13, daidzein; 14, glycitein; 15, quercetin; 16, emodin-8-O-glucoside; 17, luteolin; 18, hesperetin; 19, kaempferol; 20, baicalein; 21, alizarin; 22, galangin; 23, flavonol; 24, chalcone; 25, rhein; 26, emodin; 27, quininzarin; 28, physcion.

Fig. 4. HPLC profiles of methanolic extracts from four selected medicinal herbs: (A) phenolic acids, coumarins and flavonoids from aerial parts of Artemisia annua; (B) lignans and phenolic acid from fruits of Arctium lappa; (C) anthraquinones, stilbene and phenolic acid from rhizomes of Polygonum cuspidatum (tannins removed); and (D) flavonoids, phenolic acid and tannins from flowers of Rosa chinensis. Elution monitored at 250 nm (C), 280 nm (B and D), and 370 nm (A). subclassified as flavones (basic structure, B ring binds to the 2-position), flavonols (having a hydroxy] sroup at the 3-position), flavanones (dihydroflavones) and flavanonols (dihydroflavonols) (2—3 bond is saturated), and flavanols (flavan-3-ols and flavan-3,4-diols) (C-ring is 1-pyran), chalcones (C-ring is ypened), isoflavonoids (mainly isoflavones) (B ring binds to the 3-position), anthocyanins (anthocya- uidins) (C-ring is 1-pyran, and 1—2 and 3-4 bonds are unsaturated), and biflavonoids (dimer of flavones, lavonols, and flavanones) (Rice-Evans et al., 1996; Iwashina, 2000; Xiao et al., 2000). Flavonoids in slants are mainly present as glycosides with a sugar moiety/more sugar moieties linked through an OH sroup (O-glycosides) or through carbon-carbon bonds (C-glycosides), but some flavonoids are present is aglycones.

Antioxidant activity and total phenolic content of methanolic extracts from common vegetables and fruits (dietary plants)*

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Polyoxometalates: introduction to a class of inorganic compounds and their biomedical applications

by Bernold Hasenknopf

2005, Frontiers in Bioscience

Figure 1. Structure drawings of alpha-[MosOy¢]" .. a) Ball- and-Stick representation. b) Polyhedral representation.

Table 1. ICso values in microM for different heteropolyoxotungstates on tumor cells in vitro lactam antibiotics. (70) He discovered that a factor (named "Factor T" for Tungstate) greatly enhanced the antibacterial effect of the drug in MRSA strains, but there was no synergism of factor T with other classes of antibiotics, nor any effect on other groups of bacteria. He subsequently studied the mechanism of action of Factor T, and found that it reduced the amount of PBP 2', and thus sensitized the MRSA strains to beta-lactams. (71) Factor T was finally identified as the lacunary Keggin polyoxotungstate [PW ,O39]’, (72) and an extended investigation together with Yamase on the synergistic effect of more than 70 polyoxometalates in combination with beta-lactam antibiotics followed. (73, 74) Whereas almost no polyoxomolybdate, nor polyoxovanadate exhibited a significant effect in combination with oxacillin on MRSA strains SR3605 and ATCC43300, almost all polyoxotungstates clavulanic acid (for example Augmentin”) can restore the antibiotic effectiveness. On the other hand, hydrolytically stable penicillins such as methicillin and oxacillin have been developped. Bacteria were developing resistance against these antibiotics by modifying their Penicillin-Binding-Proteins (PBP). For instance Methicillin-Resistant-Staphylococcus Aureus (MRSA) strains produce the PBP variant PBP 2', which plays the same role in the construction of the cell wall as PBP, but is insensitive to beta-lactams. These penicillin-resistant bacteria represent a very serious threat to humans, in particular in intensive care units, and much effort is devoted to find effective antibiotics against MRSA infections.

Table 2. The antibacterial effects of polyoxotungstates alone (MIC) and in combination with oxacillin (FIC) against two different MRSA strains (73, 74) relationship between composition and activity. showed synergism. This result can be correlated with the amount of polyoxometalates found inside the cells of MRSA strains MRS394-1. (74) When these cells grown to a stationary phase were treated with 100 microg/mL of Na3[PW 2049] for 20 min, the amount of tungsten found inside the cells (mainly in the cel membrane) was 1.05+0.18 mg/g dry weight of cell (6 micromol/g). With the isostructural molybdate Na3[PMo 2040], only 0.05+0.02 mg/g dry weight o cell (0.5 micromol/g) of molybdenum are incorporated into the cell. Metavanadate and hexaniobiate are also absorbed to a lesser extent by the cells than the examined polyoxotungstates. However, there are too few studies of isostructura polyoxometalates to draw conclusions about the

Table 3. Trends in insulin-mimetic effects of polyoxotungstates (106) upon tungstate treatment. Very recently, the regeneration of pancratic beta-cell population in diabetic rats treated orally with sodium tungstate was reported. (105) effect. Among the polyoxotungstates lowering noticeably the glucose level, those with a Dawson structure (entries 2, 8, 14) produce no or little body weight loss. The authors showed furthermore by *'P NMR that [a/pha-P5W,,0¢:]° is stable at mM concentrations in water. Although these results need to be put on a larger basis, they show clearly that polyoxometalates have a potential in diabetes treatment.

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The Relationships between Sleep-Wake Cycle and Academic Performance in Medical Students

by John F Araújo

2003, Biological Rhythm Research

Survey and laboratory studies suggest that several factors, such as social and academic demands, part-time jobs and irregular school schedules, affect the sleep-wake cycle of college students. In this study, we examined the sleep-wake... more

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Lycopene: A biologically important carotenoid for humans?

by Helmut Sies

1996

used as sources for vitamin A, as food colorants, or as Lycopene is a carotenoid present in human blood feed additives.

FIG. 1. Structures of selected carotenoids.

FIG. 2. Biosynthesis of carotenoids showing the central position of lycopene. Methylene blue was also used as a sensitizer to study the consumption of carotenoids during photooxidation

FIG. 3. Suggested pathway of the formation of apo-6-lycopenal and 2-methyl-2-hepten-6-one from lycopene upon photosensitization (modified from Ref. (13)). The reduction potential of 6-carotene is such that the equilibrium with respect to oxygen lies in favor of O; , resulting in the formation of the superoxide radi- cal anion. For lycopene this reaction is less efficient, and electron transfer is observed in both directions.

FIG. 4. Typical HPLC chromatogram of carotenoid pattern of a human plasma sample (for analytical details see 9).

FIG. 5. Bioavailability of lycopene from processed and unprocessed tomato juice. Changes in lycopene serum levels after ingestion of untreated tomato juice (O) and tomato juice heated at 100°C for 1h together with 1% corn oil (@); amount of tomato juice was equivalent to a lycopene dose of 2.5 yzmol/kg body wt. The decrease in lycopene levels observed in the individuals that consumed untreated juice is due to the ingestion of a diet poor in lycopene throughout the experi- ment (modified from Ref. (54)).

FIG. 6. Structures of lycopene oxidation products. Lycopene-5,6- epoxide is the major oxidation product in the reaction with chloroper- benzoic acid. Final hydrolysis products following rearrangement are the epimers of 2,6-cyclolycopene-1,5-diol, isolated by preparative HPLC from human serum (58).

yhemical and Biochemical Properties of Lycopene and 6-Caroten¢ TABLE I azinobis(3-ethylbenzothiazoline-6-sulfonic acid—diam- monium salt (ABTS) as a radical source (20). Lycopene was the most efficient scavenger of the ABTS radical followed by cryptoxanthin, lutein, zeaxanthin, and (- carotene. Astaxanthin and canthaxanthin showed only minor effects. The radical-scavenging effect of lycopene exceeded that of trolox, a water-soluble analog of vita- min E, by a factor of 3. of human plasma and LDL? (15). In both plasma and LDL carotenoids and tocopherols were consumed, while cholesteryl ester hydroperoxides accumulated. Lyco- pene and (-carotene were more resistant to photooxi- dation in blood plasma than lutein and zeaxanthin. In contrast, the decrease of lycopene was higher in LDL and plasma when 12-(1-pyrene)dodecanoic acid was employed as photosensitizer. Exposure of blood plasma to a water-soluble 'O, generator resulted in the deple- tion of the water-soluble antioxidants ascorbate or urate, whereas the levels of the lipophilic antioxidants lycopene, 6-carotene, and a-tocopherol remained un- changed (16). The data suggest that carotenoids con- tribute to prevention of lipid peroxidation via singlet oxygen quenching.

Source. From Refs. (30-32). Lycopene Content of Fruits and Vegetables

Note. Data are given as nmol carotenoid/ml serum or plasma. * Not determined. > Mean values from these 8 studies. Carotenoid Serum or Plasma Levels (nmol/ml)

Human Lycopene and /-Carotene Tissue Levels (nmol/g wet wt)

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Sostenibilidad agropecuaria y sistemas de producción campesinos

by Elcy Corrales

2002, Cuadernos Tierra y Justicia

ISBN 958-9262-17-1 © Elcy Corrales Roa 2 CONTENIDO INTRODUCCIÓN EL PUNTO DE PARTIDA 1. GUÍA CONCEPTUAL Para moverse en la sostenibilidad • Conceptos relacionados • ¿Pueden ir juntos? 2. LA LENTE DE LA SOSTENIBILIDAD • Utilización de los... more

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The Efficiency of Translation Termination is Determined by a Synergistic Interplay Between Upstream and Downstream Sequences inSaccharomyces cerevisiae

by David Bedwell

1995, Journal of Molecular Biology

In a recent study we found that the efficiency of translation termination could be decreased several hundred fold by altering the local sequence context The University of Alabama at Birmingham, Birmingham surrounding stop codons in the... more

In a recent study we found that the efficiency of translation termination could be decreased several hundred fold by altering the local sequence context The University of Alabama at Birmingham, Birmingham surrounding stop codons in the yeast Saccharomyces cerevisiae. Suppression AL 35294, USA of termination was shown to be mediated by near-cognate tRNA mispairing with the termination codon. We have now examined in greater detail how the local sequence context affects the efficiency of translation termination in this organism. Our results indicate that the sequence immediately upstream of the termination codon plays a significant role in determining the efficiency of translation termination. An extended termination sequence (containing the stop codon and the following three nucelotides) was also found to be a major determinant of termination efficiency, with effects attributable to the fourth nucleotide being largely independent of the termination codon. For the UGA and UAA stop codons, the influence of the fourth position on termination efficiency (from most efficient to least efficient termination) was found to be G>U,A>C, while for the UAG codon it was U,A>C>G. These sequence-specific effects on the efficiency of translation termination suggest that polypeptide chain release factor (or another molecule that may play a role in translation termination, such as rRNA) recognizes an extended termination sequence in yeast. A previous study found a statistically significant bias toward certain tetranucleotide sequences (containing the stop codon and the first distal nucleotide) in several organisms. We found that tetranucleotide sequences most frequently used in yeast are among the most efficient at mediating translation termination, while rare tetranucleotide sequences mediate much less efficient termination. Taken together, our results indicate that upstream and downstream components of an extended sequence context act synergistically to determine the overall efficiency of translation termination in yeast.

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Roles of TGF-β in hepatic fibrosis

by Katja Breitkopf-Heinlein

Frontiers in Bioscience

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The biochemistry of environmental heavy metal uptake by plants: Implications for the food chain

by Laura Lopez

2009, International Journal of Biochemistry & Cell Biology

Plants absorb a number of elements from soil, some of which have no known biological function and some are known to be toxic at low concentrations. As plants constitute the foundation of the food chain, some concerns have been raised... more

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Overview on techniques in cluster analysis

by Rune Matthiesen

2010, Methods in molecular biology

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Role of reactive oxygen species (ROS) in apoptosis induction

by An Ro

2000, Apoptosis

Reactive oxygen species (ROS) and mitochondria play an important role in apoptosis induction under both physiologic and pathologic conditions. Interestingly, mitochondria are both source and target of ROS. Cytochrome c release from... more

Figure 1. A proposed model showing the mitochondria as both source and target of ROS and the role in apoptosis induction. is the nitrosylation of essential components of the apop- tosis machinery such as caspases."

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Electromagnetic cellular interactions

by Ashkan Farhadi

2011, Progress in Biophysics and Molecular Biology

Chemical and electrical interaction within and between cells is well established. Just the opposite is true about cellular interactions via other physical fields. The most probable candidate for an other form of cellular interaction is... more

This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Provided for non-commercial research and education use. Not for reproduction, distribution or commercial use.

Fig. 1. The range of the electromagnetic (EM) spectrum covers different frequencies including visible light. The radiofrequency (3 Hz—300 GHz) wavelengths are named originally based on their use in technology for radio communication and broadcasting. However, radiofrequencies are used for many other applications nowadays. The visible part of the EM spectrum of light is sandwiched between the infra-red (IR) and ultraviolet (UV) regions and is sometimes denoted as the optical part of the EM spectrum.

Fig. 4. Histogram of the strength of the mirror cythopathic effect (dependent on UV EMF cellular interaction) in August, the statistically most favorable month. The abscissa shows the strength of the effect in individual experiments, the ordinate is the number of experiments with a given strength. An average of more than 12 000 experiments over a period of 10 years on 12 cell lines. Adapted from Kaznacheev and Mikhailova (1981).

Fig. 3. Strength of the mirror cytopathic effect averaged from more than 12 000 experiments over the period of 10 years on 12 cell lines. Adapted from Kaznacheev and Mikhailova (1981). M. Cifra et al. / Progress in Biophysics and Molecular Biology 105 (2011) 223—246

Fig. 5. Histogram of the strength of the mirror cythopathic effect (dependent on UV EMF cellular interactions) in November, statistically the least favorable month. The abscissa shows the strength of the effect in individual experiments, ordinate is the number of experiments with a given strength. An average of more than 12 000 experiments over a period of 10 years on 12 cell lines. Adapted from Kaznacheev and Mikhailova (1981).

Corresponding author. Institute of Photonics and Electronics, Academy of Sciences of the Czech Republic, Prague, Czech Republic. Tel.: +420 266 773 528. E-mail address: cifra@ufe.cz (M. Cifra). TIRT: Attn: //wrwrw iufe c7/—cifra/ Chemical and electrical interaction within and between cells is well established. Just the opposite is true about cellular interactions via other physical fields. The most probable candidate for an other form of cellular interaction is the electromagnetic field. We review theories and experiments on how cells can generate and detect electromagnetic fields generally, and if the cell-generated electromagnetic field can mediate cellular interactions. We do not limit here ourselves to specialized electro-excitable cells. Rather we describe physical processes that are of a more general nature and probably present in almost every type of living cell. The spectral range included is broad; from kHz to the visible part of the electro- magnetic spectrum. We show that there is a rather large number of theories on how cells can generate and detect electromagnetic fields and discuss experimental evidence on electromagnetic cellular inter- actions in the modern scientific literature. Although small, it is continuously accumulating.

Direct electronic detection of EMF cellular signals. Indirect detection of cellular EMF, for instance by its dieletrophoretic effect, is not included. Table 1

lectromagnetic distant interactions of biosystems. Quartz is transparent basically for wavelengths of EMFs longer than 170 nm, normal glass is transparent usually for wavelength: ger than 350 nm. The upper limit of transparency is in near the infra-red at wavelengths of about 2000 nm. Exact transmission depends on the composition of the glass and it: lickness.

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An estimation of the number of cells in the human body

by Federica Facchin and

2013, Annals of Human Biology

Background: All living organisms are made of individual and identifiable cells, whose number, together with their size and type, ultimately defines the structure and functions of an organism. While the total cell number of lower organisms... more

An approximation of the cell/organ volume was obtained by the following formula:

*References are cited by the specific ‘‘Original article’’. {References are cited by the specific ‘‘Website’’. Table Al. Estimations of human total cell number from bibliographical search.

Table B1. Total cell number of organs or cell types.

Bibliographical method is highlighted with *, while an integration of methods with 7.

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A New Generation of the IMAGIC Image Processing System

by Elena C

1996, Journal of Structural Biology

One of the aims of modern microscopy is to quantify two-, three-, or even four-dimensional phenomena in biology, medicine, and material sciences. The requirements imposed on software by such data processing are exemplified by the design... more

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Multiple UPGMA and Neighbor-joining Trees and the Performance of Some Computer Packages

by Thierry Backeljau

Although the unweighted pair-group method using arithmetic averages (UPGMA) and neighbor-joining (NJ) algorithms are designed to produce single trees, they may derive more than one topology from a single matrix, depending on the order of... more

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Primary Charge Separation Routes in the BChl:BPhe Heterodimer Reaction Centers of Rhodobacter sphaeroides

by M. Van Brederode and

1999, Biochemistry

Energy transfer and the primary charge separation process are studied as a function of excitation wavelength in membrane-bound reaction centers of Rhodobacter sphaeroides in which the excitonically coupled bacteriochlorophyll homodimer is... more

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Free radicals, metals and antioxidants in oxidative stress-induced cancer

by inter milan

2006, Chemico-biological Interactions

Oxygen-free radicals, more generally known as reactive oxygen species (ROS) along with reactive nitrogen species (RNS) are well recognised for playing a dual role as both deleterious and beneficial species. The "two-faced" character of... more

Oxygen-free radicals, more generally known as reactive oxygen species (ROS) along with reactive nitrogen species (RNS) are well recognised for playing a dual role as both deleterious and beneficial species. The "two-faced" character of ROS is substantiated by growing body of evidence that ROS within cells act as secondary messengers in intracellular signalling cascades, which induce and maintain the oncogenic phenotype of cancer cells, however, ROS can also induce cellular senescence and apoptosis and can therefore function as anti-tumourigenic species. The cumulative production of ROS/RNS through either endogenous or exogenous insults is termed oxidative stress and is common for many types of cancer cell that are linked with altered redox regulation of cellular signalling pathways. Oxidative stress induces a cellular redox imbalance which has been found to be present in various cancer cells compared with normal cells; the redox imbalance thus may be related to oncogenic stimulation. DNA mutation is a critical step in carcinogenesis and elevated levels of oxidative DNA lesions (8-OH-G) have been noted in various tumours, strongly implicating such damage in the etiology of cancer. It appears that the DNA damage is predominantly linked with the initiation process. This review examines the evidence for involvement of the oxidative stress in the carcinogenesis process. Attention is focused on structural, chemical and biochemical aspects of free radicals, the endogenous and exogenous sources of their generation, the metal (iron, copper, chromium, cobalt, vanadium, cadmium, arsenic, nickel)-mediated formation of free radicals (e.g. Fenton chemistry), the DNA damage (both mitochondrial and nuclear), the damage to lipids and proteins by free radicals, the phenomenon of oxidative stress, cancer and the redox environment of a cell, the mechanisms of carcinogenesis and the role of signalling cascades by ROS; in particular, ROS activation of AP-1 (activator protein) and NF-B (nuclear factor kappa B) signal transduction pathways, which in turn lead to the transcription of genes involved in cell growth regulatory pathways. The role of enzymatic (superoxide dismutase (Cu, Zn-SOD, Mn-SOD), catalase, glutathione peroxidase) and non-enzymatic antioxidants (Vitamin C, Vitamin E, carotenoids, thiol antioxidants (glutathione, thioredoxin and lipoic acid), flavonoids, selenium and others) in the process of carcinogenesis as well as the antioxidant interactions with various regulatory factors, including Ref-1, NF-B, AP-1 are also reviewed.

Fig. 1. Biological reductants of Cr(V1) and its reactions (for description, see the text).

Fig. 2. Reaction of guanine with hydroxyl radical.

Fig. 3. Various pathways of lipid peroxidation. The methylene groups of polyunsaturated fatty acids are highly susceptible to oxidation and their hydrogen atoms, after the interaction with radical R*, are removed to form carbon-centred radicals 1° (reaction (1)). Carbon-centred radicals react with molecular dioxygen to form peroxy] radicals (reactions (2) and (3)). If the peroxyl! radical is located at one of the ends of the double bond (3°) it is reduced to a hydroperoxide which is relatively stable in the absence of metals (reaction (4)). A peroxyl] radical located in the internal position of the fatty acid (2°) can react by cyclisation to produce a cyclic peroxide adjacent to a carbon-centred radical (reaction (5)). This can then either be reduced to form a hydroperoxide (reaction (6)) or through reaction (7) it can undergo a second cyclisation to form a bicyclic peroxide which after coupling to dioxygen and reduction yields a molecule structurally analogous to the endoperoxide. Compound 7 is an intermediate product for the production of malondialdehyde (reaction (8)). Malondialdehyde can react with DNA bases G, A, and C to form adducts MiG, MjA and M,C (reactions (9)-(11)). Peroxy! radicals located in the internal position of the fatty acid (2°) can, besides cyclisation reactions, (reaction (5)) also abstract hydrogen from the neighbouring fatty acid molecule, creating thus lipid hydroperoxides (reaction (12)). They can further react with redox metals (e.g. iron) to produce reactive alkoxy] radicals (RO®*) (reaction (13)) which, after cleavage (reaction (14)) may form, e.g. gaseous pentane; a good marker of lipid peroxidation.

Fig. 4. ROS and metal ions-induced signalling pathways. Cells communicate with each other and respond to extracellular stimuli through biological mechanisms called cell signalling or signal transduction [4,135]. Sig- nal transduction is a process enabling information to be transmitted from the outside of a cell to various functional elements inside the cell. Signal transduction is triggered by extracellular signals such as hormones, growth factors, cytokines and neurotransmitters [136]. Signals sent to the transcription machinery responsible for expression of certain genes are normally transmitted to the cell nucleus by a class of proteins called tran- scription factors. By binding to specific DNA sequences, these factors regulate the activity of RNA polymerase II. These signal transduction processes can induce var- While ROS are predominantly implicated in causing cell damage, they also play a major physiological role in several aspects of intracellular signalling and regula- tion [138]. It has been clearly demonstrated that ROS interfere with the expression of a number of genes and signal transduction pathways [135]. Because ROS are oxidants by nature, they influence the redox status and may, according to their concentration, cause either a positive response (cell proliferation) or a negative cel response (growtl tioned above, w Nn arrest radica proliferation and cell types. ROSc an thus hile hig cell death or even necrosis, the effects of ROS on cel proliferation occurred exclusively at low or transien concentrations of oxide radical and hydrogen peroxide in fact stimulate enhanced survival in a wide variety of or cell death). As already men- h concentrations of ROS cause s. Low concentrations of super- play avery important physiolog- ical role as secondary messengers [139]. Other examples include regulation of the cytosolic calcium concentration (which itself regulates the above-mentioned biological activities), regulation of protein phosphorylation, and activation of certain transcription factors such as NF-«B and the AP-1 family factors [140].

Fig. 5. Three stages model of carcinogenesis and the level of carcinogenic effect vs. level of free radicals at various stages of carcinogenic process (inset A). Initiation involves a non-lethal mutation in DNA that produces an altered cell followed by at least one round of DNA synthesis to fix the damage (e.g. 8-OH-G) pro- duced during the initiation (Fig. 5); if dividing cells are damaged for whatever reason, they are able to interrupt temporarily their cell cycle at stage G1, S, or G2 (“check- The promotion stage is characterised by the clonal expansion of initiated cells by the induction of cell pro- liferation and/or inhibition of programmed cell death (apoptosis). This process results in the formation of an identifiable focal lesion. This stage dose-dependently requires the continuous presence of the tumour promo- tion stimulus and therefore it is a reversible process [212]. Many tumour promoters have a strong inhibit- ing effect on cellular antioxidant defence systems such as SOD, catalase, glutathione, etc. While a high level of oxidative stress is cytotoxic to the cell and halts prolifer. ation by inducing apoptosis or even necrosis, a low level of oxidative stress can in fact stimulate the cell division in the promotion stage and thus stimulate the promotion of tumour growth [213]. This implies that production of ROS during this stage of carcinogenesis is the main line of ROS-related tumour promotion.

Fig. 6. Various forms of ascorbic acid (Vitamin C) and its reaction with radicals (R°).

Fig. 7. Structures of reduced (GSH) and oxidised (GSSG) glutathione.

‘ig. 9. The various pathways of glutathione (GSH) and other antioxidants (Vitamin E, Vitamin C, lipoic acid) in the management of oxidative tress. (Equations are not balanced.) Reaction (1): superoxide is dismutated by the superoxide dismutase (SOD) to hydrogen peroxide. Reaction (2). 1ydrogen peroxide is most efficiently scavenged by the enzyme glutathione peroxidase (GPx) which requires GSH as the electron donor. Reactior 3): the oxidised glutathione (GSSG) is reduced back to GSH by the enzyme glutathione reductase (Gred) which uses NADPH as the electror lonor. Reaction (4): some transition metals (e.g. Fe2*+, Cu* and others) can breakdown hydrogen peroxide to the reactive hydroxyl radical (Fentor eaction). Reaction (5): the hydroxy! radical can abstract an electron from polyunsaturated fatty acid (LH) to give rise to a carbon-centred lipic adical (L*). Reaction (6): the lipid radical (L*) can further interact with molecular oxygen to give a lipid peroxyl! radical (LOO®). Reaction (7) he lipid peroxyl radical (LOO*) is reduced within the membrane by the reduced form of vitamin E (T-OH) resulting in the formation of a lipic ry droperoxide and a radical of Vitamin E (T-O*). Reaction (8): the regeneration of Vitamin E by Vitamin C: the Vitamin E radical (T-O°) is reducec ack to Vitamin E (T-OH) by ascorbic acid (the physiological form of ascorbate is ascorbate monoanion, AscH~ ) leaving behind the ascorby] radical Asc*—). Reaction (9): the regeneration of Vitamin E by GSH: the oxidised Vitamin E radical (T-O°) is reduced by GSH. Reaction (10): The oxidisec jlutathione (GSSG) and the ascorby] radical (Asc*~) are reduced back to GSH and ascorbate monoanion, AscH, respectively, by the dihydrolipoic cid (DHLA) which is itself converted to «-lipoic acid (ALA). Reaction (11): the regeneration of DHLA from ALA using NADPH. Reaction (12) ipid hydroperoxides can break down into aldehydes, such as the strong oxidant 4-hydroxynonenal. Reaction (13): 4-hydroxynonenal is renderec nto an innocuous glutathiy] adduct (GST: glutathione S-transferase). Reaction (14): lipid hydroperoxides are reduced to alcohols and dioxygen by 3Px using GSH as the electron donor. the catalytic action of glutathionperoxidase; (iv) glu- tathione is able to regenerate the most important antiox- idants, vitamins C and E back to their active forms glutathione can reduce the tocopherol radical of Vita- min E directly, or indirectly, via reduction of semidehy- droascorbate to ascorbate (Fig. 9). The capacity of glutathione to regenerate the most important antioxidants is linked with the redox state of the glutathione disulphide-glutathione couple (GSSG/2GSH) [246]. This, in turn, has a high impact on the overall redox environment of the cell. The values of the half-cell reduction potential for the GSSG/2GSH

Fig. 8. Role of GSH in oxidation of protein sulphydryl groups.

Fig. 12. Structure of a flavonoid quercetin. (M: coordinated metal ion).

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On the mechanism of nitrogen photofixation at nanostructured iron titanate films

by Fabio Orecchini

2006, Photochemical & Photobiological Sciences

The photofixation of dinitrogen to ammonia at a nanostructured iron titanate thin film, prepared from iron(III) chloride and titanium tetraisopropylate, was established by isotopic labeling employing (15,15)N(2). It is found that traces... more

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Fluorine in Medicinal Chemistry

by Steve Swallow

2004, ChemBioChem

Scheme 2. Development of the COX 2 inhibitor Celecoxib." Replacement of a fluorine group by a methyl group reduces the very long half-life to an accepta- ble level. Scheme 1. Development of Ezetimibe (SCH58235) by optimization of the lead $CH48461.!"23! As part of the optimization, two metabolically labile sites are blocked by flu- orine substituents.

Figure 1. Effect of pK, value on the bioavailability and receptor binding for a set of 5HT;p agonists.” The nonfluorinated parent compound is a very potent receptor ligand, but has c very low bioavailability. The monofluorinated compound has a lower pK, that is still com- patible with the requirements for receptor binding, but now results in a compound of sub- stantially increased bioavaliability. The difluoro compound has a pK, of 6.7. This compound is no longer basic enough to achieve high binding affinity for the 5HT, receptor.

Figure 2. Histogram of change in logD observed upon substitution of a hydro- gen atom by a fluorine atom. On average, logD is increased by roughly 0.25.

Scheme 3. Chemical substructures observed in compounds for which a fluorine substituent decreases logD. The concept of increased lipophilicity due to H/F exchange does not appear to hold in general and should therefore be used with care. Moreover, our results might point to strategies to reduce the lipo- philicity of a compound while, at the same time, in- creasing its metabolic stability.

Figure 3. Binding of a fluorinated inhibitor to p38 kinase (pdb refcode 1au9""’). The fluorine is in close proximity to two carbonyl groups of the protein. The dis: tances between the fluorine atom and the carbon atoms of the C=O units are 3.21 and 3.47 A. Oxygen atoms are in red, nitrogen atoms in blue, carbon atoms are light gray, fluorine atoms are green, and sulfur atoms are shown in yellow. Interestingly, a very similar structural arrangement has also been observed in some other protein-ligand complexes with fluorinated ligands, for example in many fluorinated inhibitors of p38 kinase.“°*2] One example"! is shown in Figure 3. A simi- lar interaction pattern for fluorine was also observed for a factor Xa inhibitor.

Figure 5. Structure of two inhibitors with and without fluorine bound to thrombin. In the right-hand structure, th F--N distance is 3.47 A. compound is a good inhibitor of thrombin with k= 260 nm. The compound without fluorine is six times less potent (K,= 1.6 wm). We determined the X-ray structures of both com- pounds bound to human thrombin. They are shown side-by- side in Figure 5. Interestingly, there is a conformational change of the ligand on going from R=H to R=F. In the fluorinated compound, the fluorine is within hydrogen-bonding distance of the N-H group of Gly216 of thrombin, although the dis- tance is somewhat at the upper end of what would be consid- ered to be geometrically compatible with a hydrogen bond (Rey = 3.47 A). Therefore, this interaction mode certainly consti- tutes a favorable dipolar interaction. Whether one wants to call this a hydrogen bond remains a matter of personal taste.

Figure 4. Structure and binding affinity of a pair of thrombin inhibitors with and without fluorine substituent. our effort to discover novel serine protease inhibitors with antithrombotic activities, we synthesized a pair of molecules (Figure 4) that differ just by one fluorine atom. The fluorinated

Figure 6. Structure of two inhibitors of the serine protease factor Vlla with pyrazinone and benzene core structures. A similar interaction of fluorine with a protein N—H group in a series of inhibitors for the serine protease complex Tissue Factor/Factor Vila (TF/Vlla) has been described by Parlow et al.“°*”, They report a fluorinated compound (Figure 6) with

Scheme 4. Chemical structures of the DNA gyrase inhibitors nalidixic acid (left) and ciprofloxacin (right).

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Yogurt as probiotic carrier food

by Bennie Viljoen

2001, International Dairy Journal

This paper reviews the history of the development of probiotics and the effect on the human gastrointestinal microecology. Furthermore, the application of probiotics to yogurt, commonly referred to as bio-yogurt and the effectiveness of... more

Fig. 1. Changes of intestinal flora with age (Mitsuoka, 1982): (---->) Welch’s Bacilli (C. perfringens), (—-») Coliform bacteria and enterococci, (----») Bifidobacteria, (—---@) Lactobacilli, (-—-@) acter- oides, eubacteria and anaerobic streptococci. Considerable changes in the intestinal microflora occur from the day a baby is born until he or she becomes an adult. Benno, Sawada, and Mitsuoka (1984) and others studied the development of intestinal microflora in newborn babies and the changes occurring with age. The intestine of a newborn infant is devoid of intestinal flora, but immediately after birth colonisation by many bacteria begins. Within one to two days, coliforms, enterococci, clostridia and lactobacilli are detected in the faeces; within three to four days, bifidobacteria appear and become predominant around the fifth day. The coliforms and other bacteria are restricted and decrease in response to the increase of bifidobacteria (Fig. 1). Bifidobacteria counts of 10!°— 10''cfug~! faeces are common in breast-fed infants (Modler, McKellar, & Yaguchi, 1990) representing 25% of the intestinal bacteria. Lactococci, enterococci and coliforms represent less than 1% of the intestinal population, and normally Bacteroides, clostridia and other organisms are absent (Rasic, 1983). Bottle-fed babies normally have 1-log count less of bifidobacteria (10°-10'° 1/g) present in their faecal samples than breast-fed babies (Braun, 1981), and there is a tendency for bottle-fed babies to have higher levels of enterobac- teriaceae, streptococci, and other putrefactive bacteria (Yuhara, Isojima, Tsuchiya, & Mitsuoka, 1983). This

Fig. 2. The interrelationship between intestinal bacteria and human health as proposed by Mitsuoka (Ishibashi & Shimamura, 1993). In 1987, Mitsuoka proposed a hypothetical scheme in which he illustrates the interrelationship between intestinal bacteria and human health (Fig. 2) (Ishibashi & Shimamura, 1993). The intestinal bacteria were classified into three categories, namely harmful, bene- ficial, or neutral with respect to human health. Among the beneficial bacteria are Bifidobacterium and Lactoba- cilli. Harmful bacteria are Escherichia coli, Clostridium, Proteus and types of Bacteroides. These bacteria produce a variety of harmful substances, such as amines, indole, hydrogen sulfide, or phenols, from food compo- nents and cause certain intestinal problems. These

Selective/differential media for enumeration of L. acidophilus and Bifidobacterium species in the presence of yogurt starter bacteria Table 2

“A: L. acidophilus, B: Bifidobacteria, Yogurt culture: S. thermophilus and L. bulgaricus. Some examples of probiotic dairy products available on the world market*

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Voltammetric techniques for the assay of pharmaceuticals—A review

by Vinod Kumar Gupta

2011, Analytical Biochemistry

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Geoffrey's 'Very Old Book' and Penda of Mercia

by Edwin Pace

2012, Arthuriana

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The impact of cognitive training and mental stimulation on cognitive and everyday functioning of healthy older adults: A systematic review and meta-analysis

by David Loughrey and

2014, Ageing Research Reviews

This systematic review and meta-analysis investigates the impact of cognitive training and general mental stimulation on the cognitive and everyday functioning of older adults without known cognitive impairment. We examine transfer and... more

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Hypoglycemic and hypolipidemic effects and antioxidant activity of fruit extracts from Lycium barbarum

by Harold Corke

2004, Life sciences (New York, NY: …

The hypoglycemic and hypolipidemic effects of Lycium barbarum fruit water decoction, crude polysaccharide extracts (crude LBP), and purified polysaccharide fractions (LBP-X) in alloxan-induced diabetic or hyperlipidemic rabbits were... more

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