Oscillation frequency

This document illustrates how the wave motion of a shark swimming through water can be modeled mathematically and how the same principles of oscillatory motion and vortex formation can inform the design of warp-field bubbles. Both involve traveling waves, energy-efficient motion, and resonant frequencies that minimize drag or instability.

Methylammonium lead iodide (CH3NH3PbI3) hybrid perovskite in the tetragonal and orthorhombic phases have different exciton binding energies and demonstrate different excitation kinetics. Here, we explore the role that crystal structure plays in the kinetics via fluence dependent transient absorption spectroscopy. We observe stronger saturation of the free carrier concentration under high pump energy density in the orthorhombic phase relative to the tetragonal phase. We attribute this phenomenon to small dielectric constant, large exciton binding energy, and weak Coulomb screening, which results in difficult exciton dissociation under high light intensity in the orthorhombic phase. At higher excitation intensities, we observe a coherent phonon with an oscillation frequency of 23.4 cm(-1) at 77 K, whose amplitude tracks the increase of the first-order lifetime.

We measure the relative rate of production of orbitally excited (Lϭ1) states of B mesons (B**) by observing their decays into B Ϯ. We reconstruct B mesons through semileptonic decay channels using data collected in pp collisions at ͱsϭ1.8 TeV. The fraction of light B mesons that are produced as Lϭ1B** states is measured to be 0.28Ϯ0.06͑stat͒Ϯ0.03͑syst͒. We also measure the collective mass of the B** states, and quantify the result by quoting the ͑model-dependent͒ mass of the lowest B** state to be m(B 1)ϭ5.71 Ϯ0.02 GeV/c 2 .

Context. PG 1159-035, a pre-white dwarf with T eff 140 000 K, is the prototype of both two classes: the PG 1159 spectroscopic class and the DOV pulsating class. Previous studies of PG 1159-035 photometric data obtained with the Whole Earth Telescope (WET) showed a rich frequency spectrum allowing the identification of 122 pulsation modes. Analyzing the periods of pulsation, it is possible to measure the stellar mass, the rotational period and the inclination of the rotation axis, to estimate an upper limit for the magnetic field, and even to obtain information about the inner stratification of the star. Aims. We have three principal aims: to increase the number of detected and identified pulsation modes in PG 1159-035, study trapping of the star's pulsation modes, and to improve or constrain the determination of stellar parameters. Methods. We used all available WET photometric data from 1983, 1985, 1989, 1993 and 2002 to identify the pulsation periods. Results. We identified 76 additional pulsation modes, increasing to 198 the number of known pulsation modes in PG 1159-035, the largest number of modes detected in any star besides the Sun. From the period spacing we estimated a mass M/M = 0.59 ± 0.02 for PG 1159-035, with the uncertainty dominated by the models, not the observation. Deviations in the regular period spacing suggest that some of the pulsation modes are trapped, even though the star is a pre-white dwarf and the gravitational settling is ongoing. The position of the transition zone that causes the mode trapping was calculated at r c /R = 0.83 ± 0.05. From the multiplet splitting, we calculated the rotational period P rot = 1.3920 ± 0.0008 days and an upper limit for the magnetic field, B < 2000 G. The total power of the pulsation modes at the stellar surface changed less than 30% for = 1 modes and less than 50% for = 2 modes. We find no evidence of linear combinations between the 198 pulsation mode frequencies. PG 1159-035 models have not significative convection zones, supporting the hypothesis that nonlinearity arises in the convection zones in cooler pulsating white dwarf stars.

Recent observations, reported by Warner and Woudt, of Dwarf Nova Oscillations (DNOs) exhibiting frequency drift, period doubling, and 1:2:3 harmonic structure, can be understood as disc oscillations that are excited by perturbations at the spin frequency of the white dwarf or of its equatorial layers. Similar quasi-periodic disc oscillations in black hole low-mass X-ray binary (LMXB) transients in a 2:3 frequency ratio show no evidence of frequency drift and correspond to two separate modes of disc oscillation excited by an internal resonance. Just as no effects of general relativity play a role in white dwarf DNOs, no stellar surface or magnetic field effects need be invoked to explain the black hole QPOs.

We measure the relative rate of production of orbitally excited (Lϭ1) states of B mesons (B**) by observing their decays into B Ϯ. We reconstruct B mesons through semileptonic decay channels using data collected in pp collisions at ͱsϭ1.8 TeV. The fraction of light B mesons that are produced as Lϭ1B** states is measured to be 0.28Ϯ0.06͑stat͒Ϯ0.03͑syst͒. We also measure the collective mass of the B** states, and quantify the result by quoting the ͑model-dependent͒ mass of the lowest B** state to be m(B 1)ϭ5.71 Ϯ0.02 GeV/c 2 .

Methylammonium lead iodide (CH3NH3PbI3) hybrid perovskite in the tetragonal and orthorhombic phases have different exciton binding energies and demonstrate different excitation kinetics. Here, we explore the role that crystal structure plays in the kinetics via fluence dependent transient absorption spectroscopy. We observe stronger saturation of the free carrier concentration under high pump energy density in the orthorhombic phase relative to the tetragonal phase. We attribute this phenomenon to small dielectric constant, large exciton binding energy, and weak Coulomb screening, which results in difficult exciton dissociation under high light intensity in the orthorhombic phase. At higher excitation intensities, we observe a coherent phonon with an oscillation frequency of 23.4 cm(-1) at 77 K, whose amplitude tracks the increase of the first-order lifetime.

Context. PG 1159-035, a pre-white dwarf with T eff 140 000 K, is the prototype of both two classes: the PG 1159 spectroscopic class and the DOV pulsating class. Previous studies of PG 1159-035 photometric data obtained with the Whole Earth Telescope (WET) showed a rich frequency spectrum allowing the identification of 122 pulsation modes. Analyzing the periods of pulsation, it is possible to measure the stellar mass, the rotational period and the inclination of the rotation axis, to estimate an upper limit for the magnetic field, and even to obtain information about the inner stratification of the star. Aims. We have three principal aims: to increase the number of detected and identified pulsation modes in PG 1159-035, study trapping of the star's pulsation modes, and to improve or constrain the determination of stellar parameters. Methods. We used all available WET photometric data from 1983, 1985, 1989, 1993 and 2002 to identify the pulsation periods. Results. We identified 76 additional pulsation modes, increasing to 198 the number of known pulsation modes in PG 1159-035, the largest number of modes detected in any star besides the Sun. From the period spacing we estimated a mass M/M = 0.59 ± 0.02 for PG 1159-035, with the uncertainty dominated by the models, not the observation. Deviations in the regular period spacing suggest that some of the pulsation modes are trapped, even though the star is a pre-white dwarf and the gravitational settling is ongoing. The position of the transition zone that causes the mode trapping was calculated at r c /R = 0.83 ± 0.05. From the multiplet splitting, we calculated the rotational period P rot = 1.3920 ± 0.0008 days and an upper limit for the magnetic field, B < 2000 G. The total power of the pulsation modes at the stellar surface changed less than 30% for = 1 modes and less than 50% for = 2 modes. We find no evidence of linear combinations between the 198 pulsation mode frequencies. PG 1159-035 models have not significative convection zones, supporting the hypothesis that nonlinearity arises in the convection zones in cooler pulsating white dwarf stars.

We measure the relative rate of production of orbitally excited (Lϭ1) states of B mesons (B**) by observing their decays into B Ϯ. We reconstruct B mesons through semileptonic decay channels using data collected in pp collisions at ͱsϭ1.8 TeV. The fraction of light B mesons that are produced as Lϭ1B** states is measured to be 0.28Ϯ0.06͑stat͒Ϯ0.03͑syst͒. We also measure the collective mass of the B** states, and quantify the result by quoting the ͑model-dependent͒ mass of the lowest B** state to be m(B 1)ϭ5.71 Ϯ0.02 GeV/c 2 .

A novel digital oscillator topology for microelectromechanical systems (MEMS) based on bandpass sigma-delta modulation is presented. Short pulses of force of the same amplitude maintain the oscillation and the associated bit-stream output serves to know the oscillation frequency which, for low mechanical losses, is very close to the natural frequency of the MEMS resonator. Position-sensing requirements are extremely simplified because, at each sampling time, it is only necessary to know whether the resonator position is above or below the steady-state position. Continuous-time simulations are presented showing the behavior of the oscillator for different sampling frequencies and mechanical damping losses. Experimental results from an oscillator using a MEMS resonator with thermoelectric actuation and piezoresitive position sensing are presented. It is concluded that the quality of the oscillator response depends on the resonator damping losses and on the sampling frequency. The experimental results agree with the analytical and simulation results.

Methylammonium lead iodide (CH3NH3PbI3) hybrid perovskite in the tetragonal and orthorhombic phases have different exciton binding energies and demonstrate different excitation kinetics. Here, we explore the role that crystal structure plays in the kinetics via fluence dependent transient absorption spectroscopy. We observe stronger saturation of the free carrier concentration under high pump energy density in the orthorhombic phase relative to the tetragonal phase. We attribute this phenomenon to small dielectric constant, large exciton binding energy, and weak Coulomb screening, which results in difficult exciton dissociation under high light intensity in the orthorhombic phase. At higher excitation intensities, we observe a coherent phonon with an oscillation frequency of 23.4 cm(-1) at 77 K, whose amplitude tracks the increase of the first-order lifetime.

Context. PG 1159-035, a pre-white dwarf with T eff 140 000 K, is the prototype of both two classes: the PG 1159 spectroscopic class and the DOV pulsating class. Previous studies of PG 1159-035 photometric data obtained with the Whole Earth Telescope (WET) showed a rich frequency spectrum allowing the identification of 122 pulsation modes. Analyzing the periods of pulsation, it is possible to measure the stellar mass, the rotational period and the inclination of the rotation axis, to estimate an upper limit for the magnetic field, and even to obtain information about the inner stratification of the star. Aims. We have three principal aims: to increase the number of detected and identified pulsation modes in PG 1159-035, study trapping of the star's pulsation modes, and to improve or constrain the determination of stellar parameters. Methods. We used all available WET photometric data from 1983, 1985, 1989, 1993 and 2002 to identify the pulsation periods. Results. We identified 76 additional pulsation modes, increasing to 198 the number of known pulsation modes in PG 1159-035, the largest number of modes detected in any star besides the Sun. From the period spacing we estimated a mass M/M = 0.59 ± 0.02 for PG 1159-035, with the uncertainty dominated by the models, not the observation. Deviations in the regular period spacing suggest that some of the pulsation modes are trapped, even though the star is a pre-white dwarf and the gravitational settling is ongoing. The position of the transition zone that causes the mode trapping was calculated at r c /R = 0.83 ± 0.05. From the multiplet splitting, we calculated the rotational period P rot = 1.3920 ± 0.0008 days and an upper limit for the magnetic field, B < 2000 G. The total power of the pulsation modes at the stellar surface changed less than 30% for = 1 modes and less than 50% for = 2 modes. We find no evidence of linear combinations between the 198 pulsation mode frequencies. PG 1159-035 models have not significative convection zones, supporting the hypothesis that nonlinearity arises in the convection zones in cooler pulsating white dwarf stars.

We measure the relative rate of production of orbitally excited (Lϭ1) states of B mesons (B**) by observing their decays into B Ϯ. We reconstruct B mesons through semileptonic decay channels using data collected in pp collisions at ͱsϭ1.8 TeV. The fraction of light B mesons that are produced as Lϭ1B** states is measured to be 0.28Ϯ0.06͑stat͒Ϯ0.03͑syst͒. We also measure the collective mass of the B** states, and quantify the result by quoting the ͑model-dependent͒ mass of the lowest B** state to be m(B 1)ϭ5.71 Ϯ0.02 GeV/c 2 .

The aim of the present work is to assess and to demonstrate the benefits of adopting optimal experimental design theory and techniques in order to enhance the potential of field data recorded using conventional geodetic instruments. More specifically, this research focuses on Robotic Total Stations (RTS) and in kinematic applications of geodetic positioning that exhibit a cyclic/periodic pattern of motion. The computational approach adopted follows from the principles of c-and D-optimal design criteria. Data processing involves computing the amplitude of motion in two ways; (a) using a sample of consecutively ordered data recordings and (b) using a sample respecting the optimal design criteria. Analysis, confirms the utility of the method resulting an improvement (i.e. a reduction) of the oscillation amplitude variance. This conclusion applies particularly at higher frequencies of oscillations (>1 Hz). This is important as at higher frequencies the performance of RTS deteriorates, and hence large variances occur.

We measure the relative rate of production of orbitally excited (Lϭ1) states of B mesons (B**) by observing their decays into B Ϯ. We reconstruct B mesons through semileptonic decay channels using data collected in pp collisions at ͱsϭ1.8 TeV. The fraction of light B mesons that are produced as Lϭ1B** states is measured to be 0.28Ϯ0.06͑stat͒Ϯ0.03͑syst͒. We also measure the collective mass of the B** states, and quantify the result by quoting the ͑model-dependent͒ mass of the lowest B** state to be m(B 1)ϭ5.71 Ϯ0.02 GeV/c 2 .

Methylammonium lead iodide (CH3NH3PbI3) hybrid perovskite in the tetragonal and orthorhombic phases have different exciton binding energies and demonstrate different excitation kinetics. Here, we explore the role that crystal structure plays in the kinetics via fluence dependent transient absorption spectroscopy. We observe stronger saturation of the free carrier concentration under high pump energy density in the orthorhombic phase relative to the tetragonal phase. We attribute this phenomenon to small dielectric constant, large exciton binding energy, and weak Coulomb screening, which results in difficult exciton dissociation under high light intensity in the orthorhombic phase. At higher excitation intensities, we observe a coherent phonon with an oscillation frequency of 23.4 cm(-1) at 77 K, whose amplitude tracks the increase of the first-order lifetime.

Mesons comprising a beauty quark and a strange quark can oscillate between particle ($B^{0}_{s}$) and antiparticle ($\bar{B}^{0}_{s}$) flavour eigenstates, with a frequency given by the mass difference between heavy and light mass eigenstates, $\Delta m_s$. Here we present a measurement of $\Delta m_s$ using $B^{0}_{s} \to D_{s}^{-} \pi^{+}$ decays produced in proton-proton collisions collected with the LHCb detector at the Large Hadron Collider. This measurement improves upon the current $\Delta m_s$ precision by a factor of two. The oscillation frequency is found to be $\Delta m_s = 17.7683 \pm 0.0051 \pm 0.0032$ ps$^{-1}$ where the first uncertainty is statistical and the second systematic. We combine this result with previous LHCb measurements to determine $\Delta m_s = 17.7656 \pm 0.0057$ ps$^{-1}$.

This paper performs a fundamental study of very low frequency oscillations characterized by a common mode shape at all system busses (same magnitude and phase). Also known as global or frequency control oscillation mode (below 0.1 Hz), it determines frequency response performance according to NERC requirements. When poorly damped, it poses a serious threat to small signal stability in islanded interconnections (e.g., Quebec and Texas) or hydro-dominated low-inertia systems (e.g., Columbia and Ecuador). Building on the classical damping and synchronizing torque concept, an improved understanding of underlying mechanisms behind common oscillation mode apparition and its frequency and damping are achieved through analytical assessment of the impact of turbine-governor types, load voltage sensitivity as well as system inertia. By revisiting frequency stability definition in light of the damping-synchronizing torque concept, the paper in essence uncovers the important yet poorly understood notion of small-signal (oscillatory) frequency stability.

Stimulus-induced changes in oscillation frequencies may affect information flow in the brain. We investigated whether the oscillation frequency of spiking activity in cat area 17 changes as a function of the drifting direction of sinusoidal gratings. Oscillation frequencies were tuned to specific drifting directions, such that some directions induced higher oscillation frequencies than others. When activity from the same neurons was recorded at a later time point, the average oscillation frequency with which the neurons responded had also often changed. However, the direction tuning of the neurons' oscillation frequencies remained constant. Thus, while the overall oscillation frequency, across all drift directions, was state-dependent, the relative change in oscillation frequencies induced by stimulus properties was not, the tuning remaining stable.

Wavefunction at the origin with the incorporation of relativistic effect leads to singularity in a specific potential model. To regularise the wavefunction, we introduce a short distance scale here and use it to estimate masses and decay constants of B d and B s mesons within the QCD potential model.These values are then used to compute the oscillation frequency ∆m B of B d and B s mesons. The values are found to be in good agreement with experiment and other theoretical values.

The paper describes a specific case of power oscillations problem of hydroelectric power units with double regulated bulb turbine. Results of previous research are summarized and discussed. Measurements of characteristic quantities of generator and turbine are presented and analyzed in detail for few cases. Different aspects of the phenomenon are discussed and explained, and finally treatment of oscillations during operation is defined. Keywords— electromechanical oscillations; hydroelectric unit; bulb turbine

This paper performs a fundamental study of very low frequency oscillations characterized by a common mode shape at all system busses (same magnitude and phase). Also known as global or frequency control oscillation mode (below 0.1 Hz), it determines frequency response performance according to NERC requirements. When poorly damped, it poses a serious threat to small signal stability in islanded interconnections (e.g., Quebec and Texas) or hydro-dominated low-inertia systems (e.g., Columbia and Ecuador). Building on the classical damping and synchronizing torque concept, an improved understanding of underlying mechanisms behind common oscillation mode apparition and its frequency and damping are achieved through analytical assessment of the impact of turbine-governor types, load voltage sensitivity as well as system inertia. By revisiting frequency stability definition in light of the damping-synchronizing torque concept, the paper in essence uncovers the important yet poorly understood notion of small-signal (oscillatory) frequency stability.

Future power systems are more vulnerable to contingencies due to the fluctuating power generation arising from the integration of renewable resources with intermittent patterns. Aside from their intermittent nature, most of these resources can not participate in system reserves and in the entire system inertia. Therefore, higher amount of frequency deviation is foreseeable in future power systems with large penetration of renewable energy sources. In this paper, enjoying the smart load technology, a virtual inertia-based load modulation strategy is presented and compared to the conventional load modulation approach. Simulation results indicate that virtual inertia-based load modulation can achieve better generalization performance with minimum performance sacrifice compared to the conventional strategy. The detailed simulation is performed using SimPowerSystems (SPS) toolbox, in phasor mode, on the IEEE 39-bus New England test system

—Nowadays the interest in smart load technologies for primary frequency regulation is spurred due to the increasing penetration of renewable energy resources. In this paper, an improved optimal load control (improved OLC) is introduced by applying a multiobjective optimization-based gain-tuning method to the conventional OLC approach. The objective is to minimize the frequency nadir, time response, steady-state error, total load shed, and aggregated disutility of controllable loads subject to power balance over the network. Simulation results indicate that enabling a multiobjective optimization-based gain-tuning procedure in the OLC approach can provide better power system frequency regulation. Time-domain analysis confirms the superior performance of improved OLC in terms of frequency nadir (Hz), steady-state error (Hz), control effort, and NERC-based performance metrics (MW/0.1 Hz), with detailed load and wind farm models. Furthermore , small-signal analysis demonstrates that the improved OLC enhances the system closed-loop performance and stability margins by increasing the damping ratio of the system's critical modes. Index Terms—Damping control, demand response, low frequency oscillations, optimal load control, primary frequency response , spinning reserve, smart load.