Direct generation of all-optical random numbers from optical pulse amplitude chaos.

Science.gov (United States)

Li, Pu; Wang, Yun-Cai; Wang, An-Bang; Yang, Ling-Zhen; Zhang, Ming-Jiang; Zhang, Jian-Zhong

2012-02-13

We propose and theoretically demonstrate an all-optical method for directly generating all-optical random numbers from pulse amplitude chaos produced by a mode-locked fiber ring laser. Under an appropriate pump intensity, the mode-locked laser can experience a quasi-periodic route to chaos. Such a chaos consists of a stream of pulses with a fixed repetition frequency but random intensities. In this method, we do not require sampling procedure and external triggered clocks but directly quantize the chaotic pulses stream into random number sequence via an all-optical flip-flop. Moreover, our simulation results show that the pulse amplitude chaos has no periodicity and possesses a highly symmetric distribution of amplitude. Thus, in theory, the obtained random number sequence without post-processing has a high-quality randomness verified by industry-standard statistical tests.

Experimental control of Stewart's theoretical model of large amplitude moving striations

International Nuclear Information System (INIS)

Berge, G. van den; Vanmarcke, M.

1977-01-01

The longitudinal variation of the electron concentration in large amplitude moving striations, computed theoretically by Stewart, has been tested experimentally. The measurements are carried out by means of a sampling probe technique in the glow discharge of neon (I = 105 mA, 2R = 5.6 cm, p 0 = 0.79 torr) and of argon (I = 75 mA, 2R = 5.7 cm, p 0 = 0.46 torr). It is found that the measured dependence of the concentration is not consistent with the theory. (Auth.)

Theoretical and experimental analysis of amplitude control ablation and bipolar ablation in creating linear lesion and discrete lesions for treating atrial fibrillation.

Science.gov (United States)

Yan, Shengjie; Wu, Xiaomei; Wang, Weiqi

2017-09-01

Radiofrequency (RF) energy is often used to create a linear lesion or discrete lesions for blocking the accessory conduction pathways for treating atrial fibrillation. By using finite element analysis, we study the ablation effect of amplitude control ablation mode (AcM) and bipolar ablation mode (BiM) in creating a linear lesion and discrete lesions in a 5-mm-thick atrial wall; particularly, the characteristic of lesion shape has been investigated in amplitude control ablation. Computer models of multipolar catheter were developed to study the lesion dimensions in atrial walls created through AcM, BiM and special electrodes activated ablation methods in AcM and BiM. To validate the theoretical results in this study, an in vitro experiment with porcine cardiac tissue was performed. At 40 V/20 V root mean squared (RMS) of the RF voltage for AcM, the continuous and transmural lesion was created by AcM-15s, AcM-5s and AcM-ad-20V ablation in 5-mm-thick atrial wall. At 20 V RMS for BiM, the continuous but not transmural lesion was created. AcM ablation yielded asymmetrical and discrete lesions shape, whereas the lesion shape turned to more symmetrical and continuous as the electrodes alternative activated period decreased from 15 s to 5 s. Two discrete lesions were created when using AcM, AcM-ad-40V, BiM-ad-20V and BiM-ad-40V. The experimental and computational thermal lesion shapes created in cardiac tissue were in agreement. Amplitude control ablation technology and bipolar ablation technology are feasible methods to create continuous lesion or discrete for pulmonary veins isolation.

Theoretical and experimental investigations of thickness- stretch modes in 1-3 piezoelectric composites

International Nuclear Information System (INIS)

Yang, Z T; Zeng, D P; He, M; Wang, H

2015-01-01

Bulk piezoelectric ceramics operating in thickness-stretch (TSt) modes have been widely used in acoustic-related devices. However, the fundamental TSt waves are always coupled with other modes, and the occurrence of these spurious modes in bulk piezoelectric ceramics affects its performance. To suppress the spurious modes, 1-3 piezoelectric composites are promising candidates. However, theoretical modeling of multiphase ceramic composite objects is very complex. In this study, a 1-3 piezoelectric composite sample and a bulk piezoelectric sample are fabricated. The electrical impedance of these two samples are compared. A simple analytical TSt vibration mode from the three dimensional equations of linear piezoelectricity is used to model the performance of 1-3 piezoelectric composites. The theoretical results agree well with the experimental results. (paper)

Calibration and fluctuation of the secular frequency peak amplitude versus initial condition distribution of the ion cloud confined into a three-dimensional quadrupole ion trap using a fourier transform operating mode and a steady ion flow injection mode

International Nuclear Information System (INIS)

Janulyte, A.; Andre, J.; Carette, M.; Mercury, M.; Reynard, C; Zerega, Y.

2009-01-01

A specific Fourier transform operating mode is applied to a 3-dimensional quadrupolar ion trap for mass analysis (Fourier Transform Quadrupolar Ion Trap (FTQIT) Operating Mode or Mass Spectrometer). With this operating mode, an image signal, which is representative of the collective motion of simultaneously confined ions, is made up from a set of recorded time-of-flight histograms. In an ion trap, the secular frequency of ion motion depends on m/Z ratio of the ion. By Fourier transformation of the image signal, one observes the frequency peak of each confined ionic species. When only one ionic species is confined, the peak amplitude is proportional to the maximal amplitude of the image signal. The maximal amplitude of the image signal is expressed according to the operating parameters, the initial conditions of the ions and the number of ions. Simulation tools lead to fluctuation calculation of the maximal amplitude of the image signal. Two origins are explored: (1) the fluctuation of the numbers of ions according to the steady ion flow injection mode (SIFIM) used with this operating mode and (2) the distribution fluctuation of the initial positions and velocities. Initial confinement conditions, obtained with SIFIM injection mode, lead to optimal detection with small fluctuations of the peak amplitude for Fourier transform operating mode applied to an ion trap. (authors)

Improving the theoretical foundations of the multi-mode transport model

International Nuclear Information System (INIS)

Bateman, G.; Kritz, A.H.; Redd, A.J.; Erba, M.; Rewoldt, G.; Weiland, J.; Strand, P.; Kinsey, J.E.; Scott, B.

1999-01-01

A new version of the Multi-Mode transport model, designated MMM98, is being developed with improved theoretical foundations, in an ongoing effort to predict the temperature and density profiles in tokamaks. For transport near the edge of the plasma, MMM98 uses a new model based on 3-D nonlinear simulations of drift Alfven mode turbulence. Flow shear stabilization effects have been added to the Weiland model for Ion Temperature Gradient and Trapped Electron Modes, which usually dominates in most of the plasma core. For transport near the magnetic axis at high beta, a new kinetic ballooning mode model has been constructed based on FULL stability code computations. (author)

Improving the theoretical foundations of the multi-mode transport model

International Nuclear Information System (INIS)

Bateman, G.; Kritz, A.H.; Redd, A.J.; Erba, M.; Rewoldt, G.; Weiland, J.; Strand, P.; Kinsey, J.E.; Scott, B.

2001-01-01

A new version of the Multi-Mode transport model, designated MMM98, is being developed with improved theoretical foundations, in an ongoing effort to predict the temperature and density profiles in tokamaks. For transport near the edge of the plasma, MMM98 uses a new model based on 3-D nonlinear simulations of drift Alfven mode turbulence. Flow shear stabilization effects have been added to the Weiland model for Ion Temperature Gradient and Trapped Electron Modes, which usually dominates in most of the plasma core. For transport near the magnetic axis at high beta, a new kinetic ballooning mode model has been constructed based on FULL stability code computations. (author)

Theoretical analysis of mode instability in high-power fiber amplifiers

DEFF Research Database (Denmark)

Hansen, Kristian Rymann; Alkeskjold, Thomas Tanggaard; Broeng, Jes

2013-01-01

We present a simple theoretical model of transverse mode instability in high-power rare-earth doped fiber amplifiers. The model shows that efficient power transfer between the fundamental and higher-order modes of the fiber can be induced by a nonlinear interaction mediated through the thermo......-optic effect, leading to transverse mode instability. The temporal and spectral characteristics of the instability dynamics are investigated, and it is shown that the instability can be seeded by both quantum noise and signal intensity noise, while pure phase noise of the signal does not induce instability...

Two-photon spectral amplitude of entangled states resolved in separable Schmidt modes

International Nuclear Information System (INIS)

Avella, A; Brida, G; Gramegna, M; Shurupov, A; Genovese, M; Chekhova, M

2015-01-01

The ability to access high dimensionality in Hilbert spaces represents a demanding key-stone for state-of-the-art quantum information. The manipulation of entangled states in continuous variables, wavevector as well frequency, represents a powerful resource in this sense. The number of dimensions of the Hilbert space that can be used in practical information protocols can be determined by the number of Schmidt modes that it is possible to address one by one. In the case of wavevector variables, the Schmidt modes can be losslessly selected using single-mode fibre and a spatial light modulator, but no similar procedure exists for the frequency space. The aim of this work is to present a technique to engineer the spectral properties of biphoton light, emitted via ultrafast spontaneous parametric down conversion, in such a way that the two-photon spectral amplitude (TPSA) contains several non-overlapping Schmidt modes, each of which can be filtered losslessly in frequency variables. Such TPSA manipulation is operated by a fine balancing of parameters like the pump frequency, the shaping of pump pulse spectrum, the dispersion dependence of spontaneous parametric down-conversion crystals as well as their length. Measurements have been performed exploiting the group velocity dispersion induced by the passage of optical fields through dispersive media, operating a frequency-to-time two-dimensional Fourier transform of the TPSA. Exploiting this kind of measurement we experimentally demonstrate the ability to control the Schmidt modes structure in TPSA through the pump spectrum manipulation. (paper)

Amplitudes of solar p modes: Modelling of the eddy time-correlation function

Energy Technology Data Exchange (ETDEWEB)

Belkacem, K [Institut d' Astrophysique et de Geophysique, Universite de Liege, Allee du 6 Aout 17-B 4000 Liege (Belgium); Samadi, R; Goupil, M J, E-mail: Kevin.Belkacem@ulg.ac.BE [LESIA, UMR8109, Universite Pierre et Marie Curie, Universite Denis Diderot, Obs. de Paris, 92195 Meudon Cedex (France)

2011-01-01

Modelling amplitudes of stochastically excited oscillations in stars is a powerful tool for understanding the properties of the convective zones. For instance, it gives us information on the way turbulent eddies are temporally correlated in a very large Reynolds number regime. We discuss the way the time correlation between eddies is modelled and we present recent theoretical developments as well as observational results. Eventually, we discuss the physical underlying meaning of the results by introducing the Ornstein-Uhlenbeck process, which is a sub-class of a Gaussian Markov process.

Variability of phase and amplitude fronts due to horizontal refraction in shallow water.

Science.gov (United States)

Katsnelson, Boris G; Grigorev, Valery A; Lynch, James F

2018-01-01

The variability of the interference pattern of a narrow-band sound signal in a shallow water waveguide in the horizontal plane in the presence of horizontal stratification, in particular due to linear internal waves, is studied. It is shown that lines of constant phase (a phase front) and lines of constant amplitude/envelope (an amplitude front) for each waveguide mode may have different directions in the spatial vicinity of the point of reception. The angle between them depends on the waveguide's parameters, the mode number, and the sound frequency. Theoretical estimates and data processing methodology for obtaining these angles from experimental data recorded by a horizontal line array are proposed. The behavior of the angles, which are obtained for two episodes from the Shallow Water 2006 (SW06) experiment, show agreement with the theory presented.

Monitoring and manipulating Higgs and Goldstone modes in a supersolid quantum gas.

Science.gov (United States)

Léonard, Julian; Morales, Andrea; Zupancic, Philip; Donner, Tobias; Esslinger, Tilman

2017-12-15

Higgs and Goldstone modes are collective excitations of the amplitude and phase of an order parameter that is related to the breaking of a continuous symmetry. We directly studied these modes in a supersolid quantum gas created by coupling a Bose-Einstein condensate to two optical cavities, whose field amplitudes form the real and imaginary parts of a U(1)-symmetric order parameter. Monitoring the cavity fields in real time allowed us to observe the dynamics of the associated Higgs and Goldstone modes and revealed their amplitude and phase nature. We used a spectroscopic method to measure their frequencies, and we gave a tunable mass to the Goldstone mode by exploring the crossover between continuous and discrete symmetry. Our experiments link spectroscopic measurements to the theoretical concept of Higgs and Goldstone modes. Copyright © 2017 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.

Theoretical analysis of ejector refrigeration system performance under overall modes

International Nuclear Information System (INIS)

Chen, Weixiong; Shi, Chaoyin; Zhang, Shuangping; Chen, Huiqiang; Chong, Daotong; Yan, Junjie

2017-01-01

Highlights: • Real gas theoretical model is used to get ejector performance at critical/sub-critical modes. • The model has a better accuracy against the experiment results compared to ideal gas model. • The overall performances of two refrigerants are analyzed based on the parameter analysis. - Abstract: The ejector refrigeration integrated in the air-conditioning system is a promising technology, because it could be driven by the low grade energy. In the present study, a theoretical calculation based on the real gas property is put forward to estimate the ejector refrigeration system performance under overall modes (critical/sub-critical modes). The experimental data from literature are applied to validate the proposed model. The findings show that the proposed model has higher accuracy compared to the model using the ideal gas law, especially when the ejector operates at sub-critical mode. Then, the performances of the ejector refrigeration circle using different refrigerants are analyzed. R290 and R134a are selected as typical refrigerants by considering the aspects of COP, environmental impact, safety and economy. Finally, the ejector refrigeration performance is investigated under variable operation conditions with R290 and R134a as refrigerants. The results show that the R290 ejector circle has higher COP under critical mode and could operate at low evaporator temperature. However, the performance would decrease rapidly at high condenser temperature. The performance of R134a ejector circle is the opposite, with relatively lower COP, and higher COP at high condenser temperature compared to R290.

Theoretical and experimental study of modes associated to ion cyclotron heating on TFR

International Nuclear Information System (INIS)

Pignol, L.

1985-05-01

In this work, the ion cyclotron wave evolution is followed thanks to a coherent scattering device using carbon dioxide laser radiation. A theoretical part presents the dispersion equation that obey the waves excited in the plasma by antenna emitting ion cyclotron frequency. Then measurements given by the diagnostic are given. Fast and slow waves evidenced theoretically, are experimentally observed. Two simple theoretical models allow to extract physical quantities characteristics of the two modes. These two modes are followed along the radial coordinate of the tore and their behavior through the hybrid curve is studied. measured spectra shape is shown to confirm the described numerical code validity. Time study of the slow wave shows of internal relaxation phenomenon of plasma [fr

Amplitude Modulation in the δ Sct star KIC 7106205

Directory of Open Access Journals (Sweden)

Bowman Dominic. M.

2015-01-01

Full Text Available The δ Sct star KIC 7106205 showed amplitude modulation in a single p mode, whilst all other p and g modes remained stable in amplitude and phase over 1470 d of the Kepler dataset. The data were divided into 30 time bins of equal length and a series of consecutive Fourier transforms was calculated. A fixed frequency, calculated from a least-squares fit of all data, allowed amplitude and phase for every mode in each time bin to be tracked. The missing p mode energy was not transferred to any other visible modes.

Relaxation oscillations induced by amplitude-dependent frequency in dissipative trapped electron mode turbulence

International Nuclear Information System (INIS)

Terry, P.W.; Ware, A.S.; Newman, D.E.

1994-01-01

A nonlinear frequency shift in dissipative trapped electron mode turbulence is shown to give rise to a relaxation oscillation in the saturated power density spectrum. A simple non-Markovian closure for the coupled evolution of ion momentum and electron density response is developed to describe the oscillations. From solutions of a nonlinear oscillator model based on the closure, it is found that the oscillation is driven by the growth rate, as modified by the amplitude-dependent frequency shift, with inertia provided by the memory of the growth rate of prior amplitudes. This memory arises from time-history integrals common to statistical closures. The memory associated with a finite time of energy transfer between coupled spectrum components does not sustain the oscillation in the simple model. Solutions of the model agree qualitatively with the time-dependent numerical solutions of the original dissipative trapped electron model, yielding oscillations with the proper phase relationship between the fluctuation energy and the frequency shift, the proper evolution of the wave number spectrum shape and particle flux, and a realistic period

Amplitudes of solar-like oscillations in red giants: Departures from the quasi-adiabatic approximation

Directory of Open Access Journals (Sweden)

Barban C.

2013-03-01

Full Text Available CoRoT and Kepler measurements reveal us that the amplitudes of solar-like oscillations detected in red giant stars scale from stars to stars in a characteristic way. This observed scaling relation is not yet fully understood but constitutes potentially a powerful diagnostic about mode physics. Quasi-adiabatic theoretical scaling relations in terms of mode amplitudes result in systematic and large differences with the measurements performed for red giant stars. The use of a non-adiabatic intensity-velocity relation derived from a non-adiabatic pulsation code significantly reduces the discrepancy with the CoRoT measurements. The origin of the remaining difference is still unknown. Departure from adiabatic eigenfunction is a very likely explanation that is investigated in the present work using a 3D hydrodynamical model of the surface layers of a representative red giant star.

Suppressed phase variations in a high amplitude rapidly oscillating Ap star pulsating in a distorted quadrupole mode

Science.gov (United States)

Holdsworth, Daniel L.; Saio, H.; Bowman, D. M.; Kurtz, D. W.; Sefako, R. R.; Joyce, M.; Lambert, T.; Smalley, B.

2018-05-01

We present the results of a multisite photometric observing campaign on the rapidly oscillating Ap (roAp) star 2MASS 16400299-0737293 (J1640; V = 12.7). We analyse photometric B data to show the star pulsates at a frequency of 151.93 d-1 (1758.45 μHz; P = 9.5 min) with a peak-to-peak amplitude of 20.68 mmag, making it one of the highest amplitude roAp stars. No further pulsation modes are detected. The stellar rotation period is measured at 3.674 7 ± 0.000 5 d, and we show that rotational modulation due to spots is in antiphase between broad-band and B observations. Analysis and modelling of the pulsation reveals this star to be pulsating in a distorted quadrupole mode, but with a strong spherically symmetric component. The pulsational phase variation in this star is suppressed, leading to the conclusion that the contribution of ℓ > 2 components dictate the shape of phase variations in roAp stars that pulsate in quadrupole modes. This is only the fourth time such a strong pulsation phase suppression has been observed, leading us to question the mechanisms at work in these stars. We classify J1640 as an A7 Vp SrEu(Cr) star through analysis of classification resolution spectra.

How to adapt broad-band gravitational-wave searches for r-modes

International Nuclear Information System (INIS)

Owen, Benjamin J.

2010-01-01

Up to now there has been no search for gravitational waves from the r-modes of neutron stars in spite of the theoretical interest in the subject. Several oddities of r-modes must be addressed to obtain an observational result: The gravitational radiation field is dominated by the mass current (gravitomagnetic) quadrupole rather than the usual mass quadrupole, and the consequent difference in polarization affects detection statistics and parameter estimation. To astrophysically interpret a detection or upper limit it is necessary to convert the gravitational-wave amplitude to an r-mode amplitude. Also, it is helpful to know indirect limits on gravitational-wave emission to gauge the interest of various searches. Here I address these issues, thereby providing the ingredients to adapt broad-band searches for continuous gravitational waves to obtain r-mode results. I also show that searches of existing data can already have interesting sensitivities to r-modes.

CONSTRAINING THE R-MODE SATURATION AMPLITUDE FROM A HYPOTHETICAL DETECTION OF R-MODE GRAVITATIONAL WAVES FROM A NEWBORN NEUTRON STAR: SENSITIVITY STUDY

International Nuclear Information System (INIS)

Mytidis, Antonis; Whiting, Bernard; Coughlin, Michael

2015-01-01

This paper consists of two related parts: in the first part we derive an expression of the moment of inertia (MOI) of a neutron star as a function of observables from a hypothetical r-mode gravitational-wave detection. For a given r-mode detection we show how the value of the MOI of a neutron star constrains the equation of state (EOS) of the matter in the core of the neutron star. Subsequently, for each candidate EOS, we derive a possible value of the saturation amplitude, α, of the r-mode oscillations on the neutron star. Additionally, we argue that an r-mode detection will provide clues about the cooling rate mechanism of the neutron star. The above physics that can be derived from a hypothetical r-mode detection constitutes our motivation for the second part of the paper. In that part we present a detection strategy to efficiently search for r-modes in gravitational-wave data. R-mode signals were injected into simulated noise colored with the advanced LIGO (aLIGO) and Einstein Telescope (ET) sensitivity curves. The r-mode waveforms used are those predicted by early theories based on polytropic EOS neutron star matter. In our best case scenario (α of order 10 −1 ), the maximum detection distance when using the aLIGO sensitivity curve is ∼1 Mpc (supernova event rate of 3–4 per century) while the maximum detection distance when using the ET sensitivity curve is ∼10 Mpc (supernova event rate of 1–2 per year)

Nonlinear behavior of multiple-helicity resistive interchange modes near marginally stable states

International Nuclear Information System (INIS)

Sugama, Hideo; Nakajima, Noriyoshi; Wakatani, Masahiro.

1991-05-01

Nonlinear behavior of resistive interchange modes near marginally stable states is theoretically studied under the multiple-helicity condition. Reduced fluid equations in the sheared slab configuration are used in order to treat a local transport problem. With the use of the invariance property of local reduced fluid model equations under a transformation between the modes with different rational surfaces, weakly nonlinear theories for single-helicity modes by Hamaguchi and Nakajima are extended to the multiple-helicity case and applied to the resistive interchange modes. We derive the nonlinear amplitude equations of the multiple-helicity modes, from which the convective transport in the saturated state is obtained. It is shown how the convective transport is enhanced by nonlinear interaction between modes with different rational surfaces compared with the single-helicity case. We confirm that theoretical results are in good agreement with direct numerical simulations. (author)

Introduction to focus issue: Mixed mode oscillations: Experiment, computation, and analysis

DEFF Research Database (Denmark)

Brøns, Morten; Kaper, T.J.; Rotstein, H.G.

2008-01-01

Mixed mode oscillations ( MMOs ) occur when a dynamical system switches between fast and slow motion and small and large amplitude. MMOs appear in a variety of systems in nature, and may be simple or complex. This focus issue presents a series of articles on theoretical, numerical, and experiment...

Theoretic base of Edge Local Mode triggering by vertical displacements

Energy Technology Data Exchange (ETDEWEB)

Wang, Z. T. [Southwestern Institute of Physics, Chengdu 610041 (China); College of Physics Science and Technology, Sichuan University, Chengdu 610065 (China); He, Z. X.; Wang, Z. H. [Southwestern Institute of Physics, Chengdu 610041 (China); Wu, N.; Tang, C. J. [College of Physics Science and Technology, Sichuan University, Chengdu 610065 (China)

2015-05-15

Vertical instability is studied with R-dependent displacement. For Solovev's configuration, the stability boundary of the vertical instability is calculated. The pressure gradient is a destabilizing factor which is contrary to Rebhan's result. Equilibrium parallel current density, j{sub //}, at plasma boundary is a drive of the vertical instability similar to Peeling-ballooning modes; however, the vertical instability cannot be stabilized by the magnetic shear which tends towards infinity near the separatrix. The induced current observed in the Edge Local Mode (ELM) triggering experiment by vertical modulation is derived. The theory provides some theoretic explanation for the mitigation of type-I ELMS on ASDEX Upgrade. The principle could be also used for ITER.

Relationships between gastric slow wave frequency, velocity, and extracellular amplitude studied by a joint experimental-theoretical approach.

Science.gov (United States)

Wang, T H-H; Du, P; Angeli, T R; Paskaranandavadivel, N; Erickson, J C; Abell, T L; Cheng, L K; O'Grady, G

2018-01-01

Gastric slow wave dysrhythmias are accompanied by deviations in frequency, velocity, and extracellular amplitude, but the inherent association between these parameters in normal activity still requires clarification. This study quantified these associations using a joint experimental-theoretical approach. Gastric pacing was conducted in pigs with simultaneous high-resolution slow wave mapping (32-256 electrodes; 4-7.6 mm spacing). Relationships between period, velocity, and amplitude were quantified and correlated for each wavefront. Human data from two existing mapping control cohorts were analyzed to extract and correlate these same parameters. A validated biophysically based ICC model was also applied in silico to quantify velocity-period relationships during entrainment simulations and velocity-amplitude relationships from membrane potential equations. Porcine pacing studies identified positive correlations for velocity-period (0.13 mm s -1 per 1 s, r 2 =.63, Prelationships and demonstrated dependence on the slow wave recovery phase. Simulated membrane potential relationships were close to these experimental results (100 μV per 1 mm s -1 ). These data quantify the relationships between slow wave frequency, velocity, and extracellular amplitude. The results from both human and porcine studies were in keeping with biophysical models, demonstrating concordance with ICC biophysics. These relationships are important in the regulation of gastric motility and will help to guide interpretations of dysrhythmias. © 2017 John Wiley & Sons Ltd.

Kepler observations of the high-amplitude δ Scuti star V2367 Cyg

DEFF Research Database (Denmark)

Balona, L. A.; Lenz, P.; Antoci, V.

2012-01-01

We analyse Kepler observations of the high-amplitude δ Scuti (HADS) star V2367 Cyg (KIC 9408694). The variations are dominated by a mode with frequency f1= 5.6611 d−1. Two other independent modes with f2= 7.1490 d−1 and f3= 7.7756 d−1 have amplitudes an order of magnitude smaller than f1. Nearly...... all the light variation is due to these three modes and their combination frequencies, but several hundred other frequencies of very low amplitude are also present. The amplitudes of the principal modes may vary slightly with time. The star has twice the projected rotational velocity of any other HADS...... star, which makes it unusual. We find a correlation between the phases of the combination frequencies and their pulsation frequencies, which is not understood. Since modes of highest amplitude in HADS stars are normally radial modes, we assumed that this would also be true in this star. However...

Online channel operation mode: Game theoretical analysis from the supply chain power structure

Directory of Open Access Journals (Sweden)

Song Huang

2015-11-01

Full Text Available Purpose: Dual-channels have been widely used in practice, and the pricing decisions and the online channel operation mode choice have been the core problems in dual-channel supply chain management. This paper focuses on the online channel operation mode choice from the supply chain power structures based on game theoretical analysis. Design/methodology/approach: This paper utilizes three kinds of game theoretical models to analyze the impact of supply chain power structures on the optimal pricing and online channel operation mode choice. Findings: Results derived in this paper indicate that when the self-price elasticity is large, the power structures have no direct impact on the decisions. However, when the self-price elasticity is small and customers’ preference for the online channel is low, then in the MS market, it is better for the retailer to operate the online channel, while in the RS market or in the VN market, it is better for the manufacturer to operate the online channel. Research limitations/implications: In this paper, we do not consider stochastic demand and asymmetric information, which may not well suit the reality. Originality/value: This paper provides a different perspective to analyze the impact of supply chain power structures on the pricing decisions and online channel operation mode choice. The comparison of these two online channel operation modes in this paper is also a unique point.

Revealing Extremely Low Energy Amplitude Modes in the Charge-Density-Wave Compound LaAgSb_{2}.

Science.gov (United States)

Chen, R Y; Zhang, S J; Zhang, M Y; Dong, T; Wang, N L

2017-03-10

Using infrared spectroscopy and ultrafast pump probe measurement, we have studied the two charge-density-wave (CDW) instabilities in the layered compound LaAgSb_{2}. The development of CDW energy gaps was clearly observed by optical spectroscopy, which removed most of the free carrier spectral weight. More interestingly, our time-resolved measurements revealed two coherent oscillations that softened by approaching the two phase transition temperatures, respectively. We addressed that these two oscillations come from the amplitude modes of CDW collective excitations, the surprisingly low energies (0.12 THz and 0.34 THz for the higher and lower temperature ones, respectively) of which are associated with the extremely small nesting wave vectors. Additionally, the amplitude and relaxation time of photoinduced reflectivity of LaAgSb_{2} single crystals stayed unchanged across the CDW phase transitions, which is quite rare and deserves further investigation.

Adaptive suboptimal second-order sliding mode control for microgrids

Science.gov (United States)

Incremona, Gian Paolo; Cucuzzella, Michele; Ferrara, Antonella

2016-09-01

This paper deals with the design of adaptive suboptimal second-order sliding mode (ASSOSM) control laws for grid-connected microgrids. Due to the presence of the inverter, of unpredicted load changes, of switching among different renewable energy sources, and of electrical parameters variations, the microgrid model is usually affected by uncertain terms which are bounded, but with unknown upper bounds. To theoretically frame the control problem, the class of second-order systems in Brunovsky canonical form, characterised by the presence of matched uncertain terms with unknown bounds, is first considered. Four adaptive strategies are designed, analysed and compared to select the most effective ones to be applied to the microgrid case study. In the first two strategies, the control amplitude is continuously adjusted, so as to arrive at dominating the effect of the uncertainty on the controlled system. When a suitable control amplitude is attained, the origin of the state space of the auxiliary system becomes attractive. In the other two strategies, a suitable blend between two components, one mainly working during the reaching phase, the other being the predominant one in a vicinity of the sliding manifold, is generated, so as to reduce the control amplitude in steady state. The microgrid system in a grid-connected operation mode, controlled via the selected ASSOSM control strategies, exhibits appreciable stability properties, as proved theoretically and shown in simulation.

FM-AM Conversion Induced by Polarization Mode Dispersion in Fiber Systems

International Nuclear Information System (INIS)

Xiao-Dong, Huang; Sheng-Zhi, Zhao; Jian-Jun, Wang; Ming-Zhong, Li; Dang-Peng, Xu; Hong-Huan, Lin; Rui, Zhang; Ying, Deng; Xiao-Min, Zhang

2010-01-01

The conversion of the frequency modulated pulse induced from frequency modulation (FM) to amplitude modulation (AM) by the polarization mode dispersion (PMD) is theoretically and experimentally investigated. When there is no polarizer at the output end of a fiber system, the amplitude modulation depth is stable by 8%. Random amplitude modulation is observed when a polarizer is placed at the output end of the fiber system. The observed minimum and maximum modulation depths in our experiment are 5% and 80%, respectively. Simulation results show that the amplitude modulation is stable by 4% induced mainly by group velocity dispersion (GVD) when there is no polarizer, and the amplitude modulation depth displays the random variation character induced by the GVD and PMD. Lastly, a new fiber system scheme is proposed and little amplitude modulation is observed at the top of the output pulse

Basic mode of nonlinear spin-wave resonance in normally magnetized ferrite films

International Nuclear Information System (INIS)

Gulyaev, Yu.V.; Zil'berman, P.E.; Timiryazev, A.G.; Tikhomirova, M.P.

2000-01-01

Modes of nonlinear and spin-wave resonance (SWR) in the normally magnetized ferrite films were studied both theoretically and experimentally. The particular emphasis was placed on the basic mode of SWR. One showed theoretically that with the growth of the precession amplitude the profile of the basic mode changed. The nonlinear shift of the resonance field depends on the parameters of fixing of the surface spins. Films of ferroyttrium garnet (FYG) with strong gradient of the single-axis anisotropy field along the film thickness, as well as, FYG films of the submicron thickness where investigated experimentally. With the intensification of Uhf-power one observed the sublinear shift of the basic mode resonance field following by the superlinear growth of the absorbed power. That kind of behaviour is explained by variation of the profile of the varying magnetization space distribution [ru

Charmless B{sub (s)} → VV decays in factorization-assisted topological-amplitude approach

Energy Technology Data Exchange (ETDEWEB)

Wang, Chao; Zhang, Qi-An [CAS, Institute of High Energy Physics, P.O. Box 918, Beijing (China); University of Chinese Academy of Sciences, School of Physics, Beijing (China); Li, Ying [Yantai University, Department of Physics, Yantai (China); CAS, State Key Laboratory of Theoretical Physics, Institute of Theoretical Physics, Beijing (China); Lue, Cai-Dian [CAS, Institute of High Energy Physics, P.O. Box 918, Beijing (China); University of Chinese Academy of Sciences, School of Physics, Beijing (China); CAS, State Key Laboratory of Theoretical Physics, Institute of Theoretical Physics, Beijing (China)

2017-05-15

Within the factorization-assisted topological-amplitude approach, we studied the 33 charmless B{sub (s)} → VV decays, where V stands for a light vector meson. According to the flavor flows, the amplitude of each process can be decomposed into eight different topologies. In contrast to the conventional flavor diagrammatic approach, we further factorize each topological amplitude into decay constant, form factors and unknown universal parameters. By χ{sup 2} fitting 46 experimental observables, we extracted 10 theoretical parameters with χ{sup 2} per degree of freedom around 2. Using the fitted parameters, we calculated the branching fractions, polarization fractions, CP asymmetries and relative phases between polarization amplitudes of each decay mode. The decay channels dominated by tree diagram have large branching fractions and large longitudinal polarization fraction. The branching fractions and longitudinal polarization fractions of color-suppressed decays become smaller. Current experimental data of large transverse polarization fractions in the penguin dominant decay channels can be explained by only one transverse amplitude of penguin annihilation diagram. Our predictions of the not yet measured channels can be tested in the ongoing LHCb experiment and the Belle-II experiment in the future. (orig.)

TMX tandem-mirror experiments and thermal-barrier theoretical studies

International Nuclear Information System (INIS)

Simonen, T.C.; Baldwin, D.E.; Allen, S.L.

1982-01-01

This paper describes recent analysis of energy confinement in the Tandem Mirror Experiment (TMX). TMX data also indicates that warm plasma limits the amplitude of the anisotropy driven Alfven ion cyclotron (AIC) mode. Theoretical calculations show strong AIC stabilization with off-normal beam injection as planned in TMX-U and MFTF-B. This paper reports results of theoretical analysis of hot electrons in thermal barriers including electron heating calculations by Monte Carlo and Fokker-Planck codes and analysis of hot electron MHD and microinstability. Initial results from the TMX-U experiment are presented which show the presence of sloshing ions

Destabilization of a peeling-ballooning mode by a toroidal rotation in tokamaks

International Nuclear Information System (INIS)

Aiba, N.; Hirota, M.; Tokuda, S.; Furukawa, M.

2009-01-01

Full text: From the viewpoint of the heat load on the divertor, Type-I edge localized mode (ELM) needs to be suppressed or the amplitude of this ELM needs to be reduced. In JT-60U, some experimental results showed that the ELM frequency depends on the toroidal rotation, and the rapid rotation in the counter direction of the plasma current changes from Type-I ELM to Grassy ELM, whose frequency is high and the amplitude is small. Recent experimental and theoretical/numerical studies in a static system have identified that both Type-I and Grassy ELMs are considered ideal magnetohydrodynamic (MHD) modes destabilizing near the plasma surface, called peeling-ballooning modes. To investigate the mechanism of the change of ELM frequency by a toroidal rotation, theoretical and numerical analyses are important for understanding the toroidal rotation effects on the peeling-ballooning mode. Previous works about the toroidal rotation effect on the edge MHD stability have illustrated that the toroidal rotation with shear can destabilize low/intermediate-n (<50) modes but can stabilize high-n modes, where n is the toroidal mode number. The stabilization of the high-n mode can be understood qualitatively in analogy with the infinite-n ballooning mode case. However, the destabilizing mechanism of the low/intermediate-n mode is not still clarified, and to understand the stability property related to ELM suppression/mitigation, it is important to clarify this destabilizing mechanism. In this paper, we investigate numerically the destabilizing effect of a toroidal rotation on the peeling-ballooning mode with a newly developed code MINERVA, which solves the Frieman-Rotenberg equation. Particularly, we pay attention to the effect of the centrifuged force on not only equilibrium but also change of equation of motion. (author)

Dynamic force microscopy with quartz tuning forks at high oscillation amplitudes

International Nuclear Information System (INIS)

Labardi, M

2007-01-01

Dynamic force microscopy (DFM) with the self-oscillator (SO) method allows reasonably high scanning rates even with high Q-factors of the resonant force sensor, typical of cantilevers in ultra-high vacuum and of quartz tuning forks. However, due to simpler interpretation of force spectroscopy measurements, small oscillation amplitudes (sub-nm level) are generally preferred. In applications like 'apertureless' scanning near-field optical microscopy (SNOM), oscillation amplitudes of the order of 5-10 nm are needed to increase optical sensitivity and to apply standard optical artefact suppression methods. This motivates the study of the behaviour of tuning forks driven at such high amplitudes, as compared to usual air-operated cantilevers. Both constant-excitation-amplitude (CE) and constant-oscillation-amplitude (CA) modes of SO-DFM are analysed, since the CA mode is more convenient for SNOM applications, denoting remarkable differences. In particular, possible instability effects, previously found in CE mode, are not anticipated for CA mode. It is shown how resonance and approach ('isophase') curves in both modes can be conveniently described in terms of the usual 'normalized frequency shift' γ and of a 'normalized gain' η, defined as a measurement of surface dissipation

Error Field Assessment from Driven Mode Rotation: Results from Extrap-T2R Reversed-Field-Pinch and Perspectives for ITER

Science.gov (United States)

Volpe, F. A.; Frassinetti, L.; Brunsell, P. R.; Drake, J. R.; Olofsson, K. E. J.

2012-10-01

A new ITER-relevant non-disruptive error field (EF) assessment technique not restricted to low density and thus low beta was demonstrated at the Extrap-T2R reversed field pinch. Resistive Wall Modes (RWMs) were generated and their rotation sustained by rotating magnetic perturbations. In particular, stable modes of toroidal mode number n=8 and 10 and unstable modes of n=1 were used in this experiment. Due to finite EFs, and in spite of the applied perturbations rotating uniformly and having constant amplitude, the RWMs were observed to rotate non-uniformly and be modulated in amplitude (in the case of unstable modes, the observed oscillation was superimposed to the mode growth). This behavior was used to infer the amplitude and toroidal phase of n=1, 8 and 10 EFs. The method was first tested against known, deliberately applied EFs, and then against actual intrinsic EFs. Applying equal and opposite corrections resulted in longer discharges and more uniform mode rotation, indicating good EF compensation. The results agree with a simple theoretical model. Extensions to tearing modes, to the non-uniform plasma response to rotating perturbations, and to tokamaks, including ITER, will be discussed.

Dual-Mode Measurement and Theoretical Analysis of Evaporation Kinetics of Binary Mixtures

Science.gov (United States)

Song, Hanyu; He, Chi-Ruei; Basdeo, Carl; Li, Ji-Qin; Ye, Dezhuang; Kalonia, Devendra; Li, Si-Yu; Fan, Tai-Hsi

Theoretical and experimental investigations are presented for the precision measurement of evaporation kinetics of binary mixtures using a quartz crystal resonator. A thin layer of light alcohol mixture including a volatile (methanol) and a much less volatile (1-butanol) components is deployed on top of the resonator. The normal or acoustic mode is to detect the moving liquid-vapor interface due to evaporation with a great spatial precision on the order of microns, and simultaneously the shear mode is used for in-situ detection of point viscosity or concentration of the mixture near the resonator. A one-dimensional theoretical model is developed to describe the underlying mass transfer and interfacial transport phenomena. Along with the modeling results, the transient evaporation kinetics, moving interface, and the stratification of viscosity of the liquid mixture during evaporation are simultaneously measured by the impedance response of the shear and longitudinal waves emitted from the resonator. The system can be used to characterize complicated evaporation kinetics involving multi-component fuels. American Chemical Society Petroleum Research Fund, NSF CMMI-0952646.

Theoretical analysis of the mode coupling induced by heat of large-pitch micro-structured fibers

International Nuclear Information System (INIS)

Zhang Hai-Tao; Hao Jie; Yan Ping; Gong Ma-Li; Chen Dan

2015-01-01

In this paper, a theoretical model to analyze the mode coupling induced by heat, when the fiber amplifier works at high power configuration, is proposed. The model mainly takes into consideration the mode field change due to the thermally induced refractive index change and the coupling between modes. A method to predict the largest average output power of fiber is also proposed according to the mode coupling theory. The largest average output power of a large pitch fiber with a core diameter of 190 μm and an available pulse energy of 100 mJ is predicted to be 540 W, which is the highest in large mode field fibers. (paper)

Amplitude saturation of MEMS resonators explained by autoparametric resonance

International Nuclear Information System (INIS)

Van der Avoort, C; Bontemps, J J M; Steeneken, P G; Le Phan, K; Van Beek, J T M; Van der Hout, R; Hulshof, J; Fey, R H B

2010-01-01

This paper describes a phenomenon that limits the power handling of MEMS resonators. It is observed that above a certain driving level, the resonance amplitude becomes independent of the driving level. In contrast to previous studies of power handling of MEMS resonators, it is found that this amplitude saturation cannot be explained by nonlinear terms in the spring constant or electrostatic force. Instead we show that the amplitude in our experiments is limited by nonlinear terms in the equation of motion which couple the in-plane length-extensional resonance mode to one or more out-of-plane (OOP) bending modes. We present experimental evidence for the autoparametric excitation of these OOP modes using a vibrometer. The measurements are compared to a model that can be used to predict a power-handling limit for MEMS resonators

Amplitude saturation of MEMS resonators explained by autoparametric resonance

Energy Technology Data Exchange (ETDEWEB)

Van der Avoort, C; Bontemps, J J M; Steeneken, P G; Le Phan, K; Van Beek, J T M [NXP Research, Eindhoven (Netherlands); Van der Hout, R; Hulshof, J [Department of Mathematics, VU University—Faculty of Sciences, De Boelelaan 1081a, 1081 HV Amsterdam (Netherlands); Fey, R H B, E-mail: cas.van.der.avoort@nxp.com [Department of Mechanical Engineering, Eindhoven University of Technology, PO Box 513, 5600 MB, Eindhoven (Netherlands)

2010-10-15

This paper describes a phenomenon that limits the power handling of MEMS resonators. It is observed that above a certain driving level, the resonance amplitude becomes independent of the driving level. In contrast to previous studies of power handling of MEMS resonators, it is found that this amplitude saturation cannot be explained by nonlinear terms in the spring constant or electrostatic force. Instead we show that the amplitude in our experiments is limited by nonlinear terms in the equation of motion which couple the in-plane length-extensional resonance mode to one or more out-of-plane (OOP) bending modes. We present experimental evidence for the autoparametric excitation of these OOP modes using a vibrometer. The measurements are compared to a model that can be used to predict a power-handling limit for MEMS resonators.

Suppression of an acoustic mode by an elastic mode of a liquid-filled spherical shell resonator.

Science.gov (United States)

Lonzaga, Joel B; Raymond, Jason L; Mobley, Joel; Gaitan, D Felipe

2011-02-01

The purpose of this paper is to report on the suppression of an approximately radial (radially symmetric) acoustic mode by an elastic mode of a water-filled, spherical shell resonator. The resonator, which has a 1-in. wall thickness and a 9.5-in. outer diameter, was externally driven by a small transducer bolted to the external wall. Experiments showed that for the range of drive frequencies (19.7-20.6 kHz) and sound speeds in water (1520-1570 m/s) considered in this paper, a nonradial (radially nonsymmetric) mode was also excited, in addition to the radial mode. Furthermore, as the sound speed in the liquid was changed, the resonance frequency of the nonradial mode crossed with that of the radial one and the amplitude of the latter was greatly reduced near the crossing point. The crossing of the eigenfrequency curves of these two modes was also predicted theoretically. Further calculations demonstrated that while the radial mode is an acoustic one associated with the interior fluid, the nonradial mode is an elastic one associated with the shell. Thus, the suppression of the radial acoustic mode is apparently caused by the overlapping with the nonradial elastic mode near the crossing point.

2-D modeling of dual-mode acoustic phonon excitation of a triangular nanoplate

Science.gov (United States)

Tai, Po-Tse; Yu, Pyng; Tang, Jau

2010-08-01

In this theoretical work, we investigated coherent phonon excitation of a triangular nanoplate based on 2-D Fermi-Pasta-Ulam lattice model. Based on the two-temperature model commonly used in description of laser heating of metals, we considered two kinds of forces related to electronic and lattice stresses. Based on extensive simulation and analysis, we identified two major planar phonon modes, namely, a standing wave mode related to the triangle bisector and another mode corresponding to half of the side length. This work elucidates the roles of laser-induced electronic stress and lattice stress in controlling the initial phase and the amplitude ratio between these two phonon modes.

Transverse magnetic field impact on waveguide modes of photonic crystals.

Science.gov (United States)

Sylgacheva, Daria; Khokhlov, Nikolai; Kalish, Andrey; Dagesyan, Sarkis; Prokopov, Anatoly; Shaposhnikov, Alexandr; Berzhansky, Vladimir; Nur-E-Alam, Mohammad; Vasiliev, Mikhail; Alameh, Kamal; Belotelov, Vladimir

2016-08-15

This Letter presents a theoretical and experimental study of waveguide modes of one-dimensional magneto-photonic crystals magnetized in the in-plane direction. It is shown that the propagation constants of the TM waveguide modes are sensitive to the transverse magnetization and the spectrum of the transverse magneto-optical Kerr effect has resonant features at mode excitation frequencies. Two types of structures are considered: a non-magnetic photonic crystal with an additional magnetic layer on top and a magneto-photonic crystal with a magnetic layer within each period. We found that the magneto-optical non-reciprocity effect is greater in the first case: it has a magnitude of δ∼10-4, while the second structure type demonstrates δ∼10-5 only, due to the higher asymmetry of the claddings of the magnetic layer. Experimental observations show resonant features in the optical and magneto-optical Kerr effect spectra. The measured dispersion properties are in good agreement with the theoretical predictions. An amplitude of light intensity modulation of up to 2.5% was observed for waveguide mode excitation within the magnetic top layer of the non-magnetic photonic crystal structure. The presented theoretical approach may be utilized for the design of magneto-optical sensors and modulators requiring pre-determined spectral features.

On spurious resonant modes in the MOT solution of time domain EFIE

KAUST Repository

Shi, Yifei

2013-07-01

Theoretically, internal resonant modes should not be induced in the marching-on-in-time (MOT) solution of the time domain electric field integral equation since zero initial conditions are enforced at the beginning of time marching and the internal resonant modes do not satisfy these initial conditions. However, these spurious modes are always observed in the MOT solution. It has been conjectured in the past that numerical errors might establish the necessary initial conditions and allow the incident field to induce the internal resonant modes. Systematic numerical experiments carried out in this work prove this conjecture by demonstrating that the internal resonant modes\\' amplitudes are indeed dictated by the numerical errors and the spectrum of the incident field. © 2013 IEEE.

Amplitude oscillations in a non-equilibrium polariton condensate

Science.gov (United States)

Brierley, Richard; Littlewood, Peter; Eastham, Paul

2011-03-01

Like cold atomic gases, semiconductor nanostructures provide new opportunities for exploring non-equilibrium quantum dynamics. In semiconductor microcavities the strong coupling between trapped photons and excitons produces new quasiparticles, polaritons, which can undergo Bose-Einstein condensation. Quantum quenches can be realised by rapidly creating cold exciton populations with a laser [Eastham and Phillips, PRB 79 165303 (2009)]. The mean field theory of non-equilibrium polariton condensates predicts oscillations in the condensate amplitude due to the excitation of a Higgs mode. These oscillations are the analogs of those predicted in quenched cold atomic gases and may occur in the polariton system after performing a quench or by direct excitation of the amplitude mode. We have studied the stability of these oscillations beyond mean field theory. We show that homogeneous amplitude oscillations are unstable to decay into lower energy phase modes at finite wavevectors, suggesting the onset of chaotic behaviour. The resulting hierarchy of decay processes can be understood by analogy to optical parametric oscillators in microcavities. Polariton systems thus provide an interesting opportunity to study the dynamics of Higgs-like modes in a solid state system.

Restudy of the open-superstring tree amplitudes by looking at their field-theoretical limits

International Nuclear Information System (INIS)

Hsu, R.; Yeung, W.B.; Yu, H.L.

1987-01-01

We carry out complete computations of some open- and closed-superstring tree amplitudes by using the bosonized covariant vertices. Some open-superstring amplitudes so obtained are shown to be different from those obtained in the light-cone gauge approach by some numerical factors. The low-energy limits of our five open-superstring amplitudes are then shown to match the five super Yang-Mills field amplitudes while the five light-cone gauge open-superstring amplitudes fail to do so

A non-radial oscillation mode in an accreting millisecond pulsar?

Energy Technology Data Exchange (ETDEWEB)

Strohmayer, Tod [Astrophysics Science Division and Joint Space-Science Institute, NASA' s Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Mahmoodifar, Simin [Department of Physics and Joint Space-Science Institute, University of Maryland College Park, MD 20742 (United States)

2014-03-20

We present results of targeted searches for signatures of non-radial oscillation modes (such as r- and g-modes) in neutron stars using RXTE data from several accreting millisecond X-ray pulsars (AMXPs). We search for potentially coherent signals in the neutron star rest frame by first removing the phase delays associated with the star's binary motion and computing fast Fourier transform power spectra of continuous light curves with up to 2{sup 30} time bins. We search a range of frequencies in which both r- and g-modes are theoretically expected to reside. Using data from the discovery outburst of the 435 Hz pulsar XTE J1751–305 we find a single candidate, coherent oscillation with a frequency of 0.5727597 × ν{sub spin} = 249.332609 Hz, and a fractional Fourier amplitude of 7.46 × 10{sup –4}. We estimate the significance of this feature at the 1.6 × 10{sup –3} level, slightly better than a 3σ detection. Based on the observed frequency we argue that possible mode identifications include rotationally modified g-modes associated with either a helium-rich surface layer or a density discontinuity due to electron captures on hydrogen in the accreted ocean. In the latter case the presence of sufficient hydrogen in this ultracompact system with a likely helium-rich donor would present an interesting puzzle. Alternatively, the frequency could be identified with that of an inertial mode or a core r-mode modified by the presence of a solid crust; however, the r-mode amplitude required to account for the observed modulation amplitude would induce a large spin-down rate inconsistent with the observed pulse timing measurements. For the AMXPs XTE J1814–338 and NGC 6440 X–2 we do not find any candidate oscillation signals, and we place upper limits on the fractional Fourier amplitude of any coherent oscillations in our frequency search range of 7.8 × 10{sup –4} and 5.6 × 10{sup –3}, respectively. We briefly discuss the prospects and sensitivity for

Latitudinal amplitude-phase structure of MHD waves: STARE radar observations and modeling

Directory of Open Access Journals (Sweden)

Pilipenko V.

2016-09-01

Full Text Available We have developed a numerical model that yields a steady-state distribution of field components of MHD wave in an inhomogeneous plasma box simulating the realistic magnetosphere. The problem of adequate boundary condition at the ionosphere–magnetosphere interface for coupled MHD mode is considered. To justify the model’s assumptions, we have derived the explicit inequality showing when the ionospheric inductive Hall effect can be neglected upon the consideration of Alfven wave reflection from the ionospheric boundaries. The model predicts a feature of the ULF spatial amplitude/phase distribution that has not been noticed by the field line resonance theory: the existence of a region with opposite phase delays on the source side of the resonance. This theoretical prediction is supported by the amplitude-phase latitudinal structures of Pc5 waves observed by STARE radar and IMAGE magnetometers. A gradual decrease in azimuthal wave number m at smaller L-shells was observed at longitudinally separated radar beams.

A possible explanation for the divergent projection of ENSO amplitude change under global warming

Science.gov (United States)

Chen, Lin; Li, Tim; Yu, Yongqiang; Behera, Swadhin K.

2017-12-01

The El Niño-Southern Oscillation (ENSO) is the greatest climate variability on interannual time scale, yet what controls ENSO amplitude changes under global warming (GW) is uncertain. Here we show that the fundamental factor that controls the divergent projections of ENSO amplitude change within 20 coupled general circulation models that participated in the Coupled Model Intercomparison Project phase-5 is the change of climatologic mean Pacific subtropical cell (STC), whose strength determines the meridional structure of ENSO perturbations and thus the anomalous thermocline response to the wind forcing. The change of the thermocline response is a key factor regulating the strength of Bjerknes thermocline and zonal advective feedbacks, which ultimately lead to the divergent changes in ENSO amplitude. Furthermore, by forcing an ocean general circulation mode with the change of zonal mean zonal wind stress estimated by a simple theoretical model, a weakening of the STC in future is obtained. Such a change implies that ENSO variability might strengthen under GW, which could have a profound socio-economic consequence.

Stabilization of the (2,1) tearing mode and of the current disruption in the W VII-A stellarator

International Nuclear Information System (INIS)

Bartlett, D.V.; Cannici, G.; Cattanei, G.

1980-01-01

A numerical code based on a Δ'-analysis is applied to calculate the saturated amplitude of tearing modes dependent on the current density profile. The only stellarator effect included is the additional, shearless external rotational transform in the safety factor profile q(r). In this way, the stellarator field shifts the resonant q=2 surface toward the outside, where the current density gradient is smaller, and stabilizes the (2,1) mode as observed experimentally. Also the measured dependence of the (2,1) mode amplitude on electron density and plasma current can be absolutely predicted by the calculations. - In addition to stabilizing the (2,1) tearing mode, the current disruption is suppressed in Ohmically heated W VII-A discharges for approximately >0.15. The experimental findings, together with the calculated island widths, are compared with the predictions of a theoretical model proposed by several authors to explain the current disruption. (author)

THEORETICAL MODELING OF THE FEEDBACK STABILIZATION OF EXTERNAL MHD MODES IN TOROIDAL GEOMETRY

International Nuclear Information System (INIS)

CHANCE, M.S.; CHU, M.S.; OKABAYASHI, M.; TURNBULL, A.D.

2001-02-01

OAK-B135 A theoretical framework for understanding the feedback mechanism against external MHD modes has been formulated. Efficient computational tools--the GATO stability code coupled with a substantially modified VACUUM code--have been developed to effectively design viable feedback systems against these modes. The analysis assumed a thin resistive shell and a feedback coil structure accurately modeled in θ, with only a single harmonic variation in φ. Time constants and induced currents in the enclosing resistive shell are calculated. An optimized configuration based on an idealized model have been computed for the DIII-D device. Up to 90% of the effectiveness of an ideal wall can be achieved

Bimodal atomic force microscopy driving the higher eigenmode in frequency-modulation mode: Implementation, advantages, disadvantages and comparison to the open-loop case.

Science.gov (United States)

Ebeling, Daniel; Solares, Santiago D

2013-01-01

We present an overview of the bimodal amplitude-frequency-modulation (AM-FM) imaging mode of atomic force microscopy (AFM), whereby the fundamental eigenmode is driven by using the amplitude-modulation technique (AM-AFM) while a higher eigenmode is driven by using either the constant-excitation or the constant-amplitude variant of the frequency-modulation (FM-AFM) technique. We also offer a comparison to the original bimodal AFM method, in which the higher eigenmode is driven with constant frequency and constant excitation amplitude. General as well as particular characteristics of the different driving schemes are highlighted from theoretical and experimental points of view, revealing the advantages and disadvantages of each. This study provides information and guidelines that can be useful in selecting the most appropriate operation mode to characterize different samples in the most efficient and reliable way.

Three-mode resonant coupling of collective excitations in a Bose-Einstein condensate

International Nuclear Information System (INIS)

Ma Yongli; Huang, Guoxiang; Hu Bambi

2005-01-01

We make a systematic study of the resonant mode coupling of the collective excitations at zero temperature in a Bose-Einstein condensate (BEC). (i) Based on the Gross-Pitaevskii equation we derive a set of nonlinearly coupled envelope equations for a three-mode resonant interaction (TMRI) by means of a method of multiple scales. (ii) We calculate the coupling matrix elements for the TMRI and show that the divergence appearing in previous studies can be eliminated completely by using a Fetter-like variational approximation for the ground-state wave function of the condensate. (iii) We provide the selection rules in mode-mode interaction processes [including TMRI and second-harmonic generation (SHG)] according to the symmetry of the excitations. (iv) By solving the nonlinearly coupled envelope equations we obtain divergence-free nonlinear amplitudes for the TMRI and SHG processes and show that our theoretical results on the shape oscillations of the condensate agree well with the experimental ones. We suggest also an experiment to check the theoretical prediction of the present study on the TMRI of collective excitations in a BEC

Factorization and resummation: A new paradigm to improve gravitational wave amplitudes. II. The higher multipolar modes

Science.gov (United States)

Messina, Francesco; Maldarella, Alberto; Nagar, Alessandro

2018-04-01

The factorization and resummation approach of Nagar and Shah [Phys. Rev. D 94, 104017 (2016), 10.1103/PhysRevD.94.104017], designed to improve the strong-field behavior of the post-Newtonian (PN) residual waveform amplitudes fℓm's entering the effective-one-body, circularized, gravitational waveform for spinning coalescing binaries, is improved and generalized here to all multipoles up to ℓ=6 . For a test particle orbiting a Kerr black hole, each multipolar amplitude is truncated at relative 6 PN order, both for the orbital (nonspinning) and spin factors. By taking a certain Padé approximant (typically the P24 one) of the orbital factor in conjunction with the inverse Taylor (iResum) representation of the spin factor, it is possible to push the analytical/numerical agreement of the energy flux at the level of 5% at the last-stable orbit for a quasimaximally spinning black hole with dimensionless spin parameter +0.99 . When the procedure is generalized to comparable-mass binaries, each orbital factor is kept at relative 3+3 PN order; i.e., the globally 3 PN-accurate comparable-mass terms are hybridized with higher-PN test-particle terms up to 6 PN relative order in each mode. The same Padé resummation is used for continuity. By contrast, the spin factor is only kept at the highest comparable-mass PN order currently available. We illustrate that the consistency between different truncations in the spin content of the waveform amplitudes is more marked in the resummed case than when using the standard Taylor-expanded form of Pan et al. [Phys. Rev. D 83, 064003 (2011), 10.1103/PhysRevD.83.064003]. We finally introduce a method to consistently hybridize comparable-mass and test-particle information also in the presence of spin (including the spin of the particle), discussing it explicitly for the ℓ=m =2 spin-orbit and spin-square terms. The improved, factorized and resummed, multipolar waveform amplitudes presented here are expected to set a new standard for

Understanding the amplitudes of noise correlation measurements

Science.gov (United States)

Tsai, Victor C.

2011-01-01

Cross correlation of ambient seismic noise is known to result in time series from which station-station travel-time measurements can be made. Part of the reason that these cross-correlation travel-time measurements are reliable is that there exists a theoretical framework that quantifies how these travel times depend on the features of the ambient noise. However, corresponding theoretical results do not currently exist to describe how the amplitudes of the cross correlation depend on such features. For example, currently it is not possible to take a given distribution of noise sources and calculate the cross correlation amplitudes one would expect from such a distribution. Here, we provide a ray-theoretical framework for calculating cross correlations. This framework differs from previous work in that it explicitly accounts for attenuation as well as the spatial distribution of sources and therefore can address the issue of quantifying amplitudes in noise correlation measurements. After introducing the general framework, we apply it to two specific problems. First, we show that we can quantify the amplitudes of coherency measurements, and find that the decay of coherency with station-station spacing depends crucially on the distribution of noise sources. We suggest that researchers interested in performing attenuation measurements from noise coherency should first determine how the dominant sources of noise are distributed. Second, we show that we can quantify the signal-to-noise ratio of noise correlations more precisely than previous work, and that these signal-to-noise ratios can be estimated for given situations prior to the deployment of seismometers. It is expected that there are applications of the theoretical framework beyond the two specific cases considered, but these applications await future work.

Effect of frequency on amplitude-dependent internal friction in niobium

International Nuclear Information System (INIS)

Ide, Naoki; Atsumi, Tomohiro; Nishino, Yoichi

2006-01-01

Amplitude-dependent internal friction (ADIF) was measured in a polycrystalline niobium using four modes of flexural vibration from the fundamental to the third-order resonance at room temperature. The ADIF was detected in each vibration mode. The internal-friction versus strain-amplitude curve of the ADIF shifted to a larger strain-amplitude range as frequency increased. The stress-strain curves were derived from the ADIF data, and the microplastic flow stress defined as the stress required to produce a plastic strain of 1 x 10 -9 was read from the stress-strain curves. It was found that the microplastic flow stress was proportional to the frequency

Effect of frequency on amplitude-dependent internal friction in niobium

Energy Technology Data Exchange (ETDEWEB)

Ide, Naoki [Department of Materials Science and Engineering, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555 (Japan)]. E-mail: ide@nitech.ac.jp; Atsumi, Tomohiro [Department of Materials Science and Engineering, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555 (Japan); Nishino, Yoichi [Department of Materials Science and Engineering, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555 (Japan)

2006-12-20

Amplitude-dependent internal friction (ADIF) was measured in a polycrystalline niobium using four modes of flexural vibration from the fundamental to the third-order resonance at room temperature. The ADIF was detected in each vibration mode. The internal-friction versus strain-amplitude curve of the ADIF shifted to a larger strain-amplitude range as frequency increased. The stress-strain curves were derived from the ADIF data, and the microplastic flow stress defined as the stress required to produce a plastic strain of 1 x 10{sup -9} was read from the stress-strain curves. It was found that the microplastic flow stress was proportional to the frequency.

Violin mode amplitude glitch monitor for the presence of excess noise on the monolithic silica suspensions of GEO 600

Energy Technology Data Exchange (ETDEWEB)

Sorazu, B; Strain, K A; Heng, I S; Kumar, R, E-mail: b.sorazu@physics.gla.ac.u [Department of Physics and Astronomy, University of Glasgow, University Avenue, Glasgow G12 8QQ (United Kingdom)

2010-08-07

Non-Gaussian features of data from gravitational wave detectors are of interest as unpredictable 'glitches' limit the sensitivity of searches for many kinds of signal. We consider events due to non-random excitations of the test masses and their suspension fibres. These events could, for example, be related to acoustic emissions in the fibres due to the presence and propagation of cracks or another type of structural perturbation, and they would generate excess noise above the Gaussian background, which matches the level expected due to thermal noise. We look for excess noise in the fundamental violin modes of the monolithic silica suspension fibres of GEO 600. We describe the algorithm used to monitor the violin mode amplitude for glitches, present our results and consider how these may be applied to advanced detectors. The conclusion of our analysis is that no excess noise above what was considered to be thermal noise was observed for several days of h(t) data analysed at the frequency of the selected violin modes.

Violin mode amplitude glitch monitor for the presence of excess noise on the monolithic silica suspensions of GEO 600

International Nuclear Information System (INIS)

Sorazu, B; Strain, K A; Heng, I S; Kumar, R

2010-01-01

Non-Gaussian features of data from gravitational wave detectors are of interest as unpredictable 'glitches' limit the sensitivity of searches for many kinds of signal. We consider events due to non-random excitations of the test masses and their suspension fibres. These events could, for example, be related to acoustic emissions in the fibres due to the presence and propagation of cracks or another type of structural perturbation, and they would generate excess noise above the Gaussian background, which matches the level expected due to thermal noise. We look for excess noise in the fundamental violin modes of the monolithic silica suspension fibres of GEO 600. We describe the algorithm used to monitor the violin mode amplitude for glitches, present our results and consider how these may be applied to advanced detectors. The conclusion of our analysis is that no excess noise above what was considered to be thermal noise was observed for several days of h(t) data analysed at the frequency of the selected violin modes.

Violin mode amplitude glitch monitor for the presence of excess noise on the monolithic silica suspensions of GEO 600

Science.gov (United States)

Sorazu, B.; Strain, K. A.; Heng, I. S.; Kumar, R.

2010-08-01

Non-Gaussian features of data from gravitational wave detectors are of interest as unpredictable 'glitches' limit the sensitivity of searches for many kinds of signal. We consider events due to non-random excitations of the test masses and their suspension fibres. These events could, for example, be related to acoustic emissions in the fibres due to the presence and propagation of cracks or another type of structural perturbation, and they would generate excess noise above the Gaussian background, which matches the level expected due to thermal noise. We look for excess noise in the fundamental violin modes of the monolithic silica suspension fibres of GEO 600. We describe the algorithm used to monitor the violin mode amplitude for glitches, present our results and consider how these may be applied to advanced detectors. The conclusion of our analysis is that no excess noise above what was considered to be thermal noise was observed for several days of h(t) data analysed at the frequency of the selected violin modes.

Amplitude-modulated fiber-ring laser

DEFF Research Database (Denmark)

Caputo, J. G.; Clausen, Carl A. Balslev; Sørensen, Mads Peter

2000-01-01

Soliton pulses generated by a fiber-ring laser are investigated by numerical simulation and perturbation methods. The mathematical modeling is based on the nonlinear Schrödinger equation with perturbative terms. We show that active mode locking with an amplitude modulator leads to a self......-starting of stable solitonic pulses from small random noise, provided the modulation depth is small. The perturbative analysis leads to a nonlinear coupled return map for the amplitude, phase, and position of the soliton pulses circulating in the fiber-ring laser. We established the validity of this approach...

Effects of mode coupling between low-mode radiation flux asymmetry and intermediate-mode ablator roughness on ignition capsule implosions

Directory of Open Access Journals (Sweden)

Jianfa Gu

2017-01-01

Full Text Available The low-mode shell asymmetry and high-mode hot spot mixing appear to be the main reasons for the performance degradation of the National Ignition Facility (NIF implosion experiments. The effects of the mode coupling between low-mode P2 radiation flux asymmetry and intermediate-mode L = 24 capsule roughness on the implosion performance of ignition capsule are investigated by two-dimensional radiation hydrodynamic simulations. It is shown that the amplitudes of new modes generated by the mode coupling are in good agreement with the second-order mode coupling equation during the acceleration phase. The later flow field not only shows large areal density P2 asymmetry in the main fuel, but also generates large-amplitude spikes and bubbles. In the deceleration phase, the increasing mode coupling generates more new modes, and the perturbation spectrum on the hot spot boundary is mainly from the strong mode interactions rather than the initial perturbation conditions. The combination of the low-mode and high-mode perturbations breaks up the capsule shell, resulting in a significant reduction of the hot spot temperature and implosion performance.

Tree-level amplitudes and dual superconformal symmetry

Energy Technology Data Exchange (ETDEWEB)

Drummond, J M, E-mail: drummond@lapp.in2p3.fr [PH-TH Division, CERN, CH-1211, Geneva 23 (Switzerland); LAPTH, Universite de Savoie, CNRS, B.P. 110, F-74941 Annecy-le-Vieux Cedex (France)

2011-11-11

We review the structure of gauge theory scattering amplitudes at tree level and describe how a compact expression can be found which encodes all the tree-level amplitudes in the maximally supersymmetric N=4 theory. The expressions for the amplitudes reveal a dual superconformal symmetry. We describe how these ideas can be extended to leading singularities and the loop integrand in the planar theory and discuss the appearance of dual conformal symmetry in higher-dimensional gauge theories. This paper is an invited review for a special issue of Journal of Physics A: Mathematical and Theoretical devoted to 'Scattering amplitudes in gauge theories'. (review)

Theoretical modeling of the feedback stabilization of external MHD modes of toroidal geometry

International Nuclear Information System (INIS)

Chance, M.S.; Chu, M.S.; Okabayashi, M.

2001-01-01

A theoretical framework for understanding the feedback mechanism against external MHD modes has been formulated. Efficient computational tools - the GATO stability code coupled with a substantially modified VACUUM code - have been developed to effectively design viable feedback systems against these modes. The analysis assumed a thin resistive shell and a feedback coil structure accurately modeled in θ, with only a single harmonic variation in φ. An optimized configuration and placement of the feedback and sensor coils as well as the time constants and induced currents in the enclosing resistive shell have been computed for the DIII-D device. Up to 90% of the effectiveness of an ideal wall can be achieved. (author)

Generation of three-mode continuous-variable entanglement by cascaded nonlinear interactions in a quasiperiodic superlattice

International Nuclear Information System (INIS)

Yu, Y. B.; Xie, Z. D.; Yu, X. Q.; Li, H. X.; Xu, P.; Yao, H. M.; Zhu, S. N.

2006-01-01

The generation of three-mode continuous-variable entanglement in a quasiperiodically optical superlattice is studied theoretically in this paper. This work is based on the previous experiment result in which three-color light generated from a quasiperiodically optical superlattice through a stimulated parametric down-conversion cascaded with a sum-frequency process. The degree of quadrature phase amplitude correlations, a nonclassical characteristic, among the three mode was discussed by a sufficient inseparability criterion for continuous-variable entanglement, which was proposed by van Loock and Furusawa

Mode instability in one-dimensional anharmonic lattices: Variational equation approach

Science.gov (United States)

Yoshimura, K.

1999-03-01

The stability of normal mode oscillations has been studied in detail under the single-mode excitation condition for the Fermi-Pasta-Ulam-β lattice. Numerical experiments indicate that the mode stability depends strongly on k/N, where k is the wave number of the initially excited mode and N is the number of degrees of freedom in the system. It has been found that this feature does not change when N increases. We propose an average variational equation - approximate version of the variational equation - as a theoretical tool to facilitate a linear stability analysis. It is shown that this strong k/N dependence of the mode stability can be explained from the view point of the linear stability of the relevant orbits. We introduce a low-dimensional approximation of the average variational equation, which approximately describes the time evolution of variations in four normal mode amplitudes. The linear stability analysis based on this four-mode approximation demonstrates that the parametric instability mechanism plays a crucial role in the strong k/N dependence of the mode stability.

Experimental studies of tearing mode and resistive wall mode dynamics in the reversed field pinch configuration

International Nuclear Information System (INIS)

Malmberg, Jenny-Ann

2003-06-01

It is relatively straightforward to establish equilibrium in magnetically confined plasmas, but the plasma is frequently susceptible to a variety of instabilities that are driven by the free energy in the magnetic field or in the pressure gradient. These unstable modes exhibit effects that affect the particle, momentum and heat confinement properties of the configuration. Studies of the dynamics of several of the most important modes are the subject of this thesis. The studies are carried out on plasmas in the reversed field pinch (RFP) configuration. One phenomenon commonly observed in RFPs is mode wall locking. The localized nature of these phase- and wall locked structures results in localized power loads on the wall which are detrimental for confinement. A detailed study of the wall locked mode phenomenon is performed based on magnetic measurements from three RFP devices. The two possible mechanisms for wall locking are investigated. Locking as a result of tearing modes interacting with a static field error and locking due to the presence of a non-ideal boundary. The characteristics of the wall locked mode are qualitatively similar in a device with a conducting shell system (TPE-RX) compared to a device with a resistive shell (Extrap T2). A theoretical model is used for evaluating the threshold values for wall locking due to eddy currents in the vacuum vessel in these devices. A good correlation with experiment is observed for the conducting shell device. The possibility of successfully sustaining discharges in a resistive shell RFP is introduced in the recently rebuilt device Extrap T2R. Fast spontaneous mode rotation is observed, resulting in low magnetic fluctuations, low loop voltage and improved confinement. Wall locking is rarely observed. The low tearing mode amplitudes allow for the theoretically predicted internal non-resonant on-axis resistive wall modes to be observed. These modes have not previously been distinguished due to the formation of wall

Electrostatic lower hybrid waves excited by electromagnetic whistler mode waves scattering from planar magnetic-field-aligned plasma density irregularities

International Nuclear Information System (INIS)

Bell, T.F.; Ngo, H.D.

1990-01-01

Recent satellite observations demonstrate that high amplitude, short wavelength (5 m ≤ λ ≤ 100 m) electrostatic waves are commonly excited by electromagnetic whistler mode waves propagating in regions of the magnetosphere and topside ionosphere where small-scale magnetic-field-aligned plasma density irregularities are thought to exist. A new theoretical model of this phenomenon is presented, based upon passive linear scattering in a cold magnetoplasma. In this model the electrostatic waves are excited by linear mode coupling as the incident electromagnetic whistler mode waves scatter from the magnetic-field-aligned plasma density irregularities. The excited short wavelength waves are quasi-electrostatic whistler mode waves, a type of lower hybrid wave, whose wave normal lies near the whistler mode resonance cone where the wave refractive index becomes very large. The amplitude of the excited electrostatic lower hybrid waves is calculated for a wide range of values of input electromagnetic wave frequency, wave normal direction, electron plasma frequency, gyrofrequency, ion composition, and irregularity scale and density enhancement. Results indicate that high amplitude lower hybrid waves can be excited over a wide range of parameters for irregularity density enhancements as low as 5% whenever the scale of the irregularity is of the same order as the lower hybrid wavelength

Global multiresolution models of surface wave propagation: comparing equivalently regularized Born and ray theoretical solutions

Science.gov (United States)

Boschi, Lapo

2006-10-01

I invert a large set of teleseismic phase-anomaly observations, to derive tomographic maps of fundamental-mode surface wave phase velocity, first via ray theory, then accounting for finite-frequency effects through scattering theory, in the far-field approximation and neglecting mode coupling. I make use of a multiple-resolution pixel parametrization which, in the assumption of sufficient data coverage, should be adequate to represent strongly oscillatory Fréchet kernels. The parametrization is finer over North America, a region particularly well covered by the data. For each surface-wave mode where phase-anomaly observations are available, I derive a wide spectrum of plausible, differently damped solutions; I then conduct a trade-off analysis, and select as optimal solution model the one associated with the point of maximum curvature on the trade-off curve. I repeat this exercise in both theoretical frameworks, to find that selected scattering and ray theoretical phase-velocity maps are coincident in pattern, and differ only slightly in amplitude.

Comparisons of theoretically predicted transport from ion temperature gradient instabilities to L-mode tokamak experiments

International Nuclear Information System (INIS)

Kotschenreuther, M.; Wong, H.V.; Lyster, P.L.; Berk, H.L.; Denton, R.; Miner, W.H.; Valanju, P.

1991-12-01

The theoretical transport from kinetic micro-instabilities driven by ion temperature gradients is a sheared slab is compared to experimentally inferred transport in L-mode tokamaks. Low noise gyrokinetic simulation techniques are used to obtain the ion thermal transport coefficient X. This X is much smaller than in experiments, and so cannot explain L-mode confinement. Previous predictions based on fluid models gave much greater X than experiments. Linear and nonlinear comparisons with the fluid model show that it greatly overestimates transport for experimental parameters. In addition, disagreements among previous analytic and simulation calculations of X in the fluid model are reconciled

Particle simulations of nonlinear whistler and Alfven wave instabilities - Amplitude modulation, decay, soliton and inverse cascading

International Nuclear Information System (INIS)

Omura, Yoshiharu; Matsumoto, Hiroshi.

1989-01-01

Past theoretical and numerical studies of the nonlinear evolution of electromagnetic cyclotron waves are reviewed. Such waves are commonly observed in space plasmas such as Alfven waves in the solar wind or VLF whistler mode waves in the magnetosphere. The use of an electromagnetic full-particle code to study an electron cyclotron wave and of an electromagnetic hybrid code to study an ion cyclotron wave is demonstrated. Recent achievements in the simulations of nonlinear revolution of electromagnetic cyclotron waves are discussed. The inverse cascading processes of finite-amplitude whistler and Alfven waves is interpreted in terms of physical elementary processes. 65 refs

Source of low frequency modulation of ENSO amplitude in a CGCM

Energy Technology Data Exchange (ETDEWEB)

Moon, Byung-Kwon [Chonbuk National University, Division of Science Education/Institute of Science Education, Jeonju (Korea); Yeh, Sang-Wook [Korea Ocean Research and Development Institute, Ansan (Korea); Dewitte, Boris [Laboratoire d' Etude en Geophysique et Oceanographie Spatiale, Toulouse (France); Jhun, Jong-Ghap [Seoul National University, School of Earth and Environmental Sciences, Seoul (Korea); Kang, In-Sik [Seoul National University, Climate Environment System Research Center (CES), Seoul (Korea)

2007-07-15

We study the relationship between changes in equatorial stratification and low frequency El Nino/Southern Oscillation (ENSO) amplitude modulation in a coupled general circulation model (CGCM) that uses an anomaly coupling strategy to prevent climate drifts in the mean state. The stratification is intensified at upper levels in the western and central equatorial Pacific during periods of high ENSO amplitude. Furthermore, changes in equatorial stratification are connected with subsurface temperature anomalies originating from the central south tropical Pacific. The correlation analysis of ocean temperature anomalies against an index for the ENSO modulation supports the hypothesis of the existence of an oceanic ''tunnel'' that connects the south tropical Pacific to the equatorial wave guide. Further analysis of the wind stress projection coefficient onto the oceanic baroclinic modes suggests that the low frequency modulation of ENSO amplitude is associated with a significant contribution of higher-order modes in the western and central equatorial Pacific. In the light of these results, we suggest that, in the CGCM, change in the baroclinic mode energy distribution associated with low frequency ENSO amplitude modulation have its source in the central south tropical Pacific. (orig.)

A novel oscillation control for MEMS vibratory gyroscopes using a modified electromechanical amplitude modulation technique

International Nuclear Information System (INIS)

Ma, Wei; Lin, Yiyu; Liu, Siqi; Zheng, Xudong; Jin, Zhonghe

2017-01-01

This paper reports a novel oscillation control algorithm for MEMS vibratory gyroscopes using a modified electromechanical amplitude modulation (MEAM) technique, which enhances the robustness against the frequency variation of the driving mode, compared to the conventional EAM (CEAM) scheme. In this approach, the carrier voltage exerted on the proof mass is frequency-modulated by the drive resonant frequency. Accordingly, the pick-up signal from the interface circuit involves a constant-frequency component that contains the amplitude and phase information of the vibration displacement. In other words, this informational detection signal is independent of the mechanical resonant frequency, which varies due to different batches, imprecise micro-fabrication and changing environmental temperature. In this paper, the automatic gain control loop together with the phase-locked loop are simultaneously analyzed using the averaging method and Routh–Hurwitz criterion, deriving the stability condition and the parameter optimization rules of the transient response. Then, a simulation model based on the real system is set up to evaluate the control algorithm. Further, the proposed MEAM method is tested using a field-programmable-gate-array based digital platform on a capacitive vibratory gyroscope. By optimizing the control parameters, the transient response of the drive amplitude reveals a settling time of 45.2 ms without overshoot, according well with the theoretical prediction and simulation results. The first measurement results show that the amplitude variance of the drive displacement is 12 ppm in an hour while the phase standard deviation is as low as 0.0004°. The mode-split gyroscope operating under atmospheric pressure demonstrates an outstanding performance. By virtue of the proposed MEAM method, the bias instability and angle random walk are measured to be 0.9° h −1 (improved by 2.4 times compared to the CEAM method) and 0.068° (√h) −1 (improved by 1

Excitation mechanisms for Jovian seismic modes

Science.gov (United States)

Markham, Steve; Stevenson, Dave

2018-05-01

Recent (2011) results from the Nice Observatory indicate the existence of global seismic modes on Jupiter in the frequency range between 0.7 and 1.5 mHz with amplitudes of tens of cm/s. Currently, the driving force behind these modes is a mystery; the measured amplitudes are many orders of magnitude larger than anticipated based on theory analogous to helioseismology (that is, turbulent convection as a source of stochastic excitation). One of the most promising hypotheses is that these modes are driven by Jovian storms. This work constructs a framework to analytically model the expected equilibrium normal mode amplitudes arising from convective columns in storms. We also place rough constraints on Jupiter's seismic modal quality factor. Using this model, neither meteor strikes, turbulent convection, nor water storms can feasibly excite the order of magnitude of observed amplitudes. Next we speculate about the potential role of rock storms deeper in Jupiter's atmosphere, because the rock storms' expected energy scales make them promising candidates to be the chief source of excitation for Jovian seismic modes, based on simple scaling arguments. We also suggest some general trends in the expected partition of energy between different frequency modes. Finally we supply some commentary on potential applications to gravity, Juno, Cassini and Saturn, and future missions to Uranus and Neptune.

Mechanical detection and mode shape imaging of vibrational modes of micro and nanomechanical resonators by dynamic force microscopy

International Nuclear Information System (INIS)

Paulo, A S; GarcIa-Sanchez, D; Perez-Murano, F; Bachtold, A; Black, J; Bokor, J; Esplandiu, M J; Aguasca, A

2008-01-01

We describe a method based on the use of higher order bending modes of the cantilever of a dynamic force microscope to characterize vibrations of micro and nanomechanical resonators at arbitrarily large resonance frequencies. Our method consists on using a particular cantilever eigenmode for standard feedback control in amplitude modulation operation while another mode is used for detecting and imaging the resonator vibration. In addition, the resonating sample device is driven at or near its resonance frequency with a signal modulated in amplitude at a frequency that matches the resonance of the cantilever eigenmode used for vibration detection. In consequence, this cantilever mode is excited with an amplitude proportional to the resonator vibration, which is detected with an external lock-in amplifier. We show two different application examples of this method. In the first one, acoustic wave vibrations of a film bulk acoustic resonator around 1.6 GHz are imaged. In the second example, bending modes of carbon nanotube resonators up to 3.1 GHz are characterized. In both cases, the method provides subnanometer-scale sensitivity and the capability of providing otherwise inaccessible information about mechanical resonance frequencies, vibration amplitude values and mode shapes

Kinetic Alfven Waves at the Magnetopause-Mode Conversion, Transport and Formation of LLBL; TOPICAL

International Nuclear Information System (INIS)

Jay R. Johnson; C.Z. Cheng

2002-01-01

At the magnetopause, large amplitude, low-frequency (ULF), transverse MHD waves are nearly always observed. These waves likely result from mode conversion of compressional MHD waves observed in the magnetosheath to kinetic Alfven waves at the magnetopause where there is a steep gradient in the Alfven velocity[Johnson and Cheng, Geophys. Res. Lett. 24 (1997) 1423]. The mode-conversion process can explain the following wave observations typically found during satellite crossings of the magnetopause: (1) a dramatic change in wave polarization from compressional in the magnetosheath to transverse at the magnetopause, (2) an amplification of wave amplitude at the magnetopause, (3) a change in Poynting flux from cross-field in the magnetosheath to field-aligned at the magnetopause, and (4) a steepening in the wave power spectrum at the magnetopause. We examine magnetic field data from a set of ISEE1, ISEE2, and WIND magnetopause crossings and compare with the predictions of theoretical wave solutions based on the kinetic-fluid model with particular attention to the role of magnetic field rotation across the magnetopause. The results of the study suggest a good qualitative agreement between the observations and the theory of mode conversion to kinetic Alfven waves. Because mode-converted kinetic Alfven waves readily decouple particles from the magnetic field lines, efficient quasilinear transport (D(approx) 109m2/s) can occur. Moreover, if the wave amplitude is sufficiently large (Bwave/B0 and gt; 0.2) stochastic particle transport also occurs. This wave-induced transport can lead to significant heating and particle entry into the low latitude boundary layer across closed field lines.At the magnetopause, large amplitude, low-frequency (ULF), transverse MHD waves are nearly always observed. These waves likely result from mode conversion of compressional MHD waves observed in the magnetosheath to kinetic Alfven waves at the magnetopause where there is a steep gradient in

Stabilization of the hypersonic boundary layer by finite-amplitude streaks

Science.gov (United States)

Ren, Jie; Fu, Song; Hanifi, Ardeshir

2016-02-01

Stabilization of two-dimensional disturbances in hypersonic boundary layer flows by finite-amplitude streaks is investigated using nonlinear parabolized stability equations. The boundary-layer flows at Mach numbers 4.5 and 6.0 are studied in which both first and second modes are supported. The streaks considered here are driven either by the so-called optimal perturbations (Klebanoff-type) or the centrifugal instability (Görtler-type). When the streak amplitude is in an appropriate range, i.e., large enough to modulate the laminar boundary layer but low enough to not trigger secondary instability, both first and second modes can effectively be suppressed.

Solving theoretical and empirical conundrums in international strategy research by matching foreign entry mode choices and performance

NARCIS (Netherlands)

Martin, Xavier

2013-01-01

Several theoretical and empirical developments in the literature on foreign entry mode and performance, and on (international) strategy more generally, were influenced or prefigured by Brouthers’ (2002) JIBS Decade Award winning paper. Regarding theory, Brouthers is an archetype of the integration

Cluster polylogarithms for scattering amplitudes

International Nuclear Information System (INIS)

Golden, John; Paulos, Miguel F; Spradlin, Marcus; Volovich, Anastasia

2014-01-01

Motivated by the cluster structure of two-loop scattering amplitudes in N=4 Yang-Mills theory we define cluster polylogarithm functions. We find that all such functions of weight four are made up of a single simple building block associated with the A 2 cluster algebra. Adding the requirement of locality on generalized Stasheff polytopes, we find that these A 2 building blocks arrange themselves to form a unique function associated with the A 3 cluster algebra. This A 3 function manifests all of the cluster algebraic structure of the two-loop n-particle MHV amplitudes for all n, and we use it to provide an explicit representation for the most complicated part of the n = 7 amplitude as an example. This article is part of a special issue of Journal of Physics A: Mathematical and Theoretical devoted to ‘Cluster algebras in mathematical physics’. (paper)

Determination of electromagnetic modes in oversized corrugated waveguides on the electron cyclotron resonance heating installation at the tokamak Tore Supra; Determination de modes electromagnetiques de guides d'ondes corrugues surdimensionnes sur l'installation de chauffage des electrons de tokamak Tore Supra

Energy Technology Data Exchange (ETDEWEB)

Courtois, L

2001-03-09

Electron cyclotron resonance heating (ECRH) in the Tore Supra tokamak constitutes an important step in the research aimed at obtaining thermonuclear fusion reactions. Electron heating is achieved by transmitting an electromagnetic wave from the oscillators (gyrotrons) to the plasma via the fundamental mode, propagating in oversized corrugated waveguides. Maximizing the proportion of the gyrotron power coupled to the fundamental waveguide mode is essential for the good functioning of the transmission line and for maximizing the effect on the plasma. This thesis gives all necessary tools for finding the proportion of the fundamental mode and all other modes present in passive components and at the output of the gyrotron as installed in the Tore Supra ECRH plant. This characterisation is based on obtaining amplitude and phase diagrams of the electric field on a plane transverse to the propagation axis. The most difficult part of obtaining these diagrams is measuring the phase which, despite the very short wavelength, is measured directly at low power levels. At high power levels the phase is numerically reconstructed from amplitude measurements for gyrotron characterisation. A complete theoretical study of the phase reconstruction code is given including its validation with theoretical diagrams. This study allows the realisation of a modal characterisation unit electromagnetic for measurement of radiated beams and usable in each part of the ECRH installation. At the end, the complete modal characterisation is given at low level for a mode converter and also at high level for the first series gyrotron installed at TORE SUPRA. (author)

Stabilization of tearing modes to suppress major disruptions in tokamaks

International Nuclear Information System (INIS)

Holmes, J.A.; Carreras, B.; Hicks, H.R.; Lynch, S.J.; Waddell, B.V.

1979-02-01

It is shown, for q-profiles which lead to a disruption, that the control of the amplitude of the 2/1 tearing mode avoids the disruption. Q-profiles measured in T-4 and PLT before a major disruption were studied. Two methods of controlling the 2/1 mode amplitude have been considered: (1) Feedback stabilization with the feedback signal locked in phase with the 2/1 mode. (2) Heating slightly outside the q = 2 surface. In both cases it is only necessary to decrease the 2/1 mode amplitude to suppress the disruption. It is not always necessary to stabilize the unstable modes fully

SEARCH FOR GLOBAL f-MODES AND p-MODES IN THE {sup 8}B NEUTRINO FLUX

Energy Technology Data Exchange (ETDEWEB)

Lopes, Ilídio, E-mail: ilidio.lopes@ist.utl.pt, E-mail: ilopes@uevora.pt [Centro Multidisciplinar de Astrofísica, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1049-001 Lisboa (Portugal); Departamento de Física, Escola de Ciências e Tecnologia, Universidade de Évora, Colégio Luis António Verney, 7002-554 Évora (Portugal)

2013-11-01

The impact of global acoustic modes on the {sup 8}B neutrino flux time series is computed for the first time. It is shown that the time fluctuations of the {sup 8}B neutrino flux depend on the amplitude of acoustic eigenfunctions in the region where the {sup 8}B neutrino flux is produced: modes with low n (or order) that have eigenfunctions with a relatively large amplitude in the Sun's core strongly affect the neutrino flux; conversely, modes with high n that have eigenfunctions with a minimal amplitude in the Sun's core have a very small impact on the neutrino flux. It was found that the global modes with a larger impact on the {sup 8}B neutrino flux have a frequency of oscillation in the interval 250 μHz to 500 μHz (or a period in the interval 30 minutes to 70 minutes), such as the f-modes (n = 0) for the low degrees, radial modes of order n ≤ 3, and the dipole mode of order n = 1. Their corresponding neutrino eigenfunctions are very sensitive to the solar inner core and are unaffected by the variability of the external layers of the solar surface. If time variability of neutrinos is observed for these modes, it will lead to new ways of improving the sound speed profile inversion in the central region of the Sun.

Theoretical and experimental study of Gaussian beam and mode propagation in over-dimensioned circular guides

International Nuclear Information System (INIS)

Crenn, J.P.

1984-06-01

A theoretical study of modes in circular hollow over-dimensioned waveguides is developed; it shows the interest of dielectric or weakly conducting wall guide use. An optical model computing the transmitted power of gaussian beams through these guides, for different types of walls, is established. The formulas obtained allow to optimize the guide and to adapt the beam. Applied to the EH 11 mode this optical model leads to new results. Systematical measurements of gaussian beam propagation in over-dimensioned guides are realised; they are concerned with beam power transmission, polarization, its structure and its radiation at the guide exit in function of the different characteristics of the beam and the guide [fr

Nonlinear drift tearing mode. Strong mode of excitation and stabilization mechanisms

International Nuclear Information System (INIS)

Galeev, A.A.; Zelenyj, L.M.; Kuznetsova, M.M.

1985-01-01

A nonlinear theory of magnetic disturbance development in collisionless configurations with magnetic field shear is considered. The instability evolution is investigated with account for the dynamics of ions and potential electric fields which determine the mode stabilization. It has been found that the drift tearing mode possesses metastable properties: in a nonlinear mode even the growth of linearly stable disturbances of the finite amplitude is possible

Injection-locked single-mode VCSEL for orthogonal multiplexing and amplitude noise suppression

DEFF Research Database (Denmark)

Chipouline, Arkadi; Lyubopytov, Vladimir S.; Malekizandi, Mohammadreza

2017-01-01

It has been shown earlier, that the injection locked semiconductor lasers enable effective amplitude noise suppression [1] and makes possible an extra level of signal multiplexing-orthogonal modulation [2], where DPSK and ASK NRZ channels propagate at the same wavelength [3]. In our work we use...... an injection-locked 1550 nm VCSEL as a slave laser providing separation of amplitude and phase modulations, carrying independent information flows. To validate the possibility of phase modulation extraction by an injection-locked VCSEL, an experimental setup shown in Fig. 1 has been built....

Enhanced Electroweak Penguin Amplitude in B→VV Decays

International Nuclear Information System (INIS)

Beneke, M.; Rohrer, J.; Yang, D.

2006-01-01

We discuss a novel electromagnetic penguin contribution to the transverse helicity amplitudes in B decays to two vector mesons, which is enhanced by two powers of m B /Λ relative to the standard penguin amplitudes. This leads to unique polarization signatures in penguin-dominated decay modes such as B→ρK* similar to polarization effects in the radiative decay B→K*γ and offers new opportunities to probe the magnitude and chirality of flavor-changing neutral current couplings to photons

Stability of coupled tearing and twisting modes in tokamaks

International Nuclear Information System (INIS)

Fitzpatrick, R.

1994-03-01

A dispersion relation is derived for resistive modes of arbitrary parity in a tokamak plasma. At low mode amplitude, tearing and twisting modes which have nonideal MHD behavior at only one rational surface at a time in the plasma are decoupled via sheared rotation and diamagnetic flows. At higher amplitude, more unstable open-quote compound close-quote modes develop which have nonideal behavior simultaneously at many surfaces. Such modes possess tearing parity layers at some of the nonideal surfaces, and twisting parity layers at others, but mixed parity layers are generally disallowed. At low mode number, open-quote compound close-quote modes are likely to have tearing parity layers at all of the nonideal surfaces in a very low-β plasma, but twisting parity layers become more probable as the plasma β is increased. At high mode number, unstable twisting modes which exceed a critical amplitude drive conventional magnetic island chains on alternate rational surfaces, to form an interlocking structure in which the O-points and X-points of neighboring chains line up

Amplitude modulation in δ Sct stars: statistics from an ensemble of Kepler targets

Science.gov (United States)

Bowman, Dominic M.; Kurtz, Donald W.; Breger, Michel; Murphy, Simon J.; Holdsworth, Daniel L.

2017-10-01

The results of a search for amplitude modulation of pulsation modes in 983 δ Sct stars, which have effective temperatures between 6400 ⩽ Teff ⩽ 10 000 K in the Kepler Input Catalogue and were continuously observed by the Kepler Space Telescope for 4 yr, are presented. A total of 603 δ Sct stars (61.3 per cent) are found to exhibit at least one pulsation mode that varies significantly in amplitude over 4 yr. Furthermore, it is found that amplitude modulation is not restricted to a specific region within the classical instability strip in the HR diagram, therefore its cause is not necessarily dependent on stellar parameters such as Teff or log g. On the other hand, many δ Sct stars show constant pulsation amplitudes demonstrating that the cause of pulsational non-linearity in these stars is not well understood.

Numerical study of the quasinormal mode excitation of Kerr black holes

International Nuclear Information System (INIS)

Dorband, Ernst Nils; Diener, Peter; Tiglio, Manuel; Berti, Emanuele; Schnetter, Erik

2006-01-01

We present numerical results from three-dimensional evolutions of scalar perturbations of Kerr black holes. Our simulations make use of a high-order accurate multiblock code which naturally allows for adapted grids and smooth inner (excision) and outer boundaries. We focus on the quasinormal ringing phase, presenting a systematic method for extraction of the quasinormal mode frequencies and amplitudes and comparing our results against perturbation theory. The detection of a single mode in a ringdown waveform allows for a measurement of the mass and spin of a black hole; a multimode detection would allow a test of the Kerr nature of the source. Since the possibility of a multimode detection depends on the relative mode amplitude, we study this topic in some detail. The amplitude of each mode depends exponentially on the starting time of the quasinormal regime, which is not defined unambiguously. We show that this time-shift problem can be circumvented by looking at appropriately chosen relative mode amplitudes. From our simulations we extract the quasinormal frequencies and the relative and absolute amplitudes of corotating and counterrotating modes (including overtones in the corotating case). We study the dependence of these amplitudes on the shape of the initial perturbation, the angular dependence of the mode, and the black hole spin, comparing against results from perturbation theory in the so-called asymptotic approximation. We also compare the quasinormal frequencies from our numerical simulations with predictions from perturbation theory, finding excellent agreement. For rapidly rotating black holes (of spin j=0.98) we can extract the quasinormal frequencies of not only the fundamental mode, but also of the first two overtones. Finally we study under what conditions the relative amplitude between given pairs of modes gets maximally excited and present a quantitative analysis of rotational mode-mode coupling. The main conclusions and techniques of our

On the evolutionary status and pulsations of the recently discovered blue large-amplitude pulsators (BLAPs)

Science.gov (United States)

Romero, Alejandra D.; Córsico, A. H.; Althaus, L. G.; Pelisoli, I.; Kepler, S. O.

2018-06-01

The blue large-amplitude pulsators (BLAPs) constitute a new class of pulsating stars. They are hot stars with effective temperatures of ˜30 000 K and surface gravities of log g ˜ 4.9, that pulsate with periods in the range 20-40 min. Until now, their origin and evolutionary state, as well as the nature of their pulsations, were not been unveiled. In this paper, we propose that the BLAPs are the hot counterpart of the already known pulsating pre-extremely low mass (pre-ELM) white dwarf (WD) stars, that are He-core low-mass stars resulting from interacting binary evolution. Using fully evolutionary sequences, we show that the BLAPs are well represented by pre-ELM WD models with high effective temperature and stellar masses ˜0.34 M⊙. From the analysis of their pulsational properties, we find that the observed variabilities can be explained by high-order non-radial g-mode pulsations or, in the case of the shortest periods, also by low-order radial modes, including the fundamental radial mode. The theoretical modes with periods in the observed range are unstable due to the κ mechanism associated with the Z-bump in the opacity at log T ˜ 5.25.

Capillary forces in tapping mode atomic force microscopy

NARCIS (Netherlands)

Zitzler, L.; Herminghaus, S.; Mugele, Friedrich Gunther

2002-01-01

We investigated the influence of the relative humidity on amplitude and phase of the cantilever oscillation while operating an atomic force microscope (AFM) in the tapping mode. If the free oscillation amplitude A0 exceeds a certain critical amplitude Ac, the amplitude- and phase-distance curves

High Frequency Amplitude Detector for GMI Magnetic Sensors

Directory of Open Access Journals (Sweden)

Aktham Asfour

2014-12-01

Full Text Available A new concept of a high-frequency amplitude detector and demodulator for Giant-Magneto-Impedance (GMI sensors is presented. This concept combines a half wave rectifier, with outstanding capabilities and high speed, and a feedback approach that ensures the amplitude detection with easily adjustable gain. The developed detector is capable of measuring high-frequency and very low amplitude signals without the use of diode-based active rectifiers or analog multipliers. The performances of this detector are addressed throughout the paper. The full circuitry of the design is given, together with a comprehensive theoretical study of the concept and experimental validation. The detector has been used for the amplitude measurement of both single frequency and pulsed signals and for the demodulation of amplitude-modulated signals. It has also been successfully integrated in a GMI sensor prototype. Magnetic field and electrical current measurements in open- and closed-loop of this sensor have also been conducted.

Pulsations of the High-Amplitude δ Scuti star YZ Bootis

Science.gov (United States)

Yang, Tao-Zhi; Esamdin, Ali; Fu, Jian-Ning; Niu, Hu-Biao; Feng, Guo-Jie; Song, Fang-Fang; Liu, Jin-Zhong; Ma, Lu

2018-01-01

We present a study on pulsations of the high-amplitude δ Scuti star YZ Boo based on photometric observations in Johnson V and R bands with both the Nanshan 1-m telescope of Xinjiang AstronomicalObservatory (XAO) and the Xinglong 85-cmtelescope of NationalAstronomical Observatories, Chinese Academy of Sciences (NAOC). Fourier analysis of the light curves reveals the fundamental radial mode and its five harmonics, with the fourth and fifth being newly detected. Thirty-nine new times of maximum light are determined from the light curves, and combined with those in the literature, we construct the O ‑ C diagram, derive a new ephemeris and determine a new value for the updated period of 0.104091579(2). In addition, the O ‑ C diagram reveals an increasing rate of period change for YZ Boo. Theoretical models are calculated and constrained with the observationally determined parameters of YZ Boo. The mass and age of YZ Boo are hence derived as M = 1.61±0.05 M ⊙ and age = (1.44±0.14)×109 yr, respectively.With both the frequency of the fundamental radial mode and the rate of period change, YZ Boo is located at the post main sequence stage.

Heavy quark effective theory, interpolating fields and Bethe-Salpeter amplitudes

International Nuclear Information System (INIS)

Hussain, F.; Thomspon, G.

1994-07-01

We use the LSZ reduction theorem and interpolating fields, along with the heavy quark effective theory, to investigate the structure of the Bethe-Salpeter amplitude for heavy hadrons. We show how a simple form of this amplitude, used extensively in heavy hadron decay calculations, follows naturally up to O(1/M) from these field theoretic considerations. (author). 13 refs, 1 tab

Unusual magnetic excitations in the weakly ordered spin- 12 chain antiferromagnet Sr2CuO3: Possible evidence for Goldstone magnon coupled with the amplitude mode

International Nuclear Information System (INIS)

Sergeicheva, E. G.; Sosin, S. S.; Prozorova, L. A.; Gu, G. D.; Zaliznyak, I. A.

2017-01-01

We report on an electron spin resonance (ESR) study of a nearly one-dimensional (1D) spin-1/2 chain antiferromagnet, Sr 2 CuO 3 , with extremely weak magnetic ordering. The ESR spectra at T > T N , in the disordered Luttinger-spin-liquid phase, reveal nearly ideal Heisenberg-chain behavior with only a very small, field-independent linewidth, ~1/T. In the ordered state, below T N , we identify field-dependent antiferromagnetic resonance modes, which are well described by pseudo-Goldstone magnons in the model of a collinear biaxial antiferromagnet. Additionally, we observe a major resonant mode with unusual and strongly anisotropic properties, which is not anticipated by the conventional theory of Goldstone spin waves. Lastly, we propose that this unexpected magnetic excitation can be attributed to a field-independent magnon mode renormalized due to its interaction with the high-energy amplitude (Higgs) mode in the regime of weak spontaneous symmetry breaking.

Formation of large-amplitude dust ion-acoustic shocks in dusty plasmas

International Nuclear Information System (INIS)

Eliasson, B.; Shukla, P.K.

2005-01-01

Theoretical and numerical studies of self-steepening and shock formation of large-amplitude dust ion-acoustic waves in dusty plasmas are presented. A comparison is made between the nondispersive two fluid model, which predicts the formation of large-amplitude compressive and rarefactive dust ion-acoustic shocks, Vlasov simulations, and recent laboratory experiments

2-D modeling of dual-mode acoustic phonon excitation of a triangular nanoplate

International Nuclear Information System (INIS)

Tai, Po-Tse; Yu, Pyng; Tang, Jau

2010-01-01

Graphical abstract: Modeling the lattice dynamics of a triangular plate with the arrows indicating the direction of impulsive thermal stress. We investigated ultrafast structural dynamics of triangular nanoplates based on 2-D Fermi-Pasta-Ulam model to explain coherent acoustic phonon excitation in nanoprisms. - Abstract: In this theoretical work, we investigated coherent phonon excitation of a triangular nanoplate based on 2-D Fermi-Pasta-Ulam lattice model. Based on the two-temperature model commonly used in description of laser heating of metals, we considered two kinds of forces related to electronic and lattice stresses. Based on extensive simulation and analysis, we identified two major planar phonon modes, namely, a standing wave mode related to the triangle bisector and another mode corresponding to half of the side length. This work elucidates the roles of laser-induced electronic stress and lattice stress in controlling the initial phase and the amplitude ratio between these two phonon modes.

Numerical Predictions of Mode Reflections in an Open Circular Duct: Comparison with Theory

Science.gov (United States)

Dahl, Milo D.; Hixon, Ray

2015-01-01

The NASA Broadband Aeroacoustic Stator Simulation code was used to compute the acoustic field for higher-order modes in a circular duct geometry. To test the accuracy of the results computed by the code, the duct was terminated by an open end with an infinite flange or no flange. Both open end conditions have a theoretical solution that was used to compare with the computed results. Excellent comparison for reflection matrix values was achieved after suitable refinement of the grid at the open end. The study also revealed issues with the level of the mode amplitude introduced into the acoustic held from the source boundary and the amount of reflection that occurred at the source boundary when a general nonreflecting boundary condition was applied.

Nonlinear mode coupling in rotating stars and the r-mode instability in neutron stars

International Nuclear Information System (INIS)

Schenk, A.K.; Arras, P.; Flanagan, E.E.; Teukolsky, S.A.; Wasserman, I.

2002-01-01

We develop the formalism required to study the nonlinear interaction of modes in rotating Newtonian stars, assuming that the mode amplitudes are only mildly nonlinear. The formalism is simpler than previous treatments of mode-mode interactions for spherical stars, and simplifies and corrects previous treatments for rotating stars. At linear order, we elucidate and extend slightly a formalism due to Schutz, show how to decompose a general motion of a rotating star into a sum over modes, and obtain uncoupled equations of motion for the mode amplitudes under the influence of an external force. Nonlinear effects are added perturbatively via three-mode couplings, which suffices for moderate amplitude modal excitations; the formalism is easy to extend to higher order couplings. We describe a new, efficient way to compute the modal coupling coefficients, to zeroth order in the stellar rotation rate, using spin-weighted spherical harmonics. The formalism is general enough to allow computation of the initial trends in the evolution of the spin frequency and differential rotation of the background star. We apply this formalism to derive some properties of the coupling coefficients relevant to the nonlinear interactions of unstable r modes in neutron stars, postponing numerical integrations of the coupled equations of motion to a later paper. First, we clarify some aspects of the expansion in stellar rotation frequency Ω that is often used to compute approximate mode functions. We show that, in zero-buoyancy stars, the rotational modes (those modes whose frequencies vanish as Ω→0) are orthogonal to zeroth order in Ω. From an astrophysical viewpoint, the most interesting result of this paper is that many couplings of r modes to other rotational modes are small: either they vanish altogether because of various selection rules, or they vanish to lowest order in Ω or in compressibility. In particular, in zero-buoyancy stars, the coupling of three r modes is forbidden

Frequency and amplitude stabilization in MEMS and NEMS oscillators

Science.gov (United States)

Chen, Changyao; Lopez, Omar Daniel; Czaplewski, David A.

2017-06-14

This invention comprises a nonlinear micro- and nano-mechanical resonator that can maintain frequency of operation and amplitude of operation for a period of time after all external power has been removed from the device. Utilizing specific nonlinear dynamics of the micromechanical resonator, mechanical energy at low frequencies can be input and stored in higher frequencies modes, thus using the multiple degrees of freedom of the resonator to extend its energy storage capacity. Furthermore, the energy stored in multiple vibrational modes can be used to maintain the resonator oscillating for a fixed period of time, even without an external power supply. This is the first demonstration of an "autonomous" frequency source that can maintain a constant frequency and vibrating amplitude when no external power is provided, making it ideal for applications requiring an oscillator in low power, or limited and intermittent power supplies.

Theoretical study of the mode of the mass-selective nonstable axial output ions from the nonlinear trap

International Nuclear Information System (INIS)

Sudakov, M.Yu.

2000-01-01

One studied theoretically the mode of mass-selective unstable output of ions from three-dimensional quadrupole ion trap. One developed a method represent coordinates of ions per one period of supplying HF voltage with regard to nonlinear distortions of quadrupole potential. One derived equation for an envelope of ion oscillations in the form of motion equation of mass point in the efficient force field. One explained the effect of output delay of ions at presence of the field negative even harmonics. One proved that the positive even distortions of quadrupole potential favored realization of that mode and studied the dynamics of ions in the course of output [ru

Photoacoustic microbeam-oscillator with tunable resonance direction and amplitude

Science.gov (United States)

Wu, Qingjun; Li, Fanghao; Wang, Bo; Yi, Futing; Jiang, J. Z.; Zhang, Dongxian

2018-01-01

We successfully design one photoacoustic microbeam-oscillator actuated by nanosecond laser, which exhibits tunable resonance direction and amplitude. The mechanism of laser induced oscillation is systematically analyzed. Both simulation and experimental results reveal that the laser induced acoustic wave propagates in a multi-reflected mode, resulting in resonance in the oscillator. This newly-fabricated micrometer-sized beam-oscillator has an excellent actuation function, i.e., by tuning the laser frequency, the direction and amplitude of actuation can be efficiently altered, which will have potential industrial applications.

A comparative study of the single-mode Richtmyer-Meshkov instability

Science.gov (United States)

Bai, X.; Deng, X.-L.; Jiang, L.

2017-11-01

In this work, the single-mode Richtmyer-Meshkov instability is studied numerically to find a reasonable nonlinear theoretical model which can be applied to predict the interface evolution from the linear stage to the early nonlinear stage. The cut-cell-based sharp-interface methods MuSiC+ (Chang et al. in J Comput Phys 242:946-990, 2013) and CCGF (Bai and Deng in Adv Appl Math Mech 9(5):1052-1075, 2017) are applied to generate numerical results for comparisons. Classical Air-SF6 and Air-Helium conditions are applied in this study, and initial amplitude and Atwood number are varied for comparison. Comparisons to the simulation results from the literature show the applicability of MuSiC+ and CCGF. Comparisons to the nonlinear theoretical models show that ZS (Zhang and Sohn in Phys Lett A 212:149-155, 1996; Phys Fluids 9:1106-1124, 1997), SEA (Sadot et al. in Phys Rev Lett 80:1654-1657, 1998), and DR (Dimonte and Ramaprabhu in Phys Fluids 22:014104, 2010) models are valid for both spike and bubble growth rates, and MIK (Mikaelian in Phys Rev E 67:026319, 2003) and ZG (Zhang and Guo in J Fluid Mech 786:47-61, 2016) models are valid for bubble growth rate, when the initial perturbation is small and the Atwood number is low, but only the DR model is applicable for both spike and bubble growth rates when the initial perturbation amplitude and the Atwood number are large. A new term of non-dimensional initial perturbation amplitude is presented and multiplied to the DR model to get a unified fitted DR model, which gives consistent results to the simulation ones for small and large initial amplitudes.

Scattering amplitudes in open superstring theory

Energy Technology Data Exchange (ETDEWEB)

Schlotterer, Oliver

2011-07-15

with regards to the duality between group-theoretical and kinematic contributions to tree-level amplitudes observed in the field theory.

Scattering amplitudes in open superstring theory

International Nuclear Information System (INIS)

Schlotterer, Oliver

2011-01-01

with regards to the duality between group-theoretical and kinematic contributions to tree-level amplitudes observed in the field theory.

Chimera distribution amplitudes for the pion and the longitudinally polarized ρ-meson

Energy Technology Data Exchange (ETDEWEB)

Stefanis, N.G., E-mail: stefanis@tp2.ruhr-uni-bochum.de [Institut für Theoretische Physik II, Ruhr-Universität Bochum, D-44780 Bochum (Germany); Pimikov, A.V., E-mail: pimikov@theor.jinr.ru [Bogoliubov Laboratory of Theoretical Physics, JINR, 141980 Dubna (Russian Federation); Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou, 730000 (China)

2016-01-15

Using QCD sum rules with nonlocal condensates, we show that the distribution amplitude of the longitudinally polarized ρ-meson may have a shorttailed platykurtic profile in close analogy to our recently proposed platykurtic distribution amplitude for the pion. Such a chimera distribution de facto amalgamates the broad unimodal profile of the distribution amplitude, obtained with a Dyson–Schwinger equations-based computational scheme, with the suppressed tails characterizing the bimodal distribution amplitudes derived from QCD sum rules with nonlocal condensates. We argue that pattern formation, emerging from the collective synchronization of coupled oscillators, can provide a single theoretical scaffolding to study unimodal and bimodal distribution amplitudes of light mesons without recourse to particular computational schemes and the reasons for them.

The transmission of finite amplitude sound beam in multi-layered biological media

Science.gov (United States)

Liu, Xiaozhou; Li, Junlun; Yin, Chang; Gong, Xiufen; Zhang, Dong; Xue, Honghui

2007-02-01

Based on the Khokhlov Zabolotskaya Kuznetsov (KZK) equation, a model in the frequency domain is given to describe the transmission of finite amplitude sound beam in multi-layered biological media. Favorable agreement between the theoretical analyses and the measured results shows this approach could effectively describe the transmission of finite amplitude sound wave in multi-layered biological media.

The transmission of finite amplitude sound beam in multi-layered biological media

Energy Technology Data Exchange (ETDEWEB)

Liu, Xiaozhou [Key Lab of Modern Acoustics, Institute of Acoustics, Nanjing University, Nanjing 210093 (China)]. E-mail: xzliu@nju.edu.cn; Li, Junlun [Key Lab of Modern Acoustics, Institute of Acoustics, Nanjing University, Nanjing 210093 (China); Yin, Chang [Key Lab of Modern Acoustics, Institute of Acoustics, Nanjing University, Nanjing 210093 (China); Gong, Xiufen [Key Lab of Modern Acoustics, Institute of Acoustics, Nanjing University, Nanjing 210093 (China); Zhang, Dong [Key Lab of Modern Acoustics, Institute of Acoustics, Nanjing University, Nanjing 210093 (China); Xue, Honghui [Key Lab of Modern Acoustics, Institute of Acoustics, Nanjing University, Nanjing 210093 (China)

2007-02-19

Based on the Khokhlov-Zabolotskaya-Kuznetsov (KZK) equation, a model in the frequency domain is given to describe the transmission of finite amplitude sound beam in multi-layered biological media. Favorable agreement between the theoretical analyses and the measured results shows this approach could effectively describe the transmission of finite amplitude sound wave in multi-layered biological media.

The transmission of finite amplitude sound beam in multi-layered biological media

International Nuclear Information System (INIS)

Liu, Xiaozhou; Li, Junlun; Yin, Chang; Gong, Xiufen; Zhang, Dong; Xue, Honghui

2007-01-01

Based on the Khokhlov-Zabolotskaya-Kuznetsov (KZK) equation, a model in the frequency domain is given to describe the transmission of finite amplitude sound beam in multi-layered biological media. Favorable agreement between the theoretical analyses and the measured results shows this approach could effectively describe the transmission of finite amplitude sound wave in multi-layered biological media

A study of tearing modes via electron cyclotron emission from tokamak plasmas

International Nuclear Information System (INIS)

Ren, C.

1998-07-01

This thesis studies several tearing mode problems from both theoretical and experimental points of view. A major part of this thesis is to demonstrate that Electron Cyclotron Emission (ECE) is an excellent diagnostic for studying an MHD mode structure and its properties in a tokamak plasma. It is shown that an MHD mode can be detected from the electron temperature fluctuations measured by ECE. The amplitude and phase profiles of the fluctuations contain detailed information about the mode structure. The ECE fluctuation phase profile indicates the magnetic island deformation due to the combination of sheared flow and viscosity. A model is presented to relate qualitatively the observed phase gradient to the local magnetic field, flow velocity shear and viscosity in a 2D slab geometry, using an ideal Ohm's law and the plasma momentum equation including flow and viscosity. Numerical solution of the resultant Grad-Shafranov-like equation describing the deformed island shows that the experimentally observed value of the phase gradient can be obtained under realistic parameters for the shear in the flow velocity and viscosity. A new approach to the tearing mode stability boundary and saturation level is also presented

A study of tearing modes via electron cyclotron emission from tokamak plasmas

Energy Technology Data Exchange (ETDEWEB)

Ren, Chuang [Univ. of Wisconsin, Madison, WI (United States)

1998-07-01

This thesis studies several tearing mode problems from both theoretical and experimental points of view. A major part of this thesis is to demonstrate that Electron Cyclotron Emission (ECE) is an excellent diagnostic for studying an MHD mode structure and its properties in a tokamak plasma. It is shown that an MHD mode can be detected from the electron temperature fluctuations measured by ECE. The amplitude and phase profiles of the fluctuations contain detailed information about the mode structure. The ECE fluctuation phase profile indicates the magnetic island deformation due to the combination of sheared flow and viscosity. A model is presented to relate qualitatively the observed phase gradient to the local magnetic field, flow velocity shear and viscosity in a 2D slab geometry, using an ideal Ohm`s law and the plasma momentum equation including flow and viscosity. Numerical solution of the resultant Grad-Shafranov-like equation describing the deformed island shows that the experimentally observed value of the phase gradient can be obtained under realistic parameters for the shear in the flow velocity and viscosity. A new approach to the tearing mode stability boundary and saturation level is also presented.

Detection of B-mode polarization in the cosmic microwave background with data from the South Pole Telescope.

Science.gov (United States)

Hanson, D; Hoover, S; Crites, A; Ade, P A R; Aird, K A; Austermann, J E; Beall, J A; Bender, A N; Benson, B A; Bleem, L E; Bock, J J; Carlstrom, J E; Chang, C L; Chiang, H C; Cho, H-M; Conley, A; Crawford, T M; de Haan, T; Dobbs, M A; Everett, W; Gallicchio, J; Gao, J; George, E M; Halverson, N W; Harrington, N; Henning, J W; Hilton, G C; Holder, G P; Holzapfel, W L; Hrubes, J D; Huang, N; Hubmayr, J; Irwin, K D; Keisler, R; Knox, L; Lee, A T; Leitch, E; Li, D; Liang, C; Luong-Van, D; Marsden, G; McMahon, J J; Mehl, J; Meyer, S S; Mocanu, L; Montroy, T E; Natoli, T; Nibarger, J P; Novosad, V; Padin, S; Pryke, C; Reichardt, C L; Ruhl, J E; Saliwanchik, B R; Sayre, J T; Schaffer, K K; Schulz, B; Smecher, G; Stark, A A; Story, K T; Tucker, C; Vanderlinde, K; Vieira, J D; Viero, M P; Wang, G; Yefremenko, V; Zahn, O; Zemcov, M

2013-10-04

Gravitational lensing of the cosmic microwave background generates a curl pattern in the observed polarization. This "B-mode" signal provides a measure of the projected mass distribution over the entire observable Universe and also acts as a contaminant for the measurement of primordial gravity-wave signals. In this Letter we present the first detection of gravitational lensing B modes, using first-season data from the polarization-sensitive receiver on the South Pole Telescope (SPTpol). We construct a template for the lensing B-mode signal by combining E-mode polarization measured by SPTpol with estimates of the lensing potential from a Herschel-SPIRE map of the cosmic infrared background. We compare this template to the B modes measured directly by SPTpol, finding a nonzero correlation at 7.7σ significance. The correlation has an amplitude and scale dependence consistent with theoretical expectations, is robust with respect to analysis choices, and constitutes the first measurement of a powerful cosmological observable.

Modal effects on amplitude perturbations on subionospheric signals (trimpis) deduced from two-frequency measurements

International Nuclear Information System (INIS)

Dowden, R.L.; Adams, C.D.D.

1989-01-01

Interference between the first two modes of Earth-ionosphere waveguide propagation at the high end of the VLF band (> 18 kHz) increases with distance from the transmitter out to very large distances and can add amplitude perturbations to the phase perturbations (trimpis) produced by lightning-induced electron precipitation (LEP) on the great circle path. Since the two modes have slightly different phase velocities, an interference pattern or standing wave is formed which is shifted slightly along the propagation path by the LEP-induced change in differential phase velocity. The model effect at the receiver depends on the local gradient (along the great circle path) of amplitude with respect to the differential phase. Since this differential or mode beat phase varies with frequency, measurement of the resultant amplitude at two close frequencies enables an estimation of the modal effects. In this study, measurements were made at Dunedin at the two MSK frequencies, 22,250 Hz and 22,350 Hz, of the transmitter NWC, during a night of frequent one-dimensional trimpis (i.e., those produced by large-area LEP occurring close to the great circle path) and of strong and varying modal interference. Modal generation or modification of trimpi amplitude was related to the local gradient of amplitude as expected. From these results it was deduced that modal modification of echo trimpis (those produced by small area LEP occurring well off the great circle path), even under extreme conditions, is insignificant

In-situ piezoresponse force microscopy cantilever mode shape profiling

International Nuclear Information System (INIS)

Proksch, R.

2015-01-01

The frequency-dependent amplitude and phase in piezoresponse force microscopy (PFM) measurements are shown to be a consequence of the Euler-Bernoulli (EB) dynamics of atomic force microscope (AFM) cantilever beams used to make the measurements. Changes in the cantilever mode shape as a function of changes in the boundary conditions determine the sensitivity of cantilevers to forces between the tip and the sample. Conventional PFM and AFM measurements are made with the motion of the cantilever measured at one optical beam detector (OBD) spot location. A single OBD spot location provides a limited picture of the total cantilever motion, and in fact, experimentally observed cantilever amplitude and phase are shown to be strongly dependent on the OBD spot position for many measurements. In this work, the commonly observed frequency dependence of PFM response is explained through experimental measurements and analytic theoretical EB modeling of the PFM response as a function of both frequency and OBD spot location on a periodically poled lithium niobate sample. One notable conclusion is that a common choice of OBD spot location—at or near the tip of the cantilever—is particularly vulnerable to frequency dependent amplitude and phase variations stemming from dynamics of the cantilever sensor rather than from the piezoresponse of the sample

Further Development of Rotating Rake Mode Measurement Data Analysis

Science.gov (United States)

Dahl, Milo D.; Hixon, Ray; Sutliff, Daniel L.

2013-01-01

The Rotating Rake mode measurement system was designed to measure acoustic duct modes generated by a fan stage. After analysis of the measured data, the mode amplitudes and phases were quantified. For low-speed fans within axisymmetric ducts, mode power levels computed from rotating rake measured data would agree with the far-field power levels on a tone by tone basis. However, this agreement required that the sound from the noise sources within the duct propagated outward from the duct exit without reflection at the exit and previous studies suggested conditions could exist where significant reflections could occur. To directly measure the modes propagating in both directions within a duct, a second rake was mounted to the rotating system with an offset in both the axial and the azimuthal directions. The rotating rake data analysis technique was extended to include the data measured by the second rake. The analysis resulted in a set of circumferential mode levels at each of the two rake microphone locations. Radial basis functions were then least-squares fit to this data to obtain the radial mode amplitudes for the modes propagating in both directions within the duct. The fit equations were also modified to allow evanescent mode amplitudes to be computed. This extension of the rotating rake data analysis technique was tested using simulated data, numerical code produced data, and preliminary in-duct measured data.

Theoretical Study of Amplitude Modulation Application during Radio Frequency Electrocoagulation

Directory of Open Access Journals (Sweden)

V. A. Karpuhin

2015-01-01

Full Text Available This article concerns the investigation results of influence of the amplitude-modulated acting signal parameters on the thermoelectric characteristics of biological tissues for a specified geometry of the working electrode section during RF mono-polar electrocoagulation. The geometric model ‘electrode - a biological tissue’ was suggested to study the distribution of power and temperature fields in biological tissue during mono-polar coagulation. The model of biological tissue is represented as a cylinder and the needle electrode is an ellipsoid immersed in the biological tissue. The heat and quasi-electrostatics equations are used as a mathematical model. These equations are solved in Comsol Multiphysics environment.As a result, we have got the following findings: the technique of calculating parameters of the PAM acting signal which has a fixed carrier frequency for the needle electrode of a specified geometry and the immersion depth in biological tissues is suggested. Parameters of PAM signal are determined for this electrode geometry. These parameters provide a 60 ... 80°C heating range of biological tissues near the working part of the tool for different amplitudes of acting signal during RF coagulation. It has been found out that both the temperature and the relaxation frequency of biological tissue depend on exposure time for the needle electrode of a specified geometry and immersion depth of the working part of tool into biological tissue.It is shown that the relaxation frequency of the biological tissue, subjected to the radiofrequency pulses, linearly depends on its heating temperature and can be used as a numerical criterion for maintaining the specified temperature conditions. It is found that the relaxation frequency of the biological tissue depends on the contact area of the tool working part and biological tissues. To reduce this dependence it is necessary to provide automatic current control of the output action.

High-Energy String Scattering Amplitudes and Signless Stirling Number Identity

Directory of Open Access Journals (Sweden)

Jen-Chi Lee

2012-07-01

Full Text Available We give a complete proof of a set of identities (7 proposed recently from calculation of high-energy string scattering amplitudes. These identities allow one to extract ratios among high-energy string scattering amplitudes in the fixed angle regime from high-energy amplitudes in the Regge regime. The proof is based on a signless Stirling number identity in combinatorial theory. The results are valid for arbitrary real values L rather than only for L=0,1 proved previously. The identities for non-integer real value L were recently shown to be realized in high-energy compactified string scattering amplitudes [He S., Lee J.C., Yang Y., arXiv:1012.3158]. The parameter L is related to the mass level of an excited string state and can take non-integer values for Kaluza-Klein modes.

True amplitude wave equation migration arising from true amplitude one-way wave equations

Science.gov (United States)

Zhang, Yu; Zhang, Guanquan; Bleistein, Norman

2003-10-01

One-way wave operators are powerful tools for use in forward modelling and inversion. Their implementation, however, involves introduction of the square root of an operator as a pseudo-differential operator. Furthermore, a simple factoring of the wave operator produces one-way wave equations that yield the same travel times as the full wave equation, but do not yield accurate amplitudes except for homogeneous media and for almost all points in heterogeneous media. Here, we present augmented one-way wave equations. We show that these equations yield solutions for which the leading order asymptotic amplitude as well as the travel time satisfy the same differential equations as the corresponding functions for the full wave equation. Exact representations of the square-root operator appearing in these differential equations are elusive, except in cases in which the heterogeneity of the medium is independent of the transverse spatial variables. Here, we address the fully heterogeneous case. Singling out depth as the preferred direction of propagation, we introduce a representation of the square-root operator as an integral in which a rational function of the transverse Laplacian appears in the integrand. This allows us to carry out explicit asymptotic analysis of the resulting one-way wave equations. To do this, we introduce an auxiliary function that satisfies a lower dimensional wave equation in transverse spatial variables only. We prove that ray theory for these one-way wave equations leads to one-way eikonal equations and the correct leading order transport equation for the full wave equation. We then introduce appropriate boundary conditions at z = 0 to generate waves at depth whose quotient leads to a reflector map and an estimate of the ray theoretical reflection coefficient on the reflector. Thus, these true amplitude one-way wave equations lead to a 'true amplitude wave equation migration' (WEM) method. In fact, we prove that applying the WEM imaging condition

A design of a mode converter for electron cyclotron heating by the method of normal mode expansion

International Nuclear Information System (INIS)

Hoshino, Katsumichi; Kawashima, Hisato; Hata, Kenichiro; Yamamoto, Takumi

1983-09-01

Mode conversion of electromagnetic wave propagating in the over-size circular waveguide is attained by giving a periodical perturbation in the guide wall. Mode coupling equation is expressed by ''generalized telegraphist's equations'' which are derived from the Maxwell's equations using a normal mode expansion. A computer code to solve the coupling equations is developed and mode amplitude, conversion efficiency, etc. of a particular type of mode converter for the 60 GHz electron cyclotron heating are obtained. (author)

Source-Space Cross-Frequency Amplitude-Amplitude Coupling in Tinnitus

Directory of Open Access Journals (Sweden)

Oliver Zobay

2015-01-01

Full Text Available The thalamocortical dysrhythmia (TCD model has been influential in the development of theoretical explanations for the neurological mechanisms of tinnitus. It asserts that thalamocortical oscillations lock a region in the auditory cortex into an ectopic slow-wave theta rhythm (4–8 Hz. The cortical area surrounding this region is hypothesized to generate abnormal gamma (>30 Hz oscillations (“edge effect” giving rise to the tinnitus percept. Consequently, the model predicts enhanced cross-frequency coherence in a broad range between theta and gamma. In this magnetoencephalography study involving tinnitus and control cohorts, we investigated this prediction. Using beamforming, cross-frequency amplitude-amplitude coupling (AAC was computed within the auditory cortices for frequencies (f1,f2 between 2 and 80 Hz. We find the AAC signal to decompose into two distinct components at low (f1,f230 Hz frequencies, respectively. Studying the correlation of AAC with several key covariates (age, hearing level (HL, tinnitus handicap and duration, and HL at tinnitus frequency, we observe a statistically significant association between age and low-frequency AAC. Contrary to the TCD predictions, however, we do not find any indication of statistical differences in AAC between tinnitus and controls and thus no evidence for the predicted enhancement of cross-frequency coupling in tinnitus.

Non-linear radial spinwave modes in thin magnetic disks

International Nuclear Information System (INIS)

Helsen, M.; De Clercq, J.; Vansteenkiste, A.; Van Waeyenberge, B.; Gangwar, A.; Back, C. H.; Weigand, M.

2015-01-01

We present an experimental investigation of radial spin-wave modes in magnetic nano-disks with a vortex ground state. The spin-wave amplitude was measured using a frequency-resolved magneto-optical spectrum analyzer, allowing for high-resolution resonance curves to be recorded. It was found that with increasing excitation amplitude up to about 10 mT, the lowest-order mode behaves strongly non-linearly as the mode frequency redshifts and the resonance peak strongly deforms. This behavior was quantitatively reproduced by micromagnetic simulations. Micromagnetic simulations showed that at higher excitation amplitudes, the spinwaves are transformed into a soliton by self-focusing, and collapse onto the vortex core, dispersing the energy in short-wavelength spinwaves. Additionally, this process can lead to switching of the vortex polarization through the injection of a Bloch point

Non-adiabatic study of the Kepler subgiant KIC 6442183

Directory of Open Access Journals (Sweden)

Grosjean M.

2015-01-01

Full Text Available Thanks to the precision of Kepler observations, [3] were able to measure the linewidth and amplitude of individual modes (including mixed modes in several subgiant power spectra. We perform a forward modelling of a Kepler subgiant based on surface properties and observed frequencies. Non-adiabatic computations including a time- dependent treatment of convection give the lifetimes of radial and non-radial modes. Next, combining the lifetimes and inertias with a stochastic excitation model gives the amplitudes of the modes. We can now directly compare theoretical and observed linewidths and amplitudes of mixed-modes to obtain new constraints on our theoretical models.

Chirally motivated separable potential model for eta N amplitudes

Czech Academy of Sciences Publication Activity Database

Cieplý, Aleš; Smejkal, J.

2013-01-01

Roč. 919, DEC (2013), s. 46-66 ISSN 0375-9474 R&D Projects: GA ČR(CZ) GAP203/12/2126 Institutional support: RVO:61389005 Keywords : Chrial model * eta-nucleon amplitude * Baryon resonances Subject RIV: BE - Theoretical Physics Impact factor: 2.499, year: 2013

Automated force controller for amplitude modulation atomic force microscopy

Energy Technology Data Exchange (ETDEWEB)

Miyagi, Atsushi, E-mail: atsushi.miyagi@inserm.fr, E-mail: simon.scheuring@inserm.fr; Scheuring, Simon, E-mail: atsushi.miyagi@inserm.fr, E-mail: simon.scheuring@inserm.fr [U1006 INSERM, Université Aix-Marseille, Parc Scientifique et Technologique de Luminy, 163 Avenue de Luminy, 13009 Marseille (France)

2016-05-15

Atomic Force Microscopy (AFM) is widely used in physics, chemistry, and biology to analyze the topography of a sample at nanometer resolution. Controlling precisely the force applied by the AFM tip to the sample is a prerequisite for faithful and reproducible imaging. In amplitude modulation (oscillating) mode AFM, the applied force depends on the free and the setpoint amplitudes of the cantilever oscillation. Therefore, for keeping the applied force constant, not only the setpoint amplitude but also the free amplitude must be kept constant. While the AFM user defines the setpoint amplitude, the free amplitude is typically subject to uncontrollable drift, and hence, unfortunately, the real applied force is permanently drifting during an experiment. This is particularly harmful in biological sciences where increased force destroys the soft biological matter. Here, we have developed a strategy and an electronic circuit that analyzes permanently the free amplitude of oscillation and readjusts the excitation to maintain the free amplitude constant. As a consequence, the real applied force is permanently and automatically controlled with picoNewton precision. With this circuit associated to a high-speed AFM, we illustrate the power of the development through imaging over long-duration and at various forces. The development is applicable for all AFMs and will widen the applicability of AFM to a larger range of samples and to a larger range of (non-specialist) users. Furthermore, from controlled force imaging experiments, the interaction strength between biomolecules can be analyzed.

Tacoma mode

International Nuclear Information System (INIS)

Courant, E.D.; Ruth, R.D.; Wang, J.M.

1979-01-01

The name Tacoma refers to the Tacoma Narrows Bridge which collapsed on November 8, 1940 due to massive oscillations caused by high winds. One of the destructive modes was a torsion mode which was excited by transverse wind, a dipole force, and continued until the bridge collapsed. The name is used to refer to a coherent mode of oscillation of a spectrum of oscillators in which the amplitude vs frequency graph contains one node, where the node occurs near the driving frequency and a(ω) is not symmetric about zero. When this result is applied to vertical instabilities in coasting beams, it implies the existence of a coherent skew quadrupole moment, whenever a coherent dipole oscillation exists

Functional dependence of resonant harmonics on nanomechanical parameters in dynamic mode atomic force microscopy.

Science.gov (United States)

Gramazio, Federico; Lorenzoni, Matteo; Pérez-Murano, Francesc; Rull Trinidad, Enrique; Staufer, Urs; Fraxedas, Jordi

2017-01-01

We present a combined theoretical and experimental study of the dependence of resonant higher harmonics of rectangular cantilevers of an atomic force microscope (AFM) as a function of relevant parameters such as the cantilever force constant, tip radius and free oscillation amplitude as well as the stiffness of the sample's surface. The simulations reveal a universal functional dependence of the amplitude of the 6th harmonic (in resonance with the 2nd flexural mode) on these parameters, which can be expressed in terms of a gun-shaped function. This analytical expression can be regarded as a practical tool for extracting qualitative information from AFM measurements and it can be extended to any resonant harmonics. The experiments confirm the predicted dependence in the explored 3-45 N/m force constant range and 2-345 GPa sample's stiffness range. For force constants around 25 N/m, the amplitude of the 6th harmonic exhibits the largest sensitivity for ultrasharp tips (tip radius below 10 nm) and polymers (Young's modulus below 20 GPa).

Linear stability of microtearing modes in ASDEX

International Nuclear Information System (INIS)

Giannone, L.

1987-12-01

The linear stability of microtearing modes in typical ASDEX discharges have been calculated. In the case of Ohmic discharges it was found that unstable modes are predicted to be located towards the centre of the plasma. For L and H discharges the zone of instability shifts towards the plasma edge. The interpretation of an increase or decrease in the amplitude of broadband magnetic fluctuations during L and H discharges must be interpreted with caution, since the amplitude observed is strongly dependent on the radial position of the instability. (orig./GG)

Influence of transverse mode on retinal spot size and retinal injury effect: A theoretical analysis on 532-nm laser

Directory of Open Access Journals (Sweden)

Jia-Rui Wang

2014-05-01

Full Text Available The fundamental transverse mode (TEM00 is preferable for experimental and theoretical study on the laser-induced retinal injury effect, for it can produce the minimal retinal image and establish the most strict laser safety standards. But actually lasers with higher order mode were frequently used in both earlier and recent studies. Generally higher order mode leads to larger retinal spot size and so higher damage threshold, but there are few quantitative analyses on this problem. In this paper, a four-surface schematic eye model is established for human and macaque. The propagation of 532-nm laser in schematic eye is analyzed by the ABCD law of Gaussian optics. It is shown that retinal spot size increases with laser transverse mode order. For relative lower mode order, the retinal spot diameter will not exceed the minimum laser-induced retinal lesion (25 ~ 30 μm in diameter, and so has little effect on retinal damage threshold. While for higher order mode, the larger retinal spot requires more energy to induce injury and so the damage threshold increases. When beam divergence is lowered, the retinal spot size decreases correspondingly, so the effect of mode order can be compensated. The retinal spot size of macaque is slightly smaller than that of human and the ratio between them is independent of mode order. We conclude that the laser mode order has significant influence on retinal spot size but limited influence on the retinal injury effect.

Mode shape and natural frequency identification for seismic analysis from background vibration

International Nuclear Information System (INIS)

Bhan, S.; Wozniak, Z.

1986-02-01

The feasibility of calculating natural frequencies and mode shapes of major equipment in a CANDU reactor from the measurements of their response to background excitation has been studied. A review of vibration data measured at various locations in CANDU plants shows that structures responded to a combination of random and harmonic background excitation. Amplitude of measured vibration is sufficient to allow meaningful data analysis. Frequency content in the 0 to 50-Hz range, which is of interest for earthquake response, is present in some of the vibration measurements studied. Spectral techniques have been developed for determining the response function of structures from measured vibration response to background excitation. The natural frequencies and mode shapes are then evaluated graphically from the frequency function plots. The methodology has been tested on a simple cantilever beam with known natural frequencies and mode shapes. The comparison between the theoretical and the computed natural frequencies and mode shapes is good for the lower modes. However, better curve-fitting techniques will be required in future, especially for higher modes. Readily available equipment necessary for the measurement of background vibration in a CANDU plant (which is commercially available) has been identified. An experimental program has been proposed to verify the methodology developed in this study. Recommendations are also made to study methods to improve the accuracy of the mode shape and natural frequency prediction

String amplitudes: from field theories to number theory

CERN Multimedia

CERN. Geneva

2017-01-01

In a variety of recent developments, scattering amplitudes hint at new symmetries of and unexpected connections between physical theories which are otherwise invisible in their conventional description via Feynman diagrams or Lagrangians. Yet, many of these hidden structures are conveniently accessible to string theory where gauge interactions and gravity arise as the low-energy excitations of open and closed strings. In this talk, I will give an intuitive picture of gravity as a double copy of gauge interactions and extend the web of relations to scalar field theories including chiral Lagrangians for Goldstone bosons. The string corrections to gauge and gravity amplitudes beyond their point-particle limit exhibit elegant mathematical structures and offer a convenient laboratory to explore modern number-theoretic concepts in a simple context. As a common theme with Feynman integrals, string amplitudes introduce a variety of periods and special functions including multiple zeta values and polylogarithms, orga...

Theoretical treatment of high-frequency, large-amplitude ac voltammetry applied to ideal surface-confined redox systems

International Nuclear Information System (INIS)

Bell, Christopher G.; Anastassiou, Costas A.; O’Hare, Danny; Parker, Kim H.; Siggers, Jennifer H.

2012-01-01

Highlights: ► Theory of ac voltammetry on ideal surface-confined redox systems. ► Analytical description of the harmonics and transient of the current response. ► Solution valid for high frequency, large-amplitude sinusoidal input voltage. ► Protocol for determining system parameters from experimental current responses. - Abstract: Large-amplitude ac voltammetry, where the applied voltage is a large-amplitude sinusoidal waveform superimposed onto a dc ramp, is a powerful method for investigating the reaction kinetics of surface-confined redox species. Here we consider the large-amplitude ac voltammetric current response of a quasi-reversible, ideal, surface-confined redox system, for which the redox reaction is described by Butler–Volmer theory. We derive an approximate analytical solution, which is valid whenever the angular frequency of the sine-wave is much larger than the rate of the dc ramp and the standard kinetic rate constant of the redox reaction. We demonstrate how the third harmonic and the initial transient of the current response can be used to estimate parameters of the electrochemical system, namely the kinetic rate constant, the electron transfer coefficient, the adsorption formal potential, the initial proportion of oxidised molecules and the linear double-layer capacitance.

On the role of resonances in double-mode pulsation

International Nuclear Information System (INIS)

Dziembowski, W.; Kovacs, G.

1984-01-01

Simultaneous effects of resonant coupling and non-linear saturation of linear driving mechanism on the finite amplitude solution of multi-modal pulsation problem and on its stability are investigated. Both effects are calculated in the lowest order of approximation in terms of amplitudes. It is shown that the 2:1 resonance between one of the two linearly unstable modes and a higher frequency mode causes double-mode (fundamental and first overtone) pulsation. In a certain range of parameters, such as the frequency mismatch, the linear growth and damping rates, it is the only stable solution of the problem. (author)

Secondary Instability of Second Modes in Hypersonic Boundary Layers

Science.gov (United States)

Li, Fei; Choudhari, Meelan M.; Chang, Chau-Lyan; White, Jeffery A.

2012-01-01

Second mode disturbances dominate the primary instability stage of transition in a number of hypersonic flow configurations. The highest amplification rates of second mode disturbances are usually associated with 2D (or axisymmetric) perturbations and, therefore, a likely scenario for the onset of the three-dimensionality required for laminar-turbulent transition corresponds to the parametric amplification of 3D secondary instabilities in the presence of 2D, finite amplitude second mode disturbances. The secondary instability of second mode disturbances is studied for selected canonical flow configurations. The basic state for the secondary instability analysis is obtained by tracking the linear and nonlinear evolution of 2D, second mode disturbances using nonlinear parabolized stability equations. Unlike in previous studies, the selection of primary disturbances used for the secondary instability analysis was based on their potential relevance to transition in a low disturbance environment and the effects of nonlinearity on the evolution of primary disturbances was accounted for. Strongly nonlinear effects related to the self-interaction of second mode disturbances lead to an upstream shift in the upper branch neutral location. Secondary instability computations confirm the previously known dominance of subharmonic modes at relatively small primary amplitudes. However, for the Purdue Mach 6 compression cone configuration, it was shown that a strong fundamental secondary instability can exist for a range of initial amplitudes of the most amplified second mode disturbance, indicating that the exclusive focus on subharmonic modes in the previous applications of secondary instability theory to second mode primary instability may not have been fully justified.

Tapping mode imaging and measurements with an inverted atomic force microscope.

Science.gov (United States)

Chan, Sandra S F; Green, John-Bruce D

2006-07-18

This report demonstrates the successful use of the inverted atomic force microscope (i-AFM) for tapping mode AFM imaging of cantilever-supported samples. i-AFM is a mode of AFM operation in which a sample supported on a tipless cantilever is imaged by one of many tips in a microfabricated tip array. Tapping mode is an intermittent contact mode whereby the cantilever is oscillated at or near its resonance frequency, and the amplitude and/or phase are used to image the sample. In the process of demonstrating that tapping mode images could be obtained in the i-AFM design, it was observed that the amplitude of the cantilever oscillation decreased markedly as the cantilever and tip array were approached. The source of this damping of the cantilever oscillations was identified to be the well-known "squeeze film damping", and the extent of damping was a direct consequence of the relatively shorter tip heights for the tip arrays, as compared to those of commercially available tapping mode cantilevers with integrated tips. The functional form for the distance dependence of the damping coefficient is in excellent agreement with previously published models for squeeze film damping, and the values for the fitting parameters make physical sense. Although the severe damping reduces the cantilever free amplitude substantially, we found that we were still able to access the low-amplitude regime of oscillation necessary for attractive tapping mode imaging of fragile molecules.

Experimental and theoretical studies of active control of resistive wall mode growth in the EXTRAP T2R reversed-field pinch

International Nuclear Information System (INIS)

Drake, J.R.; Brunsell, P.R.; Yadikin, D.; Cecconello, M.; Malmberg, J.A.; Gregoratto, D.; Paccagnella, R.; Bolzonella, T.; Manduchi, G.; Marrelli, L.; Ortolani, S.; Spizzo, G.; Zanca, P.; Bondeson, A.; Liu, Y.Q.

2005-01-01

Active feedback control of resistive wall modes (RWMs) has been demonstrated on the EXTRAP T2R reversed-field pinch experiment. The control system includes a sensor consisting of an array of magnetic coils (measuring mode harmonics) and an actuator consisting of a saddle coil array (producing control harmonics). Closed-loop (feedback) experiments using a digital controller based on a real time Fourier transform of sensor data have been studied for cases where the feedback gain was constant and real for all harmonics (intelligent-shell) and cases where the feedback gain could be set for selected harmonics, with both real or complex values (targeted-harmonics). The growth of the dominant RWMs can be suppressed by feedback for both the intelligent-shell and targeted-harmonic control systems. Because the number of toroidal positions of saddle coils in the array is half the number of sensors, it is predicted and observed experimentally that the control harmonic spectrum has sidebands. As a result, each control harmonic has to control simultaneously two mode harmonics. Real gains can stabilize non-rotating RWMs, while complex gains give better results for (slowly) rotating RWMs. In addition open loop experiments have been used to observe the effects of resonant field errors applied to unstable, marginally stable and robustly stable modes. The observed effects of field errors are consistent with the thin-wall model, where mode growth is proportional to the resonant field error amplitude and the wall penetration time for that mode harmonic. (author)

The locking and unlocking thresholds for tearing modes in a cylindrical tokamak

Energy Technology Data Exchange (ETDEWEB)

Huang, Wenlong [CAS Key Laboratory of Geospace Environment and Department of Modern Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China); Zhu, Ping, E-mail: pzhu@ustc.edu.cn [CAS Key Laboratory of Geospace Environment and Department of Modern Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China); Department of Engineering Physics, University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States)

2016-03-15

The locking and unlocking thresholds for tearing modes are in general different. In this work, the physics origin for this difference is illustrated from theory analysis, and a numerical procedure is developed to find both locking and unlocking thresholds. In particular, a new scaling law for the unlocking threshold that is valid in both weak and strong rotation regimes has been derived from the lowest amplitude of the RMP (resonant magnetic perturbation) allowed for the locked-mode solution. Above the unlocking threshold, the criterion for the phase-flip instability is extended to identify the entire locked-mode states. Two different regimes of the RMP amplitude in terms of the accessibility of the locked-mode states have been found. In the first regime, the locked-mode state may or may not be accessible depending on the initial conditions of an evolving island. In the second regime, the locked-mode state can always be reached regardless of the initial conditions of the tearing mode. The lowest RMP amplitude for the second regime is determined to be the mode-locking threshold. The different characteristics of the two regimes above the unlocking threshold reveal the underlying physics for the gap between the locking and unlocking thresholds and provide an explanation for the closely related and widely observed hysteresis phenomena in island evolution during the sweeping process of the RMP amplitude up and down across that threshold gap.

Production of enhanced beam halos via collective modes and colored noise

Directory of Open Access Journals (Sweden)

Ioannis V. Sideris

2004-10-01

Full Text Available We investigate how collective modes and colored noise conspire to produce a beam halo with much larger amplitude than could be generated by either phenomenon separately. The collective modes are lowest-order radial eigenmodes calculated self-consistently for a configuration corresponding to a direct-current, cylindrically symmetric, warm-fluid Kapchinskij-Vladimirskij equilibrium. The colored noise arises from unavoidable machine errors and influences the internal space-charge force. Its presence quickly launches statistically rare particles to ever-growing amplitudes by continually kicking them back into phase with the collective-mode oscillations. The halo amplitude is essentially the same for purely radial orbits as for orbits that are initially purely azimuthal; orbital angular momentum has no statistically significant impact. Factors that do have an impact include the amplitudes of the collective modes and the strength and autocorrelation time of the colored noise. The underlying dynamics ensues because the noise breaks the Kolmogorov-Arnol’d-Moser tori that otherwise would confine the beam. These tori are fragile; even very weak noise will eventually break them, though the time scale for their disintegration depends on the noise strength. Both collective modes and noise are therefore centrally important to the dynamics of halo formation in real beams.

Comparison of Three Methods in Extracting Coherent Modes from a Doppler Backscatter System

International Nuclear Information System (INIS)

Zhang Xiao-Hui; Liu A-Di; Zhou Chu; Hu Jian-Qiang; Wang Ming-Yuan; Yu Chang-Xuan; Liu Wan-Dong; Li Hong; Lan Tao; Xie Jin-Lin

2015-01-01

We compare three different methods to extract coherent modes from Doppler backscattering (DBS), which are center of gravity (COG) of the complex amplitude spectrum, spectrum of DBS phase derivative (phase derivative method), and phase spectrum, respectively. These three methods are all feasible to extract coherent modes, for example, geodesic acoustic mode oscillation. However, there are still differences between dealing with high frequency modes (several hundred kHz) and low frequency modes (several kHz) hiding in DBS signal. There is a significant amount of power at low frequencies in the phase spectrum, which can be removed by using the phase derivative method and COG. High frequency modes are clearer by using the COG and the phase derivative method than the phase spectrum. The spectrum of DBS amplitude does not show the coherent modes detected by using COG, phase derivative method and phase spectrum. When two Doppler shifted peaks exist, coherent modes and their harmonics appear in the spectrum of DBS amplitude, which are introduced by the DBS phase. (paper)

Tacoma mode

International Nuclear Information System (INIS)

Courant, E.D.; Ruth, R.D.; Wang, J.M.

1979-01-01

The name Tacoma refers to the Tacoma Narrows Bridge which collapsed on November 8, 1940 due to massive oscillations caused by high winds. One of the destructive modes was a torsion mode which was excited by transverse wind, a dipole force, and continued until the bridge collapsed. The name is used to refer to a coherent mode of oscillation of a spectrum of oscillators in which the amplitude vs frequency graph contains one node, where the node occurs near the driving frequency and a ω is not symmetric about zero. When this result is applied to vertical instabilities in coasting beams, it implies the existence of a coherent skew quadrupole moment, Q/sub xy/, whenever a coherent dipole oscillation exists

Higher-order spin effects in the amplitude and phase of gravitational waveforms emitted by inspiraling compact binaries: Ready-to-use gravitational waveforms

International Nuclear Information System (INIS)

Arun, K. G.; Buonanno, Alessandra; Ochsner, Evan; Faye, Guillaume

2009-01-01

We provide ready-to-use time-domain gravitational waveforms for spinning compact binaries with precession effects through 1.5 post-Newtonian (PN) order in amplitude, and compute their mode decomposition using spin-weighted -2 spherical harmonics. In the presence of precession, the gravitational-wave modes (l,m) contain harmonics originating from combinations of the orbital frequency and precession frequencies. We find that the gravitational radiation from binary systems with large mass asymmetry and large inclination angle can be distributed among several modes. For example, during the last stages of inspiral, for some maximally spinning configurations, the amplitude of the (2, 0) and (2, 1) modes can be comparable to the amplitude of the (2, 2) mode. If the mass ratio is not too extreme, the l=3 and l=4 modes are generally 1 or 2 orders of magnitude smaller than the l=2 modes. Restricting ourselves to spinning, nonprecessing compact binaries, we apply the stationary-phase approximation and derive the frequency-domain gravitational waveforms including spin-orbit and spin(1)-spin(2) effects through 1.5PN and 2PN order, respectively, in amplitude, and 2.5PN order in phase. Since spin effects in the amplitude through 2PN order affect only the first and second harmonics of the orbital phase, they do not extend the mass reach of gravitational-wave detectors. However, they can interfere with other harmonics and lower or raise the signal-to-noise ratio depending on the spin orientation. These ready-to-use waveforms could be employed in the data analysis of the spinning, inspiraling binaries as well as in comparison studies at the interface between analytical and numerical relativity.

Saturation and postsaturation phenomena of Rayleigh-Taylor instability with adjacent modes

International Nuclear Information System (INIS)

Ikegawa, Tadashi; Nishihara, Katsunobu

2003-01-01

A weakly nonlinear theory has been developed for the classical Rayleigh-Taylor instability with a finite bandwidth taken into account self-consistently. The theory includes up to third order nonlinearity, which results in the saturation of linear growth and determines subsequent weakly nonlinear growth. Analytical results are shown to agree fairly well with two-dimensional hydrodynamic simulations. There are generally many local peaks of a perturbation with a finite bandwidth due to the interference of modes. Since a local amplitude is determined from phases among the modes as well as the bandwidth, we have investigated an onset of the linear growth saturation and the subsequent weakly nonlinear growth for different bandwidths and phases. It is shown that the saturation of the linear growth occurs locally, i.e., each of the local maximum amplitudes (LMAs) grows exponentially until it reaches almost the same saturation amplitude. In the random phase case, the root mean square amplitude thus saturates with almost the same amplitude as the LMA, after most of the LMAs have saturated. The saturation amplitude of the LMA is found to be independent of the bandwidth and depends on the Atwood number. We derive a formula of the saturation amplitude of modes based on the results obtained, and discuss its relation with Haan's formula [Phys. Rev. A 39, 5812 (1989)]. The LMAs grow linearly in time after the saturation and their speeds are approximated by the product of the linear growth rate and the saturation amplitude. We investigate the Atwood number dependence of both the saturation amplitude and the weakly nonlinear growth

External amplitude and frequency modulation of a terahertz quantum cascade laser using metamaterial/graphene devices.

Science.gov (United States)

Kindness, S J; Jessop, D S; Wei, B; Wallis, R; Kamboj, V S; Xiao, L; Ren, Y; Braeuninger-Weimer, P; Aria, A I; Hofmann, S; Beere, H E; Ritchie, D A; Degl'Innocenti, R

2017-08-09

Active control of the amplitude and frequency of terahertz sources is an essential prerequisite for exploiting a myriad of terahertz applications in imaging, spectroscopy, and communications. Here we present a optoelectronic, external modulation technique applied to a terahertz quantum cascade laser which holds the promise of addressing a number of important challenges in this research area. A hybrid metamaterial/graphene device is implemented into an external cavity set-up allowing for optoelectronic tuning of feedback into a quantum cascade laser. We demonstrate powerful, all-electronic, control over the amplitude and frequency of the laser output. Full laser switching is performed by electrostatic gating of the metamaterial/graphene device, demonstrating a modulation depth of 100%. External control of the emission spectrum is also achieved, highlighting the flexibility of this feedback method. By taking advantage of the frequency dispersive reflectivity of the metamaterial array, different modes of the QCL output are selectively suppressed using lithographic tuning and single mode operation of the multi-mode laser is enforced. Side mode suppression is electrically modulated from ~6 dB to ~21 dB, demonstrating active, optoelectronic modulation of the laser frequency content between multi-mode and single mode operation.

Effect of removing the common mode errors on linear regression analysis of noise amplitudes in position time series of a regional GPS network & a case study of GPS stations in Southern California

Science.gov (United States)

Jiang, Weiping; Ma, Jun; Li, Zhao; Zhou, Xiaohui; Zhou, Boye

2018-05-01

The analysis of the correlations between the noise in different components of GPS stations has positive significance to those trying to obtain more accurate uncertainty of velocity with respect to station motion. Previous research into noise in GPS position time series focused mainly on single component evaluation, which affects the acquisition of precise station positions, the velocity field, and its uncertainty. In this study, before and after removing the common-mode error (CME), we performed one-dimensional linear regression analysis of the noise amplitude vectors in different components of 126 GPS stations with a combination of white noise, flicker noise, and random walking noise in Southern California. The results show that, on the one hand, there are above-moderate degrees of correlation between the white noise amplitude vectors in all components of the stations before and after removal of the CME, while the correlations between flicker noise amplitude vectors in horizontal and vertical components are enhanced from un-correlated to moderately correlated by removing the CME. On the other hand, the significance tests show that, all of the obtained linear regression equations, which represent a unique function of the noise amplitude in any two components, are of practical value after removing the CME. According to the noise amplitude estimates in two components and the linear regression equations, more accurate noise amplitudes can be acquired in the two components.

Minimal formulation of the linear spatial analysis of capillary jets: Validity of the two-mode approach

Science.gov (United States)

González, H.; Vazquez, P. A.; García, F. J.; Guerrero, J.

2018-04-01

A rigorous and complete formulation of the linear evolution of harmonically stimulated capillary jets should include infinitely many spatial modes to account for arbitrary exit conditions [J. Guerrero et al., J. Fluid Mech. 702, 354 (2012), 10.1017/jfm.2012.182]. However, it is not rare to find works in which only the downstream capillary dominant mode, the sole unstable one, is retained, with amplitude determined by the jet deformation at the exit. This procedure constitutes an oversimplification, unable to handle a flow rate perturbation without jet deformation at the exit (the most usual conditions). In spite of its decaying behavior, the other capillary mode (subdominant) must be included in what can be called a "minimal linear formulation." Deformation and mean axial velocity amplitudes at the jet exit are the two relevant parameters to simultaneously find the amplitudes of both capillary modes. Only once these amplitudes are found, the calculation of the breakup length may be eventually simplified by disregarding the subdominant mode. Simple recipes are provided for predicting the breakup length, which are checked against our own numerical simulations. The agreement is better than in previous attempts in the literature. Besides, the limits of validity of the linear formulation are explored in terms of the exit velocity amplitude, the wave number, the Weber number, and the Ohnesorge number. Including the subdominant mode extends the range of amplitudes for which the linear model gives accurate predictions, the criterion for keeping this mode being that the breakup time must be shorter than a given formula. It has been generally assumed that the shortest intact length happens for the stimulation frequency with the highest growth rate. However, we show that this correlation is not strict because the amplitude of the dominant mode has a role in the breakup process and it depends on the stimulation frequency.

Ozil IP torsional mode versus combined torsional/longitudinal microcoaxial phacoemulsification.

Science.gov (United States)

Helvacioglu, Firat; Tunc, Zeki; Yeter, Celal; Oguzhan, Hasan; Sencan, Sadik

2012-01-01

To compare the safety and efficacy of microcoaxial phacoemulsification surgeries performed with the Ozil Intelligent Phaco (IP) torsional mode and combined torsional/longitudinal ultrasound (US) mode using the Infiniti Vision System (Alcon Laboratories). In this prospective randomized comparative study, 60 eyes were assigned to 2.2-mm microcoaxial phacoemulsification using the Ozil IP torsional mode (group 1) or combined torsional/longitudinal US mode (group 2). The primary outcome measures were US time (UST), cumulative dissipated energy (CDE), longitudinal and torsional ultrasound amplitudes, mean operation time, mean volume of balanced salt solution (BSS) used, and surgical complications. Both groups included 30 eyes. Mean UST, CDE, and longitudinal and torsional ultrasound amplitudes in group 1 were 1 minute 15±34.33 seconds, 8.74±5.64, 0.43±0.74, and 25.56±8.56, respectively, and these parameters in group 2 were 1 minute 40±51.44 seconds, 9.28±5.99, 3.64±1.55, and 3.71±1.34, respectively. UST and longitudinal amplitudes were found to be significantly low in group 1 (p<0.001, p<0.001), whereas torsional amplitude was found to be significantly high in this group (p=0.001). Mean volumes of BSS used in groups 1 and 2 were 63.30±18.00 cc and 84.50±28.65 cc, respectively (p=0.001). The Ozil IP torsional mode may provide more effective lens removal than the combined torsional/longitudinal US mode with a lower UST and volume of BSS used.

Separation of musical instruments based on amplitude and frequency comodulation

Science.gov (United States)

Jacobson, Barry D.; Cauwenberghs, Gert; Quatieri, Thomas F.

2002-05-01

In previous work, amplitude comodulation was investigated as a basis for monaural source separation. Amplitude comodulation refers to similarities in amplitude envelopes of individual spectral components emitted by particular types of sources. In many types of musical instruments, amplitudes of all resonant modes rise/fall, and start/stop together during the course of normal playing. We found that under certain well-defined conditions, a mixture of constant frequency, amplitude comodulated sources can unambiguously be decomposed into its constituents on the basis of these similarities. In this work, system performance was improved by relaxing the constant frequency requirement. String instruments, for example, which are normally played with vibrato, are both amplitude and frequency comodulated sources, and could not be properly tracked under the constant frequency assumption upon which our original algorithm was based. Frequency comodulation refers to similarities in frequency variations of individual harmonics emitted by these types of sources. The analytical difficulty is in defining a representation of the source which properly tracks frequency varying components. A simple, fixed filter bank can only track an individual spectral component for the duration in which it is within the passband of one of the filters. Alternatives are therefore explored which are amenable to real-time implementation.

The Dynamics of Large-Amplitude Motion in Energized Molecules

Energy Technology Data Exchange (ETDEWEB)

Perry, David S. [Univ. of Akron, OH (United States). Dept. of Chemistry

2016-05-27

Chemical reactions involve large-amplitude nuclear motion along the reaction coordinate that serves to distinguish reactants from products. Some reactions, such as roaming reactions and reactions proceeding through a loose transition state, involve more than one large-amplitude degree of freedom. Because of the limitation of exact quantum nuclear dynamics to small systems, one must, in general, define the active degrees of freedom and separate them in some way from the other degrees of freedom. In this project, we use large-amplitude motion in bound model systems to investigate the coupling of large-amplitude degrees of freedom to other nuclear degrees of freedom. This approach allows us to use the precision and power of high-resolution molecular spectroscopy to probe the specific coupling mechanisms involved, and to apply the associated theoretical tools. In addition to slit-jet spectra at the University of Akron, the current project period has involved collaboration with Michel Herman and Nathalie Vaeck of the Université Libre de Bruxelles, and with Brant Billinghurst at the Canadian Light Source (CLS).

Multiplexing of spatial modes in the mid-IR region

Science.gov (United States)

Gailele, Lucas; Maweza, Loyiso; Dudley, Angela; Ndagano, Bienvenu; Rosales-Guzman, Carmelo; Forbes, Andrew

2017-02-01

Traditional optical communication systems optimize multiplexing in polarization and wavelength both trans- mitted in fiber and free-space to attain high bandwidth data communication. Yet despite these technologies, we are expected to reach a bandwidth ceiling in the near future. Communications using orbital angular momentum (OAM) carrying modes offers infinite dimensional states, providing means to increase link capacity by multiplexing spatially overlapping modes in both the azimuthal and radial degrees of freedom. OAM modes are multiplexed and de-multiplexed by the use of spatial light modulators (SLM). Implementation of complex amplitude modulation is employed on laser beams phase and amplitude to generate Laguerre-Gaussian (LG) modes. Modal decomposition is employed to detect these modes due to their orthogonality as they propagate in space. We demonstrate data transfer by sending images as a proof-of concept in a lab-based scheme. We demonstrate the creation and detection of OAM modes in the mid-IR region as a precursor to a mid-IR free-space communication link.

Coupling of tearing modes in tokamaks

International Nuclear Information System (INIS)

Finn, J.M.

1977-01-01

The simultaneous presence of tearing modes of different helical pitches leads to the destruction of magnetic surfaces, which has been suggested as the mechanism leading to the onset of the disruptive instability in tokamaks. For current profiles in which the m = 2 mode is unstable, but the m = 3 is stable, the coupling of the m = 3 to the m = 2 through the poloidal variation of the toroidal field can drive the m = 3 amplitude psi 3 to order psi 2 times the inverse aspect ratio. Detailed calculations, both analytical and numerical, have been performed for two models for the equilibrium and m = 2 mode structure. A slab model and incompressible m = 3 perturbations are assumed. The m = 3 amplitude increases with shear, up to a point, showing that as the current channel shrinks, overlap of resonances becomes more likely. The results also apply qualitatively to other m, m +- 1 interactions

A simple theory of linear mode conversion

International Nuclear Information System (INIS)

Cairns, R.A.; Lashmore-Davies, C.N.; Woods, A.M.

1984-01-01

A summary is given of the basic theory of linear mode conversion involving the construction of differential equations for the mode amplitudes based on the properties of the dispersion relation in the neighbourhood of the mode conversion point. As an example the transmission coefficient for tunneling from the upper hybrid resonance through the evanescent region to the adjacent cut-off is treated. 7 refs, 3 figs

Nonlinear surface elastic modes in crystals

Science.gov (United States)

Gorentsveig, V. I.; Kivshar, Yu. S.; Kosevich, A. M.; Syrkin, E. S.

1990-03-01

The influence of nonlinearity on shear horizontal surface elastic waves in crystals is described on the basis of the effective nonlinear Schrödinger equation. It is shown that the corresponding solutions form a set of surface modes and the simplest mode coincides with the solution proposed by Mozhaev. The higher order modes have internal frequencies caused by the nonlinearity. All these modes decay in the crystal as uoexp(- z/ zo) atz≫ zo- u o-1 ( z is the distance from the crystal surface, uo the wave amplitude at the surface). The creation of the modes from a localized surface excitation has a threshold. The stability of the modes is discussed.

Mixed-Mode Crack Growth in Wood

Directory of Open Access Journals (Sweden)

Octavian POP

2012-09-01

Full Text Available In timber elements the mixed mode dependsessentially of wood anatomy and load configuration.In these conditions, in order to evaluate the materialbehavior and the fracture process, it’s necessary toseparate the part of each mode. The mixed modeseparation allows evaluating the amplitude offracture mode. In the present paper, using a mixedmodecrack growth specimen made in Douglas fir,the mixed mode crack growth process is studythanks to marks tracking method. Using the markstracking method the characteristic displacementsassociated to opening and shear mode aremeasured. From the experimental measurements,the energy release rate associated to opening andshear modes is calculated into to account the crackadvancement during the test.

Damage detection in composite panels based on mode-converted Lamb waves sensed using 3D laser scanning vibrometer

Science.gov (United States)

Pieczonka, Łukasz; Ambroziński, Łukasz; Staszewski, Wiesław J.; Barnoncel, David; Pérès, Patrick

2017-12-01

This paper introduces damage identification approach based on guided ultrasonic waves and 3D laser Doppler vibrometry. The method is based on the fact that the symmetric and antisymmetric Lamb wave modes differ in amplitude of the in-plane and out-of-plane vibrations. Moreover, the modes differ also in group velocities and normally they are well separated in time. For a given time window both modes can occur simultaneously only close to the wave source or to a defect that leads to mode conversion. By making the comparison between the in-plane and out-of-plane wave vector components the detection of mode conversion is possible, allowing for superior and reliable damage detection. Experimental verification of the proposed damage identification procedure is performed on fuel tank elements of Reusable Launch Vehicles designed for space exploration. Lamb waves are excited using low-profile, surface-bonded piezoceramic transducers and 3D scanning laser Doppler vibrometer is used to characterize the Lamb wave propagation field. The paper presents theoretical background of the proposed damage identification technique as well as experimental arrangements and results.

Comparison of methods for extracting annual cycle with changing amplitude in climate science

Science.gov (United States)

Deng, Q.; Fu, Z.

2017-12-01

Changes of annual cycle gains a growing concern recently. The basic hypothesis regards annual cycle as constant. Climatology mean within a time period is usually used to depict the annual cycle. Obviously this hypothesis contradicts with the fact that annual cycle is changing every year. For the lack of a unified definition about annual cycle, the approaches adopted in extracting annual cycle are various and may lead to different results. The precision and validity of these methods need to be examined. In this work we numerical experiments with known monofrequent annual cycle are set to evaluate five popular extracting methods: fitting sinusoids, complex demodulation, Ensemble Empirical Mode Decomposition (EEMD), Nonlinear Mode Decomposition (NMD) and Seasonal trend decomposition procedure based on loess (STL). Three different types of changing amplitude will be generated: steady, linear increasing and nonlinearly varying. Comparing the annual cycle extracted by these methods with the generated annual cycle, we find that (1) NMD performs best in depicting annual cycle itself and its amplitude change, (2) fitting sinusoids, complex demodulation and EEMD methods are more sensitive to long-term memory(LTM) of generated time series thus lead to overfitting annual cycle and too noisy amplitude, oppositely the result of STL underestimate the amplitude variation (3)all of them can present the amplitude trend correctly in long-time scale but the errors on account of noise and LTM are common in some methods over short time scales.

The pressure distribution for biharmonic transmitting array: theoretical study

Science.gov (United States)

Baranowska, A.

2005-03-01

The aim of the paper is theoretical analysis of the finite amplitude waves interaction problem for the biharmonic transmitting array. We assume that the array consists of 16 circular pistons of the same dimensions that regrouped in two sections. Two different arrangements of radiating elements were considered. In this situation the radiating surface is non-continuous without axial symmetry. The mathematical model was built on the basis of the Khokhlov - Zabolotskaya - Kuznetsov (KZK) equation. To solve the problem the finite-difference method was applied. On-axis pressure amplitude for different frequency waves as a function of distance from the source, transverse pressure distribution of these waves at fixed distances from the source and pressure amplitude distribution for them at fixed planes were examined. Especially changes of normalized pressure amplitude for difference frequency were studied. The paper presents mathematical model and some results of theoretical investigations obtained for different values of source parameters.

Modification of H-Mode Pedestal Instabilities in the DIII-D Tokamak

International Nuclear Information System (INIS)

J.R. Ferron; M.S. Chu; G.L. Jackson; L.L. Lao; R.L. Miller; T.H. Osborne; P.B. Snyder; E.J. Strait; T.S. Taylor; A.D. Turnbull; A.M. Garofalo; M.A. Makowski; B.W. Rice; M.S. Chance; L.R. Baylor; M. Murakami; M.R. Wade

1999-01-01

Through comparison of experiment and ideal magnetohydrodynamic (MHD) theory, modes driven in the edge region of tokamak H-mode discharges [Type I edge-localized modes (ELMs)] are shown to result from low toroidal mode number (n) instabilities driven by pressure gradient and current density. The mode amplitude and frequency are functions of the discharge shape. Reductions in mode amplitude are observed in discharge shapes with either high squareness or low triangularity where the low-n stability threshold in the edge pressure gradient is predicted to be reduced and the most unstable mode is expected to have higher values of n. The importance of access to the ballooning mode second stability regime is demonstrated through the changes in the ELM character that occur when second regime access is not available. An edge stability model is presented that predicts that there is a threshold value of n for second regime access and that the most unstable mode has n near this threshold

Phase Coherence of Large Amplitude MHD Waves in the Earth's Foreshock: Geotail Observations

International Nuclear Information System (INIS)

Hada, Tohru; Koga, Daiki; Yamamoto, Eiko

2003-01-01

Large amplitude MHD turbulence is commonly found in the earth's foreshock region. It can be represented as a superposition of Fourier modes with characteristic frequency, amplitude, and phase. Nonlinear interactions between the Fourier modes are likely to produce finite correlation among the wave phases. For discussions of various transport processes of energetic particles, it is fundamentally important to determine whether the wave phases are randomly distributed (as assumed in quasi-linear theories) or they have a finite coherence. However, naive inspection of wave phases does not reveal anything, as the wave phase is sensitively related to the choice of origin of the coordinate, which should be arbitrary. Using a method based on a surrogate data technique and a fractal analysis, we analyzed Geotail magnetic field data to evaluate the phase coherence among the MHD waves in the earth's foreshock region. We show that the correlation of wave phases does exist, indicating that the nonlinear interactions between the waves is in progress. Furthermore, by introducing an index to represent the degree of the phase coherence, we discuss that the wave phases become more coherent as the turbulence amplitude increases, and also as the propagation angle of the most dominant wave mode becomes oblique. Details of the analysis as well as implications of the present results to transport processes of energetic particles will be discussed

Magnetorheological dampers in shear mode

International Nuclear Information System (INIS)

Wereley, N M; Cho, J U; Choi, Y T; Choi, S B

2008-01-01

In this study, three types of shear mode damper using magnetorheological (MR) fluids are theoretically analyzed: linear, rotary drum, and rotary disk dampers. The damping performance of these shear mode MR dampers is characterized in terms of the damping coefficient, which is the ratio of the equivalent viscous damping at field-on status to the damping at field-off status. For these three types of shear mode MR damper, the damping coefficient or dynamic range is derived using three different constitutive models: the Bingham–plastic, biviscous, and Herschel–Bulkley models. The impact of constitutive behavior on shear mode MR dampers is theoretically presented and compared

On the joint distribution of excursion duration and amplitude of a narrow-band Gaussian process

DEFF Research Database (Denmark)

Ghane, Mahdi; Gao, Zhen; Blanke, Mogens

2018-01-01

of amplitude and period are limited to excursion through a mean-level or to describe the asymptotic behavior of high level excursions. This paper extends the knowledge by presenting a theoretical derivation of probability of wave exceedance amplitude and duration, for a narrow-band Gaussian process......The probability density of crest amplitude and of duration of exceeding a given level are used in many theoretical and practical problems in engineering. The joint density is essential for design of constructions that are subjected to waves and wind. The presently available joint distributions...... distribution, as expected, and that the marginal distribution of excursion duration works both for asymptotic and non-asymptotic cases. The suggested model is found to be a good replacement for the empirical distributions that are widely used. Results from simulations of narrow-band Gaussian processes, real...

Direct amplitude detuning measurement with ac dipole

Directory of Open Access Journals (Sweden)

S. White

2013-07-01

Full Text Available In circular machines, nonlinear dynamics can impact parameters such as beam lifetime and could result in limitations on the performance reach of the accelerator. Assessing and understanding these effects in experiments is essential to confirm the accuracy of the magnetic model and improve the machine performance. A direct measurement of the machine nonlinearities can be obtained by characterizing the dependency of the tune as a function of the amplitude of oscillations (usually defined as amplitude detuning. The conventional technique is to excite the beam to large amplitudes with a single kick and derive the tune from turn-by-turn data acquired with beam position monitors. Although this provides a very precise tune measurement it has the significant disadvantage of being destructive. An alternative, nondestructive way of exciting large amplitude oscillations is to use an ac dipole. The perturbation Hamiltonian in the presence of an ac dipole excitation shows a distinct behavior compared to the free oscillations which should be correctly taken into account in the interpretation of experimental data. The use of an ac dipole for direct amplitude detuning measurement requires careful data processing allowing one to observe the natural tune of the machine; the feasibility of such a measurement is demonstrated using experimental data from the Large Hadron Collider. An experimental proof of the theoretical derivations based on measurements performed at injection energy is provided as well as an application of this technique at top energy using a large number of excitations on the same beam.

Higher order mode optical fiber Raman amplifiers

DEFF Research Database (Denmark)

Rottwitt, Karsten; Friis, Søren Michael Mørk; Usuga Castaneda, Mario A.

2016-01-01

We review higher order mode Raman amplifiers and discuss recent theoretical as well as experimental results including system demonstrations.......We review higher order mode Raman amplifiers and discuss recent theoretical as well as experimental results including system demonstrations....

Evidence of resonant mode coupling and the relationship between low and high frequencies in a rapidly rotating a star

International Nuclear Information System (INIS)

Breger, M.; Montgomery, M. H.

2014-01-01

In the theory of resonant mode coupling, the parent and child modes are directly related in frequency and phase. The oscillations present in the fast rotating δ Sct star KIC 8054146 allow us to test the most general and generic aspects of such a theory. The only direct way to separate the parent and coupled (child) modes is to examine the correlations in amplitude variability between the different frequencies. For the dominant family of related frequencies, only a single mode and a triplet are the origins of nine dominant frequency peaks ranging from 2.93 to 66.30 cycles day –1 (as well as dozens of small-amplitude combination modes and a predicted and detected third high-frequency triplet). The mode-coupling model correctly predicts the large amplitude variations of the coupled modes as a product of the amplitudes of the parent modes, while the phase changes are also correctly modeled. This differs from the behavior of 'normal' combination frequencies in that the amplitudes are three orders of magnitude larger and may exceed even the amplitudes of the parent modes. We show that two dominant low frequencies at 5.86 and 2.93 cycles day –1 in the gravity-mode region are not harmonics of each other, and their properties follow those of the almost equidistant high-frequency triplet. We note that the previously puzzling situation of finding two strong peaks in the low-frequency region related by nearly a factor of two in frequency has been seen in other δ Sct stars as well.

Evidence of resonant mode coupling and the relationship between low and high frequencies in a rapidly rotating a star

Energy Technology Data Exchange (ETDEWEB)

Breger, M.; Montgomery, M. H. [Department of Astronomy, University of Texas, Austin, TX 78712 (United States)

2014-03-10

In the theory of resonant mode coupling, the parent and child modes are directly related in frequency and phase. The oscillations present in the fast rotating δ Sct star KIC 8054146 allow us to test the most general and generic aspects of such a theory. The only direct way to separate the parent and coupled (child) modes is to examine the correlations in amplitude variability between the different frequencies. For the dominant family of related frequencies, only a single mode and a triplet are the origins of nine dominant frequency peaks ranging from 2.93 to 66.30 cycles day{sup –1} (as well as dozens of small-amplitude combination modes and a predicted and detected third high-frequency triplet). The mode-coupling model correctly predicts the large amplitude variations of the coupled modes as a product of the amplitudes of the parent modes, while the phase changes are also correctly modeled. This differs from the behavior of 'normal' combination frequencies in that the amplitudes are three orders of magnitude larger and may exceed even the amplitudes of the parent modes. We show that two dominant low frequencies at 5.86 and 2.93 cycles day{sup –1} in the gravity-mode region are not harmonics of each other, and their properties follow those of the almost equidistant high-frequency triplet. We note that the previously puzzling situation of finding two strong peaks in the low-frequency region related by nearly a factor of two in frequency has been seen in other δ Sct stars as well.

Characterization of peeling modes in a low aspect ratio tokamak

Science.gov (United States)

Bongard, M. W.; Thome, K. E.; Barr, J. L.; Burke, M. G.; Fonck, R. J.; Hinson, E. T.; Redd, A. J.; Schlossberg, D. J.

2014-11-01

Peeling modes are observed at the plasma edge in the Pegasus Toroidal Experiment under conditions of high edge current density (Jedge ˜ 0.1 MA m-2) and low magnetic field (B ˜ 0.1 T) present at near-unity aspect ratio. Their macroscopic properties are measured using external Mirnov coil arrays, Langmuir probes and high-speed visible imaging. The modest edge parameters and short pulse lengths of Pegasus discharges permit direct measurement of the internal magnetic field structure with an insertable array of Hall-effect sensors, providing the current profile and its temporal evolution. Peeling modes generate coherent, edge-localized electromagnetic activity with low toroidal mode numbers n ⩽ 3 and high poloidal mode numbers, in agreement with theoretical expectations of a low-n external kink structure. Coherent MHD fluctuation amplitudes are found to be strongly dependent on the experimentally measured Jedge/B peeling instability drive, consistent with theory. Peeling modes nonlinearly generate ELM-like, field-aligned filamentary structures that detach from the edge and propagate radially outward. The KFIT equilibrium code is extended with an Akima spline profile parameterization and an improved model for induced toroidal wall current estimation to obtain a reconstruction during peeling activity with its current profile constrained by internal Hall measurements. It is used to test the analytic peeling stability criterion and numerically evaluate ideal MHD stability. Both approaches predict instability, in agreement with experiment, with the latter identifying an unstable external kink.

A Study on Scattered Wave Amplitude Closed-Form Solution Calculation of Torsional Wave Mode by Reciprocity Theorem

International Nuclear Information System (INIS)

Lee, Jaesun; Cho, Younho; Achenbach, Jan D.

2016-01-01

Guided waves can be used for the inspection of long range pipelines. Surface corrosion is often found as a major defect type in pipelines. The reciprocity relation is a well-established theorem by which one can simplify complicated mathematical expressions. The approach has been already applied to plate and half-space structures to obtain the closed-form solutions of scattered amplitude. However, results for the case of cylindrical structures have not been reported yet. In this paper, the scattering of torsional waves, which is widely used in commercial applications, is explored by the reciprocity theorem approach. Obtaining closed-form solutions of the amplitudes of propagating waves is much simplified by using the reciprocal relation. The scattered amplitudes for elliptical and rectangular defect shapes are calculated with respect to defect depth and width, at frequencies between 0 and 500 kHz. The amplitude shows the periodic result as a function of frequency. The derived closed-form solutions can play a significant role in quantitative signal interpretation

A Study on Scattered Wave Amplitude Closed-Form Solution Calculation of Torsional Wave Mode by Reciprocity Theorem

Energy Technology Data Exchange (ETDEWEB)

Lee, Jaesun; Cho, Younho [Pusan National Univ., Pusan (Korea, Republic of); Achenbach, Jan D. [Northwestern Univ., Everston (United States)

2016-07-15

Guided waves can be used for the inspection of long range pipelines. Surface corrosion is often found as a major defect type in pipelines. The reciprocity relation is a well-established theorem by which one can simplify complicated mathematical expressions. The approach has been already applied to plate and half-space structures to obtain the closed-form solutions of scattered amplitude. However, results for the case of cylindrical structures have not been reported yet. In this paper, the scattering of torsional waves, which is widely used in commercial applications, is explored by the reciprocity theorem approach. Obtaining closed-form solutions of the amplitudes of propagating waves is much simplified by using the reciprocal relation. The scattered amplitudes for elliptical and rectangular defect shapes are calculated with respect to defect depth and width, at frequencies between 0 and 500 kHz. The amplitude shows the periodic result as a function of frequency. The derived closed-form solutions can play a significant role in quantitative signal interpretation.

Theoretical and experimental studies on a magnetorheological brake operating under compression plus shear mode

International Nuclear Information System (INIS)

Sarkar, C; Hirani, H

2013-01-01

The torque characteristics of magnetorheological brakes, consisting of rotating disks immersed in a MR fluid and enclosed in an electromagnetic casing, are controlled by regulating the yield stress of the MR fluid. An increase in yield stress increases the braking torque, which means that the higher the yield strength of the MR fluid, the better the performance of the MR brake will be. In the present research an application of compressive force on MR fluid has been proposed to increase the torque capacity of MR brakes. The mathematical expressions to estimate the torque values for MR brake, operating under compression plus shear mode accounting Herschel–Bulkley shear thinning model, have been detailed. The required compressive force on MR fluid of the proposed brake has been applied using an electromagnetic actuator. The development of a single-plate MR disk brake and an experimental test rig are described. Experiments have been performed to illustrate braking torque under different control currents (0.0–2.0 A). The torque results have been plotted and compared with theoretical study. Experimental results as well as theoretical calculations indicate that the braking torque of the proposed MR brake is higher than that of the MR brake operating only under shear. (paper)

A discrete model of the development and relaxation of a local microbreakdown in silicon avalanche photodiodes operating in the Geiger mode

International Nuclear Information System (INIS)

Vanyushin, I. V.; Gergel, V. A.; Gontar', V. M.; Zimoglyad, V. A.; Tishin, Yu. I.; Kholodnov, V. A.; Shcheleva, I. M.

2007-01-01

A new discrete theoretical model of the development and relaxation of a local microbreakdown in silicon avalanche photodiodes operating in the Geiger mode is developed. It is shown that the spreading resistance in the substrate profoundly affects both the amplitude of a single-photon electrical pulse and the possibility of attaining the steady-state form of the avalanche breakdown excluding the Geiger mode of the photodiode's operation. The model is employed to interpret the experimental data obtained using test single-photon cells of avalanche photodiodes fabricated on the basis of the 0.25-μm silicon technology with the use of deep implantation to form the region of avalanche multiplication for the charge carriers. Excellent functional properties of the studied type of the single-photon (Geiger) cell are noted. A typical amplitude characteristic of the cell for optical radiation with the wavelength λ = 0.56 μm in the irradiance range of 10 -3 -10 2 lx is presented; this characteristic indicates that the quantum efficiency of photoconversion is extremely high

THEMIS Observations of the Magnetopause Electron Diffusion Region: Large Amplitude Waves and Heated Electrons

Science.gov (United States)

Tang, Xiangwei; Cattell, Cynthia; Dombeck, John; Dai, Lei; Wilson, Lynn B. III; Breneman, Aaron; Hupack, Adam

2013-01-01

We present the first observations of large amplitude waves in a well-defined electron diffusion region based on the criteria described by Scudder et al at the subsolar magnetopause using data from one Time History of Events and Macroscale Interactions during Substorms (THEMIS) satellite. These waves identified as whistler mode waves, electrostatic solitary waves, lower hybrid waves, and electrostatic electron cyclotron waves, are observed in the same 12 s waveform capture and in association with signatures of active magnetic reconnection. The large amplitude waves in the electron diffusion region are coincident with abrupt increases in electron parallel temperature suggesting strong wave heating. The whistler mode waves, which are at the electron scale and which enable us to probe electron dynamics in the diffusion region were analyzed in detail. The energetic electrons (approx. 30 keV) within the electron diffusion region have anisotropic distributions with T(sub e(right angle))/T(sub e(parallel)) > 1 that may provide the free energy for the whistler mode waves. The energetic anisotropic electrons may be produced during the reconnection process. The whistler mode waves propagate away from the center of the "X-line" along magnetic field lines, suggesting that the electron diffusion region is a possible source region of the whistler mode waves.

Experimental and theoretical studies of active control of resistive wall mode growth in the EXTRAP T2R reversed-field pinch

Science.gov (United States)

Drake, J. R.; Brunsell, P. R.; Yadikin, D.; Cecconello, M.; Malmberg, J. A.; Gregoratto, D.; Paccagnella, R.; Bolzonella, T.; Manduchi, G.; Marrelli, L.; Ortolani, S.; Spizzo, G.; Zanca, P.; Bondeson, A.; Liu, Y. Q.

2005-07-01

Active feedback control of resistive wall modes (RWMs) has been demonstrated in the EXTRAP T2R reversed-field pinch experiment. The control system includes a sensor consisting of an array of magnetic coils (measuring mode harmonics) and an actuator consisting of a saddle coil array (producing control harmonics). Closed-loop (feedback) experiments using a digital controller based on a real time Fourier transform of sensor data have been studied for cases where the feedback gain was constant and real for all harmonics (corresponding to an intelligent-shell) and cases where the feedback gain could be set for selected harmonics, with both real and complex values (targeted harmonics). The growth of the dominant RWMs can be reduced by feedback for both the intelligent-shell and targeted-harmonic control systems. Because the number of toroidal positions of the saddle coils in the array is half the number of the sensors, it is predicted and observed experimentally that the control harmonic spectrum has sidebands. Individual unstable harmonics can be controlled with real gains. However if there are two unstable mode harmonics coupled by the sideband effect, control is much less effective with real gains. According to the theory, complex gains give better results for (slowly) rotating RWMs, and experiments support this prediction. In addition, open loop experiments have been used to observe the effects of resonant field errors applied to unstable, marginally stable and robustly stable modes. The observed effects of field errors are consistent with the thin-wall model, where mode growth is proportional to the resonant field error amplitude and the wall penetration time for that mode harmonic.

Experimental and theoretical studies of active control of resistive wall mode growth in the EXTRAP T2R reversed-field pinch

International Nuclear Information System (INIS)

Drake, J.R.; Brunsell, P.R.; Yadikin, D.

2005-01-01

Active feedback control of resistive wall modes (RWMs) has been demonstrated in the EXTRAP T2R reversed-field pinch experiment. The control system includes a sensor consisting of an array of magnetic coils (measuring mode harmonics) and an actuator consisting of a saddle coil array (producing control harmonics). Closed-loop (feedback) experiments using a digital controller based on a real time Fourier transform of sensor data have been studied for cases where the feedback gain was constant and real for all harmonics (corresponding to an intelligent-shell) and cases where the feedback gain could be set for selected harmonics, with both real and complex values (targeted harmonics). The growth of the dominant RWMs can be reduced by feedback for both the intelligent-shell and targeted-harmonic control systems. Because the number of toroidal positions of the saddle coils in the array is half the number of the sensors, it is predicted and observed experimentally that the control harmonic spectrum has sidebands. Individual unstable harmonics can be controlled with real gains. However if there are two unstable mode harmonics coupled by the sideband effect, control is much less effective with real gains. According to the theory, complex gains give better results for (slowly) rotating RWMs, and experiments support this prediction. In addition, open loop experiments have been used to observe the effects of resonant field errors applied to unstable, marginally stable and robustly stable modes. The observed effects of field errors are consistent with the thin-wall model, where mode growth is proportional to the resonant field error amplitude and the wall penetration time for that mode harmonic

The generation of flat-top beams by complex amplitude modulation with a phase-only spatial light modulator

CSIR Research Space (South Africa)

Hendriks, A

2012-08-01

Full Text Available amplitude modulation of the light, i.e., in amplitude and phase. We outline the theoretical concept, and then illustrate its use with the example of the laser beam shaping of Gaussian beams into flat-top beams. We quantify the performance of this approach...

The MACHO Project Sample of Galactic Bulge High-Amplitude Scuti Stars: Pulsation Behavior and Stellar Properties

International Nuclear Information System (INIS)

Bennett, D.P.; Cook, K.H.; Freeman, K.C.; Geha, M.; Griest, K.; Lehner, M.J.; Marshall, S.L.; McNamara, B.J.; Minniti, D.; Nelson, C.; Peterson, B.A.; Popowski, P.; Pratt, M.R.; Quinn, P.J.; Rodgers, A.W.; Sutherland, W.; Templeton, M.R.; Vandehei, T.; Welch, D.L.

1999-01-01

We have detected 90 objects with periods and lightcurve structure similar to those of field(delta) Scuti stars, using the Massive Compact Halo Object (MACHO) Project database of Galactic bulge photometry. If we assume similar extinction values for all candidates and absolute magnitudes similar to those of other field high-amplitude(delta) Scuti stars (HADS), the majority of these objects lie in or near the Galactic bulge. At least two of these objects are likely foreground(delta) Scuti stars, one of which may be an evolved nonradial pulsator, similar to other evolved, disk-population(delta) Scuti stars. We have analyzed the light curves of these objects and find that they are similar to the light curves of field(delta) Scuti stars and the(delta) Scuti stars found by the Optical Gravitational Lens Experiment (OGLE). However, the amplitude distribution of these sources lies between those of low- and high-amplitude(delta) Scuti stars, which suggests that they may be an intermediate population. We have found nine double-mode HADS with frequency ratios ranging from 0.75 to 0.79, four probable double- and multiple-mode objects, and another four objects with marginal detections of secondary modes. The low frequencies (5-14 cycles d(sup -1)) and the observed period ratios of(approx)0.77 suggest that the majority of these objects are evolved stars pulsating in fundamental or first overtone radial modes

Low-m magnetic modes activity and disruptions in Tokamaks discharges

International Nuclear Information System (INIS)

Cotsaftis, Michel.

1982-01-01

It has been possible to follow the evolution of the low-m modes and discuss the various patterns of their interactions. The structure of the non linear mode has been studied, and shown to possess a periodic time dependence which, on a rational magnetic surface where q = m/n, and large aspect ratio case, reduces to the sum of two pure oscillations with different frequencies. The amplitude of the mode has been evaluated, and it is further shown that, in the limit cycle regime, the modes amplitudes is small enough for them not to interact. This is not the case when the limit cycle becomes unstable, where the modes can now intermix by direct coupling or overlapping, and create a disruption. For this reason, stability criteria, both linear and nonlinear, respectively corresponding to the beginning and the end of the existence of the limit cycle, have been explicitely set down, showing the three domains corresponding to the three previous steps in an adapted parameter space. It is possible to follow the detailed evolution of the low-m modes all along the discharge duration. For regular enough profiles, the mode (m = 2, n = 1) is shown to largely dominate and, when becoming nonlinearly unstable, to drive the disruptions ending the discharges. In other words, in the present picture, the disruption is interpreted as the instability of a limit cycle rather than the usual linear instability of the zero amplitude mode, ie, corresponds to a second branching, and not to a first one

Theoretical investigation of flute modes in a magnetic quadrupole

International Nuclear Information System (INIS)

Wu, H.S.

1988-01-01

This research developed theories and conducted numerical investigations of electrostatic flute modes in a plasma confined in a magnetic quadrupole. Chapter I presents the discussion of relevant background. Chapter II contains a brief discussion of the basic flute-mode operator L 0 for intermediate- and low-frequency regimes. Chapter III develops a simple theory for a flute mode with frequency between the electron and ion bounce frequencies in the uniform density and temperature regions of a magnetic quadrupole. The frequency is predicted to be inversely proportional to the wave number. Chapter IV describes the kinetic approach. Chapter V contains the derivation of an eigenvalue equation for electrostatic waves with frequencies below the ion frequency in the private flux region of a magnetic quadrupole. Chapter VI develops a theory for electrostatic waves with frequency below the ion bounce frequency in the shared flux region of a magnetic quadrupole. Chapter VII contains the derivation of a dispersion equation for flute modes with frequencies between the electron and ion bounce frequencies in a plasma confined to a magnetic quadrupole. Chapter VIII presents a summary of the research described

Finite amplitude effects on drop levitation for material properties measurement

Science.gov (United States)

Ansari Hosseinzadeh, Vahideh; Holt, R. Glynn

2017-05-01

The method of exciting shape oscillation of drops to extract material properties has a long history, which is most often coupled with the technique of acoustic levitation to achieve non-contact manipulation of the drop sample. We revisit this method with application to the inference of bulk shear viscosity and surface tension. The literature is replete with references to a "10% oscillation amplitude" as a sufficient condition for the application of Lamb's analytical expressions for the shape oscillations of viscous liquids. Our results show that even a 10% oscillation amplitude leads to dynamic effects which render Lamb's results inapplicable. By comparison with samples of known viscosity and surface tension, we illustrate the complicating finite-amplitude effects (mode-splitting and excess dissipation associated with vorticity) that can occur and then show that sufficiently small oscillations allow us to recover the correct material properties using Lamb's formula.

Time-Dependent Amplitude Analysis of B0→KS0π+π- decays with the BaBar Experiment and constraints on the CKM matrix using the B→K*π and B→ρK modes

International Nuclear Information System (INIS)

Perez Perez, L.A.

2008-12-01

A time-dependent amplitude analysis of B 0 → K S 0 π + π - decays is performed to extract the CP violation parameters of f 0 (980)K S 0 and ρ 0 (770)K S 0 , and direct CP asymmetries of K * (892) ± π ± . The results are obtained from a data sample of (383 ± 3)*10 6 BB-bar decays, collected with the BaBar detector at the PEP-II asymmetric-energy B factory at SLAC. Two solutions are found, with equivalent goodness-of-fit merits. Including systematic and Dalitz plot model uncertainties, the combined confidence interval for values of β(eff) in B 0 decays to f 0 (980)K S 0 is 18 degrees 0 decays to f 0 (980)K S 0 is excluded at 3.5 σ, including systematics. For B 0 decays to ρ 0 (770)K S 0 , the combined confidence interval is -9 degrees * (892) ± π ± the measured direct CP asymmetry parameter is A(CP) -0.20 ± 0.10 ± 0.01 ± 0.02. The measured phase difference between the decay amplitudes of B 0 → K * (892) + π - and B-bar 0 → K * (892) - π + excludes the [-132 degrees: +25 degrees] interval (at 95% C.L.). Branching fractions and CP asymmetries are measured for all significant intermediate resonant modes. The measurements on ρ 0 (770)K S 0 and K *± (892)π ± are used as inputs to a phenomenological analysis of B → K * π and B → ρK decays based solely on SU(2) isospin symmetry. Adding external information on the CKM matrix, constraints on the hadronic parameter space are set. For B → K * π, the preferred intervals for color-allowed electroweak penguins are marginally compatible with theoretical expectations. The constraints on CKM parameters are dominated by theoretical uncertainties. A prospective study, based on the expected increase in precision from measurements at LHCb, and at future programs such as Super-B or Belle-upgrade, illustrates the physics potential of this approach. (author)

Tapping mode SPM local oxidation nanolithography with sub-10 nm resolution

International Nuclear Information System (INIS)

Nishimura, S; Ogino, T; Shirakashi, J; Takemura, Y

2008-01-01

Tapping mode SPM local oxidation nanolithography with sub-10 nm resolution is investigated by optimizing the applied bias voltage (V), scanning speed (S) and the oscillation amplitude of the cantilever (A). We fabricated Si oxide wires with an average width of 9.8 nm (V = 17.5 V, S 250 nm/s, A = 292 nm). In SPM local oxidation with tapping mode operation, it is possible to decrease the size of the water meniscus by enhancing the oscillation amplitude of cantilever. Hence, it seems that the water meniscus with sub-10 nm dimensions could be formed by precisely optimizing the oxidation conditions. Moreover, we quantitatively explain the size (width and height) of Si oxide wires with a model based on the oxidation ratio, which is defined as the oxidation time divided by the period of the cantilever oscillation. The model allows us to understand the mechanism of local oxidation in tapping mode operation with amplitude modulation. The results imply that the sub-10 nm resolution could be achieved using tapping mode SPM local oxidation technique with the optimization of the cantilever dynamics

Role of interbranch pumping on the quantum-statistical behavior of multi-mode magnons in ferromagnetic nanowires

Science.gov (United States)

Haghshenasfard, Zahra; Cottam, M. G.

2018-01-01

Theoretical studies are reported for the quantum-statistical properties of microwave-driven multi-mode magnon systems as represented by ferromagnetic nanowires with a stripe geometry. Effects of both the exchange and the dipole-dipole interactions, as well as a Zeeman term for an external applied field, are included in the magnetic Hamiltonian. The model also contains the time-dependent nonlinear effects due to parallel pumping with an electromagnetic field. Using a coherent magnon state representation in terms of creation and annihilation operators, we investigate the effects of parallel pumping on the temporal evolution of various nonclassical properties of the system. A focus is on the interbranch mixing produced by the pumping field when there are three or more modes. In particular, the occupation magnon number and the multi-mode cross correlations between magnon modes are studied. Manipulation of the collapse and revival phenomena of the average magnon occupation number and the control of the cross correlation between the magnon modes are demonstrated through tuning of the parallel pumping field amplitude and appropriate choices for the coherent magnon states. The cross correlations are a direct consequence of the interbranch pumping effects and do not appear in the corresponding one- or two-mode magnon systems.

Amplitude modulation of charge-density-wave domains in 1T-TaS2 at 300 K

International Nuclear Information System (INIS)

Coleman, R.V.; McNairy, W.W.; Slough, C.G.

1991-01-01

Measurements of the charge-density-wave (CDW) amplitude modulation in 1T-TaS 2 at room temperature have been made using a scanning tunneling microscope (STM) operating in the constant current mode. The amplitude profiles are in good agreement with the profile predicated by the CDW domain model of Nakanishi and Shiba. Interference effects between the atomic and CDW lattices have been analyzed and do not modify these profiles significantly. They represent the true CDW amplitude variation connected with the CDW domain structure

Nonlinear response of dense colloidal suspensions under oscillatory shear: mode-coupling theory and Fourier transform rheology experiments.

Science.gov (United States)

Brader, J M; Siebenbürger, M; Ballauff, M; Reinheimer, K; Wilhelm, M; Frey, S J; Weysser, F; Fuchs, M

2010-12-01

Using a combination of theory, experiment, and simulation we investigate the nonlinear response of dense colloidal suspensions to large amplitude oscillatory shear flow. The time-dependent stress response is calculated using a recently developed schematic mode-coupling-type theory describing colloidal suspensions under externally applied flow. For finite strain amplitudes the theory generates a nonlinear response, characterized by significant higher harmonic contributions. An important feature of the theory is the prediction of an ideal glass transition at sufficiently strong coupling, which is accompanied by the discontinuous appearance of a dynamic yield stress. For the oscillatory shear flow under consideration we find that the yield stress plays an important role in determining the nonlinearity of the time-dependent stress response. Our theoretical findings are strongly supported by both large amplitude oscillatory experiments (with Fourier transform rheology analysis) on suspensions of thermosensitive core-shell particles dispersed in water and Brownian dynamics simulations performed on a two-dimensional binary hard-disk mixture. In particular, theory predicts nontrivial values of the exponents governing the final decay of the storage and loss moduli as a function of strain amplitude which are in good agreement with both simulation and experiment. A consistent set of parameters in the presented schematic model achieves to jointly describe linear moduli, nonlinear flow curves, and large amplitude oscillatory spectroscopy.

Scaling Fiber Lasers to Large Mode Area: An Investigation of Passive Mode-Locking Using a Multi-Mode Fiber.

Science.gov (United States)

Ding, Edwin; Lefrancois, Simon; Kutz, Jose Nathan; Wise, Frank W

2011-01-01

The mode-locking of dissipative soliton fiber lasers using large mode area fiber supporting multiple transverse modes is studied experimentally and theoretically. The averaged mode-locking dynamics in a multi-mode fiber are studied using a distributed model. The co-propagation of multiple transverse modes is governed by a system of coupled Ginzburg-Landau equations. Simulations show that stable and robust mode-locked pulses can be produced. However, the mode-locking can be destabilized by excessive higher-order mode content. Experiments using large core step-index fiber, photonic crystal fiber, and chirally-coupled core fiber show that mode-locking can be significantly disturbed in the presence of higher-order modes, resulting in lower maximum single-pulse energies. In practice, spatial mode content must be carefully controlled to achieve full pulse energy scaling. This paper demonstrates that mode-locking performance is very sensitive to the presence of multiple waveguide modes when compared to systems such as amplifiers and continuous-wave lasers.

Multichannel amplitude analyser for nuclear spectrometry

International Nuclear Information System (INIS)

Jankovic, S.; Milovanovic, B.

2003-01-01

A multichannel amplitude analyser with 4096 channels was designed. It is based on a fast 12-bit analog-to-digital converter. The intended purpose of the instrument is recording nuclear spectra by means of scintillation detectors. The computer link is established through an opto-isolated serial connection cable, thus reducing instrument sensitivity to disturbances originating from digital circuitry. Refreshing of the data displayed on the screen occurs on every 2.5 seconds. The impulse peak detection is implemented through the differentiation of the amplified input signal, while the synchronization with the data coming from the converter output is established by taking advantage of the internal 'pipeline' structure of the converter itself. The mode of operation of the built-in microcontroller provides that there are no missed impulses, and the simple logic network prevents the initiation of the amplitude reading sequence for the next impulse in case it appears shortly after its precedent. The solution proposed here demonstrated a good performance at a comparatively low manufacturing cost, and is thus suitable for educational purposes (author)

Experimental evidence and theory for the interaction of superthermal electrons with the MHD modes during ECRH

International Nuclear Information System (INIS)

Lazaros, Avrilios

2000-01-01

The interaction of ECRH with the m/n=2/1 tearing mode, which was observed in toroidal plasmas, is attributed to the superthermal electrons which are produced on the EC resonance by the ECRH. Superthermal electrons diffusing across the q=2 surface, exchange power with the m/n=2/1 MHD mode which is either suppressed or enhanced. When the EC resonance is outside the rational surface, the mode is always suppressed. When the EC resonance is inside the rational surface, modes with large amplitude are enhanced while modes with small amplitude are suppressed. (author)

Tearing mode instability due to anomalous resistivity

International Nuclear Information System (INIS)

Furuya, Atsushi; Itoh, Sanae I.; Yagi, Masatoshi

2000-01-01

Tearing mode instability in the presence of microscopic truculence is investigates. The effects of microscopic turbulence on tearing mode are taken as drags which are calculated by one-point renormalization method and mean-field approximation. These effects are reduced to effective diffusivities in reduced MHD equations. Using these equations, the stability analyses of the tearing mode are performed. It is shown that a finite amplitude of fluctuation enhances the growth rate of tearing mode. For very high values of turbulent diffusivities, marginally stable state exists. The effects of each turbulent diffusivity on mode stability are examined near marginal stability boundary. Parameter dependence of the resistive ballooning mode turbulence on tearing mode is analyzed as an example. (author)

Electronically Tunable Quadrature Sinusoidal Oscillator with Equal Output Amplitudes during Frequency Tuning Process

Directory of Open Access Journals (Sweden)

Den Satipar

2017-01-01

Full Text Available A new configuration of voltage-mode quadrature sinusoidal oscillator is proposed. The proposed oscillator employs two voltage differencing current conveyors (VDCCs, two resistors, and two grounded capacitors. In this design, the use of multiple/dual output terminal active building block is not required. The tuning of frequency of oscillation (FO can be done electronically by adjusting the bias current of active device without affecting condition of oscillation (CO. The electronic tuning can be done by controlling the bias current using a digital circuit. The amplitude of two sinusoidal outputs is equal when the frequency of oscillation is tuned. This makes the sinusoidal output voltages meet good total harmonic distortions (THD. Moreover, the proposed circuit can provide the sinusoidal output current with high impedance which is connected to external load or to another circuit without the use of buffer device. To confirm that the oscillator can generate the quadrature sinusoidal output signal, the experimental results using VDCC constructed from commercially available ICs are also included. The experimental results agree well with theoretical anticipation.

Nuclear-Mechanical Coupling: Small Amplitude Mechanical Vibrations and High Amplitude Power Oscillations in Nuclear Reactors

International Nuclear Information System (INIS)

Suarez Antola, R.

2008-11-01

The cores of nuclear reactors, including its structural parts and cooling fluids, are complex mechanical systems able to vibrate in a set of normal modes and frequencies, if suitable perturbed. The cyclic variations in the strain state of the core materials may produce changes in density. Changes in density modify the reactivity. Changes in reactivity modify thermal power. Modifications in thermal power produce variations in temperature fields. Variations in temperature produce variations in strain due to thermal-elastic effects. If the variation of the temperature field is fast enough and if the Doppler Effect and other stabilizing prompt effects in the fuel are weak enough, a fast oscillatory instability could be produced, coupled with mechanical vibrations of small amplitude. A recently constructed, simple mathematical model of nuclear reactor kinetics, that improves the one due to A.S. Thompson, is reviewed. It was constructed in order to study, in a first approximation, the stability of the reactor: a nonlinear nuclear-thermal oscillator (that corresponds to reactor point kinetics with thermal-elastic feedback and with frozen delayed neutron effects) is coupled nonlinearly with a linear mechanical-thermal oscillator (that corresponds to the first normal mode of mechanical vibrations excited by thermo-elastic effects). This mathematical model is studied here from the standpoint of mechanical vibrations. It is shown how, under certain conditions, a suitable mechanical perturbation could elicit fast and growing oscillatory instabilities in the reactor power. Applying the asymptotic method due to Krylov, Bogoliubov and Mitropolsky, analytical formulae that may be used in the calculation of the time varying amplitude and phase of the mechanical oscillations are given, as functions of the mechanical, thermal and nuclear parameters of the reactor. The consequences for the mechanical integrity of the reactor are assessed. Some conditions, mainly, but not exclusively

H-mode physics

International Nuclear Information System (INIS)

Itoh, Sanae.

1991-06-01

After the discovery of the H-mode in ASDEX ( a tokamak in Germany ) the transition between the L-mode ( Low confinement mode ) and H-mode ( High confinement mode ) has been observed in many tokamaks in the world. The H-mode has made a breakthrough in improving the plasma parameters and has been recognized to be a universal phenomena. Since its discovery, the extensive studies both in experiments and in theory have been made. The research on H-mode has been casting new problems of an anomalous transport across the magnetic surface. This series of lectures will provide a brief review of experiments for explaining H-mode and a model theory of H-mode transition based on the electric field bifurcation. If the time is available, a new theoretical model of the temporal evolution of the H-mode will be given. (author)

A study of oscillation amplitude settling transients in a molecular beam maser

International Nuclear Information System (INIS)

Lefrere, P.R.; Laine, D.C.

1977-01-01

The dynamic behaviour of oscillation amplitude build-up from noise has been studied in a molecular beam maser (MBM). The three forms of growth curve, predicted theoretically, namely exponential, aperiodic and damped periodic have been observed with their associated 'times of silence'. (Auth.)

Recovery of seismic attributes by using the amplitude zero offset migration; Recuperacao de atributos sismicos utilizando a migracao para afastamento nulo em verdadeira amplitude

Energy Technology Data Exchange (ETDEWEB)

Vasquez, Angela Cristina Romero

1999-07-01

In the present work a method was developed to extract reflections coefficients after applying amplitude zero offset migration (TA MZO) on synthetic seismic data composed of several common offset sections. Sorting to the common mid point domain (CMP) provides the conventional amplitude versus offset curve directly. A second MZO application with different weights provides an estimation of incident angles, transforming AVO in AVA. Four models were developed with this objective, which basic difference is the structural complexity. One of these models is based on Brazilian turbidity reservoir of Neo-Albian age and proves the wide applicability of this methodology on reservoir characterization. Final, AVA results were compared with the theoretical AVA, quantifying the relative errors between them.

Soliton formation and evolution in passively-mode-locked lasers with ultralong anomalous-dispersion fibers

International Nuclear Information System (INIS)

Liu Xueming

2011-01-01

The soliton formation and evolution are numerically and experimentally investigated in passively-mode-locked lasers where pulses encounter ultralong anomalous-dispersion fibers. The pulse formation and evolution in lasers are determined by two balances, namely, nonlinearity and anomalous-dispersion balance and intracavity filtering and self-amplitude modulation balance. It is numerically found that a higher-energy soliton can be split into identical lower-energy multisolitons with exactly the same physical properties. Simulation results show that the separation of neighboring solitons is variational in the temporal domain. The temporal and spectral characteristics of solitons have large variations throughout the laser cavity, qualitatively distinct from the steady state of conventional solitons. The experimental observations confirm the theoretical predictions.

Low-frequency oscillations in default mode subnetworks are associated with episodic memory impairments in Alzheimer's disease.

Science.gov (United States)

Veldsman, Michele; Egorova, Natalia; Singh, Baljeet; Mungas, Dan; DeCarli, Charles; Brodtmann, Amy

2017-11-01

Disruptions to functional connectivity in subsystems of the default mode network are evident in Alzheimer's disease (AD). Functional connectivity estimates correlations in the time course of low-frequency activity. Much less is known about other potential perturbations to this activity, such as changes in the amplitude of oscillations and how this relates to cognition. We examined the amplitude of low-frequency fluctuations in 44 AD patients and 128 cognitively normal participants and related this to episodic memory, the core deficit in AD. We show higher amplitudes of low-frequency oscillations in AD patients. Rather than being compensatory, this appears to be maladaptive, with greater amplitude in the ventral default mode subnetwork associated with poorer episodic memory. Perturbations to default mode subnetworks in AD are evident in the amplitude of low-frequency oscillations in the resting brain. These disruptions are associated with episodic memory demonstrating their behavioral and clinical relevance in AD. Copyright © 2017 Elsevier Inc. All rights reserved.

Ballooning mode stabilization by moderate sheared rotation

International Nuclear Information System (INIS)

Hameiri, E.

1996-01-01

Sheared toroidal plasma rotation has been known for some time to have a stabilizing effect on the ballooning modes. A recent calculation showed that a large flow shear, with dΩ/dq of the order of the Alfven toroidal frequency, can stabilize the ballooning modes. This latest result is, in fact, not so optimistic. For observed flows with Mach number of order unity one gets dΩ/dq smaller by a factor O(√β) from the required level (if the flow shear length is of the same order as the magnetic shear length). Moreover, the calculation does not take into account a possibly large transient growth of the mode amplitude due to its Floquet structures We show here that, in fact, there is a general tendency of the ballooning mode to stabilize as soon as the flow shear dΩ/dq exceeds the (O√β smaller) open-quotes slowclose quotes magnetosonic wave frequency. Our analysis is perturbative, where the small parameter is related to the small coupling between the slow and Alfven waves-as is the case in a high aspect-ratio tokamak. (In the perturbation it is important to take the Hamiltonian nature of the governing equations into account.) Moreover, our results apply to the relevant transient growth of the mode amplitude

Theoretical and experimental investigation of multispectral photoacoustic osteoporosis detection method

Science.gov (United States)

Steinberg, Idan; Hershkovich, Hadas Sara; Gannot, Israel; Eyal, Avishay

2014-03-01

Osteoporosis is a widespread disorder, which has a catastrophic impact on patients lives and overwhelming related to healthcare costs. Recently, we proposed a multispectral photoacoustic technique for early detection of osteoporosis. Such technique has great advantages over pure ultrasonic or optical methods as it allows the deduction of both bone functionality from the bone absorption spectrum and bone resistance to fracture from the characteristics of the ultrasound propagation. We demonstrated the propagation of multiple acoustic modes in animal bones in-vitro. To further investigate the effects of multiple wavelength excitations and of induced osteoporosis on the PA signal a multispectral photoacoustic system is presented. The experimental investigation is based on measuring the interference of multiple acoustic modes. The performance of the system is evaluated and a simple two mode theoretical model is fitted to the measured phase signals. The results show that such PA technique is accurate and repeatable. Then a multiple wavelength excitation is tested. It is shown that the PA response due to different excitation wavelengths revels that absorption by the different bone constitutes has a profound effect on the mode generation. The PA response is measured in single wavelength before and after induced osteoporosis. Results show that induced osteoporosis alters the measured amplitude and phase in a consistent manner which allows the detection of the onset of osteoporosis. These results suggest that a complete characterization of the bone over a region of both acoustic and optical frequencies might be used as a powerful tool for in-vivo bone evaluation.

Predictive transport modelling of type I ELMy H-mode dynamics using a theory-motivated combined ballooning-peeling model

International Nuclear Information System (INIS)

Loennroth, J-S; Parail, V; Dnestrovskij, A; Figarella, C; Garbet, X; Wilson, H

2004-01-01

This paper discusses predictive transport simulations of the type I ELMy high confinement mode (H-mode) with a theory-motivated edge localized mode (ELM) model based on linear ballooning and peeling mode stability theory. In the model, a total mode amplitude is calculated as a sum of the individual mode amplitudes given by two separate linear differential equations for the ballooning and peeling mode amplitudes. The ballooning and peeling mode growth rates are represented by mutually analogous terms, which differ from zero upon the violation of a critical pressure gradient and an analytical peeling mode stability criterion, respectively. The damping of the modes due to non-ideal magnetohydrodynamic effects is controlled by a term driving the mode amplitude towards the level of background fluctuations. Coupled to simulations with the JETTO transport code, the model qualitatively reproduces the experimental dynamics of type I ELMy H-mode, including an ELM frequency that increases with the external heating power. The dynamics of individual ELM cycles is studied. Each ELM is usually triggered by a ballooning mode instability. The ballooning phase of the ELM reduces the pressure gradient enough to make the plasma peeling unstable, whereby the ELM continues driven by the peeling mode instability, until the edge current density has been depleted to a stable level. Simulations with current ramp-up and ramp-down are studied as examples of situations in which pure peeling and pure ballooning mode ELMs, respectively, can be obtained. The sensitivity with respect to the ballooning and peeling mode growth rates is investigated. Some consideration is also given to an alternative formulation of the model as well as to a pure peeling model

Nonlinear Longitudinal Mode Instability in Liquid Propellant Rocket Engine Preburners

Science.gov (United States)

Sims, J. D. (Technical Monitor); Flandro, Gary A.; Majdalani, Joseph; Sims, Joseph D.

2004-01-01

Nonlinear pressure oscillations have been observed in liquid propellant rocket instability preburner devices. Unlike the familiar transverse mode instabilities that characterize primary combustion chambers, these oscillations appear as longitudinal gas motions with frequencies that are typical of the chamber axial acoustic modes. In several respects, the phenomenon is similar to longitudinal mode combustion instability appearing in low-smoke solid propellant motors. An important feature is evidence of steep-fronted wave motions with very high amplitude. Clearly, gas motions of this type threaten the mechanical integrity of associated engine components and create unacceptably high vibration levels. This paper focuses on development of the analytical tools needed to predict, diagnose, and correct instabilities of this type. For this purpose, mechanisms that lead to steep-fronted, high-amplitude pressure waves are described in detail. It is shown that such gas motions are the outcome of the natural steepening process in which initially low amplitude standing acoustic waves grow into shock-like disturbances. The energy source that promotes this behavior is a combination of unsteady combustion energy release and interactions with the quasi-steady mean chamber flow. Since shock waves characterize the gas motions, detonation-like mechanisms may well control the unsteady combustion processes. When the energy gains exceed the losses (represented mainly by nozzle and viscous damping), the waves can rapidly grow to a finite amplitude limit cycle. Analytical tools are described that allow the prediction of the limit cycle amplitude and show the dependence of this wave amplitude on the system geometry and other design parameters. This information can be used to guide corrective procedures that mitigate or eliminate the oscillations.

Theoretical and Experimental Investigations of the Rotor Vibration Amplitude of the Turbocharger and Bearings Temperature

Directory of Open Access Journals (Sweden)

E. Zadorozhnaya

2017-12-01

Full Text Available One of the most urgent issues of the modern world and domestic automobile and tractor production is the problem of the production of efficient and reliable turbochargers. The rotor bearings largely determine the reliable operation of the turbocharger. By increasing the degree of the forcing of the engine the turbocharger rotor speed and the load increases significantly. Working conditions of bearings also complicated because of the temperature rise. In this case the bearing of the turbine and the compressor bearing works in different thermal conditions. The definition of the thermal state of the bearings can be performed experimentally. However, to perform these studies the sophisticated experimental equipment must be used. Researchers can't perform experiments for each type of turbocharger. Therefore, the applying of the theoretical approaches becomes more relevant. The peculiarity of the considered problem is the design of the bearings, which are made in the form of multilayer bearings with floating rings. Such designs increase the number of the parameters that affect the behaviour of the rotor. For the calculation of the multilayer bearings and turbocharger rotor dynamics a method and calculation algorithm was developed. A plan of the experiment based on the orthogonal central composite plan was drawn up. The regression equations for rotor amplitude and bearing temperature were obtained. As variable parameters the clearances (external and internal, rotor speed, pressure and lubricant temperature were used. The results of the calculation were compared with experimental results obtained at the plant. Non-Newtonian properties of the lubricants were taken into account in the calculations. Comparative results showed good agreement. In this way the resulting function can be applied to studies of the similarly multilayer bearings without complicated experimental studies.

Analysis of stationary power/amplitude distributions for multiple channels of sampled FBGs.

Science.gov (United States)

Xing, Ya; Zou, Xihua; Pan, Wei; Yan, Lianshan; Luo, Bin; Shao, Liyang

2015-08-10

Stationary power/amplitude distributions for multiple channels of the sampled fiber Bragg grating (SFBG) along the grating length are analyzed. Unlike a uniform FBG, the SFBG has multiple channels in the reflection spectrum, not a single channel. Thus, the stationary power/amplitude distributions for these multiple channels are analyzed by using two different theoretical models. In the first model, the SFBG is regarded as a set of grating sections and non-grating sections, which are alternately stacked. A step-like distribution is obtained for the corresponding power/amplitude of each channel along the grating length. While, in the second model, the SFBG is decomposed into multiple uniform "ghost" gratings, and a continuous distribution is obtained for each ghost grating (i.e., each channel). After a comparison, the distributions obtained in the two models are identical, and the equivalence between the two models is demonstrated. In addition, the impacts of the duty cycle on the power/amplitude distributions of multiple channels of SFBG are presented.

Correlations between locked modes and impurity influxes

Energy Technology Data Exchange (ETDEWEB)

Fishpool, G M [Commission of the European Communities, Abingdon (United Kingdom). JET Joint Undertaking; Lawson, K D [UKAEA Culham Lab., Abingdon (United Kingdom)

1994-07-01

An analysis of pulses that were disturbed by medium Z impurity influxes (Cl, Cr, Fe and Ni) recorded during the 91/92 JET operations, has demonstrated that such influxes can result in MHD modes which subsequently ``lock``. A correlation is found between the power radiated by the influx and the time difference between the start of the influx and the beginning of the locked mode. The growth in the amplitude of the locked mode itself can lead to further impurity influxes. A correlation is noted between intense influxes (superior to 10 MW) and the mode ``unlocking``. (authors). 4 refs., 4 figs.

Small amplitude variable charge dust Bernstein-Greene-Kruskal double layers

Energy Technology Data Exchange (ETDEWEB)

Amour, Rabia [Plasma Physics Group, Theoretical Physics Laboratory, Faculty of Sciences - Physics, U.S.T.H.B, Bab-Ezzouar, B.P. 32, El Alia, Algiers 16111 (Algeria); Tribeche, Mouloud [Plasma Physics Group, Theoretical Physics Laboratory, Faculty of Sciences - Physics, U.S.T.H.B, Bab-Ezzouar, B.P. 32, El Alia, Algiers 16111 (Algeria)], E-mail: mouloud-tribeche@lycos.com

2009-05-11

A first theoretical attempt is made to investigate small amplitude, variable charge dust Bernstein-Greene-Kruskal (BGK) double layers (DLs). The nature of the dust BGK-DLs (compressive or rarefactive), their strength and thickness depend sensitively on the net negative charge residing on the grain surface, the dust grain dynamics and, more interestingly, on the ion-to-electron temperatures ratio.

Small amplitude variable charge dust Bernstein-Greene-Kruskal double layers

International Nuclear Information System (INIS)

Amour, Rabia; Tribeche, Mouloud

2009-01-01

A first theoretical attempt is made to investigate small amplitude, variable charge dust Bernstein-Greene-Kruskal (BGK) double layers (DLs). The nature of the dust BGK-DLs (compressive or rarefactive), their strength and thickness depend sensitively on the net negative charge residing on the grain surface, the dust grain dynamics and, more interestingly, on the ion-to-electron temperatures ratio.

Double-wavelet approach to study frequency and amplitude modulation in renal autoregulation

DEFF Research Database (Denmark)

Sosnovtseva, Olga; Pavlov, A N; Mosekilde, E

2004-01-01

Biological time series often display complex oscillations with several interacting rhythmic components. Renal autoregulation, for instance, involves at least two separate mechanisms both of which can produce oscillatory variations in the pressures and flows of the individual nephrons. Using double......-wavelet analysis we propose a method to examine how the instantaneous frequency and amplitude of a fast mode is modulated by the presence of a slower mode. Our method is applied both to experimental data from normotensive and hypertensive rats showing different oscillatory patterns and to simulation results...

Amplitude based feedback control for NTM stabilisation at ASDEX Upgrade

Energy Technology Data Exchange (ETDEWEB)

Rapson, Christopher, E-mail: chris.rapson@ipp.mpg.de; Giannone, Louis; Maraschek, Marc; Reich, Matthias; Stober, Joerg; Treutterer, Wolfgang

2014-05-15

Highlights: • Two algorithms have been developed which use the NTM amplitude to control ECCD deposition and stabilise NTMs. • Both algorithms were tested and tuned in a simulation of the full feedback loop including an MRE. • Both algorithms have been successfully deployed in ASDEX Upgrade experiments. • Use of the NTM amplitude adds considerable robustness, which is necessary when trying to target ECCD to within 1 cm of the island location. • This is part of ongoing work to reliably and quickly stabilise NTMs in any plasma scenario. - Abstract: Neoclassical Tearing Modes (NTMs) degrade the confinement in tokamak plasmas at high beta, placing a major limitation on the projected fusion performance. Furthermore, NTMs can lead to disruptions with even more severe consequences. Therefore methods to stabilise NTMs are being developed with high priority at several research institutes worldwide. The favoured method is to deposit Electron Cyclotron Current Drive (ECCD) precisely at the mode location by controlling a movable mirror in the ECCD launcher. This method requires both the mode location and the deposition location to be known with high accuracy in real time. The required accuracy is given by half of the marginal island width, or approximately 1 cm for a m/n = 3/2 NTM at ASDEX Upgrade. Despite considerable development on a range of diagnostics, it remains challenging to provide the necessary accuracy reliably and in real time. To relax the accuracy requirements and add robustness, the feedback controller can additionally consider the effect of ECCD on the NTM amplitude directly. Then the optimal deposition location is simply where the NTM amplitude is minimised. The simplest implementation sweeps the ECCD beam across the expected NTM location. After the sweep, the beam can be returned to the optimal location and held there to stabilise the NTM. Unfortunately, waiting for a full sweep takes too long. Therefore a second method assesses the NTM growth every

Amplitude modulation control of escape from a potential well

International Nuclear Information System (INIS)

Chacón, R.; Martínez García-Hoz, A.; Miralles, J.J.; Martínez, P.J.

2014-01-01

We demonstrate the effectiveness of periodic amplitude modulations in controlling (suppressing and enhancing) escape from a potential well through the universal model of a damped Helmholtz oscillator subjected to an external periodic excitation (the escape-inducing excitation) whose amplitude is periodically modulated (the escape-controlling excitation). Analytical and numerical results show that this multiplicative control works reliably for different subharmonic resonances between the two periodic excitations involved, and that its effectiveness is comparable to those of different methods of additive control. Additionally, we demonstrate the robustness of the multiplicative control against the presence of low-intensity Gaussian noise. -- Highlights: •Multiplicative control of escape from a potential well has been demonstrated. •Theoretical predictions are obtained from a Melnikov analysis. •It has been shown the robustness of the multiplicative control against noise.

Cluster observations of trapped ions interacting with magnetosheath mirror modes

Directory of Open Access Journals (Sweden)

J. Soucek

2011-06-01

Full Text Available Mirror modes are among the most intense low frequency plasma wave phenomena observed in the magnetosheaths of magnetized planets. They appear as large amplitude non-propagating fluctuations in the magnetic field magnitude and plasma density. These structures are widely accepted to represent a non-linear stage of the mirror instability, dominant in plasmas with large ion beta and a significant ion temperature anisotropy T⊥/T∥>1. It has long been recognized that the mirror instability both in the linear and non-linear stage is a kinetic process and that the behavior of resonant particles at small parallel velocities is crucial for its development and saturation. While the dynamics of the instability and the effect of trapped particles have been studied extensively in theoretical models and numerical simulations, only spurious observations of the trapped ions were published to date. In this work we used data from the Cluster spacecraft to perform the first detailed experimental study of ion velocity distribution associated with mirror mode oscillations. We show a conclusive evidence for the predicted cooling of resonant ions at small parallel velocities and heating of trapped ions at intermediate pitch angles.

Instability of surface electron cyclotron TM-modes influenced by non-monochromatic alternating electric field

International Nuclear Information System (INIS)

Girka, I. O.; Girka, V. O.; Sydora, R. D.; Thumm, M.

2016-01-01

The influence of non-monochromaticity of an external alternating electric field on excitation of TM eigenmodes at harmonics of the electron cyclotron frequency is considered here. These TM-modes propagate along the plasma interface in a metal waveguide. An external static constant magnetic field is oriented perpendicularly to the plasma interface. The problem is solved theoretically using the kinetic Vlasov-Boltzmann equation for description of plasma particles motion and the Maxwell equations for description of the electromagnetic mode fields. The external alternating electric field is supposed to be a superposition of two waves, whose amplitudes are different and their frequencies correlate as 2:1. An infinite set of equations for electric field harmonics of these modes is derived with the aid of nonlinear boundary conditions. This set is solved using the wave packet approach consisting of the main harmonic frequency and two nearest satellite temporal harmonics. Analytical studies of the obtained set of equations allow one to find two different regimes of parametric instability, namely, enhancement and suppression of the instability. Numerical analysis of the instability is carried out for the three first electron cyclotron harmonics.

Effect of Nonlinearity by the Amplitude Variation in coherent transmission in Laser Heterodyne Interferometric

International Nuclear Information System (INIS)

Chen, H F; Ding, X M; Zhong, Z; Xie, Z L; Yue, H

2006-01-01

To reduce the nonlinearity of nanometer measurement in laser heterodyne interferometric, the influence mechanics of the amplitude variation in coherent transmission upon nonlinearity must be confirmed. Based on the mechanics of nonlinearity, the models about how first-harmonic and second-harmonic nonlinearity caused by the amplitude variation in coherent transmission are proposed. The emulation result shows that different amplitude between measurement arm and reference arm increases the first-harmonic nonlinearity when laser beams nonorthogonality errors exist, but it doesn't change the relationship between nonlinearity and half wavelength. When the rotation angle error β of polarizing beam splitter (PBS) exists, amplitude variation only affects the first-harmonic nonlinearity. With a constant rotation angle of PBS β = 4 0 , when the amplitude factor of measurement arm reduces from 1 to 0.6, the nonlinearity increases from 0.25 nm to 3.81 nm, and the nonlinearity is simple superposition of first-harmonic and second-harmonic. Theoretic analysis and emulation show that the reduction of amplitude variation in coherent transmission can reduce influence on nonlinearity

The MACHO Project Sample of Galactic Bulge High-Amplitude {delta} Scuti Stars: Pulsation Behavior and Stellar Properties

Energy Technology Data Exchange (ETDEWEB)

Alcock, C.; Allsman, R. A.; Alves, D. R.; Axelrod, T. S.; Becker, A. C.; Bennett, D. P.; Cook, K. H.; Freeman, K. C.; Geha, M.; Griest, K. (and others)

2000-06-20

We have detected 90 objects with periods and light-curve structures similar to those of field {delta} Scuti stars using the Massive Compact Halo Object (MACHO) Project database of Galactic bulge photometry. If we assume similar extinction values for all candidates and absolute magnitudes similar to those of other field high-amplitude {delta} Scuti stars (HADS), the majority of these objects lie in or near the Galactic bulge. At least two of these objects are likely foreground {delta} Scuti stars, one of which may be an evolved nonradial pulsator, similar to other evolved, disk-population {delta} Scuti stars. We have analyzed the light curves of these objects and find that they are similar to the light curves of field {delta} Scuti stars and the {delta} Scuti stars found by the Optical Gravitational Lens Experiment (OGLE). However, the amplitude distribution of these sources lies between those of low- and high-amplitude {delta} Scuti stars, which suggests that they may be an intermediate population. We have found nine double-mode HADS with frequency ratios ranging from 0.75 to 0.79, four probable double- and multiple-mode objects, and another four objects with marginal detections of secondary modes. The low frequencies (5-14 cycles day-1) and the observed period ratios of {approx}0.77 suggest that the majority of these objects are evolved stars pulsating in fundamental or first overtone radial modes. (c) 2000 The American Astronomical Society.

Nonlinear nano-scale localized breather modes in a discrete weak ferromagnetic spin lattice

International Nuclear Information System (INIS)

Kavitha, L.; Parasuraman, E.; Gopi, D.; Prabhu, A.; Vicencio, Rodrigo A.

2016-01-01

We investigate the propagation dynamics of highly localized discrete breather modes in a weak ferromagnetic spin lattice with on-site easy axis anisotropy due to crystal field effect. We derive the discrete nonlinear equation of motion by employing boson mappings and p-representation. We explore the onset of modulational instability both analytically in the framework of linear stability analysis and numerically by means of molecular dynamics (MD) simulations, and a perfect agreement was demonstrated. It is also explored that how the antisymmetric nature of the canted ferromagnetic lattice supports highly localized discrete breather (DBs) modes as shown in the stability/instability windows. The energy exchange between low amplitude discrete breathers favours the growth of higher amplitude DBs, resulting eventually in the formation of few long-lived high amplitude DBs. - Highlights: • The effects of DM and anisotropy interaction on the DB modes are studied. • The antisymmetric nature of the canted ferromagnetic medium supports the DB modes. • Dynamics of ferromagnetic chain is governed by boson mappings and p-representation.

Mode-locking behavior of Izhikevich neurons under periodic external forcing

Science.gov (United States)

Farokhniaee, AmirAli; Large, Edward W.

2017-06-01

Many neurons in the auditory system of the brain must encode periodic signals. These neurons under periodic stimulation display rich dynamical states including mode locking and chaotic responses. Periodic stimuli such as sinusoidal waves and amplitude modulated sounds can lead to various forms of n :m mode-locked states, in which a neuron fires n action potentials per m cycles of the stimulus. Here, we study mode-locking in the Izhikevich neurons, a reduced model of the Hodgkin-Huxley neurons. The Izhikevich model is much simpler in terms of the dimension of the coupled nonlinear differential equations compared with other existing models, but excellent for generating the complex spiking patterns observed in real neurons. We obtained the regions of existence of the various mode-locked states on the frequency-amplitude plane, called Arnold tongues, for the Izhikevich neurons. Arnold tongue analysis provides useful insight into the organization of mode-locking behavior of neurons under periodic forcing. We find these tongues for both class-1 and class-2 excitable neurons in both deterministic and noisy regimes.

A modulation model for mode splitting of magnetic perturbations in the Mega Ampere Spherical Tokamak

International Nuclear Information System (INIS)

Hole, M J; Appel, L C

2009-01-01

Recent observations of magnetic fluctuation activity in the Mega Ampere Spherical Tokamak (MAST) reveal the presence of plasmas with bands of both low and high frequency magnetic fluctuations. Such plasmas exhibit a spectrum of low frequency modes with adjacent toroidal mode numbers, for which the measured frequency is near the Doppler shifted rotation frequency of the plasma. These are thought to be tearing modes. Also present are a spectrum of high frequency modes (e.g. Alfven, fishbone and/or ICE). The frequency and mode number of the tearing mode and its harmonics is identical to the frequency and mode number splitting of the high frequency MHD activity, strongly suggesting that the high frequency splitting is produced by modulation of the high and low frequency modes. We describe a strong modulation model, in which the nonlinear terms are fitted to produce the amplitude envelope profile of the tearing mode. A bispectral analysis proves that the low frequency modes are indeed in phase with the fundamental, while Fourier-SVD mode analysis confirms the mode numbers are toroidal harmonics. Employing this model, the sideband amplitude profile of the high frequency modes is predicted, and found to be in good agreement with experimental observations. Also, toroidal mode number splitting of the high frequency activity matches the mode number of the tearing mode. Weak evidence is found to indicate the Alfvenic sidebands are in phase with the Alfven eigenmode fundamental. The findings support predictions of a strong modulation model, and suggest a need to further develop nonlinear MHD theory to predict the amplitude of coupled sidebands, and so corroborate the observed nonlinear plasma response.

Field theory of large amplitude collective motion. A schematic model

International Nuclear Information System (INIS)

Reinhardt, H.

1978-01-01

By using path integral methods the equation for large amplitude collective motion for a schematic two-level model is derived. The original fermion theory is reformulated in terms of a collective (Bose) field. The classical equation of motion for the collective field coincides with the time-dependent Hartree-Fock equation. Its classical solution is quantized by means of the field-theoretical generalization of the WKB method. (author)

Global structure of mirror modes in the magnetosheath

International Nuclear Information System (INIS)

Johnson, J.R.; Cheng, C.Z.

1996-01-01

A global stability analysis of mirror modes in the magnetosheath is presented. The analysis is based upon the kinetic-MHD formulation which includes relevant kinetic effects such as Landau resonance and gradient drift effects related to inhomogeneities in the background density, temperature, pressure and its anisotropy, magnetic field, and plasma flow velocity. Pressure anisotropy provides the free energy for the global mirror mode. The local theory of mirror modes predicts purely growing modes confined in the unstable magnetosheath region; however, the nonlocal theory that includes the effects of gradients and plasma flow predicts modes with real frequencies which propagate with the flow from the magnetosheath toward the magnetopause boundary. The real frequency is on the order of a combination of the diamagnetic drift frequency and the Doppler shift frequency associated with plasma flow. The diamagnetic drift frequency provides a wave phase velocity in the direction of the magnetopause so that wave energy accumulates against the magnetopause boundary, and the amplitude is skewed in that direction. On the other hand, plasma flow also gives rise to a real phase velocity, but the phase velocity is smaller than the flow velocity. As a result, the wave amplitude is increased in the wake of the plasma flow and piles up against the bow shock boundary

Global structure of mirror modes in the magnetosheath

Energy Technology Data Exchange (ETDEWEB)

Johnson, J.R.; Cheng, C.Z.

1996-11-01

A global stability analysis of mirror modes in the magnetosheath is presented. The analysis is based upon the kinetic-MHD formulation which includes relevant kinetic effects such as Landau resonance and gradient drift effects related to inhomogeneities in the background density, temperature, pressure and its anisotropy, magnetic field, and plasma flow velocity. Pressure anisotropy provides the free energy for the global mirror mode. The local theory of mirror modes predicts purely growing modes confined in the unstable magnetosheath region; however, the nonlocal theory that includes the effects of gradients and plasma flow predicts modes with real frequencies which propagate with the flow from the magnetosheath toward the magnetopause boundary. The real frequency is on the order of a combination of the diamagnetic drift frequency and the Doppler shift frequency associated with plasma flow. The diamagnetic drift frequency provides a wave phase velocity in the direction of the magnetopause so that wave energy accumulates against the magnetopause boundary, and the amplitude is skewed in that direction. On the other hand, plasma flow also gives rise to a real phase velocity, but the phase velocity is smaller than the flow velocity. As a result, the wave amplitude is increased in the wake of the plasma flow and piles up against the bow shock boundary.

Amplitude characteristics of a solid-state ring laser with active mode locking

Energy Technology Data Exchange (ETDEWEB)

Belkina, E.M.; Klochan, E.L.; Lariontsev, E.G.

1986-09-01

A system of equations is obtained for the parameters of ultrashort light pulses (USLP) in a solid-state ring laser (SSRL) with periodic loss modulation. Allowance is made for the coupling between counterpropagating USLP due to backscattering in the modulator. The regime of counter-propagating wave frequency capture (CPWFC) is studied. It is shown that the coupling of counterpropagating waves due to backscattering at the modulator ends leads to the suppression of one of the counterpropagating waves during an increase in the detuning of the modulation frequency relative to its optimal value. The influence of rotation on the amplitude characteristics of an SSRL in the CPWFC regime is studied. 9 references.

Small-action Particles in a Tokamak in the Presence of an n = 1 Mode

International Nuclear Information System (INIS)

White, R.B.; Lutsenko, V.V.; Kolesnichenko, Ya. I.; Yakovenko, Yu. V.

1999-01-01

It is found that an m = n = 1 mode with the amplitude exceeding a certain threshold can lead to stochastic motion of energetic ions in tokamaks, the large orbit width particles (potatoes) being most easily affected. An n = 1 mode can redistribute particles also in the absence of stochasticity but only when the perturbation is quickly switched on/off, e.g., due to sawtooth crash. In the latter case, the perturbation results in regular motion of particles around a certain helical orbit, at which a resonance driven by the mode but having no amplitude threshold takes place

Small--radiation-amplitude dynamical voltage model of an irradiated, externally unbiased Josephson tunnel junction

International Nuclear Information System (INIS)

McAdory, R.T. Jr.

1988-01-01

A theory is presented for the nonequilibrium voltage states of an irradiated Josephson junction shunted by an external resistor but with no external current or voltage biasing. This device, referred to as a free-running Josephson junction, is modeled in a small--radiation-amplitude, deterministic regime extending the previous work of Shenoy and Agarwal. The time-averaged induced voltage is treated as a dynamical variable, the external radiation is modeled as a current source, and the induced junction-radiation vector potential, with and without a mode structure, is treated to first order in the driving currents. A dynamical equation for the time-averaged induced voltage yields a (nonequilibrium) steady-state relation between the time-averaged induced voltage and the incident radiation amplitude valid for a wide range of voltages, including zero. Regions of bistability occur in the voltage--versus--incident-amplitude curves, some of which are dependent on the external resistor. The zero-voltage state breaks down, as the external radiation amplitude is increased, at a critical value of the incident-radiation amplitude inversely proportional to the external resistance

Oscillation Mode Variability in Evolved Compact Pulsators from Kepler Photometry. I. The Hot B Subdwarf Star KIC 3527751

Science.gov (United States)

Zong, Weikai; Charpinet, Stéphane; Fu, Jian-Ning; Vauclair, Gérard; Niu, Jia-Shu; Su, Jie

2018-02-01

We present the first results of an ensemble and systematic survey of oscillation mode variability in pulsating hot B subdwarf (sdB) and white dwarf stars observed with the original Kepler mission. The satellite provides uninterrupted high-quality photometric data with a time baseline that can reach up to 4 yr collected on pulsating stars. This is a unique opportunity to characterize long-term behaviors of oscillation modes. A mode modulation in amplitude and frequency can be independently inferred by its fine structure in the Fourier spectrum, from the sLSP, or with prewhitening methods applied to various parts of the light curve. We apply all these techniques to the sdB star KIC 3527751, a long-period-dominated hybrid pulsator. We find that all the detected modes with sufficiently large amplitudes to be thoroughly studied show amplitude and/or frequency variations. Components of three identified quintuplets around 92, 114, and 253 μHz show signatures that can be linked to nonlinear interactions according to the resonant mode coupling theory. This interpretation is further supported by the fact that many oscillation modes are found to have amplitudes and frequencies showing correlated or anticorrelated variations, a behavior that can be linked to the amplitude equation formalism, where nonlinear frequency corrections are determined by their amplitude variations. Our results suggest that oscillation modes varying with diverse patterns are a very common phenomenon in pulsating sdB stars. Close structures around main frequencies therefore need to be carefully interpreted in light of this finding to secure a robust identification of real eigenfrequencies, which is crucial for seismic modeling. The various modulation patterns uncovered should encourage further developments in the field of nonlinear stellar oscillation theory. It also raises a warning to any long-term project aiming at measuring the rate of period change of pulsations caused by stellar evolution, or at

Amplitude calculations for 3D Gaussian beam migration using complex-valued traveltimes

International Nuclear Information System (INIS)

Bleistein, Norman; Gray, Samuel H

2010-01-01

Gaussian beams are often used to represent Green's functions in three-dimensional Kirchhoff-type true-amplitude migrations because such migrations made using Gaussian beams yield superior images to similar migrations using classical ray-theoretic Green's functions. Typically, the integrand of a migration formula consists of two Green's functions—each describing propagation to the image point—one from the source and the other from the receiver position. The use of Gaussian beams to represent each of these Green's functions in 3D introduces two additional double integrals when compared to a Kirchhoff migration using ray-theoretic Green's functions, thereby adding a significant computational burden. Hill (2001 Geophysics 66 1240–50) proposed a method for reducing those four integrals to two, compromising slightly on the full potential quality of the Gaussian beam representations for the sake of more efficient computation. That approach requires a two-dimensional steepest descent analysis for the asymptotic evaluation of a double integral. The method requires evaluation of the complex traveltimes of the Gaussian beams as well as the amplitudes of the integrands at the determined saddle points. In addition, it is necessary to evaluate the determinant of a certain (Hessian) matrix of second derivatives. Hill (2001 Geophysics 66 1240–50) did not report on this last part; thus, his proposed migration formula is kinematically correct but lacks correct amplitude behavior. In this paper, we derive a formula for that Hessian matrix in terms of dynamic ray tracing quantities. We also show in a simple example how the integral that we analyze here arises in a true amplitude migration formula

Spatial light modulation for mode conditioning

DEFF Research Database (Denmark)

Glückstad, Jesper; Palima, Darwin

We demonstrate patented techniques for generating tuneable complex field distributions for controllable coupling to high-order guided modes of micro-structured fibres. The optical Fourier transform of binary phase-only patterns which are encoded on a computer-controlled spatial light modulator......, generates complex field distributions for selective launching of a desired mode. Both the amplitude and the phase of the programmable fields are modulated by straightforward and fast adjustments of simple pre-defined binary phase-only diffractive patterns. Experiments demonstrate tuneable coupling...

Amplitude modulation of quantum-ion-acoustic wavepackets in electron-positron-ion plasmas: Modulational instability, envelope modes, extreme wavesa)

Science.gov (United States)

Rahman, Ata-ur-; Kerr, Michael Mc; El-Taibany, Wael F.; Kourakis, Ioannis; Qamar, A.

2015-02-01

A semirelativistic fluid model is employed to describe the nonlinear amplitude modulation of low-frequency (ionic scale) electrostatic waves in an unmagnetized electron-positron-ion plasma. Electrons and positrons are assumed to be degenerated and inertialess, whereas ions are warm and classical. A multiscale perturbation method is used to derive a nonlinear Schrödinger equation for the envelope amplitude, based on which the occurrence of modulational instability is investigated in detail. Various types of localized ion acoustic excitations are shown to exist, in the form of either bright type envelope solitons (envelope pulses) or dark-type envelope solitons (voids, holes). The plasma configurational parameters (namely, the relativistic degeneracy parameter, the positron concentration, and the ionic temperature) are shown to affect the conditions for modulational instability significantly, in fact modifying the associated threshold as well as the instability growth rate. In particular, the relativistic degeneracy parameter leads to an enhancement of the modulational instability mechanism. Furthermore, the effect of different relevant plasma parameters on the characteristics (amplitude, width) of these envelope solitary structures is also presented in detail. Finally, the occurrence of extreme amplitude excitation (rogue waves) is also discussed briefly. Our results aim at elucidating the formation and dynamics of nonlinear electrostatic excitations in superdense astrophysical regimes.

Amplitude modulation of quantum-ion-acoustic wavepackets in electron-positron-ion plasmas: Modulational instability, envelope modes, extreme waves

Energy Technology Data Exchange (ETDEWEB)

Rahman, Ata-ur-, E-mail: ata797@yahoo.com [Department of Physics, University of Peshawar, Peshawar 25000 (Pakistan); Department of Physics, Islamia College Peshawar, Khyber Pakhtunkhwa (Pakistan); Kerr, Michael Mc, E-mail: mjamckerr@gmail.com; Kourakis, Ioannis, E-mail: IoannisKourakisSci@gmail.com [Centre for Plasma Physics, Department of Physics and Astronomy, Queen' s University Belfast, BT7 1NN Northern Ireland (United Kingdom); El-Taibany, Wael F., E-mail: eltaibany@hotmail.com [Department of Physics, Faculty of Science, Damietta University, New Damietta, P.O. Box 34517 (Egypt); Department of Physics, College of Science for Girls in Abha, King Khalid University, P.O. Box 960, Abha (Saudi Arabia); Qamar, A., E-mail: anisaqamar@gmail.com [Department of Physics, University of Peshawar, Peshawar 25000 (Pakistan)

2015-02-15

A semirelativistic fluid model is employed to describe the nonlinear amplitude modulation of low-frequency (ionic scale) electrostatic waves in an unmagnetized electron-positron-ion plasma. Electrons and positrons are assumed to be degenerated and inertialess, whereas ions are warm and classical. A multiscale perturbation method is used to derive a nonlinear Schrödinger equation for the envelope amplitude, based on which the occurrence of modulational instability is investigated in detail. Various types of localized ion acoustic excitations are shown to exist, in the form of either bright type envelope solitons (envelope pulses) or dark-type envelope solitons (voids, holes). The plasma configurational parameters (namely, the relativistic degeneracy parameter, the positron concentration, and the ionic temperature) are shown to affect the conditions for modulational instability significantly, in fact modifying the associated threshold as well as the instability growth rate. In particular, the relativistic degeneracy parameter leads to an enhancement of the modulational instability mechanism. Furthermore, the effect of different relevant plasma parameters on the characteristics (amplitude, width) of these envelope solitary structures is also presented in detail. Finally, the occurrence of extreme amplitude excitation (rogue waves) is also discussed briefly. Our results aim at elucidating the formation and dynamics of nonlinear electrostatic excitations in superdense astrophysical regimes.

Active Control of Compressor Stall inception: A Bifurcation-Theoretic Approach

National Research Council Canada - National Science Library

Liaw, Der-Cherng; Abed, Eyad H

1994-01-01

...). This model consists of three ordinary differential equations with state variables being the mass flow rate, pressure rise, and the amplitude of the first harmonic mode of the asymmetric component...

Observations of core modes during RF-generated internal transport barriers in Alcator C-Mod

Energy Technology Data Exchange (ETDEWEB)

Lynn, A G [Fusion Research Center, University of Texas at Austin, Austin, TX (United States); Phillips, P E [Fusion Research Center, University of Texas at Austin, Austin, TX (United States); Hubbard, A E [Plasma Science and Fusion Center, MIT, Cambridge, MA (United States); Wukitch, S J [Plasma Science and Fusion Center, MIT, Cambridge, MA (United States)

2004-05-01

In the Alcator C-Mod tokamak, a high-resolution heterodyne ECE radiometer has been used to measure the electron temperature in plasma discharges with internal transport barriers (ITBs). ITBs are formed by the application of off-axis (r/a {approx} 0.5) ICRF power. Strong density peaking indicates the formation of the ITB. When the ITB is formed, the ECE radiometer detects a small amplitude mode localized near the magnetic axis. Surprisingly, as this mode amplitude grows a dip in the temperature profile is clearly observed at the same location. If sawteeth are present, the mode amplitude appears to be suppressed by the sawtooth crash and no dip in the temperate profiles is observed. TORAY, a ray-tracing code, has been used to investigate the possible refractive effects of the steep density gradients in the ITB and its effects on the ECE observations. The results show that refractive effects can explain the observed local changes in temperature. Ray-tracing also indicates that the observed modes are density fluctuations. Observations of broadband density fluctuations during 4.5 T ITBs are also described.

Design and numerical optimization of a mode multiplexer based on few-mode fiber couplers

International Nuclear Information System (INIS)

Xie, Yiwei; Fu, Songnian; Liu, Hai; Zhang, Hailiang; Tang, Ming; Liu, Deming; Shum, P

2013-01-01

Mode division multiplexing (MDM) transmission based on few-mode fibers (FMFs) appears to be an alternative solution for overcoming the capacity limit of single-mode fibers (SMFs). A FMF coupler-based mode division multiplexer/demultiplexer (MMUX/DeMMUX) is proposed and theoretically investigated after the fabricated FMF is characterized. MMUXs/DeMMUXs with a mode contrast ratio (MCR) of more than 20 dB can be obtained for two-mode multiplexing and three-mode multiplexing over a wavelength span of 60 and 10 nm, respectively. We numerically verify the proposed MMUX/DeMMUX which has the advantages of high MCR, easy fabrication and maintenance, and low wavelength dependence. (paper)

Large Amplitude Low Frequency Waves in a Magnetized Nonuniform Electron-Positron-Ion Plasma

Institute of Scientific and Technical Information of China (English)

Q. Haque; H. Saleem

2004-01-01

@@ It is shown that the large amplitude low-frequency electromagnetic drift waves in electron-positron-ion plasmas might give rise to dipolar vortices. A linear dispersion relation of several coupled electrostatic and electromagnetic low-frequency modes is obtained. The relevance of this work to both laboratory and astrophysical situations is pointed out.

Color guided amplitudes

Energy Technology Data Exchange (ETDEWEB)

Broedel, Johannes [Stanford Institute for Theoretical Physics and Department of Physics, Stanford University, Stanford, CA (United States); Dixon, Lance J. [SLAC National Accelerator Laboratory, Stanford University, Stanford, CA (United States)

2012-07-01

Amplitudes in gauge thoeries obtain contributions from color and kinematics. While these two parts of the amplitude seem to exhibit different symmetry structures, it turns out that they can be reorganized in a way to behave equally, which leads to the so-called color-kinematic dual representations of amplitudes. Astonishingly, the existence of those representations allows squaring to related gravitational theories right away. Contrary to the Kawaii-Levellen-Tye relations, which have been used to relate gauge theories and gravity previously, this method is applicable not only to tree amplitudes but also at loop level. In this talk, the basic technique is introduced followed by a discussion of the existence of color-kinematic dual representations for amplitudes derived from gauge theory actions which are deformed by higher-operator insertions. In addition, it is commented on the implications for deformed gravitational theories.

Response of ENSO amplitude to global warming in CESM large ensemble: uncertainty due to internal variability

Science.gov (United States)

Zheng, Xiao-Tong; Hui, Chang; Yeh, Sang-Wook

2018-06-01

El Niño-Southern Oscillation (ENSO) is the dominant mode of variability in the coupled ocean-atmospheric system. Future projections of ENSO change under global warming are highly uncertain among models. In this study, the effect of internal variability on ENSO amplitude change in future climate projections is investigated based on a 40-member ensemble from the Community Earth System Model Large Ensemble (CESM-LE) project. A large uncertainty is identified among ensemble members due to internal variability. The inter-member diversity is associated with a zonal dipole pattern of sea surface temperature (SST) change in the mean along the equator, which is similar to the second empirical orthogonal function (EOF) mode of tropical Pacific decadal variability (TPDV) in the unforced control simulation. The uncertainty in CESM-LE is comparable in magnitude to that among models of the Coupled Model Intercomparison Project phase 5 (CMIP5), suggesting the contribution of internal variability to the intermodel uncertainty in ENSO amplitude change. However, the causations between changes in ENSO amplitude and the mean state are distinct between CESM-LE and CMIP5 ensemble. The CESM-LE results indicate that a large ensemble of 15 members is needed to separate the relative contributions to ENSO amplitude change over the twenty-first century between forced response and internal variability.

Trapped Mode Study in the LHC Rotatable Collimator

CERN Document Server

Xiao, L; Smith, J C; Caspers, F

2010-01-01

A rotatable collimator is proposed for the LHC phase II collimation upgrade. When the beam crosses the collimator, trapped modes will be excited that result in beam energy loss and collimator power dissipation. Some of the trapped modes can also generate transverse kick on the beam and affect the beam operation. In this paper the parallel eigensolver code Omega3P is used to search for all the trapped modes below 2GHz in the collimator, including longitudinal modes and transverse modes. The loss factors and kick factors of the trapped modes are calculated as function of the jaw positions. The amplitude ratio between transverse and longitudinal trapped mode intensity can be used as a direct measure of the position of the beam. We present simulation results and discuss the results.

Spin-selective coupling to Majorana zero modes in mixed singlet and triplet superconducting nanowires

Science.gov (United States)

Paul, Ganesh C.; Saha, Arijit; Das, Sourin

2018-05-01

We theoretically investigate the transport properties of a quasi-one-dimensional ferromagnet-superconductor junction where the superconductor consists of mixed singlet and triplet pairings. We show that the relative orientation of the Stoner field (h ˜) in the ferromagnetic lead and the d vector of the superconductor acts like a on-off switch for the zero bias conductance of the device. In the regime, where triplet pairing amplitude dominates over the singlet counterpart (topological phase), a pair of Majorana zero modes appear at each end of the superconducting part of the nanowire. When h ˜ is parallel or antiparallel to the d vector, transport gets completely blocked due to blockage in pairing while, when h ˜ and d are perpendicular to each other, the zero energy two terminal differential conductance spectra exhibits sharp transition from 4 e2/h to 2 e2/h as the magnetization strength in the lead becomes larger than the chemical potential indicating the spin-selective coupling of a pair of Majorana zero modes to the lead.

Responses to amplitude modulated infrared stimuli in the guinea pig inferior colliculus

Science.gov (United States)

Richter, Claus-Peter; Young, Hunter

2013-03-01

Responses of units in the central nucleus of the inferior colliculus of the guinea pig were recorded with tungsten electrodes. The set of data presented here is limited to high stimulus levels. The effect of changing the modulation frequency and the modulation depth was explored for acoustic and laser stimuli. The selected units responded to sinusoidal amplitude modulated (AM) tones, AM trains of clicks, and AM trains of laser pulses with a modulation of their spike discharge. At modulation frequencies of 20 Hz, some units tended to respond with 40 Hz to the acoustic stimuli, but only at 20 Hz for the trains of laser pulses. For all modes of stimulation the responses revealed a dominant response to the first cycle of the modulation, with decreasing number of action potential during successive cycles. While amplitude modulated tone bursts and amplitude modulated trains of acoustic clicks showed similar patterns, the response to trains of laser pulses was different.

Frequency shift and hysteresis suppression in contact-mode AFM using contact stiffness modulation

Directory of Open Access Journals (Sweden)

Belhaq M.

2012-07-01

Full Text Available In this paper the frequency response shift and hysteresis suppression of contact-mode atomic force microscopy is investigated using parametric modulation of the contact stiffness. Based on the Hertzian contact theory, a lumped single degree of freedom oscillator is considered for modeling the cantilever dynamics contact-mode atomic force microscopy. We use the technique of direct partition of motion and the method of multiple scales to obtain, respectively, the slow dynamic and the corresponding slow flow of the system. As results, this study shows that the amplitude of the contact stiffness modulation has a significant effect on the frequency response. Specifically, increasing the amplitude of the stiffness modulation suppresses hysteresis, decreases the peak amplitude and produces shifts towards higher and lower frequencies.

Modeling and experimental study on near-field acoustic levitation by flexural mode.

Science.gov (United States)

Liu, Pinkuan; Li, Jin; Ding, Han; Cao, Wenwu

2009-12-01

Near-field acoustic levitation (NFAL) has been used in noncontact handling and transportation of small objects to avoid contamination. We have performed a theoretical analysis based on nonuniform vibrating surface to quantify the levitation force produced by the air film and also conducted experimental tests to verify our model. Modal analysis was performed using ANSYS on the flexural plate radiator to obtain its natural frequency of desired mode, which is used to design the measurement system. Then, the levitation force was calculated as a function of levitation distance based on squeeze gas film theory using measured amplitude and phase distributions on the vibrator surface. Compared with previous fluid-structural analyses using a uniform piston motion, our model based on the nonuniform radiating surface of the vibrator is more realistic and fits better with experimentally measured levitation force.

Collective modes in superconducting rhombohedral graphite

Energy Technology Data Exchange (ETDEWEB)

Kauppila, Ville [O.V. Lounasmaa Laboratory, Aalto University (Finland); Hyart, Timo; Heikkilae, Tero [University of Jyvaeskylae (Finland)

2015-07-01

Recently it was realized that coupling particles with a Dirac dispersion (such as electrons in graphene) can lead to a topologically protected state with flat band dispersion. Such a state could support superconductivity with unusually high critical temperatures. Perhaps the most promising way to realize such coupling in real materials is in the surface of rhombohedrally stacked graphite. We consider collective excitations (i.e. the Higgs modes) in surface superconducting rhombohedral graphite. We find two amplitude and two phase modes corresponding to the two surfaces of the graphite where the superconductivity lives. We calculate the dispersion of these modes. We also derive the Ginzburg-Landau theory for this material. We show that in superconducting rhombohedral graphite, the collective modes, unlike in conventional BCS superconductors, give a large contribution to thermodynamic properties of the material.

There is a continuum ambiguity for elastic πN amplitudes

International Nuclear Information System (INIS)

Atkinson, D.; Roo, M. de; Polman, T.J.T.M.

1984-01-01

The implicit-function method of constructing phase-factor continuum ambiguities in phase-shift analysis is briefly reviewed, and new numerical examples are given of ambiguities in πN phase shifts at 1997 MeV. Since the ambiguous amplitudes differ by more than 5%, while the corresponding cross sections and polarizations are equal, to better than a computational accuracy of 0.007%, numerical credence is given to the theoretical claim that the continuum ambiguity exists. (orig.)

A microwave FEL [free electron laser] code using waveguide modes

International Nuclear Information System (INIS)

Byers, J.A.; Cohen, R.H.

1987-08-01

A free electron laser code, GFEL, is being developed for application to the LLNL tokamak current drive experiment, MTX. This single frequency code solves for the slowly varying complex field amplitude using the usual wiggler-averaged equations of existing codes, in particular FRED, except that it describes the fields by a 2D expansion in the rectangular waveguide modes, using coupling coefficients similar to those developed by Wurtele, which include effects of spatial variations in the fields seen by the wiggler motion of the particles. Our coefficients differ from those of Wurtele in two respects. First, we have found a missing √2γ/a/sub w/ factor in his C/sub z/; when corrected this increases the effect of the E/sub z/ field component and this in turn reduces the amplitude of the TM mode. Second, we have consistently retained all terms of second order in the wiggle amplitude. Both corrections are necessary for accurate computation. GFEL has the capability of following the TE/sub 0n/ and TE(M)/sub m1/ modes simultaneously. GFEL produces results nearly identical to those from FRED if the coupling coefficients are adjusted to equal those implied by the algorithm in FRED. Normally, the two codes produce results that are similar but different in detail due to the different treatment of modes higher than TE/sub 01/. 5 refs., 2 figs., 1 tab

Modified Clemmow-Mullaly-Allis diagram for large-amplitude electromagnetic waves in magnetoplasmas

International Nuclear Information System (INIS)

Minami, K.; Mori, Y.; Takeda, S.

1975-02-01

A possible modification to the well known Clemmow- Mullaly-Allis diagram is analysed taking into account the radiation pressure force due to a large-amplitude electromagnetic field E in magnetoplasmas. We restrict ourselves here to the propagations parallel (the right and left-hand circularly polarized waves) and/or perpendicular (the ordinary and extraordinary modes) to the static magnetic field Bsub(o). We analyse electromagnetic waves incident normally on a semi-infinite uniform plasma, on which Bsub(o) is applied parallel and/or perpendicular to the surface. Considerations are limited to a cold collisionless plasma where the incident waves are evanescent. Simple expressions are obtained for the cut-off conditions of the waves except the extraordinary mode. In the latter case, the cut-off condition is calculated numerically solving an integral equation. The results are demonstrated in the usual Clemmow-Mullaly-Allis diagram for the various values of b=2Esub(i) 2 e 2 /mω 2 kappaTsub(e') where Esub(i) and ω are, respectively, the amplitude and the angular frequency of the incident wave. The cut-off lines are shown to move towards the higher densities with increasing b. (auth.)

Non linear interaction between a Langmuir wave and a ballistic perturbation

International Nuclear Information System (INIS)

Gervais, F.; Olivain, J.; Quemeneur, A.; Trocheris, M.

1979-05-01

The theoretical solutions of the Landau-Vlasov initial value problem giving mode-mode coupling usually neglect the free-streaming contribution. We solve theoretically this problem including the ballistic terms. We find that a new mode appears resulting from the nonlinear interaction between the Landau component and the ballistic perturbation. The amplitude of this mode is calculated as a function of distance and compared with experimental results in a plasma column

Particle-Hole Character of the Higgs and Goldstone Modes in Strongly Interacting Lattice Bosons

Science.gov (United States)

Di Liberto, M.; Recati, A.; Trivedi, N.; Carusotto, I.; Menotti, C.

2018-02-01

We study the low-energy excitations of the Bose-Hubbard model in the strongly interacting superfluid phase using a Gutzwiller approach. We extract the single-particle and single-hole excitation amplitudes for each mode and report emergent mode-dependent particle-hole symmetry on specific arc-shaped lines in the phase diagram connecting the well-known Lorentz-invariant limits of the Bose-Hubbard model. By tracking the in-phase particle-hole symmetric oscillations of the order parameter, we provide an answer to the long-standing question about the fate of the pure amplitude Higgs mode away from the integer-density critical point. Furthermore, we point out that out-of-phase symmetric oscillations in the gapless Goldstone mode are responsible for a full suppression of the condensate density oscillations. Possible detection protocols are also discussed.

Observing mode propagation inside a laser cavity

CSIR Research Space (South Africa)

Naidoo, Darryl

2012-05-01

Full Text Available components, to study the forward and backward propagating waves everywhere inside a laser cavity. We verify the previous theoretical-only prediction that the two fields may differ substantially in their amplitude profile, even for stable resonator systems, a...

Non-dissipative kinetic simulation and analytical solution of three-mode equations of ion temperature gradient instability

International Nuclear Information System (INIS)

Watanabe, T.-H.; Sugama, H.; Sato, T.

1999-12-01

A non-dissipative drift kinetic simulation scheme, which rigorously satisfies the time-reversibility, is applied to the three-mode coupling problem of the ion temperature gradient (ITG) instability. It is found from the simulation that the three-mode ITG system repeats growth and decay with a period which shows a logarithmic divergence for infinitesimal initial perturbations. Accordingly, time average of the mode amplitude vanishes, as the initial amplitude approaches to zero. An exact solution is analytically given for a class of initial conditions. An excellent agreement is confirmed between the analytical solution and numerical results. The results obtained here provide a useful reference for basic benchmarking of theories and simulation of the ITG modes. (author)

Observation of precursor magnetic oscillations to the H-mode transition of ASDEX

International Nuclear Information System (INIS)

Toi, K.; Gernhardt, J.; Klueber, O.; Kornherr, M.

1988-05-01

Precursor oscillations to the H-mode transition are identified in magnetic fluctuations of the ASDEX H-mode discharges initiated without a sawtooth. This precursor is m=4/n=1 mode, rotating with f ≅ 10 kHz in the opposite direction to co-injected neutral beams. Time behaviour of the amplitude suggests that the H-mode transition is caused, not by the edge electron temperature, but by the edge current density. (orig.)

Hysteresis in the tearing mode locking/unlocking due to resonant magnetic perturbations in EXTRAP T2R

Science.gov (United States)

Fridström, R.; Frassinetti, L.; Brunsell, P. R.

2015-10-01

The physical mechanisms behind the hysteresis in the tearing mode locking and unlocking to a resonant magnetic perturbation (RMP) are experimentally studied in EXTRAP T2R reversed-field pinch. The experiments show that the electromagnetic and the viscous torque increase with increasing perturbation amplitude until the mode locks to the wall. At the wall-locking, the plasma velocity reduction profile is peaked at the radius where the RMP is resonant. Thereafter, the viscous torque drops due to the relaxation of the velocity in the central plasma. This is the main reason for the hysteresis in the RMP locking and unlocking amplitude. The increased amplitude of the locked tearing mode produces further deepening of the hysteresis. Both experimental results are in qualitative agreement with the model in Fitzpatrick et al (2001 Phys. Plasmas 8 4489)

Properties of solar gravity mode signals in total irradiance observations

International Nuclear Information System (INIS)

Kroll, R.J.; Chen, J.; Hill, H.A.

1988-01-01

Further evidence has been found that a significant fraction of the gravity mode power density in the total irradiance observations appears in sidebands of classified eigenfrequencies. These sidebands whose amplitudes vary from year to year are interpreted as harmonics of the rotational frequencies of the nonuniform solar surface. These findings are for non axisymmetric modes and corroborate the findings of Kroll, Hill and Chen for axisymmetric modes. It is demonstrated the the generation of the sidebands lifts the usual restriction on the parity of the eigenfunctions for modes detectable in total irradiance observations. 14 refs

Real part of amplitude and hadron scattering cross section at superhigh energies

International Nuclear Information System (INIS)

Troshin, S.M.; Tyurin, N.E.

1987-01-01

New data on measuring the ratio of the real to imaginary part of the forward scattering amplitude: ρ pp-bar (√s=546 GeV)=0.24±0.04 have been considered. This result is shown to agree with the behaviour of σ tot (s), predicted by the U-matrix model. A possibility of transition to antishadow scattering mode at superhigh energies is stated

Scaling of the MHD perturbation amplitude required to trigger a disruption and predictions for ITER

Science.gov (United States)

de Vries, P. C.; Pautasso, G.; Nardon, E.; Cahyna, P.; Gerasimov, S.; Havlicek, J.; Hender, T. C.; Huijsmans, G. T. A.; Lehnen, M.; Maraschek, M.; Markovič, T.; Snipes, J. A.; the COMPASS Team; the ASDEX Upgrade Team; Contributors, JET

2016-02-01

The amplitude of locked instabilities, likely magnetic islands, seen as precursors to disruptions has been studied using data from the JET, ASDEX Upgrade and COMPASS tokamaks. It was found that the thermal quench, that often initiates the disruption, is triggered when the amplitude has reached a distinct level. This information can be used to determine thresholds for simple disruption prediction schemes. The measured amplitude in part depends on the distance of the perturbation to the measurement coils. Hence the threshold for the measured amplitude depends on the mode location (i.e. the rational q-surface) and thus indirectly on parameters such as the edge safety factor, q 95, and the internal inductance, li(3), that determine the shape of the q-profile. These dependencies can be used to set the disruption thresholds more precisely. For the ITER baseline scenario, with typically q 95  =  3.2, li(3)  =  0.9 and taking into account the position of the measurement coils on ITER, the maximum allowable measured locked mode amplitude normalized to engineering parameters was estimated to be a·B ML(r c)/I p  =  0.92 m mT/MA, or directly as a fraction edge poloidal magnetic field: B ML(r c)/B θ (a)  =  5 · 10-3. But these values decrease for operation at higher q 95 or lower li(3). The analysis found furthermore that the above empirical criterion to trigger a thermal quench is more consistent with a criterion derived with the concept of a critical island size, i.e. the thermal quench seemed to be triggered at a distinct island width.

Theory of anomalous transport in H-mode plasmas

International Nuclear Information System (INIS)

Itoh, S.; Itoh, K.; Fukuyama, A.; Yagi, M.

1993-05-01

Theory of the anomalous transport is developed, and the unified formula for the L- and H-mode plasmas is presented. The self-sustained ballooning-mode turbulence is solved in the presence of the inhomogeneous radial electric field, E r . Reductions in transport coefficients and the amplitude and decorrelation length of fluctuations due to E r ' are quantitatively analyzed. Combined with the E r -bifurcation model, the thickness of the transport barrier is simultaneously determined. (author)

Frequency and amplitude modulation of ultra-compact terahertz quantum cascade lasers using an integrated avalanche diode oscillator.

Science.gov (United States)

Castellano, Fabrizio; Li, Lianhe; Linfield, Edmund H; Davies, A Giles; Vitiello, Miriam S

2016-03-15

Mode-locked comb sources operating at optical frequencies underpin applications ranging from spectroscopy and ultrafast physics, through to absolute frequency measurements and atomic clocks. Extending their operation into the terahertz frequency range would greatly benefit from the availability of compact semiconductor-based sources. However, the development of any compact mode-locked THz laser, which itself is inherently a frequency comb, has yet to be achieved without the use of an external stimulus. High-power, electrically pumped quantum cascade lasers (QCLs) have recently emerged as a promising solution, owing to their octave spanning bandwidths, the ability to achieve group-velocity dispersion compensation and the possibility of obtaining active mode-locking. Here, we propose an unprecedented compact architecture to induce both frequency and amplitude self-modulation in a THz QCL. By engineering a microwave avalanche oscillator into the laser cavity, which provides a 10 GHz self-modulation of the bias current and output power, we demonstrate multimode laser emission centered around 3 THz, with distinct multiple sidebands. The resulting microwave amplitude and frequency self-modulation of THz QCLs opens up intriguing perspectives, for engineering integrated self-mode-locked THz lasers, with impact in fields such as nano- and ultrafast photonics and optical metrology.

Investigation of equilibrium, global modes and microinstabilities in the stellarator W7-AS

International Nuclear Information System (INIS)

Weller, A.; Anton, M.; Brakel, R.

1999-01-01

Equilibrium and stability properties in the WENDELSTEIN 7-AS stellarator are investigated experimentally and compared with theoretical predictions for particular cases. The topology of equilibrium magnetic surfaces and of global MHD modes is inferred from X-ray tomography. The predicted effects of externally driven currents and internal currents on the equilibrium surfaces could be confirmed experimentally. In particular the reduced Shafranov shift due to reduced Pfirsch-Schlueter currents in W7-AS could be verified. Up to the maximum accessible β ((β) ∼ 2%) plasmas can be confined without significant deterioration by pressure driven MHD-activity. However, global modes in the stable MHD spectrum such as global and toroidal Alfven eigenmodes (GAE, TAE) can be destabilised by energetic ions from neutral beam heating. These instabilities appear as very coherent low frequency modes (≤ 40 kHz) in the lower β regime without significant impact on the global confinement. At medium β very strong particle driven MHD modes with frequencies up to the range of 500 kHz can be observed. These modes can show nonlinear behaviour including periodic bursting and frequency chirping in combination with significant plasma energy losses. With increasing β Alfven modes are widely stable, because under these conditions the damping relative to the particle drive is increased. Besides the global mode activity small scale turbulent structures have been investigated in the plasma core and at the edge. The measured data of electron temperature, density and magnetic fluctuations do not yet allow to assess turbulence driven transport fluxes. However, correlations with the global confinement have been found, and the measured amplitudes are in the range expected to be relevant for anomalous transport. The observed dependence of the confinement on the edge rotational transform and magnetic shear can be explained in terms of enhanced transport at rational surfaces, however, the underlying

Investigation of equilibrium, global modes and microinstabilities in the stellarator W7-AS

International Nuclear Information System (INIS)

Weller, A.; Anton, M.; Brakel, R.

2001-01-01

Equilibrium and stability properties in the WENDELSTEIN 7-AS stellarator are investigated experimentally and compared with theoretical predictions for particular cases. The topology of equilibrium magnetic surfaces and of global MHD modes is inferred from X-ray tomography. The predicted effects of externally driven currents and internal currents on the equilibrium surfaces could be confirmed experimentally. In particular the reduced Shafranov shift due to reduced Pfirsch-Schlueter currents in W7-AS could be verified. Up to the maximum accessible β ( ∼2%) plasmas can be confined without significant deterioration by pressure driven MHD-activity. However, global modes in the stable MHD spectrum such as global and toroidal Alfven eigenmodes (GAE, TAE) can be destabilised by energetic ions from neutral beam heating. These instabilities appear as very coherent low frequency modes (≤40 kHz) in the lower β regime without significant impact on the global confinement. At medium β very strong particle driven MHD modes with frequencies up to the range of 500 kHz can be observed. These modes can show nonlinear behaviour including periodic bursting and frequency chirping in combination with significant plasma energy losses. With increasing β Alfven modes are widely stable, because under these conditions the damping relative to the particle drive is increased. Besides the global mode activity small scale turbulent structures have been investigated in the plasma core and at the edge. The measured data of electron temperature, density and magnetic fluctuations do not yet allow to assess turbulence driven transport fluxes. However, correlations with the global confinement have been found, and the measured amplitudes are in the range expected to be relevant for anomalous transport. The observed dependence of the confinement on the edge rotational transform and magnetic shear can be explained in terms of enhanced transport at rational surfaces, however, the underlying

Nonlinear saturation of the trapped-ion mode by mode coupling in two dimensions

International Nuclear Information System (INIS)

Cohen, B.I.; Tang, W.M.

1977-01-01

A study of the nonlinear saturation by mode coupling of the dissipative trapped-ion mode is presented in which both radial and poloidal variations are considered. The saturation mechanism consists of the nonlinear coupling via E x B convection of energy from linearly unstable modes to stable modes. Stabilization is provided at short poloidal wavelengths by Landau damping from trapped and circulating ions, at short radial wavelengths by effects associated with the finite ion banana excursions and at long wavelengths by ion collisions. A one-dimensional, nonlinear partial differential equation for the electrostatic potential derived in earlier work is extended to two dimensions and to third order in amplitude. Included systematically are kinetic effects, e.g., Landau damping and its spatial dependence due to magnetic shear. The stability and accessibility of equilibria are considered in detail for cases far from as well as close to marginal stability. In the first case three-wave interactions are found to be important when the spectrum of unstable modes is sufficiently narrow. In the latter case, it is found that for a single unstable mode, a four-wave interaction can provide the dominant saturation mechanism. Cross-field transport is calculated, and the scaling of results is considered for tokamak parameters

Field-theoretic calculation of kinetic helicity flux

Indian Academy of Sciences (India)

Given all these practical aspects, kinetic helicity is an important quantity to study in fluid turbulence. Turbulence involves millions of interacting modes. It is very difficult to analyze these modes theoretically as well as numerically. In recent times, a new numeri- cal procedure called 'large eddy simulations' (LES) has become ...

Influences of multiple low-n modes on n=1 resistive wall mode identification and feedback control

International Nuclear Information System (INIS)

In, Y.; Kim, J.; Kim, J. S.; Garofalo, A. M.; Jackson, G. L.; La Haye, R. J.; Strait, E. J.; Okabayashi, M.; Reimerdes, H.

2008-01-01

It is well known in theory that even after the n=1 resistive wall mode (RWM) is suppressed, the other low-n modes, such as n=2 or 3, can appear sequentially, as β increases. In recent DIII-D experiments [J. L. Luxon, Nucl. Fusion 42, 614 (2002)], we found such an example that supports the theoretical prediction: while the n=1 mode was suppressed, an n=3 mode grew dominant, leading to a β collapse. The n=1 RWM suppression was likely due to a combination of rotational stabilization and n=1 RWM feedback. The multiple RWM identification was performed using an expanded matched filter, where n=1 and n=3 RWM basis vectors are simultaneously considered. Taking advantage of the expanded matched filter, we found that an n=3 mode following an edge-localized-mode burst grew almost linearly for several milliseconds without being hindered. This n=3 mode appeared responsible for the β collapse (down to the n=3 no-wall limit), as well as for a drop in toroidal rotation. A preliminary analysis suggests that the identity of the n=3 mode could be related to the n=3 RWM (possibly the first observation in tokamak experiments), while the impact of the n=3 mode was not as destructive as that of n=1 RWM. A numerical postprocessing of Mirnov probes showed that the n=2 mode was also unstable, consistent with the theoretical prediction. In practice, since the presence of an n=3 mode can interfere with the existing n=1 RWM identification, multiple low-n mode identification is deemed essential not only to detect n>1 mode, but also to provide accurate n=1 RWM identification and feedback control.

Effect of initial perturbation amplitude on Richtmyer-Meshkov flows induced by strong shocks

Energy Technology Data Exchange (ETDEWEB)

Dell, Z.; Abarzhi, S. I., E-mail: snezhana.abarzhi@gmail.com, E-mail: sabarji@andrew.cmu.edu [Mellon College of Science and Carnegie Mellon University – Qatar, Carnegie Mellon University, Pittsburgh, Pennsylvania 15231 (United States); Stellingwerf, R. F. [Stellingwerf Consulting, Huntsville, Alabama 35803 (United States)

2015-09-15

We systematically study the effect of the initial perturbation on Richtmyer-Meshkov (RM) flows induced by strong shocks in fluids with contrasting densities. Smooth Particle Hydrodynamics simulations are employed. A broad range of shock strengths and density ratios is considered. The amplitude of the initial single mode sinusoidal perturbation of the interface varies from 0% to 100% of its wavelength. The simulations results are compared, wherever possible, with four rigorous theories, and with other experiments and simulations, achieving good quantitative and qualitative agreement. Our study is focused on early time dynamics of the Richtmyer-Meshkov instability (RMI). We analyze the initial growth-rate of RMI immediately after the shock passage, when the perturbation amplitude increases linearly with time. For the first time, to the authors' knowledge, we find that the initial growth-rate of RMI is a non-monotone function of the initial perturbation amplitude, thus restraining the amount of energy that can be deposited by the shock at the interface. The maximum value of the initial growth-rate depends on the shock strength and the density ratio, whereas the corresponding value of the initial perturbation amplitude depends only slightly on the shock strength and density ratio.

Nonlinear evolution of Mack modes in a hypersonic boundary layer

Science.gov (United States)

Chokani, Ndaona

2005-01-01

In hypersonic boundary layer flows the nonlinear disturbance evolution occurs relatively slowly over a very long length scale and has a profound effect on boundary layer transition. In the case of low-level freestream disturbances and negligible surface roughness, the transition is due to the modal growth of exponentially growing Mack modes that are destabilized by wall cooling. Cross-bicoherence measurements, derived from hot-wire data acquired in a quiet hypersonic tunnel, are used to identify and quantify phase-locked, quadratic sum and difference interactions involving the Mack modes. In the early stages of the nonlinear disturbance evolution, cross-bicoherence measurements indicate that the energy exchange between the Mack mode and the mean flow first occurs to broaden the sidebands; this is immediately followed by a sum interaction of the Mack mode to generate the first harmonic. In the next stages of the nonlinear disturbance evolution, there is a difference interaction of the first harmonic, which is also thought to contribute to the mean flow distortion. This difference interaction, in the latter stages, is also accompanied by a difference interaction between Mack mode and first harmonic, and a sum interaction, which forces the second harmonic. Analysis using the digital complex demodulation technique, shows that the low-frequency, phase-locked interaction that is identified in the cross bicoherence when the Mack mode and first harmonic have large amplitudes, arises due to the amplitude modulation of Mack mode and first harmonic.

Local measurement of error field using naturally rotating tearing mode dynamics in EXTRAP T2R

Science.gov (United States)

Sweeney, R. M.; Frassinetti, L.; Brunsell, P.; Fridström, R.; Volpe, F. A.

2016-12-01

An error field (EF) detection technique using the amplitude modulation of a naturally rotating tearing mode (TM) is developed and validated in the EXTRAP T2R reversed field pinch. The technique was used to identify intrinsic EFs of m/n  =  1/-12, where m and n are the poloidal and toroidal mode numbers. The effect of the EF and of a resonant magnetic perturbation (RMP) on the TM, in particular on amplitude modulation, is modeled with a first-order solution of the modified Rutherford equation. In the experiment, the TM amplitude is measured as a function of the toroidal angle as the TM rotates rapidly in the presence of an unknown EF and a known, deliberately applied RMP. The RMP amplitude is fixed while the toroidal phase is varied from one discharge to the other, completing a full toroidal scan. Using three such scans with different RMP amplitudes, the EF amplitude and phase are inferred from the phases at which the TM amplitude maximizes. The estimated EF amplitude is consistent with other estimates (e.g. based on the best EF-cancelling RMP, resulting in the fastest TM rotation). A passive variant of this technique is also presented, where no RMPs are applied, and the EF phase is deduced.

Mapping the upper mantle beneath North American continent with joint inversion of surface-wave phase and amplitude

Science.gov (United States)

Yoshizawa, K.; Hamada, K.

2017-12-01

A new 3-D S-wave model of the North American upper mantle is constructed from a large number of inter-station phase and amplitude measurements of surface waves. A fully nonlinear waveform fitting method by Hamada and Yoshizawa (2015, GJI) is applied to USArray for measuring inter-station phase speeds and amplitude ratios of the fundamental-mode Rayleigh and Love waves. We employed the seismic events from 2007 - 2014 with Mw 6.0 or greater, and collected a large-number of inter-station phase speed data (about 130,000 for Rayleigh and 85,000 for Love waves) and amplitude ratio data (about 75,000 for Rayleigh waves) in a period range from 30 to 130 s for fundamental-mode surface waves. Typical inter-station distances are mostly in a range between 300 and 800 km, which can be of help in enhancing the lateral resolution of a regional tomography model. We first invert Rayleigh-wave phase speeds and amplitudes simultaneously for phase speed maps as well as local amplification factors at receiver locations. The isotropic 3-D S-wave model constructed from these phase speed maps incorporating both phase and amplitude data exhibits better recovery of the strength of velocity perturbations. In particular, local tectonic features characterized by strong velocity gradients, such as Rio Grande Rift, Colorado Plateau and New Madrid Seismic Zone, are more enhanced than conventional models derived from phase information only. The results indicate that surface-wave amplitude, which is sensitive to the second derivative of phase speeds, can be of great help in retrieving small-scale heterogeneity in the upper mantle. We also obtain a radial anisotropy model from the simultaneous inversions of Rayleigh and Love waves (without amplitude information). The model has shown faster SH wave speed anomalies than SV above the depth of 100 km, particularly in tectonically active regions in the western and central U.S., representing the effects of current and former tectonic processes on

Amplitude and frequency stabilized solid-state lasers in the near infrared

International Nuclear Information System (INIS)

Laporta, P.; Taccheo, S.; Marano, M.; Svelto, O.; Bava, E.; Galzerano, G.; Svelto, C.

2001-01-01

In this article we present a comprehensive review of the work done by our group on the amplitude and frequency stabilization of diode-pumped near-infrared solid-state lasers. In particular, we describe experiments based on single-mode Nd:YAG (1064 nm), Er-Yb:glass (1530-1560 nm), and Tm-Ho:YAG (2097 nm) lasers, end-pumped by semiconductor laser diodes. Amplitude stabilization is achieved by means of optoelectronic control loops sensing the laser intensity fluctuations and feeding back the error signal to the current of the pump diodes. Frequency stabilization is pursued using rovibrational molecular lines as absolute frequency references by means of various frequency locking techniques. The most interesting stability results are described in some detail whereas the wide literature cited through the paper provides for a useful reference list of related topics and experiments. (author)

Two-Loop Splitting Amplitudes

International Nuclear Information System (INIS)

Bern, Z.

2004-01-01

Splitting amplitudes govern the behavior of scattering amplitudes at the momenta of external legs become collinear. In this talk we outline the calculation of two-loop splitting amplitudes via the unitarity sewing method. This method retains the simple factorization properties of light-cone gauge, but avoids the need for prescriptions such as the principal value or Mandelstam-Leibbrandt ones. The encountered loop momentum integrals are then evaluated using integration-by-parts and Lorentz invariance identities. We outline a variety of applications for these splitting amplitudes

Two-loop splitting amplitudes

International Nuclear Information System (INIS)

Bern, Z.; Dixon, L.J.; Kosower, D.A.

2004-01-01

Splitting amplitudes govern the behavior of scattering amplitudes at the momenta of external legs become collinear. In this talk we outline the calculation of two-loop splitting amplitudes via the unitarity sewing method. This method retains the simple factorization properties of light-cone gauge, but avoids the need for prescriptions such as the principal value or Mandelstam-Leibbrandt ones. The encountered loop momentum integrals are then evaluated using integration-by-parts and Lorentz invariance identities. We outline a variety of applications for these splitting amplitudes

Problems in nonlinear acoustics: Scattering of sound by sound, parametric receiving arrays, nonlinear effects in asymmetric sound beams and pulsed finite amplitude sound beams

Science.gov (United States)

Hamilton, Mark F.

1989-08-01

Four projects are discussed in this annual summary report, all of which involve basic research in nonlinear acoustics: Scattering of Sound by Sound, a theoretical study of two nonconlinear Gaussian beams which interact to produce sum and difference frequency sound; Parametric Receiving Arrays, a theoretical study of parametric reception in a reverberant environment; Nonlinear Effects in Asymmetric Sound Beams, a numerical study of two dimensional finite amplitude sound fields; and Pulsed Finite Amplitude Sound Beams, a numerical time domain solution of the KZK equation.

Joint Manipulation: Toward a General Theory of High-Velocity, Low-Amplitude Thrust Techniques.

Science.gov (United States)

Harwich, Andrew S

2017-12-01

The objective of this study was to describe the initial stage of a generalized theory of high-velocity, low-amplitude thrust (HVLAT) techniques for joint manipulation. This study examined the movements described by authors from the fields of osteopathy, chiropractic, and physical therapy to produce joint cavitation in both the metacarpophalangeal (MCP) joint and the cervical spine apophysial joint. This study qualitatively compared the kinetics, the similarities, and the differences between MCP cavitation and cervical facet joint cavitation. A qualitative vector analysis of forces and movements was undertaken by constructing computer-generated, simplified graphical models of the MCP joint and a typical cervical apophysial joint and imposing the motions dictated by the clinical technique. Comparing the path to cavitation of 2 modes of HVLAT for the MCP joint, namely, distraction and hyperflexion, it was found that the hyperflexion method requires an axis of rotation, the hinge axis, which is also required for cervical HVLAT. These results show that there is an analogue of cervical HVLAT in one of the MCP joint HVLATs. The study demonstrated that in a theoretical model, the path to joint cavitation is the same for asymmetric separation of the joint surfaces in the cervical spine and the MCP joints.

Mode-Selective Photon Counting Via Quantum Frequency Conversion Using Spectrally-Engineered Pump Pulses

Science.gov (United States)

Manurkar, Paritosh

Most of the existing protocols for quantum communication operate in a two-dimensional Hilbert space where their manipulation and measurement have been routinely investigated. Moving to higher-dimensional Hilbert spaces is desirable because of advantages in terms of longer distance communication capabilities, higher channel capacity and better information security. We can exploit the spatio-temporal degrees of freedom for the quantum optical signals to provide the higher-dimensional signals. But this necessitates the need for measurement and manipulation of multidimensional quantum states. To that end, there have been significant theoretical studies based on quantum frequency conversion (QFC) in recent years even though the experimental progress has been limited. QFC is a process that allows preservation of the quantum information while changing the frequency of the input quantum state. It has deservedly garnered a lot of attention because it serves as the connecting bridge between the communications band (C-band near 1550 nm) where the fiber-optic infrastructure is already established and the visible spectrum where high efficiency single-photon detectors and optical memories have been demonstrated. In this experimental work, we demonstrate mode-selective frequency conversion as a means to measure and manipulate photonic signals occupying d -dimensional Hilbert spaces where d=2 and 4. In the d=2 case, we demonstrate mode contrast between two temporal modes (TMs) which serves as the proof-of-concept demonstration. In the d=4 version, we employ six different TMs for our detailed experimental study. These TMs also include superposition modes which are a crucial component in many quantum key distribution protocols. Our method is based on producing pump pulses which allow us to upconvert the TM of interest while ideally preserving the other modes. We use MATLAB simulations to determine the pump pulse shapes which are subsequently produced by controlling the amplitude and

4D scattering amplitudes and asymptotic symmetries from 2D CFT

Science.gov (United States)

Cheung, Clifford; de la Fuente, Anton; Sundrum, Raman

2017-01-01

We reformulate the scattering amplitudes of 4D flat space gauge theory and gravity in the language of a 2D CFT on the celestial sphere. The resulting CFT structure exhibits an OPE constructed from 4D collinear singularities, as well as infinite-dimensional Kac-Moody and Virasoro algebras encoding the asymptotic symmetries of 4D flat space. We derive these results by recasting 4D dynamics in terms of a convenient foliation of flat space into 3D Euclidean AdS and Lorentzian dS geometries. Tree-level scattering amplitudes take the form of Witten diagrams for a continuum of (A)dS modes, which are in turn equivalent to CFT correlators via the (A)dS/CFT dictionary. The Ward identities for the 2D conserved currents are dual to 4D soft theorems, while the bulk-boundary propagators of massless (A)dS modes are superpositions of the leading and subleading Weinberg soft factors of gauge theory and gravity. In general, the massless (A)dS modes are 3D Chern-Simons gauge fields describing the soft, single helicity sectors of 4D gauge theory and gravity. Consistent with the topological nature of Chern-Simons theory, Aharonov-Bohm effects record the "tracks" of hard particles in the soft radiation, leading to a simple characterization of gauge and gravitational memories. Soft particle exchanges between hard processes define the Kac-Moody level and Virasoro central charge, which are thereby related to the 4D gauge coupling and gravitational strength in units of an infrared cutoff. Finally, we discuss a toy model for black hole horizons via a restriction to the Rindler region.

Nonlinear amplitude dynamics in flagellar beating.

Science.gov (United States)

Oriola, David; Gadêlha, Hermes; Casademunt, Jaume

2017-03-01

The physical basis of flagellar and ciliary beating is a major problem in biology which is still far from completely understood. The fundamental cytoskeleton structure of cilia and flagella is the axoneme, a cylindrical array of microtubule doublets connected by passive cross-linkers and dynein motor proteins. The complex interplay of these elements leads to the generation of self-organized bending waves. Although many mathematical models have been proposed to understand this process, few attempts have been made to assess the role of dyneins on the nonlinear nature of the axoneme. Here, we investigate the nonlinear dynamics of flagella by considering an axonemal sliding control mechanism for dynein activity. This approach unveils the nonlinear selection of the oscillation amplitudes, which are typically either missed or prescribed in mathematical models. The explicit set of nonlinear equations are derived and solved numerically. Our analysis reveals the spatio-temporal dynamics of dynein populations and flagellum shape for different regimes of motor activity, medium viscosity and flagellum elasticity. Unstable modes saturate via the coupling of dynein kinetics and flagellum shape without the need of invoking a nonlinear axonemal response. Hence, our work reveals a novel mechanism for the saturation of unstable modes in axonemal beating.

Force reconstruction from tapping mode force microscopy experiments

International Nuclear Information System (INIS)

Payam, Amir F; Martin-Jimenez, Daniel; Garcia, Ricardo

2015-01-01

Fast, accurate, and robust nanomechanical measurements are intensely studied in materials science, applied physics, and molecular biology. Amplitude modulation force microscopy (tapping mode) is the most established nanoscale characterization technique of surfaces for air and liquid environments. However, its quantitative capabilities lag behind its high spatial resolution and robustness. We develop a general method to transform the observables into quantitative force measurements. The force reconstruction algorithm has been deduced on the assumption that the observables (amplitude and phase shift) are slowly varying functions of the tip–surface separation. The accuracy and applicability of the method is validated by numerical simulations and experiments. The method is valid for liquid and air environments, small and large free amplitudes, compliant and rigid materials, and conservative and non-conservative forces. (paper)

Small-amplitude vibrations at a finite temperature in the liquid drop model

International Nuclear Information System (INIS)

Providencia, J. da Jr.

1991-01-01

The ground state of a hot nucleus is studied in the classical limit. The equations of motion and boundary conditions of the liquid drop model are derived from the variational principle. The effect of the surface tension is taken into account. The temperature dependence of small-amplitude vibrations in the liquid drop model is investigated. It is shown that the breathing mode suffers a 6.3% decrease in energy when the temperature increases from 0 to 5 MeV. The present model allows for a description of surface modes with an A -1/2 dependence of the energy. It is also found that the surface modes will show an appreciable temperature dependence if a reasonable temperature dependence of the surface tension is postulated. It is shown that the model satisfies the energy-weighted sum rule and the inverse energy-weighted sum rule. (orig.)D

Amplitudes, acquisition and imaging

Energy Technology Data Exchange (ETDEWEB)

Bloor, Robert

1998-12-31

Accurate seismic amplitude information is important for the successful evaluation of many prospects and the importance of such amplitude information is increasing with the advent of time lapse seismic techniques. It is now widely accepted that the proper treatment of amplitudes requires seismic imaging in the form of either time or depth migration. A key factor in seismic imaging is the spatial sampling of the data and its relationship to the imaging algorithms. This presentation demonstrates that acquisition caused spatial sampling irregularity can affect the seismic imaging and perturb amplitudes. Equalization helps to balance the amplitudes, and the dealing strategy improves the imaging further when there are azimuth variations. Equalization and dealiasing can also help with the acquisition irregularities caused by shot and receiver dislocation or missing traces. 2 refs., 2 figs.

Evolution of the squeezing-enhanced vacuum state in the amplitude dissipative channel

Science.gov (United States)

Ren, Gang; Du, Jian-ming; Zhang, Wen-hai

2018-05-01

We study the evolution of the squeezing-enhanced vacuum state (SEVS) in the amplitude dissipative channel by using the two-mode entangled state in the Fock space and Kraus operator. The explicit formulation of the output state is also given. It is found that the output state does not exhibit sub-Poissonian behavior for the nonnegative value of the Mandel's Q-parameters in a wide range of values of squeezing parameter and dissipation factor. It is interesting to see that second-order correlation function is independent of the dissipation factor. However, the photon-number distribution of the output quantum state shows remarkable oscillations with respect to the dissipation factor. The shape of Wigner function and the degree of squeezing show that the initial SEVS is dissipated by the amplitude dissipative channel.

Photo-acoustic sensor based on an inexpensive piezoelectric film transducer and an amplitude-stabilized single-mode external cavity diode laser for in vitro measurements of glucose concentration

Science.gov (United States)

Bayrakli, Ismail; Erdogan, Yasar Kemal

2018-06-01

The present paper focuses on development of a compact photo-acoustic sensor using inexpensive components for glucose analysis. An amplitude-stabilized wavelength-tunable single-mode external cavity diode laser operating around 1050 nm was realized and characterized for the use of laser beam as an excitation light source. In the established setup, a fine tuning range of 9 GHz was achieved. The glucose solution was obtained by diluting D-glucose in sterile water. The acoustic signal generated by the optical excitation was detected via a chip piezoelectric film transducer. A detection limit of 50 mM (900 mg/dl) was achieved. The device may be of great interest for its applications in medicine and health monitoring. The sensor is promising for non-invasive in vivo glucose measurements from interstitial fluid.

First results from the 'Violin-Mode' tests on an advanced LIGO suspension at MIT

International Nuclear Information System (INIS)

Lockerbie, N A; Tokmakov, K V; Carbone, L; Shapiro, B; Bell, A; Strain, K A

2011-01-01

This paper describes the first results from 'Violin-Mode' measurements made on the four suspension fibres of a fully suspended 40 kg test mass. These measurements were made at the LIGO lab, Gravitational Wave Observatory test facility, at MIT. Here, an aluminium-alloy (dummy) test mass, simulating an advanced LIGO (Laser Interferometer Gravitational Wave Observatory) test mass/mirror, had been suspended in air from a test suspension by four fused-silica suspension fibres, each measuring 400 μm in diameter x 600 mm long. Violin-Mode measurements were made on these highly tensioned fibres by retrofitting a prototype system of four novel shadow sensors to the test suspension, one per fibre, these sensors having, collectively, a displacement sensitivity of (6.9 ± 1.3) x 10 -11 m (rms) Hz -1/2 , at 500 Hz, over a measuring span of ±0.1 mm. Violin-Mode fundamental resonances were detected in all four fibres: with frequencies ∼ 485 Hz when the test mass was supported lightly from below, and at ∼500 Hz when it was fully suspended. In the latter case the Violin-Mode detection took place whilst the test mass, together with its suspension fibres, was undergoing relatively large-amplitude 'pendulum-mode' motion, at ∼0.6 Hz. This motion was measured to have a peak-peak amplitude at one of the suspension fibres of up to ∼140 μm (35 μm, rms) the shadow sensors each having subsidiary outputs for monitoring such low-frequency, large amplitude, motion. Under fully suspended conditions, a calibrated Violin-Mode 'free-oscillation' amplitude of 430 ± 20 picometres, rms, was measured at 500.875 Hz, in the same suspension fibre which was found to be undergoing, simultaneously, the ∼140 μm peak-peak motion. Over the bandwidth monitored (dc to 3.2 kHz), Violin-Mode harmonics up to the sixth were recorded in an evoked response. It was concluded that the prototype system had demonstrated amply its practical viability as a detector of Violin-Mode resonances in the test

Passive, active, and hybrid mode-locking in a self-optimized ultrafast diode laser

Science.gov (United States)

Alloush, M. Ali; Pilny, Rouven H.; Brenner, Carsten; Klehr, Andreas; Knigge, Andrea; Tränkle, Günther; Hofmann, Martin R.

2018-02-01

Semiconductor lasers are promising sources for generating ultrashort pulses. They are directly electrically pumped, allow for a compact design, and therefore they are cost-effective alternatives to established solid-state systems. Additionally, their emission wavelength depends on the bandgap which can be tuned by changing the semiconductor materials. Theoretically, the obtained pulse width can be few tens of femtoseconds. However, the generated pulses are typically in the range of several hundred femtoseconds only. Recently, it was shown that by implementing a spatial light modulator (SLM) for phase and amplitude control inside the resonator the optical bandwidth can be optimized. Consequently, by using an external pulse compressor shorter pulses can be obtained. We present a Fourier-Transform-External-Cavity setup which utilizes an ultrafast edge-emitting diode laser. The used InGaAsP diode is 1 mm long and emits at a center wavelength of 850 nm. We investigate the best conditions for passive, active and hybrid mode-locking operation using the method of self-adaptive pulse shaping. For passive mode-locking, the bandwidth is increased from 2.34 nm to 7.2 nm and ultrashort pulses with a pulse width of 216 fs are achieved after external pulse compression. For active and hybrid mode-locking, we also increased the bandwidth. It is increased from 0.26 nm to 5.06 nm for active mode-locking and from 3.21 nm to 8.7 nm for hybrid mode-locking. As the pulse width is strongly correlated with the bandwidth of the laser, we expect further reduction in the pulse duration by increasing the bandwidth.

Relative amplitude preservation processing utilizing surface consistent amplitude correction. Part 4; Surface consistent amplitude correction wo mochiita sotai shinpuku hozon shori. 4

Energy Technology Data Exchange (ETDEWEB)

Saeki, T [Japan National Oil Corp., Tokyo (Japan). Technology Research Center

1997-10-22

Discussions were given on seismic exploration from the ground surface using the reflection method, for surface consistent amplitude correction from among effects imposed from the ground surface and a surface layer. Amplitude distribution on the reflection wave zone is complex. Therefore, items to be considered in making an analysis are multiple, such as estimation of spherical surface divergence effect and exponential attenuation effect, not only amplitude change through the surface layer. If all of these items are taken into consideration, burden of the work becomes excessive. As a method to solve this problem, utilization of amplitude in initial movement of a diffraction wave may be conceived. Distribution of the amplitude in initial movement of the diffraction wave shows a value relatively close to distribution of the vibration transmitting and receiving points. The reason for this is thought because characteristics of the vibration transmitting and receiving points related with waveline paths in the vicinity of the ground surface have no great difference both on the diffraction waves and on the reflection waves. The lecture described in this paper introduces an attempt of improving the efficiency of the surface consistent amplitude correction by utilizing the analysis of amplitude in initial movement of the diffraction wave. 4 refs., 2 figs.

Failure Modes of thin supported Membranes

DEFF Research Database (Denmark)

Hendriksen, Peter Vang; Høgsberg, J.R.; Kjeldsen, Ane Mette

2007-01-01

Four different failure modes relevant to tubular supported membranes (thin dense films on a thick porous support) were analyzed. The failure modes were: 1) Structural collapse due to external pressure 2) burst of locally unsupported areas, 3) formation of surface cracks in the membrane due to TEC......-mismatches, and finally 4) delamination between membrane and support due to expansion of the membrane on use. Design criteria to minimize risk of failure by the four different modes are discussed. The theoretical analysis of the two last failure modes is compared to failures observed on actual components....

W-Band Circularly Polarized TE11 Mode Transducer

Science.gov (United States)

Zhan, Mingzhou; He, Wangdong; Wang, Lei

2018-06-01

This paper presents a balanced sidewall exciting approach to realize the circularly polarized TE11 mode transducer. We used a voltage vector transfer matrix to establish the relationship between input and output vectors, then we analyzed amplitude and phase errors to estimate the isolation of degenerate mode. A mode transducer with a sidewall exciter was designed based on the results. In the 88-100 GHz frequency range, the simulated axial ratio is less than 1.05 and the isolation of linearly polarization TE11 mode is higher than 30 dBc. In back-to-back measurements, the return loss is generally greater than 20 dB with a typical insertion loss of 1.2 dB. Back-to-back transmission measurements are in excellent agreement with simulations.

ac driving amplitude dependent systematic error in scanning Kelvin probe microscope measurements: Detection and correction

International Nuclear Information System (INIS)

Wu Yan; Shannon, Mark A.

2006-01-01

The dependence of the contact potential difference (CPD) reading on the ac driving amplitude in scanning Kelvin probe microscope (SKPM) hinders researchers from quantifying true material properties. We show theoretically and demonstrate experimentally that an ac driving amplitude dependence in the SKPM measurement can come from a systematic error, and it is common for all tip sample systems as long as there is a nonzero tracking error in the feedback control loop of the instrument. We further propose a methodology to detect and to correct the ac driving amplitude dependent systematic error in SKPM measurements. The true contact potential difference can be found by applying a linear regression to the measured CPD versus one over ac driving amplitude data. Two scenarios are studied: (a) when the surface being scanned by SKPM is not semiconducting and there is an ac driving amplitude dependent systematic error; (b) when a semiconductor surface is probed and asymmetric band bending occurs when the systematic error is present. Experiments are conducted using a commercial SKPM and CPD measurement results of two systems: platinum-iridium/gap/gold and platinum-iridium/gap/thermal oxide/silicon are discussed

Multi-modal vibration amplitudes of taut inclined cables due to direct and/or parametric excitation

Science.gov (United States)

Macdonald, J. H. G.

2016-02-01

Cables are often prone to potentially damaging large amplitude vibrations. The dynamic excitation may be from external loading or motion of the cable ends, the latter including direct excitation, normally from components of end motion transverse to the cable, and parametric excitation induced by axial components of end motion causing dynamic tension variations. Geometric nonlinearity can be important, causing stiffening behaviour and nonlinear modal coupling. Previous analyses of the vibrations, often neglecting sag, have generally dealt with direct and parametric excitation separately or have reverted to numerical solutions of the responses. Here a nonlinear cable model is adopted, applicable to taut cables such as on cable-stayed bridges, that allows for cable inclination, small sag (such that the vibration modes are similar to those of a taut string), multiple modes in both planes and end motion and/or external forcing close to any natural frequency. Based on the method of scaling and averaging it is found that, for sinusoidal inputs and positive damping, non-zero steady state responses can only occur in the modes in each plane with natural frequencies close to the excitation frequency and those with natural frequencies close to half this frequency. Analytical solutions, in the form of non-dimensional polynomial equations, are derived for the steady state vibration amplitudes in up to three modes simultaneously: the directly excited mode, the corresponding nonlinearly coupled mode in the orthogonal plane and a parametrically excited mode with half the natural frequency. The stability of the solutions is also identified. The outputs of the equations are consistent with previous results, where available. Example results from the analytical solutions are presented for a typical inclined bridge cable subject to vertical excitation of the lower end, and they are validated by numerical integration of the equations of motion and against some previous experimental

Signal Based Mixing Analysis for the magnetohydrodynamic mode reconstruction from homodyne microwave reflectometry

International Nuclear Information System (INIS)

Ejiri, Akira; Sakakibara, Satoru; Kawahata, Kazuo.

1995-03-01

A new method 'Signal Based Mixing Analysis', to extract the components which are coherent to a certain reference signal from a noisy signal, has been developed. The method is applied to homodyne microwave reflectometry to reconstruct the radial structure of a magnetohydrodynamic (MHD) mode in heliotron/torsatron Compact Helical System (CHS) [K. Matsuoka et al. Plasma Phys. Control. Nuclear Fusion Research 1988 Vol. 2, IAEA, Vienna 411 (1989)]. In CHS plasmas, MHD fluctuations measured with magnetic probes show bursts, in which the amplitude and frequency quasi-periodically vary. The signal based mixing analysis uses a set of functions which have the same amplitude and the harmonic frequency as those of the magnetic fluctuations. The product (mixing) of the signal of reflectometer and the functions yields the amplitude and phase of the coherent components. When the plasma density gradually increases, the measuring position moves radially outward. Thus, the radial structure of MHD modes can be obtained by this method. The analysis indicates several peaks and nodes inside the resonance surface of the MHD mode. In addition, the structure does not propagate radially during a burst. (author)

A digital laser for on-demand laser modes

CSIR Research Space (South Africa)

Ngcobo, S

2013-08-01

Full Text Available -cavity digitally addressed holographic mirror. The phase and amplitude of the holographic mirror may be controlled simply by writing a computer- generated hologram in the form of a grey-scale image to the device, for on-demand laser modes. We show that we can...

Exclusive two-photon processes: Tests of QCD at the amplitude level

International Nuclear Information System (INIS)

Brodsky, S.J.

1992-07-01

Exclusive two-photon processes at large momentum transfer, particularly Compton scattering γp→γp and its crossed-channel reactions γγ→ bar pp and bar pp→γγ, can provide definitive information on the bound-state distributions of quarks in hadrons at the amplitude level. Recent theoretical work has shown that QCD predictions based on the factorization of long and short distance physics are already applicable at momentum transfers of order of a few GeV

Spectroscopic identification of ethanol-water conformers by large-amplitude hydrogen bond librational modes

DEFF Research Database (Denmark)

Andersen, Jonas; Heimdal, J.; Larsen, René Wugt

2015-01-01

⋯HO hydrogen bond acceptor in the two most stable conformations. In the most stable conformation, the water subunit forces the ethanol molecule into its less stable gauche configuration upon dimerization owing to a cooperative secondary weak O⋯HC hydrogen bondinteraction evidenced by a significantly blue......-shift of the low-frequency in-plane donor OH librational band origin. The strong correlation between the low-frequency in-plane donor OH librational motion and the secondary intermolecular O⋯HC hydrogen bond is demonstrated by electronic structure calculations. The experimental findings are further supported...... by CCSD(T)-F12/aug-cc-pVQZ calculations of the conformationalenergy differences together with second-order vibrational perturbation theory calculations of the large-amplitude donor OH librational band origins....

Computational investigation of single mode vs multimode Rayleigh endash Taylor seeding in Z-pinch implosions

International Nuclear Information System (INIS)

Douglas, M.R.; Deeney, C.; Roderick, N.F.

1998-01-01

A series of two-dimensional magnetohydrodynamic calculations have been carried out to investigate single and multimode growth and mode coupling for magnetically-driven Rayleigh endash Taylor instabilities in Z pinches. Wavelengths ranging from 5.0 mm down to 1.25 mm were considered. Such wavelengths are comparable to those observed at stagnation using a random density open-quotes seedingclose quotes method. The calculations show that wavelengths resolved by less than 10 cells exhibit an artificial decrease in initial Fourier spectrum amplitudes and a reduction in the corresponding amplitude growth. Single mode evolution exhibits linear exponential growth and the development of higher harmonics as the mode transitions into the nonlinear phase. The mode growth continues to exponentiate but at a slower rate than determined by linear hydrodynamic theory. In the two and three mode case, there is clear evidence of mode coupling and inverse cascade. In addition, distinct modal patterns are observed late in the implosion, resulting from finite shell thickness and magnetic field effects. copyright 1998 American Institute of Physics. thinsp

Collective Lyapunov modes

International Nuclear Information System (INIS)

Takeuchi, Kazumasa A; Chaté, Hugues

2013-01-01

We show, using covariant Lyapunov vectors in addition to standard Lyapunov analysis, that there exists a set of collective Lyapunov modes in large chaotic systems exhibiting collective dynamics. Associated with delocalized Lyapunov vectors, they act collectively on the trajectory and hence characterize the instability of its collective dynamics. We further develop, for globally coupled systems, a connection between these collective modes and the Lyapunov modes in the corresponding Perron–Frobenius equation. We thereby address the fundamental question of the effective dimension of collective dynamics and discuss the extensivity of chaos in the presence of collective dynamics. This article is part of a special issue of Journal of Physics A: Mathematical and Theoretical devoted to ‘Lyapunov analysis: from dynamical systems theory to applications’. (paper)

Wavelength selection in injection-driven Hele-Shaw flows: A maximum amplitude criterion

Science.gov (United States)

Dias, Eduardo; Miranda, Jose

2013-11-01

As in most interfacial flow problems, the standard theoretical procedure to establish wavelength selection in the viscous fingering instability is to maximize the linear growth rate. However, there are important discrepancies between previous theoretical predictions and existing experimental data. In this work we perform a linear stability analysis of the radial Hele-Shaw flow system that takes into account the combined action of viscous normal stresses and wetting effects. Most importantly, we introduce an alternative selection criterion for which the selected wavelength is determined by the maximum of the interfacial perturbation amplitude. The effectiveness of such a criterion is substantiated by the significantly improved agreement between theory and experiments. We thank CNPq (Brazilian Sponsor) for financial support.

Fusion oriented plasma research in Bangladesh: theoretical study on low-frequency dust modes and edge plasma control experiment in tandem mirror

International Nuclear Information System (INIS)

Khairul Islam, Md.; Salimullah, Mohammed; Yatsu, Kiyoshi; Nakashima, Yousuke; Ishimoto, Yuki

2003-01-01

A collaboration with a Japanese institute in the field of plasma-wall interaction and dusty plasma has been formed in order to understand the physical properties of edge plasma. Results of the theoretical study on dusty plasma and the experimental study on GAMMA10 plasma are presented in this paper. Part A deals with the results obtained from the theoretical investigation of the properties and excitation of low-frequency electrostatic dust modes, e.g. the dust-acoustic (DA) and dust-lower-hybrid (DLH) waves, using the fluid models. In this study, dust grain charge is considered as a dynamic variable in streaming magnetized dusty plasmas with a background of neutral atoms. Dust charge fluctuation, collisional and streaming effects on DA and DLH modes are discussed. Part B deals with the results of the plasma control experiment in a non-axisymmetric magnetic field region of the anchor cell of GAMMA10. The observations, which indicate the comparatively low-temperature plasma formation in the anchor cell, are explained from the viewpoint of enhanced outgassing from the wall due to the interaction of the drifted-out ions. The drifting of ions is thought to be due to the effect of a local non-axisymmetric magnetic field. Experimental results on the control of the wall-plasma interaction by covering the flux tube of a non-axisymmetric magnetic field region by conducting plates are given. Possible influences of the asymmetric magnetic field and conducting plates on the GAMMA10 plasma parameters are discussed. (author)

Quasiadiabatic modes from viscous inhomogeneities

CERN Document Server

Giovannini, Massimo

2016-04-20

The viscous inhomogeneities of a relativistic plasma determine a further class of entropic modes whose amplitude must be sufficiently small since curvature perturbations are observed to be predominantly adiabatic and Gaussian over large scales. When the viscous coefficients only depend on the energy density of the fluid the corresponding curvature fluctuations are shown to be almost adiabatic. After addressing the problem in a gauge-invariant perturbative expansion, the same analysis is repeated at a non-perturbative level by investigating the nonlinear curvature inhomogeneities induced by the spatial variation of the viscous coefficients. It is demonstrated that the quasiadiabatic modes are suppressed in comparison with a bona fide adiabatic solution. Because of its anomalously large tensor to scalar ratio the quasiadiabatic mode cannot be a substitute for the conventional adiabatic paradigm so that, ultimately, the present findings seems to exclude the possibility of a successful accelerated dynamics solely...

Reflection of oblique electron thermal modes in an inhomogeneous plasma

International Nuclear Information System (INIS)

Ohnuma, T.; Watanabe, T.; Sanuki, H.

1980-04-01

In an inhomogeneous magnetoplasma, reflection of an oblique electron thermal mode radiated from a local source is investigated experimentally and theoretically near the electron plasma frequency layer. The experimental observation of reflection in the lower plasma density region than the f sub(p)-layer is found to be in qualitative accord with the theoretical reflection, which is obtained from a kinetic theory in an inhomogeneous magnetoplasma. The reflection of the thermal mode is also compared with that of an electromagnetic mode at the f sub(p)-layer. (author)

Evidence of Boundary Reflection of Kelvin and First-Mode Rossby Waves from Topex/Poseidon Sea Level Data

Science.gov (United States)

Boulanger, Jean-Philippe; Fu, Lee-Lueng

1996-01-01

The TOPEX/POSEIDON sea level data lead to new opportunities to investigate some theoretical mechanisms suggested to be involved in the El Nino-Southern Oscillation phenomenon in the tropical Pacific ocean. In particular, we are interested in studying the western boundary reflection, a process crucial for the delayed action oscillator theory, by using the TOPEX/POSEIDON data from November 1992 to May 1995. We first projected the sea level data onto Kelvin and first-mode Ross waves. Then we estimated the contribution of wind forcing to these waves by using a single baroclinic mode simple wave model forced by the ERS-1 wind data. Wave propagation was clearly observed with amplitudes well explained by the wind forcing in the ocean interior. Evidence of wave reflection was detected at both the western and eastern boundaries of the tropical Pacific ocean. At the eastern boundary, Kelvin waves were seen to reflect as first-mode Rossby waves during the entire period. The reflection efficiency (in terms of wave amplitude) of the South American coasts was estimated to be 80% of that of an infinite meridional wall. At the western boundary, reflection was observed in April-August 1993, in January-June 1994, and, later, in December 1994 to February 1995. Although the general roles of these reflection events in the variability observed in the equatorial Pacific ocean are not clear, the data suggest that the reflections in January-June 1994 have played a role in the onset of the warm conditions observed in late 1994 to early 1995. Indeed, during the January-June 1994 period, as strong downwelling first-mode Rossby waves reflected into downwelling Kelvin waves, easterly wind and cold sea surface temperature anomalies located near the date line weakened and eventually reversed in June-July 1994. The presence of the warm anomalies near the date line then favored convection and westerly wind anomalies that triggered strong downwelling Kelvin waves propagating throughout the basin

Influence of mode competition on beam quality of fiber amplifier

International Nuclear Information System (INIS)

Xiao Qi-Rong; Yan Ping; Sun Jun-Yi; Chen Xiao; Ren Hai-Cui; Gong Ma-Li

2014-01-01

Theoretical and experimental studies of the influence of the mode competition on the output beam quality of fiber amplifiers are presented. Rate equations and modal decomposition method are used in the theoretical model. In the experiment, the output beam-quality factor of a fiber amplifier, which is based on a Yb-doped double-clad large mode area fiber as a function of the seed beam quality and the pump power of the amplifier, is measured. The experimental results are consistent with the theoretical analysis. (electromagnetism, optics, acoustics, heat transfer, classical mechanics, and fluid dynamics)

Piezoelectric transducer parameter selection for exciting a single mode from multiple modes of Lamb waves

International Nuclear Information System (INIS)

Zhang Hai-Yan; Yu Jian-Bo

2011-01-01

Excitation and propagation of Lamb waves by using rectangular and circular piezoelectric transducers surface-bonded to an isotropic plate are investigated in this work. Analytical stain wave solutions are derived for the two transducer shapes, giving the responses of these transducers in Lamb wave fields. The analytical study is supported by a numerical simulation using the finite element method. Symmetric and antisymmetric components in the wave propagation responses are inspected in detail with respect to test parameters such as the transducer geometry, the length and the excitation frequency. By placing only one piezoelectric transducer on the top or the bottom surface of the plate and weakening the strength of one mode while enhancing the strength of the other modes to find the centre frequency, with which the peak wave amplitude ratio between the S0 and A0 modes is maximum, a single mode excitation from the multiple modes of the Lamb waves can be achieved approximately. Experimental data are presented to show the validity of the analyses. The results are used to optimize the Lamb wave detection system. (electromagnetism, optics, acoustics, heat transfer, classical mechanics, and fluid dynamics)

Higher order modes excitation of electrostatically actuated clamped–clamped microbeams: experimental and analytical investigation

KAUST Repository

Jaber, Nizar

2016-01-06

© 2016 IOP Publishing Ltd. In this study, we demonstrate analytically and experimentally the excitations of the higher order modes of vibrations in electrostatically actuated clamped-clamped microbeam resonators. The concept is based on using partial electrodes with shapes that induce strong excitation of the mode of interest. The devices are fabricated using polyimide as a structural layer coated with nickel from the top and chrome and gold layers from the bottom. Experimentally, frequency sweeps with different electro-dynamical loading conditions are shown to demonstrate the excitation of the higher order modes of vibration. Using a half electrode, the second mode is excited with high amplitude of vibration compared with almost zero response using the full electrode. Also, using a two-third electrode configuration is shown to amplify the third mode resonance amplitude compared with the full electrode under the same electrical loading conditions. An analytical model is developed based on the Euler-Bernollui beam model and the Galerkin method to simulate the device response. Good agreement between the simulation results and the experimental data is reported.

Diphoton generalized distribution amplitudes

International Nuclear Information System (INIS)

El Beiyad, M.; Pire, B.; Szymanowski, L.; Wallon, S.

2008-01-01

We calculate the leading order diphoton generalized distribution amplitudes by calculating the amplitude of the process γ*γ→γγ in the low energy and high photon virtuality region at the Born order and in the leading logarithmic approximation. As in the case of the anomalous photon structure functions, the γγ generalized distribution amplitudes exhibit a characteristic lnQ 2 behavior and obey inhomogeneous QCD evolution equations.

Analyticity properties of two-body helicity amplitudes; Proprietes d'analyticite des amplitudes d'helicite a deux corps

Energy Technology Data Exchange (ETDEWEB)

Navelet-Noualhier, H [Commissariat a l' Energie Atomique, Saclay (France). Centre d' Etudes Nucleaires

1967-06-15

Helicity amplitudes are expressed via the spinor amplitudes in terms of the Joos invariant which have been shown by Williams to be free from kinematical singularities. This procedure allows to analyze the kinematical singularities of helicity amplitudes and separate them out, which results into the definition of regularized helicity amplitudes. A crossing matrix for helicity amplitudes, is written down, corresponding to the continuation path used to cross spinor amplitudes. We verify explicitly that the corresponding crossing matrix for regularized helicity amplitudes is uniform as it should be. Kinematical constraints which generalize, to the case of arbitrary spins and masses, relations which must hold between helicity amplitudes at some values of the energy variable in {pi}N {yields} {pi}N, {pi}{pi} {yields} NN-bar and NN-bar {yields} NN-bar reactions, appear as a consequence of the existence of poles in the crossing matrix between regularized helicity amplitudes. An english version of this work has been written with G. Cohen-Tannoudji and A. Morel and submitted for publication to Annals of Physics. (author) [French] Les amplitudes d'helicite pour une reaction a deux corps sont exprimees, par l'intermediaire des amplitudes spinorielles, en fonction d'amplitudes invariantes de Joos qui sont, comme l'a montre Williams, sans singularites cinematiques. Ce procede nous permet d'analyser puis d'eliminer les singularites cinematiques des amplitudes d'helicite. Ceci nous conduit a la definition d'amplitudes d'helicite 'regularisees'. Une relation de 'croisement' entre amplitudes d'helicite est ecrite; elle realise leur prolongement analytique le long du chemin utilise pour 'croiser' les amplitudes spinorielles. Nous verifions que les elements de la matrice de croisement entre amplitudes d'helicite 'regularisees' sont bien uniformes. Les contraintes cinematiques qui generalisent, au cas de masses et de spins arbitraires, les relations obtenues dans les reactions {pi

Excitation of large-amplitude parametric resonance by the mechanical stiffness modulation of a microstructure

International Nuclear Information System (INIS)

Krylov, Slava; Gerson, Yuval; Nachmias, Tali; Keren, Uri

2010-01-01

In this work we report on an approach allowing efficient parametric excitation of large-amplitude stable oscillations of a microstructure operated by a parallel-plate electrode, and present results of a theoretical and experimental investigation of the device. The frame-type structure, fabricated from a silicon on insulator (SOI) substrate using deep reactive ion etching (DRIE), consists a pair of cantilever-type suspensions connected at their ends by a link. The time-varying electrostatic force applied to the link by a parallel-plate electrode is transformed into a periodic tension of the beams, resulting in the modulation of their flexural stiffness and consequently the mechanical parametric excitation of the structure. The lateral compliance of the beams allows for large-amplitude in-plane oscillations in the direction parallel to the electrode while high axial stiffness prevents undesirable instabilities. The lumped model of the device, considered as an assembly of geometrically nonlinear massless flexures and a rigid massive link and built using the Rayleigh–Ritz method, predicted the feasibility of the excitation approach. The fabricated devices were operated in ambient air conditions by a combination of a steady (dc) and time-dependent (ac) components of voltage and the large-amplitude responses, up to 75 µm, in the vicinity of the principal parametric and primary resonances were registered by means of video acquisition and image processing. The shapes of the experimental resonant curves were consistent with those predicted by the model. The location and size of the instability regions on the frequency–voltage plane (parametric tongues) were quantitatively in good agrement with the model results. Theoretical and experimental results indicate that the suggested approach can be efficiently used for excitation of various types of microdevices where stable resonant operation combined with robustness and large vibrational amplitudes are desirable

A Bayesian network model for predicting aquatic toxicity mode of action using two dimensional theoretical molecular descriptors

Energy Technology Data Exchange (ETDEWEB)

Carriger, John F. [U.S. Environmental Protection Agency, Office of Research and Development, Gulf Ecology Division, Gulf Breeze, FL, 32561 (United States); Martin, Todd M. [U.S. Environmental Protection Agency, Office of Research and Development, Sustainable Technology Division, Cincinnati, OH, 45220 (United States); Barron, Mace G., E-mail: barron.mace@epa.gov [U.S. Environmental Protection Agency, Office of Research and Development, Gulf Ecology Division, Gulf Breeze, FL, 32561 (United States)

2016-11-15

Highlights: • A Bayesian network was developed to classify chemical mode of action (MoA). • The network was based on the aquatic toxicity MoA for over 1000 chemicals. • A Markov blanket algorithm selected a subset of theoretical molecular descriptors. • Sensitivity analyses found influential descriptors for classifying the MoAs. • Overall precision of the Bayesian MoA classification model was 80%. - Abstract: The mode of toxic action (MoA) has been recognized as a key determinant of chemical toxicity, but development of predictive MoA classification models in aquatic toxicology has been limited. We developed a Bayesian network model to classify aquatic toxicity MoA using a recently published dataset containing over one thousand chemicals with MoA assignments for aquatic animal toxicity. Two dimensional theoretical chemical descriptors were generated for each chemical using the Toxicity Estimation Software Tool. The model was developed through augmented Markov blanket discovery from the dataset of 1098 chemicals with the MoA broad classifications as a target node. From cross validation, the overall precision for the model was 80.2%. The best precision was for the AChEI MoA (93.5%) where 257 chemicals out of 275 were correctly classified. Model precision was poorest for the reactivity MoA (48.5%) where 48 out of 99 reactive chemicals were correctly classified. Narcosis represented the largest class within the MoA dataset and had a precision and reliability of 80.0%, reflecting the global precision across all of the MoAs. False negatives for narcosis most often fell into electron transport inhibition, neurotoxicity or reactivity MoAs. False negatives for all other MoAs were most often narcosis. A probabilistic sensitivity analysis was undertaken for each MoA to examine the sensitivity to individual and multiple descriptor findings. The results show that the Markov blanket of a structurally complex dataset can simplify analysis and interpretation by

Real topological string amplitudes

Energy Technology Data Exchange (ETDEWEB)

Narain, K.S. [The Abdus Salam International Centre for Theoretical Physics (ICTP),Strada Costiera 11, Trieste, 34151 (Italy); Piazzalunga, N. [Simons Center for Geometry and Physics, State University of New York,Stony Brook, NY, 11794-3636 (United States); International School for Advanced Studies (SISSA) and INFN, Sez. di Trieste,via Bonomea 265, Trieste, 34136 (Italy); Tanzini, A. [International School for Advanced Studies (SISSA) and INFN, Sez. di Trieste,via Bonomea 265, Trieste, 34136 (Italy)

2017-03-15

We discuss the physical superstring correlation functions in type I theory (or equivalently type II with orientifold) that compute real topological string amplitudes. We consider the correlator corresponding to holomorphic derivative of the real topological amplitude G{sub χ}, at fixed worldsheet Euler characteristic χ. This corresponds in the low-energy effective action to N=2 Weyl multiplet, appropriately reduced to the orientifold invariant part, and raised to the power g{sup ′}=−χ+1. We show that the physical string correlator gives precisely the holomorphic derivative of topological amplitude. Finally, we apply this method to the standard closed oriented case as well, and prove a similar statement for the topological amplitude F{sub g}.

Asymptotic properties of Born-improved amplitudes with gauge bosons in the final state

CERN Document Server

Papavassiliou, J

1999-01-01

For processes with gauge bosons in the final state we show how to continuously connect with a single Born-improved amplitude the resonant region, where resummation effects are important, with the asymptotic region far away from the resonance, where the amplitude must reduce to its tree-level form. While doing so all known field-theoretical constraints are respected, most notably gauge-invariance, unitarity and the equivalence theorem. The calculations presented are based on the process $f\\bar{f}\\to ZZ$, mediated by a possibly resonant Higgs boson; this process captures all the essential features, and can serve as a prototype for a variety of similar calculations. By virtue of massive cancellations the resulting closed expressions for the differential and total cross-sections are particularly compact.

Arbitrary amplitude nucleus-acoustic solitons in multi-ion quantum plasmas with relativistically degenerate electrons

Science.gov (United States)

Sultana, S.; Schlickeiser, R.

2018-02-01

A three component degenerate relativistic quantum plasma (consisting of relativistically degenerate electrons, nondegenerate inertial light nuclei, and stationary heavy nuclei) is considered to model the linear wave and also the electrostatic solitary waves in the light nuclei-scale length. A well-known normal mode analysis is employed to investigate the linear wave properties. A mechanical-motion analog (Sagdeev-type) pseudo-potential approach, which reveals the existence of large amplitude solitary excitations, is adopted to study the nonlinear wave properties. Only the positive potential solitary excitations are found to exist in the plasma medium under consideration. The basic properties of the arbitrary amplitude electrostatic acoustic modes in the light nuclei-scale length and their existence domain in terms of soliton speed (Mach number) are examined. The modifications of solitary wave characteristics and their existence domain with the variation of different key plasma configuration parameters (e.g., electrons degeneracy parameter, inertial light nuclei number density, and degenerate electron number density) are also analyzed. Our results, which may be helpful to explain the basic features of the nonlinear wave propagation in multi-component degenerate quantum plasmas, in connection with astrophysical compact objects (e.g., white dwarfs) are briefly discussed.

One-way mode transmission in one-dimensional phononic crystal plates

Science.gov (United States)

Zhu, Xuefeng; Zou, Xinye; Liang, Bin; Cheng, Jianchun

2010-12-01

We investigate theoretically the band structures of one-dimensional phononic crystal (PC) plates with both antisymmetric and symmetric structures, and show how unidirectional transmission behavior can be obtained for either antisymmetric waves (A modes) or symmetric waves (S modes) by exploiting mode conversion and selection in the linear plate systems. The theoretical approach is illustrated for one PC plate example where unidirectional transmission behavior is obtained in certain frequency bands. Employing harmonic frequency analysis, we numerically demonstrate the one-way mode transmission for the PC plate with finite superlattice by calculating the steady-state displacement fields under A modes source (or S modes source) in forward and backward direction, respectively. The results show that the incident waves from A modes source (or S modes source) are transformed into S modes waves (or A modes waves) after passing through the superlattice in the forward direction and the Lamb wave rejections in the backward direction are striking with a power extinction ratio of more than 1000. The present structure can be easily extended to two-dimensional PC plate and efficiently encourage practical studies of experimental realization which is believed to have much significance for one-way Lamb wave mode transmission.

Pulse-amplitude modulation of optical injection-locked quantum-dot lasers

Science.gov (United States)

Zhou, Yue-Guang; Wang, Cheng

2018-02-01

This work theoretically investigates the four-level pulse-amplitude modulation characteristics of quantum dot lasers subject to optical injection. The rate equation model takes into account carrier dynamics in the carrier reservoir, in the excited state, and in the ground state, as well as photon dynamics and phase dynamics of the electric field. It is found that the optical injection significantly improves the eye diagram quality through suppressing the relaxation oscillation, while the extinction ratio is reduced as well. In addition, both the adiabatic chirp and the transient chirp of the signal are substantially suppressed.

Turbulence and Solar p-Mode Oscillations

Science.gov (United States)

Bi, S. L.; Xu, H. Y.

The discrepancy between observed and theoretical mode frequencies can be used to examine the reliability of the standard solar model as a faithful representation of solar real situation. With the help of an improved time-dependent convective model that takes into account contribution of the full spatial and temporal turbulent energy spectrum, we study the influence of turbulent pressure on structure and solar p-mode frequencies. For the radial modes we find that the Reynolds stress produces signification modifications in structure and p-mode spectrum. Compared with an adiabatic approximation, the discrepancy is largely removed by the turbulent correction.

Unifying relations for scattering amplitudes

Science.gov (United States)

Cheung, Clifford; Shen, Chia-Hsien; Wen, Congkao

2018-02-01

We derive new amplitudes relations revealing a hidden unity among a wideranging variety of theories in arbitrary spacetime dimensions. Our results rely on a set of Lorentz invariant differential operators which transmute physical tree-level scattering amplitudes into new ones. By transmuting the amplitudes of gravity coupled to a dilaton and two-form, we generate all the amplitudes of Einstein-Yang-Mills theory, Dirac-Born-Infield theory, special Galileon, nonlinear sigma model, and biadjoint scalar theory. Transmutation also relates amplitudes in string theory and its variants. As a corollary, celebrated aspects of gluon and graviton scattering like color-kinematics duality, the KLT relations, and the CHY construction are inherited traits of the transmuted amplitudes. Transmutation recasts the Adler zero as a trivial consequence of the Weinberg soft theorem and implies new subleading soft theorems for certain scalar theories.

Equilibrium calculations and mode analysis

International Nuclear Information System (INIS)

Herrnegger, F.

1987-01-01

The STEP asymptotic stellarator expansion procedure was used to study the MHD equilibrium and stability properties of stellarator configurations without longitudinal net-current, which also apply to advanced stellarators. The effects of toroidal curvature and magnetic well, and the Shafranov shift were investigated. A classification of unstable modes in toroidal stellarators is given. For WVII-A coil-field configurations having a β value of 1% and a parabolic pressure profile, no free-boundary modes are found. This agrees with the experimental fact that unstable behavior of the plasma column is not observed for this parameter range. So a theoretical β-limit for stability against ideal MHD modes can be estimated by mode analysis for the WVII-A device

Analysis of Energy Transmission Modes of Flyback Converter

Directory of Open Access Journals (Sweden)

GONG Shu

2014-08-01

Full Text Available It is of significance to investigate energy transmission modes of a flyback converter for its optimum design. In this paper, the ETMs of a flyback converter are divided into three modes, which are continuous conduction mode-complete inductor supply mode, continuous conduction mode- incomplete inductor supply mode and discontinuous conduction mode-incomplete inductor supply mode, respectively. A deep analysis of the operation is made, a reduction of the boundary condition between the modes is conducted and a comparison of current stress, transformer AP and output ripple voltage between the modes is performed. A 30W prototype is developed and its experiment is done. The experiment results are in agreement with the theoretical analysis quite well.

Finite toroidal flow generated by unstable tearing mode in a toroidal plasma

Energy Technology Data Exchange (ETDEWEB)

Hao, G. Z., E-mail: haogz@swip.ac.cn; Wang, A. K.; Xu, Y. H.; He, H. D.; Xu, M.; Qu, H. P.; Peng, X. D.; Xu, J. Q.; Qiu, X. M. [Southwestern Institute of Physics, P.O. Box 432, Chengdu 610041 (China); Liu, Y. Q. [Culham Centre for Fusion Energy, Culham Science Centre, Abingdon OX14 3DB (United Kingdom); Sun, Y. [Institute of Plasma Physics, Chinese Academic of Sciences, P.O. Box 1126, Hefei 230031 (China); Cui, S. Y. [School of Mathematics and Statistics Science, Ludong University, Yantai 264025 (China)

2014-12-15

The neoclassical toroidal plasma viscosity torque and electromagnetic torque, generated by tearing mode (TM) in a toroidal plasma, are numerically investigated using the MARS-Q code [Liu et al., Phys. Plasmas 20, 042503 (2013)]. It is found that an initially unstable tearing mode can intrinsically drive a toroidal plasma flow resulting in a steady state solution, in the absence of the external momentum input and external magnetic field perturbation. The saturated flow is in the order of 0.5%ω{sub A} at the q=2 rational surface in the considered case, with q and ω{sub A} being the safety factor and the Alfven frequency at the magnetic axis, respectively. The generation of the toroidal flow is robust, being insensitive to the given amplitude of the perturbation at initial state. On the other hand, the flow amplitude increases with increasing the plasma resistivity. Furthermore, the initially unstable tearing mode is fully stabilized by non-linear interaction with the self-generated toroidal flow.

An instability due to the nonlinear coupling of p-modes to g-modes: Implications for coalescing neutron star binaries

International Nuclear Information System (INIS)

Weinberg, Nevin N.; Arras, Phil; Burkart, Joshua

2013-01-01

A weakly nonlinear fluid wave propagating within a star can be unstable to three-wave interactions. The resonant parametric instability is a well-known form of three-wave interaction in which a primary wave of frequency ω a excites a pair of secondary waves of frequency ω b + ω c ≅ ω a . Here we consider a nonresonant form of three-wave interaction in which a low-frequency primary wave excites a high-frequency p-mode and a low-frequency g-mode such that ω b + ω c >> ω a . We show that a p-mode can couple so strongly to a g-mode of similar radial wavelength that this type of nonresonant interaction is unstable even if the primary wave amplitude is small. As an application, we analyze the stability of the tide in coalescing neutron star binaries to p-g mode coupling. We find that the equilibrium tide and dynamical tide are both p-g unstable at gravitational wave frequencies f gw ≳ 20 Hz and drive short wavelength p-g mode pairs to significant energies on very short timescales (much less than the orbital decay time due to gravitational radiation). Resonant parametric coupling to the tide is, by contrast, either stable or drives modes at a much smaller rate. We do not solve for the saturation of the p-g instability and therefore we cannot say precisely how it influences the evolution of neutron star binaries. However, we show that if even a single daughter mode saturates near its wave breaking amplitude, the p-g instability of the equilibrium tide will (1) induce significant orbital phase errors (Δφ ≳ 1 radian) that accumulate primarily at low frequencies (f gw ≲ 50 Hz) and (2) heat the neutron star core to a temperature of T ∼ 10 10 K. Since there are at least ∼100 unstable p-g daughter pairs, Δφ and T are potentially much larger than these values. Tides might therefore significantly influence the gravitational wave signal and electromagnetic emission from coalescing neutron star binaries at much larger orbital separations than previously

Rippling modes in the edge of a tokamak plasma

International Nuclear Information System (INIS)

Carreras, B.A.; Callen, J.D.; Gaffney, P.W.; Hicks, H.R.

1982-02-01

A promising resistive magnetohydrodynamic candidate for the underlying cause of turbulence in the edge of a tokamak plasma is the rippling instability. In this paper we develop a computational model for these modes in the cylindrical tokamak approximation and explore the linear growth and single-helicity quasi-linear saturation phases of the rippling modes for parameters appropriate to the edge of a tokamak plasma. Large parallel heat conduction does not stabilize these modes; it only reduces their growth rate by a factor scaling as k/sub parallel//sup -4/3/. Nonlinearly, individual rippling modes are found to saturate by quasi-linear flattening of the resistivity profile. The saturated amplitude of the modes scales as m/sup -1/, and the radial extent of these modes grows linearly with time due to radial Vector E x Vector B 0 convection. This evolution is found to be terminated by parallel heat conduction

Rippling modes in the edge of a tokamak plasma

International Nuclear Information System (INIS)

Carreras, B.A.; Gaffney, P.W.; Hicks, H.R.; Callan, J.D.

1982-01-01

A promising resistive magnetohydrodynamic candidate for the underlying cause of turbulence in the edge of a tokamak plasma is the rippling instability. In this paper a computational model for these modes in the cylindrical tokamak approximation was developed and the linear growth and single-helicity quasi-linear saturation phases of the rippling modes for parameters appropriate to the edge of a tokamak plasma were explored. Large parallel heat conduction does not stabilize these modes; it only reduces their growth rate by a factor sacling as K/sup -4/3//sub parallel/. Nonlinearly, individual rippling modes are found to saturate by quasi-linear flattening of the resistivity profile. The saturated amplitude of the modes scales as m -1 , and the radial extent of these modes grows linearly with time due to radial E x B 0 convection. This evolution is found to be terminated by parallel heat conduction

Decoding Mode-mixing in Black-hole Merger Ringdown

Science.gov (United States)

Kelly, Bernard J.; Baker, John G.

2013-01-01

Optimal extraction of information from gravitational-wave observations of binary black-hole coalescences requires detailed knowledge of the waveforms. Current approaches for representing waveform information are based on spin-weighted spherical harmonic decomposition. Higher-order harmonic modes carrying a few percent of the total power output near merger can supply information critical to determining intrinsic and extrinsic parameters of the binary. One obstacle to constructing a full multi-mode template of merger waveforms is the apparently complicated behavior of some of these modes; instead of settling down to a simple quasinormal frequency with decaying amplitude, some |m| = modes show periodic bumps characteristic of mode-mixing. We analyze the strongest of these modes the anomalous (3, 2) harmonic mode measured in a set of binary black-hole merger waveform simulations, and show that to leading order, they are due to a mismatch between the spherical harmonic basis used for extraction in 3D numerical relativity simulations, and the spheroidal harmonics adapted to the perturbation theory of Kerr black holes. Other causes of mode-mixing arising from gauge ambiguities and physical properties of the quasinormal ringdown modes are also considered and found to be small for the waveforms studied here.

Fatigue behaviour of fiberglass wind turbine blade material under variable amplitude loading

Energy Technology Data Exchange (ETDEWEB)

Delft, D R.V. Van; Winkel, G.D. de [Delft Univ. of Technology, STEVIN Lab., Delft (Netherlands); Joosse, P A [Stork Product Engineering b.v., Amsterdam (Netherlands)

1996-09-01

In the work presented here fatigue tests with the WISPER and WISPERX load sequence have been carried out and analysed. The test programme includes tests at low stress levels which results in fatigue lives of 50 millions of cycles. The results are compared with constant amplitude tests in the very high cycle range, carried out in a previous programme. The results are also compared with ECN results in the lower cycle range (on identical specimens). It appeared, that the difference between the fatigue life of the specimens tested with the WISPER and the WISPERX load sequence is larger than can be expected from the theoretical damage rates. Moreover, the slope of the S-N data differs from theoretical values obtained by using commonly applied design rules. (au)

Field-theoretic model of Harari's two component phenomenological theory of high energy hadron scattering

International Nuclear Information System (INIS)

Dymski, T.C.

1976-01-01

For high energy scattering of pseudoscalar particles on spin 1 / 2 particles, the transition amplitude (for a given signature) is constructed as an infinite sum over spin of boson exchange graphs of the Feynman type, each of which has impact parameters up to some value R completely removed. This amplitude is advanced as a field theoretic realization of the nondiffractive component of Harari's dual absorption model. Comparing with π/sup +-/p→π/sup +-/p and π - p→π 0 n data shows that the imaginary parts of both helicity amplitudes are excellent, for either signature

Pulse-amplitude multipliers using logarithmic amplitude-to-time conversion; Amplificateurs d'impulsions utilisant une conversion logarithmique temps-amplitude; Ob umnozhitelyakh amplitudy impul'sov s ispol'zovaniem logarifmicheskogo preobrazovaniya amplitudy vo vremya; Multiplicadores de amplitud de impulso usando una conversion logaritmica de amplitud en tiempo

Energy Technology Data Exchange (ETDEWEB)

Konrad, M [Institut Rudjer Boskovic, Zagreb, Yugoslavia (Croatia)

1962-04-15

The accuracy and limitations of multipliers based on logarithmic amplitude-to-time conversion using RC pulse stretchers are discussed with respect to their application for determining whether the amplitude product of two coincident pulses has a given value. Some possible circuits are given. (author) [French] L'auteur etudie la precision et les limitations des amplificateurs fondes sur la conversion logarithmique temps-amplitude et utilisant des allongeurs d'impulsions RC, afin d'etablir si ces appareils peuvent servir a determiner la valeur du produit des amplitudes de deux impulsions coincidentes. Il decrit en outre plusieurs circuits possibles. (author) [Spanish] La memoria discute la precision y limitaciones de los multiplicadores basados en la conversion logaritmica de amplitud en tiempo empleando circuitos alargadores de resistencia-capacidad en relacion con su aplicacion para determinar si el producto de las amplitudes de dos impulsos coincidentes tiene un valor determinado. Indica algunos circuitos posibles. (author) [Russian] Obsuzhdayutsya predel pogreshnosti i ogranicheniya umnozhitelej, osnovannykh na logarifmicheskom preobrazovanii amplitudy vo vremya, s ispol'zovaniem rasshiritelej impul'sov RC; ehto delaetsya v svyazi s ikh primeneniem dlya vyyasneniya voprosa o tom, imeet li opredelennuyu velichinu proizvedenie amplitud dvukh sovpadayushchikh impul'sov. Privodyatsya nekotorye vozmozhnye blok-skhemy. (author)

Time-amplitude converter; Convertisseur temps-amplitude

Energy Technology Data Exchange (ETDEWEB)

Banner, M [Commissariat a l' Energie Atomique, Saclay (France).Centre d' Etudes Nucleaires

1961-07-01

It is normal in high energy physics to measure the time of flight of a particle in order to determine its mass. This can be done by the method which consists in transforming the time measurement into an analysis of amplitude, which is easier; a time-amplitude converter has therefore been built for this purpose. The apparatus here described uses a double grid control tube 6 BN 6 whose resolution time, as measured with a pulse generator, is 5 x 10{sup -11} s. The analysis of the response of a particle counter, made up of a scintillator and a photomultiplier, indicates that a time of resolution of 5 x 10{sup -10} s. can be obtained. A time of this order of magnitude is obtained experimentally with the converter. This converter has been used in the study of the time of flight of particles in a secondary beam of the accelerator Saturne. It has thus been possible to measure the energy spectrum of {pi}-mesons, of protons, and of deutons emitted from a polyethylene target bombarded by 1,4 and 2 GeV protons. (author) [French] Pour determiner la masse d'une particule, il est courant, en physique des hautes energies, de mesurer le temps de vol de cette particule. Cela peut etre fait par la methode qui consiste a transformer la mesure d'un temps en une analyse d'amplitude, plus aisee; aussi a-t-on, a cet effet, cree un convertisseur temps-amplitude. L'appareillage decrit dans cet article utilise un tube a double grille de commande 6 BN 6 dont le temps de resolution mesure avec un generateur d'impulsion est de 5.10{sup -11} s. L'analyse de la reponse d'un compteur de particules, constitue par un scintillateur et un photomultiplicateur, indique qu'un temps de resolution de 5.10{sup -10} s peut etre obtenu. Un temps de cet ordre est atteint experimentalement avec le convertisseur. Ce convertisseur a servi a l'etude du temps de vol des particules dans un faisceau secondaire de l'accelerateur Saturne. On a mesure ainsi le spectre d'energie des mesons {pi}, des protons, des deutons

Speech rhythm analysis with decomposition of the amplitude envelope: characterizing rhythmic patterns within and across languages.

Science.gov (United States)

Tilsen, Sam; Arvaniti, Amalia

2013-07-01

This study presents a method for analyzing speech rhythm using empirical mode decomposition of the speech amplitude envelope, which allows for extraction and quantification of syllabic- and supra-syllabic time-scale components of the envelope. The method of empirical mode decomposition of a vocalic energy amplitude envelope is illustrated in detail, and several types of rhythm metrics derived from this method are presented. Spontaneous speech extracted from the Buckeye Corpus is used to assess the effect of utterance length on metrics, and it is shown how metrics representing variability in the supra-syllabic time-scale components of the envelope can be used to identify stretches of speech with targeted rhythmic characteristics. Furthermore, the envelope-based metrics are used to characterize cross-linguistic differences in speech rhythm in the UC San Diego Speech Lab corpus of English, German, Greek, Italian, Korean, and Spanish speech elicited in read sentences, read passages, and spontaneous speech. The envelope-based metrics exhibit significant effects of language and elicitation method that argue for a nuanced view of cross-linguistic rhythm patterns.

Attitude tracking control of flexible spacecraft with large amplitude slosh

Science.gov (United States)

Deng, Mingle; Yue, Baozeng

2017-12-01

This paper is focused on attitude tracking control of a spacecraft that is equipped with flexible appendage and partially filled liquid propellant tank. The large amplitude liquid slosh is included by using a moving pulsating ball model that is further improved to estimate the settling location of liquid in microgravity or a zero-g environment. The flexible appendage is modelled as a three-dimensional Bernoulli-Euler beam, and the assumed modal method is employed. A hybrid controller that combines sliding mode control with an adaptive algorithm is designed for spacecraft to perform attitude tracking. The proposed controller has proved to be asymptotically stable. A nonlinear model for the overall coupled system including spacecraft attitude dynamics, liquid slosh, structural vibration and control action is established. Numerical simulation results are presented to show the dynamic behaviors of the coupled system and to verify the effectiveness of the control approach when the spacecraft undergoes the disturbance produced by large amplitude slosh and appendage vibration. Lastly, the designed adaptive algorithm is found to be effective to improve the precision of attitude tracking.

Update on Linear Mode Photon Counting with the HgCdTe Linear Mode Avalanche Photodiode

Science.gov (United States)

Beck, Jeffrey D.; Kinch, Mike; Sun, Xiaoli

2014-01-01

The behavior of the gain-voltage characteristic of the mid-wavelength infrared cutoff HgCdTe linear mode avalanche photodiode (e-APD) is discussed both experimentally and theoretically as a function of the width of the multiplication region. Data are shown that demonstrate a strong dependence of the gain at a given bias voltage on the width of the n- gain region. Geometrical and fundamental theoretical models are examined to explain this behavior. The geometrical model takes into account the gain-dependent optical fill factor of the cylindrical APD. The theoretical model is based on the ballistic ionization model being developed for the HgCdTe APD. It is concluded that the fundamental theoretical explanation is the dominant effect. A model is developed that combines both the geometrical and fundamental effects. The model also takes into account the effect of the varying multiplication width in the low bias region of the gain-voltage curve. It is concluded that the lower than expected gain seen in the first 2 × 8 HgCdTe linear mode photon counting APD arrays, and higher excess noise factor, was very likely due to the larger than typical multiplication region length in the photon counting APD pixel design. The implications of these effects on device photon counting performance are discussed.

Unified treatment: analyticity, Regge trajectories, Veneziano amplitude, fundamental regions and Moebius transformations

International Nuclear Information System (INIS)

Choudhary, A.R.

2003-01-01

In this paper we present a unified treatment that combines the analyticity properties of the scattering amplitudes, the threshold and asymptotic behaviors, the invariance group of Moebius transformations, the automorphic functions defined over this invariance group, the fundamental region in (Poincare) geometry, and the generators of the invariance group as they relate to the fundamental region. Using these concepts and techniques, we provide a theoretical basis for Veneziano type amplitudes with the ghost elimination condition built in, related the Regge trajectory functions to the generators of the invariance group, constrained the values of the Regge trajectories to take only inverse integer values at the threshold, used the threshold behavior in the forward direction to deduce the Pomeranchuk trajectory as well as other relations. The enabling tool for this unified treatment came from the multi-sheet conformal mapping techniques that map the physical sheet to a fundamental region which in turn defines a Riemann surface on which a global uniformization variable for the scattering amplitude is calculated via an automorphic function, which in turn can be constructed as a quotient of two automorphic forms of the same dimension. (orig.)

Dictionary-Based Stochastic Expectation–Maximization for SAR Amplitude Probability Density Function Estimation

OpenAIRE

Moser , Gabriele; Zerubia , Josiane; Serpico , Sebastiano B.

2006-01-01

International audience; In remotely sensed data analysis, a crucial problem is represented by the need to develop accurate models for the statistics of the pixel intensities. This paper deals with the problem of probability density function (pdf) estimation in the context of synthetic aperture radar (SAR) amplitude data analysis. Several theoretical and heuristic models for the pdfs of SAR data have been proposed in the literature, which have been proved to be effective for different land-cov...

Response of the Higgs amplitude mode of superfluid Bose gases in a three-dimensional optical lattice

Science.gov (United States)

Nagao, Kazuma; Takahashi, Yoshiro; Danshita, Ippei

2018-04-01

We study the Higgs mode of superfluid Bose gases in a three-dimensional optical lattice, which emerges near the quantum phase transition to the Mott insulator at commensurate fillings. Specifically, we consider responses of the Higgs mode to temporal modulations of the onsite interaction and the hopping energy. In order to calculate the response functions including the effects of quantum and thermal fluctuations, we map the Bose-Hubbard model onto an effective pseudospin-1 model and use a perturbative expansion based on the imaginary-time Green's function theory. We also include the effects of an inhomogeneous trapping potential by means of a local density approximation. We find that the response function for the hopping modulation is equal to that for the interaction modulation within our approximation. At the unit filling rate and in the absence of a trapping potential, we show that the Higgs mode can exist as a sharp resonance peak in the dynamical susceptibilities at typical temperatures. However, the resonance peak is significantly broadened due to the trapping potential when the modulations are applied globally to the entire system. We suggest that the Higgs mode can be detected as a sharp resonance peak by partial modulations around the trap center.

Choice of Foreign Market Entry Mode - Cognitions from Empirical and Theoretical Studies

OpenAIRE

Zhao, Xuemin; Decker, Reinhold

2004-01-01

This paper analyzes critically five basic theories on market entry mode decision with respect to existing strengths and weaknesses and the results of corresponding empirical studies. Starting from conflictions both in theories and empirical studies dealing with the entry mode choice problem we motivate a significant need of further research in this important area of international marketing. Furthermore we provide implications for managers in practice and outline emerging trends in market entr...

Rock Fracture Toughness Study Under Mixed Mode I/III Loading

Science.gov (United States)

Aliha, M. R. M.; Bahmani, A.

2017-07-01

Fracture growth in underground rock structures occurs under complex stress states, which typically include the in- and out-of-plane sliding deformation of jointed rock masses before catastrophic failure. However, the lack of a comprehensive theoretical and experimental fracture toughness study for rocks under contributions of out-of plane deformations (i.e. mode III) is one of the shortcomings of this field. Therefore, in this research the mixed mode I/III fracture toughness of a typical rock material is investigated experimentally by means of a novel cracked disc specimen subjected to bend loading. It was shown that the specimen can provide full combinations of modes I and III and consequently a complete set of mixed mode I/III fracture toughness data were determined for the tested marble rock. By moving from pure mode I towards pure mode III, fracture load was increased; however, the corresponding fracture toughness value became smaller. The obtained experimental fracture toughness results were finally predicted using theoretical and empirical fracture models.

From dressed particle to dressed mode in plasmas

Energy Technology Data Exchange (ETDEWEB)

Itoh, Sanae-I. [Kyushu Univ., Research Inst. for Applied Mechanics, Kasuga, Fukuoka (Japan); Itoh, Kimitaka [National Inst. for Fusion Science, Toki, Gifu (Japan)

2002-05-01

A theoretical method to analyze the strong turbulence in far-nonequilibrium plasma is discussed. In this approach, a test mode is treated being dressed with interactions with other modes. Nonlinear dispersion relation of the dressed mode and statistical treatment of turbulence is briefly explained. Analogue to the method of dressed particle, which has given Balescu-Lenard collision operator for inter-particle collisions, is mentioned. (author)

Multi-Mode Cavity Accelerator Structure

Energy Technology Data Exchange (ETDEWEB)

Jiang, Yong [Yale Univ., New Haven, CT (United States); Hirshfield, Jay Leonard [Omega-P R& D, Inc., New Haven, CT (United States)

2016-11-10

This project aimed to develop a prototype for a novel accelerator structure comprising coupled cavities that are tuned to support modes with harmonically-related eigenfrequencies, with the goal of reaching an acceleration gradient >200 MeV/m and a breakdown rate <10^-7/pulse/meter. Phase I involved computations, design, and preliminary engineering of a prototype multi-harmonic cavity accelerator structure; plus tests of a bimodal cavity. A computational procedure was used to design an optimized profile for a bimodal cavity with high shunt impedance and low surface fields to maximize the reduction in temperature rise ΔT. This cavity supports the TM010 mode and its 2nd harmonic TM011 mode. Its fundamental frequency is at 12 GHz, to benchmark against the empirical criteria proposed within the worldwide High Gradient collaboration for X-band copper structures; namely, a surface electric field E_sur^max< 260 MV/m and pulsed surface heating ΔT^max< 56 °K. With optimized geometry, amplitude and relative phase of the two modes, reductions are found in surface pulsed heating, modified Poynting vector, and total RF power—as compared with operation at the same acceleration gradient using only the fundamental mode.

Multi-Mode Cavity Accelerator Structure

International Nuclear Information System (INIS)

Jiang, Yong; Hirshfield, Jay Leonard

2016-01-01

This project aimed to develop a prototype for a novel accelerator structure comprising coupled cavities that are tuned to support modes with harmonically-related eigenfrequencies, with the goal of reaching an acceleration gradient >200 MeV/m and a breakdown rate <10"-"7/pulse/meter. Phase I involved computations, design, and preliminary engineering of a prototype multi-harmonic cavity accelerator structure; plus tests of a bimodal cavity. A computational procedure was used to design an optimized profile for a bimodal cavity with high shunt impedance and low surface fields to maximize the reduction in temperature rise Δ T. This cavity supports the TM010 mode and its 2nd harmonic TM011 mode. Its fundamental frequency is at 12 GHz, to benchmark against the empirical criteria proposed within the worldwide High Gradient collaboration for X-band copper structures; namely, a surface electric field E_s_u_r"m"a"x< 260 MV/m and pulsed surface heating Δ T"m"a"x< 56 °K. With optimized geometry, amplitude and relative phase of the two modes, reductions are found in surface pulsed heating, modified Poynting vector, and total RF power - as compared with operation at the same acceleration gradient using only the fundamental mode.

Effect of Dynamical Phase on the Resonant Interaction Among Tsunami Edge Wave Modes

Science.gov (United States)

Geist, Eric L.

2018-04-01

Different modes of tsunami edge waves can interact through nonlinear resonance. During this process, edge waves that have very small initial amplitude can grow to be as large or larger than the initially dominant edge wave modes. In this study, the effects of dynamical phase are established for a single triad of edge waves that participate in resonant interactions. In previous studies, Jacobi elliptic functions were used to describe the slow variation in amplitude associated with the interaction. This analytical approach assumes that one of the edge waves in the triad has zero initial amplitude and that the combined phase of the three waves φ = θ 1 + θ 2 - θ 3 is constant at the value for maximum energy exchange ( φ = 0). To obtain a more general solution, dynamical phase effects and non-zero initial amplitudes for all three waves are incorporated using numerical methods for the governing differential equations. Results were obtained using initial conditions calculated from a subduction zone, inter-plate thrust fault geometry and a stochastic earthquake slip model. The effect of dynamical phase is most apparent when the initial amplitudes and frequencies of the three waves are within an order of magnitude. In this case, non-zero initial phase results in a marked decrease in energy exchange and a slight decrease in the period of the interaction. When there are large differences in frequency and/or initial amplitude, dynamical phase has less of an effect and typically one wave of the triad has very little energy exchange with the other two waves. Results from this study help elucidate under what conditions edge waves might be implicated in late, large-amplitude arrivals.

Effect of Dynamical Phase on the Resonant Interaction Among Tsunami Edge Wave Modes

Science.gov (United States)

Geist, Eric L.

2018-02-01

Different modes of tsunami edge waves can interact through nonlinear resonance. During this process, edge waves that have very small initial amplitude can grow to be as large or larger than the initially dominant edge wave modes. In this study, the effects of dynamical phase are established for a single triad of edge waves that participate in resonant interactions. In previous studies, Jacobi elliptic functions were used to describe the slow variation in amplitude associated with the interaction. This analytical approach assumes that one of the edge waves in the triad has zero initial amplitude and that the combined phase of the three waves φ = θ 1 + θ 2 - θ 3 is constant at the value for maximum energy exchange (φ = 0). To obtain a more general solution, dynamical phase effects and non-zero initial amplitudes for all three waves are incorporated using numerical methods for the governing differential equations. Results were obtained using initial conditions calculated from a subduction zone, inter-plate thrust fault geometry and a stochastic earthquake slip model. The effect of dynamical phase is most apparent when the initial amplitudes and frequencies of the three waves are within an order of magnitude. In this case, non-zero initial phase results in a marked decrease in energy exchange and a slight decrease in the period of the interaction. When there are large differences in frequency and/or initial amplitude, dynamical phase has less of an effect and typically one wave of the triad has very little energy exchange with the other two waves. Results from this study help elucidate under what conditions edge waves might be implicated in late, large-amplitude arrivals.

NOTE ON TRAVEL TIME SHIFTS DUE TO AMPLITUDE MODULATION IN TIME-DISTANCE HELIOSEISMOLOGY MEASUREMENTS

International Nuclear Information System (INIS)

Nigam, R.; Kosovichev, A. G.

2010-01-01

Correct interpretation of acoustic travel times measured by time-distance helioseismology is essential to get an accurate understanding of the solar properties that are inferred from them. It has long been observed that sunspots suppress p-mode amplitude, but its implications on travel times have not been fully investigated so far. It has been found in test measurements using a 'masking' procedure, in which the solar Doppler signal in a localized quiet region of the Sun is artificially suppressed by a spatial function, and using numerical simulations that the amplitude modulations in combination with the phase-speed filtering may cause systematic shifts of acoustic travel times. To understand the properties of this procedure, we derive an analytical expression for the cross-covariance of a signal that has been modulated locally by a spatial function that has azimuthal symmetry and then filtered by a phase-speed filter typically used in time-distance helioseismology. Comparing this expression to the Gabor wavelet fitting formula without this effect, we find that there is a shift in the travel times that is introduced by the amplitude modulation. The analytical model presented in this paper can be useful also for interpretation of travel time measurements for the non-uniform distribution of oscillation amplitude due to observational effects.

Coupling of Higgs and Leggett modes in non-equilibrium superconductors.

Science.gov (United States)

Krull, H; Bittner, N; Uhrig, G S; Manske, D; Schnyder, A P

2016-06-21

In equilibrium systems amplitude and phase collective modes are decoupled, as they are mutually orthogonal excitations. The direct detection of these Higgs and Leggett collective modes by linear-response measurements is not possible, because they do not couple directly to the electromagnetic field. In this work, using numerical exact simulations we show for the case of two-gap superconductors, that optical pump-probe experiments excite both Higgs and Leggett modes out of equilibrium. We find that this non-adiabatic excitation process introduces a strong interaction between the collective modes, which is absent in equilibrium. Moreover, we propose a type of pump-probe experiment, which allows to probe and coherently control the Higgs and Leggett modes, and thus the order parameter directly. These findings go beyond two-band superconductors and apply to general collective modes in quantum materials.

Universal amplitude ratios in the 3D Ising model

International Nuclear Information System (INIS)

Caselle, M.; Hasenbusch, M.

1998-01-01

We present a high precision Monte Carlo study of various universal amplitude ratios of the three dimensional Ising spin model. Using state of the art simulation techniques we studied the model close to criticality in both phases. Great care was taken to control systematic errors due to finite size effects and correction to scaling terms. We obtain C + /C - =4.75(3), f +,2nd /f -,2nd =1.95(2) and u * =14.3(1). Our results are compatible with those obtained by field theoretic methods applied to the φ 4 theory and high and low temperature series expansions of the Ising model. (orig.)

Lamb wave tuning curve calibration for surface-bonded piezoelectric transducers

International Nuclear Information System (INIS)

Sohn, Hoon; Lee, Sang Jun

2010-01-01

Surface-bonded lead zirconate titanate (PZT) transducers have been widely used for guided wave generation and measurement. For selective actuation and sensing of Lamb wave modes, the sizes of the transducers and the driving frequency of the input waveform should be tuned. For this purpose, a theoretical Lamb wave tuning curve (LWTC) of a specific transducer size is generally obtained. Here, the LWTC plots each Lamb wave mode' amplitude as a function of the driving frequency. However, a discrepancy between experimental and existing theoretical LWTCs has been observed due to little consideration of the bonding layer and the energy distribution between Lamb wave modes. In this study, calibration techniques for theoretical LWTCs are proposed. First, a theoretical LWTC is developed when circular PZT transducers are used for both Lamb wave excitation and sensing. Then, the LWTC is calibrated by estimating the effective PZT size with PZT admittance measurement. Finally, the energy distributions among symmetric and antisymmetric modes are taken into account for better prediction of the relative amplitudes between Lamb wave modes. The effectiveness of the proposed calibration techniques is examined through numerical simulations and experimental estimation of the LWTC using the circular PZT transducers instrumented on an aluminum plate

Segmentation of a Vibro-Shock Cantilever-Type Piezoelectric Energy Harvester Operating in Higher Transverse Vibration Modes

Directory of Open Access Journals (Sweden)

Darius Zizys

2015-12-01

Full Text Available The piezoelectric transduction mechanism is a common vibration-to-electric energy harvesting approach. Piezoelectric energy harvesters are typically mounted on a vibrating host structure, whereby alternating voltage output is generated by a dynamic strain field. A design target in this case is to match the natural frequency of the harvester to the ambient excitation frequency for the device to operate in resonance mode, thus significantly increasing vibration amplitudes and, as a result, energy output. Other fundamental vibration modes have strain nodes, where the dynamic strain field changes sign in the direction of the cantilever length. The paper reports on a dimensionless numerical transient analysis of a cantilever of a constant cross-section and an optimally-shaped cantilever with the objective to accurately predict the position of a strain node. Total effective strain produced by both cantilevers segmented at the strain node is calculated via transient analysis and compared to the strain output produced by the cantilevers segmented at strain nodes obtained from modal analysis, demonstrating a 7% increase in energy output. Theoretical results were experimentally verified by using open-circuit voltage values measured for the cantilevers segmented at optimal and suboptimal segmentation lines.

On Kinetic Slow Modes, Fluid Slow Modes, and Pressure-balanced Structures in the Solar Wind

Energy Technology Data Exchange (ETDEWEB)

Verscharen, Daniel [Space Science Center and Department of Physics, University of New Hampshire, Durham, NH 03824 (United States); Chen, Christopher H. K. [Department of Physics, Imperial College London, London SW7 2AZ (United Kingdom); Wicks, Robert T., E-mail: daniel.verscharen@unh.edu, E-mail: christopher.chen@imperial.ac.uk, E-mail: r.wicks@ucl.ac.uk [Mullard Space Science Laboratory, University College London, London WC1E 6BT (United Kingdom)

2017-05-10

Observations in the solar wind suggest that the compressive component of inertial-range solar-wind turbulence is dominated by slow modes. The low collisionality of the solar wind allows for nonthermal features to survive, which suggests the requirement of a kinetic plasma description. The least-damped kinetic slow mode is associated with the ion-acoustic (IA) wave and a nonpropagating (NP) mode. We derive analytical expressions for the IA-wave dispersion relation in an anisotropic plasma in the framework of gyrokinetics and then compare them to fully kinetic numerical calculations, results from two-fluid theory, and magnetohydrodynamics (MHD). This comparison shows major discrepancies in the predicted wave phase speeds from MHD and kinetic theory at moderate to high β . MHD and kinetic theory also dictate that all plasma normal modes exhibit a unique signature in terms of their polarization. We quantify the relative amplitude of fluctuations in the three lowest particle velocity moments associated with IA and NP modes in the gyrokinetic limit and compare these predictions with MHD results and in situ observations of the solar-wind turbulence. The agreement between the observations of the wave polarization and our MHD predictions is better than the kinetic predictions, which suggests that the plasma behaves more like a fluid in the solar wind than expected.

On Kinetic Slow Modes, Fluid Slow Modes, and Pressure-balanced Structures in the Solar Wind

International Nuclear Information System (INIS)

Verscharen, Daniel; Chen, Christopher H. K.; Wicks, Robert T.

2017-01-01

Observations in the solar wind suggest that the compressive component of inertial-range solar-wind turbulence is dominated by slow modes. The low collisionality of the solar wind allows for nonthermal features to survive, which suggests the requirement of a kinetic plasma description. The least-damped kinetic slow mode is associated with the ion-acoustic (IA) wave and a nonpropagating (NP) mode. We derive analytical expressions for the IA-wave dispersion relation in an anisotropic plasma in the framework of gyrokinetics and then compare them to fully kinetic numerical calculations, results from two-fluid theory, and magnetohydrodynamics (MHD). This comparison shows major discrepancies in the predicted wave phase speeds from MHD and kinetic theory at moderate to high β . MHD and kinetic theory also dictate that all plasma normal modes exhibit a unique signature in terms of their polarization. We quantify the relative amplitude of fluctuations in the three lowest particle velocity moments associated with IA and NP modes in the gyrokinetic limit and compare these predictions with MHD results and in situ observations of the solar-wind turbulence. The agreement between the observations of the wave polarization and our MHD predictions is better than the kinetic predictions, which suggests that the plasma behaves more like a fluid in the solar wind than expected.

Non-linear coupling of drift modes in a quadrupole

International Nuclear Information System (INIS)

Elliott, J.A.; Sandeman, J.C.; Tessema, G.Y.

1990-01-01

We report continuing experimental studies of non-linear interactions of drift waves, with direct evidence of a growth saturation mechanism by transfer of energy to lower frequency modes. Wave launching experiments show that the decay rate of drift waves can be strongly amplitude dependent. (author) 9 refs., 5 figs

Analysis of dynamic cantilever behavior in tapping mode atomic force microscopy.

Science.gov (United States)

Deng, Wenqi; Zhang, Guang-Ming; Murphy, Mark F; Lilley, Francis; Harvey, David M; Burton, David R

2015-10-01

Tapping mode atomic force microscopy (AFM) provides phase images in addition to height and amplitude images. Although the behavior of tapping mode AFM has been investigated using mathematical modeling, comprehensive understanding of the behavior of tapping mode AFM still poses a significant challenge to the AFM community, involving issues such as the correct interpretation of the phase images. In this paper, the cantilever's dynamic behavior in tapping mode AFM is studied through a three dimensional finite element method. The cantilever's dynamic displacement responses are firstly obtained via simulation under different tip-sample separations, and for different tip-sample interaction forces, such as elastic force, adhesion force, viscosity force, and the van der Waals force, which correspond to the cantilever's action upon various different representative computer-generated test samples. Simulated results show that the dynamic cantilever displacement response can be divided into three zones: a free vibration zone, a transition zone, and a contact vibration zone. Phase trajectory, phase shift, transition time, pseudo stable amplitude, and frequency changes are then analyzed from the dynamic displacement responses that are obtained. Finally, experiments are carried out on a real AFM system to support the findings of the simulations. © 2015 Wiley Periodicals, Inc.

Available pressure amplitude of linear compressor based on phasor triangle model

Science.gov (United States)

Duan, C. X.; Jiang, X.; Zhi, X. Q.; You, X. K.; Qiu, L. M.

2017-12-01

The linear compressor for cryocoolers possess the advantages of long-life operation, high efficiency, low vibration and compact structure. It is significant to study the match mechanisms between the compressor and the cold finger, which determines the working efficiency of the cryocooler. However, the output characteristics of linear compressor are complicated since it is affected by many interacting parameters. The existing matching methods are simplified and mainly focus on the compressor efficiency and output acoustic power, while neglecting the important output parameter of pressure amplitude. In this study, a phasor triangle model basing on analyzing the forces of the piston is proposed. It can be used to predict not only the output acoustic power, the efficiency, but also the pressure amplitude of the linear compressor. Calculated results agree well with the measurement results of the experiment. By this phasor triangle model, the theoretical maximum output pressure amplitude of the linear compressor can be calculated simply based on a known charging pressure and operating frequency. Compared with the mechanical and electrical model of the linear compressor, the new model can provide an intuitionistic understanding on the match mechanism with faster computational process. The model can also explain the experimental phenomenon of the proportional relationship between the output pressure amplitude and the piston displacement in experiments. By further model analysis, such phenomenon is confirmed as an expression of the unmatched design of the compressor. The phasor triangle model may provide an alternative method for the compressor design and matching with the cold finger.

Dispersion of strongly confined channel plasmon polariton modes

DEFF Research Database (Denmark)

Zenin, Vladimir; Volkov, Valentyn S.; Han, Zhanghua

2011-01-01

We report on experimental (by use of scanning near-field optical microscopy) and theoretical investigations of strongly confined (∼λ/5) channel plasmon polariton (CPP) modes propagating at telecom wavelengths (1425–1630 nm) along V-grooves cut in a gold film. The main CPP characteristics (mode in...

Hidden beauty in multiloop amplitudes

International Nuclear Information System (INIS)

Cachazo, Freddy; Spradlin, Marcus; Volovich, Anastasia

2006-01-01

Planar L-loop maximally helicity violating amplitudes in N = 4 supersymmetric Yang-Mills theory are believed to possess the remarkable property of satisfying iteration relations in L. We propose a simple new method for studying iteration relations for four-particle amplitudes which involves the use of certain linear differential operators and eliminates the need to fully evaluate any loop integrals. We carry out this procedure in explicit detail for the two-loop amplitude and prove that this method can be applied to any multiloop integral, allowing a conjectured iteration relation for any given amplitude to be tested up to polynomials in logarithms

An analysis of plasma ion toroidal rotation during large amplitude MHD activity in JET

International Nuclear Information System (INIS)

Snipes, J.A.; Esch, H.P.L. de; Lazzaro, E.; Stork, D.; Hellermann, M. von; Galvao, R.; Hender, T.C.; Zasche, D.

1989-01-01

A detailed study of plasma ion toroidal rotation in JET during large amplitude MHD activity has revealed a strong viscous force that couples plasma ions to MHD modes. Depending on the MHD modes present, this force can couple across all of the plasma cross section, across only the central region, roughly within the q=1 surface, or across only the outer region outside the q=1.5 surface. The force acts to flatten the ion toroidal rotation frequency profile, measured by the JET active charge exchange spectroscopy diagnostic, across the coupled region of plasma. The frequency of rotation in this region agrees with the MHD oscillation frequency measured by magnetic pick-up coils at the wall. The strength of the force between the ions and modes becomes evident during high power NBI when the mode locks and drags the ion toroidal rotation frequency to zero, within the errors of the measurements. The present theories of plasma rotation either ignore MHD effects entirely, consider only moderate n toroidal field ripple, or low n ripple effects. (author) 7 refs., 3 figs

Spectral Amplitude Coding (SAC)-OCDMA Network with 8DPSK

Science.gov (United States)

Aldhaibani, A. O.; Aljunid, S. A.; Fadhil, Hilal A.; Anuar, M. S.

2013-09-01

Optical code division multiple access (OCDMA) technique is required to meet the increased demand for high speed, large capacity communications in optical networks. In this paper, the transmission performance of a spectral amplitude coding (SAC)-OCDMA network is investigated when a conventional single-mode fiber (SMF) is used as the transmission link using 8DPSK modulation. The DW has a fixed weight of two. Simulation results reveal that the transmission distance is limited mainly by the fiber dispersion when high coding chip rate is used. For a two-user SAC-OCDMA network operating with 2 Gbit/s data rate and two wavelengths for each user, the maximum allowable transmission distance is about 15 km.

The Influence of Second Harmonic Phase and Amplitude Variation in Cyclically Pitching Wings

Science.gov (United States)

Culler, Ethan; Farnsworth, John

2017-11-01

From wind tunnel testing of a cyber-physical wing model, it has been found that the pitch trajectory for stall flutter is described by an array of higher harmonic frequencies with decaying energy content. These frequencies distort the stall flutter motion from that of a pure sinusoidal oscillation in pitch and can have a significant effect on the resulting force production. In order to understand how these higher harmonic frequencies contribute to the overall pitching moment characteristics of a wing in stall flutter, a rigid finite span wing model, with aspect ratio four, was pitched in the wind tunnel. The prescribed motion of the pitch cycle was varied by changing the amplitude ratio and phase of the second harmonic of the oscillation frequency. The second harmonic represents the second highest energy mode in the pitching cycle spectra. Pitching moment and planar particle image velocimetry data was collected. From these pitching trajectories, a significant dependence of pitching moment on both the phase and amplitude of the prescribed waveforms was found. Specifically, for the same amplitude ratio, variations in the phase produced changes of approximately 30 percent in the phase averaged pitching moment.

Empirical Mode Decomposition of the atmospheric wave field

Directory of Open Access Journals (Sweden)

A. J. McDonald

2007-03-01

Full Text Available This study examines the utility of the Empirical Mode Decomposition (EMD time-series analysis technique to separate the horizontal wind field observed by the Scott Base MF radar (78° S, 167° E into its constituent parts made up of the mean wind, gravity waves, tides, planetary waves and instrumental noise. Analysis suggests that EMD effectively separates the wind field into a set of Intrinsic Mode Functions (IMFs which can be related to atmospheric waves with different temporal scales. The Intrinsic Mode Functions resultant from application of the EMD technique to Monte-Carlo simulations of white- and red-noise processes are compared to those obtained from the measurements and are shown to be significantly different statistically. Thus, application of the EMD technique to the MF radar horizontal wind data can be used to prove that this data contains information on internal gravity waves, tides and planetary wave motions.

Examination also suggests that the EMD technique has the ability to highlight amplitude and frequency modulations in these signals. Closer examination of one of these regions of amplitude modulation associated with dominant periods close to 12 h is suggested to be related to a wave-wave interaction between the semi-diurnal tide and a planetary wave. Application of the Hilbert transform to the IMFs forms a Hilbert-Huang spectrum which provides a way of viewing the data in a similar manner to the analysis from a continuous wavelet transform. However, the fact that the basis function of EMD is data-driven and does not need to be selected a priori is a major advantage. In addition, the skeleton diagrams, produced from the results of the Hilbert-Huang spectrum, provide a method of presentation which allows quantitative information on the instantaneous period and amplitude squared to be displayed as a function of time. Thus, it provides a novel way to view frequency and amplitude-modulated wave phenomena and potentially non

Mode locking and spatiotemporal chaos in periodically driven Gunn diodes

DEFF Research Database (Denmark)

Mosekilde, Erik; Feldberg, Rasmus; Knudsen, Carsten

1990-01-01

oscillation entrains with the external signal. This produces a devil’s staircase of frequency-locked solutions. At higher microwave amplitudes, period doubling and other forms of mode-converting bifurcations can be seen. In this interval the diode also exhibits spatiotemporal chaos. At still higher microwave...

Vibrational mode and sound radiation of electrostatic speakers using circular and annular diaphragms

Science.gov (United States)

Huang, Yu-Hsi; Chiang, Hsin-Yuan

2016-06-01

This study modeled two diaphragms comprising a pair of indium tin oxide (ITO) transparent plates sandwiching a vibrating diaphragm to create circular (30 mm radius) and annular (30 mm outer and 3 mm inner radius) push-pull electrostatic speakers. We then measured the displacement amplitudes and mode shapes produced by the devices. Vibration characteristics were used to predict sound pressure levels (SPLs) using the lumped parameter method (LPM) and distributed parameter method (DPM). The two measurement results obtained using a laser system were compared to the SPLs obtained using traditional acoustic measurement (AM) from 20 Hz to 20 kHz in order to verify our predictions. When using LPM and DPM, the SPL prediction results in the first three symmetric modes were in good agreement with the AM results. Under the assumption of linear operations, the DPM and amplitude-fluctuation electronic speckle pattern interferometry (ESPI) techniques proved effective in determining the visualization of mode shape (0,1)-(0,3). The use of ITO plates is a practical technique for the prediction of SPL, as well as measurement of mode shapes. The four evaluation methods, i.e. LPM, DPM, ESPI and AM, present a high degree of consistency with regard to vibrational mode and sound radiation characteristics.

Off-shell CHY amplitudes

Energy Technology Data Exchange (ETDEWEB)

Lam, C.S., E-mail: Lam@physics.mcgill.ca [Department of Physics, McGill University, Montreal, Q.C., H3A 2T8 (Canada); Department of Physics and Astronomy, University of British Columbia, Vancouver, BC, V6T 1Z1 (Canada); Yao, York-Peng, E-mail: yyao@umich.edu [Department of Physics, The University of Michigan Ann Arbor, MI 48109 (United States)

2016-06-15

The Cachazo–He–Yuan (CHY) formula for on-shell scattering amplitudes is extended off-shell. The off-shell amplitudes (amputated Green's functions) are Möbius invariant, and have the same momentum poles as the on-shell amplitudes. The working principles which drive the modifications to the scattering equations are mainly Möbius covariance and energy momentum conservation in off-shell kinematics. The same technique is also used to obtain off-shell massive scalars. A simple off-shell extension of the CHY gauge formula which is Möbius invariant is proposed, but its true nature awaits further study.

On-coil multiple channel transmit system based on class-D amplification and pre-amplification with current amplitude feedback.

Science.gov (United States)

Gudino, Natalia; Heilman, Jeremiah A; Riffe, Matthew J; Heid, Oliver; Vester, Markus; Griswold, Mark A

2013-07-01

A complete high-efficiency transmit amplifier unit designed to be implemented in on-coil transmit arrays is presented. High power capability, low power dissipation, scalability, and cost minimization were some of the requirements imposed to the design. The system is composed of a current mode class-D amplifier output stage and a voltage mode class-D preamplification stage. The amplitude information of the radio frequency pulse was added through a customized step-down DC-DC converter with current amplitude feedback that connects to the current mode class-D stage. Benchtop measurements and imaging experiments were carried out to analyze system performance. Direct control of B1 was possible and its load sensitivity was reduced to less than 10% variation from unloaded to full loaded condition. When using the amplifiers in an array configuration, isolation above 20 dB was achieved between neighboring coils by the amplifier decoupling method. High output current operation of the transmitter was proved on the benchtop through output power measurements and in a 1.5T scanner through flip angle quantification. Finally, single and multiple channel excitations with the new hardware were demonstrated by receiving signal with the body coil of the scanner. Copyright © 2012 Wiley Periodicals, Inc.

Changes in the Amplitude and Phase of the Annual Cycle: quantifying from surface wind series in China

Science.gov (United States)

Feng, Tao

2013-04-01

Climate change is not only reflected in the changes in annual means of climate variables but also in the changes in their annual cycles (seasonality), especially in the regions outside the tropics. Changes in the timing of seasons, especially the wind season, have gained much attention worldwide in recent decade or so. We introduce long-range correlated surrogate data to Ensemble Empirical Mode Decomposition method, which represent the statistic characteristics of data better than white noise. The new method we named Ensemble Empirical Mode Decomposition with Long-range Correlated noise (EEMD-LRC) and applied to 600 station wind speed records. This new method is applied to investigate the trend in the amplitude of the annual cycle of China's daily mean surface wind speed for the period 1971-2005. The amplitude of seasonal variation decrease significantly in the past half century over China, which can be well explained by Annual Cycle component from EEMD-LRC. Furthermore, the phase change of annual cycle lead to strongly shorten of wind season in spring, and corresponding with strong windy day frequency change over Northern China.

MHD activity in the ISX-B tokamak: experimental results and theoretical interpretation

Energy Technology Data Exchange (ETDEWEB)

Carreras, B.A.; Dunlap, J.L.; Bell, J.D.; Charlton, L.A.; Cooper, W.A.; Dory, R.A.; Hender, T.C.; Hicks, H.R.; Holmes, J.A.; Lynch, V.E.

1982-01-01

The observed spectrum of MHD fluctuations in the ISX-B tokamak is clearly dominated by the n=1 mode when the q=1 surface is in the plasma. This fact agrees well with theoretical predictions based on 3-D resistive MHD calculations. They show that the (m=1; n=1) mode is then the dominant instability. It drives other n=1 modes through toroidal coupling and n>1 modes through nonlinear couplings. These theoretically predicted mode structures have been compared in detail with the experimentally measured wave forms (using arrays of soft x-ray detectors). The agreement is excellent. More detailed comparisons between theory and experiment have required careful reconstructions of the ISX-B equilibria. The equilibria so constructed have permitted a precise evaluation of the ideal MHD stability properties of ISX-B. The present results indicate that the high ..beta.. ISX-B equilibria are marginally stable to finite eta ideal MHD modes. The resistive MHD calculations also show that at finite ..beta.. there are unstable resistive pressure driven modes.

Influence of the nuclear matter equation of state on the r-mode instability using the finite-range simple effective interaction

Science.gov (United States)

Pattnaik, S. P.; Routray, T. R.; Viñas, X.; Basu, D. N.; Centelles, M.; Madhuri, K.; Behera, B.

2018-05-01

The characteristic physical properties of rotating neutron stars under the r-mode oscillation are evaluated using the finite-range simple effective interaction. Emphasis is given on examining the influence of the stiffness of both the symmetric and asymmetric parts of the nuclear equation of state on these properties. The amplitude of the r-mode at saturation is calculated using the data of particular neutron stars from the considerations of ‘spin equilibrium’ and ‘thermal equilibrium’. The upper limit of the r-mode saturation amplitude is found to lie in the range 10‑8–10‑6, in agreement with the predictions of earlier work.

Soft modes and structural phase transitions

Energy Technology Data Exchange (ETDEWEB)

Venkataraman, G [Reactor Research Centre, Kalpakkam (India)

1979-12-01

A survey of soft modes and their relationship to structural phase transitions is presented. After introducing the concept of a soft mode, the origin of softening is considered from a lattice-dynamical point. The Landau theory approach to structural transitions is then discussed, followed by a generalisation of the soft-mode concept through the use of the dynamic order-parameter susceptibility. The relationship of soft modes to broken symmetry is also examined. Experimental results for several classes of crystals are next presented, bringing out various features such as the co-operative Jahn-Teller effect. The survey concludes with a discussion of the central peak, touching upon both the experimental results and the theoretical speculations.

Effect of dynamical phase on the resonant interaction among tsunami edge wave modes

Science.gov (United States)

Geist, Eric L.

2018-01-01

Different modes of tsunami edge waves can interact through nonlinear resonance. During this process, edge waves that have very small initial amplitude can grow to be as large or larger than the initially dominant edge wave modes. In this study, the effects of dynamical phase are established for a single triad of edge waves that participate in resonant interactions. In previous studies, Jacobi elliptic functions were used to describe the slow variation in amplitude associated with the interaction. This analytical approach assumes that one of the edge waves in the triad has zero initial amplitude and that the combined phase of the three waves φ = θ1 + θ2 − θ3 is constant at the value for maximum energy exchange (φ = 0). To obtain a more general solution, dynamical phase effects and non-zero initial amplitudes for all three waves are incorporated using numerical methods for the governing differential equations. Results were obtained using initial conditions calculated from a subduction zone, inter-plate thrust fault geometry and a stochastic earthquake slip model. The effect of dynamical phase is most apparent when the initial amplitudes and frequencies of the three waves are within an order of magnitude. In this case, non-zero initial phase results in a marked decrease in energy exchange and a slight decrease in the period of the interaction. When there are large differences in frequency and/or initial amplitude, dynamical phase has less of an effect and typically one wave of the triad has very little energy exchange with the other two waves. Results from this study help elucidate under what conditions edge waves might be implicated in late, large-amplitude arrivals.

THE THEORETICAL FOUNDATIONS OF VIBRATION DAMPERS BY ROLLING FRICTION

Directory of Open Access Journals (Sweden)

L. M. Bondarenko

2015-06-01

Full Text Available Purpose. There are some unresolved issues in vibration damping – the lack of engineering calculations for the vibration dampers by rolling friction; the absence of evidence of their application appropriateness. Considering this fact, the authors suggest to prove that the dampers based on rolling friction, are similar in rate of oscillation damping by hydraulic shock absorbers. At the same time, they are easier for the hydraulic design, and easily amenable to manual adjustment, both in automatic and manual mode. Methodology. Fixed techniques of practice in order to determine amplitudes of the oscillations of a shock absorber led to a predetermined result and will apply this theory in the calculation of other vibration dampers. Findings. Analysis of the formulas and graphs leads to the following conclusions and recommendations: 1 the nature of the oscillation damping at vibration dampers by rolling friction is close to their decay in the viscous resistance; 2 when conducting the necessary experiments the shock absorber rolling can be recommended as alternatives to hydraulic ones. The research results of this task will help implement the new trend in reduction of dynamic loads in vehicles. Originality. With the help of theoretical curves to determine the coefficients of rolling friction the dependences for determining the amplitudes of the oscillations in the vertical movement of cargo were obtained. At the same time, the previously proposed analytical dependence for determining the coefficient of rolling friction contains only conventional mechanical constants of the contacting bodies and there geometrical dimensions. Practical value. Due to the existing well-known disadvantages of hydraulic shock absorbers it would be logical to apply shock absorbers that are technologically convenient in manufacturing and easy to adjust the damping rate. The proposed theory can be used in the design of shock absorbers rolling as an alternative to the hydraulic

Parametric resonance of intrinsic localized modes in coupled cantilever arrays

International Nuclear Information System (INIS)

Kimura, Masayuki; Matsushita, Yasuo; Hikihara, Takashi

2016-01-01

In this study, the parametric resonances of pinned intrinsic localized modes (ILMs) were investigated by computing the unstable regions in parameter space consisting of parametric excitation amplitude and frequency. In the unstable regions, the pinned ILMs were observed to lose stability and begin to fluctuate. A nonlinear Klein–Gordon, Fermi–Pasta–Ulam-like, and mixed lattices were investigated. The pinned ILMs, particularly in the mixed lattice, were destabilized by parametric resonances, which were determined by comparing the shapes of the unstable regions with those in the Mathieu differential equation. In addition, traveling ILMs could be generated by parametric excitation. - Highlights: • Destabilization of intrinsic localized modes (ILMs) by parametric excitation is investigated for FPU, NKG, and mixed lattices. • Frequency and amplitude of parametric excitation is determined based on characteristic multipliers of ILMs. • Unstable regions for the mixed lattice case show very similar shape to those of the Mathieu equation. • ILMs become unstable by causing parametric resonance.

Parametric resonance of intrinsic localized modes in coupled cantilever arrays

Energy Technology Data Exchange (ETDEWEB)

Kimura, Masayuki, E-mail: kimura.masayuki.8c@kyoto-u.ac.jp [Department of Electrical Engineering, Kyoto University, Katsura, Nishikyo-ku, Kyoto 615-8510 (Japan); Matsushita, Yasuo [Advanced Mathematical Institute, Osaka City University, 3-3-138 Sughimoto, Sumiyoshi-ku, Osaka 558-8585 (Japan); Hikihara, Takashi [Department of Electrical Engineering, Kyoto University, Katsura, Nishikyo-ku, Kyoto 615-8510 (Japan)

2016-08-19

In this study, the parametric resonances of pinned intrinsic localized modes (ILMs) were investigated by computing the unstable regions in parameter space consisting of parametric excitation amplitude and frequency. In the unstable regions, the pinned ILMs were observed to lose stability and begin to fluctuate. A nonlinear Klein–Gordon, Fermi–Pasta–Ulam-like, and mixed lattices were investigated. The pinned ILMs, particularly in the mixed lattice, were destabilized by parametric resonances, which were determined by comparing the shapes of the unstable regions with those in the Mathieu differential equation. In addition, traveling ILMs could be generated by parametric excitation. - Highlights: • Destabilization of intrinsic localized modes (ILMs) by parametric excitation is investigated for FPU, NKG, and mixed lattices. • Frequency and amplitude of parametric excitation is determined based on characteristic multipliers of ILMs. • Unstable regions for the mixed lattice case show very similar shape to those of the Mathieu equation. • ILMs become unstable by causing parametric resonance.

Optical property of few-mode fiber with non-uniform refractive index for cylindrical vector beam generation

Science.gov (United States)

Li, Hongye; Wan, Hongdan; Zhang, Zuxing; Sun, Bing; Zhang, Lin

2016-10-01

This paper investigates optical properties of few-mode fiber with non-uniform refractive index, namely: the few mode fiber with U-shape refractive index and the two-mode and four-mode few-mode fiber with bent radius. Finite element method is used to analyze the mode distributions based on their non-uniform refractive index. Effective mode control can be achieved through these few mode fibers to achieve vector beam generation. Finally, reflection spectra of a few-mode fiber Bragg grating are calculated theoretically and then measured under different bending conditions. Experimental results are in good accordance with the theoretical ones. These few mode fibers show potential applications in generation of cylindrical vector beam both for optical lasing and sensing systems.

Comprehensive comparison of macro-strain mode and displacement mode based on different sensing technologies

Science.gov (United States)

Hong, Wan; Zhang, Jian; Wu, Gang; Wu, Zhishen

2015-01-01

A comprehensive comparison of macro-strain mode and displacement mode obtained from distributed macro-strain sensing and high-density point sensing (such as accelerometers) technologies is presented in this paper. Theoretical derivation reveals that displacement mode shape from accelerometers and modal macro-strain from distributed macro-strain sensors can be converted into each other. However, it is realized that displacement mode shape as global behavior of a structure can still be calculated with high-precision from modal macro-strain considering measurement errors in practical monitoring, whereas modal macro-strain can hardly be accurately achieved from displacement mode shape when signals are corrupted with noise in practical monitoring. Simulation and experiment results show that the calculated displacement mode shapes are very close to the actual ones even if the noise level reaches 5%. Meanwhile, damage index using measured modal macro-strain is still effective when the measurements are corrupted with 5% noise which is reliable for damage detection in practical monitoring. Calculating modal macro-strain from noise-polluted displacement mode shape will cause an unacceptable error if the noise level reaches only 0.5%, which has been verified in the simulation.

A 900-channel coincidence pulse-amplitude analyser; Selecteur d'amplitudes d'impulsions a coincidence a trois dimensions; Devyatisotkanal'nyj amplitudnyj analizator impul'sov sovpadeniya; Analizador de amplitud de impulsos de coincidencia con 900 canales

Energy Technology Data Exchange (ETDEWEB)

Alexander, T K; Robinson, L B [Atomic Energy of Canada Limited, Chalk River, Ontario (Canada)

1962-04-15

An analyser designed for correlation studies of pulse-height distributions from two scintillation counters is described. The analyser consists of two separate transistorized units; a dual-channel analogue-to-digital encoder and a 900-channel, 2{sup 16}-per-channel capacity ferrite-core store. The display and control unit for the instrument is separate and can be situated away from the analyser. The analysis mode of operation for coincident pulses on the A and B inputs of the encoder can be selected to be 30 by 30, 100 by 9 or 300 channels by 3 distributions. In the last two modes the base lines and the widths of the pulse-amplitude ''windows'' on distribution A can be selected by the operator. With 100 channels for pulse-amplitude analysis, eight ''windows'' in distribution A define eight groups of 100 channels for the B distributions. In this case we have, in effect, one 100-channel analyser for distribution A and eight separate 100-channel analysers to which B can be routed. A description of the basic circuits of the encoder and the logic of the store and display units is given. (author) [French] Le memoire decrit un selecteur concu pour etudier la correlation des distributions en amplitude des impulsions fournies par deux compteurs a scintillations. L'analyseur se compose de deux parties distinctes transistorisees: un codeur analogique/numerique a deux voies et une memoire a ferrites, a 900 canaux d'une capacite de 2{sup 16} par canal. Les tableaux d'enregistrement et les commandes de l'appareil forment un element autonome qui peut etre installe a une certaine distance du selecteur. Pour l'analyse des impulsions de coincidence aux entrees A et B du codeur, on peut combiner les canaux de trois manieres differentes: 30 x 30, 100 x 9 ou 300 x 3. Dans les deux derniers cas, l'operateur peut choisir les lignes de base et la largeur des des amplitudes d'impulsion pour la distribution A. Lorsque l'analyse de l'amplitude d'impulsion se fait avec 100 canaux

Theoretical perspectives on strange physics

International Nuclear Information System (INIS)

Ellis, J.

1983-04-01

Kaons are heavy enough to have an interesting range of decay modes available to them, and light enough to be produced in sufficient numbers to explore rare modes with satisfying statistics. Kaons and their decays have provided at least two major breakthroughs in our knowledge of fundamental physics. They have revealed to us CP violation, and their lack of flavor-changing neutral interactions warned us to expect charm. In addition, K 0 -anti K 0 mixing has provided us with one of our most elegant and sensitive laboratories for testing quantum mechanics. There is every reason to expect that future generations of kaon experiments with intense sources would add further to our knowledge of fundamental physics. This talk attempts to set future kaon experiments in a general theoretical context, and indicate how they may bear upon fundamental theoretical issues. A survey of different experiments which would be done with an Intense Medium Energy Source of Strangeness, including rare K decays, probes of the nature of CP isolation, μ decays, hyperon decays and neutrino physics is given

Two- and three-loop amplitudes in covariant loop calculus

International Nuclear Information System (INIS)

Roland, K.

1988-04-01

We study 2- and 3-loop vacuum-amplitudes for the closed bosonic string. We compare two sets of expressions for the corresponding density on moduli space: One, based on the covariant Reggeon loop calculus (where modular invariance is not manifest). The other, based on analytic geometry. We want to prove identity between the two sets of expressions. Quite apart from demonstrating modular invariance of the Reggeon results, this would in itself be a remarkable mathematical feature. Identity is established to 'high' order in some moduli and exactly in others. The expansions reveal an essentially number-theoretical structure. Agreement is found only by exploiting the connection between the 4 Jacobi θ-functions and number theory. (orig.)

Two- and three-loop amplitudes in covariant loop calculus

International Nuclear Information System (INIS)

Roland, K.

1989-01-01

We study two- and three-loop vacuum amplitudes for the closed bosonic string. We compare two sets of expressions for the corresponding density on moduli space. One is based on the covariant reggeon loop calculus (where modular invariance is not manifest). The other is based on analytic geometry. We want to prove identity between the two sets of expressions. Quite apart from demonstrating modular invariance of the reggeon results, this would in itself be a remarkable mathematical feature. Identity is established to ''high'' order in some moduli and exactly in others. The expansions reveal an essentially number-theoretic structure. Agreement is found only by exploiting the connection between the four Jacobi θ-functions and number theory. (orig.)

New relations for Einstein–Yang–Mills amplitudes

International Nuclear Information System (INIS)

Stieberger, Stephan; Taylor, Tomasz R.

2016-01-01

We obtain new relations between Einstein–Yang–Mills (EYM) amplitudes involving N gauge bosons plus a single graviton and pure Yang–Mills amplitudes involving N gauge bosons plus one additional vector boson inserted in a way typical for a gauge boson of a “spectator” group commuting with the group associated to original N gauge bosons. We show that such EYM amplitudes satisfy U(1) decoupling relations similar to Kleiss–Kuijf relations for Yang–Mills amplitudes. We consider a D-brane embedding of EYM amplitudes in the framework of disk amplitudes involving open and closed strings. A new set of monodromy relations is derived for mixed open–closed amplitudes with one closed string inserted on the disk world-sheet and a number of open strings at the boundary. These relations allow expressing the latter in terms of pure open string amplitudes and, in the field-theory limit, they yield the U(1) decoupling relations for EYM amplitudes.

Oblique propagation of electron thermal modes below the electron plasma frequency without boundary effects

International Nuclear Information System (INIS)

Ohnuma, T.; Watanabe, T.; Sanuki, H.

1981-08-01

Propagation characteristics and refractive effects of an oblique electron thermal mode without boundary effects below the electron plasma frequency are studied experimentally and theoretically in an inhomogeneous magnetized plasma. The behavior of this mode observed experimentally was confirmed by the theoretical analysis based on a new type of ray theory. (author)

Large-amplitude internal tides, solitary waves, and turbulence in the central Bay of Biscay

Science.gov (United States)

Xie, X. H.; Cuypers, Y.; Bouruet-Aubertot, P.; Ferron, B.; Pichon, A.; LourençO, A.; Cortes, N.

2013-06-01

and fine-scale measurements collected in the central Bay of Biscay during the MOUTON experiment are analyzed to investigate the dynamics of internal waves and associated mixing. Large-amplitude internal tides (ITs) that excite internal solitary waves (ISWs) in the thermocline are observed. ITs are dominated by modes 3 and 4, while ISWs projected on mode 1 that is trapped in the thermocline. Therein, ITs generate a persistent narrow shear band, which is strongly correlated with the enhanced dissipation rate in the thermocline. This strong dissipation rate is further reinforced in the presence of ISWs. Dissipation rates during the period without ISWs largely agree with the MacKinnon-Gregg scaling proposed for internal wavefields dominated by a low-frequency mode, while they show poor agreement with the Gregg-Henyey parameterization valid for internal wavefields close to the Garrett-Munk model. The agreement with the MacKinnon-Gregg scaling is consistent with the fact that turbulent mixing here is driven by the low-frequency internal tidal shear.

Joint Inversion of Phase and Amplitude Data of Surface Waves for North American Upper Mantle

Science.gov (United States)

Hamada, K.; Yoshizawa, K.

2015-12-01

For the reconstruction of the laterally heterogeneous upper-mantle structure using surface waves, we generally use phase delay information of seismograms, which represents the average phase velocity perturbation along a ray path, while the amplitude information has been rarely used in the velocity mapping. Amplitude anomalies of surface waves contain a variety of information such as anelastic attenuation, elastic focusing/defocusing, geometrical spreading, and receiver effects. The effects of elastic focusing/defocusing are dependent on the second derivative of phase velocity across the ray path, and thus, are sensitive to shorter-wavelength structure than the conventional phase data. Therefore, suitably-corrected amplitude data of surface waves can be useful for improving the lateral resolution of phase velocity models. In this study, we collect a large-number of inter-station phase velocity and amplitude ratio data for fundamental-mode surface waves with a non-linear waveform fitting between two stations of USArray. The measured inter-station phase velocity and amplitude ratios are then inverted simultaneously for phase velocity maps and local amplification factor at receiver locations in North America. The synthetic experiments suggest that, while the phase velocity maps derived from phase data only reflect large-scale tectonic features, those from phase and amplitude data tend to exhibit better recovery of the strength of velocity perturbations, which emphasizes local-scale tectonic features with larger lateral velocity gradients; e.g., slow anomalies in Snake River Plain and Rio Grande Rift, where significant local amplification due to elastic focusing are observed. Also, the spatial distribution of receiver amplification factor shows a clear correlation with the velocity structure. Our results indicate that inter-station amplitude-ratio data can be of help in reconstructing shorter-wavelength structures of the upper mantle.

Observations of neutral beam and ICRF tail ion losses due to Alfven modes in TFTR

International Nuclear Information System (INIS)

Darrow, D.S.; Zweben, S.J.; Chang, Z.

1996-04-01

Fast ion losses resulting from MHD modes at the Alfven frequency, such as the TAE, have been observed in TFTR. The modes have been driven both by neutral beam ions, at low B T , and by H-minority ICRF tail ions at higher B T . The measurements indicate that the loss rate varies linearly with the mode amplitude, and that the fast ion losses during the mode activity can be significant, e.g. up to 10% of the input power is lost in the worst case

Motivic amplitudes and cluster coordinates

International Nuclear Information System (INIS)

Golden, J.K.; Goncharov, A.B.; Spradlin, M.; Vergu, C.; Volovich, A.

2014-01-01

In this paper we study motivic amplitudes — objects which contain all of the essential mathematical content of scattering amplitudes in planar SYM theory in a completely canonical way, free from the ambiguities inherent in any attempt to choose particular functional representatives. We find that the cluster structure on the kinematic configuration space Conf n (ℙ 3 ) underlies the structure of motivic amplitudes. Specifically, we compute explicitly the coproduct of the two-loop seven-particle MHV motivic amplitude A 7,2 M and find that like the previously known six-particle amplitude, it depends only on certain preferred coordinates known in the mathematics literature as cluster X-coordinates on Conf n (ℙ 3 ). We also find intriguing relations between motivic amplitudes and the geometry of generalized associahedrons, to which cluster coordinates have a natural combinatoric connection. For example, the obstruction to A 7,2 M being expressible in terms of classical polylogarithms is most naturally represented by certain quadrilateral faces of the appropriate associahedron. We also find and prove the first known functional equation for the trilogarithm in which all 40 arguments are cluster X-coordinates of a single algebra. In this respect it is similar to Abel’s 5-term dilogarithm identity

Modelling and mitigation of wheel squeal noise amplitude

Science.gov (United States)

Meehan, Paul A.; Liu, Xiaogang

2018-01-01

The prediction of vibration amplitude and sound pressure level of wheel squeal noise is investigated using a concise mathematical model that is verified with measurements from both a rolling contact two disk test rig and a field case study. The model is used to perform an energy-based analysis to determine a closed form solution to the steady state limit cycle amplitude of creep and vibration oscillations during squealing. The analytical solution compares well with a numerical solution using an experimentally tuned creep curve with full nonlinear shape. The predicted squeal sound level trend also compares well with that recorded at various crabbing velocities (proportional to angle of attack) for the test rig at different rolling speeds. In addition, further verification is performed against many field recordings of wheel squeal on a sharp curve of 300 m. A comparison with a simplified modified result from Rudd [1] is also provided and highlights the accuracy and advantages of the present efficient model. The analytical solution provides insight into why the sound pressure level of squeal noise increases with crabbing velocity (or angle of attack) as well as how the amplitude is affected by the critical squeal parameters including a detailed investigation of modal damping. Finally, the efficient model is used to perform a parametric investigation into means of achieving a 6 dB decrease in squeal noise. The results highlight the primary importance of crabbing velocity (and angle of attack) as well as the creep curve parameters that may be controlled using third body control (ie friction modifiers). The results concur with experimental and field observations and provide important theoretical insight into the useful mechanisms of mitigating wheel squeal and quantifying their relative merits.

School of Analytic Computing in Theoretical High-Energy Physics

CERN Document Server

2015-01-01

In recent years, a huge progress has been made on computing rates for production processes of direct relevance to experiments at the Large Hadron Collider (LHC). Crucial to that remarkable advance has been our understanding and ability to compute scattering amplitudes and cross sections. The aim of the School is to bring together young theorists working on the phenomenology of LHC physics with those working in more formal areas, and to provide them the analytic tools to compute amplitudes in gauge theories. The school is addressed to Ph.D. students and post-docs in Theoretical High-Energy Physics. 30 hours of lectures and 4 hours of tutorials will be delivered over the 6 days of the School.

Theoretical study of the Raman active CDW gap mode in manganites

International Nuclear Information System (INIS)

Rout, G C; Panda, Saswati; Behera, S N

2010-01-01

We report here the microscopic theory of the Raman spectra of the colossal magnetoresistive (CMR) manganite systems. The system is described by a model Hamiltonian consisting of the double exchange interaction in addition to the charge ordering interaction in the e g band and spin-spin interaction among the t 2g core electrons. Further the phonon coupling to the conduction electron density is incorporated in the model for phonons in the harmonic approximation. The spectral density function for the Raman spectra is calculated from the imaginary part of the phonon Green's function. The calculated spectra display the Raman active bare phonon peak along with the charge ordering peak. The magnetic field and temperature dependence of the charge ordering peak agrees with the 480 cm -1 JT mode observed in the experiments. The evolution of this mode is investigated in the report.

Physics of the H-mode

International Nuclear Information System (INIS)

Hinton, F.L.; Chu, M.S.; Dominguez, R.R.

1985-01-01

A theoretical picture of the H-mode is proposed which explains some of the most important features of this good confinement mode in neutral beam heated plasmas with divertors. From consideration of the transport through the separatrix and along the open field lines outside the separatrix, as well as the stability of the plasma inside the separatrix, we show that a bifurcation in the operating parameters is possible. At high edge temperatures, very large particle confinement times are possible because of the Ware pinch. The transport of particles and heat along the open field lines to the divertor region depends on temperature in a non-monotonic way, and the bifurcation of the thermal equilibrium which is implied may correspond to the L- to H-mode transition. The improvement of the interior confinement in the H-mode, when the edge temperature is higher, is shown to follow from the tearing mode stability properties of current profiles with pedestals. (author)

Two Photon Distribution Amplitudes

International Nuclear Information System (INIS)

El Beiyad, M.; Pire, B.; Szymanowski, L.; Wallon, S.

2008-01-01

The factorization of the amplitude of the process γ*γ→γγ in the low energy and high photon virtuality region is demonstrated at the Born order and in the leading logarithmic approximation. The leading order two photon (generalized) distribution amplitudes exhibit a characteristic ln Q 2 behaviour and obey new inhomogeneous evolution equations

Fundamental uncertainty in the BAO scale from isocurvature modes

Energy Technology Data Exchange (ETDEWEB)

Zunckel, C., E-mail: caroline.zunckel@gmail.co [Astrophysics and Cosmology Research Unit, School of Mathematical Sciences, University of Kwazulu-Natal, Durban 4041 (South Africa); Astrophysics Department, Princeton University, Peyton Hall, 4 Ivy Lane, NJ 08544 (United States); Okouma, P. [Department of Maths and Applied Maths, University of Cape Town, Rondebosch 7701, Cape Town (South Africa); Centre for High Performance Computing, CSIR Campus, 15 Lower Hope St., Rosebank, Cape Town (South Africa); South African Astronomical Observatory, Observatory, Cape Town (South Africa); African Institute for Mathematical Sciences, 6-8 Melrose Road, Muizenberg, Cape Town (South Africa); Muya Kasanda, S.; Moodley, K. [Astrophysics and Cosmology Research Unit, School of Mathematical Sciences, University of Kwazulu-Natal, Durban 4041 (South Africa); Centre for High Performance Computing, CSIR Campus, 15 Lower Hope St., Rosebank, Cape Town (South Africa); Bassett, B.A. [Department of Maths and Applied Maths, University of Cape Town, Rondebosch 7701, Cape Town (South Africa); Centre for High Performance Computing, CSIR Campus, 15 Lower Hope St., Rosebank, Cape Town (South Africa); South African Astronomical Observatory, Observatory, Cape Town (South Africa); African Institute for Mathematical Sciences, 6-8 Melrose Road, Muizenberg, Cape Town (South Africa)

2011-02-14

Small fractions of isocurvature perturbations correlated with the dominant adiabatic mode are shown to be a significant primordial systematic for Baryon Acoustic Oscillation (BAO) surveys which must be accounted for in future surveys. Isocurvature modes distort the standard ruler distance by broadening and shifting the peak in the galaxy correlation function. While a single isocurvature mode does not significantly degrade dark energy constraints, the general case with multiple isocurvature modes leads to biases that exceed 7{sigma} on average in the dark energy parameters even for isocurvature amplitudes undetectable by PLANCK. Accounting for all isocurvature modes corrects for this bias but degrades the dark energy figure of merit by at least 50% in the case of the BOSS experiment. However the BAO data in turn provides significantly stronger constraints on the nature of the primordial perturbations. Future large galaxy surveys will thus be powerful probes of exotic physics in the early Universe in addition to helping pin down the nature of dark energy.

Scissors mode with a simple Hamiltonians

International Nuclear Information System (INIS)

Bal'butsev, E.B.; ); Shuk, P.

2002-01-01

The system of the motion bound equation for the nucleus angular moment and its quadrupole moments in the coordinate and pulse spaces is derived from the equation of the Hartree-Fock time-dependent theory. The formulae for the energy, B(M1)- and B(E2)-factors of the scissors mode are obtained in the approximation of low amplitudes; the physical nature of the event is explained. The calculation results qualitatively agree with the experiment [ru

Robust fiber optic flexure sensor exploiting mode coupling in few-mode fiber

Science.gov (United States)

Nelsen, Bryan; Rudek, Florian; Taudt, Christopher; Baselt, Tobias; Hartmann, Peter

2015-05-01

Few-mode fiber (FMF) has become very popular for use in multiplexing telecommunications data over fiber optics. The simplicity of producing FMF and the relative robustness of the optical modes, coupled with the simplicity of reading out the information make this fiber a natural choice for communications. However, little work has been done to take advantage of this type of fiber for sensors. Here, we demonstrate the feasibility of using FMF properties as a mechanism for detecting flexure by exploiting mode coupling between modes when the cylindrical symmetry of the fiber is perturbed. The theoretical calculations shown here are used to understand the coupling between the lowest order linearly polarized mode (LP01) and the next higher mode (LP11x or LP11y) under the action of bending. Twisting is also evaluated as a means to detect flexure and was determined to be the most reliable and effective method when observing the LP21 mode. Experimental results of twisted fiber and observations of the LP21 mode are presented here. These types of fiber flexure sensors are practical in high voltage, high magnetic field, or high temperature medical or industrial environments where typical electronic flexure sensors would normally fail. Other types of flexure measurement systems that utilize fiber, such as Rayleigh back-scattering [1], are complicated and expensive and often provide a higher-than necessary sensitivity for the task at hand.

Kinetic slow mode-type solitons

Directory of Open Access Journals (Sweden)

K. Baumgärtel

2005-01-01

Full Text Available One-dimensional hybrid code simulations are presented, carried out in order both to study solitary waves of the slow mode branch in an isotropic, collisionless, medium-β plasma (βi=0.25 and to test the fluid based soliton interpretation of Cluster observed strong magnetic depressions (Stasiewicz et al., 2003; Stasiewicz, 2004 against kinetic theory. In the simulations, a variety of strongly oblique, large amplitude, solitons are seen, including solitons with Alfvenic polarization, similar to those predicted by the Hall-MHD theory, and robust, almost non-propagating, solitary structures of slow magnetosonic type with strong magnetic field depressions and perpendicular ion heating, which have no counterpart in fluid theory. The results support the soliton-based interpretation of the Cluster observations, but reveal substantial deficiencies of Hall-MHD theory in describing slow mode-type solitons in a plasma of moderate beta.

Effects of initial radius of the interface and Atwood number on nonlinear saturation amplitudes in cylindrical Rayleigh-Taylor instability

International Nuclear Information System (INIS)

Liu, Wanhai; Yu, Changping; Li, Xinliang

2014-01-01

Nonlinear saturation amplitudes (NSAs) of the first two harmonics in classical Rayleigh-Taylor instability (RTI) in cylindrical geometry for arbitrary Atwood numbers have been analytically investigated considering nonlinear corrections up to the fourth-order. The NSA of the fundamental mode is defined as the linear (purely exponential) growth amplitude of the fundamental mode at the saturation time when the growth of the fundamental mode (first harmonic) is reduced by 10% in comparison to its corresponding linear growth, and the NSA of the second harmonic can be obtained in the same way. The analytic results indicate that the effects of the initial radius of the interface (r 0 ) and the Atwood number (A) play an important role in the NSAs of the first two harmonics in cylindrical RTI. On the one hand, the NSA of the fundamental mode first increases slightly and then decreases quickly with increasing A. For given A, the smaller the r 0 /λ (with λ perturbation wavelength) is, the larger the NSA of the fundamental mode is. When r 0 /λ is large enough (r 0 ≫λ), the NSA of the fundamental mode is reduced to the prediction of previous literatures within the framework of third-order perturbation theory [J. W. Jacobs and I. Catton, J. Fluid Mech. 187, 329 (1988); S. W. Haan, Phys. Fluids B 3, 2349 (1991)]. On the other hand, the NSA of the second harmonic first decreases quickly with increasing A, reaching a minimum, and then increases slowly. Furthermore, the r 0 can reduce the NSA of the second harmonic for arbitrary A at r 0 ≲2λ while increase it for A ≲ 0.6 at r 0 ≳2λ. Thus, it should be included in applications where the NSA has a role, such as inertial confinement fusion ignition target design

ASTEROSEISMOLOGY OF THE NEARBY SN II PROGENITOR RIGEL. II. {epsilon}-MECHANISM TRIGGERING GRAVITY-MODE PULSATIONS?

Energy Technology Data Exchange (ETDEWEB)

Moravveji, Ehsan [Department of Physics, Institute for Advanced Studies in Basic Sciences (IASBS), Zanjan 45137-66731 (Iran, Islamic Republic of); Moya, Andres [Departamento de Astrofisica, Centro de Astrobiologia (INTA-CSIC), P.O. Box 78, 28691 Villanueva de la Canada, Madrid (Spain); Guinan, Edward F., E-mail: moravveji@iasbs.ac.ir [Department of Astronomy, Villanova University, 800 Lancaster Avenue, Villanova, PA (United States)

2012-04-10

The cores of luminous B- and A-type (BA) supergiant stars are the seeds of later core-collapse supernovae. Thus, constraining the near-core conditions in this class of stars can place tighter constraints on the size, mass, and chemical composition of supernova remnants. Asteroseismology of these massive stars is one possible approach into such investigations. Recently, Moravveji et al. in 2012 (hereafter Paper I) extracted 19 significant frequencies from a 6-year radial velocity monitoring of Rigel ({beta} Ori, B8 Ia). The periods they determined broadly range from 1.22 to 74.74 days. Based on our differentially rotating stellar structure and evolution model, Rigel, at its current evolutionary state, is undergoing core He burning and shell H burning. Linear fully non-adiabatic non-radial stability analyses result in the excitation of a dense spectrum of non-radial gravity-dominated mixed modes. The fundamental radial mode (l = 0) and its overtones are all stable. When the hydrogen-burning shell is located even partially in the radiative zone, a favorable condition for destabilization of g-modes through the so-called {epsilon}-mechanism becomes viable. Only those g-modes that have high relative amplitudes in the hydrogen-burning (radiative) zone can survive the strong radiative damping. From the entire observed range of variability periods of Rigel (found in Paper I), and based on our model, only those modes with periods ranging between 21 and 127 days can be theoretically explained by the {epsilon}-mechanism. The origin of the short-period variations (found in Paper I) still remains unexplained. Because Rigel is similar to other massive BA supergiants, we believe that the {epsilon}-mechanism may be able to explain the long-period variations in {alpha} Cygni class of pulsating stars.

Narrow-band modulation of semiconductor lasers at millimeter wave frequencies (7100 GHz) by mode locking

International Nuclear Information System (INIS)

Lau, K.Y.

1990-01-01

This paper reports on the possibility of mode locking a semiconductor laser at millimeter wave frequencies approaching and beyond 100 GHz which was investigated theoretically and experimentally. It is found that there are no fundamental theoretical limitations in mode locking at frequencies below 100 GHz. AT these high frequencies, only a few modes are locked and the output usually takes the form of a deep sinusoidal modulation which is synchronized in phase with the externally applied modulation at the intermodal heat frequency. This can be regarded for practical purposes as a highly efficient means of directly modulating an optical carrier over a narrow band at millimeter wave frequencies. Both active and passive mode locking are theoretically possible. Experimentally, predictions on active mode locking have been verified in prior publications up to 40 GHz. For passive mode locking, evidence consistent with passive mode locking was observed in an inhomogeneously pumped GaAIAs laser at a frequency of approximately 70 GHz. A large differential gain-absorption ratio such as that present in an inhomogeneously pumped single quantum well laser is necessary for pushing the passive mode-locking frequency beyond 100 GHz

Amplitude modulation of atomic wave functions. Final report

Energy Technology Data Exchange (ETDEWEB)

NONE

1998-11-01

The major theoretical advance has been to show that one can modulate Rydberg wave functions using either of two methods: (1) the amplitude modulation technique which depends on autoionization to deplete part of the wave function, or (2) a phase modulation method, which uses a change in the core potential to create a localized phase shift in the wave function. Essentially, these two methods can both be seen as using the core potential to change the Rydberg wave function, using the imaginary part of the potential to do amplitude modulation, or using the real part of the potential to do phase modulation. This work will be published as the authors acquire experimental results which show the differences between the two methods. One of the results of this theoretical study is that the initial proposal to study Barium 6snd states had a significant flaw. Neither the autoionization time, nor the quantum defect shifts are very large in these cases. This means that the modulation is relatively small. This shows itself primarily in the difficulty of seeing significant population redistribution into different 6snd states. The authors intend to correct this in the next funding cycle either: (a) by using the more quickly decaying Ba 6pnf states to modulate 6snd states, or (b) by using Sr 5 snd states, as outlined in this report. Their first, low power experiments are complete. These experiments have used two pulses to do a temporal version of the Ramsey separated oscillatory fields excitation. The two pulses are generated by passing the single pulse through a Michelson-Morley interferometer, which is computer controlled to sweep one arm through 2.5 {micro}m in steps of 10 nm. The second pulse`s excitation interferes with that of the first pulse, and so the total excitation has a sinusoidal variation (with a time period equal to the optical period) on top of a constant background. The amplitude of the total variation should decay at half of the rate decay rate of the autoionizing

Nonlinear interaction between a pair of oblique modes in a supersonic mixing layer: Long-wave limit

Science.gov (United States)

Balsa, Thomas F.; Gartside, James

1995-01-01

The nonlinear interaction between a pair of symmetric, oblique, and spatial instability modes is studied in the long-wave limit using asymptotic methods. The base flow is taken to be a supersonic mixing layer whose Mach number is such that the corresponding vortex sheet is marginally stable according to Miles' criterion. It is shown that the amplitude of the mode obeys a nonlinear integro-differential equation. Numerical solutions of this equation show that, when the obliqueness angle is less than pi/4, the effect of the nonlinearity is to enhance the growth rate of the instability. The solution terminates in a singularity at a finite streamwise location. This result is reminiscent of that obtained in the vicinity of the neutral point by other authors in several different types of flows. On the other hand, when the obliqueness angle is more than pi/4, the streamwise development of the amplitude is characterized by a series of modulations. This arises from the fact that the nonlinear term in the amplitude equation may be either stabilizing or destabilizing, depending on the value of the streamwise coordinate. However, even in this case the amplitude of the disturbance increases, though not as rapidly as in the case for which the angle is less than pi/4. Quite generally then, the nonlinear interaction between two oblique modes in a supersonic mixing layer enhances the growth of the disturbance.

Turbulent edge transport in the Princeton Beta Experiment-Modified high confinement mode

Science.gov (United States)

Tynan, G. R.; Schmitz, L.; Blush, L.; Boedo, J. A.; Conn, R. W.; Doerner, R.; Lehmer, R.; Moyer, R.; Kugel, H.; Bell, R.; Kaye, S.; Okabayashi, M.; Sesnic, S.; Sun, Y.

1994-10-01

The first probe measurements of edge turbulence and transport in a neutral beam induced high confinement mode (H-mode) are reported. A strong negative radial electric field is directly observed in H-mode. A transient suppression of normalized ion saturation and floating potential fluctuation levels occurs at the low confinement mode to high confinement mode (L-H) transition, followed by a recovery to near low mode (L-mode) levels. The average poloidal wave number and the poloidal wave-number spectral width are decreased, and the correlation between fluctuating density and potential is reduced. A large-amplitude coherent oscillation, localized to the strong radial electric field region, is observed in H-mode but does not cause transport. In H-mode the effective turbulent diffusion coefficient is reduced by an order of magnitude inside the last closed flux surface and in the scrape-off layer. The results are compared with a heuristic model of turbulence suppression by velocity-shear stabilization.

Theoretical studies in elementary particle physics: [Progress report for the period June 1986 to February 1987

International Nuclear Information System (INIS)

Collins, J.C.

1987-01-01

Theoretical research on elementary particles is reported, with progress discussed in these areas: heavy quark production, the cosmic rays observed from Cygnus X-3, hadron-hadron collisions at small values of x, Monte Carlo event generators for hadron-hadron collisions, review of perturbative QCD theorems, direct computation of helicity amplitudes for tree diagrams, and application of the factorization of helicity amplitudes to the effective W approximation

Localized solutions for a nonlocal discrete NLS equation

International Nuclear Information System (INIS)

Ben, Roberto I.; Cisneros Ake, Luís; Minzoni, A.A.; Panayotaros, Panayotis

2015-01-01

We study spatially localized time-periodic solutions of breather type for a cubic discrete NLS equation with a nonlocal nonlinearity that models light propagation in a liquid crystal waveguide array. We show the existence of breather solutions in the limit where both linear and nonlinear intersite couplings vanish, and in the limit where the linear coupling vanishes with arbitrary nonlinear intersite coupling. Breathers of this nonlocal regime exhibit some interesting features that depart from what is seen in the NLS breathers with power nonlinearity. One property we see theoretically is the presence of higher amplitude at interfaces between sites with zero and nonzero amplitude in the vanishing linear coupling limit. A numerical study also suggests the presence of internal modes of orbitally stable localized modes. - Highlights: • Show existence of spatially localized solutions in nonlocal discrete NLS model. • Study spatial properties of localized solutions for arbitrary nonlinear nonlocal coupling. • Present numerical evidence that nonlocality leads to internal modes around stable breathers. • Present theoretical and numerical evidence for amplitude maxima at interfaces

Localized solutions for a nonlocal discrete NLS equation

Energy Technology Data Exchange (ETDEWEB)

Ben, Roberto I. [Instituto de Desarrollo Humano, Universidad Nacional de General Sarmiento, J.M. Gutiérrez 1150, 1613 Los Polvorines (Argentina); Cisneros Ake, Luís [Department of Mathematics, ESFM, Instituto Politécnico Nacional, Unidad Profesional Adolfo López Mateos Edificio 9, 07738 México D.F. (Mexico); Minzoni, A.A. [Depto. Matemáticas y Mecánica, I.I.M.A.S.-U.N.A.M., Apdo. Postal 20-726, 01000 México D.F. (Mexico); Panayotaros, Panayotis, E-mail: panos@mym.iimas.unam.mx [Depto. Matemáticas y Mecánica, I.I.M.A.S.-U.N.A.M., Apdo. Postal 20-726, 01000 México D.F. (Mexico)

2015-09-04

We study spatially localized time-periodic solutions of breather type for a cubic discrete NLS equation with a nonlocal nonlinearity that models light propagation in a liquid crystal waveguide array. We show the existence of breather solutions in the limit where both linear and nonlinear intersite couplings vanish, and in the limit where the linear coupling vanishes with arbitrary nonlinear intersite coupling. Breathers of this nonlocal regime exhibit some interesting features that depart from what is seen in the NLS breathers with power nonlinearity. One property we see theoretically is the presence of higher amplitude at interfaces between sites with zero and nonzero amplitude in the vanishing linear coupling limit. A numerical study also suggests the presence of internal modes of orbitally stable localized modes. - Highlights: • Show existence of spatially localized solutions in nonlocal discrete NLS model. • Study spatial properties of localized solutions for arbitrary nonlinear nonlocal coupling. • Present numerical evidence that nonlocality leads to internal modes around stable breathers. • Present theoretical and numerical evidence for amplitude maxima at interfaces.

Surface Loving and Surface Avoiding modes

OpenAIRE

Combe, Nicolas; Huntzinger, Jean Roch; Morillo, Joseph

2008-01-01

International audience; We theoretically study the propagation of sound waves in GaAs/AlAs superlattices focussing on periodic modes in the vicinity of the band gaps. Based on analytical and numerical calculations, we show that these modes are the product of a quickly oscillating function times a slowly varying envelope function. We carefully study the phase of the envelope function compared to the surface of a semi-infinite superlattice. Especially, the dephasing of the superlattice compared...

Acoustic mode coupling induced by shallow water nonlinear internal waves: sensitivity to environmental conditions and space-time scales of internal waves.

Science.gov (United States)

Colosi, John A

2008-09-01

While many results have been intuited from numerical simulation studies, the precise connections between shallow-water acoustic variability and the space-time scales of nonlinear internal waves (NLIWs) as well as the background environmental conditions have not been clearly established analytically. Two-dimensional coupled mode propagation through NLIWs is examined using a perturbation series solution in which each order n is associated with nth-order multiple scattering. Importantly, the perturbation solution gives resonance conditions that pick out specific NLIW scales that cause coupling, and seabed attenuation is demonstrated to broaden these resonances, fundamentally changing the coupling behavior at low frequency. Sound-speed inhomogeneities caused by internal solitary waves (ISWs) are primarily considered and the dependence of mode coupling on ISW amplitude, range width, depth structure, location relative to the source, and packet characteristics are delineated as a function of acoustic frequency. In addition, it is seen that significant energy transfer to modes with initially low or zero energy involves at least a second order scattering process. Under moderate scattering conditions, comparisons of first order, single scattering theoretical predictions to direct numerical simulation demonstrate the accuracy of the approach for acoustic frequencies upto 400 Hz and for single as well as multiple ISW wave packets.

Transformation and Modes of Production

DEFF Research Database (Denmark)

Høst, Jeppe Engset

2015-01-01

modes of production and examine the ways of life that are enabled by the two modes of production. The central questions are around how market-based fisheries management transforms the principal preconditions for the self-employed fishers; and, in turn, why capitalist organized large-scale fisheries......The introduction of private and individual transferable quotas is widely considered to have a negative impact on small- and medium-sized fishing operations. In this chapter, I set out to explore this in a theoretical manner. I discuss the differences in the fishing operations as two contrasting...

Effect of a static external magnetic perturbation on resistive mode stability in tokamaks

International Nuclear Information System (INIS)

Fitzpatrick, R.

1994-03-01

The influence of a general static external magnetic perturbation on the stability of resistive modes in a tokamak plasma is examined. There are three main parts to this investigation. Firstly, the vacuum perturbation is expanded as a set of well-behaved toroidal ring functions and is, thereafter, specified by the coefficients of this expansion. Secondly, a dispersion relation is derived for resistive plasma instabilities in the presence of a general external perturbation and finally, this dispersion relation is solved for the amplitudes of the tearing and twisting modes driven in the plasma by a specific perturbation. It is found that the amplitudes of driven tearing and twisting modes are negligible until a certain critical perturbation strength is exceeded. Only tearing modes are driven in low-β plasmas with εβ p p ∼>1. For error-field perturbations made up of a large number of different poloidal and toroidal harmonics the critical strength to drive locked modes has a open-quote staircase close-quote variation with edge-q, characterized by strong discontinuities as coupled rational surfaces enter or leave the plasma. For single harmonic perturbations the variation with edge-q is far smoother. Both types of behaviour have been observed experimentally. The critical perturbation strength is found to decrease strongly close to an ideal external kink stability boundary. This is also in agreement with experimental observations

Thermally induced high frequency random amplitude fatigue damage at sharp notches

International Nuclear Information System (INIS)

Lewis, M.W.J.

1992-01-01

Experiments have been performed using the SUPERSOMITE facility to investigate the initiation and growth of fatigue cracks at the tips of sharp surface notches subjected to random thermally-induced stress. The experimental situation is complex involving plasticity, random amplitude loading and heat transfer medium/surface coupling. Crack initiation and growth prediction have been considered using the Creager and Neuber methods to compute the strain ranges in the vicinity of the notch root. Good agreement has been obtained between the experimental results and theoretical predictions. The paper reports the results of the analysis of the notch behavior

Nonlinear ω*-stabilization of the m = 1 mode in tokamaks

International Nuclear Information System (INIS)

Rogers, B.; Zakharov, L.

1995-08-01

Earlier studies of sawtooth oscillations in Tokamak Fusion Test Reactor supershots (Levinton et al, Phys. Rev. Lett. 72, 2895 (1994); Zakharov, et al, Plasma Phys. and Contr. Nucl. Fus. Res., Proc. 15th Int. Conf., Seville 1994, Vienna) have found an apparent contradiction between conventional linear theory and experiment: even in sawtooth-free discharges, the theory typically predicts instability due to a nearly ideal m = 1 mode. Here, the nonlinear evolution of such mode is analyzed using numerical simulations of a two-fluid magnetohydrodynamic (MHD) model. We find the mode saturates nonlinearly at a small amplitude provided the ion and electron drift-frequencies ω* i,e are somewhat above the linear stability threshold of the collisionless m = 1 reconnecting mode. The comparison of the simulation results to m = 1 mode activity in TFTR suggests additional, stabilizing effects outside the present model are also important

Relative amplitude preservation processing utilizing surface consistent amplitude correction. Part 3; Surface consistent amplitude correction wo mochiita sotai shinpuku hozon shori. 3

Energy Technology Data Exchange (ETDEWEB)

Saeki, T [Japan National Oil Corporation, Tokyo (Japan). Technology Research Center

1996-10-01

For the seismic reflection method conducted on the ground surface, generator and geophone are set on the surface. The observed waveforms are affected by the ground surface and surface layer. Therefore, it is required for discussing physical properties of the deep underground to remove the influence of surface layer, preliminarily. For the surface consistent amplitude correction, properties of the generator and geophone were removed by assuming that the observed waveforms can be expressed by equations of convolution. This is a correction method to obtain records without affected by the surface conditions. In response to analysis and correction of waveforms, wavelet conversion was examined. Using the amplitude patterns after correction, the significant signal region, noise dominant region, and surface wave dominant region would be separated each other. Since the amplitude values after correction of values in the significant signal region have only small variation, a representative value can be given. This can be used for analyzing the surface consistent amplitude correction. Efficiency of the process can be enhanced by considering the change of frequency. 3 refs., 5 figs.

Resistance-driven bunching mode of an accelerated ion pulse

International Nuclear Information System (INIS)

Lee, E.P.

1981-01-01

Amplification of a longitudinal perturbation of an ion pulse in a linear induction accelerator is calculated. The simplified accelerator model consists only of an applied field (E/sub a/), distributed gap impedance per meter (R) and beam-pipe capacity per meter (C). The beam is treated as a cold, one-dimensional fluid. It is found that normal mode frequencies are nearly real, with only a very small damping rate proportional to R. This result is valid for a general current profile and is not restricted to small R. However, the mode structure exhibits spatial amplification from pulse head to tail by the factor exp(RCLv/sub o//2), where L is pulse length and v 0 is drift velocity. This factor is very large for typical HIF parameters. An initially small disturbance, when expanded in terms of the normal modes, is found to oscillate with maximum amplitude proportional to the amplification factor. Unlike the analogous problem in a circular machine, linear growth is limited in amplitude bntegrating the void fraction profile and comparing the cross-sectionally averaged void fraction with direct measurements using two quick closing valves. Results on the calibration of combinations of full-flow turbine meters, Pitot tube rakes and gamma densitometers for measuring cross-sectionally averaged mass velocity in steady steam-water flow are presented. The results are interpreted ntation

New relations for gauge-theory amplitudes

International Nuclear Information System (INIS)

Bern, Z.; Carrasco, J. J. M.; Johansson, H.

2008-01-01

We present an identity satisfied by the kinematic factors of diagrams describing the tree amplitudes of massless gauge theories. This identity is a kinematic analog of the Jacobi identity for color factors. Using this we find new relations between color-ordered partial amplitudes. We discuss applications to multiloop calculations via the unitarity method. In particular, we illustrate the relations between different contributions to a two-loop four-point QCD amplitude. We also use this identity to reorganize gravity tree amplitudes diagram by diagram, offering new insight into the structure of the Kawai-Lewellen-Tye (KLT) relations between gauge and gravity tree amplitudes. This insight leads to similar but novel relations. We expect this to be helpful in higher-loop studies of the ultraviolet properties of gravity theories.

Vp-Vs relationship and amplitude variation with offset modelling of glauconitic greensand

DEFF Research Database (Denmark)

Hossain, Zakir; Mukerji, Tapan; Fabricius, Ida Lykke

2012-01-01

The relationship between Vp and Vs may be used to predict Vs where only Vp is known. Vp/Vs is also used to identify pore fluids from seismic data and amplitude variation with offset analysis. Theoretical, physical, as well as statistical empirical Vp-Vs relationships have been proposed...... modelling works well for greensand shear-wave velocity prediction. We model the seismic response of glauconitic greensand by using laboratory data from the Nini field. Our studies here reveal that brine-saturated glauconitic greensand can have a similar seismic response to that from oil-saturated quartzitic...

Multiscalar production amplitudes beyond threshold

CERN Document Server

Argyres, E N; Kleiss, R H

1993-01-01

We present exact tree-order amplitudes for $H^* \\to n~H$, for final states containing one or two particles with non-zero three-momentum, for various interaction potentials. We show that there are potentials leading to tree amplitudes that satisfy unitarity, not only at threshold but also in the above kinematical configurations and probably beyond. As a by-product, we also calculate $2\\to n$ tree amplitudes at threshold and show that for the unbroken $\\phi^4$ theory they vanish for $n>4~$, for the Standard Model Higgs they vanish for $n\\ge 3~$ and for a model potential, respecting tree-order unitarity, for $n$ even and $n>4~$. Finally, we calculate the imaginary part of the one-loop $1\\to n$ amplitude in both symmetric and spontaneously broken $\\phi^4$ theory.

Theory of tokamak resistive fishbone modes

International Nuclear Information System (INIS)

Shi Bingren; Sui Guofang

1995-12-01

A special kind of internal kink mode, the fishbone, can be excited by the energetic particles in tokamak plasmas. Theoretical analyses of fishbone modes based on the ideal MHD framework have predicted that two branches of modes exists. One is the Chen-White branch with ω∼ω-bar dm , corresponding to a higher threshold in β h ; the other is the Coppis branch with ω∼ω *i , and a much lower threshold in β h . The latter mode would put a rather unfavourable restriction on heating efficiency and on plasma confinement. However. It is found that the resistivity effect is essential for this mode. In this paper, a new resistive fishbone mode analysis is carried out. In the (γ mhd ,β H ) space, the stability diagram shows complicate structure, the Coppis branch is replaced by a weakly unstable mode and there is no longer closed stable region. The growth rate of this mode varies with β h , its peak value is still very low compared to other internal modes. The implications of these results to future tokamak experiments are discussed. (8 figs.)

ON THE SATURATION OF THE MAGNETOROTATIONAL INSTABILITY VIA PARASITIC MODES

International Nuclear Information System (INIS)

Pessah, Martin E.; Goodman, Jeremy

2009-01-01

We investigate the stability of incompressible, exact, non-ideal magnetorotational (MRI) modes against parasitic instabilities. Both Kelvin-Helmholtz and tearing-mode parasitic instabilities may occur in the dissipative regimes accessible to current numerical simulations. We suppose that a primary MRI mode saturates at an amplitude such that its fastest parasite has a growth rate comparable to its own. The predicted alpha parameter then depends critically on whether the fastest primary and parasitic modes fit within the computational domain and whether non-axisymmetric parasitic modes are allowed. Hence, even simulations that resolve viscous and resistive scales may not saturate properly unless the numerical domain is large enough to allow the free evolution of both MRI and parasitic modes. To minimally satisfy these requirements in simulations with vertical background fields, the vertical extent of the domain should accommodate the fastest growing MRI mode while the radial and azimuthal extents must be twice as large. The fastest parasites have horizontal wavelengths roughly twice as long as the vertical wavelength of the primary.

A Note on Standing Internal Inertial Gravity Waves of Finite Amplitude

Science.gov (United States)

Thorpe, S. A.

2003-01-01

The effects of finite amplitude are examined in two-dimensional, standing, internal gravity waves in a rectangular container which rotates about a vertical axis at frequency f/2. Expressions are given for the velocity components, density fluctuations and isopycnal displacements to second order in the wave steepness in fluids with buoyancy frequency, N, of general form, and the effect of finite amplitude on wave frequency is given in an expansion to third order. The first order solutions, and the solutions to second order in the absence of rotation, are shown to conserve energy during a wave cycle. Analytical solutions are found to second order for the first two modes in a deep fluid with N proportional to sech(az), where z is the upward vertical coordinate and a is scaling factor. In the absence of rotation, results for the first mode in the latter stratification are found to be consistent with those for interfacial waves. An analytical solution to fourth order in a fluid with constant N is given and used to examine the effects of rotation on the development of static instability or of conditions in which shear instability may occur. As in progressive internal waves, an effect of rotation is to enhance the possibility of shear instability for waves with frequencies close to f. The analysis points to a significant difference between the dynamics of standing waves in containers of limited size and progressive internal waves in an unlimited fluid; the effect of boundaries on standing waves may inhibit the onset of instability. A possible application of the analysis is to transverse oscillations in long, narrow, steep-sided lakes such as Loch Ness, Scotland.

Amplitude structure of off-shell processes

International Nuclear Information System (INIS)

Fearing, H.W.; Goldstein, G.R.; Moravcsik, M.J.

1984-01-01

The structure of M matrices, or scattering amplitudes, and of potentials for off-shell processes is discussed with the objective of determining how one can obtain information on off-shell amplitudes of a process in terms of the physical observables of a larger process in which the first process is embedded. The procedure found is inevitably model dependent, but within a particular model for embedding, a determination of the physically measurable amplitudes of the larger process is able to yield a determination of the off-shell amplitudes of the embedded process

Elevator mode convection in flows with strong magnetic fields

Energy Technology Data Exchange (ETDEWEB)

Liu, Li; Zikanov, Oleg, E-mail: zikanov@umich.edu [Department of Mechanical Engineering, University of Michigan-Dearborn, 48128-1491 Michigan (United States)

2015-04-15

Instability modes in the form of axially uniform vertical jets, also called “elevator modes,” are known to be the solutions of thermal convection problems for vertically unbounded systems. Typically, their relevance to the actual flow state is limited by three-dimensional breakdown caused by rapid growth of secondary instabilities. We consider a flow of a liquid metal in a vertical duct with a heated wall and strong transverse magnetic field and find elevator modes that are stable and, thus, not just relevant, but a dominant feature of the flow. We then explore the hypothesis suggested by recent experimental data that an analogous instability to modes of slow axial variation develops in finite-length ducts, where it causes large-amplitude fluctuations of temperature. The implications for liquid metal blankets for tokamak fusion reactors that potentially invalidate some of the currently pursued design concepts are discussed.

Dynamic rotor mode in antiferromagnetic nanoparticles

DEFF Research Database (Denmark)

Lefmann, Kim; Jacobsen, H.; Garde, J.

2015-01-01

We present experimental, numerical, and theoretical evidence for an unusual mode of antiferromagnetic dynamics in nanoparticles. Elastic neutron scattering experiments on 8-nm particles of hematite display a loss of diffraction intensity with temperature, the intensity vanishing around 150 K...

Entanglement of two-mode Gaussian states: characterization and experimental production and manipulation

Energy Technology Data Exchange (ETDEWEB)

Laurat, Julien [Laboratoire Kastler Brossel, Case 74, Universite Pierre et Marie curie, 4 Place Jussieu, 75252 Paris cedex 05 (France); Keller, Gaelle [Laboratoire Kastler Brossel, Case 74, Universite Pierre et Marie curie, 4 Place Jussieu, 75252 Paris cedex 05 (France); Oliveira-Huguenin, Jose Augusto [Laboratoire Kastler Brossel, Case 74, Universite Pierre et Marie curie, 4 Place Jussieu, 75252 Paris cedex 05 (France); Fabre, Claude [Laboratoire Kastler Brossel, Case 74, Universite Pierre et Marie curie, 4 Place Jussieu, 75252 Paris cedex 05 (France); Coudreau, Thomas [Laboratoire Kastler Brossel, Case 74, Universite Pierre et Marie curie, 4 Place Jussieu, 75252 Paris cedex 05 (France); Laboratoire Materiaux et Phenomenes Quantiques, Case 7021, Universite Denis Diderot, 2 Place Jussieu, 75251 Paris cedex 05 (France); Serafini, Alessio [Dipartimento di Fisica ' E R Caianiello' , Universita di Salerno (Italy); CNR-Coherentia, Gruppo di Salerno (Italy); and INFN Sezione di Napoli-Gruppo Collegato di Salerno, Via S Allende, 84081 Baronissi (Saudi Arabia) (Italy); Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT (United Kingdom); Adesso, Gerardo [Dipartimento di Fisica ' E R Caianiello' , Universita di Salerno (Italy); CNR-Coherentia, Gruppo di Salerno (Italy); and INFN Sezione di Napoli-Gruppo Collegato di Salerno, Via S Allende, 84081 Baronissi (Saudi Arabia) (Italy); Illuminati, Fabrizio [Dipartimento di Fisica ' E R Caianiello' , Universita di Salerno (Italy) and CNR-Coherentia, Gruppo di Salerno (Italy) and INFN Sezione di Napoli-Gruppo Collegato di Salerno, Via S Allende, 84081 Baronissi (SA) (Italy)

2005-12-01

A powerful theoretical structure has emerged in recent years on the characterization and quantification of entanglement in continuous-variable systems. After reviewing this framework, we will illustrate it with an original set-up based on a type-II OPO (optical parametric oscillator) with adjustable mode coupling. Experimental results allow a direct verification of many theoretical predictions and provide a sharp insight into the general properties of two-mode Gaussian states and entanglement resource manipulation.

Entanglement of two-mode Gaussian states: characterization and experimental production and manipulation

International Nuclear Information System (INIS)

Laurat, Julien; Keller, Gaelle; Oliveira-Huguenin, Jose Augusto; Fabre, Claude; Coudreau, Thomas; Serafini, Alessio; Adesso, Gerardo; Illuminati, Fabrizio

2005-01-01

A powerful theoretical structure has emerged in recent years on the characterization and quantification of entanglement in continuous-variable systems. After reviewing this framework, we will illustrate it with an original set-up based on a type-II OPO (optical parametric oscillator) with adjustable mode coupling. Experimental results allow a direct verification of many theoretical predictions and provide a sharp insight into the general properties of two-mode Gaussian states and entanglement resource manipulation

Digital control of laser modes with an intra-cavity spatial light modulator

CSIR Research Space (South Africa)

Ngcobo, S

2014-02-01

Full Text Available addressed holographic end-mirror. We show that on-demand digitally controlled laser modes are possible by changing the phase and amplitude of the computer generated hologram in a form of a grey-scale image on the holographic mirror. We demonstrate...

Theoretical approach to the phonon modes and specific heat of germanium nanowires

Energy Technology Data Exchange (ETDEWEB)

Trejo, A.; López-Palacios, L.; Vázquez-Medina, R.; Cruz-Irisson, M., E-mail: irisson@ipn.mx

2014-11-15

The phonon modes and specific heat of Ge nanowires were computed using a first principles density functional theory scheme with a generalized gradient approximation and finite-displacement supercell algorithms. The nanowires were modeled in three different directions: [001], [111], and [110], using the supercell technique. All surface dangling bonds were saturated with Hydrogen atoms. The results show that the specific heat of the GeNWs at room temperature increases as the nanowire diameter decreases, regardless the orientation due to the phonon confinement and surface passivation. Also the phonon confinement effects could be observed since the highest optical phonon modes in the Ge vibration interval shifted to a lower frequency compared to their bulk counterparts.

Higher‐order mode absorption measurement of X-band choke-mode cavities in a radial line structure

International Nuclear Information System (INIS)

Zha, Hao; Shi, Jiaru; Wu, Xiaowei; Chen, Huaibi

2016-01-01

An experiment is presented to study the higher-order mode (HOM) suppression of X-band choke-mode structures with a vector network analyzer (VNA). Specific radial line disks were built to test the reflection from the corresponding damping load and different choke geometries. The mismatch between the radial lines and the VNA was calibrated through a special multi-short-load calibration method. The measured reflections of different choke geometries showed good agreement with the theoretical calculations and verified the HOM absorption feature of each geometric design.

Higher‐order mode absorption measurement of X-band choke-mode cavities in a radial line structure

Energy Technology Data Exchange (ETDEWEB)

Zha, Hao [Department of Engineering Physics, Tsinghua University, Beijing CN-100086 (China); Key Laboratory of Particle and Radiation Imaging, Tsinghua University, Ministry of Education, Beijing (China); The European Organization for Nuclear Research, Geneva CH-1211 (Switzerland); Shi, Jiaru, E-mail: shij@mail.tsinghua.edu.cn [Department of Engineering Physics, Tsinghua University, Beijing CN-100086 (China); Key Laboratory of Particle and Radiation Imaging, Tsinghua University, Ministry of Education, Beijing (China); The European Organization for Nuclear Research, Geneva CH-1211 (Switzerland); Wu, Xiaowei; Chen, Huaibi [Department of Engineering Physics, Tsinghua University, Beijing CN-100086 (China); Key Laboratory of Particle and Radiation Imaging, Tsinghua University, Ministry of Education, Beijing (China)

2016-04-01

An experiment is presented to study the higher-order mode (HOM) suppression of X-band choke-mode structures with a vector network analyzer (VNA). Specific radial line disks were built to test the reflection from the corresponding damping load and different choke geometries. The mismatch between the radial lines and the VNA was calibrated through a special multi-short-load calibration method. The measured reflections of different choke geometries showed good agreement with the theoretical calculations and verified the HOM absorption feature of each geometric design.

High frequency switched-mode stimulation can evoke postsynaptic responses in cerebellar principal neurons

Directory of Open Access Journals (Sweden)

Marijn Van Dongen

2015-03-01

Full Text Available This paper investigates the efficacy of high frequency switched-mode neural stimulation. Instead of using a constant stimulation amplitude, the stimulus is switched on and off repeatedly with a high frequency (up to 100kHz duty cycled signal. By means of tissue modeling that includes the dynamic properties of both the tissue material as well as the axon membrane, it is first shown that switched-mode stimulation depolarizes the cell membrane in a similar way as classical constant amplitude stimulation.These findings are subsequently verified using in vitro experiments in which the response of a Purkinje cell is measured due to a stimulation signal in the molecular layer of the cerebellum of a mouse. For this purpose a stimulator circuit is developed that is able to produce a monophasic high frequency switched-mode stimulation signal. The results confirm the modeling by showing that switched-mode stimulation is able to induce similar responses in the Purkinje cell as classical stimulation using a constant current source. This conclusion opens up possibilities for novel stimulation designs that can improve the performance of the stimulator circuitry. Care has to be taken to avoid losses in the system due to the higher operating frequency.

Non-supersymmetric loop amplitudes and MHV vertices

International Nuclear Information System (INIS)

Bedford, James; Brandhuber, Andreas; Spence, Bill; Travaglini, Gabriele

2005-01-01

We show how the MHV diagram description of Yang-Mills theories can be used to study non-supersymmetric loop amplitudes. In particular, we derive a compact expression for the cut-constructible part of the general one-loop MHV multi-gluon scattering amplitude in pure Yang-Mills theory. We show that in special cases this expression reduces to known amplitudes-the amplitude with adjacent negative-helicity gluons, and the five gluon non-adjacent amplitude. Finally, we briefly discuss the twistor space interpretation of our result

Why the Real Part of the Proton-Proton Forward Scattering Amplitude Should be Measured at the LHC

CERN Document Server

Bourrely, C.; Martin, Andre; Soffer, Jacques; Wu, Tai Tsun

2006-01-01

For the energy of 14 TeV, to be reached at the Large Hadron Collider (LHC), we have had for some time accurate predictions for both the real and imaginary parts of the forward proton-proton elastic scattering amplitude. LHC is now scheduled to start operating in two years, and it is timely to discuss some of the important consequences of the measurements of both the total cross-section and the ratio of the real to the imaginary part. We stress the importance of measuring the real part of the proton-proton forward scattering amplitude at LHC, because a deviation from existing theoretical predictions could be a strong sign for new physics.

Composition Dependence of Surface Phonon Polariton Mode in Wurtzite InxGa1−xN (0 ≤ x ≤ 1) Ternary Alloy

International Nuclear Information System (INIS)

Ng, S. S.; Hassan, Z.; Hassan, H. Abu

2008-01-01

We present a theoretical study on the composition dependence of the surface phonon polariton (SPP) mode in wurtzite structure α-In x Ga 1-x N ternary alloy over the whole composition range. The SPP modes are obtained by the theoretical simulations by means of an anisotropy model. The results reveal that the SPP mode of α-In x Ga 1-x N semiconductors exhibits one-mode behaviour. From these data, composition dependence of the SPP mode with bowing parameter of −28.9 cm −1 is theoretically obtained

Experimental Lamb mode identification in a plate containing a hole using dual signal processing

International Nuclear Information System (INIS)

Grondel, Sébastien; Assaad, Jamal; Youbi, Faysal El; Moulin, Emmanuel; Leyla, Najib Abou

2008-01-01

The identification of Lamb mode amplitude variation as a function of the damage evolution is still the most difficult step in the process of damage monitoring using embedded Lamb wave-based systems. The aim of this paper is to propose a simple system based on the generation of two different frequencies in order to better identify Lamb mode amplitude and to avoid false data interpretation in plates containing a hole of variable diameter. This identification is based on a simple relation between the short-time Fourier transform and the two-dimensional Fourier transform. Experimentally, a 3 mm thick aluminium plate is used and the two frequencies have been chosen equal to 400 kHz and 600 kHz in order to generate the two first fundamental Lamb waves

Effects of resonant magnetic perturbation on the triggering and the evolution of double-tearing mode

Science.gov (United States)

Wang, L.; Lin, W. B.; Wang, X. Q.

2018-02-01

The effects of resonant magnetic perturbation on the triggering and the evolution of the double-tearing mode are investigated by using nonlinear magnetohydrodynamics simulations in a slab geometry. It is found that the double-tearing mode can be destabilized by boundary magnetic perturbation. Moreover, the mode has three typical development stages before it reaches saturation: the linear stable stage, the linear-growth stage, and the exponential-growth stage. The onset and growth of the double-tearing mode significantly depend on the boundary magnetic perturbations, particularly in the early development stage of the mode. The influences of the magnetic perturbation amplitude on the mode for different separations of the two rational surfaces are also discussed.

Beam orbit control in TESLA superconducting cavities from dipole mode measurements

International Nuclear Information System (INIS)

Paparella, R.

2006-09-01

The knowledge of the electromagnetic interaction between a beam and the surrounding vacuum chamber is necessary in order to optimize the accelerator performance in terms of stored current. Many instability phenomena may occur in the machine because of the fields produced by the beam and acting back on itself. Basically, these fields, wake-fields, produce an extra voltage, affecting the longitudinal dynamics, and a transverse kick which deflects the beam. In this thesis we present the results of theoretical and experimental investigations to demonstrate the possibility of using the dipolar wake fields of the superconducting accelerating to measure the beam transverse position. After an introduction to the ILC project and to the TESLA technology, of superconducting RF cavities, we will approach the problem from an analytical point of view in chapter 2. The expression of the wake fields in a cylindrical cavity will be investigated and the electromagnetic field modes derived from Maxwell equations in an original way. Graphical solutions of a Matlab program simulating the fields due to a particle passing through a pill-box cavity along a generic path will be shown. The interaction of the beam with higher order modes (HOM) in the TESLA cavities has been studied in the past at the TESLA Test Facility (TTF) in order to determine whether the modes with the highest loss factor are sufficiently damped. Starting from the results obtained before 2003, HOM signals has been better observed and examined in order to use dipole modes to find the electric center of each cavity in the first TTF accelerating module. The results presented in chapter 3 will show that by monitoring the HOM signal amplitude for two polarizations of a dipole mode, one can measure electrical center of the modes with a resolution of 50 μm. Moreover, a misalignment of the first TTF module with respect to the gun axis has been predicted using cavity dipole modes. Alternatives to this method are described in

Amplitudes of solar-like oscillations: Constraints from red giants in open clusters observed by Kepler

DEFF Research Database (Denmark)

Stello, Dennis; Huber, Daniel; Kallinger, Thomas

2011-01-01

implies that the stellar parameters can be measured to much higher precision than what is usually achievable for single stars. This makes clusters ideal for exploring the relation between the mode amplitude of solar-like oscillations and the global stellar properties. We have analyzed data obtained......Scaling relations that link asteroseismic quantities to global stellar properties are important for gaining understanding of the intricate physics that underpins stellar pulsations. The common notion that all stars in an open cluster have essentially the same distance, age, and initial composition...... with NASA's Kepler space telescope to study solar-like oscillations in 100 red giant stars located in either of the three open clusters, NGC 6791, NGC 6819, and NGC 6811. By fitting the measured amplitudes to predictions from simple scaling relations that depend on luminosity, mass, and effective...

Spread F bubbles - Nonlinear Rayleigh-Taylor mode in two dimensions

Science.gov (United States)

Hudson, M. K.

1978-01-01

The paper discusses long-wavelength developed bottomside spread F which has been attributed to the Rayleigh-Taylor instability. The nonlinear saturation amplitude and the k spectrum of the inertia-dominated Rayleigh-Taylor instability is found in two directions: east-west and vertical. As in the collisional case (Chaturvedi and Ossakow, 1977), the dominant nonlinearity is found to be two-dimensional. It is found that the linearly most unstable modes, which are primarily horizontal, saturate by the nonlinear generation of vertical spatial harmonics. The harmonics are damped by diffusion or recombination. The resulting amplitude spectrum indicates that bubbles are vertically elongated in both inertial and collisional regimes.

Radial mode structure of curvature-driven instabilities in EBT

International Nuclear Information System (INIS)

Spong, D.A.

1983-01-01

Viewgraphs describe the theoretical treatment of the radial mode structure of plasma instabilities in the Elmo Bumpy Torus. The calculation retains nonlocal structure of the modes, connects inner and outer ring regions together, uses a self-consistent finite β, includes the relativistic effects for the hot electron ring, and examines a wide range of parameters

Nonlinear dynamics of tearing modes in the reversed field pinch

International Nuclear Information System (INIS)

Holmes, J.A.; Carreras, B.A.; Diamond, P.H.; Lynch, V.E.

1988-01-01

The results of investigations of nonlinear tearing-mode dynamics in reversed field pinch plasmas are described. The linear instabilities have poloidal mode number m = 1 and toroidal mode numbers 10approx. < napprox. <20, and the resonant surfaces are therefore in the plasma core. The nonlinear dynamics result in dual cascade processes. The first process is a rapid m = 1 spectral broadening toward high n, with a simultaneous spreading of magnetic turbulence radially outward toward the field-reversal surface. Global m = 0 perturbations, which are driven to large amplitudes by the m = 1 instabilities, in turn trigger the m = 1 spectral broadening by back coupling to the higher n. The second process is a cascade toward large m and is mediated by m = 2 modes. The m = 2 perturbations have the structure of localized, driven current sheets and nonlinearly stabilize the m = 1 modes by transferring m = 1 energy to small-scale dissipation. The calculated spectrum has many of the qualitative features observed in experiments

Scattering amplitudes in gauge theories

CERN Document Server

Henn, Johannes M

2014-01-01

At the fundamental level, the interactions of elementary particles are described by quantum gauge field theory. The quantitative implications of these interactions are captured by scattering amplitudes, traditionally computed using Feynman diagrams. In the past decade tremendous progress has been made in our understanding of and computational abilities with regard to scattering amplitudes in gauge theories, going beyond the traditional textbook approach. These advances build upon on-shell methods that focus on the analytic structure of the amplitudes, as well as on their recently discovered hidden symmetries. In fact, when expressed in suitable variables the amplitudes are much simpler than anticipated and hidden patterns emerge.   These modern methods are of increasing importance in phenomenological applications arising from the need for high-precision predictions for the experiments carried out at the Large Hadron Collider, as well as in foundational mathematical physics studies on the S-matrix in quantum ...

Analytical properties of multiple production amplitudes

Energy Technology Data Exchange (ETDEWEB)

Medvedev, B V; Pavlov, V P; Polivanov, M K; Sukhanov, A D [Gosudarstvennyj Komitet po Ispol' zovaniyu Atomnoj Ehnergii SSSR, Moscow. Inst. Teoreticheskoj i Ehksperimental' noj Fiziki; AN SSSR, Moscow. Matematicheskij Inst.)

1984-05-01

Local analytical properties of amplitudes 2..-->..3 and 2..-->..4 are studied. The amplitudes are shown to be analytical functions of total and partial energies at fixed momentum transfers in the neighbourhood of any physical point on the energy shell 14 (for the 2..-->..3 case) and 242 (for the 2..-->..4 case) boundary values are expressed through the amplitudes of real processes.

Mode splitting effect in FEMs with oversized Bragg resonators

Energy Technology Data Exchange (ETDEWEB)

Peskov, N. Yu.; Sergeev, A. S. [Institute of Applied Physics Russian Academy of Sciences, Nizhny Novgorod (Russian Federation); Kaminsky, A. K.; Perelstein, E. A.; Sedykh, S. N. [Joint Institute for Nuclear Research, Dubna (Russian Federation); Kuzikov, S. V. [Institute of Applied Physics Russian Academy of Sciences, Nizhny Novgorod (Russian Federation); Nizhegorodsky State University, Nizhny Novgorod (Russian Federation)

2016-07-15

Splitting of the fundamental mode in an oversized Bragg resonator with a step of the corrugation phase, which operates over the feedback loop involving the waveguide waves of different transverse structures, was found to be the result of mutual influence of the neighboring zones of the Bragg scattering. Theoretical description of this effect was developed within the framework of the advanced (four-wave) coupled-wave approach. It is shown that mode splitting reduces the selective properties, restricts the output power, and decreases the stability of the narrow-band operating regime in the free-electron maser (FEM) oscillators based on such resonators. The results of the theoretical analysis were confirmed by 3D simulations and “cold” microwave tests. Experimental data on Bragg resonators with different parameters in a 30-GHz FEM are presented. The possibility of reducing the mode splitting by profiling the corrugation parameters is shown. The use of the mode splitting effect for the output power enhancement by passive compression of the double-frequency pulse generated in the FEM with such a resonator is discussed.

Extended holomorphic anomaly and loop amplitudes in open topological string

International Nuclear Information System (INIS)