Residual Amplitude Modulation in Interferometric Gravitational Wave Detectors
Kokeyama, Keiko; Korth, William Z; Smith-Lefebvre, Nicolas; Arai, Koji; Adhikari, Rana X
2013-01-01
The effects of residual amplitude modulation (RAM) in laser interferometers using heterodyne sensing can be substantial and difficult to mitigate. In this work, we analyze the effects of RAM on a complex laser interferometer used for gravitational wave detection. The RAM introduces unwanted offsets in the cavity length signals and thereby shifts the operating point of the optical cavities from the nominal point via feedback control. This shift causes variations in the sensing matrix, and leads to degradation in the performance of the precision noise subtraction scheme of the multiple-degree-of-freedom control system. In addition, such detuned optical cavities produce an opto-mechanical spring, which also varies the sensing matrix. We use our simulations to derive requirements on RAM for the Advanced LIGO detectors, and show that the RAM expected in Advanced LIGO will not limit its sensitivity.
Residual amplitude modulation in interferometric gravitational wave detectors.
Kokeyama, Keiko; Izumi, Kiwamu; Korth, William Z; Smith-Lefebvre, Nicolas; Arai, Koji; Adhikari, Rana X
2014-01-01
The effects of residual amplitude modulation (RAM) in laser interferometers using heterodyne sensing can be substantial and difficult to mitigate. In this work, we analyze the effects of RAM on a complex laser interferometer used for gravitational wave detection. The RAM introduces unwanted offsets in the cavity length signals and thereby shifts the operating point of the optical cavities from the nominal point via feedback control. This shift causes variations in the sensing matrix, and leads to degradation in the performance of the precision noise subtraction scheme of the multiple-degree-of-freedom control system. In addition, such detuned optical cavities produce an optomechanical spring, which also perturbs the sensing matrix. We use our simulations to derive requirements on RAM for the Advanced LIGO (aLIGO) detectors, and show that the RAM expected in aLIGO will not limit its sensitivity. PMID:24561943
Yu, Yinan; Wang, Yicheng; Pratt, Jon R.
2016-03-01
Residual amplitude modulation (RAM) is one of the most common noise sources known to degrade the sensitivity of frequency modulation spectroscopy. RAM can arise as a result of the temperature dependent birefringence of the modulator crystal, which causes the orientation of the crystal's optical axis to shift with respect to the polarization of the incident light with temperature. In the fiber-based optical interferometer used on the National Institute of Standards and Technology calculable capacitor, RAM degrades the measured laser frequency stability and correlates with the environmental temperature fluctuations. We have demonstrated a simple approach that cancels out excessive RAM due to polarization mismatch between the light and the optical axis of the crystal. The approach allows us to measure the frequency noise of a heterodyne beat between two lasers individually locked to different resonant modes of a cavity with an accuracy better than 0.5 ppm, which meets the requirement to further determine the longitudinal mode number of the cavity length. Also, this approach has substantially mitigated the temperature dependency of the measurements of the cavity length and consequently the capacitance.
Our results demonstrate that photorefractive residual amplitude modulation (RAM) noise in electro-optic modulators (EOMs) can be reduced by modifying the incident beam intensity distribution. Here we report an order of magnitude reduction in RAM when beams with uniform intensity (flat-top) profiles, generated with an LCOS-SLM, are used instead of the usual fundamental Gaussian mode (TEM00). RAM arises from the photorefractive amplified scatter noise off the defects and impurities within the crystal. A reduction in RAM is observed with increasing intensity uniformity (flatness), which is attributed to a reduction in space charge field on the beam axis. The level of RAM reduction that can be achieved is physically limited by clipping at EOM apertures, with the observed results agreeing well with a simple model. These results are particularly important in applications where the reduction of residual amplitude modulation to 10−6 is essential. (paper)
Sathian, Juna; Jaatinen, Esa
2013-12-01
Our results demonstrate that photorefractive residual amplitude modulation (RAM) noise in electro-optic modulators (EOMs) can be reduced by modifying the incident beam intensity distribution. Here we report an order of magnitude reduction in RAM when beams with uniform intensity (flat-top) profiles, generated with an LCOS-SLM, are used instead of the usual fundamental Gaussian mode (TEM00). RAM arises from the photorefractive amplified scatter noise off the defects and impurities within the crystal. A reduction in RAM is observed with increasing intensity uniformity (flatness), which is attributed to a reduction in space charge field on the beam axis. The level of RAM reduction that can be achieved is physically limited by clipping at EOM apertures, with the observed results agreeing well with a simple model. These results are particularly important in applications where the reduction of residual amplitude modulation to 10-6 is essential.
Pulse amplitude modulated chlorophyll fluorometer
Greenbaum, Elias; Wu, Jie
2015-12-29
Chlorophyll fluorometry may be used for detecting toxins in a sample because of changes in micro algae. A portable lab on a chip ("LOAC") based chlorophyll fluorometer may be used for toxin detection and environmental monitoring. In particular, the system may include a microfluidic pulse amplitude modulated ("PAM") chlorophyll fluorometer. The LOAC PAM chlorophyll fluorometer may analyze microalgae and cyanobacteria that grow naturally in source drinking water.
Amplitude modulation reflectometer for FTU
Amplitude modulation (AM) reflectometry is a modification of the classical frequency sweep technique which allows to perform unambiguous phase delay measurements. An eight-channel AM reflectometer has been realized for the measurement of density profiles on the FTU tokamak in the range. The characteristics of the instrument have been determined in extensive laboratory tests; particular attention has been devoted to the effect of interference with parasitic reflections. The reflectometer is now operating on FTU. Some examples of the first experimental data are discussed
Alternating-phase focusing with amplitude modulation
Sagalovsky, L.; Delayen, J.R.
1993-08-01
We have previously developed a model of alternating-phase focusing (APF) applicable to ion linacs comprised of short independently controlled cavities. The main beam dynamical aspects of APF are adequately described by four parameters: Equilibrium synchronous phase, phase modulation amplitude, length of APF period, and incremental energy gain. In this paper we report on an extension of the analysis to include simultaneous modulation of the accelerating field amplitude. Two additional parameters are included: Relative phase between the amplitude and phase modulation and magnitude of the amplitude modulation. The effects of amplitude modulation on the stable regions and longitudinal acceptance are discussed.
Speech production in amplitude-modulated noise
Macdonald, Ewen N; Raufer, Stefan
2013-01-01
consequences of temporally fluctuating noise. In the present study, 20 talkers produced speech in a variety of noise conditions, including both steady-state and amplitude-modulated white noise. While listening to noise over headphones, talkers produced randomly generated five word sentences. Similar to...... previous studies, talkers raised the level of their voice in steady-state noise. While talkers also increased the level of their voice in amplitude-modulated noise, the increase was not as large as that observed in steady-state noise. Importantly, for the 2 and 4 Hz amplitude-modulated noise conditions...
Amplitude-modulated fiber-ring laser
Caputo, J. G.; Clausen, Carl A. Balslev; Sørensen, Mads Peter; Bischoff, Svend
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...
Amplitude modulation of wind turbine noise
Makarewicz, Rufin
2013-01-01
Due to swish and thump amplitude modulation, the noise of wind turbines cause more annoyance than other environmental noise of the same average level. The wind shear accounts for the thump modulation (van den Berg effect). Making use of the wind speed measurements at the hub height, as well as at the top and the bottom of the rotor disc (Fig.1), the non-standard wind profile is applied. It causes variations in the A-weighted sound pressure level, LpA. The difference between the maximum and minimum of LpA characterizes thump modulation (Fig.2).
Amplitude and phase modulation with waveguide optics
We have developed amplitude and phase modulation systems for glass lasers using integrated electro-optic modulators and solid state high-speed electronics. The present and future generation of lasers for Inertial Confinement Fusion require laser beams with complex temporal and phase shaping to compensate for laser gain saturation, mitigate parametric processes such as transverse stimulated Brillouin scattering in optics, and to provide specialized drive to the fusion targets. These functions can be performed using bulk optoelectronic modulators, however using high-speed electronics to drive low voltage integrated optical modulators has many practical advantages. In particular, we utilize microwave GaAs transistors to perform precision, 250 ps resolution temporal shaping. Optical bandwidth is generated using a microwave oscillator at 3 GHz amplified by a solid state amplifier. This drives an integrated electrooptic modulator to achieve laser bandwidths exceeding 30 GHz
Amplitude modulation of wind turbine noise
Makarewicz, Rufin; Golebiewski, Roman
2013-01-01
Due to swish and thump amplitude modulation, the noise of wind turbines cause more annoyance than other environmental noise of the same average level. The wind shear accounts for the thump modulation (van den Berg effect). Making use of the wind speed measurements at the hub height, as well as at the top and the bottom of the rotor disc (Fig.1), the non-standard wind profile is applied. It causes variations in the A-weighted sound pressure level, LpA. The difference between the maximum and mi...
Amplitude-modulated fiber-ring laser
Caputo, J. G.; Clausen, Carl A. Balslev; Sørensen, Mads Peter; Bischoff, Svend
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......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...... by comparison with the full numerical simulations. Finally, we discuss possible sources of instability that are due to resonances in the device....
All-optical PT-symmetric conversion of amplitude (phase) modulation to phase (amplitude) modulation.
Gutiérrez, Oscar Ignacio Zaragoza; Mendoza, Luis Felipe Salinas; Rodríguez-Lara, B M
2016-02-22
We study electromagnetic field propagation through a planar three-waveguide coupler with linear gain or loss in a configuration that is the optical analog of a quantum PT-symmetric system. This model is experimentally feasible on at least four proven architectures: lossy waveguide couplers, pumped waveguides couplers, non-Hermitian electronics and coupled pumped whispering gallery mode resonators. We show that our device provides all-optical amplitude (phase) to phase (amplitude) conversion in the PT-symmetric regime at given propagation lenghts. The device has a π amplitude to phase conversion range if an extra binary phase is allowed in the reference signal, and a phase to amplitude conversion range that depends linearly on the gain-to-coupling ratio of the system. Our scheme may prove valuable in implementing phase shift keying formats, which have longer unrepeated transmission distance than intensity modulation schemes. PMID:26907051
Log-Likelihood Classification Of Quadrature Amplitude Modulation
Savita Kamboj
2013-10-01
Full Text Available This paper is concerned with amplitude-based log likelihood classification for quadrature amplitude modulation. We derive the amplitude density functions of received QAM signals first, then develop the required statistics for signal classification based on the maximum a posteriori probability criterion and demonstrate a schematic structure of classifier for M-ary QAM signals. It is illustrated successful classification rate reaches 100% for SNR>=15.
Mechanisms of amplitude modulation in wind turbine noise
Smith, Malcom; Bullmore, Andrew; CAND, Matthew; Davis, Robert
2012-01-01
The noise produced by wind turbines is inherently time varying. This amplitude modulation is normally due to the directivity of the dominant trailing edge noise sources combined with the changing position and orientation of the rotating blades. In some circumstances the level and character of the amplitude modulation is altered and this paper outlines results from a Renewable UK funded research programme into the possible causes. Besides the variability of the normal trailing edge noise mecha...
Parasitic amplitude modulation of stabilized CO/sub 2/ lasers
Bazarov, E.; Gerasimov, G.; Gubin, V.; Starostin, N.; Fomin, V.
1981-07-01
An experimental investigation was made of parasitic amplitude modulation in a CO/sub 2/ laser with intracavity frequency modulation. This effect was due to periodic misalignment of the laser cavity during operation of a piezoelectric ceramic modulator. A method for controlling and minimizing the parasitic modulation was developed. Relationships were derived for the shift of the stabilized frequency due to such parasitic amplitude modulation and estimates were obtained for the case of a stabilized CO/sub 2//OsO/sub 4/ laser. It was found that the parasitic modulation could give rise to a dependence of the stabilized frequency on the phase relationships in the case of phase-sensitive detection in an automatic frequency control system of the laser.
Amplitude modulation detection by human listeners in sound fields
Zahorik, Pavel; Kim, Duck O.; Kuwada, Shigeyuki; Anderson, Paul W.; Brandewie, Eugene; Srinivasan, Nirmal
2011-01-01
The temporal modulation transfer function (TMTF) approach allows techniques from linear systems analysis to be used to predict how the auditory system will respond to arbitrary patterns of amplitude modulation (AM). Although this approach forms the basis for a standard method of predicting speech intelligibility based on estimates of the acoustical modulation transfer function (MTF) between source and receiver, human sensitivity to AM as characterized by the TMTF has not been extensively stud...
Amplitude Modulation in the δ Sct star KIC 7106205
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.
CARRIER-FREQUENCY HARMONIZATION STRUCTURE FOR ENHANCED AMPLITUDE MODULATION FUNCTION
B.V.Subba Rao
2013-06-01
Full Text Available Amplitude Modulation was the major method of influencing sound on a radio signal and is still extensively used in the present days. The characteristic amplitude modulation radio receivers’ automatic gain-control to circumvent bass distortion, generally reacts extreme moreover slowly to average out or overwhelm these intercarrier beat modulations as a result, these extremely aggravating modulation effects are mainly distributed on unbroken to the eavesdropper. A GPS-referenced frequency-synchronizer unit could be organized at transmitter sites capable of holding both current and big transmitters as a result basically eradicating carrier beat interference between co-channel amplitude modulation stations. The beat-related properties are a main aspect in the deprivation of dusk and night-time amplitude modulation fringe-area function excellence and the subsequent damage of hearers for effectively all stations. Commonly, an amplitude modulation radio listener for the duration of the sundown and nightfall hours and to a slighter amount in the first day break, obtains undesired sky wave indications from numerous distant locations as well as the desired local signal. The simple oscillator is naturally a predictable high-stability quartz-crystal kind, temperature compensated. To stand long-term drifts, advanced years effects, and loading-circuit variations, the simple oscillator is somewhat adjusted through electronic or mechanical resources to path a high-precision cause of standard frequency. The steady local reference frequency is then used as a timer for a typical numerically applied frequency synthesizer, which is planned to create the speciﬁc receiver carrier frequency expected.
Effects of dust on amplitude modulation of kinetic Alfven waves
Effects of dust on the amplitude modulation of two possible types of kinetic Alfven waves, modified and dust kinetic Alfven waves, in a magnetized dusty plasma have been investigated. The appropriate nonlinear dispersion relations of the amplitude modulation predict that the carrier kinetic Alfven waves are modulationally unstable for long wave-length perturbations. It has been found that the parameter σ plays a significant role on the amplitude modulation of the waves, where σ is the ratio of the equilibrium number densities of the ions and the electrons and is a measure of the charge carried by the dust component. The maximum growth rate of the modulational instability increases with the parameter σ, whereas, the range of the perpendicular component of the modulation wavenumber K perpendicularto of the unstable wave remains almost constant for the case of dust kinetic Alfven waves. On the other hand, the maximum growth rate is almost constant with σ, while the range of K perpendicularto of the unstable wave drastically decreases for the case of modified kinetic Alfven waves. (orig.)
Amplitude Modulated Sinusoidal Signal Decomposition for Audio Coding
Christensen, M. G.; Jacobson, A.; Andersen, S. V.; Jensen, Søren Holdt
2006-01-01
In this paper, we present a decomposition for sinusoidal coding of audio, based on an amplitude modulation of sinusoids via a linear combination of arbitrary basis vectors. The proposed method, which incorporates a perceptual distortion measure, is based on a relaxation of a nonlinear least...
Amplitude modulated drift wave packets in a nonuniform magnetoplasma
Shukla, P.K., E-mail: profshukla@yahoo.de [International Centre for Advanced Studies in Physical Sciences and Institute for Theoretical Physics, Faculty of Physics and Astronomy, Ruhr University Bochum, D-447 80 Bochum (Germany); Misra, A.P., E-mail: apmisra@gmail.com [Department of Mathematics, Siksha Bhavana, Visva-Bharati University, Santiniketan 731 235 (India)
2012-08-06
We consider the amplitude modulation of low-frequency, long wavelength electrostatic drift wave packets in a nonuniform magnetoplasma with the effects of equilibrium density, electron temperature and magnetic field inhomogeneities. The dynamics of the modulated drift wave packet is governed by a nonlinear Schrödinger equation. The latter is used to study the modulational instability of a Stoke's wave train to a small longitudinal perturbation. It is shown that the drift wave packet is stable (unstable) against the modulation when the drift wave number lies in 0
About the Phasor Pathways in Analogical Amplitude Modulation
de Oliveira, H M
2015-01-01
The Phasor diagrams have long been used in Physics and Engineering. In telecommunications, this is particularly useful to clarify how the modulations work. This paper addresses rotating phasor pathways derived from different standard Amplitude Modulation Systems (e.g. A3E, H3E, J3E, C3F). A cornucopia of algebraic curves is then derived assuming a single tone or a double tone modulation signal. The ratio of the frequency of the tone modulator (fm) and carrier frequency (fc) is considered in two distinct cases, namely: fm/fc=1. The geometric figures are some sort of Lissajours figures. Different shapes appear looking like epicycloids (including cardioids), rhodonea curves, Lemniscates, folium of Descartes or Lam\\'e curves. The role played by the modulation index is elucidated in each case.
Graphene based plasmonic terahertz amplitude modulator operating above 100 MHz
Jessop, D. S.; Kindness, S. J.; Xiao, L.; Braeuninger-Weimer, P.; Lin, H.; Ren, Y.; Ren, C. X.; Hofmann, S.; Zeitler, J. A.; Beere, H. E.; Ritchie, D. A.; Degl'Innocenti, R.
2016-04-01
The terahertz (THz) region of the electromagnetic spectrum holds great potential in many fields of study, from spectroscopy to biomedical imaging, remote gas sensing, and high speed communication. To fully exploit this potential, fast optoelectronic devices such as amplitude and phase modulators must be developed. In this work, we present a room temperature external THz amplitude modulator based on plasmonic bow-tie antenna arrays with graphene. By applying a modulating bias to a back gate electrode, the conductivity of graphene is changed, which modifies the reflection characteristics of the incoming THz radiation. The broadband response of the device was characterized by using THz time-domain spectroscopy, and the modulation characteristics such as the modulation depth and cut-off frequency were investigated with a 2.0 THz single frequency emission quantum cascade laser. An optical modulation cut-off frequency of 105 ± 15 MHz is reported. The results agree well with a lumped element circuit model developed to describe the device.
Multisensory interaction in vibrotactile detection and discrimination of amplitude modulation
Teodorescu, Kinneret; Bouchigny, Sylvain; Hoffmann, Pablo F.; Korman, Maria
-tactile modulations in relevant stimuli ranges. Altogether, our results provide basis to assume that during acquisition of mandibular drilling skill, trainees may benefit from training of relevant basic aspects of touch perception - sensitivity to vibration and accompanying modulations of sound.......Perception of vibration during drilling demands integration of haptic and auditory information with force information. In this study we explored the ability to detect and discriminate changes in vibrotactile stimuli amplitude based either on purely haptic feedback or together with congruent...... synthesized auditory cues in groups of naive subjects and expert surgeons. Our results point toward the complex influence of multimodal experience during vibration perception. First, in naive subjects, we showed that detection and discrimination of amplitude change in complex vibro-tactile stimulus is...
Amplitude Modulation in the ZZ Ceti Star GD 244
Bognár, Zs.; Paparó, M.; Molnár, L.; Plachy, E.; Sódor, Á.
2015-06-01
Previous studies of GD 244 revealed seven pulsation frequencies (two doublets and three single periods) in the light variations of the star. The data obtained at McDonald Observatory between 2003 and 2006, and our additional measurements in 2006 and 2007 at Konkoly Observatory, allow the investigation of the long-term pulsational behaviour of GD 244. We found that the 307.1 s period component of one of the doublets show long-term, periodic amplitude modulation with a time scale of ˜ 740 days. Possible explanations are that nonlinear resonant mode coupling is operating among the rotationally split frequency components, or two modes, unresolved in the yearly data are excited at ˜ 307.1 s. This is the first time that such long-term periodic amplitude modulation is published on a ZZ Ceti star.
Multi-hit time-to-amplitude CAMAC module (MTAC)
A Multi-Hit Time-to-Amplitude Module (MTAC) for the SLAC Mark III drift chamber system has been designed to measure drift time by converting time-proportional chamber signals into analog levels, and converting the analog data by slow readout via a semi-autonomous controller in a CAMAC crate. The single width CAMAC module has 16 wire channels, each with a 4-hit capacity. An externally generated common start initiates an internal precision ramp voltage which is then sampled using a novel shift register gating scheme and CMOS sampling switches. The detailed design and performance specifications are described
Amplitude modulation of atomic wave functions. Final report
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 microm 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 state, so this produces a time-resolved measurement of the very rapid autoionization decay. Although this does not yet show that the atom stores modulations in the bound coherent state, it does demonstrate that the atom can be excited to an autoionizing state with high efficiency, and then brought back to a bound state at a later time. The second set of experiments takes the previous work to the strong coupling regime
Amplitude modulation of atomic wave functions. Final report
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 state, so this produces a time-resolved measurement of the very rapid autoionization decay. Although this does not yet show that the atom stores modulations in the bound coherent state, it does demonstrate that the atom can be excited to an autoionizing state with high efficiency, and then brought back to a bound state at a later time. The second set of experiments takes the previous work to the strong coupling regime.
Modulational instability of a large-amplitude lower hybrid wave
Modulation instability of a longwave low-hybride high amplitude wave is considered. A new method for investigating the cold plasma parametric instabilities, based on regularization of finiteless determinants by the Hill method is developed, using which an obvious expression for instability increment is obtained without making use of low parameters. It is shown that without regard to plasma particle thermal spread, increment grows monotonously with the growth of Bessel function argument. Instability increment calculations for plasma with Maxwell distribution by rates are performed using a numeric solution of a standard system describing parametric instabilities. 10 refs.; 6 figs
Dispersion interferometer using modulation amplitudes on LHD (invited)
Akiyama, T., E-mail: takiyama@lhd.nifs.ac.jp; Yasuhara, R.; Kawahata, K. [National Institute for Fusion Science, 322-6 Oroshi-cho, Toki-shi, Gifu 509-5292 (Japan); Okajima, S.; Nakayama, K. [Chubu University, Matsumoto-cho, Kasugai-shi, Aichi 487-8501 (Japan)
2014-11-15
Since a dispersion interferometer is insensitive to mechanical vibrations, a vibration compensation system is not necessary. The CO{sub 2} laser dispersion interferometer with phase modulations on the Large Helical Device utilizes the new phase extraction method which uses modulation amplitudes and can improve a disadvantage of the original dispersion interferometer: measurement errors caused by variations of detected intensities. The phase variation within ±2 × 10{sup 17} m{sup −3} is obtained without vibration compensation system. The measured line averaged electron density with the dispersion interferometer shows good agreement with that with the existing far infrared laser interferometer. Fringe jump errors in high density ranging up to 1.5 × 10{sup 20} m{sup −3} can be overcome by a sufficient sampling rate of about 100 kHz.
Dispersion interferometer using modulation amplitudes on LHD (invited)
Akiyama, T.; Yasuhara, R.; Kawahata, K.; Okajima, S.; Nakayama, K.
2014-11-01
Since a dispersion interferometer is insensitive to mechanical vibrations, a vibration compensation system is not necessary. The CO2 laser dispersion interferometer with phase modulations on the Large Helical Device utilizes the new phase extraction method which uses modulation amplitudes and can improve a disadvantage of the original dispersion interferometer: measurement errors caused by variations of detected intensities. The phase variation within 2 1017 m-3 is obtained without vibration compensation system. The measured line averaged electron density with the dispersion interferometer shows good agreement with that with the existing far infrared laser interferometer. Fringe jump errors in high density ranging up to 1.5 1020 m-3 can be overcome by a sufficient sampling rate of about 100 kHz.
Amplitude and polarization modulated hyperspectral Stimulated Raman Scattering Microscopy.
Andreana, Marco; Houle, Marie-Andre; Moffatt, Douglas J; Ridsdale, Andrew; Buettner, Edlef; Lgar, Franois; Stolow, Albert
2015-11-01
We present a simple hyperspectral Stimulated Raman Scattering (SRS) microscopy method based on spectral focusing of chirped femtosecond pulses, combined with amplitude (AM) and polarization (PM) modulation. This approach permits the imaging of low concentration components with reduced background signals, combined with good hyperspectral resolution and rapid spectral scanning. We demonstrate, using PM-SRS in a Raman loss configuration, the spectrally resolved detection of deuterated dimethyl sulfoxide (DMSO-d6) at concentrations as low as 0.039 % (5.5 mM). In general, background signals due to cross-phase modulation (XPM), two-photon absorption (TPA) and thermal lensing (TL) can reduce the contrast in SRS microscopy. We show that the nonresonant background signal contributing to the SRS signal is, in our case, largely due to XPM. Polarization modulation of the Stokes beam eliminates the nonresonant XPM background, yielding high quality hyperspectral scans at low analyte concentration. The flexibility of our combined AM-PM approach, together with the use of variable modulation frequency and lock-in phase, should allow for optimization of SRS imaging in more complex samples. PMID:26561083
Research proposal on : amplitude modulated reflectometry system for JET divertor
Amplitude Modulated reflectometry is presented here as a tool for density profile measurements in the JET divertor plasmas. One of the main problems which has been presented in most reflectometers during the last years is the need for a coherent tracking of the phase delay: fast density fluctuations and strong modulation on the amplitude of the reflected signal usually bring to fringe jumps' in the phase signal, which are a big problem when the phase values are much larger than 2 pi. The conditions in the JET divertor plasmas: plasma geometry, access and long oversized broad-band waveguide paths makes very difficult the phase measurements at the millimeter wave range. AM reflectometry is to some extension an intermediate solution between the classical phase delay reflectometry, so far applied to small distances, and the time domain reflectometry, used for ionospheric studies and recently also proposed for fusion plasma. the main advantage is to allow the use of millimeter wave reflectometry with moderate phase shifts (approx 2 pi). (author)
Cusack, B J; Shaddock, D A; Gray, M B; Lam, P K; Whitcomb, S E; Cusack, Benedict J; Gray, Malcolm B; Lam, Ping Koy; Shaddock, Daniel A; Sheard, Benjamin S; Whitcomb, Stan E
2003-01-01
We report on the analysis and prototype-characterization of a dual-electrode electro-optic modulator that can generate both amplitude and phase modulations with a selectable relative phase, termed a universally tunable modulator (UTM). All modulation states can be reached by tuning only the electrical inputs, facilitating real-time tuning, and the device is shown to have good suppression and stability properties. A mathematical analysis is presented, including the development of a geometric phase representation for modulation. The experimental characterization of the device shows that relative suppressions of 38 dB, 39 dB and 30 dB for phase, single-sideband and carrier-suppressed modulations, respectively, can be obtained, as well as showing the device is well-behaved when scanning continuously through the parameter space of modulations. Uses for the device are discussed, including the tuning of lock points in optical locking schemes, single sideband applications, modulation fast-switching applications, and ...
Linear solutions for the frequency and amplitude modulation of ENSO by the annual cycle
An, Soon-Il; Jin, Fei-Fei
2011-01-01
We obtained linear solutions for the frequency and amplitude modulations of the El Niño-Southern Oscillation (ENSO) by the annual cycle using a modified harmonic oscillator equation. The frequency modulation by the annual cycle was capable of changing the ENSO phases and dominant frequency, but could not modify the ENSO amplitude. On the other hand, the amplitude modulation by the annual cycle intensifies the ENSO variability and also induces seasonal amplitude locking. The intensification ra...
Phonological awareness and sinusoidal amplitude modulation in phonological dislexia
Yolanda Peñaloza-López
2016-04-01
Full Text Available ABSTRACT Objective Dyslexia is the difficulty of children in learning to read and write as results of neurological deficiencies. The objective was to test the Phonological awareness (PA and Sinusoidal amplitude modulation (SAM threshold in children with Phonological dyslexia (PD. Methods We performed a case-control, analytic, cross sectional study. We studied 14 children with PD and 14 control children from 7 to 11 years of age, by means of PA measurement and by SAM test. The mean age of dyslexic children was 8.39 years and in the control group was 8.15. Results Children with PD exhibited inadequate skills in PA, and SAM. We found significant correlations between PA and SAM at 4 Hertz frequency, and calculated regression equations that predicts between one-fourth and one-third of variance of measurements. Conclusion Alterations in PA and SAM found can help to explain basis of deficient language processing exhibited by children with PD.
Phonological awareness and sinusoidal amplitude modulation in phonological dislexia.
Peñaloza-López, Yolanda; Herrera-Rangel, Aline; Pérez-Ruiz, Santiago J; Poblano, Adrián
2016-04-01
Objective Dyslexia is the difficulty of children in learning to read and write as results of neurological deficiencies. The objective was to test the Phonological awareness (PA) and Sinusoidal amplitude modulation (SAM) threshold in children with Phonological dyslexia (PD). Methods We performed a case-control, analytic, cross sectional study. We studied 14 children with PD and 14 control children from 7 to 11 years of age, by means of PA measurement and by SAM test. The mean age of dyslexic children was 8.39 years and in the control group was 8.15. Results Children with PD exhibited inadequate skills in PA, and SAM. We found significant correlations between PA and SAM at 4 Hertz frequency, and calculated regression equations that predicts between one-fourth and one-third of variance of measurements. Conclusion Alterations in PA and SAM found can help to explain basis of deficient language processing exhibited by children with PD. PMID:27097001
Decadal amplitude modulation of two types of ENSO and its relationship with the mean state
Choi, Jung; An, Soon-Il [Yonsei University, Department of Atmospheric Sciences, Global Environmental Laboratory, Seoul (Korea, Republic of); Yeh, Sang-Wook [Hanyang University, Department of Environmental Marine Science, Ansan (Korea, Republic of)
2012-06-15
In this study, we classified two types of El Nino-Southern Oscillation (ENSO) events within the decadal ENSO amplitude modulation cycle using a long-term coupled general circulation model simulation. We defined two climate states - strong and weak ENSO amplitude periods - and separated the characteristics of ENSO that occurred in both periods. There are two major features in the characteristics of ENSO: the first is the asymmetric spatial structure between El Nino and La Nina events; the second is that the El Nino-La Nina asymmetry is reversed during strong and weak ENSO amplitude periods. El Nino events during strong (weak) ENSO amplitude periods resemble the Eastern Pacific (Central Pacific) El Nino in terms of the spatial distribution of sea surface temperature anomalies (SSTA) and physical characteristics based on heat budget analysis. The spatial pattern of the thermocline depth anomaly for strong (weak) El Nino is identical to that for weak (strong) La Nina, but for an opposite sign and slightly different amplitude. The accumulated residuals of these asymmetric anomalies dominated by an east-west contrast structure could feed into the tropical Pacific mean state. Moreover, the residual pattern associated with El Nino-La Nina asymmetry resembles the first principal component analysis (PCA) mode of tropical Pacific decadal variability, indicating that the accumulated residuals could generate the change in climate state. Thus, the intensified ENSO amplitude yields the warm residuals due to strong El Nino and weak La Nina over the eastern tropical Pacific. This linear relationship between ENSO and the mean state is strong during the mature phases of decadal oscillation, but it is weak during the transition phases. Furthermore, the second PCA mode of tropical Pacific decadal variability plays an important role in changing the phase of the first mode. Consequently, the feedback between ENSO and the mean state is positive feedback to amplify the first PCA mode, whereas the second PCA mode is a negative feedback to lead the phase change of the first PCA mode due to their lead-lag relationship. These features could be regarded as evidence that the decadal change in properties of ENSO could be generated by the nonlinear interaction between ENSO and the mean state on a decadal-to-interdecadal time scale. (orig.)
Amplitude modulation in $\\delta$ Sct stars: statistics from an ensemble study of Kepler targets
Bowman, Dominic M; Breger, Michel; Murphy, Simon J; Holdsworth, Daniel L
2016-01-01
We present the results of a search for amplitude modulation of pulsation mode frequencies in 983 $\\delta$ Sct stars, which have effective temperatures between 6400 $\\leq T_{\\rm eff} \\leq$ 10 000 K in the Kepler Input Catalogue and were continuously observed by the Kepler Space Telescope for 4 yr. We demonstrate the diversity in pulsational behaviour observed, in particular nonlinearity, which is predicted for $\\delta$ Sct stars. We analyse and discuss examples of $\\delta$ Sct stars with constant amplitudes and phases; those that exhibit amplitude modulation caused by beating of close-frequency pulsation modes; those that exhibit pure amplitude modulation (with no associated phase variation); those that exhibit phase modulation caused by binarity; and those that exhibit amplitude modulation caused by nonlinearity. Using models and examples of individual stars, we demonstrate that observations of the changes in amplitude and phase of pulsation modes can be used to distinguish among the different scenarios. We f...
Ma, Zong-Min; Mu, Ji-Liang; Tang, Jun; XUE, HUI; ZHANG, Huan; Xue, Chen-Yang; Liu, Jun; Li, Yan-jun
2013-01-01
In this paper, the potential sensitivity in Kelvin probe force microscopy (KPFM) was investigated in frequency modulation (FM) and heterodyne amplitude modulation (AM) modes. We showed theoretically that the minimum detectable contact potential difference (CPD) in FM-KPFM is higher than in heterodyne AM-KPFM. We experimentally confirmed that the signal-to-noise ratio in FM-KPFM is lower than that in heterodyne AM-KPFM, which is due to the higher minimum detectable CPD dependence in FM-KPFM. W...
Blaaberg, Søren; Mørk, Jesper
2009-01-01
We present theoretical results that show conversion of phase modulated signals to amplitude modulated signals in an SOA. Large-signal and small-signal calculations show significant conversion responses caused by even minute reflections at the end mirrors.......We present theoretical results that show conversion of phase modulated signals to amplitude modulated signals in an SOA. Large-signal and small-signal calculations show significant conversion responses caused by even minute reflections at the end mirrors....
ERP responses to processing prosodic phrasing of sentences in amplitude modulated noise.
Carroll, Rebecca; Ruigendijk, Esther
2016-02-01
Intonation phrase boundaries (IPBs) were hypothesized to be especially difficult to process in the presence of an amplitude modulated noise masker because of a potential rhythmic competition. In an event-related potential study, IPBs were presented in silence, stationary, and amplitude modulated noise. We elicited centro-parietal Closure Positive Shifts (CPS) in 23 young adults with normal hearing at IPBs in all acoustic conditions, albeit with some differences. CPS peak amplitudes were highest in stationary noise, followed by modulated noise, and lowest in silence. Both noise types elicited CPS delays, slightly more so in stationary compared to amplitude modulated noise. These data suggest that amplitude modulation is not tantamount to a rhythmic competitor for prosodic phrasing but rather supports an assumed speech perception benefit due to local release from masking. The duration of CPS time windows was, however, not only longer in noise compared to silence, but also longer for amplitude modulated compared to stationary noise. This is interpreted as support for additional processing load associated with amplitude modulation for the CPS component. Taken together, processing prosodic phrasing of sentences in amplitude modulated noise seems to involve the same issues that have been observed for the perception and processing of segmental information that are related to lexical items presented in noise: a benefit from local release from masking, even for prosodic cues, and a detrimental additional processing load that is associated with either stream segregation or signal reconstruction. PMID:26776233
All-optical $\\mathcal{PT}$-symmetric amplitude to phase modulator
Gutiérrez, Oscar Ignacio Zaragoza; Rodríguez-Lara, B M
2015-01-01
We study electromagnetic field propagation through a planar three-waveguide coupler with linear gain and loss, in a configuration that is the optical analog of a quantum $\\mathcal{PT}$-symmetric system, and provide its closed-form analytic propagator. At an specific propagation length, we show that the device provides all-optical amplitude to phase modulation with a $\\pi$ modulation range, if an extra binary phase is allowed in the reference signal, as well as phase to amplitude modulation, with an amplitude modulation range that depends linearly on the gain-to-coupling ratio of the system.
Stepp, Cara E; Matsuoka, Yoky
2012-01-01
Incorporating sensory feedback with prosthetic devices is now possible, but the optimal methods of providing such feedback are still unknown. The relative utility of amplitude and pulse train frequency modulated stimulation paradigms for providing vibrotactile feedback for object manipulation was assessed in 10 participants. The two approaches were studied during virtual object manipulation using a robotic interface as a function of presentation order and a simultaneous cognitive load. Despite the potential pragmatic benefits associated with pulse train frequency modulated vibrotactile stimulation, comparison of the approach with amplitude modulation indicates that amplitude modulation vibrotactile stimulation provides superior feedback for object manipulation. PMID:21997322
Trellis-coded pulse amplitude modulation for indoor visible light communication
Wang, Yu; Yang, Aiying; Wu, Yongsheng; Feng, Lihui; Sun, Yu-nan; Li, Yankun
2013-12-01
Trellis-coded pulse-amplitude modulation (TC-PAM) is applied in visible light communication (VLC) system using RGB-LED. Based on natural modulation, we propose a modified modulation to yield performance enhancement. Further, a decoding method of combing soft-decision Viterbi algorithm with most significant bit (MSB) decoding is developed. Finally, the results of Monte-Carlo simulation are presented to verify the best modulation and decoding method among the mentioned modulation and decoding techniques.
Quadrature amplitude modulation (QAM) using binary-driven coupling-modulated rings
Karimelahi, Samira; Sheikholeslami, Ali
2016-05-01
We propose and fully analyze a compact structure for DAC-free pure optical QAM modulation. The proposed structure is the first ring resonator-based DAC-free QAM modulator reported in the literature, to the best of our knowledge. The device consists of two segmented add-drop Mach Zehnder interferometer-assisted ring modulators (MZIARM) in an IQ configuration. The proposed architecture is investigated based on the parameters from SOI technology where various key design considerations are discussed. We have included the loss in the MZI arms in our analysis of phase and amplitude modulation using MZIARM for the first time and show that the imbalanced loss results in a phase error. The output level linearity is also studied for both QAM-16 and QAM-64 not only based on optimizing RF segment lengths but also by optimizing the number of segments. In QAM-16, linearity among levels is achievable with two segments while in QAM-64 an additional segment may be required.
A novel microcomputer-based ultrasonic distance measurement system is presented. This study proposes an efficient algorithm which combines both the amplitude modulation (AM) and the phase modulation (PM) of the pulse-echo technique. The proposed system can reduce error caused by inertia delay and amplitude attenuation effect when using the AM and PM envelope square wave form (APESW). The APESW ultrasonic driving wave form causes a phase inversion phenomenon in the relative wave form of the receiver. The phase inversion phenomenon sufficiently identifies the ''measurement pulse'' in the received wave forms, which can be used for accurate time-of-flight (TOF) measurement. In addition, combining a countertechnique to compute the phase shifts of the last cycle for TOF, the presented system can obtain distance resolution of 0.1% of the wavelength corresponding to the 40 kHz frequency of the ultrasonic wave. The standard uncertainty of the proposed distance measurement system is found to be 0.2 mm at a range of 50-500 mm. The APESW signal generator and phase detector of this measuring system are designed on a complex programmable logic device, which is used to govern the TOF measurement and send the data to a personal computer for distance calibration and examination. The main advantages of this APESW system are high resolution, low cost, narrow bandwidth requirement, and ease of implementation
Transport Enhancement of Irregular Optical Lattices with Polychromatic Amplitude Modulation
Pepino, R. A.; Teh, W. P.; Magness, L. J.
2015-01-01
We demonstrate that the transport characteristics of deep optical lattices with one or multiple off-resonant external energy offsets can be greatly-enhanced by modulating the lattice depth in an exotic way. We derive effective stationary models for our proposed modulation schemes in the strongly interacting limit, where only one particle can occupy any given site. Afterwards we discuss the modifications necessary to recover transport when more than one particle may occupy the lattice sites. F...
Predistortion of quadrature amplitude modulation signals using Volterra series approximation
Donovan, Michael T.
1996-01-01
Modern digital communication systems are being called upon to move ever increasing amounts of information over decreasingly available bandwidth. This requires that communication systems employ bandwidth-efficient modulation schemes to conserve bandwidth while moving the information at higher data rates. A major stumbling block to using higher order modulation schemes in long haul communication is the distortion caused by high power amplifiers. These high power amplifiers are required to ampli...
Modulational instability of finite-amplitude, circularly polarized Alfven waves
Derby, N. F., Jr.
1978-01-01
The simple theory of the decay instability of Alfven waves is strictly applicable only to a small-amplitude parent wave in a low-beta plasma, but, if the parent wave is circularly polarized, it is possible to analyze the situation without either of these restrictions. Results show that a large-amplitude circularly polarized wave is unstable with respect to decay into three waves, one longitudinal and one transverse wave propagating parallel to the parent wave and one transverse wave propagating antiparallel. The transverse decay products appear at frequencies which are the sum and difference of the frequencies of the parent wave and the longitudinal wave. The decay products are not familiar MHD modes except in the limit of small beta and small amplitude of the parent wave, in which case the decay products are a forward-propagating sound wave and a backward-propagating circularly polarized wave. In this limit the other transverse wave disappears. The effect of finite beta is to reduce the linear growth rate of the instability from the value suggested by the simple theory. Possible applications of these results to the theory of the solar wind are briefly touched upon.
Analyses of the mechanisms of amplitude modulation of aero-acoustic wind turbine sound
Fischer, Andreas; Aagaard Madsen, Helge; Kragh, Knud Abildgaard; Bertagnolio, Franck
2014-01-01
This paper explores the source mechanism which cause amplitude modulation of the emitted sound of a wind turbine at large distances from the turbine, named as other amplitude modulation. Measurements of the fluctuating surface pressure on a 2.3MW wind turbine showed a considerable variation over ...... give further evidence that transient stall is a main mechanism to cause other amplitude modulation. Wind shear was identified as a critical condition to cause angle of attack variations. Dierent control strategies to mitigate other amplitude modulation were proposed....... blade revolution in the presence of angle of attack variations. If the blade undergoes transient stall, the variation of the surface pressure spectrum was enhanced and shifted to frequencies below 200Hz. The surface pressure spectra could be directly related to the emitted far eld sound. These ndings...
Uncovering signals from measurement noise by electro mechanical amplitude modulation
We present an electromechanical parametric scheme to improve the low-frequency signal-to-noise ratio of energy buffering type transducers. The method is based on periodic modulation of the stiffness in the sensory system which produces upconverted replicas of the signals of interest at frequencies where measurement is less troubled by noise or other detrimental effects. We demonstrate this principle by means of capacitive biomimetic hair flow sensors, where we modulate the rotational spring stiffness by periodic electrostatic spring softening, such that a replica of the original signal is formed around the modulation frequency. Using this replica we gain up to a 25-fold improvement of the low-frequency signal-to-noise ratio and sensing threshold. For transient measurements we demonstrate that tiny signals, which are below the noise-levels in the base-band, are revealed well when upconverted to higher frequencies. (paper)
Uncovering signals from measurement noise by electro mechanical amplitude modulation
Droogendijk, H.; Sanders, R. G. P.; Krijnen, G. J. M.
2013-05-01
We present an electromechanical parametric scheme to improve the low-frequency signal-to-noise ratio of energy buffering type transducers. The method is based on periodic modulation of the stiffness in the sensory system which produces upconverted replicas of the signals of interest at frequencies where measurement is less troubled by noise or other detrimental effects. We demonstrate this principle by means of capacitive biomimetic hair flow sensors, where we modulate the rotational spring stiffness by periodic electrostatic spring softening, such that a replica of the original signal is formed around the modulation frequency. Using this replica we gain up to a 25-fold improvement of the low-frequency signal-to-noise ratio and sensing threshold. For transient measurements we demonstrate that tiny signals, which are below the noise-levels in the base-band, are revealed well when upconverted to higher frequencies.
Amplitude control of solid-state modulators for precision fast kicker applications
A solid-state modulator with very fast rise and fall times, pulse width agility, and multi-pulse burst and intra-pulse amplitude adjustment capability for use with high speed electron beam kickers has been designed and tested at LLNL (Lawrence Livermore National Laboratory). The modulator uses multiple solid-state modules stacked in an inductive-adder configuration. Amplitude adjustment is provided by controlling individual modules in the adder, and is used to compensate for transverse e-beam motion as well as the dynamic response and beam-induced steering effects associated with the kicker structure. A control algorithm calculates a voltage based on measured e-beam displacement and adjusts the modulator to regulate beam centroid position. This paper presents design details of amplitude control along with measured performance data from kicker operation on the ETA-II accelerator at LLNL. (author)
Amplitude Control of Solid-State Modulators for Precision Fast Kicker Applications
A solid-state modulator with very fast rise and fall times, pulse width agility, and multi-pulse burst and intra-pulse amplitude adjustment capability for use with high speed electron beam kickers has been designed and tested at LLNL. The modulator uses multiple solid-state modules stacked in an inductive-adder configuration. Amplitude adjustment is provided by controlling individual modules in the adder, and is used to compensate for transverse e-beam motion as well as the dynamic response and beam-induced steering effects associated with the kicker structure. A control algorithm calculates a voltage based on measured e-beam displacement and adjusts the modulator to regulate beam centroid position. This paper presents design details of amplitude control along with measured performance data from kicker operation on the ETA-II accelerator at LLNL
Pokorný, Pavel; Náhlík, Luboš; Hutař, Pavel
Vol. C. Amsterdam : Elsevier Ltd, 2015 - (Papuga, J.; Ružička, M.), s. 380-385 ISSN 1877-7058. - (Procedia Engineering. 101). [VAL 2015 - International Conference on Material and Component Performance under Variable Amplitude Loading /3./. Praha (CZ), 23.03.2015-26.03.2015] R&D Projects: GA MŠk(CZ) EE2.3.20.0214 Institutional support: RVO:68081723 Keywords : railway axle * residual fatigue lifetime * fatigue crack * EA4T Subject RIV: JL - Materials Fatigue, Friction Mechanics http://www.sciencedirect.com/science/article/pii/S187770581500644X
Inspection of complex amplitudes of spatial light modulators using moiré techniques
Calderón-Hermosillo, C. Y.; Alcalá Ochoa, Noé; Noé Arias, E.; García-Márquez, J.
2013-05-01
We propose a method to get the phase and amplitude modes of an electrically driven spatial light modulator (SLM) device using the formation of moiré patterns. It is found to be a fast experimental method to visualize the complex amplitude of the SLM and it may be an excellent guide to find specific complex configurations of amplitude and phase. Experimental results and limitations of the proposal are presented using a reflective liquid crystal on silicon (LCoS SLM) modulator. With this method it has been found experimentally a phase-mostly configuration using only one polarizer, without an analyzer.
Ghoreishy, Hoda; Varjani, Ali Yazdian; Mohamadian, Mustafa; Farhangi, Shahrokh; Zhang, Zhe
2013-01-01
Compared to the conventional selective harmonic elimination-pulse width modulation (SHE-PWM), the selective harmonic elimination-pulse width and amplitude modulation (SHE-PWAM) control strategy results in significant improvements in the performance of CHB inverters. This fact is due to considerin...
A comparison of the effects of continuous wave, sinusoidal-amplitude modulated, and pulsed square-wave-modulated 591-MHz microwave exposures on brain energy metabolism was made in male Sprague Dawley rats (175-225g). Brain NADH fluorescence, adensine triphosphate (ATP) concentrat...
Plasma based optical guiding of an amplitude-modulated electromagnetic beam
Singh, Mamta; Gupta, D. N.
2015-06-01
We propose the stronger optical guiding of an electromagnetic beam in a plasma by considering the amplitude modulation of the fundamental beam. With the advent of high power source of electromagnetic radiation, the electron velocity in a plasma may become quite large (comparable to the light velocity in free space). Thus, the effect of relativistic mass variation must be taken into account. The relativistic effect of the laser propagation in a plasma leads to self-focusing because of the dielectric constant of a plasma being an increasing function of the intensity. The ponderomotive force of the laser beam pushes the electrons out of the region of high intensity, which reduces the local electron density and increases the plasma dielectric function further, leading to even more selffocusing of the laser. In this work, we consider a short pulse laser of finite spot size as an amplitude modulation in time. Our findings show an efficient optical guiding mechanism based on amplitude modulation signal propagation in plasmas. Medium nonlinearity becomes stronger if an amplitude modulated beam is introduced, which contributes significantly in laser guiding in plasmas. Furthermore, the rate of laser self-focusing is increased with modulation index due the fact of stronger Kerr effect. The study related to amplitude modulated optical signal may be useful for communication technology.
Observations on auditory learning in amplitude- and frequency-modulation rate discrimination
Hoffmann, Pablo F.
2010-01-01
Because amplitude- and frequency-modulated sounds can be the basis for the synthesis of many complex sounds, they can be good candidates in the design of training systems aiming at improving the acquisition of perceptual skills that can benefit from information provided via the auditory channel......-training, training, a post-training stages. During training, listeners were divided into two groups; one group trained on amplitude-modulation rate discrimination and the other group trained on frequency-modulation rate discrimination. Results will be discussed in terms of their implications for training...
Diffusion-induced periodic transition between oscillatory modes in amplitude-modulated patterns
Tang, Xiaodong; He, Yuxiu; Wang, Shaorong; Gao, Qingyu, E-mail: gaoqy@cumt.edu.cn [College of Chemical Engineering, China University of Mining and Technology, Xuzhou 221008 (China); Epstein, Irving R., E-mail: epstein@brandeis.edu [Department of Chemistry and Volen Center for Complex Systems, MS 015, Brandeis University, Waltham, Massachusetts 02454-9110 (United States); Wang, Qun [School of Physics and Electronic Engineering, Jiangsu Normal University, Xuzhou 221116 (China)
2014-06-15
We study amplitude-modulated waves, e.g., wave packets in one dimension, overtarget spirals and superspirals in two dimensions, under mixed-mode oscillatory conditions in a three-variable reaction-diffusion model. New transition zones, not seen in the homogeneous system, are found, in which periodic transitions occur between local 1{sup N−1} and 1{sup N} oscillations. Amplitude-modulated complex patterns result from periodic transition between (N − 1)-armed and N-armed waves. Spatial recurrence rates provide a useful guide to the stability of these modulated patterns.
Diffusion-induced periodic transition between oscillatory modes in amplitude-modulated patterns.
Tang, Xiaodong; He, Yuxiu; Epstein, Irving R; Wang, Qun; Wang, Shaorong; Gao, Qingyu
2014-06-01
We study amplitude-modulated waves, e.g., wave packets in one dimension, overtarget spirals and superspirals in two dimensions, under mixed-mode oscillatory conditions in a three-variable reaction-diffusion model. New transition zones, not seen in the homogeneous system, are found, in which periodic transitions occur between local 1(N-1) and 1(N) oscillations. Amplitude-modulated complex patterns result from periodic transition between (N - 1)-armed and N-armed waves. Spatial recurrence rates provide a useful guide to the stability of these modulated patterns. PMID:24985423
Optical modulation using anti-crossing between paired amplitude and phase resonators.
Green, William M J; Rooks, Michael J; Sekaric, Lidija; Vlasov, Yurii A
2007-12-10
An optical modulator design based upon anti-crossing between coupled silicon microrings with independent amplitude and phase functionality is presented. The device exhibits over 25x improvement in sensitivity to an input drive signal when compared with previously studied microring modulators based on control of waveguide-resonator coupling. The new design also demonstrates an ON-OFF contrast of 14 dB, and has an ultra-compact footprint of 0.003 mm(2). The observed sensitivity enhancement suggests that this modulator may be driven directly by digital CMOS electrical signals with less than 1 V amplitude. PMID:19551020
Basic causes of amplitude modulation in climatic/weather parameters
The continuous interaction between the Earth's spinning motion and energy from the Sun gives rise to some (heat) energy oscillations in the Earth-atmosphere system (Njau, 1985a; 1985b; 1986a; 1986b). Recent results of large scale analysis of East African climatic records have proved that these oscillations significantly link the Sun to climatic/weather variations by systematically modulating key climatic/weather parameters like rainfall and air temperature (Njau, 1987a; 1987b; 1987c; 1987e; 1987f). In this paper, we re-develop the latter proof using a very different approach based upon theoretical analysis. The analysis has confirmed a general law suggested earlier (Njau, 1987d), that, with an exception of the diurnal cycle, any permanent cycle in the net solar energy incident upon a given part of the Earth-Atmosphere system gives rise to a quasi-permanent cycle whose period is approximately twice that of the former. Quasi-biennial as well as double sunspot cycles are shown to be a possible result of this general law. (author). 35 refs, 1 fig., 2 tabs
Extending single molecule fluorescence observation time by amplitude-modulated excitation
We present a hardware-based method that can improve single molecule fluorophore observation time by up to 1500% and super-localization by 47% for the experimental conditions used. The excitation was modulated using an acousto-optic modulator (AOM) synchronized to the data acquisition and inherent data conversion time of the detector. The observation time and precision in super-localization of four commonly used fluorophores were compared under modulated and traditional continuous excitation, including direct total internal reflectance excitation of Alexa 555 and Cy3, non-radiative Frster resonance energy transfer (FRET) excited Cy5, and direct epi-fluorescence wide field excitation of Rhodamine 6G. The proposed amplitude-modulated excitation does not perturb the chemical makeup of the system or sacrifice signal and is compatible with multiple types of fluorophores. Amplitude-modulated excitation has practical applications for any fluorescent study utilizing an instrumental setup with time-delayed detectors. (technical note)
Analysis of amplitude modulation atomic force microscopy in aqueous salt solutions
Karayaylalı, Pınar [Department of Mechanical Engineering, Bilkent University, Ankara 06800 (Turkey); Baykara, Mehmet Z., E-mail: mehmet.baykara@bilkent.edu.tr [Department of Mechanical Engineering, Bilkent University, Ankara 06800 (Turkey); UNAM-Institute of Materials Science and Nanotechnology, Bilkent University, Ankara 06800 (Turkey)
2014-11-01
Highlights: • Imaging contrast during AM-AFM performed in salt solutions is numerically analyzed. • Imaging contrast is only marginally improved (∼15%) at high amplitude setpoints. • Sample indentation and maximum interaction force values remain relatively unaffected. - Abstract: We present a numerical analysis of amplitude modulation atomic force microscopy in aqueous salt solutions, by considering the interaction of the microscope tip with a model sample surface consisting of a hard substrate and soft biological material through Hertz and electrostatic double layer forces. Despite the significant improvements reported in the literature concerning contact-mode atomic force microscopy measurements of biological material due to electrostatic interactions in aqueous solutions, our results reveal that only modest gains of ∼15% in imaging contrast at high amplitude setpoints are expected under typical experimental conditions for amplitude modulation atomic force microscopy, together with relatively unaffected sample indentation and maximum tip–sample interaction values.
Encoding and decoding amplitude-modulated cochlear implant stimuli--a point process analysis.
Goldwyn, Joshua H; Shea-Brown, Eric; Rubinstein, Jay T
2010-06-01
Cochlear implant speech processors stimulate the auditory nerve by delivering amplitude-modulated electrical pulse trains to intracochlear electrodes. Studying how auditory nerve cells encode modulation information is of fundamental importance, therefore, to understanding cochlear implant function and improving speech perception in cochlear implant users. In this paper, we analyze simulated responses of the auditory nerve to amplitude-modulated cochlear implant stimuli using a point process model. First, we quantify the information encoded in the spike trains by testing an ideal observer's ability to detect amplitude modulation in a two-alternative forced-choice task. We vary the amount of information available to the observer to probe how spike timing and averaged firing rate encode modulation. Second, we construct a neural decoding method that predicts several qualitative trends observed in psychophysical tests of amplitude modulation detection in cochlear implant listeners. We find that modulation information is primarily available in the sequence of spike times. The performance of an ideal observer, however, is inconsistent with observed trends in psychophysical data. Using a neural decoding method that jitters spike times to degrade its temporal resolution and then computes a common measure of phase locking from spike trains of a heterogeneous population of model nerve cells, we predict the correct qualitative dependence of modulation detection thresholds on modulation frequency and stimulus level. The decoder does not predict the observed loss of modulation sensitivity at high carrier pulse rates, but this framework can be applied to future models that better represent auditory nerve responses to high carrier pulse rate stimuli. The supplemental material of this article contains the article's data in an active, re-usable format. PMID:20177761
Amplitude modulation of sound from wind turbines under various meteorological conditions.
Larsson, Conny; hlund, Olof
2014-01-01
Wind turbine (WT) sound annoys some people even though the sound levels are relatively low. This could be because of the amplitude modulated "swishing" characteristic of the turbine sound, which is not taken into account by standard procedures for measuring average sound levels. Studies of sound immission from WTs were conducted continually between 19 August 2011 and 19 August 2012 at two sites in Sweden. A method for quantifying the degree and strength of amplitude modulation (AM) is introduced here. The method reveals that AM at the immission points occur under specific meteorological conditions. For WT sound immission, the wind direction and sound speed gradient are crucial for the occurrence of AM. Interference between two or more WTs could probably enhance AM. The mechanisms by which WT sound is amplitude modulated are not fully understood. PMID:24437746
Ow, Y.S., E-mail: g0601170@nus.edu.s [Physics Department, National University of Singapore, Lower Kent Ridge Road, Singapore 119260 (Singapore); Breese, M.B.H.; Leng, Y.R.; Azimi, S.; Teo, E.J. [Physics Department, National University of Singapore, Lower Kent Ridge Road, Singapore 119260 (Singapore); Sun, X.W. [School of Electrical and Electronic Engineering, Nanyang Technological University, Nanyang Avenue, Singapore 639798 (Singapore)
2010-05-01
Silicon has been machined on lateral resolutions of micrometers and on depth resolutions of nanometers using a recently-developed process based on ion irradiation and electrochemical anodisation. Here we investigate its use as a recording medium for computer generated hologram patterns. We describe the fabrication of both amplitude and phase binary modulated reflective computer generated hologram patterns on a silicon surface with pixel sizes of 5 mum. We further discuss the use of micromachined silicon to variably modulate both amplitude and phase in a continuous, rather than a binary fashion.
Silicon has been machined on lateral resolutions of micrometers and on depth resolutions of nanometers using a recently-developed process based on ion irradiation and electrochemical anodisation. Here we investigate its use as a recording medium for computer generated hologram patterns. We describe the fabrication of both amplitude and phase binary modulated reflective computer generated hologram patterns on a silicon surface with pixel sizes of 5 μm. We further discuss the use of micromachined silicon to variably modulate both amplitude and phase in a continuous, rather than a binary fashion.
Characterizing Alzheimers Disease Severity via Resting-Awake EEG Amplitude Modulation Analysis
Fraga, Francisco J.; Falk, Tiago H.; Kanda, Paulo A. M.; Anghinah, Renato
2013-01-01
Changes in electroencephalography (EEG) amplitude modulations have recently been linked with early-stage Alzheimers disease (AD). Existing tools available to perform such analysis (e.g., detrended fluctuation analysis), however, provide limited gains in discriminability power over traditional spectral based EEG analysis. In this paper, we explore the use of an innovative EEG amplitude modulation analysis technique based on spectro-temporal signal processing. More specifically, full-band EEG signals are first decomposed into the five well-known frequency bands and the envelopes are then extracted via a Hilbert transform. Each of the five envelopes are further decomposed into four so-called modulation bands, which were chosen to coincide with the delta, theta, alpha and beta frequency bands. Experiments on a resting-awake EEG dataset collected from 76 participants (27 healthy controls, 27 diagnosed with mild-AD, and 22 with moderate-AD) showed significant differences in amplitude modulations between the three groups. Most notably, i) delta modulation of the beta frequency band disappeared with an increase in disease severity (from mild to moderate AD), ii) delta modulation of the theta band appeared with an increase in severity, and iii) delta modulation of the beta frequency band showed to be a reliable discriminant feature between healthy controls and mild-AD patients. Taken together, it is hoped that the developed tool can be used to assist clinicians not only with early detection of Alzheimers disease, but also to monitor its progression. PMID:24015222
Human Neuromagnetic Steady-State Responses to Amplitude-Modulated Tones, Speech, and Music
Parkkonen, Lauri; Hari, Riitta
2014-01-01
Objectives: Auditory steady-state responses that can be elicited by various periodic sounds inform about subcortical and early cortical auditory processing. Steady-state responses to amplitude-modulated pure tones have been used to scrutinize binaural interaction by frequency-tagging the two ears’ inputs at different frequencies. Unlike pure tones, speech and music are physically very complex, as they include many frequency components, pauses, and large temporal variations. To examine the utility of magnetoencephalographic (MEG) steady-state fields (SSFs) in the study of early cortical processing of complex natural sounds, the authors tested the extent to which amplitude-modulated speech and music can elicit reliable SSFs. Design: MEG responses were recorded to 90-s-long binaural tones, speech, and music, amplitude-modulated at 41.1 Hz at four different depths (25, 50, 75, and 100%). The subjects were 11 healthy, normal-hearing adults. MEG signals were averaged in phase with the modulation frequency, and the sources of the resulting SSFs were modeled by current dipoles. After the MEG recording, intelligibility of the speech, musical quality of the music stimuli, naturalness of music and speech stimuli, and the perceived deterioration caused by the modulation were evaluated on visual analog scales. Results: The perceived quality of the stimuli decreased as a function of increasing modulation depth, more strongly for music than speech; yet, all subjects considered the speech intelligible even at the 100% modulation. SSFs were the strongest to tones and the weakest to speech stimuli; the amplitudes increased with increasing modulation depth for all stimuli. SSFs to tones were reliably detectable at all modulation depths (in all subjects in the right hemisphere, in 9 subjects in the left hemisphere) and to music stimuli at 50 to 100% depths, whereas speech usually elicited clear SSFs only at 100% depth. The hemispheric balance of SSFs was toward the right hemisphere for tones and speech, whereas SSFs to music showed no lateralization. In addition, the right lateralization of SSFs to the speech stimuli decreased with decreasing modulation depth. Conclusions: The results showed that SSFs can be reliably measured to amplitude-modulated natural sounds, with slightly different hemispheric lateralization for different carrier sounds. With speech stimuli, modulation at 100% depth is required, whereas for music the 75% or even 50% modulation depths provide a reasonable compromise between the signal-to-noise ratio of SSFs and sound quality or perceptual requirements. SSF recordings thus seem feasible for assessing the early cortical processing of natural sounds. PMID:24603544
Focusing through a turbid medium by amplitude modulation with genetic algorithm
Dai, Weijia; Peng, Ligen; Shao, Xiaopeng
2014-05-01
Multiple scattering of light in opaque materials such as white paint and human tissue forms a volume speckle field, will greatly reduce the imaging depth and degrade the imaging quality. A novel approach is proposed to focus light through a turbid medium using amplitude modulation with genetic algorithm (GA) from speckle patterns. Compared with phase modulation method, amplitude modulation approach, in which the each element of spatial light modulator (SLM) is either zero or one, is much easier to achieve. Theoretical and experimental results show that, the advantage of GA is more suitable for low the signal to noise ratio (SNR) environments in comparison to the existing amplitude control algorithms such as binary amplitude modulation. The circular Gaussian distribution model and Rayleigh Sommerfeld diffraction theory are employed in our simulations to describe the turbid medium and light propagation between optical devices, respectively. It is demonstrated that the GA technique can achieve a higher overall enhancement, and converge much faster than others, and outperform all algorithms at high noise. Focusing through a turbid medium has potential in the observation of cells and protein molecules in biological tissues and other structures in micro/nano scale.
Dual Amplitude-Width Pulse Interval Modulation for Optical Wireless Communications
Mehdi Rouissat
2012-05-01
Full Text Available In this paper, a new modified digital pulse interval modulation called Dual Amplitude-Width Pulse Interval Modulation (DAWPIM is presented, on the basis of Pulse Amplitude Modulation (PAM and Pulse Width Modulation (PWM, and its properties are presented. After introducing symbol structure, data rate improvement, average normalized power requirement and bandwidth efficiency are studied. The proposed concept showed to be well suited to use in Optical Wireless Communications links by virtue of its increased data rate, high spectral efficiency and the absence of receiver synchronization problems. We present theoretical expressions of spectral efficiency, power requirements, and the data rate improvement normalized to PPM, and we present comparison results to DPIM and the hybrid PAM-DPIM.
Ghoreishy, Hoda; Varjani, Ali Yazdian; Mohamadian, Mustafa; Farhangi, Shahrokh; Zhang, Zhe
2013-01-01
Compared to the conventional selective harmonic elimination-pulse width modulation (SHE-PWM), the selective harmonic elimination-pulse width and amplitude modulation (SHE-PWAM) control strategy results in significant improvements in the performance of CHB inverters. This fact is due to considering the optimization of the CHB dc sources’ values along with the optimized switching angles. This paper proposes a new SHE-PWAM control strategy and its realization in a drive application. Analysis and...
Residual fatigue life estimation using a nonlinear ultrasound modulation method
Predicting the residual fatigue life of a material is not a simple task and requires the development and association of many variables that as standalone tasks can be difficult to determine. This work develops a modulated nonlinear elastic wave spectroscopy method for the evaluation of a metallic components residual fatigue life. An aluminium specimen (AA6082-T6) was tested at predetermined fatigue stages throughout its fatigue life using a dual-frequency ultrasound method. A modulated nonlinear parameter was derived, which described the relationship between the generation of modulated (sideband) responses of a dual frequency signal and the linear response. The sideband generation from the dual frequency (two signal output system) was shown to increase as the residual fatigue life decreased, and as a standalone measurement method it can be used to show an increase in a materials damage. A baseline-free method was developed by linking a theoretical model, obtained by combining the Paris law and the Nazarov–Sutin crack equation, to experimental nonlinear modulation measurements. The results showed good correlation between the derived theoretical model and the modulated nonlinear parameter, allowing for baseline-free material residual fatigue life estimation. Advantages and disadvantages of these methods are discussed, as well as presenting further methods that would lead to increased accuracy of residual fatigue life detection. (paper)
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
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.
Transmission of Waveforms Determined by 7 Eigenvalues with PSK-Modulated Spectral Amplitudes
Buelow, Henning; Idler, Wilfried
2016-01-01
2-ns waveforms with 7 eigenvalues and their QPSK-modulated spectral amplitudes were optimized by taking constraints of link, transmitter, and receiver into account. In experiment these signals were transmitted with a BER of 3.2E-3 over 1440-km of NZ-DSF fiber spans.
Puerta Ramírez, Rafael; Rommel, Simon; Altabas, Jose A.; Pyndt, Line; Idrissa, Raya; Sultanov, Albert Kh.
2016-01-01
We report on the first experimental demonstration of carrierless amplitude/phase modulation in a flexible multiband approach for ultrawideband high-data-rate wireless communications. An effective bitrate of 2 GB/s is achieved while complying with the restrictions on the effective radiated power e...
Radar transponder operation with compensation for distortion due to amplitude modulation
Ormesher, Richard C.; Tise, Bertice L.; Axline, Jr., Robert M.
2011-01-04
In radar transponder operation, a variably delayed gating signal is used to gate a received radar pulse and thereby produce a corresponding gated radar pulse for transmission back to the source of the received radar pulse. This compensates for signal distortion due to amplitude modulation on the retransmitted pulse.
Source of low frequency modulation of ENSO amplitude in a CGCM
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.)
Annoyance of wind-turbine noise as a function of amplitude-modulation parameters
Ioannidou, Christina; Santurette, Sébastien; Jeong, Cheol-Ho
Amplitude modulation (AM) has been suggested as an important factor for the perceived annoyance of wind-turbine noise (WTN). Two AM types, typically referred to as “normal AM” and “other AM,” depending on the AM extent and frequency region, have been proposed to characterize WTN AM. The extent to...
Hediger, S.; Meier, B. H.; Ernst, R. R.
1993-10-01
Amplitude-modulated cross-polarization (AMCP) schemes that can greatly improve the transfer efficiency under fast magic angle spinning are discussed. A novel class of pulse sequences (S-AMCP) that employ an amplitude-modulated spin-lock field on the S-spin channel only and cw irradiation on the I-spin channel is introduced. It leads to efficient cross polarization at the standard Hartmann-Hahn condition while maintaining good spin-lock properties. S-AMCP does, however, not decrease the sensitivity to exact Hartmann-Hahn matching that can become critical under fast rotation. A double amplitude modulation scheme (D-AMCP) that uses amplitude modulation on both radiofrequency channels and significantly broadens the Hartmann-Hahn matching condition is presented. It can, however, be applied only to spin systems with relatively low I-spin homonuclear dipolar interactions due to the absence of an effective spin-locking field. S-AMCP pulse sequences, in contrast, are generally applicable and yield cross-polarization efficiencies that are always better than or equal to the standard continuous-wave cross-polarization experiment.
Super-oscillation focusing lens based on continuous amplitude and binary phase modulation.
Wen, Zhongquan; He, Yinghu; Li, Yuyan; Chen, Li; Chen, Gang
2014-09-01
In this paper, we numerically demonstrate the advantage of utilizing continuous amplitude and phase modulation in super-oscillation focusing lens design. Numerical results show that compared with simple binary amplitude modulation, continuous amplitude and phase modulation can greatly improve the super-oscillation focusing performance by increasing the central lobe intensity and the ratio of its energy to the total energy, reducing the sidelobe intensity, and substantially extending the field of view. Our study also reveals the role of phase distribution in reducing the spatial frequency bandwidth of the super-oscillation optical field on the focal plane. Based on continuous amplitude and binary phase modulation, a lens was designed with double layer metal slit array for wavelength of 4.6 m. COMSOL is used to carry out the 2D simulation. The lens focal length is 40.18? and the focal spot FWHM is 0.308?. Two largest sidelobes are located right next to the central lobe with intensity about 40% of the central lobe intensity. Except for the two sidelobes, other sidelobes have intensity less than 25% of the central lobe intensity, which leads to a clear field of view on the whole focal plane. PMID:25321591
Influence of stimulus intensity on the soleus H-reflex amplitude and modulation during locomotion
Simonsen, Erik B; Alkjær, Tine; Raffalt, Peter C
2013-01-01
Diverging results have been reported regarding the modulation and amplitude of the soleus H-reflex measured during human walking and running. A possible explanation to this could be the use of too high stimulus strength in some studies while not in others. During activities like walking and runni...
Atomic force microscopy force-distance curves with small amplitude ultrasonic modulation.
Ma, Chengfu; Chen, Yuhang; Wang, Tian; Chu, Jiaru
2015-01-01
Force-distance curves were acquired on a highly oriented pyrolytic graphite (HOPG) specimen and a gold film specimen under ultrasonic modulation in atomic force microscopy (AFM). Measurements demonstrated that small amplitude ultrasonic oscillation of either the cantilever or the sample has significant impacts on the characteristics of force-distance curves. With the increase of excitation amplitude, the apparent pull-off force decreased gradually and the hysteresis between the approach and retraction curves reduced significantly. Furthermore, the decrease of the pull-off force was determined to be also relevant to the excitation frequency. With the assistance of contact resonance spectra, the pull-off force was verified to have a near-linear relationship with the cantilever contact oscillation amplitude. Theoretical analysis and subsequent numerical simulations well interpreted the experimental results. The emergence of large oscillating contact forces under ultrasonic modulation altered the force-distance curves, and such a mechanism was ascertained by further ultrasonic AFM imaging. PMID:25917870
Determination of nanovibration amplitudes using frequency-modulated semiconductor laser autodyne
Usanov, D A; Skripal, A V; Astakhov, E I [Saratov State University named after N.G.Chernyshevsky, Saratov (Russian Federation)
2014-02-28
The method for measuring nanovibration amplitudes using the autodyne signal of a semiconductor laser at several laser radiation wavelengths is described. The theoretical description of the frequency-modulated autodyne signal under harmonic vibrations of the reflector is presented and the relations for its spectral components are derived using the expansions into the Fourier and Bessel series. The results of numerical modelling based on the proposed method for measuring the reflector nanovibration amplitudes are presented that make use of the low-frequency spectrum of the autodyne signal from the frequency-modulated laser autodyne and the solution of the appropriate inverse problem. The experimental setup is described; the results of the measurements are presented for the nanovibration amplitudes and the autodyne signal spectra under the reflector nanovibrations. (laser applications and other topics in quantum electronics)
Determination of nanovibration amplitudes using frequency-modulated semiconductor laser autodyne
The method for measuring nanovibration amplitudes using the autodyne signal of a semiconductor laser at several laser radiation wavelengths is described. The theoretical description of the frequency-modulated autodyne signal under harmonic vibrations of the reflector is presented and the relations for its spectral components are derived using the expansions into the Fourier and Bessel series. The results of numerical modelling based on the proposed method for measuring the reflector nanovibration amplitudes are presented that make use of the low-frequency spectrum of the autodyne signal from the frequency-modulated laser autodyne and the solution of the appropriate inverse problem. The experimental setup is described; the results of the measurements are presented for the nanovibration amplitudes and the autodyne signal spectra under the reflector nanovibrations. (laser applications and other topics in quantum electronics)
Mark S. Leeson
2007-03-01
Full Text Available
Modulation techniques have attracted increasing attention in optical wireless communications. Basic schemes such as on off keying (OOK, pulse amplitude modulation (PAM and pulse position modulation (PPM have been validated as suitable for the optical wireless channel. This paper starts from the analysis of these three modulation schemes in terms of their power and bandwidth requirements. As a result, a new tunable hybrid modulation technique is proposed. The proposed modulation scheme takes the real time channel conditions into account, which is different from other schemes. By employing amplitude and position modulation selectively, a guaranteed system performance can be secured, without compromising power and bandwidth efficiency. This is also a new approach to realize reliable optical wireless links.
NOTE ON TRAVEL TIME SHIFTS DUE TO AMPLITUDE MODULATION IN TIME-DISTANCE HELIOSEISMOLOGY MEASUREMENTS
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.
Cyclic pitch for the control of wind turbine noise amplitude modulation
Bertagnolio, Franck; Aagaard Madsen , Helge; Fischer, Andreas; Bak, Christian
2014-01-01
Using experimental data acquired during a wind turbine measurement campaign, it is shown that amplitude modulation of aerodynamic noise can be generated by the rotating blades in conjunction with the atmospheric wind shear. As an attempt to alleviate this phenomenon, a control strategy is designed in form of a cyclic pitch of the blades. As a side effect, it is shown that it is also possible to reduce fatigue load on the blade using this cyclic pitch. The main goal is to reduce both amplitude...
A Compact QPSK Modulator with Low Amplitude and Phase Imbalance for Remote Sensing Applications
Ghaffar, Farhan Abdul
2012-09-30
A new, compact and wide-band Quadrature Phase Shift Keying (QPSK) modulator is presented for remote sensing applications. The microstrip-based modulator employs quadrature hybrid coupler, Wilkinson divider, rat race coupler and GaAs MESFET switches. It is designed to be part of an X band remote sensing transmitter with a center frequency of 8.25GHz. The fabricated module demonstrates the lowest reported amplitude and phase imbalances (0.1dB and 0.4° respectively) around its center frequency. The modulation, tested up to 160 Mbps data rate, displays carrier suppression greater than 30 dB. With negligible DC power consumption and low insertion loss, it operates for a wide bandwidth of 3 GHz (7-10 GHz). The effect of amplitude and phase imbalance is investigated on the performance of the modulator. Finally, a transmitter employing this modulator exhibits an excellent overall Error Vector Magnitude (EVM) of around 8 % that is considerably low as compared to the typically obtained values for such transmitters.
Liljedahl, C. D. M.; ZANELLATO, O; Fitzpatrick, M. E.; Lin, J; Edwards, L.
2010-01-01
In this work the evolution of the residual stresses in a MIG-welded 2024-T3 aluminium alloy M(T) specimen during in situ fatigue crack growth at constant load amplitude has been measured with neutron diffraction. The plastic relaxation and plasticity-induced residual stresses associated with the fatigue loading were found to be small compared with the stresses arising due to elastic re-distribution of the initial residual stress field. The elastic re-distribution was modelled with a finite el...
Latifa Lazzouni
2008-12-01
Full Text Available Cortical auditory steady-state responses to amplitude modulated tones oscillate at the stimulation rhythm and show important spectral energy peaks in temporal areas at the modulation frequencies of the stimuli. Our objective is to show that spectral peaks can be used to asses the effects of blindfolding in temporal and occipital areas and that rapid cortical reorganisation is possible after short term sensory deprivation. Stimuli were amplitude modulated tones lasting 2 seconds (standard tones. The carrier frequency was 1000 Hz, at 2 modulation frequencies. Stimuli were presented monaurally left, right and binaurally (39 Hz right ear, 41 Hz left ear. Six subjects discriminated a deviant tone occurring 10% of the time, right hand pressing a button. The deviant differed from the standard by its carrier frequency (950 Hz and duration (150ms. Subject were tested a day before the blindfolding procedure for the control condition. The next day they were blindfolded using a night mask for a period of six hours. MEG data were recorded with a 275 channel whole head system. For each subject, 200 two-second epochs (pre-processed for ocular artefacts and baseline corrected were averaged and band-pass filtered (30-48 Hz to obtain Auditory Steady State Responses (ASSR. Spectral analysis was performed using Fast Fourier Transformations. Peaks at the modulation frequencies were calculated on the sensors covering the left and right temporal and occipital areas for each subject and condition. Statistical analyses used repeated measures ANOVA testing for factors: Area (temporal, occipital, Delay (before, after deprivation and Hemisphere (left, right. Results showed that spectral peaks in the temporal areas were significantly larger than those in the occipital areas. Moreover, there was a modulation of the peak amplitudes of the ASSR responses after a blindfold of six hours. A significant Area/Delay effect was also found with peaks in the occipital areas being larger after blindfolding. A significant Area/Hemisphere effect showed larger responses in the right hemisphere. In conclusion, we used spectral energy of the ASSR to amplitude modulated tones before and after a transient sensory visual deprivation to determine whether cortical reorganisation is possible after only six hours of total blindfolding. Results showed significant increases of the amplitude of the spectral peaks in occipital areas following the deprivation, suggesting fairly rapid functional reorganization.
On the modulational instability of large amplitude waves in supersonic boundary layers
Hall, Philip; Papageorgiou, Demetrios T.
1995-01-01
The evolution of large amplitude Tollmien-Schlichting waves in a supersonic boundary layer is investigated. Disturbances which have their wavenumber and frequency slowly varying in time and space are described using a phase equation type of approach. Unlike the incompressible case we find that the initial bifurcation to a finite amplitude Tollmien-Schlichting wave is subcritical for most Mach numbers. In fact the bifurcation is only supercritical for a small range of Mach numbers and even then for only a finite range of wave propagation angles. The modulational instability of large amplitude wavetrains is considered and is shown to be governed by an equation similar to Burgers equation but with the viscous term replaced by a fractional derivative. A numerical investigation of the solution of this equation is described. It is shown that uniform wavetrains are unstable.
Cyclic pitch for the control of wind turbine noise amplitude modulation
Bertagnolio, Franck; Aagaard Madsen, Helge; Fischer, Andreas; Bak, Christian
2014-01-01
Using experimental data acquired during a wind turbine measurement campaign, it is shown that amplitude modulation of aerodynamic noise can be generated by the rotating blades in conjunction with the atmospheric wind shear. As an attempt to alleviate this phenomenon, a control strategy is designed...... in form of a cyclic pitch of the blades. As a side effect, it is shown that it is also possible to reduce fatigue load on the blade using this cyclic pitch. The main goal is to reduce both amplitude modulation and fatigue load without compromising the energy harvested from the wind. A simulation tool...... such a strategy is to be implemented on an actual wind turbine, though at the expense of an increased wear and tear of the pitch control system....
Stimulus-frequency otoacoustic emissions measured with amplitude-modulated suppressor tones
Neely, Stephen T.; Johnson, Tiffany A.; Garner, Cassie A.; Gorga, Michael P.
2005-01-01
Stimulus-frequency otoacoustic emissions (SFOAE) are typically derived as the difference in sound pressure in the ear canal with and without a suppressor tone added to the probe tone. A novel variation of this method applies a sinusoidal amplitude modulation (AM) to the suppressor tone, which causes the SFOAE to also be modulated. The AM-SFOAE can be separated from the probe frequency using spectral methods. AM-SFOAE measurements are described for four normal-hearing subjects using 6-Hz AM. B...
The imaging spectrometer based on dual photoelastic modulator of unequal retardation amplitudes
Zhang, Rui; Wang, Zhi-bin; Wen, Ting-dun; Wang, Yao-li; Li, Ke-wu
2015-10-01
As the existing photoelastic modulator (PEM) resonant frequency is high (tens to hundreds of kHz), the interference signal frequency is up to hundreds of MHz, even to several GHz. Signal frequency is so high that they can not effectively be detected by charge coupled device (CCD). This paper reports a method for measuring spectroscopy using two PEMs at different frequencies. The difference frequency of dual-PEM system is 2~3 orders of magnitude lower than any one modulation frequency of the two PEMs. Operating the PEMs at slightly different resonant frequencies f1 and f2 respectively, the dual-PEM system generates a difference frequency modulation signal. Therefore, interference signal contains low frequency modulation components which carry the information of the incident light. And low frequency modulation component consists of a series of frequency-multiplier signals whose fundamental frequency is equal to (f1-f2)/2. The low frequency modulation components can be detected by ordinary CCD. Through Fourier transform, modulation signal of CCD is to get a series of frequency-multiplier signals amplitude. Then the incident light spectra can be obtained by the corresponding matrix operations. Furthermore, this method is to realize object imaging spectral measurement by the way of combining with CCD. The peak retardation amplitude of two PEMs does not require being complete equal, and modulation frequencies f1 and f2 do not also require equality. So this can reduce the difficulty of the PEM processing. What's more, the method makes the traditional PEM have both imaging and spectroscopy measurement functions. The basic principle is introduced, the basic equations is derived, and the feasibility is verified through the corresponding numerical simulation and experiment.
Sato, Aya; Torii, Tetsuya; Iwahashi, Masakuni; Itoh, Yuji; Iramina, Keiji
2014-05-01
The present study analyzed the effects of monophasic magnetic stimulation to the motor cortex. The effects of magnetic stimulation were evaluated by analyzing the motor evoked potentials (MEPs). The amplitude and latency of MEPs on the abductor pollicis brevis muscle were used to evaluate the effects of repetitive magnetic stimulation. A figure eight-shaped flat coil was used to stimulate the region over the primary motor cortex. The intensity of magnetic stimulation was 120% of the resting motor threshold, and the frequency of magnetic stimulation was 0.1 Hz. In addition, the direction of the current in the brain was posterior-anterior (PA) or anterior-posterior (AP). The latency of MEP was compared with PA and AP on initial magnetic stimulation. The results demonstrated that a stimulus in the AP direction increased the latency of the MEP by approximately 2.5 ms. MEP amplitude was also compared with PA and AP during 60 magnetic stimulations. The results showed that a stimulus in the PA direction gradually increased the amplitude of the MEP. However, a stimulus in the AP direction did not modulate the MEP amplitude. The average MEP amplitude induced from every 10 magnetic pulses was normalized by the average amplitude of the first 10 stimuli. These results demonstrated that the normalized MEP amplitude increased up to approximately 150%. In terms of pyramidal neuron indirect waves (I waves), magnetic stimulation inducing current flowing backward to the anterior preferentially elicited an I1 wave, and current flowing forward to the posterior elicited an I3 wave. It has been reported that the latency of the I3 wave is approximately 2.5 ms longer than the I1 wave elicitation, so the resulting difference in latency may be caused by this phenomenon. It has also been reported that there is no alteration of MEP amplitude at a frequency of 0.1 Hz. However, this study suggested that the modulation of MEP amplitude depends on stimulation strength and stimulation direction.
Acua, Alonso M.; Joris J. Snellenburg; Gwizdala, Michal; Kirilovsky, Diana; van Grondelle, Rienk; van Stokkum, Ivo H M
2015-01-01
Pulse-amplitude modulated (PAM) fluorometry is extensively used to characterize photosynthetic organisms on the slow time-scale (11000s). The saturation pulse method allows determination of the quantum yields of maximal (FM) and minimal fluorescence (F0), parameters related to the activity of the photosynthetic apparatus. Also, when the sample undergoes a certain light treatment during the measurement, the fluorescence quantum yields of the unquenched and the quenched states can be determin...
Hydrostatic Vibratory Drive of the Test Stand for Excitation of the Amplitude-Modulated Vibrations
Nizhegorodov, A. I.; Gavrilin, A. N.; Moyzes, B. B.
2016-01-01
The article reviews the problems arising during the development of the test stand hydrostatic vibratory drive, which synthesize controlled amplitude-modulated vibrations required testing of vibration strength and vibrostability of technological devices. The newly developed modification can adequately simulate the transport vibration and vibration of the operating power-supply units of technological machinery vibration by means of implementing of a continuous frequency spectrum of the vibration exposure in the desired frequency range.
Tian, Yuan; Cotté, Benjamin; Chaigne, Antoine
2014-01-01
Aeroacoustic noise from a wind turbine is mainly caused by the interaction between the wind turbine blade and the air flow. For a modern wind turbine, trailing edge noise is often the dominant noise source. In this paper, a detailed study of trailing edge noise is carried out using Amiet's frequency domain analytical source model. Model results are compared with experimental data. Features of wind turbine noise, such as amplitude modulation, ground directivity, influence of blade twist and pi...
Lin, C-C K; Liu, W-C; Chan, C-C; Ju, M-S
2012-04-01
The main goal of this study was to study the performance of fuzzy logic controllers combined with simplified hybrid amplitude/pulse-width (AM/PW) modulation to regulate muscle force via nerve electrical stimulation. The recruitment curves with AM/PW and AM modulations were constructed for the calf muscles of rabbits. Integrated with the modulation methods, a proportional-integral-derivative (PID) and three fuzzy logic controllers were designed and applied for the electrical stimulation of tibial nerves to control the ankle torque under isometric conditions. The performance of the two modulation methods combined with the four controllers was compared when the ankle was fixed at three positions for both in vivo experiments and model simulations using a nonlinear muscle model. For the animal experiments, AM/PW modulation performed better than AM modulation alone. The fuzzy PI controller performed marginally better and was resistant to external noises, though it tended to have a larger overshoot. The performance of the controllers had a similar trend in the three different joint positions, and the simulation results with the nonlinear model matched the experimental results well. In conclusion, AM/PW modulation improved controller performance, while the contribution of fuzzy logic was only marginal. PMID:22422279
Lin, C.-C. K.; Liu, W.-C.; Chan, C.-C.; Ju, M.-S.
2012-04-01
The main goal of this study was to study the performance of fuzzy logic controllers combined with simplified hybrid amplitude/pulse-width (AM/PW) modulation to regulate muscle force via nerve electrical stimulation. The recruitment curves with AM/PW and AM modulations were constructed for the calf muscles of rabbits. Integrated with the modulation methods, a proportional-integral-derivative (PID) and three fuzzy logic controllers were designed and applied for the electrical stimulation of tibial nerves to control the ankle torque under isometric conditions. The performance of the two modulation methods combined with the four controllers was compared when the ankle was fixed at three positions for both in vivo experiments and model simulations using a nonlinear muscle model. For the animal experiments, AM/PW modulation performed better than AM modulation alone. The fuzzy PI controller performed marginally better and was resistant to external noises, though it tended to have a larger overshoot. The performance of the controllers had a similar trend in the three different joint positions, and the simulation results with the nonlinear model matched the experimental results well. In conclusion, AM/PW modulation improved controller performance, while the contribution of fuzzy logic was only marginal.
Differential pulse amplitude modulation for multiple-input single-output OWVLC
Yang, S. H.; Kwon, D. H.; Kim, S. J.; Son, Y. H.; Han, S. K.
2015-01-01
White light-emitting diodes (LEDs) are widely used for lighting due to their energy efficiency, eco-friendly, and small size than previously light sources such as incandescent, fluorescent bulbs and so on. Optical wireless visible light communication (OWVLC) based on LED merges lighting and communications in applications such as indoor lighting, traffic signals, vehicles, and underwater communications because LED can be easily modulated. However, physical bandwidth of LED is limited about several MHz by slow time constant of the phosphor and characteristics of device. Therefore, using the simplest modulation format which is non-return-zero on-off-keying (NRZ-OOK), the data rate reaches only to dozens Mbit/s. Thus, to improve the transmission capacity, optical filtering and pre-, post-equalizer are adapted. Also, high-speed wireless connectivity is implemented using spectrally efficient modulation methods: orthogonal frequency division multiplexing (OFDM) or discrete multi-tone (DMT). However, these modulation methods need additional digital signal processing such as FFT and IFFT, thus complexity of transmitter and receiver is increasing. To reduce the complexity of transmitter and receiver, we proposed a novel modulation scheme which is named differential pulse amplitude modulation. The proposed modulation scheme transmits different NRZ-OOK signals with same amplitude and unit time delay using each LED chip, respectively. The `N' parallel signals from LEDs are overlapped and directly detected at optical receiver. Received signal is demodulated by power difference between unit time slots. The proposed scheme can overcome the bandwidth limitation of LEDs and data rate can be improved according to number of LEDs without complex digital signal processing.
Amplitude and phase modulation of radiation in a travelling-wave amplifier based on a laser diode
An analytical solution (in quadratures) to the problem of propagation of quasi-monochromatic optical signal in a semiconductor amplifier under harmonic modulation of its pump current is obtained for the first time. It is shown that the modulation of the output radiation has amplitude and phase features. The relation is found between the coefficients of the amplitude and phase modulation with the effect of gain saturation taken into account. Adequacy of the results obtained is confirmed experimentally. (control of laser radiation parameters)
Shading of holographic reconstructed image by two-dimensional amplitude modulation of zone plates
Kurihara, Takayuki; Takaki, Yasuhiro
2012-03-01
We propose a technique to shade reconstructed images of electronic holography. Our technique modifies the zone plate technique, which represents a three-dimensional object as an aggregate of object points and zone plates, which generate object points, are summed to calculate a hologram. Our technique is based on the Phong reflection model developed for computer graphics, which assumes that light reflected from an object consists of three components: diffuse, specular, and ambient reflection light. Among these components, only the specular component depends on the position of the camera (or the eye). A holographic reconstructed image changes depending on the viewing direction. Therefore, the specular component changes for different viewing directions. Because light modulated by a zone plate converges to an object point, we assumed that light is redirected differently at each point on the zone plate. Therefore, two-dimensional amplitude modulation of the zone plate would generate an object point that emits light with different intensities in different directions. The proposed two-dimensional amplitude modulation comprises variable and constant modulations: the former one controls the specular component and the latter one controls the diffuse and ambient components. We experimentally verified the proposed technique.
Abdul Latif Memon
2014-04-01
Full Text Available SAC (Spectral Amplitude Coding is a technique of OCDMA (Optical Code Division Multiple Access to encode and decode data bits by utilizing spectral components of the broadband source. Usually OOK (ON-Off-Keying modulation format is used in this encoding scheme. To make SAC OCDMA network spectrally efficient, advanced modulation format of DQPSK (Differential Quaternary Phase Shift Keying is applied, simulated and analyzed. m-sequence code is encoded in the simulated setup. Performance regarding various lengths of m-sequence code is also analyzed and displayed in the pictorial form. The results of the simulation are evaluated with the help of electrical constellation diagram, eye diagram and bit error rate graph. All the graphs indicate better transmission quality in case of advanced modulation format of DQPSK used in SAC OCDMA network as compared with OOK
SAC (Spectral Amplitude Coding) is a technique of OCDMA (Optical Code Division Multiple Access) to encode and decode data bits by utilizing spectral components of the broadband source. Usually OOK (ON-Off-Keying) modulation format is used in this encoding scheme. To make SAC OCDMA network spectrally efficient, advanced modulation format of DQPSK (Differential Quaternary Phase Shift Keying) is applied, simulated and analyzed, m-sequence code is encoded in the simulated setup. Performance regarding various lengths of m-sequence code is also analyzed and displayed in the pictorial form. The results of the simulation are evaluated with the help of electrical constellation diagram, eye diagram and bit error rate graph. All the graphs indicate better transmission quality in case of advanced modulation format of DQPSK used in SAC OCDMA network as compared with OOK. (author)
A 32x32 pixel focal plane array ladar system using chirped amplitude modulation
Stann, Barry L.; Aliberti, Keith; Carothers, Daniel; Dammann, John; Dang, Gerard; Giza, Mark M.; Lawler, William B.; Redman, Brian C.; Simon, Deborah R.
2004-09-01
The Army Research Laboratory is researching system architectures and components required to build a 32x32 pixel scannerless ladar breadboard. The 32x32 pixel architecture achieves ranging based on a frequency modulation/continuous wave (FM/cw) technique implemented by directly amplitude modulating a near-IR diode laser transmitter with a radio frequency (RF) subcarrier that is linearly frequency modulated (i.e. chirped amplitude modulation). The backscattered light is focused onto an array of metal-semiconductor-metal (MSM) detectors where it is detected and mixed with a delayed replica of the laser modulation signal that modulates the responsivity of each detector. The output of each detector is an intermediate frequency (IF) signal (a product of the mixing process) whose frequency is proportional to the target range. Pixel read-out is achieved using code division multiple access techniques as opposed to the usual time-multiplexed techniques to attain high effective frame rates. The raw data is captured with analog-to-digital converters and fed into a PC to demux the pixel data, compute the target ranges, and display the imagery. Last year we demonstrated system proof-of-principle for the first time and displayed an image of a scene collected in the lab that was somewhat corrupted by pixel-to-pixel cross-talk. This year we report on system modifications that reduced pixel-to-pixel cross-talk and new hardware and display codes that enable near real-time stereo display of imagery on the ladar's control computer. The results of imaging tests in the laboratory will also be presented.
Amplitude modulation of hydromagnetic waves and associated rogue waves in magnetoplasmas.
Sabry, R; Moslem, W M; Shukla, P K
2012-09-01
It is shown that the dynamics of amplitude-modulated compressional dispersive Alfvénic (CDA) waves in a collisional megnetoplasma is governed by a complex Ginzburg-Landau (CGL) equation. The nonlinear dispersion relation for the modulational instability of the CDA waves is derived and investigated numerically. It is found that the growth rate of the modulational instability decreases (increases) with the increase of the normalized electron-ion collision frequency α (the plasma β). The modulational instability criterion for the CGL equation is defined precisely and investigated numerically. The region of the modulational instability becomes narrower with the increase of α and β, indicating that the system dissipates the wave energy by collisions, and a stable CDA wave envelope packet in the form of a hole will be a dominant localized pulse. For a collisionless plasma, i.e., α=0, the CGL equation reduces to the standard nonlinear Schrödinger (NLS) equation. The latter is used to investigate the modulational (in)stability region for the CDA waves in a collisionless magnetoplasma. It is shown that, within unstable regions, a random set of nonlinearly interacting CDA perturbations leads to the formation of CDA rogue waves. In order to demonstrate that the characteristics of the CDA rogue waves are influenced by the plasma β, the relevant numerical analysis of the appropriate nonlinear solution of the NLS equation is presented. The application of our investigation to space and laboratory magnetoplasmas is discussed. PMID:23031035
Limitations on accurate shape determination using amplitude modulation atomic force microscopy
The limitations of amplitude modulation atomic force microscopy to accurately measure the shape or form of features are investigated. The control feedback loop and the dynamics of the cantilever limit the response time of the atomic force microscope. Simply subtracting appropriately scaled amplitude (error) signal from the topography data significantly improves the accuracy of the data and can correct for the slow response time of the feedback loop. Two mechanisms were found to induce topographic errors independent of scan speed. The first is the change in tip/surface interaction at a step edge observed by comparison with results from a ‘virtual’ sample. The second is due to friction between the probe and sample but only for a specifically oriented step edge determined by the direction of oscillation of the cantilever. -- Highlights: ► Three sources of error that effect shape measurements using an AFM are discussed. ► Focus is solely on amplitude modulation AFM. ► A simple scheme corrects for errors due to limitations in the feedback loop. ► Effect of changing tip-surface interaction at step edge to shape is quantified. ► Friction between tip and sample distorts measured shape.
Direct summands of syzygy modules of the residue class field
Takahashi, Ryo
2008-01-01
Let $R$ be a commutative Noetherian local ring. This paper deals with the problem asking whether $R$ is Gorenstein if the $n$th syzygy module of the residue class field of $R$ has a non-trivial direct summand of finite G-dimension for some $n$. It is proved that if $n$ is at most two then it is true, and moreover, the structure of the ring $R$ is determined essentially uniquely.
Tip radius preservation for high resolution imaging in amplitude modulation atomic force microscopy
The acquisition of high resolution images in atomic force microscopy (AFM) is correlated to the cantilever's tip shape, size, and imaging conditions. In this work, relative tip wear is quantified based on the evolution of a direct experimental observable in amplitude modulation atomic force microscopy, i.e., the critical amplitude. We further show that the scanning parameters required to guarantee a maximum compressive stress that is lower than the yield/fracture stress of the tip can be estimated via experimental observables. In both counts, the optimized parameters to acquire AFM images while preserving the tip are discussed. The results are validated experimentally by employing IgG antibodies as a model system.
Mauras, N; Blizzard, R M; Link, K; Johnson, M L; Rogol, A D; Veldhuis, J D
1987-03-01
The augmentation of GH secretion that occurs during puberty has been attributed to changes in sex steroid levels that enhance the frequency and amplitude of GH pulses. To investigate the specific GH pulse characteristics responsible for such augmentation we analyzed the serum GH concentration profiles of 10 boys in Tanner stages I-II of sexual development (group A; aged 10 5/12-15 1/12 yr) and compared their GH pulse characteristics with those of 5 boys at Tanner stages IV-V of development (group B; aged 14 8/12-15 1/12 yr). We also reanalyzed previously reported data from 5 prepubertal boys (group C; aged 13 6/12-15 5/12 yr) before and after 10 weeks of treatment with testosterone enanthate (100 mg/4 weeks, im). Using a pulse detection algorithm that constrains the false positive pulse detection rate to less than 5% (Cluster), we found that group B boys had a significantly higher mean serum GH pulse amplitude compared to group A boys (17.1 +/- 2.6 vs. 8.6 +/- 1.7 ng/mL; P = 0.012), but both groups had the same mean GH pulse frequency (group B, 5.4 +/- 0.5 pulses/24 h vs. group A, 5.5 +/- 0.4 pulses/24 h; P greater than 0.05). Similar changes were found in group C boys before and after testosterone therapy; there was no significant change in GH pulse frequency (6.6 +/- 0.9 before vs. 7.6 +/- 0.5 pulses/24 h after treatment; P greater than 0.05), but there was a significant increase in the GH pulse amplitude after therapy (6.8 +/- 1.6 before vs. 15.4 +/- 2.4 ng/mL after treatment; P = 0.04). When the 24-h GH concentration profiles were analyzed using a mathematically distinct method for the estimation of pulse amplitudes, namely the Fourier expansion time series, we confirmed a significant increase in GH pulse amplitude with later stages of puberty and androgen treatment. We conclude that the augmentation in GH secretion that occurs during either spontaneous puberty or exogenous testosterone therapy is an amplitude-modulated phenomenon, relatively independent of changes in pulse frequency. Such an effect may be secondary to the action of sex steroid hormones modulating either the responsivity of somatotrophs to endogenous GH-releasing hormone, the amount of GH-releasing hormone secreted, or the tonic inhibitory tone of somatostatin. PMID:3493255
Gramse, G.; Edwards, M. A.; Fumagalli, L.; Gomila, G.
2013-10-01
A theoretical analysis of amplitude modulated electrostatic force microscopy (AM-EFM) in liquid media at MHz frequencies, based on a simple tip-sample parallel plate model, is presented. The model qualitatively explains the main features of AM-EFM in liquid media and provides a simple explanation of how the measured electric forces are affected by: the frequency of the applied voltage, the tip-sample distance, the ionic concentration, the relative dielectric constant of the solution, and the relative dielectric constant and thickness of the sample. These results provide a simple framework for the design of AM-EFM measurements for localized dielectric characterization in liquid media.
A theoretical analysis of amplitude modulated electrostatic force microscopy (AM-EFM) in liquid media at MHz frequencies, based on a simple tip–sample parallel plate model, is presented. The model qualitatively explains the main features of AM-EFM in liquid media and provides a simple explanation of how the measured electric forces are affected by: the frequency of the applied voltage, the tip–sample distance, the ionic concentration, the relative dielectric constant of the solution, and the relative dielectric constant and thickness of the sample. These results provide a simple framework for the design of AM-EFM measurements for localized dielectric characterization in liquid media. (paper)
Amplitude modulation reflectometer for FTU; Riflettometro a modulazione di ampiezza per FTU
Zerbini, M.; Buratti, P.; Centioli, C. [ENEA, Centro Ricerche Frascati, Rome (Italy). Dip. Energia; Amadeo, P.
1995-06-01
Amplitude modulation (AM) reflectometry is a modification of the classical frequency sweep technique which allows to perform unambiguous phase delay measurements. An eight-channel AM reflectometer has been realized for the measurement of density profiles on the FTU tokamak in the range. The characteristics of the instrument have been determined in extensive laboratory tests; particular attention has been devoted to the effect of interference with parasitic reflections. The reflectometer is now operating on FTU. Some examples of the first experimental data are discussed.
Sensitive detection of vortex-core resonance using amplitude-modulated magnetic field
Cui, Xiaomin; Hu, Shaojie; Hidegara, Makoto; Yakata, Satoshi; Kimura, Takashi
2015-12-01
Understanding and manipulating the dynamic properties of the magnetic vortices stabilized in patterned ferromagnetic structures are of great interest owing to the superior resonant features with the high thermal stability and their flexible tunability. So far, numerous methods for investigating the dynamic properties of the magnetic vortex have been proposed and demonstrated. However, those techniques have some regulations such as spatial resolution, experimental facility and sensitivity. Here, we develop a simple and sensitive method for investigating the vortex-core dynamics by using the electrically separated excitation and detection circuits. We demonstrate that the resonant oscillation of the magnetic vortex induced by the amplitude- modulated alternating-sign magnetic field is efficiently picked up by the lock-in detection with the modulated frequency. By extending this method, we also investigate the size dependence and the influence of the magneto-static interaction in the resonant property of the magnetic vortex.
Tokle, Torger; Serbay, Murat; Jensen, Jesper Bevensee; Geng, Yan; Rosenkranz, Werner; Jeppesen, Palle
2006-01-01
We present experimental investigations of the receiver sensitivity and dispersion tolerance of multilevel optical communication systems with a symbol rate of 40 Gbaud. Four- and eight-level communication is obtained by combining binary amplitude modulation with either binary or quadrature...... differential phase modulation. We experimentally compare the dispersion tolerance, and show that multilevel modulation formats offer much better dispersion tolerance compared to binary formats. By combining multilevel modulation with polarization multiplexing, bit rates up to 240 Gb/s were obtained. We...
Hwang, Chi-Young; Yi, Yoonsik; Choi, Choon-Gi
2016-03-01
We present a method for reflection-type spatial amplitude modulation using a sub-wavelength plasmonic absorber structure that can operate in the visible region. We utilize a pixelated array of absorbing elements based on a two-dimensional sub-wavelength metal grating, and the reflectance of each pixel is controlled by simple structural modification. For the purpose of validation, numerical simulations were performed on an amplitude modulation hologram fabricated using our method. PMID:26974098
Prado-Gutierrez, Pavel; Castro-Fariñas, Anisleidy; Morgado-Rodriguez, Lisbet; Velarde-Reyes, Ernesto; Martínez, Agustín D.; Martínez-Montes, Eduardo
2015-01-01
Generation of the auditory steady state responses (ASSR) is commonly explained by the linear combination of random background noise activity and the stationary response. Based on this model, the decrease of amplitude that occurs over the sequential averaging of epochs of the raw data has been exclusively linked to the cancelation of noise. Nevertheless, this behavior might also reflect the non-stationary response of the ASSR generators. We tested this hypothesis by characterizing the ASSR time course in rats with different auditory maturational stages. ASSR were evoked by 8-kHz tones of different supra-threshold intensities, modulated in amplitude at 115 Hz. Results show that the ASSR amplitude habituated to the sustained stimulation and that dishabituation occurred when deviant stimuli were presented. ASSR habituation increased as animals became adults, suggesting that the ability to filter acoustic stimuli with no-relevant temporal information increased with age. Results are discussed in terms of the current model of the ASSR generation and analysis procedures. They might have implications for audiometric tests designed to assess hearing in subjects who cannot provide reliable results in the psychophysical trials. PMID:26557360
Improvement of the Spatial Amplitude Isotropy of a ^4He Magnetometer Using a Modulated Pumping Beam
Chéron, B.; Gilles, H.; Hamel, J.; Moreau, O.; Noël, E.
1997-08-01
Optically pumped magnetometers are scalar magnetometers. Contrary to vectoriel magnetometers, they measure the total magnetic field whatever the direction of the sensor. However, for some orientations of the magnetometer with respect to the magnetic field direction, the resonant signal vanishes and the measurement is impossible. In this paper we present a simple solution to reduce the amplitude spatial anisotropy and apply it to a ^4He magnetometer developed in our Laboratory. Les magnétomètres à pompage optique sont des magnétomètres scalaires. Contrairement aux magnétomètres vectoriels, ils mesurent le module du champ magnétique quelle que soit l'orientation du capteur dans l'espace. Cependant, pour certaines orientations du magnétomètre par rapport à la direction du champ à mesurer, l'amplitude du signal de résonance s'annule et la mesure devient impossible. Dans cet article, nous présentons une solution simple pour réduire l'anisotropie spatiale d'amplitude et nous l'appliquons à un magnétomètre à hélium-4 développé dans notre Laboratoire.
Travel Time Shifts due to Amplitude Modulation in Time-Distance Helioseismology
Nigam, R
2009-01-01
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 has 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 wave...
Amplitude modulation depth discrimination in hearing-impaired and normal-hearing listeners
Ewert, Stephan D.; Volmer, Jutta; Dau, Torsten; Verhey, Jesko
2008-01-01
The processing of amplitude modulations (AM) of sounds is assumed to be crucial for decoding and understanding of speech in humans. Since hearing-impaired (HI) listeners often suffer from severely hampered speech intelligibility, particularly in reverberant or noisy environments, they might also ...... appeared to be an increased internal noise in the AM-depth domain. Consequences for speech perception are discussed....... investigates the differential processing of amplitude modulation depth in HI and NH listeners. AM-depth discrimination of a 4-, 8-, and 30-Hz sinusoidal AM, imposed on a 1- or 4-kHz pure-tone carrier, was measured. The AM of the standard ranged from being well detectable to near threshold. AM-depth...... discrimination thresholds strongly varied among HI listeners and were elevated in comparison to NH for high standard depths. A model of AM processing is suggested incorporating an individually adjusted simulation of the auditory periphery. To account for the data of HI listeners, however, the key element...
Edge density profile measurements by amplitude modulation reflectometry on PBX-M tokamak
A reflectometer, based on the amplitude modulation technique, has been developed and operated on a PBX-M for the measurement of electron density profile. The system, operating with the extraordinary mode in the range of 32-50 GHz, is able to measure the density profile in the plasma edge from the scrape-off layer up to typically r/a = 0.7. The determination of the time delay for each frequency is achieved by measuring the phase delay of a 200 MHz amplitude modulation envelope superimposed on the millimetre wave probing signal. The system has a final bandwidth of 40 kHz and is able to obtain the edge profile during a 1 ms sweep of the microwave source. High quality profiles are obtained in systematic good agreement with Thomson scattering measurements. The profile reconstruction from the raw data is direct, with only a need for minimal data processing. Profiles have been measured for ohmic, RF and NBI heated discharges. Features of the profile changes in the L-H transition are shown. One of the goals of the instrument has been the measurement of the slight modifications to the edge density profile produced by the injection of ion Bernstein waves. These changes have been clearly observed and are in agreement with theoretical expectations. (Author)
Noise-immunity processing of digital multilevel pulse-amplitude modulation signals
A. S. Makarenko
2015-12-01
Full Text Available Introduction. The main properties and features of spectral-effective multi-level pulse amplitude modulation digital signals at coherent reception are presented. It is shown that the phase locked loop circuit (PLL circuit used in the receiver is able to work at SNR > 5 dB.Object of the paper. We propose a new scheme of noise compensator at an intermediate frequency, allowing us to obtain increasing of SNR on 15–25 dB when error of PLL is equal zero. The noise compensator has the gain 8–18 dB at error of PLL = 33° that is able to work at SNR = 5 dB. As result, we can obtain a required SNR for determined BER in systems with multi-level PAM.Conclusions. This technical solution makes a spectrally-efficient system using multi-level amplitude modulation is also energy efficient, forward-looking and competitive. The power transmitters of cell phones and radio relay lines of mobile communication systems can be reduced by 10 times or at the same transmitter power improvement the quality of communication or range is presented.
Regime of a wideband phase-amplitude modulation in a CW magnetron transmitter with a phase control
Kazakevich, G; Chase, B; Pasquinelli, R; Yakovlev, V
2014-01-01
A model of the CW high-power transmitter, utilizing frequency-locked magnetrons with a phase control studied initially as a prototype of controllable in phase and power an RF source for intensity-frontier superconducting linacs, was considered for telecommunication as a model of magnetron source, acceptable for a wideband phase-amplitude modulation at a precisely stable carrier frequency. The R&D conducted with CW, 2.45 GHz, 1 kW, microwave oven magnetrons demonstrated that the frequency locking of the magnetrons by the phase-modulated signal provides wideband phase and amplitude modulation at the modulating frequency at least up to 3 MHz and large magnitude, keeping the carrier frequency precisely stable, without broadening of the spectral line width. Performed experiments with power combining verified applicability of the transmitter based on the frequency-locked magnetrons for wideband phase and amplitude modulation, which may be used for telecommunication. Results of the experiments are described in t...
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
Frederico P. Costa
2013-11-01
Full Text Available In the past century, there have been many attempts to treat cancer with low levels of electric and magnetic fields. We have developed noninvasive biofeedback examination devices and techniques and discovered that patients with the same tumor type exhibit biofeedback responses to the same, precise frequencies. Intrabuccal administration of 27.12 MHz radiofrequency (RF electromagnetic fields (EMF, which are amplitude-modulated at tumor-specific frequencies, results in long-term objective responses in patients with cancer and is not associated with any significant adverse effects. Intrabuccal administration allows for therapeutic delivery of very low and safe levels of EMF throughout the body as exemplified by responses observed in the femur, liver, adrenal glands, and lungs. In vitro studies have demonstrated that tumor-specific frequencies identified in patients with various forms of cancer are capable of blocking the growth of tumor cells in a tissue- and tumor-specific fashion. Current experimental evidence suggests that tumor-specific modulation frequencies regulate the expression of genes involved in migration and invasion and disrupt the mitotic spindle. This novel targeted treatment approach is emerging as an appealing therapeutic option for patients with advanced cancer given its excellent tolerability. Dissection of the molecular mechanisms accounting for the anti-cancer effects of tumor-specific modulation frequencies is likely to lead to the discovery of novel pathways in cancer.
Acousto-optic tomography using amplitude-modulated focused ultrasound and a near-IR laser
A novel tomographic method that can be applied in strongly scattering optical media is proposed. 1-MHz focused ultrasound is used to tag the scattering photons in the biological tissue; it carries a 10-KHz sinusoidal wave to act as a detection wave through amplitude-modulation (AM). The scattering photons that come from the focused zone carry the modulated information. Their optoelectronic signal is demodulated by real-time FFT. By detecting and discriminating ultrasound-modulated information carried by scattered photons, the optical tomographic images of the media simulating biological tissue and of a buried object are reconstructed by the AM spectral intensity. This ultrasound-tagged optical tomography can be applied to tissue structures with different optical parameters. For the first time, by using this method, we obtained the tomographic image of a 5 mm-wide soft rubber cube buried in a biological tissue-simulating media with a detecting depth of 30 mm. (laser applications and other topics in quantum electronics)
Khaleghi, Salman
Technology has empowered people in all walks of life to generate, store, and communicate enormous amounts of data. Recent technological advances in high-speed backbone data networks, together with the growing trend toward bandwidth-demanding applications such as data and video sharing, cloud computing, and data collection systems, have created a need for higher capacities in signal transmission and signal processing. Optical communication systems have long benefited from the large bandwidth of optical signals (beyond tera-hertz) to transmit information. Through the use of optical signal processing techniques, this Ph.D. dissertation explores the potential of very-high-speed optics to assist electronics in processing huge amounts of data at high speeds. Optical signal processing brings together various fields of optics and signal processing---nonlinear devices and processes, analog and digital signals, and advanced data modulation formats---to achieve high-speed signal processing functions that can potentially operate at the line rate of fiber optic communications. Information can be encoded in amplitude, phase, wavelength, polarization, and spatial features of an optical wave to achieve high-capacity transmission. Many advances in the key enabling technologies have led to recent research in optical signal processing for digital signals that are encoded in one or more of these dimensions. Optical Kerr nonlinearities have femto-second response times that have been exploited for fast processing of optical signals. Various optical nonlinearities and chromatic dispersions have enabled key sub-system applications such as wavelength conversion, multicasting, multiplexing, demultiplexing, and tunable optical delays. In this Ph.D. dissertation, we employ these recent advances in the enabling technologies for high-speed optical signal processing to demonstrate various techniques that can process phase- and amplitude-encoded optical signals at the line rate of optics. We use nonlinear media, such as highly nonlinear fiber, periodically poled lithium niobate, and semiconductor optical amplifiers, for nonlinear mixing of optical signals. We propose and experimentally demonstrate a novel, fully tunable optical tapped-delay-line that is a key building block for signal processing functions. Applications such as finite impulse response filtering, equalization, correlation (pattern recognition), discrete Fourier transform, digital-to-analog conversion, and flexible optical signal conversion and generation are shown. The phase- and amplitude-preserving nature of the demonstrated techniques, together with their wide-tuning range, allows for processing of optical signals that carry different modulation formats with different data rates. The reconfigurability may apply to future optical networks that carry heterogeneous traffic with different modulation formats and baud rates.
First Results with a Fast Phase and Amplitude Modulator for High Power RF Application
Frischholz, Hans; Valuch, D; Weil, C
2004-01-01
In a high energy and high power superconducting proton linac, it is more economical to drive several cavities with a single high power transmitter rather than to use one transmitter per cavity. However, this option has the disadvantage of not permitting individual control for each cavity, which potentially leads to instabilities. Provided that it can be built at a reasonable cost, a fast phase and amplitude modulator inserted into each cavity feeder line can provide the necessary control capability. A prototype of such a device has been built, based on two fast and compact high power RF phase-shifters, magnetically biased by external coils. The design is described, together with the results obtained at high and low power levels.
Decoding Finger Flexion using amplitude modulation from band-specific ECoG
Liang, Nanying
2009-01-01
EEG-BCIs have been well studied in the past decades and implemented into several famous applications, like P300 speller and wheelchair controller. However, these interfaces are indirect due to low spatial resolution of EEG. Recently, direct ECoG-BCIs attract intensive attention because ECoG provides a higher spatial resolution and signal quality. This makes possible localization of the source of neural signals with respect to certain brain functions. In this article, we present a realization of ECoG-BCIs for finger flexion prediction provided by BCI competition IV. Methods for finger flexion prediction including feature extraction and selection are provided in this article. Results show that the predicted finger movement is highly correlated with the true movement when we use band-specific amplitude modulation.
Parthasarathy, Aravindakshan; Lai, Jesyin; Bartlett, Edward L
2016-04-01
Listening conditions in the real world involve segregating the stimuli of interest from competing auditory stimuli that differ in their sound level and spectral content. It is in these conditions of complex spectro-temporal processing that listeners with age-related hearing loss experience the most difficulties. Envelope following responses (EFRs) provide objective neurophysiological measures of auditory processing. EFRs were obtained to two simultaneous sinusoidally amplitude modulated (sAM) tones from young and aged Fischer-344 rats. One was held at a fixed suprathreshold sound level (sAM1FL) while the second varied in sound level (sAM2VL) and carrier frequency. EFR amplitudes to sAM1FL in the young decreased with signal-to-noise ratio (SNR), and this reduction was more pronounced when the sAM2VL carrier frequency was spectrally separated from sAM1FL. Aged animals showed similar trends, while having decreased overall response amplitudes compared to the young. These results were replicated using an established computational model of the auditory nerve. The trends observed in the EFRs were shown to be due to the contributions of the low-frequency tails of high-frequency neurons, rather than neurons tuned to the sAM1FL carrier frequency. Modeling changes in threshold and neural loss reproduced some of the changes seen with age, but accuracy improved when combined with an additional decrease representing synaptic loss of auditory nerve neurons. Sound segregation in this case derives primarily from peripheral processing, regardless of age. Contributions by more central neural mechanisms are likely to occur only at low SNRs. PMID:26905273
Cal Francis Rabang
2012-11-01
Full Text Available The inferior colliculus (IC receives ascending excitatory and inhibitory inputs from multiple sources, but how these auditory inputs converge to generate IC spike patterns is poorly understood. Simulating patterns of in vivo spike train data from cellular and synaptic models creates a powerful framework to identify factors that contribute to changes in IC responses, such as those resulting in age-related loss of temporal processing. A conductance-based single neuron IC model was constructed, and its responses were compared to those observed during in vivo IC recordings in rats. IC spike patterns were evoked using amplitude-modulated (AM tone or noise carriers at 20-40 dB above threshold and were classified as low-pass, band-pass, band-reject, all-pass, or complex based on their rate modulation transfer function (rMTF tuning shape. Their temporal modulation transfer functions (tMTFs were also measured. These spike patterns provided experimental measures of rate, vector strength and firing pattern for comparison with model outputs. Patterns of excitatory and inhibitory synaptic convergence to IC neurons were based on anatomical studies and generalized input tuning for modulation frequency. Responses of modeled ascending inputs were derived from experimental data from previous studies. Adapting and sustained IC intrinsic models were created, with adaptation created via calcium-activated potassium currents. Short-term synaptic plasticity was incorporated into the model in the form of synaptic depression, which was shown to have a substantial effect on the magnitude and time course of the IC response. The most commonly observed IC response subtypes were recreated and enabled dissociation of inherited response properties from those that were generated in IC. Furthermore, the model was used to make predictions about the consequences of reduction in inhibition for age-related loss of temporal processing due to a reduction in GABA seen anatomically with age.
Differential Amplitude Pulse-Position Modulation for Indoor Wireless Optical Communications
Sethakaset Ubolthip
2005-01-01
Full Text Available We propose a novel differential amplitude pulse-position modulation (DAPPM for indoor optical wireless communications. DAPPM yields advantages over PPM, DPPM, and DH-PIM in terms of bandwidth requirements, capacity, and peak-to-average power ratio (PAPR. The performance of a DAPPM system with an unequalized receiver is examined over nondispersive and dispersive channels. DAPPM can provide better bandwidth and/or power efficiency than PAM, PPM, DPPM, and DH-PIM depending on the number of amplitude levels and the maximum length of a symbol. We also show that, given the same maximum length, DAPPM has better bandwidth efficiency but requires about and more power than PPM and DPPM, respectively, at high bit rates over a dispersive channel. Conversely, DAPPM requires less power than DH-PIM . When the number of bits per symbol is the same, PAM requires more power, and DH-PIM less power, than DAPPM. Finally, it is shown that the performance of DAPPM can be improved with MLSD, chip-rate DFE, and multichip-rate DFE.
Differential Amplitude Pulse-Position Modulation for Indoor Wireless Optical Communications
Sethakaset Ubolthip
2005-01-01
Full Text Available We propose a novel differential amplitude pulse-position modulation (DAPPM for indoor optical wireless communications. DAPPM yields advantages over PPM, DPPM, and DH-PIM α in terms of bandwidth requirements, capacity, and peak-to-average power ratio (PAPR. The performance of a DAPPM system with an unequalized receiver is examined over nondispersive and dispersive channels. DAPPM can provide better bandwidth and/or power efficiency than PAM, PPM, DPPM, and DH-PIM α depending on the number of amplitude levels A and the maximum length L of a symbol. We also show that, given the same maximum length, DAPPM has better bandwidth efficiency but requires about 1 dB and 1.5 dB more power than PPM and DPPM, respectively, at high bit rates over a dispersive channel. Conversely, DAPPM requires less power than DH-PIM 2 . When the number of bits per symbol is the same, PAM requires more power, and DH-PIM 2 less power, than DAPPM. Finally, it is shown that the performance of DAPPM can be improved with MLSD, chip-rate DFE, and multichip-rate DFE.
Shaping symmetric Airy beam through binary amplitude modulation for ultralong needle focus
Needle-like electromagnetic field has various advantages for the applications in high-resolution imaging, Raman spectroscopy, as well as long-distance optical transportation. The realization of such field often requires high numerical aperture (NA) objective lens and the transmission masks. We demonstrate an ultralong needle-like focus in the optical range produced with an ordinary lens. This is achieved by focusing a symmetric Airy beam (SAB) generated via binary spectral modulation with a digital micromirror device. Such amplitude modulation technique is able to shape traditional Airy beams, SABs, as well as the dynamic transition modes between the one-dimensional and two-dimensional (2D) symmetric Airy modes. The created 2D SAB was characterized through measurement of the propagating fields with one of the four main lobes blocked by an opaque mask. The 2D SAB was verified to exhibit self-healing property against propagation with the obstructed major lobe reconstructed after a certain distance. We further produced an elongated focal line by concentrating the SAB via lenses with different NAs and achieved an ultralong longitudinal needle focus. The produced long needle focus will be applied in optical, chemical, and biological sciences
Shaping symmetric Airy beam through binary amplitude modulation for ultralong needle focus
Fang, Zhao-Xiang; Ren, Yu-Xuan; Gong, Lei; Vaveliuk, Pablo; Chen, Yue; Lu, Rong-De
2015-11-01
Needle-like electromagnetic field has various advantages for the applications in high-resolution imaging, Raman spectroscopy, as well as long-distance optical transportation. The realization of such field often requires high numerical aperture (NA) objective lens and the transmission masks. We demonstrate an ultralong needle-like focus in the optical range produced with an ordinary lens. This is achieved by focusing a symmetric Airy beam (SAB) generated via binary spectral modulation with a digital micromirror device. Such amplitude modulation technique is able to shape traditional Airy beams, SABs, as well as the dynamic transition modes between the one-dimensional and two-dimensional (2D) symmetric Airy modes. The created 2D SAB was characterized through measurement of the propagating fields with one of the four main lobes blocked by an opaque mask. The 2D SAB was verified to exhibit self-healing property against propagation with the obstructed major lobe reconstructed after a certain distance. We further produced an elongated focal line by concentrating the SAB via lenses with different NAs and achieved an ultralong longitudinal needle focus. The produced long needle focus will be applied in optical, chemical, and biological sciences.
Shaping symmetric Airy beam through binary amplitude modulation for ultralong needle focus
Fang, Zhao-Xiang; Gong, Lei; Vaveliuk, Pablo; Chen, Yue; Lu, Rong-De
2015-01-01
Needle-like electromagnetic fields has various advantages for the applications in high-resolution imaging, Raman Spectroscopy, as well as long-distance optical transportation. The realization of such field often requires high numerical aperture (NA) objective lens and the transmission masks. We demonstrate an ultralong needle-like focus in the optical range produced with an ordinary lens. This is achieved by focusing a symmetric Airy beam (SAB) generated via binary spectral modulation with a digital micromirror device(DMD). Such amplitude modulation technique is able to shape traditional Airy beams, SABs, as well as the dynamic transition modes between the one-dimensional(1D) and two-dimensional (2D) symmetric Airy modes. The created 2D SAB was characterized through measurement of the propagating fields with one of the four main lobes blocked by an opaque mask. The 2D SAB was verified to exhibit self-healing property against propagation with the obstructed major lobe reconstructed after a certain distance. We...
EEG amplitude modulation analysis for semi-automated diagnosis of Alzheimer's disease
Falk, Tiago H.; Fraga, Francisco J.; Trambaiolli, Lucas; Anghinah, Renato
2012-12-01
Recent experimental evidence has suggested a neuromodulatory deficit in Alzheimer's disease (AD). In this paper, we present a new electroencephalogram (EEG) based metric to quantitatively characterize neuromodulatory activity. More specifically, the short-term EEG amplitude modulation rate-of-change (i.e., modulation frequency) is computed for five EEG subband signals. To test the performance of the proposed metric, a classification task was performed on a database of 32 participants partitioned into three groups of approximately equal size: healthy controls, patients diagnosed with mild AD, and those with moderate-to-severe AD. To gauge the benefits of the proposed metric, performance results were compared with those obtained using EEG spectral peak parameters which were recently shown to outperform other conventional EEG measures. Using a simple feature selection algorithm based on area-under-the-curve maximization and a support vector machine classifier, the proposed parameters resulted in accuracy gains, relative to spectral peak parameters, of 21.3% when discriminating between the three groups and by 50% when mild and moderate-to-severe groups were merged into one. The preliminary findings reported herein provide promising insights that automated tools may be developed to assist physicians in very early diagnosis of AD as well as provide researchers with a tool to automatically characterize cross-frequency interactions and their changes with disease.
Position of the pole and residue in the Msub(1+)sup(3/2) amplitude of the ?p?N? reaction
Coordinates of the pole and the residue for the Msub(1+)sup(3/2) amplitude of the ?p ? N? reaction are estimated in the framework of various models. These quantities are compared with those for the ?N scattering. The coincidence of the phases of residues in the ?N scattering and the photoproduction is indicated
Amplitude modulation of charge-density-wave domains in 1T-TaS2 at 300 K
Measurements of the charge-density-wave (CDW) amplitude modulation in 1T-TaS2 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
Nishihara, Masato; Kai, Yutaka; Tanaka, Toshiki; Takahara, Tomoo; Li, Lei; Yan, Weizhen; Liu, Bo; Tao, Zhenning; Rasmussen, Jens C.
2013-12-01
Advanced multi-level modulation is an attractive modulation technique for beyond 100 Gbps short reach optical transmission system. Above all, discrete multi-tone (DMT) technique and pulse amplitude modulation (PAM) technique are the strong candidates. We compared the 100 Gbps transmission characteristics of DMT and PAM by simulation and experiment. The comparison was done by using same devices and only the digital signal processing was changed. We studied the transmission distance dependence for 0.5 to 40 km and the impact of the frequency responses of the optical devices. Finally we discuss the features of the both modulation techniques.
Justin R. Timora
2013-11-01
Full Text Available Aims: Modulation masking refers to a disruption in the ability to detect amplitude modulation (AM in sound in the presence of an auditory masker with a similar temporal pattern. Previously, we have shown that multisensory presentations of acoustic and vibrotactile AM stimuli increase auditory and vibrotactile AM detection thresholds, suggesting a cross-modal modulation masking effect. Prior psychoacoustic research suggests that this masking effect is dependent on the phase of the AM masker. This study aimed to determine whether cross-modal phase differences for simultaneously presented acoustic and vibrotactile AM stimuli increase AM detection thresholds and whether this is reflected in the steady-state response (SSR elicited by the same multisensory stimulus combinations. Method: A 2I-3AFC psychophysical procedure was used to estimate AM detection thresholds for auditory and vibrotactile stimuli at two AM rates (27 and 40 Hz and three cross-modal phase conditions: None (AM stimulation in the target modality only; Same (AM in both modalities /no cross-modal phase difference; Different (AM stimulation in both modalities/180? phase difference. In a separate EEG session SSR activity was measured to the same stimulus combinations. Results: Vibrotactile AM thresholds significantly varied according to Phase F(2,28= 4.81,p = .02. Thresholds for the Same condition were higher relative to None F(1,14 = 8.06, p =.01. Differences between None and Different were non-significant. The influence of Phase on auditory 27 and 40 Hz SSR activity significantly varied according to AM rate F(2,16 = 8.65, p =.003, F(2,16 = 6.43, p=.01, with greater increases in activity at the EEG frequency corresponding to the AM rate. Conclusions: The increased sensitivity to vibrotactile AM stimuli resulting from a cross-modal phase difference suggests a release from masking and provides further evidence of cross-modal modulation masking. Cross-modal AM stimulation increases auditory SSR activity at the frequency of stimulation but has no effect on vibrotactile SSR activity which suggests a dissociation between SSR activity and AM detection.
Hayrapetyan, Armen G; Goette, Joerg B
2015-01-01
We study the impact of spatially homogeneous yet non-stationary PT-symmetric dielectric permittivity in dynamical and spectral properties of light. For such a time-reversal optical system, we analytically construct the instantaneous amplitude and angular frequency of waves within the framework of Maxwell's equations and demonstrate PT modulations of light amplification and attenuation associated with the well-defined regions of gain and loss, respectively. Particularly strong enhancement of amplitude modulation towards the loss domain is shown to be expected depending on fine tuning of parameters of the complex permittivity profile. Moreover, we predict the split of extrema of angular frequency modulation and demonstrate the shrinkage of the modulation period. Our theory can be extended for investigating similar time-dependent effects with matter and acoustic waves in PT-symmetric structures.
A Psychophysical and EEG Investigation of Cross-Modal Amplitude Modulation
Justin R Timora
2014-10-01
Full Text Available It is well established that both auditory and tactile perceptual processing is dependent on the temporally dynamic features of sensory stimulation. Much less is known about how these temporal features are integrated across sensory modalities. According to the temporal principle of multisensory integration greater cross-modal temporal correspondence should enhance the integration of multisensory stimulation. Aim: Investigate how cross-modal temporal correspondence of amplitude modulation (AM rate of multimodal presentations of acoustic and vibrotactile AM stimuli influence perceptual sensitivity for both psychophysical and EEG steady state measures of multisensory integration. Method: A psychophysical procedure was used to estimate auditory and vibrotactile AM detection thresholds for a 32 Hz AM target stimuli while the cross-modal modulation rate was varied across six conditions (0, 8, 16, 32, 64 and 128 Hz. In a separate session EEG activity was recorded while participants were presented with the same stimulus conditions. FFT was then used to measure EEG entrainment at the frequency corresponding to AM rate of stimulation. Results: Cross-modal AM rate significantly influenced auditory thresholds with polynomial contrasts indicating a significant quadratic trend. Cross-modal AM rate also significantly influenced vibrotactile thresholds with polynomial contrasts revealing a significant linear trend. Analysis of the 32 Hz SSR activity revealed no significant effect of cross-modal AM rate on the magnitude of 32 Hz SSR activity. Conclusions: Results of the psychophysical analysis suggest that perceptual sensitivity to AM stimuli varied with cross-modal AM rate. Contrary to prior literature, auditory sensitivity was worst when the cross-modal AM rates matched while sensitivity to vibrotactile AM stimuli decreased as the cross-modal AM rate increased. SSR activity was not influenced by cross-modal AM rate suggesting that the oscillatory activity as measured by the SSR may not reflect entrained activity involved in multisensory integration.
Xing, Xiangjun; Jin, Qingli; Li, Shuwei
2015-02-01
Spin-wave devices are regarded as one of the most promising candidates for future computation and data processing. How to manipulate spin-wave propagation is a key issue in realizing the functionality of these of devices. The existing manipulation methods have serious drawbacks for constructing practical spin-wave devices. Here, we propose an approach to harness the amplitude and mode excitation of traveling spin waves by introducing unique micromagnetic textures in a permalloy waveguide directly exchange-coupled to a pair of cobalt nanomagnets. We demonstrate that the imprinted micromagnetic textures, i.e., the 360 domain wall and magnetic buckle, which play different roles in spin-wave manipulation, can be interchanged with each other repeatedly by using a sequence of homogeneous magnetic fields. Moreover, the suggested architecture could easily be tailored to implement fundamental logic-NOT operation. In light of the internal-field profile of the micromagnetic textures, speculation is offered concerning the physical origin underlying the observed spin-wave modulation phenomena.
Spinwave devices are regarded as one of the most promising candidates for future computation and data processing. How to manipulate spinwave propagation is a key issue in realizing the functionality of these of devices. The existing manipulation methods have serious drawbacks for constructing practical spinwave devices. Here, we propose an approach to harness the amplitude and mode excitation of traveling spin waves by introducing unique micromagnetic textures in a permalloy waveguide directly exchange-coupled to a pair of cobalt nanomagnets. We demonstrate that the imprinted micromagnetic textures, i.e., the 360 domain wall and magnetic buckle, which play different roles in spinwave manipulation, can be interchanged with each other repeatedly by using a sequence of homogeneous magnetic fields. Moreover, the suggested architecture could easily be tailored to implement fundamental logic-NOT operation. In light of the internal-field profile of the micromagnetic textures, speculation is offered concerning the physical origin underlying the observed spinwave modulation phenomena. (paper)
Colaux, Henri; Dawson, Daniel M; Ashbrook, Sharon E
2014-08-01
The conversion between multiple- and single-quantum coherences is integral to many nuclear magnetic resonance (NMR) experiments of quadrupolar nuclei. This conversion is relatively inefficient when effected by a single pulse, and many composite pulse schemes have been developed to improve this efficiency. To provide the maximum improvement, such schemes typically require time-consuming experimental optimization. Here, we demonstrate an approach for generating amplitude-modulated pulses to enhance the efficiency of the triple- to single-quantum conversion. The optimization is performed using the SIMPSON and MATLAB packages and results in efficient pulses that can be used without experimental reoptimisation. Most significant signal enhancements are obtained when good estimates of the inherent radio-frequency nutation rate and the magnitude of the quadrupolar coupling are used as input to the optimization, but the pulses appear robust to reasonable variations in either parameter, producing significant enhancements compared to a single-pulse conversion, and also comparable or improved efficiency over other commonly used approaches. In all cases, the ease of implementation of our method is advantageous, particularly for cases with low sensitivity, where the improvement is most needed (e.g., low gyromagnetic ratio or high quadrupolar coupling). Our approach offers the potential to routinely improve the sensitivity of high-resolution NMR spectra of nuclei and systems that would, perhaps, otherwise be deemed "too challenging". PMID:25047226
Puerta Ramírez, Rafael; Rommel, Simon; Vegas Olmos, Juan José; Tafur Monroy, Idelfonso
2016-01-01
In this paper, for the first time, a record UWB transmission of 10Gb/s is experimentally demonstrated employing a multi-band approach of carrierless amplitude phase modulation (MultiCAP). The proposed solution complies with the restrictions on the effective radiated power established by both the ...
Rodes Lopez, Roberto; Wieckowski, Marcin; Pham, Tien Thang; Jensen, Jesper Bevensee; Turkiewicz, Jarek; Siuzdak, Jerzy; Tafur Monroy, Idelfonso
2011-01-01
We experimentally demonstrate successful performance of VCSEL-based WDM link supporting advanced 16-level carrierless amplitude/phase modulation up to 1.25 Gbps, over 26 km SSMF with spectral efficiency of 4 bit/s/Hz for application in high capacity PONs. 2011 Optical Society of America....
Rodes Lopez, Roberto; Wieckowski, Marcin; Pham, Tien Thang; Jensen, Jesper Bevensee; Turkiewicz, Jarek; Siuzdak, Jerzy; Tafur Monroy, Idelfonso
2011-01-01
We experimentally demonstrate successful performance of VCSEL-based WDM link supporting advanced 16-level carrierless amplitude/phase modulation up to 1.25 Gbps, over 26 km SSMF with spectral efficiency of 4 bit/s/Hz for application in high capacity PONs. © 2011 Optical Society of America.
Low-temperature Aharonov–Bohm oscillations in the magnetoresistance of mesoscopic interferometric rings patterned on an InGaAs/InAlAs heterostructure are investigated for their dependence on excitation current and temperature. The rings have an average radius of 650 nm, and a lithographic arm width of 300 nm, yielding pronounced interference oscillations over a wide range of magnetic fields. Apart from a current and temperature dependence, the oscillation amplitude also shows a quasi-periodic modulation with applied magnetic field. The phase coherence length is extracted by analysis of the fundamental and higher Fourier components of the oscillations, and by direct analysis of the amplitude and its dependence on parameters. It is concluded that the Thouless energy forms the measure of excitation energies for quantum decoherence. The amplitude modulation finds an explanation in the effect of the magnetic flux threading the finite width of the interferometer arms. (paper)
Nony, Laurent; Bocquet, Franck; Loppacher, Christian; Glatzel, Thilo
2009-01-01
The influence of short-range electrostatic forces on the measured local Contact Potential Difference (CPD) by means of Amplitude Modulation- and Frequency Modulation-Kelvin Probe Force Microscopy (AM- and FM-KPFM) is discussed on the base of numeric and analytic descriptions of both methods. The goal of this work is to help interpreting recent experimental results reporting atomically-resolved CPD images, in particular on bulk insulating samples. The discussion is carried out on the base of s...
Acua, Alonso M; Snellenburg, Joris J; Gwizdala, Michal; Kirilovsky, Diana; van Grondelle, Rienk; van Stokkum, Ivo H M
2016-01-01
Pulse-amplitude modulated (PAM) fluorometry is extensively used to characterize photosynthetic organisms on the slow time-scale (1-1000s). The saturation pulse method allows determination of the quantum yields of maximal (F M) and minimal fluorescence (F 0), parameters related to the activity of the photosynthetic apparatus. Also, when the sample undergoes a certain light treatment during the measurement, the fluorescence quantum yields of the unquenched and the quenched states can be determined. In the case of cyanobacteria, however, the recorded fluorescence does not exclusively stem from the chlorophylla in photosystem II (PSII). The phycobilins, the pigments of the cyanobacterial light-harvesting complexes, the phycobilisomes (PB), also contribute to the PAM signal, and therefore, F 0 and F M are no longer related to PSII only. We present a functional model that takes into account the presence of several fluorescent species whose concentrations can be resolved provided their fluorescence quantum yields are known. Data analysis of PAM measurements on in vivo cells of our model organism Synechocystis PCC6803 is discussed. Three different components are found necessary to fit the data: uncoupled PB (PBfree), PB-PSII complexes, and free PSI. The free PSII contribution was negligible. The PBfree contribution substantially increased in the mutants that lack the core terminal emitter subunits allophycocyanin D or allophycocyanin F. A positive correlation was found between the amount of PBfree and the rate constants describing the binding of the activated orange carotenoid protein to PB, responsible for non-photochemical quenching. PMID:25893897
Gorb, Yuliya
2010-11-01
We model and analyze the response of nonlinear, residually stressed elastic bodies subjected to small amplitude vibrations superimposed upon large deformations. The problem derives from modeling the use of intravascular ultrasound (IVUS) imaging to interrogate atherosclerotic plaques in vivo in large arteries. The goal of this investigation is twofold: (i) introduce a modeling framework for residual stress that unlike traditional Fung type classical opening angle models may be used for a diseased artery, and (ii) investigate the sensitivity of the spectra of small amplitude high frequency time harmonic vibrations superimposed on a large deformation to the details of the residual stress stored in arteries through a numerical simulation using physiologic parameter values under both low and high blood pressure loadings. The modeling framework also points the way towards an inverse problem using IVUS techniques to estimate residual stress in healthy and diseased arteries. © 2010 Elsevier Ltd. All rights reserved.
Borisov, Vladimir; Veniaminov, Andrey
2015-10-01
Amplitude and phase contributions to mixed volume holographic gratings were extracted from measured contours of angular selectivity. Holograms for the investigation were recorded in the glassy polymer material with phenan-threnequinone (PQ) using the DPSS CW laser (532 nm) and then self-developed due to molecular diffusion of PQ, reaching diffraction efficiency about 40%. Refractive index and absorbance modulation amplitudes of those holograms were obtained as adjustable parameters from theoretical equations by fitting angular dependencies of zeros and 1st orders diffraction efficiency measured at 450, 473, 532, and 633 nm at the different stages of hologram development. Mixed gratings manifest themselves in asymmetrical transmittance selectivity contours with one minimum and one maximum shifted with respect to the Bragg angle, while symmetrical contours with a minimum or a maximum at the Bragg angle are characteristic of pure phase and amplitude gratings, respectively. In the course of a hologram development, it converts from a predominantly amplitude-mixed to almost purely phase one in the case of readout using a light within the absorption band of PQ and maintains the phase nature besides it. The value of refractive index amplitude is ranging from 5×10-6 to 10-4 and the value of absorbance amplitude is up to 140 m-1.
A 25 J -1.053 μm pulse in 0.45 ps (a0= 2.2) was injected into a gas jet. This excited a large amplitude self-modulated wakefield. By increasing the pulse length from 0.45 to to 1.2 ps, the wakefield grew close to the wave-breaking limit, which sustained a 350 ± 150 GV/m acceleration field over a 1 mm dephasing distance along the laser axis in a plasma with density 2 x 1019 cm-3. This resulted in electrons accelerated to 300 MeV. The amplitude saturation of the wakefield is explained by a pump depletion effect to the large amplitude forward Raman instability. The Petawatt Laser is completed, which will be used to accelerate electrons above one GeV
Herlory, Olivier, E-mail: olivier.herlory@gmail.com [IRSN-Laboratoire d’Ecotoxicologie des Radionucléides, Centre de Cadarache, BP3, 13115 Saint Paul lez Durance (France); Bonzom, Jean-Marc, E-mail: jean-marc.bonzom@irsn.fr [IRSN-Laboratoire d’Ecotoxicologie des Radionucléides, Centre de Cadarache, BP3, 13115 Saint Paul lez Durance (France); Gilbin, Rodolphe, E-mail: rodolphe.gilbin@irsn.fr [IRSN-Laboratoire de Biogéochimie, Biodisponibilité et Transferts des Radionucléides, Centre de Cadarache, BP3, 13115 Saint Paul lez Durance (France)
2013-09-15
Highlights: •Our study addressed the toxicity thresholds of uranium on microalgae using PAM fluorometry. •The oxygen-evolving complex (OEC) of PSII was identified as the primary action site of uranium. •Uranium impaired the electron flux between the photosystems until almost complete inhibition. •Non-photochemical quenching was identified as the most sensitive fluorescence parameter. •PAM fluorometry provided a rapid and reasonably sensitive method for assessing stress response. -- Abstract: Although ecotoxicological studies tend to address the toxicity thresholds of uranium in freshwaters, there is a lack of information on the effects of the metal on physiological processes, particularly in aquatic plants. Knowing that uranium alters photosynthesis via impairment of the water photo-oxidation process, we determined whether pulse amplitude modulated (PAM) fluorometry was a relevant tool for assessing the impact of uranium on the green alga Chlamydomonas reinhardtii and investigated how and to what extent uranium hampered photosynthetic performance. Photosynthetic activity and quenching were assessed from fluorescence induction curves generated by PAM fluorometry, after 1 and 5 h of uranium exposure in controlled conditions. The oxygen-evolving complex (OEC) of PSII was identified as the primary action site of uranium, through alteration of the water photo-oxidation process as revealed by F{sub 0}/F{sub v}. Limiting re-oxidation of the plastoquinone pool, uranium impaired the electron flux between the photosystems until almost complete inhibition of the PSII quantum efficiency (F{sup ′}{sub q}/F{sup ′}{sub m}, EC{sub 50} = 303 ± 64 μg U L{sup −1} after 5 h of exposure) was observed. Non-photochemical quenching (qN) was identified as the most sensitive fluorescence parameter (EC{sub 50} = 142 ± 98 μg U L{sup −1} after 5 h of exposure), indicating that light energy not used in photochemistry was dissipated in non-radiative processes. It was shown that parameters which stemmed from fluorescence induction kinetics are valuable indicators for evaluating the impact of uranium on PSII in green algae. PAM fluorometry provided a rapid and reasonably sensitive method for assessing stress response to uranium in microalgae.
Highlights: •Our study addressed the toxicity thresholds of uranium on microalgae using PAM fluorometry. •The oxygen-evolving complex (OEC) of PSII was identified as the primary action site of uranium. •Uranium impaired the electron flux between the photosystems until almost complete inhibition. •Non-photochemical quenching was identified as the most sensitive fluorescence parameter. •PAM fluorometry provided a rapid and reasonably sensitive method for assessing stress response. -- Abstract: Although ecotoxicological studies tend to address the toxicity thresholds of uranium in freshwaters, there is a lack of information on the effects of the metal on physiological processes, particularly in aquatic plants. Knowing that uranium alters photosynthesis via impairment of the water photo-oxidation process, we determined whether pulse amplitude modulated (PAM) fluorometry was a relevant tool for assessing the impact of uranium on the green alga Chlamydomonas reinhardtii and investigated how and to what extent uranium hampered photosynthetic performance. Photosynthetic activity and quenching were assessed from fluorescence induction curves generated by PAM fluorometry, after 1 and 5 h of uranium exposure in controlled conditions. The oxygen-evolving complex (OEC) of PSII was identified as the primary action site of uranium, through alteration of the water photo-oxidation process as revealed by F0/Fv. Limiting re-oxidation of the plastoquinone pool, uranium impaired the electron flux between the photosystems until almost complete inhibition of the PSII quantum efficiency (F′q/F′m, EC50 = 303 ± 64 μg U L−1 after 5 h of exposure) was observed. Non-photochemical quenching (qN) was identified as the most sensitive fluorescence parameter (EC50 = 142 ± 98 μg U L−1 after 5 h of exposure), indicating that light energy not used in photochemistry was dissipated in non-radiative processes. It was shown that parameters which stemmed from fluorescence induction kinetics are valuable indicators for evaluating the impact of uranium on PSII in green algae. PAM fluorometry provided a rapid and reasonably sensitive method for assessing stress response to uranium in microalgae
Pezzopane, M.; Pignalberi, A.; Pietrella, M.
2016-01-01
Spectral analyses are employed to investigate how the diurnal periodicity of the critical frequency of the sporadic E (Es) layer varies with solar activity. The study is based on ionograms recorded at the ionospheric station of Rome (41.8°N, 12.5°E), Italy, from 1976 to 2009, a period of time covering three solar cycles. It was confirmed that the diurnal periodicity is always affected by an amplitude modulation with periods of several days, which is the proof that Es layers are affected indirectly by planetary waves through their nonlinear interaction with atmospheric tides at lower altitudes. The most striking features coming out from this study is however that this amplitude modulation is greater for high-solar activity than for low-solar activity.
Stein, A.; Ewert, Stephan; Wiegrebe, L.
2005-01-01
(<33 Hz). Predictions of a generic implementation of a modulation-filterbank model and an autocorrelation model are compared to the data. Both models were too insensitive to high-frequency envelope or carrier periodicity and to infra-pitch carrier periodicity. Additionally, both models simulated......Recent temporal models of pitch and amplitude modulation perception converge on a relatively realistic implementation of cochlear processing followed by a temporal analysis of periodicity. However, for modulation perception, a modulation filterbank is applied whereas for pitch perception......, autocorrelation is applied. Considering the large overlap in pitch and modulation perception, this is not parsimonious. Two experiments are presented to investigate the interaction between carrier periodicity, which produces strong pitch sensations, and envelope periodicity using broadband stimuli. Results show...
The effects of amplitude modulation (AM) on an atmospheric pressure microwave argon jet is investigated using time-resolved optical emission spectroscopy, passive acoustic diagnostic and digital camera imaging. These techniques show significant changes of the effluent plasma properties with varying AM frequency. Operation in AM mode can enhance the plasma jet length or width over continuous-wave mode with the same mean power, which could be advantageous in many practical applications of plasma jets. (paper)
Cerebral cortex tissue slices and cerebral hemispheres prepared from Gallus domesticus chicks were exposed to 147 MHz radiofrequency radiation, amplitude modulated at 16 Hz and applied at a power density of 0.75 mW/cm2, to determine the effect of such exposure of 45Ca2+ efflux from the avian brain tissue. Statistical analysis of these data demonstrates that such exposure has no significant effect on 45Ca2+ efflux
The onion fly modulates the adult eclosion time in response to amplitude of temperature cycle
Tanaka, Kazuhiro; Watari, Yasuhiko
2011-08-01
To confirm whether the amplitude of diel temperature cycles causes a phase shift of adult eclosion rhythm of the onion fly, Delia antiqua, the peak time ( E) of adult eclosion was determined under various thermoperiods with a fixed temperature either in the warm or cool phase and temperature differences ranging from 1C to 4C between the two phases. Irrespective of the temperature level during the warm or cool phase, E occurred earlier with decreasing amplitude of the temperature cycle. The results strongly support the previous conclusion of Tanaka and Watari (Naturwissenschaften 90:76-79, 2003) that D. antiqua responds to the amplitude of temperature cycle as a cue for the circadian adult eclosion timing. The phase advance was larger in thermoperiods with a fixed warm-phase temperature than in those with a fixed cool-phase temperature. This might be ascribed to the interaction between the amplitude and level of temperature in the thermoperiodic regimes.
Peucheret, Christophe; Lorenzen, Michael Rodas; Seoane, Jorge; Noordegraaf, Danny; Nielsen, Carsten Vandel; Grüner-Nielsen, Lars; Rottwitt, Karsten
2008-01-01
Input power dynamic range enhancement and amplitude regeneration of highly distorted signals are demonstrated experimentally for 40 Gbit/s RZ-DPSK in a single-pump fibre parametric amplifier with 22 dB smallsignal gain.
Characterizations of regular local rings via syzygy modules of the residue field
Ghosh, Dipankar; Gupta, Anjan; Puthenpurakal, Tony J.
2015-01-01
Let $R$ be a commutative Noetherian local ring with residue field $k$. We show that if a finite direct sum of syzygy modules of $k$ surjects onto `a semidualizing module' or `a non-zero maximal Cohen-Macaulay module of finite injective dimension', then $R$ is regular. We also prove that $R$ is regular if and only if some syzygy module of $k$ has a non-zero direct summand of finite injective dimension.
Zhang, Qiushi; Zhao, Xiaojie; Zhu, Chaozhe; Yang, Xueqian; Yao, Li
2015-03-01
The functional magnetic resonance imaging (fMRI) researches on working memory have found that activation of cortical areas appeared dependent on memory load, and event-related potentials (ERP) studies have demonstrated that amplitudes of P300 decreased significantly when working memory load increased. However, the cortical activities related with P300 amplitudes under different memory loads remains unclear. Joint fMRI and EEG analysis which fusions the time and spatial information in simultaneous EEG-fMRI recording can reveal the regional activation at each ERP time point. In this paper, we first used wavelet transform to obtain the single-trial amplitudes of P300 caused by a digital N-back task in the simultaneous EEG-fMRI recording as the ERP feature sequences. Then the feature sequences in 1-back condition and 3-back condition were introduced into general linear model (GLM) separately as parametric modulations to compare the cortical activation under different memory loads. The results showed that the average amplitudes of P300 in 3-back significantly decreased than that in 1-back, and the activities induced by ERP feature sequences in 3-back also significantly decreased than that in the 1-back, including the insular, anterior cingulate cortex, right inferior frontal gyrus, and medial frontal gyrus, which were relevant to the storage, monitoring, and manipulation of information in working memory task. Moreover, the difference in the activation caused by ERP feature showed a positive correlation with the difference in behavioral performance. These findings demonstrated the locations of P300 amplitudes differences modulated by the memory load and its relationship with the behavioral performance.
Anderson, Richard I
2014-01-01
[Abridged] I report the discovery of modulations in radial velocity (RV) curves of four Galactic classical Cepheids and investigate their impact as a systematic uncertainty for Baade-Wesselink distances. Highly precise Doppler measurements were obtained using the Coralie high-resolution spectrograph since 2011. Particular care was taken to sample all phase points in order to very accurately trace the RV curve during multiple epochs and to search for differences in linear radius variations derived from observations obtained at different epochs. Different timescales are sampled, ranging from cycle-to-cycle to months and years. The unprecedented combination of excellent phase coverage obtained during multiple epochs and high precision enabled the discovery of significant modulation in the RV curves of the short-period s-Cepheids QZ Normae and V335 Puppis, as well as the long-period fundamental mode Cepheids l Carinae and RS Puppis. The modulations manifest as shape and amplitude variations that vary smoothly on ...
Lechinger, Julia; Heib, Dominik Philip Johannes; Gruber, Walter; Schabus, Manuel; Klimesch, Wolfgang
2015-11-01
Based on physiological models of neurovisceral integration, different studies have shown how cognitive processes modulate heart rate and how the heartbeat, on the other hand, modulates brain activity. We tried to further determine interactions between cardiac and electrical brain activity by means of EEG. We investigated how the heartbeat modulates EEG in 23 healthy controls from wakefulness to deep sleep and showed that frontocentral heartbeat evoked EEG amplitude and phase locking (as measured by intertrial phase locking), at about 300-400 ms after the R peak, decreased with increasing sleep depth with a renewed increase during REM sleep, which underpins the assumption that the heartbeat evoked positivity constitutes an active frontocortical response to the heartbeat. Additionally, we found that individual heart rate was correlated with the frequency of the EEG's spectral peak (i.e., alpha peak frequency during wakefulness). This correlation was strongest during wakefulness and declined linearly with increasing sleep depth. Furthermore, we show that the QRS complex modulates spindle phase possibly related to the correspondence between the frequency of the QRS complex and the spindle frequency of about 12-15 Hz. Finally, during deep sleep stages, a loose temporal coupling between heartbeats and slow oscillation (0.8 Hz) could be observed. These findings indicate that cardiac activity such as heart rate or individual heartbeats can modulate or be modulated by ongoing oscillatory brain activity. PMID:26268858
Pfabigan, Daniela M.; Zeiler, Michael; Lamm, Claus; Sailer, Uta
2014-01-01
ERP responses to feedback stimuli with explicit or assigned valence information were investigated with blocked or randomized trial presentation modes.Only P3b, but not feedback-related negativity amplitudes were affected by feedback type for both presentation modes.Results suggest using blocked design when using different types of feedback stimuli.
Hassan Farhan Rashag
2013-04-01
Full Text Available Various aspects related to controlling induction motor are investigated. Direct torque control is an original high performance control strategy in the field of AC drive. In this proposed method, the control system is based on Space Vector Modulation (SVM, amplitude of voltage in direct- quadrature reference frame (d-q reference and angle of stator flux. Amplitude of stator voltage is controlled by PI torque and PI flux controller. The stator flux angle is adjusted by rotor angular frequency and slip angular frequency. Then, the reference torque and the estimated torque is applied to the input of PI torque controller and the control quadrature axis voltage is determined. The control d-axis voltage is determined from the flux calculator. These q and d axis voltage are converted into amplitude voltage. By applying polar to Cartesian on amplitude voltage and stator flux angle, direct voltage and quadratures voltage are generated. The reference stator voltages in d-q are calculated based on forcing the stator voltage error to zero at next sampling period. By applying inverse park transformation on d-q voltages, the stator voltages in &alpha and &beta frame are generated and apply to SVM. From the output of SVM, the motor control signal is generated and the speed of the induction motor regulated toward the rated speed. The simulation Results have demonstrated exceptional performance in steady and transient states and shows that decrease of torque and flux ripples is achieved in a complete speed range.
Castellano, Fabrizio; Li, Lianhe; Linfield, Edmund H.; Davies, A. Giles; Vitiello, Miriam S.
2016-03-01
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.
Castellano, Fabrizio; Li, Lianhe; Linfield, Edmund H; Davies, A Giles; Vitiello, Miriam S
2016-01-01
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. PMID:26976199
Travel Time Shifts due to Amplitude Modulation in Time-Distance Helioseismology
Nigam, R.; Kosovichev, A. G.
2009-01-01
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 has 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 suppres...
Bellgowan, P.S.F; Saad, Z. S.; Bandettini, P. A.
2003-01-01
Estimates of hemodynamic amplitude, delay, and width were combined to investigate system dynamics involved in lexical decision making. Subjects performed a lexical decision task using word and nonword stimuli rotated 0°, 60°, or 120°. Averaged hemodynamic responses to repeated stimulation were fit to a Gamma-variate function convolved with a heavyside function of varying onset and duration to estimate each voxel's activation delay and width. Consistent with prolonged reaction times for the ro...
Phase dependent modulation of tremor amplitude in essential tremor through thalamic stimulation
Cagnan, Hayriye; Brittain, John-Stuart; Little, Simon; Foltynie, Thomas; Limousin, Patricia; Zrinzo, Ludvic; Hariz, Marwan; Joint, Carole; Fitzgerald, James; Green, Alexander L.; Aziz, Tipu; Brown, Peter
2013-01-01
High frequency deep brain stimulation of the thalamus can help ameliorate severe essential tremor. Here we explore how the efficacy, efficiency and selectivity of thalamic deep brain stimulation might be improved in this condition. We started from the hypothesis that the effects of electrical stimulation on essential tremor may be phase dependent, and that, in particular, there are tremor phases at which stimuli preferentially lead to a reduction in the amplitude of tremor. The latter could b...
Line shape of amplitude or frequency-modulated spectral profiles including resonator distortions.
Suter, Martin; Quack, Martin
2015-05-10
We report experiments and an improved method of analysis for any harmonics of frequency-modulated spectral line shapes allowing for very precise determinations of the resonance frequency of single absorption lines for gigahertz spectroscopy in the gas phase. Resonator perturbations are implemented into the formalism of modulation spectroscopy by means of a full complex transmission function being able to model the asymmetrically distorted absorption line shapes for arbitrary modulation depths, modulation frequencies, and resonator reflectivities. Exact equations of the in-phase and the quadrature modulation signal, taking into account a full resonator transmission function, are simultaneously adjusted to two-channel lock-in measurements performed in the gigahertz regime to obtain the spectral line position. The determination of the absorption line position of the rotational transition J' = 7 ? J" = 6 of (16)O(12)C(32)S in the vibrational ground state is investigated while changing the resonator distortions. The results are subjected to the approach proposed here and compared to standard methods known from the literature. PMID:25967497
van Dijk, Hanneke; van der Werf, Jurrian; Mazaheri, Ali; Medendorp, W. Pieter; Jensen, Ole
2009-01-01
Event-related responses and oscillatory activity are typically regarded as manifestations of different neural processes. Recent work has nevertheless revealed a mechanism by which slow event-related responses are created as a direct consequence of modulations in brain oscillations with nonsinusoidal properties. It remains unknown if this mechanism applies to cognitively relevant event-related responses. Here, we investigated whether sustained event-related fields (ERFs) measured during working memory maintenance can be explained by modulations in oscillatory power. In particular, we focused on contralateral delayed activity (CDA) typically observed in working memory tasks in which hemifield specific attention is manipulated. Using magnetoencephalography, we observed sustained posterior ERFs following the presentation of the memory target. These ERFs were systematically lateralized with respect to the hemisphere in which the target was presented. A strikingly similar pattern emerged for modulations in alpha (913 Hz) power. The alpha power and ERF lateralization were strongly correlated over subjects. Based on a mechanistic argument pertaining to the nonsinusoidal properties of the alpha activity, we conclude that the ERFs modulated by working memory are likely to be directly produced by the modulations in oscillatory alpha activity. Given that posterior alpha activity typically reflects disengagement, we conclude that the CDA is not attributable to an additive process reflecting memory maintenance per se but, rather, is a consequence of how attentional resources are allocated. PMID:20080773
Francucci M
2010-01-01
Full Text Available Amplitude-modulated (AM laser imaging is a promising technology for the production of accurate three-dimensional (3D images of submerged scenes. The main challenge is that radiation scattered off water gives rise to a disturbing signal (optical noise that degrades more and more the quality of 3D images for increasing turbidity. In this paper, we summarize a series of theoretical findings, that provide valuable hints for the development of experimental methods enabling a partial rejection of optical noise in underwater imaging systems. In order to assess the effectiveness of these methods, which range from modulation/demodulation to polarimetry, we carried out a series of experiments by using the laboratory prototype of an AM 3D imager ( = 405?nm for marine archaeology surveys, in course of realization at the ENEA Artificial Vision Laboratory (Frascati, Rome. The obtained results confirm the validity of the proposed methods for optical noise rejection.
We present a family of soliton solutions of the quasi-one-dimensional Bose-Einstein condensates with time-dependent scattering length, by developing multiple-scale method combined with truncated Painleve expansion. Then, by numerical calculating the solutions, it is shown that there exhibit two types of dark solitons-black soliton (the zero minimum amplitude at its center) and gray soliton (the minimum density does not drop to zero) in a repulsive condensate. Furthermore, we propose experimental protocols to realize the exchange between black and gray solitons by varying the scattering length via the Feshbach resonance in currently experimental conditions
Phase-amplitude coupling characteristics in directly modulated quantum dot lasers
WANG, Cheng; Osi?ski, M; Even, J; Grillot, F
2014-01-01
We present a semi-analytical model for studying the phase-amplitude coupling (a-factor) in quantum dot (QD) semiconductor lasers, which takes into account the influence of carrier populations in the excited state and in the two-dimensional carrier reservoir on the refractive index change. Calculations of the a-factor based on the amplified spontaneous emission method and on the "FM/AM" technique are both investigated. It is shown that the a-factor of a QD laser strongly depends on the energy ...
Comparison of carrierless amplitude-phase (CAP) and discrete multitone (DMT) modulation
Othman, M. B.; Pham, Tien-Thang; Deng, Lei; Jensen, Jesper Bo; Tafur Monroy, Idelfonso
We compare the transmission of 1.25 Gb/s CAP-16 and 909.2 Mb/s 16-QAM-DMT modulation formats over 2.4 km of MMF with 850 nm DM-CSELs. CAP displays 0.7-1.1 dB better sensitivity than DMT in this experiment....
Korman Maria
2011-12-01
Full Text Available Perception of vibration during drilling demands integration of haptic and auditory information with force information. In this study we explored the ability to detect and discriminate changes in vibrotactile stimuli amplitude based either on purely haptic feedback or together with congruent synthesized auditory cues in groups of naive subjects and expert surgeons. Our results point toward the complex influence of multimodal experience during vibration perception. First, in naive subjects, we showed that detection and discrimination of amplitude change in complex vibro-tactile stimulus is selectively sensitive to combination of modality and previous experience. In the domain of discrimination, our results suggest that bi-modal performance is always better than uni-modal performance regardless of order of experience. Second, experiments with expert surgeons revealed that expertise in complex skill of maxilla-facial surgery strongly relies on enhanced touch perception, as measured in reaction times and discrimination ability in bi-modal vibro-auditory conditions. These observations suggest that acquisition of mandibular surgery skill has brought to an enhanced representation of vibro-tactile modulations in relevant stimuli ranges. Altogether, our results provide basis to assume that during acquisition of mandibular drilling skill, trainees may benefit from training of relevant basic aspects of touch perception - sensitivity to vibration and accompanying modulations of sound.
Shaping symmetric Airy beam through binary amplitude modulation for ultralong needle focus
Fang, Zhao-Xiang; Ren, Yu-Xuan; Gong, Lei; Vaveliuk, Pablo; Chen, Yue; Lu, Rong-De
2015-01-01
Needle-like electromagnetic fields has various advantages for the applications in high-resolution imaging, Raman Spectroscopy, as well as long-distance optical transportation. The realization of such field often requires high numerical aperture (NA) objective lens and the transmission masks. We demonstrate an ultralong needle-like focus in the optical range produced with an ordinary lens. This is achieved by focusing a symmetric Airy beam (SAB) generated via binary spectral modulation with a ...
Phase-amplitude coupling characteristics in directly modulated quantum dot lasers
We present a semi-analytical model for studying the phase-amplitude coupling (α-factor) in quantum dot (QD) semiconductor lasers, which takes into account the influence of carrier populations in the excited state and in the two-dimensional carrier reservoir on the refractive index change. Calculations of the α-factor based on the amplified spontaneous emission method and on the “FM/AM” technique are both investigated. It is shown that the α-factor of a QD laser strongly depends on the energy separation between the ground state and the off-resonant states. Through band structure engineering, the α-factor can be reduced by enlarging this energy separation
Self-amplitude and self-phase modulation of the charcoal mode-locked erbium-doped fiber lasers.
Lin, Yung-Hsiang; Lo, Jui-Yung; Tseng, Wei-Hsuan; Wu, Chih-I; Lin, Gong-Ru
2013-10-21
With the intra-cavity nano-scale charcoal powder based saturable absorber, the 455-fs passive mode-locking of an L-band erbium-doped fiber laser (EDFL) is demonstrated. The size reduction of charcoal nano-particle is implemented with a simple imprinting-exfoliation-wiping method, which assists to increase the transmittance up to 0.91 with corresponding modulation depth of 26%. By detuning the power gain from 17 to 21 dB and cavity dispersion from -0.004 to -0.156 ps of the EDFL, the shortening of mode-locked pulsewidth from picosecond to sub-picosecond by the transformation of the pulse forming mechanism from self-amplitude modulation (SAM) to the combining effect of self-phase modulation (SPM) and group delay dispersion (GDD) is observed. A narrower spectrum with 3-dB linewidth of 1.83-nm is in the SAM case, whereas the spectral linewidth broadens to 5.86 nm with significant Kelly sideband pair can be observed if the EDFL enters into the SPM regime. The mode-locking mechanism transferred from SAM to SPM/GDD dominates the pulse shortening procedure in the EDFL, whereas the intrinsic defects in charcoal nano-particle only affect the pulse formation at initial stage. The minor role of the saturable absorber played in the EDFL cavity with strongest SPM is observed. PMID:24150360
An installation is described for measuring the Hall electromotive force and the magnetorsistance ΔR(B)/R of low-resistance materials by means of the amplitude modulation method with double synchronous detection. An active filter, synchronous detectors, a phase shifter, rejector filter, scale amplifier and squarelaw generator are the basic units of the installation. The installation permits to record ΔR(B)/R approximately 10-5 and the minimum Hall electromotive force of 10-9. Measurement results of the resistivity temperature dependencies, of the Hall coefficient and of the magnetoresistance of a Bisub(2)Tesub(2,7)Sesub(0.3) sample in the temperature range of 77-300 K are given
Vahdat, Vahid; Carpick, Robert W
2013-11-26
Amplitude modulation atomic force microscopy (AM-AFM) is one of the most popular AFM modes because of the reduced tip-sample interaction, compared to contact mode AFM, and the ability to acquire high-resolution images while interrogating the sample's material composition through phase imaging. Despite the reduced tip-sample interaction, tip and sample wear can occur through gradual atomic scale processes that can significantly accumulate due to the high frequency of the tip-sample interaction and through high intermittent contact stresses. Starting from existing analytical formulations, we introduce a method for selecting an appropriate probe and free oscillation amplitude that avoids exceeding a critical contact stress to minimize tip/sample damage. The approach is presented for the case of both a Hertzian- and a Derjaguin-Müller-Toporov-like tip-sample contact. Stress maps and related simplified formulas are provided that enable one to determine allowable free oscillation amplitudes to stay below a target contact stress for given cantilever and sample parameters (combined into a single "cantilever-sample constant" that we introduce). Experimental results show how sharp silicon tips, either uncoated or coated with diamond-like carbon and silicon nitride, interacting with a hard and wear-resistant sample (ultrananocrystalline diamond) can be preserved while attaining high-quality AM-AFM images by using our proposed scheme. We also show that using our analysis to select parameters that exceed the target contact stress indeed leads to significant tip wear. This method provides AM-AFM users with a better understanding of contact stresses and enables selection of AM-AFM cantilevers and experimental parameters that preserve the tip for long periods of use and prevents the sample from damage. PMID:24131354
The dynamics of the oscillating microcantilever for amplitude modulation atomic force microscopy (AM AFM) operating in air is well understood theoretically but the experimental outcomes are still emerging. We use double-stranded DNA on mica as a model biomolecular system for investigating the connection between theory and experiment. A demonstration that the switching between the two cantilever oscillation states is stochastic in nature is achieved, and it can be induced by means of topographical anomalies on the surface. Whether one or the other attractor basin is accessed depends on the tip-sample separation history used to achieve the imaging conditions, and we show that the behaviour is reproducible when the tip is stable and well characterized. Emergence of background noise occurs in certain regions of parameter space regardless of whether two cantilever oscillation states coexist. The low state has been explored in detail and we note that at low to intermediate values of the free amplitude, noise-free imaging is achieved. The outcomes shown here are general and demonstrate that a thorough and systematic experimental approach in conjunction with standard modelling gives insight into the mechanisms behind image contrast formation in AM AFM in air.
Low-amplitude rotational modulation rather than pulsations in the CoRoT B-type supergiant HD 46769
Aerts, C; Catala, C; Neiner, C; Briquet, M; Castro, N; Schmid, V S; Scardia, M; Rainer, M; Poretti, E; Papics, I; Degroote, P; Bloemen, S; Oestensen, R H; Auvergne, M; Baglin, A; Baudin, F; Michel, E; Samadi, R
2013-01-01
{We aim to detect and interpret photometric and spectroscopic variability of the bright CoRoT B-type supergiant target HD\\,46769 ($V=5.79$). We also attempt to detect a magnetic field in the target.} {We analyse a 23-day oversampled CoRoT light curve after detrending, as well as spectroscopic follow-up data, by using standard Fourier analysis and Phase Dispersion Minimization methods. We determine the fundamental parameters of the star, as well as its abundances from the most prominent spectral lines. We perform a Monte Carlo analysis of spectropolarimetric data to obtain an upper limit of the polar magnetic field, assumping a dipole field.} {In the CoRoT data, we detect a dominant period of 4.84\\,d with an amplitude of 87\\,ppm, and some of its (sub-)multiples. Given the shape of the phase-folded light curve and the absence of binary motion, we interpret the dominant variability in terms of rotational modulation, with a rotation period of 9.69\\,d. Subtraction of the rotational modulation signal does not revea...
Alexandra de Oliveira, Claro; Bruna Akie, Kanezawa; Michele de, Camargo; Vanessa Maria, Paes; Jos Luiz Marinho, Portolez; Gladson Ricardo Flor, Bertolini.
2014-09-01
Full Text Available JUSTIFICATIVA E OBJETIVOS: A corrente interferencial um mtodo de eletroestimulao bastante utilizado com finalidades analgsicas, porm, existem controvrsias com relao aos seus parmetros de uso. O objetivo do estudo foi comparar diferentes frequncias de amplitude modulada, da corrente inte [...] rferencial, sobre o limiar de dor presso e ao frio, em voluntrios saudveis. MTODOS: Trata-se de um ensaio cruzado, aleatrio e com avaliadores e avaliados encobertos, de carter quantitativo. Participaram deste estudo 20 voluntrios subdivididos em quatro grupos, que durante quatro semanas passaram por diferentes frequncias de amplitude modulada. Foram avaliados os limiares da dor presso e ao frio em quatro momentos distintos - no incio, logo aps eletroestimulao, 20 e 60 minutos aps. Como forma de eletroestimulao foi utilizada a corrente interferencial nas frequncias de amplitude modulada de 1Hz, 10Hz e 100Hz, com frequncia de base de 4.000Hz, sendo que em uma determinada semana os voluntrios recebiam placebo (0Hz). RESULTADOS: No houve diferena significativa nas comparaes dentro das frequncias, nem entre elas e o grupo placebo. CONCLUSO: O uso da corrente interferencial nas frequncias de amplitude modulada de 1Hz, 10Hz e 100Hz no produziu alteraes nos limiares de dor ao frio e presso, semelhante ao encontrado para o grupo placebo. Abstract in english BACKGROUND AND OBJECTIVES: The interferential current is an electrical stimulation method widely used with analgesic purposes; however, there are controversies regarding their usage parameters. The aim of this study was to compare different amplitude modulated frequencies of the interferential curr [...] ent on the pressure and cold pain threshold in healthy volunteers. METHODS: This is a crossover, randomized and blinded evaluators and evaluated in quantitative character test. Participants were 20 volunteers divided into four groups, who for four weeks were subject to different modulated frequencies. Thresholds of pressure and cold pain in four different times were evaluated - at the beginning, right after electric stimulation, 20 and 60 minutes after. As a form of electrical stimulation, interferential current was used at modulated amplitude frequencies of 1Hz, 10Hz and 100Hz with base frequency of 4,000Hz, being that in a particular week volunteers received placebo (0Hz). RESULTS: There has been no significant difference in comparisons within frequencies or between them and the placebo group. CONCLUSION: The use of amplitude modulated frequencies of interferential current of 1Hz, 10Hz and 100Hz did not change cold and pressure pain thresholds, similar to what has been found for the placebo group
Ishimura, Shota; Kikuchi, Kazuro
2015-03-01
We apply the eight-state trellis-coded modulation (TCM) using signal constellations of four-dimensional M-ary quadrature-amplitude modulation (4D-MQAM) to optical communication systems for the first time to our knowledge. In the TCM scheme, the free distance of the trellis diagram is equal to the minimum distance between constellation points in partitioned subsets, which enlarges the coding gain effectively. In fact, its asymptotic power efficiency is 3-dB larger than that of the set-partitioned 4D-MQAM (SP-4D-MQAM) format, while their spectral efficiencies are the same. Such theoretical predictions are confirmed through computer simulations on eight-state TCM with constellations of 4D-4QAM (i.e., 4D quadrature phase-shift keying: 4D-QPSK) and 4D-16QAM. In particular, eight-state TCM with 4D-QPSK constellations is practically important because of its simple encoder structure, relatively low computational cost, and high coding gain against dual-polarization QPSK (DP-QPSK) and SP-4D-QPSK. Through measurements of its bit-error rate (BER) performance, we confirm that the coding gain against DP-QPSK is about 3 dB at BER=10(-3). PMID:25836886
The characterization of deep surface trenches with atomic force microscopy (AFM) presents significant challenges due to the sharp step edges that disturb the instrument and prevent it from faithfully reproducing the sample topography. Previous authors have developed AFM methodologies to successfully characterize semiconductor surface trenches with dimensions on the order of tens of nanometers. However, the study of imaging fidelity for features with dimensions smaller than 10 nm has not yet received sufficient attention. Such a study is necessary because small features in some cases lead to apparently high-quality images that are distorted due to tip and sample mechanical deformation. This paper presents multi-scale simulations, illustrating common artifacts affecting images of nanoscale trenches taken with fine carbon nanotube probes within amplitude-modulation and frequency-force-modulation AFM (AM-AFM and FFM-AFM, respectively). It also describes a methodology combining FFM-AFM with a step-in/step-out algorithm analogous to that developed by other groups for larger trenches, which can eliminate the observed artifacts. Finally, an overview of the AFM simulation methods is provided. These methods, based on atomistic and continuum simulation, have been previously used to study a variety of samples including silicon surfaces, carbon nanotubes and biomolecules
Solares, Santiago D.
2008-01-01
The characterization of deep surface trenches with atomic force microscopy (AFM) presents significant challenges due to the sharp step edges that disturb the instrument and prevent it from faithfully reproducing the sample topography. Previous authors have developed AFM methodologies to successfully characterize semiconductor surface trenches with dimensions on the order of tens of nanometers. However, the study of imaging fidelity for features with dimensions smaller than 10 nm has not yet received sufficient attention. Such a study is necessary because small features in some cases lead to apparently high-quality images that are distorted due to tip and sample mechanical deformation. This paper presents multi-scale simulations, illustrating common artifacts affecting images of nanoscale trenches taken with fine carbon nanotube probes within amplitude-modulation and frequency-force-modulation AFM (AM-AFM and FFM-AFM, respectively). It also describes a methodology combining FFM-AFM with a step-in/step-out algorithm analogous to that developed by other groups for larger trenches, which can eliminate the observed artifacts. Finally, an overview of the AFM simulation methods is provided. These methods, based on atomistic and continuum simulation, have been previously used to study a variety of samples including silicon surfaces, carbon nanotubes and biomolecules.
Loizou, C P; Murray, V; Pattichis, M S; Pantziaris, M; Nicolaides, A N; Pattichis, C S
2014-01-01
The intima-media thickness (IMT) of the common carotid artery (CCA) is widely used as an early indicator of cardiovascular disease (CVD). Typically, the IMT grows with age and this is used as a sign of increased risk of CVD. Beyond thickness, there is also clinical interest in identifying how the composition and texture of the intima-media complex (IMC) changed and how these textural changes grow into atherosclerotic plaques that can cause stroke. Clearly though texture analysis of ultrasound images can be greatly affected by speckle noise, our goal here is to develop effective despeckle noise methods that can recover image texture associated with increased rates of atherosclerosis disease. In this study, we perform a comparative evaluation of several despeckle filtering methods, on 100 ultrasound images of the CCA, based on the extracted multiscale Amplitude-Modulation Frequency-Modulation (AM-FM) texture features and visual image quality assessment by two clinical experts. Texture features were extracted from the automatically segmented IMC for three different age groups. The despeckle filters hybrid median and the homogeneous mask area filter showed the best performance by improving the class separation between the three age groups and also yielded significantly improved image quality. PMID:24734038
Alvarez, Clarisa E; Detarsio, Enrique; Moreno, Silvia; Andreo, Carlos S; Drincovich, Mara F
2012-06-01
Two highly similar plastidic NADP-malic enzymes (NADP-MEs) are found in the C(4) species maize (Zea mays); one exclusively expressed in the bundle sheath cells (BSCs) and involved in C(4) photosynthesis (ZmC(4)-NADP-ME); and the other (ZmnonC(4)-NADP-ME) with housekeeping roles. In the present work, these two NADP-MEs were analyzed regarding their redox-dependent activity modulation. The results clearly show that ZmC(4)-NADP-ME is the only one modulated by redox status, and that its oxidation produces a conformational change limiting the catalytic process, although inducing higher affinity binding of the substrates. The reversal of ZmC(4)-NADP-ME oxidation by chemical reductants suggests the presence of thiol groups able to form disulfide bonds. In order to identify the cysteine residues involved in the activity modulation, site-directed mutagenesis and MALDI-TOF (matrix-assisted laser desorption ionization-time of flight) analysis of ZmC(4)-NADP-ME were performed. The results obtained allowed the identification of Cys192, Cys246 (not conserved in ZmnonC(4)-NADP-ME), Cys270 and Cys410 as directly or indirectly implicated in ZmC(4)-NADP-ME redox modulation. These residues may be involved in forming disulfide bridge(s) or in the modulation of the oxidation of critical residues. Overall, the results indicate that, besides having acquired a high level of expression and localization in BSCs, ZmC(4)-NADP-ME displays a particular redox modulation, which may be required to accomplish the C(4) photosynthetic metabolism. Therefore, the present work could provide new insights into the regulatory mechanisms potentially involved in the recruitment of genes for the C(4) pathway during evolution. PMID:22514092
Wydro, Marc J; Warr, Gregory G; Atkin, Rob
2015-05-19
Amplitude-modulated atomic force microscopy (AM-AFM) has been used to study the nanostructure of cetylpyridinium chloride (CPCl)-hexanol-0.2 M NaCl sponge (L3) and lamellar (L?) phases near a mica surface. For both phases, membrane volume fractions of 22, 27, and 32 vol % were investigated, with the L3 or L? phase selected by adjusting the co-surfactant/surfactant ratio (hexanol/CPCl). For the L3 phase, the presence of the surface flattens the three-dimensional bulk structure. AM-AFM clearly resolves the membrane and solvent passages in the near surface layer. Increasing the membrane volume fraction decreases the size of the image features because of the lower solvent content. Within error, the average passage sizes in the near surface layer are the same as those in the bulk at the same concentration. Images of the L? phase reveal undulating near surface sheets. At the highest membrane concentration, the image is very smooth, because the lamellar sheet is confined between the surface and the next near surface layer, which is in close proximity as a result of the low solvent content. As the membrane concentration is reduced, the space between layers is increased and undulations appear in the near surface lamellar structure. Undulations are more pronounced at the lowest membrane volume fraction. PMID:25906083
P. A. Janakiraman
2010-01-01
Full Text Available An accurate ultrasonic range finder employing Sliding Discrete Fourier Transform (SDFT based restructured phase-locked loop (RPLL, which is an improved version of the recently proposed integrated phase-locking scheme (IPLL, has been expounded. This range finder principally utilizes amplitude-modulated ultrasonic waves assisted by an infrared (IR pilot signal. The phase shift between the envelope of the reference IR pilot signal and that of the received ultrasonic signal is proportional to the range. The extracted envelopes are filtered by SDFT without introducing any additional phase shift. A new RPLL is described in which the phase error is driven to zero using the quadrature signal derived from the SDFT. Further, the quadrature signal is reinforced by another cosine signal derived from a lookup table (LUT. The pulse frequency of the numerically controlled oscillator (NCO is extremely accurate, enabling fine tuning of the SDFT and RPLL also improves the lock time for the 50 Hz input signal to 0.04 s. The percentage phase error for the range 0.6 m to 6 m is about 0.2%. The VHDL codes generated for the various signal processing steps were downloaded into a Cyclone FPGA chip around which the ultrasonic ranger had been built.
Calcite, the most stable modification of calcium carbonate, is a major mineral in nature. It is, therefore, highly relevant in a broad range of fields such as biomineralization, sea water desalination and oil production. Knowledge of the surface structure and reactivity of the most stable cleavage plane, calcite (10.4), is pivotal for understanding the role of calcite in these diverse areas. Given the fact that most biological processes and technical applications take place in an aqueous environment, perhaps the most basic—yet decisive—question addresses the interaction of water molecules with the calcite (10.4) surface. In this work, amplitude modulation atomic force microscopy is used for three-dimensional (3D) mapping of the surface structure and the hydration layers above the surface. An easy-to-use scanning protocol is implemented for collecting reliable 3D data. We carefully discuss a comprehensible criterion for identifying the solid–liquid interface within our data. In our data three hydration layers form a characteristic pattern that is commensurate with the underlying calcite surface. (paper)
Madhu, P. K.; Johannessen, Ole G.; Pike, Kevin J.; Dupree, Ray; Smith, Mark E.; Levitt, Malcolm H.
2003-08-01
We report pulse sequences for the sensitivity enhancement of magic-angle spinning and multiple-quantum magic-angle spinning spectra of spin- {7}/{2} systems. Sensitivity enhancement is obtained with the use of fast amplitude-modulated (FAM) radiofrequency pulses. In one-dimensional magic-angle spinning experiments, signal enhancement of 3 is obtained by a FAM pulse followed by a soft 90° pulse. In two-dimensional multiple-quantum magic-angle spinning experiments, FAM pulses are used for both the excitation of multiple-quantum coherences and for their conversion into observable single-quantum coherences. The observed signal enhancements are 2.2 in 3Q experiments, 3.1 in 5Q experiments, and 4.1 in 7Q experiments, compared to the conventional two-pulse scheme. The pulse schemes are demonstrated on the 45Sc NMR of Sc 2(SO 4) 3 · 5H 2O and the 139La NMR of LaAlO 3. We also demonstrate the generation of FAM pulses by double-frequency irradiation.
We use a prototypical alkane film (n-C32H66 or C32) adsorbed on a SiO2 surface to compare step heights measured by amplitude modulation atomic force microscopy (AM-AFM) with those measured in the contact mode. The C32 film exhibits layers in which the molecules are oriented with their long axis parallel to the SiO2 surface followed by partial layers of perpendicular molecules. We show that step heights measured in the AM and contact modes agree in all cases except where the step is between a surface formed by a layer of parallel molecules and one of perpendicular molecules. In this case, the AM mode gives a false step height that is as much as 20% lower than that measured in the contact mode and inferred from synchrotron X-ray specular reflectivity measurements. We propose that the weaker van der Waals forces between the AFM tip and a perpendicular layer compared to a parallel layer causes this discrepancy. We show how to correct the false step height by using the approximately linear relationship observed between phase angle (cantilever oscillation relative to the drive signal) and cantilever height measured in an approach curve
Caroselli, Erik; Falini, Giuseppe; Goffredo, Stefano; Dubinsky, Zvy; Levy, Oren
2015-01-01
Balanophyllia europaea is a shallow water solitary zooxanthellate coral, endemic to the Mediterranean Sea. Extensive field studies across a latitudinal temperature gradient highlight detrimental effects of rising temperatures on its growth, demography, and skeletal characteristics, suggesting that depression of photosynthesis at high temperatures might cause these negative effects. Here we test this hypothesis by analyzing, by means of pulse amplitude modulation fluorometry, the photosyntheti...
Hancke, Kasper; Hancke, Torunn; Olsen, Lasse M.; Johnsen, Geir; Glud, Ronnie N.
2008-01-01
decreased slightly with increasing temperature. Absolute rates of O2 production were calculated from pulse-amplitude-modulated (PAM) fluorometry measurements in combination with biooptical determination of absorbed quanta in PSII. The relationship between PAM-based O2 production and measured O2 production...
The influence of short-range electrostatic forces on the measured local contact potential difference (CPD) by means of amplitude-modulation and frequency-modulation Kelvin probe force microscopy (AM- and FM-KPFM) is discussed on the base of numerical and analytical descriptions of both methods. The goal of this work is to help in interpreting recent experimental results reporting atomically resolved CPD images, in particular on bulk insulating samples. The discussion is carried out on the basis of spectroscopic curves. The expression of the bias-dependent electrostatic force is derived from a previous work and is estimated between a tip with simple geometry and the (001) facet of a perfect alkali halide single crystal. The force, with a short-range character, scales as a second-order polynomial function of the bias voltage. It is stated that the linear term is responsible for the occurrence of the atomic-scale CPD contrast, while the quadratic one, involving the sample polarization, accounts for the detected signal by the KPFM methods. Nevertheless, analytical and numerical approaches stress the influence of the linear term on the measured CPD which intrinsically hinders the possibility to perform quantitative CPD measurements, but also makes the measured 'pseudo-CPD' strongly deviating from the surface potential. Hence, in the short-range regime, AM- or FM-KPFM measurements neither reflect the CPD nor the local surface potential, but rather an effective value which is convoluted by the geometric parameters of the tip, the so-called local CPD. It is also stated that the local CPD measured by means of AM- or FM-KPFM differs when sub-nanometer vibration amplitudes of the cantilever are used. Otherwise, AM- and FM-KPFM measurements should be almost similar. At last, the influence of long-range, capacitive, electrostatic forces is discussed in conjunction with the short-range ones. This allows us to draw conclusions regarding the distance dependence of the local CPD which then exhibits a resonant behavior as a function of the tip-surface separation. This phenomenon is expected to play a role in the KPFM imaging process.
Giannoula, Alexia; Cobbold, Richard; Bezerianos, Anastasios
2014-02-01
A modulated acoustic radiation force, produced by two confocal tone-burst ultrasound beams of slightly different frequencies (i.e. 2.0 MHz ± Δf/2, where Δf is the difference frequency), can be used to remotely generate modulated low-frequency (Δf ≤ 500 Hz) shear waves in attenuating media. By appropriately selecting the duration of the two beams, the energy of the generated shear waves can be concentrated around the difference frequency (i.e., Δf ± Δf/2). In this manner, neither their amplitude nor their phase information is distorted by frequency-dependent effects, thereby, enabling a more accurate reconstruction of the viscoelastic properties. Assuming a Voigt viscoelastic model, this paper describes the use of a finite-element-method model to simulate three-dimensional (3-D) shear-wave propagation in viscoelastic media containing a spherical inclusion. Nonlinear propagation is assumed for the two ultrasound beams, so that higher harmonics are developed in the force and shear spectrum. Finally, an inverse reconstruction algorithm is used to extract 3-D maps of the local shear modulus and viscosity from the simulated shear-displacement fields based on the fundamental and second-harmonic component. The quality of the reconstructed maps is evaluated using the contrast between the inclusion and the background and the contrast-to-noise ratio (CNR). It is shown that the shear modulus can be accurately reconstructed based on the fundamental component, such that the observed contrast deviates from the true contrast by a root-mean-square-error (RMSE) of only 0.38 and the CNR is greater than 30 dB. If the second-harmonic component is used, the RMSE becomes 1.54 and the corresponding CNR decreases by approximately 10-15 dB. The reconstructed shear viscosity maps based on the second harmonic are shown to be of higher quality than those based on the fundamental. The effects of noise are also investigated and a fusion operation between the two spectral components is applied to enhance the reconstruction quality. Finally, a modified shear-wave spectroscopy technique, shown to be more robust to noise, is described for the estimation of the viscoelastic properties inside and outside the spherical inclusion under conditions of increased noise. PMID:24011778
Archan B. Patel
2015-11-01
Full Text Available Inverters using pulse width modulation techniques generates common mode voltages in induction motor drives which can cause shaft voltages and bearing currents resulting into failure of motor. A two level and five level inverter topology with amplitude modulation technique is proposed in this paper which completely eliminates the above problems. Also losses in switching devices and stress is reduced. Using proposed topology total harmonic distortion (THD is reduced and improved overall harmonic profile is achieved. The system is modelled with the help of MATLAB Simulink software for two level and five level inverter with proposed AM technique. Experimental results shown for the proposed topology which indicates lower total harmonic distortion.
Residual stress modulation in the diamond-like carbon coatings with incorporation of gold nanoparticles was studied critically. The films were deposited on glass and Si (1 0 0) substrates by using capacitatively coupled plasma chemical vapor deposition. Stresses in the films were determined from the broadening of the optical absorption tail and were found to decrease from 2.3 GPa to 0.48 GPa with increasing gold content (2-7 at.% Au) in the DLC matrix. Gold incorporation also made the films harder than the corresponding DLC coatings. Modulation of stress with nanocrystalline gold content in the DLC matrix was related to the relative amount of sp2/sp3 content in the DLC films.
Anderson, Richard I.
2014-01-01
I report on the recent discovery of modulation in the radial velocity curves in four classical Cepheids. This discovery may enable significant improvements in the accuracy of Baade-Wesselink distances by revealing a not previously considered systematic source of uncertainty.
Wu, Yan; Gupta, Chaitanya; Shannon, Mark A
2008-10-01
The dynamic response of amplitude-modulated atomic force microscopy (AM-AFM) is studied at the solid/water interface with respect to changes in ionic concentration, applied surface potential, and surface protonation. Each affects the electric double layer in the solution, charge on the tip and the sample surface, and thus the forces affecting the dynamic response. A theoretical model is developed to relate the effective stiffness and hydrodynamic damping of the AFM cantilever that is due to the tip/surface interaction with the phase and amplitude signals measured in the AM-AFM experiments. The phase and amplitude of an oscillating cantilever are measured as a function of tip-sample distance in three experiments: mica surface in potassium nitrate solutions with different concentrations, biased gold surface in potassium nitrate solution, and carboxylic acid-terminated self-assembled monolayers (SAMs) on gold in potassium nitrate pH buffers. Results show that, over the range where the higher harmonic modes of the oscillation are negligible, the effective stiffness of the AFM cantilever increases to a maximum as the tip approaches the surface before declining again as a result of the repulsive electrical double layer interaction. For attractive electrical double-layer interactions, the effective stiffness declines monotonically as the tip approaches the surface. Similarly, the hydrodynamic damping of the tip increases and then decreases as the tip approaches the solid/water interface, with the magnitude depending on the species present in the solution. PMID:18763814
Syzygies Probing Scattering Amplitudes
Chen, Gang; Xie, Ruofei; Zhang, Hao; Zhou, Yehao
2015-01-01
We propose a new efficient algorithm to obtain the linearly independent basis of syzygies for an ideal, which are widely used in the current study of scattering amplitudes. This new algorithm, which can deal with more syzygies effectively owing to a new generation of syzygy in each step is given to verify the independence, is described in detail. We generalize this efficient algorithm to the module case, and partially guarantee the basis independence of the module. We also show a typical example to illustrate the potential application of this method in scattering amplitudes, especially the IBP relations of characteristic two-loop diagrams in the Yang-Mills theory.
A. K. Sinha
Full Text Available Ionospheric scintillations of radio waves at low-latitudes are associated with electron density irregularities. These irregularities are field-aligned and can provide excitation energy all along the field line to non-local field-aligned oscillations, such as the local field line oscillations. Eigen-periods of toroidal field line oscillations at low-latitudes, computed by using the dipole magnetic field and ion distributions obtained from the International Reference Ionosphere (IRI for typical nighttime conditions, fall in the range of 20–25 s. When subjected to spectral analysis, signal strength of the radio waves recorded on the 250 MHz beacon at Pondicherry (4.5° N dip, Mumbai (13.4° N dip and Ujjain (18.6° N dip exhibit periodicities in the same range. For the single event for which simultaneous ground magnetic data were available, the geomagnetic field also oscillated at the same periodicity. The systematic presence of a significant peak in the 20–25 s range during periods of strong radio wave scintillations, and its absence otherwise suggests the possibility that field line oscillations are endogenously excited by the irregularities, and the oscillations associated with the excited field line generate the modulation characteristics of the radio waves received on the ground. The frequency of modulation is found to be much lower than the characteristic frequencies that define the main body of scintillations, and they probably correspond to scales that are much larger than the typical Fresnel scale. It is possible that the refractive mechanism associated with larger scale long-lived irregularities could be responsible for the observed phenomenon. Results of a preliminary numerical experiment that uses a sinusoidal phase irregularity in the ionosphere as a refracting media are presented. The results show that phase variations which are large enough to produce a focal plane close to the ground can reproduce features that are not inconsistent with our observations.
Key words. Magnetospheric physics (magnetosphere – ionosphere interactions Ionosphere (ionosphere – magnetoshere interactions; ionospheric irregularities
Branstetter, Brian K; DeLong, Caroline M; Dziedzic, Brandon; Black, Amy; Bakhtiari, Kimberly
2016-01-01
Bottlenose dolphins (Tursiops truncatus) use the frequency contour of whistles produced by conspecifics for individual recognition. Here we tested a bottlenose dolphin's (Tursiops truncatus) ability to recognize frequency modulated whistle-like sounds using a three alternative matching-to-sample paradigm. The dolphin was first trained to select a specific object (object A) in response to a specific sound (sound A) for a total of three object-sound associations. The sounds were then transformed by amplitude, duration, or frequency transposition while still preserving the frequency contour of each sound. For comparison purposes, 30 human participants completed an identical task with the same sounds, objects, and training procedure. The dolphin's ability to correctly match objects to sounds was robust to changes in amplitude with only a minor decrement in performance for short durations. The dolphin failed to recognize sounds that were frequency transposed by plus or minus ½ octaves. Human participants demonstrated robust recognition with all acoustic transformations. The results indicate that this dolphin's acoustic recognition of whistle-like sounds was constrained by absolute pitch. Unlike human speech, which varies considerably in average frequency, signature whistles are relatively stable in frequency, which may have selected for a whistle recognition system invariant to frequency transposition. PMID:26863519
Sui, Liansheng; Liu, Benqing; Wang, Qiang; Li, Ye; Liang, Junli
2015-12-01
A color image encryption scheme is proposed based on Yang-Gu mixture amplitude-phase retrieval algorithm and two-coupled logistic map in gyrator transform domain. First, the color plaintext image is decomposed into red, green and blue components, which are scrambled individually by three random sequences generated by using the two-dimensional Sine logistic modulation map. Second, each scrambled component is encrypted into a real-valued function with stationary white noise distribution in the iterative amplitude-phase retrieval process in the gyrator transform domain, and then three obtained functions are considered as red, green and blue channels to form the color ciphertext image. Obviously, the ciphertext image is real-valued function and more convenient for storing and transmitting. In the encryption and decryption processes, the chaotic random phase mask generated based on logistic map is employed as the phase key, which means that only the initial values are used as private key and the cryptosystem has high convenience on key management. Meanwhile, the security of the cryptosystem is enhanced greatly because of high sensitivity of the private keys. Simulation results are presented to prove the security and robustness of the proposed scheme.
A. Bali?ski
2013-01-01
Full Text Available Describes how to obtain a soluble sodium silicate with a density of 1.40 g/cm3, 1.45 g/cm3, 1.50 g/cm3, and silica module M = 2.1obtained from the silica- sodium glass with module M = 3.3 and M = 2.1. Residual (final strength of molding samples made with thesebinders, were determined at temperatures corresponding to the characteristic temperatures of phase and temperature transitions of silica gel. Indicated the type of soluble sodium silicate capable of obtain the smallest value of the final strength of molding sand in the specified range of temperatures.
Protein thermal denaturation is modulated by central residues in the protein structure network.
Souza, Valquiria P; Ikegami, Cecília M; Arantes, Guilherme M; Marana, Sandro R
2016-03-01
Network structural analysis, known as residue interaction networks or graphs (RIN or RIG, respectively) or protein structural networks or graphs (PSN or PSG, respectively), comprises a useful tool for detecting important residues for protein function, stability, folding and allostery. In RIN, the tertiary structure is represented by a network in which residues (nodes) are connected by interactions (edges). Such structural networks have consistently presented a few central residues that are important for shortening the pathways linking any two residues in a protein structure. To experimentally demonstrate that central residues effectively participate in protein properties, mutations were directed to seven central residues of the β-glucosidase Sfβgly (β-d-glucoside glucohydrolase; EC 3.2.1.21). These mutations reduced the thermal stability of the enzyme, as evaluated by changes in transition temperature (Tm ) and the denaturation rate at 45 °C. Moreover, mutations directed to the vicinity of a central residue also caused significant decreases in the Tm of Sfβgly and clearly increased the unfolding rate constant at 45 °C. However, mutations at noncentral residues or at surrounding residues did not affect the thermal stability of Sfβgly. Therefore, the data reported in the present study suggest that the perturbation of the central residues reduced the stability of the native structure of Sfβgly. These results are in agreement with previous findings showing that networks are robust, whereas attacks on central nodes cause network failure. Finally, the present study demonstrates that central residues underlie the functional properties of proteins. PMID:26785700
Munz, M., E-mail: martin.munz@npl.co.uk
2013-08-15
In this study, atomic force microscopy (AFM) has been employed to image a photopolymerized poly(ethylene glycol) diacrylate (PEG-DA) hydrogel. The same area was imaged both in amplitude modulation (AM) and in frequency modulation (FM) mode and the latter allowed for excellent resolution of the hydrogel microstructure. It shows globular domains with typical diameters in the range of ?10100 nm. The hydrogel morphology has been analysed using grain size analysis as well as roughness analysis. Based on AFM topography images of hydrogel nano-domains, a set of roughness parameters has been identified which can be readily used as descriptors for spatial resolution. It includes the density of summits, S{sub ds}, the mean summit curvature, S{sub sc}, the surface area ratio, S{sub dr}, and the correlation length parameter, S{sub cl37}. The latter describes the length over which the autocorrelation function decays to 37% of its peak value. These parameters allow for better discrimination than the widely used root-mean-square (RMS) roughness, S{sub q}, and are available with common image processing software packages. Systematic variation of the virtual tilt angle has indicated that these parameters are robust to small variations in plane levelling. Such image processing is frequently needed to separate the inherent surface microstructure from the global topography related to sample tilt or surface waviness. Hydrogels are an important group of biomaterials as they find numerous applications in biomedical engineering, ranging from adhesives, to controlled release of water-soluble drugs, to encapsulation of cells, to tissue engineering. Optimisation of their interactions with bioentities, such as bacteria, cells or proteins, requires accurate surface characterisation.
In this study, atomic force microscopy (AFM) has been employed to image a photopolymerized poly(ethylene glycol) diacrylate (PEG-DA) hydrogel. The same area was imaged both in amplitude modulation (AM) and in frequency modulation (FM) mode and the latter allowed for excellent resolution of the hydrogel microstructure. It shows globular domains with typical diameters in the range of ∼10–100 nm. The hydrogel morphology has been analysed using grain size analysis as well as roughness analysis. Based on AFM topography images of hydrogel nano-domains, a set of roughness parameters has been identified which can be readily used as descriptors for spatial resolution. It includes the density of summits, Sds, the mean summit curvature, Ssc, the surface area ratio, Sdr, and the correlation length parameter, Scl37. The latter describes the length over which the autocorrelation function decays to 37% of its peak value. These parameters allow for better discrimination than the widely used root-mean-square (RMS) roughness, Sq, and are available with common image processing software packages. Systematic variation of the virtual tilt angle has indicated that these parameters are robust to small variations in plane levelling. Such image processing is frequently needed to separate the inherent surface microstructure from the global topography related to sample tilt or surface waviness. Hydrogels are an important group of biomaterials as they find numerous applications in biomedical engineering, ranging from adhesives, to controlled release of water-soluble drugs, to encapsulation of cells, to tissue engineering. Optimisation of their interactions with bioentities, such as bacteria, cells or proteins, requires accurate surface characterisation.
Jinkins, K.; Farina, L.; Wu, Y., E-mail: wuy@uwplatt.edu [Engineering Physics Department, University of Wisconsin-Platteville, 1 University Plaza, Platteville, Wisconsin 53818 (United States); Camacho, J. [Mechanical Engineering Department, University of Wisconsin-Platteville, 1 University Plaza, Platteville, Wisconsin 53818 (United States)
2015-12-14
The properties of Few-Layer Graphene (FLG) change with the number of layers and Amplitude Modulation (AM) Atomic Force Microscopy (AFM) is commonly used to determine the thickness of FLG. However, AFM measurements have been shown to be sensitive to environmental conditions such as relative humidity (RH). In the present study, AM-AFM is used to measure the thickness and loss tangent of exfoliated graphene on silicon dioxide (SiO{sub 2}) as RH is increased from 10% to 80%. We show that the measured thickness of graphene is dependent on RH. The loss tangent values of the graphene and oxide regions are both affected by humidity, with generally higher loss tangent for graphene than SiO{sub 2}. As RH increases, we observe the loss tangent of both materials approaches the same value. We hypothesize that there is a layer of water trapped between the graphene and SiO{sub 2} substrate to explain this observation. Using this interpretation, the loss tangent images also indicate movement and change in this trapped water layer as RH increases, which impacts the measured thickness of graphene using AM-AFM.
Jinkins, K.; Camacho, J.; Farina, L.; Wu, Y.
2015-12-01
The properties of Few-Layer Graphene (FLG) change with the number of layers and Amplitude Modulation (AM) Atomic Force Microscopy (AFM) is commonly used to determine the thickness of FLG. However, AFM measurements have been shown to be sensitive to environmental conditions such as relative humidity (RH). In the present study, AM-AFM is used to measure the thickness and loss tangent of exfoliated graphene on silicon dioxide (SiO2) as RH is increased from 10% to 80%. We show that the measured thickness of graphene is dependent on RH. The loss tangent values of the graphene and oxide regions are both affected by humidity, with generally higher loss tangent for graphene than SiO2. As RH increases, we observe the loss tangent of both materials approaches the same value. We hypothesize that there is a layer of water trapped between the graphene and SiO2 substrate to explain this observation. Using this interpretation, the loss tangent images also indicate movement and change in this trapped water layer as RH increases, which impacts the measured thickness of graphene using AM-AFM.
Avila, Mislay; Khosravi, Mojtaba; Alves, Lisa; Ader-Ebert, Nadine; Bringolf, Fanny; Zurbriggen, Andreas; Plemper, Richard K; Plattet, Philippe
2015-01-15
Membrane fusion for morbillivirus cell entry relies on critical interactions between the viral fusion (F) and attachment (H) envelope glycoproteins. Through extensive mutagenesis of an F cavity recently proposed to contribute to F's interaction with the H protein, we identified two neighboring hydrophobic residues responsible for severe F-to-H binding and fusion-triggering deficiencies when they were mutated in combination. Since both residues reside on one side of the F cavity, the data suggest that H binds the F globular head domain sideways. PMID:25355896
Caroselli, Erik; Falini, Giuseppe; Goffredo, Stefano; Dubinsky, Zvy; Levy, Oren
2015-01-01
Balanophyllia europaea is a shallow water solitary zooxanthellate coral, endemic to the Mediterranean Sea. Extensive field studies across a latitudinal temperature gradient highlight detrimental effects of rising temperatures on its growth, demography, and skeletal characteristics, suggesting that depression of photosynthesis at high temperatures might cause these negative effects. Here we test this hypothesis by analyzing, by means of pulse amplitude modulation fluorometry, the photosynthetic efficiency of B. europaea specimens exposed in aquaria to the annual range of temperatures experienced in the field (13, 18, and 28C), and two extreme temperatures expected for 2100 as a consequence of global warming (29 and 32C). The indicators of photosynthetic performance analyzed (maximum and effective quantum yield) showed that maximum efficiency was reached at 20.0-21.6C, slightly higher than the annual mean temperature in the field (18C). Photosynthetic efficiency decreased from 20.0 to 13C and even more strongly from 21.6 to 32C. An unusual form of bleaching was observed, with a maximum zooxanthellae density at 18C that strongly decreased from 18 to 32C. Chlorophyll a concentration per zooxanthellae cell showed an opposite trend as it was minimal at 18C and increased from 18 to 32C. Since the areal chlorophyll concentration is the product of the zooxanthellae density and its cellular content, these trends resulted in a homogeneous chlorophyll concentration per coral surface across temperature treatments. This confirms that B. europaea photosynthesis is progressively depressed at temperatures >21.6C, supporting previous hypotheses raised by the studies on growth and demography of this species. This study also confirms the threats posed to this species by the ongoing seawater warming. PMID:26582993
Highlights: • Residual stresses were determined in a welded EUROFER blanket assembly with integrated cooling channels. • Good agreement was seen between experimentally determined and predicted stresses. • We show that microstructure changes that occur in EUROFER steels during welding must be considered for residual stress determination. • An experimental route is proposed for validation of predicted stresses in reactor components using non-destructive diffraction techniques. - Abstract: Whilst the structural integrity and lifetime considerations in welded joints for blanket modules can be predicted using finite element software, it is essential to prove the validity of these simulations. This paper provides detailed analysis for the first time, of the residual stress state in a laser-welded sample with integral cooling channels. State-of-the-art non-destructive neutron diffraction was employed to determine the triaxial stress state and to understand microstructural changes around the heat affected zone. Synchrotron X-ray diffraction was used to probe the variation of strain-free lattice reference parameter around the weld zone allowing correction of the neutron measurements. This paper details an important experimental route to validation of predicted stresses in complex safety-critical reactor components for future applications
Price, Kerry L; Lummis, Sarah C R
2014-10-18
GABA-activated RDL receptors are the insect equivalent of mammalian GABAA receptors, and play a vital role in neurotransmission and insecticide action. Here we clone the pore lining M2 region of the Varroa mite RDL receptor and show that it has 4 atypical residues when compared to M2 regions of most other insects, including bees, which are the major host of Varroa mites. We create mutant Drosophila RDL receptors containing these substitutions and characterise their effects on function. Using two electrode voltage clamp electrophysiology we show that one substitution (T6'M) ablates picrotoxin inhibition and increases the potency of GABA. This mutation also alters the effect of thymol, which enhances both insect and mammalian GABA responses, and is widely used as a miticide. Thymol decreases the GABA EC50 of WT receptors, enhancing responses, but in T6'M-containing receptors it is inhibitory. The other 3 atypical residues have no major effects on either the GABA EC50, the picrotoxin potency or the effect of thymol. In conclusion we show that the RDL 6' residue is important for channel block, activation and modulation, and understanding its function also has the potential to prove useful in the design of Varroa-specific insecticidal agents. PMID:25460510
Hughes, D.J., E-mail: d.hughes@warwick.ac.uk [WMG, University of Warwick, Coventry CV4 7AL (United Kingdom); Koukovini-Platia, E. [CERN, CH-1211 Geneva 23 (Switzerland); Heeley, E.L. [Department of Physical Sciences, Open University, Walton Hall, Milton Keynes MK7 6AA (United Kingdom)
2014-02-15
Highlights: Residual stresses were determined in a welded EUROFER blanket assembly with integrated cooling channels. Good agreement was seen between experimentally determined and predicted stresses. We show that microstructure changes that occur in EUROFER steels during welding must be considered for residual stress determination. An experimental route is proposed for validation of predicted stresses in reactor components using non-destructive diffraction techniques. - Abstract: Whilst the structural integrity and lifetime considerations in welded joints for blanket modules can be predicted using finite element software, it is essential to prove the validity of these simulations. This paper provides detailed analysis for the first time, of the residual stress state in a laser-welded sample with integral cooling channels. State-of-the-art non-destructive neutron diffraction was employed to determine the triaxial stress state and to understand microstructural changes around the heat affected zone. Synchrotron X-ray diffraction was used to probe the variation of strain-free lattice reference parameter around the weld zone allowing correction of the neutron measurements. This paper details an important experimental route to validation of predicted stresses in complex safety-critical reactor components for future applications.
Limon, Agenor; Estrada-Mondragón, Argel; Ruiz, Jorge M Reyes; Miledi, Ricardo
2016-04-01
Dipicrylamine (DPA) is a commonly used acceptor agent in Förster resonance energy transfer experiments that allows the study of high-frequency neuronal activity in the optical monitoring of voltage in living cells. However, DPA potently antagonizes GABAA receptors that contain α1 and β2 subunits by a mechanism which is not clearly understood. In this work, we aimed to determine whether DPA modulation is a general phenomenon of Cys-loop ligand-gated ion channels (LGICs), and whether this modulation depends on particular amino acid residues. For this, we studied the effects of DPA on human homomeric GABAρ1, α7 nicotinic, and 5-HT3A serotonin receptors expressed in Xenopus oocytes. Our results indicate that DPA is an allosteric modulator of GABAρ1 receptors with an IC50 of 1.6 µM, an enhancer of α7 nicotinic receptors at relatively high concentrations of DPA, and has little, if any, effect on 5-HT3A receptors. DPA antagonism of GABAρ1 was strongly enhanced by preincubation, was slightly voltage-dependent, and its washout was accelerated by bovine serum albumin. These results indicate that DPA modulation is not a general phenomenon of LGICs, and structural differences between receptors may account for disparities in DPA effects. In silico modeling of DPA docking to GABAρ1, α7 nicotinic, and 5-HT3A receptors suggests that a hydrophobic pocket within the Cys-loop and the M4 segment in GABAρ1, located at the extracellular/membrane interface, facilitates the interaction with DPA that leads to inhibition of the receptor. Functional examinations of mutant receptors support the involvement of the M4 segment in the allosteric modulation of GABAρ1 by DPA. PMID:26869399
Michael R Markham
2012-04-01
Full Text Available Energetic demands of action potential (AP generation are a major cost of electrical signaling by excitable cells in the central nervous system and periphery. Energy consumption by AP generation is particularly acute in the electric organ (EO of weakly electric fish, and some species regulate AP energetic demands by dynamically regulating AP amplitude. These fish navigate and communicate by generating and sensing electric fields, known as electric organ discharges (EODs produced by the synchronized action potentials (APs of electrogenic cells (electrocytes in the EO. Electrocyte ionic currents are often several microAmperes, many orders of magnitude larger than currents in central neurons, creating significant energetic costs of AP generation. One class of South American electric fish, wave-type fish, generate sinusoidal waveforms produced by EODs emitted at highly regular rates with interpulse intervals equal to the EOD duration. Most wave-type fish generate EODs at individually-fixed frequencies throughout the lifespan, creating high energetic demands and predation risk from electroreceptive predators. We have shown previously that the wave-type fish Sternopygus macrurus (EOD frequencies 70-150 Hz manages EOD energetic/predation costs by reducing EOD amplitude during times of inactivity and increasing EOD amplitude during active periods and social interaction. These circadian and socially-induced EOD modulations are produced by rapid changes in AP amplitude controlled by circulating melanocortin hormones that up-regulate Na+ channel trafficking into the electrocyte membrane. The increased Na+ current magnitude also broadens AP and EOD pulse width with little consequence because of the relatively long intervals (5-8 ms between individual EODs. Here we investigated the ionic mechanisms of EOD amplitude modulation in Eigenmannia virescens, a related gymnotiform fish that discharges at much higher frequencies (200-600 Hz likely incurring increased energetic demands of EOD generation. EOD amplitude in this species appears to be particularly sensitive to energetic constraints, and E. virescens exhibits large day-night changes in EOD amplitude, potentially a mechanism of energetic regulation. The ionic currents of its electrocytes are not known nor have the ionic mechanisms of EOD amplitude modulation been determined. We also studied Eigenmannia because its high electrocyte AP frequencies require mechanisms for changing EOD amplitude while maintaining stable EOD pulse width. With inter-pulse intervals less than 2 ms, increases in AP width would shorten the interpulse interval, preventing recovery of Na+ channels sufficient to maintain EOD waveform. We found that melanocortin peptides applied in vitro increased electrocyte AP amplitude but not AP width. E. virescens electrocytes exhibited a voltage-gated Na+ current with extremely rapid kinetics, an inwardly rectifying K+ current, and a Na+-activated K+ current (KNa that has not been identified in any gymnotiform species to date. Melanocortin peptides increased the magnitude of all three currents, but increased KNa current is a direct function of enhanced Na+ influx. Numerical simulations suggest that KNa channels are necessary for maintaining stable AP width during AP amplitude modulations. Thus, E. virescens overcomes the challenges of modulating EOD amplitude in a high-frequency signal through ultra-rapid Na+ channel kinetics and a KNa channel that scales repolarizing K+ currents to the magnitude of Na+ currents.
Aguilera, Paulina; Marcoleta, Andrs; Lobos-Ruiz, Pablo; Arranz, Roco; Valpuesta, Jos M.; Monasterio, Octavio; Lagos, Rosalba
2016-01-01
Microcin E492 (MccE492) is a pore-forming bacteriocin produced and exported by Klebsiella pneumoniae RYC492. Besides its antibacterial activity, excreted MccE492 can form amyloid fibrils in vivo as well as in vitro. It has been proposed that bacterial amyloids can be functional playing a biological role, and in the particular case of MccE492 it would control the antibacterial activity. MccE492 amyloid fibrils morphology and formation kinetics in vitro have been well-characterized, however, it is not known which amino acid residues determine its amyloidogenic propensity, nor if it forms intracellular amyloid inclusions as has been reported for other bacterial amyloids. In this work we found the conditions in which MccE492 forms intracellular amyloids in Escherichia coli cells, that were visualized as round-shaped inclusion bodies recognized by two amyloidophilic probes, 2-4?-methylaminophenyl benzothiazole and thioflavin-S. We used this property to perform a flow cytometry-based assay to evaluate the aggregation propensity of MccE492 mutants, that were designed using an in silico prediction of putative aggregation hotspots. We established that the predicted amino acid residues 5463, effectively act as a pro-amyloidogenic stretch. As in the case of other amyloidogenic proteins, this region presented two gatekeeper residues (P57 and P59), which disfavor both intracellular and in vitro MccE492 amyloid formation, preventing an uncontrolled aggregation. Mutants in each of these gatekeeper residues showed faster in vitro aggregation and bactericidal inactivation kinetics, and the two mutants were accumulated as dense amyloid inclusions in more than 80% of E. coli cells expressing these variants. In contrast, the MccE492 mutant lacking residues 5463 showed a significantly lower intracellular aggregation propensity and slower in vitro polymerization kinetics. Electron microscopy analysis of the amyloids formed in vitro by these mutants revealed that, although with different efficiency, all formed fibrils morphologically similar to wild-type MccE492. The physiological implication of MccE492 intracellular amyloid formation is probably similar to the inactivation process observed for extracellular amyloids, and could be used as a mean of sequestering potentially toxic species inside the cell when this bacteriocin is produced in large amounts.
Hydrophilic Aromatic Residue and in silico Structure for Carbohydrate Binding Module
Chou, Wei-Yao; Pai, Tun-Wen; Jiang, Ting-Ying; Chou, Wei-I; Tang, Chuan-Yi; Chang, Margaret Dah-Tsyr
2011-01-01
Carbohydrate binding modules (CBMs) are found in polysaccharide-targeting enzymes and increase catalytic efficiency. Because only a relatively small number of CBM structures have been solved, computational modeling represents an alternative approach in conjunction with experimental assessment of CBM functionality and ligand-binding properties. An accurate target-template sequence alignment is the crucial step during homology modeling. However, low sequence identities between target/template s...
Danilov, G S
2003-01-01
Widely spread cruel misconceptions and mistakes in the calculation of multi-loop superstring amplitudes are exposed. Correct calculations are given. It is shown that the cardinal mistake in the gauge fixing procedure presents ab ovo in the Verlinde papers. The mistake was reproduced in following proposals including the recent papers. The modular symmetry of the multi-loop superstring amplitudes is clarified, an incorrectness of previous conjectures being shown. It is shown that the Berezin-type integral versus boson and fermion moduli is doubt under non-split transformations mixing fermion integration variables to the boson integration ones. In particular, due to singularities in moduli of the given spin structure, the integral can be finite or divergent dependently on the integration variables employed. Hence, unlike naive expectations, the multi-loop superstring amplitude is ambiguous. Nevertheless, the ambiguity is totally resolved by the requirement to preserve local symmetries of the superstring amplitud...
Hughes, D J; Heeley, E L
2014-01-01
Whilst the structural integrity and lifetime considerations in welded joints for blanket modules can be predicted using finite element software, it is essential to prove the validity of these simulations. This paper provides detailed analysis for the first time, of the residual stress state in a laser-welded sample with integral cooling channels. State-of-the-art non-destructive neutron diffraction was employed to determine the triaxial stress state and to understand microstructural changes around the heat affected zone. Synchrotron X-ray diffraction was used to probe the variation of strain-free lattice reference parameter around the weld zone allowing correction of the neutron measurements. This paper details an important experimental route to validation of predicted stresses in complex safety-critical reactor components for future applications.
ITER-India, the Indian domestic agency for ITER project, is responsible to deliver one of the packages, called ICH and CD Radio Frequency Power Sources (RFPS). Total 20 MW of RF power is required for ITER plasma from RFPS system using 8 nos. of identical sources. Each power source is capable to deliver 2.5 MW @ 35 to 65 MHz frequency range with a load condition up to VSWR 2:1 and any reflection coefficient of phase angle. Each source should be operated independently as well as in slave mode with synchronization of central plant control system of ITER. To fulfill the desired specifications of constant power and fixed relative phase, the real time control loop is required. The real time control loops would be used for maintaining the Amplitude and Phase as requested from central plant control system. Since, there are methods available for the measurement of amplitude and phase but the accuracy and linearity of the measurement is one of the important parameters, thus after survey and analysis ITER-India has chosen a digital I-Q demodulator based technique for amplitude and phase detection. In this paper, Amplitude and Phase measurement of RF signal with DIQDM technique using PXI system is described in detail, with various test results with dummy signals and low power RF systems
Hanzo, Lajos
2004-01-01
"Now fully revised and updated, with more than 300 pages of new material, this new edition presents the wide range of recent developments in the field and places particular emphasis on the family of coded modulation aided OFDM and CDMA schemes. In addition, it also includes a fully revised chapter on adaptive modulation and a new chapter characterizing the design trade-offs of adaptive modulation and space-time coding." "In summary, this volume amalgamates a comprehensive textbook with a deep research monograph on the topic of QAM, ensuring it has a wide-ranging appeal for both senior undergraduate and postgraduate students as well as practicing engineers and researchers."--Jacket.
Kubinyi, G.; Thuroczy, G.; Bakos, J.; Boeloeni, E.; Sinay, H.; Szabo, L.D. [National Frederic Joliot-Curie Research Inst. for Radiobiology and Radiohygiene, Budapest (Hungary)
1996-12-31
Investigations have been carried out concerning the effects of microwave (MW) exposure on the aminoacyl-transfer ribonucleic acid (tRNA) synthetase of the progeny of females that were exposed during their entire period of gestation (19 days). The changes caused by continuous-wave (CW) and amplitude-modulated (AM) MW radiation have been compared. CFLP mice were exposed to MW radiation for 100 min each day in an anechoic room. The MW frequency was 2.45 GHz, and the amplitude modulation had a 50 Hz rectangular waveform (on/off ratio, 50/50%). The average power density exposure was 3 mW/cm{sup 2}, and the whole body specific absorption rate (SAR) was 4.23 {+-} 0.63 W/kg. The weight and mortality of the progeny were followed until postnatal day 24. Aminoacyl-tRNA synthetase enzymes and tRNA from the brains and livers of the offspring (461 exposed, 487 control) were isolated. The aminoacyl-tRNA synthetase activities were determined. The postnatal increase of body weight and organ weight was not influenced by the prenatal MW radiation. The activity of enzyme isolated form the brain showed a significant decrease after CW MW exposure, but the changes were not significant after 50 Hz AM MW exposure. The activity of the enzyme isolated from liver increased under CW and 50 Hz modulated MW.
Guo, Ying; Yu, Xuemei; Rihani, Kayla; Wang, Qing-Yin; Rong, Lijun
2004-04-16
One common feature of the more than 1,000 complement-type repeats (or low density lipoprotein (LDL)-A modules) found in LDL receptor and the other members of the LDL receptor superfamily is a cluster of five highly conserved acidic residues in the C-terminal region, DXXXDXXDXXDE. However, the role of the third conserved aspartate of these LDL-A modules in protein folding and ligand recognition has not been elucidated. In this report, using a model LDL-A module and several experimental approaches, we demonstrate that this acidic residue, like the other four conserved acidic residues, is involved in calcium-dependent protein folding. These results suggest an alternative calcium coordination conformation for the LDL-A modules. The proposed model provides a plausible explanation for the conservation of this acidic residue among the LDL-A modules. Furthermore, the model can explain why mutations of this residue in human LDL receptor cause familial hypercholesterolemia. PMID:14749324
Scattering Amplitudes in Gauge Theories
Schubert, Ulrich
2014-01-01
This thesis is focused on the development of new mathematical methods for computing multi-loop scattering amplitudes in gauge theories. In this work we combine, for the first time, the unitarity-based construction for integrands, and the recently introduced integrand-reduction through multivariate polynomial division. After discussing the generic features of this novel reduction algorithm, we will apply it to the one- and two-loop five-point amplitudes in ${\\cal N}=4$ sYM. The integrands of the multiple-cuts are generated from products of tree-level amplitudes within the super-amplitudes formalism. The corresponding expressions will be used for the analytic reconstruction of the polynomial residues. Their parametric form is known a priori, as derived by means of successive polynomial divisions using the Gr\\"obner basis associated to the on-shell denominators. The integrand reduction method will be exploited to investigate the color-kinematic duality for multi-loop ${\\cal N}=4$ sYM scattering amplitudes. Our a...
Pahari, Mayukh; Mukherjee, Arunava; Yadav, J S; Pandey, S K
2013-01-01
Using the flux resolved spectroscopy for the first time, we analyse the RXTE/PCA data of the black hole X-ray binaries GRS 1915+105 and IGR J17091-3624, when both sources show large amplitude, quasi-regular oscillations in 2.0-60.0 keV X-ray light curves. For different observations, we extract spectra during the peak (spectrally soft) and dip (spectrally hard) intervals of the oscillation, and find that their spectra are phenomenologically complex, requiring at least two distinct spectral components. Besides a thermal Comptonization component, we find that the disc emission is better modelled by an index-free multicolour disc blackbody component (p-free disc model) rather than that from a standard accretion disc. While the peak and dip spectra are complex, remarkably, their difference spectra constructed by treating dip spectra as the background spectra of the peak spectra, can be modelled as a single p-free disc component. Moreover, the variability at different time-scales and energy bands of the peak flux l...
Pahari, Mayukh; Misra, Ranjeev; Mukherjee, Arunava; Yadav, J. S.; Pandey, S. K.
2013-12-01
Using the flux resolved spectroscopy for the first time, we analyse the RXTE/PCA data of the black hole X-ray binaries GRS 1915+105 and IGR J17091-3624, when both sources show large-amplitude, quasi-regular oscillations in 2.0-60.0 keV X-ray light curves (similar to the κ and λ classes in GRS 1915+105). For different observations, we extract spectra during the peak (spectrally soft) and dip (spectrally hard) intervals of the oscillation, and find that their spectra are phenomenologically complex, requiring at least two distinct spectral components. Besides a thermal Comptonization component, we find that the disc emission is better modelled by an index-free multicolour disc blackbody component (p-free disc model) rather than that from a standard accretion disc. While the peak and dip spectra are complex, remarkably, their difference spectra, constructed by treating dip spectra as the background spectra of the peak spectra, can be modelled as a single p-free disc component. Moreover, the variability at different time-scales and energy bands of the peak flux level is always greater than or equal to the variability of the dip flux level, which strengthens the possibility that the peak flux level may be due to an independent spectral component added to the dip one. Using joint spectral analysis of peak and dip spectra with a variable emission component, we verify that the variable component is consistent with p-free disc blackbody and its spectral parameters are similar to that found from the difference spectral analysis. In contrast, we show that for oscillations in the θ class where soft dips are observed, the difference spectra cannot be similarly fitted. Our result substantiates the standard hypothesis that the oscillations are due to the limit cycle behaviour of an unstable radiation pressure dominated inner disc. However, in this interpretation, the flux variation of the unstable disc can be several order of magnitudes as expected from some theoretical simulations and need not be fine tuned to match the factor of ˜10 variation seen between the peak and dip levels.
Cluster decomposition of Veneziano amplitudes
Chan Hong Mo; Ruuskanen, P V
1972-01-01
A simple general rule is given for writing down the factorized form of an N-point Veneziano amplitude when it is decomposed into several clusters separated by high energies. It is hoped that while the explicit form of the cluster vertices may be useful phenomenologically, the manner in which they are obtained may also be instructive when considering the factorization of N-point functions in general. Note that factorization along trajectories as considered here differs in meaning from that of residues at resonance poles as embodied in the operator formalism. (7 refs).
Assentoft, Mette; Larsen, Brian R; Olesen, Emma T B; Fenton, Robert A; MacAulay, Nanna
2014-01-01
. Phosphorylation of aquaporins can regulate plasma membrane localization and, possibly, the unit water permeability via gating of the AQP channel itself. In vivo phosphorylation of six serine residues in the COOH terminus of AQP4 has been detected by mass spectrometry: Ser(276), Ser(285), Ser(315), Ser(316), Ser......(321), and Ser(322). To address the role of these phosphorylation sites for AQP4 function, serine-to-alanine mutants were created to abolish the phosphorylation sites. All mutants were detected at the plasma membrane of transfected C6 cells, with the fraction of the total cellular AQP4 expressed at the...... heterologous expression in Xenopus laevis oocytes (along with serine-to-aspartate mutants of the same residues to mimic a phosphorylation). None of the mutant AQP4 constructs displayed alterations in the unit water permeability. Thus phosphorylation of six different serine residues in the COOH terminus of AQP4...
Calculating scattering amplitudes efficiently
Dixon, L.
1996-01-01
We review techniques for more efficient computation of perturbative scattering amplitudes in gauge theory, in particular tree and one- loop multi-parton amplitudes in QCD. We emphasize the advantages of (1) using color and helicity information to decompose amplitudes into smaller gauge-invariant pieces, and (2) exploiting the analytic properties of these pieces, namely their cuts and poles. Other useful tools include recursion relations, special gauges and supersymmetric rearrangements. 46 refs., 11 figs.
Periods and Feynman amplitudes
Brown, Francis
2016-01-01
Feynman amplitudes in perturbation theory form the basis for most predictions in particle collider experiments. The mathematical quantities which occur as amplitudes include values of the Riemann zeta function and relate to fundamental objects in number theory and algebraic geometry. This talk reviews some of the recent developments in this field, and explains how new ideas from algebraic geometry have led to much progress in our understanding of amplitudes. In particular, the idea that certain transcendental numbers, such as $\\pi$, can be viewed as a representation of a group, provides a powerful framework to study amplitudes which reveals many hidden structures.
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.
Amplitudes, acquisition and imaging
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.
Correlation of amplitude modulation to inflow characteristics
Aagaard Madsen, Helge; Bertagnolio, Franck; Fischer, Andreas; Bak, Christian
2014-01-01
research by RenewableUK the hypothesis has been that one of the causes of OAM is transient stall on the blade due to non uniform inflow such as shear. Part of the RenewableUK research work was a contribution by DTU on analysis of data from the DANAERO MW experiment from 2009. In the DANAERO experiment a...
Gearbox Vibration Signal Amplitude and Frequency Modulation
Fakher Chaari; Walter Bartelmus; Radoslaw Zimroz; Tahar Fakhfakh; Mohamed Haddar
2012-01-01
Gearboxes usually run under fluctuating load conditions during service, however most of papers available in the literature describe models of gearboxes under stationary load conditions. Main task of published papers is fault modeling for their detection. Considering real situation from industry, the assumption of stationarity of load conditions cannot be longer kept. Vibration signals issued from monitoring in maintenance operations differ from mentioned models (due to load non-stationarity) ...
O. Uchino
2012-07-01
Full Text Available Simultaneous measurements of the partial column-averaged dry air mixing ratio of CO2 (q and target range were demonstrated using airborne amplitude-modulated 1.57 μm differential laser absorption spectrometry (LAS. The LAS system is useful for discriminating between ground and cloud return signals and has a demonstrated ability to suppress the impact of integrated aerosol signals on differential absorption optical depth (Δτ measurements. A high correlation coefficient (R of 0.99 between Δτ observed by LAS and Δτ calculated from in-situ measurements of CO2 was obtained. The averaged difference in q obtained from LAS (qLAS and validation data (qval was within 1.5 ppm for all spiral measurements. A significant profile was observed for both qLAS and qval, in which lower altitude CO2 decreases compared to higher altitude CO2 attributed to the photosynthesis over grassland in the summer. In the case of an urban area where CO2 and aerosol are highly distributed in the lower atmosphere in the winter, the difference of qLAS to qval is −1.5 ppm, and evaluated qLAS is in agreement with qval within the measurement precision of 2.4 ppm (1σ.
Zvorykin, V. D.; Ionin, Andrei A.; Levchenko, A. O.; Mesyats, Gennadii A.; Seleznev, L. V.; Sinitsyn, D. V.; Smetanin, Igor V.; Sunchugasheva, E. S.; Ustinovskii, N. N.; Shutov, A. V.
2013-04-01
The problem of the production of extended (~1 m) plasma channels is studied in atmospheric air by amplitude-modulated laser pulses of UV radiation, which are a superposition of a subpicosecond USP train amplified in a regenerative KrF amplifier with an unstable confocal resonator and a quasi-stationary lasing pulse. The USPs possess a high (0.2-0.3 TW) peak power and efficiently ionise oxygen molecules due to multiphoton ionisation, and the quasi-stationary lasing pulse, which has a relatively long duration (~100 ns), maintains the electron density at a level ne = (3-5) × 1014 cm—3 by suppressing electron attachment to oxygen. Experiments in laser triggering of high-voltage electric discharges suggest that the use of combined pulses results in a significant lowering of the breakdown threshold and enables controlling the discharge trajectory with a higher efficiency in comparison with smooth pulses. It was shown that controlled breakdowns may develop with a delay of tens of microseconds relative to the laser pulse, which is many orders of magnitude greater than the lifetime of free electrons in the laser-induced plasma. We propose a mechanism for this breakdown, which involves speeding-up of the avalanche ionisation of the air by negative molecular oxygen ions with a low electron binding energy (~0.5 eV) and a long lifetime (~1 ms), which are produced upon cessation of the laser pulse.
The problem of the production of extended (∼1 m) plasma channels is studied in atmospheric air by amplitude-modulated laser pulses of UV radiation, which are a superposition of a subpicosecond USP train amplified in a regenerative KrF amplifier with an unstable confocal resonator and a quasi-stationary lasing pulse. The USPs possess a high (0.2–0.3 TW) peak power and efficiently ionise oxygen molecules due to multiphoton ionisation, and the quasi-stationary lasing pulse, which has a relatively long duration (∼100 ns), maintains the electron density at a level ne = (3–5) × 1014 cm—3 by suppressing electron attachment to oxygen. Experiments in laser triggering of high-voltage electric discharges suggest that the use of combined pulses results in a significant lowering of the breakdown threshold and enables controlling the discharge trajectory with a higher efficiency in comparison with smooth pulses. It was shown that controlled breakdowns may develop with a delay of tens of microseconds relative to the laser pulse, which is many orders of magnitude greater than the lifetime of free electrons in the laser-induced plasma. We propose a mechanism for this breakdown, which involves speeding-up of the avalanche ionisation of the air by negative molecular oxygen ions with a low electron binding energy (∼0.5 eV) and a long lifetime (∼1 ms), which are produced upon cessation of the laser pulse. (extreme light fields and their applications)
Residues in the 5th module of the low-density lipoprotein receptor that bind apoE and apoB-100
Full text: The low-density lipoprotein receptor (LDLR) binds and removes cholesterol-rich lipoproteins from the circulation. Its ligand-binding (LB) domain consists of seven cysteine-rich LB modules that bind apoB-100 and apoE. These modules fold into well-defined structures with three disulfide bonds, in the presence of Ca2+. The 5th module (LB5) is unique in that it is required to bind both apoB-100 and apoE. The aim of the current study was to map residues in human LB5 that are required for ligand binding. This was done by alanine mutagenesis of a series of residues that are conserved in human, mouse, rat and rabbit LB5 (E9, S14, E16, H19, S21, K31, and K33), but not in the other six modules. E37 (R37 in the rabbit) was included, since it has been previously hypothesized to play a role in binding. The variant LB5 modules were first produced as recombinant peptides, and subjected to oxidative folding to determine whether the mutations interfered with Ca2+'-dependent folding. Only the S14A and E16A mutations interfered significantly with folding, suggesting that S14 and E16 are required for the structural framework of LB5 and that their substitution in the LDLR may interfere with its folding. The native LDLR and E9A, H19A, S21A, K31A, K33A and E37A LDLRs were expressed in LDLR negative IdlA-7 CHO cells. Labeling with 125I-lgG-C7 showed that all receptors were expressed on the cell surface. Binding of Dil-labeled LDL (Dil-LDL) and Dil-labeled DMPC, complexed with the N-terminal receptor-binding domain of apoE3 (Dil-E3), at 4 deg C, was used to assess receptor binding. Binding of Dil-E3 (0.1 ?/ml) to the H19A, S21A, K31A, K33A and E37A LDLRs was 65-92% of binding to the native LDLR. In contrast, the E9A LDLR only bound 3% of that of the native LDLR. The binding of Dil-LDL (0.5 Ag/ml) to the E9A LDLR was 23% of that of the native LDLR, while binding to the remaining variant LDLRs ranged from 44-70% of what of the native LDLR. We conclude that (i) E9 of LB5 plays a key role in the binding of apoE and LDL, consistent with ionic interactions with basic residues on apoE and apoB-100. (ii) that H19, S21, K31, and K33 and E37 play a minor role in binding apoE, and (iii) that these residues play a small, but significant role in the binding of LDL
Assentoft, Mette; Larsen, Brian R; Olesen, Emma T B; Fenton, Robert A; MacAulay, Nanna
2014-11-15
Aquaporin 4 (AQP4) is the predominant water channel in the mammalian brain and is mainly expressed in the perivascular glial endfeet at the brain-blood interface. AQP4 serves as a water entry site during brain edema formation, and regulation of AQP4 may therefore be of therapeutic interest. Phosphorylation of aquaporins can regulate plasma membrane localization and, possibly, the unit water permeability via gating of the AQP channel itself. In vivo phosphorylation of six serine residues in the COOH terminus of AQP4 has been detected by mass spectrometry: Ser(276), Ser(285), Ser(315), Ser(316), Ser(321), and Ser(322). To address the role of these phosphorylation sites for AQP4 function, serine-to-alanine mutants were created to abolish the phosphorylation sites. All mutants were detected at the plasma membrane of transfected C6 cells, with the fraction of the total cellular AQP4 expressed at the plasma membrane of transfected C6 cells being similar between the wild-type (WT) and mutant forms of AQP4. Activation of protein kinases A, C, and G in primary astrocytic cultures did not affect the plasma membrane abundance of AQP4. The unit water permeability was determined for the mutant AQP4s upon heterologous expression in Xenopus laevis oocytes (along with serine-to-aspartate mutants of the same residues to mimic a phosphorylation). None of the mutant AQP4 constructs displayed alterations in the unit water permeability. Thus phosphorylation of six different serine residues in the COOH terminus of AQP4 appears not to be required for proper plasma membrane localization of AQP4 or to act as a molecular switch to gate the water channel. PMID:25231107
Greenblatt, M.H.
1958-03-25
This patent pertains to pulse amplitude analyzers for sorting and counting a serles of pulses, and specifically discloses an analyzer which ls simple in construction and presents the puise height distribution visually on an oscilloscope screen. According to the invention, the pulses are applied to the vertical deflection plates of an oscilloscope and trigger the horizontal sweep. Each pulse starts at the same point on the screen and has a maximum amplitude substantially along the same vertical line. A mask is placed over the screen except for a slot running along the line where the maximum amplitudes of the pulses appear. After the slot has been scanned by a photocell in combination with a slotted rotating disk, the photocell signal is displayed on an auxiliary oscilloscope as vertical deflection along a horizontal time base to portray the pulse amplitude distribution.
Worldgraph approach to amplitudes
Dai, Peng
String theory uses the first-quantized method (quantum mechanics) to derive scattering amplitudes. External states are considered as vertex operators inserted on the worldsheet generated by an internal string and the amplitudes are calculated perturbatively by calculating vacuum expectation values (vevs) of these vertex operators on worldsheets with different topologies. This approach is different from the common approach of particle theories in which the second-quantized method (quantum field theory) is adopted to calculate amplitudes. A natural question to ask is whether there exists a first-quantization formalism for particles that gives particle amplitudes to all orders. This thesis presents the recent research in answering this question. In the first-quantized approach for particles, amplitudes are considered as the vevs of vertex operators inserted on different graphs generated by an internal particle. I refer to these graphs as worldgraphs and first-quantized approach for particles as worldgraph approach. To evaluate these vevs, vertex operators for several external states and Green functions on different worldgraphs are needed. In this thesis, various vertex operators are considered and a general method to obtain scalar Green functions on different worldgraphs is obtained. Some examples of the worldgraph approach to amplitudes in scalar theory and Yang-Mills theory are presented.
Detecting Pesticide Residue by Using Modulating Temperature Over a Single SnO2-Based Gas Sensor
Zengliang Yu
2003-09-01
Full Text Available A new rapid detecting method (called dynamic measurements was reported to detect and distinguish the presence of two pesticide gases in the ambient atmosphere. The method employed only a single SnO2-based gas sensor in a rectangular temperature mode to perform the qualitative analysis of a binary gas mixture (acephate and trichlorphon in air. Polar plots was used for quantitative analysis which the feature extraction was performed by FFT. Experimental results showed that high selectivity of the sensor achieved in the range of 250~3000C and modulating frequency 20mHz, one can easily observe the qualitative difference among the response to pure acephate and trichlorphon gases of the same concentration and to the mixture, and the concentration of pesticide gases can be obtained based on the changes of polar plots.
Resonant ?+? ??+?0 Amplitude from Quantum Chromodynamics
Briceo, Ral A.; Dudek, Jozef J.; Edwards, Robert G.; Shultz, Christian J.; Thomas, Christopher E.; Wilson, David J.; Hadron Spectrum Collaboration
2015-12-01
We present the first ab initio calculation of a radiative transition of a hadronic resonance within quantum chromodynamics (QCD). We compute the amplitude for ? ? ?? ??, as a function of the energy of the ? ? pair and the virtuality of the photon, in the kinematic regime where ? ? couples strongly to the unstable ? resonance. This exploratory calculation is performed using a lattice discretization of QCD with quark masses corresponding to m??400 MeV . We obtain a description of the energy dependence of the transition amplitude, constrained at 48 kinematic points, that we can analytically continue to the ? pole and identify from its residue the ? ?? ?? form factor.
Yu, Junru; Haldar, Manas; Mallik, Sanku; Srivastava, D. K.
2016-01-01
Sirtuins are emerging as the key regulators of metabolism and aging, and their potential activators and inhibitors are being explored as therapeutics for improving health and treating associated diseases. Despite the global structural similarity among all seven isoforms of sirtuins (of which most of them catalyze the deacetylation reaction), SIRT5 is the only isoform that catalyzes the cleavage of negatively charged acylated substrates, and the latter feature appears to be encoded by the presence of Tyr102 and Arg105 residues at the active site pocket of the enzyme. To determine the contributions of the above residues in SIRT5 (vis a vis the corresponding residues of SIRT1) on substrate selectivity, inhibition by EX527 and nicotinamide, secondary structural features and thermal stability of the enzymes, we created single and double mutations (viz. Y102A, R105l, and Y102A/R105I) in SIRT5. The kinetic data revealed that while Y102A mutant enzyme catalyzed both deacetylation and desuccinylation reactions with comparable efficiencies, R105I and Y102A/R105I mutant enzymes favored the deacetylase reaction. Like SIRT1, the nicotinamide inhibition of SIRT5 double mutant (Y102A/R105I) exhibited the mixed non-competitive behavior. On the other hand, the desuccinylation reaction of both wild-type and Y102A mutant enzymes conformed to the competitive inhibition model. The inhibitory potency of EX527 progressively increased from Y102A, R105I, to Y102A/R105 mutant enzymes in SIRT5, but it did not reach to the level obtained with SIRT1. The CD spectroscopic data for the wild-type and mutant enzymes revealed changes in the secondary structural features of the enzymes, and such changes were more pronounced on examining their thermal denaturation patterns. A cumulative account of our experimental data reveal mutual cooperation between Y102 and R105 residues in promoting the desuccinylation versus deacetylation reaction in SIRT5, and the overall catalytic feature of the enzyme is manifested via the mutation induced modulation in the protein structure. PMID:27023330
Amplitude interference and interferometry
The performance of the electron beam interformeter are discussed. When the interferometer is based on the observation of an interference pattern the original incident beam has to be well-collimated and the allowable misalignment is small. This allowable misalignment increasing with the angle spread of the incident electron beams a convergent electron beam can be used. The electron interferometer based on amplitude interferences is more advantageous. The amplitude interference may be accomplished through the Fraunhofer diffraction of two coherent beams by a crystal, a convergent electron beam is also used
Multilevel Modulation formats for Optical Communication
Jensen, Jesper Bevensee
2008-01-01
This thesis studies the use of multilevel modulation formats for optical communication systems. Multilevel modulation is an attractive method of increasing the spectral efficiency of optical communication systems. Various modulation formats employing phase modulation, amplitude modulation or a...
Amodeo, Giuseppe Federico; Scorciapino, Mariano Andrea; Messina, Angela; De Pinto, Vito; Ceccarelli, Matteo
2014-01-01
Voltage Dependent Anion-selective Channels (VDACs) are pore-forming proteins located in the outer mitochondrial membrane. They are responsible for the access of ions and energetic metabolites into the inner membrane transport systems. Three VDAC isoforms exist in mammalian, but their specific role is unknown. In this work we have performed extensive (overall ?5 s) Molecular Dynamics (MD) simulations of the human VDAC isoforms to detect structural and conformational variations among them, possibly related to specific functional roles of these proteins. Secondary structure analysis of the N-terminal domain shows a high similarity among the three human isoforms of VDAC but with a different plasticity. In particular, the N-terminal domain of the hVDAC1 is characterized by a higher plasticity, with a ?20% occurrence for the 'unstructured' conformation throughout the folded segment, while hVDAC2, containing a peculiar extension of 11 amino acids at the N-terminal end, presents an additional 310-helical folded portion comprising residues 10' to 3, adhering to the barrel wall. The N-terminal sequences of hVDAC isoforms are predicted to have a low flexibility, with possible consequences in the dynamics of the human VDACs. Clear differences were found between hVDAC1 and hVDAC3 against hVDAC2: a significantly modified dynamics with possible important consequence on the voltage-gating mechanism. Charge distribution inside and at the mouth of the pore is responsible for a different preferential localization of ions with opposite charge and provide a valuable rationale for hVDAC1 and hVDAC3 having a Cl-/K+ selectivity ratio of 1.8, whereas hVDAC2 of 1.4. Our conclusion is that hVDAC isoforms, despite sharing a similar scaffold, have modified working features and a biological work is now requested to give evidence to the described dissimilarities. PMID:25084457
Sewing closed string amplitudes
Carlip, S.
1988-08-11
We give a prescription for combining the Polyakov amplitudes for two string world-sheets with boundary by functionally integrating over boundary values of the embedding and ghost fields. The relationship between the moduli of the sewn surface and its components is investigated, and implications for string field theory are discussed.
Sewing closed string amplitudes
We give a prescription for combining the Polyakov amplitudes for two string world-sheets with boundary by functionally integrating over boundary values of the embedding and ghost fields. The relationship between the moduli of the sewn surface and its components is investigated, and implications for string field theory are discussed. (orig.)
Sewing closed string amplitudes
Carlip, Steven
1988-08-01
We give a prescription for combining the Polyakov amplitudes for two string world-sheets with boundary by functionally integrating over boundary values of the embedding and ghost fields. The relationship between the moduli of the sewn surface and its components is investigated, and implications for string field theory are discussed.
Lewis, Martin A; Hunihan, Lisa; Watson, John; Gentles, Robert G; Hu, Shuanghua; Huang, Yazhong; Bronson, Joanne; Macor, John E; Beno, Brett R; Ferrante, Meredith; Hendricson, Adam; Knox, Ronald J; Molski, Thaddeus F; Kong, Yan; Cvijic, Mary Ellen; Rockwell, Kristin L; Weed, Michael R; Cacace, Angela M; Westphal, Ryan S; Alt, Andrew; Brown, Jeffrey M
2015-09-01
The present studies represent the first published report of a dopamine D1 positive allosteric modulator (PAM). D1 receptors have been proposed as a therapeutic target for the treatment of cognitive deficits associated with schizophrenia. However, the clinical utility of orthosteric agonist compounds is limited by cardiovascular side effects, poor pharmacokinetics, lack of D1 selectivity, and an inverted dose response. A number of these challenges may be overcome by utilization of a selective D1 PAM. The current studies describe two chemically distinct D1 PAMs: Compound A [1-((rel-1S,3R,6R)-6-(benzo[d][1,3]dioxol-5-yl)bicyclo[4.1.0]heptan-3-yl)-4-(2-bromo-5-chlorobenzyl)piperazine] and Compound B [rel-(9R,10R,12S)-N-(2,6-dichloro-3-methylphenyl)-12-methyl-9,10-dihydro-9,10-ethanoanthracene-12-carboxamide]. Compound A shows pure PAM activity, with an EC50 of 230 nM and agonist activity at the D2 receptor in D2-expressing human embryonic kidney cells. Compound B shows superior potency (EC50 of 43 nM) and selectivity for D1 versus D2 dopamine receptors. Unlike Compound A, Compound B is selective for human and nonhuman primate D1 receptors, but lacks activity at the rodent (rat and mouse) D1 receptors. Using molecular biology techniques, a single amino acid was identified at position 130, which mediates the species selectivity of Compound B. These data represent the first described D1-selective PAMs and define critical amino acids that regulate species selectivity. PMID:26109678
Multiplex measuring of amplitude and time parameters
The methods and apparatus for spectrometry and diagnosis of high-speed processes with a great number of measured and analysed amplitude and time parameters are briefly considered. Some characteristics of measuring channels with the interrogation time of 100 and 10 ?s per a given parameter are presented. The channels comprise multiplexers of analog signals of high level; analog converters of amplitude and time intervals into voltage signal. The modules are realized in the CAMAC standard and they can process data from more than 100 channels
Light Meson Distribution Amplitudes
Arthur, R; Brommel, D; Donnellan, M A; Flynn, J M; Juttner, A; de Lima, H Pedroso; Rae, T D; Sachrajda, C T; Samways, B
2010-01-01
We calculated the first two moments of the light-cone distribution amplitudes for the pseudoscalar mesons ($\\pi$ and $K$) and the longitudinally polarised vector mesons ($\\rho$, $K^*$ and $\\phi$) as part of the UKQCD and RBC collaborations' $N_f=2+1$ domain-wall fermion phenomenology programme. These quantities were obtained with a good precision and, in particular, the expected effects of $SU(3)$-flavour symmetry breaking were observed. Operators were renormalised non-perturbatively and extrapolations to the physical point were made, guided by leading order chiral perturbation theory. The main results presented are for two volumes, $16^3\\times 32$ and $24^3\\times 64$, with a common lattice spacing. Preliminary results for a lattice with a finer lattice spacing, $32^3\\times64$, are discussed and a first look is taken at the use of twisted boundary conditions to extract distribution amplitudes.
Periods and Superstring Amplitudes
Stieberger, S
2016-01-01
Scattering amplitudes which describe the interaction of physical states play an important role in determining physical observables. In string theory the physical states are given by vibrations of open and closed strings and their interactions are described (at the leading order in perturbation theory) by a world-sheet given by the topology of a disk or sphere, respectively. Formally, for scattering of N strings this leads to N-3-dimensional iterated real integrals along the compactified real axis or N-3-dimensional complex sphere integrals, respectively. As a consequence the physical observables are described by periods on M_{0,N} - the moduli space of Riemann spheres of N ordered marked points. The mathematical structure of these string amplitudes share many recent advances in arithmetic algebraic geometry and number theory like multiple zeta values, single-valued multiple zeta values, Drinfeld, Deligne associators, Hopf algebra and Lie algebra structures related to Grothendiecks Galois theory. We review the...
Quantitative Seismic Amplitude Analysis
Dey, A.K.
2011-01-01
The Seismic Value Chain quantifies the cyclic interaction between seismic acquisition, imaging and reservoir characterization. Modern seismic innovation to address the global imbalance in hydrocarbon supply and demand requires such cyclic interaction of both feed-forward and feed-back processes. Currently, the seismic value chain paradigm is in a feed-forward mode. Modern seismic data now have the potential to yield the best images in terms of spatial resolution, amplitude accuracy, and incre...
Quantitative Seismic Amplitude Analysis:
Dey, A.K.
2011-01-01
The Seismic Value Chain quantifies the cyclic interaction between seismic acquisition, imaging and reservoir characterization. Modern seismic innovation to address the global imbalance in hydrocarbon supply and demand requires such cyclic interaction of both feed-forward and feed-back processes. Currently, the seismic value chain paradigm is in a feed-forward mode. Modern seismic data now have the potential to yield the best images in terms of spatial resolution, amplitude accuracy, and incre...
HIGH AMPLITUDE PROPAGATED CONTRACTIONS
Bharucha, Adil E.
2012-01-01
While most colonic motor activity is segmental and non-propulsive, colonic high amplitude propagated contractions (HAPC) can transfer colonic contents over long distances and often precede defecation. HAPC occur spontaneously, in response to pharmacological agents or colonic distention. In this issue of Neurogastroenterology and Motility, Rodriguez and colleagues report that anal relaxation during spontaneous and bisacodyl-induced HAPC exceeds anal relaxation during rectal distention in const...
About amplitude fluctuations of the Pi1C geomagnetic pulsations
Amplitude fluctuations of the Pi1C geomagnetic pulsations are analyzed. Applicability of the Landau theory for describing this type of pulsations is verified. The conclusion is made that in the case of Pi1C the Landau theory should be supplemented by a special hypothesis of the origin of chaotic modulation of the oscillation amplitude
It has been shown that the process du-bar ? W-? has a radiation amplitude zero and, hence, the angular distribution is very sensitive to the magnetic-moment parameter ? of the W boson. Sharp dips persist in p anti p or pp ? W-?X and also in the higher-order processes du-bar ? W?g and p anti p or pp ? W-?gX. Here, we study the energy-dependence of these processes. We find that for du-bar ? W-?, pp ? W-?X and pp ? W-?gX the dips are enhanced with increasing energy, whereas for p anti p ? W-?X, du-bar ? W-?g and p anti p ? W-?gX the magnitude of the dips is decreased with increasing energy. (author)
Closed string amplitudes as single-valued open string amplitudes
We show that the single trace heterotic N-point tree-level gauge amplitude ANHET can be obtained from the corresponding type I amplitude ANI by the single-valued (sv) projection: ANHET=sv(ANI). This projection maps multiple zeta values to single-valued multiple zeta values. The latter represent a subclass of multiple zeta values originating from single-valued multiple polylogarithms at unity. Similar relations between open and closed string amplitudes or amplitudes of different string vacua can be established. As a consequence the α′-expansion of a closed string amplitude is dictated by that of the corresponding open string amplitude. The combination of single-valued projections, Kawai–Lewellen–Tye relations and Mellin correspondence reveal a unity of all tree-level open and closed superstring amplitudes together with the maximally supersymmetric Yang–Mills and supergravity theories
Poretti, Ennio; Weiss, Werner W; Bognar, Zsofia; Moya, Andy; Niemczura, Ewa; Suarez, Juan Carlos; Auvergne, Michel; Baglin, Annie; Baudin, Frederic; Benko, Jozsef M; Debosscher, Jonas; Garrido, Rafa; Mantegazza, Luciano; Paparo, Margit
2011-01-01
The detection of small-amplitude nonradial modes in high-amplitude Delta Sct (HADS) variables has been very elusive until at least five of them were detected in the light curve of V974 Oph obtained from ground-based observations. The combination of radial and nonradial modes has a high asteroseismic potential, thanks to the strong constraints we can put in the modelling. The continuous monitoring of ASAS 192647-0030.0=CoRoT 101155310 (P=0.1258 d, V=13.4) ensured from space by the CoRoT (Convection, Rotation and planetary Transits) mission constitutes a unique opportunity to exploit such potential. The 22270 CoRoT measurements were performed in the chromatic mode. They span 152 d and cover 1208 consecutive cycles. After the correction for one jump and the long-term drift, the level of the noise turned out to be 29 micromag. The phase shifts and amplitude ratios of the coloured CoRoT data, the HARPS spectra, and the period-luminosity relation were used to determine a self-consistent physical model. In turn, it ...
Full one-loop amplitudes from tree amplitudes
Giele, Walter T.; /Fermilab; Kunszt, Zoltan; /Zurich, ETH; Melnikov, Kirill; /Hawaii U.
2008-01-01
We establish an efficient polynomial-complexity algorithm for one-loop calculations, based on generalized D-dimensional unitarity. It allows automated computations of both cut-constructible and rational parts of one-loop scattering amplitudes from on-shell tree amplitudes. We illustrate the method by (re)-computing all four-, five- and six-gluon scattering amplitudes in QCD at one-loop.
Apostol, Marcin I.; Sawaya, Michael R.; Cascio, Duilio; Eisenberg, David (UCLA)
2010-09-23
A single nucleotide polymorphism (SNP) in codon 129 of the human prion gene, leading to a change from methionine to valine at residue 129 of prion protein (PrP), has been shown to be a determinant in the susceptibility to prion disease. However, the molecular basis of this effect remains unexplained. In the current study, we determined crystal structures of prion segments having either Met or Val at residue 129. These 6-residue segments of PrP centered on residue 129 are 'steric zippers,' pairs of interacting {beta}-sheets. Both structures of these 'homozygous steric zippers' reveal direct intermolecular interactions between Met or Val in one sheet and the identical residue in the mating sheet. These two structures, plus a structure-based model of the heterozygous Met-Val steric zipper, suggest an explanation for the previously observed effects of this locus on prion disease susceptibility and progression.
CHY formula and MHV amplitudes
Du, Yi-jian; Wu, Yong-shi
2016-01-01
In this paper, we study the relation between the Cachazo-He-Yuan (CHY) formula and the maximal-helicity-violating (MHV) amplitudes of Yang-Mills and gravity in four dimensions. We prove that only one special rational solution of the scattering equations found by Weinzierl support the MHV amplitudes. Namely, localized at this solution, the integrated CHY formula reproduces the Parke-Taylor formula for Yang-Mills amplitudes as well as the Hodges formula for gravitational amplitudes. This is achieved by developing techniques, in a manifestly M\\"obius covariant formalism, to explicitly compute relevant reduced Pfaffians/determinants. We observe and prove two interesting properties (or identities), which facilitate the computations. We also check that all the other $(n-3)!-1$ solutions to the scattering equations do not support the MHV amplitudes, and prove analytically that this is indeed true for the other special rational solution proposed by Weinzierl, that actually supports the anti-MHV amplitudes.
Hidden Beauty in Multiloop Amplitudes
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 the 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 argue that t...
Amplitude oscillation of DCLC mode
A quasilinear model and a simulation code taking into account the electron bounce resonance damping have been developed to describe the amplitude oscillation of the drift cyclotron loss-cone mode, which has been observed in mirror experiments. It was found that this oscillatory behavior of the amplitude is caused by the temporal variation of the growth rate and the effect of electron bounce resonance damping on the amplitude of this mode. (author)
Model selection for amplitude analysis
Guegan, Baptiste; Hardin, John; Stevens, Justin; Williams, Mike
2015-01-01
Model complexity in amplitude analyses is often a priori under-constrained since the underlying theory permits a large number of possible amplitudes to contribute to most physical processes. The use of an overly complex model results in reduced predictive power and worse resolution on unknown parameters of interest. Therefore, it is common to reduce the complexity by removing from consideration some subset of the allowed amplitudes. This paper studies a method for limiting model complexity fr...
Amplitude dependent closest tune approach
Tomas Garcia, Rogelio; Franchi, Andrea; Maclean, Ewen Hamish; CERN. Geneva. ATS Department
2016-01-01
Recent observations in the LHC point to the existence of an amplitude dependent closest tune approach. However this dynamical behavior and its underlying mechanism remain unknown. This effect is highly relevant for the LHC as an unexpectedly closest tune approach varying with amplitude modifies the frequency content of the beam and, hence, the Landau damping. Furthermore the single particle stability would also be affected by this effect as it would modify how particles with varying amplitudes approach and cross resonances. We present analytic derivations that lead to a mechanism generating an amplitude dependent closest tune approach.
Graviton amplitudes from collinear limits of gauge amplitudes
We express all tree-level graviton amplitudes in Einstein's gravity as the collinear limits of a linear combination of pure Yang–Mills amplitudes in which each graviton is represented by two gauge bosons, each of them carrying exactly one half of graviton's momentum and helicity
Graviton amplitudes from collinear limits of gauge amplitudes
Stephan Stieberger
2015-05-01
Full Text Available We express all tree-level graviton amplitudes in Einstein's gravity as the collinear limits of a linear combination of pure Yang–Mills amplitudes in which each graviton is represented by two gauge bosons, each of them carrying exactly one half of graviton's momentum and helicity.
Graviton amplitudes from collinear limits of gauge amplitudes
Stephan Stieberger; Taylor, Tomasz R.
2015-01-01
We express all tree-level graviton amplitudes in Einstein's gravity as the collinear limits of a linear combination of pure Yang–Mills amplitudes in which each graviton is represented by two gauge bosons, each of them carrying exactly one half of graviton's momentum and helicity.
Scattering amplitudes from multivariate polynomial division
Mastrolia, Pierpaolo, E-mail: pierpaolo.mastrolia@cern.ch [Max-Planck-Institut fuer Physik, Foehringer Ring 6, 80805 Muenchen (Germany); Dipartimento di Fisica e Astronomia, Universita di Padova, Padova (Italy); INFN Sezione di Padova, via Marzolo 8, 35131 Padova (Italy); Mirabella, Edoardo, E-mail: mirabell@mppmu.mpg.de [Max-Planck-Institut fuer Physik, Foehringer Ring 6, 80805 Muenchen (Germany); Ossola, Giovanni, E-mail: GOssola@citytech.cuny.edu [New York City College of Technology, City University of New York, 300 Jay Street, Brooklyn, NY 11201 (United States); Graduate School and University Center, City University of New York, 365 Fifth Avenue, New York, NY 10016 (United States); Peraro, Tiziano, E-mail: peraro@mppmu.mpg.de [Max-Planck-Institut fuer Physik, Foehringer Ring 6, 80805 Muenchen (Germany)
2012-11-15
We show that the evaluation of scattering amplitudes can be formulated as a problem of multivariate polynomial division, with the components of the integration-momenta as indeterminates. We present a recurrence relation which, independently of the number of loops, leads to the multi-particle pole decomposition of the integrands of the scattering amplitudes. The recursive algorithm is based on the weak Nullstellensatz theorem and on the division modulo the Groebner basis associated to all possible multi-particle cuts. We apply it to dimensionally regulated one-loop amplitudes, recovering the well-known integrand-decomposition formula. Finally, we focus on the maximum-cut, defined as a system of on-shell conditions constraining the components of all the integration-momenta. By means of the Finiteness Theorem and of the Shape Lemma, we prove that the residue at the maximum-cut is parametrized by a number of coefficients equal to the number of solutions of the cut itself.
High Frequency Amplitude Detector for GMI Magnetic Sensors
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.
Closed string amplitudes as single-valued open string amplitudes
Stieberger, Stephan, E-mail: stephan.stieberger@mpp.mpg.de [Max-Planck-Institut fr Physik, Werner-Heisenberg-Institut, 80805 Mnchen (Germany); Taylor, Tomasz R. [Department of Physics, Northeastern University, Boston, MA 02115 (United States)
2014-04-15
We show that the single trace heterotic N-point tree-level gauge amplitude A{sub N}{sup HET} can be obtained from the corresponding type I amplitude A{sub N}{sup I} by the single-valued (sv) projection: A{sub N}{sup HET}=sv(A{sub N}{sup I}). This projection maps multiple zeta values to single-valued multiple zeta values. The latter represent a subclass of multiple zeta values originating from single-valued multiple polylogarithms at unity. Similar relations between open and closed string amplitudes or amplitudes of different string vacua can be established. As a consequence the ?{sup ?}-expansion of a closed string amplitude is dictated by that of the corresponding open string amplitude. The combination of single-valued projections, KawaiLewellenTye relations and Mellin correspondence reveal a unity of all tree-level open and closed superstring amplitudes together with the maximally supersymmetric YangMills and supergravity theories.
Experimental generation of amplitude squeezed vector beams
Chille, Vanessa; Semmler, Marion; Banzer, Peter; Aiello, Andrea; Leuchs, Gerd; Marquardt, Christoph
2016-01-01
We present an experimental method for the generation of amplitude squeezed high-order vector beams. The light is modified twice by a spatial light modulator such that the vector beam is created by means of a collinear interferometric technique. A major advantage of this approach is that it avoids systematic losses, which are detrimental as they cause decoherence in continuous-variable quantum systems. The utilisation of a spatial light modulator (SLM) gives the flexibility to switch between arbitrary mode orders. The conversion efficiency with our setup is only limited by the efficiency of the SLM. We show the experimental generation of Laguerre-Gauss (LG) modes with radial indices up to 1 and azimuthal indices up to 3 with complex polarization structures and a quantum noise reduction up to -0.9dB$\\pm$0.1dB. The corresponding polarization structures are studied in detail by measuring the spatial distribution of the Stokes parameters.
Main results on the RF amplitude and phase regulation systems in operation at GANIL
The general features of the amplitude and phase regulations and their control systems are briefly reviewed. These feedback control systems are fully under the control of the main computer aided by dedicated CAMAC microprocessors for actions such as starting, parameters tuning or phase stability surveying. Numerous results obtained with spectrum analysis method give the actual RF purity and the residual modulation and crossmodulation noise level for all RF signals picked up in the RF resonators. A typical value for the noise immunity is .80 dB below the carrier at 100 Hz deviation. Another set of results gives the actual long term phase drift between resonators (<0.2 RF degree within 6 hours). The stability of the RF phases is confirmed by on line beam phase measurements
Connection between the period and the amplitude of the Blazhko effect
Benkő József M.
2015-01-01
Full Text Available We found a possible relationship between the modulation period and the amplitude of the Blazhko RR Lyrae stars: long modulation period generally implies high modulation amplitude while the short modulation period results in small amplitude. Although this effect is much more a tendency than a strict rule, it can be detected easily in the space-born time series data produced by Kepler and CoRoT. Good quality ground-based data show this relation, too. This phenomenon could give us constraints for the physics of the Blazhko effect.
The pulsed amplitude unit for the SLC
There is a recurring requirement in the SLC for the control of devices such as magnets, phase shifters, and attenuators on a beam-by-beam basis. The Pulsed Amplitude Unit (PAU) is a single width CAMAC module developed for this purpose. It provides digitally programmed analog output voltages on a beam-by-beam basis. Up to 32 preprogrammed values of output voltage are available from the single analog output of the module, and any of these values can be associated with any of the 256 possible SLC beam definitions. A 12-bit Analog-to-Digital Converter (ADC) digitizes an analog input signal at the appropriate beam time and stores it in a buffer memory. This feature is normally used to monitor the response of the device being controlled by the PAU at each beam time. Initial application of the PAU is a part of the system that controls the output of Klystrons in the SLC. The PAU combines several different functions in a single module. In order to accommodate these functions in a single width CAMAC module, field programmed logic is used extensively. Field Programmable Logic Arrays, Programmed Array Logic, and a Field Programmable Logic Sequencer are employed
Teleporting Superpositions of Chiral Amplitudes
Maierle, C S; Harris, R A; Maierle, Christopher S.; Lidar, Daniel A.; Harris, Robert A.
1998-01-01
Chiral molecules may exist in superpositions of left- and right-handed states. We show how the amplitudes of such superpositions may be teleported to the polarization degrees of freedom of a photon. Two experimental schemes are proposed, one leading to perfect, the other to state-dependent teleportation. Both methods yield complete information about the amplitudes. This is the first explicit example of "inter-species" teleportation, where the amplitudes of the quantum superposition of one species are transferred at the end of the process to a different species. The latter is then easily accessible for measurement.
Positive Amplitudes In The Amplituhedron
Arkani-Hamed, Nima; Trnka, Jaroslav
2014-01-01
The all-loop integrand for scattering amplitudes in planar N = 4 SYM is determined by an "amplitude form" with logarithmic singularities on the boundary of the amplituhedron. In this note we provide strong evidence for a new striking property of the superamplitude, which we conjecture to be true to all loop orders: the amplitude form is positive when evaluated inside the amplituhedron. The statement is sensibly formulated thanks to the natural "bosonization" of the superamplitude associated with the amplituhedron geometry. However this positivity is not manifest in any of the current approaches to scattering amplitudes, and in particular not in the cellulations of the amplituhedron related to on-shell diagrams and the positive grassmannian. The surprising positivity of the form suggests the existence of a "dual amplituhedron" formulation where this feature would be made obvious. We also suggest that the positivity is associated with an extended picture of amplituhedron geometry, with the amplituhedron sitting...
Model selection for amplitude analysis
Guegan, B.; Hardin, J.; Stevens, J.; Williams, M.
2015-09-01
Model complexity in amplitude analyses is often a priori under-constrained since the underlying theory permits a large number of possible amplitudes to contribute to most physical processes. The use of an overly complex model results in reduced predictive power and worse resolution on unknown parameters of interest. Therefore, it is common to reduce the complexity by removing from consideration some subset of the allowed amplitudes. This paper studies a method for limiting model complexity from the data sample itself through regularization during regression in the context of a multivariate (Dalitz-plot) analysis. The regularization technique applied greatly improves the performance. An outline of how to obtain the significance of a resonance in a multivariate amplitude analysis is also provided.
The Bs oscillation amplitude analysis
The properties of the amplitude method for Bs oscillation analyses are studied in detail. The world combination of measured amplitudes is converted into a likelihood profile as a function of oscillation frequency. A procedure is proposed to estimate the probability that the minimum observed is due to a statistical fluctuation. This method, applied to the data available at the time of 1999 Winter Conferences, gives 1 - C.L. /∼ 0.03. (author)
Analytic Scattering Amplitudes for QCD
Vaman, Diana
2008-01-01
By analytically continuing QCD scattering amplitudes through specific complexified momenta, one can study and learn about the nature and the consequences of factorization and unitarity. In some cases, when coupled with the largest time equation and gauge invariance requirement, this approach leads to recursion relations, which greatly simplify the construction of multi-gluon scattering amplitudes. The setting for this discussion is in the space-cone gauge.
Beenstock, Jonah; Melamed, Dganit; Mooshayef, Navit; Mordechay, Dafna; Garfinkel, Benjamin P; Ahn, Natalie G; Admon, Arie; Engelberg, David
2016-05-15
Many enzymes are self-regulated and can either inhibit or enhance their own catalytic activity. Enzymes that do both are extremely rare. Many protein kinases autoactivate by autophosphorylating specific sites at their activation loop and are inactivated by phosphatases. Although mitogen-activated protein kinases (MAPKs) are usually activated by dual phosphorylation catalyzed by MAPK kinases (MAPKKs), the MAPK p38β is exceptional and is capable of self-activation by cis autophosphorylation of its activation loop residue T180. We discovered that p38β also autophosphorylates in trans two previously unknown sites residing within a MAPK-specific structural element known as the MAPK insert: T241 and S261. Whereas phosphorylation of T180 evokes catalytic activity, phosphorylation of S261 reduces the activity of T180-phosphorylated p38β, and phosphorylation of T241 reduces its autophosphorylation in trans Both phosphorylations do not affect the activity of dually phosphorylated p38β. T241 of p38β is found phosphorylated in vivo in bone and muscle tissues. In myogenic cell lines, phosphorylation of p38β residue T241 is correlated with differentiation to myotubes. T241 and S261 are also autophosphorylated in intrinsically active variants of p38α, but in this protein, they probably play a different role. We conclude that p38β is an unusual enzyme that automodulates its basal, MAPKK-independent activity by several autophosphorylation events, which enhance and suppress its catalytic activity. PMID:26976637
The scattering amplitude for four off-shell tachyons from functional integrals
We use functional integral techniques to calculate the scattering amplitude for four open off-shell tachyons in Witten's string field theory and show that the residues of the first three poles agree with those obtained using oscillator methods. (orig.)
Cattani, Eduardo; Dickenstein, Alicia; Sturmfels, Bernd
2000-01-01
A binomial residue is a rational function defined by a hypergeometric integral whose kernel is singular along binomial divisors. Binomial residues provide an integral representation for rational solutions of A-hypergeometric systems of Lawrence type. The space of binomial residues of a given degree, modulo those which are polynomial in some variable, has dimension equal to the Euler characteristic of the matroid associated with A.
Grassmannian origin of scattering amplitudes
Trnka, Jaroslav
Quantum field theory (QFT) is our central theoretical framework to describe the microscopic world, arising from the union of quantum mechanics and special relativity. Since QFTs play such a central role in our understanding of Nature, a deeper study of their physical properties is one of the most exciting directions of research in theoretical physics. This has led to the discovery of many important theoretical concepts, such as supersymmetry and string theory. One of the most prominent physical observable in any QFT is the scattering amplitude, which describes scattering processes of elementary particles. Theoretical progress in understanding and computing scattering amplitudes has accelerated in last few years with the discovery of amazing new mathematical structures in a close cousin of QCD, known as N=4 Super-Yang-Mills theory (SYM). In the first chapter we study integrands of loop amplitudes in planar N=4 SYM and show their astonishing simplicity when written in terms of special set of chiral integrals. In chapter two we show how to reconstruct the multi-loop integrand recursively starting from tree-level amplitudes. This approach makes the long-hidden Yangian symmetry of the theory completely manifest and provides a Lagrangian-independent approach for determining the integrand at any loop order. In chapter three we demonstrate that the problem of calculating of scattering amplitudes in planar N=4 SYM can be completely reformulated in a new framework in terms of on-shell diagrams and integrals over the positive Grassmannian G(k,n). Remarkably, the building blocks for amplitudes play a fundamental role in an active area of research in mathematics spanning algebraic geometry to combinatorics. In chapter four we sketch the argument that the amplitude itself is represented by a single geometrical object defined purely using a new striking property -- positivity -- and all physical concepts like unitarity and locality emerge as derived concepts, each having a sharp geometric interpretation.
Generator coordinate amplitude for scattering
Mihailovic, M.V.; Poljsak, M. (Institut Jozef Stefan, Ljubljana (Yugoslavia))
1982-10-25
In the generator coordinate method for scattering the proper boundary conditions is accomplished by requiring the GC amplitude to satisfy an integral equation of the first kind. Attempts to solve this problem are first reviewed and then an improved approximation is proposed which is applicable to a wider class of scattering problems in addition to the Coulomb scattering. A better approximation is obtained in the asymptotic region, where the generator coordinate, i.e., the distance between two shell-model wells of the fragments, is larger than the touching distance of the colliding nuclei, by deriving partial differential equations of first order for the terms of an asymptotic series in 1/E, where E is the scattering energy. Extracting the information on the GC amplitude for small values of the generator parameter from the integral equation of the first kind is an ill-posed problem. It is shown that the method of statistical regularization offers a powerful and controllable procedure to uncover the GC amplitude. The unknown GC amplitude is treated as a random function with an a priori distribution of probability which is based on the assumption that the amplitude is bounded and that the errors in the input are random with zero expectation value. A useful procedure is found for fixing parameters of the a priori distribution. The solution for small values of the GC parameter is expressed in the form of a Dini series. The method is applied to the calculation of the GC amplitude for scattering of two ..cap alpha..-particles at 15 MeV c.m. energy. The measure of the accuracy is the difference between the input wave function of relative motion and the result of folding of the GC amplitude with the kernel of the integral equation. The prescribed accuracy is reached with this method on a much larger interval than with any previously proposed method.
Generator coordinate amplitude for scattering
In the generator coordinate method for scattering the proper boundary conditions is accomplished by requiring the GC amplitude to satisfy an integral equation of the first kind. Attempts to solve this problem are first reviewed and then an improved approximation is proposed which is applicable to a wider class of scattering problems in addition to the Coulomb scattering. A better approximation is obtained in the asymptotic region, where the generator coordinate, i.e., the distance between two shell-model wells of the fragments, is larger than the touching distance of the colliding nuclei, by deriving partial differential equations of first order for the terms of an asymptotic series in 1/E, where E is the scattering energy. Extracting the information on the GC amplitude for small values of the generator parameter from the integral equation of the first kind is an ill-posed problem. It is shown that the method of statistical regularization offers a powerful and controllable procedure to uncover the GC amplitude. The unknown GC amplitude is treated as a random function with an a priori distribution of probability which is based on the assumption that the amplitude is bounded and that the errors in the input are random with zero expectation value. A useful procedure is found for fixing parameters of the a priori distribution. The solution for small values of the GC parameter is expressed in the form of a Dini series. The method is applied to the calculation of the GC amplitude for scattering of two α-particles at 15 MeV c.m. energy. The measure of the accuracy is the difference between the input wave function of relative motion and the result of folding of the GC amplitude with the kernel of the integral equation. The prescribed accuracy is reached with this method on a much larger interval than with any previously proposed method. (orig.)
Blyth, T S; Sneddon, I N; Stark, M
1972-01-01
Residuation Theory aims to contribute to literature in the field of ordered algebraic structures, especially on the subject of residual mappings. The book is divided into three chapters. Chapter 1 focuses on ordered sets; directed sets; semilattices; lattices; and complete lattices. Chapter 2 tackles Baer rings; Baer semigroups; Foulis semigroups; residual mappings; the notion of involution; and Boolean algebras. Chapter 3 covers residuated groupoids and semigroups; group homomorphic and isotone homomorphic Boolean images of ordered semigroups; Dubreil-Jacotin and Brouwer semigroups; and loli
Price, Kerry; Lummis, Sarah C R
2014-01-01
GABA-activated RDL receptors are the insect equivalent of mammalian GABAA receptors, and play a vital role in neurotransmission and insecticide action. Here we clone the pore lining M2 region of the Varroa mite RDL receptor and show that it has 4 atypical residues when compared to M2 regions of most other insects, including bees, which are the major host of Varroa mites. We create mutant Drosophila RDL receptors containing these substitutions and characterise their effects on function. Using ...
Pion-pion scattering amplitude
We obtain reliable ππ scattering amplitudes consistent with experimental data, both at low and high energies, and fulfilling appropriate analyticity properties. We do this by first fitting experimental low energy (s1/2≤1.42 GeV) phase shifts and inelasticities with expressions that incorporate analyticity and unitarity. In particular, for the S wave with isospin 0, we discuss in detail several sets of experimental data. This provides low energy partial wave amplitudes that summarize the known experimental information. Then, we impose Regge behavior as follows from factorization and experimental data for the imaginary parts of the scattering amplitudes at higher energy, and check fulfillment of dispersion relations up to 0.925 GeV. This allows us to improve our fits. The ensuing ππ scattering amplitudes are then shown to verify dispersion relations up to 1.42 GeV, as well as s-t-u crossing sum rules and other consistency conditions. The improved parametrizations therefore provide a reliable representation of pion-pion amplitudes with which one can test chiral perturbation theory calculations, pionium decays, or use as input for CP-violating K decays. In this respect, we find [a0(0)-a0(2)]2=(0.077±0.008)Mπ-2 and δ0(0)(mK2)-δ0(2)(mK2)=52.9±1.6o
Chen, Hao; Ding, Jianping; Li, Guoqiang
2015-01-01
We present an approach that enables complete control over the amplitude, phase and arbitrary polarization state on the Poincar\\'e sphere of an optical beam in a 4-f system with a spatial light modulator (SLM). The beams can be constructed from a coaxial superposition of x- and y-linearly polarized light, each carrying structured amplitude profile and phase distributions by using an amplitude-modulated mask imposed on the SLM. The amplitude, phase and polarization distribution of vector beams with four free parameters can be tailored independently and simultaneously by the SLM.
Nonsinglet pentagons and NMHV amplitudes
A.V. Belitsky
2015-07-01
Full Text Available Scattering amplitudes in maximally supersymmetric gauge theory receive a dual description in terms of the expectation value of the super Wilson loop stretched on a null polygonal contour. This makes the analysis amenable to nonperturbative techniques. Presently, we elaborate on a refined form of the operator product expansion in terms of pentagon transitions to compute twist-two contributions to NMHV amplitudes. To start with, we provide a novel derivation of scattering matrices starting from Baxter equations for flux-tube excitations propagating on magnon background. We propose bootstrap equations obeyed by pentagon form factors with nonsinglet quantum numbers with respect to the R-symmetry group and provide solutions to them to all orders in 't Hooft coupling. These are then successfully confronted against available perturbative calculations for NMHV amplitudes to four-loop order.
Nonsinglet pentagons and NHMV amplitudes
Belitsky, A V
2014-01-01
Scattering amplitudes in maximally supersymmetric gauge theory receive a dual description in terms of the expectation value of the super Wilson loop stretched on a null polygonal contour. This makes the analysis amenable to nonperturbative techniques. Presently, we elaborate on a refined form of the operator product expansion in terms of pentagon transitions to compute twist-two contributions to NMHV amplitudes. To start with, we provide a novel derivation of scattering matrices starting from Baxter equations for flux-tube excitations propagating on magnon background. We propose bootstrap equations obeyed by pentagon form factors with nonsinglet quantum numbers with respected to the R-symmetry group and provide solutions to them to all orders in 't Hooft coupling. These are then successfully confronted against available low-loop perturbative calculations for NMHV amplitudes.
Factorization of Chiral String Amplitudes
Huang, Yu-tin; Yuan, Ellis Ye
2016-01-01
We re-examine a closed-string model defined by altering the boundary conditions for one handedness of two-dimensional propagators in otherwise-standard string theory. We evaluate the amplitudes using Kawai-Lewellen-Tye factorization into open-string amplitudes. The only modification to standard string theory is effectively that the spacetime Minkowski metric changes overall sign in one open-string factor. This cancels all but a finite number of states: As found in earlier approaches, with enough supersymmetry (e.g., type II) the tree amplitudes reproduce those of the massless truncation of ordinary string theory. However, we now find for the other cases that additional fields, formerly thought to be auxiliary, describe new spin-2 states at the two adjacent mass levels (tachyonic and tardyonic). The tachyon is always a ghost, but can be avoided in the heterotic case.
Topological amplitudes in string theory
We show that certain type II string amplitudes at genus g are given by the topological partition Fg discussed recently by Bershadsky, Cecotti, Ooguri and Vafa. These amplitudes give rise to a term in the four-dimensional effective action of the form ?gFgW2g, where W is the chiral superfield of N = 2 supergravitational multiplet. The holomorphic anomaly of Fg is related to non-localities of the effective action due to the propagation of massless states. This result generalizes the holomorphic anomaly of the one loop case which is known to lead to non-harmonic gravitational couplings. (author). 22 refs, 2 figs
OPE for all Helicity Amplitudes
Basso, Benjamin; Cordova, Lucia; Sever, Amit; Vieira, Pedro
2014-01-01
We extend the Operator Product Expansion (OPE) for scattering amplitudes in planar N=4 SYM to account for all possible helicities of the external states. This is done by constructing a simple map between helicity configurations and so-called charged pentagon transitions. These OPE building blocks are generalizations of the bosonic pentagons entering MHV amplitudes and they can be bootstrapped at finite coupling from the integrable dynamics of the color flux tube. A byproduct of our map is a simple realization of parity in the super Wilson loop picture.
Scattering amplitudes in gauge theories
First monographical text on this fundamental topic. Course-tested, pedagogical and self-contained exposition. Includes exercises and solutions. 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 field theory. Bridging the gap between introductory courses on quantum field theory and state-of-the-art research, these concise yet self-contained and course-tested lecture notes are well-suited for a one-semester graduate level course or as a self-study guide for anyone interested in fundamental aspects of quantum field theory and its applications. The numerous exercises and solutions included will help readers to embrace and apply the material presented in the main text.
Discontinuity formulas for multiparticle amplitudes
It is shown how discontinuity formulas for multiparticle scattering amplitudes are derived from unitarity and analyticity. The assumed analyticity property is the normal analytic structure, which was shown to be equivalent to the space-time macrocausality condition. The discontinuity formulas to be derived are the basis of multi-particle fixed-t dispersion relations
Work on the derivation of an explicit perturbation series for string and superstring amplitudes is reviewed. The light-cone approach is emphasized, but some work on the Polyakov approach is also mentioned, and the two methods are compared. The calculation of the measure factor is outlined in the interacting-string picture
Mapping Pn amplitude spreading and attenuation in Asia
Yang, Xiaoning [Los Alamos National Laboratory; Phillips, William S [Los Alamos National Laboratory; Stead, Richard J [Los Alamos National Laboratory
2010-12-06
Pn travels most of its path in the mantle lid. Mapping the lateral variation of Pn amplitude attenuation sheds light on material properties and dynamics of the uppermost region of the mantle. Pn amplitude variation depends on the wavefront geometric spreading as well as material attenuation. We investigated Pn geometric spreading, which is much more complex than a traditionally assumed power-law spreading model, using both synthetic and observed amplitude data collected in Asia. We derived a new Pn spreading model based on the formulation that was proposed previously to account for the spherical shape of the Earth (Yang et. al., BSSA, 2007). New parameters derived for the spreading model provide much better correction for Pn amplitudes in terms of residual behavior. Because we used observed Pn amplitudes to construct the model, the model incorporates not only the effect of the Earth's spherical shape, but also the effect of potential upper-mantle velocity gradients in the region. Using the new spreading model, we corrected Pn amplitudes measured at 1, 2, 4 and 6 Hz and conducted attenuation tomography. The resulting Pn attenuation model correlates well with the regional geology. We see high attenuation in regions such as northern Tibetan Plateau and the western Pacific subduction zone, and low attenuation for stable blocks such as Sichuan and Tarim basins.
N=4 scattering amplitudes and the deformed Gramannian
Ferro, Livia, E-mail: livia.ferro@lmu.de [Arnold-Sommerfeld-Center for Theoretical Physics, Fakultt fr Physik, Ludwig-Maximilians-Universitt Mnchen, Theresienstrae 37, 80333 Mnchen (Germany); ?ukowski, Tomasz, E-mail: lukowski@maths.ox.ac.uk [Mathematical Institute, University of Oxford, Andrew Wiles Building, Radcliffe Observatory Quarter, Oxford, OX2 6GG (United Kingdom); Staudacher, Matthias, E-mail: staudacher@mathematik.hu-berlin.de [Institut fr Mathematik, Institut fr Physik und IRIS Adlershof, Humboldt-Universitt zu Berlin, Zum Groen Windkanal 6, 12489 Berlin (Germany); Max-Planck Institut fr Gravitationsphysik, Albert-Einstein-Institut, Am Mhlenberg 1, 14476 Potsdam (Germany); Theory Group, Physics Department, CERN, 1211 Geneva 23 (Switzerland)
2014-12-15
Some time ago the general tree-level scattering amplitudes of N=4 Super YangMills theory were expressed as certain Gramannian contour integrals. These remarkable formulas allow to clearly expose the super-conformal, dual super-conformal, and Yangian symmetries of the amplitudes. Using ideas from integrability it was recently shown that the building blocks of the amplitudes permit a natural multi-parameter deformation. However, this approach had been criticized by the observation that it seemed impossible to reassemble the building blocks into Yangian-invariant deformed non-MHV amplitudes. In this note we demonstrate that the deformations may be succinctly summarized by a simple modification of the measure of the Gramannian integrals, leading to a Yangian-invariant deformation of the general tree-level amplitudes. Interestingly, the deformed building blocks appear as residues of poles in the spectral parameter planes. Given that the contour integrals also contain information on the amplitudes at loop-level, we expect the deformations to be useful there as well. In particular, applying meromorphicity arguments, they may be expected to regulate all notorious infrared divergences. We also point out relations to Gelfand hypergeometric functions and the quantum KnizhnikZamolodchikov equations.
Loop Integrands for Scattering Amplitudes from the Riemann Sphere.
Geyer, Yvonne; Mason, Lionel; Monteiro, Ricardo; Tourkine, Piotr
2015-09-18
The scattering equations on the Riemann sphere give rise to remarkable formulas for tree-level gauge theory and gravity amplitudes. Adamo, Casali, and Skinner conjectured a one-loop formula for supergravity amplitudes based on scattering equations on a torus. We use a residue theorem to transform this into a formula on the Riemann sphere. What emerges is a framework for loop integrands on the Riemann sphere that promises to have a wide application, based on off-shell scattering equations that depend on the loop momentum. We present new formulas, checked explicitly at low points, for supergravity and super-Yang-Mills amplitudes and for n-gon integrands at one loop. Finally, we show that the off-shell scattering equations naturally extend to arbitrary loop order, and we give a proposal for the all-loop integrands for supergravity and planar super-Yang-Mills theory. PMID:26430983
Loop Integrands for Scattering Amplitudes from the Riemann Sphere
Geyer, Yvonne; Mason, Lionel; Monteiro, Ricardo; Tourkine, Piotr
2015-09-01
The scattering equations on the Riemann sphere give rise to remarkable formulas for tree-level gauge theory and gravity amplitudes. Adamo, Casali, and Skinner conjectured a one-loop formula for supergravity amplitudes based on scattering equations on a torus. We use a residue theorem to transform this into a formula on the Riemann sphere. What emerges is a framework for loop integrands on the Riemann sphere that promises to have a wide application, based on off-shell scattering equations that depend on the loop momentum. We present new formulas, checked explicitly at low points, for supergravity and super-Yang-Mills amplitudes and for n -gon integrands at one loop. Finally, we show that the off-shell scattering equations naturally extend to arbitrary loop order, and we give a proposal for the all-loop integrands for supergravity and planar super-Yang-Mills theory.
All-fibre source of amplitude squeezed light pulses
An all-fibre source of amplitude squeezed solitons utilizing the self-phase modulation in an asymmetric Sagnac interferometer is experimentally demonstrated. The asymmetry of the interferometer is passively controlled by an integrated fibre coupler, allowing for the optimization of the noise reduction. We have carefully studied the dependence of the amplitude noise on the asymmetry and the power launched into the Sagnac interferometer. Qualitatively, we find good agreement between the experimental results, a semi-classical theory and earlier numerical calculations (Schmitt et al 1998 Phys. Rev. Lett. 81 2446). The stability and flexibility of this all-fibre source makes it particularly well suited to applications in quantum information science
Gauge and Gravity Amplitude Relations
Carrasco, John Joseph M
2015-01-01
In these lectures I talk about simplifications and universalities found in scattering amplitudes for gauge and gravity theories. In contrast to Ward identities, which are understood to arise from familiar symmetries of the classical action, these structures are currently only understood in terms of graphical organizational principles, such as the gauge-theoretic color-kinematics duality and the gravitational double-copy structure, for local representations of multi-loop S-matrix elements. These graphical principles make manifest new relationships in and between gauge and gravity scattering amplitudes. My lectures will focus on arriving at such graphical organizations for generic theories with examples presented from maximal supersymmetry, and their use in unitarity-based multi-loop integrand construction.
Infrared singularities in QCD amplitudes
Gardi, Einan
2009-01-01
We review recent progress in determining the infrared singularity structure of on-shell scattering amplitudes in massless gauge theories. We present a simple ansatz where soft singularities of any scattering amplitude of massless partons, to any loop order, are written as a sum over colour dipoles, governed by the cusp anomalous dimension. We explain how this formula was obtained, as the simplest solution to a newly-derived set of equations constraining the singularity structure to all orders. We emphasize the physical ideas underlying this derivation: the factorization of soft and collinear modes, the special properties of soft gluon interactions, and the notion of the cusp anomaly. Finally, we briefly discuss potential multi-loop contributions going beyond the sum-over-dipoles formula, which cannot be excluded at present.
Multiscalar amplitudes in perturbation theory
It is shown that the high-multiplicity limit of amplitudes involving scalar particles (Higgs) does not respect unitary bounds at any order in perturbation theory. Possible restoration of a unitary-respecting behaviour within the Standard Model is discussed. It relies on the existence of relations that express the masses of all known elementary particles in terms of the mass of the Higgs particle. 1 fig., 14 refs
Patients with locally advanced head and neck cancer (LAHNC) undergo life-changing treatments that can seriously affect quality of life (QoL). This prospective study examined the key QoL domains during the first year after intensity-modulated radiotherapy (IMRT) and identified predictors of these changes in order to improve patient outcomes. A consecutive series of patients with LAHNC completed the European Organisation for Research and Treatment of Cancer (EORTC) Quality of Life Questionnaire Core module (QLQ-C30) and the HNC-specific QLQ-HN35 before (t0) and at the end (t1) of definitive or adjuvant IMRT, then at 6-8 weeks (t2), 6 months (t3), and 1 year (t4) after IMRT. Patients (n = 111) completing questionnaires at all five time points were included (baseline response rate: 99 %; dropout rate between t0 and t4: 5 %). QoL deteriorated in all domains during IMRT and improved slowly during the first year thereafter. Many domains recovered to baseline values after 1 year but problems with smelling and tasting, dry mouth, and sticky saliva remained issues at this time. Increases in problems with sticky saliva were greater after 1 year in patients with definitive versus adjuvant IMRT (F = 3.5, P = 0.05). QoL in patients with LAHNC receiving IMRT takes approximately 1 year to return to baseline; some domains remain compromised after 1 year. Although IMRT aims to maintain function and QoL, patients experience long-term dry mouth and sticky saliva, particularly following definitive IMRT. Patients should be counseled at the start of therapy to reduce disappointment with the pace of recovery. (orig.)
Cavity enhanced terahertz modulation
Born, N., E-mail: norman.born@physik.uni-marburg.de [College of Optical Sciences, University of Arizona, 1630 E University Boulevard, Tucson, Arizona 85721 (United States); Faculty of Physics and Material Sciences Center, Philipps-Universitt Marburg, Renthof 5, 35032 Marburg (Germany); Scheller, M.; Moloney, J. V. [College of Optical Sciences, University of Arizona, 1630 E University Boulevard, Tucson, Arizona 85721 (United States); Koch, M. [Faculty of Physics and Material Sciences Center, Philipps-Universitt Marburg, Renthof 5, 35032 Marburg (Germany)
2014-03-10
We present a versatile concept for all optical terahertz (THz) amplitude modulators based on a Fabry-Prot semiconductor cavity design. Employing the high reflectivity of two parallel meta-surfaces allows for trapping selected THz photons within the cavity and thus only a weak optical modulation of the semiconductor absorbance is required to significantly damp the field within the cavity. The optical switching yields to modulation depths of more than 90% with insertion efficiencies of 80%.
A summary is presented of the many investigations that have been done on solid residues of atmospheric fluid bed combustion (AFBC). These residues are bed ash, cyclone ash and bag filter ash. Physical and chemical properties are discussed and then the various uses of residues (in fillers, bricks, gravel, and for recovery of aluminium) are summarised. Toxicological properties of fly ash and stack ash are discussed as are risks of pneumoconiosis for workers handling fly ash, and contamination of water by ashes. On the basis of present information it is concluded that risks to public health from exposure to emissions of coal fly ash from AFBC appear small or negligible as are health risk to workers in the coal fly ash processing industry. 35 refs., 5 figs., 12 tabs
Thin Photoresponding Elements with Frequency and Amplitude Modulations
Klusoň, Petr; Morozová, Magdalena; Dzik, P.; Veselý, M.
Praha : Česká společnost chemického inženýrství, 2013, s. 83. ISBN 978-80-02-02500-9. [Konference chemického a procesního inženýrství CHISA 2013 /60./. Srní, Šumava (CZ), 14.10.2013-17.10.2013] Institutional support: RVO:67985858 Keywords : metal oxide * electrochemical properties * photoelectrocatalytic activity Subject RIV: CI - Industrial Chemistry, Chemical Engineering www.chisa.cz/2013
Modulated electron bunch with amplitude front tilt in an undulator
Geloni, Gianluca [European XFEL GmbH, Hamburg (Germany); Kocharyan, Vitali; Saldin, Evgeni [Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany)
2015-12-15
In a previous paper we discussed the physics of a microbunched electron beam kicked by the dipole field of a corrector magnet by describing the kinematics of coherent undulator radiation after the kick. We demonstrated that the effect of aberration of light supplies the basis for understanding phenomena like the deflection of coherent undulator radiation by a dipole magnet. We illustrated this fact by examining the operation of an XFEL under the steady state assumption, that is a harmonic time dependence. We argued that in this particular case the microbunch front tilt has no objective meaning; in other words, there is no experiment that can discriminate whether an electron beam is endowed with a microbunch front tilt of not. In this paper we extend our considerations to time-dependent phenomena related with a finite electron bunch duration, or SASE mode of operation. We focus our attention on the spatiotemporal distortions of an X-ray pulse. Spatiotemporal coupling arises naturally in coherent undulator radiation behind the kick, because the deflection process involves the introduction of a tilt of the bunch profile. This tilt of the bunch profile leads to radiation pulse front tilt, which is equivalent to angular dispersion of the output radiation. We remark that our exact results can potentially be useful to developers of new generation XFEL codes for cross-checking their results.
Modulated Electron Bunch with Amplitude Front Tilt in an Undulator
Geloni, Gianluca; Saldin, Evgeni
2015-01-01
In a previous paper we discussed the physics of a microbunched electron beam kicked by the dipole field of a corrector magnet by describing the kinematics of coherent undulator radiation after the kick. We demonstrated that the effect of aberration of light supplies the basis for understanding phenomena like the deflection of coherent undulator radiation by a dipole magnet. We illustrated this fact by examining the operation of an XFEL under the steady state assumption, that is a harmonic time dependence. We argued that in this particular case the microbunch front tilt has no objective meaning; in other words, there is no experiment that can discriminate whether an electron beam is endowed with a microbunch front tilt of not. In this paper we extend our considerations to time-dependent phenomena related with a finite electron bunch duration, or SASE mode of operation. We focus our attention on the spatiotemporal distortions of an X-ray pulse. Spatiotemporal coupling arises naturally in coherent undulator radi...
Modulated electron bunch with amplitude front tilt in an undulator
In a previous paper we discussed the physics of a microbunched electron beam kicked by the dipole field of a corrector magnet by describing the kinematics of coherent undulator radiation after the kick. We demonstrated that the effect of aberration of light supplies the basis for understanding phenomena like the deflection of coherent undulator radiation by a dipole magnet. We illustrated this fact by examining the operation of an XFEL under the steady state assumption, that is a harmonic time dependence. We argued that in this particular case the microbunch front tilt has no objective meaning; in other words, there is no experiment that can discriminate whether an electron beam is endowed with a microbunch front tilt of not. In this paper we extend our considerations to time-dependent phenomena related with a finite electron bunch duration, or SASE mode of operation. We focus our attention on the spatiotemporal distortions of an X-ray pulse. Spatiotemporal coupling arises naturally in coherent undulator radiation behind the kick, because the deflection process involves the introduction of a tilt of the bunch profile. This tilt of the bunch profile leads to radiation pulse front tilt, which is equivalent to angular dispersion of the output radiation. We remark that our exact results can potentially be useful to developers of new generation XFEL codes for cross-checking their results.
Adamson, Justus
2012-02-01
PURPOSE: To quantify the dosimetric effect and margins required to account for prostate intrafractional translation and residual setup error in a cone beam computed tomography (CBCT)-guided hypofractionated radiotherapy protocol. METHODS AND MATERIALS: Prostate position after online correction was measured during dose delivery using simultaneous kV fluoroscopy and posttreatment CBCT in 572 fractions to 30 patients. We reconstructed the dose distribution to the clinical tumor volume (CTV) using a convolution of the static dose with a probability density function (PDF) based on the kV fluoroscopy, and we calculated the minimum dose received by 99% of the CTV (D(99)). We compared reconstructed doses when the convolution was performed per beam, per patient, and when the PDF was created using posttreatment CBCT. We determined the minimum axis-specific margins to limit CTV D(99) reduction to 1%. RESULTS: For 3-mm margins, D(99) reduction was <\\/=5% for 29\\/30 patients. Using post-CBCT rather than localizations at treatment delivery exaggerated dosimetric effects by ~47%, while there was no such bias between the dose convolved with a beam-specific and patient-specific PDF. After eight fractions, final cumulative D(99) could be predicted with a root mean square error of <1%. For 90% of patients, the required margins were <\\/=2, 4, and 3 mm, with 70%, 40%, and 33% of patients requiring no right-left (RL), anteroposterior (AP), and superoinferior margins, respectively. CONCLUSIONS: For protocols with CBCT guidance, RL, AP, and SI margins of 2, 4, and 3 mm are sufficient to account for translational errors; however, the large variation in patient-specific margins suggests that adaptive management may be beneficial.
VCSEL with intracavity modulator: fast modulation options
Yakimov, M.; Tokranov, V.; Sergeev, A.; Oktyabrsky, S.
2009-02-01
An integrated optoelectronic device, comprising VCSEL and intracavity electro-absorption modulator within the same epitaxial structure, has been previously developed by several research groups. Such a combination device, despite having relatively weak DC modulation, exhibits strong optical feedback, resulting in strong optoelectronic resonance feature in small-signal modulation response characteristic . At large modulation amplitude, device demonstrates pulsed response. Similar to Q-switching operation, energy accumulated in the gain medium over full modulation cycle is released in a single short pulse once cavity Q-factor is increased. As a result, traditional NRZ amplitude modulation becomes ineffective. We are proposing a phase-pulse modulation approach to drive this device, when strong optical feedback is used for obtaining very fast rise and fall times of short pulses. Such transient times can be on the order of few photon lifetimes, e.g. few picoseconds. Gain medium depletion can be avoided by variation of Q-factor both above and below steady-state value and keeping total emitted energy per cycle at a constant level. Data showing modulation properties (pulse energy >100 fJ, FWHM 40 ps non-controlled pulse length at 4 GHz,) and device characteristics, along with numerical analysis of such device for different modulation waveforms is presented.
Superstring amplitudes and contact interactions
We show that scattering amplitudes computed from light-cone superstring field theory are divergent at tree level. The divergences can be eliminated, and supersymmetry restored, by the addition of certain counter terms to the light-cone Hamiltonian. These counter terms have the form of local contact interactions, whose existence we had previously deduced on grounds of vacuum stability, and closure of the super-Poincare algebra. The quartic contact interactions required in Type I and Type IIB superstring theories are constructed in detail. (orig.)
Perturbative Gravity from QCD Amplitudes
Bern, Z.; Grant, A. K.
1999-01-01
We demonstrate that QCD gluon amplitudes can be used to construct a Lagrangian for gravity. This procedure makes use of perturbative `squaring' relations between gravity and gauge theory that follow from string theory. We explicitly carry out the construction for up to five-point interactions and discuss a set of field variables in the Einstein-Hilbert Lagrangian for interpreting the Lagrangian obtained from QCD. A spin-off from our analysis is that it can be used to provide simpler tree-leve...
Large amplitude oscillatory elongation flow
Rasmussen, Henrik K.; Laillé, Philippe; Yu, Kaijia
2008-01-01
+ Lambda[1 - cos( 2 pi Omega(epsilon) over dot(0)t)] where epsilon is the Hencky strain, (epsilon) over dot(0) is a constant elongational rate for the base elongational flow, Lambda the strain amplitude ( Lambda >= 0), and Omega the strain frequency. A narrow molecular mass distribution linear polystyrene...... with a molecular weight of 145 kg/ mol was subjected to the oscillative flow. The onset of the steady periodic regime is reached at the same Hencky strain as the onset of the steady elongational viscosity ( Lambda = 0). The integral molecular stress function formulation within the 'interchain pressure...
Forward amplitude in pion deuteron
The data on total cross section for ?d scattering is analysed in terms of a single scattering calculation with Fermi motion dependence, in order to obtain a criterion to fix the value of the energy entering the two body meson nucleon amplitude. It is found that the prescription derived from the non-relativistic three body kinematics gives reasonable results. The introduction of a shift in the energy value, possibly representing nuclear binding effects, leads to a very good fitting of the data. The results are compared with those obtained in direct calculations of Faddeev equations and with the Brueckner model of fixed scatterers. (Author)
Tribius, Silke; Raguse, Marieclaire; Voigt, Christian; Petersen, Cordula; Kruell, Andreas [University Medical Center Hamburg-Eppendorf, Department of Radiation Oncology, Hamburg (Germany); Muenscher, Adrian [University Medical Center Hamburg-Eppendorf, Department of Otorhinolaryngology and Head and Neck Surgery, Hamburg (Germany); Groebe, Alexander [University Medical Center Hamburg-Eppendorf, Department of Maxillofacial Surgery, Hamburg (Germany); Bergelt, Corinna [University Medical Center Hamburg-Eppendorf, Department of Medical Psychology, Hamburg (Germany); Singer, Susanne [University Medical Center Mainz, Institute of Medical Biostatistics, Epidemiology and Informatics (IMBEI), Mainz (Germany)
2015-03-08
Patients with locally advanced head and neck cancer (LAHNC) undergo life-changing treatments that can seriously affect quality of life (QoL). This prospective study examined the key QoL domains during the first year after intensity-modulated radiotherapy (IMRT) and identified predictors of these changes in order to improve patient outcomes. A consecutive series of patients with LAHNC completed the European Organisation for Research and Treatment of Cancer (EORTC) Quality of Life Questionnaire Core module (QLQ-C30) and the HNC-specific QLQ-HN35 before (t0) and at the end (t1) of definitive or adjuvant IMRT, then at 6-8 weeks (t2), 6 months (t3), and 1 year (t4) after IMRT. Patients (n = 111) completing questionnaires at all five time points were included (baseline response rate: 99 %; dropout rate between t0 and t4: 5 %). QoL deteriorated in all domains during IMRT and improved slowly during the first year thereafter. Many domains recovered to baseline values after 1 year but problems with smelling and tasting, dry mouth, and sticky saliva remained issues at this time. Increases in problems with sticky saliva were greater after 1 year in patients with definitive versus adjuvant IMRT (F = 3.5, P = 0.05). QoL in patients with LAHNC receiving IMRT takes approximately 1 year to return to baseline; some domains remain compromised after 1 year. Although IMRT aims to maintain function and QoL, patients experience long-term dry mouth and sticky saliva, particularly following definitive IMRT. Patients should be counseled at the start of therapy to reduce disappointment with the pace of recovery. (orig.) [German] Die Therapie von Patienten mit lokal fortgeschrittenen Kopf-Hals-Tumoren (LFKHT) geht mit einschneidenden Veraenderungen einher und beeinflusst die Lebensqualitaet (LQ) erheblich. Diese prospektive Studie untersucht die LQ waehrend des ersten Jahres nach intensitaetsmodulierter Strahlentherapie (IMRT) und hat Praediktoren dieser Veraenderungen herausgearbeitet, um Therapieergebnisse verbessern zu koennen. Patienten mit LFKHT fuellten Lebensqualitaetsfrageboegen der European Organisation for Research and Treatment of Cancer (EORTC) aus; Hauptfragebogen (QLQ-C30) und Kopf-Hals-Tumor-Fragebogen (QLQ-HN35) jeweils vor definitiver oder adjuvanter IMRT (t0), am Ende der IMRT (t1), nach weiteren 6-8 Wochen (t2), 6 Monaten (t3) und nach 1 Jahr (t4). Insgesamt haben 111 Patienten zu allen fuenf Zeitpunkten die Frageboegen ausgefuellt und wurden in die Studie eingeschlossen (Responserate t0: 99%; Ausfallrate t0-t4: 5 %). Waehrend der IMRT verschlechterten sich alle Domaenen der LQ und besserten sich langsam ueber das erste Folgejahr. Viele Lebensqualitaetswerte kehrten zum Ausgangsniveau zurueck, waehrend Probleme mit Riechen und Schmecken, trockener Mund und klebriger Speichel problematisch blieben. Probleme mit klebrigem Speichel wurden von Patienten nach definitiver IMRT haeufiger berichtet als von Patienten nach adjuvanter Therapie (F = 3,5; P = 0,05). Nach einer IMRT dauert es bei Patienten mit Kopf-Hals-Tumoren bis zu 1 Jahr bis die LQ wieder ihr Ausgangsniveau erreicht; einige Domaenen bleiben auch noch nach 1 Jahr darunter. Obwohl es Ziel der IMRT ist, Funktion und LQ zu erhalten, bleiben trockener Mund und klebriger Speichel teilweise als Langzeiteffekte bestehen, insbesondere bei Patienten nach primaerer IMRT. Patienten sollten diesbezueglich vor Beginn der Therapie aufgeklaert werden, um ihnen Unzufriedenheit mit der Geschwindigkeit der Rekonvaleszenz zu ersparen. (orig.)
This paper discusses when and how the Verlinde dimensions of a rational conformal field theory can be expressed as correlation functions in a topical LG theory. It is seen that a necessary condition is that the RCFT fusion rules must exhibit an extra symmetry. The authors consider two particular perturbations of the Grassmannian superpotentials. The topological LG residues in one perturbation, introduced by Gepner, are shown to be a twisted version of the SU(N)k Verlinde dimensions. The residues in the other perturbations are the twisted Verlinde dimensions of another RCFT; these topological LG correlation functions are conjectured to be the correlation functions of the corresponding Grassmannian topological sigma model with a coupling in the action to instanton number
Holonomy-flux spinfoam amplitude
Perini, Claudio
2012-01-01
We introduce a holomorphic representation for the Lorentzian EPRL spinfoam on arbitrary 2-complexes. The representation is obtained via the Ashtekar-Lewandowski-Marolf-Mour\\~ao-Thiemann heat kernel coherent state transform. The new variables are classical holonomy-flux phase space variables $(h,X)\\simeq \\mathcal T^*SU(2)$ of Hamiltonian loop quantum gravity prescribing the holonomies of the Ashtekar connection $A=\\Gamma + \\gamma K$, and their conjugate gravitational fluxes. For small heat kernel `time' the spinfoam amplitude is peaked on classical space-time geometries, where at most countably many curvatures are allowed for non-zero Barbero-Immirzi parameter. We briefly comment on the possibility to use the alternative flipped classical limit.
Grassmannian geometry of scattering amplitudes
Arkani-Hamed, Nima; Cachazo, Freddy; Goncharov, Alexander; Postnikov, Alexander; Trnka, Jaroslav
2016-01-01
Outlining a revolutionary reformulation of the foundations of perturbative quantum field theory, this book is a self-contained and authoritative analysis of the application of this new formulation to the case of planar, maximally supersymmetric YangMills theory. The book begins by deriving connections between scattering amplitudes and Grassmannian geometry from first principles before introducing novel physical and mathematical ideas in a systematic manner accessible to both physicists and mathematicians. The principle players in this process are on-shell functions which are closely related to certain sub-strata of Grassmannian manifolds called positroids - in terms of which the classification of on-shell functions and their relations becomes combinatorially manifest. This is an essential introduction to the geometry and combinatorics of the positroid stratification of the Grassmannian and an ideal text for advanced students and researchers working in the areas of field theory, high energy physics, and the...
Exploration for uranium carried out over a major portion of the Rio Grande do Sul Shield has revealed a number of small residual basins developed along glacially eroded channels of pre-Permian age. Mineralization of uranium occurs in two distinct sedimentary units. The lower unit consists of rhythmites overlain by a sequence of black shales, siltstones and coal seams, while the upper one is dominated by sandstones of probable fluvial origin. (Author)
BCFW construction of the Veneziano Amplitude
A. Fotopoulos
2010-01-01
In this note we demonstrate how one can compute the Veneziano amplitude for bosonic string theory using the BCFW method. We use an educated ansatz for the cubic amplitude of two tachyons and an arbitrary level string state.
Constructing Amplitudes from Their Soft Limits
Boucher-Veronneau, Camille; Larkoski, Andrew J.; /SLAC
2011-12-09
The existence of universal soft limits for gauge-theory and gravity amplitudes has been known for a long time. The properties of the soft limits have been exploited in numerous ways; in particular for relating an n-point amplitude to an (n-1)-point amplitude by removing a soft particle. Recently, a procedure called inverse soft was developed by which 'soft' particles can be systematically added to an amplitude to construct a higher-point amplitude for generic kinematics. We review this procedure and relate it to Britto-Cachazo-Feng-Witten recursion. We show that all tree-level amplitudes in gauge theory and gravity up through seven points can be constructed in this way, as well as certain classes of NMHV gauge-theory amplitudes with any number of external legs. This provides us with a systematic procedure for constructing amplitudes solely from their soft limits.
New identities among gauge theory amplitudes
Color-ordered amplitudes in gauge theories satisfy non-linear identities involving amplitude products of different helicity configurations. We consider the origin of such identities and connect them to the Kawai-Lewellen-Tye (KLT) relations between gravity and gauge theory amplitudes. Extensions are made to one-loop order of the full N=4 super Yang-Mills multiplet.
Computational Prediction of Hot Spot Residues
Morrow, John Kenneth; Zhang, Shuxing
2012-01-01
Most biological processes involve multiple proteins interacting with each other. It has been recently discovered that certain residues in these protein-protein interactions, which are called hot spots, contribute more significantly to binding affinity than others. Hot spot residues have unique and diverse energetic properties that make them challenging yet important targets in the modulation of protein-protein complexes. Design of therapeutic agents that interact with hot spot residues has pr...
2006-01-01
10 May 2006 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a summertime view of the south polar residual cap of Mars. In this image, mesas composed largely of solid carbon dioxide are separated from one another by irregularly-shaped depressions. The variation in brightness across this scene is a function of several factors including, but not limited to, varying proportions of dust and solid carbon dioxide, undulating topography, and differences in the roughness of the slopes versus the flat surfaces. Location near: 86.7oS, 343.3oW Image width: 3 km (1.9 mi) Illumination from: upper left Season: Southern Summer
Lifetime and residual strength of materials
Nielsen, Lauge Fuglsang
1997-01-01
of load amplitude, load average, fractional time under maximum load, and load frequency.The analysis includes prediction of residual strength (re-cycle strength) during the process of load cycling. It is concluded that number of cycles to failure is a very poor design criterion. It is demonstrated...
S-Duality and Helicity Amplitudes
Colwell, Kitran
2015-01-01
We examine interacting Abelian theories at low energies and show that holomorphically normalized photon helicity amplitudes transform into dual amplitudes under SL(2,Z) as modular forms with weights that depend on the number of positive and negative helicity photons and on the number of internal photon lines. Moreover, canonically normalized helicity amplitudes transform by a phase, so that even though the amplitudes are not duality invariant, their squares are duality invariant. We explicitly verify the duality transformation at one loop by comparing the amplitudes in the case of an electron and the dyon that is its SL(2,Z) image, and extend the invariance of squared amplitudes order by order in perturbation theory. We demonstrate that S-duality is property of all low-energy effective Abelian theories with electric and/or magnetic charges and see how the duality generically breaks down at high energies.
All-fibre source of amplitude-squeezed light pulses
Meissner, M; Heersink, J; Gaber, T; Wietfeld, A; Leuchs, G; Andersen, U L; Meissner, Markus; Marquardt, Christoph; Heersink, Joel; Gaber, Tobias; Wietfeld, Andr\\'e; Leuchs, Gerd; Andersen, Ulrik L.
2004-01-01
An all-fibre source of amplitude squeezed solitons utilizing the self-phase modulation in an asymmetric Sagnac interferometer is experimentally demonstrated. The asymmetry of the interferometer is passively controlled by an integrated fibre coupler, allowing for the optimisation of the noise reduction. We have carefully studied the dependence of the amplitude noise on the asymmetry and the power launched into the Sagnac interferometer. Qualitatively, we find good agreement between the experimental results, a semi-classical theory and earlier numerical calculations [Schmitt etl.al., PRL Vol. 81, p.2446, (1998)]. The stability and flexibility of this all-fibre source makes it particularly well suited to applications in quantum information science.
Amplitude Dependency of Synchrony Codes
Jan Grewe
2012-05-01
Full Text Available Synchronous activity among neurons in a population is usually associated with the occurrence of specific features in the common stimulus. We investigate the synchrony code in the context of the encoding of electrosensory information in the weakly electric fish Apteronotus leptorhynchus. Middleton et al., 2009 showed that the extraction of synchronous spikes from a population of input neurons shifts the range of encoded signals to higher frequencies and thus can be understood as a way to separarte coding channels. In the electrosensory world this separation roughly matches the frequency ranges used for the two purposes of active electrosensation, i.e. navigation and prey detection, in the lower range, and communication in the high frequency range. Here, we compare experimental results from in vivo recordings of p-unit electroreceptors with predictions from linear response theory in the limit of weak stimuli. Analytical expressions are derived for the coherence of both the synchronous spikes, as a coincidence detector would read them out, and the integrated spike trains. The theoretical results show how the synchrony code depends on stimulus amplitude and the power-spectrum of baseline firing. Theory predicts that any cell that has a regular baseline firing rate and contains a certain amount of intrinsic noise can employ a synchrony code and thus separate coding channels. Furthermore the separation of the frequency bands of integrated and synchronous responses dependes on the stimulus intensity. Weak stimuli lead to a clear separation that becomes weaker with increasing stimulus intensity. Our experimental results from the electrosensory systems of the weakly electric fish support these predictions. In irregular spiking P-units of the active electrosensory system the observed separation of the coding channels indeed shows the predicted stimulus dependency. On the other hand, ampullary receptors of the passive electrosensory system exhibit a much more regular baseline firing rate than those of the active system. Here the coding ranges of the synchronous and integrated responses are not shifted relative to each other. Thus, the receptors of the passive system do not have a sufficient level of intrinsic noise, although a distinction of synchronous and non-synchronous spikes is still possible. Again, these results are in line with the predictions of the theory.
Gupta, Tejpal, E-mail: tejpalgupta@rediffmail.com [Department of Radiation Oncology, ACTREC/TMH, Tata Memorial Centre, Kharghar, Navi Mumbai (India); Wadasadawala, Tabassum; Master, Zubin; Phurailatpam, Reena; Pai-Shetty, Rajershi; Jalali, Rakesh [Department of Radiation Oncology, ACTREC/TMH, Tata Memorial Centre, Kharghar, Navi Mumbai (India)
2012-02-01
Purpose: To report early clinical outcomes of helical tomotherapy (HT)-based image-guided intensity-modulated radiation therapy (IMRT) in brain tumors of varying shape, size, and location. Materials and Methods: Patients with residual, recurrent, and/or progressive low-grade intracranial and skull-base tumors were treated on a prospective protocol of HT-based IMRT and followed clinicoradiologically. Standardized metrics were used for plan evaluation and outcome analysis. Results: Twenty-seven patients with 30 lesions were treated to a median radiotherapy dose of 54 Gy in 30 fractions. All HT plans resulted in excellent target volume coverage with steep dose-gradients. The mean (standard deviation) dose homogeneity index and conformity index was 0.07 (0.05) and 0.71 (0.08) respectively. At first response assessment, 20 of 30 lesions were stable, whereas 9 showed partial regression. One patient with a recurrent clival chordoma though neurologically stable showed imaging-defined progression, whereas another patient with stable disease on serial imaging had sustained neurologic worsening. With a median follow-up of 19 months (interquartile range, 11-26 months), the 2-year clinicoradiological progression-free survival and overall survival was 93.3% and 100% respectively. Conclusions: Careful selection of radiotherapy technique is warranted for benign/low-grade brain tumors to achieve durable local control with minimum long-term morbidity. Large or complex-shaped tumors benefit most from IMRT. Our early clinical experience of HT-based IMRT for brain tumors has been encouraging.
On the singularities of massive superstring amplitudes
Superstring one-loop amplitudes with massive external states are shown to be in general ill-defined due to internal on-shell propagators. However, we argue that since any massive string state (in the uncompactified theory) has a finite lifetime to decay into massless particles, such amplitudes are not terms in the perturbative expansion of physical S-matrix elements: These can be defined only with massless external states. Consistent massive amplitudes repuire an off-shell formalism. (orig.)
On the singularities of massive superstring amplitudes
Foda, O.
1987-06-04
Superstring one-loop amplitudes with massive external states are shown to be in general ill-defined due to internal on-shell propagators. However, we argue that since any massive string state (in the uncompactified theory) has a finite lifetime to decay into massless particles, such amplitudes are not terms in the perturbative expansion of physical S-matrix elements: These can be defined only with massless external states. Consistent massive amplitudes repuire an off-shell formalism.
On the singularities of massive superstring amplitudes
Foda, O.
1987-01-01
Superstring one-loop amplitudes with massive external states are shown to be in general ill-defined due to internal on-shell propagators. However, we argue that since any massive string state (in the uncompactified theory) has a finite lifetime to decay into massless particles, such amplitudes are not terms in the perturbative expansion of physical S-matrix elements: these can be defined only with massless external states. Consistent massive amplitudes require an off-shell formalism.
Discontinuities of multi-Regge amplitudes
Fadin, V S
2014-01-01
In the BFKL approach, discontinuities of multiple production amplitudes in invariant masses of produced particles are discussed. It turns out that they are in evident contradiction with the BDS ansatz for $n$-gluon amplitudes in the planar $N$=4 SYM at $n\\ge 6$. An explicit expression for the NLO discontinuity of the two-to-four amplitude in the invariant mass of two produced gluons is is presented.
Gravity and Yang-Mills amplitude relations
Using only general features of the S matrix and quantum field theory, we prove by induction the Kawai-Lewellen-Tye relations that link products of gauge theory amplitudes to gravity amplitudes at tree level. As a bonus of our analysis, we provide a novel and more symmetric form of these relations. We also establish an infinite tower of new identities between amplitudes in gauge theories.
Modulation of ultrasound to produce multifrequency radiation force1
Urban, Matthew W.; Fatemi, Mostafa; Greenleaf, James F.
2010-01-01
Dynamic radiation force has been used in several types of applications, and is performed by modulating ultrasound with different methods. By modulating ultrasound, energy can be transmitted to tissue, in this case a dynamic force to elicit a low frequency cyclic displacement to inspect the material properties of the tissue. In this paper, different types of modulation are explored including amplitude modulation (AM), double sideband suppressed carrier amplitude modulation AM, linear frequency...
Klagyivik, Peter
2009-01-01
Aims: We attempt to revise the period-amplitude (P-A) relationship of Galactic Cepheids based on multi-colour photometric and radial velocity data. Reliable P-A graphs for Galactic Cepheids constructed for the U, B, V, R_C, and I_C photometric bands and pulsational radial velocity variations facilitate investigations of previously poorly studied interrelations between observable amplitudes. The effects of both binarity and metallicity on the observed amplitude, and the dichotomy between short- and long-period Cepheids can both be studied. Results: Large amplitude Cepheids with companions exhibit smaller photometric amplitudes on average than solitary ones, as expected, while s-Cepheids pulsate with an rbitrary (although small) amplitude. The ratio of the observed radial velocity to blue photometric amplitudes, A_V_RAD/A_B, is not as good an indicator of the ulsation mode as predicted theoretically. This may be caused by an incorrect mode assignment to a number of small amplitude Cepheids, which are not ecessa...
Modulational instabilities in discrete lattices
We study analytically and numerically modulational instabilities in discrete nonlinear chains, taking the discrete Klein-Gordon model as an example. We show that discreteness can drastically change the conditions for modulational instability; e.g., at small wave numbers a nonlinear carrier wave is unstable to all possible modulations of its amplitude if the wave amplitude exceeds a certain threshold value. Numerical simulations show the validity of the analytical approach for the initial stage of the time evolution, provided that the harmonics generated by the nonlinear terms are considered. The long-term evolution exhibits chaoticlike states
Singularity Structure of Maximally Supersymmetric Scattering Amplitudes
Arkani-Hamed, Nima; Bourjaily, Jacob L.; Cachazo, Freddy; Trnka, Jaroslav
2014-01-01
We present evidence that loop amplitudes in maximally supersymmetric (N=4) Yang-Mills theory (SYM) beyond the planar limit share some of the remarkable structures of the planar theory. In particular, we show that through two loops, the four-particle amplitude in full N=4 SYM has only logarithmic ...
Production amplitude for a single scalar resonance
We derive a simple expression for the production amplitude of two pseudoscalar mesons involving a single scalar resonance. This amplitude is determined by a combination of Watson's phase δ(s) and another phase ω(s), related to an unambiguous two-meson propagator. With a lagrangian model, we study the σππ system
Finite amplitude dynamic motion of viscoelastic materials.
Yen, H.-C.; Mcintire, L. V.
1972-01-01
It is shown that an integral constitutive relation containing a memory function depending on strain tensor invariants can describe the rheological behavior of finite amplitude oscillatory motion of polymer solutions both qualitatively and quantitatively. Values of the material constants are obtained by a numerical technique of simultaneously curve fitting simple shearing viscosity, first normal stress difference, and small amplitude oscillatory motion data.
Six-Photon Amplitudes in Scalar QED
Bernicot, C; Guillet, J. -Ph.
2007-01-01
The analytical result for the six-photon helicity amplitudes in scalar QED is presented. To compute the loop, a recently developed method based on multiple cuts is used. The amplitudes for QED and $QED^{\\caln=1}$ are also derived using the supersymmetric decomposition linking the three theories.
Scattering Amplitudes via Algebraic Geometry Methods
Søgaard, Mads
Feynman diagrams. The study of multiloop scattering amplitudes is crucial for the new era of precision phenomenology at the Large Hadron Collider (LHC) at CERN. Loop-level scattering amplitudes can be reduced to a basis of linearly independent integrals whose coefficients are extracted from generalized...
Agafonov, A V
2001-01-01
It is proposed to use a dynatron effect to modulate the voltage across the vacuum inverted coaxial diode with magnetic insulation supplied by an external pulsed high-voltage source connected to the modulator via the RL-circuit. Oscillations of the voltage due to oscillating regime of diode charging and/or azimuthal instability of a rotating electron flow simulates back-bombardment electron flow to the cathode and leads to power spikes of secondary emission current exceeding the primary one. As a result,the amplitude of oscillations grows and the system can turn the modulator and its possible applications.
Three particle superstring amplitudes with massive legs
Boels, Rutger H
2012-01-01
On-shell superspaces and associated spinor helicity techniques give an efficient formulation of the Ward identities of on-shell supersymmetry for scattering amplitudes and supply tools to construct their solutions. Based on these techniques in this paper the general solutions of the Ward identities are presented for three particle scattering amplitudes with one, two or three massive legs for simple supersymmetry in ten and eight dimensions. It is shown in examples how these solutions may be used to obtain concrete amplitudes for the closed (IIB) and open superstring in a flat background. Explicit results include all three point amplitudes with one massive leg whose functional form is shown to be dictated completely by super-Poincare symmetry. The resulting surprisingly simple series only involves massive superfields labelled by completely symmetric little group representations. The extension to more general explicit three and higher point amplitudes in string theory is initiated. In appendices the field conte...
New relations for gauge-theory amplitudes
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.
The Lorentzian proper vertex amplitude: Asymptotics
Engle, Jonathan; Zipfel, Antonia
2015-01-01
In previous work, the Lorentzian proper vertex amplitude for a spin-foam model of quantum gravity was derived. In the present work, the asymptotics of this amplitude are studied in the semi-classical limit. The starting point of the analysis is an expression for the amplitude as an action integral with action differing from that in the EPRL case by an extra `projector' term which scales linearly with spins only in the asymptotic limit. New tools are introduced to generalize stationary phase methods to this case. For the case of boundary data which can be glued to a non-degenerate Lorentzian 4-simplex, the asymptotic limit of the amplitude is shown to equal the single Feynman term, showing that the extra term in the asymptotics of the EPRL amplitude has been eliminated.
Multipole modes in deformed nuclei within the finite amplitude method
Kortelainen, M; Nazarewicz, W
2015-01-01
Background: To access selected excited states of nuclei, within the framework of nuclear density functional theory, the quasiparticle random phase approximation (QRPA) is commonly used. Purpose: We present a computationally efficient, fully self-consistent framework to compute the QRPA transition strength function of an arbitrary multipole operator in axially-deformed superfluid nuclei. Methods: The method is based on the finite amplitude method (FAM) QRPA, allowing fast iterative solution of QRPA equations. A numerical implementation of the FAM-QRPA solver module has been carried out for deformed nuclei. Results: The practical feasibility of the deformed FAM module has been demonstrated. In particular, we calculate the quadrupole and octupole strength in a heavy deformed nucleus $^{240}$Pu, without any truncations in the quasiparticle space. To demonstrate the capability to calculate individual QRPA modes, we also compute low-lying negative-parity collective states in $^{154}$Sm. Conclusions: The new FAM imp...
Is the effect of tinnitus on auditory steady-state response amplitude mediated by attention?
Eugen Diesch
2012-05-01
Full Text Available Objectives: The amplitude of the auditory steady-state response (ASSR is enhanced in tinnitus. As ASSR ampli¬tude is also enhanced by attention, the effect of tinnitus on ASSR amplitude could be interpreted as an effect of attention mediated by tinnitus. As attention effects on the N1 are signi¬fi¬cantly larger than those on the ASSR, if the effect of tinnitus on ASSR amplitude were due to attention, there should be similar amplitude enhancement effects in tinnitus for the N1 component of the auditory evoked response. Methods: MEG recordings of auditory evoked responses which were previously examined for the ASSR (Diesch et al. 2010 were analysed with respect to the N1m component. Like the ASSR previously, the N1m was analysed in the source domain (source space projection. Stimuli were amplitude-modulated tones with one of three carrier fre¬quen¬cies matching the tinnitus frequency or a surrogate frequency 1½ octaves above the audio¬metric edge frequency in con¬trols, the audiometric edge frequency, and a frequency below the audio¬metric edge Results: In the earlier ASSR study (Diesch et al., 2010, the ASSR amplitude in tinnitus patients, but not in controls, was significantly larger in the (surrogate tinnitus condition than in the edge condition. In the present study, both tinnitus patients and healthy controls show an N1m-amplitude profile identical to the one of ASSR amplitudes in healthy controls. N1m amplitudes elicited by tonal frequencies located at the audiometric edge and at the (surrogate tinnitus frequency are smaller than N1m amplitudes elicited by sub-edge tones and do not differ among each other. Conclusions: There is no N1-amplitude enhancement effect in tinnitus. The enhancement effect of tinnitus on ASSR amplitude cannot be accounted for in terms of attention induced by tinnitus.
Amplitude regeneration of RZ-DPSK signals in single-pump fiber-optic parametric amplifiers
Peucheret, Christophe; Lorenzen, Michael Rodas; Seoane, Jorge; Noordegraaf, Danny; Nielsen, Carsten Vandel; Grüner-Nielsen, Lars; Rottwitt, Karsten
2009-01-01
The input power tolerance of a single-pump fiber-optic parametric amplifier (FOPA) is experimentally shown to be enhanced for return-to-zero differential phase-shift keying (RZ-DPSK) modulation compared to RZ ON–OFF keying modulation at 40 Gb/s. The improved nonlinear tolerance is exploited to demonstrate amplitude regeneration of a distorted RZ-DPSK signal in a gain-saturated FOPA. An optical signal-to-noise ratio penalty of 3.5 dB after amplitude distortion is shown to be reduced to 0.2 dB ...
Parameters estimation of a noisy sinusoidal signal with time-varying amplitude
Liu, Da-Yan; Perruquetti, Wilfrid
2011-01-01
In this paper, we give estimators of the frequency, amplitude and phase of a noisy sinusoidal signal with time-varying amplitude by using the algebraic parametric techniques introduced by Fliess and Sira-Ramirez. We apply a similar strategy to estimate these parameters by using modulating functions method. The convergence of the noise error part due to a large class of noises is studied to show the robustness and the stability of these methods. We also show that the estimators obtained by modulating functions method are robust to "large" sampling period and to non zero-mean noises.
Polynomial reduction and evaluation of tree- and loop-level CHY amplitudes
Zlotnikov, Michael
2016-01-01
We develop a polynomial reduction procedure that transforms any gauge fixed CHY amplitude integrand for $n$ scattering particles into a $\\sigma$-moduli multivariate polynomial of what we call the $\\textit{standard form}$. We show that a standard form polynomial must have a specific $\\textit{ladder type}$ monomial structure, which has finite size at any $n$, with highest multivariate degree given by $\\frac{(n-3)(n-4)}{2}$. This set of monomials spans a complete basis for polynomials with rational coefficients in kinematic data on the support of scattering equations. Subsequently, at tree and one-loop level, we employ the global residue theorem to derive a prescription that evaluates any CHY amplitude by means of collecting simple residues at infinity only. The prescription is then applied explicitly to some tree and one-loop amplitude examples.
On the Integrand-Reduction Method for Two-Loop Scattering Amplitudes
Mastrolia, Pierpaolo
2011-01-01
We propose a first implementation of the integrand-reduction method for two-loop scattering amplitudes. We show that the residues of the amplitudes on multi-particle cuts are polynomials in the irreducible scalar products involving the loop momenta, and that the reduction of the amplitudes in terms of master integrals can be realized through polynomial fitting of the integrand, without any apriori knowledge of the integral basis. We discuss how the polynomial shapes of the residues determine the basis of master integrals appearing in the final result. We present a four-dimensional constructive algorithm that we apply to planar and non-planar contributions to the 4- and 5-point MHV amplitudes in N=4 SYM. The technique hereby discussed extends the well-established analogous method holding for one-loop amplitudes, and can be considered a preliminary study towards the systematic reduction at the integrand-level of two-loop amplitudes in any gauge theory, suitable for their automated semianalytic evaluation.
DETERMINISTIC COMPONENTS IN THE LIGHT CURVE AMPLITUDE OF Y OPH
About two decades after the discovery of the amplitude decline of the light curve of the classical Cepheid Y Oph, its study is resumed using an increased amount of homogenized data and an extended time base. In our approach, the investigation of different time series concerning the light curve amplitude of Y Oph is not only the reason for the present study, but also a stimulus for developing a coherent methodology for studying long- and short-term variability phenomena in variable stars, taking into account the details of concrete observing conditions: amount of data, data sampling, time base, and individual errors of observational data. The statistical significance of this decreasing trend was estimated by assuming its linearity. We approached the decision-making process by formulating adequate null and alternative hypotheses, and testing the value of the regression line slope for different data sets via Monte Carlo simulations. A variability analysis, through various methods, of the original data and of the residuals obtained after removing the linear trend was performed. We also proposed a new statistical test, based on amplitude spectrum analysis and Monte Carlo simulations, intended to evaluate how detectible is a given (linear) trend in well-defined observing conditions: the trend detection probability. The main conclusion of our study on Y Oph is that, even if the false alarm probability is low enough to consider the decreasing trend to be statistically significant, the available data do not allow us to obtain a reasonably powerful test. We are able to confirm the light curve amplitude decline, and the order of magnitude of its slope with a better statistical substantiation. According to the obtained values of the trend detection probability, it seems that the trend we are dealing with is marked by a low detectibility. Our attempt to find signs of possible variability phenomena at shorter timescales ended by emphasizing the relative constancy of our data, within their precision limits.
Effects of strength training on mechanomyographic amplitude
The aim of the present study was to determine if the patterns of mechanomyographic (MMG) amplitude across force would change with strength training. Twenty-two healthy men completed an 8-week strength training program. During three separate testing visits (pre-test, week 4, and week 8), the MMG signal was detected from the vastus lateralis as the subjects performed isometric step muscle actions of the leg extensors from 10–100% of maximal voluntary contraction (MVC). During pre-testing, the MMG amplitude increased linearly with force to 66% MVC and then plateaued. Conversely, weeks 4 and 8 demonstrated an increase in MMG amplitude up to ∼85% of the subject's original MVC before plateauing. Furthermore, seven of the ten force levels (30–60% and 80–100%) showed a significant decrease in mean MMG amplitude values after training, which consequently led to a decrease in the slope of the MMG amplitude/force relationship. The decreases in MMG amplitude at lower force levels are indicative of hypertrophy, since fewer motor units would be required to produce the same absolute force if the motor units increased in size. However, despite the clear changes in the mean values, analyses of individual subjects revealed that only 55% of the subjects demonstrated a significant decrease in the slope of the MMG amplitude/force relationship. (paper)
Softness and Amplitudes' Positivity for Spinning Particles
Bellazzini, Brando
2016-01-01
We derive positivity bounds for scattering amplitudes of particles with arbitrary spin using unitarity, analyticity and crossing symmetry. The bounds imply the positivity of certain low-energy coefficients of the effective action that controls the dynamics of the light degrees of freedom. We show that low-energy amplitudes strictly softer than $O(p^4)$ do not admit unitary ultraviolet completions unless the theory is free. This enforces a bound on the energy growth of scattering amplitudes in the region of validity of the effective theory. We discuss explicit examples including the Goldstino from spontaneous supersymmetry breaking, and the theory of a spin-1/2 fermion with a shift symmetry.
Form Factor and Boundary Contribution of Amplitude
Huang, Rijun; Feng, Bo
2016-01-01
The boundary contribution of an amplitude in the BCFW recursion relation can be considered as a form factor involving boundary operator and unshifted particles. At the tree-level, we show that by suitable construction of Lagrangian, one can relate the leading order term of boundary operators to some composite operators of N=4 super-Yang-Mills theory, then the computation of form factors is translated to the computation of amplitudes. We compute the form factors of these composite operators through the computation of corresponding double trace amplitudes.
High Energy Hadron Spin Flip Amplitude
Selyugin, O V
2015-01-01
The high energy part of the hadron spin flip amplitude is examined in the framework of the new high energy general structure (HEGS) model of the elastic hadron scattering at high energies. The different forms of the hadron spin flip amplitude are compared in the impact parameters representation. It is shown that the existing experimental data of the proton-proton and proton-antiproton elastic scattering at high energy in the region of the diffraction minimum and at large momentum transfer give support in the presence of the energy-independent part of the hadron spin flip amplitude with the momentum dependence proposed in the works by Galynskii-Kuraev.
This paper investigates the nonlinear vibro-acoustic modulation technique for damage detection in metallic structures. Surface-bonded, low-profile piezoceramic actuators are used to introduce a high-frequency ultrasonic wave and low-frequency modal vibration into an aluminium specimen. The response of the vibro-acoustic interaction is monitored by a third low-profile piezoceramic transducer. In contrast to previous applications analysing the response in the frequency domain, current investigations focus on the instantaneous characteristics of the response using the Hilbert–Huang transform. The study shows that both modulations, i.e. amplitude and frequency, are present in the acoustical responses when the aluminium plate is cracked. The intensity of amplitude modulation correlates far better with crack lengths than the intensity of frequency modulations
Attitude Maneuvers of CTS-like Spacecraft Using PD based Constant-Amplitude Inputs
Edward Halawa
2012-01-01
Full Text Available Attitude maneuvers of a Communication Technology Satellite (CTS-like spacecraft using constant-amplitude thrusters is of great importance. The spacecraft consists of a rigid main body and two symmetrical solar panels. When the panels are large, they cannot be treated as rigid bodies anymore. They are supposed to behave structural flexibility. To discrete their motion, the finite element method is followed. Under constant-amplitude thrusts, steady-state attitude angle oscillations may occur in large amplitude after the maneuvers. Since, the spacecraft should point to the earth precisely, these oscillations must be reduced into small permissible values. To reduce residual attitude angle oscillations, Proportional Derivative (PD based constant-amplitude input shaping logic is proposed to determine time locations of thruster switching. Then, under such inputs, attitude maneuvers of the spacecraft are simulated numerically. Results of simulations show that the precise orientation of the satellite can be achieved.
Scattering equations and global duality of residues
Søgaard, Mads; Zhang, Yang
2016-05-01
We examine the polynomial form of the scattering equations by means of computational algebraic geometry. The scattering equations are the backbone of the Cachazo-He-Yuan (CHY) representation of the S-matrix. We explain how the Bezoutian matrix facilitates the calculation of amplitudes in the CHY formalism, without explicitly solving the scattering equations or summing over the individual residues. Since for n -particle scattering the size of the Bezoutian matrix grows only as (n -3 )×(n -3 ), our algorithm is very efficient for analytic and numeric amplitude computations.
Off-shell amplitudes in superstring theory
Sen, Ashoke [Harish-Chandra Research Institute, Chhatnag Road, Jhusi, Allahabad, 211019 (India)
2015-04-01
Computing the renormalized masses and S-matrix elements in string theory, involving states whose masses are not protected from quantum corrections, requires defining off-shell amplitude with certain factorization properties. While in the bosonic string theory one can in principle construct such an amplitude from string field theory, there is no fully consistent field theory for type II and heterotic string theory. In this paper we give a practical construction of off-shell amplitudes satisfying the desired factorization property using the formalism of picture changing operators. We describe a systematic procedure for dealing with the spurious singularities of the integration measure that we encounter in superstring perturbation theory. This procedure is also useful for computing on-shell amplitudes, as we demonstrate by computing the effect of Fayet-Iliopoulos D-terms in four dimensional heterotic string theory compactifications using this formalism. (copyright 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
Open string amplitudes of closed topological vertex
Takasaki, Kanehisa
2016-01-01
The closed topological vertex is the simplest "off-strip" case of non-compact toric Calabi-Yau threefolds with acyclic web diagrams. By the diagrammatic method of topological vertex, open string amplitudes of topological string theory therein can be obtained by gluing a single topological vertex to an "on-strip" subdiagram of the tree-like web diagram. If non-trivial partitions are assigned to just two parallel external lines of the web diagram, the amplitudes can be calculated with the aid of techniques borrowed from the melting crystal models. These amplitudes are thereby expressed as matrix elements, modified by simple prefactors, of an operator product on the Fock space of 2D charged free fermions. This fermionic expression can be used to derive $q$-difference equations for generating functions of special subsets of the amplitudes. These $q$-difference equations may be interpreted as the defining equation of a quantum mirror curve.
Stora's fine notion of divergent amplitudes
Várilly, Joseph C
2016-01-01
Stora and coworkers refined the notion of divergent quantum amplitude, somewhat upsetting the standard power-counting recipe. This unexpectedly clears the way to new prototypes for free and interacting field theories of bosons of any mass and spin.
Lectures on Scattering Amplitudes in String Theory
Staessens, Wieland
2010-01-01
In these lecture notes, we take a closer look at the calculation of scattering amplitudes for the bosonic string. It is believed that string theories form the UV completions of (super)gravity theories. Support for this claim can be found in the (on-shell) scattering amplitudes of strings. On the other hand, studying these string scattering amplitudes opens a window on the UV behavior of the string theories themselves. In these short set of lectures, we discuss the two-dimensional Polyakov path integral for the string, and its gauge symmetries, the connection to Riemann surfaces and how to obtain some of the simplest string scattering amplitudes. We end with some comments on more advanced topics. For simplicity we limit ourselves to bosonic open string theory in 26 dimensions.
Open String Amplitudes in Various Gauges
Fuji, H; Suzuki, H; Fuji, Hiroyuki; Nakayama, Shinsaku; Suzuki, Hisao
2007-01-01
Recently, Schnabl constructed the analytic solution of the open string tachyon. Subsequently, the absence of the physical states at the vacuum was proved. The development relies heavily on the use of the gauge condition different from the ordinary one. It was shown that the choice of gauge simplifies the analysis drastically. When we perform the calculation of the amplitudes in Schnabl gauge, we find that the off-shell amplitudes of the Schnabl gauge is still very complicated. In this paper, we propose the use of the propagator in the modified Schnabl gauge and show that this modified use of the Schnabl gauge simplifies the computation of the off-shell amplitudes drastically. We also compute the amplitudes of open superstring in this gauge.
The singular behavior of massive QCD amplitudes
We discuss the structure of infrared singularities in on-shell QCD amplitudes with massive partons and present a general factorization formula in the limit of small parton masses. The factorization formula gives rise to an all-order exponentiation of both, the soft poles in dimensional regularization and the large collinear logarithms of the parton masses. Moreover, it provides a universal relation between any on-shell amplitude with massive external partons and its corresponding massless amplitude. For the form factor of a heavy quark we present explicit results including the fixed-order expansion up to three loops in the small mass limit. For general scattering processes we show how our constructive method applies to the computation of all singularities as well as the constant (mass-independent) terms of a generic massive n-parton QCD amplitude up to the next-to-next-to-leading order corrections. (orig.)
Amplitude-Integrated EEG in the Newborn
J. Gordon Millichap
2008-01-01
Th value of amplitude-integrated electroencephalography (aEEG) in the newborn is explored by researchers at Washington University, St Louis; Wilhelmina Children’s Hospital, Utrecht, Netherlands; and Uppsala University Hospital, Sweden.
Open string amplitudes of closed topological vertex
Takasaki, Kanehisa; Nakatsu, Toshio
2016-01-01
The closed topological vertex is the simplest off-strip case of non-compact toric CalabiYau threefolds with acyclic web diagrams. By the diagrammatic method of topological vertex, open string amplitudes of topological string theory therein can be obtained by gluing a single topological vertex to an on-strip subdiagram of the tree-like web diagram. If non-trivial partitions are assigned to just two parallel external lines of the web diagram, the amplitudes can be calculated with the aid of techniques borrowed from the melting crystal models. These amplitudes are thereby expressed as matrix elements, modified by simple prefactors, of an operator product on the Fock space of 2D charged free fermions. This fermionic expression can be used to derive q-difference equations for generating functions of special subsets of the amplitudes. These q-difference equations may be interpreted as the defining equation of a quantum mirror curve.
An analysis of heavy ion scattering amplitudes
A heurisht method is derived for the analysis of light heavy ion systems. It consists in splitting an oscillatory amplitude into subamplitudes each of them being smooth, at least in modulus. Applications are given
Amplitudes for left-handed strings
Siegel, W
2015-01-01
We consider a class of string-like models introduced previously where all modes are left-handed, all states are massless, T-duality is manifest, and only a finite number of orders in the string tension can appear. These theories arise from standard string theories by a singular gauge limit and associated change in worldsheet boundary conditions. In this paper we show how to calculate amplitudes by using the gauge parameter as an infrared regulator. The amplitudes produce the Cachazo-He-Yuan delta-functions after some modular integration; the Mason-Skinner string-like action and amplitudes arise from the zero-tension (infinite-slope) limit. However, without the limit the amplitudes have the same problems as found in the Mason-Skinner formalism.
Amplitude distribution of eigenfunctions in mixed systems
Baecker, Arnd [School of Mathematics, University of Bristol, Bristol (United Kingdom) and BRIMS, Hewlett-Packard Laboratories, Bristol (United Kingdom)]. E-mail: a.backer@bristol.ac.uk; Schubert, Roman [Abteilung Theoretische Physik, Universitaet Ulm, Ulm (Germany)]. E-mail: roman.schubert@physik.uni-ulm.de
2002-01-25
We study the amplitude distribution of irregular eigenfunctions in systems with mixed classical phase space. For an appropriately restricted random wave model, a theoretical prediction for the amplitude distribution is derived and a good agreement with numerical computations for the family of limacon billiards is found. The natural extension of our result to more general systems, e.g. with a potential, is also discussed. (author)
Quartic amplitudes for Minkowski higher spin
Bengtsson, Anders K H
2016-01-01
The problem of finding general quartic interaction terms between fields of higher helicities on the light-front is discussed from the point of view of calculating the corresponding amplitudes directly from the cubic vertices using BCFW recursion. Amplitude based no-go results that has appeared in the literature are reviewed and discussed and it is pointed out how they may perhaps be circumvented.
Modified Amplitude of Gravitational Waves Spectrum
Ghayour, Basem; Suresh, P. K.
2012-01-01
The spectrum of thermal gravitational waves is obtained by including the high frequency thermal gravitons created from extra-dimensional effect and is a new feature of the spectrum. The amplitude and spectral energy density of gravitational waves in thermal vacuum state are found enhanced. The amplitude of the waves get modified in the frequency range (10$^{-16}$ -10 $^{8}$ Hz) but the corresponding spectral energy density is less than the upper bound of various estimated results. With the ad...
Effective gluon interactions from superstring disk amplitudes
In this thesis an efficient method for the calculation of the N-point tree-level string amplitudes is presented. Furthermore it is shown that the six-gluon open-superstring disk amplitude can be expressed by a basis of six triple hypergeometric functions, which encode the full α' dependence. In this connection material for obtaining the α' expansion of these functions is derived. Hereby many Euler-Zagier sums are calculated including multiple harmonic series. (HSI)
Nucleon distribution amplitudes from lattice QCD
Goeckeler, M. [Regensburg Univ. (Germany). Inst. fuer Theoretische Physik; Horsley, R. [Edinburgh Univ. (United Kingdom). School of Physics; Kaltenbrunner, T. [Deutsches Elektronen-Synchrotron (DESY), Zeuthen (DE). John von Neumann-Inst. fuer Computing NIC] (and others)
2008-04-15
We calculate low moments of the leading-twist and next-to-leading twist nucleon distribution amplitudes on the lattice using two flavors of clover fermions. The results are presented in the MS scheme at a scale of 2 GeV and can be immediately applied in phenomenological studies. We find that the deviation of the leading-twist nucleon distribution amplitude from its asymptotic form is less pronounced than sometimes claimed in the literature. (orig.)
Nucleon Distribution Amplitudes from Lattice QCD
We calculate low moments of the leading-twist and next-to-leading-twist nucleon distribution amplitudes on the lattice using two flavors of clover fermions. The results are presented in the MS scheme at a scale of 2 GeV and can be immediately applied in phenomenological studies. We find that the deviation of the leading-twist nucleon distribution amplitude from its asymptotic form is less pronounced than sometimes claimed in the literature
Nucleon distribution amplitudes from lattice QCD
Göckeler, Meinulf; Kaltenbrunner, Thomas; Nakamura, Yoshifumi; Pleiter, Dirk; Rakow, Paul E L; Schäfer, Andreas; Schierholz, Gerrit; Stüben, Hinnerk; Warkentin, Nikolaus; Zanotti, James M
2008-01-01
We calculate low moments of the leading-twist and next-to-leading twist nucleon distribution amplitudes on the lattice using two flavors of clover fermions. The results are presented in the MSbar scheme at a scale of 2 GeV and can be immediately applied in phenomenological studies. We find that the deviation of the leading-twist nucleon distribution amplitude from its asymptotic form is less pronounced than sometimes claimed in the literature.
Effective gluon interactions from superstring disk amplitudes
Oprisa, D.
2006-05-15
In this thesis an efficient method for the calculation of the N-point tree-level string amplitudes is presented. Furthermore it is shown that the six-gluon open-superstring disk amplitude can be expressed by a basis of six triple hypergeometric functions, which encode the full {alpha}' dependence. In this connection material for obtaining the {alpha}' expansion of these functions is derived. Hereby many Euler-Zagier sums are calculated including multiple harmonic series. (HSI)
Employing Helicity Amplitudes for Resummation in SCET
Moult, Ian; Tackmann, Frank J; Waalewijn, Wouter J
2016-01-01
Helicity amplitudes are the fundamental ingredients of many QCD calculations for multi-leg processes. We describe how these can seamlessly be combined with resummation in Soft-Collinear Effective Theory (SCET), by constructing a helicity operator basis for which the Wilson coefficients are directly given in terms of color-ordered helicity amplitudes. This basis is crossing symmetric and has simple transformation properties under discrete symmetries.
Duality between Wilson Loops and Scattering Amplitudes
Henn, Johannes
2008-01-01
We summarise the status of an intriguing new duality between planar maximally helicity violating scattering amplitudes and light-like Wilson loops in N=4 super Yang-Mills. In particular, we focus on the role played by (dual) conformal symmetry, which is made predictive by deriving anomalous conformal Ward identities for the Wilson loops. Assuming the duality, the conformal symmetry of the dual Wilson loops becomes an unexpected new symmetry of scattering amplitudes in N=4 SYM.
Dependence of diffuse ultrasonic backscatter on residual stress in 1080 steel.
Du, Hualong; Turner, Joseph A
2016-04-01
In this article, the effects of residual stress on the ultrasonic scattering in a quenched steel sample are investigated by calculating the change of spatial variance amplitudes of ultrasonic signals after removing residual stress via annealing. The experimental results show that the average spatial variance amplitude decreases by about 11.89% for a scan area on the quenched surface after removing residual stress. This quantity was used to estimate the residual stress based on the developed stress-dependent backscatter model. In addition, the residual stress on the whole scan area was mapped by calculating the change of the spatial variance amplitude for each subarea after annealing, respectively. Diffuse ultrasonic backscatter signals show a high sensitivity to residual stress such that this technique has potential as a non-destructive method for measuring residual stress. PMID:26784273
Amplitudes for Multiple M5 Branes
Czech, Bartlomiej; Rozali, Moshe
2011-01-01
We study N=(n,0) super-Poincare invariant six-dimensional massless and five-dimensional massive on-shell amplitudes. We demonstrate that in six dimensions all possible three-point amplitudes involving tensor multiplets are uniquely determined by super-Poincare invariance and are necessarily embedded in gravitational theories. For non-gravitational amplitudes we consider instead five-dimensional massive amplitudes with N=(2,0) supersymmetry, corresponding to compactifying the theory on a circle. Super-Poincare invariance and constraints motivated by four-dimensional S-duality uniquely fix the amplitude as well as the participating multiplets. The on-shell degrees of freedom are shown to match those of the massive particle states that arise from self-dual strings wrapping a circle. Along the way we find interesting hints of a fermionic symmetry in the (2,0) theory, which accompanies the self-dual tensor gauge symmetry. We also discuss novel theories with (3,0) and (4,0) supersymmetry. The three-point amplitudes...
Modulation properties of VCSEL with intracavity modulator
van Eisden, J.; Yakimov, M.; Tokranov, V.; Varanasi, M.; Mohammed, E. M.; Young, I. A.; Oktyabrsky, S.
2007-02-01
We have studied the modulation properties of VCSEL with intracavity multiple quantum well (MQW) electroabsorption modulator integrated into the top distributed Bragg reflector (DBR) [1]. Small signal analysis of rate equations for loss modulation shows an intrinsic high-frequency roll-off slope of 1/ω instead of 1/ω2 in directly modulated laser diodes, and consequently bandwidths in excess of 40 GHz are obtainable with this configuration [2]. Possible limiting factors to high bandwidth were examined by fitting high frequency characteristics to a multi-pole transfer function, and include RC delay and carrier drift-limited time of flight (TOF) in the modulator intrinsic region. Intracavity loss modulation shows a strong (+20dB) relaxation oscillation resonant feature in both theory and experiment. As demonstrated, this feature can be significantly reduced in amplitude using parasitics. We have extracted relative contribution of TOF and parasitic capacitance by varying the modulator intrinsic region width (105 and 210 nm) and lateral size of the modulator (18 and 12μm). It was estimated that the small size modulator exhibits parasitics f -3dB at 8GHz. To estimate the carrier TOF contribution to bandwidth limits, low temperature growth of a 210 nm absorber i-region and MQW was employed to reduce photogenerated carrier lifetime. Bandwidth limitations were found to be mostly due to diode and metallization capacitances, in addition to one pole set by the optoelectronic resonance frequency. We have used p-modulation doping of the gain region to increase the relaxation frequency. Pronounced active Q-switching was observed, yielding pulse widths of 40 ps at a 4 GHz rate.
Gang Fang
2009-01-01
Abstract: In this paper, we discuss the upgrade problem of module, and introduce the concepts of the power module, regular power module and uniform power module. We give some results of them． Key words: power group; power module; regular power module; uniform power module
Single SOA based simultaneous amplitude regeneration for WDM-PDM RZ-PSK signals.
Wu, Wenhan; Yu, Yu; Zou, Bingrong; Yang, Weili; Zhang, Xinliang
2013-03-25
We propose and demonstrate all-optical amplitude regeneration for the wavelength division multiplexing and polarization division multiplexing (WDM-PDM) return-to-zero phase shift keying (RZ-PSK) signals using a single semiconductor optical amplifier (SOA) and subsequent filtering. The regeneration is based on the cross phase modulation (XPM) effect in the saturated SOA and the subsequent narrow filtering. The spectrum of the distorted signal can be broadened due to the phase modulation induced by the synchronous optical clock signal. A narrow band pass filter is utilized to extract part of the broadened spectrum and remove the amplitude noise, while preserving the phase information. The working principle for multi-channel and polarization orthogonality preserving is analyzed. 4-channel dual polarization signals can be simultaneously amplitude regenerated without introducing wavelength and polarization demultiplexing. An average power penalty improvement of 1.75dB can be achieved for the WDM-PDM signals. PMID:23546053
Understanding and Ameliorating Non-Linear Phase and Amplitude Responses in AMCW Lidar
John P. Godbaz
2011-12-01
Full Text Available Amplitude modulated continuous wave (AMCW lidar systems commonly suffer from non-linear phase and amplitude responses due to a number of known factors such as aliasing and multipath inteference. In order to produce useful range and intensity information it is necessary to remove these perturbations from the measurements. We review the known causes of non-linearity, namely aliasing, temporal variation in correlation waveform shape and mixed pixels/multipath inteference. We also introduce other sources of non-linearity, including crosstalk, modulation waveform envelope decay and non-circularly symmetric noise statistics, that have been ignored in the literature. An experimental study is conducted to evaluate techniques for mitigation of non-linearity, and it is found that harmonic cancellation provides a significant improvement in phase and amplitude linearity.
Effects of low-frequency biasing on spontaneous otoacoustic emissions: Frequency modulation
Bian, Lin
2008-01-01
It was previously reported that low-frequency biasing of cochlear structures can suppress and modulate the amplitudes of spontaneous otoacoustic emissions (SOAEs) in humans [Bian, L. and Watts, K. L. (2008). “Effects of low-frequency biasing on spontaneous otoacoustic emissions: Amplitude modulation,” J. Acoust. Soc. Am. 123, 887–898]. In addition to amplitude modulation, the bias tone produced an upward shift of the SOAE frequency and a frequency modulation. These frequency effects usually o...
Scattering amplitudes in open superstring theory
Schlotterer, Oliver
2011-07-15
The present thesis deals with the theme field of the scattering amplitudes in theories of open superstrings. Especially two different formalisms for the handling of superstrings are introduced and applied for the calaculation of tree-level amplitudes - the Ramond- Neveu-Schwarz (RNS) and the Pure-Spinor (PS) formalism. The RNS approach is proved as flexible in order to describe compactification of the initially ten flat space-time dimensions to four dimensions. We solve the technical problems, which result from the interacting basing world-sheet theory with conformal symmetry. This is used to calculate phenomenologically relevant scattering amplitudes of gluons and quarks as well as production rates of massive harmonic vibrations, which were already identified as virtual exchange particles on the massless level. In the case of a low string mass scale in the range of some Tev the string-specific signatures in parton collisions can be observed in the near future in the LHC experiment at CERN and indicated as first experimental proof of the string theory. THose string effects occur universally for a wide class of string ground states respectively internal geometries and represent an elegant way to avoid the so-called landscape problem of the string theory. A further theme complex in this thesis is based on the PS formalism, which allows a manifestly supersymmetric treatment of scattering amplitudes in ten space-time dimension with sixteen supercharges. We introduce a family of superfields, which occur in massless amplitudes of the open string and can be naturally identified with diagrams of three-valued knots. Thereby we reach not only a compact superspace representation of the n-point field-theory amplitude but can also write the complete superstring n-point amplitude as minimal linear combination of partial amplitudes of the field theory as well as hypergeometric functions. The latter carry the string effects and are analyzed from different perspectives, above all 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
The present thesis deals with the theme field of the scattering amplitudes in theories of open superstrings. Especially two different formalisms for the handling of superstrings are introduced and applied for the calaculation of tree-level amplitudes - the Ramond- Neveu-Schwarz (RNS) and the Pure-Spinor (PS) formalism. The RNS approach is proved as flexible in order to describe compactification of the initially ten flat space-time dimensions to four dimensions. We solve the technical problems, which result from the interacting basing world-sheet theory with conformal symmetry. This is used to calculate phenomenologically relevant scattering amplitudes of gluons and quarks as well as production rates of massive harmonic vibrations, which were already identified as virtual exchange particles on the massless level. In the case of a low string mass scale in the range of some Tev the string-specific signatures in parton collisions can be observed in the near future in the LHC experiment at CERN and indicated as first experimental proof of the string theory. THose string effects occur universally for a wide class of string ground states respectively internal geometries and represent an elegant way to avoid the so-called landscape problem of the string theory. A further theme complex in this thesis is based on the PS formalism, which allows a manifestly supersymmetric treatment of scattering amplitudes in ten space-time dimension with sixteen supercharges. We introduce a family of superfields, which occur in massless amplitudes of the open string and can be naturally identified with diagrams of three-valued knots. Thereby we reach not only a compact superspace representation of the n-point field-theory amplitude but can also write the complete superstring n-point amplitude as minimal linear combination of partial amplitudes of the field theory as well as hypergeometric functions. The latter carry the string effects and are analyzed from different perspectives, above all with regards to the duality between group-theoretical and kinematic contributions to tree-level amplitudes observed in the field theory.
Three particle superstring amplitudes with massive legs
Boels, Rutger H.
2012-06-01
On-shell superspaces and associated spinor helicity techniques give an efficient formulation of the Ward identities of on-shell supersymmetry for scattering amplitudes and supply tools to construct their solutions. Based on these techniques in this paper the general solutions of the Ward identities are presented for three particle scattering amplitudes with one, two or three massive legs for simple supersymmetry in ten and eight dimensions. It is shown in examples how these solutions may be used to obtain concrete amplitudes for the closed (IIB) and open superstring in a flat background. Explicit results include all three point amplitudes with one massive leg whose functional form is shown to be dictated completely by super-Poincare symmetry. The resulting surprisingly simple series only involves massive superfields labelled by completely symmetric little group representations. The extension to more general explicit three and higher point amplitudes in string theory is initiated. In appendices the field content of the fundamental massive superfields of the open and closed superstring are listed in terms of the Dynkin labels of a variety of groups which may be of independent interest.
Evaluation of Cavitation Characteristics of 5083-O Al Alloy with Amplitude
With recent advances in engineering and technology, a damage on industrial machinery performing high-speed and high-power requirements has become a problem. There is an increasing possibility of cavitation damage, especially in pumps, propellers and high-speed vessels in a flowing liquid accordingly. There are several factors affecting cavitation damage on materials, including viscosity, pressure, temperature, amplitude applied. In this study, effects of cavity pressure in seawater on the damage for 5083-O aluminium alloy were evaluated by modulating amplitude. Trend of the damage with respect to time and amplitude was analyzed comparatively, and surface degradation of specimens was investigated by using Scanning Electron Microscope(SEM) and 3D microscope. The result reveals that the amount of the damage increased consistently with the increase in time and amplitude while the plastic deformation zone where no appreciable damage occurred was in less than 30 minutes
Perturbative type II amplitudes for BPS interactions
Basu, Anirban
2015-01-01
We consider the perturbative contributions to the R^4, D^4 R^4 and D^6 R^4 interactions in toroidally compactified type II string theory. These BPS interactions do not receive perturbative contributions beyond genus three. We derive Poisson equations satisfied by these moduli dependent string amplitudes. These T--duality invariant equations have eigenvalues that are completely determined by the structure of the integrands of the multi--loop amplitudes. The source terms are given by boundary terms of the moduli space of Riemann surfaces corresponding to both separating and non--separating nodes. These are determined directly from the string amplitudes, as well as from the logarithmic divergences of maximal supergravity. We explicitly solve these Poisson equations in nine and eight dimensions.
Perturbative type II amplitudes for BPS interactions
Basu, Anirban
2016-02-01
We consider the perturbative contributions to the {{ R }}4, {D}4{{ R }}4 and {D}6{{ R }}4 interactions in toroidally compactified type II string theory. These BPS interactions do not receive perturbative contributions beyond genus three. We derive Poisson equations satisfied by these moduli dependent string amplitudes. These T-duality invariant equations have eigenvalues that are completely determined by the structure of the integrands of the multi-loop amplitudes. The source terms are given by boundary terms of the moduli space of Riemann surfaces corresponding to both separating and non-separating nodes. These are determined directly from the string amplitudes, as well as from U-duality constraints and logarithmic divergences of maximal supergravity. We explicitly solve these Poisson equations in nine and eight-dimensions.
Duality and effective amplitudes in quantum chromodynamics
This work is an attempt to relate the partonic and hadronic phases of strong interactions by means of a model of effective string amplitudes which take into account color coherence without the need to restrict the phase-space. The basic idea of this approach is to construct, from open superstrings, string amplitudes which give, at the zero slope limit, QCD amplitudes. The running parameters (coupling and slope) of the model are constrained by perturbative QCD and by the consistency of string quantization. When the running slope becomes equal to the hadronic one, the model can be used in the hadronic sector. This approach could provide some hints about the effective string theory of QCD, and a better understanding of the parton-hadron duality
Relativistic amplitudes in terms of wave functions
In the framework of the invariant diagram technique which arises at the formulation of the fueld theory on the light front the question about conditions at which the relativistic amplitudes may be expressed through the wave functions is investigated. The amplitudes obtained depend on four-vector ω, determining the light front surface. The way is shown to find such values of the four-vector ω, at which the contribution of diagrams not expressed through wave functions is minimal. The investigation carried out is equivalent to the study of the dependence of amplitudes of the old-fashioned perturbation theory in the in the infinite momentum frame on direction of the infinite momentum
Amplitude dependent damping from granular viscoelastics
The ability of a granular medium to dissipate vibrational energy is studied at different frequencies and amplitudes. The filler comprises relatively large particles with significant viscoelasticity and is placed in a rectangular box-shaped container and vibrated perpendicular to the direction of gravity. The performance of a model based on wave behaviour that is suitable for very low amplitude vibrations is compared with discrete elements and experimental results. Frequency dependent behaviour for the viscoelastic material is taken into account. The effects of vibration amplitude on performance are considered carefully especially at the point where particles begin to move relative to each other. One interesting finding is that internal and interface loss mechanisms are closely interrelated reduction in internal loss increases the mobility of individual particles and therefore more energy dissipation via friction. As a result, the overall effectiveness of the granular medium is less sensitive to material and configurationally parameters than might be expected.
Analytic Representations of Yang-Mills Amplitudes
Bjerrum-Bohr, N E J; Damgaard, Poul H; Feng, Bo
2016-01-01
Scattering amplitudes in Yang-Mills theory can be represented in the formalism of Cachazo, He and Yuan (CHY) as integrals over an auxiliary projective space---fully localized on the support of the scattering equations. Because solving the scattering equations is difficult and summing over the solutions algebraically complex, a method of directly integrating the terms that appear in this representation has long been sought. We solve this important open problem by first rewriting the terms in a manifestly Mobius-invariant form and then using monodromy relations (inspired by analogy to string theory) to decompose terms into those for which combinatorial rules of integration are known. The result is a systematic procedure to obtain analytic, covariant forms of Yang-Mills tree-amplitudes for any number of external legs and in any number of dimensions. As examples, we provide compact analytic expressions for amplitudes involving up to six gluons of arbitrary helicities.
Scaling of saturation amplitudes in baroclinic instability
By using finite-amplitude conservation laws for pseudomomentum and pseudoenergy, rigorous upper bounds have been derived on the saturation amplitudes in baroclinic instability for layered and continuously-stratified quasi-geostrophic models. Bounds have been obtained for both the eddy energy and the eddy potential enstrophy. The bounds apply to conservative (inviscid, unforced) flow, as well as to forced-dissipative flow when the dissipation is proportional to the potential vorticity. This approach provides an efficient way of extracting an analytical estimate of the dynamical scalings of the saturation amplitudes in terms of crucial non-dimensional parameters. A possible use is in constructing eddy parameterization schemes for zonally-averaged climate models. The scaling dependences are summarized, and compared with those derived from weakly-nonlinear theory and from baroclinic-adjustment estimates
Online tracking of instantaneous frequency and amplitude of dynamical system response
Frank Pai, P.
2010-05-01
This paper presents a sliding-window tracking (SWT) method for accurate tracking of the instantaneous frequency and amplitude of arbitrary dynamic response by processing only three (or more) most recent data points. Teager-Kaiser algorithm (TKA) is a well-known four-point method for online tracking of frequency and amplitude. Because finite difference is used in TKA, its accuracy is easily destroyed by measurement and/or signal-processing noise. Moreover, because TKA assumes the processed signal to be a pure harmonic, any moving average in the signal can destroy the accuracy of TKA. On the other hand, because SWT uses a constant and a pair of windowed regular harmonics to fit the data and estimate the instantaneous frequency and amplitude, the influence of any moving average is eliminated. Moreover, noise filtering is an implicit capability of SWT when more than three data points are used, and this capability increases with the number of processed data points. To compare the accuracy of SWT and TKA, Hilbert-Huang transform is used to extract accurate time-varying frequencies and amplitudes by processing the whole data set without assuming the signal to be harmonic. Frequency and amplitude trackings of different amplitude- and frequency-modulated signals, vibrato in music, and nonlinear stationary and non-stationary dynamic signals are studied. Results show that SWT is more accurate, robust, and versatile than TKA for online tracking of frequency and amplitude.
Simulation of Digital Modulation Techniques Using MATLAB
Neha Sharma, Yogendra Yadav
2012-01-01
In Digital modulation the message signal is in the digital form and the carrier wave is in sinusoidal form. In this technique the Amplitude, Frequency or Phase of carrier varies according to message (Baseband) signal. There are various type of digital modulation technique like Amplitude Shift Keying (ASK), Phase Shift Keying (PSK), Frequency Shift Keying (FSK), Quadature Phase Shift Keying (QPSK), Differential Phase Shift Keying (DPSK) and other digital demodulation technique. Simulation is t...
Magnetization of compositionally modulated CuNi films
We report static magnetization measurements on the compositionally modulated ferromagnetic alloy Cu/Ni, which, contrary to earlier ferromagnetic resonance measurements, show the moment per Ni atom is reduced relative to pure Ni. The low-temperature magnetization is found to vary linearly with modulation amplitude, but, surprisingly, the Curie temperature is found to be almost amplitude independent
Massive QCD amplitudes at higher orders
We consider the factorization properties of on-shell QCD amplitudes with massive partons in the limit when all kinematical invariants are large compared to the parton mass and discuss the structure of their infrared singularities. The dimensionally regulated soft poles and the large collinear logarithms of the parton masses exponentiate to all orders. Based on this factorization a simple relation between massless and massive scattering amplitudes in gauge theories can be established. We present recent applications of this relation for the calculation of the two-loop virtual QCD corrections to the hadro-production of heavy quarks. (orig.)
Dual amplitude pulse generator for radiation detectors
Hoggan, Jerry M. (Idaho Falls, ID); Kynaston, Ronnie L. (Blackfoot, ID); Johnson, Larry O. (Island Park, ID)
2001-01-01
A pulsing circuit for producing an output signal having a high amplitude pulse and a low amplitude pulse may comprise a current source for providing a high current signal and a low current signal. A gate circuit connected to the current source includes a trigger signal input that is responsive to a first trigger signal and a second trigger signal. The first trigger signal causes the gate circuit to connect the high current signal to a pulse output terminal whereas the second trigger signal causes the gate circuit to connect the low current signal to the pulse output terminal.
Microwave Imaging using Amplitude-only Data
Rubk, Tonny; Zhurbenko, Vitaliy
2010-01-01
This paper discuss how the performance of an imaging system is affected when the phase information of the measurements are removed from the data, leaving only amplitude information as input for the imaging algorithm. Simulated data are used for this purpose, and the images resulting from using...... amplitude-only data are compared with images obtained using the same data sets in which the phase information has been retained. In addition to this, some modifications for the imaging algorithm is presented which to some extent counters the effects of excluding the phase information in the reconstruction....
Amplitude Equations for Electrostatic Waves: multiple species
Crawford, John David; Jayaraman, Anandhan
1997-01-01
The amplitude equation for an unstable electrostatic wave is analyzed using an expansion in the mode amplitude $A(t)$. In the limit of weak instability, i.e. $\\gamma\\to 0^+$ where $\\gamma$ is the linear growth rate, the nonlinear coefficients are singular and their singularities predict the dependence of $A(t)$ on $\\gamma$. Generically the scaling $|A(t)|=\\gamma^{5/2}r(\\gamma t)$ as $\\gamma\\to 0^+$ is required to cancel the coefficient singularities to all orders. This result predicts the ele...
A Method and an Apparatus for Generating a Phase-Modulated Wave Front of Electromagnetic Radiation
The present invention provides a method and a system for generating a phase-modulated wave front. According to the present invention, the spatial phase-modulation is not performed on the different parts of the wave front individually as in known POSLMs. Rather, the spatial phase-modulation of the...... present invention is performed by generating an amplitude modulation in the wave front, Fourier or Fresnel transforming the amplitude modulated wave front, filtering Fourier or Fresnel components of the Fourier or Fresnel distribution with a spatial filter such as a phase contrast filter, and regenerating...... the wave front whereby the initial amplitude modulation has transformed into a phase-modulation....
Amplitude regeneration of RZ-DPSK signals in single-pump fiber-optic parametric amplifiers
Peucheret, Christophe; Lorenzen, Michael Rodas; Seoane, Jorge; Noordegraaf, Danny; Nielsen, Carsten Vandel; Grner-Nielsen, Lars; Rottwitt, Karsten
2009-01-01
The input power tolerance of a single-pump fiber-optic parametric amplifier (FOPA) is experimentally shown to be enhanced for return-to-zero differential phase-shift keying (RZ-DPSK) modulation compared to RZ ONOFF keying modulation at 40 Gb/s. The improved nonlinear tolerance is exploited to...... demonstrate amplitude regeneration of a distorted RZ-DPSK signal in a gain-saturated FOPA. An optical signal-to-noise ratio penalty of 3.5 dB after amplitude distortion is shown to be reduced to 0.2 dB after the FOPA, thus clearly demonstrating the regenerative nature of saturated FOPAs for RZ-DPSK modulation....
Spectral Amplitude Coding (SAC)-OCDMA Network with 8DPSK
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.
On Calculation of Amplitudes in Quantum Electrodynamics
Karplyuk, Kostyantyn
2012-01-01
A new method of calculation of amplitudes of different processes in quantum electrodynamics is proposed. The method does not use the Feynman technique of trace of product of matrices calculation. The method strongly simplifies calculation of cross sections for different processes. The effectiveness of the method is shown on the cross-section calculation of Coulomb scattering, Compton scattering and electron-positron annihilation.
Fatigue Reliability under Multiple-Amplitude Loads
Talreja, R.
1979-01-01
A method to determine the fatigue of structures subjected to multiple-amplitude loads is presented. Unlike the more common cumulative damage methods, which are usually based on fatigue life data, the proposed method is based on tensile strength data. Assuming the Weibull distribution for the...
Coherent states, transition amplitudes and embeddings
Berceanu, S
1997-01-01
The transition amplitudes between coherent states on a coherent state manifold are expressed in terms of the embedding of the coherent state manifold into a projective Hilbert space. Consequences for the dimension of projective Hilbert space and a simple geometric interpretation of Calabi's diastasis follows.
Particle Distribution Modification by Low Amplitude Modes
White, R. B.; Gorelenkov, N.; Heidbrink, W. W.; Van Zeeland, M. A.
2009-08-28
Modification of a high energy particle distribution by a spectrum of low amplitude modes is investigated using a guiding center code. Only through resonance are modes effective in modifying the distribution. Diagnostics are used to illustrate the mode-particle interaction and to find which effects are relevant in producing significant resonance, including kinetic Poincare plots and plots showing those orbits with time averaged mode-particle energy transfer. Effects of pitch angle scattering and drag are studied, as well as plasma rotation and time dependence of the equilibrium and mode frequencies. A specific example of changes observed in a DIII-D deuterium beam distribution in the presence of low amplitude experimentally validated Toroidal Alfven (TAE) eigenmodes and Reversed Shear Alfven (RSAE) eigenmodes is examined in detail. Comparison with experimental data shows that multiple low amplitude modes can account for significant modification of high energy beam particle distributions. It is found that there is a stochastic threshold for beam profile modification, and that the experimental amplitudes are only slightly above this threshold.
Scattering amplitudes in super-renormalizable gravity
Don, Pietro; Giaccari, Stefano; Modesto, Leonardo; Rachwal, Leslaw; Zhu, Yiwei
2015-08-01
We explicitly compute the tree-level on-shell four-graviton amplitudes in four, five and six dimensions for local and weakly nonlocal gravitational theories that are quadratic in both, the Ricci and scalar curvature with form factors of the d'Alembertian operator inserted between. More specifically we are interested in renormalizable, super-renormalizable or finite theories. The scattering amplitudes for these theories turn out to be the same as the ones of Einstein gravity regardless of the explicit form of the form factors. As a special case the four-graviton scattering amplitudes in Weyl conformal gravity are identically zero. Using a field redefinition, we prove that the outcome is correct for any number of external gravitons (on-shell n-point functions) and in any dimension for a large class of theories. However, when an operator quadratic in the Riemann tensor is added in any dimension (with the exception of the Gauss-Bonnet term in four dimensions) the result is completely altered, and the scattering amplitudes depend on all the form factors introduced in the action.
Optical twists in phase and amplitude
Daria, Vincent R.; Palima, Darwin; Glückstad, Jesper
2011-01-01
Light beams with helical phase profile correspond to photons having orbital angular momentum (OAM). A Laguerre-Gaussian (LG) beam is an example where its helical phase sets a phase-singularity at the optical axis and forms a ring-shaped transverse amplitude profile. Here, we describe a unique beam...
Semileptonic Bc decays and charmonium distribution amplitude
In this paper we study the semileptonic decays of the Bc meson in the light-cone sum rule (LCSR) approach. The result for each channel depends on the corresponding distribution amplitude (DA) of the final meson. For the case of Bc decaying into a pseudoscalar meson, to twist-3 accuracy only the leading twist distribution amplitude is involved if we start from a chiral current. If we choose a suitable chiral current in the vector meson case, the main twist-3 contributions are also eliminated and we can consider the leading twist contribution only. The leading twist distribution amplitudes of the charmonium and other heavy mesons are given by a model approach in a reasonable way. Employing this charmonium distribution amplitude we find a cross section ?(e+e-?J/?+?c)?22.8 fb that is consistent with Belle and BaBar data. Based on this model, we calculate the form factors for various Bc decay modes in the corresponding regions. Extrapolating the form factors to the whole kinetic regions, we get the decay widths and branching ratios for various Bc decay modes including their ? modes when they are kinematically accessible. (orig.)
Kaon decay amplitudes using staggered fermions
A status report is given of an attempt, using staggered fermions to calculate the real and imaginary parts of the amplitudes for K → ππ,. Semi-quantitative results are found for the imaginary parts, and these suggest that ε' might be smaller than previously expected in the standard model
Hyperlogarithms and periods in Feynman amplitudes
Todorov, Ivan
2016-01-01
The role of hyperlogarithms and multiple zeta values (and their generalizations) in Feynman amplitudes is being gradually recognized since the mid 1990's. The present lecture provides a concise introduction to a fast developing subjects that attracts the attention to a wide range of specialists - from number theorists to particle physicists.
Amplitude Correction Factors of KVN Observations
Lee, Sang-Sung; Oh, Chung Sik; Kim, Hyo Ryoung; Kim, Jongsoo; Jung, Taehyun; Oh, Se-Jin; Roh, Duk-Gyoo; Jung, Dong-Kyu; Yeom, Jae-Hwan
2015-01-01
We report results of investigation of amplitude calibration for very long baseline interferometry (VLBI) observations with Korean VLBI Network (KVN). Amplitude correction factors are estimated based on comparison of KVN observations at 22~GHz correlated by Daejeon hardware correlator and DiFX software correlator in Korea Astronomy and Space Science Institute (KASI) with Very Long Baseline Array (VLBA) observations at 22~GHz by DiFX software correlator in National Radio Astronomy Observatory (NRAO). We used the observations for compact radio sources, 3C~454.3 and NRAO~512, which are almost unresolved for baselines in a range of 350-477~km. Visibility data of the sources obtained with similar baselines at KVN and VLBA are selected, fringe-fitted, calibrated, and compared for their amplitudes. We found that visibility amplitudes of KVN observations should be corrected by factors of 1.10 and 1.35 when correlated by DiFX and Daejeon correlators, respectively. These correction factors are attributed to the combinat...
Generalised Unitarity for Dimensionally Regulated Amplitudes
Bobadilla, W J Torres; Mastrolia, P; Mirabella, E
2015-01-01
We present a novel set of Feynman rules and generalised unitarity cut-conditions for computing one-loop amplitudes via d-dimensional integrand reduction algorithm. Our algorithm is suited for analytic as well as numerical result, because all ingredients turn out to have a four-dimensional representation. We will apply this formalism to NLO QCD corrections.
Calculating real Delbrueck amplitudes on parallel processors
Kahane, S. (Physics Dept., Nuclear Research Center-Negev, Beer Sheva (Israel))
1991-12-01
Calculation of the real Delbrueck scattering amplitudes is parallelized by concurrent evaluation of 20 four-dimensional integrals. Two approaches were used: (a) a farm of master and workers tasks, and (b) the Cubix concept of parallelization. We discuss load balancing, timing and the efficiency of the implementation. (orig.).
Calculating real Delbrck amplitudes on parallel processors
Kahane, Sylvian
1991-12-01
Calculation of the real Delbrck scattering amplitudes is parallelized by concurent evaluation of 20 four-dimensional integrals. Two approaches were used: (a) a farm of master and workers tasks, and (b) the Cubix concept of parallelization. We discuss load balancing, timing and the efficiency of the implementation.
Calculating real Delbrueck amplitudes on parallel processors
Calculation of the real Delbrueck scattering amplitudes is parallelized by concurrent evaluation of 20 four-dimensional integrals. Two approaches were used: (a) a farm of master and workers tasks, and (b) the Cubix concept of parallelization. We discuss load balancing, timing and the efficiency of the implementation. (orig.)
Attenuation of ground-motion spectral amplitudes in southeastern Australia
Allen, T.I.; Cummins, P.R.; Dhu, T.; Schneider, J.F.
2007-01-01
A dataset comprising some 1200 weak- and strong-motion records from 84 earthquakes is compiled to develop a regional ground-motion model for southeastern Australia (SEA). Events were recorded from 1993 to 2004 and range in size from moment magnitude 2.0 ??? M ??? 4.7. The decay of vertical-component Fourier spectral amplitudes is modeled by trilinear geometrical spreading. The decay of low-frequency spectral amplitudes can be approximated by the coefficient of R-1.3 (where R is hypocentral distance) within 90 km of the seismic source. From approximately 90 to 160 km, we observe a transition zone in which the seismic coda are affected by postcritical reflections from midcrustal and Moho discontinuities. In this hypocentral distance range, geometrical spreading is approximately R+0.1. Beyond 160 km, low-frequency seismic energy attenuates rapidly with source-receiver distance, having a geometrical spreading coefficient of R-1.6. The associated regional seismic-quality factor can be expressed by the polynomial: log Q(f) = 3.66 - 1.44 log f + 0.768 (log f)2 + 0.058 (log f)3 for frequencies 0.78 ??? f ??? 19.9 Hz. Fourier spectral amplitudes, corrected for geometrical spreading and anelastic attenuation, are regressed with M to obtain quadratic source scaling coefficients. Modeled vertical-component displacement spectra fit the observed data well. Amplitude residuals are, on average, relatively small and do not vary with hypocentral distance. Predicted source spectra (i.e., at R = 1 km) are consistent with eastern North American (ENA) Models at low frequencies (f less than approximately 2 Hz) indicating that moment magnitudes calculated for SEA earthquakes are consistent with moment magnitude scales used in ENA over the observed magnitude range. The models presented represent the first spectral ground-motion prediction equations develooed for the southeastern Australian region. This work provides a useful framework for the development of regional ground-motion relations for earthquake hazard and risk assessment in SEA.
The modulational instability of colinear waves
A brief review is given of the modulational instability of a single wave. Some aspects of the modulational instability of two colinear waves are then studied. In general, the waves are modulationally unstable with a maximal growth rate which is larger than the modulational growth rate of either wave alone. Moreover, waves which are modulationally stable by themselves are often unstable in the other's presence. This is true for both copropagating and counterpropagating waves. An important property of an instability is whether it is absolute of convective in nature. The modulational instability of two equal-amplitude copropagating waves is usually, but not always, convective. The modulational instability of two equal-amplitude counter-propagating waves is always absolute. Some applications of current interest are discussed. (orig.)
Absolute frequency references at 1529 nm and 1560 nm using modulation transfer spectroscopy
de Escobar, Y Natali Martinez; Coop, Simon; Vanderbruggen, Thomas; Kaczmarek, Krzysztof T; Mitchell, Morgan W
2015-01-01
We demonstrate a double optical frequency reference (1529 nm and 1560 nm) for the telecom C-band using $^{87}$Rb modulation transfer spectroscopy. The two reference frequencies are defined by the 5S$_{1/2} F=2 \\rightarrow $ 5P$_{3/2} F'=3$ two-level and 5S$_{1/2} F=2 \\rightarrow $ 5P$_{3/2} F'=3 \\rightarrow $ 4D$_{5/2} F"=4$ ladder transitions. We examine the sensitivity of the frequency stabilization to probe power and magnetic field fluctuations, calculate its frequency shift due to residual amplitude modulation, and estimate its shift due to gas collisions. The short-term Allan deviation was estimated from the error signal slope for the two transitions. Our scheme provides a simple and high performing system for references at these important wavelengths. We estimate an absolute accuracy of $\\sim$ 1 kHz is realistic.
Absolute frequency references at 1529 and 1560 nm using modulation transfer spectroscopy.
Martinez de Escobar, Y Natali; Palacios lvarez, Silvana; Coop, Simon; Vanderbruggen, Thomas; Kaczmarek, Krzysztof T; Mitchell, Morgan W
2015-10-15
We demonstrate a double optical frequency reference (1529 and 1560 nm) for the telecom C-band using 87Rb modulation transfer spectroscopy. The two reference frequencies are defined by the 5S(1/2)F=2?5P(3/2)F'=3 two-level and 5S(1/2)F=2?5P(3/2)F'=3?4D(5/2)F''=4 ladder transitions. We examine the sensitivity of the frequency stabilization to probe power and magnetic field fluctuations, calculate its frequency shift due to residual amplitude modulation, and estimate its shift due to gas collisions. The short-term Allan deviation was estimated from the error signal slope for the two transitions. Our scheme provides a simple and high performing system for references at these important wavelengths. We estimate that an absolute accuracy of ?1 kHz is realistic. PMID:26469606
Modulations in the light of the firefly
Anurup Gohain Barua
2013-03-01
Continuous light could be produced from the firefly by making it inhale vapours of ethyl acetate. Here we perform such a control experiment on the Indian species of the firefly Luciola praeusta Kiesenwetter 1874 (Coleoptera : Lampyridae : Luciolinae), and analyse the light in the microsecond time scale. The amplitude of the continuous train of triangular pulses is apparently altered in accordance with the instantaneous values of a hypothetical signal, which exhibits pulse amplitude modulation (PAM). In addition to sampling in amplitude, this scheme apparently provides sampling in time, representing pulse width modulation (PWM). A Fourier transform spectrum of this waveform shows the `carrier’ frequency and the accompanying `side bands’.
Stabilization of the hypersonic boundary layer by finite-amplitude streaks
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.
Kinematic numerators and a double-copy formula for N=4 super-Yang-Mills residues
Litsey, Sean; Stankowicz, James
2014-07-01
Recent work by Cachazo et al.arXiv:1309.0885 shows that connected prescription residues obey the global identities of N=4 super-Yang-Mills amplitudes. In particular, they obey the Bern-Carrasco-Johansson (BCJ) amplitude identities. Here we offer a new way of interpreting this result via objects that we call residue numerators. These objects behave like the kinematic numerators introduced by BCJ except that they are associated with individual residues. In particular, these new objects satisfy a double-copy formula relating them to the residues appearing in recently discovered analogs of the connected prescription integrals for N=8 supergravity. Along the way, we show that the BCJ amplitude identities are equivalent to the consistency condition that allows kinematic numerators to be expressed as amplitudes using a generalized inverse.
Evaluation of the CHY Gauge Amplitude
Lam, C S
2016-01-01
The Cachazo-He-Yuan (CHY) formula for $n$-gluon scattering is known to give the same amplitude as the one obtained from Feynman diagrams, though the former contains neither vertices nor propagators explicitly. The equivalence was shown by indirect means, not by a direct evaluation of the $(n\\! - \\!3)$-dimensional integral in the CHY formula. The purpose of this paper is to discuss how such a direct evaluation can be carried out. There are two basic difficulties in the calculation: how to handle the large number of terms in the reduced Pfaffian, and how to carry out the integrations in the presence of a $\\sigma$-dependence much more complicated than the Parke-Taylor form found in a CHY double-color scalar amplitude. We have solved both of these problems, and have formulated a method that can be applied to any $n$. Many examples are provided to illustrate these calculations.
Differential equations, associators, and recurrences for amplitudes
Georg Puhlfürst
2016-01-01
Full Text Available We provide new methods to straightforwardly obtain compact and analytic expressions for ϵ-expansions of functions appearing in both field and string theory amplitudes. An algebraic method is presented to explicitly solve for recurrence relations connecting different ϵ-orders of a power series solution in ϵ of a differential equation. This strategy generalizes the usual iteration by Picard's method. Our tools are demonstrated for generalized hypergeometric functions. Furthermore, we match the ϵ-expansion of specific generalized hypergeometric functions with the underlying Drinfeld associator with proper Lie algebra and monodromy representations. We also apply our tools for computing ϵ-expansions for solutions to generic first-order Fuchsian equations (Schlesinger system. Finally, we set up our methods to systematically get compact and explicit α′-expansions of tree-level superstring amplitudes to any order in α′.
Integrable spin chains and scattering amplitudes
In this review, we show that the multi-particle scattering amplitudes in N=4 SYM at large Nc and in the multi-Regge kinematics for some physical regions have the high energy behavior appearing from the contribution of the Mandelstam cuts in the complex angular momentum plane of the corresponding t-channel partial waves. These Mandelstam cuts or Regge cuts result from gluon composite states in the adjoint representation of the gauge group SU(Nc). In the leading logarithmic approximation (LLA), their contribution to the six-point amplitude is in full agreement with the known two-loop result. The Hamiltonian for the Mandelstam states constructed from n gluons in LLA coincides with the local Hamiltonian of an integrable open spin chain. We construct the corresponding wavefunctions using the integrals of motion and the BaxterSklyanin approach. (review)
Quadrupole and monopole large amplitude vibrations
A set of nonlinear dynamical equations for quadrupole and monopole moments of nuclei is derived from the TDHF equation with the help of the so-called Wigner function moments. It allows the description of coupled large amplitude monopole and quadrupole vibrations. These equations are solved numerically for 208Pb and 40Ca in a model with separable forces. The giant quadrupole and monopole resonances are reproduced very well. However the essential feature of the large amplitude motion is the existence of multiphonon states. They are analyzed in detail. The classical and quantum aspects of the analytically solvable one-dimensional pure monopole model are studied to clarify the problem of the anharmonicity of the collective spectrum. 26 refs., 2 figs., 2 tabs
Relation of QCD and dual resonance amplitudes
The dual resonance amplitudes are derived basing on the main QCD principles. The expression for the wave function of the extended system (anti qq) is applied to show that the vertices of the dual resonance model (DRM) play the role of the string (meson) production operators. Maxwell solution of Yang-Mills equations in the form of waves propagating along the extended sources is used. The DRM vertices are generalized to the case of color degrees of freedom. It is found that only singlet color (angi qq) states correspond to the poles of the scattering amplitude in the physical energy region. The problem of states with a negative norm is briefly discussed. The way of solving it is the same as in the electrodynamics
Differential equations, associators, and recurrences for amplitudes
Puhlfürst, Georg; Stieberger, Stephan
2016-01-01
We provide new methods to straightforwardly obtain compact and analytic expressions for ɛ-expansions of functions appearing in both field and string theory amplitudes. An algebraic method is presented to explicitly solve for recurrence relations connecting different ɛ-orders of a power series solution in ɛ of a differential equation. This strategy generalizes the usual iteration by Picard's method. Our tools are demonstrated for generalized hypergeometric functions. Furthermore, we match the ɛ-expansion of specific generalized hypergeometric functions with the underlying Drinfeld associator with proper Lie algebra and monodromy representations. We also apply our tools for computing ɛ-expansions for solutions to generic first-order Fuchsian equations (Schlesinger system). Finally, we set up our methods to systematically get compact and explicit α‧-expansions of tree-level superstring amplitudes to any order in α‧.
Differential Equations, Associators, and Recurrences for Amplitudes
Puhlfuerst, Georg
2015-01-01
We provide new methods to straightforwardly obtain compact and analytic expressions for epsilon-expansions of functions appearing in both field and string theory amplitudes. An algebraic method is presented to explicitly solve for recurrence relations connecting different epsilon-orders of a power series solution in epsilon of a differential equation. This strategy generalizes the usual iteration by Picard's method. Our tools are demonstrated for generalized hypergeometric functions. Furthermore, we match the epsilon-expansion of specific generalized hypergeometric functions with the underlying Drinfeld associator with proper Lie algebra and monodromy representations. We also setup up our tools for computing epsilon-expansions for solutions to generic first-order Fuchsian equations (Schlesinger system). Finally, we apply our methods to systematically get compact and explicit alpha'-expansions of tree-level superstring amplitudes to any order in alpha'.
Limit on the pion distribution amplitude
Luna, E G S
2014-01-01
The pion distribution amplitude (DA) can be related to the fundamental QCD Green's functions as a function of the quark self-energy and the quark-pion vertex, which in turn are associated with the pion wave function through the Bethe-Salpeter equation. Considering the extreme hard asymptotic behavior in momentum space allowed for a pseudoscalar wave function, which is limited by its normalization condition, we compute the pion DA and its second moment. From the resulting amplitude, representing the field theoretical upper limit on the DA behavior, we calculate the photon-pion transition form factor $F_{\\pi\\gamma\\gamma^{\\ast}}(Q^{2})$. The resulting upper limit on the pion transition form factor is compared with existing data published by CLEO, BaBar and Belle collaborations.
Integrable spin chains and scattering amplitudes
Bartels, J.; Prygarin, A. [Hamburg Univ. (Germany). 2. Inst. fuer Theoretische Physik; Lipatov, L.N. [Hamburg Univ. (Germany). 2. Inst. fuer Theoretische Physik; Petersburg Nuclear Physics Institute (Russian Federation); Sankt-Peterburgskij Univ., St. Petersburg (Russian Federation)
2011-04-15
In this review we show that the multi-particle scattering amplitudes in N=4 SYM at large N{sub c} and in the multi-Regge kinematics for some physical regions have the high energy behavior appearing from the contribution of the Mandelstam cuts in the complex angular momentum plane of the corresponding t-channel partial waves. These Mandelstam cuts or Regge cuts are resulting from gluon composite states in the adjoint representation of the gauge group SU(N{sub c}). In the leading logarithmic approximation (LLA) their contribution to the six point amplitude is in full agreement with the known two-loop result. The Hamiltonian for the Mandelstam states constructed from n gluons in LLA coincides with the local Hamiltonian of an integrable open spin chain. We construct the corresponding wave functions using the integrals of motion and the Baxter-Sklyanin approach. (orig.)
New structures in scattering amplitudes: a review
Benincasa, Paolo
2013-01-01
We review some recent developments in the understanding of field theories in the perturbative regime. In particular, we discuss the notions of analyticity, unitarity and locality, and therefore the singularity structure of scattering amplitudes in general interacting theories. We describe their tree-level structure and their on-shell representations, as well as the links between the tree-level structure itself and the structure of the loop amplitudes. Finally, we describe the on-shell diagrammatics recently proposed both on general grounds and in the remarkable example of planar supersymmetric theories. This review is partially based on lectures given at: Dipartimento di Fisica and INFN, Universit\\`a di Bologna; Departamento de F{\\i}sica de Part{\\i}culas, Universidade de Santiago de Compostela; and as part of the program Strings@ar Lectures on Advanced Topics of High Energy Physics held at the IAFE
Modified amplitude of the gravitational wave spectrum
Ghayour, Basem; Suresh, P. K.
2012-09-01
The spectrum of thermal gravitational waves is obtained by including the high-frequency thermal gravitons created from extra-dimensional effects and is a new feature of the spectrum. The amplitude and spectral energy density of gravitational waves in a thermal vacuum state are found to be enhanced. The amplitude of the waves is modified in the frequency range (10-16-108 Hz) but the corresponding spectral energy density is less than the upper bound of various estimated results. With the addition of higher frequency thermal waves, the obtained spectral energy density of the wave in the thermal vacuum state does not exceed the upper bound put by the nucleosynthesis rate. The existence of cosmologically originated thermal gravitational waves due to extra dimension is not ruled out.
Modified Amplitude of Gravitational Waves Spectrum
Ghayour, Basem
2012-01-01
The spectrum of thermal gravitational waves is obtained by including the high frequency thermal gravitons created from extra-dimensional effect and is a new feature of the spectrum. The amplitude and spectral energy density of gravitational waves in thermal vacuum state are found enhanced. The amplitude of the waves get modified in the frequency range (10$^{-16}$ -10 $^{8}$ Hz) but the corresponding spectral energy density is less than the upper bound of various estimated results. With the addition of higher frequency thermal waves, the obtained spectral energy density of the wave in thermal vacuum state does not exceed the upper bound put by nucleosynthesis rate. The existence of cosmologically originated thermal gravitational waves due to extra dimension is not ruled out.
Nanosecond time-to-amplitude converter
A description is given of a modified time-to-amplitude converter intended for operation under great counting rates (5x106 pls/s). The converter is a part of the time-of-flight system used on the JINR synchrocyclotron. Basic circuits of the instrument analog and logic part are given. The converter uses mainly integrated circuits of the 138 series. The gating stage of the instrument analog part is based on a SHF transistor. The voltage-to-current converter is based on an operational amplifier. The duration of amplifier output pulses can be controlled from 0.2 to 2 ?s. The output signal maximum amplitude in the linear range is +-5 V. The temperature instability is 0.1 %/deg C, the output resistance - 50 Ohm. The measurement range of the described converter is 25 and 50 ns
Constructing QCD one-loop amplitudes
In the context of constructing one-loop amplitudes using a unitarity bootstrap approach we discuss a general systematic procedure for obtaining the coefficients of the scalar bubble and triangle integral functions of one-loop amplitudes. Coefficients are extracted after examining the behavior of the cut integrand as the unconstrained parameters of a specifically chosen parameterization of the cut loop momentum approach infinity. Measurements of new physics at the forthcoming experimental program at CERN's Large Hadron Collider (LHC) will require a precise understanding of processes at next-to-leading order (NLO). This places increased demands for the computation of new one-loop amplitudes. This in turn has spurred recent developments towards improved calculational techniques. Direct calculations using Feynman diagrams are in general inefficient. Developments of more efficient techniques have usually centered around unitarity techniques [1], where tree amplitudes are effectively 'glued' together to form loops. The most straightforward application of this method, in which the cut loop momentum is in D = 4, allows for the computation of 'cut-constructible' terms only, i.e. (poly)logarithmic containing terms and any related constants. QCD amplitudes contain, in addition to such terms, rational pieces which cannot be derived using such cuts. These 'missing' rational parts can be extracted using cut loop momenta in D = 4-2 (varepsilon). The greater difficulty of such calculations has restricted the application of this approach, although recent developments [3, 4] have provided new promise for this technique. Recently the application of on-shell recursion relations [5] to obtaining the 'missing' rational parts of one-loop processes [6] has provided an alternative very promising solution to this problem. In combination with unitarity methods an 'on-shell bootstrap' approach provides an efficient technique for computing complete one-loop QCD amplitudes [7]. Additionally other new methods have also proved fruitful for calculating rational terms [8]. Such developments have again refocused attention on the optimization of the derivation of the cut-constructable pieces of the amplitude. Deriving cut-constructible terms for any one-loop amplitude reduces to the computation of coefficients of a set of scalar bubble, scalar triangle and scalar box integral functions. Box coefficients may be found with very little work, directly from the quadruple cut of the relevant box function [9]. A unique box coefficient contributes to each distinct quadruple cut. Unfortunately triangle and bubble coefficients cannot be derived in quite so direct a manner. Multiple scalar integral coefficients appear inside a two-particle cut or triple cut. It is therefore necessary to disentangle the relevant bubble or triangle coefficients from any other coefficients sharing the same cut [1, 4, 10, 11]. The large number of NLO processes of interest for the LHC suggests that a completely automated computational procedure is highly desired. To this end we discuss, in this proceeding, a recently proposed method [12, 13] for the direct, efficient and systematic extraction of bubble and triangle coefficients which is well suited to automation
Effects of rTMS on EEG phase-amplitude coupling
Chie Nakatani
2015-10-01
Full Text Available The EEG signal has multiple frequency bands, which emerge as a result of interactions among different neural populations. Couplings between these bands, in particular Phase-Amplitude Coupling, are observed within and across brain regions. Phase-Amplitude Coupling is believed to have a crucial role in processing and transfer of information across brain regions. As a result, Phase-Amplitude Coupling has received considerable attention recently. We hypothesized that Phase-Amplitude Coupling would be decreased when neuronal populations are fatigued by repetitive Trans-cranial Magnetic Stimulation (rTMS. We applied rTMS to intraparietal sulcus, temporal-parietal junction, and lateral occipital complex of healthy volunteers. Stimulating the intraparietal sulcus decreased Phase-Amplitude Coupling between theta and gamma bands. In the temporal-parietal junction condition, no change was observed. However, in the lateral occipital complex condition, Phase-Amplitude Coupling increased between the alpha and beta bands of the EEG. The increase could be explained by relative increase in alpha band activity; this activity is known to modulate fast activity[1]. Alternatively, the coupling might increase because of increased connectivity between neural populations, e.g., pyramidal and fast inhibitory interneurons, due to activity forcing [2].
Injection coupling with high amplitude transverse modes: Experimentation and simulation
Mery, Yoann; Ducruix, Sébastien; Scouflaire, Philippe; Candel, Sébastien
2009-06-01
High frequency combustion instabilities have technical importance in the design of liquid rocket engines. These phenomena involve a strong coupling between transverse acoustic modes and combustion. They are currently being investigated by combining experimentation and numerical simulations. On the experimental level, the coupling is examined in a model scale system featuring a multiple injector combustor (MIC) comprising five coaxial injectors fed with liquid oxygen and gaseous methane. This system is equipped with a novel VHAM actuator (Very High Amplitude Modulator) which comprises two nozzles and a rotating toothed wheel blocking the nozzles in an alternate fashion. This device was designed to obtain the highest possible levels of transverse oscillation in the MIC. After a brief review of the VHAM, this article reports cold flow experiments using this modulator. Velocity maps obtained under resonant conditions using the VHAM are examined at different instants during a cycle of oscillation. Experimental data are compared with numerical pressure and velocity fields obtained from an acoustic solver. The good agreement observed in the nozzle vicinity indicates that numerical simulations can be used to analyze the complex flow field generated by the VHAM. To cite this article: Y. Mery et al., C. R. Mecanique 337 (2009).
Multipole modes in deformed nuclei within the finite amplitude method
Kortelainen, M.; Hinohara, N.; Nazarewicz, W.
2015-11-01
Background: To access selected excited states of nuclei, within the framework of nuclear density functional theory, the quasiparticle random phase approximation (QRPA) is commonly used. Purpose: We present a computationally efficient, fully self-consistent framework to compute the QRPA transition strength function of an arbitrary multipole operator in axially deformed superfluid nuclei. Methods: The method is based on the finite amplitude method (FAM) QRPA, allowing fast iterative solution of QRPA equations. A numerical implementation of the FAM-QRPA solver module has been carried out for deformed nuclei. Results: The practical feasibility of the deformed FAM module has been demonstrated. In particular, we calculate the quadrupole and octupole strengths in a heavy deformed nucleus 240Pu, without any truncations in the quasiparticle space. To demonstrate the capability to calculate individual QRPA modes, we also compute low-lying negative-parity collective states in 154Sm. Conclusions: The new FAM implementation enables calculations of the QRPA strength function throughout the nuclear landscape. This will facilitate global surveys of multipole modes and ? decays and will open new avenues for constraining the nuclear energy density functional.
Infrared Observations of Large Amplitude Pulsating Stars
Whitelock, Patricia A
1997-01-01
Our understanding of large amplitude pulsating stars and their status in stellar evolution is briefly reviewed. The paper then describes the near-infrared light curves of various asymptotic giant branch stars, concentrating on possible evidence for changing mass-loss rates. The stars discussed include oxygen- and carbon-rich Miras, OH/IR stars, thick-shelled carbon stars and symbiotic Miras. Finally a newly discovered Mira variable in the Sagittarius Dwarf Galaxy is described.
Ward identities for amplitudes with reggeized gluons
Bartles, J. [Hamburg Univ. (Germany). 2. Inst. fuer Theoretische Physik; Universidad Tecnica Federico Santa Maria, Valparaiso (Chile). Dept. de Fisica; Lipatov, L.N. [Hamburg Univ. (Germany). 2. Inst. fuer Theoretische Physik; St. Petersburg Nuclear Physics Institute (Russian Federation); Vacca, G.P. [INFN, Sezione di Bologna (Italy)
2012-05-15
Starting from the effective action of high energy QCD we derive Ward identities for Green's functions of reggeized gluons. They follow from the gauge invariance of the effective action, and allow to derive new representations of amplitudes containing physical particles as well as reggeized gluons. We explicitly demonstrate their validity for the BFKL kernel, and we present a new derivation of the kernel.
A note on Coulomb scattering amplitude
Ahmed, Zafar
2003-01-01
The summation of the partial wave series for Coulomb scattering amplitude, $f^C(\\theta)$ is avoided because the series is oscillatorily and divergent. Instead, $f^C(\\theta)$ is obtained by solving the Schr{\\"o}dinger equation in parabolic cylindrical co-ordinates which is not a general method. Here, we show that a reconstructed series, $(1-\\cos\\theta) ^2f^C(\\theta)$, is both convergent and analytically summable.
Finiteness of type II superstring amplitudes
All possible divergences arising from vanishing dividing or handle geodesics are analysed for massless amplitudes for type II superstrings. In particular putative divergences arising from coincidence of interaction vertices are shown to cancel on integration over phases. Nor do any infinities arise when there are vanishing dividing geodesics. We conclude that type II superstrings are finite, and are excellent candidates to give a finite theory of quantum gravity. (orig.)
Automatic Generation of Tree Level Helicity Amplitudes
Stelzer, T.; Long, W. F.
1994-01-01
The program MadGraph is presented which automatically generates postscript Feynman diagrams and Fortran code to calculate arbitrary tree level helicity amplitudes by calling HELAS[1] subroutines. The program is written in Fortran and is available in Unix and VMS versions. MadGraph currently includes standard model interactions of QCD and QFD, but is easily modified to include additional models such as supersymmetry.
On the infinities of closed superstring amplitudes
We present an analysis of possible infinities that may be present in uncompactified multi-loop heterotic and type II superstring amplitudes constructed, without use of the short-string limit, in the light-cone gauge, and with use of a closed SUSY field theory algebra. Various types of degenerations of the integrand are discussed on the string world-sheet. No infinities are found, modulo (for type II) a particular identity for Green's functions. (author). 13 refs
Zeroing in on Supersymmetric Radiation Amplitude Zeros
Hewett, JoAnne L.; Ismail, Ahmed; Rizzo, Thomas G.; /SLAC
2012-02-15
Radiation amplitude zeros have long been used to test the Standard Model. Here, we consider the supersymmetric radiation amplitude zero in chargino-neutralino associated production, which can be observed at the luminosity upgraded LHC. Such an amplitude zero only occurs if the neutralino has a large wino fraction and hence this observable can be used to determine the neutralino eigenstate content. We find that this observable can be measured by comparing the p{sub T} spectrum of the softest lepton in the trilepton {tilde {chi}}{sub 1}{sup {+-}} {tilde {chi}}{sub 2}{sup 0} decay channel to that of a control process such as {tilde {chi}}{sub 1}{sup +} {tilde {chi}}{sub 1}{sup -} or {tilde {chi}}{sub 2}{sup 0} {tilde {chi}}{sub 2}{sup 0}. We test this technique on a previously generated model sample of the 19 dimensional parameter space of the phenomenological MSSM, and find that it is effective in determining the wino content of the neutralino.
Transversity Amplitudes in Hypercharge Exchange Processes
' In this work we present several techniques developed for the extraction of the. Transversity amplitudes governing quasi two-body meson baryon reactions with hypercharge exchange. We review the methods used in processes having a pure spin configuration, as well as the more relevant results obtained with data from Kp and Tp interactions at intermediate energies. The predictions of the additive quark model and the ones following from exchange degeneracy and etoxicity are discussed. We present a formalism for amplitude analysis developed for reactions with mixed spin configurations and discuss the methods of parametric estimation of the moduli and phases of the amplitudes, as well as the various tests employed to check the goodness of the fits. The calculation of the generalized joint density matrices is given and we propose a method based on the generalization of the idea of multipole moments, which allows to investigate the structure of the decay angular correlations and establishes the quality of the fits and the validity of the simplifying assumptions currently used in this type of studies. (Author) 43 refs
Connecting physical resonant amplitudes and lattice QCD
Bolton, Daniel R. [Univ. of Colorado, Boulder, CO (United States); Baylor Univ., Waco, TX (United States); Briceño, Raúl A. [Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States); Wilson, David J. [Old Dominion Univ., Norfolk, VA (United States)
2016-03-01
We present a determination of the isovector, $P$-wave $\\pi\\pi$ scattering phase shift obtained by extrapolating recent lattice QCD results from the Hadron Spectrum Collaboration using $m_\\pi =236$ MeV. The finite volume spectra are described using extensions of L\\"uscher's method to determine the infinite volume Unitarized Chiral Perturbation Theory scattering amplitude. We exploit the pion mass dependence of this effective theory to obtain the scattering amplitude at $m_\\pi= 140$ MeV. The scattering phase shift is found to be in good agreement with experiment up to center of mass energies of 1.2 GeV. The analytic continuation of the scattering amplitude to the complex plane yields a $\\rho$-resonance pole at $E_\\rho= \\left[755(2)(1)(^{20}_{02})-\\frac{i}{2}\\,129(3)(1)(^{7}_{1})\\right]~{\\rm MeV}$. The techniques presented illustrate a possible pathway towards connecting lattice QCD observables of few-body, strongly interacting systems to experimentally accessible quantities.
Coding stimulus amplitude by correlated neural activity
Metzen, Michael G.; vila-kerberg, Oscar; Chacron, Maurice J.
2015-04-01
While correlated activity is observed ubiquitously in the brain, its role in neural coding has remained controversial. Recent experimental results have demonstrated that correlated but not single-neuron activity can encode the detailed time course of the instantaneous amplitude (i.e., envelope) of a stimulus. These have furthermore demonstrated that such coding required and was optimal for a nonzero level of neural variability. However, a theoretical understanding of these results is still lacking. Here we provide a comprehensive theoretical framework explaining these experimental findings. Specifically, we use linear response theory to derive an expression relating the correlation coefficient to the instantaneous stimulus amplitude, which takes into account key single-neuron properties such as firing rate and variability as quantified by the coefficient of variation. The theoretical prediction was in excellent agreement with numerical simulations of various integrate-and-fire type neuron models for various parameter values. Further, we demonstrate a form of stochastic resonance as optimal coding of stimulus variance by correlated activity occurs for a nonzero value of noise intensity. Thus, our results provide a theoretical explanation of the phenomenon by which correlated but not single-neuron activity can code for stimulus amplitude and how key single-neuron properties such as firing rate and variability influence such coding. Correlation coding by correlated but not single-neuron activity is thus predicted to be a ubiquitous feature of sensory processing for neurons responding to weak input.
Residues of neoasozine in rice grain were determined by neutron activation and colorimetric techniques. Twice application of the chemical before flowering did not lead to increased residue levels while 4-times application resulted in significant increase in the residue level (up to 0.4-0.5 mg/kg). The neutron activation technique was advantageous because of its high sensitivity and the smaller sample amounts required for analysis. The partition ratio of arsenic residues into grain and bran was 73:27 in 100% polished rice. Most of the residue in the bran was transferred to the oilcake fraction. (author)
Complete N-point superstring disk amplitude II. Amplitude and hypergeometric function structure
Mafra, Carlos R., E-mail: crmafra@aei.mpg.de [Max-Planck-Institut fr Gravitationsphysik, Albert-Einstein-Institut, 14476 Potsdam (Germany); Kavli Institute for Theoretical Physics, University of California, Santa Barbara, CA 93106 (United States); Schlotterer, Oliver, E-mail: olivers@mppmu.mpg.de [Kavli Institute for Theoretical Physics, University of California, Santa Barbara, CA 93106 (United States); Max-Planck-Institut fr Physik, Werner-Heisenberg-Institut, 80805 Mnchen (Germany); Stieberger, Stephan, E-mail: stephan.stieberger@mpp.mpg.de [Kavli Institute for Theoretical Physics, University of California, Santa Barbara, CA 93106 (United States); Max-Planck-Institut fr Physik, Werner-Heisenberg-Institut, 80805 Mnchen (Germany)
2013-08-21
Using the pure spinor formalism in part I (Mafra et al., preprint [1]) we compute the complete tree-level amplitude of N massless open strings and find a striking simple and compact form in terms of minimal building blocks: the full N-point amplitude is expressed by a sum over (N?3)! YangMills partial subamplitudes each multiplying a multiple Gaussian hypergeometric function. While the former capture the spacetime kinematics of the amplitude the latter encode the string effects. This result disguises a lot of structure linking aspects of gauge amplitudes as color and kinematics with properties of generalized Euler integrals. In this part II the structure of the multiple hypergeometric functions is analyzed in detail: their relations to monodromy equations, their minimal basis structure, and methods to determine their poles and transcendentality properties are proposed. Finally, a Grbner basis analysis provides independent sets of rational functions in the Euler integrals.
Phase and amplitude considerations for the Two-Beam Accelerator
Phase and amplitude considerations are made for a Two-Beam Accelerator and analytic formulas are obtained expressing the phase and amplitude errors in terms of magnetic wiggler errors, beam energy errors, beam current errors, and microwave field amplitude errors. The necessity of phase and amplitude control is shown and schemes are proposed which can accomplish this control
Coding of amplitude information by the time-locked electrosensory system of Brachyhypopomus
Masashi Kawasaki
2012-04-01
Full Text Available A pulse-type gymnotiform electric fish, Brachyhypopomus gauderio, emits short electrical pulses from its electric organ in the tail and senses the feedback signals with the tuberous electroreceptors in the skin for electrolocation and electrocommunication. The feedback signals are captured and processed by two distinct pathways, the amplitude and time-locked electrosensory systems. While the amplitude system is driven by the electroreceptors, the burst duration coders, which generate action potentials at variable rates according to the amplitude of the electrosensory signals, the time-locked system is driven by the pulse markers, which generate a single action potential in response to a feedback pulse regardless of its amplitude. The response latency of the action potentials of pulse markers and their ascending higher order time-locked neurons in the midbrain, however, may depend on the amplitude of stimulus pulses. In this study, (1 we measured the amplitude of the self stimulation by fish's own electric organ discharges in an in vivo preparation, (2 recorded the latencies and accuracy (jitter of time-locked neurons in the midbrain in response to artificial electric organ discharges with various waveforms and amplitudes, and (3 compared the slope of the amplitude-latency function with the sensitivity of a behavioral response to time differences between feedback pulses. The time-locked neurons in the midbrain fired their action potentials with short latency (~0.9 msec and with accurate timing (a few microseconds. The natural waveform, polarity (outward monophasic waveform, and higher repetition rates of the stimulus pulses produced smaller jitter. The slope of the amplitude-latency function indicated that amplitude modulation of sensory signals at 20% shifted the latency of the midbrain time locked neurons by ~40 microseconds on average, which was large enough to cause novelty responses. Novelty responses were recorded when stimulus pulses with equal amplitudes were delivered with microsecond time differences. We propose that the timing system of Brachyhypoopomus encodes and utilizes time information in the microsecond range which are resulted not only from capacitance of electrolocation objects but also from the changes in amplitude of feedback signals caused by resistive components of electrolocation objects, surrounding environment, and relative geometrical positions of the electric organ of itself or neighboring fish.
Pulse-train modulation in a picosecond self-mode-locked laser
Pulse-train modulation was observed in a picosecond self-mode-locked Ti:sapphire laser with pump-power dependence when it was operated around the degenerate cavity configuration. By increasing the optical pumping power, the envelope of the periodic amplitude modulation splits into two or three clusters with enhanced modulation depth, and the amplitude modulation eventually becomes disordered at higher pump power. The amplitude modulation may be supported by exciting two sets of non-degenerate longitudinally mode-locked supermodes due to spatially inhomogeneous gain modulation in the Ti:sapphire crystal.
Alcaraz-Pelegrina, J.M., E-mail: fa1alpej@uco.e [Departamento de Fisica, Facultad de Ciencias, Universidad de Cordoba, Campus de Rabanales, Ctra de Madrid N-IV-a, km 396, 14071 Cordoba (Spain); Rodriguez-Garcia, P. [Departamento de Fisica, Facultad de Ciencias, Universidad de Cordoba, Campus de Rabanales, Ctra de Madrid N-IV-a, km 396, 14071 Cordoba (Spain)
2010-03-29
Modulation instability is investigated in two cubic-quintic Ginzburg-Landau equations coupled with a cross phase modulation type term. After carrying out a stability analysis an expression for gain is obtained. Some direct simulations to see the evolution of different continuous wave states are reported. These show the formation of modulation instability pulses as well as transitions from lower amplitude continuous wave states to higher amplitude continuous wave states.
Simulation study of the interaction between large-amplitude HF radio waves and the ionosphere
Eliasson, B; Eliasson, Bengt; Thid\\'e, Bo
2006-01-01
The time evolution of a large-amplitude electromagnetic (EM) wave injected vertically into the overhead ionosphere is studied numerically. The EM wave has a carrier frequency of 5 MHz and is modulated as a Gaussian pulse with a width of ca 0.1 milliseconds and a vacuum amplitude of 1.5 V/m. The pulse is propagated through the neutral atmosphere to the critical points of the magnetosphere where the ordinary (O) and extraordinary (X) modes are reflected, and back to the neutral atmosphere. We observe mode conversion of the O mode to electrostatic waves, as well as harmonic generation at the turning points of both the X and O modes, where their amplitudes rise to several times the original ones. The study has relevance for ionospheric interaction experiments in combination with ground-based and satellite or rocket observations.
Extended Kalman filtering for joint mitigation of phase and amplitude noise in coherent QAM systems.
Pakala, Lalitha; Schmauss, Bernhard
2016-03-21
We numerically investigate our proposed carrier phase and amplitude noise estimation (CPANE) algorithm using extend Kalman filter (EKF) for joint mitigation of linear and non-linear phase noise as well as amplitude noise on 4, 16 and 64 polarization multiplexed (PM) quadrature amplitude modulation (QAM) 224 Gb/s systems. The results are compared to decision directed (DD) carrier phase estimation (CPE), DD phase locked loop (PLL) and universal CPE (U-CPE) algorithms. Besides eliminating the necessity of phase unwrapping function, EKF-CPANE shows improved performance for both back-to-back (BTB) and transmission scenarios compared to the aforementioned algorithms. We further propose a weighted innovation approach (WIA) of the EKF-CPANE which gives an improvement of 0.3 dB in the Q-factor, compared to the original algorithm. PMID:27136830
Variability in mode amplitudes in the rapidly oscillating Ap star HR 1217
White, T R; Stello, D; Kurtz, D W; Cunha, M S; Gough, D O
2011-01-01
HR 1217 is one of the best-studied rapidly oscillating Ap (roAp) stars, with eight known oscillation modes that are distorted by a strong, global magnetic field. We have reanalysed the multisite observations of HR 1217 taken in 1986 and 2000. We determined a weighting scheme for the 1986 and 2000 data to minimize the noise level. A wavelet analysis of the data has found that the modulation of the amplitude due to rotation for all frequencies is, in general, consistent with the expected modulation for modified l=1, 2 or 3 modes. Unexpected variations in the rotational modulation are also seen, with variations in the modulation profile, time of maximal pulsation, and pulsational energy in each mode. Interestingly, these changes take place on a short timescale, of the order of days. We consider potential explanations for these behaviours.
Enhanced modulation rates via field modulation in spin torque nano-oscillators
Purbawati, A.; Garcia-Sanchez, F.; Buda-Prejbeanu, L. D.; Ebels, U.
2016-03-01
Spin Transfer Nano-Oscillators (STNOs) are promising candidates for telecommunications applications due to their frequency tuning capabilities via either a dc current or an applied field. This frequency tuning is of interest for Frequency Shift Keying concepts to be used in wireless communication schemes or in read head applications. For these technological applications, one important parameter is the characterization of the maximum achievable rate at which an STNO can respond to a modulating signal, such as current or field. Previous studies of in-plane magnetized STNOs on frequency modulation via an rf current revealed that the maximum achievable rate is limited by the amplitude relaxation rate Γp, which gives the time scale over which amplitude fluctuations are damped out. This might be a limitation for applications. Here, we demonstrate via numerical simulation that application of an additional rf field is an alternative way for modulation of the in-plane magnetized STNO configuration, which has the advantage that frequency modulation is not limited by the amplitude relaxation rate, so that higher modulation rates above GHz are achievable. This occurs when the modulating rf field is oriented along the easy axis (longitudinal rf field). Tilting the direction of the modulating rf field in-plane and perpendicularly with respect to the easy axis (transverse rf field), the modulation is again limited by the amplitude relaxation rate similar to the response observed in current modulation.
Ethnic differences in electrocardiographic amplitude measurements
There is a controversy regarding ethnic differences in electrocardiographic (ECG) patterns because of the potentially confounding socioeconomic, nutritional, environmental and occupational factors. We reviewed the first 1000 medical files of a multiethnic community, where all individuals shared similar living conditions. Only healthy adults age 15 to 60 years were included. Wave amplitudes were measured manually from the standard 12lead ECG. Minnesota coding was used. ECG from 597 subjects were included in the study: 350 Saudi Arabians, 95 Indians, 17 Sri-Lankans, 39 Filipinos, and 57 Caucasians; 349 were men. the mean +-SD of Sokolow-Lyon voltage (SLV) in men was signifcantly different among ethnic groups (2.9+-0.86, 2.64+-0.79, 2.73+-0.72, 3.23+-0.61, 2.94+-0.6, 2.58+-0.79 mV, P=0.0006, for Saudi's, Indians, Jordanians, Filipinos, Sri-Lankans, and Caucasians, respectively). SLV was similar among ethnic groups in women. The prevalence of early transition pattern was also different among ethnic groups in men but not women (15.8%, 34.6%, 17.9%, 21.7%, 35.3%, 26.8% in Suadi, Indian, Jordanian, Filipino, Sri-Lankan, and Caucasian, respectively, P=0.037). T wave amplitude was significantly different among ethnic groups in selected lead. ECG wave amplitude differs with ethnic region even when other factors are similar. Using SLV of 3.5 mV as a criterion may overestimate the incidence of left ventricular hypertrophy in some ethnic groups. The pattern of high R wave in lead V1is common in healthy adults in certain ethnic groups. T wave height differs with ethnic origin and sex. (author)
Pion Distribution Amplitude from Lattice QCD
V.M. Braun; COLLINS S.; Göckeler, M.; Pérez-Rubio, P.; A. Schäfer; Schiel, R. W.; Sternbeck, A.
2015-01-01
We have calculated the second moment of the pion light-cone distribution amplitude using two flavors of dynamical (clover) fermions on lattices of different volumes, lattice spacings between $0.06 \\, \\mathrm {fm}$ and $0.08 \\, \\mathrm {fm}$ and pion masses down to $m_\\pi\\sim 150 \\, \\mathrm {MeV}$. Our result for the second Gegenbauer coefficient is $a_2 = 0.1364(154)(145)$ and for the width parameter $\\langle \\xi^2 \\rangle = 0.2361(41)(39)$. Both numbers refer to the scale $\\mu=2 \\, \\mathrm {...
Amplitude squeezed light from a laser
Hart, D. L.; Kennedy, T. A. B.
1992-01-01
Intensity squeezed light was successfully generated using semiconductor lasers with sub-Poissonian pumping. Control of the pumping statistics is crucial and is achieved by a large series resistor which regulates the pump current; its sub-Poissonian statistics are then transferred to the laser output. The sub-Poissonian pumping of other laser systems is not so simple, however, and their potential as squeezed states sources is apparently diminished. We consider a conventional laser incoherently pumped well above threshold, and allow for pump depletion of the ground state. In this regime, sub-Poissonian photon statistics and squeezed amplitude fluctuations are produced.
Revisiting soliton contributions to perturbative amplitudes
Papageorgakis, Constantinos; Royston, Andrew B.
2014-09-01
It is often said that soliton contributions to perturbative processes in QFT are exponentially suppressed by a form factor. We provide a derivation of this form factor by studying the soliton-antisoliton pair production amplitude for a class of scalar theories with generic soliton moduli. This reduces to the calculation of a matrix element in the quantum mechanics on the soliton moduli space. We investigate the conditions under which the latter leads to suppression. Extending this framework to instanton-solitons in five-dimensional Yang-Mills theory leaves open the possibility that such contributions will not be suppressed.
Inverse amplitude method and Adler zeros
The inverse amplitude method is a powerful unitarization technique to enlarge the energy applicability region of effective Lagrangians. It has been widely used to describe resonances in hadronic physics, combined with chiral perturbation theory, as well as in the strongly interacting symmetry breaking sector. In this work we show how it can be slightly modified to also account for the subthreshold region, incorporating correctly the Adler zeros required by chiral symmetry and eliminating spurious poles. These improvements produce negligible effects on the physical region.
Second moment of the pion's distribution amplitude
We present preliminary results from the QCDSF/UKQCD collaborations for the second moment of the pion's distribution amplitude with two flavours of dynamical fermions. We use nonperturbatively determined renormalisation coefficients to convert our results to the MS scheme at 5 GeV2. Employing a linear chiral extrapolation from our large pion masses > 550 MeV, we find left angle ξ2 right angle = 0.281(28), leading to a value of α2 = 0.236(82) for the second Gegenbauer moment. (orig.)
Multiloop integrand reduction for dimensionally regulated amplitudes
Mastrolia, Pierpaolo, E-mail: pierpaolo.mastrolia@cern.ch [Max-Planck-Institut fr Physik, Fhringer Ring 6, 80805 Mnchen (Germany); Dipartimento di Fisica e Astronomia, Universit di Padova, and INFN Sezione di Padova, via Marzolo 8, 35131 Padova (Italy); Mirabella, Edoardo, E-mail: mirabell@mppmu.mpg.de [Max-Planck-Institut fr Physik, Fhringer Ring 6, 80805 Mnchen (Germany); Ossola, Giovanni, E-mail: GOssola@citytech.cuny.edu [Physics Department, New York City College of Technology, The City University of New York, 300 Jay Street Brooklyn, New York 11201 (United States); The Graduate School and University Center, The City University of New York, 365 Fifth Avenue, New York, New York 10016 (United States); Peraro, Tiziano, E-mail: peraro@mppmu.mpg.de [Max-Planck-Institut fr Physik, Fhringer Ring 6, 80805 Mnchen (Germany)
2013-12-18
We present the integrand reduction via multivariate polynomial division as a natural technique to encode the unitarity conditions of Feynman amplitudes. We derive a recursive formula for the integrand reduction, valid for arbitrary dimensionally regulated loop integrals with any number of loops and external legs, which can be used to obtain the decomposition of any integrand analytically with a finite number of algebraic operations. The general results are illustrated by applications to two-loop Feynman diagrams in QED and QCD, showing that the proposed reduction algorithm can also be seamlessly applied to integrands with denominators appearing with arbitrary powers.