Lewis, I.A.D.
1956-05-15
This patent pentains to an electrical pulse amplitude analyzer, capable of accepting input pulses having a separation between adjacent pulses in the order of one microsecond while providing a large number of channels of classification. In its broad aspect the described pulse amplitude analyzer utilizes a storage cathode ray tube und control circuitry whereby the amplitude of the analyzed pulses controls both the intensity and vertical defiection of the beam to charge particular spots in horizontal sectors of the tube face as the beam is moved horizontally across the tube face. As soon as the beam has swept the length of the tube the information stored therein is read out by scanning individually each horizontal sector corresponding to a certain range of pulse amplitudes and applying the output signal from each scan to separate indicating means.
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.
Real topological string amplitudes
NASA Astrophysics Data System (ADS)
Narain, K. S.; Piazzalunga, N.; Tanzini, A.
2017-03-01
We discuss the physical superstring correlation functions in type I theory (or equivalently type II with orientifold) that compute real topological string amplitudes. We consider the correlator corresponding to holomorphic derivative of the real topological amplitude G_{χ } , at fixed worldsheet Euler characteristic χ. This corresponds in the low-energy effective action to N=2 Weyl multiplet, appropriately reduced to the orientifold invariant part, and raised to the power g' = -χ + 1. We show that the physical string correlator gives precisely the holomorphic derivative of topological amplitude. Finally, we apply this method to the standard closed oriented case as well, and prove a similar statement for the topological amplitude F_g.
Protostring scattering amplitudes
NASA Astrophysics Data System (ADS)
Thorn, Charles B.
2016-11-01
We calculate some tree-level scattering amplitudes for a generalization of the protostring, which is a novel string model implied by the simplest string bit models. These bit models produce a light-cone world sheet which supports s integer moded Grassmann fields. In the generalization we supplement this Grassmann world-sheet system with d =24 -s transverse coordinate world-sheet fields. The protostring corresponds to s =24 and the bosonic string to s =0 . The interaction vertex is a simple overlap with no operator insertions at the break/join point. Assuming that s is even we calculate the multistring scattering amplitudes by bosonizing the Grassmann fields, each pair equivalent to one compactified bosonic field, and applying Mandelstam's interacting string formalism to a system of s /2 compactified and d uncompactified bosonic world-sheet fields. We obtain all amplitudes for open strings with no oscillator excitations and for closed strings with no oscillator excitations and zero winding number. We then study in detail some simple special cases. Multistring processes with maximal helicity violation have much simpler amplitudes. We also specialize to general four-string amplitudes and discuss their high energy behavior. Most of these models are not covariant under the full Lorentz group O (d +1 ,1 ). The exceptions are the bosonic string whose Lorentz group is O (25 ,1 ) and the protostring whose Lorentz group is O (1 ,1 ). The models in between only enjoy an O (1 ,1 )×O (d ) spacetime symmetry.
Feng Bo
2007-11-20
In this talk, we will present recent progresses in perturbative calculations of scattering amplitudes at tree and one-loop levels. At tree level, we will discuss MHV-diagram method and on-shell recursion relation. At one-loop level, we will establish the framework of Unitarity cut method.
Reinforcing Saccadic Amplitude Variability
ERIC Educational Resources Information Center
Paeye, Celine; Madelain, Laurent
2011-01-01
Saccadic endpoint variability is often viewed as the outcome of neural noise occurring during sensorimotor processing. However, part of this variability might result from operant learning. We tested this hypothesis by reinforcing dispersions of saccadic amplitude distributions, while maintaining constant their medians. In a first experiment we…
NASA Astrophysics Data System (ADS)
Taylor, Tomasz R.
2017-05-01
This a pedagogical introduction to scattering amplitudes in gauge theories. It proceeds from Dirac equation and Weyl fermions to the two pivot points of current developments: the recursion relations of Britto, Cachazo, Feng and Witten, and the unitarity cut method pioneered by Bern, Dixon, Dunbar and Kosower. In ten lectures, it covers the basic elements of on-shell methods.
Planar amplitude ammonia sensor
NASA Astrophysics Data System (ADS)
Karasinski, Pawel; Rogozinski, Roman
2004-09-01
The paper presents the results of investigation involving the influence of the change of launching conditions on the characteristics of amplitude ammonia sensors produced with the application of strip waveguides of different refractive profiles. Strip waveguides were produced using ion exchange technique, and the absorption sensitive films were produced using sol-gel technology.
Weak boson production amplitude zeros; equalities of the helicity amplitudes
NASA Astrophysics Data System (ADS)
Mamedov, Fizuli
2002-08-01
We investigate the radiation amplitude zeros exhibited by many standard model amplitudes for triple weak gauge boson production processes. We show that WZγ production amplitudes have an especially rich structure in terms of zeros; these amplitudes have zeros originating from several different sources. It is also shown that the type-I current null zone is the special case of the equality of the specific helicity amplitudes.
NASA Astrophysics Data System (ADS)
Can, T. V.; Weber, R. T.; Walish, J. J.; Swager, T. M.; Griffin, R. G.
2017-04-01
We present a pulsed dynamic nuclear polarization (DNP) study using a ramped-amplitude nuclear orientation via electron spin locking (RA-NOVEL) sequence that utilizes a fast arbitrary waveform generator (AWG) to modulate the microwave pulses together with samples doped with narrow-line radicals such as 1,3-bisdiphenylene-2-phenylallyl (BDPA), sulfonated-BDPA (SA-BDPA), and trityl-OX063. Similar to ramped-amplitude cross polarization in solid-state nuclear magnetic resonance, RA-NOVEL improves the DNP efficiency by a factor of up to 1.6 compared to constant-amplitude NOVEL (CA-NOVEL) but requires a longer mixing time. For example, at τmix = 8 μs, the DNP efficiency reaches a plateau at a ramp amplitude of ˜20 MHz for both SA-BDPA and trityl-OX063, regardless of the ramp profile (linear vs. tangent). At shorter mixing times (τmix = 0.8 μs), we found that the tangent ramp is superior to its linear counterpart and in both cases there exists an optimum ramp size and therefore ramp rate. Our results suggest that RA-NOVEL should be used instead of CA-NOVEL as long as the electronic spin lattice relaxation T1e is sufficiently long and/or the duty cycle of the microwave amplifier is not exceeded. To the best of our knowledge, this is the first example of a time domain DNP experiment that utilizes modulated microwave pulses. Our results also suggest that a precise modulation of the microwave pulses can play an important role in optimizing the efficiency of pulsed DNP experiments and an AWG is an elegant instrumental solution for this purpose.
Erbert, G
2009-09-01
The Amplitude Modulator Chassis (AMC) is the final component in the MOR system and connects directly to the PAM input through a 100-meter fiber. The 48 AMCs temporally shape the 48 outputs of the MOR using an arbitrary waveform generator coupled to an amplitude modulator. The amplitude modulation element is a two stage, Lithium Niobate waveguide device, where the intensity of the light passing through the device is a function of the electrical drive applied. The first stage of the modulator is connected to a programmable high performance Arbitrary Waveform Generator (AWG) consisting of 140 impulse generators space 250 ps apart. An arbitrary waveform is generated by independently varying the amplitude of each impulse generator and then summing the impulses together. In addition to the AWG a short pulse generator is also connected to the first stage of the modulator to provide a sub 100-ps pulse used for timing experiments. The second stage of the modulator is connect to a square pulse generator used to further attenuate any pre or post pulse light passing through the first stage of the modulator. The fast rise and fall time of the square pulse generator is also used to produce fast rise and fall times of the AWG by clipping the AWG pulse. For maximum extinction, a pulse bias voltage is applied to each stage of the modulator. A pulse voltage is applied as opposed to a DC voltage to prevent charge buildup on the modulator. Each bias voltage is adjustable to provide a minimum of 50-dB extinction. The AMC is controlled through ICCS to generate the desired temporal pulse shape. This process involves a closed-loop control algorithm, which compares the desired temporal waveform to the produced optical pulse, and iterates the programming of the AWG until the two waveforms agree within an allowable tolerance.
High amplitude propagated contractions.
Bharucha, A E
2012-11-01
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. High amplitude propagated contractions occur spontaneously, in response to pharmacological agents or colonic distention. A subset of patients with slow transit constipation have fewer HAPC. In this issue of Neurogastroenterology and Motility, Rodriguez et al. report that anal relaxation during spontaneous and bisacodyl-induced HAPC exceeds anal relaxation during rectal distention in constipated children undergoing colonic manometry. Moreover, and consistent with a neural mechanism, anal relaxation often precedes arrival of HAPC in the left colon. High amplitude propagated contractions are also used to evaluate the motor response to a meal and pharmacological stimuli (e.g., bisacodyl, neostigmine) and to identify colonic inertia during colonic motility testing in chronic constipation. This editorial comprehensively reviews the characteristics, physiology and pharmacology of HAPC, their assessment by manometry, and relevance to constipation and diarrhea. © 2012 Blackwell Publishing Ltd.
Amplitudes of Spiral Perturbations
NASA Astrophysics Data System (ADS)
Grosbol, P.; Patsis, P. A.
2014-03-01
It has proven very difficult to estimate the amplitudes of spiral perturbations in disk galaxies from observations due to the variation of mass-to-light ratio and extinction across spiral arms. Deep, near-infrared images of grand-design spiral galaxies obtained with HAWK-I/VLT were used to analyze the azimuthal amplitude and shape of arms, which, even in the K-band may, be significantly biased by the presence of young stellar populations. Several techniques were applied to evaluate the relative importance of young stars across the arms, such as surface brightness of the disk with light from clusters subtracted, number density of clusters detected, and texture of the disk. The modulation of the texture measurement, which correlates with the number density of faint clusters, yields amplitudes of the spiral perturbation in the range 0.1-0.2. This estimate gives a better estimate of the mass perturbation in the spiral arms, since it is dominated by old clusters.
Gray, G.W.; Jensen, A.S.
1957-10-22
A pulse-height analyzer system of improved design for sorting and counting a series of pulses, such as provided by a scintillation detector in nuclear radiation measurements, is described. The analyzer comprises a main transmission line, a cathode-ray tube for each section of the line with its deflection plates acting as the line capacitance; means to bias the respective cathode ray tubes so that the beam strikes a target only when a prearranged pulse amplitude is applied, with each tube progressively biased to respond to smaller amplitudes; pulse generating and counting means associated with each tube to respond when the beam is deflected; a control transmission line having the same time constant as the first line per section with pulse generating means for each tube for initiating a pulse on the second transmission line when a pulse triggers the tube of corresponding amplitude response, the former pulse acting to prevent successive tubes from responding to the pulse under test. This arrangement permits greater deflection sensitivity in the cathode ray tube and overcomes many of the disadvantages of prior art pulse-height analyzer circuits.
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 constipated children undergoing colonic manometry. Moreover, and consistent with a neural mechanism, anal relaxation often precedes arrival of HAPC in the left colon. This editorial comprehensively reviews the characteristics, physiology and pharmacology of HAPC, their assessment by manometry, and relevance to constipation and diarrhea. PMID:23057554
Pion distribution amplitude and quasidistributions
Radyushkin, Anatoly V.
2017-03-27
We extend our analysis of quasidistributions onto the pion distribution amplitude. Using the formalism of parton virtuality distribution amplitudes, we establish a connection between the pion transverse momentum dependent distribution amplitude Ψ(x,k2⊥) and the pion quasidistribution amplitude (QDA) Qπ(y,p3). We build models for the QDAs from the virtuality-distribution-amplitude-based models for soft transverse momentum dependent distribution amplitudes, and analyze the p3 dependence of the resulting QDAs. As there are many models claimed to describe the primordial shape of the pion distribution amplitude, we present the p3-evolution patterns for models producing some popular proposals: Chernyak-Zhitnitsky, flat, and asymptotic distribution amplitude. Finally, ourmore » results may be used as a guide for future studies of the pion distribution amplitude on the lattice using the quasidistribution approach.« less
PULSE AMPLITUDE DISTRIBUTION RECORDER
Cowper, G.
1958-08-12
A device is described for automatica1ly recording pulse annplitude distribution received from a counter. The novelty of the device consists of the over-all arrangement of conventional circuit elements to provide an easy to read permanent record of the pulse amplitude distribution during a certain time period. In the device a pulse analyzer separates the pulses according to annplitude into several channels. A scaler in each channel counts the pulses and operates a pen marker positioned over a drivable recorder sheet. Since the scalers in each channel have the sanne capacity, the control circuitry permits counting of the incoming pulses until one scaler reaches capacity, whereupon the input is removed and an internal oscillator supplies the necessary pulses to fill up the other scalers. Movement of the chart sheet is initiated wben the first scaler reaches capacity to thereby give a series of marks at spacings proportional to the time required to fill the remaining scalers, and accessory equipment marks calibration points on the recorder sheet to facilitate direct reading of the number of external pulses supplied to each scaler.
Invariant amplitudes for pion electroproduction
NASA Astrophysics Data System (ADS)
Pasquini, B.; Drechsel, D.; Tiator, L.
2007-12-01
The invariant amplitudes for pion electroproduction on the nucleon are evaluated by dispersion relations at constant t with MAID as input for the imaginary parts of these amplitudes. In the threshold region these amplitudes are confronted with the predictions of several low-energy theorems derived in the soft-pion limit. In general agreement with chiral perturbation theory, the dispersive approach yields large corrections to these theorems because of the finite pion mass.
Amplitude variations in coarticulated vowels
Jacewicz, Ewa; Fox, Robert Allen
2008-01-01
This paper seeks to characterize the nature, size, and range of acoustic amplitude variation in naturally produced coarticulated vowels in order to determine its potential contribution and relevance to vowel perception. The study is a partial replication and extension of the pioneering work by House and Fairbanks [J. Acoust. Soc. Am. 22, 105–113 (1953)], who reported large variation in vowel amplitude as a function of consonantal context. Eight American English vowels spoken by men and women were recorded in ten symmetrical CVC consonantal contexts. Acoustic amplitude measures included overall rms amplitude, amplitude of the rms peak along with its relative location in the CVC-word, and the amplitudes of individual formants F1–F4 along with their frequencies. House and Fairbanks’ amplitude results were not replicated: Neither the overall rms nor the rms peak varied appreciably as a function of consonantal context. However, consonantal context was shown to affect significantly and systematically the amplitudes of individual formants at the vowel nucleus. These effects persisted in the auditory representation of the vowel signal. Auditory spectra showed that the pattern of spectral amplitude variation as a function of contextual effects may still be encoded and represented at early stages of processing by the peripheral auditory system. PMID:18529192
On the Period-Amplitude and Amplitude-Period Relationships
NASA Technical Reports Server (NTRS)
Wilson, Robert M.; Hathaway, David H.
2008-01-01
Examined are Period-Amplitude and Amplitude-Period relationships based on the cyclic behavior of the 12-month moving averages of monthly mean sunspot numbers for cycles 0.23, both in terms of Fisher's exact tests for 2x2 contingency tables and linear regression analyses. Concerning the Period-Amplitude relationship (same cycle), because cycle 23's maximum amplitude is known to be 120.8, the inferred regressions (90-percent prediction intervals) suggest that its period will be 131 +/- 24 months (using all cycles) or 131 +/- 18 months (ignoring cycles 2 and 4, which have the extremes of period, 108 and 164 months, respectively). Because cycle 23 has already persisted for 142 months (May 1996 through February 2008), based on the latter prediction, it should end before September 2008. Concerning the Amplitude-Period relationship (following cycle maximum amplitude versus preceding cycle period), because cycle 23's period is known to be at least 142 months, the inferred regressions (90-percent prediction intervals) suggest that cycle 24's maximum amplitude will be about less than or equal to 96.1 +/- 55.0 (using all cycle pairs) or less than or equal to 91.0 +/- 36.7 (ignoring statistical outlier cycle pairs). Hence, cycle 24's maximum amplitude is expected to be less than 151, perhaps even less than 128, unless cycle pair 23/24 proves to be a statistical outlier.
Substorm statistics: Occurrences and amplitudes
Borovsky, J.E.; Nemzek, R.J.
1994-05-01
The occurrences and amplitudes of substorms are statistically investigated with the use of three data sets: the AL index, the Los Alamos 3-satellite geosynchronous energetic-electron measurements, and the GOES-5 and -6 geosynchronous magnetic-field measurements. The investigation utilizes {approximately} 13,800 substorms in AL, {approximately} 1400 substorms in the energetic-electron flux, and {approximately} 100 substorms in the magnetic field. The rate of occurrence of substorms is determined as a function of the time of day, the time of year, the amount of magnetotail bending, the orientation of the geomagnetic dipole, the toward/away configuration of the IMF, and the parameters of the solar wind. The relative roles of dayside reconnection and viscous coupling in the production of substorms are assessed. Three amplitudes are defined for a substorms: the jump in the AL index, the peak of the >30-keV integral electron flux at geosynchronous orbit near midnight, and the angle of rotation of the geosynchronous magnetic field near midnight. The substorm amplitudes are statistically analyzed, the amplitude measurements are cross correlated with each other, and the substorm amplitudes are determined as functions of the solar-wind parameters. Periodically occurring and randomly occurring substorms are analyzed separately. The energetic-particle-flux amplitudes are consistent with unloading and the AL amplitudes are consistent with direct driving plus unloading.
Small amplitude quasibreathers and oscillons
Fodor, Gyula; Lukacs, Arpad; Forgacs, Peter; Horvath, Zalan
2008-07-15
Quasibreathers (QB) are time-periodic solutions with weak spatial localization introduced in G. Fodor et al. in [Phys. Rev. D 74, 124003 (2006)]. QB's provide a simple description of oscillons (very long-living spatially localized time dependent solutions). The small amplitude limit of QB's is worked out in a large class of scalar theories with a general self-interaction potential, in D spatial dimensions. It is shown that the problem of small amplitude QB's is reduced to a universal elliptic partial differential equation. It is also found that there is the critical dimension, D{sub crit}=4, above which no small amplitude QB's exist. The QB's obtained this way are shown to provide very good initial data for oscillons. Thus these QB's provide the solution of the complicated, nonlinear time dependent problem of small amplitude oscillons in scalar theories.
Large Amplitude Oscillations in Prominences
NASA Astrophysics Data System (ADS)
Tripathi, D.; Isobe, H.; Jain, R.
2009-12-01
Since the first reports of oscillations in prominences in the 1930s, there have been major theoretical and observational developments to understand the nature of these oscillatory phenomena, leading to the whole new field of the so-called “prominence seismology”. There are two types of oscillatory phenomena observed in prominences; “small-amplitude oscillations” (2-3 km s-1), which are quite common, and “large-amplitude oscillations” (>20 km s-1) for which observations are scarce. Large-amplitude oscillations have been found as “winking filament” in H α as well as motion in the plane-of-sky in H α, EUV, micro-wave and He 10830 observations. Historically, it has been suggested that the large-amplitude oscillations in prominences were triggered by disturbances such as fast-mode MHD waves (Moreton wave) produced by remote flares. Recent observations show, in addition, that near-by flares or jets can also create such large-amplitude oscillations in prominences. Large-amplitude oscillations, which are observed both in transverse as well as longitudinal direction, have a range of periods varying from tens of minutes to a few hours. Using the observed period of oscillation and simple theoretical models, the obtained magnetic field in prominences has shown quite a good agreement with directly measured one and, therefore, justifies prominence seismology as a powerful diagnostic tool. On rare occasions, when the large-amplitude oscillations have been observed before or during the eruption, the oscillations may be applied to diagnose the stability and the eruption mechanism. Here we review the recent developments and understanding in the observational properties of large-amplitude oscillations and their trigger mechanisms and stability in the context of prominence seismology.
Tempo and amplitude in growth.
Hermanussen, Michael
2011-01-01
Growth is defined as an increase of size over time with time usually defined as physical time. Yet, the rigid metric of physical time is not directly relevant to the internal dynamics of growth. Growth is linked to maturation. Children and adolescents differ in the tempo at which they mature. One calendar year differs in its meaning in a fast maturing, and in a slow maturing child. The slow child needs more calendar years for completing the same stage of maturity. Many characteristics in the human growth curve are tempo characteristics. Tempo - being fast or slow maturing - has to be carefully separated from amplitude - being tall or short. Several characteristic phenomena such as catch-up growth after periods of illness and starvation are largely tempo phenomena, and do usually not affect the amplitude component of growth. Applying Functional Data Analysis and Principal Component Analysis, the two main sources of height variance: tempo and amplitude can statistically be separate and quantified. Tempo appears to be more sensitive than amplitude to nutrition, health and environmental stress. An appropriate analysis of growth requires disentangling its two major components: amplitude and tempo. The assessment of the developmental tempo thus is an integral part of assessing child and adolescent growth. Though an Internet portal is currently available to process small amounts of height data (www.willi-will-wachsen.com) for separately determining amplitude and tempo in growth, there is urgent need of better and practical solutions for analyzing individual growth.
Grassmannian origin of scattering amplitudes
NASA Astrophysics Data System (ADS)
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
Computing Maximally Supersymmetric Scattering Amplitudes
NASA Astrophysics Data System (ADS)
Stankowicz, James Michael, Jr.
This dissertation reviews work in computing N = 4 super-Yang--Mills (sYM) and N = 8 maximally supersymmetric gravity (mSUGRA) scattering amplitudes in D = 4 spacetime dimensions in novel ways. After a brief introduction and overview in Ch. 1, the various techniques used to construct amplitudes in the remainder of the dissertation are discussed in Ch. 2. This includes several new concepts such as d log and pure integrand bases, as well as how to construct the amplitude using exactly one kinematic point where it vanishes. Also included in this chapter is an outline of the Mathematica package on shell diagrams and numerics.m (osdn) that was developed for the computations herein. The rest of the dissertation is devoted to explicit examples. In Ch. 3, the starting point is tree-level sYM amplitudes that have integral representations with residues that obey amplitude relations. These residues are shown to have corresponding residue numerators that allow a double copy prescription that results in mSUGRA residues. In Ch. 4, the two-loop four-point sYM amplitude is constructed in several ways, showcasing many of the techniques of Ch. 2; this includes an example of how to use osdn. The two-loop five-point amplitude is also presented in a pure integrand representation with comments on how it was constructed from one homogeneous cut of the amplitude. On-going work on the two-loop n-point amplitude is presented at the end of Ch. 4. In Ch. 5, the three-loop four-point amplitude is presented in the d log representation and in the pure integrand representation. In Ch. 6, there are several examples of four- through seven-loop planar diagrams that illustrate how considerations of the singularity structure of the amplitude underpin dual-conformal invariance. Taken with the previous examples, this is additional evidence that the structure known to exist in the planar sector extends to the full theory. At the end of this chapter is a proof that all mSUGRA amplitudes have a pole at
Lorentzian proper vertex amplitude: Asymptotics
NASA Astrophysics Data System (ADS)
Engle, Jonathan; Vilensky, Ilya; Zipfel, Antonia
2016-09-01
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 semiclassical limit. The starting point of the analysis is an expression for the amplitude as an action integral with action differing from that in the Engle-Pereira-Rovelli-Livine (EPRL) case by an extra "projector" term. This extra term scales linearly with spins only in the asymptotic limit, and is discontinuous on a (lower dimensional) submanifold of the integration domain in the sense that its value at each such point depends on the direction of approach. New tools are introduced to generalize stationary phase methods to this case. For the case of boundary data which can be glued to a nondegenerate 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.
Factorization of chiral string amplitudes
NASA Astrophysics Data System (ADS)
Huang, Yu-tin; Siegel, Warren; Yuan, Ellis Ye
2016-09-01
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.
Large amplitude drop shape oscillations
NASA Technical Reports Server (NTRS)
Trinh, E. H.; Wang, T. G.
1982-01-01
An experimental study of large amplitude drop shape oscillation was conducted in immiscible liquids systems and with levitated free liquid drops in air. In liquid-liquid systems the results indicate the existence of familiar characteristics of nonlinear phenomena. The resonance frequency of the fundamental quadrupole mode of stationary, low viscosity Silicone oil drops acoustically levitated in water falls to noticeably low values as the amplitude of oscillation is increased. A typical, experimentally determined relative frequency decrease of a 0.5 cubic centimeters drop would be about 10% when the maximum deformed shape is characterized by a major to minor axial ratio of 1.9. On the other hand, no change in the fundamental mode frequency could be detected for 1 mm drops levitated in air. The experimental data for the decay constant of the quadrupole mode of drops immersed in a liquid host indicate a slight increase for larger oscillation amplitudes. A qualitative investigation of the internal fluid flows for such drops revealed the existence of steady internal circulation within drops oscillating in the fundamental and higher modes. The flow field configuration in the outer host liquid is also significantly altered when the drop oscillation amplitude becomes large.
Toward complete pion nucleon amplitudes
Mathieu, Vincent; Danilkin, Igor V.; Fernández-Ramírez, Cesar; ...
2015-10-05
We compare the low-energy partial wave analyses πN scattering with a high-energy data via finite energy sum rules. We also construct a new set of amplitudes by matching the imaginary part from the low-energy analysis with the high-energy, Regge parametrization and then reconstruct the real parts using dispersion relations.
Toward complete pion nucleon amplitudes
Mathieu, Vincent; Danilkin, Igor V.; Fernández-Ramírez, Cesar; Pennington, Michael R.; Schott, Diane M.; Szczepaniak, Adam P.; Fox, G.
2015-10-05
We compare the low-energy partial wave analyses πN scattering with a high-energy data via finite energy sum rules. We also construct a new set of amplitudes by matching the imaginary part from the low-energy analysis with the high-energy, Regge parametrization and then reconstruct the real parts using dispersion relations.
True amplitude prestack depth migration
NASA Astrophysics Data System (ADS)
Deng, Feng
Reliable analysis of amplitude variation with offset (or with angle) requires accurate amplitudes from prestack migration. In routine seismic data processing, amplitude balancing and automatic gain control are often used to reduce amplitude lateral variations. However, these methods are empirical and lack a solid physical basis; thus, there are uncertainties that might produce erroneous conclusions, and hence cause economic loss. During wavefield propagation, geometrical spreading, intrinsic attenuation, transmission losses and the energy conversion significantly distort the wavefield amplitude. Most current true-amplitude migrations usually compensate only for geometrical spreading. A new prestack depth migration based on the framework of reverse-time migration in the time-space domain was developed in this dissertation with the aim of compensating all of the propagation effects in one integrated algorithm. Geometrical spreading is automatically included because of the use of full two-way wave extrapolation. Viscoelastic wave equations are solved to handle the intrinsic attenuation with a priori quality factor. Transmission losses for both up- and down-going waves are compensated using a two-pass, recursive procedure based on extracting the angle-dependent reflection/transmission coefficients from prestack migration. The losses caused by the conversion of energy from one elastic model to another are accounted for through elastic wave extrapolation; the influence of the S wave velocity contrast on the P wave reflection coefficient is implicitly included by using the Zoeppritz equations to describe the reflection and transmission at an elastic interface. Only smooth background models are assumed to be known. The contrasts/ratios of the model parameters can be estimated by fitting the compensated angle-dependent reflection coefficients obtained from data for multiple sources. This is one useful by-product of the algorithm. Numerical tests on both 2D and 3D scalar
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.
Genus dependence of superstring amplitudes
Davis, Simon
2006-11-15
The problem of the consistency of the finiteness of the supermoduli space integral in the limit of vanishing super-fixed point distance and the genus-dependence of the integral over the super-Schottky coordinates in the fundamental region containing a neighborhood of |K{sub n}|=0 is resolved. Given a choice of the categories of isometric circles representing the integration region, the exponential form of bounds for superstring amplitudes is derived.
Phase variation of hadronic amplitudes
Dedonder, J.-P.; Gibbs, W. R.; Nuseirat, Mutazz
2008-04-15
The phase variation with angle of hadronic amplitudes is studied with a view to understanding the underlying physical quantities that control it and how well it can be determined in free space. We find that unitarity forces a moderately accurate determination of the phase in standard amplitude analyses but that the nucleon-nucleon analyses done to date do not give the phase variation needed to achieve a good representation of the data in multiple scattering calculations. Models are examined that suggest its behavior near forward angles is related to the radii of the real and absorptive parts of the interaction. The dependence of this phase on model parameters is such that if these radii are modified in the nuclear medium (in combination with the change due to the shift in energy of the effective amplitude in the medium) then the larger magnitudes of the phase needed to fit the data might be attainable but only for negative values of the phase variation parameter.
Crisis in Amplitude Control Hides in Multistability
NASA Astrophysics Data System (ADS)
Li, Chunbiao; Sprott, Julien Clinton; Xing, Hongyan
2016-12-01
A crisis of amplitude control can occur when a system is multistable. This paper proposes a new chaotic system with a line of equilibria to demonstrate the threat to amplitude control from multistability. The new symmetric system has two coefficients for amplitude control, one of which is a partial amplitude controller, while the other is a total amplitude controller that simultaneously controls the frequency. The amplitude parameter rescales the basins of attraction and triggers a state switch among different states resulting in a failure of amplitude control to the desired state.
Calculation of multi-loop superstring amplitudes
NASA Astrophysics Data System (ADS)
Danilov, G. S.
2016-12-01
The multi-loop interaction amplitudes in the closed, oriented superstring theory are obtained by the integration of local amplitudes. The local amplitude is represented by a sum over the spinning string local amplitudes. The spinning string local amplitudes are given explicitly through super-Schottky group parameters and through interaction vertex coordinates on the (1| 1) complex, non-split supermanifold. The obtained amplitudes are free from divergences. They are consistent with the world-sheet spinning string symmetries. The vacuum amplitude vanishes along with 1-, 2- and 3-point amplitudes of massless states. The vanishing of the above-mentioned amplitude occurs after the integration of the corresponding local amplitude has been performed over the super-Schottky group limiting points and over interaction vertex coordinate, except for those (3| 2) variables which are fixed due to SL(2)-symmetry.
Quasidistribution amplitude of heavy quarkonia
NASA Astrophysics Data System (ADS)
Jia, Yu; Xiong, Xiaonu
2016-11-01
The recently proposed quasidistributions point out a promising direction for lattice QCD to investigate the light-cone correlators, such as parton distribution functions and distribution amplitudes (DAs), directly in the x space. Owing to its excessive simplicity, heavy quarkonium can serve as an ideal theoretical laboratory to ascertain certain features of quasi-DAs. In the framework of nonrelativistic QCD factorization, we compute the order-αs correction to both light-cone distribution amplitudes (LCDAs) and quasi-DAs associated with the lowest-lying quarkonia, with the transverse-momentum UV cutoff interpreted as the renormalization scale. We confirm analytically that the quasi-DA of a quarkonium does reduce to the respective LCDA in the infinite-momentum limit. We also observe that, provided that the momentum of a charmonium reaches about 2-3 times its mass, the quasi-DAs already converge to the LCDAs to a decent level. These results might provide some useful guidance for the future lattice study of quasidistributions.
Large amplitude relativistic plasma waves
Coffey, Timothy
2010-05-15
Relativistic, longitudinal plasma oscillations are studied for the case of a simple water bag distribution of electrons having cylindrical symmetry in momentum space with the axis of the cylinder parallel to the velocity of wave propagation. The plasma is required to obey the relativistic Vlasov-Poisson equations, and solutions are sought in the wave frame. An exact solution for the plasma density as a function of the electrostatic field is derived. The maximum electric field is presented in terms of an integral over the known density. It is shown that when the perpendicular momentum is neglected, the maximum electric field approaches infinity as the wave phase velocity approaches the speed of light. It is also shown that for any nonzero perpendicular momentum, the maximum electric field will remain finite as the wave phase velocity approaches the speed of light. The relationship to previously published solutions is discussed as is some recent controversy regarding the proper modeling of large amplitude relativistic plasma waves.
Expansion of Einstein-Yang-Mills amplitude
NASA Astrophysics Data System (ADS)
Fu, Chih-Hao; Du, Yi-Jian; Huang, Rijun; Feng, Bo
2017-09-01
In this paper, we study from various perspectives the expansion of tree level single trace Einstein-Yang-Mills amplitudes into linear combination of color-ordered Yang-Mills amplitudes. By applying the gauge invariance principle, a programable recursive construction is devised to expand EYM amplitude with arbitrary number of gravitons into EYM amplitudes with fewer gravitons. Based on this recursive technique we write down the complete expansion of any single trace EYM amplitude in the basis of color-order Yang-Mills amplitude. As a byproduct, an algorithm for constructing a polynomial form of the BCJ numerator for Yang-Mills amplitudes is also outlined in this paper. In addition, by applying BCFW recursion relation we show how to arrive at the same EYM amplitude expansion from the on-shell perspective. And we examine the EYM expansion using KLT relations and show how to evaluate the expansion coefficients efficiently.
Constructing amplitudes from their soft limits
NASA Astrophysics Data System (ADS)
Boucher-Veronneau, Camille; Larkoski, Andrew J.
2011-09-01
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.
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.
Tsunami Focusing and Leading Amplitude
NASA Astrophysics Data System (ADS)
Kanoglu, U.
2016-12-01
Tsunamis transform substantially through spatial and temporal spreading from their source region. This substantial spreading might result unique maximum tsunami wave heights which might be attributed to the source configuration, directivity, the waveguide structures of mid-ocean ridges and continental shelves, focusing and defocusing through submarine seamounts, random focusing due to small changes in bathymetry, dispersion, and, most likely, combination of some of these effects. In terms of the maximum tsunami wave height, after Okal and Synolakis (2016 Geophys. J. Int. 204, 719-735), it is clear that dispersion would be one of the reasons to drive the leading wave amplitude in a tsunami wave train. Okal and Synolakis (2016), referring to this phenomenon as sequencing -later waves in the train becoming higher than the leading one, considered Hammack's (1972, Ph.D. Dissertation, Calif. Inst. Tech., 261 pp) formalism, in addition to LeMéhauté and Wang's (1995 Water waves generated by underwater explosion, World Scientific, 367 pp), to evaluate linear dispersive tsunami propagation from a circular plug uplifted on an ocean of constant depth. They identified transition distance, as the second wave being larger, performing parametric study for the radius of the plug and the depth of the ocean. Here, we extend Okal and Synolakis' (2016) analysis to an initial wave field with a finite crest length and, in addition, to a most common tsunami initial wave form of N-wave (Tadepalli and Synolakis, 1994 Proc. R. Soc. A: Math. Phys. Eng. Sci. 445, 99-112). First, we investigate the focusing feature in the leading-depression side, which enhance tsunami wave height as presented by Kanoglu et al. (2013 Proc. R. Soc. A: Math. Phys. Eng. Sci. 469, 20130015). We then discuss the results in terms of leading wave amplitude presenting a parametric study and identify a simple relation for the transition distance. The solution presented here could be used to better analyze dispersive
The relationship between sensory latency and amplitude.
Bodofsky, Elliot B; Cohen, Stephen J; Kumar, Rohini J; Schindelheim, Adam; Gaughan, John
2016-12-01
To prove that the relationship between sensory latencies and amplitudes is useful in determining the severity of neuropathies. This is achieved by deriving a mathematical relationship between sensory distal latency and amplitude. Determine whether sensory amplitudes below predicted correlate with a worse pathology. Patients seen for Nerve Conduction Studies by the Department of Physical Medicine and Rehabilitation at Cooper University Hospital between 12/1/12 and 12/31/14 were invited to participate in a prospective database. The median, ulnar and sural sensory latencies and amplitudes were analyzed with both linear and power regression. Patients with amplitudes above and below the regression curve were compared for latency, amplitude and velocity of other nerves. Carpal Tunnel Patients were analyzed to determine whether Median sensory amplitude below predicted correlated with more severe disease. For the Median nerve, Power Regression Analysis showed a stronger correlation (R(2)=0.54) than linear regression (R(2)=0.34). Patients with Median sensory amplitude below the power correlation curve showed significantly longer ulnar sensory latency, and lower sensory amplitude than those above. Carpal Tunnel Syndrome patients with Median sensory amplitude well below predicted by the power relationship showed more advanced disease. For the ulnar and sural sensory nerve, the difference between power and linear regression was not significant. A power regression curve correlates sensory latency and amplitude better than linear regression. The latency amplitude relationship correlates with other parameters of nerve function and severity of Carpal Tunnel Syndrome. This implies that below predicted sensory amplitude may indicate worse disease, and could be a useful diagnostic tool. Copyright Â© 2016 Elsevier Ltd. All rights reserved.
Amplitude-dependent station magnitude
NASA Astrophysics Data System (ADS)
Radzyner, Yael; Ben Horin, Yochai; Steinberg, David M.
2016-04-01
Magnitude, a concept first presented by Gutenberg and Richter, adjusts measurements of ground motion for epicentral distance and source depth. Following this principle, the IDC defines the j'th station body wave magnitude for event i as mb(stai,j) = log 10(Aj,i/Tj,i) + V C(Δj,i,hi) , where VC is the Veith-Clawson (VC) correction to compensate for the epicentral distance of the station and the depth of the source. The network magnitude is calculated as the average of station magnitudes. The IDC magnitude estimation is used for event characterization and discrimination and it should be as accurate as possible. Ideally, the network magnitude should be close in value to the station magnitudes. In reality, it is observed that the residuals range between -1 and 1 mu or ±25% of a given mb(neti) value. We show that the residual, mb(neti) -mb(staj,i), depends linearly on log 10(Aj,i/Tj,i), and we correct for this dependence using the following procedure: Calculate a "jackknifed" network magnitude, mbj,n(neti), i.e. an average over all participating stations except station n. Using all measurements at station n, calculate the parameters an, bn of the linear fit of the residual mbj,n(neti) - mb(stan,i to log 10(An,i/Tn,i). For each event i at station n calculate the new station magnitude mbnew(stan,i) = (an + 1)log(An,i/Tn,i) + V C(Δn,i,hi) + bn Calculate the new network magnitude: mbnew(neti) = 1N- ∑ n=1nmbnew(stan,i) The procedure was used on more than two million station-event pairs. Correcting for the station-specific dependence on log amplitude reduces the residuals by roughly a third. We have calculated the spread of the distributions, and compared the original values and those for the corrected magnitudes. The spread is the ratio between the variance of the network magnitudes, and the variance of the residual. Calculations show an increase in the ratio of the variance, meaning that the correction process presented in this document did not lead to loss of variance
Gravity and Yang-Mills amplitude relations
Bjerrum-Bohr, N. E. J.; Damgaard, Poul H.; Soendergaard, Thomas; FengBo
2010-11-15
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.
Minimal Basis for Gauge Theory Amplitudes
Bjerrum-Bohr, N. E. J.; Damgaard, Poul H.; Vanhove, Pierre
2009-10-16
Identities based on monodromy for integrations in string theory are used to derive relations between different color-ordered tree-level amplitudes in both bosonic and supersymmetric string theory. These relations imply that the color-ordered tree-level n-point gauge theory amplitudes can be expanded in a minimal basis of (n-3)exclamation amplitudes. This result holds for any choice of polarizations of the external states and in any number of dimensions.
Discontinuities of multi-Regge amplitudes
NASA Astrophysics Data System (ADS)
Fadin, V. S.
2015-04-01
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 ≥ 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.
DVCS amplitude with kinematical twist-3 terms
Radyushkin, A.V.; Weiss, C.
2000-08-01
The authors compute the amplitude of deeply virtual Compton scattering (DVCS) using the calculus of QCD string operators in coordinate representation. To restore the electromagnetic gauge invariance (transversality) of the twist-2 amplitude they include the operators of twist-3 which appear as total derivatives of twist-2 operators. The results are equivalent to a Wandzura-Wilczek approximation for twist-3 skewed parton distributions. They find that this approximation gives a finite result for the amplitude of a longitudinally polarized virtual photon, while the amplitude for transverse polarization is divergent, i.e., factorization breaks down in this term.
Secondary threshold amplitudes for sinuous streak breakdown
NASA Astrophysics Data System (ADS)
Cossu, Carlo; Brandt, Luca; Bagheri, Shervin; Henningson, Dan S.
2011-07-01
The nonlinear stability of laminar sinuously bent streaks is studied for the plane Couette flow at Re = 500 in a nearly minimal box and for the Blasius boundary layer at Reδ*=700. The initial perturbations are nonlinearly saturated streamwise streaks of amplitude AU perturbed with sinuous perturbations of amplitude AW. The local boundary of the basin of attraction of the linearly stable laminar flow is computed by bisection and projected in the AU - AW plane providing a well defined critical curve. Different streak transition scenarios are seen to correspond to different regions of the critical curve. The modal instability of the streaks is responsible for transition for AU = 25%-27% for the considered flows, where sinuous perturbations of amplitude below AW ≈ 1%-2% are sufficient to counteract the streak viscous dissipation and induce breakdown. The critical amplitude of the sinuous perturbations increases when the streamwise streak amplitude is decreased. With secondary perturbations amplitude AW ≈ 4%, breakdown is induced on stable streamwise streaks with AU ≈ 13%, following the secondary transient growth scenario first examined by Schoppa and Hussain [J. Fluid Mech. 453, 57 (2002)]. A cross-over, where the critical amplitude of the sinuous perturbation becomes larger than the amplitude of streamwise streaks, is observed for streaks of small amplitude AU < 5%-6%. In this case, the transition is induced by an initial transient amplification of streamwise vortices, forced by the decaying sinuous mode. This is followed by the growth of the streaks and final breakdown. The shape of the critical AU - AW curve is very similar for Couette and boundary layer flows and seems to be relatively insensitive to the nature of the edge states on the basin boundary. The shape of this critical curve indicates that the stability of streamwise streaks should always be assessed in terms of both the streak amplitude and the amplitude of spanwise velocity perturbations.
Off-shell amplitudes and Grassmannians
NASA Astrophysics Data System (ADS)
Bork, L. V.; Onishchenko, A. I.
2017-09-01
The Grassmannian representation for gauge-invariant amplitudes for arbitrary number of legs with one of them being off-shell is derived for the case of N = 4 SYM. The obtained formula are successfully checked against known BCFW results for MHV n , NMHV4 and NMHV5 amplitudes.
BCFW construction of the Veneziano amplitude
NASA Astrophysics Data System (ADS)
Fotopoulos, Angelos
2011-06-01
In this paper we demonstrate how one can compute the Veneziano amplitude for bosonic string theory using the Britto-Cachazo-Feng-Witten method. We use an educated ansatz for the cubic amplitude of two tachyons and an arbitrary level string state.
Formant Amplitude of Children with Down's Syndrome.
ERIC Educational Resources Information Center
Pentz, Arthur L., Jr.
1987-01-01
The sustained vowel sounds of 14 noninstitutionalized 7- to 10-year-old children with Down's syndrome were analyzed acoustically for vowel formant amplitude levels. The subjects with Down's syndrome had formant amplitude intensity levels significantly lower than those of a similar group of speakers without Down's syndrome. (Author/DB)
Amplitude image processing by diffractive optics.
Cagigal, Manuel P; Valle, Pedro J; Canales, V F
2016-02-22
In contrast to the standard digital image processing, which operates over the detected image intensity, we propose to perform amplitude image processing. Amplitude processing, like low pass or high pass filtering, is carried out using diffractive optics elements (DOE) since it allows to operate over the field complex amplitude before it has been detected. We show the procedure for designing the DOE that corresponds to each operation. Furthermore, we accomplish an analysis of amplitude image processing performances. In particular, a DOE Laplacian filter is applied to simulated astronomical images for detecting two stars one Airy ring apart. We also check by numerical simulations that the use of a Laplacian amplitude filter produces less noisy images than the standard digital image processing.
Magnetospheric chorus - Amplitude and growth rate
NASA Technical Reports Server (NTRS)
Burtis, W. J.; Helliwell, R. A.
1975-01-01
A new study of the amplitude of magnetospheric chorus with 1966-1967 data from the Stanford University/Stanford Research Institute VLF receivers on Ogo 1 and Ogo 3 has confirmed the band-limited character of magnetospheric chorus in general and the double-banding of near-equatorial chorus. Chorus amplitude tended to be inversely correlated with frequency, implying lower intensities at lower L values. Individual chorus emissions often showed a characteristic amplitude variation, with rise times of 10 to 300 ms, a short duration at peak amplitude, and decay times of 100 to 3000 msec. Growth was often approximately exponential, with rates from 200 to nearly 2000 dB/sec. Rate of change of frequency was found in many cases to be independent of emission amplitude, in agreement with the cyclotron feedback theory of chorus (Helliwell, 1967, 1970).
Thermal cracking and amplitude dependent attenuation
Johnston, D.H.; Toksoez, M.N.
1980-02-10
The role of crack and grain boundary contacts in determining seismic wave attenuation in rock is investigated by examining Q as a function of thermal cycling (cracking) and wave strain amplitude. Q values are obtained using a longitudinal resonant bar technique in the 10- to 20-kHz range for maximum strain amplitudes varying from roughly 10/sup -8/ to 10/sup -5/. The samples studied include the Berea and Navajo sandstones, Plexiglas, Westerly granite, Solenhofen limestone, and Frederick diabase, the latter two relatively crack free in their virgin state. Measurements were made at room temperature and pressure in air. Q values for both sandstones are constant at low strains (<10/sup -6/) but decrease rapidly with amplitude at higher strains. There is no hysteresis of Q with amplitude. Q values for Plexiglas show no indication of amplitude dependent behavior. The granite, limestone, and diabase are thermally cycled at both fast and slow heating rates in order to induce cracking. Samples slowly cycled at 400/sup 0/C show a marked increase in Q that cannot be entirely explained by outgassing of volatiles. Cycling may also widen thin cracks and grain boundaries, reducing contact areas. Samples heated beyond 400/sup 0/C, or rapidly heated, result in generally decreasing Q values. The amplitude dependence of Q is found to be coupled to the effects of thermal cycling. For rock slowly cycled 400)C or less, the transition from low-amplitude contant Q to high-amplitude variable Q behavior decreases to lower amplitudes as a function of maximum temperature. Above 400/sup 0/C, and possibly in th rapidly heated samples also, the transition moves to higher amplitudes.
Color-kinematics duality for QCD amplitudes
NASA Astrophysics Data System (ADS)
Johansson, Henrik; Ochirov, Alexander
2016-01-01
We show that color-kinematics duality is present in tree-level amplitudes of quantum chromodynamics with massive flavored quarks. Starting with the color structure of QCD, we work out a new color decomposition for n-point tree amplitudes in a reduced basis of primitive amplitudes. These primitives, with k quark-antiquark pairs and ( n - 2 k) gluons, are taken in the ( n - 2)! /k! Melia basis, and are independent under the color-algebra Kleiss-Kuijf relations. This generalizes the color decomposition of Del Duca, Dixon, and Maltoni to an arbitrary number of quarks. The color coefficients in the new decomposition are given by compact expressions valid for arbitrary gauge group and representation. Considering the kinematic structure, we show through explicit calculations that color-kinematics duality holds for amplitudes with general configurations of gluons and massive quarks. The new (massive) amplitude relations that follow from the duality can be mapped to a well-defined subset of the familiar BCJ relations for gluons. They restrict the amplitude basis further down to ( n - 3)!(2 k - 2) /k! primitives, for two or more quark lines. We give a decomposition of the full amplitude in that basis. The presented results provide strong evidence that QCD obeys the color-kinematics duality, at least at tree level. The results are also applicable to supersymmetric and D-dimensional extensions of QCD.
Amplitude- and rise-time-compensated filters
Nowlin, Charles H.
1984-01-01
An amplitude-compensated rise-time-compensated filter for a pulse time-of-occurrence (TOOC) measurement system is disclosed. The filter converts an input pulse, having the characteristics of random amplitudes and random, non-zero rise times, to a bipolar output pulse wherein the output pulse has a zero-crossing time that is independent of the rise time and amplitude of the input pulse. The filter differentiates the input pulse, along the linear leading edge of the input pulse, and subtracts therefrom a pulse fractionally proportional to the input pulse. The filter of the present invention can use discrete circuit components and avoids the use of delay lines.
Hidden simplicity of gauge theory amplitudes
NASA Astrophysics Data System (ADS)
Drummond, J. M.
2010-11-01
These notes were given as lectures at the CERN Winter School on Supergravity, Strings and Gauge Theory 2010. We describe the structure of scattering amplitudes in gauge theories, focussing on the maximally supersymmetric theory to highlight the hidden symmetries which appear. Using the Britto, Cachzo, Feng and Witten (BCFW) recursion relations we solve the tree-level S-matrix in \\ {N}=4 super Yang-Mills theory and describe how it produces a sum of invariants of a large symmetry algebra. We review amplitudes in the planar theory beyond tree level, describing the connection between amplitudes and Wilson loops, and discuss the implications of the hidden symmetries.
A recursion relation for gravity amplitudes
NASA Astrophysics Data System (ADS)
Bedford, James; Brandhuber, Andreas; Spence, Bill; Travaglini, Gabriele
2005-08-01
Britto, Cachazo and Feng have recently derived a recursion relation for tree-level scattering amplitudes in Yang-Mills. This relation has a bilinear structure inherited from factorisation on multi-particle poles of the scattering amplitudes—a rather generic feature of field theory. Motivated by this, we propose a new recursion relation for scattering amplitudes of gravitons at tree level. Using this, we derive a new general formula for the MHV tree-level scattering amplitude for n gravitons. Finally, we comment on the existence of recursion relations in general field theories.
Phase and amplitude errors in FM radars
NASA Astrophysics Data System (ADS)
Griffiths, Hugh D.
The constraints on phase and amplitude errors are determined for various types of FM radar by calculating the range sidelobe levels on the point target response due to the phase and amplitude modulation of the target echo. It is shown that under certain circumstances the constraints on phase linearity appropriate for conventional pulse compression radars are unnecessarily stringent, and quite large phase errors can be tolerated provided the relative delay of the local oscillator with respect to the target echo is small compared with the periodicity of the phase error characteristic. The constraints on amplitude flatness, however, are severe under almost all circumstances.
A link representation for gravity amplitudes
NASA Astrophysics Data System (ADS)
He, Song
2013-10-01
We derive a link representation for all tree amplitudes in supergravity, from a recent conjecture by Cachazo and Skinner. The new formula explicitly writes amplitudes as contour integrals over constrained link variables, with an integrand naturally expressed in terms of determinants, or equivalently tree diagrams. Important symmetries of the amplitude, such as supersymmetry, parity and (partial) permutation invariance, are kept manifest in the formulation. We also comment on rewriting the formula in a GL( k)-invariant manner, which may serve as a starting point for the generalization to possible Grassmannian contour integrals.
Amplitude dynamics favors synchronization in complex networks
Gambuzza, Lucia Valentina; Gómez-Gardeñes, Jesus; Frasca, Mattia
2016-01-01
In this paper we study phase synchronization in random complex networks of coupled periodic oscillators. In particular, we show that, when amplitude dynamics is not negligible, phase synchronization may be enhanced. To illustrate this, we compare the behavior of heterogeneous units with both amplitude and phase dynamics and pure (Kuramoto) phase oscillators. We find that in small network motifs the behavior crucially depends on the topology and on the node frequency distribution. Surprisingly, the microscopic structures for which the amplitude dynamics improves synchronization are those that are statistically more abundant in random complex networks. Thus, amplitude dynamics leads to a general lowering of the synchronization threshold in arbitrary random topologies. Finally, we show that this synchronization enhancement is generic of oscillators close to Hopf bifurcations. To this aim we consider coupled FitzHugh-Nagumo units modeling neuron dynamics. PMID:27108847
Stable ac phase and amplitude comparator
NASA Technical Reports Server (NTRS)
Bruce, H. P.
1967-01-01
Stable ac phase and amplitude comparator detects excessive vehicle maneuvering or vibration. It has phase demodulation, low-pass filter, and multiple threshold-setting capability designed specifically for low drifts over a wide range of temperatures.
Pion distribution amplitude from lattice QCD
NASA Astrophysics Data System (ADS)
Zhang, Jian-Hui; Chen, Jiunn-Wei; Ji, Xiangdong; Jin, Luchang; Lin, Huey-Wen
2017-05-01
We present the first lattice-QCD calculation of the pion distribution amplitude using the large-momentum effective field theory (LaMET) approach, which allows us to extract light cone parton observables from a Euclidean lattice. The mass corrections needed to extract the pion distribution amplitude from this approach are calculated to all orders in mπ2/Pz2 . We also implement the Wilson-line renormalization which is crucial to remove the power divergences in this approach, and find that it reduces the oscillation at the end points of the distribution amplitude. Our exploratory result at 310-MeV pion mass favors a single-hump form broader than the asymptotic form of the pion distribution amplitude.
The periods and amplitudes of TU Cas
NASA Technical Reports Server (NTRS)
Hodson, S. W.; Cox, A. N.
1980-01-01
Light curve observations of the double-mode Cepheid TU Cas obtained by 10 different sets of observers on several photometric systems over a time span of 67 years were carefully studied to determine the fundamental and first overtone periods and their amplitudes on the V magnitude scale. The presence of a second overtone radial pulsation is discussed, and it is concluded that a previous detection of this mode was spurious due to the lack of a proper zero point correction for two groups of observations. The amplitudes of the two modes are shown to possibly vary during the entire observing period with the fundamental mode amplitude of 0.69 + or - 0.03 and the overtone amplitude decreasing about 0.2 or 0.3 magnitude. If this Cepheid displays the two pulsation modes because it is mode switching, this switching time scale might be less than a hundred years.
Amplitude dynamics favors synchronization in complex networks
NASA Astrophysics Data System (ADS)
Gambuzza, Lucia Valentina; Gómez-Gardeñes, Jesus; Frasca, Mattia
2016-04-01
In this paper we study phase synchronization in random complex networks of coupled periodic oscillators. In particular, we show that, when amplitude dynamics is not negligible, phase synchronization may be enhanced. To illustrate this, we compare the behavior of heterogeneous units with both amplitude and phase dynamics and pure (Kuramoto) phase oscillators. We find that in small network motifs the behavior crucially depends on the topology and on the node frequency distribution. Surprisingly, the microscopic structures for which the amplitude dynamics improves synchronization are those that are statistically more abundant in random complex networks. Thus, amplitude dynamics leads to a general lowering of the synchronization threshold in arbitrary random topologies. Finally, we show that this synchronization enhancement is generic of oscillators close to Hopf bifurcations. To this aim we consider coupled FitzHugh-Nagumo units modeling neuron dynamics.
Large Amplitude Oscillations of a Double Pendulum
NASA Astrophysics Data System (ADS)
Gerres, Jeffrey M.; Jacobs, Robert M.; Kasun, Sara F.; Bacon, Margaret E.; Nagolu, Chakravarthi M.; Owens, Erin L.; Siehl, Kevin F.; Thomsen, Marshall; Troyer, Jon S.
2008-03-01
The nature of the normal modes of oscillation in the small angle regime of a double pendulum is well established. However, for large amplitude oscillations, a closed form solution of the differential equations of motion does not exist. Using Lagrange formalism, we explore both the in-phase and out-of-phase normal modes of oscillation of a double pendulum as a function of the mass ratio of the two bobs and their initial angular positions. We conduct the analysis using MatLab, where we initially verify our code in the known small amplitude limit. Among our results we find that certain symmetries between the in-phase and out-of-phase normal modes that exist in the small amplitude limit are no longer present at large amplitudes.
Quartic Amplitudes for Minkowski Higher Spin
NASA Astrophysics Data System (ADS)
Bengtsson, Anders K. H.
The old 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.
Amplitude metrics for cellular circadian bioluminescence reporters.
St John, Peter C; Taylor, Stephanie R; Abel, John H; Doyle, Francis J
2014-12-02
Bioluminescence rhythms from cellular reporters have become the most common method used to quantify oscillations in circadian gene expression. These experimental systems can reveal phase and amplitude change resulting from circadian disturbances, and can be used in conjunction with mathematical models to lend further insight into the mechanistic basis of clock amplitude regulation. However, bioluminescence experiments track the mean output from thousands of noisy, uncoupled oscillators, obscuring the direct effect of a given stimulus on the genetic regulatory network. In many cases, it is unclear whether changes in amplitude are due to individual changes in gene expression level or to a change in coherence of the population. Although such systems can be modeled using explicit stochastic simulations, these models are computationally cumbersome and limit analytical insight into the mechanisms of amplitude change. We therefore develop theoretical and computational tools to approximate the mean expression level in large populations of noninteracting oscillators, and further define computationally efficient amplitude response calculations to describe phase-dependent amplitude change. At the single-cell level, a mechanistic nonlinear ordinary differential equation model is used to calculate the transient response of each cell to a perturbation, whereas population-level dynamics are captured by coupling this detailed model to a phase density function. Our analysis reveals that amplitude changes mediated at either the individual-cell or the population level can be distinguished in tissue-level bioluminescence data without the need for single-cell measurements. We demonstrate the effectiveness of the method by modeling experimental bioluminescence profiles of light-sensitive fibroblasts, reconciling the conclusions of two seemingly contradictory studies. This modeling framework allows a direct comparison between in vitro bioluminescence experiments and in silico ordinary
Seismic directional beamforming using cosine amplitude distribution
NASA Astrophysics Data System (ADS)
Jiang, T.; Xu, X.; Song, J.; Jia, H.; Ge, L.
2013-12-01
o improve the signal-to-noise ratio in seismic exploration, we studied the method of time domain seismic beam-forming based on receiver array (TSBBRA). TSBBRA is useful to extract reflected waves from some target layers and decrease noise from other direction. When noise is strong enough, the control parameter of the method of TSBBRA need to be increased. It means that we have to use more raw records to form a directional seismic record. Therefore, the signal energy in beam is much denser, and the beam becomes narrower accordingly. When the beam can not cover the receiver array, the signal-to-noise ratios in different traces are quite unbalanced and average quality of data probably is still quite low. Therefore, this paper proposes seismic directional beamforming using the cosine amplitude distribution (SDBCAD). SDBCAD can adjust seismic beam shape by introducing cosine amplitude distribution, an amplitude weighting method, in the procedure of beamforming. We studied cosine amplitude weighting function, analyzed the characteristics of uniform and cosine amplitude distribution in beamforming, and compared directivity of beams from the two kind of amplitude pattern. It shows that the main beam of cosine-weighted amplitude is different from uniform distribution. The coverage of main beam from SDBCAD is wider than uniform amplitude, and the width of beam is varied with different number of cosine order. So we simulated the seismic raw record, and used TSBBRA and SDBCAD to process simulated data at the receiving array. The results show that SDBCAD can broaden directional beam, and the main beam from SDBCAD can cover the entire traces instead of partial coverage in TSBBRA. The average signal-to-noise ratio increased 0.2~4.5dB. It concludes that SDBCAD is competent to stretch beam reasonable, and it is useful to boost signal-to-noise ratio when beam from TSBBRA is too narrow to illuminate receiver array properly. Updated results will be presented at the meeting.
Nucleon Distribution Amplitudes from Lattice QCD
Goeckeler, Meinulf; Kaltenbrunner, Thomas; Warkentin, Nikolaus; Horsley, Roger; Zanotti, James M.; Nakamura, Yoshifumi; Pleiter, Dirk; Schierholz, Gerrit; Rakow, Paul E. L.; Schaefer, Andreas; Stueben, Hinnerk
2008-09-12
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.
Amplitude Metrics for Cellular Circadian Bioluminescence Reporters
St. John, Peter C.; Taylor, Stephanie R.; Abel, John H.; Doyle, Francis J.
2014-01-01
Bioluminescence rhythms from cellular reporters have become the most common method used to quantify oscillations in circadian gene expression. These experimental systems can reveal phase and amplitude change resulting from circadian disturbances, and can be used in conjunction with mathematical models to lend further insight into the mechanistic basis of clock amplitude regulation. However, bioluminescence experiments track the mean output from thousands of noisy, uncoupled oscillators, obscuring the direct effect of a given stimulus on the genetic regulatory network. In many cases, it is unclear whether changes in amplitude are due to individual changes in gene expression level or to a change in coherence of the population. Although such systems can be modeled using explicit stochastic simulations, these models are computationally cumbersome and limit analytical insight into the mechanisms of amplitude change. We therefore develop theoretical and computational tools to approximate the mean expression level in large populations of noninteracting oscillators, and further define computationally efficient amplitude response calculations to describe phase-dependent amplitude change. At the single-cell level, a mechanistic nonlinear ordinary differential equation model is used to calculate the transient response of each cell to a perturbation, whereas population-level dynamics are captured by coupling this detailed model to a phase density function. Our analysis reveals that amplitude changes mediated at either the individual-cell or the population level can be distinguished in tissue-level bioluminescence data without the need for single-cell measurements. We demonstrate the effectiveness of the method by modeling experimental bioluminescence profiles of light-sensitive fibroblasts, reconciling the conclusions of two seemingly contradictory studies. This modeling framework allows a direct comparison between in vitro bioluminescence experiments and in silico ordinary
Bootstrapping One-Loop QCD Amplitudes
Berger, Carola F.; /SLAC
2006-09-08
We review the recently developed bootstrap method for the computation of high-multiplicity QCD amplitudes at one loop. We illustrate the general algorithm step by step with a six-point example. The method combines (generalized) unitarity with on-shell recursion relations to determine the not cut-constructible, rational terms of these amplitudes. Our bootstrap approach works for arbitrary configurations of gluon helicities and arbitrary numbers of external legs.
Feynman amplitudes and limits of heights
NASA Astrophysics Data System (ADS)
Amini, O.; Bloch, S. J.; Burgos Gil, J. I.; Fresán, J.
2016-10-01
We investigate from a mathematical perspective how Feynman amplitudes appear in the low-energy limit of string amplitudes. In this paper, we prove the convergence of the integrands. We derive this from results describing the asymptotic behaviour of the height pairing between degree-zero divisors, as a family of curves degenerates. These are obtained by means of the nilpotent orbit theorem in Hodge theory.
Vowel identification by amplitude and phase contrast.
Molis, Michelle R; Diedesch, Anna; Gallun, Frederick; Leek, Marjorie R
2013-02-01
Vowel identification is largely dependent on listeners' access to the frequency of two or three peaks in the amplitude spectrum. Earlier work has demonstrated that, whereas normal-hearing listeners can identify harmonic complexes with vowel-like spectral shapes even with very little amplitude contrast between "formant" components and remaining harmonic components, listeners with hearing loss require greater amplitude differences. This is likely the result of the poor frequency resolution that often accompanies hearing loss. Here, we describe an additional acoustic dimension for emphasizing formant versus non-formant harmonics that may supplement amplitude contrast information. The purpose of this study was to determine whether listeners were able to identify "vowel-like" sounds using temporal (component phase) contrast, which may be less affected by cochlear loss than spectral cues, and whether overall identification improves when congruent temporal and spectral information are provided together. Five normal-hearing and five hearing-impaired listeners identified three vowels over many presentations. Harmonics representing formant peaks were varied in amplitude, phase, or a combination of both. In addition to requiring less amplitude contrast, normal-hearing listeners could accurately identify the sounds with less phase contrast than required by people with hearing loss. However, both normal-hearing and hearing-impaired groups demonstrated the ability to identify vowel-like sounds based solely on component phase shifts, with no amplitude contrast information, and they also showed improved performance when congruent phase and amplitude cues were combined. For nearly all listeners, the combination of spectral and temporal information improved identification in comparison to either dimension alone.
Twistor-strings and gravity tree amplitudes
NASA Astrophysics Data System (ADS)
Adamo, Tim; Mason, Lionel
2013-04-01
Recently we discussed how Einstein supergravity tree amplitudes might be obtained from the original Witten and Berkovits twistor-string theory when external conformal gravitons are restricted to be Einstein gravitons. Here we obtain a more systematic understanding of the relationship between conformal and Einstein gravity amplitudes in that twistor-string theory. We show that although it does not in general yield Einstein amplitudes, we can nevertheless obtain some partial twistor-string interpretation of the remarkable formulae recently been found by Hodges and generalized to all tree amplitudes by Cachazo and Skinner. The Hodges matrix and its higher degree generalizations encode the world sheet correlators of the twistor string. These matrices control both Einstein amplitudes and those of the conformal gravity arising from the Witten and Berkovits twistor-string. Amplitudes in the latter case arise from products of the diagonal elements of the generalized Hodges matrices and reduced determinants give the former. The reduced determinants arise if the contractions in the worldsheet correlator are restricted to form connected trees at MHV. The (generalized) Hodges matrices arise as weighted Laplacian matrices for the graph of possible contractions in the correlators and the reduced determinants of these weighted Laplacian matrices give the sum of the connected tree contributions by an extension of the matrix-tree theorem.
Amplitude Modulations of Acoustic Communication Signals
NASA Astrophysics Data System (ADS)
Turesson, Hjalmar K.
2011-12-01
In human speech, amplitude modulations at 3 -- 8 Hz are important for discrimination and detection. Two different neurophysiological theories have been proposed to explain this effect. The first theory proposes that, as a consequence of neocortical synaptic dynamics, signals that are amplitude modulated at 3 -- 8 Hz are propagated better than un-modulated signals, or signals modulated above 8 Hz. This suggests that neural activity elicited by vocalizations modulated at 3 -- 8 Hz is optimally transmitted, and the vocalizations better discriminated and detected. The second theory proposes that 3 -- 8 Hz amplitude modulations interact with spontaneous neocortical oscillations. Specifically, vocalizations modulated at 3 -- 8 Hz entrain local populations of neurons, which in turn, modulate the amplitude of high frequency gamma oscillations. This suggests that vocalizations modulated at 3 -- 8 Hz should induce stronger cross-frequency coupling. Similar to human speech, we found that macaque monkey vocalizations also are amplitude modulated between 3 and 8 Hz. Humans and macaque monkeys share similarities in vocal production, implying that the auditory systems subserving perception of acoustic communication signals also share similarities. Based on the similarities between human speech and macaque monkey vocalizations, we addressed how amplitude modulated vocalizations are processed in the auditory cortex of macaque monkeys, and what behavioral relevance modulations may have. Recording single neuron activity, as well as, the activity of local populations of neurons allowed us to test both of the neurophysiological theories presented above. We found that single neuron responses to vocalizations amplitude modulated at 3 -- 8 Hz resulted in better stimulus discrimination than vocalizations lacking 3 -- 8 Hz modulations, and that the effect most likely was mediated by synaptic dynamics. In contrast, we failed to find support for the oscillation-based model proposing a
Periodic amplitude variations in Jovian continuum radiation
NASA Technical Reports Server (NTRS)
Kurth, W. S.; Gurnett, D. A.; Scarf, F. L.
1986-01-01
An analysis of periodic variations in the amplitude of continuum radiation near 3 kHz trapped in the Jovian magnetosphere shows structure with periods near both five and ten hours. Contrary to a plausible initial idea, the continuum amplitudes are not organized by position of the observer relative to the dense plasma sheet. Instead, there seem to be preferred orientations of system III longitude with respect to the direction to the sun which account for the peaks. This implies a clock-like modulation of the continuum radiation intensity as opposed to a searchlight effect. The importance of the dipole longitude-solar wind alignment to the amplitude of the continuum radiation implies the source region of the radiation is near the magnetopause and may indirectly tie the generation of the radio waves to the clocklike modulation of energetic electron fluxes from Jupiter.
Analytic representations of Yang-Mills amplitudes
NASA Astrophysics Data System (ADS)
Bjerrum-Bohr, N. E. J.; Bourjaily, Jacob L.; Damgaard, Poul H.; Feng, Bo
2016-12-01
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 Möbius-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 the foundations of 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.
Cut-constructible part of QCD amplitudes
Britto, Ruth; Feng Bo; Mastrolia, Pierpaolo
2006-05-15
Unitarity cuts are widely used in analytic computation of loop amplitudes in gauge theories such as QCD. We expand upon the technique introduced in hep-ph/0503132 to carry out any finite unitarity cut integral. This technique naturally separates the contributions of bubble, triangle and box integrals in one-loop amplitudes and is not constrained to any particular helicity configurations. Loop momentum integration is reduced to a sequence of algebraic operations. We discuss the extraction of the residues at higher-order poles. Additionally, we offer concise algebraic formulas for expressing coefficients of three-mass triangle integrals. As an application, we compute all remaining coefficients of bubble and triangle integrals for nonsupersymmetric six-gluon amplitudes.
Amplitude-coded color doppler: clinical applications.
Turetschek, K; Kollmann, C; Dorffner, R; Wunderbaldinger, P; Mostbeck, G
1999-01-01
Amplitude-coded color Doppler sonography (ACD) has become an useful adjunct to gray-scale US and conventional color Doppler sonography (CD) for the assessment of vascular diseases and pathologic conditions that might affect or alter tissue vascularization or perfusion. Basically, all US units that generate conventional color Doppler information through autocorrelation technique are capable of displaying ACD. This technique is also referred to as power Doppler, amplitude-mode color Doppler US, color Doppler energy (CDE), or US angiography. Amplitude-coded color Doppler sonography has already emerged as a valuable adjunct to conventional CD, particularly for evaluating flow in parts of the body where CD signal is weak because of slow flow, small blood vessels, or both.
A description of seismic amplitude techniques
NASA Astrophysics Data System (ADS)
Shadlow, James
2014-02-01
The acquisition of seismic data is a non-invasive technique used for determining the sub surface geology. Changes in lithology and fluid fill affect the seismic wavelet. Analysing seismic data for direct hydrocarbon indicators (DHIs), such as full stack amplitude anomalies, or amplitude variation with offset (AVO), can help a seismic interpreter relate the geophysical response to real geology and, more importantly, to distinguish the presence of hydrocarbons. Inversion is another commonly used technique that attempts to tie the seismic data back to the geology. Much has been written about these techniques, and attempting to gain an understanding on the theory and application of them by reading through various journals can be quite daunting. The purpose of this paper is to briefly outline DHI analysis, including full stack amplitude anomalies, AVO and inversion and show the relationship between all three. The equations presented have been included for completeness, but the reader can pass over the mathematical detail.
Modified π π amplitude with σ pole
NASA Astrophysics Data System (ADS)
Bydžovský, P.; Kamiński, R.; Nazari, V.
2014-12-01
A set of well-known once subtracted dispersion relations with imposed crossing symmetry condition is used to modify unitary multichannel S (π π , K K ¯, and η η ) and P (π π , ρ 2 π , and ρ σ ) wave amplitudes mostly below 1 GeV. Before the modifications, these amplitudes significantly did not satisfy the crossing symmetry condition and did not describe the π π threshold region. Moreover, the pole of the S wave amplitude related with the f0(500 ) meson (former f0(600 ) or σ ) had much smaller imaginary part and bigger real one in comparison with those in the newest Particle Data Group Tables. Here, these amplitudes are supplemented by near threshold expansion polynomials and refitted to the experimental data in the effective two pion mass from the threshold to 1.8 GeV and to the dispersion relations up to 1.1 GeV. In result the self consistent, i.e., unitary and fulfilling the crossing symmetry condition, S and P wave amplitudes are formed and the σ pole becomes much narrower and lighter. To eliminate doubts about the uniqueness of the so obtained sigma pole position short and purely mathematical proof of the uniqueness of the results is also presented. This analysis is addressed to a wide group of physicists and aims at providing a very effective and easy method of modification of, many presently used, π π amplitudes with a heavy and broad σ meson without changing of their original mathematical structure.
Nonlinear (super)symmetries and amplitudes
NASA Astrophysics Data System (ADS)
Kallosh, Renata
2017-03-01
There is an increasing interest in nonlinear supersymmetries in cosmological model building. Independently, elegant expressions for the all-tree amplitudes in models with nonlinear symmetries, like D3 brane Dirac-Born-Infeld-Volkov-Akulov theory, were recently discovered. Using the generalized background field method we show how, in general, nonlinear symmetries of the action, bosonic and fermionic, constrain amplitudes beyond soft limits. The same identities control, for example, bosonic E 7(7) scalar sector symmetries as well as the fermionic goldstino symmetries.
Coherent quantum states from classical oscillator amplitudes
NASA Astrophysics Data System (ADS)
Briggs, John S.; Eisfeld, Alexander
2012-05-01
In the first days of quantum mechanics Dirac pointed out an analogy between the time-dependent coefficients of an expansion of the Schrödinger equation and the classical position and momentum variables solving Hamilton's equations. Here it is shown that the analogy can be made an equivalence in that, in principle, systems of classical oscillators can be constructed whose position and momenta variables form time-dependent amplitudes which are identical to the complex quantum amplitudes of the coupled wave function of an N-level quantum system with real coupling matrix elements. Hence classical motion can reproduce quantum coherence.
Constructing Chaotic Systems with Total Amplitude Control
NASA Astrophysics Data System (ADS)
Li, Chunbiao; Sprott, Julien Clinton; Yuan, Zeshi; Li, Hongtao
A general method is introduced for controlling the amplitude of the variables in chaotic systems by modifying the degree of one or more of the terms in the governing equations. The method is applied to the Sprott B system as an example to show its flexibility and generality. The method may introduce infinite lines of equilibrium points, which influence the dynamics in the neighborhood of the equilibria and reorganize the basins of attraction, altering the multistability. However, the isolated equilibrium points of the original system and their stability are retained with their basic properties. Electrical circuit implementation shows the convenience of amplitude control, and the resulting oscillations agree well with results from simulation.
Topographic quantitative EEG amplitude in recovered alcoholics.
Pollock, V E; Schneider, L S; Zemansky, M F; Gleason, R P; Pawluczyk, S
1992-05-01
Topographic measures of electroencephalographic (EEG) amplitude were used to compare recovered alcoholics (n = 14) with sex- and age-matched control subjects. Delta, alpha, and beta activity did not distinguish the groups, but regional differences in theta distribution did. Recovered alcoholics showed more uniform distributions of theta amplitudes in bilateral anterior and posterior regions compared with controls. Because a minimum of 5 years had elapsed since the recovered alcoholic subjects fulfilled DSM-III-R criteria for alcohol abuse or dependence, it is unlikely these EEG theta differences reflect the effects of withdrawal.
Amplitude Models for Discrimination and Yield Estimation
Phillips, William Scott
2016-09-01
This seminar presentation describes amplitude models and yield estimations that look at the data in order to inform legislation. The following points were brought forth in the summary: global models that will predict three-component amplitudes (R-T-Z) were produced; Q models match regional geology; corrected source spectra can be used for discrimination and yield estimation; three-component data increase coverage and reduce scatter in source spectral estimates; three-component efforts must include distance-dependent effects; a community effort on instrument calibration is needed.
Dual amplitude pulse generator for radiation detectors
Hoggan, Jerry M.; Kynaston, Ronnie L.; Johnson, Larry O.
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.
Singularity structure of maximally supersymmetric scattering amplitudes.
Arkani-Hamed, Nima; Bourjaily, Jacob L; Cachazo, Freddy; Trnka, Jaroslav
2014-12-31
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 singularities and is free of any poles at infinity--properties closely related to uniform transcendentality and the UV finiteness of the theory. We also briefly comment on implications for maximal (N=8) supergravity theory (SUGRA).
Amplitude for N-Gluon Superstring Scattering
Stieberger, Stephan; Taylor, Tomasz R.
2006-11-24
We consider scattering processes involving N gluonic massless states of open superstrings with a certain Regge slope {alpha}{sup '}. At the semiclassical level, the string world-sheet sweeps a disk and N gluons are created or annihilated at the boundary. We present exact expressions for the corresponding amplitudes, valid to all orders in {alpha}{sup '}, for the so-called maximally helicity violating configurations, with N=4, 5 and N=6. We also obtain the leading O({alpha}{sup '2}) string corrections to the zero-slope N-gluon Yang-Mills amplitudes.
Amplitude for N-gluon superstring scattering.
Stieberger, Stephan; Taylor, Tomasz R
2006-11-24
We consider scattering processes involving N gluonic massless states of open superstrings with a certain Regge slope alpha'. At the semiclassical level, the string world-sheet sweeps a disk and N gluons are created or annihilated at the boundary. We present exact expressions for the corresponding amplitudes, valid to all orders in alpha', for the so-called maximally helicity violating configurations, with N = 4, 5 and N = 6. We also obtain the leading O(alpha '2) string corrections to the zero-slope N-gluon Yang-Mills amplitudes.
Travel-Time and Amplitude Sensitivity Kernels
2011-09-01
amplitude sensitivity kernels shown in the lower panels concentrate about the corresponding eigenrays . Each 3D kernel exhibits a broad negative...in 2 and 3 dimensions have similar 11 shapes to corresponding travel-time sensitivity kernels (TSKs), centered about the respective eigenrays
Connected formulas for amplitudes in standard model
NASA Astrophysics Data System (ADS)
He, Song; Zhang, Yong
2017-03-01
Witten's twistor string theory has led to new representations of S-matrix in massless QFT as a single object, including Cachazo-He-Yuan formulas in general and connected formulas in four dimensions. As a first step towards more realistic processes of the standard model, we extend the construction to QCD tree amplitudes with massless quarks and those with a Higgs boson. For both cases, we find connected formulas in four dimensions for all multiplicities which are very similar to the one for Yang-Mills amplitudes. The formula for quark-gluon color-ordered amplitudes differs from the pure-gluon case only by a Jacobian factor that depends on flavors and orderings of the quarks. In the formula for Higgs plus multi-parton amplitudes, the massive Higgs boson is effectively described by two additional massless legs which do not appear in the Parke-Taylor factor. The latter also represents the first twistor-string/connected formula for form factors.
The CMU Baryon Amplitude Analysis Program
Matt Bellis
2007-10-01
The PWA group at Carnegie Mellon University has developed a comprehensive approach and analysis package for the purpose of extracting the amplitudes for photoproduced baryon resonances. The end goal is to identify any missing resonances that are predicted by the constituent quark model, but not definitively observed in experiments. The data comes from the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Lab.
Consonant confusions in amplitude-expanded speech.
Freyman, R L; Nerbonne, G P
1996-12-01
The perceptual consequences of expanding the amplitude variations in speech were studied under conditions in which spectral information was obscured by signal correlated noise that had an envelope correlated with the speech envelope, but had a flat amplitude spectrum. The noise samples, created individually from 22 vowel-consonant-vowel nonsense words, were used as maskers of those words, with signal-to-noise ratios ranging from -15 to 0 dB. Amplitude expansion was by a factor of 3.0 in terms of decibels. In the first experiment, presentation level for speech peaks was 80 dB SPL. Consonant recognition performance for expanded speech by 50 listeners with normal hearing was as much as 30 percentage points poorer than for unexpanded speech and the types of errors were dramatically different, especially in the midrange of S-N ratios. In a second experiment presentation level was varied to determine whether reductions in consonant levels produced by expansion were responsible for the differences between conditions. Recognition performance for unexpanded speech at 40 dB SPL was nearly equivalent to that for expanded speech at 80 dB SPL. The error patterns obtained in these two conditions were different, suggesting that the differences between conditions in Experiment 1 were due largely to expanded amplitude envelopes rather than differences in audibility.
Scattering amplitudes for dark and bright excitons
NASA Astrophysics Data System (ADS)
Shiau, Shiue-Yuan; Combescot, Monique; Combescot, Roland; Dubin, François; Chang, Yia-Chung
2017-05-01
Using the composite boson many-body formalism that takes single-exciton states rather than free carrier states as a basis, we derive the integral equation fulfilled by the exciton-exciton effective scattering from which the role of fermion exchanges can be unraveled. For excitons made of (+/-1/2) -spin electrons and (+/-3/2) -spin holes, as in GaAs heterostructures, one major result is that most spin configurations lead to brightness-conserving scatterings with equal amplitude Δ, despite differences in the carrier exchanges involved. A brightness-changing channel also exists when two opposite-spin excitons scatter: dark excitons (2,-2) can end either in the same dark states with an amplitude Δe , or in opposite-spin bright states (1,-1) , with a different amplitude Δo , the number of carrier exchanges involved in these scatterings being even or odd, respectively. Another major result is that these amplitudes are linked by a striking relation, Δ_e+Δ_o=Δ , which has decisive consequence on exciton Bose-Einstein condensation. By using Born values, we show that the exciton condensate can be optically observed through a bright part when excitons have large dipole only, that is, when the electrons and holes are in two well-separated layers, as in current experiments.
Audio steganography by amplitude or phase modification
NASA Astrophysics Data System (ADS)
Gopalan, Kaliappan; Wenndt, Stanley J.; Adams, Scott F.; Haddad, Darren M.
2003-06-01
This paper presents the results of embedding short covert message utterances on a host, or cover, utterance by modifying the phase or amplitude of perceptually masked or significant regions of the host. In the first method, the absolute phase at selected, perceptually masked frequency indices was changed to fixed, covert data-dependent values. Embedded bits were retrieved at the receiver from the phase at the selected frequency indices. Tests on embedding a GSM-coded covert utterance on clean and noisy host utterances showed no noticeable difference in the stego compared to the hosts in speech quality or spectrogram. A bit error rate of 2 out of 2800 was observed for a clean host utterance while no error occurred for a noisy host. In the second method, the absolute phase of 10 or fewer perceptually significant points in the host was set in accordance with covert data. This resulted in a stego with successful data retrieval and a slightly noticeable degradation in speech quality. Modifying the amplitude of perceptually significant points caused perceptible differences in the stego even with small changes of amplitude made at five points per frame. Finally, the stego obtained by altering the amplitude at perceptually masked points showed barely noticeable differences and excellent data recovery.
The CMU Baryon Amplitude Analysis Program
NASA Astrophysics Data System (ADS)
Bellis, Matt
2007-05-01
The PWA group at Carnegie Mellon University has developed a comprehensive approach and analysis package for the purpose of extracting the amplitudes for photoproduced baryon resonances. The end goal is to identify any missing resonances that are predicted by the constituent quark model, but not definitively observed in experiments. The data comes from the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Lab.
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.
Amplitude Frequency Response Measurement: A Simple Technique
ERIC Educational Resources Information Center
Satish, L.; Vora, S. C.
2010-01-01
A simple method is described to combine a modern function generator and a digital oscilloscope to configure a setup that can directly measure the amplitude frequency response of a system. This is achieved by synchronously triggering both instruments, with the function generator operated in the "Linear-Sweep" frequency mode, while the oscilloscope…
Large Amplitude Patterns for Two Competing Species.
1980-06-01
scalar equation arising in population genetics . Mimura and Nishiura, [14], have obtained small amplitude spatial patterns for a system arising in...A nonlinear eigenvalue problem occuring in population genetics , preprint. [17] Peletier, L. A., Fife, P.: Nonlinear diffusion in population genetics . Arch
Holographic corrections to the Veneziano amplitude
NASA Astrophysics Data System (ADS)
Armoni, Adi; Ireson, Edwin
2017-08-01
We propose a holographic computation of the 2 → 2 meson scattering in a curved string background, dual to a QCD-like theory. We recover the Veneziano amplitude and compute a perturbative correction due to the background curvature. The result implies a small deviation from a linear trajectory, which is a requirement of the UV regime of QCD.
Amplitude Frequency Response Measurement: A Simple Technique
ERIC Educational Resources Information Center
Satish, L.; Vora, S. C.
2010-01-01
A simple method is described to combine a modern function generator and a digital oscilloscope to configure a setup that can directly measure the amplitude frequency response of a system. This is achieved by synchronously triggering both instruments, with the function generator operated in the "Linear-Sweep" frequency mode, while the oscilloscope…
Amplitude of Supersonic Diffuser Flow Pulsations
NASA Technical Reports Server (NTRS)
Sterbentz, William H.; Davids, Joseph
1952-01-01
A theoretical method for evaluating the stability characteristics and the amplitude and the frequency of pulsation of ram-jet engines without heat addition is presented herein. Experimental verification of the theoretical results are included where data were available. Theory and experiment show that the pulsation amplitude of a high mass-flow-ratio diffuser having no cone surface flow separation increases with decreasing mass flow. The theoretical trends for changes in amplitude, frequency, and mean-pressure recovery with changes in plenum-chamber volume were experimentally confirmed. For perforated convergent-divergent-type diffusers, a stability hysteresis loop was predicted on the pressure-recovery mass-flow-ratio curve. At a given mean mass-flow ratio, the higher.value of mean pressure recovery corresponded to oscillatory flow in the diffuser while the lower branch was stable. This hysteresis has been observed experimentally. The theory indicates that for a ram-jet engine of given diameter, the amplitude of pulsation of a supersonic diffuser is increased by decreasing the relative size of the plenum chamber with respect to the diffuser volume down to a critical value at which oscillations cease. In the region of these critical values, the stable mass-flow range of the diffuser may be increased either by decreasing the combustion chamber volume or by increasing the length of the diffuser.
ABJM amplitudes and the positive orthogonal Grassmannian
NASA Astrophysics Data System (ADS)
Huang, Yu-tin; Wen, CongKao
2014-02-01
A remarkable connection between perturbative scattering amplitudes of four dimensional planar SYM, and the stratification of the positive Grassmannian, was revealed in the seminal work of Arkani-Hamed et al. Similar extension for three-dimensional ABJM theory was proposed. Here we establish a direct connection between planar scattering amplitudes of ABJM theory, and singularities thereof, to the stratification of the positive orthogonal Grassmannian. In particular, scattering processes are constructed through on-shell diagrams, which are simply iterative gluing of the fundamental four-point amplitude. Each diagram is then equivalent to the merging of fundamental OG2 orthogonal Grassmannian to form a larger OG k , where 2 k is the number of external particles. The invariant information that is encoded in each diagram is precisely this stratification. This information can be easily read off via permutation paths of the on-shell diagram, which also can be used to derive a canonical representation of OG k that manifests the vanishing of consecutive minors as the singularity of all on-shell diagrams. Quite remarkably, for the BCFW recursion representation of the tree-level amplitudes, the on-shell diagram manifests the presence of all physical factorization poles, as well as the cancellation of the spurious poles. After analytically continuing the orthogonal Grassmannian to split signature, we reveal that each on-shell diagram in fact resides in the positive cell of the orthogonal Grassmannian, where all minors are positive. In this language, the amplitudes of ABJM theory is simply an integral of a product of d log forms, over the positive orthogonal Grassmannian.
Quantitative laryngeal electromyography: turns and amplitude analysis.
Statham, Melissa McCarty; Rosen, Clark A; Nandedkar, Sanjeev D; Munin, Michael C
2010-10-01
Laryngeal electromyography (LEMG) is primarily a qualitative examination, with no standardized approach to interpretation. The objectives of our study were to establish quantitative norms for motor unit recruitment in controls and to compare with interference pattern analysis in patients with unilateral vocal fold paralysis (VFP). Retrospective case-control study We performed LEMG of the thyroarytenoid-lateral cricoarytenoid muscle complex (TA-LCA) in 21 controls and 16 patients with unilateral VFP. Our standardized protocol used a concentric needle electrode with subjects performing variable force TA-LCA contraction. To quantify the interference pattern density, we measured turns and mean amplitude per turn for ≥10 epochs (each 500 milliseconds). Logarithmic regression analysis between amplitude and turns was used to calculate slope and intercept. Standard deviation was calculated to further define the confidence interval, enabling generation of a linear-scale graphical "cloud" of activity containing ≥90% of data points for controls and patients. Median age of controls and patients was similar (50.7 vs. 48.5 years). In controls, TA-LCA amplitude with variable contraction ranged from 145-1112 μV, and regression analysis comparing mean amplitude per turn to root-mean-square amplitude demonstrated high correlation (R = 0.82). In controls performing variable contraction, median turns per second was significantly higher compared to patients (450 vs. 290, P = .002). We first present interference pattern analysis in the TA-LCA in healthy adults and patients with unilateral VFP. Our findings indicate that motor unit recruitment can be quantitatively measured within the TA-LCA. Additionally, patients with unilateral VFP had significantly reduced turns when compared with controls.
Optical factors influencing the amplitude of accommodation.
López-Alcón, Diego; Marín-Franch, Iván; Fernández-Sánchez, Vicente; López-Gil, Norberto
2016-09-23
The purpose of this work was to find plausible predictors among optical parameters that may explain the inter-individual differences in subjective amplitude of accommodation not explained by age. An exploratory multivariable regression analysis was carried out retrospectively on a dataset with 180 eyes from 97 subjects (ages ranged from 20 to 58years). Subjective amplitudes of accommodation were recorded with the use of a custom-made Badal system. A commercial aberrometer was used to obtain each eye's wavefront during the full range of accommodation. The plausible predictors under study were pupil diameter in the unaccommodated eye, its reduction with accommodation; fourth- and six-order Zernike spherical aberration, their reduction with accommodation, and subjective refraction. At a significance level of 0.05, only fourth- and sixth-order Zernike spherical aberration were found to be predictors of subjective amplitude of accommodation not explained by age, each explaining on their own less than 5% of the variance, and about 9% together. All other optical parameters explained less than 2%. Spherical aberration did not explain the greater variability for younger eyes than for older eyes. The remainder variability in amplitude of accommodation not explained by age or spherical aberration was about ±2.6D for 20year-old subjects, ±1.5D for 40year-old subjects, and about ±0.6D for 55year-old subjects. Optical factors do not seem to account for much of the inter-individual differences in subjective amplitude of accommodation. Most of the variability not explained by age must be due to anatomical differences and physiological, psychological, or other factors. Copyright © 2016 The Authors. Published by Elsevier Ltd.. All rights reserved.
NASA Astrophysics Data System (ADS)
Paulo, Álvaro San; García, Ricardo
2001-11-01
Amplitude-modulation (tapping mode) atomic force microscopy is a technique for high resolution imaging of a wide variety of surfaces in air and liquid environments. Here by using the virial theorem and energy conservation principles we have derived analytical relationships between the oscillation amplitude, phase shift, and average tip-surface forces. We find that the average value of the interaction force and oscillation and the average power dissipated by the tip-surface interaction are the quantities that control the amplitude reduction. The agreement obtained between analytical and numerical results supports the analytical method.
Stability of amplitude chimeras in oscillator networks
NASA Astrophysics Data System (ADS)
Tumash, L.; Zakharova, A.; Lehnert, J.; Just, W.; Schöll, E.
2017-01-01
We show that amplitude chimeras in ring networks of Stuart-Landau oscillators with symmetry-breaking nonlocal coupling represent saddle-states in the underlying phase space of the network. Chimera states are composed of coexisting spatial domains of coherent and of incoherent oscillations. We calculate the Floquet exponents and the corresponding eigenvectors in dependence upon the coupling strength and range, and discuss the implications for the phase-space structure. The existence of at least one positive real part of the Floquet exponents indicates an unstable manifold in phase space, which explains the nature of these states as long-living transients. Additionally, we find a Stuart-Landau network of minimum size N = 12 exhibiting amplitude chimeras.
Multilayered models for electromagnetic reflection amplitudes
NASA Technical Reports Server (NTRS)
Linlor, W. I.
1976-01-01
The remote sensing of snowpack characteristics with surface installations or with an airborne system could have important applications in water resource management and flood prediction. To derive some insight into such applications, the electromagnetic response of multilayer snow models is analyzed. Normally incident plane waves are assumed at frequencies ranging from 10 to the 6th power to 10 to the 10th power Hz, and amplitude reflection coefficients are calculated for models having various snow-layer combinations, including ice sheets. Layers are defined by a thickness, permittivity, and conductivity; the electrical parameters are constant or prescribed functions of frequency. To illustrate the effect of various layering combinations, results are given in the form of curves of amplitude reflection coefficients, versus frequency for a variety of models. Under simplifying assumptions, the snow thickness and effective dielectric constant can be estimated from the reflection coefficient variations as a function of frequency.
Constructing QCD one-loop amplitudes
Forde, Darren; /SLAC /UCLA
2008-02-22
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 {var_epsilon}. 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
Amplitudes of MHD Waves in Sunspots
NASA Astrophysics Data System (ADS)
Norton, Aimee Ann; Cally, Paul; Baldner, Charles; Kleint, Lucia; Tarbell, Theodore D.; De Pontieu, Bart; Scherrer, Philip H.; Rajaguru, Paul
2016-05-01
The conversion of p-modes into MHD waves by strong magnetic fields occurs mainly in the sub-photospheric layers. The photospheric signatures of MHD waves are weak due to low amplitudes at the beta=1 equipartion level where mode-conversion occurs. We report on small amplitude oscillations observed in the photosphere with Hinode SOT/SP in which we analyze time series for sunspots ARs 12186 (11.10.2014) and 12434 (17.10.2015). No significant magnetic field oscillations are recovered in the umbra or penumbra in the ME inversion. However, periodicities in the inclination angle are found at the umbral/penumbral boundary with 5 minute periods. Upward propagating waves are indicated in the intensity signals correlated between HMI and AIA at different heights. We compare SP results with the oscillations observed in HMI data. Simultaneous IRIS data shows transition region brightening above the umbral core.
Is DAMAs modulation amplitude changing with time?
NASA Astrophysics Data System (ADS)
Kelso, Chris
2016-06-01
If dark matter is composed of weakly interacting particles, Earth's orbital motion induces a small annual variation in the rate at which these particles interact in a terrestrial detector. The DAMA collaboration has identified at a 9.3σ confidence level (CL) such an annual modulation in their event rate over two detector iterations, DAMA/NaI and DAMA/LIBRA, each with about 7 years of observations. We examine the nature of this modulation signal and find the modulation amplitude for the two detectors is inconsistent at the 3σ CL over 2-6 keVee. Such a time-dependence in the modulation amplitude is unexpected behavior for a dark matter signal, at least for dark matter halo morphologies consistent with the DAMA signal. We also find unusual behavior over the 5-6 keVee energy range that might indicate problems with the data.
Photon Counting Chirped Amplitude Modulation Ladar
2008-03-01
135 S. Taylor Ave., Room 103, Louisville, CO 80027-3025 14. ABSTRACT This work developed a method using Geiger - mode avalanche photodiode (GM-APD...effort to develop a method using Geiger - mode avalanche photodiode (GM-APD) photon counting detectors in the U.S. Army Research Laboratory’s chirped...architecture are discussed. 15. SUBJECT TERMS laser radar, ladar, avalanche photo-detectors, Geiger mode detectors, chirped amplitude modulation
Chiral extrapolation of SU(3) amplitudes
Ecker, Gerhard
2011-05-23
Approximations of chiral SU(3) amplitudes at NNLO are proposed to facilitate the extrapolation of lattice data to the physical meson masses. Inclusion of NNLO terms is essential for investigating convergence properties of chiral SU(3) and for determining low-energy constants in a controllable fashion. The approximations are tested with recent lattice data for the ratio of decay constants F{sub K}/F{sub {pi}}.
Automatic generation of tree level helicity amplitudes
NASA Astrophysics Data System (ADS)
Stelzer, T.; Long, W. F.
1994-11-01
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.
Automatic generation of tree level helicity amplitudes
NASA Astrophysics Data System (ADS)
Stelzer, T.; Long, W. F.
1994-07-01
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.
Large Amplitude Oscillatory Shear near Jamming
NASA Astrophysics Data System (ADS)
Tighe, Brian; Dagois-Bohy, Simon; Somfai, Ellak; van Hecke, Martin
2014-11-01
Jammed solids such as foams and emulsions can be driven with oscillatory shear at finite strain amplitude and frequency. On a macro scale, this induces nonlinearities such as strain softening and shear thinning. On the micro scale one observes the onset of irreversibility, caging, and long-time diffusion. Using simulations of soft viscous spheres, we systematically vary the distance to the jamming transition. We correlate crossovers in the microscopic and macroscopic response, and construct scaling arguments to explain their relationships.
Amplitude calibration experiment for SIR-B
NASA Technical Reports Server (NTRS)
Held, D. N.; Ulaby, F. T.
1984-01-01
The objectives, approach, and expected results of the amplitude calibration experiment for the Shuttle Imaging Radar-B (SIR-B) are outlined. Specific objectives include: (1) the determination of the repeatability (stability) of the SIR-B; (2) the absolute and relative calibration of the system; and (3) the ground truth verification of the calibration accuracy using measurements made by a ground spectrometer and an airborne synthetic aperture radar.
Understanding the amplitudes of noise correlation measurements
Tsai, Victor C.
2011-01-01
Cross correlation of ambient seismic noise is known to result in time series from which station-station travel-time measurements can be made. Part of the reason that these cross-correlation travel-time measurements are reliable is that there exists a theoretical framework that quantifies how these travel times depend on the features of the ambient noise. However, corresponding theoretical results do not currently exist to describe how the amplitudes of the cross correlation depend on such features. For example, currently it is not possible to take a given distribution of noise sources and calculate the cross correlation amplitudes one would expect from such a distribution. Here, we provide a ray-theoretical framework for calculating cross correlations. This framework differs from previous work in that it explicitly accounts for attenuation as well as the spatial distribution of sources and therefore can address the issue of quantifying amplitudes in noise correlation measurements. After introducing the general framework, we apply it to two specific problems. First, we show that we can quantify the amplitudes of coherency measurements, and find that the decay of coherency with station-station spacing depends crucially on the distribution of noise sources. We suggest that researchers interested in performing attenuation measurements from noise coherency should first determine how the dominant sources of noise are distributed. Second, we show that we can quantify the signal-to-noise ratio of noise correlations more precisely than previous work, and that these signal-to-noise ratios can be estimated for given situations prior to the deployment of seismometers. It is expected that there are applications of the theoretical framework beyond the two specific cases considered, but these applications await future work.
[Amplitude modulation in sound signals by mammals].
Nikol'skiĭ, A A
2012-01-01
Periodic variations in amplitude of a signal, or amplitude modulation (AM), affect the structure of communicative messages spectrum. Within the spectrum of AM-signals, side frequencies are formed both above and below the carrier frequency that is subjected to modulation. In case of harmonic signal structure they are presented near fundamental frequency as well as near harmonics. Thus, AM may by viewed as a relatively simple mechanism for controlling the spectrum of messages transmitted by mammals. Examples of AM affecting the spectrum structure of functionally different sound signals are discussed as applied to representatives of four orders of mammals: rodents (Reodentia), duplicidentates (Lagomorpha), pinnipeds (Pinnipedia), and paridigitates (Artiodactia). For the first time, the classification of AM in animals' sound signals is given. Five forms of AM are picked out in sound signals by mammals: absence of AM, continuous AM, fragmented, heterogeneous, and multilevel one. AM presence/absence is related neither with belonging to any specific order nor with some particular function of a signal. Similar forms of AM can occur in different orders of mammals in parallel. On the contrary, different forms of AM can be detected in signals meant for similar functions. The assumption is made about AM-signals facilitating information encoding and jamprotection of messages transmitted by mammals. Preliminry analysis indicates that hard-driving amplitude modulation is incompatible with hard-driving frequency modulation.
Prominence Seismology Using Small Amplitude Oscillations
NASA Astrophysics Data System (ADS)
Oliver, Ramón
2009-12-01
Quiescent prominences can be modeled as thin slabs of cold, dense plasma embedded in the much hotter and rarer solar corona. Although their global shape is rather irregular, they are often characterised by an internal structure consisting of a large number of thin, parallel threads piled together. Prominences often display periodic disturbances mostly observed in the Doppler displacement of spectral lines and with an amplitude typically of the order of or smaller than 2-3 km s-1, a value which seems to be much smaller than the characteristic speeds of the prominence plasma (namely the Alfvén and sound velocities). Two particular features of these small amplitude prominence oscillations are that they seem to damp in a few periods and that they seem not to affect the whole prominence structure. In addition, in high spatial resolution observations, in which threads can be discerned, small amplitude oscillations appear to be clearly associated to these fine structure constituents. Prominence seismology tries to bring together the results from these observations (e.g. periods, wavelengths, damping times) and their theoretical modeling (by means of the magnetohydrodynamic theory) to gain insight into physical properties of prominences that cannot be derived from direct observation. In this paper we discuss works that have not been described in previous reviews, namely the first seismological application to solar prominences and theoretical advances on the attenuation of prominence oscillations.
Continuous phase and amplitude holographic elements
NASA Technical Reports Server (NTRS)
Maker, Paul D. (Inventor); Muller, Richard E. (Inventor)
1995-01-01
A method for producing a phase hologram using e-beam lithography provides n-ary levels of phase and amplitude by first producing an amplitude hologram on a transparent substrate by e-beam exposure of a resist over a film of metal by exposing n is less than or equal to m x m spots of an array of spots for each pixel, where the spots are randomly selected in proportion to the amplitude assigned to each pixel, and then after developing and etching the metal film producing a phase hologram by e-beam lithography using a low contrast resist, such as PMMA, and n-ary levels of low doses less than approximately 200 micro-C/sq cm and preferably in the range of 20-200 micro-C/sq cm, and aggressive development using pure acetone for an empirically determined time (about 6 s) controlled to within 1/10 s to produce partial development of each pixel in proportion to the n-ary level of dose assigned to it.
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.
Mellin amplitudes for dual conformal integrals
NASA Astrophysics Data System (ADS)
Paulos, Miguel F.; Spradlin, Marcus; Volovich, Anastasia
2012-08-01
Motivated by recent work on the utility of Mellin space for representing conformal correlators in AdS/CFT, we study its suitability for representing dual conformal integrals of the type which appear in perturbative scattering amplitudes in super-Yang-Mills theory. We discuss Feynman-like rules for writing Mellin amplitudes for a large class of integrals in any dimension, and find explicit representations for several familiar toy integrals. However we show that the power of Mellin space is that it provides simple representations even for fully massive integrals, which except for the single case of the 4-mass box have not yet been computed by any available technology. Mellin space is also useful for exhibiting differential relations between various multi-loop integrals, and we show that certain higher-loop integrals may be written as integral operators acting on the fully massive scalar n-gon in n dimensions, whose Mellin amplitude is exactly 1. Our chief example is a very simple formula expressing the 6-mass double box as a single integral of the 6-mass scalar hexagon in 6 dimensions.
Nonlinear amplitude approximation for bilinear systems
NASA Astrophysics Data System (ADS)
Jung, Chulwoo; D'Souza, Kiran; Epureanu, Bogdan I.
2014-06-01
An efficient method to predict vibration amplitudes at the resonant frequencies of dynamical systems with piecewise-linear nonlinearity is developed. This technique is referred to as bilinear amplitude approximation (BAA). BAA constructs a single vibration cycle at each resonant frequency to approximate the periodic steady-state response of the system. It is postulated that the steady-state response is piece-wise linear and can be approximated by analyzing the response over two time intervals during which the system behaves linearly. Overall the dynamics is nonlinear, but the system is in a distinct linear state during each of the two time intervals. Thus, the approximated vibration cycle is constructed using linear analyses. The equation of motion for analyzing the vibration of each state is projected along the overlapping space spanned by the linear mode shapes active in each of the states. This overlapping space is where the vibratory energy is transferred from one state to the other when the system switches from one state to the other. The overlapping space can be obtained using singular value decomposition. The space where the energy is transferred is used together with transition conditions of displacement and velocity compatibility to construct a single vibration cycle and to compute the amplitude of the dynamics. Since the BAA method does not require numerical integration of nonlinear models, computational costs are very low. In this paper, the BAA method is first applied to a single-degree-of-freedom system. Then, a three-degree-of-freedom system is introduced to demonstrate a more general application of BAA. Finally, the BAA method is applied to a full bladed disk with a crack. Results comparing numerical solutions from full-order nonlinear analysis and results obtained using BAA are presented for all systems.
Loop-quantum-gravity vertex amplitude.
Engle, Jonathan; Pereira, Roberto; Rovelli, Carlo
2007-10-19
Spin foam models are hoped to provide the dynamics of loop-quantum gravity. However, the most popular of these, the Barrett-Crane model, does not have the good boundary state space and there are indications that it fails to yield good low-energy n-point functions. We present an alternative dynamics that can be derived as a quantization of a Regge discretization of Euclidean general relativity, where second class constraints are imposed weakly. Its state space matches the SO(3) loop gravity one and it yields an SO(4)-covariant vertex amplitude for Euclidean loop gravity.
Fatigue damage analysis under variable amplitude cycling
NASA Technical Reports Server (NTRS)
Leis, B. N.; Forte, T. P.
1983-01-01
This paper explores the suitability of a recently proposed mean stress parameter and introduces a nonlinear damage accumulation procedure. Data covering a range of positive and negative stress ratios from +0.6 to -2.66, for several aluminum alloys and steels, are assembled and shown to be well correlated by a simple damage parameter. A nonlinear damage accumulation postulate is advanced to replace the usual linear procedure. Results of critical experiments performed to assess the suitability of the postulate are introduced and shown to support a non-linear criterion. The implications of this work related to variable amplitude life prediction are discussed.
Fatigue crack growth under variable amplitude loading
NASA Astrophysics Data System (ADS)
Sidawi, Jihad A.
1994-09-01
Fatigue crack growth tests were conducted on an Fe 510 E C-Mn steel and a submerged arc welded joint from the same material under constant, variable, and random loading amplitudes. Paris-Erdogan's crack growth rate law was tested for the evaluation of m and C using the stress intensity factor K, the J-integral, the effective stress intensity factor K(sub eff), and the root mean square stress intensity factor K(sub rms) fracture mechanics concepts. The effect of retardation and residual stresses resulting from welding was also considered. It was found that all concepts gave good life predictions in all cases.
Fatigue crack growth under variable amplitude loading
NASA Technical Reports Server (NTRS)
Sidawi, Jihad A.
1994-01-01
Fatigue crack growth tests were conducted on an Fe 510 E C-Mn steel and a submerged arc welded joint from the same material under constant, variable, and random loading amplitudes. Paris-Erdogan's crack growth rate law was tested for the evaluation of m and C using the stress intensity factor K, the J-integral, the effective stress intensity factor K(sub eff), and the root mean square stress intensity factor K(sub rms) fracture mechanics concepts. The effect of retardation and residual stresses resulting from welding was also considered. It was found that all concepts gave good life predictions in all cases.
Phase amplitude conformal symmetry in Fourier transforms
NASA Astrophysics Data System (ADS)
Kuwata, S.
2015-04-01
For the Fourier transform ℑ : L2(R) → L2(R) of a complex-valued even or odd function ψ, it is found that the amplitude invariance |ℑψ| = |ψ| leads to a phase invariance or inversion as arg(ℑψ) = ±argψ + θ (θ = constant). The converse holds unless arg ψ = constant. The condition |ψ| = |ℑψ| is required in dealing with, for example, the minimum uncertainty relation between position and momentum. Without the evenness or oddness of ψ, |ℑψ| = |ψ| does not necessarily imply arg(ℑψ) = ±argψ + θ, nor is the converse.
In-Medium Pion Valence Distribution Amplitude
NASA Astrophysics Data System (ADS)
Tsushima, K.; de Melo, J. P. B. C.
2017-03-01
After a brief review of the quark-based model for nuclear matter, and some pion properties in medium presented in our previous works, we report new results for the pion valence wave function as well as the valence distribution amplitude in medium, which are presented in our recent article. We find that both the in-medium pion valence distribution and the in-medium pion valence wave function, are substantially modified at normal nuclear matter density, due to the reduction in the pion decay constant.
The small amplitude magnetohydrodynamic Riemann problem
NASA Technical Reports Server (NTRS)
Wu, C. C.; Kennel, C. F.
1993-01-01
The small-amplitude MHD Riemann problem is studied using the Cohen-Kulsrud-Burgers equations. Unlike the coplanar Riemann problem, the evolution of noncoplanar Riemann problems is not self-similar and its flow structures could change in time. But its large-time behavior is very simple and a time-dependent 2 - 3 intermediate shock is always involved for the noncoplanar field rotations. The time-dependent 2 - 3 intermediate shock has a well-defined structure and exists for any degree of field rotation.
Stochastic aspects of nuclear large amplitude motion
Kolomietz, V.M.
1995-08-01
A consistent description of the macroscopic large amplitude dynamics and processes of internal excitation of a nucleus is suggested. The cranking model approach is used for the calculation of the response function of the nucleus in a moving frame. Using spectral statistics smearing, the collective mass, friction, and diffusion coefficients are derived. The relation of the response function in a moving frame to the correlation function in a classical chaotic system is established. The rate of dissipation due to the Landau-Zener transitions and through the Kubo mechanism is considered.
PERIOD AND AMPLITUDE VARIABILITY OF THE HIGH-AMPLITUDE {delta} SCUTI STAR GP ANDROMEDAE
Zhou, A.-Y.; Jiang, S.-Y.
2011-10-15
Extensive differential time-series CCD photometry has been carried out between 2003 and 2009 for the high-amplitude {delta} Scuti (HADS) star GP And. We acquired 12,583 new measurements consisting of 41 nights (153.3 hr) spanning over 2221 days. This is the largest time-series data set to date for the star. Based upon these data and others available in the literature, a comprehensive analysis has been conducted to investigate the pulsational properties of the star. Except for the known fundamental period and its harmonics we failed to detect any additional pulsation periods either radial or nonradial. We show clear amplitude variability, but we failed to verify the previously claimed periodic amplitude modulation. Classic O-C analysis indicates that the fundamental pulsation period of GP And is slowly increasing at a rate of P-dot /P = (5.49 {+-} 0.1)x10{sup -8} yr{sup -1} in accordance with the predictions of stellar evolutionary models. Findings of nonradial oscillations in previously known radial high-amplitude pulsators are being increasingly reported. We have briefly reviewed the current status of multiperiodicity and nonradial pulsation features among the high-amplitude pulsators in the classic instability strip.
Small-amplitude synchrotron tune near transition
Ng, K.Y.; /Fermilab
2010-05-01
The separatrices of the rf buckets near transition are mapped when the synchronous phase is neither 0 or {pi}. The small-amplitude synchronous tune is derived when the rf frequency is changed. Synchrotron radiation is present in all electron storage ring. As a result, the synchronous phase is always offset from {phi}{sub s} = {pi} to compensate for the power loss. Even for proton storage rings with negligible synchrotron radiation, the synchronous phase is also required to be offset from {phi}{sub s} = 0 or {pi} slightly to compensate for beam loading. Thus for all storage rings operating near transition, beam particles reside in accelerating buckets instead of stationary bucket. It is of interest to map these buckets and see how they evolve near transition. When the rf frequency is varied, the closed orbit is pushed radially inward or outward. The momentum of the particle synchronous with the rf is thus changed. By measuring the small-amplitude synchrotron tune as a function of the rf frequency, the lowest first few orders of the slip factor can be inferred. Here, we derive this relationship up to the lowest first three orders of the slip factor when the particle velocity is not ultra-relativistic.
Amplitude enhancement by a gold dimer
NASA Astrophysics Data System (ADS)
Hong, Xin; Wang, Jingxin; Jin, Zheng
2016-10-01
The unique optical properties such as brightness, non-bleaching, good bio-compatibility make gold particles ideal label candidates for molecular probes. Due to the strongly enhanced field, aggregation of gold nanoparticles finds themselves plenty of applications in bio-imaging. But limited by its small cross-section associated with nanometer sized particle, it is a big challenge to employ it in a single molecular detection. The field enhancement results from the effect of plasmonic coupling between two closely attached gold nanoparticle under the right excitation condition. With the aim to apply the gold dimer probe to find the molecules in our recently established optical detection method, we compared of the amplitude enhancement by the dimer relative to a single particle. The amplitude distribution under a highly focused illumination objective was calculated, whose results suggest that at the optimized excitation condition, the local field can be enhanced 190 fold. In consequence, experimental detection was carried out. Gold dimers were linked together by the hybridization of two single chain DNAs. Dimer and single particle probes were mixed together in one detection. Overwhelming contrast between these two kinds of probes were clearly exhibited in the experimental detection image. This method can provide a way to a high specific detection in early diagnosis.
Wrist Proprioception: Amplitude or Position Coding?
Marini, Francesca; Squeri, Valentina; Morasso, Pietro; Masia, Lorenzo
2016-01-01
This work examines physiological mechanisms underlying the position sense of the wrist, namely, the codification of proprioceptive information related to pointing movements of the wrist toward kinesthetic targets. Twenty-four healthy subjects participated to a robot-aided assessment of their wrist proprioceptive acuity to investigate if the sensorimotor transformation involved in matching targets located by proprioceptive receptors relies on amplitude or positional cues. A joint position matching test was performed in order to explore such dichotomy. In this test, the wrist of a blindfolded participant is passively moved by a robotic device to a preset target position and, after a removal movement from this position, the participant has to actively replicate and match it as accurately as possible. The test involved two separate conditions: in the first, the matching movements started from the same initial location; in the second one, the initial location was randomly assigned. Target matching accuracy, precision, and bias in the two conditions were then compared. Overall results showed a consistent higher performance in the former condition than in the latter, thus supporting the hypothesis that the joint position sense is based on vectorial or amplitude coding rather than positional. PMID:27807417
Color-kinematic duality in ABJM theory without amplitude relations
NASA Astrophysics Data System (ADS)
Sivaramakrishnan, Allic
2017-01-01
We explicitly show that the Bern-Carrasco-Johansson color-kinematic duality holds at tree level through at least eight points in Aharony-Bergman-Jafferis-Maldacena theory with gauge group SU(N) × SU(N). At six points we give the explicit form of numerators in terms of amplitudes, displaying the generalized gauge freedom that leads to amplitude relations. However, at eight points no amplitude relations follow from the duality, so the diagram numerators are fixed unique functions of partial amplitudes. We provide the explicit amplitude-numerator decomposition and the numerator relations for eight-point amplitudes.
Spurious cross-frequency amplitude-amplitude coupling in nonstationary, nonlinear signals
NASA Astrophysics Data System (ADS)
Yeh, Chien-Hung; Lo, Men-Tzung; Hu, Kun
2016-07-01
Recent studies of brain activities show that cross-frequency coupling (CFC) plays an important role in memory and learning. Many measures have been proposed to investigate the CFC phenomenon, including the correlation between the amplitude envelopes of two brain waves at different frequencies - cross-frequency amplitude-amplitude coupling (AAC). In this short communication, we describe how nonstationary, nonlinear oscillatory signals may produce spurious cross-frequency AAC. Utilizing the empirical mode decomposition, we also propose a new method for assessment of AAC that can potentially reduce the effects of nonlinearity and nonstationarity and, thus, help to avoid the detection of artificial AACs. We compare the performances of this new method and the traditional Fourier-based AAC method. We also discuss the strategies to identify potential spurious AACs.
Evaluation of new spin foam vertex amplitudes
NASA Astrophysics Data System (ADS)
Khavkine, Igor
2009-06-01
The Christensen-Egan algorithm is extended and generalized to efficiently evaluate new spin foam vertex amplitudes proposed by Engle, Pereira and Rovelli and Freidel and Krasnov, with or without (factored) boundary states. A concrete pragmatic proposal is made for comparing the different models using uniform methodologies, applicable to the behavior of large spin asymptotics and of expectation values of specific semiclassical observables. The asymptotics of the new models exhibit non-oscillatory, power-law decay similar to that of the Barrett-Crane model, though with different exponents. Also, an analysis of the semiclassical wave packet propagation problem indicates that the Magliaro, Rovelli and Perini's conjecture of good semiclassical behavior of the new models does not hold for generic factored states, which neglect spin-spin correlations.
Amplitude Scaling of Active Separation Control
NASA Technical Reports Server (NTRS)
Stalnov, Oksana; Seifert, Avraham
2010-01-01
Three existing and two new excitation magnitude scaling options for active separation control at Reynolds numbers below one Million. The physical background for the scaling options was discussed and their relevance was evaluated using two different sets of experimental data. For F+ approx. 1, 2D excitation: a) The traditional VR and C(mu) - do not scale the data. b) Only the Re*C(mu) is valid. This conclusion is also limited for positive lift increment.. For F+ > 10, 3D excitation, the Re corrected C(mu), the St corrected velocity ratio and the vorticity flux coefficient, all scale the amplitudes equally well. Therefore, the Reynolds weighted C(mu) is the preferred choice, relevant to both excitation modes. Incidence also considered, using Ue from local Cp.
Low Amplitude Impact of Damaged PBX 9501
NASA Astrophysics Data System (ADS)
Idar, Deanne
1999-06-01
Low amplitude impact tests on damaged, baseline and aged, PBX 9501 specimens have been performed to determine the critical impact-velocity threshold for violent reaction. Tests were performed using 3.0-in. diameter, 2 kg. mild-steel projectiles launched from a spigot gun at lightly confined modified Steven targets. Prior damage on the seven targets was induced by a single impact ranging in velocity from 36.9 to 52.7 m/s. External blast gauge data were coupled with ballistic pendulum data to evaluate the level of reaction violence relative to a steady-state detonation. Strain gage data were used to evaluate the response of the explosive to impact and characterize subsequent reaction profiles. The effect of PBX 9501 lots, age, and prior level of damage on threshold behavior will be discussed and compared to single impact test results.
Speech recognition with amplitude and frequency modulations
NASA Astrophysics Data System (ADS)
Zeng, Fan-Gang; Nie, Kaibao; Stickney, Ginger S.; Kong, Ying-Yee; Vongphoe, Michael; Bhargave, Ashish; Wei, Chaogang; Cao, Keli
2005-02-01
Amplitude modulation (AM) and frequency modulation (FM) are commonly used in communication, but their relative contributions to speech recognition have not been fully explored. To bridge this gap, we derived slowly varying AM and FM from speech sounds and conducted listening tests using stimuli with different modulations in normal-hearing and cochlear-implant subjects. We found that although AM from a limited number of spectral bands may be sufficient for speech recognition in quiet, FM significantly enhances speech recognition in noise, as well as speaker and tone recognition. Additional speech reception threshold measures revealed that FM is particularly critical for speech recognition with a competing voice and is independent of spectral resolution and similarity. These results suggest that AM and FM provide independent yet complementary contributions to support robust speech recognition under realistic listening situations. Encoding FM may improve auditory scene analysis, cochlear-implant, and audiocoding performance. auditory analysis | cochlear implant | neural code | phase | scene analysis
Presynaptic spike broadening reduces junctional potential amplitude.
Spencer, A N; Przysiezniak, J; Acosta-Urquidi, J; Basarsky, T A
1989-08-24
Presynaptic modulation of action potential duration may regulate synaptic transmission in both vertebrates and invertebrates. Such synaptic plasticity is brought about by modifications to membrane currents at presynaptic release sites, which, in turn, lead to changes in the concentration of cytosolic calcium available for mediating transmitter release. The 'primitive' neuromuscular junction of the jellyfish Polyorchis penicillatus is a useful model of presynaptic modulation. In this study, we show that the durations of action potentials in the motor neurons of this jellyfish are negatively correlated with the amplitude of excitatory junctional potentials. We present data from in vitro voltage-clamp experiments showing that short duration voltage spikes, which elicit large excitatory junctional potentials in vivo, produce larger and briefer calcium currents than do long duration action potentials, which elicit small excitatory junctional potentials.
Conformal basis for flat space amplitudes
NASA Astrophysics Data System (ADS)
Pasterski, Sabrina; Shao, Shu-Heng
2017-09-01
We study solutions of the Klein-Gordon, Maxwell, and linearized Einstein equations in R1 ,d +1 that transform as d -dimensional conformal primaries under the Lorentz group S O (1 ,d +1 ). Such solutions, called conformal primary wavefunctions, are labeled by a conformal dimension Δ and a point in Rd, rather than an on-shell (d +2 )-dimensional momentum. We show that the continuum of scalar conformal primary wavefunctions on the principal continuous series Δ ∈d/2 +i R of S O (1 ,d +1 ) spans a complete set of normalizable solutions to the wave equation. In the massless case, with or without spin, the transition from momentum space to conformal primary wavefunctions is implemented by a Mellin transform. As a consequence of this construction, scattering amplitudes in this basis transform covariantly under S O (1 ,d +1 ) as d -dimensional conformal correlators.
Amplitude envelope synchronization in coupled chaotic oscillators.
Gonzalez-Miranda, J M
2002-03-01
A peculiar type of synchronization has been found when two Van der Pol-Duffing oscillators, evolving in different chaotic attractors, are coupled. As the coupling increases, the frequencies of the two oscillators remain different, while a synchronized modulation of the amplitudes of a signal of each system develops, and a null Lyapunov exponent of the uncoupled systems becomes negative and gradually larger in absolute value. This phenomenon is characterized by an appropriate correlation function between the returns of the signals, and interpreted in terms of the mutual excitation of new frequencies in the oscillators power spectra. This form of synchronization also occurs in other systems, but it shows up mixed with or screened by other forms of synchronization, as illustrated in this paper by means of the examples of the dynamic behavior observed for three other different models of chaotic oscillators.
Bootstrapping an NMHV amplitude through three loops
NASA Astrophysics Data System (ADS)
Dixon, Lance J.; von Hippel, Matt
2014-10-01
We extend the hexagon function bootstrap to the next-to-maximally-helicity-violating (NMHV) configuration for six-point scattering in planar = 4 super-Yang-Mills theory at three loops. Constraints from the differential equation, from the operator product expansion (OPE) for Wilson loops with operator insertions, and from multi-Regge factorization, lead to a unique answer for the three-loop ratio function. The three-loop result also predicts additional terms in the OPE expansion, as well as the behavior of NMHV amplitudes in the multi-Regge limit at one higher logarithmic accuracy (NNLL) than was used as input. Both predictions are in agreement with recent results from the flux-tube approach. We also study the multi-particle factorization of multi-loop amplitudes for the first time. We find that the function controlling this factorization is purely logarithmic through three loops. We show that a function U , which is closely related to the parity-even part of the ratio function V , is remarkably simple; only five of the nine possible final entries in its symbol are non-vanishing. We study the analytic and numerical behavior of both the parity-even and parity-odd parts of the ratio function on simple lines traversing the space of cross ratios ( u, v, w), as well as on a few two-dimensional planes. Finally, we present an empirical formula for V in terms of elements of the coproduct of the six-gluon MHV remainder function R 6 at one higher loop, which works through three loops for V (four loops for R 6).
Compositions of bosonic string amplitudes with cylinder topology
Trisnadi, J.I.
1989-01-01
Many issues in string theory are conveniently addressed and handled in a quantum fleld theoretical framework, from which Feynman rules can then be derived. Although at present a generally acceptable quantum field theory of closed strings does not yet exist, the Feynman rules are known. This is due to another development in string theory, namely, the Polyakov path integral approach. In this approach, scattering amplitudes are calculated directly without appealing to the quantum fleld theoretical description. It is therefore important to examine if the scattering amplitude can be reconstructed by composing propagators and vertices. In general, the author is interested in knowing if Polyakov amplitudes can be consistently composed. Composition of amplitudes in general has been studied formally. Explicit composition, however, is limited to amplitudes that have been calculated explicitly. Among them is the amplitude with cylinder topology. In this dissertation, the author will rederive this cylinder amplitude. The author uses the action principle in the evaluation of the path integral. This way, the contributions of the ghost zero modes, which are usually introduced by hand, come out automatically. Then, the author studies three compositions of the cylinder amplitude: two cylinder amplitudes into one, a single cylinder amplitude into a torus amplitude, and a cylinder amplitude into a Klein-bottle amplitude. The author shows that the resulting amplitudes agree with known results. Using the cylinder amplitude, the author also demonstrates the derivation of the (imaginary time) Schrodinger equation for the free closed bosonic string. Finally, the author applies the techniques to derive the composable transition amplitude of gravity in a Friedmann-RobertsonWalker cosmology.
Localized finite-amplitude disturbances and selection of solitary waves
Kliakhandler; Porubov; Velarde
2000-10-01
It turns out that evolution of localized finite-amplitude disturbances in perturbed KdV equation is qualitatively different compared with conventional small-amplitude initial conditions. Namely, relatively fast solitary waves, with one and the same amplitude and velocity, are formed ahead of conventional chaotic-like irregular structures. The amplitude and velocity of the waves, obtained from the asymptotic theory, are in excellent agreement with numerics.
Chiral closed strings: four massless states scattering amplitude
NASA Astrophysics Data System (ADS)
Leite, Marcelo M.; Siegel, Warren
2017-01-01
We compute the scattering amplitudes of four massless states for chiral (closed) bosonic and type II superstrings using the Kawai-Lewellen-Tye ( KLT ) factorization method. The amplitude in the chiral bosonic case is identical to a field theory amplitude corresponding to the spin-2 tachyon, massless gravitational sector and massive spin-2 tardyon states of the spectrum. Chiral type II superstrings amplitude only possess poles associated with the massless gravitational sector. We briefly discuss the extension of the calculation to heterotic superstrings.
Feed-forward digital phase and amplitude correction system
Yu, D.U.L.; Conway, P.H.
1994-11-15
Phase and amplitude modifications in repeatable RF pulses at the output of a high power pulsed microwave amplifier are made utilizing a digital feed-forward correction system. A controlled amount of the output power is coupled to a correction system for processing of phase and amplitude information. The correction system comprises circuitry to compare the detected phase and amplitude with the desired phase and amplitude, respectively, and a digitally programmable phase shifter and attenuator and digital logic circuitry to control the phase shifter and attenuator. The phase and amplitude of subsequent are modified by output signals from the correction system. 11 figs.
Feed-forward digital phase and amplitude correction system
Yu, David U. L.; Conway, Patrick H.
1994-01-01
Phase and amplitude modifications in repeatable RF pulses at the output of a high power pulsed microwave amplifier are made utilizing a digital feed-forward correction system. A controlled amount of the output power is coupled to a correction system for processing of phase and amplitude information. The correction system comprises circuitry to compare the detected phase and amplitude with the desired phase and amplitude, respectively, and a digitally programmable phase shifter and attenuator and digital logic circuitry to control the phase shifter and attenuator. The Phase and amplitude of subsequent are modified by output signals from the correction system.
Leading Wave Amplitude of a Tsunami
NASA Astrophysics Data System (ADS)
Kanoglu, U.
2015-12-01
Okal and Synolakis (EGU General Assembly 2015, Geophysical Research Abstracts-Vol. 17-7622) recently discussed that why the maximum amplitude of a tsunami might not occur for the first wave. Okal and Synolakis list observations from 2011 Japan tsunami, which reached to Papeete, Tahiti with a fourth wave being largest and 72 min later after the first wave; 1960 Chilean tsunami reached Hilo, Hawaii with a maximum wave arriving 1 hour later with a height of 5m, first wave being only 1.2m. Largest later waves is a problem not only for local authorities both in terms of warning to the public and rescue efforts but also mislead the public thinking that it is safe to return shoreline or evacuated site after arrival of the first wave. Okal and Synolakis considered Hammack's (1972, Ph.D. Dissertation, Calif. Inst. Tech., 261 pp., Pasadena) linear dispersive analytical solution with a tsunami generation through an uplifting of a circular plug on the ocean floor. They performed parametric study for the radius of the plug and the depth of the ocean since these are the independent scaling lengths in the problem. They identified transition distance, as the second wave being larger, regarding the parameters of the problem. Here, we extend their analysis to an initial wave field with a finite crest length and, in addition, to a most common tsunami initial wave form of N-wave as presented by Tadepalli and Synolakis (1994, Proc. R. Soc. A: Math. Phys. Eng. Sci., 445, 99-112). We compare our results with non-dispersive linear shallow water wave results as presented by Kanoglu et al. (2013, Proc. R. Soc. A: Math. Phys. Eng. Sci., 469, 20130015), investigating focusing feature. We discuss the results both in terms of leading wave amplitude and tsunami focusing. Acknowledgment: The research leading to these results has received funding from the European Union's Seventh Framework Programme (FP7/2007-2013) under grant agreement no 603839 (Project ASTARTE - Assessment, Strategy and Risk
Amplitude interpretation and visualization of three-dimensional reflection data
Enachescu, M.E. )
1994-07-01
Digital recording and processing of modern three-dimensional surveys allow for relative good preservation and correct spatial positioning of seismic reflection amplitude. A four-dimensional seismic reflection field matrix R (x,y,t,A), which can be computer visualized (i.e., real-time interactively rendered, edited, and animated), is now available to the interpreter. The amplitude contains encoded geological information indirectly related to lithologies and reservoir properties. The magnitude of the amplitude depends not only on the acoustic impedance contrast across a boundary, but is also strongly affected by the shape of the reflective boundary. This allows the interpreter to image subtle tectonic and structural elements not obvious on time-structure maps. The use of modern workstations allows for appropriate color coding of the total available amplitude range, routine on-screen time/amplitude extraction, and late display of horizon amplitude maps (horizon slices) or complex amplitude-structure spatial visualization. Stratigraphic, structural, tectonic, fluid distribution, and paleogeographic information are commonly obtained by displaying the amplitude variation A = A(x,y,t) associated with a particular reflective surface or seismic interval. As illustrated with several case histories, traditional structural and stratigraphic interpretation combined with a detailed amplitude study generally greatly enhance extraction of subsurface geological information from a reflection data volume. In the context of three-dimensional seismic surveys, the horizon amplitude map (horizon slice), amplitude attachment to structure and [open quotes]bright clouds[close quotes] displays are very powerful tools available to the interpreter.
Writing CFT correlation functions as AdS scattering amplitudes
NASA Astrophysics Data System (ADS)
Penedones, Joao
2011-03-01
We explore the Mellin representation of conformal correlation functions recently proposed by Mack. Examples in the AdS/CFT context reinforce the analogy between Mellin amplitudes and scattering amplitudes. We conjecture a simple formula relating the bulk scattering amplitudes to the asymptotic behavior of Mellin amplitudes and show that previous results on the flat space limit of AdS follow from our new formula. We find that the Mellin amplitudes are particularly useful in the case of conformal gauge theories in the planar limit. In this case, the four point Mellin amplitudes are meromorphic functions whose poles and their residues are entirely determined by two and three point functions of single-trace operators. This makes the Mellin amplitudes the ideal objects to attempt the conformal bootstrap program in higher dimensions.
Efficient reverse time migration with amplitude encoding
NASA Astrophysics Data System (ADS)
Hu, Jiangtao; Wang, Huazhong; Zhao, Lei; Shao, Yu; Wang, Meixia; Osen, Are
2015-08-01
Reverse time migration (RTM) is an accurate seismic imaging method for imaging the complex subsurface structure. Traditional common shot RTM suffers from low efficiency due to the large number of single shot gathers, especially for marine seismic data. Phase encoding is commonly used to reduce the computational cost of RTM. Phase encoding in the frequency domain is usually related to time shift in the time domain. Therefore, phase-encoding-based RTM needs time padding to avoid information loss which degrades the efficiency of the time-domain wavefield extrapolator. In this paper, an efficient time-domain RTM scheme based on the amplitude encoding is proposed. This scheme uses the orthogonal cosine basis as the encoding function, which has similar physical meaning to plane wave encoding (i.e. plane-wave components with different surface shooting angles). The proposed scheme can generate a qualified imaging result as well as common shot RTM but with less computational cost. Since this scheme does not need time padding, it is more efficient than the phase encoding schemes and can be conveniently implemented in the time domain. Numerical examples on the Sigsbee2a synthetic dataset demonstrate the feasibility of the proposed method.
[Amplitude modulation following responses in audiological diagnostics].
Pethe, J; Mühler, R; von Specht, H
2002-12-01
The registration of brainstem potentials currently represents one of the most common methods in objective audiological diagnostics. However, regardless of their use, they are still known to possess important disadvantages, such as low specificity and validity in the lower frequency range due to broadband stimuli, or uncertainties due to the need for subjective evaluation. One potential solution to these problems could involve the registration of amplitude modulation following responses (AMFR). These potentials are being discussed much more regularly within the anglo-american literature due to their known frequency specificity within the high frequency range (resulting from a very narrow frequency band of stimulation), and also their ability to permit assessment of the hearing threshold at lower frequencies. Another additional advantage of AMFR results from the simple statistical verification of its presence.Extensive studies on the influence of both stimulating and recording parameters have also shown that the registration of AMFR could prove to be a very promising audiological tool, with past interest being focussed primarily on the optimal modulation frequency, the influence of vigilance of the generation of potentials, and the precise assessment of an objective threshold.
A generalized fidelity amplitude for open systems.
Gorin, T; Moreno, H J; Seligman, T H
2016-06-13
We consider a central system which is coupled via dephasing to an open system, i.e. an intermediate system which in turn is coupled to another environment. Considering the intermediate and far environment as one composite system, the coherences in the central system are given in the form of fidelity amplitudes for a certain perturbed echo dynamics in the composite environment. On the basis of the Born-Markov approximation, we derive a master equation for the reduction of that dynamics to the intermediate system alone. In distinction to an earlier paper (Moreno et al 2015 Phys. Rev. A 92, 030104. (doi:10.1103/PhysRevA.92.030104)), where we discussed the stabilizing effect of the far environment on the decoherence in the central system, we focus here on the possibility of using the measurable coherences in the central system for probing the open quantum dynamics in the intermediate system. We illustrate our results for the case of chaotic dynamics in the near environment, where we compare random matrix simulations with our analytical result. © 2016 The Author(s).
Nonlinear amplitude dynamics in flagellar beating
NASA Astrophysics Data System (ADS)
Oriola, David; Gadêlha, Hermes; Casademunt, Jaume
2017-03-01
The physical basis of flagellar and ciliary beating is a major problem in biology which is still far from completely understood. The fundamental cytoskeleton structure of cilia and flagella is the axoneme, a cylindrical array of microtubule doublets connected by passive cross-linkers and dynein motor proteins. The complex interplay of these elements leads to the generation of self-organized bending waves. Although many mathematical models have been proposed to understand this process, few attempts have been made to assess the role of dyneins on the nonlinear nature of the axoneme. Here, we investigate the nonlinear dynamics of flagella by considering an axonemal sliding control mechanism for dynein activity. This approach unveils the nonlinear selection of the oscillation amplitudes, which are typically either missed or prescribed in mathematical models. The explicit set of nonlinear equations are derived and solved numerically. Our analysis reveals the spatio-temporal dynamics of dynein populations and flagellum shape for different regimes of motor activity, medium viscosity and flagellum elasticity. Unstable modes saturate via the coupling of dynein kinetics and flagellum shape without the need of invoking a nonlinear axonemal response. Hence, our work reveals a novel mechanism for the saturation of unstable modes in axonemal beating.
Sensitivity to changes in amplitude envelope
NASA Astrophysics Data System (ADS)
Gallun, Erick; Hafter, Ervin R.; Bonnel, Anne-Marie
2002-05-01
Detection of a brief increment in a tonal pedestal is less well predicted by energy-detection (e.g., Macmillan, 1973; Bonnel and Hafter, 1997) than by sensitivity to changes in the stimulus envelope. As this implies a mechanism similar to an envelope extractor (Viemeister, 1979), sinusoidal amplitude modulation was used to mask a single ramped increment (10, 45, or 70 ms) added to a 1000-ms pedestal with carrier frequency (cf)=477 Hz. As in informational masking (Neff, 1994) and ``modulation-detection interference'' (Yost and Sheft, 1989), interference occurred with masker cfs of 477 and 2013 Hz. While slight masking was found with modulation frequencies (mfs) from 16 to 96 Hz, masking grew inversely with still lower mfs, being greatest for mf=4 Hz. This division is reminiscent of that said to separate sensations of ``roughness'' and ``beats,'' respectively (Terhardt, 1974), with the latter also being related to durations associated with auditory groupings in music and speech. Importantly, this result held for all of the signal durations and onset-offset ramps tested, suggesting that an increment on a pedestal is treated as a single auditory object whose detection is most difficult in the presence of other objects (in this case, ``beats'').
Baseline blood oxygenation modulates response amplitude
Lu, Hanzhang; Zhao, Chenguang; Ge, Yulin; Lewis-Amezcua, Kelly
2008-01-01
Although BOLD fMRI provides a useful tool for probing neuronal activities, large inter-subject variations in signal amplitude are commonly observed. Understanding the physiologic basis for these variations will have a significant impact on many fMRI studies. First, the physiologic modulator can be used as a regressor to reduce variations across subjects, thereby improving statistical power for detecting group differences. Second, if a pathologic condition or a drug treatment is shown to change fMRI responses, monitoring this modulatory parameter is useful in correctly interpreting the fMRI changes to neuronal deficits/recruitments. Here we present evidence that the task-evoked fMRI signals are modulated by baseline blood oxygenation. To measure global blood oxygenation, we used a recently developed technique, T2-Relaxation-Under-Spin-Tagging MRI, yielding baseline oxygenation of 63.7±7.2% in sagittal sinus with an estimation error of 1.3%. It was found that individuals with higher baseline oxygenation tend to have a smaller fMRI signal and vice versa. For every 10% difference in baseline oxygenation across subjects, the BOLD and cerebral blood flow signal differ by -0.4% and -30.0%, respectively, when using visual stimulation. TRUST MRI is a useful measurement for fMRI studies to control for the modulatory effects of baseline oxygenation that are unique to each subject. PMID:18666103
Nonlinear amplitude dynamics in flagellar beating
Casademunt, Jaume
2017-01-01
The physical basis of flagellar and ciliary beating is a major problem in biology which is still far from completely understood. The fundamental cytoskeleton structure of cilia and flagella is the axoneme, a cylindrical array of microtubule doublets connected by passive cross-linkers and dynein motor proteins. The complex interplay of these elements leads to the generation of self-organized bending waves. Although many mathematical models have been proposed to understand this process, few attempts have been made to assess the role of dyneins on the nonlinear nature of the axoneme. Here, we investigate the nonlinear dynamics of flagella by considering an axonemal sliding control mechanism for dynein activity. This approach unveils the nonlinear selection of the oscillation amplitudes, which are typically either missed or prescribed in mathematical models. The explicit set of nonlinear equations are derived and solved numerically. Our analysis reveals the spatio-temporal dynamics of dynein populations and flagellum shape for different regimes of motor activity, medium viscosity and flagellum elasticity. Unstable modes saturate via the coupling of dynein kinetics and flagellum shape without the need of invoking a nonlinear axonemal response. Hence, our work reveals a novel mechanism for the saturation of unstable modes in axonemal beating. PMID:28405357
The pulsed amplitude unit for the SLC
Rolfe, J.; Browne, M.J.; Jobe, R.K.
1987-02-01
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.
An amplitude modulated radio frequency plasma generator
NASA Astrophysics Data System (ADS)
Lei, Fan; Li, Xiaoping; Liu, Yanming; Liu, Donglin; Yang, Min; Xie, Kai; Yao, Bo
2017-04-01
A glow discharge plasma generator and diagnostic system has been developed to study the effects of rapidly variable plasmas on electromagnetic wave propagation, mimicking the plasma sheath conditions encountered in space vehicle reentry. The plasma chamber is 400 mm in diameter and 240 mm in length, with a 300-mm-diameter unobstructed clear aperture. Electron densities produced are in the mid 1010 electrons/cm3. An 800 W radio frequency (RF) generator is capacitively coupled through an RF matcher to an internally cooled stainless steel electrode to form the plasma. The RF power is amplitude modulated by a waveform generator that operates at different frequencies. The resulting plasma contains electron density modulations caused by the varying power levels. A 10 GHz microwave horn antenna pair situated on opposite sides of the chamber serves as the source and detector of probe radiation. The microwave power feed to the source horn is split and one portion is sent directly to a high-speed recording oscilloscope. On mixing this with the signal from the pickup horn antenna, the plasma-induced phase shift between the two signals gives the path-integrated electron density with its complete time dependent variation. Care is taken to avoid microwave reflections and extensive shielding is in place to minimize electronic pickup. Data clearly show the low frequency modulation of the electron density as well as higher harmonics and plasma fluctuations.
Surface Wave Amplitude Anomalies in the Western United States
NASA Astrophysics Data System (ADS)
Eddy, C.; Ekstrom, G.
2011-12-01
We determine maps of local surface wave amplitude factors across the Western United States for Rayleigh and Love waves at discrete periods between 25 and 125s. Measurements of raw amplitude anomalies are made from data recorded at 1161 USArray stations for minor arc arrivals of earthquakes with Mw>5.5 occurring between 2006 and 2010. We take the difference between high-quality amplitude anomaly measurements for events recorded on station pairs less than 2 degrees apart. The mean of these differences for each station pair is taken as the datum. Surface wave amplitudes are controlled by four separate mechanisms: focusing due to elastic structure, attenuation due to anelastic structure, source effects, and receiver effects. By taking the mean of the differences of amplitude anomalies for neighboring stations, we reduce the effects of focusing, attenuation, and the seismic source, thus isolating amplitude anomalies due to near-receiver amplitude effects. We determine local amplitude factors for each USArray station by standard linear inversion of the differential data set. The individual station amplitude factors explain the majority of the variance of the data. For example, derived station amplitude factors for 50s Rayleigh waves explain 92% of the variance of the data. We explore correlations between derived station amplitude factors and local amplitude factors predicted by crust and upper mantle models. Maps of local amplitude factors show spatial correlation with topography and geologic structures in the Western United States, particularly for maps derived from Rayleigh wave amplitude anomalies. A NW-SE trending high in amplitude factors in Eastern California is evident in the 50s map, corresponding to the location of the Sierra Nevada Mountains. High amplitude factors are observed in Colorado and New Mexico in the 50s-125s maps in the location of the highest peaks of the Rocky Mountains. High amplitude factors are also seen in Southern Idaho and Eastern Wyoming in
[Dependence of "amplitude modulation following response" on attention].
Pethe, J; Mühler, R; von Specht, H
2001-03-01
Amplitude modulation following responses (AMFR) allows good estimation of the hearing threshold due to the very narrow band excitation of the cochlea. Audiological use of AMFR requires knowledge of the relationship of these responses to the state of vigilance. The few studies published compared only qualitatively the amplitude of AMFR recorded in awake subjects to that recorded in sleeping subjects. A quantitative determination of the level of vigilance on the basis of recorded physiological parameters has not yet been carried out. In the present study, the relationship between the amplitude of AMFR and the level of vigilance was investigated quantitatively. In eight adults with normal hearing, the relationship between the AMFR amplitude and EEG amplitude in the delta- and theta-band was determined. The amplitude in both frequency bands was used to indicate the state of vigilance. The subjects were studied during natural and drug-induced sleep. A 1-kHz carrier tone with a sinusoidally modulated amplitude of 40 Hz or 80 Hz was used as stimulus. At 40-Hz modulation frequency, the AMFR amplitude correlates with the EEG amplitude both in natural and drug-induced sleep. An increase in EEG activity is paralleled by a significant reduction of AMFR amplitude. At 80-Hz modulation frequency, no relationship between AMFR amplitude and EEG activity could be detected. Under all conditions, the amplitudes of AMFR evoked by a modulation frequency of 80 Hz were significantly lower than those evoked by 40 Hz. These results suggest that for an audiological use of the 40-Hz AMFR the state of vigilance should be stabilised at a constantly high level. In spite of the lower influence of vigilance on the 80-Hz AMFR, this response appears less ideal for threshold estimation in adults due to the significantly smaller amplitudes.
Amplitude death induced by fractional derivatives in nonlinear coupled oscillators
NASA Astrophysics Data System (ADS)
Liu, Q. X.; Liu, J. K.; Chen, Y. M.
2017-07-01
This paper presents a study on amplitude death in nonlinear coupled oscillators containing fractional derivatives. Analytical criterion for amplitude death region is obtained by eigenvalue analysis and verified by numerical results. It is found that amplitude death regions can be enlarged to a large extent by fractional derivatives. For this reason, amplitude death can be detected in fractional Stuart-Landau systems with weak coupling strength and low frequency, whereas it never appears in integer-order systems. Interestingly, the widening of amplitude death region induced by fractional derivative is shared by a variety of oscillators with different types of coupling mechanisms. An interpretation for the underlying mechanism of this phenomenon is briefly addressed, based on which we further suggest a coupling organization leading to amplitude death only in fractional oscillators.
Image measurement technique on vibration amplitude of ultrasonic horn
NASA Astrophysics Data System (ADS)
Zhang, Yong-bin; Wu, Zhi-qun; Zhu, Jian-ping; He, Jian-guo; Liu, Guang-min
2013-10-01
The paper proposes a method to measure vibration amplitude of ultrasonic horn which is a very important component in the spindle for micro-electrical-chemical discharging machining. The method of image measuring amplitude on high frequency vibration is introduced. Non-contact measurement system based on vision technology is constructed. High precision location algorithm on image centroid, quadratic location algorithm, is presented to find the center of little light spot. Measurement experiments have been done to show the effect of image measurement technique on vibration amplitude of ultrasonic horn. In the experiments, precise calibration of the vision system is implemented using a normal graticule to obtain the scale factor between image pixel and real distance. The vibration amplitude of ultrasonic horn is changed by modifying the voltage amplitude of pulse power supply. The image of feature on ultrasonic horn is captured and image processing is carried out. The vibration amplitudes are got at different voltages.
Detection of combined frequency and amplitude modulation.
Moore, B C; Sek, A
1992-12-01
This article is concerned with the detection of mixed modulation (MM), i.e., simultaneously occurring amplitude modulation (AM) and frequency modulation (FM). In experiment 1, an adaptive two-alternative forced-choice task was used to determine thresholds for detecting AM alone. Then, thresholds for detecting FM were determined for stimuli which had a fixed amount of AM in the signal interval only. The amount of AM was always less than the threshold for detecting AM alone. The FM thresholds depended significantly on the magnitude of the coexisting AM. For low modulation rates (4, 16, and 64 Hz), the FM thresholds did not depend significantly on the relative phase of modulation for the FM and AM. For a high modulation rate (256 Hz) strong effects of modulator phase were observed. These phase effects are as predicted by the model proposed by Hartmann and Hnath [Acustica 50, 297-312 (1982)], which assumes that detection of modulation at modulation frequencies higher than the critical modulation frequency is based on detection of the lower sideband in the modulated signal's spectrum. In the second experiment, psychometric functions were measured for the detection of AM alone and FM alone, using modulation rates of 4 and 16 Hz. Results showed that, for each type of modulation, d' is approximately a linear function of the square of the modulation index. Application of this finding to the results of experiment 1 suggested that, at low modulation rates, FM and AM are not detected by completely independent mechanisms. In the third experiment, psychometric functions were again measured for the detection of AM alone and FM alone, using a 10-Hz modulation rate. Detectability was then measured for combined AM and FM, with modulation depths selected so that each type of modulation would be equally detectable if presented alone. Significant effects of relative modulator phase were found when detectability was relatively high. These effects were not correctly predicted by either a
Log-periodic Critical Amplitudes: A Perturbative Approach
NASA Astrophysics Data System (ADS)
Derrida, Bernard; Giacomin, Giambattista
2013-06-01
Log-periodic amplitudes appear in the critical behavior of a large class of systems, in particular when a discrete scale invariance is present. Here we show how to compute these critical amplitudes perturbatively when they originate from a renormalization map which is close to a monomial. In this case, the log-periodic amplitudes of the subdominant corrections to the leading critical behavior can also be calculated.
N >= 4 Supergravity Amplitudes from Gauge Theory at One Loop
Bern, Z.; Boucher-Veronneau, C.; Johansson, H.; /Saclay
2011-08-19
We expose simple and practical relations between the integrated four- and five-point one-loop amplitudes of N {ge} 4 supergravity and the corresponding (super-)Yang-Mills amplitudes. The link between the amplitudes is simply understood using the recently uncovered duality between color and kinematics that leads to a double-copy structure for gravity. These examples provide additional direct confirmations of the duality and double-copy properties at loop level for a sample of different theories.
Calculation and modular properties of multiloop superstring amplitudes
Danilov, G. S.
2013-06-15
Multiloop superstring amplitudes are calculated within an extensively used gauge where the two-dimensional gravitino field carries Grassmann moduli. In general, the amplitudes possess, instead of modular symmetry, symmetry with respect to modular transformation supplemented with appropriate transformations of two-dimensional local supersymmetry. If the number of loops is larger than three, the integrationmeasures are notmodular forms, while the expression for the amplitude contains integrals along the boundary of the fundamental region of the modular group.
Mass of nonrelativistic meson from leading twist distribution amplitudes
NASA Astrophysics Data System (ADS)
Braguta, V. V.
2011-01-01
In this paper distribution amplitudes of pseudoscalar and vector nonrelativistic mesons are considered. Using equations of motion for the distribution amplitudes, relations are derived which allow one to calculate the masses of nonrelativistic pseudoscalar and vector meson if the leading twist distribution amplitudes are known. These relations can be also rewritten as relations between the masses of nonrelativistic mesons and infinite series of QCD operators, what can be considered as an exact version of Gremm-Kapustin relation in NRQCD.
Tree-level split helicity amplitudes in ambitwistor space
NASA Astrophysics Data System (ADS)
Chen, Bin; Wu, Jun-Bao
2009-12-01
We study all tree-level split helicity gluon amplitudes by using the recently proposed Britto-Cachazo-Feng-Witten recursion relation and Hodges diagrams in ambitwistor space. We pick out the contributing diagrams and find that all of them can be divided into triangles in a suitable way. We give the explicit expressions for all of these amplitudes. As an example, we reproduce the six-gluon split next-to-maximally-helicity-violating amplitudes in momentum space.
Scattering amplitudes and BCFW recursion in twistor space
NASA Astrophysics Data System (ADS)
Mason, Lionel; Skinner, David
2010-01-01
Twistor ideas have led to a number of recent advances in our understanding of scattering amplitudes. Much of this work has been indirect, determining the twistor space support of scattering amplitudes by examining the amplitudes in momentum space. In this paper, we construct the actual twistor scattering amplitudes themselves. We show that the recursion relations of Britto, Cachazo, Feng and Witten have a natural twistor formulation that, together with the three-point seed amplitudes, allows us to recursively construct general tree amplitudes in twistor space. We obtain explicit formulae for n-particle MHV and NMHV super-amplitudes, their CPT conjugates (whose representations are distinct in our chiral framework), and the eight particle N2MHV super-amplitude. We also give simple closed form formulae for the mathcal{N} = 8 supergravity recursion and the MHV and overline {text{MHV}} amplitudes. This gives a formulation of scattering amplitudes in maximally supersymmetric theories in which superconformal symmetry and its breaking is manifest. For N k MHV, the amplitudes are given by 2 n - 4 integrals in the form of Hilbert transforms of a product of n - k - 2 purely geometric, superconformally invariant twistor delta functions, dressed by certain sign operators. These sign operators subtly violate conformal invariance, even for tree-level amplitudes in mathcal{N} = 4 super Yang-Mills, and we trace their origin to a topological property of split signature space-time. We develop the twistor transform to relate our work to the ambidextrous twistor diagram approach of Hodges and of Arkani-Hamed, Cachazo, Cheung and Kaplan.
Amplitude-modulated circular-harmonic filter for pattern recognition.
Chen, X W; Chen, Z P
1995-02-10
An amplitude-modulated circular-harmonic filter is proposed for rotation-invariant pattern recognition. We investigate the filter characteristics by varying two design parameters, A(ρ) and B(ρ), and select optimum values to design an amplitude-modulated circular-harmonic filter. When compared with the phase-only circular-harmonic filter, the amplitude-modulated circular-harmonic filter is found to yield a sharper correlation peak, a better noise tolerance, and an improved correlation discrimination.
Amplitudes and Ultraviolet Behavior of N = 8 Supergravity
Bern, Zvi; Carrasco, John Joseph; Dixon, Lance J.; Johansson, Henrik; Roiban, Radu; /Penn State U.
2011-05-20
In this contribution we describe computational tools that permit the evaluation of multi-loop scattering amplitudes in N = 8 supergravity, in terms of amplitudes in N = 4 super-Yang-Mills theory. We also discuss the remarkable ultraviolet behavior of N = 8 supergravity, which follows from these amplitudes, and is as good as that of N = 4 super-Yang-Mills theory through at least four loops.
Cluster functions and scattering amplitudes for six and seven points
NASA Astrophysics Data System (ADS)
Harrington, Thomas; Spradlin, Marcus
2017-07-01
Scattering amplitudes in planar super-Yang-Mills theory satisfy several basic physical and mathematical constraints, including physical constraints on their branch cut structure and various empirically discovered connections to the mathematics of cluster algebras. The power of the bootstrap program for amplitudes is inversely proportional to the size of the intersection between these physical and mathematical constraints: ideally we would like a list of constraints which determine scattering amplitudes uniquely. We explore this intersection quantitatively for two-loop six- and seven-point amplitudes by providing a complete taxonomy of the Gr(4, 6) and Gr(4, 7) cluster polylogarithm functions of [15] at weight 4.
Method of differential-phase/absolute-amplitude QAM
Dimsdle, Jeffrey William [Overland Park, KS
2008-10-21
A method of quadrature amplitude modulation involving encoding phase differentially and amplitude absolutely, allowing for a high data rate and spectral efficiency in data transmission and other communication applications, and allowing for amplitude scaling to facilitate data recovery; amplitude scale tracking to track-out rapid and severe scale variations and facilitate successful demodulation and data retrieval; 2.sup.N power carrier recovery; incoherent demodulation where coherent carrier recovery is not possible or practical due to signal degradation; coherent demodulation; multipath equalization to equalize frequency dependent multipath; and demodulation filtering.
Method of differential-phase/absolute-amplitude QAM
Dimsdle, Jeffrey William
2007-07-03
A method of quadrature amplitude modulation involving encoding phase differentially and amplitude absolutely, allowing for a high data rate and spectral efficiency in data transmission and other communication applications, and allowing for amplitude scaling to facilitate data recovery; amplitude scale tracking to track-out rapid and severe scale variations and facilitate successful demodulation and data retrieval; 2.sup.N power carrier recovery; incoherent demodulation where coherent carrier recovery is not possible or practical due to signal degradation; coherent demodulation; multipath equalization to equalize frequency dependent multipath; and demodulation filtering.
Method of differential-phase/absolute-amplitude QAM
Dimsdle, Jeffrey William
2007-10-02
A method of quadrature amplitude modulation involving encoding phase differentially and amplitude absolutely, allowing for a high data rate and spectral efficiency in data transmission and other communication applications, and allowing for amplitude scaling to facilitate data recovery; amplitude scale tracking to track-out rapid and severe scale variations and facilitate successful demodulation and data retrieval; 2.sup.N power carrier recovery; incoherent demodulation where coherent carrier recovery is not possible or practical due to signal degradation; coherent demodulation; multipath equalization to equalize frequency dependent multipath; and demodulation filtering.
Method of differential-phase/absolute-amplitude QAM
Dimsdle, Jeffrey William
2007-07-17
A method of quadrature amplitude modulation involving encoding phase differentially and amplitude absolutely, allowing for a high data rate and spectral efficiency in data transmission and other communication applications, and allowing for amplitude scaling to facilitate data recovery; amplitude scale tracking to track-out rapid and severe scale variations and facilitate successful demodulation and data retrieval; 2.sup.N power carrier recovery; incoherent demodulation where coherent carrier recovery is not possible or practical due to signal degradation; coherent demodulation; multipath equalization to equalize frequency dependent multipath; and demodulation filtering.
Method of differential-phase/absolute-amplitude QAM
Dimsdle, Jeffrey William [Overland Park, KS
2009-09-01
A method of quadrature amplitude modulation involving encoding phase differentially and amplitude absolutely, allowing for a high data rate and spectral efficiency in data transmission and other communication applications, and allowing for amplitude scaling to facilitate data recovery; amplitude scale tracking to track-out rapid and severe scale variations and facilitate successful demodulation and data retrieval; 2.sup.N power carrier recovery; incoherent demodulation where coherent carrier recovery is not possible or practical due to signal degradation; coherent demodulation; multipath equalization to equalize frequency dependent multipath; and demodulation filtering.
Method of differential-phase/absolute-amplitude QAM
Dimsdle, Jeffrey William
2007-07-03
A method of quadrature amplitude modulation involving encoding phase differentially and amplitude absolutely, allowing for a high data rate and spectral efficiency in data transmission and other communication applications, and allowing for amplitude scaling to facilitate data recovery; amplitude scale tracking to track-out rapid and severe scale variations and facilitate successful demodulation and data retrieval; 2.sup.N power carrier recovery; incoherent demodulation where coherent carrier recovery is not possible or practical due to signal degradation; coherent demodulation; multipath equalization to equalize frequency dependent multipath; and demodulation filtering.
Phase and amplitude control system for Stanford Linear Accelerator
Yoo, S.J.
1983-09-26
The computer controlled phase and amplitude detection system measures the instantaneous phase and amplitude of a 1 micro-second 2856 MHz rf pulse at a 180 Hz rate. This will be used for phase feedback control, and also for phase and amplitude jitter measurement. The program, which was originally written by John Fox and Keith Jobe, has been modified to improve the function of the system. The software algorithms used in the measurement are described, as is the performance of the prototype phase and amplitude detector system.
Cluster functions and scattering amplitudes for six and seven points
Harrington, Thomas; Spradlin, Marcus
2017-07-05
Scattering amplitudes in planar super-Yang-Mills theory satisfy several basic physical and mathematical constraints, including physical constraints on their branch cut structure and various empirically discovered connections to the mathematics of cluster algebras. The power of the bootstrap program for amplitudes is inversely proportional to the size of the intersection between these physical and mathematical constraints: ideally we would like a list of constraints which determine scattering amplitudes uniquely. Here, we explore this intersection quantitatively for two-loop six- and seven-point amplitudes by providing a complete taxonomy of the Gr(4, 6) and Gr(4, 7) cluster polylogarithm functions of [15] at weight 4.
Source-Space Cross-Frequency Amplitude-Amplitude Coupling in Tinnitus
Zobay, Oliver; Adjamian, Peyman
2015-01-01
The thalamocortical dysrhythmia (TCD) model has been influential in the development of theoretical explanations for the neurological mechanisms of tinnitus. It asserts that thalamocortical oscillations lock a region in the auditory cortex into an ectopic slow-wave theta rhythm (4–8 Hz). The cortical area surrounding this region is hypothesized to generate abnormal gamma (>30 Hz) oscillations (“edge effect”) giving rise to the tinnitus percept. Consequently, the model predicts enhanced cross-frequency coherence in a broad range between theta and gamma. In this magnetoencephalography study involving tinnitus and control cohorts, we investigated this prediction. Using beamforming, cross-frequency amplitude-amplitude coupling (AAC) was computed within the auditory cortices for frequencies (f1, f2) between 2 and 80 Hz. We find the AAC signal to decompose into two distinct components at low (f1, f2 < 30 Hz) and high (f1, f2 > 30 Hz) frequencies, respectively. Studying the correlation of AAC with several key covariates (age, hearing level (HL), tinnitus handicap and duration, and HL at tinnitus frequency), we observe a statistically significant association between age and low-frequency AAC. Contrary to the TCD predictions, however, we do not find any indication of statistical differences in AAC between tinnitus and controls and thus no evidence for the predicted enhancement of cross-frequency coupling in tinnitus. PMID:26665004
NASA Astrophysics Data System (ADS)
Roiban, Radu; Spradlin, Marcus; Volovich, Anastasia
2011-11-01
This issue aims to serve as an introduction to our current understanding of the structure of scattering amplitudes in gauge theory, an area which has seen particularly rapid advances in recent years following decades of steady progress. The articles contained herein provide a snapshot of the latest developments which we hope will serve as a valuable resource for graduate students and other scientists wishing to learn about the current state of the field, even if our continually evolving understanding of the subject might soon render this compilation incomplete. Why the fascination with scattering amplitudes, which have attracted the imagination and dedicated effort of so many physicists? Part of it stems from the belief, supported now by numerous examples, that unexpected simplifications of otherwise apparently complicated calculations do not happen by accident. Instead they provide a strong motivation to seek out an underlying explanation. The insight thereby gained can subsequently be used to make the next class of seemingly impossible calculations not only possible, but in some cases even trivial. This two-pronged strategy of exploring and exploiting the structure of gauge theory amplitudes appeals to a wide audience from formal theorists interested in mathematical structure for the sake of its own beauty to more phenomenologically-minded physicists eager to speed up the next generation of analysis software. Understandably it is the maximally supersymmetric 𝒩 = 4 Yang-Mills theory (SYM) which has the simplest structure and has correspondingly received the most attention. Rarely in theoretical physics are we fortunate enough to encounter a toy model which is simple enough to be solved completely yet rich enough to possess interesting non-trivial structure while simultaneously, and most importantly, being applicable (even if only as a good approximation) to a wide range of 'real' systems. The canonical example in quantum mechanics is of course the harmonic
Graph Diagrams in Transition Amplitudes of Dipole Cosmology
NASA Astrophysics Data System (ADS)
Kisielowski, Marcin; Lewandowski, Jerzy; Puchta, Jacek
2015-01-01
The Operator Spin-network Diagrams is a new framework that enables to express Spin-foam amplitudes in a clear graphical way. Within this framework it is easy to find and characterise all the spin-foams with a given fixed boundary graph. We used this technique to characterise transition amplitudes in Dipole Cosmology in higher order in the vertex expansion.
Amplitudes in N = 4 Super-Yang-Mills Theory
NASA Astrophysics Data System (ADS)
Spradlin, Marcus
These lecture notes provide a lightning introduction to some aspects of scattering amplitudes in maximally supersymmetric theory, aimed at the audience of students attending the 2014 TASI summer school "Journeys Through the Precision Frontier: Amplitudes for Colliders". Emphasis is placed on explaining modern terminology so that students needing to delve further may more easily access the available literature.
Proof of a new colour decomposition for QCD amplitudes
NASA Astrophysics Data System (ADS)
Melia, Tom
2015-12-01
Recently, Johansson and Ochirov conjectured the form of a new colour decom-position for QCD tree-level amplitudes. This note provides a proof of that conjecture. The proof is based on `Mario World' Feynman diagrams, which exhibit the hierarchical Dyck structure previously found to be very useful when dealing with multi-quark amplitudes.
Proof of a new colour decomposition for QCD amplitudes
Melia, Tom
2015-12-16
Recently, Johansson and Ochirov conjectured the form of a new colour decom-position for QCD tree-level amplitudes. This note provides a proof of that conjecture. The proof is based on ‘Mario World’ Feynman diagrams, which exhibit the hierarchical Dyck structure previously found to be very useful when dealing with multi-quark amplitudes.
Simple parametrization of the π-N amplitude
NASA Astrophysics Data System (ADS)
McLeod, R. J.; Afnan, I. R.
1985-07-01
We present a simple parametrization of the S-, P-, and D-wave π-N amplitudes using separable potentials for Tπ<1 GeV. The effect of the inelasticity is included in the Green's function while maintaining consistency with unitarity. The P11 amplitude is written as a pole plus nonpole in order to describe pion absorption in A>=2.
Miracles in Scattering Amplitudes: from QCD to Gravity
Volovich, Anastasia
2016-10-09
The goal of my research project "Miracles in Scattering Amplitudes: from QCD to Gravity" involves deepening our understanding of gauge and gravity theories by exploring hidden structures in scattering amplitudes and using these rich structures as much as possible to aid practical calculations.
Abnormal Selective Attention Normalizes P3 Amplitudes in PDD
ERIC Educational Resources Information Center
Hoeksma, Marco R.; Kemner, Chantal; Kenemans, J. Leon; van Engeland, Herman
2006-01-01
This paper studied whether abnormal P3 amplitudes in PDD are a corollary of abnormalities in ERP components related to selective attention in visual and auditory tasks. Furthermore, this study sought to clarify possible age differences in such abnormalities. Children with PDD showed smaller P3 amplitudes than controls, but no abnormalities in…
Automated force controller for amplitude modulation atomic force microscopy
Miyagi, Atsushi E-mail: simon.scheuring@inserm.fr; Scheuring, Simon E-mail: simon.scheuring@inserm.fr
2016-05-15
Atomic Force Microscopy (AFM) is widely used in physics, chemistry, and biology to analyze the topography of a sample at nanometer resolution. Controlling precisely the force applied by the AFM tip to the sample is a prerequisite for faithful and reproducible imaging. In amplitude modulation (oscillating) mode AFM, the applied force depends on the free and the setpoint amplitudes of the cantilever oscillation. Therefore, for keeping the applied force constant, not only the setpoint amplitude but also the free amplitude must be kept constant. While the AFM user defines the setpoint amplitude, the free amplitude is typically subject to uncontrollable drift, and hence, unfortunately, the real applied force is permanently drifting during an experiment. This is particularly harmful in biological sciences where increased force destroys the soft biological matter. Here, we have developed a strategy and an electronic circuit that analyzes permanently the free amplitude of oscillation and readjusts the excitation to maintain the free amplitude constant. As a consequence, the real applied force is permanently and automatically controlled with picoNewton precision. With this circuit associated to a high-speed AFM, we illustrate the power of the development through imaging over long-duration and at various forces. The development is applicable for all AFMs and will widen the applicability of AFM to a larger range of samples and to a larger range of (non-specialist) users. Furthermore, from controlled force imaging experiments, the interaction strength between biomolecules can be analyzed.
Amplitude transitions of swimmers and flexors in viscoelastic fluids
NASA Astrophysics Data System (ADS)
Guy, Robert; Thomases, Becca
2015-11-01
In both theoretical and experimental studies of the effect of fluid elasticity on micro-organism swimming, very different behavior has been observed for small and large amplitude strokes. We present simulations of an undulatory swimmer in an Oldroyd-B fluid and show that the resulting viscoelastic stresses are a nonlinear function of the amplitude. Specifically, there appears to be an amplitude dependent transition that is key to obtaining a speed-up over the Newtonian swimming speed. To understand the physical mechanism of the transition, we examine the stresses in a time-symmetric oscillatory bending beam, or flexor. We compare the flow in a neighborhood of the flexor tips with a large-amplitude oscillatory extensional flow, and we see similar amplitude dependent transitions. We relate these transitions to observed speed-ups in viscoelastic swimmers.
High frequency amplitude detector for GMI magnetic sensors.
Asfour, Aktham; Zidi, Manel; Yonnet, Jean-Paul
2014-12-19
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.
High Frequency Amplitude Detector for GMI Magnetic Sensors
Asfour, Aktham; Zidi, Manel; Yonnet, Jean-Paul
2014-01-01
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. PMID:25536003
Reinforcing saccadic amplitude variability in a visual search task.
Paeye, Céline; Madelain, Laurent
2014-11-20
Human observers often adopt rigid scanning strategies in visual search tasks, even though this may lead to suboptimal performance. Here we ask whether specific levels of saccadic amplitude variability may be induced in a visual search task using reinforcement learning. We designed a new gaze-contingent visual foraging task in which finding a target among distractors was made contingent upon specific saccadic amplitudes. When saccades of rare amplitudes led to displaying the target, the U values (measuring uncertainty) increased by 54.89% on average. They decreased by 41.21% when reinforcing frequent amplitudes. In a noncontingent control group no consistent change in variability occurred. A second experiment revealed that this learning transferred to conventional visual search trials. These results provide experimental support for the importance of reinforcement learning for saccadic amplitude variability in visual search. © 2014 ARVO.
Discontinuities of BFKL amplitudes and the BDS ansatz
NASA Astrophysics Data System (ADS)
Fadin, V. S.; Fiore, R.
2015-12-01
We perform an examination of discontinuities of multiple production amplitudes, which are required for further development of the BFKL approach. It turns out that the discontinuities of 2 → 2 + n amplitudes obtained in the BFKL approach contradict to the BDS ansatz for amplitudes with maximal helicity violation in N = 4 supersymmetric Yang-Mills theory with large number of colors starting with n = 2. Explicit expressions for the discontinuities of the 2 → 3 and 2 → 4 amplitudes in the invariant mass of pairs of produced gluons are obtained in the planar N = 4 SYM in the next-to-leading logarithmic approximation. These expressions can be used for checking the conjectured duality between the light-like Wilson loops and the MHV amplitudes.
Effective Field Theories from Soft Limits of Scattering Amplitudes.
Cheung, Clifford; Kampf, Karol; Novotny, Jiri; Trnka, Jaroslav
2015-06-05
We derive scalar effective field theories-Lagrangians, symmetries, and all-from on-shell scattering amplitudes constructed purely from Lorentz invariance, factorization, a fixed power counting order in derivatives, and a fixed order at which amplitudes vanish in the soft limit. These constraints leave free parameters in the amplitude which are the coupling constants of well-known theories: Nambu-Goldstone bosons, Dirac-Born-Infeld scalars, and Galilean internal shift symmetries. Moreover, soft limits imply conditions on the Noether current which can then be inverted to derive Lagrangians for each theory. We propose a natural classification of all scalar effective field theories according to two numbers which encode the derivative power counting and soft behavior of the corresponding amplitudes. In those cases where there is no consistent amplitude, the corresponding theory does not exist.
New formulas for amplitudes from higher-dimensional operators
NASA Astrophysics Data System (ADS)
He, Song; Zhang, Yong
2017-02-01
In this paper we study tree-level amplitudes from higher-dimensional operators, including F 3 operator of gauge theory, and R 2, R 3 operators of gravity, in the Cachazo-He-Yuan formulation. As a generalization of the reduced Pfaffian in Yang-Mills theory, we find a new, gauge-invariant object that leads to gluon amplitudes with a single insertion of F 3, and gravity amplitudes by Kawai-Lewellen-Tye relations. When reduced to four dimensions for given helicities, the new object vanishes for any solution of scattering equations on which the reduced Pfaffian is non-vanishing. This intriguing behavior in four dimensions explains the vanishing of graviton helicity amplitudes produced by the Gauss-Bonnet R 2 term, and provides a scattering-equation origin of the decomposition into self-dual and anti-self-dual parts for F 3 and R 3 amplitudes.
Gravity Amplitudes as Generalized Double Copies of Gauge-Theory Amplitudes
NASA Astrophysics Data System (ADS)
Bern, Zvi; Carrasco, John Joseph; Chen, Wei-Ming; Johansson, Henrik; Roiban, Radu
2017-05-01
Whenever the integrand of a gauge-theory loop amplitude can be arranged into a form where the Bern-Carrasco-Johansson duality between color and kinematics is manifest, a corresponding gravity integrand can be obtained simply via the double-copy procedure. However, finding such gauge-theory representations can be challenging, especially at high loop orders. Here, we show that we can, instead, start from generic gauge-theory integrands, where the duality is not manifest, and apply a modified double-copy procedure to obtain gravity integrands that include contact terms generated by violations of dual Jacobi identities. We illustrate this with three-, four- and five-loop examples in N =8 supergravity.
Gravity Amplitudes as Generalized Double Copies of Gauge-Theory Amplitudes.
Bern, Zvi; Carrasco, John Joseph; Chen, Wei-Ming; Johansson, Henrik; Roiban, Radu
2017-05-05
Whenever the integrand of a gauge-theory loop amplitude can be arranged into a form where the Bern-Carrasco-Johansson duality between color and kinematics is manifest, a corresponding gravity integrand can be obtained simply via the double-copy procedure. However, finding such gauge-theory representations can be challenging, especially at high loop orders. Here, we show that we can, instead, start from generic gauge-theory integrands, where the duality is not manifest, and apply a modified double-copy procedure to obtain gravity integrands that include contact terms generated by violations of dual Jacobi identities. We illustrate this with three-, four- and five-loop examples in N=8 supergravity.
Amplitude path corrections for regional phases in China
Phillips, W.S.; Velasco, A.A.; Taylor, S.R.; Randall, G.E.
1998-12-31
The authors investigate the effectiveness of amplitude path corrections for regional phases on seismic event discrimination and magnitude estimation. Waveform data from digital stations in China for regional, shallow (< 50 km) events were obtained from the IRIS Data Management Center (DMC) for years 1986 to 1996 using the USGS Preliminary Determination of Epicenters (PDE) and the Chinese State Seismological Bureau (SSB) catalogs. For each event, the amplitudes for each regional phase (P{sub n}, P{sub g}, S{sub n}, L{sub g}) were measured, as well as the P{sub g} and L{sub g} coda. Measured amplitudes were corrected for source scaling using estimates of m{sub b} and for distance using a power law that accounts for attenuation and spreading. The amplitude residuals were interpolated and mapped as 2-D amplitude correction surfaces. The authors employ several methods to create the amplitude correction surfaces: a waveguide method, and two interpolation methods (Baysian kriging and a circular moving window mean smoother). They explore the sensitivities of the surfaces to the method and to regional propagation, and apply these surfaces to correct amplitude data to reduce scatter in discrimination ratios and magnitude estimates.
Amplitude Dispersion Compensation for Damage Detection Using Ultrasonic Guided Waves
Zeng, Liang; Lin, Jing; Huang, Liping; Zhao, Ming
2016-01-01
Besides the phase and group velocities, the amplitude of guided wave mode is also frequency dependent. This amplitude dispersion also influences the performance of guided wave methods in nondestructive evaluation (NDE) and structural health monitoring (SHM). In this paper, the effects of amplitude dispersion to the spectrum and waveform of a propagating wave-packet are investigated. It is shown that the amplitude dispersion results in distortion in the spectrum of guided wave response, and thus influences the waveform of the wave-packet. To remove these effects, an amplitude dispersion compensation method is established on the basis of Vold–Kalman filter and Taylor series expansion. The performance of that method is then investigated by experimental examples. The results show that with the application of the amplitude dispersion compensation, the time reversibility could be preserved, which ensures the applicability of the time reversal method for damage detection. Besides, through amplitude dispersion compensation, the testing resolution of guided waves could be improved, so that the structural features located in the close proximity may be separately identified. PMID:27706067
Discriminating simulated vocal tremor source using amplitude modulation spectra.
Carbonell, Kathy M; Lester, Rosemary A; Story, Brad H; Lotto, Andrew J
2015-03-01
Sources of vocal tremor are difficult to categorize perceptually and acoustically. This article describes a preliminary attempt to discriminate vocal tremor sources through the use of spectral measures of the amplitude envelope. The hypothesis is that different vocal tremor sources are associated with distinct patterns of acoustic amplitude modulations. Statistical categorization methods (discriminant function analysis) were used to discriminate signals from simulated vocal tremor with different sources using only acoustic measures derived from the amplitude envelopes. Simulations of vocal tremor were created by modulating parameters of a vocal fold model corresponding to oscillations of respiratory driving pressure (respiratory tremor), degree of vocal fold adduction (adductory tremor), and fundamental frequency of vocal fold vibration (F0 tremor). The acoustic measures were based on spectral analyses of the amplitude envelope computed across the entire signal and within select frequency bands. The signals could be categorized (with accuracy well above chance) in terms of the simulated tremor source using only measures of the amplitude envelope spectrum even when multiple sources of tremor were included. These results supply initial support for an amplitude-envelope-based approach to identify the source of vocal tremor and provide further evidence for the rich information about talker characteristics present in the temporal structure of the amplitude envelope. Copyright © 2015 The Voice Foundation. Published by Elsevier Inc. All rights reserved.
Bootstrapping Multi-Parton Loop Amplitudes in QCD
Bern, Zvi; Dixon, Lance J.; Kosower, David A.; /Saclay, SPhT
2005-07-06
The authors present a new method for computing complete one-loop amplitudes, including their rational parts, in non-supersymmetric gauge theory. This method merges the unitarity method with on-shell recursion relations. It systematizes a unitarity-factorization bootstrap approach previously applied by the authors to the one-loop amplitudes required for next-to-leading order QCD corrections to the processes e{sup +}e{sup -} {yields} Z, {gamma}* {yields} 4 jets and pp {yields} W + 2 jets. We illustrate the method by reproducing the one-loop color-ordered five-gluon helicity amplitudes in QCD that interfere with the tree amplitude, namely A{sub 5;1}(1{sup -}, 2{sup -}, 3{sup +}, 4{sup +}, 5{sup +}) and A{sub 5;1}(1{sup -}, 2{sup +}, 3{sup -}, 4{sup +}, 5{sup +}). Then we describe the construction of the six- and seven-gluon amplitudes with two adjacent negative-helicity gluons, A{sub 6;1}(1{sup -}, 2{sup -}, 3{sup +}, 4{sup +}, 5{sup +}, 6{sup +}) and A{sub 7;1}(1{sup -}, 2{sup -}, 3{sup +}, 4{sup +}, 5{sup +}, 6{sup +}, 7{sup +}), which uses the previously-computed logarithmic parts of the amplitudes as input. They present a compact expression for the six-gluon amplitude. No loop integrals are required to obtain the rational parts.
Frequency adaptation for enhanced radiation force amplitude in dynamic elastography.
Ouared, Abderrahmane; Montagnon, Emmanuel; Kazemirad, Siavash; Gaboury, Louis; Robidoux, André; Cloutier, Guy
2015-08-01
In remote dynamic elastography, the amplitude of the generated displacement field is directly related to the amplitude of the radiation force. Therefore, displacement improvement for better tissue characterization requires the optimization of the radiation force amplitude by increasing the push duration and/or the excitation amplitude applied on the transducer. The main problem of these approaches is that the Food and Drug Administration (FDA) thresholds for medical applications and transducer limitations may be easily exceeded. In the present study, the effect of the frequency used for the generation of the radiation force on the amplitude of the displacement field was investigated. We found that amplitudes of displacements generated by adapted radiation force sequences were greater than those generated by standard nonadapted ones (i.e., single push acoustic radiation force impulse and supersonic shear imaging). Gains in magnitude were between 20 to 158% for in vitro measurements on agar-gelatin phantoms, and 170 to 336% for ex vivo measurements on a human breast sample, depending on focus depths and attenuations of tested samples. The signal-to-noise ratio was also improved more than 4-fold with adapted sequences. We conclude that frequency adaptation is a complementary technique that is efficient for the optimization of displacement amplitudes. This technique can be used safely to optimize the deposited local acoustic energy without increasing the risk of damaging tissues and transducer elements.
Large amplitude ion-acoustic solitons in dusty plasmas
Tiwari, R. S.; Jain, S. L.; Mishra, M. K.
2011-08-15
Characteristics of ion-acoustic soliton in dusty plasma, including the dynamics of heavily charged massive dust grains, are investigated following the Sagdeev Potential formalism. Retaining fourth order nonlinearities of electric potential in the expansion of the Sagdeev Potential in the energy equation for a pseudo particle and integrating the resulting energy equation, large amplitude soliton solution is determined. Variation of amplitude (A), half width (W) at half maxima and the product P = AW{sup 2} of the Korteweg-deVries (KdV), dressed and large amplitude soliton as a function of wide range of dust concentration are numerically studied for recently observed parameters of dusty plasmas. We have also presented the region of existence of large amplitude ion-acoustic soliton in the dusty plasma by analyzing the structure of the pseudo potential. It is found that in the presence of positively charged dust grains, system supports only compressive solitons, on the other hand, in the presence of negatively charged dust grains, the system supports compressive solitons up to certain critical concentration of dust grains and above this critical concentration, the system can support rarefactive solitons also. The effects of dust concentration, charge, and mass of the dust grains, on the characteristics of KdV, dressed and large amplitude the soliton, i.e., amplitude (A), half width at half maxima (W), and product of amplitude (A) and half width at half maxima (P = AW{sup 2}), are discussed in detail.
Broadband metasurface holograms: toward complete phase and amplitude engineering
Wang, Qiu; Zhang, Xueqian; Xu, Yuehong; Gu, Jianqiang; Li, Yanfeng; Tian, Zhen; Singh, Ranjan; Zhang, Shuang; Han, Jiaguang; Zhang, Weili
2016-01-01
As a revolutionary three-dimensional imaging technique, holography has attracted wide attention for its ability to photographically record a light field. However, traditional phase-only or amplitude-only modulation holograms have limited image quality and resolution to reappear both amplitude and phase information required of the objects. Recent advances in metasurfaces have shown tremendous opportunities for using a planar design of artificial meta-atoms to shape the wave front of light by optimal control of both its phase and amplitude. Inspired by the concept of designer metasurfaces, we demonstrate a novel amplitude-phase modulation hologram with simultaneous five-level amplitude modulation and eight-level phase modulation. Such a design approach seeks to turn the perceived disadvantages of the traditional phase or amplitude holograms, and thus enable enhanced performance in resolution, homogeneity of amplitude distribution, precision, and signal-to-noise ratio. In particular, the unique holographic approach exhibits broadband characteristics. The method introduced here delivers more degrees of freedom, and allows for encoding highly complex information into designer metasurfaces, thus having the potential to drive next-generation technological breakthroughs in holography. PMID:27615519
Discriminating Simulated Vocal Tremor Source Using Amplitude Modulation Spectra
Carbonell, Kathy M.; Lester, Rosemary A.; Story, Brad H.; Lotto, Andrew J.
2014-01-01
Objectives/Hypothesis Sources of vocal tremor are difficult to categorize perceptually and acoustically. This paper describes a preliminary attempt to discriminate vocal tremor sources through the use of spectral measures of the amplitude envelope. The hypothesis is that different vocal tremor sources are associated with distinct patterns of acoustic amplitude modulations. Study Design Statistical categorization methods (discriminant function analysis) were used to discriminate signals from simulated vocal tremor with different sources using only acoustic measures derived from the amplitude envelopes. Methods Simulations of vocal tremor were created by modulating parameters of a vocal fold model corresponding to oscillations of respiratory driving pressure (respiratory tremor), degree of vocal fold adduction (adductory tremor) and fundamental frequency of vocal fold vibration (F0 tremor). The acoustic measures were based on spectral analyses of the amplitude envelope computed across the entire signal and within select frequency bands. Results The signals could be categorized (with accuracy well above chance) in terms of the simulated tremor source using only measures of the amplitude envelope spectrum even when multiple sources of tremor were included. Conclusions These results supply initial support for an amplitude-envelope based approach to identify the source of vocal tremor and provide further evidence for the rich information about talker characteristics present in the temporal structure of the amplitude envelope. PMID:25532813
Broadband metasurface holograms: toward complete phase and amplitude engineering
NASA Astrophysics Data System (ADS)
Wang, Qiu; Zhang, Xueqian; Xu, Yuehong; Gu, Jianqiang; Li, Yanfeng; Tian, Zhen; Singh, Ranjan; Zhang, Shuang; Han, Jiaguang; Zhang, Weili
2016-09-01
As a revolutionary three-dimensional imaging technique, holography has attracted wide attention for its ability to photographically record a light field. However, traditional phase-only or amplitude-only modulation holograms have limited image quality and resolution to reappear both amplitude and phase information required of the objects. Recent advances in metasurfaces have shown tremendous opportunities for using a planar design of artificial meta-atoms to shape the wave front of light by optimal control of both its phase and amplitude. Inspired by the concept of designer metasurfaces, we demonstrate a novel amplitude-phase modulation hologram with simultaneous five-level amplitude modulation and eight-level phase modulation. Such a design approach seeks to turn the perceived disadvantages of the traditional phase or amplitude holograms, and thus enable enhanced performance in resolution, homogeneity of amplitude distribution, precision, and signal-to-noise ratio. In particular, the unique holographic approach exhibits broadband characteristics. The method introduced here delivers more degrees of freedom, and allows for encoding highly complex information into designer metasurfaces, thus having the potential to drive next-generation technological breakthroughs in holography.
Amplitude Dispersion Compensation for Damage Detection Using Ultrasonic Guided Waves.
Zeng, Liang; Lin, Jing; Huang, Liping; Zhao, Ming
2016-09-30
Besides the phase and group velocities, the amplitude of guided wave mode is also frequency dependent. This amplitude dispersion also influences the performance of guided wave methods in nondestructive evaluation (NDE) and structural health monitoring (SHM). In this paper, the effects of amplitude dispersion to the spectrum and waveform of a propagating wave-packet are investigated. It is shown that the amplitude dispersion results in distortion in the spectrum of guided wave response, and thus influences the waveform of the wave-packet. To remove these effects, an amplitude dispersion compensation method is established on the basis of Vold-Kalman filter and Taylor series expansion. The performance of that method is then investigated by experimental examples. The results show that with the application of the amplitude dispersion compensation, the time reversibility could be preserved, which ensures the applicability of the time reversal method for damage detection. Besides, through amplitude dispersion compensation, the testing resolution of guided waves could be improved, so that the structural features located in the close proximity may be separately identified.
Coronagraphic Amplitude and Phase Correction for Detecting Planets
NASA Technical Reports Server (NTRS)
Woodgate, Bruce E.; Bowers, Charles W.
2003-01-01
Detection of earth-like planets around other stars using coronagraphy requires the optical beam into the coronagraph to be extremely uniform in both phase and amplitude. Errors in phase can be corrected using a deformable mirror, and error in amplitude can be corrected using a spatial light modulator, both in the pupil plan,a. These corrections can be combined using a Michelson interferometer. If amplitude corrections of only a few percent range are needed, the required accuracy of 10 (circumflex) -4 can be obtained with spatial light modulators with the modest dynamic range of 8 bits.
Direct Calculation of the Scattering Amplitude Without Partial Wave Analysis
NASA Technical Reports Server (NTRS)
Shertzer, J.; Temkin, A.; Fisher, Richard R. (Technical Monitor)
2001-01-01
Two new developments in scattering theory are reported. We show, in a practical way, how one can calculate the full scattering amplitude without invoking a partial wave expansion. First, the integral expression for the scattering amplitude f(theta) is simplified by an analytic integration over the azimuthal angle. Second, the full scattering wavefunction which appears in the integral expression for f(theta) is obtained by solving the Schrodinger equation with the finite element method (FEM). As an example, we calculate electron scattering from the Hartree potential. With minimal computational effort, we obtain accurate and stable results for the scattering amplitude.
Direct numerical approach to one-loop amplitudes
NASA Astrophysics Data System (ADS)
Duplančić, G.; Klajn, B.
2017-01-01
We present a completely numerical method of calculating one-loop amplitudes. Our approach is built upon two different existing methods: the contour deformation and the extrapolation methods. Taking the best features of each of them, we devise an intuitive, stable and robust procedure which circumvents the problem of large cancellations and related numerical instabilities by calculating the complete amplitude at once. As a proof of concept, we use our method to calculate the 2 γ →(N -2 )γ benchmark process, as well as the Higgs decay amplitude H →γ γ .
Analytical formula for three points sinusoidal signals amplitude estimation errors
NASA Astrophysics Data System (ADS)
Nicolae Vizireanu, Dragos; Viorica Halunga, Simona
2012-01-01
In this note, we show that the amplitude estimation of sinusoidal signals proposed in Wu and Hong [Wu, S.T., and Hong, J.L. (2010), 'Five-point Amplitude Estimation of Sinusoidal Signals: With Application to LVDT Signal Conditioning', IEEE Transactions on Instrumentation and Measurement, 59, 623-630] is a particular case of Vizireanu and Halunga [Vizireanu, D.N, and Halunga, S.V. (2011), 'Single Sine Wave Parameters Estimation Method Based on Four Equally Spaced Samples', International Journal of Electronics, 98(7), pp. 941-948]. An analytical formula for amplitude estimation errors as effects of sampling period deviation is obtained.
One-loop amplitudes of gluons in supersymmetric QCD
Britto, Ruth; Buchbinder, Evgeny; Cachazo, Freddy; Feng Bo
2005-09-15
One-loop amplitudes of gluons in supersymmetric Yang-Mills are four-dimensional cut-constructible. This means that they can be determined from their unitarity cuts. We present a new systematic procedure to explicitly carry out any finite unitarity cut integral. The procedure naturally separates the contributions from bubble, triangle and box scalar integrals. This technique allows the systematic calculation of N=1 amplitudes of gluons. As an application we compute all next-to-MHV six-gluon amplitudes in N=1 super-Yang-Mills.
Phase Synchronization of Coupled Rossler Oscillators: Amplitude Effect
NASA Astrophysics Data System (ADS)
Li, Xiao-Wen; Zheng, Zhi-Gang
2007-02-01
Phase synchronization of two linearly coupled Rossler oscillators with parameter misfits is explored. It is found that depending on parameter mismatches, the synchronization of phases exhibits different manners. The synchronization regime can be divided into three regimes. For small mismatches, the amplitude-insensitive regime gives the phase-dominant synchronization; When the parameter misfit increases, the amplitudes and phases of oscillators are correlated, and the amplitudes will dominate the synchronous dynamics for very large mismatches. The lag time among phases exhibits a power law when phase synchronization is achieved.
Scattering Amplitudes: The Most Perfect Microscopic Structures in the Universe
Dixon, Lance J.; /CERN /SLAC
2011-11-04
This article gives an overview of many of the recent developments in understanding the structure of relativistic scattering amplitudes in gauge theories ranging from QCD to N = 4 super-Yang-Mills theory, as well as (super)gravity. I also provide a pedagogical introduction to some of the basic tools used to organize and illuminate the color and kinematic structure of amplitudes. This article is an invited review introducing a special issue of Journal of Physics A devoted to 'Scattering Amplitudes in Gauge Theories'.
Renormalization Scale-Fixing for Complex Scattering Amplitudes
Brodsky, Stanley J.; Llanes-Estrada, Felipe J.; /Madrid U.
2005-12-21
We show how to fix the renormalization scale for hard-scattering exclusive processes such as deeply virtual meson electroproduction by applying the BLM prescription to the imaginary part of the scattering amplitude and employing a fixed-t dispersion relation to obtain the scale-fixed real part. In this way we resolve the ambiguity in BLM renormalization scale-setting for complex scattering amplitudes. We illustrate this by computing the H generalized parton distribution at leading twist in an analytic quark-diquark model for the parton-proton scattering amplitude which can incorporate Regge exchange contributions characteristic of the deep inelastic structure functions.
Segmentation Of Multifrequency Complex-Amplitude SAR Data
NASA Technical Reports Server (NTRS)
Rignot, Eric J.; Chellappa, Ramalingam
1994-01-01
Several mathematical models and associated algorithms implement method of segmenting multifrequency, highly speckled, high-resolution, complex-amplitude (amplitude and phase) synthetic-aperture-radar (SAR) digitized image into regions, within each of which radar backscattering characteristics are similar or homogeneous from place to place. Typically, each region represents different type of terrain or other surface; e.g., forest, agricultural land, sea ice, or water. Method of segmentation of SAR scene into regions is product of generalization, to multifrequency case, of single-frequency method described in "Algorithms for Segmentation of Complex-Amplitude SAR Data" (NPO-18524).
Two-color pyrometry for low amplitude periodic heating
NASA Astrophysics Data System (ADS)
Bennett, T. D.; Silveira, V. B.; Valdes, R.
2017-02-01
Specimens subject to periodic heating must be probed for a calibrated temperature response if standard measurements of thermal diffusivity are to be extended to determine thermal conductivity. A variation on two-color pyrometry is developed to measure both the offset and harmonic amplitudes of temperature fluctuations caused by periodic heating. The requisite pyrometric formulae are derived for low amplitude heating using an expansion of the nonlinear thermal emission. Well-defined uncertainties in the temperature values are determined from experimental uncertainties in radiometric measurements. The accuracy demonstrated in this work is better than 2% for the temperature offset and 3%-8% for the fluctuating temperature amplitude.
Some tree-level string amplitudes in the NSR formalism
NASA Astrophysics Data System (ADS)
Becker, Katrin; Becker, Melanie; Melnikov, Ilarion V.; Robbins, Daniel; Royston, Andrew B.
2015-12-01
We calculate tree level scattering amplitudes for open strings using the NSR formalism. We present a streamlined symmetry-based and pedagogical approach to the computations, which we first develop by checking two-, three-, and four-point functions involving bosons and fermions. We calculate the five-point amplitude for massless gluons and find agreement with an earlier result by Brandt, Machado and Medina. We then compute the five-point amplitudes involving two and four fermions respectively, the general form of which has not been previously obtained in the NSR formalism. The results nicely confirm expectations from the supersymmetric F 4 effective action. Finally we use the prescription of Kawai, Lewellen and Tye (KLT) to compute the amplitudes for the closed string sector.
Movement amplitude and tempo change in piano performance
NASA Astrophysics Data System (ADS)
Palmer, Caroline
2004-05-01
Music performance places stringent temporal and cognitive demands on individuals that should yield large speed/accuracy tradeoffs. Skilled piano performance, however, shows consistently high accuracy across a wide variety of rates. Movement amplitude may affect the speed/accuracy tradeoff, so that high accuracy can be obtained even at very fast tempi. The contribution of movement amplitude changes in rate (tempo) is investigated with motion capture. Cameras recorded pianists with passive markers on hands and fingers, who performed on an electronic (MIDI) keyboard. Pianists performed short melodies at faster and faster tempi until they made errors (altering the speed/accuracy function). Variability of finger movements in the three motion planes indicated most change in the plane perpendicular to the keyboard across tempi. Surprisingly, peak amplitudes of motion before striking the keys increased as tempo increased. Increased movement amplitudes at faster rates may reduce or compensate for speed/accuracy tradeoffs. [Work supported by Canada Research Chairs program, HIMH R01 45764.
Amplitude and phase chimeras in an ensemble of chaotic oscillators
NASA Astrophysics Data System (ADS)
Bogomolov, S. A.; Strelkova, G. I.; Schöll, E.; Anishchenko, V. S.
2016-07-01
The transition from coherence to incoherence in an ensemble of nonlocally coupled logistic maps is considered. Chimera states of two types (amplitude and phase) are found. The mechanism and conditions of their appearance are determined.
Amplitude chimeras and chimera death in dynamical networks
NASA Astrophysics Data System (ADS)
Zakharova, Anna; Kapeller, Marie; Schöll, Eckehard
2016-06-01
We find chimera states with respect to amplitude dynamics in a network of Stuart- Landau oscillators. These partially coherent and partially incoherent spatio-temporal patterns appear due to the interplay of nonlocal network topology and symmetry-breaking coupling. As the coupling range is increased, the oscillations are quenched, amplitude chimeras disappear and the network enters a symmetry-breaking stationary state. This particular regime is a novel pattern which we call chimera death. It is characterized by the coexistence of spatially coherent and incoherent inhomogeneous steady states and therefore combines the features of chimera state and oscillation death. Additionally, we show two different transition scenarios from amplitude chimera to chimera death. Moreover, for amplitude chimeras we uncover the mechanism of transition towards in-phase synchronized regime and discuss the role of initial conditions.
Effect of vibration amplitude on vapor cavitation in journal bearings
NASA Technical Reports Server (NTRS)
Brewe, D. E.; Jacobson, B. O.
1986-01-01
Computational movies were used to analyze the formation and collapse of vapor cavitation bubbles in a submerged journal bearing. The effect of vibration amplitude on vapor cavitation was studied for a journal undergoing circular whirl. The boundary conditions were implemented using Elrod's algorithm, which conserves mass flow through the cavitation bubble as well as through the oil-film region of the bearing. The vibration amplitudes for the different cases studied resulted in maximum eccentricity ratios ranging from 0.4 to 0.9. The minimum eccentricity ratio reached in each case was 0.1. For the least vibration amplitude studied in which the eccentricity ratio varied between 0.1 and 0.4, no vapor cavitation occurred. The largest vibration amplitude (i.e., eccentricity ratios of 0.1 to 0.9) resulted in vapor cavitation present 76 percent of one complete orbit.
Amplitude analysis of the charmed decay D0 to KKpipi
NASA Astrophysics Data System (ADS)
Skidmore, Nicola
2017-01-01
An amplitude analysis of the 4-body charmed decay D0 -> KKππ is presented using data collected from electron-positron collisions at the CLEO experiment. Both flavour tagged and CP tagged data are utilized in the analysis making it unique from amplitude analyses performed at other colliders and providing extra sensitivity to the phases of the amplitude components. The amplitude model is used to search for CP violation in the D0 decay by analysing D0 and D0 decays separately. The model is also crucial input for a model-dependent measurement of the CP-violating phase γ using B+/- ->D0(-> KKππ) K+/- decays, which remains one of the least constrained parameters of the Standard Model. Forum on International Physics Distinguished Student Seminar Program, and European Research Council
Amplitude death of identical oscillators in networks with direct coupling
NASA Astrophysics Data System (ADS)
Illing, Lucas
2016-08-01
It is known that amplitude death can occur in networks of coupled identical oscillators if they interact via diffusive time-delayed coupling links. Here we consider networks of oscillators that interact via direct time-delayed coupling links. It is shown analytically that amplitude death is impossible for directly coupled Stuart-Landau oscillators, in contradistinction to the case of diffusive coupling. We demonstrate that amplitude death in the strict sense does become possible in directly coupled networks if the node dynamics is governed by second-order delay differential equations. Finally, we analyze in detail directly coupled nodes whose dynamics are described by first-order delay differential equations and find that, while amplitude death in the strict sense is impossible, other interesting oscillation quenching scenarios exist.
N >= 4 Supergravity Amplitudes from Gauge Theory at Two Loops
Boucher-Veronneau, C.; Dixon, L.J.; /SLAC
2012-02-15
We present the full two-loop four-graviton amplitudes in N = 4, 5, 6 supergravity. These results were obtained using the double-copy structure of gravity, which follows from the recently conjectured color-kinematics duality in gauge theory. The two-loop four-gluon scattering amplitudes in N = 0, 1, 2 supersymmetric gauge theory are a second essential ingredient. The gravity amplitudes have the expected infrared behavior: the two-loop divergences are given in terms of the squares of the corresponding one-loop amplitudes. The finite remainders are presented in a compact form. The finite remainder for N = 8 supergravity is also presented, in a form that utilizes a pure function with a very simple symbol.
Off-Shell Amplitudes for Nonoriented Closed Strings
NASA Astrophysics Data System (ADS)
Cappiello, Luigi; Marotta, Raffaele; Pettorino, Roberto; Pezzella, Franco
In the context of the bosonic closed string theory, by using the operatorial formalism, we give a simple expression of the off-shell amplitude with an arbitrary number of external massless states inserted on the Klein bottle.
Properties of scattering amplitudes at very high energies
NASA Technical Reports Server (NTRS)
Mickens, R. E.
1975-01-01
The research is reported concerning the (1) total cross sections as the energy becomes infinite, (2) elastic scattering amplitude for nonforward directions, and (3) upper bound of neutrino scattering cross sections.
Modelling of grain boundary dynamics using amplitude equations
NASA Astrophysics Data System (ADS)
Hüter, Claas; Neugebauer, Jörg; Boussinot, Guillaume; Svendsen, Bob; Prahl, Ulrich; Spatschek, Robert
2017-07-01
We discuss the modelling of grain boundary dynamics within an amplitude equations description, which is derived from classical density functional theory or the phase field crystal model. The relation between the conditions for periodicity of the system and coincidence site lattices at grain boundaries is investigated. Within the amplitude equations framework, we recover predictions of the geometrical model by Cahn and Taylor for coupled grain boundary motion, and find both {<100\\rangle} and {<110\\rangle} coupling. No spontaneous transition between these modes occurs due to restrictions related to the rotational invariance of the amplitude equations. Grain rotation due to coupled motion is also in agreement with theoretical predictions. Whereas linear elasticity is correctly captured by the amplitude equations model, open questions remain for the case of nonlinear deformations.
Moments of pseudoscalar meson distribution amplitudes from the lattice
Braun, V. M.; Goeckeler, M.; Horsley, R.; Zanotti, J. M.; Perlt, H.; Schiller, A.; Pleiter, D.; Schroers, W.; Schierholz, G.; Stueben, H.
2006-10-01
Based on lattice simulations with two flavors of dynamical, O(a)-improved Wilson fermions we present results for the first two moments of the distribution amplitudes of pseudoscalar mesons at several values of the valence quark masses. By extrapolating our results to the physical masses of up/down and strange quarks, we find the first two moments of the K{sup +} distribution amplitude and the second moment of the {pi}{sup +} distribution amplitude. We use nonperturbatively determined renormalization coefficients to obtain results in the MS scheme. At a scale of 4 GeV{sup 2} we find a{sub 2}{sup {pi}}=0.201(114) for the second Gegenbauer moment of the pion's distribution amplitude, while for the kaon, a{sub 1}{sup K}=0.0453(9)(29) and a{sub 2}{sup K}=0.175(18)(47)
Interdecadal Modulation of ENSO Amplitude During the Last Millennium
NASA Astrophysics Data System (ADS)
Li, J.; Xie, S.; Cook, E.; Huang, G.; D'Arrigo, R.; Liu, F.; Ma, J.; Zheng, X.
2010-12-01
El Niño/Southern Oscillation (ENSO) is the dominant mode of interannual variability, and affects climate around the globe. ENSO amplitude displays considerable variations on the instrumental record, and its future change is highly uncertain. Here we analyze a newly updated version of the tree-ring derived North American Drought Atlas (NADA) for the past 1100 years, and show that ENSO variance displays a quasi-regular cycle of 50-90 years. Interannual variability and its low-frequency amplitude modulation in NADA are in broad agreement with independent proxy records in the Pacific and surrounding regions. Large volcanic eruptions tend to trigger El Niño, but for the past millennium solar variations seem to drive amplitude modulation of ENSO. Simulating the quasi-periodic ENSO amplitude modulation may hold the key to improving models and their prediction of ENSO behavior in global warming.
Amplitude sorting of oscillatory burst signals by sampling
Davis, Thomas J.
1977-01-01
A method and apparatus for amplitude sorting of oscillatory burst signals is described in which the burst signal is detected to produce a burst envelope signal and an intermediate or midportion of such envelope signal is sampled to provide a sample pulse output. The height of the sample pulse is proportional to the amplitude of the envelope signal and to the maximum burst signal amplitude. The sample pulses are fed to a pulse height analyzer for sorting. The present invention is used in an acoustic emission testing system to convert the amplitude of the acoustic emission burst signals into sample pulse heights which are measured by a pulse height analyzer for sorting the pulses in groups according to their height in order to identify the material anomalies in the test material which emit the acoustic signals.
Laser beam complex amplitude measurement by phase diversity.
Védrenne, Nicolas; Mugnier, Laurent M; Michau, Vincent; Velluet, Marie-Thérèse; Bierent, Rudolph
2014-02-24
The control of the optical quality of a laser beam requires a complex amplitude measurement able to deal with strong modulus variations and potentially highly perturbed wavefronts. The method proposed here consists in an extension of phase diversity to complex amplitude measurements that is effective for highly perturbed beams. Named camelot for Complex Amplitude MEasurement by a Likelihood Optimization Tool, it relies on the acquisition and processing of few images of the beam section taken along the optical path. The complex amplitude of the beam is retrieved from the images by the minimization of a Maximum a Posteriori error metric between the images and a model of the beam propagation. The analytical formalism of the method and its experimental validation are presented. The modulus of the beam is compared to a measurement of the beam profile, the phase of the beam is compared to a conventional phase diversity estimate. The precision of the experimental measurements is investigated by numerical simulations.
High Amplitude (delta)-Scutis in the Large Magellanic Cloud
Garg, A; Cook, K H; Nikolaev, S; Huber, M E; Rest, A; Becker, A C; Challis, P; Clocchiatti, A; Miknaitis, G; Minniti, D; Morelli, L; Olsen, K; Prieto, J L; Suntzeff, N B; Welch, D L; Wood-Vasey, W M
2010-01-25
The authors present 2323 High-Amplitude {delta}-Scutis (HADS) candidates discovered in the Large Magellanic Cloud (LMC) by the SuperMACHO survey (Rest et al. 2005). Frequency analyses of these candidates reveal that several are multimode pulsators, including 119 whose largest amplitude of pulsation is in the fundamental (F) mode and 19 whose largest amplitude of pulsation is in the first overtone (FO) mode. Using Fourier decomposition of the HADS light curves, they find that the period-luminosity (PL) relation defined by the FO pulsators does not show a clear separation from the PL-relation defined by the F pulsators. This differs from other instability strip pulsators such as type c RR Lyrae. They also present evidence for a larger amplitude, subluminous population of HADS similar to that observed in Fornax (Poretti et al. 2008).
The Last of the Finite Loop Amplitudes in QCD
Bern, Zvi; Dixon, Lance J.; Kosower, David A.
2005-05-31
We use on-shell recursion relations to determine the one-loop QCD scattering amplitudes with a massless external quark pair and an arbitrary number (n - 2) of positive-helicity gluons. These amplitudes are the last of the unknown infrared- and ultraviolet-finite loop amplitudes of QCD. The recursion relations are similar to ones applied at tree level, but contain new non-trivial features corresponding to poles present for complex momentum arguments but absent for real momenta. We present the relations and the compact solutions to them, valid for all n. We also present compact forms for the previously-computed one-loop n-gluon amplitudes with a single negative helicity and the rest positive helicity.
Euclidean to Minkowski Bethe-Salpeter amplitude and observables
NASA Astrophysics Data System (ADS)
Carbonell, J.; Frederico, T.; Karmanov, V. A.
2017-01-01
We propose a method to reconstruct the Bethe-Salpeter amplitude in Minkowski space given the Euclidean Bethe-Salpeter amplitude - or alternatively the light-front wave function - as input. The method is based on the numerical inversion of the Nakanishi integral representation and computing the corresponding weight function. This inversion procedure is, in general, rather unstable, and we propose several ways to considerably reduce the instabilities. In terms of the Nakanishi weight function, one can easily compute the BS amplitude, the LF wave function and the electromagnetic form factor. The latter ones are very stable in spite of residual instabilities in the weight function. This procedure allows both, to continue the Euclidean BS solution in the Minkowski space and to obtain a BS amplitude from a LF wave function.
Non-perturbative QCD amplitudes in quenched and eikonal approximations
Fried, H.M.; Grandou, T.; Sheu, Y.-M.
2014-05-15
Even though approximated, strong coupling non-perturbative QCD amplitudes remain very difficult to obtain. In this article, in eikonal and quenched approximations at least, physical insights are presented that rely on the newly-discovered property of effective locality. The present article also provides a more rigorous mathematical basis for the crude approximations used in the previous derivation of the binding potential of quarks and nucleons. Furthermore, the techniques of Random Matrix calculus along with Meijer G-functions are applied to analyze the generic structure of fermionic amplitudes in QCD. - Highlights: • We discuss the physical insight of effective locality to QCD fermionic amplitudes. • We show that an unavoidable delta function goes along with the effective locality property. • The generic structure of QCD fermion amplitudes is obtained through Random Matrix calculus.
A Pn Spreading Model Constrained with Observed Amplitudes in Asia
2011-09-01
of observed Pn amplitudes from the tectonically active regions of Asia to evaluate the performance of Y2007 and to develop new, observation-based...a set of observed Pn amplitudes from the tectonically active regions of Asia to evaluate the performance of Y2007 and to develop new observation-based...tomographic inversions to map the lateral Pn attenuation variation. RESEARCH ACCOMPLISHED Introduction It has long been recognized that the
Bootstrapping a five-loop amplitude using Steinmann relations
Caron-Huot, Simon; Dixon, Lance J.; McLeod, Andrew; ...
2016-12-05
Here, the analytic structure of scattering amplitudes is restricted by Steinmann relations, which enforce the vanishing of certain discontinuities of discontinuities. We show that these relations dramatically simplify the function space for the hexagon function bootstrap in planar maximally supersymmetric Yang-Mills theory. Armed with this simplification, along with the constraints of dual conformal symmetry and Regge exponentiation, we obtain the complete five-loop six-particle amplitude.
Bootstrapping a Five-Loop Amplitude Using Steinmann Relations.
Caron-Huot, Simon; Dixon, Lance J; McLeod, Andrew; von Hippel, Matt
2016-12-09
The analytic structure of scattering amplitudes is restricted by Steinmann relations, which enforce the vanishing of certain discontinuities of discontinuities. We show that these relations dramatically simplify the function space for the hexagon function bootstrap in planar maximally supersymmetric Yang-Mills theory. Armed with this simplification, along with the constraints of dual conformal symmetry and Regge exponentiation, we obtain the complete five-loop six-particle amplitude.
T-wave amplitude is related to physical fitness status.
Arbel, Yaron; Birati, Edo Y; Shapira, Itzhak; Topilsky, Yan; Wirguin, Michal; Canaani M D, Jonathan
2012-07-01
Abnormalities in repolarization may reflect underlying myocardial pathology and play a prominent role in arrhythmogenesis The T-wave amplitude has been associated with cardiovascular outcome in patients with acute myocardial infarction (MI) Additionally, T-wave amplitude is considered a predictor of arrhythmias, as well as being related to an individual's inflammatory status. The combined influence of different variables, such as inflammation, cardiovascular risk factors and physical fitness status, on the T-wave amplitude has not been evaluated to date. The aim of this study was to identify factors that affect the T-wave amplitude. Data from 255 consecutive apparently healthy individuals included in the Tel Aviv Medical Center Inflammation Survey (TAMCIS) were reviewed. All patients had undergone a physical examination and an exercise stress test, and different inflammatory and metabolic biomarkers (fibrinogen, potassium, and high-sensitivity C-reactive protein) were measured. Multivariate stepwise analysis revealed that the body mass index and the resting heart rate were significantly associated with the T-wave amplitude (β=-0.34, P < 0.001; β=-0.19, P = 0.03, respectively) in males, while the recovery rate and the usage of statins significantly affected the T-wave amplitude in females (β= 0.36, P = 0.002; β= 0.35, P = 0.002, respectively). Inflammatory variables had no significant affect on the T-wave amplitude of either gender. In conclusion, the T-wave amplitude is linked to an individual's physical fitness and not to his/her inflammatory status. ©2012, Wiley Periodicals, Inc.
A cluster bootstrap for two-loop MHV amplitudes
NASA Astrophysics Data System (ADS)
Golden, John; Spradlin, Marcus
2015-02-01
We apply a bootstrap procedure to two-loop MHV amplitudes in planar super-Yang-Mills theory. We argue that the mathematically most complicated part (the Λ2 B 2 coproduct component) of the n-particle amplitude is uniquely determined by a simple cluster algebra property together with a few physical constraints (dihedral symmetry, analytic structure, supersymmetry, and well-defined collinear limits). We present a concise, closed-form expression which manifests these properties for all n.
Three-point disc amplitudes in the RNS formalism
NASA Astrophysics Data System (ADS)
Becker, Katrin; Becker, Melanie; Robbins, Daniel; Su, Ning
2016-06-01
We calculate all tree level string theory vacuum to Dp-brane disc amplitudes involving an arbitrary RR-state and two NS-NS vertex operators. This computation was earlier performed by K. Becker, Guo, and Robbins for the simplest case of a RR-state of type C (p - 3). Here we use the aid of a computer to calculate all possible three-point amplitudes involving a RR-vertex operator of type C (p + 1 + 2 k).
PAPR Advantage of Amplitude Clipped OFDM/TDM
NASA Astrophysics Data System (ADS)
Gacanin, Haris; Adachi, Fumiyuki
OFDM combined with TDM (OFDM/TDM) can be used to reduce a high peak-to-average power ratio (PAPR) of OFDM, but the PAPR reduction is not sufficient. To further reduce the PAPR, an amplitude clipping can be applied. In this letter, we investigate the effect of clipping on OFDM/TDM with and without channel coding. It is shown that amplitude clipped OFDM/TDM has an advantage over clipped OFDM with respect to the PAPR.
Wilson loops and QCD/string scattering amplitudes
Makeenko, Yuri; Olesen, Poul
2009-07-15
We generalize modern ideas about the duality between Wilson loops and scattering amplitudes in N=4 super Yang-Mills theory to large N QCD by deriving a general relation between QCD meson scattering amplitudes and Wilson loops. We then investigate properties of the open-string disk amplitude integrated over reparametrizations. When the Wilson-loop is approximated by the area behavior, we find that the QCD scattering amplitude is a convolution of the standard Koba-Nielsen integrand and a kernel. As usual poles originate from the first factor, whereas no (momentum-dependent) poles can arise from the kernel. We show that the kernel becomes a constant when the number of external particles becomes large. The usual Veneziano amplitude then emerges in the kinematical regime, where the Wilson loop can be reliably approximated by the area behavior. In this case, we obtain a direct duality between Wilson loops and scattering amplitudes when spatial variables and momenta are interchanged, in analogy with the N=4 super Yang-Mills theory case.
Light Diffraction by Large Amplitude Ultrasonic Waves in Liquids
NASA Technical Reports Server (NTRS)
Adler, Laszlo; Cantrell, John H.; Yost, William T.
2016-01-01
Light diffraction from ultrasound, which can be used to investigate nonlinear acoustic phenomena in liquids, is reported for wave amplitudes larger than that typically reported in the literature. Large amplitude waves result in waveform distortion due to the nonlinearity of the medium that generates harmonics and produces asymmetries in the light diffraction pattern. For standing waves with amplitudes above a threshold value, subharmonics are generated in addition to the harmonics and produce additional diffraction orders of the incident light. With increasing drive amplitude above the threshold a cascade of period-doubling subharmonics are generated, terminating in a region characterized by a random, incoherent (chaotic) diffraction pattern. To explain the experimental results a toy model is introduced, which is derived from traveling wave solutions of the nonlinear wave equation corresponding to the fundamental and second harmonic standing waves. The toy model reduces the nonlinear partial differential equation to a mathematically more tractable nonlinear ordinary differential equation. The model predicts the experimentally observed cascade of period-doubling subharmonics terminating in chaos that occurs with increasing drive amplitudes above the threshold value. The calculated threshold amplitude is consistent with the value estimated from the experimental data.
A proposed physical analog for a quantum probability amplitude
NASA Astrophysics Data System (ADS)
Boyd, Jeffrey
What is the physical analog of a probability amplitude? All quantum mathematics, including quantum information, is built on amplitudes. Every other science uses probabilities; QM alone uses their square root. Why? This question has been asked for a century, but no one previously has proposed an answer. We will present cylindrical helices moving toward a particle source, which particles follow backwards. Consider Feynman's book QED. He speaks of amplitudes moving through space like the hand of a spinning clock. His hand is a complex vector. It traces a cylindrical helix in Cartesian space. The Theory of Elementary Waves changes direction so Feynman's clock faces move toward the particle source. Particles follow amplitudes (quantum waves) backwards. This contradicts wave particle duality. We will present empirical evidence that wave particle duality is wrong about the direction of particles versus waves. This involves a paradigm shift; which are always controversial. We believe that our model is the ONLY proposal ever made for the physical foundations of probability amplitudes. We will show that our ``probability amplitudes'' in physical nature form a Hilbert vector space with adjoints, an inner product and support both linear algebra and Dirac notation.
Scattering amplitudes and Wilson loops in twistor space
NASA Astrophysics Data System (ADS)
Adamo, Tim; Bullimore, Mathew; Mason, Lionel; Skinner, David
2011-11-01
This paper reviews the recent progress in twistor approaches to Wilson loops, amplitudes and their duality for {N}=4 super-Yang-Mills. Wilson loops and amplitudes are derived from first principles using the twistor action for maximally supersymmetric Yang-Mills theory. We start by deriving the MHV rules for gauge theory amplitudes from the twistor action in an axial gauge in twistor space, and show that this gives rise to the original momentum space version given by Cachazo, Svrček and Witten. We then go on to obtain from these the construction of the momentum twistor space loop integrand using (planar) MHV rules and show how it arises as the expectation value of a holomorphic Wilson loop in twistor space. We explain the connection between the holomorphic Wilson loop and certain light-cone limits of correlation functions. We give a brief review of other ideas in connection with amplitudes in twistor space: twistor-strings, recursion in twistor space, the Grassmannian residue formula for leading singularities and amplitudes as polytopes. This paper is an invited review for a special issue of Journal of Physics A: Mathematical and Theoretical devoted to ‘Scattering amplitudes in gauge theories’.
Amplitude relations in non-linear sigma model
NASA Astrophysics Data System (ADS)
Chen, Gang; Du, Yi-Jian
2014-01-01
In this paper, we investigate tree-level scattering amplitude relations in U( N) non-linear sigma model. We use Cayley parametrization. As was shown in the recent works [23,24], both on-shell amplitudes and off-shell currents with odd points have to vanish under Cayley parametrization. We prove the off-shell U(1) identity and fundamental BCJ relation for even-point currents. By taking the on-shell limits of the off-shell relations, we show that the color-ordered tree amplitudes with even points satisfy U(1)-decoupling identity and fundamental BCJ relation, which have the same formations within Yang-Mills theory. We further state that all the on-shell general KK, BCJ relations as well as the minimal-basis expansion are also satisfied by color-ordered tree amplitudes. As a consequence of the relations among color-ordered amplitudes, the total 2 m-point tree amplitudes satisfy DDM form of color decomposition as well as KLT relation.
Ball bearing vibrations amplitude modeling and test comparisons
NASA Technical Reports Server (NTRS)
Hightower, Richard A., III; Bailey, Dave
1995-01-01
Bearings generate disturbances that, when combined with structural gains of a momentum wheel, contribute to induced vibration in the wheel. The frequencies generated by a ball bearing are defined by the bearing's geometry and defects. The amplitudes at these frequencies are dependent upon the actual geometry variations from perfection; therefore, a geometrically perfect bearing will produce no amplitudes at the kinematic frequencies that the design generates. Because perfect geometry can only be approached, emitted vibrations do occur. The most significant vibration is at the spin frequency and can be balanced out in the build process. Other frequencies' amplitudes, however, cannot be balanced out. Momentum wheels are usually the single largest source of vibrations in a spacecraft and can contribute to pointing inaccuracies if emitted vibrations ring the structure or are in the high-gain bandwidth of a sensitive pointing control loop. It is therefore important to be able to provide an a priori knowledge of possible amplitudes that are singular in source or are a result of interacting defects that do not reveal themselves in normal frequency prediction equations. This paper will describe the computer model that provides for the incorporation of bearing geometry errors and then develops an estimation of actual amplitudes and frequencies. Test results were correlated with the model. A momentum wheel was producing an unacceptable 74 Hz amplitude. The model was used to simulate geometry errors and proved successful in identifying a cause that was verified when the parts were inspected.
Dependence of kink oscillation damping on the amplitude
NASA Astrophysics Data System (ADS)
Goddard, C. R.; Nakariakov, V. M.
2016-05-01
Context. Kink oscillations of coronal loops are one of the most intensively studied oscillatory phenomena in the solar corona. In the large-amplitude rapidly damped regime, these oscillations are observed to have a low quality factor with only a few cycles of oscillation detected before they are damped. The specific mechanism responsible for rapid damping is commonly accepted to be associated with the linear coupling between collective kink oscillations and localised torsional oscillations, the phenomenon of resonant absorption of the kink mode. The role of finite amplitude effects, however, is still not clear. Aims: We investigated the empirical dependence of the kink oscillation damping time and its quality factor, which is defined as the ratio of damping time to oscillation period, on the oscillation amplitude. Methods: We analysed decaying kink oscillation events detected previously with TRACE, SDO/AIA and and STEREO/EUVI in the extreme ultraviolet (EUV) 171 Å band. Results: We found that the ratio of the kink oscillation damping time to the oscillation period systematically decreases with the oscillation amplitude. We approximated the quality factor dependence on the oscillation displacement amplitude via the power-law dependence with the exponent of -1/2, however we stress that this is a by-eye estimate, and a more rigorous estimation of the scaling law requires more accurate measurements and increased statistics. We conclude that damping of kink oscillations of coronal loops depends on the oscillation amplitude, indicating the possible role of non-linear mechanisms for damping.
Composite representation invariants and unoriented topological string amplitudes
NASA Astrophysics Data System (ADS)
Paul, Chandrima; Borhade, Pravina; Ramadevi, P.
2010-12-01
Sinha and Vafa [1] had conjectured that the SO Chern-Simons gauge theory on S must be dual to the closed A-model topological string on the orientifold of a resolved conifold. Though the Chern-Simons free energy could be rewritten in terms of the topological string amplitudes providing evidence for the conjecture, we needed a novel idea in the context of Wilson loop observables to extract cross-cap c=0,1,2 topological amplitudes. Recent paper of Marino [2] based on the work of Morton and Ryder [3] has clearly shown that the composite representation placed on the knots and links plays a crucial role to rewrite the topological string cross-cap c=0 amplitude. This enables extracting the unoriented cross-cap c=2 topological amplitude. In this paper, we have explicitly worked out the composite invariants for some framed knots and links carrying composite representations in U(N) Chern-Simons theory. We have verified generalised Rudolph's theorem, which relates composite invariants to the invariants in SO(N) Chern-Simons theory, and also verified Marino's conjectures on the integrality properties of the topological string amplitudes. For some framed knots and links, we have tabulated the BPS integer invariants for cross-cap c=0 and c=2 giving the open-string topological amplitude on the orientifold of the resolved conifold.
Mapping Pn amplitude spreading and attenuation in Asia
Yang, Xiaoning; Phillips, William S; Stead, Richard J
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.
Keenan, Kevin G.; Valero-Cuevas, Francisco J.
2008-01-01
Researchers and clinicians routinely rely on interference electromyograms (EMGs) to estimate muscle forces and command signals in the neuromuscular system (e.g., amplitude, timing, and frequency content). The amplitude cancellation intrinsic to interference EMG, however, raises important questions about how to optimize these estimates. For example, what should the length of the epoch (time window) be to average an EMG signal to reliably estimate muscle forces and command signals? Shorter epochs are most practical, and significant reductions in epoch have been reported with high-pass filtering and whitening. Given that this processing attenuates power at frequencies of interest (< 250 Hz), however, it is unclear how it improves the extraction of physiologically-relevant information. We examined the influence of amplitude cancellation and high-pass filtering on the epoch necessary to accurately estimate the “true” average EMG amplitude calculated from a 28 s EMG trace (EMGref) during simulated constant isometric conditions. Monte Carlo iterations of a motor-unit model simulating 28 s of surface EMG produced 245 simulations under 2 conditions: with and without amplitude cancellation. For each simulation, we calculated the epoch necessary to generate average full-wave rectified EMG amplitudes that settled within 5% of EMGref. For the no-cancellation EMG, the necessary epochs were short (e.g., < 100 ms). For the more realistic interference EMG (i.e., cancellation condition), epochs shortened dramatically after using high-pass filter cutoffs above 250 Hz, producing epochs short enough to be practical (i.e., < 500 ms). We conclude that the need to use long epochs to accurately estimate EMG amplitude is likely the result of unavoidable amplitude cancellation, which helps to clarify why high-pass filtering (> 250 Hz) improves EMG estimates. PMID:19081815
Retrieving impulse response function amplitudes from the ambient seismic field
NASA Astrophysics Data System (ADS)
Viens, Loïc; Denolle, Marine; Miyake, Hiroe; Sakai, Shin'ichi; Nakagawa, Shigeki
2017-07-01
Seismic interferometry is now widely used to retrieve the impulse response function of the Earth between two distant seismometers. The phase information has been the focus of most passive imaging studies, as conventional seismic tomography uses traveltime measurements. The amplitude information, however, is harder to interpret because it strongly depends on the distribution of ambient seismic field sources and on the multitude of processing methods. Our study focuses on the latter by comparing the amplitudes of the impulse response functions calculated between seismic stations in the Kanto sedimentary basin, Japan, using several processing techniques. This region provides a unique natural laboratory to test the reliability of the amplitudes with complex wave propagation through the basin, and dense observations from the Metropolitan Seismic Observation network. We compute the impulse response functions using the cross correlation, coherency and deconvolution techniques of the raw ambient seismic field and the cross correlation of 1-bit normalized data. To validate the amplitudes of the impulse response functions, we use a shallow Mw 5.8 earthquake that occurred on the eastern edge of Kanto Basin and close to a station that is used as the virtual source. Both S and surface waves are retrieved in the causal part of the impulse response functions computed with all the different techniques. However, the amplitudes obtained from the deconvolution method agree better with those of the earthquake. Despite the expected wave attenuation due to the soft sediments of the Kanto Basin, seismic amplification caused by the basin geometry dominates the amplitudes of S and surface waves and is captured by the ambient seismic field. To test whether or not the anticausal part of the impulse response functions from deconvolution also contains reliable amplitude information, we use another virtual source located on the western edge of the basin. We show that the surface wave amplitudes
Forecasting Wave Amplitudes after the Arrival of a Tsunami
NASA Astrophysics Data System (ADS)
Nyland, David; Huang, Paul
2014-12-01
The destructive Pacific Ocean tsunami generated off the east coast of Honshu, Japan, on 11 March 2011 prompted the West Coast and Alaska Tsunami Warning Center (WCATWC) to issue a tsunami warning and advisory for the coastal regions of Alaska, British Columbia, Washington, Oregon, and California. Estimating the length of time the warning or advisory would remain in effect proved difficult. To address this problem, the WCATWC developed a technique to estimate the amplitude decay of a tsunami recorded at tide stations within the Warning Center's Area of Responsibly (AOR). At many sites along the West Coast of North America, the tsunami wave amplitudes will decay exponentially following the arrival of the maximum wave ( Mofjeld et al., Nat Hazards 22:71-89, 2000). To estimate the time it will take before wave amplitudes drop to safe levels, the real-time tide gauge data are filtered to remove the effects of tidal variations. The analytic envelope is computed and a 2 h sequence of amplitude values following the tsunami peak is used to obtain a least squares fit to an exponential function. This yields a decay curve which is then combined with an average West Coast decay function to provide an initial tsunami amplitude-duration forecast. This information may then be provided to emergency managers to assist with response planning.
Bagolini glasses: do they affect the horizontal prism fusion amplitude?
Schultinga, L; Burggraaf, F; Polling, J R; Gutter, M
2013-06-01
Bagolini striated glasses (BSG) can be used while performing the prism fusion amplitude to verify the maintenance of binocularity. The aim of this clinical study was to evaluate whether these glasses affect the prism fusion amplitude. Fifty-six subjects were examined at the Eye Care Clinic at the University of Applied Sciences Utrecht. The positive and negative prism fusion amplitudes were measured, incorporating the BSG at random, for both near and distance, with right and left eye fixating. Fifty-two normal subjects with a mean age of 21 years (range 17-28) were recruited. The median prism fusion amplitude at near was 10 BI to 33 BO with the BSG and 13 BI to 38 BO without (p < 0.001). At distance the median amplitude was 8 BI to 33 BO both with and without these glasses (p = 0.104). Although BSG are useful to verify whether binocularity is maintained, significantly smaller fusional ranges were obtained during measurements at near. In clinical terms, fusional ranges can vary significantly when using the BSG.
Name that percussive tune: Associative memory and amplitude envelope.
Schutz, Michael; Stefanucci, Jeanine K; H Baum, Sarah; Roth, Amber
2017-07-01
A series of experiments demonstrated novel effects of amplitude envelope on associative memory, with tones exhibiting naturally decaying amplitude envelopes (e.g., those made by two wine glasses clinking) better associated with target objects than amplitude-invariant tones. In Experiment 1 participants learned associations between household objects and 4-note tone sequences constructed of spectrally matched pure tones with either "flat" or "percussive" amplitude envelopes. Those hearing percussive tones correctly recalled significantly more sequence-object associations. Experiment 2 demonstrated that participants hearing percussive tones learned the associations more quickly. Experiment 3 used "reverse percussive" tones (percussive tones played backwards) to test whether differences in overall energy might account for this effect, finding they did not lead to the same level of performance as percussive tones. Experiment 4 varied the envelope at encoding and retrieval to determine which stage of the task was most affected by the envelope manipulation. Participants hearing percussive tones at both encoding and retrieval performed significantly better than the other three groups (i.e., flat at encoding/percussive at retrieval, etc.). We conclude that amplitude envelope plays an important role in learning and memory, a finding with relevance to psychological research on audition and associative memory, as well as practical relevance for improving human-computer interface design.
Brain and human pain: topographic EEG amplitude and coherence mapping.
Chen, A C; Rappelsberger, P
1994-01-01
Nineteen young healthy volunteers (8 males and 11 females) participated in an experimental ice-cube cold pressor test to study topographic changes of EEG parameters in response to painful stimulation. EEG was recorded with 19 electrodes and quantified by amplitude and coherence analyses. Mean amplitudes and values for local (between adjacent electrodes) and interhemispheric (between electrodes on homologous sites of both hemispheres) coherences were computed for six frequency bands. For the evaluation of changes between EEG at rest (baseline) and EEG during painful stimulation (right or left hand), non-parametric paired Wilcoxon tests were performed. The obtained descriptive error probabilities were presented in probability maps. In the behavioural pain tolerance and subjective pain ratings, no difference in gender or stimulation condition was observed. Under painful stimulation the results showed: (A) most pronounced decrease of Alpha amplitude in the central areas and some increase of high Beta amplitude; (B) increase of local coherence for Alpha and Beta 2 mainly in central regions and centro-frontal leads; and (C) increase of interhemispheric coherence for Alpha and Beta 2 in the central areas. The results of this study indicate clearly that peripheral painful stimulation is reflected by EEG changes. Decrease of EEG amplitude and simultaneous increase of EEG coherence in the central regions can be cortical correlates of human pain.
All Tree-level Amplitudes in Massless QCD
Dixon, Lance J.; Henn, Johannes M.; Plefka, Jan; Schuster, Theodor; /Humboldt U., Berlin
2010-10-25
We derive compact analytical formulae for all tree-level color-ordered gauge theory amplitudes involving any number of external gluons and up to three massless quark-anti-quark pairs. A general formula is presented based on the combinatorics of paths along a rooted tree and associated determinants. Explicit expressions are displayed for the next-to-maximally helicity violating (NMHV) and next-to-next-to-maximally helicity violating (NNMHV) gauge theory amplitudes. Our results are obtained by projecting the previously-found expressions for the super-amplitudes of the maximally supersymmetric Yang-Mills theory (N = 4 SYM) onto the relevant components yielding all gluon-gluino tree amplitudes in N = 4 SYM. We show how these results carry over to the corresponding QCD amplitudes, including massless quarks of different flavors as well as a single electroweak vector boson. The public Mathematica package GGT is described, which encodes the results of this work and yields analytical formulae for all N = 4 SYM gluon-gluino trees. These in turn yield all QCD trees with up to four external arbitrary-flavored massless quark-anti-quark-pairs.
Simulation of absolute amplitudes of ultrasound signals using equivalent circuits.
Johansson, Jonny; Martinsson, Pär-Erik; Delsing, Jerker
2007-10-01
Equivalent circuits for piezoelectric devices and ultrasonic transmission media can be used to cosimulate electronics and ultrasound parts in simulators originally intended for electronics. To achieve efficient system-level optimization, it is important to simulate correct, absolute amplitude of the ultrasound signal in the system, as this determines the requirements on the electronics regarding dynamic range, circuit noise, and power consumption. This paper presents methods to achieve correct, absolute amplitude of an ultrasound signal in a simulation of a pulse-echo system using equivalent circuits. This is achieved by taking into consideration loss due to diffraction and the effect of the cable that connects the electronics and the piezoelectric transducer. The conductive loss in the transmission line that models the propagation media of the ultrasound pulse is used to model the loss due to diffraction. Results show that the simulated amplitude of the echo follows measured values well in both near and far fields, with an offset of about 10%. The use of a coaxial cable introduces inductance and capacitance that affect the amplitude of a received echo. Amplitude variations of 60% were observed when the cable length was varied between 0.07 m and 2.3 m, with simulations predicting similar variations. The high precision in the achieved results show that electronic design and system optimization can rely on system simulations alone. This will simplify the development of integrated electronics aimed at ultrasound systems.
Three beams phase-shifting interferometry by their amplitude variation
NASA Astrophysics Data System (ADS)
Meneses-Fabian, Cruz; Rivera-Ortega, Uriel
2011-10-01
A novel phase shifting interferometry method based on the variation of the electric field under the scheme of a three beams interferometer is proposed. One beam contains the object under study, that makes this beam the probe beam; the other two will be consider as the reference beams with a phase difference of p 2 . Due to this, one of the three resulting interference terms will be cancelled and the two remaining will be in quadrature. Applying some trigonometric identities, we show that the resulting interference pattern could become modeled by the interfering of two beams with an additional phase term; we obtain that the tangent function of the additional phase depends on the division of the amplitude of the third field divided by the amplitude of the first, and it is possible to group the sum of the squares of these fields in a square amplitude. To recover the phase by using the phase shifting interferometry techniques it is necessary to keep constant the visibility of the interference pattern, at first sight we can think that this is not possible because the variations of the field amplitude affect the visibility of the patterns. However this problem is solved if the values of the amplitude corresponding to the fields one and three are seen as an ordered pair contained over an arc segment at the first quadrant. We justify the viability of this method by a theoretical analysis and a numerical simulation of the interference of three beams under the conditions mentioned above.
Amplitude death of coupled hair bundles with stochastic channel noise
NASA Astrophysics Data System (ADS)
Kim, Kyung-Joong; Ahn, Kang-Hun
2014-04-01
Hair cells conduct auditory transduction in vertebrates. In lower vertebrates such as frogs and turtles, due to the active mechanism in hair cells, hair bundles (stereocilia) can be spontaneously oscillating or quiescent. Recently an amplitude death phenomenon has been proposed [K.-H. Ahn, J. R. Soc. Interface, 10, 20130525 (2013)] as a mechanism for auditory transduction in frog hair-cell bundles, where sudden cessation of the oscillations arises due to the coupling between nonidentical hair bundles. The gating of the ion channel is intrinsically stochastic due to the stochastic nature of the configuration change of the channel. The strength of the noise due to the channel gating can be comparable to the thermal Brownian noise of hair bundles. Thus, we perform stochastic simulations of the elastically coupled hair bundles. In spite of stray noisy fluctuations due to its stochastic dynamics, our simulation shows the transition from collective oscillation to amplitude death as interbundle coupling strength increases. In its stochastic dynamics, the formation of the amplitude death state of coupled hair bundles can be seen as a sudden suppression of the displacement fluctuation of the hair bundles as the coupling strength increases. The enhancement of the signal-to-noise ratio through the amplitude death phenomenon is clearly seen in the stochastic dynamics. Our numerical results demonstrate that the multiple number of transduction channels per hair bundle is an important factor to the amplitude death phenomenon, because the phenomenon may disappear for a small number of transduction channels due to strong gating noise.
Ultraviolet divergences and factorization for coordinate-space amplitudes
NASA Astrophysics Data System (ADS)
Erdoǧan, Ozan; Sterman, George
2015-03-01
We consider the coordinate-space matrix elements that correspond to fixed-angle scattering amplitudes involving partons and Wilson lines in coordinate space, working in Feynman gauge. In coordinate space, both collinear and short-distance limits produce ultraviolet divergences. We classify singularities in coordinate space, and identify neighborhoods associated unambiguously with individual subspaces (pinch surfaces) where the integrals are singular. The set of such regions is finite for any diagram. Within each of these regions, coordinate-space soft-collinear and hard-collinear approximations reproduce singular behavior. Based on this classification of regions and approximations, we develop a series of nested subtraction approximations by analogy to the formalism in momentum space. This enables us to rewrite each amplitude as a sum of terms to which gauge-theory Ward identities can be applied, factorizing them into hard, jet and soft factors, and to confirm the multiplicative renormalizability of products of lightlike Wilson lines. We study in some detail the simplest case, the color-singlet cusp linking two Wilson lines, and show that the logarithm of this amplitude, which is a sum of diagrams known as webs, is closely related to the corresponding subtracted amplitude order by order in perturbation theory. This enables us to confirm that the logarithm of the cusp can be written as the integral of an ultraviolet-finite function over a surface. We study to what extent this result generalizes to amplitudes involving multiple Wilson lines.
Joint amplitude and frequency analysis of tremor activity.
Foerster, F; Smeja, M
1999-01-01
Clinical tremor analysis mostly is used for the measurement of tremor frequency. The analysis is based on short segments of EMG recordings and on clinical ratings of tremor intensity. Accelerometry appears to have some practical advantages. The present study was concerned with the development of a methodology for assessing tremor activity using the three parameters, frequency (Hz), amplitude (g), and occurrence of tremor (in per cent of time). These parameters were derived from joint amplitude frequency analysis of the calibrated accelerometer raw signal and from appropriate decision rules. This methodology was used in connection with 27 patients with Parkinson's disease, to investigate the aforesaid parameters of tremor activity. Postural tremor had a higher occurrence time (right-hand only) and higher frequency (left-hand only) than resting tremor, however, the average amplitudes did not differ. The correlations between right-hand and left-hand measures were higher during postural tremor test. Frequency was not correlated to amplitude or occurrence time, however, moderate correlations did exist between amplitude and occurrence time. In addition to the assessment of tremor activity, multi-channel accelerometry may be used for the detection of posture and motion. Further applications of this methodology, for example, in 24 hr ambulatory monitoring of tremor, are discussed.
Coupling of Large Amplitude Inversion with Other States
NASA Astrophysics Data System (ADS)
Pearson, John; Yu, Shanshan
2016-06-01
The coupling of a large amplitude motion with a small amplitude vibration remains one of the least well characterized problems in molecular physics. Molecular inversion poses a few unique and not intuitively obvious challenges to the large amplitude motion problem. In spite of several decades of theoretical work numerous challenges in calculation of transition frequencies and more importantly intensities persist. The most challenging aspect of this problem is that the inversion coordinate is a unique function of the overall vibrational state including both the large and small amplitude modes. As a result, the r-axis system and the meaning of the K-quantum number in the rotational basis set are unique to each vibrational state of large or small amplitude motion. This unfortunate reality has profound consequences to calculation of intensities and the coupling of nearly degenerate vibrational states. The case of NH3 inversion and inversion through a plane of symmetry in alcohols will be examined to find a general path forward.
Lorentz constraints on massive three-point amplitudes
NASA Astrophysics Data System (ADS)
Conde, Eduardo; Marzolla, Andrea
2016-09-01
Using the helicity-spinor language we explore the non-perturbative constraints that Lorentz symmetry imposes on three-point amplitudes where the asymptotic states can be massive. As it is well known, in the case of only massless states the three-point amplitude is fixed up to a coupling constant by these constraints plus some physical requirements. We find that a similar statement can be made when some of the particles have mass. We derive the generic functional form of the three-point amplitude by virtue of Lorentz symmetry, which displays several functional structures accompanied by arbitrary constants. These constants can be related to the coupling constants of the theory, but in an unambiguous fashion only in the case of one massive particle. Constraints on these constants are obtained by imposing that in the UV limit the massive amplitude matches the massless one. In particular, there is a certain Lorentz frame, which corresponds to projecting all the massive momenta along the same null momentum, where the three-point massive amplitude is fully fixed, and has a universal form.
Propagation and amplitude decay mechanisms of internal solitary waves
NASA Astrophysics Data System (ADS)
Wang, Ling-ling; Wang, Chun-ling; Tang, Hong-wu; Chen, Hong
2016-12-01
In this paper, a modified dynamic coherent eddy model (DCEM) of large eddy simulation is applied to study internal solitary waves in a numerical flume. The model was verified by physical experiment and applied to investigate the potential influence factors on internal wave amplitude. In addition, we discussed the energy loss of internal solitary wave as well as hydrodynamics in the propagation. The results of our study show that (1) Step-depth is the most sensitive factor on wave amplitude for the "step-pool" internal wave generation method and the wave amplitudes obey a linear increase with step depth, and the increase rate is about 0.4. (2) Wave energy loss obeys a linear decrease with the propagation distance and its loss rate of large amplitude waves is smaller than that of small amplitude waves. (3) Loss of kinetic energy in wave valley is larger than that near the interface due to relative high fluctuating frequency. (4) Discovered boundary jet-flow can intensify the bottom shear, which might be one of the mechanisms of substance transportation, and the boundary layers of jet flows are easily influenced by the adjacent waves.
Optimization of phase contrast in bimodal amplitude modulation AFM
Damircheli, Mehrnoosh; Payam, Amir F
2015-01-01
Summary Bimodal force microscopy has expanded the capabilities of atomic force microscopy (AFM) by providing high spatial resolution images, compositional contrast and quantitative mapping of material properties without compromising the data acquisition speed. In the first bimodal AFM configuration, an amplitude feedback loop keeps constant the amplitude of the first mode while the observables of the second mode have not feedback restrictions (bimodal AM). Here we study the conditions to enhance the compositional contrast in bimodal AM while imaging heterogeneous materials. The contrast has a maximum by decreasing the amplitude of the second mode. We demonstrate that the roles of the excited modes are asymmetric. The operational range of bimodal AM is maximized when the second mode is free to follow changes in the force. We also study the contrast in trimodal AFM by analyzing the kinetic energy ratios. The phase contrast improves by decreasing the energy of second mode relative to those of the first and third modes. PMID:26114079
Calculating phases between B{yields}K*{pi} amplitudes
Gronau, Michael; Pirjol, Dan; Rosner, Jonathan L.
2010-05-01
A phase {Delta}{Phi} between amplitudes for B{sup 0{yields}}K*{sup 0{pi}0} and B{sup 0{yields}}K*{sup +{pi}-} plays a crucial role in a method for constraining Cabibbo-Kobayashi-Maskawa parameters. We present a general argument for destructive interference between amplitudes for B{sup 0{yields}}K*{sup +{pi}-} and B{sup 0{yields}}K*{sup 0{pi}0} forming together a smaller I(K*{pi})=3/2 amplitude. Applying flavor SU(3) and allowing for conservative theoretical uncertainties, we obtain lower limits on |{Delta}{Phi}| and its charge conjugate. Values of these two phases favored by the BABAR collaboration are in good agreement with our bounds.
Phase and amplitude stabilization of beam-loaded superconducting resonators
Delayen, J.R.
1992-01-01
A model has been developed to analyze the static and dynamic behavior of superconducting accelerating cavities operated in self-excited loops in the presence of phase and amplitude feedback, ponderomotive effects, and beam loading. This is an extension of an earlier analysis of the stabilization of superconducting cavities which has been the basis of the control system of several superconducting accelerators but did not include beam loading. Conditions have been derived to ensure static and dynamic stability in the presence of ponderomotive effects (coupling between the mechanical and electromagnetic modes of the cavity through the radiation pressure). Expressions for the effect of fluctuations of cavity frequency and beam amplitude and phase on the cavity-field amplitude and phase and beam-energy gain have been obtained.
Phase and amplitude stabilization of beam-loaded superconducting resonators
Delayen, J.R.
1992-10-01
A model has been developed to analyze the static and dynamic behavior of superconducting accelerating cavities operated in self-excited loops in the presence of phase and amplitude feedback, ponderomotive effects, and beam loading. This is an extension of an earlier analysis of the stabilization of superconducting cavities which has been the basis of the control system of several superconducting accelerators but did not include beam loading. Conditions have been derived to ensure static and dynamic stability in the presence of ponderomotive effects (coupling between the mechanical and electromagnetic modes of the cavity through the radiation pressure). Expressions for the effect of fluctuations of cavity frequency and beam amplitude and phase on the cavity-field amplitude and phase and beam-energy gain have been obtained.
Mammalian cycles: internally defined periods and interaction-driven amplitudes
Krebs, CJ
2015-01-01
The cause of mammalian cycles—the rise and fall of populations over a predictable period of time—has remained controversial since these patterns were first observed over a century ago. In spite of extensive work on observable mammalian cycles, the field has remained divided upon what the true cause is, with a majority of opinions attributing it to either predation or to intra-species mechanisms. Here we unite the eigenperiod hypothesis, which describes an internal, maternal effect-based mechanism to explain the cycles’ periods with a recent generalization explaining the amplitude of snowshoe hare cycles in northwestern North America based on initial predator abundance. By explaining the period and the amplitude of the cycle with separate mechanisms, a unified and consistent view of the causation of cycles is reached. Based on our suggested theory, we forecast the next snowshoe hare cycle (predicted peak in 2016) to be of extraordinarily low amplitude. PMID:26339557
Amplitude Noise Reduction of Ion Lasers with Optical Feedback
NASA Technical Reports Server (NTRS)
Herring, Gregory C.
2011-01-01
A reduction in amplitude noise on the output of a multi-mode continuous-wave Ar-ion laser was previously demonstrated when a fraction of the output power was retroreflected back into the laser cavity. This result was reproduced in the present work and a Fabry-Perot etalon was used to monitor the longitudinal mode structure of the laser. A decrease in the number of operating longitudinal cavity modes was observed simultaneously with the introduction of the optical feedback and the onset of the amplitude noise reduction. The noise reduction is a result of a reduced number of lasing modes, resulting in less mode beating and amplitude fluctuations of the laser output power.
Frequency, phase, and amplitude changes of the hydrogen maser oscillation
NASA Technical Reports Server (NTRS)
Audoin, Claude; Diener, William A.
1992-01-01
The frequency, the phase, and the amplitude changes of the hydrogen maser oscillation, which are induced by the modulation of the cavity resonant frequency, are considered. The results obtained apply specifically to one of the H-maser cavity autotuning methods which is actually implemented, namely the cavity frequency-switching method. The frequency, the phase, and the amplitude changes are analyzed theoretically. The phase and the amplitude variations are measured experimentally. It is shown, in particular, that the phase of oscillation is subjected to abrupt jumps at the times of the cavity frequency switching, whose magnitude is specified. The results given can be used for the design of a phase-locked loop (PLL) aimed at minimizing the transfer of the phase modulation to the slaved VCXO.
Chronotaxic systems with separable amplitude and phase dynamics
NASA Astrophysics Data System (ADS)
Suprunenko, Yevhen F.; Clemson, Philip T.; Stefanovska, Aneta
2014-01-01
Until recently, deterministic nonautonomous oscillatory systems with stable amplitudes and time-varying frequencies were not recognized as such and have often been mistreated as stochastic. These systems, named chronotaxic, were introduced in Phys. Rev. Lett. 111, 024101 (2013), 10.1103/PhysRevLett.111.024101. In contrast to conventional limit cycle models of self-sustained oscillators, these systems posses a time-dependent point attractor or steady state. This allows oscillations with time-varying frequencies to resist perturbations, a phenomenon which is ubiquitous in living systems. In this work a detailed theory of chronotaxic systems is presented, specifically in the case of separable amplitude and phase dynamics. The theory is extended by the introduction of chronotaxic amplitude dynamics. The wide applicability of chronotaxic systems to a range of fields from biological and condensed matter systems to robotics and control theory is discussed.
Control of amplitude chimeras by time delay in oscillator networks
NASA Astrophysics Data System (ADS)
Gjurchinovski, Aleksandar; Schöll, Eckehard; Zakharova, Anna
2017-04-01
We investigate the influence of time-delayed coupling in a ring network of nonlocally coupled Stuart-Landau oscillators upon chimera states, i.e., space-time patterns with coexisting partially coherent and partially incoherent domains. We focus on amplitude chimeras, which exhibit incoherent behavior with respect to the amplitude rather than the phase and are transient patterns, and we show that their lifetime can be significantly enhanced by coupling delay. To characterize their transition to phase-lag synchronization (coherent traveling waves) and other coherent structures, we generalize the Kuramoto order parameter. Contrasting the results for instantaneous coupling with those for constant coupling delay, for time-varying delay, and for distributed-delay coupling, we demonstrate that the lifetime of amplitude chimera states and related partially incoherent states can be controlled, i.e., deliberately reduced or increased, depending upon the type of coupling delay.
Amplitudes of solar-like oscillations: a new scaling relation
NASA Astrophysics Data System (ADS)
Kjeldsen, H.; Bedding, T. R.
2011-05-01
Solar-like oscillations are excited by near-surface convection and are being observed in growing numbers of stars using ground- and space-based telescopes. We have previously suggested an empirical scaling relation to predict their amplitudes. This relation has found widespread use but it predicts amplitudes in F-type stars that are higher than observed. Here we present a new scaling relation that is based on the postulate that the power in velocity fluctuations due to p-mode oscillations scales with stellar parameters in the same way as the power in velocity fluctuations due to granulation. The new relation includes a dependence on the damping rate via the mode lifetime and should be testable using observations from the CoRoT and Kepler missions. We also suggest scaling relations for the properties of the background power due to granulation and argue that both these and the amplitude relations should be applicable to red giant stars.
Finite amplitude effects on drop levitation for material properties measurement
NASA Astrophysics Data System (ADS)
Ansari Hosseinzadeh, Vahideh; Holt, R. Glynn
2017-05-01
The method of exciting shape oscillation of drops to extract material properties has a long history, which is most often coupled with the technique of acoustic levitation to achieve non-contact manipulation of the drop sample. We revisit this method with application to the inference of bulk shear viscosity and surface tension. The literature is replete with references to a "10% oscillation amplitude" as a sufficient condition for the application of Lamb's analytical expressions for the shape oscillations of viscous liquids. Our results show that even a 10% oscillation amplitude leads to dynamic effects which render Lamb's results inapplicable. By comparison with samples of known viscosity and surface tension, we illustrate the complicating finite-amplitude effects (mode-splitting and excess dissipation associated with vorticity) that can occur and then show that sufficiently small oscillations allow us to recover the correct material properties using Lamb's formula.
Frequency, phase, and amplitude changes of the hydrogen maser oscillation
NASA Technical Reports Server (NTRS)
Audoin, Claude; Diener, William A.
1992-01-01
The frequency, the phase, and the amplitude changes of the hydrogen maser oscillation, which are induced by the modulation of the cavity resonant frequency, are considered. The results obtained apply specifically to one of the H-maser cavity autotuning methods which is actually implemented, namely the cavity frequency-switching method. The frequency, the phase, and the amplitude changes are analyzed theoretically. The phase and the amplitude variations are measured experimentally. It is shown, in particular, that the phase of oscillation is subjected to abrupt jumps at the times of the cavity frequency switching, whose magnitude is specified. The results given can be used for the design of a phase-locked loop (PLL) aimed at minimizing the transfer of the phase modulation to the slaved VCXO.
Top Quark Amplitudes with an Anomolous Magnetic Moment
Larkoski, Andrew J.; Peskin, Michael E.; /SLAC
2011-06-23
The anomalous magnetic moment of the top quark may be measured during the first run of the LHC at 7 TeV. For these measurements, it will be useful to have available tree amplitudes with t{bar t} and arbitrarily many photons and gluons, including both QED and color anomalous magnetic moments. In this paper, we present a method for computing these amplitudes using the Britto-Cachazo-Feng-Witten recursion formula. Because we deal with an effective theory with higher-dimension couplings, there are roadblocks to a direct computation with the Britto-Cachazo-Feng-Witten method. We evade these by using an auxiliary scalar theory to compute a subset of the amplitudes.
Amplitude variations on the Extreme Adaptive Optics testbed
Evans, J; Thomas, S; Dillon, D; Gavel, D; Phillion, D; Macintosh, B
2007-08-14
High-contrast adaptive optics systems, such as those needed to image extrasolar planets, are known to require excellent wavefront control and diffraction suppression. At the Laboratory for Adaptive Optics on the Extreme Adaptive Optics testbed, we have already demonstrated wavefront control of better than 1 nm rms within controllable spatial frequencies. Corresponding contrast measurements, however, are limited by amplitude variations, including those introduced by the micro-electrical-mechanical-systems (MEMS) deformable mirror. Results from experimental measurements and wave optic simulations of amplitude variations on the ExAO testbed are presented. We find systematic intensity variations of about 2% rms, and intensity variations with the MEMS to be 6%. Some errors are introduced by phase and amplitude mixing because the MEMS is not conjugate to the pupil, but independent measurements of MEMS reflectivity suggest that some error is introduced by small non-uniformities in the reflectivity.
Einstein-Yang-Mills from pure Yang-Mills amplitudes
NASA Astrophysics Data System (ADS)
Nandan, Dhritiman; Plefka, Jan; Schlotterer, Oliver; Wen, Congkao
2016-10-01
We present new relations for scattering amplitudes of color ordered gluons and gravitons in Einstein-Yang-Mills theory. Tree-level amplitudes of arbitrary multiplicities and polarizations involving up to three gravitons and up to two color traces are reduced to partial amplitudes of pure Yang-Mills theory. In fact, the double-trace identities apply to Einstein-Yang-Mills extended by a dilaton and a B-field. Our results generalize recent work of Stieberger and Taylor for the single graviton case with a single color trace. As the derivation is made in the dimension-agnostic Cachazo-He-Yuan formalism, our results are valid for external bosons in any number of spacetime dimensions. Moreover, they generalize to the superamplitudes in theories with 16 supercharges.
Amplitude and polarization asymmetries in a ring laser
NASA Technical Reports Server (NTRS)
Campbell, L. L.; Buholz, N. E.
1971-01-01
Asymmetric amplitude effects between the oppositely directed traveling waves in a He-Ne ring laser are analyzed both theoretically and experimentally. These effects make it possible to detect angular orientations of an inner-cavity bar with respect to the plane of the ring cavity. The amplitude asymmetries occur when a birefringent bar is placed in the three-mirror ring cavity, and an axial magnetic field is applied to the active medium. A simplified theoretical analysis is performed by using a first order perturbation theory to derive an expression for the polarization of the active medium, and a set of self-consistent equations are derived to predict threshold conditions. Polarization asymmetries between the oppositely directed waves are also predicted. Amplitude asymmetries similar in nature to those predicted at threshold occur when the laser is operating in 12-15 free-running modes, and polarization asymmetry occurs simultaneously.
Amplitude and phase-shaping effects in beamwaveguides
NASA Technical Reports Server (NTRS)
Rengarajan, Sembiam R.; Galindo-Israel, Victor; Imbriale, William A.
1991-01-01
Results are presented of an investigation on improvements in a geometrical optics (GO) design of a beam-waveguide antenna for operation at multiple frequency bands. Improvements might be possible by changing the design of the lower-frequency input pattern to the beam waveguide. The effects of amplitude and phase shaping the input pattern have been studied with an aperture diffraction model. Accurate vector near-field computations were made rapidly with a spherical wave expansion of the input and scattered fields. Numerical results indicate that for aperture sizes of less than 30 wavelengths, there is insufficient control on defocusing due to amplitude and phase shaping. Design tradeoffs on spillover loss and defocusing are possible by changing the amplitude and phase distribution of the input wavefront for larger size apertures.
Berends-Giele recursion for double-color-ordered amplitudes
NASA Astrophysics Data System (ADS)
Mafra, Carlos R.
2016-07-01
Tree-level double-color-ordered amplitudes are computed using Berends-Giele recursion relations applied to the bi-adjoint cubic scalar theory. The standard notion of Berends-Giele currents is generalized to double-currents and their recursions are derived from a perturbiner expansion of linearized fields that solve the non-linear field equations. Two applications are given. Firstly, we prove that the entries of the inverse KLT matrix are equal to Berends-Giele double-currents (and are therefore easy to compute). And secondly, a simple formula to generate tree-level BCJ-satisfying numerators for arbitrary multiplicity is proposed by evaluating the field-theory limit of tree-level string amplitudes for various color orderings using double-color-ordered amplitudes.
Large amplitude stationary Rossby waves in the Southern Hemisphere
NASA Technical Reports Server (NTRS)
Kalnay, E.; Halem, M.
1981-01-01
Large Amplitude stationary waves downstream of South America, and in the lee of Australia were investigated using Tiros N photographs. These waves appear to be Rossby lee waves associated with anomalous poleward flow over the Andes and by continental heating over Australia. The waves have a maximum amplitude near 300 mb between 20 and 40 deg S and correlate well with observed precipitation bands in the Atlantic and Pacific Oceans. The orientation of these waves is such that they transfer zonal momentum to the roaring forties latitudes. Stationary Rossby waves, in the Northern Hemisphere, have a characteristic wavelength of the order of 120 deg longitude. In January the observed stationary wavelengths have a wavelength of less than 60 deg longitude with an amplitude in the upper tropospheric meridional wind of more than 15 m sec E-1.
Amplitude-dependent Lamb wave dispersion in nonlinear plates.
Packo, Pawel; Uhl, Tadeusz; Staszewski, Wieslaw J; Leamy, Michael J
2016-08-01
The paper presents a perturbation approach for calculating amplitude-dependent Lamb wave dispersion in nonlinear plates. Nonlinear dispersion relationships are derived in closed form using a hyperelastic stress-strain constitutive relationship, the Green-Lagrange strain measure, and the partial wave technique integrated with a Lindstedt-Poincaré perturbation approach. Solvability conditions are derived using an operator formalism with inner product projections applied against solutions to the adjoint problem. When applied to the first- and second-order problems, these solvability conditions lead to amplitude-dependent, nonlinear dispersion corrections for frequency as a function of wavenumber. Numerical simulations verify the predicted dispersion shifts for an example nonlinear plate. The analysis and identification of amplitude-dependent, nonlinear Lamb wave dispersion complements recent research focusing on higher harmonic generation and internally resonant waves, which require precise dispersion relationships for frequency-wavenumber matching.
Amplitude envelope onsets and developmental dyslexia: A new hypothesis.
Goswami, Usha; Thomson, Jennifer; Richardson, Ulla; Stainthorp, Rhona; Hughes, Diana; Rosen, Stuart; Scott, Sophie K
2002-08-06
A core difficulty in developmental dyslexia is the accurate specification and neural representation of speech. We argue that a likely perceptual cause of this difficulty is a deficit in the perceptual experience of rhythmic timing. Speech rhythm is one of the earliest cues used by infants to discriminate syllables and is determined principally by the acoustic structure of amplitude modulation at relatively low rates in the signal. We show significant differences between dyslexic and normally reading children, and between young early readers and normal developers, in amplitude envelope onset detection. We further show that individual differences in sensitivity to the shape of amplitude modulation account for 25% of the variance in reading and spelling acquisition even after controlling for individual differences in age, nonverbal IQ, and vocabulary. A possible causal explanation dependent on perceptual-center detection and the onset-rime representation of syllables is discussed.
Top quark amplitudes with an anomalous magnetic moment
NASA Astrophysics Data System (ADS)
Larkoski, Andrew J.; Peskin, Michael E.
2011-02-01
The anomalous magnetic moment of the top quark may be measured during the first run of the LHC at 7 TeV. For these measurements, it will be useful to have available tree amplitudes with tt¯ and arbitrarily many photons and gluons, including both QED and color anomalous magnetic moments. In this paper, we present a method for computing these amplitudes using the Britto-Cachazo-Feng-Witten recursion formula. Because we deal with an effective theory with higher-dimension couplings, there are roadblocks to a direct computation with the Britto-Cachazo-Feng-Witten method. We evade these by using an auxiliary scalar theory to compute a subset of the amplitudes.
Kernel phase and kernel amplitude in Fizeau imaging
NASA Astrophysics Data System (ADS)
Pope, Benjamin J. S.
2016-12-01
Kernel phase interferometry is an approach to high angular resolution imaging which enhances the performance of speckle imaging with adaptive optics. Kernel phases are self-calibrating observables that generalize the idea of closure phases from non-redundant arrays to telescopes with arbitrarily shaped pupils, by considering a matrix-based approximation to the diffraction problem. In this paper I discuss the recent history of kernel phase, in particular in the matrix-based study of sparse arrays, and propose an analogous generalization of the closure amplitude to kernel amplitudes. This new approach can self-calibrate throughput and scintillation errors in optical imaging, which extends the power of kernel phase-like methods to symmetric targets where amplitude and not phase calibration can be a significant limitation, and will enable further developments in high angular resolution astronomy.
Thermodynamic constraints on the amplitude of quantum oscillations
NASA Astrophysics Data System (ADS)
Shekhter, Arkady; Modic, K. A.; McDonald, R. D.; Ramshaw, B. J.
2017-03-01
Magneto-quantum oscillation experiments in high-temperature superconductors show a strong thermally induced suppression of the oscillation amplitude approaching the critical dopings [B. J. Ramshaw et al., Science 348, 317 (2014), 10.1126/science.aaa4990; H. Shishido et al., Phys. Rev. Lett. 104, 057008 (2010), 10.1103/PhysRevLett.104.057008; P. Walmsley et al., Phys. Rev. Lett. 110, 257002 (2013), 10.1103/PhysRevLett.110.257002]—in support of a quantum-critical origin of their phase diagrams. We suggest that, in addition to a thermodynamic mass enhancement, these experiments may directly indicate the increasing role of quantum fluctuations that suppress the quantum oscillation amplitude through inelastic scattering. We show that the traditional theoretical approaches beyond Lifshitz-Kosevich to calculate the oscillation amplitude in correlated metals result in a contradiction with the third law of thermodynamics and suggest a way to rectify this problem.
Discriminating Valid from Spurious Indices of Phase-Amplitude Coupling
Spaak, Eelke
2016-01-01
Abstract Recently there has been a strong interest in cross-frequency coupling, the interaction between neuronal oscillations in different frequency bands. In particular, measures quantifying the coupling between the phase of slow oscillations and the amplitude of fast oscillations have been applied to a wide range of data recorded from animals and humans. Some of the measures applied to detect phase-amplitude coupling have been criticized for being sensitive to nonsinusoidal properties of the oscillations and thus spuriously indicate the presence of coupling. While such instances of spurious identification of coupling have been observed, in this commentary we give concrete examples illustrating cases when the identification of cross-frequency coupling can be trusted. These examples are based on control analyses and empirical observations rather than signal-processing tools. Finally, we provide concrete advice on how to determine when measures of phase-amplitude coupling can be considered trustworthy. PMID:28101528
Operator form of the three-nucleon scattering amplitude
NASA Astrophysics Data System (ADS)
Topolnicki, Kacper; Golak, Jacek; Skibiński, Roman; Witała, Henryk
2017-07-01
To extend the applications of the so-called "three-dimensional" formalism to the description of three-nucleon scattering within the Faddeev formalism, we develop a general form of the three-nucleon scattering amplitude. This form significantly decreases the numerical complexity of the "three-dimensional" calculations by reducing the scattering amplitude to a linear combination of momentum-dependent spin operators and scalar functions of momenta. The number and structure of the spin operators is fixed and the scalar functions can be represented numerically using standard methods such as multidimensional arrays. In this paper, we show that all orders of the iterated Faddeev equation can be written in this general form. We argue that calculations utilizing the three-nucleon force will also conform to the same general form. Additionally, we show how the general form of the scattering amplitude can be used to transform the Faddeev equation to make it suitable for numerical calculations using iterative methods.
Superstring disk amplitudes in a rolling tachyon background
Jokela, Niko; Majumder, Jaydeep; Keski-Vakkuri, Esko
2006-02-15
We study the tree level scattering or emission of n closed superstrings from a decaying non-BPS brane in Type II superstring theory. We attempt to calculate generic n-point superstring disk amplitudes in the rolling tachyon background. We show that these can be written as infinite power series of Toeplitz determinants, related to expectation values of a periodic function in Circular Unitary Ensembles. Further analytical progress is possible in the special case of bulk-boundary disk amplitudes. These are interpreted as probability amplitudes for emission of a closed string with initial conditions perturbed by the addition of an open string vertex operator. This calculation has been performed previously in bosonic string theory, here we extend the analysis for superstrings. We obtain a result for the average energy of closed superstrings produced in the perturbed background.
Loop Integrands for Scattering Amplitudes from the Riemann Sphere
NASA Astrophysics Data System (ADS)
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.
Large-amplitude Longitudinal Oscillations in a Solar Filament
NASA Astrophysics Data System (ADS)
Zhang, Q. M.; Li, T.; Zheng, R. S.; Su, Y. N.; Ji, H. S.
2017-06-01
In this paper, we report our multiwavelength observations of the large-amplitude longitudinal oscillations of a filament observed on 2015 May 3. Located next to active region 12335, the sigmoidal filament was observed by the ground-based Hα telescopes from the Global Oscillation Network Group and by the Atmospheric Imaging Assembly instrument on board the Solar Dynamics Observatory. The filament oscillations were most probably triggered by the magnetic reconnection in the filament channel, which is characterized by the bidirectional flows, brightenings in EUV and soft X-ray, and magnetic cancellation in the photosphere. The directions of oscillations have angles of 4°-36° with respect to the filament axis. The whole filament did not oscillate in phase as a rigid body. Meanwhile, the oscillation periods (3100-4400 s) have a spatial dependence, implying that the curvature radii (R) of the magnetic dips are different at different positions. The values of R are estimated to be 69.4-133.9 Mm, and the minimum transverse magnetic field of the dips is estimated to be 15 G. The amplitudes of S5-S8 grew with time, while the amplitudes of S9-S14 damped with time. The oscillation amplitudes range from a few to ten Mm, and the maximum velocity can reach 30 km s-1. Interestingly, the filament experienced mass drainage southward at a speed of ˜27 km s-1. The oscillations continued after the mass drainage and lasted for more than 11 hr. After the mass drainage, the oscillation phases did not change much. The periods of S5-S8 decreased, while the periods of S9-S14 increased. The amplitudes of S5-S8 damped with time, while the amplitudes of S9-S14 grew. Most of the damping (growing) ratios are between -9 and 14. We offer a schematic cartoon to explain the complex behaviors of oscillations by introducing thread-thread interaction.
Quasi-steady, marginally unstable electron cyclotron harmonic wave amplitudes
NASA Astrophysics Data System (ADS)
Zhang, Xiaojia; Angelopoulos, Vassilis; Ni, Binbin; Thorne, Richard M.; Horne, Richard B.
2013-06-01
Electron cyclotron harmonic (ECH) waves have long been considered a potential driver of diffuse aurora in Earth's magnetotail. However, the scarcity of intense ECH emissions in the outer magnetotail suggests that our understanding of the amplification and the relative importance of these waves for electron scattering is lacking. We conduct a comprehensive study of wave growth and quasi-linear diffusion to estimate the amplitude of loss-cone-driven ECH waves once diffusion and growth balance but before convection or losses alter the background hot plasma sheet population. We expect this to be the most common state of the plasma sheet between episodes of fast convection. For any given wave amplitude, we model electron diffusion caused by interaction with ECH waves using a 2-D bounce-averaged Fokker-Planck equation. After fitting the resultant electron distributions as a superposition of multicomponent subtracted bi-Maxwellians, we estimate the maximum path-integrated gain using the HOTRAY ray-tracing code. We argue that the wave amplitude during quasi-steady state is the inflection point on a gain-amplitude curve. During quasi-steady state, ECH wave amplitudes can be significant (~1 mV/m) at L ~ 8 but drop to very low values (<~0.1 mV/m) in the outer magnetotail (L ~ 16) and likely fall below the sensitivity of typical instrumentation relatively close to Earth mainly because of the smallness of the loss cone. Our result reinforces the potentially important role of ECH waves in driving diffuse aurora and suggests that careful comparison of theoretical wave amplitude estimates and observations is required for resolving the equatorial scattering mechanism of diffuse auroral precipitation.
Unambiguous ionization amplitudes for electron-hydrogen scattering
Bartlett, P. L.; Bray, I.; Jones, S.; Stelbovics, A. T.; Kadyrov, A. S.; Bartschat, K.; Ver Steeg, G. L.; Scott, M. P.; Burke, P. G.
2003-08-01
According to quantum collision theory, scattering amplitudes are complex numbers, which are completely defined by their magnitude and phase. Although the phase information is generally not determined entirely in collision experiments, the phases are well defined and can be used to check computational models. We use four state-of-the-art approaches to calculate the magnitude and phase of the electron-hydrogen ionization amplitude in the Temkin-Poet S-wave model. We demonstrate that the correct phase can be extracted for each method by using the appropriate final-state continuum functions.
Enhanced Electroweak Penguin Amplitude in B{yields}VV Decays
Beneke, M.; Rohrer, J.; Yang, D.
2006-04-14
We discuss a novel electromagnetic penguin contribution to the transverse helicity amplitudes in B decays to two vector mesons, which is enhanced by two powers of m{sub B}/{lambda} relative to the standard penguin amplitudes. This leads to unique polarization signatures in penguin-dominated decay modes such as B{yields}{rho}K* similar to polarization effects in the radiative decay B{yields}K*{gamma} and offers new opportunities to probe the magnitude and chirality of flavor-changing neutral current couplings to photons.
Scattering amplitudes for the rationally extended PT symmetric complex potentials
NASA Astrophysics Data System (ADS)
Kumari, Nisha; Yadav, Rajesh Kumar; Khare, Avinash; Bagchi, Bijan; Mandal, Bhabani Prasad
2016-10-01
In this paper, we consider the rational extensions of two different classes of PT symmetric complex potentials namely the asymptotically vanishing Scarf II and asymptotically non-vanishing Rosen-Morse II [ RM-II] and obtain the accompanying bound state eigenfunctions in terms of the exceptional Xm Jacobi polynomials and a certain class of orthogonal polynomials. By considering the asymptotic behavior of the exceptional polynomials, we also derive the reflection and transmission amplitudes for them and discuss the various novel properties of the corresponding amplitudes.
Amplitude of primeval fluctuations from cosmological mass density reconstructions
NASA Technical Reports Server (NTRS)
Seljak, Uros; Bertschinger, Edmund
1994-01-01
We use the POTENT reconstruction of the mass density field in the nearby universe to estimate the amplitude of the density fluctuation power spectrum for various cosmological models. We find that sigma(sub 8) Omega(sub m sup 0.6) = 1.3(sub -0.3 sup +0.4), almost independently of the power spectrum. This value agrees well with the Cosmic Background Explorer (COBE) normalization for the standard cold dark matter model, while alternative models predict an excessive amplitude compared with COBE. Flat, low Omega(sub m) models and tilted models with spectral index n less than 0.8 are particularly discordant.
Modulated Source Interferometry with Combined Amplitude and Frequency Modulation
NASA Technical Reports Server (NTRS)
Gutierrez, Roman C. (Inventor)
1998-01-01
An improved interferometer is produced by modifying a conventional interferometer to include amplitude and/or frequency modulation of a coherent light source at radio or higher frequencies. The phase of the modulation signal can be detected in an interfering beam from an interferometer and can be used to determine the actual optical phase of the beam. As such, this improvement can be adapted to virtually any two-beam interferometer, including: Michelson, Mach-Zehnder, and Sagnac interferometers. The use of an amplitude modulated coherent tight source results in an interferometer that combines the wide range advantages of coherent interferometry with the precise distance measurement advantages of white light interferometry.
Baryon-to-Meson Transition Distribution Amplitudes: Formalism and Models
NASA Astrophysics Data System (ADS)
Pire, B.; Semenov-Tian-Shansky, K.; Szymanowski, L.
2017-03-01
In specific kinematics, hard exclusive amplitudes may be factorized into a short distance dominated part computable in a perturbative way on the one hand, and universal, confinement related hadronic matrix elements on the other hand. The extension of this description to processes such as backward meson electroproduction and forward meson production in antiproton-nucleon scattering leads to define new hadronic matrix elements of three quark operators on the light cone, the nucleon-to-meson transition distribution amplitudes, which shed a new light on the nucleon structure.
Calculation of the Scattering Amplitude Without Partial Wave Expansion
NASA Technical Reports Server (NTRS)
Shertzer, J.; Temkin, Aaron; Fisher, Richard R. (Technical Monitor)
2001-01-01
Two developments in the direct calculation of the angular differential scattering amplitude have been implemented: (a) The integral expansion of the scattering amplitude is simplified by analytically integration over the azimuthal angle. (b) The resulting integral as a function of scattering angle is calculated by using the numerically generated wave function from a finite element method calculation. Results for electron-hydrogen scattering in the static approximation will be shown to be as accurate as a partial wave expansion with as many l's as is necessary for convergence at the incident energy being calculated.
Amplitude-Modulated Bursting: A Novel Class of Bursting Rhythms
NASA Astrophysics Data System (ADS)
Vo, Theodore; Kramer, Mark A.; Kaper, Tasso J.
2016-12-01
We report on the discovery of a novel class of bursting rhythms, called amplitude-modulated bursting (AMB), in a model for intracellular calcium dynamics. We find that these rhythms are robust and exist on open parameter sets. We develop a new mathematical framework with broad applicability to detect, classify, and rigorously analyze AMB. Here we illustrate this framework in the context of AMB in a model of intracellular calcium dynamics. In the process, we discover a novel family of singularities, called toral folded singularities, which are the organizing centers for the amplitude modulation and exist generically in slow-fast systems with two or more slow variables.
Very low luminosity stars with very large amplitude flares
Schaefer, B.E. )
1990-04-01
CCD frames of CZ Cnc, KY Cep, the gamma-ray burster optical transient, and NSV 12006 are analyzed. Also studied are 549 archival photographic plates of the CZ Cnc field. These observations are compared with the data of Lovas (1976). Flare events on CZ Cnc are examined. Based on the data it is noted that CZ Cnc is a main-sequence star, has a magnitude of 16.1, a distance of 100 pc, occasional large-amplitude flares, and frequent flares with amplitudes greater than 4 mag. 36 refs.
Universal patterns in sound amplitudes of songs and music genres.
Mendes, R S; Ribeiro, H V; Freire, F C M; Tateishi, A A; Lenzi, E K
2011-01-01
We report a statistical analysis of more than eight thousand songs. Specifically, we investigated the probability distribution of the normalized sound amplitudes. Our findings suggest a universal form of distribution that agrees well with a one-parameter stretched Gaussian. We also argue that this parameter can give information on music complexity, and consequently it helps classify songs as well as music genres. Additionally, we present statistical evidence that correlation aspects of the songs are directly related to the non-Gaussian nature of their sound amplitude distributions.
Universal patterns in sound amplitudes of songs and music genres
NASA Astrophysics Data System (ADS)
Mendes, R. S.; Ribeiro, H. V.; Freire, F. C. M.; Tateishi, A. A.; Lenzi, E. K.
2011-01-01
We report a statistical analysis of more than eight thousand songs. Specifically, we investigated the probability distribution of the normalized sound amplitudes. Our findings suggest a universal form of distribution that agrees well with a one-parameter stretched Gaussian. We also argue that this parameter can give information on music complexity, and consequently it helps classify songs as well as music genres. Additionally, we present statistical evidence that correlation aspects of the songs are directly related to the non-Gaussian nature of their sound amplitude distributions.
Closed-form decomposition of one-loop massive amplitudes
Britto, Ruth; Feng Bo; Mastrolia, Pierpaolo
2008-07-15
We present formulas for the coefficients of 2-, 3-, 4-, and 5-point master integrals for one-loop massive amplitudes. The coefficients are derived from unitarity cuts in D dimensions. The input parameters can be read off from any unitarity-cut integrand, as assembled from tree-level expressions, after simple algebraic manipulations. The formulas presented here are suitable for analytical as well as numerical evaluation. Their validity is confirmed in two known cases of helicity amplitudes contributing to gg{yields}gg and gg{yields}gH, where the masses of the Higgs and the fermion circulating in the loop are kept as free parameters.
Explaining the discrepancy between forced fold amplitude and sill thickness.
NASA Astrophysics Data System (ADS)
Hoggett, Murray; Jones, Stephen M.; Reston, Timothy; Magee, Craig; Jackson, Christopher AL
2017-04-01
Understanding the behaviour of Earth's surface in response to movement and emplacement of magma underground is important because it assists calculation of subsurface magma volumes, and could feed into eruption forecasting. Studies of seismic reflection data have observed that the amplitude of a forced fold above an igneous sill is usually smaller than the thickness of the sill itself. This observation implies that fold amplitude alone provides only a lower bound for magma volume, and an understanding of the mechanism(s) behind the fold amplitude/sill thickness discrepancy is also required to obtain a true estimate of magma volume. Mechanisms suggested to explain the discrepancy include problems with seismic imaging and varying strain behaviour of the host rock. Here we examine the extent to which host-rock compaction can explain the fold amplitude/sill thickness discrepancy. This mechanism operates in cases where a sill is injected into the upper few kilometres of sedimentary rock that contain significant porosity. Accumulation of sediment after sill intrusion reduces the amplitude of the forced fold by compaction, but the sill itself undergoes little compaction since its starting porosity is almost zero. We compiled a database of good-quality 2D and 3D seismic observations where sill thickness has been measured independently of forced fold geometry. We then backstripped the post-intrusion sedimentary section to reconstruct the amplitude of the forced fold at the time of intrusion. We used the standard compaction model in which porosity decays exponentially below the sediment surface. In all examples we studied, post-sill-emplacement compaction can explain all of the fold amplitude/sill thickness discrepancy, subject to uncertainty in compaction model parameters. This result leads directly to an improved method of predicting magma volume from fold amplitude, including how uncertainty in compaction parameters maps onto uncertainty in magma volume. Our work implies
Large amplitude internal waves in three-layer flows
NASA Astrophysics Data System (ADS)
Barros, Ricardo
2017-04-01
Large amplitude internal waves in a three-layer flow confined between two rigid walls will be examined in this talk. The mathematical model under consideration is an extension of the two-layer MCC (Miyata-Choi-Camassa) model, which can be derived without imposing any smallness assumption on the wave amplitudes and is well-suited to describe internal waves within a strongly nonlinear regime. Solitary-wave solutions will be investigated and some of their properties will be unveiled by carrying out a detailed critical point analysis of the underlying dynamical system. A particular emphasis will be given to mode-2 waves.
Theoretical analysis of the Ca2+ spark amplitude distribution.
Izu, L T; Wier, W G; Balke, C W
1998-01-01
A difficulty of using confocal microscopy to study Ca2+ sparks is the uncertainty of the linescan position with respect to the source of Ca2+ release. Random placement of the linescan is expected to result in a broad distribution of measured Ca2+ spark amplitudes (a) even if all Ca2+ sparks were generated identically. Thus variations in Ca2+ spark amplitude due to positional differences between confocal linescans and Ca2+ release site are intertwined with variations due to intrinsic differences in Ca2+ release properties. To separate these two sources of variations on the Ca2+ spark amplitude, we determined the effect changes of channel current or channel open time--collectively called the source strength, alpha--had on the measured Ca2+ spark amplitude histogram, N(a). This was done by 1) simulating Ca2+ release, Ca2+ and fluo-3 diffusion, and Ca2+ binding reactions; 2) simulation of image formation of the Ca2+ spark by a confocal microscope; and 3) using a novel automatic Ca2+ spark detector. From these results we derived an integral equation relating the probability density function of source strengths, f alpha (alpha), to N(a), which takes into account random positional variations between the source and linescan. In the special, but important, case that the spatial distribution of Ca(2+)-bound fluo-3 is Gaussian, we show the following: 1) variations of Ca2+ spark amplitude due to positional or intrinsic differences can be separated, and 2) f alpha (alpha) can, in principle, be calculated from the Ca2+ spark amplitude histogram since N(a) is the sum of shifted hyperbolas, where the magnitudes of the shifts and weights depend on f alpha (alpha). In particular, if all Ca2+ sparks were generated identically, then the plot of 1/N(a) against a will be a straight line. Multiple populations of channels carrying distinct currents are revealed by discontinuities in the 1/N(a) plot. 3) Although the inverse relationship between Ca2+ spark amplitude and decay time might be
Solar corona and prediction of the solar cycle 24 amplitude..
NASA Astrophysics Data System (ADS)
Pishkalo, M.
2012-12-01
Investigation of the solar cycle amplitude dependence on such quantitative parameters of shape and structure of the solar corona as indexes of photometrical and geometrical flattening and extension of polar coronal rays along the solar limb have been made. Observation of the solar corona during total solar eclipses in solar cycles 11-23 were used. The amplitude of solar cycle 24 was predicted on the basis of the parameters values at the cycle minimum. Solar cycle 24 is expected to be weaker than previous cycle 23. The Wolf number in the cycle maximum will amount to 83-113.
Nanometer Accuracy Amplitude Modulation Sensor Technique Used For Roundness Measurement
NASA Astrophysics Data System (ADS)
Zhang, H.
2006-10-01
This paper introduces the advantage of digital phase sensitivity demodulation technique based on analyzing the errors of the analog phase sensitivity demodulation technique. And the digital phase sensitivity demodulation technique is used in the amplitude modulation sensor circuit for roundness measurement. The digital phase sensitivity demodulation technique can simplify the circuit design and improve the reliability. The experiment shows the amplitude modulation sensor circuit using the digital phase sensitivity demodulation technique can reach nanometer precision, so it can be used to accomplish the high precision roundness measurement.
Very low luminosity stars with very large amplitude flares
NASA Technical Reports Server (NTRS)
Schaefer, Bradley E.
1990-01-01
CCD frames of CZ Cnc, KY Cep, the gamma-ray burster optical transient, and NSV 12006 are analyzed. Also studied are 549 archival photographic plates of the CZ Cnc field. These observations are compared with the data of Lovas (1976). Flare events on CZ Cnc are examined. Based on the data it is noted that CZ Cnc is a main-sequence star, has a magnitude of 16.1, a distance of 100 pc, occasional large-amplitude flares, and frequent flares with amplitudes greater than 4 mag.
Amplitude of primeval fluctuations from cosmological mass density reconstructions
NASA Technical Reports Server (NTRS)
Seljak, Uros; Bertschinger, Edmund
1994-01-01
We use the POTENT reconstruction of the mass density field in the nearby universe to estimate the amplitude of the density fluctuation power spectrum for various cosmological models. We find that sigma(sub 8) Omega(sub m sup 0.6) = 1.3(sub -0.3 sup +0.4), almost independently of the power spectrum. This value agrees well with the Cosmic Background Explorer (COBE) normalization for the standard cold dark matter model, while alternative models predict an excessive amplitude compared with COBE. Flat, low Omega(sub m) models and tilted models with spectral index n less than 0.8 are particularly discordant.
Traveling surface waves of moderate amplitude in shallow water
Gasull, Armengol; Geyer, Anna
2014-01-01
We study traveling wave solutions of an equation for surface waves of moderate amplitude arising as a shallow water approximation of the Euler equations for inviscid, incompressible and homogeneous fluids. We obtain solitary waves of elevation and depression, including a family of solitary waves with compact support, where the amplitude may increase or decrease with respect to the wave speed. Our approach is based on techniques from dynamical systems and relies on a reformulation of the evolution equation as an autonomous Hamiltonian system which facilitates an explicit expression for bounded orbits in the phase plane to establish existence of the corresponding periodic and solitary traveling wave solutions. PMID:24895474
From maximal to minimal supersymmetry in string loop amplitudes
NASA Astrophysics Data System (ADS)
Berg, Marcus; Buchberger, Igor; Schlotterer, Oliver
2017-04-01
We calculate one-loop string amplitudes of open and closed strings with N = 1 , 2 , 4 supersymmetry in four and six dimensions, by compactification on Calabi-Yau and K3 orbifolds. In particular, we develop a method to combine contributions from all spin structures for arbitrary number of legs at minimal supersymmetry. Each amplitude is cast into a compact form by reorganizing the kinematic building blocks and casting the worldsheet integrals in a basis. Infrared regularization plays an important role to exhibit the expected factorization limits. We comment on implications for the one-loop string effective action.
NASA Astrophysics Data System (ADS)
Ito, Kazuhito; Nakagawa, Seiji
2015-07-01
A novel hearing aid system utilizing amplitude-modulated bone-conducted ultrasound (AM-BCU) is being developed for use by profoundly deaf people. However, there is a lack of research on the acoustic aspects of AM-BCU hearing. In this study, acoustic fields in the ear canal under AM-BCU stimulation were examined with respect to the self-demodulation effect of amplitude-modulated signal components generated in the ear canal. We found self-demodulated signals with an audible sound pressure level related to the amplitude-modulated signal components of bone-conducted ultrasonic stimulation. In addition, the increases in the self-demodulated signal levels at low frequencies in the ear canal after occluding the ear canal opening, i.e., the positive occlusion effect, indicate the existence of a pathway by which the self-demodulated signals pass through the aural cartilage and soft tissue, and radiate into the ear canal.
Volume Functions of Historical Texts and the Amplitude Correlation Principle.
ERIC Educational Resources Information Center
Fomenko, Anatoliy T.; Rachev, Svetlozar T.
1990-01-01
Proposes an empirico-statistical model to differentiate dependent and independent historical texts. Formulates a regard for information principle and an amplitude correlation principle. Experimentally examines and validates the model and both principles using specific historical texts. Includes tables and graphs. Appends further discussion of the…
End point behaviour of the pion distribution amplitude
NASA Astrophysics Data System (ADS)
Szcepaniak, Adam; Mankiewicz, Lech
1991-08-01
We study the end point structure of the pion distribution amplitude and reexamine the perturbative analysis of the high-Q2 pion form factor in the factorization approach. Permanent address: Nicolaus Copernicus Astronomical Centre, Bartycka 18, PL-00-716 Warsaw, Poland.
Gauge and Gravity Scattering Amplitudes from CHY Formalism
NASA Astrophysics Data System (ADS)
Teng, Fei
In this dissertation, we first review some recent progress on exploring the nature of scattering amplitudes. Then we present our recent work on direct evaluation of tree level maximally helicity violating (MHV) amplitudes by Cachazo-He-Yuan (CHY) formula, which naturally reproduce the Parke-Taylor and Hodges formula, respectively, for gauge and gravity. We also verify that they are supported only by one single solution to the scattering equation. In addition, we derive a new compact formula for tree level single trace MHV amplitudes for Einstein-Yang-Mills theory, which is equivalent to, but much simpler than the known Selivanov-Bern-De Freitas-Wong (SBDW) formula. It can be shown that other solutions do not contribute to the MHV amplitudes of Yang-Mills, gravity and Einstein-Yang-Mills theory. We further propose a method to characterize the solutions to the scattering equations using the rank of two discriminant matrices. In four dimensions, such a characterization can be used to understand the correspondence between the helicity configurations of external scattering particles and the solutions to the scattering equation.
High amplitude surging and plunging motions at low Reynolds number
NASA Astrophysics Data System (ADS)
Choi, Jeesoon; Colonius, Tim; Williams, David; Caltech Collaboration; IIT Collaboration
2014-11-01
Aerodynamic forces and flow structures associated with high amplitude oscillations of an airfoil in the streamwise (surging) and transverse (plunging) direction are investigated in two-dimensional simulations at low Reynolds number (Re = 102 ~ 103). While the unsteady aerodynamic forces for low-amplitude motions were mainly affected by the leading-edge vortex (LEV) acting in- or out-of phase with the quasi-component of velocity, large-amplitude motions involve complex vortex interactions of LEVs and trailing-edge vortices (TEVs) with the moving body. For high-amplitude surging, the TEV, instead of the LEV, induces low-pressure regions above the airfoil during the retreating portion of the cycle near the reduced frequency, k = 0.5, and enhances the time-average forces. The time required for the LEV to convect along the chord becomes an intrinsic time scale, and for plunging motions, there is a sudden change of flow structure when the period of the motion is not long enough for the LEV to convect through the whole chord.
Oscillations of a Simple Pendulum with Extremely Large Amplitudes
ERIC Educational Resources Information Center
Butikov, Eugene I.
2012-01-01
Large oscillations of a simple rigid pendulum with amplitudes close to 180[degrees] are treated on the basis of a physically justified approach in which the cycle of oscillation is divided into several stages. The major part of the almost closed circular path of the pendulum is approximated by the limiting motion, while the motion in the vicinity…
Contextual Modulation of N400 Amplitude to Lexically Ambiguous Words
ERIC Educational Resources Information Center
Titone, Debra A.; Salisbury, Dean F.
2004-01-01
Through much is known about the N400 component, an event-related EEG potential that is sensitive to semantic manipulations, it is unclear whether modulations of N400 amplitude reflect automatic processing, controlled processing, or both. We examined this issue using a semantic judgment task that manipulated local and global contextual cues. Word…
The Effect of Speed of Processing Training on Microsaccade Amplitude
Layfield, Stephen; Burge, Wesley; Mitchell, William; Ross, Lesley; Denning, Christine; Amthor, Frank; Visscher, Kristina
2014-01-01
Older adults experience cognitive deficits that can lead to driving errors and a loss of mobility. Fortunately, some of these deficits can be ameliorated with targeted interventions which improve the speed and accuracy of simultaneous attention to a central and a peripheral stimulus called Speed of Processing training. To date, the mechanisms behind this effective training are unknown. We hypothesized that one potential mechanism underlying this training is a change in distribution of eye movements of different amplitudes. Microsaccades are small amplitude eye movements made when fixating on a stimulus, and are thought to counteract the “visual fading” that occurs when static stimuli are presented. Due to retinal anatomy, larger microsaccadic eye movements are needed to move a peripheral stimulus between receptive fields and counteract visual fading. Alternatively, larger microsaccades may decrease performance due to neural suppression. Because larger microsaccades could aid or hinder peripheral vision, we examine the distribution of microsaccades during stimulus presentation. Our results indicate that there is no statistically significant change in the proportion of large amplitude microsaccades during a Useful Field of View-like task after training in a small sample of older adults. Speed of Processing training does not appear to result in changes in microsaccade amplitude, suggesting that the mechanism underlying Speed of Processing training is unlikely to rely on microsaccades. PMID:25248099
Cross-Channel Amplitude Sweeps Are Crucial to Speech Intelligibility
ERIC Educational Resources Information Center
Prendergast, Garreth; Green, Gary G. R.
2012-01-01
Classical views of speech perception argue that the static and dynamic characteristics of spectral energy peaks (formants) are the acoustic features that underpin phoneme recognition. Here we use representations where the amplitude modulations of sub-band filtered speech are described, precisely, in terms of co-sinusoidal pulses. These pulses are…
Light-Front Holography and Hadronization at the Amplitude Level
Brodsky, Stanley J.; Teramond, Guy F. de; Shrock, Robert
2008-10-13
The correspondence between theories in anti-de Sitter space and conformal field theories in physical space-time leads to an analytic, semiclassical model for strongly-coupled QCD which has scale invariance at short distances and color confinement at large distances. Light-front holography is a remarkable feature of AdS/CFT: it allows hadronic amplitudes in the AdS fifth dimension to be mapped to frame-independent light-front wavefunctions of hadrons in physical space-time, thus providing a relativistic description of hadrons at the amplitude level. Some novel features of QCD are discussed, including the consequences of confinement for quark and gluon condensates and the behavior of the QCD coupling in the infrared. We suggest that the spatial support of QCD condensates is restricted to the interior of hadrons, since they arise due to the interactions of confined quarks and gluons. Chiral symmetry is thus broken in a limited domain of size 1/m{sub {pi}}, in analogy to the limited physical extent of superconductor phases. A new method for computing the hadronization of quark and gluon jets at the amplitude level, an event amplitude generator, is outlined.
The Dynamics of Large-Amplitude Motion in Energized Molecules
Perry, David S.
2016-05-27
Chemical reactions involve large-amplitude nuclear motion along the reaction coordinate that serves to distinguish reactants from products. Some reactions, such as roaming reactions and reactions proceeding through a loose transition state, involve more than one large-amplitude degree of freedom. Because of the limitation of exact quantum nuclear dynamics to small systems, one must, in general, define the active degrees of freedom and separate them in some way from the other degrees of freedom. In this project, we use large-amplitude motion in bound model systems to investigate the coupling of large-amplitude degrees of freedom to other nuclear degrees of freedom. This approach allows us to use the precision and power of high-resolution molecular spectroscopy to probe the specific coupling mechanisms involved, and to apply the associated theoretical tools. In addition to slit-jet spectra at the University of Akron, the current project period has involved collaboration with Michel Herman and Nathalie Vaeck of the Université Libre de Bruxelles, and with Brant Billinghurst at the Canadian Light Source (CLS).
Path integral approach to the quantum fidelity amplitude
2016-01-01
The Loschmidt echo is a measure of quantum irreversibility and is determined by the fidelity amplitude of an imperfect time-reversal protocol. Fidelity amplitude plays an important role both in the foundations of quantum mechanics and in its applications, such as time-resolved electronic spectroscopy. We derive an exact path integral formula for the fidelity amplitude and use it to obtain a series of increasingly accurate semiclassical approximations by truncating an exact expansion of the path integral exponent. While the zeroth-order expansion results in a remarkably simple, yet non-trivial approximation for the fidelity amplitude, the first-order expansion yields an alternative derivation of the so-called ‘dephasing representation,’ circumventing the use of a semiclassical propagator as in the original derivation. We also obtain an approximate expression for fidelity based on the second-order expansion, which resolves several shortcomings of the dephasing representation. The rigorous derivation from the path integral permits the identification of sufficient conditions under which various approximations obtained become exact. PMID:27140973
Amplitude-modulation detection by gerbils in reverberant sound fields.
Lingner, Andrea; Kugler, Kathrin; Grothe, Benedikt; Wiegrebe, Lutz
2013-08-01
Reverberation can dramatically reduce the depth of amplitude modulations which are critical for speech intelligibility. Psychophysical experiments indicate that humans' sensitivity to amplitude modulation in reverberation is better than predicted from the acoustic modulation depth at the receiver position. Electrophysiological studies on reverberation in rabbits highlight the contribution of neurons sensitive to interaural correlation. Here, we use a prepulse-inhibition paradigm to quantify the gerbils' amplitude modulation threshold in both anechoic and reverberant virtual environments. Data show that prepulse inhibition provides a reliable method for determining the gerbils' AM sensitivity. However, we find no evidence for perceptual restoration of amplitude modulation in reverberation. Instead, the deterioration of AM sensitivity in reverberant conditions can be quantitatively explained by the reduced modulation depth at the receiver position. We suggest that the lack of perceptual restoration is related to physical properties of the gerbil's ear input signals and inner-ear processing as opposed to shortcomings of their binaural neural processing. Copyright © 2013 Elsevier B.V. All rights reserved.
Generalized quantum counting algorithm for non-uniform amplitude distribution
NASA Astrophysics Data System (ADS)
Tan, Jianing; Ruan, Yue; Li, Xi; Chen, Hanwu
2017-03-01
We give generalized quantum counting algorithm to increase universality of quantum counting algorithm. Non-uniform initial amplitude distribution is possible due to the diversity of situations on counting problems or external noise in the amplitude initialization procedure. We give the reason why quantum counting algorithm is invalid on this situation. By modeling in three-dimensional space spanned by unmarked state, marked state and free state to the entire Hilbert space of n qubits, we find Grover iteration can be regarded as improper rotation in the space. This allows us to give formula to solve counting problem. Furthermore, we express initial amplitude distribution in the eigenvector basis of improper rotation matrix. This is necessary to obtain mathematical analysis of counting problem on various situations. Finally, we design four simulation experiments, the results of which show that compared with original quantum counting algorithm, generalized quantum counting algorithm wins great satisfaction from three aspects: (1) Whether initial amplitude distribution is uniform; (2) the diversity of situations on counting problems; and (3) whether phase estimation technique can get phase exactly.
Large-amplitude motion in polymer crystals and mesophases
Wunderlich, B. |
1994-12-31
Large-amplitude motion of macromolecules involves mainly rotation about bonds (conformational motion). In the liquid phases, the large- amplitude motion is coupled with disorder and accounts for the flow and viscoelastic behavior. Perfectly ordered crystals, in contrast, permit only little large-amplitude motion. The mesophases are intermediate in order and mobility. In crystals, large-amplitude motion leads initially to gauche defects and kinks (conformational defects), and ultimately may produce conformationally disordered crystals (conis crystals). Molecular dynamics simulations of crystals with up to 30,000 atoms have been carried out and show the mechanism of defect formation, permit the study of the distribution of defects, and the visualization of hexagonal crystals. Distinction between main-chain liquid-crystalline macromolecules and condis crystals, the two mesophases of polymers, can be done on basis of analysis of phase separation (partial crystallinity), present in condis crystals and not in liquid crystals. Solid state NMR is the tool of choice for detecting mobile and rigid phases. In highly drawn fibers one can find four different states of order and mobility. Besides the (defect) crystalline phase and the isotropic amorphous phase, an intermediate oriented phase and a rigid amorphous phase exists.
Reconnaissance amplitude versus offset techniques in the Niger Delta
Barton, J.; Gullette, K.
1996-08-01
Reconnaissance AVO (amplitude vs. offset) techniques have been invaluable in allowing the analyses and mapping of AVO on large-volume data sets in the Nigerian Niger Delta. Forward modelling of rock properties derived from well data on the shelf and regional ties of common depth point gathers to well control show that a shale on hydrocarbon bearing sand typically generates increasing amplitude with offset [Class 2 and Class 3 type anomalies of the Rutherford and Williams (1989) classification]. Consequently, processing and display techniques have been developed that distinguish the increasing amplitude with offset response associated with hydrocarbon bearing sands from the flatter AVO response of background water wet sands and shales. Attributes are created from angle stacks rather than by analyses of individual common depth point gathers over an entire data set. We show examples of a new AVO attribute which we call the Enhanced Restricted Gradient that highlights Class 2 and Class 3 type AVO anomalies more clearly than some of the standard AVO attributes used in the industry. The techniques described here provide a cost-effective and practical way of evaluating AVO character on large volume 2D and 3D data sets and should also be useful in other areas worldwide where hydrocarbon bearing reservoirs generate increasing amplitude with offset.
Nonlinear Saturation Amplitude in Classical Planar Richtmyer-Meshkov Instability
NASA Astrophysics Data System (ADS)
Liu, Wan-Hai; Wang, Xiang; Jiang, Hong-Bin; Ma, Wen-Fang
2016-04-01
The classical planar Richtmyer-Meshkov instability (RMI) at a fluid interface supported by a constant pressure is investigated by a formal perturbation expansion up to the third order, and then according to definition of nonlinear saturation amplitude (NSA) in Rayleigh-Taylor instability (RTI), the NSA in planar RMI is obtained explicitly. It is found that the NSA in planar RMI is affected by the initial perturbation wavelength and the initial amplitude of the interface, while the effect of the initial amplitude of the interface on the NSA is less than that of the initial perturbation wavelength. Without marginal influence of the initial amplitude, the NSA increases linearly with wavelength. The NSA normalized by the wavelength in planar RMI is about 0.11, larger than that corresponding to RTI. Supported by the National Natural Science Foundation of China under Grant Nos. 11472278 and 11372330, the Scientific Research Foundation of Education Department of Sichuan Province under Grant No. 15ZA0296, the Scientific Research Foundation of Mianyang Normal University under Grant Nos. QD2014A009 and 2014A02, and the National High-Tech ICF Committee
Amplitude Correction Factors of Korean VLBI Network Observations
NASA Astrophysics Data System (ADS)
Lee, Sang-Sung; Byun, Do-Young; Oh, Chung Sik; Kim, Hyo Ryoung; Kim, Jongsoo; Jung, Taehyun; Oh, Se-Jin; Roh, Duk-Gyoo; Jung, Dong-Kyu; Yeom, Jae-Hwan
2015-10-01
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, NRAO~512, OJ 287, BL Lac, 3C 279, 1633+382, and 1510-089, 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 find 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 combination of two steps of 2-bit quantization in KVN observing systems and characteristics of Daejeon correlator.
Finite amplitude wave interaction with premixed laminar flames
NASA Astrophysics Data System (ADS)
Aslani, Mohamad; Regele, Jonathan D.
2014-11-01
The physics underlying combustion instability is an active area of research because of its detrimental impact in many combustion devices, such as turbines, jet engines, and liquid rocket engines. Pressure waves, ranging from acoustic waves to strong shocks, are potential sources of these disturbances. Literature on flame-disturbance interactions are primarily focused on either acoustics or strong shock wave interactions, with little information about the wide spectrum of behaviors that may exist between these two extremes. For example, the interaction between a flame and a finite amplitude compression wave is not well characterized. This phenomenon is difficult to study numerically due to the wide range of scales that need to be captured, requiring powerful and efficient numerical techniques. In this work, the interaction of a perturbed laminar premixed flame with a finite amplitude compression wave is investigated using the Parallel Adaptive Wavelet Collocation Method (PAWCM). This method optimally solves the fully compressible Navier-Stokes equations while capturing the essential scales. The results show that depending on the amplitude and duration of a finite amplitude disturbance, the interaction between these waves and premixed flames can produce a broad range of responses.
Large-amplitude inviscid fluid motion in an accelerating container
NASA Technical Reports Server (NTRS)
Perko, L. M.
1968-01-01
Study of dynamic behavior of the liquid-vapor interface of an inviscid fluid in an accelerating cylindrical container includes an analytical-numerical method for determining large amplitude motion. The method is based on the expansion of the velocity potential in a series of harmonic functions with time dependent coefficients.
Amplitude modulation reduces loudness adaptation to high-frequency tones
Wynne, Dwight P.; George, Sahara E.; Zeng, Fan-Gang
2015-01-01
Long-term loudness perception of a sound has been presumed to depend on the spatial distribution of activated auditory nerve fibers as well as their temporal firing pattern. The relative contributions of those two factors were investigated by measuring loudness adaptation to sinusoidally amplitude-modulated 12-kHz tones. The tones had a total duration of 180 s and were either unmodulated or 100%-modulated at one of three frequencies (4, 20, or 100 Hz), and additionally varied in modulation depth from 0% to 100% at the 4-Hz frequency only. Every 30 s, normal-hearing subjects estimated the loudness of one of the stimuli played at 15 dB above threshold in random order. Without any amplitude modulation, the loudness of the unmodulated tone after 180 s was only 20% of the loudness at the onset of the stimulus. Amplitude modulation systematically reduced the amount of loudness adaptation, with the 100%-modulated stimuli, regardless of modulation frequency, maintaining on average 55%–80% of the loudness at onset after 180 s. Because the present low-frequency amplitude modulation produced minimal changes in long-term spectral cues affecting the spatial distribution of excitation produced by a 12-kHz pure tone, the present result indicates that neural synchronization is critical to maintaining loudness perception over time. PMID:26233027
Amplitude-squeezed light from quantum-well lasers.
Freeman, M J; Wang, H; Steel, D G; Craig, R; Scifres, D R
1993-03-01
High-impedance pump noise suppression was used to generate amplitude squeezing in an index-guided quantumwell laser. Light exhibiting photon-number noise 1.4 dB below the shot-noise limit was observed, and the corresponding polarization properties were examined. an unsaturated detector revealed 2.9 dB of squeezing.
Light-Front Holography and Hadronization at the Amplitude Level
Brodsky, Stanley J.; de Teramond, Guy; Shrock, Robert
2008-07-25
The correspondence between theories in anti-de Sitter space and conformal field theories in physical space-time leads to an analytic, semiclassical model for strongly-coupled QCD which has scale invariance at short distances and color confinement at large distances. Light-front holography is a remarkable feature of AdS/CFT: it allows hadronic amplitudes in the AdS fifth dimension to be mapped to frame-independent light-front wavefunctions of hadrons in physical space-time, thus providing a relativistic description of hadrons at the amplitude level. Some novel features of QCD are discussed, including the consequences of confinement for quark and gluon condensates and the behavior of the QCD coupling in the infrared. We suggest that the spatial support of QCD condensates is restricted to the interior of hadrons, since they arise due to the interactions of confined quarks and gluons. Chiral symmetry is thus broken in a limited domain of size 1=m{sub {pi}} in analogy to the limited physical extent of superconductor phases. A new method for computing the hadronization of quark and gluon jets at the amplitude level, an event amplitude generator, is outlined.
T Dwarf Variability Amplitudes Are Likely Stronger in the Optical
NASA Astrophysics Data System (ADS)
Heinze, Aren; Metchev, Stanimir; Kellogg, Kendra
2015-01-01
We have monitored twelve T dwarfs using an f814w filter (0.7-0.95 microns) to place in context the remarkable 10-20% variability exhibited by the nearby T dwarf Luhman 16B in this wavelength regime. The motivation was the poorly known red optical behavior of T dwarfs, which have been monitored almost exclusively at infrared wavelengths, where variability amplitudes greater than 10% have been found to be very rare. We detect highly significant variability in two T dwarfs. The T2.5 dwarf 2MASS 13243559+6358284 shows consistent ~17% variability on two consecutive nights. The T2 dwarf 2MASS J16291840+0335371 exhibits ~10% variability that may evolve from night to night, similarly to Luhman 16B. Both objects were previously known to be variable in the infrared, but with considerably lower amplitudes. We also find evidence for variability in the T6 dwarf J162414.37+002915.6, but since it has lower significance, we conservatively refrain from claiming this object as a variable. We explore and rule out various telluric effects, demonstrating that the variations we detect are astrophysically real. We suggest that high-amplitude photometric variability for T dwarfs is likely more common in the red optical than at longer wavelengths. The two new members of the growing class of high-amplitude variable T dwarfs offer excellent prospects for further study of cloud structures and their evolution.
Saturation amplitude of the f-mode instability
Kastaun, Wolfgang; Willburger, Beatrix; Kokkotas, Kostas D.
2010-11-15
We investigate strong nonlinear damping effects which occur during high amplitude oscillations of neutron stars, and the gravitational waves they produce. For this, we use a general relativistic nonlinear hydrodynamics code in conjunction with a fixed spacetime (Cowling approximation) and a polytropic equation of state (EOS). Gravitational waves are estimated using the quadrupole formula. Our main interest are l=m=2 f modes subject to the CFS (Chandrasekhar, Friedman, Schutz) instability, but we also investigate axisymmetric and quasiradial modes. We study various models to determine the influence of rotation rate and EOS. We find that axisymmetric oscillations at high amplitudes are predominantly damped by shock formation, while the nonaxisymmetric f modes are mainly damped by wave breaking and, for rapidly rotating models, coupling to nonaxisymmetric inertial modes. From the observed nonlinear damping, we derive upper limits for the saturation amplitude of CFS-unstable f modes. Finally, we estimate that the corresponding gravitational waves for an oscillation amplitude at the upper limit should be detectable with the advanced LIGO (Laser Interferometer Gravitational Wave Observatory) and VIRGO interferometers at distances above 10 Mpc. This strongly depends on the stellar model, in particular, on the mode frequency.
The Determination of Pseudoscalar Meson Photoproduction Amplitudes from Complete Experiments
A. M. Sandorfi, S. Hoblit, H. Kamano, and T-S. H. Lee
2011-10-01
A new generation of complete experiments is currently underway with the goal of performing a high precision extraction of pseudoscalar meson photo-production amplitudes. Here we review the most general analytic form of the cross section, dependent upon the three polarization vectors of the beam, target and recoil baryon, including all single, double and triple-polarization terms involving 16 spin-dependent observables. Analytic expressions that determine the recoil baryon polarization are also presented. Different conventions are in use in the literature and we have used a numerical calculation of cross sections from Chew-Goldberger-Low-Nambu amplitudes with arbitrary spin projections to clarify apparent sign differences. As an illustration of the use of this machinery, we carry out a multipole analysis of the gammap --> K+Lambda reaction and examine the impact of recently published polarization measurements. In fitting multipoles, we use a combined Monte Carlo sampling of the amplitude space, with gradient minimization, and find a shallow chi2 valley pitted with a very large number of local minima, despite the inclusion of recent data on 8 different observables. We conclude that, while a mathematical solution to the problem of determining an amplitude free of ambiguities may require 8 observables, as has been pointed out in the literature, experiments with realistically achievable uncertainties will require a significantly larger number.
Ward identities and high energy scattering amplitudes in string theory
NASA Astrophysics Data System (ADS)
Chan, Chuan-Tsung; Ho, Pei-Ming; Lee, Jen-Chi
2005-02-01
High-energy limit α→∞ of stringy Ward identities derived from the decoupling of two types of zero-norm states in the old covariant first quantized (OCFQ) spectrum of open bosonic string are used to check the consistency of saddle point calculations of high energy scattering amplitudes of Gross and Mende and Gross and Manes. Some inconsistencies of their saddle point calculations are found even for the string-tree scattering amplitudes of the excited string states. We discuss and calculate the missing terms of the calculation by those authors to recover the stringy Ward identities. In addition, based on the tree-level stringy Ward identities, we give the proof of a general formula, which was proposed previously, of all high energy four-point string-tree amplitudes of arbitrary particles in the string spectrum. In this formula all such scattering amplitudes are expressed in terms of those of tachyons as conjectured by Gross. The formula is extremely simple which manifestly demonstrates the universal high energy behavior of the interactions among all string states.
Amplitude requirements, visual information, and the spatial structure of movement.
Slifkin, Andrew B; Eder, Jeffrey R
2012-08-01
Studies using a variety of experimental tasks have established that when humans repeatedly produce an action, the amount of variability in system output is distributed across a range of time scales or frequencies. A finding of particular interest is that fluctuations in the output of cognitive systems are the highest at the lowest frequencies with fluctuation magnitude (power) systematically declining as frequency increases. Such time-series structure--captured by spectral analysis--is termed pink noise. However, the appearance of pink noise seems to be limited to tasks where action is executed in the absence of external, task-related feedback. In contrast, a few studies have demonstrated that when action was executed in the presence of external, task-related feedback, power was evenly distributed across all spectral frequencies--that is, a white-noise time-series structure was revealed. Here, we sought to determine if the time-series structure of movement amplitude values would change when movement amplitude requirements increased (6.35, 12.70, 25.40, 50.80, and 101.60 mm) under conditions of full visual feedback. Given that increases in movement amplitude requirements are known to induce increased reliance on the available visual feedback, we predicted an amplitude-requirement-induced shift in time-series structure from pink to white noise. Indeed, those results were revealed. Last, the main findings were captured by a computer simulation that was based on established principles of motor control.
Modeling of Pulses Having Arbitrary Amplitude and Frequency Modulation.
1980-03-01
function, fi(t), has been discussed in great detail in Section II. The linearized amplitude modulation, 1(t), is given by: (IV-6) vo A +h( -) TO’ # where "A...10. LCDR Francis Martin Lunney, USN 6143 Gatsby Green Columbia, Maryland 21045 149
Oscillations of a Simple Pendulum with Extremely Large Amplitudes
ERIC Educational Resources Information Center
Butikov, Eugene I.
2012-01-01
Large oscillations of a simple rigid pendulum with amplitudes close to 180[degrees] are treated on the basis of a physically justified approach in which the cycle of oscillation is divided into several stages. The major part of the almost closed circular path of the pendulum is approximated by the limiting motion, while the motion in the vicinity…
Cross-Channel Amplitude Sweeps Are Crucial to Speech Intelligibility
ERIC Educational Resources Information Center
Prendergast, Garreth; Green, Gary G. R.
2012-01-01
Classical views of speech perception argue that the static and dynamic characteristics of spectral energy peaks (formants) are the acoustic features that underpin phoneme recognition. Here we use representations where the amplitude modulations of sub-band filtered speech are described, precisely, in terms of co-sinusoidal pulses. These pulses are…
The Accretion Rate Dependence of Burst Oscillation Amplitude
NASA Astrophysics Data System (ADS)
Ootes, Laura S.; Watts, Anna L.; Galloway, Duncan K.; Wijnands, Rudy
2017-01-01
Neutron stars in low-mass X-ray binaries exhibit oscillations during thermonuclear bursts, attributed to asymmetric brightness patterns on the burning surfaces. All models that have been proposed to explain the origin of these asymmetries (spreading hotspots, surface waves, and cooling wakes) depend on the accretion rate. By analysis of archival RXTE data of six oscillation sources, we investigate the accretion rate dependence of the amplitude of burst oscillations. This more than doubles the size of the sample analyzed previously by Muno et al., who found indications for a relationship between accretion rate and oscillation amplitudes. We find that burst oscillation signals can be detected at all observed accretion rates. Moreover, oscillations at low accretion rates are found to have relatively small amplitudes ({A}{{rms}}≤slant 0.10) while oscillations detected in bursts observed at high accretion rates cover a broad spread in amplitudes (0.05≤slant {A}{{rms}}≤slant 0.20). In this paper we present the results of our analysis and discuss these in the light of current burst oscillation models. Additionally, we investigate the bursts of two sources without previously detected oscillations. Despite the fact that these sources have been observed at accretion rates where burst oscillations might be expected, we find their behavior not to be anomalous compared to oscillation sources.
Amplitude and phase reconstruction by radial shearing interferometry.
López Lago, Elena; de la Fuente, Raúl
2008-01-20
We describe a new procedure for retrieving both amplitude and phase of an optical beam from radial shearing measurements. Information from the sheared interferogram is used to estimate and improve the beam and wavefront shape in successive iterations. We present computer simulations and experimental results that show the performance of the method.
Contextual Modulation of N400 Amplitude to Lexically Ambiguous Words
ERIC Educational Resources Information Center
Titone, Debra A.; Salisbury, Dean F.
2004-01-01
Through much is known about the N400 component, an event-related EEG potential that is sensitive to semantic manipulations, it is unclear whether modulations of N400 amplitude reflect automatic processing, controlled processing, or both. We examined this issue using a semantic judgment task that manipulated local and global contextual cues. Word…
Resolving High Amplitude Surface Motion with Diffusing Light
NASA Technical Reports Server (NTRS)
Wright, W.; Budakian, R.; Putterman, Seth J.
1996-01-01
A new technique has been developed for the purpose of imaging high amplitude surface motion. With this method one can quantitatively measure the transition to ripple wave turbulence. In addition, one can measure the phase of the turbulent state. These experiments reveal strong coherent structures in turbulent range of motion.
Maximally supersymmetric planar Yang-Mills amplitudes at five loops
Bern, Z.; Carrasco, J. J. M.; Johansson, H.; Kosower, D. A.
2007-12-15
We present an Ansatz for the planar five-loop four-point amplitude in maximally supersymmetric Yang-Mills theory in terms of loop integrals. This Ansatz exploits the recently observed correspondence between integrals with simple conformal properties and those found in the four-point amplitudes of the theory through four loops. We explain how to identify all such integrals systematically. We make use of generalized unitarity in both four and D dimensions to determine the coefficients of each of these integrals in the amplitude. Maximal cuts, in which we cut all propagators of a given integral, are an especially effective means for determining these coefficients. The set of integrals and coefficients determined here will be useful for computing the five-loop cusp anomalous dimension of the theory which is of interest for nontrivial checks of the AdS/CFT duality conjecture. It will also be useful for checking a conjecture that the amplitudes have an iterative structure allowing for their all-loop resummation, whose link to a recent string-side computation by Alday and Maldacena opens a new venue for quantitative AdS/CFT comparisons.
Path integral approach to the quantum fidelity amplitude.
Vaníček, Jiří; Cohen, Doron
2016-06-13
The Loschmidt echo is a measure of quantum irreversibility and is determined by the fidelity amplitude of an imperfect time-reversal protocol. Fidelity amplitude plays an important role both in the foundations of quantum mechanics and in its applications, such as time-resolved electronic spectroscopy. We derive an exact path integral formula for the fidelity amplitude and use it to obtain a series of increasingly accurate semiclassical approximations by truncating an exact expansion of the path integral exponent. While the zeroth-order expansion results in a remarkably simple, yet non-trivial approximation for the fidelity amplitude, the first-order expansion yields an alternative derivation of the so-called 'dephasing representation,' circumventing the use of a semiclassical propagator as in the original derivation. We also obtain an approximate expression for fidelity based on the second-order expansion, which resolves several shortcomings of the dephasing representation. The rigorous derivation from the path integral permits the identification of sufficient conditions under which various approximations obtained become exact.
Joint inversion of surface and borehole magnetic amplitude data
NASA Astrophysics Data System (ADS)
Li, Zelin; Yao, Changli; Zheng, Yuanman; Yuan, Xiaoyu
2016-04-01
3D magnetic inversion for susceptibility distribution is a powerful tool in quantitative interpretation of magnetic data in mineral exploration. However, the inversion and interpretation of such data are faced with two problems. One problem is the poor imaging results of deep sources when only surface data are inverted. The other is the unknown total magnetization directions of sources when strong remanence exists. To deal with these problems simultaneously, we propose a method through the joint inversion of surface and borehole magnetic amplitude data. In this method, we first transform both surface and borehole magnetic data to magnetic amplitude data that are less sensitive to the directions of total magnetization, and then preform a joint inversion of the whole amplitude data to generate a 3D susceptibility distribution. The amplitude inversion algorithm uses Tikhonov regularization and imposes a positivity constraint on the effective susceptibility defined as the ratio of magnetization magnitude over the geomagnetic field strength. In addition, a distance-based weighting function is used to make the algorithm applicable to joint data sets. To solve this positivity-constraint inversion problem efficiently, an appropriate optimization method must be chosen. We first use an interior-point method to incorporate the positivity constraint into the total objective function, and then minimize the objective function via a Gauss-Newton method due to the nonlinearity introduced by the positivity constraint and the amplitude data. To further improve the efficiency of the inversion algorithm, we use a conjugate gradient method to carry out the fast matrix-vector multiplication during the minimization. To verify the utility of the proposed method, we invert the synthetic and field data using three inversion methods, including the joint inversion of surface and borehole three-component magnetic data, the inversion of surface magnetic amplitude data, and the proposed joint
Measuring finite-frequency body-wave amplitudes and traveltimes
NASA Astrophysics Data System (ADS)
Sigloch, Karin; Nolet, Guust
2006-10-01
We have developed a method to measure finite-frequency amplitude and traveltime anomalies of teleseismic P waves. We use a matched filtering approach that models the first 25 s of a seismogram after the P arrival, which includes the depth phases pP and sP. Given a set of broad-band seismograms from a teleseismic event, we compute synthetic Green's functions using published moment tensor solutions. We jointly deconvolve global or regional sets of seismograms with their Green's functions to obtain the broad-band source time function. The matched filter of a seismogram is the convolution of the Green's function with the source time function. Traveltimes are computed by cross-correlating each seismogram with its matched filter. Amplitude anomalies are defined as the multiplicative factors that minimize the RMS misfit between matched filters and data. The procedure is implemented in an iterative fashion, which allows for joint inversion for the source time function, amplitudes, and a correction to the moment tensor. Cluster analysis is used to identify azimuthally distinct groups of seismograms when source effects with azimuthal dependence are prominent. We then invert for one source time function per group. We implement this inversion for a range of source depths to determine the most likely depth, as indicated by the overall RMS misfit, and by the non-negativity and compactness of the source time function. Finite-frequency measurements are obtained by filtering broad-band data and matched filters through a bank of passband filters. The method is validated on a set of 15 events of magnitude 5.8 to 6.9. Our focus is on the densely instrumented Western US. Quasi-duplet events (`quplets') are used to estimate measurement uncertainty on real data. Robust results are achieved for wave periods between 24 and 2 s. Traveltime dispersion is on the order of 0.5 s. Amplitude anomalies are on the order of 1 db in the lowest bands and 3 db in the highest bands, corresponding to
Nonlinear amplitude frequency characteristics of attenuation in rock under pressure
NASA Astrophysics Data System (ADS)
Mashinskii, E. I.
2006-12-01
Laboratory experiments have been carried out to investigate the influence of change in strain amplitude on the frequency dependence of attenuation in samples of sandstone, smoky quartz and duralumin. The measurements were performed using the reflection method on pulse frequency of 1 MHz in the strain range ~(0.3-2.0) × 10-6 under a confining pressure of 20 MPa. The attenuation in rocks is nonlinearly dependent on frequency and strain amplitude. In sandstone for P-waves and in smoky quartz for P- and S-waves, the dependences Q-1p(f) and Q-1s(f) have the attenuation peak. With increasing amplitude, the peak frequency can shift towards both the lower and the higher frequencies. It depends on the location of the frequency of an incident (input) pulse with respect to the peak frequency on the frequency axis. For sandstone the peak frequency of P-waves shifts towards the higher frequencies. For smoky quartz the shift of peak frequency is absent in P-waves, and S-waves shift towards the lower frequencies. The attenuation at the incident frequency always monotonically decreases with amplitude, and the other frequency components have complex or monotonic characters depending on the location of the incident frequency in the relaxation spectrum. Q-1p(f) in duralumin has monotonic character, i.e. a relaxation peak in the measurement frequency band is absent. Attenuation strongly decreases with increasing frequency and weakly depends on strain amplitude. The curve Q-1s(f) has an attenuation peak, and its character essentially depends on strain amplitude. With increasing amplitude, the peak frequency shifts towards the lower frequencies. The unusual increase of peak frequency of the P-wave spectrum in the bottom reflection in comparison with peak frequency in spectrum of the initial reflection is detected. The unusual behaviour of attenuation is explained by features of the joint action of viscoelastic and microplastic mechanisms. These results can be used for improving methods
Global oscillation amplitudes excited by the Jupiter-comet collision
NASA Technical Reports Server (NTRS)
Lee, U.; Van Horn, H. M.
1994-01-01
The energy released during the collision of fragments of comet Shoemaker-Levy 9 with Jupiter in 1994 July may excite a spectrum of global oscillation modes. We estimate the maximum amplitudes to which the p-modes, discontinuity modes, inertial modes, and r-modes can be excited by assuming that the full kinetic energy of the fragment, which we take to be 10(exp 30) ergs, is converted into the energy of each individual mode. We have used two realistics Jovian models as the basis for our estimates: one with and one without the predicted 'plasma phase transition' (PPT) of hydrogen. A density discontinuity in the planet's hydrogen-helium envelope is associated with the PPT. We find that high-frequency p-modes, with periods approximately less than 15 minutes, may be excited to sufficiently large amplitudes to be observable as Doppler shifts (velocity amplitudes approximately greater than serveral m/s) or temperature variations (delta(T) approximately greater than 0.01 K) at the planetary surface. Inertial modes may also be observable. If the PPT exists in Jupiter, inertial modes with periods approximately 8 hr or approximately 2.2 days trapped in the surface region of the planet, above the PPT, may be detectable as temperature fluctuations of order delta(T) approximately 0.01 K. Inertial modes with periods of order 8-8.5 hr appear to be particularly strongly excited if the PPT exists. If the PPT does not exist in Jupiter, intertial modes with periods approximately 8-8.5 hr have much lower amplitudes. In this case, inertial modes with periods longer than approximately 18 hr may produce temperature fluctuations of order delta(T) approximately 0.01 K. Discontinuity modes associated with the PPT and r-modes unfortunately may not reach observable amplitudes.
Accommodative amplitude using the minus lens at different near distances.
Momeni-Moghaddam, Hamed; Ng, Jason S; Cesana, Bruno Mario; Yekta, Abbas Ali; Sedaghat, Mohammad Reza
2017-03-01
The purpose of this study was to compare the mean findings and the repeatability of the minus lens (ML) amplitude of accommodation (AA) at 33 cm and 40 cm. AA was measured from the dominant eye of 120 fully corrected subjects using the ML procedure when viewing the target at both 33 and 40 cm. Each measurement was repeated between 24 and 48 hours after the first trial. Mean AA when tested at 33 cm and 40 cm was 10.20 diopter (D) (standard deviation [SD] =1.24) and 8.85 D (SD = 1.23), respectively (P < 0.001). The limits of agreement of the measured amplitude calculated with taking into account of the replicates at 33 and 40 cm were - 0.19 (95% confidence interval [CI]: -0.34 to -0.04) and 2.53 (95% CI: 2.38 to 2.68), respectively. The repeatability of testing at the two distances 33 and 40 cm was ± 1.24 and ± 0.99, respectively. In addition, the retest reliability of measured amplitude using the intraclass correlation coefficient was 0.87 (95% CI: 0.789-0.920) at 33 cm and 0.91 (95% CI: 0.872-0.945) at 40 cm. There is no agreement in the obtained amplitude at the two measurement distances. Testing the ML AA at 40 cm may be superior given that a lower repeatability coefficient was observed. However, it is unclear whether the larger amplitude measured at 33 cm reflects a larger increase in accommodation (greater proximity effect) or a decrease in the ability to perceive the first slight sustained blur.
Observing rapid quasi-wave ionospheric disturbance using amplitude charts
NASA Astrophysics Data System (ADS)
Kurkin, Vladimir; Laryunin, Oleg; Podlesnyi, Alexey
Data from vertical (quasi-vertical) sounding are traditionally used for determining a number of ionospheric parameters such as critical frequencies of E and F layers, peaks of these layers, and for reconstructing electron density profiles. In this respect, radio sounding is not used to its full capacity. Modern ionosondes provide additional information encoded in ionospheric echoes, including information on reflected-signal amplitude. The time dependence of the amplitude-frequency characteristic of reflected signal has been named "amplitude chart" (A-chart). Ionosondes used by the ISTP SB RAS Geophysical Observatory for constructing A-charts employ the frequency-modulated continuous-wave (FMCW) signal in a range 1.3-15 MHz. One-minute sounding interval allows a more detailed study of dynamic processes in the ionosphere. The ionosonde has a direct digital synthesizer and direct sampling receiver without automatic gain control (AGC). The absence of AGC and the high dynamic range enable determination of the relative field strength at a receiving point and registration of relative long-term variations in reflected-signal amplitude over the entire range of operating frequencies of the ionosonde. We have revealed that the passage of travelling ionospheric disturbances (TID) along with height-frequency distortion modulates amplitude characteristics of signal. The characteristic depth of the modulation reaches 40 dB. The pronounced alternate vertical stripes typical for A-charts are likely to be associated with focusing properties of TID. In order to examine the space-time structure of TID able to induce such a focusing of the radio waves, we performed ray tracing simulations. We used geometrical-optics approximation, took magneto-ionic effects into account and prescribed electron density to be a stratified electron density profile on which an undulating disturbance was superimposed. This work was supported by the RFBR grant №14-05-00259-а.
Asymptotics of spinfoam amplitude on simplicial manifold: Lorentzian theory
NASA Astrophysics Data System (ADS)
Han, Muxin; Zhang, Mingyi
2013-08-01
This paper studies the large-j asymptotics of the Lorentzian Engle-Pereira-Rovelli-Livine (EPRL) spinfoam amplitude on a 4D simplicial complex with an arbitrary number of simplices. The asymptotics of the spinfoam amplitude is determined by the critical configurations. Here we show that, given a critical configuration in general, there exists a partition of the simplicial complex into three types of regions {R}_{Nondeg}, {R}_{{Deg{-}A}} and {R}_{{Deg{-}B}}, where the three regions are simplicial sub-complexes with boundaries. The critical configuration implies different types of geometries in different types of regions, i.e. (1) the critical configuration restricted to {R}_{Nondeg} implies a nondegenerate discrete Lorentzian geometry, (2) the critical configuration restricted to {R}_{{Deg{-}A}} is degenerate of type-A in our definition of degeneracy, but it implies a nondegenerate discrete Euclidean geometry in {R}_{{Deg{-}A}}, (3) the critical configuration restricted to {R}_{{Deg{-}B}} is degenerate of type-B, and it implies a vector geometry in {R}_{{Deg{-}B}}. With the critical configuration, we further make a subdivision of the regions {R}_{Nondeg} and {R}_{{Deg{-}A}} into sub-complexes (with boundaries) according to their Lorentzian/Euclidean oriented 4-volume V4(v) of the 4-simplices, such that sgn(V4(v)) is a constant sign on each sub-complex. Then in each sub-complex {R}_{Nondeg} or {R}_{{Deg{-}A}}, the spinfoam amplitude at the critical configuration gives the Regge action in a Lorentzian signature or an Euclidean signature respectively. The Regge action reproduced here contains a sign prefactor sgn(V4(v)) related to the oriented 4-volume of the 4-simplices. Therefore the Regge action reproduced here can be viewed as a discretized Palatini action with an on-shell connection. Finally, the asymptotic formula of the spinfoam amplitude is given by a sum of the amplitudes evaluated at all possible critical configurations, which are the products of the
On statistics of electric field amplitudes in Langmuir turbulence
NASA Astrophysics Data System (ADS)
Voshchepynets, Andrii; Volokitin, Alexander; Krasnoselskikh, Vladimir; Krafft, Catherine
2017-04-01
A systematic study of the properties of Langmuir wave turbulence generated by electron beams via bump-on-tail instabilities in strongly non-homogeneous plasmas is presented. A statistical analysis of the Langmuir waves' fields' amplitudes using numerical simulations based on two different theoretical models is performed : a probabilistic one and a dynamical one. The former describes the self-consistent dynamics of wave-particle and wave-wave interactions in inhomogeneous plasmas. The latter is a modified version of the standard quasi-linear theory which requires much less computational resources. To analyze the simulation data provided by the probabilistic model, a Pearson technique is used to classify the calculated probability distribution functions (PDFs) of the logarithm of the wave fields' intensities. It is demonstrated that the core parts of the PDFs belong to the Pearson types I, IV and VI distributions, depending on the spatial profiles of the density fluctuations, rather than to the normal distribution. Moreover it is shown that the high-amplitude parts of the PDFs follow power-law or exponential decay distributions, depending on the type of the corresponding cores' distributions. The PDFs of the fields' amplitudes calculated using the numerical simulations based on the dynamical model are in the whole consistent with those provided by the probabilistic model. Moreover, these simulations lead to a series of additional results. First, in the small fields' amplitudes' parts of the PDFs (i.e. in the linear stage of the system's evolution), an universal scaling parameter is found, with a value not depending on the average levels of the density fluctuations and of the Langmuir turbulence. Second, the PDFs are obtained in the presence of wave 28 decay processes, which are not taken into account in the probabilistic model. When those are weak, the PDFs show at large fields' amplitudes an exponential asymptotic behavior; during the time evolution, the
Positroid stratification of orthogonal Grassmannian and ABJM amplitudes
NASA Astrophysics Data System (ADS)
Kim, Joonho; Lee, Sangmin
2014-09-01
A novel understanding of scattering amplitudes in terms of on-shell diagrams and positive Grassmannian has been recently established for four dimensional Yang-Mills theories and three dimensional Chern-Simons theories of ABJM type. We give a detailed construction of the positroid stratification of orthogonal Grassmannian relevant for ABJM amplitudes. On-shell diagrams are classified by pairing of external particles. We introduce a combinatorial aid called `OG tableaux' and map each equivalence class of on-shell diagrams to a unique tableau. The on-shell diagrams related to each other through BCFW bridging are naturally grouped by the OG tableaux. Introducing suitably ordered BCFW bridges and positive coordinates, we construct the complete coordinate charts to cover the entire positive orthogonal Grassmannian for arbitrary number of external particles. The graded counting of OG tableaux suggests that the positive orthogonal Grassmannian constitutes a combinatorial polytope.
Amplitude analysis of resonant production in three pions
NASA Astrophysics Data System (ADS)
Jackura, Andrew; Mikhasenko, Mikhail; Szczepaniak, Adam
2016-11-01
We present some results on the analysis of three pion resonances. The analyses are motivated by the recent release of the largest data set on diffractively produced three pions by the COMPASS collaboration. We construct reaction amplitudes that satisfy fundamental S -matrix principles, which allows the use of models that have physical constraints to be used in fitting data. The models are motivated by the isobar model that satisfy unitarity constraints. The model consist of a Deck production amplitude with which final state interactions are constrained by unitarity. We employ the isobar model where two of the pions form a quasi-stable particle. The analysis is performed in the high-energy, single Regge limit. We specifically discuss the examples of the three pion JPC = 2-+ resonance in the ρπ and f2π channels.
CESR feedback system using a constant amplitude pulser
Codner, G.; Billing, M.; Meller, R.; Patten, R.; Rogers, J.; Sikora, J.; Sloand, M.; Strohman, C.
1998-12-10
Particle beam feedback system using constant-amplitude, 1000 V, 12 ns pulses has been built to provide longitudinal and horizontal feedback for stabilizing 14 ns spaced bunches for use in CESR (Cornell Electron Storage Ring). The pulse rate is modulated to obtain proportional amplitude control and the pulse arrival time is modulated to obtain both positive and negative kicks. The average repetition rate is limited by pulser power dissipation, but the instantaneous rate may be increased to full duty cycle for short periods of time to handle transients. The pulser drives a 50-ohm stripline kicker so the equivalent peak power at 1000 V is 10 kW. The characteristics of the pulser and its modulator will be described along with the system's operation.
Harmonic R matrices for scattering amplitudes and spectral regularization.
Ferro, Livia; Łukowski, Tomasz; Meneghelli, Carlo; Plefka, Jan; Staudacher, Matthias
2013-03-22
Planar N = 4 supersymmetric Yang-Mills theory appears to be integrable. While this allows one to find this theory's exact spectrum, integrability has hitherto been of no direct use for scattering amplitudes. To remedy this, we deform all scattering amplitudes by a spectral parameter. The deformed tree-level four-point function turns out to be essentially the one-loop R matrix of the integrable N = 4 spin chain satisfying the Yang-Baxter equation. Deformed on-shell three-point functions yield novel three-leg R matrices satisfying bootstrap equations. Finally, we supply initial evidence that the spectral parameter might find its use as a novel symmetry-respecting regulator replacing dimensional regularization. Its physical meaning is a local deformation of particle helicity, a fact which might be useful for a much larger class of nonintegrable four-dimensional field theories.
Light-induced suppression of endogenous circadian amplitude in humans
NASA Technical Reports Server (NTRS)
Jewett, Megan; Czeisler, Charles A.; Kronauer, Richard E.
1991-01-01
A recent demonstration that the phase of the human circadian pacemaker could be inverted using an unconventional three-cycle stimulus has led to an investigation of whether critically timed exposure to a more moderate stimulus could drive that oscillator toward its singularity, a phaseless position at which the amplitude of circadian oscillation is zero. It is reported here that exposure of humans to fewer cycles of bright light, centered around the time at which the human circadian pacemaker is most sensitive to light-induced phase shifts, can markedly attenuate endogenous cicadian amplitude. In some cases this results in an apparent loss of rhythmicity, as expected to occur in the region of singularity.
Towards an amplitude analysis of exclusive. gamma gamma. processes
Pennington, M.R.
1988-06-01
The potential of two photon processes to shed light on the parton content of resonances, we maintain, can only be realized in practice by moving towards an Amplitude Analysis of experimental data. By using the process ..gamma gamma.. ..-->.. ..pi pi.. as an example, the way to do this is discussed. Presently claimed uncertainties in the ..gamma gamma.. width of even the well-known f/sub 2/ (1270) are shown to be over-optimistic and the fitted couplings of the overlapping scalar states in the 1 GeV region meaningless. Only the use of Amplitude Analysis techniques on the new higher statistics data from SLAC and DESY can resolve these uncertainties and lead to definite and significant results. 37 refs., 18 figs.
Vertex amplitudes in spin foam loop quantum cosmology
NASA Astrophysics Data System (ADS)
Craig, David
2016-03-01
We discuss properties of the vertex expansion for homogeneous, isotropic loop quantum cosmological models sourced by a massless, minimally coupled scalar field, which in this model plays the role of an internal matter ``clock''. We show that the vertex expansion, first written down by Ashtekar, Campiglia and Henderson, must be thought of as a short-time expansion in the sense that the amplitude for volume transitions is constrained both by the order of the expansion and by the elapsed scalar field. To calculate the amplitude for significant volume changes or between large differences in the value of the scalar field requires the expansion be evaluated to very high order. This contribution describes work in collaboration with P. Singh.
3D dynamic holographic display by modulating complex amplitude experimentally.
Li, Xin; Liu, Juan; Jia, Jia; Pan, Yijie; Wang, Yongtian
2013-09-09
Complex amplitude modulation method is presented theoretically and performed experimentally for three-dimensional (3D) dynamic holographic display with reduced speckle using a single phase-only spatial light modulator. The determination of essential factors is discussed based on the basic principle and theory. The numerical simulations and optical experiments are performed, where the static and animated objects without refinement on the surfaces and without random initial phases are reconstructed successfully. The results indicate that this method can reduce the speckle in reconstructed images effectively; furthermore, it will not cause the internal structure in the reconstructed pixels. Since the complex amplitude modulation is based on the principle of phase-only hologram, it does not need the stringent alignment of pixels. This method can be used for high resolution imaging or measurement in various optical areas.
Amplitude or Higgs modes in d-wave superconductors
NASA Astrophysics Data System (ADS)
Barlas, Yafis; Varma, C. M.
2013-02-01
In Lorentz-invariant systems spontaneously broken gauge symmetry results in three types of fundamental excitations: density excitations, Higgs bosons (amplitude modes), and Goldstone bosons (phase modes). The density and phase modes are coupled by electromagnetic interactions while the amplitude modes are not. In s-wave superconductors, the Higgs mode, which can be observed only under special conditions, has been detected. We show that unconventional d-wave superconductors, such as the high-temperature cuprate superconductors, should have a rich assortment of Higgs bosons, each in a different irreducible representation of the point-group symmetry of the lattice. We also show that these modes have a characteristic singular spectral structure and discuss conditions for their observability.
Phase-shifting interferometry by wave amplitude modulation.
Meneses-Fabian, Cruz; Rivera-Ortega, Uriel
2011-07-01
A new method for phase-shifting interferometry based on wave amplitude modulation is proposed and discussed. This proposal is based on the interference of three waves, where two waves attend as two reference waves and the other wave attends as a probe wave. Thereby, three interference terms are obtained, but because a phase difference of π/2 between the two references is kept constant, one of the three terms will be dropped, while the two remaining will be put in quadrature. Under these conditions, the resulting pattern is mathematically modeled by an interferogram of two waves, where an additional phase is given by the amplitude variations of the reference waves. In this Letter, both a theoretical model and some numerical simulations are presented.
Light-induced suppression of endogenous circadian amplitude in humans
NASA Technical Reports Server (NTRS)
Jewett, Megan; Czeisler, Charles A.; Kronauer, Richard E.
1991-01-01
A recent demonstration that the phase of the human circadian pacemaker could be inverted using an unconventional three-cycle stimulus has led to an investigation of whether critically timed exposure to a more moderate stimulus could drive that oscillator toward its singularity, a phaseless position at which the amplitude of circadian oscillation is zero. It is reported here that exposure of humans to fewer cycles of bright light, centered around the time at which the human circadian pacemaker is most sensitive to light-induced phase shifts, can markedly attenuate endogenous cicadian amplitude. In some cases this results in an apparent loss of rhythmicity, as expected to occur in the region of singularity.
Tunable metasurfaces via subwavelength phase shifters with uniform amplitude
NASA Astrophysics Data System (ADS)
Colburn, Shane; Zhan, Alan; Majumdar, Arka
2017-01-01
Metasurfaces with tunable spatial phase functions could benefit numerous applications. Currently, most approaches to tuning rely on mechanical stretching which cannot control phase locally, or by modulating the refractive index to exploit rapid phase changes with the drawback of also modulating amplitude. Here, we propose a method to realize phase modulation at subwavelength length scales while maintaining unity amplitude. Our device is inspired by an asymmetric Fabry-Perot resonator, with pixels comprising a scattering nanopost on top of a distributed Bragg reflector, capable of providing a nearly 2π nonlinear phase shift with less than 2% refractive index modulation. Using the designed pixels, we simulate a tunable metasurface composed of an array of moderately coupled nanopost resonators, realizing axicons, vortex beam generators, and aspherical lenses with both variable focal length and in-plane scanning capability, achieving nearly diffraction-limited performance. The experimental feasibility of the proposed method is also discussed.
Tunable metasurfaces via subwavelength phase shifters with uniform amplitude.
Colburn, Shane; Zhan, Alan; Majumdar, Arka
2017-01-05
Metasurfaces with tunable spatial phase functions could benefit numerous applications. Currently, most approaches to tuning rely on mechanical stretching which cannot control phase locally, or by modulating the refractive index to exploit rapid phase changes with the drawback of also modulating amplitude. Here, we propose a method to realize phase modulation at subwavelength length scales while maintaining unity amplitude. Our device is inspired by an asymmetric Fabry-Perot resonator, with pixels comprising a scattering nanopost on top of a distributed Bragg reflector, capable of providing a nearly 2π nonlinear phase shift with less than 2% refractive index modulation. Using the designed pixels, we simulate a tunable metasurface composed of an array of moderately coupled nanopost resonators, realizing axicons, vortex beam generators, and aspherical lenses with both variable focal length and in-plane scanning capability, achieving nearly diffraction-limited performance. The experimental feasibility of the proposed method is also discussed.
Dielectric interfaces and mirrors in the amplitude and phase representation
NASA Astrophysics Data System (ADS)
Fernández-Guasti, M.
2015-02-01
Reflection and refraction at an abrupt dielectric interface at normal incidence are evaluated using an amplitude and phase (amph) formalism. The optical properties of a stack with two quarter-wavelength layers are then calculated. The characteristics of a mirror constructed with quarter-wavelength layers are discussed using the amplitude and phase representation. Floquet nonlinear theorem is invoked to describe the multi-layered system. Results are consistent with Fresnel formulae and conventional matrix methods for stratified periodic media. However, the amph formalism offers several advantages: (i) it is capable of showing the field properties as it propagates though the stack, (ii) it gives a lucid physical insight because the variables involved have a clear physical meaning, and (iii) the mathematical description is simple.
Analytic Evolution of Singular Distribution Amplitudes in QCD
Radyushkin, Anatoly V.; Tandogan Kunkel, Asli
2014-03-01
We describe a method of analytic evolution of distribution amplitudes (DA) that have singularities, such as non-zero values at the end-points of the support region, jumps at some points inside the support region and cusps. We illustrate the method by applying it to the evolution of a flat (constant) DA, anti-symmetric at DA and then use it for evolution of the two-photon generalized distribution amplitude. Our approach has advantages over the standard method of expansion in Gegenbauer polynomials, which requires infinite number of terms in order to accurately reproduce functions in the vicinity of singular points, and over a straightforward iteration of an initial distribution with evolution kernel. The latter produces logarithmically divergent terms at each iteration, while in our method the logarithmic singularities are summed from the start, which immediately produces a continuous curve, with only one or two iterations needed afterwards in order to get rather precise results.
Interaction imaging with amplitude-dependence force spectroscopy.
Platz, Daniel; Forchheimer, Daniel; Tholén, Erik A; Haviland, David B
2013-01-01
Knowledge of surface forces is the key to understanding a large number of processes in fields ranging from physics to material science and biology. The most common method to study surfaces is dynamic atomic force microscopy (AFM). Dynamic AFM has been enormously successful in imaging surface topography, even to atomic resolution, but the force between the AFM tip and the surface remains unknown during imaging. Here we present a new approach that combines high-accuracy force measurements and high-resolution scanning. The method, called amplitude-dependence force spectroscopy (ADFS), is based on the amplitude dependence of the cantilever's response near resonance and allows for separate determination of both conservative and dissipative tip-surface interactions. We use ADFS to quantitatively study and map the nano-mechanical interaction between the AFM tip and heterogeneous polymer surfaces. ADFS is compatible with commercial atomic force microscopes and we anticipate its widespread use in taking AFM toward quantitative microscopy.
Einstein-Yang-Mills scattering amplitudes from scattering equations
NASA Astrophysics Data System (ADS)
Cachazo, Freddy; He, Song; Yuan, Ellis Ye
2015-01-01
We present the building blocks that can be combined to produce tree-level S-matrix elements of a variety of theories with various spins mixed in arbitrary dimensions. The new formulas for the scattering of n massless particles are given by integrals over the positions of n points on a sphere restricted to satisfy the scattering equations. As applications, we obtain all single-trace amplitudes in Einstein-Yang-Mills (EYM) theory, and generalizations to include scalars. Also in EYM but extended by a B-field and a dilaton, we present all double-trace gluon amplitudes. The building blocks are made of Pfaffians and Parke-Taylor-like factors of subsets of particle labels.
Small-amplitude supersolitons near supercritical plasma compositions
NASA Astrophysics Data System (ADS)
Olivier, Carel P.; Verheest, Frank; Maharaj, Shimul K.
2017-08-01
Supercritical plasma compositions in parameter space are considered for a general fluid model consisting of an arbitrary number of species. This is done by applying a Taylor series expansion of the Sagdeev potential about the acoustic speed and the equilibrium electrostatic potential. A novel finding in this study is the description of small-amplitude supersolitons. Our analysis allows us to determine the plasma compositional criteria for such structures, as well as lower and upper bounds of their velocities and amplitudes. We therefore establish an interesting link between supercritical plasma compositions and the existence of supersolitons. The results are illustrated via a case study where plasmas consisting of cold ions and two Boltzmann electron species are considered.
Molecular dynamics simulation of amplitude modulation atomic force microscopy.
Hu, Xiaoli; Egberts, Philip; Dong, Yalin; Martini, Ashlie
2015-06-12
Molecular dynamics (MD) simulations were used to model amplitude modulation atomic force microscopy (AM-AFM). In this novel simulation, the model AFM tip responds to both tip-substrate interactions and to a sinusoidal excitation signal. The amplitude and phase shift of the tip oscillation observed in the simulation and their variation with tip-sample distance were found to be consistent with previously reported trends from experiments and theory. These simulation results were also fit to an expression enabling estimation of the energy dissipation, which was found to be smaller than that in a corresponding experiment. The difference was analyzed in terms of the effects of tip size and substrate thickness. Development of this model is the first step toward using MD to gain insight into the atomic-scale phenomena that occur during an AM-AFM measurement.
Full colour for loop amplitudes in Yang-Mills theory
NASA Astrophysics Data System (ADS)
Ochirov, Alexander; Page, Ben
2017-02-01
We present a general method to account for full colour dependence Yang-Mills amplitudes at loop level. The method fits most naturally into the framework of multi-loop integrand reduction and in a nutshell amounts to consistently retaining the colour structures of the unitarity cuts from which the integrand is gradually constructed. This technique has already been used in the recent calculation of the two-loop five-gluon amplitude in pure Yang-Mills theory with all positive helicities, JHEP 10 (2015) 064. In this note, we give a careful exposition of the method and discuss its connection to looplevel Kleiss-Kuijf relations. We also explore its implications for cancellation of nontrivial symmetry factors at two loops. As an example of its generality, we show how it applies to the three-loop case in supersymmetric Yang-Mills case.
Stability of a steady, large amplitude whistler wave.
NASA Technical Reports Server (NTRS)
Palmadesso, P. J.; Schmidt, G.
1972-01-01
Study of the behavior of weak electrostatic waves in a collisionless magnetoplasma supporting a steady large amplitude whistler wave. All waves are assumed to propagate parallel to a uniform background magnetic field B sub zero. In the presence of the whistler wave fields each particle executes an oscillatory motion parallel to B sub zero, in addition to a translation along B sub zero and transverse motions. This oscillation causes the Landau resonance to be replaced by a series of new resonances between particles and the electrostatic modes. A distribution function for the perturbed plasma is constructed by solving the Vlasov equation, linearized in the electrostatic wave amplitudes. A dispersion relation is obtained and solved approximately for the growth/damping rate of the perturbations. Growing electrostatic modes are found to be approximately uncoupled. Trapped particles have a strong influence on the stability of the system.
Gain degradation and amplitude scintillation due to tropospheric turbulence
NASA Technical Reports Server (NTRS)
Theobold, D. M.; Hodge, D. B.
1978-01-01
It is shown that a simple physical model is adequate for the prediction of the long term statistics of both the reduced signal levels and increased peak-to-peak fluctuations. The model is based on conventional atmospheric turbulence theory and incorporates both amplitude and angle of arrival fluctuations. This model predicts the average variance of signals observed under clear air conditions at low elevation angles on earth-space paths at 2, 7.3, 20 and 30 GHz. Design curves based on this model for gain degradation, realizable gain, amplitude fluctuation as a function of antenna aperture size, frequency, and either terrestrial path length or earth-space path elevation angle are presented.
Amplitude death in coupled robust-chaos oscillators
NASA Astrophysics Data System (ADS)
Palazzi, M. J.; Cosenza, M. G.
2014-12-01
We investigate the synchronization behavior of a system of globally coupled, continuous-time oscillators possessing robust chaos. The local dynamics corresponds to the Shimizu-Morioka model where the occurrence of robust chaos in a region of its parameter space has been recently discovered. We show that the global coupling can drive the oscillators to synchronization into a fixed point created by the coupling, resulting in amplitude death in the system. The existence of robust chaos allows to introduce heterogeneity in the local parameters, while guaranteeing the functioning of all the oscillators in a chaotic mode. In this case, the system reaches a state of oscillation death, with coexisting clusters of oscillators in different steady states. The phenomena of amplitude death or oscillation death in coupled robust-chaos flows could be employed as mechanisms for stabilization and control in systems that require reliable operation under chaos.
Excitation of nearly steady finite-amplitude barotropic waves
NASA Technical Reports Server (NTRS)
Hou, A. Y.; Farrell, B. F.
1986-01-01
An exact nonlinear stationary solution is obtained for barotropic waves in a beta-plane channel and it is shown that it can be excited under a range of initial conditions. Results show that a finite-amplitude wave in a constant shear flow, given an initial phase tilt against the shear and a sufficient initial amplitude, interacts with the mean flow to produce a nearly steady state close to the exact stationary solution. This equilibration process involves nonlinear transients; in particular, as the flow equilibrates, the emergence of critical levels is accompanied by the neutralization of local mean vorticity gradients at these levels, thus allowing the solution to attain a nonsingular modal structure.
Tunable metasurfaces via subwavelength phase shifters with uniform amplitude
Colburn, Shane; Zhan, Alan; Majumdar, Arka
2017-01-01
Metasurfaces with tunable spatial phase functions could benefit numerous applications. Currently, most approaches to tuning rely on mechanical stretching which cannot control phase locally, or by modulating the refractive index to exploit rapid phase changes with the drawback of also modulating amplitude. Here, we propose a method to realize phase modulation at subwavelength length scales while maintaining unity amplitude. Our device is inspired by an asymmetric Fabry-Perot resonator, with pixels comprising a scattering nanopost on top of a distributed Bragg reflector, capable of providing a nearly 2π nonlinear phase shift with less than 2% refractive index modulation. Using the designed pixels, we simulate a tunable metasurface composed of an array of moderately coupled nanopost resonators, realizing axicons, vortex beam generators, and aspherical lenses with both variable focal length and in-plane scanning capability, achieving nearly diffraction-limited performance. The experimental feasibility of the proposed method is also discussed. PMID:28054662
Nonrelativistic Dynamics of the Amplitude (Higgs) Mode in Superconductors.
Cea, T; Castellani, C; Seibold, G; Benfatto, L
2015-10-09
Despite the formal analogy with the Higgs particle, the amplitude fluctuations of the order parameter in weakly coupled superconductors do not identify a real mode with a Lorentz-invariant dynamics. Indeed, its resonance occurs at 2Δ_{0}, which coincides with the threshold 2E_{gap} for quasiparticle excitations that spoil any relativistic dynamics. Here we investigate the fate of the Higgs mode in the unconventional case where 2E_{gap} becomes larger than 2Δ_{0}, as due to strong coupling or strong disorder. We show that also in this situation, the amplitude fluctuations never identify a real mode at 2Δ_{0}, since such a "bosonic" limit is always reached via strong mixing with the phase fluctuations, which dominate the low-energy part of the spectrum. Our results have direct implications for the interpretation of the subgap optical absorption in disordered superconductors.
Infrared singularities of scattering amplitudes in perturbative QCD
Becher, Thomas; Neubert, Matthias
2013-11-01
An exact formula is derived for the infrared singularities of dimensionally regularized scattering amplitudes in massless QCD with an arbitrary number of legs, valid at any number of loops. It is based on the conjecture that the anomalous-dimension matrix of n-jet operators in soft-collinear effective theory contains only a single non-trivial color structure, whose coefficient is the cusp anomalous dimension of Wilson loops with light-like segments. Its color-diagonal part is characterized by two anomalous dimensions, which are extracted to three-loop order from known perturbative results for the quark and gluon form factors. This allows us to predict the three-loop coefficients of all 1/epsilon^k poles for an arbitrary n-parton scattering amplitudes, generalizing existing two-loop results.
Amplitude suppression and chaos control in epileptic EEG signals.
Majumdar, Kaushik; Myers, Mark H
2006-03-01
In this paper we have proposed a novel amplitude suppression algorithm for EEG signals collected during epileptic seizure. Then we have proposed a measure of chaoticity for a chaotic signal, which is somewhat similar to measuring sensitive dependence on initial conditions by measuring Lyapunov exponent in a chaotic dynamical system. We have shown that with respect to this measure the amplitude suppression algorithm reduces chaoticity in a chaotic signal (EEG signal is chaotic). We have compared our measure with the estimated largest Lyapunov exponent measure by the largelyap function, which is similar to Wolf's algorithm. They fit closely for all but one of the cases. How the algorithm can help to improve patient specific dosage titration during vagus nerve stimulation therapy has been outlined.
Vibrations of moderately thick shallow spherical shells at large amplitudes
NASA Astrophysics Data System (ADS)
Sathyamoorthy, M.
1994-04-01
A shallow shell theory is presented for the geometrically nonlinear analysis of moderately thick isotropic spherical shells. Effects of transverse shear deformation and rotatory inertia are included in the governing equations of motion by means of tracing constants. When these effects are ignored, the governing equations readily reduce to those applicable for thin shallow spherical shells. Solutions to the system of thick shell equations are obtained by means of Galerkin's method and the numerical Runge-Kutta procedure. Numerical results are presented for certain cases of shallow spherical shells considering different geometric shell parameters. Transverse shear and rotatory inertia effects are found to be important in linear as well as nonlinear responses of shallow spherical shells. The nonlinear frequency-amplitude behavior is of the softening type for shallow spherical shells and of the hardening type for circular plates. Frequency ratios are lower at any given amplitude when the effects of transverse shear and rotatory inertia are included in the analysis.
Pump pulse duration dependence of coherent phonon amplitudes in antimony
Misochko, O. V.
2016-08-15
Coherent optical phonons of A{sub 1k} and E{sub k} symmetry in antimony have been studied using the femtosecond pump–probe technique. By varying the pump-pulse duration and keeping the probe duration constant, it was shown that the amplitude of coherent phonons of both symmetries exponentially decreases with increasing pulse width. It was found that the amplitude decay rate for the fully symmetric phonons with larger frequency is greater than that of the doubly degenerate phonons, whereas the frequency and lifetime for coherent phonons of both symmetries do not depend on the pump-pulse duration. Based on this data, the possibility of separation between dynamic and kinematic contributions to the generation mechanism of coherent phonons is discussed.
Amplitude analysis of resonant production in three pions
Jackura, Andrew; Mikhasenko, Mikhail; Szczepaniak, Adam
2016-11-29
We present some results on the analysis of three pion resonances. The analyses are motivated by the recent release of the largest data set on diffractively produced three pions by the COMPASS collaboration. We construct reaction amplitudes that satisfy fundamental $S$-matrix principles, which allows the use of models that have physical constraints to be used in fitting data. The models are motivated by the isobar model that satisfy unitarity constraints. The model consist of a Deck production amplitude with which final state interactions are constrained by unitarity. We employ the isobar model where two of the pions form a quasi-stable particle. The analysis is performed in the high-energy, single Regge limit. We specifically discuss the examples of the three pion $J^{PC}=2^{-+}$ resonance in the $\\rho\\pi$ and $f_2\\pi$ channels.
The discovery of an extremely low amplitude Cepheid?
NASA Technical Reports Server (NTRS)
Butler, R. P.
1992-01-01
Extremely low amplitude periodic radial velocity variations are found for HR 7796 (F8 Ib), thought to be a non-Cepheid in (or near) the instability strip. Two and one-half complete cycles have been monitored over three observing runs. The period is found to be 11.874 +/- 0.02 days. Observations of the reference star HR 509 (G8 V) taken on the same nights show no periodicities and a scatter of just 20 m/s. A first-order approximation shows that HR 7796 does appear to follow the Cepheid period-luminosity relation. If HR 7796 is a Cepheid, it is the smallest amplitude Cepheid by more than an order of magnitude.
Finite-amplitude solutions in rotating Hagen-Poiseuille flow
NASA Astrophysics Data System (ADS)
Pier, Benoît; Kumar, Abhishek; Govindarajan, Rama
2015-11-01
While the pipe Poiseuille base flow is linearly stable at all Reynolds numbers, a small amount of rotation of the pipe around its axis induces linear instability beyond a low critical Reynolds number Rc ~= 83 [Pedley, J. Fluid Mech. 1969]. More recently [Fernandez-Feria and del Pino, Phys. Fluids 2002], this configuration has been shown to become absolutely unstable at Reynolds numbers of the same order of magnitude. Using direct numerical simulations, we investigate here finite-amplitude solutions resulting from saturation of exponentially growing small-amplitude initial perturbations. The base flow depends on two dynamical parameters (axial Reynolds number and rotation rate) and the initial perturbation is characterized by its axial wavenumber and its azimuthal mode number. The range of nonlinear waves prevailing in this configuration, the associated nonlinear dispersion relation and the spatial structure of these solutions are systematically obtained by exploring the parameter space. Funding from CEFIPRA is gratefully acknowledged.
Photoinduced Enhancement of the Charge Density Wave Amplitude
NASA Astrophysics Data System (ADS)
Singer, A.; Patel, S. K. K.; Kukreja, R.; Uhlíř, V.; Wingert, J.; Festersen, S.; Zhu, D.; Glownia, J. M.; Lemke, H. T.; Nelson, S.; Kozina, M.; Rossnagel, K.; Bauer, M.; Murphy, B. M.; Magnussen, O. M.; Fullerton, E. E.; Shpyrko, O. G.
2016-07-01
Symmetry breaking and the emergence of order is one of the most fascinating phenomena in condensed matter physics. It leads to a plethora of intriguing ground states found in antiferromagnets, Mott insulators, superconductors, and density-wave systems. Exploiting states of matter far from equilibrium can provide even more striking routes to symmetry-lowered, ordered states. Here, we demonstrate for the case of elemental chromium that moderate ultrafast photoexcitation can transiently enhance the charge-density-wave (CDW) amplitude by up to 30% above its equilibrium value, while strong excitations lead to an oscillating, large-amplitude CDW state that persists above the equilibrium transition temperature. Both effects result from dynamic electron-phonon interactions, providing an efficient mechanism to selectively transform a broad excitation of the electronic order into a well-defined, long-lived coherent lattice vibration. This mechanism may be exploited to transiently enhance order parameters in other systems with coupled degrees of freedom.
Multiplexing technique using amplitude-modulated chirped fiber Bragg gratings
NASA Astrophysics Data System (ADS)
Wong, Allan C. L.; Childs, Paul A.; Peng, Gang-Ding
2007-07-01
We propose a new multiplexing technique using amplitude-modulated chirped fiber Bragg gratings that have an identical center Bragg wavelength. Each grating is inscribed with a unique amplitude modulation that allows them to be multiplexed with complete overlapping within a certain bandwidth. To demodulate the multiplexed signal, the discrete wavelet transform is employed. Concurrently, a wavelet denoising technique is used to reduce the noise. This proposed multiplexing technique has been verified through strain measurements. Experimental results showed that for strains applied up to 1250 μɛ the absolute error and cross-talk are within ±20 μɛ and 16 μɛ, respectively. A strain resolution of 4 μɛ is obtained.
Small-amplitude viscous motion on arbitrary potential flows
NASA Astrophysics Data System (ADS)
Goldstein, M. E.
1984-02-01
This paper is concerned with small-amplitude, unsteady, vortical and entropic motion imposed on steady potential flows. It is restricted to the case where the spatial scale of the unsteady motion is small compared to that of the mean flow. Under such conditions, the unsteady motion may be influenced by viscosity even if the mean flow is not. An exact high-frequency (small-wavelength) solution is obtained for the small-amplitude viscous motion imposed on a steady potential flow. It generalizes the one obtained by Pearson (1959) for the homogeneous-strain case to the case of quasi-homogeneous strain. This result is used to study the effect of viscosity on rapidly distorted turbulent flows. Specific numerical results are given for a turbulent flow near a two-dimensional stagnation point.
K- nuclear potentials based on chiral meson-baryon amplitudes
NASA Astrophysics Data System (ADS)
Mareš, J.; Cieplý, A.; Gazda, D.; Friedman, E.; Gal, A.
2012-09-01
K- nuclear optical potentials are constructed from in-medium subthreshold K¯N scattering amplitudes within a chirally motivated coupled-channel model. We demonstrate how the strong energy and density dependence of the scattering amplitudes at and below threshold leads to a deep K- nuclear potential VK- for kaonic atoms and K- nuclear quasibound states. Selfconsistent evaluations yield K- potential depths -ReVK- (ρ0) of order 100 MeV. Allowing for K- NN absorption, better agreement with K- atoms data is achieved, leading to increased potential depths, -ReVK- (ρ0) ˜ 175 MeV, in accord with density dependent potentials obtained in purely phenomenological fits. Self consistent dynamical calculations of K- nuclear quasibound states are reported and discussed, as well.
K+-nucleus potentials from K+-nucleon amplitudes
NASA Astrophysics Data System (ADS)
Friedman, E.
2016-10-01
Optical potentials for K+-nucleus interactions are constructed from K+-nucleon amplitudes using recently developed algorithm based on K+-N kinematics in the nuclear medium. With the deep penetration of K+ mesons into the nucleus at momenta below 800 MeV / c it is possible to test this approach with greater sensitivity than hitherto done with K- and pions. The energy-dependence of experimental reaction and total cross sections on nuclei is better reproduced with this approach compared to fixed-energy amplitudes. The inclusion of Pauli correlations in the medium also improves the agreement between calculation and experiment. The absolute scale of the cross sections is reproduced very well for 6Li but for C, Si and Ca calculated cross sections are (23 ± 4)% smaller than experiment, in agreement with earlier analyses. Two phenomenological models that produce such missing strength suggest that the imaginary part of the potential needs about 40% enhancement.
Geomagnetic Activity Indicates Large Amplitude for Sunspot Cycle 24
NASA Technical Reports Server (NTRS)
Hathaway, D. H.; Wilson, R. M.
2006-01-01
The level of geomagnetic activity near the time of solar activity minimum has been shown to be a reliable indicator for the amplitude of the following solar activity maximum. The geomagnetic activity index aa can be split into two components: one associated with solar flares, prominence eruptions, and coronal mass ejections which follows the solar activity cycle and a second component associated with recurrent high speed solar wind streams which is out of phase with the solar activity cycle. This second component often peaks before solar activity minimum and has been one of the most reliable indicators for the amplitude of the following maximum. The size of the recent maximum in this second component indicates that solar activity cycle 24 will be much higher than average - similar in size to cycles 21 and 22.
Frequency and amplitude stabilization in MEMS and NEMS oscillators
Chen, Changyao; Lopez, Omar Daniel; Czaplewski, David A.
2017-06-14
This invention comprises a nonlinear micro- and nano-mechanical resonator that can maintain frequency of operation and amplitude of operation for a period of time after all external power has been removed from the device. Utilizing specific nonlinear dynamics of the micromechanical resonator, mechanical energy at low frequencies can be input and stored in higher frequencies modes, thus using the multiple degrees of freedom of the resonator to extend its energy storage capacity. Furthermore, the energy stored in multiple vibrational modes can be used to maintain the resonator oscillating for a fixed period of time, even without an external power supply. This is the first demonstration of an "autonomous" frequency source that can maintain a constant frequency and vibrating amplitude when no external power is provided, making it ideal for applications requiring an oscillator in low power, or limited and intermittent power supplies.
Phase, amplitude, and polarization microscopy with a sampling field sensor.
Tumbar, Remy
2008-07-01
I describe an improved implementation of a previously reported interferometric device, the sampling field sensor (SFS) [Appl. Opt.47, B32-B43 (2008)]. It provides X, Y, and XY shearing interferometric information simultaneously (space multiplexed) with amplitude and polarization information while using time-multiplexed phase shifting. Its simple common-path configuration makes it compact and vibration insensitive, as demonstrated by the ~lambda/125 phase estimation repeatability that was below the coherent noise floor (estimated at ~lambda/50). The SFS may be viewed as an efficient, robust and accurate full-field optical-digital interface, easy to integrate with traditional imaging systems. This is demonstrated by using the sensor as the focal plane array of a transmitted-light microscope in a straightforward setup using an illumination path polarization phase shifter. This work is focused on a qualitative demonstration and presents phase, amplitude, and polarization images of different types of human cheek cells and Caenorhabditiselegans larvae.
BPS amplitudes, helicity supertraces and membranes in M-theory
NASA Astrophysics Data System (ADS)
Wit, B. d.; Lüst, D.
2000-03-01
We study BPS dominated loop amplitudes in M-theory on T2. For this purpose we generalize the concept of helicity supertraces to nine spacetime dimensions. These traces distinguish between various massive supermultiplets and appear as coefficients in their one-loop contributions to n-graviton scattering amplitudes. This can be used to show that only ultrashort BPS multiplets contribute to the R4 term in the effective action, which was first computed by Green, Gutperle and Vanhove. There are two inequivalent ultrashort BPS multiplets which describe the Kaluza-Klein states and the wrapped membranes that cover the torus a number of times. From the perspective of the type-II strings they correspond to momentum and winding states and D0 or D1 branes.
Abnormal selective attention normalizes P3 amplitudes in PDD.
Hoeksma, Marco R; Kemner, Chantal; Kenemans, J Leon; van Engeland, Herman
2006-07-01
This paper studied whether abnormal P3 amplitudes in PDD are a corollary of abnormalities in ERP components related to selective attention in visual and auditory tasks. Furthermore, this study sought to clarify possible age differences in such abnormalities. Children with PDD showed smaller P3 amplitudes than controls, but no abnormalities in selective attention. Adolescents with PDD showed abnormal selective attention, as reflected by larger auditory Processing Negativity (PN) and visual N2b, but no P3 abnormalities. Dipole localizations revealed that the locations of PN generators in subjects with PDD differed from controls. It was concluded that the abnormalities in selective attention in adolescents with PDD have a normalizing effect on P3, and possibly act as a compensatory process.
Optical resolution improvement by nanoparticle's amplitude and phase pattern
NASA Astrophysics Data System (ADS)
Hong, Xin; Sun, Xiaoyaun
2016-11-01
Optical detection of nanoparticle with ultra-high sensitivity plays an important role in bio- / nano- and their relative research fields. In our recently developed method, each single particle exhibits unique 4-lobes pattern both in the amplitude and phase images respectively, based on which we explored the possibility of resolution improvement by a particle pair. In this paper two polystyrene beads at the diameter of 100nm were employed with the gap distance ranging from 100-400nm. The amplitude and phase images of the particle pair were simulated by FDTD solver. The images are sensitive to geometrical parameters of the two particles, such as gap distance and direction. The simulation results lead to a resolution of 100nm.
TASI 2014: Lectures on Gauge and Gravity Amplitude Relations
NASA Astrophysics Data System (ADS)
Carrasco, John Joseph M.
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 multiloop integrand construction.
Renormalization of position space amplitudes in a massless QFT
NASA Astrophysics Data System (ADS)
Todorov, Ivan
2017-03-01
Ultraviolet renormalization of position space massless Feynman amplitudes has been shown to yield associate homogeneous distributions. Their degree is determined by the degree of divergence while their order—the highest power of logarithm in the dilation anomaly—is given by the number of (sub)divergences. In the present paper we review these results and observe that (convergent) integration over internal vertices does not alter the total degree of (superficial) ultraviolet divergence. For a conformally invariant theory internal integration is also proven to preserve the order of associate homogeneity. The renormalized 4-point amplitudes in the φ4 theory (in four space-time dimensions) are written as (non-analytic) translation invariant functions of four complex variables with calculable conformal anomaly. Our conclusion concerning the (off-shell) infrared finiteness of the ultraviolet renormalized massless φ4 theory agrees with the old result of Lowenstein and Zimmermann [23].
On-Shell Unitarity Bootstrap for QCD Amplitudes
Berger, Carola F.; Bern, Zvi; Dixon, Lance J.; Forde, Darren; Kosower, David A.
2006-10-17
Seeking and measuring new physics at the imminent Large Hadron Collider (LHC) will require extensive calculations of high-multiplicity backgrounds in perturbative QCD to next-to-leading order (NLO). The Les Houches 2005 workshop defined a target list, reproduced in table 1, for theorists to attack. In addition to the processes in the table, one would also like to compute processes such as W, Z + 4 jets, which are important backgrounds to searches for supersymmetry and other models of new electroweak physics. Such computations require one-loop amplitudes with seven external particles, including the vector boson, as depicted in figure 1. These are challenging calculations and Feynman-diagrammatic computations have only recently reached six-point amplitudes. Some of this progress has been described in this conference.
Symbol rate identification for auxiliary amplitude modulation optical signal
NASA Astrophysics Data System (ADS)
Wei, Junyu; Dong, Zhi; Huang, Zhiping; Zhang, Yimeng
2016-09-01
In this paper, we creatively propose and demonstrate a method for symbol rate identification (SRI) of auxiliary amplitude modulation (AAM) optical signal based on asynchronous delay-tap sampling (ADTS) and average magnitude difference function (AMDF). The method can accurately estimate symbol rate and has large transmission impairments tolerance. Furthermore, it can be realized in the digital signal processor (DSP) with low logical resources because of multiplication-free. In order to improve the accuracy of SRI, the peak to valley ratio (PTVR) of AMDF is introduced into our method for blind chromatic dispersion (CD) compensation. The results of the numerical simulations show that the overall maximum SRI error is smaller 0.079% for return-to-zero (RZ) on-off keying (OOK), RZ differential phase-shift keying (DPSK), RZ differential quadrature phase-shift keying (DQPSK) and RZ 16-ary quadrature amplitude modulation (QAM) with 50% duty cycles.
Detailed Study of Amplitude Nonlinearity in Piezoresistive Force Sensors
Paredes-Madrid, Leonel; Emmi, Luis; Garcia, Elena; de Santos, Pablo Gonzalez
2011-01-01
This article upgrades the RC linear model presented for piezoresistive force sensors. Amplitude nonlinearity is found in sensor conductance, and a characteristic equation is formulated for modeling its response under DC-driving voltages below 1 V. The feasibility of such equation is tested on four FlexiForce model A201-100 piezoresistive sensors by varying the sourcing voltage and the applied forces. Since the characteristic equation proves to be valid, a method is presented for obtaining a specific sensitivity in sensor response by calculating the appropriate sourcing voltage and feedback resistor in the driving circuit; this provides plug-and-play capabilities to the device and reduces the start-up time of new applications where piezoresistive devices are to be used. Finally, a method for bypassing the amplitude nonlinearity is presented with the aim of reading sensor capacitance. PMID:22164109
Detailed study of amplitude nonlinearity in piezoresistive force sensors.
Paredes-Madrid, Leonel; Emmi, Luis; Garcia, Elena; de Santos, Pablo Gonzalez
2011-01-01
This article upgrades the RC linear model presented for piezoresistive force sensors. Amplitude nonlinearity is found in sensor conductance, and a characteristic equation is formulated for modeling its response under DC-driving voltages below 1 V. The feasibility of such equation is tested on four FlexiForce model A201-100 piezoresistive sensors by varying the sourcing voltage and the applied forces. Since the characteristic equation proves to be valid, a method is presented for obtaining a specific sensitivity in sensor response by calculating the appropriate sourcing voltage and feedback resistor in the driving circuit; this provides plug-and-play capabilities to the device and reduces the start-up time of new applications where piezoresistive devices are to be used. Finally, a method for bypassing the amplitude nonlinearity is presented with the aim of reading sensor capacitance.
Radiation Belt Electron Dynamics Driven by Large-Amplitude Whistlers
NASA Technical Reports Server (NTRS)
Khazanov, G. V.; Tel'nikhin, A. A.; Kronberg, T. K.
2013-01-01
Acceleration of radiation belt electrons driven by oblique large-amplitude whistler waves is studied. We show analytically and numerically that this is a stochastic process; the intensity of which depends on the wave power modified by Bessel functions. The type of this dependence is determined by the character of the nonlinear interaction due to coupling between action and phase. The results show that physically significant quantities have a relatively weak dependence on the wave power.
Multifractal analysis based on amplitude extrema of intrinsic mode functions
NASA Astrophysics Data System (ADS)
Welter, Guilherme S.; Esquef, Paulo A. A.
2013-03-01
In this study, a multifractal formalism based on the empirical mode decomposition is proposed. Scaling exponents are estimated from statistical moments computed over a discrete set of multiresolution parameters, namely, the dominant amplitude coefficients, which are selected among the local maxima observed across the set of envelopes of the intrinsic mode functions. Analyses of synthetic fractal and multifractal processes demonstrate that the proposed technique is capable of overcoming the negative moment divergence problem, and is competitive with other multifractal formalisms.
Contextual modulation of N400 amplitude to lexically ambiguous words.
Titone, Debra A; Salisbury, Dean F
2004-08-01
Though much is known about the N400 component, an event-related EEG potential that is sensitive to semantic manipulations, it is unclear whether modulations of N400 amplitude reflect automatic processing, controlled processing, or both. We examined this issue using a semantic judgment task that manipulated local and global contextual cues. Word triplets (prime-noun-target, e.g., finance-bank-money) were sequentially presented on a computer screen (500 ms duration, 1000 ms stimulus onset asynchrony), in which the second word was a homograph. The first word (prime) created a neutral-, dominant-meaning- or subordinate-meaning-biased "global context," and the third word (target) created a dominant- or subordinate-biased "local context" that was either congruent or incongruent with the "global context" established by the first prime word. Participants were instructed to read all three words but to decide only whether the second and third words were semantically related. Event-related potentials (ERPs), specifically the N400, were recorded to the third terminal word. N400 amplitudes evoked by dominant meaning-related third words incongruent with the globally biased subordinate context (e.g., river-bridge-money) were significantly more negative than dominant endings in neutral contexts (e.g., taxi-bank-money), but not different from unrelated filler triplets. In addition, there was some indication that left hemisphere, temporal-parietal electrode sites were associated with greater N400 negativity for dominant targets in conflicting subordinate global contexts than homologous right hemisphere electrode sites, the latter of which showed significant activation to subordinate meanings in cooperating contexts. Thus, N400 amplitude was more affected by global than local context suggesting that controlled processes may take priority over automatic processes in modulating N400 amplitude, especially for left hemisphere electrode sites.
Microwave Power Combiners for Signals of Arbitrary Amplitude
NASA Technical Reports Server (NTRS)
Conroy, Bruce; Hoppe, Daniel
2009-01-01
Schemes for combining power from coherent microwave sources of arbitrary (unequal or equal) amplitude have been proposed. Most prior microwave-power-combining schemes are limited to sources of equal amplitude. The basic principle of the schemes now proposed is to use quasi-optical components to manipulate the polarizations and phases of two arbitrary-amplitude input signals in such a way as to combine them into one output signal having a specified, fixed polarization. To combine power from more than two sources, one could use multiple powercombining stages based on this principle, feeding the outputs of lower-power stages as inputs to higher-power stages. Quasi-optical components suitable for implementing these schemes include grids of parallel wires, vane polarizers, and a variety of waveguide structures. For the sake of brevity, the remainder of this article illustrates the basic principle by focusing on one scheme in which a wire grid and two vane polarizers would be used. Wire grids are the key quasi-optical elements in many prior equal-power combiners. In somewhat oversimplified terms, a wire grid reflects an incident beam having an electric field parallel to the wires and passes an incident beam having an electric field perpendicular to the wires. In a typical prior equal-power combining scheme, one provides for two properly phased, equal-amplitude signals having mutually perpendicular linear polarizations to impinge from two mutually perpendicular directions on a wire grid in a plane oriented at an angle of 45 with respect to both beam axes. The wires in the grid are oriented to pass one of the incident beams straight through onto the output path and to reflect the other incident beam onto the output path along with the first-mentioned beam.
Multipartite correlation degradation in amplitude-damping quantum channels
NASA Astrophysics Data System (ADS)
Batle, J.; Farouk, A.; Alkhambashi, M.; Abdalla, S.
2017-04-01
Multipartite correlations, such as entanglement and non-locality, are considered when particles pass through a generalized amplitude-damping channel. Results for pure and mixed states for two qubits suggest that initial mixed states can still be considered provided that their degree of mixture is low enough. Also, the ensuing small values for non-locality suggest that instances involving more than three parties cannot easily be considered for practical purposes.
Respiratory Amplitude Guided 4-Dimensional Magnetic Resonance Imaging
Hu, Yanle; Caruthers, Shelton D.; Low, Daniel A.; Parikh, Parag J.; Mutic, Sasa
2013-05-01
Purpose: To evaluate the feasibility of prospectively guiding 4-dimensional (4D) magnetic resonance imaging (MRI) image acquisition using triggers at preselected respiratory amplitudes to achieve T{sub 2} weighting for abdominal motion tracking. Methods and Materials: A respiratory amplitude-based triggering system was developed and integrated into a commercial turbo spin echo MRI sequence. Initial feasibility tests were performed on healthy human study participants. Four respiratory states, the middle and the end of inhalation and exhalation, were used to trigger 4D MRI image acquisition of the liver. To achieve T{sub 2} weighting, the echo time and repetition time were set to 75 milliseconds and 4108 milliseconds, respectively. Single-shot acquisition, together with parallel imaging and partial k-space imaging techniques, was used to improve image acquisition efficiency. 4D MRI image sets composed of axial or sagittal slices were acquired. Results: Respiratory data measured and logged by the MRI scanner showed that the triggers occurred at the appropriate respiratory levels. Liver motion could be easily observed on both 4D MRI image datasets by sensing either the change of liver in size and shape (axial) or diaphragm motion (sagittal). Both 4D MRI image datasets were T{sub 2}-weighted as expected. Conclusions: This study demonstrated the feasibility of achieving T{sub 2}-weighted 4D MRI images using amplitude-based respiratory triggers. With the aid of the respiratory amplitude-based triggering system, the proposed method is compatible with most MRI sequences and therefore has the potential to improve tumor-tissue contrast in abdominal tumor motion imaging.
The torus and the Klein bottle amplitude of permutation orbifolds
NASA Astrophysics Data System (ADS)
Kadar, Z.
2000-07-01
The torus and the Klein bottle amplitude coefficients are computed in permutation orbifolds of RCFT's in terms of the same quantities in the original theory and the twist group. An explicit expression is presented for the number of self conjugate primaries in the orbifold as a polynomial of the total number of primaries and the number of self conjugate ones in the parent theory. The formulae in the Z2 orbifold illustrate the general results.
Dynamical Selection of the Primordial Density Fluctuation Amplitude
Lehners, Jean-Luc; Steinhardt, Paul J.
2011-02-25
In inflationary models, the predicted amplitude of primordial density perturbations Q is much larger than the observed value ({approx}10{sup -5}) for natural choices of parameters. To explain the requisite exponential fine-tuning, anthropic selection is often invoked, especially in cases where microphysics is expected to produce a complex energy landscape. By contrast, we find examples of ekpyrotic models based on heterotic M theory for which dynamical selection naturally favors the observed value of Q.
Binary components of food reinforcement: Amplitude and persistence.
Epstein, Leonard H; Stein, Jeffrey S; Paluch, Rocco A; MacKillop, James; Bickel, Warren K
2017-08-26
Demand curves provide an index of how reinforcing a food is. Research examining the latent structure of alcohol and tobacco reinforcement identified two underlying components of reinforcement, amplitude and persistence. No research has assessed latent structure of food reinforcement and how these factors are related to BMI. Participants were 297 adults from two studies that completed food purchasing tasks to assess the following measures of relative reinforcing efficacy (RRE) of food: intensity (Q0): purchases made when the food was free or of very minimal price, Omax: maximum expenditure (purchases*price), Pmax: price point where maximum expenditure was observed, breakpoint: first price where 0 purchases are made, and demand elasticity (α): quantitative non-linear relationship between purchasing and price. Principal components analysis was used to examine the factor structure of RRE for food across samples and types of food. Both studies revealed two factor solutions, with Pmax, Omax, breakpoint and α loading on factor 1 (persistence) and intensity (Q0) loading on factor 2 (amplitude) across both high and low energy dense foods. Persistence reflects an aggregate measure of price sensitivity and amplitude reflects the preferred volume of consumption (how long vs. how much). The two factors accounted for between 91.7 and 95.4% of the variance in food reinforcement. Intensity for high energy dense foods predicted BMI for both studies (r = 0.18 and r = 0.22, p's < 0.05). The latent factor structure was similar across two significantly different independent samples and across low and high energy dense snack foods. In addition, the amplitude of the demand curve, but not persistence, was related to BMI. These results suggest specific aspects of food reinforcement that can be targeted to alter food intake. Copyright © 2017. Published by Elsevier Ltd.
Constraints on scattering amplitudes in multistate Landau-Zener theory
Sinitsyn, Nikolai A.; Lin, Jeffmin; Chernyak, Vladimir Y.
2017-01-30
Here, we derive a set of constraints, which we will call hierarchy constraints, on scattering amplitudes of an arbitrary multistate Landau-Zener model (MLZM). The presence of additional symmetries can transform such constraints into nontrivial relations between elements of the transition probability matrix. This observation can be used to derive complete solutions of some MLZMs or, for models that cannot be solved completely, to reduce the number of independent elements of the transition probability matrix.
Massive quark-gluon scattering amplitudes at tree level
NASA Astrophysics Data System (ADS)
Hall, Anthony
2008-01-01
Results for four-, five-, and six-parton tree amplitudes for massive quark-antiquark scattering with gluons are calculated using the recursion relations of Britto, Cachazo, Feng, and Witten. The required diagrams are generated using shifts of the momenta of a pair of massless legs to complex values. Checks verifying the calculations are described, and a simple formula for the shifted spinors of an internal gluon is presented.
Classical radiation zeros in gauge-theory amplitudes
Brown, R.W.; Kowalski, K.L.; Brodsky, S.J.
1983-08-01
The electromagnetic radiation from classical convection currents in relativistic n-particle collisions is shown to vanish in certain kinematical zones, due to complete destructive interference of the classical radiation patterns of the incoming and outgoing charged lines. We prove that quantum tree photon amplitudes vanish in the same zones, at arbitrary photon momenta including spin, seagull, and internal-line currents, provided only that the electromagnetic couplings and any other derivative couplings are as prescribed by renormalizable local gauge theory (spins < or =1). In particular, the existence of this new class of amplitude zeros requires the familiar gyromagnetic-ratio value g = 2 for all particles. The location of the zeros is spin independent, depending only on the charges and momenta of the external particles. Such null zones are the relativistic generalization of the well-known absence of electric and magnetic dipole radiation for nonrelativistic collisions involving particles with the same charge-to-mass ratio and g factor. The origin of zeros in reactions such as ud-bar..-->..W/sup +/..gamma.. is thus explained and examples with more particles are discussed. Conditions for the null zones to lie in physical regions are established. A new radiation representation, with the zeros manifest and of practical utility independently of whether the null zones are in physical regions is derived for the complete single-photon amplitude in tree approximation, using a gauge-invariant vertex expansion stemming from new internal-radiation decomposition identities. The question of whether amplitudes with closed loops can vanish in null zones is addressed. The null zone and these relations are discussed in terms of the Bargmann-Michel-Telegdi equation. The extension from photons to general massless gauge bosons is carried out.
Inherent Angular Tracking Error in an Amplitude Comparison Monopulse Radar.
1984-12-01
antennas is assumed. It is demonstrated that the cross over angle of the rantenna assembly and the target angular span are essential parameters for...Gaussian radiation pattern for the antennas is assumed. It is demonstrated that the cross over angle of the antenna assembly and the target angular...spherically symmetric in either amplitude or phase. A phase comparison tracking radar is constrained to have individual feeds in its antenna assembly at
Simplified theory of large-amplitude wave propagation
NASA Technical Reports Server (NTRS)
Kim, H.
1976-01-01
An orbit perturbation procedure was applied to the description of monochromatic, large-amplitude, electrostatic plasma wave propagation. In the lowest order approximation, untrapped electrons were assumed to follow constant-velocity orbits and trapped electrons were assumed to execute simple harmonic motion. The deviations of these orbits from the actual orbits were regarded as perturbations. The nonlinear damping rate and frequency shift were then obtained in terms of simple functions. The results are in good agreement with previous less approximate analyses.
Radiation Belt Electron Dynamics Driven by Large-Amplitude Whistlers
NASA Technical Reports Server (NTRS)
Khazanov, G. V.; Tel'nikhin, A. A.; Kronberg, T. K.
2013-01-01
Acceleration of radiation belt electrons driven by oblique large-amplitude whistler waves is studied. We show analytically and numerically that this is a stochastic process; the intensity of which depends on the wave power modified by Bessel functions. The type of this dependence is determined by the character of the nonlinear interaction due to coupling between action and phase. The results show that physically significant quantities have a relatively weak dependence on the wave power.
Constraints on scattering amplitudes in multistate Landau-Zener theory
NASA Astrophysics Data System (ADS)
Sinitsyn, Nikolai A.; Lin, Jeffmin; Chernyak, Vladimir Y.
2017-01-01
We derive a set of constraints, which we will call hierarchy constraints, on scattering amplitudes of an arbitrary multistate Landau-Zener model (MLZM). The presence of additional symmetries can transform such constraints into nontrivial relations between elements of the transition probability matrix. This observation can be used to derive complete solutions of some MLZMs or, for models that cannot be solved completely, to reduce the number of independent elements of the transition probability matrix.
Protecting Quantum Correlation from Correlated Amplitude Damping Channel
NASA Astrophysics Data System (ADS)
Huang, Zhiming; Zhang, Cai
2017-08-01
In this work, we investigate the dynamics of quantum correlation measured by measurement-induced nonlocality (MIN) and local quantum uncertainty (LQU) in correlated amplitude damping (CAD) channel. We find that the memory parameter brings different influences on MIN and LQU. In addition, we propose a scheme to protect quantum correlation by executing prior weak measurement (WM) and post-measurement reversal (MR). However, better protection of quantum correlation by the scheme implies a lower success probability (SP).
Small-amplitude oscillatory shear magnetorheology of inverse ferrofluids.
Ramos, Jose; de Vicente, Juan; Hidalgo-Alvarez, Roque
2010-06-15
A comprehensive investigation is performed on highly monodisperse silica-based inverse ferrofluids under small-amplitude oscillatory shear in the presence of external magnetic fields up to 1 T. The effect of particle volume fraction and continuous medium Newtonian viscosity is thoroughly investigated. Experimental results for storage modulus are used to validate existing micromechanical magnetorheological models assuming different particle-level field-induced structures.
Baryon to meson transition distribution amplitudes and their spectral representation
Pire, B.; Semenov-Tian-Shansky, K.; Szymanowski, L.
2011-07-15
We consider the problem of construction of a spectral representation for nucleon to meson transition distribution amplitudes (TDAs), non-diagonal matrix elements of nonlocal three quark operators between a nucleon and a meson states. We introduce the notion of quadruple distributions and generalize Radyshkin's factorized Ansatz for this issue. Modelling of baryon to meson TDAs in the complete domain of their definition opens the way to quantitative estimates of cross-sections for various hard exclusive reactions.
Wigner function and transition amplitude of three mutually coupled oscillators
NASA Astrophysics Data System (ADS)
Nassar, M. M.; Sebawe Abdalla, M.
2007-04-01
A full quantum mechanical treatment of three electromagnetic fields is considered. The proposed model consists of three different coupling parameters for which the rotating and counter-rotating terms are retained. An exact solution of the wave function in the Schrödinger picture is obtained and the connection with the coherent states wave function is given. The symmetrical ordered quasi-probability distribution function ( W-Wigner function) is calculated via the wave function in the coherent states representation. The squeezing phenomenon is also examined for both single mode and squared-amplitude, where the collapse and revival phenomena are observed. For the case in which λ3=0 and ω1=ω2=ω3 (exact resonances) we find that the late phenomenon is apparent but only after long period of the time considered. The transition amplitude between two different coherent states (a state in which all the coupling parameters are involved and a state when the coupling parameter λ3=0) is calculated. It is shown that the probability amplitude is sensitive to the variation of the mean photon numbers, and the coupling parameters as well as to the field frequencies.
Mechanical annealing under low-amplitude cyclic loading in micropillars
NASA Astrophysics Data System (ADS)
Cui, Yi-nan; Liu, Zhan-li; Wang, Zhang-jie; Zhuang, Zhuo
2016-04-01
Mechanical annealing has been demonstrated to be an effective method for decreasing the overall dislocation density in submicron single crystal. However, simultaneously significant shape change always unexpectedly happens under extremely high monotonic loading to drive the pre-existing dislocations out of the free surfaces. In the present work, through in situ TEM experiments it is found that cyclic loading with low stress amplitude can drive most dislocations out of the submicron sample with virtually little change of the shape. The underlying dislocation mechanism is revealed by carrying out discrete dislocation dynamic (DDD) simulations. The simulation results indicate that the dislocation density decreases within cycles, while the accumulated plastic strain is small. By comparing the evolution of dislocation junction under monotonic, cyclic and relaxation deformation, the cumulative irreversible slip is found to be the key factor of promoting junction destruction and dislocation annihilation at free surface under low-amplitude cyclic loading condition. By introducing this mechanics into dislocation density evolution equations, the critical conditions for mechanical annealing under cyclic and monotonic loadings are discussed. Low-amplitude cyclic loading which strengthens the single crystal without seriously disturbing the structure has the potential applications in the manufacture of defect-free nano-devices.
Segmental high amplitude peristaltic contractions in the distal esophagus.
Freidin, N; Mittal, R K; Traube, M; McCallum, R W
1989-06-01
High amplitude peristaltic contractions in the distal esophagus ("nutcracker esophagus") is the most common manometric disorder seen in patients with noncardiac chest pain. Although this abnormality is found in the distal esophagus, the definition regarding its precise level in the esophagus is unclear. A careful analysis of 99 consecutive manometric tracings performed during a 1-yr period revealed that in patients with noncardiac chest pain and/or dysphagia, the location of the abnormal esophageal contractions varied: 1) in 11 patients the esophageal contractions were abnormal at 2 cm, as well as 7 cm, above the lower esophageal sphincter (LES); 2) the abnormality was limited to the 2-cm location above the LES in six patients; and 3) was confined to the 7-cm location above the LES in five patients. If the conventional criteria of averaging the distal esophageal contraction amplitudes at 2 and 7 cm above the LES were adopted, six of the 11 patients with segmental esophageal contraction abnormality would not have been identified. We suggest that, by inspection of each location of the distal esophagus separately, localized high amplitude contractions can be identified, and the distal 2 cm segment of the esophagus should be routinely included in the manometric evaluation.
Dependence of seismoelectric amplitudes on water content - a field study
NASA Astrophysics Data System (ADS)
Strahser, M. H. P.; Matthey, P.-D.; Jouniaux, L.; Sailhac, P.
2009-04-01
In porous saturated media, seismic compressional waves can cause seismoelectric and seismoelectromagnetic signals through electrokinetic coupling. It has been observed that these measureable signals also occur in partially saturated media, but the theory is largely unknown for these circumstances. Seismoelectromagnetic tomography is expected to combine the sensitivity of electrical properties to water-content and permeability, to the high spatial resolution of seismic surveys. A better understanding of the physical processes and a reliable quantification of the conversion between seismic and electric energy are necessary and need to take into account the effect of water-content, especially for shallow subsurface investigations. In order to quantify seismoelectric signals with changing water content, we repeated seismoelectric and seismic measurements on the same profile in the Vosges Mountains during several months. The electrical resistivity was also monitored to take into account the water-content variations. We show that an exponential relation can be established between the seismoelectric amplitudes normalized with the seismic amplitudes and the resistivity which in turn is related to the saturation: Increasing resistivity (decreasing water content) leads to decreasing normalized seismoelectric amplitudes. These results imply that the electrokinetic coefficient should increase with water-saturation, as measured in laboratory, but not predicted by theory. This work was funded by CNRS and Université Louis Pasteur de Strasbourg.
Factors that control amplitude of EPSPs in dendritic neurons.
Lev-Tov, A; Miller, J P; Burke, R E; Rall, W
1983-08-01
We have used a computer-based mathematical model of alpha-motoneurons and of group Ia synaptic input to them, based on anatomical and electrophysiological data from the cat spinal cord, in order to examine the effects of variations in neuron size and input resistance and of conductance magnitude and duration on the generation of excitatory postsynaptic potentials (EPSPs). The first set of calculations were designed to test the possible role of nonlinear EPSP summation in producing a differential distribution of posttetanic potentiation of group Ia EPSPs, described in the preceding paper (25; see also Refs. 26, 27). The results suggest that the negative correlations observed between the degree of posttetanic potentiation of Ia EPSPs and initial (pretetanic) EPSP amplitude as well as with the input resistance of the postsynaptic motoneurons can be explained in part by the inherent non-linearity between conductance change and the resultant potential change at chemical synapses. In a second set of calculations, we used the same model system to evaluate the effects produced by variations in neuronal membrane area, input resistance, and specific membrane resistivity, as well as of the density of excitatory synaptic input on the peak amplitude of EPSPs. With parameters constrained to match the properties of alpha-motoneurons and group Ia synaptic input, EPSP amplitudes were most sensitive to changes in synaptic density and were much less sensitive to alterations in neuron input resistance and specific membrane resistivity when synaptic density was constant.
Spectral saliency via automatic adaptive amplitude spectrum analysis
NASA Astrophysics Data System (ADS)
Wang, Xiaodong; Dai, Jialun; Zhu, Yafei; Zheng, Haiyong; Qiao, Xiaoyan
2016-03-01
Suppressing nonsalient patterns by smoothing the amplitude spectrum at an appropriate scale has been shown to effectively detect the visual saliency in the frequency domain. Different filter scales are required for different types of salient objects. We observe that the optimal scale for smoothing amplitude spectrum shares a specific relation with the size of the salient region. Based on this observation and the bottom-up saliency detection characterized by spectrum scale-space analysis for natural images, we propose to detect visual saliency, especially with salient objects of different sizes and locations via automatic adaptive amplitude spectrum analysis. We not only provide a new criterion for automatic optimal scale selection but also reserve the saliency maps corresponding to different salient objects with meaningful saliency information by adaptive weighted combination. The performance of quantitative and qualitative comparisons is evaluated by three different kinds of metrics on the four most widely used datasets and one up-to-date large-scale dataset. The experimental results validate that our method outperforms the existing state-of-the-art saliency models for predicting human eye fixations in terms of accuracy and robustness.
Feelings of helplessness increase ERN amplitudes in healthy individuals.
Pfabigan, D M; Pintzinger, N M; Siedek, D R; Lamm, C; Derntl, B; Sailer, U
2013-03-01
Experiencing feelings of helplessness has repeatedly been reported to contribute to depressive symptoms and negative affect. In turn, depression and negative affective states are associated, among others, with impairments in performance monitoring. Thus, the question arises whether performance monitoring is also affected by feelings of helplessness. To this end, after the induction of feelings of helplessness via an unsolvable reasoning task, 37 participants (20 females) performed a modified version of a Flanker task. Based on a previously validated questionnaire, 17 participants were classified as helpless and 20 as not-helpless. Behavioral measures revealed no differences between helpless and not-helpless individuals. However, we observed enhanced Error-Related Negativity (ERN) amplitude differences between erroneous and correct responses in the helpless compared to the not-helpless group. Furthermore, correlational analysis revealed that higher scores of helplessness were associated with increased ERN difference scores. No influence of feelings of helplessness on later stages of performance monitoring was observed as indicated by Error-Positivity (Pe) amplitude. The present study is the first to demonstrate that feelings of helplessness modulate the neuronal correlates of performance monitoring. Thus, even a short-lasting subjective state manipulation can lead to ERN amplitude variation, probably via modulation of mesencephalic dopamine activity.
Amplitude Demodulation of Entrained Sway to Analyze Human Postural Control
Bhatkar, Viprali V.; Pilkar, Rakesh B.; Storey, Christopher M.; Robinson, Charles J.
2008-01-01
This paper presents an innovative technique to study postural control. Our translating platform, the Sliding Linear Investigative Platform For Analyzing Lower Limb Stability and Simultaneous Tracking, EMG and Pressure mapping (SLIP-FALLS-STEPm), makes precise, vibration movements under controlled conditions. We look at the psychophysical thresholds to the perception of a sinusoidally induced sway. In the Sine Lock experiments described, an induced sinusoidal perturbation locks the subject's natural sway pattern at the frequency of the perturbation. The input / output system is treated as an Amplitude Shift Key (ASK) modulated signal modulating a carrier frequency (at or about a subject's natural sway frequency). The Position signal (input) and the Anterior-Posterior Center of Pressure (APCOP) signal (output) or the ankle angle are demodulated by mixing them with the pure sine wave carrier at the frequency of underlying oscillation and then low-pass filtering it to detect the amplitude envelope. These detected envelopes elucidate that the square pulse increase in the position sine wave amplitude yields a triangular increase in APCOP demodulated signal. PMID:18003110
Amplitude demodulation of entrained sway to analyze human postural control.
Bhatkar, Viprali V; Pilkar, Rakesh B; Storey, Christopher M; Robinson, Charles J
2007-01-01
This paper presents an innovative technique to study postural control. Our translating platform, the Sliding Linear Investigative Platform For Analyzing Lower Limb Stability and Simultaneous Tracking, EMG and Pressure mapping (SLIP-FALLS-STEPm), makes precise, vibration movements under controlled conditions. We look at the psychophysical thresholds to the perception of a sinusoidally induced sway. In the Sine Lock experiments described, an induced sinusoidal perturbation locks the subject's natural sway pattern at the frequency of the perturbation. The input / output system is treated as an Amplitude Shift Key (ASK) modulated signal modulating a carrier frequency (at or about a subject's natural sway frequency). The Position signal (input) and the Anterior-Posterior Center of Pressure (APCOP) signal (output) or the ankle angle are demodulated by mixing them with the pure sine wave carrier at the frequency of underlying oscillation and then low-pass filtering it to detect the amplitude envelope. These detected envelopes elucidate that the square pulse increase in the position sine wave amplitude yields a triangular increase in APCOP demodulated signal.
Thread amplitudes and frequencies in a fluid mechanical `sewing machine'
NASA Astrophysics Data System (ADS)
Morris, Stephen W.; Dawes, J. H. P.; Lister, John; Dalziel, Stuart
2006-11-01
A viscous thread falling on a surface exhibits the famous rope- coiling effect, in which the thread buckles to form loops. If the surface is replaced by a belt moving at speed U, the rotational symmetry of the buckling instability is broken and a wealth of interesting states are observed (1). We experimentally studied this fluid mechanical `sewing machine' in a new, more precise apparatus. As U is reduced, the stretched thread bifurcates into a meandering state in which the thread displacements are only transverse to the motion of the belt. We measured the amplitudes A and frequency φ of the meandering close to the bifurcation. For small U, single- frequency meandering bifurcates to a two-frequency `figure 8' state, which contains a significant 2φ component and parallel as well as transverse displacements. This eventually reverts to single-frequency coiling at smaller U. More complex, highly hysteretic states with additional harmonics are observed for larger nozzle heights. We propose to understand this zoology in terms of the generic amplitude equations appropriate for resonant interactions between three oscillatory modes with frequencies φ, 2φ and 3φ. The form of the amplitude equations captures both the axisymmetry of the U=0 coiling state and the symmetry-breaking effects induced by the moving belt.(1) Chiu-Webster and Lister, J. Fluid Mech., in press.
Mapping High Latitude Gravity Wave Amplitudes over Antarctica during Summer
NASA Astrophysics Data System (ADS)
Badenhausen, P.; Millan, R. M.; Gerrard, A. J.
2015-12-01
Appropriate inclusion of gravity wave amplitudes into general circulation models is required to get accurate atmospheric circulation characteristics. However, high latitude gravity wave amplitudes are particularly difficult to obtain due to the challenging experimental and logistical constraints in these regions. In this study, we present gravity wave climatology of high latitudes during austral summer conditions over the Antarctic continent. These data were obtained using high-resolution GPS measurements aboard long duration high altitude balloon flights that were flown as part of the NASA Balloon Array for Radiation-belt Relativistic Electron Losses (BARREL) mission in December 2013-February 2014 and December 2012-February 2013. The results show increased gravity wave activity along the coast of the Antarctic continent, particularly over the Peninsula and Halley Bay, whereas at higher latitudes, particularly over regions near the South Pole, gravity wave amplitudes decrease substantially. Through use of horizontal winds data, we obtained measurements of the vertical transport of horizontal momentum fluxes, which were unusually high for the summer high latitude lower stratosphere. Such unique measurements as these are immediately applicable to understanding of upwelling in the summer middle atmosphere as well as to the formation of overlaying mesospheric clouds formation.
Vibrational energy relaxation of large-amplitude vibrations in liquids.
Zhang, Baofeng; Stratt, Richard M
2012-07-14
Given the limited intermolecular spaces available in dense liquids, the large amplitudes of highly excited, low frequency vibrational modes pose an interesting dilemma for large molecules in solution. We carry out molecular dynamics calculations of the lowest frequency ("warping") mode of perylene dissolved in liquid argon, and demonstrate that vibrational excitation of this mode should cause identifiable changes in local solvation shell structure. But while the same kinds of solvent structural rearrangements can cause the non-equilibrium relaxation dynamics of highly excited diatomic rotors in liquids to differ substantially from equilibrium dynamics, our simulations also indicate that the non-equilibrium vibrational energy relaxation of large-amplitude vibrational overtones in liquids should show no such deviations from linear response. This observation seems to be a generic feature of large-moment-arm vibrational degrees of freedom and is therefore probably not specific to our choice of model system: The lowest frequency (largest amplitude) cases probably dissipate energy too quickly and the higher frequency (more slowly relaxing) cases most likely have solvent displacements too small to generate significant nonlinearities in simple nonpolar solvents. Vibrational kinetic energy relaxation, in particular, seems to be especially and surprisingly linear.
A Generic Receiver Tracking Model for GPS Ionospheric Amplitude Scintillation
NASA Astrophysics Data System (ADS)
Paula, E. R.; Moraes, A. D.; Perrella, W. J.; Galera Monico, J. F.
2012-12-01
Ionospheric scintillations result in rapid variations in phase and amplitude of the radio signal, which propagates through the ionosphere. Depending on the temporal and spatial situation, the scintillation can represent a problem in the availability and precision of the Global Navigation Satellite Systems (GNSS). Scintillations affect the receiver performance, specially the tracking loop level. Depending on the scintillation level, the receiver might increase the measurement errors or even can lead to a loss of lock of the carrier and code loops. In extreme cases, the scintillation can result in full disrupting of the receiver. In this work we introduce a generic model to evaluate the effects of ionospheric amplitude scintillation on GPS receiver tracking loops. This model is based on α-μ distribution, which can be seen as a generalized fading model, that includes a variety of distributions such as Gamma, Nakagami-m, Exponential, Weibull, one-sided Gaussian and Rayleigh. Differently from the model based only on Nakagami-m, this one is not limited to S4< 0,71 which allows using it to predict amplitude scintillation effects for stronger scenarios. The estimation of α-μ coefficients, the empirical parameterization based on field measurements and the typical values estimated based on observations made during the last solar maximum are presented and discussed.
Model equation for strongly focused finite-amplitude sound beams
Kamakura; Ishiwata; Matsuda
2000-06-01
A model equation that describes the propagation of sound beams in a fluid is developed using the oblate spheroidal coordinate system. This spheroidal beam equation (SBE) is a parabolic equation and has a specific application to a theoretical prediction on focused, high-frequency beams from a circular aperture. The aperture angle does not have to be small. The theoretical background is basically along the same analytical lines as the composite method (CM) reported previously [B. Ystad and J. Berntsen, Acustica 82, 698-706 (1996)]. Numerical examples are displayed for the amplitudes of sound pressure along and across the beam axis when sinusoidal waves are radiated from the source with uniform amplitude distribution. The primitive approach to linear field analysis is readily extended to the case where harmonic generation in finite-amplitude sound beams becomes significant due to the inherent nonlinearity of the medium. The theory provides the propagation and beam pattern profiles that differ from the CM solution for each harmonic component.
Amplitude-dependent contraction/elongation of nonlinear Lamb waves
NASA Astrophysics Data System (ADS)
Packo, Pawel; Staszewski, Wieslaw J.; Uhl, Tadeusz; Leamy, Michael J.
2016-04-01
Nonlinear elastic guided waves find application in various disciplines of science and engineering, such as non- destructive testing and structural health monitoring. Recent recognition and quantification of their amplitude- dependent changes in spectral properties has contributed to the development of new monitoring concepts for mechanical structures. The focus of this work is to investigate and predict amplitude-dependent shifts in Lamb wave dispersion curves. The theory for frequency/wavenumber shifts for plate waves, based on a Lindstedt-Poincaré perturbation approach, was presented by the authors in previous years. Equivalently, spectral properties changes can be seen as wavelength contraction/elongation. Within the proposed framework, the wavelength of a Lamb wave depends on several factors; e.g., wave amplitude and second-, third- and fourth-order elastic constants, and others. Various types of nonlinear effects are considered in presented studies. Sensitivity studies for model parameters, i.e. higher-order elastic constants, are performed to quantify their influence on Lamb wave frequency/wavenumber shifting, and to identify the key parameters governing wavelength tuning.
Spectroscopic determination of the internal amplitude of frequency sweeping TAE
NASA Astrophysics Data System (ADS)
Pinches, S. D.; Berk, H. L.; Gryaznevich, M. P.; Sharapov, S. E.; Contributors, JET-EFDA
2004-07-01
From an understanding of the processes that cause a marginally unstable eigenmode of the system to sweep in frequency, it is shown how the absolute peak amplitude of the mode can be determined from the spectroscopic measurements of the frequency sweeping rate, e.g. with Mirnov coils outside the plasma. In a first attempt to implement such a diagnostic calculation, the MISHKA code (Mikhailovskii A B et al 1997 Plasma Phys. Rep. 23 844) is used to determine the global mode structure of toroidal Alfvén eigenmodes (TAEs) (Cheng C Z et al 1985 Ann. Phys. (NY) 161 21) observed in the MAST spherical tokamak (Sykes A et al 2001 Nucl. Fusion 41 1423). Simulations using the HAGIS code (Pinches S D 1996 PhD Thesis The University of Nottingham, Pinches S D et al 1998 Comput. Phys. Commun. 111 131) are then made, replicating the experimentally observed sweeping phenomena. The fundamental theory is then used together with these simulation results to predict the internal field amplitude from the observed frequency sweeping. The calculated mode amplitude is shown to agree with that obtained from Mirnov coil measurements.
Compensating temperature-induced ultrasonic phase and amplitude changes
NASA Astrophysics Data System (ADS)
Gong, Peng; Hay, Thomas R.; Greve, David W.; Junker, Warren R.; Oppenheim, Irving J.
2016-04-01
In ultrasonic structural health monitoring (SHM), environmental and operational conditions, especially temperature, can significantly affect the propagation of ultrasonic waves and thus degrade damage detection. Typically, temperature effects are compensated using optimal baseline selection (OBS) or optimal signal stretch (OSS). The OSS method achieves compensation by adjusting phase shifts caused by temperature, but it does not fully compensate phase shifts and it does not compensate for accompanying signal amplitude changes. In this paper, we develop a new temperature compensation strategy to address both phase shifts and amplitude changes. In this strategy, OSS is first used to compensate some of the phase shifts and to quantify the temperature effects by stretching factors. Based on stretching factors, empirical adjusting factors for a damage indicator are then applied to compensate for the temperature induced remaining phase shifts and amplitude changes. The empirical adjusting factors can be trained from baseline data with temperature variations in the absence of incremental damage. We applied this temperature compensation approach to detect volume loss in a thick wall aluminum tube with multiple damage levels and temperature variations. Our specimen is a thick-walled short tube, with dimensions closely comparable to the outlet region of a frac iron elbow where flow-induced erosion produces the volume loss that governs the service life of that component, and our experimental sequence simulates the erosion process by removing material in small damage steps. Our results show that damage detection is greatly improved when this new temperature compensation strategy, termed modified-OSS, is implemented.
AMPLITUDE AND TIME MEASUREMENT ASIC WITH ANALOG DERANDOMIZATION.
O CONNOR,P.; DE GERONIMO,G.; KANDASAMY,A.
2002-11-10
We describe a new ASIC for accurate and efficient processing of high-rate pulse signals from highly segmented detectors. In contrast to conventional approaches, this circuit affords a dramatic reduction in data volume through the use of analog techniques (precision peak detectors and time-to-amplitude converters) together with fast arbitration and sequencing logic to concentrate the data before digitization. In operation the circuit functions like a data-driven analog first-in, first-out (FIFO) memory between the preamplifiers and the ADC. Peak amplitudes of pulses arriving at any one of the 32 inputs are sampled, stored, and queued for readout and digitization through a single output port. Hit timing, pulse risetime, and channel address are also available at the output. Prototype chips have been fabricated in 0.35 micron CMOS and tested. First results indicate proper functionality for pulses down to 30 ns peaking time and input rates up to 1.6 MHz/channel. Amplitude accuracy of the peak detect and hold circuit is 0.3% (absolute). TAC accuracy is within 0.3% of full scale. Power consumption is less than 2 mW/channel. Compared with conventional techniques such as track-and-hold and analog memory, this new ASIC will enable efficient pulse height measurement at 20 to 300 times higher rates.
Three applications of a bonus relation for gravity amplitudes
NASA Astrophysics Data System (ADS)
Spradlin, Marcus; Volovich, Anastasia; Wen, Congkao
2009-04-01
Arkani-Hamed et al. have recently shown that all tree-level scattering amplitudes in maximal supergravity exhibit exceptionally soft behavior when two supermomenta are taken to infinity in a particular complex direction, and that this behavior implies new non-trivial relations amongst amplitudes in addition to the well-known on-shell recursion relations. We consider the application of these new 'bonus relations' to MHV amplitudes, showing that they can be used quite generally to relate (n - 2) !-term formulas typically obtained from recursion relations to (n - 3) !-term formulas related to the original BGK conjecture. Specifically we provide (1) a direct proof of a formula presented by Elvang and Freedman, (2) a new formula based on one due to Bedford et al., and (3) an alternate proof of a formula recently obtained by Mason and Skinner. Our results also provide the first direct proof that the conjectured BGK formula, only very recently proven via completely different methods, satisfies the on-shell recursion.
Type I/heterotic duality and M-theory amplitudes
NASA Astrophysics Data System (ADS)
Green, Michael B.; Rudra, Arnab
2016-12-01
This paper investigates relationships between low-energy four-particle scattering amplitudes with external gauge particles and gravitons in the E 8 × E 8 and SO(32) heterotic string theories and the type I and type IA superstring theories by considering a variety of tree level and one-loop Feynman diagrams describing such amplitudes in eleven-dimensional supergravity in a Horava-Witten background compactified on a circle. This accounts for a number of perturbative and non-perturbative aspects of low order higher derivative terms in the low-energy expansion of string theory amplitudes, which are expected to be protected by half maximal supersymmetry from receiving corrections beyond one or two loops. It also suggests the manner in which type I/heterotic duality may be realised for certain higher derivative interactions that are not so obviously protected. For example, our considerations suggest that R 4 interactions (where R is the Riemann curvature) might receive no perturbative corrections beyond one loop by virtue of a conspiracy involving contributions from (non-BPS) {Z}_2 D-instantons in the type I and heterotic SO(32) theories.
Phase and Pupil Amplitude Recovery for JWST Space-Optics Control
NASA Technical Reports Server (NTRS)
Dean, B. H.; Zielinski, T. P.; Smith, J. S.; Bolcar, M. R.; Aronstein, D. L.; Fienup, J. R.
2010-01-01
This slide presentation reviews the phase and pupil amplitude recovery for the James Webb Space Telescope (JWST) Near Infrared Camera (NIRCam). It includes views of the Integrated Science Instrument Module (ISIM), the NIRCam, examples of Phase Retrieval Data, Ghost Irradiance, Pupil Amplitude Estimation, Amplitude Retrieval, Initial Plate Scale Estimation using the Modulation Transfer Function (MTF), Pupil Amplitude Estimation vs lambda, Pupil Amplitude Estimation vs. number of Images, Pupil Amplitude Estimation vs Rotation (clocking), and Typical Phase Retrieval Results Also included is information about the phase retrieval approach, Non-Linear Optimization (NLO) Optimized Diversity Functions, and Least Square Error vs. Starting Pupil Amplitude.
Bakhtiari, Zahra; Sawchuk, Alexander A
2015-04-20
We describe and demonstrate an all-optical tunable phase- preserving scheme for multilevel amplitude regeneration based on coherent optical wave mixing using a polarizer for optical star 8-quadrature-amplitude modulation (star-8QAM) and star-16QAM signals with a power ratio of 1:5. Amplitude noise can be efficiently suppressed on both amplitude levels. A regeneration factor of nearly 5 for the higher-amplitude level of star-8QAM and 3 for lower-amplitude level are achieved. The system robustness against nonlinear phase noise originating from the Gordon-Mollenauer effect in a 150 km transmission line is investigated using the proposed amplitude regenerator.
High Amplitude Events in relation to Interplanetary disturbances
NASA Astrophysics Data System (ADS)
Mishra, Rajesh Kumar; Agarwal Mishra, Rekha
2012-07-01
The Sun emits the variable solar wind which interacts with the very local interstellar medium to form the heliosphere. Hence variations in solar activity strongly influence interplanetary space, from the Sun's surface out to the edge of the heliosphere. Superimposed on the solar wind are mass ejections from the Sun and/or its corona which, disturb the interplanetary medium - hence the name "interplanetary disturbances". Interplanetary disturbances are the sources of large-scale particle acceleration, of disturbances in the Earth's magnetosphere, of modulations of galactic cosmic rays in short, they are the prime focus for space weather studies. The investigation deals with the study of cosmic ray intensity, solar wind plasma and interplanetary magnetic field parameters variation due to interplanetary disturbances (magnetic clouds) during an unusual class of days i.e. high amplitude anisotropic wave train events. The high amplitude anisotropic wave train events in cosmic ray intensity has been identified using the data of ground based Goose Bay neutron monitor and studied during the period 1981-94. Even though, the occurrence of high amplitude anisotropic wave trains does not depend on the onset of interplanetary magnetic clouds. But the possibility of occurrence of these events cannot be overlooked during the periods of interplanetary magnetic cloud events. It is observed that solar wind velocity remains higher (> 300) than normal and interplanetary magnetic field B remains lower than normal on the onset of interplanetary magnetic cloud during the passage of these events. It is also noted from the superposed epoch analysis of cosmic ray intensity and geomagnetic activity for high amplitude anisotropic wave train events during the onset of interplanetary magnetic clouds that the increase in cosmic ray intensity and decrease in geomagnetic activity start not at the onset of magnetic clouds but after few days. The north south component of IMF (Bz), IMF (B), proton
Calculation of multiloop amplitudes in the theory of closed oriented superstrings
NASA Astrophysics Data System (ADS)
Danilov, G. S.
2017-05-01
Multiloop superstring amplitudes are obtained upon integrating local amplitudes with respect to modular parameters of the Schottky supergroup and with respect to vertex coordinates in the nonsplit (1|1) complex supermanifold. Ambiguities in this integration are removed by the condition requiring that the local symmetries of the amplitudes under discussion be conserved. Local superstring amplitudes are calculated by summing local fermion-string amplitudes. The resulting superstring amplitudes are free from divergencies. The vacuum amplitude is zero, in just the same way as the one-, two-, and three-point massless-boson amplitudes are. The amplitudes in question vanish after integration of corresponding local amplitudes with respect to interaction-vertex coordinates and with respect to the limiting points of the Schottky supergroup, with the exception of those (3|2) points that are fixed by SL(2) symmetry.
Berger, Carola F.; Del Duca, Vittorio; Dixon, Lance J.
2006-08-18
We consider a scalar field, such as the Higgs boson H, coupled to gluons via the effective operator H tr G{sub {mu}{nu}} G{sup {mu}{nu}} induced by a heavy-quark loop. We treat H as the real part of a complex field {phi} which couples to the self-dual part of the gluon field-strength, via the operator {phi} tr G{sub SD {mu}{nu}} G{sub SD}{sup {mu}{nu}}, whereas the conjugate field {phi} couples to the anti-self-dual part. There are three infinite sequences of amplitudes coupling {phi} to quarks and gluons that vanish at tree level, and hence are finite at one loop, in the QCD coupling. Using on-shell recursion relations, we find compact expressions for these three sequences of amplitudes and discuss their analytic properties.
Topics in Nonsupersymmetric Scattering Amplitudes in Gauge and Gravity Theories
NASA Astrophysics Data System (ADS)
Nohle, Joshua David
In Chapters 1 and 2, we introduce and review the duality between color and kinematics in Yang-Mills theory uncovered by Bern, Carrasco and Johansson (BCJ). In Chapter 3, we provide evidence in favor of the conjectured duality between color and kinematics for the case of nonsupersymmetric pure Yang-Mills amplitudes by constructing a form of the one-loop four-point amplitude of this theory that makes the duality manifest. Our construction is valid in any dimension. We also describe a duality-satisfying representation for the two-loop four-point amplitude with identical four-dimensional external helicities. We use these results to obtain corresponding gravity integrands for a theory containing a graviton, dilaton, and antisymmetric tensor, simply by replacing color factors with specified diagram numerators. Using this, we give explicit forms of ultraviolet divergences at one loop in four, six, and eight dimensions, and at two loops in four dimensions. In Chapter 4, we extend the four-point one-loop nonsupersymmetric pure Yang-Mills discussion of Chapter 3 to include fermions and scalars circulating in the loop with all external gluons. This gives another nontrivial loop-level example showing that the duality between color and kinematics holds in nonsupersymmetric gauge theory. The construction is valid in any spacetime dimension and written in terms of formal polarization vectors. We also convert these expressions into a four-dimensional form with explicit external helicity states. Using this, we compare our results to one-loop duality-satisfying amplitudes that are already present in literature. In Chapter 5, we switch from the topic of color-kinematics duality to discuss the recently renewed interest in the soft behavior of gravitons and gluons. Specifically, we discuss the subleading low-energy behavior. Cachazo and Strominger recently proposed an extension of the soft-graviton theorem found by Weinberg. In addition, they proved the validity of their extension at
Combrisson, Etienne; Perrone-Bertolotti, Marcela; Soto, Juan Lp; Alamian, Golnoush; Kahane, Philippe; Lachaux, Jean-Philippe; Guillot, Aymeric; Jerbi, Karim
2017-02-15
Goal-directed motor behavior is associated with changes in patterns of rhythmic neuronal activity across widely distributed brain areas. In particular, movement initiation and execution are mediated by patterns of synchronization and desynchronization that occur concurrently across distinct frequency bands and across multiple motor cortical areas. To date, motor-related local oscillatory modulations have been predominantly examined by quantifying increases or suppressions in spectral power. However, beyond signal power, spectral properties such as phase and phase-amplitude coupling (PAC) have also been shown to carry information with regards to the oscillatory dynamics underlying motor processes. Yet, the distinct functional roles of phase, amplitude and PAC across the planning and execution of goal-directed motor behavior remain largely elusive. Here, we address this question with unprecedented resolution thanks to multi-site intracerebral EEG recordings in human subjects while they performed a delayed motor task. To compare the roles of phase, amplitude and PAC, we monitored intracranial brain signals from 748 sites across six medically intractable epilepsy patients at movement execution, and during the delay period where motor intention is present but execution is withheld. In particular, we used a machine-learning framework to identify the key contributions of various neuronal responses. We found a high degree of overlap between brain network patterns observed during planning and those present during execution. Prominent amplitude increases in the delta (2-4Hz) and high gamma (60-200Hz) bands were observed during both planning and execution. In contrast, motor alpha (8-13Hz) and beta (13-30Hz) power were suppressed during execution, but enhanced during the delay period. Interestingly, single-trial classification revealed that low-frequency phase information, rather than spectral power change, was the most discriminant feature in dissociating action from
Comparing Moment Release and Tremor Amplitudes in Cascadia ETS Events
NASA Astrophysics Data System (ADS)
Hall, K.; Schmidt, D. A.; Houston, H.
2016-12-01
A proposed relationship between the moment release of ETS and tremor duration. [Aguiar et al., 2009] compared moment from static inversions of slip with the overall duration of the entire ETS, finding a linear relationship between moment release and tremor duration. There is a logical relationship between the processes that generate slip and those that generate tremor. Spatially, we have seen that slip may occur up-dip of tremor [Houston, 2012] and [Hall and Houston, 2014] in Northern Cascadia. On the other hand, Bartlow et al. [2011] did not resolve a spatio-temporal difference between tremor and slow slip for the 2009 ETS in mid-Cascadia. This raises the possibility that there could be an as-yet-unrecognized regional difference. In order to explore spatio-temporal relationships between tremor and slow slip, I used the Extended Network Inversion Filter (ENIF) [Segall and Matthews, 1997] together with PNSN tremor locations. Preliminary results for the 2010 ETS event yield a M6.8 event that begins near Seattle on August 8th and propagates mainly to the north with some smaller slip to the south, following the propagation of the tremor, a pattern consistent with our static inversion results. The slip-pulse nature of the ETS process is clearly imaged, with some fault patches continuing to slip for several days after tremor has passed through, but not for the entire duration of the event. I then looked at tremor amplitudes [Ulberg and Creager, AGU Abs, 2013], which represent the amount of energy released in a five-minute tremor window. Because the tremor catalog has much finer temporal resolution than the GPS data, I sum the daily tremor amplitudes and compare to daily moment-rates from the time-dependent inversion, obtaining a correlation between moment-rate and tremor amplitude rate. This suggests that the energy released by tremor may be a direct proxy for energy released by slip.
Clinical application of amplitude processing of echocardiographic images.
Logan-Sinclair, R; Wong, C M; Gibson, D G
1981-01-01
In order to assess the possible clinical value of measuring regional amplitude of ultrasound reflected from intracardiac structures, two-dimensional echocardiographic images from 20 normal subjects and 70 patients with heart disease were processed by modulation of both colour and intensity to represent grey scale. Maximum echo intensity was consistently recorded from the pericardial interface behind the posterior left ventricular wall, and this was taken as 100 per cent. In the normal heart, central fibrous body reflected at 64 +/- 5 per cent, and mitral and aortic valves at 35 +/- 5 per cent and 36 +/- 8 per cent, respectively. Normal septal myocardium gave a valve of 33 +/- 8 per cent and posterior wall of 23 +/- 6 per cent. Consistent increases were recorded from prosthetic mitral valves in 20 patients, and also from the anterior cusp of the mitral valve (54 +/- 11%) in 20 patients with rheumatic heart diseases. In all of 15 patients with left ventricular involvement caused by coronary artery disease, septal echo amplitude was increased in all to 71 +/- 11 per cent, and localised increases were also noted in the posterior wall, subendocardially, or in one or both papillary muscles. Similar focal changes were noted in five, and increases in septal density in 10 of 15 patients with left ventricular hypertrophy and in 12 of those with mitral valve disease. Thus, measurement of regional echo amplitude is possible without degradation of the quality from standard two-dimensional cardiac images. Abnormalities are particularly common in left ventricular disease where their distribution corresponds to that described for fibrous tissue. Images PMID:6455136
Proposed proper Engle-Pereira-Rovelli-Livine vertex amplitude
NASA Astrophysics Data System (ADS)
Engle, Jonathan
2013-04-01
As established in a prior work of the author, the linear simplicity constraints used in the construction of the so-called “new” spin-foam models mix three of the five sectors of Plebanski theory as well as two dynamical orientations, and this is the reason for multiple terms in the asymptotics of the Engle-Pereira-Rovelli-Livine vertex amplitude as calculated by Barrett et al. Specifically, the term equal to the usual exponential of i times the Regge action corresponds to configurations either in sector (II+) with positive orientation or sector (II-) with negative orientation. The presence of the other terms beyond this cause problems in the semiclassical limit of the spin-foam model when considering multiple 4-simplices due to the fact that the different terms for different 4-simplices mix in the semiclassical limit, leading in general to a non-Regge action and hence non-Regge and nongravitational configurations persisting in the semiclassical limit. To correct this problem, we propose to modify the vertex so its asymptotics include only the one term of the form eiSRegge. To do this, an explicit classical discrete condition is derived that isolates the desired gravitational sector corresponding to this one term. This condition is quantized and used to modify the vertex amplitude, yielding what we call the “proper Engle-Pereira-Rovelli-Livine vertex amplitude.” This vertex still depends only on standard SU(2) spin-network data on the boundary, is SU(2) gauge-invariant, and is linear in the boundary state, as required. In addition, the asymptotics now consist in the single desired term of the form eiSRegge, and all degenerate configurations are exponentially suppressed. A natural generalization to the Lorentzian signature is also presented.
On Statistics of Electric Field Amplitudes in the Langmuir Turbulence
NASA Astrophysics Data System (ADS)
Krasnoselskikh, V.; Voshchepynets, A.; Volokitin, A.; Krafft, C.
2016-12-01
We present a systematic study of the properties of the Langmuir wave turbulence generated by bump-on-tail instability in strongly non-homogeneous plasma. This type of turbulence occurs in numerous processes involving electrons beams in space plasmas. We analyse the synthetic data obtained in the numerical simulation based on two different approaches: the Hamiltonian model, and so-called probabilistic model. The Hamiltonian model describes in the self-consistent manner the wave-particle and wave-wave interactions in inhomogeneous magnetized plasmas. The model enables us to study the general properties of the distributions of the amplitudes of the Langmuir waves driven by the high-velocity electron beams in the fluctuating plasma. We pay special attention to the study of statistics of Languir waves under conditions when the decay instability, involving ion-sound waves, is developed. The probabilistic model, being modified version of the standard quasi-linear theory requires much less computational resources. Due to this it enables us to performed a detailed analysis of the statistics of the amplitudes of the Langmuir waves in the plasma with density fluctuations. To analyze data obtained in both numerical models, a Pearson technique was used to classify the probability distribution functions (PDF) of the logarithm of wave intensity. It was shown that core parts the PDF's belong to Pearson types I,IV and VI, depending on the spatial profiles of the density fluctuations, rather than to the normal distribution. The study also showed that the high-amplitude parts of the distributions follow power-low or exponential decay, depending on the type of core distribution.
The Detection of Phase Amplitude Coupling during Sensory Processing.
Seymour, Robert A; Rippon, Gina; Kessler, Klaus
2017-01-01
There is increasing interest in understanding how the phase and amplitude of distinct neural oscillations might interact to support dynamic communication within the brain. In particular, previous work has demonstrated a coupling between the phase of low frequency oscillations and the amplitude (or power) of high frequency oscillations during certain tasks, termed phase amplitude coupling (PAC). For instance, during visual processing in humans, PAC has been reliably observed between ongoing alpha (8-13 Hz) and gamma-band (>40 Hz) activity. However, the application of PAC metrics to electrophysiological data can be challenging due to numerous methodological issues and lack of coherent approaches within the field. Therefore, in this article we outline the various analysis steps involved in detecting PAC, using an openly available MEG dataset from 16 participants performing an interactive visual task. Firstly, we localized gamma and alpha-band power using the Fieldtrip toolbox, and extracted time courses from area V1, defined using a multimodal parcelation scheme. These V1 responses were analyzed for changes in alpha-gamma PAC, using four common algorithms. Results showed an increase in alpha (7-13 Hz)-gamma (40-100 Hz) PAC in response to the visual grating stimulus, though specific patterns of coupling were somewhat dependent upon the algorithm employed. Additionally, post-hoc analyses showed that these results were not driven by the presence of non-sinusoidal oscillations, and that trial length was sufficient to obtain reliable PAC estimates. Finally, throughout the article, methodological issues and practical guidelines for ongoing PAC research will be discussed.
Finite amplitude method for the quasiparticle random-phase approximation
Avogadro, Paolo; Nakatsukasa, Takashi
2011-07-15
We present the finite amplitude method (FAM), originally proposed in Ref. [17], for superfluid systems. A Hartree-Fock-Bogoliubov code may be transformed into a code of the quasiparticle-random-phase approximation (QRPA) with simple modifications. This technique has advantages over the conventional QRPA calculations, such as coding feasibility and computational cost. We perform the fully self-consistent linear-response calculation for the spherical neutron-rich nucleus {sup 174}Sn, modifying the hfbrad code, to demonstrate the accuracy, feasibility, and usefulness of the FAM.
Non-gauge phase transformations in quantum transition amplitudes
NASA Technical Reports Server (NTRS)
Reiss, H. R.
1993-01-01
The prescription for introducing a gauge transformation into a quantum transition amplitude, nominally well known, contains an ambiguous feature. It is presumed by some authors that an appropriate transformation of the phase of a wave function will generate the associated gauge transformation. It is shown that this is a necessary but not sufficient step. Examples from the literature are cited to show the consequences of the failure of this procedure. One must distinguish between true gauge transformations and unitary transformations within a fixed gauge.
Phase coherence and pairing amplitude in photo-excited superconductors
NASA Astrophysics Data System (ADS)
Perfetti, Luca; Piovera, Christian; Zhang, Zailan
2016-05-01
New data on Bi2Sr2CaCu2O8+δ (Bi2212) reveal interesting aspects of photoexcited superconductors. The electrons dynamics show that inelastic scattering by nodal quasiparticles decreases when the temperature is lowered below the critical value of the superconducting phase transition. This drop of electronic dissipation is astonishingly robust and survives to photoexcitation densities much larger than the value sustained by long-range superconductivity. The unconventional behavior of quasiparticle scattering is ascribed to superconducting correlations extending on a length scale comparable to the inelastic mean-free path. Our measurements indicate that strongly driven superconductors enter in a regime without phase coherence but finite pairing amplitude.
Transition from Amplitude to Oscillation Death via Turing Bifurcation
NASA Astrophysics Data System (ADS)
Koseska, Aneta; Volkov, Evgenii; Kurths, Jürgen
2013-07-01
Coupled oscillators are shown to experience two structurally different oscillation quenching types: amplitude death (AD) and oscillation death (OD). We demonstrate that both AD and OD can occur in one system and find that the transition between them underlies a classical, Turing-type bifurcation, providing a clear classification of these significantly different dynamical regimes. The implications of obtaining a homogeneous (AD) or inhomogeneous (OD) steady state, as well as their significance for physical and biological applications and control studies, are also pointed out.
Fluidic Oscillator Having Decoupled Frequency and Amplitude Control
NASA Technical Reports Server (NTRS)
Koklu, Mehti (Inventor)
2016-01-01
A fluidic oscillator having independent frequency and amplitude control includes a fluidic-oscillator main flow channel having a main flow inlet, a main flow outlet, and first and second control ports disposed at opposing sides thereof. A fluidic-oscillator controller has an inlet and outlet. A volume defined by the main flow channel is greater than the volume defined by the controller. A flow diverter coupled to the outlet of the controller defines a first fluid flow path from the controller's outlet to the first control port and defines a second fluid flow path from the controller's outlet to the second control port.
A psychometric assessment of the Circadian Amplitude and Phase Scale.
Di Milia, Lee; Folkard, Simon; Hill, Joanne; Walker, Curtis
2011-02-01
The Circadian Amplitude and Phase Scale (CAPS) is a new self-report tool that aims to assess amplitude and phase. The CAPS consists of three factors made up of 38 items. Amplitude is posited to be assessed via two of these factors: time awareness (TA) and/or strength of preference (SOP). The remaining factor, phase, is assessed via the existing Preferences Scale (PS). Given there is no published research using this measure, the authors undertook two studies to examine its psychometric properties and construct validity. In a sample of 351 North American students, the authors identified a three-factor 34-item model using principal components analysis. The components explained 39% of the variance, and scale reliability ranged from 0.73 (SOP) to 0.88 (PS). The correlations between the components were small, suggesting they are each assessing different constructs. Thus, it is unlikely TA and SOP may both be indicators of amplitude. The distributions for each scale were divided into two groups (≤ 25th and ≥ 75th percentiles), and these groups were used to assess construct validity using alertness ratings by time-of-day. The results from a multivariate general linear model indicated a significant difference (p < .001) in sleepiness ratings by time-of-day for the PS scale only. In the second study, the authors applied confirmatory factor analysis in an attempt to replicate the factor structure identified in the student sample in a working sample (n = 388). The results suggested the model fit was not optimal. Subsequent analysis suggested a 26-item model was a better fit, but it also was not optimal. The intercorrelations between the factors were larger than in the student sample but again small, indicating the constructs are independent measures. The inability to replicate the factor structure is most likely explained by the differences in the sample characteristics of age, sex, and perhaps difficulty in interpreting the items. The limitations of these studies
Emergence of amplitude and oscillation death in identical coupled oscillators.
Zou, Wei; Senthilkumar, D V; Duan, Jinqiao; Kurths, Jürgen
2014-09-01
We deduce rigorous conditions for the onset of amplitude death (AD) and oscillation death (OD) in a system of identical coupled paradigmatic Stuart-Landau oscillators. A nonscalar coupling and high frequency are beneficial for the onset of AD. In strong contrast, scalar diffusive coupling and low intrinsic frequency are in favor of the emergence of OD. Our finding contributes to clearly distinguish intrinsic geneses for AD and OD, and further substantially corroborates that AD and OD are indeed two dynamically distinct oscillation quenching phenomena due to distinctly different mechanisms.
Algorithms For Segmentation Of Complex-Amplitude SAR Data
NASA Technical Reports Server (NTRS)
Rignot, Eric J. M.; Chellappa, Ramalingam
1993-01-01
Several algorithms implement improved method of segmenting highly speckled, high-resolution, complex-amplitude synthetic-aperture-radar (SAR) digitized images into regions, within each backscattering characteristics similar or homogeneous from place to place. Method provides for approximate, deterministic solution by two alternative algorithms almost always converging to local minimums: one, Iterative Conditional Modes (ICM) algorithm, which locally maximizes posterior probability density of region labels; other, Maximum Posterior Marginal (MPM) algorithm, which maximizes posterior marginal density of region labels at each pixel location. ICM algorithm optimizes reconstruction of underlying scene. MPM algorithm minimizes expected number of misclassified pixels, possibly better in remote sensing of natural scenes.
The Chandler wobble of the poles and its amplitude modulation
NASA Astrophysics Data System (ADS)
Sidorenkov, N.
2015-08-01
It is shown that the period of the Chandler wobble of the poles (CWP) is a combined oscillation caused by three periodic processes experienced by the Earth: (a) lunisolar tides, (b) the precession of the orbit of the Earth's monthly revolution around the barycenter of the Earth-Moon system, and (c) the motion of the perigee of this orbit. The addition of the 1.20 - year Chandler wobble to sidereal, anomalistic, and synodic lunar yearly forcing gives rise slow periodic variations in the CWP amplitude with periods of 32 to 51 years.
Electroglottographic Quasi-open quotient and amplitude in crescendo phonation.
Hacki, T
1996-12-01
Crescendo phonation (swelltone) was used to evaluate the laryngeal tensioning behavior of seven normal speakers and of 12 dysphonic patients. EGG quasi-open quotient (qOq), stroboscopic open quotient, and vocal sound pressure level (SPL) were measured, and EGG amplitude and the mucosal wave were assessed qualitatively. For normal speakers, the qOq decreased greatly as vocal intensity increased. The same tendency was observed, but to a lesser extent, among hyperfunctional dysphonics. In contrast, qOq increased with vocal intensity among the hypofunctional dysphonics. The crescendo task combined with EGG assessment appears to offer a valid approach to the classification of laryngeal dysfunctions.
Simultaneous phase, amplitude, and polarization control of femtosecond laser pulses
NASA Astrophysics Data System (ADS)
Lindinger, A.; Weber, S. M.; Plewicki, M.; Weise, F.
2012-12-01
We present a serial pulse shaper design which allows us to shape the phase, amplitude, and polarization of fs laser pulses independently and simultaneously. The capabilities of this setup are demonstrated by implementing a method for generating parametrically tailored laser pulses. This method is applied on the ionization of NaK molecules by feedback loop optimization, employing a temporal sub pulse encoding. Moreover, we introduce and characterize a further development of this common path pulse shaper scheme for full control of all light field parameters.
Transient Cavitation Induced by High Amplitude Diagnostic Ultrasound.
NASA Astrophysics Data System (ADS)
Ayme, Eveline J.
1988-07-01
Study of the response of gaseous microbubbles to medical ultrasound is essential to apprehend the potentially dangerous effects of transient cavitation on living tissues. However, the prediction of such response is complicated by the finite -amplitude distortion associated with high amplitude acoustic fields. Through a combination of theoretical developments, computer simulations, and experiments, this dissertation investigates the consequences of the interaction between finite-amplitude distortion and transient cavitation, in the context of a diagnostic ultrasonic field. The theoretical approach is to synthesize the asymmetry between compression and rarefaction half-cycles which characterizes a typical nonlinearly distorted pulse obtained at the focus of a diagnostic transducer immersed in water. The synthetic pulse is used to drive a theoretical model for nonlinear bubble dynamics. Comparison with sinusoidal pulses "equivalent" to the distorted pulse as measured by a selection of descriptive parameters shows that: (i) the peak-positive pressure (P_{+} ) in the distorted pulse is a very poor predictor of transient cavitation, (ii) the peak-negative pressure (P_{-}) is a better indicator but underestimates the actual bubble response, (iii) the best predictor is the pressure amplitude of the fundamental (P_{F}) in a Fourier series representation of the distorted pulse. These predictions are tested experimentally on Drosophila larvae. The larvae are exposed to pulsed, symmetric, sinusoidal fields and to pulsed, asymmetric, distorted fields. The killing ratio of the larvae is plotted as a function of the same selection of descriptive parameters, namely P_{+}, P_{ -}, and P_{F}. The resulting curves are compared with the killing ratio plotted against the peak pressure in the sinusoidal, undistorted pulse (P_{A}). If the distorted pulse is described in terms of P_ {-} or P_{+} , the killing ratios are significantly different; if the distorted pulse is described in terms
Partial synchronization and partial amplitude death in mesoscale network motifs
NASA Astrophysics Data System (ADS)
Poel, Winnie; Zakharova, Anna; Schöll, Eckehard
2015-02-01
We study the interplay between network topology and complex space-time patterns and introduce a concept to analytically predict complex patterns in networks of Stuart-Landau oscillators with linear symmetric and instantaneous coupling based solely on the network topology. These patterns consist of partial amplitude death and partial synchronization and are found to exist in large variety for all undirected networks of up to 5 nodes. The underlying concept is proved to be robust with respect to frequency mismatch and can also be extended to larger networks. In addition it directly links the stability of complete in-phase synchronization to only a small subset of topological eigenvalues of a network.
Demodulation techniques for the amplitude modulated laser imager.
Mullen, Linda; Laux, Alan; Cochenour, Brandon; Zege, Eleonora P; Katsev, Iosif L; Prikhach, Alexander S
2007-10-20
A new technique has been found that uses in-phase and quadrature phase (I/Q) demodulation to optimize the images produced with an amplitude-modulated laser imaging system. An I/Q demodulator was used to collect the I/Q components of the received modulation envelope. It was discovered that by adjusting the local oscillator phase and the modulation frequency, the backscatter and target signals can be analyzed separately via the I/Q components. This new approach enhances image contrast beyond what was achieved with a previous design that processed only the composite magnitude information.
Estimation of amplitude and standard deviation of noisy sinusoidal signals
NASA Astrophysics Data System (ADS)
Juarez-Salazar, Rigoberto; Diaz-Ramirez, Victor H.
2017-01-01
A simple method to estimate the amplitude and standard deviation of sinusoidal signals corrupted with additive Gaussian noise is proposed. For this, a two-parameter model is developed by sorting the samples of the signal. This reduced parametric model allows robust parameter estimation, even if the phase function of the sinusoid is nonlinear, discontinuous, and unknown. The functionality and performance of the proposed method are analyzed by several computer simulations; the used GNU Octave program is provided. The proposed method can be useful for unbiased envelope estimation in fringe pattern normalization among other potential applications.
Amplitude-dependent orbital period in alternating gradient accelerators
Machida, S.; Kelliher, D. J.; Edmonds, C. S.; Kirkman, I. W.; Berg, J. S.; Jones, J. K.; Muratori, B. D.; Garland, J. M.
2016-03-16
Orbital period in a ring accelerator and time of flight in a linear accelerator depend on the amplitude of betatron oscillations. The variation is negligible in ordinary particle accelerators with relatively small beam emittance. In an accelerator for large emittance beams like muons and unstable nuclei, however, this effect cannot be ignored. In this study, we measured orbital period in a linear non-scaling fixed-field alternating-gradient accelerator, which is a candidate for muon acceleration, and compared it with the theoretical prediction. The good agreement between them gives important ground for the design of particle accelerators for a new generation of particle and nuclear physics experiments.
Short Large-Amplitude Magnetic Structures (SLAMS) at Venus
NASA Technical Reports Server (NTRS)
Collinson, G. A.; Wilson, L. B.; Sibeck, D. G.; Shane, N.; Zhang, T. L.; Moore, T. E.; Coates, A. J.; Barabash, S.
2012-01-01
We present the first observation of magnetic fluctuations consistent with Short Large-Amplitude Magnetic Structures (SLAMS) in the foreshock of the planet Venus. Three monolithic magnetic field spikes were observed by the Venus Express on the 11th of April 2009. The structures were approx.1.5->11s in duration, had magnetic compression ratios between approx.3->6, and exhibited elliptical polarization. These characteristics are consistent with the SLAMS observed at Earth, Jupiter, and Comet Giacobini-Zinner, and thus we hypothesize that it is possible SLAMS may be found at any celestial body with a foreshock.
Compressional and torsional wave amplitudes in rods with periodic structures
NASA Astrophysics Data System (ADS)
Morales, A.; Flores, J.; Gutierrez, L.; Mendez-Sanchez, R. A.
2002-11-01
To measure and detect elastic waves in metallic rods a low-frequency electromagnetic-acoustic transducer has been developed. Frequencies range from a few hertz up to hundreds of kilohertz. With appropriate configuration of the transducer, compressional or torsional waves can be selectively excited or detected. Although the transducer can be used in many different situations, it has been tested and applied to a locally periodic rod, which consists of a finite number of unit cells. The measured wave amplitudes are compared with theoretical ones, obtained with the one-dimensional transfer matrix method, and excellent agreement is obtained. copyright 2002 Acoustical Society of America.
Transition Distribution Amplitudes for γ⋆γ collisions
NASA Astrophysics Data System (ADS)
Lansberg, J. P.; Pire, B.; Szymanowski, L.
2008-11-01
We study the exclusive production of ππ and ρπ in hard γ⋆γ scattering in the forward kinematical region where the virtuality of one photon provides us with a hard scale in the process. The newly introduced concept of Transition Distribution Amplitudes (TDA) is used to perform a QCD calculation of these reactions thanks to two simple models for TDAs. The sizable cross sections for ρπ and ππ production may be tested at intense electron-positron colliders such as CLEO and B factories (Belle and BABAR).
Amplitude analysis and the nature of the Zc(3900)
NASA Astrophysics Data System (ADS)
Pilloni, A.; Fernández-Ramírez, C.; Jackura, A.; Mathieu, V.; Mikhasenko, M.; Nys, J.; Szczepaniak, A. P.
2017-09-01
The microscopic nature of the XYZ states remains an unsettled topic. We show how a thorough amplitude analysis of the data can help constraining models of these states. Specifically, we consider the case of the Zc (3900) peak and discuss possible scenarios of a QCD state, virtual state, or a kinematical enhancement. We conclude that current data are not precise enough to distinguish between these hypotheses, however, the method we propose, when applied to the forthcoming high-statistics measurements should shed light on the nature of these exotic enhancements.
Arrangement of multiple UV filaments by periodic amplitude masks
NASA Astrophysics Data System (ADS)
Zvorykin, V. D.; Goncharov, S. A.; Ionin, A. A.; Mokrousova, D. V.; Ryabchuk, S. V.; Seleznev, L. V.; Smetanin, I. V.; Shutov, A. V.; Sunchugasheva, E. S.; Ustinovskii, N. N.
2017-07-01
Nonlinear self-focusing of sub-TW power, sub-ps UV pulses generated by Ti:Sapphire/KrF GARPUN-MTW laser facility produces a few hundred randomly distributed filament-like weakly ionized plasma channels in atmospheric air. Arrangement of occasional multiple filaments has been demonstrated by means of amplitude masks with periodic circular and square apertures introduced in the light beam. Diffraction on the apertures overcomes natural stochastic and deterministic radiation inhomogeneities and builds up a regular array of a few hundred filaments persisting over 20 m.
Equidistribution rates, closed string amplitudes, and the Riemann hypothesis
NASA Astrophysics Data System (ADS)
Cacciatori, Sergio L.; Cardella, Matteo
2010-12-01
We study asymptotic relations connecting unipotent averages of {text{Sp}}left( {2g,mathbb{Z}} right) automorphic forms to their integrals over the moduli space of principally polarized abelian varieties. We obtain reformulations of the Riemann hypothesis as a class of problems concerning the computation of the equidistribution convergence rate in those asymptotic relations. We discuss applications of our results to closed string amplitudes. Remarkably, the Riemann hypothesis can be rephrased in terms of ultraviolet relations occurring in perturbative closed string theory.
Superposed pulse amplitude modulation for visible light communication.
Li, J F; Huang, Z T; Zhang, R Q; Zeng, F X; Jiang, M; Ji, Y F
2013-12-16
We propose and experimentally demonstrate a novel modulation scheme called superposed pulse amplitude modulation (SPAM) which is low-cost, insensitive to non-linearity of light emitting diode (LED). Multiple optical pulses transmit parallelly from different spatial position in the LED array and overlap linearly in free space to realize SPAM. With LED arrangement, the experimental results show that using the modulation we proposed the data rate of 120 Mbit/s with BER 1 × 10(-3) can be achieved with an optical blue filter and RC post-equalization.
Amplitude analysis and the nature of the Zc(3900)
Pilloni, A.; Fernandez-Ramirez, C.; Jackura, A.; ...
2017-06-21
The microscopic nature of the XYZ states remains an unsettled topic. We show how a thorough amplitude analysis of the data can help constraining models of these states. Specifically, we consider the case of the Zc(3900) peak and discuss possible scenarios of a QCD state, virtual state, or a kinematical enhancement. Here, we conclude that current data are not precise enough to distinguish between these hypotheses, however, the method we propose, when applied to the forthcoming high-statistics measurements should shed light on the nature of these exotic enhancements.
Born amplitudes and seagull term in meson-soliton scattering
NASA Astrophysics Data System (ADS)
Liang, Y. G.; Li, B. A.; Liu, K. F.; Su, R. K.
1990-06-01
The meson-soliton scattering for the ⊘ 4 theory in 1 + 1 dimensions is calculated. We show that when the seagull term from the equal time commutator is included in addition to the Born amplitudes, the t-matrix from the reduction formula approach is identical to that of the potential scattering with small quantum fluctuations to leading order in weak coupling. The seagull term is equal to the Born term in the potential scattering. This confirms the speculation that the leading order Yukawa coupling is derivable from the classical soliton.