Beating Effect Research Articles

Large parity violating effects in atomic dysprosium with nearly degenerate Floquet eigenvalues

In this article we study effects of parity nonconservation in atomic dysprosium, where one has a pair of nearly degenerate levels of opposite parity. We consider the time evolution of this two-level system within oscillatory electric and magnetic fields. These are chosen to have a periodical structure with the same period, such that a Floquet matrix describes the time evolution of the quantum states. We show that, if the states are unstable, the eigenvalues of the Floquet matrix may have contributions proportional to the square root of the parity violating interaction matrix element $H_w$ while they are almost degenerate in their parity even part. This leads to beat frequencies proportional to $\sqrt{H_w}$ which are expected to be larger by several orders of magnitude compared to ordinary P-violating contributions which are of order $H_w$. However, for the simple field configurations we considered, it still seems to be difficult to observe these P-violating beat effects, since the states decay too fast. On the other hand, we found that, within only a few Floquet cycles, very large parity violating asymmetries with respect to experimental setups of opposite chirality may be obtained. The electric and magnetic fields as well as the time intervals necessary for this are in an experimentally accessible range. For statistically significant effects beyond one standard deviation a number of about $10^7$ atoms is required. Our ideas may be applied directly to other 2-level atomic systems and different field configurations. We hope that these ideas will stimulate experimental work in this direction.

X-ray standing-wave study of(AlAs)m(GaAs)nshort-period superlattices

X-ray standing-waves (XSW) are used for an investigation of the structure of $(\mathrm{AlAs}{)}_{m}(\mathrm{GaAs}{)}_{n}$ short-period superlattices (SL's). The XSW induced modulation of x-ray fluorescence from the Al, As, and Ga atoms and the total photoelectron yield are monitored around the 0th order SL satellite (AlAs)(GaAs)(004,0) and the GaAs(004) substrate Bragg reflection. From the specific shape of these modulations and the sample reflectivity, an atomic model about the interfaces is derived. This is accomplished by comparing the experimental data with dynamical calculations of x-ray wavefield distribution and reflectivity, which are based on the Takagi-Taupin equation. The fluorescence measurements at the 0th order SL satellite reveal a high crystalline order in the AlAs layers of the short-period SL, whereas in the GaAs layers, a fraction of the Ga and As atoms is not on the ideal lattice positions. From the analysis, a model of the atomic distribution along the [001] direction can be determined. This reveals that at each internal interface in the GaAs layers, two Ga atom planes are shifted by up to 0.035 nm and one As atom plane by 0.023 nm. At each interface, the shifts are directed towards the substrate. In addition, the XSW field at the GaAs(004) substrate reflection results in a moir\'e or beating effect in the SL structure, which can be used to determine the information depth ${\ensuremath{\Lambda}}_{e}$ of total electron-yield measurements in a more detailed approach.

THEORETICAL STUDY OF THE FIFTH-ORDER POLARIZA-TION BEATS IN A FOUR-LEVEL SYSTEM

We have studied theoretically a beat effect in a four-level system due to fifth-order optical polarization, and considered the cases that the pump beams have either narrowband or broadband linewidth. We have found that the accuracy for the energy-level splitting meaurement is determined by the homogeneous linewidths of the optical transitions. That is to say, this technique can achieve Doppler-free precision in the measurement of the eaergy level splitting between two excited states which are dipolar forbidden from the ground state.

Wannier--Bloch Oscillators

We consider a Wannier–Stark problem with only one ladder for weak field. We prove that a generic first-band state is a metastable state (Wannier–Bloch oscillator) oscillating because of a beating effect and decaying at the rate given by the imaginary part of the Wannier-Stark resonances. By this result we have at the same time the realization of the ideas of Bloch about the oscillations, of Wannier about the approximate quantization and of Zener about the metastability. Such oscillators, which generically perform a breathing mode motion in a large spatial region, have been experimentally observed.

Dispersion induced multiple signal peak splitting in partial coherence interferometry

Dispersion is known to increase the width of the coherence envelope and therefore to decrease the resolution in partial coherence interferometry (PCI). If the thickness of a thin foil located behind a dispersive medium is to be measured, a further effect occurs. Because of the different refractive indices of different wavelengths in the dispersive medium, the period of the intensity oscillations of the interference fringes varies within the signal signature. This causes a beat effect which can lead to a multiple splitting of the PCI signal peaks. We demonstrate this effect experimentally and compare the experimental results with computer simulations. Furthermore, we discuss the implications of this effect for PCI and optical coherence tomography of the human retina. Care has to be taken to not confuse the peak splitting with real multilayer structures. Finally, we show how this effect can be used to improve the precision of thickness measurements of thin foils.

Before and after retrofit – response of a building during ambient and strong motions

Abstract This paper presents results obtained from ambient vibration and strong-motion responses of a thirteen-story, moment-resisting steel framed Santa Clara County Office Building (SCCOB) before being retrofitted by visco-elastic dampers and from ambient vibration response following the retrofit. Understanding the cumulative structural and site characteristics that affect the response of SCCOB before and after the retrofit is important in assessing earthquake hazards to other similar buildings and decision making in retrofitting them. The results emphasize the need to better evaluate structural and site characteristics in developing earthquake resisting designs that avoid resonating effects. Various studies of the strong-motion response records from the SCCOB during the 24 April 1984 (MHE) Morgan Hill ( M s =6.1), the 31 March 1986 (MLE) Mt. Lewis ( M s =6.1) and the 17 October 1989 (LPE) Loma Prieta ( M s =7.1) earthquakes show that the dynamic characteristics of the building are such that it (a) resonated (b) responded with a beating effect due to close-coupling of its translational and torsional frequencies, and (c) had a long-duration response due to low-damping. During each of these earthquakes, there was considerable contents damage and the occupants felt the rigorous vibration of the building. Ambient tests of SCCOB performed following LPE showed that both translational and torsional periods of the building are smaller than those derived from strong motions. Ambient tests performed following the retrofit of the building with visco-elastic dampers show that the structural fundamental mode frequency of the building has increased. The increased frequency implies a stiffer structure. Strong-motion response of the building during future earthquakes will ultimately validate the effectiveness of the retrofit method.

Coherent lidar at low signal powers: Basic considerations on optical heterodyning

In a number of optical heterodyne systems it may happen that the signal power is so low that only a few, or even fractions of, photons enter the receiver in a characteristic time interval. As the heterodyne receiver basically employs the beating effect, such intricate questions as “is there still a beating between the (many) local oscillator photons and the few return photons?” or “how can a single photon produce an intermediate frequency?” arise. We show that the semiclassical theory, which provides exact results as long as optical fields with an adequate classical description are used, is capable of answering those questions. The term “photon” must thereby be assigned its (semiclassically) correct meaning, which is an abbreviation for “discrete interaction of light and matter.” We illustrate our discussion by providing a numerical example related to a space-borne CO2 Doppler wind lidar instrument.

Mutualistic and Commensal Organization of Avian Mixed-Species Foraging Flocks in a Forest of Western Madagascar

I examined the feeding rates and foraging niches of seven species regularly participating in heterospecific avian flocks in a deciduous dry forest of western Madagascar in two different social situations, viz. when the species was foraging alone or with conspecifics, and in heterospecific flocks, respectively. The species responded differently to mixed-flocking. A change in feeding sites and/or techniques was found in six species, five of which increased their feeding rates when foraging in heterospecific flocks. In mixed flocks, they tended to use similar substrates. That such interspecific convergence enhanced feeding rate might be explained by social learning, kleptoparasitism or a beating effect. Benefits gained through these effects were greatest in two species consistently acting as followers, Crested Drongo Dicrurus forficatus and Paradise Flycatcher Tersiphone mutata. Although as leaders, Newtonia Newtonia brunneicauda and Long-billed Greenbul Phyllastrephus madagascariensis often attracted other species, they also increased their feeding rates through some mutualistic effects. Another leader, Rufous Vanga Shetba rufa was the only species that neither changed foraging niche nor feeding efficiency in different social situations. Its participation in heterospecific associations probably resulted from other species exploiting the vanga's ability to detect predators. Therefore, the organization of multispecies flocks in Madagascar was mainly based on mutualism and commensalism which increased feeding efficiency.

Binaural Auditory Beats Affect Vigilance Performance and Mood

LANE, J. D., S. J. KASIAN, J. E. OWENS AND G. R. MARSH.Binaural auditory beats affect vigilance performance and mood. PHYSIOL BEHAV 63(2) 249–252, 1998.—When two tones of slightly different frequency are presented separately to the left and right ears the listener perceives a single tone that varies in amplitude at a frequency equal to the frequency difference between the two tones, a perceptual phenomenon known as the binaural auditory beat. Anecdotal reports suggest that binaural auditory beats within the electroencephalograph frequency range can entrain EEG activity and may affect states of consciousness, although few scientific studies have been published. This study compared the effects of binaural auditory beats in the EEG beta and EEG theta/delta frequency ranges on mood and on performance of a vigilance task to investigate their effects on subjective and objective measures of arousal. Participants (n = 29) performed a 30-min visual vigilance task on three different days while listening to pink noise containing simple tones or binaural beats either in the beta range (16 and 24 Hz) or the theta/delta range (1.5 and 4 Hz). However, participants were kept blind to the presence of binaural beats to control expectation effects. Presentation of beta-frequency binaural beats yielded more correct target detections and fewer false alarms than presentation of theta/delta frequency binaural beats. In addition, the beta-frequency beats were associated with less negative mood. Results suggest that the presentation of binaural auditory beats can affect psychomotor performance and mood. This technology may have applications for the control of attention and arousal and the enhancement of human performance.

Exact Response Analysis and Dynamic Design of Cam-Follower Systems Using Laplace Transforms

This article presents Laplace transforms utilizing methods to determine response of follower systems to motions machined on cams. The exact response of a follower system at any cycle, at any time, or in any time zone is directly determined without the need for numerical integrations. The method permits the study of response for many cycles to determine beat effect, the critical cam speeds, and possible follower jump conditions. Cam profile is corrected to eliminate static error and oscillate follower about exact position. Disk cams with translating roller followers with one and two degrees of freedom are considered in the article. Numerical illustrations are included, where results by other numerical methods (matrix exponential and phase plane-6) are compared.

High-accuracy wavelength-change measurement system based on a Wollaston interferometer, incorporating a self-referencing scheme

A novel wavelength-difference measurement scheme with a Wollaston prism is presented. By using a suitable reference wavelength, a small variation in the signal wavelength can be converted into a relatively larger change in the modulated wavelength, as a result of the so-called fringe beating effect, resulting in enhanced measurement sensitivity by use of autocorrelation and Gaussian filtering techniques. From the results of a simulation carried out, we observed a wavelength variation of 0.01 nm over 15 nm or 0.1 nm over 60 nm for a typical pair of laser diodes with wavelengths of 785 and 810 nm, and wavelength variations of 0.5 nm over 40 nm or 1 nm over 110 nm for 671-and 785-nm wavelengths. These results were partially verified by the experimental results obtained for which a resolution of 0.01 nm over a range of 2.5 nm for the first pair and 0.5 nm over 4 nm for the second pair of laser diodes was seen. The results have applications to the determination of wavelength variations in a wavelength-division multiplexing system or measurement of the wavelength changes induced in a range of optical sensors.

Mutualism and Commensalism in Avian Mixed-Species Flocks in a Western Forest of Madagascar

I examined the feeding rates and feeding niches of regular partcipating species of avian mixd-species flocks in a western forest of Madagascar in different social situations. The regular species were, Crested Drongo, Common Newtonia, Madagascar Paradise Flycatcher, Rufous Vanga, Blue Vanga, Long-billed Greenbul and Ashy Cuckoo Shrike. All of the species responded differently to mixed-flocking and thus it is suggested that the effects of association varied among species. The changing of feeding sites and/or technique was found in six species, five of which increased feeding rates. When participating in mixed flocks, they tended to use similar height and increased variations of location and/or technique. The interspecific convergence enhancing feeding rate, contrary to that expected from a competition may be explained from a social learning effect. The effect appeared to be greatest in Drongo, which increased feeding efficiency by changing not only foraging habits but also prey menu when foraging with other species. In Drongo, kleptoparasitism also appeared to contribut to increase feeding effisiency in mixed-flocks. Paradise Flycatcher also benefitted much from foraging in mixed flocks by a beating effect. The two species' consistently-following tactics in mixed-flocks is greatly paid through these effects. Although Newtonia and Greenbul often attracted other species as leaders, then, they increased feeding rates through some mutualistic effects. Rufous Vanga was the only species that changed neither feeding habits and feeding efficiency in different social situations. Most individuals of this species foraged in cohesive conspecific breeding groups, and frequently gave alarm calls and even direct attacks against predators. These characteristics of Rufous Vanga suggest that its conspecific groups moved independently of other species and that its association with heterospecifics probably resulted from other species following it to exploit its ability to detect predators.

Multimode laser model with coupled cavities and quantum noise

A stochastic, semiclassical model is developed for a multimode, homogeneously broadened laser with rapid dipole dephasing, appropriate for semiconductor, Ti:sapphire, or dye lasers. The theory self-consistently incorporates population dynamics including temporal beating effects and relaxation oscillations, spatial hole burning, coherent-wave mixing, and quantum noise. The model is valid for single- and compound-cavity lasers in which the mode frequencies are well defined. We pay particular attention to finding a useful mode basis in the case that the gain medium does not completely fill the cavity. This situation can lead to coupled-cavity effects. For typical systems the model is valid for pump rates up to several times threshold and is tractable for numerical simulations. The theoretical development described in this paper is applied to an experimental system in a companion paper (J. Opt. Soc. Am. B14, 180 (1997)].

Fringe beating effects induced by misalignment in a white-light interferometer

The profile of the interference fringe packet obtained in interferometry, especially in the topical area of white-light interferometry, may be dramatically altered by the presence of the so-called `fringe beating effect' due to the poor quality of the collimation lens or the misalignment of the optical arrangement. In the worst cases, the peak value of the central fringe will be equal to or even less than that of the other fringes and in consequence will give an erroneous result for the determination of the central fringe position in the visibility profile. This effect is considered using a simple computer simulation model and the results both from the computer simulation and from experiment are discussed and compared to find means of eliminating such effects.

Reswelling Capability of Pulp Fibers in Paper Sheet.

Water-reswelling capability of pulp fibers was studied by water retention value applied to paper sheet. (WRV-PS) Optimum conditions for determining WRV-PS were first examined, and the WRV-PS obtained by centrifugation at 3000 G for 15min can be regarded as a peculiar value for characterizing reswelling properties of paper sheets. Effects of beating, couching, pressing and drying in handsheet-making on reswelling capability of paper sheet were sensitively and clearly detected by the WRV-PS, in comparison with equilibrium moisture content or specific surface area. A decrease in WRVs-PS by pressing and/or drying reflected the formation of hydrogen bonds of pulp fibers in paper sheet. Furthermore, the decrease in WRVs-PS or the formation of hydrogen bonds in pulp fibers occurred in pressing or dried paper web at water content below the fiber saturation point. Therefore, WRV-PS is widely applicable to evaluation of reswelling properties of paper sheet.

Implications of myocardial lactate metabolism during coronary artery bypass grafting (CABG): Adverse effects of empty beating on the hearts of patients with left main trunk disease (LMTD)

Implications of myocardial lactate metabolism during coronary artery bypass grafting (CABG): Adverse effects of empty beating on the hearts of patients with left main trunk disease (LMTD)

The effects of laboratory beating on cellulose structure

The effects of laboratory beating on cellulose structure

Exact treatment of beating phenomena in EXAFS

Beating occurs when two coordination shells are closely spaced ( δR ≈ 0.1 A ̊ ). Analyzing two such shells by curve fitting is difficult because the fit parameters exhibit enhanced correlation due to the reduced number of degrees of freedom. Analyzing the combined phase of the two shells in k-space, or its derivative with respect to k, can be performed with a reduced number of fit parameters because only the ratio of the two coordination numbers is required and, with a minor approximation, only the difference of the two EXAFS Debye-Waller factors is needed. Since the beating effect leads to structure that occurs localized in k-space and because this beating structure is usually at the high- k end (for very closely spaced coordination shells) one may neglect the effects of the energy corrections ΔE 1 and ΔE 2 for the origins of the two k-scales, thus reducing the number of fit parameters by another two. The beating effect can be investigated conveniently by analyzing the derivative of the combined phase of the two coordination shells in k-space. Then the occurrence of beating manifest itself by peaks or dips in the derivative function. This structure, however, can be modified significantly by effects resulting from the Fourier transform. In the present paper such Fourier transform artifacts, the effects of window functions and k-space weighting are taken into account.

Effects of ventricular arrhythmia on the cerebral microcirculation in cats.

To test the widely believed but poorly proved hypothesis that the cerebral symptoms observed during ventricular arrhythmia are caused by a reduced cerebral blood supply, we examined the effects of single and multiple ectopic ventricular beats (or ventricular tachycardia of short duration) on the cerebral microcirculation. Six anesthetized cats were used. Ectopic ventricular systoles of various sequences were produced by electrically stimulating the ventricle through a bipolar needle-type electrode for 1 to 50 times at a rate of 300/min. The local cerebral blood volume (CBV) and blood flow (CBFLD) in the cortex were measured continuously employing the photoelectric and laser Doppler methods. CBV reflects the cumulative dimensions of the cerebrocortical microvessels. Ectopic ventricular contractions, as confirmed by electrocardiograms, always reduced the CBV and arterial blood pressure in a total of 104 attempts. The CBV reductions ranged from 0.20 +/- 0.03 vol% for a single ectopic beat to approximately 0.6-0.8 vol% for runs of 8 or more beats. The CBFLD reductions measured with the laser Doppler flowmeter were 10-35%. The reductions in CBV and CBFLD during the ventricular arrhythmia could be attributed to the abrupt and marked reductions in arterial blood pressure. Runs of ectopic ventricular beats have significant effects on the cerebral microcirculation, whether clinically apparent or not.

Characterization of the excitable gap in a functionally determined reentrant circuit. Studies in the sterile pericarditis model of atrial flutter.

Single premature beats were introduced in the reentrant circuit during stable atrial flutter in the canine sterile pericarditis model to test the hypotheses that (1) despite the fact that the reentrant circuit is functionally determined, there is a fully excitable gap; (2) the excitable gap in the reentrant circuit is not uniform; and (3) inhomogeneities of conduction in the reentrant circuit explain the effects of premature beats. A multiplexing system was used to record 190 unipolar electrograms from the right atrial free wall during 18 atrial flutter episodes in 9 dogs. In all 18 episodes, premature stimuli captured the atrial flutter reentrant circuit. At the longest coupling intervals, the return cycle at the site closest to the pacing site did not prolong. As the coupling interval of the premature stimulus decreased, the return cycle then progressively increased, associated with changes in conduction in the reentrant circuit that were not uniform. The result was that coupling intervals associated with introduction of the premature beat also were not constant. The mean duration of the total (ie, fully plus partially) excitable gap was 12 +/- 4 ms in areas of slow conduction, and it was always shorter than the total excitable gap in other areas (22 +/- 6 ms, P < .001). The mean duration of the fully excitable gap based on analysis of the return cycle was 4 +/- 1 ms in the reentrant circuit. In 13 of 18 atrial flutter episodes, a premature stimulus terminated atrial flutter by causing block of the orthodromic wave front of the premature beat in an area of slow conduction. The mean coupling interval that caused orthodromic block was 113 +/- 5 ms (recorded at the site just proximal to the area of block), and it was always longer than the delivered stimulus coupling interval at the pacing site (96 +/- 8 ms, P < .001). We conclude that in this functionally determined atrial flutter reentrant circuit in the canine sterile pericarditis model, (1) a fully excitable gap is present in at least part of the reentrant circuit; (2) the duration of the excitable gap in the reentrant circuit is shortest in areas of slow conduction; and (3) when a premature beat encounters the partially excitable gap of the reentrant circuit, it results in changes in conduction such that the coupling intervals are not uniform throughout in the reentrant circuit.