Conical diffraction from a multi-crystal cascade: experimental observations

The cascade conical diffraction phenomenon from up to four crystals is experimentally demonstrated. Less than one year ago M.V. Berry predicted that the focus pattern of conical diffraction from an N-crystal cascade is the superposition of 2 ^N−1 single-crystal concentric conical diffraction patterns (rings), whose ring radii are a combination of those from the individual crystals in cascade. The experimental observations presented here are in full agreement with these theoretical predictions.     

运动后人体心肺节律同步关系及信号的耦合方向

研究运动后青年心肺系统的耦合关系.通过提取在校学生运动后的心跳和呼吸信号,采用经验模态分解的方法对信号进行滤波,分析了心肺信号的相同步行为和心肺节律间耦合作用的相对强弱关系.结果表明,人体在运动后仍然存在心肺系统节律同步现象.这种同步比例不仅因人而异,而且因时而异.由传递熵的计算结果得知,呼吸对于心跳的耦合作用相对较大.     

On the observations of muons in the direction of Cyg X-3

The binary X-ray source Cyg X-3, a known gamma ray emitter, was recently seen to be emmitting a new type of neutral radiation producing muons detected in deep underground experiments. Here an explanation is offered for the deviation of the observed muon directions from that of Cyg X-3. A new underground experiment is suggested to verify the explanation. The new observations enjoying reduced backgrounds will help establish the phenomenon with enormously improved statistical significance. The nature of the neutral radiation, however, remains obscure.     

Revealing direction of coupling between neuronal oscillators from time series: phase dynamics modeling versus partial directed coherence

The problem of determining directional coupling between neuronal oscillators from their time series is addressed. We compare performance of the two well-established approaches: partial directed coherence and phase dynamics modeling. They represent linear and nonlinear time series analysis techniques, respectively. In numerical experiments, we found each of them to be applicable and superior under appropriate conditions: The latter technique is superior if the observed behavior is "closer" to limit-cycle dynamics, the former is better in cases that are closer to linear stochastic processes.     

TM-mode coupling in anisotropic optical waveguides caused by periodic variation optic-axis direction

The problem of mode coupling caused by a small periodic variation of the opticaxis direction in an anisotropic optical waveguide is reduced to a pair of coupled differential equations and an expression for the coupling coefficient is given. For a periodically perturbed section of the waveguide the coupled-mode equations are solved subject to suitable boundary conditions, and the coupling between the forward TM mode and the backward TM mode is analysed. A perturbed section of an anisotropic waveguide acts as a frequency selective reflection filter for TM modes only.     

Synchronization of organ pipes: experimental observations and modeling

We report measurements on the synchronization properties of organ pipes. First, we investigate influence of an external acoustical signal from a loudspeaker on the sound of an organ pipe. Second, the mutual influence of two pipes with different pitch is analyzed. In analogy to the externally driven, or mutually coupled self-sustained oscillators, one observes a frequency locking, which can be explained by synchronization theory. Further, we measure the dependence of the frequency of the signals emitted by two mutually detuned pipes with varying distance between the pipes. The spectrum shows a broad "hump" structure, not found for coupled oscillators. This indicates a complex coupling of the two organ pipes leading to nonlinear beat phenomena.     

Phase transitions of nanoemulsions using ultrasound: experimental observations

The ultrasound-induced transformation of perfluorocarbon liquids to gases is of interest in the area of drug and gene delivery. In this study, three independent parameters (temperature, size, and perfluorocarbon species) were selected to investigate the effects of 476-kHz and 20-kHz ultrasound on nanoemulsion phase transition. Two levels of each factor (low and high) were considered at each frequency. The acoustic intensities at gas bubble formation and at the onset of inertial cavitation were recorded and subsequently correlated with the acoustic parameters. Experimental data showed that low frequencies are more effective in forming and collapsing a bubble. Additionally, as the size of the emulsion droplet increased, the intensity required for bubble formation decreased. As expected, perfluorohexane emulsions require greater intensity to form cavitating bubbles than perfluoropentane emulsions.     

Theoretical and experimental studies of carbon nanotube electromechanical coupling

We present an investigation into electromechanical coupling in carbon nanotubes by focusing on phonon frequency shifts as a result of charge injection. A nearest-neighbor, tight-binding theoretical model is accompanied by a computational explication carried out using the Vienna ab initio simulation package density functional theory code. Raman spectroscopic measurements of the electromechanic couplings under varied but controlled charge injection conditions are also carried out, and the close agreement between the model results and the measured Raman peak shifts suggests that geometrical changes of charged carbon nanotubes previously observed or speculated in different experiments can indeed originate from the simple quantum effects described herein.     

The control of near-field optics: imposing direction through coupling with off-resonant laser light

The well-known spatially distributed form of the near field, associated with a dipolar source, is usually unsuitable for effecting the excitation of a location-specific detector in the vicinity. It is of interest, therefore, to identify a means of producing a much more greatly directed character to such a near field, imposing features that are more commonly associated with longer-range, wave-zone electromagnetic propagation. In this paper, it is shown that nonlinear optical coupling with off-resonant, throughput laser light can achieve this effect. Based on a quantum electrodynamical analysis it is shown that two mechanisms contribute; one requires both the source and detector to be irradiated by the throughput radiation, the other can operate with the source alone irradiated. The analysis leads to results identifying the dependence of each mechanism on the relative directions of the laser beam and the source–detector displacement. Contour maps of the ensuing near field, at the source emission frequency, exhibit a directionality that grows with the off-resonant beam intensity. The phenomenon affords a means of achieving optical control over the near-field distribution.     

Determination of the electron-phonon coupling constants from the experimental temperature dependences of superconducting gaps in MgB2

Experimental temperature dependences Δ_{σ, π}(T) of the energy of superconducting gaps for MgB₂ samples with the critical temperatures 22 K < T _c < 41 K have been fitted by selecting the renormalized electron-phonon coupling constants λ _ij with the use of the Moskalenko-Shul system of equations, the expression for the frequency of collective plasma oscillations obtained by Leggett for two-gap superconductors, and two fitting parameters. We previously obtained the dependences Δ_{σ, π}(T) by the multiple Andreev reflection spectroscopy of superconductor-constriction-superconductor junctions based on MgB₂ with various degree of disorder of the crystal structure. It has been shown that the intraband pairing constants are decisive for the superconductivity mechanism in MgB₂; in this case, √V _σσ V _ππ/V _σπ = 8–22 and the ratio of the interband constants α can range from 3 to 11. The set of the Eliashberg coupling constants λ _ij ⁰ has been qualitatively determined for relatively pure MgB₂ with maximum values T _c ≈ 40 K. The leading constant is 0.7 < λ _σσ ⁰ ≈ λ _eff ⁰ < 0.9 and depends on the choice of the upper integration limit in the Bardeen-Cooper-Schrieffer (BCS) model and the effective Coulomb repulsion μ _iff ^* . The characteristic ratio for the gap in the σ band is 2Δ_σ/k _B T _c = 5.0–6.5.     

Theoretical and experimental studies on spin-orbit coupling in caffeine

We compute the radiative phosphorescence lifetime of caffeine using CNDO/S wavefunctions. The importance of nπ*, πσ* and σπ* singlet and triplet states is considered. The calculated values are in good agreement with experimental determinations. The role played by two-electron terms is briefly discussed.     

Determination of the strong coupling constant using available experimental data

We determine the strong coupling constant α s up to 4-loop in perturbative QCD.Testing QCD requires the measurement of α s over ranges of energy scales.In this analysis,the value of α s is determined from the unpolarized structure functions data points by minimizing the χ ^2 function between the theory result and experimental data.Using perturbative QCD calculations from threshold corrections,we obtain α s （M 2 Z ） = 0.1139±0.0020 at N ^3 LO which is in good agreement with the very recently results from the inclusive jet cross section in pp collisions at√ s=1.96 TeV.     

Determination of the strong coupling constant using available experimental data

We determine the strong coupling constant α s up to 4-loop in perturbative QCD.Testing QCD requires the measurement of α s over ranges of energy scales.In this analysis,the value of α s is determined from the unpolarized structure functions data points by minimizing the χ 2 function between the theory result and experimental data.Using perturbative QCD calculations from threshold corrections,we obtain α s (M 2 Z ) = 0.1139±0.0020 at N 3 LO which is in good agreement with the very recently results from the inclusive jet cross section in pp collisions at√ s=1.96 TeV.     

Measuring direction in the coupling of biological oscillators: a case study for electroreceptors of paddlefish

Recently developed methods for estimating directionality in the coupling between oscillators were tested on experimental time series data from electroreceptors of paddlefish, because each electroreceptor contains two distinct types of noisy oscillators. One type of oscillator is in the sensory epithelia, and another type is in the terminals of afferent neurons. Based on morphological organization and our previous work, we expected unidirectional coupling, whereby epithelial oscillations synaptically influence the spiking oscillators of afferent neurons. Using directionality analysis we confirmed unidirectional coupling of oscillators embedded in electroreceptors. We studied the performance of directionality algorithms for decreasing length of data. Also, we experimentally varied the strength of oscillator coupling, to test the effect of coupling strength on directionality algorithms.     

An experimental study on antipersonnel landmine detection using acoustic-to-seismic coupling

An acoustic-to-seismic system to detect buried antipersonnel mines exploits airborne acoustic waves penetrating the surface of the ground. Acoustic waves radiating from a sound source above the ground excite Biot type I and II compressional waves in the porous soil. The type I wave and type II waves refract toward the normal and cause air and soil particle motion. If a landmine is buried below the surface of the insonified area, these waves are scattered or reflected by the target, resulting in distinct changes to the acoustically coupled ground motion. A scanning laser Doppler vibrometer measures the motion of the ground surface. In the past, this technique has been employed with remarkable success in locating antitank mines during blind field tests [Sabatier and Xiang, IEEE Trans. Geosci. Remote Sens. 39, 1146-1154 (2001)]. The humanitarian demining mission requires an ability to locate antipersonnel mines, requiring a surmounting of additional challenges due to a plethora of shapes and smaller sizes. This paper describes an experimental study on the methods used to locate antipersonnel landmines in recent field measurements.     

Characterizing dusky dolphin sounds from Argentina and New Zealand

Dusky dolphin (Lagenorhynchus obscurus) acoustic sounds were characterized by analyzing narrowband recordings [0-16 kHz in New Zealand (NZ) and 0-24 kHz in Argentina], and sounds in broadband recordings (0-200 kHz) were compared to their counterparts in down-sampled narrowband recordings (0-16 kHz). The most robust similarity between sounds present in broadband recordings and their counterparts in the down-sampled narrowband recordings was inter-click interval (ICI); ICI was therefore primarily used to characterize click sounds in narrowband recordings. In NZ and Argentina, distribution of ICIs was a continuum, although the distribution of ICIs in NZ had a somewhat bimodal tendency. In NZ, sounds that had smaller mean ICIs were more likely to have constant ICIs, and less likely to have increasing or decreasing ICIs. Similar to some other delphinids, dusky dolphins may use single, short duration sounds that have a constant ICI and closely spaced clicks for communication. No whistles were documented at either study site. Temporally structured sequences of burst pulses (i.e., sounds with ICI < about 10 ms) also occurred at both study sites, and these sequences contained 2-14 burst pulses that appeared closely matched aurally and in spectrograms and waveforms.     

基于金属结构单元间耦合的左手材料的设计及实验验证

提出了基于金属结构单元间耦合进行左手材料设计的思想,并建立了理论分析模型.通过合理选择结构单元的结构参数并通过单元之间的耦合,使电谐振等效电路的谐振频率与磁谐振等效电路的谐振频率相等,从而最大限度地实现宽左手频带.加工、制作并测试了基于金属结构单元间耦合的左手材料.实验结果表明,测试样品具有相等的电谐振频率和磁谐振频率,其左手频带的带宽为24 GHz.实验结果与理论分析一致,验证了基于金属结构单元间耦合的左手材料设计思想. 关键词： 左手材料 单元间耦合 等谐振频率 宽频带