Feasible "Kochen-Specker" experiment with single particles

We present a simple experimental scheme which can be used to demonstrate an all-or-nothing-type contradiction between noncontextual hidden variables and quantum mechanics. The scheme, which is inspired by recent ideas by Cabello and Garcia-Alcaine, shows that even for a single particle, path and spin information cannot be predetermined in a noncontextual way.     

Comment on "Auditory-nerve first-spike latency and auditory absolute threshold: a computer model" [J. Acoust. Soc. Am. 119, 406-417 (2006)

A recent paper by Meddis [J. Acoust. Soc. Am. 119, 406-417 (2006)] shows that an existing model of the auditory nerve [Meddis and O'Mard, J. Acoust. Soc. Am. 117, 3787-3798 (2005)] is consistent with experimentally-measured first-spike latencies in the auditory nerve [Heil and Neubauer, J. Neurosci. 21, 7404-7415 (2001)]. The paper states that this consistency emerges because in the model, the calcium concentration inside the inner hair cell builds up over long periods of time (up to at least 200 ms) during tone presentation. It further states that integration over long time-scales happens despite the very short time constants (< 1 ms) used for the calcium dynamics. This letter demonstrates that these statements are incorrect. It is shown by simulation that calcium concentration inside the hair cell stage of the Meddis model rapidly reaches a steady state within a few milliseconds of a stimulus onset, exactly as expected from the short time-constant in the simple first-order differential equation used to model the calcium concentration. The success of the Meddis model in fitting experimental data actually confirms earlier results [Krishna, J. Comput. Neurosci. 13, 71-91 (2002a)] that show that the experimental data are a natural result of stochasticity in the synaptic events leading up to spike-generation in the auditory nerve; integration over long time scales is not necessary to model the experimental data.     

如何“写”出平面简谐波的波函数

介绍了大学物理课堂中讲授平面简谐波波函数的一种教学设计,其核心是在课堂教学中归纳总结出平面简谐波波函数的一般形式,为学生提供处理波函数问题的简单方法,该方法只要给定任意点的振动方程及波的传播方向,就可依据一般形式"写"出平面简谐波的波函数.     

Adaptability and "intermediate phase" in randomly connected networks

We present a simple model that enables us to analytically characterize a floppy to rigid transition and an associated self-adaptive intermediate phase in a random bond network. In this intermediate phase, the network adapts itself to lower the stress due to constraints. Our simulations verify this picture. We use these insights to identify applications of these ideas in computational problems such as vertex cover and K-satisfiability.     

"Ideal" optical delay lines based on tailored-coupling and reflecting, coupled-resonator optical waveguides

We present a design of "ideal" optical delay lines (i.e., constant amplitude and constant group delay over the desired bandwidth). They are based on reflection from coupled-resonator optical waveguides (CROWs). The inter-resonator coupling coefficients are tailored and decrease monotonically with the distance from the input to realize all-pass Bessel filters. The tailored coupling coefficients result in a frequency-dependent propagating distance which compensates for the group velocity dispersion of CROWs. We present a simple formalism for deriving the time-domain coupling coefficients and convert these coefficients to field coupling coefficients of ring resonators. The reflecting CROWs possess a delay-bandwidth product of 0.5 per resonator, larger than that of any kind of transmitting CROW. In the presence of uniform gain, the gain enhanced by slow light propagation and the constant group delay result in efficient and dispersion-free amplifiers.     

"BEST" homonuclear adiabatic decoupling for 13C- and 15N-double-labeled proteins.

The cyclic irradiation sidebands appearing in homonuclear adiabatic decoupling are calculated in detail, which reveals the origin of the antisymmetric sidebands. The sidebands can be inverted by inserting an initial decoupling with a different period, but the same f1rms as the main decoupling that is required for Bloch-Siegert shift compensation. The sidebands can be eliminated in a broad decoupling range by adding spectra of opposite sidebands. Based on this scheme, an offset-independent double-adiabatic decoupling, named Bloch-Siegert Shift Eliminated and Cyclic Sideband Trimmed Double-Adiabatic Decoupling, or "BEST" decoupling for short, is constructed, which not only compensates the Bloch-Siegert shift as shown earlier by Zhang and Gorenstein (1998) but also eliminates residual sidebands effectively.     

基于“猫眼效应”的目标识别

 阐述了“猫眼效应”的基本原理，并在此基础上对“猫眼效应”进行了实验验证。实验结果表明，光电探测器的确存在“猫眼效应”。利用“猫眼效应”进行远距离的目标探测与识别能够简化系统并有效提高目标探测识别的概率，对今后选取合适的方案进行空间目标捕获、跟踪和瞄准有一定的参考意义。     

Comments on "Effects of Noise on Speech Production: Acoustic and Perceptual Analyses" [J. Acoust. Soc. Am. 84, 917-928 (1988)

The effect of background noise on speech production is an important issue, both from the practical standpoint of developing speech recognition algorithms and from the theoretical standpoint of understanding how speech is tuned to the environment in which it is spoken. Summers et al. [J. Acoust. Soc. Am. 84, 917-928 (1988]) address this issue by experimentally manipulating the level of noise delivered through headphones to two talkers and making several kinds of acoustic measurements on the resulting speech. They indicate that they have replicated effects on amplitude, duration, and pitch and have found effects on spectral tilt and first-formant frequency (F1). The authors regard these acoustic changes as effects in themselves rather than as consequences of a change in vocal effort, and thus treat equally the change in spectral tilt and the change in F1. In fact, the change in spectral tilt is a well-documented and understood consequence of the change in the glottal waveform, which is known to occur with increased effort. The situation with F1 is less clear and is made difficult by measurement problems. The bias in linear predictive coding (LPC) techniques related to two of the other changes-fundamental frequency and spectral tilt-is discussed.     

Kinematics,equilibrium, and shape in Hamiltonian systems: the "LAB" effect

We demonstrate that a system of a finite number of particles in a container with a "typical" shape does not get mixed in the sense that in an (asymptotic) steady state distribution the particles are not equally likely to occupy (almost) any position inside the container. Our incomplete mixing result should be contrasted with the complete mixing of noninteracting or elastically colliding particles in a box, which does occur because the box is not a "typical" shape. The effect we describe does not disappear in the limit of infinitely many particles. However, it is unlikely to be observed in nature but rather in laboratory (the "LAB" effect) experiments. Ideal gas in a container, which is a product of billiards, serves as a transparent model to understand the "LAB" (look at billiards) effect.     

On chaotic dynamics in "pseudobilliard" Hamiltonian systems with two degrees of freedom

A new class of Hamiltonian dynamical systems with two degrees of freedom is studied, for which the Hamiltonian function is a linear form with respect to moduli of both momenta. For different potentials such systems can be either completely integrable or behave just as normal nonintegrable Hamiltonian systems with two degrees of freedom: one observes many of the phenomena characteristic of the latter ones, such as a breakdown of invariant tori as soon as the integrability is violated; a formation of stochastic layers around destroyed separatrices; bifurcations of periodic orbits, etc. At the same time, the equations of motion are simply integrated on subsequent adjacent time intervals, as in billiard systems; i.e., all the trajectories can be calculated explicitly: Given an initial data, the state of the system is uniquely determined for any moment. This feature of systems in interest makes them very attractive models for a study of nonlinear phenomena in finite-dimensional Hamiltonian systems. A simple representative model of this class (a model with quadratic potential), whose dynamics is typical, is studied in detail. (c) 1997 American Institute of Physics.     

Comment on “Questioning the Recent Observation of Quantum Hawking Radiation” [Ann. Phys. (Berlin) 2018, 530, 1700114]

The observation of quantum Hawking radiation and its entanglement in an analogue black hole was recently reported. A subsequent article presented critical comments of the study. The article suffers from technical difficulties which invalidate its claims. These include the misunderstanding of a simple Fourier transform, the unnecessary modification of experimental data, and the assertion that the experiment measured a strictly‐zero population.     

All-optical generation of states for "Encoding a qubit in an oscillator"

Most quantum computation schemes propose encoding qubits in two-level systems. Others exploit the use of an infinite-dimensional system. In "Encoding a qubit in an oscillator" [Phys. Rev. A 64, 012310 (2001)], Gottesman, Kitaev, and Preskill (GKP) combined these approaches when they proposed a fault-tolerant quantum computation scheme in which a qubit is encoded in the continuous position and momentum degrees of freedom of an oscillator. One advantage of this scheme is that it can be performed by use of relatively simple linear optical devices, squeezing, and homodyne detection. However, we lack a practical method to prepare the initial GKP states. Here we propose the generation of an approximate GKP state by using superpositions of optical coherent states (sometimes called "Schr?dinger cat states"), squeezing, linear optical devices, and homodyne detection.     

E.S.R. spectroscopy of non-cyclic enones

The π-bond model is applied to the calculation of the proton chemical shifts of a range of benzenoid hydrocarbons. The simple calculations give results which compare well with experiment and with calculations based on the ring current model. Least squares fitting of the predicted chemical shifts to the observed values can give an indication of the occurrence of local aromatic groups in larger molecules. This procedure also yields an empirically adjusted estimate of the anisotropy in the molar magnetic susceptibility from the experimental proton chemical shifts. A simple criterion for aromaticity is also given. The overall results suggest that there is no need to associate a special ring current attribute to π conjugation in aromatic molecules.     

Principles of Adaptive Optics, 3rd edn., by Robert K. Tyson

A review is made of the quantum effects which are observed in the transport coefficients of semiconductors. Quantization of the free carriers in semiconductors is produced whenever an external potential acts on an otherwise uniform and perfect crystal. Typical examples are a magnetic field, an electric field or the physical boundaries of the sample. A magnetic field quantizes the electron and hole states into a ladder of equally spaced Landau levels. This gives rise to the Shubnikov–de Haas, magnetophonon and magneto-impurity effects, where the positions of the Landau levels resonate with the Fermi, phonon, or impurity energies present in the sample. A series of oscillations in the magneto-resistance of many different types of materials results. Electric fields applied to the surface of metal oxide semiconductor (MOS) devices result in a set of quantum levels for motion perpendicular to the surface. At low temperatures the charge carriers are bound to the surface and behave as if they were two-dimensional. This is shown to give rise to very dramatic oscillatory metal–insulator behaviour in high magnetic fields. Quantization is also shown to occur in very thin layers of semiconductors which act like a simple square well potential, the energy levels of which can be studied as a function of layer thickness. The carriers are confined within the layers, and also show two-dimensional behaviour.     

Evidence for microbunching "sidebands" in a saturated free-electron laser using coherent optical transition radiation

We report the first measurements of z-dependent coherent optical transition radiation (COTR) due to electron-beam microbunching at high gains ( >10(4)) including saturation of a self-amplified spontaneous emission free-electron laser (FEL). In these experiments the fundamental wavelength was near 530 nm, and the COTR spectra exhibit the transition from simple spectra to complex spectra ( 5% spectral width) after saturation. The COTR intensity growth and angular distribution data are reported as well as the evidence for transverse spectral dependencies and an "effective" core of the beam being involved in microbunching.     

"Development of REDOR rotational-echo double-resonance NMR" by Terry Gullion and Jacob Schaefer [J. Magn. Reson. 81 (1989) 196-200

The popularity of rotational-echo double-resonance (REDOR) NMR arises from its ability to measure weak dipolar couplings and long-range heteronuclear distances accurately. This ability was not anticipated in the first REDOR experiments and resulted from the effectiveness of a simple radiofrequency phase alternation scheme to suppress amplitude and phase distortions in echo trains even after hundreds of pi pulses.     

A history of scanning electron microscopy developments: towards "wet-STEM" imaging

A recently developed imaging mode called "wet-STEM" and new developments in environmental scanning electron microscopy (ESEM) allows the observation of nano-objects suspended in a liquid phase, with a few manometers resolution and a good signal to noise ratio. The idea behind this technique is simply to perform STEM-in-SEM, that is SEM in transmission mode, in an environmental SEM. The purpose of the present contribution is to highlight the main advances that contributed to development of the wet-STEM technique. Although simple in principle, the wet-STEM imaging mode would have been limited before high brightness electron sources became available, and needed some progresses and improvements in ESEM. This new technique extends the scope of SEM as a high-resolution microscope, relatively cheap and widely available imaging tool, for a wider variety of samples.     

"Learn on the fly": a hybrid classical and quantum-mechanical molecular dynamics simulation

We describe and test a novel molecular dynamics method which combines quantum-mechanical embedding and classical force model optimization into a unified scheme free of the boundary region, and the transferability problems which these techniques, taken separately, involve. The scheme is based on the idea of augmenting a unique, simple parametrized force model by incorporating in it, at run time, the quantum-mechanical information necessary to ensure accurate trajectories. The scheme is tested on a number of silicon systems composed of up to approximately 200 000 atoms.