Magnetic properties of cuprate superconductors based on a phase separation theory

There is a great debate concerning the hole of the inhomogeneities in high critical temperature superconductors (HTS). Several experiments indicate a possible electronic phase separation (PS). However, there is not a method to quantify how such transition occurs and how it develops. Here we show that the Cahn–Hilliard (CH) theory of phase separation provides a way to trace the phase separation process as a function of temperature. We connect these calculations with the Bogoliubov–deGennes (BdG) approach to an inhomogeneous superconductor and derive many HTS properties of the La_2−xSrCuO₄ (LSCO) system. The results yield: an onset of superconductivity that follows close the Nernst signal, the leading edge shift is close to the zero temperature average gap, and the superconducting phase is achieved by percolation. Our approach reproduces also the experimental measurements of the H_c2 field.     

Time shifts and correlations in synchronized chaos

We introduce a new method for predicting characteristics of the synchronized state achieved by a wide class of unidirectional coupling schemes. Specifically, we derive a transfer function from the coupling model that provides estimates of the correlation between the drive and response waveforms, and of the time shift (i.e., lag or anticipation) of the synchronized state. To demonstrate the method, we apply it to a simulated system of coupled Rossler oscillators as well as to an experimental system of coupled chaotic electronic circuits. Finally, we show that the transfer function can be exploited to design novel coupling schemes that significantly improve the correlation and increase the maximum achievable time shift.     

Attenuation,scattering, and depolarization of light by gold nanorods with silver shells

Gold nanoparticles with silver nanoshells are obtained by synthesizing gold nanorods in a growing solution containing cetyltrimethylammonium bromide, subsequent separation in a concentration gradient of glycerol, and reduction of silver nitrate by ascorbic acid under alkaline conditions in the presence of polyvinylpyrrolidone. The formation of silver nanoshells was monitored by the shift of plasmon resonances of extinction and differential light scattering, by the appearance of characteristics peaks of silver in the energy dispersive X-ray (EDX) spectra of samples, by the data of transmission electron microscopy, and by visual changes in the color of colloids. The spectrum of the intensity ratio of the co- and cross-polarized compo- nents of light scattered by gold-silver nanorods is measured for the first time, and it is observed that the maximum is shifted by 80–100 nm compared to previously published spectra of gold nanorods (Khlebtsov et al., J. Phys. Chem. C 112, 12760 (2008)). The extinction and light scattering spectra are calculated by the method of separation of variables using the model of a confocal two-layer spheroid and these calculations are found to agree with spectral measurements. A method for determining the thickness of a silver nanolayer by the spectral shift of an extinction longitudinal resonance is described. The obtained data of optical spectroscopy and transmission electron microscopy and estimations of the mass of the deposited metal show that the aver-age thickness of the silver layer varies from 0.12 to 4 nm as the Ag/Au ratio changes from 2/80 to 90/80 μg/μg.     

Effect of strain on hole tunneling dynamics in double barrier heterostructures

A study of the effects of strain due to external stress and lattice mismatch on hole tunneling times in double barrier heterostructures is presented. The band structure of holes is calculated based on a k·p method within the envelope function approximation, including band mixing effects. The phase delay time is obtained from the energy derivative of the total phase shift of the wave function upon tunneling and is used to estimate the hole tunneling time. The results demonstrate that strain can be utilized to tailor hole tunneling times by changing the energy separation and, consequently, the mixing between heavy hole and light hole states in the quantum well.     

利用声场频谱频率漂移监测内波的算法改进和实验验证

声场频谱的频率漂移曲线可以用来监测内波。由于简正波幅度剧烈起伏带来的干扰,目前尚无从实验数据中提取频移曲线的有效算法.提出了一种依据实测声学传播数据提取频移曲线的算法。借助于简正波过滤技术,该算法利用相关法从简正波相角之差中提取频率漂移曲线。利用该算法提取的频移曲线与内波导致的跃层起伏具有很高的相似性,这在2011年黄海实验中得到了验证。该算法的优点是可以保留简正波相位差变化导致的频移曲线信息,同时又能有效地抑制简正波幅度起伏带来的干扰,但是需要良好的接收阵阵型来保证简正波分离。     

Electric-field effect on shallow impurity ground state in nanowire superlattice

We have developed a variational formalism to analyze the effect of electric field on the donor ground state in a nanowire superlattice with cylindrical cross-section. The trial function is taken as a product of the free-electron ground state wave function with an envelope function that is a solution of a differential equation arising from the Schrödinger variational principle. We establish a close relationship between the donor ground state energy and density of charge induced by the unbound electron at the point of donor location. Also, we show that electric field applied along the crystal growth direction can easily shift the peak position of the free-electron density distribution from the central well toward one of the nanowire ends, providing a variation of the average electron-ion separation and a considerable alteration of the donor ground state energy.     

Solution of Electromagnetic Wave in Time-Varying Media in Two-Dimensional Space

The analytical solution of gradual change media in two-dimensional free space is studied. Using separation of variables, the solution of electromagnetic wave in time-varying media, which is an exponential function of time, is derived in two-dimensional space. The rationality of the solution is verified indirectly. According to the solution, the figures of the wave are depicted. Based on these figures, the character of the wave in time-varying media is obtained, which shows frequency shift and changes of phase velocity and amplitude.     

Time shifting chaotic signals using synchronization

In this paper we examine couplings that produce time-shifted synchronization. We find a surprising variety of time-shifted states can be attained without including an explicit time-delay term in the coupling. We characterize the observed synchronization by determining the dependence of the time shift and cross correlation between the drive and response oscillators on a tunable parameter. Our observations agree well with a recently introduced method for estimating the time shift and cross correlation using a transfer function.     

Singular scaling functions in clustering phenomena

We study clustering in a stochastic system of particles sliding down a fluctuating surface in one and two dimensions. In steady state, the density-density correlation function is a scaling function of separation and system size. This scaling function is singular for small argument — it exhibits a cusp singularity for particles with mutual exclusion, and a divergence for noninteracting particles. The steady state is characterized by giant fluctuations which do not damp down in the thermodynamic limit. The autocorrelation function is a singular scaling function of time and system size. The scaling properties are surprisingly similar to those for particles moving in a quenched disordered environment that results if the surface is frozen.     

Biexcitonic effects in the time integrated four-wave mixing with picosecond pulses

We propose a simple method to estimate the biexcitonic contribution to the excitonic non-linearity. The method is based on the time integrated four-wave mixing (TI FWM) with picosecond pulses. The TI FWM signal, which is measured as a function of the delay between pump and test pulses, shows shift towards positive and negative time delay when the laser is tuned at the exciton and biexciton resonance, respectively. We show theoretically that the magnitude of the shift allows us to estimate the biexcitonic contribution to the third-order non-linearity at the fundamental band edge.     

电子在圆柱形半导体量子线中的行为研究

用计算一维势阱波函数的方法简化了圆柱形量子线波函数的计算, 得出了量子线中电子的能态、 能级图和波函数。 在确定温度条件下, 讨论了量子线的线宽与它的光谱蓝移、 能级分离或兼并以及电子能态的关系。The wave function of column quantum wires has been calculated with the means of calculation for the quantum wave function in one dimensional potential well. The energy state, energy level diagram and wave function of column quantum wire have gained. Under assured temperature, the relations of column quantum wire diameter to its spectrum blue shift, separation or annexation of energy level, and electrons energy state have been discussed.     

Photon-echo profile in the ultrashort time region for pentacene molecules in crystals

Photon-echo behavior in the ultrashort time region is studied for pentacene molecules in p-terphenyl crystals at 1.7 K by means of the accumulated three-pulse echo. We show highly resolved echo spectra with a parameter of time separation and also time behavior of echo intensity as a function of pulse separation measured at various frequencies near the peak position of the absorption line of the S₀–S₁ transition. We demonstrate various features of echo profile in both time and frequency domains, which are dependent on the time region of observation.     

面向脑血管分割的改进型非局部均值滤波算法研究

介绍了经典非局部均值滤波算法与Manjón非局部均值滤波算法,改进了非局部均值滤波方法的相似度权值,使算法在具有旋转平移不变性,保持时间复杂度的同时优化了视觉效果与信噪比。实验通过添加噪声标准差从10~100不等的高斯加性噪声,比较了改进后的算法与传统滤波算法以及Manjón非均值滤波算法,结果表明,改进后的算法无论从视觉上还是数值上都优于Manjón非均值滤波算法。     

Two-photon coherent propagation,transmission of 90° phase-shifted pulses,and application to isotope separation

Most single photon coherent propagation effects are shown to have their two-photon analogue. The case of zero-area pulse propagation (90° phase shifted in the two-photon situation), frequency shift with distance, and selective optical excitation for isotope separation are considered. Selective two-photon pumping is shown to occur even when the pulse spectrum overlaps the various isotope shifted lines. An application to radiation pressure isotope separation is proposed.     

Real-time cosmology

In recent years, improved astrometric and spectroscopic techniques have opened the possibility of measuring the temporal change of radial and transverse position of sources in the sky over relatively short time intervals. This has made at least conceivable to establish a novel research domain, which we dub “real-time cosmology”. We review for the first time most of the work already done in this field, analysing the theoretical framework as well as some foreseeable observational strategies and their capability to constrain models. We first focus on real-time measurements of the overall redshift drift and angular separation shift in distant sources, which allows the observer to trace the background cosmic expansion and large scale anisotropy, respectively. We then examine the possibility of employing the same kind of observations to probe peculiar and proper accelerations in clustered systems, and therefore their gravitational potential. The last two sections are devoted to the future change of the cosmic microwave background on “short” time scales, as well as to the temporal shift of the temperature anisotropy power spectrum and maps. We conclude revisiting in this context the usefulness of upcoming experiments (like CODEX and Gaia) for real-time observations.     

Universal Ratio of Coulomb Interaction to Geometric Quantization in (In,Ga)As/GaAs Quantum Dots

We study the photoluminescence of self-assembled (In,Ga)As/GaAs quantum dot ensembles with varying confinement potential height. The low energy shift of the s-shell emission with increasing excitation power gives a measure of the Coulomb interaction in these structures as it results from carrier–carrier interactions between the optically injected exciton complexes. When dividing this shift by the dot level splitting, determined by the geometric confinement, we obtain a universal function of the number of involved excitons that is independent of the confinement potential height. This shows an identical scaling of Coulomb interaction and geometric quantization with varying confinement.     

Demonstration of partial erasing of picosecond temporal optical data by use of accumulated photon echoes

We demonstrated partial erasing of temporal optical data on a picosecond time scale by use of accumulated photon echoes. In a photon-echo memory the temporal data at time tau are stored as a frequency grating of period 1/tau in the absorption spectrum of a material. Partial erasing of the temporal data is achieved by irradiation of the material with a pulse pair at time separation tau , but the phase of one of the pulses is shifted 180 degrees . This process does not produce a frequency grating, and no echo is emitted. The experiment was performed with a dye-doped polymer film. The 180 degrees phase shift was obtained by use of a half-wave plate.     

Sub-wavelength interference in the field assisted by surface plasmons

We present a theoretical study of the optical transmission from a thin metallic double slit. The second-order correlation function as a function of the displacement of the detectors for different values of slit separation is studied. It is shown that surface plasmons excited at one slit and propagating to the other slit modulate the coincidence counts with the variation of slit separation. Sub-wavelength interference effect has also been observed for the field assisted by surface plasmons. It is also shown that the second order interference-diffraction pattern changes with slit separation and at some particular value of slit separation it changes into the Hanbury Brown and Twiss (HBT) effect.     

Shift multiplexing with a two-dimensional lens array

We propose a new shift multiplexing method to reduce the cross-talk noise and increase the holographic storage density. We use spherical waves emerging from a two-dimensional lens array as reference beams to multiple holograms. The theoretical results indicate that the sidelobes of the diffraction intensity can sharply be reduced to near-zero and the spatial separation of adjacent holograms can also be reduced, resulting in higher holographic storage density than conventional shift multiplexing methods.     

A 1H/19F minicoil NMR probe for solid-state NMR: application to 5-fluoroindoles

We show that it is feasible to use a minicoil for solid-state 19F 1H NMR experiments that has short pulse widths, good RF homogeneity, and excellent signal-to-noise for small samples while using low power amplifiers typical to liquid-state NMR. The closely spaced resonant frequencies of 1H and 19F and the ubiquitous use of fluorine in modern plastics and electronic components present two major challenges in the design of a high-sensitivity, high-field 1H/19F probe. Through the selection of specific components, circuit design, and pulse sequence, we were able to build a probe that has low 19F background and excellent separation of 1H and 19F signals. We determine the principle components of the chemical shift anisotropy tensor of 5-fluoroindole-3-acetic acid (5FIAA) and 5-fluorotryptophan. We also solve the crystal structure of 5FIAA, determine the orientation dependence of the chemical shift of a single crystal of 5FIAA, and predict the 19F chemical shift based on the orientation of the fluorine in the crystal. The results show that this 1H/19F probe is suitable for solid-state NMR experiments with low amounts of biological molecules that have been labeled with 19F.