Tilt of pancake vortex stacks in layered superconductors in the crossing lattice regime

We study crossing vortices in strongly anisotropic Bi2Sr2CaCu2O8+delta single crystals. Using scanning Hall probe microscopy and Bitter decoration techniques, we find an asymmetry of magnetic field profiles produced by pancake vortices (PVs), which are interacting with Josephson vortices (JVs), near the surface of the crystal. We attribute the observed asymmetry to a substantial tilt (14-18 degrees) of PV stacks, which is produced by the torque due to the surface currents and JVs. We calculate the tilt angle and obtain agreement with experimental data when the irreversible in-plane magnetization is included. A further refinement to the model is considered which accounts for a reduction in the PV stack line tension near the sample surface.     

Investigating the vortex melting phenomenon in BSCCO crystals using magneto-optical imaging technique

Using a novel differential magneto-optical imaging technique we investigate the phenomenon of vortex lattice melting in crystals of Bi₂Sr₂CaCu₂O₈ (BSCCO). The images of melting reveal complex patterns in the formation and evolution of the vortex solid-liquid interface with varying field (H)/temperature (T). We believe that the complex melting patterns are due to a random distribution of material disorder/inhomogeneities across the sample, which create fluctuations in the local melting temperature or field value. To study the fluctuations in the local melting temperature/field, we have constructed maps of the melting landscape T _m(H, r), viz., the melting temperature (T _m) at a given location (r) in the sample at a given field (H). A study of these melting landscapes reveals an unexpected feature: the melting landscape is not fixed, but changes rather dramatically with varying field and temperature along the melting line. It is concluded that the changes in both the scale and shape of the landscape result from the competing contributions of different types of quenched disorder which have opposite effects on the local melting transition.     

Theory of direct-interband-transition line shapes based on Mori’s method

Summary A theory of direct interband optical transitions in the electronphonon system is introduced on the basis of the Kubo formalism and by using Mori’s method of calculation. The line shape functions are introduced in two different ways and are compared with those obtained by Choi and Chung based on Argyres and Sigel’s projection technique.

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Riassunto S’introduce una teoria delle transizioni ottiche dirette d’interbanda nei sistemi elettronefonone sulla base del formalismo di Kubo e usando il metodo di calcolo di Mori. Le funzioni di forma della linea s’introducono in due diversi modi e sono paragonate a quelle ottenute da Choi e Chung basate sulla tecnica di proiezione di Argyres e Sigel.

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Резюме Развивается теория прямых межзонных оптических переходов в электрон-фононных системах на основе формализма Кубо и, используя метод вычислений Мори. Выводятся функции для форм линий двумя различными способами. Полученные результаты сравниваются с результатами Чоя и Чунга, которые основаны на технике проектирования Аргиреса и Сигеля.

     

A simple approach for immobilization of gold nanoparticles on graphene oxide sheets by covalent bonding

Amino—functionalized gold nanoparticles with a diameter of around 5 nm were immobilized onto the surface of graphene oxide sheets (GOS) by covalent bonding through a simple amidation reaction. Pristine graphite was firstly oxidized and exfoliated to obtain GOS, which further were acylated with thionyl chloride to give acyl chloride bound GOS. Gold nanoparticles (AuNPs) were functionalized using 4-aminothiophenol in a single-phase system to introduce amino groups on their surface through the well-developed Au-S chemistry. Subsequently, amino groups of AuNPs were reacted with acyl chloride groups of GOS to form a novel hybrid material containing GOS and AuNPs. Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), energy dispersive X-ray (EDX) spectroscopy, ultraviolet-visible (UV-Vis) spectroscopy were used to study the changes in surface functionalities and demonstrate the successful immobilization of AuNPs on GOS surface. High resolution transmission electron microscopy (HR-TEM), field emission scanning electronic microscopy (FE-SEM), and atomic force microscopy (AFM) were employed to investigate the morphologies of prepared AuNPs and their distribution onto the GOS surface. Thermogravimetric analysis (TGA) was used to characterize the thermal stability of the samples on heating.     

Superintense laser fields in circular array: effects of phase and pulse jitters

Extremely intense laser field that makes nonlinear quantum vacuum can be generated by coherent superposition of multiple lasers in circular configuration that incorporates optical fibers synchronization scheme and piecewise mirrors in circular array operating below typical damage threshold. Coherent amplification and large laser beams can produce intensity reaching nonlinear quantum vacuum regime. The effects of phase jitter and envelope timing of the pulses due to imperfect synchronization are simulated and analyzed for both linear and circularly polarized pulses. We obtain simple analytical expressions that well describe the envelope jitter and phase jitter. Several practical aspects are discussed, including implications of scaling the laser dimension and pulse duration, with possibility for giant laser facility.     

Measuring gravitational effect of superintense laser by spin-squeezed Bose—Einstein condensates interferometer

We consider an extremely intense laser, enclosed by an atom interferometer. The gravitational potential generated from the high-intensity laser is solved from the Einstein field equation under the Newtonian limit. We compute the strength of the gravitational force and study the feasibility of measuring the force by the atom interferometer. The intense laser field from the laser pulse can induce a phase change in the interferometer with Bose-Einstein condensates. We push up the sensitivity limit of the interferometer with Bose-Einstein condensates by spin-squeezing effect and determine the sensitivity gap for measuring the gravitational effect from intense laser by atom interferometer.     

Analysis of time delay effects on a linear bubble chain system

A chain of vertically rising discrete air bubbles represents a transition phenomenon from individual to continuum behavior in a bubbly liquid. Previous studies have reported that there is a preference for acoustic energy to propagate along the bubble chain and that this behavior could be explained by a coupled-oscillator model. However, it has recently been demonstrated that quantitative results from the coupled-oscillator model do not match experimental data. In this paper, it is shown how adding time delays to the coupled-oscillator model can produce results that are in better agreement with experimental data. In addition, the effects of time delays on the natural frequencies and damping of individual eigenmodes of the vertical bubble chain are also investigated. It was found that adding time delays can dramatically change the damping of the different modes of the system while having less dramatic impact on the natural frequencies of the individual eigenmodes. Counterintuitively, it is found that the effects of time delays appear to be more important when the bubbles are closer together than when they are farther apart.     

Antidot diameter dependence of matching effect in Bi2Sr2CaCu2O8+y with antidot array

To explore vortex states and their dynamics in superconductors with large thermal fluctuation and artificial pinning potentials, we have studied the influence of periodic arrays of antidots in high-T_c superconductor Bi₂Sr₂CaCu₂O_8+y (Bi2212). The diameter dependence of the matching effect in Bi2212 without a change of the thickness and oxygen doping level was investigated using one Bi2212 single-crystal film of homogeneous thickness in which several different-diameter antidot arrays were introduced. The matching effect observed by vortex-flow resistance measurements changed systematically depending on the diameter. The antidot-diameter dependence of the irreversibility lines was examined.     

Impact of a finite elastic-viscoplastic bar

A method for predicting the response of strain-rate sensitive structures under dynamic loading is developed. It is based on a finite difference method, the incremental theory of plasticity, and an elastic work-hardening viscoplastic material idealization. The strain-rate effect, loading and unloading conditions, and wave interactions are automatically accounted for, and adjusted if necessary, as the deformation proceeds. No iteration is required even if the field equations are nonlinear (e.g. non-linear constitutive equations, large deformation, or complicated geometry). We solve as an example the small deflection of a finite bar with a concentrated tip mass. The accuracy is comparable to that obtained by the well-known method of characteristics, a powerful tool for solving elastic-viscoplastic wave problems but which is restricted to small deflections and simple geometry. Because of the form of the constitutive relation selected (elastic work-hardening visco-plastic), several important new features of the dynamics response are brought out. These features are not revealed when simpler, computationally-convenient constitutive relations, such as rigid ideal-viscoplastic, rigid work-hardening viscoplastic and elastic ideal-viscoplastic are used.     

On certain pairs of <Emphasis Type="Italic">q</Emphasis>-series identities

Hirschhorn recently proved a pair of q-series identities that interlinked the coefficients of two infinite products. We use the theory of modular forms to extend his results from \(p=5\) to other primes and provide other examples of infinite products sharing similar properties.