Quantum Monte Carlo Simulations of?the?Kosterlitz-Thouless Transition for?Two-Dimensional Disordered Bose-Hubbard Model

In two-dimensional (2D) Bose systems, it is well known that Koterlitz-Thouless (KT) transition occurs. In this report, we perform quantum Monte Carlo simulations to investigate the 2D disordered Bose-Hubbard model. The chemical potential is assumed to depend on the site randomly and its distribution is given by a Gaussian distribution. The KT transition is confirmed from the finite-size analysis of superfluid density and the critical exponent of correlation function. By changing the variance of the Gaussian distribution, we found that the transition temperature decreases as the variance increases. The phase diagram is obtained to show the superfluid and the disordered phases. We try to understand our results by using the concept of ??percolation??.     

What Went Wrong with Home Hemodialysis in the United States and What Can Be Done Now?

In 1973, almost 40% of the more than 10 000 dialysis patients were treated by home hemodialysis. Today, with more than a quarter of a million dialysis patients in the United States, fewer than 2000 are on home hemodialysis. A number of factors have contributed to this change. First, many nephrologists and administrators who were developing new dialysis units had little or no practical experience with dialysis for chronic renal failure. Second, more elderly and diabetic patients were admitted to treatment. Home hemodialysis was more difficult for such patients, and often their helpers were themselves were elderly. Third, hemodialysis machines were difficult to learn and operate. Fourth, following publication of the results of the National Cooperative Dialysis Study, there developed the erroneous concept that a Kt/V equal to 1.0 was “adequate dialysis.” As bigger dialyzers became available, there was a widespread shortening of dialysis time. This decrease in time was embraced by for‐profit dialysis facilities and inadequately educated patients, and assembly‐line dialysis became generally accepted. Finally, continuous ambulatory peritoneal dialysis, with its simplicity and short training time, began to fill the need of many patients for home dialysis and independence, at least temporarily. Fortunately, the trend is now reversing. Two developments clearly have benefits for home hemodialysis. The first is an increasing interest in the use of more frequent dialysis. The second is the development of new equipment designed specifically for use by the patient, and requiring a minimum of effort on the patient's part.     

Does the Phenomenological Approach Contradict the Quantum Theory of Exciton-Polariton Spatial Dispersion?

This paper clarifies the controversial issue over 40 years between the quantum approach by Pekar and the phenomenological approach by Ginzburg about the exciton-polariton spatial dispersion theory. For an isotropic nongyrotropic medium, the analytical explicit function of the impermeability tensor \(\eta _{ij} (\omega ,\mathop k\limits^ \to )\) (the inverse of the permittivity tensor) is obtained from the anisotropic undamped-wave harmonic oscillator model. After expanding \(\eta _{ij} (\omega ,\mathop k\limits^ \to )\) with respect to small parameters within it rather than to wavevector \(\mathop k\limits^ \to\), the approximate refractive indices can be determined from the eigenvalue equation. By this treatment, the phenomenological approach is proved to be the approximation of the quantum approach near the resonance frequency. The condition for the approximation is discussed.     

Fatigue of metals – What the designer needs?

Engineering designers have to tackle various fatigue problems in their routine work. Some problems are simple and other are complex. Most of the designers have been taught only a small part of the suitable fatigue knowledge needed to successfully deal with many of these problems except for the most trivial ones. The main reason is the vast amount and complexity of the fatigue discipline, and lack of a clear integrated approach to the main fatigue problems that may be conveniently utilized by designers. An integrated approach to fatigue, that has been introduced by one of the authors in the past, is here extended, simplified and proposed as a comprehensive fatigue design tool for engineers. The whole fatigue domain is divided into six zones that include different fatigue regimes. The propagating crack length is considered as the sole parameter to evaluate safe fatigue life, including the use of an “equivalent crack propagation rate”, which averages the intense variations of CPR in the vicinity of grain boundaries. Contrary to the many unified relations to evaluate fatigue crack propagation that were proposed in the past, the current study is based on separation. For each fatigue zone a unique prediction relation is presented. Flow chart of comprehensive software for calculation of crack propagation in the whole fatigue domain is explained, and simulation results show good fit to published test results. The method is claimed to fit for use mainly by design engineers, but possibly by fatigue experts as well.     

The “Composite Polarons” Interesting Objects in the Physics of the Superconducting Materials?

We generalize the Landau Pekar theory of polarons by taking account of the screening of the Coulomb interactions, and of the coupling of the electrons with the acoustical phonons. We give a criterium of existence of polarons in the presence of screening. This criterium is probably not satisfied in metals, but it can be in anisotropic materials like the cuprates. Moreover, the composite polarons may attract each other at large distance. Finally, the screening lowers significantly the effective mass of the polarons.     

What Remains Unexplained about the Properties of Halide Perovskites?

The notion that halide perovskite crystals (ABX₃, where X is a halide) exhibit unique structural and optoelectronic behavior deserves serious scrutiny. After decades of steady and half a decade of intense research, the question which attributes of these materials are unusual, is discussed, with an emphasis on the identification of the most important remaining issues. The goal is to stimulate discussion rather than to merely present a community consensus.     

Laboratory for Surface Physics of Academia Sinica (LSPAS)

1.ObjectivesLaboratory for Surface Physics ofAcademia Sinica(LSPAS)was establishedin 1987 for enhancing the research activity insurface sciences,according to the NationalLaboratory Project of the State PlanningCommittee.During the last 30 years,we have wit-nessed a tremendous development in surfacephysics.Photoemission spectroscopy(1981Nobel prize to Siegbahn for ESCA)offers     

What is the best article publishing strategy for early career scientists?

Scientometrics - To date, it remains unclear how different approaches to early career publishing behaviors (e.g., publishing papers in the same journal or in different journals) may benefit a young...     

What is the role of the accessibility of wood hydroxyl groups in controlling moisture content?

It has often been claimed that the equilibrium moisture content (EMC) of wood is controlled by the available hydroxyl group content and their accessibility, but this has not been proven. In the present study, the accessibility of the hydroxyl groups were analysed by deuterium exchange in a dynamic vapour sorption apparatus, and generally poor correlation with the EMC and hydroxyl group accessibility was found. Therefore, the role of the accessibility of wood hydroxyl groups in relation to exerting sole influence on the EMC is disputable. It is concluded that there has to be an additional mechanism to exercise control over the EMC in addition to hydroxyl group accessibility.     

What determines the mobility of charge carriers in conjugated polymers?

In a conjugated polymer, the mobility of charge carriers is not a well-defined coefficient of a particular material as it is in an inorganic crystalline semiconductor but depends on the time domain of detection. On a time-scale of typically 100 fs, the on-chain mobility is ultra-high and controlled by the electronic band width of the polymer chain. When a carrier hits a chain imperfection, subsequent mesoscopic on-chain motion is retarded and controlled by intrachain disorder to which the chain environment contributes. Macroscopic transport commences after a time when interchain carrier jumps become rate limiting. It is routinely probed by time-of-flight experiments and can be rationalized in terms of random walk within a rough energy landscape. Experimental signatures of the various modes of transport are discussed.     

Quantum dynamics of the phase of a Bose–Einstein condensate

Abstract

In this review we discuss the dynamics of the phase of trapped Bose–Einstein condensates. In particular we consider the phenomena of phase decoherence (termed also as phase collapse, or diffusion), and phase revival in systems of interacting atoms. We analyse the dependence of the collapse and revival times on the trap potential, dimensionality of the gas, atom number fluctuations, and on the coherent dynamics of the condensate. We show that in a class of experimentally relevant systems, the collapse time is relatively short, and in some cases vanishes in the limit of a large number of atoms, implying that the trapped Bose gas cannot sustain a well-defined quantum phase, and that the phase memory is lost on a relatively short time scale. Furthermore, we calculate the relative atom number fluctuations or a model of two interacting condensates, and show that the fluctuations are generically sub-Poissonian.     

A Tunable Hybrid Electro-magnetomotive NEMS Device for?Low Temperature Physics

Microfabrication techniques have made possible the realization of mechanical devices with dimensions in the micro- and nano-scale domain. At low temperatures, one can operate and study these devices in well-controlled conditions, namely low electrical noise and cryogenic vacuum, with the ability to use high magnetic fields and superconducting coating metals (Collin et al. in J. Low Temp. Phys. 150(5?C6):739, 2008). Moreover, the temperature turns out to be a control parameter in the experimental study of mechanical dissipation processes, with the cryogenic environment ensuring that only low energy states are thermally populated. Immersed in a quantum fluid, these MEMS and NEMS devices (micro and nano electro-mechanical systems) can probe the excitations of the liquid at a smaller scale, with higher frequencies and better resolution than ??classical?? techniques (Triqueneaux et al. in Physica B 284:2141, 2000). We present experimental results obtained in vacuum on cantilever NEMS structures which can be both magnetomotive and electrostatically driven. The device is extremely sensitive with resolved displacements down to 1 Å using conventional room-temperature electronics. It is calibrated in situ, and frequency/non-linearity can be tuned electrostatically. The design should allow parametric amplification to be used.     

What makes the first forward citation of a patent occur earlier?

Identifying the economic value of a patent is crucial to technology management. It also facilitates the commercialization and transactions of patents. As a proxy of patent value, forward citation counting is widely used, but it takes a long time for a patent to be sufficiently cited. In this context, we suggest the first citation lag, namely the time taken until the first citation, as a proxy of patent value, as it is positively correlated with the patent value and considers the fact that important patents with a high economic value tend to receive many citations in a short space of time. We explore the influential patent attributes related to the first citation lag to build a model to predict the patent value. By using the Cox proportional hazard model on green inventory patent data, we find that patents with a shorter technology cycle time and a larger number of IPC four-digit classes, claims, patent family, and backward citations are associated with the shorter first citation lag, while a patent’s science linkage has an inverse U-shaped relationship with the first citation lag. Further, patents having an unconventional technological core have a longer first citation lag and among patents having an unconventional technological core, the presence of a novel element makes the first citation earlier. Our study is expected to help patent evaluation in the early stage of technology transfer.     

What is the tensile strength of a ceramic to be used in numerical models for predicting crack initiation?

Criteria for predicting initiation of cracks in brittle materials like ceramics are based on two parameters: the material fracture toughness and the tensile strength. Standardized experiments exist to estimate the former. However, the tensile strength is often taken from experiments (mainly uniaxial bending) on specimens with various geometries and surface finish, usually tested under ambient conditions at a given loading rate. The reported strength is commonly the Weibull characteristic strength, which scatters due to the critical defect size distribution on the tested specimen. In this work, we propose a definition of the “inherent” or “intrinsic” tensile strength to be used in numerical models, making a distinction between extrinsic defects due to manufacturing and intrinsic ones relying on the microstructure. Our approach is based on the Finite Fracture Mechanics theory and the Coupled Criterion applied to small surface flaws and its influence on the measured (extrinsic) strength. Numerical results are compared with experiments on alumina reported in the literature. In addition, a model for the Petch law (strength vs. grain size) in polycrystalline materials is proposed using the Coupled Criterion, which predicts an initial crack length of increasing numbers of grains as the grain size decreases.     

Self Organization of Inorganic Nanocrystals： anew Challenge for a New Physics

2008年10月23—27日，“2008第七届中国纳米科技（武汉）研讨会”在湖北大学隆重召开。欧洲科学院院士M．P．Pileni应邀出席并做了题为“Self organization of inorganic nanocrystals：a new challenge for a new physics”的大会特邀主题报告，摘要如下：     

Bad-Metal Behavior: Exotic Physics or a Consequence of Microstructure?

A geometric renormalization associated with microstructure in coalescing silver films is shown to be responsible for metallic behavior on anomalously high resistivity scales. The signature for this effect, a proportional enhancement of residual resistivity and the temperature slope, may help determine the relevance of microstructure to other band metal systems.