Short-range plasma model for intermediate spectral statistics

We propose a plasma model for spectral statistics displaying level repulsion without long-range spectral rigidity, i.e. statistics intermediate between random matrix and Poisson statistics similar to the ones found numerically at the critical point of the Anderson metal-insulator transition in disordered systems and in certain dynamical systems. The model emerges from Dysons one-dimensional gas corresponding to the eigenvalue distribution of the classical random matrix ensembles by restricting the logarithmic pair interaction to a finite number k of nearest neighbors. We calculate analytically the spacing distributions and the two-level statistics. In particular we show that the number variance has the asymptotic form Σ²(L) ∼χL for large L and the nearest-neighbor distribution decreases exponentially when s→∞, P(s) ∼ exp(- Λs) with Λ = 1/χ = kβ + 1, where β is the inverse temperature of the gas (β = 1, 2 and 4 for the orthogonal, unitary and symplectic symmetry class respectively). In the simplest case of k = β = 1, the model leads to the so-called Semi-Poisson statistics characterized by particular simple correlation functions e.g. P(s) = 4s exp(- 2s). Furthermore we investigate the spectral statistics of several pseudointegrable quantum billiards numerically and compare them to the Semi-Poisson statistics. Received 13 September 2000     

Binding effects in pion-nucleus scattering

The pion nucleus optical potential is evaluated for a pion scattered by a nucleon bound in a potential well. Total cross sections for π-¹⁶O scattering are computed supposing an S-wave separable two body interaction. The comparison with impulse and static approximations shows that they are not justified in a resonance region.     

高Tc超导体YBCO磁通钉扎的计算机模拟研究

临界电流密度Jc是影响高温超导体在强电领域应用的一个重要参数,在实际应用中,特别在外加磁场下,临界电流密度与超导材料的磁通钉扎性质密切相关.因此,磁通钉扎一直是高温超导体研究中的一个重要领域.由于高温超导体磁通钉扎力密度Fp的标度律存在,本文根据D.Dew-Hughes总结的钉扎力函数,主要存在两种主要作用类型(正常相和△K).我们将D.Dew-HugBes给出的钉扎力密度Fp标度函数改进为一个简化的具有物理意义的函数表达式.结合文献中已有的实验数据,我们对YBcO进行了计算机模拟,确定了它的磁通钉扎类型,模拟的研究结果与实际情况比较吻合.     

A novel approach to high-sensitivity grating interferometry

The authors propose a new approach for obtaining information about in-plane and out-of-plane displacements of an object tested using high-sensitivity grating interferometry. The interferences of each of the specimen grating diffraction orders with a reference beam are recorded separately. Computer addition and subtraction of the phase functions calculated from the interferograms give the in-plane and out-of-plane displacement values, respectively. The authors present their experimental work, and then compare their results with those obtained using a conventional grating interferometry approach.     

Interferometric profiling of microcantilevers in liquid

Silicon micro cantilevers are used as highly sensitive transducers for a wide range of physical, chemical and biochemical stimuli. Vibrating the cantilevers at higher-order resonant modes can achieve extra sensitivity, but the difficulty lies in determining exactly which modes are excited in the cantilever. This problem is exacerbated for cantilever sensors operating in liquid where the computational analysis of the resonance modes is very challenging. Using strobed interferometric microscopy, we are able to image the dynamic behavior of individual (100×500×1 μm³) cantilevers in an eight cantilever array over frequencies from 0–1 MHz. We show how some modifications to the interferometric microscope allow for the spatial visualization of 16 longitudinal modes of cantilevers working in liquid with nanometer-scale amplitudes. We also compare the shift in frequency response and reduction in quality factor for cantilevers resonating in liquid versus in air and simulations in vacuum. Because the resonant frequency spectrum is fairly complex and does not follow simple intuition, our work maps the actual behavior of cantilevers without having any specific knowledge of the sample and environment parameters and without the necessity of involved simulations and calculations.     

Impact of ligand spacer and counter-anion in selected 1D iron(II) spin crossover coordination polymers

A new 1D coordination polymer [Fe(βAlatrz)₃](ClO₄)₂ ? H₂O (1) with a neutral bidentate ligand, βAlatrz = 4H-1,2,4-triazol-4-yl-propionate, was prepared and its magnetic behavior was investigated by temperature dependent magnetic susceptibility measurements and ⁵⁷Fe M?ssbauer spectroscopy. The temperature dependence of the high-spin molar fraction derived from ⁵⁷Fe M?ssbauer spectroscopy recorded on cooling below room temperature reveals a gradual single step transition with T_1/2 = 173?K between high-spin and low-spin states in agreement with magnetic susceptibility measurements. 1 presents striking reversible thermochromism from white, at room temperature, to pink on quench cooling to liquid nitrogen. The phase transition is of first order as deduced from differential scanning calorimetry, with T_1/2 matching the one determined by both SQUID and ⁵⁷Fe M?ssbauer spectroscopy. A brief assessment has been made among closely related 1D coordination polymers to perceive the effect of ligand spacer length and anion effect on the spin crossover behavior of these new materials.