“Massive” perturbative QCD, Regular in the IR limit

The goal of the research is to devise a modification of the perturbative QCD (pQCD) that should be regular in the low-energy region and could serve as a practical means for the analysis of data below 1 GeV down to the IR limit. Recent observation of the four-loop pQCD series “blow-up” in the region below 1 GeV for the Bjorken Sum Rule gave an impetus to this attempt. The proposed “massive” analytic pQCD has two sources. It can be treated as the common logarithmic pQCD with only one parameter added, the effective “glueball mass” m _gl ? 1 GeV, serving as an IR regulator. At the same time, it looks like a modification of Analytic Perturbation Theory (APT) comprising nonpower perturbative expansion that makes it compatible with linear integral transformations. Figuratively (with minor reservations), the proposed MAPT differs from the minimal APT by simple ansatz Q ² → Q ² + m _g1 ² .     

Anomalous dynamical light scattering in soft glassy gels

We compute the dynamical structure factor S(q,τ) of an elastic medium where force dipoles appear at random in space and in time, due to “micro-collapses” of the structure. Various regimes are found, depending on the wave vector q and the collapse time θ. In an early time regime, the logarithm of the structure factor behaves as (qτ)^3/2, as predicted in (L. Cipelletti et al., Phys. Rev Lett. 84, 2275 (2000)) using heuristic arguments. However, in an intermediate-time regime we rather obtain a (qτ)^5/4 behaviour. Finally, the asymptotic long-time regime is found to behave as q ^3/2τ. We also give a plausible scenario for aging, in terms of a strain-dependent energy barrier for micro-collapses. The relaxation time is found to grow with the age t_w, quasi-exponentially at first, and then as t _w ^4/5 with logarithmic corrections. Received 15 April 2002     

A study of π states of H2 + in the one centre approach

The statistical theory of the elastic constants of nematic liquid crystals is applied to detailed calculations based on well-defined approximations for the direct correlation function of Ornstein and Zernike and for the singlet orientational distribution. The model of hard spherocylinders with superimposed r ^-6 attraction modulated by a Maier-Saupe P ₂(cos ?_{1 2}) term, is used. The dependence on temperature, on the order parameter and on the length to breadth ratio, of the reduced elastic constants K* _i (i=1, 2, 3), is discussed in some detail and comparison with experiment is included.     

Anomalous dynamical light scattering in soft glassy gels

We compute the dynamical structure factor S(q,τ) of an elastic medium where force dipoles appear at random in space and in time, due to “micro-collapses” of the structure. Various regimes are found, depending on the wave vector q and the collapse time θ. In an early-time regime, the logarithm of the structure factor behaves as (qτ)^3/2, as predicted in L. Cipelletti, S. Manley, R.C. Ball, D.A. Weitz, Phys. Rev. Lett. 84, 2275 (2000) using heuristic arguments. However, in an intermediate-time regime we rather obtain a (qτ)^5/4 behaviour. Finally, the asymptotic long-time regime is found to behave as q ^3/2τ. We also give a plausible scenario for aging, in terms of a strain-dependent energy barrier for micro-collapses. The relaxation time is found to grow with the age t _w, quasi-exponentially at first, and then as t _w ^4/5 with logarithmic corrections. Received 23 July 2001     

Level density fluctuations and characterization of chaos in the realistic model spectra for odd-odd nuclei

Statistical properties of the realistic energy spectra of the odd-odd nuclei¹⁰⁶Ag,¹⁹⁸Au,¹³⁴Cs,⁴⁰K and⁹⁴Rb, calculated within the Interacting Boson Fermion Fermion Model, are investigated by means of theΔ ₃ statistics and the Nearest Neighbor Spacing Distribution method. New probability distribution function, which describes well the calculated results and enables the characterization of chaos with a physically meaningfull parameter, is proposed. Level spacing fluctuations of the examined nuclei exhibit the transitional behavior between Poisson and GOE limits, revealing different degrees of chaoticity in their dynamics. Communicated by X. Campi     

ESR study of some Cu(II)-oxazepam complexes

The CuL₂X₂ (L = 7-chlor-l,3-dihydro-3-hydroxi-5-phenyl-2H-l,4-benzodiazepin-2-one, also known as oxazepam, X = Cl, Br) complexes were prepared and investigated by ESR (electron spin resonance) method. Powder ESR spectra of CuL₂X₂ compounds at room temperature show the presence of monomeric species having an axial symmetry with a small rhombic distortion. In case of compounds with Cl there is a superposition of two nonequivalent mononuclear species, one with ad_{x² - y²} d_{x^2 - y^2 } ground state and another with ad_z² d_{z^2 } ground state. In pyridine (Py) and dimethylformamide (DMF) solutions the monomeric species prevail. Two different monomeric species, one with pseudotetrahedral (T_d) and the other with elongated tetrahedral-octahedral symmetry, were evidenced in DMF solutions adsorbed on NaY zeolite. In Py-DMF solutions two monomeric species were also identified. Dimeric species appear in DMF and Py solutions adsorbed on NaY zeolite through the coordination of two Cu(II) ions at the same keto-oxygen from one oxazepam molecule.     

A six-dimensional approach to microtexture analysis

A mathematical framework is presented for microtexture derivation and analysis. A six-dimensional space is introduced, defined as the product of direct space (x, y, z) and orientation space, parametrized by the Rodrigues vector (r ₁, r ₂, r ₃). The framework is adapted to diffraction experiments, where orientation information from many grains or deformation microstructures is recorded in parallel, with the prime aim of allowing fast measurements and thus the ability to study microstructure dynamics. Assuming the use of a monochromatic beam the geometry of the projection surfaces is deduced. The derivation of the microtexture is formulated as an inverse problem similar to reconstruction problems in absorption or emission tomography. The applicability of the two major types of reconstruction algorithm, namely transform methods and algebraic methods, is discussed. An explicit solution in terms of the iterative algebraic reconstruction technique algorithm is given. The choice of basis function is discussed. Furthermore, the framework is applied to a number of important simplifying cases. These include grain-by-grain reconstruction, classical pole figure inversion and the generation of three-dimensional maps of non-deformed grains.     

Modeling of clusters by a molecular dynamics model using a fast tree method

The dynamics of clusters irradiated by a high-intensity ultrashort pulse laser has been studied using a fully relativistic three-dimensional Molecular Dynamics Model. A fast three-dimensional tree algorithm for computing the electrostatic force has been developed and compared with the conventional particle-particle method. The particle-particle method requires computation time, which scales as O(N_p ²), and it is faster for small number of particles N_p <10³. In the opposite case of relatively large ensemble of particles N_p >10³, the preferred method is the tree algorithm whose computation time scales as O(N_p log N_p). The tree algorithm has been benchmarked against the particle-particle method for clusters composed of xenon and deuterium atoms and its accuracy and computation time have been analyzed. The optimum free parameter of the tree method has been determined to be θ≈0.5. We addressed the effects of boundary conditions by studying the contribution of adjacent clusters to the total electromagnetic force exerted on individual particles. We found that the adjacent clusters play a minor role in the overall cluster dynamics.     

Multivariate Image Analysis of Magnetic Resonance Images with the Direct Exponential Curve Resolution Algorithm (DECRA): Part 2: Application to Human Brain Images

Owing to the heterogeneity of living tissues, it is challenging to quantify tissue properties using magnetic resonance imaging. Within a single voxel, contributions to the signal may result from several types of¹H nuclei with varied chemical (e.g., −CH₂−, −OH) and physical environments (e.g., tissue density, compartmentalization). Therefore, mixtures of¹H environments are prevalent. Furthermore, each unique type of¹H environment may possess a unique and characteristic spin–lattice relaxation time (T₁) and spin–spin relaxation time (T₂). A method for resolving these unique exponentials is introduced in a separate paper (Part 1. Algorithm and Model System) and uses the direct exponential curve resolution algorithm (DECRA). We present results from an analysis of images of the human head comprising brain tissues.     

Relation between the internal stress measured in creep and the stress generated by the dislocation structure in the fcc metals

From the steady-state creep rate data treated as a function of the applied and the measured effective stress and temperature, a phenomenological dependence of the internal stress on the applied stress and temperature was derived. The result determined the expected character of the applied stress- and temperature dependences of the dislocation density, which was considered the microstructure parameter of the internal stress σ _i?=?α MGbρ ^1/2 (σ_i is the internal stress, α the dislocation interaction factor, M the Taylor factor, G the shear modulus, b the Burgers vector length and ρ the dislocation density). A scaling of the expected dislocation density by fitting it to measured dislocation density data yielded reasonable values of the parameter α in the Taylor formula, but the experimental data indicated a weaker applied stress dependence of the measured dislocation density than that of the expected dependence. An admission of an empirical formula fitting the dependence of dislocation density on the applied stress and temperature leads to a suggestion that the parameter α might be dependent on applied stress and temperature.     

Three-dimensional nuclear dynamics in the quantized ATDHF approach

The quantized adiabatic time-dependent Hartree-Fock theory is numerically applied to the low energy large amplitude collective dynamics of heavy ion systems ranging from α + α to ¹⁶O + ¹⁶O. The problem is reduced to three successive steps. First, for the lowest mode the optimal, i.e., maximally decoupled, collective path {φ_q} is evaluated by solving a coupled set of nonlinear differential equations for the single-particle wave functions _q^(a)(r) of φ_q, depending on the collective coordinate q and three spatial coordinates. A density-dependent interaction with a direct finite range Yukawa-term is employed and three-dimensional coordinate- and momentum-grid techniques are used, including fast Fourier methods. In a second step the quantized collective Hamiltonian H_c(q, d/dq) is extracted from {φ_q} by means of generator coordinate techniques involving, besides q, a conjugate variable p. Starting from {φ} this procedure includes the numerical evaluation of the classical potential, (q), of the intertia parameter, (q), of the quantum corrections with regard to rotation, translation and collective q-motion, (q), and of the centrifugal potential. The third step consists of actually calculating the subbarrier fusion cross section by means of WKB methods applied to the collective Hamiltonian H_c(q, d/dq). The theoretical numbers are compared with results from Hartree-Fock calculations with quadrupole constraint, and with experimental data. The microscopic aspects of the dynamics, the relation to other theories, and the practical and conceptual problems arising from the quantized ATDHF theory are discussed in detail.     

Pyridine-2-yl Quinoxaline (2-CPQ) Derivative As a Novel Pink Fluorophore: Synthesis,and Chemiluminescence Characteristics

Quinoxaline derivatives are well-known N-heterocycles with pharmacological and fluorescence activities. Almost all quinoxaline derivatives with extensive π-conjugation have been introduced as fluorophores which emit blue and green light. For the first time, we designed and synthesized 6-chloro-2,3 di(Pyridine-2yl) quinoxaline (2-CPQ) as a pink fluorophore in acetonitrile medium by simple route at room temperature whitin 30 min. The synthesized quinoxaline was identified using ¹H, ¹³C NMR, MS, and FT-IR spectroscopy. Our results showed that the iodine-catalyzed method for both oxidation and cyclization during the synthesis of quinoxaline from pyridine 2-carbaldehyde was straightforward, efficient, and clean. All of the mentioned characterization devices confirmed the synthesis of 2-CPQ.

Moreover, we studied the photophysical properties of the synthesized fluorophore in which The UV–Vis absorption spectrum of 2-CPQ in DMF were three peaks at 451, 518 and 556 nm. Based on photophysical properties investigation, 2-CPQ shows good fluorescence with maximum peaks 607 and 653 nm in DMF as solvent (ф_F?=?0.21). Hence, the fluorophore was applied in the peroxyoxalate chemiluminescence system. The reaction of imidazole, H₂O_2, and bis (2,4,6-trichlorophenyl) oxalate (TCPO) can transfer energy to a 6-chloro-2,3 di(pyridine-2yl) quinoxaline. In this process, dioxetane was synthesized, which chemically initiated the electron exchange luminescence (CIEEL) mechanism and led to pink light emission. We anticipate our synthesized fluorophores 2-CPQ will have great potential applications in imaging and medical markers.

     

Sonochemical temperature controlled synthesis of pellet-, laminate- and rice grain-like morphologies of a Cu(II) porous metal–organic framework nano-structures

Nano-structures of the Cu(II) metal–organic framework, {Cu(BDT)(DMF)·CH₃OH·0.25DMF}_n (1), which BDT²⁻ is 1,4-benzeneditetrazolate, have been synthesized by the reaction of H₂BDT with Cu(NO₃)₂·6H₂O via ultrasonic irradiation in three different temperatures, which causes different morphologies. The products were characterized by IR spectroscopy, elemental analysis, scanning electron microscopy and X-ray powder diffraction. This study demonstrates that sonochemistry is a suitable method for preparation of metal–organic framework nano-structures and temperature is an effective parameter on morphologies of Cu(II) metal–organic framework nano-structures.     

Solvation structure of magnesium,zinc, and alkaline earth metal ions in N,N‐dimethylformamide,N,N‐dimethylacetamide,and their mixtures studied by means of Raman spectroscopy and DFT calculations—Ionic size and electronic effects on steric congestion

The solvation structure of magnesium, zinc(II), and alkaline earth metal ions in N,N‐dimethylformamide (DMF) and N,N‐dimethylacetamide (DMA), and their mixtures has been studied by means of Raman spectroscopy and DFT calculations. The solvation number is revealed to be 6, 7, 8, and 8 for Mg²⁺, Ca²⁺, Sr²⁺, and Ba²⁺, respectively, in both DMF and DMA. The δ (O C N) vibration of DMF shifts to a higher wavenumber upon binding to the metal ions and the shift Δν(= ν_bound − ν_free) becomes larger, when the ionic radius of the metal ion becomes smaller. The ν (N CH₃) vibration of DMA also shifts to a higher wavenumber upon binding to the metal ions. However, the shift Δν saturates for small ions, as well as the transition‐metal (II) ions, implying that steric congestion among solvent molecules takes place in the coordination sphere. It is also indicated that, despite the magnesium ion having practically the same ionic radius as the zinc(II) ion of six‐coordination, their solvation numbers in DMA are significantly different. DFT calculations for these metalsolvate clusters of varying solvation numbers revealed that not only solvent–solvent interaction through space but also the bonding nature of the metal ion plays an essential role in the steric congestion. The individual solvation number and the Raman shift Δν in DMF–DMA mixtures indicate that steric congestion is significant for the magnesium ion, but not appreciable for calcium, strontium, and barium ions, despite the solvation number of these metal ions being large. Copyright © 2006 John Wiley & Sons, Ltd.     

Laterally patterned high mobility two-dimensional electron gases obtained by overgrowth of focused ion beam implanted Al1−xGaxAs

The use of focused ion beam implantation doping of an inverted GaAs/Al_1−xGa_xAs heterostructure during a growth interruption allows for the lateral modulation of the heterostructure doping. Hence, laterally patterned two dimensional electron gases (2DEGs) are obtained with no further processing steps required. We have performed the direct writing of a 2DEG with a Hall-bar pattern, such that only the application of ohmic contacts was necessary and the sample surface remained unharmed otherwise. The 2DEG has an electron density of 3.6×10¹¹ cm⁻² and an electron mobility of 4.8×10⁵ cm²/V s, as determined by magnetotransport measurements. A conventional mesa-etched Hall-bar with almost identical electronic properties has also been studied. Different behaviour of the longitudinal as well as the transversal magnetoresistance for the two Hall-bars is observed and can be concluded to be due to a different confinement potential.     

无标度网络上队列资源分配研究

研究了节点队列资源有限的条件下,无标度网络上的信息流动力学过程,发现了网络由自由流通到拥塞的相变现象,提出了一种基于节点度的队列资源分配模型.模型的核心是使节点i的队列长度与kβi成正比(ki为节点i的度,β为分配参数).仿真结果表明,在网络使用最短路径算法进行信息包传送的条件下,β近似等于1.25时队列资源分配最合理,网络容量最大,且该最佳值与队列总资源多少以及网络的规模无关.     

A Heuristic algorithm for reducing wavelength number of optical WDM networks

This paper proposes a Heuristic algorithm in order to reduce the total number of wavelengths required to accommodate light-paths in a WDM networks with static traffic loading. Proposed algorithm is compared with Dijkstra's algorithm for average light-path length and wavelength number of network. To see the efficiency of this 01algorithm new parameter, reduced wavelength cost (RC_X) has been defined.     

Ab initio calculation of the geometric,electronic and magnetic properties of neutral and anionic Au n Pd (n = 1–9) clusters

The ab initio method based on density functional theory at the B3PW91 level has been applied to study the geometric, electronic, and magnetic properties of neutral and anionic Au _n Pd (n?=?1–9) clusters. The results show that the most stable geometric structures adopt a three-dimensional structure for neutral Au₇Pd and Au₈Pd clusters, but for anionic clusters, no three-dimensional lowest-energy structures were obtained. The relative stabilities of neutral and anionic Au _n Pd clusters were analysed by means of the dependent relationships between the binding energies per atom, the dissociation energies, the second-order difference of energies, the HOMO–LUMO energy gaps and the cluster size n, and a local odd–even alternation phenomenon was found. Natural population analysis indicates the sequential transfer from the Pd atom to the Au _n frame in Au_1,2,3,5Pd and Au_2,3Pd^? clusters, and from the Au _n frame to the Pd atom in other clusters. Much to our surprise, irrespective of whether it is the total magnetic moment or the local magnetic moment, the magnetic moment presents an odd–even alternation phenomenon as a function of the cluster size n. The magnetic effects are mainly localized on the various atoms (Au or Pd) for different cluster size n.     

Effect of absorbed pump power on the quality of output beam from monolithic microchip lasers

The dependence of the beam propagation factor (M ² parameter) with the absorbed pump power in the case of monolithic microchip laser under face-cooled configuration is extensively studied. Our investigations show that the M ₂ parameter is related to the absorbed pump power through two parameters (α and β) whose values depend on the laser material properties and laser configuration. We have shown that one parameter arises due to the oscillation of higher order modes in the microchip cavity and the other parameter accounts for the spherical aberration associated with the thermal lens induced by the pump beam. Such dependency of M ² parameter with the absorbed pump power is experimentally verified for a face-cooled monolithic microchip laser based on Nd³⁺ -doped GdVO₄ crystal and the values of α and β parameters were estimated from the experimentally measured data points.     

Determination of Internucleotide JHN Couplings by the Modified 2D JNN-Correlated [N, H] TROSY

Recent developments in the direct observation of J couplings across hydrogen bonds in proteins and nucleic acids provide additional information for structure and function studies of these molecules by NMR spectroscopy. A J_NN-correlated [¹⁵N, ¹H] TROSY experiment proposed by Pervushin et al. (Proc. Natl. Acad. Sci. USA 95, 14147–14151, 1998) can be applied to measure ^hJ_HN in smaller nucleic acids in an E.COSY manner. However, it cannot be effectively applied to large nucleic acids, such as tRNA^Trp, since one of the peaks corresponding to a fast relaxing component will be too weak to be observed in the spectra of large molecules. In this Communication, we proposed a modified J_NN-correlated [¹⁵N, ¹H] TROSY experiment which enables direct measurement of ^hJ_HN in large nucleic acids.