Capacitive discharge mode transition in moderate and atmospheric pressure

Current–voltage characteristics of α- and γ-modes were investigated in moderate and atmospheric pressure capacitive discharges. The α- and γ-modes, the co-existence of both modes, and the α- to γ- and γ- to α-mode transitions were observed with the changes in voltage, current, and plasma volume. Changing of gas pressure, (100–760) Torr, the α to γ and the γ to α transition occurred with respect to input power increasing and decreasing, respectively. The hysteresis in current and voltage curve was observed and became more evident at higher pressure. Using a simple electrical circuit model, the relation between the gas pressure and the α-sheath thickness before mode transition was described.     

Theoretical Study of the Second－order Nonlinear Generation in Glass with Crystallization

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Reconstruction at a metallic interface studied by field ion and field emission microscopy

Reconstruction of a tungsten surface by adsorbed layers of gold, silver and copper has been studied by field emission and field ion microscopy. Gold reconstructs the surface in three ways, termed the α, β and γ rearrangements. The α rearrangement, which results in a smoothing of the tungsten surface, takes place at around 400° K with gold coverages of 5 monolayers (5θ), and is thought to be an increase in structural perfection of the tungsten surface by gold-assisted surface diffusion of tungsten atoms, β-reconstruction takes place in the temperature range 480–950°K at coverages ? 1.7θ, producing a faceted surface which comprises {211} and {110} facets, and is thought to result from the need to minimise the free energy at the gold/tungsten interface. The γ structure, which appears above 1400°K, is believed to represent a change in the shape of the tip by transport of tungsten to the (110) locality. Adsorbed silver produces neither β nor γ structures, and the degree of α rearrangement is very small, being confined to the {230} regions of the substrate. Copper lies between silver and gold in its ability to rearrange the tungsten surface, some degree of α rearrangement is detectable, and the β structure is very poorly developed unlike the γ structure which is clearly formed. The binding strength of copper to tungsten is greater than that of silver, but less than that of gold; the capacity of an adsorbate, to reconstruct the tungsten substrate is therefore thought to be related to the strength of the adsorbate-substrate bond.     

The Van Cittert-Zernike theorem for optical fibres

The Van Cittert-Zernike theorem determines the degree of coherence γ of light from a source radiating in a uniform medium in terms of the angular size α of the source. For the fields within an optical fibre far from the source, γ is found by replacing α by the critical angle for total internal reflection.     

10B-editing 1H-detection and 19F MRI strategies to optimize boron neutron capture therapy

Boron neutron capture therapy (BNCT) is a binary radiation therapy used to treat malignant brain tumours. It is based on the nuclear reaction (10B + n th --> [11B*] --> alpha + 7Li + 2.79 MeV) that occurs when 10B captures a thermal neutron to yield alpha particles and recoiling 7Li nuclei, both responsible of tumour cells destruction by short range and high ionization energy release. The clinical success of the therapy depends on the selective accumulation of the 10B carriers in the tumour and on the high thermal neutron capture cross-section of 10B. Magnetic resonance imaging (MRI) methods provide the possibility of monitoring, through 10B nuclei, the metabolic and physiological processes suitable to optimize the BNCT procedure. In this study, spatial distribution mapping of borocaptate (BSH) and 4-borono-phenylalanine (BPA), the two boron carriers used in clinical trials, has been obtained. The BSH map in excised rat brain and the 19F-BPA image in vivo rat brain, representative of BPA spatial distribution, were reported. The BSH image was obtained by means of double-resonance 10B-editing 1H-detection sequence, named M-Bend, exploiting the J-coupling interaction between 10B and 1H nuclei. Conversely, the BPA map was obtained by 19F-BPA using 19F-MRI. Both images were obtained at 7 T, in C6 glioma-bearing rat brain. Our results demonstrate the powerful of non conventional MRI techniques to optimize the BNCT procedure.     

Phase transformations of 2,4,6,8,10,12-hexanitrohexaazaisowurtzitane: the role played by water, dislocations, and density

A comparative study of the kinetics and mechanisms of the α → γ and ? → γ polymorphic transitions in polycrystalline haxanitrohexaazaisowurtzitane was performed using electron and optical microscopy, calorimetry, IR spectroscopy, and quantitative X-ray phase analysis. The kinetics of both processes is complex because of the morphology of the crystals, their defect structure, and impurities. As distinct from the ? → γ process, which always occurs as a single crystal-polycrystal transition (through nucleation by the dislocation mechanism with subsequent movement of the phase separation front), the α → γ process can also follow the quasi-homogeneous mechanism and occur as a single crystal-single crystal transition.     

Fluctuations with a 1/f α spectrum in nonequilibrium phase transitions in a spatially distributed system

Statistics of fluctuations in a spatially distributed system describing the interaction of nonequilibrium phase transitions is studied. It is shown that for a certain value of the intensity of external white noise acting on phase transitions, the time and spatial spectra of fluctuations exhibit power dependences S(f) ～ f ^?α and S(k) ～ k ^?γ. The dependence of exponents α and γ on the diffusion coefficient determining the spatial interaction of fluctuations is determined. Extremal low-frequency fluctuations are singled out and the distribution functions of their duration (P(τ) ～ τ^?β) and size (P(s) ～ s^?ν)) are constructed. It is found that exponent α in the time spectral dependence and exponent β in the duration of fluctuations are connected via the relation α + β = 2. Exponents γ and ν in the spatial spectral dependence and in the size distribution function are connected via an analogous relation (γ + ν = 2).     

红外杂化单光束谱的性质

同一样品不同厚度(b₁和b₂)的两单光束谱ø_b1和ø_b2经线性组合得到杂化单光束谱ø_α=αø_b1+(1-α)ø_b2=αø₀e-Kb₁+(1-α)ø₀e-Kb₂,α为杂化系数。通过改变杂化系数α,就可获得任意强度的杂化谱ø_α。系统研究了杂化光谱ø_α的性质。研究表明,只要控制合适的条件,则厚度为(b₂-αb₂+αb₁)的真实样品的单光束谱ø_b(b=b₂-αb₂+αb₁)与杂化谱ø_α高度相似,ø_α的失真程度可忽略不计。也就是说,厚度在b₁～b₂间任一厚度b的真实样品的单光束谱都可用杂化谱ø_α来表达,ø_α≈ø_b。因此,不需制备厚度为b的样品,通过改变杂化系数α就可获得研究者所希望强度的单光束谱ø_b。杂化谱方法有望在扣除背景干扰等方面得到广泛应用。     

散射相函数的高阶光学参量研究

漫反射光谱技术被广泛应用于无创测量生物组织光学性质。当光源与探测器很近时,仅仅依靠吸收系数μ_a和约化散射系数μ′_s不能准确描述光源附近光的传播状态。而二阶光学参量γ的引入改善了近光源光的传播状态的描述。本文将生物组织的散射等效成特定球形颗粒的散射,基于Mie散射理论,计算了与散射相函数p(θ)有关的单粒子和多分散系粒子的二阶光学参量γ,研究了γ随尺度参数α和相对折射率m的变化规律,描述了γ与组织结构参量之间的联系,并阐述了γ对粒子特征的表征能力。研究表明,参量γ对尺度参数α小于2的微粒尺寸的改变是敏感的,并呈二次函数关系,其系数与相对折射率呈线性关系;对于相对折射率和尺度参数都不相同的两个粒子,他们的各向异性因子g相同时,二阶光学参量γ却不同,粒子越大,γ表征粒子特征的能力越强。这对于无创探究组织微观形态具有深远的意义。     

On the Spatial Distribution of Temporal Complexity in Resting State and Task Functional MRI

Measuring the temporal complexity of functional MRI (fMRI) time series is one approach to assess how brain activity changes over time. In fact, hemodynamic response of the brain is known to exhibit critical behaviour at the edge between order and disorder. In this study, we aimed to revisit the spatial distribution of temporal complexity in resting state and task fMRI of 100 unrelated subjects from the Human Connectome Project (HCP). First, we compared two common choices of complexity measures, i.e., Hurst exponent and multiscale entropy, and observed a high spatial similarity between them. Second, we considered four tasks in the HCP dataset (Language, Motor, Social, and Working Memory) and found high task-specific complexity, even when the task design was regressed out. For the significance thresholding of brain complexity maps, we used a statistical framework based on graph signal processing that incorporates the structural connectome to develop the null distributions of fMRI complexity. The results suggest that the frontoparietal, dorsal attention, visual, and default mode networks represent stronger complex behaviour than the rest of the brain, irrespective of the task engagement. In sum, the findings support the hypothesis of fMRI temporal complexity as a marker of cognition.     

Anomalous Behavior of an α → γ Phase Transition in Iron: Results of In Situ Neutron Diffraction Experiment

Neutron diffraction studies of a α → γ structural phase transition (T_c ≈ 911°C) in iron samples at different initial states have been performed. The anomalous disappearance of a diffraction pattern is observed in iron in the region of the α → γ phase transition. At repeated heating processes of an as cast sample, this effect becomes less pronounced and it is absent at the heating of iron powder. The observed effects have been assumingly attributed to the formation of small paracrystalline clusters with a large dispersion of the cell parameters in the process of phase transition. The kinetics of formation of clusters is slowed in as cast samples, which leads to the temporal disappearance of the diffraction pattern. These results make it possible to reconsider the atomic processes in the α → γ phase transition in iron.     

Effect of Temperature and Comonomer Content on Thermal Behavior and Crystallization Property of the Propylene–Ethylene Random Copolymers

The effects of ethylene units content and crystallization temperature on the conformations, and the thermal and crystallization behavior were investigated by a combination of Fourier transform infrared (FTIR) spectroscopy, wide angle X-ray diffraction (WAXD), and differential scanning calorimetry (DSC). The characterization of FTIR spectroscopy proves that the longer helical conformation sequences of the propylene–ethylene random (PER) samples decrease, whereas the shorter helical conformation sequences increase with the increase in ethylene units content. The increase of the shorter helical conformation sequences is favorable for the formation of the γ-phase in the crystals. A group of broad endothermic peaks can be seen clearly in the DSC curves of PER copolymers, which may be associated with the melting of mixtures of the α- and γ-forms in the crystals. The melting point, crystallization temperature, and crystallinity degree of the PER copolymers decrease with the increase in ethylene units contents. Three typical melting peaks of the PER copolymers crystallized isothermally between 80°C and 130°C were observed. The two higher melting peaks result from melting of the α- and γ-phase in the crystals, whereas the materials crystallized on quenching give the lowest peak. The WAXD results confirm that the PER copolymers crystallize from the melt, as mixtures of α and γ forms, in a wide temperature range. The critical number ζ_lim of the crystallizable units for the α-form increases with the increase in crystallization temperature for PER copolymers, which is favorable for the formation of the γ phases. The amount of γ-form increases with the increase in crystallization temperature at the expense of its α component, then reaches a maximum value at the crystallization temperature of 115°C, and finally decreases with further increase in the crystallization temperature.     

银-锡-铝三元系富银合金固相平衡圖

银—锡—铅三元系富银合金固相平衡图已经用X-射线及金相显微镜两种方法测定了出来。并且每一相区的相边介都经过用X-射线方法作了精密确定。合金含量最高到30wt％锡及30wt％铝。室温相截面由四个单相(即α,β,μ及γ)相区,五个变相(即α+β,α+μ,β+γ,β+μ及β+δ)相区及两个三相(即α+β+μ及β+γ+δ)相区所构成。所有四个单相与二元系Ag-Sn及Ag-Al所存在的单相相同,没有新的单相出现。     

T-P diagram of cerium: The lattice instability lines of gamma and alpha phases

Abstract

The compressibility and thermal expansion coeffocients of γ Ce and α Ce were measured in the 290-480 K temperature range at truly hydrostatic pressures up to 20 kbar. The lines of absolute lattice instability for γ- and α-phases were determined.     

Infrared studies of chain folding in polymers. X. polycaprolactam

The 1210-, 1233-, and 1288—cm^?1 infrared bands in the α form of nylon 6 are shown to result from a unique conformation in a tightly folded chain with adjacent reentry. The assignment of the 1210- and 1288-cm^?1 bands to motions of a gauche nitrogen-methylene group in the fold and the 1233-cm^?1 band to motions of a gauche carboxyl-methylene group in the fold is supported by the infrared studies of the α form of nylon 6, the γ form of nylon 6, poly-D(-)β-methyl- ? -caproamide (PBCA), and the high- and low-temperature forms of the cyclic dimer of nylon 6. The γ- form of nylon 6 and PBCA do not exhibit a unique conformation in the fold. The 1198-cm^?1 band can be assigned to the trans conformation of the amide group which exists in the normal planar zigzag conformation in the α-form crystal. A mechanism for the α to γ iodine-induced transition in nylon 6 is proposed showing the role of the fold in maintaining a minimum of molecular disordering during the transformation.     

具有幂率度分布的因特网平均最短路径长度估计

针对具有幂律度分布的复杂网络的平均最短路径长度进行了研究.给出了一个计算因特网平 均最短路径长度的公式.提出因特网的整体构造实质是以最小代价换取最大收益，从此出 发通过对因特网这类复杂网络平均最短路径长度影响因素分析，推断出网络最短路径长度分 布P(l)的基本性质，进而构造了一个只含参数α的P(l)的简洁形式，直接打通了拓扑具有幂 律度分布的因特网的度分布P(k)与网络最短路径长度分布P(l)之间的关系.然后说明了导出 的公式的物理意义，即参数α代表网络节点连接方式和网络的总边数对平均最短路径长 度的影响.此公式意味着只要掌握幂律P(k)～k-α中α值，就可以直接计算相应网 络的平均最短路径长度.通过对已知数据的计算，验证了公式的有效性.阐明了参数 α对网络设计的重要性和对网络功能的影响. 关键词： 复杂网络 幂律 度分布 平均最短路径长度     

Linear baryons and SU(3) breaking

The recently proposed mechanism of dynamical SU(3) symmetry breaking in linear baryons is applied to the α-γ sector after taking into account two types of α and γ trajectories. The observed splitting pattern of leading strange baryon trajectories is qualitatively explained. The implications of the scheme for ground state baryons are discussed.     

Cascading failures in congested complex networks with feedback

In this article, we investigate cascading failures in complex networks by introducing a feedback. To characterize the effect of the feedback, we define a procedure that involves a self-organization of trip distribution during the process of cascading failures. For this purpose, user equilibrium with variable demand is used as an alternative way to determine the traffic flow pattern throughout the network. Under the attack, cost function dynamics are introduced to discuss edge overload in complex networks, where each edge is assigned a finite capacity (controlled by parameter α). We find that scale-free networks without considering the effect of the feedback are expected to be very sensitive to α as compared with random networks, while this situation is largely improved after introducing the feedback.     

Statical critical properties of gadolinium models

Microscopic models of real ferromagnetic gadolinium are proposed, and their critical properties are studied by the Monte Carlo method. The critical exponents α (heat capacity), γ (susceptibility), and β (magnetization) are calculated. The α, β, and γ exponents are determined by the approximation of the data on the basis of traditional power functions and in the framework of the finite-size scaling theory. It is revealed that the critical behavior of gadolinium is affected by the dipole-dipole interactions. It is shown that the Monte Carlo method is a powerful tool for investigations into the critical properties of complex models in which two types of weak relativistic interactions are jointly taken into account against the background of each of these interactions.     

Infrared studies of single crystals of polycaprolactam

Infrared studies of the α-crystalline form of polycaprolactam (nylon 6) have confirmed the assignment of the 1288 and 1210-cm^?1 bands to a unique fold conformation. The γ-crystalline phase has a band at 1212 cm^?1 which overlaps the 1210-cm^?1 fold band in samples containing both α and γ phases. The 1288-cm^?1 band was, therefore, used to monitor regular fold content. No unique fold bands were detected in the γ form. Irregular folds present in solution-grown crystals regularize to the unique fold conformation upon annealing. Crystals which originally exhibit slight differences in regular folding as a result of different crystallization history have similar amounts of regular folds upon annealing at 220°C. Crystals grown from solutions of very dilute concentrations of polymer have different amounts of regular folding. The annealing behavior of crystals prepared from two different solution concentrations reflect the processes of regularization and long period increase.