Flow field topology of transient mixing driven by buoyancy

Transient mixing driven by buoyancy occurs through the birth of a symmetric Rayleigh-Taylor morphology (RTM) structure for large length scales. Beyond its critical bifurcation the RTM structure exhibits self-similarity and occurs on smaller and smaller length scales. The dynamics of the RTM structure, its nonlinear growth and internal collision, show that its genesis occurs from an explosive bifurcation which leads to the overlap of resonance regions in phase space. This event shows the coexistence of regular and chaotic regions in phase space which is corroborated with the existence of horseshoe maps. A measure of local chaos given by the topological entropy indicates that as the system evolves there is growth of uncertainty. Breakdown of the dissipative RTM structure occurs during the transition from explosive to catastrophic bifurcation; this event gives rise to annihilation of the separatrices which drives overlap of resonance regions. The global bifurcation of explosive and catastrophic events in phase space for the large length scale of the RTM structure serves as a template for which mixing occurs on smaller and smaller length scales.     

Pionization structure function

We analyze the properties of a pionization structure function. Making some general assumptions about the analyticity structure of amplitudes describing inclusive processes (which are valid in a large class of models and are expected to be valid for the true amplitudes) we derive a general form of this structure function.     

Resonant states in the electronic structure of the high performance thermoelectrics AgPbmSbTe2+m: the role of Ag-Sb microstructures

Ab initio electronic structure calculations based on gradient corrected density-functional theory were performed on a class of novel quaternary compounds AgPb(m)SbTe(2+m), which were found to be excellent high temperature thermoelctrics with a large figure of merit ZT approximately 2.2 at 800 K. We find that resonant states appear near the top of the valence and bottom of the conduction bands of bulk PbTe when Ag and Sb replace Pb. These states can be understood in terms of modified Te-Ag(Sb) bonds. The electronic structure near the gap depends sensitively on the microstructural arrangements of Ag-Sb atoms, suggesting that large ZT values may originate from the nature of these ordering arrangements.     

Study of scattering from turbulence structure generated by propeller with FLUENT

In this article, the turbulence structure generated by a propeller is simulated with the computational fluid dynamics (CFD) software FLUENT. With the method of moments, the backscattering radar cross sections (RCS) of the turbulence structure are calculated. The scattering results can reflect the turbulent intensity of the wave profiles. For the wake turbulence with low rotating speed, the scattering intensity of HH polarization is much smaller than VV polarization at large incident angles. When the turbulence becomes stronger with high rotating speed, the scattering intensity of HH polarization also becomes stronger at large incident angles, which is almost the same with VV polarization. And also, the bistatic scattering of the turbulence structure has the similar situation. These scattering results indicate that the turbulence structure can also give rise to an anomaly compared with traditional sea surface. The study of electromagnetic (EM) scattering from turbulence structure generated by the propeller can help in better understanding of the scattering from different kinds of waves and provide more bases to explain the anomalies of EM scattering from sea surfaces.     

Anisotropic transport of charge and complexified duality

Charge transport in two dimensions provides an ideal laboratory for investigating parameter space geometries. The Onsager relations for anisotropic transport in a parity-violating external field endow these spaces with a highly nontrivial complex (and Kähler) structure, which can be given a simple geometrical interpretation. A large class of Coulomb gases exhibiting this structure have a generalized Kramers-Wannier symmetry (complexfield duality) which is contained in the modular group. Knowledge of this symmetry and the degrees of freedom encoded in the Coulomb gas appear to be sufficient to determine the global phase diagram and the renormalization group fixed-point structure, including the critical exponents. This accounts for all the scaling behavior observed so far in the quantum Hall system.     

Interrelation between optical and magneto-optical properties of MnSbBi(Pt,Co) films

Results of the study of optical and magneto-optical properties of MnSbBi(Pt, Co) films in a spectral region of 360–820 nm are reported. It is shown that the multilayer MnSbBi(Pt, Co) films obtained by magnetron sputtering possess considerable optical rotation in the geometry of the polar Kerr effect, which is as large as 0.5°–0.7° upon 5-h annealing of the films at 350°C. The spectral dependences measured for the magnitude of the polar Kerr effect showed that these films may be used for laser data recording in the short-wavelength spectral region, which substantially increases the recording density. Studies of the film structure by X-ray and electron diffraction analysis showed that the films have a polycrystalline structure, with granules 15–40 nm in size. Possible causes of a large magnitude of Kerr effect are analyzed.     

Superconducting high pressure phase of germane

High-pressure structures of germane (GeH4) are explored through ab initio evolutionary methodology to reveal a metallic monoclinic structure of C2/c (4 molecules/cell). The C2/c structure consists of layerlike motifs containing novel "H2" units. Enthalpy calculations suggest a remarkably wide decomposition (Ge+H2) pressure range of 0-196 GPa, above which C2/c structure is stable. Perturbative linear-response calculations for C2/c GeH4 at 220 GPa predict a large electron-phonon coupling parameter lambda of 1.12 and the resulting superconducting critical temperature reaches 64 K.     

Three-dimensional isotropic metamaterial consisting of domain-structure

Whether an artificially designed negative-index structure could be regarded as a homogeneous medium or not rests with the ratio of its structural unit (man-made atom) over the operation wavelength. However, this definition is ambiguous, and usually the ratio is too large to rigorously meet the effective medium theory. In this paper a three-dimensional (3D) isotropic structure is presented which is obtained from a two-dimensional (2D) isotropic structure rotating on its axis for a circle, and the material is silver. Numerical studies confirm that both the 2D and 3D structures can realize a negative refractive index at microwave wavelengths. Observing the monitored surface current distributions and analogizing the molecular current and the magnetic domain, we suggest a new concept of domain-structure to explain the interior structure of this metamaterial, and finally conclude that the 3D structure is a kind of domain-structured and isotropic metamaterial.     

Non-equilibrium cation distribution and enhanced spin disorder in hollow CoFe2O4 nanoparticles

We present magnetic properties of hollow and solid CoFe(2)O(4) nanoparticles that were obtained by annealing of Co(33)Fe(67)/CoFe(2)O(4) (core/shell) nanoparticles. Hollow nanoparticles were polycrystalline whereas the solid nanoparticles were mostly single crystal. Electronic structure studies were performed by photoemission which revealed that particles with hollow morphology have a higher degree of inversion compared to solid nanoparticles and the bulk counterpart. Electronic structure and the magnetic measurements show that particles have uncompensated spins. Quantitative comparison of saturation magnetization (M(S )), assuming bulk Néel type spin structure with cationic distribution, calculated from quantitative XPS analysis, is presented. The thickness of uncompensated spins is calculated to be significantly large for particles with hollow morphology compared to solid nanoparticles. Both morphologies show a lack of saturation up to 7 T. Moreover magnetic irreversibility exists up to 7 T of cooling fields for the entire temperature range (10-300 K). These effects are due to the large bulk anisotropy constant of CoFe(2)O(4) which is the highest among the cubic spinel ferrites. The effect of the uncompensated spins for hollow nanoparticles was investigated by cooling the sample in large fields of up to 9 T. The magnitude of horizontal shift resulting from the unidirectional anisotropy was more than three times larger than that of solid nanoparticles. As an indication signature of uncompensated spin structure, 11% vertical shift for hollow nanoparticles is observed, whereas solid nanoparticles do not show a similar shift. Deconvolution of the hysteresis response recorded at 300 K reveals the presence of a significant paramagnetic component for particles with hollow morphology which further confirms enhanced spin disorder.     

The photoemission study of NdNiO3/NdGaO3 thin films, through the metal-insulator transition

The electronic structure of thin films NdNiO₃/NdGaO₃ with various thicknesses (from 17 nm to 150 nm), have been studied by photoemission spectroscopy at 300 K and 169 K. The XPS results are consistent with the literature ab initio calculations of the NdNiO₃ electronic structure. A noticeable variation attributed to the metal-insulator (MI) transition has been found only for the films with relatively high thickness (150 nm). Furthermore, the photoemission spectra and their temperature dependence have been discussed with regard to the results of dc electrical resistivity measurements which also exhibit large thickness dependence. Finally, these new results support a possible large hetero-epitaxial effect on the thinnest sample (17 nm) which could stress the NdNiO₃ structure and consequently makes its electronic structure nearly stabilized.     

Large negative lateral shifts due to negative refraction

When a thin structure in which negative refraction occurs (a metallo-dielectric structure or a photonic crystal) is illuminated by a beam, the reflected and transmitted beam can undergo a large negative lateral shift. This phenomenon can be seen as an interferential enhancement of the geometrical shift and can be considered a signature of negative refraction.     

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给出了EAST极向场磁体电源失超保护系统的设计方案,描述了两种失超保护开关——直流快速开关和爆炸开关采用的两级换流结构的设计和工作原理,分析了这种结构在换流过程中的规律,该结构有效地解决了开关开断直流大电流的难点。通过模拟实验证明了该失超保护系统满足设计要求。     

Impact of the liquid phase shape on the structure of III-V nanowires

The III-V nanowire structure (zinc blende or wurtzite) grown by the vapor-liquid-solid process is shown to be highly dependent on the parameters which shape the droplet at the top of the nanowire. Under conditions that the droplet volume does not exceed a certain value, it is demonstrated that when the nucleation of the solid starts at the solid-liquid-vapor triple line, a relatively large droplet volume and low wetting angle favor the formation of the wurtzite structure. We show that the effective V/III flux ratio is the primary parameter controlling the structure.     

遗传算法结合密度泛函理论研究Cu13团簇的几何结构

基于Gupta 多体势采用遗传算法详细计算了金属团簇Cu13的几何结构,对所得到的大量低能（基态及低激发态）结构,利用密度泛函理论方法作进一步优化计算。结果表明：尽管遗传算法所得基于Gupta原子间多体势的基态结构（Ih高对称性的紧致结构）并不对应第一性原理计算结果（非紧致低对称性基态）,但遗传算法给予的大量候选结构经密度泛函理论再次计算仍然可以高效地得到真实基态结构,体现出遗传算法在计算具有非紧致低对称性基态体系时的有效性。     

Identification and visualization of coherent structures in rayleigh-bénard convection with a time-dependent RANS

A time-dependent Reynolds-average-Navier-Stokes (TRANS) method is applied to capture and analyze the large-scale coherent structure in Rayleigh-Bénard (RB) convection over a flat and wavy bottom wall at a range of Rayleigh numbers. The method can be regarded as a Very Large Eddy Simulation (VLES) in which the unresolved random motion is modelled using a low-Re-number $k - \varepsilon - \bar \theta ^2 $ algebraic stress/flux single-point closure model. The large scale motion, which is the major mode of heat and momentum transfer in the bulk central region, is fully resolved by the time solution. In contrast to LES, the contribution of both modes to the turbulent fluctuations are of the same order of magnitude. The approach was assessed by comparison with the Direct Numerical Simulations (DNS) and experimental data using several criteria: visual observation of the large structure morphology, different structure identification criteria, and long-term averaged mean flow and turbulence properties. A visible similarity with large structures in DNS was observed, confirming the suitability of TRANS approach to reproduce the flows dominated by large coherent motions.     

便携式投影仪投影物镜设计

针对当前投影仪光源功耗大,光投影稳定性差,系统结构大的缺点,利用Zemax软件,设计出了一款大视场,短焦距,结构紧凑,适用于便携式投影仪的投影物镜系统。经过优化处理,最终获得的结构具有良好的成像质量,在空间频率为80 lp/mm处中心视场MTF≥0.7,0.8视场MTF≥0.6,边缘视场处MTF≥0.48,畸变小于3%,满足给出的设计指标。并且在规定和要求的像元尺寸范围内能量集中度大于85%,照度曲线0.8倍视场以内整体高于90%,能量集中度高,照度均匀性好,与便携式投影仪能很好地搭配使用。     

遗传算法结合密度泛函理论研究Cu13团簇的几何结构

基于Gupta 多体势采用遗传算法详细计算了金属团簇Cu13的几何结构,对所得到的大量低能（基态及低激发态）结构,利用密度泛函理论方法作进一步优化计算。结果表明：尽管遗传算法所得基于Gupta原子间多体势的基态结构（Ih高对称性的紧致结构）并不对应第一性原理计算结果（非紧致低对称性基态）,但遗传算法给予的大量候选结构经密度泛函理论再次计算仍然可以高效地得到真实基态结构,体现出遗传算法在计算具有非紧致低对称性基态体系时的有效性。     

全息制作不同晶面取向光子晶体模板

用单向光入射和单次曝光的激光全息技术制作了类金刚石结构, 此类金刚石结构有宽完全带隙和低介质折射率要求等优点. 在同一种光束配置下，引入恰当的匹配棱镜，用激光全息技术制作了大面积的类金刚石光学晶格不同晶面取向的亚微米周期结构. 满足如负折射效应等研究中所需的特殊晶面取向要求. 关键词： 激光全息技术 光学晶格 光子晶体     

High resolution numerical simulation of the structure of 2-D gaseous detonations

Two dimensional numerical simulation of the structure of gaseous detonation is investigated by utilizing the single step Arrhenius kinetic reaction mechanism in both high and low activation energy mixtures, characterized by their irregular and regular detonation structure, respectively. All the computations are performed on a small Beowulf cluster with six nodes. The dependency of the structure on the grid resolution is performed and it is found that, resolution of more than 300 cells per hrl is required to demonstrate the role of hydrodynamic instabilities, (KH and RM instabilities) in detonation propagation in irregular structures, while due to the absence of fine-scale structures, resolution of 50 cells per hrl, gives the physical structure of detonation with regular structures. Results show that the transverse waves in irregular structure are significantly stronger than the transverse wave in regular structure detonation, which can enhance the burning rate of the unburned pockets behind the shock front. Results for resolution of 600 cells per hrl illustrate that, in addition to the primary mode, the interaction of large vortices with the shock front provides secondary modes in the structure which leads to the irregularity of the structure in high activation energy mixture. In contrast with the results obtained for regular structure, which no unburned gas pockets and vortices observed behind the front, the results for irregular structure reveal that most portions of the gases, escape from shock compression and create large unburned gas pockets behind the both weak section of the Mach stem and the incident wave, which will burn eventually by the turbulent mixing due to the vortices associated with hydrodynamic instabilities. Therefore, the ignition mechanism in irregular structure is due to the both shock compression and by turbulent mixing associated with hydrodynamic instabilities, while the shock compression yields the ignition mechanism in regular structure detonation.     

Anomalous double peak structure in superconductor/ferromagnet tunneling density of states

We have experimentally investigated the density of states (DOS) in Nb/Ni (S/F) bilayers as a function of Ni thickness, d(F). Our thinnest samples show the usual DOS peak at +/- Delta(0), whereas intermediate-thickness samples have an anomalous "double-peak" structure. For thicker samples (d(F) > or =3.5 nm), we see an inverted DOS, which has previously only been reported in superconductor or weak-ferromagnet structures. We analyze the data using the self-consistent nonlinear Usadel equation and find that we are able to quantitatively fit the features at +/- Delta(0) -- in particular the thickness at which the inversion occurs -- only if we include a large amount of spin-orbit scattering in the model. Interestingly, we are unable to reproduce the subgap structure through the addition of any parameter(s). Therefore, the observed anomalous subgap structure represents new physics beyond that contained in the present Usadel theory.