Symmetric Directions Research Articles

A diffraction-based technique for determination of interband absorption coefficients in bulk 3C-, 4H- and 6H-SiC crystals

Knowledge of absorption coefficient values for wavelengths above the bandgap and the injected carrier density profile is an important issue for analysis of carrier dynamics in highly excited semiconductors, e.g. for evaluation of the carrier density in photoexcited layer, density-dependent recombination rate and diffusivity. In this work we present a novel way for determining the interband absorption coefficient α for SiC crystals in a wide temperature range. The proposed method is based on recording of a transient free carrier grating in a bulk semiconductor by strongly absorbed light and measurements of probe beam diffraction efficiencies on the grating for the Bragg and symmetric anti-Bragg directions. The method was applied for 3C-, 6H-, 4H-SiC polytypes at 351 nm wavelength and revealed 3 to 10-fold increase in the interband absorption coefficients in the 80–800 K temperature range. Increase in absorption coefficients with temperature was simulated by bandgap shrinkage and increase in phonon density. A good agreement of the determined α values with a priori known room-temperature data verified validation of this technique.

Effect of dispersion and damping of thermal phonon states on the longitudinal ultrasonic absorption in germanium crystals

A method has been proposed for approximating a phonon spectrum of cubic crystals, which has been obtained from data on inelastic neutron scattering for symmetric directions, over the entire Brillouin zone in the form appropriate for studying relaxation characteristics of phonon systems. The effect of dispersion and damping of thermal phonon states on the longitudinal ultrasonic absorption in anharmonic processes of scattering with the participation of three longitudinal phonons has been investigated for germanium crystals. It has been shown that the inclusion of the dispersion leads to a decrease in the anisotropy of ultrasonic absorption in the LLL relaxation mechanism and makes it possible to fit the results obtained from calculations of the ultrasonic absorption coefficients to the experimental data in the low-temperature range. The temperature dependence and anisotropy of the relaxation rate of longitudinal thermal phonons in germanium crystals have been determined from experimental data on ultrasonic absorption. The performed analysis has refined values of the relaxation parameters obtained from the interpretation of the data on thermal conductivity of germanium crystals with different isotopic compositions in the isotropic-medium model.

Extremely efficient and deterministic approach to generating optimal ordering of diffusion MRI measurements

Diffusion MRI measurements are typically acquired sequentially with unit gradient directions that are distributed uniformly on the unit sphere. The ordering of the gradient directions has significant effect on the quality of dMRI-derived quantities. Even though several methods have been proposed to generate optimal orderings of gradient directions, these methods are not widely used in clinical studies because of the two major problems. The first problem is that the existing methods for generating highly uniform and antipodally symmetric gradient directions are inefficient. The second problem is that the existing methods for generating optimal orderings of gradient directions are also highly inefficient. In this work, the authors propose two extremely efficient and deterministic methods to solve these two problems. The method for generating nearly uniform point set on the unit sphere (with antipodal symmetry) is based upon the notion that the spacing between two consecutive points on the same latitude should be equal to the spacing between two consecutive latitudes. The method for generating optimal ordering of diffusion gradient directions is based on the idea that each subset of incremental sample size, which is derived from the prescribed and full set of gradient directions, must be as uniform as possible in terms of the modified electrostatic energy designed for antipodally symmetric point set. The proposed method outperformed the state-of-the-art method in terms of computational efficiency by about six orders of magnitude. Two extremely efficient and deterministic methods have been developed for solving the problem of optimal ordering of diffusion gradient directions. The proposed strategy is also applicable to optimal view-ordering in three-dimensional radial MRI.

Fine structure and magnetism of the cubic oxide compound Ni0.3Zn0.7O

The fine structure and spin system of the cubic oxide Ni0.3Zn0.7O compound prepared from the initial hexagonal phase by quenching a sample with a high temperature and applying an external hydrostatic pressure to it have been studied using magnetic measurements, synchrotron and X-ray diffraction. It has been revealed that the diffraction patterns of this compound contain a system of weak diffuse maxima with the wave vectors q = (1/6 1/6 1/6)2π/a and (1/3 1/3 1/3)2π/a, along with strong Bragg peaks of the cubic phase. It has been shown that the origin of the diffuse peaks is due to longitudinal and transverse displacements of ions with respect to symmetric crystallographic directions of the {111} type. The reasons for the ion displacement and specific features of the structure of the spin system of the strongly correlated oxide Ni0.3Zn0.7O compound have been briefly discussed.

Hydrothermal synthesis of copper selenides with controllable phases and morphologies from an ionic liquid precursor

Cu2−xSe nanocrystals and CuSe nanoflakes are successfully synthesized through a convenient hydrothermal method from an ionic liquid precursor 1-n-butyl-3-ethylimidazolium methylselenite ([BMIm][SeO2(OCH3)]). The phases and morphologies of the copper selenides can be controlled by simply changing the atom ratio of Cu/Se in the reactants and reaction temperature. Furthermore, it is found that the [BMIm][SeO2(OCH3)] not only serves as Se source but also has influence on the shapes of CuSe nanoflakes. The adsorption of alkyl imidazolium rings ([BMIm]+) onto the (0001) facets of covellite CuSe prohibits the growth in the [0001] direction, and CuSe nuclei growth mainly processes along the six symmetric directions (±[011], ±[10], and ±[100]) to form flakelike CuSe. The obtained copper selenides are characterized by XRD, SEM, EDS, XPS, TEM, and HRTEM. The results indicate that the Cu2−xSe nanocrystals are nearly spherical particles with an average diameter of about 20 nm, the hexagonal CuSe nanoflakes are single crystals with an edge length of 100–400 nm and a thickness of 25–50 nm. The potential formation mechanism of the copper selenides is also proposed.

Difference of Directions Between External Driving Force and Movement Direction of Center of Mass

Driven dynamics of a two-dimensional Frenkel-Kontorova model is studied in the paper. In our numerical simulations, it is found that the movement direction of the center of mass is not consistent with that of the external driving force except for some special symmetric directions at the lower driving force. Our results also indicate that the movement direction of the center of mass strongly depends on both the magnitude and the direction of the external driving force as well as the misfit angle between two layers.

Analysis of Asymmetric Valve Control Asymmetric Cylinder System of Hydraulic Leveler

Symmetric valve controlled asymmetric cylinder which is applied to force down system of hydraulic leveler. In this case, the flow metering-in is not equal with metering-out universally in proportional or servo control hydraulic system, "pressure jump" will appear at the time of symmetric valve changing direction[1,2]. To deal with this disadvantage well and improve the system, the disadvantage of symmetric valve controlled asymmetric cylinder is altered by the solution that asymmetric valve controlled asymmetric cylinder. In this paper, the mathematic model of the solution has been worked out actually and the transfer function has been constructed. Finally using simulink software of MATLAB to simulate the system and analyze the stability of closed-loop.

Competitive market for multiple firms and economic crisis

The origin of economic crises is a key problem for economics. We present a model of long-run competitive markets to show that the multiplicity of behaviors in an economic system, over a long time scale, emerge as statistical regularities (perfectly competitive markets obey Bose-Einstein statistics and purely monopolistic-competitive markets obey Boltzmann statistics) and that how interaction among firms influences the evolutionary of competitive markets. It has been widely accepted that perfect competition is most efficient. Our study shows that the perfectly competitive system, as an extreme case of competitive markets, is most efficient but not stable, and gives rise to economic crises as society reaches full employment. In the economic crisis revealed by our model, many firms condense (collapse) into the lowest supply level (zero supply, namely, bankruptcy status), in analogy to Bose-Einstein condensation. This curious phenomenon arises because perfect competition (homogeneous competitions) equals symmetric (indistinguishable) investment direction, a fact abhorred by nature. Therefore, we urge the promotion of monopolistic competition (heterogeneous competitions) rather than perfect competition. To provide early warning of economic crises, we introduce a resolving index of investment, which approaches zero in the run-up to an economic crisis. On the other hand, our model discloses, as a profound conclusion, that the technological level for a long-run social or economic system is proportional to the freedom (disorder) of this system; in other words, technology equals the entropy of system. As an application of this concept, we give a possible answer to the Needham question: "Why was it that despite the immense achievements of traditional China it had been in Europe and not in China that the scientific and industrial revolutions occurred?"

Synthesis of Hierarchical Porous ZnO Disklike Nanostructures for Improved Photovoltaic Properties of Dye-Sensitized Solar Cells

We report on the synthesis of a porous hierarchical disklike ZnO nanostructure fabricated via a simple low-temperature hydrothermal method for photovoltaic applications. The hierarchical ZnO nanostructures consist of porous ZnO nanowires growing in six symmetric directions and form a disklike shape. Owing to the enlarged surface area and natural electron collection routes of the ZnO hierarchical nanostructures, dye-sensitized solar cells based on these structures exhibit improved photovoltaic performance compared with that of the ZnO nanowire arrays. Our results suggest that porous hierarchical nanomaterials are promising materials for applications in dye-sensitized solar cells.

Trivial Connections on Discrete Surfaces

AbstractThis paper presents a straightforward algorithm for constructing connections on discrete surfaces that are as smooth as possible everywhere but on a set of isolated singularities with given index. We compute these connections by solving a single linear system built from standard operators. The solution can be used to design rotationally symmetric direction fields with user‐specified singularities and directional constraints.

족관절 테이핑이 자세 균형과 요부 유연성에 미치는 영향

Purpose : This study identifies the effect of ankle-taping on limb asymmetry, postural sway and lumbar flexibility. Ankle-taping was applied for participants of this study and the results were compared to the control group. Methods : This study targets 46 adults, in which 25 composed the test group and 21 composed the control group. All participants were interviewed. For the test group, inflexible tapes of 5mm width were applied as designed by Danaka Nobudaka while the tapes for the control group were arranged in a symmetric direction to the direction of the test group. Postural balance was measured using Mediance (Human Tech Inc, Korea) and to identify lumbar flexibility, the trunk flexion is targeted. Results : 1. The postural inclination of both the groups decreased, but a statistically significant difference is not found (p>0.05). 2. Both the groups increased, but no statistically significant difference is found (p>0.05). 3. Both the groups increased, and a statistically significant change is found (p

Low-Symmetry Phases in Ferroelectric Nanowires

Ferroelectric nanostructures have recently attracted much attention due to the quest of miniaturizing devices and discovering novel phenomena. In particular, studies conducted on two-dimensional and zero-dimensional ferroelectrics have revealed original properties and their dependences on mechanical and electrical boundary conditions. Meanwhile, researches aimed at discovering and understanding properties of one-dimensional ferroelectric nanostructures are scarce. The determination of the structural phase and of the direction of the polarization in one-dimensional ferroelectrics is of technological importance, since, e.g., a low-symmetry phase in which the polarization lies away from a highly symmetric direction typically generates phenomenal dielectric and electromechanical responses. Here, we investigate the phase transition sequence of nanowires made of KNbO(3) and BaTiO(3) perovskites, by combining X-ray diffraction, Raman spectroscopy, and first-principles-based calculations. We provide evidence of a previously unreported ferroelectric ground state of monoclinic symmetry and the tuning of the polarization's direction by varying factors inherent to the nanoscale.

Distortion theorems for univalent meromorphic functions on an annulus

We apply the capacity and symmetrization methods to distortion theorems for analytic functions in an annulus. We show that the classical Teichmuller estimate for the capacity of a doubly-connected domain yields a series of the already known and new inequalities for univalent functions. In particular, we supplement the results of Grotzsch, Duren, and Huckemann. Using the dissymmetrization of condensers we establish sharp estimates for local distortion and the distortion of level curves in n ≥ 2 symmetric directions. In terms of Robin functions we give an analog of the Nehari inequality: some general distortion theorem for several points taking into account the boundary behavior of the function and describing the cases of equalities. As a corollary we give analogs of some inequalities of Solynin, Pommerenke, and Vasil’ev that were obtained previously for univalent and bounded functions in a disk. We prove a distortion theorem that involves the Schwarzian derivatives at symmetric points on the unit circle.

A New Class of Large Neighborhood Path-Following Interior Point Algorithms for Semidefinite Optimization with $O(\sqrt{n}\log\frac{\mathrm{Tr}(X^0S^0)}{\epsilon})$ Iteration Complexity

In this paper, we extend the Ai-Zhang direction to the class of semidefinite optimization problems. We define a new wide neighborhood $\mathcal{N}(\tau_1,\tau_2,\eta)$, and, as usual but with a small change, we make use of the scaled Newton equations for symmetric search directions. After defining the “positive part” and the “negative part” of a symmetric matrix, we recommend solving the Newton equation with its right-hand side replaced first by its positive part and then by its negative part, respectively. In such a way, we obtain a decomposition of the classical Newton direction and use different step lengths for each of them. Starting with a feasible point $(X^0,y^0,S^0)$ in $\mathcal{N}(\tau_1,\tau_2,\eta)$, the algorithm terminates in at most $O(\eta\sqrt{\kappa_{\infty}n}\log({Tr}(X^0S^0)/\epsilon))$ iterations, where $\kappa_{\infty}$ is a parameter associated with the scaling matrix $P$ and $\epsilon$ is the required precision. To our best knowledge, when the parameter $\eta$ is a constant, this is the first large neighborhood path-following interior point method (IPM) with the same complexity as small neighborhood path-following IPMs for semidefinite optimization that use the Nesterov-Todd direction. In the case where $\eta$ is chosen to be in the order of $\sqrt{n}$, our result coincides with the results for classical large neighborhood IPMs. Some preliminary numerical results also confirm the efficiency of the algorithm.

On the orientation of plane tensegrity cytoskeletons under biaxial substrate stretching

Two different simple cases of plane tensegrity cytoskeleton geometries are presented and investigated in terms of stability. The tensegrity frames are used to model adherent cell cytoskeletal behaviour under the application of plane substrate stretching and describe thoroughly the experimentally observed reorientation phenomenon. Both models comprise two elastic bars (microtubules), four elastic strings (actin filaments) and are attached on an elastic substrate. In the absence of external loading shape stability of the cytoskeleton is dominated by its prestress. Upon application of external loading, the cytoskeleton is reorganized in a new direction such that its total potential energy is rendered a global minimum. Considering linear constitutive relations, yet large deformations, it is revealed that the reorientation phenomenon can be successfully treated as a problem of ma- thematical stability. It is found that apart from the magnitude of contractile prestress and the magnitude of extracellular stretching, the reorientation is strongly shape–dependent as well. Numerical applications not only justify laboratory data reported in literature but such experimental evidence as the concurrent appearance of two distinct and symmetric directions of orientation, indicating the cellular coexistence of phases phenomenon, are clearly detected and incorporated in the proposed mathematical treatment.

Fast vertical alignment mode with continuous multi-domains for a liquid crystal display

We proposed a fast liquid crystal display (LCD) in a vertical alignment (VA) mode with continuous multi-domains for wide-viewing characteristics. The fast VA LCD was fabricated by the mixed vertical alignment layer with UV curable reactive mesogen (RM) polymer memorizing the switching directions of the LC molecules. The wide-viewing and fast response characteristics were obtained by axially symmetric switching directions and the memorization of them without any specific electrode patterns or surface structures.

The influence of technical and tactical training with symmetric direction on the efficiency of young boxers` strokes

ВВЕДЕНИЕ Современный бокс характеризуется возросшей интенсивностью боя и жестко-стью выполняемых ударов. Соответственно, успешное выступление в поединке требу-ет от боксеров адекватного уровня подготовленности не только в физическом и функ-циональном отношении, но и в технико-тактическом компоненте, определяющем уро-вень специальной подготовленности спортсменов к соревнованиям. Одним из возмож-ных вариантов совершенствования методики тренировки юных боксеров может быть симметричный подход в технико-тактической подготовке. Данный подход может быть полезен для формирования более прочных и вариативных двигательных навыков, что соответствует основным задачам начальных этапов обучения [1], [2], [3], [5]. Вместе с тем, есть и опасение, которое заключается в том, что, обучая боксеров-новичков бое-вым приемам сразу в двух стойках, можно ввести в процесс обучения дезорганизую-щий фактор, проявляющийся в отвлечении спортсмена от ведущей – доминантной стороны, в результате чего, они не смогут освоить необходимый начальный уровень технико-тактических действий в основную сторону, в то же время, обучение в одной стойке значительно ограничивает возможность овладения разнообразной техникой и тактикой. Поэтому, при разработке методики симметричной направленности (билате-рального обучения), по мере возможности, были учтены мнения всех специалистов. МЕТОДИКА Основными элементом методики симметричной направленности были выбраны упражнения специального и специально-подготовительного характера, направленные на обучение спортсмена двигательным действиям, выполняемым обеими руками.

Improving Accuracy of Sample Surface Topography by Atomic Force Microscopy

We describe method for improving the accuracy of sample surface topography by atomic force microscopy (AFM). It takes into account the effect of the AFM tip shape and image reconstruction on the acquired AFM images. The dilation effect due to the use of a finite-sized tip shape can be minimized by using a sharp AFM tip and scanning at the most symmetric direction of tip geometry. Reconstruction of AFM image could produce more accurate sample surface features. The method is useful to AFM measurement and is significant because AFM has become a fundamental tool in nanoscience and nanotechnology with multiple applications in a wide range of disciplines ranging from biology to physics and material science.

Effect of the higher d-wave gap harmonics and possible s-wave component on spin dynamics in electron-doped high- [formula omitted] superconductors

In this paper, we examine the effect on spin dynamics of three kinds of possible superconducting (SC) gap in electron-doped high- T c systems, that is, the d x 2 - y 2 -wave, the mixed d x 2 - y 2 + higher d-wave harmonics ( cos ( 6 ϕ ) ) , and the d x 2 - y 2 + is -wave. Starting from the slave-boson mean-field approach to the t - t ′ - J model, a higher d-wave gap term and an is-wave component are included in a phenomenological form, respectively. With the random-phase approximation (RPA), we present a detailed analysis of the momentum, frequency and doping dependence of the spin susceptibility. It is found that at low frequencies, the spin response is commensurate in the SC state and there is a crossover frequency ω c above which the spin response begins to be incommensurate, and the crossover frequency ω c increases with doping. So the dispersion of the excitation is different from the hole-doped cuprates, in which a hourglass-like dispersion is observed. We also find that a spin resonance appears in the underdoped and optimally doped regime. These similar characters for the three kinds of superconducting gap suggest the underlying importance of Fermi surface (FS) topology. On the other hand, the incommensurate spin fluctuation at high frequencies is found to exhibit a ring structure around ( π , π ) for the mixed cos ( 2 ϕ ) + cos ( 6 ϕ ) -wave, while others show maxima along the ( π , π + δ π ) and its symmetric directions. Below ω c , the spin response remains to be commensurate all along to the lowest frequency for the d x 2 - y 2 + is -wave, while the others cross to a small incommensurate structure with further decreasing the frequency. These may be taken to probe the possible subdominant SC components.

Zinc oxide nanostructures: epitaxially growing from hexagonal zinc nanostructures

The epitaxial growth of ZnO nanosheets and nanoneedles from a Zn/ZnO core/shellstructure is verified by an experiment in which the ZnO nanoneedles andnanosheets are synthesized in air within an ultra-low temperature range from 250 to400 °C by thermal oxidation of Zn films made up of hexagonal nanodiscs or nanoprisms. Thehexagonal Zn structures are oxidized to form a Zn/ZnO core/shell structure withan epitaxial relationship; ZnO nanoneedles and nanosheets are found to growepitaxially from the ZnO shell, along sixfold symmetric directions, showing the same lattice orientation as the Zn core. The stability differenceamong different facets of hexagonal Zn crystal structures plays a key role in the formationof ZnO nanosheets, nanoneedles and the Zn/ZnO core/shell structure, as well as ZnOhollow structures. A vapor–solid mechanism is suggested to explain the epitaxial growthprocess of the ZnO products. Photoluminescence properties of the ZnO nanostructures arealso explored.