2,162 research outputs found
Anisotropic optical response of nanocrystalline v2O5 thin films and effects of oxygen vacancy formation
We report a high sensitivity to oxygen vacancy formation as well as the temperature dependence of anisotropic optical properties of a nanocrystalline V2O5 thin film. Spectroscopic ellipsometry data show that the film has a uniaxial optical anisotropy due to a highly ordered nanocrystalline layer structure. The anisotropic optical properties of the film begin to change at 400 K in a high vacuum and can be linked to the changes in the electronic structure of the film upon reduction. An increase in the refractive indices, anisotropic changes of the optical conductivities, and a decrease in film thickness are observed after vacuum heating and are recovered to original values by heating in air up to 480 K. The experimental results are supported by the previous theoretical studies on the stability of reduced V2O5 surface through the formation of oxygen vacancies. We discuss the formation of oxygen vacancies, vacancy-induced structural relaxations, and changes in the electronic structure of V2O5 in conjunction with the experimental results.1441sciescopu
Development of wirelessly-powered, extracranial brain activator (ECBA) in a large animal model for the future non-invasive human neuromodulation
As transcranial electrical stimulation (tES) is an emerging and promising technique for neuromodulation, we developed a novel device; wirelessly-powered, extracranial brain activator (ECBA), which is mounted subcutaneously, and its neuromodulation effect was investigated. The oscillatory changes in electrocorticography (EcoG) were analyzed from two types of stimulation. Two weeks prior to the recording experiment, we underwent surgery for implantation of subdural strips and ECBA module over centroparietal regions of anesthetized beagles. Low-frequency stimulation (LFS) and subsequent high-frequency stimulation (HFS) protocols (600 pulses respectively) were applied. Then, the power changes before and after each stimulation in five different bands were compared. A significantly larger voltage difference with subcutaneous than transcutaneous stimulation measured at EcoG channels indicated a substantial current attenuation between the skin and skull. Compared with the baseline, all subjects showed consistently decreased delta power and increased gamma power after HFS. LFS also induced a similar, but opposite, pattern of power change in four beagles. The results from this study indicate that LFS and HFS with our novel ECBA can consistently and effectively modulate neural activity of the cortex, inducing neural inhibition and facilitation functions, respectively. Future studies are necessary to further ensuring a consistent efficacy and long-term safety.11Ysciescopu
Advances in single crystal growth and annealing treatment of electron-doped HTSC
High quality electron-doped HTSC single crystals of and have been
successfully grown by the container-free traveling solvent floating zone
technique. The optimally doped and crystals have transition temperatures
of \,K and \,K, respectively, with a transition width of less than
\,K. We found a strong dependence of the optimal growth parameters on the Ce
content . We discuss the optimization of the post-growth annealing treatment
of the samples, the doping extension of the superconducting dome for both
compounds as well as the role of excess oxygen. The absolute oxygen content of
the as-grown crystals is determined from thermogravimetric experiments and is
found to be . This oxygen surplus is nearly completely removed by a
post-growth annealing treatment. The reduction process is reversible as
demonstrated by magnetization measurements. In as-grown samples the excess
oxygen resides on the apical site O(3). This apical oxygen has nearly no doping
effect, but rather influences the evolution of superconductivity by inducing
additional disorder in the CuO layers. The very high crystal quality of
is particularly manifest in magnetic quantum
oscillations observed on several samples at different doping levels. They
provide a unique opportunity of studying the Fermi surface and its dependence
on the carrier concentration in the bulk of the crystals.Comment: 19 pages, 7 figures, submitted to Eur. Phys. J.
Thermoelectric power of MgBBe
We investigated thermoelectric power of MgBBe (,
0.2, 0.3, 0.4, and 0.6). decreases systematically with , suggesting
that the hole density increases. Our band calculation shows that the increase
occurs in the -band. With the hole-doping, decreases.
Implication of this phenomenon is discussed within the BCS framework. While the
Mott formula explains only the linear part of at low temperature,
incorporation of electron-phonon interaction enables us to explain over
wide temperature range including the anomalous behavior at high temperature.Comment: 4 pages, 4 figure
Numerical studies towards practical large-eddy simulation
Large-eddy simulation developments and validations are presented for an
improved simulation of turbulent internal flows. Numerical methods are proposed
according to two competing criteria: numerical qualities (precision and
spectral characteristics), and adaptability to complex configurations. First,
methods are tested on academic test-cases, in order to abridge with fundamental
studies. Consistent results are obtained using adaptable finite volume method,
with higher order advection fluxes, implicit grid filtering and "low-cost"
shear-improved Smagorinsky model. This analysis particularly focuses on mean
flow, fluctuations, two-point correlations and spectra. Moreover, it is shown
that exponential averaging is a promising tool for LES implementation in
complex geometry with deterministic unsteadiness. Finally, adaptability of the
method is demonstrated by application to a configuration representative of
blade-tip clearance flow in a turbomachine
The Modeling of Anisotropic Fuselage Lining Material
In this paper a theoretical model that can account for the effect of lining anisotropy on sound transmission through fuselage structures is developed. The model allows for anisotropic flow resistivity, tortuosity and elastic moduli. Implicit to the theory is a characteristic dispersion relation of sixth order that yields the allowed wave numbers for wave propagation in anisotropic elastic porous media. In addition, explicit expressions for field variables such as displacements and stresses appropriate for anisotropic foams are derived. Predictions of random incidence sound transmission loss for double panels with anisotropic linings have been performed. To verify the prediction, the theoretical results have been compared with random incidence transmission loss measurements
Tangential intersection of branches of motion
The branches of motion in the configuration space of a reconfigurable linkage can intersect in different ways leading to different types of singularities. In the vast majority of reported linkages whose configuration spaces contain multiple branches of motion the intersection happens transversally, allowing local methods, like the computation of its tangent cone, to identify different branches by means of their tangents. However, if these branches are of the same dimension and they intersect tangentially, it is not possible to identify them by means of the tangent cone at the singularity as the tangent spaces to the branches are the same. Although this possibility has been mentioned by a few researchers, whether linkages with this kind of tangent intersection of branches of motion exist is still an open question. In this paper, it is shown that the answer to this question is yes: A local method is proposed for the effective identification of branches of motion intersecting tangentially, and a method for the type synthesis of linkages that exhibit this particular type of singularity is presente
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