29,540 research outputs found
Effects of Geometric Phases in Josephson Junction Arrays
We show that the en route vortex velocity dependent part of the Magnus force
in a Josephson junction array is effectively zero, and predict zero Hall effect
in the classical limit. However, geometric phases due to the finite superfluid
density at superconductor grains have a profound influence on the quantum
dynamics of vortices. Subsequently we find rich and complex Hall behaviors
analogous to the Thouless-Kohmoto-Nightingale-den Nijs effect in the quantum
regime.Comment: Latex, 11 pages, appeared in Phys. Rev. Lett. v.77, 562 (1996) with
minor change
Work Function of Single-wall Silicon Carbide Nanotube
Using first-principles calculations, we study the work function of single
wall silicon carbide nanotube (SiCNT). The work function is found to be highly
dependent on the tube chirality and diameter. It increases with decreasing the
tube diameter. The work function of zigzag SiCNT is always larger than that of
armchair SiCNT. We reveal that the difference between the work function of
zigzag and armchair SiCNT comes from their different intrinsic electronic
structures, for which the singly degenerate energy band above the Fermi level
of zigzag SiCNT is specifically responsible. Our finding offers potential
usages of SiCNT in field-emission devices.Comment: 3 pages, 3 figure
Application of symbolic computations to the constitutive modeling of structural materials
In applications involving elevated temperatures, the derivation of mathematical expressions (constitutive equations) describing the material behavior can be quite time consuming, involved and error-prone. Therefore intelligent application of symbolic systems to faciliate this tedious process can be of significant benefit. Presented here is a problem oriented, self contained symbolic expert system, named SDICE, which is capable of efficiently deriving potential based constitutive models in analytical form. This package, running under DOE MACSYMA, has the following features: (1) potential differentiation (chain rule), (2) tensor computations (utilizing index notation) including both algebraic and calculus; (3) efficient solution of sparse systems of equations; (4) automatic expression substitution and simplification; (5) back substitution of invariant and tensorial relations; (6) the ability to form the Jacobian and Hessian matrix; and (7) a relational data base. Limited aspects of invariant theory were also incorporated into SDICE due to the utilization of potentials as a starting point and the desire for these potentials to be frame invariant (objective). The uniqueness of SDICE resides in its ability to manipulate expressions in a general yet pre-defined order and simplify expressions so as to limit expression growth. Results are displayed, when applicable, utilizing index notation. SDICE was designed to aid and complement the human constitutive model developer. A number of examples are utilized to illustrate the various features contained within SDICE. It is expected that this symbolic package can and will provide a significant incentive to the development of new constitutive theories
Computer simulation of the mathematical modeling involved in constitutive equation development: Via symbolic computations
Development of new material models for describing the high temperature constitutive behavior of real materials represents an important area of research in engineering disciplines. Derivation of mathematical expressions (constitutive equations) which describe this high temperature material behavior can be quite time consuming, involved and error prone; thus intelligent application of symbolic systems to facilitate this tedious process can be of significant benefit. A computerized procedure (SDICE) capable of efficiently deriving potential based constitutive models, in analytical form is presented. This package, running under MACSYMA, has the following features: partial differentiation, tensor computations, automatic grouping and labeling of common factors, expression substitution and simplification, back substitution of invariant and tensorial relations and a relational data base. Also limited aspects of invariant theory were incorporated into SDICE due to the utilization of potentials as a starting point and the desire for these potentials to be frame invariant (objective). Finally not only calculation of flow and/or evolutionary laws were accomplished but also the determination of history independent nonphysical coefficients in terms of physically measurable parameters, e.g., Young's modulus, was achieved. The uniqueness of SDICE resides in its ability to manipulate expressions in a general yet predefined order and simplify expressions so as to limit expression growth. Results are displayed when applicable utilizing index notation
Mgb2 Nonlinear Properties Investigated under Localized High RF Magnetic Field Excitation
In order to increase the accelerating gradient of Superconducting Radio
Frequency (SRF) cavities, Magnesium Diboride (MgB2) opens up hope because of
its high transition temperature and potential for low surface resistance in the
high RF field regime. However, due to the presence of the small superconducting
gap in the {\pi} band, the nonlinear response of MgB2 is potentially quite
large compared to a single gap s-wave superconductor (SC) such as Nb.
Understanding the mechanisms of nonlinearity coming from the two-band structure
of MgB2, as well as extrinsic sources, is an urgent requirement. A localized
and strong RF magnetic field, created by a magnetic write head, is integrated
into our nonlinear-Meissner-effect scanning microwave microscope [1]. MgB2
films with thickness 50 nm, fabricated by a hybrid physical-chemical vapor
deposition technique on dielectric substrates, are measured at a fixed location
and show a strongly temperature-dependent third harmonic response. We propose
that at least two mechanisms are responsible for this nonlinear response, one
of which involves vortex nucleation and penetration into the film. [1] T. M.
Tai, X. X. Xi, C. G. Zhuang, D. I. Mircea, S. M. Anlage, "Nonlinear Near-Field
Microwave Microscope for RF Defect Localization in Superconductors", IEEE
Trans. Appl. Supercond. 21, 2615 (2011).Comment: 6 pages, 6 figure
QUANTITATIVE MONITORING OF CEFRADINE IN HUMAN URINE USING A LUMINOL/SULFOBUTYLETHER-beta-CYCLODEXTRIN CHEMILUMINESCENCE SYSTEM
In this paper, a sensitive, rapid, and simple flow-injection chemiluminescence (FI-CL) technique is described for determining cefradine in human urine and capsule samples at the picogram level. The results show that cefradine within 0.1-100.0 nmol/L quantitatively quenches the CL intensity of the luminol/sulfo butylether-beta-cyclodextrin (SBE-beta-CD) system, with a relative correlation coefficient r of 0.9931. Subsequently, the possible mechanism for the quenching phenomenon is discussed in detail using the FI-CL and molecular docking methods. The proposed CL method, with a detection limit of 0.03 nmol/L (3 sigma) and relative standard deviations < 3.0% (N = 7), is then implemented to monitor the excretion of cefradine in human urine. After orally administration, the cefradine reaches a maximum value of 1.37 +/- 0.02 mg/mL at 2.0 h in urine, and the total excretion is 4.41 +/- 0.03 mg/mL within 8.0 h. The absorption rate constant k(a), the elimination rate constant k(e), and the half-life t(1/2) are 0.670 +/- 0.008 h(-1), 0.744 +/- 0.005 h(-1), and 0.93 +/- 0.05 h, respectively
Performance of Photosensors in the PandaX-I Experiment
We report the long term performance of the photosensors, 143 one-inch
R8520-406 and 37 three-inch R11410-MOD photomultipliers from Hamamatsu, in the
first phase of the PandaX dual-phase xenon dark matter experiment. This is the
first time that a significant number of R11410 photomultiplier tubes were
operated in liquid xenon for an extended period, providing important guidance
to the future large xenon-based dark matter experiments.Comment: v3 as accepted by JINST with modifications based on reviewers'
comment
Roles of intrinsic anisotropy and pi-band pairbreaking effects on critical currents in tilted c-axis MgB2 films probed by magneto-optical and transport measurements
Investigations of MgB2 and Fe-based superconductors in recent years have
revealed many unusual effects of multiband superconductivity but manifestations
of anisotropic multiband effects in the critical current density Jc have not
been addressed experimentally, mostly because of the difficulties to measure Jc
along the c-axis. To investigate the effect of very different intrinsic
anisotropies of sigma and pi electron bands in MgB2 on current transport, we
grew epitaxial films with tilted c-axis (THETA ~ 19.5{\deg}), which enabled us
to measure the components of Jc both along the ab-plane and the c-axis using
magneto-optical and transport techniques. These measurements were combined with
scanning and transmission electron microscopy, which revealed terraced steps on
the surface of the c-axis tilted films. The measured field and temperature
dependencies of the anisotropic Jc(H) show that Jc,L parallel to the terraced
steps is higher than Jc,T perpendicular to the terraced steps, and Jc of
thinner films (50 nm) obtained from transport experiments at 0.1 T reaches ~10%
of the depairing current density Jd in the ab plane, while magneto-optical
imaging revealed much higher Jc at lower fields. To analyze the experimental
data we developed a model of anisotropic vortex pinning which accounts for the
observed behavior of Jc in the c-axis tilted films and suggests that the
apparent anisotropy of Jc is affected by current pairbreaking effects in the
weaker {\pi} band. Our results indicate that the out-of-plane current transport
mediated by the {\pi} band could set the ultimate limit of Jc in MgB2
polycrystals.Comment: 21 pges, 13 figure
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