1,423 research outputs found
Ablation of carbonaceous materials in a hydrogen-helium arc-jet flow
The stagnation-point ablation rates of a graphite, a carbon-carbon composite, and four carbon-phenolic materials are measured in an arc-jet wind tunnel with a 50% hydrogen-50% helium mixture as the test gas. Flow environments are determined through measurements of static and impact pressures, heat-transfer rates to a calorimeter, and radiation spectra, and through numerical calculation of the flow through the wind tunnel, spectra, and heat-transfer rates. The environments so determined are: impact pressure approx. 3 atm, Mach number approx. 2.1, convective heat-transfer rate approx. 14 kw/sq cm, and radiative heat-transfer rate approx. 7 kw/sq cm in the absence of ablation. Ablation rates are determined from the measured rates of mass loss and recession of the ablation specimens. Compared with the predicted ablation rates obtained by running RASLE and CMA codes, the measured rates are higher by about 15% for all tested materials
Zero-energy Andreev surface bound states in the lattice model
The conditions for zero-energy Andreev surface bound states to exist are
found for the lattice model of d-wave superconductor with arbitrary surface
orientation. Both nearest neighbors and next nearest neighbors models are
considered. It is shown that the results are very sensitive to the surface
orientation. In particular, for half-filled -surface zero-energy Andreev
surface states only appear under the condition that and are odd
simultaneouslyComment: 9 pages, 1 figur
Current Issues in Legal Education
Six current issues in legal education, of wide general interest and importance, were posed by the Editors of this review to leading legal educators.These questions were and are frankly difficult and controversial, but their answers are important to our system of legal education and to our society. Capsule answers given by these distinguished legal educators are believed to be interesting and significant. Each is a personal rather than representative opinion. Brief answers such as these, of course, are not expected to be, nor do they pretend to be, complete or profound. Their purpose is to indicate succinctly the approach of outstanding American opinion makers to difficult problems of legal education
Spontaneous flux in a d-wave superconductor with time-reversal-symmetry-broken pairing state at {110} boundaries
The induction of an s-wave component in a d-wave superconductor is
considered. Near the {110}-oriented edges of such a sample, the induced s-wave
order parameter together with d-wave component forms a complex combination
d+e^{i\phi} s, which breaks the time reversal symmetry (BTRS) of the pairing
state. As a result, the spontaneous current is created. We numerically study
the current distribution and the formation of the spontaneous flux induced by
the current. We show that the spontaneous flux formed from a number of defect
lines with {110} orientation has a measurable strength. This result may provide
a unambiguous way to check the existence of BTRS pairing state at
{110}-oriented boundaries.Comment: 4 pages, 2 ps-figures, content changed, references adde
Discrete-Lattice Model for Surface Bound States and Tunneling in d-Wave Superconductors
Surface bound states in a discrete-lattice model of a cuprate
superconductor are shown to be, in general, coherent superpositions of an
incoming excitation and more than one outgoing excitation, and a simple
graphical construction based on a surface Brillouin zone is developed to
describe their nature. In addition, a momentum-dependent lifetime contribution
to the width of these bound states as observed in tunneling experiments is
derived and elucidated in physical terms.Comment: 4 pages, 1 figure, revte
Phase-sensitive Evidence for d-wave Pairing Symmetry in Electron-doped Cuprate Superconductors
We present phase-sensitive evidence that the electron-doped cuprates
Nd1.85Ce0.15CuO4-y (NCCO) and Pr1.85Ce0.15CuO4-y (PCCO) have d-wave pairing
symmetry. This evidence was obtained by observing the half-flux quantum effect,
using a scanning SQUID microscope, in c-axis oriented films of NCCO or PCCO
epitaxially grown on tricrystal [100] SrTiO3 substrates designed to be
frustrated for a d(x2-y2) order parameter. Samples with two other
configurations, designed to b unfrustrated for a d-wave superconductor, do not
show the half-flux quantum effect.Comment: 4 pages, Latex, 4 figure
Realistic Surface Scattering and Surface Bound State Formation in the High T_c Superconductor YBa_2Cu_3O_{6+x}
Surface Umklapp scattering of quasiparticles, and surface roughness are shown
to play essential roles in the formation of the surface bound states in
realistic models for YBa_2Cu_3O_{6+x}. The results account for the shape, the
impurity dependence of the height, and for a proposed universal width of the
zero bias conductance peak.Comment: 4 pages, 1 figur
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