25,121 research outputs found
Bogoliubov quasiparticle spectra of the effective d-wave model for cuprate superconductivity
An exact-diagonalization technique on finite-size clusters is used to study
the ground state and excitation spectra of the two-dimensional effective
fermion model, a fictious model of hole quasiparticles derived from numerical
studies of the two-dimensional t-J model at low doping. We show that there is
actually a reasonable range of parameter values where the -wave
pairing of holes occurs and the low-lying excitation can be described by the
picture of Bogoliubov quasiparticles in the BCS pairing theory. The gap
parameter of a size (where is the attractive
interaction between holes) is estimated at low doping levels. The paired state
gives way to the state of clustering of holes for some stronger attractions.Comment: 4 pages, RevTeX. Figures available upon request to
[email protected]. To be published in Phys. Rev.
Heat transfer on accreting ice surfaces
Based on previous observations of glaze ice accretion on aircraft surfaces, a multizone model with distinct zones of different surface roughness is demonstrated. The use of surface roughness in the LEWICE ice accretion prediction code is examined. It was found that roughness is used in two ways: (1) to determine the laminar to turbulent boundary-layer transition location; and (2) to calculate the convective turbulent heat-transfer coefficient. A two-zone version of the multizone model is implemented in the LEWICE code, and compared with experimental convective heat-transfer coefficient and ice accretion results. The analysis of the boundary-layer transition, surface roughness, and viscous flowfield effects significantly increased the accuracy in predicting heat-transfer coefficients. The multizone model was found to significantly improve the ice accretion prediction for the cases compared
Hydrogen dissociation on the Mg(0001) surface from quantum Monte Carlo calculations
We have used diffusion Monte Carlo (DMC) simulations to calculate the energy
barrier for H dissociation on the Mg(0001) surface. The calculations employ
pseudopotentials and systematically improvable B-spline basis sets to expand
the single particle orbitals used to construct the trial wavefunctions.
Extensive tests on system size, time step, and other sources of errors,
performed on periodically repeated systems of up to 550 atoms, show that all
these errors together can be reduced to eV. The DMC dissociation
barrier is calculated to be eV, and is compared to those
obtained with density functional theory using various exchange-correlation
functionals, with values ranging between 0.44 and 1.07 eV.Comment: 6 pages, 4 figures, to appear in Physical Review
Cosmological evolution of cosmic strings with time-dependent tension
We discuss the cosmological evolution of cosmic strings with time-dependent
tension. We show that, in the case that the tension changes as a power of time,
the cosmic string network obeys the scaling solution: the characteristic scale
of the string network grows with the time. But due to the time dependence of
the tension, the ratio of the energy density of infinite strings to that of the
background universe is {\it not} necessarily constant.Comment: 9 pages, to appear in Phys. Rev.
D-term chaotic inflation in supergravity
Even though the chaotic inflation is one of the most popular inflation models
for its simple dynamics and compelling resolutions to the initial condition
problems, its realization in supergravity has been considered a challenging
task. We discuss how the chaotic inflation dominated by the D-term can be
induced in supergravity, which would give a new perspective on the inflation
model building in supergravity.Comment: 5 pages, to appear in Phys. Rev.
Deterministic multi-zone ice accretion modeling
The focus here is on a deterministic model of the surface roughness transition behavior of glaze ice. The initial smooth/rough transition location, bead formation, and the propagation of the transition location are analyzed. Based on the hypothesis that the smooth/rough transition location coincides with the laminar/turbulent boundary layer transition location, a multizone model is implemented in the LEWICE code. In order to verify the effectiveness of the model, ice accretion predictions for simple cylinders calculated by the multizone LEWICE are compared to experimental ice shapes. The glaze ice shapes are found to be sensitive to the laminar surface roughness and bead thickness parameters controlling the transition location, while the ice shapes are found to be insensitive to the turbulent surface roughness
Multiple buoyancy driven flows in a vertical cylinder heated from below
The structure of axisymmetric buoyancy-driven convection in a vertical cylinder heated from below is probed by finite element solution of the Boussinesq equations coupled with computed-implemented perturbation techniques for detecting and tracking multiple flows and for determining flow stability. Results are reported for fluids with Prandtl number of one and for cylinders with aspect ratio (Lambda) (defined as the height to radius of the cylinder) between 0.5 and 2.25. Extensive calculations of the neutral stability curve for the static solution and of the nonlinear motions along the bifurcating flow families show a continuous evolution of the primary cellular motion from a single toroidal cell to two and three cells nested radially in the cylinder, instead of the sharp transitions found for a cylinder with shear-free sidewalls. The smooth transitions in flow structure with Rayleigh number and lambda are explained by nonlinear connectivity between the first two bifurcating flow families formed either by a secondary bifurcation point for Lambda or = Lambda * approximately 0.80 or by a limit point for Lambda Lambda *. The transition between these two modes may be described by the theory of multiple limit point bifurcation
New Universality of Lyapunov Spectra in Hamiltonian Systems
A new universality of Lyapunov spectra {\lambda_i} is shown for Hamiltonian
systems. The universality appears in middle energy regime and is different from
another universality which can be reproduced by random matrices in the
following two points. One is that the new universality appears in a limited
range of large i/N rather than the whole range, where N is degrees of freedom.
The other is Lyapunov spectra do not behave linearly while random matrices give
linear behavior even on 3D lattice. Quadratic terms with smaller nonlinear
terms of potential functions play an intrinsic role in the new universality.Comment: 19 pages, 16 Encapsulated Postscript figures, LaTeX (100 kb
The \gamma-ray production in neutral-current neutrino oxygen interaction in the energy range above 100 MeV
We calculate the cross section of the gamma-ray production from
neutral-current neutrino-oxygen quasi-elastic interaction, , or , in
which the residual nuclei (15N* or 15O*) lead to the gamma-ray emission with
gamma-ray energy >6 MeV at the branching ratio of 41%. Above 200 MeV, this
cross section dominates over that of gamma-ray production from the inelastic
reaction, . In the present calculation, spectral
function and the spectroscopic factors of
states are essential. The gamma-ray production is dominated by the deexcitation
of state of the residual nucleus
Elemental Abundances in the Possible Type Ia Supernova Remnant G344.7-0.1
Recent studies on the Galactic supernova remnant (SNR) G344.7-0.1 have
commonly claimed its origin to be a core-collapse supernova (SN) explosion,
based on its highly asymmetric morphology and/or proximity to a star forming
region. In this paper, however, we present an X-ray spectroscopic study of this
SNR using Suzaku, which is supportive of a Type Ia origin. Strong K-shell
emission from lowly ionized Fe has clearly been detected, and its origin is
determined, for the first time, to be the Fe-rich SN ejecta. The abundance
pattern is highly consistent with that expected for a somewhat-evolved Type Ia
SNR. It is suggested, therefore, that the X-ray point-like source CXOU
J170357.8-414302 located at the SNR's geometrical center is not associated with
the SNR but is likely to be a foreground object. Our result further indicates
that G344.7-0.1 is the first possible Type Ia SNR categorized as a member of
the so-called "mixed-morphology" class. In addition, we have detected emission
from He-like Al at ~1.6 keV, the first clear detection of this element in the
spectrum of an extended X-ray source. The possible enhancement of the Al/Mg
abundance ratio from the solar value suggests that the ambient interstellar
medium has a relatively high metallicity (not less than 10% of the solar
value), if this SNR has indeed a Type Ia origin. We also report marginal
detection of Cr and Mn, although the measured fluxes have large statistical and
systematic uncertainties.Comment: ApJ in pres
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