95,911 research outputs found
Density oscillations in trapped dipolar condensates
We investigated the ground state wave function and free expansion of a
trapped dipolar condensate. We find that dipolar interaction may induce both
biconcave and dumbbell density profiles in, respectively, the pancake- and
cigar-shaped traps. On the parameter plane of the interaction strengths, the
density oscillation occurs only when the interaction parameters fall into
certain isolated areas. The relation between the positions of these areas and
the trap geometry is explored. By studying the free expansion of the condensate
with density oscillation, we show that the density oscillation is detectable
from the time-of-flight image.Comment: 7 pages, 9 figure
The breakage prediction for hydromechanical deep drawing based on local bifurcation theory
A criterion of sheet metal localized necking under plane stress was established based on the bifurcation theory and the characteristics theory of differential equation. In order to be capable to incorporate the directional dependence of the plastic strain rate on stress rate, Ito-Goya’s constitutive equation which gave a one to one relationship between stress rate component and plastic strain rate component was employed. The hydromechanical deep drawing process of a cylindrical cup part was simulated using the commercial software ABAQUS IMPLICIT. The onset of breakage of the part during the forming process was predicted by combining the simulation results with the local necking criterion. The proposed method is applied to the hydro-mechanical deep drawing process for A2219 aluminum alloy sheet metal to predict the breakage of the cylindrical cup part. The proposed method can be applied to the prediction of breakage in the forming of the automotive bodies
Black Holes in Higher-Derivative Gravity
Extensions of Einstein gravity with higher-order derivative terms arise in
string theory and other effective theories, as well as being of interest in
their own right. In this paper we study static black-hole solutions in the
example of Einstein gravity with additional quadratic curvature terms. A
Lichnerowicz-type theorem simplifies the analysis by establishing that they
must have vanishing Ricci scalar curvature. By numerical methods we then
demonstrate the existence of further black-hole solutions over and above the
Schwarzschild solution. We discuss some of their thermodynamic properties, and
show that they obey the first law of thermodynamics.Comment: Typos corrected, discussion added, figure changed. 4 pages, 6 figure
Spectrum-generating Symmetries for BPS Solitons
We show that there exist nonlinearly realised duality symmetries that are
independent of the standard supergravity global symmetries, and which provide
active spectrum-generating symmetries for the fundamental BPS solitons. The
additional ingredient, in any spacetime dimension, is a single scaling
transformation that allows one to map between BPS solitons with different
masses. Without the inclusion of this additional transformation, which is a
symmetry of the classical equations of motion, but not the action, it is not
possible to find a spectrum-generating symmetry. The necessity of including
this scaling transformation highlights the vulnerability of duality multiplets
to quantum anomalies. We argue that fundamental BPS solitons may be immune to
this threat.Comment: References added. Latex, 29 page
Lichnerowicz Modes and Black Hole Families in Ricci Quadratic Gravity
A new branch of black hole solutions occurs along with the standard
Schwarzschild branch in -dimensional extensions of general relativity
including terms quadratic in the Ricci tensor. The standard and new branches
cross at a point determined by a static negative-eigenvalue eigenfunction of
the Lichnerowicz operator, analogous to the Gross-Perry-Yaffe eigenfunction for
the Schwarzschild solution in standard dimensional general relativity.
This static eigenfunction has two r\^oles: both as a perturbation away from
Schwarzschild along the new black-hole branch and also as a threshold unstable
mode lying at the edge of a domain of Gregory-Laflamme-type instability of the
Schwarzschild solution for small-radius black holes. A thermodynamic analogy
with the Gubser and Mitra conjecture on the relation between quantum
thermodynamic and classical dynamical instabilities leads to a suggestion that
there may be a switch of stability properties between the old and new
black-hole branches for small black holes with radii below the branch crossing
point.Comment: 33 pages, 8 figure
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