83,043 research outputs found
Higher-spin Realisations of the Bosonic String
It has been shown that certain algebras can be linearised by the
inclusion of a spin--1 current. This provides a way of obtaining new
realisations of the algebras. Recently such new realisations of were
used in order to embed the bosonic string in the critical and non-critical
strings. In this paper, we consider similar embeddings in and
strings. The linearisation of is already known, and can be
achieved for all values of central charge. We use this to embed the bosonic
string in critical and non-critical strings. We then derive the
linearisation of using a spin--1 current, which turns out to be
possible only at central charge . We use this to embed the bosonic
string in a non-critical string.Comment: 8 pages. CTP TAMU-10/95
Domain wall switching: optimizing the energy landscape
It has recently been suggested that exchange spring media offer a way to
increase media density without causing thermal instability
(superparamagnetism), by using a hard and a soft layer coupled by exchange.
Victora has suggested a figure of merit xi = 2 E_b/mu_0 m_s H_sw, the ratio of
the energy barrier to that of a Stoner-Wohlfarth system with the same switching
field, which is 1 for a Stoner-Wohlfarth (coherently switching) particle and 2
for an optimal two-layer composite medium. A number of theoretical approaches
have been used for this problem (e.g., various numbers of coupled
Stoner-Wohlfarth layers and continuum micromagnetics). In this paper we show
that many of these approaches can be regarded as special cases or
approximations to a variational formulation of the problem, in which the energy
is minimized for fixed magnetization. The results can be easily visualized in
terms of a plot of the energy as a function of magnetic moment m_z, in which
both the switching field [the maximum slope of E(m_z)] and the stability
(determined by the energy barrier E_b) are geometrically visible. In this
formulation we can prove a rigorous limit on the figure of merit xi, which can
be no higher than 4. We also show that a quadratic anistropy suggested by Suess
et al comes very close to this limit.Comment: Acccepted for proceedings of Jan. 2007 MMM Meeting, paper BE-0
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
Liouville and Toda Solitons in M-theory
We study the general form of the equations for isotropic single-scalar,
multi-scalar and dyonic -branes in superstring theory and M-theory, and show
that they can be cast into the form of Liouville, Toda (or Toda-like)
equations. The general solutions describe non-extremal isotropic -branes,
reducing to the previously-known extremal solutions in limiting cases. In the
non-extremal case, the dilatonic scalar fields are finite at the outer event
horizon.Comment: Latex, 10 pages. Minor corrections to text and titl
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