1,369 research outputs found
Supersymmetry and the Systematics of T-duality Rotations in Type-II Superstring Theories
We describe a systematic method of studying the action of the T-duality group
O(d,d) on space-time fermions and R-R field strengths and potentials in type-II
string theories, based on space-time supersymmetry. The formalism is then used
to show that the couplings of non-Abelian D-brane charges to R-R potentials can
be described by an appropriate Clifford multiplication.Comment: 6 pages, LaTeX, uses espcrc2.sty; Contribution to the proceedings of
the D. V. Volkov memorial conference on ``Supersymmetry and Quantum Field
Theory'', Kharkov, July 25-29, 2000 (to appear in the Nucl. Phys. B
Conference Supplements
Evaluation of functions on microcomputers: rational approximation of kth roots
AbstractThis paper describes the implementation of rational approximation algorithms for evaluation of kth roots in short wordlength machines. The emphasis is on maintaining full machine precision in computers that use fixed point, truncated binary arithmetic with at most 16 bits of wordlength. Included is a table of coefficients for evaluation of kth roots on a 16 bit machine with 3 †k †11
Influence of pretreatment on surface interaction between Cu and anatase-TiO2 in the simultaneous photoremediation of nitrate and oxalic acid
This research work was partly supported by the Petroleum Technology Development Fund (PTDF) of Nigeria. We are grateful to Abubakar Tafawa Balewa University, Bauchi-Nigeria for the award of fellowship to Haruna Adamu.Peer reviewedPostprin
Gauge Theory Description of D-brane Black Holes: Emergence of the Effective SCFT and Hawking Radiation
We study the hypermultiplet moduli space of an N=4, U(Q_1)xU(Q_5) gauge
theory in 1+1 dimensions to extract the effective SCFT description of near
extremal 5-dimensional black holes modelled by a collection of D1- and
D5-branes. On the moduli space, excitations with fractional momenta arise due
to a residual discrete gauge invariance. It is argued that, in the infra-red,
the lowest energy excitations are described by an effective c=6, N=4 SCFT on
T^4, also valid in the large black hole regime. The ``effective string
tension'' is obtained using T-duality covariance. While at the microscopic
level, minimal scalars do not couple to (1,5) strings, in the effective theory
a coupling is induced by (1,1) and (5,5) strings, leading to Hawking radiation.
These considerations imply that, at least for such black holes, the calculation
of the Hawking decay rate for minimal scalars has a sound foundation in string
theory and statistical mechanics and, hence, there is no information loss.Comment: 24 pages, LaTeX, very minor changes, to appear in Nucl. Phys.
Detection and modelling of contacts in explicit finite-element simulation of soft tissue biomechanics
Realistic modelling of soft-tissue biomechanics and mechanical interactions between tissues is an important part of surgical simulation, and may become a valuable asset in
surgical image-guidance. Unfortunately, it is also computationally very demanding. Explicit
matrix-free FEM solvers have been shown to be a good choice for fast tissue simulation,
however little work has been done on contact algorithms for such FEM solvers.
This work introduces such an algorithm that is capable of handling the scenarios typically encountered in image-guidance. The responses are computed with an evolution of
the Lagrange-multiplier method first used by Taylor and Flanagan in PRONTO 3D with
spatio-temporal smoothing heuristics for improved stability with coarser meshes and larger
time steps. For contact search, a bounding-volume hierarchy (BVH) capable of identifying self collisions, and which is optimised for the small time steps by reducing the number
of bounding-volume refittings between iterations through identification of geometry areas
with mostly rigid motion and negligible deformation, is introduced. Further optimisation is
achieved by integrating the self-collision criterion in the BVH creation and updating algorithms.
The effectiveness of the algorithm is demonstrated on a number of artificial test cases
and meshes derived from medical image data
On fluctuations of closed string tachyon solitons
We discuss fluctuations on solitons in the dilaton/graviton/tachyon system
using the low energy effective field theory approach. It is shown that closed
string solitons are free of tachyons in this approximation, regardless of the
exact shape of the tachyon potential.Comment: 13 pages, 1 figure, uses JHEP3.cl
An observation of spin-valve effects in a semiconductor field effect transistor: a novel spintronic device
We present the first spintronic semiconductor field effect transistor.
The injector and collector contacts of this device were made from magnetic
permalloy thin films with different coercive fields so that they could be
magnetized either parallel or antiparallel to each other in different applied
magnetic fields. The conducting medium was a two dimensional electron gas
(2DEG) formed in an AlSb/InAs quantum well.
Data from this device suggest that its resistance is controlled by two
different types of spin-valve effect: the first occurring at the
ferromagnet-2DEG interfaces; and the second occuring in direct propagation
between contacts.Comment: 4 pages, 2 figure
Excited Fermion Contribution to Z Physics at One Loop
We investigate the effects induced by excited leptons at the one-loop level
in the observables measured on the peak at LEP. Using a general effective
Lagrangian approach to describe the couplings of the excited leptons, we
compute their contributions to both oblique parameters and partial widths.
Our results show that the new effects are comparable to the present
experimental sensitivity, but they do not lead to a significant improvement on
the available constraints on the couplings and masses of these states.Comment: 25 pages 6 figure
A Lifshitz Black Hole in Four Dimensional R^2 Gravity
We consider a higher derivative gravity theory in four dimensions with a
negative cosmological constant and show that vacuum solutions of both Lifshitz
type and Schr\"{o}dinger type with arbitrary dynamical exponent z exist in this
system. Then we find an analytic black hole solution which asymptotes to the
vacuum Lifshitz solution with z=3/2 at a specific value of the coupling
constant. We analyze the thermodynamic behavior of this black hole and find
that the black hole has zero entropy while non-zero temperature, which is very
similar to the case of BTZ black holes in new massive gravity at a specific
coupling. In addition, we find that the three dimensional Lifshitz black hole
recently found by E. Ayon-Beato et al. has a negative entropy and mass when the
Newton constant is taken to be positive.Comment: 11 pages, no figure; v2, a minor error correcte
The clustering instability of inertial particles spatial distribution in turbulent flows
A theory of clustering of inertial particles advected by a turbulent velocity
field caused by an instability of their spatial distribution is suggested. The
reason for the clustering instability is a combined effect of the particles
inertia and a finite correlation time of the velocity field. The crucial
parameter for the clustering instability is a size of the particles. The
critical size is estimated for a strong clustering (with a finite fraction of
particles in clusters) associated with the growth of the mean absolute value of
the particles number density and for a weak clustering associated with the
growth of the second and higher moments. A new concept of compressibility of
the turbulent diffusion tensor caused by a finite correlation time of an
incompressible velocity field is introduced. In this model of the velocity
field, the field of Lagrangian trajectories is not divergence-free. A mechanism
of saturation of the clustering instability associated with the particles
collisions in the clusters is suggested. Applications of the analyzed effects
to the dynamics of droplets in the turbulent atmosphere are discussed. An
estimated nonlinear level of the saturation of the droplets number density in
clouds exceeds by the orders of magnitude their mean number density. The
critical size of cloud droplets required for clusters formation is more than
m.Comment: REVTeX 4, 15 pages, 2 figures(included), PRE submitte
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