7,636 research outputs found
SPH Simulations with Reconfigurable Hardware Accelerator
We present a novel approach to accelerate astrophysical hydrodynamical
simulations. In astrophysical many-body simulations, GRAPE (GRAvity piPE)
system has been widely used by many researchers. However, in the GRAPE systems,
its function is completely fixed because specially developed LSI is used as a
computing engine. Instead of using such LSI, we are developing a special
purpose computing system using Field Programmable Gate Array (FPGA) chips as
the computing engine. Together with our developed programming system, we have
implemented computing pipelines for the Smoothed Particle Hydrodynamics (SPH)
method on our PROGRAPE-3 system. The SPH pipelines running on PROGRAPE-3 system
have the peak speed of 85 GFLOPS and in a realistic setup, the SPH calculation
using one PROGRAPE-3 board is 5-10 times faster than the calculation on the
host computer. Our results clearly shows for the first time that we can
accelerate the speed of the SPH simulations of a simple astrophysical phenomena
using considerable computing power offered by the hardware.Comment: 27 pages, 13 figures, submitted to PAS
Grand-Canonical simulation of 4D simplicial quantum gravity
A thorough numerical examination for the field theory of 4D quantum gravity
(QG) with a special emphasis on the conformal mode dependence has been studied.
More clearly than before, we obtain the string susceptibility exponent of the
partition function by using the Grand-Canonical Monte-Carlo method. Taking
thorough care of the update method, the simulation is made for 4D Euclidean
simplicial manifold coupled to scalar fields and U(1) gauge fields.
The numerical results suggest that 4D simplicial quantum gravity (SQG) can be
reached to the continuum theory of 4D QG. We discuss the significant property
of 4D SQG.Comment: 3 pages, 2 figures, LaTeX, Lattice2002(Gravity
Vertex Operators in 4D Quantum Gravity Formulated as CFT
We study vertex operators in 4D conformal field theory derived from quantized
gravity, whose dynamics is governed by the Wess-Zumino action by Riegert and
the Weyl action. Conformal symmetry is equal to diffeomorphism symmetry in the
ultraviolet limit, which mixes positive-metric and negative-metric modes of the
gravitational field and thus these modes cannot be treated separately in
physical operators. In this paper, we construct gravitational vertex operators
such as the Ricci scalar, defined as space-time volume integrals of them are
invariant under conformal transformations. Short distance singularities of
these operator products are computed and it is shown that their coefficients
have physically correct sign. Furthermore, we show that conformal algebra holds
even in the system perturbed by the cosmological constant vertex operator as in
the case of the Liouville theory shown by Curtright and Thorn.Comment: 26 pages, rewrote review part concisely, added explanation
Space-Time and Matter in IIB Matrix Model - gauge symmetry and diffeomorphism -
We pursue the study of the type IIB matrix model as a constructive definition
of superstring. In this paper, we justify the interpretation of space-time as
distribution of eigenvalues of the matrices by showing that some low energy
excitations indeed propagate in it. In particular, we show that if the
distribution consists of small clusters of size , low energy theory acquires
local SU(n) gauge symmetry and a plaquette action for the associated gauge
boson is induced, in addition to a gauge invariant kinetic term for a massless
fermion in the adjoint representation of the SU(n). We finally argue a possible
identification of the diffeomorphism symmetry with permutation group acting on
the set of eigenvalues, and show that the general covariance is realized in the
low energy effective theory even though we do not have a manifest general
covariance in the IIB matrix model action.Comment: 25 page
Construction of Some Optimal Ternary Linear Codes and the Uniqueness of [294, 6, 195; 3]-Codes Meeting the Griesmer Bound
AbstractLet nq(k, d) denote the smallest value of n for which there exists an [n, k, d; q]-code. It is known (cf. (J. Combin. Inform. Syst. Sci.18, 1993, 161â191)) that (1) n3(6, 195) â {294, 295}, n3(6, 194) â {293, 294}, n3(6, 193) â {292, 293}, n3(6, 192) â {290, 291}, n3(6, 191) â {289, 290}, n3(6, 165) â {250, 251} and (2) there is a one-to-one correspondence between the set of all nonequivalent [294, 6, 195; 3]-codes meeting the Griesmer bound and the set of all {v2 + 2v3 + v4, v1 + 2v2 + v3; 5, 3}-minihypers, where vi = (3i â 1)/(3 â 1) for any integer i â„ 0. The purpose of this paper is to show that (1) n3(6, 195) = 294, n3(6, 194) = 293, n3(6, 193) = 292, n3(6, 192) = 290, n3(6, 191) = 289, n3(6, 165) = 250 and (2) a [294, 6, 195; 3]-code is unique up to equivalence using a characterization of the corresponding {v2 + 2v3 + v4, v1 + 2v2 + v3; 5, 3}-minihypers
External-fiber-grating vertical-cavity surface-emitting lasers
A Bragg grating in graded-index multimode fiber was coupled to a 0.8-/spl mu/m VCSEL. By using a fiber Bragg grating, the spectral width of the VCSEL decreased to 1/2-1/3 of the initial value, depending on the temperature of the fiber Bragg grating. The minimum spectral width was less than 0.1 nm FWHM. Data transmission using 1-km graded-index multimode fiber was investigated at 700 Mb/s. The power penalty decreased by using the fiber Bragg grating. The decrease was 2 dB for the optimum grating temperature at a bit error rate of 10/sup -9/
Supersymmetric Wilson Loops in IIB Matrix Model
We show that the supersymmetric Wilson loops in IIB matrix model give a
transition operator from reduced supersymmetric Yang-Mills theory to
supersymmetric space-time theory. In comparison with Green-Schwarz superstring
we identify the supersymmetric Wilson loops with the asymptotic states of IIB
superstring. It is pointed out that the supersymmetry transformation law of the
Wilson loops is the inverse of that for the vertex operators of massless modes
in the U(N) open superstring with Dirichlet boundary condition.Comment: 10 pages, Latex, minor typos correcte
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