13,798 research outputs found
Null particle solutions in three-dimensional (anti-) de Sitter spaces
We obtain a class of exact solutions representing null particles moving in
three-dimensional (anti-) de Sitter spaces by boosting the corresponding static
point source solutions given by Deser and Jackiw. In de Sitter space the
resulting solution describes two null particles moving on the (circular)
cosmological horizon, while in anti-de Sitter space it describes a single null
particle propagating from one side of the universe to the other. We also boost
the BTZ black hole solution to the ultrarelativistic limit and obtain the
solution for a spinning null particle moving in anti-de Sitter space. We find
that the ultrarelativistic geometry of the black hole is exactly the same as
that resulting from boosting the Deser-Jackiw solution when the angular
momentum of the hole vanishes. A general class of solutions is also obtained
which represents several null particles propagating in the Deser-Jackiw
background. The differences between the three-dimensional and four-dimensional
cases are also discussed.Comment: 11 pages, LaTeX, To appear in J. Math. Phy
Effective potential for composite operators and for an auxiliary scalar field in a Nambu-Jona-Lasinio model
We derive the effective potentials for composite operators in a
Nambu-Jona-Lasinio (NJL) model at zero and finite temperature and show that in
each case they are equivalent to the corresponding effective potentials based
on an auxiliary scalar field. The both effective potentials could lead to the
same possible spontaneous breaking and restoration of symmetries including
chiral symmetry if the momentum cutoff in the loop integrals is large enough,
and can be transformed to each other when the Schwinger-Dyson (SD) equation of
the dynamical fermion mass from the fermion-antifermion vacuum (or thermal)
condensates is used. The results also generally indicate that two effective
potentials with the same single order parameter but rather different
mathematical expressions can still be considered physically equivalent if the
SD equation corresponding to the extreme value conditions of the two potentials
have the same form.Comment: 7 pages, no figur
Accurate a priori signal integrity estimation using a multilevel dynamic interconnect model for deep submicron VLSI design.
A multilevel dynamic interconnect model was derived for accurate a priori signal integrity estimates. Cross-talk and delay estimations over interconnects in deep submicron technology were analyzed systematically using this model. Good accuracy and excellent time-efficiency were found compared with electromagnetic simulations. We aim to build a dynamic interconnect library with this model to facilitate the interconnect issues for future VLSI design
Optimising bandwidth over deep sub-micron interconnect.
In deep sub-micron (DSM) circuits proper analysis of interconnect delay is very important. When relatively long wires are placed in parallel, it is essential to include the effects of cross-talk on delay. In a parallel wire structure, the exact spacing and size of the wires determine both the resistance and the distribution of the capacitance between the ground plane and the adjacent signal carrying conductors, and have a direct effect on the delay. Repeater insertion depending on whether it is optimal or constrained, affects the delay in different ways. Considering all these effects we show that there is a clear optimum configuration for the wires which maximises the total bandwidth. Our analysis is valid for lossy interconnects as are typical of wires in DSM technologies
DISTINGUISHING BETWEEN EQUILIBRIUM AND INTEGRATION IN MARKETS ANALYSIS
This paper introduces a new market analysis methodology based on maximum likelihood estimation of a mixture distribution model incorporating price, transfer cost, and trade flow data. Not only does this method obviate statistical problems associated with conventional price analysis methods, it also permits differentiation between market integration and competitive market equilibrium. The model generates estimates of the frequency of alternative regimes, combinations of which provide useful, intuitive measures of intermarket tradability, competitive market equilibrium, perfect integration, segmented equilibrium, and segmented disequilibrium. An application to trade in soybean meal among Pacific Rim economies demonstrates the usefulness of the method.international trade, law of one price, market integration, spatial equilibrium, International Relations/Trade,
Crystalline and Electronic Structures of Molecular Solid CCl: First-Principles Calculation
A molecular solid CCl with possible crystalline structures,
including the hexagonal-close-packed (hcp) phase, the face-centered cubic (fcc)
phase, and a hexagonal monolayer, is predicted in terms of first-principles
calculation within the density functional theory. The stable structures are
determined from the total-energy calculations, where the hcp phase is uncovered
more stable than the fcc phase and the hexagonal monolayer in energy per
molecule. The energy bands and density of states for hcp and fcc
CCl are presented. The results show that CCl%
molecules can form either a hcp or fcc indirect-gap band insulator or an
insulating hexagonal monolayer.Comment: 5 pages, 6 figure
On the Entropy Function and the Attractor Mechanism for Spherically Symmetric Extremal Black Holes
In this paper we elaborate on the relation between the entropy formula of
Wald and the "entropy function" method proposed by A. Sen. For spherically
symmetric extremal black holes, it is shown that the expression of extremal
black hole entropy given by A. Sen can be derived from the general entropy
definition of Wald, without help of the treatment of rescaling the AdS_2 part
of near horizon geometry of extremal black holes. In our procedure, we only
require that the surface gravity approaches to zero, and it is easy to
understand the Legendre transformation of f, the integration of Lagrangian
density on the horizon, with respect to the electric charges. Since the Noether
charge form can be defined in an "off-shell" form, we define a corresponding
entropy function, with which one can discuss the attractor mechanism for
extremal black holes with scalar fields.Comment: v3: Revtex4, 19 pages, discussion added, mistakes corrected, final
version; to appear in Phys. Rev.
Extending systems-on-chip to the third dimension : performance, cost and technological tradeoffs.
Because of the today's market demand for high-performance, high-density portable hand-held applications, electronic system design technology has shifted the focus from 2-D planar SoC single-chip solutions to different alternative options as tiled silicon and single-level embedded modules as well as 3-D integration. Among the various choices, finding an optimal solution for system implementation dealt usually with cost, performance and other technological trade-off analysis at the system conceptual level. It has been identified that the decisions made within the first 20% of the total design cycle time will ultimately result up to 80% of the final product cost. In this paper, we discuss appropriate and realistic metric for performance and cost trade-off analysis both at system conceptual level (up-front in the design phase) and at implementation phase for verification in the three-dimensional integration. In order to validate the methodology, two ubiquitous electronic systems are analyzed under various implementation schemes and discuss the pros and cons of each of them
A global wire planning scheme for Network-on-Chip.
As technology scales down, the interconnect for on-chip global communication becomes the delay bottleneck. In order to provide well-controlled global wire delay and efficient global communication, a packet switched Network-on-Chip (NoC) architecture was proposed by different authors. In this paper, the NoC system parameters constrained by the interconnections are studied. Predictions on scaled system parameters such as clock frequency, resource size, global communication bandwidth and inter-resource delay are made for future technologies. Based on these parameters, a global wire planning scheme is proposed
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