16,619 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
Quantum Phases of the Shastry-Sutherland Kondo Lattice: Implications for the Global Phase Diagram of Heavy Fermion Metals
Considerable recent theoretical and experimental efforts have been devoted to
the study of quantum criticality and novel phases of antiferromagnetic
heavy-fermion metals. In particular, quantum phase transitions have been
discovered in the compound YbPtPb. These developments have motivated us
to study the competition between the RKKY and Kondo interactions on the
Shastry-Sutherland lattice. We determine the zero-temperature phase diagram as
a function of magnetic frustration and Kondo coupling within a slave-fermion
approach. Pertinent phases include the Shastry-Sutherland valence bond solid
and heavy Fermi liquid. In the presence of antiferromagnetic order, our
zero-temperature phase diagram is remarkably similar to the global phase
diagram proposed earlier based on general grounds. We discuss the implications
of our results for the experiments on YbPtPb and other geometrically
frustrated heavy fermion compounds.Comment: 5 pages 4 figures - Supplementary Material 4 pages 6 figures. Updated
with published versio
Determination of and Extraction of from Semileptonic Decays
By globally analyzing all existing measured branching fractions and partial
rates in different four momentum transfer-squared bins of decays, we obtain the product of the form factor and magnitude of
CKM matrix element to be . With this
product, we determine the semileptonic form factor
in conjunction with the value of
determined from the SM global fit. Alternately, with the product together with
the input of the form factor calculated in lattice QCD recently, we
extract , where the error is
still dominated by the uncertainty of the form factor calculated in lattice
QCD. Combining the
extracted from all existing measurements of decays and
together, we find the most
precisely determined to be , which improves
the accuracy of the PDG'2014 value by
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
Size-dependent spin-reorientation transition in Nd2Fe14B nanoparticles
Nd2Fe14B magnetic nanoparticles have been successfully produced using a
surfactant-assisted ball milling technique. The nanoparticles with different
size about 6, 20 and 300 nm were obtained by a size-selection process.
Spin-reorientation transition temperature of the NdFeB nanoparticles was then
determined by measuring the temperature dependence of DC and AC magnetic
susceptibility. It was found that the spin-reorientation transition temperature
(Tsr) of the nanoparticles is strongly size dependent, i.e., Tsr of the 300 nm
particles is lower than that of raw materials and a significant decrease was
observed in the 20 nm particles
The long-range interactions between branes in diverse dimensions
We calculate the long-range interactions between two simple branes placed
parallel at a separation in diverse dimensions via an effective field theory
approach. We also compute for the first time the explicit long-range
interaction between two D-branes with each carrying a world-volume non-abelian
magnetic flux in three special cases, respectively. In particular, we
demonstrate that the half-string creation between a D-brane and a
D-brane continues to hold even in the present context, therefore lending
further support to the previous assertion of this. Our computations re-raise
also the issue in one case on whether so constructed (D, D) bound state
is actually a marginal one.Comment: 28 pages, various discussions expanded and references adde
On-line planning and scheduling: an application to controlling modular printers
We present a case study of artificial intelligence techniques applied to the control of production printing equipment. Like many other real-world applications, this complex domain requires high-speed autonomous decision-making and robust continual operation. To our knowledge, this work represents the first successful industrial application of embedded domain-independent temporal planning. Our system handles execution failures and multi-objective preferences. At its heart is an on-line algorithm that combines techniques from state-space planning and partial-order scheduling. We suggest that this general architecture may prove useful in other applications as more intelligent systems operate in continual, on-line settings. Our system has been used to drive several commercial prototypes and has enabled a new product architecture for our industrial partner. When compared with state-of-the-art off-line planners, our system is hundreds of times faster and often finds better plans. Our experience demonstrates that domain-independent AI planning based on heuristic search can flexibly handle time, resources, replanning, and multiple objectives in a high-speed practical application without requiring hand-coded control knowledge
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