18,895 research outputs found
The use of field-programmable gate arrays for the hardware acceleration of design automation tasks
This paper investigates the possibility of using Field-Programmable Gate Arrays (Fr’GAS) as
reconfigurable co-processors for workstations to produce moderate speedups for most tasks
in the design process, resulting in a worthwhile overall design process speedup at low cost
and allowing algorithm upgrades with no hardware modification. The use of FPGAS as hardware
accelerators is reviewed and then achievable speedups are predicted for logic simulation
and VLSI design rule checking tasks for various FPGA co-processor arrangements
Ladder-like optical conductivity in the spin-fermion model
In the nested limit of the spin-fermion model for the cuprates,
one-dimensional physics in the form of half-filled two-leg ladders emerges. We
show that the renormalization group flow of the corresponding ladder is towards
the d-Mott phase, a gapped spin-liquid with short-ranged d-wave pairing
correlations, and reveals an intermediate SO(5)SO(3) symmetry. We use
the results of the renormalization group in combination with a memory-function
approach to calculate the optical conductivity of the spin-fermion model in the
high-frequency regime, where processes within the hot spot region dominate the
transport. We argue that umklapp processes play a major role. For finite
temperatures, we determine the resistivity in the zero-frequency (dc) limit.
Our results show an approximate linear temperature dependence of the
resistivity and a conductivity that follows a non-universal power law. A
comparison to experimental data supports our assumption that the conductivity
is dominated by the antinodal contribution above the pseudogap.Comment: 11+2 pages, 8 figure
Flexible Integration of Alternative Energy Sources for Autonomous Sensing
Recent developments in energy harvesting and autonomous sensing mean that it is now possible to power sensors solely from energy harvested from the environment. Clearly this is dependent on sufficient environmental energy being present. The range of feasible environments for operation can be extended by combining multiple energy sources on a sensor node. The effective monitoring of their energy resources is also important to deliver sustained and effective operation. This paper outlines the issues concerned with combining and managing multiple energy sources on sensor nodes. This problem is approached from both a hardware and embedded software viewpoint. A complete system is described in which energy is harvested from both light and vibration, stored in a common energy store, and interrogated and managed by the node
Fabrication and Electrical Characterization of Fully CMOS Si Single Electron Devices
We present electrical data of silicon single electron devices fabricated with
CMOS techniques and protocols. The easily tuned devices show clean Coulomb
diamonds at T = 30 mK and charge offset drift of 0.01 e over eight days. In
addition, the devices exhibit robust transistor characteristics including
uniformity within about 0.5 V in the threshold voltage, gate resistances
greater than 10 G{\Omega}, and immunity to dielectric breakdown in electric
fields as high as 4 MV/cm. These results highlight the benefits in device
performance of a fully CMOS process for single electron device fabrication.Comment: 7 pages, 7 figure
Tachyon Defect Formation and Reheating in Brane-Antibrane Inflation
We study analytically the dynamical formation of lower dimensional branes at
the endpoint of brane-antibrane inflation through the condensation of
topological defects of the tachyon field which describes the instability of the
initial state. We then use this information to quantify the efficiency of the
reheating which is due to the coupling of time dependent tachyon background to
massless gauge fields which will be localized on the final state branes. We
improve upon previous estimates indicating that this can be an efficient
reheating mechanism for observers on the brane.Comment: 9 pages. Talk given at the 26th annual
Montreal-Rochester-Syracuse-Toronto Conference on High-Energy Physics: MRST
200
The use of a formal sensitivity analysis on epidemic models with immune protection from maternally acquired antibodies
This paper considers the outcome of a formal sensitivity analysis on a series of epidemic model structures developed to study the population level effects of maternal antibodies. The analysis is used to compare the potential influence of maternally acquired immunity on various age and time domain observations of infection and serology, with and without seasonality. The results of the analysis indicate that time series observations are largely insensitive to variations in the average duration of this protection, and that age related empirical data are likely to be most appropriate for estimating these characteristics
Motion of a distinguishable impurity in the Bose gas: Arrested expansion without a lattice and impurity snaking
We consider the real time dynamics of an initially localized distinguishable
impurity injected into the ground state of the Lieb-Liniger model. Focusing on
the case where integrability is preserved, we numerically compute the time
evolution of the impurity density operator in regimes far from analytically
tractable limits. We find that the injected impurity undergoes a stuttering
motion as it moves and expands. For an initially stationary impurity, the
interaction-driven formation of a quasibound state with a hole in the
background gas leads to arrested expansion -- a period of quasistationary
behavior. When the impurity is injected with a finite center of mass momentum,
the impurity moves through the background gas in a snaking manner, arising from
a quantum Newton's cradle-like scenario where momentum is exchanged
back-and-forth between the impurity and the background gas.Comment: v1: 13 pages, 10 figures; v2: 14 pages, 13 figures and change of
titl
Ringing the eigenmodes from compact manifolds
We present a method for finding the eigenmodes of the Laplace operator acting
on any compact manifold. The procedure can be used to simulate cosmic microwave
background fluctuations in multi-connected cosmological models. Other
applications include studies of chaotic mixing and quantum chaos.Comment: 11 pages, 8 figures, IOP format. To be published in the proceedings
of the Cleveland Cosmology and Topology Workshop 17-19 Oct 1997. Submitted to
Class. Quant. Gra
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