24,909 research outputs found
Gaseous He Nuclear Magnetic Resonance Probe for Cryogenic Environments
Normal nuclear magnetic resonance (NMR) probes cannot be used to make high
frequency resolution measurements in a cryogenic environment because they lose
their frequency resolution when the liquid sample in the probe freezes. A
gaseous He NMR probe, designed and constructed to work naturally in such
cryogenic environments, is demonstrated at 4.2 K and 5.3 Tesla to have a
frequency resolution better than 0.4 part per billion. As a demonstration of
its usefulness, the cryogenic probe is used to shim a superconducting solenoid
with a cryogenic interior to produce a magnetic field with a high spatial
homogeneity, and to measure the magnetic field stability.Comment: 9 pages, 11 figure
Towards an Improved Test of the Standard Model's Most Precise Prediction
The electron and positron magnetic moments are the most precise prediction of
the standard model of particle physics. The most accurate measurement of a
property of an elementary particle has been made to test this result. A new
experimental method is now being employed in an attempt to improve the
measurement accuracy by an order of magnitude. Positrons from a "student
source" now suffice for the experiment. Progress toward a new measurement is
summarized
Frequency-tunable metamaterials using broadside-coupled split ring resonators
We present frequency tunable metamaterial designs at terahertz (THz)
frequencies using broadside-coupled split ring resonator (BC-SRR) arrays.
Frequency tuning, arising from changes in near field coupling, is obtained by
in-plane horizontal or vertical displacements of the two SRR layers. For
electrical excitation, the resonance frequency continuously redshifts as a
function of displacement. The maximum frequency shift occurs for displacement
of half a unit cell, with vertical displacement resulting in a shift of 663 GHz
(51% of f0) and horizontal displacement yielding a shift of 270 GHz (20% of
f0). We also discuss the significant differences in tuning that arise for
electrical excitation in comparison to magnetic excitation of BC-SRRs
An energetic blast wave from the December 27 giant flare of the soft gamma-ray repeater 1806-20
Recent follow-up observations of the December 27 giant flare of SGR 1806-20
have detected a multiple-frequency radio afterglow from 240 MHz to 8.46 GHz,
extending in time from a week to about a month after the flare. The angular
size of the source was also measured for the first time. Here we show that this
radio afterglow gives the first piece of clear evidence that an energetic blast
wave sweeps up its surrounding medium and produces a synchrotron afterglow, the
same mechanism as established for gamma-ray burst afterglows. The optical
afterglow is expected to be intrinsically as bright as at t\la
0.1 days after the flare, but very heavy extinction makes the detection
difficult because of the low galactic latitude of the source. Rapid infrared
follow-up observations to giant flares are therefore crucial for the
low-latitude SGRs, while for high-latitude SGRs (e.g. SGR 0526-66), rapid
follow-ups should result in identification of their possible optical
afterglows. Rapid multi-wavelength follow-ups will also provide more detailed
information of the early evolution of a fireball as well as its composition.Comment: Updated version, accepted for publication in ApJ Letter
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GALS for Bursty Data Transfer based on Clock Coupling
In this paper we introduce a novel burst-mode GALS technique. The goal of this technique is improving the performance of the GALS approach for systems with predominantly bursty data transfer. This new technique has been used to implement a GALS-based version of a hardware accelerator of a 60 GHz OFDM baseband processor. The simulation results show a significant performance improvement in comparison with a classical implementation of GALS using pausible clocking. © 2009 Elsevier B.V. All rights reserved
GALS for Bursty Data Transfer based on Clock Coupling
In this paper we introduce a novel burst-mode GALS technique. The goal of this technique is improving the performance of the GALS approach for systems with predominantly bursty data transfer. This new technique has been used to implement a GALS-based version of a hardware accelerator of a 60 GHz OFDM baseband processor. The simulation results show a significant performance improvement in comparison with a classical implementation of GALS using pausible clocking. © 2009 Elsevier B.V. All rights reserved
k-Component q-deformed charge coherent states and their nonclassical properties
k-Component q-deformed charge coherent states are constructed, their
(over)completeness proved and their generation explored. The q-deformed charge
coherent states and the even (odd) q-deformed charge coherent states are the
two special cases of them as k becomes 1 and 2, respectively. A D-algebra
realization of the SU(1,1) generators is given in terms of them. Their
nonclassical properties are studied and it is shown that for , they
exhibit two-mode q-antibunching, but neither SU(1,1) squeezing, nor one- or
two-mode q-squeezing.Comment: LaTeX, 29 pages, 2 Postscript figures, minor change
A network-based structure-preserving dynamical model for the study of cascading failures in power grids
In this work we show that simple classic models of power grids, albeit frequently utilized in many applications, may not be reliable for investigating cascading failures problems. For this purpose, we develop a novel model, based on a structure-preserving approach, to obtain a network-based description of a power grid, where nodes correspond to generators and buses, while the links correspond to the physical lines connecting them. In addition, we also consider classic voltage and frequency protection mechanisms for lines and buses. Considering the Italian power grid as a case study of interest, we then investigate the propagation of an initial failure of any line of the power system, and compare the predicted impact of the failure according to different assumptions in the model such as the presence or absence of protection mechanisms and a simplified description of the system dynamics. In particular, it can be observed that more realistic models are crucial to determine the size of the cascading failure, as well as the sequence of links that may be involved in the cascade
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