38,082 research outputs found
Fully Coherent X-ray Pulses from a Regenerative Amplifier Free Electron Laser
We propose and analyze a novel regenerative amplifier free electron laser
(FEL) to produce fully coherent x-ray pulses. The method makes use of
narrow-bandwidth Bragg crystals to form an x-ray feedback loop around a
relatively short undulator. Self-amplified spontaneous emission (SASE) from the
leading electron bunch in a bunch train is spectrally filtered by the Bragg
reflectors and is brought back to the beginning of the undulator to interact
repeatedly with subsequent bunches in the bunch train. The FEL interaction with
these short bunches not only amplifies the radiation intensity but also
broadens its spectrum, allowing for effective transmission of the x-rays
outside the crystal bandwidth. The spectral brightness of these x-ray pulses is
about two to three orders of magnitude higher than that from a single-pass SASE
FEL.Comment: 11 pages, 6 figure
Further investigation of a contactless patient-electrode interface of an Electrical Impedance Mammography system
The Sussex Mk4 Electrical Impedance Mammography (EIM) system is a novel instrument, designed for the detection of early breast cancer, based upon Electrical Impedance Tomography (EIT). Many innovations in the field have been incorporated in the design improving both signal distribution and response. This paper investigates the behaviour of the contactless patient-electrode interface. The interface was studied in detail using phantom and healthy volunteer, in-vivo, data. Our findings show the necessity for the careful design of electrode enclosure so that the response of the system is not affected by the unpredictable positioning of the breast; it closely mimics those conditions seen when using the phantom. The paper includes a number of possible designs and their individual characteristics. In addition an explanation on the unanticipated effects and solutions for such are described. © 2010 IOP Publishing Ltd
Large Deviations in the Superstable Weakly Imperfect Bose Gas
The superstable Weakly Imperfect Bose Gas {(WIBG)} was originally derived to
solve the inconsistency of the Bogoliubov theory of superfluidity. Its
grand-canonical thermodynamics was recently solved but not at {point of} the
{(first order)} phase transition. This paper proposes to close this gap by
using the large deviations formalism and in particular the analysis of the Kac
distribution function. It turns out that, as a function of the chemical
potential, the discontinuity of the Bose condensate density at the phase
transition {point} disappears as a function of the particle density. Indeed,
the Bose condensate continuously starts at the first critical particle density
and progressively grows but the free-energy per particle stays constant until
the second critical density is reached. At higher particle densities, the Bose
condensate density as well as the free-energy per particle both increase
{monotonously}
Markov modeling of moving target defense games
We introduce a Markov-model-based framework for Moving Target Defense (MTD) analysis. The framework allows modeling of broad range of MTD strategies, provides general theorems about how the probability of a successful adversary defeating an MTD strategy is related to the amount of time/cost spent by the adversary, and shows how a multi-level composition of MTD strategies can be analyzed by a straightforward combination of the analysis for each one of these strategies. Within the proposed framework we define the concept of security capacity which measures the strength or effectiveness of an MTD strategy: the security capacity depends on MTD specific parameters and more general system parameters. We apply our framework to two concrete MTD strategies
Approximations of Sobolev norms in Carnot groups
This paper deals with a notion of Sobolev space introduced by
J.Bourgain, H.Brezis and P.Mironescu by means of a seminorm involving local
averages of finite differences. This seminorm was subsequently used by A.Ponce
to obtain a Poincar\'e-type inequality. The main results that we present are a
generalization of these two works to a non-Euclidean setting, namely that of
Carnot groups. We show that the seminorm expressd in terms of the intrinsic
distance is equivalent to the norm of the intrinsic gradient, and provide
a Poincar\'e-type inequality on Carnot groups by means of a constructive
approach which relies on one-dimensional estimates. Self-improving properties
are also studied for some cases of interest
First Direct Measurement of Jets in GeV Heavy Ion Collisions by STAR
We present the first measurement of reconstructed jets in ultra-relativistic
heavy ion collisions. Utilizing the large coverage of the STAR Time Projection
Chamber and Electromagnetic Calorimeter, we apply several modern jet
reconstruction algorithms and background subtraction techniques and explore
their systematic uncertainties in heavy ion events. The differential spectrum
for inclusive jet production in central Au+Au collisions at GeV is presented. In order to assess the jet reconstruction biases, this
spectrum is compared with the jet cross section measured in GeV
p+p collisions scaled by the number of binary N-N collisions to account for
nuclear geometric effects.Comment: Proceedings of the 3rd International Conference on Hard and Electro-
Magnetic Probes of High-Energy Nuclear Collisions 8-14 June 2008, Illa da
Toxa (Galicia-Spain
Hyperspherical Harmonics, Separation of Variables and the Bethe Ansatz
The relation between solutions to Helmholtz's equation on the sphere
and the [{\gr sl}(2)]^n Gaudin spin chain is clarified. The joint
eigenfuctions of the Laplacian and a complete set of commuting second order
operators suggested by the --matrix approach to integrable systems, based on
the loop algebra \wt{sl}(2)_R, are found in terms of homogeneous polynomials
in the ambient space. The relation of this method of determining a basis of
harmonic functions on to the Bethe ansatz approach to integrable
systems is explained.Comment: 14 pgs, Plain Tex, preprint CRM--2174 (May, 1994
Paper Session I-A - Weather Impacts on Space Operations
The 45th Weather Squadron of the United States Air Force provides weather support to Patrick Air Force Base, Cape Canaveral Air Force Station (CCAFS), Eastern Range, and Kennedy Space Center (KSC). The support includes weather observations, forecasts, climatological studies and consultant services to a wide variety of Range users. The most visible to the general public is weather support to space vehicles, particularly the Space Shuttle. That support includes resource protection, ground processing, launch, and Ferry Flight; as well as consultant to the Spaceflight Meteorology Group (at Johnson Space Center) for landing forecasts
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