6,581 research outputs found
Rigorous theory of nuclear fusion rates in a plasma
Real-time thermal field theory is used to reveal the structure of plasma
corrections to nuclear reactions. Previous results are recovered in a fashion
that clarifies their nature, and new extensions are made. Brown and Yaffe have
introduced the methods of effective quantum field theory into plasma physics.
They are used here to treat the interesting limiting case of dilute but very
highly charged particles reacting in a dilute, one-component plasma. The highly
charged particles are very strongly coupled to this background plasma. The
effective field theory proves that this mean field solution plus the one-loop
term dominate; higher loop corrections are negligible even though the problem
involves strong coupling. Such analytic results for very strong coupling are
rarely available, and they can serve as benchmarks for testing computer models.Comment: 4 pages and 2 figures, presented at SCCS 2005, June 20-25, Moscow,
Russi
PRODUCTION DISTORTIONS IN THE SLOVAKIAN GRAIN SECTOR RESULTING FROM AGRICULTURAL SUBSIDIES
A Policy Analysis Method, based on social benefit-cost analysis, is applied to five production areas of the Slovak Republic to analyze production distortions resulting from direct systematic subsidies in Slovakia. Three grains are analyzed: wheat, barley, and corn. Results indicate that currently applied policies have significant distortion effects, but those effects are not homogeneous across commodities and production areas.Agricultural and Food Policy, Productivity Analysis,
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The Stac Fada “impact ejecta” layer: not what it seems
The Stac Fada Member (SFM) forms part of the Stoer Group of the Torridonian of NW Scotland. The SFM is unique in the Torridonian, being characterized by the presence of greenish altered glass clasts. Its origin has been debated for decades with several hypotheses being proposed but all invoking some connection with volcanic activity in the region. More recently, Amor et al. suggested that the SFM represents “a chord section through the continuous ejecta blanket surrounding an impact crater”. Here, we confirm the presence of shocked material within the SFM and then discuss its origin
Searching for low mass objects around nearby dMe radio stars
Nearby M-dwarfs are best suited for searches of low mass companions. VLBI
phase-referencing observations with sensitive telescopes are able to detect
radio star flux-densities of tenths of mJy as well as to position the star on
the sky with submilliarcsecond precision. We have initiated a long-term
observational program, using EVN telescopes in combination with NASA DSN
dishes, to revisit the kinematics of nearby, single M dwarfs. The precision of
the astrometry allows us to search for possible companions with masses down to
1 Jupiter mass. In this contribution we report preliminary results of the first
observation epochs, in which we could detect some of the radio stars included
in our program.Comment: Proceedings of the 6th European VLBI Network Symposium, Ros E.,
Porcas R.W., Lobanov A.P., & Zensus J.A. (eds.), MPIfR, Bonn, Germany, p.
255-258 (2002). 4 pages, 3 figures, needs evn2002.cl
An Audible Demonstration Of The Speed Of Sound In Bubbly Liquids
The speed of sound in a bubbly liquid is strongly dependent upon the volume fraction of the gas phase, the bubble size distribution, and the frequency of the acoustic excitation. At sufficiently low frequencies, the speed of sound depends primarily on the gas volume fraction. This effect can be audibly demonstrated using a one-dimensional acoustic waveguide, in which the flow rate of air bubbles injected into a water-filled tube is varied by the user. The normal modes of the waveguide are excited by the sound of the bubbles being injected into the tube. As the flow rate is varied, the speed of sound varies as well, and hence, the resonance frequencies shift. This can be clearly heard through the use of an amplified hydrophone and the user can create aesthetically pleasing and even musical sounds. In addition, the apparatus can be used to verify a simple mathematical model known as Wood's equation that relates the speed of sound of a bubbly liquid to its void fraction. (c) 2008 American Association of Physics Teachers.Mechanical Engineerin
Brueckner-Hartree-Fock study of circular quantum dots
We calculate ground state energies in the Brueckner-Hartree-Fock theory for
electrons (with ) confined to a circular quantum dot and in
presence of a static magnetic field. Comparison with the predictions of
Hartree-Fock, local-spin-density and exact configuration-interaction theories
is made. We find that the correlations taken into account in
Brueckner-Hartree-Fock calculations give an important contribution to the
ground state energies, specially in strongly confined dots. In this
high-density range, corresponding in practice to self-assembled quantum dots,
the results of Brueckner-Hartree-Fock calculations are close to the exact
values and better than those obtained in the local-spin-density approximation.Comment: Regular articl
The energy partitioning of non-thermal particles in a plasma: or the Coulomb logarithm revisited
The charged particle stopping power in a highly ionized and weakly to
moderately coupled plasma has been calculated to leading and next-to-leading
order by Brown, Preston, and Singleton (BPS). After reviewing the main ideas
behind this calculation, we use a Fokker-Planck equation derived by BPS to
compute the electron-ion energy partitioning of a charged particle traversing a
plasma. The motivation for this application is ignition for inertial
confinement fusion -- more energy delivered to the ions means a better chance
of ignition, and conversely. It is therefore important to calculate the
fractional energy loss to electrons and ions as accurately as possible, as this
could have implications for the Laser Megajoule (LMJ) facility in France and
the National Ignition Facility (NIF) in the United States. The traditional
method by which one calculates the electron-ion energy splitting of a charged
particle traversing a plasma involves integrating the stopping power dE/dx.
However, as the charged particle slows down and becomes thermalized into the
background plasma, this method of calculating the electron-ion energy splitting
breaks down. As a result, the method suffers a systematic error of order T/E0,
where T is the plasma temperature and E0 is the initial energy of the charged
particle. In the case of DT fusion, for example, this can lead to uncertainties
as high as 10% or so. The formalism presented here is designed to account for
the thermalization process, and in contrast, it provides results that are
near-exact.Comment: 10 pages, 3 figures, invited talk at the 35th European Physical
Society meeting on plasma physic
MMP-9 cleaves SP-D and abrogates its innate immune functions in vitro
Possession of a properly functioning innate immune system in the lung is vital to prevent infections due to the ongoing exposure of the lung to pathogens. While mechanisms of pulmonary innate immunity have been well studied, our knowledge of how these systems are altered in disease states, leading to increased susceptibility to infections, is limited. One innate immune protein in the lung, the pulmonary collectin SP-D, has been shown to be important in innate immune defense, as well as clearance of allergens and apoptotic cells. MMP-9 is a protease with a wide variety of substrates, and has been found to be dysregulated in a myriad of lung diseases ranging from asthma to cystic fibrosis; in many of these conditions, there are decreased levels of SP-D. Our results indicate that MMP-9 is able to cleave SP-D in vitro and this cleavage leads to loss of its innate immune functions, including its abilities to aggregate bacteria and increase phagocytosis by mouse alveolar macrophages. However, MMP-9-cleaved SP-D was still detected in a solid-phase E. coli LPS-binding assay, while NE-cleaved SP-D was not. In addition, MMP-9 seems to cleave SP-D much more efficiently than NE at physiological levels of calcium. Previous studies have shown that in several diseases, including cystic fibrosis and asthma, patients have increased expression of MMP-9 in the lungs as well as decreased levels of intact SP-D. As patients suffering from many of the diseases in which MMP-9 is over-expressed can be more susceptible to pulmonary infections, it is possible that MMP-9 cleavage of SP-D may contribute to this phenotype
Continuing a Chandra Survey of Quasar Radio Jets
We are conducting an X-ray survey of flat spectrum radio quasars (FSRQs) with
extended radio structures. We summarize our results from the first stage of our
survey, then we present findings from its continuation.
We have discovered jet X-ray emission from 12 of our first 20 Chandra
targets, establishing that strong 0.5-7.0 keV emission is a common feature of
FSRQ jets. The X-ray morphology is varied, but in general closely matches the
radio structure until the first sharp radio bend. In the sources with optical
data as well as X-ray detections we rule out simple synchrotron models for
X-ray emission, suggesting these systems may instead be dominated by inverse
Compton (IC) scattering. Fitting models of IC scattering of cosmic microwave
background photons suggests that these jets are aligned within a few degrees of
our line of sight, with bulk Lorentz factors of a few to ten and magnetic
fields a bit stronger than G.
In the weeks prior to this meeting, we have discovered two new X-ray jets at
. One (PKS B1055+201) has a dramatic, -long jet. The other (PKS
B1421-490) appears unremarkable at radio frequencies, but at higher frequencies
the jet is uniquely powerful: its optically-dominated, with jet/core flux
ratios of 3.7 at 1 keV and 380 at 480 nm.Comment: 4 pages, 8 figures. To appear in `X-Ray and Radio Connections', ed.
L.O. Sjouwerman and K.K. Dyer (published electronicly at
http://www.aoc.nrao.edu/events/xraydio/). Additional material and higher
resolution figures may be found at http://space.mit.edu/home/jonathan/jets
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