450 research outputs found
The influence of strong magnetic field on photon-neutrino reactions
The two-photon two-neutrino interaction induced by magnetic field is
investigated. In particular the processes and
are studied in the presence of strong magnetic
field. An effective Lagrangian and partial amplitudes of the processes are
presented. Neutrino emissivities due to the reactions and are calculated taking into
account of the photon dispersion and large radiative corrections. A comparison
of the results obtained with previous estimations and another inducing
mechanisms of the processes under consideration is made.Comment: 16 pages, LATEX, 3 EPS figures, based on the talk presented at XXXI
ITEP Winter School of Physics, Moscow, Russia, February 18 - 26, 200
Toward an analytic determination of the deconfinement temperature in SU(2) L.G.T.
We consider the SU(2) lattice gauge theory at finite temperature in (d+1)
dimensions, with different couplings and for timelike and
spacelike plaquettes. By using the character expansion of the Wilson action and
performing the integrals over space-like link variables, we find an effective
action for the Polyakov loops which is exact to all orders in and to
the first non-trivial order in . The critical coupling for the
deconfinement transition is determined in the (3+1) dimensional case, by the
mean field method, for different values of the lattice size in the
compactified time direction and of the asymmetry parameter . We find good agreement with Montecarlo simulations in
the range , and good qualitative agreement in the same range
with the logarithmic scaling law of QCD. Moreover the dependence of the results
from the parameter is in excellent agreement with previous theoretical
predictions.Comment: uuencoded latex file of 32 pages plus 3 ps figure
Simple de Sitter Solutions
We present a framework for de Sitter model building in type IIA string
theory, illustrated with specific examples. We find metastable dS minima of the
potential for moduli obtained from a compactification on a product of two Nil
three-manifolds (which have negative scalar curvature) combined with
orientifolds, branes, fractional Chern-Simons forms, and fluxes. As a discrete
quantum number is taken large, the curvature, field strengths, inverse volume,
and four dimensional string coupling become parametrically small, and the de
Sitter Hubble scale can be tuned parametrically smaller than the scales of the
moduli, KK, and winding mode masses. A subtle point in the construction is that
although the curvature remains consistently weak, the circle fibers of the
nilmanifolds become very small in this limit (though this is avoided in
illustrative solutions at modest values of the parameters). In the simplest
version of the construction, the heaviest moduli masses are parametrically of
the same order as the lightest KK and winding masses. However, we provide a
method for separating these marginally overlapping scales, and more generally
the underlying supersymmetry of the model protects against large corrections to
the low-energy moduli potential.Comment: 37 pages, harvmac big, 4 figures. v3: small correction
The influence of a combined strain-heat treatment on the features of electromagnetic testing of fatigue degradation of quenched constructional steel
Two-Point Functions and S-Parameter in QCD-like Theories
We calculated the vector, axial-vector, scalar and pseudo-scalar two-point
functions up to two-loop level in the low-energy effective field theory for
three different QCD-like theories. In addition we also calculated the
pseudo-scalar decay constant . The QCD-like theories we used are those
with fermions in a complex, real or pseudo-real representation with in general
n flavours. These case correspond to global symmetry breaking pattern of
, or .
We also estimated the S parameter for those different theories.Comment: 29 page
Meson-meson Scattering in QCD-like Theories
We discuss meson-meson scattering at next-to-next-to-leading order in the
chiral expansion for QCD-like theories with general degenerate flavours for
the cases with a complex, real and pseudo-real representation. I.e. with global
symmetry and breaking pattern , and . We obtain fully analytical expressions for all
these cases. We discuss the general structure of the amplitude and the
structure of the possible intermediate channels for all three cases. We derive
the expressions for the lowest partial wave scattering length in each channel
and present some representative numerical results. We also show various
relations between the different cases in the limit of large .Comment: 61 page
Extreme Technicolor & The Walking Critical Temperature
We map the phase diagram of gauge theories of fundamental interactions in the
flavor-temperature plane using chiral perturbation theory to estimate the
relation between the pion decaying constant and the critical temperature above
which chiral symmetry is restored. We then investigate the impact of our
results on models of dynamical electroweak symmetry breaking and therefore on
the electroweak early universe phase transition.Comment: RevTeX, 18 pages, 3 figure
The Evolution of Compact Binary Star Systems
We review the formation and evolution of compact binary stars consisting of
white dwarfs (WDs), neutron stars (NSs), and black holes (BHs). Binary NSs and
BHs are thought to be the primary astrophysical sources of gravitational waves
(GWs) within the frequency band of ground-based detectors, while compact
binaries of WDs are important sources of GWs at lower frequencies to be covered
by space interferometers (LISA). Major uncertainties in the current
understanding of properties of NSs and BHs most relevant to the GW studies are
discussed, including the treatment of the natal kicks which compact stellar
remnants acquire during the core collapse of massive stars and the common
envelope phase of binary evolution. We discuss the coalescence rates of binary
NSs and BHs and prospects for their detections, the formation and evolution of
binary WDs and their observational manifestations. Special attention is given
to AM CVn-stars -- compact binaries in which the Roche lobe is filled by
another WD or a low-mass partially degenerate helium-star, as these stars are
thought to be the best LISA verification binary GW sources.Comment: 105 pages, 18 figure
Pten dependence distinguishes haematopoietic stem cells from leukaemia-initiating cells
Recent advances have highlighted extensive phenotypic and functional similarities between normal stem cells and cancer stem cells. This raises the question of whether disease therapies can be developed that eliminate cancer stem cells without eliminating normal stem cells. Here we address this issue by conditionally deleting the Pten tumour suppressor gene in adult haematopoietic cells. This led to myeloproliferative disease within days and transplantable leukaemias within weeks. Pten deletion also promoted haematopoietic stem cell (HSC) proliferation. However, this led to HSC depletion via a cell-autonomous mechanism, preventing these cells from stably reconstituting irradiated mice. In contrast to leukaemia-initiating cells, HSCs were therefore unable to maintain themselves without Pten. These effects were mostly mediated by mTOR as they were inhibited by rapamycin. Rapamycin not only depleted leukaemia-initiating cells but also restored normal HSC function. Mechanistic differences between normal stem cells and cancer stem cells can thus be targeted to deplete cancer stem cells without damaging normal stem cells.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/62514/1/nature04703.pd
Deficit of circulating stem – progenitor cells in opiate addiction: a pilot study
A substantial literature describes the capacity of all addictive drugs to slow cell growth and potentiate apoptosis. Flow cytometry was used as a means to compare two lineages of circulating progenitor cells in addicted patients. Buprenorphine treated opiate addicts were compared with medical patients. Peripheral venous blood CD34+ CD45+ double positive cells were counted as haemopoietic stem cells (HSC's), and CD34+ KDR+ (VEGFR2+) cells were taken as endothelial progenitor cells (EPC's). 10 opiate dependent patients with substance use disorder (SUD) and 11 non-addicted (N-SUD) were studied. The ages were (mean + S.D.) 36.2 + 8.6 and 56.4 + 18.6 respectively (P <0.01). HSC's were not different in the SUD (2.38 + 1.09 Vs. 3.40 + 4.56 cells/mcl). EPC's were however significantly lower in the SUD (0.09 + 0.14 Vs. 0.26 + 0.20 cells/mcl; No. > 0.15, OR = 0.09, 95% C.I. 0.01–0.97), a finding of some interest given the substantially older age of the N-SUD group. These laboratory data are thus consistent with clinical data suggesting accelerated ageing in addicted humans and implicate the important stem cell pool in both addiction toxicology and ageing. They carry important policy implications for understanding the fundamental toxicology of addiction, and suggest that the toxicity both of addiction itself and of indefinite agonist maintenance therapies may have been seriously underestimated
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