578 research outputs found
Navigation/traffic control satellite mission study. Volume 3 - System concepts
Satellite network for air traffic control, solar flare warning, and collision avoidanc
Vector meson couplings to vector and tensor currents in extended NJL quark model
A simple explanation of the dynamic properties of vector mesons is given in
the framework of extended Nambu - Jona-Lasinio quark model. New mass relations
among the hadron vector resonances are derived. The results of this approach
are in good accordance with the QCD sum rules, the lattice calculations and the
experimental data.Comment: 4 pages, 2 figure
Regulation of human mTOR complexes by DEPTOR
The vertebrate-specific DEP domain-containing mTOR interacting protein (DEPTOR), an oncoprotein or tumor suppressor, has important roles in metabolism, immunity, and cancer. It is the only protein that binds and regulates both complexes of mammalian target of rapamycin (mTOR), a central regulator of cell growth. Biochemical analysis and cryo-EM reconstructions of DEPTOR bound to human mTOR complex 1 (mTORC1) and mTORC2 reveal that both structured regions of DEPTOR, the PDZ domain and the DEP domain tandem (DEPt), are involved in mTOR interaction. The PDZ domain binds tightly with mildly activating effect, but then acts as an anchor for DEPt association that allosterically suppresses mTOR activation. The binding interfaces of the PDZ domain and DEPt also support further regulation by other signaling pathways. A separate, substrate-like mode of interaction for DEPTOR phosphorylation by mTOR complexes rationalizes inhibition of non-stimulated mTOR activity at higher DEPTOR concentrations. The multifaceted interplay between DEPTOR and mTOR provides a basis for understanding the divergent roles of DEPTOR in physiology and opens new routes for targeting the mTOR-DEPTOR interaction in disease
Formalism for dilepton production via virtual photon bremsstrahlung in hadronic reactions
We derive a set of new formulas for various distributions in dilepton
production via virtual photon bremsstrahlung from pseudoscalar mesons and
unpolarized spin-one-half fermions. These formulas correspond to the leading
and sub-leading terms in the Low-Burnett-Kroll expansion for real photon
bremsstrahlung. The relation of our leading-term formulas to previous works is
also shown. Existing formulas are examined in the light of Lorentz covariance
and gauge invariance. Numerical comparison is made in a simple example, where
an "exact" formula and real photon data exist. The results reveal large
discrepancies among different bremsstrahlung formulas. Of all the leading-term
bremsstrahlung formulas, the one derived in this work agrees best with the
exact formula. The issues of M_T-scaling and event generators are also
addressed.Comment: 37 pages, RevTeX, epsf.sty, 10 embedded figure
Quaternion Gravi-Electromagnetism
Defining the generalized charge, potential, current and generalized fields as
complex quantities where real and imaginary parts represent gravitation and
electromagnetism respectively, corresponding field equation, equation of motion
and other quantum equations are derived in manifestly covariant manner. It has
been shown that the field equations are invariant under Lorentz as well as
duality transformations. It has been shown that the quaternionic formulation
presented here remains invariant under quaternion transformations.Comment: Key Words: Quaternion, dyons, gravito-dyons, gravi-electromagnetism.
PACS No.: 04.90. +e ; 14.80. H
Pion and Rho Structure Functions from Lattice QCD
We calculate the lower moments of the deep-inelastic structure functions of
the pion and the rho meson on the lattice. Of particular interest to us are the
spin-dependent structure functions of the rho. The calculations are done with
Wilson fermions and for three values of the quark mass, so that we can perform
an extrapolation to the chiral limit.Comment: 30pp, LaTeX2e with 15 eps figures using epsfig. Postscript file also
available from ftp://ftp.th.physik.uni-frankfurt.de/pub/cbest/pionrho.ps or
http://www.th.physik.uni-frankfurt.de/~cbest/pionrho.p
Weak gauge principle and electric charge quantization
Starting from a weak gauge principle we give a new and critical revision of
the argument leading to charge quantization on arbitrary spacetimes. The main
differences of our approach with respect to previous works appear on spacetimes
with non trivial torsion elements on its second integral cohomology group. We
show that in these spacetimes there can be topologically non-trivial
configurations of charged fields which do not imply charge quantization.
However, the existence of a non-exact electromagnetic field always implies the
quantization of charges. Another consequence of the theory for spacetimes with
torsion is the fact that it gives rise to two natural quantization units that
could be identified with the electric quantization unit (realized inside the
quarks) and with the electron charge. In this framework the color charge can
have a topological origin, with the number of colors being related to the order
of the torsion subgroup. Finally, we discuss the possibility that the
quantization of charge may be due to a weak non-exact component of the
electromagnetic field extended over cosmological scales.Comment: Latex2e, 24 pages, no figure
Worldline Approach to Forward and Fixed Angle fermion-fermion Scattering in Yang-Mills Theories at High Energies
Worldline techniques are employed to study the general behaviour of the
fermion-fermion collision amplitude at very high energies in a non-abelian
gauge field theory for the forward and fixed angle scattering cases. A central
objective of this work is to demonstrate the simplicity by which the worldline
methodology isolates that sector of the full theory which carries the soft
physics, relevant to each process. Anomalous dimensions pertaining to a given
soft sector are identified and subseuently used to facilitate the
renormalization group running of the respective four point functions. Gluon
reggeization is achieved for forward, while Sudakov suppression is established
for fixed angle scattering.Comment: 28 pages, 10 figures in three file
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