1,885 research outputs found
Transfer RNA Biosynthesis: The Nucleotide Sequence of a Precursor to Serine and Proline Transfer RNAs
Hadronic Density of States from String Theory
Exactly soluble string theories describing a particular hadronic sector of
certain confining gauge theories have been obtained recently as Penrose-Gueven
limits of the dual supergravity backgrounds. The effect of taking the
Penrose-Gueven limit on the gravity side translates, in the gauge theory side,
into an effective truncation to hadrons of large U(1) charge (annulons). We
present an exact calculation of the finite temperature partition function for
the hadronic states corresponding to a Penrose-Gueven limit of the
Maldacena-Nunez embedding of N=1 SYM into string theory. It is established that
the theory exhibits a Hagedorn density of states.
Motivated by this exact calculation we propose a semiclassical string
approximation to the finite temperature partition function for confining gauge
theories admitting a supergravity dual, by performing an expansion around
classical solutions characterized by temporal windings. This semiclassical
approximation reveals a hadronic energy density of states of Hagedorn type,
with the coefficient determined by the gauge theory string tension as expected
for confining theories. We argue that our proposal captures primarily
information about states of pure N=1 SYM, given that this semiclassical
approximation does not entail a projection onto states of large U(1) charge.Comment: 15 page
The protective effect of FK506 pretreatment against renal ischemia/reperfusion injury in rats
The effect of pretreatment with FK506 on renal ischemia and reperfusion (I/R) injury was investigated using a rat model. Animals were assigned to one of two groups (20 rats each). Group 1 animals (controls) received 0.5 ml saline while group 2 animals received FK506 (0.3 mg/kg), administered intravenously 24 hr prior to the induction of renal ischemia. A 60-min period of ischemia of the right kidney was induced, and upon reperfusion a left nephrectomy was performed. Blood samples for estimation of BUN, creatinine, and tumor necrosis factor were collected on days 0 (preischemia), 1, 2, 3, 5, 7, and 10 (postischemia). Rats were sacrificed after day 10 and renal tissue was examined histologically. All animals survived the ischemic episode. FK506 pretreatment significantly reduced the serum levels of BUN (P<0.02), creatinine (P<0.02), and TNF (P<0.05) as compared with that seen in controls. Histologically, at day 10, the kidneys showed the expected sequelae of prior renal I/R with various degrees of tubular damage. However, no objective differences were evident between the two groups. Based upon these data, it can be concluded that (1) FK506 pretreatment ameliorates the functional renal injury associated with I/R, (2) renal ischemia induces the release of TNF, and (3) FK506 pretreatment results in a significant inhibition of TNF production. These data suggest that the release of TNF may be responsible for the increasing of BUN and creatinine levels seen after renal I/R and that pretreatment of renal donors with FK506 may improve renal function in the immediate post-transplant period. © 1992 by Williams and Wilkins
Duality Symmetry in Momentum Frame
Siegel's action is generalized to the D=2(p+1) (p even) dimensional
space-time. The investigation of self-duality of chiral p-forms is extended to
the momentum frame, using Siegel's action of chiral bosons in two space-time
dimensions and its generalization in higher dimensions as examples. The whole
procedure of investigation is realized in the momentum space which relates to
the configuration space through the Fourier transformation of fields. These
actions correspond to non-local Lagrangians in the momentum frame. The
self-duality of them with respect to dualization of chiral fields is uncovered.
The relationship between two self-dual tensors in momentum space, whose similar
form appears in configuration space, plays an important role in the
calculation, that is, its application realizes solving algebraically an
integral equation.Comment: 11 pages, no figures, to appear in Phys. Rev.
Vacuum Energy Cancellation in a Non-supersymmetric String
We present a nonsupersymmetric orbifold of type II string theory and show
that it has vanishing cosmological constant at the one and two loop level. We
argue heuristically that the cancellation persists at higher loops.Comment: 31 pages harvmac big, 6 figures. New version includes the 2-loop
analysis of hep-th/9810129 and elimination of one of the two heuristic
arguments for higher loop cancellatio
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Industrial application of geothermal energy in Southeast Idaho
Those phosphate related and food processing industries in Southeastern Idaho are identified which require large energy inputs and the potential for direct application of geothermal energy is assessed. The total energy demand is given along with that fractional demand that can be satisfied by a geothermal source of known temperature. The potential for geothermal resource development is analyzed by examining the location of known thermal springs and wells, the location of state and federal geothermal exploration leases, and the location of federal and state oil and gas leasing activity in Southeast Idaho. Information is also presented regarding the location of geothermal, oil, and gas exploration wells in Southeast Idaho. The location of state and federal phosphate mining leases is also presented. This information is presented in table and map formats to show the proximity of exploration and development activities to current food and phosphate processing facilities and phosphate mining activities. (MHR
On Lorentz Invariant Actions for Chiral P-Forms
We demonstrate how a Lorentz covariant formulation of the chiral p-form model
in D=2(p+1) containing infinitely many auxiliary fields is related to a Lorentz
covariant formulation with only one auxiliary scalar field entering a chiral
p-form action in a nonpolynomial way. The latter can be regarded as a
consistent Lorentz-covariant truncation of the former. We make the Hamiltonian
analysis of the model based on the nonpolynomial action and show that the Dirac
constraints have a simple form and are all of the first class. In contrast to
the Siegel model the constraints are not the square of second-class
constraints. The canonical Hamiltonian is quadratic and determines energy of a
single chiral p-form. In the case of d=2 chiral scalars the constraint can be
improved by use of `twisting' procedure (without the loss of the property to be
of the first class) in such a way that the central charge of the quantum
constraint algebra is zero. This points to possible absence of anomaly in an
appropriate quantum version of the model.Comment: RevTeX file, 7 page
Duality in Non-Trivially Compactified Heterotic Strings
We study the implications of duality symmetry on the analyticity properties
of the partition function as it depends upon the compactification length. In
order to obtain non-trivial compactifications, we give a physical prescription
to get the Helmholtz free energy for any heterotic string supersymmetric or
not. After proving that the free energy is always invariant under the duality
transformation and getting the zero temperature
theory whose partition function corresponds to the Helmholtz potential, we show
that the self-dual point is a generic singularity
as the Hagedorn one. The main difference between these two critical
compactification radii is that the term producing the singularity at the
self-dual point is finite for any . We see that this behavior at
actually implies a loss of degrees of freedom below that point.Comment: (Preprint No. FTUAM-92/12) 17 page
Yang-Mills Theory as a Deformation of Topological Field Theory, Dimensional Reduction and Quark Confinement
We propose a reformulation of Yang-Mills theory as a perturbative deformation
of a novel topological (quantum) field theory. We prove that this reformulation
of the four-dimensional QCD leads to quark confinement in the sense of area law
of the Wilson loop. First, Yang-Mills theory with a non-Abelian gauge group G
is reformulated as a deformation of a novel topological field theory. Next, a
special class of topological field theories is defined by both BRST and
anti-BRST exact action corresponding to the maximal Abelian gauge leaving the
maximal torus group H of G invariant. Then we find the topological field theory
() has a hidden supersymmetry for a choice of maximal Abelian gauge. As a
result, the D-dimensional topological field theory is equivalent to the
(D-2)-dimensional coset G/H non-linear sigma model in the sense of Parisi and
Sourlas dimensional reduction. After maximal Abelian gauge fixing, the
topological property of magnetic monopole and anti-monopole of four-dimensional
Yang-Mills theory is translated into that of instanton and anti-instanton in
two-dimensional equivalent model. It is shown that the linear static potential
in four-dimensions follows from the instanton--anti-instanton gas in the
equivalent two-dimensional non-linear sigma model obtained from the
four-dimensional topological field theory by dimensional reduction, while the
remaining Coulomb potential comes from the perturbative part in
four-dimensional Yang-Mills theory. The dimensional reduction opens a path for
applying various exact methods developed in two-dimensional quantum field
theory to study the non-perturbative problem in low-energy physics of
four-dimensional quantum field theories.Comment: 58 pages, Latex, no figures, version accepted for publication in
Phys. Rev. D (additions of Discussion, references and minor changes
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