9,511 research outputs found
Application of heat pipes to a nuclear aircraft propulsion system
Application of heat pipes to nuclear aircraft propulsion syste
Dimensional Duality
We show that string theory on a compact negatively curved manifold,
preserving a U(1)^{b_1} winding symmetry, grows at least b_1 new effective
dimensions as the space shrinks. The winding currents yield a "D-dual"
description of a Riemann surface of genus h in terms of its 2h dimensional
Jacobian torus, perturbed by a closed string tachyon arising as a potential
energy term in the worldsheet sigma model. D-branes on such negatively curved
manifolds also reveal this structure, with a classical moduli space consisting
of a b_1-torus. In particular, we present an AdS/CFT system which offers a
non-perturbative formulation of such supercritical backgrounds. Finally, we
discuss generalizations of this new string duality.Comment: 25 pages, harvmac. v2: fixed typo. v3: fixed typos and added ref
Introduction and Expression of a Rabbit β-globin Gene in Mouse Fibroblasts
The cloned chromosomal rabbit ß-globin gene has been introduced into mouse fibroblasts by DNA-mediated gene transfer (transformation). In this report, we examine the expression of the rabbit gene in six independent transformants that contain from 1 to 20 copies of the cloned globin gene. Rabbit globin transcripts were detected in two of these transformants at steady-state concentrations of 5 and 2 copies per cell. The globin transcripts from one cell line are polyadenylylated and migrate as 9S RNA on methylmercury gels. These transcripts reflect correct processing of the two intervening sequences but lack 48 ± 5 nucleotides present at the 5' terminus of rabbit erythrocyte globin mRNA
The Scaling of the No Scale Potential and de Sitter Model Building
We propose a variant of the KKLT (A)dS flux vacuum construction which does
not require an antibrane to source the volume modulus. The strategy is to find
nonzero local minima of the no-scale potential in the complex structure and
dilaton directions in moduli space. The corresponding no-scale potential
expanded about this point sources the volume modulus in the same way as does
the antibrane of the KKLT construction. We exhibit explicit examples of such
nonzero local minima of the no-scale potential in a simple toroidal orientifold
model.Comment: 11 pages, harvmac big. v2: trivial typos fixe
A New Handle on de Sitter Compactifications
We construct a large new class of de Sitter (and anti de Sitter) vacua of
critical string theory from flux compactifications on products of Riemann
surfaces. In the construction, the leading effects stabilizing the moduli are
perturbative. We show that these effects self-consistently dominate over
standard estimates for further and quantum corrections, via
tuning available from large flux and brane quantum numbers.Comment: 26 pages, harvmac big. v2: Correction generalizing specific
ingredients required for tunable negative term; conclusions and structure of
potential unchange
Preliminary Full-Scale Wind-Tunnel Investigation of Wing Ducts for Radiators, Special Report
Wing ducts for liquid-cooled engine radiators have been investigated in the N.A.C.A. full-scale wind tunnel on a large model airplane. Th e tests were made to determine the relative merits of several types of duct and radiator installations for an airplane of a particular des ign. In the test program the principal duct dimensions were system atically varied, and the results are therefore somewhat applicable to the general problems of wing duct design, although they should be co nsidered as preliminary and only indicative of the inherent possibil ities
4d Conformal Field Theories and Strings on Orbifolds
We propose correspondences between 4d quantum field theories with N=2,1,0
(super)conformal invariance and Type IIB string theory on various orbifolds. We
argue using the spacetime string theory, and check using the beta functions
(exactly for N=2,1 and so far at 1-loop for the gauge couplings in the N=0
case), that these theories have conformal fixed lines. The latter case
potentially gives well-defined non-supersymmetric vacua of string theory, with
a mechanism for making the curvature and cosmological constant small at
nontrivial string coupling. We suggest a correspondence between
nonsupersymmetric conformal fixed lines and nonsupersymmetric string vacua with
vanishing vacuum energy.Comment: 11 pages, harvmac big. Reference adde
Study of resonance light scattering for remote optical probing
Enhanced scattering and fluorescence processes in the visible and UV were investigated which will enable improved remote measurements of gas properties. The theoretical relationship between scattering and fluorescence from an isolated molecule in the approach to resonance is examined through analysis of the time dependence of re-emitted light following excitation of pulsed incident light. Quantitative estimates are developed for the relative and absolute intensities of fluorescence and resonance scattering. New results are obtained for depolarization of scattering excited by light at wavelengths within a dissociative continuum. The experimental work was performed in two separate facilities. One of these utilizes argon and krypton lasers, single moded by a tilted etalon, and a 3/4 meter double monochromator. This facility was used to determine properties of the re-emission from NO2, I2 and O3 excited by visible light. The second facility involves a narrow-line dye laser, and a 3/4 meter single monochromator. The dye laser produces pulsed light with 5 nsec pulse duration and 0.005 nm spectral width
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
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