3,893 research outputs found
pp Wave Big Bangs: Matrix Strings and Shrinking Fuzzy Spheres
We find pp wave solutions in string theory with null-like linear dilatons.
These provide toy models of big bang cosmologies. We formulate Matrix String
Theory in these backgrounds. Near the big bang ``singularity'', the string
theory becomes strongly coupled but the Yang-Mills description of the matrix
string is weakly coupled. The presence of a second length scale allows us to
focus on a specific class of non-abelian configurations, viz. fuzzy cylinders,
for a suitable regime of parameters. We show that, for a class of pp waves,
fuzzy cylinders which start out big at early times dynamically shrink into
usual strings at sufficiently late times.Comment: 29 pages, ReVTeX and AMSLaTeX. 4 Figures. v2: Typo corrected and
reference adde
Automated tracking of the Florida manatee (Trichechus manatus)
The electronic, physical, biological and environmental factors involved in the automated remote tracking of the Florida manatee (Trichechus manatus) are identified. The current status of the manatee as an endangered species is provided. Brief descriptions of existing tracking and position locating systems are presented to identify the state of the art in these fields. An analysis of energy media is conducted to identify those with the highest probability of success for this application. Logistic questions such as the means of attachment and position of any equipment to be placed on the manatee are also investigated. Power sources and manateeborne electronics encapsulation techniques are studied and the results of a compter generated DF network analysis are summarized
Did the Markman Court Ignore Fact, Substance, and the Spirit of the Constitution in Its Rush toward Uniformity
Impaired endothelial function of the retinal vasculature in hypertensive patients
<p><b>Background and Purpose:</b> Arterial hypertension constitutes a central factor in the pathogenesis of stroke. We examined endothelial function of the retinal vasculature as a model of the cerebral circulation.</p>
<p><b>Methods:</b> Thirty-eight young subjects (19 hypertensive and 19 normotensive) were treated with the AT1-receptor blocker candesartan cilexetil and placebo, each over 7 days. Retinal capillary flow and blood flow velocity in the central retinal artery were assessed with scanning laser Doppler flowmetry and pulsed Doppler ultrasound, respectively. NG-monomethyl-L-arginine (L-NMMA) was infused to inhibit nitric oxide (NO) synthesis. Diffuse luminance flicker was applied to stimulate NO release.</p>
<p><b>Results:</b> In normotensive subjects, L-NMMA decreased retinal capillary flow by 8.2%±13% (P<0.05) and flickering light increased mean blood flow velocity in the central retinal artery by 19%±29% (P<0.01). In contrast, no significant change to these provocative tests was seen in hypertensive subjects. Treatment with candesartan cilexetil restored a normal pattern of reactivity in retinal capillaries (L-NMMA: decrease in perfusion by 10%±17%, P<0.05) and the central retinal artery (flicker: increase in mean blood flow velocity by 42%±31%, P<0.001) in hypertensive patients.</p>
<p><b>Conclusions:</b> Endothelial function of the retinal vasculature is impaired in early essential hypertension but can be improved by AT1-receptor blockade.</p>
Arago (1810): the first experimental result against the ether
95 years before Special Relativity was born, Arago attempted to detect the
absolute motion of the Earth by measuring the deflection of starlight passing
through a prism fixed to the Earth. The null result of this experiment gave
rise to the Fresnel's hypothesis of an ether partly dragged by a moving
substance. In the context of Einstein's Relativity, the sole frame which is
privileged in Arago's experiment is the proper frame of the prism, and the null
result only says that Snell's law is valid in that frame. We revisit the
history of this premature first evidence against the ether theory and calculate
the Fresnel's dragging coefficient by applying the Huygens' construction in the
frame of the prism. We expose the dissimilar treatment received by the ray and
the wave front as an unavoidable consequence of the classical notions of space
and time.Comment: 16 pages. To appear in European Journal of Physic
Potential one-forms for hyperk\"ahler structures with torsion
It is shown that an HKT-space with closed parallel potential 1-form has
-symmetry. Every locally conformally hyperk\"ahler manifold
generates this type of geometry. The HKT-spaces with closed parallel potential
1-form arising in this way are characterized by their symmetries and an
inhomogeneous cubic condition on their torsion.Comment: 16 pages, Latex, no figure
Cosmologies with Null Singularities and their Gauge Theory Duals
We investigate backgrounds of Type IIB string theory with null singularities
and their duals proposed in hep-th/0602107. The dual theory is a deformed N=4
Yang-Mills theory in 3+1 dimensions with couplings dependent on a light-like
direction. We concentrate on backgrounds which become AdS_5 x S^5 at early and
late times and where the string coupling is bounded, vanishing at the
singularity. Our main conclusion is that in these cases the dual gauge theory
is nonsingular. We show this by arguing that there exists a complete set of
gauge invariant observables in the dual gauge theory whose correlation
functions are nonsingular at all times. The two-point correlator for some
operators calculated in the gauge theory does not agree with the result from
the bulk supergravity solution. However, the bulk calculation is invalid near
the singularity where corrections to the supergravity approximation become
important. We also obtain pp-waves which are suitable Penrose limits of this
general class of solutions, and construct the Matrix Membrane theory which
describes these pp-wave backgrounds.Comment: 43 pages REVTeX and AMSLaTeX. v2: references adde
Robust interferometer for the routing of light beams carrying orbital angular momentum
We have developed an interferometer requiring only minimal angular alignment for the routing of beams carrying orbital angular momentum. The Mach–Zehnder interferometer contains a Dove prism in each arm where each has a mirror plane around which the transverse phase profile is inverted. One consequence of the inversions is that the interferometer needs no alignment. Instead the interferometer defines a unique axis about which the input beam must be coupled. Experimental results are presented for the fringe contrast, reaching a maximum value of 93±1%
Superconformal Multi-Black Hole Moduli Spaces in Four Dimensions
Quantum mechanics on the moduli space of N supersymmetric Reissner-Nordstrom
black holes is shown to admit 4 supersymmetries using an unconventional
supermultiplet which contains 3N bosons and 4N fermions. A near-horizon limit
is found in which the quantum mechanics of widely separated black holes
decouples from that of strongly-interacting, near-coincident black holes. This
near-horizon theory is shown to have an enhanced D(2,1;0) superconformal
symmetry. The bosonic symmetries are SL(2,R) conformal symmetry and SU(2)xSU(2)
R-symmetry arising from spatial rotations and the R-symmetry of N=2
supergravity.Comment: 23 pages, harvmac. v2: many typos fixe
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