9,580 research outputs found
Shortage of vaccines during a yellow fever outbreak in Guinea.
A yellow fever epidemic erupted in Guinea in September, 2000. From Sept 4, 2000, to Jan 7, 2001, 688 instances of the disease and 225 deaths were reported. The diagnosis was laboratory confirmed by IgM detection in more than 40 patients. A mass vaccination campaign was limited by insufficient international stocks. After the epidemic in Guinea, the International Coordinating Group on Vaccine Provision for Epidemic Meningitis Control decided that 2 million doses of 17D yellow fever vaccine, being stored as part of a UNICEF stockpile, should be used only in response to outbreaks
Regularizing Cubic Open Neveu-Schwarz String Field Theory
After introducing non-minimal variables, the midpoint insertion of Y\bar Y in
cubic open Neveu-Schwarz string field theory can be replaced with an operator
N_\rho depending on a constant parameter \rho. As in cubic open superstring
field theory using the pure spinor formalism, the operator N_\rho is invertible
and is equal to 1 up to a BRST-trivial quantity. So unlike the linearized
equation of motion Y\bar Y QV=0 which requires truncation of the Hilbert space
in order to imply QV=0, the linearized equation N_\rho QV=0 directly implies
QV=0.Comment: 6 pages harvmac, added footnote and referenc
Scattering of a Baseball by a Bat
A ball can be hit faster if it is projected without spin but it can be hit
farther if it is projected with backspin. Measurements are presented in this
paper of the tradeoff between speed and spin for a baseball impacting a
baseball bat. The results are inconsistent with a collision model in which the
ball rolls off the bat and instead imply tangential compliance in the ball, the
bat, or both. If the results are extrapolated to the higher speeds that are
typical of the game of baseball, they suggest that a curveball can be hit with
greater backspin than a fastball, but by an amount that is less than would be
the case in the absence of tangential compliance.Comment: Accepted for publication in American Journal of Physic
Conformal Field Theory for the Superstring in a Ramond-Ramond Plane Wave Background
A quantizable worldsheet action is constructed for the superstring in a
supersymmetric plane wave background with Ramond-Ramond flux. The action is
manifestly invariant under all isometries of the background and is an exact
worldsheet conformal field theory.Comment: 13 pages harvma
Grain Boundary Loops in Graphene
Topological defects can affect the physical properties of graphene in
unexpected ways. Harnessing their influence may lead to enhanced control of
both material strength and electrical properties. Here we present a new class
of topological defects in graphene composed of a rotating sequence of
dislocations that close on themselves, forming grain boundary loops that either
conserve the number of atoms in the hexagonal lattice or accommodate
vacancy/interstitial reconstruction, while leaving no unsatisfied bonds. One
grain boundary loop is observed as a "flower" pattern in scanning tunneling
microscopy (STM) studies of epitaxial graphene grown on SiC(0001). We show that
the flower defect has the lowest energy per dislocation core of any known
topological defect in graphene, providing a natural explanation for its growth
via the coalescence of mobile dislocations.Comment: 23 pages, 7 figures. Revised title; expanded; updated reference
Elliptic Genera and 3d Gravity
We describe general constraints on the elliptic genus of a 2d supersymmetric
conformal field theory which has a gravity dual with large radius in Planck
units. We give examples of theories which do and do not satisfy the bounds we
derive, by describing the elliptic genera of symmetric product orbifolds of
, product manifolds, certain simple families of Calabi-Yau hypersurfaces,
and symmetric products of the "Monster CFT." We discuss the distinction between
theories with supergravity duals and those whose duals have strings at the
scale set by the AdS curvature. Under natural assumptions we attempt to
quantify the fraction of (2,2) supersymmetric conformal theories which admit a
weakly curved gravity description, at large central charge.Comment: 50 pages, 9 figures, v2: minor corrections to section
Supersymmetric Born-Infeld from the Pure Spinor Formalism of the Open Superstring
Classical BRST invariance in the pure spinor formalism for the open
superstring is shown to imply the supersymmetric Born-Infeld equations of
motion for the background fields. These equations are obtained by requiring
that the left and right-moving BRST currents are equal on the worldsheet
boundary in the presence of the background. The Born-Infeld equations are
expressed in N=1 D=10 superspace and include all abelian contributions to the
low-energy equations of motion, as well as the leading non-abelian
contributions.Comment: Added footnote 3 in agreement with the comments of Schiappa and
Wyllard in hep-th/050312
Inelastic collisions of ultra-cold heteronuclear molecules in an optical trap
Ultra-cold RbCs molecules in high-lying vibrational levels of the
a ground electronic state are confined in an optical trap.
Inelastic collision rates of these molecules with both Rb and Cs atoms are
determined for individual vibrational levels, across an order of magnitude of
binding energies. A simple model for the collision process is shown to
accurately reproduce the observed scattering rates
Role of coronal mass ejections in the heliospheric Hale cycle
[1] The 11-year solar cycle variation in the heliospheric magnetic field strength can be explained by the temporary buildup of closed flux released by coronal mass ejections (CMEs). If this explanation is correct, and the total open magnetic flux is conserved, then the interplanetary-CME closed flux must eventually open via reconnection with open flux close to the Sun. In this case each CME will move the reconnected open flux by at least the CME footpoint separation distance. Since the polarity of CME footpoints tends to follow a pattern similar to the Hale cycle of sunspot polarity, repeated CME eruption and subsequent reconnection will naturally result in latitudinal transport of open solar flux. We demonstrate how this process can reverse the coronal and heliospheric fields, and we calculate that the amount of flux involved is sufficient to accomplish the reversal within the 11 years of the solar cycle
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