415 research outputs found
Negative Energy, Superluminosity and Holography
The holographic connection between large Super Yang Mills theory and
gravity in anti deSitter space requires unfamiliar behavior of the SYM theory
in the limit that the curvature of the AdS geometry becomes small. The
paradoxical behavior includes superluminal oscillations and negative energy
density. These effects typically occur in the SYM description of events which
take place far from the boundary of AdS when the signal from the event arrives
at the boundary. The paradoxes can be resolved by assuming a very rich
collection of hidden degrees of freedom of the SYM theory which store
information but give rise to no local energy density. These degrees of freedom,
called precursors, are needed to make possible sudden apparently acausal energy
momentum flows. Such behavior would be impossible in classical field theory as
a consequence of the positivity of the energy density. However we show that
these effects are not only allowed in quantum field theory but that we can
model them in free quantum field theory.Comment: Expanded version replacing earlier hep-th/990218
Genetic analysis of members of the species Oropouche virus and identification of a novel M segment sequence
Oropouche virus (OROV) is a public health threat in South America, and in particular Northern Brazil, causing frequent outbreaks of febrile illness. Using a combination of deep sequencing and Sanger sequencing approaches we have determined complete genome sequences of eight clinical isolates that were obtained from patient sera during an Oropouche fever outbreak in Amapa state, northern Brazil in 2009. We also report complete genome sequences of two OROV reassortants isolated from two marmosets in Minas Gerais state, southeast Brazil in 2012 that contain a novel M genome segment. Interestingly, all ten isolates posses a 947 nucleotide long S segment that lacks 11 residues in the S segment 3' UTR compared to the recently redetermined Brazilian prototype OROV strain BeAn19991. OROV maybe circulating more widely in Brazil and in the non-human primate population than previously appreciated and the identification of yet another reassortant highlights the importance of bunyavirus surveillance in South America
Wesson's IMT with a Weylian bulk
The foundations of Wesson's induced matter theory are analyzed. It is shown
that the 5D empty bulk must be regarded rather as a Weylian space than as a
Riemannian one.The framework of a Weyl-Dirac version of Wesson's theory is
elaborated and discussed. The bulk possesses in addition to the metric tensor a
Weylian connection vector as well Dirac's gauge function; there are no sources
(mass, current) in the bulk. On the 4D brane one obtains a geometrically based
unified theory of gravitation and electromagnetism with mass, currents and
equations induced by the 5D bulkComment: 29 page
Classical confinement of test particles in higher-dimensional models: stability criteria and a new energy condition
We review the circumstances under which test particles can be localized
around a spacetime section \Sigma_0 smoothly contained within a codimension-1
embedding space M. If such a confinement is possible, \Sigma_0 is said to be
totally geodesic. Using three different methods, we derive a stability
condition for trapped test particles in terms of intrinsic geometrical
quantities on \Sigma_0 and M; namely, confined paths are stable against
perturbations if the gravitational stress-energy density on M is larger than
that on \Sigma_0, as measured by an observed travelling along the unperturbed
trajectory. We confirm our general result explicitly in two different cases:
the warped-product metric ansatz for (n+1)-dimensional Einstein spaces, and a
known solution of the 5-dimensional vacuum field equation embedding certain
4-dimensional cosmologies. We conclude by defining a confinement energy
condition that can be used to classify geometries incorporating totally
geodesic submanifolds, such as those found in thick braneworld and other
5-dimensional scenarios.Comment: 9 pages, REVTeX4, in press in Phys. Rev.
Analysis of Basis Pursuit Via Capacity Sets
Finding the sparsest solution for an under-determined linear system
of equations is of interest in many applications. This problem is
known to be NP-hard. Recent work studied conditions on the support size of
that allow its recovery using L1-minimization, via the Basis Pursuit
algorithm. These conditions are often relying on a scalar property of
called the mutual-coherence. In this work we introduce an alternative set of
features of an arbitrarily given , called the "capacity sets". We show how
those could be used to analyze the performance of the basis pursuit, leading to
improved bounds and predictions of performance. Both theoretical and numerical
methods are presented, all using the capacity values, and shown to lead to
improved assessments of the basis pursuit success in finding the sparest
solution of
Conserved mechanisms of microtubule-stimulated ADP release, ATP binding, and force generation in transport kinesins
Kinesins are a superfamily of microtubule-based ATP-powered motors, important for multiple, essential cellular functions. How microtubule binding stimulates their ATPase and controls force generation is not understood. To address this fundamental question, we visualized microtubule-bound kinesin-1 and kinesin-3 motor domains at multiple steps in their ATPase cycles - including their nucleotide-free states - at ~7Ă
resolution using cryo-electron microscopy. In both motors, microtubule binding promotes ordered conformations of conserved loops that stimulate ADP release, enhance microtubule affinity and prime the catalytic site for ATP binding. ATP binding causes only small shifts of these nucleotide-coordinating loops but induces large conformational changes elsewhere that allow force generation and neck linker docking towards the microtubule plus end. Family-specific differences across the kinesin-microtubule interface account for the distinctive properties of each motor. Our data thus provide evidence for a conserved ATP-driven mechanism for kinesins and reveal the critical mechanistic contribution of the microtubule interface
Matrix and Stimulus Sample Sizes in the Weighted MDS Model: Empirical Metric Recovery Functions
The only guidelines for sample size that exist in the multidimensional scaling (MDS) literature are a set of heuristic "rules-of-thumb" that have failed to live up to Young's (1970) goal of finding func tional relationships between sample size and metric recovery. This paper develops answers to two im portant sample-size questions in nonmetric weight ed MDS settings, both of which are extensions of work reported in MacCallum and Cornelius (1977): (1) are the sample size requirements for number of stimuli and number of matrices compensatory? and (2) what type of functional relationships exist between the number of matrices and metric recov ery ? The graphs developed to answer the second question illustrate how such functional relation ships can be defined empirically in a wide range of MDS and other complicated nonlinear models.Yeshttps://us.sagepub.com/en-us/nam/manuscript-submission-guideline
Yang-Mills Duals for Semiclassical Strings
We consider a semiclassical multiwrapped circular string pulsating on S_5,
whose center of mass has angular momentum J on an S_3 subspace. Using the
AdS/CFT correspondence we argue that the one-loop anomalous dimension of the
dual operator is a simple rational function of J/L, where J is the R-charge and
L is the bare dimension of the operator. We then reproduce this result directly
from a super Yang-Mills computation, where we make use of the integrability of
the one-loop system to set up an integral equation that we solve. We then
verify the results of Frolov and Tseytlin for circular rotating strings with
R-charge assignment (J',J',J). In this case we solve for an integral equation
found in the O(-1) matrix model when J' J.
The latter region starts at J'=L/2 and continues down, but an apparent critical
point is reached at J'=4J. We argue that the critical point is just an artifact
of the Bethe ansatz and that the conserved charges of the underlying integrable
model are analytic for all J' and that the results from the O(-1) model
continue onto the results of the O(+1) model.Comment: 26 Pages, LaTeX; v2 Typos corrected, reference update
Deep Inelastic Scattering and Gauge/String Duality
We study deep inelastic scattering in gauge theories which have dual string
descriptions. As a function of we find a transition. For small , the
dominant operators in the OPE are the usual ones, of approximate twist two,
corresponding to scattering from weakly interacting partons. For large ,
double-trace operators dominate, corresponding to scattering from entire
hadrons (either the original `valence' hadron or part of a hadron cloud.) At
large we calculate the structure functions. As a function of Bjorken
there are three regimes: of order one, where the scattering produces only
supergravity states; small, where excited strings are produced; and,
exponentially small, where the excited strings are comparable in size to the
AdS space. The last regime requires in principle a full string calculation in
curved spacetime, but the effect of string growth can be simply obtained from
the world-sheet renormalization group.Comment: 52 pages, 10 figure
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