175 research outputs found
Ernst Mach and the Episode of the Monocular Depth Sensations
A look at Mach's work on monocular stereoscopy with relation to Mach Bands and the sensation of space
De Sitter Holography with a Finite Number of States
We investigate the possibility that, in a combined theory of quantum
mechanics and gravity, de Sitter space is described by finitely many states.
The notion of observer complementarity, which states that each observer has
complete but complementary information, implies that, for a single observer,
the complete Hilbert space describes one side of the horizon. Observer
complementarity is implemented by identifying antipodal states with outgoing
states. The de Sitter group acts on S-matrix elements. Despite the fact that
the de Sitter group has no nontrivial finite-dimensional unitary
representations, we show that it is possible to construct an S-matrix that is
finite-dimensional, unitary, and de Sitter-invariant. We present a class of
examples that realize this idea holographically in terms of spinor fields on
the boundary sphere. The finite dimensionality is due to Fermi statistics and
an `exclusion principle' that truncates the orthonormal basis in which the
spinor fields can be expanded.Comment: 23 pages, 1 eps figure, LaTe
Multiple zeta values in deformation quantization
Kontsevich's 1997 formula for the deformation quantization of Poisson
brackets is a Feynman expansion involving volume integrals over moduli spaces
of marked disks. We develop a systematic theory of integration on these moduli
spaces via suitable algebras of polylogarithms, and use it to prove that
Kontsevich's integrals can be expressed as integer-linear combinations of
multiple zeta values. Our proof gives a concrete algorithm for calculating the
integrals, which we have used to produce the first software package for the
symbolic calculation of Kontsevich's formula.Comment: 71 pages; software available at
http://bitbucket.org/bpym/starproducts/ and
https://bitbucket.org/PanzerErik/kontsevint
5D Black Holes and Matrix Strings
We derive the world-volume theory, the (non)-extremal entropy and background
geometry of black holes and black strings constructed out of the NS IIA
fivebrane within the framework of matrix theory. The CFT description of strings
propagating in the black hole geometry arises as an effective field theory.Comment: 25 pages, latex, 1 figure, extended discussion of non-extremal
entrop
Damage Detection and Self-Repair in Inflatable/Deployable Structures
Inflatable/deployable structures are under consideration for applications as varied as expansion modules for the International Space Station to destinations for space tourism to habitats for the lunar surface. Monitoring and maintaining the integrity of the physical structure is critical, particularly since these structures rely on non-traditional engineering materials such as fabrics, foams, and elastomeric polymers to provide the primary protection for the human crew. The closely related prior concept of monitoring structural integrity by use of built-in or permanently attached sensors has been applied to structures made of such standard engineering materials as metals, alloys, and rigid composites. To effect monitoring of flexible structures comprised mainly of soft goods, however, it will be necessary to solve a different set of problems - especially those of integrating power and data-transfer cabling that can withstand, and not unduly interfere with, stowage and subsequent deployment of the structures. By incorporating capabilities for self-repair along with capabilities for structural health monitoring, successful implementation of these technologies would be a significant step toward semi-autonomous structures, which need little human intervention to maintain. This would not only increase the safety of these structures, but also reduce the inspection and maintenance costs associated with more conventional structures
The distribution and mutagenesis of short coding INDELs from 1,128 whole exomes
BACKGROUND: Identifying insertion/deletion polymorphisms (INDELs) with high confidence has been intrinsically challenging in short-read sequencing data. Here we report our approach for improving INDEL calling accuracy by using a machine learning algorithm to combine call sets generated with three independent methods, and by leveraging the strengths of each individual pipeline. Utilizing this approach, we generated a consensus exome INDEL call set from a large dataset generated by the 1000 Genomes Project (1000G), maximizing both the sensitivity and the specificity of the calls. RESULTS: This consensus exome INDEL call set features 7,210 INDELs, from 1,128 individuals across 13 populations included in the 1000 Genomes Phase 1 dataset, with a false discovery rate (FDR) of about 7.0%. CONCLUSIONS: In our study we further characterize the patterns and distributions of these exonic INDELs with respect to density, allele length, and site frequency spectrum, as well as the potential mutagenic mechanisms of coding INDELs in humans. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/s12864-015-1333-7) contains supplementary material, which is available to authorized users
A Matrix Big Bang
The light-like linear dilaton background represents a particularly simple
time-dependent 1/2 BPS solution of critical type IIA superstring theory in ten
dimensions. Its lift to M-theory, as well as its Einstein frame metric, are
singular in the sense that the geometry is geodesically incomplete and the
Riemann tensor diverges along a light-like subspace of codimension one. We
study this background as a model for a big bang type singularity in string
theory/M-theory. We construct the dual Matrix theory description in terms of a
(1+1)-d supersymmetric Yang-Mills theory on a time-dependent world-sheet given
by the Milne orbifold of (1+1)-d Minkowski space. Our model provides a
framework in which the physics of the singularity appears to be under control.Comment: 25 pages, LaTeX; v2: discussion of singularity of Einstein frame
metric added, references adde
Directed geometrical worm algorithm applied to the quantum rotor model
We discuss the implementation of a directed geometrical worm algorithm for
the study of quantum link-current models. In this algorithm Monte Carlo updates
are made through the biased reptation of a worm through the lattice. A directed
algorithm is an algorithm where, during the construction of the worm, the
probability for erasing the immediately preceding part of the worm, when adding
a new part,is minimal. We introduce a simple numerical procedure for minimizing
this probability. The procedure only depends on appropriately defined local
probabilities and should be generally applicable. Furthermore we show how
correlation functions, C(r,tau) can be straightforwardly obtained from the
probability of a worm to reach a site (r,tau) away from its starting point
independent of whether or not a directed version of the algorithm is used.
Detailed analytical proofs of the validity of the Monte Carlo algorithms are
presented for both the directed and un-directed geometrical worm algorithms.
Results for auto-correlation times and Green functions are presented for the
quantum rotor model.Comment: 11 pages, 9 figures, v2 : Additional results and data calculated at
an incorrect chemical potential replaced. Conclusions unchange
Structural and Functional MRI Differences in Master Sommeliers: A Pilot Study on Expertise in the Brain
Our experiences, even as adults, shape our brains. Regional differences have been found in experts, with the regions associated with their particular skill-set. Functional differences have also been noted in brain activation patterns in some experts. This study uses multimodal techniques to assess structural and functional patterns that differ between experts and nonexperts. Sommeliers are experts in wine and thus in olfaction. We assessed differences in Master Sommeliersâ brains, compared with controls, in structure and also in functional response to olfactory and visual judgment tasks. MRI data were analyzed using voxel-based morphometry as well as automated parcellation to assess structural properties, and group differences between tasks were calculated. Results indicate enhanced volume in the right insula and entorhinal cortex, with the cortical thickness of the entorhinal correlating with experience. There were regional activation differences in a large area involving the right olfactory and memory regions, with heightened activation specifically for sommeliers during an olfactory task. Our results indicate that sommeliersâ brains show specialization in the expected regions of the olfactory and memory networks, and also in regions important in integration of internal sensory stimuli and external cues. Overall, these differences suggest that specialized expertise and training might result in enhancements in the brain well into adulthood. This is particularly important given the regions involved, which are the first to be impacted by many neurodegenerative diseases
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