37,157 research outputs found
Weak Coupling, Degeneration and Log Calabi-Yau Spaces
We establish a new weak coupling limit in F-theory. The new limit may be
thought of as the process in which a local model bubbles off from the rest of
the Calabi-Yau. The construction comes with a small deformation parameter
such that computations in the local model become exact as . More
generally, we advocate a modular approach where compact Calabi-Yau geometries
are obtained by gluing together local pieces (log Calabi-Yau spaces) into a
normal crossing variety and smoothing, in analogy with a similar cutting and
gluing approach to topological field theories. We further argue for a
holographic relation between F-theory on a degenerate Calabi-Yau and a dual
theory on its boundary, which fits nicely with the gluing construction.Comment: 59 pp, 2 figs, LaTe
Implementing Transitive Credit with JSON-LD
Science and engineering research increasingly relies on activities that
facilitate research but are not currently rewarded or recognized, such as: data
sharing; developing common data resources, software and methodologies; and
annotating data and publications. To promote and advance these activities, we
must develop mechanisms for assigning credit, facilitate the appropriate
attribution of research outcomes, devise incentives for activities that
facilitate research, and allocate funds to maximize return on investment. In
this article, we focus on addressing the issue of assigning credit for both
direct and indirect contributions, specifically by using JSON-LD to implement a
prototype transitive credit system.Comment: accepted by WSSSPE2 - http://wssspe.researchcomputing.org.uk/wssspe2
Hierarchies from D-brane instantons in globally defined Calabi-Yau Orientifolds
We construct the first globally consistent semi-realistic Type I string vacua
on an elliptically fibered manifold where the zero modes of the Euclidean
D1-instanton sector allow for the generation of non-perturbative Majorana
masses of an intermediate scale. In another class of global models, a D1-brane
instanton can generate a Polonyi-type superpotential breaking supersymmetry at
an exponentially suppressed scale.Comment: 4 pages, 4 tables, uses revtex; v2: Discussion of instanton curves
improved, typos fixed, references added; v3: version published in PR
Phase transitions, double-scaling limit, and topological strings
Topological strings on Calabi--Yau manifolds are known to undergo phase
transitions at small distances. We study this issue in the case of perturbative
topological strings on local Calabi--Yau threefolds given by a bundle over a
two-sphere. This theory can be regarded as a q--deformation of Hurwitz theory,
and it has a conjectural nonperturbative description in terms of q--deformed 2d
Yang--Mills theory. We solve the planar model and find a phase transition at
small radius in the universality class of 2d gravity. We give strong evidence
that there is a double--scaled theory at the critical point whose all genus
free energy is governed by the Painlev\'e I equation. We compare the critical
behavior of the perturbative theory to the critical behavior of its
nonperturbative description, which belongs to the universality class of 2d
supergravity. We also give evidence for a new open/closed duality relating
these Calabi--Yau backgrounds to open strings with framing.Comment: 49 pages, 3 eps figures; section added on non-perturbative proposal
and 2d gravity; minor typos correcte
Investigation of light scattering in highly reflecting pigmented coatings. Volume 2 - Classical investigations, theoretical and experimental Final report, 1 May 30 Sep. 1966
Light scattering theory applied to particle arrays to explain scattering in highly reflecting paint coating
The baryonic Tully-Fisher relation for different velocity definitions and implications for galaxy angular momentum
We study the baryonic Tully-Fisher relation (BTFR) at z=0 using 153 galaxies
from the SPARC sample. We consider different definitions of the characteristic
velocity from HI and H-alpha rotation curves, as well as HI line-widths from
single-dish observations. We reach the following results: (1) The tightest BTFR
is given by the mean velocity along the flat part of the rotation curve. The
orthogonal intrinsic scatter is extremely small (6%) and the best-fit slope is
3.85+/-0.09, but systematic uncertainties may drive the slope from 3.5 to 4.0.
Other velocity definitions lead to BTFRs with systematically higher scatters
and shallower slopes. (2) We provide statistical relations to infer the flat
rotation velocity from HI line-widths or less extended rotation curves (like
H-alpha and CO data). These can be useful to study the BTFR from large HI
surveys or the BTFR at high redshifts. (3) The BTFR is more fundamental than
the relation between angular momentum and galaxy mass (the Fall relation). The
Fall relation has about 7 times more scatter than the BTFR, which is merely
driven by the scatter in the mass-size relation of galaxies. The BTFR is
already the "fundamental plane" of galaxy discs: no value is added with a
radial variable as a third parameter.Comment: 12 pages, 6 figures, accepted for publication in MNRA
Many-Task Computing and Blue Waters
This report discusses many-task computing (MTC) generically and in the
context of the proposed Blue Waters systems, which is planned to be the largest
NSF-funded supercomputer when it begins production use in 2012. The aim of this
report is to inform the BW project about MTC, including understanding aspects
of MTC applications that can be used to characterize the domain and
understanding the implications of these aspects to middleware and policies.
Many MTC applications do not neatly fit the stereotypes of high-performance
computing (HPC) or high-throughput computing (HTC) applications. Like HTC
applications, by definition MTC applications are structured as graphs of
discrete tasks, with explicit input and output dependencies forming the graph
edges. However, MTC applications have significant features that distinguish
them from typical HTC applications. In particular, different engineering
constraints for hardware and software must be met in order to support these
applications. HTC applications have traditionally run on platforms such as
grids and clusters, through either workflow systems or parallel programming
systems. MTC applications, in contrast, will often demand a short time to
solution, may be communication intensive or data intensive, and may comprise
very short tasks. Therefore, hardware and software for MTC must be engineered
to support the additional communication and I/O and must minimize task dispatch
overheads. The hardware of large-scale HPC systems, with its high degree of
parallelism and support for intensive communication, is well suited for MTC
applications. However, HPC systems often lack a dynamic resource-provisioning
feature, are not ideal for task communication via the file system, and have an
I/O system that is not optimized for MTC-style applications. Hence, additional
software support is likely to be required to gain full benefit from the HPC
hardware
Application of advanced on-board processing concepts to future satellite communications systems
An initial definition of on-board processing requirements for an advanced satellite communications system to service domestic markets in the 1990's is presented. An exemplar system architecture with both RF on-board switching and demodulation/remodulation baseband processing was used to identify important issues related to system implementation, cost, and technology development
- …