1,333 research outputs found
A Comprehensive Survey of Brane Tilings
An infinite class of gauge theories can be engineered on
the worldvolume of D3-branes probing toric Calabi-Yau 3-folds. This kind of
setup has multiple applications, ranging from the gauge/gravity correspondence
to local model building in string phenomenology. Brane tilings fully encode the
gauge theories on the D3-branes and have substantially simplified their
connection to the probed geometries. The purpose of this paper is to push the
boundaries of computation and to produce as comprehensive a database of brane
tilings as possible. We develop efficient implementations of brane tiling tools
particularly suited for this search. We present the first complete
classification of toric Calabi-Yau 3-folds with toric diagrams up to area 8 and
the corresponding brane tilings. This classification is of interest to both
physicists and mathematicians alike.Comment: 39 pages. Link to Mathematica modules provide
CHANDRA Observations of X-ray Jet Structure on kpc to Mpc Scales
With its exquisite spatial resolution of better than 0.5 arcsecond, the
Chandra observatory is uniquely capable of resolving and studying the spatial
structure of extragalactic X-ray jets on scales of a few to a few hundred
kilo-parsec. Our analyses of four recent Chandra images of quasar jets
interpret the X-ray emission as inverse Compton scattering of high energy
electrons on the cosmic microwave background. We infer that these jets are in
bulk relativistic motion, carrying kinetic powers upwards of 10^46 ergs/s to
distances of hundreds of kpc, with very high efficiency.Comment: 4 pages, 3 figures, to be published in the proceedings of the Bologna
jet workshop, "The Physics of Relativistic Jets in the CHANDRA and XMM Era.
Understanding the Effects of Spaceflight on Head-trunk Coordination during Walking and Obstacle Avoidance
Prolonged exposure to spaceflight conditions results in a battery of physiological changes, some of which contribute to sensorimotor and neurovestibular deficits. Upon return to Earth, functional performance changes are tested using the Functional Task Test (FTT), which includes an obstacle course to observe postflight balance and postural stability, specifically during turning. The goal of this study was to quantify changes in movement strategies during turning events by observing the latency between headandtrunk coordinated movements. It was hypothesized that subjects experiencing neurovestibular adaptations would exhibit headtotrunk locking ('en bloc' movement) during turning, exhibited by a decrease in latency between head and trunk movement. FTT data samples were collected from ISS missions. Samples were analyzed three times preexposure, immediately postexposure (1 day post) and 2to3 times during recovery from the microgravity environment. Two 3D inertial measurements units (XSens MTx) were attached to subjects, one on the head and one on the upper back. This study focused primarily on the yaw movements about the subject's center of rotation. Time differences (latency) between head and trunk movement were calculated at two points on the obstacle course: the first turn to enter the obstacle course (approximately 90 turn) and averaged across a slalom obstacle portion, consisting of three turns (approximately three 90 turns). Preliminary analysis of the data shows a trend toward decreasing headtotrunk movement latency during postflight ambulation in slalom turning after reintroduction to Earth gravity in ISS astronauts. It is clear that changes in movement strategies are adopted during exposure to the microgravity environment and upon reintroduction to a gravity environment. Most ISS subjects exhibit symptoms of neurovestibular changes ('en bloc head and trunk movement) which may impact their ability to perform postflight functional tasks
Quantum driven Bounce of the future Universe
It is demonstrated that due to back-reaction of quantum effects, expansion of
the universe stops at its maximum and takes a turnaround. Later on, it
contracts to a very small size in finite future time. This phenomenon is
followed by a " bounce" with re-birth of an exponentially expanding
non-singular universe
Advances in aquatic insect systematics and biodiversity in the Neotropics: introduction
The Neotropical Region or Neotropics, contains vast expanses of rain forest and river systems representing some of the most biologically diverse ecosystems on Earth, but much of its resident biota remains undescribed and undocumented, and some of it is at risk of extirpation and extinction. Anthropogenic disturbances, especially deforestation, urbanization, and climate change, threaten the integrity of the Neotropics and its biodiversity. In the Neotropics, freshwater habitats are particularly susceptible to environmental stressors and freshwater species throughout the Neotropics have experienced marked declines greater than those of other groups when compared to marine and terrestrial systems. Advances in taxonomic descriptions, preparation of keys, and faunal assessments will aid future studies as well as conservation efforts
A Loop-Aware Search Strategy for Automated Performance Analysis
Automated online search is a powerful technique for performance diagnosis. Such a search can change the types of experiments it performs while the program is running, making decisions based on live performance data. Previous research has addressed search speed and scaling searches to large codes and many nodes. This paper explores using a finer granularity for the bottlenecks that we locate in an automated online search, i.e., refining the search to bottlenecks localized to loops. The ability to insert and remove instrumentation on-the-fly means an online search can utilize fine-grain program structure in ways that are infeasible using other performance diagnosis techniques. We automatically detect
loops in a program�s binary control flow graph and use this information to efficiently instrument loops. We implemented our new strategy in an existing automated online performance tool, Paradyn. Results for several sequential and parallel applications show that a loop-aware search strategy can increase bottleneck precision without compromising search time or cost
Condensate cosmology -- dark energy from dark matter
Imagine a scenario in which the dark energy forms via the condensation of
dark matter at some low redshift. The Compton wavelength therefore changes from
small to very large at the transition, unlike quintessence or metamorphosis. We
study CMB, large scale structure, supernova and radio galaxy constraints on
condensation by performing a 4 parameter likelihood analysis over the Hubble
constant and the three parameters associated with Q, the condensate field:
Omega_Q, w_f and z_t (energy density and equation of state today, and redshift
of transition). Condensation roughly interpolates between Lambda CDM (for large
z_t) and sCDM (low z_t) and provides a slightly better fit to the data than
Lambda CDM. We confirm that there is no degeneracy in the CMB between H and z_t
and discuss the implications of late-time transitions for the Lyman-alpha
forest. Finally we discuss the nonlinear phase of both condensation and
metamorphosis, which is much more interesting than in standard quintessence
models.Comment: 13 pages, 13 colour figures. Final version with discussion of TE
cross-correlation spectra for condensation and metamorphosis in light of the
WMAP result
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