2,197 research outputs found
Mechanics of universal horizons
Modified gravity models such as Ho\v{r}ava-Lifshitz gravity or
Einstein-{\ae}ther theory violate local Lorentz invariance and therefore
destroy the notion of a universal light cone. Despite this, in the infrared
limit both models above possess static, spherically symmetric solutions with
"universal horizons" - hypersurfaces that are causal boundaries between an
interior region and asymptotic spatial infinity. In other words, there still
exist black hole solutions. We construct a Smarr formula (the relationship
between the total energy of the spacetime and the area of the horizon) for such
a horizon in Einstein-{\ae}ther theory. We further show that a slightly
modified first law of black hole mechanics still holds with the relevant area
now a cross-section of the universal horizon. We construct new analytic
solutions for certain Einstein-{\ae}ther Lagrangians and illustrate how our
results work in these exact cases. Our results suggest that holography may be
extended to these theories despite the very different causal structure as long
as the universal horizon remains the unique causal boundary when matter fields
are added.Comment: Minor clarifications. References update
6. The 1960s
From David Moore – “I served as dean of the ILR School during the 1960s. This was a period that started in relative tranquility and ended in tumultuous disarray with students demonstrating, administrators trying to maintain control, and faculty worrying about traditional academic freedom and values.” Includes: Remembrances of Things Past – 1963-71; Creation of the Public Employment Relations Board; and Alumni Perspectives
Strains for identifying and studying individual vegetative (heterokaryon) incompatibility loci in Neurospora crassa
Genetic and molecular studies of vegetative incompatibility are proceeding in several Neurospora labs. The purpose of this note is to present an expanded list of strains in the Fungal Genetics Stock Center that are potentially useful when partial diploids are employed to identify different alleles at any of the 11 known het loci of N. crassa. Some of the strains are newly deposited in FGSC. Others have previously been listed under other categories in the stock list
Followup to Columbia Investigation: Reinforced Carbon/Carbon From the Breach Location in the Wing Leading Edge Studied
Initial estimates on the temperature and conditions of the breach in the Space Shuttle Columbia's wing focused on analyses of the slag deposits. These deposits are complex mixtures of the reinforced carbon/carbon (RCC) constituents, insulation material, and wing structural materials. Identification of melted/solidified Cerachrome insulation (Thermal Ceramics, Inc., Augusta, GA) indicated that the temperatures at the breach had exceeded 1760 C
Substitutional and Interstitial Diffusion in alpha2-Ti3Al(O)
The reaction between Al2O3 and alpha2-Ti3Al was studied with a series of Al2O3/alpha2-Ti3Al multiphase diffusion couples annealed at 900, 1000 and 1100 C. The diffusion-paths were found to strongly depend on alpha2- Ti3Al(O) composition. For alloys with low oxygen concentrations the reaction involved the reduction of Al2O3, the formation of a gamma-TiAl reaction-layer and diffusion of Al and O into the alpha2-Ti3Al substrate. Measured concentration profiles across the interaction-zone showed "up-hill" diffusion of O in alpha2-Ti3Al(O) indicating a significant thermodynamic interaction between O and Al, Ti or both. Diffusion coefficients for the interstitial O in alpha2-Ti3Al(O) were determined independently from the interdiffusion of Ti and Al on the substitutional lattice. Diffusion coefficients are reported for alpha2-Ti3Al(O) as well as gamma-TiAl. Interpretation of the results were aided with the subsequent measurement of the activities of Al, Ti and O in alpha 2-Ti3Al(O) by Knudsen effusion-cell mass spectrometry
Public Health Department Accreditation in Nebraska
https://digitalcommons.unmc.edu/coph_policy_reports/1023/thumbnail.jp
Generally covariant model of a scalar field with high frequency dispersion and the cosmological horizon problem
Short distance structure of spacetime may show up in the form of high
freqency dispersion. Although such dispersion is not locally Lorentz invariant,
we show in a scalar field model how it can nevertheless be incorporated into a
generally covariant metric theory of gravity provided the locally preferred
frame is dynamical. We evaluate the resulting energy-momentum tensor and
compute its expectation value for a quantum field in a thermal state. The
equation of state differs at high temperatures from the usual one, but not by
enough to impact the problems of a hot big bang cosmology. We show that a
superluminal dispersion relation can solve the horizon problem via superluminal
equilibration, however it cannot do so while remaining outside the Planck
regime unless the dispersion relation is artificially chosen to have a rather
steep dependence on wavevector.Comment: 4 pages, 1 figure; New section added with discussion of solution to
the cosmological horizon problem using superluminal dispersion, title changed
to reflect new content, various additional minor change
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