290 research outputs found
The Otterbein Miscellany - May 1972
https://digitalcommons.otterbein.edu/miscellany/1016/thumbnail.jp
A World-Volume Perspective on the Recombination of Intersecting Branes
We study brane recombination for supersymmetric configurations of
intersecting branes in terms of the world-volume field theory. This field
theory contains an impurity, corresponding to the degrees of freedom localized
at the intersection. The Higgs branch, on which the impurity fields condense,
consists of vacua for which the intersection is deformed into a smooth
calibrated manifold. We show this explicitly using a superspace formalism for
which the calibration equations arise naturally from F- and D-flatness.Comment: References adde
Global Patterns of Terrestrial Biological Nitrogen (N2) Fixation in Natural Ecosystems
Human activities have clearly caused dramatic alterations of the terrestrial nitrogen cycle, and analyses of the extent and effects of such changes are now common in the scientific literature. However, any attempt to evaluate N cycling processes within ecosystems, as well as anthropogenic influences on the N cycle, requires an understanding of the magnitude of inputs via biological nitrogen fixation (BNF). Although there have been many studies addressing the microbiology, physiology, and magnitude of N fixation at local scales, there are very few estimates of BNF over large scales. We utilized \u3e100 preexisting published estimates of BNF to generate biome- and global-level estimates of biological N fixation. We also used net primary productivity (NPP) and evapotranspiration (ET) estimates from the Century terrestrial ecosystem model to examine global relationships between these variables and BNF as well as to compare observed and Century-modeled BNF. Our data-based estimates showed a strong positive relationship between ecosystem ET and BNF, and our analyses suggest that while the model\u27s simple relationships for BNF predict broad scale patterns, they do not capture much of the variability or magnitude of published rates. Patterns of BNF were also similar to patterns of ecosystem NPP. Our âbest estimateâ of potential nitrogen fixation by natural ecosystems is âŒ195 Tg N yrâ1, with a range of 100â290 Tg N yrâ1. Although these estimates do not account for the decrease in natural N fixation due to cultivation, this would not dramatically alter our estimate, as the greatest reductions in area have occurred in systems characterized by relatively low rates of N fixation (e.g., grasslands). Although our estimate of BNF in natural ecosystems is similar to previously published estimates of terrestrial BNF, we believe that this study provides a more documented, constrained estimate of this important flux
De Sitter Holography and the Cosmic Microwave Background
We interpret cosmological evolution holographically as a renormalisation
group flow in a dual Euclidean field theory, as suggested by the conjectured
dS/CFT correspondence. Inflation is described by perturbing around the
infra-red fixed point of the dual field theory. The spectrum of the cosmic
microwave background radiation is determined in terms of scaling violations in
the field theory. The dark energy allows similar, albeit less predictive,
considerations. We discuss the cosmological fine-tuning problems from the
holographic perspective.Comment: 17 pages, 2 figures, uses JHEP style files; corrected and added
reference
VertNet: A New Model for Biodiversity Data Sharing
Responding to the urgent need to make biodiversity records broadly accessible, the natural history community turned to âthe cloud.
Risk factors influencing fracture characteristics in postoperative periprosthetic femoral fractures around cemented stems in total hip arthroplasty : a multicentre observational cohort study on 584 fractures.
AIMS: This study evaluates risk factors influencing fracture characteristics for postoperative periprosthetic femoral fractures (PFFs) around cemented stems in total hip arthroplasty. METHODS: Data were collected for PFF patients admitted to eight UK centres between 25 May 2006 and 1 March 2020. Radiographs were assessed for Unified Classification System (UCS) grade and AO/OTA type. Statistical comparisons investigated relationships by age, gender, and stem fixation philosophy (polished taper-slip (PTS) vs composite beam (CB)). The effect of multiple variables was estimated using multinomial logistic regression to estimate odds ratios (ORs) with 95% confidence intervals (CIs). Surgical treatment (revision vs fixation) was compared by UCS grade and AO/OTA type. RESULTS: A total of 584 cases were included. Median age was 79.1 years (interquartile range 72.0 to 86.0), 312 (53.6%) patients were female, and 495 (85.1%) stems were PTS. The commonest UCS grade was type B1 (278, 47.6%). The most common AO/OTA type was spiral (352, 60.3%). Metaphyseal split fractures occurred only with PTS stems with an incidence of 10.1%. Male sex was associated with a five-fold reduction in odds of a type C fracture (OR 0.22 (95% CI 0.12 to 0.41); p < 0.001) compared to a type B fracture. CB stems were associated with significantly increased odds of transverse fracture (OR 9.51 (95% CI 3.72 to 24.34); p < 0.001) and wedge fracture (OR 3.72 (95% CI 1.16 to 11.95); p = 0.027) compared to PTS stems. Both UCS grade and AO/OTA type differed significantly (p < 0.001 and p = 0.001, respectively) between the revision and fixation groups but a similar proportion of B1 fractures underwent revision compared to fixation (45.3% vs 50.6%). CONCLUSION: The commonest fracture types are B1 and spiral fractures. PTS stems are exclusively associated with metaphyseal split fractures, but their incidence is low. Males have lower odds of UCS grade C fractures compared to females. CB stems have higher odds of bending type fractures (transverse and wedge) compared to PTS stems. There is considerable variation in practice when treating B1 fractures around cemented stems. Cite this article: Bone Jt Open 2021;2(7):466-475
Financial Structure and Economic Welfare: Applied General Equilibrium Development Economics
This review provides a common framework for researchers thinking about the next generation of micro-founded macro models of growth, inequality, and financial deepening, as well as direction for policy makers targeting microfinance programs to alleviate poverty. Topics include treatment of financial structure general equilibrium models: testing for as-if-complete markets or other financial underpinnings; examining dual-sector models with both a perfectly intermediated sector and a sector in financial autarky, as well as a second generation of these models that embeds information problems and other obstacles to trade; designing surveys to capture measures of income, investment/savings, and flow of funds; and aggregating individuals and households to the level of network, village, or national economy. The review concludes with new directions that overcome conceptual and computational limitations.National Science Foundation (U.S.)National Institutes of Health (U.S.)Templeton FoundationBill & Melinda Gates Foundatio
Pathologies in Asymptotically Lifshitz Spacetimes
There has been significant interest in the last several years in studying
possible gravitational duals, known as Lifshitz spacetimes, to anisotropically
scaling field theories by adding matter to distort the asymptotics of an AdS
spacetime. We point out that putative ground state for the most heavily studied
example of such a spacetime, that with a flat spatial section, suffers from a
naked singularity and further point out this singularity is not resolvable by
any known stringy effect. We review the reasons one might worry that
asymptotically Lifshitz spacetimes are unstable and employ the initial data
problem to study the stability of such systems. Rather surprisingly this
question, and even the initial value problem itself, for these spacetimes turns
out to generically not be well-posed. A generic normalizable state will evolve
in such a way to violate Lifshitz asymptotics in finite time. Conversely,
enforcing the desired asymptotics at all times puts strong restrictions not
just on the metric and fields in the asymptotic region but in the deep interior
as well. Generically, even perturbations of the matter field of compact support
are not compatible with the desired asymptotics.Comment: 36 pages, 1 figure, v2: Enhanced discussion of singularity, including
relationship to Gubser's conjecture and singularity in RG flow solution, plus
minor clarification
Nonabelian Phenomena on D-branes
A remarkable feature of D-branes is the appearance of a nonabelian gauge
theory in the description of several (nearly) coincident branes. This
nonabelian structure plays an important role in realizing various geometric
effects with D-branes. In particular, the branes' transverse displacements are
described by matrix-valued scalar fields and so noncommutative geometry
naturally appears in this framework. I review the action governing this
nonabelian theory, as well as various related physical phenomena such as the
dielectric effect, giant gravitons and fuzzy funnels.Comment: Lecture at Leuven workshop on ``The quantum structure of spacetime
and the geometrical nature of fundamental interactions'' (September 13-19,
2002); ref.'s adde
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