724 research outputs found
Wideband Characteristic Basis Functions in Radiation Problems
In this paper, the use of characteristic basis function (CBF) method, augmented by the application of asymptotic waveform evaluation (AWE) technique is analyzed in the context of the application to radiation problems. Both conventional and wideband CBFs are applied to the analysis of wire and planar antennas
Supergravity Instabilities of Non-Supersymmetric Quantum Critical Points
Motivated by the recent use of certain consistent truncations of M-theory to
study condensed matter physics using holographic techniques, we study the
SU(3)-invariant sector of four-dimensional, N=8 gauged supergravity and compute
the complete scalar spectrum at each of the five non-trivial critical points.
We demonstrate that the smaller SU(4)^- sector is equivalent to a consistent
truncation studied recently by various authors and find that the critical point
in this sector, which has been proposed as the ground state of a holographic
superconductor, is unstable due to a family of scalars that violate the
Breitenlohner-Freedman bound. We also derive the origin of this instability in
eleven dimensions and comment on the generalization to other embeddings of this
critical point which involve arbitrary Sasaki-Einstein seven manifolds. In the
spirit of a resurging interest in consistent truncations, we present a formal
treatment of the SU(3)-invariant sector as a U(1)xU(1) gauged N=2 supergravity
theory coupled to one hypermultiplet.Comment: 46 page
The Influence of Multimorbidity on Leading Causes of Death in Older Adults With Cognitive Impairment
Objective: The aim of this study is to evaluate the relationship of leading causes of death with gradients of cognitive impairment and multimorbidity. Method: This is a population-based study using data from the linked 1992- 2010 Health and Retirement Study and National Death Index (n = 9,691). Multimorbidity is defined as a combination of chronic conditions, functional limitations, and geriatric syndromes. Regression trees and Random Forest identified which combinations of multimorbidity associated with causes of death. Results: Multimorbidity is common in the study population. Heart disease is the leading cause in all groups, but with a larger percentage of deaths in the mild and moderate/severe cognitively impaired groups than among the noncognitively impaired. The different âpathsâ down the regression trees show that the distribution of causes of death changes with different combinations of multimorbidity. Discussion: Understanding the considerable heterogeneity in chronic conditions, functional limitations, geriatric syndromes, and causes of death among people with cognitive impairment can target care management and resource allocation
Flowing with Eight Supersymmetries in M-Theory and F-theory
We consider holographic RG flow solutions with eight supersymmetries and
study the geometry transverse to the brane. For both M2-branes and for
D3-branes in F-theory this leads to an eight-manifold with only a four-form
flux. In both settings there is a natural four-dimensional hyper-Kahler slice
that appears on the Coulomb branch. In the IIB theory this hyper-Kahler
manifold encodes the Seiberg-Witten coupling over the Coulomb branch of a U(1)
probe theory. We focus primarily upon a new flow solution in M-theory. This
solution is first obtained using gauged supergravity and then lifted to eleven
dimensions. In this new solution, the brane probes have an Eguchi-Hanson moduli
space with the M2-branes spread over the non-trivial 2-sphere. It is also shown
that the new solution is valid for a class of orbifold theories. We discuss how
the hyper-Kahler structure on the slice extends to some form of G-structure in
the eight-manifold, and describe how this can be computed.Comment: 29 pages, 1 figure, harvma
A harmonic family of dielectric flow solutions with maximal supersymmetry
We construct a new harmonic family: dielectric flow solutions with maximal
supersymmetry in eleven-dimensional supergravity. These solutions are
asymptotically AdS_4 x S^7, while in the infra-red the M2 branes are
dielectrically polarized into M5 branes. These solutions are holographically
dual to vacua of the mass deformed theory on M2 branes. They also provide an
interesting insight on the supergravity solutions sourced by giant gravitons,
allowing one to see how supergravity solves the giant graviton puzzle.Comment: 21 pages, LaTeX. reference adde
Mergers and Typical Black Hole Microstates
We use mergers of microstates to obtain the first smooth horizonless
microstate solutions corresponding to a BPS three-charge black hole with a
classically large horizon area. These microstates have very long throats, that
become infinite in the classical limit; nevertheless, their curvature is
everywhere small. Having a classically-infinite throat makes these microstates
very similar to the typical microstates of this black hole. A rough CFT
analysis confirms this intuition, and indicates a possible class of dual CFT
microstates.
We also analyze the properties and the merging of microstates corresponding
to zero-entropy BPS black holes and black rings. We find that these solutions
have the same size as the horizon size of their classical counterparts, and we
examine the changes of internal structure of these microstates during mergers.Comment: 49 pages, 5 figures. v2 references adde
Seasonal variability of sediment controls of nitrogen cycling in an agricultural stream
Agricultural streams receive large inputs of nutrients, such as nitrate (NO3â) and ammonium (NH4+), which impact water quality and stream health. Streambed sediments are hotspots of biogeochemical reactivity, characterised by high rates of nutrient attenuation and denitrification. High concentrations of nitrous oxide (N2O) previously observed in stream sediments point to incomplete denitrification, with sediments acting as a potentially significant source of global N2O. We investigated the effect of sediment type and seasonal variation on denitrification and N2O production in the streambed of an agricultural UK stream. Denitrification was strongly controlled by sediment type, with sand-dominated sediments exhibiting potential rates of denitrification almost 10 times higher than those observed in gravel-dominated sediments (0.026â±â0.004 N2OâN ÎŒg gâ1 hâ1 for sand-dominated and 0.003â±â0.003 N2OâN ÎŒg gâ1 hâ1 for gravel-dominated). In-situ measurements supported this finding, with higher concentrations of NO3â, nitrite (NO2â) and N2O observed in the porewaters of gravel-dominated sediments. Denitrification varied substantially between seasons, with denitrification increasing from winter to autumn. Our results indicate highest NO3â reduction occurred in sand-dominated sediments whilst highest N2O concentrations occurred in gravel-dominated sediments. This suggests that finer-grained streambeds could play an important role in removing excess nitrogen from agricultural catchments without producing excess N2O
Reply to âPseudoreplication and greenhouse-gas emissions from rivers'
Tiegs et al.1 highlight the significance and relevance of the findings of Comer-Warner et al.2 on greenhouse-gas emissions from streambed sediments but raise questions about some aspects of the experimental design. We support their call for more detailed field and laboratory-based studies on this subject. However, we believe that their concerns relate to uncertainties and limitations in the experimental design that were discussed explicitly in the original paper (and accompanying transparent peer review processâavailable online), or represent criticisms related to highly improbable minor anomalies that may unnecessarily dismiss experimental results as discussed below
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