4,792 research outputs found
Minimal Basis for Gauge Theory Amplitudes
Identities based on monodromy for integrations in string theory are used to
derive relations between different color ordered tree-level amplitudes in both
bosonic and supersymmetric string theory. These relations imply that the color
ordered tree-level n-point gauge theory amplitudes can be expanded in a minimal
basis of (n-3)! amplitudes. This result holds for any choice of polarizations
of the external states and in any number of dimensions.Comment: v2: typos corrected, some rephrasing of the general discussion.
Captions to figures added. Version to appear in PRL. 4 pages, 5 figure
Non-renormalisation Conditions in Type II String Theory and Maximal Supergravity
This paper considers general features of the derivative expansion of Feynman
diagram contributions to the four-graviton scattering amplitude in
eleven-dimensional supergravity compactified on a two-torus. These are
translated into statements about interactions of the form D^2k R^4 in type II
superstring theories, assuming the standard M-theory/string theory duality
relationships, which provide powerful constraints on the effective
interactions. In the ten-dimensional IIA limit we find that there can be no
perturbative contributions beyond k string loops (for k>0). Furthermore, the
genus h=k contributions are determined exactly by the one-loop
eleven-dimensional supergravity amplitude for all values of k. A plausible
interpretation of these observations is that the sum of h-loop Feynman diagrams
of maximally extended supergravity is less divergent than might be expected and
could be ultraviolet finite in dimensions d < 4 + 6/h -- the same bound as for
N=4 Yang--Mills.Comment: 30 pages, 4 figures. v3 Some rewording, typos corrected and some
references added. v4: Abstract rephrased. More typos corrected. Version to be
publishe
Comparing the reliability of networks by spectral analysis
We provide a method for the ranking of the reliability of two networks with
the same connectance. Our method is based on the Cheeger constant linking the
topological property of a network with its spectrum. We first analyze a set of
twisted rings with the same connectance and degree distribution, and obtain the
ranking of their reliability using their eigenvalue gaps. The results are
generalized to general networks using the method of rewiring. The success of
our ranking method is verified numerically for the IEEE57, the
Erd\H{o}s-R\'enyi, and the Small-World networks.Comment: 7 pages, 3 figure
Structure, Stability, and (Non)Reactivity of the Low-Index Surfaces of Crystalline B2O3−I
Diboron trioxide (B2O 3) assumes critical importance as an effective oxidation inhibitor in prominent chemical applications. For instance, it has been extensively used in electrolysis and ceramic/glass technology. Results are presented of accurate quantum mechanical calculations using the PW1PW hybrid HF/DFT functional of four low- index surfaces of the low-pressure phase of B2O : (101), (100), (011), and (001). Bond lengths, bond angles, and net Mulliken charges of the surface atoms are analyzed in detail. Total and projected density of states as well as surface energies are discussed. The occurrence of tetrahedral BO 4 units on the lowest energy structures of two of these surfaces has been demonstrated for the first time. The corresponding surface orientations incur larger energies in reference to the two orientations featuring only BO3 units. All of the four investigated lowest energy structures have no dangling bonds, which reasonably relates to the experimentally observed low reactivity of this compound. Findings in this paper pave the way for potential interest in the perspective of future studies on the surfaces of amorphous B2O3, as well as on the hydroxylation of both crystalline and amorphous B2O3
Strong interactions in air showers
We study the role new gauge interactions in extensions of the standard model
play in air showers initiated by ultrahigh-energy cosmic rays. Hadron-hadron
events remain dominated by quantum chromodynamics, while projectiles and/or
targets from beyond the standard model permit us to see qualitative differences
arising due to the new interactions.Comment: 35 pages, 12 figures. Accepted for publication in JCA
Force balance and membrane shedding at the Red Blood Cell surface
During the aging of the red-blood cell, or under conditions of extreme
echinocytosis, membrane is shed from the cell plasma membrane in the form of
nano-vesicles. We propose that this process is the result of the
self-adaptation of the membrane surface area to the elastic stress imposed by
the spectrin cytoskeleton, via the local buckling of membrane under increasing
cytoskeleton stiffness. This model introduces the concept of force balance as a
regulatory process at the cell membrane, and quantitatively reproduces the rate
of area loss in aging red-blood cells.Comment: 4 pages, 3 figure
The Momentum Kernel of Gauge and Gravity Theories
We derive an explicit formula for factorizing an -point closed string
amplitude into open string amplitudes. Our results are phrased in terms of a
momentum kernel which in the limit of infinite string tension reduces to the
corresponding field theory kernel. The same momentum kernel encodes the
monodromy relations which lead to the minimal basis of color-ordered amplitudes
in Yang-Mills theory. There are interesting consequences of the momentum kernel
pertaining to soft limits of amplitudes. We also comment on surprising links
between gravity and certain combinations of kinematic and color factors in
gauge theory.Comment: 19 pages, 1 figur
Profil de sensibilisation aux allergènes des asthmatiques adultes à Kinshasa, RDC : Etude transversale par prick-tests: Allergen sensitization profile of adult asthmatics in Kinshasa, DRC: Cross-sectional study by prick-tests
Context. Atopy is a common feature of asthma, involving near 80% of patients. Allergen sensitization shows environmental and geographical variability worldwide. Objective. To determine the common allergen sensitization profile of adult asthmatics in Kinshasa. Methods. From June 2017 to February 2018, 216 asthmatics aged 18 and over, of both sexes, were consecutively recruited at the University Clinics of Kinshasa and in some parishes and churches around the same town. The socio-demographic variables were registered using a validated questionnaire. The prick-test was performed relaying on five standardized commercial extracts of dog and cat dander, house dust mite (Blomia tropicalis, Bt), molds (Alternaria alternata), and egg yolk. Results. The population, average age of 45.23 (SD=17.56) years, 74% female, was sensitized at least to one allergen (53%) and non -sensitized in 47%. Twenty-five percent were monosensitized and 27% plurisensitized. The sensitization profile was respectively to Blomia tropicalis (72%), cat dander (46%), dog dander (34%), Alternaria alternata (13%) and egg yolk (11%). Conclusion. The present study indicates a plurisentisization feature in many asthmatics in our milieu ; mainly to dust mites and cat dander. Futher investigations involving a larger number of subjects and using broader test batteries are needed to improve diagnostic and therapeutic approaches in our context.
Contexte. Environ 80% des asthmatiques sont atopiques. La sensibilisation aux allergènes communs présente certaines variabilités environnementales et géographiques. Objectif. Déterminer le profil de sensibilisation aux allergènes communs des asthmatiques adultes de la ville de Kinshasa. Méthodes. De juin 2017 à février 2018, 216 asthmatiques de 18 ans et plus, des 2 sexes, ont été consécutivement recrutés aux Cliniques Universitaires de Kinshasa et dans certaines paroisses et églises de réveil de la ville de Kinshasa. A l’aide d’un questionnaire validé, les variables sociodémographiques ont été précisées. Le prick-test a été réalisé avec cinq extraits commerciaux standardisés de phanères de chien et chat, l’acarien de poussière de maison (Blomia tropicalis, Bt), les moisissures (Alternaria alternata), et le jaune d’oeuf. Résultats. L’âge moyen de la population était de 45,23 (ET=17,56) ans, 74% de sexe féminin, 47 % non sensibilisés et 53% sensibilisés à au moins un allergène. Vingt-cinq pourcent étaient monosensibilisées et 27% plurisensibilisées. Le profil de sensibilisation était Blomia tropicalis (72%), phanères de chat (46%), phanères de chien (34%), Alternaria alternata (13%) et jaune d’oeuf (11%). Conclusion. Une plurisensibilisation aux allergènes communs chez les asthmatiques dans notre milieu est présente dont le profil dominé par les acariens et les phanères de chats. Des enquêtes futures incluant un plus grand nombre de sujets et recourant à des batteries de tests plus élargies s’imposent en vue d’une définition d’options diagnostiques et thérapeutiques dans notre contexte
Seasonal effects on plasma cortisol concentrations in the Bedouin buck: circadian studies and response to ACTH
Our work aims at the exploration of cortisol secretion in the Bedouin goat, native to the Algerian Sahara desert, to understand the mechanisms of adaptation to extreme hot climates. In the present study, diurnal and seasonal variations of cortisol concentrations were measured in basal conditions, as well as the response to ACTH stimulation tests across seasons in bucks. The plasma concentrations of cortisol showed no diurnal cycle but a large variation across seasons. The highest levels occurred in summer and winter when the environmental conditions are at their extreme levels. The rectal temperature showed nychthemeral and seasonal variations, and BW was also different across seasons with highest values in summer and lowest in winter. The results obtained after administration of two doses (2 or 10 ?g/kg BW) of synthetic ACTH to three different age groups (kids, adults and elderly animals) showed a strong increase in plasma cortisol concentrations under all conditions with maximum levels achieved between 15 and 120 min. The analysis of the area under the cortisol curve showed no significant difference between the responses to the two doses of ACTH and between age groups, but showed seasonal variations with the lowest response in autumn than in other seasons. We conclude that season significantly affects secretion of cortisol in both basal state and under ACTH stimulation. However, the variation of adrenal reactivity to ACTH is not sufficient to explain seasonal differences, and in particular the summer peak in basal circulating cortisol concentrations. Further research should focus on the respective contribution of environmental factors (such as day length, temperature, humidity) and the mechanisms involved in cortisol regulation
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