316 research outputs found
Cluster model of glass transition in simple liquids
On the basis of microscopic statistical mechanics of simple liquids the
orientational interaction between clusters consisting of a particle and its
nearest neighbors is estimated. It is shown that there are ranges of density
and temperature where the interaction changes sign as a function of a radius of
a cluster. The model of interacting cubic and icosahedral clusters is proposed
and solved in mean-field replica symmetric approximation. It is shown that the
glass order parameter grows smoothly upon cooling, the transition temperature
being identified with the temperature of the replica symmetry breaking. It is
shown that upon cooling a Lennard-Jones system, cubic clusters freeze first.
The transition temperature for icosahedral clusters is about ten per cent
lower. So the local structure of Lennard-Jones glass in the vicinity of glass
transition should be most probably cubic.Comment: 4 pages, 3 figure
Quantum Chaos in Quantum Wells
We develop a quantitative semiclassical theory for the resosnant tunneling
through a quantum well in a tilted magnetic field. It is shown, that in the
leading semiclassical approximation the tunneling current depends only on
periodic orbits within the quantum well. Further corrections (due to e.g.
"ghost" effect) can be expressed in terms of closed, but non-periodic orbits,
started at the "injection point". The results of the semiclassical theory are
shown to be in good agreement with both the experimental data and numerical
calculations.Comment: 25 pages, 15 figures, accepted for publication in Physica
Quantificação do carbono das substâncias húmicas em diferentes sistemas de uso do solo e Êpocas de avaliação.
A quantificação do carbono nas diferentes fraçþes da matĂŠria orgânica do solo (MOS) torna-se necessĂĄria devido ao interesse de se conhecer o potencial de captura e armazenamento do carbono nos diferentes sistemas de uso do solo. O objetivo deste trabalho foi quantificar o carbono das substâncias hĂşmicas em diferentes sistemas de uso do solo e ĂŠpocas de avaliação e correlacionĂĄ-lo com algumas propriedades quĂmicas e fĂsicas do solo. Os sistemas selecionados foram: preparo convencional (PC-milho/feijĂŁo), plantio direto (PD-berinjela/milho), consĂłrcio maracujĂĄ/Desmodium sp, cultivo com figo e sistema agroflorestal. As amostras de solo foram coletadas em duas profundidades (0-5 e 5-10 cm) e ĂŠpocas (17/11/2005âverĂŁo e 23/6/2006-inverno). Foi determinado o carbono orgânico total (COT) e realizado o fracionamento quĂmico da MOS, quantificando-se o carbono da fração humina (C-HUM), fração ĂĄcido hĂşmico (C-FAH) e fração ĂĄcido fĂşlvico (C-FAF). O C-HUM constituiu a maior parte do COT, havendo correlação significativa com o COT em todos os sistemas avaliados e estaçþes. Analisando o C-FAH foi possĂvel identificar alteraçþes no solo relacionadas aos sistemas de uso, na profundidade de 0-5 cm e no verĂŁo, destacando-se o PD com os maiores teores. Com o C-FAF ocorreu este mesmo comportamento, mas na profundidade de 5-10 cm e no inverno, destacando-se o PC com maiores valores. Foram verificadas correlaçþes significativas entre Valor S, Valor T e DMP em todos os sistemas, com exceção da ĂĄrea de PC. O PD aumenta os teores de C-FAH, nas duas profundidades e nas duas estaçþes, quando comparado ao PC do solo
Aedes species (Diptera: Culicidae) ecological and host feeding patterns in the north-eastern parts of South Africa, 2014â2018
BACKGROUND: There is a paucity of recent data and knowledge on mosquito diversity and potential vectors of arboviruses in South Africa, with most of the available data dating back to the 1950sâ1970s. Aedes and Culex species are the
major vectors of some of the principal arboviruses which have emerged and re-emerged in the past few decades.
METHODS: In this study we used entomological surveillance in selected areas in the north-eastern parts of South
Africa from 2014 to 2018 to assess mosquito diversity, with special emphasis on the Aedes species. The impact of trap
types and environmental conditions was also investigated. Identifcation of the blood meal sources of engorged
females collected during the study period was carried out, and DNA barcodes were generated for selected species.
RESULTS: Overall, 18.5% of the total Culicidae mosquitoes collected belonged to the genus Aedes, with 14 species recognised or suspected vectors of arboviruses. Species belonging to the Neomelaniconion subgenus were commonly
collected in the Bushveld savanna at conservation areas, especially Aedes mcintoshi and Aedes circumluteolus. Aedes
aegypti was present in all sites, albeit in low numbers. Temperature was a limiting factor for the Aedes population, and
they were almost exclusively collected at temperatures between 18 °C and 27 °C. The cytochrome oxidase subunit
I (COI) barcode fragment was amplifed for 21 Aedes species, and for nine of these species it was the frst sequence
information uploaded on GenBank.
CONCLUSION: This study provides a better understanding of the diversity and relative abundance of Aedes species in
the north-east of South Africa. The information provided here will contribute to future arboviral research and implementation of efcient vector control and prevention strategies.The Centers for Disease Control and Preventionhttp://www.parasitesandvectors.compm2022Medical VirologyUP Centre for Sustainable Malaria Control (UP CSMC
Search for a W' boson decaying to a bottom quark and a top quark in pp collisions at sqrt(s) = 7 TeV
Results are presented from a search for a W' boson using a dataset
corresponding to 5.0 inverse femtobarns of integrated luminosity collected
during 2011 by the CMS experiment at the LHC in pp collisions at sqrt(s)=7 TeV.
The W' boson is modeled as a heavy W boson, but different scenarios for the
couplings to fermions are considered, involving both left-handed and
right-handed chiral projections of the fermions, as well as an arbitrary
mixture of the two. The search is performed in the decay channel W' to t b,
leading to a final state signature with a single lepton (e, mu), missing
transverse energy, and jets, at least one of which is tagged as a b-jet. A W'
boson that couples to fermions with the same coupling constant as the W, but to
the right-handed rather than left-handed chiral projections, is excluded for
masses below 1.85 TeV at the 95% confidence level. For the first time using LHC
data, constraints on the W' gauge coupling for a set of left- and right-handed
coupling combinations have been placed. These results represent a significant
improvement over previously published limits.Comment: Submitted to Physics Letters B. Replaced with version publishe
Search for the standard model Higgs boson decaying into two photons in pp collisions at sqrt(s)=7 TeV
A search for a Higgs boson decaying into two photons is described. The
analysis is performed using a dataset recorded by the CMS experiment at the LHC
from pp collisions at a centre-of-mass energy of 7 TeV, which corresponds to an
integrated luminosity of 4.8 inverse femtobarns. Limits are set on the cross
section of the standard model Higgs boson decaying to two photons. The expected
exclusion limit at 95% confidence level is between 1.4 and 2.4 times the
standard model cross section in the mass range between 110 and 150 GeV. The
analysis of the data excludes, at 95% confidence level, the standard model
Higgs boson decaying into two photons in the mass range 128 to 132 GeV. The
largest excess of events above the expected standard model background is
observed for a Higgs boson mass hypothesis of 124 GeV with a local significance
of 3.1 sigma. The global significance of observing an excess with a local
significance greater than 3.1 sigma anywhere in the search range 110-150 GeV is
estimated to be 1.8 sigma. More data are required to ascertain the origin of
this excess.Comment: Submitted to Physics Letters
Search for new physics in events with opposite-sign leptons, jets, and missing transverse energy in pp collisions at sqrt(s) = 7 TeV
A search is presented for physics beyond the standard model (BSM) in final
states with a pair of opposite-sign isolated leptons accompanied by jets and
missing transverse energy. The search uses LHC data recorded at a
center-of-mass energy sqrt(s) = 7 TeV with the CMS detector, corresponding to
an integrated luminosity of approximately 5 inverse femtobarns. Two
complementary search strategies are employed. The first probes models with a
specific dilepton production mechanism that leads to a characteristic kinematic
edge in the dilepton mass distribution. The second strategy probes models of
dilepton production with heavy, colored objects that decay to final states
including invisible particles, leading to very large hadronic activity and
missing transverse energy. No evidence for an event yield in excess of the
standard model expectations is found. Upper limits on the BSM contributions to
the signal regions are deduced from the results, which are used to exclude a
region of the parameter space of the constrained minimal supersymmetric
extension of the standard model. Additional information related to detector
efficiencies and response is provided to allow testing specific models of BSM
physics not considered in this paper.Comment: Replaced with published version. Added journal reference and DO
Measurement of the Lambda(b) cross section and the anti-Lambda(b) to Lambda(b) ratio with Lambda(b) to J/Psi Lambda decays in pp collisions at sqrt(s) = 7 TeV
The Lambda(b) differential production cross section and the cross section
ratio anti-Lambda(b)/Lambda(b) are measured as functions of transverse momentum
pt(Lambda(b)) and rapidity abs(y(Lambda(b))) in pp collisions at sqrt(s) = 7
TeV using data collected by the CMS experiment at the LHC. The measurements are
based on Lambda(b) decays reconstructed in the exclusive final state J/Psi
Lambda, with the subsequent decays J/Psi to an opposite-sign muon pair and
Lambda to proton pion, using a data sample corresponding to an integrated
luminosity of 1.9 inverse femtobarns. The product of the cross section times
the branching ratio for Lambda(b) to J/Psi Lambda versus pt(Lambda(b)) falls
faster than that of b mesons. The measured value of the cross section times the
branching ratio for pt(Lambda(b)) > 10 GeV and abs(y(Lambda(b))) < 2.0 is 1.06
+/- 0.06 +/- 0.12 nb, and the integrated cross section ratio for
anti-Lambda(b)/Lambda(b) is 1.02 +/- 0.07 +/- 0.09, where the uncertainties are
statistical and systematic, respectively.Comment: Submitted to Physics Letters
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