175 research outputs found
Magnetospheric convection electric field dynamics and stormtime particle energization: Case study of the magnetic storm of 4 May 1998
It is shown that narrow channels of high electric field are an effective mechanism for injecting plasma into the inner magnetosphere. Analytical expressions for the electric field cannot produce these channels of intense plasma flow, and thus, result in less entry and adiabatic energization of the plasma sheet into near-Earth space. For the ions, omission of these channels leads to an underprediction of the strength of the stormtime ring current and therefore, an underestimation of the geoeffectiveness of the storm event. For the electrons, omission of these channels leads to the inability to create a seed population of 10-100 keV electrons deep in the inner magnetosphere. These electrons can eventually be accelerated into MeV radiation belt particles. To examine this, the 1-7 May 1998 magnetic storm is studied with a plasma transport model by using three different convection electric field models: Volland-Stern, Weimer, and AMIE. It is found that the AMIE model can produce particle fluxes that are several orders of magnitude higher in the <i>L</i> = 2 â 4 range of the inner magnetosphere, even for a similar total cross-tail potential difference. <br><br><b>Key words.</b> Space plasma physics (charged particle motion and acceleration) â Magnetospheric physics (electric fields, storms and substorms
Absorption and quasinormal modes of classical fields propagating on 3D and 4D de Sitter spacetime
We extensively study the exact solutions of the massless Dirac equation in 3D
de Sitter spacetime that we published recently. Using the Newman-Penrose
formalism, we find exact solutions of the equations of motion for the massless
classical fields of spin s=1/2,1,2 and to the massive Dirac equation in 4D de
Sitter metric. Employing these solutions, we analyze the absorption by the
cosmological horizon and de Sitter quasinormal modes. We also comment on the
results given by other authors.Comment: 31 page
Critical exponents and equation of state of the three-dimensional Heisenberg universality class
We improve the theoretical estimates of the critical exponents for the
three-dimensional Heisenberg universality class. We find gamma=1.3960(9),
nu=0.7112(5), eta=0.0375(5), alpha=-0.1336(15), beta=0.3689(3), and
delta=4.783(3). We consider an improved lattice phi^4 Hamiltonian with
suppressed leading scaling corrections. Our results are obtained by combining
Monte Carlo simulations based on finite-size scaling methods and
high-temperature expansions. The critical exponents are computed from
high-temperature expansions specialized to the phi^4 improved model. By the
same technique we determine the coefficients of the small-magnetization
expansion of the equation of state. This expansion is extended analytically by
means of approximate parametric representations, obtaining the equation of
state in the whole critical region. We also determine a number of universal
amplitude ratios.Comment: 40 pages, final version. In publication in Phys. Rev.
Can forest management based on natural disturbances maintain ecological resilience?
Given the increasingly global stresses on forests, many ecologists argue that managers must maintain ecological resilience: the capacity of ecosystems to absorb disturbances without undergoing fundamental change. In this review we ask: Can the emerging paradigm of natural-disturbance-based management (NDBM) maintain ecological resilience in managed forests? Applying resilience theory requires careful articulation of the ecosystem state under consideration, the disturbances and stresses that affect the persistence of possible alternative states, and the spatial and temporal scales of management relevance. Implementing NDBM while maintaining resilience means recognizing that (i) biodiversity is important for long-term ecosystem persistence, (ii) natural disturbances play a critical role as a generator of structural and compositional heterogeneity at multiple scales, and (iii) traditional management tends to produce forests more homogeneous than those disturbed naturally and increases the likelihood of unexpected catastrophic change by constraining variation of key environmental processes. NDBM may maintain resilience if silvicultural strategies retain the structures and processes that perpetuate desired states while reducing those that enhance resilience of undesirable states. Such strategies require an understanding of harvesting impacts on slow ecosystem processes, such as seed-bank or nutrient dynamics, which in the long term can lead to ecological surprises by altering the forest's capacity to reorganize after disturbance
Nonperturbative renormalization group approach to frustrated magnets
This article is devoted to the study of the critical properties of classical
XY and Heisenberg frustrated magnets in three dimensions. We first analyze the
experimental and numerical situations. We show that the unusual behaviors
encountered in these systems, typically nonuniversal scaling, are hardly
compatible with the hypothesis of a second order phase transition. We then
review the various perturbative and early nonperturbative approaches used to
investigate these systems. We argue that none of them provides a completely
satisfactory description of the three-dimensional critical behavior. We then
recall the principles of the nonperturbative approach - the effective average
action method - that we have used to investigate the physics of frustrated
magnets. First, we recall the treatment of the unfrustrated - O(N) - case with
this method. This allows to introduce its technical aspects. Then, we show how
this method unables to clarify most of the problems encountered in the previous
theoretical descriptions of frustrated magnets. Firstly, we get an explanation
of the long-standing mismatch between different perturbative approaches which
consists in a nonperturbative mechanism of annihilation of fixed points between
two and three dimensions. Secondly, we get a coherent picture of the physics of
frustrated magnets in qualitative and (semi-) quantitative agreement with the
numerical and experimental results. The central feature that emerges from our
approach is the existence of scaling behaviors without fixed or pseudo-fixed
point and that relies on a slowing-down of the renormalization group flow in a
whole region in the coupling constants space. This phenomenon allows to explain
the occurence of generic weak first order behaviors and to understand the
absence of universality in the critical behavior of frustrated magnets.Comment: 58 pages, 15 PS figure
Search for direct production of charginos and neutralinos in events with three leptons and missing transverse momentum in âs = 7 TeV pp collisions with the ATLAS detector
A search for the direct production of charginos and neutralinos in final states with three electrons or muons and missing transverse momentum is presented. The analysis is based on 4.7 fbâ1 of protonâproton collision data delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with Standard Model expectations in three signal regions that are either depleted or enriched in Z-boson decays. Upper limits at 95% confidence level are set in R-parity conserving phenomenological minimal supersymmetric models and in simplified models, significantly extending previous results
Jet size dependence of single jet suppression in lead-lead collisions at sqrt(s(NN)) = 2.76 TeV with the ATLAS detector at the LHC
Measurements of inclusive jet suppression in heavy ion collisions at the LHC
provide direct sensitivity to the physics of jet quenching. In a sample of
lead-lead collisions at sqrt(s) = 2.76 TeV corresponding to an integrated
luminosity of approximately 7 inverse microbarns, ATLAS has measured jets with
a calorimeter over the pseudorapidity interval |eta| < 2.1 and over the
transverse momentum range 38 < pT < 210 GeV. Jets were reconstructed using the
anti-kt algorithm with values for the distance parameter that determines the
nominal jet radius of R = 0.2, 0.3, 0.4 and 0.5. The centrality dependence of
the jet yield is characterized by the jet "central-to-peripheral ratio," Rcp.
Jet production is found to be suppressed by approximately a factor of two in
the 10% most central collisions relative to peripheral collisions. Rcp varies
smoothly with centrality as characterized by the number of participating
nucleons. The observed suppression is only weakly dependent on jet radius and
transverse momentum. These results provide the first direct measurement of
inclusive jet suppression in heavy ion collisions and complement previous
measurements of dijet transverse energy imbalance at the LHC.Comment: 15 pages plus author list (30 pages total), 8 figures, 2 tables,
submitted to Physics Letters B. All figures including auxiliary figures are
available at
http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HION-2011-02
In search of disorders: internalizing symptom networks in a large clinical sample.
Background
The coâoccurrence of internalizing disorders is a common form of psychiatric comorbidity, raising questions about the boundaries between these diagnostic categories. We employ network psychometrics in order to: (a) determine whether internalizing symptoms cluster in a manner reflecting DSM diagnostic criteria, (b) gauge how distinct these diagnostic clusters are and (c) examine whether this network structure changes from childhood to early and then late adolescence.
Method
Symptomâlevel data were obtained for service users in publicly funded mental health services in England between 2011 and 2015 (N = 37,162). A symptom network (i.e. Gaussian graphical model) was estimated, and a community detection algorithm was used to explore the clustering of symptoms.
Results
The estimated network was densely connected and characterized by a multitude of weak associations between symptoms. Six communities of symptoms were identified; however, they were weakly demarcated. Two of these communities corresponded to social phobia and panic disorder, and four did not clearly correspond with DSM diagnostic categories. The network structure was largely consistent by sex and across three age groups (8â11, 12â14 and 15â18 years). Symptom connectivity in the two older age groups was significantly greater compared to the youngest group and there were differences in centrality across the age groups, highlighting the ageâspecific relevance of certain symptoms.
Conclusions
These findings clearly demonstrate the interconnected nature of internalizing symptoms, challenging the view that such pathology takes the form of distinct disorders
Cianoacrilato na colagem de BrĂĄquetes ortodĂŽnticos em resina acrĂlica: hĂĄ maior adesĂŁo?
Pacientes em tratamento ortodĂŽntico apresentam restauraçÔes provisĂłrias com frequĂȘncia. No entanto, poucos estudos avaliam a influĂȘncia dos adesivos na resistĂȘncia ao cisalhamento dos brĂĄquetes nessas superfĂcies. A resina acrĂlica Ă© comumente indicada para colagem de brĂĄquetes, porĂ©m o uso do cianoacrilato como adesivo ortodĂŽntico Ă© uma opção analisada. O objetivo do presente trabalho foi avaliar o desempenho do cianoacrilato associado aos materiais comumente utilizados para a fixação de brĂĄquetes metĂĄlicos em restauraçÔes provisĂłrias de resina acrĂlica. Quarenta amostras em resina acrĂlica foram preparadas e as superfĂcies homogeinizadas com lixas de carboneto de silĂcio (320 e 600). Em seguida, as amostras foram divididas aleatoriamente em quatro grupos (n=10) com base no tratamento de superfĂcie e agente de uniĂŁo: G1 - brĂĄquetes colados com resina acrĂlica; G2 - brĂĄquetes colados com resina acrĂlica e aplicação de cianoacrilato; G3 - brĂĄquetes colados com Transbond(tm) XT; G4 - brĂĄquetes colados com Transbond(tm) XT e aplicação de cianoacrilato. Foram utilizados brĂĄquetes ortodĂŽnticos de aço inoxidĂĄvel, prescrição Roth, Kirium (3M/Abzil) para incisivos centrais superiores direitos, slot 022. ApĂłs colagem, as amostras foram submetidas ao teste de cisalhamento a uma velocidade de 0,5mm/min em uma mĂĄquina de ensaios universal (EMIC DL-1000). Os dados foram coletados e submetidos Ă anĂĄlise estatĂstica pelo teste ANOVA com nĂvel de significĂąncia de 5%. A associação de resina acrĂlica ao cianoacrilato (G2) resultou na maior resistĂȘncia ao cisalhamento (13,76 MPa), mas nĂŁo significativa em comparação aos valores obtidos para a resina acrĂlica (G1= 7,76 MPa). O mesmo pĂŽde ser observado para a associação Transbond(tm) XT e cianoacrilato (G4= 4,03 MPa) em relação a utilização da Transbond(tm) XT de forma isolada (G3= 3,87 MPa) e resina acrĂlica. O tratamento de superfĂcie tem efeito significativo na resistĂȘncia da uniĂŁo dos brĂĄquetes colados aos materiais provisĂłrios. A associação de cianoacrilato ao monĂŽmero de metilmetacrilato apresentou maior resistĂȘncia ao cisalhamento, sendo mais indicada clinicamente
Search for the Standard Model Higgs boson decaying into bbÂŻ produced in association with top quarks decaying hadronically in pp collisions at âs = 8 TeV with the ATLAS detector
A search for Higgs boson production in association with a pair of top quarks (ttÂŻ H) is performed, where the Higgs boson decays to bbÂŻ, and both top quarks decay hadronically. The data used correspond to an integrated luminosity of 20.3 fbâ1 of pp collisions at âs = 8 TeV collected with the ATLAS detector at the Large Hadron Collider. The search selects events with at least six energetic jets and uses a boosted decision tree algorithm to discriminate between signal and Standard Model background. The dominant multijet background is estimated using a dedicated data-driven technique. For a Higgs boson mass of 125 GeV, an upper limit of 6.4 (5.4) times the Standard Model cross section is observed (expected) at 95% confidence level. The best-fit value for the signal strength is ÎŒ = 1.6 ± 2.6 times the Standard Model expectation for mH = 125 GeV. Combining all ttÂŻ H searches carried out by ATLAS at âs = 8 and 7 TeV, an observed (expected) upper limit of 3.1 (1.4) times the Standard Model expectation is obtained at 95% confidence level, with a signal strength ÎŒ = 1.7 ± 0.8
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