2,903 research outputs found
Coexistence of Spin Density Wave and Triplet Superconductivity
We discuss the possibility of coexistence of spin density wave
(antiferromagnetism) and triplet superconductivity as a particular example of a
broad class of systems where the interplay of magnetism and superconductivity
is important. We focus on the case of quasi-one-dimensional metals, where it is
known experimentally that antiferromagnetism is in close proximity to triplet
superconductivity in the temperature versus pressure phase diagram. Over a
narrow range of pressures, we propose an intermediate non-uniform phase
consisting of alternating antiferromagnetic and triplet superconducting
stripes. Within the non-uniform phase there are also changes between two and
three dimensional behavior.Comment: Revtex4, 4 pages, 5 figure
Density Induced Quantum Phase Transitions in Triplet Superconductors
We consider the possibility of quantum phase transitions in the ground state
of triplet superconductors where particle density is the tunning parameter. For
definiteness, we focus on the case of one band quasi-one-dimensional triplet
superconductors but many of our conclusions regarding the nature of the
transition are quite general. Within the functional integral formulation, we
calculate the electronic compressibility and superfluid density tensor as a
function of the particle density for various triplet order parameter symmetries
and find that these quantities are non-analytic when a critical value of the
particle density is reached.Comment: 4 pages, 3 figure
Radiative accretion shocks along nonuniform stellar magnetic fields in classical T Tauri stars
(abridged) AIMS. We investigate the dynamics and stability of post-shock
plasma streaming along nonuniform stellar magnetic fields at the impact region
of accretion columns. We study how the magnetic field configuration and
strength determine the structure, geometry, and location of the shock-heated
plasma. METHODS. We model the impact of an accretion stream onto the
chromosphere of a CTTS by 2D axisymmetric magnetohydrodynamic simulations. Our
model takes into account the gravity, the radiative cooling, and the
magnetic-field-oriented thermal conduction. RESULTS. The structure, stability,
and location of the shocked plasma strongly depend on the configuration and
strength of the magnetic field. For weak magnetic fields, a large component of
B may develop perpendicular to the stream at the base of the accretion column,
limiting the sinking of the shocked plasma into the chromosphere. An envelope
of dense and cold chromospheric material may also develop around the shocked
column. For strong magnetic fields, the field configuration determines the
position of the shock and its stand-off height. If the field is strongly
tapered close to the chromosphere, an oblique shock may form well above the
stellar surface. In general, a nonuniform magnetic field makes the distribution
of emission measure vs. temperature of the shocked plasma lower than in the
case of uniform magnetic field. CONCLUSIONS. The initial strength and
configuration of the magnetic field in the impact region of the stream are
expected to influence the chromospheric absorption and, therefore, the
observability of the shock-heated plasma in the X-ray band. The field strength
and configuration influence also the energy balance of the shocked plasma, its
emission measure at T > 1 MK being lower than expected for a uniform field. The
above effects contribute in underestimating the mass accretion rates derived in
the X-ray band.Comment: 11 pages, 11 Figures; accepted for publication on A&A. Version with
full resolution images can be found at
http://www.astropa.unipa.it/~orlando/PREPRINTS/sorlando_accretion_shocks.pd
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In silico modeling of oxygen-enhanced MRI of specific ventilation.
Specific ventilation imaging (SVI) proposes that using oxygen-enhanced 1H MRI to capture signal change as subjects alternatively breathe room air and 100% O2 provides an estimate of specific ventilation distribution in the lung. How well this technique measures SV and the effect of currently adopted approaches of the technique on resulting SV measurement is open for further exploration. We investigated (1) How well does imaging a single sagittal lung slice represent whole lung SV? (2) What is the influence of pulmonary venous blood on the measured MRI signal and resultant SVI measure? and (3) How does inclusion of misaligned images affect SVI measurement? In this study, we utilized two patient-based in silico models of ventilation, perfusion, and gas exchange to address these questions for normal healthy lungs. Simulation results from the two healthy young subjects show that imaging a single slice is generally representative of whole lung SV distribution, with a calculated SV gradient within 90% of that calculated for whole lung distributions. Contribution of O2 from the venous circulation results in overestimation of SV at a regional level where major pulmonary veins cross the imaging plane, resulting in a 10% increase in SV gradient for the imaging slice. A worst-case scenario simulation of image misalignment increased the SV gradient by 11.4% for the imaged slice
Correlation equalities and upper bounds for the transverse Ising model
Starting from an exact formal identity for the two-state transverse Ising
model and using correlation inequalities rigorous upper bounds for the critical
temperature and the critical transverse field are obtained which improve
effective results.Comment: 8 pages, 1 figur
Prospecção de espécies vegetais potencialmente acumuladoras de fósforo: uma estratégia para a melhoria da sustentabilidade de sistemas agroflorestais seqüenciais no nordeste Paraense.
Cópia de trabalho editado em CD-ROM
Nova ocorrência da Cochonilha-do-carmim em Opuntia spp. (Cactaceae) em Santa Catarina, Brasil.
O objetivo deste trabalho foi o levantamento dos inimigos naturais desta cochonilha que infesta Opuntia spp. no litoral de Santa Catarina
Relações hídricas do açaizeiro em mata de várzea do estuário do Amazonas.
As relações hídricas do açaizeiro(Euterpe oleracea Mart.) foram avaliadas em plantas adultas, vegetando em ecossistemas típicos de mata inundável do estuário amazônico, com o objetivo de verificar os possíveis efeitos da inundação periódica total ou parcial dos sistemas radiculares e de outros fatores ambientais sobre o fluxo de água no sistema solo-planta-atmosfera. Foram avaliados, nas épocas chuvosa e seca, a condutância estomática ao fluxo de vapor d?água, o potencial hídrico foliar, o teor relativo de água dos tecidos foliares e o teor relativo de água no ponto de perda de turgor dos tecidos dos folíolos, relacionando-os com o défice de pressão de vapor d?água da atmosfera (DPV), radiação solar e altura das marés. O açaizeiro tem uma condutância máxima baixa (0,160 mol.m-2.s-1) em relação a outras palmeiras e os seus estômatos respondem mais à radiação solar do que ao DPV. Observou-se também que a espécie é adaptada a ambientes de hipoxia do sistema radicular e que as inundações periódicas, por efeito das marés, não afetam a absorção de água pelas raízes. Também na época seca (estação das marés baixas), esta espécie mantem a absorção de água em níveis suficientes para suprir a demanda transpiratória
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