3,461 research outputs found
Hall conductance of a pinned vortex lattice in a high magnetic field
We calculate the quasiparticle contribution to the zero temperature Hall
conductance of two-dimensional extreme type-II superconductors in a high
magnetic field, using the Landau basis. As one enters the superconducting phase
the Hall conductance is renormalized to smaller values, with respect to the
normal state result, until a quantum level-crossing transition is reached. At
high values of the order parameter, where the quasiparticles are bound to the
vortex cores, the Hall conductance is expected to tend to zero due to a theorem
of Thouless.Comment: To appear in Journ. Phys. : Cond. Matte
Identifying fear of childbirth in a UK population: qualitative examination of the clarity and acceptability of existing measurement tools in a small UK sample
Background: Fear of childbirth is related to but not synonymous with general anxiety, and represents a superior predictor for maternal and infant outcomes. There is a need to improve the identification and provision of support for women experiencing high fear of childbirth. However it is uncertain as to whether existing measurement tools have appropriate content validity (i.e. cover the relevant domains within the construct), practical utility, and whether they are acceptable for use with a UK population. This study aimed to (1) identify the utility and acceptability of existing measures of fear of childbirth (FOC) with a small UK sample and (2) map the content of existing measures to the key concepts of fear of childbirth established by previous research.
Methods: Ten pregnant women; five with high and five with low fear of childbirth participated in a cognitive interview covering four most commonly used measures of fear of childbirth: 1. The Wijma Delivery Expectancy Questionnaire (WDEQ A), 2. The Oxford Worries about Labour Scale (OWLS), 3. The Slade-Pais Expectations of Childbirth Scale – fear subscale (SPECS) and 4. The Fear of Birth scale (FOBS). Each measure was also reviewed by participants for ease and clarity of understanding and acceptability. The measures were then reviewed against the key domains identified in the fear of childbirth literature to ascertain the adequacy of content validity of each measure. Interviews were analysed using thematic analysis for each scale item.
Results: All measures except the FOBS, included items that either women did not understand or, if where there was understanding the meanings were inconsistent across women. All measures demonstrated limited acceptability and content validity for the specific construct of FOC. Therefore, none of the measurement tools currently used within the UK met criteria for understanding, acceptability and content validity for measurement of FOC.
Conclusions: Findings emphasise a need to develop a specific fear of childbirth tool with good clarity which demonstrates appropriate content validity, and that is acceptable in presentation and length for pregnant women in a UK population
Hall Effect in the mixed state of moderately clean superconductors
The Hall conductivity in the mixed state of a clean () type-II
s-wave superconductor is determined from a microscopic calculation within a
quasiclassical approximation. We find that below the superconducting transition
the contribution to the transverse conductivity due to dynamical fluctuations
of the order parameter is compensated by the modification of the quasiparticle
contribution. In this regime the nonlinear behaviour of the Hall angle is
governed by the change in the effective quasiparticle scattering rate due to
the reduction in the density of states at the Fermi level. The connection with
experimental results is discussed
Quasiparticle thermal conductivity in the vortex state of high-T cuprates
We present the results of a microscopic calculation of the longitudinal
thermal conductivity, , of a d-wave superconductor in the mixed state.
Our results show an increase in the thermal conductivity with the applied field
at low temperatures, and a decrease followed by a nearly field independent
at higher temperatures, in qualitative agreement with the
experimental results. We discuss the relationship between the slope of the
superconducting gap and the plateau in .Comment: 4 pages, 3 figures, very minor changes to text, published versio
Parabolic negative magnetoresistance in p-Ge/Ge1-xSix heterostructures
Quantum corrections to the conductivity due to the weak localization (WL) and
the disorder-modified electron-electron interaction (EEI) are investigated for
the high-mobility multilayer p-Ge/Ge1-xSix heterostructures at T = (0.1 -
20.0)K in magnetic field B up to 1.5T. Negative magnetoresistance with
logarithmic dependence on T and linear in B^2 is observed for B >= 0.1T. Such a
behavior is attributed to the interplay of the classical cyclotron motion and
the EEI effect. The Hartree part of the interaction constant is estimated
(F_/sigma = 0.44) and the WL and EEI contributions to the total quantum
correction /Delta /sigma at B = 0 are separated (/Delta /sigma_{WL} ~ 0.3/Delta
/sigma; /Delta /sigma_{EEI} ~ 0.7/Delta /sigma).Comment: 3 pages, 4 figure
Symmetric Skyrmions
We present candidates for the global minimum energy solitons of charge one to
nine in the Skyrme model, generated using sophisticated numerical algorithms.
Assuming the Skyrme model accurately represents the low energy limit of QCD,
these configurations correspond to the classical nuclear ground states of the
light elements. The solitons found are particularly symmetric, for example, the
charge seven skyrmion has icosahedral symmetry, and the shapes are shown to fit
a remarkable sequence defined by a geometric energy minimization (GEM) rule. We
also calculate the energies and sizes to within at least a few percent
accuracy. These calculations provide the basis for a future investigation of
the low energy vibrational modes of skyrmions and hence the possibility of
testing the Skyrme model against experiment.Comment: latex, 9 pages, 1 figure (fig1.gif
1958 Ohio Farm Income: Estimated Cash Receipts From Farm Marketing and Government Payments, by Counties and Major Commodity Groups
Interchain coherence of coupled Luttinger liquids at all orders in perturbation theory
We analyze the problem of Luttinger liquids coupled via a single-particle
hopping \tp and introduce a systematic diagrammatic expansion in powers of
\tp. An analysis of the scaling of the diagrams at each order allows us to
determine the power-law behavior versus \tp of the interchain hopping and of
the Fermi surface warp. In particular, for strong interactions, we find that
the exponents are dominated by higher-order diagrams producing an enhanced
coherence and a failure of linear-response theory. Our results are valid at any
finite order in \tp for the self-energy.Comment: 4 pages, 3 ps figures. Accepted for publication in Phys. Rev. Let
Charge-Spin Separation in 2D Fermi Systems: Singular Interactions as Modified Commutators, and Solution of 2D Hubbard Model in Bosonized Approximation
The general 2-dimensional fermion system with repulsive interactions
(typified by the Hubbard Model) is bosonized, taking into account the finite
on-shell forward scattering phase shift derived in earlier papers. By taking
this phase shift into account in the bosonic commutation relations a consistent
picture emerges showing the charge-spin separation and anomalous exponents of
the Luttinger liquid.Comment: Latex file 14 pages. email: [email protected]
- …