1,189 research outputs found
GINZBURG-LANDAU THEORY OF VORTICES IN -WAVE SUPERCONDUCTORS
Ginzburg-Landau theory is used to study the properties of single vortices and
of the Abrikosov vortex lattice in a superconductor. For a single
vortex, the -wave order parameter has the expected four-lobe structure in a
ring around the core and falls off like at large distances. The
topological structure of the -wave order parameter consists of one
counter-rotating unit vortex, centered at the core, surrounded by four
symmetrically placed positive unit vortices. The Abrikosov lattice is shown to
have a triangular structure close to and an oblique structure at lower
temperatures. Comparison is made to recent neutron scattering data.Comment: 4 pages, REVTeX, 3 figures available upon reques
Antibody responses to nasopharyngeal carriage of Streptococcus pneumoniae in adults: A longitudinal household study
Background. Natural immunity to Streptococcus pneumoniae is thought to be induced by exposure to S. pneumoniae or cross-reactive antigens. No longitudinal studies of carriage of and immune responses to S. pneumoniae have been conducted using sophisticated immunological laboratory techniques.Methods. We enrolled 121 families with young children into this study. Nasopharyngeal (NP) swabs were collected monthly for 10 months from all family members and were cultured in a standard fashion. Cultured S. pneumoniae isolates were serotyped. At the beginning (month 0) and end (month 10) of the study, venous blood was collected from family members 118 years old. Serotype-specific antipolysaccharide immunoglobulin G (IgG) and functional antibody and antibodies to pneumolysin, pneumococcal surface protein A (PspA), and pneumococcal surface antigen A (PsaA) were measured in paired serum samples.Results. Levels of anticapsular IgG increased significantly after carriage of serotypes 9V, 14, 18C, 19F, and 23F by an individual or family member. For serotype 14, a higher level of anticapsular IgG at the beginning of the study was associated with reduced odds of carriage (P = .0006). There was a small (similar to 20%) but significant increase in titers of antibodies to PsaA and pneumolysin but no change in titers of antibody to PspA.Conclusions. Adults respond to NP carriage by mounting anticapsular and weak antiprotein antibody responses, and naturally induced anticapsular IgG can prevent carriage
Understanding the effect of cognitive/brain reserve and depression on regional atrophy in early Alzheimer’s disease
Introduction: Depression in patients with mild cognitive impairment (MCI) and dementia of the Alzheimer’s type (AD) is associated with worse prognosis. Indeed, depressed MCI patients have worse cognitive performance and greater loss of gray-matter volume in several brain areas. To date, knowledge of the factors that can mitigate this detrimental effect is still limited. The aim of the present study was to understand in what way cognitive reserve/brain reserve and depression interact and are linked to regional atrophy in early stage AD.
Methods: Depression was evaluated with the Patient Health Questionnaire-9 in 90 patients with early AD, and a cutoff of ≥ 5 was used to separate depressed (n = 44) from non-depressed (n = 46) patients. Each group was further stratified into high/low cognitive reserve/brain reserve. Cognitive reserve was calculated using years of education as proxy, while normalized parenchymal volumes were used to estimate brain reserve. Voxel-based morphometry was carried out to extract and analyze gray-matter maps. 2 × 2 ANCOVAs were run to test the effect of the reserve-by-depression interaction on gray matter. Age and hippocampal ratio were used as covariates. Composite indices of major cognitive domains were also analyzed with comparable models.
Results: No reserve-by-depression interaction was found in the analytical models of gray matter. Depression was associated with less gray matter volume in the cerebellum and parahippocampal gyrus. The brain reserve-by-depression interaction was a significant predictor of executive functioning. Among those with high brain reserve, depressed patients had poorer executive skills. No significant results were found in association with cognitive reserve.
Conclusion: These findings suggest that brain reserve may modulate the association between neurodegeneration and depression in patients with MCI and dementia of the AD type, influencing in particular executive functioning
Biochem Soc Trans
Abnormal protein aggregation and intracellular or extracellular accumulation of misfolded and aggregated proteins are key events in the pathogenesis of different neurodegenerative diseases. Furthermore, endoplasmic reticulum stress and impairment of the ubiquitin-proteasome system probably contribute to neurodegeneration in these diseases. A characteristic feature of AD (Alzheimer's disease) is the abnormal accumulation of Abeta (amyloid beta-peptide) in the brain. Evidence shows that the AD-associated PS (presenilin) also forms aggregates under certain conditions and that another AD-associated protein, ubiquilin-1, controls protein aggregation and deposition of aggregated proteins. Here, we review the current knowledge of ubiquilin-1 and PS in protein aggregation and related events that potentially influence neurodegeneration
Field induced state and marginal stability of high-Tc superconductors
It is shown that the {\em complex} component is generated in d-wave
superconductor in the magnetic field. As one enters superconducting state at
finite field the normal to superconducting transition occurs into bulk
state . The driving force for the transition is the
linear coupling between magnetic field and non zero magnetization of the
condensate. The external magnetic field violates parity
and time reversal symmetries and the nodal quasiparticle states respond by
generating the component of the order parameter, with the magnitude
estimated to be on the order of few Kelvin. Parity (P) and time reversal (T)
symmetries are violated in this state.Comment: 4 pages, latex file with two eps figure file
Ginzburg Landau theory for d-wave pairing and fourfold symmetric vortex core structure
The Ginzburg Landau theory for d_{x^2-y^2}-wave superconductors is
constructed, by starting from the Gor'kov equation with including correction
terms up to the next order of ln(T_c/T). Some of the non-local correction terms
are found to break the cylindrical symmetry and lead to the fourfold symmetric
core structure, reflecting the internal degree of freedom in the pair
potential. Using this extended Ginzburg Landau theory, we investigate the
fourfold symmetric structure of the pair potential, current and magnetic field
around an isolated single vortex, and clarify concretely how the vortex core
structure deviates from the cylindrical symmetry in the d_{x^2-y^2}-wave
superconductors.Comment: 12 pages including 8 eps figs, LaTeX with jpsj.sty & epsfi
X-ray Raman scattering study of aligned polyfluorene
We present a non-resonant inelastic x-ray scattering study at the carbon
K-edge on aligned poly[9,9-bis(2-ethylhexyl)-fluorene-2,7-diyl] and show that
the x-ray Raman scattering technique can be used as a practical alternative to
x-ray absorption measurements. We demonstrate that this novel method can be
applied to studies on aligned -conjugated polymers complementing
diffraction and optical studies. Combining the experimental data and a very
recently proposed theoretical scheme we demonstrate a unique property of x-ray
Raman scattering by performing the symmetry decomposition on the density of
unoccupied electronic states into - and -type symmetry contributions.Comment: 19 pages, 8 figure
The Effects of Phase Separation in the Cuprate Superconductors
Phase separation has been observed by several different experiments and it is
believed to be closely related with the physics of cuprates but its exactly
role is not yet well known. We propose that the onset of pseudogap phenomenon
or the upper pseudogap temperature has its origin in a spontaneous phase
separation transition at the temperature . In order to perform
quantitative calculations, we use a Cahn-Hilliard (CH) differential equation
originally proposed to the studies of alloys and on a spinodal decomposition
mechanism. Solving numerically the CH equation it is possible to follow the
time evolution of a coarse-grained order parameter which satisfies a
Ginzburg-Landau free-energy functional commonly used to model superconductors.
In this approach, we follow the process of charge segregation into two main
equilibrium hole density branches and the energy gap normally attributed to the
upper pseudogap arises as the free-energy potential barrier between these two
equilibrium densities below . This simulation provides quantitative
results %on the hole doping and temperature %dependence of the degree of the
charge inhomogeneity in agreement with %some experiments and the simulations
reproduce the observed stripe and granular pattern of segregation. Furthermore,
with a Bogoliubov-deGennes (BdG) local superconducting critical temperature
calculation for the lower pseudogap or the onset of local superconductivity, it
yields novel interpretation of several non-conventional measurements on
cuprates.Comment: Published versio
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