130 research outputs found
Importance of In-Plane Anisotropy in the Quasi Two-Dimensional Antiferromagnet BaNiVO
The phase diagram of the quasi two-dimensional antiferromagnet
BaNiVO is studied by specific heat, thermal expansion,
magnetostriction, and magnetization for magnetic fields applied perpendicular
to . At T, a crossover to a high-field state,
where increases linearly, arises from a competition of intrinsic and
field-induced in-plane anisotropies. The pressure dependences of and
are interpreted using the picture of a pressure-induced in-plane
anisotropy. Even at zero field and ambient pressure, in-plane anisotropy cannot
be neglected, which implies deviations from pure
Berezinskii-Kosterlitz-Thouless behavior.Comment: 4 pages, 4 figure
Double superconducting transition in the filled skutterudite PrOs4Sb12 and sample characterizations
A thorough characterization of many samples of the filled skutterudite
compound PrOs4Sb12 is provided. We find that the double superconducting
transition in the specific heat Tc1~1.89K and Tc2~1.72K tends to appear in
samples with a large residual resistivity ratio, large specific heat jump at
the superconducting transition and with the highest absolute value of the
specific heat above Tc1. However, we present evidence which casts doubt on the
intrinsic nature of the double superconducting transition. The ratio of the two
specific heat jumps \Delta C(Tc1)/\Delta C(Tc2) shows a wide range of values on
crystals from different batches but also within the same batch. This ratio was
strongly reduced by polishing a sample down to 120um. Remarkably, three samples
exhibit a single sharp transition of ~15mK in width at Tc~1.7K. The normalized
specific heat jump (C-Cnormal)/Cnormal at Tc of two of them is higher than ~32%
so larger than the sum of the two specific heat jumps when a double transition
exists. As an evidence of better quality, the slope in the transition is at
least two time steeper.
We discuss the origins of the double transition; in particular we consider,
based on X-ray diffraction results, a scenario involving Pr-vacancies. The
superconducting phase diagram under magnetic field of a sample with a single
transition is fitted with a two-band model taking into account the good values
for the gap as deduced from thermal conductivity measurements.Comment: 10 pages, 9 figures, 2 tables, submitted to Physical review
Differential regulation of wild-type and mutant alpha-synuclein binding to synaptic membranes by cytosolic factors
BACKGROUND: Alpha-Synuclein (alpha-syn), a 140 amino acid protein associated with presynaptic membranes in brain, is a major constituent of Lewy bodies in Parkinson's disease (PD). Three missense mutations (A30P, A53T and E46K) in the alpha-syn gene are associated with rare autosomal dominant forms of familial PD. However, the regulation of alpha-syn's cellular localization in neurons and the effects of the PD-linked mutations are poorly understood. RESULTS: In the present study, we analysed the ability of cytosolic factors to regulate alpha-syn binding to synaptic membranes. We show that co-incubation with brain cytosol significantly increases the membrane binding of normal and PD-linked mutant alpha-syn. To characterize cytosolic factor(s) that modulate alpha-syn binding properties, we investigated the ability of proteins, lipids, ATP and calcium to modulate alpha-syn membrane interactions. We report that lipids and ATP are two of the principal cytosolic components that modulate Wt and A53T alpha-syn binding to the synaptic membrane. We further show that 1-O-hexadecyl-2-acetyl-sn-glycero-3-phosphocholine (C16:0 PAF) is one of the principal lipids found in complex with cytosolic proteins and is required to enhance alpha-syn interaction with synaptic membrane. In addition, the impaired membrane binding observed for A30P alpha-syn was significantly mitigated by the presence of protease-sensitive factors in brain cytosol. CONCLUSION: These findings suggest that endogenous brain cytosolic factors regulate Wt and mutant alpha-syn membrane binding, and could represent potential targets to influence alpha-syn solubility in brain
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