382 research outputs found
Study made of corrosion resistance of stainless steel and nickel alloys in nuclear reactor superheaters
Experiments performed under conditions found in nuclear reactor superheaters determine the corrosion rate of stainless steel and nickel alloys used in them. Electropolishing was the primary surface treatment before the corrosion test. Corrosion is determined by weight loss of specimens after defilming
Doping and Irradiation Controlled Vortex Pinning Behavior in BaFe2(As1-xPx)2 Single Crystals
We report on the systematic evolution of vortex pinning behavior in isovalent
doped single crystals of BaFe2(As1-xPx)2. Proceeding from optimal doped to
ovedoped samples, we find a clear transfor- mation of the magnetization
hysteresis from a fishtail behavior to a distinct peak effect followed by a
reversible magnetization and Bean Livingston surface barriers. Strong point
pinning dominates the vortex behavior at low fields whereas weak collective
pinning determines the behavior at higher fields. In addition to doping
effects, we show that particle irradiation by energetic protons can tune vortex
pinning in these materials.Comment: 4 pages, 4 figures,significant change of eraly version, accepted by
PRB rapid communication
Associations between Proprioceptive Neural Pathway Structural Connectivity and Balance in People with Multiple Sclerosis
Mobility and balance impairments are a hallmark of multiple sclerosis (MS), affecting nearly half of patients at presentation and resulting in decreased activity and participation, falls, injuries, and reduced quality of life. A growing body of work suggests that balance impairments in people with mild MS are primarily the result of deficits in proprioception, the ability to determine body position in space in the absence of vision. A better understanding of the pathophysiology of balance disturbances in MS is needed to develop evidence-based rehabilitation approaches. The purpose of the current study was to (1) map the cortical proprioceptive pathway in vivo using diffusion-weighted imaging and (2) assess associations between proprioceptive pathway white matter microstructural integrity and performance on clinical and behavioral balance tasks. We hypothesized that people with MS (PwMS) would have reduced integrity of cerebral proprioceptive pathways, and that reduced white matter microstructure within these tracts would be strongly related to proprioceptive-based balance deficits. We found poorer balance control on proprioceptive-based tasks and reduced white matter microstructural integrity of the cortical proprioceptive tracts in PwMS compared with age-matched healthy controls (HC). Microstructural integrity of this pathway in the right hemisphere was also strongly associated with proprioceptive-based balance control in PwMS and controls. Conversely, while white matter integrity of the right hemisphere’s proprioceptive pathway was significantly correlated with overall balance performance in HC, there was no such relationship in PwMS. These results augment existing literature suggesting that balance control in PwMS may become more dependent upon (1) cerebellar-regulated proprioceptive control, (2) the vestibular system, and/or (3) the visual system
Comparison of the Fermi-surface topologies of kappa-(BEDT-TTF)_2 Cu(NCS)_2 and its deuterated analogue
We have measured details of the quasi one-dimensional Fermi-surface sections
in the organic superconductor kappa-(BEDT-TTF)_2 Cu(NCS)_2 and its deuterated
analogue using angle-dependent millimetre-wave techniques. There are
significant differences in the corrugations of the Fermi surfaces in the
deuterated and undeuterated salts. We suggest that this is important in
understanding the inverse isotope effect, where the superconducting transition
temperature rises on deuteration. The data support models for superconductivity
which invoke electron-electron interactions depending on the topological
properties of the Fermi surface
Magnetic properties of the S=1/2 quasi square lattice antiferromagnet CuF2(H2O)2(pyz) (pyz=pyrazine) investigated by neutron scattering
We have performed elastic and inelastic neutron experiments on single crystal
samples of the coordination polymer compound CuF2(H2O)2(pyz) (pyz=pyrazine) to
study the magnetic structure and excitations. The elastic neutron diffraction
measurements indicate a collinear antiferromagnetic structure with moments
oriented along the [0.7 0 1] real-space direction and an ordered moment of 0.60
+/- 0.03 muB/Cu. This value is significantly smaller than the single ion
magnetic moment, reflecting the presence of strong quantum fluctuations. The
spin wave dispersion from magnetic zone center to the zone boundary points (0.5
1.5 0) and (0.5 0 1.5) can be described by a two dimensional Heisenberg model
with a nearest neighbor magnetic exchange constant J2d = 0.934 +/-0.0025 meV.
The inter-layer interaction Jperp in this compound is less than 1.5% of J2d.
The spin excitation energy at the (0.5 0.5 0.5) zone boundary point is reduced
when compared to the (0.5 1 0.5) zone boundary point by ~10.3 +/- 1.4 %. This
zone boundary dispersion is consistent with quantum Monte Carlo and series
expansion calculations which include corrections for quantum fluctuations to
linear spin wave theory.Comment: 7 pages, 6 figure
Test for interlayer coherence in a quasi-two-dimensional superconductor
Peaks in the magnetoresistivity of the layered superconductor
-(BEDT-TTF)Cu(NCS), measured in fields T applied
within the layers, show that the Fermi surface is extended in the interlayer
direction and enable the interlayer transfer integral (
meV) to be deduced. However, the quasiparticle scattering rate is
such that , implying that
-(BEDT-TTF)Cu(NCS) meets the criterion used to identify
interlayer incoherence. The applicability of this criterion to anisotropic
materials is thus shown to be questionable.Comment: 5 pages, 4 figure
Resistivity studies under hydrostatic pressure on a low-resistance variant of the quasi-2D organic superconductor kappa-(BEDT-TTF)2Cu[N(CN)2]Br: quest for intrinsic scattering contributions
Resistivity measurements have been performed on a low (LR)- and high
(HR)-resistance variant of the kappa-(BEDT-TTF)_2Cu[N(CN)_2]Br superconductor.
While the HR sample was synthesized following the standard procedure, the LR
crystal is a result of a somewhat modified synthesis route. According to their
residual resistivities and residual resistivity ratios, the LR crystal is of
distinctly superior quality. He-gas pressure was used to study the effect of
hydrostatic pressure on the different transport regimes for both variants. The
main results of these comparative investigations are (i) a significant part of
the inelastic-scattering contribution, which causes the anomalous rho(T)
maximum in standard HR crystals around 90 K, is sample dependent, i.e.
extrinsic in nature, (ii) the abrupt change in rho(T) at T* approx. 40 K from a
strongly temperature-dependent behavior at T > T* to an only weakly T-dependent
rho(T) at T < T* is unaffected by this scattering contribution and thus marks
an independent property, most likely a second-order phase transition, (iii)
both variants reveal a rho(T) proportional to AT^2 dependence at low
temperatures, i.e. for T_c < T < T_0, although with strongly sample-dependent
coefficients A and upper bounds for the T^2 behavior measured by T_0. The
latter result is inconsistent with the T^2 dependence originating from coherent
Fermi-liquid excitations.Comment: 8 pages, 6 figure
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