1,189 research outputs found
Ipsilateral common iliac artery plus femoral artery clamping for inducing sciatic nerve ischemia/reperfusion injury in rats: a reliable and simple method
The aim of this study was to develop a practical model of sciatic ischemia reperfusion (I/R) injury producing serious neurologic deficits and being technically feasible compared with the current time consuming or ineffective models. Thirty rats were divided into 6 groups (n = 5). Animal were anesthetized by using ketamine (50 mg/kg) and xylazine (4 mg/kg). Experimental groups included a sham-operated group and five I/R groups with different reperfusion time intervals (0 h, 3 h, 1 d, 4 d, 7 d). In I/R groups, the right common iliac artery and the right femoral artery were clamped for 3 hrs. Sham-operated animals underwent only laparotomy without induction of ischemia. Just before euthanasia, behavioral scores (based on gait, grasp, paw position, and pinch sensitivity) were obtained and then sciatic nerves were removed for light-microscopy studies (for ischemic fiber degeneration (IFD) and edema). Behavioral score deteriorated among the ischemic groups compared with the control group (p < 0.01), with maximal behavioral deficit occurring at 4 days of reperfusion. Axonal swelling and IFD were found to happen only after 4 and 7 days, respectively. Our observations led to an easy-to-use but strong enough method for inducing and studying I/R injury in peripheral nerves
Selenium uptake, translocation and speciation in wheat supplied with selenate or selenite
Selenite can be a dominant form of selenium (Se) in aerobic soils; however, unlike selenate, the mechanism of selenite uptake by plants remains unclear. Uptake, translocation and Se speciation in wheat (Triticum aestivum) supplied with selenate or selenite, or both, were investigated in hydroponic experiments. The kinetics of selenite influx was determined in short-term (30 min) experiments. Selenium speciation in the water-extractable fraction of roots and shoots was determined by HPLC-ICPMS. Plants absorbed similar amounts of Se within 1 d when supplied with selenite or selenate. Selenate and selenite uptake were enhanced in sulphur-starved and phosphorus-starved plants, respectively. Phosphate markedly increased K-m of the selenite influx. Selenate and selenite uptake were both metabolically dependent. Selenite was rapidly converted to organic forms in roots, with limited translocation to shoots. Selenomethionine, selenomethionine Se-oxide, Se-methyl-selenocysteine and several other unidentified Se species were detected in the root extracts and xylem sap from selenite-treated plants. Selenate was highly mobile in xylem transport, but little was assimilated to organic forms in 1 d. The presence of selenite decreased selenate uptake and xylem transport. Selenite uptake is an active process likely mediated, at least partly, by phosphate transporters. Selenite and selenate differ greatly in the ease of assimilation and xylem transport
Two Energy Scales and two Quasiparticle Dynamics in the Superconducting State of Underdoped Cuprates
The superconducting state of underdoped cuprates is often described in terms
of a single energy-scale, associated with the maximum of the (d-wave) gap.
Here, we report on electronic Raman scattering results, which show that the gap
function in the underdoped regime is characterized by two energy scales,
depending on doping in opposite manners. Their ratios to the maximum critical
temperature are found to be universal in cuprates. Our experimental results
also reveal two different quasiparticle dynamics in the underdoped
superconducting state, associated with two regions of momentum space: nodal
regions near the zeros of the superconducting gap and antinodal regions. While
antinodal quasiparticles quickly loose coherence as doping is reduced, coherent
nodal quasiparticles persist down to low doping levels. A theoretical analysis
using a new sum-rule allows us to relate the low-frequency-dependence of the
Raman response to the temperature-dependence of the superfluid density, both
controlled by nodal excitations.Comment: 16 pages, 5 figure
The A-B transition in superfluid helium-3 under confinement in a thin slab geometry
The influence of confinement on the topological phases of superfluid 3He is
studied using the torsional pendulum method. We focus on the phase transition
between the chiral A-phase and the time-reversal-invariant B-phase, motivated
by the prediction of a spatiallymodulated (stripe) phase at the A-B phase
boundary. We confine superfluid 3He to a single 1.08 {\mu}m thick nanofluidic
cavity incorporated into a high-precision torsion pendulum, and map the phase
diagram between 0.1 and 5.6 bar. We observe only small supercooling of the
A-phase, in comparison to bulk or when confined in aerogel. This has a
non-monotonic pressure dependence, suggesting that a new intrinsic B-phase
nucleation mechanism operates under confinement, mediated by the putative
stripe phase. Both the phase diagram and the relative superfluid fraction of
the A and B phases, show that strong coupling is present at all pressures, with
implications for the stability of the stripe phase.Comment: 6 figures, 1 table + supplemental informatio
Optical Lattices: Theory
This chapter presents an overview of the properties of a Bose-Einstein
condensate (BEC) trapped in a periodic potential. This system has attracted a
wide interest in the last years, and a few excellent reviews of the field have
already appeared in the literature (see, for instance, [1-3] and references
therein). For this reason, and because of the huge amount of published results,
we do not pretend here to be comprehensive, but we will be content to provide a
flavor of the richness of this subject, together with some useful references.
On the other hand, there are good reasons for our effort. Probably, the most
significant is that BEC in periodic potentials is a truly interdisciplinary
problem, with obvious connections with electrons in crystal lattices, polarons
and photons in optical fibers. Moreover, the BEC experimentalists have reached
such a high level of accuracy to create in the lab, so to speak, paradigmatic
Hamiltonians, which were first introduced as idealized theoretical models to
study, among others, dynamical instabilities or quantum phase transitions.Comment: Chapter 13 in Part VIII: "Optical Lattices" of "Emergent Nonlinear
Phenomena in Bose-Einstein Condensates: Theory and Experiment," edited by P.
G. Kevrekidis, D. J. Frantzeskakis, and R. Carretero-Gonzalez (Springer
Series on Atomic, Optical, and Plasma Physics, 2007) - pages 247-26
Surface features, rotation and atmospheric variability of ultra cool dwarfs
Photometric I band light curves of 21 ultra cool M and L dwarfs are
presented. Variability with amplitudes of 0.01 to 0.055 magnitudes (RMS) with
typical timescales of an hour to several hours are discovered in half of these
objects. Periodic variability is discovered in a few cases, but interestingly
several variable objects show no significant periods, even though the
observations were almost certainly sensitive to the expected rotation periods.
It is argued that in these cases the variability is due to the evolution of the
surface features on timescales of a few hours. This is supported in the case of
2M1145 for which no common period is found in two separate light curves. It is
speculated that these features are photospheric dust clouds, with their
evolution possibly driven by rotation and turbulence. An alternative
possibility is magnetically-induced surface features. However, chromospheric
activity undergoes a sharp decrease between M7 and L1, whereas a greater
occurrence of variability is observed in objects later than M9, lending support
to the dust interpretation.Comment: To appear in "Ultracool Dwarf Stars" (Lecture Notes in Physics),
H.R.A. Jones, I. Steele (eds), Springer-Verlag, 2001. Also available from
http://www.mpia-hd.mpg.de/homes/calj/ultra.htm
Dementia Caregiver Burden: A Research Update and Critical Analysis
Purpose of Review: This article provides an updated review of the determinants of caregiver burden and depression, with a focus on care demands and especially the differential effects of various neuropsychiatric symptoms or symptom clusters. Moreover, studies on caregivers for frontotemporal and Lewy body dementias were referred to in order to identify differences and similarities with the mainstream literature based largely on Alzheimer caregivers. Recent Findings: As a group, neuropsychiatric symptoms are most predictive of caregiver burden and depression regardless of dementia diagnosis, but the effects appear to be driven primarily by disruptive behaviors (e.g., agitation, aggression, disinhibition), followed by delusions and mood disturbance. Disruptive behaviors are more disturbing partly because of the adverse impact on the emotional connection between the caregiver and the care-recipient and partly because they exacerbate difficulties in other domains (e.g., caring for activities of daily living). In behavioral variant frontotemporal dementia, not only are these disruptive behaviors more prominent but they are also more disturbing due to the care-recipient’s insensitivity to others’ feelings. In Lewy body dementia, visual hallucinations also appear to be distressing. Summary: The disturbing nature of disruptive behaviors cuts across dementia conditions, but the roles played by symptoms that are unique or particularly serious in a certain condition need to be explored further
Dislocations and vortices in pair density wave superconductors
With the ground breaking work of the Fulde, Ferell, Larkin, and Ovchinnikov
(FFLO), it was realized that superconducting order can also break translational
invariance; leading to a phase in which the Cooper pairs develop a coherent
periodic spatially oscillating structure. Such pair density wave (PDW)
superconductivity has become relevant in a diverse range of systems, including
cuprates, organic superconductors, heavy fermion superconductors, cold atoms,
and high density quark matter. Here we show that, in addition to charge density
wave (CDW) order, there are PDW ground states that induce spin density wave
(SDW) order when there is no applied magnetic field. Furthermore, we show that
PDW phases support topological defects that combine dislocations in the induced
CDW/SDW order with a fractional vortex in the usual superconducting order.
These defects provide a mechanism for fluctuation driven non-superconducting
CDW/SDW phases and conventional vortices with CDW/SDW order in the core.Comment: 6 pages,1 figure, 1 tabl
Reaction rates and transport in neutron stars
Understanding signals from neutron stars requires knowledge about the
transport inside the star. We review the transport properties and the
underlying reaction rates of dense hadronic and quark matter in the crust and
the core of neutron stars and point out open problems and future directions.Comment: 74 pages; commissioned for the book "Physics and Astrophysics of
Neutron Stars", NewCompStar COST Action MP1304; version 3: minor changes,
references updated, overview graphic added in the introduction, improvements
in Sec IV.A.
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