10,588 research outputs found
Sodium Entry during Action Potentials of Mammalian Neurons: Incomplete Inactivation and Reduced Metabolic Efficiency in Fast-Spiking Neurons
SummaryWe measured the time course of sodium entry during action potentials of mouse central neurons at 37°C to examine how efficiently sodium entry is coupled to depolarization. In cortical pyramidal neurons, sodium entry was nearly completely confined to the rising phase of the spike: only ∼25% more sodium enters than the theoretical minimum necessary for spike depolarization. However, in fast-spiking GABAergic neurons (cerebellar Purkinje cells and cortical interneurons), twice as much sodium enters as the theoretical minimum. The extra entry occurs because sodium channel inactivation is incomplete during the falling phase of the spike. The efficiency of sodium entry in different cell types is primarily a function of action potential shape and not cell-type-specific differences in sodium channel kinetics. The narrow spikes of fast-spiking GABAergic neurons result in incomplete inactivation of sodium channels; this reduces metabolic efficiency but likely enhances the ability to fire spikes at high frequency
Vector magnetic hysteresis of hard superconductors
Critical state problems which incorporate more than one component for the
magnetization vector of hard superconductors are investigated. The theory is
based on the minimization of a cost functional
which weighs the changes of the magnetic field vector within the sample. We
show that Bean's simplest prescription of choosing the correct sign for the
critical current density in one dimensional problems is just a particular
case of finding the components of the vector . is
determined by minimizing under the constraint , with a bounded set. Upon the selection of
different sets we discuss existing crossed field measurements and
predict new observable features. It is shown that a complex behavior in the
magnetization curves may be controlled by a single external parameter, i.e.:
the maximum value of the applied magnetic field .Comment: 10 pages, 9 figures, accepted in Phys. Rev.
Cosmon dark matter?
We investigate if the fluctuations of the scalar field mediating quintessence
-- the cosmon -- can play an important role in cosmology. Small fluctuations
with short wavelength behave similar to a relativistic gas. In contrast, the
contribution to the energy density from horizon size fluctuations may decrease
less rapidly than radiation. We discuss the possibility that the cosmon
fluctuations grow nonlinearly, form lumps and constitute the clustering dark
matter of the universe. Cosmon dark matter would lead to interesting
consequences for the equation of state and the coupling between quintessence
and dark matter.Comment: Published version,correction in appendix A, 43 pages, LaTe
Superconductivity in Dense Wires
becomes superconducting just below 40 K. Whereas porous
polycrystalline samples of can be synthesized from boron powders, in
this letter we demonstrate that dense wires of can be prepared by
exposing boron filaments to vapor. The resulting wires have a diameter of
160 , are better than 80% dense and manifest the full shielding in the superconducting state. Temperature-dependent
resistivity measurements indicate that is a highly conducting metal in
the normal state with = 0.38 -. Using this value, an
electronic mean free path, can be estimated, indicating
that wires are well within the clean limit. , , and
data indicate that manifests comparable or better superconducting
properties in dense wire form than it manifests as a sintered pellet.Comment: Figures' layout fixe
Comparing Infrared Dirac-Born-Infeld Brane Inflation to Observations
We compare the Infrared Dirac-Born-Infeld (IR DBI) brane inflation model to
observations using a Bayesian analysis. The current data cannot distinguish it
from the \LambdaCDM model, but is able to give interesting constraints on
various microscopic parameters including the mass of the brane moduli
potential, the fundamental string scale, the charge or warp factor of throats,
and the number of the mobile branes. We quantify some distinctive testable
predictions with stringy signatures, such as the large non-Gaussianity, and the
large, but regional, running of the spectral index. These results illustrate
how we may be able to probe aspects of string theory using cosmological
observations.Comment: 54 pages, 13 figures. v2: non-Gaussianity constraint has been applied
to the model; parameter constraints have tightened significantly, conclusions
unchanged. References added; v3, minor revision, PRD versio
Magnetization Relaxation via Quantum and Classical Vortex Motion in a Bose Glass Superconductor
I show that in Bose Glass superconductor with high and at low the
magnetization relaxation (S), dominated by quantum tunneling, is , which crosses over to the conventional classical rate at
higher and lower , with the crossover . I argue
that due to interactions between flux lines there exist three relaxation
regimes, depending on whether ,
corresponding to Strongly-pinned Bose Glass (SBG) with large , Mott
Insulator (MI) with vanishing S, and Weakly-pinned Bose Glass (WBG)
characterized by small . I discuss the effects of interactions on
and focus attention on the recent experiment which is consistently described by
the theory.Comment: 4 pages, self-unpacking uuencoded compressed postscript file with
figures already inside text; to appear in Phys. Rev. Lett.(1995
The Adiabatic Instability on Cosmology's Dark Side
We consider theories with a nontrivial coupling between the matter and dark
energy sectors. We describe a small scale instability that can occur in such
models when the coupling is strong compared to gravity, generalizing and
correcting earlier treatments. The instability is characterized by a negative
sound speed squared of an effective coupled dark matter/dark energy fluid. Our
results are general, and applicable to a wide class of coupled models and
provide a powerful, redshift-dependent tool, complementary to other
constraints, with which to rule many of them out. A detailed analysis and
applications to a range of models are presented in a longer companion paper.Comment: 4 pages, 1 figur
Intra- and interobserver reproducibility of pelvic ultrasound for the detection and measurement of endometriotic lesions
STUDY QUESTION: What is the interobserver and intraobserver reproducibility of pelvic ultrasound for the detection of endometriotic lesions? SUMMARY ANSWER: Pelvic ultrasound is highly reproducible for the detection of pelvic endometriotic lesions. WHAT IS KNOWN ALREADY: Transvaginal ultrasound (TVS) has been widely adopted as the first-line assessment for the diagnosis and assessment of pelvic endometriosis. Severity of endometriosis as assessed by ultrasound has been shown to have good concordance with laparoscopy (kappa 0.79). The reproducibility of TVS for assessment of ovarian mobility and pouch of Douglas obliteration using the 'sliding sign' has already been described in the literature. However, there is no available data in the literature to demonstrate the intraobserver repeatability of measurements for endometriotic cysts and nodules. STUDY DESIGN SIZE DURATION: This was a prospective observational cross-sectional study conducted over a period of 12 months. We included 50 consecutive women who were all examined by two operators (A and B) during their clinic attendance. PARTICIPANTS/MATERIALS SETTING METHODS: The study was carried out in a specialist endometriosis centre. We included all consecutive women who had ultrasound scans performed independently by two experienced operators during the same visit to the clinic. The outcomes of interest were the inter- and intraobserver reproducibility for the detection of endometriotic lesions. We also assessed repeatability of the measurements of lesion size. MAIN RESULTS AND THE ROLE OF CHANCE: There was a good level of agreement between operator A and operator B in detecting the presence of pelvic endometriotic lesions (k = 0.72). There was a very good level of agreement between operators in identifying endometriotic cysts (k = 0.88) and a good level of agreement in identifying endometriotic nodules (k = 0.61). The inter- and intraobserver repeatability of measuring endometriotic cysts was excellent (intra-class correlation (ICC) ≥ 0.98). There was good interobserver measurement repeatability for bowel nodules (ICC 0.88), but the results for nodules in the posterior compartment were poor (ICC 0.41). The intraobserver repeatability for nodule size measurements was good for both operators (ICC ≥0.86). LIMITATIONS REASONS FOR CAUTION: Within this cohort, there was insufficient data to perform a separate analysis for nodule size in the anterior compartment. All examinations were performed within a specialised unit with a high prevalence of deep endometriosis. Our findings may not apply to operators without intensive ultrasound training in the diagnosis of pelvic endometriosis. WIDER IMPLICATIONS OF THE FINDINGS: These findings are important because ultrasound has been widely accepted as the first-line investigation for the diagnosis of pelvic endometriosis, which often determines the need for future investigations and treatment. The detection and measurement of bowel nodules is essential for anticipation of surgical risk and planning surgical excision. STUDY FUNDING/COMPETING INTERESTS: The authors have no conflict of interest. No funding was obtained for this work
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