524 research outputs found
Effects of Elevated H\u3csup\u3e+\u3c/sup\u3e And P\u3csub\u3ei\u3c/sub\u3e on The Contractile Mechanics of Skeletal Muscle Fibres From Young and Old Men: Implications for Muscle Fatigue in Humans
The present study aimed to identify the mechanisms responsible for the loss in muscle power and increased fatigability with ageing by integrating measures of wholeâmuscle function with single fibre contractile mechanics. After adjusting for the 22% smaller muscle mass in old (73â89 years, n = 6) compared to young men (20â29 years, n = 6), isometric torque and power output of the knee extensors were, respectively, 38% and 53% lower with age. Fatigability was âŒ2.7âfold greater with age and strongly associated with reductions in the electricallyâevoked contractile properties. To test whether crossâbridge mechanisms could explain ageârelated decrements in knee extensor function, we exposed myofibres (n = 254) from the vastus lateralis to conditions mimicking quiescent muscle and fatiguing levels of acidosis (H+) (pH 6.2) and inorganic phosphate (Pi) (30 mm). The fatigueâmimicking condition caused marked reductions in force, shortening velocity and power and inhibited the lowâ to highâforce state of the crossâbridge cycle, confirming findings from nonâhuman studies that these ions act synergistically to impair crossâbridge function. Other than severe ageârelated atrophy of fast fibres (â55%), contractile function and the depressive effects of the fatigueâmimicking condition did not differ in fibres from young and old men. The selective loss of fast myosin heavy chain II muscle was strongly associated with the ageârelated decrease in isometric torque (r = 0.785) and power (r = 0.861). These data suggest that the ageârelated loss in muscle strength and power are primarily determined by the atrophy of fast fibres, but the ageârelated increased fatigability cannot be explained by an increased sensitivity of the crossâbridge to H+ and Pi
Glasslike Arrest in Spinodal Decomposition as a Route to Colloidal Gelation
Colloid-polymer mixtures can undergo spinodal decomposition into colloid-rich
and colloid-poor regions. Gelation results when interconnected colloid-rich
regions solidify. We show that this occurs when these regions undergo a glass
transition, leading to dynamic arrest of the spinodal decomposition. The
characteristic length scale of the gel decreases with increasing quench depth,
and the nonergodicity parameter exhibits a pronounced dependence on scattering
vector. Mode coupling theory gives a good description of the dynamics, provided
we use the full static structure as input.Comment: 14 pages, 4 figures; replaced with published versio
Generality of shear thickening in suspensions
Suspensions are of wide interest and form the basis for many smart fluids.
For most suspensions, the viscosity decreases with increasing shear rate, i.e.
they shear thin. Few are reported to do the opposite, i.e. shear thicken,
despite the longstanding expectation that shear thickening is a generic type of
suspension behavior. Here we resolve this apparent contradiction. We
demonstrate that shear thickening can be masked by a yield stress and can be
recovered when the yield stress is decreased below a threshold. We show the
generality of this argument and quantify the threshold in rheology experiments
where we control yield stresses arising from a variety of sources, such as
attractions from particle surface interactions, induced dipoles from applied
electric and magnetic fields, as well as confinement of hard particles at high
packing fractions. These findings open up possibilities for the design of smart
suspensions that combine shear thickening with electro- or magnetorheological
response.Comment: 11 pages, 9 figures, accepted for publication in Nature Material
Reexamination of Quantum Bit Commitment: the Possible and the Impossible
Bit commitment protocols whose security is based on the laws of quantum
mechanics alone are generally held to be impossible. In this paper we give a
strengthened and explicit proof of this result. We extend its scope to a much
larger variety of protocols, which may have an arbitrary number of rounds, in
which both classical and quantum information is exchanged, and which may
include aborts and resets. Moreover, we do not consider the receiver to be
bound to a fixed "honest" strategy, so that "anonymous state protocols", which
were recently suggested as a possible way to beat the known no-go results are
also covered. We show that any concealing protocol allows the sender to find a
cheating strategy, which is universal in the sense that it works against any
strategy of the receiver. Moreover, if the concealing property holds only
approximately, the cheat goes undetected with a high probability, which we
explicitly estimate. The proof uses an explicit formalization of general two
party protocols, which is applicable to more general situations, and a new
estimate about the continuity of the Stinespring dilation of a general quantum
channel. The result also provides a natural characterization of protocols that
fall outside the standard setting of unlimited available technology, and thus
may allow secure bit commitment. We present a new such protocol whose security,
perhaps surprisingly, relies on decoherence in the receiver's lab.Comment: v1: 26 pages, 4 eps figures. v2: 31 pages, 5 eps figures; replaced
with published version; title changed to comply with puzzling Phys. Rev.
regulations; impossibility proof extended to protocols with infinitely many
rounds or a continuous communication tree; security proof of decoherence
monster protocol expanded; presentation clarifie
Reversal of infall in SgrB2(M) revealed by Herschel/HIFI observations of HCN lines at THz frequencies
To investigate the accretion and feedback processes in massive star
formation, we analyze the shapes of emission lines from hot molecular cores,
whose asymmetries trace infall and expansion motions. The high-mass star
forming region SgrB2(M) was observed with Herschel/HIFI (HEXOS key project) in
various lines of HCN and its isotopologues, complemented by APEX data. The
observations are compared to spherically symmetric, centrally heated models
with density power-law gradient and different velocity fields (infall or
infall+expansion), using the radiative transfer code RATRAN. The HCN line
profiles are asymmetric, with the emission peak shifting from blue to red with
increasing J and decreasing line opacity (HCN to HCN). This is most
evident in the HCN 12--11 line at 1062 GHz. These line shapes are reproduced by
a model whose velocity field changes from infall in the outer part to expansion
in the inner part. The qualitative reproduction of the HCN lines suggests that
infall dominates in the colder, outer regions, but expansion dominates in the
warmer, inner regions. We are thus witnessing the onset of feedback in massive
star formation, starting to reverse the infall and finally disrupting the whole
molecular cloud. To obtain our result, the THz lines uniquely covered by HIFI
were critically important.Comment: A&A, HIFI special issue, accepte
Studies on the clinical significance of nonesterified and total cholesterol in urine
Gas-liquid chromatographic determinations of nonesterified and total urinary cholesterol were performed in 137 normals, 264 patients with various internal diseases without evidence of neoplasias or diseases of the kidney or urinary tract, 497 patients with malignancies and 236 patients with diseases of the kidney, urinary tract infections or prostatic adenoma with residual urine. A normal range (mean±2 SD) of 0.2â2.2 mg/24 hours nonesterified cholesterol (NEC) and of 0.3â3.0 mg/24 hours total cholesterol (TC) was calculated.
Values of urinary cholesterol excretion were independent of age and sex and did not correlate with cholesterol levels in plasma. Patients with various internal diseases, without evidence of neoplasias nor diseases of the kidney or obstruction of the urinary tract, showed normal urinary cholesterol excretions, as did patients with infections of the urinary tract.
However, elevated urinary cholesterol was found in patients with diseases of the kidney or urinary tract obstruction (prostatic adenoma with residual urine), malignant diseases of the urogenital tract and metastasing carcinoma of the breast. In patients with other malignant diseases urinary cholesterol was usually normal.
Lesions of the urothelial cell membranes are considered to be the most likely cause of urinary cholesterol hyperexcretion. The clinical value of urinary cholesterol determinations as a possible screening test for urogenital carcinomas in unselected populations is limited by lacking specificity, expensive methodology and low prevalence of the mentioned carcinomas, although elevated urinary cholesterol excretions have been observed in early clinical stages of urogenital cancers
Herschel observations of deuterated water towards Sgr B2(M)
Observations of HDO are an important complement for studies of water, because
they give strong constraints on the formation processes -- grain surfaces
versus energetic process in the gas phase, e.g. in shocks. The HIFI
observations of multiple transitions of HDO in Sgr~B2(M) presented here allow
the determination of the HDO abundance throughout the envelope, which has not
been possible before with ground-based observations only. The abundance
structure has been modeled with the spherical Monte Carlo radiative transfer
code RATRAN, which also takes radiative pumping by continuum emission from dust
into account. The modeling reveals that the abundance of HDO rises steeply with
temperature from a low abundance () in the outer envelope
at temperatures below 100~K through a medium abundance () in
the inner envelope/outer core, at temperatures between 100 and 200~K, and
finally a high abundance () at temperatures above 200~K in
the hot core.Comment: A&A HIFI special issue, accepte
Fluctuations in the coarsening dynamics of the O(N) model: are they similar to those in glassy systems?
We study spatio-temporal fluctuations in the non-equilibrium dynamics of the
d dimensional O(N) in the large N limit. We analyse the invariance of the
dynamic equations for the global correlation and response in the slow ageing
regime under transformations of time. We find that these equations are
invariant under scale transformations. We extend this study to the action in
the dynamic generating functional finding similar results. This model therefore
falls into a different category from glassy problems in which full
time-reparametrisation invariance, a larger symmetry that emcompasses time
scale invariance, is expected to be realised asymptotically. Consequently, the
spatio-temporal fluctuations of the large N O(N) model should follow a
different pattern from that of glassy systems. We compute the fluctuations of
local, as well as spatially separated, two-field composite operators and
responses, and we confront our results with the ones found numerically for the
3d Edwards-Anderson model and kinetically constrained lattice gases. We analyse
the dependence of the fluctuations of the composite operators on the growing
domain length and we compare to what has been found in super-cooled liquids and
glasses. Finally, we show that the development of time-reparametrisation
invariance in glassy systems is intimately related to a well-defined and finite
effective temperature, specified from the modification of the
fluctuation-dissipation theorem out of equilibrium. We then conjecture that the
global asymptotic time-reparametrisation invariance is broken down to time
scale invariance in all coarsening systems.Comment: 57 pages, 5 figure
Herschel observations of EXtra-Ordinary Sources: The Terahertz spectrum of Orion KL seen at high spectral resolution
We present the first high spectral resolution observations of Orion KL in the
frequency ranges 1573.4 - 1702.8 GHz (band 6b) and 1788.4 - 1906.8 GHz (band
7b) obtained using the HIFI instrument on board the Herschel Space Observatory.
We characterize the main emission lines found in the spectrum, which primarily
arise from a range of components associated with Orion KL including the hot
core, but also see widespread emission from components associated with
molecular outflows traced by H2O, SO2, and OH. We find that the density of
observed emission lines is significantly diminished in these bands compared to
lower frequency Herschel/HIFI bands.Comment: Accepted for publication in the Herschel HIFI special issue of
Astronomy and Astrophysics Letters, 5 pages, 3 figure
Herschel observations of extra-ordinary sources: Detection of Hydrogen Fluoride in absorption towards Orion~KL
We report a detection of the fundamental rotational transition of hydrogen
fluoride in absorption towards Orion KL using Herschel/HIFI. After the removal
of contaminating features associated with common molecules ("weeds"), the HF
spectrum shows a P-Cygni profile, with weak redshifted emission and strong
blue-shifted absorption, associated with the low-velocity molecular outflow. We
derive an estimate of 2.9 x 10^13 cm^-2 for the HF column density responsible
for the broad absorption component. Using our best estimate of the H2 column
density within the low-velocity molecular outflow, we obtain a lower limit of
~1.6 x 10^-10 for the HF abundance relative to hydrogen nuclei, corresponding
to 0.6% of the solar abundance of fluorine. This value is close to that
inferred from previous ISO observations of HF J=2--1 absorption towards Sgr B2,
but is in sharp contrast to the lower limit of 6 x 10^-9 derived by Neufeld et
al. (2010) for cold, foreground clouds on the line of sight towards G10.6-0.4.Comment: 5 pages, 3 figures, paper to be published in the Herschel special
issue of A&A letter
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