6,813 research outputs found
The validity of capillary blood sampling in the determination of human growth hormone concentration during exercise in men
This is an open access article - Copyright © 2004 BMJ Publishing Group LtdBACKGROUND: Studies measuring human growth hormone (hGH) in blood during exercise have mainly used venous sampling. The invasive nature of this procedure makes evaluation of hGH impossible in various exercise environments.
OBJECTIVE: To determine whether capillary sampling could offer an alternative sampling method.
METHODS: Capillary and venous blood samples were collected for determination of hGH at the end of each exercise stage during an incremental exercise test in 16 male club level competitive cyclists (mean (SD) age 30.8 (8.0) years, body mass 72.2 (7.1) kg, body fat 12.9 (3.5)%, peak oxygen consumption 4.18 (0.46) lâ
minâ1). Linear regression, from a plot of venous v capillary blood hGH concentration, showed a correlation coefficient of r = 0.986 (p<0.001). When geometric means and log transformations were used, a coefficient of variation of 14.2% was demonstrated between venous and capillary flow for hGH concentration. The mean ratio limits of agreement were 0.62 (1.72)âthat is, 95% of the ratios were contained between 0.36 and 1.07, with a mean of 0.62.
CONCLUSIONS: Capillary blood sampling is an acceptable alternative to venous sampling for determining hGH concentration during rest and exercise. Sample sites should not be used interchangeably: one site should be chosen and its use standardised
Two-stage clustering in genotype-by-environment analyses with missing data
Cluster analysis has been commonly used in genotype-by-environment (G x E) analyses, but current methods are inadequate when the data matrix is incomplete. This paper proposes a new method, referred to as two-stage clustering, which relies on a partitioning of squared Euclidean distance into
two independent components, the G x E interaction and the genotype main effect. These components are used in the first and second stages of clustering respectively. Two-stage clustering forms the basis for imputing missing values in the G x E matrix so that a more complete data array is available for other GxE analyses. Imputation for a given genotype uses information from genotypes with similar interaction profiles. This imputation method is shown to improve on an existing nearest cluster method that confounds the G x E interaction and the genotype main effect
Properties of the Strange Axial Mesons in the Relativized Quark Model
We studied properties of the strange axial mesons in the relativized quark
model. We calculated the decay constant in the quark model and showed how
it can be used to extract the mixing angle
() from the weak decay . The ratio is the most sensitive
measurement and also the most reliable since the largest of the theoretical
uncertainties factor out. However the current bounds extracted from the
TPC/Two-Gamma collaboration measurements are rather weak: we typically obtain
at 68\% C.L. We also calculated the
strong OZI-allowed decays in the pseudoscalar emission model and the flux-tube
breaking model and extracted a mixing angle of . Our analysis also indicates that the heavy quark limit does not give a
good description of the strange mesons.Comment: Revised version to be published in Phys. Rev. D. Minor changes. Latex
file uses revtex version 3 and epsfig, 4 postcript figures are attached. The
full postcript version with embedded figures is available at
ftp://ftp.physics.carleton.ca/pub/theory/godfrey/ocipc9512.ps.
The Effect of a Magnetic Field on the Acoustoelectric current in a Narrow Channel
The effect of a perpendicular magnetic field on the quantized current induced
by a surface acoustic wave in a quasi-1D channel is studied. The channel has
been produced experimentally in a GaAs heterostructure by shallow etching
techniques and by the application of a negative gate voltage to Schottky split
gates. Commensurability oscillations of the quantized current in this
constriction have been observed in the interval of current between quantized
plateaus. The results can be understood in terms of a moving quantum dot with
the electron in the dot tunneling into the adjacent two-dimensional region. The
goal is to explain qualitatively the mechanism for the steplike nature of the
acoustoelectric current as a function of gate voltage and the oscillations when
a magnetic field is applied. A transfer Hamiltonian formalism is employed.Comment: 5 pages, 2 figure
Spin-dependent Scattering by a Potential Barrier on a Nanotube
The electron spin effects on the surface of a nanotube have been considered
through the spin-orbit interaction (SOI), arising from the electron confinement
on the surface of the nanotube. This is of the same nature as the
Rashba-Bychkov SOI at a semiconductor heterojunction. We estimate the effect of
disorder within a potential barrier on the transmission probability. Using a
continuum model, we obtained analytic expressions for the spin-split energy
bands for electrons on the surface of nanotubes in the presence of SOI. First
we calculate analytically the scattering amplitudes from a potential barrier
located around the axis of the nanotube into spin-dependent states. The effect
of disorder on the scattering process is included phenomenologically and
induces a reduction in the transition probability. We analyzed the relative
role of SOI and disorder on the transmission probability which depends on the
angular and linear momentum of the incoming particle, and its spin orientation.
We demonstrated that in the presence of disorder perfect transmission may not
be achieved for finite barrier heights.Comment: 16 pages, 15 figure
LOFAR observations of 4C+19.44. On the discovery of low frequency spectral curvature in relativistic jet knots
We present the first LOFAR observations of the radio jet in the quasar
4C+19.44 (a.k.a. PKS 1354+19) obtained with the long baselines. The achieved
resolution is very well matched to that of archival Jansky Very Large Array
(JVLA) observations at higher radio frequencies as well as the archival X-ray
images obtained with {\it Chandra}. We found that, for several knots along the
jet, the radio flux densities measured at hundreds of MHz lie well below the
values estimated by extrapolating the GHz spectra. This clearly indicates the
presence of spectral curvature. Radio spectral curvature has been already
observed in different source classes and/or extended radio structures and it
has been often interpreted as due to intrinsic processes, as a curved particle
energy distribution, rather than absorption mechanisms ({ Razin-Tsytovich}
effect, free-free or synchrotron self absorption to name a few). Here we
discuss our results according to the scenario where particles undergo
stochastic acceleration mechanisms also in quasar jet knots.Comment: 13 pages, 4 tables, 4 figures, pre-proof version, published on the
Astrophysical Journal (Harris, et al. 2019 ApJ, 873, 21
Novel technique for monitoring the performance of the LAT instrument on board the GLAST satellite
The Gamma-ray Large Area Space Telescope (GLAST) is an observatory designed
to perform gamma-ray astronomy in the energy range 20 MeV to 300 GeV, with
supporting measurements for gamma-ray bursts from 10 keV to 25 MeV. GLAST will
be launched at the end of 2007, opening a new and important window on a wide
variety of high energy astrophysical phenomena . The main instrument of GLAST
is the Large Area Telescope (LAT), which provides break-through high-energy
measurements using techniques typically used in particle detectors for collider
experiments. The LAT consists of 16 identical towers in a four-by-four grid,
each one containing a pair conversion tracker and a hodoscopic crystal
calorimeter, all covered by a segmented plastic scintillator anti-coincidence
shield. The scientific return of the instrument depends very much on how
accurately we know its performance, and how well we can monitor it and correct
potential problems promptly. We report on a novel technique that we are
developing to help in the characterization and monitoring of LAT by using the
power of classification trees to pinpoint in a short time potential problems in
the recorded data. The same technique could also be used to evaluate the effect
on the overall LAT performance produced by potential instrumental problems.Comment: 2 pages, 1 figure, manuscript submitted on behalf of the GLAST/LAT
collaboration to First GLAST symposium proceeding
The running mass at low scalefrom the heavy-light meson decay constants
It is shown that a 25(20)% difference between the decay constants
and occurs due to large differences in the pole
masses of the and quarks. The values , recently observed in the CLEO experiment, and
, obtained in unquenched lattice QCD, can be
reached only if the running mass at low scale is GeV) MeV. Our results follow from the analytical expression for the
pseudoscalar decay constant based on the path-integral
representation of the meson Green's function.Comment: 6 pages, no figures; revtex
Spectroscopy of B_c Mesons in the Relativized Quark Model
We calculate the spectrum of the charm-beauty mesons using the relativized
quark model. Using the wavefunctions from this model we compute the radiative
widths of excited c\bar{b} states. The hadronic transition rates between
c\bar{b} states are estimated using the Kuang-Yan approach and are combined
with the radiative widths to give estimates of the relative branching ratios.
These results are combined with production rates at the Tevatron and the LHC to
suggest promising signals for excited B_c states. Our results are compared with
other models to gauge the reliability of the predictions and point out
differences.Comment: 15 pages, 1 fig. uses revtex4. References adde
Just a different place to graze? An unusual occurrence of the echinoid feeding trace Gnathichnus pentax on a marine vertebrate coprolite (Miocene, Italy) and its palaeoethological implications
Faeces produced by marine vertebrates and macro-invertebrates contain sufficient organic matter to represent a usable food source for a wide array of macroscopic animals. In some extant marine environments, coprophagy even represents a crucial trophic interaction in food webs. In ancient ecosystems, coprophagy by macroscopic animals is occasionally exemplified by coprolites that exhibit biting traces or burrows. Here, we report Gnathichnus pentax on an exquisitely preserved vertebrate-bitten vertebrate coprolite from the marine calcareous deposits of the Pietra leccese (Miocene, southern Italy). This unusual occurrence is interpreted as evidence of the feeding activity of a regular echi-noid; in particular, it may represent either exploratory coprophagy or the browsing of an algal (microbial) film that locally developed on the exterior of the faeces. Strengthening the former interpretation, the development of microbial communities on submerged faeces often leads to their destruction; furthermore, some extant Antarctic echinoderms are well known to ordinarily feed on vertebrate faeces, and coprophagy is believed to be fairly widespread among sea urchins. Supporting the algal browsing hypothesis, in turn, only a limited area of the external surface of the faeces was subject to grazing, and the resulting trace is neatly defined, which suggest that the feeding sea urchin targeted a precise location on the dung's exterior when the latter was already rather firm. To our knowledge, the G. pentax specimen studied here represents the first published record of this ichnotaxon on a coprolite
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