342 research outputs found
Phenomenological glass model for vibratory granular compaction
A model for weakly excited granular media is derived by combining the free
volume argument of Nowak et al. [Phys. Rev. E 57, 1971 (1998)] and the
phenomenological model for supercooled liquids of Adam and Gibbs [J. Chem.
Phys. 43, 139 (1965)]. This is made possible by relating the granular
excitation parameter \Gamma, defined as the peak acceleration of the driving
pulse scaled by gravity, to a temperature-like parameter \eta(\Gamma). The
resulting master equation is formally identical to that of Bouchaud's trap
model for glasses [J. Phys. I 2, 1705 (1992)]. Analytic and simulation results
are shown to compare favourably with a range of known experimental behaviour.
This includes the logarithmic densification and power spectrum of fluctuations
under constant \eta, the annealing curve when \eta is varied cyclically in
time, and memory effects observed for a discontinuous shift in \eta. Finally,
we discuss the physical interpretation of the model parameters and suggest
further experiments for this class of systems.Comment: 2 references added; some figure labels tweaked. To appear in PR
Prenatal cortisol exposure impairs adrenal function but not glucose metabolism in adult sheep
Adverse environmental conditions before birth are known to program adult metabolic and endocrine phenotype in several species. However, whether increments in fetal cortisol
concentrations of the magnitude commonly seen in these conditions can cause
developmental programming remains unknown. Thus, this study investigated the outcome
of physiological increases in fetal cortisol concentrations on glucose-insulin dynamics and
pituitary-adrenal function in adult sheep. Compared to saline treatment, intravenous fetal
cortisol infusion for 5 days in late gestation did not affect birthweight but increased lamb
body weight at 1-2 weeks after birth. Adult glucose dynamics, insulin sensitivity and insulin
secretion were unaffected by prenatal cortisol overexposure, assessed by glucose tolerance
tests, hyperinsulinaemic-euglycaemic clamps and acute insulin administration. In contrast,
prenatal cortisol infusion induced adrenal hypo-responsiveness in adulthood with
significantly reduced cortisol responses to insulin-induced hypoglycaemia and exogenous
adrenocorticotropic hormone (ACTH) administration relative to saline treatment. The area of
adrenal cortex expressed as a percentage of the total cross-sectional area of the adult adrenal
gland was also lower after prenatal cortisol than saline infusion. In adulthood, basal
circulating ACTH but not cortisol concentrations were significantly higher in the cortisol than
saline treated group. The results show that cortisol overexposure before birth programs
pituitary-adrenal development with consequences for adult stress responses. Physiological
variations in cortisol concentrations before birth may, therefore, have an important role in
determining adult phenotypical diversity and adaptability to environmental challenges
Compaction of Rods: Relaxation and Ordering in Vibrated, Anisotropic Granular Material
We report on experiments to measure the temporal and spatial evolution of
packing arrangements of anisotropic, cylindrical granular material, using
high-resolution capacitive monitoring. In these experiments, the particle
configurations start from an initially disordered, low-packing-fraction state
and under vertical vibrations evolve to a dense, highly ordered, nematic state
in which the long particle axes align with the vertical tube walls. We find
that the orientational ordering process is reflected in a characteristic, steep
rise in the local packing fraction. At any given height inside the packing, the
ordering is initiated at the container walls and proceeds inward. We explore
the evolution of the local as well as the height-averaged packing fraction as a
function of vibration parameters and compare our results to relaxation
experiments conducted on spherically shaped granular materials.Comment: 9 pages incl. 7 figure
alpha-decay of excited states in 11C and 11B
Studies of the 16O(9Be,alpha7Be)14C and 7Li(9Be,alpha7Li)5He reactions at
E{beam}=70 MeV have been performed using resonant particle spectroscopy
techniques. The 11C excited states decaying into alpha+7Be(gs) are observed at
8.65, 9.85, 10.7 and 12.1 MeV as well as possible states at 12.6 and 13.4 MeV.
This result is the first observation of alpha-decay for excited states above 9
MeV. The alpha+7Li(gs) decay of 11B excited states at 9.2, 10.3, 10.55, 11.2,
(11.4), 11.8, 12.5,(13.0), 13.1, (14.0), 14.35, (17.4) and (18.6) MeV is
observed. The decay processes are used to indicate the possible three-centre
2alpha+3He(3H) cluster structure of observed states. Two rotational bands
corresponding to very deformed structures are suggested for the positive-parity
states. Excitations of some observed T=1/2 resonances coincide with the
energies of T=3/2 states which are the isobaric analogs of the lowest 11Be
states. Some of these states may have mixed isospin.Comment: accepted for publication in Nuclear Physics
Big GABA II: Water-referenced edited MR spectroscopy at 25 research sites
Accurate and reliable quantification of brain metabolites measured in vivo using 1H magnetic resonance spectroscopy (MRS) is a topic of continued interest. Aside from differences in the basic approach to quantification, the quantification of metabolite data acquired at different sites and on different platforms poses an additional methodological challenge. In this study, spectrally edited Îł-aminobutyric acid (GABA) MRS data were analyzed and GABA levels were quantified relative to an internal tissue water reference. Data from 284 volunteers scanned across 25 research sites were collected using GABA+ (GABA + co-edited macromolecules (MM)) and MM-suppressed GABA editing. The unsuppressed water signal from the volume of interest was acquired for concentration referencing. Whole-brain T1-weighted structural images were acquired and segmented to determine gray matter, white matter and cerebrospinal fluid voxel tissue fractions. Water-referenced GABA measurements were fully corrected for tissue-dependent signal relaxation and water visibility effects. The cohort-wide coefficient of variation was 17% for the GABA + data and 29% for the MM-suppressed GABA data. The mean within-site coefficient of variation was 10% for the GABA + data and 19% for the MM-suppressed GABA data. Vendor differences contributed 53% to the total variance in the GABA + data, while the remaining variance was attributed to site- (11%) and participant-level (36%) effects. For the MM-suppressed data, 54% of the variance was attributed to site differences, while the remaining 46% was attributed to participant differences. Results from an exploratory analysis suggested that the vendor differences were related to the unsuppressed water signal acquisition. Discounting the observed vendor-specific effects, water-referenced GABA measurements exhibit similar levels of variance to creatine-referenced GABA measurements. It is concluded that quantification using internal tissue water referencing is a viable and reliable method for the quantification of in vivo GABA levels
Perspectives in visual imaging for marine biology and ecology: from acquisition to understanding
Durden J, Schoening T, Althaus F, et al. Perspectives in Visual Imaging for Marine Biology and Ecology: From Acquisition to Understanding. In: Hughes RN, Hughes DJ, Smith IP, Dale AC, eds. Oceanography and Marine Biology: An Annual Review. 54. Boca Raton: CRC Press; 2016: 1-72
Linear Collider Physics Resource Book for Snowmass 2001, 3: Studies of Exotic and Standard Model Physics
This Resource Book reviews the physics opportunities of a next-generation e+e- linear collider and discusses options for the experimental program. Part 3 reviews the possible experiments on that can be done at a linear collider on strongly coupled electroweak symmetry breaking, exotic particles, and extra dimensions, and on the top quark, QCD, and two-photon physics. It also discusses the improved precision electroweak measurements that this collider will make available.This Resource Book reviews the physics opportunities of a next-generation e+e- linear collider and discusses options for the experimental program. Part 3 reviews the possible experiments on that can be done at a linear collider on strongly coupled electroweak symmetry breaking, exotic particles, and extra dimensions, and on the top quark, QCD, and two-photon physics. It also discusses the improved precision electroweak measurements that this collider will make available
Effects of maternal high fat intake during pregnancy and lactation on total cholesterol and adipose tissue in neonatal rats
Search for long-lived doubly charged Higgs bosons in p(p)over-bar collisions at root s=1.96 TeV
We present a search for long-lived doubly charged Higgs bosons (H+/-+/-), with signatures of high ionization energy loss and muonlike penetration. We use 292 pb(-1) of data collected in p (p) over bar collisions at root s=1.96 TeV by the CDF II detector at the Fermilab Tevatron. Observing no evidence of long-lived doubly charged particle production, we exclude H-L(+/-+/-) and H-R(+/-+/-) bosons with masses below 133 GeV/c(2) and 109 GeV/c(2), respectively. In the degenerate case we exclude H+/-+/- mass below 146 GeV/c(2). All limits are quoted at the 95% confidence level
- …