670 research outputs found
Neonatal oxytocin administration and weaning onto a gruel based diet reduce weight loss at weaning and enhance gastric leptin expression
Administering oxytocin to neonatal rats has positive long-term effects on growth and development (Uvnas-Moberg and Petersson, 2005). These effects include a reduction in the stress response to weaning, increased post-weaning feed intake and alterations in the expression of gastrointestinal (GI) hormones regulating feed intake (Uvnas-Moberg et al., 1998; Sohlstrom et al., 1999). Two GI hormones of importance in regulating feed intake are ghrelin and leptin, which have antagonistic actions. Ghrelin expression is increased in response to fasting and leptin expression increases rapidly in response to feed intake. Since weaning the piglet is associated with stress and growth restriction, this study examined whether oxytocin given to young pigs could reduce the extent of the post-weaning growth check, along with any associated changes in ghrelin and leptin expression
Steady non-ideal detonations in cylindrical sticks of expolsives
Numerical simulations of detonations in cylindrical rate-sticks of highly
non-ideal explosives are performed, using a simple model with a weakly pressure
dependent rate law and a pseudo-polytropic equation of state. Some numerical issues
with such simulations are investigated, and it is shown that very high resolution
(hundreds of points in the reaction zone) are required for highly accurate (converged)
solutions. High resolution simulations are then used to investigate the qualitative
dependences of the detonation driving zone structure on the diameter and degree of
confinement of the explosive charge. The simulation results are used to show that,
given the radius of curvature of the shock at the charge axis, the steady detonation
speed and the axial solution are accurately predicted by a quasi-one-dimensional
theory, even for cases where the detonation propagates at speeds significantly below
the Chapman-Jouguet speed. Given reaction rate and equation of state models, this
quasi-one-dimensional theory offers a significant improvement to Wood-Kirkwood
theories currently used in industry
Periodic orbit resonances in layered metals in tilted magnetic fields
The frequency dependence of the interlayer conductivity of a layered Fermi
liquid in a magnetic field which is tilted away from the normal to the layers
is considered. For both quasi-one- and quasi-two-dimensional systems resonances
occur when the frequency is a harmonic of the frequency at which the magnetic
field causes the electrons to oscillate on the Fermi surface within the layers.
The intensity of the different harmonic resonances varies significantly with
the direction of the field. The resonances occur for both coherent and weakly
incoherent interlayer transport and so their observation does not imply the
existence of a three-dimensional Fermi surface.Comment: 4 pages, RevTeX + epsf, 2 figures. Discussion of other work revised.
To appear in Phys. Rev. B, Rapid Commun., October 1
B(E1) Strengths from Coulomb Excitation of 11Be
The (E1;) strength for Be has been extracted from
intermediate energy Coulomb excitation measurements, over a range of beam
energies using a new reaction model, the extended continuum discretized coupled
channels (XCDCC) method. In addition, a measurement of the excitation cross
section for Be+Pb at 38.6 MeV/nucleon is reported. The (E1)
strength of 0.105(12) efm derived from this measurement is consistent
with those made previously at 60 and 64 MeV/nucleon, i n contrast to an
anomalously low result obtained at 43 MeV/nucleon. By coupling a
multi-configuration description of the projectile structure with realistic
reaction theory, the XCDCC model provides for the first time a fully quantum
mechanical description of Coulomb excitation. The XCDCC calculations reveal
that the excitation process involves significant contributions from nuclear,
continuum, and higher-order effects. An analysis of the present and two earlier
intermediate energy measurements yields a combined B(E1) strength of 0.105(7)
efm. This value is in good agreement with the value deduced
independently from the lifetime of the state in Be, and has a
comparable p recision.Comment: 5 pages, 2 figures, accepted for publication in Phys. Lett.
Magnetic field-dependent interplay between incoherent and Fermi liquid transport mechanisms in low-dimensional tau phase organic conductors
We present an electrical transport study of the 2-dimensional (2D) organic
conductor tau-(P-(S,S)-DMEDT-TTF)_2(AuBr)_2(AuBr_2)_y (y = 0.75) at low
temperatures and high magnetic fields. The inter-plane resistivity rho_zz
increases with decreasing temperature, with the exception of a slight anomaly
at 12 K. Under a magnetic field B, both rho_zz and the in-plane resistivity
plane rho_xx show a pronounced negative and hysteretic magnetoresistance with
Shubnikov de Haas (SdH)oscillations being observed in some (high
quality)samples above 15 T. Contrary to the predicted single, star-shaped,
closed orbit Fermi surface from band structure calculations (with an expected
approximate area of 12.5% of A_FBZ), two fundamental frequencies F_l and F_h
are detected in the SdH signal. These orbits correspond to 2.4% and 6.8% of the
area of the first Brillouin zone(A_FBZ), with effective masses F_l = 4.0 +/-
0.5 and F_h = 7.3 +/- 0.1. The angular dependence, in tilted magnetic fields of
F_l and F_h, reveals the 2D character of the FS and Angular dependent
magnetoresistance (AMRO) further suggests a FS which is strictly 2-D where the
inter-plane hopping t_c is virtually absent or incoherent. The Hall constant
R_xy is field independent, and the Hall mobility increases by a factor of 3
under moderate magnetic fields. Our observations suggest a unique physical
situation where a stable 2D Fermi liquid state in the molecular layers are
incoherently coupled along the least conducting direction. The magnetic field
not only reduces the inelastic scattering between the 2D metallic layers, but
it also reveals the incoherent nature of interplane transport in the AMRO
spectrum. The apparent ferromagnetism of the hysteretic magnetoresistance
remains an unsolved problem.Comment: 33 pages, 11 figure
New results from the NA57 experiment
We report results from the experiment NA57 at CERN SPS on hyperon production
at midrapidity in Pb-Pb collisions at 158 GeV/ and 40 GeV/.
, and yields are compared with those from the STAR
experiment at the higher energy of the BNL RHIC. , , \
and preliminary transverse mass spectra are presented and interpreted
within the framework of a hydro-dynamical blast wave model.Comment: 8 pages, 3 figures, contribution to the proceedings of The XXXVIIIth
Rencontres de Moriond "QCD and High Energy Hadronic Interactions
Expansion dynamics of Pb-Pb collisions at 40 A GeV/c viewed by negatively charged hadrons
In this paper we present results on transverse mass spectra and Hanbury-Brown
and Twiss correlation functions of negatively charged hadrons, which are
expected to be mostly negative pions, measured in Pb-Pb collisions at 40 A
GeV/c beam momentum. Based on these data, the collision dynamics and the
space-time extent of the system at the thermal freeze-out are studied over a
centrality range corresponding to the most central 53% of the Pb--Pb inelastic
cross section. Comparisons with freeze-out conditions of strange particles and
HBT results from other experiments are discussed.Comment: 29 pages, 18 figure
Results on hyperon production from the NA57 experiment
Recent results on hyperon production in Pb--Pb collisions from the NA57
experiment are reported. Strangeness enhancement and the transverse mass
spectra properties at 158 GeV per nucleon are described.Comment: submitted to Acta Phys. Hung. A (Heavy Ion Physics
Jupiter's X-ray Emission 2007 Part 2:Comparisons with UV and Radio Emissions and In-Situ Solar Wind Measurements
We compare Chandra and XMMâNewton Xâray observations of Jupiter during 2007 with a rich multiâinstrument dataset including: upstream inâsitu solar wind measurements from the New Horizons spacecraft, radio emissions from the Nançay Decametric Array and Wind/Waves, and UV observations from the Hubble Space Telescope. New Horizons data revealed two corotating interaction regions (CIRs) impacted Jupiter during these observations. NonâIo decametric bursts and UV emissions brightened together and varied in phase with the CIRs. We characterise 3 types of Xâray aurorae: hard Xâray bremsstrahlung main emission, pulsed/flared soft Xâray emissions and a newly identified dim flickering (varying on shortâtimescales, but quasiâcontinuously present) aurora. For most observations, the Xâray aurorae were dominated by pulsed/flaring emissions, with ion spectral lines that were best fit by Iogenic plasma. However, the brightest Xâray aurora was coincident with a magnetosphere expansion. For this observation, the aurorae were produced by both flickering emission and erratic pulses/flares. Auroral spectral models for this observation required the addition of solar wind ions to attain good fits, suggesting solar wind entry into the outer magnetosphere or directly into the pole for this particularly bright observation. Xâray bremsstrahlung from high energy electrons was only bright for one observation, which was during a forward shock. This bremsstrahlung was spatially coincident with bright UV main emission (power> 1TW) and Xâray ion spectral line dusk emission, suggesting closening of upward and downward current systems during the shock. Otherwise, the bremsstrahlung was dim and UV main emission power was also lower(<700 GW), suggesting their power scaled together
Strange particle production in 158 and 40 GeV/ Pb-Pb and p-Be collisions
Results on strange particle production in Pb-Pb collisions at 158 and 40
GeV/ beam momentum from the NA57 experiment at CERN SPS are presented.
Particle yields and ratios are compared with those measured at RHIC.
Strangeness enhancements with respect to p-Be reactions at the same beam
momenta have been also measured: results about their dependence on centrality
and collision energy are reported and discussed.Comment: Contribution to the proceedings of the "Hot Quarks 2004" Conference,
July 18-24 2004, New Mexico, USA, submitted to Journal of Physics G 7 pages,
5 figure
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