790 research outputs found
Logistic Barriers to U.S.–Mexico Grain and Soybean Trade
Fourteen years after the implementation of the North American Free Trade Agreement (NAFTA), border-crossing restrictions still remain with Mexico. Although studies have analyzed the impact of NAFTA trade liberalization, there has only been limited research on effects of informal trade barriers on U.S.–Mexico grain and soybean flows. This paper quantitatively measures the impact of logistic barriers impeding U.S.–Mexico grain and soybean trade. A conditional model testing for the presence of asymmetries in grain trade suggests that logistic barriers and transshipments are correlated. Econometric analysis rejects the null hypoInternational Relations/Trade,
Weak Pion Production off the Nucleon
We develop a model for the weak pion production off the nucleon, which
besides the Delta pole mechanism (weak excitation of the
resonance and its subsequent decay into ), includes also some background
terms required by chiral symmetry. We re-fit the form factor to
the flux averaged ANL differential cross
section data, finding a substantially smaller contribution of the Delta pole
mechanism than traditionally assumed in the literature. Within this scheme, we
calculate several differential and integrated cross sections, including pion
angular distributions, induced by neutrinos and antineutrinos and driven both
by charged and neutral currents. In all cases we find that the background terms
produce quite significant effects and that they lead to an overall improved
description of the data, as compared to the case where only the Delta pole
mechanism is considered. We also show that the interference between the Delta
pole and the background terms produces parity-violating contributions to the
pion angular differential cross section, which are intimately linked to odd
correlations in the contraction between the leptonic and hadronic tensors.
However, these latter correlations do not imply a genuine violation of time
reversal invariance because of the existence of strong final state interaction
effects.Comment: Typos corrected; comments adde
Experimental and numerical investigations of flow structure and momentum transport in a turbulent buoyancy-driven flow inside a tilted tube.
Buoyancy-driven turbulent mixing of fluids of slightly different densities [At = Δρ/(2〈ρ〉) = 1.15×10−2] in a long circular tube tilted at an angle θ = 15° from the vertical is studied at the local scale, both experimentally from particle image velocimetry and laser induced fluorescence measurements in the vertical diametrical plane and numerically throughout the tube using direct numerical simulation. In a given cross section of the tube, the axial mean velocity and the mean concentration both vary linearly with the crosswise distance z from the tube axis in the central 70% of the diameter. A small crosswise velocity component is detected in the measurement plane and is found to result from a four-cell mean secondary flow associated with a nonzero streamwise component of the vorticity. In the central region of the tube cross section, the intensities of the three turbulent velocity fluctuations are found to be strongly different, that of the streamwise fluctuation being more than twice larger than that of the spanwise fluctuation which itself is about 50% larger than that of the crosswise fluctuation. This marked anisotropy indicates that the turbulent structure is close to that observed in homogeneous turbulent shear flows. Still in the central region, the turbulent shear stress dominates over the viscous stress and reaches a maximum on the tube axis. Its crosswise variation is approximately accounted for by a mixing length whose value is about one-tenth of the tube diameter. The momentum exchange in the core of the cross section takes place between its lower and higher density parts and there is no net momentum exchange between the core and the near-wall regions. A sizable part of this transfer is due both to the mean secondary flow and to the spanwise turbulent shear stress. Near-wall regions located beyond the location of the extrema of the axial velocity (|z|≳0.36 d) are dominated by viscous stresses which transfer momentum toward (from) the wall near the top (bottom) of the tube
Disentangling the effect of dietary restriction on mitochondrial function using recombinant inbred mice
Dietary restriction (DR) extends lifespan and healthspan in many species, but precisely how it elicits its beneficial effects is unclear. We investigated the impact of DR on mitochondrial function within liver and skeletal muscle of female ILSXISS mice that exhibit strain-specific variation in lifespan under 40% DR. Strains TejJ89 (lifespan increased under DR), TejJ48 (lifespan unaffected by DR) and TejJ114 (lifespan decreased under DR) were studied following 10 months of 40% DR (13 months of age). Oxygen consumption rates (OCR) within isolated liver mitochondria were unaffected by DR in TejJ89 and TejJ48, but decreased by DR in TejJ114. DR had no effect on hepatic protein levels of PGC-1a, TFAM, and OXPHOS complexes IV. Mitonuclear protein imbalance (nDNA:mtDNA ratio) was unaffected by DR, but HSP90 protein levels were reduced in TejJ114 under DR. Surprisingly hepatic mitochondrial hydrogen peroxide (H2O2) production was elevated by DR in TejJ89, with total superoxide dismutase activity and protein carbonyls increased by DR in both TejJ89 and TejJ114. In skeletal muscle, DR had no effect on mitochondrial OCR, OXPHOS complexes or mitonuclear protein imbalance, but H2O2 production was decreased in TejJ114 and nuclear PGC-1a increased in TejJ89 under DR. Our findings indicate that hepatic mitochondrial dysfunction associated with reduced lifespan of TejJ114 mice under 40% DR, but similar dysfunction was not apparent in skeletal muscle mitochondria. We highlight tissue-specific differences in the mitochondrial response in ILSXISS mice to DR, and underline the importance and challenges of exploiting genetic heterogeneity to help understand mechanisms of ageing
Ultra low energy results and their impact to dark matter and low energy neutrino physics
We present ultra low energy results taken with the novel Spherical
Proportional Counter. The energy threshold has been pushed down to about 25 eV
and single electrons are clearly collected and detected. To reach such
performance low energy calibration systems have been successfully developed: -
A pulsed UV lamp extracting photoelectrons from the inner surface of the
detector - Various radioactive sources allowing low energy peaks through
fluorescence processes. The bench mark result is the observation of a well
resolved peak at 270 eV due to carbon fluorescence which is unique performance
for such large-massive detector. It opens a new window in dark matter and low
energy neutrino search and may allow detection of neutrinos from a nuclear
reactor or from supernova via neutrino-nucleus elastic scatteringComment: 14 pages,16 figure
Energy resolution of alpha particles in a microbulk Micromegas detector at high pressure Argon and Xenon mixtures
The latest Micromesh Gas Amplification Structures (Micromegas) are achieving
outstanding energy resolution for low energy photons, with values as low as 11%
FWHM for the 5.9 keV line of Fe in argon/isobutane mixtures at
atmospheric pressure. At higher energies (MeV scale), these measurements are
more complicated due to the difficulty in confining the events in the chamber,
although there is no fundamental reason why resolutions of 1% FWHM or below
could not be reached. There is much motivation to demonstrate experimentally
this fact in Xe mixtures due to the possible application of Micromegas readouts
to the Double Beta Decay search of Xe, or in other experiments needing
calorimetry and topology in the same detector. In this paper, we report on
systematic measurements of energy resolution with state-of-the-art Micromegas
using a 5.5 MeV alpha source in high pressure Ar/isobutane mixtures. Values as
low as 1.8% FWHM have been obtained, with possible evidence that better
resolutions are achievable. Similar measurements in Xe, of which a preliminary
result is also shown here, are under progress.Comment: 16 pages, 19 figures, version after referees comments. Accepted for
publication in Nuclear Instruments and Methods
A 1.85 Ga volcanic arc offshore the proto-continent Fennoscandia in southern Sweden
The Fröderyd Group forms part of the Vetlanda-Oskarshamn belt (also known as the Oskarshamn-Jönköping Belt), which is a piece of Palaeoproterozoic crust that is completely encapsulated by 1.81–1.77 Ga granitoids of the Transscandinavian Igneous Belt in the southern part of the Fennoscandian Shield. New U-Pb zircon data from a felsic metavolcanic rock in the Fröderyd Group have been acquired using LA-ICP-MS single collector. The age is determined to 1853 ± 11 Ma. The Fröderyd Group is interpreted to represent a volcanic arc that was located southwest of the margin to the proto-continent Fennoscandia. Tonalitic magma, identified in the Eksjö-Bäckaby regions, formed the middle crust in this arc complex and intruded the volcanic arc rocks at ca. 1.83–1.82 Ga. When this arc complex gradually approached the margin to the proto-continent Fennoscandia, parts of it were uplifted above sea level and initiated lacustrine sedimentation in restricted basins, which now are found in the Vetlanda region. Parallel with the development of this arc complex, 1.86–1.85 Ga granitoids intruded the margin to the proto-continent Fennoscandia and 1.87–1.86 Ga clastic metasedimentary rocks in the Västervik area in an Andean-type active continental margin.It can be concluded that the Vetlanda and Västervik sedimentary basins formed in two completely different geological environments during two separate events. The Västervik sediments formed along the margin to the proto-continent Fennoscandia before the Fröderyd arc system had developed while the Vetlanda sediments formed in a post-arc environment outboard to the southwest of the margin to the proto-continent Fennoscandia. It is suggested that the mafic volcanic rocks close to the lake Nömmen should be excluded from the Vetlanda supergroup and instead be related in time to the Fröderyd Group. This paper presents an interpretation of the tectonic evolution including volcanic arc and rifted volcanic arc during the 1.87 to 1.77 Ga time span with relevance to the evolution of the active southwestern margin of the proto-continent Fennoscandia depicted as a sequence of schematic profiles.</p
MEMPHYS:A large scale water Cerenkov detector at Fr\'ejus
A water \v{C}erenkov detector project, of megaton scale, to be installed in
the Fr\'ejus underground site and dedicated to nucleon decay, neutrinos from
supernovae, solar and atmospheric neutrinos, as well as neutrinos from a
super-beam and/or a beta-beam coming from CERN, is presented and compared with
competitor projects in Japan and in the USA. The performances of the European
project are discussed, including the possibility to measure the mixing angle
and the CP-violating phase .Comment: 1+33 pages, 14 figures, Expression of Interest of MEMPHYS projec
Micromegas in a Bulk
In this paper we present a novel way to manufacture the bulk Micromegas
detector. A simple process based on the PCB (Printed Circuit Board) technology
is employed to produce the entire sensitive detector. Such fabrication process
could be extended to very large area detectors made by the industry. The low
cost fabrication together with the robustness of the electrode materials will
make it extremely attractive for several applications ranging from particle
physics and astrophysics to medicineComment: 6 pages, 4 figure
Resonance production by neutrinos: I. J=3/2 Resonances
The article contains general formulas for the production of J=3/2 resonances
by neutrinos and antineutrinos. It specializes to the P_{33}(1232) resonance
whose form factors are determined by theory and experiment and then are
compared with experimental results at low and high energies. It is shown that
the minimum in the low Q^2 region is a consequence of a combined effect from
the vanishing of the vector form factors, the muon mass and Pauli blocking.
Several improvements for the future investigations are suggested.Comment: 10 pages, LaTeX, misprints corrected, 1 reference adde
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