863 research outputs found
Progressing social prescribing with a focus on process of connection : evidence-informed guidance for robust evaluation and evidence synthesis
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The Proton Spin and Flavor Structure in the Chiral Quark Model
After a pedagogical review of the simple constituent quark model and deep
inelastic sum rules, we describe how a quark sea as produced by the emission of
internal Goldstone bosons by the valence quarks can account for the observed
features of proton spin and flavor structures. Some issues concerning the
strange quark content of the nucleon are also discussed.Comment: 59 pages with table of contents, Lecture delivered at the Schladming
Winter School (March 1997), to be published by Springer-Verlag under the
title "Computing Particle Properties" (eds. C. B. Lang and H. Gausterer
Schottky barrier heights at polar metal/semiconductor interfaces
Using a first-principle pseudopotential approach, we have investigated the
Schottky barrier heights of abrupt Al/Ge, Al/GaAs, Al/AlAs, and Al/ZnSe (100)
junctions, and their dependence on the semiconductor chemical composition and
surface termination. A model based on linear-response theory is developed,
which provides a simple, yet accurate description of the barrier-height
variations with the chemical composition of the semiconductor. The larger
barrier values found for the anion- than for the cation-terminated surfaces are
explained in terms of the screened charge of the polar semiconductor surface
and its image charge at the metal surface. Atomic scale computations show how
the classical image charge concept, valid for charges placed at large distances
from the metal, extends to distances shorter than the decay length of the
metal-induced-gap states.Comment: REVTeX 4, 11 pages, 6 EPS figure
Near infrared reflectance spectroscopy for the determination of free gossypol in cottonseed meal
Gossypol is a toxic polyphenolic compound produced by the pigment glands of the cotton
plant. The free gossypol content of cottonseed meal (CSM) is commonly determined by the
American Oil Chemistsâ Society (AOCS) wet chemistry method. The AOCS method, however,
laboratory-intensive, time-consuming, and therefore, not practical for quick field analyses.
To determine if the free gossypol content of CSM could be predicted by near infrared reflectance
spectroscopy (NIRS), CSM samples were collected from all over the world. All CSM samples
were ground and a portion of each analyzed for free gossypol by the AOCS procedure (reference
data) and by NIRS (reflectance data). Both reflectance and reference data were combined in
calibration. The coefficient of determination (r2) and standard error of prediction (SEP) were
used to assess the calibration accuracy. The r2 was 0.728, and the SEP was 0.034 for the
initial calibration that included samples from all over the world. However, the r2 and SEP
improved to 0.921 and 0.014, respectively, if the calibration was made using CSM samples
only from the United States. These results indicate that a general prediction equation can be
developed to predict the free gossypol content of CSM by NIRS. From a practical standpoint,
NIRS technology provides a method for quickly assessing whether a particular batch of CSM
has a free gossypol content low enough to be suitable for use in poultry diets.This research was supported in part by grant 05-635GA from the Georgian Cotton Commission, Perry, G
Ocean forests: breakthrough yields for macroalgae
The US Department of Energy Advanced Research Projects Agency - Energy (ARPA-E) MacroAlgae Research Inspiring Novel Energy Research (MARINER) program is encouraging technologies for the sustainable harvest of large funding research of macroalgae for biofuels at less than $80 per dry metric ton (DMT). The Ocean Forests team, led by the University of Southern Mississippi, is developing a complete managed ecosystem where nutrients are transformed and recycled. The teamâs designs address major bottlenecks in profitability of offshore aquaculture systems including economical moored structures that can withstand storms, efficient planting, managing and harvesting systems, and sustainable nutrient supply. The work is inspired by Lapointe who reported yields of Gracilaria tikvahiae equivalent to 127 DMT per hectare per year (compared with standard aquaculture systems in the range of 20 to 40 DMT/ha/yr). This approach offers the potential for breakthrough yields for many macroalgae species. Moreover, mini-ecosystems in offshore waters create communities of macroalgae, shellfish, and penned finfish, supplemented by visiting free-range fish that can increase productivity, produce quality products, and create jobs and income for aquafarmers. Additional benefits include reduced disease in fish pens, cleaning contaminated coastal waters, and
maximizing nutrient recycling. Cost projections for a successful, intensive, scaled system are competitive with current prices for fossil fuels
Global Study of Nuclear Structure Functions
We present the results of a phenomenological study of unpolarized nuclear
structure functions for a wide kinematical region of x and Q^2. As a basis of
our phenomenology we develop a model which takes into account a number of
different nuclear effects including nuclear shadowing, Fermi motion and
binding, nuclear pion excess and off-shell correction to bound nucleon
structure functions. Within this approach we perform a statistical analysis of
available data on the ratio of the nuclear structure functions F_2 for
different nuclei in the range from the deuteron to the lead. We express the
off-shell effect and the effective scattering amplitude describing nuclear
shadowing in terms of few parameters which are common to all nuclei and have a
clear physical interpretation. The parameters are then extracted from
statistical analysis of data. As a result, we obtain an excellent overall
agreement between our calculations and data in the entire kinematical region of
x and Q^2. We discuss a number of applications of our model which include the
calculation of the deuteron structure functions, nuclear valence and sea quark
distributions and nuclear structure functions for neutrino charged-current
scattering.Comment: 67 pages, 18 figures (v3: updated text and references, a new section
with discussion about relation between off-shell effect and modification of
the nucleon size in nuclei, accepted for publication in Nucl. Phys. A
CP asymmetries in the supersymmetric trilepton signal at the LHC
In the CP-violating Minimal Supersymmetric Standard Model, we study the
production of a neutralino-chargino pair at the LHC. For their decays into
three leptons, we analyze CP asymmetries which are sensitive to the CP phases
of the neutralino and chargino sector. We present analytical formulas for the
entire production and decay process, and identify the CP-violating
contributions in the spin correlation terms. This allows us to define the
optimal CP asymmetries. We present a detailed numerical analysis of the cross
sections, branching ratios, and the CP observables. For light neutralinos,
charginos, and squarks, the asymmetries can reach several 10%. We estimate the
discovery potential for the LHC to observe CP violation in the trilepton
channel.Comment: 39 pages, 8 figures, version to appear in EPJC, discussion(s) added,
typo in (D.79), (D.118) corrected, new Fig. 7; The European Physical Journal
C, Volume 72, Issue 3, 201
The chemical enrichment of the ICM from hydrodynamical simulations
The study of the metal enrichment of the intra-cluster and inter-galactic
media (ICM and IGM) represents a direct means to reconstruct the past history
of star formation, the role of feedback processes and the gas-dynamical
processes which determine the evolution of the cosmic baryons. In this paper we
review the approaches that have been followed so far to model the enrichment of
the ICM in a cosmological context. While our presentation will be focused on
the role played by hydrodynamical simulations, we will also discuss other
approaches based on semi-analytical models of galaxy formation, also critically
discussing pros and cons of the different methods. We will first review the
concept of the model of chemical evolution to be implemented in any
chemo-dynamical description. We will emphasise how the predictions of this
model critically depend on the choice of the stellar initial mass function, on
the stellar life-times and on the stellar yields. We will then overview the
comparisons presented so far between X-ray observations of the ICM enrichment
and model predictions. We will show how the most recent chemo-dynamical models
are able to capture the basic features of the observed metal content of the ICM
and its evolution. We will conclude by highlighting the open questions in this
study and the direction of improvements for cosmological chemo-dynamical models
of the next generation.Comment: 25 pages, 11 figures, accepted for publication in Space Science
Reviews, special issue "Clusters of galaxies: beyond the thermal view",
Editor J.S. Kaastra, Chapter 18; work done by an international team at the
International Space Science Institute (ISSI), Bern, organised by J.S.
Kaastra, A.M. Bykov, S. Schindler & J.A.M. Bleeke
Adding tree rings to North America's National Forest Inventories: an essential tool to guide drawdown of atmospheric CO2
Tree-ring time series provide long-term, annually resolved information on the growth of trees. When sampled in a systematic context, tree-ring data can be scaled to estimate the forest carbon capture and storage of landscapes, biomes, and-ultimately-the globe. A systematic effort to sample tree rings in national forest inventories would yield unprecedented temporal and spatial resolution of forest carbon dynamics and help resolve key scientific uncertainties, which we highlight in terms of evidence for forest greening (enhanced growth) versus browning (reduced growth, increased mortality). We describe jump-starting a tree-ring collection across the continent of North America, given the commitments of Canada, the United States, and Mexico to visit forest inventory plots, along with existing legacy collections. Failing to do so would be a missed opportunity to help chart an evidence-based path toward meeting national commitments to reduce net greenhouse gas emissions, urgently needed for climate stabilization and repair.Published versio
Monte Carlo Methods for Estimating Interfacial Free Energies and Line Tensions
Excess contributions to the free energy due to interfaces occur for many
problems encountered in the statistical physics of condensed matter when
coexistence between different phases is possible (e.g. wetting phenomena,
nucleation, crystal growth, etc.). This article reviews two methods to estimate
both interfacial free energies and line tensions by Monte Carlo simulations of
simple models, (e.g. the Ising model, a symmetrical binary Lennard-Jones fluid
exhibiting a miscibility gap, and a simple Lennard-Jones fluid). One method is
based on thermodynamic integration. This method is useful to study flat and
inclined interfaces for Ising lattices, allowing also the estimation of line
tensions of three-phase contact lines, when the interfaces meet walls (where
"surface fields" may act). A generalization to off-lattice systems is described
as well.
The second method is based on the sampling of the order parameter
distribution of the system throughout the two-phase coexistence region of the
model. Both the interface free energies of flat interfaces and of (spherical or
cylindrical) droplets (or bubbles) can be estimated, including also systems
with walls, where sphere-cap shaped wall-attached droplets occur. The
curvature-dependence of the interfacial free energy is discussed, and estimates
for the line tensions are compared to results from the thermodynamic
integration method. Basic limitations of all these methods are critically
discussed, and an outlook on other approaches is given
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