2,960 research outputs found
Inelastic scattering of protons from He and Li in a folding model approach
The proton-inelastic scattering from He and Li nuclei are
studied in a folding model approach. A finite-range, momentum, density and
isospin dependent nucleon-nucleon interaction (SBM) is folded with realistic
density distributions of the above nuclei. The renormalization factors N
and N on the real and volume imaginary part of the folded potentials are
obtained by analyzing the respective elastic scattering data and kept unaltered
for the inelastic analysis at the same energy. The form factors are generated
by taking derivatives of the folded potentials and therefore required
renormalizations. The values are extracted by fitting the p +
He,Li inelastic angular distributions. The present analysis of
p + He inelastic scattering to the 3.57 MeV excited state, including
unpublished forward angle data (RIKEN) confirms L = 2 transition. Similar
analysis of the p + He inelastic scattering angular distribution leading to
the 1.8 MeV (L = 2) excited state fails to satisfactorily reproduce the data.Comment: one LaTeX file, five PostScript figure
Barrier and internal wave contributions to the quantum probability density and flux in light heavy-ion elastic scattering
We investigate the properties of the optical model wave function for light
heavy-ion systems where absorption is incomplete, such as Ca
and O around 30 MeV incident energy. Strong focusing effects
are predicted to occur well inside the nucleus, where the probability density
can reach values much higher than that of the incident wave. This focusing is
shown to be correlated with the presence at back angles of a strong enhancement
in the elastic cross section, the so-called ALAS (anomalous large angle
scattering) phenomenon; this is substantiated by calculations of the quantum
probability flux and of classical trajectories. To clarify this mechanism, we
decompose the scattering wave function and the associated probability flux into
their barrier and internal wave contributions within a fully quantal
calculation. Finally, a calculation of the divergence of the quantum flux shows
that when absorption is incomplete, the focal region gives a sizeable
contribution to nonelastic processes.Comment: 16 pages, 15 figures. RevTeX file. To appear in Phys. Rev. C. The
figures are only available via anonynous FTP on
ftp://umhsp02.umh.ac.be/pub/ftp_pnt/figscat
A preliminary study of genetic factors that influence susceptibility to bovine tuberculosis in the British cattle herd
Associations between specific host genes and susceptibility to Mycobacterial infections such as tuberculosis have been reported in several species. Bovine tuberculosis (bTB) impacts greatly the UK cattle industry, yet genetic predispositions have yet to be identified. We therefore used a candidate gene approach to study 384 cattle of which 160 had reacted positively to an antigenic skin test (‘reactors’). Our approach was unusual in that it used microsatellite markers, embraced high breed diversity and focused particularly on detecting genes showing heterozygote advantage, a mode of action often overlooked in SNP-based studies. A panel of neutral markers was used to control for population substructure and using a general linear model-based approach we were also able to control for age. We found that substructure was surprisingly weak and identified two genomic regions that were strongly associated with reactor status, identified by markers INRA111 and BMS2753. In general the strength of association detected tended to vary depending on whether age was included in the model. At INRA111 a single genotype appears strongly protective with an overall odds ratio of 2.2, the effect being consistent across nine diverse breeds. Our results suggest that breeding strategies could be devised that would appreciably increase genetic resistance of cattle to bTB (strictly, reduce the frequency of incidence of reactors) with implications for the current debate concerning badger-culling
Continuum Model for River Networks
The effects of erosion, avalanching and random precipitation are captured in
a simple stochastic partial differential equation for modelling the evolution
of river networks. Our model leads to a self-organized structured landscape and
to abstraction and piracy of the smaller tributaries as the evolution proceeds.
An algebraic distribution of the average basin areas and a power law
relationship between the drainage basin area and the river length are found.Comment: 9 pages, Revtex 3.0, 7 figures in compressed format using uufiles
command, to appear in Phys. Rev. Lett., for an hard copy or problems e-mail
to [email protected]
The D0 Run IIb Luminosity Measurement
An assessment of the recorded integrated luminosity is presented for data
collected with the D0 detector at the Fermilab Tevatron Collider from June 2006
to September 2011 (Run IIb). In addition, a measurement of the effective cross
section for inelastic interactions, also referred to as the luminosity
constant, is reported. This measurement incorporates new features that lead to
a substantial improvement in the precision of the result. A luminosity constant
of \sigma_{LM} = 48.3\pm1.9\pm0.6 mb is obtained, where the first uncertainty
is due to the accuracy of the inelastic cross section used by both CDF and D0,
and the second uncertainty is due to D0 sources. The recorded luminosity for
the highest E_T jet trigger is L_rec = 9.2 \pm 0.4 fb^{-1}, with a relative
uncertainty of 4.3%.Comment: 20 pages, 23 figure
Network Structures from Selection Principles
We present an analysis of the topologies of a class of networks which are
optimal in terms of the requirements of having as short a route as possible
between any two nodes while yet keeping the congestion in the network as low as
possible. Strikingly, we find a variety of distinct topologies and novel phase
transitions between them on varying the number of links per node. Our results
suggest that the emergence of the topologies observed in nature may arise both
from growth mechanisms and the interplay of dynamical mechanisms with a
selection process.Comment: 4 pages, 5 figure
Effective measures of tailored learning support for Engineering Work-Based Learners in HE: A Case study
Since 2004, Aston University has been delivering work-based learning (WBL) engineering degrees to key UK Energy sector employers, such as National Grid. National measures for widening participation in HE, such as the Degree Apprenticeship Levy, have led to significant changes in learning background diversity of WBL cohorts, consequently increasing student requirement for additional learning-support in HE Institutions (HEIs). To address these challenges, an intervention strategy was formulated in collaboration with Aston University's Learning Development Centre. Our methodology gradually embedded a provision of tailored learning-support sessions/workshops in mathematics and effective communication skills within WBL curricula. Integrating this support has led to marked increases in student engagement,grade-attainment, and stakeholder satisfaction. This case study is pertinent to HE's current STEM sector focus on developing WBL programmes, where the flexible methodologies established here can serve as practical models for other HEIs in the delivery of ‘in-employment’ education, in response to the fast-changing workplace
Nucleon-Nucleon Optical Model for Energies to 3 GeV
Several nucleon-nucleon potentials, Paris, Nijmegen, Argonne, and those
derived by quantum inversion, which describe the NN interaction for T-lab below
300$ MeV are extended in their range of application as NN optical models.
Extensions are made in r-space using complex separable potentials definable
with a wide range of form factor options including those of boundary condition
models. We use the latest phase shift analyses SP00 (FA00, WI00) of Arndt et
al. from 300 MeV to 3 GeV to determine these extensions. The imaginary parts of
the optical model interactions account for loss of flux into direct or resonant
production processes. The optical potential approach is of particular value as
it permits one to visualize fusion, and subsequent fission, of nucleons when
T-lab above 2 GeV. We do so by calculating the scattering wave functions to
specify the energy and radial dependences of flux losses and of probability
distributions. Furthermore, half-off the energy shell t-matrices are presented
as they are readily deduced with this approach. Such t-matrices are required
for studies of few- and many-body nuclear reactions.Comment: Latex, 40 postscript pages including 17 figure
Protein design in a lattice model of hydrophobic and polar amino acids
A general strategy is described for finding which amino acid sequences have
native states in a desired conformation (inverse design). The approach is used
to design sequences of 48 hydrophobic and polar aminoacids on three-dimensional
lattice structures. Previous studies employing a sequence-space Monte-Carlo
technique resulted in the successful design of one sequence in ten attempts.
The present work also entails the exploration of conformations that compete
significantly with the target structure for being its ground state. The design
procedure is successful in all the ten cases.Comment: RevTeX, 12 pages, 1 figur
- …