1,108 research outputs found
Coulomb breakup of 22C in a four-body model
Breakup cross sections are determined for the Borromean nucleus 22C by using
a four-body eikonal model, including Coulomb corrections. Bound and continuum
states are constructed within a 20C + n + n three-body model in hyperspherical
coordinates. We compute continuum states with the correct asymptotic behavior
through the R-matrix method. For the n+ n potential, we use the Minnesota
interaction. As there is no precise experimental information on 21C, we define
different parameter sets for the 20C + n potentials. These parameter sets
provide different scattering lengths, and resonance energies of an expected
3/2+ excited state. Then we analyze the 22C ground-state energy and rms radius,
as well as E1 strength distributions and breakup cross sections. The E1
strength distribution presents an enhancement at low energies. Its amplitude is
associated with the low binding energy, rather than with a three-body
resonance. We show that the shape of the cross section at low energies is
sensitive to the ground-state properties. In addition, we suggest the existence
of a low-energy 2+ resonance, which should be observable in breakup
experiments
Microscopic description of Li in the and elastic scattering at high energies
We employ a microscopic continuum-discretized coupled-channels reaction
framework (MCDCC) to study the elastic angular distribution of the
Li nucleus colliding with C and Si targets at
=350 MeV. In this framework, the Li projectile is described
in a microscopic cluster model and impinges on non-composite targets. The
diagonal and coupling potentials are constructed from nucleon-target
interactions and Li microscopic wave functions. We obtain a fair
description of the experimental data, in the whole angular range studied, when
continuum channels are included. The inelastic and breakup angular
distributions on the lightest target are also investigated. In addition, we
compute LiC MCDCC elastic cross sections at energies much higher
than the Coulomb barrier and we use them as reference calculations to test the
validity of multichannel eikonal cross sections.Comment: 9 Pages, 6 Figure
Current rectification in a single molecule diode: the role of electrode coupling
We demonstrate large rectification ratios (> 100) in single-molecule
junctions based on a metal-oxide cluster (polyoxometalate), using a scanning
tunneling microscope (STM) both at ambient conditions and at low temperature.
These rectification ratios are the largest ever observed in a single-molecule
junction, and in addition these junctions sustain current densities larger than
10^5 A/cm^2. By following the variation of the I-V characteristics with
tip-molecule separation we demonstrate unambiguously that rectification is due
to asymmetric coupling to the electrodes of a molecule with an asymmetric level
structure. This mechanism can be implemented in other type of molecular
junctions using both organic and inorganic molecules and provides a simple
strategy for the rational design of molecular diodes
Condensate Fraction of a Two-Dimensional Attractive Fermi Gas
We investigate the Bose-Einstein condensation of fermionic pairs in a
two-dimensional uniform two-component Fermi superfluid obtaining an explicit
formula for the condensate density as a function of the chemical potential and
the energy gap. By using the mean-field extended BCS theory, we analyze, as a
function of the bound-state energy, the off-diagonal long-range order in the
crossover from the Bardeen-Cooper-Schrieffer (BCS) state of weakly-bound Cooper
pairs to the Bose-Einstein Condensate (BEC) of strongly-bound molecular dimers.Comment: 4 pages, 2 figures, accepted for publication in Phys. Rev.
Molecular Dynamics Simulation of Polymer-Metal Bonds
Molecular simulation is becoming a very powerful tool for studying dynamic phenomena in materials. The simulation yields information about interaction at length and time scales unattainable by experimental measurements and unpredictable by continuum theories. This is especially meaningful when referring to bonding between a polymer and a metal substrate. A very important characteristic of polymers is that their physical properties do not rely on the detailed chemical structure of the molecular chains but only on their flexibility, and accordingly they will be able to adopt different conformations. In this paper, a molecular simulation of the bonding between vinyl ester polymer and steel is presented. Four different polymers with increasing chain lengths have been studied. Atomic co-ordinates are adjusted in order to reduce the molecular energy. Conformational changes in the macromolecules have been followed to obtain the polymer pair correlation function. Radius of gyration and end-to-end distance distributions of the individual chains have been used as a quantitative measurement of their flexibility. There exists a correlation between flexibility of the molecular chains and the energy of adhesion between the polymer and the metal substrate. Close contacts between the two materials are established at certain points but every atom up to a certain distance from the interface contributes to the total value of the adhesion energy of the system
UV and Visible Light-Driven Production of Hydroxyl Radicals by Reduced Forms of N, F, and P Codoped Titanium Dioxide
The photocatalytic activities of reduced titanium dioxide (TiO2) materials have been investigated by measuring their ability to produce hydroxyl radicals under UV and visible light irradiation. Degussa P25 TiO2 was doped with nitrogen (N), fluorine (F), and/or phosphorus (P) and then subjected to surface modification employing a thermo-physicochemical process in the presence of reducing agent sodium borohydride (NaBH4). The reduced TiO2 materials were characterized by a number of X-ray, spectroscopic and imaging methods. Surface doping of TiO2 was employed to modulate the band gap energies into the visible wavelength region for better overlap with the solar spectrum. Hydroxyl radical generation, central to TiO2 photocatalytic water purification applications, was quantitated using coumarin as a trap under UV and visible light irradiation of the reduced TiO2 materials. At 350 nm irradiation, the yield of hydroxyl radicals generated by the reduced forms of TiO2 was nearly 90% of hydroxyl radicals generated by the Degussa P25 TiO2. Hydroxyl radical generation by these reduced forms of TiO2 was also observed under visible light irradiation (419 and 450 nm). These results demonstrated that simple surface modification of doped TiO2 can lead to visible light activity, which is important for more economical solar-driven applications of TiO2 photocatalysis
Visible spectroscopy of the new ESO Large Program on trans-Neptunian objects and Centaurs: final results
A second large programme (LP) for the physical studies of TNOs and Centaurs,
started at ESO Cerro Paranal on October 2006 to obtain high-quality data, has
recently been concluded. In this paper we present the spectra of these pristine
bodies obtained in the visible range during the last two semesters of the LP.
We investigate the spectral behaviour of the TNOs and Centaurs observed, and we
analyse the spectral slopes distribution of the full data set coming from this
LP and from the literature. We computed the spectral slope for each observed
object, and searched for possible weak absorption features. A statistical
analysis was performed on a total sample of 73 TNOs and Centaurs to look for
possible correlations between dynamical classes, orbital parameters, and
spectral gradient. We obtained new spectra for 28 bodies, 15 of which were
observed for the first time. All the new presented spectra are featureless,
including 2003 AZ84, for which a faint and broad absorption band possibly
attributed to hydrated silicates on its surface has been reported. The data
confirm a wide variety of spectral behaviours, with neutral--grey to very red
gradients. An analysis of the spectral slopes available from this LP and in the
literature for a total sample of 73 Centaurs and TNOs shows that there is a
lack of very red objects in the classical population. We present the results of
the statistical analysis of the spectral slope distribution versus orbital
parameters. In particular, we confirm a strong anticorrelation between spectral
slope and orbital inclination for the classical population. A strong
correlation is also found between the spectral slope and orbital eccentricity
for resonant TNOs, with objects having higher spectral slope values with
increasing eccentricity.Comment: 11 pages, 9 figure
Multiline operation from a single plasmon-assisted laser
The demonstration of plasmon-assisted lasing by associating optical gain media with plasmonic nanostructures has led to a new generation of nanophotonic devices with unprecedented performances. However, despite the variety of designs demonstrated so far, the operation of these systems is in most cases limited to a single output wavelength, and some reports on multiline emission refer to mixing single nanolasers with the subsequent limitation in compactness. Here, we show multiline operation from a single plasmon-assisted nonlinear solid-state laser on which a linear chain of Ag nanoparticles is deposited. The system provides lasing at 1.08 μm, which is self-converted to the visible range through different parametric frequency-mixing processes generated at metal-dielectric interfaces. Near infrared and simultaneously green and tunable blue radiation with a subwavelength confinement in the direction perpendicular to the nanoparticle chain, are obtained at room temperature in CW regime. The results demonstrate the possibility of multifunctional operation from a single plasmon-assisted laser and offer new avenues for the development of highly integrable sources of coherent radiationThis work has been supported by the Spanish Ministry of Economy and Competitiveness (MINECO) under Projects MAT201343301-R, MAT2015-66128-R and MAT2016-76106-R and by Comunidad de Madrid under Grant S2013/MIT-274
Prion protein gene sequence and chronic wasting disease susceptibility in white-tailed deer (Odocoileus virginianus)
The sequence of the prion protein gene (PRNP) affects susceptibility to spongiform encephalopathies, or prion diseases in many species. In white-tailed deer, both coding and non-coding single nucleotide polymorphisms have been identified in this gene that correlate to chronic wasting disease (CWD) susceptibility. Previous studies examined individual nucleotide or amino acid mutations; here we examine all nucleotide polymorphisms and their combined effects on CWD. A 626 bp region of PRNP was examined from 703 free-ranging white-tailed deer. Deer were sampled between 2002 and 2010 by hunter harvest or government culling in Illinois and Wisconsin. Fourteen variable nucleotide positions were identified (4 new and 10 previously reported). We identified 68 diplotypes comprised of 24 predicted haplotypes, with the most common diplotype occurring in 123 individuals. Diplotypes that were found exclusively among positive or negative animals were rare, each occurring in less than 1% of the deer studied. Only one haplotype (C, odds ratio 0.240) and 2 diplotypes (AC and BC, odds ratios of 0.161 and 0.108 respectively) has significant associations with CWD resistance. Each contains mutations (one synonymous nucleotide 555C/T and one nonsynonymous nucleotide 286G/A) at positions reported to be significantly associated with reduced CWD susceptibility. Results suggest that deer populations with higher frequencies of haplotype C or diplotypes AC and BC might have a reduced risk for CWD infection – while populations with lower frequencies may have higher risk for infection. Understanding the genetic basis of CWD has improved our ability to assess herd susceptibility and direct management efforts within CWD infected areas.https://digitalcommons.snc.edu/faculty_staff_works/1029/thumbnail.jp
Results of the activity of the Spanish Teratology Information Services (SITTE and SITE) during 2006 and analysis of the maternal age and the number of planned pregnancies
Resultados de otras actividades del ECEMCWe present a summary of the activity of the two Teratology Information Services: SITTE (for health professionals) and SITE (for the general
population) during 2006. We also include a comparative analysis on maternal age and number of planned pregnancies between the
population of mothers who called to SITE and the mothers of the ECEMC's controls (as a representative group of the general population).
The total number of calls received in both services was 4,876 (898 and 3,978 from SITTE and SITE respectively).N
- …