1,175 research outputs found
Extended Optical Model Analyses of Elastic Scattering and Fusion Cross Sections for 6Li + 208Pb System at Near-Coulomb-Barrier Energies by using Folding Potential
Based on the extended optical model approach in which the polarization
potential is decomposed into direct reaction (DR) and fusion parts,
simultaneous analyses are performed for elastic scattering and
fusion cross section data for the Li+Pb system at
near-Coulomb-barrier energies. A folding potential is used as the bare
potential. It is found that the real part of the resultant DR part of the
polarization potential is repulsive, which is consistent with the results from
the Continuum Discretized Coupled Channel (CDCC) calculations and the
normalization factors needed for the folding potentials. Further, it is found
that both DR and fusion parts of the polarization potential satisfy separately
the dispersion relation.Comment: 6 figure
Extended Optical Model Analyses of Elastic Scattering, Direct Reaction, and Fusion Cross Sections for the 9Be + 208Pb System at Near-Coulomb-Barrier Energies
Based on the extended optical model approach in which the polarization
potential is decomposed into direct reaction (DR) and fusion parts,
simultaneous analyses are performed for elastic scattering, DR, and
fusion cross section data for the Be+Pb system at
near-Coulomb-barrier energies. Similar analyses are also performed
by only taking into account the elastic scattering and fusion data as was
previously done by the present authors, and the results are compared with those
of the full analysis including the DR cross section data as well. We find that
the analyses using only elastic scattering and fusion data can produce very
consistent and reliable predictions of cross sections particularly when the DR
cross section data are not complete. Discussions are also given on the results
obtained from similar analyses made earlier for the Be+Bi system.Comment: 5 figure
State of the Climate in 2016: Global Ocean Phytoplankton
Marine phytoplankton contribute roughly half the net primary production (NPP) on Earth, fixing atmospheric CO2 into food that fuels global ocean ecosystems and drives biogeochemical cycles. Satellite ocean color sensors, such as SeaWiFS, MODIS, and VIIRS, provide observations of sufficient frequency and geographic coverage to globally monitor changes in the near-surface concentrations of the phytoplankton pigment chlorophyll-a (Chla; mg -cu m) that serve as a proxy for phytoplankton abundance. Here, global Chla distributions for 2016 are evaluated within the context of the 19-year continuous record provided through the combined observations of SeaWiFS (19972010), MODIS on Aqua (MODISA, 2002present), and VIIRS on Suomi-NPP (2011present). All Chla data used in this analysis correspond to version R2014.0, which utilized common algorithms and calibration methods to maximize consistency in the multi-mission satellite record
Geochemical and biochemical evidence of lake overturn and fish-kill at Lake Averno, Italy.
Lake Averno is situated in the homonymous crater in the northwestern sector of the Campi Flegrei active
volcanic system in Campania region, Italy. In February 2005 a fish kill event was observed in the lake,
prompting a geochemical survey to ascertain the possible cause. In February 2005 a geochemical survey
revealed that the lake water was unstratified chemically and isotopically, presumable, as a result of lake
overturn. This fish-kill phenomenon was recorded at least two other times in the past. In contrast to the
February 2005 results, data collected in October 2005, shows the Lake Averno to be stratified, with an oxic
epilimnion (surface to 6 m) and an anoxic hypolimnion (6 m to lake bottom at about 33 m).
Chemical and isotopic composition of Lake Averno waters suggests an origin by mixing of shallow waters
with a Na-Cl hydrothermal component coupled with an active evaporation process. The isotopic composition
of Dissolved Inorganic Carbon, as well as the composition of the non-reactive dissolved gas species again
supports the occurrence of this mixing process.
Decreasing levels of SO4 and increasing levels of H2S and CH4 contents in lake water with depth, strongly
suggests anaerobic bacterial processes are occurring through decomposition of organic matter under anoxic
conditions in the sediment and in the water column. Sulfate reduction and methanogenesis processes coexist
and play a pivotal role in the anaerobic environment of the Lake Averno. The sulfate reducing bacterial
activity has been estimated in the range of 14-22 ÎŒmol.m-2.day-1.
Total gas pressure of dissolved gases ranges between 800 and 1400 mbar, well below the hydrostatic
pressure throughout the water column, excluding the possibility, at least at the survey time, of a limnic
eruption.
Vertical changes in the density of lake waters indicate that overturn may be triggered by cooling of
epilimnetic waters below 7°C. This is a possible phenomenon in winter periods if atmospheric temperatures
remain frosty for enough time, as occurred in February 2005.
The bulk of these results strongly support the hypothesis that fish kill was caused by a series of events that
began with the cooling of the epilimnetic waters with breaking of the thermal stratification, followed by lake
overturn and the rise of toxic levels of H2S from the reduced waters near the lake bottom
Fusion versus Breakup: Observation of Large Fusion Suppression for ^9Be + ^{208}Pb
Complete fusion excitation functions for Be + Pb have been
measured to high precision at near barrier energies. The experimental fusion
barrier distribution extracted from these data allows reliable prediction of
the expected complete fusion cross-sections. However, the measured
cross-sections are only 68% of those predicted. The large cross-sections
observed for incomplete fusion products support the interpretation that this
suppression of fusion is caused by Be breaking up into charged fragments
before reaching the fusion barrier. Implications for the fusion of radioactive
nuclei are discussed.Comment: RevTex, 11 pages, 2 postscript figures, to appear in PR
Human Polyomaviruses in the Cerebrospinal Fluid of Neurological Patients.
BACKGROUND:
Central nervous system (CNS) infections by human polyomaviruses (HPyVs), with the exception of JC (JCPyV), have been poorly studied.
METHODS:
In total, 234 cerebrospinal fluid (CSF) samples were collected from patients affected with neurological disorders. DNA was isolated and subjected to quantitative real-time PCR (Q-PCR) for the detection of six HPyVs: JCPyV, BKPyV, Merkel cell PyV (MCPyV), HPyV6, HPyV7, and HPyV9. Where possible, the molecular characterization of the viral strains was carried out by nested PCR and automated sequencing.
RESULTS:
JCPyV was detected in 3/234 (1.3%), BKPyV in 15/234 (6.4%), MCPyV in 22/234 (9.4%), and HPyV6 in 1/234 (0.4%) CSF samples. JCPyV was detected at the highest (p < 0.05) mean load (3.7
7 107 copies/mL), followed by BKPyV (1.9
7 106 copies/mL), MCPyV (1.9
7 105 copies/mL), and HPyV6 (3.3
7 104 copies/mL). The noncoding control regions (NCCRs) of the sequenced viral strains were rearranged.
CONCLUSIONS:
HPyVs other than JCPyV were found in the CSF of patients affected with different neurological diseases, probably as bystanders, rather than etiological agents of the disease. However, the fact that they can be latent in the CNS should be considered, especially in immunosuppressed patients
Simultaneous Optical Model Analyses of Elastic Scattering, Breakup, and Fusion Cross Section Data for the He + Bi System at Near-Coulomb-Barrier Energies
Based on an approach recently proposed by us, simultaneous
-analyses are performed for elastic scattering, direct reaction (DR)
and fusion cross sections data for the He+Bi system at
near-Coulomb-barrier energies to determine the parameters of the polarization
potential consisting of DR and fusion parts. We show that the data are well
reproduced by the resultant potential, which also satisfies the proper
dispersion relation. A discussion is given of the nature of the threshold
anomaly seen in the potential
A smart and sustainable future for viticulture is rooted in soil: How to face cu toxicity
In recent decades, agriculture has faced the fundamental challenge of needing to increase food production and quality in order to meet the requirements of a growing global population. Similarly, viticulture has also been undergoing change. Several countries are reducing their vineyard areas, and several others are increasing them. In addition, viticulture is moving towards higher altitudes and latitudes due to climate change. Furthermore, global warming is also exacerbating the incidence of fungal diseases in vineyards, forcing farmers to apply agrochemicals to preserve production yields and quality. The repeated application of copper (Cu)-based fungicides in con-ventional and organic farming has caused a stepwise accumulation of Cu in vineyard soils, posing environmental and toxicological threats. High Cu concentrations in soils can have multiple impacts on agricultural systems. In fact, it can (i) alter the chemical-physical properties of soils, thus com-promising their fertility; (ii) induce toxicity phenomena in plants, producing detrimental effects on growth and productivity; and (iii) affect the microbial biodiversity of soils, thereby influencing some microbial-driven soil processes. However, several indirect (e.g., management of rhizosphere processes through intercropping and/or fertilization strategies) and direct (e.g., exploitation of vine resistant genotypes) strategies have been proposed to restrain Cu accumulation in soils. Furthermore, the application of precision and smart viticulture paradigms and their related technologies could allow a timely, localized and balanced distribution of agrochemicals to achieve the required goals. The present review highlights the necessity of applying multidisciplinary approaches to meet the requisites of sustainability demanded of modern viticulture
Test of mode coupling theory for a supercooled liquid of diatomic molecules.I. Translational degrees of freedom
A molecular dynamics simulation is performed for a supercooled liquid of
rigid diatomic molecules. The time-dependent self and collective density
correlators of the molecular centers of mass are determined and compared with
the predictions of the ideal mode coupling theory (MCT) for simple liquids.
This is done in real as well as in momentum space. One of the main results is
the existence of a unique transition temperature T_c, where the dynamics
crosses over from an ergodic to a quasi-nonergodic behavior. The value for T_c
agrees with that found earlier for the orientational dynamics within the error
bars. In the beta- regime of MCT the factorization of space- and time
dependence is satisfactorily fulfilled for both types of correlations. The
first scaling law of ideal MCT holds in the von Schweidler regime, only, since
the validity of the critical law can not be confirmed, due to a strong
interference with the microscopic dynamics. In this first scaling regime a
consistent description within ideal MCT emerges only, if the next order
correction to the asymptotic law is taken into account. This correction is
almost negligible for q=q_max, the position of the main peak in the static
structure factor S(q), but becomes important for q=q_min, the position of its
first minimum. The second scaling law, i.e. the time-temperature superposition
principle, holds reasonably well for the self and collective density
correlators and different values for q. The alpha-relaxation times tau_q^(s)
and tau_q follow a power law in T-T_c over 2 -- 3 decades. The corresponding
exponent gamma is weakly q-dependent and is around 2.55. This value is in
agreement with the one predicted by MCT from the value of the von Schweidler
exponent but at variance with the corresponding exponent gammaComment: 14 pages of RevTex, 19 figure
Towards an effective potential for the monomer, dimer, hexamer, solid and liquid forms of hydrogen fluoride
We present an attempt to build up a new two-body effective potential for
hydrogen fluoride, fitted to theoretical and experimental data relevant not
only to the gas and liquid phases, but also to the crystal. The model is simple
enough to be used in Molecular Dynamics and Monte Carlo simulations. The
potential consists of: a) an intra-molecular contribution, allowing for
variations of the molecular length, plus b) an inter-molecular part, with three
charged sites on each monomer and a Buckingham "exp-6" interaction between
fluorines. The model is able to reproduce a significant number of observables
on the monomer, dimer, hexamer, solid and liquid forms of HF. The shortcomings
of the model are pointed out and possible improvements are finally discussed.Comment: LaTeX, 24 pages, 2 figures. For related papers see also
http://www.chim.unifi.it:8080/~valle
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