785 research outputs found
Laboratory and field measurements of enantiomeric monoterpene emissions as a function of chemotype, light and temperature
Plants emit significant amounts of monoterpenes into the
earth's atmosphere, where they react rapidly to form a multitude of gas phase
species and particles. Many monoterpenes exist in mirror-image forms or
enantiomers. In this study the enantiomeric monoterpene profile for several
representative plants (<i>Quercus ilex L., Rosmarinus officinalis L.</i>,
and <i>Pinus halepensis Mill.</i>) was investigated as a function of
chemotype, light and temperature both in the laboratory and in the field.
Analysis of enantiomeric monoterpenes from 19 <i>Quercus ilex</i>
individuals from Southern France and Spain revealed four regiospecific
chemotypes (genetically fixed emission patterns). In agreement with previous
work, only <i>Quercus ilex</i> emissions increased strongly with light.
However, for all three plant species no consistent enantiomeric variation was
observed as a function of light, and the enantiomeric ratio of α-pinene was found to vary by less than 20% from 100 and
1000 μmol m<sup>−2</sup> s<sup>−1</sup> PAR (photosynthetically active
radiation). The rate of monoterpene emission increased with temperature from
all three plant species, but little variation in the enantiomeric
distribution of α-pinene was observed with temperature. There was
more enantiomeric variability between individuals of the same species than
could be induced by either light or temperature. Field measurements of
α-pinene enantiomer mixing ratios in the air, taken at a
<i>Quercus ilex</i> forest in Southern France, and several other previously
reported field enantiomeric ratio diel cycle profiles are compared. All show
smoothly varying diel cycles (some positive and some negative) even over
changing wind directions. This is surprising in comparison with variations of
enantiomeric emission patterns shown by individuals of the same species
Nuclear signatures in high-harmonic generation from laser-driven muonic atoms
High-harmonic generation from muonic atoms exposed to intense laser fields is
considered. Our particular interest lies in effects arising from the finite
nuclear mass and size. We numerically perform a fully quantum mechanical
treatment of the muon-nucleus dynamics by employing modified soft-core and
hard-core potentials. It is shown that the position of the high-energy cutoff
of the harmonic spectrum depends on the nuclear mass, while the height of the
spectral plateau is sensitive to the nuclear radius. We also demonstrate that
-ray harmonics can be generated from muonic atoms in ultrastrong VUV
fields, which have potential to induce photo-nuclear reactions.Comment: 5 pages, 3 figure
Direct neutron capture of 48Ca at kT = 52 keV
The neutron capture cross section of 48Ca was measured relative to the known
gold cross section at kT = 52 keV using the fast cyclic activation technique.
The experiment was performed at the Van-de-Graaff accelerator, Universitaet
Tuebingen. The new experimental result is in good agreement with a calculation
using the direct capture model. The 1/v behaviour of the capture cross section
at thermonuclear energies is confirmed, and the adopted reaction rate which is
based on several previous experimental investigations remains unchanged.Comment: 9 pages (uses Revtex), 2 postscript figures, accepted for publication
as Brief Report in Phys. Rev.
Origin of atomic clusters during ion sputtering
Previous studies have shown that the size distributions of small clusters ( n<=40 n = number of atoms/cluster) generated by sputtering obey an inverse power law with an exponent between -8 and -4. Here we report electron microscopy studies of the size distributions of larger clusters ( n>=500) sputtered by high-energy ion impacts. These new measurements also yield an inverse power law, but one with an exponent of -2 and one independent of sputtering yield, indicating that the large clusters are produced when shock waves, generated by subsurface displacement cascades, ablate the surface
Shell Model Study of the Double Beta Decays of Ge, Se and Xe
The lifetimes for the double beta decays of Ge, Se and
Xe are calculated using very large shell model spaces. The two neutrino
matrix elements obtained are in good agreement with the present experimental
data. For eV we predict the following upper bounds to the
half-lives for the neutrinoless mode: , and . These results are the first from a new generation of Shell
Model calculations reaching O(10) dimensions
Neutrinoless Double Beta Decay within QRPA with Proton-Neutron Pairing
We have investigated the role of proton-neutron pairing in the context of the
Quasiparticle Random Phase approximation formalism. This way the neutrinoless
double beta decay matrix elements of the experimentally interesting A= 48, 76,
82, 96, 100, 116, 128, 130 and 136 systems have been calculated. We have found
that the inclusion of proton-neutron pairing influences the neutrinoless double
beta decay rates significantly, in all cases allowing for larger values of the
expectation value of light neutrino masses. Using the best presently available
experimental limits on the half life-time of neutrinoless double beta decay we
have extracted the limits on lepton number violating parameters.Comment: 16 RevTex page
Neutrinoless Double Beta Decay in Supersymmetric Seesaw model
Inspired by the recent HEIDELBERG-MOSCOW double beta decay experiment, we
discuss the neutrinoless double beta decay in the supersymmetric seesaw model.
Our numerical analysis indicates that we can naturally explain the data of the
observed neutrinoless double beta decay, as well as that of the solar and
atmospheric neutrino experiments with at least one Majorana-like sneutrino of
middle energy scale in the model.Comment: latex, 25 pages, include 5 figures, final version in Phys. Rev.
The melanoma-specific graded prognostic assessment does not adequately discriminate prognosis in a modern population with brain metastases from malignant melanoma
The melanoma-specific graded prognostic assessment (msGPA) assigns patients with brain metastases from malignant melanoma to 1 of 4 prognostic groups. It was largely derived using clinical data from patients treated in the era that preceded the development of newer therapies such as BRAF, MEK and immune checkpoint inhibitors. Therefore, its current relevance to patients diagnosed with brain metastases from malignant melanoma is unclear. This study is an external validation of the msGPA in two temporally distinct British populations.Performance of the msGPA was assessed in Cohort I (1997-2008, n=231) and Cohort II (2008-2013, n=162) using Kaplan-Meier methods and Harrell's c-index of concordance. Cox regression was used to explore additional factors that may have prognostic relevance.The msGPA does not perform well as a prognostic score outside of the derivation cohort, with suboptimal statistical calibration and discrimination, particularly in those patients with an intermediate prognosis. Extra-cerebral metastases, leptomeningeal disease, age and potential use of novel targeted agents after brain metastases are diagnosed, should be incorporated into future prognostic models.An improved prognostic score is required to underpin high-quality randomised controlled trials in an area with a wide disparity in clinical care
Constraining Almost Degenerate Three-Flavor Neutrinos
We discuss constraints on a scenario of almost degenerate three-flavor
neutrinos imposed by the solar and the atmospheric neutrino anomalies, hot dark
matter, and neutrinoless double decays. It is found that in the
Majorana version of the model the region with relatively large is
favored and a constraint on the CP violating phases is obtained.Comment: 19 pages (uses revtex), including 6 figures (uses epsf
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