527 research outputs found
Three kinematical methods to identify local galactic structures
Method one: by combining a sampling parameter related to an isolating integral of the stellar motion, an optimisation of
the mixture approach, and a maximisation of the partition entropy for the constituent populations of the stellar sample.
Method two: by segregating into different kinematical components in terms of the stellar orbital parameters.
Method three: by approaching a maximum entropy velocity distribution to samples selected in terms of stellar eccentricity
layers.
Working samples: HIPPARCOS and Geneva-Copenhagen survey catalog.
Results: kinematical characterisation of large-scale structures, such as thin disc, thick disc and halo, and identification of
small-scale structures, such as moving groups in the solar neighbourhood.
Consequences: confirmation of the Titius-Bode-like law for radial velocity dispersions and explanation of the apparent
vertex deviation of the disc from the swinging of two major kinematic groups around the LSR, by predicting a continuously
changing orientation of the disc pseudo ellipsoid.Postprint (published version
Recommended from our members
Osmotic and Activity Coefficients of the {xZnCl2 + (1 - x)ZnSO4}(aq) System at 298.15 K
Isopiestic vapor pressure measurements were made for (xZnCl{sub 2} + (1 - x)ZnSO{sub 4})(aq) solutions with ZnCl{sub 2} molality fractions of x = (0, 0.3062, 0.5730, 0.7969, and 1) at the temperature 298.15 K, using KCl(aq) as the reference standard. These measurements cover the water activity range 0.901-0.919 {le} a{sub w} {le} 0.978. The experimental osmotic coefficients were used to evaluate the parameters of an extended ion-interaction (Pitzer) model for these mixed electrolyte solutions. A similar analysis was made of the available activity data for ZnCl{sub 2}(aq) at 298.15 K, while assuming the presence of equilibrium amounts of ZnCl{sup +}(aq) ion-pairs, to derive the ion-interaction parameters for the hypothetical pure binary electrolytes (Zn{sup 2+}, 2Cl{sup -}) and (ZnCl{sup +},Cl{sup -}). These parameters are required for the analysis of the mixture results. Although significant concentrations of higher-order zinc chloride complexes may also be present in these solutions, it was possible to represent the osmotic coefficients accurately by explicitly including only the predominant complex ZnCl{sup +}(aq) and the completely dissociated ions. The ionic activity coefficients and osmotic coefficients were calculated over the investigated molality range using the evaluated extended Pitzer model parameters
Influence of Annealing on the Optical and Scintillation Properties of CaWO Single Crystals
We investigate the influence of oxygen annealing on the room temperature
optical and scintillation properties of CaWO single crystals that are being
produced for direct Dark Matter search experiments. The applied annealing
procedure reduces the absorption coefficient at the peak position of the
scintillation spectrum ( nm) by a factor of and leads to an
even larger reduction of the scattering coefficient. Furthermore, the annealing
has no significant influence on the \emph{intrinsic} light yield. An additional
absorption occurring at nm suggests the formation of O hole
centers. Light-yield measurements at room temperature where one crystal surface
was mechanically roughened showed an increase of the \emph{measured} light
yield by and an improvement of the energy resolution at 59.5 keV by
for the annealed crystal. We ascribe this result to the reduction of
the absorption coefficient while the surface roughening is needed to compensate
for the also observed reduction of the scattering coefficient after annealing
The CRESST Dark Matter Search
We present first competitive results on WIMP dark matter using the
phonon-light-detection technique. A particularly strong limit for WIMPs with
coherent scattering results from selecting a region of the phonon-light plane
corresponding to tungsten recoils. The observed count rate in the neutron band
is compatible with the rate expected from neutron background. CRESST is
presently being upgraded with a 66 channel SQUID readout system, a neutron
shield and a muon veto system. This results in a significant improvement in
sensitivity.Comment: 6 pages, 3 figures, to be published in the proceedings of the 5th
International Workshop on the Identification and Detection of Dark Matter IDM
2004, Edinburgh, Sept. 2004, World Scientifi
The HARE chip for efficient time-resolved serial synchrotron crystallography
Serial synchrotron crystallography (SSX) is an emerging technique for static and time-resolved protein structure determination. Using specifically patterned silicon chips for sample delivery, the `hit-and-return' (HARE) protocol allows for efficient time-resolved data collection. The specific pattern of the crystal wells in the HARE chip provides direct access to many discrete time points. HARE chips allow for optical excitation as well as on-chip mixing for reaction initiation, making a large number of protein systems amenable to time-resolved studies. Loading of protein microcrystals onto the HARE chip is streamlined by a novel vacuum loading platform that allows fine-tuning of suction strength while maintaining a humid environment to prevent crystal dehydration. To enable the widespread use of time-resolved serial synchrotron crystallography (TR-SSX), detailed technical descriptions of a set of accessories that facilitate TR-SSX workflows are provided
Effect of within-species plant genotype mixing on habitat preference of a polyphagous insect predator
The effects of within-species plant genotype mixing on the habitat preference of a polyphagous ladybird were studied. Plant species diversity is often claimed to positively affect habitat preferences of insect predators, but the effects of within-species genotype diversity have not been extensively studied. In a field experiment with different barley (Hordeum vulgare) genotypes in mixed and pure stands, adult seven-spot ladybird Coccinella septempunctata, a polyphagous predator, preferred a specific combination of genotypes over the single genotypes alone before aphids had arrived in the crop, and again when aphids were emigrating. In laboratory experiments on adult ladybird orientation to odour from barley, ladybirds were attracted/arrested by the mixed odour of the same barley genotype mixture that was preferred in the field. Exposure of one barley genotype to volatiles from the other also caused the odour of the exposed plants to become more attractive to ladybirds. The results support the hypothesis that plant volatiles may attract or arrest foraging adult ladybirds, contributing to the selection of favourable habitats, and they show that within-species plant genotype mixing can shape interactions within multitrophic communities
Detection of the Natural Alpha Decay of Tungsten
The natural alpha decay of 180W has been unambiguously detected for the first
time. The alpha peak is found in a (gamma,beta and neutron)-free background
spectrum. This has been achieved by the simultaneous measurement of phonon and
light signals with the CRESST cryogenic detectors. A half-life of T1/2 = (1.8
+- 0.2) x 10^18 y and an energy release of Q = (2516.4 +- 1.1 (stat.) +- 1.2
(sys.)) keV have been measured. New limits are also set on the half-lives of
the other naturally occurring tungsten isotopes.Comment: Submitted to Physical Review C Revised versio
- âŠ