192 research outputs found
Classical Effects of Laser Pulse Duration on Strong-field Double Ionization
We use classical electron ensembles and the aligned-electron approximation to
examine the effect of laser pulse duration on the dynamics of strong-field
double ionization. We cover the range of intensities
for the laser wavelength 780 nm. The classical scenario suggests that the
highest rate of recollision occurs early in the pulse and promotes double
ionization production in few-cycle pulses. In addition, the purely classical
ensemble calculation predicts an exponentially decreasing recollision rate with
each subsequent half cycle. We confirm the exponential behavior by trajectory
back-analysis
Measurement campaign on the JRC Ispra decommissioning site
The purpose of this document is to describe the measurement campaign with the Free Release Measurement Facility (FRMF) at building 41m âInterim Storage Facilityâ (ISF) of material clearable according to existing licenses as part of the collaborative research project MetroDecom.
The description of the measurement campaign includes the technical requirements and safety implementations necessary for carrying out this project.
The Free Release Measurement Facility (FRMF) was designed as a state of the art facility for measurement of low gamma-ray activity waste packages. Gamma spectrometric method for free release measurment was developed. The complemented with passive neutron counting method. The both methods are used for different nuclide contents in the waste and are complementary.
For this purpose the instrument incorporates:
â Three passive neutron counters (design of JRC)
â A gamma-ray detection system HPGe Interchangeable Detector Module IDM-200-V (ORTEC)
â NuDET Plastic Scintillation Detectors (design of NUVIA)
Decommissioning unit delivered seventy containers with material clearable according to existing JRC licenses. JRC G.II.7 performed the testing of the free release measurement system. The document contains the overview of that measurement campaign. The detailed measurement protocols, spectra generated by FRMF software are shared with MetroDecom Partners.JRC.G.II.7-Nuclear securit
A theoretical approach for the interpretation of pulsating PMS intermediate-mass stars
The investigation of the pulsation properties of pre-main-sequence
intermediate-mass stars is a promising tool to evaluate the intrinsic
properties of these stars and to constrain current evolutionary models. Many
new candidates of this class have been discovered during the last decade and
very accurate data are expected from space observations obtained for example
with the CoRoT satellite. In this context we aim at developing a theoretical
approach for the interpretation of observed frequencies, both from the already
available ground-based observations and from the future more accurate and
extensive CoRoT results. To this purpose we have started a project devoted to
the computations of fine and extensive grids of asteroseismic models of
intermediate mass pre-main-sequence stars. The obtained frequencies are used to
derive an analytical relation between the large frequency separation and the
stellar luminosity and effective temperature and to develop a tool to compare
theory and observations in the echelle diagram. The predictive capabilities of
the proposed method are verified through the application to two test stars. As
a second step, we apply the procedure to two true observations from multisite
campaigns and we are able to constrain their stellar parameters, in particular
the mass, in spite of the small number of frequencies. We expect that with a
significantly higher number of frequencies both the stellar mass and age could
be constrained and, at the same time, the physics of the models could be
tested.Comment: Accepted for publication on A&
Effect of Heart Structure on Ventricular Fibrillation in the Rabbit: A Simulation Study
Ventricular fibrillation (VF) is a lethal condition that affects millions worldwide. The mechanism underlying VF is unstable reentrant electrical waves rotating around lines called filaments. These complex spatio-temporal patterns can be studied using both experimental and numerical methods. Computer simulations provide unique insights including high resolution dynamics throughout the heart and systematic control of quantities such as fiber orientation and cellular kinetics that are not feasible experimentally. Here we study filament dynamics using two bi-ventricular 3-D high-resolution rabbit heart geometries, one with detailed fine structure and another without fine structure. We studied filament dynamics using anisotropic and isotropic conductivities, and with four cellular action potential models with different recovery kinetics. Spiral wave dynamics observed in isotropic two-dimensional sheets were not predictive of the behavior in the whole heart. In 2-D the four cell models exhibited stable reentry, meandering spiral waves, and spiral-wave breakup. In the whole heart with fine structure, all simulation results exhibited complex dynamics reminiscent of fibrillation observed experimentally. In the whole heart without fine structure, anisotropy acted to destabilize filament dynamics although the number of filaments was reduced compared to the heart with structure. In addition, in isotropic hearts without structure the two cell models that exhibited meandering spiral waves in 2-D, stabilized into figure-of-eight surface patterns. We also studied the sensitivity of filament dynamics to computer system configuration and initial conditions. After large simulation times, different macroscopic results sometimes occurred across different system configurations, likely due to a lack of bitwise reproducibility. The study conclusions were insensitive to initial condition perturbations, however, the exact number of filaments over time and their trends were altered by these changes. In summary, we present the following new results. First, we provide a new cell model that resembles the surface patterns of VF in the rabbit heart both qualitatively and quantitatively. Second, filament dynamics in the whole heart cannot be predicted from spiral wave dynamics in 2-D and we identified anisotropy as one destabilizing factor. Third, the exact dynamics of filaments are sensitive to a variety of factors, so we suggest caution in their interpretation and their quantitative analyses
Potential of Endangered Local Donkey Breeds in Meat and Milk Production
The problem of the erosion of animal genetic resources is evident in certain local donkey breeds, and their long-term sustainability can be achieved by economically repositioning them. To develop alternative and sustainable commercial programs, the meat and milk production characteristics of Istrian donkey and Littoral Dinaric donkey breeds were investigated. The meat production characteristics were examined in mature males, whose carcasses were dissected, and meat composition was determined using NIT spectrophotometry and gas chromatography. Milk yield and milk composition were determined in jennies in second or subsequent lactations by measuring milk volume and using infrared spectrometry and gas chromatography. Compared to the Littoral Dinaric donkey, the Istrian donkey has a higher carcass weight and dressing percentage (p < 0.001). The share of boneless meat in relation to live weight was 28.27% in the Istrian donkey and 26.18% in the Littoral Dinaric donkey. The absolute masses of primal cuts of meat in E, I, and II classes were significantly greater in Istrian donkeys than in Littoral Dinaric donkeys (p < 0.01), although the differences in the proportions of primal cuts were not significant. The breed did not have a significant impact on the color, pH, or meat composition. A significant influence of breed on milk yield, lactose, protein, and the fat content of milk was observed (p < 0.01). A significant influence of breed on the ratio of n-6/n-3 PUFA fatty acids in donkey milk was observed (p = 0.002). The values of the atherogenic and thrombogenic indexes were favorable, considering potential beneficial effects of donkey milk and meat on consumer health. The findings of this research suggest that local donkey breeds hold significant potential for meat and milk production, focusing on the uniqueness and quality of their products rather than the quantity of meat and milk they can produce
Disentangling discrepancies between stellar evolution theory and sub-solar mass stars. The influence of the mixing length parameter for the UV Psc binary
Serious discrepancies have recently been observed between predictions of
stellar evolution models in the 0.7-1.1 M_sun mass range and accurately
measured properties of binary stars with components in this mass range. We
study one of these objects, the eclipsing binary UV Piscium, which is
particularly interesting because Popper (1997) derived age estimates for each
component which differed by more than a factor of two. In an attempt to solve
this significant discrepancy (a difference in age of 11 Gyr), we compute a
large grid of stellar evolution models with the CESAM code for each component.
By fixing the masses to their accurately determined values (relative error
smaller than 1% for both stars), we consider a wide range of possible
metallicities Z (0.01 to 0.05), and Helium content Y (0.25 to 0.34)
uncorrelated to Z. In addition, the mixing length parameter alpha_MLT is left
as another free parameter. We obtain a best fit in the T_eff-radius diagram for
a common chemical composition (Z, Y)=(0.012, 0.31), but a different MLT
parameter alpha_MLT_A = 0.95+-0.12(statistical)+0.30(systematic) and
alpha_MLT_B = 0.65+-0.07(stat)+0.10(syst). The apparent age discrepancy found
by Popper (1997) disappears with this solution, the components being coeval to
within 1%. This suggests that fixing alpha_MLT to its solar value (~1.6), a
common hypothesis assumed in most stellar evolutionary models, may not be
correct. Secondly, since alpha_MLT is smaller for the less massive component,
this suggests that the MLT parameter may decrease with stellar mass, showing
yet another shortcoming of the mixing length theory to explain stellar
convection. This trend needs further confirmation with other binary stars with
accurate data.Comment: 8 pages, accepted for publication in Astronomy & Astrophysic
Inter-comparison of the g-, f- and p-modes calculated using different oscillation codes for a given stellar model
In order to make astroseismology a powerful tool to explore stellar
interiors, different numerical codes should give the same oscillation
frequencies for the same input physics. This work is devoted to test, compare
and, if needed, optimize the seismic codes used to calculate the
eigenfrequencies to be finally compared with observations. The oscillation
codes of nine research groups in the field have been used in this study. The
same physics has been imposed for all the codes in order to isolate the
non-physical dependence of any possible difference. Two equilibrium models with
different grids, 2172 and 4042 mesh points, have been used, and the latter
model includes an explicit modelling of semiconvection just outside the
convective core. Comparing the results for these two models illustrates the
effect of the number of mesh points and their distribution in particularly
critical parts of the model, such as the steep composition gradient outside the
convective core. A comprehensive study of the frequency differences found for
the different codes is given as well. These differences are mainly due to the
use of different numerical integration schemes. The use of a second-order
integration scheme plus a Richardson extrapolation provides similar results to
a fourth-order integration scheme. The proper numerical description of the
Brunt-Vaisala frequency in the equilibrium model is also critical for some
modes. An unexpected result of this study is the high sensitivity of the
frequency differences to the inconsistent use of values of the gravitational
constant (G) in the oscillation codes, within the range of the experimentally
determined ones, which differ from the value used to compute the equilibrium
model.Comment: 18 pages, 34 figure
Correlated multi-electron dynamics in ultrafast laser pulse - atom interactions
We present the results of the detailed experimental study of multiple
ionization of Ne and Ar by 25 and 7 fs laser pulses. For Ne the highly
correlated "instantaneous" emission of up to four electrons is triggered by a
recollisional electron impact, whereas in multiple ionization of Ar different
mechanisms, involving field ionization steps and recollision-induced
excitations, play a major role. Using few-cycle pulses we are able to suppress
those processes that occur on time scales longer than one laser cycle.Comment: 9 pages, 4 figure
Asteroseismic fundamental properties of solar-type stars observed by the NASA Kepler Mission
We use asteroseismic data obtained by the NASA Kepler Mission to estimate the
fundamental properties of more than 500 main-sequence and sub-giant stars. Data
obtained during the first 10 months of Kepler science operations were used for
this work, when these solar-type targets were observed for one month each in a
survey mode. Stellar properties have been estimated using two global
asteroseismic parameters and complementary photometric and spectroscopic data.
Homogeneous sets of effective temperatures were available for the entire
ensemble from complementary photometry; spectroscopic estimates of T_eff and
[Fe/H] were available from a homogeneous analysis of ground-based data on a
subset of 87 stars. [Abbreviated version... see paper for full abstract.]Comment: Accepted for publication in ApJS; 90 pages, 22 figures, 6 tables.
Units on rho in tables now listed correctly as rho(Sun
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