1,441 research outputs found
Les modèles numériques des microhabitats des passons : application et nouveaux développements
L'estimation des stocks de poissons que peut abriter un secteur de cours d'eau non pollué nécessite le calcul de sa capacité d'accueil en terme d'espace et de nourriture. Le premier volet a donné lieu aux Etats-Unis à la mise en place de modèles de comportement de différentes espèces de poissons en fonction de variables physiques et de modèles hydrauliques décrivant l'évolution temporelle de ces variables.Les hypothèses sous-jacentes sont discutées. Une modification du calcul de la perte de charge linéaire est préconisée pour le modèle hydraulique dans le cas des rivières à truites, et l'utilisation de méthodes multivariées est proposée pour décrire avec une meilleure fiabilité les relations entre densités de poissons et variables physiques des cours d'eau.Quelques cas d'application illustrent l'intérêt de cette démarche pour répondre à des questions posées par les gestionnaires, tant en matière de prévision des impacts piscicoles des aménagements que d'optimisation des repeuplements.When evaluating the potential fish stock that an unpolluted reach of a stream can accomodate, the load capacity with regard to space and food available must be assessed. It is for this purpose that the Instream Flow Incremental Methodology has been developed in the United States.The assumptions on which behavioural and hydraulic models are based are discussed and modifications are suggested to improve the efficiency of this methodology.The use of the Manning equation to compute the energy loss is misleading in the case of trout streams and results from simulation are more reliable when using resistance equations designed for mountain rivers.For biological monitoring, multivariate data analysis is an interesting alternative to drawing one-dimensional preference curves. Qualitative variables can be used and redundancy or dependence between parameters no longer distorts the results. The relations between physical variables of streams and a probability of the presence of fish are estimated with greater accuracy.Examples of the application of this methodology are presented with a view to assessing the effects of water abstraction on fish populations and to optimizing the restocking of trout streams
Experimental and Theoretical Results for Weak Charge Current Backward Proton Production
In this paper, we do three things in the study of deuteron break-up by high
energy neutrino beams. (1) We present previously unpublished data on neutrino
induced backward protons from deuteron targets; (2) we calculate the
contributions from both the two-nucleon (2N) and six-quark (6q) deuteron
components, which depend upon the overall normalization of the part that is 6q;
and (3) we suggest other signatures for distinguishing the 2N and 6q clusters.
We conclude that the 6q cluster easily explains the shape of the high momentum
backward proton spectrum, and its size is nicely explained if the amount of 6q
is one or a few percent by normalization of the deuteron. There is a crossover,
above which the 6q contribution is important or dominant, at 300--400 MeV/c
backward proton momentum.Comment: 8 pages, 5 figure
Skyrmions and the Nuclear Force
The derivation of the nucleon-nucleon force from the Skyrme model is
reexamined. Starting from previous results for the potential energy of
quasistatic solutions, we show that a calculation using the Born-Oppenheimer
approximation properly taking into account the mixing of nucleon resonances,
leads to substantial central attraction. We obtain a potential that is in
qualitative agreement with phenomenological potentials. We also study the
non-adiabatic corrections, such as the velocity dependent transition
potentials, and discuss their importance.Comment: 24 pages, UPR-0124M
The Transient Dendritic Solidification Experiment (TDSE)
The study of steady-state dendritic growth has both validated many element of transport phenomena in dendritic growth, and yielded many new insights. Further development in simulation and modeling are needed, as is further understanding of the role of selection or scaling in dendritic growth. The TDSE contributes to the further study of dendritic phenomena by carefully measuring and modeling transient effects on dendritic growth. The major challenge encountered in measuring and analyzing the transient behavior of isothermal dendrites is defining precisely the initial conditions from which or to which the dendrite evolves. Our proposed pressure-mediated TDSE microgravity experiment, obviates this difficulty, because the transient occurs between two well-characterized steady-states, rather than between an ill-defined initial state and the final steady state. The major results expected are unique data on transient behavior that will extend the scientific bounds from the now well-understood thermal effects, and provide insight into interfacial dynamics where open questions remain
The Isothermal Dendritic Growth Experiment (IDGE)
The Isothermal Dendritic Growth Experiment (IDGE) constituted a series of three NASA-supported microgravity experiments, all of which flew aboard the space shuttle, Columbia. This experimental space flight series was designed and operated to grow and record dendrite solidification in the absence of gravity-induced convective heat transfer, and thereby produce a wealth of benchmark-quality data for testing solidification scaling laws. The data and analysis performed on the dendritic growth speed and tip size in Succinontrie (SCN) demonstrates that although the theory yields predictions that are reasonably in agreement with experiment, there are significant discrepancies. However, some of these discrepancies can be explained by accurately describing the diffusion of heat. The key finding involves recognition that the actual three-dimensional shape of dendrites includes time-dependent side-branching and a tip region that is not a paraboloid of revolution. Thus, the role of heat transfer in dendritic growth is validated, with the caveat that a more realistic model of the dendrite then a paraboloid is needed to account for heat flow in an experimentally observed dendrite. We are currently conducting additional analysis to further confirm and demonstrate these conclusions. The data and analyses for the growth selection physics remain much less definitive. From the first flight, the data indicated that the selection parameter, sigma*, is not exactly a constant, but exhibits a slight dependence on the supercooling. Additional data from the second flight are being examined to investigate the selection of a unique dendrite speed, tip size and shape. The IDGE flight series is now complete. We are currently completing analyses and moving towards final data archiving. It is gratifying to see that the IDGE published results and archived data sets are being used actively by other scientists and engineers. In addition, we are also pleased to report that the techniques and IDGE hardware system that the authors developed with NASA, are being currently employed on both designated flight experiments, like EDSE, and on flight definition experiments, like TDSE
On the K^+D Interaction at Low Energies
The Kd reactions are considered in the impulse approximation with NN
final-state interactions (NN FSI) taken into account. The realistic parameters
for the KN phase shifts are used. The "quasi-elastic" energy region, in which
the elementary KN interaction is predominantly elastic, is considered. The
theoretical predictions are compared with the data on the K^+d->K^+pn,
K^+d->K^0pp, K^+d->K^+d and K^+d total cross sections. The NN FSI effect in the
reaction K^+d->K^+pn has been found to be large. The predictions for the Kd
cross sections are also given for slow kaons, produced from phi(1020) decays,
as the functions of the isoscalar KN scattering length a_0. These predictions
can be used to extract the value of a_0 from the data.Comment: 22 pages, 5 figure
Magnetic field turbulence in the solar wind at sub-ion scales: in situ observations and numerical simulations
We investigate the transition of the solar wind turbulent cascade from MHD to
sub-ion range by means of a detail comparison between in situ observations and
hybrid numerical simulations. In particular we focus on the properties of the
magnetic field and its component anisotropy in Cluster measurements and hybrid
2D simulations. First, we address the angular distribution of wave-vectors in
the kinetic range between ion and electron scales by studying the variance
anisotropy of the magnetic field components. When taking into account the
single-direction sampling performed by spacecraft in the solar wind, the main
properties of the fluctuations observed in situ are also recovered in our
numerical description. This result confirms that solar wind turbulence in the
sub-ion range is characterized by a quasi-2D gyrotropic distribution of
k-vectors around the mean field. We then consider the magnetic compressibility
associated with the turbulent cascade and its evolution from large-MHD to
sub-ion scales. The ratio of field-aligned to perpendicular fluctuations,
typically low in the MHD inertial range, increases significantly when crossing
ion scales and its value in the sub-ion range is a function of the total plasma
beta only, as expected from theoretical predictions, with higher magnetic
compressibility for higher beta. Moreover, we observe that this increase has a
gradual trend from low to high beta values in the in situ data; this behaviour
is well captured by the numerical simulations. The level of magnetic field
compressibility that is observed in situ and in the simulations is in fairly
good agreement with theoretical predictions, especially at high beta,
suggesting that in the kinetic range explored the turbulence is supported by
low-frequency and highly-oblique fluctuations in pressure balance, like kinetic
Alfv\'en waves or other slowly evolving coherent structures.Comment: Manuscript submitted to Frontiers Astronomy and Space Sciences,
Research Topic: Improving the Understanding of Kinetic Processes in Solar
Wind and Magnetosphere: From CLUSTER to MM
Development of standardized method for the determination of the degradation of nitric oxide (NO) in the air by photocatalytic materials: Inter-laboratory validation tests
International audienceThe need of a uniform experimental procedure for assessing the performance of photocatalytic inorganic materials contained in building materials led the European Committee for Standardization (CEN/TC386/WG2) to elaborate a Technical Specification (TS).Taking into consideration the importance of the effects which will be of possible variations in the implementation of the reference method, parallel photocatalytic tests according to the TS were performed in the current study. 6 European labs were participated in an inter-laboratory exercise where the experiments had to be done in a special design CEN reactor using LED system. The experimental procedure and conditions were taken from the draft TS and were referred to the average irradiance, inlet NO & NO 2 concentration, T o C and RH inside the reactor, flow and reactor net volume. Identical photocatalytic samples were provided to all participants. The results obtained from the 6 labs showed a variation between 18% and 31% on the photocatalytic NO conversion while the mean value was 26%. The corresponding photocatalytic rate was ranged between 2600 μg/m 2 h and 4100 μg/m 2 h presenting a mean value of 3400 μg/m 2 h. The homogeneity of the lamp and the homogeneity of the deposition of TiO 2 are the main factors impacting the results
The Breathing Mode in Extended Skyrme Model
We study an extended Skyrme model which includes fourth and sixth-order
terms. We explore some static properties like the -nucleon mass
splitting and investigate the Skyrmion breathing mode in the framework of the
linear response theory. We find that the monopole response function has a
pronounced peak located at 400 MeV, which we identify to the Roper
resonance . As compared to the standard one, the extended Skyrme model
provides a more accurate description of baryon properties.Comment: 12 pages of plain Latex and 3 figures (available from the authors),
preprint IPNO/TH 93-0
THz packaging solution for low cost si-based 40 Gb/s wireless link system
This paper presents an innovative low-cost transmitter solution aimed at improving telecommunication networks capacities in order to support the massive data traffic growth. Sub-THz frequencies > 200 GHz are considered to target at least 40 Gb/s. The proposed transmitter consists of a Silicon Photonic integrated sub-THz source and an industrial antenna integrated in HDI organic packaging substrate. As these components were experimentally evaluated, a real-time error free wireless data transmission of 10 Gb/s was successfully achieved and an antenna gain of 5.5 dBi was measured in the broadside direction from 220 GHz to 240 GHz (8.7% relative bandwidth). With the addition of a low-cost dielectric lens, a gain of 17 dBi was reached.info:eu-repo/semantics/acceptedVersio
- …