Dynamic Compaction Using Select Fill Displacement Methods

Since its development as a full-fledged soil compaction technique by Louis Menard in the late 1960s, the Dynamic Compaction method has evolved considerably and has become an increasingly efficient ground improvement system. Among the special techniques borne out of this evolution is the use of Dynamic Compaction to create large-diameter columns using select granular material. This method serves to not only provide increased support and better distribution of imposed loads through the columns themselves, but also augments the capability of the process in improving the host soils to a depth and degree not possible using conventional DC methods. Three case histories are presented to illustrate this technique and its benefits in terms of increased effectiveness and range of application

Microparasite species richness in rodents is higher at lower latitudes and is associated with reduced litter size

Parasite species loads are expected to be higher in the tropics and higher parasite species richness to have cumulative effects on host physiology or demography. Despite being regularly assumed or predicted, empirical evidence on specieslatitude patterns is scarce or contradictory and studies on the impacts of concomitant infections have mainly been done at host intra-specific level. Broad generalizations are then very hard, if not spurious. By focusing on rodent species and their non-eukaryotic microparasites (i.e. viruses and bacteria), we investigated, using a comparative approach, microparasite species richness across rodent species according to the latitude where they occur. We also explored the links between rodents' reproductive traits, latitude and microparasite species richness. We find for the first time in rodents that virus species richness increases towards tropical latitudes, and that rodent litter size seems to decrease when microparasite species richness increases independently from the latitude. These results support the hypotheses that rodent species in the tropics effectively harbour higher parasite species loads, at least in terms of species richness for viruses, and that parasite species richness influences rodent life-history traits. Although some other factors, such as seasonality, were not taken into account due the lack of data, our study stresses the idea that chronic microparasite infections may have detrimental effects on their rodent host reservoirs, notably by affecting litter size

Magnetic reversals in a simple model of MHD

We study a simple magnetohydrodynamical approach in which hydrodynamics and MHD turbulence are coupled in a shell model, with given dynamo constrains in the large scales. We consider the case of a low Prandtl number fluid for which the inertial range of the velocity field is much wider than that of the magnetic field. Random reversals of the magnetic field are observed and it shown that the magnetic field has a non trivial evolution linked to the nature of the hydrodynamics turbulence.Comment: 4 pages, submitted to PR

Viscous photons in relativistic heavy ion collisions

Theoretical studies of the production of real thermal photons in relativistic heavy ion collisions at the Relativistic Heavy Ion Collider (RHIC) are performed. The space-time evolution of the colliding system is modelled using MUSIC, a 3+1D relativistic hydrodynamic simulation, using both its ideal and viscous versions. The inclusive spectrum and its azimuthal angular anisotropy are studied separately, and the relative contributions of the different photon sources are highlighted. It is shown that the photon v2 coefficient is especially sensitive to the details of the microscopic dynamics like the equation of state, the ratio of shear viscosity over entropy density, eta/s, and to the morphology of the initial state.Comment: 15 pages, 12 figures. References updated and discussion adde

Salicylic Acid, an Ambimobile Molecule Exhibiting a High Ability to Accumulate in the Phloem

International audienceThe ability of exogenous salicylic acid (SA) to accumulate in castor bean (Ricinus communis) phloem was evaluated by HPLC and liquid scintillation spectrometry analyses of phloem sap collected from the severed apical part of seedlings. Time-course experiments indicated that SA was transported to the root system via the phloem and redistributed upward in small amounts via the xylem. This helps to explain the peculiarities of SA distribution within the plant in response to biotic stress and exogenous SA application. Phloem loading of SA at 1, 10, or 100 mM was dependent on the pH of the cotyledon incubating solution, and accumulation in the phloem sap was the highest (about 10-fold) at the most acidic pH values tested (pH 4.6 and 5.0). As in animal cells, SA uptake still occurred at pH values close to neutrality (i.e. when SA is only in its dissociated form according to the calculations made by ACD LogD suite software). The analog 3,5-dichlorosalicylic acid, which is predicted to be nonmobile according to the models of Bromilow and Kleier, also moved in the sieve tubes. These discrepancies and other data may give rise to the hypothesis of a possible involvement of a pH-dependent carrier system translocating aromatic monocarboxylic acids in addition to the ion-trap mechanism

Determination of the dynamic tensile response and dissipated fracture energy of concrete with a cohesive element model

International audienc

Feller property and infinitesimal generator of the exploration process

We consider the exploration process associated to the continuous random tree (CRT) built using a Levy process with no negative jumps. This process has been studied by Duquesne, Le Gall and Le Jan. This measure-valued Markov process is a useful tool to study CRT as well as super-Brownian motion with general branching mechanism. In this paper we prove this process is Feller, and we compute its infinitesimal generator on exponential functionals and give the corresponding martingale

A systematic study of supersonic jet noise

December 1971Includes bibliographical references (leaves 39-40)The purpose of this work is to study the acoustic fields associated with two different nozzle configurations; a rectangular and a circular. Both nozzles are designed with the same exit Mach number and have an identical momentum and energy flux. By presenting a comparison of the two nozzles, it proposed to establish and identify the dominant noise generating mechanisms. A basic difference in shape changes the relative importance of different noise mechanisms. The other main aim of this study is to establish scaling laws of supersonic jet noise. A shock tube is a very versatile apparatus for such an analysis. By first changing the driver, driven pressure and molecular weights, a wide range of stagnation pressures and temperatures could be achieved. The case with which these conditions are simulated is, however, traded off with the short test time, of the order of milliseconds. A short test time allows the use of a heat sink nozzle and eliminates the use of an anechoic chamber.So far tests have been made in the range of 1000-5000°R, for different levels of expansion and an exit Mach number of 2.7. In comparing the two nozzles, it is found that the rectangular nozzle is indeed quieter than the circular nozzle. The rectangular nozzle is more effective under overexpanded conditions, and a factor of 1.6 in acoustic efficiency at low temperature (1200°R) and about 3 at high temperature is related to a rapid deceleration of the jet through a system of strong shocks. The low acoustic efficiency of the overexpanded rectangular jet is related to a rapid deceleration of the jet through a system of strong shocks. At high temperature, this effect is not observed because an important density ratio exists across the shear layer which becomes very unstable due to the Taylor instability.For both the circular and rectangular nozzle, the effect of temperature showed an increase in the directivity angle at high temperature which is correlated to an increase in eddy convective velocity, rather than refraction due to density gradients, which seems to play a secondary role. The low temperature overexpanded jet showed a difference of about 2.6 db in the OPWL between the two nozzles. However, at this condition, for the rectangular nozzle, a difference of 8 db between the maximum and minimum noise direction is observed. Hence, a suitable orientation of the nozzle could cause a considerable reduction in the noise level. The rectangular nozzle seems to be very effective under overexpanded conditions. The scaling laws, which are in the preliminary stages, were developed for the change in the OPWL as a function of stagnation pressure. For the circular nozzle, additional scaling was done for temperature and acoustic efficiency.These scaling laws need to be verified for additional temperatures. Also, further work should be initiated in the potential use of the rectangular nozzle as a noise suppressor and as a model for better comprehension of noise generating mechanisms.Office of Noise Abatement, Dept. of Transportation. DOT-TSC-14