Jet propulsion without inertia

A body immersed in a highly viscous fluid can locomote by drawing in and expelling fluid through pores at its surface. We consider this mechanism of jet propulsion without inertia in the case of spheroidal bodies, and derive both the swimming velocity and the hydrodynamic efficiency. Elementary examples are presented, and exact axisymmetric solutions for spherical, prolate spheroidal, and oblate spheroidal body shapes are provided. In each case, entirely and partially porous (i.e. jetting) surfaces are considered, and the optimal jetting flow profiles at the surface for maximizing the hydrodynamic efficiency are determined computationally. The maximal efficiency which may be achieved by a sphere using such jet propulsion is 12.5%, a significant improvement upon traditional flagella-based means of locomotion at zero Reynolds number. Unlike other swimming mechanisms which rely on the presentation of a small cross section in the direction of motion, the efficiency of a jetting body at low Reynolds number increases as the body becomes more oblate, and limits to approximately 162% in the case of a flat plate swimming along its axis of symmetry. Our results are discussed in the light of slime extrusion mechanisms occurring in many cyanobacteria

MiniBooNE

The physics motivations, design, and status of the Booster Neutrino Experiment at Fermilab, MiniBooNE, are briefly discussed. Particular emphasis is given on the ongoing preparatory work that is needed for the MiniBooNE muon neutrino to electron neutrino oscillation appearance search. This search aims to confirm or refute in a definitive and independent way the evidence for neutrino oscillations reported by the LSND experiment.Comment: 3 pages, no figures, to appear in the proceedings of the 9th International Conference on Astroparticle and Underground Physics (TAUP 2005), Zaragoza, Spain, 10-14 Sep 200

Hydraulic interactions between fractures and bedding planes in a carbonate aquifer studied by means of experimentally induced water-table fluctuations (Coaraze experimental site, southeastern France)

International audienceIn aquifers with variable permeability, the water exchanges between high and low permeability regions are controlled by the hydraulic head gradient. Past studies have addressed this problem mainly considering steadystate hydraulic conditions. To study such exchanges during water-table fluctuations, a spring was equipped with a water-gate that creates 10-meter artificial fluctuations of the water table. The water exchanges are discussed with respect to hydrochemical and pressure measurements in the groundwater. With successive water-table fluctuations the mineralization and pH decrease, but the bicarbonate content increases in response to carbon dioxide dissolution . At this scale of single fractures and surroundings, the hydrochemistry allows water flows from low or high permeability discontinuities to be discriminated. During hydraulic head fluctuations, the waters from low and high permeability discontinuities become mixed. During water-table rise, the low-permeability matrix contributed to the refilling of the permeable faults and to the mixing of the waters. Dynamic flows in the opposite direction to the hydraulic gradient can expel mineralized water, pushing it towards permeable discontinuities. This mechanism could be the cause of the peak in the mineralisation recorded in some karst springs at the start of flood events

Bayesian Autoregressive Frailty Models for Inference in Recurrent Events

We propose autoregressive Bayesian semi-parametric models for gap times between recurrent events. The aim is two-fold: inference on the effect of possibly time-varying covariates on the gap times and clustering of individuals based on the time trajectory of the recurrent event. Time-dependency between gap times is taken into account through the specification of an autoregressive component for the frailty parameters influencing the response at different times. The order of the autoregression may be assumed unknown and is an object of inference. We consider two alternative approaches to perform model selection under this scenario. Covariates may be easily included in the regression framework and censoring and missing data are easily accounted for. As the proposed methodologies lie within the class of Dirichlet process mixtures, posterior inference can be performed through efficient MCMC algorithms. We illustrate the approach through simulations and medical applications involving recurrent hospitalizations of cancer patients and successive urinary tract infections

Hydromechanical modeling of pulse tests that measure both fluid pressure and fracture-normal displacement of the Coaraze Laboratory site, France

21International audienceIn situ fracture mechanical deformation and fluid flow interactions are investigated through a series of hydraulic pulse injection tests, using specialized borehole equipment that can simultaneously measure fluid pressure and fracture displacements. The tests were conducted in two horizontal boreholes spaced one meter apart vertically and intersecting a near-vertical highly permeable fault located within a shallow fractured carbonate rock. The field data were evaluated by conducting a series of coupled hydromechanical numerical analyses, using both distinct-element and finite-element modeling techniques and both two- and three-dimensional model representations that can incorporate various complexities in fracture network geometry. One unique feature of these pulse injection experiments is that the entire test cycle, both the initial pressure increase and subsequent pressure fall-off, is carefully monitored and used for the evaluation of the in situ hydromechanical behavior. Field test data are evaluated by plotting fracture normal displacement as a function of fluid pressure, measured at the same borehole. The resulting normal displacement-versus-pressure curves show a characteristic loop, in which the paths for loading (pressure increase) and unloading (pressure decrease) are different. By matching this characteristic loop behavior, the fracture normal stiffness and an equivalent stiffness (Young's modulus) of the surrounding rock mass can be back-calculated. Evaluation of the field tests by coupled numerical hydromechanical modeling shows that initial fracture hydraulic aperture and normal stiffness vary by a factor of 2 to 3 for the two monitoring points within the same fracture plane. Moreover, the analyses show that hydraulic aperture and the normal stiffness of the pulse-tested fracture, the stiffness of surrounding rock matrix, and the properties and geometry of the surrounding fracture network significantly affect coupled hydromechanical responses during the pulse injection test. More specifically, the pressure-increase path of the normal displacement-versus-pressure curve is highly dependent on the hydromechanical parameters of the tested fracture and the stiffness of the matrix near the injection point, whereas the pressure-decrease path is highly influenced by mechanical processes within a larger portion of the surrounding fractured rock

Stabilization of fault slip by fluid injection in the laboratory and in situ

Faults can slip seismically or aseismically depending on their hydromechanical properties, which can be measured in the laboratory. Here, we demonstrate that fault slip induced by fluid injection in a natural fault at the decametric scale is quantitatively consistent with fault slip and frictional properties measured in the laboratory. The increase in fluid pressure first induces accelerating aseismic creep and fault opening. As the fluid pressure increases further, friction becomes mainly rate strengthening, favoring aseismic slip. Our study reveals how coupling between fault slip and fluid flow promotes stable fault creep during fluid injection. Seismicity is most probably triggered indirectly by the fluid injection due to loading of nonpressurized fault patches by aseismic creep

Systematic procedure for the efficient design of folded waveguide comb-line filters

[EN] A systematic procedure for the efficient design of folded waveguide comb-line filters is presented. The proposed strategy is based on dividing the design process in more simple stages, in order to reduce the number of variables to be optimized in each step of the design process. The electrical response of an equivalent circuit model of the waveguide component considered in each step is used as a target response. Moreover, a method for obtaining an initial value for some key dimensions of the filter is also addressed. Finally, an S-band 6-pole folded comb-line filter has been successfully designed following the proposed design strategy.San-Blas, AA.; Pérez-Guijarro, J.; Boria Esbert, VE.; Guglielmi, M. (2019). Systematic procedure for the efficient design of folded waveguide comb-line filters. IEEE. 1-4. https://doi.org/10.1109/NEMO.2019.8853707S1