628 research outputs found
An experimental study of particle sedimentation using ultrasonic speckle velocimetry
Ultrasonic speckle velocimetry (USV) is a non-invasive technique that allows the measurement of fluid velocity in flow and also that of powders under sedimentation. To improve the USV method, we studied the sedimentation of polymethyl methacrylate and silica particles in water. Then, we built a sedimentation cell and characterized the diameter distribution of the particles. Subsequently, we carried out a specific study to optimize the USV procedure, the signal processing and data analysis. Space and temporal resolution and USV dynamics are also discussed with regard to the optimization conditions. We found that USV is a useful technique to measure velocities between 10â5 and 1 m sâ1, using appropriate ultrasonic transducers. The space resolution is fixed by the length and the percentage of overlapping of the analyzed speckle windows and varies between 48 and 536 ÎŒm for the different studied particle families. Furthermore, we found that a 0.1 ns temporal resolution
could be obtained after a zero padding signal processing. In the context of our sedimentation experiments, we showed that the velocities measured by USV are in close agreement with those measured by particle image velocimetry and theory
LâĂ©volution de la polygamie en milieu rural sĂ©nĂ©galais : institution en crise ou en mutation ?
On annonce depuis longtemps le dĂ©clin de la polygamie en Afrique. Pourtant, ces pratiques restent courantes dans de nombreux pays de la rĂ©gion, surtout en milieu rural. Depuis les annĂ©es 1970, la crise Ă©conomique et agricole a entraĂźnĂ© de profonds changements dans lâorganisation des mĂ©nages et laisse entrevoir une remise en question des fondements de la polygamie. LâĂ©tude de lâĂ©volution de la polygamie dans la zone dâĂ©tude de Niakhar, au SĂ©nĂ©gal, met en Ă©vidence la complexitĂ© des forces en jeu : bien que les niveaux restent stables au cours du temps, les hommes des gĂ©nĂ©rations rĂ©centes entrent en premiĂšre union polygame moins rapidement que leurs aĂźnĂ©s. En combinant des donnĂ©es qualitatives avec celles dâune enquĂȘte biographique rĂ©trospective, cette Ă©tude vise Ă identifier quels processus influent sur le calendrier dâentrĂ©e en union polygame des hommes au fil des gĂ©nĂ©rations. La confrontation des diffĂ©rentes donnĂ©es laisse croire Ă lâadoption dâattitudes visant la redĂ©finition des fondements de la polygamie plutĂŽt que sa remise en question, redĂ©finition ayant pour objectif dâen assurer la pĂ©rennitĂ©.The decline of polygyny in sub-Saharan Africa has been predicted for decades but the levels remain high in many countries, especially in rural areas. Since the 1970s, the economic and agricultural crisis has strongly affected household organization, suggesting that the bases for polygamy might be in question. The study of polygamous behaviours in the Niakhar rural area in Senegal highlights the different forces at work: despite relatively stable levels in recent decades, younger men are entering their first polygamous union later than their elders. By combining qualitative data with the results of a retrospective biographical survey, this study seeks to identify the processes that affect the timing of menâs first polygamous union across different cohorts. The results suggest an adoption of new attitudes, involving a redefinition of the bases for polygamy (rather than a questioning of polygamy), in order to ensure the continuation of such practices
Light Non-degenerate Composite Partners at the LHC
We study the implications of a large degree of compositeness for the light
generation quarks in composite pseudo-Nambu-Goldstone-boson Higgs models. We
focus in particular on viable scenarios where the right-handed up-type quarks
have a sizable mixing with the strong dynamics. For concreteness we assume the
latter to be characterized by an SO(5)/SO(4) symmetry with fermionic resonances
in the SO(4) singlet and fourplet representations. Singlet partners dominantly
decay to a Higgs boson and jets. As no dedicated searches are currently looking
for these final states, singlet partners can still be rather light. Conversely,
some fourplet partners dominantly decay to an electroweak gauge boson and a
jet, a signature which has been analyzed at the LHC. To constrain the parameter
space of this scenario we have reinterpreted various LHC analyses. In the limit
of first two generation degeneracy, as in minimal flavor violation or
U(2)-symmetric flavor models, fourplet partners need to be relatively heavy,
with masses above 1.8 TeV, or the level of compositeness needs to be rather
small. The situation is rather different in models that deviate from the first
two generation degeneracy paradigm, as the charm parton distribution functions
are suppressed relative to the up quark ones. The right-handed charm quark can
be composite and its partners being as light as 600 GeV, while the right-handed
up quark needs either to be mostly elementary or to have its partners as heavy
as 2 TeV. Models with fully composite singlet fermions are also analyzed,
leading to similar conclusions. Finally, we consider the case where both the
fourplet and the singlet states are present. In this case the bounds could be
significantly weaken due to a combination of smaller production rates and the
opening of new channels including cascade processes.Comment: 49 pages, 18 figure
Extraction sélective de la cocaïne d'échantillons biologiques avec un polymÚre à empreintes moléculaires monolithique et miniaturisé et une analyse en ligne par nano-chromatographie en phase liquide
International audienceWe report the on-line coupling of a monolithic molecularly imprinted polymer to nano-liquid chromatography for the selective analysis of cocaine and its main metabolite, benzoylecgonine, in complex biological samples. After the screening of different synthesis conditions, a monolithic molecularly imprinted polymer was in situ synthesized into a 100 ”m internal diameter fused-silica capillary using cocaine as template, methacrylic acid as functional monomer, and trimethylolpropane trimethacrylate as cross-linker. Scanning electron microscopy was used to assess the homogeneous morphology of the molecularly imprinted polymer and its permeability was measured. Its selectivity was evaluated by nano-liquid chromatography-ultraviolet, leading to imprinting factors of 3.2 ± 0.5 and 2.2 ± 0.3 for cocaine and benzoylecgonine, respectively, on polymers resulting from three independent syntheses, showing the high selectivity and the repeatability of the synthesis. After optimizing the extraction protocol to promote selectivity, the monolithic molecularly imprinted polymer was successfully on-line coupled with nano-liquid chromatography-ultraviolet for the direct extraction and analysis of cocaine present in spiked human plasma and saliva samples. The repeatability of the obtained extraction recovery, between 85.4-98.7% for a plasma sample spiked at 100 ng.mL-1 , was high with relative standard deviation values lower than 5.8% for triplicate analyses on each of the three independently synthesized molecularly imprinted polymers. A linear calibration range was achieved between 100 and 2000 ng mL-1 (R 2 = 0.999). Limits of quantification of 14.5 ng mL-1 and 6.1 ng mL-1 were achieved in plasma and urine samples, respectively. The very clean-baseline of the resulting chromatogram illustrated the high selectivity brought by the monolithic molecularly imprinted polymer that allows the removal of a huge peak corresponding to the elution of interfering compounds and the easy determination of the target analyte in these complex biological samples
Milli-PIV rheology of shear-thinning fluids
Milli-Particle Image Velocimetry (Milli-PIV), which is an application of the standard PIV has been developed to measure the velocity distribution of complex fluids in a millimetric Hele-Shaw cell. A laser sheet is sent perpendicularly to the cell and the camera observes the PIV images via an internal optical prism. We studied, with Milli-PIV, a structural series of shear thinning xanthan fluids at different injection rates. We determined the velocity profiles in the thickness of the flow cell and discussed the accuracy of measurement. Using an inverse method, we calculated the constitutive parameters and showed that they are similar to those measured by rheology. The pressure gradient characteristic of the couple experimental conditions - fluid were also calculated from modeling the velocity profile
Cosmological Consequences of Nearly Conformal Dynamics at the TeV scale
Nearly conformal dynamics at the TeV scale as motivated by the hierarchy
problem can be characterized by a stage of significant supercooling at the
electroweak epoch. This has important cosmological consequences. In particular,
a common assumption about the history of the universe is that the reheating
temperature is high, at least high enough to assume that TeV-mass particles
were once in thermal equilibrium. However, as we discuss in this paper, this
assumption is not well justified in some models of strong dynamics at the TeV
scale. We then need to reexamine how to achieve baryogenesis in these theories
as well as reconsider how the dark matter abundance is inherited. We argue that
baryonic and dark matter abundances can be explained naturally in these setups
where reheating takes place by bubble collisions at the end of the strongly
first-order phase transition characterizing conformal symmetry breaking, even
if the reheating temperature is below the electroweak scale GeV. We
also discuss inflation as well as gravity wave smoking gun signatures of this
class of models.Comment: 22 pages, 7 figure
Emergence of the N=16 shell gap in 21O
The spectroscopy of O21 has been investigated using a radioactive O20 beam and the (d,p) reaction in inverse kinematics. The ground and first excited states have been determined to be JÏ=5/2+ and 1/2+, respectively. Two neutron unbound states were observed at excitation energies of 4.77(10) and 6.17(11) MeV. The spectroscopic factor deduced for the lower of these, interpreted as a 3/2+ level, reveals a relatively pure (60%) 0d3/2 single-particle configuration, in good agreement with shell-model calculations that predict O26 to be unbound. The large energy difference between the 3/2+ and 1/2+ states is indicative of the emergence of the N=16 shell gap, which is estimated to be 5.1(11) MeV. For the higher-lying resonance, which has a character consistent with a spin-parity assignment of 3/2+ or 7/2-, a 0.71(22) branching ratio to the first 2+ state in O20 has been observed.UniĂłn Europea EURISOL 515768 RIDSNSF PHY-075809
Structure of Be probed via secondary beam reactions
The low-lying level structure of the unbound neutron-rich nucleus Be
has been investigated via breakup on a carbon target of secondary beams of
B at 35 MeV/nucleon. The coincident detection of the beam velocity
Be fragments and neutrons permitted the invariant mass of the
Be+ and Be++ systems to be reconstructed. In the case of
the breakup of B, a very narrow structure at threshold was observed in
the Be+ channel. Contrary to earlier stable beam fragmentation
studies which identified this as a strongly interacting -wave virtual state
in Be, analysis here of the Be++ events demonstrated that
this was an artifact resulting from the sequential-decay of the
Be(2) state. Single-proton removal from B was found to
populate a broad low-lying structure some 0.70 MeV above the neutron-decay
threshold in addition to a less prominent feature at around 2.4 MeV. Based on
the selectivity of the reaction and a comparison with (0-3)
shell-model calculations, the low-lying structure is concluded to most probably
arise from closely spaced J=1/2 and 5/2 resonances
(E=0.400.03 and 0.85 MeV), whilst the broad
higher-lying feature is a second 5/2 level (E=2.350.14 MeV). Taken
in conjunction with earlier studies, it would appear that the lowest 1/2
and 1/2 levels lie relatively close together below 1 MeV.Comment: 14 pages, 13 figures, 2 tables. Accepted for publication in Physical
Review
Electroweak Baryogenesis in Non-minimal Composite Higgs Models
We address electroweak baryogenesis in the context of composite Higgs models,
pointing out that modifications to the Higgs and top quark sectors can play an
important role in generating the baryon asymmetry. Our main observation is that
composite Higgs models that include a light, gauge singlet scalar in the
spectrum [as in the model based on the symmetry breaking pattern SO(6)/SO(5)],
provide all necessary ingredients for viable baryogenesis. In particular, the
singlet leads to a strongly first-order electroweak phase transition and
introduces new sources of CP violation in dimension-five operators involving
the top quark. We discuss the amount of baryon asymmetry produced and the
experimental constraints on the model.Comment: 15 pages, 7 figure
Emergence of the N=16 shell gap in ^(21)O
This is the publisher's version, also available electronically from http://journals.aps.org/prc/abstract/10.1103/PhysRevC.84.011301
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