Electrical controlled rheology of a suspension of weakly conducting particles in dielectric liquid

The properties of suspensions of fine particles in dielectric liquid (electrorheological fluids) subjected to an electric field lead to a drastic change of the apparent viscosity of the fluid. For high applied fields (~ 3-5 kV/mm) the suspension congeals to a solid gel (particles fibrillate span the electrode gap) having a finite yield stress. For moderate fields the viscosity of the suspension is continuously controlled by the electric field strength. We have roposed that in DC voltage the field distribution in the solid (particles) and liquid phases of the suspension and so the attractive induced forces between particles and the yield stress of the suspension are controlled by the conductivities of the both materials. In this paper we report investigation and results obtained with nanoelectrorheological suspensions: synthesis of coated nanoparticles (size ~ 50 to 600 nm, materials Gd2O3:Tb, SiOx...), preparation of ER fluids (nanoparticles mixed in silicone oil), electrical and rheological characterization of the ER fluids. We also propose a possible explanation of the enhanced ER effect (giant ER fluids) taking into account the combined effects of the (nano)size of the particles, the Van der Waals forces between particles in contact and the electrostatic pressure in a very thin layer of insulating liquid.Comment: Article pour la conf\'{e}rence sur les charges d'espaces (CSC 6\`{e}me \'{e}dition) qui s'est d\'{e}roul\'{e}e \`{a} Tours du 3 au 7 juillet 2006. 6page

Global and local environmental changes as drivers of Buruli ulcer emergence

International audienceMany emerging infectious diseases are caused by generalist pathogens that infect and transmit via multiple host species with multiple dissemination routes, thus confounding the understanding of pathogen transmission pathways from wildlife reservoirs to humans. The emergence of these pathogens in human populations has frequently been associated with global changes, such as socio-economic, climate or biodiversity modifications, by allowing generalist pathogens to invade and persist in new ecological niches, infect new host species, and thus change the nature of transmission pathways. Using the case of Buruli ulcer disease, we review how land-use changes, climatic patterns and biodiversity alterations contribute to disease emergence in many parts of the world. Here we clearly show that Mycobacterium ulcerans is an environmental pathogen characterized by multi-host transmission dynamics and that its infectious pathways to humans rely on the local effects of global environmental changes. We show that the interplay between habitat changes (for example, deforestation and agricultural land-use changes) and climatic patterns (for example, rainfall events), applied in a local context, can lead to abiotic environmental changes and functional changes in local biodiversity that favor the pathogen’s prevalence in the environment and may explain disease emergence

First Results from The GlueX Experiment

The GlueX experiment at Jefferson Lab ran with its first commissioning beam in late 2014 and the spring of 2015. Data were collected on both plastic and liquid hydrogen targets, and much of the detector has been commissioned. All of the detector systems are now performing at or near design specifications and events are being fully reconstructed, including exclusive production of $\pi^{0}$, $\eta$ and $\omega$ mesons. Linearly-polarized photons were successfully produced through coherent bremsstrahlung and polarization transfer to the $\rho$ has been observed.Comment: 8 pages, 6 figures, Invited contribution to the Hadron 2015 Conference, Newport News VA, September 201

Precision measurements of g1g_1 of the proton and the deuteron with 6 GeV electrons

The inclusive polarized structure functions of the proton and deuteron, g1p and g1d, were measured with high statistical precision using polarized 6 GeV electrons incident on a polarized ammonia target in Hall B at Jefferson Laboratory. Electrons scattered at lab angles between 18 and 45 degrees were detected using the CEBAF Large Acceptance Spectrometer (CLAS). For the usual DIS kinematics, Q^2>1 GeV^2 and the final-state invariant mass W>2 GeV, the ratio of polarized to unpolarized structure functions g1/F1 is found to be nearly independent of Q^2 at fixed x. Significant resonant structure is apparent at values of W up to 2.3 GeV. In the framework of perturbative QCD, the high-W results can be used to better constrain the polarization of quarks and gluons in the nucleon, as well as high-twist contributions

Measurement of Exclusive π0\pi^0 Electroproduction Structure Functions and their Relationship to Transversity GPDs

Exclusive $\pi^0$ electroproduction at a beam energy of 5.75 GeV has been measured with the Jefferson Lab CLAS spectrometer. Differential cross sections were measured at more than 1800 kinematic values in $Q^2$, $x_B$, $t$, and $\phi_\pi$, in the $Q^2$ range from 1.0 to 4.6 GeV$^2$,\ $-t$ up to 2 GeV$^2$, and $x_B$ from 0.1 to 0.58. Structure functions $\sigma_T +\epsilon \sigma_L, \sigma_{TT}$ and $\sigma_{LT}$ were extracted as functions of $t$ for each of 17 combinations of $Q^2$ and $x_B$. The data were compared directly with two handbag-based calculations including both longitudinal and transversity GPDs. Inclusion of only longitudinal GPDs very strongly underestimates $\sigma_T +\epsilon \sigma_L$ and fails to account for $\sigma_{TT}$ and $\sigma_{LT}$, while inclusion of transversity GPDs brings the calculations into substantially better agreement with the data. There is very strong sensitivity to the relative contributions of nucleon helicity flip and helicity non-flip processes. The results confirm that exclusive $\pi^0$ electroproduction offers direct experimental access to the transversity GPDs.Comment: 6 pages, 2 figure

Measurement of the neutron F2 structure function via spectator tagging with CLAS

We report on the first measurement of the F2 structure function of the neutron from semi-inclusive scattering of electrons from deuterium, with low-momentum protons detected in the backward hemisphere. Restricting the momentum of the spectator protons to < 100 MeV and their angles to < 100 degrees relative to the momentum transfer allows an interpretation of the process in terms of scattering from nearly on-shell neutrons. The F2n data collected cover the nucleon resonance and deep-inelastic regions over a wide range of Bjorken x for 0.65 < Q2 < 4.52 GeV2, with uncertainties from nuclear corrections estimated to be less than a few percent. These measurements provide the first determination of the neutron to proton structure function ratio F2n/F2p at 0.2 < x < 0.8 with little uncertainty due to nuclear effects.Comment: 6 pages, 3 page

Deep exclusive π+\pi^+ electroproduction off the proton at CLAS

The exclusive electroproduction of $\pi^+$ above the resonance region was studied using the $\rm{CEBAF}$ Large Acceptance Spectrometer ($\rm{CLAS}$) at Jefferson Laboratory by scattering a 6 GeV continuous electron beam off a hydrogen target. The large acceptance and good resolution of $\rm{CLAS}$, together with the high luminosity, allowed us to measure the cross section for the $\gamma^* p \to n \pi^+$ process in 140 ($Q^2$, $x_B$, $t$) bins: $0.16<x_B<0.58$, 1.6 GeV$^2<$$Q^2$$<4.5$ GeV$^2$ and 0.1 GeV$^2<$$-t$$<5.3$ GeV$^2$. For most bins, the statistical accuracy is on the order of a few percent. Differential cross sections are compared to two theoretical models, based either on hadronic (Regge phenomenology) or on partonic (handbag diagram) degrees of freedom. Both can describe the gross features of the data reasonably well, but differ strongly in their ingredients. If the handbag approach can be validated in this kinematical region, our data contain the interesting potential to experimentally access transversity Generalized Parton Distributions.Comment: 18pages, 21figures,2table