199 research outputs found
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
Measurement of Unpolarized and Polarized Cross Sections for Deeply Virtual Compton Scattering on the Proton at Jefferson Laboratory with CLAS
This paper reports the measurement of polarized and unpolarized cross sections for the epâeâČpâČÎł reaction, which is composed of deeply virtual Compton scattering (DVCS) and Bethe-Heitler (BH) processes, at an electron beam energy of 5.88 GeV at the Thomas Jefferson National Accelerator Facility using the Large Acceptance Spectrometer CLAS. The unpolarized cross sections and polarized cross section differences have been measured over broad kinematics, 0.10 \u3c xB \u3c 0.58, 1.0 \u3c Q2 \u3c4.8 GeV2 and 0.09\u3cât \u3c2.00 GeV2. The results are found to be consistent with previous CLAS data, and these new data are discussed in the framework of the generalized parton distribution approach. Calculations with two widely used phenomenological models are approximately compatible with the experimental results over a large portion of the kinematic range of the data
Precision measurements of 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 Electroproduction Structure Functions and their Relationship to Transversity GPDs
Exclusive 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 , , , and
, in the range from 1.0 to 4.6 GeV,\ up to 2 GeV,
and from 0.1 to 0.58. Structure functions and were extracted as functions of for each of
17 combinations of and . The data were compared directly with two
handbag-based calculations including both longitudinal and transversity GPDs.
Inclusion of only longitudinal GPDs very strongly underestimates and fails to account for and ,
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 electroproduction offers
direct experimental access to the transversity GPDs.Comment: 6 pages, 2 figure
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
, and mesons. Linearly-polarized photons were
successfully produced through coherent bremsstrahlung and polarization transfer
to the has been observed.Comment: 8 pages, 6 figures, Invited contribution to the Hadron 2015
Conference, Newport News VA, September 201
A comparison of forward and backward pp pair knockout in 3He(e,e'pp)n
Measuring nucleon-nucleon Short Range Correlations (SRC) has been a goal of
the nuclear physics community for many years. They are an important part of the
nuclear wavefunction, accounting for almost all of the high-momentum strength.
They are closely related to the EMC effect. While their overall probability has
been measured, measuring their momentum distributions is more difficult. In
order to determine the best configuration for studying SRC momentum
distributions, we measured the He reaction, looking at events
with high momentum protons ( GeV/c) and a low momentum neutron
( GeV/c). We examined two angular configurations: either both protons
emitted forward or one proton emitted forward and one backward (with respect to
the momentum transfer, ). The measured relative momentum distribution
of the events with one forward and one backward proton was much closer to the
calculated initial-state relative momentum distribution, indicating that
this is the preferred configuration for measuring SRC.Comment: 8 pages, 9 figures, submitted to Phys Rev C. Version 2 incorporates
minor corrections in response to referee comment
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
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