28,731 research outputs found
Creating Non-Maxwellian Velocity Distributions in Ultracold Plasmas
We present techniques to perturb, measure and model the ion velocity
distribution in an ultracold neutral plasma produced by photoionization of
strontium atoms. By optical pumping with circularly polarized light we promote
ions with certain velocities to a different spin ground state, and probe the
resulting perturbed velocity distribution through laser-induced fluorescence
spectroscopy. We discuss various approaches to extract the velocity
distribution from our measured spectra, and assess their quality through
comparisons with molecular dynamic simulationsComment: 13 pages, 8 figure
Velocity Relaxation in a Strongly Coupled Plasma
Collisional relaxation of Coulomb systems is studied in the strongly coupled
regime. We use an optical pump-probe approach to manipulate and monitor the
dynamics of ions in an ultracold neutral plasma, which allows direct
measurement of relaxation rates in a regime where common Landau-Spitzer theory
breaks down. Numerical simulations confirm the experimental results and display
non-Markovian dynamics at early times.Comment: 5 pages, 5 figure
Hemisphere Mixing: a Fully Data-Driven Model of QCD Multijet Backgrounds for LHC Searches
A novel method is proposed here to precisely model the multi-dimensional
features of QCD multi-jet events in hadron collisions. The method relies on the
schematization of high-pT QCD processes as 2->2 reactions made complex by
sub-leading effects. The construction of libraries of hemispheres from
experimental data and the definition of a suitable nearest-neighbor-based
association map allow for the generation of artificial events that reproduce
with surprising accuracy the kinematics of the QCD component of original data,
while remaining insensitive to small signal contaminations. The method is
succinctly described and its performance is tested in the case of the search
for the hh->bbbb process at the LHC.Comment: 4 pages plus header, 1 figure, proceedings of EPS 2017 Venic
Pressure and isotope effect on the anisotropy of MgB
We analyze the data for the pressure and boron isotope effect on the
temperature dependence of the magnetization near . Invoking the
universal scaling relation for the magnetization at fixed magnetic field it is
shown that the relative shift of , induced by pressure or boron isotope
exchange, mirrors essentially that of the anisotropy. This uncovers a novel
generic property of anisotropic type II superconductors, inexistent in the
isotropic case. For MgB it implies that the renormalization of the Fermi
surface topology due to pressure or isotope exchange is dominated by a
mechanism controlling the anisotropy.Comment: 7 pages, 3 figure
A burst with double radio spectrum observed up to 212 GHz
We study a solar flare that occurred on September 10, 2002, in active region
NOAA 10105 starting around 14:52 UT and lasting approximately 5 minutes in the
radio range. The event was classified as M2.9 in X-rays and 1N in H\alpha.
Solar Submillimeter Telescope observations, in addition to microwave data give
us a good spectral coverage between 1.415 and 212 GHz. We combine these data
with ultraviolet images, hard and soft X-rays observations and full-disk
magnetograms. Images obtained from Ramaty High Energy Solar Spectroscopic
Imaging data are used to identify the locations of X-ray sources at different
energies and to determine the X-ray spectrum, while ultra violet images allow
us to characterize the coronal flaring region. The magnetic field evolution of
the active region is analyzed using Michelson Doppler Imager magnetograms. The
burst is detected at all available radio-frequencies. X-ray images (between 12
keV and 300 keV) reveal two compact sources and 212 GHz data, used to estimate
the radio source position, show a single compact source displaced by 25" from
one of the hard X-ray footpoints. We model the radio spectra using two
homogeneous sources, and combine this analysis with that of hard X-rays to
understand the dynamics of the particles. Relativistic particles, observed at
radio wavelengths above 50 GHz, have an electron index evolving with the
typical soft-hard-soft behaviour.Comment: Submitted to Solar Physics, 20 pages, 8 fugure
Optical conductivity near finite-wavelength quantum criticality
We study the optical conductivity sigma(Omega) of an electron system near a
quantum-critical point with finite-wavelength ordering. sigma(Omega) vanishes
in clean Galilean-invariant systems, unless electrons are coupled to dynamical
collective modes, which dissipate the current. This coupling introduces a
nonuniversal energy scale. Depending on the parameters of each specific system,
a variety of responses arise near criticality: scaling peaks at a temperature-
and doping-dependent frequency, peaks at a fixed frequency, or no peaks to be
associated with criticality. Therefore the lack of scaling in the far-infrared
conductivity in cuprates does not necessarily call for new concepts of quantum
criticality.Comment: 4 pages, 4 figures; version as publishe
Desenvolvimento de ninfas Euborellia annulipes (Lucas) (Dermaptera: carcinophoridae) alimentada com Schizaphis graminum (Rondani) (Hemiptera: aphididae).
Aspectos biolĂłgicos do DĂptero Winthemia trinitatis Thompson e viabilidade do parasitismo sobre a lagarta-do-cartucho do milho Spodoptera frugiperda.
Metodologia de criação de ninfas Euborelia annulipes (Lucas) (Dermaptera: carcinophoridae).
Weak lensing analysis in three dimensions
We present a comprehensive full-sky 3-dimensional analysis of the
weak-lensing fields and their corresponding power spectra. Using the formalism
of spin-weight spherical harmonics and spherical Bessel functions, we relate
the two-point statistics of the harmonic expansion coefficients of the weak
lensing shear and convergence to the power spectrum of the matter density
perturbations, and derive small-angle limits. Such a study is relevant in view
of the next generation of large-scale weak lensing surveys which will provide
distance information about the sources through photometric redshifts. This
opens up the possibility of accurate cosmological parameter estimation via weak
lensing, with an emphasis on the equation of state of dark energy.Comment: 23 pages, 4 figures, accepted by Phys.Rev.D; replaced with revised
version, minor corrections, all figures done with better samplin
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