1,012 research outputs found
MadEvent: Automatic Event Generation with MadGraph
We present a new multi-channel integration method and its implementation in
the multi-purpose event generator MadEvent, which is based on MadGraph. Given a
process, MadGraph automatically identifies all the relevant subprocesses,
generates both the amplitudes and the mappings needed for an efficient
integration over the phase space, and passes them to MadEvent. As a result, a
process-specific, stand-alone code is produced that allows the user to
calculate cross sections and produce unweighted events in a standard output
format. Several examples are given for processes that are relevant for physics
studies at present and forthcoming colliders.Comment: 11 pages, MadGraph home page at http://madgraph.physics.uiuc.ed
FOR MONEY OR LIBERTY? THE POLITICAL ECONOMY OF MILITARY DESERTION AND REBEL RECRUITMENT IN THE SYRIAN CIVIL WAR
Asymmetric multisensory interactions of visual and somatosensory responses in a region of the rat parietal cortex
Perception greatly benefits from integrating multiple sensory cues into a unified percept. To study the neural mechanisms of sensory integration, model systems are required that allow the simultaneous assessment of activity and the use of techniques to affect individual neural processes in behaving animals. While rodents qualify for these requirements, little is known about multisensory integration and areas involved for this purpose in the rodent. Using optical imaging combined with laminar electrophysiological recordings, the rat parietal cortex was identified as an area where visual and somatosensory inputs converge and interact. Our results reveal similar response patterns to visual and somatosensory stimuli at the level of current source density (CSD) responses and multi-unit responses within a strip in parietal cortex. Surprisingly, a selective asymmetry was observed in multisensory interactions: when the somatosensory response preceded the visual response, supra-linear summation of CSD was observed, but the reverse stimulus order resulted in sub-linear effects in the CSD. This asymmetry was not present in multi-unit activity however, which showed consistently sub-linear interactions. These interactions were restricted to a specific temporal window, and pharmacological tests revealed significant local intra-cortical contributions to this phenomenon. Our results highlight the rodent parietal cortex as a system to model the neural underpinnings of multisensory processing in behaving animals and at the cellular level
Bubble nucleation and jetting inside a millimetric droplet
In this work, we present experiments and simulations on the nucleation and
successive dynamics of laser-induced bubbles inside liquid droplets in
free-fall motion, i.e. a case where the bubbles are subjected to the influence
of a free boundary in all directions. The droplets of a millimetric size are
released from a height of around 20\,cm and acquire a velocity of around 2\,m/s
at the moment the bubble is nucleated. Within this droplet, we have
investigated the nucleation of secondary bubbles induced by the rarefaction
wave that is produced when the shock wave emitted by the laser-induced plasma
reflects at the drop surface. Interestingly, three-dimensional clusters of
cavitation bubbles are observed. Their shape is compared with the negative
pressure distribution computed with a CFD model and allows us to estimate a
cavitation threshold value. High-speed recordings of the drop/bubble dynamics
are complemented by the velocity and pressure fields simulated for the same
initial conditions. The effect of the proximity of a curved free surface on the
jetting dynamics of the bubbles was qualitatively assessed by classifying the
cavitation events using a non-dimensional stand-off parameter which depends on
the drop size, the bubble maximum radius and the relative position of the
bubble inside the drop. Here, we found that the curvature of the free surface
does not play a determinant role on the jet dynamics, being the distance to the
surface the dominant parameter. The oscillation of the laser-induced bubbles
promote the onset of Rayleigh-Taylor and Rayleigh-Plateau instabilities,
observed on the drop's surface. The specific mechanisms leading to the
destabilisation of the droplet surface were identified through a careful
inspection of the high speed images
Bicudo do algodoeiro: identificaĆ§Ć£o, biologia, amostragem e tĆ”ticas de controle.
bitstream/CNPA/18282/1/CIRTEC79.pd
QFT on homothetic Killing twist deformed curved spacetimes
We study the quantum field theory (QFT) of a free, real, massless and
curvature coupled scalar field on self-similar symmetric spacetimes, which are
deformed by an abelian Drinfel'd twist constructed from a Killing and a
homothetic Killing vector field. In contrast to deformations solely by Killing
vector fields, such as the Moyal-Weyl Minkowski spacetime, the equation of
motion and Green's operators are deformed. We show that there is a *-algebra
isomorphism between the QFT on the deformed and the formal power series
extension of the QFT on the undeformed spacetime. We study the convergent
implementation of our deformations for toy-models. For these models it is found
that there is a *-isomorphism between the deformed Weyl algebra and a reduced
undeformed Weyl algebra, where certain strongly localized observables are
excluded. Thus, our models realize the intuitive physical picture that
noncommutative geometry prevents arbitrary localization in spacetime.Comment: 23 pages, no figures; v2: extended discussion of physical
consequences, compatible with version to be published in General Relativity
and Gravitatio
Effect of adding nanometre-sized heterogeneities on the structural dynamics and the excess wing of a molecular glass former
We present the relaxation dynamics of glass-forming glycerol mixed with 1.1
nm sized polyhedral oligomeric silsesquioxane (POSS) molecules using dielectric
spectroscopy (DS) and two different neutron scattering (NS) techniques. Both,
the reorientational dynamics as measured by DS and the density fluctuations
detected by NS reveal a broadening of the alpha relaxation when POSS molecules
are added. Moreover, we find a significant slowing down of the alpha-relaxation
time. These effects are in accord with the heterogeneity scenario considered
for the dynamics of glasses and supercooled liquids. The addition of POSS also
affects the excess wing in glycerol arising from a secondary relaxation
process, which seems to exhibit a dramatic increase in relative strength
compared to the alpha-relaxation.Comment: 32 pages, 7 figures, accepted for publication in the journal
Scientific Report
The Standard Model on Non-Commutative Space-Time: Electroweak Currents and Higgs Sector
In this article we review the electroweak charged and neutral currents in the
Non-Commutative Standard Model (NCSM) and compute the Higgs and Yukawa parts of
the NCSM action. With the aim to make the NCSM accessible to phenomenological
considerations, all relevant expressions are given in terms of physical fields
and Feynman rules are provided.Comment: 33 pages, axodraw.sty; shortened, comments and references added,
version to appear in EPJ
Far-Ultraviolet Color Gradients in Early-Type Galaxies
We discuss far-UV (1500 A) surface photometry and FUV-B color profiles for 8
E/S0 galaxies from images taken with the Ultraviolet Imaging Telescope,
primarily during the Astro-2 mission. In three cases, the FUV radial profiles
are more consistent with an exponential than a de Vaucouleurs function, but
there is no other evidence for the presence of a disk or of young, massive
stars. In all cases except M32 the FUV-B color becomes redder at larger radii.
There is a wide range of internal radial FUV-B color gradients. However, we
find no correlation between the FUV-B color gradients and internal metallicity
gradients based on Mg absorption features. We conclude that metallicity is not
the sole parameter controlling the "UV upturn component" in old populations.Comment: 11 pages; tar.gz file includes LaTeX text file, 3 PostScript figures.
Paper to be published in ApJ Letter
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