12,646 research outputs found
Hybrid Pixel Detector Development for the Linear Collider Vertex Tracker
In order to fully exploit the physics potential of the future high energy
e+e- linear collider, a Vertex Tracker able to provide particle track
extrapolation with very high resolution is needed. Hybrid Si pixel sensors are
an attractive technology due to their fast read-out capabilities and radiation
hardness. A novel pixel detector layout with interleaved cells has been
developed to improve the single point resolution. Results of the
characterisation of the first processed prototypes by electrostatic
measurements and charge collection studies are discussed.Comment: 5 pages, 1 figure, to appear in the Proceedings of the 9th Int.
Workshop on Vertex Detectors, Lake Michigan MI (USA), September~200
Two brains in action: joint-action coding in the primate frontal cortex
Daily life often requires the coordination of our actions with those of another partner. After sixty years (1968-2018) of behavioral neurophysiology of motor control, the neural mechanisms which allow such coordination in primates are unknown. We studied this issue by recording cell activity simultaneously from dorsal premotor cortex (PMd) of two male interacting monkeys trained to coordinate their hand forces to achieve a common goal. We found a population of 'joint-action cells' that discharged preferentially when monkeys cooperated in the task. This modulation was predictive in nature, since in most cells neural activity led in time the changes of the "own" and of the "other" behavior. These neurons encoded the joint-performance more accurately than 'canonical action-related cells', activated by the action per se, regardless of the individual vs. interactive context. A decoding of joint-action was obtained by combining the two brains activities, using cells with directional properties distinguished from those associated to the 'solo' behaviors. Action observation-related activity studied when one monkey observed the consequences of the partner's behavior, i.e. the cursor's motion on the screen, did not sharpen the accuracy of 'joint-action cells' representation, suggesting that it plays no major role in encoding joint-action. When monkeys performed with a non-interactive partner, such as a computer, 'joint-action cells' representation of the "other" (non-cooperative) behavior was significantly degraded. These findings provide evidence of how premotor neurons integrate the time-varying representation of the self-action with that of a co-actor, thus offering a neural substrate for successful visuo-motor coordination between individuals.SIGNIFICANT STATEMENTThe neural bases of inter-subject motor coordination were studied by recording cell activity simultaneously from the frontal cortex of two interacting monkeys, trained to coordinate their hand forces to achieve a common goal. We found a new class of cells, preferentially active when the monkeys cooperated, rather than when the same action was performed individually. These 'joint-action neurons' offered a neural representation of joint-behaviors by far more accurate than that provided by the canonical action-related cells, modulated by the action per se regardless of the individual/interactive context. A neural representation of joint-performance was obtained by combining the activity recorded from the two brains. Our findings offer the first evidence concerning neural mechanisms subtending interactive visuo-motor coordination between co-acting agents
Multi-Higgs boson production in the Standard Model and beyond
We present a calculation of the loop-induced processes gg -> HH and gg ->
HHH, and investigate the observability of multi-Higgs boson production at the
CERN Large Hadron Collider (LHC) in the Standard Model (SM) and beyond. While
the SM cross sections are too small to allow observation at the LHC, we
demonstrate that physics beyond the SM can lead to amplified, observable cross
sections. Furthermore, the applicability of the heavy top quark approximation
in two- and three-Higgs boson production is investigated. We conclude that
multi-Higgs boson production at the SuperLHC is an interesting probe of Higgs
sectors beyond the SM and warrants further study.Comment: 17 pages, 17 figure
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Identification and characterization of the dominant thermal resistance in lithium-ion batteries using operando 3-omega sensors
Poor thermal transport within lithium-ion batteries fundamentally limits their performance, safety, and lifetime, in spite of external thermal management systems. All prior efforts to understand the origin of batteries' mysteriously high thermal resistance have been confined to ex situ measurements without understanding the impact of battery operation. Here, we develop a frequency-domain technique that employs sensors capable of measuring spatially resolved intrinsic thermal transport properties within a live battery while it is undergoing cycling. Our results reveal that the poor battery thermal transport is due to high thermal contact resistance between the separator and both electrode layers and worsens as a result of formation cycling, degrading total battery thermal transport by up to 70%. We develop a thermal model of these contact resistances to explain their origin. These contacts account for up to 65% of the total thermal resistance inside the battery, leading to far-reaching consequences for the thermal design of batteries. Our technique unlocks new thermal measurement capabilities for future battery research
Activated Tryptophan-Kynurenine metabolic system in the human brain is associated with learned fear
Fear is widely recognized as a defensive emotion that has developed as a consequence
of its adaptive function in protecting the entire animal kingdom from danger, ensuring
the survival (Bouton, 2002; Milad and Quirk, 2002). Although fear associated with specific
stimuli is an innate emotion (e.g., a loud noise triggering fear in infants, fear of potential
predators), it can also be acquired rapidly and permanently to enable an appropriate and
adaptive response to new or unpredictable environmental situations (LeDoux, 2000; Beckers
et al., 2013)
The sizes of galaxy halos in galaxy cluster Abell 1689
The multiple images observed in galaxy cluster Abell 1689 provide strong
constraints not only on the mass distribution of the cluster but also on the
ensemble properties of the cluster galaxies. Using parametric strong lensing
models for the cluster, and by assuming well motivated scaling laws between the
truncation radius s and the velocity dispersion sigma of a cluster galaxy we
are able to derive sizes of the dark matter halos of cluster galaxies.
For the scaling law expected for galaxies in the cluster environment (s
propto sigma), we obtain s = 64^{+15}_{-14} (sigma / 220 km/s) kpc. For the
scaling law used for galaxies in the field with s propto sigma^2 we find s =
66^{+18}_{-16} (sigma / 220 km/s)^2 kpc. Compared to halos of field galaxies,
the cluster galaxy halos in Abell 1689 are strongly truncated.Comment: 12 pages, 4 figures. Accepted for publication in the Ap
Exciting dark matter in the galactic center
We reconsider the proposal of excited dark matter (DM) as an explanation for
excess 511 keV gamma rays from positrons in the galactic center. We
quantitatively compute the cross section for DM annihilation to nearby excited
states, mediated by exchange of a new light gauge boson with off-diagonal
couplings to the DM states. In models where both excited states must be heavy
enough to decay into e^+ e^- and the ground state, the predicted rate of
positron production is never large enough to agree with observations, unless
one makes extreme assumptions about the local circular velocity in the Milky
Way, or alternatively if there exists a metastable population of DM states
which can be excited through a mass gap of less than 650 keV, before decaying
into electrons and positrons.Comment: Dedicated to the memory of Lev Kofman; 16 pages, 9 figures; v3 added
refs, minor changes, accepted to PR
The Solar X-ray Limb
We describe a new technique to measure the height of the X-ray limb with
observations from occulted X-ray flare sources as observed by the RHESSI (the
Reuven Ramaty High-Energy Spectroscopic Imager) satellite. This method has
model dependencies different from those present in traditional observations at
optical wavelengths, which depend upon detailed modeling involving radiative
transfer in a medium with complicated geometry and flows. It thus provides an
independent and more rigorous measurement of the "true" solar radius, meaning
that of the mass distribution. RHESSI's measurement makes use of the flare
X-ray source's spatial Fourier components (the visibilities), which are
sensitive to the presence of the sharp edge at the lower boundary of the
occulted source. We have found a suitable flare event for analysis,
SOL2011-10-20T03:25 (M1.7), and report a first result from this novel technique
here. Using a 4-minute integration over the 3-25 keV photon energy range, we
find arcsec, at 1 AU, where
the uncertainties include statistical uncertainties from the method and a
systematic error. The standard VAL-C model predicts a value of 959.94 arcsec,
about 1 below our value.Comment: 12 pages, 5 figures, accepted for publication in Ap
Where to find a dark matter sterile neutrino?
We propose a strategy of how to look for dark matter (DM) particles
possessing a radiative decay channel and derive constraints on their parameters
from observations of X-rays from our own Galaxy and its dwarf satellites. When
applied to the sterile neutrinos in keV mass range, it allows a significant
improvement of restrictions to its parameters, as compared with previous works.Comment: 5 pp, revtex; v3: 1-sigma limits have been replaced by more
conservative 3-sigma limits, a picture illustrating the data analysis methods
has been ade
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