15,768 research outputs found
Radio/X-ray Offsets of Large Scale Jets Caused by Synchrotron Time Lags
In the internal shock scenario, we argue that electrons in most kpc (or even
larger) scale jets can be accelerated to energies high enough to emit
synchrotron X-rays, if shocks exist on these scales. These high energy
electrons emit synchrotron radiation at high frequencies and cool as they
propagate downstream along the jet, emitting at progressively lower frequencies
and resulting in time lags and hence radio/X-ray (and optical/X-ray if the
optical knot is detectable) offsets at bright knots, with the centroids of
X-ray knots being closer to the core. Taking into account strong effects of jet
expansion, the behaviour of radio/X-ray and optical/X-ray offsets at bright
knots in M87, Cen A, 3C 66B, 3C 31, 3C 273, and PKS 1127-145 is consistent with
that of synchrotron time lags due to radiative losses. This suggests that the
large scale X-ray and optical jets in these sources are due to synchrotron
emission.Comment: 4 pages, Accepted for publication in ApJ Letter
Kinetic instabilities that limit {\beta} in the edge of a tokamak plasma: a picture of an H-mode pedestal
Plasma equilibria reconstructed from the Mega-Amp Spherical Tokamak (MAST)
have sufficient resolution to capture plasma evolution during the short period
between edge-localized modes (ELMs). Immediately after the ELM steep gradients
in pressure, P, and density, ne, form pedestals close to the separatrix, and
they then expand into the core. Local gyrokinetic analysis over the ELM cycle
reveals the dominant microinstabilities at perpendicular wavelengths of the
order of the ion Larmor radius. These are kinetic ballooning modes (KBMs) in
the pedestal and microtearing modes (MTMs) in the core close to the pedestal
top. The evolving growth rate spectra, supported by gyrokinetic analysis using
artificial local equilibrium scans, suggest a new physical picture for the
formation and arrest of this pedestal.Comment: Final version as it appeared in PRL (March 2012). Minor improvements
include: shortened abstract, and better colour table for figures. 4 pages, 6
figure
Stranger Danger Awareness in Williams Syndrome
Background: The developmental disorder Williams syndrome (WS) is characterised by a distinctive cognitive profile and an intriguing social phenotype. Individuals with the disorder are often highly social engaging with familiar and unfamiliar people and once in an interaction they often show subtle abnormalities of social behaviour. Atypically increased approach to unfamiliar people is widely reported in the existing literature for both children and adults. Parents frequently report interactions with unfamiliar people as a major concern. Methods: In this study we aimed to evaluate ‘stranger danger’ awareness using a video vignette task with individuals who had WS. When linked to other components of the WS phenotype (e.g. reduced intellectual ability, increased social approach) an awareness of stranger danger is particularly important. Results: Qualitative and quantitative data showed that young people with WS have difficulties making judgements about whether or not to trust and engage in conversation with unfamiliar people. Qualitative data showed that individuals with WS often suggested that they would engage in an interaction with an unfamiliar person. Conclusions: The findings have substantial implications for the safety of young people with the disorder and emphasise the need for intervention regarding this behaviour
Incoherent Transport through Molecules on Silicon in the vicinity of a Dangling Bond
We theoretically study the effect of a localized unpaired dangling bond (DB)
on occupied molecular orbital conduction through a styrene molecule bonded to a
n++ H:Si(001)-(2x1) surface. For molecules relatively far from the DB, we find
good agreement with the reported experiment using a model that accounts for the
electrostatic contribution of the DB, provided we include some dephasing due to
low lying phonon modes. However, for molecules within 10 angstrom to the DB, we
have to include electronic contribution as well along with higher dephasing to
explain the transport features.Comment: 9 pages, 5 figure
Experimental conditions to suppress edge localised modes by magnetic perturbations in the ASDEX Upgrade tokamak
Access conditions for full suppression of Edge Localised Modes (ELMs) by
Magnetic Perturbations (MP) in low density high confinement mode (H-mode)
plasmas are studied in the ASDEX Upgrade tokamak. The main empirical
requirements for full ELM suppression in our experiments are: 1. The poloidal
spectrum of the MP must be aligned for best plasma response from weakly stable
kink-modes, which amplify the perturbation, 2. The plasma edge density must be
below a critical value, ~m. The edge collisionality
is in the range (ions) and
(electrons). However, our data does not show that the edge collisionality is
the critical parameter that governs access to ELM suppression. 3. The pedestal
pressure must be kept sufficiently low to avoid destabilisation of small ELMs.
This requirement implies a systematic reduction of pedestal pressure of
typically 30\% compared to unmitigated ELMy H-mode in otherwise similar
plasmas. 4. The edge safety factor lies within a certain window.
Within the range probed so far, , one such window,
has been identified. Within the range of plasma rotation
encountered so far, no apparent threshold of plasma rotation for ELM
suppression is found. This includes cases with large cross field electron flow
in the entire pedestal region, for which two-fluid MHD models predict that the
resistive plasma response to the applied MP is shielded
Electrical current distribution across a metal-insulator-metal structure during bistable switching
Combining scanning electron microscopy (SEM) and electron-beam-induced
current (EBIC) imaging with transport measurements, it is shown that the
current flowing across a two-terminal oxide-based capacitor-like structure is
preferentially confined in areas localized at defects. As the thin-film device
switches between two different resistance states, the distribution and
intensity of the current paths, appearing as bright spots, change. This implies
that switching and memory effects are mainly determined by the conducting
properties along such paths. A model based on the storage and release of charge
carriers within the insulator seems adequate to explain the observed memory
effect.Comment: 8 pages, 7 figures, submitted to J. Appl. Phy
The NuMAX Long Baseline Neutrino Factory Concept
A Neutrino Factory where neutrinos of all species are produced in equal
quantities by muon decay is described as a facility at the intensity frontier
for exquisite precision providing ideal conditions for ultimate neutrino
studies and the ideal complement to Long Baseline Facilities like LBNF at
Fermilab. It is foreseen to be built in stages with progressively increasing
complexity and performance, taking advantage of existing or proposed facilities
at an existing laboratory like Fermilab. A tentative layout based on a
recirculating linac providing opportunities for considerable saving is
discussed as well as its possible evolution toward a muon collider if and when
requested by Physics. Tentative parameters of the various stages are presented
as well as the necessary R&D to address the technological issues and
demonstrate their feasibility.Comment: JINST Special Issue on Muon Accelerators. arXiv admin note: text
overlap with arXiv:1308.0494, arXiv:1502.0164
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