13,450 research outputs found
Giant ultrafast Kerr effect in type-II superconductors
We study the ultrafast Kerr effect and high-harmonic generation in type-II
superconductors by formulating a new model for a time-varying electromagnetic
pulse normally incident on a thin-film superconductor. It is found that type-II
superconductors exhibit exceptionally large due to the progressive
destruction of Cooper pairs, and display high-harmonic generation at low
incident intensities, and the highest nonlinear susceptibility of all known
materials in the THz regime. Our theory opens up new avenues for accessible
analytical and numerical studies of the ultrafast dynamics of superconductors
Infrared spectra of van de Waals complexes of importance in planetary atmospheres
It has been suggested that (CO2)2 and Ar-CO2 are important constituents of the planetary atmospheres of Venus and Mars. Recent results on the laboratory spectroscopy of CO2 containing van der Waals complexes which may be of use in the modeling of the spectra of planetary atmospheres are presented. Sub-Doppler infrared spectra were obtained for (CO2)2, (CO2)3, and rare-gas-CO2 complexes in the vicinity of the CO2 Fermi diad at 2.7 micrometers using a color-center-laser optothermal spectrometer. From the spectroscopic constants the geometries of the complexes have been determined and van der Waals vibrational frequencies have been estimated. The equilibrium configurations are C2h, C3h, and C2v, for (CO2)2, (CO2)3, and the rare-gas-CO2 complexes, respectively. Most of the homogeneous linewidths for the revibrational transitions range from 0.5 to 22 MHz, indicating that predissociation is as much as four orders of magnitude faster than radiative processes for vibrational relaxation in these complexes
The Mass, Orbit, and Tidal Evolution of the Quaoar-Weywot System
Here we present new adaptive optics observations of the Quaoar-Weywot system.
With these new observations we determine an improved system orbit. Due to a
0.39 day alias that exists in available observations, four possible orbital
solutions are available with periods of , , , and
days. From the possible orbital solutions, system masses of
kg are found. These observations provide an
updated density for Quaoar of 2.7-5.0{g cm^{-3}}. In all cases, Weywot's
orbit is eccentric, with possible values . We present a
reanalysis of the tidal orbital evolution of the Quoaor-Weywot system. We have
found that Weywot has probably evolved to a state of synchronous rotation, and
have likely preserved their initial inclinations over the age of the Solar
system. We find that for plausible values of the effective tidal dissipation
factor tides produce a very slow evolution of Weywot's eccentricity and
semi-major axis. Accordingly, it appears that Weywot's eccentricity likely did
not tidally evolve to its current value from an initially circular orbit.
Rather, it seems that some other mechanism has raised its eccentricity
post-formation, or Weywot formed with a non-negligible eccentricity.Comment: Accepted to Icarus, Nov. 8 201
Potential solar axion signatures in X-ray observations with the XMM-Newton observatory
The soft X-ray flux produced by solar axions in the Earth's magnetic field is
evaluated in the context of ESA's XMM-Newton observatory. Recent calculations
of the scattering of axion-conversion X-rays suggest that the sunward
magnetosphere could be an observable source of 0.2-10 keV photons. For
XMM-Newton, any conversion X-ray intensity will be seasonally modulated by
virtue of the changing visibility of the sunward magnetic field region. A
simple model of the geomagnetic field is combined with the ephemeris of
XMM-Newton to predict the seasonal variation of the conversion X-ray intensity.
This model is compared with stacked XMM-Newton blank sky datasets from which
point sources have been systematically removed. Remarkably, a seasonally
varying X-ray background signal is observed. The EPIC count rates are in the
ratio of their X-ray grasps, indicating a non-instrumental, external photon
origin, with significances of 11(pn), 4(MOS1) and 5(MOS2) sigma. After
examining the constituent observations spatially, temporally and in terms of
the cosmic X-ray background, we conclude that this variable signal is
consistent with the conversion of solar axions in the Earth's magnetic field.
The spectrum is consistent with a solar axion spectrum dominated by
bremsstrahlung- and Compton-like processes, i.e. axion-electron coupling
dominates over axion-photon coupling and the peak of the axion spectrum is
below 1 keV. A value of 2.2e-22 /GeV is derived for the product of the
axion-photon and axion-electron coupling constants, for an axion mass in the
micro-eV range. Comparisons with limits derived from white dwarf cooling may
not be applicable, as these refer to axions in the 0.01 eV range. Preliminary
results are given of a search for axion-conversion X-ray lines, in particular
the predicted features due to silicon, sulphur and iron in the solar core, and
the 14.4 keV transition line from 57Fe.Comment: Accepted for publication in MNRAS. 67 pages total, including 39
figures, 6 table
Silica grain catalysis of methanol formation
The specific catalytic effect of a silica grain on the formation of methanol via the sequential addition of H atoms to CO adsorbed on the surface is investigated. A negatively charged defect on a siliceous edingtonite surface is found to reduce the gas phase barriers for the H + COads and H + H2C=O-ads reactions by 770 and 399 K, respectively, when compared to the same reactions in the gas phase. The catalytic effect of negatively charged surface sites could also be applicable to the hydrogenation of other adsorbed unsaturated species. However, the activation energies on the surface defect are still too large (1150 and 2230 K) for CH3OH to form efficiently at 10-20 K in the interstellar medium via a classical mechanism. It is therefore suggested that quantum mechanical tunnelling through the activation barrier is required for these hydrogen addition reactions to proceed at such temperatures. The calculations show that because the adsorption energies of CO and H2C=O on the negatively charged defect are substantial, CH3OH may form efficiently during the warm-up period in star-forming regions
The Effects of Ethostasis on Farm Animal Behavior: A Theoretical Overview
Ethostasis – the effect of constraining husbandry practices on animal behavior – is described and discussed. The review describes specific husbandry practices that may give rise to behavioral anomalies and how these anomalous behaviors may be of diagnostic value. Ready identification may facilitate correcting problems leading to lower productivity, diseases, and economic losses
Community experiences of organised crime in Scotland
The research explored community experiences of serious organised crime in Scotland (SOC). The report provides information on the nature and extent of the impact of SOC on everyday life in the community, as well as offering suggestions for policy development. The study sought to answer the following questions: 1)What are the relationships that exist between SOC and communities in Scotland? 2)What are the experiences and perceptions of residents, stakeholders and organisations of the scope and nature of SOC within their local area? and 3)How does SOC impact on community wellbeing, and to what extent can the harms associated with SOC be mitigated
The Effects of Ethostasis on Farm Animal Behavior: A Theoretical Overview
The solution of animal problems that occur on the farm requires a holistic and multidisciplinary orientation and analysis, as well as the acquisition of new investigatory tools by both veterinarians and animal scientists. Field studies may be modeled under more controlled laboratory conditions, but the most relevant investigations must take place on the farm, and the first level of analysis should be ethological. Domestic animal behavior can be monitored and quantified like any other factor in the animals\u27 environment; yet it has been virtually ignored in the development of new livestock husbandry systems.
The relationships between husbandry systems, disease problems, and behavioral factors are extremely complex but are known to be interrelated and interdependent. It is postulated that severely constricting husbandry practices can generate anomalous behavior- a phenomenon termed ethostasis. Applied ethology now has a vital and central role to play in investigating the problems that have been created by modern intensive livestock production.
The purpose of this overview, therefore, is to delineate some of the husbandry factors that can give rise to behavioral anomalies, and to describe various categories of anomalous behavior that are of diagnostic value in clinical appraisals of stressful husbandry. Ready identification may facilitate recognition and correction of problems that may lead to lowered productivity, diseases, and economic losses; it may also foster concern for the animals\u27 welfare from an ethical, as well as an economic, perspective. These circumstances highlight some of the contemporary animal husbandry problems that warrant further research and quantitative analysis
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