13,242 research outputs found
Embryo impacts and gas giant mergers II: Diversity of Hot Jupiters' internal structure
We consider the origin of compact, short-period, Jupiter-mass planets. We
propose that their diverse structure is caused by giant impacts of embryos and
super-Earths or mergers with other gas giants during the formation and
evolution of these hot Jupiters. Through a series of numerical simulations, we
show that typical head-on collisions generally lead to total coalescence of
impinging gas giants. Although extremely energetic collisions can disintegrate
the envelope of gas giants, these events seldom occur. During oblique and
moderately energetic collisions, the merger products retain higher fraction of
the colliders' cores than their envelopes. They can also deposit considerable
amount of spin angular momentum to the gas giants and desynchronize their spins
from their orbital mean motion. We find that the oblateness of gas giants can
be used to infer the impact history. Subsequent dissipation of stellar tide
inside the planets' envelope can lead to runaway inflation and potentially a
substantial loss of gas through Roche-lobe overflow. The impact of super-Earths
on parabolic orbits can also enlarge gas giant planets' envelope and elevates
their tidal dissipation rate over 100 Myr time scale. Since giant
impacts occur stochastically with a range of impactor sizes and energies, their
diverse outcomes may account for the dispersion in the mass-radius relationship
of hot Jupiters.Comment: 19 pages, 7 figures, 7 tables. Accepted for publication in MNRA
Can we evaluate population screening strategies in UK general practice? A pilot randomised controlled trial comparing postal and opportunistic screening for genital chlamydial infection
STUDY OBJECTIVE: To assess whether opportunistic and postal screening strategies for Chlamydia trachomatis can be compared with usual care in a randomised trial in general practice
DESIGN: Feasibility study for a randomised controlled trial.
SETTING: Three West of Scotland general medical practices: one rural, one urban/deprived and one urban/affluent.
PARTICIPANTS: 600 women aged 16-30 years, 200 from each of three participating practices selected at random from a sample of West of Scotland practices that had expressed interest in the study. The women could opt out of the study. Those who did not were randomly assigned to one of three groups: postal screening, opportunistic screening or usual care.
MAIN RESULTS: 38% (85/221) of the approached practices expressed interest in the study. Data were collected successfully from the 3 participating practices, although intensive support was required. There were considerable workload implications for staff, both in relation to implementing the screening strategies and managing the research process.
124 of the 600 women opted out of the study. During the four-month study period, 55% (81/146) of the control group attended their practice but none was offered screening. 59% (80/136) women in the opportunistic group attended their practice of whom 55% (44/80) were offered screening. Of those, 64% (28/44) accepted, representing 21% of the opportunistic group. 48% (59/124) of the postal group returned samples.
CONCLUSION: A randomised controlled trial comparing postal and opportunistic screening for chlamydial infection in general practice is feasible, though resource intensive. There may be problems with generalising from screening trials in which patients may opt out from the offer of screening
Variable-Frequency QPOs from the Galactic Microquasar GRS 1915+105
We show that the galactic microquasar GRS 1915+105 exhibits quasi-periodic
oscillations (QPOs) whose frequency varies continuously from 1-15 Hz, during
spectrally hard dips when the source is in a flaring state. We report here
analyses of simultaneous energy spectra and power density spectra at 4 s
intervals. The energy spectrum is well fit at each time step by an optically
thick accretion disk plus power law model, while the power density spectrum
consists of a varying red noise component plus the variable frequency QPO. The
features of both spectra are strongly correlated with one another. The 1-15 Hz
QPOs appear when the power law component becomes hard and intense, and
themselves have an energy spectrum consistent with the power law component
(with root mean square amplitudes as high as 10%). The frequency of the
oscillations, however, is most strikingly correlated with the parameters of the
thermal disk component. The tightest correlation is between QPO frequency and
the disk X-ray flux. This fact indicates that the properties of the QPO are not
determined by solely a disk or solely a corona.Comment: Accepted to ApJ Letters, 12 pages, 3 figures, AASTEX forma
Molecular Composition of the Louse Sheath
Flash pyrolysis-gas chromatography/mass spectrometry was used to assess the chemical composition of the head louse\u27s nit sheath. The pyrolyzate of the female insect\u27s secretions, which form a cement-like cylinder holding the egg onto the hair, is dominated by amino acid derivatives and fatty acids. No chitin-specific compounds were detected in the sheath. These results, contrary to previous reports, show that the polymeric complex of the sheath is composed of proteinaceous moieties, possibly cross-linked to aliphatic components. This study constitutes the first chemical characterization of the pyrolysis products of insect (louse) glue and unequivocally confirms that louse sheaths are not chitinous, as suggested by earlier histochemical studies. Development of agents that might loosen nits from the hair shaft is dependent on research that addresses the chemical composition of the nit sheath
The LWA1 Radio Telescope
LWA1 is a new radio telescope operating in the frequency range 10-88 MHz,
located in central New Mexico. The telescope consists of 258 pairs of
dipole-type antennas whose outputs are individually digitized and formed into
beams. Simultaneously, signals from all dipoles can be recorded using one of
the instrument's "all dipoles" modes, facilitating all-sky imaging. Notable
features of the instrument include high intrinsic sensitivity (about 6 kJy
zenith system equivalent flux density), large instantaneous bandwidth (up to 78
MHz), and 4 independently-steerable beams utilizing digital "true time delay"
beamforming. This paper summarizes the design of LWA1 and its performance as
determined in commissioning experiments. We describe the method currently in
use for array calibration, and report on measurements of sensitivity and
beamwidth.Comment: 9 pages, 14 figures, accepted by IEEE Trans. Antennas & Propagation.
Various minor changes from previous versio
Vibronic origin of long-lived coherence in an artificial molecular light harvester
Natural and artificial light harvesting processes have recently gained new
interest. Signatures of long lasting coherence in spectroscopic signals of
biological systems have been repeatedly observed, albeit their origin is a
matter of ongoing debate, as it is unclear how the loss of coherence due to
interaction with the noisy environments in such systems is averted. Here we
report experimental and theoretical verification of coherent
exciton-vibrational (vibronic) coupling as the origin of long-lasting coherence
in an artificial light harvester, a molecular J-aggregate. In this
macroscopically aligned tubular system, polarization controlled 2D spectroscopy
delivers an uncongested and specific optical response as an ideal foundation
for an in-depth theoretical description. We derive analytical expressions that
show under which general conditions vibronic coupling leads to prolonged
excited-state coherence
Flavor Mediation Delivers Natural SUSY
If supersymmetry (SUSY) solves the hierarchy problem, then naturalness
considerations coupled with recent LHC bounds require non-trivial superpartner
flavor structures. Such "Natural SUSY" models exhibit a large mass hierarchy
between scalars of the third and first two generations as well as degeneracy
(or alignment) among the first two generations. In this work, we show how this
specific beyond the standard model (SM) flavor structure can be tied directly
to SM flavor via "Flavor Mediation". The SM contains an anomaly-free SU(3)
flavor symmetry, broken only by Yukawa couplings. By gauging this flavor
symmetry in addition to SM gauge symmetries, we can mediate SUSY breaking via
(Higgsed) gauge mediation. This automatically delivers a natural SUSY spectrum.
Third-generation scalar masses are suppressed due to the dominant breaking of
the flavor gauge symmetry in the top direction. More subtly, the
first-two-generation scalars remain highly degenerate due to a custodial U(2)
symmetry, where the SU(2) factor arises because SU(3) is rank two. This
custodial symmetry is broken only at order (m_c/m_t)^2. SUSY gauge coupling
unification predictions are preserved, since no new charged matter is
introduced, the SM gauge structure is unaltered, and the flavor symmetry treats
all matter multiplets equally. Moreover, the uniqueness of the anomaly-free
SU(3) flavor group makes possible a number of concrete predictions for the
superpartner spectrum.Comment: 17 pages, 7 figures, 2 tables. v2 references added, minor changes to
flavor constraints and a little discussion adde
Time since fire and average fire interval are the best predictors of Phytophthora cinnamomi activity in heathlands of south-western Australia
Fires are features of ecological communities in much of Australia; however, very little is still known about the potential impact of fire on plant diseases in the natural environment. Phytophthora cinnamomi is an introduced soil-borne plant pathogen with a wide host range, affecting a large proportion of native plant species in Australia and other regions of the world, but its interaction with fire is poorly understood. An investigation of the effects of fire on P. cinnamomi activity was undertaken in the Stirling Range National Park of south-western Australia, where fire is used as a management tool to reduce the negative impact of wildfires and more than 60% of the park is infested with, and 48% of woody plant species are known to be susceptible to, P. cinnamomi. At eight sites confirmed to be infested with P. cinnamomi, the proportion of dead and dying susceptible species was used as a proxy for P. cinnamomi activity. Subset modelling was used to determine the interactive effects of latest fire interval, average fire interval, soil water-holding capacity and pH on P. cinnamomi activity. It was found that the latest and average fire interval were the variables that best explained the variation in the percentage of dead and dying susceptible species among sites, indicating that fire in P. cinnamomi-infested communities has the potential to increase both the severity and extent of disease in native plant communities
The use of touch in developing a therapeutic relationship
The use of touch within health and social care is the focus of this article. The different types
of touch will first be defined, before moving on to examine the many benefits that expressive
touch can bring to the health and social care role and to developing a supportive therapeutic
relationship between the support worker and their patient. Relevant sections of the Code of Conduct for Healthcare Support Workers and Adult Social Care Workers in England (Skills for
Care and Skills for Health, 2013) will be highlighted throughout. The important aspects of communication, compassion and empathy will be explored. Touch is not always appropriate or
welcomed by the patient, and the support worker must take into account preferences, cultural needs and beliefs while also gaining consent
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