14,198 research outputs found
Formation of terrestrial planets in close binary systems: the case of Alpha Centauri A
At present the possible existence of planets around the stars of a close
binary system is still matter of debate. Can planetary bodies form in spite of
the strong gravitational perturbations of the companion star? We study in this
paper via numerical simulation the last stage of planetary formation, from
embryos to terrestrial planets in the Alpha Cen system, the prototype of close
binary systems. We find that Earth class planets can grow around Alpha Cen A on
a time-scale of 50 Myr. In some of our numerical models the planets form
directly in the habitable zone of the star in low eccentric orbits. In one
simulation two of the final planets are in a 2:1 mean motion resonance that,
however, becomes unstable after 200 Myr. During the formation process some
planetary embryos fall into the stars possibly altering their metallicity.Comment: accepted for pubblication in A&A, 13 pages, 9 figure
BEHAVIORAL IMPLICATIONS OF COUNTER-CYCLICAL PAYMENTS AND BASE ACREAGE UPDATING UNDER THE 2002 FARM ACT
The introduction of counter-cyclical payments (CCPs) and a base acreage updating option under the 2002 Farm Act have potential supply response implications. To gain insight into the economic incentives and efficiency implications of these provisions, this paper presents the design of a 3-stage experimental market used to gauge the actual response of economic agents under conditions simulating those faced by U.S. farmers. When completed, the results of the experiment will be used to assess the impact of the CCP system and of policy uncertainty regarding future base-updating options, relative to a market revenue-only baseline.Agricultural and Food Policy,
The changing epidemiology of Staphylococcus aureus?
Strains of methicillin-resistant Staphylococcus aureus (MRSA), which had been largely confined to hospitals and long-term care facilities, are emerging in the community. The changing epidemiology of MRSA bears striking similarity to the emergence of penicillinase-mediated resistance in S. aureus decades ago. Even though the origin (hospital or the community) of the emerging MRSA strains is not known, the prevalence of these strains in the community seems likely to increase substantially
Superburst oscillations: ocean and crustal modes excited by Carbon-triggered Type I X-ray bursts
Accreting neutron stars (NS) can exhibit high frequency modulations in their
lightcurves during thermonuclear X-ray bursts, known as burst oscillations. The
frequencies can be offset from the spin frequency of the NS by several Hz, and
can drift by 1-3 Hz. One possible explanation is a mode in the bursting ocean,
the frequency of which would decrease (in the rotating frame) as the burst
cools, hence explaining the drifts. Most burst oscillations have been observed
during H/He triggered bursts, however there has been one observation of
oscillations during a superburst; hours' long Type I X-ray bursts caused by
unstable carbon burning deeper in the ocean. This paper calculates the
frequency evolution of an oceanic r-mode during a superburst. The rotating
frame frequency varies during the burst from 4-14 Hz, and is sensitive to the
background parameters, in particular the temperature of the ocean and ignition
depth. This calculation is compared to the superburst oscillations observed on
4U-1636-536. The predicted mode frequencies ( 10 Hz) would require a spin
frequency of 592 Hz to match observations; 6 Hz higher than the spin
inferred from an oceanic r-mode model for the H/He triggered burst
oscillations. This model also over-predicts the frequency drift during the
superburst by 90 %.Comment: Accepted for publication in MNRA
Progress in strain monitoring of tapestries
This paper reports interdisciplinary
research between conservators and
engineers designed to enhance the
long-term conservation of tapestries
(tapestry-weave hangings) on longterm
display. The aim is to monitor,
measure and document the strain
experienced by different areas of a
tapestry while it is hanging on display.
Initial research has established that
damage can be identified in the early
stages of its inception, i.e., before it is
visible to the naked eye. The paper also
reports initial results of strain data
visualisation that allows curators and
conservators to examine how strain
develops, thereby facilitating
predictions about the changes in the
form or condition of the tapestry.
Strain data visualisation also allows the
strain process to be recorded, thereby
facilitating the effective documentation
of display methods and conservation
interventions. The paper reports the
use of point measurements (using
silica optical fibre sensors) and full-field
monitoring (using 3-D
photogrammetry with digital image
correlation (DIC))
PBP4: A New Perspective on Staphylococcus aureus β-Lactam Resistance.
β-lactam antibiotics are excellent drugs for treatment of staphylococcal infections, due to their superior efficacy and safety compared to other drugs. Effectiveness of β-lactams is severely compromised due to resistance, which is widespread among clinical strains of Staphylococcus aureus. β-lactams inhibit bacterial cells by binding to penicillin binding proteins (PBPs), which perform the penultimate steps of bacterial cell wall synthesis. Among PBPs of S. aureus, PBP2a has received the most attention for the past several decades due to its preeminent role in conferring both high-level and broad-spectrum resistance to the entire class of β-lactam drugs. Studies on PBP2a have thus unraveled incredible details of its mechanism of action. We have recently identified that an uncanonical, low molecular weight PBP of S. aureus, PBP4, can also provide high-level and broad-spectrum resistance to the entire class of β-lactam drugs at a level similar to that of PBP2a. The role of PBP4 has typically been considered not so important for β-lactam resistance of S. aureus, and as a result its mode of action remains largely unknown. In this article, we review our current knowledge of PBP4 mediating β-lactam resistance in S. aureus
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