768 research outputs found
The Decay of Accreting Triple Systems as Brown Dwarf Formation Scenario
We investigate the dynamical decay of non-hierarchical accreting triple
systems and its implications on the ejection model as Brown Dwarf formation
scenario. A modified chain-regularization scheme is used to integrate the
equations of motion, that also allows for mass changes over time as well as for
momentum transfer from the accreted gas mass onto the bodies. We integrate an
ensemble of triple systems within a certain volume with different accretion
rates, assuming several prescriptions of how momentum is transferred onto the
bodies. We follow their evolution until the systems have decayed. We analyze
the end states and decay times of these systems and determine the fraction of
Brown Dwarfs formed, their escape speeds as well as the semi-major axis
distribution of the formed Brown Dwarf binaries. We find that the formation
probability of Brown Dwarfs depends strongly on the assumed momentum transfer
which is related to the motion of the gas. Due to ongoing accretion and
consequent shrinkage of the systems, the median escape velocity is increased by
a factor of 2 and the binary separations are decreased by a factor of 5
compared with non-accreting systems. Furthermore, the obtained semi-major axis
distribution drops off sharply to either side of the median, which is also
supported by observations. We conclude that accretion and momentum transfer of
accreted gas during the dynamical decay of triple systems is able to produce
the observed distribution of close binary Brown Dwarfs, making the ejection
model a viable option as Brown Dwarf formation scenario.Comment: 31 pages, 8 figures, accepted for publication in Ap
A Spitzer IRAC Imaging Survey for T Dwarf Companions Around M, L, and T Dwarfs: Observations, Results, and Monte Carlo Population Analyses
We report observational techniques, results, and Monte Carlo population
analyses from a Spitzer Infrared Array Camera imaging survey for substellar
companions to 117 nearby M, L, and T dwarf systems (median distance of 10 pc,
mass range of 0.6 to \sim0.05 M\odot). The two-epoch survey achieves typical
detection sensitivities to substellar companions of [4.5 {\mu}m] \leq 17.2 mag
for angular separations between about 7" and 165". Based on common proper
motion analysis, we find no evidence for new substellar companions. Using Monte
Carlo orbital simulations (assuming random inclination, random eccentricity,
and random longitude of pericenter), we conclude that the observational
sensitivities translate to an ability to detect 600-1100K brown dwarf
companions at semimajor axes greater than ~35 AU, and to detect 500-600K
companions at semimajor axes greater than ~60 AU. The simulations also estimate
a 600-1100K T dwarf companion fraction of < 3.4% for 35-1200 AU separations,
and < 12.4% for the 500-600K companions, for 60-1000 AU separations.Comment: 35 pages, 6 figure
Disc-Disc Encounters between Low-Mass Protoplanetary Accretion Discs
Simulations of the collapse and fragmentation of turbulent molecular clouds
and dense young clusters show that encounters between disc-surrounded stars are
relatively common events which should significantly influence the resulting
disc structure. In turn this should alter the accretion rate of disc matter
onto the star and the conditions under which planet formation occurs. Although
the effects of star-disc encounters have been previously investigated, very
little is known about encounters where both stars are surrounded by discs. In
this paper encounters of such disc-disc systems are studied quantitatively. It
is found that for low-mass discs (= 0.01 M_\sun) the results from
star-disc encounters can be straightforwardly generalized to disc-disc
encounters as long as there is no mass transport between the discs. Differences
to star-disc encounters occur naturally where significant amounts of matter are
transported between the discs. In this case it is found that although the mass
distribution does not change significantly, matter caught onto highly eccentric
orbits is transported surprisingly far inside the disc. The captured mass
partly replenishes the disc, but has a much lower angular momentum. This can
lead to a reduction of the angular momentum in the entire disc and thus
considerably increased accretion shortly after the encounter as well as in the
long term.Comment: 24 pages, 10 figures, accepted by Ap
Exploring recent developments in restorative policing in England and Wales
The evolution of the policing role over the last decade has led to 33 police forces in England and Wales integrating restorative justice practices, in one form or another, into their responses to minor crime committed for the first time by both youths and adults. Most recently, this reform dynamic has been used in response to more serious offences committed by persistent offenders and expanded to include all stages of the criminal justice process. Despite the significant positive rhetoric that surrounds the adoption and use of restorative justice, there are a number of procedural and cultural challenges that pose a threat to the extent to which restorative justice may become embedded within the policing response. This article explores these developments and highlights where potential problems for implementation may arise as well as some strategies to overcome them
Sugar utilization patterns and respiro-fermentative metabolism in the bakerâs yeast Torulaspora delbrueckii
The highly osmo- and cryotolerant yeast species Torulaspora delbrueckii is an important case study among the non-Saccharomyces yeast species. The strain T delbrueckii PYCC 532 1, isolated from traditional corn and rye bread dough in northern Portugal, is considered particularly interesting for the baking industry. This paper reports the sugar utilization patterns of this strain, using media with glucose, maltose and sucrose, alone or in mixtures. Kinetics of growth, biomass and ethanol yields, fermentation and respiration rates, hydrolase activities and sugar uptake rates were used to infer the potential applied relevance of this yeast in comparison to a conventional baker's strain of Saccharomyces cerevisiae. The results showed that both maltase and maltose transport in T delbrueckii were subject to glucose repression and maltose induction, whereas invertase was subject to glucose control but not dependent on sucrose induction. A comparative analysis of specific sugar consumption rates and transport capacities suggests that the transport step limits both glucose and maltose metabolism. Specific rates of CO2 production and O-2 consumption showed a significantly higher contribution of respiration to the overall metabolism in T delbrueckii than in S. cerevisiae. This was reflected in the biomass yields from batch cultures and could represent an asset for the large-scale production of the former species. This work contributes to a better understanding of the physiology of a non-conventional yeast species, with a view to the full exploitation of T delbrueckii by the baking industry.This work was partially funded by AgĂȘncia de Inovação (AdI) program
POCI2010/2.3, project âPARFERMâ. C. A.-A. and A. P. were supported
by PhD fellowships from PRAXIS XXI â BD/21543/99 and BD/13282/
2003, respectively (Fundação para a CiĂȘncia e para a Tecnologia,
Portugal).info:eu-repo/semantics/publishedVersio
A search for pre-substellar cores and proto-brown dwarf candidates in Taurus: multiwavelength analysis in the B213-L1495 clouds
In an attempt to study whether the formation of brown dwarfs (BDs) takes
place as a scaled-down version of low-mass stars, we conducted IRAM30m/MAMBO-II
observations at 1.2 mm in a sample of 12 proto-BD candidates selected from
Spitzer/IRAC data in the B213-L1495 clouds in Taurus. Subsequent observations
with the CSO at 350 micron, VLA at 3.6 and 6 cm, and IRAM30m/EMIR in the
12CO(1-0), 13CO(1-0), and N2H+(1-0) transitions were carried out toward the two
most promising Spitzer/IRAC source(s), J042118 and J041757. J042118 is
associated with a compact (<10 arcsec or <1400 AU) and faint source at 350
micron, while J041757 is associated with a partially resolved (~16 arcsec or
~2000 AU) and stronger source emitting at centimetre wavelengths with a flat
spectral index. The corresponding masses of the dust condensations are ~1 and
~5 Mjup for J042118 and J041757, respectively. In addition, about 40 arcsec to
the northeast of J041757 we detect a strong and extended submillimetre source,
J041757-NE, which is not associated with NIR/FIR emission down to our detection
limits, but is clearly detected in 13CO and N2H+ at ~7 km/s, and for which we
estimated a total mass of ~100 Mjup, close to the mass required to be
gravitationally bound. In summary, our observational strategy has allowed us to
find in B213-L1495 two proto-BD candidates and one pre-substellar core
candidate, whose properties seem to be consistent with a scaled-down version of
low-mass stars.Comment: MNRAS, 424, 2778; corrected typos, mass estimate refined in Section
3.2.1 and Section 5.3; conclusions unchange
Measuring the Initial Mass Function of Low Mass Stars and Brown Dwarfs
I review efforts to determine the form and any lower limit to the initial
mass function in the Galactic disk, using observations of low-mass stars and
brown dwarfs in the field, young clusters and star forming regions. I focus on
the methodologies that have been used and the uncertainties that exist due to
observational limitations and to systematic uncertainties in calibrations and
theoretical models. I conclude that whilst it is possible that the low-mass
IMFs deduced from the field and most young clusters are similar, there are too
many problems to be sure; there are examples of low-mass cluster IMFs that
appear to be very discrepant and the IMFs for brown dwarfs in the field and
young clusters have yet to be reconciled convincingly.Comment: From a series of lectures presented at the Evry-Schatzman school on
Low-mass stars and the transition from stars to brown dwarfs, edited by C.
Charbonnel, C. Reyle, M. Schultheis. To appear in the EAS Conference Series.
47p
Ska3 Ensures Timely Mitotic Progression by Interacting Directly With Microtubules and Ska1 Microtubule Binding Domain
The establishment of physical attachment between the kinetochore and dynamic spindle microtubules, which undergo cycles of polymerization and depolymerization generating straight and curved microtubule structures, is essential for accurate chromosome segregation. The Ndc80 and Ska complexes are the major microtubule-binding factors of the kinetochore responsible for maintaining chromosome-microtubule coupling during chromosome segregation. We previously showed that the Ska1 subunit of the Ska complex binds dynamic microtubules using multiple contact sites in a mode that allows conformation-independent binding. Here, we show that the Ska3 subunit is required to modulate the microtubule binding capability of the Ska complex (i) by directly interacting with tubulin monomers and (ii) indirectly by interacting with tubulin contacting regions of Ska1 suggesting an allosteric regulation. Perturbing either the Ska3-microtubule interaction or the Ska3-Ska1 interactions negatively influences microtubule binding by the Ska complex in vitro and affects the timely onset of anaphase in cells. Thus, Ska3 employs additional modulatory elements within the Ska complex to ensure robust kinetochore-microtubule attachments and timely progression of mitosis
Morality tales: young women's narratives on offending, self-worth and desistance
This article emerges from a study of female offendersâ participation in police-facilitated restorative justice in one county in England. The qualitative study, presented here, is based on life history interviews with twelve women and focuses on three morality tales that emerged through narrative analysis: âoffending as play,â âthe strong womanâ and âwork and a normal life.â The women used these tales to protect self-worth and justify âbadâ behavior in order to counter professional responses which they viewed as stigmatising. The paper concludes with implications for practice with girls and women who offend, which may benefit police, probation and social workers
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