1,433 research outputs found
Tidal disruption of inviscid protoplanets
Roche showed that equilibrium is impossible for a small fluid body synchronously orbiting a primary within a critical radius now termed the Roche limit. Tidal disruption of orbitally unbound bodies is a potentially important process for planetary formation through collisional accumulation, because the area of the Roche limit is considerably larger then the physical cross section of a protoplanet. Several previous studies were made of dynamical tidal disruption and different models of disruption were proposed. Because of the limitation of these analytical models, we have used a smoothed particle hydrodynamics (SPH) code to model the tidal disruption process. The code is basically the same as the one used to model giant impacts; we simply choose impact parameters large enough to avoid collisions. The primary and secondary both have iron cores and silicate mantles, and are initially isothermal at a molten temperature. The conclusions based on the analytical and numerical models are summarized
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A New Green Salamander in the Southern Appalachians: Evolutionary History of Aneides aeneus and Implications for Management and Conservation with the Description of a Cryptic Micro-endemic Species (vol 107, pg 748, 2019)
Simultaneous Triggered Collapse of the Presolar Dense Cloud Core and Injection of Short-Lived Radioisotopes by a Supernova Shock Wave
Cosmochemical evidence for the existence of short-lived radioisotopes (SLRI)
such as Al and Fe at the time of the formation of primitive
meteorites requires that these isotopes were synthesized in a massive star and
then incorporated into chondrites within yr. A supernova shock wave
has long been hypothesized to have transported the SLRI to the presolar dense
cloud core, triggered cloud collapse, and injected the isotopes. Previous
numerical calculations have shown that this scenario is plausible when the
shock wave and dense cloud core are assumed to be isothermal at K,
but not when compressional heating to K is assumed. We show here
for the first time that when calculated with the FLASH2.5 adaptive mesh
refinement (AMR) hydrodynamics code, a 20 km/sec shock wave can indeed trigger
the collapse of a 1 cloud while simultaneously injecting shock wave
isotopes into the collapsing cloud, provided that cooling by molecular species
such as HO, CO, and H is included. These calculations imply that
the supernova trigger hypothesis is the most likely mechanism for delivering
the SLRI present during the formation of the solar system.Comment: 12 pages, 4 color figures. Astrophysical Journal Letters (in press
A new upper limit on the reflected starlight from Tau Bootis b
Using improved doppler tomographic signal-analysis techniques we have carried
out a deep search for starlight reflected from the giant planet orbiting the
star Tau Bootis. We combined echelle spectra secured at the 4.2 m William
Herschel telescope in 1998 and 1999 (which yielded a tentative detection of a
reflected starlight component from the orbiting companion) with new data
obtained in 2000 (which failed to confirm the detection). The combined dataset
comprises 893 high resolution spectra with a total integration time of 75 hr 32
min spanning 17 nights. We establish an upper limit on the planet's geometric
albedo p<0.39 (at the 99.9 % significance level) at the most probable orbital
inclination i=36 degrees, assuming a grey albedo, a Venus-like phase function
and a planetary radius R_p=1.2 R_Jup. We are able to rule out some combinations
of the predicted planetary radius and atmospheric albedo models with high,
reflective cloud decks. Although a weak candidate signal appears near to the
most probable radial velocity amplitude, its statistical significance is
insufficient for us to claim a detection with any confidence.Comment: 13 pages, 18 figures, MNRAS accepted 12 June 200
Triggering Collapse of the Presolar Dense Cloud Core and Injecting Short-Lived Radioisotopes with a Shock Wave. I. Varied Shock Speeds
The discovery of decay products of a short-lived radioisotope (SLRI) in the
Allende meteorite led to the hypothesis that a supernova shock wave transported
freshly synthesized SLRI to the presolar dense cloud core, triggered its
self-gravitational collapse, and injected the SLRI into the core. Previous
multidimensional numerical calculations of the shock-cloud collision process
showed that this hypothesis is plausible when the shock wave and dense cloud
core are assumed to remain isothermal at ~10 K, but not when compressional
heating to ~1000 K is assumed. Our two-dimensional models (Boss et al. 2008)
with the FLASH2.5 adaptive mesh refinement (AMR) hydrodynamics code have shown
that a 20 km/sec shock front can simultaneously trigger collapse of a 1 solar
mass core and inject shock wave material, provided that cooling by molecular
species such as H2O, CO, and H2 is included. Here we present the results for
similar calculations with shock speeds ranging from 1 km/sec to 100 km/sec. We
find that shock speeds in the range from 5 km/sec to 70 km/sec are able to
trigger the collapse of a 2.2 solar mass cloud while simultaneously injecting
shock wave material: lower speed shocks do not achieve injection, while higher
speed shocks do not trigger sustained collapse. The calculations continue to
support the shock-wave trigger hypothesis for the formation of the solar
system, though the injection efficiencies in the present models are lower than
desired.Comment: 39 pages, 14 figures. in press, Ap
Injection of Radioactivities into the Forming Solar System
Meteorite studies have revealed the presence of short-lived radioactivities
in the early solar system. The current data suggests that the origin of at
least some of the radioactivities requires contribution from recent
nucleosynthesis at a stellar site. This sets a strict time limit on the time
available for the formation of the solar system and argues for the theory of
the triggered origin of the solar system. According to this scenario, the
formation of our planetary system was initiated by the impact of an
interstellar shock wave on a molecular cloud core. The shock wave originated
from a nearby explosive stellar event and carried with it radioactivities
produced in the stellar source. In addition to triggering the collapse of the
molecular cloud core, the shock wave also deposited some of the freshly
synthesized radioactivities into the collapsing system. The radioactivities
were then incorporated into the first solar system solids, in this manner
leaving a record of the event in the meteoritic material. The viability of the
scenario can be investigated through numerical simulations studying the
processes involved in mixing shock wave material into the collapsing system.
The high-resolution calculations presented here show that injection occurs
through Rayleigh-Taylor instabilities, the injection efficiency is
approximately 10%, and temporal and spatial heterogeneities in the abundances
of the radioactivities existed at the time of their arrival in the forming
solar system.Comment: 13 pages, including 3 figures. Better-quality figures available at
http://www.public.asu.edu/~hvanhal/pubs
New thiophene-based conjugated macrocycles for optoelectronic applications
GC acknowledges the EPSRC for funding (EP/E036244/1). JMS acknowledges the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – Brasil (CAPES) – Finance Code 001 for PhD funding. JMS also acknowledges Dr Nor Basid Adiwibawa Prasetya for helpful advice. Dr L. K. Jagadamma acknowledges support from a Marie Skłodowska-Curie Individual Fellowship (European Commission) (MCIF: No. 745776).Thiophene-based semiconductors are amongst the most successful materials in organic electronics. In this contribution, we present the synthesis and characterisation of two thiophene-based macrocycles as well as their evaluation in organic-electronic devices. McT-1 is composed of ten thiophene moieties, whereas in McT-2, four additional electron-deficient benzothiadiazole moieties are incorporated to form a donor–acceptor (D–A) π-system. Red-shifted and broadened absorption spectra as well as more positive redox potentials are observed in McT-2, whereas McT-1 displays a sharper absorption band with a higher extinction coefficient. Macrocycle McT-1 shows emission in the yellow region whereas McT-2 displays emission in the red wavelength region. DFT calculations predict the macrocycles to comprise of mainly the E,E isomers with a near-planar structure, which is further supported by the single crystal X-ray structure for McT-1. Their charge transporting properties are determined by fabricating thin-film OFETs. The photovoltaic properties of McT-1 and McT-2 are also investigated by fabricating bulk heterojunction (BHJ) devices and their potential as photodetectors has been evaluated.Publisher PDFPeer reviewe
Recent Decisions
Recent Decisions
ADMIRALTY--COGSA--BILL OF LADING CARGO DESCRIPTION AND PACKER IDENTITY DETERMINE WHEN A CONTAINER IS A PACKAGE IN COGSA LIABILITY PROCEEDINGS
Alan L. Marchisotto
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ADMIRALTY--JURISDICTION OVER AVIATION TORT CLAIMS--ADMIRALTY JURISDICTION DOES NOT EXTEND TO AVIATION TORT CLAIMS IN THE ABSENCE OF A SIGNIFICANT RELATIONSHIP BETWEEN THE TORT AND TRADITIONAL MARITIME ACTIVITIES
W. H. Schwarzschild III
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ALIENS--ALIENS MAY MAINTAIN A CAUSE OF ACTION FOR PRIVATE EMPLOYMENT DISCRIMINATION UNDER 42 U.S.C. § 1981 (1970)
Mark M. Greisberger
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ANTITRUST--ARTICLE 86 OF THE EEC TREATY APPLIES TO CERTAIN CHANGES IN INTERNAL CORPORATE STRUCTURE
Richard P. Granfield
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CONSTITUTIONAL LAW--EXECUTIVE POWER--PRESIDENTIAL AUTHORITY TO NEGOTIATE FOREIGN COMMERCIAL AGREEMENTS PURSUANT TO FOREIGN AFFAIRS POWER IS NOT CIRCUMSCRIBED ABSENT EX-PLICIT LEGISLATION
Donald B. Cameron, Jr.
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JURISDICTION--SECURITIES EXCHANGE ACT OF 1934--SECTION 10(b) APPLIES TO A TRANSACTION IN UNLISTED FOREIGN SECURITIES WHEN SIGNIFICANT FRAUDULENT CONDUCT OCCURS IN THE UNITED STATES
Isaac H. Braddock
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TARIFFS--TRADE AGREEMENT CONCESSIONS MAY BE SUSPENDED ON A MOST-FAVORED-NATION BASIS WHEN SUCH TREATMENT IS REQUIRED BY INTERNATIONAL AGREEMENTS OF THE UNITED STATES
David A. Boillo
The multicovering radius problem for some types of discrete structures
The covering radius problem is a question in coding theory concerned with
finding the minimum radius such that, given a code that is a subset of an
underlying metric space, balls of radius over its code words cover the
entire metric space. Klapper introduced a code parameter, called the
multicovering radius, which is a generalization of the covering radius. In this
paper, we introduce an analogue of the multicovering radius for permutation
codes (cf. Keevash and Ku, 2006) and for codes of perfect matchings (cf. Aw and
Ku, 2012). We apply probabilistic tools to give some lower bounds on the
multicovering radii of these codes. In the process of obtaining these results,
we also correct an error in the proof of the lower bound of the covering radius
that appeared in Keevash and Ku (2006). We conclude with a discussion of the
multicovering radius problem in an even more general context, which offers room
for further research.Comment: To appear in Designs, Codes and Cryptography (2012
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