4,510 research outputs found
The Populations of Comet-Like Bodies in the Solar system
A new classification scheme is introduced for comet-like bodies in the Solar
system. It covers the traditional comets as well as the Centaurs and
Edgeworth-Kuiper belt objects. At low inclinations, close encounters with
planets often result in near-constant perihelion or aphelion distances, or in
perihelion-aphelion interchanges, so the minor bodies can be labelled according
to the planets predominantly controlling them at perihelion and aphelion. For
example, a JN object has a perihelion under the control of Jupiter and aphelion
under the control of Neptune, and so on. This provides 20 dynamically distinct
categories of outer Solar system objects in the Jovian and trans-Jovian
regions. The Tisserand parameter with respect to the planet controlling
perihelion is also often roughly constant under orbital evolution. So, each
category can be further sub-divided according to the Tisserand parameter. The
dynamical evolution of comets, however, is dominated not by the planets nearest
at perihelion or aphelion, but by the more massive Jupiter. The comets are
separated into four categories -- Encke-type, short-period, intermediate and
long-period -- according to aphelion distance. The Tisserand parameter
categories now roughly correspond to the well-known Jupiter-family comets,
transition-types and Halley-types. In this way, the nomenclature for the
Centaurs and Edgeworth-Kuiper belt objects is based on, and consistent with,
that for comets.Comment: MNRAS, in press, 11 pages, 6 figures (1 available as postscript, 5 as
gif). Higher resolution figures available at
http://www-thphys.physics.ox.ac.uk/users/WynEvans/preprints.pd
Diffusional Relaxation in Random Sequential Deposition
The effect of diffusional relaxation on the random sequential deposition
process is studied in the limit of fast deposition. Expression for the coverage
as a function of time are analytically derived for both the short-time and
long-time regimes. These results are tested and compared with numerical
simulations.Comment: 9 pages + 2 figure
Nomenclature and placental mammal phylogeny.
An issue arising from recent progress in establishing the placental mammal Tree of Life concerns the nomenclature of high-level clades. Fortunately, there are now several well-supported clades among extant mammals that require unambiguous, stable names. Although the International Code of Zoological Nomenclature does not apply above the Linnean rank of family, and while consensus on the adoption of competing systems of nomenclature does not yet exist, there is a clear, historical basis upon which to arbitrate among competing names for high-level mammalian clades. Here, we recommend application of the principles of priority and stability, as laid down by G.G. Simpson in 1945, to discriminate among proposed names for high-level taxa. We apply these principles to specific cases among placental mammals with broad relevance for taxonomy, and close with particular emphasis on the Afrotherian family Tenrecidae. We conclude that no matter how reconstructions of the Tree of Life change in years to come, systematists should apply new names reluctantly, deferring to those already published and maximizing consistency with existing nomenclature.RIGHTS : This article is licensed under the BioMed Central licence at http://www.biomedcentral.com/about/license which is similar to the 'Creative Commons Attribution Licence'. In brief you may : copy, distribute, and display the work; make derivative works; or make commercial use of the work - under the following conditions: the original author must be given credit; for any reuse or distribution, it must be made clear to others what the license terms of this work are
Adolescents care but don't feel responsible for farm animal welfare
Adolescents are the next generation of consumers with the potential to raise standards of farm animal welfareâto theirsatisfactionâif their preferences and concerns are translated into accurate market drivers and signals. There are no published data about adolescent views of farm animal welfare to allow meaningful design, implementation, and evaluation of educational strategies to improve consideration ofâand behavior towardâfarm animals. Knowledge of farm animal welfare, as well as beliefs and attitudes about farm animal welfare and behavioral intention relevant to it were determined in a sample of ukadolescents, using a survey incorporating an extended version of the theory of planned behavior and novel assessment tools. Our results indicate that adolescents have only a limited knowledge of welfare problems for farm animals and welfare-relevant product labels. Intentions to identify welfare standards for the animals from whom their food was derived were weak. Although they cared about farm animal welfare and agreed with fundamental principlesâfor example, the provision of space and the absence of pain and sufferingâlike adults they held limited belief in the power and responsibility that they possess through their choices as consumers; responsibility was often shifted to others, such as the government and farmers
Nonlocal effects in Fock space
If a physical system contains a single particle, and if two distant detectors
test the presence of linear superpositions of one-particle and vacuum states, a
violation of classical locality can occur. It is due to the creation of a
two-particle component by the detecting process itself.Comment: final version in PRL 74 (1995) 4571; 76 (1996) 2205 (erratum
Newly-Discovered Planets Orbiting HD~5319, HD~11506, HD~75784 and HD~10442 from the N2K Consortium
Initially designed to discover short-period planets, the N2K campaign has
since evolved to discover new worlds at large separations from their host
stars. Detecting such worlds will help determine the giant planet occurrence at
semi-major axes beyond the ice line, where gas giants are thought to mostly
form. Here we report four newly-discovered gas giant planets (with minimum
masses ranging from 0.4 to 2.1 MJup) orbiting stars monitored as part of the
N2K program. Two of these planets orbit stars already known to host planets: HD
5319 and HD 11506. The remaining discoveries reside in previously-unknown
planetary systems: HD 10442 and HD 75784. The refined orbital period of the
inner planet orbiting HD 5319 is 641 days. The newly-discovered outer planet
orbits in 886 days. The large masses combined with the proximity to a 4:3 mean
motion resonance make this system a challenge to explain with current formation
and migration theories. HD 11506 has one confirmed planet, and here we confirm
a second. The outer planet has an orbital period of 1627.5 days, and the
newly-discovered inner planet orbits in 223.6 days. A planet has also been
discovered orbiting HD 75784 with an orbital period of 341.7 days. There is
evidence for a longer period signal; however, several more years of
observations are needed to put tight constraints on the Keplerian parameters
for the outer planet. Lastly, an additional planet has been detected orbiting
HD 10442 with a period of 1043 days.Comment: Accepted for publication in Ap
Gravitating monopoles in SU(3) gauge theory
We consider the Einstein-Yang-Mills-Higgs equations for an SU(3) gauge group
in a spherically symmetric ansatz. Several properties of the gravitating
monopole solutions are obtained an compared with their SU(2) counterpart.Comment: 7 pages, Latex, 3 figure
Comparison of application methods to prolong the survival of potential biocontrol bacteria on stored sugar-beet seed
Colonization of the developing rhizosphere of sugar beet seedlings by potential biocontrol agents applied as seed treatments
Aims: Poor colonization of the rhizosphere is a major constraint of seed treatment biological control. The objectives of this study were to; examine the colonization of the rhizosphere of sugar beet seedlings by selected rhizobacteria; determine the influence of the host rhizosphere and percolating water on the distribution of the bacteria; and deliver two biological control agents (BCAs) by co-inoculation. Methods and Results: Rifampicin-resistant bacterial strains (Rif(+)) applied as single treatments to seed sown in columns of field soil produced persistent populations of 5-9 log(10) cfu g(-1) in the infection court of the damping-off pathogen Aphanomyces cochlioides in a controlled environment. However, isolates varied in their ability to colonize the lower rhizosphere. Percolating water significantly increased the colonization of the upper rhizosphere. Bacterial populations in the soil profiles of "non-rhizosphere" controls declined markedly with time. There was no interaction between the two selected BCAs applied as a seed treatment mixture. Conclusions: The distribution of the bacteria resulted primarily from root colonization although percolating water may modify the colonization profiles. Co-inoculation of the sugar-beet rhizosphere is a viable proposition. Significance and Impact of Study: Potential BCAs were successfully delivered to the known infection court of A. cochloides and persisted for the infection period. This bioassay can be used as a tool for the selection of BCAs for field trials
- âŠ