7,236 research outputs found
Canonical heights on the jacobians of curves of genus 2 and the infinite descent
We give an algorithm to compute the canonical height on a Jacobian of a curve of genus 2. The computations involve only working with the Kummer surface and so lengthy computations with divisors in the Jacobian are avoided. We use this height algorithm to give an algorithm to perform the infinite descent stage of computing the Mordell-Weil group. This last stage is performed by a lattice enlarging procedure
Experiences of post-qualifying study in social work
This article is based on a research project to explore the experiences of past and current candidates for post-qualifying awards in social work in England. Also included in the study are the Leads of the post-qualifying consortia in England. The study used questionnaire survey and nominal group techniques to gather data, which were coded and categorised into themes. The main findings relate to the perceived purposes of post-qualifying study, motivations for undertaking post-qualifying study, the factors that sustain and hinder study, the advice that those who have or who are experiencing post-qualifying study would give to those about to start and future plans and hopes in this area.Post-qualifying study is generally valued, especially in relation to the opportunities it provides for professional development. The support of a mentor who has direct experience of the candidate's programme is highly prized, as are clear and consistent guidance from the programme and meaningful study time and workload relief from employers. There are also frustrations for some candidates who do not feel that their post-qualifying study has stretched them beyond qualifying standards or who experience the teaching as divorced from the realities of daily practice. The appetite for a wider choice of post-qualifying modules suggests that providers of post-qualifying study will need to collaborate within and across regions in order to achieve a critical mass of candidates for more specialist or focused learning. The study suggests a need for further research to understand the impact of post-qualifying study on candidates' social work practice.The article concludes with two checklists of questions, one for individual candidates and another for agencies and programmes. These questions arise from the findings in the research
Connections of activated hopping processes with the breakdown of the Stokes-Einstein relation and with aspects of dynamical heterogeneities
We develop a new extended version of the mode-coupling theory (MCT) for glass
transition, which incorporates activated hopping processes via the dynamical
theory originally formulated to describe diffusion-jump processes in crystals.
The dynamical-theory approach adapted here to glass-forming liquids treats
hopping as arising from vibrational fluctuations in quasi-arrested state where
particles are trapped inside their cages, and the hopping rate is formulated in
terms of the Debye-Waller factors characterizing the structure of the
quasi-arrested state. The resulting expression for the hopping rate takes an
activated form, and the barrier height for the hopping is ``self-generated'' in
the sense that it is present only in those states where the dynamics exhibits a
well defined plateau. It is discussed how such a hopping rate can be
incorporated into MCT so that the sharp nonergodic transition predicted by the
idealized version of the theory is replaced by a rapid but smooth crossover. We
then show that the developed theory accounts for the breakdown of the
Stokes-Einstein relation observed in a variety of fragile glass formers. It is
also demonstrated that characteristic features of dynamical heterogeneities
revealed by recent computer simulations are reproduced by the theory. More
specifically, a substantial increase of the non-Gaussian parameter, double-peak
structure in the probability distribution of particle displacements, and the
presence of a growing dynamic length scale are predicted by the extended MCT
developed here, which the idealized version of the theory failed to reproduce.
These results of the theory are demonstrated for a model of the Lennard-Jones
system, and are compared with related computer-simulation results and
experimental data.Comment: 13 pages, 5 figure
Effective renormalized multi-body interactions of harmonically confined ultracold neutral bosons
We calculate the renormalized effective 2-, 3-, and 4-body interactions for N
neutral ultracold bosons in the ground state of an isotropic harmonic trap,
assuming 2-body interactions modeled with the combination of a zero-range and
energy-dependent pseudopotential. We work to third-order in the scattering
length a defined at zero collision energy, which is necessary to obtain both
the leading-order effective 4-body interaction and consistently include
finite-range corrections for realistic 2-body interactions. The leading-order,
effective 3- and 4-body interaction energies are U3 = -(0.85576...)(a/l)^2 +
2.7921(1)(a/l)^3 + O[(a/l)^4] and U4 = +(2.43317...)(a/l)^3 + O[(a\l)^4], where
w and l are the harmonic oscillator frequency and length, respectively, and
energies are in units of hbar*w. The one-standard deviation error 0.0001 for
the third-order coefficient in U3 is due to numerical uncertainty in estimating
a slowly converging sum; the other two coefficients are either analytically or
numerically exact. The effective 3- and 4-body interactions can play an
important role in the dynamics of tightly confined and strongly correlated
systems. We also performed numerical simulations for a finite-range boson-boson
potential, and it was comparison to the zero-range predictions which revealed
that finite-range effects must be taken into account for a realistic
third-order treatment. In particular, we show that the energy-dependent
pseudopotential accurately captures, through third order, the finite-range
physics, and in combination with the multi-body effective interactions gives
excellent agreement with the numerical simulations, validating our theoretical
analysis and predictions.Comment: Updated introduction, correction of a few typos and sign error
Second order perturbation theory for spin-orbit resonances
We implement Lie transform perturbation theory to second order for the planar
spin-orbit problem. The perturbation parameter is the asphericity of the body,
with the orbital eccentricity entering as an additional parameter. We study
first and second order resonances for different values of these parameters. For
nearly spherical bodies like Mercury and the Moon first order perturbation
theory is adequate, whereas for highly aspherical bodies like Hyperion the spin
is mostly chaotic and perturbation theory is of limited use. However, in
between, we identify a parameter range where second order perturbation theory
is useful and where as yet unidentified objects may be in second order
resonances.Comment: To appear in A
Seedhead Suppression in Tall Fescue with Chaparral Herbicide
Tall Fescue (Lolium arundinaceum (Schreb.)) is cool-season perennial grass found in pastures throughout the Eastern US, most commonly in the transition zone. Itâs tolerance to extreme temperatures, drought, poor soil fertility, heavy grazing, and pests have made it a reliable forage base for livestock pastures. Released in 1943, âKY-31â tall fescue was quickly adopted by cattle producers and now inhabits an estimated 40 million acres in the US.
Soon after its adoption, cattle producers began to notice a reduction in animal performance and signs that animals were heat stressed following tall fescue consumption. These symptoms were an indication of an animal disorder that would later be called âfescue toxicosisâ by scientists and producers. In the late 1970s, it was discovered that the cattle health issues with tall fescue were actually caused by a fungus (Neotyphodium coenophialum) living within some plants, which produced a toxic class of compounds termed ergot alkaloids. We refer to these tall fescue plants that contain this fungus as being endophyte infected (E+) and those that do not as being endophyte free (E-)
The impact of supply chain complexity on manufacturing plant performance
This paper puts forth a model of supply chain complexity and empirically tests it using plant-level data from 209 plants across seven countries. The results show that upstream complexity, internal manufacturing complexity, and downstream complexity all have a negative impact on manufacturing plant performance. Furthermore, supply chain characteristics that drive dynamic complexity are shown to have a greater impact on performance than those that drive only detail complexity. In addition to providing a definition and empirical test of supply chain complexity, the study serves to link the systems complexity literature to the prescriptions found in the flexibility and lean production literatures. Finally, this research establishes a base from which to extend previous work linking operations strategy to organization design [Flynn, B.B., Flynn, E.J., 1999. Information-processing alternatives for coping with manufacturing environment complexity. Decision Sciences 30 (4), 1021â1052]
The use of information in online healthcare provider choice
In order to evaluate and facilitate the provision of health information online, we must first understand how it is perceived by those who use it. Two important considerations in research on patientsâ information use in online healthcare provider choice are the need for a conceptual framework for studying information types and methods for studying information use. Therefore, our first contribution lies in using Donabedian's structure-process-outcome model of healthcare quality to identify specific patterns of preference and information use in online healthcare provider choice, and differences in information use between two healthcare provider types. Our second contribution lies in identifying differences in results between data collection methods (importance rating/selection, concurrent self-report of online information use and retrospective information use) in relation to choice tasks. In a mixed-methods design, provider type (primary and secondary care) was systematically varied during participantsâ use of the infomediary NHS Choices. Participants preferred process topics over structure topics, in contrast with the results of concurrent and retrospective self-report. We conclude that the differences in results between the types of data collection method reflect underlying differences in choice task. Future research should address the use of novel infomediary user-interfaces, and infomediaries in relation to the use of other information sources and (e-)health literacy
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