26,138 research outputs found
Ionosphere/microwave beam interaction study
A solar power satellite microwave power density of 20mw sq cm was confirmed as the level where nonlinear interactions may occur in the ionosphere, particularly at 100 km altitude. Radio wave heating at this altitude, produced at the Arecibo Observatory, yielded negative results for radio wave heating of an underdense ionosphere. Overdense heating produced striations in the ionosphere which may cause severe radio frequency interference problems under certain conditions. The effects of thermal self-focusing are shown to be limited severely geographically. The aspect sensitivity of field-aligned striations makes interference-free regions above magnetic latitude about 60 deg. A test program is proposed to simulate the interaction of the SPS beam with the ionosphere, to measure the effects of the interaction on the ionosphere and on communication and navigation systems, and to interpret the results
String Breaking in Four Dimensional Lattice QCD
Virtual quark pair screening leads to breaking of the string between
fundamental representation quarks in QCD. For unquenched four dimensional
lattice QCD, this (so far elusive) phenomenon is studied using the recently
developed truncated determinant algorithm (TDA). The dynamical configurations
were generated on an Athlon 650 MHz PC. Quark eigenmodes up to 420 MeV are
included exactly in these TDA studies performed at low quark mass on large
coarse (but O() improved) lattices. A study of Wilson line correlators in
Coulomb gauge extracted from an ensemble of 1000 two-flavor dynamical
configurations reveals evidence for flattening of the string tension at
distances R approximately 1 fm.Comment: 16 pages, 5 figures, Latex (deleted extraneous eps figure file
Recommended from our members
Using shared goal setting to improve access and equity: a mixed methods study of the Good Goals intervention
Background: Access and equity in childrenâs therapy services may be improved by directing cliniciansâ use of resources toward specific goals that are important to patients. A practice-change intervention (titled âGood Goalsâ) was designed to achieve this. This study investigated uptake, adoption, and possible effects of that intervention in childrenâs occupational therapy services.
Methods: Mixed methods case studies (n = 3 services, including 46 therapists and 558 children) were conducted. The intervention was delivered over 25 weeks through face-to-face training, team workbooks, and âtools for changeâ. Data were collected before, during, and after the intervention on a range of factors using interviews, a focus group, case note analysis, routine data, document analysis, and researchersâ observations.
Results: Factors related to uptake and adoptions were: mode of intervention delivery, competing demands on therapistsâ time, and leadership by service manager. Service managers and therapists reported that the intervention: helped therapists establish a shared rationale for clinical decisions; increased clarity in service provision; and improved interactions with families and schools. During the study period, therapistsâ behaviours changed: identifying goals, odds ratio 2.4 (95% CI 1.5 to 3.8); agreeing goals, 3.5 (2.4 to 5.1); evaluating progress, 2.0 (1.1 to 3.5). Childrenâs LoT decreased by two months [95% CI â8 to +4 months] across the services. Cost per therapist trained ranged from ÂŁ1,003 to ÂŁ1,277, depending upon service size and therapistsâ salary bands.
Conclusions: Good Goals is a promising quality improvement intervention that can be delivered and adopted in practice and may have benefits. Further research is required to evaluate its: (i) impact on patient outcomes, effectiveness, cost-effectiveness, and (ii) transferability to other clinical contexts
Improved Pseudofermion Approach for All-Point Propagators
Quark propagators with arbitrary sources and sinks can be obtained more
efficiently using a pseudofermion method with a mode-shifted action.
Mode-shifting solves the problem of critical slowing down (for light quarks)
induced by low eigenmodes of the Dirac operator. The method allows the full
physical content of every gauge configuration to be extracted, and should be
especially helpful for unquenched QCD calculations. The method can be applied
for all the conventional quark actions: Wilson, Sheikoleslami-Wohlert,
Kogut-Susskind, as well as Ginsparg-Wilson compliant overlap actions. The
statistical properties of the method are examined and examples of physical
processes under study are presented.Comment: LateX, 26 pages, 10 eps figure
Regional Meeting on the Use of Ecological Guidelnies for Development in Tropical Forest Areas of South-east Asia, held at Bandung, Indonesia, 28-31 May 1974
Unquenched QCD with Light Quarks
We present recent results in unquenched lattice QCD with two degenerate light
sea quarks using the truncated determinant approximation (TDA). In the TDA the
infrared modes contributing to the quark determinant are computed exactly up to
some cutoff in quark off-shellness (typically 2). This approach
allows simulations to be performed at much lighter quark masses than possible
with conventional hybrid MonteCarlo techniques. Results for the static energy
and topological charge distributions are presented using a large ensemble
generated on very coarse (6) but physically large lattices. Preliminary
results are also reported for the static energy and meson spectrum on 10x20
lattices (lattice scale =1.15 GeV) at quark masses corresponding to
pions of mass 200 MeV. Using multiboson simulation to compute the
ultraviolet part of the quark determinant the TDA approach becomes an exact
with essentially no increase in computational effort. Some preliminary results
using this fully unquenched algorithm are presented.Comment: LateX, 39 pages, 16 eps figures, 1 ps figur
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
Automorphisms of Partially Commutative Groups II: Combinatorial Subgroups
We define several "standard" subgroups of the automorphism group Aut(G) of a
partially commutative (right-angled Artin) group and use these standard
subgroups to describe decompositions of Aut(G). If C is the commutation graph
of G, we show how Aut(G) decomposes in terms of the connected components of C:
obtaining a particularly clear decomposition theorem in the special case where
C has no isolated vertices.
If C has no vertices of a type we call dominated then we give a semi-direct
decompostion of Aut(G) into a subgroup of locally conjugating automorphisms by
the subgroup stabilising a certain lattice of "admissible subsets" of the
vertices of C. We then characterise those graphs for which Aut(G) is a product
(not necessarily semi-direct) of two such subgroups.Comment: 7 figures, 63 pages. Notation and definitions clarified and typos
corrected. 2 new figures added. Appendix containing details of presentation
and proof of a theorem adde
- âŠ