Effective Fitness Landscapes for Evolutionary Systems

In evolution theory the concept of a fitness landscape has played an important role, evolution itself being portrayed as a hill-climbing process on a rugged landscape. In this article it is shown that in general, in the presence of other genetic operators such as mutation and recombination, hill-climbing is the exception rather than the rule. This descrepency can be traced to the different ways that the concept of fitness appears --- as a measure of the number of fit offspring, or as a measure of the probability to reach reproductive age. Effective fitness models the former not the latter and gives an intuitive way to understand population dynamics as flows on an effective fitness landscape when genetic operators other than selection play an important role. The efficacy of the concept is shown using several simple analytic examples and also some more complicated cases illustrated by simulations.Comment: 11 pages, 8 postscript figure

Use of night-time positioning equipment in care home residents with postural asymmetry : a pilot study

Twenty four-hour postural care that includes the use of night-time positioning equipment (NTPE) is being increasingly recommended. However, because most of the published studies focus on children, there is a lack of evidence on the use of NTPE in adults. The aim of this pilot study was to assess the effect of NTPE use in UK care home residents with complex health conditions and postural asymmetry. Ten care home residents trialled NTPE over a 12-week period. Qualitative and quantitative data were collected before and after each trial using standardised assessment tools. Semi-structured interviews were conducted with participants and relatives after each trial. Staff's views were elicited via two focus groups at the end of the study. There were notable benefits of NTPE use in terms of participants' pain levels, sleep quality, risk of pressure ulcers, risk of choking, and weight. There was also evidence of improvements in participants' function, ability to undertake activities of daily living and quality of life. However, some equipment was abandoned during the trials because participants found it too hot or restrictive. This pilot study increases the evidence base for a personalised approach to 24-hour postural care that can support older people's health and well-being. Further empirical studies are required to determine how NTPE can be used to improve older people's quality of life. [Abstract copyright: © 2020 RCN Publishing Company Ltd. All rights reserved. Not to be copied, transmitted or recorded in any way, in whole or part, without prior permission of the publishers.

A Short Ion Path High Voltage Tube

A vacuum tube for the acceleration of charged particles is described. The total acceleration of the ions takes place in a distance of 18 inches although the total height of the tube is about 14 feet. It has been used at one million volts peak a.c. with target currents of 5 ma of electrons and 0.2 ma of positive ions

Environmentally Friendly Renormalization

We analyze the renormalization of systems whose effective degrees of freedom are described in terms of fluctuations which are ``environment'' dependent. Relevant environmental parameters considered are: temperature, system size, boundary conditions, and external fields. The points in the space of \lq\lq coupling constants'' at which such systems exhibit scale invariance coincide only with the fixed points of a global renormalization group which is necessarily environment dependent. Using such a renormalization group we give formal expressions to two loops for effective critical exponents for a generic crossover induced by a relevant mass scale $g$. These effective exponents are seen to obey scaling laws across the entire crossover, including hyperscaling, but in terms of an effective dimensionality, d\ef=4-\gl, which represents the effects of the leading irrelevant operator. We analyze the crossover of an $O(N)$ model on a $d$ dimensional layered geometry with periodic, antiperiodic and Dirichlet boundary conditions. Explicit results to two loops for effective exponents are obtained using a [2,1] Pad\'e resummed coupling, for: the ``Gaussian model'' ($N=-2$), spherical model ($N=\infty$), Ising Model ($N=1$), polymers ($N=0$), XY-model ($N=2$) and Heisenberg ($N=3$) models in four dimensions. We also give two loop Pad\'e resummed results for a three dimensional Ising ferromagnet in a transverse magnetic field and corresponding one loop results for the two dimensional model. One loop results are also presented for a three dimensional layered Ising model with Dirichlet and antiperiodic boundary conditions. Asymptotically the effective exponents are in excellent agreement with known results.Comment: 76 pages of Plain Tex, Postscript figures available upon request from [email protected], preprint numbers THU-93/14, DIAS-STP-93-1

Geometry the Renormalization Group and Gravity

We discuss the relationship between geometry, the renormalization group (RG) and gravity. We begin by reviewing our recent work on crossover problems in field theory. By crossover we mean the interpolation between different representations of the conformal group by the action of relevant operators. At the level of the RG this crossover is manifest in the flow between different fixed points induced by these operators. The description of such flows requires a RG which is capable of interpolating between qualitatively different degrees of freedom. Using the conceptual notion of course graining we construct some simple examples of such a group introducing the concept of a ``floating'' fixed point around which one constructs a perturbation theory. Our consideration of crossovers indicates that one should consider classes of field theories, described by a set of parameters, rather than focus on a particular one. The space of parameters has a natural metric structure. We examine the geometry of this space in some simple models and draw some analogies between this space, superspace and minisuperspace.Comment: 16 pages of LaTex, DIAS-STP-92-3