The physical basis for Parrondo's games

Several authors have implied that the original inspiration for Parrondo's games was a physical system called a ``flashing Brownian ratchet''. The relationship seems to be intuitively clear but, surprisingly, has not yet been established with rigor. In this paper, we apply standard finite-difference methods of numerical analysis to the Fokker-Planck equation. We derive a set of finite difference equations and show that they have the same form as Parrondo's games. Parrondo's games, are in effect, a particular way of sampling a Fokker-Planck equation. Physical Brownian ratchets have been constructed and have worked. It is hoped that the finite element method presented here will be useful in the simulation and design of flashing Brownian ratchets.Comment: 10 pages and 2 figure

A note on the estimation of confidence intervals for cost-effectiveness when costs and effects are censored

<i>Background</i>. The relation between methodological advances in estimation of confidence intervals (CIs) for incremental cost-effectiveness ratios (ICER) and estimation of cost effectiveness in the presence of censoring has not been explored. The authors address the joint problem of estimating ICER precision in the presence of censoring. <i>Methods</i>. Using patient-level data (n = 168) on cost and survival from a published placebo-controlled trial, the authors compared 2 methods of measuring uncertainty with censored data: 1)Bootstrap with censor adjustment (BCA); 2) Fieller’s method with censor adjustment (FCA). The authors estimate the FCA over all possible values for the correlation (p) between costs and effects (range= –1 to +1) and also examine the use of the correlation between cases without censoring adjustment (i.e., simple time-on-study) for costs and effects as an approximation for. <i>Results</i>. Using time-on-study, which considers all censored observations as responders (deaths), yields 0.64 life-years gained at an additional cost of 87.9 for a cost per life-year of 137 (95% CI by bootstrap –5.9 to 392). Censoring adjustment corrects for the bias in the time-on-study approach and reduces the cost per life-year estimate to 132 (=72/0.54). Confidence intervals with censor adjustment were approximately 40% wider than the base-case without adjustment. Using the Fieller method with an approximation of based on the uncensored cost and effect correlation provides a 95% CI of (–48 to 529), which is very close to the BCA interval of (–52 to 504). <i>Conclusions</i>. Adjustment for censoring is necessary in cost-effectiveness studies to obtain unbiased estimates of ICER with appropriate uncertainty limits. In this study, BCA and FCA methods, the latter with approximated covariance, are simple to compute and give similar confidence intervals

Florida's West Coast inlets: shoreline effects and recommended action

This report responds to the 1986 Beaches Bill which, in recognition of the potential deleterious impact on Florida's beaches of inlets modified for navigation, mandated a study of those inlets with identification of recommended action to reduce the impacts. This report addresses west Coast inlets; East Coast inlets are the subject of a companion report. There are 37 inlets along that portion of Florida's West Coast commencing from Pensacola Bay Entrance to Caxambas Pass at the south end of Marco Island. Compared to those on the East Coast, most West Coast inlets have not had the deleterious effects on the adjacent beaches, yet all modified inlets without proper management have the potential of impacting unfavorably on the adjacent shorelines. Moreover, at present there is interest in opening three West Coast entrances which either have been open in the past (Midnight Pass) or which have opened occasionally (Navarre Pass and Entrance to Phillips Lake). A review of inlets in their natural condition demonstrates the presence of a shallow broad outer bar across which the longshore transport Occurs. These shallow and shifting bar features were unsuitable for navigation which in many cases has led to the deepening of the channels and fixing with one or two jetty structures. Inlets in this modified state along with inappropriate maintenance practices have the potential of placing great ero$ional stress along the adjacent beaches. Moreover. channel dredging can reduce wave sheltering of the shoreline by ebb tidal shoals and alter the equilibrium of the affected shoreline segments. The ultimate in poor sand management practice is the placement of good quality beach sand in water depths too great for the sand to reenter the longshore system under natural forces; depths of 12 ft. or less are considered appropriate for Florida in order to maintain the sand in the system. With the interference of the nearshore sediment transport processes by inlets modified for navigation, if the adjacent beaches are to be stabilized there must be an active monitoring program with commitment to placement of dredged material of beach quality on shoreline segments of documented need. Several East Coast inlets have such transfer facilities; however. the quantities of sand transferred should be increased. Although an evolution and improvement in the technical capability to manage sand resources in the vicinity of inlets is expected, an adequate capability exists today and a concerted program should be made to commence a scheduled implementation of this capability at those entrances causing greatest erosional stress on the adjacent shorelines. A brief summary review for each of the 37 West Coast inlets is presented including: a scaled aerial photograph, brief historical information, several items related to sediment losses at each inlet and special characteristics relevant to State responsibilities. For each inlet, where appropriate, the above infor~tion is utilized to develop a recommenced action. (PDF has 101 pages.

Thinking outside the box: recent advances in the analysis and presentation of uncertainty in cost-effectiveness studies

As many more clinical trials collect economic information within their study design, so health economics analysts are increasingly working with patient-level data on both costs and effects. In this paper, we review recent advances in the use of statistical methods for economic analysis of information collected alongside clinical trials. In particular, we focus on the handling and presentation of uncertainty, including the importance of estimation rather than hypothesis testing, the use of the net-benefit statistic, and the presentation of cost-effectiveness acceptability curves. We also discuss the appropriate sample size calculations for cost-effectiveness analysis at the design stage of a study. Finally, we outline some of the challenges for future research in this area—particularly in relation to the appropriate use of Bayesian methods and methods for analyzing costs that are typically skewed and often incomplete

Lithospheric failure on Venus

We develop a predictive model which has the ability to explain a postulated style of episodic plate tectonics on Venus, through the periodic occurrence of lithospheric subduction events. Present-day incipient subduction zones are associated with the existence of arcuate trenches on the Venusian lithosphere. These trenches resemble terrestrial subduction zones, and occur at the rim of coronae, uplift features thought to be due to deep-mantle convective plumes. The model we adopt represents the lithosphere as the thermal boundary layer which lies above a convective plume. We assume a temperature-dependent nonlinear viscoelastic rheology, and we assume a stress-based criterion for plastic yield. In developing this latter criterion, we are led to a re-interpretation of the strength envelope which is commonly used in analysing lithospheric stress, and we propose that the plastic yield strength has meaning (and is finite) below the lithosphere, using behaviour in the Earth as our 'laboratory' justification for this view. An inferred yield stress on the Earth is ca. 300 bar (30 MPa). Our model then shows that a thickening lithosphere becomes progressively more fluid as the stresses induced by the buoyant convective plume become large. Failure occurs when the effective lithosphere viscosity becomes equal to that of the underlying mantle. We show that reasonable expected values of yield stress in the range 100-200 bar (10-20 MPa) for Venusian mantle rocks are consistent within the framework of the model with radii of coronal trenches in the range 100-1200 km, and with the approximate time (200-800 Myr) which they may take to develop

The concept of sexual exploitation in legislation relating to persons with intellectual disability

The focus of this paper is on the use of the concept of sexual exploitation in legislation concerning sexual expression by persons with mental impairment, with particular emphasis on persons with intellectual disability. Two main statutory approaches have been adopted in Australian jurisdictions. The first is prohibition of sexual acts between a person with intellectual disability and others who, by virtue of their employment, are in a position of ascendancy over that person. The second is the prohibition of sexually exploitative acts by any person towards a person with an intellectual disability. The major aim in this article is to critically examine these approaches and evaluate them according to the standards of being non-discriminatory, minimally restrictive of rights, and enforceable. It is argued that comprehensively cataloguing sexually exploitative acts is untenable, with the result that prohibition of all sexual exploitation is unenforceable. The alternative, namely legislation that prohibits sexual relations with any person employed to render any kind of service to the intellectually disabled person, would further restrict an already limited number of potential sexual partners. We suggest that a more useful approach would be to prohibit sexual activity in one-on-one relationships whose scope is commonly understood to exclude such acts, while allowing relations between workers or caregivers and the persons to whom they do not directly render services. This mechanism would have to be narrowly defined to have the desired effect of affording protection to vulnerable persons while preserving their right to sexual expression

Using the interpersonal reactivity index to assess empathy in violent offenders

The Interpersonal Reactivity Index (IRI), developed by Davis (1980), provides an excellent multidimensional measure of empathy for the general adult population, the domain for which it was developed. Its use has subsequently expanded into other areas, for example criminal psychology. In this domain empathy is a critical variable in theoretical accounts of criminality and particularly of violence. For many researchers within the field of criminal psychology, the IRI has become the instrument of choice for the assessment of empathy. However, the psychometric properties of the scale, when used with a criminal population, have not been investigated. This paper reports the results of an investigation into the reliability and component structure of the IRI using a sample of violent offenders. The Personal Distress subscale was found not to be reliable when used in an offender population. Furthermore, when used to assess offenders, principle components analysis did not confirm the four-subscale structure of the IRI. Possible explanations for these findings are discussed in relation to offender assessment in general