Sampling variability of the Kunst-Mackenbach relative index of inequality.

STUDY OBJECTIVE: To derive methods of calculating confidence limits for the relative index of inequality, defined by Kunst and Mackenbach as a measure of the influence of socioeconomic status on an adverse health index, such as mortality rate. The methods may be used for a health outcome recorded on a continuous scale, as a Poisson count or as a binomial variable. RESULTS AND CONCLUSION: The confidence limits depend on the sampling variability of both the mean mortality rate and the slope of the regression line of mortality on the socioeconomic status scale variable. The best method for a continuous health outcome is based on Fieller's theorem but a good approximation is obtained by substituting the confidence limits for the slope of the regression line into the formula for the calculation of the index, or by using the variance of the logarithmic transform of the index. The last method is the most appropriate for the construction of significance tests comparing indices. The mortality rates may show statistically significant departure from linearity, while not suggesting that a linear relation is inappropriate, and the main decision is whether to base the confidence limits on the conventional standard error of the slope derived from the regression analysis or whether to use the standard deviation of the estimates of mortality rates.

Prediction of transient temperature fields and cumulative tissue destruction for radio frequency heating of a tumor.

A therapeutic hyperthermia protocol using a radio frequency (rf) electrode placed adjacent to a bronchial wall tumor has been modeled using the finite element technique. Variable physical properties and variable blood perfusion have been assigned to the tumor and to the surrounding normal lung tissue. The Laplace equation was solved on a curvilinear grid for a single rf source electrode to determine the steady-state electric field, which in turn governs the energy deposition function. The heat generation in the tumor and in the lung tissue is then calculated from the energy deposition profile, and the bioheat equation is solved on the same finite element mesh to determine the transient temperature history. The temperatures are displayed as isothermal contours at designated times during the protocol and as temperature histories at selected points. In addition, an Arrhenius-type injury model has been implemented to predict thermally induced damage, from which equal total amounts of energy are deposited into the tissue using a constant power density for an appropriate time or using a cyclic heating pattern. The cyclic heating pattern consisted of a series of equal duration time periods during which the rf current source is alternately turned on and off (50% duty cycle). This study illustrates how a finite element model could be used to evaluate alternative protocols for heating a tumor of a specific geometry and to evaluate thermally induced damage to surrounding normal tissue.

Laser ablation of discs of agar gel.

Discs of agar gel mixed with ink were used to study ablation effects with an argon laser as a light source. Varying amounts of ink were added resulting in a variation of the attenuation coefficient between 0.45 and 6.3 mm-1. For laser beam irradiation horizontally incident on a vertical sample, the average velocity of ablation was found to be approximately constant for thicknesses up to 1.7 mm. When the laser beam was directed vertically on a sample held horizontally, the vaporized debris present in the beam attenuated the incident laser energy to such a degree that the average ablation velocity decreased by a factor of approximately five. Horizontal beam experiments for various attenuation coefficients showed that an attenuation coefficient of about 1.7 mm-1 is optimal for fast penetration of discs thicker than 4 mm. Thus, based upon the optical properties of a given tissue, there may exist an optimum laser wavelength to maximise ablation velocity.

A theoretical study of the effect of optical properties in laser ablation of tissue.

The role of optical properties in the distribution of laser light and the resulting thermodynamic processes in biological tissue is studied from a theoretical perspective. Light distribution is modeled by a discrete ordinate method and heat transfer and ablation is modeled by an immobilized finite element method. The effect of parametric variation of absorption, scattering anisotropicity on the dynamics of the ablation process is examined. The manifestation of higher than the ablation threshold temperature in the subsurface tissue is observed and discussed. Results indicate significant differences in the ablation behavior which may have important clinical implications.

Stimulus equivalence and rule following.

The present study examined the occurrence of a novel behavior pattern with respect to a novel configuration of stimuli enabled by the participation of those stimuli in equivalence classes. In Experiment 1, functional substitutabilities were established via equivalence between two independent sets of musical stimuli. Aspects of stimuli from the two sets were then compounded to produce novel stimulus configurations. Behavioral components enabled by each separate class combined to produce novel musical performances and accurate descriptions of them. In Experiment 2, the impact of experimenter-provided names for equivalence classes on the musical performances was investigated in naive subjects by establishing similar classes without experimenter-provided names. The results indicated few differences in the playing performances under these conditions. These experiments demonstrated a possible method for the analysis of rule following.

The transfer of specific and general consequential functions through simple and conditional equivalence relations.

The purpose of this study was to examine the transfer of consequential (reinforcement and punishment) functions through equivalence relations. In Experiment 1, 9 subjects acquired three three-member equivalence classes through matching-to-sample training using arbitrary visual forms. Comparison stimuli were then given conditioned reinforcement or punishment functions by pairing them with verbal feedback during a sorting task. For 8 of the 9 subjects, trained consequential functions transferred through their respective equivalence classes without additional training. In Experiment 2, transfer of function was initially tested before equivalence testing per se. Three of 4 subjects showed the transfer without a formal equivalence test. In Experiment 3, 3 subjects were given training that gave rise to six new three-member conditional equivalence classes. For 2 of the subjects, the same stimulus could have either a reinforcement or punishment function on the basis of contextual cues that defined its class membership. Experiment 4 assessed whether equivalence training had established general or specific consequential functions primarily by adding novel stimuli in the transfer test. Subjects treated even novel feedback stimuli in the transfer test as consequences, but the direction of consequential effects depended upon the transfer of specific consequential functions through equivalence relations.

The transfer of contextual control over equivalence classes through equivalence classes: a possible model of social stereotyping.

In Experiment 1, subjects acquired conditional equivalence classes controlled by three male and three female names as contextual stimuli. When equivalence relations were tested using new names not used in training (three male and three female), contextual control remained intact. Thus, generalized control of the composition of conditional equivalence classes by characteristically gender-identified names was shown. A basic analysis of this finding was tested in Experiment 2. Contextual equivalence classes were established using as contextual stimuli nonrepresentational visual figures that were members of additional pretrained three-member equivalence classes. When other stimuli in the pretrained equivalence classes were used as contextual stimuli, the conditional equivalence classes remained intact. Control subjects showed that this effect depended on the equivalence relations established in pretraining. The results show that contextual control over equivalence classes can transfer through equivalence classes. The implications of this phenomenon for social stereotyping are discussed.

Dextran-70 inhibits equine platelet aggregation induced by PAF but not by other agonists.

Dextrans of mean molecular weight 70 kDa (dextran-70) have had clinical use as anti-thrombotics in man. A major part of the anti-thrombotic action is mediated via inhibition of platelet function. Greatorex (1975, 1977) treated thromboembolic colic in horses with infusions of dextran-70 and reported a 90% recovery rate, but this treatment is nonetheless rarely used. We have used an in vitro method to examine the effect of dextran-70 on equine platelet suspensions, in the hope that understanding the mechanism of action of dextran-70 might lead to the development of alternative therapeutic agents. The effects of dextran-70 on equine platelets occurred immediately in vitro with an initial activation and shape change. Subsequent assessment of aggregation revealed a dose-dependent specific inhibition of platelet-activating factor (PAF)-induced aggregation, significant in rate of aggregation at dextran-70 concentrations >40 g/l (P<0.05) and in extent of aggregation at dextran-70 concentrations >50 g/l (P<0.05). Pre-incubation with 60 g/l dextran-70 significantly inhibited the rate and extent of aggregation in response to PAF (1 nmol/l) (P<0.001 and P = 0.003, respectively) but this was not dependent on the duration of pre-incubation (from 0 to 150 min). No effects were seen when the agonist was adenosine 5'-diphosphate (200 nmol/l), collagen (10 mg/l), 5-hydroxytryptamine (100 micromol/l) or U44069 (600 nmol/l) (all P>0.1). Analysis of PAF concentration-aggregation curves after pre-incubation with 60 g/l dextran-70 indicated significant noncompetitive inhibition by dextran-70 (P<0.001 for rate and extent of aggregation). The ability of dextran-70 to inhibit responses of equine platelets to PAF is probably an important component of its beneficial effect as an anti-thrombotic in colic cases.

Using a self-control training procedure to increase appropriate behavior.

The present study evaluated a technique for teaching self-control and increasing desirable behaviors among adults with developmental disabilities. Results showed that when participants were initially given the choice between an immediate smaller reinforcer and a larger delayed reinforcer, all participants repeatedly chose the smaller reinforcer. Concurrent fixed-duration/progressive-duration reinforcement schedules then were introduced in which initially both the smaller and larger reinforcers were available immediately. Thereafter, progressively increasing delays were introduced for the schedule associated with the larger reinforcer only. When initial short-duration requirements for access to the larger reinforcer were gradually increased, participants repeatedly selected the larger reinforcer, thereby demonstrating increased self-control.

Engaging in "illusory control" during repeated risk-taking.

Risk-taking behavior occurs when an individual chooses to engage in a game of chance. Although the outcomes of these games are completely random, many individuals believe that they can exercise some control over the outcomes. The present study examined the extent to which five undergraduate roulette players would pay additional money for opportunities to engage in an illusory activity that had no influence on the game's outcome, i.e., choosing random numbers rather than having the experimenter choose them. All five subjects engaged in this type of activity and the extent to which they did was linearly related to the player's winnings. These findings may suggest why people continue to gamble when the odds of winning are against them.

The psychological present.

The present paper compares behavior-analytic and cognitive treatments of the concept of psychological history with regard to its role in current action. Both treatments take the position that the past bears some responsibility for the present, and are thereby obligated to find a means of actualizing the past in the present. Both do so by arguing that the past is brought to bear in the present via the organism. Although the arguments of the two positions differ on this issue, neither provides a complete account. An unconventional treatment of psychological history is proposed, the logic of which is exemplified in anthropological, biological, and psychological perspectives. The unconventional treatment in psychological perspective holds that (a) the organism's interaction with its environment, not the organism itself, changes with experience; and (b) the past interactions of an organism exist as, and only as, the present interactions of that organism. This solution to the problem of psychological history provides obligations and opportunities for analysis that are not available when the more conventional positions of cognitivism and behavior analysis are adopted.

A self-capitalization model for building behavior analysis graduate programs.

The development of the Behavior Analysis Program at the University of Nevada through self-capitalization is described. With this model, both doctoral and master's degree programs were established at almost no cost to the university. Some of the problems encountered along the way, including gaining support for the original proposal, attracting and retaining high-quality faculty, engendering support from the Department of Psychology and the university, developing resources, and balancing academic with entrepreneurial demands are discussed, as are the solutions we have found for those problems.

A finite element model for phase change heat transfer in a composite tissue with blood perfusion.

This paper describes a finite element model of the thermal response of a human to extreme subfreezing environments and the transient temperature fields that are produced at specific locations within the body. This analysis includes the effects of latent heat of fusion from the liquid to the solid phase and of blood perfusion in selected tissues during the freezing process. A highly simplified physiological model is assumed. This type of analysis can be used as a predictive tool in many applications such as cryosurgery and cryopreservation of organs. The finite element model described herein has many advantages over standard numerical techniques such as finite difference methods for analyzing heat transfer problems. This method can treat very general geometries with many different tissue types, each having unique thermal properties, and unique blood perfusion and metabolic rates. This model can incorporate either convective thermal resistance at the body surface or a prescribed temperature history as a boundary condition, either of which may vary as a function of time or temperature. This analysis extends previous work by incorporating the effects of latent heat and by including a blood perfusion rate that varies with temperature in individual tissues.

A finite element model of burn injury in blood-perfused skin.

The burn process resulting from the application of a hot, cylindrical source to the skin surface was modeled using the finite element technique. A rotationally symmetric 125-element mesh was defined within the tissue beneath and outlying to an applied heating disk. The disk temperature and duration of contact were varied, respectively, between 50 and 100 degrees C for up to 30 s. Natural convection with ambient air was assumed for areas of skin surface not in direct contact with the disk. The simulated thermal history was used in a damage integral model to calculate the extent and severity of injury in the radial and axial dimensions.

Steady-state analysis of self-heated thermistors using finite elements.

The purpose of this work is to validate, using numerical, finite element methods, the thermal assumptions made in the analytical analysis of a coupled thermistor probe-tissue model upon which a thermal conductivity measurement scheme has been based. Analytic, closed form temperature profiles generated by the self-heated thermistors can be found if three simplifying assumptions are made: the thermistor is spherical; heat is generated in all regions of the bead; and heat is generated uniformly in the bead. This analytic solution is used to derive a linear relationship between tissue thermal conductivity and the ratio of thermistor temperature rise over electrical power required to maintain that temperature rise. This derived, linear relationship is used to determine thermal conductivity from the observed experimental data. However, in reality, the thermistor bead is a prolate spheroid surrounded by a passive shell, and the heating pattern in the bead is highly nonuniform. In the physical system, the exact relationship between the tissue thermal conductivity and parameters measured by the thermistor is not known. The finite element method was used to calculate the steady-state temperature profiles generated by thermistor beads with realistic geometry and heating patterns. The results of the finite element analysis show that the empirical, linear relationship remains valid when all three simplified assumptions are significantly relaxed.