Risk Communication under Conflicting Information: The Role of Confidence in Subjective Risk Assessment

In this study, we develop a model of food consumption with a focus on the subjectively assessed risk of consumers and their degree of confidence in their risk assessment and use it to examine consumer behavior in the chaotic situation created by the Fukushima nuclear accident in 2011. The data were collected in March 2012 using a mail survey for 1300 Japanese women, the primary food purchasers. The respondents were asked to evaluate the cancer risk of eating agricultural products, which were assumed to be grown in the affected area, despite meeting national regulatory standards for radioactive materials, as a measure of their risk assessment and willingness to purchase Fukushima beef. The results show that the effect of confidence in a consumer’s risk assessment on their behavior depends on the stated risk level: when stated risk is below an estimated critical value, termed the switching point, the risk perceived by a consumer without confidence exceeds that of one with confidence. On the other hand, perceived risk is inversely related to confidence when the stated risk exceeds the switching point.

Dynamic Problem of Optimal Control of Spacecraft Attitude under Restriction on Phase Variables

An analytical solution to the optimal control problem of spacecraft reorientation from an arbitrary initial angular position into a required final angular position under the restrictions on control functions and phase variables is presented (the controlling moment and angular velocity are restricted). Time of slew maneuver is minimized. The specific case was considered when maximum admissible kinetic energy of rotation is significant restriction. Constructing the optimal control of reorientation is based on Pontryagin’s maximum principle and the quaternionic variables and models. It is shown that optimal mode is piecewise-continuous control when a direction of spacecraft’s angular momentum is constant relative to the inertial coordinate system during rotation of a spacecraft; for a per forming an optimal turn, the moment of forces is parallel to a straight line fixed in inertial space. Two types of optimal control are possible depending on the given initial and final positions and spacecraft’s moments of inertia — relay control with one switching point when the controlling moment is maximal over the entire time interval of control (segments of acceleration and braking), and relay control with two switching point consisting of intensive acceleration, motion by inertia with the absented moment and an exit onto restriction of rotation energy, and then final braking with the maximum controlling moment. The analytical equations and relations for a finding the optimal control program are written down. The calculation formulas for determining the time characteristics of maneuver and computing a duration of acceleration and braking are given. The proposed algorithm of control provides maximally fast implementation of spacecraft reorientation under the limited kinetic energy of rotation. For an axially symmetric solid body (spacecraft), the optimal control problem, in dynamical statement, was solved completely — we obtained the dependences as explicit functions of time for the control variables, and relations for calculating the key parameters of the law of control are derived. The numerical example and results of mathematical simulation of spacecraft motion under the optimal control are presented, demonstrating the practical feasibility of the developed method for control of spacecraft attitude.

A Data Driven Policy to Minimize the Tuberculosis Testing Cost Among Healthcare Workers

Background The Centers for Disease Control and Prevention mandates that healthcare employees at high risk exposure to Tuberculosis (TB) undergo annual testing. Currently in the US, two methods of TB testing are commonly used: a two-step skin test or a whole-blood test. Each testing method has unique costs and considerations. Healthcare leadership’s test selection must not only account for direct cost such as material, procedure and resources, but also indirect costs such as employee workplace absence. Our purpose was to build a mathematical model to investigate the value loss perspective of these testing methods and assist leadership in their decision-making. Methods This model is based on an Upstate South Carolina healthcare employer’s costs affecting over 18,000 employees on 6 campuses. A process flow map identified the variations in TB testing methods that incorporated the varied material and procedural costs based on the Mantoux two-step tuberculin skin test (TST) and the Interferon-Gamma Release Assay test (IGRA). In addition to these direct costs, the subject’s time requirements involved with each test for 4 employee types and 6 travel-to-testing-site times were calculated. Results Regardless of direct cost variations, a switching point between testing procedures that minimized total system costs was most influenced by employee salary. In this model, an employee who is paid more than $48/hour should undergo IGRA blood testing irrespective of the travel time. As employee pay rate decreases to $30/hour, TST testing becomes more economical. Assuming an equal number of at-risk employees in each wage and travel category, switching from the current policy of 95% TST testing to integrated TST/IGRA testing would reduce TB compliance cost by 28%. Conclusions Mathematical modeling can assist healthcare system decision-makers in understanding the implications of employee TB compliance testing. This model distills the known direct costs of TST compared to IGRA testing and value loss perspectives of employee time into a definable switching point. Although actual costs and potential dollars saved depends on TB testing compliance rules and regulation, it appears that a mixed model of TB testing may be the most cost-effective approach for a large health care employer with multiple campuses.