Managing uncertainties in a safety-constrained process system for solvent selection and usage: an optimization approach with technical, economic, and risk factors

This paper addresses the problem of managing uncertainties in a safety-constrained process system for economic performance enhancement. Within such a context, a typical solvent selection problem involves a number of different solvents with nominal property values that are utilized in various process units and requires the minimization of the total operating cost while satisfying certain technical performance criteria and process safety constraints. Practically, in any process system, property values of streams are not exact; they are usually functions of operating variables and market conditions that change over time inevitably introducing irreducible uncertainties in system performance. A key aim of the present study is to systematically explore the effect of volatility in solvent prices on the economic performance of the process. Appropriate sensitivity analysis and Monte Carlo simulation work have been carried out to assist the decision maker in taking into account the continuously changing market conditions, while identifying operationally safe feasibility regions for solvents with different risk characteristics in the underlying optimization problem. The aforementioned uncertain inputs are shown to cause shifts of the associated Pareto front of optimal solutions toward feasibility regions that can be characterized in a more realistic manner. Finally, an illustrative case study that uses the permissible exposure limit as a risk factor is considered to evaluate the proposed method.     

Power to detect homework effects in psychotherapy outcome research.

Studies of homework effects in psychotherapy outcome have produced inconsistent results. Although these findings may reflect the comparability of psychotherapy with and without homework assignments, many of these studies may not have been sensitive enough to detect the effects sizes (ESs) likely to be found when examining homework effects. The present study evaluated the power of homework research and showed that, on average, current power levels are relatively weak in controlled studies ranging from 0.58 for large ESs to 0.09 for small ESs. Thus, inconsistent findings between studies may very well be due to low statistical power. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Psychologists' use of homework assignments in clinical practice.

Does the average professional psychologist use homework in clinical practice? If so, how frequently and how systematic is he or she in recommending homework? Ninety-eight percent of the 221 New Zealand practicing psychologists surveyed reported using homework assignments. Although practitioners reported using homework in an average of 57% of sessions, a higher rate (66% of sessions) was reported among those using cognitive and behavioral approaches to therapy. Despite this fact, only 25% of all psychologists reported using systematic procedures for recommending homework. The use of homework in clinical practice may need modification to ensure that clients receive maximum benefit from homework assignments. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A National Survey of Practicing Psychologists' Use and Attitudes Toward Homework in Psychotherapy.

Homework assignments have been studied extensively in psychotherapy research, but there is little data on the way in which homework is transferred to clinical practice. A survey was conducted of 827 practicing psychologists nationwide regarding their use and attitudes toward homework. Overall, 68% of the present sample indicated that they "often" or "almost always" used homework assignments. Factor analysis revealed that practitioners have a range of attitudes that can be classified as reflecting the notion that homework has (a) a negative impact on in-session therapeutic work and (b) a positive effect on therapy outcomes. More positive attitudes were reported among those with a cognitive-behavioral theoretical orientation. Nevertheless, the use of homework among psychodynamic/analytic practitioners reported in the present sample was unexpected and suggests that theoretical and empirical work is required to examine homework's effects in a range of psychotherapy approaches. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Psychologists' Use of Motion Pictures in Clinical Practice.

Do professional psychologists use motion pictures in clinical practice? If so, do they consider motion pictures to have therapeutic value? Of 827 licensed practicing psychologists, 67% reported the use of motion pictures to promote therapy gains. Most of these practitioners (88%) considered the use of motion pictures as effective in promoting treatment outcome, and only a minority (1%) reported them as potentially harmful. Compared with their psychodynamic counterparts, therapists practicing within eclectic-integrative, cognitive-behavioral, or humanistic frameworks were more likely to view or use motion pictures as therapeutic tools. Psychologists provided individual evaluations of 27 motion pictures that deal with a variety of mental health subjects, and overall they were characterized as "moderately helpful." Clinical applications and issues pertaining to using motion pictures in therapy are summarized. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Singular PDEs and the assignment of zero dynamics in nonlinear systems

The present research work aims at the development of a systematic method to arbitrarily assign the zero dynamics of a nonlinear system by constructing the requisite synthetic output maps. The minimum-phase synthetic output maps constructed can be made statically equivalent to the original output maps, and therefore, they could be directly used for nonminimum-phase compensation purposes. Specifically, the mathematical formulation of the problem is realized via a system of first-order nonlinear singular PDEs and a rather general set of necessary and sufficient conditions for solvability is derived. The solution to the above system of singular PDEs can be proven to be locally analytic and this enables the development of a series solution method that is easily programmable with the aid of a symbolic software package. The minimum-phase synthetic output maps that induce the prescribed zero dynamics for the original nonlinear system can be computed on the basis of the solution of the aforementioned system of singular PDEs. Moreover, static equivalence to the original output map can be readily established by a simple algebraic construction.