No abstract

We analyze the power and efficiency of heat engines which operate subject to irreversible heat flow. First, we consider a specific model, with a cycle for an ideal gas similar to that of a reversible Carnot engine ("isothermal cycle"), and find the maximum power, and efficiency at the point of maximum power ('YIm). for given heat bath temperatures and compression ratio. We prove that the cycle chosen produces more power than any other conceivable cycle in the limit of large compression ratio; the derivation is made for an ideal or van der Waals gas as a working fluid, but this is not restrictive in this limit. We use these results to obtain a general formulation, of upper bounds on power and 'YIm' valid for isothermal cycles to study the dependence of these quantities on the form of the law of irreversihle heat conouction. We fino that ' YIm depends only on the heat bath temperatures and the form of the irreversible rate process. but is independent of the material properties of the system. The dependence of ' YIm on the form of the rate process suggests the concept of "efficiency of rate processes." 3898

To demonstrate the safety and effectiveness of MelaFind, a noninvasive and objective computervision system designed to aid in detection of early pigmented cutaneous melanoma. Design: A prospective, multicenter, blinded study. The diagnostic performance of MelaFind and of study clinicians was evaluated using the histologic reference standard. Standard images and patient information for a subset of 50 randomly selected lesions (25 melanomas) were used in a reader study of 39 independent dermatologists to estimate clinicians' biopsy sensitivity to melanoma. Setting: Three academic and 4 community practices in the United States with expertise in management of pigmented skin lesions.

To evaluate the performance of dermoscopists in diagnosing small pigmented skin lesions (diameter Յ6 mm) compared with an automatic multispectral computer-vision system.Design: Blinded comparison study.Setting: Dermatologic hospital-based clinics and private practice offices.Patients: From a computerized skin imaging database of 990 small (Յ 6-mm) pigmented skin lesions, all 49 melanomas from 49 patients were included in this study. Fifty randomly selected nonmelanomas from 46 patients served as a control.Main Outcome Measures: Ten dermoscopists independently examined dermoscopic images of 99 pigmented skin lesions and decided whether they identified the lesions as melanoma and whether they would recommend biopsy to rule out melanoma. Diagnostic and biopsy sensitivity and specificity were computed and then compared with the results of the computervision system.Results: Dermoscopists were able to correctly identify small melanomas with an average diagnostic sensitivity of 39% and a specificity of 82% and recommended small melanomas for biopsy with a sensitivity of 71% and specificity of 49%, with only fair interobserver agreement (=0.31 for diagnosis and 0.34 for biopsy). In comparison, in recommending biopsy to rule out melanoma, the computer-vision system achieved 98% sensitivity and 44% specificity.Conclusions: Differentiation of small melanomas from small benign pigmented lesions challenges even expert physicians. Computer-vision systems can facilitate early detection of small melanomas and may limit the number of biopsies to rule out melanoma performed on benign lesions.