Realistic upper bounds can be placed on the power and efficiency of real heat engines via a relatively simple analytic treatment of primary sources of irreversibility. Generalized curves for heat engine performance, their universal nature, and quantitative evaluation of upper bounds for power and efficiency are derived for several engine types, specifically: Brayton cycle (gas turbines), Rankine cycle (steam turbines), and cycles with sizable heat leaks, such as thermoelectric generators. The key irreversibility sources include fluid friction, the constraint of the equation of state of the engine’s working fluid, and heat leak. It is demonstrated that maximum power and maximum efficiency operating points are usually relatively close, with the associated implications for the selection of optimal heat engine operating conditions. The limitations of past analyses of endoreversible cycles as models for real heat engines will be discussed and the fortuitous nature of agreement between their predictions and actual heat engine performance will be explained.

Maximum power point characteristics of heat engines as a general thermodynamic problem Am.For a general class of heat engines operating at maximum power, in which the generic sources of irreversibility are finite-rate heat transfer and friction only, we investigate ( 1) the timedependent driving functions that maximize power when heat input and heat rejection are constrained to be nonisothermal, as is the case in many conventional heat engines, and (2) the specific impact of friction on the nature of the engine cycle that maximizes power, and on the engine's power-efficiency characteristic. The extent to which maximum power is affected by the constraints on the driving function is evaluated, as well as the time divisions on the different branches of the optimal cycle. The fundamental differences in engine performance that arise from frictional losses being internally dissipative, as opposed to externally dissipative, are derived, and illustrative examples are presented.

Microscopic FTIR spectroscopy was used to investigate the spectral differences between normal cells in culture and cells infected with various members of the herpes family of viruses [Herpes simplex (HSV) and Varicella zoster (VZV)]. The main objective of this study is to evaluate the possibility of developing microscopic FTIR spectroscopy as a sensitive assay for the detection of herpetic infections at their early stages. The advantage of this method over conventional FTIR spectroscopy is that it facilitates inspection of restricted regions of tissue. Our results showed significant and consistent differences between all normal and HSV or VZV infected cells that were tested. Detectable and significant spectral differences between normal and infected cells are seen as early as 24 h postinfection, but the damage of the cells (cytopathic effect), caused by the infecting virus, can be seen by optical microscope observations at only 3 days postinfection. An impressive increase in the levels of vital cellular metabolites was seen in the herpes virus infected cells compared to normal cells. It seems that this spectral behavior is unique for infection with herpes viruses, because when these cells were infected with other viruses from different families like retroviruses, a considerable decrease in the levels of vital cellular metabolites was seen in infected cells compared to normal cells. Cluster analysis performed on FTIR mass chromatography yielded 100% accuracy in classifying control uninfected and VZV or HSV infected cells. Our data strongly support the possibility of developing FTIR microscopy as a diagnostic method for early detection of herpetic infections.

We report experimental results with a miniature fiber-optic photovoltaic concentrator with (a) deliverable power density up to 104 suns (10 W/mm2), (b) solar cell efficiencies above 30%, (c) completely passive cooling, (d) uniform and individualized cell illumination, and (e) assembly from readily available components. Measurements include the sensitivity of the conversion efficiency of tandem III–V cells to (1) power input, (2) flux distribution, and (3) the modified spectrum from the fiber-optic concentrators. Our results augur favorably for the feasibility of such designs at concentration levels as high as thousands of suns.

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