Volume 85, Issue 2, 15 January 1999
Index of content:
- GENERAL PHYSICS: NUCLEAR, ATOMIC, AND MOLECULAR (PACS 01-39)
85(1999); http://dx.doi.org/10.1063/1.369247View Description Hide Description
The thermodynamic performance of real irreversible cooling and refrigeration systems (chillers) can be summarized in simple rectangular temperature-entropy diagrams, in analogy to classic pedagogical examples for idealized reversible devices. The key to translating complex dissipative losses into this graphical framework is the process average temperature—a factor that can be calculated from nonintrusive experimental measurements, for converting entropy production into lost work. An uncomplicated thermodynamic model is used to transform the governing chiller performance equations into an easily-interpreted graph. Examples based upon actual data from commercial work-driven (reciprocating) and heat-driven (absorption) chillers are presented, and are used to highlight the predominance of internal dissipation in determining chiller efficiency. With the thermodynamic diagram representation, the relative roles of each irreversibility source, as well as the reversible and endoreversible limits, become transparent.
85(1999); http://dx.doi.org/10.1063/1.369198View Description Hide Description
The signal induced in a readout circuit connected to a pixel electrode in a semiconductorgamma-ray imaging array is calculated by solving the Laplace equation. Two approaches are presented that use Green functions in solving the boundary value problem: decomposition into basis functions, and construction of an infinite series of image charges. Another approach is developed based on the Ramo–Shockley theorem, which makes use of weighting potentials. These potentials may be readily calculated in three dimensions using a Fourier-transform propagation technique. An analytic solution is found for the special two-dimensional case of a strip detector. Experiments on CdZnTe square-pixel test structures using alpha radiation confirm the expected trends in pulse shape as a function of pixel size. Signals observed simultaneously on adjacent pixels also follow the predicted division of currents. Trends with pixel size are also confirmed in the shape of pulse-height spectra taken using a source.