[1] A new technique has been developed to operate spatially extended VLF/LF lightning detection networks in a pseudo 3-D mode in order to facilitate discrimination of intra-cloud and cloud-to-ground lightning. Time-ofarrival measurements are carried out with high precision to distinguish VLF/LF-emission regions of lightning discharges in higher altitudes and near ground, respectively. This is accomplished by utilizing deviations of arrival times measured at sensor stations close to lightning events as compared to arrival times expected on the basis of 2-D propagation paths. Successful functioning of the method in networks of common dimensions requires that both signal processing and event time tagging is achieved with an accuracy level of about 1 ms. Results are presented from a new network which has been operating continuously since May 2003 and covers southeast Germany in an area of approximately 300 Â 400 km. VLF/LF source emission heights of $5 -15 km have been identified.

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Graphite particles have been coated with Al2O3 via atomic layer deposition. Alumina content was measured via inductively coupled plasma spectrometry (ICP), LECO combustion analysis, and thermogravimetric analysis (TGA). While alumina was present, adherence was limited, and nonconformal films were deposited on the graphite particles. Coatings produced changes in particle interactions and dispersability. These changes were observed via sedimentation rates of particle suspensions in water, Zeta potential values, and particle size distributions. Alumina‐Graphite composites were sintered using coated and uncoated particles. Differences in bulk thermal properties are ascribed to enhanced dispersability of the coated particles in presintered powder mixtures. EDS mapping of the sintered composites confirms the enhanced dispersion of the coated graphite particles. Particle coating through atomic layer deposition provides a means to improve particle dispersion with low material loadings. It has been shown that changes in particle interaction characteristics can be achieved even without uniform and conformal coatings. These particle interaction changes can result in sintered composites with enhanced thermal properties.

Thermal efficiencies of the solar field of two different parabolic trough concentrator (PTC) systems are evaluated for a variety of operating conditions and geographical locations, using a detailed 3D heat transfer model. Results calculated at specific design points are compared to yearly average efficiencies determined using measured direct normal solar irradiance (DNI) data as well as an empirical correlation for DNI. It is shown that the most common choices of operating conditions at which solar field performance is evaluated, such as the equinox or the summer solstice, are inadequate for predicting the yearly average efficiency of the solar field. For a specific system and location, the different design point efficiencies vary significantly and differ by as much as 11.5% from the actual yearly average values. An alternative simple method is presented of determining a representative operating condition for solar fields through weighted averages of the incident solar radiation. For all tested PTC systems and locations, the efficiency of the solar field at the representative operating condition lies within 0.3% of the yearly average efficiency. Thus, with this procedure, it is possible to accurately predict year-round performance of PTC systems using a single design point, while saving computational effort. The importance of the design point is illustrated by an optimization study of the absorber tube diameter, where different choices of operating conditions result in different predicted optimum absorber diameters.