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P Specht

Publications and source records attributed to P Specht.

8 recordsLinked to original sources
PubMed2005

Distortion and segregation in a dislocation core region at atomic resolution.

The structure of an isolated, Ga terminated, 30 degree partial dislocation in GaAs:Be is determined by high resolution transmission electron microscopes and focal series reconstruction. The positions of atomic columns in the core region are measured to an accuracy of better than 10 pm. A quantitative comparison of the structure predicted by an ab initio electronic structure total energy calculation to the experiment indicates that theory and experiment agree to within 20 pm. Further analysis shows the deviations between theory and experiment appear to be systematic. Electron energy loss spectroscopy establishes that defects segregate to the core region, thus accounting for the systematic deviations.

Journal Article↗
PubMed2002

Direct compositional analysis of AlGaAs/GaAs heterostructures by the reciprocal space segmentation of high-resolution micrographs.

A detailed description of a combined reciprocal and real space technique for the mapping of layer compositions across interior interfaces from high-resolution electron micrographs is presented. The analysis is based on the reciprocal space extraction of chemically sensitive image information encoded in lattice images of AlGaAs/GaAs heterostructures taken under optimized imaging conditions. Analysis procedures include centering a set of apertures around chemically sensitive reflections in the Fourier transform of lattice images and performing an inverse transformation, thus extracting composition related information from experimental micrographs. It is demonstrated that this approach is characterized by the same spatial resolution as real space techniques but by improved capabilities with respect to analysing images characterized by a minor signal-to-noise ratio. For illustration purposes the stability of AlAs/GaAs multiple quantum wells grown under low-temperature conditions against thermal treatment as expressed by interfacial roughness parameters is investigated.

Journal Article↗
PubMed1988

Evaluating ultra-low volume ground applications of malathion against Aedes aegypti using landing counts in Puerto Rico, 1980-84.

Landing counts made in a residential area in San Juan, Puerto Rico during the 5-year period, 1980-84 indicated that malathion ULV applied by LECO Fog Generators was not effective against Aedes aegypti. Of 25 applications only 6 resulted in a decrease on the first day after treatment and only one remained much less than the pretreatment count on the second and third days after treatment. Daily, the number of mosquitoes landing for a 5-minute period at each of 2 stations was recorded. An ideal year created by averaging the monthly data suggested that the seasonal variation of mosquitoes was inverse to that of reported dengue incidence.

Aedes↗
PubMed1982

Automatic control of potential and agonist-induced current across the endplate membrane by drug electrophoresis.

Two techniques are described that are designed to elicit long and constant postsynaptic depolarizations or agonist-induced currents by the electrophoretic application of agonists to endplate membranes. In the first technique, which can be described as a "pharmacologic voltage clamp," the current flowing through the agonist pipette is controlled by the potential across the endplate membrane. Sustained depolarizations of constant amplitude can be obtained in this manner, while the agonist current needed to produce and maintain the response is recorded. The second technique uses a signal proportional to the current flowing across a voltage-clamped endplate membrane to control the delivery of agonist. This allows control of the intensity of the agonist-induced current. The possible application of these techniques in studying receptor desensitization and obtaining samples of post-synaptic current noise for spectral analysis is discussed.

Animals↗