Penetration of fast electrons and positrons

Abstract

A thorough investigation of Lewis' formal solution of the multiple scattering problem for an infinite medium is presented. The account includes the mean value and the longitudinal dispersion of the projected range distribution and also the transverse dispersion for 10-3000 keV electrons and positrons in a number of monatomic targets. A method for comparison with experimental data is described and applied. Approximate results for semi-infinite targets are shown to compare well with experiments even for heavy elements where the deviations relative to infinite targets are shown to be most pronounced and related to the probability of back-scattering. Finally, the authors note that an unresolved discrepancy appears to persist between theoretically and experimentally determined differences of electron and positron penetration.

Protein Phosphatases−A Phylogenetic Perspective

“…15 While the PPMs were observed to be completely disparate from the PPPs at the level of their polypeptide sequences, 99,100 X-ray crystallographic analysis has revealed a striking degree of similarity between their active sites, suggestive of convergence upon a common catalytic mechanism. 98 The PPM-family appears to be ubiquitous in eukaryotes, examples having been isolated and/or cloned from mammals, 99-101 nematodes, 102 insects, 103 plants, 104 fungi, 105 and protozoa. 106,107 With the exception of pyruvate dehydrogenase phosphatase, which is a heterodimer, 100 all other eukaryotic PPMs isolated to date have proven to be monomeric proteins that generally ranged from 31 to 65 kDa in size.…”

The Caenorhabditis elegansSex-determining Protein FEM-2 and Its Human Homologue, hFEM-2, Are Ca2+/Calmodulin-dependent Protein Kinase Phosphatases That Promote Apoptosis

“…Does hFEM-2 have a role in sex determination? This possibility seems remote as C. briggsae fem-2, which has 45% amino acid identity to C. elegans fem-2, can only weakly rescue the FEM-2-deficient phenotype in C. elegans (7), suggesting that, like many other genes in the sex determination pathway, the sex determination function of the fem-2 gene is rapidly evolving. Furthermore, hFEM-2 displayed minimal activity in rescuing the FEM-2 deficient phenotype in C. elegans.…”

“…Indeed, genes in the sex-determining pathway are known to be rapidly diverged even between two closely related species, C. elegans and Caenorhabditis briggsae (7,8). In C. elegans, many genes have been identified that affect sexual fate.…”

Harnessing Caenorhabditis Genomics for Evolutionary Developmental Biology

“…For example, degenerate PCR was used to isolate genomic fragments of C. briggsae homologues of fog-3 [68], CB5161 homologues of fem-2 and two other related PP2C phosphatases [69], and the highly divergent tra-1 homologue of the diplogasterid nematode Pristionchus pacificus [70]. Hansen and Pilgrim [71] probed genomic Southern blots at low-stringency with a C. elegans fem-2 probe, and then generated plasmid mini-libraries based on this to clone fragments of Cb-fem-2. A number of studies also used gene-specific primers to generate complete cDNAs for newly isolated homologues via RT-PCR [68,[70][71][72][73][74].…”

“…Hansen and Pilgrim [71] probed genomic Southern blots at low-stringency with a C. elegans fem-2 probe, and then generated plasmid mini-libraries based on this to clone fragments of Cb-fem-2. A number of studies also used gene-specific primers to generate complete cDNAs for newly isolated homologues via RT-PCR [68,[70][71][72][73][74]. In several cases these efforts were facilitated by the presence of either the SL1 or SL2 trans-spliced leader found at the 5' end of many nematode transcripts [75].…”