Sucrose transport through maltoporin mutants of Escherichia coli

Maltoporin (LamB) and sucrose porin (ScrY) reside in the bacterialouter membrane and facilitate the passive diffusion of maltodextrinsand sucrose, respectively. To gain further insight into thedeterminants of solute specificity, LamB mutants were designedto allow translocation of sucrose, which hardly translocatesthrough wild-type LamB. Three LamB mutants were studied. (a)Based on sequence and structure alignment of LamB with ScrY,two LamB triple mutants were generated (R109D, Y118D,D121F;R109N,Y118D,D121F) to mimic the ScrY constriction. The crystalstructure of the first of these mutants was determined to be3.2 Å and showed an increased ScrY-like cross-sectionexcept for D109 that protrudes into the channel. (b) Based onthis crystal structure a double mutant was generated by truncationof the two residues that obstruct the channel most in LamB (R109A,Y118A).Analysis of liposome swelling and in vivo sugar uptake demonstratedsubstantial sucrose permeation through all mutants with thedouble alanine mutant performing best. The triple mutants didnot show a well-defined binding site as indicated by sugar-inducedion current noise analysis, which can be explained by remainingsteric interference as deduced from the crystal structure. Binding,however, was observed for the double mutant that had the obstructingresidues truncated to alanines.     

A New Test of Image Theory

This paper investigates two hypotheses of the screening phases of two-staged multiattribute choice procedures: the editing phase in which dominated choice alternatives are eliminated and the compatibility test of image theory. As the importance weights and rejection thresholds of the compatibility test are recalcitrant to elicitation, we develop a new method to examine the compatibility phase treating importance weights and rejection thresholds as latent parameters. Our method allows a checkup of the application of a compatibility test without any knowledge of subjects' importance weights and rejection thresholds. Our experimental findings show that the compatibility test enjoys consistency rates of some 70% as compared to consistency rates of about 15% for the editing hypothesis of the elimination of dominated choice alternatives. This result is supported by applying Selten's measure of predictive success. Copyright 1998 Academic Press.     

Einschnüreffekt bei Transistoren mit Streifengeometrie (Pinch-in effect in transistors with emitter-stripe geometry)

Es wird gezeigt, da? bei ausreichend hohem Multiplikations-faktor in der Kollektorfeldzone eine punktf?rmige Einschnürung des Emitterstromes (pinch-in Effekt) auftretenk ann. Dieser Effekt, der von der Zylindergeometrie her bekannt ist, kommt dadurch zustande, da? die Gleichverteilung des Emitterstromes in L?ngsrichtung des Emitterstreifens instabil weid. This letter shows that the emitter current is concentrated at one localised spot when the multiplication factor in the collector depletion layer becomes sufficiently high. This effect, which has previously been described only for transistors with cylindrical geometry, is due to an instability of the emitter-current distribution along the emitter stripe.     

Ultrastructural studies of bones from patients with osteogenesis imperfecta

Bone samples from patients suffering from osteogenesis imperfecta (OI) types I, II, III and IV, as well as normal controls, were studied by scanning (SEM) and transmission electron microscopy (TEM). SEM views of normal bone at low magnification show coherent structure, with regular striations due to a lamellar plywood-like arrangement of the mineralized collagen fibrils. Compact lamellar bone was also found in various OI specimens, but in limited disconnected regions separated by open spaces. Furthermore, some OI, but not normal, bones have regions of loose unconnected fibers and others of apparently abnormally dense mineral deposition. High resolution TEM studies of OI bone fragments have served to elucidate the structures of these different textures. There appears to be a substantial, though reduced, proportion of normal lamellar bone even in quite severe OI. However, the regions of loose fibers are largely unmineralized and probably contain abnormal collagen. Other regions are overmineralized, with generally small unorganized apatite crystals deposited onto fibril surfaces or in separate clusters. These structural abnormalities, together with the paucity of normal bone, may explain the fragility of OI bones.     

A factor analysis of programmed learning and ability measures.

An oblique factor analysis of 23 tests of cognitive abilities and 6 measures of performance on a programed learning task given to 104 6th-graders, revealed 8 factors defined primarily by the tests and 2 defined by speed of performance on the programed task. 2 measures of program achievement, i.e., error frequency and posttest performance, did not define a separate factor but exhibited high loadings on 1 of the test factors, i.e., following directions. The intercorrelations among the 10 factors defined 2 2nd-order factors, verbal-numerical-educational and mental speed. Results indicate that measures of performance on a learning program may contain information about human abilities not assessed by tests of well-known cognitive factors. However, this new information is related at a more general level to the information provided by the tests. Results also provide some understanding of the abilities required to perform well on learning programs of the type employed here. (French summary) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A two species trap for chromium and rubidium atoms

Abstract

We realize a combined trap for bosonic chromium (⁵²Cr) and rubidium (⁸⁷Rb) atoms. Initial experiments focus on exploring a suitable loading scheme for the combined trap and on studies of new trap loss mechanisms originating from simultaneous trapping of two species. By comparing the trap loss from the ⁸⁷Rb magneto-optical trap (MOT) in the absence and presence of magnetically trapped ground state ⁵²Cr atoms we determine the scattering cross-section of σ _inel,RbCr = 5.0 ± 4.0 × 10^?18 m² for light-induced inelastic collisions between the two species. Studying the trap loss from the Rb magneto-optical trap induced by the Cr cooling-laser light, the photoionization cross-section of the excited 5P_3/1 state at an ionizing wavelength of 426 nm is measured to be σ _P = 1.1 ± 0.3 × 10^?21 m².