Electron-Phonon Coupling Origin of the resistivity in YNi_{2}B_{2}C Single Crystals

Resistivity measurements from 4.2 K up to 300 K were made on YNi_{2}B_{2}C single crystals with Tc=15.5 K. The resulting rho(T) curve shows a perfect Bloch-Grueneisen (BG) behavior, with a very small residual resistivity which indicates the low impurity content and the high cristallographic quality of the samples. The value lambda_{tr}=0.53 for the transport electron-phonon coupling constant was obtained by using the high-temperature constant value of d(rho)/dT and the plasma frequency reported in literature. The BG expression for the phononic part of the resistivity rho_{ph}(T) was then used to fit the data in the whole temperature range, by approximating alpha^{2}_{tr}F(Omega) with the experimental phonon spectral density G(Omega) multiplied by a two-step weighting function to be determined by the fit. The resulting fitting curve perfectly agrees with the experimental points. We also solved the real-axis Eliashberg equations in both s- and d-wave symmetries under the approximation alpha^{2}F(Omega)= alpha^{2}_{tr}F(Omega). We found that the value of lambda_{tr} here determined in single-band approximation is quite compatible with Tc and the gap Delta experimentally observed. Finally, we calculated the normalized tunneling conductance, whose comparison with break-junction tunnel data gives indication of the possible s-wave symmetry for the order parameter in YNi_{2}B_{2}C.Comment: 6 pages, 5 figures. Proceedings of SATT10 Conference, to be published in Int. J. Mod. Phys.

Sonographie bei intrakorporalem Drogenschmuggel

Um die Bedeutung der Sonographie zur Erfassung inkorporierter Drogenpäckchen (»body-packs«) zu überprüfen, wurden nach Erarbeitung sonographisch-diagnostischer Kriterien im Wasserbad zehn Probanden zwischen 23 und 30 Jahren, die je vier »body-packs« geschluckt hatten, sonographisch untersucht. Die »body-packs« bestanden aus mit festgepreßter Glucose gefüllten Fingerlingen mit einem Durchmesser von 1,5-1,8 cm. Im Wasserbadversuch zeigte sich als Identifikationskriterium der »body-packs« ein sichelförmiger Reflex mit dorsaler Schallauslöschung. Aufgrund dieses Kriteriums konnten bei acht der zehn Probanden 23 der 40 »body-packs« im Magen identifiziert werden. Dabei ließen sich innerhalb der ersten drei Stunden nach Ingestion bei acht Probanden 22 »body-packs« und nach etwa 17 Stunden bei vier Probanden neun »body-packs« im Magen nachweisen; nur bei einem Probanden gelang der Nachweis von zwei »body-packs« im Dünn-Dickdarm-Bereich. Da in der Praxis des intrakorporalen Drogenschmuggels zum möglichen Untersuchungszeitpunkt fast immer »body-packs« im Magen vorhanden sind, kann ein breiter Einsatz des Ultraschalls im Screening des Drogenschmuggels empfohlen werden.To evaluate the place of ultrasonography in the detection of intracorporeal drug packets (body-packs) ten volunteers were examined by ultrasound after having swallowed four body-packs each. Diagnostic criteria had first been established by ultrasound imaging of body-packs in a water bath. The body-packs contained fingerstalls, 1.5-1.8 cm in diameter, filled with hard-pressed glucose. The criterion for identification in the water-bath was shown to be a sickle-shaped echo with a dorsal echo deficit. This sign identified 23 of the 40 body-packs in eight of the ten subjects. Within the first three hours of ingestion 22 body-packs were demonstrated in eight of the subjects; after 17 hours nine body-packs were identified in the stomach of four subjects. In only one subject was it possible to identify (two) body-packs in the region of the small-large intestine. In practice, intracorporeal drug smugglers will almost always have the body-packs in the stomach at the time of likely examination. Extensive ultrasound screening of suspected smugglers is, therefore, recommended

Comparative studies on the structure of an upland African stream ecosystem

Upland stream systems have been extensively investigated in Europe, North America and Australasia and many of the central ideas concerning their function are based on these systems. One central paradigm, the river continuum concept is ultimately derived from those North American streams whose catchments remain forested with native vegetation. Streams of the tropics may or may not fit the model. They have been little studied. The Amani Nature Reserve in the East Usambara Mountains of north-eastern Tanzania offers an opportunity to bring these naturally forested systems to the attention of the ecological community. This article describes a comparison made between two lengths of the River Dodwe in this area. The work was carried out by a group of postgraduate students from eighteen European and African countries with advice from five staff members, as part of a course organised by the Tropical Biology Association. Rigorous efforts were made to standardise techniques, in a situation where equipment and laboratory facilities were very basic, through a management structure and deliberate allocation of work to specialists in each area.The article offers a summary of invertebrate communities found in the stream and its biomass. Crabs seem to be the key organism in both sections of the streams

Spectroscopy of 230Th in the (p,t) reaction

The excitation spectra in the deformed nucleus 230Th were studied by means of the (p,t) reaction, using the Q3D spectrograph facility at the Munich Tandem accelerator. The angular distributions of tritons are measured for about 200 excitations seen in the triton spectra up to 3.3 MeV. Firm 0+ assignments are made for 16 excited states by comparison of experimental angular distributions with the calculated ones using the CHUCK code. Additional assignments are possible: relatively firm for 4 states and tentative also for 4 states. Assignments up to spin $6^+$ are made for other states. Sequences of the states are selected which can be treated as rotational bands and as multiplets of excitations. Experimental data are compared with interacting boson model IBM) and quasiparticle-phonon model (QPM) calculations.Comment: 35 pages in PDF, 14 figures in text and 8 figures in appendix Extended version of the paper published in Phys.Re

αA-crystallin R49Cneo mutation influences the architecture of lens fiber cell membranes and causes posterior and nuclear cataracts in mice

<p>Abstract</p> <p>Background</p> <p>αA-crystallin (CRYAA/HSPB4), a major component of all vertebrate eye lenses, is a small heat shock protein responsible for maintaining lens transparency. The R49C mutation in the αA-crystallin protein is linked with non-syndromic, hereditary human cataracts in a four-generation Caucasian family.</p> <p>Methods</p> <p>This study describes a mouse cataract model generated by insertion of a neomycin-resistant (neo^r) gene into an intron of the gene encoding mutant R49C αA-crystallin. Mice carrying the neo^rgene and wild-type <it>Cryaa </it>were also generated as controls. Heterozygous knock-in mice containing one wild type gene and one mutated gene for αA-crystallin (WT/R49C^neo) and homozygous knock-in mice containing two mutated genes (R49C^neo/R49C^neo) were compared.</p> <p>Results</p> <p>By 3 weeks, WT/R49C^neomice exhibited large vacuoles in the cortical region 100 μm from the lens surface, and by 3 months posterior and nuclear cataracts had developed. WT/R49C^neomice demonstrated severe posterior cataracts at 9 months of age, with considerable posterior nuclear migration evident in histological sections. R49C^neo/R49C^neomice demonstrated nearly complete lens opacities by 5 months of age. In contrast, R49C mice in which the neo^rgene was deleted by breeding with CreEIIa mice developed lens abnormalities at birth, suggesting that the neo^rgene may suppress expression of mutant R49C αA-crystallin protein.</p> <p>Conclusion</p> <p>It is apparent that modification of membrane and cell-cell interactions occurs in the presence of the αA-crystallin mutation and rapidly leads to lens cell pathology <it>in vivo</it>.</p

Flavor decomposition of the sea quark helicity distributions in the nucleon from semi-inclusive deep-inelastic scattering

Double-spin asymmetries of semi-inclusive cross sections for the production of identified pions and kaons have been measured in deep-inelastic scattering of polarized positrons on a polarized deuterium target. Five helicity distributions including those for three sea quark flavors were extracted from these data together with re-analyzed previous data for identified pions from a hydrogen target. These distributions are consistent with zero for all three sea flavors. A recently predicted flavor asymmetry in the polarization of the light quark sea appears to be disfavored by the data.Comment: 5 pages, 3 figure