105,224 research outputs found
Pressure dependence of the solubility of Ar and Kr in melts of the system SiO2-NaAlSi2O6
No full textThe solubilities of Ar and Kr in supercooled melts in the system SiO2-NaAlSi2O6 have been studied at temperatures of 1200 degrees C (SiO2), 1000 and 750 degrees C (NaAlSi3O8), and 800 degrees C (NaAlSi2O6) at pressures from 200 to 6000 bar. Gas sorption experiments were performed in an internally heated pressure vessel, and noble gas concentrations in quenched samples were analyzed by absolute analytical techniques [gas chromatography (GC), and thermogravimetry (TG), gravimetry]. Comparison of the results from this study with other absolute techniques (Rutherford-backscattering, mass spectrometry) is possible for silica and exhibit excellent agreement. This agreement leads us to conclude that our silica glasses with an Ar concentration of 1.02 wt% and a Kr concentration of 0.54 wt% are suitable as standard materials. Solubility increases linearly with increasing pressure for all three compositions. In SiO2 the solubility of Ar and Kr increases with pressure with nearly parallel slopes, whereas Ar and Kr exhibit diverging slopes in NaAlSi3O8 and NaAlSi2O6. The linear relationship between fugacity and dissolved gas below 2-3 kbar, indicates that Henry's law constants (in units of 10(6) bar) for Ar in SiO2, NaAlSi3O8, and NaAlSi2O6 are 0.94, 3.15, and 5.71, respectively, and for Kr are 1.38, 5.69, and 9.28, respectively. The experimental results can be modeled by two alternative thermodynamic approaches. First, assuming mixing of noble gases with the network of the melt, partial molar volumes (in cm(3)/mol) can be calculated in SiO2, NaAlSi3O8, and NaAlSi2O6 for Ar as 25.9 +/- 1.3, 21.1 +/-. 1.6, and 21.1 +/- 0.7, respectively and for Kr as 24.3 +/- 1.8, 27.6 +/- 0.8, and 24.7 +/- 0.9, respectively. Second, assuming the volume change upon solution to be zero, a Langmuir Isotherm can be applied yielding saturation levels M (in units of 10(20) sites/cm(3) melt) in SiO2, NaAlSi3O8, and NaAlSi2O6 for Ar as 3.82 +/- 0.6, 1.33 +/- 0.2, and 0.72 +/- 0.08, respectively and for Kr as 3.49 +/- 0.7, 0.56 +/- 0.05, and 0.42 +/- 0.06, respectively. Highest solubility is observed in all three melts for Ar. Solubility decreases with increasing substitution of Si4+ by Na+ + Al3+. Th, dependence of solubility on composition supports the structural model for melts along the join SiO2-NaAlSi2O6, based on a stuffed tridymite-like structure
Changes in the electronic structure of gold particles upon thiol adsorption as a function of the mean particle size
No full textWe studied the interaction of adsorbed thiol molecules with gold nanoparticles as a function of the mean particle size. The results obtained from MXPS (monochromated X-Ray Photoelectron Spectroscopy) measurements showed that attachment of the thiol sulfur headgroup onto the cluster surface leads to a positive binding energy shift in the Au 4f core-level. The absence of line width broadening upon adsorption indicates that these changes affect the whole particle and not only the particle surface, where the actual Au-S bond is located. The positive binding energy shift depends on the cluster size and increases with decreasing diameter. A maximum shift of 0.41 eV could be measured for the smallest particles (similar to 1 nm). The valence band exhibited positive binding energy shifts similar to the Au 4f core-levels, but smaller in absolute values. Changes in the valence band shape were interpreted as re-hybridization of Au 5d electrons due to the creation of Au-S bonds. Furthermore, we observed a disappearance of the Fermi edge upon thiol adsorption, which we attribute to a sulfur-induced metal-insulator-transition of the gold cluster. (c) 2005 Elsevier B.V. All rights reserved
Motoneurons of twitch and nontwitch extraocular muscle fibers in the abducens, trochlear, and oculomotor nuclei of monkeys
No full textEye muscle fibers can be divided into two categories: nontwitch, multiply innervated muscle fibers (MIFs), and twitch, singly innervated muscle fibers (SIFs). We investigated the location of motoneurons supplying SIFs and MIFs in the six extraocular muscles of monkeys. Injections of retrograde tracers into eye muscles were placed either centrally, within the central SIF endplate zone; in an intermediate zone, outside the SIF endplate zone, targeting MIF endplates along the length of muscle fiber; or distally, into the myotendinous junction containing palisade endings. Central injections labeled large motoneurons within the abducens, trochlear or oculomotor nucleus, and smaller motoneurons lying mainly around the periphery of the motor nuclei. Intermediate injections labeled some large motoneurons within the motor nuclei but also labeled many peripheral motoneurons. Distal injections labeled small and medium-large peripheral neurons strongly and almost exclusively. The peripheral neurons labeled from the lateral rectus muscle surround the medial half of the abducens nucleus: from superior oblique, they form a cap over the dorsal trochlear nucleus; from inferior oblique and superior rectus, they are scattered bilaterally around the midline, between the oculomotor nucleus; from both medial and inferior rectus, they lie mainly in the C-group, on the dorsomedial border of oculomotor nucleus. In the medial rectus distal injections, a "C-group extension" extended up to the Edinger-Westphal nucleus and labeled dendrites within the supraoculomotor area. We conclude that large motoneurons within the motor nuclei innervate twitch fibers, whereas smaller motoneurons around the periphery innervate nontwitch, MIF fibers. The peripheral subgroups also contain medium-large neurons which may be associated with the palisade endings of global MIFs. The role of MIFs in eye movements is unclear, but the concept of a final common pathway must now be reconsidered. J. Comp. Neurol. 438:318-335, 2001. (C) 2001 Wiley-Liss, Inc
Reply from Authors re: Arthur L. Burnett. Erection Rehabilitation After Radical Prostatectomy: Definite Purpose, Indefinite Strategy. Eur Urol 2014; 65: 597-8 Although Erection Rehabilitation After Prostatectomy Remains Indefinite, the Most Effective Treatment, the Earliest Recovery, and the Preservation of Erectile Function Remain a Definite Goal
No full textDiffusivity and solubility of He in garnet: An exploratory study using nuclear reaction analysis
No full textWe have used the nuclear reaction He-3(d,p)He-4 in an exploratory study of the diffusivity and solubility of He in the mineral garnet. The garnet samples analyzed were single crystals which had been loaded with He-3 at 7000 bar pressure and temperatures of 900, 950 and 1000 degrees C. From the He-3 depth profiles measured we could deduce diffusion coefficients and solubility values. For the diffusivity the Arrhenius parameters D-0 = 7.5 x 10(9) cm(2)/s and E-a = 500 kJ/mol were found. An estimate of 11.5 at ppm was obtained for the apparent solubility, which comprises volume solubility and dislocation solubility, and an upper limit of 3 at ppm for the volume solubility. Furthermore, out-diffusion of He at room temperature occurring faster than to be expected from the high-temperature diffusivity was observed. The results are compared to those of a preceding study in which a bulk technique for measuring He-4 had been used. It can be concluded that the NRA technique is well suited to the problem in question. (c) 2005 Elsevier B.V. All rights reserved
Crystal structure of Yersinia enterocolitica type III secretion chaperone SycT
No full textButtner CR, Cornelis GR, Heinz DW, Niemann H. Crystal structure of Yersinia enterocolitica type III secretion chaperone SycT. Protein Sci. 2005;14(8):1993-2002
Gold cluster formation on a fullerene surface
No full textThe growth of Au clusters on a fullerene thin film was investigated by in situ photoelectron spectroscopy in the ultraviolet (UPS) and x-ray (XPS) regime. Due to its highly corrugated surface fullerene films provide a wide range of bonding sites which could be exploited as molecular templates and serve to create a cluster superstructure. To gain insight into the fullerene-Au interaction two types of experiments were performed: (i) the deposition of Au on a fullerene surface, and (ii) the deposition of fullerenes on a Au surface. In both experiments an island growth mode is observed. The deposition of submonolayer amounts of C-60 onto a gold film showed that the main interaction of the two species is due to chemisorption of the first C-60 monolayer. In addition a constant band bending in the fullerene film is detected, but the UPS valence-band spectra show that there is no charge transfer from the Au to the C-60 lowest unoccupied molecular orbital. In the reverse experiment, the cluster growth of Au on the corrugated C-60 surface, the analysis of the Au core level does not reveal a specific bonding or nucleation site for Au atoms and clusters. This is in contrast to observations with Si clusters, which prefer to reside in the troughs between the fullerene molecules. The Au clusters grow continually from a size of about 55 atoms for the early stages of growth up to 150 atoms for the deposition of a nominal coverage of 1.5 nm. These data are derived from an analysis of the d-band splitting and the Au 4f core-level shift due to delayed photohole relaxation. The thermal stability of the Au-clusters-covered fullerene film was investigated by annealing in situ up to temperatures of 650 degrees C. For temperatures up to 450 degrees C a continuous growth of the clusters is detected, which is accompanied by a slight drop in Au concentration in the range of XPS for annealing temperatures higher than 350 degrees C. This may be due to a ripening of the clusters. The presence of Au apparently delays fullerene sublimation. The film shows a very good thermal stability and even after annealing at 650 degrees C there is still a fullerene film detectable in the photoelectron spectroscopy spectra. (c) 2005 American Institute of Physics
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Appropriate Similarity Measures for Author Cocitation Analysis
No full textWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Matrix metalloproteinases (MMP-8,-13, and-14) interact with the clotting system and degrade fibrinogen and factor XII (hagemann factor)
No full textTschesche H, Lichte A, Hiller O, Oberpichler A, Buttner FH, Bartnik E. Matrix metalloproteinases (MMP-8,-13, and-14) interact with the clotting system and degrade fibrinogen and factor XII (hagemann factor). In: CELLULAR PEPTIDASES IN IMMUNE FUNCTIONS AND DISEASES 2. Vol 477. KLUWER ACADEMIC / PLENUM PUBL; 2000: 217-228
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