89 research outputs found
Liquid phase hydrogenation of crotonaldehyde over Pt/SiO2 catalysts
The dependence of the catalytic properties of Pt/SiO2 catalysts for the hydrogenation of crotonaldehyde on the hydrogen pressure, the reaction temperature, the nature of the solvent and the presence of several additives were investigated. Strong deactivation of the catalysts mainly caused by decarbonylation of crotonaldehyde and irreversible adsorption of CO was observed. The initial activity of the deactivated catalysts is regained by oxidation of the adsorbed CO to CO2 by purging with air. The selectivity to crotylalcohol increased with increasing number of turnovers per metal site. This is explained with preferential blocking of the nonselective sites on the metal crystallites by CO and by a slow surface modification of the aging catalyst with organic deposits. The overall rate and the selectivity to the saturated aldehyde are markedly enhanced by an increase in hydrogen pressure and by a decrease in reaction temperature. The addition of modifiers such as potassium acetate, triphenylphosphine and thiophene had only little influence on the activity and the selectivity of the catalysts
A variational approach to dislocation problems for periodic Schr\"odinger operators
As a simple model for lattice defects like grain boundaries in solid state
physics we consider potentials which are obtained from a periodic potential on with period lattice by setting
for and for , for . For
Lipschitz-continuous it is shown that the Schr\"odinger operators have spectrum (surface states) in the spectral gaps of ,
for suitable . We also discuss the density of these surface states
as compared to the density of the bulk. Our approach is variational and it is
first applied to the well-known dislocation problem [E. Korotyaev, Commun.
Math. Phys. 213 (2000), 471-489], [E. Korotyaev, Asymptotic Anal. 45 (2005),
73-97] on the real line. We then proceed to the dislocation problem for an
infinite strip and for the plane. In an appendix, we discuss regularity
properties of the eigenvalue branches in the one-dimensional dislocation
problem for suitable classes of potentials.Comment: 19 pages, 3 figure
Immunohistochemistry Reveals TRPC Channels in the Human Hearing Organ : A Novel CT-Guided Approach to the Cochlea
TRPC channels are critical players in cochlear hair cells and sensory neurons, as demonstrated in animal experiments. However, evidence for TRPC expression in the human cochlea is
still lacking. This reflects the logistic and practical difficulties in obtaining human cochleae. The
purpose of this study was to detect TRPC6, TRPC5 and TRPC3 in the human cochlea. Temporal bone
pairs were excised from ten body donors, and the inner ear was first assessed based on computed
tomography scans. Decalcification was then performed using 20% EDTA solutions. Immunohistochemistry with knockout-tested antibodies followed. The organ of Corti, the stria vascularis, the
spiral lamina, spiral ganglion neurons and cochlear nerves were specifically stained. This unique
report of TRPC channels in the human cochlea supports the hypothesis of the potentially critical
role of TRPC channels in human cochlear health and disease which has been suggested in previous
rodent experiments
TRPC6 Is Found in Distinct Compartments of the Human Kidney
In the context of renal proteinuric diseases, TRPC6 has been shown to play an important
role in ultrafiltration associated with the slit diaphragm through the control of the intracellular Ca2+
concentration in the podocytes of glomeruli. However, to date, the properties of TRPC6 have been
studied mainly in cell lines or in animal models. Therefore, the aim of the study presented here was to
investigate the presence and distribution of TRPC6 in human kidneys in order to possibly verify the
applicability of the results previously obtained in nonhuman experiments. For this purpose, kidneys
from nine cadavers were prepared for immunohistochemical staining and were supplemented with a
fresh human kidney obtained by nephrectomy. TRPC6 was detected in glomeruli and in the parietal
epithelial cells of Bowman’s capsule. Larger amounts were detected in the tubular system and
collecting ducts. In contrast to the peritubular capillary bed, which showed no immune reaction, the
cortical resistance vessels showed mild TRPC6 staining. In conclusion, our studies on the expression
of TRPC6 in human kidney tissue support the translational concept of the involvement of TRPC6 in
various renal diseases and reveal new aspects of the distribution of TRPC6 in the human kidney
Impact of Forest Seral Stage on use of Ant Communities for Rapid Assessment of Terrestrial Ecosystem Health
Bioassessment evaluates ecosystem health by using the responses of a community of organisms that integrate all aspects of the ecosystem. A variety of bioassessment methods have been applied to aquatic ecosystems; however, terrestrial methods are less advanced. The objective of this study was to examine baseline differences in ant communities at different seral stages from clear cut to mature pine plantation as a precursor to developing a broader terrestrial bioassessment protocol. Comparative sampling was conducted at nine sites having four seral stages: clearcut, 5 year recovery, 15 year recovery, and mature stands. Soil and vegetation data were also collected at each site. Ants were identified to genus. Analysis of the ant data indicated that ants respond strongly to habitat changes that accompany ecological succession in managed pine forests, and both individual genera and ant community structure can be used as indicators of successional change. Ants exhibited relatively high diversity in both early and mature seral stages. High ant diversity in mature seral stages was likely related to conditions on the forest floor favoring litter dwelling and cold climate specialists. While ants may be very useful in identifying environmental stress in managed pine forests, adjustments must be made for seral stage when comparing impacted and unimpacted forests
Structure sensitivity of the hydrogenation of crotonaldehyde over Pt/SiO2 and Pt/TiO2
Hydrogenation of crotonaldehyde has been studied over SiO2- and TiO2-supported Pt catalysts. Over Pt/SiO2, the selectivity to the primary products butyraldehyde and crotylalcohol depends critically on the Pt particle size; i.e., the selectivity to the unsaturated alcohol increases with increasing particle size. For large metal particles, the high fraction of Pt(111) surfaces is concluded to favor the adsorption of crotonaldehyde via the carbonyl bond. On small Pt particles, the high abundance of metal atoms in low coordination allows unconstrained adsorption of both double bonds. In this case, the hydrogenation of the C=C bond is kinetically favored. Activity and selectivity of Pt/TiO2catalysts after low-temperature reduction are similar to those of Pt/SiO2. After high-temperature reduction the selectivity to crotylalcohol is generally enhanced. The selectivity of Pt/TiO2catalysts is then determined by the metal particle size and the extent of decoration of Pt with TiOxparticles. The presence of coordinatively unsaturated Ti cations in these oxide particles enhances the sorption strength of the C=O bond resulting in an enhanced selectivity to crotylalcohol. The effects of metal particle size and promotion by TiOxare additive. TiOxpromotion of catalysts with small particles and the presence of unpromoted large particles allow reaching of selectivities to crotylalcohol of approximately 45%. Promotion of large Pt particles with TiOxyields 64% selectivity to crotylalcohol
Liquid phase hydrogenatin of crotonaldehyde over Pt/SiO2 catalysts
The dependence of the catalytic properties of Pt/SiO2 catalysts for the hydrogenation of crotonaldehyde on the hydrogen pressure, the reaction temperature, the nature of the solvent and the presence of several additives were investigated. Strong deactivation of the catalysts mainly caused by decarbonylation of crotonaldehyde and irreversible adsorption of CO was observed. The initial activity of the deactivated catalysts is regained by oxidation of the adsorbed CO to CO2 by purging with air. The selectivity to crotylalcohol increased with increasing number of turnovers per metal site. This is explained with preferential blocking of the nonselective sites on the metal crystallites by CO and by a slow surface modification of the aging catalyst with organic deposits. The overall rate and the selectivity to the saturated aldehyde are markedly enhanced by an increase in hydrogen pressure and by a decrease in reaction temperature. The addition of modifiers such as potassium acetate, triphenylphosphine and thiophene had only little influence on the activity and the selectivity of the catalysts
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