196,840 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
Interaction of Fe+ with the C-60 surface: A study about the feasibility of endohedral doping
No full textThe feasibility of endohedral iron doping of C-60 is studied using a mass selected ion beam to create an Fe+ beam with variable energy (60-380 eV, 1.2x10(-3) C) which is directed at a C-60 thin film. The surface is characterized by x-ray photoelectron spectroscopy, and oxidation of the samples is used to discriminate between Fe@C-60 and carbides. The fullerene cages are damaged during the irradiation, and participate in direct Fe-C bond formation. The reaction with oxygen indicates the absence of sizable amount of Fe@C-60. Comparison with reference samples composed of iron and damaged fullerene layers (by Ar+ irradiation) supports this interpretation. The experiment serves as a model study for the investigation of different metal-fullerene combinations. (C) 2004 American Institute of Physics
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
Dr. Duane M. Jackson, Morehouse College, July 2011
No full textThis video is a conversation with Dr. Duane M. Jackson. Dr. Jackson talks about his paper, "Recall and the Serial Position Effect: The Role of Primacy and Recency on Accounting Students' Performance." Jackie Daniel, AUC Woodruff Library, is the interviewer
mmunohistological studies on neoplasms of female and male Onchocerca volvulus: Filarial origin and absence of Wolbachia from tumor cells
No full textUp to 5% of untreated female Onchocerca volvulus filariae develop potentially fatal pleomorphic neoplasms, whose incidence is increased following ivermectin treatment. We studied the occurrence of 8 filarial proteins and of Wolbachia endobacteria in the tumor cells. Onchocercomas from patients, untreated and treated with antibiotics and anthelminthics, were examined by immunohistology. Neoplasms were diagnosed in 112 of 3587 female and in 2 of 1570 male O. volvulus. The following proteins and other compounds of O. volvulus were expressed in the cells of the neoplasms: glutathione S-transferase 1, lysosomal aspartic protease, cAMP-dependent protein kinase, alpha-enolase, aspartate aminotransferase, ankyrin E1, tropomyosin, heat shock protein 60, transforming growth factor-beta, and prostaglandin E2. These findings prove the filarial origin of the neoplasms and confirm the pleomorphism of the tumor cells. Signs indicating malignancy of the neoplasms are described. Wolbachia were observed in the hypodermis, oocytes, and embryos of tumor-harbouring filariae using antibodies against Wolbachia surface protein, Wolbachia HtrA-type serine protease, and Wolbachia aspartate aminotransferase. In contrast, Wolbachia were not found in the cells of the neoplasms. Further, neoplasm-containing worms were not observed after more than 10 months after the start of sufficient treatment with doxycycline or doxycycline plus ivermectin
"Reflections on the subject of Emigration from Europe with a view to Settlement in the United States" By M. Carey.
No full text"Reflections on the subject of Emigration from Europe with a view to Settlement in the United States: containing bried sketches of the moral and political character of those states.
By M. Carey, member of the American philosophical, and of the American Antiquarian Society, and author of The Olive Branch, Cindiciae Hibernicae, essays on banking, on political economy, and on internal improvement.
To which are now added the English editor's comments on the subject; together with Important Advice to Emigrants, and Cautions Against Impositions Practiced in the Outports
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Dr. Glendon Swarthout
No full textHosted by Roger M. Busfield, MSU Assistant Professor of Speech and Theater, Meet the Author is designed to introduce a general audience to a contemporary author and their work through in-depth interviews. This episode features a conversation between Dr. Glendon Swarthout, prolific author and English professor at MSU, and assistant professors Sam S. Baskett and Theodore B. Strandness
The 7 September 2008 Vulcanian explosion at Stromboli volcano: Multiparametric characterization of the event and quantification of the ejecta
No full textOn 7 September 2008 a major ash explosion occurred from the SW summit crater of Stromboli volcano. This explosive event lasted similar to 2 min and consisted of three discrete eruptive pulses, forming an eruptive ash cloud similar to 500-600 m high and similar to 300 m wide, rising with speed of 20-27 m s(-1). The event was recorded by our camera and seismic networks, as well as by two electric stations installed at a 500 m mean distance from the SW crater. The electric signals recorded by the two stations during this event were 10(6) times greater than signals recorded during the persistent Strombolian activity, and the seismic trace had a bigger amplitude and a longer duration. Camera image analysis allowed us to infer that a partial obstruction took place at the SW crater three days before the explosive event, suggesting that a constriction within the upper conduit could have likely led to magma overpressure. Data analysis, combined with previous experimental investigations, revealed that the higher energy output of the ash explosion, when compared to the persistent Strombolian activity, resulted in a greater magma fragmentation and erupted mass. Integration of the different parameters allowed us to classify the event as a Vulcanian type, and electric signal analysis enabled retrieval of the total volume of erupted ash and of the amounts of the juvenile, phreatomagmatic, and lithic components
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