X-ray absorption spectroscopic investigation of partially reduced cobalt species in Co-MCM-41 catalysts during synthesis of single-wall carbon nanotubes

Chemometric tools were employed to analyze the in-situ dynamic X-ray absorption spectroscopy data to probe the state of Co-MCM-41 catalysts during reduction in pure hydrogen and under single-wall carbon nanotube synthesis reaction conditions. The use of the progressive correlation analysis established the sequence in which changes in the spectral features near the Co K edge occurred, and the evolving factor analysis provided evidence for the formation of an intermediate Co(1+) ionic species during reduction of the Co-MCM-41 catalyst in pure hydrogen up to 720 degrees C. This intermediate species preserves the tetrahedral environment in the silica framework and is resistant to complete reduction to the metal in H(2). While the Co(2+) species is resistant to reduction in pure CO, the intermediate Co(1+) species is more reactive in CO most likely forming cobalt carbonyl-like compounds with high mobility in the MCM-41. These mobile species are the precursors of the metallic clusters growing carbon nanotubes. Controlling the rates of each step of this two-stage reduction process is key to controlling the size of the metallic Co clusters formed in Co-MCM-41 catalysts.     

Orientierung und Deformierung disperser Teilchen in strömenden Flüssigkeiten

Zusammenfassung Es wird eine Theorie über Orientierung und Deformierung disperser Teilchen in str?menden Flüssigkeiten entwickelt. Dabei ergibt sich für die Orientierung anisodimensionaler Teilchen: Die Orientierung h?ngt von zwei Dingen ab: von der Str?mung der Flüssigkeit und von der Brown'schen Bewegung der Teilchen. Bei überwiegendem Einflu? der Str?mung n?hert sich die Orientierung einem Zustand der S?ttigung, in welchem die Teilchen mit ihrer L?ngsrichtung vorzugsweise parallel der Flie?richtung liegen. Die Brown'sche Bewegung vermindert den Betrag der Orientierung und verschiebt ihre Richtung zu kleineren Winkeln. Bei überwiegender Brown'scher Bewegung ist die Orientierungsrichtung unter 45° gegen die Flie?richtung geneigt.     

Seven matched bolometers for millimeter wave observations

We have fabricated a millimeter wave observation system using an array of bolometric detectors. The performance of the system depends largely on obtaining identical performance from each bolometer. We achieved a variance in the responsivity of less than 4% except for one of the seven elements. The bolometers had an electrical NEP of 1.3×10^–16 W/Hz under radiation background loading of 30pW. We used an AC bridge readout circuit to significantly improve the stability of the array and showed that observations can be done without a mechanical beam switch. The bolometer array is now in use on the Nobeyama 45-m telescope for 150GHz observations.H. Matsuo thanks those who helped him work on bolometers during his stay in Berkeley, especially to T. Wilbanks, M. Devlin and C. Inman. The authors are also grateful to S. Sato and T. Watabe at Nagoya University for their advice on the AC bridge circuit. This work is partly supported by the Shimazdu Science Foundation.     

Excitation of degenerate vibrations in non-degenerate electronic bands

The vibrational rule structuic of the 2A'₁ band in the photoelectron spectrum of BF₃ is analyzed Using ab initio calculated coupling constants, It is shown that some lines of this spectrum represent excitation of single quanta of the degenerate stretching vibration They borrow their intensity from the adjacent 2E' state via a pseudo-Jahn-Teller interaction     

Das Mikroskop als Hilfsmittel zur Aufklärung der Färbevorgänge

Ohne Zusammenfassung(Umgearbeitet nach dem Vortrag, gehalten am Kongreß der Chemiker-Koloristen in Wien am 16–19. Mai 1912.)     

Probing Transient Conformational States of Proteins by Solid‐State R1ρ Relaxation‐Dispersion NMR Spectroscopy

The function of proteins depends on their ability to sample a variety of states differing in structure and free energy. Deciphering how the various thermally accessible conformations are connected, and understanding their structures and relative energies is crucial in rationalizing protein function. Many biomolecular reactions take place within microseconds to milliseconds, and this timescale is therefore of central functional importance. Here we show that R_1ρ relaxation dispersion experiments in magic‐angle‐spinning solid‐state NMR spectroscopy make it possible to investigate the thermodynamics and kinetics of such exchange process, and gain insight into structural features of short‐lived states.     

Impedance measurements of nanoporosity in electrodeposited ZnO films for DSSC

Porous ZnO/dye hybrid films have been deposited by cathodic electrodeposition, and their active surface area after dye desorption was evaluated by impedance measurements with the semiconducting electrode polarized in accumulation. Surface area ratios have been deduced for a large number of films from imaginary part Z″ vs. frequency measurements, having a constant rate over the frequency range from 0.5 Hz to > 50 Hz. The active surface increased by a factor of roughly 150 per every micron of film with respect to the area of a flat ZnO electrode: this linear relationship held from less than 1 µm up to 9 µm thick films.     

(n,m) Abundance evaluation of single-walled carbon nanotubes by fluorescence and absorption spectroscopy

A methodology that takes into account the (n,m) structure of single-walled carbon nanotubes (SWNTs), through an exciton-exciton resonance model and an electron-phonon interaction model, was employed in order to evaluate the semiconducting (n,m) abundance of two SWNT samples (i.e., Co-MCM-41 and HiPco). This was based on photoluminescence and near-infrared absorption data obtained on aqueous suspensions of individually dispersed SWNTs. In the absence of known (n,m) abundance SWNT samples, we resorted to determining the diameter distribution curves for both samples, which were found to obey an unsymmetrical log-normal distribution, typical for vapor-phase particle growth. Using this log-normal function, we reconstructed the near-infrared E S11 absorption spectrum of the narrow diameter distribution Co-MCM-41 SWNT sample, which in turn enabled us to assess the predictions of these two theoretical models. High spectral reconstruction accuracy was obtained from the electron-phonon interaction model when considering (11,0) and (10,0) zigzag nanotubes, along with (n,m) line widths inversely proportional to their extinction coefficients.