Acoustic source identification using a scanning laser Doppler vibrometer

This paper shows how a scanning laser Doppler vibrometer (LDV), an instrument designed to measure vibrations of structures or objects, can be used in a non-traditional fashion to identify acoustical sources. This is achieved by measuring the changes in the optical path induced by local fluctuation of the air refraction index to which the LDV is sensitive. The acoustical signal used is sinusoidal and may be recovered by scanning at a uniform rate over a subject area (continuous scan) parallel to the source axis and demodulating this signal. Due to the fact that the measured scan area is in fact a line integral over a measurement volume between the laser head and a rigid object needed to reflect the laser beam, multiple view planes around the axis of the acoustic source are usually measured. These are then passed through a tomographic algorithm, thereby reconstructing the full sound field. In this article however, only one view plane is measured, but the acoustic source is placed on a rotating surface with fixed rotational frequency, thereby imposing a modulation on the measured spectrum. Demodulation will allow reconstruction of the three-dimensional sound field.     

Determination of ephedrine and related compounds in pharmaceutical preparations by ion chromatography with direct conductivity detection

An ion chromatographic method with conductivity detection for the simultaneous determination of ephedrine, pseudoephedrine and norephedrine was developed. A mixture of 2.0 mmol/L HNO3 and 2% (v/v) acetonitrile was used as eluent. The three ephedrine-like compounds were separated and determined within 20 min. The linear ranges were 0.08-50 microg/mL for ephedrine, 0.08-40 microg/mL for pseudoephedrine and 0.06-40 microg/mL for norephedrine. The detection limits were 0.03 microg/mL for ephedrine and pseudoephedrine, and 0.02 microg/mL for norephedrine. The method has been applied successfully to the determination of these sympathomimetics in pharmaceutical preparations and in Ephedra herbs.     

The electronic structure of the isoelectronic, square-planar complexes [FeII(L)2]2- and [CoIII(L Bu)2]- (L2- and (L Bu)2-=benzene-1,2-dithiolates): an experimental and density functional theoretical study

The electronic structures of two formally isoelectronic transition-metal dithiolato complexes [Fe(L)2]2- (1) and [Co(L Bu)2]1- (2) both possessing a spin triplet ground state (St=1) have been investigated by various spectroscopic and density functional methods; H2L Bu represents the pro-ligand 3,5-di-tert-butylbenzene-1,2-dithiol and H2L is the corresponding unsubstituted benzene-1,2-dithiol. An axial zero-field splitting (D) of +32 cm(-1) for 2 has been measured independently by SQUID magnetometry, far-infrared absorption, and variable-temperature and variable-field (VTVH) magnetic circular dichroism spectroscopies. A similar D value of +28 cm(-1) is obtained for 1 on the basis of VTVH SQUID measurements. The absorption spectra of 1 and 2 are found, however, to be very different. Complex 1 is light yellow in color with no intense transition in the visible region, whereas 2 is deep blue. DFT calculations establish that the electronic structures of the [Fe(L)2](2-) and [Co(L)2]1- anions are very different and explain the observed differences in their absorption spectra. On the basis of these spectroscopic and theoretical analyses, 1 is best described as containing an intermediate spin FeII ion, whereas for the corresponding cobalt complex, oxidation states describing a d6 (CoIII) or d7 (CoII) electron configuration cannot be unambiguously assigned. The physical origin of the large zero-field splitting in both 1 and 2 is found to be due to the presence of low-energy spin-conserved d-d excitations which lead to a large Dzz through efficient spin-orbit coupling. Differential covalency effects appear to be of limited importance for this property.     

Une-application non-immersive qui possède la propriété universelle des immersions

Sans résumé     

Insights into the Reaction Mechanism of Ethanol Conversion into Hydrocarbons on H‐ZSM‐5

Ethanol dehydration to ethene is mechanistically decoupled from the production of higher hydrocarbons due to complete surface coverage by adsorbed ethanol and diethyl ether (DEE). The production of C₃₊ hydrocarbons was found to be unaffected by water present in the reaction mixture. Three routes for the production of C₃₊ hydrocarbons are identified: the dimerization of ethene to butene and two routes involving two different types of surface species categorized as aliphatic and aromatic. Evidence for the different types of species involved in the production of higher hydrocarbons is obtained via isotopic labeling, continuous flow and transient experiments complemented by UV/Vis characterization of the catalyst and ab initio microkinetic modeling.     

Toward the characterization of peptidoglycan structure and protein-peptidoglycan interactions by solid-state NMR spectroscopy

Solid-state NMR spectroscopy is applied to intact peptidoglycan sacculi of the Gram-negative bacterium Escherichia coli. High-quality solid-state NMR spectra allow atom-resolved investigation of the peptidoglycan structure and dynamics as well as the study of protein-peptidoglycan interactions.     

A Dicobalt Complex with an Unsymmetrical Quinonoid Bridge Isolated in Three Units of Charge: A Combined Structural, (Spectro)electrochemical,Magnetic and Spectroscopic Study

Quinonoid ligands are excellent bridges for generating redox‐rich dinuclear assemblies. A large majority of these bridges are symmetrically substituted, with examples of unsymmetrically substituted quinonoid bridges being extremely rare. We present here a dicobalt complex in its various redox states with an unsymmetrically substituted quinonoid bridging ligand. Two homovalent forms and one mixed‐valent form have been isolated and characterized by single crystal X‐ray diffraction. The complex displays a large comproportionation constant for the mixed‐valent state which is three orders of magnitude higher than that observed for the analogous complex with a symmetrically substituted bridge. Results from electrochemistry, UV/Vis/NIR spectroelectrochemistry, SQUID magnetometry, multi‐frequency EPR spectroscopy and FIR spectroscopy are used to probe the electronic structures of these complexes. FIR provides direct evidence of exchange coupling. The results presented here display the advantages of using an unsymmetrically substituted bridge: site specific redox chemistry, high thermodynamic stabilization of the mixed‐valent form, isolation and crystallization of various redox forms of the complex. This work represents an important step on the way to generating heterodinuclear complexes for use in cooperative catalysis.