Transverse spectra of waves in random media

We consider the statistics of the transverse spectra of forward-propagating waves in a stationary random medium. A short-range perturbation solution is used to derive the difference equations that govern the long-range evolution of the ensemble-averaged transverse wave spectrum and coherence. The conditions under which these equations may be approximated by differential and integro-differential equations are given, and it is shown that the approximation is valid for the treatment of beam propagation provided that the transverse dimension of the beam is sufficiently large, and at ranges where the transverse coherence length of the beam remains larger than a wavelength. The equations that are derived are not limited by the parabolic approximation, and are amenable to numerical solution by marching techniques. We use the equation that governs the spectral density of the total energy flux, and also the propagation of waves which are statistically homogeneous in transverse planes, to show the conditions under which previously studied approximations derive from the present formulation, and to illustrate the numerical solution of the problem.     

Quantum chemical study of the electronic structure of NaX and NaY zeolites1

The CNDO/2 method is employed to determine S_III type positions for the location of Na cations in the faujasite zeolites. The minimum energy path of Na migration between these positions exhibiting an energy banier of 20 kJ/mol has been calculated.     

Pulse propagation of acoustic waves scattered in a three-dimensional channel

Abstract

In a previous paper (Whitman et al 1999 Waves Random Media 9 1–11) we discussed the scattering of acoustic waves by random sound-speed fluctuations in a two-dimensional channel and presented an asymptotic form for an acoustic pulse propagating in the channel. Here we include the three-dimensional effect of transverse scattering. We find an asymptotic solution in which initially the two-dimensional mode-transfer effect is more important than the transverse scattering effect. However, for large enough propagation distances the transverse scattering effect dominates the pulse spread. In this paper we shall show the form of the pulse shape in both propagation ranges as well as in the transition regime. We shall begin with a discussion of the physics of the problem and then present a mathematical discussion.     

Labelled compounds as radiopharmaceuticals for radiosynoviorthesis

Radiopharmaceuticals for radiosynoviorthesis are designed as suspension (colloidal) of particles in sterile and pyrogen free form, where radionuclide (active substance) fix on carrier which is form solid particles or gel form. Generally, radionuclide and carrier have to fulfil the request of sterility, chemical purity, non toxicity, non allergen and low cost preparation. In term of the radionuclide purity, beta-emission with sufficient energy for penetration and ablation the synovial tissue and low gamma-radiation is requested. The radionuclide gold-198 in colloidal form was used as radiopharmaceutical for radiosynoviorthesis at first. Presently, beta-emitting radionuclides, which have no or only a minimal gammaemission, are used. Between such radionuclides is possible to insert: yttrium-90, rhenium-186 and radiolanthanoides — dysprosium-165, holmium-166 and erbium-169. In this paper are presented experiences with preparation [¹⁶⁶Ho] Holmium-Macroaggregates ([¹⁶⁶Ho] holmium-MA), [¹⁶⁶Ho] holmium-Polylactic Acid Microspheres ([¹⁶⁶Ho] Ho-PLA-MS) which are potential candidate for radiosynoviorhesis.     

Infrared and Raman spectroscopy of mullite‐type Bi2Ga4O9

Mullite‐type Bi₂Ga₄O₉ single‐crystals were grown by the top‐seeded solution growth (TSSG) method and investigated by vibrational spectroscopy. Polarised IR specular reflectance and attenuated total reflectance (ATR) spectra, as well as polarised micro‐Raman spectra were acquired at room temperature. Powder IR spectra of sol‐gel‐derived samples were also recorded. Using model calculations and comparison to other mullite‐type compounds, bands at ∼ 850 – 400 cm^‐1 could be assigned to stretching and bending vibrations of the structural GaO₄ and GaO₆ units. Low‐energetic modes were attributed to motions involving Bi atoms. The IR spectra of Bi₂Ga₄O₉ display close similarities to those of the mullite‐type alkali gallates (9Ga₂O₃ · Rb₂O), while their differences to those of mullite sensu stricto (3Al₂O₃ · 2SiO₂ and 2Al₂O₃ · SiO₂, repectively) are assigned to Si‐O stretching vibrations of the corresponding tetrahedral units. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Electronic spectral study of the interaction of CoNaX zeolite with C1?C5 hydrocarbons

Interaction of both satured and unsaturated hydrocarbons with tetrahedral Co²⁺ ion complexes lodged in the zeolite skeleton is reported on the basis of diffuse reflectance spectra. While saturated hydrocarbons do not affect the coordination sphere of the Co-complex, the unsaturated hydrocarbons change considerably the distortion of the tetrahedral Co-complex.

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- Co²⁺ - . - Co-, - - Co-.

     

Flow-microcalorimetric determination of enzymatic activities of the Trichoderma viridae-cellulase complex

A method for measuring enzymatic activities of the Trichoderma viridae cellulase complex is described. The LKB 2277 Thermal activity monitor and a flow-mix mode were used. Enzymatic activities of samples of a crude cellulose complex have been determined using three substrates: cellobiose, carboxymethyl cellulose (CMC) and xylan. Some kinetic constants for cellobiase activity have been evaluated from the obtained results. A process of the end-product inhibition of cellobiase resp. carboxymethyl cellulase activity by glucose has been observed too.The described method allows a direct determination of various enzymatic activities of the cellulase complex. Because of the high sensitivity and the simplicity, the method is a very suitable tool for studying the cellulase complex, determining the optimal conditions of enzymatic break-down of the cellulosic materials and observing various mechanisms of the feed-back control by products of enzymatic action. The procedure is completely general in nature and is applicable to other enzymatic systems.

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Zusammenfassung Es wird eine Methode zur Bestimmung der enzymatischen Aktivität des Trichoderma viridae Zellulase Komplexes beschrieben. Dazu wurde ein LKB 2277 Thermoaktivitätsmonitor und ein kontinuierlicher Flüsigkeitsmischer verwendet. Bei der Bestimmung der enzymatischen Aktivität von Proben des rohen Zellulasekomplexes wurden drei Substanzen verwendet: Zellobiose, Karboxymethylzellulose (CMC) und Hemizellulose. Anhand der Ergebnisse wurden einige kinetische Parameter für die Zellobiaseaktivität ermittelt. Außerdem wurde eine Endprodukt-Inhibition von Zellobiase sowie Karboxymethylzellulaseaktivität durch Glukose beobachtet.Das beschriebene Verfahren erlaubt eine direkte Bestimmung der verschiedenen Enzymaktivitäten des Zellulasekomplexes. Wegen ihrer hohen Empfindlichkeit und Einfachheit handelt es sich hier um ein sehr nützliches Werkzeug zur Untersuchung des Zellulasekomplexes, indem die optimalen Bedingungen für die enzymatische Spaltung zelluloser Substanzen bestimmt und verschiedene Mechanismen von Feedback-Kontrolle durch die Produkte der Enzymtätigkeit beobachtet werden. Das Verfahren trägt vollkommen allgemeinen Charakter und kann auch bei anderen Ezymsystemen Anwendung finden.

     

Nitrogen activation via three-coordinate molybdenum complexes: comparison of density functional theory performance with wave function based methods

Obtaining an accurate theoretical model for the activation of dinitrogen by three-coordinate molybdenum amide complexes (e.g. Mo(NH2)3) is difficult due to the interaction of various high- and low-spin open-shell complexes along the reaction coordinate which must be treated with comparable levels of accuracy in order to obtain reasonable potential energy surfaces. Density functional theory with present-day functionals is a popular choice in this situation; however, the dinitrogen activation reaction energetics vary substantially with the choice of functional. An assessment of the reaction using specialized wave function based methods indicates that although current density functionals in general agree qualitatively on the mechanistic details of the reaction, a variety of high-level electron correlation methods (including CCSD(T), OD(T), CCSD(2), KS-CCSD(T), and spin-flip CCSD) provide a consistent but slightly different representation of the system.     

Pneumatoamperometric determination of various oxidants and total dissolved chlorine

Trace levels of dissolved nitrite, chromate, permanganate, cerium(IV), bromate, chlorine and bromine are treated with iodide to produce iodine, which is then determined pneumatoamperometrically, i.e., by purging it from solution with nitrogen and quantifying it at a gold, gas-porous electrode by electro-oxidation to iodate. All the dissolved oxidants produce linear calibration curves. Detection limits range from 30 to 60 ppb. Aqueous sample sizes of 4 ml are used.