Micellar and solubilizing behaviour of Pluronic L-64 in water

The temperature effect in aqueous solutions of a polyoxyethylene—polyoxypropylene—poloxyethylene (POE—POP—POE) block copolymer, Pluronic L-64 in water, was examined by means of viscosity, sedimentation, scattering and sound velocity measurements. Micelle formation in L-64 was strongly dependent on concentration and temperature. An increase in temperature shifted the micelle formation markedly to lower concentration; the micelle grew large particularly at temperatures near the cloud point. The viscosity data were analyzed to estimate various parameters, including the hydrated micellar volume, hydration number, hydrodynamic radius, etc. An increase in diazepam solubility in L-64 micelles with increasing concentration and temperature was observed.     

Composition profile in semiconducting alloys by second derivative wavelength modulation

The wavelength (λ) and composition (x) modulations are used simultaneously in order to obtain the second derivative ∂² R/∂λ∂x of the reflectivity. A great sensitivity to a small composition difference is obtained. This method is applied to the determination of the compositional profile for a ternary alloy Mg _x Zn_1−x Te withx<0.01. A good agreement is observed with the theoretical profile calculated on the basis of a regular associated solution model.     

Ferroelectricity associated with the metastable phase “III” of AgNO3

The dielectric constant, dc resistance, D-E ferroelectric hysteresis loop and dilatometric analysis of the three phases I, II, and III of AgNO₃ single crystals has been studied over the temperature range 100–200° C. A ferroelectric behaviour of the metastable phase III was detected here for the first time similar to what happened in KNO₃. The ferroelectric is attributed here to Ag⁺-ion vacancy formation in the unit cell of AgNO₃. The energy activating the process of vacancy formation was found to beE _v=2.6 eV. It was found that an ionic shift from one lattice point to another requires an amount of energy to overcome a potential barrierE _m=0.1 eV. A model is suggested to explain such behaviour. Dilatometric analysis indicated that this metastable phase transition III is accompanied by an expansion of the unit cell.     

Spectroscopic analysis of roman wall paintings from Casa del Mitreo in Emerita Augusta, Mérida, Spain

The use of visible spectroscopy, applied to chromatic characterization of Roman wall paintings, allows an easy and trustworthy grouping of the samples studied. The use of other spectroscopic techniques such as Fourier transform infrared spectroscopy (FTIR) and energy-dispersive X-ray spectroscopy (EDS) in conjunction with X-ray diffraction (XRD) allows a good identification of the substances present in the pictorial layers that define and differentiate each chromatic group. In this paper, a study of 40 Roman wall painting samples, from Pinturas Báquicas of Casa del Mitreo in Emerita Augusta (Mérida, Spain), is described. In these samples, some pigments of high quality and cost, as well as some unusual mixtures, not described in the bibliography, have been found.     

Peculiarities of phosphorescence of complexes between aromatic molecules and β-cyclodextrin at room temperature

Luminescence of complexes between -cyclodextrin and phenanthrene, fluorene, or naphthalene-d₈ in aqueous solutions was studied at room temperature. It is found that the addition of acetone, in the absence of heavy atoms, results in the phosphorescence of these complexes at 293 K due to triplet-triplet energy transfer. The conclusion is drawn that a heavy atom is necessary for population of a triplet level, because the intersystem crossing of an aromatic molecule in the cyclodextrin cavity is suppressed due to restriction of vibration-relaxation interactions with a medium. The phosphorescence multiply increases when lightscattering polycomplexes between an aromatic molecule and cyclodextrin in the presence of a heavy atom and a sensitizer are formed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1966–1969, October, 1995.The work was financially supported by the Russian Foundation for Basic Research (Project No. 94-03-O9961).     

Verteilung von Wismut-Spuren im Korngrenzenbereich von technischem Kupfer

Kupferproben mit Gehalten von 40 bis 100 ppm Wismut, die bei 580 °C eine halbe Stunde geglüht wurden, zeigen eine groβe Anreicherung dieses Elements im Bereich der Korngrenzen. Die Abnahme des Anreicherungsgrades mit fallender Bi-Ge-halten verläuft nicht proportional. Eine Glühung bei 750 °C führt zu einer besseren Verteilung bzw. geringeren Bi-Anreicherung in diesem Bereich.     

Anwendung von Radiotracern bei der Entwicklung hydrometallurgischer Verfahren zur Aufarbeitung von Sekundärrohstoffen der NE-Metallurgie mittels Flüssig-Flüssig-Extraktion

The selective separation of Cu, Zn and Mn from various liquid secondary raw materials has been studied by the use of radionuclides. The experimental equipment allowed the establishment of equilibrium in a mixer-settler to be continuously followed. The suitability of various industrial extractants such as LIX 64 N, Acorga P-17, Kelex 100, D 2 EHPA for the extraction of those non-ferrous metals from spent zinc electrolytes and from solutions obtained by leaching Cu/Zn scrap has been determined on the basis of a new selectivity criterion. Good results have been achieved by selecting the optimum extraction and reextraction conditions.     

The generalized Dirichlet–Neumann map for linear elliptic PDEs and its numerical implementation

A new approach for analyzing boundary value problems for linear and for integrable nonlinear PDEs was introduced in Fokas [A unified transform method for solving linear and certain nonlinear PDEs, Proc. Roy. Soc. London Ser. A 53 (1997) 1411–1443]. For linear elliptic PDEs, an important aspect of this approach is the characterization of a generalized Dirichlet to Neumann map: given the derivative of the solution along a direction of an arbitrary angle to the boundary, the derivative of the solution perpendicularly to this direction is computed without solving on the interior of the domain. This is based on the analysis of the so-called global relation, an equation which couples known and unknown components of the derivative on the boundary and which is valid for all values of a complex parameter k. A collocation-type numerical method for solving the global relation for the Laplace equation in an arbitrary bounded convex polygon was introduced in Fulton et al. [An analytical method for linear elliptic PDEs and its numerical implementation, J. Comput. Appl. Math. 167 (2004) 465–483]. Here, by choosing a different set of the “collocation points” (values for k), we present a significant improvement of the results in Fulton et al. [An analytical method for linear elliptic PDEs and its numerical implementation, J. Comput. Appl. Math. 167 (2004) 465–483]. The new collocation points lead to well-conditioned collocation methods. Their combination with sine basis functions leads to a collocation matrix whose diagonal blocks are point diagonal matrices yielding efficient implementation of iterative methods; numerical experimentation suggests quadratic convergence. The choice of Chebyshev basis functions leads to higher order convergence, which for regular polygons appear to be exponential.     

Formation Dynamics of Absorbing Layers in a Two‐Stage Atomizer

An experimental spatialresolution facility for recording the formation dynamics of absorbing layers in a twostage atomizer is described. An optical scheme with a convergent raying beam in the atomizer zone and a hollow cathode as a radiation source is considered. The dynamics of the absorptivity signal at evaporation of Rb, NaCl, and a standard sample CASS2 has been investigated under different operating conditions of the atomizer. It is shown that the proposed evaporation–condensation–atomization regime considerably lowers the spatial gradients of absorptivity and the level of nonselective absorption in recording the atomic absorption signal.     

Photoacoustic characterization of phase transitions in amorphous metal alloys

Received: 24 February 1997