Relaxation and phonons in viscous and glassy orthoterphenyl by neutron scattering

We present an extended set of incoherent neutron scattering measurements on the van der Waals liquido-terphenyl, obtained by time-of-flight and backscattering spectroscopy. In the supercooled liquid regime, data from three instruments are combined and analysed in terms of the selfcorrelationS(Q, t). In the time range 1...100 ps, the crossover from -to -relaxation is well described by the masterfunction of mode coupling theory, and fitted parameters are consistent with the previously established critical temperatureT _c [Z. Phys. B83, 175 (1991)]. In the glassy regime, vibrations are harmonic and can be described by a density of states. Deviations at lowQ are quantitatively explained by a multiple scattering simulation. Throughout the article, experimental difficulties are discussed in some detail.     

Instability of the paramagnetic state towards incommensurate magnetic order in the 2-d Hubbard model

We determine the instability line separating the paramagnetic phase in the phase diagram of the 2-d Hubbard Model from a phase with incommensurate magnetic order. A mean-field approximation of the Kotliar-Ruckenstein slave boson representation is used to calculate the wave-vector dependent magnetic susceptibility. For largeU/t the instability occurs at a densityn0.37, and a wave-vector close toq=(0,). The dependence ofq onU andn is also given.     

A universe of Friedmann type with pressure

We propose a method of obtaining homogeneous and isotropic cosmological models satisfying physical conditions for 0 and . The model obtained in this way describes a universe filled with matter, the equation of state of which changes in time from the asymptotically ultrarelativistic to the asymptotically dust state.Dnepropetrovsk State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 8–12, May, 1993.     

Polyfunctional macroheterocycles. 7. Synthetic enzyme analogs. synthesis of 16- and 22-membered nitrogen and sulfur crown compounds containing exocyclic histamine and histidine fragments and carboxyl groups

The acid hydrolysis of 9,14-bis(2-methoxycarbonylethyl)-11-12-benzo-3,4-(4,5-dimethylbenzo)-10,13-dioxo-1,6-dithia-9,14-diazacyclohexadeca-3,11-diene leads to the corresponding 9,14-biscarboxy derivative. The reaction of 4,9,15,20-tetrakis-(2-methoxycarbonylethyl)-6,7,17,18-dibenzo-5,8,16,19-tetraoxo-1,12-dithia-4,9,15,20-tetraazacyclodocosa-6,17-diene with hydrazine hydrate and subsequent treatment with NaNO₂ gave the corresponding tetraazide. The reaction of this tetraazide with histamine and histidine leads to macroheterocycles, containing exocyclic histamine and histidine fragments.For Communication 6, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 130–133, January, 1993.     

Dispersity and kinetic characteristics of dissociation of mono- and hemiaquo adducts of copper N,N′-ethylenebis(acetylacetoniminate) under nonisothermal conditions

Using optical microscopy and thermogravimetry, we have established that determination of the kinetic characteristics of dissociation for the monoaquo adduct of copper N,N-ethylene-bis(acetylacetoniminate) with particle size 0.5–2 mm is hindered by self-dispersal processes. Using a piezoquartz microbalance, we have obtained the kinetic parameters for thermolysis for a phase whose crystal sizes are substantially smaller than the minimal size after self-dispersal of a block of a large crystal (0.5–2 m). For thermolysis of the hemiaquo adduct not accompanied by self-dispersal, the kinetic characteristics of the process for phases of dispersity 0.5–2 mm and 0.5–2 m are comparable.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 28, No. 3, pp. 226–231, May–June, 1992.     

Determination of polonium in aqueous media using metal-containing membranes

A rapid method has been developed for the determination of polonium in water. The samples with a volume of 0.25 to 4.0 1 were filtered at a flow rate of 2 to 3 1 h^–1 on a membrane filter impregnated with silver. Optimum conditions are 0.1M hydrochloric acid in the presence of 0.01M ascorbic acid. After the filtration the membranes are flushed, dried and measured for -activity. The detection limit for a 41 sample with a membrane diameter of 35 mm is lower corresponding to 1.5×10^–3 Bq.1^–1. The method permits activity measurement with an -radiometer or -spectrometer with an error less than 30% at a confidence level of 0.95.     

Depth-profiling of organic layers on microparticles with SNMS

Summary Previous work on the quantification and localization of organically bound elements with plasma-based SNMS for the characterization of microparticles has been continued. Relative detection factors for 10 elements have been determined. Except for lead and bromine a principle proportionality to atomic ionization probabilities is shown. A moderate matrix dependence of less than 40% variation was found even when inorganic and organic materials are included. For depth calibration, erosion rates of organic materials were determined from the time interval necessary to sputter through planar single-layers and Langmuir-Blodgett multi-layer systems with known thickness, as well as from gravimetric powder measurements. Depth propagation rates were 0.7 nm·sec^–1 for polymers and 2.3 nm·sec^–1 for aromatic compounds, when 400 eV argon ion bombardment with 0.7 mA·cm^–2 was used. A depth resolution of 30 nm has been obtained. Model particles of 5 m size have been coated with fluoranthene. Inspection with SNMS revealed an incomplete coating covering only 20% of the microparticle surface with an average thickness of the partial coating of 300 nm. Subsequent characterization using laser-induced fluorimetry confirmed the amount of fluoranthene coating measured by SNMS.     

On two methods of determining the ellipses and ellipsoids of positioning accuracy of robot manipulators

Summary When analysing the problem of the positioning accuracy of robot manipulators it is important to know how far random deviations of the hand may be from the desired position if the joint positioning errors possess a normal distribution. Two methods of determining the ellipses and ellipsoids of probability concentration are compared. The first of them is based on the standard procedure of the probability calculus. The second approximate method consists in finding at first the polygon or polyhedron of the positioning accuracy, and then in finding the ellipse or ellipsoid with principal axes and second order moments coinciding with those of the polygon or polyhedron, respectively. Examples of application demonstrate that these two methods give very close results.

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Zwei Methoden zur Bestimmung der Ellipsen und Ellipsoide der Positioniergenauigkeit von Handhabungsrobotern

Übersicht Bei der Untersuchung der Positioniergenauigkeit von Handhabungsrobotern ist es wichtig, die Größe zufälliger Abweichungen des Greifers von der erstrebten Position zu kennen, wenn die Lagefehler der Verbindungen eine Normalverteilung besitzen. Es werden zwei Methoden zur Bestimmung der Ellipsen bzw. Ellipsoide der Wahrscheinlichkeitsdichte verglichen. Die erste beruht auf dem Standardverfahren der Wahrscheinlichkeitsrechnung. Die zweite Näherungsmethode besteht darin, daß zunächst das Polygon bzw. Polyeder der Positioniergenauigkeit bestimmt wird und danach die Ellipse bzw. das Ellipsoid mit den Hauptachsen und Momenten zweiter Ordnung wie das Polygon oder Polyeder. Beispiele zeigen, daß beide Methoden zu sehr ähnlichen Ergebnissen führen.

     

On the construction and calculation of optimal nonlifting critical airfoils

Numerical calculations are carried out in the hodograph plane to construct optimal critical airfoil shapes and the flow about them. These optimal airfoil shapes give the highest free-stream Mach numberM for a given thickness ratio and tail angle _t (nonlifting) for which the flow is nowhere supersonic. A relationship betweenM and for various _t is given. Analytical and numerical solutions to the same problem are found on the basis of transonic small-disturbance theory. These results provide a limiting case asM 1, 0 and agree well with the calculations of the full problem. Using a numerical method to calculate the flow about general (subsonic) airfoils, a comparison is made between the critical free-stream Mach numbers for some standard airfoil shapes and the optimal free stream Mach number of the corresponding and _t . A significant increase in the critical free-stream Mach number is found for the optimal airfoils.