The magnetic behaviour of diluted CrAl alloys

Magnetic susceptibility as a function of temperature of binary CrAl alloys containing 0.7,1.07,1.35,1.59, 1.79,1.98, 2.18, 2.84, 3.74 and 4.36 at %A1 is investigated. Aluminium, by alloying, acts on the Néel temperature of pure chromium giving rise to a complicated phase diagram. The bahaviour of the magnetic susceptibility as a function of temperature, in the ordered phase, for the samples containing 1.28, 2.18 and 2.84 at %A1 is found to be temperature independent. In the paramagnetic region, for the samples containing between 1.07 and 2.84 at %A1, it is found a decrease of the magnetic susceptibility as a function of temperature.     

Boundary-layer flow of a micropolar fluid due to a stretching wall

Summary  A Theoretical analysis is carried out to study the boundary-layer flow over a continuously moving surface through an otherwise quiescent micropolar fluid. The transformed boundary-layer equations are solved numerically for a power-law surface velocity using the Keller-box method. The effects of the micropolar K and exponent m parameters on the velocity and microrotation field as well as on the skin-friction group are discussed in a detailed manner. It is shown that there is a near-similarity solution of this problem. The accuracy of the present solution is also discussed. Accepted for publication 1 April 1996     

On boundary layer growth past a spinning body

Summary The incompressible boundary layer growth on a body of revolution in spinning motion when the outer flow and the angular velocity of the body are expressed in powers series of √t is studied. Series at small time are established for the velocity. A simple application is presented in the case of a sphere and the separation characteristics are studied. Entrata in Redazione il 23 novembre 1970.     

Influence of composition and of activation temperature upon the adsorption and thermodesorption of ammonia on aluminium oxide-silica gels

Aluminium oxide gel and aluminium oxide-silica gels of different compositions were prepared and activated at different temperatures. The adsorption of NH₃ was studied in a McBain type balance at 20 torr and 5×10^–3 torr at 25°. The thermodesorption of NH₃ was studied at 5×10^–3 torr between 25 and 550° at a constant heating rate of 4°/min. The desorption was followed by recording the thermogravimetric curve and the pressure oscillations in the system (p — T curve). The influence of composition and activation temperature is discussed. Chemisorption of a monomolecular layer is assumed in three main types of pores, together with the formation of a second monomolecular layer held by hydrogen bonds.

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Zusammenfassung Aluminiumoxyd und Aluminiumoxyd-Kieselsäure Gele von verschiedener Zusammensetzung wurden erzeugt und bei unterschiedlichen Temperaturen aktiviert. Die Adsorption von NH₃ wurde mit Hilfe einer McBain Waage unter 20 und 5 · 10^–3 Torr Druck bei 25°, weiterhin die Thermodesorption von NH₃ unter 5 · 10^–3 Torr Druck zwischen 25 und 550° mit 4°/Min. Aufheizungsgeschwindigkeit untersucht. Die Desorption wurde durch die thermogravimetrische Kurve und durch Registrieren der Druckschwankungen in dem System (p — T Kurve) verfolgt. Man diskutiert den Einfluß von Zusammensetzung und Aktivierungstemperatur. Man nimmt eine Chemisorption einer monomolekularen Schicht in drei Porenhaupttypen gemeinsam mit der Ausbildung einer zweiten durch Wasserstoffbindungen gebundenen monomolekularen Schicht an.

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Résumé On a préparé des gels d'oxyde d'aluminium et des gels de silice et d'oxyde d'aluminium de diverses compositions; les préparations ont ensuite été activées à différentes températures. On a étudié l'adsorption de NH₃ à l'aide d'une balance de type McBain à 25° sous des pressions de 20 et de 5.10³torr ainsi que la désorption thermique sous 5.10^–3 torr entre 25 et 550° avec une vitesse de chauffage de 4°/mn. On a suivi la désorption en enregistrant les courbes thermogravimétriques et les oscillations de pression dans le système (courbesp — T). On a discuté l'influence de la composition et de la température d'activation. On suppose une chemisorption d'une couche monomoléculaire dans trois types principaux de pores ainsi que d'une seconde couche monomoléculaire maintenue par ponts d'hydrogène.

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- . (NH₃) 20 . . 5 · 10^–3 . . 25°. 5 · 10^–3 . . 25° – 550° 4°/ . (p—T ). . , , .

     

Temperature dependence of the electrical resistivity of the nickel-platinum alloy system

The temperature dependence of the electrical resistivity of Ni_1?xPt_x (x = 1, 2, 3, 4, 5, 8, 10, 15, 20, 25 and 30 at.%) between 77 and 700 K has been investigated. The experimental results are interpreted according to the theoretical model developed by Mott. It is shown that for this system Matthiessen's rule is not obeyed.     

Rheological Behavior of Some Aqueous Gels of Carbopol with Pharmaceutical Applications

The concentration and temperature dependence of the viscosity is observed for some aqueous dispersions of Carbopol. The experimental data are analyzed with the power model, and reveal non-Newtonian behavior （shear thinning） of the samples.     

Cosmology with torsion: An alternative to cosmic inflation

We propose a simple scenario which explains why our Universe appears spatially flat, homogeneous and isotropic. We use the Einstein–Cartan–Kibble–Sciama (ECKS) theory of gravity which naturally extends general relativity to include the spin of matter. The torsion of spacetime generates gravitational repulsion in the early Universe filled with quarks and leptons, preventing the cosmological singularity: the Universe expands from a state of minimum but finite radius. We show that the dynamics of the closed Universe immediately after this state naturally solves the flatness and horizon problems in cosmology because of an extremely small and negative torsion density parameter, ΩS≈−¹⁰⁻⁶⁹${\Omega }_S\approx -{10}^{-69}$. Thus the ECKS gravity provides a compelling alternative to speculative mechanisms of standard cosmic inflation. This scenario also suggests that the contraction of our Universe preceding the bounce at the minimum radius may correspond to the dynamics of matter inside a collapsing black hole existing in another universe, which could explain the origin of the Big Bang.