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 ). . , , .

     

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.     

MHD mixed convection flow near the stagnation-point on a vertical permeable surface

The steady magnetohydrodynamic (MHD) mixed convection boundary layer flow of a viscous and electrically conducting fluid near the stagnation-point on a vertical permeable surface is investigated in this study. The velocity of the external flow and the temperature of the plate surface are assumed to vary linearly with the distance from the stagnation-point. The governing partial differential equations are first transformed into ordinary differential equations, before being solved numerically by a finite-difference method. The features of the flow and heat transfer characteristics for different values of the governing parameters are analyzed and discussed. Both assisting and opposing flows are considered. It is found that dual solutions exist for both cases, and the range of the mixed convection parameter for which the solution exists increases with suction.     

Analogues of Ramanujan’s partition identities

Ramanujan discovered that $$\sum_{n=0}^\infty p(5n+4)q^n=5 \prod_{j=1}^\infty \frac{(1-q^{5j})^5}{(1-q^j)^6}, $$ where p(n) is the number of partitions of n. Recently, H.-C. Chan and S. Cooper, and H.H. Chan and P.C. Toh established several analogues of Ramanujan’s partition identities by employing the theory of modular functions. Very recently, N.D. Baruah and K.K. Ojah studied the partition function $p_{[c^{l}d^{m}]}(n)$ which is defined by $$\sum_{n=0}^\infty p_{[c^ld^m]}(n)q^n= \frac{1}{\prod_{j=1}^\infty (1-q^{cj})^{l}(1-q^{dj})^m}. $$ They discovered some analogues of Ramanujan’s partition identities and deduced several interesting partition congruences. In this paper, we provide a uniform method to prove some of their results by utilizing an addition formula. In the process, we also establish some new analogues of Ramanujan’s partition identities and congruences for $p_{[c^{l}d^{m}]}(n)$ .     

PEG–Anthracene Hydrogels as an On‐Demand Stiffening Matrix To Study Mechanobiology

There is a growing interest in materials that can dynamically change their properties in the presence of cells to study mechanobiology. Herein, we exploit the 365 nm light mediated [4+4] photodimerization of anthracene groups to develop cytocompatible PEG‐based hydrogels with tailorable initial moduli that can be further stiffened. A hydrogel formulation that can stiffen from 10 to 50 kPa, corresponding to the stiffness of a healthy and fibrotic heart, respectively, was prepared. This system was used to monitor the stiffness‐dependent localization of NFAT, a downstream target of intracellular calcium signaling using a reporter in live cardiac fibroblasts (CFbs). NFAT translocates to the nucleus of CFbs on stiffening hydrogels within 6 h, whereas it remains cytoplasmic when the CFbs are cultured on either 10 or 50 kPa static hydrogels. This finding demonstrates how dynamic changes in the mechanical properties of a material can reveal the kinetics of mechanoresponsive cell signaling pathways that may otherwise be missed in cells cultured on static substrates.