Fusion and neutron-transfer cross sections for 13C + 10B and 13C + 11B reactions at subbarrier energies

The cross sections for the ¹⁰B(¹³C, ¹²C)¹¹B neutron-transfer reaction, leading to the ¹¹B 4.45 and 6.74 MeV and ¹²C 4.44 MeV excited states, and for ¹³C + ¹⁰B fusion have been measured by the characteristic and total γ-ray yield methods, respectively, over the energy (c.m.) interval 2.4–5.8 MeV. For ¹³C + ¹¹B, with no transfer reactions present, the fusion cross sections have been measured between E_c.m. = 2.3 and 6.4 MeV. The fusion cross sections for ¹³C + ¹⁰B and ¹³C + ¹¹B are found to be almost equal and slightly enhanced with respect to those for ¹²C + ¹⁰B and ¹²C + ¹¹B.     

Free boundary problems arising in the freezing of soils in a bounded region. III. Hydrodynamics of the unfrozen phase. IV. Thermal stresses in the frozen phase

In this paper, the method of characteristics is utilized to construct unique solutions to Problems II and III stated in Part I, and we demonstrate the continuous dependence of these solutions on the respective initial and boundary data. Moreover, asymptotic estimates for the critical time of breakdown in these solutions are also obtained.     

New one step synthesis of crown compounds containing a 1,3,4‐thiadiazole moiety

New macrocyclic polyether compounds containing a 2,5‐bis(2‐hydroxyphenyl)‐1,3,4‐thiadiazole moiety have been prepared by a nucleophilic substitution reaction involving ethylene or polyethylene glycol ditosylate and a bisphenol, the 2,5‐bis(2‐hydroxyphenyl)‐1,3,4‐thiadiazole, with solid anhydrous carbonate as a base. The structures of the macrocycles obtained were firmly established by ¹H and ¹³C nmr spectroscopy and their mass spectra.     

Thermal decomposition and creation of reactive solid surfaces: IV. effect of NH4NO3 inclusion on the thermal genesis of chromia catalyst from a parent gel

The effect of NO₃^? contaminant on the thermal decomposition of chromia gel has been thoroughly investigated. NO₃^?free gel, prepared by treating a dilute solution of chromium nitrate with aqueous ammonia, and a simulated NO₃^?-contaminated one, obtained by mechanically mixing calculated amounts of the pure gel and NH₄NO₃ (4.7–33.3% by weight), have been subjected to thermogravimetric and differential thermal analyses. The thermal behaviour thus monitored has been physicochemically characterized by means of infrared and X-ray diffraction techniques. The results obtained have revealed a notable disparity between the reaction pathways conceded by the pure and the contaminated gel yielding chromias of different properties.     

A Comparative Analytical Study of Two New Liquid Crystals Used as Stationary Phases in GC

The investigation of the analytical properties of two new nematic sulphur-containing liquid crystals 5-(4-methoxyphenyl)-azophenyl)-2-butylthio-1,3,4-oxadiazole (Phase I) and 5-(4-(propoxyphenyl)-azophenyl)-2-butyl thio-1,3,4-oxadiazole (Phase II) and which comprise units of 1,3,4-oxadiazole instead of the aromatic cycles, was carried out by gas chromatography using glass capillary columns. For this purpose, many solutes belonging to various families and having different polarities and volatilities were injected. Comparison of the retention data of the studied components has shown that Phase II allowed a better separation than the other phase. The two liquid crystalline materials show a good separation of the studied isomers except for xylene.     

Accumulation of some metal ions on Bacillus licheniformis

Pure species of Bacillus licheniformis was used to remove ions from aqueous and simulated waste solutions. Metal ion accumulation on B. licheniformis was fast. Maximum uptake occurred at pH 4±0.5 and at 25±3 °C. One gram of dry B. licheniformis was found to accumulate 115 mg cerium, 34 mg copper and 11 mg cobalt from aqueous solutions. The presence of certain foreign ions such as calcium, sodium and potassium decreased the uptake of ions by B. licheniformis, while citrate and EDTA prevent the uptake. Electron microscopic investigations showed that cerium (III), copper (II) and cobalt (II) accumulated extracellulary around the surface wall of B. licheniformis cells. A bio-adsorption mechanism between the metal ions and B. licheniformis cell wall was proposed.     

Effect of the Preparation Methodof Al–Mg–O Catalysts on the Selective Decomposition of Ethanol

Summary.  Selective decomposition of ethanol was used as a test reaction at 350°C to evaluate the catalytic activity of two Al–Mg–O mixed oxides prepared by two different methods (wet impregnation and coprecipitation). The catalyst precursors were examined by TG and DTA and were calcined between 500–900°C for 5 h in air. The surface area of all catalysts was measured by N₂ sorption using the BET method. The total acidity and basicity were determined by TPD using pyridine and formic acid. The catalysts were characterized by XRD analysis. It was found that the preparation method of Al–Mg–O catalyst has a great effect on the selective decomposition of ethanol. Al–Mg–O (I) catalysts, prepared by wet impregnation, were more selective towards ethene formation during dehydration of ethanol. This is ascribed to their high total surface acidity. On the other hand, Al–Mg–O (II) catalysts, prepared by coprecipitation, were highly selective in the oxidative dehydrogenation of ethanol to yield acetaldehyde. This could be attributed to their high concentration of basic sites. In addition, the production of traces of diethyl ether was also observed (three times more for Al–Mg–O (II) than for Al–Mg–O (I)). Corresponding author. E-mail: shalawy99@yahoo.com Received October 12, 2001. Accepted (revised) January 7, 2002     

Computational parametric analysis of fuel cells: Application to PEMFC and SOFC

This study presents a numerical investigation on the proton exchange membrane fuel cell (PEMFC) and the solid oxide fuel cell (SOFC), using the aerothermal and electrochemistry equations to describe all phenomena included in both types of the fuel cells. The computational process is based on the implementation of the mathematical fuel cells models in FLUENT computational fluid dynamics code. This is in order to evaluate the temperature field, the production of the electricity, and the distribution of the water mass fraction in different region of the fuel cells. The obtained results show that the simulation is able to evaluate the physical and chemical parameters to explain the main phenomena in the fuel cells.     

Oxyfluoroborate host glass for upconversion application: phonon energy calculation

Reducing the glass phonon energy is an essential procedure to achieve high efficient radiative upconversion process. The degree of covalence of chemical bonds is responsible for the high oscillator strength of intracenter transitions in rare-earth ions. So, conversion covalent to ionic glass character is proposed as a structure-sensitive criterion that controls the phonon energy of the glasses. A series of oxyfluoro aluminum-borate host glasses used for upconversion application is prepared by the conventional melt-quenching technique. Through lithium oxide substitution by lithium fluoride, the ionic-covalent property of Li⁺ ion successes to regulate the band gap energies of the studied glasses. Furthermore, a new method to determine the glass phonon energy is offered.     

Magnetism of electrodeposited ultrathin layers: Challenges and opportunities

The magnetism in ultrathin films and multilayers is an active field of research in strong relationship with applications. Advances in the understanding of such systems came from an improved control of growth modes and detailed structural studies coupled with magnetic measurements, especially in the UHV environment. Thanks to the development of in situ methods, similar studies can now be conducted in the electrolytic environment and investigating the magnetism of nanostructures on the nanometre scale has become a reality. After a brief review of our work about the epitaxial growth and magnetism of ultrathin magnetic layers of Ni, Co and Fe on Au(1 1 1), with an emphasis on the early stages of their electrochemical growth, this article introduces ongoing works which draw attention about the specificity and the opportunities offered by the electrochemical interface.