Low-energy predictions from grand unified theories

A theoretical framework to compute low-energy processes in a spontaneously broken gauge theory is devised. It applies in any gauge and uses conventional renormalisation schemes. Application of the method to SU(5) gives a range for M_X of 4.10¹³ GeV < M_X < 1.3 · 10¹⁵ GeV with a best value of 6.6 · 10¹⁴ GeV.     

Measurement of steering gear impedance

Proper simulation of noise in hydraulic circuits requires reliable experimental data to be used in the simulations. In automotive power steering applications, obtaining reliable impedance data for both the pump and steering gear is critical for the success of any fluid-borne noise simulation program. Collecting data for power steering pumps has been the subject of various studies. Steering gears, on the other hand, have received little attention. The purpose of this paper is to present a comprehensive assessment of the need of such data and describe a test setup for obtaining the data according to recent ISO standards. This paper describes the results obtained and presents several studies. In particular, the effects of pressure, steering position, slave pump and steering fluid on rack impedance will be studied. Furthermore, repeatability and production variability of measured data will be addressed.     

Controlled Rate Thermal Analysis of kaolinite dehydroxylation: effect of water vapour pressure on the mechanism

The present kinetic study is focused on one aspect of kaolinite dehydroxylation, namely the influence of water vapour pressure in the 10⁻³ to 5 hPa range and in the presence of crystalline defects. The experimental problem of keeping, throughout the dehydroxylation, the pressure gradients negligible around and within the sample is solved by means of Controlled Rate Evolved Gas Detection (CR-EGD). The dehydroxylation rate selected is as low as 0.014 h⁻¹ (which corresponds to a duration of 70 h for the whole experiment). Moreover, more than 20 independent measurements of the apparent Arrhenius energy of activation are carried out all along the dehydroxylation, with help of the rate–jump method, and therefore, without any assumption about the rate law of the determining step. In these conditions, the apparent Arrhenius energy of activation measured during the dehydroxylation of a poorly crystallised kaolinite is shown to be constant in the range 0.02<<0.84 (under 10⁻³ hPa) and in the range 0.18<<0.80 (under 5 hPa), indicating that the rate law obeys the Arrhenius law in this range of extent of reaction. The corresponding activation energies obtained are (233±15) kJ/mol under 10⁻³ hPa and only (188±10) kJ/mol under 5 hPa. Although this decrease is in contradiction with previously published results, it can be interpreted by considering that, under 10⁻³ hPa, diffusion is the limiting step whereas, under 5 hPa, the part of water desorption probably becomes predominant.     

Quasi-equilibrium adsorption gravimetry of water on MFI- and ‘FER’-type zeolites and on an AFI-type aluminophosphate

Water adsorption at temperatures of 286 and 296 K on silicalite-I, ZSM-5 (Si/Al=16), ZSM-48 (Si/Al=50) and AlPO₄-5 is followed by gravimetry with a quasi-equilibrium continuous adsorptive introduction. The results show that all of these samples are characterized by a continuous distribution of strongly energetic water adsorption sites (from 60 to 120 kJ·mol^?1) for which the adsorption is irreversible at the experimental temperature. This probably justifies the presence of hysteresis on desorption at very low relative pressure values. Adsorption of water in these systems firstly occurs by site. This is then followed by cluster formation and it is suggested that it is the ability of the adsorbent to build up these clusters within the microporous structure which determines intracrystalline uptake. It is put forward that the zeolites, silicalite-I and ZSM-5, do not accommodate cluster formation within its microporous network. However, an external flexible microporous structure, containing Lewis sites, may be present for large crystals. This flexible secondary structure may then be able to opened (swelled) at high relative pressures. On the other hand, for the aluminophosphate AlPO₄-5, it is believed that a change in the aluminium coordination on the formation of a crystal hydrate together with capillary condensation results in a large step in the adsorption isotherm, which is itself preceded by a smaller step, revealing a brutal densification of the adsorbed phase.     

Aromatic nitrations in ionic liquids: the importance of cation choice

Aromatic substrates can be nitrated in high yields and with efficient use of the nitrating agent in ionic liquids, although a suitably inert ionic liquid cation must be used.     

A novel example of chiral counteranion induced enantioselective metal catalysis: the importance of ion-pairing in copper-catalyzed olefin aziridination and cyclopropanation

A new ion-pairing route to achieve asymmetric catalysis has been observed in the copper-catalyzed aziridination of styrene with a chiral counteranion. Structural studies suggest that enantioinduction occurs via ion-pairing of the cationic copper catalyst in the chiral pocket created by the anion. The degree of asymmetric induction can be tuned with features that affect ion-pairing, such as achiral and chiral ligands, temperature, and solvent polarity.     

Argon and nitrogen adsorption in disordered nanoporous carbons: simulation and experiment

We report experimental measurements of the isosteric heats of adsorption for argon and nitrogen in two microporous saccharose-based carbons, using a Tian-Calvet microcalorimeter. These data are used to test recently developed molecular models of these carbons, obtained by a constrained reverse Monte Carlo method. Grand canonical Monte Carlo simulation is used to calculate the adsorption isotherms and isosteric heats for these systems, and the results for the latter are compared to the experimental data. For argon, excellent quantitative agreement is obtained over the entire range of pore filling. In the case of nitrogen, very good agreement is obtained over the range of coverage 0.25 < or = gamma/gamma 0 < or = 0.85, but discrepancies are observed at lower and higher coverages. The discrepancy at low coverage may be due to the presence of oxygenated groups on the pore surfaces, which are not taken into account in the model. The differences at high coverage are believed to arise from the presence of a few mesopores, which again are not included in the model. Pair correlation functions (argon-carbon and argon-argon) are determined from the simulations and are discussed as a function of pore filling. Snapshots of the simulations are presented and provide a picture of the pore filling process.