able ( Figure 2). This places further constraints on asymmetric catalysis: (a) only the neutral histidine is effective, and (b) phosphate buffer (predominant counterion HP0:-0.2 t 0.4 -Lg k 0.6 0.8 1 .0 1.2 1.4 ? i' 7 8 9 PH -Fig. 2 Dependence of Ig k on the pH of the solution in the hydrolysis of (21 catalyzed by(12);[(12)]=1.08~ l0-'MM,[/2)]=5x 10-'M,[buffer]=0.02 M,0.47 vol.-% acetone in water; 0 (S,S)-(12), (S)-(2), borate buffer; __ phosphate buffer; D (R,S)-(lZj. (S)-V), ---borate buffer; (3 (S.SHl2). (R)-(2), borate buffer, __ phosphate buffer; + (R.S)-(IZj, (R)-/.?), _ _ _ borate buffer.at p H 7.5) is more efficacious than borate buffer (predominant counterion CIrather than H3B0, at p H 9). A model which displays these features is presented by formula (13).
Magnetic-field-assisted self-assembly of magnetic dipole moment carrying iron nanoparticles is shown to result in the formation of magnetic and mechanically stiff nanoscale rods. The cooperative behavior of an ensemble of such rods and bundles thereof exhibits self-organized pattern formation on different length scales. Pattern formation on large length scales reveals great similarity with physical systems undergoing spinodal decomposition. Possible applications for dipolar magnetic nanorods in the field of perpendicular storage media are highlighted. We discuss an aerosol-synthesis-route allowing to prepare ferrofluids (FF) with shape-anisotropic particles constituting the magnetic phase immersed in the nonmagnetic carrier fluid. These so-called nanorod FF unveil a two orders of magnitude increase of viscosity enforced by an applied field of 10mT even at shear rates larger than 10-2s. This raises prospects for applications in microfluidics and MEMS.
Comparative studies on fixed‐bed catalytic isomerization of 1‐hexene and disproportionation of 1,4‐diisopropylbenzene were performed under liquid, gaseous or supercritical conditions. The kinetic measurements show that by variation of pressure in the different fluid states catalytic surface reactions as well as mass transfer effects between catalyst and fluid phase and/or transport processes inside porous catalysts can be influenced in a very sensitive way. Conclusions are drawn in view of new possibilities for the direction of yield and selectivity of multiple reactions, for the prolongation of catalyst lifetime, and the study of deactivation mechanisms on heterogeneous catalysts.
The present paper gives experimental and theoretical results which enabel us to determine the absolute values of stacking-fault energies of face-centred cubic metals from the stress-strain-curves of single crystals. The activation energy for the crossslip of screw-dislocations is calculated as a function of the stacking-fault energyv, the applied shear stress T, and the size of the piled-up dislocation groups. An experimental value for the activation energy for cross-slip in copper is deduced from the strain-rate dependence of the shear stress TIII at the beginning of stage III of the stress-strain-curve. Comparison between experiment and theory gives VCu = 170 ergs/cm 2. The determination of the stacking-fault energy of other f.c.c, metals is possible by comparing the temperature dependence of TII I. Experimental results are given for Au and Cu. Data from the literature are used for Ag, Ni, and A1. We find YAu = 30 ergs/cm 2. The difference in stacking-fault energy of Cu and Au is much larger than was anticipated. It is substantiated, however, by a number of observations discussed in the paper. Constriction energies calculated on the basis of the newly determined stacking-fault energies are given.
Magnetic-field-assisted self-assembly of magnetic-dipole moment carrying aerosol-grown iron nanoparticles on a nonmagnetic substrate results in the formation of magnetic nanoscale rods and bundles thereof. The magnetic dipolar interaction between the bundles essentially drives the formation of regular patterns of bundle density modulations in the two-dimensional array of elastically deformable magnetic rods. This pattern formation is shown to belong to the class of physical systems undergoing spinodal decomposition. Possible applications for dipolar magnetic nanorods in the fields of perpendicular storage media and ferrofluids are highlighted. A giant magnetoviscous effect is expected.
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