Kinetic energy release distribution in the fragmentation of energy-selected iodopropane ions

The technique of threshold photoelectron-photoion coincidence (PEPICO) has been employed to determine the average kinetic energy release and the kinetic energy release distribution (KERD) for the iodine loss from 1- and 2-iodopropane ions as a function of the ion internal energy. The KERDs at all precursor-ion energies investigated (0–3 eV excess energy) have the shape of statistically expected distributions, 1-iodopropane ions which dissociate with an apparent 0.16 eV reverse activation barrier, are shown to isomerize at low energies prior to dissociation, to produce subsequently the 2-propyl C₃H₇^? structure. At high energies they may form a different C₃H₇^? isomer. The experimentally observed average kinetic energy releases are approximately a factor of 2 greater than expected statistically suggesting that not all vibrational modes participate in the energy disposal. The secondary dissociation of the C₃H₇^? isomers to C₃H₃ which is inhibited by a reverse activation barrier of = 0.4 eV indicates that the 1- and 2-iodopropane ions dissociate 75% and 60% respectively, to form the excited 1(²P_1/2) atoms.     

Vacuum-arc plasma centrifuge experiment

The authors describe the vacuum-arc plasma centrifuge developed at the Institute for Space Research (INPE) in Brazil. The experiment is characterized by its relatively small dimensions. Angular rotation frequencies in the range of 1.9×10⁵ rad/s to 3.5×10⁵ rad/s, measured with langmuir probes, are presented for a magnesium plasma. Enrichments of 15% for ²⁵Mg and 26% for ²⁶Mg were measured with a quadrupole mass spectrometer. The dependence of magnesium isotope enrichments upon the magnetic field is also presented. It is noted that the existence of an optimum value for the B field is important for future scaling laws of plasma centrifuges     

The response of a turbulent boundary layer to artificial disturbances

With periodic fluid injection through small slots, a turbulent boundary layer is artificially disturbed on scales that are of the order of those of the natural quasi-periodic events. The periodic phase-average of the streamwise fluid velocity is determined from hot-film measurements, and used to find the coherent velocity component as defined by the triple decomposition. It appears that, when a disturbance is active, the generated flow pattern is very similar to the one caused by the interaction of a crossflow and a jet. However, when it is terminated, the turbulent boundary layer returns to its undisturbed state.     

MISSED OPPORTUNITIES IN NATURAL RESOURCE MANAGEMENT

After 20 years of effort, technical approaches to natural resource management have not been effective in preventing overuse and destruction of resources. The resource modeling community can help to change our present course toward destruction by (1) recognizing and publicizing the ineffectiveness of scientific, technical and magical approaches to resource management, (2) pointing out that the resolution of environmental problems is impossible unless the social problems of excessive human population sizes and excessive consumption are effectively addressed, (3) making clear the irrationality and imprudence of current environmental decisionmaking under uncertainty, and (4) pointing out the impossibility of achieving conservation goals by management that attempts to achieve economic optima.     

The GHP conformai Killing equations and their integrability conditions,with application to twisting type N vacuum spacetimes

The conformai Killing equations in resolved form and their first and second integrability conditions are obtained in the compact spin coefficient formalism for arbitrary spacetimes. To facilitate calculations an operatorL is introduced which agrees with the Lie derivative only when operating on quantities with GHP weights (0,0). The resulting equations are used to find the conditions for the existence of a two dimensional non-Abelian group of homothetic motions in a twisting typeN vacuum spacetime. The equivalence of two such sets of metrics is established, metrics that were recently the subject of independent investigations by Herlt on the one hand and by Ludwig and Yu on the other.     

Electrooptic response of smectic O and smectic O

We present the results of our investigations on the electrooptic properties of the smectic O and O* phases of m7tac (1-methylheptyl terephthalylidene-bis-4-aminocinnamate). At low voltages, we observed striking electrochromic effects and, in O* at high voltages, a field induced phase transition. Freely suspended thick films of m7tac in the O and O* phases are weakly biaxial. A framework is proposed to account for our observations.     

Friction coefficients and directed motion of asymmetric test particles

The behavior of a test particle in a rarefied gas of classical particles is investigated. considering different interaction mechanisms (specular and diffuse reflection, respectively). For large mass ratio between test and gas particles, analytical expressions for the linear friction coefficient are derived. Moreover, the existence of directed motion of asymmetric test particles with distinct initial conditions (but in the absence of any gradients) is shown. The analytical results are supported by a numerical simulation technique applicable to systems with any mass ratio, which is described here in detail.