Raman spectroscopy of atomic fluorine

We have measured the Raman scattering cross section of atomic fluorine for transitions between the ground fine-structure electronic states. The fluorine was contained a in heated, static chamber. Gas temperature, determined from the rotational Raman spectrum of molecular fluorine, was used as an input to calculate the degree of fluorine dissociation (assuming thermodynamic and chemical equilibrium). The Raman frequency shift and depolarization ratio were also determined. Our results indicate that Raman scattering can be used as a probe for atomic fluorine.     

Insulator-based dielectrophoresis for the selective concentration and separation of live bacteria in water

Insulator-based dielectrophoresis (iDEP) was utilized to separate and concentrate selectively mixtures of two species of live bacteria simultaneously. Four species of bacteria were studied: the Gram-negative Escherichia coli and the Gram-positive Bacillus subtilis, B. cereus, and B. megaterium. Under an applied direct current (DC) electric field all the bacterial species exhibited negative dielectrophoretic behavior. The dielectrophoretic separations were carried out in a glass microchannel containing an array of insulating posts. The insulating posts in the microchannel produced nonuniformities in the electric field applied along the channel. Mixtures of two species of bacteria were introduced into the microchannel and the electric field was applied. The bacterial species exhibited different dielectrophoretic mobilities under the influence of the nonuniform field. From these experiments a trapping order was established with E. coli trapping at the weakest applied electric field, while the Bacillus species were trapped at different characteristic threshold fields. At stronger applied electric fields, the two different species of bacteria in the microchannel were dielectrophoretically trapped into two spatially distinct bands. The results showed that iDEP has the potential to selectively concentrate and separate different species of bacteria.     

Diode-laser spectroscopy of the ν3Q branch of MoF6

A diode laser has been used to measure the absorption spectrum of the ν₃ band of MoF₆ (740–750 cm^?1). A rich Q-branch spectrum was observed with natural-abundance MoF₆ and with isotopically pure samples of ⁹²MoF₆, ⁹⁶MoF₆, and ¹⁰⁰MoF₆. Q-Branch subbandheads were observed experimentally, their absolute frequencies were determined, and the spectra were compared to computer-generated simulations. From the comparison to spectral simulations, the band-center frequencies, the effective perturbations to the rotational constants, and the octahedral splitting constants for the three isotopes have been determined. A number of tests were conducted using a gas-dynamic expansion to cool the MoF₆ in order to assess the feasibility of laser isotope separation of molybdenum.     

Precision measurements of the timelike electromagnetic form factors of pion, kaon, and proton

Using 20.7 pb(-1) of e(+)e(-) annihilation data taken at sq.rt(r) = 3.671 GeV with the CLEO-c detector, precision measurements of the electromagnetic form factors of the charged pion, charged kaon, and proton have been made for timelike momentum transfer of |Q(2)| = 13.48 GeV(2) by the reaction e(+)e(-) --> h(+)h(-). The measurements are the first ever with identified pions and kaons of |Q(2)| > 4 GeV(2), with the results F(13.48 GeV(2)) = 0.075 +/- 0.008(stat) +/- 0.005(syst) and F(K)(13.48 GeV(2)) = 0.063 +/- 0.004(stat) +/- 0.001(syst). The result for the proton, assuming G(p)(E) = G(p)(M), is G(p)(M)(13.48 GeV(2)) = 0.014 +/- 0.002(stat) +/- 0.001(syst), which is in agreement with earlier results.     

Sintering of titanium dioxide nanoparticles: a comparison between molecular dynamics and phenomenological modeling

Molecular dynamics simulations were used to determine the melting points of anatase and rutile nanoparticles. The melting points decrease with decrease in particle diameter and are in reasonable agreement with the empirical formula derived by Buffat and Borel. The phenomenological model of Koch and Friedlander is unable to predict the temperature rise during initial stages of sintering with acceptable accuracy. It is argued that the Koch and Friedlander assumption of linear surface reduction rate upon sintering may be inadequate for the time scales under consideration. A theoretical model using direct area measurement from molecular dynamics simulations and a single adjustable parameter is able to predict temperature rise during initial stages of sintering within acceptable error limits.     

Random flights in Euclidean space. I. General analysis and results for flights with prescribed hit expectance density about the origin

We consider the problem of random flights in Euclidean space defined by a series of displacements, r_i, the magnitude and direction of each being independent of all the preceding ones. The displacements are not restricted to prescribed lattice sites. We begin with some new results generalizing a well-known latticewalk relation between the probability of return to the origin and the expected number of times the origin is visited in the course of a random walk. We go on to consider flights for which the hit expectancy is prescribed within a hypersphere of radiusR centered at the flight origin. For uniform hit expectance density (i.e., hit expectancy proportional to volume size) within the sphere, we solve the problem in three and five dimensions for a certain class of displacement probability densities that are prescribed only for displacement distancesr greater thanR. For each such displacement probability τ(r), we find both the value of the hit expectance density and the form of the displacement probability density forr that are dictated by the constraint of uniform hit expectance density within the sphere of radiusR. In an appendix, we show the way the common appearance of integral equations of Ornstein-Zernike type in problems of random flight, liquid and lattice-gas structure, and percolation theory yield certain corresponding results in all three areas.