Inclusive production of D-mesons in e+e− annihilation at 7 GeV

Inclusive momentum and energy spectra of neutral and charged D-mesons produced in e⁺e^? annihilation at energies near 7 GeV are presented. The slope of the energy spectrum is similar to the charged pion spectrum at the same energy. The inclusive cross section σ(e⁺e^?→ D or $\text{D}$ + anything) at 7 GeV is 4.8±1.3 nb.     

Wavelength modulation spectra of SbSI and its electronic band structure

The reflectivities of SbSI and their logarithmic derivatives between 1.8 and 4.5 eV have been measured at different temperatures. The structures in the reflectivities are compared with those calculated independently by the empirical pseudopotential method (EPM), using the pseudopotential form factors scaled from previous band structure calculations of other crystals. The large optical anisotropy of SbSI is explained. A preliminary band structure for SbSI is presented.     

Current-Driven Kink-Like Instability in Collisional Plasmas

The stability of left-hand circularly polarized waves propagating along an external magnetic field with wavelengths much larger than the ion Larmor radius is studied for fully-ionized collisional plasmas carrying a field-aligned current. It is found that, in the presence of electron-ion collisions, this "kink-like" instability has two branches of unstable wavenumbers: a main branch and a resistive branch. The resistive branch owes its existence to electron-ion collisions, but its growth rate is much smaller than that of the main branch, which is typically some fraction of the ion cyclotron frequency. The effect of collisions on the main branch is to reduce its maximum growth rate while extending the range of unstable wavenumbers to larger values. However, these changes are significant only when the electron-ion collision frequency is comparable to the electron cyclotron frequency. The dispersion relation is solved numerically for plasma and magnetic field parameters appropriate to the UCLA arcjet plasma. The results show that, within the framework of an infinite and homogeneous theory, the kink-like instability should occur in this plasma device.     

Resistive Electrostatic Ion Cyclotron Instability in Plasmas

The stability of electrostatic ion cyclotron waves propagating obliquely with respect to the background magnetic field is studied for collisional, fully-ionized plasmas in which there is a relative field-aligned streaming between electrons and ions. It is found that electron-ion collisions, in conjunction with electron streaming, provides a mechanism for instability. The role of electron streaming is to supply a source of free energy and the role of electron-ion collisions is to restrict the field-aligned mobility of the electrons, thus preventing them from establishing a Boltzmann equilibrium. Ion-ion collisions and finite ion Larmor radius are found to exert a stabilizing influence. The instability is analyzed for both current-carrying plasmas and counterstreaming-beam-plasma systems.     

The Dependence of the Air Blast Arc Characteristics on Electrode Position

The effect of the position of the upstream electrode on the characteristics of the air blast arc in a converging-diverging nozzle is investigated using a simple one-dimensional model. It is found that altering the upstream electrode position affects the pressure gradient between the electrode and the nozzle throat. The pressure gradient in this region determines to a large extent the arc area contraction rate as the arc current decreases to zero and, therefore, the interruption capability of the arc after current zero. Moreover, the upstream electrode position affects the arc diameter in the steady and transient states throughout the whole arc length. It is found that radial turbulent cooling need not be incorporated into the model to explain the experimental results. However, turbulent radial cooling, if present, is found to enhance the interruption capability of the arc by a large factor.     

Resistive lower-hybrid instability in current-carrying plasmas

Obliquely propagating lower hybrid waves are found to be unstable in a collisional, fully-ionized plasma carrying a field-aligned current.     

Fluoride determination by magnesium atomic absorption inhibition—release effects

The pH characteristics of fluoride inhibited magnesium atomic absorption signals distinguish them from other anions commonly present. The new technique involves addition of magnesium chloride and then acid to the sample solution while monitoring the magnesium atomic absorption signal. The signal enhancement due to the pH effect is proportional to flouride concentration. A sensitivity of 0.10 absorbance units/ppm F and a determination limit of 0.3 ppm F were found. Tap water fluoride determination results compare well with those for established methods. Various data point to a mechanism involving simple displacement of flouride in the refractory compound to form hydrogen fluoride.     

Electromagnetic Instability in Counterstreaming Collisional Plasmas in a Magnetic Field

The stability of low frequency electromagnetic waves is studied for collisional, counterstreaming plasmas situated in a steady magnetic field. Based on the cold fluid equations, it is found that obliquely propagating waves are unstable when the parallel component of the phase velocity is smaller than the electron streaming velocity. The frequency of the instability is of the order of but always smaller than the ion cyclotron frequency. The growth rate is proportional to the electron-ion collisional frequency.