Dielectric response of a relativistic degenerate electron plasma in a strong magnetic field

The longitudinal dielectric response of a relativistic ultra-degenerate electron plasma in a strong magnetic field is obtained via a relativistic generalization of the Hartree self-consistent field method. Dispersion relations and damping conditions for plasma oscillations both parallel and perpendicular to the magnetic field are obtained. We also give detailed results for the zero-field case. Applications to white dwarf stars and pulsars are given.     

metamagnetic behavior of linear chain pyridine compounds: Co(Pyridine)2Cl2, Fe(Pyridine)2Cl2, Fe(Pyridine)2(NCS)2 and Ni(Pyridine)2Cl2

Magnetic phase transitions in the pyridine (pyr) compounds Co(pyr)₂Cl₂, Fe(pyr)₂Cl₂, Fe(pyr)₂(NCS)₂ and Ni(pyr)₂Cl₂ have been observed at applied magnetic fields of ～0.7, 0.7, 1.1 and 2.7 kG respectively. These low field phase transitions are observed in the Fe and Ni compounds at T = 4.2 K, and in the Co compound at T < 3K, and are consistent with metamagnetic behavior. Magnetic saturation is not achieved in any of these compounds for fields of 60 kG, reflecting high anisotropy.     

Experimental verification of the quasi-steady approximation for aerodynamic sound generation by pulsating jets in tubes

Voice production involves sound generation by a confined jet flow through an orifice (the glottis) with a time-varying area. Predictive models of speech production are usually based on the so-called quasi-steady approximation. The flow rate through the time-varying orifice is assumed to be the same as a sequence of steady flows through stationary orifices for wall geometries and flow boundary conditions that instantaneously match those of the dynamic, nonstationary problem. Either the flow rate or the pressure drop can then be used to calculate the radiated sound using conventional acoustic radiation models. The quasi-steady approximation allows complex unsteady flows to be modeled as steady flows, which is more cost effective. It has been verified for pulsating open jet flows. The quasi-steady approximation, however, has not yet been rigorously validated for the full range of flows encountered in voice production. To further investigate the range of validity of the quasi-steady approximation for voice production applications, a dynamic mechanical model of the larynx was designed and built. The model dimensions approximated those of human vocal folds. Airflow was supplied by a pressurized, quiet air storage facility and modulated by a driven rubber orifice. The acoustic pressure of waves radiated upstream and downstream of the orifice was measured, along with the orifice area and other time-averaged flow variables. Calculated and measured radiated acoustic pressures were compared. A good agreement was obtained over a range of operating frequencies, flow rates, and orifice shapes, confirming the validity of the quasi-steady approximation for a class of relevant pulsating jet flows.     

Broadband sound generation by confined turbulent jets

Sound generation by confined stationary jets is of interest to the study of voice and speech production, among other applications. The generation of sound by low Mach number, confined, stationary circular jets was investigated. Experiments were performed using a quiet flow supply, muffler-terminated rigid uniform tubes, and acrylic orifice plates. A spectral decomposition method based on a linear source-filter model was used to decompose radiated nondimensional sound pressure spectra measured for various gas mixtures and mean flow velocities into the product of (1) a source spectral distribution function; (2) a function accounting for near field effects and radiation efficiency; and (3) an acoustic frequency response function. The acoustic frequency response function agreed, as expected, with the transfer function between the radiated acoustic pressure at one fixed location and the strength of an equivalent velocity source located at the orifice. The radiation efficiency function indicated a radiation efficiency of the order (kD)2 over the planar wave frequency range and (kD)4 at higher frequencies, where k is the wavenumber and D is the tube cross sectional dimension. This is consistent with theoretical predictions for the planar wave radiation efficiency of quadrupole sources in uniform rigid anechoic tubes. The effects of the Reynolds number, Re, on the source spectral distribution function were found to be insignificant over the range 20002.5. The influence of a reflective open tube termination on the source function spectral distribution was found to be insignificant, confirming the absence of a feedback mechanism.     

Measurements ofn−p correlations in the reaction of relativistic neon with uranium

We report a preliminary measurement of coincident neutron-proton pairs emitted at 45° in the interaction of 400, 530, and 650 MeV/A neon beams incident on uranium. Charged particles were identified by time of flight and momentum, as determined in a magnetic spectrometer. Neutral particles were detected using a thick plastic scintillator, and their time of flight was measured between an entrance scintillator, triggered by a charged particle, and the neutron detector. The scatter plots and contour plots of neutron momentum vs. proton momentum appear to show a slight correlation ridge above an uncorrelated background. The projections of this plane on then-p momentum difference axis are essentially flat, showing a one standard deviation enhancement for each of the three beams energies. At each beam energy, the calculated momentum correlation function for the neutron-proton pairs is enhanced near zero neutron-proton momentum difference by approximately one standard deviation over the expected value for no correlation. This enhancement is expected to occur as a consequence of the attractive final state interaction between the neutron and proton (i.e., virtual or “singlet” deuterons). The implications of these measurements are discussed.     

Binding of Fe2+ by mammalian ferritin

An average of 140 Fe²⁺ ions bind to mammalian ferritin that has an average core content of 1876 Fe³⁺ ions per molecule. The Fe²⁺ ions enter the protein interior and exchange electrons with the core Fe³⁺ ions. A non-homogeneous model for the iron-containing core of ferritin is proposed.     

Electrodynamics of bounded spatially dispersive media: The additional boundary conditions

The eigenfunction for the center of mass motion of a Mott-Wannier exciton in a bounded medium has been determined by solving asymptotically an effective mass equation, assuming electron and hole reflect perfectly from the surface: the surface potential is taken as an infinite barrier. Using this eigenfunction, the non-local susceptibility was determined. From it the relevant additional boundary condition for this model follows: the total flux associated with the sum of the polarization waves vanishes at the surface.