Method for measuring the characteristics of a gas Patent

Device for simultaneously determining density, velocity, and temperature of streaming ga

Electrostatic plasma modulator for space vehicle re-entry communication Patent

Electrostatic modulator for communicating through plasma sheath formed around spacecraft during reentr

Using Three-Body Recombination to Extract Electron Temperatures of Ultracold Plasmas

Three-body recombination, an important collisional process in plasmas, increases dramatically at low electron temperatures, with an accepted scaling of T_e^-9/2. We measure three-body recombination in an ultracold neutral xenon plasma by detecting recombination-created Rydberg atoms using a microwave-ionization technique. With the accepted theory (expected to be applicable for weakly-coupled plasmas) and our measured rates we extract the plasma temperatures, which are in reasonable agreement with previous measurements early in the plasma lifetime. The resulting electron temperatures indicate that the plasma continues to cool to temperatures below 1 K.Comment: 5 pages, 3 figure

OPserver: interactive online-computations of opacities and radiative accelerations

Codes to compute mean opacities and radiative accelerations for arbitrary chemical mixtures using the Opacity Project recently revised data have been restructured in a client--server architecture and transcribed as a subroutine library. This implementation increases efficiency in stellar modelling where element stratification due to diffusion processes is depth dependent, and thus requires repeated fast opacity reestimates. Three user modes are provided to fit different computing environments, namely a web browser, a local workstation and a distributed grid.Comment: 5 pages, 1 figur

Low-Altitude Reconnection Inflow-Outflow Observations during a 2010 November 3 Solar Eruption

For a solar flare occurring on 2010 November 3, we present observations using several SDO/AIA extreme-ultraviolet (EUV) passbands of an erupting flux rope followed by inflows sweeping into a current sheet region. The inflows are soon followed by outflows appearing to originate from near the termination point of the inflowing motion - an observation in line with standard magnetic reconnection models. We measure average inflow plane-of-sky speeds to range from ~150-690 km/s with the initial, high-temperature inflows being the fastest. Using the inflow speeds and a range of Alfven speeds, we estimate the Alfvenic Mach number which appears to decrease with time. We also provide inflow and outflow times with respect to RHESSI count rates and find that the fast, high-temperature inflows occur simultaneously with a peak in the RHESSI thermal lightcurve. Five candidate inflow-outflow pairs are identified with no more than a minute delay between detections. The inflow speeds of these pairs are measured to be 10^2 km/s with outflow speeds ranging from 10^2-10^3 km/s - indicating acceleration during the reconnection process. The fastest of these outflows are in the form of apparently traveling density enhancements along the legs of the loops rather than the loop apexes themselves. These flows could either be accelerated plasma, shocks, or waves prompted by reconnection. The measurements presented here show an order of magnitude difference between the retraction speeds of the loops and the speed of the density enhancements within the loops - presumably exiting the reconnection site.Comment: 31 pages, 13 figures, 1 table, Accepted to ApJ (expected publication ~July 2012

Line emission from gamma-ray burst environments

The time and angle dependent line and continuum emission from a dense torus around a cosmological gamma-ray burst source is simulated, taking into account photoionization, collisional ionization, recombination, and electron heating and cooling due to various processes. The importance of the hydrodynamical interaction between the torus and the expanding blast wave is stressed. Due to the rapid deceleration of the blast wave as it interacts with the dense torus, the material in the torus will be illuminated by a drastically different photon spectrum than observable through a low-column-density line of sight, and will be heated by the hydrodynamical interaction between the blast wave and the torus. A model calculation to reproduce the Fe K-alpha line emission observed in the X-ray afterglow of GRB 970508 is presented. The results indicate that ~ 10^{-4} solar masses of iron must be concentrated in a region of less than 10^{-3} pc. The illumination of the torus material due to the hydrodynamic interaction of the blast wave with the torus is the dominant heating and ionization mechanism leading to the formation of the iron line. These results suggest that misaligned GRBs may be detectable as X-ray flashes with pronounced iron emission line features.Comment: Accepted for publication in ApJ. Updated recombination rate data; discussion on element abundances added; references update

Magnetic Correlation Length and Universal Amplitude of the Lattice E_8 Ising Model

The perturbation approach is used to derive the exact correlation length $\xi$ of the dilute A_L lattice models in regimes 1 and 2 for L odd. In regime 2 the A_3 model is the E_8 lattice realisation of the two-dimensional Ising model in a magnetic field h at T=T_c. When combined with the singular part f_s of the free energy the result for the A_3 model gives the universal amplitude $f_s \xi^2 = 0.061~728...$ as $h\to 0$ in precise agreement with the result obtained by Delfino and Mussardo via the form-factor bootstrap approach.Comment: 7 pages, Late

The Ha Luminosity Function and Star Formation Rate at z\sim 0.2

We have measured the Ha+[N II] fluxes of the I-selected Canada-France Redshift Survey (CFRS) galaxies lying at a redshift z below 0.3, and hence derived the Ha luminosity function. The magnitude limits of the CFRS mean that only the galaxies with M(B) > -21 mag were observed at these redshifts. We obtained a total Ha luminosity density of at least 10^{39.44\pm 0.04} erg/s/Mpc^{3} at a mean z=0.2 for galaxies with rest-fame EW(Ha+[N II]) > 10 Angs. This is twice the value found in the local universe by Gallego et al. 1995. Our Ha star formation rate, derived from Madau (1997) is higher than the UV observations at same z, implying a UV dust extinction of about 1 mag. We found a strong correlation between the Ha luminosity and the absolute magnitude in the B-band: M(B(AB)) = 46.7 - 1.6 log L(Ha). This work will serve as a basis of future studies of Ha luminosity distributions measured from optically-selected spectroscopic surveys of the distant universe, and it will provide a better understanding of the physical processes responsible for the observed galaxy evolution.Comment: Accepted for publication in ApJ, 14 pages, LaTeX (macro aas2pp4.sty), 6 figure

An exact universal amplitude ratio for percolation

The universal amplitude ratio $\tilde{R}_{\xi}$ for percolation in two dimensions is determined exactly using results for the dilute A model in regime 1, by way of a relationship with the q-state Potts model for q<4.Comment: 5 pages, LaTeX, submitted to J. Phys. A. One paragraph rewritten to correct error

Excitation of the 3.071mm Hyperfine Line in Li-Like 57-Fe in Astrophysical Plasmas

As noted first by Sunyaev & Churazov (1984), the 3.071 mm hyperfine line from $^{57}Fe^{+23}$ might be observable in astrophysical plasmas. We assess the atomic processes which might contribute to the excitation of this line. We determine the intensity of the hyperfine line from an isothermal, coronal plasma in collisional ionization equilibrium and for a coronal plasma cooling isobarically due to its own radiation. Comparisons of the hyperfine line to other lines emitted by the same ion, Fe$^{+23}$, are shown to be useful for deriving the isotopic fraction of $^{57}$Fe. We calculate the ratios of the hyperfine line to the 2s--2p EUV lines at 192 \AA and 255 \AA, and the 2s--3p X-ray doublet at 10.6 \AA.Comment: 28 pages text+figures, Accepted to ApJ in Jan 98, also at http://www.astro.virginia.edu/~nld2n/research.htm