High speed techniques for synthetic aperture radar image formation

One possible approach to high speed synthetic aperture radar signal reconstruction involves the utilization of two dimensional real time spatial light modulators as recyclable replacements for photographic film in the input transducer plane of a modified synthetic aperture radar (SAR) coherent optical processor. Leading candidate spatial light modulators include modified Pockels readout optical modulators (PROM), charge coupled devices (CCD) addressed liquid crystal light valves, and CCD addressed membrane light modulators. The fundamental physical limitations affecting SAR processor performance characteristics of such real time devices are under investigation. Current research on PROM is focused on the effects of device operatonal mode, device constitutive parameters, electro-optic crystal orientation, writing wavelength, frame rate/data overwrite/presuming, erasure completeness, and image retention on the overall quality of SAR image formation. Both modulated laser scanning and intensified CRT temporal to spatial input approaches are being examined

A Surveillance of the Causes of Mortality in Three South Dakota Layer Flocks

A surveillance program was conducted during June 1968 through June 1969 to determine the important causes of mortality in certain South Dakota layer flocks that experienced reasonably normal mortality

Free circular introns with an unusual branchpoint in neuronal projections

The polarized structure of axons and dendrites in neuronal cells depends in part on RNA localization. Previous studies have looked at which polyadenylated RNAs are enriched in neuronal projections or at synapses, but less is known about the distribution of non-adenylated RNAs. By physically dissecting projections from cell bodies of primary rat hippocampal neurons and sequencing total RNA, we found an unexpected set of free circular introns with a non-canonical branchpoint enriched in neuronal projections. These introns appear to be tailless lariats that escape debranching. They lack ribosome occupancy, sequence conservation, and known localization signals, and their function, if any, is not known. Nonetheless, their enrichment in projections has important implications for our understanding of the mechanisms by which RNAs reach distal compartments of asymmetric cells

PKS B1545-321: Bow shocks of a relativistic jet?

Sensitive, high resolution images of the double-double radio galaxy PKS B1545-321 reveal detailed structure, which we interpret in the light of previous work on the interaction of restarted jets with pre-existing relict cocoons. We have also examined the spectral and polarization properties of the source, the color distribution in the optical host and the environment of this galaxy in order to understand its physical evolution. We propose that the restarted jets generate narrow bow shocks and that the inner lobes are a mixture of cocoon plasma reaccelerated at the bow shock and new jet material reaccelerated at the termination shock. The dynamics of the restarted jets implies that their hot spots advance at mildly relativistic speeds with external Mach numbers of at least 5. The existence of supersonic hot spot Mach numbers and bright inner lobes is the result of entrainment causing a reduction in the sound speed of the pre-existing cocoon. The interruption to jet activity in PKS B1545-321 has been brief - lasting less than a few percent of the lifetime $\sim (0.3-2)\times 10^{8} yr$ of the giant radio source. The host galaxy is located at the boundary of a large scale filamentary structure, and shows blue patches in color distribution indicative of a recent merger, which may have triggered the Mpc-scale radio galaxy.Comment: 26 pages including 1 table and 16 figures. To appear in MNRA

Equation of state and transport processes in self--similar spheres

We study the effect of transport processes (diffusion and free--streaming) on a collapsing spherically symmetric distribution of matter in a self--similar space--time. A very simple solution shows interesting features when it is matched with the Vaidya exterior solution. In the mixed case (diffusion and free--streaming), we find a barotropic equation of state in the stationary regime. In the diffusion approximation the gravitational potential at the surface is always constant; if we perturb the stationary state, the system is very stable, recovering the barotropic equation of state as time progresses. In the free--streaming case the self--similar evolution is stationary but with a non--barotropic equation of state.Comment: 9 pages, 2 figure

The Twin-Jet of NGC1052 at Radio, Optical, and X-ray Frequencies

We present results from a combined radio, optical, and X-ray study of the jet-associated emission features in NGC1052. We analyse the radio-optical morphology and find a good positional correlation between the radio jet and the optical emission cone. Two optical emission knots are directly associated with radio counterparts exhibiting a radio to X-ray broadband spectrum not compatible with synchrotron emission. We discuss the possibility that the thermal soft spectrum of the extended X-ray emission originates from jet driven shocks produced in the interaction between the jet-plasma and its surrounding medium.Comment: 4 pages, 1 figure, needs elsart.cls, to be published in ''The Physics of Relativistic Jets in the CHANDRA and XMM Era'', G. Brunetti, D.E. Harris, R.M. Sambruna, G. Setti (eds.

Convergence to a self-similar solution in general relativistic gravitational collapse

We study the spherical collapse of a perfect fluid with an equation of state $P=k\rho$ by full general relativistic numerical simulations. For 0, it has been known that there exists a general relativistic counterpart of the Larson-Penston self-similar Newtonian solution. The numerical simulations strongly suggest that, in the neighborhood of the center, generic collapse converges to this solution in an approach to a singularity and that self-similar solutions other than this solution, including a ``critical solution'' in the black hole critical behavior, are relevant only when the parameters which parametrize initial data are fine-tuned. This result is supported by a mode analysis on the pertinent self-similar solutions. Since a naked singularity forms in the general relativistic Larson-Penston solution for 0, this will be the most serious known counterexample against cosmic censorship. It also provides strong evidence for the self-similarity hypothesis in general relativistic gravitational collapse. The direct consequence is that critical phenomena will be observed in the collapse of isothermal gas in Newton gravity, and the critical exponent $\gamma$ will be given by $\gamma\approx 0.11$, though the order parameter cannot be the black hole mass.Comment: 22 pages, 15 figures, accepted for publication in Physical Review D, reference added, typos correcte

A new duality transformation for fourth-order gravity

We prove that for non-linear L = L(R), the Lagrangians L and \hat L give conformally equivalent fourth-order field equations being dual to each other. The proof represents a new application of the fact that the operator is conformally invariant.Comment: 11 pages, LaTeX, no figures. Gen. Relat. Grav. in prin

Jet-Induced Emission-Line Nebulosity and Star Formation in the High-Redshift Radio Galaxy 4C41.17

The high redshift radio galaxy 4C41.17 consists of a powerful radio source in which previous work has shown that there is strong evidence for jet-induced star formation along the radio axis. We argue that nuclear photoionization is not responsible for the excitation of the emission line clouds and we construct a jet-cloud interaction model to explain the major features revealed by the data. The interaction of a high-powered jet with a dense cloud in the halo of 4C41.17 produces shock-excited emission-line nebulosity through ~1000 km/s shocks and induces star formation. The CIII to CIV line ratio and the CIV luminosity emanating from the shock, imply that the pre-shock density in the line-emitting cloud is high enough (~1-10 cm^-3) that shock initiated star formation could proceed on a timescale of order a few x 10^6 yrs, well within the estimated dynamical age of the radio source. Broad (FWHM ~ 100 - 1400 km/s) emission lines are attributed to the disturbance of the gas cloud by a partial bow--shock and narrow emission lines (FWHM ~ 500 - 650 km/s) (in particular CIV) arise in precursor emission in relatively low metallicity gas. The implied baryonic mass ~ 8 \times 10^{10} solar masses of the cloud is high and implies that Milky Way size condensations existed in the environments of forming radio galaxies at a redshift of 3.8. Our interpretation of the data provides a physical basis for the alignment of the radio, emission-line and UV continuum images in some of the highest redshift radio galaxies and the analysis presented here may form a basis for the calculation of densities and cloud masses in other high redshift radio galaxies.Comment: 18 pages, 5 figures; uses astrobib.sty and aaspp4.sty. Better versions of figures available via anonymous from ftp://mso.anu.edu.au:pub/pub/geoff/4C41.1