Interactions of a Light Hypersonic Jet with a Non-Uniform Interstellar Medium

We present three dimensional simulations of the interaction of a light hypersonic jet with an inhomogeneous thermal and turbulently supported disk in an elliptical galaxy. We model the jet as a light, supersonic non-relativistic flow with parameters selected to be consistent with a relativistic jet with kinetic power just above the FR1/FR2 break. We identify four generic phases in the evolution of such a jet with the inhomogeneous interstellar medium: 1) an initial ``flood and channel'' phase, where progress is characterized by high pressure gas finding changing weak points in the ISM, flowing through channels that form and re-form over time, 2) a spherical, energy-driven bubble phase, were the bubble is larger than the disk scale, but the jet remains fully disrupted close to the nucleus, 3) a rapid, jet break--out phase the where jet breaks free of the last dense clouds, becomes collimated and pierces the spherical bubble, and 4) a classical phase, the jet propagates in a momentum-dominated fashion leading to the classical jet + cocoon + bow-shock structure. Mass transport in the simulations is investigated, and we propose a model for the morphology and component proper motions in the well-studied Compact Symmetric Object 4C31.04.Comment: 66 pages, 22 figures, PDFLaTeX, aastex macros, graphicx and amssymb packages, Accepted, to be published 2007 ApJ

Lasing from a circular Bragg nanocavity with an ultra-small modal volume

We demonstrate single-mode lasing at telecommunication wavelengths from a circular nanocavity employing a radial Bragg reflector. Ultra-small modal volume and Sub milliwatt pump threshold level are observed for lasers with InGaAsP quantum well active membrane. The electromagnetic field is shown to be tightly confined within the 300nm central pillar of the cavity. The quality factors of the resonator modal fields are estimated to be on the order of a few thousands.Comment: 3 pages, 4 figures Submitted to AP

Expansion of pinched hypersurfaces of the Euclidean and hyperbolic space by high powers of curvature

We prove convergence results for expanding curvature flows in the Euclidean and hyperbolic space. The flow speeds have the form $F^{-p}$, where $p>1$ and $F$ is a positive, strictly monotone and 1-homogeneous curvature function. In particular this class includes the mean curvature $F=H$. We prove that a certain initial pinching condition is preserved and the properly rescaled hypersurfaces converge smoothly to the unit sphere. We show that an example due to Andrews-McCoy-Zheng can be used to construct strictly convex initial hypersurfaces, for which the inverse mean curvature flow to the power $p>1$ loses convexity, justifying the necessity to impose a certain pinching condition on the initial hypersurface.Comment: 18 pages. We included an example for the loss of convexity and pinching. In the third version we dropped the concavity assumption on F. Comments are welcom

Constraints on the age and dilution of Pacific Exploratory Mission-Tropics biomass burning plumes from the natural radionuclide tracer 210Pb

During the NASA Global Troposphere Experiment Pacific Exploratory Mission-Tropics (PEM-Tropics) airborne sampling campaign we found unexpectedly high concentrations of aerosol-associated 210Pb throughout the free troposphere over the South Pacific. Because of the remoteness of the study region, we expected specific activities to be generally less than 35 μBq m−3 but found an average in the free troposphere of 107 μBq m−3. This average was elevated by a large number of very active (up to 405 μBq m−3) samples that were associated with biomass burning plumes encountered on nearly every PEM-Tropics flight in the southern hemisphere. We use a simple aging and dilution model, which assumes that 222Rn and primary combustion products are pumped into the free troposphere in wet convective systems over fire regions (most likely in Africa), to explain the elevated 210Pb activities. This model reproduces the observed 210Pb activities very well, and predicts the ratios of four hydrocarbon species (emitted by combustion) to CO to better than 20% in most cases. Plume ages calculated by the model depend strongly on the assumed 222Rn activities in the initial plume, but using values plausible for continental boundary layer air yields ages that are consistent with travel times from Africa to the South Pacific calculated with a back trajectory model. The model also shows that despite being easily recognized through the large enhancements of biomass burning tracers, these plumes must have entrained large fractions of the surrounding ambient air during transport

The Sagnac effect in Coupled-Resonator Slow-Light Waveguide Structures

We study the effect of rotation on the propagation of electromagnetic waves in slow-light waveguide structures consisting of coupled micro-ring resonators. We show that such configurations exhibit new a type of the Sagnac effect which can be used for the realization of highly-compact integrated rotation sensors and gyroscopes

Shocks and sonic booms in the intracluster medium: X-ray shells and radio galaxy activity

Motivated by hydrodynamic simulations, we discuss the X-ray appearance of radio galaxies embedded in the intracluster medium (ICM) of a galaxy cluster. We distinguish three regimes. In the early life of a powerful source, the entire radio cocoon is expanding supersonically and hence drives a strong shock into the ICM. Eventually, the sides of the cocoon become subsonic and the ICM is disturbed by the sonic booms of the jet's working surface. In both of these regimes, X-ray observations would find an X-ray shell. In the strong shock regime, this shell will be hot and relatively thin. However, in the weak shock (sonic-boom) regime, the shell will be approximately the same temperature as the undisturbed ICM. If a cooling flow is present, the observed shell may even be cooler than the undisturbed ICM due to the lifting of cooler material into the shell from the inner (cooler) regions of the cluster. In the third and final regime, the cocoon has collapsed and no well-defined X-ray shell will be seen. We discuss ways of estimating the power and age of the source once its regime of behavior has been determined.Comment: 4 pages, submitted for publication in Astrophysical Journal. Full paper (including figure) can be obtained from http://rocinante.Colorado.EDU/~chris/papers/xray_hydro.p

Chemical and physical properties of bulk aerosols within four sectors observed during TRACE-P

Chemical and physical aerosol data collected on the DC-8 during TRACE-P were grouped into four sectors based on back trajectories. The four sectors represent long-range transport from the west (WSW), regional circulation over the western Pacific and Southeast Asia (SE Asia), polluted transport from northern Asia with substantial sea salt at low altitudes (NNW) and a substantial amount of dust (Channel). WSW has generally low mixing ratios at both middle and high altitudes, with the bulk of the aerosol mass due to non-sea-salt water-soluble inorganic species. Low altitude SE Asia also has low mean mixing ratios in general, with the majority of the aerosol mass comprised of non-sea-salts, however, soot is also relatively important in this region. NNW had the highest mean sea salt mixing ratios, with the aerosol mass at low altitudes (\u3c2 km) evenly divided between sea salts, non-sea-salts, and dust. The highest mean mixing ratios of water-soluble ions and soot were observed at the lowest altitudes (\u3c2 km) in the Channel sector. The bulk of the aerosol mass exported from Asia emanates from Channel at both low and midaltitudes, due to the prevalence of dust compared to other sectors. Number densities show enhanced fine particles for Channel and NNW, while their volume distributions are enhanced due to sea salt and dust. Low-altitude Channel exhibits the highest condensation nuclei (CN) number densities along with enhanced scattering coefficients, compared to the other sectors. At midaltitudes (2–7 km), low mean CN number densities coupled with a high proportion of nonvolatile particles (≥65%) observed in polluted sectors (Channel and NNW) are attributed to wet scavenging which removes hygroscopic CN particles. Low single scatter albedo in SE Asia reflects enhanced soot

Discovery of a Classic FR-II Broad Absorption Line Quasar from the FIRST Survey

We have discovered a remarkable quasar, FIRST J101614.3+520916, whose optical spectrum shows unambiguous broad absorption features while its double-lobed radio morphology and luminosity clearly indicate a classic Fanaroff-Riley Type II radio source. Its radio luminosity places it at the extreme of the recently established class of radio-loud broad absorption line quasars (Becker et al. 1997, 2000; Brotherton et al. 1998). Because of its hybrid nature, we speculate that FIRST J101614.3+520916 is a typical FR-II quasar which has been rejuvenated as a broad absorption line (BAL) quasar with a Compact Steep Spectrum core. The direction of the jet axis of FIRST J101614.3+520916 can be estimated from its radio structure and optical brightness, indicating that we are viewing the system at a viewing angle of > 40 degrees. The position angles of the radio jet and optical polarization are not well-aligned, differing by 20 to 30 degrees. When combined with the evidence presented by Becker et al. (2000) for a sample of 29 BAL quasars showing that at least some BAL quasars are viewed along the jet axis, the implication is that no preferred viewing orientation is necessary to observe BAL systems in a quasar's spectrum. This, and the probable young nature of compact steep spectrum sources, leads naturally to the alternate hypothesis that BALs are an early stage in the lives of quasars.Comment: 14 pages, 6 postscript figures; accepted for publication in the Astrophysical Journa

The impact of local sources and long-range transport on aerosol properties over the northeast U.S. region during INTEX-NA

We use data collected aboard the NASA DC-8 aircraft during the summer 2004, Intercontinental Transport and Chemical Evolution Experiment over North America (INTEX-NA) field campaign to examine the origin, composition, physical and optical properties of aerosols within air masses sampled over and downwind of the northeastern U.S. We note that aerosol concentrations within the region exhibited steep vertical gradients and significant variability in both time and space. An examination of air mass chemical signatures and backward trajectories indicates that transport from four, significantly different source regions contributed to the variability: the subtropical Atlantic Ocean (AO); the U.S. west coast and eastern Pacific (WCP); the U.S. east coast and Midwestern states (EC); and northwest Canada and Alaska (CA). AO air masses were typically confined to below 2 km altitude, exhibited low pollutant contents, contained enhanced levels of sea salt, and were typically observed when the Bermuda High strengthened. The most common air mass present in the upper troposphere, WCP air often contained weak dust and aged pollution enhances from convective input occurring over the central part of the continent. CA air exhibited enhancements in anthropogenic pollution tracers below 2 km and contained some black-carbon rich haze layers between 3 and 5 km that could be traced to forest fires burning in western Canada and Alaska. EC air was prevalent at lower elevations throughout the study area and exhibited enhanced scattering along with elevated levels of sulfate aerosols and combustion tracers. There is an overall balance between the observed cations and anions for all cases, except EC air mass below 4 km