Engineering works and the tidal Chesapeake

The tidal tributaries of the ocean and coastal areas of the mid-Atlantic region and the ecological significance of engineering projects are discussed. The effects of engineering works on maritime environments and resources, with the Chesapeake Bay as the area of prime interest are examined. Significant engineering projects, both actual and proposed, are described. The conflict of navigational demands and maintenance of an estuarine environment for commercial and sport fishing and recreation is described. Specific applications of remote sensors for analyzing ecological conditions of the bay are included

Southern Chesapeake Bay water color and circulation analysis

There are no author-identified significant results in this report

Deep imaging of Eridanus II and its lone star cluster

We present deep imaging of the most distant dwarf discovered by the Dark Energy Survey, Eridanus II (Eri II). Our Magellan/Megacam stellar photometry reaches $\sim$$3$ mag deeper than previous work, and allows us to confirm the presence of a stellar cluster whose position is consistent with Eri II's center. This makes Eri II, at $M_V=-7.1$, the least luminous galaxy known to host a (possibly central) cluster. The cluster is partially resolved, and at $M_V=-3.5$ it accounts for $\sim$$4\%$ of Eri II's luminosity. We derive updated structural parameters for Eri II, which has a half-light radius of $\sim$$280$ pc and is elongated ($\epsilon$$\sim$$0.48$), at a measured distance of $D$$\sim$$370$ kpc. The color-magnitude diagram displays a blue, extended horizontal branch, as well as a less populated red horizontal branch. A central concentration of stars brighter than the old main sequence turnoff hints at a possible intermediate-age ($\sim$$3$ Gyr) population; alternatively, these sources could be blue straggler stars. A deep Green Bank Telescope observation of Eri II reveals no associated atomic gas.Comment: 7 pages, 4 figures; ApJL accepte

Phase Transitions in a Dusty Plasma with Two Distinct Particle Sizes

In semiconductor manufacturing, contamination due to particulates significantly decreases the yield and quality of device fabrication, therefore increasing the cost of production. Dust particle clouds can be found in almost all plasma processing environments including both plasma etching devices and in plasma deposition processes. Dust particles suspended within such plasmas will acquire an electric charge from collisions with free electrons in the plasma. If the ratio of inter-particle potential energy to the average kinetic energy is sufficient, the particles will form either a liquid structure with short range ordering or a crystalline structure with long range ordering. Otherwise, the dust particle system will remain in a gaseous state. Many experiments have been conducted over the past decade on such colloidal plasmas to discover the character of the systems formed, but more work is needed to fully understand these structures. The preponderance of previous experiments used monodisperse spheres to form complex plasma systems

Antlia B: A faint dwarf galaxy member of the NGC 3109 association

We report the discovery of Antlia B, a faint dwarf galaxy at a projected distance of $\sim$72 kpc from NGC 3109 ($M_{V}$$\sim$$-$15 mag), the primary galaxy of the NGC 3109 dwarf association at the edge of the Local Group. The tip of the red giant branch distance to Antlia B is $D$=1.29$\pm$0.10 Mpc, which is consistent with the distance to NGC 3109. A qualitative analysis indicates the new dwarf's stellar population has both an old, metal poor red giant branch ($\gtrsim$10 Gyr, [Fe/H]$\sim$$-$2), and a younger blue population with an age of $\sim$200-400 Myr, analogous to the original Antlia dwarf, another likely satellite of NGC 3109. Antlia B has \ion{H}{1} gas at a velocity of $v_{helio,HI}$=376 km s$^{-1}$, confirming the association with NGC 3109 ($v_{helio}$=403 km s$^{-1}$). The HI gas mass (M$_{HI}$=2.8$\pm$0.2$\times$10$^{5}$ M$_{\odot}$), stellar luminosity ($M_{V}$=$-$9.7$\pm$0.6 mag) and half light radius ($r_{h}$=273$\pm$29 pc) are all consistent with the properties of dwarf irregular and dwarf spheroidal galaxies in the Local Volume, and is most similar to the Leo P dwarf galaxy. The discovery of Antlia B is the initial result from a Dark Energy Camera survey for halo substructure and faint dwarf companions to NGC 3109 with the goal of comparing observed substructure with expectations from the $\Lambda$+Cold Dark Matter model in the sub-Milky Way regime.Comment: 7 pages, 3 figures. Submitted to ApJ

Dusty Plasma Correlation Function Experiment

Dust particles immersed within a plasma environment, such as those in protostellar clouds, planetary rings or cometary environments, will acquire an electric charge. If the ratio of the inter-particle potential energy to the average kinetic energy is high enough the particles will form either a "liquid" structure with short-range ordering or a crystalline structure with long range ordering. Many experiments have been conducted over the past several years on such colloidal plasmas to discover the nature of the crystals formed, but more work is needed to fully understand these complex colloidal systems. Most previous experiments have employed monodisperse spheres to form Coulomb crystals. However, in nature (as well as in most plasma processing environments) the distribution of particle sizes is more randomized and disperse. This paper reports experiments which were carried out in a GEC rf reference cell modified for use as a dusty plasma system, using varying sizes of particles to determine the manner in which the correlation function depends upon the overall dust grain size distribution. (The correlation function determines the overall crystalline structure of the lattice.) Two dimensional plasma crystals were formed of assorted glass spheres with specific size distributions in an argon plasma. Using various optical techniques, the pair correlation function was determined and compared to those calculated numerically.Comment: 6 pages, Presented at COSPAR '0

A Comprehensive Archival Search for Counterparts to Ultra-Compact High Velocity Clouds: Five Local Volume Dwarf Galaxies

We report five Local Volume dwarf galaxies (two of which are presented here for the first time) uncovered during a comprehensive archival search for optical counterparts to ultra-compact high velocity clouds (UCHVCs). The UCHVC population of HI clouds are thought to be candidate gas-rich, low mass halos at the edge of the Local Group and beyond, but no comprehensive search for stellar counterparts to these systems has been presented. Careful visual inspection of all publicly available optical and ultraviolet imaging at the position of the UCHVCs revealed six blue, diffuse counterparts with a morphology consistent with a faint dwarf galaxy beyond the Local Group. Optical spectroscopy of all six candidate dwarf counterparts show that five have an H$\alpha$-derived velocity consistent with the coincident HI cloud, confirming their association, the sixth diffuse counterpart is likely a background object. The size and luminosity of the UCHVC dwarfs is consistent with other known Local Volume dwarf irregular galaxies. The gas fraction ($M_{HI}/M_{star}$) of the five dwarfs are generally consistent with that of dwarf irregular galaxies in the Local Volume, although ALFALFA-Dw1 (associated with ALFALFA UCHVC HVC274.68+74.70$-$123) has a very high $M_{HI}/M_{star}$$\sim$40. Despite the heterogenous nature of our search, we demonstrate that the current dwarf companions to UCHVCs are at the edge of detectability due to their low surface brightness, and that deeper searches are likely to find more stellar systems. If more sensitive searches do not reveal further stellar counterparts to UCHVCs, then the dearth of such systems around the Local Group may be in conflict with $\Lambda$CDM simulations.Comment: 18 pages, 4 tables, 4 figures, ApJ Accepte

Vertical pairing of identical particles suspended in the plasma sheath

It is shown experimentally that vertical pairing of two identical microspheres suspended in the sheath of a radio-frequency (rf) discharge at low gas pressures (a few Pa), appears at a well defined instability threshold of the rf power. The transition is reversible, but with significant hysteresis on the second stage. A simple model, which uses measured microsphere resonance frequencies and takes into account besides Coulomb interaction between negatively charged microspheres also their interaction with positive ion wake charges, seems to explain the instability threshold quite well.Comment: 4 pages, 6 figures. to appear in Phys. Rev. Lett. 86, May 14th (2001