An evaluation of potential locations for AROD ground stations

Airborne Range and Orbit Determination tracking stations potential locations evaluation and accuracy during early minutes of fligh

Generation and measurement of nonstationary random processes technical note no. 3

Generation and measurement of nonstationary stochastic processes related to Monte Carlo studies with analog compute

The New Industrial Organization and Small Business

The small business sector is an important part of the American economic landscape, in both absolute and relative terms. Despite its absolute growth, however, the sector accounts for a diminishing share of private sector activity. But its importance, and changes in importance, vary across industrial sectors of the economy. Drawing on the theoretical and empirical insights developed in recent books by John Sutton, we suggest that the presence or absence of endogenous strategic behaviors of the larger firms with respect to advertising, promotion, research and development, and other sunk cost expenditures may well play an important role in explaining the differing levels of small business importance, both cross-sectionally and over time. We conclude the paper with suggestions for research directions that could shed further light on these ideas

Assessment of practicality of remote sensing techniques for a study of the effects of strip mining in Alabama

Because of the volume of coal produced by strip mining, the proximity of mining operations, and the diversity of mining methods (e.g. contour stripping, area stripping, multiple seam stripping, and augering, as well as underground mining), the Warrior Coal Basin seemed best suited for initial studies on the physical impact of strip mining in Alabama. Two test sites, (Cordova and Searles) representative of the various strip mining techniques and environmental problems, were chosen for intensive studies of the correlation between remote sensing and ground truth data. Efforts were eventually concentrated in the Searles Area, since it is more accessible and offers a better opportunity for study of erosional and depositional processes than the Cordova Area

Pairing Correlations in the Two-Dimensional Hubbard Model

We present the results of a quantum Monte Carlo study of the extended $s$ and the $d_{x^2-y^2}$ pairing correlation functions for the two-dimensional Hubbard model, computed with the constrained-path method. For small lattice sizes and weak interactions, we find that the $d_{x^2-y^2}$ pairing correlations are stronger than the extended $s$ pairing correlations and are positive when the pair separation exceeds several lattice constants. As the system size or the interaction strength increases, the magnitude of the long-range part of both correlation functions vanishes.Comment: 4 pages, RevTex, 4 figures included; submitted to Phys. Rev. Let

A Two-dimensional Infinte System Density Matrix Renormalization Group Algorithm

It has proved difficult to extend the density matrix renormalization group technique to large two-dimensional systems. In this Communication I present a novel approach where the calculation is done directly in two dimensions. This makes it possible to use an infinite system method, and for the first time the fixed point in two dimensions is studied. By analyzing several related blocking schemes I find that there exists an algorithm for which the local energy decreases monotonically as the system size increases, thereby showing the potential feasibility of this method.Comment: 5 pages, 6 figure

The Hubble Space Telescope high speed photometer

The Hubble Space Telescope will provide the opportunity to perform precise astronomical photometry above the disturbing effects of the atmosphere. The High Speed Photometer is designed to provide the observatory with a stable, precise photometer with wide dynamic range, broad wavelenth coverage, time resolution in the microsecond region, and polarimetric capability. Here, the scientific requirements for the instrument are examined, the unique design features of the photometer are explored, and the improvements to be expected over the performance of ground-based instruments are projected

Gemini and Chandra observations of Abell 586, a relaxed strong-lensing cluster

We analyze the mass content of the massive strong-lensing cluster Abell 586 ($z = 0.17$). We use optical data (imaging and spectroscopy) obtained with the Gemini Multi-Object Spectrograph (GMOS) mounted on the 8-m Gemini-North telescope, together with publicly available X-ray data taken with the \textit{Chandra} space telescope. Employing different techniques -- velocity distribution of galaxies, weak gravitational lensing, and X-ray spatially resolved spectroscopy -- we derive mass and velocity dispersion estimates from each of them. All estimates agree well with each other, within a 68% confidence level, indicating a velocity dispersion of 1000 -- 1250 \kms. The projected mass distributions obtained through weak-lensing and X-ray emission are strikingly similar, having nearly circular geometry. We suggest that Abell 586 is probably a truly relaxed cluster, whose last major merger occurred more than $\sim 4$ Gyr agoComment: ApJ accepted, 20 pages, 11 figures; Figure 1 fixe

Scanning Electron Microscopic Examination of Intracanal Wall Dentin: Hand Versus Laser Treatment

Conventional cleaning and shaping of root canal spaces involves the use of hand and rotary instruments with irrigation. The procedure results in the formation of a smear layer consisting of dentin shavings, organic tissue remnants and microorganisms. The laser has been suggested as an aid in root canal preparation. In this study, pulsed and continuous wave 1.06 μm wavelength Nd:YAG lasers were used to compare their abilities to clean and shape root canal spaces to conventional methods. After preparation, the test teeth were sectioned longitudinally and examined by scanning electron microscopy. The results demonstrated that the laser was capable of removing the smear layer in its entirety and could occasionally alter dentin walls

Identification of the Physical Modification Threshold of Dentin Induced by Neodymium and Holmium YAG Lasers Using Scanning Electron Microscopy

Laser application to dentin has been advocated to modify the dentin substrate for restorative procedures. We examined the minimum energy density required to physically modify the dentin surface using 1.06 μm and 1.32 μm Neodymium:Yttrium-Aluminum-Garnet (Nd: YAG) and 2.10 μm Holmium-YAG (Ho: YAG) lasers. Three millimeter thick dentin sections from the middle occlusal third of crowns of third molars were used. To determine the effect of surface preparation, the sections were ground to 240, 320, 400, 600 grit or polished to 0.5 μm. Smear layer was removed using 0.5 M EDTA for 2 minutes. Five single pulse repetitions at each laser parameter were performed. Power (W) and energy per pulse (mJ/p) were increased for each wavelength until a physical modification occurred. The energy density (J/cm2) was then held constant and the threshold was confirmed using 200, 320 and 550 μm diameter quartz contact probes. Scanning electron microscopy (SEM) was used to verify the physical modification of the dentin. The physical threshold remained constant for ground and polished surfaces. Similar surface modifications were found for the three wavelengths tested. The threshold modifications occurred at 207, 165, and 83 J/cm2 for the 1.06 μm, 1.32 μm and 2.10 μm lasers, respectively. For all emission wavelengths tested the physical threshold modification occurred at relatively low energy densities. These lasers show promise for surface modification of dentin