Means for phase locking the outputs of a surface emitting laser diode array

An array of diode lasers, either a two-dimensional array of surface emitting lasers, or a linear array of stripe lasers, is phase locked by a diode laser through a hologram which focuses the output of the diode laser into a set of distinct, spatially separated beams, each one focused onto the back facet of a separate diode laser of the array. The outputs of the diode lasers thus form an emitted coherent beam out of the front of the array

Studying the adsorption of polymers and biomolecules on surfaces using enhanced sampling methods

We discuss how to use Wang-Landau simulations in an efficient manner to investigate the statistical mechanics of individual lattice polymers and peptides adsorbed at a planar surface. For nearest neighbor interactions, we show that a single Wang-Landau simulation, recording the density of states as a function of numbers of internal contacts and of surface beads, is sufficient to give a full description of the phase behavior of both adsorbed and desorbed states of single molecules. It is not necessary to introduce a second confining wall. Moreover, moves are never rejected due to overlap with the surface. The proposed “wall-free” method has already been applied to homo-polymers and hetero-polymers (lattice peptides using the HP model) on a uniform surface, and on regularly patterned surfaces. We give here a specific example to indicate how the relative adsorption strengths of a given peptide on different surfaces may be calculated

Research study of Beta Cephei variable stars using data from OAO-2

Photometric data from the Wisconsin Experiment package on OAO-2 were obtained for six Beta Cephei variable stars. The data were reduced in accordance with the OAO 2/Wisconsin Experiment Package Photometer Users Guide. For delta Cet and gamma Peg, there were enough data points to form reliable composite light curves at seven or eight ultraviolet wavelengths. The light curves are well represented by sine waves in phase with the blue light curve for each star. The amplitude of the light variation increases with shorter wavelengths. For theta Oph, epsilon Cen, eta Sco, and Lambda Sco, mean magnitudes and light ranges were obtained at several ultraviolet wavelengths. No significant differences were found between the mean, de-reddened ultraviolet colors of the observed stars, and the mean values for standard stars computed by Bottemiller. An attempt to derive a temperature scale from a comparison of the observed ultraviolet colors with Kurucz models was unsuccessful

Mode identification in Beta Cephei stars

The essential observational characteristics related to mode identification are summarized. Major emphasis is placed on the following: both light and velocity amplitudes; typical periods in both light and radial velocity; the light curve for Beta Cephei stars in comparison to the classical Cepheids and RR Lyrae stars; the van Hoof effect with respect to the radial velocity curves in many Beta Cephei stars; and the line profiles of many Beta Cephei stars

Bredon Homology of Partition Complexes

We prove that the Bredon homology or cohomology of the partition complex with fairly general coefficients is either trivial or computable in terms of constructions with the Steinberg module. The argument involves developing a theory of Bredon homology and cohomology approximation.Comment: 48 pages. Minor revisions. A typo in the statement of Corollary 1.2 was corrected, along with other typos. Some references have been adde

A simple method for designing or analyzing an optical communication link

A simple method is described for determining the performance of a free space optical communication link. The method can be used either in the system design (synthesis) mode or in the performance evaluation (analysis) mode. Although restricted to photo counting based detection of pulse position modulated signals, the method is still sufficiently general to accommodate space-based, as well as ground-based, reception

A cost-performance model for ground-based optical communications receiving telescopes

An analytical cost-performance model for a ground-based optical communications receiving telescope is presented. The model considers costs of existing telescopes as a function of diameter and field of view. This, coupled with communication performance as a function of receiver diameter and field of view, yields the appropriate telescope cost versus communication performance curve

Matematización : la necesidad "real" de la fluidez en las representaciones

Este artículo se ha escrito como reacción al de Luis Rico y otros, acerca de los “Sistemas de representación y aprendizaje de estructuras numéricas”

Geochemical Characterization of the Louann Salt, Puma Field, Green Canyon, Gulf of Mexico Basin – Using XRF and XRD

The Jurassic-aged Louann Salt is an evaporite sequence deposited in the Gulf of Mexico Basin (GOMB). It is an important component of the GOMB petroleum system and influences the facies pattern in overlying strata and the distribution of petroleum stratigraphic traps. The Louann Salt is composed primarily of halite with intercalated anhydrites and silty or sandy-halite intervals, with overall thicknesses in excess of four kilometers (~13,000 feet). Suture zones occur intermittently within the Louann Salt, formed by the collision of allochthonous evaporite layers. The mineralogy and geochemistry of the suture zones are currently understudied and can be hazardous during drilling operations, potentially causing over-pressurization of the zone. Furthermore, these evaporite bodies are potential sources for critical minerals or Rare Earth Elements, which can also lend insight into depositional conditions during the Jurassic. The focus of this study was to determine the bulk geochemistry of the allochthonous evaporite layers within the Louann Salt in the Puma Field of the GOMB. Geochemical analyses were performed by handheld X-ray fluorescence (XRF) on approximately 600 cutting samples from the Puma West GC821-002 well, ranging from 2,057 meters to 6,528 meters (6,750 feet to 21,420 feet) below the surface. X-ray diffraction (XRD) analyses were conducted on ten samples within the suture zone to determine its mineralogy. The results of the XRF analyses delineated the upper and lower boundaries of the Louann Salt by the inverse relationship between the chlorine and silicon elemental values. XRF analyses also indicate that the Louann Salt contains Rare Earth Elements (REEs) in the hundreds of part-per-million (ppm), such as Lanthanum (La), Praseodymium (Pa), Cerium (Ce), and Neodymium (Nd). REEs in the Louann are in concentrations equivalent to those being mined for economic value. XRD results indicate that the mineralogy of the suture zone is primarily composed of quartz, hematite, and smectite, with minor amounts of other clay minerals. This study provides insight into the depositional history of the Louann Salt and characteristics of the allochthonous bodies within the Louann for future mapping of the extent of these bodies in the GOMB