Rensselaer Polytechnic Institute

About: Rensselaer Polytechnic Institute is a education organization based out in Troy, New York, United States. It is known for research contribution in the topics: Terahertz radiation & Population. The organization has 19024 authors who have published 39922 publications receiving 1414699 citations. The organization is also known as: RPI & Rensselaer Institute.

A Three-Position Spectral Line Survey of Sagittarius B2 between 218 and 263 GHZ. II. Data Analysis

Abstract: We present an analysis of the data from our Swedish-ESO Submillimetre Telescope molecular line survey in the 1.3 mm band of the N, M, and NW positions in the Sgr B2 molecular cloud. The line emissions from 42 molecular species, and some of their isotopomers, were analyzed assuming a single temperature and a homogeneous source. In cases where a source size much smaller than the antenna beam (23'') could be estimated, optical depth effects were also accounted for. In this way rotation temperatures, molecular column densities, and in several cases also source sizes, were determined. Observed and modeled intensities are presented in rotation diagrams. A few complex molecular species, NH2CHO, CH3CHO, C2H3CN, C2H5CN, and CH3OCHO, mainly in the N source, exhibit anomalously strong intensities in their intrinsically weak b- and c-type lines. We argue that this effect can hardly be explained by high optical depths alone, and therefore propose that the possibility of radiative pumping via the low-lying vibrational states of these molecules should be investigated as an alternative explanation. The highest rotation temperatures, up to about 500 K, were found for large molecules toward Sgr B2(N), closely followed by Sgr B2(M). In Sgr B2(NW), which samples the cloud envelope, the rotation temperatures are 15-50 K. For molecules with too few observed transitions to allow determination of rotation temperatures, the column density was calculated assuming optically thin emission, and we adopted rotation temperatures of 50, 50, and 20 K in M, N, and NW, respectively. Column density ratios of isotopomers were determined. After a critical discussion of the resolution-dependent H2 column density toward the observed positions, abundances relative to H2 were calculated. We discuss the chemical differences between the three observed cloud positions and compare with the hot core, compact ridge, and outflow in Orion A. Hot core-type molecules like CH2NH, NH2CN, CH3CN, C2H3CN, and C2H5CN, as well as H2CS, are more abundant in Sgr B2(N) by factors of 3-8 as compared to the M position. Large oxygen-containing species like CH3OH, CH3CHO, CH3OCHO, CH3OCH3, and NH2CHO, of compact ridge-type, show similar or slightly enhanced abundances in N as compared to M. The C2H5OH abundances are similar in N, M, and also in NW. The SO2 and SO abundances in the M core (4 × 10-7 and 1 × 10-7, respectively) are 13 and 5 times higher than in N and are very enhanced (103 and 102 times) as compared to NW. Such high SO2 and SO abundances are also found in the prominent Orion A outflow source. In M the SO18O and S18O data suggest a 16O/18O ratio of 120. The HOCO+ ion is detected in all three positions and appears to be 3 times more abundant in the NW position. HCNH+ is seen only in NW.

Mechanism of action of nalidixic acid on escherichia coli.

Abstract: Goss, William A. (Sterling-Winthrop Research Institute, Rensselaer, N.Y.), William H. Dietz, and Thomas M. Cook. Mechanism of action of nalidixic acid on Escherichia coli. J. Bacteriol. 88:1112-1118. 1964.-Nalidixic acid was lethal for proliferating cultures of Escherichia coli. Associated with this lethal effect was the formation of elongated, serpentine forms. Cultures treated with nalidixic acid were osmotically stable; lethality was observed in the presence of stabilizers. Although it was possible to demonstrate leakage of intracellular components from treated cells, this effect occurred only after 99% of the cells were nonviable. Nalidixic acid had little or no effect on respiration with glucose as substrate. If cellular growth was restricted by suboptimal temperature or nutritional deficiencies, the drug was not lethal. Chemical analysis of cellular constituents revealed that lipid, protein, and ribonucleic acid levels were of the same order of magnitude in control and drug-treated cells. Only deoxyribonucleic acid (DNA) levels were markedly lowered in drug-treated cells. These facts are consistent with the view that nalidixic acid interferes with the synthesis of E. coli DNA.

Image restoration by the method of generalized projections with application to restoration from magnitude

Abstract: The method of projections onto convex sets can be used to solve many problems in image restoration, e.g., restoration from phase, spectral extrapolation, and signal recovery in computer-aided tomography. However, image-restoration problems involving nonconvex constraints cannot be handled by the method of projection onto convex sets in a fashion that ensures convergence. The restoration-from-magnitude (RFM) problem is such a case. To handle the RFM as well as other nonconvex constraints, we describe an algorithm known as generalized projections and discuss its properties. When sets are nonconvex, it is possible for the algorithm to exhibit pathological behavior that is never manifest in convex projections. We introduce an error criterion called the summed-distance error (SDE) and show under what circumstances the SDE is a monotonically decreasing function of the number of iterations. Near-optimum performance of the algorithm is achieved by relaxation parameters. Comparisons with other RFM methods are furnished for synthetic imagery.

The discovery of a luminous z = 5.80 quasar from the sloan digital sky survey

Abstract: We present observations of SDSSp J104433.04-012502.2, a luminous quasar at z = 5.80 discovered from Sloan Digital Sky Survey (SDSS) multicolor imaging data. This object was selected as an i'-band dropout object, with i* = 21.8 ± 0.2 and z* = 19.2 ± 0.1. It has an absolute magnitude M1450 = -27.2 (H0 = 50 km s-1 Mpc-1, q0 = 0.5). The spectrum shows a strong and broad Lyα emission line, strong Lyα forest absorption lines with a mean continuum decrement DA = 0.91 and a Lyman limit system at z = 5.72. The spectrum also shows strong O I and Si IV emission lines similar to those of quasars at z 5, suggesting that these metals were produced at a redshift beyond 6. The lack of a Gunn-Peterson trough in the spectrum indicates that the universe is already highly ionized at z ~ 5.8. Using a high-resolution spectrum in the Lyα forest region, we place a conservative upper limit on the optical depth because of the Gunn-Peterson effect of τ < 0.5 in regions of minimum absorption. The Lyα forest absorption in this object is much stronger than that in quasars at z 5. The object is unresolved in a deep image with excellent seeing, implying that it is unlensed. The black hole mass of this quasar is ~3 × 109 M⊙ if we assume no lensing amplification and that it is radiating at the Eddington luminosity, implying that it resides in a very massive dark matter halo. The discovery of one quasar at M1450 < -27 in a survey area of 600 deg2 is consistent with an extrapolation of the observed luminosity function at lower redshifts. The abundance and evolution of such quasars can provide sensitive tests for models of quasar and galaxy formation.

Three-dimensional cellular microarray for high-throughput toxicology assays.

Abstract: We have developed a miniaturized 3D cell-culture array (the Data Analysis Toxicology Assay Chip or DataChip) for high-throughput toxicity screening of drug candidates and their cytochrome P450-generated metabolites. The DataChip consists of human cells encapsulated in collagen or alginate gels (as small as 20 nl) arrayed on a functionalized glass slide for spatially addressable screening against multiple compounds. A single DataChip containing 1,080 individual cell cultures, used in conjunction with the complementary human P450-containing microarray (the Metabolizing Enzyme Toxicology Assay Chip or MetaChip), simultaneously provided IC 50 values for nine compounds and their metabolites from CYP1A2, CYP2D6, and CYP3A4 and a mixture of the three P450s designed to emulate the human liver. Similar responses were obtained with the DataChip and conventional 96-well plate assays, demonstrating that the near 2,000-fold miniaturization does not influence the cytotoxicity response. The DataChip may therefore enable toxicity analyses of drug candidates and their metabolites at throughputs compatible with the availability of compounds at early-stage drug discovery.