36,408 research outputs found

    Light Element X-Ray Microanalysis in Biology

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    It is shown that both qualitative and quantitative light element X-ray microanalysis of biological samples is feasible. These analyses were carried out using ultrathin window (UTW) detectors. Quantitative analysis yields a total element analysis with H estimated by difference or guesstimated . Comparison with calculated concentrations, or concentrations obtained by chemical analysis, shows that X-ray microanalysis of sections, by the peak to continuum ratio model, give sufficiently accurate results for biological purposes. The measurement of O concentrations to yield water content is carried out using x-ray imaging techniques, so that the distribution of heavier elements can be spatially related to water and dry mass distribution. Similarly light element and heavy/light element ratios are readily visualised by X-ray imaging. These ratios can indicate the subcellular distribution of different molecular species e.g., nitrogenous compounds such as urates. It is possible to derive quantitative images of water distribution in both sections and bulk samples. Comparisons of the same sample type both as frozen sections and frozen bulk samples show that the water estimates obtained by the two different analytical methods are similar. Oxygen analysis of C films at different specimen temperatures unequivocally reveals the temperature at which ice deposition on the specimen commences. This establishes safe conditions for reducing mass loss in model samples and freeze-dried sections to minimal levels and for avoiding artefactual oxygen analyses of both frozen-hydrated and freeze-dried sections

    Iridium-coated rhenium thrusters by CVD

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    Operation of spacecraft thrusters at increased temperature reduces propellant requirements. Inasmuch as propellant comprises the bulk of a satellite's mass, even a small percentage reduction makes possible a significant enhancement of the mission in terms of increased payload. Because of its excellent high temperature strength, rhenium is often the structural material of choice. It can be fabricated into free-standing shapes by chemical vapor deposition (CVD) onto an expendable mandrel. What rhenium lacks is oxidation resistance, but this can be provided by a coating of iridium, also by CVD. This paper describes the process used by Ultramet to fabricate 22-N (5-lbf) and, more recently, 445-N (100-lbf) Ir/Re thrusters; characterizes the CVD-deposited materials; and summarizes the materials effects of firing these thrusters. Optimal propellant mixture ratios can be employed because the materials withstand an oxidizing environment up to the meltimg temperature of iridium, 2400 C (4350 F)

    Assessing Input Brand Loyalty among U.S. Agricultural Producers

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    This study explores the prevalence and determinants of brand loyalty for agricultural input products. Results suggest that loyalty for both expendable and capital inputs is high among commercial agricultural producers in the United States. Producer attitudes, beliefs, and some demographic characteristics are useful identifiers of brand loyalty among commercial producers.brand loyalty, dealer loyalty, capital inputs, expendable inputs, farmer purchase decisions, Agricultural Finance, Consumer/Household Economics, Marketing, Q10, Q13, Q14,

    Assessing Agricultural Input Brand Loyalty Among U.S. Mid-Size and Commercial Producers

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    This study explores the prevalence and determinants of brand loyalty for agricultural input products. Results suggest that loyalty for both expendable and capital inputs is high among commercial farmers. Farmer attitudes, beliefs, and some demographic characteristics are useful identifiers of brand loyal farmers.brand loyalty, capital inputs, expendable inputs, farmer purchase decisions, Farm Management,

    The Nature of Deeply Buried Ultraluminous Infrared Galaxies: A Unified Model for Highly Obscured Dusty Galaxy Emission

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    We present models of deeply buried ultraluminous infrared galaxy (ULIRG) spectral energy distributions (SEDs) and use them to construct a three-dimensional diagram for diagnosing the nature of observed ULIRGs. Our goal is to construct a suite of SEDs for a very simple model ULIRG structure, and to explore how well this simple model can (by itself) explain the full range of observed ULIRG properties. We use our diagnostic to analyze archival Spitzer Space Telescope IRS spectra of ULIRGs and find that: (1) In general, our model does provide a comprehensive explanation of the distribution of mid-IR ULIRG properties; (2) >75% (in some cases 100%) of the bolometric luminosities of the most deeply buried ULIRGs must be powered by a dust-enshrouded active galactic nucleus; (3) an unobscured "keyhole" view through <~10% of the obscuring medium surrounding a deeply buried ULIRG is sufficient to make it appear nearly unobscured in the mid-IR; and (4) the observed absence of deeply buried ULIRGs with large PAH equivalent widths is naturally explained by our models showing that deep absorption features are "filled-in" by small quantities of foreground unobscured PAH emission (e.g., from the host galaxy disk) at the level of ~1% the bolometric nuclear luminosity. The modeling and analysis we present will also serve as a powerful tool for interpreting the high angular resolution spectra of high-redshift sources to be obtained with the James Webb Space Telescope.Comment: 20 pages, 14 figures. Accepted for publication in the Ap

    Use of Ultra-Thin Window Detectors for Biological Microanalysis

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    Films and bulk samples of Nylon, gelatin, Makrofol, epoxy resin, aminoplastic resin and sodium acetate have been used as models of biological samples. It is shown that the use of ultrathin window (UTW) detectors in scanning transmission and scanning electron microsopes permits the quantitative analysis of light elements, yielding a total element analysis with hydrogen estimated by difference or guesstimated . Comparison with known concentrations or concentrations obtained by chemical analysis shows that X-ray microanalysis of sections by the peak to continuum ratio model and bulk samples by the φ(pz) model gives sufficiently accurate results for biological purposes. It is also shown that sections may be analysed by the standardless ratio model. The application of UTW detectors to total element analysis by quantitative elemental imaging is demonstrated of bulk biological samples, which have been freeze-substituted, embedded in epoxy resin and surface polished. The possibility of imaging the oxygen content of frozen-hydrated bulk tissue samples which have been surface polished is also demonstrated. This may lead to the imaging of water distribution in frozen-hydrated bulk samples of biological tissues. UTW detectors are also useful for detecting mass loss in organic samples by monitoring the decrease in oxygen counts and for detecting contamination by monitoring the increase in carbon counts. It is also shown that changes in carbon counts are good indicators of folds in sections

    A Census of X-ray gas in NGC 1068: Results from 450ks of Chandra HETG Observation

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    We present models for the X-ray spectrum of the Seyfert 2 galaxy NGC 1068. These are fitted to data obtained using the High Energy Transmission Grating (HETG) on the Chandra X-ray observatory. The data show line and radiative recombination continuum (RRC) emission from a broad range of ions and elements. The models explore the importance of excitation processes for these lines including photoionization followed by recombination, radiative excitation by absorption of continuum radiation and inner shell fluorescence. The models show that the relative importance of these processes depends on the conditions in the emitting gas, and that no single emitting component can fit the entire spectrum. In particular, the relative importance of radiative excitation and photoionization/recombination differs according to the element and ion stage emitting the line. This in turn implies a diversity of values for the ionization parameter of the various components of gas responsible for the emission, ranging from log(xi)=1 -- 3. Using this, we obtain an estimate for the total amount of gas responsible for the observed emission. The mass flux through the region included in the HETG extraction region is approximately 0.3 Msun/yr assuming ordered flow at the speed characterizing the line widths. This can be compared with what is known about this object from other techniques.Comment: 39 pages, 12 figures, Ap. J. in pres

    Scaling Symmetries of Scatterers of Classical Zero-Point Radiation

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    Classical radiation equilibrium (the blackbody problem) is investigated by the use of an analogy. Scaling symmetries are noted for systems of classical charged particles moving in circular orbits in central potentials V(r)=-k/r^n when the particles are held in uniform circular motion against radiative collapse by a circularly polarized incident plane wave. Only in the case of a Coulomb potential n=1 with fixed charge e is there a unique scale-invariant spectrum of radiation versus frequency (analogous to zero-point radiation) obtained from the stable scattering arrangement. These results suggest that non-electromagnetic potentials are not appropriate for discussions of classical radiation equilibrium.Comment: 13 page
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