5,340 research outputs found

    The Application of Laser Intracavity Absorption Detector to Gas Chromatography of Trace Organic Pollutants in Water

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    A helium-neon (HeNe) laser operating simultaneously at 3.39 um (infrared) and 0.63 um (visible) has been used as a selective detector for hydrocarbons in the effluent of a gas chromatograph. The infrared and visible laser transitions originate at the same energy level and are competitive. When a hydrocarbon enters the laser\u27s resonant cavity, the 3.39 um energy is absorbed due to the C-H stretching vibration and the visible emission is enhanced. The visible laser emission is monitored with a photodiode as a quantitative measure of the concentration of the absorbing molecule. The minimum detectable concentration for propane using the double-beam configuration is 20 pg/mL, which is 25 times lower than the best value reported for a thermal conductivity detector. In practice, the detector\u27s selectivity for hydrocarbons is modified by various substituents. The detector responds to aliphatic and aromatic hydrocarbons with aliphatic side chains, except for those substituted with halogens. The HeNe laser intracavity absorption detector may be used without prior separation in some cases (e.g., methane in coal mines). This detector operates with nitrogen carrier gas without sacrifice of sensitivity and should be useful for monitoring organic pollutants since it does not respond to water or carbon dioxide. Also, it should be possible to manufacture this detector at competitive prices

    Automorphic properties of low energy string amplitudes in various dimensions

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    This paper explores the moduli-dependent coefficients of higher derivative interactions that appear in the low-energy expansion of the four-graviton amplitude of maximally supersymmetric string theory compactified on a d-torus. These automorphic functions are determined for terms up to order D^6R^4 and various values of d by imposing a variety of consistency conditions. They satisfy Laplace eigenvalue equations with or without source terms, whose solutions are given in terms of Eisenstein series, or more general automorphic functions, for certain parabolic subgroups of the relevant U-duality groups. The ultraviolet divergences of the corresponding supergravity field theory limits are encoded in various logarithms, although the string theory expressions are finite. This analysis includes intriguing representations of SL(d) and SO(d,d) Eisenstein series in terms of toroidally compactified one and two-loop string and supergravity amplitudes.Comment: 80 pages. 1 figure. v2:Typos corrected, footnotes amended and small clarifications. v3: minor corrections. Version to appear in Phys Rev

    The Standard Model on a D-brane

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    We present a consistent string theory model which reproduces the Standard Model, consisting of a D3-brane at a simple orbifold singularity. We study some simple features of the phenomenology of the model. We find that the scale of stringy physics must be in the multi-TeV range. There are natural hierarchies in the fermion spectrum and there are several possible experimental signatures of the model.Comment: 8 pages Latex, 1 fig. v2: discussion improved, added new reference

    Constitutional Law

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    Covers cases on dams and waterpower—eminent domain—interstate commerce—municipal corporations—res judicata—state officers—the Cowlitz Dam Case (Stoebuck) and on treaties with Indians—fishing rights (Green)

    Anisotropic higher derivative gravity and inflationary universe

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    Stability analysis of the Kantowski-Sachs type universe in pure higher derivative gravity theory is studied in details. The non-redundant generalized Friedmann equation of the system is derived by introducing a reduced one dimensional generalized KS type action. This method greatly reduces the labor in deriving field equations of any complicate models. Existence and stability of inflationary solution in the presence of higher derivative terms are also studied in details. Implications to the choice of physical theories are discussed in details in this paper.Comment: 9 page

    Complement activation and protein adsorption by carbon nanotubes

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    As a first step to validate the use of carbon nanotubes as novel vaccine or drug delivery devices, their interaction with a part of the human immune system, complement, has been explored. Haemolytic assays were conducted to investigate the activation of the human serum complement system via the classical and alternative pathways. Western blot and sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) techniques were used to elucidate the mechanism of activation of complement via the classical pathway, and to analyse the interaction of complement and other plasma proteins with carbon nanotubes. We report for the first time that carbon nanotubes activate human complement via both classical and alternative pathways. We conclude that complement activation by nanotubes is consistent with reported adjuvant effects, and might also in various circumstances promote damaging effects of excessive complement activation, such as inflammation and granuloma formation. C1q binds directly to carbon nanotubes. Protein binding to carbon nanotubes is highly selective, since out of the many different proteins in plasma, very few bind to the carbon nanotubes. Fibrinogen and apolipoproteins (AI, AIV and CIII) were the proteins that bound to carbon nanotubes in greatest quantit

    Relationship between cardiovascular risk and lipid testing in one health care system: a retrospective cohort study.

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    BackgroundThe US Preventive Services Taskforce (USPSTF) recommends routine lipid screening beginning age 35 for men [1]. For women age 20 and older, as well as men age 20-34, screening is recommended if cardiovascular risk factors are present. Prior research has focused on underutilization but not overuse of lipid testing. The objective is to document over- and under-use of lipid testing in an insured population of persons at low, moderate and high cardiovascular disease (CVD) risk for persons not already on statins.MethodsThe study is a retrospective cohort study that included all adults without prior CVD who were continuously enrolled in a large integrated healthcare system from 2005 to 2010. Measures included lipid test frequency extracted from administrative data and Framingham cardiovascular risk equations applied using electronic medical record data. Five year lipid testing patterns were examined by age, sex and CVD risk. Generalized linear models were used to estimate the relative risk for over testing associated with patient characteristics.ResultsAmong males and females for whom testing is not recommended, 35.8 % and 61.5 % received at least one lipid test in the prior 5 years and 8.4 % and 24.4 % had two or more. Over-testing was associated with age, race, comorbidity, primary care use and neighborhood income. Among individuals at moderate and high-risk (not already treated with statins) and for whom screening is recommended, between 21.4 % and 25.1 % of individuals received no screening in the prior 5 years.ConclusionsBased on USPSTF lipid screening recommendations, this study documents substantial over-testing among individuals with low CVD risk and under-testing among individuals with moderate to high-risk not already on statins. Opportunity exists to better focus lipid screening efforts appropriate to CVD risk

    Modeling Changes in the In-Migration Patterns of Northern Saskatchewan Communities : a Log-Linear Approach

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    Les auteurs examinent les changements dans les types historiques de migrations au sein des petites communautés frontières du nord de la Saskatchewan durant les périodes 1927-1960, 1961-1970 et 1971-1976. Des problèmes apparaissent lorsqu'on tente de formuler des modèles d'interaction spatiale dans les régions frontières, ou en voie de développement, en particulier le faible volume de migration et le fait que certains termes agglomérés sont impropres lorsqu'utilisés comme mesures de degré d'attraction et de répulsion des communautés. Comme procédure alternative, on utilise une méthode log-linéaire, laquelle identifie, par une analyse à dimensions multiples d'une matrice de données classifiées, les composantes dans les processus d'interaction spatiale. Les résultats initiaux montrent que le sexe de l'immigrant n'a pas d'effet sur la tendance à immigrer, et que les types spatiaux d'immigration n'ont pas changé d'une période à l'autre.This paper examines changes in the historical pattern of in-migration to small frontier communities in northern Saskatchewan in three time periods: 1927-1960, 1961-1970 and 1971-1976. The problems associated with spatial interaction modeling in a developing or frontier region are noted, particularly the low volume of in-migration and the inappropriateness of mass terms as surrogate measures of nodal attractiveness and propulsiveness. As an alternative, a log-linear approach is adopted, whereby multidimensional contingency-table analysis of categorical data reveals structural components in the spatial-interaction process. Initial results indicate that the gender of the migrant has no effect on the propensity to migrate and that spatial patterns of in-migration have not changed over time

    Palatini Variational Principle for NN-Dimensional Dilaton Gravity

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    We consider a Palatini variation on a general NN-Dimensional second order, torsion-free dilaton gravity action and determine the resulting equations of motion. Consistency is checked by considering the restraint imposed due to invariance of the matter action under simple coordinate transformations, and the special case of N=2 is examined. We also examine a sub-class of theories whereby a Palatini variation dynamically coincides with that of the "ordinary" Hilbert variational principle; in particular we examine a generalized Brans-Dicke theory and the associated role of conformal transformations.Comment: 16 pages, LaTe

    The Value of Singularities

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    We point out that spacetime singularities play a useful role in gravitational theories by eliminating unphysical solutions. In particular, we argue that any modification of general relativity which is completely nonsingular cannot have a stable ground state. This argument applies both to classical extensions of general relativity, and to candidate quantum theories of gravity.Comment: 5 pages, no figures; a few clarifying comments adde
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