362 research outputs found
Photolytic modification of seasonal nitrate isotope cycles in East Antarctica
Nitrate in Antarctic snow has seasonal cycles in nitrogen and oxygen isotopic ratios that reflect its sources and atmospheric formation processes,
and as a result, nitrate archived in Antarctic ice should have great potential to record atmospheric chemistry changes over thousands of
years. However, sunlight that strikes the snow surface results in photolytic nitrate loss and isotopic fractionation that can completely obscure the
nitrate's original isotopic values. To gain insight into how photolysis overwrites the seasonal atmospheric cycles, we collected 244 snow samples
along an 850 km transect of East Antarctica during the 2013–2014 CHICTABA traverse. The CHICTABA route's limited elevation change, consistent
distance between the coast and the high interior plateau, and intermediate accumulation rates offered a gentle environmental gradient ideal for
studying the competing pre- and post-depositional influences on archived nitrate isotopes. We find that nitrate isotopes in snow along the transect
are indeed notably modified by photolysis after deposition, and drier sites have more intense photolytic impacts. Still, an imprint of the original
seasonal cycles of atmospheric nitrate isotopes is present in the top 1–2 m of the snowpack and likely preserved through archiving in
glacial ice at these sites. Despite this preservation, reconstructing past atmospheric values from archived nitrate in similar transitional regions
will remain a difficult challenge without having an independent proxy for photolytic loss to correct for post-depositional isotopic
changes. Nevertheless, nitrate isotopes should function as a proxy for snow accumulation rate in such regions if multiple years of deposition are
aggregated to remove the seasonal cycles, and this application can prove highly valuable in its own right.</p
Simulation of real-time systems with clock calculus
International audienceSafety–critical real-time systems need to be modeled and simulated early in the development of lifecycle. SIGNAL is a data-flow synchronous language with clocks widely used in modeling of such systems. Due to the synchronous features of SIGNAL, clock calculus is essential in compilation and simulation. This paper proposes a new methodology for clock calculus that takes data dependencies into consideration. In this way, simulation code can be directly generated by using a depth-first traversal algorithm. In addition, a clock insertion method based on clock-implication checking is presented to obtain an optimized control structure
Hadron Spectra for Semileptonic Heavy Quark Decay
We calculate the leading perturbative and power corrections to the hadronic
invariant mass and energy spectra in semileptonic heavy hadron decays. We apply
our results to the system. Moments of the invariant mass spectrum, which
vanish in the parton model, probe gluon bremsstrahlung and nonperturbative
effects. Combining our results with recent data on meson branching ratios,
we obtain a lower bound and an upper bound
GeV. The Brodsky-Lepage-Mackenzie scale setting
procedure suggests that higher order perturbative corrections are small for
bottom decay, and even tractable for charm decay.Comment: 24 pages, uses REVTeX, 5 EPS figures embedded with epsf.sty, slightly
modified version to appear in Phys. Rev.
Tau Lepton Physics: Theory Overview
The pure leptonic or semileptonic character of tau decays makes them a good
laboratory to test the structure of the weak currents and the universality of
their couplings to the gauge bosons. The hadronic tau decay modes constitute an
ideal tool for studying low-energy effects of the strong interactions in very
clean conditions; a well-known example is the precise determination of the QCD
coupling from tau-decay data. New physics phenomena, such as a non-zero
tau-neutrino mass or violations of (flavour / CP) conservation laws can also be
searched for with tau decays.Comment: 20 pages, latex, 5 Postscript figures, uses espcrc2.sty, Invited Talk
at the Fourth International Workshop on Tau Lepton Physics (TAU96), Colorado,
September 199
Clinical infectious outcomes associated with biofilm-related bacterial infections: a retrospective chart review
Surface engineering of poly(methylmethacrylate): Effects on fluorescence immunoassay
The authors present surface engineering modifications through chemistry of poly(methylmethacrylate) (PMMA) that have dramatic effects on the result of surface-bound fluorescence immunoassays, both for specific and nonspecific signals. The authors deduce the most important effect to be clustering of antibodies on the surface leading to significant self-quenching. Secondary effects are attributable to the formation of sparse multilayers of antibody. The authors compare PMMA as an antibody support surface with ultraviolet-ozone oxidized PMMA and also to substrates that were, after the oxidation, surface modified by a four-unit poly(ethyleneglycol) carboxylic acid (PEG4), a branched tricarboxylic acid, and a series of carboxylic acid-terminated dendrimers, from generation 1.5 to 5.5. Fluorescence immunoassay and neutron reflectometry were used to compare the apparent antibody surface loading, antigen binding and nonspecific binding on these various surfaces using anti-human IgG as a model antibody, chemically coupled to the surface by amide formation. Simple physical adsorption of the antibody on PMMA resulted in a thick antibody multilayer with small antigen binding capacity. On the carboxylated surfaces, with chemical coupling, a simple monolayer was formed. The authors deduce that antibody clustering was driven by conformational inflexibility and high carboxylate density. The PEG4-modified surface was the most conformationally flexible. The dendrimer-modified interfaces showed a collapse and densification. In fluorescence immunoassay, the optimal combination of high specific and low nonspecific fluorescence signal was found for the G3.5 dendrimer
Surface engineering of poly(methylmethacrylate): Effects on fluorescence immunoassay
The authors present surface engineering modifications through chemistry of poly(methylmethacrylate) (PMMA) that have dramatic effects on the result of surface-bound fluorescence immunoassays, both for specific and nonspecific signals. The authors deduce the most important effect to be clustering of antibodies on the surface leading to significant self-quenching. Secondary effects are attributable to the formation of sparse multilayers of antibody. The authors compare PMMA as an antibody support surface with ultraviolet-ozone oxidized PMMA and also to substrates that were, after the oxidation, surface modified by a four-unit poly(ethyleneglycol) carboxylic acid (PEG4), a branched tricarboxylic acid, and a series of carboxylic acid-terminated dendrimers, from generation 1.5 to 5.5. Fluorescence immunoassay and neutron reflectometry were used to compare the apparent antibody surface loading, antigen binding and nonspecific binding on these various surfaces using anti-human IgG as a model antibody, chemically coupled to the surface by amide formation. Simple physical adsorption of the antibody on PMMA resulted in a thick antibody multilayer with small antigen binding capacity. On the carboxylated surfaces, with chemical coupling, a simple monolayer was formed. The authors deduce that antibody clustering was driven by conformational inflexibility and high carboxylate density. The PEG4-modified surface was the most conformationally flexible. The dendrimer-modified interfaces showed a collapse and densification. In fluorescence immunoassay, the optimal combination of high specific and low nonspecific fluorescence signal was found for the G3.5 dendrimer
QCD Predictions for the Tau Hadronic Width: Determination of alpha_s(M_\tau^2)
The total hadronic width can be accurately calculated using
analyticity and the operator product expansion. The theoretical analysis of
this observable is updated to include all available perturbative and
non-perturbative corrections. The experimental determination of
and its actual uncertainties are discussed.Comment: 15 pages, LaTex: uses epsfig, twoside, fleqn, espcrc2 (included at
end, find % CUT HERE %), 1 figure (included in separate uu file). Proc. QCD9
Measurement of the Probability of Gluon Splitting into Charmed Quarks in Hadronic Z Decays
We have measured the probability, n(g->cc~), of a gluon splitting into a
charm-quark pair using 1.7 million hadronic Z decays collected by the L3
detector. Two independent methods have been applied to events with a three-jet
topology. One method relies on tagging charmed hadrons by identifying a lepton
in the lowest energy jet. The other method uses a neural network based on
global event shape parameters. Combining both methods, we measure n(g->cc~)=
[2.45 +/- 0.29 +/- 0.53]%
Measurement of the Tau Branching Fractions into Leptons
Using data collected with the L3 detector near the Z resonance, corresponding
to an integrated luminosity of 150pb-1, the branching fractions of the tau
lepton into electron and muon are measured to be
B(tau->e nu nu) = (17.806 +- 0.104 (stat.) +- 0.076 (syst.)) %,
B(tau->mu nu nu) = (17.342 +- 0.110 (stat.) +- 0.067 (syst.)) %.
From these results the ratio of the charged current coupling constants of the
muon and the electron is determined to be g_mu/g_e = 1.0007 +- 0.0051. Assuming
electron-muon universality, the Fermi constant is measured in tau lepton decays
as G_F = (1.1616 +- 0.0058) 10^{-5} GeV^{-2}. Furthermore, the coupling
constant of the strong interaction at the tau mass scale is obtained as
alpha_s(m_tau^2) = 0.322 +- 0.009 (exp.) +- 0.015 (theory)
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