6,349 research outputs found
Hygroscopicity of secondary organic aerosols formed by oxidation of cycloalkenes, monoterpenes, sesquiterpenes, and related compounds
A series of experiments has been conducted in the Caltech indoor smog chamber facility to investigate the water uptake properties of aerosol formed by oxidation of various organic precursors. Secondary organic aerosol (SOA) from simple and substituted cycloalkenes (C5-C8) is produced in dark ozonolysis experiments in a dry chamber (RH~5%). Biogenic SOA from monoterpenes, sesquiterpenes, and oxygenated terpenes is formed by photooxidation in a humid chamber (~50% RH). Using the hygroscopicity tandem differential mobility analyzer (HTDMA), we measure the diameter-based hygroscopic growth factor (GF) of the SOA as a function of time and relative humidity. All SOA studied is found to be slightly hygroscopic, with smaller water uptake than that of typical inorganic aerosol substances. The aerosol water uptake increases with time early in the experiments for the cycloalkene SOA, but decreases with time for the biogenic SOA. This behavior could indicate competing effects between the formation of more highly oxidized polar compounds (more hygroscopic), and formation of longer-chained oligomers (less hygroscopic). All SOA also exhibit a smooth water uptake with RH with no deliquescence or efflorescence. The water uptake curves are found to be fitted well with an empirical three-parameter functional form. The measured pure organic GF values at 85% RH are between 1.09–1.16 for SOA from ozonolysis of cycloalkenes, 1.01–1.04 for sesquiterpene photooxidation SOA, and 1.06–1.11 for the monoterpene and oxygenated terpene SOA. The GF of pure SOA (GForg) in experiments in which inorganic seed aerosol is used is determined by assuming volume-weighted water uptake (Zdanovskii-Stokes-Robinson or ''ZSR'' approach) and using the size-resolved organic mass fraction measured by the Aerodyne Aerosol Mass Spectrometer. Knowing the water content associated with the inorganic fraction yields GForg values. However, for each precursor, the GForg values computed from different HTDMA-classified diameters agree with each other to varying degrees. Lack of complete agreement may be a result of the non-idealities of the solutions that are not captured by the ZSR method. Comparing growth factors from different precursors, we find that GForg is inversely proportional to the precursor molecular weight and SOA yield, which is likely a result of the fact that higher-molecular weight precursors tend to produce larger and less hygroscopic oxidation products
Determination of quark-antiquark component of the photon wave function for u, d, s quarks
Based on the data for the transitions pi0, eta, eta' -> gamma gamma^*(Q^2)
and reactions of the e^+ e^- -annihilations, e^+ e^- -> rho0, omega, phi and
e^+ e^--> hadrons at 1<E_{e^+e^-}<3.7 GeV, we determine the light-quark
components of the photon wave function gamma^*(Q^2) -> q anti-q (q= u, d, s)
for the region 0< Q^2 <1 (GeV/c)^2.Comment: 17 pages, some typos correcte
Contextual factors among indiscriminate or larger attacks on food or water supplies, 1946-2015
This research updates previous inventories of malicious attacks on food and water to include data from 1946 through mid-2015. A systematic search of news reports, databases and previous inventories of poisoning events was undertaken. Incidents that threatened or were intended to achieve direct harm to humans, and that were either relatively large (number of victims > 4 or indiscriminate in intent or realisation were included. Agents could be chemical, biological or radio-nuclear. Reports of candidate incidents were subjected to systematic inclusion and exclusion criteria as well as validity analysis (not always clearly undertaken in previous inventories of such attacks). We summarise contextual aspects of the attacks that may be important for scenario prioritisation, modelling and defensive preparedness. Opportunity is key to most realised attacks, particularly access to dangerous agents. The most common motives and relative success rate in causing harm were very different between food and water attacks. The likelihood that people were made ill or died also varied by food/water mode, and according to motive and opportunity for delivery of the hazardous agent. Deaths and illness associated with attacks during food manufacture and prior to sale have been fewer than those in some other contexts. Valuable opportunities for food defence improvements are identified in other contexts, especially food prepared in private or community settings
Branching Ratio and CP Violation of B to pi pi Decays in Perturbative QCD Approach
We calculate the branching ratios and CP asymmetries for B^0 to pi^+pi^-, B^+
to pi^+pi^0 and B^0 to pi^0pi^0 decays, in a perturbative QCD approach. In this
approach, we calculate non-factorizable and annihilation type contributions, in
addition to the usual factorizable contributions. We found that the
annihilation diagram contributions are not very small as previous argument. Our
result is in agreement with the measured branching ratio of B to pi^+pi^- by
CLEO collaboration. With a non-negligible contribution from annihilation
diagrams and a large strong phase, we predict a large direct CP asymmetry in
B^0 to pi^+pi^-, and pi^0pi^0, which can be tested by the current running B
factories.Comment: Latex, 28 pages including 11 figures; added contents and figures,
corrected typo
Worldline Approach to Forward and Fixed Angle fermion-fermion Scattering in Yang-Mills Theories at High Energies
Worldline techniques are employed to study the general behaviour of the
fermion-fermion collision amplitude at very high energies in a non-abelian
gauge field theory for the forward and fixed angle scattering cases. A central
objective of this work is to demonstrate the simplicity by which the worldline
methodology isolates that sector of the full theory which carries the soft
physics, relevant to each process. Anomalous dimensions pertaining to a given
soft sector are identified and subseuently used to facilitate the
renormalization group running of the respective four point functions. Gluon
reggeization is achieved for forward, while Sudakov suppression is established
for fixed angle scattering.Comment: 28 pages, 10 figures in three file
Timelike form factors at high energy
The difference between the timelike and spacelike meson form factors is
analysed in the framework of perturbative QCD with Sudakov effects included. It
is found that integrable singularities appear but that the asymptotic behavior
is the same in the timelike and spacelike regions. The approach to asymptotia
is quite slow and a rather constant enhancement of the timelike value is
expected at measurable large . This is in agreement with the trend
shown by experimental data.Comment: 17 pages, report DAPNIA/SPhN 94 0
Off-shell effects in dilepton production from hot interacting mesons
The production of dielectrons in reactions involving a_1 mesons and pions is
studied. We compare results obtained with different phenomenological
Lagrangians that have been used in connection with hadronic matter and finite
nuclei. We insist on the necessity for those interactions to satisfy known
empirical properties of the strong interaction. Large off-shell effects in
dielectron production are found and some consequences for the interpretation of
heavy ion data are outlined. We also compare with results obtained using
experimentally-extracted spectral functions.Comment: 14 pages, LaTeX2e, 2 figure
Interpolation Formulas for the Eta-Gamma and Eta'-Gamma Transition Form Factors
The new CLEO and LEP data on the eta-gamma and eta'-gamma transition form
factors have renewed the interest in simple interpolation formulas, valid at
any value of momentum transfer. We are going to show that recent theoretical
and phenomenological results on eta-eta' mixing lead to two-pole forms, where
each pole term resembles the Brodsky/Lepage interpolation formula for the
pi-gamma case and depends on the mixing and decay parameters in a simple
fashion. The parameters, entering the occasionally used one-pole formulas, on
the other hand, cannot be interpreted theoretically in a simple way.Comment: 4 pages, 3 figures, using revtex, epsfig; to be published in
Phys.Rev.D; hypertex dvi-file available at
http://wptu38.physik.uni-wuppertal.de/~feldmann/pub/wub98_7_hyp.dv
Perturbative QCD factorization of and
We prove factorization theorem for the processes and
to leading twist in the covariant gauge by means of the
Ward identity. Soft divergences cancel and collinear divergences are grouped
into a pion wave function defined by a nonlocal matrix element. The gauge
invariance and universality of the pion wave function are confirmed. The proof
is then extended to the exclusive meson decays and
in the heavy quark limit. It is shown that a light-cone
meson wave function, though absorbing soft dynamics, can be defined in an
appropriate frame. Factorization of the decay in
space, being parton transverse momenta, is briefly discussed. We comment
on the extraction of the leading-twist pion wave function from experimental
data.Comment: 21 pages in Latex file, version to appear in Phys. Rev.
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