Delta--Excitation and Exchange Corrections for NN--Bremsstrahlung

The role of the relativistic amplitudes for a number of ${\cal O}(k)$ processes usually neglected in potential model calculations of NN--bremsstrahlung is investigated. In particular, we consider the $\Delta$--excitation pole contributions related to the one--pion and one--rho exchange and in addition include the exchange contributions induced by the radiative $\omega,\,\rho \to \pi \gamma$ decays. The contributions are calculated from relativistic Born amplitudes fitted to $\Delta$--production and absorption data in the energy range up to 1 GeV and then used to supplement potential model and soft photon calculations for nucleon--nucleon bremsstrahlung. The effects on $NN\gamma$--observables, although moderate in general, are found to be important in some kinematic domains.Comment: 15 pages in LaTex, using Revtex, 6 figures as uufile'd, compressed Postscript file included, TRIUMF preprint TRI-PP-94-9

Nucleon-nucleon bremsstrahlung: An example of the impossibility of measuring off-shell amplitudes

For nearly fifty years theoretical and experimental efforts in nucleon-nucleon bremsstrahlung (NN$\gamma$) have been devoted to measuring off-shell amplitudes and distinguishing among various NN potentials on the basis of their off-shell behavior. New experiments are underway, designed specifically to attain kinematics further off shell than in the past, and thus to be more sensitive to the off-shell behavior. This letter shows that, contrary to these expectations, and due to the invariance of the S-matrix under transformations of the fields, the off-shell NN amplitude is as a matter of principle an unmeasurable quantity in NN$\gamma$.Comment: 9 pages, Latex, using RevTeX; Minor wording changes, title changed, version to be published in Phys. Rev. Letter

Per and polyfluorinated substances in the Nordic Countries:Use, occurence and toxicology

This Tema Nord report presents a study based on open information and custom market research to review the most common perfluorinated substances (PFC) with less focus on PFOS and PFOA.The study includes three major parts: 1) Identification of relevant per-and polyfluorinated substances and their use in various industrial sectors in the Nordic market by interviews with major players and database information. 2) Emissions to and occurence in the Nordic environment of the substances described in 1). 3) A summary of knowledge of the toxic effects on humans and the environment of substances prioritized in 2). There is a lack of physical chemical data, analystical reference substances, human and environmental occurrence and toxicology data, as well as market information regarding PFCs other than PFOA and PFOS and the current legislation cannot enforce disclosure of specific PFC substance information

Proton-proton bremsstrahlung below and above pion-threshold: the influence of the Δ\Delta-isobar

The proton-proton bremsstrahlung is investigated within a coupled-channel model with the $\Delta$ degree of freedom. The model is consistent with the $NN$ scattering up to 1 GeV and the $\gamma N\Delta$ vertex determined in the study of pion photoproduction reactions. It is found that the $\Delta$ excitation can significantly improve the agreements with the $pp \rightarrow pp\gamma$ at $E_{lab}=280$ MeV. Predictions at $E_{lab}=550$ and $800$ MeV are presented for future experimental tests.Comment: 26 pages Revtex, 12 figures are available from the authors upon request ([email protected]

Field transformations and simple models illustrating the impossibility of measuring off-shell effects

In the context of simple models illustrating field transformations in Lagrangian field theories we discuss the impossibility of measuring off-shell effects in nucleon-nucleon bremsstrahlung, Compton scattering, and related processes. To that end we introduce a simple phenomenological Lagrangian describing nucleon-nucleon bremsstrahlung and perform an appropriate change of variables leading to different off-shell behavior in the nucleon-nucleon amplitude as well as the photon-nucleon vertex. As a result we obtain a class of equivalent Lagrangians, generating identical S-matrix elements, of which the original Lagrangian is but one representative. We make use of this property in order to show that what appears as an off-shell effect in an S-matrix element for one Lagrangian may originate in a contact term from an equivalent Lagrangian. By explicit calculation we demonstrate for the case of nucleon-nucleon bremsstrahlung as well as nucleon Compton scattering the equivalence of observables from which we conclude that off-shell effects cannot in any unambiguous way be extracted from an S-matrix element. Finally, we also discuss some implications of introducing off-shell effects on a phenomenological basis, resulting from the requirement that the description of one process be consistent with that of other processes described by the same Lagrangian.Comment: 19 pages, Latex, using RevTe

Car engines air filters. A useful ambient air sampler and/or a possible hazardous waste?

Car-engine air filters (CAFs) have been recently used as inexpensive alternative air sampling media for hydrophobic organic compounds such as polycyclic aromatic hydrocarbons, polychlorinated dibenzo-p-dioxins and furans and also for heavy metals. This “active-passive” sampling methodology is a promising way for urban air monitoring, being able to offer invaluable advantages. Two approaches have been proposed for the estimation of the air volume that passes through the CAFs and are herein reviewed and compared. Chemical analysis of CAFs shows that after their use in vehicles, they have accumulated a considerable amount of toxic chemicals which render CAFs as potentially hazardous materials. The CAF chemical loads are presented and evaluated and the need to characterize CAFs as special waste is discussed

Evaluation of car air filters' efficiency as active samplers for polycyclic aromatic hydrocarbons and heavy metals

In this study, an innovative and inexpensive approach, based on car engine air filters (CAFs) was used to monitor polycyclic aromatic hydrocarbons (PAHs) and heavy metals (HMs). CAFs were collected from two Taxi garages in Guangzhou and analyzed for PAHs and heavy metals. The total concentrations of eight high molecular weight PAHs (ΣPAHs) ranged from 923 to 11378 µg/CAF. The average ΣPAHs concentration in winter was slightly higher than in summer, a seasonal signal that is observed in most studies. The most abundant individual PAH was chrysene, followed by benzo[a]anthracene, benzo[b]fluoranthene and benzo[k]fluoranthene. Concentrations of benzo[a]pyrene (BaP) varied between 8.22 and 632 µg/CAF. Based on estimated air volumes that pass through each CAF, atmospheric PAHs and heavy metals were estimated. ΣPAHs ranged from ~20 to ~200 ng/m3 for the average air volume estimate, being comparable to those reported previously using a high volume air sampler. BaP-equivalent carcinogenic potency were between 1 and 15.0 ng/m3 (again, for the average scenario). The average concentrations of heavy metals in CAFs decreased in order of Zn > Cu > Pb > Cd