502 research outputs found
POLYCHLORODIBENZODIOXINS (PCDDs), POLYCHLORODIBENZO-FURANS (PCDFs), AND DIOXIN-LIKE POLYCHLOROBIPHENYLS (DL-PCBs) IN MILK, MOZZARELLA CHEESE, WHEY, AND WHEY CHEESE FROM BUFFALOES RAISED IN THE CAMPANIA REGION
Dioxins (PCDDs and PCDFs) and PCBs are a group of and toxic organo-chlorinated chemicals comprising hundreds of structurally related compounds (congeners) classified as persistent organic pollutants (POPs). It is acknowledged that 17 PCDD and PCDF congeners are of major concern due to their toxicity; 12 PCB congeners are also recognized to express dioxin-like toxicity and are thereby identified as DL-PCBs. Due to their high persistence and lipophilic nature, dioxins and PCBs tend to accumulate in fat and their bio-accumulation through the food chain may pose the risk of causing adverse effects to human health. For the general population, dietary intake is the most important pathway of exposure to the aforesaid environmental contaminants: meat, milk and dairy products, and fish and other seafood products contribute to total daily intake for more than 90 %. To prevent excessive human exposure to dioxins and DL-PCBs, the European Commission established maximum levels for dioxins and the sum of dioxins and DL-PCBs in an array of food components mainly of animal origin (Regulation EC 1881/2006). In this study, dioxins and DL-PCB concentrations were measured in buffalo milk collected from three impounded Campania farms producing milk with different contamination levels. The fate of contaminants in mozzarella cheese, whey, and whey cheese was also investigated. Analyses were carried out by HRGC-HRMS using US EPA Method 1613. The results of this study show the carry-over of the contamination from milk to its dairy products
The GAP-TPC
Several experiments have been conducted worldwide, with the goal of observing
low-energy nuclear recoils induced by WIMPs scattering off target nuclei in
ultra-sensitive, low-background detectors. In the last few decades noble liquid
detectors designed to search for dark matter in the form of WIMPs have been
extremely successful in improving their sensitivities and setting the best
limits. One of the crucial problems to be faced for the development of large
size (multi ton-scale) liquid argon experiments is the lack of reliable and low
background cryogenic PMTs: their intrinsic radioactivity, cost, and borderline
performance at 87 K rule them out as a possible candidate for photosensors. We
propose a brand new concept of liquid argon-based detector for direct dark
matter search: the Geiger-mode Avalanche Photodiode Time Projection Chamber
(GAP-TPC) optimized in terms of residual radioactivity of the photosensors,
energy and spatial resolution, light and charge collection efficiencyComment: 7 pages, 5 figures, Accepted for publication on JINS
Meson-induced correlations of nucleons in nuclear Compton scattering
The non-resonant (seagull) contribution to the nuclear Compton amplitude at
low energies is strongly influenced by nucleon correlations arising from meson
exchange. We study this problem in a modified Fermi gas model, where nuclear
correlation functions are obtained with the help of perturbation theory. The
dependence of the mesonic seagull amplitude on the nuclear radius is
investigated and the influence of a realistic nuclear density on this amplitude
is dicussed. We found that different form factors appear for the static part
(proportional to the enhancement constant ) of the mesonic seagull
amplitude and for the parts, which contain the contribution from
electromagnetic polarizabilities.Comment: 15 pages, Latex, epsf.sty, 9 eps figures
Relativistic Mean Field Model with Generalized Derivative Nucleon-Meson Couplings
The quantum hadrodynamics (QHD) model with minimal nucleon-meson couplings is
generalized by introducing couplings of mesons to derivatives of the nucleon
field in the Lagrangian density. This approach allows an effective description
of a state-dependent in-medium interaction in the mean-field approximation.
Various parametrizations for the generalized couplings are developed and
applied to infinite nuclear matter. In this approach, scalar and vector
self-energies depend on both density and momentum similarly as in the
Dirac-Brueckner theory. The Schr\"{o}diger-equivalent optical potential is much
less repulsive at high nucleon energies as compared to standard relativistic
mean field models and thus agrees better with experimental findings. The
derivative couplings in the extended model have significant effects on
properties of symmetric nuclear matter and neutron matter.Comment: 35 pages, 1 table, 10 figure
Density Dependent Hadron Field Theory
A fully covariant approach to a density dependent hadron field theory is
presented. The relation between in--medium NN interactions and
field--theoretical meson--nucleon vertices is discussed. The medium dependence
of nuclear interactions is described by a functional dependence of the
meson--nucleon vertices on the baryon field operators. As a consequence, the
Euler--Lagrange equations lead to baryon rearrangement self--energies which are
not obtained when only a parametric dependence of the vertices on the density
is assumed. It is shown that the approach is energy--momentum conserving and
thermodynamically consistent. Solutions of the field equations are studied in
the mean--field approximation. Descriptions of the medium dependence in terms
of the baryon scalar and vector density are investigated. Applications to
infinite nuclear matter and finite nuclei are discussed. Density dependent
coupling constants obtained from Dirac--Brueckner calculations with the Bonn
NN-potentials are used. Results from Hartree calculations for energy spectra,
binding energies and charge density distributions of , and
are presented. Comparisons to data strongly support the importance
of rearrangement in a relativistic density dependent field theory. Most
striking is the simultanuous improvement of charge radii, charge densities and
binding energies. The results indicate the appearance of a new "Coester line"
in the nuclear matter equation of state.Comment: 48 LateX pages, 12 Figures, figures and full paper are available as
postscript files by anonymous ftp at ftp://theorie.physik.uni-giessen.de/dd
Relativistic Brueckner-Hartree-Fock calculations with explicit intermediate negative energy states
In a relativistic Brueckner-Hartree-Fock calculation we include explicit
negative-energy states in the two-body propagator. This is achieved by using
the Gross spectator-equation, modified by medium effects. Qualitatively our
results compare well with other RBHF calculations. In some details significant
differences occur, e.g, our equation of state is stiffer and the momentum
dependence of the self-energy components is stronger than found in a reference
calculation without intermediate negative energy states.Comment: 13 pages Revtex, 5 figures included seperatel
Relativistic Contributions to Deuteron Photodisintegration in the Bethe-Salpeter Formalism
In plane wave one-body approximation the reaction of deuteron
photodisintegration is considered in the framework of the Bethe-Salpeter
formalism for two-nucleon system. Results are obtained for deuteron vertex
function, which is the solution of the homogeneous Bethe-Salpeter equation with
a multi-rank separable interaction kernel, with a given analytical form. A
comparison is presented with predictions of non-relativistic, quasipotential
approaches and the equal time approximation. It is shown that important
contributions come from the boost in the arguments of the initial state vertex
function and the boost on the relative energy in the one-particle propagator
due to recoil.Comment: 29 pages, 6 figure
Kinetics of isothermal and non-isothermal precipitation in an Al-6at%Si alloy
A novel theory which describes the progress of a thermally activated reaction under isothermal and linear heating conditions is presented. It incorporates nucleation, growth and impingement and takes account of temperaturedependent solubility. The model generally fits very well to isothermal calorimetry and differential scanning calorimetry data on precipitation in an Al-6 at.% Si alloy. Analysis of the data shows that two processes occur in this precipitation reaction: growth of large Si particles and growth of pre-existing small nuclei. Determination of the sizes of Si precipitates by transmission electron microscopy indicates that interfacial energy contributions are small and have a negligible influence on solubilit
Density dependent hadron field theory for neutron stars with antikaon condensates
We investigate and condensation in -equilibrated
hyperonic matter within a density dependent hadron field theoretical model. In
this model, baryon-baryon and (anti)kaon-baryon interactions are mediated by
the exchange of mesons. Density dependent meson-baryon coupling constants are
obtained from microscopic Dirac Brueckner calculations using Groningen and Bonn
A nucleon-nucleon potential. It is found that the threshold of antikaon
condensation is not only sensitive to the equation of state but also to
antikaon optical potential depth. Only for large values of antikaon optical
potential depth, condensation sets in even in the presence of negatively
charged hyperons. The threshold of condensation is always reached
after condensation. Antikaon condensation makes the equation of state
softer thus resulting in smaller maximum mass stars compared with the case
without any condensate.Comment: 20 pages, 7 figures; final version to appear in Physical Review
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