174 research outputs found
Determination of the Levels of Polycyclic Aromatic Hydrocarbons in Toasted Bread Using Gas Chromatography Mass Spectrometry
Concentration of 16 polycyclic aromatic hydrocarbons (PAHs) in eighteen baked bread samples using gas oven toasting were evaluated in this study. Samples were classified into the following categories: (1) bread baked from white wheat flour, (2) bread baked from brown wheat flour, and (3) sandwich bread baked from white wheat flour. Analysis was performed by GC-MS after Soxhlet extraction of the sample and clean up of the extract. The levels of B[a]P was not detected in ten of eighteen samples. In the rest of the samples, B[a]P are varied from 2.83 to 16.54 μg/kg. B[a]A, CHR, B[b]FA, B[k] FA, IP, DB[a,h]A, and B[ghi]P concentrations were found to be less than 10.0 μg/kg. However, B[a]P are not detected in original white and brown wheat flour. The total PAHs were varied in the range 1.06–44.24 μg/kg and 3.08–278.66 μg/kg for H-PAH and L-PAH, respectively. Reproducibility and repeatability of the proposed method was calculated and presented in terms of recovery and relative standard deviations (RSD, %). Recoveries were varied from 72.46% to 99.06% with RSD ± 0.28–15.01% and from 82.39% to 95.01% with RSD ±1.91–13.01% for repeatability and reproducibility, respectively. Different commercialized samples of toasted bread were collected and analyzed
Anomalous f_1 exchange in vector meson photoproduction asymmetries
We perform an analysis of the elastic production of vector mesons with
polarized photon beams at high energy in order to investigate the validity of a
recently proposed dynamical mechanism based on the dominance of the f_1
trajectory at large momentum transfer. The density matrix characterizing the
angular distributions of the vector meson decays is calculated within an
exchange model which includes the Pomeron and the f_1. The asymmetries of these
decays turn out to be very useful to disentangle the role of these exchanges
since their effect depends crucially on their quantum numbers which are
different. The observables analyzed are accessible with present experimental
facilities.Comment: 10 pages, REVTeX, 4 figures, some figures are corrected, conclusions
unchange
Vector Meson Photoproduction with an Effective Lagrangian in the Quark Model
A quark model approach to the photoproduction of vector mesons off nucleons
is proposed. Its starting point is an effective Lagrangian of the interaction
between the vector meson and the quarks inside the baryon, which generates the
non-diffractive s- and u- channel resonance contributions. Additional t-channel
and exchanges are included for the and
production respectively to account for the large diffractive behavior in the
small region as suggested by Friman and Soyeur. The numerical results are
presented for the and productions in four isospin channels with
the same set of parameters, and they are in good agreement with the available
data not only in and productions but also in the charged
productions where the additional t-channel exchange does not
contribute so that it provides an important test to this approach. The
investigation is also extended to the photoproduction, and the initial
results show that the non-diffractive behavior of the productions in the
large region can be described by the s- and u- channel contributions with
significantly smaller coupling constants, which is consistent with the findings
in the similar studies in the QHD framework. The numerical investigation has
also shown that polarization observables are essential for identifying
so-called "missing resonances".Comment: 36 pages, 10 PS figures, extended version of nucl-th/9711061 and
nucl-th/9803021, submitted to PR
An isotopic effect in phi photoproduction at a few GeV
A distinct isotopic effect in phi photoproduction at 2-5 GeV region is
identified by examining the production amplitudes due to Pomeron-exchange and
meson-exchange mechanisms. This effect is mainly caused by the pi-eta
interference constrained by SU(3) symmetry and the isotopic structure of the
gamma NN coupling in the direct phi-radiation amplitude. It can be tested
experimentally by measuring differences in the polarization observables between
the gamma-p and gamma-n reactions.Comment: 11 pages, 6 figure
The Wave Function of 2S Radially Excited Vector Mesons from Data for Diffraction Slope
In the color dipole gBFKL dynamics we predict a strikingly different Q^2 and
energy dependence of the diffraction slope for the elastic production of ground
state V(1S) and radially excited V'(2S) light vector mesons. The color dipole
model predictions for the diffraction slope for \rho^0 and \phi^0 production
are in a good agreement with the data from the fixed target and collider HERA
experiments. We present how a different form of anomalous energy and Q^2
dependence of the diffraction slope for V'(2S) production leads to a different
position of the node in radial wave function and discuss a possibility how to
determine this position from the fixed target and HERA data.Comment: 20 pages and 6 figures. Title change
Search for Millicharged Particles at SLAC
Particles with electric charge q < 10^(-3)e and masses in the range 1--100
MeV/c^2 are not excluded by present experiments. An experiment uniquely suited
to the production and detection of such "millicharged" particles has been
carried out at SLAC. This experiment is sensitive to the infrequent excitation
and ionization of matter expected from the passage of such a particle. Analysis
of the data rules out a region of mass and charge, establishing, for example, a
95%-confidence upper limit on electric charge of 4.1X10^(-5)e for millicharged
particles of mass 1 MeV/c^2 and 5.8X10^(-4)e for mass 100 MeV/c^2.Comment: 4 pages, REVTeX, multicol, 3 figures. Minor typo corrected. Submitted
to Physical Review Letter
Shadowing in the nuclear photoabsorption above the resonance region
A model based on the hadronic fluctuations of the real photon is developed to
describe the total photonucleon and photonuclear cross sections in the energy
region above the nucleon resonances. The hadronic spectral function of the
photon is derived including the finite width of vector-meson resonances and the
quark-antiquark continuum. The shadowing effect is evaluated considering the
effective interaction of the hadronic component with the bound nucleons within
a Glauber-Gribov multiple scattering theory. The low energy onset of the
shadowing effect is interpreted as a possible signature of a modification of
the hadronic spectral function in the nuclear medium. A decrease of the
-meson mass in nuclei is suggested for a better explanation of the
experimental data.Comment: 8 pages, 7 figure
Exclusive diffractive processes and the quark substructure of mesons
Exclusive diffractive processes on the nucleon are investigated within a
model in which the quark-nucleon interaction is mediated by Pomeron exchange
and the quark substructure of mesons is described within a framework based on
the Dyson-Schwinger equations of QCD. The model quark-nucleon interaction has
four parameters which are completely determined by high-energy and elastic scattering data. The model is then used to predict vector-meson
electroproduction observables. The obtained - and -meson
electroproduction cross sections are in excellent agreement with experimental
data. The predicted dependence of -meson electroproduction also
agrees with experimental data. It is shown that confined-quark dynamics play a
central role in determining the behavior of the diffractive, vector-meson
electroproduction cross section. In particular, the onset of the asymptotic
behavior of the cross section is determined by a momentum scale that is
set by the current-quark masses of the quark and antiquark inside the vector
meson. This is the origin of the striking differences between the
dependence of -, - and -meson electroproduction cross
sections observed in recent experiments.Comment: 53 pages, 23 figures, revtex and epsfig. Minor additions to tex
One-loop corrections to omega photoproduction near threshold
One-loop corrections to photoproduction near threshold have been
investigated by using the approximation that all relevant transition amplitudes
are calculated from the tree diagrams of effective Lagrangians. With the
parameters constrained by the data of , , and reactions, it is found that the one-loop effects
due to the intermediate and states can significantly change
the differential cross sections and spin observables. The results from this
exploratory investigation suggest strongly that the coupled-channel effects
should be taken into account in extracting reliable resonance parameters from
the data of vector meson photoproduction in the resonance region.Comment: 19 pages, REVTeX, 14 figures, title changed, revised version to
appear in Phys. Rev.
Nucleon resonances in omega photoproduction
The role of the nucleon resonances () in photoproduction is
investigated by using the resonance parameters predicted by Capstick and
Roberts [Phys. Rev. D {\bf 46}, 2864 (1992); {\bf 49}, 4570 (1994)]. In
contrast with the previous investigations based on the
limit of the constituent quark model, the employed and amplitudes include the configuration mixing effects due to the
residual quark-quark interactions. The contributions from the nucleon
resonances are found to be significant relative to the non-resonant amplitudes
in changing the differential cross sections at large scattering angles and
various spin observables. In particular, we suggest that a crucial test of our
predictions can be made by measuring the parity asymmetry and beam-target
double asymmetry at forward scattering angles.Comment: 18 pages, REVTeX, 8 figures, to appear in Phys. Rev.
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