441 research outputs found
Instantons, diquarks and non-leptonic weak decays of hyperons
This work is devoted to the study of the non-perturbative contributions in
non-leptonic hyperon decays. We show that the instanton-induced 't Hooft
interaction can naturally explain the Delta I=1/2 rule, by generating
quark-diquark clustering inside octet baryons. We compute P-wave and S-wave
amplitudes in the Instanton Liquid Model (ILM), and find good agreement with
experiment. We propose a model-independent procedure to test on the lattice if
the leading quark-quark attraction in the 0^+ anti-triplet channel responsible
for diquark structures in hadrons is originated by the interaction generated by
quasi-classical fields or it is predominantly due to other perturbative and/or
confining forces.Comment: Final version to appear on PR
Instantons, Chiral Dynamics and Hadronic Resonances
We use the Interacting Instanton Liquid Model (IILM) as a tool to study the
role played by the chiral interactions in the lowest-lying vector and axial
vector meson resonances. We find that narrow a1 and rho meson resonances can be
generated by instanton-induced chiral forces, even in the absence of
confinement. In the IILM, these hadrons are found to have masses only about 30%
larger than the experimental value and small width <10-50 MeV. This result
suggests that chiral interactions are very important in these systems and
provide most of their mass. We explore the decaying patterns of the rho meson,
in the absence of confinement. We argue that, in our model where only chiral
forces are switched on, this meson decays dissociating into its quark
anti-quark constituents
Are There Diquarks in the Nucleon?
This work is devoted to the study of diquark correlations inside the nucleon.
We analyze some matrix elements which encode information about the
non-perturbative forces, in different color anti-triplet diquark channels. We
suggest a lattice calculation to check the quark-diquark picture and clarify
the role of instanton-mediated interactions. We study in detail the physical
properties of the 0+ diquark, using the Random Instanton Liquid Model. We find
that instanton forces are sufficiently strong to form a diquark bound-state,
with a mass of ~500 MeV, which is compatible with earlier estimates. We also
compute its electro-magnetic form factor and find that the diquark is a broad
object, with a size comparable with that of the proton.Comment: Final version, accepted for publication on Phys. Rev.
Approximate treatment of electron Coulomb distortion in quasielastic (e,e') reactions
In this paper we address the adequacy of various approximate methods of
including Coulomb distortion effects in (e,e') reactions by comparing to an
exact treatment using Dirac-Coulomb distorted waves. In particular, we examine
approximate methods and analyses of (e,e') reactions developed by Traini et al.
using a high energy approximation of the distorted waves and phase shifts due
to Lenz and Rosenfelder. This approximation has been used in the separation of
longitudinal and transverse structure functions in a number of (e,e')
experiments including the newly published 208Pb(e,e') data from Saclay. We find
that the assumptions used by Traini and others are not valid for typical (e,e')
experiments on medium and heavy nuclei, and hence the extracted structure
functions based on this formalism are not reliable. We describe an improved
approximation which is also based on the high energy approximation of Lenz and
Rosenfelder and the analyses of Knoll and compare our results to the Saclay
data. At each step of our analyses we compare our approximate results to the
exact distorted wave results and can therefore quantify the errors made by our
approximations. We find that for light nuclei, we can get an excellent
treatment of Coulomb distortion effects on (e,e') reactions just by using a
good approximation to the distorted waves, but for medium and heavy nuclei
simple additional ad hoc factors need to be included. We describe an explicit
procedure for using our approximate analyses to extract so-called longitudinal
and transverse structure functions from (e,e') reactions in the quasielastic
region.Comment: 30 pages, 8 figures, 16 reference
new route for tizanidine administration: a pharmacokinetics and light microscope autoradiography study
Spasticity could represent a complication of several central nervous system (CNS)
disorders. Multiple sclerosis and painful paroxysmal syndromes (e.g. trigeminal
neuralgia) are pathologies in which anti-spastic drugs are used to a greater extent .
Baclofen, tizanidine (TIZ), benzodiazepines, dantrolene, and, more recently, gabapentin
are the pharmacological agents more widely used. Baclofen, TIZ, benzodiazepines,
gabapentin, clonidine but not dantrolene are active on CNS. The alpha2 adrenoceptor
agonist TIZ is one of the most eff ective and largely used anti-spastic drugs. Oral
treatment is the only route of anti-spastics administration, although it may cause
problems of bioavailability and/or compliance in spastic patients with impaired
deglutition. This study was designed to assess the possibility of develop a new route
of administration of TIZ and to identify its targets in the spinal cord.
New Zealand rabbits were treated with oral (OR , n=6), intramuscular (IM, n=6)
or intranasal (IN, n=6) TIZ (3.2 mg/kg/day). Plasma concentration was measured by
HPLC on samples collected at 0, 30, 60, 90, 120 and 480 min after treatment. Curves
of average concentrations of TIZ vs. time were constructed. In plasma, TIZ reached a
peak between 45-65 min after administration. Cmax was in the range of 268.33–1213.64
ng/ml for IM treatment, of 73.95–135.92 ng/ml for IN treatment and of 16.86–857.25
ng/ml for OR treatment. After pharmacokinetic studies, diff erent spinal cord tracts
were removed and used for radioligand binding assay and autoradiography. Using
[3H]-RX821002 ([3H]-RX) (0.1-14nM), the Kd and Bmax for every spinal cord segment
were calculated. The non-specifi c binding was obtained with 100ÎĽM of (-)-epinephrine.
[3H]-RX sites were accumulated in the superfi cial laminae of dorsal horn. Dense
[3H]-RX binding in control was seen over the superfi cial dorsal horn (laminae I-II)
and centrally located lamina X. The ventral horn showed moderate levels of binding.
[3H]-RX was displaced after TIZ treatment using diff erent administration routes. The
heaviest accumulation of silver grains (lowest displacement of TIZ) occurred after OR
administration of the compound, the lowest after IM administration. These results
suggest that both IM and IN administration of TIZ may represent routes of administration
of the drug alternative to the OR one.
Considering predictable adverse eff ects of IM treatment, the IN administration
could represent the elective route to administrate this kind of drugs
Meson exchange and nucleon polarizabilities in the quark model
Modifications to the nucleon electric polarizability induced by pion and
sigma exchange in the q-q potentials are studied by means of sum rule
techniques within a non-relativistic quark model. Contributions from meson
exchange interactions are found to be small and in general reduce the quark
core polarizability for a number of hybrid and one-boson-exchange q-q models.
These results can be explained by the constraints that the baryonic spectrum
impose on the short range behavior of the mesonic interactions.Comment: 11 pages, 1 figure added, expanded discussio
Characterisation of the secondary-neutron production in particle therapy treatments with the MONDO tracking detector
Particle Therapy (PT) is a non-invasive technique that exploits charged light ions for the irradiation of tumours that cannot be effectively treated with surgery or conventional radiotherapy. While the largest dose fraction is released to the tumour volume by the primary beam, a non-negligible amount of additional dose is due to the beam fragmentation that occurs along the path towards the target volume. In particular, the produced neutrons are particularly dangerous as they can release their energy far away from the treated area, increasing the risk of developing a radiogenic secondary malignant neoplasm after undergoing a treatment. A precise measurement of the neutron flux, energy spectrum and angular distributions is eagerly needed in order to improve the treatment planning system software, so as to predict the normal tissue toxicity in the target region and the risk of late complications in the whole body. The MONDO (MOnitor for Neutron Dose in hadrOntherapy) project is dedicated to the characterisation of the secondary ultra-fast neutrons ([20-400] MeV energy range) produced in PT. The neutron tracking system exploits the reconstruction of the recoil protons produced in two consecutive (n, p) elastic scattering interactions to measure simultaneously the neutron incoming direction and energy. The tracker active media is a matrix of thin squared scintillating fibers arranged in orthogonally oriented layers that are read out by a sensor (SBAM) based on SPAD (Single-Photon Avalanche Diode) detectors developed in collaboration with the Fondazione Bruno Kessler (FBK)
Nonperturbative versus perturbative effects in generalized parton distributions
Generalized parton distributions (GPDs) are studied at the hadronic
(nonperturbative) scale within different assumptions based on a relativistic
constituent quark model. In particular, by means of a meson-cloud model we
investigate the role of nonperturbative antiquark degrees of freedom and the
valence quark contribution. A QCD evolution of the obtained GPDs is used to add
perturbative effects and to investigate the GPDs' sensitivity to the
nonperturbative ingredients of the calculation at larger (experimental) scale.Comment: 17 pages, 10 figures; submitted to Phys. Rev.
Immunological pattern alteration in shoe, hide, and leather industry workers exposed to exavalent chromium
The aim of this work was to assess the effects of hexavalent chromium [Cr(VI)] on shoe, leather, and hide industry workers, based on the assumption that Cr(VI) can behave as an environmental immunological "stressor." The immunological patterns of 84 male subjects were studied in relation to Cr(VI) hematic and urinary levels. Cr(VI) was measured through atomic absorption. Lymphocyte subsets, mitogen-mediated lymphocyte-proliferation, cytokine levels, and natural killer (NK) cytotoxic activity were also assayed.
RESULTS: The urinary levels of the total amount of Cr(VI) were significantly higher in a subgroup of exposed subjects (group B) than in the control or in the lower exposed (group A). In group B, Cr(VI) caused a decrease in the density of
glucocorticoid receptors (GR) on peripheral blood mononuclear cells (PBMC) and a increase of IL-6. Cr(VI) did not modify NK-mediated cytotoxicity, the plasmatic levels of inflammatory cytokines and related soluble receptors, and prostaglandin levels, while it tended to increase lymphocyte sensitivity to mitogens and the production of immunomodulant cytokines (IFN-gamma, IL-4, and IL-2). The experimental addition of Cr(VI) to the in vitro lymphocyte culture determined a significant inhibition of phagocytosis percentage, index, and killing percentage. These effects were neutralized by exogenous IFN-gamma. Cr(VI) could represent an environmental immunological stressor whose
effects can be evaluated through laboratory surveys. The lymphocyte mitogen-induced proliferation, GR receptor on PBMC, and IL-6 plasma levels may represent a discriminating element between Cr(VI)-induced stress and other kinds of stress
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