218 research outputs found
N Delta - Transition Form Factors at Low Momentum Transfer
The three complex form factors entering the vertex
are calculated to in the framework of a chiral effective
theory with explicit (1232) degrees of freedom. Furthermore, the role
of presently unknown low energy constants that affect the values of EMR and CMR
is elucidated.Comment: 5 pages, 3 figures, Oral contribution given at the 8th International
Conference on the Structure of Baryons (Baryons '98), Bonn, Germany, Sept.
22-26, 199
Generalized Polarizabilities of the Nucleon in Chiral Effective Theories
Using the techniques of chiral effective field theories we evaluate the so
called generalized polarizabilities of the nucleon, which characterize the
structure dependent components in virtual Compton scattering (VCS) as probed in
the electron scattering reaction e N \to e' N gamma. Results are given for both
spin-dependent and spin-independent structure effects to O(p^3) in SU(2) Heavy
Baryon Chiral Perturbation Theory and to O(epsilon^3) in the SU(2) Small Scale
Expansion. Finally we compare our calculations with results from the pioneering
VCS experiment on the proton from Mainz.Comment: 39 pages, 12 figures, revte
Novel protein-based solutions for organophosphorus nerve agent detection and elimination
Organophosphorus (OP) nerve agents are some of the deadliest chemicals ever synthesized by man. These toxins, which include sarin, soman, cyclosarin, tabun, and VX, inhibit the neurotransmitter-regulating enzyme, acetylcholinesterase (AChE). This leads to continual acetylcholine muscarinic and nicotinic receptor stimulus and may eventually result in death due to prolonged muscles contraction and diaphragm incapacitation. Current treatments for OP poisoning include injections of atropine, to dampen acetylcholine stimulation, a strong-nucleophile oxime, such a 2-pralidoxime, to reactivate inhibited AChE, and diazepam for seizures. These treatments are limited, however, because they do not protect against poisoning, cannot be administered prior to exposure, and don't address the long-term side effects associated with nerve agent poisoning. Additionally, there is no broad-spectrum oxime effective against all nerve agents. A better therapeutic would be a prophylactic molecule capable of catalytically degrading the OP prior to AChE inhibition. Protein-based therapeutics are an emerging remedy for OP toxicity. It has been shown that pre-administration of excess AChE in mice can protein against 8-10 normally lethal doses of soman. Current enzyme therapeutics can be categorized as either stoichiometric or catalytic. Stoichiometric OP binders, such as AChE or the homologous butyrylcholinesterase (BChE), benefit from nanomolar (nM) dissociation constants, but suffer in their ability to recover after OP exposure, thereby requiring large enzyme doses for effective treatment. Catalytic protein therapeutics, including serum paraoxonase (PON1) or the bacterial organophosphate hydrolase (OPH) exhibit rapid rates of in vitro nerve agent hydrolysis, but are limited by high dissociation constants, making them ineffective in vivo. Human carboxylesterase 1 (hCE1) is a liver serine hydrolase in the same [alpha]/[beta] super family as AChE and BChE, which may have more favorable attributes as an OP bioscavenger. Indeed rodents express a serum carboxylesterase that affords them high levels of protection against OPs. Using structural and biochemical studies, we determined the stereopreference, rates of spontaneous reactivation, and availability of rapid oxime-assisted reactivation of hCE1 with nerve agents. Next, using structurally guided protein design, we engineered a form of the hCE1 that combines the benefits of both bioscavenger classes, exhibiting nM dissociation constants and enhanced rates of hydrolysis, up to 48,700-fold, against the nerve agents sarin, soman, and cyclosarin. Finally, novel mutants of hCE1 were developed that exhibit-increased rates of reactivation against specific agents, and can be utilized to detect and identify chemical agents
Complete one-loop analysis of the nucleon's spin polarizabilities
We present a complete one-loop analysis of the four nucleon spin
polarizabilities in the framework of heavy baryon chiral perturbation theory.
The first non-vanishing contributions to the isovector and first corrections to
the isoscalar spin polarizabilities are calculated. No unknown parameters enter
these predictions. We compare our results to various dispersive analyses. We
also discuss the convergence of the chiral expansion and the role of the delta
isobar.Comment: 4 pp, REVTE
Isospin violation and the proton's neutral weak magnetic form factor
The effects of isospin violation on the neutral weak magnetic form factor of
the proton are studied using two-flavour chiral perturbation theory. The first
nonzero contributions appear at O(p^4) in the small-momentum expansion, and the
O(p^5) corrections are also calculated. The leading contributions from an
explicit Delta(1232) isomultiplet are included as well. At such a high order in
the chiral expansion, one might have expected a large number of unknown
parameters to contribute. However, it is found that no unknown parameters can
appear within loop diagrams, and a single tree-level counterterm at O(p^4) is
sufficient to absorb all divergences. The momentum dependence of the neutral
weak magnetic form factor is not affected by this counterterm.Comment: 26 pages including 9 figure
Imaging of lung transplant complications
AbstractSince the late 1980s, lung transplantation has emerged as a valid treatment option for some patients with advanced non-neoplastic lung disease. Long-term survival of lung transplant recipients, however, is lower than that of patients with other types of transplantation, because of numerous specific postoperative complications. Thanks to X-ray and CT, radiologists can guide clinicians, helped in this diagnostic approach by the time between the date of injury and date of transplantation. We will detail in this pictorial review the immediate and late surgical complications, the immunological complications, the infectious complications and other late complications
Calculation of Finite Size Effects on the Nucleon Mass in Unquenched QCD using Chiral Perturbation Theory
The finite size effects on nucleon masses are calculated in relativistic
chiral perturbation theory. Results are compared with two-flavor lattice
results.Comment: talk at Confinement03, 5 pages latex, 3 figures. Assignment of 2 data
points to incorrect data sets in plot 1 and of 1 data point in plot 2
corrected. 1 fm lattice result updated. Conclusions unchange
The \Delta contribution to the parity-violating nucleon-nucleon force
Because the nucleon may be excited and transformed into a virtual
resonance easily, we consider the decuplet contribution to the parity-violating
(PV) nucleon-nucleon interaction in the chiral effective field theory. The
effective PV nucleon-nucleon potential is derived without introducing any
unknown coupling constants.Comment: 5 pages, 2 figures. The version appeared in Chinese Physics C (HEP &
NP
Effective theory of the Delta(1232) in Compton scattering off the nucleon
We formulate a new power-counting scheme for a chiral effective field theory
of nucleons, pions, and Deltas. This extends chiral perturbation theory into
the Delta-resonance region. We calculate nucleon Compton scattering up to
next-to-leading order in this theory. The resultant description of existing
p cross section data is very good for photon energies up to about 300
MeV. We also find reasonable numbers for the spin-independent polarizabilities
and .Comment: 29 pp, 9 figs. Minor revisions. To be published in PR
One-loop calculations of hyperon polarizabilities under the large N_c consistency condition
The spin-averaged electromagnetic polarizabilities of the hyperons
and are calculated within the one-loop approximation by use of the
dispersion theory. The photon and meson couplings to hyperons are determined so
as to satisfy the large N_c consistency condition. It is shown that in order
for the large N_c consistency condition to hold exotic hyperon states such as
with I=2 and J=3/2 are required in the calculation of the
magnetic polarizability of the state.Comment: 17 pages, REVTeX, no figure
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