N Delta - Transition Form Factors at Low Momentum Transfer

The three complex form factors entering the $\Delta\to N\gamma^\ast$ vertex are calculated to ${\cal O}(\epsilon^3)$ in the framework of a chiral effective theory with explicit $\Delta$(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 $\Delta$ 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 $\gamma$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 $\alpha_p$ and $\beta_p$.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 $\Lambda$ and $\Sigma$ 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 $\Sigma^{**}$ with I=2 and J=3/2 are required in the calculation of the magnetic polarizability of the $\Sigma$ state.Comment: 17 pages, REVTeX, no figure