Relativistic mean-field study of neutron-rich nuclei

A relativistic mean-field model is used to study the ground-state properties of neutron-rich nuclei. Nonlinear isoscalar-isovector terms, unconstrained by present day phenomenology, are added to the model Lagrangian in order to modify the poorly known density dependence of the symmetry energy. These new terms soften the symmetry energy and reshape the theoretical neutron drip line without compromising the agreement with existing ground-state information. A strong correlation between the neutron radius of 208Pb and the binding energy of valence orbitals is found: the smaller the neutron radius of 208Pb, the weaker the binding energy of the last occupied neutron orbital. Thus, models with the softest symmetry energy are the first ones to drip neutrons. Further, in anticipation of the upcoming one-percent measurement of the neutron radius of 208Pb at the Thomas Jefferson Laboratory, a close relationship between the neutron radius of 208Pb and neutron radii of elements of relevance to atomic parity-violating experiments is established.Comment: 14 pages, 5 figure

Parity Violating Measurements of Neutron Densities

Parity violating electron nucleus scattering is a clean and powerful tool for measuring the spatial distributions of neutrons in nuclei with unprecedented accuracy. Parity violation arises from the interference of electromagnetic and weak neutral amplitudes, and the $Z^0$ of the Standard Model couples primarily to neutrons at low $Q^2$. The data can be interpreted with as much confidence as electromagnetic scattering. After briefly reviewing the present theoretical and experimental knowledge of neutron densities, we discuss possible parity violation measurements, their theoretical interpretation, and applications. The experiments are feasible at existing facilities. We show that theoretical corrections are either small or well understood, which makes the interpretation clean. The quantitative relationship to atomic parity nonconservation observables is examined, and we show that the electron scattering asymmetries can be directly applied to atomic PNC because the observables have approximately the same dependence on nuclear shape.Comment: 38 pages, 7 ps figures, very minor changes, submitted to Phys. Rev.

Nuclear Skins and Halos in the Mean-Field Theory

Nuclei with large neutron-to-proton ratios have neutron skins, which manifest themselves in an excess of neutrons at distances greater than the radius of the proton distribution. In addition, some drip-line nuclei develop very extended halo structures. The neutron halo is a threshold effect; it appears when the valence neutrons occupy weakly bound orbits. In this study, nuclear skins and halos are analyzed within the self-consistent Skyrme-Hartree-Fock-Bogoliubov and relativistic Hartree-Bogoliubov theories for spherical shapes. It is demonstrated that skins, halos, and surface thickness can be analyzed in a model-independent way in terms of nucleonic density form factors. Such an analysis allows for defining a quantitative measure of the halo size. The systematic behavior of skins, halos, and surface thickness in even-even nuclei is discussed.Comment: 22 RevTeX pages, 22 EPS figures included, submitted to Physical Review

Biochemical Responses of Asparagus to Controlled Atmosphere Storage at 20 Degrees C

In seeking to understand the beneficial effects of controlled atmosphere (CA) storage at 20 degrees C on asparagus (Asparagus officinalis L.), biochemical responses of spear tips stored in air were compared with those of spears stored under CA (2% 02, 10% CO2). CA storage prevented the rapid loss of sucrose, increased acid invertase activity and asparagine accumulation observed in the tips of spears stored in air. CA storage also delayed changes in the levels of glutamine, malic, citric and fumaric acids, compared with those in tips of air-stored spears. Elongation observed in water-fed spears in air was reduced by CA. It is proposed that CA acted by depressing metabolism to such an extent that sucrose levels were maintained in the spear tip and this, in turn, prevented the cascade of metabolic events that contribute to spear deterioration in air

The Earth: Plasma Sources, Losses, and Transport Processes

This paper reviews the state of knowledge concerning the source of magnetospheric plasma at Earth. Source of plasma, its acceleration and transport throughout the system, its consequences on system dynamics, and its loss are all discussed. Both observational and modeling advances since the last time this subject was covered in detail (Hultqvist et al., Magnetospheric Plasma Sources and Losses, 1999) are addressed

The Cholecystectomy As A Day Case (CAAD) Score: A Validated Score of Preoperative Predictors of Successful Day-Case Cholecystectomy Using the CholeS Data Set

Background Day-case surgery is associated with significant patient and cost benefits. However, only 43% of cholecystectomy patients are discharged home the same day. One hypothesis is day-case cholecystectomy rates, defined as patients discharged the same day as their operation, may be improved by better assessment of patients using standard preoperative variables. Methods Data were extracted from a prospectively collected data set of cholecystectomy patients from 166 UK and Irish hospitals (CholeS). Cholecystectomies performed as elective procedures were divided into main (75%) and validation (25%) data sets. Preoperative predictors were identified, and a risk score of failed day case was devised using multivariate logistic regression. Receiver operating curve analysis was used to validate the score in the validation data set. Results Of the 7426 elective cholecystectomies performed, 49% of these were discharged home the same day. Same-day discharge following cholecystectomy was less likely with older patients (OR 0.18, 95% CI 0.15–0.23), higher ASA scores (OR 0.19, 95% CI 0.15–0.23), complicated cholelithiasis (OR 0.38, 95% CI 0.31 to 0.48), male gender (OR 0.66, 95% CI 0.58–0.74), previous acute gallstone-related admissions (OR 0.54, 95% CI 0.48–0.60) and preoperative endoscopic intervention (OR 0.40, 95% CI 0.34–0.47). The CAAD score was developed using these variables. When applied to the validation subgroup, a CAAD score of ≤5 was associated with 80.8% successful day-case cholecystectomy compared with 19.2% associated with a CAAD score >5 (p < 0.001). Conclusions The CAAD score which utilises data readily available from clinic letters and electronic sources can predict same-day discharges following cholecystectomy