Studies on the effect of sequential thymectomy on in vitro responses of lymphocytes in the amphibian, xenopus laevis

Spleen and thymus leucocytes from control Xenopus toadlets react similarly in vitro to classical thymus-dependent (t) mitogens (phytohaemagglutinin (PHA) and Concanavalin A) as measured by enhanced DNA synthesis. The effect of different concentrations of foetal calf serum on the dose response curves to those two mitogens is examined. The effect of sequential thymectomy on PHA responsiveness of spleen leucocytes reveals that thymectomy until stage 55of development (31 days) abrogates PHA reactivity. In contrast, thymectomy at stage 56/7 (35-40 days - just prior to metamorphosis) and in early adult life has no apparent debilitating effect on the response to this mitogen. Optimal conditions for splenic mixed leucocyte reactivity (MLR) in control Xenopus have been investigated. The use of allogeneic serum enhances MLR stimulation indices. The effect of sequential thymectomy on splenic MLR shows that thymus removal only until stage 51 (15-16 days) abrogates this allogeneic response. Thymectomy from stage 52-57 (21-40 days), and in adulthood, failed to abolish MLR. It appears that lymphocytes that can participate in MLR are established in the periphery (e.g. spleen) early in development, in contrast to the slower "emergence" of PHA- reactive cells. These studies support a concept of T cell heterogeneity in amphibians

Relativistic Calculations for Incoherent Photoproduction of Eta Mesons

We develop a relativistic model for incoherent eta-photoproduction on nuclei. The elementary process is described using an effective Lagrangian containing photons, nucleons, the S11(1535) and D13(1520) nucleon resonances, and rho, omega, and eta mesons. The nucleon and eta wavefunctions are obtained from relativistic wave equations. Final-state interactions of the outgoing particles are included via optical potentials. The effects of these interactions are found to be large and lead to reduced cross sections.The incoherent cross sections for isovector transitions are much larger than those for isoscalar ones. The dominant contributions are those from the S11 and D13 resonances. We find important interference effects between the contributions of these two resonances. We give some detailed calculations for the cross sections for incoherent eta-photoproduction on C-12. We find that the incoherent cross section for a subset of states in the excitation energy region below 17 MeV are significantly larger than those of the coherent process. These cross sections may thus be accessible experimentally.Comment: 24 pages, 7 figures, to be published in Nuclear Physics

Nuclear Medium Effects in the Relativistic Treatment of Quasifree Electron Scattering

Non-relativistic reduction of the S-matrix for the quasifree electron scattering process $A\left(~e, e'p~\right)A-1$ is studied in order to understand the source of differences between non-relativistic and relativistic models. We perform an effective Pauli reduction on the relativistic expression for the S-matrix in the one-photon exchange approximation. The reduction is applied to the nucleon current only; the electrons are treated fully relativistically. An expansion of the amplitude results in a power series in the nuclear potentials. The series is found to converge rapidly only if the nuclear potentials are included in the nuclear current operator. The results can be cast in a form which reproduces the non-relativistic amplitudes in the limit that the potentials are removed from the nuclear current operator. Large differences can be found between calculations which do and do not include the nuclear potentials in the different orders of the nuclear current operator. In the high missing momentum region we find that the non-relativistic calculations with potentials included in the nuclear current up to second order give results which are close to those of the fully relativistic calculation. This behavior is an indication of the importance of the medium modifications of the nuclear currents in this model, which are naturally built into the relativistic treatment of the reaction.Comment: Latex, 26 pages including 5 uuencoded postscript figures. accepted for publication in Phys. Rev. C

Orthogonality Effects in Relativistic Models of Nucleon Knockout Reactions

We study the effect of wave function orthogonality in the relativistic treatment of the nucleon removal reactions (gamma, p) and (e, e' p). The continuum wave function describing the outgoing nucleon is made orthogonal to the relevant bound states using the Gram-Schmidt procedure. This procedure has the advantage of preserving the asymptotic character of the continuum wave function and hence the elastic observables are unaffected. The orthogonality effects are found to be negligible for (e, e' p) reactions for missing momenta up to 700 MeV/c. This holds true for both parallel and perpendicular kinematics. By contrast the orthogonalization of the wave functions appears to have a more pronounced effect in the case of (gamma, p) reactions. We find that the orthogonality effect can be significant in this case particularly for large angles. Polarization of the outgoing protons and photon asymmetry show more sensitivity than the cross sections. If the orthogonality condition is imposed solely on this one hole state the effects are usually smaller.Comment: LaTeX, 7 postscript figure

Relativistic Calculations for Photonuclear Reactions (III): A Consistent Relativistic Analysis of the (e,e'p) and (gamma,p) Reactions

Relativistic calculations for the quasifree electron scattering process (e, e'p) and the direct knockout contribution to (gamma, p) reactions are presented. The spectroscopic factors determined from the former reaction are used to fix the magnitude of the knockout contribution to the (gamma, p) reaction at 60 MeV. The results obtained for several nuclei indicate that the knockout contributions are much larger in magnitude and hence closer to the data than predicted in an earlier comparison based on non-relativistic calculations. We discuss the sensitivity of the results to the choice of parameters for the binding and final state interactions. We find these uncertainties to be more pronounced at the larger missing momenta explored by the (gamma, p) reaction. The implications of the present results for the size of contributions due to meson exchange currents are discussed.Comment: LaTeX, 21 pages including 5 figures, submitted to Nuc. Phys.

Relativistic versus Nonrelativistic Optical Potentials in A(e,e'p)B Reactions

We investigate the role of relativistic and nonrelativistic optical potentials used in the analysis of ($e,e'p$) data. We find that the relativistic calculations produce smaller ($e,e'p$) cross sections even in the case in which both relativistic and nonrelativistic optical potentials fit equally well the elastic proton--nucleus scattering data. Compared to the nonrelativistic impulse approximation, this effect is due to a depletion in the nuclear interior of the relativistic nucleon current, which should be taken into account in the nonrelativistic treatment by a proper redefinition of the effective current operator.Comment: Added one new figure, the formalism section has been enlarged and the list of references updated. Added one appendix. This version will appear in Phys. Rev. C. Revtex 3.0, 6 figures (not included). Full postscript version of the file and figures available at http://www.nikhefk.nikhef.nl/projects/Theory/preprints

Breakup Reactions of 11Li within a Three-Body Model

We use a three-body model to investigate breakup reactions of 11Li (n+n+9Li) on a light target. The interaction parameters are constrained by known properties of the two-body subsystems, the 11Li binding energy and fragmentation data. The remaining degrees of freedom are discussed. The projectile-target interactions are described by phenomenological optical potentials. The model predicts dependence on beam energy and target, differences between longitudinal and transverse momentum distributions and provides absolute values for all computed differential cross sections. We give an almost complete series of observables and compare with corresponding measurements. Remarkably good agreement is obtained. The relative neutron-9Li p-wave content is about 40%. A p-resonance, consistent with measurements at about 0.5 MeV of width about 0.4 MeV, seems to be necessary. The widths of the momentum distributions are insensitive to target and beam energy with a tendency to increase towards lower energies. The transverse momentum distributions are broader than the longitudinal due to the diffraction process. The absolute values of the cross sections follow the neutron-target cross sections and increase strongly for beam energies decreasing below 100 MeV/u.Comment: 19 pages, 14 figures, RevTeX, psfig.st

Reducing the environmental impact of surgery on a global scale: systematic review and co-prioritization with healthcare workers in 132 countries

Background Healthcare cannot achieve net-zero carbon without addressing operating theatres. The aim of this study was to prioritize feasible interventions to reduce the environmental impact of operating theatres. Methods This study adopted a four-phase Delphi consensus co-prioritization methodology. In phase 1, a systematic review of published interventions and global consultation of perioperative healthcare professionals were used to longlist interventions. In phase 2, iterative thematic analysis consolidated comparable interventions into a shortlist. In phase 3, the shortlist was co-prioritized based on patient and clinician views on acceptability, feasibility, and safety. In phase 4, ranked lists of interventions were presented by their relevance to high-income countries and low–middle-income countries. Results In phase 1, 43 interventions were identified, which had low uptake in practice according to 3042 professionals globally. In phase 2, a shortlist of 15 intervention domains was generated. In phase 3, interventions were deemed acceptable for more than 90 per cent of patients except for reducing general anaesthesia (84 per cent) and re-sterilization of ‘single-use’ consumables (86 per cent). In phase 4, the top three shortlisted interventions for high-income countries were: introducing recycling; reducing use of anaesthetic gases; and appropriate clinical waste processing. In phase 4, the top three shortlisted interventions for low–middle-income countries were: introducing reusable surgical devices; reducing use of consumables; and reducing the use of general anaesthesia. Conclusion This is a step toward environmentally sustainable operating environments with actionable interventions applicable to both high– and low–middle–income countries

POLARIZATION EFFECTS IN A DIRAC EQUATION APPROACH TO PHOTONUCLEAR REACTIONS

Nous avons calculé, utilisant la phénoménologie de Dirac, l'amplitude de réactions photonucléaires correspondant au diagramme de premier ordre. Le mouvement du nucléon est décrit à l'aide de l'équation de Dirac, et les effets de distorsion sont pris en considération. Les calculs sont effectués pour les observables de polarization, et nous comparons avec l'expérience.The amplitude corresponding to the lowest order diagram for photonuclear reactions is calculated in the framework of Dirac phenomenology. The nucleon motion is described using the Dirac equation and distortion effects are taken into account. Calculations are carried out for the polarization observables in the reaction and some comparison with experiment is discussed

Proposed approach for developing process-based KPIs for project control during the pre-project stage

In recent years a great deal of attention has been made to measuring different aspects of construction project performance. Some of the tools used for this purpose are the Key Performance Indicators (KPIs). The main shortcoming of these however is that most of them are end product oriented and hence are of little use for controlling the project performance while it is in progress. The pre-project stage in construction is where most of the decisions that greatly influence the project as a whole are taken. To be able to monitor and influence the performance of the process at the very beginning of the project is hence very beneficial. This paper describes a theoretical framework for developing KPIs to be used for project control in the pre-project stage. The theoretical framework is based on mapping the sub-processes within the preproject stage and their main activities. The subprocesses subprocesses and their activities are identified using literature and then validated by experts. A system dynamic (SD) approach to model the link between these and the project final objectives is proposed. The paper discusses the basis of the theoretical framework and the research methodology