Explicit Ziv-Zakai lower bound for bearing estimation

The extended Ziv-Zakai bound for vector parameters is used to develop a lower bound on the mean square error in estimating the 2-D bearing of a narrowband planewave signal using planar arrays of arbitrary geometry. The bound has a simple closed-form expression that is a function of the signal wavelength, the signal-to-noise ratio (SNR), the number of data snapshots, the number of sensors in the array, and the array configuration. Analysis of the bound suggests that there are several regions of operation, and expressions for the thresholds separating the regions are provided. In the asymptotic region where the number of snapshots and/or SNR are large, estimation errors are small, and the bound approaches the inverse Fisher information. This is the same as the asymptotic performance predicted by the local Cramer-Rao bound for each value of bearing. In the a priori performance region where the number of snapshots or SNR is small, estimation errors are distributed throughout the a priori parameter space and the bound approaches the a priori covariance. In the transition region, both small and large errors occur, and the bound varies smoothly between the two extremes. Simulations of the maximum likelihood estimator (MLE) demonstrate that the bound closely predicts the performance of the MLE in all regions     

Phenotypic analysis of antigen-specific T lymphocytes

Identification and characterization of antigen-specific T lymphocytes during the course of an immune response is tedious and indirect. To address this problem, the peptide-major histocompatability complex (MHC) ligand for a given population of T cells was multimerized to make soluble peptide-MHC tetramers. Tetramers of human lymphocyte antigen A2 that were complexed with two different human immunodeficiency virus (HIV)-derived peptides or with a peptide derived from influenza A matrix protein bound to peptide-specific cytotoxic T cells in vitro and to T cells from the blood of HIV-infected individuals. In general, tetramer binding correlated well with cytotoxicity assays. This approach should be useful in the analysis of T cells specific for infectious agents, tumors, and autoantigens.     

Interface formed between visceral peritoneum and experimental polypropylene or polytetrafluoroethylene abdominal wall implants

The objective of this work was to study the healing process at the interface between biomaterial and visceral peritoneum. Implants of polytetrafluoroethylene (ePTFE) and polypropylene prostheses were introduced into the abdominal wall of New Zealand rabbits. The behaviour of the biomaterials was analysed using light and scanning electron microscopy and immunohistochemistry in which a specific anti-rabbit macrophage monoclonal antibody (RAM 11) was employed. According to macroscopic observation, there was significantly fewer adhesions prosthesis-viscera to ePTFE than to polypropylene implants. After ePTFE implantation, restoration of the peritoneum took place in an orderly fashion. When polypropylene was used, the peritoneum formed was a disorderly tissue in which small areas of haemorrhage and necrosis could be seen to coincide with the appearance of adhesions. The number of labelled macrophages peaked 14 days after ePTFE or polypropylene implantation, after which it decreased gradually. It is concluded that, given the low rate of adhesion provoked by PTFE, this material is ideal for implants contiguous to the peritoneal cavity viscera. The macrophage response does not determine the use of one material or the other. The structure of the newly formed peritoneum and development of adhesions depends on the porosity of the biomaterial.     

Hypothermic ischaemia of the liver: a re-perfusion phenomenon

BACKGROUND: The effects of hypothermic injury to the liver were investigated on an isolated perfusion circuit by comparing porcine livers with varying degrees of preservation injury. METHODS: A group of unstored livers (n = 5) were compared to livers stored in University of Wisconsin (UW) solution for 18 h (n = 5), and a group of livers stored in Hartmann's solution for 18 h (n = 5). RESULTS: We observed that the degree of platelet sequestration was directly related to the severity of the preservation injury. After 2 h of isolated liver perfusion, the perfusate platelet count fell from 148 +/- 14 x 10(9)/L to 84 +/- 13 x 10(9)/L for control livers. In comparison for livers stored in UW solution, the platelet count fell from 173 +/- 43 x 10(9)/L to 61 +/- 14 x 10(9)/L representing a 64.8% fall, while for those stored in Hartmann's solution, an even more profound fall from 152 +/- 36 x 10(9)/L to 19 +/- 9 x 10(9)/L (87.5% fall) was observed. The difference between the UW-stored and Hartmann's-stored livers was significant (P < 0.05). However, using this model, the degree of leukocyte sequestration did not differentiate the groups. Both histological and ultrastructural examination of liver biopsies taken immediately following revascularization demonstrated that for mild degrees of preservation injury following hypothermic storage, changes occur to the sinusoidal lining cells well before changes to the parenchymal elements. CONCLUSIONS: These findings substantiate the hypothesis that the primary injury associated with hypothermia involves the sinusoidal lining cells (non-parenchymal elements), that it is predominantly a reperfusion phenomenon and that efforts at improving preservation should therefore be targeted primarily at these cells and not the hepatocytes.     

The development and benefits of nursing protocols for fractured neck of femur patients

In this article the authors discuss the development, use and auditing of nursing care protocols, which have been implemented and form a guide for nurses caring for patients with fractured neck of femur in Southend Health Care NHS Trust. The development of these protocols occurred after an initial medical audit, which was followed by a far larger multidisciplinary audit, and both of these revealed there was need for changes in the clinical management of such patients; subsequently a large multidisciplinary working group worked together to develop care protocols/pathways to enable closure of the audit loop. The reasons for focusing on fractured neck of femur as a high priority condition are also discussed. All professional groups caring for these patients were involved in the multidisciplinary working group, which was formed to close the audit loop and to improve clinical practices by increasing the systemization and coordination of care. The development of the nursing protocols represented an extremely important part of this process, and the care of about 700 patients was examined during this work. The audit and associated subsequent work have resulted in direct improvements to both patient care and health outcomes, and the authors conclude that there is great value in developing multidisciplinary protocols, particularly those involving nurses, because they spend more time with patients whilst they are in hospital than any other professional group. The benefits of these nursing protocols have been multifold, in particular they have facilitated a clearer flow of patients through the hospital, increased awareness of responsibilities and reduced duplication of effort, and ensured patients receive the best possible care over the 24-hour period.     

A brief review of the ionic conductivity enhancement for selected oxide electrolytes

The advantages of lowering the operation temperature of SOFCs have attracted great interest worldwide. One of the major barriers to decreasing the operation temperature is the ohmic loss of the electrolyte. Maximizing the electrolyte ionic conductivity is of significant importance, especially in the absence of new electrolyte materials. The ionic conductivity of electrolytes can be influenced by many parameters. There has been an enormous effort in the literature for the improvement of the electrolyte ionic conductivity. From a practical point of view, this paper reviews various approaches to enhancing the ionic conductivity of polycrystalline zirconia- and ceria-based oxide electrolytes in the light of composition, microstructure, and processing. Suggestions are given for future work.