Magnetic trapping of ultracold neutrons

Three-dimensional magnetic confinement of neutrons is reported. Neutrons are loaded into an Ioffe-type superconducting magnetic trap through inelastic scattering of cold neutrons with 4He. Scattered neutrons with sufficiently low energy and in the appropriate spin state are confined by the magnetic field until they decay. The electron resulting from neutron decay produces scintillations in the liquid helium bath that results in a pulse of extreme ultraviolet light. This light is frequency downconverted to the visible and detected. Results are presented in which 500 +/- 155 neutrons are magnetically trapped in each loading cycle, consistent with theoretical predictions. The lifetime of the observed signal, 660 s +290/-170 s, is consistent with the neutron beta-decay lifetime.Comment: 17 pages, 18 figures, accepted for publication in Physical Review

Gamma Prime Precipitate Evolution During Aging of a Model Nickel-Based Superalloy

The microstructural stability of nickel-based superalloys is critical for maintaining alloy performance during service in gas turbine engines. In this study, the precipitate evolution in a model polycrystalline Ni-based superalloy during aging to 1000 hours has been studied via transmission electron microscopy, atom probe tomography and neutron diffraction. Variations in phase composition and precipitate morphology, size and volume fraction were observed during aging, whilst the constrained lattice misfit remained constant at approximately zero. The experimental composition of the γ matrix phase was consistent with thermodynamic equilibrium predictions, whilst significant differences were identified between the experimental and predicted results from the γʹ phase. These results have implications for the evolution of mechanical properties in service and their prediction using modeling methods.The authors wish to acknowledge Mrs. S. Rhodes, Dr. H.T. Pang, Dr. D.M. Collins, and Dr. O.M.D.M. Messé for their assistance with the experiments performed. Funding was provided by the EPSRC/Rolls-Royce Strategic Partnership under EP/M005607/1 and EP/H022309/1. The Oxford Atom Probe facility was funded by the EPSRC under EP/M022803/1. Neutron diffraction beam time was supported through the Canadian Neutron Beam Centre under Experiment number 1258

Disruption of Micro-organisms

Techniques for the disruption of cells have evolved and for the most part suitable methods for the solution of individual needs have been arrived at by a pragmatic approach. It is clear, however, that from the viewpoint of future developments much is to be gained from a rigorous physical and biochemical understanding of the processes involved in cell breakage. In recent years, a requirement for a greater degree of sophistication has become evident as the emphasis has shifted from the aim of quantitative enzyme release to that of the preservation of information content within the disrupted system. Many of the problems of the efficient extraction of intracellular components have been overcome via a diversity of methodological developments, it is evident that the current demands made on disruption procedures on the part of microbial physiologists engaged in fundamental studies of sub-cellular organization can only be partially satisfied. Extrapolation of data obtained with cell-free extracts to the in vivo situation requires independent confirmation. . Many of the methods used for quantitative release of enzymes from micro-organisms, especially those relying on the development of high liquid or solid shearing forces are not suitable for the release of “intact” membranes or organelles. As further information on the complexity of intracellular organization becomes available, it becomes increasingly evident that the extraction of “intact” organelles may often be an unattainable goal

A silicon microfluidic ultrasonic separator

Ultrasonic standing waves can be used to generate forces on particles within a fluid. Such forces have a number of potential applications in microfluidic devices. This paper describes such a device providing filtration on a microfluidic scale. It is microfabricated and uses ultrasound in the megahertz frequency range to concentrate particles at a node within the flow. It offers the possibility of a functional equivalent of a centrifugal separator for microfluidic systems. It is constructed using silicon and Pyrex, and hence is highly compatible with established microfabrication techniques. The modelling, design, fabrication and control of the device are discussed