Preferred conformations of enol ethers in solution: Detection of an equilibrium by kinetic nuclear overhauser effects

n.O.e. difference spectra reveal that the preferred solution conformation of methyl enol ethers has the methyl group $\text{syn}$-periplanar to the double bond; n.O.e kinetics in a methoxy—heptatriene demonstrate the presence of both possible periplanar conformations, the energy difference being $\text{ca}$ 1 kcal/mole.     

Embrittlement observed in Cr–Mo turbine bolts after service

The present paper describes a study aimed at investigating the extent of service related embrittlement suffered by a series of Cr–Mo steel turbine bolts after over 200,000 h at 450°C. A small section of material was removed from a non-critical location of all the 51 bolts. From this section, the chemical composition, average hardness and average prior austenite grain size were measured. The toughness of the bolts was measured by Charpy impact testing and/or Auger electron spectroscopy. From the various parameters investigated, it was established that grain size and phosphorus level were the only factors which consistently identified whether a bolt was embrittled or non-embrittled. Indeed it was established that bolt embrittlement could be predicted using the simple product of microstructure grain size d (μm's) and bulk phosphorus content. Finally, it was observed that bolt embrittlement could be predicted using the simple product of microstructure grain size and bulk phosphorus level and that such a trend indicated the importance of grain boundary area available for service induced phosphorus segregation.     

Examining the feasibility of using a modelling tool to assess resilience across a health-care system and assist with decisions concerning service reconfiguration

Changes in medical practice, demographic shifts and financial pressures are all examples of factors that may contribute to demand for periodic changes in the configuration of health services. When reconfiguring a service, health planners often take into account projected demand for services, patient access criteria and budgetary constraints (among other things), but typically give little consideration regarding its resilience to deliver services during and after external disruptions to its capability to deliver. In this paper we discuss a study conducted in response to a direct request from the National Health Service (NHS) Resilience Project within the Department of Health to explore the feasibility of assessing resilience across local services within the NHS and developing a computer software tool to assess resilience of different service reconfigurations. We give an account of the modelling process used, including the analytical framework we developed using both optimisation and heuristic methods, and an illustrative example of usage of a prototype software tool. We also highlight the key lessons that emerged during this project, which may be helpful to OR analysts working on similar projects regarding resilience in the public sector.     

Spiral demystified

Spiral acquisition schemes offer unique advantages such as flow compensation, efficient k-space sampling and robustness against motion that make this option a viable choice among other non-Cartesian sampling schemes. For this reason, the main applications of spiral imaging lie in dynamic magnetic resonance imaging such as cardiac imaging and functional brain imaging. However, these advantages are counterbalanced by practical difficulties that render spiral imaging quite challenging. Firstly, the design of gradient waveforms and its hardware requires specific attention. Secondly, the reconstruction of such data is no longer straightforward because k-space samples are no longer aligned on a Cartesian grid. Thirdly, to take advantage of parallel imaging techniques, the common generalized autocalibrating partially parallel acquisitions (GRAPPA) or sensitivity encoding (SENSE) algorithms need to be extended. Finally, and most notably, spiral images are prone to particular artifacts such as blurring due to gradient deviations and off-resonance effects caused by B₀ inhomogeneity and concomitant gradient fields. In this article, various difficulties that spiral imaging brings along, and the solutions, which have been developed and proposed in literature, will be reviewed in detail.     

Rotating orthogonal polarization imaging

Surface reflections often present a problem in the polarization difference imaging of tissue. The technique described involves illumination in a single polarization state and detection in the orthogonal polarization state. Synchronously rotating both the illumination and orthogonal detection states provides an image free from surface reflections that is sensitive to the polarization properties of the underlying tissue. Results on tissue phantoms demonstrate that polarization sensitive measurements of a test target can be made up to a depth of 12 mean free paths within a scattering medium. Preliminary images of bovine tendon are also demonstrated.     

Creating responsive surfaces with tailored wettability switching kinetics and reconstruction reversibility

We report on the formation of responsive surfaces with tailorable surface reconstruction kinetics and switching hysteresis by thiolene radical addition of mercaptoalkanols with variable lengths to poly(vinylmethylsiloxane) networks. Exposing these elastomer surfaces to water results in rearrangement of the hydrophilic alkanes at the surface. The rearrangement kinetics decreases with increasing number of the methylene spacers (n) in the mercaptoalkanol. The response kinetics is found to be very fast for n = 2 and 6. For instance, upon exposing to water, the water contact angle on 3-mercaptopropanol-based surfaces decreases by approximately 35 degrees at the rate of 2 degrees /s. The high flexibility of the siloxane backbone endows these materials with switching longevity; the materials were able to switch their wettability over 10 cycles with minimum hysteresis. Increasing the number of methylene spacers to n = 11 decreases the surface reorganization dramatically. Formation of semicrystalline regions in such materials (detected via IR) is responsible for initial "sluggish" kinetics and eventual surface "freezing".     

Model-independent source imaging using two-pion correlations in (2 to 8)a GeV Au+Au collisions

We report a particle source imaging analysis based on two-pion correlations in high multiplicity Au+Au collisions at beam energies between 2A and 8A GeV. We apply the imaging technique introduced by Brown and Danielewicz, which allows a model-independent extraction of source functions with useful accuracy out to relative pion separations of about 20 fm. The extracted source functions have Gaussian shapes. Values of source functions at zero separation are almost constant across the energy range under study. Imaging results are found to be consistent with conventional source parameters obtained from a multidimensional Hanburg-Brown-Twiss analysis.