A probability-conserving cross-section biasing mechanism for variance reduction in Monte Carlo particle transport calculations

In Monte Carlo particle transport codes, it is often important to adjust reaction cross sections to reduce the variance of calculations of relatively rare events, in a technique known as non-analogous Monte Carlo. We present the theory and sample code for a Geant4 process which allows the cross section of a G4VDiscreteProcess to be scaled, while adjusting track weights so as to mitigate the effects of altered primary beam depletion induced by the cross section change. This makes it possible to increase the cross section of nuclear reactions by factors exceeding 10^4 (in appropriate cases), without distorting the results of energy deposition calculations or coincidence rates. The procedure is also valid for bias factors less than unity, which is useful, for example, in problems that involve computation of particle penetration deep into a target, such as occurs in atmospheric showers or in shielding

Wind-tunnel tests of wide-chord teetering rotors with and without outboard flapping hinges

Wind tunnel tests of aeroelastically designed helicopter rotor models were conducted to obtain rotor aerodynamic performance and dynamic response data pertaining to two-bladed teetering rotors with a wider chord and lower hover tip speed than currently employed on production helicopters. The effects of a flapping hinge at 62 percent radius were also studied. Finally, the effects of changing tip mass on operating characteristics of the rotor with the outboard flapping hinge were examined. The models were tested at several shaft angles of attack for five advance ratios, 0.15, 0.25, 0.35, 0.40, and 0.45. For each combination of shaft angle and advance ratio, the rotor lift was varied over a wide range to include simulated maneuver conditions. At each test condition, rotor aerodynamic performance and dynamic response data were obtained. From these tests, it was found that wide-chord rotors may be subject to large control forces. An outboard flapping hinge may be used to reduce beamwise bending moments over a significant part of the blade radius without significantly affecting the chordwise bending moments

An improved computational procedure for determining helicopter rotor blade natural modes

An existing computer program, used for predicting the natural frequencies and mode shapes of helicopter rotor blades, was refined to improve program accuracy and versatility. The program is based on the Holzer-Myklestad approach adapted for rotating beams. Coupled vertical (out-of-plane), horizontal (in-plane), and torsional mode characteristics were determined for a variety of hub and blade configurations. The resulting program is documented by presenting the recursion equations and techniques for determining natural frequencies and mode shapes, input data requirements, and descriptions of various program outputs. The accuracy of the program is demonstrated by comparing computed results with exact solutions to classical problems and experimental data

Magnetic properties of PrCu2_2 at high pressure

We report a study of the low-temperature high-pressure phase diagram of the intermetallic compound PrCu$_2$, by means of molecular-field calculations and $^{63,65}$Cu nuclear-quadrupole-resonance (NQR) measurements under pressure. The pressure-induced magnetically-ordered phase can be accounted for by considering the influence of the crystal electric field on the $4f$ electron orbitals of the Pr$^{3+}$ ions and by introducing a pressure-dependent exchange interaction between the corresponding local magnetic moments. Our experimental data suggest that the order in the induced antiferromagnetic phase is incommensurate. The role of magnetic fluctuations both at high and low pressures is also discussed.Comment: 7 pages, 6 figures, submitted to Eur. Phys. J.

Moral Hazard and the US Stockmarket: Analyzing the "Greenspan Put"

When the risk premium in the US stock market fell far below its historic level, Shiller (2000) attributed this to a bubble driven by psychological factors. As an alternative explanation, we point out that the observed risk premium may be reduced by one-sided intervention policy on the part of the Federal Reserve, which leads investors into the erroneous belief that they are insured against downside risk. By allowing for partial credibility and state dependent risk aversion, we show that this "insurance" - referred to as the Greenspan put - is consistent with the observation that implied volatility rises as the market falls. Our bubble, like Shiller's, involves market psychology, but what we describe is not so much "irrational exuberance" as exaggerated faith in the stabilizing power of Mr. Greenspan.

Evaluation study of the IHM project on the evaluation of the accreditation of health and social care managers: a pilot.

This evaluation report was commissioned by the Institute of Healthcare Management (IHM) in March 2009 and is based on the accredited manager pilot project that started in May 2009. The IHM pilot project was funded by the Department of Health (Estates). The pilot project aimed to offer managers for the health and social care sectors the opportunity to gain accredited manager status based upon their previous performance and achievements towards nine core manager behaviours1. The pilot project was intended to develop and implement materials that would support the managers in completion of a portfolio of achievement to demonstrate competence in the behaviours (Sugden, 2009). The evaluation study of the pilot project has aimed to include the experiences of the main stakeholders, namely; the candidates (Healthcare and Social), the pilot project team, a representative from the Department of Health (Estates), representing the commissioning body for the project, and the assessors of the candidate portfolios and viva voce examinations. The candidates were drawn mainly from the field of estates and facilities managers within the healthcare sector, with two participants for the social care sector. The project was prompted by the recognition that many managers in the health and social care sector may encounter difficulties in finding the time to attend conventionally delivered training and development programmes. There was also recognition of the need for experienced managers to be able to demonstrate their competence towards good practice behaviours rather than have to undertake taught delivery

Oxygen and light sensitive field-effect transistors based on ZnO nanoparticles attached to individual double-wall carbon nanotubes

The attachment of semiconducting nanoparticles to carbon nanotubes is one of the most challenging subjects in nanotechnology. Successful high coverage attachment and control over the charge transfer mechanism and photo-current generation opens a wide field of new applications such as highly effective solar cells and fibre-enhanced polymers. In this work we study the charge transfer in individual double-wall carbon nanotubes highly covered with uniform ZnO nanoparticles. The synthetic colloidal procedure was chosen to avoid long-chained ligands at the nanoparticle-nanotube interface. The resulting composite material was used as conductive channel in a field effect transistor device and the electrical photo-response was analysed under various conditions. By means of the transfer characteristics we could elucidate the mechanism of charge transfer from non-covalently attached semiconducting nanoparticles to carbon nanotubes. The role of positive charges remaining on the nanoparticles is discussed in terms of a gating effect.Comment: 6 pages, 4 figure

Power, participation and partnership: methodological reflection on researching professional doctorate candidates' experiences of researching in the workplace

This study aimed to explore the candidate experience in order to understand more deeply aspects of the development in work based research. Delphi technique was chosen as an approach in order to capture a range of experience and data, to inform how we may best support candidates on practice based doctorates. Many such programmes include a stakeholder learning agreement between the candidate, the university and the employer organisation with the common aim to bring about transformational and sustainable change. Our research to date indicates a disparity within the agreement in the level of stakeholder participation. Where the organisation stakeholder is not fully engaged and involved in supporting the research, there is a potential threat to the effectiveness of any change outcome. Current practice based doctoral research participants were invited to relate to a range of temporal themes in their research project cycle, for example: setting up the project; implementing the project; changes/ contingency planning within the project; project completion and post completion. Of particular interest in relation to the above was the availability of resources and how they were used within the project life cycle. In this respect, resources are deemed to include, human, material, time, personal and organisational culture influence. The allocation, manipulation and distribution of such resources can be understood in terms of power relationships. The paper presents our experience and reflections from two iterative Delphi cycles and proposes a final stage of greater integration with existing academic resources within the professional doctorate programme. The study has enabled the researchers to gain a new understanding of how power may operate in a work based research project through the experience of undertaking the Delphi approach. Furthermore, by thinking about affordances of the project life cycle, it may help us to better understand needs and strategy for the curriculum in order to more effectively support candidates through their transformational learning experience. The consequences of such change might have implications for participation and power distribution within the management and leadership of doctoral work base research projects

The light chain of tetanus toxin inhibits calcium-dependent vasopressin release from permeabilized nerve endings

The effects of tetanus toxin and its light and heavy chain subunits on vasopressin release were investigated in digitonin-permeabilized neurosecretory nerve terminals isolated from the neural lobe of the rat pituitary gland. Exocytosis was induced by challenging the permeabilized nerve endings with micromolar calcium concentrations. Tetanus toxin inhibited vasopressin release only in the presence of the reducing agent dithiothreitol. This effect was irreversible. The purified light chain of tetanus toxin strongly inhibited exocytosis in a dose-dependent manner with half-maximal effect at c. 10 nM. The action of the light chain was observed after only 2.5 min of preincubation. Separated heavy chain subunit had no effect on hormone secretion. Inhibition of vasopressin release could be prevented by preincubating the light chain of tetanus toxin with an immune serum against tetanus toxin. The data clearly demonstrate that in mammalian neurosecretory nerve endings tetanus toxin acts at a step downstream from the activation by Ca2+ of the exocytotic machinery and that the functional domain of this toxin is confined to its light chain