1,166 research outputs found

    Magnetic strong coupling in a spin-photon system and transition to classical regime

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    We study the energy level structure of the Tavis-Cumming model applied to an ensemble of independent magnetic spins s=1/2s=1/2 coupled to a variable number of photons. Rabi splittings are calculated and their distribution is analyzed as a functin of photon number nmaxn_{\rm max} and spin system size NN. A sharp transition in the distribution of the Rabi frequency is found at nmax≈Nn_{\rm max}\approx N. The width of the Rabi frequency spectrum diverges as N\sqrt{N} at this point. For increased number of photons nmax>Nn_{\rm max}>N, the Rabi frequencies converge to a value proportional to nmax\sqrt{n_{\rm max}}. This behavior is interpreted as analogous to the classical spin resonance mechanism where the photon is treated as a classical field and one resonance peak is expected. We also present experimental data demonstrating cooperative, magnetic strong coupling between a spin system and photons, measured at room temperature. This points towards quantum computing implementation with magnetic spins, using cavity quantum-electrodynamics techniques.Comment: Received 8 April 2010; revised manuscript received 17 June 2010; published 14 July 201

    Liposomal amphotericin B twice weekly as antifungal prophylaxis in paediatric haematological malignancy patients

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    AbstractData on antifungal prophylaxis in paediatric cancer patients at high risk for invasive fungal disease (IFD) are scant. Intermittent administration of liposomal amphotericin B (LAMB) has been shown to be safe and effective in adult patients with haematological malignancies. We prospectively evaluated the safety and efficacy of prophylactic LAMB at a dosage of 2.5 mg/kg twice weekly in children at high risk for IFD. Efficacy was compared with that in a historical control group of patients with similar demographic characteristics not receiving LAMB prophylaxis. A total of 46 high-risk patients (24 boys; mean age, 7.7 years) with 187 episodes of antifungal prophylaxis were analysed. The median duration of neutropenia (<500/”L) was 10 days. LAMB was discontinued in four patients because of acute allergic reactions. Median values for creatinine and liver enzymes at end of treatment did not differ significantly from those at baseline. Hypokalaemia (<3.0 mmol/L) occurred with 13.5% of the prophylactic episodes, but was usually mild and always reversible. No proven/probable IFD occurred in patients receiving LAMB prophylaxis. In comparison, five proven and two probable IFDs were observed in 45 historical controls not receiving LAMB prophylaxis (p 0.01). LAMB prophylaxis had no impact on the use of empirical antifungal therapy. Systemic antifungal prophylaxis with LAMB 2.5 mg/kg twice weekly is feasible and safe, and seems to be an effective approach for antifungal prophylaxis in high-risk paediatric cancer patients

    Effect of high temperature heat treatments on the quality factor of a large-grain superconducting radio-frequency niobium cavity

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    Large-grain Nb has become a viable alternative to fine-grain Nb for the fabrication of superconducting radio-frequency cavities. In this contribution we report the results from a heat treatment study of a large-grain 1.5 GHz single-cell cavity made of "medium purity" Nb. The baseline surface preparation prior to heat treatment consisted of standard buffered chemical polishing. The heat treatment in the range 800 - 1400 C was done in a newly designed vacuum induction furnace. Q0 values of the order of 2x1010 at 2.0 K and peak surface magnetic field (Bp) of 90 mT were achieved reproducibly. A Q0-value of (5+-1)1010 at 2.0 K and Bp = 90 mT was obtained after heat treatment at 1400 C. This is the highest value ever reported at this temperature, frequency and field. Samples heat treated with the cavity at 1400 C were analyzed by secondary ion mass spectrometry, secondary electron microscopy, energy dispersive X-ray, point contact tunneling and X-ray diffraction and revealed a complex surface composition which includes titanium oxide, increased carbon and nitrogen content but reduced hydrogen concentration compared to a non heat-treated sample

    Experimental Testing and Modeling of 5 kW Oil-Free Open Drive Scroll Expander Using R245fa

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    Organic Rankine Cycles (ORC) are thermodynamic power cycles designed to generate work from low temperature sources, typically between 80 °C to 270 °C.  The low temperature heat input makes this technology attractive for applications in waste heat recovery from industrial processes, exhaust gas from diesel engines, solar systems, geothermal systems, and others.  The expander has the greatest effect on increasing the efficiency of an ORC. The operating  conditions that the expander is subjected to are directed related to its efficiency.  The performance of a 5 kW scroll expander with a displacement of 73.6 cm3 per revolution, operating at speeds from 500 to 3600 rpm, and using R245fa as the working fluid in a traditional Organic Ranking cycle is experimentally investigated In this paper. Tests were conducted varying the mass flow rate of the working fluid and varying source temperatures, while measuring the effective expander power production and the isentropic efficiency.  The experimental data was then used to develop a model of the scroll expander. Using this model, thermodynamic simulations were carried out for applications similar to exhaust gas waste heat recovery from internal combustion engines

    Generalised joint regression for count data: a penalty extension for competitive settings

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    We propose a versatile joint regression framework for count responses. The method is implemented in the R add-on package GJRM and allows for modelling linear and non-linear dependence through the use of several copulae. Moreover, the parameters of the marginal distributions of the count responses and of the copula can be specified as flexible functions of covariates. Motivated by competitive settings, we also discuss an extension which forces the regression coefficients of the marginal (linear) predictors to be equal via a suitable penalisation. Model fitting is based on a trust region algorithm which estimates simultaneously all the parameters of the joint models. We investigate the proposal’s empirical performance in two simulation studies, the first one designed for arbitrary count data, the other one reflecting competitive settings. Finally, the method is applied to football data, showing its benefits compared to the standard approach with regard to predictive performance

    Thermodynamic Comparison of Organic Rankine Cycles Employing Liquid-Flooded Expansion or a Solution Circuit

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    Two modifications to a conventional Organic Rankine Cycle (ORC) are investigated: an Organic Rankine Cycle with Liquid-Flooded Expansion (ORCLFE), and an Organic Rankine Cycle with Solution Circuit (ORCSC). The ORCLFE involves “flooding” the expansion device with a liquid that is in thermal equilibrium with the primary working fluid, while simultaneously expanding the primary working fluid through the same device. The ORCSC employs a zeotropic mixture consisting of two components with a large boiling point difference. The more volatile component in the vapor phase is separated from the absorbent in the liquid phase; the vapor then flows through the expansion device, whereas the liquid absorbent gives rise to a regenerative solution circuit. A thermodynamic model is used to compare these modified ORCs with conventional ORC technology for a range of working fluids including ammonia, water, CO2, acetone, pentane, R134a and R245fa. The working fluid pairs considered for the ORCSC are ammoniaewater and CO2eacetone. Based purely on thermodynamic considerations, the conventional ORC using water as the working fluid is found to be more efficient than ORCs that use other working fluids. It yields almost 65% of the Carnot efficiency for a source and sink temperature of 200C and 20C, respectively. However, the use of water requires low expander exhaust quality, large pressure ratios, and a large expander due to its low density at the expander exhaust. Thus, the practical challenges of using water as a working fluid at typical ORC input temperatures may make its use prohibitive. The ORCLFE always leads to improved cycle efficiency when compared to an ORC for a given working fluid, but it requires the use of a positive displacement expander. The ORCSC shows the lowest efficiencies for the working fluid pairs studied. There are significant practical advantages intrinsic to both the ORCLFE and the ORCSC. For example, the more isothermal expansion of the ORCLFE eliminates the concern of low expander exhaust quality for wet working fluids. The ORCSC provides the ability to use the two-phase temperature glide to match source and sink temperature profiles, facilitates intrinsic capacity control, and can have significantly lower working pressures than an ORC. Ultimately, the overall best choice of cycle and working fluid is highly application-specific and should balance the tradeoffs between efficiency and practical concerns. The thermodynamic analysis presented in this work represents a step toward identifying an optimal ORC solution for an application where the temperature glides of the source and sink fluids are sufficiently small to approximate a thermal energy reservoir

    Flight performance of actively foraging honey bees is reduced by a common pathogen

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    ArticleSudden and severe declines in honey bee (Apis mellifera) colony health in the US and Europe have been attributed, in part, to emergent microbial pathogens, however, the mechanisms behind the impact are unclear. Using roundabout flight mills, we measured the flight distance and duration of actively foraging, healthy-looking honey bees sampled from standard colonies, before quantifying the level of infection by Nosema ceranae and Deformed Wing Virus complex (DWV) for each bee. Neither the presence nor quantity of N. ceranae at low, natural levels of infection had any effect on flight distance or duration, but presence of DWV reduced flight distance by two thirds and duration by one half. Quantity of DWV was shown to have a significant, but weakly positive relation with flight distance and duration, however, the low amount of variation that was accounted for suggests further investigation by dose-response assays is required. We conclude that widespread, naturally occurring levels of infection by DWV weaken the flight ability of honey bees and high levels of within-colony prevalence are likely to reduce efficiency and increase the cost of resource acquisition. Predictions of implications of pathogens on colony health and function should take account of sub-lethal effects on flight performance.This work was funded by the Insect Pollinators Initiative (IPI) grants BB/I000100/1, BB/I000097/1 and BB/I000097/2, C.B. Dennis British Beekeepers' Research Trust and the High Wycombe Beekeepers’ Association. The IPI is funded jointly by the BBSRC, Defra, NERC, The Scottish Government and The Wellcome Trust, under the LWEC Partnership. Rothamsted Research is a national institute of bioscience strategically funded by the BBSRC

    Flight performance of actively foraging honey bees is reduced by a common pathogen

    Get PDF
    Sudden and severe declines in honey bee (Apis mellifera) colony health in the US and Europe have been attributed, in part, to emergent microbial pathogens, however, the mechanisms behind the impact are unclear. Using roundabout flight mills, we measured the flight distance and duration of actively foraging, healthy‐looking honey bees sampled from standard colonies, before quantifying the level of infection by Nosema ceranae and Deformed Wing Virus complex (DWV) for each bee. Neither the presence nor the quantity of N. ceranae were at low, natural levels of infection had any effect on flight distance or duration, but presence of DWV reduced flight distance by two thirds and duration by one half. Quantity of DWV was shown to have a significant, but weakly positive relation with flight distance and duration, however, the low amount of variation that was accounted for suggests further investigation by dose‐response assays is required. We conclude that widespread, naturally occurring levels of infection by DWV weaken the flight ability of honey bees and high levels of within‐colony prevalence are likely to reduce efficiency and increase the cost of resource acquisition. Predictions of implications of pathogens on colony health and function should take account of sublethal effects on flight performance
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