In-situ Magnesium Diboride Superconducting Thin Films grown by Pulsed Laser Deposition

Superconducting thin films of MgB2 were deposited by Pulsed Laser Deposition on magnesium oxide and sapphire substrates. Samples grown at 450C in an argon buffer pressure of about 10-2 mbar by using a magnesium enriched target resulted to be superconducting with a transition temperature of about 25 K. Film deposited from a MgB2 sintered pellet target in ultra high vacuum conditions showed poor metallic or weak semiconducting behavior and they became superconducting only after an ex-situ annealing in Mg vapor atmosphere. Up to now, no difference in the superconducting properties of the films obtained by these two procedures has been evidenced.Comment: 10 pages, 4 figure

Exploring the interdependencies of research funders in the UK

Investment in medical research is vital to the continuing improvement of the UK's health and wealth. It is through research that we expand our understanding of disease and develop new treatments for patients. Medical research charities currently contribute over £1 billion annually to medical research in the UK, of which over £350 million is provided by Cancer Research UK. Many charities, including Cancer Research UK, receive no government funding for their research activity. Cancer Research UK is engaged in a programme of work in order to better understand the medical research funding environment and demonstrate the importance of sustained investment. A key part of that is the Office of Health Economics‟ (OHE) 2011 report “Exploring the interdependency between public and charitable medical research”. This study found that there are substantial benefits, both financial and qualitative, from the existence of a variety of funders and that reductions in the level of government financial support for medical research are likely to have broader negative effects. This contributed to other evidence which found that the activities and funding of the charity, public and private sectors respectively are complementary, i.e. mutually reinforcing, rather than duplicative or merely substituting for one another. “Exploring the interdependencies of research funders in the UK” by the Office of Health Economics (OHE) and SPRU: Science and Technology Policy Research at the University of Sussex, represents a continued effort to build the evidence base around the funding of medical research. This report uncovers the extent to which funders of cancer research are interdependent, nationally and internationally. Key figures show that two thirds of publications acknowledging external support have relied on multiple funders, while just under half benefited from overseas funding, and almost a fifth are also supported by industry. In addition the analysis shows that the general public would not want tax funding of cancer research to be reduced, but would not donate enough to charities to compensate for any such reduction

2N+4-rule and an atlas of bulk optical resonances of zigzag graphene nanoribbons

Development of on-chip integrated carbon-based optoelectronic nanocircuits requires fast and non-invasive structural characterization of their building blocks. Recent advances in synthesis of single wall carbon nanotubes and graphene nanoribbons allow for their use as atomically precise building blocks. However, while cataloged experimental data are available for the structural characterization of carbon nanotubes, such an atlas is absent for graphene nanoribbons. Here we theoretically investigate the optical absorption resonances of armchair carbon nanotubes and zigzag graphene nanoribbons continuously spanning the tube (ribbon) transverse sizes from 0.5(0.4) nm to 8.1(12.8) nm. We show that the linear mapping is guaranteed between the tube and ribbon bulk resonance when the number of atoms in the tube unit cell is 2 N+ 4 , where N is the number of atoms in the ribbon unit cell. Thus, an atlas of carbon nanotubes optical transitions can be mapped to an atlas of zigzag graphene nanoribbons

Growth methods of c-axis oriented MgB2 thin films by pulsed laser deposition

High quality MgB2 thin films have been obtained by pulsed laser deposition both on MgO and on Al2O3 substrates using different methods. In the standard two-step procedure, an amorphous precursor layer is deposited at room temperature starting both from stoichiometric target and from boron target: after this first step, it is annealed in magnesium atmosphere in order to crystallize the superconducting phase. The so obtained films show a strong c-axis orientation, evidenced by XRD analysis, a critical temperature up to 38 K and very high critical fields along the basal planes, up to 22T at 15K. Also an in situ one step technique for the realization of superconducting MgB2 thin films has been developed. In this case, the presence of an argon buffer gas during deposition is crucial and we observe a strong dependence of the quality of the deposited film on the background gas pressure. The influence of the Ar atmosphere has been confirmed by time and space-resolved spectroscopy measurements on the emission spectrum of the plume. The Ar pressure modifies strongly the plasma kinetics by promoting excitation and ionization of the plume species, especially of the most volatile Mg atoms, increasing their internal energy.Comment: Paper presented at Boromag Workshop, Genoa 17-19 June 2002, in press on SUS

Low Temperature Fabrication of MgB2

We report the fabrication of MgB2 with bulk superconducting properties by conventional solid state methods at temperatures as low as 550 C. Mg deficiencies of the type Mg1-xB2 were tested. Tc was found to decrease by about 1K at large x, though the amount of non-stoichiometry, if any, is likely to be very small. For specific processing conditions, indications of the 25-30 K transition often seen in thin films were seen in the bulk materials. The lower temperature transition may be associated with the grain boundaries. These results indicate that it should be possible to fabricate MgB2 with bulk properties in in-situ thin films at temperatures of 600 C or less.Comment: 3 pages, 5 figures (submitted to Journal of Applied Physics

Acidity and nucleophilic reactivity of glutathione persulfide

Persulfides (RSSH/RSS2) participate in sulfur trafficking and metabolic processes, and are proposed to mediate the signaling effects of hydrogen sulfide (H2S). Despite their growing relevance, their chemical properties are poorly understood. Herein, we studied experimentally and computationally the formation, acidity, and nucleophilicity of glutathione persulfide (GSSH/ GSS2), the derivative of the abundant cellular thiol glutathione (GSH). We characterized the kinetics and equilibrium of GSSH formation from glutathione disulfide and H2S. A pKa of 5.45 for GSSH was determined, which is 3.49 units below that of GSH. The reactions of GSSH with the physiologically relevant electrophiles peroxynitrite and hydrogen peroxide, and with the probe monobromobimane, were studied and compared with those of thiols. These reactions occurred through SN2 mechanisms. At neutral pH, GSSH reacted faster than GSH because of increased availability of the anion and, depending on the electrophile, increased reactivity. In addition, GSS2 presented higher nucleophilicity with respect to a thiolate with similar basicity. This can be interpreted in terms of the so-called a effect, i.e. the increased reactivity of a nucleophile when the atom adjacent to the nucleophilic atom has high electron density. The magnitude of the a effect correlated with the Brønsted nucleophilic factor, bnuc, for the reactions with thiolates and with the ability of the leaving group. Our study constitutes the first determination of the pKa of a biological persulfide and the first examination of the a effect in sulfur nucleophiles, and sheds light on the chemical basis of the biological properties of persulfides.Fil: Benchoam, Dayana. Universidad de la República; UruguayFil: Semelak, Jonathan Alexis. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; ArgentinaFil: Cuevasanta, Ernesto. Universidad de la República; UruguayFil: Mastrogiovanni, Mauricio. Universidad de la Republica; UruguayFil: Grassano, Juan S.. Universidad de Buenos Aires; ArgentinaFil: Ferrer-Sueta, Gerardo. Universidad de la Republica; UruguayFil: Zeida Camacho, Ari Fernando. Universidad de la Republica; UruguayFil: Trujillo, Madia. Universidad de la Republica; UruguayFil: Möller, Matías N.. Universidad de la Republica; UruguayFil: Estrin, Dario Ariel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; ArgentinaFil: Alvarez, Beatriz. Universidad de la Republica; Urugua

On farm agronomic and first environmental evaluation of oil crops for sustainable bioenergy chains.

Energy crops, and in particular oil crops, could be an important occasion for developing new non food production rows for a new multi-functional agriculture in Italy. In this view, the use of local biomass is a fundamental starting point for the development of a virtuous energy chain that should pursue not only agricultural profitability, but also chain sustainability and that is less dependent on the global market, characterized by instability in terms of biomass availability and price. From this perspective, particular attention must be paid to crop choice on the basis of its rusticity and of its adaptability to local growing conditions and to low input cropping systems. In this context, alike woody and herbaceous biomasses, oil crops such as sunflower and rapeseed should be able to support local agricultural bioenergy chain in Italy. In addition, in a local bioenergy chain, the role of the farmers should not be limited just to grain production; but also grain processing should be performed at farm or consortium level in oilseed extraction plants well proportioned to the cropped surface. In this way, by means of a simple power generator, farmer could thus produce its own thermal and electric energy from the oil, maximizing his profit. This objective could also be achieved through the exploitation of the total biomass, including crop residues and defatted seed meals, that may be considered as fundamental additional economic and/or environmental benefits of the chain. This paper reports some results of three-years on-farm experiments on oil crop chain carried out in the framework of "Bioenergie" project, that was focused to enhance farmers awareness of these criteria and to the feasibility at open field scale of low-input cultivation of rapeseed, sunflower and Brassica carinata in seven Italian regions. In several on-farm experiences, these crops produced more than 800 kg ha-1 of oil with good energy properties. Defatted seed meals could be interesting as organic fertilizers and, in the case of B. carinata, as a biofumigant amendment that could offer a total or partial alternative to some chemicals in agriculture. Furthermore, biomass soil incorporation could contribute to C sequestration, catching CO2 from atmosphere and sinking a part in soil as stable humus. Finally, four different open field experiences carried out again in the second year of the project, have been analysed in order to evaluate their energy and greenhouse gasses balance after cultivation phase

In situ annealing of superconducting MgB2 films prepared by pulsed laser deposition

The in situ annealing conditions of pulsed laser deposited MgB2 films were studied. The precursor films were deposited at 250 C from a stoichiometric MgB2 target in a 120mTorr Ar atmosphere. The films were then in situ annealed at a temperature from 450 C to 800 C and an annealing time from 1 minute to 10 minutes. We found that the superconducting properties depend in a crucial way on the annealing conditions: temperature, heating rate and time. The best film with a thickness of ~600nm was obtained under the following annealing conditions: Tanneal=680-690 C, tanneal=1 min, heating rate= 38 C/min. The Tc onset of the film is 28K with a transition width of ~10K. The hysteresis loop of magnetic moment of the film indicates weak field dependence in high fields. Magneto-optical imaging of the film showed quite homogeneous magnetic flux penetration, indicating structural homogeneity. The films without annealing showed no superconductivity.Comment: 12 pages, 6 figure

Fossil energy in economic growth: A study of the energy direction of technical change, 1950-2012

Climate change mitigation challenges national economies to increase productivity while reducing fossil energy consumption. Fossil energy-saving technical change has been assumed to accomplish this, yet empirical evidence is scarce. This paper investigates the long-run relationship between the rate and direction of technical change with respect to fossil energy and labor in the world economy. Growth rates of labor productivity and the fossil energy-labor ratio are examined for more than 95 of world output between 1950 and 2012. The average elasticity of the energy-labor ratio with respect to labor productivity is close to one, implying highly energy-using technical change, but no trade-o between factor productivity growth rates. This stylized fact suggests the importance of a cheap, abundant energy supply for robust global growth, and a more important role for renewable energy. Integrated assessment models do not incorporate this restriction which may result in poorly speci ed baseline scenarios