High-performance light-weight electrodes for hydrogen-oxygen fuel cells

High performance light weight electrodes for hydrogen oxygen fuel cell

Gaining from Improved Dairy Cow Nutrition: Economic, environmental and animal health benefits

A majority of UK dairy herds have the potential to increase profitability by improving the ration of their cows. This paper reports that gains averaging around £100 per cow have been made within one year of adopting the Keenan Hi-Fibre ration by 239 UK herds in 2006 and 2007. Larger gains have been made by herds in France. The key performance indicator underlying these gains is Feed Conversion Efficiency, whereby the same, or even a smaller amount of Dry Matter Intake generates higher yields per cow. Importantly, the gains are associated with large improvements in animal health and reductions in greenhouse gases per litre of milk produced.Feed conversion efficiency, cattle nutrition, greenhouse gas emissions, animal health., Livestock Production/Industries,

Concentrations and snow-atmosphere fluxes of reactive nitrogen at Summit, Greenland

Concentrations and fluxes of NOy (total reactive nitrogen), ozone concentrations and fluxes of sensible heat, water vapor, and momentum were measured from May 1 to July 20, 1995 at Summit, Greenland. Median NOy concentrations declined from 947 ppt in May to 444 ppt by July. NOy fluxes were observed into and out of the snow, but the magnitudes were usually below 1 μmol m−2 h−1 because of the low HNO3 concentration and weak turbulence over the snow surface. Some of the highest observed fluxes may be due to temporary storage by equilibrium sorption of peroxyacetylnitrate (PAN) or other organic nitrogen species on ice surfaces in the upper snowpack. Sublimation of snow at the surface or during blowing snow events is associated with efflux of NOy from the snowpack. Because the NOy fluxes during summer at Summit are bidirectional and small in magnitude, the net result of turbulent NOyexchange is insignificant compared to the 2 μmol m−2 d−1 mean input from fresh snow during the summer months. If the arctic NOy reservoir is predominantly PAN (or compounds with similar properties), thermal dissociation of this NOy is sufficient to support the observed flux of nitrate in fresh snow. Very low HNO3 concentrations in the surface layer (1% of total NOy) reflect the poor ventilation of the surface layer over the snowpack combined with the relatively rapid uptake of HNO3 by fog, falling snow, and direct deposition to the snowpack

IrSr_2Sm_{1.15}Ce_{0.85}Cu_{2.175}O_{10}: A Novel Reentrant Spin-Glass Material

A new iridium containing layered cuprate material, IrSr_2Sm_{1.15}Ce_{0.85}Cu_{2.175}O_{10, has been synthesized by conventional ambient-pressure solid-state techniques. The material's structure has been fully characterized by Rietveld refinement of high resolution synchrotron X-ray diffraction data; tilts and rotations of the IrO_6 octahedra are observed as a result of a bond mismatch between in-plane Ir-O and Cu-O bond lengths. DC-susceptibility measurements evidence a complex set of magnetic transitions upon cooling that are characteristic of a reentrant spin-glass ground-state. The glassy character of the lowest temperature, Tg=10 K, transition is further confirmed by AC-susceptibility measurements, showing a characteristic frequency dependence that can be well fitted by the Vogel-Fulcher law and yields a value of \Delta_(T_f)/[T_f \Delta log({\omega})] =0.015(1), typical of dilute magnetic systems. Electronic transport measurements show the material to be semiconducting at all temperatures with no transition to a superconducting state. Negative magnetoresistance is observed when the material is cooled below 25 K, and the magnitude of this magnetoresistance is seen to increase upon cooling to a value of MR = -9 % at 8 K

The resistance of randomly grown trees

Copyright @ 2011 IOP Publishing Ltd. This is a preprint version of the published article which can be accessed from the link below.An electrical network with the structure of a random tree is considered: starting from a root vertex, in one iteration each leaf (a vertex with zero or one adjacent edges) of the tree is extended by either a single edge with probability p or two edges with probability 1 − p. With each edge having a resistance equal to 1 omega, the total resistance Rn between the root vertex and a busbar connecting all the vertices at the nth level is considered. A dynamical system is presented which approximates Rn, it is shown that the mean value (Rn) for this system approaches (1 + p)/(1 − p) as n → ∞, the distribution of Rn at large n is also examined. Additionally, a random sequence construction akin to a random Fibonacci sequence is used to approximate Rn; this sequence is shown to be related to the Legendre polynomials and its mean is shown to converge with |(Rn) − (1 + p)/(1 − p)| ∼ n−1/2.Engineering and Physical Sciences Research Council (EPSRC

Spin dynamics and disorder effects in the S=1/2 kagome Heisenberg spin liquid phase of kapellasite

We report $^{35}$Cl NMR, ESR, $\mu$SR and specific heat measurements on the $S=1/2$ frustrated kagom\'e magnet kapellasite, $\alpha-$Cu$_3$Zn(OH)$_6$Cl$_2$, where a gapless spin liquid phase is stabilized by a set of competing exchange interactions. Our measurements confirm the ferromagnetic character of the nearest-neighbour exchange interaction $J_1$ and give an energy scale for the competing interactions $|J| \sim 10$ K. The study of the temperature-dependent ESR lineshift reveals a moderate symmetric exchange anisotropy term $D$, with $|D/J|\sim 3$%. These findings validate a posteriori the use of the $J_1 - J_2 - J_d$ Heisenberg model to describe the magnetic properties of kapellasite [Bernu et al., Phys. Rev. B 87, 155107 (2013)]. We further confirm that the main deviation from this model is the severe random depletion of the magnetic kagom\'e lattice by 27%, due to Cu/Zn site mixing, and specifically address the effect of this disorder by $^{35}$Cl NMR, performed on an oriented polycrystalline sample. Surprisingly, while being very sensitive to local structural deformations, our NMR measurements demonstrate that the system remains homogeneous with a unique spin susceptibility at high temperature, despite a variety of magnetic environments. Unconventional spin dynamics is further revealed by NMR and $\mu$SR in the low-$T$, correlated, spin liquid regime, where a broad distribution of spin-lattice relaxation times is observed. We ascribe this to the presence of local low-energy modes.Comment: 15 pages, 11 figures. To appear in Phys. Rev.

Messages Do Diffuse Faster Than Messengers: Reconciling disparate estimates of the morphogen Bicoid diffusion coefficient

The gradient of Bicoid (Bcd) is key for the establishment of the anterior-posterior axis in Drosophila embryos. The gradient properties are compatible with the SDD model in which Bcd is synthesized at the anterior pole and then diffuses into the embryo and is degraded with a characteristic time. Within this model, the Bcd diffusion coefficient is critical to set the timescale of gradient formation. This coefficient has been measured using two optical techniques, Fluorescence Recovery After Photobleaching (FRAP) and Fluorescence Correlation Spectroscopy (FCS), obtaining estimates in which the FCS value is an order of magnitude larger than the FRAP one. This discrepancy raises the following questions: which estimate is ?correct?; what is the reason for the disparity; and can the SDD model explain Bcd gradient formation within the experimentally observed times. In this paper, we use a simple biophysical model in which Bcd diffuses and interacts with binding sites to show that both the FRAP and the FCS estimates may be correct and compatible with the observed timescale of gradient formation. The discrepancy arises from the fact that FCS and FRAP report on different effective (concentration dependent) diffusion coefficients, one of which describes the spreading rate of the individual Bcd molecules (the messengers) and the other one that of their concentration (the message). The latter is the one that is more relevant for the gradient establishment and is compatible with its formation within the experimentally observed times.Fil: Sigaut, Lorena. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Pearson, John E.. Los Alamos National Laboratory;Fil: Colman Lerner, Alejandro Ariel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Fisiología, Biología Molecular y Neurociencias. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Fisiología, Biología Molecular y Neurociencias; ArgentinaFil: Ponce Dawson, Silvina Martha. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; Argentin

Causes of irregularities in trends of global mean surface temperature since the late 19th century

The time series of monthly global mean surface temperature (GST) since 1891 is successfully reconstructed from known natural and anthropogenic forcing factors, including internal climate variability, using a multiple regression technique. Comparisons are made with the performance of 40 CMIP5 models in predicting GST. The relative contributions of the various forcing factors to GST changes vary in time, but most of the warming since 1891 is found to be attributable to the net influence of increasing greenhouse gases and anthropogenic aerosols. Separate statistically independent analyses are also carried out for three periods of GST slowdown (1896–1910, 1941–1975, and 1998–2013 and subperiods); two periods of strong warming (1911–1940 and 1976–1997) are also analyzed. A reduction in total incident solar radiation forcing played a significant cooling role over 2001–2010. The only serious disagreements between the reconstructions and observations occur during the Second World War, especially in the period 1944–1945, when observed near-worldwide sea surface temperatures (SSTs) may be significantly warm-biased. In contrast, reconstructions of near-worldwide SSTs were rather warmer than those observed between about 1907 and 1910. However, the generally high reconstruction accuracy shows that known external and internal forcing factors explain all the main variations in GST between 1891 and 2015, allowing for our current understanding of their uncertainties. Accordingly, no important additional factors are needed to explain the two main warming and three main slowdown periods during this epoch