2,076 research outputs found

    Leptogenesis from Pseudo-Scalar Driven Inflation

    Full text link
    We examine recent claims for a considerable amount of leptogenesis, in some inflationary scenarios, through the gravitational anomaly in the lepton number current. We find that when the short distances contributions are properly included the amount of lepton number generated is actually much smaller.Comment: JHEP style, 11 pages. Corrected typ

    Decomposition of wheat and barley straw treated with urea-sulfuric acid

    Get PDF
    Wheat straw treated with 0.5 or 1.0 ml/g urea-sulfuric acid (1 : 1 acid in water v/v) and incubated in Protneuf or Woodburn silt loam soils in the laboratory decomposed faster than nontreated straw the first 4-6 weeks but at 12 weeks the nontreated straw had decomposed 25% ‚Äď 45% more. In a field experiment, urea-sulfuric acid treated straw, removed at 40-day intervals over 160 days, decomposed faster than nontreated straw. The differences were attributed to salt buildup in the laboratory samples, where electrical conductivities up to 17.6 dS/m were observed. In the field, leaching removed the excess salts. Nitrification produced up to 1875 mg NO3-N/kg Portneuf silt loam soil in the laboratory, indicating that nitrifying bacteria were not suppressed by the salt. Total plate counts with no straw were 1.8 x 10^6 microorganisms/g and with urea-sulfuric acid treated straw were 15.7 x 10^6/g soil after 14 days incubation. The respective actinomycete counts were 0.3 x 10^6 and 6.7 x 10^6/g for the no straw and straw-treated soils, respectively. The urea-sulfuric acid treatments suppressed straw decomposition in the laboratory and accelerated straw decomposition in the field

    Theoretical investigation on the possibility of preparing left-handed materials in metallic magnetic granular composites

    Full text link
    We investigate the possibility of preparing left-handed materials in metallic magnetic granular composites. Based on the effective medium approximation, we show that by incorporating metallic magnetic nanoparticles into an appropriate insulating matrix and controlling the directions of magnetization of metallic magnetic components and their volume fraction, it may be possible to prepare a composite medium of low eddy current loss which is left-handed for electromagnetic waves propagating in some special direction and polarization in a frequency region near the ferromagnetic resonance frequency. This composite may be easier to make on an industrial scale. In addition, its physical properties may be easily tuned by rotating the magnetization locally.Comment: 5 figure

    Thermal conductivity enhancement of laser induced graphene foam upon P3HT infiltration

    Get PDF
    Significant research has been dedicated to the exploration of high¬†thermal conductivity¬†polymer¬†composite materials¬†with¬†conductive¬†filler particles for use in heat transfer applications. However, poor particle dispersibility and interfacial phonon scattering have limited the effective¬†composite¬†thermal conductivity.¬†Three-dimensional¬†foams¬†with high ligament¬†thermal conductivity¬†offer a potential solution to the two aforementioned problems but are traditionally fabricated through expensive and/or complex manufacturing methods. Here, laser induced¬†graphene¬†foams,¬†fabricated through a simple and cost effective laser ablation method, are infiltrated with poly(3-hexylthiophene) in a step-wise fashion to demonstrate the impact of¬†polymer¬†on the¬†thermal conductivity¬†of the¬†composite¬†system. Surprisingly, the addition of¬†polymer¬†results in a drastic (250%) improvement in¬†material¬†thermal conductivity,¬†enhancing the¬†graphene¬†foam's¬†thermal conductivity¬†from 0.68‚ÄČW/m-K to 1.72‚ÄČW/m-K for the fully infiltrated¬†composite material.¬†Graphene¬†foam¬†density measurements and theoretical¬†models¬†are utilized to estimate the effective ribbon¬†thermal conductivity¬†as a function of¬†polymer¬†filling. Here, it is proposed that the¬†polymer¬†solution acts as a binding¬†material,¬†which draws¬†graphene¬†ligaments together through elastocapillary coalescence and bonds these ligaments upon drying, resulting in greatly reduced contact resistance within the¬†foam¬†and an effective¬†thermal conductivity¬†improvement greater than what would be expected from the addition of¬†polymer¬†alone

    Solar system tests do rule out 1/R gravity

    Get PDF
    Shortly after the addition of a 1/R term to the Einstein-Hilbert action was proposed as a solution to the cosmic-acceleration puzzle, Chiba showed that such a theory violates Solar System tests of gravity. A flurry of recent papers have called Chiba's result into question. They argue that the spherically-symmetric vacuum spacetime in this theory is the Schwarzschild-de Sitter solution, making this theory consistent with Solar System tests. We point out that although the Schwarzschild-de Sitter solution exists in this theory, it is not the unique spherically-symmetric vacuum solution, and it is not the solution that describes the spacetime in the Solar System. The solution that correctly matches onto the stellar-interior solution differs from Schwarzschild-de Sitter in a way consistent with Chiba's claims. Thus, 1/R gravity is ruled out by Solar System tests

    Reply to "Comment on 'Solar System constraints to general f(R) gravity'"

    Get PDF
    Here we respond to the Comment by Faraoni and Lanahan-Tremblay on our paper. We show that the criticisms of our paper presented in this Comment are incorrect

    Solar System constraints to general f(R) gravity

    Get PDF
    It has been proposed that cosmic acceleration or inflation can be driven by replacing the Einstein-Hilbert action of general relativity with a function f(R) of the Ricci scalar R. Such f(R) gravity theories have been shown to be equivalent to scalar-tensor theories of gravity that are incompatible with Solar System tests of general relativity, as long as the scalar field propagates over Solar System scales. Specifically, the parameterized post-Newtonian (PPN) parameter in the equivalent scalar-tensor theory is ő≥=1/2, which is far outside the range allowed by observations. In response to a flurry of papers that questioned the equivalence of f(R) theory to scalar-tensor theories, it was recently shown explicitly, without resorting to the scalar-tensor equivalence, that the vacuum field equations for 1/R gravity around a spherically symmetric mass also yield ő≥=1/2. Here we generalize this analysis to f(R) gravity and enumerate the conditions that, when satisfied by the function f(R), lead to the prediction that ő≥=1/2

    String-Inspired Chern-Simons Modified Gravity In 4-Dimensions

    Full text link
    Chern-Simons modified gravity models in 4-dimensions are shown to be special cases of low energy effective string models to first order in the string constant.Comment: To appear in the European Physics Journal

    An improved approach to characterize potash-bearing evaporite deposits, evidenced in North Yorkshire, United Kingdom

    Get PDF
    Traditionally, potash mineral deposits have been characterized using downhole geophysical logging in tandem with geochemical analysis of core samples to establish the critical potassium (% K2O) content. These techniques have been employed in a recent exploration study of the Permian evaporite succession of North Yorkshire, United Kingdom, but the characterization of these complex deposits has been led by mineralogical analysis, using quantitative X-ray diffraction (QXRD). The novel QXRD approach provides data on K content with the level of confidence needed for reliable reporting of resources and also identifies and quantifies more precisely the nature of the K-bearing minerals. Errors have also been identified when employing traditional geochemical approaches for this deposit, which would have resulted in underestimated potash grades. QXRD analysis has consistently identified polyhalite (K2Ca2Mg(SO4)4·2(H2O) in the Fordon (Evaporite) Formation and sylvite (KCl) in the Boulby Potash and Sneaton Potash members as the principal K-bearing host minerals in North Yorkshire. However, other K hosts, including kalistrontite (K2Sr(SO4)2) a first recorded occurrence in the UK, and a range of boron-bearing minerals have also been detected. Application of the QXRD-led characterization program across the evaporitic basin has helped to produce a descriptive, empirical model for the deposits, including the polyhalite-bearing Shelf and Basin seams and two, newly discovered sylvite-bearing bittern salt horizons, the Pasture Beck and Gough seams. The characterization program has enabled a polyhalite mineral inventory in excess of 2.5 billion metric tons (Bt) to be identified, suggesting that this region possesses the world’s largest known resource of polyhalite. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution and reproduction in any medium provided that the original work is properly attributed

    Explaining participation in regional transnational social movement organizations

    Get PDF
    Since the late 1980s, governments have focused intensely on formalizing political and economic relationships within regions. There has also been a concurrent rise in transnational, regional level organizing among social movement activists globally, suggesting the regionalization of 'global civil society.' However, opportunities for participation in transnational associations vary widely across countries. In this article, we examine the influence of international (both global and regional) institutional contexts, citizen participation in international society, and national level factors on varying levels of participation in regional transnational social movement organizations (TSMOs). We use negative binomial regression to examine relationships among these factors at three time points: 1980, 1990, and 2000. We find that in the early time period, citizen network connections to international society facilitated the formation of and participation in regionally organized TSMOs. Over time, however, regional and global institutional contexts were more predictive of participation in regional TSMOs than were international network ties. Our analysis also uncovered how qualitatively different forms of regionalism translated into significantly different levels of TSMO regionalization. In Europe, where the regional institutional structure is more elaborated than elsewhere in the world, the number of regional TSMOs in which citizens participated greatly outpaced that found elsewhere. Irrespective of international, institutional factors, however, state-level features remained crucial to explaining the development of regional TSMO sectors and the variable levels of participation in them. Citizens in states with restrictions on political rights and civil liberties had significantly lower participation in these organizations in 1990 and 2000. Even so, over time, citizens in states with more ties to global and regional multilateral processes found more ways to overcome this disadvantage and strengthen their participation in regional, transnational civil society. © 2007 SAGE Publications
    • ‚Ķ
    corecore