184 research outputs found

    Diploptene δ13C values from contemporary thermokarst lake sediments show complex spatial variation

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    Cryospheric changes in northern high latitudes are linked to significant greenhouse gas flux to the atmosphere, for example, methane that originates from organic matter decomposition in thermokarst lakes. The set of pathways that link methane production in sediments, via oxidation in the lake system, to the flux of residual methane to the atmosphere is complex and exhibits temporal and spatial variation. The isotopic signal of bacterial biomarkers (hopanoids, e.g. diploptene) in sediments has been used to identify contemporary ocean-floor methane seeps and, in the geological record, periods of enhanced methane production (e.g. the PETM). The biomarker approach could potentially be used to assess temporal changes in lake emissions through the Holocene via the sedimentary biomarker record. However, there are no data on the consistency of the signal of isotopic depletion in relation to source or on the amount of noise (unexplained variation) in biomarker values from modern lake sediments. We assessed methane oxidation as represented by the isotopic signal of biomarkers from methane oxidising bacteria (MOB) in multiple surface sediment samples in three distinct areas known to emit varying levels of methane in two shallow Alaskan thermokarst lakes. Diploptene was present and had δ13C values lower than -38g‰ in all sediments analysed, suggesting methane oxidation was widespread. However, there was considerable variation in δ13C values within each area. The most 13C-depleted diploptene was found in an area of high methane ebullition in Ace Lake (diploptene δ13C values between -68.2 and -50.1‰). In contrast, significantly higher diploptene δ13C values (between -42.9 and -38.8g‰) were found in an area of methane ebullition in Smith Lake. δ13C values of diploptene between -56.8 and -46.9g‰ were found in the centre of Smith Lake, where ebullition rates are low but diffusive methane efflux occurs. The small-scale heterogeneity of the samples may reflect patchy distribution of substrate and/or MOB within the sediments. The two ebullition areas differ in age and type of organic carbon substrate, which may affect methane production, transport, and subsequent oxidation. Given the high amount of variation in surface samples, a more extensive calibration of modern sediment properties, within and among lakes, is required before down-core records of hopanoid isotopic signatures are developed. © Author(s) 2016

    Nutrição mineral de hortaliças: XXXVIII. deficiências de macronutrientes em alface (Juactuoa sativa L.), cv. Brasil e Clause's Aurélia

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    This research was carried out in order to study the symptomalogical chart of macronutrient deficiencies and verify the analytical level of the macronutrients. in lettuce plants under mineral deficiency conditions. Lettuce seedlings were cultivated and irrigated with nutrient solutions in the greenhouse. The treatments were: complete solution and solutions lacking N or P, K, Ca, Mg and S. Whenever the plants showed evidency and clear deficiency symptoms, they were harvested and analysed for the respective elements. The nutrient deficiencies were observed and easily identified, except for S, The macronutrient concentrations in the leaves of cv. Brasil 48 were: Normal plants: N (3-37%), P (0.44%), K (5-54%), Ca (0.97%), Mg (0.35%), and S (0.16%); Undernourished plants: N (1.86%), P (0.16%), K (1.32%), Cu (0.20%), Mg (0.05%), and S (1.16%). The concentration of the macronutrients in the leaves of cv. Clause's Aurelia were: Normal plants: N (3-02%), P (0.71%), K (7-70%); Cu t(1.47%), Mg (0.43%), and S (0.24%); Undernourished plants: N (2.68%), P (0.19%), K (1.54%), Mg (0.10%), and S (0.24%).Com os objetivos de: a) obter o quadro síntomatológico das deficiências de macronutrientes; b) relacionar o quadro sintomatológico a composição química das plantas, foi conduzido um ensaio em casa de vegetação, cultivando o cv. Brasil 48 e Clause's Aurélia em solução nutritiva, tendo como substrato silica finamente moida. Os tratamentos foram: completo, omissão de nitrogênio, omissão de fósforo, omissão de potássio, omissão de cálcio, omissão de magnésio e omissão de enxofre. Os autores observaram e identificaram as deficiências de nutrientes que se traduziram por sintomas típicos e facilmente identificáveis, com exceção do enxofre. As concentrações de macronutrientes nas folhas para plantas sem sintomas e com sintomas para o cultivar Brasil 48 foram: N% 3,37 a 1,86; P% 0,44 a 0,16; K% 5,54 a 1,32; Ca% 0,97 a 0,20; Mg% 0,35 a 0,05. As concentrações de S% foram iguais a 0,16. Para o cv. Clause's Aurélia, as concentrações nas folhas correspondentes a plantas sem e com deficiências foram: N% 3,02 a 2,68; P% 0,71 a 0,19; K% 7,7 a 1,54; Ca% 1 ,47 a 0,31; Mg% 0,43 a 0,10 e S% 0,25 a 0,24

    An alternative approach to the construction of Schur-Weyl transform

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    We propose an alternative approach for the construction of the unitary matrix which performs generalized unitary rotations of the system consisting of independent identical subsystems (for example spin system). This matrix, when applied to the system, results in a change of degrees of freedom, uncovering the information hidden in non-local degrees of freedom. This information can be used, inter alia, to study the structure of entangled states, their classification and may be useful for construction of quantum algorithms.Comment: 6 page

    Influence of Coulomb and Phonon Interaction on the Exciton Formation Dynamics in Semiconductor Heterostructures

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    A microscopic theory is developed to analyze the dynamics of exciton formation out of incoherent carriers in semiconductor heterostructures. The carrier Coulomb and phonon interaction is included consistently. A cluster expansion method is used to systematically truncate the hierarchy problem. By including all correlations up to the four-point (i.e. two-particle) level, the fundamental fermionic substructure of excitons is fully included. The analysis shows that the exciton formation is an intricate process where Coulomb correlations rapidly build up on a picosecond time scale while phonon dynamics leads to true exciton formation on a slow nanosecond time scale.Comment: 18 pages, 7 figure

    Proof of a conjecture of Polya on the zeros of successive derivatives of real entire functions

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    We prove Polya's conjecture of 1943: For a real entire function of order greater than 2, with finitely many non-real zeros, the number of non-real zeros of the n-th derivative tends to infinity with n. We use the saddle point method and potential theory, combined with the theory of analytic functions with positive imaginary part in the upper half-plane.Comment: 26 page

    Reachability in Biochemical Dynamical Systems by Quantitative Discrete Approximation (extended abstract)

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    In this paper, a novel computational technique for finite discrete approximation of continuous dynamical systems suitable for a significant class of biochemical dynamical systems is introduced. The method is parameterized in order to affect the imposed level of approximation provided that with increasing parameter value the approximation converges to the original continuous system. By employing this approximation technique, we present algorithms solving the reachability problem for biochemical dynamical systems. The presented method and algorithms are evaluated on several exemplary biological models and on a real case study.Comment: In Proceedings CompMod 2011, arXiv:1109.104

    Second harmonic generation and birefringence of some ternary pnictide semiconductors

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    A first-principles study of the birefringence and the frequency dependent second harmonic generation (SHG) coefficients of the ternary pnictide semiconductors with formula ABC2_2 (A = Zn, Cd; B = Si, Ge; C = As, P) with the chalcopyrite structures was carried out. We show that a simple empirical observation that a smaller value of the gap is correlated with larger value of SHG is qualitatively true. However, simple inverse power scaling laws between gaps and SHG were not found. Instead, the real value of the nonlinear response is a result of a very delicate balance between different intraband and interband terms.Comment: 13 pages, 12 figure

    Exciton swapping in a twisted graphene bilayer as a solid-state realization of a two-brane model

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    It is shown that exciton swapping between two graphene sheets may occur under specific conditions. A magnetically tunable optical filter is described to demonstrate this new effect. Mathematically, it is shown that two turbostratic graphene layers can be described as a "noncommutative" two-sheeted (2+1)-spacetime thanks to a formalism previously introduced for the study of braneworlds in high energy physics. The Hamiltonian of the model contains a coupling term connecting the two layers which is similar to the coupling existing between two braneworlds at a quantum level. In the present case, this term is related to a K-K' intervalley coupling. In addition, the experimental observation of this effect could be a way to assess the relevance of some theoretical concepts of the braneworld hypothesis.Comment: 15 pages, 3 figures, final version published in European Physical Journal

    Geriatric oncology health services research: Cancer and Aging Research Group infrastructure core

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    Founded by the late Dr. Arti Hurria, the Cancer and Aging Research Group (CARG) is a collaborative, interdisciplinary team of investigators dedicated to improving the care of older adults with cancer through research, advocacy, and other scholarly initiatives.1 As part of the CARG National Institute on Aging R21/R33 infrastructure grant to harness the available expertise and prioritize the development of high-impact research, the Health Services Research (HSR) Core was developed to foster and advance HSR in geriatric oncology. The mission of the HSR Core is to support clinical investigators to design and conduct highquality HSR focused on older adults with cancer and their caregivers including patterns of care, comparative effectiveness, and care delivery. At the first R21/R33 conference held at City of Hope in October 2018, Dr. Harvey Jay Cohen (Chair, CARG Oversight Board and HSR Core) led the development of this Core. In this perspective paper, we present a review of HSR in geriatric oncology to build a foundation for the Core rationale; proposed Core function, workflow, policies, and procedures; anticipated interactions with other CARG Cores; and proposed plans for sustainabilit
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