13,454 research outputs found

    The complex AGM, periods of elliptic curves over C and complex elliptic logarithms

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    We give an account of the complex Arithmetic-Geometric Mean (AGM), as first studied by Gauss, together with details of its relationship with the theory of elliptic curves over \C, their period lattices and complex parametrisation. As an application, we present efficient methods for computing bases for the period lattices and elliptic logarithms of points, for arbitrary elliptic curves defined over \C. Earlier authors have only treated the case of elliptic curves defined over the real numbers; here, the multi-valued nature of the complex AGM plays an important role. Our method, which we have implemented in both \Magma\ and \Sage, is illustrated with several examples using elliptic curves defined over number fields with real and complex embeddings.Comment: The addional file elog_ex.sage contains a Sage script for the examples in the last section of the paper, and the file elog_ex.out contains the result of running that script with Sage version 5.

    La valeur de la méthode otolithométrique pour la détermination de l'age du Merlu (<i>Merlucius merlucius</i> - Pisces, Gadidae) en Méditerranée

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    The otolithometric method rests on 2 (1) the agreement between the number of annual rings and the age of the fish and (2) the length of the fish being proportional to that of the otolith. The length of the fish may be grouped into 5 classes, ranging from 16, 18, 20, 25 to 27 cm though some degree of overlapping is observed. Using 300 otoliths and grouping the individuals according to the number of annual rings their otoliths bear it was possible to determine the frequency of individuals of varying lengths within a particular class. Although the results obtained by the author helped him to verify the 2nd parameter, numerous shortcomings were seen in this method. No consistent unity of measurement, which could be used for comparison, has been adopted by other workers; aberrant results were obtained by considering all the rings as being equivalent; the difficulty in interpreting an annual ring and the uncertainty of these deposits being regular and annual. It is strongly recommended that the otolithometric method be used only after its validity has been determined and a standard for reference in interpreting annual rings has been established

    Production of hydrogen by unmixed steam reforming of methane

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    Unmixed steam reforming is an alternative method of catalytic steam reforming that uses separate air and fuel–steam feeds, producing a reformate high in H2 content using a single reactor and a variety of fuels. It claims insensitivity to carbon formation and can operate autothermally. The high H2 content is achieved by in situ N2 separation from the air using an oxygen transfer material (OTM), and by CO2 capture using a solid sorbent. The OTM and CO2 sorbent are regenerated during the fuel–steam feed and the air feed, respectively, within the same reactor. This paper describes the steps taken to choose a suitable CO2-sorbent material for this process when using methane fuel with the help of microreactor tests, and the study of the carbonation efficiency and regeneration ability of the materials tested. Elemental balances from bench scale experiments using the best OTM in the absence of the CO2 sorbent allow identifying the sequence of the chemical reaction mechanism. The effect of reactor temperature between 600 and on the process outputs is investigated. Temperatures of 600 and under the fuel–steam feed were each found to offer a different set of desirable outputs. Two stages during the fuel–steam feed were characterised by a different set of global reactions, an initial stage where the OTM is reduced directly by methane, and indirectly by hydrogen produced by methane thermal decomposition, in the second stage, steam reforming takes over once sufficient OTM has been reduced. The implications of these stages on the process desirable outputs such as efficiency of reactants conversion, reformate gas quality, and transient effects are discussed

    Long-lived quantum memory with nuclear atomic spins

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    We propose to store non-classical states of light into the macroscopic collective nuclear spin (101810^{18} atoms) of a 3^3He vapor, using metastability exchange collisions. These collisions, commonly used to transfer orientation from the metastable state 23S_12^{3}S\_1 to the ground state state of 3^3He, can also transfer quantum correlations. This gives a possible experimental scheme to map a squeezed vacuum field state onto a nuclear spin state with very long storage times (hours).Comment: 4 page

    Uniform Commercial Code

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    Momentum and scalar transport within a vegetation canopy following atmospheric stability and seasonal canopy changes: the CHATS experiment

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    Momentum and scalar (heat and water vapor) transfer between a walnut canopy and the overlying atmosphere are investigated for two seasonal periods (before and after leaf-out), and for five thermal stability regimes (free and forced convection, near-neutral condition, transition to stable, and stable). Quadrant and octant analyses of momentum and scalar fluxes followed by space-time autocorrelations of observations from the Canopy Horizontal Array Turbulence Study's (CHATS) thirty meter tower help characterize the motions exchanging momentum, heat, and moisture between the canopy layers and aloft. &lt;br&gt;&lt;br&gt; During sufficiently windy conditions, i.e. in forced convection, near-neutral and transition to stable regimes, momentum and scalars are generally transported by sweep and ejection motions associated with the well-known canopy-top "shear-driven" coherent eddy structures. During extreme stability conditions (both unstable and stable), the role of these "shear-driven" structures in transporting scalars decreases, inducing notable dissimilarity between momentum and scalar transport. &lt;br&gt;&lt;br&gt; In unstable conditions, "shear-driven" coherent structures are progressively replaced by "buo-yantly-driven" structures, known as thermal plumes; which appear very efficient at transporting scalars, especially upward thermal plumes above the canopy. Within the canopy, downward thermal plumes become more efficient at transporting scalars than upward thermal plumes if scalar sources are located in the upper canopy. We explain these features by suggesting that: (i) downward plumes within the canopy correspond to large downward plumes coming from above, and (ii) upward plumes within the canopy are local small plumes induced by canopy heat sources where passive scalars are first injected if there sources are at the same location as heat sources. Above the canopy, these small upward thermal plumes aggregate to form larger scale upward thermal plumes. Furthermore, scalar quantities carried by downward plumes are not modified when penetrating the canopy and crossing upper scalar sources. Consequently, scalars appear to be preferentially injected into upward thermal plumes as opposed to in downward thermal plumes. &lt;br&gt;&lt;br&gt; In stable conditions, intermittent downward and upward motions probably related to elevated shear layers are responsible for canopy-top heat and water vapor transport through the initiation of turbulent instabilities, but this transport remains small. During the foliated period, lower-canopy heat and water vapor transport occurs through thermal plumes associated with a subcanopy unstable layer

    Integrated Regulatory and Metabolic Networks of the Marine Diatom Phaeodactylum tricornutum Predict the Response to Rising CO2 Levels.

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    Diatoms are eukaryotic microalgae that are responsible for up to 40% of the ocean's primary productivity. How diatoms respond to environmental perturbations such as elevated carbon concentrations in the atmosphere is currently poorly understood. We developed a transcriptional regulatory network based on various transcriptome sequencing expression libraries for different environmental responses to gain insight into the marine diatom's metabolic and regulatory interactions and provide a comprehensive framework of responses to increasing atmospheric carbon levels. This transcriptional regulatory network was integrated with a recently published genome-scale metabolic model of Phaeodactylum tricornutum to explore the connectivity of the regulatory network and shared metabolites. The integrated regulatory and metabolic model revealed highly connected modules within carbon and nitrogen metabolism. P. tricornutum's response to rising carbon levels was analyzed by using the recent genome-scale metabolic model with cross comparison to experimental manipulations of carbon dioxide. IMPORTANCE Using a systems biology approach, we studied the response of the marine diatom Phaeodactylum tricornutum to changing atmospheric carbon concentrations on an ocean-wide scale. By integrating an available genome-scale metabolic model and a newly developed transcriptional regulatory network inferred from transcriptome sequencing expression data, we demonstrate that carbon metabolism and nitrogen metabolism are strongly connected and the genes involved are coregulated in this model diatom. These tight regulatory constraints could play a major role during the adaptation of P. tricornutum to increasing carbon levels. The transcriptional regulatory network developed can be further used to study the effects of different environmental perturbations on P. tricornutum's metabolism

    Enhancement of Gap Junction Function During Acute Myocardial Infarction Modifies Healing and Reduces Late Ventricular Arrhythmia Susceptibility

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    Objectives: To investigate the effects of enhancing gap junction (GJ) coupling during acute myocardial infarction (MI) on the healed infarct scar morphology and late post-MI arrhythmia susceptibility. Background: Increased heterogeneity of myocardial scarring after MI is associated with greater arrhythmia susceptibility. We hypothesized that short-term enhancement of GJ coupling during acute MI can produce more homogeneous infarct scars, reducing late susceptibility to post-MI arrhythmias. Methods: Following arrhythmic characterisation of the rat 4-week post-MI model (n=24), a further 27 Sprague-Dawley rats were randomised to receive rotigaptide to enhance GJ coupling (n=13) or saline control (n=14) by osmotic minipump immediately prior to, and for the first 7 days following surgical MI. At 4 weeks post-MI, hearts were explanted for ex vivo programmed electrical stimulation (PES) and optical mapping. Heterogeneity of infarct border zone (IBZ) scarring was quantified by histomorphometry. Results: Despite no detectable difference in infarct size at 4 weeks post-MI, rotigaptide-treated hearts had reduced arrhythmia susceptibility during PES (Inducibility score: rotigaptide 2.40.8, control 5.00.6, p=0.02) and less heterogeneous IBZ scarring (standard deviation of IBZ Complexity Score: rotigaptide 1.10.1, control 1.40.1, p=0.04), associated with an improvement in IBZ conduction velocity (rotigaptide 43.13.4 cm/s, control 34.82.0 cm/s, p=0.04). Conclusions: Enhancement of GJ coupling for only 7 days at the time of acute MI produced more homogeneous IBZ scarring and reduced arrhythmia susceptibility at 4 weeks post-MI. Short-term GJ modulation at the time of MI may represent a novel treatment strategy to modify the healed infarct scar morphology and reduce late post-MI arrhythmic risk

    Universal spin dynamics in infinite-temperature one-dimensional quantum magnets

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    We address the nature of spin dynamics in various integrable and non-integrable, isotropic and anisotropic quantum spin-SS chains, beyond the paradigmatic S=1/2S=1/2 Heisenberg model. In particular, we investigate the algebraic long-time decay ∝t−1/z\propto t^{-1/z} of the spin-spin correlation function at infinite temperature, using state-of-the-art simulations based on tensor network methods. We identify three universal regimes for the spin transport, independent of the exact microscopic model: (i) superdiffusive with z=3/2z=3/2, as in the Kardar-Parisi-Zhang universality class, when the model is integrable with extra symmetries such as spin isotropy that drive the Drude weight to zero, (ii) ballistic with z=1z=1 when the model is integrable with a finite Drude weight, and (iii) diffusive with z=2z=2 with easy-axis anisotropy or without integrability, at variance with previous observations.Comment: 7 pages, 3 figures, supplemental material included (7 pages, 6 figures
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