1,295 research outputs found
Titan Atmospheric Chemistry Revealed by Low-temperature N2-CH4 Plasma Discharge Experiments
Chemistry in Titan's N2-CH4 atmosphere produces complex organic aerosols. The
chemical processes and the resulting organic compounds are still far from
understood, although extensive observations, laboratory, and theoretical
simulations have greatly improved physical and chemical constraints on Titan's
atmosphere. Here, we conduct a series of Titan atmosphere simulation
experiments with N2-CH4 gas mixtures and investigate the effect of initial CH4
ratio, pressure, and flow rate on the production rates and composition of the
gas and solid products at a Titan relevant temperature (100 K) for the first
time. We find that the production rate of the gas and solid products increases
with increasing CH4 ratio. The nitrogen-containing species have much higher
yield than hydrocarbons in the gas products, and the N-to-C ratio of the solid
products appears to be the highest compared to previous plasma simulations with
the same CH4 ratio. The greater degree of nitrogen incorporation in the low
temperature simulation experiments suggests temperature may play an important
role in nitrogen incorporation in Titan's cold atmosphere. We also find that H2
is the dominant gas product and serves as an indicator of the production rate
of new organic molecules in the experiment, and that CH2NH may greatly
contribute to the incorporation of both carbon and nitrogen into the solid
particles. The pressure and flow rate affect the amount of time of the gas
mixture exposed to the energy source and therefore impact the N2-CH4 chemistry
initiated by the plasma discharge, emphasizing the influence of the energy flux
in Titan atmospheric chemistry.Comment: Accepted in ACS Earth and Space Chemistry, 6 figure
Continuous Equilibrium in Affine and Information-Based Capital Asset Pricing Models
We consider a class of generalized capital asset pricing models in continuous
time with a finite number of agents and tradable securities. The securities may
not be sufficient to span all sources of uncertainty. If the agents have
exponential utility functions and the individual endowments are spanned by the
securities, an equilibrium exists and the agents' optimal trading strategies
are constant. Affine processes, and the theory of information-based asset
pricing are used to model the endogenous asset price dynamics and the terminal
payoff. The derived semi-explicit pricing formulae are applied to numerically
analyze the impact of the agents' risk aversion on the implied volatility of
simultaneously-traded European-style options.Comment: 24 pages, 4 figure
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On the Equivalence of Nonnegative Matrix Factorization and K-means- Spectral Clustering
We provide a systematic analysis of nonnegative matrix factorization (NMF) relating to data clustering. We generalize the usual X = FG{sup T} decomposition to the symmetric W = HH{sup T} and W = HSH{sup T} decompositions. We show that (1) W = HH{sup T} is equivalent to Kernel K-means clustering and the Laplacian-based spectral clustering. (2) X = FG{sup T} is equivalent to simultaneous clustering of rows and columns of a bipartite graph. We emphasizes the importance of orthogonality in NMF and soft clustering nature of NMF. These results are verified with experiments on face images and newsgroups
Localization of the succinate receptor in the distal nephron and its signaling in polarized MDCK cells
When the succinate receptor (SUCNR1) is activated in the afferent arterioles of the glomerulus it increases renin release and induces hypertension. To study its location in other nephron segments and its role in kidney function, we performed immunohistochemical analysis and found that SUCNR1 is located in the luminal membrane of macula densa cells of the juxtaglomerular apparatus in close proximity to renin-producing granular cells, the cortical thick ascending limb, and cortical and inner medullary collecting duct cells. In order to study its signaling, SUCNR1 was stably expressed in Madin-Darby Canine Kidney (MDCK) cells, where it localized to the apical membrane. Activation of the cells by succinate caused Gq and Gi-mediated intracellular calcium mobilization, transient phosphorylation of extracellular regulated kinase (ERK)1/2 and the release of arachidonic acid along with prostaglandins E2 and I2. Signaling was desensitized without receptor internalization but rapidly resensitized upon succinate removal. Immunohistochemical evidence of phosphorylated ERK1/2 was found in cortical collecting duct cells of wild type but not SUCNR1 knockout streptozotocin-induced diabetic mice, indicating in vivo relevance. Since urinary succinate concentrations in health and disease are in the activation range of the SUCNR1, this receptor can sense succinate in the luminal fluid. Our study suggests that changes in the luminal succinate concentration may regulate several aspects of renal function
Growth and reductive transformation of a gold shell around pyramidal cadmium selenide nanocrystals
We report the growth of an unstable shell-like gold structure around
dihexagonal pyramidal CdSe nanocrystals in organic solution and the structural
transformation to spherical domains by two means: i) electron beam irradiation
(in situ) and (ii) addition of a strong reducing agent during synthesis. By
varying the conditions of gold deposition, such as ligands present or the
geometry of the CdSe nanocrystals, we were able to tune the gold domain size
between 1.4 nm to 3.9 nm and gain important information on the role of surface
chemistry in hetero nanoparticle synthesis and seed reactivity, both of which
are crucial points regarding the chemical design of new materials for
photocatalysis and optoelectronic applications.Comment: 5 pages, 4 figure
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Thermoelectric Properties of Novel Semimetals: A Case Study of YbMnSb2
The emerging class of topological materials provides a platform to engineer exotic electronic structures for a variety of applications. As complex band structures and Fermi surfaces can directly benefit thermoelectric performance it is important to identify the role of featured topological bands in thermoelectrics particularly when there are coexisting classic regular bands. In this work, the contribution of Dirac bands to thermoelectric performance and their ability to concurrently achieve large thermopower and low resistivity in novel semimetals is investigated. By examining the YbMnSb2 nodal line semimetal as an example, the Dirac bands appear to provide a low resistivity along the direction in which they are highly dispersive. Moreover, because of the regular-band-provided density of states, a large Seebeck coefficient over 160 µV K−1 at 300 K is achieved in both directions, which is very high for a semimetal with high carrier concentration. The combined highly dispersive Dirac and regular bands lead to ten times increase in power factor, reaching a value of 2.1 mW m−1 K−2 at 300 K. The present work highlights the potential of such novel semimetals for unusual electronic transport properties and guides strategies towards high thermoelectric performance. © 2020 The Authors. Advanced Materials published by Wiley-VCH Gmb
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