8,513 research outputs found
Separate ways: The Mass-Metallicity Relation does not strongly correlate with Star Formation Rate in SDSS-IV MaNGA galaxies
We present the integrated stellar mass-metallicity relation (MZR) for more
than 1700 galaxies included in the integral field area SDSS-IV MaNGA survey.
The spatially resolved data allow us to determine the metallicity at the same
physical scale (effective radius in arcsecs, ) using a
heterogeneous set of ten abundance calibrators. Besides scale factors, the
shape of the MZR is similar for all calibrators, consistent with those reported
previously using single-fiber and integral field spectroscopy. We compare the
residuals of this relation against the star formation rate (SFR) and specific
SFR (sSFR). We do not find a strong secondary relation of the MZR with either
SFR or the sSFR for any of the calibrators, in contrast with previous
single-fiber spectroscopic studies. Our results agree with an scenario in which
metal enrichment happens at local scales, with global outflows playing a
secondary role in shaping the chemistry of galaxies and cold-gas inflows
regulating the stellar formation.Comment: 10 pages, 9 Figures. Accepted for publication in Ap
On numerical solution of Fredholm and Hammerstein integral equations via Nystr\"{o}m method and Gaussian quadrature rules for splines
Nystr\"{o}m method is a standard numerical technique to solve Fredholm integral equations of the second kind where the integration of the kernel is approximated using a quadrature formula. Traditionally, the quadrature rule used is the classical polynomial Gauss quadrature. Motivated by the observation that a given function can be better approximated by a spline function of a lower degree than a single polynomial piece of a higher degree, in this work, we investigate the use of Gaussian rules for splines in the Nystr\"{o}m method. We show that, for continuous kernels, the approximate solution of linear Fredholm integral equations computed using spline Gaussian quadrature rules converges to the exact solution for , being the number of quadrature points. Our numerical results also show that, when fixing the same number of quadrature points, the approximation is more accurate using spline Gaussian rules than using the classical polynomial Gauss rules. We also investigate the non-linear case, considering Hammerstein integral equations, and present some numerical tests.RYC-2017-2264
Solving boundary value problems via the Nyström method using spline Gauss rules
We propose to use spline Gauss quadrature rules for solving boundary value problems (BVPs) using the Nyström method. When solving BVPs, one converts the corresponding partial differential equation inside a domain into the Fredholm integral equation of the second kind on the boundary in the sense of boundary integral equation (BIE). The Fredholm integral equation is then solved using the Nyström method, which involves the use of a particular quadrature rule, thus, converting the BIE problem to a linear system. We demonstrate this concept on the 2D Laplace problem over domains with smooth boundary as well as domains containing corners. We validate our approach on benchmark examples and the results indicate that, for a fixed number of quadrature points (i.e., the same computational effort), the spline Gauss quadratures return an approximation that is by one to two orders of magnitude more accurate compared to the solution obtained by traditional polynomial Gauss counterparts
Solving Boundary Value Problems Via the Nyström Method Using Spline Gauss Rules
We propose to use spline Gauss quadrature rules for solving boundary value problems (BVPs) using the Nyström method. When solving BVPs, one converts the corresponding partial differential equation inside a domain into the Fredholm integral equation of the second kind on the boundary in the sense of boundary integral equation (BIE). The Fredholm integral equation is then solved using the Nyström method, which involves a use of a particular quadrature rule, thus, converting the BIE problem to a linear system. We demonstrate this concept on the 2D Laplace problem over domains with smooth boundary as well as domains containing corners. We validate our approach on benchmark examples and the results indicate that, for a fixed number of quadrature points (i.e., the same computational effort), the spline Gauss quadratures return an approximation that is by one to two orders of magnitude more accurate compared to the solution obtained by traditional polynomial Gauss counterparts
UniPROBE, update 2015: new tools and content for the online database of protein-binding microarray data on protein-DNA interactions
The Universal PBM Resource for Oligonucleotide Binding Evaluation (UniPROBE) serves as a convenient source of information on published data generated using universal protein-binding microarray (PBM) technology, which provides in vitro data about the relative DNA-binding preferences of transcription factors for all possible sequence variants of a length k (‘k-mers’). The database displays important information about the proteins and displays their DNA-binding specificity data in terms of k-mers, position weight matrices and graphical sequence logos. This update to the database documents the growth of UniPROBE since the last update 4 years ago, and introduces a variety of new features and tools, including a new streamlined pipeline that facilitates data deposition by universal PBM data generators in the research community, a tool that generates putative nonbinding (i.e. negative control) DNA sequences for one or more proteins and novel motifs obtained by analyzing the PBM data using the BEEML-PBM algorithm for motif inference. The UniPROBE database is available at http://uniprobe.org.National Institutes of Health (U.S.) (R01 HG003985)National Science Foundation (U.S.). Graduate Research Fellowship Progra
Negative thermal expansion of MgB in the superconducting state and anomalous behavior of the bulk Gr\"uneisen function
The thermal expansion coefficient of MgB is revealed to change
from positive to negative on cooling through the superconducting transition
temperature . The Gr\"uneisen function also becomes negative at
followed by a dramatic increase to large positive values at low temperature.
The results suggest anomalous coupling between superconducting electrons and
low-energy phonons.Comment: 5 figures. submitted to Phys. Rev. Let
Expression of Microbial Enzymes in Mammalian Astrocytes to Modulate Lactate Release
Astrocytes support and modulate neuronal activity through the release of L-lactate. The
suggested roles of astrocytic lactate in the brain encompass an expanding range of vital functions,
including central control of respiration and cardiovascular performance, learning, memory, executive
behaviour and regulation of mood. Studying the effects of astrocytic lactate requires tools that limit
the release of lactate selectively from astrocytes. Here, we report the validation in vitro of novel
molecular constructs derived from enzymes originally found in bacteria, that when expressed in
astrocytes, interfere with lactate handling. When lactate 2-monooxygenase derived from M. smegmatis
was specifically expressed in astrocytes, it reduced intracellular lactate pools as well as lactate release
upon stimulation. D-lactate dehydrogenase derived from L. bulgaricus diverts pyruvate towards
D-lactate production and release by astrocytes, which may affect signalling properties of lactate in
the brain. Together with lactate oxidase, which we have previously described, this set of transgenic
tools can be employed to better understand astrocytic lactate release and its role in the regulation of
neuronal activity in different behavioural contexts
Giant room temperature piezoresistance in a metal/silicon hybrid
Metal/semiconductor hybrids are artificially created structures presenting
novel properties not exhibited by either of the component materials alone. Here
we present a giant piezoresistance effect in a hybrid formed from silicon and
aluminum. The maximum piezoresistive gage factor (GF) of 843, measured at room
temperature, compares with a GF of -93 measured in the bulk homogeneous
silicon. This piezoresistance boost is not due to the silicon/aluminum
interface, but results from a stress induced anisotropy in the silicon
conductivity that acts to switch current away from the highly conductive
aluminum for uniaxial tensile strains. Its magnitude is shown, via the
calculation of hybrid resistivity weighting functions, to depend only on the
geometrical arrangement of the component parts of the hybrid.Comment: 4 pages, 4 figures, accepted for publication in Physical Review
Letter
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