4,336 research outputs found
Label Transfer from APOGEE to LAMOST: Precise Stellar Parameters for 450,000 LAMOST Giants
In this era of large-scale stellar spectroscopic surveys, measurements of
stellar attributes ("labels," i.e. parameters and abundances) must be made
precise and consistent across surveys. Here, we demonstrate that this can be
achieved by a data-driven approach to spectral modeling. With The Cannon, we
transfer information from the APOGEE survey to determine precise Teff, log g,
[Fe/H], and [/M] from the spectra of 450,000 LAMOST giants. The Cannon
fits a predictive model for LAMOST spectra using 9952 stars observed in common
between the two surveys, taking five labels from APOGEE DR12 as ground truth:
Teff, log g, [Fe/H], [\alpha/M], and K-band extinction . The model is then
used to infer Teff, log g, [Fe/H], and [/M] for 454,180 giants, 20% of
the LAMOST DR2 stellar sample. These are the first [/M] values for the
full set of LAMOST giants, and the largest catalog of [/M] for giant
stars to date. Furthermore, these labels are by construction on the APOGEE
label scale; for spectra with S/N > 50, cross-validation of the model yields
typical uncertainties of 70K in Teff, 0.1 in log g, 0.1 in [Fe/H], and 0.04 in
[/M], values comparable to the broadly stated, conservative APOGEE DR12
uncertainties. Thus, by using "label transfer" to tie low-resolution (LAMOST R
1800) spectra to the label scale of a much higher-resolution (APOGEE R
22,500) survey, we substantially reduce the inconsistencies between
labels measured by the individual survey pipelines. This demonstrates that
label transfer with The Cannon can successfully bring different surveys onto
the same physical scale.Comment: 27 pages, 14 figures. Accepted by ApJ on 16 Dec 2016, implementing
suggestions from the referee reports. Associated code available at
https://github.com/annayqho/TheCanno
Three Different Types of Galaxy Alignment within Dark Matter Halos
Using a large galaxy group catalogue based on the Sloan Digital Sky Survey
Data Release 4 we measure three different types of intrinsic galaxy alignment
within groups: halo alignment between the orientation of the brightest group
galaxies (BGG) and the distribution of its satellite galaxies, radial alignment
between the orientation of a satellite galaxy and the direction towards its
BGG, and direct alignment between the orientation of the BGG and that of its
satellites. In agreement with previous studies we find that satellite galaxies
are preferentially located along the major axis. In addition, on scales r < 0.7
Rvir we find that red satellites are preferentially aligned radially with the
direction to the BGG. The orientations of blue satellites, however, are
perfectly consistent with being isotropic. Finally, on scales r < 0.1 \Rvir, we
find a weak but significant indication for direct alignment between satellites
and BGGs. We briefly discuss the implications for weak lensing measurements.Comment: 4 pages, 4 figures, ApJL accepte
Spatial and kinematic alignments between central and satellite halos
Based on a cosmological N-body simulation we analyze spatial and kinematic
alignments of satellite halos within six times the virial radius of group size
host halos (Rvir). We measure three different types of spatial alignment: halo
alignment between the orientation of the group central substructure (GCS) and
the distribution of its satellites, radial alignment between the orientation of
a satellite and the direction towards its GCS, and direct alignment between the
orientation of the GCS and that of its satellites. In analogy we use the
directions of satellite velocities and probe three further types of alignment:
the radial velocity alignment between the satellite velocity and connecting
line between satellite and GCS, the halo velocity alignment between the
orientation of the GCS and satellite velocities and the auto velocity alignment
between the satellites orientations and their velocities. We find that
satellites are preferentially located along the major axis of the GCS within at
least 6 Rvir (the range probed here). Furthermore, satellites preferentially
point towards the GCS. The most pronounced signal is detected on small scales
but a detectable signal extends out to 6 Rvir. The direct alignment signal is
weaker, however a systematic trend is visible at distances < 2 Rvir. All
velocity alignments are highly significant on small scales. Our results suggest
that the halo alignment reflects the filamentary large scale structure which
extends far beyond the virial radii of the groups. In contrast, the main
contribution to the radial alignment arises from the adjustment of the
satellite orientations in the group tidal field. The projected data reveal good
agreement with recent results derived from large galaxy surveys. (abridged)Comment: accepted for publication in Ap
Penrose type inequalities for asymptotically hyperbolic graphs
In this paper we study asymptotically hyperbolic manifolds given as graphs of
asymptotically constant functions over hyperbolic space \bH^n. The graphs are
considered as subsets of \bH^{n+1} and carry the induced metric. For such
manifolds the scalar curvature appears in the divergence of a 1-form involving
the integrand for the asymptotically hyperbolic mass. Integrating this
divergence we estimate the mass by an integral over an inner boundary. In case
the inner boundary satisfies a convexity condition this can in turn be
estimated in terms of the area of the inner boundary. The resulting estimates
are similar to the conjectured Penrose inequality for asymptotically hyperbolic
manifolds. The work presented here is inspired by Lam's article concerning the
asymptotically Euclidean case.Comment: 29 pages, no figure, includes a proof of the equality cas
Synthesis of Mesoporous Silica@Co–Al Layered Double Hydroxide Spheres: Layer-by-Layer Method and Their Effects on the Flame Retardancy of Epoxy Resins
Hierarchical mesoporous silica@Co–Al layered double hydroxide (m-SiO2@Co–Al LDH) spheres were prepared through a layer-by-layer assembly process, in order to integrate their excellent physical and chemical functionalities. TEM results depicted that, due to the electrostatic potential difference between m-SiO2 and Co–Al LDH, the synthetic m-SiO2@Co–Al LDH hybrids exhibited that m-SiO2 spheres were packaged by the Co–Al LDH nanosheets. Subsequently, the m-SiO2@Co–Al LDH spheres were incorporated into epoxy resin (EP) to prepare specimens for investigation of their flame-retardant performance. Cone results indicated that m-SiO2@Co–Al LDH incorporated obviously improved fire retardant of EP. A plausible mechanism of fire retardant was hypothesized based on the analyses of thermal conductivity, char residues, and pyrolysis fragments. Labyrinth effect of m-SiO2 and formation of graphitized carbon char catalyzed by Co–Al LDH play pivotal roles in the flame retardance enhancement
Asymptotically hyperbolic manifolds with small mass
For asymptotically hyperbolic manifolds of dimension with scalar
curvature at least equal to the conjectured positive mass theorem
states that the mass is non-negative, and vanishes only if the manifold is
isometric to hyperbolic space. In this paper we study asymptotically hyperbolic
manifolds which are also conformally hyperbolic outside a ball of fixed radius,
and for which the positive mass theorem holds. For such manifolds we show that
the conformal factor tends to one as the mass tends to zero
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Fast and slow shifts of the zonal-mean intertropical convergence zone in response to an idealized anthropogenic aerosol
Previous modeling work showed that aerosol can affect the position of the tropical rain belt, i.e., the intertropical convergence zone (ITCZ). Yet it remains unclear which aspects of the aerosol impact are robust across models, and which are not. Here we present simulations with seven comprehensive atmosphere models that study the fast and slow impacts of an idealized anthropogenic aerosol on the zonal-mean ITCZ position. The fast impact, which results from aerosol atmospheric heating and land cooling before sea-surface temperature (SST) has time to respond, causes a northward ITCZ shift. Yet the fast impact is compensated locally by decreased evaporation over the ocean, and a clear northward shift is only found for an unrealistically large aerosol forcing. The local compensation implies that while models differ in atmospheric aerosol heating, this does not contribute to model differences in the ITCZ shift. The slow impact includes the aerosol impact on the ocean surface energy balance and is mediated by SST changes. The slow impact is an order of magnitude more effective than the fast impact and causes a clear southward ITCZ shift for realistic aerosol forcing. Models agree well on the slow ITCZ shift when perturbed with the same SST pattern. However, an energetic analysis suggests that the slow ITCZ shifts would be substantially more model-dependent in interactive-SST setups due to model differences in clear-sky radiative transfer and clouds. We also discuss implications for the representation of aerosol in climate models and attributions of recent observed ITCZ shifts to aerosol
Phenotypical microRNA screen reveals a noncanonical role of CDK2 in regulating neutrophil migration
Neutrophil migration is essential for inflammatory responses to kill pathogens; however, excessive neutrophilic inflammation also leads to tissue injury and adverse effects. To discover novel therapeutic targets that modulate neutrophil migration, we performed a neutrophil-specific microRNA (miRNA) overexpression screen in zebrafish and identified 8 miRNAs as potent suppressors of neutrophil migration. Among those, miR-199 decreases neutrophil chemotaxis in zebrafish and human neutrophil-like cells. Intriguingly, in terminally differentiated neutrophils, miR-199 alters the cell cycle-related pathways and directly suppresses cyclin-dependent kinase 2 (Cdk2), whose known activity is restricted to cell cycle progression and cell differentiation. Inhibiting Cdk2, but not DNA replication, disrupts cell polarity and chemotaxis of zebrafish neutrophils without inducing cell death. Human neutrophil-like cells deficient in CDK2 fail to polarize and display altered signaling downstream of the formyl peptide receptor. Chemotaxis of primary human neutrophils is also reduced upon CDK2 inhibition. Furthermore, miR-199 overexpression or CDK2 inhibition significantly improves the outcome of lethal systemic inflammation challenges in zebrafish. Our results therefore reveal previously unknown functions of miR-199 and CDK2 in regulating neutrophil migration and provide directions in alleviating systemic inflammation
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