14,466 research outputs found
Direct observation of pitting corrosion evolutions on carbon steel surfaces at the nano-to-micro- scales.
The Cl--induced corrosion of metals and alloys is of relevance to a wide range of engineered materials, structures, and systems. Because of the challenges in studying pitting corrosion in a quantitative and statistically significant manner, its kinetics remain poorly understood. Herein, by direct, nano- to micro-scale observations using vertical scanning interferometry (VSI), we examine the temporal evolution of pitting corrosion on AISI 1045 carbon steel over large surface areas in Cl--free, and Cl--enriched solutions. Special focus is paid to examine the nucleation and growth of pits, and the associated formation of roughened regions on steel surfaces. By statistical analysis of hundreds of individual pits, three stages of pitting corrosion, namely, induction, propagation, and saturation, are quantitatively distinguished. By quantifying the kinetics of these processes, we contextualize our current understanding of electrochemical corrosion within a framework that considers spatial dynamics and morphology evolutions. In the presence of Cl- ions, corrosion is highly accelerated due to multiple autocatalytic factors including destabilization of protective surface oxide films and preservation of aggressive microenvironments within the pits, both of which promote continued pit nucleation and growth. These findings offer new insights into predicting and modeling steel corrosion processes in mid-pH aqueous environments
Global existence and decay rates to a self-consistent chemotaxis-fluid system
In this paper, we investigate a chemotaxis-fluid system involving both the effect of potential force on cells and the effect of chemotactic force on fluid:
∂tn + u · ∇n = ∆n − ∇ · (χ(c)n∇c) + ∇ · (n∇ϕ),
∂tc + u · ∇c = ∆c − nf(c),
∂tu + κ(u · ∇)u + ∇P = ∆u − n∇ϕ + χ(c)n∇c,
∇ · u = 0
in Rd × (0, T) (d = 2, 3). One of the novelties and difficulties here is that the coupling in this model is stronger and more nonlinear than the most-studied chemotaxis-fluid model due to the additional term χ(c)n∇c in the third equation. We will first establish several extensibility criteria of classical solutions, which ensure us to extend the local solutions to global ones in the three dimensional chemotaxis-Stokes case and in the two dimensional chemotaxis-Navier-Stokes version under suitable smallness assumption on ∥c0∥L∞ with the help of a new entropy functional inequality. Some further decay estimates are also obtained under some suitable growth restriction on the potential ∇ϕ at infinity. As a byproduct of the entropy functional inequality, we also establish the global-in-time existence of weak solutions to the three dimensional chemotaxis-Navier-Stokes system. To the best of our knowledge, this seems to be the first work addressing the global well-posedness and decay property of solutions to the Cauchy problem of self-consistent chemotaxis-fluid system
Multiple large shareholders, excess leverage and tunneling: evidence from an emerging market
The file attached to this record is the author's final peer reviewed version. The Publisher's final version can be found by following the DOI link.Manuscript Type: Empirical
Research Question/Issue: Past empirical efforts in corporate governance have examined the effects of large shareholders with the excess control rights on tunneling activities. However, no study has systematically investigated the effects of multiple large shareholders on excess leverage policies and tunneling in an emerging country environment where minority rights protection is weak. In this study, we examine the role of multiple large shareholders and the effects of control contestability of multiple large shareholders on firm excess leverage decision and tunneling by controlling shareholders.
Research Findings/Insights: Using a sample of 2,341 Chinese firms for the years 2001 to 2013, we document that the contestability of multiple non-controlling large shareholders relative to controlling shareholders reduces the adoption of excess leverage policies, tunneling and enhances capital investment. Another intriguing finding is that the government as a controlling shareholder exerts significant influence and reduces the monitoring effectiveness of multiple larger shareholders.
Theoretical/Academic Implications: By addressing the role of multiple large shareholders on excess leverage decisions, this study makes an important contribution to the corporate governance literature. We extend the recent developments in agency theory regarding the role of multiple large shareholders in constraining expropriation of controlling shareholders with excess control rights and their effect on firm leverage decisions. Our results support the theoretical models which indicate that the presence of multiple large shareholders is an important and efficient internal governance mechanism that mitigates a firm’s agency costs, particularly, in an emerging market environment where corporate governance is weak and inadequate to curb tunneling problem.
JEL classification: G15; G34; G3
Characterization of received signal strength perturbations using Allan variance
This is the author accepted manuscript. The final version is available from IEEE via the DOI in this record.The received signal strength (RSS) of wireless signals
conveys important information that has been widely used in wireless
communications, localisation and tracking. Traditional RSS-based
research and applications model the RSS signal using a deterministic
component plus a white noise term. This paper investigates the
assumption of white noise to have a further understanding of the
RSS signal and proposes a methodology based on the Allan Variance
(AVAR) to characterise it. Using AVAR, we model the RSS unknown
perturbations as correlated random terms. These terms can account
for both coloured noise or other effects such as shadowing or smallscale
fading. Our results confirm that AVAR can be used to obtain
a flexible model of the RSS perturbations, as expressed by coloured
noise components . The study is complemented by introducing two
straightforward applications of the proposed methodology: 1) The
modelling and simulation of RSS noise using Wiener processes, and
2) RSS localisation using the extended Kalman filterThis paper is sponsored by the Royal Society-MOST Grant
(No. 185730) and the Royal Society of Edinburgh-NSFC Grant
(NNS/INT 15-16 Casaseca). Thanks are also given to the Scottish
Funding Council and the Centre for Excellence in Sensor and
Imaging System (CENSIS, project ref. CAF-0036) and the Digital
Health and Care Institute (DHI, project Smartcough-MacMasters)
for partially covering Dr. Luo’s (CENSIS) and Dr. Casasecade-la-Higuera’s
(CENSIS and DHI) time. The Royal Society of
Edinburgh is also acknowledged for funding associated to project
HIV
Hubble Space Telescope WFC3 Grism Spectroscopy and Imaging of a Growing Compact Galaxy at z=1.9
We present HST/WFC3 grism spectroscopy of the brightest galaxy at z>1.5 in
the GOODS-South WFC3 Early Release Science grism pointing, covering the
wavelength range 0.9-1.7 micron. The spectrum is of remarkable quality and
shows the redshifted Balmer lines Hbeta, Hgamma, and Hdelta in absorption at
z=1.902, correcting previous erroneous redshift measurements from the
rest-frame UV. The average rest-frame equivalent width of the Balmer lines is
8+-1 Angstrom, which can be produced by a post-starburst stellar population
with a luminosity-weighted age of ~0.5 Gyr. The M/L ratio inferred from the
spectrum implies a stellar mass of ~4x10^11 Msun. We determine the morphology
of the galaxy from a deep WFC3 F160W image. Similar to other massive galaxies
at z~2 the galaxy is compact, with an effective radius of 2.1+-0.3 kpc.
Although most of the light is in a compact core, the galaxy has two red, smooth
spiral arms that appear to be tidally-induced. The spatially-resolved
spectroscopy demonstrates that the center of the galaxy is quiescent and the
surrounding disk is forming stars, as it shows Hbeta in emission. The galaxy is
interacting with a companion at a projected distance of 18 kpc, which also
shows prominent tidal features. The companion has a slightly redder spectrum
than the primary galaxy but is a factor of ~10 fainter and may have a lower
metallicity. It is tempting to interpret these observations as "smoking gun"
evidence for the growth of compact, quiescent high redshift galaxies through
minor mergers, which has been proposed by several recent observational and
theoretical studies. Interestingly both objects host luminous AGNs, as
indicated by their X-ray luminosities, which implies that these mergers can be
accompanied by significant black hole growth. This study illustrates the power
of moderate dispersion, low background near-IR spectroscopy at HST resolution,
which is now available with the WFC3 grism.Comment: 5 pages, 5 figures. Submitted to ApJ Letters
The spatial distribution and origin of the FUV excess in early-type galaxies
We present surface photometry of a sample of 52 galaxies from the GALEX and
2MASS data archives, these include 32 normal elliptical galaxies, 10
ellipticals with weak Liner or other nuclear activity, and 10 star forming
ellipticals or early-type spirals. We examine the spatial distribution of the
Far Ultra-Violet excess in these galaxies, and its correlation with dynamical
and stellar population properties of the galaxies. From aperture photometry we
find that all galaxies except for recent major remnants and galaxies with
ongoing star formation show a positive gradient in the (FUV-NUV) colour
determined from the GALEX images. The logarithmic gradient does not correlate
with any stellar population parameter, but it does correlate with the central
velocity dispersion. The strength of the excess on the other hand, correlates
with both [alpha/Fe] and [Z/H], but more strongly with the former. We derive
models of the underlying stellar population from the 2MASS H-band images, and
the residual of the image from this model reveals a map of the centrally
concentrated FUV excess. We examine a possible hypothesis for generating the
FUV excess and the radial gradient in its strength, involving a helium
abundance gradient set up early in the formation process of the galaxies. If
this hypothesis is correct, the persistence of the gradients to the present day
places a strong limit on the importance of dry mergers in the formation of
ellipticals.Comment: 36 pages, accepted for publication in MNRAS. Appendices will appear
in online journal only. This version has reduced resolution for the figure in
Appendix B to comply with arXiv size limit
Superdense massive galaxies in the Nearby Universe
Superdense massive galaxies (r_e~1 kpc; M~10^{11} Msun) were common in the
early universe (z>1.5). Within some hierarchical merging scenarios, a
non-negligible fraction (1-10%) of these galaxies is expected to survive since
that epoch retaining their compactness and presenting old stellar populations
in the present universe. Using the NYU Value-Added Galaxy Catalog from the SDSS
Data Release 6 we find only a tiny fraction of galaxies (~0.03%) with r_e<1.5
kpc and M_*>8x10^{10} Msun in the local Universe (z<0.2). Surprinsingly, they
are relatively young (~2 Gyr) and metal-rich ([Z/H]~0.2). The consequences of
these findings within the current two competing size evolution scenarios for
the most massive galaxies ("dry" mergers vs "puffing up" due to quasar
activity) are discussed.Comment: Accepted for publication in ApJ Letters; 3 figure
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