5,797 research outputs found
Stress state influence on nonlocal interactions in damage modelling
This paper presents a modification of an integral nonlocal damage model used to describe concrete behaviour. It aims at providing a better treatment of areas close to a boundary and a fracture process zone where the interactions between points should vanish. Modifications on the original integral nonlocal model are introduced by considering the stress state of points in the weight function used to compute the nonlocal variables. Computations show that local information such as strain or damage profiles are significantly different, leading to a narrower region where damage equal to 1 in the case of the modified nonlocal model. It allows to better approach a discontinuity of the displacement field upon failure and thus, improves the estimation of the crack opening that has been developed in post-processing for this type of calculation
The Discovery of the Most Metal-Rich White Dwarf: Composition of a Tidally Disrupted Extrasolar Dwarf Planet
Cool white dwarf stars are usually found to have an outer atmosphere that is
practically pure in hydrogen or helium. However, a small fraction have traces
of heavy elements that must originate from the accretion of extrinsic material,
most probably circumstellar matter. Upon examining thousands of Sloan Digital
Sky Survey spectra, we discovered that the helium-atmosphere white dwarf SDSS
J073842.56+183509.6 shows the most severe metal pollution ever seen in the
outermost layers of such stars. We present here a quantitative analysis of this
exciting star by combining high S/N follow-up spectroscopic and photometric
observations with model atmospheres and evolutionary models. We determine the
global structural properties of our target star, as well as the abundances of
the most significant pollutants in its atmosphere, i.e., H, O, Na, Mg, Si, Ca,
and Fe. The relative abundances of these elements imply that the source of the
accreted material has a composition similar to that of Bulk Earth. We also
report the signature of a circumstellar disk revealed through a large infrared
excess in JHK photometry. Combined with our inferred estimate of the mass of
the accreted material, this strongly suggests that we are witnessing the
remains of a tidally disrupted extrasolar body that was as large as Ceres.Comment: 7 pages in emulateapj, 5 figures, accepted for publication in Ap
Geometry of integrable dynamical systems on 2-dimensional surfaces
This paper is devoted to the problem of classification, up to smooth
isomorphisms or up to orbital equivalence, of smooth integrable vector fields
on 2-dimensional surfaces, under some nondegeneracy conditions. The main
continuous invariants involved in this classification are the left equivalence
classes of period or monodromy functions, and the cohomology classes of period
cocycles, which can be expressed in terms of Puiseux series. We also study the
problem of Hamiltonianization of these integrable vector fields by a compatible
symplectic or Poisson structure.Comment: 31 pages, 12 figures, submitted to a special issue of Acta
Mathematica Vietnamic
Multiwavelength Observations of the Hot DB Star PG 0112+104
We present a comprehensive multiwavelength analysis of the hot DB white dwarf
PG 0112+104. Our analysis relies on newly-acquired FUSE observations, on
medium-resolution FOS and GHRS data, on archival high-resolution GHRS
observations, on optical spectrophotometry both in the blue and around Halpha,
as well as on time-resolved photometry. From the optical data, we derive a
self-consistent effective temperature of 31,300+-500 K, a surface gravity of
log g = 7.8 +- 0.1 (M=0.52 Msun), and a hydrogen abundance of log N(H)/N(He) <
-4.0. The FUSE spectra reveal the presence of CII and CIII lines that
complement the previous detection of CII transitions with the GHRS. The
improved carbon abundance in this hot object is log N(C)/N(He) = -6.15 +- 0.23.
No photospheric features associated with other heavy elements are detected. We
reconsider the role of PG 0112+104 in the definition of the blue edge of the
V777 Her instability strip in light of our high-speed photometry, and contrast
our results with those of previous observations carried out at the McDonald
Observatory.Comment: 10 pages in emulateapj, 9 figures, accepted for publication in Ap
Identification-Robust Inference for Endogeneity Parameters in Linear Structural Models
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