40 research outputs found
Dislocation density and graphitization of diamond crystals
Two sets of diamond specimens compressed at 2 GPa at temperatures varying between 1060 K and 1760 K were prepared; one in which graphitization was promoted by the presence of water and another in which graphitization of diamond was practically absent. X-ray diffraction peak profiles of both sets were analyzed for the microstructure by using the modified Williamson-Hall method and by fitting the Fourier coefficients of the measured profiles by theoretical functions for crystallite size and lattice strain. The procedures determined mean size and size distribution of crystallites as well as the density and the character of the dislocations. The same experimental conditions resulted in different microstructures for the two sets of samples. They were explained in terms of hydrostatic conditions present in the graphitized samples
Binary-induced magnetic activity? Time-series echelle spectroscopy and photometry of HD123351 = CZ CVn
We present a first and detailed study of the bright and active K0IV-III star
HD 123351. The star is found to be a single-lined spectroscopic binary with a
period of 147.8919+-0.0003 days and a large eccentricity of e=0.8086+-0.0001.
The rms of the orbital solution is just 47 m/s, making it the most precise
orbit ever obtained for an active binary system. The rotation period is
constrained from long-term photometry to be 58.32+-0.01 days. It shows that HD
123351 is a very asynchronous rotator, rotating five times slower than the
expected pseudo-synchronous value. Two spotted regions persisted throughout the
12 years of our observations. Four years of Halpha, CaII H&K and HeI D3
monitoring identifies the same main periodicity as the photometry but dynamic
spectra also indicate that there is an intermittent dependence on the orbital
period, in particular for Ca ii H&K in 2008. Line-profile inversions of a pair
of Zeeman sensitive/insensitive iron lines yield an average surface
magnetic-flux density of 542+-72 G. The time series for 2008 is modulated by
the stellar rotation as well as the orbital motion, such that the magnetic flux
is generally weaker during times of periastron and that the chromospheric
emissions vary in anti-phase with the magnetic flux. We also identify a broad
and asymmetric lithium line profile and measure an abundance of log n(Li) =
1.70+-0.05. The star's position in the H-R diagram indicates a mass of 1.2+-0.1
Msun and an age of 6-7 Gyr. We interpret the anti-phase relation of the
magnetic flux with the chromospheric emissions as evidence that there are two
magnetic fields present at the same time, a localized surface magnetic field
associated with spots and a global field that is oriented towards the
(low-mass) secondary component
Multiple and changing cycles of active stars II. Results
We study the time variations of the cycles of 20 active stars based on
decades-long photometric or spectroscopic observations. A method of
time-frequency analysis, as discussed in a companion paper, is applied to the
data. Fifteen stars definitely show multiple cycles; the records of the rest
are too short to verify a timescale for a second cycle. The cycles typically
show systematic changes. For three stars, we found two cycles in each of them
that are not harmonics, and which vary in parallel, indicating that a common
physical mechanism arising from a dynamo construct. The positive relation
between the rotational and cycle periods is confirmed for the inhomogeneous set
of active stars. Stellar activity cycles are generally multiple and variable.Comment: Accepted to Astronomy and Astrophysic
Effect of Mo addition on the microstructure and hardness of ultrafine-grained Ni alloys processed by a combination of cryorolling and high-pressure torsion
Microstructure, phase composition and hardness evolution in 316L stainless steel processed by high-pressure torsion
Dislocation densities and crystallite size distributions in nanocrystalline ball-milled fluorides, M F 2 ( M = Ca, Sr, Ba and Cd), determined by X-ray diffraction line-profile analysis
International audienc
The density and the character of dislocations in cubic and hexagonal polycrystals determined by X-ray diffraction
The density and the character of dislocations in cubic and hexagonal polycrystals were determined by a new procedure of X-ray diffraction profile analysis. The anisotropic strain broadening of diffraction profiles was accounted for by dislocation contrast factors. The screw or edge character of dislocations in a severely deformed copper specimen was determined by analysing the dislocation contrast factors. Comparing the contrast effect of the possible dislocation slip systems in hexagonal crystals with that determined experimentally for a sintered tungsten carbide sample, it was found that the dominant slip system in this specimen is {0001}. The dislocation density was calculated for both samples by the modfied Warren-Averbach procedure