86,840 research outputs found
Experimental study of the compression behavior of mask image projection based on stereolithography manufactured parts
The article presents the results of a series of compression tests on samples manufactured by means of the mask image projection based on stereolithography additive manufacturing technique (MIP-SL). Recent studies demonstrate the orthotropic nature of the MIP-SL materials. A research is initiated by the authors to attempt to predict the degree of anisotropy from the manufacturing parameters of the MIP-SL parts. The article focuses mainly on the development of the experimental compression tests of the first stage of the research. Special attention is paid to the four methods used to obtain the stress-strain curve of the material: strain gages, 2D Digital Image Correlation, extensometer measurements and crosshead displacement measurements. The article shows the advantages and limitations of each method. Finally, the anisotropic behaviour is verified and a testing procedure is set to obtain the constitutive parameters of the MIP-SL tested materialsPeer ReviewedPostprint (published version
The catalogue of positions of optically bright extragalactic radio sources OBRS-1
It is expected that the European Space Agency mission Gaia will make possible
to determine coordinates in the optical domain of more than 500000 quasars. In
2006, a radio astrometry project was launched with the overall goal to make
comparison of coordinate systems derived from future space-born astrometry
instruments with the coordinate system constructed from analysis of the global
very long baseline interferometry (VLBI) more robust. Investigation of their
rotation, zonal errors, and the non-alignment of the radio and optical
positions caused by both radio and optical structures are important for
validation of both techniques. In order to support these studies, the
densification of the list of compact extragalactic objects that are bright in
both radio and optical ranges is desirable. A set of 105 objects from the list
of 398 compact extragalactic radio sources with declination > -10 deg was
observed with the VLBA+EVN with the primary goal of producing their images with
milliarcsecond resolution. These sources are brighter than 18 magnitude at V
band, and they were previously detected at the European VLBI network. In this
paper coordinates of observed sources have been derived with milliarcsecond
accuracies from analysis of these VLBI observations following the method of
absolute astrometry. The catalogue of positions of 105 target sources is
presented. The accuracies of sources coordinates are in the range of 0.3 to 7
mas, with the median 1.1 mas.Comment: 6 pages, 1 figure, accepted by the Astronomical Journal, ID:
AJ-10606. Electronic table 2 with the catalogue is available in the source
code of this submissio
An investigation of the optimal conditions of rocket motion in the vicinity of a planet
Optimal control of points of motion for mass transfer in vacuums in gravitational fiel
An Advanced, Three-Dimensional Plotting Library for Astronomy
We present a new, three-dimensional (3D) plotting library with advanced
features, and support for standard and enhanced display devices. The library -
S2PLOT - is written in C and can be used by C, C++ and FORTRAN programs on
GNU/Linux and Apple/OSX systems. S2PLOT draws objects in a 3D (x,y,z) Cartesian
space and the user interactively controls how this space is rendered at run
time. With a PGPLOT inspired interface, S2PLOT provides astronomers with
elegant techniques for displaying and exploring 3D data sets directly from
their program code, and the potential to use stereoscopic and dome display
devices. The S2PLOT architecture supports dynamic geometry and can be used to
plot time-evolving data sets, such as might be produced by simulation codes. In
this paper, we introduce S2PLOT to the astronomical community, describe its
potential applications, and present some example uses of the library.Comment: 12 pages, 10 eps figures (higher resolution versions available from
http://astronomy.swin.edu.au/s2plot/paperfigures). The S2PLOT library is
available for download from http://astronomy.swin.edu.au/s2plo
The Three-Dimensional Mass Distribution in NGC 1700
A variety of modeling techniques is used with surface photometry from the
literature and recently acquired high-accuracy stellar kinematic data to
constrain the three-dimensional mass distribution in the luminous cuspy
elliptical galaxy NGC 1700. First, we model the radial velocity field and
photometry, and, using a Bayesian technique, estimate the triaxiality T and
short-to-long axis ratio c in five concentric annuli between approximately 1
and 3 effective radii. The results are completely consistent with T being
constant inside about 2.5 r_e (36 arcsec; 6.7/h kpc). Adding an assumption of
constant T as prior information gives an upper limit of T < 0.16 (95%
confidence); this relaxes to T < 0.22 if it is also assumed that there is
perfect alignment between the angular momentum and the galaxy's intrinsic short
axis. Near axisymmetry permits us then to use axisymmetric models to constrain
the radial mass profile. Using the Jeans (moment) equations, we demonstrate
that 2-integral, constant-M/L models cannot fit the data; but a 2-integral
model in which the cumulative enclosed M/L increases by a factor of roughly 2
from the center out to 12/h kpc can. Three-integral models constructed by
quadratic programming show that, in fact, no constant-M/L model is consistent
with the kinematics. Anisotropic 3-integral models with variable M/L, while not
uniquely establishing a minimum acceptable halo mass, imply, as do the moment
models, a cumulative M/L_B approximately 10 h at 12/h kpc. We conclude that NGC
1700 represents the best stellar dynamical evidence to date for dark matter in
elliptical galaxies.Comment: 26 pages, Latex, AASTeX v4.0, with 11 eps figures. To appear in The
Astronomical Journal, January 1999. Figures 1 and 3 are color but are
readable in b/
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