760 research outputs found
High-Resolution spectroscopy of the low-mass X-ray binary EXO 0748-67
We present initial results from observations of the low-mass X-ray binary EXO
0748-67 with the Reflection Grating Spectrometer on board the XMM-Newton
Observatory. The spectra exhibit discrete structure due to absorption and
emission from ionized neon, oxygen, and nitrogen. We use the quantitative
constraints imposed by the spectral features to develop an empirical model of
the circumsource material. This consists of a thickened accretion disk with
emission and absorption in the plasma orbiting high above the binary plane.
This model presents challenges to current theories of accretion in X-ray binary
systems.Comment: 5 pages, 4 figures, accepted by A&A letters, XMM special issu
The interstellar oxygen-K absorption edge as observed by XMM-Newton
High resolution X-ray spectra of the Reflection Grating Spectrometer (RGS) on
board the XMM satellite are used to resolve the oxygen K absorption edge. By
combining spectra of low and high extinction sources, the observed absorption
edge can be split in the true interstellar (ISM) extinction and the
instrumental absorption. The detailed ISM edge structure closely follows the
edge structure of neutral oxygen as derived by theoretical R-matrix
calculations. However, the position of the theoretical edge requires a
wavelength shift. In addition the detailed instrumental RGS absorption edge
structure is presented. All results are verified by comparing to a subset of
Chandra LETG-HRC observations.Comment: LaTeX2e A&A style, 10 pages, 12 postscript figures, accepted for
publication in Astronomy and Astrophysic
Harnessing Elastic Energy to Transfer Reciprocating Actuation into Rotary Motion
The ability to convert reciprocating, i.e., alternating, actuation into
rotary motion using linkages is hindered fundamentally by their poor torque
transmission capability around kinematic singularity configurations. Here, we
harness the elastic potential energy of a linear spring attached to the coupler
link of four-bar mechanisms to manipulate force transmission around the
kinematic singularities. We developed a theoretical model to explore the
parameter space for proper force transmission in slider-crank and rocker-crank
four-bar kinematics. Finally, we verified the proposed model and methodology by
building and testing a macro-scale prototype of a slider-crank mechanism. We
expect this approach to enable the development of small-scale rotary engines
and robotic devices with closed kinematic chains dealing with serial kinematic
singularities, such as linkages and parallel manipulators.Comment: 8 pages, 5 figures, journal article submitted to Mechanisms and
Machine Theor
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