5 research outputs found
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
Planar And Spatial Gravity Balancing With Normal Springs
Very often, spring-to-gravity-balancing mechanisms are conceived with ideal (zero-free-length l0 =0) springs. However, the use of ideal springs in the conception phase tends to lead to more complex mechanisms because the ideal spring functionality has to be approximated with normal springs. To facilitate construction of (gravity) balancers, employing normal springs (l0 ≠0) directly mounted between the link attachment points of the mechanism in the conception phase therefore seems beneficiary. This paper discusses spring mechanisms that enable perfect balancing of gravity acting on an inverted pendulum while employing normal springs between the spring-attachment points: The design synthesis of such mechanisms will be explained and balancing conditions will be derived, using a potential energy consideration
Multi-epoch X-ray observations of the Seyfert 1.2 galaxy Mrk 79: bulk motion of the illuminating X-ray source
Multi-epoch X-ray spectroscopy (0.3-25 keV) of the Seyfert 1.2 galaxy Mrk 79
(UGC 3973) spanning nearly eight years and a factor of three in broadband flux
are analysed. The data are obtained at seven epochs with either XMM-Newton or
Suzaku. Comparison with contemporaneous RXTE monitoring indicate that all flux
states of Mrk 79 are represented by the data. The spectra are fitted in a
self-consistent manner adopting a power law and ionised reflection to describe
the broadband continuum. Modification of the spectra by a distant photoionised
medium, seen predominantly in emission, are also included. Under the assumption
that the inner disk is at the innermost stable circular orbit, our blurred
reflection models give a spin of a = 0.7+/-0.1. The reflection component in
each spectrum is weaker than predicted by simple reflection models. If the
illuminating X-ray emission is produced by flares above the disk that move at
mildly relativistic velocities, however, diminished reflection is expected.
Light bending due to strong gravity near black holes can influence how the
illuminating and reflected flux are observed; variations in Mrk 79 do not
suggest that light bending is important in this source.Comment: 13 pages. Accepted for publication in MNRA
The quasar PG 0844+349 in an X-ray weak state
In March 2009 the well-studied quasar, PG 0844+349, was discovered with Swift
to be in an X-ray weak state. A follow-up XMM-Newton observation several weeks
later generated a good quality spectrum of the source, showing substantial
curvature and spectral hardening. In combination with archival data at two
previous epochs when the source was in a bright state, we examine the long-term
spectral and timing properties of PG 0844+349 spanning nearly ten years and a
factor of ten in brightness. Partial covering and blurred reflection models are
compared to the data at each flux state while attempting to maintain
consistency between the various epochs. In terms of the blurred reflection
model, PG 0844+349 is in a reflection dominated state during the 2009 X-ray
weak observations, which can be understood in terms of light bending. Moreover,
the light bending scenario can also account for the short-term (i.e. ~1000s)
spectral variability in the source. Other models cannot be decisively ruled
out, but we note distinguishing features of the models that can be explored for
in higher signal-to-noise data from current and future observatories.Comment: 11 pages. Accepted for publication in MNRA
X-ray spectral variability in PG1535+547: the changing-look of a 'soft X-ray weak' AGN
PG1535+547 is a bright NLS1 galaxy, whose high energy emission shows strong
variability in shape and flux. ROSAT data classified it as soft X-ray weak QSO
(objects whose X-ray-to-optical flux ratio is smaller than in typical QSO):
their X-ray spectra are often characterized by highly ionized, complex
absorbers and/or reflection from the disk, whose relative importance is
currently debated. In both cases, the presence of such features implies that we
are looking at matter located in the innermost regions of the AGN. In this
paper we want to clarify the nature of the X-ray emission of PG1535+547, and
constrain the physical properties of regions where the emission originates. We
present new XMM observations, from which we obtained 2 spectra separated by
about 1 week, that we compare with a previous XMM observation. The data support
the complex and variable nature of the X-ray emission. The broad band flux
increases by a factor ~2.3 in 3 years, and then decreases by a factor ~1.3 in
about 1 week. In the new EPIC spectra strong absorption features at E<3keV and
a complex spectral shape in the Fe line energy range are evident, coupled with
a drop in the emission at higher energies. We describe all the states assuming
either a warm absorber plus a relativistically blurred ionized reflection, or a
two-phase warm absorber partially covering the source plus a scattered
component. The variability is ascribed to the warm absorbers, that vary their
physical properties on timescales of years and days. In the reflection scenario
all the states require a high fraction of reflection. The strong variability in
the X-ray band opposed to a more constant optical emission implies that
PG1535+547 can not actually be classified as a soft X-ray weak AGN.Comment: 14 pages, 7 figures, A&A latex manuscript; accepted for publication
in Astronomy & Astrophysic