63 research outputs found
Reconstructing the projected gravitational potential of Abell 1689 from X-ray measurements
Context. Galaxy clusters can be used as cosmological probes, but to this end,
they need to be thoroughly understood. Combining all cluster observables in a
consistent way will help us to understand their global properties and their
internal structure. Aims. We provide proof of the concept that the projected
gravitational potential of galaxy clusters can directly be reconstructed from
X-ray observations. We also show that this joint analysis can be used to
locally test the validity of the equilibrium assumptions in galaxy clusters.
Methods. We used a newly developed reconstruction method, based on
Richardson-Lucy deprojection, that allows reconstructing projected
gravitational potentials of galaxy clusters directly from X-ray observations.
We applied this algorithm to the well-studied cluster Abell 1689 and compared
the gravitational potential reconstructed from X-ray observables to the
potential obtained from gravitational lensing measurements. [...] Results.
Assuming spherical symmetry and hydrostatic equilibrium, the potentials
recovered from gravitational lensing and from X-ray emission agree very well
beyond 500 kpc. Owing to the fact that the Richardson-Lucy deprojection
algorithm allows deprojecting each line of sight independently, this result may
indicate that non-gravitational effects and/or asphericity are strong in the
central regions of the clusters. Conclusions. We demonstrate the robustness of
the potential reconstruction method based on the Richardson-Lucy deprojection
algorithm and show that gravitational lensing and X-ray emission lead to
consistent gravitational potentials. Our results illustrate the power of
combining galaxy-cluster observables in a single, non-parametric, joint
reconstruction of consistent cluster potentials that can be used to locally
constrain the physical state of the gas.Comment: 8 pages, 4 figures. Accepted in A&
Joint reconstruction of galaxy clusters from gravitational lensing and thermal gas I. Outline of a non-parametric method
We present a method to estimate the lensing potential from massive galaxy
clusters for given observational X-ray data. The concepts developed and applied
in this work can easily be combined with other techniques to infer the lensing
potential, e.g. weak gravitational lensing or galaxy kinematics, to obtain an
overall best fit model for the lensing potential. After elaborating on the
physical details and assumptions the method is based on, we explain how the
numerical algorithm itself is implemented with a Richardson-Lucy algorithm as a
central part. Our reconstruction method is tested on simulated galaxy clusters
with a spherically symmetric NFW density profile filled with gas in hydrostatic
equilibrium. We describe in detail how these simulated observational data sets
are created and how they need to be fed into our algorithm. We test the
robustness of the algorithm against small parameter changes and estimate the
quality of the reconstructed lensing potentials. As it turns out we achieve a
very high degree of accuracy in reconstructing the lensing potential. The
statistical errors remain below 2.0% whereas the systematical error does not
exceed 1.0%.Comment: 7 pages, 5 figures. To appear in A&
Reconstructing the projected gravitational potential of galaxy clusters from galaxy kinematics
We develop a method for reconstructing the two-dimensional, projected
gravitational potential of galaxy clusters from observed line-of-sight velocity
dispersions of cluster galaxies. It is the third of an intended series of
papers aiming at a unique reconstruction method for cluster potentials
combining lensing, X-ray, Sunyaev-Zel'dovich and kinematic data. The observed
galaxy velocity dispersions are deprojected using the Richardson-Lucy
algorithm. The obtained radial velocity dispersions are then related to the
gravitational potential by using the tested assumption of a polytropic relation
between the effective galaxy pressure and the density. Once the gravitational
potential is obtained in three dimensions, projection along the line-of-sight
yields the two-dimensional potential. For simplicity we adopt spherical
symmetry and a known profile for the anisotropy parameter of the galaxy
velocity dispersions. We test the method with a numerically simulated galaxy
cluster and galaxies identified therein. We extract a projected
velocity-dispersion profile from the simulated cluster and pass it through our
algorithm, showing that the deviation between the true and the reconstructed
gravitational potential is less then 10% within approximately 1.2 Mpc/h from
the cluster centre.Comment: 8 pages, submitted to A&
Directed transport born from chaos in asymmetric antidot structures
It is shown that a polarized microwave radiation creates directed transport
in an asymmetric antidot superlattice in a two dimensional electron gas. A
numerical method is developed that allows to establish the dependence of this
ratchet effect on several parameters relevant for real experimental studies. It
is applied to the concrete case of a semidisk Galton board where the electron
dynamics is chaotic in the absence of microwave driving. The obtained results
show that high currents can be reached at a relatively low microwave power.
This effect opens new possibilities for microwave control of transport in
asymmetric superlattices.Comment: 8 pages, 10 figure
Photogalvanic current in artificial asymmetric nanostructures
We develop a theoretic description of the photogalvanic current induced by a
high frequency radiation in asymmetric nanostructures and show that it
describes well the results of numerical simulations. Our studies allow to
understand the origin of the electronic ratchet transport in such systems and
show that they can be used for creation of new types of detectors operating at
room temperature in a terahertz radiation range.Comment: 11 pages, 9 figs, EPJ latex styl
Perception versus polysomnographic assessment of sleep in CFS and non-fatigued control subjects: results from a population-based study
<p>Abstract</p> <p>Background</p> <p>Complaints of unrefreshing sleep are a prominent component of chronic fatigue syndrome (CFS); yet, polysomnographic studies have not consistently documented sleep abnormalities in CFS patients. We conducted this study to determine whether alterations in objective sleep characteristics are associated with subjective measures of poor sleep quality in persons with CFS.</p> <p>Methods</p> <p>We examined the relationship between perceived sleep quality and polysomnographic measures of nighttime and daytime sleep in 35 people with CFS and 40 non-fatigued control subjects, identified from the general population of Wichita, Kansas and defined by empiric criteria. Perceived sleep quality and daytime sleepiness were assessed using clinical sleep questionnaires. Objective sleep characteristics were assessed by nocturnal polysomnography and daytime multiple sleep latency testing.</p> <p>Results</p> <p>Participants with CFS reported unrefreshing sleep and problems sleeping during the preceding month significantly more often than did non-fatigued controls. Participants with CFS also rated their quality of sleep during the overnight sleep study as significantly worse than did control subjects. Control subjects reported significantly longer sleep onset latency than latency to fall asleep as measured by PSG and MSLT. There were no significant differences in sleep pathology or architecture between subjects with CFS and control subjects.</p> <p>Conclusion</p> <p>People with CFS reported sleep problems significantly more often than control subjects. Yet, when measured these parameters and sleep architecture did not differ between the two subject groups. A unique finding requiring further study is that control, but not CFS subjects, significantly over reported sleep latency suggesting CFS subjects may have an increased appreciation of sleep behaviour that may contribute to their perception of sleep problems.</p
Brownian motors
In systems possessing a spatial or dynamical symmetry breaking thermal
Brownian motion combined with unbiased, non-equilibrium noise gives rise to a
channelling of chance that can be used to exercise control over systems at the
micro- and even on the nano-scale. This theme is known as ``Brownian motor''
concept. The constructive role of (the generally overdamped) Brownian motion is
exemplified for a noise-induced transport of particles within various set-ups.
We first present the working principles and characteristics with a
proof-of-principle device, a diffusive temperature Brownian motor. Next, we
consider very recent applications based on the phenomenon of signal mixing. The
latter is particularly simple to implement experimentally in order to optimize
and selectively control a rich variety of directed transport behaviors. The
subtleties and also the potential for Brownian motors operating in the quantum
regime are outlined and some state-of-the-art applications, together with
future roadways, are presented.Comment: 20 pages, 9 figures (slightly changed version
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