2,610 research outputs found
Development of a real-time full-field range imaging system
This article describes the development of a full-field range imaging system employing a high frequency amplitude modulated light source and image sensor. Depth images are produced at video frame rates in which each pixel in the image represents distance from the sensor to objects in the scene.
The various hardware subsystems are described as are the details about the firmware and software implementation for processing the images in real-time. The system is flexible in that precision can be traded off for decreased acquisition time. Results are reported to illustrate this versatility for both high-speed (reduced precision) and high-precision operating modes
Stably free modules over virtually free groups
Let be the free group on generators and let be a finite
nilpotent group of non square-free order; we show that for each the
integral group ring has infinitely many stably free
modules of rank 1.Comment: 9 pages. The final publication is available at
http://www.springerlink.com doi:10.1007/s00013-012-0432-
On the Discovery of Monocular Rivalry by Tscherning in 1898:Translation and Review
Monocular rivalry was named by Breese in 1899. He made prolonged observation of superimposed orthogonal gratings; they fluctuated in clarity with either one or the other grating occasionally being visible alone. A year earlier, Tscherning observed similar fluctuations with a grid of vertical and horizontal lines and with other stimuli; we draw attention to his prior account. Monocular rivalry has since been shown to occur with a wide variety of superimposed patterns with several independent rediscoveries of it. We also argue that Helmholtz described some phenomenon other than monocular rivalry in 1867
Optical mapping and optogenetics in cardiac electrophysiology research and therapy:a state-of-the-art review
State-of-the-art innovations in optical cardiac electrophysiology are significantly enhancing cardiac research. A potential leap into patient care is now on the horizon. Optical mapping, using fluorescent probes and high-speed cameras, offers detailed insights into cardiac activity and arrhythmias by analysing electrical signals, calcium dynamics, and metabolism. Optogenetics utilizes light-sensitive ion channels and pumps to realize contactless, cell-selective cardiac actuation for modelling arrhythmia, restoring sinus rhythm, and probing complex cellâcell interactions. The merging of optogenetics and optical mapping techniques for âall-opticalâ electrophysiology marks a significant step forward. This combination allows for the contactless actuation and sensing of cardiac electrophysiology, offering unprecedented spatialâtemporal resolution and control. Recent studies have performed all-optical imaging ex vivo and achieved reliable optogenetic pacing in vivo, narrowing the gap for clinical use. Progress in optical electrophysiology continues at pace. Advances in motion tracking methods are removing the necessity of motion uncoupling, a key limitation of optical mapping. Innovations in optoelectronics, including miniaturized, biocompatible illumination and circuitry, are enabling the creation of implantable cardiac pacemakers and defibrillators with optoelectrical closed-loop systems. Computational modelling and machine learning are emerging as pivotal tools in enhancing optical techniques, offering new avenues for analysing complex data and optimizing therapeutic strategies. However, key challenges remain including opsin delivery, real-time data processing, longevity, and chronic effects of optoelectronic devices. This review provides a comprehensive overview of recent advances in optical mapping and optogenetics and outlines the promising future of optics in reshaping cardiac electrophysiology and therapeutic strategies
Searching for the earliest galaxies in the 21 cm forest
We use a model developed by Xu et al. (2010) to compute the 21 cm line
absorption signatures imprinted by star-forming dwarf galaxies (DGs) and
starless minihalos (MHs). The method, based on a statistical comparison of the
equivalent width (W_\nu) distribution and flux correlation function, allows us
to derive a simple selection criteria for candidate DGs at very high (z >= 8)
redshift. We find that ~ 18% of the total number of DGs along a line of sight
to a target radio source (GRB or quasar) can be identified by the condition
W_\nu < 0; these objects correspond to the high-mass tail of the DG
distribution at high redshift, and are embedded in large HII regions. The
criterion W_\nu > 0.37 kHz instead selects ~ 11% of MHs. Selected candidate DGs
could later be re-observed in the near-IR by the JWST with high efficiency,
thus providing a direct probe of the most likely reionization sources.Comment: 8 pages, 3 figures. Accepted for publication in Science in China
Series
Observation and Modeling of the Solar Transition Region: II. Solutions of the Quasi-Static Loop Model
In the present work we undertake a study of the quasi-static loop model and
the observational consequences of the various solutions found. We obtain the
most general solutions consistent with certain initial conditions. Great care
is exercised in choosing these conditions to be physically plausible (motivated
by observations). We show that the assumptions of previous quasi-static loop
models, such as the models of Rosner, Tucker and Vaiana (1978) and Veseckey,
Antiochos and Underwood (1979), are not necessarily valid for small loops at
transition region temperatures. We find three general classes of solutions for
the quasi-static loop model, which we denote, radiation dominated loops,
conduction dominated loops and classical loops. These solutions are then
compared with observations. Departures from the classical scaling law of RTV
are found for the solutions obtained. It is shown that loops of the type that
we model here can make a significant contribution to lower transition region
emission via thermal conduction from the upper transition region.Comment: 30 pages, 3 figures, Submitted to ApJ, Microsoft Word File 6.0/9
Multi-component measurements of the Jefferson Lab energy recovery linac electron beam using optical transition and diffraction radiation
High brightness electron accelerators, such as energy recovery linacs (ERL),
often have complex particle distributions that can create difficulties in beam
transport as well as matching to devices such as wigglers used to generate
radiation from the beam. Optical transition radiation (OTR), OTR interferometry
(OTRI) and optical diffraction-transition radiation interferometry (ODTRI) have
proven to be effective tools for diagnosing both the spatial and angular
distributions of charged particle beams. OTRI and ODTRI have been used to
measure rms divergences and optical transverse phase space mapping has been
demonstrated using OTRI. In this work we present the results of diagnostic
experiments using OTR and ODR conducted at the Jefferson Laboratory 115 MeV ERL
which show the presence of two separate components within the spatial and
angular distributions of the beam. By assuming a correlation between the
spatial and angular features we estimate an rms emittance value for each of the
two components.Comment: 25 pages, 10 figures; accepted for publication in PRSTAB; minor
formatting errors correcte
Phase Mixing of Alfvén Waves Near a 2D Magnetic Null Point
The propagation of linear Alfvén wave pulses in an inhomogeneous plasma near a 2D coronal null point is investigated. When a uniform plasma density is considered, it is seen that an initially planar Alfvén wavefront remains planar, despite the varying equilibrium Alfvén speed, and that all the wave collects at the separatrices. Thus, in the non-ideal case, these Alfvénic disturbances preferentially dissipate their energy at these locations. For a non-uniform equilibrium density, it is found that the Alfvén wavefront is significantly distorted away from the initially planar geometry, inviting the possibility of dissipation due to phase mixing. Despite this however, we conclude that for the Alfvén wave, current density accumulation and preferential heating still primarily occur at the separatrices, even when an extremely non-uniform density profile is considered
Reionization after Planck: the derived growth of the cosmic ionizing emissivity now matches the growth of the galaxy UV luminosity density
Thomson optical depth tau measurements from Planck provide new insights into
the reionization of the universe. In pursuit of model-independent constraints
on the properties of the ionising sources, we determine the empirical evolution
of the cosmic ionizing emissivity. We use a simple two-parameter model to map
out the evolution in the emissivity at z>~6 from the new Planck optical depth
tau measurements, from the constraints provided by quasar absorption spectra
and from the prevalence of Ly-alpha emission in z~7-8 galaxies. We find the
redshift evolution in the emissivity dot{N}_{ion}(z) required by the
observations to be d(log Nion)/dz=-0.15(-0.11)(+0.08), largely independent of
the assumed clumping factor C_{HII} and entirely independent of the nature of
the ionising sources. The trend in dot{N}_{ion}(z) is well-matched by the
evolution of the galaxy UV-luminosity density (dlog_{10}
rho_UV/dz=-0.11+/-0.04) to a magnitude limit >~-13 mag, suggesting that
galaxies are the sources that drive the reionization of the universe. The role
of galaxies is further strengthened by the conversion from the UV luminosity
density rho_UV to dot(N)_{ion}(z) being possible for physically-plausible
values of the escape fraction f_{esc}, the Lyman-continuum photon production
efficiency xi_{ion}, and faint-end cut-off to the luminosity
function. Quasars/AGN appear to match neither the redshift evolution nor
normalization of the ionizing emissivity. Based on the inferred evolution in
the ionizing emissivity, we estimate that the z~10 UV-luminosity density is
8(-4)(+15)x lower than at $z~6, consistent with the observations. The present
approach of contrasting the inferred evolution of the ionizing emissivity with
that of the galaxy UV luminosity density adds to the growing observational
evidence that faint, star-forming galaxies drive the reionization of the
universe.Comment: 20 pages, 12 figures, 5 tables, Astrophysical Journal, updated to
match version in press, Figure 6 shows the main result of the pape
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