3,036 research outputs found
Metastability-Containing Circuits
Communication across unsynchronized clock domains is inherently vulnerable to metastable upsets; no digital circuit can deterministically avoid, resolve, or detect metastability (Marino, 1981). Traditionally, a possibly metastable input is stored in synchronizers, decreasing the odds of maintained metastability over time. This approach costs time, and does not guarantee success. We propose a fundamentally different approach: It is possible to \emph{contain} metastability by logical masking, so that it cannot infect the entire circuit. This technique guarantees a limited degree of metastability in---and uncertainty about---the output. We present a synchronizer-free, fault-tolerant clock synchronization algorithm as application, synchronizing clock domains and thus enabling metastability-free communication. At the heart of our approach lies a model for metastability in synchronous clocked digital circuits. Metastability is propagated in a worst-case fashion, allowing to derive deterministic guarantees, without and unlike synchronizers. The proposed model permits positive results while at the same time reproducing established impossibility results regarding avoidance, resolution, and detection of metastability. Furthermore, we fully classify which functions can be computed by synchronous circuits with standard registers, and show that masking registers are computationally strictly more powerful
Mid-Infrared Instrumentation for the European Extremely Large Telescope
MIDIR is the proposed thermal/mid-IR imager and spectrograph for the European
Extremely Large Telescope (E-ELT). It will cover the wavelength range of 3 to
at least 20 microns. Designed for diffraction-limited performance over the
entire wavelength range, MIDIR will require an adaptive optics system; a
cryogenically cooled system could offer optimal performance in the IR, and this
is a critical aspect of the instrument design. We present here an overview of
the project, including a discussion of MIDIR's science goals and a comparison
with other infrared (IR) facilities planned in the next decade; top level
requirements derived from these goals are outlined. We describe the optical and
mechanical design work carried out in the context of a conceptual design study,
and discuss some important issues to emerge from this work, related to the
design, operation and calibration of the instrument. The impact of telescope
optical design choices on the requirements for the MIDIR instrument is
demonstrated.Comment: for publication in SPIE Proceedings vol. 6692, Cryogenic Optical
Systems and Instrumentation XII, eds. J.B. Heaney and L.G. Burriesci, San
Diego, Aug 200
Near-Optimal Approximate Shortest Paths and Transshipment in Distributed and Streaming Models
We present a method for solving the shortest transshipment problem-also known as uncapacitated minimum cost flow-up to a multiplicative error of 1 + Ï” in undirected graphs with non-negative integer edge weights using a tailored gradient descent algorithm. Our gradient descent algorithm takes Ï”-3 polylog n iterations, and in each iteration it needs to solve an instance of the transshipment problem up to a multiplicative error of polylog n, where n is the number of nodes. In particular, this allows us to perform a single iteration by computing a solution on a sparse spanner of logarithmic stretch. Using a careful white-box analysis, we can further extend the method to finding approximate solutions for the single-source shortest paths (SSSP) problem. As a consequence, we improve prior work by obtaining the following results: 1. Broadcast CONGEST model: (1+")-approximate SSSP using Ă((â n+D) · Ï”-O(1)) rounds, 1 where D is the (hop) diameter of the network. 2. Broadcast congested clique model: (1+Ï”)-approximate shortest transshipment and SSSP using Ă (Ï”-O(1)) rounds. 3. Multipass streaming model: (1+Ï”)-approximate shortest transshipment and SSSP using Ă (n) space and Ă(Ï”-O(1)) passes. The previously fastest SSSP algorithms for these models leverage sparse hop sets. We bypass the hop set construction; computing a spanner is sufficient with our method. The above bounds assume non-negative integer edge weights that are polynomially bounded in n; for general nonnegative weights, running times scale with the logarithm of the maximum ratio between non-zero weights. In case of asymmetric costs for traversing an edge in opposite directions, running times scale with the maximum ratio between the costs of both directions over all edges
Automatic detection of arcs and arclets formed by gravitational lensing
We present an algorithm developed particularly to detect gravitationally
lensed arcs in clusters of galaxies. This algorithm is suited for automated
surveys as well as individual arc detections. New methods are used for image
smoothing and source detection. The smoothing is performed by so-called
anisotropic diffusion, which maintains the shape of the arcs and does not
disperse them. The algorithm is much more efficient in detecting arcs than
other source finding algorithms and the detection by eye.Comment: A&A in press, 12 pages, 16 figure
Discovery of a nearby young brown dwarf binary candidate
In near-infrared NaCo observations of the young brown dwarf 2MASS
J0041353-562112, we discovered a companion a little less than a magnitude
fainter than the primary. The binary candidate has a separation of 143 mas, the
spectral types are M6.5 and M9.0 for the two components. Colors and flux ratios
are consistent with the components being located at the same distance
minimizing the probability of the secondary being a background object. The
brown dwarf is known to show Li absorption constraining the age to less than
~200 Myr, and it was suspected to show ongoing accretion, indicating an age as
low as ~10 Myr. We estimate distance and orbital parameters of the binary as a
function of age. For an age of 10 Myr, the distance to the system is 50 pc, the
orbital period is 126 yr, and the masses of the components are ~30 and ~15
MJup. The binary brown dwarf fills a so far unoccupied region in the parameters
mass and age; it is a valuable new benchmark object for brown dwarf atmospheric
and evolutionary models.Comment: 4 pages, 2 figures, accepted by A&
Tackling 3D ToF Artifacts Through Learning and the FLAT Dataset
Scene motion, multiple reflections, and sensor noise introduce artifacts in
the depth reconstruction performed by time-of-flight cameras. We propose a
two-stage, deep-learning approach to address all of these sources of artifacts
simultaneously. We also introduce FLAT, a synthetic dataset of 2000 ToF
measurements that capture all of these nonidealities, and allows to simulate
different camera hardware. Using the Kinect 2 camera as a baseline, we show
improved reconstruction errors over state-of-the-art methods, on both simulated
and real data.Comment: ECCV 201
Applying consumer responsibility principle in evaluating environmental load of carbon emissions
There is a need for a proper indicator in order to assess the environmental impact of international
trade, therefore using the carbon footprint as an indicator can be relevant and useful. The aim of this
study is to show from a methodological perspective how the carbon footprint, combined with input-
output models can be used for analysing the impacts of international trade on the sustainable use
of national resources in a country. The use of the input-output approach has the essential advantage
of being able to track the transformation of goods through the economy. The study examines the environmental
impact of consumption related to international trade, using the consumer responsibility
principle. In this study the use of the carbon footprint and input-output methodology is shown on the
example of the Hungarian consumption and the impact of international trade. Moving from a production-
based approach in climate policy to a consumption-perspective principle and allocation,
would also help to increase the efficiency of emission reduction targets and the evaluation of the
ecological impacts of international trade
One More Awareness Gap? The BehaviourâImpact Gap Problem
Preceding research has made hardly any attempt to measure the ecological impacts of pro-environmental behaviour in an objective way. Those impacts were rather supposed or calculated. The research described herein scrutinized the ecological impact reductions achieved through pro-environmental behaviour and raised the question how much of a reduction in carbon footprint can be achieved through voluntary action without actually affecting the socio-economic determinants of life. A survey was carried out in order to measure the difference between the ecological footprint of âgreenâ and âbrownâ consumers. No significant difference was found between the ecological footprints of the two groupsâsuggesting that individual pro-environmental attitudes and behaviour do not always reduce the environmental impacts of consumption. This finding resulted in the formulation of a new proposition called the BIG (behaviourâimpact gap) problem, which is an interesting addition to research in the field of environmental awareness gaps
A direct and differential imaging search for sub-stellar companions to epsilon Indi A
We have carried out a direct and differential imaging search for sub-stellar
companions to eps Indi A using the adaptive optics system NACO at the ESO VLT.
The observations were carried out in September 2004 with NACO/SDI as well as
with NACO's S27 camera in the H and Ks filters. The SDI data cover an area of
\~2.8" around eps Indi A. No detection was achieved in the inner neighbourhood
down to 53 Mj (5 sigma confidence level) at a separation > 0.4" (1.45 AU) and
down to 21 Mj for separations > 1.3" (4.7 AU). To cover a wider field of view,
observations with the S27 camera and a coronagraphic mask were obtained. We
detected a faint source at a separation of (7.3 +/- 0.1)" and a position angle
of (302.9 +/- 0.8) degree. The photometry for the candidate companion yields
m(H)=(16.45 +/- 0.04)mag and m(Ks) = (15.41 +/- 0.06)mag, respectively. Those
magnitudes and the resulting color (H-Ks) = (1.04 +/- 0.07)mag fit best to a
spectral type of L5 - L9.5 if it is bound. Observations done with HST/NICMOS by
M. Endl have shown the source to be a background object.Comment: 6 pages, 5 figures, accepted by A&
On the Parity Problem in One-Dimensional Cellular Automata
We consider the parity problem in one-dimensional, binary, circular cellular
automata: if the initial configuration contains an odd number of 1s, the
lattice should converge to all 1s; otherwise, it should converge to all 0s. It
is easy to see that the problem is ill-defined for even-sized lattices (which,
by definition, would never be able to converge to 1). We then consider only odd
lattices.
We are interested in determining the minimal neighbourhood that allows the
problem to be solvable for any initial configuration. On the one hand, we show
that radius 2 is not sufficient, proving that there exists no radius 2 rule
that can possibly solve the parity problem from arbitrary initial
configurations. On the other hand, we design a radius 4 rule that converges
correctly for any initial configuration and we formally prove its correctness.
Whether or not there exists a radius 3 rule that solves the parity problem
remains an open problem.Comment: In Proceedings AUTOMATA&JAC 2012, arXiv:1208.249
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