2,933 research outputs found
Compositional uniformity, domain patterning and the mechanism underlying nano-chessboard arrays
We propose that systems exhibiting compositional patterning at the nanoscale,
so far assumed to be due to some kind of ordered phase segregation, can be
understood instead in terms of coherent, single phase ordering of minority
motifs, caused by some constrained drive for uniformity. The essential features
of this type of arrangements can be reproduced using a superspace construction
typical of uniformity-driven orderings, which only requires the knowledge of
the modulation vectors observed in the diffraction patterns. The idea is
discussed in terms of a simple two dimensional lattice-gas model that simulates
a binary system in which the dilution of the minority component is favored.
This simple model already exhibits a hierarchy of arrangements similar to the
experimentally observed nano-chessboard and nano-diamond patterns, which are
described as occupational modulated structures with two independent modulation
wave vectors and simple step-like occupation modulation functions.Comment: Preprint. 11 pages, 11 figure
Real-Time Trajectory Planning Method Based On N-Order Curve Optimization
In recent years, many functionalities were developed for Automated Vehicles (AVs) and some of them with close-to-market prototypes. A required topic is the generation of continuous trajectories that reduces the amount of discrete and pre-coded instructions while leading the vehicle safely. Consequently, this work presents a novel real-time trajectory planning approach based on numerical optimization of n-order Bézier curves and lane-based information. The generation of a feasible trajectory considers the vehicle dimension while driving into a lane-corridor. The nonlinear optimization problem was solved with the Bound Optimization BY Quadratic Approximation method (BOBYQA), and it uses the passengers' comfort, safety, and vehicle dynamics as constraints of the problem. The solution is validated in a simulation environment using a bus with a length of 12 meters. Moreover, the validation considered the roundabouts due to its complexity, nevertheless, the solution is scalable to other scenarios.H2020 SHOW No 87553
New sub-millimeter limits on dust in the 55 Cancri planetary system
We present new, high-sensitivity sub-millimeter observations towards 55
Cancri, a nearby G8 star with one, or possibly two, known planetary
companion(s). Our 850 m map, obtained with the SCUBA instrument on the
James Clerk Maxwell Telescope, shows three peaks of emission at the 2.5 mJy
level in the vicinity of the star's position. However, the observed peaks are
25\arcsec--40\arcsec away from the star and a deep -band optical image
reveals faint point sources that coincide with two of the sub-millimeter peaks.
Thus, we do not find evidence for dust emission spatially associated with 55
Cancri. The excess 60 m emission detected with ISO may originate from one
or more of the 850 m peaks that we attribute to background sources. Our
new results, together with the HST/NICMOS coronographic images in the
near-infrared, place stringent limits on the amount of dust in this planetary
system, and argue against the existence of a detectable circumstellar dust disk
around 55 Cnc.Comment: 11 pages, 2 PostScript figures, to appear in The Astrophysical
Journal Letter
Dust in the 55 Cancri planetary system
The presence of debris disks around 1-Gyr-old main sequence stars
suggests that an appreciable amount of dust may persist even in mature
planetary systems. Here we report the detection of dust emission from 55
Cancri, a star with one, or possibly two, planetary companions detected through
radial velocity measurements. Our observations at 850m and 450m imply
a dust mass of 0.0008-0.005 Earth masses, somewhat higher than that in the the
Kuiper Belt of our solar system. The estimated temperature of the dust grains
and a simple model fit both indicate a central disk hole of at least 10 AU in
radius. Thus, the region where the planets are detected is likely to be
significantly depleted of dust. Our results suggest that far-infrared and
sub-millimeter observations are powerful tools for probing the outer regions of
extrasolar planetary systems.Comment: 8 pages and 2 figures, to appear in the Astrophysical Journa
Virtual synchronous-machine control of voltage-source converters in a low-voltage microgrid
In order to facilitate the further integration of distributed renewable generation into existing power systems, enhanced control schemes for grid-tied power electronic converters are necessary to ensure non-synchronous power sources can provide power and support to the grid. The virtual-synchronous-machine concept proposes the use of control schemes to enable static generators to operate with the dynamics of rotating synchronous generators. In this paper, a control scheme is presented based on the principle of active-power synchronization to regulate the active power of a grid-tied voltage-source converter based on an emulation of the synchronous-machine swing equation. Design of a cascaded inner-loop voltage and resonant current control is presented to regulate the output voltage as specified via the outer-loop virtual-machine control scheme responsible for power regulation. The performance of this control scheme is investigated within the context of microgrid operation for the provision of active and reactive power to the system, and microgrid frequency support. Experimental validation is provided via the use of a 15 kVA three-phase VSC in a 90 kVA 400V microgrid
Using the amplitude variation of a reverberation chamber channel to predict the synchronization of a wireless digital communication test system
We discuss the use of a metric based on the amplitude variation of a channel in the signal bandwidth to predict whether or not a digital wireless communication test system receiver will be able to demodulate a test signal. This metric is compared to another method consisting of the correlation calculated across the channel. A logistic regression analysis is used to provide a normalized assessment of the effectiveness of each metric as a predictive tool. We show that both metrics provide similar predictive capabilities, with the peak-to-minimum being significantly easier to calculate
- …