405 research outputs found
Comment on "Deuterium--tritium fusion reactors without external fusion breeding" by Eliezer et al
Inclusion of inverse Compton effects in the calculation of
deuterium-deuterium burn under the extreme conditions considered by Eliezer et
al. [Phys. Lett. A 243 (1998) 298] are shown to decrease the maximum burn
temperature from about 300 keV to only 100--150 keV. This decrease is such that
tritium breeding by the DD --> T + p reaction is not sufficient to replace the
small amount of tritium that is initially added to the deuterium plasma in
order to trigger ignition at less than 10 keV.Comment: 6 pages, 1 tabl
Terrain Sculptor: generalizing terrain models for relief shading
Shaded relief derived from high-resolution terrain models often contains distracting terrain details that need to be removed for medium- and small- scale mapping. When standard raster filter operations are applied to digital terrain data, important ridge tops and valley edges are blurred, altering the characteristic shape of these features in the resulting shaded relief. This paper introduces Terrain Sculptor, a software application that prepares generalized terrain models for relief shading. The application uses a generalization methodology based on a succession of raster operations. Curvature coefficients detect and accentuate important relief features. Terrain Sculptor offers a graphical user interface to adjust the algorithm to various scales and terrain resolutions
A Pseudospectral Optimal Motion Planner for Autonomous Unmanned Vehicles
2010 American Control Conference, Marriott Waterfront, Baltimore, MD, USA, June 30-July 02, 2010This paper presents a pseudospectral (PS) optimal
control algorithm for the autonomous motion planning of a fleet
of unmanned ground vehicles (UGVs). The UGVs must traverse
an obstacle-cluttered environment while maintaining robustness
against possible collisions. The generality of the algorithm
comes from a binary logic that modifies the cost function for
various motion planning modes. Typical scenarios including
path following and multi-vehicle pursuit are demonstrated.
The proposed framework enables the availability of real-time
information to be exploited by real-time reformulation of the
optimal control problem combined with real-time computation.
This allows the each vehicle to accommodate potential changes
in the mission/environment and uncertain conditions. Experimental
results are presented to substantiate the utility of the
approach on a typical planning scenario
Cornelius Lanczos's derivation of the usual action integral of classical electrodynamics
The usual action integral of classical electrodynamics is derived starting
from Lanczos's electrodynamics -- a pure field theory in which charged
particles are identified with singularities of the homogeneous Maxwell's
equations interpreted as a generalization of the Cauchy-Riemann regularity
conditions from complex to biquaternion functions of four complex variables. It
is shown that contrary to the usual theory based on the inhomogeneous Maxwell's
equations, in which charged particles are identified with the sources, there is
no divergence in the self-interaction so that the mass is finite, and that the
only approximation made in the derivation are the usual conditions required for
the internal consistency of classical electrodynamics. Moreover, it is found
that the radius of the boundary surface enclosing a singularity interpreted as
an electron is on the same order as that of the hypothetical "bag" confining
the quarks in a hadron, so that Lanczos's electrodynamics is engaging the
reconsideration of many fundamental concepts related to the nature of
elementary particles.Comment: 16 pages. Final version to be published in "Foundations of Physics
Inferring Implicit 3D Representations from Human Figures on Pictorial Maps
In this work, we present an automated workflow to bring human figures, one of
the most frequently appearing entities on pictorial maps, to the third
dimension. Our workflow is based on training data and neural networks for
single-view 3D reconstruction of real humans from photos. We first let a
network consisting of fully connected layers estimate the depth coordinate of
2D pose points. The gained 3D pose points are inputted together with 2D masks
of body parts into a deep implicit surface network to infer 3D signed distance
fields (SDFs). By assembling all body parts, we derive 2D depth images and body
part masks of the whole figure for different views, which are fed into a fully
convolutional network to predict UV images. These UV images and the texture for
the given perspective are inserted into a generative network to inpaint the
textures for the other views. The textures are enhanced by a cartoonization
network and facial details are resynthesized by an autoencoder. Finally, the
generated textures are assigned to the inferred body parts in a ray marcher. We
test our workflow with 12 pictorial human figures after having validated
several network configurations. The created 3D models look generally promising,
especially when considering the challenges of silhouette-based 3D recovery and
real-time rendering of the implicit SDFs. Further improvement is needed to
reduce gaps between the body parts and to add pictorial details to the
textures. Overall, the constructed figures may be used for animation and
storytelling in digital 3D maps.Comment: to be published in 'Cartography and Geographic Information Science
Design and Manufacture of a Highly Reliable, Miniaturized and Low Mass Shutter Mechanism
This paper describes the development, manufacturing and testing of a lightweight shutter mechanism made of titanium for the MERTIS Instrument. MERTIS is a thermal infrared imaging spectrometer onboard ESA's future BepiColombo mission to Mercury. The mechanism is built as a parallelogram arrangement of flexible hinges, actuated by a voice coil. In a first test run, it was shown that the selected EDM processing led to the generation of titanium oxides and an oxygen-enriched surface layer on the substrate (so called alpha-case layer). In the revised version of the shutter, it was possible to manufacture the complex geometry by micro-milling and an adjacent pickling procedure. The adequacy of this approach was verified by lifetime and vibration testing
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