1,738 research outputs found
Aerodynamic mitigation of extreme wind loading on low-rise buildings
Hurricanes and other extreme wind events cause immense devastation to our economy every year. Modern buildings should be designed to withstand extreme wind so that it reduces the financial strain on the economy. An experimental study was performed to compare aerodynamic performance of new roof designs. Traditional roof shapes were also included in this study to determine if the new designs had any merit in aerodynamic roof load mitigation. An atmospheric boundary layer wind tunnel was used with the characteristic wind of a suburban boundary terrain. The force results obtained from measurement of the roof loads showed that the largest reduction was achieved with the leading-edge spoiler, which resulted in 32.3% reduction of roof uplift. A few other methods also demonstrated adequate roof load mitigation. The aerodynamic modification of buildings provides a cost effective solution to reducing the economic impact of hurricanes and other extreme wind phenomena
Implications of National Climate Targets on the Energy-Water Nexus in Germany: A Case Study
The German energy transition is not only a challenge for the technical system transformation but will also imply changes in the water system and reallocation of resource usage. This paper analyses which interactions provide valuable information for the energy system and how future water use projection could be conducted with the help of energy system modelling. It was assumed that different national climate policy
scenarios for the energy system influence the water projections. The interactions considered for the German case study are: water demand for cooling technologies, irrigation practices of energy crops, as well as literature based assessments of total water demand and renewable water availability. Based on the energy scenario analysis, water use for the energy system will shift over time from cooling water use to irrigation water use for energy crops and the amount of irrigation water use is dependent on the demand of biomass which increases for stricter climate targets. There is a small risk of future water stress that can be eliminated through the use of recycled water for irrigation
In-medium dependence and Coulomb effects of the pion production in heavy ion collisions
The properties of the high energy pions observed in heavy ion collisions, in
particular in the system Au on Au at 1 GeV/nucleon are investigated. The
reaction dynamics is described within the Quantum Molecular Dynamics (QMD)
approach. It is shown that high energy pions freeze out early and originate
from the hot, compressed matter. --resonances are found to give an
important contribution toward the high energy tail of the pion. Further the
role of in-medium effects in the description of charged pion yields and spectra
is investigated using a microscopic potential derived from the Brueckner
G-matrix which is obtained with the Reid soft-core potential. It is seen that
the high energy part of the spectra is relatively more suppressed due to
in-medium effects as compared to the low energy part. A comparision to
experiments further demonstrates that the present calculations describe
reasonably well the neutral (TAPS) and charged (FOPI) pion spectra. The
observed energy dependence of the ratio, i.e. deviations from the
isobar model prediction, is due to Coulomb effects and again indicate that high
energy pions probe the hot and dense phase of the reaction. These findings are
confirmed independently by a simple phase space analysis.Comment: 28 pages Latex, prepared with elsevier-style, 13 PS-figure
Temperature and thermodynamic instabilities in heavy ion collisions
We investigate thermodynamic properties and instability conditions in
intermediate energy heavy ion reactions. We define locally thermodynamic
variables, i.e. density, pressure and temperature, directly from the phase
space distribution of a relativistic transport calculation. In particular,
temperatures are determined by a fit to two covariant hot Fermi distributions
thus taking into account possible anisotropic momentum configurations. We
define instability independent from the nuclear matter spinodal by the
criterion that the effective compressibility becomes negative. The method is
applied to a semi-central Au on Au reaction at 600 MeV/nucleon. We investigate
in particular the center of the participant and the spectator matter. In the
latter we find a clear indication of instability with conditions of density and
temperature that are consistent with experimental determinations.Comment: 20 pages latex, 5 PS-figures, revised version (minor changes)
accepted for publication in Nucl. Phys.
Heavy ion collisions with non-equilibrium Dirac-Brueckner mean fields
The influence of realistic interactions on the reaction dynamics in
intermediate energy heavy ion collisions is investigated. The mean field in
relativistic transport calculations is derived from microscopic Dirac-Brueckner
(DB) self-energies, taking non-equilibrium effects, in particular the
anisotropy of the local phase space configurations, into account. Thus this
approach goes beyond the local density approximation. A detailed analysis of
various in-plane and out-of-plane flow observables is presented for Au on Au
reactions at incident energies ranging from 250 to 800 A.MeV and the results
are compared to recent measurements of the FOPI collaboration. An overall good
agreement with in-plane flow data and a reasonable description of the
out-of-plane emission is achieved. For these results the intrinsic momentum
dependence of the non-equilibrium mean fields is important. On the other hand,
the local density approximation with the same underlying DB forces as well as a
standard non-linear version of the model are less successful in
describing the present data. This gives evidence of the applicability of self
energies derived from the DB approach to nuclear matter also far from
saturation and equilibrium.Comment: 63 pages Latex, using Elsevier style, 20 ps-figures, to appear in
Nucl. Phys.
Covariant representations of the relativistic Brueckner T-matrix and the nuclear matter problem
We investigate nuclear matter properties in the relativistic Brueckner
approach. The in-medium on-shell T-matrix is represented covariantly by five
Lorentz invariant amplitudes from which we deduce directly the nucleon
self-energy. We discuss the ambiguities of this approach and the failure of
previously used covariant representations in reproducing the nucleon
self-energies on the Hartree-Fock level. To enforce correct Hartree-Fock
results we develop a subtraction scheme which treats the bare nucleon-nucleon
potential exactly in accordance to the different types of meson exchanges. For
the remaining ladder kernel, which contains the higher order correlations, we
employ then two different covariant representations in order to study the
uncertainty inherent in the approach. The nuclear matter bulk properties are
only slightly sensitive on the explicit representation used for the kernel.
However, we obtain new Coester lines for the various Bonn potentials which are
shifted towards the empirical region of saturation. In addition the nuclear
equation-of-state turns out to be significantly softer in the new approach.Comment: 39 pages Latex using Elsevier style, 16 PS figure
Change of Scenery: Unsupervised LiDAR Change Detection for Mobile Robots
This paper presents a fully unsupervised deep change detection approach for
mobile robots with 3D LiDAR. In unstructured environments, it is infeasible to
define a closed set of semantic classes. Instead, semantic segmentation is
reformulated as binary change detection. We develop a neural network,
RangeNetCD, that uses an existing point-cloud map and a live LiDAR scan to
detect scene changes with respect to the map. Using a novel loss function,
existing point-cloud semantic segmentation networks can be trained to perform
change detection without any labels or assumptions about local semantics. We
demonstrate the performance of this approach on data from challenging terrains;
mean intersection over union (mIoU) scores range between 67.4% and 82.2%
depending on the amount of environmental structure. This outperforms the
geometric baseline used in all experiments. The neural network runs faster than
10Hz and is integrated into a robot's autonomy stack to allow safe navigation
around obstacles that intersect the planned path. In addition, a novel method
for the rapid automated acquisition of per-point ground-truth labels is
described. Covering changed parts of the scene with retroreflective materials
and applying a threshold filter to the intensity channel of the LiDAR allows
for quantitative evaluation of the change detector.Comment: 7 pages (6 content, 1 references). 7 figures, submitted to the 2024
IEEE International Conference on Robotics and Automation (ICRA
Off the Beaten Track: Laterally Weighted Motion Planning for Local Obstacle Avoidance
We extend the behaviour of generic sample-based motion planners to support
obstacle avoidance during long-range path following by introducing a new
edge-cost metric paired with a curvilinear planning space. The resulting
planner generates naturally smooth paths that avoid local obstacles while
minimizing lateral path deviation to best exploit prior terrain knowledge from
the reference path. In this adaptation, we explore the nuances of planning in
the curvilinear configuration space and describe a mechanism for natural
singularity handling to improve generality. We then shift our focus to the
trajectory generation problem, proposing a novel Model Predictive Control (MPC)
architecture to best exploit our path planner for improved obstacle avoidance.
Through rigorous field robotics trials over 5 km, we compare our approach to
the more common direct path-tracking MPC method and discuss the promise of
these techniques for reliable long-term autonomous operations.Comment: 15 pages, 21 Figures, 3 Tables. Manuscript was submitted to IEEE
Transactions on Robotics on September 17th, 202
- âŠ