11,827 research outputs found
3D simulations of self-propelled, reconstructed jellyfish using vortex methods
We present simulations of the vortex dynamics associated with the
self-propelled motion of jellyfish. The geometry is obtained from image
segmentation of video recordings from live jellyfish. The numerical simulations
are performed using three-dimensional viscous, vortex particle methods with
Brinkman penalization to impose the kinematics of the jellyfish motion. We
study two types of strokes recorded in the experiment1. The first type (stroke
A) produces two vortex rings during the stroke: one outside the bell during the
power stroke and one inside the bell during the recovery stroke. The second
type (stroke B) produces three vortex rings: one ring during the power stroke
and two vortex rings during the recovery stroke. Both strokes propel the
jellyfish, with stroke B producing the highest velocity. The speed of the
jellyfish scales with the square root of the Reynolds number. The simulations
are visualized in a fluid dynamics video.Comment: 1 page, 1 figur
Real-Time Predictive Modeling and Robust Avoidance of Pedestrians with Uncertain, Changing Intentions
To plan safe trajectories in urban environments, autonomous vehicles must be
able to quickly assess the future intentions of dynamic agents. Pedestrians are
particularly challenging to model, as their motion patterns are often uncertain
and/or unknown a priori. This paper presents a novel changepoint detection and
clustering algorithm that, when coupled with offline unsupervised learning of a
Gaussian process mixture model (DPGP), enables quick detection of changes in
intent and online learning of motion patterns not seen in prior training data.
The resulting long-term movement predictions demonstrate improved accuracy
relative to offline learning alone, in terms of both intent and trajectory
prediction. By embedding these predictions within a chance-constrained motion
planner, trajectories which are probabilistically safe to pedestrian motions
can be identified in real-time. Hardware experiments demonstrate that this
approach can accurately predict pedestrian motion patterns from onboard
sensor/perception data and facilitate robust navigation within a dynamic
environment.Comment: Submitted to 2014 International Workshop on the Algorithmic
Foundations of Robotic
Parameters influencing potency of Bacillus thuringiensis var. israelensis products
Bioassays of products based on #Bacillus thuringiensis var. #israelensis have been carried out according to standard protocols. Theses analyses revealed that the slopes of the log-probit transformed concentration mortality curves of various products were different from that of the international standards (IPS82 for #Bacillus thuringiensis israelensis). For statistical reasons, this invalidates the tests. Products giving various slopes of the concentration mortality curves will obtain different potencies when estimated at a LC90 level than when estimated at LC50 level, as normally done. The LC90 level is probably pore relevant for the field effect. Changing the median particle size of a product in a non destructive way results in change of slope and LC50 and thereby potency. Therefore, potency of a product as measured in these bioassays is not just a measure of the quantity of #B. thuringiensis israelensis crystal protein present, but a function of product parameters like median particle size. Biochemical methods for quantification of toxin can therefore not relate simply to potency of the products obtained with this method. It is suggested that standard protocols for bioassay may be changed to assure equal particle size of products and samples to obtain parallel close response. (Résumé d'auteur
Three-Dimensional Elastic Compatibility: Twinning in Martensites
We show how the St.Venant compatibility relations for strain in three
dimensions lead to twinning for the cubic to tetragonal transition in
martensitic materials within a Ginzburg-Landau model in terms of the six
components of the symmetric strain tensor. The compatibility constraints
generate an anisotropic long-range interaction in the order parameter
(deviatoric strain) components. In contrast to two dimensions, the free energy
is characterized by a "landscape" of competing metastable states. We find a
variety of textures, which result from the elastic frustration due to the
effects of compatibility. Our results are also applicable to structural phase
transitions in improper ferroelastics such as ferroelectrics and
magnetoelastics, where strain acts as a secondary order parameter
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Unsaturated Flow and Transport Through Fractured Rock Related to High-Level Waste Repositories; Final Report, Phase 3
Research results are summarized for a US Nuclear Regulatory Commission contract with the University of Arizona focusing on field and laboratory methods for characterizing unsaturated fluid flow and solute transport related to high-level radioactive waste repositories. Characterization activities are presented for the Apache Leap Tuff field site. The field site is located in unsaturated, fractured tuff in central Arizona. Hydraulic, pneumatic, and thermal characteristics of the tuff are summarized, along with methodologies employed to monitor and sample hydrologic and geochemical processes at the field site. Thermohydrologic experiments are reported which provide laboratory and field data related to the effects conditions and flow and transport in unsaturated, fractured rock. 29 refs., 17 figs., 21 tabs
Studying the WHIM Content of the Galaxy Large-Scale Structures along the Line of Sight to H 2356-309
We make use of a 500ks Chandra HRC-S/LETG spectrum of the blazar H2356-309,
combined with a lower S/N spectrum of the same target, to search for the
presence of warm-hot absorbing gas associated with two Large-Scale Structures
(LSSs) crossed by this sightline at z=0.062 (the Pisces-Cetus Supercluster,
PCS) and at z=0.128 ("Farther Sculptor Wall", FSW). No statistically
significant (>=3sigma) individual absorption is detected from any of the strong
He- or H-like transitions of C, O and Ne at the redshifts of the structures.
However we are still able to constrain the physical and geometrical parameters
of the associated putative absorbing gas, by performing joint spectral fit of
marginal detections and upper limits of the strongest expected lines with our
self-consistent hybrid ionization WHIM spectral model. At the redshift of the
PCS we identify a warm phase with logT=5.35_-0.13^+0.07 K and log N_H
=19.1+/-0.2 cm^-2 possibly coexisting with a hotter and less significant phase
with logT=6.9^+0.1_-0.8 K and log N_H=20.1^+0.3_-1.7 cm^-2 (1sigma errors). For
the FSW we estimate logT=6.6_-0.2^+0.1 K and log N_H=19.8_-0.8^+0.4 cm^-2. Our
constraints allow us to estimate the cumulative number density per unit
redshifts of OVII WHIM absorbers. We also estimate the cosmological mass
density obtaining Omega_b(WHIM)=(0.021^+0.031_-0.018) (Z/Z_sun)^-1, consistent
with the mass density of the intergalactic 'missing baryons' for high
metallicities.Comment: 29 pages, 8 figures, 4 tables. Accepted for publication in Ap
Digestibility in selected rainbow trout families and modelling of growth from the specific intake of digestible protein
The experiments aimed to clarify variations in digestibility of dietary nutrients in rainbow trout. Furthermore, the objective was to study how differences in digestibility might be related to growth and feed utilisation at various growth rates. When comparing the results from the experiments it appeared that particularly protein digestibility was closely related to specific growth rate and feed conversion ratio at high growth rates. As a tool to visualise the relationship between protein digestibility and growth of rainbow trout a growth model was developed based on the specific intake of digestible protein, and general assumptions on protein content and protein retention efficiency in rainbow trout. The model indicated that increased protein digestibility only partly explained growth increase and that additional factors were important for growth increment
On the CFT duals for near-extremal black holes
We consider Kerr-Newman-AdS-dS black holes near extremality and work out the
near-horizon geometry of these near-extremal black holes. We identify the exact
U(1)_L x U(1)_R isometries of the near-horizon geometry and provide boundary
conditions enhancing them to a pair of commuting Virasoro algebras. The
conserved charges of the corresponding asymptotic symmetries are found to be
well defined and non-vanishing and to yield central charges c_L\neq0 and c_R=0.
The Cardy formula subsequently reproduces the Bekenstein-Hawking entropy of the
black hole. This suggests that the near-extremal Kerr-Newman-AdS-dS black hole
is holographically dual to a non-chiral two-dimensional conformal field theory.Comment: 11 page
A comparison of statistical emulation methodologies for multi-wave calibration of environmental models
Expensive computer codes, particularly those used simulating environmental or geological processes such as climate models, require calibration (sometimes called tuning). When calibrating expensive simulators using uncertainty quantification methods, it is usually necessary to use a statistical model called an emulator in place of the computer code when running the calibration algorithm. Though emulators based on Gaussian processes are typically many orders of magnitude faster to evaluate than the simulator they mimic, many applications have sought to speed up the computations by using regression-only emulators within the calculations instead, arguing that the extra sophistication brought using the Gaussian process is not worth the extra computational power. This was the case for the analysis that produced the UK climate projections in 2009. In this paper we compare the effectiveness of both emulation approaches upon a multi-wave calibration framework that is becoming popular in the climate modelling community called \history matching". We find that Gaussian processes offer significant benefits to the reduction of parametric uncertainty over regression-only approaches. We find that in a multi-wave experiment, a combination of regression-only emulators initially, followed by Gaussian process emulators for refocussing experiments can be nearly as effective as using Gaussian processes throughout for a fraction of the computational cost. We also discover a number of design and emulator-dependent features of the multi-wave history matching approach that can cause apparent, yet premature, convergence of our estimates of parametric uncertainty. We compare these approaches to calibration in idealised examples and apply it to a well-known geological reservoir mode
A near-NHEK/CFT correspondence
We consider excitations around the recently introduced near-NHEK metric
describing the near-horizon geometry of the near-extremal four-dimensional Kerr
black hole. This geometry has a U(1)_L x U(1)_R isometry group which can be
enhanced to a pair of commuting Virasoro algebras. We present boundary
conditions for which the conserved charges of the corresponding asymptotic
symmetries are well defined and non-vanishing and find the central charges
c_L=12J/hbar and c_R=0 where J is the angular momentum of the black hole.
Applying the Cardy formula reproduces the Bekenstein-Hawking entropy of the
black hole. This suggests that the near-extremal Kerr black hole is
holographically dual to a non-chiral two-dimensional conformal field theory.Comment: 11 pages, v2: references updated, adde
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