1,858 research outputs found
When the path is never shortest: a reality check on shortest path biocomputation
Shortest path problems are a touchstone for evaluating the computing
performance and functional range of novel computing substrates. Much has been
published in recent years regarding the use of biocomputers to solve minimal
path problems such as route optimisation and labyrinth navigation, but their
outputs are typically difficult to reproduce and somewhat abstract in nature,
suggesting that both experimental design and analysis in the field require
standardising. This chapter details laboratory experimental data which probe
the path finding process in two single-celled protistic model organisms,
Physarum polycephalum and Paramecium caudatum, comprising a shortest path
problem and labyrinth navigation, respectively. The results presented
illustrate several of the key difficulties that are encountered in categorising
biological behaviours in the language of computing, including biological
variability, non-halting operations and adverse reactions to experimental
stimuli. It is concluded that neither organism examined are able to efficiently
or reproducibly solve shortest path problems in the specific experimental
conditions that were tested. Data presented are contextualised with biological
theory and design principles for maximising the usefulness of experimental
biocomputer prototypes.Comment: To appear in: Adamatzky, A (Ed.) Shortest path solvers. From software
to wetware. Springer, 201
Results from a set of three-dimensional numerical experiments of a hot Jupiter atmosphere
We present highlights from a large set of simulations of a hot Jupiter
atmosphere, nominally based on HD 209458b, aimed at exploring both the
evolution of the deep atmosphere, and the acceleration of the zonal flow or
jet. We find the occurrence of a super-rotating equatorial jet is robust to
changes in various parameters, and over long timescales, even in the absence of
strong inner or bottom boundary drag. This jet is diminished in one simulation
only, where we strongly force the deep atmosphere equator-to-pole temperature
gradient over long timescales. Finally, although the eddy momentum fluxes in
our atmosphere show similarities with the proposed mechanism for accelerating
jets on tidally-locked planets, the picture appears more complex. We present
tentative evidence for a jet driven by a combination of eddy momentum transport
and mean flow.Comment: 26 pages, 22 Figures. Accepted for publication in Astronomy and
Astrophysic
The Impact of Phase Equilibrium Cloud Models on GCM Simulations of GJ~1214b
We investigate the impact of clouds on the atmosphere of GJ~1214b using the
radiatively-coupled, phase-equilibrium cloud model {\sc EddySed} coupled to the
{\sc Unified Model} general circulation model. We find that, consistent with
previous investigations, high metallicity ( solar) and clouds with
large vertical extents (a sedimentation factor of ) are
required to best match the observations, although metallicities even higher
than those investigated here may be required to improve agreement further. We
additionally find that in our case which best matches the observations
(), the velocity structures change relative to the clear
sky case with the formation of a superrotating jet being suppressed, although
further investigation is required to understand the cause of the suppression.
The increase in cloud extent with results in a cooler planet
due to a higher albedo, causing the atmosphere to contract. This also results
in a reduced day-night contrast seen in the phase curves, although the
introduction of cloud still results in a reduction of the phase offset. We
additionally investigate the impact the the {\sc Unified Model}'s
pseudo-spherical irradiation scheme on the calculation of heating rates,
finding that the introduction of nightside shortwave heating results in slower
mid-latitude jets compared to the plane parallel irradiation scheme used in
previous works. We also consider the impact of a gamma distribution, as opposed
to a log-normal distribution, for the distribution of cloud particle radii and
find the impact to be relatively minor.Comment: Accepted to MNRA
The Limits of the Primitive Equations of Dynamics for Warm, Slowly Rotating Small Neptunes and Super Earths (article)
This is the author accepted manuscript. The final version is available from American Astronomical Society / IOP Publishing via the DOI in this record.The dataset associated with this article is located in ORE at: https://doi.org/10.24378/exe.1023We present significant differences in the simulated atmospheric flow for warm, tidally-locked small
Neptunes and super Earths (based on a nominal GJ 1214b) when solving the simplified, and commonly
used, primitive dynamical equations or the full Navier-Stokes equations. The dominant prograde,
superrotating zonal jet is markedly different between the simulations which are performed using practically identical numerical setups, within the same model. The differences arise due to the breakdown of the so-called `shallow-fluid' and traditional approximations, which worsens when rotation rates are slowed, and day{night temperature contrasts are increased. The changes in the zonal advection between simulations solving the full and simplified equations, give rise to significant differences in the atmospheric redistribution of heat, altering the position of the hottest part of the atmosphere and temperature contrast between the day and night sides. The implications for the atmospheric chemistry and, therefore, observations need to be studied with a model including a more detailed treatment of
the radiative transfer and chemistry. Small Neptunes and super Earths are extremely abundant and
important, potentially bridging the structural properties (mass, radius, composition) of terrestrial and
gas giant planets. Our results indicate care is required when interpreting the output of models solving
the primitive equations of motion for such planets.Leverhulme TrustScience and Technology Facilities CouncilEuropean Research Counci
Overcast on Osiris: 3D radiative-hydrodynamical simulations of a cloudy hot Jupiter using the parametrized, phase-equilibrium cloud formation code EDDYSED (article)
This is the final version. Available from OUP via the DOI in this recordThe dataset associated with this article is available in ORE: https://doi.org/10.24378/exe.1483We present results from 3D radiative-hydrodynamical simulations of HD 209458b with a fully coupled treatment of clouds using the EDDYSED code, critically, including cloud radiative feedback via absorption and scattering. We demonstrate that the thermal and optical structure of the simulated atmosphere is markedly different, for the majority of our simulations, when including cloud radiative effects, suggesting this important mechanism cannot be neglected. Additionally, we further demonstrate that the cloud structure is sensitive to not only the cloud sedimentation efficiency (termed fsed in EDDYSED), but also the temperature–pressure profile of the deeper atmosphere. We briefly discuss the large difference between the resolved cloud structures of this work, adopting a phase-equilibrium and parametrized cloud model, and our previous work incorporating a cloud microphysical model, although a fairer comparison where, for example, the same list of constituent condensates is included in both treatments is reserved for a future work. Our results underline the importance of further study into the potential condensate size distributions and vertical structures, as both strongly influence the radiative impact of clouds on the atmosphere. Finally, we present synthetic observations from our simulations reporting an improved match, over our previous cloud-free simulations, to the observed transmission, HST WFC3 emission, and 4.5 μm Spitzer phase curve of HD 209458b. Additionally, we find all our cloudy simulations have an apparent albedo consistent with observations.Leverhulme TrustScience and Technology Facilities Council (STFC
Effect of anisotropy and destructuration on behavior of Haarajoki test embankment
This paper investigates the influence of anisotropy and destructuration on the behavior of Haarajoki test embankment, which was built by the Finnish National Road Administration as a noise barrier in 1997 on a soft clay deposit. Half of the embankment is constructed on an area improved with prefabricated vertical drains, while the other half is constructed on the natural deposit without any ground improvement. The construction and consolidation of the embankment is analyzed with the finite-element method using three different constitutive models to represent the soft clay. Two recently proposed constitutive models, namely S-CLAY1 which accounts for initial and plastic strain induced anisotropy, and its extension, called S-CLAY1S which accounts, additionally, for interparticle bonding and degradation of bonds, were used in the analysis. For comparison, the problem is also analyzed with the isotropic modified cam clay model. The results of the numerical analyses are compared with the field measurements. The simulations reveal the influence that anisotropy and destructuration have on the behavior of an embankment on soft clay
Sex and gender differences in the management of chronic kidney disease and hypertension
No abstract available
Performance of Sensitivity based NMPC Updates in Automotive Applications
In this work we consider a half car model which is subject to unknown but
measurable disturbances. To control this system, we impose a combination of
model predictive control without stabilizing terminal constraints or cost to
generate a nominal solution and sensitivity updates to handle the disturbances.
For this approach, stability of the resulting closed loop can be guaranteed
using a relaxed Lyapunov argument on the nominal system and Lipschitz
conditions on the open loop change of the optimal value function and the stage
costs. For the considered example, the proposed approach is realtime applicable
and corresponding results show significant performance improvements of the
updated solution with respect to comfort and handling properties.Comment: 6 pages, 2 figure
Nonparametric nonlinear model predictive control
Model Predictive Control (MPC) has recently found wide acceptance in industrial applications, but its potential has been much impeded by linear models due to the lack of a similarly accepted nonlinear modeling or databased technique. Aimed at solving this problem, the paper addresses three issues: (i) extending second-order Volterra nonlinear MPC (NMPC) to higher-order for improved prediction and control; (ii) formulating NMPC directly with plant data without needing for parametric modeling, which has hindered the progress of NMPC; and (iii) incorporating an error estimator directly in the formulation and hence eliminating the need for a nonlinear state observer. Following analysis of NMPC objectives and existing solutions, nonparametric NMPC is derived in discrete-time using multidimensional convolution between plant data and Volterra kernel measurements. This approach is validated against the benchmark van de Vusse nonlinear process control problem and is applied to an industrial polymerization process by using Volterra kernels of up to the third order. Results show that the nonparametric approach is very efficient and effective and considerably outperforms existing methods, while retaining the original data-based spirit and characteristics of linear MPC
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