10,777 research outputs found
Adaptive driver modelling in ADAS to improve user acceptance: A study using naturalistic data
Accurate understanding of driver behaviour is crucial for future Advanced Driver Assistance Systems (ADAS) and autonomous driving. For user acceptance it is important that ADAS respect individual driving styles and adapt accordingly. Using data collected during a naturalistic driving study carried out at the University of Southampton, we assess existing models of driver acceleration and speed choice during car following and when cornering. We observe that existing models of driver behaviour that specify a preferred inter-vehicle spacing in car-following situations appear to be too prescriptive, with a wide range of acceptable spacings visible in the naturalistic data. Bounds on lateral acceleration during cornering from the literature are visible in the data, but appear to be influenced by the minimum cornering radii specified in design codes for UK roadway geometry. This analysis of existing driver models is used to suggest a small set of parameters that are sufficient to characterise driver behaviour in car-following and curve driving, which may be estimated in real-time by an ADAS to adapt to changing driver behaviour. Finally, we discuss applications to adaptive ADAS with the objectives of improving road safety and promoting eco-driving, and suggest directions for future researc
Coupled systems of fractional equations related to sound propagation: analysis and discussion
In this note we analyse the propagation of a small density perturbation in a
one-dimensional compressible fluid by means of fractional calculus modelling,
replacing thus the ordinary time derivative with the Caputo fractional
derivative in the constitutive equations. By doing so, we embrace a vast
phenomenology, including subdiffusive, superdiffusive and also memoryless
processes like classical diffusions. From a mathematical point of view, we
study systems of coupled fractional equations, leading to fractional diffusion
equations or to equations with sequential fractional derivatives. In this
framework we also propose a method to solve partial differential equations with
sequential fractional derivatives by analysing the corresponding coupled system
of equations
Electromagnetic field fluctuations near a dielectric-vacuum boundary and surface divergences in the ideal conductor limit
We consider the electric and magnetic field fluctuations in the vacuum state
in the region external to a half-space filled with a homogeneous
non-dissipative dielectric. We discuss an appropriate limit to an ideal metal
and concentrate our interest on the renormalized field fluctuations, or
equivalently to renormalized electric and magnetic energy densities, in the
proximity of the dielectric-vacuum interface. We show that surface divergences
of field fluctuations arise at the interface in an appropriate ideal conductor
limit, and that our limiting procedure allows to discuss in detail their
structure. Field fluctuations close to the surface can be investigated through
the retarded Casimir-Polder interaction with an appropriate polarizable body.Comment: 6 pages, 2 figure
A new near-IR window of low extinction in the Galactic plane
Reproduced with permission from Astronomy & Astrophysics. © 2018 ESO. Comments: 6 pages, 6 figures. Accepted for publication in Astronomy & AstrophysicsAims. The windows of low extinction in the Milky Way (MW) plane are rare but important because they enable us to place structural constraints on the opposite side of the Galaxy, which has hither to been done rarely. Methods. We use the near-infrared (near-IR) images of the VISTA Variables in the Vía Láctea (VVV) Survey to build extinction maps and to identify low extinction windows towards the Southern Galactic plane. Here we report the discovery of VVV WIN 1713-3939, a very interesting window with relatively uniform and low extinction conveniently placed very close to the Galactic plane. Results. The new window of roughly 30 arcmin diameter is located at Galactic coordinates (l, b) = (347.4, -0.4) deg. We analyse the VVV near-IR colour-magnitude diagrams in this window. The mean total near-IR extinction and reddening values measured for this window are A Ks = 0.46 and E(J - K s) = 0.95. The red clump giants within the window show a bimodal magnitude distribution in the K s band, with peaks at K s = 14.1 and 14.8 mag, corresponding to mean distances of D = 11.0 ± 2.4 and 14.8 ± 3.6 kpc, respectively. We discuss the origin of these red clump overdensities within the context of the MW disk structure.Peer reviewe
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Covalent targeting of the vacuolar H+-ATPase activates autophagy via mTORC1 inhibition.
Autophagy is a lysosomal degradation pathway that eliminates aggregated proteins and damaged organelles to maintain cellular homeostasis. A major route for activating autophagy involves inhibition of the mTORC1 kinase, but current mTORC1-targeting compounds do not allow complete and selective mTORC1 blockade. Here, we have coupled screening of a covalent ligand library with activity-based protein profiling to discover EN6, a small-molecule in vivo activator of autophagy that covalently targets cysteine 277 in the ATP6V1A subunit of the lysosomal v-ATPase, which activates mTORC1 via the Rag guanosine triphosphatases. EN6-mediated ATP6V1A modification decouples the v-ATPase from the Rags, leading to inhibition of mTORC1 signaling, increased lysosomal acidification and activation of autophagy. Consistently, EN6 clears TDP-43 aggregates, a causative agent in frontotemporal dementia, in a lysosome-dependent manner. Our results provide insight into how the v-ATPase regulates mTORC1, and reveal a unique approach for enhancing cellular clearance based on covalent inhibition of lysosomal mTORC1 signaling
Optimizing 3d printed metallic object’s postprocessing : a case of gamma‐tial alloys
Gamma‐TiAl (γ‐TiAl) alloys can be used in high‐end products relevant to the aerospace, defense, biomedical, and marine industries. Fabricating objects made of γ‐TiAl alloys needs an additive manufacturing process called Electron Beam Melting (EBM) or other similar processes because these alloys are difficult‐to‐cut materials. An object fabricated by EBM exhibits poor surface finish and must undergo postprocessing. In this study, cylindrical specimens were fabricated by EBM and post‐processed by turning at different cutting conditions (cutting speed, depth of cut, feed rate, insert radius, and coolant flowrate). The EBM conditions were as follows: average powder size 110 μm, acceleration voltage 60 kV, beam current 10 mA, beam scanning speed 2200 mm/s, and beam focus offset 0.20 mm. The surface roughness and cutting force were recorded for each set of cutting conditions. The values of the cutting conditions were set by the L36 Design of Experiment approach. The effects of the cutting conditions on surface roughness and cutting force are elucidated by constructing the possibility distributions (triangular fuzzy numbers) from the experimental data. Finally, the optimal cutting conditions to improve the surface finish of specimens made of γ‐TiAl alloys are determined using the possibility distributions. Thus, this study’s outcomes can be used to develop intelligent systems for optimizing additive manufacturing processes. © 2021 by the authors. Licensee MDPI, Basel, Switzerland
Heat transfer mechanisms in bubbly Rayleigh-Benard convection
The heat transfer mechanism in Rayleigh-Benard convection in a liquid with a
mean temperature close to its boiling point is studied through numerical
simulations with point-like vapor bubbles, which are allowed to grow or shrink
through evaporation and condensation and which act back on the flow both
thermally and mechanically. It is shown that the effect of the bubbles is
strongly dependent on the ratio of the sensible heat to the latent heat as
embodied in the Jacob number Ja. For very small Ja the bubbles stabilize the
flow by absorbing heat in the warmer regions and releasing it in the colder
regions. With an increase in Ja, the added buoyancy due to the bubble growth
destabilizes the flow with respect to single-phase convection and considerably
increases the Nusselt number.Comment: 11 pages, 14 figure
Exact Solution of the one-impurity quantum Hall problem
The problem of a non-relativistic electron in the presence of a uniform
electromagnetic field and of one impurity, described by means of an
Aharonov-Bohm point-like vortex, is studied. The exact solution is found and
the quantum Hall's conductance turns out to be the same as in the impurity-free
case. This exactly solvable model seems to give indications, concerning the
possible microscopic mechanisms underlying the integer quantum Hall effect,
which sensibly deviate from some proposals available in the literature.Comment: 25 pages, TeX, to appear in J. Phys.
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