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Kant, Kamal y Steven W. Zucker. "Toward Efficient Trajectory Planning: The Path-Velocity Decomposition". International Journal of Robotics Research 5, n.º 3 (septiembre de 1986): 72–89. http://dx.doi.org/10.1177/027836498600500304.
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Pham, Quang-Cuong, Stéphane Caron, Puttichai Lertkultanon y Yoshihiko Nakamura. "Admissible velocity propagation: Beyond quasi-static path planning for high-dimensional robots". International Journal of Robotics Research 36, n.º 1 (2 de noviembre de 2016): 44–67. http://dx.doi.org/10.1177/0278364916675419.
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Path-velocity decomposition is an intuitive yet powerful approach to addressing the complexity of kinodynamic motion planning. The difficult trajectory planning problem is solved in two separate, simpler steps: first, a path is found in the configuration space that satisfies the geometric constraints (path planning), and second, a time-parameterization of that path satisfying the kinodynamic constraints is found. A fundamental requirement is that the path found in the first step must be time-parameterizable. Most existing works fulfill this requirement by enforcing quasi-static constraints during the path planning step, resulting in an important loss in completeness. We propose a method that enables path-velocity decomposition to discover truly dynamic motions, i.e. motions that are not quasi-statically executable. At the heart of the proposed method is a new algorithm – Admissible Velocity Propagation – which, given a path and an interval of reachable velocities at the beginning of that path, computes exactly and efficiently the interval of all the velocities the system can reach after traversing the path, while respecting the system’s kinodynamic constraints. Combining this algorithm with usual sampling-based planners then gives rise to a family of new trajectory planners that can appropriately handle kinodynamic constraints while retaining the advantages associated with path-velocity decomposition. We demonstrate the efficiency of the proposed method on some difficult kinodynamic planning problems, where, in particular, quasi-static methods are guaranteed to fail.
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Jain, Vasundhara, Uli Kolbe, Gabi Breuel y Christoph Stiller. "Collision Avoidance for Multiple Static Obstacles using Path-Velocity Decomposition". IFAC-PapersOnLine 52, n.º 8 (2019): 265–70. http://dx.doi.org/10.1016/j.ifacol.2019.08.081.
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Wang, Dier y Jun Zhang. "Two improved scanning path planning algorithms and a 3D printing control system with circular motion controller". Rapid Prototyping Journal 28, n.º 4 (28 de diciembre de 2021): 695–703. http://dx.doi.org/10.1108/rpj-08-2020-0190.
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Purpose This paper aims to improve the infilling efficiency and the quality of parts forming. It proposes two improved scanning path planning algorithm based on velocity orthogonal decomposition. Design/methodology/approach The algorithms this paper proposes replace empty paths and corners with circular segments, driving each axis synchronously according to the SIN or COS velocity curve to make the extruder always moves at a constant speed at maximum during the infilling process. Also, to support the improved algorithms, a three-dimensional (3D) printing control system based on circular motion controller is also designed. Findings The simulation and experiment results show that the improved algorithms are effective, and the printing time is shortened more significantly, especially in the case of small or complex models. What’s more, the optimized algorithm is not only compact in shape but also not obvious in edge warping. Research limitations/implications The algorithms in this paper are not applicable to traditional motion controllers. Practical implications The algorithms in this paper improve the infilling efficiency and the quality of parts forming. Social implications There are no social implications in this paper. Originality/value The specific optimization method of parallel-line scanning algorithm based on velocity orthogonal decomposition is replacing the empty paths with arc corners. And the specific optimization method of contour offsetting algorithm based on velocity orthogonal decomposition is to add connection paths between adjacent contours and turn all straight corners into arcs. What’s more, the 3D printing control system based on the circular motion controller can achieve multi-axis parallel motion to support these two improved path scanning algorithms.
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Thyri, Emil H., Morten Breivik y Anastasios M. Lekkas. "A Path-Velocity Decomposition Approach to Collision Avoidance for Autonomous Passenger Ferries in Confined Waters". IFAC-PapersOnLine 53, n.º 2 (2020): 14628–35. http://dx.doi.org/10.1016/j.ifacol.2020.12.1472.
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Chen, Yixiao, Xinzhi Zhou, Jialiang Zhu, Chenlong Dong, Tao Xu y Hailin Wang. "Measured Regional Division Optimization for Acoustic Tomography Velocity Field Reconstruction in a Circular Area". Sensors 24, n.º 6 (21 de marzo de 2024): 2008. http://dx.doi.org/10.3390/s24062008.
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The acoustic tomography (AT) velocity field reconstruction technique has become a research hotspot in recent years due to its noninvasive nature, high accuracy, and real-time measurement advantages. However, most of the existing studies are limited to the reconstruction of the velocity field in a rectangular area, and there are very few studies on a circular area, mainly because the layout of acoustic transducers, selection of acoustic paths, and division of measured regions are more difficult in a circular area than in a rectangular area. Therefore, based on AT and using the reconstruction algorithm of the Markov function and singular value decomposition (MK-SVD), this paper proposes a measured regional division optimization algorithm for velocity field reconstruction in a circular area. First, an acoustic path distribution based on the multipath effect is designed to solve the problem of the limited emission angle of the acoustic transducer. On this basis, this paper proposes an adaptive optimization algorithm for measurement area division based on multiple sub-objectives. The steps are as follows: first, two optimization objectives, the condition number of coefficient matrix and the uniformity of acoustic path distribution, were designed. Then, the weights of each sub-objective are calculated using the coefficient of variation (CV). Finally, the measured regional division is optimized based on particle swarm optimization (PSO). The reconstruction effect of the algorithm and the anti-interference ability are verified through the reconstruction experiments of the model velocity field and the simulated velocity field.
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Liu, Ke, Guanzheng Wen, Yao Fu y Honglin Wang. "A Hierarchical Lane-Changing Trajectory Planning Method Based on the Least Action Principle". Actuators 13, n.º 1 (26 de diciembre de 2023): 10. http://dx.doi.org/10.3390/act13010010.
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This paper presents a hierarchical lane-changing trajectory planner based on the least action principle for autonomous driving. Our approach aims to achieve reliable real-time avoidance of static and moving obstacles in multi-vehicle interaction scenarios on structured urban roads. Unlike previous studies that rely on subjective weight allocation and single weighting methods, we propose a novel trajectory planning strategy that decomposes the process into two stages: candidate trajectory generation and optimal trajectory decision-making. The candidate trajectory generation employs a path-velocity decomposition method, using B-spline curves to generate a multi-objective optimal lane-changing candidate path. Collision checking eliminates paths at risk of collision with static obstacles. Dynamic programming (DP) and quadratic programming (QP) are then used to plan the velocity of safe paths, generating candidate lane-changing trajectories based on curvature checking. The optimal trajectory decision-making process follows the decision mechanism of excellent drivers. We introduce a comprehensive evaluation function, the average action, which considers safety, comfort, and efficiency based on the least action principle. Feasible trajectories are ranked based on their average action, and the trajectory with the minimum average action and no collision risk with moving obstacles is selected as the tracking target. The effectiveness of the proposed method is validated through two common lane-changing scenarios. The results demonstrate that our approach enables smooth, efficient, and safe lane-changing while effectively tracking the planned velocity and path. This method offers a solution to local trajectory planning problems in complex environments and holds promising prospects in the field of autonomous driving.
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Wu, Jianwei, Deer Bin, Xiaobing Feng, Zhongpu Wen y Yin Zhang. "GA Based Adaptive Singularity-Robust Path Planning of Space Robot for On-Orbit Detection". Complexity 2018 (28 de mayo de 2018): 1–11. http://dx.doi.org/10.1155/2018/3702916.
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As a new on-orbit detection platform, the space robot could ensure stable and reliable operation of spacecraft in complex space environments. The tracking accuracy of the space manipulator end-effector is crucial to the detection precision. In this paper, the Cartesian path planning method of velocity level inverse kinematics based on generalized Jacobian matrix (GJM) is proposed. The GJM will come across singularity issue in path planning, which leads to the infinite or incalculable joint velocity. To solve this issue, firstly, the singular value decomposition (SVD) is used for exposition of the singularity avoidance principle of the damped least squares (DLS) method. After that, the DLS method is improved by introducing an adaptive damping factor which changes with the singularity. Finally, in order to improve the tracking accuracy of the singularity-robust algorithm, the objective function is established, and two adaptive parameters are optimized by genetic algorithm (GA). The simulation of a 6-DOF free-floating space robot is carried out, and the results show that, compared with DLS method, the proposed method could improve the tracking accuracy of space manipulator end-effector.
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Cercignani, Carlo, Irene M. Gamba, Joseph W. Jerome y Chi-Wang Shu. "Applicability of the High Field Model: An Analytical Study Via Asymptotic Parameters Defining Domain Decomposition". VLSI Design 8, n.º 1-4 (1 de enero de 1998): 135–41. http://dx.doi.org/10.1155/1998/54618.
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In this paper, we present a mesoscopic-macroscopic model of self-consistent charge transport. It is based upon an asymptotic expansion of solutions of the Boltzmann Transport Equation (BTE). We identify three dimensionless parameters from the BTE. These parameters are, respectively, the quotient of reference scales for drift and thermal velocities, the scaled mean free path, and the scaled Debye length. Such parameters induce domain dependent macroscopic approximations. Particular focus is placed upon the so-called high field model, defined by the regime where drift velocity dominates thermal velocity. This model incorporates kinetic transition layers, linking mesoscopic to macroscopic states. Reference scalings are defined by the background doping levels and distinct, experimentally measured mobility expressions, as well as locally determined ranges for the electric fields. The mobilities reflect a coarse substitute for reference scales of scattering mechanisms. See [9] for elaboration.The high field approximation is a formally derived modification of the augmented drift-diffusion model originally introduced by Thornber some fifteen years ago [25]. We are able to compare our approach with the earlier kinetic approach of Baranger and Wilkins [5] and the macroscopic approach of Kan, Ravaioli and Kerkhoven [20].
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Lin, Minghui, Sabyasachi Roy y Matthias Militzer. "In situ measurement of austenite grain growth and recrystallization using laser ultrasonics". Journal of Physics: Conference Series 2635, n.º 1 (1 de noviembre de 2023): 012039. http://dx.doi.org/10.1088/1742-6596/2635/1/012039.
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Abstract The development of next generation process models and advanced high-strength steel products for thin slab casting and direct rolling requires quantification of microstructure evolution during thermomechanical processing. Laser ultrasonics is a non-contact in-situ method to record grain growth, recrystallization and phase transformations in metals and alloys. Here, we will present an improved experimental design that facilitates a continuous microstructure measurement through the various stages of simulated hot rolling from reheating to runout table cooling using a Gleeble thermomechanical simulator equipped with a laser ultrasonics for metallurgy (LUMet) system. Austenite grain growth and static recrystallization after hot deformation are quantified based on attenuation of the ultrasound waves whereas austenite decomposition can be recorded with the changes in ultrasound velocity during the phase transformation. Further, the LUMet results for a microalloyed low carbon steel are validated with conventional techniques including optical and electron microscopy as well as double-hit tests. These experimental studies demonstrate the capabilities of laser ultrasonics in the identification of both normal and abnormal grain growth, non-recrystallization temperature, recrystallization, and austenite decomposition kinetics in a single test for a given processing path, as well as its potential for accelerated optimization of process control under industrial rolling conditions.
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Wang, Yi, Xueyi Shang, Zewei Wang y Rui Gao. "High-Accuracy Location of Microseismic Events in a Strong Inhomogeneous Mining Environment by Optimized Global Full Waveform Inversion". Applied Sciences 10, n.º 20 (15 de octubre de 2020): 7205. http://dx.doi.org/10.3390/app10207205.
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High-accuracy determination of a microseismic (MS) location is the core task in MS monitoring. In this study, a 3D multi-scale grid Green’s function database, depending on recording wavefield frequency band for the target mining area, is pre-generated based on the reciprocity theorem and 3D spectral element method (SEM). Then, a multi-scale global grid search strategy is performed based on this pre-stored Green’s function database, which can be effectively and hierarchically processed by searching for the spatial location. Numerical wavefield modeling by SEM effectively overcomes difficulties in traditional and simplified ray tracing modeling, such as difficult wavefield amplitude and multi-path modeling in 3D focusing and defusing velocity regions. In addition, as a key step for broadband waveform simulation, the source-time function estimated from a new data-driven singular value decomposition averaged fractional derivative based wavelet function (DD-SVD-FD wavelet) was proposed to generate high-precision synthetic waveforms for better fitting observed broadband waveform than those by simple and traditional source-time function. Combining these sophisticated processing procedures, a new robust grid search and waveform inversion-based location (GSWI location) approach is integrated. In the synthetic test, we discuss and demonstrate the importance of 3D velocity model accuracy to waveform inversion-based location results for a practical MS monitoring configuration. Furthermore, the average location error of the 3D GSWI location for eight real blasting events is only 15.0 m, which is smaller than error from 3D ray tracing-based location (26.2 m) under the same velocity model. These synthetic and field application investigations prove the crucial role of 3D velocity model, finite-frequency travel-time sensitivity kernel characteristics and accurate numerical 3D broadband wavefield modeling for successful MS location in a strong heterogeneous velocity model that are induced by the presence of ore body, host rocks, complex tunnels, and large excavations.
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Wang, Wei, Yang Wang y Tieshan Li. "Distributed Formation Maneuvering Quantized Control of Under-Actuated Unmanned Surface Vehicles with Collision and Velocity Constraints". Journal of Marine Science and Engineering 12, n.º 5 (20 de mayo de 2024): 848. http://dx.doi.org/10.3390/jmse12050848.
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This paper focuses on a distributed cooperative time-varying formation maneuvering issue of under-actuated unmanned surface vehicles (USVs). A fleet of USVs is guided by a parameterized path with a time-varying formation while avoiding collisions and preserving the connectivity in the environment with multiple obstacles. In some surface missions, due to the obstacles in the external environment, the bandwidth limitations of the communication channel, and the hardware components/performance constraints of the USVs themselves, each vehicle is considered to be subject to model uncertainty, actuator quantization, sensor dead zone, and velocity constraints. During the control design process, the radial basis function (RBF) neural networks (NNs) are utilized to deal with nonlinear terms. Based on a nonlinear decomposition method, the relationship between the control signal and the quantization one is established, which overcomes the difficulty arising from actuator quantization. A Nussbaum function is introduced to handle the unknown output dead zone problem caused by reduced sensor sensitivity. Moreover, a universal-constrained function is employed to satisfy both the constrained and unconstrained requirements during formation keeping and obstacle avoidance. The Lyapunov stability theory confirmed that the error signals are uniformly ultimately bounded (UUB). The simulation results demonstrate the effectiveness of the proposed distributed formation control of multiple USVs.
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Morse, David L., Edwin D. Waddington y L. A. Rasmussen. "Ice deformation in the vicinity of the ice-core site at Taylor Dome, Antarctica, and a derived accumulation rate history". Journal of Glaciology 53, n.º 182 (2007): 449–60. http://dx.doi.org/10.3189/002214307783258530.
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AbstractKnowledge of ice flow and strain rate in the vicinity of the Taylor Dome (East Antarctica) ice-core site enhances interpretation of the paleoclimate information from the ice core. We measured surface ice motion by repeated optical and GPS surveys of a network of 253 markers. We developed a robust data reduction method that uses least squares based on singular value decomposition, to simultaneously calculate positions and velocities of these markers in a geocentric coordinate system. Constrained by these surface velocities, we used a finite-element model to compute the modern ice velocity field at depth. As the geometry of Taylor Dome appears to have been steady through the Holocene, we used particle paths from a steady-state model to track ice particles to the ice core from their points of origin on the surface. By removing the effects of path-dependent vertical strain, we derived past accumulation rates at the origin points of those particle paths from measured layer thicknesses in the ice core. Comparison with accumulation rates estimated from concentrations of 10Be and SO4 in the core suggests that significant amounts of snow were lost by wind scouring during the Last Glacial Maximum and at ~50kyr BP.
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Mason, Carolyn R., Lalin S. Theverapperuma, Claudia M. Hendrix y Timothy J. Ebner. "Monkey Hand Postural Synergies During Reach-to-Grasp in the Absence of Vision of the Hand and Object". Journal of Neurophysiology 91, n.º 6 (junio de 2004): 2826–37. http://dx.doi.org/10.1152/jn.00653.2003.
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Understanding how the CNS controls reach-to-grasp will require behavioral and neurophysiological studies of reach-to-grasp in the monkey, including the evaluation of whole-hand grasp with explicit force requirements. In this study, monkeys performed a reach-to-grasp task in which the size, shape, and orientation of the objects were varied. The monkeys were required to grasp each object at five force levels based on visual feedback. Seventeen positions on the wrist and hand were monitored to quantify kinematics. Hand shaping began with initiation of reach and continued throughout the reach, matching object properties even without vision of the hand or object. Grasp aperture scaled to object size. Singular value decomposition analysis of the marker positions identified two dominant hand postures. The first eigenvector or “eigenposture” consisted of an open hand configuration midway between flexion and extension that explained >93% of the variance. The second eigenposture consisted of hyperextension of all joints that accounted for another 4–5% of the variance. The two eigenpostures were similar across force levels and between monkeys. Reach kinematics consisted of a U-shaped hand path with a bell-shaped velocity profile. Trajectory and speed were independent of grasp force and object properties. In summary, hand shaping during the reach occurred without vision of the hand or object, and hand kinematics were not dependent on grasp force. Furthermore, the reach was independent of grasp force and object properties. These observations imply that the kinematics of reach-to-grasp and grasp force are controlled independently. Similar to humans, monkeys may use a simplifying strategy to reduce the degrees of freedom of the hand during reach-to-grasp.
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Delman, Andrew S., Julie L. McClean, Janet Sprintall, Lynne D. Talley, Elena Yulaeva y Steven R. Jayne. "Effects of Eddy Vorticity Forcing on the Mean State of the Kuroshio Extension". Journal of Physical Oceanography 45, n.º 5 (mayo de 2015): 1356–75. http://dx.doi.org/10.1175/jpo-d-13-0259.1.
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AbstractEddy–mean flow interactions along the Kuroshio Extension (KE) jet are investigated using a vorticity budget of a high-resolution ocean model simulation, averaged over a 13-yr period. The simulation explicitly resolves mesoscale eddies in the KE and is forced with air–sea fluxes representing the years 1995–2007. A mean-eddy decomposition in a jet-following coordinate system removes the variability of the jet path from the eddy components of velocity; thus, eddy kinetic energy in the jet reference frame is substantially lower than in geographic coordinates and exhibits a cross-jet asymmetry that is consistent with the baroclinic instability criterion of the long-term mean field. The vorticity budget is computed in both geographic (i.e., Eulerian) and jet reference frames; the jet frame budget reveals several patterns of eddy forcing that are largely attributed to varicose modes of variability. Eddies tend to diffuse the relative vorticity minima/maxima that flank the jet, removing momentum from the fast-moving jet core and reinforcing the quasi-permanent meridional meanders in the mean jet. A pattern associated with the vertical stretching of relative vorticity in eddies indicates a deceleration (acceleration) of the jet coincident with northward (southward) quasi-permanent meanders. Eddy relative vorticity advection outside of the eastward jet core is balanced mostly by vertical stretching of the mean flow, which through baroclinic adjustment helps to drive the flanking recirculation gyres. The jet frame vorticity budget presents a well-defined picture of eddy activity, illustrating along-jet variations in eddy–mean flow interaction that may have implications for the jet’s dynamics and cross-frontal tracer fluxes.
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Guo, Wusong, Hao Yan y Hanshuang Chen. "Extremal statistics for first-passage trajectories of drifted Brownian motion under stochastic resetting". Journal of Statistical Mechanics: Theory and Experiment 2024, n.º 2 (19 de febrero de 2024): 023209. http://dx.doi.org/10.1088/1742-5468/ad2678.
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Abstract We study the extreme value statistics of first-passage trajectories generated from a one-dimensional drifted Brownian motion subject to stochastic resetting to the starting point with a constant rate r. Each stochastic trajectory starts from a positive position x 0 and terminates whenever the particle hits the origin for the first time. We obtain an exact expression for the marginal distribution P r ( M | x 0 ) of the maximum displacement M. We find that stochastic resetting has a profound impact on P r ( M | x 0 ) and the expected value ⟨ M ⟩ of M. Depending on the drift velocity v, ⟨ M ⟩ shows three distinct trends of change with r. For v ⩾ 0 , ⟨ M ⟩ decreases monotonically with r, and tends to 2 x 0 as r → ∞ . For v c < v < 0 , ⟨ M ⟩ shows a nonmonotonic dependence on r, in which a minimum ⟨ M ⟩ exists for an intermediate level of r. For v ⩽ v c , ⟨ M ⟩ increases monotonically with r. Moreover, by deriving the propagator and using a path decomposition technique, we obtain, in the Laplace domain, the joint distribution of M and the time tm at which the maximum M is reached. Interestingly, the dependence of the expected value ⟨ t m ⟩ of tm on r is either monotonic or nonmonotonic, depending on the value of v. For v > v m , there is a nonzero resetting rate at which ⟨ t m ⟩ attains its minimum. Otherwise, ⟨ t m ⟩ increases monotonically with r. We provide an analytical determination of two critical values of v, v c ≈ − 1.694 15 D / x 0 and v m ≈ − 1.661 02 D / x 0 , where D is the diffusion constant. Finally, numerical simulations are performed to support our theoretical results.
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Mattern, M., J. Kainulainen, M. Zhang y H. Beuther. "Structure and fragmentation of a high line-mass filament: Nessie". Astronomy & Astrophysics 616 (agosto de 2018): A78. http://dx.doi.org/10.1051/0004-6361/201731778.
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Context. An increasing number of hundred-parsec-scale, high line-mass filaments are being detected in the Galaxy. Their evolutionary path, including fragmentation towards star formation, is virtually unknown. Aims. We characterize the fragmentation within the hundred-parsec-scale, high line-mass Nessie filament, covering size-scales in the range ~0.1–100 pc. We also connect the small-scale fragments to the star-forming potential of the cloud. Methods. We combine near-infrared data from the VISTA Variables in the Via Lactea (VVV) survey with mid-infrared Spitzer/GLIMPSE data to derive a high-resolution dust extinction map for Nessie. We then apply a wavelet decomposition technique on the map to analyze the fragmentation characteristics of the cloud. The characteristics are then compared with predictions from gravitational fragmentation models. We compare the detected objects to those identified at a resolution approximately ten times lower from ATLASGAL 870 μm dust emission data. Results. We present a high-resolution extinction map of Nessie (2″ full-width-half-max, FWHM, corresponding to 0.03 pc). We estimate the mean line mass of Nessie to be ~627 M⊙ pc−1 and the distance to be ~3.5 kpc. We find that Nessie shows fragmentation at multiple size scales. The median nearest-neighbor separations of the fragments at all scales are within a factor of two of the Jeans’ length at that scale. However, the relationship between the mean densities of the fragments and their separations is significantly shallower than expected for Jeans’ fragmentation. The relationship is similar to the one predicted for a filament that exhibits a Larson-like scaling between size-scale and velocity dispersion; such a scaling may result from turbulent support. Based on the number of young stellar objects (YSOs) in the cloud, we estimate that the star formation rate (SFR) of Nessie is ~371 M⊙ Myr−1; similar values result if using the number of dense cores, or the amount of dense gas, as the proxy of star formation. The star formation efficiency is 0.017. These numbers indicate that by its star-forming content, Nessie is comparable to the Solar neighborhood giant molecular clouds like Orion A.
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Kułacz, Karol, Michał Pocheć, Aneta Jezierska y Jarosław J. Panek. "Naphthazarin Derivatives in the Light of Intra- and Intermolecular Forces". Molecules 26, n.º 18 (17 de septiembre de 2021): 5642. http://dx.doi.org/10.3390/molecules26185642.
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Our long-term investigations have been devoted the characterization of intramolecular hydrogen bonds in cyclic compounds. Our previous work covers naphthazarin, the parent compound of two systems discussed in the current work: 2,3-dimethylnaphthazarin (1) and 2,3-dimethoxy-6-methylnaphthazarin (2). Intramolecular hydrogen bonds and substituent effects in these compounds were analyzed on the basis of Density Functional Theory (DFT), Møller–Plesset second-order perturbation theory (MP2), Coupled Clusters with Singles and Doubles (CCSD) and Car-Parrinello Molecular Dynamics (CPMD). The simulations were carried out in the gas and crystalline phases. The nuclear quantum effects were incorporated a posteriori using the snapshots taken from ab initio trajectories. Further, they were used to solve a vibrational Schrödinger equation. The proton reaction path was studied using B3LYP, ωB97XD and PBE functionals with a 6-311++G(2d,2p) basis set. Two energy minima (deep and shallow) were found, indicating that the proton transfer phenomena could occur in the electronic ground state. Next, the electronic structure and topology were examined in the molecular and proton transferred (PT) forms. The Atoms In Molecules (AIM) theory was employed for this purpose. It was found that the hydrogen bond is stronger in the proton transferred (PT) forms. In order to estimate the dimers’ stabilization and forces responsible for it, the Symmetry-Adapted Perturbation Theory (SAPT) was applied. The energy decomposition revealed that dispersion is the primary factor stabilizing the dimeric forms and crystal structure of both compounds. The CPMD results showed that the proton transfer phenomena occurred in both studied compounds, as well as in both phases. In the case of compound 2, the proton transfer events are more frequent in the solid state, indicating an influence of the environmental effects on the bridged proton dynamics. Finally, the vibrational signatures were computed for both compounds using the CPMD trajectories. The Fourier transformation of the autocorrelation function of atomic velocity was applied to obtain the power spectra. The IR spectra show very broad absorption regions between 700 cm−1–1700 cm−1 and 2300 cm−1–3400 cm−1 in the gas phase and 600 cm−1–1800 cm−1 and 2200 cm−1–3400 cm−1 in the solid state for compound 1. The absorption regions for compound 2 were found as follows: 700 cm−1–1700 cm−1 and 2300 cm−1–3300 cm−1 for the gas phase and one broad absorption region in the solid state between 700 cm−1 and 3100 cm−1. The obtained spectroscopic features confirmed a strong mobility of the bridged protons. The inclusion of nuclear quantum effects showed a stronger delocalization of the bridged protons.
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Fraichard, Th. "Trajectory Planning Amidst Moving Obstacles: Path-Velocity Decomposition Revisited". Journal of the Brazilian Computer Society 4, n.º 3 (abril de 1998). http://dx.doi.org/10.1590/s0104-65001998000100002.
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Yücesan, Sencer, Daniel Wildt, Philipp Gmeiner, Johannes Schobesberger, Christoph Hauer, Christine Sindelar, Helmut Habersack y Michael Tritthart. "Turbulent secondary flows in low aspect ratio open-channels over heterogeneous surfaces: Anisotropy in forces". Physics of Fluids, 29 de diciembre de 2022. http://dx.doi.org/10.1063/5.0131020.
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Studies of turbulent flows over heterogeneous surfaces revealed elevated turbulent kinetic energy and Reynolds shear stress in low-momentum-path (LMP) regions. These regions induce large-scale multi-cellular secondary flows. The aim of the current study is to analyse the influence of these regions on drag, lift and lateral forces acting on spherical particles at different exposure levels, thereby addressing the hitherto unknown contribution of the spanwise inhomogeneities. For this reason, numerical simulations of turbulent open-channel flow with varying aspect ratio ( AR = 1, 3, 5) over single-sized spherical particles with diameter D was studied. Ensemble-averaged cross-flow velocity vectors showed large-scale secondary flows to penetrate in-between the spherical particles, therefore stretching over the entire flow depth. Their magnitude above 0.8 D was observed to range between 12.9% − 14.9% of U. Strong tertiary vortices in the vicinity of the lateral walls were identified by analysis of swirl strength. Triple decomposition of streamwise velocity fluctuations showed strong backflow at the trailing edge of the spherical particles in high-momentum-path (HMP) regions. Furthermore, it was found that drag forces are higher in HMPs, which is attributed to the larger streamwise pressure gradient.
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Merrill, Reid J., Michael G. Bostock, Simon M. Peacock y David S. Chapman. "Optimal Multichannel Stretch Factors for Estimating Changes in Seismic Velocity: Application to the 2012 Mw 7.8 Haida Gwaii Earthquake". Bulletin of the Seismological Society of America, 8 de marzo de 2023. http://dx.doi.org/10.1785/0120220250.
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ABSTRACT We propose new methods for assessing temporal changes in seismic velocity using the S-wave coda for repeating earthquakes and cross-correlation functions of ambient noise. For a pair of seismic waveforms representing a common source–receiver path, the relative change in path-averaged velocity over the corresponding time interval is directly proportional to the factor by which one waveform needs to be stretched or compressed with respect to the other to achieve maximum coherence. For an arbitrary number of waveforms, initial pair-wise stretch factors determined through standard approaches can be improved through solution of an overdetermined system and further refined through an iterative approach exploiting the singular value decomposition to minimize rank of the stretched waveform section. We apply this combined approach to both repeating earthquakes and ambient noise correlations for Haida Gwaii in western Canada, the site of a Mw 7.8 thrust earthquake in 2012. Optimal stretch factors for repeating earthquake families indicate that path-averaged S velocities dropped by up to 0.16% after the earthquake. Ambient noise correlations indicate that velocities dropped by between 0.26% and 0.39%, which we interpret to be more pronounced in the uppermost levels of the crust. We explore these results in terms of changes in crustal porosity and hydrogeologic conditions by considering the observation that hot spring activity on Haida Gwaii ceased following the 2012 mainshock and recovered over the next several years.
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Fan, Di, Yang Xu, Hongping Wang y Jinjun Wang. "Comparative assessment for pressure field reconstruction based on physics-informed neural network". Physics of Fluids 35, n.º 7 (1 de julio de 2023). http://dx.doi.org/10.1063/5.0157753.
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In this paper, a physics-informed neural network (PINN) is used to determine pressure fields from the experimentally measured velocity data. As a novel method of data assimilation, PINN can simultaneously optimize velocity and solve pressure by embedding the Navier–Stokes equations into the loss function. The PINN method is compared with two traditional pressure reconstruction algorithms, i.e., spectral decomposition-based fast pressure integration and irrotation correction on pressure gradient and orthogonal-path integration, and its performance is numerically assessed using two kinds of flow motions, namely, Taylor's decaying vortices and forced isotropic turbulence. In the case of two-dimensional decaying vortices, critical parameters of PINN have been investigated with and without considering measurement errors. Regarding the forced isotropic turbulence, the influence of spatial resolution and out-of-plane motion on pressure reconstruction is assessed. Finally, in an experimental case of a synthetic jet impinging on a solid wall, the PINN is used to determine the pressure from the velocity fields obtained by the planar particle image velocimetry. All results show that the PINN-based pressure reconstruction is superior to other methods even if the velocity fields are significantly contaminated by the measurement errors.
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Ebert, Carola, Julien Weiss, Maarten Uijt de Haag, Christopher Ruwisch y Flavio J. Silvestre. "Trajectory Planning in Windy Urban Environment Using Gappy Proper Orthogonal Decomposition for Wind Estimates". AIAA Journal, 8 de mayo de 2023, 1–12. http://dx.doi.org/10.2514/1.j062049.
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A trajectory planning algorithm based on the traditional A* formulation is designed to determine the minimum-energy path from a start to a final location taking into account the prevailing wind conditions. To obtain average wind conditions in an urban environment, full-scale Reynolds-averaged Navier–Stokes simulations are first performed using OpenFoam® for various inlet wind directions on a computational model representing complex buildings on the campus of the Technical University of Berlin. The proper orthogonal decomposition (POD) modes of the full database are then calculated in an offline stage with the wind direction as a parameter. Next, the online reconstruction of the complete urban wind field is performed by Gappy POD using simulated pointwise measurements obtained by sparse sensors. Finally, the trajectory planning algorithm is applied to the reconstructed wind field and validated by comparison with the trajectory computed on the full-order computational fluid dynamics (CFD) model. The main conclusion is that the error made by calculating the energy requirements for a specific trajectory based on an inexpensive reduced-order model of the wind field instead of an expensive full-order CFD database is only a few percent in all investigated cases. Therefore, a reliable and trustworthy trajectory can be calculated from the inexpensive reduced-order model obtained with only a few velocity sensors. Furthermore, it is shown that the energy consumption along a trajectory could be reduced by up to 20% by taking the prevailing wind field into consideration instead of considering the shortest path.
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Hoseinzadeh, Siamak y Davide Astiaso Garcia. "Numerical Analysis of Thermal, Fluid, and Electrical Performance of a Photovoltaic Thermal Collector at New Micro-Channels Geometry". Journal of Energy Resources Technology 144, n.º 6 (28 de octubre de 2021). http://dx.doi.org/10.1115/1.4052672.
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Abstract In this article, different paths (direct, spiral, and curved) for water flow in a photovoltaic/thermal (PV/T) system are studied, and they are compared together. The intensity of radiation to the cell surface is taken 800 W/m2, and the fluid flow is considered to be laminar in the micro-channels. The PV cell absorbing radiation is of an aluminum type. The numerical solution of the three geometries is carried out using the finite volume method using ansys-fluent software. The pressure decomposition, momentum and energy discretization, and the solution of the pressure–velocity coupling are performed based on the standard method, the second-order upwind method, and the semi-implicit method for pressure-linked equations (SIMPLE) method, respectively. The convergence factor is considered to be respected and for continuity and energy equations. The results indicate that the cell surface temperature and the outlet fluid temperature decrease by increasing the Reynolds (Re) number. Moreover, electricity efficiency increases with the increased Reynolds number. The curved path has the highest electrical efficiency in comparison to other two paths. The decrease in fluid pressure of the curved path in Re = 600 is 4% and 1.3% higher than the direct and spiral paths, respectively.
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"Influence of train-generated vibrations on embankment". Acta Montanistica Slovaca 28, n.º v28/i3 (1 de noviembre de 2023): 678–86. http://dx.doi.org/10.46544/ams.v28i3.12.
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Roads and railway lines are often constructed on different geotechnical structures such as tunnels, cuttings, and/or embankments. Three main parts are necessary to consider to evaluate vibration: the source of vibrations, vibration propagation path, and receiver of the signal. This paper describes a review of the influence of train-generated vibrations on an embankment and a building in the surroundings. The first presented case study documents an interpretation of seismic signal in the frequency domain using wavelet transform. The algorithm, which we apply to the computation of the wavelet transform of the velocity component record, is based on the pyramidal algorithm, and the result of this procedure is used for an interpretation of data. The discrete wavelet transform was applied to the construction of a 3-dimension mapping of the time-frequency decomposition. An example of the numerical model on the FEM method (the MIDAS GTS software) shows the vertical displacement of the embankment body during the movement of a train. The creation of these models is strictly based on the results of experimental seismological measurements. Then, the source of vibration is represented by a typical train/vehicle that runs on the nearest part of the railway/road at the most efficient velocity.
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Pátý, Marek y Sergio Lavagnoli. "A Novel Vortex Identification Technique Applied to the 3D Flow Field of a High-Pressure Turbine". Journal of Turbomachinery 142, n.º 3 (20 de febrero de 2020). http://dx.doi.org/10.1115/1.4045471.
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Abstract The efficiency of modern axial turbomachinery is strongly driven by the secondary flows within the vane or blade passages. The secondary flows are characterized by a complex pattern of vortical structures that origin, interact, and dissipate along the turbine gas path. The endwall flows are responsible for the generation of a significant part of the overall turbine loss because of the dissipation of secondary kinetic energy and mixing out of nonuniform momentum flows. The understanding and analysis of secondary flows requires a reliable vortex identification technique to predict and analyze the impact of specific turbine designs on the turbine performance. However, the literature shows a remarkable lack of general methods to detect vortices and to determine the location of their cores and to quantify their strength. This paper presents a novel technique for the identification of vortical structures in a general 3D flow field. The method operates on the local flow field, and it is based on a triple decomposition of motion proposed by Kolář. In contrast to a decomposition of velocity gradient into the strain and vorticity tensors, this method considers a third, pure shear component. The subtraction of the pure shear tensor from the velocity gradient remedies the inherent flaw of vorticity-based techniques, which cannot distinguish between rigid rotation and shear. The triple decomposition of motion serves to obtain a 3D field of residual vorticity whose magnitude is used to define vortex regions. The present method allows to locate automatically the core of each vortex, to quantify its strength, and to determine the vortex bounding surface. The output may be used to visualize the turbine vortical structures for the purpose of interpreting the complex three-dimensional viscous flow field and to highlight any case-to-case variations by quantifying the vortex strength and location. The vortex identification method is applied to a high-pressure turbine with three optimized blade tip geometries. The 3D flow field is obtained by computational fluid dynamics (CFD) computations performed with Numeca FINE/Open. The computational model uses steady-state Reynolds-averaged Navier–Stokes (RANS) equations closed by the Spalart-Allmaras turbulence model. Although developed for turbomachinery applications, the vortex identification method proposed in this work is of general applicability to any three-dimensional flow field.
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Shi, Fenghao, Mengqi Liu, David L. S. Hung, Xuesong Li y Min Xu. "Valve Vibration Induced Intake Air Flow Dynamics Analysis Using Near Valve PIV". Journal of Engineering for Gas Turbines and Power, 18 de julio de 2022. http://dx.doi.org/10.1115/1.4055021.
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Abstract The transient dynamics of air flow running through the moving intake valve gaps in combustion cylinders is crucial to the performance of SIDI engines. However, research on the air flow behavior in the vicinity of valve exits is still limited. In this work, transient air flow characteristics of a custom-designed dual-valve system under the operating conditions of a fixed valve lift and a vibrating valve lift at two frequencies are experimentally investigated. The velocity vector field measured using planar particle image velocimetry (PIV) is first analyzed in time domain based on temporal mean and root mean square (RMS) values. Comparison of temporal mean flow fields reveals the difference in flow pattern while RMS represents the variation of intake air jet velocity along the inlet path of the vibration-affected jet. Instantaneous snapshots provide direct analysis of the valve vibration-induced intake air jet behavior. Furthermore, investigation in frequency domain extends insights into the dominant spectral components of flow structures. Fast Fourier Transform applied to every vector on the velocity field yields a vibration frequency affected zone, indicating the regions where the effect of valve vibration is significant. By employing dynamic mode decomposition method, the spatio-temporal PIV results are decomposed into modes with specific frequencies. Reconstructed flow field using modes with the valve operating frequency visually unveils a cyclic vortex structure near the valve exit. In summary, this study elucidates the mechanism of near-valve intake air flow impingement and interaction behavior induced by the valve vibrating motion.
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Cao, Jian, Peng Wang y Yingzheng Liu. "Influence of dual purging jets on interferometric measurement of optical path difference". Physics of Fluids 36, n.º 1 (1 de enero de 2024). http://dx.doi.org/10.1063/5.0182342.
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Incompressible large eddy simulations of dual purging jets at three Reynolds numbers of ReL = 1500, 1000, and 500 are performed, providing the database for simulated interferometric measurements subjected to the spatiotemporally varying temperature fields. The temperature is modeled as a passive scalar, and the index-of-refraction field is calculated from the air temperature and pressure using the modified Edlén equation. Based on wave optics, wavefront distortions of laser beams traversing the flow field are computed, and the optical path difference measurement is simulated. Statistical results of the velocity and temperature indicate distinctly different flow patterns at three Reynolds numbers. Spectral proper orthogonal decomposition is adopted to analyze the relationship between coherent flow structures and temperature wavepackets. There is a dominant frequency (St = 0.29) at ReL = 1500 and 1000, which is attributed to the Kelvin–Helmholtz instability, whereas the two jets have notable flapping behaviors at ReL = 500. The wavefront distortions are found to be insensitive to the Reynolds number. The effects of the flow region and tracing distance are examined, and the optical performances of different beam pairs for interferometry are evaluated. The optical beams passing through the outer shear layers of the dual jets and wall jets are distorted severely, resulting in large systematic and random errors in the interferometric measurement.
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Ito, Sosuke. "Geometric thermodynamics for the Fokker–Planck equation: stochastic thermodynamic links between information geometry and optimal transport". Information Geometry, 9 de marzo de 2023. http://dx.doi.org/10.1007/s41884-023-00102-3.
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AbstractWe propose a geometric theory of non-equilibrium thermodynamics, namely geometric thermodynamics, using our recent developments of differential-geometric aspects of entropy production rate in non-equilibrium thermodynamics. By revisiting our recent results on geometrical aspects of entropy production rate in stochastic thermodynamics for the Fokker–Planck equation, we introduce a geometric framework of non-equilibrium thermodynamics in terms of information geometry and optimal transport theory. We show that the proposed geometric framework is useful for obtaining several non-equilibrium thermodynamic relations, such as thermodynamic trade-off relations between the thermodynamic cost and the fluctuation of the observable, optimal protocols for the minimum thermodynamic cost and the decomposition of the entropy production rate for the non-equilibrium system. We clarify several stochastic-thermodynamic links between information geometry and optimal transport theory via the excess entropy production rate based on a relation between the gradient flow expression and information geometry in the space of probability densities and a relation between the velocity field in optimal transport and information geometry in the space of path probability densities.
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Lian, Jie, Xu Yuan, Jiadong Lou, Li Chen, Hao Wang y Nianfeng Tzeng. "Room-Scale Location Trace Tracking via Continuous Acoustic Waves". ACM Transactions on Sensor Networks, 20 de febrero de 2024. http://dx.doi.org/10.1145/3649136.
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The increasing prevalence of smart devices spurs the development of emerging indoor localization technologies for supporting diverse personalized applications at home. Given marked drawbacks of popular chirp signal-based approaches, we aim to develop a novel device-free localization system via the continuous wave of the inaudible frequency. To achieve this goal, solutions are developed for fine-grained analyses, able to precisely locate moving human traces in the room-scale environment. In particular, a smart speaker is controlled to emit continuous waves at inaudible 20 kHz , with a co-located microphone array to record their Doppler reflections for localization. We first develop solutions to remove potential noises and then propose a novel idea by slicing signals into a set of narrowband signals, each of which is likely to include at most one body segment’s reflection. Different from previous studies, which take original signals themselves as the baseband, our solutions employ the Doppler frequency of a narrowband signal to estimate the velocity first and apply it to get the accurate baseband frequency, which permits a precise phase measurement after I-Q (i.e., in-phase and quadrature) decomposition. A signal model is then developed, able to formulate the phase with body segment’s velocity, range, and angle. We next develop novel solutions to estimate the motion state in each narrowband signal, cluster the motion states for different body segments corresponding to the same person, and locate the moving traces while mitigating multi-path effects. Our system is implemented with commodity devices in room environments for performance evaluation. The experimental results exhibit that our system can conduct effective localization for up to three persons in a room, with the average errors of 7.49 cm for a single person, with 24.06 cm for two persons, with 51.15 cm for three persons.
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Dekker, Hasse N. J., Woutijn J. Baars, Fulvio Scarano, Marthijn Tuinstra y Daniele Ragni. "Unsteady flow behaviour of multi-rotors in ground proximity". Flow 3 (2023). http://dx.doi.org/10.1017/flo.2023.21.
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The unsteady flow behaviour of two side-by-side rotors in ground proximity is experimentally investigated. The rotors induce a velocity distribution interacting with the ground causing the radial expansion of the rotor wakes. In between the rotors, an interaction of the two wakes takes place, resulting in an upward flow similar to a fountain. Two types of flow topologies are examined and correspond to two different stand-off heights between the rotors and the ground: the first one where the height of the fountain remains below the rotor disks, and a second one where it emerges above, being re-ingested. The fountain unsteadiness is shown to increase when re-ingestion takes place, determining a location switch from one rotor disk to the other, multiple times during acquisition. Consequently, variable inflow conditions are imposed on each of the two rotors. The fountain dynamics is observed at a frequency that is about two orders of magnitude lower than the blade passing frequency. The dominant characteristic time scale is linked to the flow recirculation path, relating this to system parameters of thrust and ground stand-off height. The flow field is analysed using proper orthogonal decomposition, in which coupled modes are identified. Results from the modal analysis are used to formulate a simple dynamic flow model of the re-ingestion switching cycle.
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Singh, Prashant, Saikat Santra y Anupam Kundu. "Extremal statistics of a one dimensional run and tumble particle with an absorbing wall". Journal of Physics A: Mathematical and Theoretical, 11 de noviembre de 2022. http://dx.doi.org/10.1088/1751-8121/aca230.
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Abstract We study the extreme value statistics of a run and tumble particle (RTP) in one dimension till its first passage to the origin starting from the position $x_0~(>0)$. This model has recently drawn a lot of interest due to its biological application in modelling the motion of certain species of bacteria. Herein, we analytically study the exact time-dependent propagators for a single RTP in a finite interval with absorbing conditions at its two ends. By exploiting a path decomposition technique, we use these propagators appropriately to compute the joint distribution $\mathscr{P}(M,t_m)$ of the maximum displacement $M$ till first-passage and the time $t_m$ at which this maximum is achieved exactly. The corresponding marginal distributions $\mathbb{P}_M(M)$ and $P_M(t_m)$ are studied separately and verified numerically. In particular, we find that the marginal distribution $P_M(t_m)$ has interesting asymptotic forms for large and small $t_m$. While for small $t_m$, the distribution $P_M(t_m)$ depends sensitively on the initial velocity direction $\sigma _i$ and is completely different from the Brownian motion, the large $t_m$ decay of $P_M(t_m)$ is same as that of the Brownian motion although the amplitude crucially depends on the initial conditions $x_0$ and $\sigma _i$. We verify all our analytical results to high precision by numerical simulations.
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Sailellah, Sardila Nurulhikmah y Yo Fukushima. "Comparison of tropospheric delay correction methods for InSAR analysis using a mesoscale meteorological model: a case study from Japan". Earth, Planets and Space 75, n.º 1 (2 de febrero de 2023). http://dx.doi.org/10.1186/s40623-023-01773-z.
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AbstractA major source of error in interferometric synthetic aperture radar (InSAR), used for mapping ground deformation, is the delay caused by changes in the propagation velocity of radar microwaves in the troposphere. Correcting this tropospheric delay noise using numerical weather models is common because of their global availability. Various correction methods and tools exist; selecting the most appropriate one by considering weather models, delay models, and delay calculation algorithms is essential for specific applications. We compared the performance of two tropospheric delay correction methods applied to Advanced Land Observing Satellite-2 (ALOS-2) data acquired over Japan, where the atmospheric field is complex with significant seasonal variation. We tested: (1) a method of delay integration along the slant radar line-of-sight (LOS) path using the mesoscale model (MSM) provided by the Japan Meteorological Agency and (2) the Generic Atmospheric Correction Online Service (GACOS) for InSAR, which estimates delay using the high-resolution forecast (HRES)-European Centre for Medium-Range Weather Forecasts (ECMWF) products along with an iterative decomposition approach. The results showed that the tropospheric delay correction using the slant-delay integration approach with MSM, which has a finer temporal and spatial resolution, performed slightly better than GACOS. We further found that the differences in the refractivity models would have limited significance, suggesting that the difference in performance mainly originates from differences in the numerical weather models being used. This study highlights the importance of using the best-available numerical weather model data for tropospheric delay calculations. Graphical Abstract