Large amplitude problem of BGK model: Relaxation to quadratic nonlinearity

Bhatnagar-Gross-Krook (BGK) equation is a relaxation model of the Boltzmann equation which is widely used in place of the Boltzmann equation for the simulation of various kinetic flow problems. In this work, we study the asymptotic stability of the BGK model when the initial data is not necessarily close to the global equilibrium pointwisely. Due to the highly nonlinear structure of the relaxation operator, the argument developed to derive the bootstrap estimate for the Boltzmann equation leads to a weaker estimate in the case of the BGK model, which does not exclude the possible blow-up of the perturbation. To overcome this issue, we carry out a refined analysis of the macroscopic fields to guarantee that the system transits from a highly nonlinear regime into a quadratic nonlinear regime after a long but finite time, in which the highly nonlinear perturbative term relaxes to essentially quadratic nonlinearity.Comment: 34 pages, 1 figure

Numerical schemes for a multi-species quantum BGK model

We consider a kinetic model of an N-species gas mixture modeled with quantum Bhatnagar-Gross-Krook (BGK) collision operators. The collision operators consist of a relaxation to a Maxwell distribution in the classical case, a Fermi distribution for fermions and a Bose-Einstein distribution for bosons. In this paper we present a numerical method for simulating this model, which uses an Implicit-Explicit (IMEX) scheme to minimize a certain potential function. This is motivated by theoretical considerations coming from entropy minimization. We show that theoretical properties such as conservation of mass, total momentum and total energy as well as positivity of the distribution functions are preserved by the numerical method presented in this paper, and illustrate its usefulness and effectiveness with numerical examplesComment: arXiv admin note: text overlap with arXiv:2202.0565

Image or Information? Examining the Nature and Impact of Visualization Perceptual Classification

How do people internalize visualizations: as images or information? In this study, we investigate the nature of internalization for visualizations (i.e., how the mind encodes visualizations in memory) and how memory encoding affects its retrieval. This exploratory work examines the influence of various design elements on a user's perception of a chart. Specifically, which design elements lead to perceptions of visualization as an image or as information? Understanding how design elements contribute to viewers perceiving a visualization more as an image or information will help designers decide which elements to include to achieve their communication goals. For this study, we annotated 500 visualizations and analyzed the responses of 250 online participants, who rated the visualizations on a bilinear scale as image or information. We then conducted an in-person study (n = 101) using a free recall task to examine how the image/information ratings and design elements impact memory. The results revealed several interesting findings: Image-rated visualizations were perceived as more aesthetically appealing, enjoyable, and pleasing. Information-rated visualizations were perceived as less difficult to understand and more aesthetically likable and nice, though participants expressed higher positive sentiment when viewing image-rated visualizations and felt less guided to a conclusion. We also found different patterns among participants that were older. Importantly, we show that visualizations internalized as images are less effective in conveying trends and messages, though they elicit a more positive emotional judgment, while informative visualizations exhibit annotation focused recall and elicit a more positive design judgment. We discuss the implications of this dissociation between aesthetic pleasure and perceived ease of use in visualization design.Comment: 11 pages, 10 figures, 3 tables, accepted at IEEE Vis 202

Correspondence computations in visual cognition

15 behavioral experiments were conducted to investigate the role of object correspondence computations in visual cognition. Correspondence computations refer, here, to algorithms that identify relationships between objects in temporally separate encounters. In Experiment 1-5, I hypothesized that tracking failures occur because of correspondence failures during close encounters of targets and nontargets. To test this idea, I provided observers with different surface feature information to nontargets whenever they approached within 4° of a target (Experiment 1). This manipulation significantly improved performance by alleviating correspondence challenges. Two control experiments showed that this color change benefit is not merely due to target recovery (Experiment 2 and 4). A follow-up experiment measured the distance at which objects correspondence becomes challenging (Experiment 3). And an additional experiment demonstrated that the overall frequency of target-nontarget close encounters predict human performance (Experiment 5). Experiment 6-10 explored the role of object correspondence in the context of spatial working memory. Experiment 6 supplied evidence of object correspondences in a typical spatial working memory task through a trial specific analysis. In addition, a model that implements correspondence algorithms successfully predicted human performance without assuming any independent memory-related limits. Experiments 7 and 8 employed a preview display that indirectly provided information about memory location to be tested. This manipulation improved SWM performance dramatically (e.g. performance with 8 objects were comparable to 2 objects). A control experiment showed that the improved performance is not due to mere reactivation of memory representations (Experiment 9). Additional experiment showed that object colors do not support correspondence computations in this context. Experiment 11-15 employed integral features to prevent correspondence failures in a visual working memory task. I reasoned that integral features can be used to solve correspondence problems by preventing confusions between objects. Experiment 11 and 12 independently identified integral features using perceptual sorting experiments. When these features were used in change judgment tasks, working memory with two objects produced performance as precise as with one (Experiments 13-15). Taken together, these results suggest that object correspondence play a crucial role in the constraints typically observed in visual cognition

Experimental study on the effect of initial liquid droplet size on the evaporation in a heterogeneous droplet

[EN] In the present work, we experimentally investigated the effect of initial liquid droplet size on the evaporation in the heterogeneous droplet. Spherical carbon and water were used for particle and liquid droplet comprising the heterogeneous droplet. four initial droplet volumes of 1, 2, 3 and 4 μl were considered when the diameter of the particle was 5 mm. The heterogeneous droplet was suspended with a rod at 20 cm away from the radiator which surface temperature was fixed to 473 K. Ambient temperature and relative humidity remained 296 K and 40 %, respectively, during the experiment. As the results, the evaporation rate of 4 μl case increased about 1.8 times compared with that of 1 μl case. The evaporation rate increased almost linearly with the volume ratio, and that is related closely with the contact surface between particle and water droplet. Contact surface area remained almost constantly with time, whereas it increased with the initial volume of water droplet. The energy from radiator can be accumulated at the contact surface at the side of particle, thereby intensifying the evaporation of water droplet because more heat transfers from particle to droplet through the contact surface. Consequently, the initial volume of liquid droplet is one of the influence factors on the evaporation rate in the heterogenous droplet.This research was supported by the Fire Fighting Safety & 119 Rescue Technology Research and Development Program funded by the Ministry of Public Safety and Security (NEMA-NG-2014-46) and Research Project of Air Sampling Detector funded by Alllitelife co. Inc..Sung, KH.; Nam, JS.; Hong, GB.; Ryou, HS. (2017). Experimental study on the effect of initial liquid droplet size on the evaporation in a heterogeneous droplet. En Ilass Europe. 28th european conference on Liquid Atomization and Spray Systems. Editorial Universitat Politècnica de València. 290-295. https://doi.org/10.4995/ILASS2017.2017.4744OCS29029

A Study on Teleoperation of a Mobile Robot Using Haptic Feedback

Abstract. Haptic feedback force is often suggested to complement visual information through the sense of touch to improve efficiency and safety in the teleoperation of mobile robot. The efficiency and safety of teleoperation are strongly dependent upon how haptic feedback is presented to the operator. In this study a haptic feedback scheme for teleoperation of mobile robot is developed and its effectiveness is experimentally verified. Experimental results show that the developed scheme improves the quality of mobile robot teleoperation in terms of improvement in efficiency and safety