Is Our Archiving Reliable? Multiobjective Archiving Methods on “Simple” Artificial Input Sequences

In evolutionary multiobjective optimisation ( EMO ), archiving is a common component that maintains an (external or internal) set during the search process, typically with a fixed size, in order to provide a good representation of high-quality solutions produced. Such an archive set can be used solely to store the final results shown to the decision maker, but in many cases may participate in the process of producing solutions (e.g., as a solution pool where the parental solutions are selected). Over the last three decades, archiving stands as an important issue in EMO, leading to the emergence of various methods such as those based on Pareto, indicator, or decomposition criteria. Such methods have demonstrated their effectiveness in literature and have been believed to be good options to many problems, particularly those having a regular Pareto front shape, e.g., a simplex shape. In this article, we challenge this belief. We do this through artificially constructing several sequences with extremely simple shapes, i.e., 1D/2D simplex Pareto front. We show the struggle of predominantly used archiving methods which have been deemed to well handle such shapes. This reveals that the order of solutions entering the archive matters, and that current EMO algorithms may not be fully capable of maintaining a representative population on problems with linear Pareto fronts even in the case that all of their optimal solutions can be found.

Controlling wave fronts with tunable disordered non-Hermitian multilayers

Unique and flexible properties of non-Hermitian photonic systems attract ever-increasing attention via delivering a whole bunch of novel optical effects and allowing for efficient tuning light-matter interactions on nano- and microscales. Together with an increasing demand for the fast and spatially compact methods of light governing, this peculiar approach paves a broad avenue to novel optical applications. Here, unifying the approaches of disordered metamaterials and non-Hermitian photonics, we propose a conceptually new and simple architecture driven by disordered loss-gain multilayers and, therefore, providing a powerful tool to control both the passage time and the wave-front shape of incident light with different switching times. For the first time we show the possibility to switch on and off kink formation by changing the level of disorder in the case of adiabatically raising wave fronts. At the same time, we deliver flexible tuning of the output intensity by using the nonlinear effect of loss and gain saturation. Since the disorder strength in our system can be conveniently controlled with the power of the external pump, our approach can be considered as a basis for different active photonic devices.

Redesign the Front Shape of the Sedan Car for Pedestrian Safety and Mitigating Leg Injuries at Accidents

The number of fatal and non-fatal pedestrian injuries, due to car accidents, has increased. For this reason, design of least possible harm cars (i.e. pedestrian friendly cars) has attracted the interest of many researchers and companies in order to reduce mortality and mitigate injuries. The use of friendly cars can also lead to the reduction of the expensive medical treatment costs for pedestrian injuries and consequently alleviates the financial burdens of the governments and insurance companies. In the sedan cars accidents, the common first pedestrian body part which experiences impact is the legs. In this research, a simulation study is conducted for investigating the effects of car bumper profile and plastic grille tilt angle on the severity of collision. LS-Dyna software is used to simulate, numerically investigate and analyze the mechanism of collision between a simulated leg and a vehicle bumper. In this simulation, three parameters are considered, impact line between pedestrian leg and car bumper, the height of the bumper relative to the knee, and the plastic grille tilt angle. The results of this study showed that the increase of impact line, increase of bumper height and decrease the plastic grille tilt angle alleviate the severity of pedestrians leg injuries.

Hydromechanic instability of crystals growth by Czochralski method

Рассмотрен один из механизмов гидромеханической неустойчивости при выращивании кристаллов из расплава методом Чохральского, связанный с явлением образования «холодных термиков» в подкристальной области. С этой целью проанализированы результаты, полученные по двум математическим моделям: 1 - без и 2 - с учетом процесса кристаллизации. В первом случае модельной жидкостью был этанол, а положение фронта кристаллизации задавалось изотермой кристаллизации и было неизменным. В рамках такого подхода были исследованы особенности перехода от стационарного течения жидкости к его неустойчивым модам, сопровождающимся формированием, развитием и отрывом «холодного термика» от фронта (изотермы) кристаллизации. Во втором случае модельными расплавами были два материала с температурой плавления, близкой к комнатной: гептадекан и галлий, которые существенно различаются коэффициентами теплопроводности. В этом случае было изучено влияние термомеханических параметров на формирование формы фронта кристаллизации и возникновение гидромеханической неустойчивости в виде «холодных термиков». The mechanism of hydromechanical instability during Czochralski crystal growth from a melt is considered, which is associated with the formation of “cold plumes” under the crystal. For this purpose, the results obtained by two mathematical models: 1 - without and 2 - taking into account the crystallization process are analyzed. In the first case, an ethanol was as the model fluid, and the position of the crystallization front was set by the crystallization isotherm and was unchanged. Within the framework of this approach, the features of a transition from a stationary fluid flow to its unstable modes were studied, which are accompanied by the formation, development, and separation of “cold plumes” from the crystallization front (isotherm). In the second case, the model melts were as two materials with a melting point close to room temperature: heptadecane and gallium, which significantly differ in thermal conductivity. In this case, the influence of thermomechanical parameters on the formation of the crystallization front shape and the occurrence of hydromechanical instability in the form of "cold plumes"was studied.

Numerical Simulation Study on the Front Shape and Thermal Stresses in Growing Multicrystalline Silicon Ingot: Process and Structural Design

In this paper, a transient numerical simulation method is used to investigate the effects of the two furnace configurations on the thermal field: the shape of the melt–crystal (M/C) interface and the thermal stress in the growing multicrystalline ingot. First, four different power ratios (top power to side power) are investigated, and then three positions (i.e., the vertical, angled, and horizontal positions) of the insulation block are compared with the conventional setup. The power ratio simulation results show that with a descending power ratio, the M/C interface becomes flatter and the thermal stress in the solidified ingot is lower. In our cases, a power ratio of 1:3–1:4 is more feasible for high-quality ingot. The block’s position simulation results indicate that the horizontal block can more effectively reduce the radial temperature gradient, resulting in a flatter M/C interface and lower thermal stress.

Low-cost ultrasonic based object detection and collision avoidance method for autonomous robots

This work focuses on the development of an effective collision avoidance algorithm that detects and avoids obstacles autonomously in the vicinity of a potential collision by using a single ultrasonic sensor and controlling the movement of the vehicle. The objectives are to minimise the deviation from the vehicle’s original path and also the development of an algorithm utilising one of the cheapest sensors available for very lost cost systems. For instance, in a scenario where the main ranging sensor malfunctions, a backup low cost sensor is required for safe navigation of the vehicle while keeping the deviation to a minimum. The developed algorithm utilises only one ultrasonic sensor and approximates the front shape of the detected object by sweeping the sensor mounted on top of the unmanned vehicle. In this proposed approach, the sensor is rotated for shape approximation and edge detection instead of moving the robot around the encountered obstacle. It has been tested in various indoor situations using different shapes of objects, stationary objects, moving objects, and soft or irregularly shaped objects. The results show that the algorithm provides satisfactory outcomes by entirely avoiding obstacles and rerouting the vehicle with a minimal deviation.

Investigation of the Weather Conditions During the Collapse of the Morandi Bridge in Genoa on 14 August 2018 Using Field Observations and WRF Model

On 14 August 2018, Morandi Bridge in Genoa, Italy, collapsed to the ground that was 40 m below. This tragedy killed 43 people. Preliminary investigations indicated poor design, questionable building practices, and insufficient maintenance—or a combination of these factors—as a possible cause of the collapse. However, around the collapse time, a thunderstorm associated with strong winds, lightning, and rain also developed over the city. While it is unclear if this thunderstorm played a role in the collapse, the present study examines the weather conditions before and during the bridge collapse. The study particularly focuses on the analysis of a downburst that was observed around the collapse time and a few kilometers away from the bridge. Direct and remote sensing measurements are used to describe the evolution of the thunderstorm during its approached from the sea to the city. The Doppler lidar measurements allowed the reconstruction of the gust front shape and the evaluation of its displacement velocity of 6.6 m s−1 towards the lidar. The Weather Research and Forecasting simulations highlighted that it is still challenging to forecast localized thunderstorms with operational setups. The study has shown that assimilation of radar reflectivity improves the timing and reconstruction of the gust front observed by local measurements.

Visualization of Quench Front Propagation on Heated Rod Through Single Jet Impingement

Quench front characteristics and flow physics have been observed for single jet impingement using de-ionized (DI) water and various oxide-based nanofluids. Quench front velocity, shape, intensities of sputtering, and postquench front phenomenon have been observed through the high-speed camera. Quench front velocity is higher in the case of nanofluids than DI water due to the presence of nanoparticles in nanofluids. However, quench front shape also differs in the case of nanofluids due to the rupture of the boundary layer, which depends on agglomeration characteristics and the nanomicroporous layer formed on the solid surface of the heater. A better understanding of quench behavior, for a very low concentration of nanofluids, will make it a viable technology for emergency core cooling system (ECCS) for upcoming nuclear reactors in India.

How Does a Tumor Get Its Shape? MicroRNAs Act as Morphogens at the Cancer Invasion Front

The generation and organization of the invasion front shape of neoplasms is an intriguing problem. The intimate mechanism is not yet understood, but the prevailing theory is that it represents an example of morphogenesis. Morphogenesis requires the presence of specific molecules, known as morphogens (activators and inhibitors), which can diffuse and elicit dose-dependent responses in their target cells. Due to their ability to modulate most of the coding transcriptome, their well-established role in embryogenesis, and their capacity to rapidly move between neighboring and distant cells, we propose microRNAs as inhibitors that could shape the cancer invasion front. In order to explain the genesis of the tumor border, we use Alan Turing’s reaction diffusion model, refined by Meinhardt and Gierer. This assumes the existence of an activator called a, and an inhibitor called h, which we hypothesize could be a freely moving microRNA. We used the fractal dimension as a measure of tumor border irregularity. We observed that the change in fractal dimension associates with variations in the diffusion coefficient of the activator (Da) or the inhibitor (Dh). We determined that the fractal dimension remains constant (i.e., the irregularity of the tumor border does not change) across a Dh interval, which becomes narrower as Da rises. We therefore conclude that a change in fractal dimension occurs when the balance between Da and Dh is disrupted. Biologically, this could be explained by a faulty distribution of the inhibitor caused by an abnormal density of the intercellular connection network. From a translational perspective, if experimentally confirmed, our observations can be used for a better diagnosis of cancer aggressiveness.