ShadowDeNet: A Moving Target Shadow Detection Network for Video SAR

Most existing SAR moving target shadow detectors not only tend to generate missed detections because of their limited feature extraction capacity among complex scenes, but also tend to bring about numerous perishing false alarms due to their poor foreground–background discrimination capacity. Therefore, to solve these problems, this paper proposes a novel deep learning network called “ShadowDeNet” for better shadow detection of moving ground targets on video synthetic aperture radar (SAR) images. It utilizes five major tools to guarantee its superior detection performance, i.e., (1) histogram equalization shadow enhancement (HESE) for enhancing shadow saliency to facilitate feature extraction, (2) transformer self-attention mechanism (TSAM) for focusing on regions of interests to suppress clutter interferences, (3) shape deformation adaptive learning (SDAL) for learning moving target deformed shadows to conquer motion speed variations, (4) semantic-guided anchor-adaptive learning (SGAAL) for generating optimized anchors to match shadow location and shape, and (5) online hard-example mining (OHEM) for selecting typical difficult negative samples to improve background discrimination capacity. We conduct extensive ablation studies to confirm the effectiveness of the above each contribution. We perform experiments on the public Sandia National Laboratories (SNL) video SAR data. Experimental results reveal the state-of-the-art performance of ShadowDeNet, with a 66.01% best f1 accuracy, in contrast to the other five competitive methods. Specifically, ShadowDeNet is superior to the experimental baseline Faster R-CNN by a 9.00% f1 accuracy, and superior to the existing first-best model by a 4.96% f1 accuracy. Furthermore, ShadowDeNet merely sacrifices a slight detection speed in an acceptable range.

Wits: An Efficient Wi-Fi Based Indoor Positioning and Tracking System

With the development of wireless communication technology, indoor tracking technology has been rapidly developed. Wits presents a new indoor positioning and tracking algorithm with channel state information of Wi-Fi signals. Wits tracks using motion speed. Firstly, it eliminates static path interference and calibrates the phase information. Then, the maximum likelihood of the phase is used to estimate the radial Doppler velocity of the target. Experiments were conducted, and two sets of receiving antennas were used to determine the velocity of a human. Finally, speed and time intervals were used to track the target. Experimental results show that Wits can achieve the mean error of 0.235 m in two different environments with a known starting point. If the starting point is unknown, the mean error is 0.410 m. Wits has good accuracy and efficiency for practical applications.

Territorial Displays of the Ctenophorus decresii Complex: A Story of Local Adaptations

Closely related species make for interesting model systems to study the evolution of signaling behavior because they share evolutionary history but have also diverged to the point of reproductive isolation. This means that while they may have some behavioral traits in common, courtesy of a common ancestor, they are also likely to show local adaptations. The Ctenophorus decresii complex is such a system, and comprises six closely related agamid lizard species from Australia: C. decresii, C. fionni, C. mirrityana, C. modestus, C. tjanjalka, and C. vadnappa. In this study, we analyze the motion displays of five members of the C. decresii complex in the context of their respective habitats by comparing signal structure, habitat characteristics and signal contrast between all species. Motor pattern use and the temporal sequence of motor patterns did not differ greatly, but the motion speed distributions generated during the displays were different for all species. There was also variation in the extent to which signals contrasted with plant motion, with C. vadnappa performing better than the other species at all habitats. Overall, this study provides evidence that members of the C. decresii complex exhibit local adaptations in signaling behavior to their respective habitat, but they also maintain some morphological and behavioral traits in common, which is likely a consequence from the ancestral state.

A large-stroke rapid motion controller for servo applications with speed and control constraints

Large-stroke rapid motion is required in many industrial servo systems (e.g. pick-and-place applications), on which constraints of control input and motion speed are usually imposed. This paper presents a hybrid control scheme for large-stroke rapid motion in such systems. The controller resorts to the time-optimal control (TOC) for maximum acceleration initially and then switches into a linear control law to achieve smooth settling. A speed regulation stage is inserted in the tracking process to prevent violating the speed constraint. To tackle the unmeasured speed and unknown disturbance, an extended state observer (ESO) can be included in the controller. The controller is applied to a permanent magnet synchronous motor (PMSM) servo system for large-stroke position regulation. Digital simulation via MATLAB is conducted first, followed by an experimental verification using a TMS320F28335 board. The results confirm that the proposed controller can track a wide range of target references with desirable performance under speed constraint and load disturbance and has a competitive advantage over the popular active disturbance-rejection control (ADRC) scheme.

Analyzing Sea Surface Wind Distribution Characteristics of Tropical Cyclone Based on Sentinel-1 SAR Images

The spaceborne synthetic aperture radar (SAR) cross-polarization signal remains sensitive to sea surface wind speed with high signal-to-noise ratio under tropical cyclone (TC) conditions. It has the capability of observing TC intensity and size information over the ocean with large coverage and high spatial resolution. In this paper, TC wind distribution characteristics were studied based on SAR images. We collected 41 Sentinel-1A/B cross-polarization images covering TC eye, which were acquired between 2016 and 2020. For each case, sea surface wind speeds were retrieved by the modified MS1A model in a spatial resolution of 1 km. After deriving the value and location of maximum wind speed, wind fields were simulated symmetrically within a 200 km radius. Two new methodologies were proposed to calculate the decay index and the symmetry index based on the retrieved and simulated wind fields. Characteristics of the two indices were analyzed with respect to maximum wind. In addition, the maximum and averaged wind speeds of the right, back and left side of the motion direction were compared with TC intensity and storm motion speed. Statistical results indicate that right-side wind speed is the strongest for maximum and average, the wind difference between the left and right side is dependent on storm motion speed.

Perceptual judgments for the softness of materials under indentation

Humans can judge the softness of elastic materials through only visual cues. However, factors contributing to the judgement of visual softness are not yet fully understood. We conducted a psychophysical experiment to determine which factors and motion features contribute to the apparent softness of materials. Observers watched video clips in which materials were indented from the top surface to a certain depth, and reported the apparent softness of the materials. The depth and speed of indentation were systematically manipulated. As physical characteristics of materials, compliance was also controlled. It was found that higher indentation speeds resulted in larger softness rating scores and the variation with the indentation speed was successfully explained by the image motion speed. The indentation depth had a powerful effect on the softness rating scores whose variation with the indentation depth was consistently explained by motion features related to overall deformation. Higher material compliance resulted in higher rating scores while their effect was not straightforwardly explained by the motion features. We conclude that the brain makes visual judgments about the softness of materials under indentation on the basis of the motion speed and deformation magnitude while motion features related to material compliance require further study.

Coupling mechanism of materials and screen surface motion in multi-stage variable inclination equal thickness screening process

Multi-stage variable inclination equal-thickness screen (MSVIETS) is widely used in separating coal and mineral particles because of its large production capacity and good screening performance. In this study, the kinematic characteristics of infeed and outfeed ends surface under the conditions of load and no load was investigated by using a high-speed camera analysis system. The motion speed of the screen surface at the infeed end was approximately 5 times higher under load than under no-load conditions, and motion speed of the screen surface at the outfeed end was approximately 4 times higher than under no-load conditions. The mechanism of coupled motion of material and screen surface in the process of multi-stage variable inclination equal thickness screening was elucidated, and the energy coupling transfer law was “strong in and weak out”.

Airflow simulation when braking with a disc brake

With an increase in train motion speed, the issue of improving braking systems becomes more and more important, since braking systems have a direct impact on safety of traffic. At high travel speeds, the friction elements heat up strongly, so heat dissipation from the brake discs is essential. Therefore, an important task is to study the aerodynamics of brake discs. To achieve these goals, experimental measurements on a special test bench, or simulation in specialized software packages can be used. The article discusses methods for studying air flow when braking with a disc brake. The simulation methods, turbulence models and software packages used for simulation are considered. The influence of the internal geometry of the discs on ventilation and heat dissipation is considered. Also, the geometry of the disc is analysed using simulation in the specialized software. Based on the simulation results, a conclusion about the influence of the internal disc geometry on the air flow through it is drawn.

TIME REPRESENTATION IN SCIENTIFIC DIAGRAMS: GALILEO GALILEI’S SOLUTION TO THE PROBLEM OF THE MOTION OF A FALLING BODY

Рассматриваются способы научного изображения темпоральных явлений на примере чертежей Галилео Галилея, при помощи которых он описывает и исследует равноускоренное движение. Для анализа применяется концептуальная рамка теории изобразительной и неизобразительной репрезентации Грегори Карри. Показано, что в случае научных диаграмм и графиков, представляющих время как одно из измерений пространства, основанием для геометрической изобразимости времени становится полагаемый изоморфизм между временем как континуумом мгновений и линией как континуумом точек. Парадигму такого структурного сопоставления мы находим в математическом мышлении Галилея, наиболее ярко проявляющемся в доказательстве формулы равноускоренного движения, представленном в «Беседах и математических доказательствах». The textbook narrative of the scientific revolution of the 17th century says that the early modern transformation of physics and mechanics was grounded in mathematization, that is, the application of mathematical principles and procedures to physical entities and events. However, such a transformation faces a major obstacle: compared to geometry, mechanics includes an additional dimension, namely, time. When temporality of motion is to be represented geometrically, a question arises on how a temporal succession can be expressed by a static image. The problem of representation of temporal events is not limited to science. In my paper, I apply a conceptual tool elaborated by Gregory Currie for the analysis of temporal representations in art, especially in cinema, to the analysis of scientific diagrams. In his book Image and Mind. Film, Philosophy, and Cognitive Science (1995), Currie distinguishes depictive and nondepictive representations, arguing that depictive representation requires similarity and homomorphism between an object ant its representation. Thus, it seems that any non-temporal image of temporal processes would lack the required similarity and cannot be a depictive representation. However, taking into account explanations given by Galileo Galilei for his famous diagrams of accelerated motion, I argue that the representation of time in scientific diagrams as a geometrical line is grounded in isomorphism between time as a continuous structure and continuous structure of a geometrical line. The main temporal process studied by mechanics is motion. Motion can be represented in two main ways: as a trajectory of a body over some period of time or as a functional relation of various parameters of motion (speed, path, acceleration) versus time. In the latter case, time is usually represented in a diagram as a geometrical line. We can find the origin of this type of representation in the late medieval doctrine of ‘intensio et remissio qualitatum’, intension and remission of qualities, in the context of which first diagrams representing intensity and extension of velocity of nonuniform motion as a changing quality over time were produced (Nicolas Oresme). We can find very similar graphical schemes in Galileo Galilei’s works, especially in Discorsi e dimostrazioni matematiche intorno a due nuove scienze (1638). In this work, Galileo announces with all clarity that he considers time to be the same aggregate of temporal moments as a line is an aggregate of points: every moment of time has a corresponding point on the geometrical line. This allows us to establish a homomorphic similarity between temporal duration and spatial (geometrical) extension. Thus, the essential requirement for depictive representation is met. Concluding, I have to point out that the homomorphic relation in this case is established between not real but abstract entities. The visible line itself is a representation of non-visible abstract geometrical line; in the same way, time consisting of non-divisible moments is just an abstract construction which refers to physical of psychological time-duration. However, the established relation between abstract time and abstract geometrical lines is a grounding event of the modern physical science.