Letteratura scientifica selezionata sul tema "Taches satellites"

Dans la région d’El Kala (extrême Nord-Est algérien), Acacia mearnsii De Wild. a été introduit lors des reboisements de 1970, en mélange à 20 % avec l'eucalyptus. Or, depuis quelques décennies, il est constaté un développement de taches d’invasion par cette espèce australienne dans cette même contrée du pays. L’utilisation d’outils tels qu’un système d'information géographique (SIG), avec des informations spatiales à jour, est nécessaire pour mieux comprendre l'invasion et identifier les écosystèmes potentiels à haut risque. Ainsi, le présent travail a été orienté vers la cartographie afin de procéder à l’étude de la répartition de l’invasion de cette espèce. Deux approches ont été adoptées, la première faisant appel aux données collectées sur le terrain et la seconde aux techniques de télédétection, en appliquant la méthode de classification supervisée sur une image Landsat 8. Les résultats obtenus par les deux méthodes montrent que la superficie envahie avoisine les 3 200 ha, répartis en quatre sites. La quasi-totalité de la surface envahie est occupée par l’eucalyptaie et la suberaie (respectivement 65,0 % et 17,9 % de la superficie totale). La classification de l’image satellite n’a permis de détecter que les paysages fortement envahis, tandis que la méthode des relevés effectués sur le terrain a permis de cartographier sa répartition totale. Toutefois, la superposition des deux cartes montre qu’elles sont majoritairement identiques (0,90 ≤ R ≤ 1). Pour conclure, l’utilisation des données spatialisées, couplées à des données ponctuelles (relevés de terrain), a permis, d’une part, de réduire les contraintes liées à la résolution de l’image Landsat et, d’autre part, de montrer l’importance des méthodologies basées sur les travaux de terrain.

A novel ultra-wideband (UWB) KAYI-shaped and common KITE-shaped ground plane tri-port antenna is proposed. The proposed research work has a small size of (30 × 30 × 1.6 mm3). The MIMO antenna elements are placed in a KAYI-shaped (Y-shaped) with a symmetric phase shift of 120∘ between the nearby MIMO antennas element improving the isolation. The antenna’s gain is more than 5 dBi for the entire bands of WiMax, WLAN, and X-band satellite communication. The suggested work includes notches at 3.2 GHz, 5.2 GHz, and 8.9 GHz, respectively. The notching characteristics are made possible by L-shaped slits for the WiMax band, the inverted U-shaped slot for WLAN, while the third is created by the interaction between the L-shaped and U-shaped notching elements. Results were measured after making the prototype antenna on the FR-4 substrate. The proposed antenna has good impedance matching for 2–20 GHz and three notching characteristics with high isolation among the MIMO elements. Mean effective gain (MEG), envelope correlation coefficient (ECC), and total active reflection coefficient (TARC) are the diversity metrics of MIMO antennas which are in good comparison to the proposed antenna. The antenna is a good candidate for deployment in wireless communication and MIMO applications.

Today, interaction between people and objects, including industrial ones, has become an integral part of our everyday life. Access to communications, finance, and all forms of information management and permission to use them can be obtained from almost anywhere using compact devices. For example, operators can remotely control individual sectors and control operations in several areas at the same time, surgeons can operate on patients thousands of miles away, and car manufacturers can detect when one of their vehicles has been in an accident within a few seconds after the accident. As a result of the spread of the Internet and wireless data networks, the interconnection of so much data, technology and network equipment and devices has quickly become the basis of modern society. At present, we have become a knowledge-based society that often relies on technology to execute or support almost all tasks and functions of human life. Undoubtedly, this has greatly expanded the range of tasks to be solved, but at the same time, the society became much more vulnerable to threats in information and communication systems. The vulnerability is explained by the fact that at some point most of the production of different directions and industries is supported by the introduction, storage and search of data/information in a interconnected network of hard disks and data servers, locally or remotely located. And at each of these stages there is an opportunity to steal data, bypass protection, manipulate or replace information. But the risks associated with unintentional accidents caused by human errors, system failures, incompatibility or other unexpected problems, as well as “natural disasters,” must also be taken into account. Therefore, the security of computer or cyber systems is a matter of national security. Actually, cyber-threats are so great that more and more security experts are pointing out that protection of cyber systems and data is more of a problem than terrorism. Given the scale of the threat (in terms of cyberattacks) and the actual damage it can be argued, certain systems and structures are at risk [1, 2]. It is proved that hackers can break into government and business websites, steal personal data, change the traffic light scheme, accelerate and slow down travel, and much more. As an example, the implementation of a specially created malware program - Stuxnet. The effects of its use were the self-destruction in 2010 of dozens of centrifuges, which supported Iranʼs nuclear program [3, 4]. Some experts think that Stuxnet was created not by independent attackers and possibly with the support of the government. Thus, as a conclusion, it can be confirmed that hackers operate from anywhere in the world, and the links and boundaries between cyberspace and physical systems are sufficiently leveled. Thus, as a conclusion, it can be confirmed that intruders operate from anywhere in the world, and the links and borders between cyberspace and physical systems are sufficiently leveled. Society is increasingly faced with the fact that a group or even a person armed with a complex computer virus or knowledge about the vulnerability of software or hardware can cause a lot of physical damage to people’s lives or physical destruction, impose significant social or economic damage, and so on. For example, there are facts published by the Financial times on May 8, 2012 (http://on.ft.com/1wviXHW) that an unknown group for many years is trying to penetrate into the systems of managing the networks of gas pipelines of the USA. At the end of 2014, the National Oceanic and Atmospheric Administration of the United States announced that hackers from China successfully broke and destroyed American satellite networks, causing loss of services related to the prediction of various natural cataclysms, air flight corridors, navigation and other industries within a few days (http://wapo.st/1u7N9dJ). As a rule, the critical infrastructure includes power and transport main networks, oil and gas pipelines, sea ports, high-speed and governmental communication channels, systems of life support (water and heat supply) of mega-cities, waste management, emergency services and emergency response services, high-tech enterprises and enterprises of military-industrial complex, as well as central authorities. The government critical information infrastructure is only one of many important systems and networks that create our modern society. Therefore, the state and society are fully dependent on the functioning of different objects and subjects of critical information infrastructure, and the loss of integrity of any of them can lead to various kinds of failures (termination of production and transfer of electricity, temporary and long-term interruptions, improper access to medical care, and much more). Each state is a separate critical information infrastructure, but cooperation between states takes place within the framework of global critical information infrastructure. At the same time, large investments in each sector of critical information infrastructure have led to an increase in economic development rates and improvement in the quality of life.

Ce travail fournit des informations sur la synthèse de feuillets nanométriques ultrafins composés de Bi₂O₂CO₃, ci-après dénommé BOC. La synthèse est réalisée par une technique rapide et simple connue sous le signe EDDL correspondant au procédé de décharges électriques dans les liquides diélectriques. Pour assurer la reproductibilité de la synthèse, une méthode de prétraitement impliquant la gravure d'électrodes de bismuth avec du Nital a été employée. Le processus choisi consiste à initier des décharges électriques entre ces électrodes alors qu'elles sont immergées soit dans l'azote liquide, soit dans l'eau. Fait remarquable, les deux liquides conduisent à des nanostructures identiques, une similitude validée par spectroscopie d'émission optique, technique qui a permis de confirmer la nature métallique de la décharge dans les deux milieux. Après cette étape, les nanofeuillets subissent une oxydation et une carbonatation rapides lorsqu'ils sont exposés à l'air. Le mécanisme de croissance proposé est étroitement lié au mécanisme connu sous le nom de « ledge mechanism », en raison de la présence de « kinks » et de « jogs » clairement visibles le long des bords des nanofeuillets. Ces nanostructures bidimensionnelles émergent d'abord à la surface de la cathode et croissent ensuite verticalement. Cette croissance anisotrope est rendue possible par l'assistance ionique dans les régions qui ressemblent à des motifs en forme de peigne formés pendant l'étape de gravure chimique, condition préalable nécessaire à une forte reproductibilité du processus de croissance. La caractérisation cristallographique détaillée des nanofeuillets de BOC a été réalisée à l'aide d'une série de techniques, notamment la microscopie électronique en transmission (TEM), la microscopie électronique en transmission à balayage (STEM), la microscopie électronique en transmission à haute résolution (HRTEM), la spectroscopie de rayons X à dispersion d'énergie (EDX), la diffraction d'électrons en aire sélectionnée (SAED), la diffraction d'électrons en faisceau convergent (CBED), la microscopie électronique en transmission filtrée en énergie (EFTEM) et la spectroscopie de perte d'énergie des électrons (EELS). L'étude révèle que la structure cristallographique du BOC est conforme au groupe spatial I4/mmm, avec des paramètres de réseau a=3,91 Å et c=13,77 Å, une détermination qui a été confirmée par diffraction des rayons X (DRX). L'étude clarifie également l'origine potentielle des taches satellites qui sont régulièrement observées dans les motifs SAED le long de l'axe de zone [001]. Dans cette étude, ces taches ont été principalement attribuées à deux phénomènes : la diffraction multiple et les transformations locales ordre-désordre qui se produisent dans la structure cristalline du BOC. Cette transformation implique une transition d'une structure quadratique centrée vers un réseau primitif de Bravais. Afin d'évaluer leur utilité pratique, nous avons mesuré la performance photocatalytique des nanofeuillets de BOC synthétisés à l'aide de la méthode EDDL et nous avons constaté qu'elle était comparable à elle de BOCs obtenus par d'autres méthodes. En outre, nous avons évalué la performance électronique des BOC dans le but de découvrir leur potentiel dans les applications liées à des nanodispositifs
This work provides information on the synthesis of ultrathin nanosheets composed of Bi₂O₂CO₃, hereafter referred to as BOC. The synthesis is achieved through the rapid and straightforward technique known as Electrical Discharges in Dielectric Liquids (EDDL). To ensure the reproducibility of the synthesis, a pre-treatment method involving the etching of bismuth electrodes with Nital was employed. The chosen process entails initiating electrical discharges between these electrodes while submerged in either liquid nitrogen or water. Remarkably, both liquids produced identical nanostructures, a similarity validated by optical emission spectroscopy, which confirmed the metallic nature of the discharge in both environments. Following this stage, the nanosheets undergo rapid oxidation and carbonation upon exposure to air. The proposed growth mechanism is closely linked to the ledge mechanism, considering the presence of clearly visible kinks and jogs along the edges of the nanosheets. These two-dimensional nanostructures first emerge on the cathode's surface and then grow vertically. This anisotropic growth is made possible by ion assistance in regions that exhibit comb-like patterns formed during the chemical etching step, which is a necessary precondition for high reproducibility of the discharge process. Detailed crystallographic characterization of BOC nanosheets was achieved through a range of techniques, including Transmission Electron Microscopy (TEM), Scanning Transmission Electron Microscopy (STEM), High-Resolution TEM Transmission Electron Microscopy (HRTEM), Energy-Dispersive X-ray Spectroscopy (EDX), Selected Area Electron Diffraction (SAED), Convergent Beam Electron Diffraction (CBED), Energy Filtered Transmission Electron Microscopy (EFTEM), and Electron Energy-Loss Spectroscopy (EELS). The investigation reveals that the crystallographic structure of BOC conforms to the space group I4/mmm, with lattice parameters a=3.91 Å and c=13.77 Å, a determination that was confirmed by X-ray Diffraction (XRD). The study also clarifies the potential origin of satellite spots that are consistently observed in SAED patterns along the [001] zone axis. In this research, these spots were primarily attributed to two phenomena: multiple diffraction and local disorder-to-order transformations occurring within the BOC crystal structure. This transformation entails a transition from a body-centered tetragonal structure to a primitive Bravais lattice. To gauge their practical usefulness, we assessed the photocatalytic performance of BOC nanosheets synthesized using the EDDL method and found it to be consistent with BOC obtained through alternative methods. Furthermore, we explored the electronic performance of BOC with the goal of uncovering their potential in nanodevice applications

La sequence de l'arn-2 de l'isolat s comporte une seule phase de lecture ouverte qui correspond a une proteine de p. M. 150 k. La proteine de la coque est localisee dans la region c terminale de la proteine 150 k. Une proteine "de diffusion" se situerait en amont de la proteine de la capside. Les sequences des arn satellites issus d'isolats appartenant aux serotypes s (s et l) et g (g, e et c) comportent toutes une seule phase de lecture ouverte correspondant a une proteine de 48 k. La comparaison des sequences permet de distinguer 2 groupes: les arn s et l d'une part, les arn g, e et c, d'autre part. A l'interieur de chaque groupe, les arn presentent plus de 90% d'homologie de sequence tandis que 63% des nucleotides sont communs aux 5 arn etudies

Crowdsourcing is being researched as a problem-solving technique by issuing open calls for solutions to large crowds of people with the incentive of prizes. This paper tackles the dual objectives of building cluster flight software and educating students using collaborative competition, both in virtual simulation environments and on real hardware in space. The concept is demonstrated using the SPHERES Zero Robotics Program, a robotics programming competition where the robots are nano-satellites called SPHERES onboard the International Space Station (ISS), traditionally used as a Guidance, Navigation and Control testbed in microgravity. Zero Robotics allows students to program SPHERES to play a game through a web-based interface and the most robust projects are evaluated on the ISS hardware, supervised by astronauts. The apparatus to investigate the influence of collaboration was developed by (1) building new web infrastructure where intensive inter-participant collaboration is possible, (2) designing a game that incentivizes collaboration with opponents, to solve a relevant formation flight problem and (3) structuring a tournament such that inter-team collaboration is mandated. The web infrastructure was also built using collaborative competitions, to demonstrate feasibility of building space software end-to-end by crowdsourcing.

This chapter tackles the issues of simultaneous localization and mapping (SLAM) using laser scanners or vision as a viable alternative to the accurate modes of satellite-based localization, which are popular and easy to implement with modern technology but might fail in many urban scenarios. This chapter considers two state-of-the-art localization algorithms, LOAM and ORB-SLAM3 that use the optimization-based formulation of SLAM and utilize laser and vision sensing, respectively. The focus is on the practical aspects of localization and the accuracy of the obtained trajectories. It contributes to a series of experiments conducted using an electric car equipped with a carefully calibrated multisensory setup with a 3D laser scanner, camera, and a smartphone for collecting the exteroceptive measurements. Results of applying the two different SLAM algorithms to the data sequences collected with the vehicle-based multisensory setup clearly demonstrate that not only the expensive laser sensors but also monocular vision, including the commodity smartphone camera, can be used to obtain off-line reasonably accurate vehicle trajectories in an urban environment.