МОДЕЛИРОВАНИЕ ОТКАЗОВ В АВТОМАТИЗИРОВАННОЙ СИСТЕМЕ УПРАВЛЕНИЯ ВОЗДУШНЫМ СУДНОМ

This article is devoted to studying of fault diagnosis of an aircraft control surfaces using fault models to identify specific causes. Such failures as jamming, vibration, extreme run out and performance decrease are covered.It is proved that in case of an actuator failure or flight control structural damage, the aircraft performance decreases significantly. Commercial aircraft frequently appear in the areas of military conflicts and terrorist activity, where the risk of shooting attack is high, for example in Syria, Iraq, South Sudan etc. Accordingly, it is necessary to create and assess the fault model to identify the flight control failures.The research results demonstrate that the adequate fault model is the first step towards the managing the challenges of loss of aircraft controllability. This model is also an element of adaptive failure-resistant management model.The research considers the relationship between the parameters of an i th state of a control surface and its angular rate, also parameters classification associated with specific control surfaces in order to avoid conflict/inconsistency in the determination of a faulty control surface and its condition.The results of the method obtained in this article can be used in the design of an aircraft automated control system for timely identification of fault/failure of a specific control surface, that would contribute to an effective role aimed at increasing the survivability of an aircraft and increasing the acceptable level of safety due to loss of control.Исследуется вопрос управляемости воздушного судна при допущении отказов органов управления (ОУ) путем моделирования характеристики управления с учетом особенности его системы автоматического управления. Приводятся виды отказов органов управления самолетом, такие как клинение, колебание, увод в крайнее положение и снижение производительности.Обосновано, что при допущении отказа вследствие потери привода (actuator) или разрушения конструкции ОУ эксплуатационно-летные характеристики самолета значительно ухудшаются. Гражданские воздушные суда (ВС) нередко могут находиться в зонах конфликтов и террористической активности, где не исключена вероятность обстрела, например, в Сирии, Ираке, Южном Судане и т. д. Следовательно, необходима модель отказов, способная идентифицировать отказы вследствие разрушения конструкций и отказов компонентов, органов управления.Результаты данного исследования показывают, что адекватная модель отказов является первым шагом в сторону решения задач потери управляемости ВС при допущении отказов и частью дальнейшей адаптационной модели управления. Таким образом, можно обеспечить высокую эксплуатационную живучесть и надежность ВС, а также экономически рационально повысить уровень безопасности его полетов (БП).Результаты исследования, полученные в данной статье на основе моделирования нелинейного движения ВС при стабилизации углов по тангажу и крену, позволят в дальнейшем разработать алгоритм своевременного выявления отказа конкретной ОУ, который будет использован при проектировании автоматизированной системы управления самолета и на стадии разработки перспективных бортовых систем управления (БСУ). Внедрение полученных результатов позволит эффективно повысить отказоустойчивость ОУ, надежность элементов конструкции ЛА и поддерживать приемлемый уровень БП при допущении частичной или полной потери управляемости ВС из-за разрушения конструктивных компонентов органов управления и отказов ОУ ВС

Direct evidence for flat bands in twisted bilayer graphene from nano-ARPES

Transport experiments in twisted bilayer graphene revealed multiple superconducting domes separated by correlated insulating states. These properties are generally associated with strongly correlated states in a flat mini-band of the hexagonal moir\'e superlattice as it was predicted by band structure calculations. Evidence for such a flat band comes from local tunneling spectroscopy and electronic compressibility measurements, reporting two or more sharp peaks in the density of states that may be associated with closely spaced van Hove singularities. Direct momentum resolved measurements proved difficult though. Here, we combine different imaging techniques and angle resolved photoemission with simultaneous real and momentum space resolution (nano-ARPES) to directly map the band dispersion in twisted bilayer graphene devices near charge neutrality. Our experiments reveal large areas with homogeneous twist angle that support a flat band with spectral weight that is highly localized in momentum space. The flat band is separated from the dispersive Dirac bands which show multiple moir\'e hybridization gaps. These data establish the salient features of the twisted bilayer graphene band structure.Comment: Submitted to Nature Materials. Nat. Phys. (2020

Second asymptomatic carotid surgery trial (ACST-2): a randomised comparison of carotid artery stenting versus carotid endarterectomy

Background: Among asymptomatic patients with severe carotid artery stenosis but no recent stroke or transient cerebral ischaemia, either carotid artery stenting (CAS) or carotid endarterectomy (CEA) can restore patency and reduce long-term stroke risks. However, from recent national registry data, each option causes about 1% procedural risk of disabling stroke or death. Comparison of their long-term protective effects requires large-scale randomised evidence. Methods: ACST-2 is an international multicentre randomised trial of CAS versus CEA among asymptomatic patients with severe stenosis thought to require intervention, interpreted with all other relevant trials. Patients were eligible if they had severe unilateral or bilateral carotid artery stenosis and both doctor and patient agreed that a carotid procedure should be undertaken, but they were substantially uncertain which one to choose. Patients were randomly allocated to CAS or CEA and followed up at 1 month and then annually, for a mean 5 years. Procedural events were those within 30 days of the intervention. Intention-to-treat analyses are provided. Analyses including procedural hazards use tabular methods. Analyses and meta-analyses of non-procedural strokes use Kaplan-Meier and log-rank methods. The trial is registered with the ISRCTN registry, ISRCTN21144362. Findings: Between Jan 15, 2008, and Dec 31, 2020, 3625 patients in 130 centres were randomly allocated, 1811 to CAS and 1814 to CEA, with good compliance, good medical therapy and a mean 5 years of follow-up. Overall, 1% had disabling stroke or death procedurally (15 allocated to CAS and 18 to CEA) and 2% had non-disabling procedural stroke (48 allocated to CAS and 29 to CEA). Kaplan-Meier estimates of 5-year non-procedural stroke were 2·5% in each group for fatal or disabling stroke, and 5·3% with CAS versus 4·5% with CEA for any stroke (rate ratio [RR] 1·16, 95% CI 0·86–1·57; p=0·33). Combining RRs for any non-procedural stroke in all CAS versus CEA trials, the RR was similar in symptomatic and asymptomatic patients (overall RR 1·11, 95% CI 0·91–1·32; p=0·21). Interpretation: Serious complications are similarly uncommon after competent CAS and CEA, and the long-term effects of these two carotid artery procedures on fatal or disabling stroke are comparable. Funding: UK Medical Research Council and Health Technology Assessment Programme

Inhomogeneous electronic states associated with charge-orbital order/disorder in BaV10O15 probed by photoemission spectromicroscopy

We have performed scanning photoemission spectromicroscopy of BaV10O15 across the metal-insulator transition at 123 K, which is accompanied by V 3d charge/orbital order and V trimerization. Nucleation of metallic domains is observed at the cleaved surface of BaV10O15 single crystals, similar to Cr-doped V2O3 in which electronic configurations of Cr3+ and V3+ are the same as those of V2+ and V3+ in BaV10O15. Typical domain size is similar to 5- 10 mu m at 150 K, just above the transition temperature. The metallic domains continuously grow up to 240 K, well above the transition temperature. The temperature evolution of the metallic phase in BaV10O15 is different from that of Cr-doped V2O3, probably due to the charge degrees of freedom in BaV10O15

Temperature-dependent evolution of Ti 3d spectral features at surface of BaxTi8 O16+δ

We have studied temperature-driven effects on photoemission spectra of hollandite-type BaxTi8O16+δ across its metal-insulator transition (MIT) at 220 K by using surface-sensitive photon energies from 27 to 70 eV. The surface Ti 3d spectral weight was suppressed and shifted towards higher binding energy from the bulk if the surface was obtained by cleavage above the MIT temperature. The Ti 3d spectral weight was recovered once the sample was cooled across the MIT, indicating a transfer of Ti 3d electrons from the bulk to the surface across the MIT. The recovered Ti 3d spectral shape is consistent with the bulk-sensitive result and indicates strong localization character of the Ti 3d electron even in the metallic phase. Resonant photoemission spectroscopy with absorption from the Ti 3p core level exhibits resonances of the O 2p-Ti 3d and O 2p-Ti 4s,p hybridized states. The result suggests that the O 2p-Ti 4s,p hybridization plays a role in the interplay between the bulk and the surface in BaxTi8O16+δ

Observation and control of the weak topological insulator state in ZrTe5

A quantum spin Hall (QSH) insulator hosts topological states at the one-dimensional (1D) edge, along which backscattering by nonmagnetic impurities is strictly prohibited. Its 3D analogue, a weak topological insulator (WTI), possesses similar quasi-1D topological states confined at side surfaces. The enhanced confinement could provide a route for dissipationless current and better advantages for applications relative to strong topological insulators (STIs). However, the topological side surface is usually not cleavable and is thus hard to observe. Here, we visualize the topological states of the WTI candidate ZrTe5 by spin and angle-resolved photoemission spectroscopy (ARPES): a quasi-1D band with spin-momentum locking was revealed on the side surface. We further demonstrate that the bulk band gap is controlled by external strain, realizing a more stable WTI state or an ideal Dirac semimetal (DS) state. The highly directional spin-current and the tunable band gap in ZrTe5 will provide an excellent platform for applications