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Deformation,fragmentation and acceleration of a controlled fragmentation charge casing

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Defence Technology（防务技术） 2019年第5期15卷 786-795页

作者： Andreas Helte Olof Andersson patrik Lundberg FOI Defence and SecuritySystems and Technology

Two different finite element software,LS-DYNA and Impetus,have been evaluated to test their ability to predict the deformation,fragmentation and acceleration of a controlled fragmentation charge *** general-purpose program LS-DYNA was used with a multi-material ALE formulation and a masspreserving erosion criterion coupled to a Johnson-Cook fracture *** the Impetus simulations,a third order Lagrangian element formulation was used for the casing and a node-splitting element erosion treatment coupled to a Cockcroft-Latham failure criterion was used to describe casing *** high-explosive gases were described by a discrete particle *** order to acquire data to validate our computational tools and constitutive models,a series of experiments have been performed using a laboratory charge with an internal grooved *** the test series,the charge geometry was fixed except that the groove depth were varied from very shallow to very deep resulting in different deformation patterns,fracture modes and terminal *** diagnostic tools captured the different stages of the expansion and fragmentation of the casing.A high-speed framing camera depicted the deformation pattern before fragmentation and was used to determine the moment when the casing *** different complementary techniques were used to follow the acceleration of the fragments;a Photon Doppler velocimetry to determine the initial acceleration of the casing,double exposed radiographs to estimate the fragment velocity after break-up and a high-speed video to determine the terminal velocity of the fragment after leaving the *** addition,the fragments were soft recovered in a set of sawdust pit tests and their final shape and weight were measured.A SEM was used to characterise the fracture surfaces and to determine the modus of fracture(tensile or shear failure).Comparisons to experiments show that both software can predict the change in deformation behaviour

关键词： Controlled fragmentation Fracture mechanics LS-DYNA Impetus

A novel feature extraction methodology using Siamese convolutional neural networks for intrusion detection

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Cybersecurity 2018年第1期1卷 847-859页

作者： Serafeim Moustakidis patrik Karlsson AIDEAS OU Narva mnt 5TallinnHarju maakondEstonia

Intrusion detection systems(IDS)can play a significant role in detecting security threats or malicious attacks that aim to steal information and/or corrupt network *** deal with the dynamic and complex nature of cyber-attacks,advanced intelligent tools have been applied resulting into powerful and automated IDS that rely on the latest advances of machine learning(ML)and deep learning(DL).Most of the reported effort has been devoted on building complex ML/DL architectures adopting a brute force approach towards the maximization of their detection ***,just a limited number of studies have focused on the identification or extraction of user-friendly risk indicators that could be easily used by security *** papers have explored various dimensionality reduction algorithms,however a large number of selected features is still required to detect the attacks successfully,which humans cannot intuitively or immediately *** enhance user’s trust and understanding on data without sacrificing on accuracy,this paper contributes to the transformation of the available data collected by IDS into a single actionable and easy-to-understand risk *** achieve this,a novel feature extraction pipeline was implemented consisting of the following components:(i)a fuzzy allocation scheme that transforms raw data to fuzzy class memberships,(ii)a novel modality transformation mechanism for converting feature vectors to images(Vec2im)and(iii)a dimensionality reduction module that makes use of Siamese convolutional neural networks that finally reduces the input data dimensionality into a 1-d feature *** performance of the proposed methodology was validated with respect to detection accuracy,dimensionality reduction performance and execution time on the NSL-KDD dataset via a thorough comparative analysis that demonstrated its effectiveness(86.64%testing accuracy using only one feature)over a number of well-known feature selection(FS)and extracti

关键词： Feature extraction Siamese convolutional neural networks Machine learning Intrusion detection

Influence of confining prestress on the transition from interface defeat topenetration in ceramic targets

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Defence Technology（防务技术） 2016年第3期12卷 263-271页

作者： patrik LUNDBERG RenéRENSTROM Olof ANDERSSON FOI Swedish Defence Research AgencySE-164 90 StockholmSweden

Replica scaled impact experiments with unconfined ceramic targets have shown that the transition velocity,i.e.,the impact velocity at which interface defeat ceases and ceramic penetration occurs,decreased as the length scale increased.A possible explanation of how this scale effect is related to the formation of a cone crack in the ceramic has been presented by the authors in an earlier ***,the influence of confinement and prestress on cone cracking and transition velocity is *** hypothesis is that prestress will suppress the formation and growth of the cone crack by lowering the driving stress.A set of impact experiments has been performed in which the transition velocity for four different levels of prestress has been *** transition velocities as a function of the level of confining prestress is compared to an analytical model for the influence of prestress on the formation and extension of the cone crack in the ceramic *** experiments and model indicate that prestress has a strong influence on the transition from interface defeat to penetration,although the model underestimates the influence of prestress.

关键词： Impact Ceramic Armour Interface defeat Dwell Confinement Prestress

Beyond dichotomies in species and speciation

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National Science Review 2022年第12期9卷 15-17页

作者： Jeffrey L.Feder patrik Nosil Department of Biological Sciences University of Notre Dame Centre d'Ecologie Fonctionnelle et Evolutive University MontpellierCNRS EPHE IRD

Speciation is not as mysterious as D arwin once described it [1].Nevertheless,important questions *** discussed by Wu[2] and highlighted in a series of papers in National Science Review (NSR),these issues equate with imposing dichotomous perspectives on speciation,when the nature of species and the processes creating them can complicate discrete categorization.

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Production and decay of polarized hyperon-antihyperon pairs

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Chinese Physics C 2023年第5期47卷 29-48页

作者： Karin Schonning Varvara Batozskaya patrik Adlarson 周小蓉 Department of Physics and Astronomy Uppsala University Uppsala Sweden Institute of High Energy Physics Chinese Academy of SciencesBeijing 100049China National Centre for Nuclear Research WarsawPoland University of Science and Technology of China Hefei 230026China

Polarized hyperon-antihyperon pairs shed light on various unresolved puzzles in contemporary physics:How the strong interaction confines quarks into hadrons, how accurately the Standard Model describes microcosmos and even why our universe consists of so much more matter than antimatter. Thanks to their weak, parity violating decays, hyperons reveal their spin properties. This can be exploited e.g. the decomposition of the electromagnetic structure of hyperons, precision tests of flavour symmetry and searches for CP violation. At the BESⅢ experiment at BEPC-Ⅱ, Beijing, China, hyperon-antihyperon pairs can be produced in abundance. Recently collected large data samples have triggered the development of new methods that provide unprecedented precision and a plethora of new results have emerged. When applied at future high-intensity facilities like PANDA and STCF, precision physics will be taken to a new level which can contribute to the solution to the aforementioned puzzles.

关键词： hyperon polarization CP violation form factors

Interruption limits of mechanical circuit breakers and circuit upgrades for current injection in HVDC circuit breakers

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High Voltage 2020年第3期5卷 334-342页

作者： Tim Schultz patrik Herzog Christian Michael Franck High Voltage Laboratory ETH ZurichPhysikstrasse 38092 ZurichSwitzerland

Current injection circuit breakers consist of a mechanical interrupter(MI)with a current injection and an energy dissipation branch in *** performance of the complete device is largely determined by mechanical operation time and interruption performance of the *** the standard configuration,current injection is realised using a pre-charged inductor–capacitor circuit.A higher interruption performance of the MI makes it possible to scale down the resonant injection circuit,and thus have a more economical ***,the implementation of more complex injection circuits that quickly create zero crossings,while maintaining favourable conditions for interruption,can lead to economic *** this study,the interruption performance of a model gas interrupter as part of a current injection topology is *** results are used to verify a corresponding simulation model and two-dimensional upgrade circuits that influence the injection current to increase the range of interruptible fault *** the basis of experimental results,the simulation model is used to investigate the performance of upgrade circuits for the use in high-voltage direct current(HVDC)*** results indicate that using improved injection circuits can considerably increase the economic advantage of current injection circuit breakers compared with other topologies.

关键词： injection resonant branch

Determination of frequencies of oscillations of cloud cavitation on a 2-D hydrofoil from high-speed camera observations

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Journal of Hydrodynamics 2016年第3期28卷 369-378页

作者： patrik ZIMA Tomas FURST Milan SEDLAR Martin KOMAREK Rostislav HUZLIK Institute of Thermomechanics of the CAS v.v.i.PragueCzech RepublicE-mail:zimap@it.cas.cz Faculty of Science Palacky University in OlomoucOlomoucCzech Republic Centre of Hydraulic Research LutinCzech Republic Faculty of Electrical Engineering and Communication Brno University of TechnologyBrnoCzech Republic

A method is presented to determine significant frequencies of oscillations of cavitation structures from high-speed camera recordings of a flow around a 2-D hydrofoil. The top view of the suction side of an NACA 2412 hydrofoil is studied in a transparent test section of a cavitation tunnel for selected cloud cavitation regimes with strong oscillations induced by the leading-edge cavity shedding. The ability of the method to accurately determine the dominant oscillation frequencies is confirmed by pressure measure- ments. The method can resolve subtle flow characteristics that are not visible to the naked eye. The method can be used for non- invasive experimental studies of oscillations in cavitating flows with adequate visual access when pressure measurements are not available or when such measurements would disturb the flow.

关键词： unsteady cavitation oscillation frequency high-speed camera observation

Backstepping approach for design of PID controller with guaranteed performance for micro-air UAV

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Control Theory and Technology 2020年第1期18卷 19-33页

作者： Yusuf KARTAL patrik KOLARIC Victor LOPEZ Atilla DOGAN Frank LEWIS University of Texas at Arlington Research Institute Forth Worth 76118TXU.S.A. ZDepartment of Mechanical and Aerospace Engineering University of Texas at ArlingtonTKU.S.A.

Flight controllers for micro-air UAVs are generally designed using proportional-integral-derivative(PID)methods,where the tuning of gains is difficult and time-consuming,and performance is not *** this paper,we develop a rigorous method based on the sliding mode analysis and nonlinear backstepping to design a PID controller with guaranteed *** technique provides the structure and gains for the PID controller,such that a robust and fast response of the UAV(unmanned aerial vehicle)for trajectory tracking is ***,the second-order sliding variable errors are used in a rigorous nonlinear backstepping design to obtain guaranteed performance for the nonlinear UAV ***,using a small angle approximation and rigorous geometric manipulations,this nonlinear design is converted into a PID controller whose structure is naturally determined through the backstepping *** gains that guarantee robust UAV performance are finally computed from the sliding mode gains and from stabilizing gains for tracking error *** prove that the desired Euler angles of the inner attitude controller loop are related to the dynamics of the outer backstepping tracker loop by inverse kinematics,which provides a seamless connection with existing built-in UAV attitude *** implement the proposed method on actual UAV,and experimental flight tests prove the validity of these *** is seen that our PID design procedure yields tighter UAV performance than an existing popular PID control technique.

关键词： Quadrotor nonlinear controller trajectory tracking backstepping controller inverse kinematics

Consensus controller for multi-UAV navigation

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Control Theory and Technology 2018年第2期16卷 110-121页

作者： patrik KOLARIC Ci CHEN Ankur DALAL Frank L. LEWIS UTA Research Institute University of Texas at Arlington 7300 Jack Newell Bird S Fort Worth TX 76118 U.S.A. School of Automation Guangdong University of Technology Guangdong Key Laboratory of loT Information Technology Guangzhou Guangzhou 510006 China State Key Laboratory of Synthetical Automation for Process Industries Northeastern University Shenyang Liaoning 110819 China

In this paper, we design consensus algorithms for multiple unmanned aerial vehicles （UAV）. We mainly focus on the control design in the face of measurement noise and propose a position consensus controller based on the sliding mode control by using the distributed UAV information. Within the framework of Lyapunov theory, it is shown that all signals in the closed-loop multi- UAV systems are stabilized by the proposed algorithm, while consensus errors are uniformly ultimately bounded. Moreover, for each local UAV, we propose a mechanism to define the trustworthiness, based on which the edge weights are tuned to eliminate negative influence from stubborn agents or agents exposed to extremely noisy measurement. Finally, we develop software for a nano UAV platform, based on which we implement our algorithms to address measurement noises in UAV flight tests. The experimental results validate the effectiveness of the proposed algorithms.

关键词： Consensus control multi-agent system quadrotor Lyapunov stability distributed system