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The dual nature of Janus particles confers fascinating properties such as a response to multiple stimuli. In this communication, we systematically study the sensitivity to a uniform external magnetic field of isolated Janus rod-shaped and spherical particles in water confined to two dimensions. The Janus asymmetry of the particles is given by magnetic [Co(0.28 nm)/Pd(0.90 nm)]

We study the interaction of surface acoustic waves (SAWs) with spin waves (SWs) in a ${\mathrm{Co}}_{40}{\mathrm{Fe}}_{40}{\mathrm{B}}_{20}$/$\mathrm{Au}$/${\mathrm{Ni}}_{81}{\mathrm{Fe}}_{19}$ system composed of two ferromagnetic layers separated by a nonmagnetic $\mathrm{Au}$ spacer layer. Because of interlayer magnetic dipolar coupling between the two ferromagnetic layers, a symmetric and an antisymmetric SW mode form, which both show a highly nondegenerate dispersion relation for oppositely propagating SWs. Due to magnetoacoustic SAW-SW interaction, we observe highly nonreciprocal SAW transmission in the piezoelectric-ferromagnetic hybrid device. We experimentally and theoretically characterize the magnetoacoustic wave propagation as a function of frequency, wave vector, and external magnetic field magnitude and orientation. Additionally, we demonstrate that the nonreciprocal SW dispersion of a coupled magnetic bilayer is highly tuneable and not limited to ultrathin magnetic films, in contrast to the nonreciprocity induced by the interfacial Dzyaloshinskii-Moriya interaction. Therefore, magnetoacoustic coupling in ferromagnetic multilayers provides a promising route towards building efficient acoustic isolators.

We study the interaction of Rayleigh and shear horizontal surface acoustic waves (SAWs) with spin waves in thin $\mathrm{Ni}$ films on a piezoelectric ${\mathrm{Li}\mathrm{Ta}\mathrm{O}}_{3}$ substrate, which supports both SAW modes simultaneously. Because Rayleigh and shear horizontal modes induce different strain components in the $\mathrm{Ni}$ thin films, the symmetries of the magnetoelastic driving fields, of the magnetoelastic response, and of the transmission nonreciprocity differ for both SAW modes. Our experimental findings are well explained by a theoretical model based on a modified Landau-Lifshitz-Gilbert approach. We show that the symmetries of the magnetoelastic response driven by Rayleigh and shear horizontal SAWs complement each other, which makes it possible to excite spin waves for any relative orientation of magnetization and SAW propagation direction and, moreover, can be utilized to characterize surface strain components of unknown acoustic wave modes.

Colloidal Janus microparticles can be propelled by controlled chemical reactions on their surfaces. Such microswimmers have been used as model systems for the behavior on the microscale and as carriers for cargo to well-defined positions in hard-to-access areas. Here we demonstrate the propagation motion of clusters of magnetic Janus particles driven by the catalytic decomposition of $$\hbox {H}_2\hbox {O}_2$$ on their metallic caps. The magnetic moments of their caps lead to certain spatial arrangements of Janus particles, which can be influenced by external magnetic fields. We investigate how the arrangement of the particles and caps determines the driven motion of the particle clusters. In addition, we show the influence of confining walls on the cluster motion, which will be encountered in any real-life biological system.

V několika posledních letech se metody strojového učení (zvláště ty zabývající se detekcí odlehlých hodnot) v oblasti kyberbezpečnosti opíraly o zjišťování anomálií síťového provozu spočívajících v nových schématech útoků. Avšak všudypřítomnost masivních průběžně generovaných datových toků představuje ohromnou výzvu pro účinná detekční schémata a vyžaduje rychlé paměťově nenáročné online algoritmy schopné se potýkat se změnami konceptu. Volba vlastností hraje důležitou roli při zlepšování detekce odlehlých hodnot identifikací zašuměných dat, která obsahují nerelevantní nebo nadbytečné vlastnosti. Současný výzkum se zaměřuje buď na výběr vlastností bez učitele pro průběžně přicházející data nebo na (offline) detekci odlehlých hodnot. V této práci jsou zformulovány podstatné požadavky na kombinaci obou přístupů a dále jsou porovnány s existujícími řešeními. Obsáhlá rešerše odhalila mezeru ve výběru vlastností bez učitele pro zlepšování již hotových metod detekce odlehlých hodnot v datových tocích. Takže navrhujeme nový algoritmus volby vlastností bez učitele pro detekci odlehlých hodnot v průběžně přicházejících datech označovaný jako UFSSOD, který je schopen takové hodnoty automaticky odhalovat. Navíc umí zjišťovat množství nejlepších vlastností shlukováním jejich vypočítaných hodnot. Následně odvozujeme generický koncept, který ukazuje dva aplikační scénáře UFSSOD ve spojení s již hotovými online algoritmy detekce odlehlých hodnot. Rozsáhlé experimenty ukázaly, že slibný mechanismus volby vlastností pro průběžně přicházející data není v oblasti detekce odlehlých hodnot k dispozici. Nadto UFSSOD coby algoritmus schopný online zpracování vykazuje srovnatelné výsledky jako současná nejlepší offline metoda upravená pro detekci odlehlých hodnot. Over the past couple of years, machine learning methods—especially the outlier detection ones—have anchored in the cybersecurity field to detect network-based anomalies rooted in novel attack patterns. However, the ubiquity of massive continuously generated data streams poses an enormous challenge to efficient detection schemes and demands fast, memory-constrained online algorithms that are capable to deal with concept drifts. Feature selection plays an important role when it comes to improve outlier detection in terms of identifying noisy data that contain irrelevant or redundant features. State-of-the-art work either focuses on unsupervised feature selection for data streams or (offline) outlier detection. Substantial requirements to combine both fields are derived and compared with existing approaches. The comprehensive review reveals a research gap in unsupervised feature selection for the improvement of outlier detection methods in data streams. Thus, a novel algorithm for Unsupervised Feature Selection for Streaming Outlier Detection, denoted as UFSSOD, will be proposed, which is able to perform unsupervised feature selection for the purpose of outlier detection on streaming data. Furthermore, it is able to determine the amount of top-performing features by clustering their score values. A generic concept that shows two application scenarios of UFSSOD in conjunction with off-the-shell online outlier detection algorithms has been derived. Extensive experiments have shown that a promising feature selection mechanism for streaming data is not applicable in the field of outlier detection. Moreover, UFSSOD, as an online capable algorithm, yields comparable results to a state-of-the-art offline method trimmed for outlier detection.

Light-induced magnetization changes, such as all-optical switching, skyrmion nucleation, and intersite spin transfer, unfold on temporal and spatial scales down to femtoseconds and nanometers, respectively. Pump-probe spectroscopy and diffraction studies indicate that spatio-temporal dynamics may drastically affect the non-equilibrium magnetic evolution. Yet, direct real-space magnetic imaging on the relevant timescale has remained challenging. Here, we demonstrate ultrafast high-harmonic nanoscopy employing circularly polarized high-harmonic radiation for real-space imaging of femtosecond magnetization dynamics. We observe the reversible and irreversible evolution of nanoscale spin textures following femtosecond laser excitation. Specifically, we map quenched magnetic domains and localized spin structures in Co/Pd multilayers with a sub-wavelength spatial resolution down to 16 nm, and strobosocopically trace the local magnetization dynamics with 40 fs temporal resolution. Our approach enables the highest spatio-temporal resolution of magneto-optical imaging to date. Facilitating ultrafast imaging with an extreme sensitivity to various microscopic degrees of freedom expressed in chiral and linear dichroism, we envisage a wide range of applications spanning magnetism, phase transitions, and carrier dynamics., 14 pages, 4 figures

Colloidal Janus microparticles can be propelled by controlled chemical reactions on their surfaces. Such microswimmers have been used as model systems for the behavior on the microscale and as carriers for cargo to well-defined positions in hard-to-access areas. Here we demonstrate the propagation motion of clusters of magnetic Janus particles driven by the catalytic decomposition of [Formula: see text] on their metallic caps. The magnetic moments of their caps lead to certain spatial arrangements of Janus particles, which can be influenced by external magnetic fields. We investigate how the arrangement of the particles and caps determines the driven motion of the particle clusters. In addition, we show the influence of confining walls on the cluster motion, which will be encountered in any real-life biological system.

It was hypothesized that strontium (Sr)-doped &beta, tricalcium phosphate (TCP)-based scaffolds have a positive effect on the regeneration of large bone defects (LBD). Readouts in our mice models were nuclear factor-kappa beta (NF-&kappa, B) activity and vascular endothelial growth factor receptor-2 (VEGFR-2) promoter activity during the healing process. A 2-mm critical-size femoral fracture was performed in transgenic NF-&kappa, B- and VEGFR-2-luciferase reporter mice. The fracture was filled with a 3D-printed &beta, TCP scaffold with or without Sr. A bioluminescence in-vivo imaging system was used to sequentially investigate NF-&kappa, B and VEGFR-2 expression for two months. After sacrifice, soft and osseous tissue formation in the fracture sites was histologically examined. NF-&kappa, B activity increased in the &beta, TCP + Sr group in the latter stage (day 40&ndash, 60). VEGFR-2 activity increased in the + Sr group from days 0&ndash, 15 but decreased and showed significantly less activity than the &beta, TCP and non-scaffold groups from days 40&ndash, 60. The new bone formation and soft tissue formation in the + Sr group were significantly higher than in the &beta, TCP group, whereas the percentage of osseous tissue formation in the &beta, TCP group was significantly higher than in the &beta, TCP + Sr group. We analyzed longitudinal VEGFR-2 promoter activity and NF-&kappa, B activity profiles, as respective agents of angiogenesis and inflammation, during LBD healing. The extended inflammation phase and eventually more rapid resorption of scaffold caused by the addition of strontium accelerates temporary bridging of the fracture gaps. This finding has the potential to inform an improved treatment strategy for patients who suffer from osteoporosis.

We present the first nanoscale imaging of femtosecond phenomena using high-harmonic radiation that combines these extreme scales. Capturing the ultrafast spin dynamics in real-space reveals simultaneously local demagnetization and nonlocal phenomena at the domain boundaries.

Exchange-coupled structures consisting of ferromagnetic and ferrimagnetic layers become technologically more and more important. We show experimentally the occurrence of completely reversible, hysteresis-free minor loops of [Co(0.2 nm)/Ni(0.4 nm)/Pt(0.6 nm)]$_N$ multilayers exchange-coupled to a 20 nm thick ferrimagnetic Tb$_{28}$Co$_{14}$Fe$_{58}$ layer, acting as hard magnetic pinning layer. Furthermore, we present detailed theoretical investigations by means of micromagnetic simulations and most important a purely analytical derivation for the condition of the occurrence of full reversibility in magnetization reversal. Hysteresis-free loops always occur if a domain wall is formed during the reversal of the ferromagnetic layer and generates an intrinsic hard-axis bias field that overcomes the magnetic anisotropy field of the ferromagnetic layer. The derived condition further reveals that the magnetic anisotropy and the bulk exchange of both layers, as well as the exchange coupling strength and the thickness of the ferromagnetic layer play an important role for its reversibility., Comment: 9 pages, 7 figures

Giant exchange bias shifts of several Tesla have been reported in ferrimagnetic/ferromagnetic bilayer systems, which could be highly beneficial for contemporary high energy density permanent magnets and spintronic devices. However, the lack of microscopic studies of the reversal owing to the difficulty of measuring few nanometer-wide magnetic structures in high fields precludes the assessment of the lateral size of the inhomogeneity in relation to the intended application. In this study, the magnetic reversal process of nanoscale exchange-coupled bilayer systems, consisting of a ferrimagnetic TbFeCo alloy layer and a ferromagnetic [Co/Ni/Pt]N multilayer, was investigated. In particular, minor loop measurements, probing solely on the reversal characteristics of the softer ferromagnetic layer, reveal two distinct reversal mechanisms, which depend critically on the thickness of the ferromagnetic layer. For thick layers, irreversible switching of the macroscopic minor loop is observed. The underlying microscopic origin of this reversal process was studied in detail by high-resolution magnetic force microscopy, showing that the reversal is triggered by in-plane domain walls propagating through the ferromagnetic layer. In contrast, thin ferromagnetic layers show a hysteresis-free reversal, which is nucleation-dominated due to grain-to-grain variations in magnetic anisotropy of the Co/Ni/Pt multilayer and an inhomogeneous exchange coupling with the magnetically hard TbFeCo layer, as confirmed by micromagnetic simulations.

We study the interaction of surface acoustic waves with spin waves in ultra-thin CoFeB/Pt bilayers. Due to the interfacial Dzyaloshinskii-Moriya interaction (DMI), the spin wave dispersion is non-degenerate for oppositely propagating spin waves in CoFeB/Pt. In combination with the additional nonreciprocity of the magnetoacoustic coupling itself, highly nonreciprocal acoustic wave transmission through the magnetic film is observed. We systematically characterize the magnetoacoustic wave propagation in a thickness series of CoFeB($d$)/Pt samples as a function of magnetic field magnitude and direction, and at frequencies up to 7 GHz. We quantitatively model our results to extract the strength of the DMI and magnetoacoustic driving fields., Comment: 6 pages, 4 figures

In this study, the influence of Pd and Pt insertion layers in Co/Ni multilayers (MLs) on their magnetic properties, e.g., magnetic anisotropies, saturation magnetization, coercivity, magnetic domain size, and Curie temperature, is investigated. We compare three series of [Co/Ni/X] N ML systems ( X = Pd, Pt, no insertion layer), varying the individual Co layer thickness as well as the repetition number N. All three systems behave very similarly for the different Co layer thicknesses. For all systems, a maximum effective magnetic anisotropy was achieved for MLs with a Co layer thickness between 0.15 and 0.25 nm. The transition from an out-of-plane to an in-plane system occurs at about 0.4 nm of Co. While [Co(0.2 nm)/Ni(0.4 nm)] N MLs change their preferred easy magnetization axis from out-of-plane to in-plane after six bilayer repetitions, insertion of Pd and Pt results in an extension of this transition beyond 15 repetitions. The maximum effective magnetic anisotropy was more than doubled from 105 kJ/m 3 for [Co/Ni] 3 to 275 and 186 kJ/m 3 for Pt and Pd, respectively. Furthermore, the insertion layers strongly reduce the initial saturation magnetization of 1100 kA/m of Co/Ni MLs and lower the Curie temperature from 720 to around 500 K.

Skyrmions and antiskyrmions are topologically protected spin structures with opposite vorticities. Particularly in coexisting phases, these two types of magnetic quasi-particles may show fascinating physics and potential for spintronic devices. While skyrmions are observed in a wide range of materials, until now antiskyrmions were exclusive to materials with D2d symmetry. In this work, we show first and second-order antiskyrmions stabilized by magnetic dipole–dipole interaction in Fe/Gd-based multilayers. We modify the magnetic properties of the multilayers by Ir insertion layers. Using Lorentz transmission electron microscopy imaging, we observe coexisting antiskyrmions, Bloch skyrmions, and type-2 bubbles and determine the range of material properties and magnetic fields where the different spin objects form and dissipate. We perform micromagnetic simulations to obtain more insight into the studied system and conclude that the reduction of saturation magnetization and uniaxial magnetic anisotropy leads to the existence of this zoo of different spin objects and that they are primarily stabilized by dipolar interaction. Antiskyrmions are topological spin textures with negative vorticity. Like skyrmions, they have considerable technological promise, but have only been stabilised in Heusler compounds. Here, Heigl et al. succeed in stabilising first and second order antiskyrmions in a new class of materials.

In the emerging IoT ecosystem in which the internetworking will reach a totally new dimension the crucial role of efficient security solutions for embedded devices will be without controversy. Typically IoT-enabled devices are equipped with integrated circuits, such as ASICs or FPGAs to achieve highly specific tasks. Such devices must have cryptographic layers implemented and must be able to access cryptographic functions for encrypting/decrypting and signing/verifying data using various algorithms and generate true random numbers, random primes, and cryptographic keys. In the context of a limited amount of resources that typical IoT devices will exhibit, due to energy efficiency requirements, efficient hardware structures in terms of time, area, and power consumption must be deployed. In this paper, we describe a scalable word-based multivendor-capable cryptographic core, being able to perform arithmetic operations in prime and binary extension finite fields based on Montgomery Arithmetic. The functional range comprises the calculation of modular additions and subtractions, the determination of the Montgomery Parameters, and the execution of Montgomery Multiplications and Montgomery Exponentiations. A prototype implementation of the adaptable arithmetic core is detailed. Furthermore, the decomposition of cryptographic algorithms to be used together with the proposed core is stated and a performance analysis is given.

Future-oriented networking infrastructures are characterized by highly dynamic Streaming Data (SD) whose volume, speed and number of dimensions increased significantly over the past couple of years, energized by trends such as Software-Defined Networking or Artificial Intelligence. As an essential core component of network security, Intrusion Detection Systems (IDS) help to uncover malicious activity. In particular, consecutively applied alert correlation methods can aid in mining attack patterns based on the alerts generated by IDS. However, most of the existing methods lack the functionality to deal with SD data affected by the phenomenon called concept drift and are mainly designed to operate on the output from signature-based IDS. Although unsupervised Outlier Detection (OD) methods have the ability to detect yet unknown attacks, most of the alert correlation methods cannot handle the outcome of such anomaly-based IDS. In this paper, we introduce a novel framework called Streaming Outlier Analysis and Attack Pattern Recognition, denoted as SOAAPR, which is able to process the output of various online unsupervised OD methods in a streaming fashion to extract information about novel attack patterns. Three different privacy-preserving, fingerprint-like signatures are computed from the clustered set of correlated alerts by SOAAPR, which characterizes and represents the potential attack scenarios with respect to their communication relations, their manifestation in the data's features and their temporal behavior. Beyond the recognition of known attacks, comparing derived signatures, they can be leveraged to find similarities between yet unknown and novel attack patterns. The evaluation, which is split into two parts, takes advantage of attack scenarios from the widely-used and popular CICIDS2017 and CSE‐CIC‐IDS2018 datasets. Firstly, the streaming alert correlation capability is evaluated on CICIDS2017 and compared to a state-of-the-art offline algorithm, called Graph-based Alert Correlation (GAC), which has the potential to deal with the outcome of anomaly-based IDS. Secondly, the three types of signatures are computed from attack scenarios in the datasets and compared to each other. The discussion of results, on the one hand, shows that SOAAPR can compete with GAC in terms of alert correlation capability leveraging four different metrics and outperforms it significantly in terms of processing time by an average factor of 70 in 11 attack scenarios. On the other hand, in most cases, all three types of signatures seem to reliably characterize attack scenarios such that similar ones are grouped together, with up to 99.05% similarity between the FTP and SSH Patator attack.intrusion detection, alert analysis, alert correlation, outlier detection, attack scenario, streaming data, network security

In this study, we have investigated amorphous 20-nm-thick Tb/Fe80Co20 multilayer samples with different individual layer thicknesses and their corresponding alloy counterpart. In particular, the structural and magnetic properties were analyzed upon post-annealing. Up to a certain critical thickness of the individual layers in the multilayer, no significant difference between the multilayers and the alloy is observed in their as-deposited states, which indicates the importance of interfacial intermixing. With a further increase in thicknesses of the individual layers, regions with significant larger Tb content emerge, resulting in a reduced effective Tb moment. The loss in perpendicular magnetic anisotropy upon annealing seems to be delayed for multilayers with thin individual layers compared to the alloy sample. We contribute this behavior to the underlying anisotropic short-range order enforced by the multilayer structure, which hinders the structural relaxation process. At higher temperatures, the multilayers strongly intermix and Fe and Co diffuse through the capping layer. This process leads to a strong enhancement of the saturation magnetization at a certain annealing temperature, due to the formation of separated FeCo and Tb-rich TbFeCo alloy layers, until the sample gets oxidized.

V posledních letech se detekce anomálií v počítačových sítích reálného světa stala stále obtížnější kvůli trvalému nárůstu vysoce objemných, rychlých a dimenzionálních průběžně přicházejících dat, pro která nejsou k dispozici obecně uznané a pravdivé informace o anomalitě. Účinná detekční schémata pro vestavěná síťová zařízení musejí být rychlá a paměťově nenáročná a musejí být schopna se potýkat se změnami konceptu, když se vyskytnou. Pro online detekci anomálií bez učitele byly navrženy různé přístupy, které za těchto podmínek spolehlivě identifikují zlovolnou aktivitu. V tomto příspěvku představujeme nový aplikační rámec nazvaný PCB-iForest, jenž je obecně schopen využít jakoukoliv online metodu pro detekci extrémních hodnot založenou na množinách dat tak, aby fungovala na průběžně přicházejících datech. Pečlivě zformulované požadavky srovnáváme s nejpopulárnějšími stávajícími uznávanými online metodami se zvláštním zřetelem na varianty široce přijímaného algoritmu izolovaného lesa a ukazujeme při tom, že dosud neexistovalo flexibilní a výkonné řešení, které přináší až algoritmus PCB-iForest. Proto do tohoto algoritmu integrujeme dvě varianty – zlepšení izolovaného lesa, jež se nazývá rozšířený izolovaný les, a klasickou variantu izolovaného lesa vybavenou funkcionalitou k ohodnocení vlastností podle jejich přispění k anomalitě datového vzorku. Provádíme rozsáhlé experimenty na 23 multidisciplinárních datových sadách týkajících se bezpečnostní problematiky reálného světa za účelem podrobného srovnání naší implementace s již existujícími metodami. Diskuse našich výsledků zahrnující indikátory AUC, F1 a průměrnou dobu zpracování ukazuje, že PCB-iForest jasně překonává už zavedené konkurenční metody v 61 % případů a dokonce dosahuje ještě slibnějších výsledků co do vyváženosti mezi výpočetními náklady na klasifikaci a její úspěšností. In recent years, detecting anomalies in real-world computer networks has become a more and more challenging task due to the steady increase of high-volume, high-speed and high-dimensional streaming data, for which ground truth information is not available. Efficient detection schemes applied on networked embedded devices need to be fast and memory-constrained and must be capable of dealing with concept drifts when they occur. Different approaches for unsupervised online outlier detection have been designed to deal with these circumstances in order to reliably detect malicious activity. In this paper, we introduce a novel framework called PCB-iForest, which generalized, is able to incorporate any ensemble-based online OD method to function on streaming data. Carefully engineered requirements are compared to the most popular state-of-the-art online methods with an in-depth focus on variants based on the widely accepted isolation forest algorithm, thereby highlighting the lack of a flexible and efficient solution which is satisfied by PCB-iForest. Therefore, we integrate two variants into PCB-iForest—an isolation forest improvement called extended isolation forest and a classic isolation forest variant equipped with the functionality to score features according to their contributions to a sample’s anomalousness. Extensive experiments were performed on 23 different multi-disciplinary and security-related real-world datasets in order to comprehensively evaluate the performance of our implementation compared with off-the-shelf methods. The discussion of results, including AUC, F1 score and averaged execution time metric, shows that PCB-iForest clearly outperformed the state-of-the-art competitors in 61% of cases and even achieved more promising results in terms of the tradeoff between classification and computational costs.

Magnetic bistability between vortex and single domain states in nanostructures are of great interest from both fundamental and technological perspectives. In soft magnetic nanostructures, the transition from a uniform collinear magnetic state to a vortex state (or vice versa) induced by a magnetic field involves an energy barrier. If the thermal energy is large enough for overcoming this energy barrier, magnetic bistability with a hysteresis-free switching occurs between the two magnetic states. In this work, we tune this energy barrier by tailoring the composition of FePd alloys, which were deposited onto self-assembled particle arrays forming magnetic vortex structures on top of the particles. The bifurcation temperature, where a hysteresis-free transition occurs, was extracted from the temperature dependence of the annihilation and nucleation field which increases almost linearly with Fe content of the magnetic alloy. This study provides insights into the magnetization reversal process associated with magnetic bistability, which allows adjusting the bifurcation temperature range by the material properties of the nanosystem.

Všudypřítomné propojování přístrojů ve všech sférách života je podporováno různými trendy, jako je např. Internet věcí. Slibné technologie, jež mohou být používány pro taková budoucí prostředí, pocházejí z bezdrátových senzorových sítí. Ty zajišťují konektivitu mezi distribuovanými, malými a jednoduchými senzorovými uzly a také senzorovými uzly a základními stanicemi za účelem monitorování fyzických a environmentálních podmínek jako např. vibrací, teploty nebo pohybu. Bezpečnost pohraje stále významnější úlohu v následujících desetiletích, v nichž se útočné strategie stanou více a více sofistikovanými. Současné kryptografické mechanismy budou v blízké budoucnosti čelit velké hrozbě ze strany kvantových počítačů a spolu se systémy pro detekci vniknutí jsou jen sotva aplikovatelné na senzory kvůli přílišným nárokům na zdroje. Proto v této práci navrhujeme odlehčený a zdrojově úsporný bezpečnostní koncept budoucnosti pro senzorické sítě, který ve fázi zpracování využívá pronikavého filtrovací mechanismu. Zvláštní pozornost při hodnocení tohoto konceptu je upřena na nový filtr založený na tzv. magických číslech, jenž zmírňuje určité druhy útoku typu Denial-of-Service (odepření služby) provedené na mikrokontrolérových deskách CC1350 LaunchPad ARM Cortex-M3. Operational direct current grids (ODCG) are one of the most important components of many power plants and substations, for example, hydroelectric power plants. They are designed for power supply of relay protection devices, signalization and automation, and for the power supply of important equipment, emergency lighting, drives of high-voltage switches, etc. The importance of this type of equipment leads to high-reliability demands of the ODCG. Quality of cable insulation of the ODCG is crucial. The research conducted in this field shows that both gradual and sudden short-term insulation resistance fluctuations depend on many factors. Among them are the mode of operation, network load, state of cable channels, and state of switching equipment. The results of five-year observations on insulation resistance of open distribution unit ODU-110/330 kV Dniester HPP-1, an distribution unit of DU-35 kV HPP-2 and a complete distribution unit CDU-330 kV of a pumping station in 2012-2017 are analyzed.

Kvůli efektivní ochraně komunikace v bezdrátových senzorických sítích (WSN), jež bude v blízké budoucnosti čelit mj. hrozbám pocházejícím od kvantových počítačů, je na tomto poli nezbytné prozkoumat použitelnost kvantově rezistentních mechanismů. Účelem tohoto článku je přinést přehled možných schémat použitelných v senzorických uzlech a porovnat energetickou spotřebu zvolených volně dostupných softwarových implementací mikrokontrolérovou deskou Texas Instruments CC1350 LaunchPad ARM® Cortex®-M3 vhodnou pro WSN. For an effective protection of the communication in Wireless Sensor Networks (WSN) facing e.g. threats by quantum computers in the near future, it is necessary to examine the applicability of quantum-resistant mechanisms in this field. It is the aim of this article to survey possible candidate schemes utilizable on sensor nodes and to compare the energy consumption of a selection of freely-available software implementations using a WSN-ready Texas Instruments CC1350 LaunchPad ARM® Cortex®-M3 microcontroller board.

Piezoelectric surface acoustic waves are employed to induce radio frequency spatiotemporal dynamics of photogenerated electrons and holes in the GaAs core of individual GaAs/AlGaAs core/shell semiconductor nanowires. Comparison of the time-dependent interband optical recombination to numerical simulations allow to determine the charge carrier transport mobilities of electrons, μe = 500–250+500 cm2/(V s), holes, μh = 50–30+50 cm2/(V s) and their ratio μe:μh = (20 ± 5):1. Our method probes carrier transport at low carrier density. Thus, the obtained values represent the native material limit of these nanowires, determined by their structural properties. We show that for near-pristine nanowires, individual twin defects do not significantly affect electrical transport, in strong contrast to polytypic nanowires. In the acoustoelectrically modulated emission, we observe unambiguous signatures of (i) hole localization within long wurtzite-rich segments and (ii) electrons in zinc blende regions being reflected at...

A class of artifacts manifesting as soft magnetic components are revealed from magnetometry measurements of rare earth-transition metal (TbFe) thin films prepared by magnetron sputtering. They are not inherent to TbFe, but are a direct result of the manner in which the substrates are mounted prior to sample fabrication, with a material deposited at the substrate sides giving rise to a significant magnetic moment. The authors find the same artifacts to also be present in rare earth-free [Co/Pt] multilayers. Trying to supress the appearance of this type of artifact has an influence on the coercivity and, in some cases, on the shape of the reversal curves. Care needs to be taken during fabrication to ensure reliable and reproducible samples so that sensitive magnetic parameters, such as coercivity and compensation points, can be extracted accurately and that data are not misinterpreted for even more complex systems. This type of artifact is not limited to samples prepared by sputtering but can extend to other conventional thin-film deposition methods.

The protection of internetworked systems by cryptographic techniques have crystallized as a fundamental aspect in establishing secure systems. Complementary, detection mechanisms for instance based on Intrusion Detection Systems has established itself as a fundamental part in holistic security eco-systems in the previous years. However, the interpretation of and reaction on detected incidents is still a challenging task. In this paper an incident handling environment with relevant components and exemplary functionality is proposed that involves the processes from the detection of incidents over their analysis to the execution of appropriate reactions. An evaluation of a selection of implemented interacting components using technology such as OpenFlow or Snort generally proofs the concept.

We demonstrate high-resolution magneto-optical imaging using circularly-polarized high-harmonic radiation. We quantitatively map amplitude and phase of the x-ray magnetic circular dichroism at the Co M-edge using coherent diffractive imaging.

The quality of TRNG designs mainly depends on the grade of the noise source from which the entropy will be harvested to extract randomness. Especially for purely digital noise sources suitable for FPGA implementations the use of Ring Oscillators is suggested in many scientific publications. Standard Ring Oscillator based noise sources however have earned some criticism regarding the amount of entropy generated. On this account different enhancements have been proposed, with Fibonacci Ring Oscillators (FIROs) and Galois Ring Oscillators (GAROs) being prominent examples, which under some circumstances are able to sustain a chaotic oscillation suitable for entropy extraction. This paper deals with the assessment of fully constrained FIRO and GARO noise source designs for a specific target FPGA. Due to the restrictive placement of ring elements the assessment yielded new criteria for choosing proper FIRO/GARO feedback configurations and an enhanced sampling method for entropy extraction has been derived.

Today's trend of an increasing number of networked embedded devices pervades many areas. Ranging from home automation, industrial or automotive applications with a large number of different protocols, low resources and often high demands on real-time make it difficult to secure the communication of such systems. A concept of an uncoupled MAC which is able to ensure the authenticity and integrity of communication flows between two network parties can be used. This is in particular of advance for outdated legacy components still participating in the network. In this paper a assessment simulation model of the mechanism behind this technology is described. It outlines the probability of detecting an attack depending on the message authentication overhead. The model considers all control variables and performs measurements based on random data traffic. The results of the statistical analysis state that a high attack detection rate can be obtained even with a small communication overhead.

We probe and control the optical properties of emission centers forming in radial het- erostructure GaAs-Al0.3Ga0.7As nanowires and show that these emitters, located in Al0.3Ga0.7As layers, can exhibit quantum-dot like characteristics. We employ a radio frequency surface acoustic wave to dynamically control their emission energy and occupancy state on a nanosec- ond timescale. In the spectral oscillations we identify unambiguous signatures arising from both the mechanical and electrical component of the surface acoustic wave. In addition, differ- ent emission lines of a single quantum dot exhibit pronounced anti-correlated intensity oscilla- tions during the acoustic cycle. These arise from a dynamically triggered carrier extraction out of the quantum dot to a continuum in the radial heterostructure. Using finite element modeling and Wentzel-Kramers-Brillouin theory we identify quantum tunneling as the underlying mech- anism. These simulation results quantitatively reproduce the observed switching and show that in our systems these quantum dots are spatially separated from the continuum by > 10.5 nm., This document is the unedited Author's version of a Submitted Work that was subsequently accepted for publication in Nano Letters, copyright \c{copyright} American Chemical Society after peer review. To access the final edited and published work see http://pubs.acs.org/doi/abs/10.1021/nl4040434

With Ethernet as an ubiquitous technology also emerging in industrial networks, security is becoming one of the most important aspects. Whereas IT-networks together with their security features in the office domain are subject of a dynamic change, networks in the industrial environment have a long operational time and therefore are more vulnerable to unauthorized access due to outdated hard- and software components. IT-threats such as Stuxnet are targeted to these areas and in the case of a failure of, e.g., a critical infrastructure this can directly harm the public security. Hence, in this paper a concept of an embedded plug-in device is proposed that secures the authentication and integrity of communication flows between two communicating network parties. A key focus of the development is the message authentication mechanism without neglecting the safety aspect imperative for industrial networks.

The excitonic occupancy state of a single, nanowire-based, heterostructure quantum dot is dynamically programmed by a surface acoustic wave. The quantum dot is formed by an interface or thickness fluctuation of a GaAs QW embedded in a AlGaAs shell of a GaAs-AlGaAs core-shell nanowire. As we tune the time at which carriers are photogenerated during the acoustic cycle, we find pronounced intensity oscillations of neutral and negatively charged excitons. At high acoustic power levels these oscillations become anticorrelated which enables direct acoustic programming of the dot's charge configuration, emission intensity and emission wavelength. Numerical simulations confirm that the observed modulations arise from acoustically controlled modulations of the electron and electron-hole-pair concentrations at the position of the quantum dot., Revised manuscript, 12 pages, submitted to J. Phys. D as a contribution in a Special Issue on Nanowires

We demonstrate nanoscale magnetic imaging with sub-20 nm spatial resolution using high-harmonic radiation. This first demonstration will allow for comprehensive studies of ultrafast spin dynamics with nanometer spatial and femtosecond temporal resolution using a lab-scale source.

Compact radiation sources based on high harmonic generation (HHG) enable access to ultrafast phenomena with femtosecond and even attosecond temporal resolution [1]. While both ultrafast spectroscopy and real-space imaging with high-harmonic radiation are rather established techniques [2,3], the combination of nano-imaging with femtosecond temporal resolution has remained challenging. Here, we demonstrate the first imaging of femtosecond dynamics using ultrafast high-harmonic generation microscopy, harnessing both the femtosecond duration and the nanometric wavelength of HHG. We quantitatively map demagnetization dynamics in self-organized networks of nanoscale magnetic domains upon excitation with femtosecond laser pulses [see Fig. 1(a)]. In the experiment, scattering patterns from the sample are recorded as a function of pump-probe delay using the 38th harmonic order (wavelength 21 nm) with both left- and right-handed circular polarization [4]. Each diffraction pattern is reconstructed by holographically-enhanced coherent diffractive imaging [3]. The ratio of the reconstructed exit wave amplitudes forms a dichroic image of the magnetic pattern [c.f. dichroic phase maps in Fig. 1(c)]. An overall measure of the magnetization in the worm-like domain pattern is obtained from the standard deviation of the magnetization across all image pixels, which is displayed in Fig. 1(b) as a function of delay. The temporal trace exhibits the well-known features of ultrafast demagnetization curve, with a rapid drop within a few hundreds of femtoseconds and a subsequent partial re-magnetization on a picosecond time scale [5]. The images in Fig. 1 represent snap-shots from a magnetization-dynamics movie with 30 nm spatial- and 50 fs temporal resolution. Generally, for magnetic dichroic imaging using HHG we demonstrate a spatial resolution of 19 nm at the illumination wavelength of 21 nm.