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The embedding of microwave devices is treated by applying the finite-difference method to three-dimensional shielded structures. A program package was developed to evaluate electromagnetic fields inside arbitrary transmission-line connecting structures and to compute the scattering matrix. The air bridge, the transition through a wall, and the bond wire are examined as interconnecting structures. Detailed results are given and discussed regarding the fundamental behavior of embedding.
A new yield function for lamellar gray cast iron materials is proposed. The new model is able to describe the results of recently performed microstructure-based finite-element computations that resolve the three dimensional yield surface of three different gray cast irons. The yield function requires only the yield stress in tension and compression of the respective material as model parameters. Furthermore, the algorithmic formulation of the new model is assessed for numerical robustness and efficiency.
In this study, a high-performance controller is proposed for single-phase grid-tied energy storage systems (ESSs). To control power factor and current harmonics and manage time-shifting of energy, the ESS is required to have low steady-state error and fast transient response. It is well known that fast controllers often lack the required steady-state accuracy and trade-off is inevitable. A hybrid control system is therefore presented that combines a simple yet fast proportional derivative controller with a repetitive controller which is a type of learning controller with small steady-state error, suitable for applications with periodic grid current harmonic waveforms. This results in an improved system with distortion-free, high power factor grid current. The proposed controller model is developed and design parameters are presented. The stability analysis for the proposed system is provided and the theoretical analysis is verified through stability, transient and steady-state simulations.
Exploiting Dissent: Towards Fuzzing-based Differential Black Box Testing of TLS Implementations
(2017)
The Transport Layer Security (TLS) protocol is one of the most widely used security protocols on the internet. Yet do implementations of TLS keep on suffering from bugs and security vulnerabilities. In large part is this due to the protocol's complexity which makes implementing and testing TLS notoriously difficult. In this paper, we present our work on using differential testing as effective means to detect issues in black-box implementations of the TLS handshake protocol. We introduce a novel fuzzing algorithm for generating large and diverse corpuses of mostly-valid TLS handshake messages. Stimulating TLS servers when expecting a ClientHello message, we find messages generated with our algorithm to induce more response discrepancies and to achieve a higher code coverage than those generated with American Fuzzy Lop, TLS-Attacker, or NEZHA. In particular, we apply our approach to OpenssL, BoringSSL, WolfSSL, mbedTLS, and MatrixSSL, and find several real implementation bugs; among them a serious vulnerability in MatrixSSL 3.8.4. Besides do our findings point to imprecision in the TLS specification. We see our approach as present in this paper as the first step towards fully interactive differential testing of black-box TLS protocol implementations. Our software tools are publicly available as open source projects.
The automatic classification of the modulation format of a detected signal is the intermediate step between signal detection and demodulation. If neither the transmitted data nor other signal parameters such as the frequency offset, phase offset and timing information are known, then automatic modulation classification (AMC) is a challenging task in radio monitoring systems. The approach of clustering algorithms is a new trend in AMC for digital modulations. A novel algorithm called `highest constellation pattern matching' is introduced to identify quadrature amplitude modulation and phase shift keying signals. The obtained simulation and measurement results outperform the existing algorithms for AMC based on clustering. Finally, it is shown that the proposed algorithm works in a real monitoring environment.
The instability of ultra-thin films of an electrolyte bordering a dielectric gas in an external tangential electric field is scrutinized. The solid wall is assumed to be either a conducting or charged dielectric surface. The problem has a steady one-dimensional solution. The theoretical results for a plug-like velocity profile are successfully compared with available experimental data. The linear stability of the steady-state flow is investigated analytically and numerically. Asymptotic long-wave expansion has a triple-zero singularity for a dielectric wall and a quadruple-zero singularity for a conducting wall, and four (for a conducting wall) or three (for a charged dielectric wall) different eigenfunctions. For infinitely small wave numbers, these eigenfunctions have a clear physical meaning: perturbations of the film thickness, of the surface charge, of the bulk conductivity, and of the bulk charge. The numerical analysis provides an important result: the appearance of a strong short-wave instability. At increasing Debye numbers, the short-wave instability region becomes isolated and eventually disappears. For infinitely large Weber numbers, the long-wave instability disappears, while the short-wave instability persists. The linear stability analysis is complemented by a nonlinear direct numerical simulation. The perturbations evolve into coherent structures; for a relatively small external electric field, these are large-amplitude surface solitary pulses, while for a sufficiently strong electric field, these are short-wave inner coherent structures, which do not disturb the surface.
A wide range catalyst screening with noble metal and oxide catalysts for a metal–air battery with an aqueous alkaline electrolyte was carried out. Suitable catalysts reduce overpotentials during the charge and discharge process, and therefore improve the round-trip efficiency of the battery. In this case, the electrodes will be used as optimized cathodes for a future lithium–air battery with an aqueous alkaline electrolyte. Oxide catalysts were synthesized via atmospheric plasma spraying. The screening showed that IrO2, RuO2, La0.6Ca0.4Co3, Mn3O4, and Co3O4 are promising bi-functional catalysts. Considering the high price for the noble metal catalysts further investigations of the oxide catalysts were carried out to analyze their electrochemical behavior at varied temperatures, molarities, and in case of La1−x Ca x CoO3 a varying calcium content. Additionally all catalysts were tested in a longterm test to proof cyclability at varied molarities. Further investigations showed that Co3O4 seems to be the most promising bi-functional catalyst of the tested oxide catalysts. Furthermore, it was shown that a calcium content of x = 0.4 in LCCO has the best performance.
Private households constitute a considerable share of Europe's electricity consumption. The current electricity distribution system treats them as effectively passive individual units. In the future, however, users of the electricity grid will be involved more actively in the grid operation and can become part of intelligent networked collaborations. They can then contribute the demand and supply flexibility that they dispose of and, as a result, help to better integrate renewable energy in-feed into the distribution grids.
High-precision signal processing algorithm to evaluate SAW properties as a function of temperature
(2013)
This paper presents a signal processing algorithm which accurately evaluates the SAW properties of a substrate as functions of temperature. The investigated acoustic properties are group velocity, phase velocity, propagation loss, and coupling coefficient. With several measurements carried out at different temperatures, we obtain the temperature dependency of the SAW properties. The analysis algorithm starts by reading the transfer functions of short and long delay lines. The analysis algorithm determines the center frequency of the delay lines and obtains the delay time difference between the short and long delay lines. The extracted parameters are then used to calculate the acoustic properties of the SAW material. To validate the algorithm, its accuracy is studied by determining the error in the calculating delay time difference, center frequency, and group velocity.