120 research outputs found
FedKNOW: Federated Continual Learning with Signature Task Knowledge Integration at Edge
No full textDeep Neural Networks (DNNs) have been ubiquitously adopted in internet of things and are becoming an integral of our daily life. When tackling the evolving learning tasks in real world, such as classifying different types of objects, DNNs face the challenge to continually retrain themselves according to the tasks on different edge devices. Federated continual learning is a promising technique that offers partial solutions but yet to overcome the following difficulties: the significant accuracy loss due to the limited on-device processing, the negative knowledge transfer caused by the limited communication of non-IID data, and the limited scalability on the tasks and edge devices. In this paper, we propose FedKNOW, an accurate and scalable federated continual learning framework, via a novel concept of signature task knowledge. FedKNOW is a client side solution that continuously extracts and integrates the knowledge of signature tasks which are highly influenced by the current task. Each client of FedKNOW is composed of a knowledge extractor, a gradient restorer and, most importantly, a gradient integrator. Upon training for a new task, the gradient integrator ensures the prevention of catastrophic forgetting and mitigation of negative knowledge transfer by effectively combining signature tasks identified from the past local tasks and other clients' current tasks through the global model. We implement FedKNOW in PyTorch and extensively evaluate it against state-of-the-art techniques using popular federated continual learning benchmarks. Extensive evaluation results on heterogeneous edge devices show that FedKNOW improves model accuracy by 63.24% without increasing model training time, reduces communication cost by 34.28%, and achieves more improvements under difficult scenarios such as large numbers of tasks or clients, and training different complex networks. Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Data-Intensive System
Design of a Test Setup to Measure Magnetic Signature Reduction
No full textIn order to avoid detection by sea mines, the magnetic signature of merchant and naval vessels can be reduced by running a current through a set of on-board copper coils. This process is called degaussing. Studies have shown that the volume, weight and energy losses of a degaussing system can be reduced by replacing the copper coils with high temperature superconductive (HTS) coils. Moreover, since the technology and production of HTS has matured and the material is highly available, the use of HTS for degaussing coils is a serious option. As a preliminary study towards an HTS degaussing test setup, this paper presents the design of a table-top demonstration with copper degaussing coils. The goal of the demonstration is to measure the magnetic signature and the magnetic signature reduction of a cylindrical object. The design choices of the test setup and the measuring system are discussed. The magnetic signature of the table-top model is calculated as well as the optimal placement of the degaussing coils and the optimal degaussing currents. These results are compared with measurements of the magnetic flux density around the demonstrator.DC systems, Energy conversion & StorageTransport Engineering and Logistic
UAV visual signature suppression via adaptive materials
No full textVisual signature suppression (VSS) methods for several classes of aircraft from WWII on are examined and historically summarized. This study shows that for some classes of uninhabited aerial vehicles (UAVs), primary mission threats do not stem from infrared or radar signatures, but from the amount that an aircraft visually stands out against the sky. The paper shows that such visual mismatch can often jeopardize mission success and/or induce the destruction of the entire aircraft. A psycho-physioptical study was conducted to establish the definition and benchmarks of a Visual Cross Section (VCS) for airborne objects. This study was centered on combining the effects of size, shape, color and luminosity or effective illumance (EI) of a given aircraft to arrive at a VCS. A series of tests were conducted with a 6.6ft (2m) UAV which was fitted with optically adaptive electroluminescent sheets at altitudes of up to 1000 ft (300m). It was shown that with proper tailoring of the color and luminosity, the VCS of the aircraft dropped from more than 4,200cm2 to less than 1.8cm2 at 100m (the observed lower limit of the 20-20 human eye in this study). In laypersons terms this indicated that the UAV essentially “disappeared.” This study concludes with an assessment of the weight and volume impact of such a Visual Suppression System (VSS) on the UAV, showing that VCS levels on this class UAV can be suppressed to below 1.8cm2 for aircraft gross weight penalties of only 9.8%.Aerospace Science for Sustainable Engineering and TechnologyAerospace Engineerin
Phylogenomics of vertebrate serpins
No full textKumar A. Phylogenomics of vertebrate serpins. Bielefeld (Germany): Bielefeld University; 2010.The serpins constitute a superfamily of proteins that fold into a conserved tertiary structure and employ a sophisticated, irreversible suicide-mechanism of inhibition. More than 6000 serpins have been identified, occurring in all three forms of the life - the eukaryotes, the prokaryotes and the archea. Vertebrate serpins can be conveniently classified into six groups (V1 - V6), based on three independent biological features - gene organization, diagnostic amino acid sites and rare indels. In the present work, the phylogenetic relationships of serpins from Nematostella vectensis, Strongylocentrotus purpuratus, Ciona intestinalis, four fish species, frog, chicken and mammals were investigated, using gene architecture analyses and stringent criteria for identification of orthologs. With some deviations, all vertebrate serpin genes fit into one of the six exon/intron gene classes previously identified, dating the existence and maintenance of these gene organizations before or close to the divergence of fishes. Group V1 and V2 gene families underwent rapid adaptive radiation along the lineages leading to mammals as indicated by an up to nine-fold increased number of family members, accompanied by a rapid functional diversification. In contrast, gene groups V3 to V6 display a rather conservative evolution with little changes since the divergence of fishes and the other vertebrates. The orthology assessment indicates that all vertebrates are equipped with a subset of strongly conserved serpins with functions that can be clearly correlated with basic vertebrate-specific physiology.
None of serpin genes from C. intestinalis shares a common exon-intron architecture organisation with any of the vertebrate serpin gene classes, nor was it possible to identify orthologs of vertebrates. The lack of gene architecture similarity and the complete absence of orthology between urochordate and vertebrate serpins indicate that major changes with bursts of character acquisition must have occurred during evolution of serpins in the time interval separating urochordates from chordates, indicating massive intron gains or losses and events providing C and N-terminal sequence extensions characteristic for today's vertebrate serpins. Lancelets and sea urchin genomes, in contrast, share one orthologous serpin with vertebrates. Rare genomic characters are used to show that orthologs of neuroserpin, a prominent representative of vertebrate group V3 serpin genes, exist in early diverging deuterostomes and probably also in cnidarians, indicating that the origin of a mammalian serpin can be traced back far in the history of eumetazoans. A C-terminal address code assigning association with secretory pathway organelles is present in all neuroserpin orthologs, suggesting that supervision of cellular export/import routes by antiproteolytic serpins is an ancient trait.
Phylogenomic comparisons show that, after establishment of canonical exon-intron patterns in the serpin superfamily at the dawn of vertebrate evolution, multiple intron acquisition events have occurred during diversification of a lineage of actinopterygian fishes. The novel introns were acquired within a limited time interval (on an evolutionary timescale), and no such events were observed in other groups of vertebrates. Examination of the sequences flanking the intron insertion points revealed that the genetic requirements for acquisition of novel introns might be less stringent than previously suggested. Finally, we argue that genome compaction, a phenomenon associated with the fish lineage depicting preferential intron gain, might promote intron acquisition
Wind Turbine Generator Condition Monitoring via the Generator Control Loop
No full textThis thesis focuses on the development of condition monitoring techniques for application in wind turbines, particularly for offshore wind turbine driven doubly fed
induction generators. The work describes the significant development of a physical condition monitoring Test Rig and its MATLAB Simulink model to represent modern variable speed wind turbine and the innovation and application of the rotor side control signals for the generator fault detection. Work has been carried out to develop a physical condition monitoring Test Rig from open loop control, with a wound rotor induction generator, into closed loop control with a doubly fed induction generator. This included designing and building the rotor side converter, installing the back-to-back converter and other new instrumentation. Moreover, the MATLAB Simulink model of the Test Rig has been developed to represent the closed loop control, with more detailed information on the Rig components and instrumentation and has been validated against the physical system in the time and frequency domains. A fault detection technique has been proposed by the author based on frequency analysis of the rotor-side control signals, namely; d-rotor current error, q-rotor current error and q-rotor current, for wind turbine generator fault detection. This technique has been investigated for rotor electrical asymmetry on the physical Test Rig and its MATLAB Simulink model at different fixed and variable speed conditions. The sensitivity of the each proposed signal has been studied under different operating conditions. Measured and simulated results are presented, a comparison with the results from using stator current and total power has been addressed and the improvement in condition monitoring detection performance has been demonstrated in comparison with previous methods, looking at current, power and vibration analysis
Demonstration of degaussing by copper and HTS windings
No full textDue to their permeability, merchant and naval vessels distort Earth’s magnetic field which leaves a magnetic signature. These anomalies in the magnetic field may be detected by mines leaving the vessel exposed. To avoid detection by magnetic sensors, the vessels magnetic signature can be reduced in several ways. One of them is degaussing: a technique where a set of on-board coils produces a magnetic field to cancel the magnetic signature. Modelling studies have shown that the performance of a degaussing system can be improved by replacing the copper with high temperature superconductor (HTS) coils in terms of volume, weight and energy efficiency. This study aims to compare the degaussing functionality of copper and HTS windings. A table-top demonstration model is presented which is equipped with both copper and HTS degaussing coils. The demonstrator is prepared by removing the permanent magnetisation. The two degaussing topologies are compared in terms of functionality, efficiency, controllability and mutual inductances.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.DC systems, Energy conversion & StorageTransport Engineering and Logistic
The changing face of the Constantia Valley a temporal study of land use change in a heritage landscape
No full textIncludes bibliographical references.The study of land use change and urban morphology requires a multi-layered approach. Case studies are needed to gain an understanding of the local factors that are driving land use change and forming urban landscapes. This study will provide a temporal perspective on land use change in the Constantia Valley, a high income suburb on the outskirts of Cape Town. It will contextualise the efforts to conserve its heritage and, furthermore, attempt to explain the factors underlying the observed changes in the urban form. This study, through the use of Geographic Information System (GIS) mapping and a series of interviews, examines how and why the urban form of the Constantia Valley has changed. Finally, based on the findings the possible future urban form of Constantia will be considered
A New Look at Blockchain Leader Election: Simple, Efficient, Sustainable and Post-Quantum
No full textIn this work, we study the blockchain leader election problem. The purpose of such protocols is to elect a leader who decides on the next block to be appended to the blockchain, for each block proposal round. Solutions to this problem are vital for the security of blockchain systems. We introduce an efficient blockchain leader election method with security based solely on standard assumptions for cryptographic hash functions (rather than public-key cryptographic assumptions) and that does not involve a racing condition as in Proof-of-Work based approaches. Thanks to the former feature, our solution provides the highest confidence in security, even in the post-quantum era. A particularly scalable application of our solution is in the Proof-of-Stake setting, and we investigate our solution in the Algorand blockchain system. We believe our leader election approach can be easily adapted to a range of other blockchain settings. At the core of Algorand's leader election is a verifiable random function (VRF). Our approach is based on introducing a simpler primitive which still suffices for the blockchain leader election problem. In particular, we analyze the concrete requirements in an Algorand-like blockchain setting to accomplish leader election, which leads to the introduction of indexed VRF (iVRF). An iVRF satisfies modified uniqueness and pseudorandomness properties (versus a full-fledged VRF) that enable an efficient instantiation based on a hash function without requiring any complicated zero-knowledge proofs of correct PRF evaluation. We further extend iVRF to an authenticated iVRF with forward-security, which meets all the requirements to establish an Algorand-like consensus. Our solution is simple, flexible and incurs only a 32-byte additional overhead when combined with the current best solution to constructing a forward-secure signature (in the post-quantum setting). We implemented our (authenticated) iVRF proposal in C language on a standard computer and show that it significantly outperforms other quantum-safe VRF proposals in almost all metrics. Particularly, iVRF evaluation and verification can be executed in 0.02 ms, which is even faster than ECVRF used in Algorand.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Cyber Securit
Do proton pump inhibitors reduce the incidence of pharyngocutaneous fistulae following total laryngectomy?
No full textIncludes abstract.Includes bibliographical references.Pharyngocutaneous fistula is a common complication of total laryngectomy. We hypothesised that perioperative proton pump inhibitor (PPI) treatment could reduce the incidence of pharyngocutaneous fistulae. This prospective placebo-controlled double-blind randomised controlled trial compared PPI treatment (14 days enteral omeprazole) with a placebo in patients undergoing primary total laryngectomy. The incidence of pharyngocutaneous fistula was recorded
- …
