458 research outputs found
Correction: Ntakolia et al. An Explainable Machine Learning Approach for COVID-19’s Impact on Mood States of Children and Adolescents during the First Lockdown in Greece. Healthcare 2022, 10, 149
No full textExclusion of an Author Argyris Stringaris was initially included as an author in the original publication [1]. However, due to his personal decision, we have excluded him from the authors and we added his contribution to the acknowledgments section. The corrected Author Contributions and Acknowledgments are shown below. Author Contributions: Conceptualization, C.N.; methodology, C.N.; software, C.N.; validation, C.N.; formal analysis, C.N., I.R., I.G., A.S. and E.L.; data curation, C.N., D.P., K.M., I.G., K.K., A.S., E.T., A.G., K.L., I.K., N.S. and G.O.; writing—original draft prepara-tion, C.N., D.P., I.R., A.S., E.L. and M.C.-T.; writing—review and editing, C.N., I.R., I.G. and M.C.-T.; visualization, C.N.; supervision, E.L.; project administration, E.L. All authors have read and agreed to the published version of the manuscript. © 2022 by the authors. Licensee MDPI, Basel, Switzerland
Ultra Linear Low-loss Varactors & Circuits for Adaptive RF Systems
No full textWith the evolution of wireless communication, varactors can play an important role in enabling adaptive transceivers as well as phase-diversity systems. This thesis presents various varactor diode-based circuit topologies that facilitate RF adaptivity. The proposed varactor configurations can act as variable capacitors with high tuning range, low losses and ultra-low distortion, while being continuously tunable and facilitating fast modulation. Making use of these special components, we dealt with various RF applications that can benefit from their unique features, like power and impedance control in the mobile systems and multiple-standard modulators for transceivers and phase diversity systems. Chapter 1 provides an overview of challenges associated with the evolution of wireless communication. Through several case studies, it has been addressed how linear variable reactors (varactors) can enable RF reconfigurability for future telecommunication systems. The challenges on varactors for these applications are brought out, which suggests an urgent need for high-performance varactors. This chapter ends with a descriptive and flow-graph-like outline of the thesis. Chapter 2 presents an overview of the state-of-the-art tunable elements such as BST varactors, MEMS based switches and varactors, and currently available semiconductor switches and varactors. Their advantages and drawbacks are extensively discussed. These surveys clarify the motivation and goal of this thesis, and can at the same time be used as a reference to place this research with respect to the existing literature. To overcome the limitations of currently available tunable elements, Chapter 3 deals with the theory of two novel extremely linear varactor diode configurations with complementary linearity properties in a single varactor diode technology. Both varactor configurations use anti-series varactor diode configurations, where the diodes share the same exponential C(VR) depletion capacitance relation. However, the proposed structures differ in their harmonic terminations and varactor area ratios, resulting in a fundamentally different linearity behavior versus tone spacing. It is this feature that makes it possible to address different requirements of transmit and receive chains in one single technology. In Chapter 4, all varactor configurations, aiming for the cancellation of third-order intermodulation distortion, are summarized and their performance are compared. It is shown that the unique feature of the narrow tone-spacing varactor stack, compared to other “infinite” impedance center-tapped varactor stacks and MEMS varactors, is its high modulation frequency for operation and high linearity for signals with low tone spacing, making it perfectly suitable for many dynamic RF modulation applications. The wide tone-spacing varactor stack, which can be implemented in the same process technology as the narrow tone-spacing varactor stack, offers a complementary linearity behavior in terms of tone spacing and it can be regarded as a bonus, provided that the use of the narrow tone-spacing varactor stack is compulsory. In addition, their exponential C(VR) relationship generally yields larger tuning range compared to the uniformly doped varactors, i.e., the distortion-free varactor stack. When the multi-stack topology is used to further improve the IM5 dominated linearity and power handling capability, it turns out that this stacking yields a linearity improvement that is the double of what is generally found for IM3 dominated devices. The system-level responses of the different varactor configurations are investigated under different bandwidth or data-rate conditions. It reveals that the narrow tone-spacing varactor stack is suitable for both moderate and high data-rate applications, while varactor configurations with linearity limitations at low tone spacings, like the distortion-free varactor stack, may raise some in-band distortion when the bandwidth under consideration is relatively small. Chapter 5 discusses the technology implementation issues and provides the experimental verification of the proposed varactor configurations. The measurement results provide the experimental evidence for the predicted IM3 cancellation, as well as, for the complementary linearity behavior of the narrow tone-spacing varactor stack and wide tone-spacing varactor stack. Their usability in practical circuit conditions was demonstrated through source-pull simulations and measurements, illustrating that high linearity can be maintained in all cases. The multi-stack topology is used to further reduce the IM5 dominated nonlinearity of the narrow tone-spacing varactor stack, yielding a record high linearity for continuously tunable capacitances. Using the ability to adjust the C-VR relationship through the doping profile, the desired capacitance control range and related control voltage are achieved for various practical applications. In particular, the measured data of Skyworks’ pre-production GaAs varactors represent the current state-of-the-art in tuning range, linearity and quality factor among all existing continuously tunable elements. As two application examples of the novel varactors, the adaptive matching networks for mobile handsets are demonstrated in Chapter 6, while a phase shifter and amplitude modulator are given in Chapter 7. The demonstrated adaptive matching networks in Chapter 6 are focused on the efficiency enhancement of the power amplifier in the presence of antenna mismatch. Making use of a varactor-based approach, the resulting networks are capable of dynamically correcting the antenna mismatch with the VSWR of 10 over the whole Smith-chart. For all these conditions, an optimum loading for a power level between 0.5 W and 1 W is offered to the power amplifier stage along with a relatively high operating power gain. The proposed “whole Smith-chart” solution will ease the design of the RF frontend and antennas, yielding a significant reduction in the time-to-market of mobile phones. As another application example, given in Chapter 7, ultra linear low-loss varactors are applied for the implementation of amplitude and phase modulators, which can be used in phase diversity systems. The designed structures allow rapid amplitude and phase modulation with a very low distortion. These components can not only improve the performance of existing RF systems, like phased-array antennas and active load-pull system, but also facilitate other new circuit implementations or RF applications. As a demonstration, a novel polar modulator is proposed that can considerably simplify the structure of the traditional transmitter architecture, while being capable of generating the complex signals, which are typically in use in wireless communication systems. Chapter 8 presents the conclusions and recommendations of this research. The most important conclusion is that the linearization techniques proposed in this thesis has enabled the implementation of ultra linear low-loss varactors. Making use of these varactors, various adaptive circuits can be designed for adaptive RF systems.Microelectronics & Computer EngineeringElectrical Engineering, Mathematics and Computer Scienc
Technical improvement of arthroscopic techniques
No full textMechanical Maritime and Materials Engineerin
Finding cancer genes in copy number data and insertional mutagenesis data
No full textCancer is a genetic disease. Step-wise alteration of genes that have a normal function in the cell can lead to the transformation of a healthy cell into a malignant cancer cell. Cancer genes provide several traits to the cell that allow it to become malignant. These traits have been researched for many years, and currently one knows quite well what has to change in a normal cell before a tumor can be formed. For example, cells must divide continuously, escape the immune system and cause the growth of new blood vessels among others. There are many genes that can cause these processes when deregulated, and each individual tumor alters a different combination of genes to acquire its tumorigenic traits. Knowing which combination of mutations was sustained by a tumor is important as this might make the tumor susceptible or resistant to certain treatments. There are many ways in which cancer genes get mutated. This thesis studies two ways in which cancer genes are mutated. The first way of mutation comes from gains and losses of gene DNA called DNA copy number alterations (CNAs). These alterations occur due to the fact that tumors generally lose their ability to correctly repair damage to their DNA. CNAs can alter the expression of cancer genes and thereby cause cancer. Not only cancer-related genes will be affected by CNAs, also non-related DNA can be damaged. The challenge is to separate the truly oncogenic CNAs from the non-oncogenic passenger CNAs, as these oncogenic CNAs point to novel cancer genes that can be new drug targets. This thesis introduces two methods of finding cancer genes by examining DNA copy number alterations. Multiple comparable tumor samples are used to detect regions in the DNA that are altered significantly more often than other regions, indicating that they are more important for tumor development and therefore probably causative. Analogously, a novel method is introduced to find pairwise regions in the DNA that are preferentially lost or gained together (co-occurring) or preferentially not together (mutually exclusive). It is shown that co-occurring CNAs primarily target genes that are highly similar in function. A detailed analysis of a group of three mutually exclusive CNAs made it possible to associate a novel function to a known cancer gene. The second source of mutations concerns insertions of viral or transposon DNA. These agents insert their DNA in the host genome, which can cause activation or inactivation of host genes. Occasionally they can perturb genes that allow the cell to acquire cancer-related traits. In the end these insertions will cause a tumor. By carefully examining the tumor DNA one is able to reconstruct which genes caused the cancer. Of course, not all insertions were instrumental in the development of the cancer, so also in this case the passenger events and truly causal events have to be separated. This thesis used a novel approach called Shear-Splink that allows determination of the relative number of integrations in a single tumor. Each tumor will present a variety of insertions, each with its own abundance. By examining this abundance it is possible to distinguish between insertions that happened early in tumor development (and are therefore highly abundant) and insertions that are simple passengers or only essential for a small number of cells in the tumor (who will be lowly abundant). In this thesis this has been applied to a study of mouse mammary tumor virus (MMTV), a retrovirus that causes breast cancer in mice through insertion of its DNA in the mouse genome. Results show that by examining the insertion abundance a model through which the tumor has developed can be recovered. Overall this thesis contributes to the analysis of tumor-causing events and especially to the determination of which combination of events is necessary to cause a tumor.Pattern Recognition and BioinformaticsElectrical Engineering, Mathematics and Computer Scienc
Figure 13 from: Seregin AP (2021) Contribution to the "Atlas of the Russian Flora": Twelve local floras of European Russia. Biodiversity Data Journal 9: e73013. https://doi.org/10.3897/BDJ.9.e73013
No full textFigure 13 Typical plant communities of the Patakino local flora (Vladimir Oblast, Russia): broadleaved forest (Querco-Fagetea) dominated by Pteridium pinetorum C.N. Page & R.R. Mill. Photo by the author (2013)
Localization microscopy of constrained fluorescent molecules: Pushing towards Ångström-scale resolution through cryogenics
No full textLocalization microscopy has circumvented the diffraction limit by sequentially imaging individual light emitting molecules at a time. The position of these individual molecules can be determined and a super-resolution reconstruction is made with improved resolution. Normally freely rotating emitters are used such that the point spread function (PSF) is rotationally symmetric and only minor errors in the localization process are made by approximating the PSF with a Gaussian. The precision with which the individual emitters can be localized scales with the 1/√N, N the number of detected photons so that more detected photons leads to a better localization precision. However, the emission of fluorescent molecules is limited by photobleaching, a light induced chemical reaction to a permanent non-fluorescent state. In this thesis we investigate the effect of cooling the sample to cryogenic temperatures with liquid nitrogen. This reduces the chemical reaction rates and improves photostability more than 100 fold. To use localization microscopy it is necessary to switch the fluorescent molecules between an on-state and off-state, this turns out to be difficult at cryogenic temperatures. Standard methods used at room temperature in aqueous media do not work. As the molecules are frozen in place at cryogenic temperatures we use polarized light to selectively image molecules with certain orientations at a time. To realize this it is necessary to generate pure linear polarization with an arbitrary orientation in the sample plane. By calibrating the phase difference induced by the dichroic mirrors this can be achieved, effectively modulating the fluorescence of fixed dipole emitters at cryogenic temperatures. The addition of an orthogonal linearly polarized stimulated emission depletion (STED) beam narrows the orientational distribution of fluorescing molecules. This method does induce some degree of sparsity, however, it is not enough for localization microscopy of dense biological samples. Furthermore, the STED process reduces the photon yield of single molecules. This is presumably caused by the long dark-state recovery measured on fluorescent molecules in vacuum and at cryogenic temperatures. Localization microscopy of fixed or orientationally constrained emitters has long been avoided as the orientation of individual molecules leads to bias in the localizations. There are various ways to eliminate this bias but they reduce the amount of information that can be extracted from the sample. By fixing the orientation of fluorescent emitters to biomolecules of interest they become reporters for the orientation of the biomolecules. We have devised the so-called Vortex PSF with which the orientation, 3D position and degree of rotational constraint can be extracted from a single image. Alternatively the orientation of single-molecules can be probed with varying polarization states over multiple frames achieving a better precision with less photons.ImPhys/Computational Imagin
Conceptual Design of High Subsonic Prandtl Planes
No full textThe increasing airtraffic demands on aircraft capacity, sustainability and profitability, require the investigation of unconventional aircraft configurations with high aerodynamic efficiency, as the commonly applied fuselage-wing-tail configuration shows to reach an optimum in that respect which cannot be further improved using current technology. The application of the box wing system, following from the Best Wing System theory presented by Ludwig Prandtl in 1924, theoretically results in an aircraft configuration generating minimum induced drag, named Prandtl Plane. A balanced performance analysis and comparison is performed in this research, in terms of fuel burn, structural weight and cost benefits, to indicate the types of missions in which the Prandtl Plane could provide a superior alternative to conventional aircraft. For the purpose of this research, the Initiator has been used as the design and analysis environment. Methods applied specifically for the design and analysis of the Prandtl Plane configuration have been implemented in the tool, to compare the performance with respect to conventional aircraft, in the high subsonic transport category. Parametric studies have been performed on the wing design variables to assess the sensitivity of the Prandtl Plane performance. The aspect ratio of the total wing system showed to have the largest influence on the aerodynamic performance, where a large AR results in high aerodynamic efficiency, however at the same time this yields a high wing weight. Three comparison studies have been performed between a PrP and conventional aircraft, designed using the Initiator to perform a single aisle - medium range mission typically covered by an A320-200 (144 pax, range of 4,000 km), a twin aisle - long range mission typically flown by an A340-300 (270 pax, 10,500 km) and finally a high payload - low range mission (514 pax, 2,500 km) for which no conventional aircraft are specifically designed, but large aircraft such as the A380 are exploited. On each of these missions, the PrP design shows lower induced drag during cruise, as expected, and a lower fuselage weight due to distributed bending loads from the double-wing system. An a single aisle – medium range mission this results in 8% savings in fuel burn, on the long range mission in 10% savings in fuel burn and 9% on DOC. Due to a smaller wing span, the capacity of this type of Prandtl Plane can be increased further without exceeding the dimensional constraints on wing span, and could therefore be a competitor of the A380 which currently marks the maximum capabilities of aircraft in terms of maximum range and payload capacity, due to span restrictions imposed by gate dimensions on existing airports. Prandtl planes with a higher passenger capacity could be exploited on existing routes, while meeting identical airport restrictions.Flight Performance and PropulsionFlight Performance and PropulsionAerospace Engineerin
A study on TCP-SYN attacks and their effects on a network infrastructure
No full textOver the years, the Internet has evolved from a tool for the research community to an indispensable network connecting over a billion nodes world wide. There are many security threats existing on the Internet, one of them is the denial-of-service attack (DoS). In this thesis, we study effect of denial-of-service attacks arising from TCP SYN flooding. SYN flooding attack has been widely observed world-wide, and occupies about 90% of the DoS attacks. We examine the effects of the attacks on individual host, and the underlying network infrastructure carrying the SYN flood packets. In laboratory, we deploy isolated network set-ups, to test the effects of the attacks on both the network and host. Finally, we design a queuing upper bound model to estimate the probability of connection loss on a host under a SYN flood attack. We compare the results from our upper bound model with results from selected models in the literature.Computer EngineeringElectrical Engineering, Mathematics and Computer Scienc
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