1,355,608 research outputs found
A Computationally Efficient Approach for Velocity Estimation of Ground Moving Targets
No full textIn this paper, a novel algorithm for the parameters estimation of chirp signals is proposed. Chirp rate and centroid frequency of chirp signals are estimated based on a one-dimensional dechirp optimization problem (DOP). The proposed DOP algorithm is useful for synthetic aperture radar (SAR) systems since the azimuth signal of a moving target represents chirp properties, so the along-track and across-track velocities of moving targets can be efficiently estimated. The distinctive feature of the proposed DOP algorithm, as compared with other motion parameters estimators, is its efficiency from the computational point of view. This is obtained by converting the traditional two-dimensional search to an efficient and simple one-dimensional optimization problem. Finally, simulations are presented to validate the theoretical investigations
ENID 2023 Data Table
No full textData tables related to the article sent to the ENID2023 conference are available in the attached files
Enhanced Azimuth Resolution in Synthetic Aperture Radar Using the MUSIC Algorithm
No full textThis paper addresses a considerable improvement of azimuth resolution in the stripmap mode of synthetic aperture radar (SAR) using the multiple-signal classification (MUSIC) algorithm. At first, the range compression and range migration correction are performed. Azimuth chirp signals of stationary targets will be resolved by conventional azimuth compression operation if the signals have slow-time separation larger than the reciprocal of their frequency bandwidth. Otherwise, they will be merged together and appear as a single stationary target in the SAR imaging. The scenario of close targets is modelled as a multipath problem and the corresponding time-delays are estimated using the super-resolution MUSIC algorithm. Therefore, stationary targets with close centers, which were merged by conventional azimuth compression operation, will be resolved and the azimuth resolution is considerably improved. Numerical results are presented to validate the theoretical discussions
On integral input-to-state stability for a feedback interconnection of parameterised discrete-time systems
No full textThis paper addresses integral input-to-state stability (iISS) for a feedback interconnection of parameterised discrete-time systems involving two subsystems. Particularly, we give a construction for a smooth iISS Lyapunov function for the whole system from the sum of nonlinearly weighted Lyapunov functions of individual subsystems. Motivations for such a construction are given. We consider two main cases. The first one investigates iISS for the whole system when both subsystems are iISS. The second one gives iISS for the interconnected system when one of subsystems is allowed to be input-to-state stable. The approach is also valid for both discrete-time cascades and a feedback interconnection of iISS and static systems. Examples are given to illustrate the effectiveness of the results
An authenticated theoretical modeling of electrified fluid jet in core--shell nanofibers production
No full text\textcopyright 2017, \textcopyright The Author(s) 2017. Control and optimization of coaxial electrospinning process is a serious concern due to its multiparameter effectiveness. This study is concerned with modeling and simulation of process by solving the governing equations of electrified jet using FEniCS software packages applying Cahn--Hilliard and Newton solvers for finite element method. Jet diameter, solvent evaporation, electrical field, and velocity changes are focused in this model as the most effective parameters on final nanostructures quality. An experimental core--shell nanofiber production (polyvinyl alcohol) in the same spinning condition with simulated spinning is applied to validate the model. Both theoretical and experimental results demonstrate that core and shell diameter increases by increase in nozzle diameter and polymer solution concentration. Relative error shows that for the higher nozzle diameter, the model can have an acceptable prediction for final diameter which is more accurate for shell diameter part. The simulation results for jet velocity indicate a sharp sinusoidal increase during jet motion. Electric field simulation also shows a result similar to Feng's model with an increase near the nozzle and a very slow decline at the end which both are confirmed by other experimental and numerical studies. It is also concluded that by enlargement of nozzle diameter, solvent evaporation takes more time and as a result, the inhomogeneity and diameter increase which have the same trend as experimental results. The relative error of evaporation time decreases in nanojets with higher diameter. And the model has an acceptable compatibility with experimental results especially for nozzle diameters more than 50 µm
Meshfree radial point interpolation method for the vibration and buckling analysis of FG-GPLRC perforated plates under an in-plane loading
No full textA meshfree radial point interpolation method (RPIM) based on a higher-order shear deformation theory (HSDT) is here developed to investigate the free vibration and buckling behavior of multilayer functionally graded graphene platelets reinforced composite (FG-GPLRC) perforated plates under an in-plane edge loading. The non-uniform initial stresses in the multilayer FG-GPLRC perforated plates are evaluated accurately by solving the equilibrium equations derived from the same approach. The mixed collocation-Lagrange multiplayer technique is employed to enforce the various boundary conditions. The multilayer FG-GPLRC plates are built up as perfectly-bonded composite layers reinforced with a uniform distribution of graphene platelets (GPLs), randomly oriented. Perforated plates with three different cut-out shapes are analyzed. Several numerical examples are provided to demonstrate the high performance, the fast convergence rate and the high accuracy of the proposed method. Then, we study the influence of different GPLs distribution patterns, GPLs weight fraction, shape and size of cut-outs on the free vibration and buckling behavior of the multilayer FG-GPLRC perforated plates under an in-plane edge loading
A Reconfigurable GPS/Galileo Receiver Front-end for Space Applications
No full textThe trend of space technology developments is moving from high power consuming, bulky and costly systems towards low-power, small, low-cost and flexible systems. Thus, the spacecraft can benefit from multi-purpose and flexible systems which can be low-power and low-cost by employing new technology. One example of such system is a GNSS receiver capable of adapting the number of used frequency bands depending on its power constraint and the required accuracy. In the past, a Global Navigation Satellite System (GNSS) receiver has primarily been used for navigation purposes. However, as the number of available GNSS systems has increased, the potential of introducing new applications using these systems has also increased. Such applications become more robust and their performance can be improved if the GNSS receiver can operate with more than one GNSS system. On the other hand, extensive research and developments in state-of-the-art integrated circuit (IC) technology facilitates the integration of complex systems in a very compact and efficient manner. This miniaturization can be spun into space applications which are very complex systems by itself. Using this potential leads to new approaches in spacecraft design as well as potentially new space applications which may require short time-to-market. The research objective of this thesis is to develop a space-capable, flexible, multipurpose, low-power and low-cost GNSS receiver front-end. This front-end shall be able to process GNSS signals from different GNSS systems and different frequency bands. In chapter 1, an overview of navigation systems along with applications of GNSS systems is presented. This chapter also provides and introduction to state-of-the art IC technology and its advantages and disadvantages for using it in space. Thesis objectives and research questions conclude this chapter. Chapter 2 covers the fundamentals of satellite positioning system and provides a detailed explanation of GPS and Galileo signal structures followed by investigating a generic GNSS receiver architecture. This chapter is concluded with explanation of requirements for designing a space capable GNSS receiver. In chapter 3, existing radio receiver front-end architectures are reviewed and compared. The most suitable architecture, i.e. zero-IF, is selected. Finally, an innovative and flexible architecture for GNSS receiver front-end based on zero-IF is proposed. Chapter 4 begins with technology selection and calculations of link budget of the proposed receiver front-end. It is followed by reviewing various implementations of building blocks of the front-end and their comparison. In this chapter an innovative mixer architecture for zero-IF architecture is proposed which overcomes its two main problems, the DC offset and flicker noise. The chapter concludes by selecting the most suitable circuits for mixer, quadrature oscillator and analog to digital converter (ADC) for this receiver front-end. In chapter 5, the circuits of the mixer, quadrature oscillator, amplifier and ADC are developed in transistor level followed by verification simulations. The results of the simulations verify the expected behavior of the proposed mixer as well as the quadrature oscillator, amplifier and ADC. The thesis is concluded in chapter 6 with summary of the results, recommendations and future outlook.Earth Observation and Space SystemsAerospace Engineerin
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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