1,720,955 research outputs found
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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
High order sliding mode control of a flexible-link robot arm
Get PDFUcunda yük bulunan bir Esnek-Mafsallı Robot Kol (EMRK) hareket kontrolu için Kayma Kipli Kontrol (KKK) ve Yüksek Dereceli Kayma Kipli Kontrol (YDKKK) yöntemleri uygulanmıştır. Esnek kolun istenen bir noktada konumlandırma ve yörünge izleme kontrolu için KKK ve 2nci dereceden YDKKK (2-YDKKK) yöntemleri kullanılarak kontrol algoritmaları türetilmiştir. 1-SD (Serbestlik Dereceli) esnek mafsallı robot kolun hassas hareket kontrolu problemi, özellikle hafif ve esnek yapısı ile matematiksel modelinde yer alan şekil kipleri dikkate alındığında; aşırı doğrusal olmayan ve ayrışmayan dinamik denklemleri ile kontrol alanında oldukça zorlayıcı bir çalışma konusudur. Doğrudan Tahrikli (DT) eklem motoruna sahip EMRK çalışma esnasında oluşan esneme, titreşimler ve farklı kütlelere sahip uç yükü ile birlikte hareket kontrolunun sadece eklem motoruna uygula-nabilen kontrol işareti ile sağlandığı düşünülürse yüksek performanslı kontrolör gerektirdiği açıktır. Dayanıklı kontrol yöntemlerinden, sistem belirsizliklerine karşı etkili ve sistem parametre deği-şimlerinden bağımsız olan KKK yöntemi kullanılmıştır. Yöntemin olumsuzluğu olan çatırtı problemi ise 2-YDKKK yöntemi ile türetilen kontrolör ile giderilmeye çalışılmıştır. Her iki yöntemin deneysel olarak karşılaştırılması ve kontrolörlerin gerçeklenmesi bir Donanımlı Simülatör (Dsim) kullanılarak yapılmıştır. Donanımlı simülatör donanım ve yazılıma sahiptir. Dsim de bulunan donanımlar gerçek sistemin önemli bölümlerini içerir. Bu nedenle doğrudan tahrikli iki motor Dsim de yer almaktadır ve millerinden birbirine akuple bağlanmışlardır. Bu sistemle yapılan deneysel çalışmalara göre 2-YDKKK yönteminin KKK yöntemine göre EMRK hareket kontrolunda daha etkili olduğu gö-rülmüştür. Kontrolörlerin doğrudan tahrikli motor moment salınımlarını bastırmadaki etkinliği harmonik analizi ile karşılaştırılmıştır. Anahtar Kelimeler: Kayma Kipli Kontrol, Yüksek Dereceli Kayma Kipli Kontrol, Esnek-Mafsallı Robot kol, donanımlı simülatör, moment salınım analizi.In this study, Sliding Mode Control (SMC) and High Order Sliding Mode Control (HOSMC) me-thods are applied to a single Flexible Link Robot Arm (FLA) with payload. A sliding mode and high order sliding mode controllers are designed to achieve set point precision positioning control and trajectory tracking control for a FLA. Flexible robot arms have structural flexibilities and resulting high number of passive degrees-of-freedom. They cannot be decoupled due to the highly nonlinear structure. Since the flexible systems have highly nonlinear structure and coupled dynamics, the sliding mode based control approach is chosen a powerful me-thod to overcome the unmodeled and parametric uncertainties. One of the proposed controllers is 2nd order HOSMC method is compared with classical SMC method. Comparison of the methods is experimentally fulfilled using HIL simulator, and additionally torque ripple analysis is made to evaluate of the methods aspect from system harmonics. Direct drive motors are used as actuator in controlled systems. Of all system dynamics affect system harmonics via motor shaft due to the direct drive system that is no gear box. Therefore, harmonics analysis is crucial to in-vestigate of designed controllers effects on system harmonics. To precise set-point and trajectory tracking con-trol of 1-DOF DD FLA has been derived SMC and HOSMC. Sliding Mode Controllers (SMCs) have the robustness properties, while also increasing accuracy by reducing chattering effects. The performance of the designed control methods are tested for the precise position and targeting control of a 1-DOF-DD-FLA system under heavy uncertainties. Comparative results of both methods have been evaluated in real-time using a Hardware-in-the-Loop (HIL) simulator designed for robotics. Especially, HIL simulator for this system includes DD motors and obtained results can be evaluated more realistically according to pure computer simulations. Additionally, torque ripples of whole system with HIL simulator have been determined and their eliminations using for both methods are introduced. HIL simulator is used to implement designed con-troller for a flexible-link arm. Direct drive joint motors are important parts of the direct drive underactuated robot manipulators. Therefore two DD motors take part in HIL simulator and couple through their shaft. One of the motors represents joint actuator, while the other motor is used for generation of the dynamics of the controlled sys-tem via the torque applied to the shaft. The two motors acting as "actuator" and "load torque simulator" are driven separately by a high per-formance controller board. HIL Simulator is ex-pressed briefly as software that is modeled control algorithm and system dynamic model via controller board is integrated with hardware. HIL simulation differs from computer simulation as it involves actual hardware and is not limited with a software-based representation of the system. Main aim is to use HIL Simulator is able to make more realistic analysis about behaviors of the system dynamics in real-time. It is over computer simulation since the simulator incorporates some of the crucial hardware of the actual system that takes part in the loop. For this purpose defined HIL simulation environment is useful to test, analysis and performance evaluation of designed controllers for unde-ractuated robot manipulators. The major contribution of this study is experimen-tal evaluation of 2nd order HOSM controller and SMC for tracking accuracy and robustness against internal and external uncertainties of DD flexible-link arm with the consideration of the full system dynamics effects. The HIL experimental results confirm and depict that the 2-HOSMC me-thod has robust and accurate performance as expected from the HOSM controllers. Additionally, torque ripples of whole system with HIL simulator have been determined and their eliminations using for both methods are introduced. According to the HIL experimental results and torque ripple analysis, using 2-HOSMC has advantages an increased accuracy over the SMC. Keywords: Sliding Mode Control, High Order Sliding Mode Control, Flexible-Link Robot Arm, Hardware in the Loop simulator, torque ripple analysis
Speed sensorless direct vector control of the IM
Get PDFBu çalışmada, Sincap Kafesli Asenkron Motorların (SKASM’lerin) algılayıcısız kontrolünde başarımı olumsuz yönde etkileyen modele ait elektriksel ve mekanik yana ilişkin parametre belirsizliklerini çözmek üzere Genişletilmiş Kalman Filtresi (GKF) tabanlı gözlemleyici algoritmaları tasarlanarak gerçeklenmiştir. Doğrudan vektör kontrol sistemi ya da vektör kontrollü a.a sürücüsü ile başarımları test edilen bu algoritmalar ile herhangi yüksek frekanslı bir işaret eklemeksizin ve başlangıç değerleri bilinmediği varsayımıyla algılayıcısız kontrol için gerekli tüm durumlar, sabit sürtünme –viskoz– terimini de içeren yük momenti ve değeri bilinmeyen rotor direnci eş zamanlı olarak kestirilebilmiştir. Benzetim/deney sonuçları önerilen yöntemlerin oldukça etkin ve dayanıklı olduğunu göstermiştir. Bu yönleriyle, literatürde bilinen ilk çalışmadır.Anahtar Kelimeler: Genişletilmiş Kalman filtresi, gözlemleyici, kestirici, hız algılayıcısız vektör kontrol, asenkron motor.This paper offers a solution to the performance deteriorating effect of uncertainties in the sensorless control of induction motors (IMs). The major contribution of the study is the development and implementation of a Extended Kalman Filter (EKF) algorithms that take electrical and mechanical uncertainties into account. Also, unlike previous EKF based estimation studies taking the angular velocity, wm, into consideration as a constant parameter, in this study, wm, is estimated as a state with the utilization of the equation of motion. In this regard, this is the first known study to estimate the mechanical uncertainties together with the estimation of the rotor resistance, without injecting high frequency signals. The EKF algorithms also estimate the rotor flux, angular velocity and stator currents with no apriori knowledge on the states and initial values taken as zero. Experiments performed under unknown load torque and with rotor resistance variations up to twice the rated value, demonstrate the good performance and robustness of the estimation methods. The algorithms also estimate the mechanical uncertainties as a constant state to capture the unknown viscous and Coulomb friction in steady state, therefore, could be used to improve the performance of the velocity or position control of IM's, if utilized in combination with a compensation scheme.Keywords: Extended Kalman filter, observer, estimator, speed sensorless vector control, induction motor
Implementation of adaptive fuzzy logic based methods on parallel active filter systems
Get PDFParalel Aktif Filtreler (PAF), lineer olmayan yüklerin üç fazlı alternatif akım (AA) güç sistemlerinde yarattığı harmonik akım, reaktif güç gibi elektrik enerji kalitesini bozan etkilerini azaltmada oldukça başarılıdır. PAF’nin yük akım kompanzasyon yeteneği, güç yapısında yer alan pasif elemanlar kadar, gerilim ve akım kontrol çevrimlerinde kullanılan kontrol yöntemlerine de bağlıdır. Bu çalışmada PAF sisteminin doğru akım (DA) gerilim kontrol çevriminde kullanılan farklı kontrolörlerin performansları karşılaştırmalı olarak verilmiştir. Klasik Bulanık Mantık temelli PI (BPI) kontrolörünün performansı, kontrol parametrelerinin adaptasyonu ile arttırılabilir. Bu çalışmada, BPI kontrolörünün sadece çıkış ölçeklendirme katsayısının bir kazanç ayar mekanizması yardımıyla adaptasyonu incelenecektir.Anahtar Kelimeler: Paralel aktif filtre, harmonik, güç faktörü, bulanık mantık. Power Electronics based equipment characterised by non-linear and time varying operation are the common sources of current/voltage harmonics and reactive power in electric power systems. To reduce the effects of harmonic currents and reactive power, which significantly degrade the performance and efficiency of the electric power distribution system, three phase Parallel Active Filter (PAF) in which a Current Controlled, Voltage Source PWM IGBT power converter is the core element is connected in parallel with the non-linear load to compensate the load harmonic currents and reactive power drawn from the mains utility. In principle, PAF improves the electric power quality by drawing the same magnitude, but opposite phase harmonic and reactive current components consumed by the non-linear type power electronics loads and keeping the supply currents sinusoidal and in-phase with the related phase voltages. In this paper, classic and Adaptive Fuzzy Logic based PI controllers as well as linear PI controller are employed in the dc voltage control loop and their performances are compared. Two different adaptation methods for scaling factors of fuzzy controllers are studied. It has been found that self tuning adaptive fuzzy logic based controllers perform better than their classic fuzzy logic based counterparts in which input and output scaling factors are constant. Matlab 6.1 software package has been used in simulation studies. Keywords: Parallel active filter, harmonic, power factor, fuzzy logic
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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