Mixed order robust adaptive control for general linear time invariant systems     

Javier A. Gallegos  Manuel A. Duarte-Mermoud  Rafael Castro-Linares 《Journal of The Franklin Institute》2018,355(8):3399-3422

We provide a solution to the adaptive control problem of an unknown linear system of a given derivation order, using a reference model or desired poles defined in a possibly different derivation order and employing continuous adjustment of parameters ruled by possibly another different derivation order. To this purpose, we present an extension for the fractional settings of the Bezout’s lemma and gradient steepest descent adjustment. We analyze both the direct and indirect approaches to adaptive control. We discuss some robustness advantages/disadvantages of the fractional adjustment of parameters in comparison with the integer one and, through simulations, the possibility to define optimal derivation order controllers.  相似文献   

Technological dependence and the failure of educational institutions to support development     

Rafael L. Irizarry 《International Journal of Educational Development》1983,3(2):163-181

Academics, foundations and international agencies concerned with development have repeatedly pointed out the failure of educational institutions to support economic development in underdeveloped countries, particularly in providing the occupational skills and research knowledge in science and technology required by the productive sectors of the economy. The causal factors of this failure have been attributed to institutional deficiencies and traditionalism of backward societies where ‘desk’ jobs and independent professions enjoy higher esteem than technology-related occupations.This paper argues that such educational patterns are rooted in the structures of dependency of the underdeveloped countries. First, employment is concentrated in the non-productive services sector of the economy where desk jobs abound. Second, dependent industrialization entails the predominance of external linkages of industry to developed countries, and technological dependency both in its organic and intellectual components. Industry in underdeveloped countries does not carry out the more complex technological operations of the production cycle or research and development activities for new technology, both of which are done in developed countries. In the absence of this activity, educational institutions cannot ‘learn’ and keep abreast of the modern technological knowledge and processes required for jobs in industry.  相似文献   

Kinematics used by world class tennis players to produce high-velocity serves     

Fleisig G  Nicholls R  Elliott B  Escamilla R 《Sports biomechanics / International Society of Biomechanics in Sports》2003,2(1):51-64

The purpose of this study was to quantify ranges and speeds of movement, from shoulder external rotation to ball impact, in the tennis service actions of world class players. Two electronically synchronised 200 Hz video cameras were used to record 20 tennis players during singles competition at the Sydney 2000 Olympic games. Three-dimensional motion of 20 landmarks on each player and racquet were manually digitized. Based upon the mean values for this group, the elbow flexed to 104 degrees and the upper arm rotated into 172 degrees of shoulder external rotation as the front knee extended. From this cocked position, there was a rapid sequence of segment rotations. The order of maximum angular velocities was trunk tilt (280 degrees/s), upper torso rotation (870 degrees/s), pelvis rotation (440 degrees/s), elbow extension (1510 degrees/s), wrist flexion (1950 degrees/s), and shoulder internal rotation. Shoulder internal rotation was greater for males (2420 degrees/s) than females (1370 degrees/s), which may be related to the faster ball velocity produced by the males (50.8 m/s) than the females (41.5 m/s). Although both genders produced segment rotations in the same order, maximum upper torso velocity occurred earlier for females (0.075 s before impact) than for males (0.058 s). At impact, the trunk was tilted 48 degrees above horizontal, the arm was abducted 101 degrees and the elbow, wrist, and lead knee were slightly flexed. Male and female players should be trained to develop the kinematics measured in this study in order to produce effective high-velocity serves.  相似文献   

Kinematic and kinetic comparisons between American and Korean professional baseball pitchers     

Escamilla R  Fleisig G  Barrentine S  Andrews J  Moorman C 《Sports biomechanics / International Society of Biomechanics in Sports》2002,1(2):213-228

The purpose of this study was to quantify and compare kinematic, temporal, and kinetic characteristics of American and Korean professional pitchers in order to investigate differences in pitching mechanics, performance, and injury risks among two different cultures and populations of baseball pitchers. Eleven American and eight Korean healthy professional baseball pitchers threw multiple fastball pitches off an indoor throwing mound positioned at regulation distance from home plate. A Motion Analysis three-dimensional automatic digitizing system was used to collect 200 Hz video data from four electronically synchronized cameras. Twenty kinematic, six temporal, and 11 kinetic variables were analyzed at lead foot contact, during the arm cocking and arm acceleration phases, at ball release, and during the arm deceleration phase. A radar gun was used to quantify ball velocity. At lead foot contact, the American pitchers had significantly greater horizontal abduction of the throwing shoulder, while Korean pitchers exhibited significantly greater abduction and external rotation of the throwing shoulder. During arm cocking, the American pitchers displayed significantly greater maximum shoulder external rotation and maximum pelvis angular velocity. At the instant of ball release, the American pitchers had significantly greater forward trunk tilt and ball velocity and significantly less knee flexion, which help explain why the American pitchers had 10% greater ball velocity compared to the Korean pitchers. The American pitchers had significantly greater maximum shoulder internal rotation torque and maximum elbow varus torque during arm cocking, significantly greater elbow flexion torque during arm acceleration, and significantly greater shoulder and elbow proximal forces during arm deceleration. While greater shoulder and elbow forces and torques generated in the American pitchers helped generate greater ball velocity for the American group, these greater kinetics may predispose this group to a higher risk of shoulder and elbow injuries.  相似文献   

The Progression of Prospective Primary Teachers’ Conceptions of the Methodology of Teaching     

Ana Rivero  Pilar Azcárate  Rafael Porlán  Rosa Martín del Pozo  Joao Harres 《Research in Science Education》2011,41(5):739-769

This article describes the evolution of prospective primary teachers’ conceptions of the methodology of teaching. Three categories were analyzed: the concept of activity, the organization of activities, and the concept of teaching resources. The study was conducted with five teams of prospective teachers, who were participating in teacher education courses of a constructivist orientation. The results showed very different itineraries in the processes of change, and the presence of two major obstacles—the belief that teaching is the direct cause of learning, and epistemological absolutism. The study allows us to deduce some implications for initial teacher education.  相似文献   

If PLOS ONE were really 101 different specialized journals: A proposed approach to the evaluation of multidisciplinary megajournals     

Rafael Repiso  Alicia Moreno‐Delgado  Daniel Torres‐Salinas 《Learned Publishing》2020,33(2):96-103

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Radical student participation: lessons from an urban government primary school in Tigray,Ethiopia     

Rafael Mitchell 《Compare》2019,49(1):98-114

Recent policies in Ethiopia put students at the heart of school improvement through structures for peer leadership and school-level consultation, evaluation and decision-making. This article draws on an ethnographic study of a government school in Tigray, Ethiopia, to explore how the participation and influence of students is achieved and mediated by structures and processes in school. Three key contexts of student participation are explored: positions of peer leadership (monitor, ‘one-to-five’ network leader); public evaluation sessions (gim gima); and the Parent Student Teacher Association (PSTA). Recommendations are made for sharing and strengthening democratic practices and for future research.  相似文献   

How and where is artificial intelligence in the public sector going? A literature review and research agenda     

Weslei Gomes de Sousa  Elis Regina Pereira de Melo  Paulo Henrique De Souza Bermejo  Rafael Araújo Sousa Farias  Adalmir Oliveira Gomes 《Government Information Quarterly》2019,36(4):101392

To obtain benefits in the provision of public services, managers of public organizations have considerably increased the adoption of artificial intelligence (AI) systems. However, research on AI is still scarce, and the advance of this technology in the public sector, as well as the applications and results of this strategy, need to be systematized. With this goal in mind, this paper examines research related to AI as applied to the public sector. A review of the literature covering articles available in five research databases was completed using the PRISMA protocol for literature reviews. The search process yielded 59 articles within the scope of the study out of a total of 1682 studies. Results show a growing trend of interest in AI in the public sector, with India and the US as the most active countries. General public service, economic affairs, and environmental protection are the functions of government with the most studies related to AI. The Artificial Neural Networks (ANN) technique is the most recurrent in the investigated studies and was pointed out as a technique that provides positive results in several areas of its application. A research framework for AI solutions for the public sector is presented, where it is demonstrated that policies and ethical implications of the use of AI permeate all layers of application of this technology and the solutions can generate value for functions of government. However, for this, a prior debate with society about the use of AI in the public sector is recommended.  相似文献   

The Progression of Prospective Teachers’ Conceptions of School Science Content     

Rosa Martín del Pozo  Rafael Porlán  Ana Rivero 《Journal of Science Teacher Education》2011,22(4):291-312

The purpose of the present work is to describe the progression in the conceptions of prospective primary teachers about school science content while they were participating in three teacher education courses following the same constructivist oriented strategy. The participants’ written output was analyzed in various categories—selection of content, types of content and their relationships, levels of complexity, and presentation of content to pupils. There was evidence for some progress in their conceptions of the content from a traditional view to another that we termed intermediate since it did not reach the vision that we consider to be the most complex. Finally, we present a General Itinerary of Progression on school content that could serve as a referent for initial teacher education.  相似文献   

DNA-library assembly programmed by on-demand nano-liter droplets from a custom microfluidic chip     

Uwe Tangen  Gabriel Antonio S. Minero  Abhishek Sharma  Patrick F. Wagler  Rafael Cohen  Ofir Raz  Tzipy Marx  Tuval Ben-Yehezkel  John S. McCaskill 《Biomicrofluidics》2015,9(4)

Nanoscale synthetic biology can benefit from programmable nanoliter-scale processing of DNA in microfluidic chips if they are interfaced effectively to biochemical arrays such as microwell plates. Whereas active microvalve chips require complex fabrication and operation, we show here how a passive and readily fabricated microchip can be employed for customizable nanoliter scale pipetting and reaction control involving DNA. This recently developed passive microfluidic device, supporting nanoliter scale combinatorial droplet generation and mixing, is here used to generate a DNA test library with one member per droplet exported to addressed locations on microwell plates. Standard DNA assembly techniques, such as Gibson assembly, compatible with isothermal on-chip operation, are employed and checked using off-chip PCR and assembly PCR. The control of output droplet sequences and mixing performance was verified using dyes and fluorescently labeled DNA solutions, both on-chip and in external capillary channels. Gel electrophoresis of products and DNA sequencing were employed to further verify controlled combination and functional enzymatic assembly. The scalability of the results to larger DNA libraries is also addressed by combinatorial input expansion using sequential injection plugs from a multiwell plate. Hence, the paper establishes a proof of principle of the production of functional combinatorial mixtures at the nanoliter scale for one sequence per well DNA libraries.  相似文献