950 resultados para Traction of Force


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La presente investigación tiene como objetivo explicar cuáles son los efectos de la gramática de la Guerra contra el Terrorismo en el proceso de construcción del “Nuevo Orden Mundial” tras la caída de la Unión Soviética. Para ello, la investigación sostiene que la Guerra contra el Terrorismo se caracteriza por una serie de transformaciones de los principios del uso de la fuerza, cuyos efectos sobre el proceso de construcción del Nuevo Orden Mundial, están dados por un ejercicio desinstitucionalizado y transnacional de la violencia política en el que la Guerra se convierte en una forma de globalización unilateral. Para la elaboración de esta monografía se adoptará una metodología cualitativa de índole no experimental.

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Esta investigación aborda las condiciones bajo las que se llevó a cabo en Colombia, en el primer gobierno del presidente Álvaro Uribe Vélez (2002-2006), la negociación entre el Estado y los grupos paramilitares. Se establecen las características de ese proceso de paz, su correspondencia con modelos tradicionales de negociación y sus alcances sobre el proceso de Desmovilización, Desarme y Reinserción (DDR) de las organizaciones paramilitares.

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Este es un estudio sobre la estrategia de guerra estadounidense en Medio Oriente basada en el uso sistemático de drones durante el periodo comprendido entre 2009 y 2013. Se busca explicar de qué manera puede considerarse el uso de este tipo de armamento como una práctica basada en la proyección de poder sin mayor vulnerabilidad. Los casos de Pakistán y Yemen son abordados, ya que evidencian las características de las operaciones selectivas por las que ha abogado el Presidente Obama. El estudio se inscribe dentro del realismo ofensivo, haciendo también referencia a sus limitaciones explicativas. Empero, se afirma que las dinámicas y consecuencias de la utilización de drones son intrínsecas a la necesidad estadounidense de combatir actores no estatales mediante prácticas que garanticen su seguridad y pretensiones hegemónicas a pesar de las implicaciones políticas , legales y sociales en las que puede incurrir.

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El cáncer de próstata es el cáncer más frecuente en los hombres en muchos países industrializados. Considerando el porcentaje de supervivencia relativa a los 5 años (76,5%) y el estado de morbilidad que generan los tratamientos vigentes, el concepto de Calidad de Vida (CdV) del hombre mayor con cáncer de próstata pasa a ser un objetivo prioritario en la intervención sociosanitaria. Clásicamente la evaluación del impacto que generan los síntomas se ha determinado por la frecuencia y el número de síntomas asociados a la enfermedad y al tratamiento. A nuestro parecer, lo más apropiado es realizar el análisis objetivando además el impacto que generan en la actividad de vida diaria de los afectados. Este artículo tiene un doble objetivo. Primero, evaluar los beneficios de un programa de ejercicio de fuerza adaptado a la enfermedad y al tratamiento de cáncer de próstata. Segundo, identificar los síntomas más relevantes del cáncer de próstata desde la perspectiva del paciente y el impacto que generan a la Calidad de Vida del hombre mayor. La propuesta metodológica se basa en la triangulación metodológica entre métodos secuencial, (cuantitativo y cualitativo). En los resultados se observa una mejora significativa de la Calidad de Vida del enfermo, mediado indirectamente por la mejora del síntoma de incontinencia y el dolor. Así mismo se observa una mejora de la capacidad de la fuerza y resistencia muscular más evidente en las extremidades inferiores. Queda científicamente demostrada la eficacia de un programa de ejercicio físico de fuerza adaptado a los síntomas que genera la enfermedad y el tratamiento de cáncer de próstata en la mejora de la Calidad de Vida de la persona mayor.

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The assumption that negligible work is involved in the formation of new surfaces in the machining of ductile metals, is re-examined in the light of both current Finite Element Method (FEM) simulations of cutting and modern ductile fracture mechanics. The work associated with separation criteria in FEM models is shown to be in the kJ/m2 range rather than the few J/m2 of the surface energy (surface tension) employed by Shaw in his pioneering study of 1954 following which consideration of surface work has been omitted from analyses of metal cutting. The much greater values of surface specific work are not surprising in terms of ductile fracture mechanics where kJ/m2 values of fracture toughness are typical of the ductile metals involved in machining studies. This paper shows that when even the simple Ernst–Merchant analysis is generalised to include significant surface work, many of the experimental observations for which traditional ‘plasticity and friction only’ analyses seem to have no quantitative explanation, are now given meaning. In particular, the primary shear plane angle φ becomes material-dependent. The experimental increase of φ up to a saturated level, as the uncut chip thickness is increased, is predicted. The positive intercepts found in plots of cutting force vs. depth of cut, and in plots of force resolved along the primary shear plane vs. area of shear plane, are shown to be measures of the specific surface work. It is demonstrated that neglect of these intercepts in cutting analyses is the reason why anomalously high values of shear yield stress are derived at those very small uncut chip thicknesses at which the so-called size effect becomes evident. The material toughness/strength ratio, combined with the depth of cut to form a non-dimensional parameter, is shown to control ductile cutting mechanics. The toughness/strength ratio of a given material will change with rate, temperature, and thermomechanical treatment and the influence of such changes, together with changes in depth of cut, on the character of machining is discussed. Strength or hardness alone is insufficient to describe machining. The failure of the Ernst–Merchant theory seems less to do with problems of uniqueness and the validity of minimum work, and more to do with the problem not being properly posed. The new analysis compares favourably and consistently with the wide body of experimental results available in the literature. Why considerable progress in the understanding of metal cutting has been achieved without reference to significant surface work is also discussed.

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In over forty years of research robots have made very little progress still largely confined to industrial manufacture and cute toys, yet in the same period computing has followed Moores Law where the capacity double roughly every two years. So why is there no Moores Law for robots? Two areas stand out as worthy of research to speedup progress. The first is to get a greater understanding of how human and animal brains control movement, the second to build a new generation of robots that have greater haptic sense, that is a better ability to adapt to the environment as it is encountered. A remarkable property of the cognitive-motor system in humans and animals is that it is slow. Recognising an object may take 250 mS, a reaction time of 150 mS is considered fast. Yet despite this slow system we are well designed to allow contact with the world in a variety of ways. We can anticipate an encounter, use the change of force as a means of communication and ignore sensory cues when they are not relevant. A better understanding of these process has allowed us to build haptic interfaces to mimic the interaction. Emerging from this understanding are new ways to control the contact between robots, the user and the environment. Rehabilitation robotics has all the elements in the subject to not only enable and change the lives of people with disabilities, but also to facilitate revolution change in classic robotics.

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For individuals with upper-extremity motor disabilities, the head-stick is a simple and intuitive means of performing manipulations because it provides direct proprioceptive information to the user. Through practice and use of inherent proprioceptive cues, users may become quite adept at using the head-stick for a number of different tasks. The traditional head-stick is limited, however, to the user's achievable range of head motion and force generation, which may be insufficient for many tasks. The authors describe an interface to a robot system which emulates the proprioceptive qualities of a traditional head-stick while also allowing for augmented end-effector ranges of force and motion. The design and implementation of the system in terms of coordinate transforms, bilateral telemanipulator architecture, safety systems, and system identification of the master is described, in addition to preliminary evaluation results.

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Haptic computer interfaces provide users with feedback through the sense of touch, thereby allowing users to feel a graphical user interface. Force feedback gravity wells, i.e. attractive basins that can pull the cursor toward a target, are one type of haptic effect that have been shown to provide improvements in "point and click" tasks. For motion-impaired users, gravity wells could improve times by as much as 50%. It has been reported that the presentation of information to multiple sensory modalities, e.g. haptics and vision, can provide performance benefits. However, previous studies investigating the use of force feedback gravity wells have generally not provided visual representations of the haptic effect. Where force fields extend beyond clickable targets, the addition of visual cues may affect performance. This paper investigates how the performance of motion-impaired computer users is affected by having visual representations of force feedback gravity wells presented on-screen. Results indicate that the visual representation does not affect times and errors in a "point and click" task involving multiple targets.

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This paper examines the physiological mechanisms responsible for differences in the amplitude of force fluctuations between young and old adults. Because muscle force is a consequence of motor unit activity, the potential mechanisms include both motor unit properties and the behavior of motor unit populations. The force fluctuations, however, depend not only on the age of the individual but also on the muscle group performing the task, the type and intensity of the muscle contraction, and the physical activity status of the individual. Computer simulations and experimental findings performed on tasks that involved single agonist and antagonist muscles suggest that differences in force fluctuations are not attributable to motor unit twitch force, motor unit number, or nonuniform activation of the agonist muscle, but that they are influenced by the variability and common modulation of motor unit discharge in both the agonist and antagonist muscles. Because the amplitude of the force fluctuations does not vary linearly with muscle activation, these results suggest that multiple mechanisms contribute to the differences in force fluctuations between young and old adults, although the boundary conditions for each mechanism remain to be determined.

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The aim of this preliminary study was to investigate motor cortex (cortical) excitability between a similar fine visuomotor task of varying difficulty. Ten healthy adults (three female, seven male; 20–45 years of age) participated in the study. Participants were instructed to perform a fine visuomotor task by statically abducting their first index finger against a force transducer which displayed the level of force (represented as a marker) on a computer monitor. This marker was to be maintained between two stationary bars, also displayed on the computer monitor. The level of difficulty was increased by amplifying the position of the marker, making the task more difficult to control. Cortical measures of motor evoked potential (MEP) and silent period (SP) duration in first dorsal interosseous (FDI) muscle were obtained using transcranial magnetic stimulation (TMS) while the participant maintained the “easy” or “difficult” static task. An 11.8% increase in MEP amplitude was observed when subjects undertook the “difficult” task, but no differences in MEP latency or SP duration. The results from this preliminary study suggest that cortical excitability increases reflect the demand required to perform tasks requiring greater precision with suggestions for further research discussed.

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The researcher worked closely with two biology-trained teachers to plan three teaching sequences in the topics of forces, substances and astronomy that were subsequently taught to Year 7 students. The sequences sought to develop a model of classroom practice that foregrounds students’ negotiation of conceptual representations.

The difficulties encountered by individuals in learning science point to the need for a very strong emphasis of the role of representations in learning. There is a need for learners to use their own representational, cultural and cognitive resources to engage with the subject-specific representational practices of science. Researchers who have undertaken classroom studies whereby students have constructed and used their own representations have pointed to several principles in the planning, execution and assessment of student learning (diSessa, 2004; Greeno & Hall, 1997). A key principle is that teachers need to identify big ideas, key concepts, of the topic at the planning stage in order to guide refinement of representational work. These researchers also point out the need for students to engage with multiple representations in different modes that are both teacher and student generated. A representation can only partially explain a particular phenomenon or process and has both positive and negative attributes to the target that it represents. The issue of the partial nature of representations needs to be a component of classroom practice (Greeno & Hall, 1997) in terms of students critiquing representations for their limitations and affordances and explicitly linking multiple representations to construct a fuller understanding of the phenomenon or process under study. The classroom practice should also provide opportunities for students to manipulate representations as reasoning tools (Cox, 1999) in constructing the scientifically acceptable ideas and communicating them.

Research question: What impact was there on the participating teacher’s practice through the adoption of a representational focus to teaching science?

Data collection included video sequences of classroom practice and student responses, student work, field notes, tape records of meetings and discussions, and student and teacher interviews based in some cases on video stimulated recall. Video analysis software was used to capture the variety of representations used, and sequences of representational negotiation.

The teachers in this study reported substantial shifts in their classroom practices, and in the quality of classroom discussions, arising from adopting a representational focus. The shifts were reported by them as a three-fold challenge. First, there was an epistemological challenge as they came to terms with the culturally produced nature of representations in the topics of force, substance and astronomy and their flexibility and power as tools for analysis and communication, as opposed to their previous assumption that this was given knowledge to be learnt as an end point. The second challenge was pedagogical, in that this approach was acknowledged to place much greater agency in the hands of students, and this brought a need to learn to run longer and more structured discussions around conceptual problems. The third challenge related to content coverage. The teachers sacrificed coverage for the greater depth offered by this approach, and were unanimous in their judgment that this had been a change that had paid dividends in terms of student learning.

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The intended outcome of Information Operations appears to be a favourable change (to the instigator) in attitudes or belief systems of the target, however, the relationship between attitude and behaviour is tenuous. Propaganda and other methods of ‘influence’ are difficult to assess as the cause and effect relationship is complicated. The short term effects of psychological warfare where force is used in conjunction with influence techniques can be easily assessed; at least at a superficial level. Even in the latter case, the actual causes and effects could be solely the force used or some other factors rather than the psychological techniques per se. Influence Operations attempt to win the hearts and minds of the target audience but, even if successful, the lasting effects of a campaign are problematic. It is further complicated because if a person has a particular view, it does not mean that the ensuing behaviours will reflect that view. Also, there is evidence that the use of force on one set of people produces attitudes and behaviours that instigate radical beliefs and behaviours in another set. So psychological warfare techniques on one group that may or may not produce compliant behaviour stimulates another group to empathise with the victims thus producing an overall practical negative influence. Influence campaigns cannot be separated from the physical environment in which they are executed. If good politics requires good influence campaigns then good influence campaigns require good politics to back them up. This paper will examine the relationships between short term influence campaigns and compare them with the more long term socialising effects such as early education, family and physical attributes that have on attitudes and beliefs which result in the development of such behaviours as terrorism.

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In exercising vision we employ strategies to perceive space and to distinguish the objects of attention. Some processes however remain invisible to us; how we process binocular vision; and how we resolve vision in motion. This work images invisible motion perspective. Revelation of invisible mechanisms of vision exposes the haptic qualities of sight and their contribution to proprioception and ʻaffordanceʼ. Figuring the ʻvortex of visionʼ also releases symbolic and metaphoric potentials. This innovative outcome of practical research develops imagery which depicts relative movement in space using the principles of motion perspective (Herschel) and optic flow (J. J. Gibson); the locative awareness of volumes in space through the dimensions of time and space presented in 2D imagery. The mural scale (3.5 metres) work presented in 'Circle', a group show of work around the idea of 'the circle' curated by Melinda Capp is derived from a large production of digital photographs made in the London Underground. In this work, the circle is associated with the orbit of the commuter which bends around the twin poles of home and employment, work and rest, circulating in an ellipse around the Ideal Life. Each traveller's path is a braid woven through gyrations of force and resistance. Optic flow, emulated with the rotating lens, tracing the moving subject, makes this visible.

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Although it is now well known that there is a disproportionate number of people with mental illnesses in the criminal justice system, surprising little attention has been paid to the challenges faced by policing people with mental illnesses in the community. This article provides an overview of some of the key findings from a programme of research undertaken in Victoria to further understand and develop a best practice model at this interface. The areas covered will include the prevalence of psychiatric symptoms and mental illnesses among police cell detainees; the existing knowledge base and attitudes of police towards mentally ill people; the relationship between mental illness and offending; the frequency and nature of police apprehensions of mentally ill people under the Mental Health Act; the association among mental disorder, police shootings, and other injuries to people as a result of these encounters; and police interactions with victims of crime. The work highlights the need for ongoing improvements in policing people with mental illnesses, and particularly the need for improved inter-agency practices for dealing with them.