This paper reviews different approaches for explaining body sway while quiet standing that directly address the instability of the human inverted pendulum. We argue that both stiffness control [Winter, D. A., Patla, A. E., Riedtyk, S., & Ishac, M. (2001). Ankle muscle stiffness in the control of balance during quiet standing. Journal of Neurophysiology, 85, 2630-2633] and continuous feedback control by means of a PID (Proportional, Integral, Derivative) mechanism [Peterka, R. J. (2000). Postural control model interpretation of stabilogram diffusion analysis. Biological Cybernetics, 83, 335-343.] can guarantee asymptotic stability of controlled posture at the expense of unrealistic assumptions: the level of intrinsic muscle stiffness in the former case, and the level of background noise in the latter, which also determines an unrealistic level of jerkiness in the sway. We show that the decomposition of the control action into a slow and a fast component (rambling and trembling, respectively, as proposed by [Zatsiorsky, V. M., & Duarte, M. (1999). Instant equilibrium point and its migration in standing tasks: Rambling and trembling components of the stabilogram. Motor Control, 4, 185-200; Zatsiorsky, V. M., & Duarte, M. (2000). Rambling and trembling in quiet standing. Motor Control, 4, 185-200.]) is useful but must be modified in order to take into account that rambling is not a stable equilibrium trajectory. We address the possibility of a form of stability weaker than asymptotic stability in light of the intermittent stabilization mechanism outlined by [Loram, I. D., & Lakie, M. (2002a). Human balancing of an inverted pendulum: position control by small, ballistic-like, throw and catch movements. Journal of Physiology, 540, 1111-1124.], and propose an indicator of intermittent stabilization that is related to the phase portrait of the human inverted pendulum. This indicator provides a further argument against the plausibility of PID-like control mechanisms. Finally, we draw attention to the sliding mode control theory that provides a useful theoretical framework for formulating realistic intermittent, stabilization models. 相似文献
This article proposes to analyse some aspects of the appropriation of New School thinking in Brazil, particularly Deweyan pragmatism, in the 1950s and 1960s. The analysis is based on the assumption that the developmentalist ideology that punctuated the debate on the economic, political and social restructuring of the country in these two decades constituted fertile ground for the return and expansion of pragmatist thinking amongst Brazilian educators, articulating itself, sometimes in contradictory ways, with this ideology. The focus of the analysis will be on the writings of the group of educators which circulated around the figure of Anísio Teixeira, at the time director of the National Institute for Pedagogic Studies (INEP), an organ linked to the Ministry of Education and Culture (MEC), which set itself the task of producing research that would support public policy in the field of education, as well as constituting itself as a center for teacher education and the stimulus and development of innovative experiences in the public school system. The appropriation of Deweyan pragmatism, in this context, had a triple perspective: pragmatism as scientific method, implying a specific conception of science, particularly the social sciences, with emphasis on the application of scientific knowledge in the solution of practical problems; as a way of democratic life; and as a synonym for experimentalism, in the sphere of schooling. 相似文献
Surface color is traditionally measured by matching methods. However, in some conditions, the color of certain surfaces cannot be measured: The surface simply looks brighter or darker than all the patches on a matching scale. We studied the reliability, validity, and range of application of three different types of simulated Munsell scales (white-, black-, and split-surrounded) as methods for measuring surface colors in simple disk-ring displays. All the scales were equally reliable for matching both increments and decrements, but about 20% of the increments were unmatchable on the white-surrounded scale, about 13% of the decrements were unmatchable on the black-surrounded scale, and about 9% of the increments were unmatchable on the split-surrounded scale. However, matches on all the scales were linearly related. Therefore, it is possible to convert them to common units, using regression parameters. These units provide an extended metric for measuring all increments and decrements in the stimulus space, effectively removing ceiling and floor effects, and providing measures even for surfaces that were perceived as out of range on some of the scales. 相似文献
We compared reasoners' inferences from conditionals based on possibilities in the present or the past (e.g., "If Linda had been in Dublin then Cathy would have been in Galway") with their inferences based on facts in the present or the past (e.g., "If Linda was in Dublin then Cathy was in Galway"). We propose that people construct a richer representation of conditionals that deal with possibilities rather than facts: Their models make explicit not only the suppositional case, in which Linda is in Dublin and Cathy is in Galway, but also the presupposed case, in which Linda is not in Dublin and Cathy is not in Galway. We report the results of four experiments that corroborate this model theory. The experiments show that reasoners make more inferences from conditionals based on possibilities rather than on facts when the inferences depend on the presupposed case. The results also show that reasoners generate different situations to verify and falsify conditionals based on possibilities and facts. 相似文献
The Christian evaluation of homosexuality is based primarily on a model which can view homosexuality only as aberrational. From a Christian theological point of view this model articulates an inadequate vision of the dignity of human being. In its deliberations on the process of church, Vatican Council II implicitly developed a relational-progressive model for understanding the salvific engagement of the complete gift of Godlife and creation. This model, in turn, provides a new basis for understanding human dignity and evaluating homosexuality. Viewed from this perspective homosexuality is able to be considered a sacramental embodiment of Godlife. 相似文献
Chronic consumption of ethanol during pregnancy and lactation may lead to abnormalities in the fetus or infant. A group of female Wistar rats was submitted to ethanol treatment over a period of a month. A pair-fed control group received sucrose solution isocaloric to ethanol and the control group received water “ad libitum.” Afterward, the females were mated with males over a period of 20 days. At birth, each litter was maximized to eight pups and the remaining ones were decapitated to remove the fetal blood and brains. No significant difference was observed in fetal body and brain weight at birth. During lactation the ethanol and pair-fed groups gained less weight than the control group. After weaning, their weight became similar. Fetal blood glucose levels were decreased in the ethanol-treated group. One hundred percent of the pair-fed and control females delivered live fetuses at term and all survived; only 40% of the females in the ethanol group delivered, and one pup did not survive. Chronic ethanol treatment pointed to a possible reduction in the fertility. It seems likely that the change in body weight of ethanol-fed dams was caused by undernutrition. 相似文献
A sentence construction experiment examining the effect of part of speech and phonological form in written-word comprehension is reported. Normal and aphasic subjects had to write sentences incorporating a given word pair, one word was a homograph (e.g., “bank”) whose meaning was context-biased by the other (e.g., “money”/“river”). The effect of three psycholinguistic factors on subjects' performance was questioned: (i) The relative frequency of one meaning of the homograph as compared to the other meaning; (ii) The lexical/syntactic ambiguity (“ball”/“can”); (iii) The same/different phonological forms of the two meanings (“fair”/“bass”). The results are discussed in the framework of a model in which multiple special-purpose procedures are involved in normal processing, some of them being differentially impaired by brain disease in Broca's and Wernicke's aphasics. 相似文献
This paper focuses on (an interpretation of) the Enkratic principle of rationality, according to which rationality requires that if an agent sincerely and with conviction believes she ought to X, then X-ing is a goal in her plan. We analyze the logical structure of Enkrasia and its implications for deontic logic. To do so, we elaborate on the distinction between basic and derived oughts, and provide a multi-modal neighborhood logic with three characteristic operators: a non-normal operator for basic oughts, a non-normal operator for goals in plans, and a normal operator for derived oughts. We prove two completeness theorems for the resulting logic, and provide a dynamic extension of the logic by means of product updates. We illustrate how this setting informs deontic logic by considering issues related to the filtering of inconsistent oughts, the restricted validity of deontic closure, and the stability of oughts and goals under dynamics.