Optimal jumping strategies from compliant surfaces: a simple model of springboard standing jumps

A simple model of standing dives is used to investigate optimal jumping strategies from compliant surfaces and applied to springboard diving. The human model consists of a massless leg actuated by knee torque, and a lumped torso mass centered above the leg. The springboard is modeled as a mass-spring system. Maximum jump height for a male and a female is calculated by controlling knee-torque activation level as a function of time. The optimization includes constraints on minimum and maximum knee angle, rate of change of normalized activation level, and contact duration. Simulation results for maximal springboard depression and diver takeoff velocity agree reasonably with experimental data, even though larger board tip velocities are necessarily predicted earlier during the contact period. Qualitatively similar multiple pulse knee-torque activation patterns are found over various conditions and are different from those in rigid-surface jumping. The model is less able to predict accurately jump height at high fulcrum number since jumpers may have difficulty behaving optimally at non-preferred fulcrum settings. If strength is proportional to the product of mass and leg length, increasing leg length is more effective in increasing jump height than is increasing mass.     

Functional variability in the takeoff phase of one metre springboard forward dives

In springboard diving consistency of body orientation at water entry is necessary for a good dive and is likely to be dependent on the consistency of conditions at takeoff. The aim of the present study was to investigate whether a diver modifies his technique from dive to dive during the board contact phase in order to be more consistent at takeoff in one metre springboard forward dives. Two-dimensional video analysis was used to calculate orientation and configuration angles of 12 forward pike dives and 12 forward 2½ somersault pike dives, performed by an international diver. A computer simulation model of a diver and springboard during board contact was used to obtain matching simulations of the performances and to calculate the rotation potential (angular momentum × flight time) for each dive. Simulations were used to determine the variation in conditions at maximum board depression arising from variation in touchdown conditions, and the variation in takeoff conditions arising from the variability in conditions at maximum board depression. A comparison of the simulated and performance variations implied that adjustments were made during the board contact phase for both the pike dives and the 2½ somersault pike dives. In the board depression phase, adjustments reduced the variability in the mass centre horizontal velocity at the lowest point. In the board recoil phase, adjustments reduced the variability in the horizontal velocity and rotation potential at takeoff.     

Chronometric comparisons of imagery to action: visualizing versus physically performing springboard dives

Motor imagery research emphasizes similarities between the mental imagery of an action and its physical execution. In this study, temporal differences between motor imagery and its physical performance as a function of performer expertise, skill complexity, and spatial ability were investigated. Physical execution times for springboard dives were compared with visualized execution times. Results indicate that physical and visualized performance times were not identical: Their relation is a function of dive complexity and diver expertise, but not their interaction. Relative to physical time, visualization time increased with increased complexity, suggesting the involvement of capacity-limited working memory. A nonmonotonic relation was found for expertise: Unlike experts or novices, visualization time for intermediates was significantly slower than physical time. These temporal differences are most consistent with schematic differences in skill representation. Intermediates may be relatively slowed by greater amounts of nonautomatized knowledge, as compared with the automatized knowledge of experts or the sparse knowledge of novices.     

Modality of postural movement in men and women with both arms flexed during standing.

We investigated postural movement associated with bilateral arm flexion in response to a light signal during standing in 179 healthy men and women to assess whether individual and sex differences arc evident in the postural movement pattern. The following results were obtained. (a) A correlation of -.87 was noted between movement angles of the foot-leg and leg-trunk. (b) Individual differences in movement angle were approximately twice as large in the hip joint as in the ankle and knee joints, and the movement angle of the leg trunk showed approximately half the number of extension as flexion movements. (c) The postural movement pattern was categorized on the basis of the movement angle of the foot leg and leg trunk into the following three patterns: hip flexion, backward leaning, and hip extension. The percentages of subjects showing these patterns were 59.2%, 33.5%, and 7.3%, respectively. (d) The inclination angle reflecting the righting response showed a gradual increase in size in the order of trunk, head, and neck. However, the righting response was not controlled precisely enough to enable subjects to maintain the inclination angle in a quiet standing posture. (e) We identified a significant sex difference in the relative frequency of subjects in the postural movement pattern.     

Role of a striatal slowly inactivating potassium current in short-term facilitation of corticostriatal inputs: a computer simulation study

Striatal output neurons (SONs) integrate glutamatergic synaptic inputs originating from the cerebral cortex. In vivo electrophysiological data have shown that a prior depolarization of SONs induced a short-term (相似文献   

Jewish rural settlement in Cyprus 1882–1935: a “springboard” or a destiny?

After its transfer to British rule in 1878, Cyprus became an object of Jewish settlement. The island was seen as a reasonable alternative at a time when aliyah and land purchase in Eretz-Israel were problematic. Three attempts were made by different groups to settle Jews in rural sites between 1882 and 1935. The first, near Pathos, was initiated by a millenarian British association. It lasted barely a year and focused on helping immigrants from Russia. The second, in the years 1892–1898, fostered by a pre-Zionist group of London Jews, and with the assistance of JCA, led to the purchase of Margo, an agricultural site located between Larnaka and Nicosia. The third attempt, the longest, between 1898 and 1935, was sponsored by the JCA itself, which settled about 35 families and offered continuing professional assistance. Ultimate failure was assured, nonetheless, by the proximity of Eretz-Israel, which exerted an irresistible allure on the younger, second, generation. For a short time, Cyprus was thought by some to be a political alternative to Eretz-Israel. The so-called “Trietsch Project” of 1898 interested even Herzl himself.     

Factor analysis of ipsative data: a simulation study

This paper introduces a summary on how to proceed to conduct a factor analysis when the input data are ipsative. The classical factor analysis procedures cannot be used because the covariance matrix is singular. Additionally, previous research on the optimal conditions to conduct factor analysis for ipsatized data is reviewed, and the results of a simulation study are presented. The study includes conditions of sample size, model complexity, and model specification (correct vs. incorrect). The results suggest that researchers should be careful when factor analyzing ipsatized data, particularly if they suspect that the model is incorrectly specified and includes a smaller number of factors.     

Aspects of a compliant container: Considering narcissistic personality configurations1

Attempts to expand Bion's container‐contained model and to use it as an instrument for investigating psychic disorders arising in the analytical context have led the author to conjecture about the model's dynamics. In this paper, she illustrates a hypothetical compliant container by clinical material, in order to describe a psychic structure that contains only what is pleasant, only that which does not cause confl ict or pain. Through a dynamic of ideal accommodation, a compliant container makes any disagreements, contradictions, limits and differences disappear, recognizing only what is very familiar and commonplace. The results are misleading, pseudological thoughts and concepts founded on strategic plans to maintain a narcissistic defensive system.     

Arsenic adsorption onto silicon stepped surfaces: a study at semiempirical level

As adsorption onto Si surfaces vicinal to (100) has been studied using the Hartree–Fock method at a semiempirical level and a cluster model of the surface steps. The simulation conditions apply to the dilute limit of the adsorbate concentration. Accordingly, one As atom is placed on the step in a substitutional or interstitial location, either above or below the surface. The optimal configuration of the system is evaluated from a steepest-descent energy minimization. The central finding is that As is preferably adsorbed in the interstitial location and the physical explanation is that this location allows both a stronger electrostatic coupling with the surface and a lower stress than in the case of the substitutional impurity. This result represents a significant divergence with respect to the known properties of the bulk impurity. It can, however, consistently account for known features of heteroepitaxial growth of As on Si(100).     

Reading a standing wave: Figure-ground-alternation masking of primes in evaluative priming

We propose a new masking technique for masking word stimuli. Drawing on the phenomena of metacontrast and paracontrast, we alternately presented two prime displays of the same word with the background color in one display matching the font color in the other display and vice versa. The sequence of twenty alterations (spanning approx. 267ms) was sandwich-masked by structure masks. Using this masking technique, we conducted evaluative priming experiments with positive and negative target and prime words. Significant priming effects were found - for primes and targets drawn from the same as well as from different word sets. Priming effects were independent of prime discrimination performance in direct tests and they were still significant after the sample was restricted to those participants who showed random responding in the direct test.     

The role of motor simulation in action perception: a neuropsychological case study

Research on embodied cognition stresses that bodily and motor processes constrain how we perceive others. Regarding action perception the most prominent hypothesis is that observed actions are matched to the observer’s own motor representations. Previous findings demonstrate that the motor laws that constrain one’s performance also constrain one’s perception of others’ actions. The present neuropsychological case study asked whether neurological impairments affect a person’s performance and action perception in the same way. The results showed that patient DS, who suffers from a frontal brain lesion, not only ignored target size when performing movements but also when asked to judge whether others can perform the same movements. In other words DS showed the same violation of Fitts’s law when performing and observing actions. These results further support the assumption of close perception action links and the assumption that these links recruit predictive mechanisms residing in the motor system.     

Analysing multisource feedback with multilevel structural equation models: Pitfalls and recommendations from a simulation study

When multisource feedback instruments, for example, 360-degree feedback tools, are validated, multilevel structural equation models are the method of choice to quantify the amount of reliability as well as convergent and discriminant validity. A non-standard multilevel structural equation model that incorporates self-ratings (level-2 variables) and others’ ratings from different additional perspectives (level-1 variables), for example, peers and subordinates, has recently been presented. In a Monte Carlo simulation study, we determine the minimal required sample sizes for this model. Model parameters are accurately estimated even with the smallest simulated sample size of 100 self-ratings and two ratings of peers and of subordinates. The precise estimation of standard errors necessitates sample sizes of 400 self-ratings or at least four ratings of peers and subordinates. However, if sample sizes are smaller, mainly standard errors concerning common method factors are biased. Interestingly, there are trade-off effects between the sample sizes of self-ratings and others’ ratings in their effect on estimation bias. The degree of convergent and discriminant validity has no effect on the accuracy of model estimates. The χ² test statistic does not follow the expected distribution. Therefore, we suggest using a corrected level-specific standardized root mean square residual to analyse model fit and conclude with further recommendations for applied organizational research.     

Measurement of active rotation in standing: reliability of a simple test protocol

Interrater and intrarater reliability were evaluated for a test measuring active rotation range in a standing position. Subjects stood with their feet comfortably apart while a horizontal bar rested on their shoulders. A plumb bob attached to the end of the bar was allowed to drop to the floor, indicating maximal rotation range achieved. Two raters measured 24 subjects (M age = 35 +/- 14 yr.), who were sedentary office workers and active recreational golfers, on two occasions separated by two weeks to obtain values for left and right trunk rotation range. The test had good intrarater and interrater reliabilities, with standard error of measurement values varying from 5.6 degrees to 8.6 degrees against an overall mean range of 128 degrees. This simple active rotation test requires inexpensive equipment and could be incorporated into clinical examinations when there is a need to assess active rotation in standing with minimal constraints.     

Anatomy of a DATASIM simulation: The Doob and Gross horn-honking study

The program DATASIM is used to simulate the classic “horn-honking” study by Doob and Gross (1968). In a 2×2 field experiment, Doob and Gross investigated the effects of status of frustrator—a low- or high-status car blocking an intersection—on the latency to honk among male and female drivers. The present paper illustrates how to extract the values of simulation parameters from the published study, how to initialize the simulation in DATASIM, and how to generate and analyze the simulated data. Certain complications arise because the latency data collected by Doob and Gross were nonnormally distributed, cell variances were heterogeneous, and sample sizes were unequal. DATASIM is able to incorporate these features in the simulation, and several methods for assessing the quality of the simulation are illustrated. In addition, sampling experiments are reported, which were performed to assess the joint and individual effects of nonnormality and heterogeneity on the Type I and Type II error rates of theF test. The paper concludes with some practical suggestions regarding how researchers can evaluate, and adjust for, the effects of such violations.     

Psychological study of a crew in long-term space flight simulation

This research derives from a 60-day isolation study realized for the European Space Agency (ESA) as a simulation of space flights. Three goals were pursued in this study: (a) to study individual and group responses to the stress factors specific to the simulation; (b) to make a critical comparison of a variety of tools and methods used for this purpose; and (c) to express recommendations for future research. Direct methods (questionnaires, tests) and indirect methods (observation) were used in an individual and a whole group assessment. The group did not show important stress manifestations during the isolation period. It maintained its cohesion by opposing the external authority. Some tools were more efficient than others: The qualitative and indirect methods have revealed much more information than the quantitative or direct methods that reinforced one's defense to avoid criticism.     

Role of motor imitation in traversability of surfaces by walking infants.

The ecological approach by Gibson stressed the role of visual cues in toddlers' locomotor activities. In particular, a rigid surface offers more traversability "affordances" to walkers (13-16 mo. old) than a deformable surface. On the other hand, imitation plays a relevant role in human behaviors. In our study a group of 17 walking infants (12-19 mo.) were asked to choose between locomoting on a rigid versus a deformable surface after having seen an older child walking on the deformable surface. A control group of 19 infants were asked to do the same task without having seen a model. The task was repeated three times. No relevant differences appeared between the two groups as to the choice of surfaces: the rigid surface was preferred by both groups. Some slight differences in the behavior of the experimental group were seen as a result of observing the model. Clearly, however, social stimulus. such as the sight of an older child performing a specific task, does not overcome the affordances which induce infants not to walk on the deformable surface.     

Populations of spiking neurons for reservoir computing: Closed loop control of a compliant quadruped

Compliant robots can be more versatile than traditional robots, but their control is more complex. The dynamics of compliant bodies can however be turned into an advantage using the physical reservoir computing framework. By feeding sensor signals to the reservoir and extracting motor signals from the reservoir, closed loop robot control is possible. Here, we present a novel framework for implementing central pattern generators with spiking neural networks to obtain closed loop robot control. Using the FORCE learning paradigm, we train a reservoir of spiking neuron populations to act as a central pattern generator. We demonstrate the learning of predefined gait patterns, speed control and gait transition on a simulated model of a compliant quadrupedal robot.     

Generalized canonical correlation analysis of matrices with missing rows: a simulation study

A method is presented for generalized canonical correlation analysis of two or more matrices with missing rows. The method is a combination of Carroll’s (1968) method and the missing data approach of the OVERALS technique (Van der Burg, 1988). In a simulation study we assess the performance of the method and compare it to an existing procedure called GENCOM, proposed by Green and Carroll (1988). We find that the proposed method outperforms the GENCOM algorithm both with respect to model fit and recovery of the true structure. The research of Michel van de Velden was partly funded through EU Grant HPMF-CT-2000-00664. The authors would like to thank the associate editor and three anonymous referees for their constructive comments and suggestions that led to a considerable improvement of the paper.