Differential Method of Characterizing Gait Strategies From Step Lengths and Frequencies: Strategy of Velocity Modulation

The differential method consists of the analysis of the variation of gait parameters length, frequency, and velocity with respect to their mean values, respectively, ΔL = L — L_m , Δf = f — f_m , and Δv = v – v_m , where L_m , f_m , and v_m represent the mean values of those parameters. Assuming that the strategy of modulation of velocity implies that L and f are functions of v and that statistical analyses of ratios ΔL/Δv and Δf/Δv have established that there is a very significant linear correlation, close to 1, between those ratios, the mathematical procedure allows one to determine the equation of step length, L = a · f + b · v + K, where a and b are the slope and the intercept of the linear regression and K is close to L_m . The equation was experimentally tested on 140 gait sequences performed by 6 participants and for gait velocities ranging from 0.6 to 2.2 m/s and was found to be very representative of all individual values. The differential method provides another way of using the derivative of velocity, v = L·f, to characterize the strategy of velocity modulation, which then permits one to determine the linear equation of velocity, v = f · L_m + L · f_m — L_m · f_m , and to show that the respective parts played by each parameter in the progression velocity are approximately equal. The author establishes the uniqueness of the different linear adjustments and discusses the differential method's own modes of use, that is, interindividually or globally.     

Foam coarsening under forced drainage

A monodisperse liquid foam is allowed to coarsen while subject to a constant flow of liquid. The average bubble size is indirectly monitored by measurement of the velocity of forced drainage waves. After an initial period the average bubble diameter is found to increase with the square root of time. The rate of this increase is a function of the flow rate; coarsening is slower in wet foams. This rate is linked to the variation in the film area in a foam as a function of liquid fraction.     

Specifically objective stochastic latency mechanisms

A two parameter additive model for psychological response latencies f_vi(t) = (θ_v + ?_i) exp(?(θ_v + ?_i)t) is suggested. Conditional inference procedures are derived for the psychometric latency model. If the model is considered as a theory for speed test construction the unrestricted comparability of measurements obtained under “speed” and “power” conditions is an attractive feature of the model. An extension of the parametric structure gives the “linear exponential model” f_vi(t) = (θ_v + Σ_ι^ma_iιη_ι) exp(?(θ_v + Σ_ι^ma_iιη_ι)t), where the time constants of the latencies are conceived as linear combinations of “basic parameters” corresponding to the experimental conditions of the latency situations. The linear exponential model includes as special cases some well known series latency mechanisms. Some generalizations of the distributional assumptions are discussed, especially the Weibull distributions. The estimation of parameters by conditional inference procedures and the evaluation of the fit of the model by conditional likelihood ratio tests is illustrated by means of the numerical data from a free recall experiment.     

Gleason's Theorem Has a Constructive Proof

Gleason's theorem for R ³ says that if f is a nonnegative function on the unit sphere with the property that f(x) + f(y) + f(z) is a fixed constant for each triple x,y,z of mutually orthogonal unit vectors, then f is a quadratic form. We examine the issues raised by discussions in this journal regarding the possibility of a constructive proof of Gleason"s theorem in light of the recent publication of such a proof.     

Masking by combination tones and bands

Masking of a pure tone by a cubic difference tone or band generated by two pure tones or by a pure tone and a narrow band of noise as a function of the level of the masker was measured for three subjects at three ratios of f₂/f₁, 1.125, 1,2, and 1.3. The three maskers used were f₁ alone, f₁ + f₂, and f₁ + NBN (60-Hz band of noise centered at f₂). At ratio 1.125, the amounts of masking produced by f₁ alone and f₁ + NBN were not significantly different for all subjects. For ratios = 1.125 and 1.2, f₁ + f₂ produced the least masking at least in two of the subjects. f₁ + NBN was the best masker at ratios 1.2 and 1.3. These results show that the masking data on cubic difference tone at very small ratios of f₂/f₁ are not reliable due to the masking effect contributed by f₁. For higher ratios, the combination band has to be used instead of combination tone because of the interaction between the signal and the cubic difference tone. Also the divergence of the effectiveness in masking by the three maskers gives an estimation of the levels of primaries at which the cubic difference tone is generated.     

Thermophysical properties of undercooled liquid cobalt

The surface tension of undercooled liquid cobalt has been measured by the oscillating-drop technique combined with electromagnetic levitation. The accuracy of the method was verified by measurements of the surface tension of liquid nickel. The liquid cobalt was undercooled by up to 231K (0.13T _m), and its surface tension determined to be σ_Co =1875 0.348(T-T _m)mNm^-1. From this result, the viscosity, self-diffusion coefficient, density and thermal diffusivity of undercooled liquid cobalt were derived. Using these thermophysical parameters, the growth velocity of cobalt dendrite is calculated and shown to agree well with experimental results. Furthermore, the Marangoni number and the Rayleigh number are calculated; these increase slowly with increasing degree of undercooling.     

Deposition-rate dependence of granular size distribution in Cu aggregate on liquid substrate studied by atomic force microscopy

In this article, we report an atomic force microscopy study on the microstructure and the deposition-rate dependence of granular size distribution in copper (Cu) ramified aggregates on a liquid substrate. This study shows that the ramified Cu aggregates are composed of Gaussian size distribution granules, which form immediately after the Cu atoms are deposited. The interesting phenomenon is that the mean diameter Φ_m of the granules exponentially decays and approaches a stable value Φ_c with an increase in the deposition rate f. The granular mean diameter Φ_m slightly changes with the time interval Δt during which the film is kept in the vacuum chamber, owing to the large diffusion coefficient of the Cu granules on the liquid substrates. The experimental behavior strongly depends on the properties of the liquid substrate.     

An extension of special relativity to accelerating frames and some of its philosophical implications

A rigorous extension of the full Lorentz group is found which is parameterized by interframe velocities v(t) and which reduces to Special Relativity for acceleration-free cases and to Galilean relativity for low velocity cases. Full group properties are exhibited. Four-momentum is defined and particle masses are shown to be invariants. Four-force is introduced and pseudoforces are shown to enter the equations of particle dynamics. Maxwell's equations are shown to take on pseudocurrent terms in accelerating frames. A four-vector Green function solution to the modified Maxwell equations is presented. Finally, a discussion is offered concerning philosophical questions such as the operational definition of time.     

The role of f 0 and formant frequencies in distinguishing the voices of men and women

The purpose of the present study was to determine the contributions of fundamental frequency (f ₀) and formants in cuing the distinction between men’s and women’s voices. A source-filter synthesizer was used to create four versions of 25 sentences spoken by men: (1) unmodified synthesis, (2) f ₀ only shifted up toward values typical of women, (3) formants only shifted up toward values typical of women, and (4) both f ₀ and formants shifted up. Identical methods were used to generate four corresponding versions of 25 sentences spoken by women, but with downward shifts. Listening tests showed that (1) shifting both f ₀ and formants was usually effective (～82%) in changing the perceived sex of the utterance, and (2) shifting either f ₀ or formants alone was usually ineffective in changing the perceived sex. Both f ₀ and formants are apparently needed to specify speaker sex, though even together these cues are not entirely effective. Results also suggested that f ₀ is somewhat more important than formants. A second experiment used the same methods, but isolated /hVd/ syllables were used as test signals. Results were broadly similar, with the important exception that, on average, the syllables were more likely to shift perceived talker sex with shifts in f ₀ and/or formants.     

Yield drop in high-strain-rate superplastic deformation of ZrO2-30 vol% MgAl2O4 spinel composite

The origin of a sudden yield drop in a tetragonal ZrO₂ dispersed with 30 vol% MgAl₂O₄ spinel composite has been examined. The present ZrO₂-spinel composite exhibits yield drop in superplastic flow at high strain rates of 0.2s^?1 or greater, where the flow behaviour is characterized by a stress exponent of about 3.5 and a grain-size exponent of about 1.0. Experimental examination suggests that a sudden increase in the mobile dislocation density within spinel grains is responsible for the yield drop.     

The anomalous flow behaviour in the layered Ti3SiC2 ceramic

The temperature dependence of flow stress for polycrystalline titanium silicon carbide (Ti₃SiC₂) has been investigated from room temperature to 1423K. An anomalous positive temperature dependence of flow stress was observed in this ceramic. This anomalous phenomenon is attributed to the change in the mechanism controlling the flow stress. However, it is not in good agreement with the widely accepted Kear-Wilsdorf mechanism.     

Velocity perception for sounds moving in frequency space

In three experiments, we considered the relative contribution of frequency change (Δf) and time change (Δt) to perceived velocity (Δf/Δt) for sounds that moved either continuously in frequency space (Experiment 1) or in discrete steps (Experiments 2 and 3). In all the experiments, participants estimated “how quickly stimuli changed in pitch” on a scale ranging from 0 (not changing at all) to 100 (changing very quickly). Objective frequency velocity was specified in terms of semitones per second (ST/s), with ascending and descending stimuli presented on each trial at one of seven velocities (2, 4, 6, 8, 10, 12, and 14 ST/s). Separate contributions of frequency change (Δf) and time change (Δt) to perceived velocity were assessed by holding total Δt constant and varying Δf or vice versa. For tone glides that moved continuously in frequency space, both Δf and Δt cues contributed approximately equally to perceived velocity. For tone sequences, in contrast, perceived velocity was based almost entirely on Δt, with surprisingly little contribution from Δf. Experiment 3 considered separate judgments about Δf and Δt in order to rule out the possibility that the results of Experiment 2 were due to the inability to judge frequency change in tone sequences.     

Interfacial structure in SiC/Si3N4 composite whiskers

Abstract

High-resolution TEM techniques have been used to investigate the interfacial structure in SiC/Si₃N₄ composite whiskers grown by a vapour–liquid–solid process. On one side of the whisker a coherent interface with the relationship of (111)β-SiC∥(102) α-Si₃N₄ has been observed, on the other side the interface is (111)β-SiC∥(114)α-Si₃N₄.     

Frequency-temperature dependent dynamics of dielectrics in ferric oxoborate Fe3BO6 of cocktail structure of nanorods

Oxoborates have both dielectric and magnetic properties useful for magnetodielectric devices, sensors, or biological tools. Such compounds Fe₂BO₄, Fe₃BO₅, or Fe₃BO₆ are known to grow easily as single crystals in a liquid flux. A polycrystalline phase forms only on controlled conditions of a solid state reaction of the basic oxides. In this study, we report highly dielectric Fe₃BO₆ when grown in a specific shape of nanorods (～200?nm diameter and 50–100?µm length) from an iron borate glass, which offers devisable shapes of sheets, discs, and fibers. Frequency (f)-temperature reliant dynamics of dielectric constant ε_r is studied over 25–300°C at 0.1–10^3?kHz frequencies. At low frequency such as 100?Hz, a large ε_r -value 40,000, better than most of high ε_r -value ferroelectrics, incurs at room temperature. At f?≥?50?kHz, although only an order of diminished ε_r -value lasts, it increases steadily with temperature, possibly due to increasing electrical conductivity in a specific resistor–capacitor network. Suppressed dielectric relaxation and spin-flops share a merely weak spin-reorientation transition near 160°C. A stable power loss ≤0.5 lasts at f?>?10?kHz useful for possible applications of magnetodielectric materials.     

How attentional focus on body sway affects postural control during quiet standing

The purpose of this study was to investigate how attentional focus on body sway affects postural control during quiet standing. To address this issue, sixteen young healthy adults were asked to stand upright as immobile as possible on a force platform in both Control and Attention conditions. In the latter condition, participants were instructed to deliberately focus their attention on their body sways and to increase their active intervention into postural control. The critical analysis was focused on elementary motions computed from the centre of pressure (CoP) trajectories: (1) the vertical projection of the centre of gravity (CoG_v) and (2) the difference between CoP and CoG_v (CoP–CoG_v). The former is recognised as an index of performance in this postural task, whilst the latter constitutes a fair expression of the ankle joint stiffness and is linked to the level of neuromuscular activity of the lower limb muscles required for controlling posture. A frequency-domain analysis showed increased amplitudes and frequencies of CoP–CoG_v motions in the Attention relative to the Control condition, whereas non-significant changes were observed for the CoG_v motions. Altogether, the present findings suggest that attentional focus on body sway, induced by the instructions, promoted the use of less automatic control process and hampered the efficiency for controlling posture during quiet standing.     

Lexicographic additive differences

Several authors have identified sets of axioms for a preference relation ? on a two-factor set A × X which imply that ? can be represented by specific types of numerical structures. Perhaps the two best-known of these are the additive representation, for which there are real valued functions f_A on A and f_X on X such that (a, x) ? (b, y) if and only if f_A(a) + f_X(x) > f_A(b) + f_X(y), and the lexicographic representation which, with A as the dominant factor, has (a, x) ? (b, y) if and only if f_A(a) > f_A(b) or {f_A(a) = f_A(b) and f_X(x) > f_X(y)}. Recently, Duncan Luce has combined the additive and lexicographic notions in a model for which A is the dominant factor if the difference between a and b is sufficiently large but which adheres to the additive representation when the difference between a and b lies within what might be referred to as a lexicographic threshold. The present paper specifies axioms for ? which lead to a numerical model which also has a lexicographic component but whose local tradeoff structure is governed by the additive-difference model instead of the additive model. Although the additive-difference model includes the additive model as a special case, the new lexicographic additive-difference model is not more general than Luce's model since the former has a “constant” lexicographic threshold whereas Luce's model has a “variable” lexicographic threshold. Realizations of the new model range from the completely lexicographic representation to the regular additive-difference model with no genuine lexicographic component. Axioms for the latter model are obtained from the general axioms with one slight modification.     

Multilinear representations for ordinal utility functions

An ordinal utility function u over two attributes X₁, X₂ is additive if there exists a strictly monotonic function ϕ such that ϕ(u) = v₁(x₂) + v₂(x₂) for some functions v₁, v₂. Here we consider the class of ordinal utility functions over n attributes for which each pair of attributes is additive, but not necessarily separable, for any fixed levels of the remaining attributes. We show that while this class is more general than those that are ordinally additive, the assessment task is of the same order of difficulty, and involves a hierarchy of multilinear rather than additive decompositions.     

Central auditory processing : IV. Ear dominance—Spatial and temporal complexity

Ear dominance for dichotically presented tones was measured in 63 right-handed subjects when the frequency difference (Δf) was small compared to the center frequency (f_c) and again when it was large. Although two-thirds of the population exhibited a left-ear dominance in both conditions, a shift toward right-ear dominance occurred when the Δf was increased. An additional study, employing the alternating tone illusion described by Deutsch, revealed the same general effect, i.e., a shift toward right-ear dominance with increasing values of Δf/f_c. The results of these experiments, coupled with a review of previously published data of other dichotic experiments, indicate that as the ratio of Δf/f_c increases, the subjective complexity of the sound image increases, and there is a progressive emergence of a “right-ear advantage” (or ear dominance). A tentative explanation relates these results to the effects of anatomical asymmetries of primary and auditory association cortex and the efferent temporal lobe enhancement mechanism described by R. Efron, P. H. Crandall, B. Koss, P. L. Divenyi, and E. W. Yund (Brain and Language, 1983, 19, 254–263.     

Order from chaos? 1/f noise predicts performance on reaction time measures

In repetitive tasks, latencies typically display non-random variation called 1/f noise, but the magnitude of 1/f noise can depend on effort. Between-participant variation in 1/f noise might therefore predict differences in performance for tasks that are sensitive to effort. Feedback was manipulated to suggest that participants had (or had not) shown bias on a preliminary task. Participants then completed a computer-based measure of prejudice. Consistent with an ironic process account, participants who were falsely informed that they had shown bias ultimately did show increased prejudice. But ironic processes should depend on control-related effort. Taking 1/f noise as a proxy for effort, results show that the effect of the feedback was moderated by 1/f noise. Participants demonstrating a low-effort 1/f pattern were unaffected by the manipulation (η_p² < .01), whereas those demonstrating a high-effort 1/f pattern showed larger effects (η_p² = .19). Results thus suggest that 1/f noise can provide novel explanatory power regarding behavior.