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PubMed1997

Human arm stiffness and equilibrium-point trajectory during multi-joint movement.

By using a newly designed high-performance manipulandum and a new estimation algorithm, we measured human multi-joint arm stiffness parameters during multi-joint point-to-point movements on a horizontal plane. This manipulandum allows us to apply a sufficient perturbation to subject's arm within a brief period during movement. Arm stiffness parameters were reliably estimated using a new algorithm, in which all unknown structural parameters could be estimated independent of arm posture (i.e., constant values under any arm posture). Arm stiffness during transverse movement was considerably greater than that during corresponding posture, but not during a longitudinal movement. Although the ratios of elbow, shoulder, and double-joint stiffness were varied in time, the orientation of stiffness ellipses during the movement did not change much. Equilibrium-point trajectories that were predicted from measured stiffness parameters and actual trajectories were slightly sinusoidally curved in Cartesian space and their velocity profiles were quite different from the velocity profiles of actual hand trajectories. This result contradicts the hypothesis that the brain does not take the dynamics into account in movement control depending on the neuromuscular servo mechanism; rather, it implies that the brain needs to acquire some internal models of controlled objects.

Adult↗

PubMed2003

Bioprocess control from a multivariate process trajectory.

A multivariate bioprocess control approach, capable of tracking a pre-set process trajectory correlated to the biomass or product concentration in the bioprocess is described. The trajectory was either a latent variable derived from multivariate statistical process monitoring (MSPC) based on partial least squares (PLS) modeling, or the absolute value of the process variable. In the control algorithm the substrate feed pump rate was calculated from on-line analyzer data. The only parameters needed were the substrate feed concentration and the substrate yield of the growth-limiting substrate. On-line near-infrared spectroscopy data were used to demonstrate the performance of the control algorithm on an Escherichia coli fed-batch cultivation for tryptophan production. The controller showed good ability to track a defined biomass trajectory during varying process dynamics. The robustness of the control was high, despite significant external disturbances on the cultivation and control parameters.

Algorithms↗

PubMed2003

Characteristics of trajectory in the migration of Amoeba proteus.

We investigated the behavior of migration of Amoeba proteus in an isotropic environment. We found that the trajectory in the migration of A. proteus is smooth in the observation time of 500-1000 s, but its migration every second (the cell velocity) on the trajectory randomly changes. Stochastic analysis of the cell velocity and the turn angle of the trajectory has shown that the histograms of the both variables well fit to Gaussian curves. Supposing a simple model equation for the cell motion, we have estimated the motive force of the migrating cell, which is of the order of piconewton. Furthermore, we have found that the cell velocity and the turn angle have a negative cross-correlation coefficient, which suggests that the amoeba explores better environment by changing frequently its migrating direction at a low speed and it moves rectilinearly to the best environment at a high speed. On the other hand, the model equation has simulated the negative correlation between the cell velocity and the turn angle. This indicates that the apparently rational behavior comes from intrinsic characteristics in the dynamical system where the motive force is not torquelike.

Amoeba↗

PubMed2006

Change trajectories in women's STD/HIV risk behaviors following intervention.

Three 16-month sexual risk-taking trajectories were identified in 287 women in an STD/HIV intervention study. The Risk Eliminator group reported no sex risk following intervention while the Risk Reducer group reported continuous drops over time. The High Risk group reported higher initial risk than the other two and no subsequent changes. The trajectory groups showed no between- or within-group effects of intervention exposure. Trajectory groups were compared on baseline characteristics. No differences were seen in demographics or STD/HIV knowledge. Compared to one or both of the other groups, the High Risk women reported more lifetime partners, recent paying partners, adult rape, and recent substance use. Their steady partners were more likely to be abusive, intoxicated during sex (as were the women themselves), and believed to be non-monogamous. The Risk Eliminator group differed from the other two by being less likely to report a history of childhood sexual abuse.

Adolescent↗

PubMed1986

Systolic direction of right ventricular contrast trajectories in the detection of ventricular septal defect with left-to-right shunt.

Abnormal systolic direction of contrast flow toward the transducer within the right ventricle was demonstrated on M-mode echocardiograms in patients with ventricular septal defect (VSD) and left-to-right shunt. The usefulness of this new technique was tested in 30 patients with VSD proved at catheterization and in 300 control subjects. In all subjects, 2-dimensional (2-D) visualization of the defect, 2-D negative contrast effect and M-mode demonstration of positive contrast within the left ventricular (LV) cavity were also performed. Sensitivity and specificity for each technique and each hemodynamic subgroup of patients were determined and compared. A sensitivity of 100% for the diagnosis of VSD by anterior right ventricular (RV) systolic direction of contrast trajectories was achieved in 20 patients with relatively small VSDs and mild to moderate elevation of RV pressure (RV-LV pressure ratio 60%) and mean pulmonary to systemic blood flow ratio of 1.7. Sensitivities of 2-D echocardiography, 2-D negative contrast technique and positive LV contrast appearance on M-mode echocardiography were 63%, 71% and 53%, respectively. Sensitivity of 100% for systolic anterior direction of contrast trajectories was also calculated in 6 patients with RV-LV pressure ratios from 61 to 80% and mean pulmonary to systemic blood flow ratio of 2.7. Sensitivities of 2-D echocardiography, 2-D negative contrast technique and positive contrast appearance in the LV cavity by M-mode echocardiography were 75%, 60% and 86%, respectively. In 4 patients with systemic or nearly systemic RV pressure, sensitivity of systolic anterior direction of RV contrast trajectories decreased drastically, to only 67%.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗

PubMed1985

Three-channel Lissajous' trajectory of human auditory brain-stem evoked potentials. I. Normative measures.

Three-channel Lissajous' trajectories (3-CLTs) of auditory brainstem evoked potentials (ABEPs) were obtained from 14 humans (28 ears) in response to 75 dB nHL, 10/sec alternating polarity clicks. A normative set of 3-CLT quantitative measures was calculated and compared with amplitudes and latencies of the simultaneously recorded, single-channel, vertex-mastoid ABEP. The comparison included average values as well as intersubject variability. The 3-CLT measures included: apex latencies; planar segment durations, orientation, size and shape; trajectory-amplitude peaks and their latencies. Apex latencies of 3-CLT were comparable to peak latencies of the vertex-mastoid records, both in absolute values and in intersubject variability. Durations of planar segments were approximately 0.7 msec and their standard deviations were about a half of their average. Individual planar segment orientations were typically within 50 degrees of the normative average. Trajectory amplitudes were, in general, somewhat larger than peak amplitudes of the vertex-mastoid records, while their intersubject variabilities were comparable. Size and shape measures of planar segments were variable across subjects, making their clinical use, in their present form, questionable. The quantitative study of the 3-CLT of auditory brain-stem evoked potentials will enable evaluation of normal, as well as pathological, evoked potentials, to further the understanding and utility of this comprehensive representation of brain-stem function.

Adult↗

PubMed1986

Three-channel Lissajous' trajectory of human auditory brain-stem evoked potentials. II. Effects of click intensity.

Three-channel Lissajous' trajectories (3-CLT) of the human auditory brain-stem evoked potentials (ABEP) were recorded from 14 adult subjects at 15, 45, and 75 dB (nHL). The 3-CLTs were analysed and described in terms of their constituent planar segments and their trajectory amplitudes at each stimulus level. At 75 dB, 9 planar segments were observed, each having unique apex latency, boundaries, duration, shape, size and orientation in voltage space. As stimulus levels were lowered, changes were noted in apex latency and trajectory amplitude which parallelled changes seen under similar experimental conditions using single-channel ABEP. In addition, changes were seen in planar segment number, boundaries, duration, shape, size and orientation, all of which could be related to decreased generator activity. It is proposed that at high stimulus levels, there is significant temporal overlap of generator activity which results in a larger number of planar segments and single-channel peaks than at low stimulus levels. This may be important to the identification of the specific generators of the ABEP and their appropriate clinical usage.

Brain Stem↗

PubMed1986

Three-channel Lissajous' trajectory of human auditory brain-stem evoked potentials. III. Effects of click rate.

Three-channel Lissajous' trajectories (3-CLT) of the human auditory brain-stem evoked potentials (ABEPs) were recorded from 14 adult subjects using click rates of 10, 55 and 80/sec. The 3-CLTs were analysed and described in terms of their constituent planar segments and their trajectory amplitudes at each stimulus rate. Increasing stimulus rate resulted in an increase of planar segment duration which was more pronounced for segments 'a' and 'e', an increase in apex latency which was more pronounced the later the component and a decrease in planar segment size and peak trajectory amplitude which was more pronounced the earlier the component. These findings support the involvement of synaptic efficacy changes in the effects of stimulus rate on ABEP. The results are explained by overlapping convergence and divergence in the ascending auditory pathway. These results support the notion that the principal generator of each component is activated by the principal generator of the previous component, with some temporal overlap of their activities. Such temporal overlap may be minimized by using low intensity high rate stimuli.

Brain Stem↗

PubMed1987

Three-channel Lissajous' trajectory of auditory brain-stem potentials evoked by specific frequency bands (derived responses).

Three-channel Lissajous' trajectories (3-CLT) of the auditory brain-stem evoked potentials were recorded from 14 adult subjects in response to different frequency bands as well as to unmasked clicks. The frequency bands (8 kHz and above, 4-8 kHz, 2-4 kHz, 1-2 kHz and 1 kHz and under) were obtained by subtraction of wave forms to clicks with high-pass masking at these frequencies (derived responses). The 3-CLTs were analysed and described in terms of their geometrical measures. All 3-CLTs included 5 planar segments whose latencies progressively increased with decreasing stimulus frequency, and whose durations and orientations did not change across frequencies. Apex trajectory amplitudes as well as planar segment sizes decreased between unmasked clicks and specific frequency bands, and with decreasing frequency. The changes noted for apex latency and trajectory amplitude were paralleled with corresponding changes in amplitude and latency of single-channel records. The changes in 3-CLT measures with changes in stimulus frequency reflect the contribution of different parts of the cochlea. The unchanged measures may be attributed to the unchanged anatomy of the generators under the different stimulus conditions. The results of this study do not support the wide band of stimuli as responsible for the planarity of 3-CLT segments. In addition, these results indicate that different cochlear processes are responsible for the latency changes observed across stimulus intensities and for those associated with stimulus frequency.

Adolescent↗

PubMed1984

Optimal javelin trajectories.

A companion paper has treated computer simulation of javelin flight using measured lift, drag and pitching moments. In the present paper we present, categorize and discuss the relative significance of various initial conditions in such a simulation. Since the differential equations describing flight are autonomous, the eventual javelin range and entry angle are unique functions of the initial conditions. A series of successively less constrained optimum solutions is defined, the last of which is the global optimum javelin trajectory. Sensitivities of these trajectories to perturbations from the optima and their implications for throwers are discussed. Finally, we investigate the effects of some design and environmental parameters on optimal initial conditions and trajectories.

Computers↗

PubMed1991

Real-time interactive frequency filtering of molecular dynamics trajectories.

Molecular dynamics simulations of atomic motion in protein and nucleic acid molecules must be done on a femtosecond time-scale. Much of this rapid motion is unimportant for the slower changes that are most relevant to biological function (conformational changes, substrate binding, protein folding). The high-frequency motion makes simulations computationally expensive. More importantly, the high frequencies obscure visualization of the relevant dynamics processes. Sessions, Dauber-Osguthorpe and Osguthorpe presented a method for removing high-frequency motions from atomic co-ordinates of trajectories generated by simulation. While that study used fast Fourier methods and emphasized the use of filtering for analysis of trajectories, this communication describes a new method that makes it much easier to use frequency filtering in programs that display trajectories as a sequence of moving images. Tests of the method on systems extending from pure water to proteins and nucleic acid molecules in vacuo and in solution have demonstrated its general utility. Impressed with the power and simplicity of the new method, we wish to present it in sufficient detail to allow others to implement it themselves.

Fourier Analysis↗

PubMed1989

Trabecular structure compared to stress trajectories in the proximal femur and the calcaneus.

The theory that the trabecular structure within bones follows the principal stress trajectories, is investigated by two-dimensional finite element models of increasing complexity. This is done for the proximal femur of the human and for the calcaneus of the horse. In both cases, a simple model with well-chosen loading and boundary conditions gives good agreement between the observed trabecular structure and the calculated stress trajectories. It is shown that this stress trajectory theory has a mechanically founded explanation.

Adaptation, Biological↗

PubMedDate not supplied

Three-channel Lissajous' trajectories of auditory event-related potentials to target stimuli.

Three orthogonal recordings ('X,' 'Y' and 'Z') of event-related potentials (ERPs) evoked by auditory target stimuli were represented in 3-dimensional voltage-space, to produce 3-channel Lissajous' trajectories (3-CLTs). Stimuli were verbal or non-verbal and were differentiated by their pitch, phonemic or phonetic attributes. Visual inspection and quantitative evaluations unexpectedly revealed that the 3-CLT of these ERPs strongly resembles a 'hair-pin' trajectory. This trajectory titled in space at characteristic angles with each of the analysis axes: 133 degrees with the 'X' axis, 87 degrees with the 'Y' axis, and 54 degrees with the 'Z' axis. The relatively small inter-subject variability observed in the geometrical measures, particularly in orientation, may be attributed to the slight variation in the underlying generators. 3-CLT analysis could be useful in future clinical as well as source studies of ERP generators.

Acoustic Stimulation↗

PubMed1990

Microcomputer analysis of three-channel Lissajous' trajectory of auditory brainstem evoked potentials.

A software package for the IBM PC computer is presented to facilitate the analysis of three-channel Lissajous' trajectories (3CLT) of auditory brainstem potentials. The program deals with 4-channel numeric or ASCII files, including three orthogonal X, Y, Z channels and standard vertex-mastoid on the stimulated side. The 3CLT analysis program implements standard measurements of peak latencies, voltage amplitude and curvature plots computed from the three orthogonal channels, interactive three-dimensional rotations of the trajectory and planar segment analysis. Parameter estimates of the best-fit plane are computed for any part of the trajectory limited by two latency cursors. Results are displayed and stored in a table including segment bounds and duration, sight vector orientation, plane equation parameters and adjustment criteria.

Evoked Potentials, Auditory↗

PubMed1995

Stigma, HIV and AIDS: an exploration and elaboration of a stigma trajectory.

Stigma is a social construction which dramatically affects the life experiences of the individuals infected with the human immunodeficiency virus (HIV) and their partners, family and friends. While it has been generally recognized that the nature of stigma varies across illnesses, it has usually not been considered as changing and emerging over the course of a single illness. In this paper, HIV/AIDS is analyzed in terms of a stigma trajectory. The primary purpose is to conceptualize how individuals with HIV/AIDS experience stigma and to demonstrate how these experiences are affected by changes in the biophysical dimensions of HIV/AIDS. Four phases of the HIV/AIDS stigma trajectory are depicted: (1) at risk: pre-stigma and the worried well; (2) diagnosis: confronting an altered identity; (3) latent: living between illness and health; and (4) manifest: passage to social and physical death. The essential processes through which individuals personalize the illness, dilemmas encountered in interpersonal relations, strategies that are used to avoid or minimize HIV-related stigma, and subcultural networks and ideologies that are drawn upon to construct, avow, and adapt to an HIV identity are considered across the stigma trajectory.

Acquired Immunodeficiency Syndrome↗

PubMed1982

Trajectory determines movement dynamics.

The relation between figural and kimematic aspects of movement was studied in handwriting and drawing. It was found that, throughout the movement, the tangential velocity. V is proportional to the radius of curvature r of the trajectory: V= kr, or, equivalently, that the angular velocity is constant: dalpha(t)/dt = K. However, the constant k generally takes several distinct values during the movement, the changes being abrupt. These changes suggest a clear segmentation of the movement into units of action which overlap but do not coincide with the figural units as defined by the discontinuities of the movement (cuspids, points of inflection). This organisational principle holds even when movements are mechanically constrained or are executed under strict visuo-motor guidance. Moreover, the segmentation of a given trajectory is invariant with respect to the total duration of the movement. A tentative interpretation of the principle is proposed which results from the assumption that the actual movement is produced as a continuous approximation to an intended movement, and that the well known relationship between movement speed and extent in rectilinear trajectories (Fitts' law) also applies to such continuous approximation.

Biomechanical Phenomena↗

PubMed1992

Virtual trajectories of single-joint movements performed under two basic strategies.

The framework of the equilibrium point hypothesis has been used to analyse motor control processes for single-joint movements. Virtual trajectories and joint stiffness were reconstructed for different movement speeds and distances when subjects were instructed either to move "as fast as possible" or to intentionally vary movement speed. These instructions are assumed to be associated with similar or different rates of change of hypothetical central control variables (corresponding to the speed-sensitive and speed-insensitive strategies). The subjects were trained to perform relatively slow, moderately fast and very fast (nominal movement times 800, 400 and 250 ms) single-joint elbow flexion movements against a constant extending torque bias. They were instructed to reproduce the motor command for a series of movements while ignoring possible changes in the external torque which could slowly and unpredictably increase, decrease, or remain constant. The total muscle torque was calculated as a sum of external and inertial components. Fast movements over different distances were made with the speed-insensitive strategy. They were characterized by an increase in joint stiffness near the midpoint of the movements which was relatively independent of movement amplitude. Their virtual trajectories had a non-monotonic N-shape. All three arms of the N-shape scaled with movement amplitude. Movements over one distance at different speeds were made with a speed-sensitive strategy. They demonstrated different patterns of virtual trajectories and joint stiffness that depended on movement speed. The N-shape became less apparent for moderately fast movements and virtually disappeared for the slow movements. Slow movements showed no visible increase in joint stiffness.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗

PubMed1996

Quantitative analysis of human walking trajectory on a circular path in darkness.

Thirteen normal (eight young and five older) subjects and a patient who was removed left sided acoustic neurinoma were tested to walk blindfolded along circular paths. They were asked to walk completing two revolutions and to stop when they judged they had returned to the initial position with their head faced to the initial directions. Movements of two markers on the subjects head were recorded by three dimensional motion analyzing system (ELITE system) at 50 Hz which allowed us to measure (a) total walked distance, (b) average radius of the trajectory, and (c) cumulative angle of rotation. Eight young subjects were tested on three circles with radii 0.5, 0.9, and 1.15 m, in two conditions (control, and with mental arythmetic), only to clockwise direction. Five older subjects and a patient were tested on a circle of 0.9 m radius in two conditions, but to both directions, counterclockwise and clockwise. Walked trajectories of young subjects were smooth, whereas those of older subjects tended to be polygonal. Young subjects overshot the ideal distance (6.6%) and ideal radius (9.5%), whereas they undershot the ideal angle (5.1%). There was no effect of circle size or condition on these variables. On the other hand, there was a significant effect of condition on average radius in the older group. The performance of older subjects seemed to be affected by the concurrent mental task. Comparing the counterclockwise walk, the older subjects undershot the turning angle much more than the young subjects which suggest deficits in the vestibular function with aging. The patient showed larger radius and smaller angle while she turned to the healthy side (clockwise) than to the affected side (counterclockwise). Lack of unilateral vestibular information seemed to have affected the circular walking trajectory.

Adult↗