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PubMed2006

Developmental trajectories in cottonwood phytochemistry.

We examined the hypothesis that ecologically important phytochemical traits differ predictably among various developmental zones of trees (i.e., mature and juvenile zones of individual trees and juvenile ramets that sprout from roots) and that the slope of this phytochemical gradient represents a "developmental trajectory." We focused on Populus fremontii (Fremont cottonwood), P. angustifolia (narrowleaf cottonwood), and their natural hybrids. Two major patterns emerged. First, within narrowleaf and hybrids, concentrations of important phytochemicals (condensed tannins and phenolic glycosides) differ greatly and predictably between developmental zones. Second, developmental trajectories differ greatly among these cottonwood species and their hybrids: Fremont exhibits a flat trajectory, narrowleaf a steep trajectory, and hybrids an intermediate trajectory, suggesting an additive genetic component and an ontogenetic basis to this phytochemical variation. Because diverse herbivorous species respond to the phytochemistry of their host plants, we predict that the developmental trajectories of plants play a major role in mediating ecological interactions and structuring communities, and that biodiversity in a stand of trees is determined by both interplant genetic diversity and intraplant ontogenetic diversity.

Crosses, Genetic↗

PubMed1986

Three-channel Lissajous' trajectory of the human short latency visual evoked potentials.

Three orthogonally derived voltage-time records, when plotted simultaneously on three-dimensional voltage-voltage-voltage coordinates, produce a 3-Channel Lissajous' Trajectory (3CLT). 3CLTs of short latency visual evoked potentials (SVEP) were obtained for 8 adult humans (16 eyes) in response to monocular flash stimulation. Intersubject variability of 3CLT of SVEP was small enough to enable identification along the trajectory of comparable planar-segments of approx. 3-5 ms duration across subjects. In each planar-segment, the point at which the trajectory exhibited marked bending was noted. These points were called apices and they corresponded to maxima in the trajectory's distance from the origin (Trajectory Amplitude). Intersubject variability in apex latencies was comparable to, or smaller than, peak latency variability of single-channel records. 3CLT of SVEP consisted of 8 planar-segments in each of the latency ranges of 0-40, 40-70 and 70-100 ms. Analysis of 3CLT, combining the criteria of segment planarity, apices and trajectory amplitude peaks, enabled differentiation between components that had been considered the same in surface distribution studies. 3CLT of SVEP seemed to be influenced by the direction of propagation along the visual pathway.

Adult↗

PubMed1989

Filtering molecular dynamics trajectories to reveal low-frequency collective motions: phospholipase A2.

A novel method for analysing molecular dynamics trajectories has been developed, which filters out high frequencies using digital signal processing techniques and facilitates focusing on the low-frequency collective motions of proteins. These motions involve low energy slow motions, which lead to important biological phenomena such as domain closure and allosteric effects in enzymes. The filtering method treats each of the atomic trajectories obtained from the molecular dynamics simulation as a "signal". The trajectories of each of the atoms in the system (or any subset of interest) are Fourier transformed to the frequency domain, a filtering function is applied and then an inverse transformation back to the time domain yields the filtered trajectory. The filtering method has been used to study the dynamics of the enzyme phospholipase A2. In the filtered trajectory, all the high frequency bond and valence angle vibrations were eliminated, leaving only low-frequency motion, mainly fluctuations in torsions and conformational transitions. Analysis of this trajectory revealed interesting motions of the protein, including concerted movements of helices, and changes in shape of the active site cavity. Unlike normal mode analysis, which has been used to study the motion of proteins, this method does not require converged minimizations or diagonalization of a matrix of second derivatives. In addition, anharmonicity, multiple minima and conformational transitions are treated explicitly. Thus, the filtering method avoids most of the approximations implicit in other investigations of the dynamic behaviour of large systems.

Binding Sites↗

PubMed1995

Detecting a trajectory embedded in random-direction motion noise.

Human observers can easily detect a signal dot moving, in apparent motion, on a trajectory embedded in a background of random-direction motion noise. A high detection rate is possible even though the spatial and temporal characteristics (step size and frame rate) of the signal are identical to the noise, making the signal indistinguishable from the noise on the basis of a single pair of frames. The success rate for detecting the signal dot was as high as 90% when the probability of mismatch from frame-to-frame, based on nearest-neighbor matching, was 0.3. Control experiments showed that trajectory detection is not based on detecting a "string" of collinear dots, i.e. a stationary position cue. Nor is a trajectory detected because it produces stronger signals in single independent motion detectors. For one thing, trajectory detection improves with increases in duration, up to 250-400 msec, a duration longer than the integration typically associated with a single motion detector. For another, the signal dot need not travel in a straight line to be detectable. The signal dot was as reliably detected when it changed its direction a small amount (about 30 deg or less) each frame. Consistent with this, circular paths of sufficiently low curvature were as detectable as straight trajectories. Our data suggest that trajectory motion is highly detectable in motion noise because the component local motion signals are enhanced when motion detectors with similar directional tuning are stimulated in a sequence along their preferred direction.

Cues↗

PubMed2006

Walking trajectory in neglect patients.

A lateral deviation of the walking trajectory is often observed in stroke patients with unilateral spatial neglect. However, existing research appears to be contradictory regarding the direction of this deviation. The aim of the present study was to gain more insight into the walking trajectory of neglect patients. Twelve right hemisphere stroke patients (six neglect, six no neglect), eight left hemisphere stroke patients (none neglect) and 10 healthy control subjects were instructed to walk towards a target while a two-dimensional ultrasonic positioning system recorded their walking trajectory. Patients' recovery of walking ability was assessed and they were tested for the presence of neglect. Neglect patients showed a larger lateral deviation in their walking trajectory compared to stroke patients without neglect or controls. Neglect patients with good walking ability showed a deviation to the contralesional side. Neglect patients with limited walking ability showed a deviation to the ipsilesional side. Within the neglect group we found no relation between the severity of neglect and lateral deviation. Differences in walking ability may account for the contradictory results between studies regarding the lateral deviation in neglect patients' walking trajectory. We suggest that when a neglect patient's walking ability is limited, walking towards a target becomes a dual task: heading control and walking. A limited walking ability will cause a higher task priority of walking compared to heading control. This shift in task priority may be causing the change in walking trajectory deviation.

Adult↗

PubMed2026

"Abrazos, no Balazos": Intensity of Risk for Exposure to Violence and Armed Conflict Trajectories for Adolescents and Young Adults in México 2018-2024.

PURPOSE: "Abrazos, no balazos" (Hugs, not gunshots) is the approach to violence used by the Federal Mexican government from 2018 to 2024. This study identifies distinct conceptually useful latent class growth trajectories in the annual intensity of risk for exposure to events and fatalities from violence against civilians and battles for adolescents and young adults (AYAs) in México from 2018 to 2024. METHODS: Data are from the Armed Conflict Location and Event Data project. Latent class growth analyses were conducted with four longitudinal dependent variables assessed in seven sequential years (2018-2024). RESULTS: In most of the Mexican states, AYAs experienced low intensity-flat trajectories (p >.096) in the annual intensity of risk for exposure to events and fatalities from violence against civilians and battles. AYAs who lived in states with extremely, markedly, or moderately elevated 2018 intensities of risk for exposure to violence experienced decreasing trajectories (p =.000). One latent class with a mildly elevated-increasing trajectory (p =.000) in the annual intensity of risk for exposure to violence was identified for each of the four longitudinal dependent variables. DISCUSSION: During the time that the Federal Mexican government used the "Abrazos, no balazos" approach, AYAs in the majority of the states in México had intensity of risk for exposure to violence and armed conflict trajectories that were consistent with the goals of primary and secondary violence prevention. Violence prevention efforts should be augmented in states with unfavorable trajectories.

Humans↗

PubMed1997

Minimum energy trajectories of the swing ankle when stepping over obstacles of different heights.

This study was performed to test the hypothesis that the motion of the lower extremities when stepping over obstacles is governed by the criterion of minimum mechanical energy. The trajectories of the swing ankle during level walking and when stepping over obstacles of 51, 102, 153, and 204 mm heights were predicted and measured for eight healthy young adults. The predictions were made with a planar, seven-link linkage model based on the criterion of minimum mechanical energy using the method of dynamic programming. When stepping over obstacles, the predicted trajectories of the swing ankle were just high enough for the swing toe to clear the obstacles. The clearances measured between the obstacle and toe were significantly larger than those predicted. When stepping over obstacles the levels of work required to generate the measured trajectories were significantly larger (p < or = 0.002) than those required to produce the predicted trajectories. The amount of work necessary to generate the measured or predicted trajectories increased linearly (significant at p < or = 0.022) with obstacle height and, except when predicting the trajectory for the lowest obstacle, was significantly greater than that required when walking on level ground (p < 0.02). Thus, conservation of energy was found to become a less dominant criterion for governing the motion of the body when crossing obstacles than when walking on level ground.

Acceleration↗

PubMed2000

Perception of two-dimensional, simulated ego-motion trajectories from optic flow.

A veridical percept of ego-motion is normally derived from a combination of visual, vestibular, and proprioceptive signals. A previous study showed that blindfolded subjects can accurately perceive passively travelled straight or curved trajectories provided that the orientation of the head remained constant along the trajectory. When they were turned (whole-body, head-fixed) relative to the trajectory, errors occurred. We ask whether vision allows for better path perception in that situation, to correct or complement vestibular perception. Seated, stationary subjects wore a head mounted display showing optic flow stimuli which simulated linear or curvilinear 2D trajectories over a horizontal ground plane. The observer's orientation was either fixed in space, fixed relative to the path, or changed relative to both. After presentation, subjects reproduced the perceived movement with a model vehicle, of which position and orientation were recorded. They tended to correctly perceive ego-rotation (yaw), but they perceive orientation as fixed relative to trajectory or (unlike in the vestibular study) to space. This caused trajectory misperception when body rotation was wrongly attributed to a rotation of the path. Visual perception was very similar to vestibular perception.

Head Movements↗

PubMed2000

Coordinate roles for LIM homeobox genes in directing the dorsoventral trajectory of motor axons in the vertebrate limb.

Motor neurons extend axons along specific trajectories, but the molecules that control their pathfinding remain poorly defined. We show that two LIM homeodomain transcription factors, Lim1 and Lmx1b, control the initial trajectory of motor axons in the developing mammalian limb. The expression of Lim1 by a lateral set of lateral motor column (LMC) neurons ensures that their axons select a dorsal trajectory in the limb. In a complementary manner, the expression of Lmx1b by dorsal limb mesenchymal cells controls the dorsal and ventral axonal trajectories of medial and lateral LMC neurons. In the absence of these two proteins, motor axons appear to select dorsal and ventral trajectories at random. Thus, LIM homeodomain proteins act within motor neurons and cells that guide motor axons to establish the fidelity of a binary choice in axonal trajectory.

Animals↗

PubMed2005

A quasiclassical trajectory study of the reaction H + O2 <==> OH + O with the O2 reagent vibrationally excited.

Quasiclassical trajectories have been computed on the Melius-Blint (MB) Potential Energy Surface (PES) and on the Double Many-Body Expansion (DMBE) IV PES of Pastrana et al. describing the H + O(2) <==> OH + O reaction with the nonrotating (J = 0) O(2) reagent vibrationally excited to levels v = 6, 7, 8, 9, and 10 at four temperatures: 1000, 2000, 3000, and 4000 K. The vibrational energy levels were selected by using a semiclassical Einstein-Brillouin-Keller (EBK) quantization procedure while the relative translational energy was sampled from a Boltzmann weighted distribution. The rate coefficient for the formation of the OH + O products is seen to increase monotonically with quantum number and nearly monotonically with temperature. On the MB PES, at T = 1000 K, the total rate coefficient increases by a factor of 5.2 as the initial vibrational quantum number of the O(2) diatom increases from v = 6 to v = 10. For T = 2000 K, this factor drops to 3.3, to 2.9 for T = 3000 K, and to 2.5 for T = 4000 K. On the DMBE IV PES, at T = 1000 K the total rate coefficient increases by a factor of 4.1 as the initial vibrational quantum number of the O(2) diatom increases from v = 6 to v = 10. For T = 2000 K, this factor drops to 3.5, to 2.1 for T = 3000 K, and to 2.0 for T = 4000 K. The less-direct group (defined below) of trajectories is sensitive to the initial O(2) vibrational excitation in several different temperature ranges, apparently retaining the effect of reagent vibrational excitation. The more-direct group (defined below) of trajectories does not exhibit this behavior. Reagent vibrational excitation does not increase the total rate coefficients for the title reaction more than the increase due to a simple temperature increase. The less-direct and more-direct groups of trajectories differ in their contribution to the rate coefficient for the title reaction. In particular, at T = 4000 K, the two PESs used in this work differ dramatically in the roles of the less-direct and more-direct trajectories. The behavior of the more-direct and less-direct groups of trajectories can be understood in terms of the efficiency of intramolecular vibrational energy transfer. This work utilizes the recently introduced PES Library, POTLIB 2001, which made the comparisons between the two PESs discussed in this work possible in a very straightforward way.

Journal Article↗

PubMed2003

Developmental trajectories toward violence in middle childhood: course, demographic differences, and response to school-based intervention.

The present study addressed 3 questions concerning (a) the course of developmental trajectories toward violence over middle childhood, (b) whether and how the course of these trajectories differed by demographic subgroups of children, and (c) how responsive these trajectories were to a universal, school-based preventive intervention. Four waves of data on features of children's social-emotional development known to forecast aggression/violence were collected in the fall and spring over 2 years for a highly representative sample of 1st to 6th grade children from New York City public elementary schools (N = 11,160). Using hierarchical linear modeling techniques, synthetic growth curves were estimated for the entire sample and were conditioned on child demographic characteristics (gender, family economic resources, race/ethnicity) and amount of exposure to components of the preventive intervention. Three patterns of growth--positive linear, late acceleration, and gradual deceleration--characterized the children's trajectories, and these trajectories varied meaningfully by child demographic characteristics. Most important, children whose teachers taught a high number of lessons in the conflict resolution curriculum demonstrated positive changes in their social-emotional developmental trajectories and deflections from a path toward future aggression and violence.

Adolescent↗

PubMed1983

Quantifying the cognitive trajectories of extrapolated movements.

Subjects' extrapolations of a piecewise constant-velocity trajectory and a constant-acceleration trajectory were mapped out over a sequence of trials that required only a button-press response. Without any performance feedback, subjects' extrapolations of both trajectories approximated an acceleration segment followed by a constant-velocity segment. With performance feedback, subjects' extrapolations of the constant-acceleration trajectory approached optimal performance. Subsequent withdrawal of the feedback shifted the entire extrapolated trajectory. These feedback-related changes in the extrapolated trajectory can be interpreted as changes in two parameters of a cognitive representation of the movement pattern.

Cognition↗

PubMed2005

Optical trajectories and the informational basis of fly ball catching.

D. M. Shaffer and M. K. McBeath (see record 2002-02027-006) plotted the optical trajectories of uncatchable fly balls and concluded that linear optical trajectory is the informational basis of the actions taken to catch these balls. P. McLeod, N. Reed, and Z. Dienes (see record 2002-11140-016) replotted these trajectories in terms of changes in the tangent of optical angle over time and concluded that optical acceleration is the informational basis of fielder actions. Neither of these conclusions is warranted, however, because the optical trajectories of even uncatchable balls confound the information that is the basis of fielder action with the effects of those same actions on these trajectories. To determine the informational basis of fielder action, it is necessary to do the control-theory-based Test for the Controlled Variable, in which the informational basis of catching is found by looking for features of optical trajectories that are protected from experimentally or naturally applied disturbances.

Baseball↗

PubMed2026

Early-childhood temperament trajectories map onto transdiagnostic psychiatric risk.

Early-childhood temperament is associated with later mental health. Temperament continues to develop throughout the first years of life, and a single assessment cannot capture its trajectory. Whether departures from an individual's developmental trajectory carry psychiatric risk remains unknown. Using data from more than 50,000 children in the Norwegian Mother, Father and Child Cohort Study, we modeled longitudinal temperament at 1.5, 3, and 5 years of age with the FEMA-Long mixed-effects framework. We then quantified each child's departures from their predicted trajectories. Multivariate analysis revealed two transdiagnostic dimensions linking trajectory departures to psychiatric diagnoses across childhood and adolescence. Higher scores on the first dimension were associated with an increased hazard of subsequent ADHD diagnosis (hazard ratio = 1.54), and higher scores on the second with an increased hazard of Asperger syndrome (hazard ratio = 1.64). To examine the genetic basis of these associations, we performed longitudinal GWAS of temperament and conjunctional FDR analysis to detect loci shared with the associated diagnoses. The effects of these loci changed across early childhood, with some strengthening and others attenuating with age. These findings show that departures from predicted temperament trajectories reflect transdiagnostic psychiatric risk with a shared genetic basis. Longitudinal, trajectory-based monitoring could help identify children at elevated psychiatric risk.

Journal Article↗

PubMed2003

The last 2 years of life: functional trajectories of frail older people.

OBJECTIVES: To characterize the functional trajectories during the last 2 years of life of patients with progressive frailty, with and without cognitive impairment, and to assess whether it was possible to identify discrete functional indicators that signal the end of life. DESIGN: A retrospective analysis of functional trajectories during the last 24 months of life. SETTING: Twelve demonstration sites of the Program of All-inclusive Care for the Elderly (PACE). PACE cares for frail older people who meet criteria for nursing home placement, with the goal of keeping the patient at home. PARTICIPANTS: Nine hundred seventeen patients who died while enrolled in PACE. MEASURES: At PACE entry and every 3 months thereafter, data were collected about the degree of dependence (none, partial, or full) in bathing, eating, and walking and the degree of incontinence (none, bladder, or bowel). Cognitive impairment was defined as six or more errors on the Short Portable Mental Status Questionnaire. To describe the end-of-life trajectories of patients, data were analyzed from observational windows of time, beginning with the patients' dates of death and extending backward in time to 24 months before death. Each analytical window was 3 months in duration. For each of the functional measures, the probability of functional deterioration in the last 2 years of life in patients with (64%) and without (36%) cognitive impairment was also compared. RESULTS: The mean age at death was 84; 69% of patients were women. For patients with and without cognitive impairment, a prolonged, steady increase in the rates of functional dependence that were evident at least 1 year before death, rather than sudden increases in functional dependence shortly before death, characterized the functional trajectories. It was not possible for any of the four measures to detect a time point before death at which there was an abrupt decline in function likely to signal impending death. For each measure, patients with cognitive impairment declined earlier, were more likely than patients without cognitive impairment to have the maximal level of dependence in the 0- to 3-month window before death (e.g., 56% vs 30% for mobility, P <.001), and were more likely to decline in the 2 years before death (e.g., 56% vs 36% for mobility, P <.001). CONCLUSION: Patients with advanced frailty, with or without cognitive impairment, have an end-of-life functional course marked by slowly progressive functional deterioration, with only a slight acceleration in the trajectory of functional loss as death approaches. Patients with cognitive impairment have particularly high rates of functional impairment at the time of death. These results suggest that end-of-life care systems that are targeted toward patients with functional trajectories clearly suggesting impending death (such as the Medicare hospice benefit) are poorly suited to older people dying with progressive frailty.

Activities of Daily Living↗

PubMed2004

Trajectory approach to dissipative quantum phase space dynamics: Application to barrier scattering.

The Caldeira-Leggett master equation, expressed in Lindblad form, has been used in the numerical study of the effect of a thermal environment on the dynamics of the scattering of a wave packet from a repulsive Eckart barrier. The dynamics are studied in terms of phase space trajectories associated with the distribution function, W(q,p,t). The equations of motion for the trajectories include quantum terms that introduce nonlocality into the motion, which imply that an ensemble of correlated trajectories needs to be propagated. However, use of the derivative propagation method (DPM) allows each trajectory to be propagated individually. This is achieved by deriving equations of motion for the partial derivatives of W(q,p,t) that appear in the master equation. The effects of dissipation on the trajectories are studied and results are shown for the transmission probability. On short time scales, decoherence is demonstrated by a swelling of trajectories into momentum space. For a nondissipative system, a comparison is made of the DPM with the "exact" transmission probability calculated from a fixed grid calculation.

Journal Article↗

PubMed2005

Extended quantization condition for constructive and destructive interferences and trajectories dominating molecular vibrational eigenstates.

The role of destructive quantum interference in semiclassical quantization of molecular vibrational states is studied. This aspect is crucial for correct quantization, since failure in the appropriate treatment of destructive interference quite often results in many spurious peaks and broad background to hide the true peaks. We first study the time-Fourier transform of the autocorrelation function without performing summation over the trajectories. The resultant quantity, the prespectrum which is a function of individual classical trajectories, provides a clear view about how destructive interference among the trajectories should function. It turns out that the prespectrum is oscillatory but never a random noise. On the contrary, it bears a systematic and regular structure, which is sometimes characterized in terms of very sharp and high peaks in the energy space of the sampled classical trajectories. We have found an extended quantization condition that is responsible for generating these peaks in the prespectrum, which we call the prior quantization condition. Integration of the prespectrum over the trajectory space is supposed to give "zero" (practically a small value of the order of the Planck constant) at a noneigenvalue energy, which is actually a materialization of the destructive interference. Besides, certain finite peaks in the prespectrum survive after the integration to form the true spikes (eigenvalues) in the final spectrum, if they satisfy an additional resonance condition. For these resonance components, the prior quantization condition is reduced to the Einstein-Brillouin-Keller quantization condition. Based on these analyses, we propose a rather conventional filtering technique to efficiently handle tedious computation for destructive interference, and numerically verify that it works well even for multidimensional chaotic systems. This filtering technique is further utilized to extract a few trajectories that dominate an eigenstate of molecular vibration.

Journal Article↗

PubMed2005

Labor market trajectories and health: a four-year follow-up study of initially fixed-term employees.

With the growth of atypical employment, there is increasing concern about the potential health-damaging effects of unstable employment. This prospective study of Finnish public-sector employees in 1998-2002 examined labor market trajectories and changes in health. At entry, all participants had a fixed-term job contract. Trajectories were measured by exposure to unstable employment during follow-up, destination employment status at the end of follow-up, and the way in which these elements were combined. Nonoptimal self-rated health at baseline was associated with high exposure to unstable employment and unemployment as the destination. After adjustment for health and psychological distress at baseline, a trajectory with stable employment as the destination was associated with a decreased risk of psychological distress at follow-up (odds ratio = 0.68, 95% confidence interval: 0.46, 0.98), whereas a trajectory toward the labor market periphery was related to increased risk of nonoptimal health (odds ratio = 2.54, 95% confidence interval: 1.47, 4.39) when compared with remaining in fixed-term employment. A significant dose-response relation was seen between the measure combining exposure to instability with destination employment status and nonoptimal health. This longitudinal study provides evidence of health-related selection into employment trajectories and suggests that the trajectories themselves carry different health risks.

Adult↗