Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “trajectory”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 487 records · Page 27Linked to original sources
PubMed2003

Facial nerve in rhytidoplasty: anatomic study of its trajectory in the overlying skin and the most common sites of injury.

The anatomic study of the facial nerve is closely related to the prevention of nerve injury that may occur in facial surgeries. The purpose of this study is to analyze the most susceptible areas in the face regarding the probability of facial nerve injury, based on the demarcation of its trajectory in the overlying skin. Three hundred cadaveric hemifaces were dissected (172 male, 128 female) and the facial nerve trajectory was followed from the stylomastoids foramen to the mimic muscles. The trajectory of the facial branches was delimited in the overlying skin by six diverging lines, with the following reference points: the upper and lower portions of the tragus, the most cranial wrinkle of the frontal region, the lower facial wrinkle of the frontal muscle, the nasal midpoint, an imaginary point 1 cm caudal to the oral commisura, another imaginary point also caudal to the oral commisura at the lower margin of mandible, and the clavicle midpoint. The temporal branches have the highest probability of being injured, followed by the mandibular marginal and buccal branches. The areas with greater risk of injury are the temporofrontal region (between the hairline and the lateral limit of the frontal muscle), the area near the angle of the mandible, and the preparotid region.

Facial Nerve↗
PubMed2001

Trajectory versus probability density entropy.

We show that the widely accepted conviction that a connection can be established between the probability density entropy and the Kolmogorov-Sinai (KS) entropy is questionable. We adopt the definition of density entropy as a functional of a distribution density whose time evolution is determined by a transport equation, conceived as the only prescription to use for the calculation. Although the transport equation is built up for the purpose of affording a picture equivalent to that stemming from trajectory dynamics, no direct use of trajectory time evolution is allowed, once the transport equation is defined. With this definition in mind we prove that the detection of a time regime of increase of the density entropy with a rate identical to the KS entropy is possible only in a limited number of cases. The proposals made by some authors to establish a connection between the two entropies in general, violate our definition of density entropy and imply the concept of trajectory, which is foreign to that of density entropy.

Journal Article↗
PubMed2001

Trajectories in phase diagrams, growth processes, and computational complexity: how search algorithms solve the 3-satisfiability problem.

Decision and optimization problems typically fall into one of two categories for any particular solving algorithm. The problem is either solved quickly (easy) or demands an impractically long computational effort (hard). Here we show that some characteristic parameters of problems can be tracked during a run of the algorithm defining a trajectory through the parameter space. Focusing on 3-satisfiability, a recognized representative of hard problems, we analyze trajectories generated by search algorithms. These trajectories can cross well-defined phases, corresponding to domains of easy or hard instances, and allow one to successfully predict the times of resolution.

Journal Article↗
PubMed2005

Langevin trajectories between fixed concentrations.

We consider the trajectories of particles diffusing between two infinite baths of fixed concentrations connected by a channel, e.g., a protein channel of a biological membrane. The steady state influx and efflux of Langevin trajectories at the boundaries of a finite volume containing the channel and parts of the two baths is replicated by termination of outgoing trajectories and injection according to a residual phase space density. We present a simulation scheme that maintains averaged fixed concentrations without creating spurious boundary layers, consistent with the assumed physics.

Biophysics↗
PubMed2006

Piecewise parametric interpolation for temporal compression of multijoint movement trajectories.

Computer animation of sign language used by deaf individuals has been produced from 51 time-varying trajectories of the fingertips, the centers of rotation of the joints of the hands and arms, and facial landmarks. These trajectories are sampled at 1/5th the National Television Systems Committee (NTSC) video frame rate and interpolated using piecewise sequences of cubic Bezier splines. The resulting trajectories are used to control sparse, stick figure animations of sign language resulting in considerable spatiotemporal compression with intelligibility in the range of 90%. This method introduces an additional 5:1 compression in the temporal domain that has not been previously exploited, and is potentially useful in sign language telecommunication, multimedia presentations, and gesture recognition.

Arm↗
PubMed2003

Single-shot MR imaging using trapezoidal-gradient-based Lissajous trajectories.

A novel single-shot trapezoidal-gradient-based Lissajous trajectory is described and implemented on a 3-tesla magnetic resonance (MR) scanner. A feature of this trajectory is that its sampling points are located on a nonequidistant rectangular grid, which permits the usage of one-dimensional optimal algorithms to increase the robustness and speed of image reconstruction. Another advantage of the trajectory is that two images with different effective echo times can be obtained within a single excitation, which might be used for fast T2* mapping, in functional MR imaging scanning of brain activity associated with mental processes. Potential artifacts in reconstructed images were investigated and methods for suppressing these artifacts were developed. Experiments on normal subjects at rest and during brain activation were performed to demonstrate the feasibility of the new sequence.

Algorithms↗
PubMed2006

Movement trajectories and habitat partitioning of small mammals in logged and unlogged rain forests on Borneo.

1. Non-volant animals in tropical rain forests differ in their ability to exploit the habitat above the forest floor and also in their response to habitat variability. It is predicted that specific movement trajectories are determined both by intrinsic factors such as ecological specialization, morphology and body size and by structural features of the surrounding habitat such as undergrowth and availability of supportive structures. 2. We applied spool-and-line tracking in order to describe movement trajectories and habitat segregation of eight species of small mammals from an assemblage of Muridae, Tupaiidae and Sciuridae in the rain forest of Borneo where we followed a total of 13,525 m path. We also analysed specific changes in the movement patterns of the small mammals in relation to habitat stratification between logged and unlogged forests. Variables related to climbing activity of the tracked species as well as the supportive structures of the vegetation and undergrowth density were measured along their tracks. 3. Movement patterns of the small mammals differed significantly between species. Most similarities were found in congeneric species that converged strongly in body size and morphology. All species were affected in their movement patterns by the altered forest structure in logged forests with most differences found in Leopoldamys sabanus. However, the large proportions of short step lengths found in all species for both forest types and similar path tortuosity suggest that the main movement strategies of the small mammals were not influenced by logging but comprised generally a response to the heterogeneous habitat as opposed to random movement strategies predicted for homogeneous environments. 4. Overall shifts in microhabitat use showed no coherent trend among species. Multivariate (principal component) analysis revealed contrasting trends for convergent species, in particular for Maxomys rajah and M. surifer as well as for Tupaia longipes and T. tana, suggesting that each species was uniquely affected in its movement trajectories by a multiple set of environmental and intrinsic features.

Animals↗
PubMedDate not supplied

Conditions for young infants' perception of object trajectories.

When an object moves behind an occluder and re-emerges, 4-month-old infants perceive trajectory continuity only when the occluder is narrow, raising the question of whether time or distance out of sight is the important constraining variable. One hundred and forty 4-month-olds were tested in five experiments aimed to disambiguate time and distance out of sight. Manipulating the object's visible speed had no effect on infants' responses, but reducing occlusion time by increasing object speed while occluded induced perception of trajectory continuity. In contrast, slowing the ball while it was behind a narrow or intermediate screen did not modify performance. It is concluded that 4-month-olds perceive trajectory continuity when time or distance out of sight is short.

Child Development↗
PubMedDate not supplied

Longitudinal trajectories of ethnic identity among urban Black and Latino adolescents.

The current study modeled developmental trajectories of ethnic identity exploration and affirmation and belonging from middle to late adolescence (ages 15-18) and examined how these trajectories varied according to ethnicity, gender, immigrant status, and perceived level of discrimination. The sample consisted of 135 urban low-income Black and Latino adolescents (42% male, 34% Black, 66% Latino). Consistent with developmental theory, individual growth modeling identified an average quadratic trajectory of ethnic identity exploration characterized by decelerating levels of exploration after 10th grade. However, ethnicity and perceived discrimination by peers moderated this pattern. No uniform growth pattern in affirmation was found and Black and Latino adolescents displayed equally high levels of affirmation over time.

Adolescent↗
PubMedDate not supplied

Developmental trajectories of personal and collective self-concept among American Indian adolescents.

Developmental trajectories of personal and collective self-concept were examined among American Indian adolescents. Personal self-concept (self-esteem) and collective self-concept (American Indian identity, Euro-American identity, community-mindedness) were assessed 6 times over 3 years in 4 cohorts of adolescents from 3 American Indian cultural groups (N=1,252). An accelerated longitudinal design was used to estimate developmental trajectories from 14 to 19 years; parallel-process and covariate models were used to examine variation in trajectories. Both personal and collective self-concepts were generally positive and showed small gains; they were moderately related to one another and differentially related to cultural group, gender, and perceived social support. The findings highlight the complexity of self-concept for American Indian youth and the significance of both personal and collective identity.

Adolescent↗
PubMed2006

Trajectories of aggression from toddlerhood to age 9 predict academic and social functioning through age 12.

BACKGROUND: Using longitudinal data from the NICHD Study of Early Child Care and Youth Development, we examined behavior problems and social and academic outcomes from ages 9 through 12 in children classified into five trajectories of physical aggression, on the basis of maternal ratings obtained from 24 months through 9 years (N = 1195). METHODS: Outcome data were obtained from teacher reports, observations of children's behavior, and children's self-reports. RESULTS: Children on the high-stable aggression trajectory (3% of sample) showed the most severe adjustment problems, including poorer social skills, higher levels of externalizing problems, and more self-reported peer problems; those on the moderate-stable aggression trajectory (15%) showed poor regulation and inattention. Although children with moderate levels of early aggression that decreased sharply by school entry (12%) appeared well adjusted at follow-up, those who showed a low level of stable aggression (25%) evidenced some unanticipated social and behavior problems. Children in the contrast group (45%) were consistently very low in aggression from toddlerhood onward. CONCLUSIONS: Results highlight links between different patterns (stable or decreasing) and levels (high, moderate, low, very low) of aggression across childhood and children's later adjustment. For example, even quite low aggression that is stable appears to be a risk factor for some social problems; in contrast, moderate aggression that decreases sharply to no aggression by school entry is associated with good adjustment at age 12.

Age Factors↗
PubMed2005

Time-varying functional regression for predicting remaining lifetime distributions from longitudinal trajectories.

A recurring objective in longitudinal studies on aging and longevity has been the investigation of the relationship between age-at-death and current values of a longitudinal covariate trajectory that quantifies reproductive or other behavioral activity. We propose a novel technique for predicting age-at-death distributions for situations where an entire covariate history is included in the predictor. The predictor trajectories up to current time are represented by time-varying functional principal component scores, which are continuously updated as time progresses and are considered to be time-varying predictor variables that are entered into a class of time-varying functional regression models that we propose. We demonstrate for biodemographic data how these methods can be applied to obtain predictions for age-at-death and estimates of remaining lifetime distributions, including estimates of quantiles and of prediction intervals for remaining lifetime. Estimates and predictions are obtained for individual subjects, based on their observed behavioral trajectories, and include a dimension-reduction step that is implemented by projecting on a single index. The proposed techniques are illustrated with data on longitudinal daily egg-laying for female medflies, predicting remaining lifetime and age-at-death distributions from individual event histories observed up to current time.

Animals↗
PubMed2004

A filtered backprojection algorithm for cone beam reconstruction using rotational filtering under helical source trajectory.

With the evolution from multi-detector-row CT to cone beam (CB) volumetric CT, maintaining reconstruction accuracy becomes more challenging. To combat the severe artifacts caused by a large cone angle in CB volumetric CT, three-dimensional reconstruction algorithms have to be utilized. In practice, filtered backprojection (FBP) reconstruction algorithms are more desirable due to their computational structure and image generation efficiency. One of the CB-FBP reconstruction algorithms is the well-known FDK algorithm that was originally derived for a circular x-ray source trajectory by heuristically extending its two-dimensional (2-D) counterpart. Later on, a general CB-FBP reconstruction algorithm was derived for noncircular, such as helical, source trajectories. It has been recognized that a filtering operation in the projection data along the tangential direction of a helical x-ray source trajectory can significantly improve the reconstruction accuracy of helical CB volumetric CT. However, the tangential filtering encounters latitudinal data truncation, resulting in degraded noise characteristics or data manipulation inefficiency. A CB-FBP reconstruction algorithm using one-dimensional rotational filtering across detector rows (namely CB-RFBP) is proposed in this paper. Although the proposed CB-RFBP reconstruction algorithm is approximate, it approaches the reconstruction accuracy that can be achieved by exact helical CB-FBP reconstruction algorithms for moderate cone angles. Unlike most exact CB-FBP reconstruction algorithms in which the redundant data are usually discarded, the proposed CB-RFBP reconstruction algorithm make use of all available projection data, resulting in significantly improved noise characteristics and dose efficiency. Moreover, the rotational filtering across detector rows not only survives the so-called long object problem, but also avoids latitudinal data truncation existing in other helical CB-FBP reconstruction algorithm in which a tangential filtering is carried out, providing better noise characteristics, dose efficiency and data manipulation efficiency.

Algorithms↗
PubMed2000

Observations on the trajectory of the bullet in 15 horses euthanased by free bullet.

The trajectories taken by the free bullets used to euthanase 15 horses were examined. The point of entry of the bullet relative to the recommended site was measured, together with the angle of the trajectory of the bullet relative to a tangent to its point of entry, the deviation of the trajectory from the midline of the brain, the structures of the brain that were damaged and the extent of this damage. Despite a reasonably consistent point of entry, there were wide variations in the damage inflicted, ranging from the total destruction of the hindbrain to injury to the cerebral cortex alone. The extent of the bullet's lateral deviation from the midline appeared to be the most significant factor affecting the level of destruction to the hindbrain, suggesting that angular direction may be more important than precise surface location in effecting a satisfactory kill.

Animal Welfare↗
PubMed2005

A hybrid genetic algorithm and expectation maximization method for global gene trajectory clustering.

Clustering time-course gene expression data (gene trajectories) is an important step towards solving the complex problem of gene regulatory network modeling and discovery as it significantly reduces the dimensionality of the gene space required for analysis. Traditional clustering methods that perform hill-climbing from randomly initialized cluster centers are prone to produce inconsistent and sub-optimal cluster solutions over different runs. This paper introduces a novel method that hybridizes genetic algorithm (GA) and expectation maximization algorithms (EM) for clustering gene trajectories with the mixtures of multiple linear regression models (MLRs), with the objective of improving the global optimality and consistency of the clustering performance. The proposed method is applied to cluster the human fibroblasts and the yeast time-course gene expression data based on their trajectory similarities. It outperforms the standard EM method significantly in terms of both clustering accuracy and consistency. The biological implications of the improved clustering performance are demonstrated.

Algorithms↗
PubMed2001

Comparing personal trajectories and drawing causal inferences from longitudinal data.

This review considers statistical analysis of data from studies that obtain repeated measures on each of many participants. Such studies aim to describe the average change in populations and to illuminate individual differences in trajectories of change. A person-specific model for the trajectory of each participant is viewed as the foundation of any analysis having these aims. A second, between-person model describes how persons very in their trajectories. This two-stage modeling framework is common to a variety of popular analytic approaches variously labeled hierarchical models, multilevel models, latent growth models, and random coefficient models. Selected published examples reveal how the approach can be flexibly adapted to represent development in domains as diverse as vocabulary growth in early childhood, academic learning, and antisocial propensity during adolescence. The review then considers the problem of drawing causal inferences from repeated measures data.

Adolescent↗
PubMed2005

Trajectory interpretation by supplementary eye field neurons during ocular baseball.

Good performance in the sport of baseball shows that humans can determine the trajectory of a moving object and act on it under the constraint of a rule. We report here on neuronal activity in the supplementary eye field (SEF) of monkeys performing an eye movement task inspired by baseball. In "ocular baseball," a pursuit eye movement to a target is executed or withheld based on the target's trajectory. We found that a subset of neurons in the SEF interpreted the trajectory according to the task rule. Other neurons specified at a later time the command to pursue the target with the eyes. The results suggest that the SEF can interpret sensory signals about target motion in the context of a rule to guide voluntary eye movement initiation.

Animals↗
PubMed2006

Time course of oculomotor inhibition revealed by saccade trajectory modulation.

Selecting a stimulus as the target for a goal-directed movement involves inhibiting other competing possible responses. Both target and distractor stimuli activate populations of neurons in topographic oculomotor maps such as the superior colliculus. Local inhibitory interconnections between these populations ensure only one saccade target is selected. Suppressing saccades to distractors may additionally involve inhibiting corresponding map regions to bias the local competition. Behavioral evidence of these inhibitory processes comes from the effects of distractors on oculomotor and manual trajectories. Individual saccades may initially deviate either toward or away from a distractor, but the source of this variability has not been investigated. Here we investigate the relation between distractor-related deviation of trajectory and saccade latency. Targets were presented with, or without, distractors, and the deviation of saccade trajectories arising from the presence of distractors was measured. A fixation gap paradigm was used to manipulate latency independently of the influence of competing distractors. Shorter-latency saccades deviated toward distractors and longer-latency saccades deviated away from distractors. The transition between deviation toward or away from distractors occurred at a saccade latency of around 200 ms. This shows that the time course of the inhibitory process involved in distractor related suppression is relatively slow.

Fixation, Ocular↗