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PubMed2002

Control of foot trajectory in human locomotion: role of ground contact forces in simulated reduced gravity.

We studied the changes of vertical contact forces, lower limb kinematics, and electromyographic activity (EMG) at different speeds and gravitational loads. To this end healthy subjects were asked to walk on a motorized treadmill while the percentage of body weight unloaded (body weight support, BWS) was modified in steps by means of a well-characterized unloading system. BWS was set at 0, 35, 50, 75, 95, or 100% of body weight. Walking speed was 0.7, 1.1, 2, 3, or 5 km/h. We found that changing BWS between 0 and 95% resulted in drastic changes of kinetic parameters but in limited changes of the kinematic coordination. In particular, the peak vertical contact forces decreased proportionally to BWS; at 95%-BWS they were 20-fold smaller than at 0% and were applied at the forefoot only. Also, there were considerable changes of the amplitude of EMG activity of all tested lower limb muscles and a complex re-organization of the pattern of activity of thigh muscles. By contrast, the corresponding variation of the parameters that describe shape and variability of the foot path was very limited, always <30% of the corresponding values at 0 BWS. Moreover, the planar co-variation of the elevation angles was obeyed at all speed and BWS values. Minimum variance of limb trajectory occurred at 3 km/h. At 100% BWS, subjects stepped in the air, their feet oscillating back and forth just above but never contacting the treadmill. In this case, step-to-step variability of foot path was much greater than at all other BWS levels but was restored to lower values when minimal surrogate contact forces were provided during the "stance" phase. The results did not depend on the specific instruction given to the subject. Therefore we conclude that minimal contact forces are sufficient for accurate foot trajectory control.

Adult↗
PubMed1987

Technique of stereotactic biopsy of two cranial target employing spherical coordinates to define a single trajectory.

A 'spherical coordinate system' has been developed to allow either stereotactic biopsy of two intracranial lesions using a single predetermined trajectory or biopsy of a single lesion through an existing burr hole. By means of the Gildenberg technique, the CT coordinates of the targets (or target and burr hole) are obtained. These are employed in three simple trigonometric equations to give three coordinates-two angles for the probe carrier (theta and alpha) and the radius (T) of a sphere, defined by one target as the center and the other target on the surface. These can be utilized in the Todd-Wells stereotactic frame. This system was evaluated using hollow skulls and crossed 30-gauge wire for phantom targets. The system was tried on ten different target combinations, and eight successful trajectories were obtained to within 3 mm. Two target combinations were inaccessible because of technical limitations of the Todd-Wells frame. This 'spherical coordinate system' can decrease the time to localize multiple targets as well as minimize the number of passes.

Biopsy↗
PubMed1985

Altered myelinated fiber trajectory at various postnatal days in the cerebral cortex of reeler mice by immunohistochemical stain with MBP antiserum.

The cerebral cortex of reeler mutant mice characterized by the derangement of cell position was analyzed by an immunohistochemical staining technique using antiserum against myelin basic protein. All the myelins of the myelinated fibers were stained, so that the fiber trajectories could be clearly traced. In the present study the changes in the fiber trajectories were accompanied by changes in myelination sites. Myelinated fibers were localized in the central white matter and gradually became sparser toward the surface of the normal cerebral cortex, while in the reeler myelinated fibers were observed throughout the cortical plane. From the immunohistochemical analysis of the changes occurring in the myelinated fiber pathways in developmental sequence, it was also shown that the fiber bundle accumulation was thin at the earlier stages (e.g. the 15th postnatal day) and became thick as the animal grew, and the timing of myelination in the reeler was similar to that of the control.

Animals↗
PubMed1996

Application of the minimum jerk model to formation of the trajectory of the centre of mass during multijoint limb movements.

Smoothness of movement is an inherent characteristic of the motor repertoire of primates. According to the minimum hand jerk model, a major feature of motor coordination in two-joint upper limb movements by humans in the horizontal plane is the production of the smoothest possible movement of the end effector, the hand ('hand version'). In the present study, this model was extended to the formation of the trajectory of the centre of mass (CMt) of the whole arm system ('CMt version'), and its importance for the shaping of multijoint movements was tested against the classical 'hand version'. During point-to-point movements between many pairs of targets in the work space, the movements of the CMt showed lower changes of torque than in movements of the hand on a straight path. Furthermore, the CMt version of the minimum jerk model reproduced the curved hand trajectory that can be observed in actual human performance. Under the assumption that the smoothness criterion is induced by a high-level motor coordination, our results suggest that CMt-based planning can be an alternative strategy for joint coordination. It offers the advantage of the simplified scaling of joint torques which are suitable for execution of planned movements.

Computer Simulation↗
PubMed2004

Tracking the trajectories of evolution.

This article proposes a method of visualizing and measuring evolution in artificial life simulations. The evolving population of agents is treated as a dynamical system. The proposed method is inspired by the notion of trajectory. The article provides examples of tracking of trajectories of evolutionary systems in the spaces of genotypes, strategies, and some global characteristics. Visualization similar to a bifurcation diagram is used to represent results of a series of simulations.

Artificial Intelligence↗
PubMed2006

Role of focal attention on latencies and trajectories of visually guided manual pointing.

Previous studies have shown that an odd-colored target among uniformly colored distractors can be rapidly detected and localized using broadly distributed attention over an entire display. In the current study, we show that such a broadly distributed attentional allocation is not sufficient for seemingly effortless goal-directed manual pointing. Latencies and movement durations of manual pointing in odd-colored search tasks become shorter and curved trajectories decreased as the number of distractors increase or target color repetitions increases. Because these manipulations have been shown to facilitate the deployment of narrowly focused attention to a target but not for distributed attention, this adds further support to the view that focal attention is necessary for goal-directed action. In addition, the presence of highly curved movement trajectories, directed first to a distractor then to the target reflects ongoing changes in focal attentional deployment and target selection.

Attention↗
PubMed2025

Distinct evolutionary trajectories of subgenomic centromeres in polyploid wheat.

BACKGROUND: Centromeres are crucial for precise chromosome segregation and maintaining genome stability during cell division. However, their evolutionary dynamics, particularly in polyploid organisms with complex genomic architectures, remain largely enigmatic. Allopolyploid wheat, with its well-defined hierarchical ploidy series and recent polyploidization history, serves as an excellent model to explore centromere evolution. RESULTS: In this study, we perform a systematic comparative analysis of centromeres in common wheat and its corresponding ancestral species, utilizing the latest comprehensive reference genome assembly available. Our findings reveal that wheat centromeres predominantly consist of five types of centromeric-specific retrotransposon elements (CRWs), with CRW1 and CRW2 being the most prevalent. We identify distinct evolutionary trajectories in the functional centromeres of each subgenome, characterized by variations in copy number, insertion age, and CRW composition. By utilizing CENH3-ChIP data across various ploidy levels, we uncover a series of CRW invasion events that have shaped the evolution of AA subgenome centromeres. Conversely, the evolutionary process of the DD subgenome centromeres involves their expansion from diploid to hexaploid wheat, facilitating adaptation to a larger genomic context. Integration of complete einkorn centromere assemblies and Aegilops tauschii pan-genomes further revealed subgenome-specific centromere evolutionary trajectories. By inclusion of synthetic hexaploid from S2-S3 generations, alongside 2x/6&#x2009;&#xd7;&#x2009;natural accessions, we demonstrate that DD subgenome centromere expansion represents a gradual evolutionary process rather than an immediate response to polyploidization. CONCLUSIONS: Our study provides a comprehensive landscape of centromere adaptation, evolution, and maturation, along with insights into how retrotransposon invasions drive centromere evolution in polyploid wheat.

Centromere↗
PubMed2002

The trajectory of fatigue in adult patients with breast and ovarian cancer receiving chemotherapy.

PURPOSE/OBJECTIVES: To describe the trajectory of fatigue and determine the feasibility of exploring physiologic mechanisms of fatigue in adult patients receiving chemotherapy for breast and ovarian cancer. DESIGN: Descriptive, longitudinal, repeated measures. SETTING: Outpatient ambulatory cancer centers within two large, academic, teaching hospitals with overnight hospital stays in general clinical research centers. SAMPLE: Seventeen adult participants with either early-stage breast or ovarian cancer receiving chemotherapy for the first time. METHODS: Demographic questionnaire; Piper Fatigue Scale (PFS); hemoglobin, bilirubin, melatonin, and weight change were measured at baseline, three months, and approximately six months. PFS also was collected at three additional two-week nadir, post-treatment, measurement points. Descriptive statistics and repeated analysis of variance measures were used to analyze data. MAIN RESEARCH VARIABLES: Fatigue, hemoglobin, bilirubin, melatonin, and presence of other comorbid disease. FINDINGS: Subjective fatigue was experienced by the majority of patients receiving chemotherapy. It was irregular over time, intensified at three months, and continued after treatment ended. The physiologic trajectory of fatigue from baseline to three months indicated a significant change over time in hemoglobin in the breast cancer group (p = 0.02) and in nighttime melatonin levels for both breast and ovarian cancer groups (p = 0.03). Although not significant, daytime melatonin levels changed over time from baseline to six months. CONCLUSIONS: Fatigue fluctuates during the course of chemotherapy treatment and does not cease after treatment ends. Preliminary findings suggest that fatigue mechanisms may have an undetermined physiologic basis. IMPLICATIONS FOR NURSING: Assessment of cancer treatment-related fatigue must be ongoing, even after treatment ends. Findings suggest an awareness of the importance of understanding fatigue mechanisms to enable future testing of research-based interventions.

Adult↗
PubMed2004

Trajectories of alcohol use and electrophysiological and morphological indices of brain development: distinguishing causes from consequences.

Alcoholism is a major public health problem. Patterns of drinking during adolescence can influence the likelihood of this outcome. Both environmental variation and familial/genetic susceptibility play important roles in this process. While there is some evidence to suggest that metabolic factors play a role in whether some individuals are protected from developing alcohol problems, there is substantial reason to look for cognitive factors that are associated with increased susceptibility. Developmental trajectories for information processing that can be reflected in P300 amplitude changes over time, as well as trajectories describing acquisition of postural control when compared in offspring from families with multiple cases of alcoholism or those with none or few, suggest that brain development provides a clue to why some individuals are more susceptible to becoming alcoholic. Finally, differences seen in amygdala volume between high- and low-risk adolescents suggest that functional differences seen in electrophysiological responding or neuropsychological test performance may have anatomical correlates.

Adolescent↗
PubMed2005

Trajectory design for space missions to libration point L2.

This work is focused on the detection and computation of "free" transfer trajectories from parking orbits around the Earth to quasiperiodic orbits around the collinear libration point L(2), in the Sun-Earth system; no correction or insertion maneuvers into the final orbits have been considered. The circular restricted three-body problem is the mathematical model used to describe the motion of a spacecraft, in the gravitational field of the two primaries, computed by integrating the nonlinearized equations of motion. A shooting method has been designed and developed to determine the increment of velocity required for the perigee maneuver, which injects a spacecraft into its transfer trajectory: first the velocity boundary for the Earth escape/capture condition is detected and then an iterative bisection method is applied until the burnout velocity, tangential to the parking orbit, leads the spacecraft to its final Lissajous orbit. For a launch from Kourou at local noon, Ariane5 GTO and Soyuz GTO "equivalent" have been studied and compared, considering fuel minimization for the transfer maneuver and general mission constraints, as maximum excursion of the final Lissajous orbit from the ecliptic plane and eclipses avoidance during the mission. This analysis highlights advantages and drawbacks of various parking orbits. Mission goals are the key factor for the tradeoff among orbit selection, launch options, and the other constraints, fixed by mission requirements.

Journal Article↗
PubMed2002

The C. elegans even-skipped homologue, vab-7, specifies DB motoneurone identity and axon trajectory.

Locomotory activity is defined by the specification of motoneurone subtypes. In the nematode, C. elegans, DA and DB motoneurones innervate dorsal muscles and function to induce movement in the backwards or forwards direction, respectively. These two neurone classes express separate sets of genes and extend axons with oppositely directed trajectories; anterior (DA) versus posterior (DB). The DA-specific homeoprotein UNC-4 interacts with UNC-37/Groucho to repress the DB gene, acr-5 (nicotinic acetylcholine receptor subunit). We show that the C. elegans even-skipped-like homoedomain protein, VAB-7, coordinately regulates different aspects of the DB motoneurone fate, in part by repressing unc-4. Wild-type DB motoneurones express VAB-7, have posteriorly directed axons, express ACR-5 and lack expression of the homeodomain protein UNC-4. In a vab-7 mutant, ectopic UNC-4 represses acr-5 and induces an anteriorly directed DB axon trajectory. Thus, vab-7 indirectly promotes DB-specific gene expression and posteriorly directed axon outgrowth by preventing UNC-4 repression of DB differentiation. Ectopic expression of VAB-7 also induces DB traits in an unc-4-independent manner, suggesting that VAB-7 can act through a parallel pathway. This work supports a model in which a complementary pair of homeodomain transcription factors (VAB-7 and UNC-4) specifies differences between DA and DB neurones through inhibition of the alternative fates. The recent findings that Even-skipped transcriptional repressor activity specifies neurone identity and axon guidance in the mouse and Drosophila motoneurone circuit points to an ancient origin for homeoprotein-dependent mechanisms of neuronal differentiation in the metazoan nerve cord.

Animals↗
PubMed1991

How stimulus direction determines the trajectory of the Mauthner-initiated escape response in a teleost fish.

Fishes use the Mauthner-initiated C-start for short-latency evasion of predators. C-starts consist of a sudden turn (stage 1) and a rapid acceleration (stage 2). We analyzed high-speed ciné films of goldfish C-starts elicited by dropping a ball into the water. It was previously thought that stage 1 angle does not vary concomitantly with the angle of the threatening stimulus relative to the position of the fish. We found, however, a significant inverse relationship between the direction of the impact of the ball and the angle turned by the end of stage 1. When starting near a wall, or when its usual trajectory was blocked by a wall, the fish used an escape route that was not predictable from the stimulus angle. The fish did not appear to correct its trajectory if it began to turn towards the ball. This behavioral evidence supports the previous notion that the underlying neural command is ballistic and does not use sensory information from the stimulus once the movement begins. If this is so, the fish probably utilizes information on obstacle location in the interval leading up to the trigger stimulus.

Animals↗
PubMed1998

Determinants of the center of mass trajectory in human walking and running.

Walking is often modeled as an inverted pendulum system in which the center of mass vaults over the rigid stance limb. Running is modeled as a simple spring-mass system in which the center of mass bounces along on the compliant stance limb. In these models, differences in stance-limb behavior lead to nearly opposite patterns of vertical movements of the center of mass in the two gaits. Our goal was to quantify the importance of stance-limb behavior and other factors in determining the trajectory of the center of mass during walking and running. We collected kinematic and force platform data during human walking and running. Virtual stance-limb compression (i.e. reduction in the distance between the point of foot-ground contact and the center of mass during the first half of the stance phase) was only 26% lower for walking (0.091 m) than for running (0.123 m) at speeds near the gait transition speed. In spite of this relatively small difference, the center of mass moved upwards by 0.031 m during the first half of the stance phase during walking and moved downwards by 0.073 m during the first half of the stance phase during running. The most important reason for this difference was that the stance limb swept through a larger angle during walking (30.4 degrees) than during running (19.2 degrees). We conclude that stance-limb touchdown angle and virtual stance-limb compression both play important roles in determining the trajectory of the center of mass and whether a gait is a walk or a run.

Biomechanical Phenomena↗
PubMed1999

Escape trajectories of the brown shrimp crangon crangon, and a theoretical consideration of initial escape angles from predators

Tail-flip escape trajectories of the brown shrimp Crangon crangon have been investigated in response to a natural predator, the cod Gadus morhua, and an artificial stimulus. Shrimps escaped by rolling to their left or right during the initial tail-flip of a response, and thereafter swam on their side. As a result of the laterally directed first tail-flip, initial escape angles always lay between 75 degrees and 156 degrees with respect to the (pre-escape) longitudinal axis (anterior=0 degrees) of the shrimp. Symmetrical attacks from either head-on or tail-on produced escapes to the shrimp's left or right in equal proportions, although a contralateral bias did occur if the shrimp experienced a looming object from one side before a symmetrical attack was applied. Lateral attacks produced a significantly greater proportion of contralateral responses than ipsilateral ones. Empirical and theoretical analyses indicate that the initial escape direction is influenced by an interaction between the range of first tail-flip escape angles that the shrimp is capable of performing and the risk of being intercepted by a predator during the initial stage of an escape. Thus, the unpredictability ('protean behaviour') of the response may be affected by the conditions of the interaction. Subsequent tail-flips of an escape usually directed the response away from the stimulus, but sometimes escapes were instead steered to the side of the stimulus and then behind it. The probability of each type of escape occurring changed with attack direction. The elements of protean behaviour that have been identified in both the initial and subsequent stages of the escape may prevent predators from learning a fixed pattern of response, but a trade-off occurs when escape trajectories infringe upon zones of high capture risk.

Journal Article↗
PubMed2003

Pathogen survival trajectories: an eco-environmental approach to the modeling of human campylobacteriosis ecology.

Campylobacteriosis, like many human diseases, has its own ecology in which the propagation of human infection and disease depends on pathogen survival and finding new hosts in order to replicate and sustain the pathogen population. The complexity of this process, a process common to other enteric pathogens, has hampered control efforts. Many unknowns remain, resulting in a poorly understood disease ecology. To provide structure to these unknowns and help direct further research and intervention, we propose an eco-environmental modeling approach for campylobacteriosis. This modeling approach follows the pathogen population as it moves through the environments that define the physical structure of its ecology. In this paper, we term the ecologic processes and environments through which these populations move "pathogen survival trajectories." Although such a modeling approach could have veterinary applications, our emphasis is on human campylobacteriosis and focuses on human exposures to Campylobacter through feces, food, and aquatic environments. The pathogen survival trajectories that lead to human exposure include ecologic filters that limit population size, e.g., cooking food to kill Campylobacter. Environmental factors that influence the size of the pathogen reservoirs include temperature, nutrient availability, and moisture availability during the period of time the pathogen population is moving through the environment between infected and susceptible hosts. We anticipate that the modeling approach proposed here will work symbiotically with traditional epidemiologic and microbiologic research to help guide and evaluate the acquisition of new knowledge about the ecology, eventual intervention, and control of campylobacteriosis.

Animals↗
PubMed2003

The academic trajectories of immigrant youths: analysis within and across cohorts.

Two nationally representative cohorts--from the National Educational Longitudinal Study (NELS) and High School and Beyond (HSB)--were used to examine the effects of generation and duration of residence on students' performance on standardized tests over a two-year period. In multivariate models, generational status predicts variation in students' performance on baseline (sophomore) tests, with effects stronger for the later age cohort (NELS) than for the earlier age cohort (HSB). With regard to the trajectory of achievement, generational status has a greatly reduced role for both cohorts. The best predictors of the trajectory of achievement are not those that are based on nativity per se, but those that reflect the social environment experienced in the United States (i.e., ethnicity and family's socioeconomic status).

Acculturation↗
PubMed2006

Trajectory of end-stage heart failure: the influence of technology and implications for policy change.

Patients with end-stage heart failure have a trajectory of illness characterized by an overall gradual decline in function punctuated by periods of symptom exacerbation followed by a return nearly to their baseline. These exacerbations are not predictable. Death may come suddenly and unexpectedly for each patient, even though predictive models can draw an accurate survival curve by averaging the experience of a substantial number of people with heart failure. Heart failure patients often have treatable symptoms, such as dyspnea, fatigue, and generalized pain. In this article, we explain the trajectory of patients with heart failure, illustrate the importance of advance care planning for these patients, discuss the impact of choices to use or forgo new technologies, and suggest ways to improve the care system. Only by reexamining our health care spending priorities can we create a sustainable care system that allows patients to live both long and comfortably, reaching a balance that serves them and their communities well.

Advance Care Planning↗
PubMed2004

Adolescent heavy episodic drinking trajectories and health in young adulthood.

OBJECTIVE: This study examined the association of trajectories of heavy episodic drinking (at least five alcoholic drinks on one occasion) during adolescence with health status and practices at age 24. METHOD: Semiparametric group-based modeling and logistic regressions were used to analyze data from a longitudinal panel of 808 youths interviewed between 10 and 24 years of age. RESULTS: Four distinct trajectories of adolescent heavy episodic drinking were identified: nonheavy drinkers, late onsetters, escalators and chronic heavy drinkers. Overall, young adults who did not engage in heavy episodic drinking during adolescence had the lowest occurrence of health problems and were most likely to engage in safe health behaviors at age 24. Chronic and late-onset heavy episodic drinking during adolescence had negative effects on health status and practices at age 24. Adolescent chronic heavy drinkers were more likely to be overweight or obese and to have high blood pressure at age 24 than those who did not drink heavily in adolescence. Late-onset heavy drinkers were less likely to engage in safe driving practices at age 24 and were more likely to have been ill in the past year than adolescents who did not drink heavily. These health disparities remained even after current frequency of heavy episodic drinking at age 24, other adolescent drug use, ethnicity, gender and family poverty were controlled. CONCLUSIONS: Heavy episodic alcohol use during adolescence has long-term, negative health consequences. Distinct patterns of adolescent heavy drinking affect health status and practices in young adulthood differently.

Adolescent↗