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At least 631 records · Page 35Linked to original sources
PubMed1999

Evaluation of a semiburied, fixed-trajectory, curvilinear, distraction device in an animal model.

PURPOSE: This study evaluated a new small, buried distractor, capable of curvilinear movement while following a fixed trajectory. The geometrical basis for such devices and the 3-dimensional treatment planning system required to make buried distractors practical are discussed. MATERIALS AND METHODS: A curved rack and worm-gear device, based on the design of a hose clamp, was constructed to produce a curved distraction path, and this distractor was tested in 2 minipigs using a protocol with zero latency and 1 mm/d x 7 days of distraction. Serial standardized lateral cephalograms were used to verify distractor function and path. RESULTS: Curvilinear distraction was documented by clinical examination and serial cephalometric analysis in the 2 minipigs. Observed angulation of the margins of the wedge-shaped distraction gap conformed to the calculated angulation based on the fixed radius of curvature of the distractor. CONCLUSION: Distraction along a curved trajectory using a small, semiburied, curvilinear device of novel design is feasible in the minipig mandible.

Animals↗
PubMed1999

Risk-informed selection of a highway trajectory in the neighborhood of an oil-refinery.

A methodology for characterizing alternative trajectories of a new highway in the neighborhood of an oil-refinery with respect to the risk to public health is presented. The approach is based on a quantitative assessment of the risk that the storage facilities of flammable materials of the refinery pose to the users of the highway. Physical phenomena with a potential for detrimental consequences to public health such as BLEVE (Boiling Liquid Expanding Vapor Explosion), Unconfined Vapor Cloud Explosion, flash fire and pool fire are considered. Methodological and procedural steps for assessing the individual risk around the tank farm of the oil-refinery are presented. Based on the individual risk, group risk for each alternative highway trajectory is determined.

Decision Support Techniques↗
PubMed1997

Trajectory formation of the center-of-mass of the arm during reaching movements.

We attempted to identify the invariant kinematic properties of multijoint arm reaching movements in the horizontal plane to explore the planning variable(s) involved in their coordination. Different targets were placed near the perimeter of the workspace boundary, thereby causing variation of size and orientation of the hand stroke. We have a special interest in the trajectory characteristics of the most massive point within the arm system, the center-of-mass of the entire arm system, in addition to those of the hand or joints. The motion of the individual segments (the forearm plus hand and the upper arm) or joints (shoulder and elbow) was modulated in a different way depending on the tasks; thus, there was no invariance in the relationships between paired variables (displacement or velocity) for segment or joint motions. For relatively short hand strokes, the trajectory of the hand and the center-of-mass of the entire arm system were characterized by a nearly straight path, and a smooth, bell-shaped velocity curve along the path, symmetrical about the mid-portion of the movement, starting from nearly zero, growing to a single peak and declining again to nearly zero. However, in large hand strokes the hand path was highly curved and the velocity curve was asymmetric. Although the path of the center-of-mass of the entire arm system also tended to be curved with the increase of the hand stroke, a bell-shaped velocity curve along the path and its typical symmetry were preserved over a wide range of stroke sizes and orientations, and its peak was scaled in proportion to movement distance and movement time. Our findings indicate that it is not valid to postulate solely the joint- or hand-based planning strategies which have been proposed previously. Rather, the planning of the spatial aspects of the motion is largely dependent on the interaction of multiple variables, including those not analysed in this study. The bell-shaped pattern of the center-of-mass velocity profile represents a certain efficiency of movement, since it corresponds to a single accelerative and a decelerative phase of a mass over the movement, with no intermediate force reversals. The simple structure of the center-of-mass velocity profiles may reflect a fundamental organization principle underlying the temporal aspects of movement planning.

Adult↗
PubMed1997

An algorithm for numerical calculation of the k-space data-weighting for polarly sampled trajectories: application to spiral imaging.

Image reconstruction of data sampled into a non-uniform k-space grid requires appropriate data weighting and, for spiral-scan raw data, this weighting is usually calculated analytically under the assumption of uniform radial k-space sampling. This paper presents a simple and efficient algorithm for explicit numerical calculation of the data weighting for generalised polarly sampled k-space trajectories. The algorithm has been tested against both simulated data and data from experimental spiral-scan imaging and clearly provides significant improvements in image reconstruction when the radial uniformity of the k-space trajectory is poor.

Algorithms↗
PubMed1997

Spatial reconstruction of marker trajectories from high-speed video image sequences.

A novel method is presented for the spatial reconstruction of marker trajectories, which describe the motion of articulating segments of the human or animal body or of a technical construction. In human motion analysis, such markers may be attached to landmark points defining the configuration of the subject. A high-speed video-recording system comprising two cameras is used for motion data acquisition. The particular images are composed of the synchronous recordings of both cameras; the resolution of one image is 239 x 192 pixels, which is comparatively low. To obtain high precision, a new centre estimation method has been developed to calculate the image coordinates of the centres of the recorded spherical markers to subpixel precision. Image coordinates of the centres in subsequent frames are obtained by first applying a tracing algorithm, which calculates the position of a marker to pixel precision, and then using the new centre estimation method. The reconstruction of the spatial coordinates from the image coordinates is based on a three-dimensional photogrammetric calibration and results in deviations of about 0.1%. The instantaneous acceleration of a falling ball has been calculated. The average deviation from the gravitational constant was comparatively small. From the accuracy of the results, it can be concluded that the novel method is applicable in connection with the high-speed video-recording system presently used. Moreover, the techniques are suitable for reconstructing three-dimensional marker trajectories from any low-resolution video image sequences recorded simultaneous with at least two cameras.

Algorithms↗
PubMed2000

Vestibular rehabilitation outcomes: velocity trajectory analysis of repeated bench stepping.

OBJECTIVES: To quantify vestibular rehabilitation (VR) outcomes in patients with vestibulospinal reflex pathology (VSP) using a new technique, high curvature analysis (HCA), that measures space trajectory stability. METHODS: Twelve patients with VSP and 10 healthy controls performed a repeated stepping task in a motion analysis laboratory. Patients with VSP were tested before and after a 12 week VR program. Three dimensional whole body center of gravity (CG) was captured during repeated bench stepping trials (step up forward/step down backward), and the resulting horizontal plane CG velocity trajectories were analyzed using HCA. RESULTS: VSP patients were significantly less stable than healthy subjects prior to VR (P=0.022), but these differences disappeared following VR (P=0.148). The stability of the VSP patients during the stepping task at 3 months increased significantly from baseline values (P=0.013). CONCLUSIONS: Evaluating the efficacy of VR requires analysis techniques that are sensitive to changes in stability. We conclude that HCA can be used for assessing improvements in CG stability of VSP patients while performing a repeated bench stepping activity.

Adult↗
PubMed2002

A logistic mixture model for characterizing genetic determinants causing differentiation in growth trajectories.

The logistic or S-shaped curve of growth is one of the few universal laws in biology. It is certain that there exist specific genes affecting growth curves, but, due to a lack of statistical models, it is unclear how these genes cause phenotypic differentiation in growth and developmental trajectories. In this paper we present a statistical model for detecting major genes responsible for growth trajectories. This model is incorporated with pervasive logistic growth curves under the maximum likelihood framework and, thus, is expected to improve over previous models in both parameter estimation and inference. The power of this model is demonstrated by an example using forest tree data, in which evidence of major genes affecting stem growth processes is successfully detected. The implications for this model and its extensions are discussed.

Crosses, Genetic↗
PubMed2003

Quantitative trait loci for growth trajectories in Populus.

Growth trajectories are a biological process important to plant and animal breeding, and to evolutionary genetic studies. In this article, we report the detection of quantitative trait loci (QTLs) responsible for growth trajectories in poplars that are used as a model system for the study of forest biology. These QTLs were localized on a genetic linkage map of polymorphic markers using a statistical mapping method incorporating growth-curve models. The effects of the QTLs on growth are described as a function of age, so that age-specific changes in QTL effects can be readily projected throughout the entire growth process. The QTLs identified display increased effects on growth when trees age, yet the timing of QTL activation is earlier for stem height than diameter, which is consistent with the ecological viewpoint of canopy competition. The implications of the results for breeding and silviculture are discussed.

Genetic Linkage↗
PubMed1990

Trajectory analysis of winds and eastern equine encephalitis in USA, 1980-5.

Backward trajectories of winds were determined to identify possible sources of eastern equine encephalitis virus associated with isolation of virus from mosquitoes or birds or outbreaks in horses between 1980 and 1985 in Maryland, New Jersey, New York and Michigan, USA. The results of the trajectory analyses suggested that eastern equine encephalitis virus could have been carried by infected mosquitoes on surface winds at temperatures 13 degrees C or higher from North Carolina north-eastwards along the Atlantic Coast to Maryland and New Jersey and thence to upstate New York and from western Kentucky to Michigan. Landing of mosquitoes was associated with the presence of a cold front and rain leading to variations in the location and timing of outbreaks from year to year. The mosquito responsible was most likely to have been Culiseta melanura, but Coquillettidia perturbans and Aedes sollicitans could also have been involved. There may be a continual cycle of eastern equine encephalitis virus in mosquitoes and birds in south-eastern USA, from where the virus could be distributed by infected mosquitoes on the wind along the Gulf and Atlantic Coasts and up the Mississippi Valley.

Air Movements↗
PubMed2001

Structure and variability in the developmental trajectory of children's externalizing problems: impact of infant attachment, maternal depressive symptomatology, and child sex.

This study explores the developmental trajectory of externalizing problems in a sample of 101 children of adolescent mothers from preschool through third grade using hierarchical linear models (HLM). First, a detailed assessment of the structure of the developmental trajectory of externalizing problems is provided. Second, the impact of three risk factors (infant attachment, maternal depressive symptomatology, and child sex) on the developmental course of externalizing problems is assessed. Both avoidant and disorganized attachment and higher levels of maternal depressive symptomatology were associated with higher levels of externalizing problems at 9 years of age. Girls also showed higher externalizing problems relative to their same-sex peers than did boys. In addition, maternal depressive symptomatology related to the rate of change in these problems over time: the greater the mother's depression, the faster externalizing problems tended to increase. Although the overall level of maternal depressive symptomatology was related to children's externalizing problems for secure, avoidant, and disorganized groups, changes in maternal depressive symptomatology over time predicted levels of externalizing problems only for children with avoidant insecure attachments.

Child Behavior↗
PubMed2003

Implications of latent trajectory models for the study of developmental psychopathology.

The field of developmental psychopathology is faced with a dual challenge. On the one hand, we must build interdisciplinary theoretical models that adequately reflect the complexity of normal and abnormal human development over time. On the other hand, to remain a viable empirical science, we must rigorously evaluate these theories using statistical methods that fully capture this complexity. The degree to which our statistical models fail to correspond to our theoretical models undermines our ability to validly test developmental theory. The broad class of random coefficient trajectory (or growth curve) models allow us to test our theories in ways not previously possible. Despite these advantages, there remain certain limits with regard to the types of questions these models can currently evaluate. We explore these issues through the pursuit of three goals. First, we provide an overview of a variety of trajectory models that can be used for rigorously testing many hypotheses in developmental psychopathology. Second, we highlight what types of research questions are well tested using these methods and what types of questions currently are not. Third, we describe areas for future statistical development and encourage the ongoing interchange between developmental theory and quantitative methodology.

Child↗
PubMed2004

Developmental trajectories and ecological transitions: a two-step procedure to aid in the choice of prevention and promotion interventions.

The confluence of two different types of transitional processes is explored: human development and normative ecological transitions. There are periods of greater vulnerability than others in the developmental life course as well as particular normative ecological transitions that are more disruptive than others. When there is a confluence of developmental vulnerability and a disruptive ecological transition, a "turning point" in development may ensue. This can take the form of an opportunity for growth and development or a developmental mismatch. Consequently, such turning points may represent opportune times and places at which to launch prevention/promotion programs. A two-step analytic procedure, nomothetic analyses followed by idiographic analyses, is described and illustrated to test the utility of this framework. First, these issues are illustrated using the self-esteem trajectories of low-income, urban public school students making a normative school transition to a junior and senior high school. Second, new data are presented on the early adolescent self-esteem trajectories and their association with long-term psychopathology. Third, the significance of this two-step procedure is discussed in regard to several normative ecological transitions that are common when older adolescents make the developmental transition into adulthood (e.g., into full-time employment, marriage).

Adolescent↗
PubMed2005

Developmental trajectories of offending: validation and prediction to young adult alcohol use, drug use, and depressive symptoms.

This longitudinal study extended previous work of Wiesner and Capaldi by examining the validity of differing offending pathways and the prediction from the pathways to substance use and depressive symptoms for 204 young men. Findings from this study indicated good external validity of the offending trajectories. Further, substance use and depressive symptoms in young adulthood (i.e., ages 23-24 through 25-26 years) varied depending on different trajectories of offending from early adolescence to young adulthood (i.e., ages 12-13 through 23-24 years), even after controlling for antisocial propensity, parental criminality, demographic factors, and prior levels of each outcome. Specifically, chronic high-level offenders had higher levels of depressive symptoms and engaged more often in drug use compared with very rare, decreasing low-level, and decreasing high-level offenders. Chronic low-level offenders, in contrast, displayed fewer systematic differences compared with the two decreasing offender groups and the chronic high-level offenders. The findings supported the contention that varying courses of offending may have plausible causal effects on young adult outcomes beyond the effects of an underlying propensity for crime.

Adolescent↗
PubMed2006

Trajectories of depressive symptoms and stressful life events among male and female adolescents in divorced and nondivorced families.

This 11-year longitudinal study models the trajectories of depressive symptoms among approximately 550 females and males raised in divorced and nondivorced families in the rural Midwest. Using multilevel analyses, we demonstrate that, first, depressive symptoms changed according to a curvilinear pattern, especially for females; they increased during early to midadolescence and then declined in late adolescence to young adulthood. Second, compared with males, females experienced a greater number of depressive symptoms in adolescence and early adulthood. Third, children who experienced parental divorce by age 15 manifested a sharper increase in depressive symptoms compared to those from nondivorced families. Fourth, stressful life events children experienced shortly after parental divorce mediated the effect of parental divorce on depressive symptoms. Fifth and finally, time-varying stressful life events, particularly those related to relationship and personal loss, were significantly associated with the trajectories of depressive symptoms.

Adolescent↗
PubMed1998

Variables that initiate and maintain an early-onset trajectory for juvenile offending.

A trajectory defined by three time-ordered events was offered as a useful adjunct to building a development theory about antisocial behaviors. A sequence was defined with significant linkages between antisocial childhood behavior and early arrest and between early arrest and chronic offending. The majority of chronic offenders traveled through all three events in the sequence. Each event in the sequence shared a common process of disrupted family process plus frequent family transitions and marked social disadvantage. The findings support the hypothesis that the process that leads to antisocial behaviors at grade four may also maintain the entire sequence. The level of disrupted process at initiation and a time-based measure of involvement with deviant peers predicted which individuals moved forward in the sequence and which did not. The findings are consistent with the idea that the majority of chronic offending juveniles follow a trajectory that can be explained by a single theory.

Adolescent↗
PubMed2006

Saccadic trajectory in Huntington's disease.

Trajectories of saccadic eye movements can be modulated by the presence of a competing visual distractor. It is proposed that the superior colliculus (SC) controls the initial deviation through competitive lateral interactions. Given the ramifications of connections between basal ganglia (BG) thalamo-cortical circuitry and the SC, it was anticipated that this modulation would be differentially effected in those with Huntington's disease, which in its early stages is primarily a disorder of the BG. Horizontal deviation was determined for exogenously driven and endogenously driven vertical saccades in the presence of peripheral distractors. For neurologically healthy participants, the initial trajectories of both saccade types curved away from distractor locations, as predicted. However, for HD participants exogenous saccades consistently deviated leftwards, irrespective of distractor location. Endogenous saccades also revealed anomalous horizontal deviation, with significant leftward deviation evident for saccades directed upward and significant rightward deviation for saccades directed downward. Further, both groups generated a comparable proportion of erroneous responses to distractor stimuli, but only neurologically healthy participants demonstrated a response time advantage for compatible target/distractor presentation. These results suggest anomalous regulation of distractor-related activity in HD.

Adult↗
PubMed2001

Band-trajectory model for temperature-programmed series-coupled column ensembles with pressure-tunable selectivity.

A model and a spreadsheet algorithm is described for the prediction of solute-band migration trajectories in a series-coupled combination of two capillary GC columns with pressure-tunable and -programmable selectivity and operated under temperature-programmed conditions. The model takes into account the acceleration of carrier gas in the two columns as a result of decompression effects, the deceleration of carrier gas as a result of the increase in viscosity during temperature programming, the decrease in solute retention factors with increasing temperature during the temperature program, the differences in retention factors for the two columns, and programmed changes in the carrier-gas flow rates in the two columns during selectivity programming. In the model, the 20-meter-long column ensemble is divided into 1-cm-long intervals, and the carrier-gas velocity and column temperature are assummed to be constant in any interval. Migration times for all of the mixture solutes are computed for each column interval, and the solute-band positons in the column ensemble are plotted versus the running sum of these migration times to obtain band trajectory plots. The sum of these migration times for all 2,000 intervals gives the ensemble retention times for the solutes. Isothermal retention factors (k) for all of the mixture components at various column temperatures (Tc) are used as imput to the algorithm. Slope and intercept values of In(k) vs 1/Tc plots are used in the algorithm. General features of the model are tested using a mixture of C12-C24 normal alkanes. A mixture of polar and nonpolar compounds is used to test the utility of the model for the predicition of peak separations and retention times with pressure-tunable and -programmable selectivity. Good agreement is observed in all cases.

Journal Article↗
PubMed2002

Measuring the number of independent emitters in single-molecule fluorescence images and trajectories using coincident photons.

A simple new approach is described and demonstrated for measuring the number of independent emitters along with the fluorescence intensity, lifetime, and emission wavelength for trajectories and images of single molecules and multichromophoric systems using a single PC plug-in card for time-correlated single-photon counting. The number of independent emitters present in the detection volume can be determined using the interphoton times in a manner similar to classical antibunching experiments. In contrast to traditional coincidence analysis based on pulsed laser excitation and direct measurement of coincident photon pairs using a time-to-amplitude converter, the interphoton distances are retrieved afterward by recording the absolute arrival time of each photon with nanosecond time resolution on two spectrally separated detectors. Intensity changes that result from fluctuations of a photophysical parameter can be distinguished from fluctuations due to changes in the number of emitters (e.g., photobleaching) in single chromophore and multichromophore intensity trajectories. This is the first report to demonstrate imaging with contrast based on the number of independently emitting species within the detection volume.

Journal Article↗