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PubMed2002

Fertilization has little effect on light-interception efficiency of Picea abies shoots.

We investigated effects of nutrient availability on shoot structure and light-interception efficiency based on data from control (C) and irrigated + fertilized (IL) trees of Norway spruce (Picea abies (L.) Karst.). The sampling of 1-year-old shoots was designed to cover the variation in canopy exposure within the live crown zone, where current-year shoots were still found. Canopy openness was used as a measure of light availability at the shoot's position. Openness values for the sample shoots ranged from 0.02 to 0.77 on the IL plot, and from 0.10 to 0.96 on the C plot. Among needle dimensions, needle width increased most with canopy openness. At fixed canopy openness, needle width was larger, and the ratio of needle thickness to width was smaller in IL trees than in C trees. Specific needle area (SNA) and the ratio of shoot silhouette area to total needle area (STAR) decreased with canopy openness, so that the combined effect was a threefold decrease in the ratio of shoot silhouette area to unit dry mass (SMR = STAR x SNA) along the studied range of openness values. This means that the light-interception efficiency of shoots per unit needle dry mass was three times higher for the most shaded shoots than for sun shoots. A test of the effect of fertilization on the relationships of SNA, STAR and SMR indicated statistically significant differences in both slope and intercept for SNA and STAR, and in the intercept for SMR. However, the differences partly cancelled each other so that, at medium values of canopy openness, differences between treatments in predicted SNA, STAR and SMR were small. At 0.5 canopy openness, predicted STAR of IL shoots was 6.1% larger than STAR of C shoots, but SMR of IL shoots was 10% smaller than that of C shoots. The results suggest that light-interception efficiency per unit needle area or mass of the shoots is not greatly affected by fertilization.

Light↗
PubMed1997

The feasibility of a street-intercept survey method in an African-American community.

OBJECTIVES: This study evaluates the feasibility of a nonquota, street-intercept survey method that utilized random selection of interview sites. METHODS: The street-intercept survey was compared with a random digit-dial telephone survey conducted in the same catchment area among African-American adults aged 18 or older. RESULTS: The street-intercept survey's response rate was 80.2%; residence rate, 85.3%; interview completion rate, 97.9%; interference rate, 4.0%; and yield rate, 2.5 interviews per interviewer per hour. The street-intercept method produced more representative distributions of age and sex than the random-digit-dial survey. CONCLUSIONS: The street-intercept method is a feasible alternative to traditional population survey methods and may provide better access to harder-to-reach segments of the urban population in a safe manner.

Adolescent↗
PubMed2000

[Rainfall interception capacity of forest canopy between two different stands].

Based on the observation data, the rainfall interception capacity of the canopy in plantation and natural forest stands and its relation to rainfall were examined using the method of taking maximum under the same rainfall. The results showed that the rainfall interception capacity of plantation forest increased rapidly with the increase of rainfall, because of its even distribution of branches and leaves, which was higher under low rainfall less than 30 mm, and the saturation interception capacity was easily reached, depending on the quantity of branches and leaves in the canopy. Although the interception capacity of natural forest was relatively weak under low rainfall less than 30 mm, compared with plantation forest, it was much stronger under heavy rainfall more than 30 mm. The saturation interception of natural forest was larger than that of plantation forest.

Ecosystem↗
PubMed2004

Neurophysiology of the parieto-frontal system during target interception.

We studied the functional properties of neurons of two elements of the parieto-frontal system: area 7a of the PPC and the motor cortex (M1), during an interception task of stimuli moving in real (RM) and apparent motion (AM). The stimulus moved along a circular path with one of 5 speeds, and was intercepted at 6 o'clock by exerting a force pulse on a joystick. A smooth stimulus motion was produced in RM, whereas in AM 5 stimuli were flashed successively at the vertices of a pentagon. The results showed, that a group of neurons in both areas above responded not only during the interception but also during a NOGO task in which the same stimuli were presented in the absence of a motor response. Most of these neurons were tuned to the stimulus angular position. In addition, we found that the time-varying neuronal activity in both areas was related to various aspects of stimulus motion and hand force, with stimulus-related activity prevailing in area 7a and hand-related activity prevailing in M1. Interestingly, the neural activity was selectively associated with the stimulus angle during RM, whereas it was tightly correlated to the time-to-contact during AM. Thus, the results suggest that area 7a was processing high level features of the circularly moving stimuli and was involved in the production of an early command signal for stimulus interception, whereas M1 was still processing some aspect of the visual stimulus that were used to trigger the interception movement using a predictive mechanism.

Animals↗
PubMed2005

[Rainffall interception model of forest canopy: a preliminary study].

Canopy interception is an important hydrological process in forest ecosystem, and its modelling is of significance to understand and estimate the rainfall interception by the canopy. In this paper, a canopy rainfall interception model was established by dividing a rain incident into a set of short period, calculating the rainfall distribution intercepted by the canopy, and educing the process of the rain incident. This model considered the effects of the dryness of canopy and trunk on the evaporation from wet canopy and trunk during one rain incident, and introduced two factors, leaf area index (LAI) and surface area of trunk per unit area of ground (SAI), when computing the evaporation. The application of the model to simulate the rainfall interception process in a Larix principis-rupprechtii plantation in Guyuan, south Ningxia Hui autonomous region of China showed that the simulated and measured throughfall were identical, and the absolute deviation between simulated and measured results was within +/- 1 mm. But, when the precipitation was smaller than 6 mm, the simulated throughfall was lower than the measured one. The values of simulated stemflow were lower than the measured values, and the relative deviation between simulated and measured values was smaller when the precipitation was larger. The process of throughfall in the forest was also simulated, with the results fitted well to the measured one.

Ecosystem↗
PubMed2004

Role of interceptive orthodontics in early mixed dentition.

Early orthodontic interventions are often initiated in the developing dentition to promote favourable developmental changes and remove or suppress those that are unfavourable. Early interceptive orthodontics can eliminate or reduce the severity of a developing malocclusion, the complexity of orthodontic treatment, overall treatment time and cost. It also improves self-esteem in the subjects and parental satisfaction. Early detection and appropriate referral of cases requiring interceptive orthodontics are important. However, lack of awareness among school children, parents and primary-care personnel (dental nurses and dental officers) may result in patients not being referred for timely interceptive intervention. This article presents a general view of the scope of interceptive orthodontics that can be carried out in early mixed dentition, i.e. when the permanent incisors and molars are erupting into the oral cavity.

Age Factors↗
PubMed2004

The perceptual control of goal-directed locomotion: a common control architecture for interception and navigation?

Intercepting a moving object while locomoting is a highly complex and demanding ability. Notwithstanding the identification of several informational candidates, the role of perceptual variables in the control process underlying such skills remains an open question. In this study we used a virtual reality set-up for studying locomotor interception of a moving ball. The subject had to walk along a straight path and could freely modify forward velocity, if necessary, in order to intercept-with the head-a ball moving along a straight path that led it to cross the agent's displacement axis. In a series of experiments we manipulated a local (ball size) and a global (focus of expansion) component of the visual flow but also the egocentric orientation of the ball. The experimental observations are well captured by a dynamic model linking the locomotor acceleration to properties of both global flow and egocentric direction. More precisely the changes in locomotor velocity depend on a linear combination of the change in bearing angle and the change in egocentric orientation, allowing the emergence of adaptive behavior under a variety of circumstances. We conclude that the mechanisms underlying the control of different goal-directed locomotion tasks (i.e. steering and interceptive tasks) could share a common architecture.

Acceleration↗
PubMed2006

Use of visual information in the correction of interceptive actions.

Use of visual information in interceptive actions requiring large-scale changes to movement timing was investigated. The task consisted of intercepting a moving target on a monitor screen through an angular arm movement. In half of the trials, the initial target velocity of 8 cm/s was unexpectedly decreased to 4 cm/s or increased to 12 cm/s, leaving 800 ms to target arrival after velocity change. Visual information about target displacement was manipulated by interpolating full vision with occlusion of the last 200, 400, or 600 ms before the due time of interception. The results revealed that reduction of visual exposure of target displacement affected movement variability, but not arm velocity or directional trend of temporal errors. This finding supports the concept that motor control in interception is based on an internal representation of target displacement, formed during the initial portion of visual exposure following velocity change, which is updated by further visual information of target displacement.

Adult↗
PubMed2005

Perception-action coupling and expertise in interceptive actions.

The goal of this experiment was to show that expertise in interceptive actions can be explained by a shorter delay in movement regulation. In this contribution, we tested tennis experts and non-experts using a simulated interceptive task. The experimental device simulated linear motion of an object toward a target on a horizontal runway. Participants had to intercept the simulated moving object with their right hand holding a cart that could slide along a horizontal track perpendicular to the runway. Three different velocity conditions were used: a constant velocity condition that maintained the initial velocity (2m/s) constant until arriving on the target; the decelerated and accelerated velocity conditions, in which the velocity suddenly changed (400 ms before its arrival on the target) from 2 to 1m/s or 3m/s, respectively. Timing accuracy and movement correction after the unexpected velocity change were analysed. The experts were more accurate in the decelerative case (-29 and -124 ms respectively), in the accelerative case (69 and 116 ms respectively), but not in the constant velocity case (2 and 13 ms respectively). Findings can be explained by the shorter visuo-motor delay (VMD: the time required to adapt the movement to the new velocity) for the experts (162 ms) than for the non-experts (221 ms). This shorter VMD offers more time to adapt the interceptive movement to the new velocity. These results can be interpreted as an optimization of the perception-action coupling with expertise.

Adolescent↗
PubMed2001

Interception, retention and translocation under greenhouse conditions of radiocaesium and radiostrontium from a simulated accidental source.

The behaviour of radioactive aerosols released from a severely damaged nuclear reactor and deposited on cereals was simulated under controlled conditions. 137Cs- and 90Sr-labelled aerosols were generated by volatilisation at high temperature of an artificially spiked pellet of depleted UO2. After cooling and maturation the aerosols were allowed to deposit on spring wheat (Triticum aestivum L. var. Arbon) cultures grown on lysimeters under greenhouse conditions. At the time of contamination the wheat plants were at different stages of development, from early vegetative growth (two leaves) until nearly mature (end of flowering). The estimated interception coefficient (micro) amounted to 13.1 m2 kg(-1); such a high value may be explained by the experimental conditions that created an over-saturated atmosphere during the contamination process and wet leaf surfaces. The first simulated rain, applied 6 days after the contamination, removed four times more 137Cs (54%+/-12 of the intercepted radionuclides) than 90Sr (15%+/-20) from the aerial parts. At harvest approximately 2% of the Sr and less than 1% of the Cs initially intercepted by the aerial parts is recovered for plants contaminated during the early development stages. A significantly higher proportion of the intercepted activity is still present for plants contaminated in the late development stages. The translocation to grains (TLF) increases when deposit occurs closer to the mature stage of the plant. The initial decrease of TLF values that we observed for strontium contamination in the earliest development stages is most probably due to the contribution of root uptake. Ploughing and re-sowing after the first rain, applied as a countermeasure reduced the 137Cs content in leaves and stems at harvest approximately 3 times but had no effect on the 90Sr content in vegetative organs. It reduced the 137Cs-contamination level in edible parts (grain) by a factor of 2 compared to the unploughed control, but doubled the 90Sr content.

Aerosols↗
PubMed2003

The information for catching fly balls: judging and intercepting virtual balls in a CAVE.

Visually guided action implies the existence of information as well as a control law relating that information to movement. For ball catching, the Chapman Strategy--keeping constant the rate of change of the tangent of the elevation angle (d(tan(alpha))/dt)--leads a catcher to the right location at the right time to intercept a fly ball. Previous studies showed the ability to detect the information and the consistency of running patterns with the use of the strategy. However, only direct manipulation of information can show its use. Participants were asked to intercept virtual balls in a Cave Automated Virtual Environment (CAVE) or to judge whether balls would pass behind or in front of them. Catchers in the CAVE successfully intercepted virtual balls with their forehead. Furthermore, the timing of judgments was related to the patterns of changing d(tan(alpha))/dt. The advantages and disadvantages of a CAVE as a tool for studying interceptive action are discussed.

Adult↗
PubMed2006

Muscular proprioception contributes to the control of interceptive actions.

The authors proposed a model of the control of interceptive action over a ground plane (Chardenon, Montagne, Laurent, & Bootsma, 2004). This model is based on the cancellation of the rate of change of the angle between the current position of the target and the direction of displacement (i.e., the bearing angle). While several sources of visual information specify this angle, the contribution of proprioceptive information has not been directly tested. In this study, the authors used a virtual reality setup to study the role of proprioception when intercepting a moving target. In a series of experiments, the authors manipulated proprioceptive information by using the tendon vibration paradigm. The results revealed that proprioception is crucial not only to locate a moving target with respect to the body but also, and more importantly, to produce online displacement velocity changes to intercept a moving target. These findings emphasize the importance of proprioception in the control of interceptive action and illustrate the relevance of our model to account for the regulations produced by the participants.

Adult↗
PubMed2004

Visual guidance of intercepting a moving target on foot.

How do people walk to a moving target, and what visual information do they use to do so? Under a pursuit strategy, one would head toward the target's current position, whereas under an interception strategy, one would lead the target, ideally by maintaining a constant target-heading angle (or constant bearing angle). Either strategy may be guided by the egocentric direction of the target, local optic flow from the target, or global optic flow from the background. In four experiments, participants walked through a virtual environment to reach a target moving at a constant velocity. Regardless of the initial conditions, they walked ahead of the target for most of a trial at a fairly constant speed, consistent with an interception strategy (experiment 1). This behavior can be explained by trying to maintain a constant target-heading angle while trying to walk a straight path, with transient steering dynamics. In contrast to previous results for stationary targets, manipulation of the local optic flow from the target (experiment 2) and the global optic flow of the background (experiments 3 and 4) failed to influence interception behavior. Relative motion between the target and the background did affect the path slightly, presumably owing to its effect on perceived target motion. We conclude that humans use an interception strategy based on the egocentric direction of a moving target.

Adult↗
PubMed2001

A method for estimating light interception by a conifer shoot.

We present an operational method for estimating the amount of PAR intercepted by a coniferous shoot. Interception of PAR by a shoot is divided into three components: the amount of radiation coming from the sky, the transmission of radiation through the surrounding vegetation, and the shoot' s silhouette area facing the direction of the incoming radiation. All three components usually vary with direction. Radiation incident from the sky consists of direct and diffuse radiation. The well-known equation of motion for the sun and Beer' s Law for atmospheric transmittance are used to simulate the directional distribution of direct sunlight for any given period of time. The diffuse component is assumed to be uniform. Meteorological field measurements are used to calibrate the absolute amounts of the direct and diffuse components. The gap fraction (proportion of visible sky) in different directions around a shoot is measured by analyzing a hemispherical fish-eye photograph, taken at the location of the shoot, with an image processing program. Similarly, the shoot silhouette area (SSA) is measured by photographing the shoot from many different directions. The measurements of SSA are interpolated by a method called trigonometric interpolation to obtain the directional distribution of SSA over the entire hemisphere. This distribution is then rotated according to the shoot' s position in the canopy. Multiplying incoming PAR, canopy gap fraction and SSA in different directions, and summing over all directions, gives an estimate of PAR intercepted by the shoot during the chosen period of time. The method is described step by step, and applied, as an example, to a shoot from a Scots pine (Pinus sylvestris L.) stand in central Finland. Differences in radiation interception properties between sun and shade shoots and their relevance to canopy-scale models are discussed.

Cycadopsida↗
PubMedDate not supplied

Performance of a canopy light interception model for conifer shoots, trees and stands.

A hierarchical approach was used to evaluate the behavior of a canopy light interception model using submodels for interception at levels of the shoot, crown and stand. Mean silhouette areas of individual shoots of lodgepole pine (Pinus contorta var. latifolia Engelm.) calculated assuming spherical shoot orientation agreed well with silhouette areas measured with a video projection system. A theoretical mean silhouette to total leaf area ratio (STAR) calculated using measured shoot characteristics and a model of shoot geometry agreed reasonably well with STAR values from measured shoot silhouette and leaf areas, although the range of calculated STAR values was slightly lower than that of the measured values. The shadow areas of tree crowns were underestimated for lodgepole pine; however, a model using regular shoot dispersion in the crown gave better agreement than a model based on random shoot dispersion. The underestimates may have been caused by underestimation either of leaf or branch area for the crowns or of the extinction coefficient. Two equations used to calculate leaf area from sapwood area measurements both underestimated leaf area. Accordingly, there are too many uncertainties to determine whether crown interception is best represented by a random or regular distribution of shoots. Mean canopy transmission in the Engelmann spruce (Picea engelmannii Parry ex Engelm.) stand was estimated very well by a random (Poisson) model of the spatial distribution of trees, whereas, in the lodgepole pine stand, a regular (hexagonal) model gave the best results. The Engelmann spruce stand had less regular tree spacing than the lodgepole pine stand. Taken as a whole, the weakest submodel for calculating canopy interception was the model for individual crown transmission, which underestimated crown shadow areas. However, the problem may be in leaf area estimates rather than in model performance.

Journal Article↗
PubMed1990

An analysis of vegetation interception data pertaining to close-in weapons test fallout.

This paper reports an analysis of literature data pertaining to the fraction of particles resulting from regional weapons fallout intercepted by vegetation. A simple model for the interception parameter, alpha, was developed that predicted an increasing interception fraction with increasing distance from detonation site. The predicted values of alpha close to the detonation site are much smaller than most accepted values that pertain to aerosols and gases. The apparent dependence of the interception parameter on distance is believed to partially reflect the changes of the particle-size distribution of the fallout cloud with the time aloft and the ability of vegetation surfaces to better retain particles of small size. The validity of a set of predicted values was tested using an assessment model and literature data of radioiodine concentrations in milk following a nuclear test.

Environmental Exposure↗
PubMed2005

Quality control of slope-intercept measurements of glomerular filtration rate using single-sample estimates.

OBJECTIVES: Measurement of glomerular filtration rate (GFR) using the slope-intercept technique determines the plasma clearance curve by fitting a straight line to the logarithm of sample count rate. When two samples are used there is no check on the validity of curve fitting. GFR may also be estimated from single-sample concentrations. This study describes a method of quality control for the two-sample technique using the agreement between the one-sample and two-sample estimates. METHODS: GFR measurements using Tc-DTPA were performed on 225 adults and 100 children using two samples taken between 2 h and 4 h post-injection. The two-sample values obtained using the British Nuclear Medicine Guidelines slope-intercept technique were compared to one-sample estimates obtained using a new general equation. Equations describing the variation of GFR error with GFR value were defined. These were used to determine action levels giving the limits of expected agreement between slope-intercept and single-sample values. The use of these action levels for quality control was demonstrated in a further 120 GFR measurements. RESULTS: The variation of single-sample error estimate with GFR depended both on the time of sample and body surface area. For specific sample groups, the error variation with GFR could be approximated using a truncated quadratic equation. Four studies were identified as failing quality control in the dataset used to define the error equations. Two studies failed in the test dataset. CONCLUSIONS: One-sample equations give reliable estimates of GFR, which may be used for quality control of slope-intercept GFR assessment.

Adult↗
PubMed2004

Evaluation of processing characteristics of photochemically treated pooled platelets: target requirements for the INTERCEPT Blood System comply with routine use after process optimization.

To ensure good performance of pathogen inactivation with the INTERCEPT blood system, specific target requirements must be met for platelet dose, volume, plasma content and residual red blood cells (RBCs) prior to photochemical treatment (PCT). A two-arm in vitro study was conducted to compare quality parameters of pooled platelet concentrates (PCs), either treated (test units) or nontreated (control units). PCs meeting European requirements were evaluated with reference to their compliance with INTERCEPT guard bands. Of 50 PCs (25 tests and 25 controls) meeting European quality requirements, 24% (three test and three controls units) did not reach INTERCEPT requirements, particularly in terms of sufficient volumes and RBC contamination. The buffy-coat optimization procedure assessed prior to this study ensured plasma contents well within target limits of 30 to 45%. Due to PCT-related in-process loss of 11% in volume (34.38 +/- 3.94) and in platelet dose (0.41 +/- 0.14), the mean platelet dose was significantly (P < 0.001) lower in test units: 3.1 +/- 0.3 versus 3.6 +/- 0.4 x 10(11). After treatment, six of the overall 25 test units (25%) would not have met the European guideline for platelet dose (3.0 x 10(11)). Before implementation of techniques for pathogen reduction, each centre should optimize processing steps during a validation procedure to ensure PC complying with INTERCEPT targets before and European targets after treatment. Besides buffy-coat optimization for sufficient plasma reduction, centrifugation profiles need to be optimized as well to prevent PC with low volumes and, in particular, with higher than acceptable RBC contamination.

Blood Banking↗