Trajectory Duration Research Articles

Précision et moment de frappe de balle chez le joueur de tennis expert

Introduction. – This study investigates the effect of post-rebound’s trajectory duration on the precision of the forehand stroke in tennis. Subjects and Methods. – The experimental device was composed of a ball-delivery robot, different time captors and a target. During the first experiment, six high level players are submitted to a free striking condition (C1) and a condition where they have to hit the ball before 500 ms after the rebound (C2). The second experiment explore the effects of various ejection’s angles and trajectories when high-level players have no constraint on their hitting moment. Results. – In the first experiment, the players hit the ball in the (550–600 ms) interval under C1 et have a better precision than in C2. Moreover, subjects who hit the ball during the (400–450 ms) interval under C2 have a lower precision than those using the (100–400 ms) interval. In the 2nd experiment, the (400–450 ms) interval is still unexploited under the six conditions. Conclusion. – An explanation to the existence of the (400–450 ms) critical interval could be the transition from one modality of visual information pick-up to another.

Trajectory hunting as an effective technique to validate multiplatform measurements: Analysis of the MLS, HALOE, SAGE‐II, ILAS, and POAM‐II data in October–November 1996

The goal of this study is to show that trajectory hunting is an effective technique for comparison of multiplatform measurements. In order to achieve this goal, we (1) describe in detail the trajectory hunting technique (THT), (2) perform several consistency tests for THT (self‐hunting and reversibility), (3) estimate uncertainties of this technique, and (4) validate THT results against those obtained by the traditional correlative analysis (TCA). THT launches backward and forward trajectories from the locations of measurements and finds air parcels sampled at least twice within a prescribed match criterion during the course of several days. TCA finds matched profiles for a chosen match criterion, averages them for each instrument separately, and compares the averaged profiles. As an example, we consider the 22 October to 30 November 1996 period in the Southern Hemisphere and compare the latest versions of relevant measurements made by the following five instruments: Microwave Limb Sounder (MLS, version 5 (v.5)), Halogen Occultation Experiment (HALOE, v.19), Polar Ozone and Aerosol Measurement II (POAM‐II, v.6), Stratospheric Aerosol and Gas Experiment II (SAGE‐II, v.6.1), and Improved Limb Atmospheric Spectrometer (ILAS, v.5.20). We present results for O3, H2O, CH4, HNO3, and NO2, which show that (1) ozone measurements from all five instruments agree to better than 0.4 (0.2) ppmv below (above) 30 km; (2) water vapor measurements agree within ±5–10% above 22 km; (3) methane measurements by HALOE and ILAS agree to better than 10% above 30 km with a possible positive offset of up to 10–15% by ILAS in the lower stratosphere; (4) MLS HNO3 data corrected to account for some excited vibrational lines omitted in the v.5 HNO3 retrieval agree with ILAS HNO3 measurements to within ∼0.5 ppbv (∼10–20%) over the range ∼450–750 K; (5) ILAS sunset NO2 measurements are larger than both POAM‐II and SAGE‐II values by up to 10–15% below 30 km. The self‐hunting tests show that the THT RMS noise is of the order of 1–2% for O3, CH4, and H2O and 4% for NO2 and HNO3 measurements in the stratosphere. Total THT‐related uncertainties may be 3–5% for O3 measurements when photochemical effects and sensitivities of the results to duration of trajectories and match criteria are taken into account. Good agreement is found between the THT and TCA results for each of these products and for each possible pair of instruments, with considerably better statistics (typically by at least an order of magnitude) in the THT case. This agreement validates the THT results.

Life Course, Households and Institutions: Brazil and Mexico

This paper analyzes how increases in life expectancy have, in several ways, reorganized the individual life-course during the last century ( 1900-1990) in Brazil and Mexico. In each society, couple and family relationships, domestic positions, household’s composition and structure, domestic resources and institutional mediations are in interplay with survival and generational patterns. A higher life expectancy extends the duration of the individual trajectories, successive cohorts of men and women survive longer, different generations survive together, differences by gender emerge, and domestic relationships conform a mix of types of households. The household structure has changed while people survive until advanced ages, their adult children leave the parents’ household and older people live alone as a couple and then, after the death of one of the partners, they live as a widow or widower. On the other hand, socioeconomic and institutional conditions are different in each society, drafting specific settings that can promote or limit the household members’ opportunities. Individuals of different cohorts reproduce norms and resources according to different phases of the demographic transition and institutional properties in specific historical time.

Brownian Dynamics Simulations of Aldolase Binding Glyceraldehyde 3-Phosphate Dehydrogenase and the Possibility of Substrate Channeling

Brownian dynamics (BD) simulations test for channeling of the substrate, glyceraldehyde 3-phosphate (GAP), as it passes between the enzymes fructose-1,6-bisphosphate aldolase (aldolase) and glyceraldehyde 3-phosphate dehydrogenase (GAPDH). First, BD simulations determined the favorable complexes between aldolase and GAPDH; two adjacent subunits of GAPDH form salt bridges with two subunits of aldolase. These intermolecular contacts provide a strong electrostatic interaction between the enzymes. Second, BD simulates GAP moving out of the active site of the A or D aldolase subunit and entering any of the four active sites of GAPDH. The efficiency of transfer is determined as the relative number of BD trajectories that reached any active site of GAPDH. The distribution functions of the transfer time were calculated based on the duration of successful trajectories. BD simulations of the GAP binding from solution to aldolase/GAPDH complex were compared to the channeling simulations. The efficiency of transfer of GAP within an aldolase/GAPDH complex was 2 to 3% compared to 1.3% when GAP was binding to GAPDH from solution. There is a preference for GAP channeling between aldolase and GAPDH when compared to binding from solution. However, this preference is not large enough to be considered as a theoretical proof of channeling between these proteins.

Postcoincidence trajectory duration affects motion event perception.

In a two-dimensional display, identical visual targets moving toward and across each other with equal, constant speed can be perceived either to reverse their motion directions at the coincidence point (bouncing percept) or to stream through one another (streaming percept). Although there is a strong tendency to perceive the streaming percept, various factors have been reported to induce the bouncing percept, such as a sound or a visual flash at the moment of the visual target coincidence. By changing duration of the postcoincidence trajectory (PCT), we investigated how long it would take for such bounce-inducing factors to be maximally effective after the visual coincidence. With bounce-inducing factors, the percentage of the bouncing percept did not reach its maximal level immediately after the coincidence but increased as a function of PCT duration up to 150-200 msec. The results clearly reject the possibility of the cognitive-bias hypothesis about the bounce-inducing effect and suggest rather that the bounce-inducing factors have to interact with the PCT for some period after the coincidence to be maximally effective.

Trajectory mapping: A tool for validation of trace gas observations

We investigate the effectiveness of trajectory mapping (TM) as a data validation tool. TM combines a dynamical model of the atmosphere with trace gas observations to provide more statistically robust estimates of instrument performance over much broader geographic areas than traditional techniques are able to provide. We present four detailed case studies selected so that the traditional techniques are expected to work well. In each case the TM results are equivalent to or improve upon the measurement comparisons performed with traditional approaches. The TM results are statistically more robust than those achieved using traditional approaches since the TM comparisons occur over a much larger range of geophysical variability. In the first case study we compare ozone data from the Halogen Occultation Experiment (HALOE) with Microwave Limb Sounder (MLS). TM comparisons appear to introduce little to no error as compared to the traditional approach. In the second case study we compare ozone data from HALOE with that from the Stratospheric Aerosol and Gas Experiment II (SAGE II). TM results in differences of less than 5% as compared to the traditional approach at altitudes between 18 and 25 km and less than 10% at altitudes between 25 and 40 km. In the third case study we show that ozone profiles generated from HALOE data using TM compare well with profiles from five European ozonesondes. In the fourth case study we evaluate the precision of MLS H2O using TM and find typical precision uncertainties of 3–7% at most latitudes and altitudes. The TM results agree well with previous estimates but are the result of a global analysis of the data rather than an analysis in the limited latitude bands in which traditional approaches work. Finally, sensitivity studies using the MLS H2O data show the following: (1) a combination of forward and backward trajectory calculations minimize uncertainties in isentropic TM; (2) although the uncertainty of the technique increases with trajectory duration, TM calculations of up to 14 days can provide reliable information for use in data validation studies; (3) a correlation coincidence criterion of 400 km produces the best TM results under most circumstances; (4) TM performs well compared to (and sometimes better than) traditional approaches at all latitudes and in most seasons; and (5) TM introduces no statistically significant biases at altitudes between 22 and 40 km.

Windborne displacements of Desert Locusts from Africa to the Caribbean and South America

The Desert Locust is a major pest of agriculture in Africa, the Middle East and South-West Asia and swarms are known to make downwind flights over hundreds and thousands of kilometres between seasonal breeding areas. At the end of summer in 1988, swarms of locusts were moving north and south along the western margins of North Africa and in October and November, swarms crossed the Atlantic Ocean and invaded the Caribbean and neighbouring parts of South America for the first recorded time. Because of the extent of the migration and the evolutionary significance of linkages between Old and New World species of locusts, the weather associated with the migrations was studied and trajectory analysis was used to identify the source areas and estimate the flight times. Locusts were moving offshore from western North Africa throughout the autumn and on three occasions migrated west of 40° W with easterly Trade winds. Two trans-Atlantic crossings coincided with the passage of easterly waves. Over 100 trajectories were constructed at 950 and 850 hPa and within the time limit used (≤ 144-h), 28% successfully linked source and receptor areas. Minimum trajectory duration was 93-h, which is one-and-a-half times longer than the previously longest flight duration, derived for a similar migration to the British Isles in 1954. Upwind trajectories from the arrival areas, identified sources between 27 and 6° N in Africa, with most end-points located in Mauritania, Senegal, Gambia and Guinea-Bissau. Interspersed with the Atlantic crossings were a northward movement of locusts and an incursion of Saharan dust into Europe within the circulations of frontal depressions. While offshore migrations from northern Africa are common in autumn, the immigrants in the Caribbean and South America were probably at the extreme limits of flight endurance for the species. The results tend to confirm earlier hypotheses that New World species of locusts may have evolved from ancestral migrants from Africa.

Target speed alone influences the latency and temporal accuracy of interceptive action.

When intercepting a mobile object or an apparent movement, participants show a temporal bias. They are in advance when dealing with a slow-moving stimulus and late with a fast-moving one. We studied participants intercepting an apparent movement by sliding a disk on a table. Using a fast and a slow stimulus speed, we varied three factors: duration of presentation of the stimulus, distance covered by the stimulus, and speed context (constant or varied) of stimulus presentation. In addition to the temporal bias, spatial accuracy and kinematic measures were collected. The temporal bias created by speed was evident across all three factors. Speed, in addition to strongly determining the temporal bias, significantly affected the throwing strategy adopted by the participants, as revealed by latency, movement time, and disk trajectory duration.

Stochastic trajectory modeling and sentence searching for continuous speech recognition

The paper first points out a defect in hidden Markov modeling (HMM) of continuous speech, referred as trajectory folding phenomenon. A new approach to modeling phoneme-based speech units is then proposed, which represents the acoustic observations of a phoneme as clusters of trajectories in a parameter space. The trajectories are modeled by a mixture of probability density functions of a random sequence of states. Each state is associated with a multivariate Gaussian density function, optimized at the state sequence level. Conditional trajectory duration probability is integrated in the modeling. An efficient sentence search procedure based on trajectory modeling is also formulated. Experiments with a speaker-dependent, 2010-word continuous speech recognition application with a word-pair perplexity of 50, using vocabulary-independent acoustic training, monophone models trained with 80 sentences per speaker, reported about a 1% word error rate. The new models were experimentally compared to continuous density mixture HMM (CDHMM) on the same recognition task, and gave significantly smaller word error rates. These results suggest that the stochastic trajectory model provides a more in-depth modeling of continuous speech signals.

Dynamic single machine equivalent techniques for on-line transient stability assessment

According to the post-fault trajectory duration characteristics, power system disturbances, which may cause transient stability problems, are classified into three types: short, long and extremely long duration ones. An improved method using dynamic single machine equivalent system (SMES) model for on-line first swing critical clearing time (CCT) estimation for both short and long duration disturbances on multi-machine power systems is developed in this paper. This dynamic SMES model substitutes for a large power system to provide fast, on-line transient stability assessment (TSA). Techniques such as assessment of energy margin, identification of a group of machines called the ‘dominant critical machines’ and an interpolation formula for CCT evaluation are proposed in this method to achieve high speed and accuracy in TSA. Test results on real size power systems are reported to show that the method is reliable for CCT assessment of both short and long post-fault duration disturbances.

Alternative Production and Protection Practices for Pistachios

Pistachios are the single most-successful plant introduction to the United States in the 20th century. Part of this success is due to the alternative production practices that have made this crop more economical to grow. Controlled deficit irrigation (CDI) can produce 25% savings in irrigation water with no adverse effects. Reclaimed drainage water can be used for in-season irrigation up to 6 dS/m. Nitrogen applications can be adjusted for crop load and alternate bearing. Foliar sprays of boron, copper, and zinc can replace heavy ground applications to alleviated these micronutrient deficiencies. Some early season insect damage can be tolerated due to the tree's ability to compensate for the damage by filling a higher percentage of the remaining nuts, Maintaining a clean orchard floor can limit some insect pests. Mechanical pruning has been demonstrated to be cheaper and cause no loss in yield. Foliar fungal diseases can be partially controlled by limiting trajectory angle, frequency, and duration of irrigation or by using buried drip irrigation systems. Soil-borne fungal diseases and nematode damage are controlled by using resistant rootstocks.

Articulatory dynamics in long and short vowel pairs

In English, several vowels, such as /i/ and /ı/ may be said to form pairs. The members have been described as “tense” and “lax” because, while they are believed to be grossly similar in vocal tract topography, the lax member of the pair is shorter in acoustic duration and represents a less extreme tract deformation. Temporal and configurational aspects of “tense” and “lax” pairs were investigated by an x-ray microbeam technique using the facilities at the University of Tokyo. Tongue, lip, and jaw trajectories were examined for a single speaker, producing multiple utterances of the form /əpVp/. Preliminary analysis showed that the duration of tongue movement trajectories reflected acoustic duration differences, but configurational differences were more complex. [This research was supported, in part, by grants from NINCDS and the Voice Foundation. The collaboration of the staff of the Institute of Logopedics and Phoniatrics, University of Tokyo, is gratefully acknowledged.]

The acoustic signature for intelligibility test words.

As part of a research program that aims to develop an explicit acoustic basis for a single-word intelligibility test, an initial attempt to characterize the formant trajectories and segment durations of seven test words produced by 30 normal speakers is described. These characterizations are referred to as "acoustic signatures." The data indicate that: (1) formant trajectories show two sex effects, namely, that females are more variable as a group than males and tend to have greater slopes for the transitional segment of the second-formant trajectories and that these effects are consistent across words; (2) Bark transformations of the frequency data do not seem to eliminate the interspeaker differences in formant trajectories, nor do they eliminate either of the sex effects described above; and (3) segment durations have different variabilities depending on the syllabic structure of the word; no sex effect was noted here. The discussion focuses on the appropriate form for the acoustic signatures, as well as factors that should be considered in selecting words for signature development. To demonstrate the potential application of these data, formant trajectory and segment duration data from 18 speakers with amyotrophic lateral sclerosis and varying degrees of dysarthria are compared to the acoustic signature for the word wax.