Correction of ultrasonic array images to improve reflector sizing and location in inhomogeneous materials using a ray-tracing model.

The use of ultrasonic arrays has increased dramatically within recent years due to their ability to perform multiple types of inspection and to produce images of the structure through post-processing of received signals. Phased arrays offer many advantages over conventional transducers in the inspection of materials that are inhomogeneous with spatially varying anisotropic properties. In this paper, the arrays are focused on austenitic steel welds as a representative inhomogeneous material. The method of ray-tracing through a previously developed model of an inhomogeneous weld is shown, with particular emphasis on the difficulties presented by material inhomogeneity. The delay laws for the structure are computed and are used to perform synthetic focusing at the post-processing stage of signal data acquired by the array. It is demonstrated for a simulated austenitic weld that by taking material inhomogeneity and anisotropy into account, superior reflector location (and hence, superior sizing) results when compared to cases where these are ignored. The image is thus said to have been corrected. Typical images are produced from both analytical data in the frequency domain and data from finite element simulations in the time domain in a variety of wave modes, including cases with mode conversion and reflections.

Long-term effects of an early childhood intervention on educational achievement and juvenile arrest: A 15-year follow-up of low-income children in public schools.

CONTEXT: Most studies of the long-term effects of early childhood educational interventions are of demonstration programs rather than large-scale public programs. Previous studies of one of the oldest federally funded preschool programs have reported positive effects on school performance, but effects on educational attainment and crime are unknown. OBJECTIVE: To determine the long-term effectiveness of a federal center-based preschool and school-based intervention program for urban low-income children. DESIGN, SETTING, AND PARTICIPANTS: Fifteen-year follow-up of a nonrandomized, matched-group cohort of 1539 low-income, mostly black children born in 1980 and enrolled in alternative early childhood programs in 25 sites in Chicago, Ill. INTERVENTIONS: The Chicago Child-Parent Center (CPC) Program (n = 989 children) provides comprehensive education, family, and health services and includes half-day preschool at ages 3 to 4 years, half- or full-day kindergarten, and school-age services in linked elementary schools at ages 6 to 9 years. The comparison group (n = 550) consisted of children who participated in alternative early childhood programs (full-day kindergarten): 374 in the preschool comparison group from 5 randomly selected schools plus 2 others that provided full-day kindergarten and additional instructional resources and 176 who attended full-day kindergartens in 6 CPCs without preschool participation. MAIN OUTCOME MEASURES: Rates of high school completion and school dropout by age 20 years, juvenile arrests for violent and nonviolent offenses, and grade retention and special education placement by age 18 years. RESULTS: Relative to the preschool comparison group and adjusted for several covariates, children who participated in the preschool intervention for 1 or 2 years had a higher rate of high school completion (49.7 % vs 38.5%; P =.01); more years of completed education (10.6 vs 10.2; P =.03); and lower rates of juvenile arrest (16.9% vs 25.1%; P =.003), violent arrests (9.0% vs 15.3%; P =.002), and school dropout (46.7% vs 55.0%; P =.047). Both preschool and school-age participation were significantly associated with lower rates of grade retention and special education services. The effects of preschool participation on educational attainment were greater for boys than girls, especially in reducing school dropout rates (P =.03). Relative to less extensive participation, children with extended program participation from preschool through second or third grade also experienced lower rates of grade retention (21.9% vs 32.3%; P =.001) and special education (13.5% vs 20.7%; P =.004). CONCLUSIONS: Participation in an established early childhood intervention for low-income children was associated with better educational and social outcomes up to age 20 years. These findings are among the strongest evidence that established programs administered through public schools can promote children's long-term success.

Early childhood intervention and juvenile delinquency. An exploratory analysis of the Chicago Child-Parent Centers.

We investigated the relation between participation in the Child-Parent Center and Expansion Program during preschool to third grade and measures of adolescent delinquency for low-income, mostly Black youths in the Chicago Longitudinal Study. Based on analyses of 1,262 program and comparison-group children, duration of program participation (0 to 6 years) and extensive participation in the program were significantly associated with lower rates of school-reported delinquency infractions at ages 13 and 14. Extended program participation was only marginally associated with a lower rate of delinquency infractions over ages 12 to 16. Preschool participation alone had no systematic relation with delinquency but was marginally associated with delinquency reports at ages 15 and 16. Reductions in school-reported delinquency were due to less frequent mobility and to postprogram parent involvement in school. Given the high cost of crime to society, even the relatively modest effects of early childhood intervention on delinquency suggest that such programs can provide another weapon in the war on crime.

Extended early childhood intervention and school achievement: age thirteen findings from the Chicago Longitudinal Study.

We evaluated the effects of participation in an extended program of compensatory education for 559 low-income, inner-city African American children up to seventh grade. The intervention is the federal and state-funded Chicago Child-Parent Center and Expansion Program, which began in 1967. Groups included 426 children who participated in the program from preschool to grades 2 or 3 and 133 children whose participation ceased in kindergarten. After taking into account initial differences in achievement at kindergarten entry and at the end of kindergarten, and after taking into account sample selection bias, program participation for 2 or 3 years after preschool and kindergarten was associated with significantly higher reading achievement up to seventh grade and with lower rates of cumulative grade retention and special education placement (4 to 5 years postprogram). Children participating in the follow-on program for 3 years had significantly higher reading achievement in seventh grade and a lower rate of grade retention than 3 year participants. Only 3 year participants had significantly higher math achievement than the comparison group. Study findings provide rare longitudinal evidence of the beneficial effects of a large-scale community-based program of extended early childhood intervention.

Ultrasonic propagation in slurries.

Experimental measurements have been made of the ultrasonic velocity and attenuation in some simple suspensions of, mainly, silicon carbide in water and in ethylene glycol. These are compared with theoretical predictions based on a novel hydrodynamic model. Predicted ultrasonic velocities are in excellent agreement with the measured values. Predicted and measured ultrasonic attenuations do not agree as well. However, the suspensions give rise to excess attenuations rising to a few hundred nepers per metre and special experimental techniques were needed to measure ultrasonic properties. To predict attenuations to within, say, 20% for mixtures such as these is a major achievement.

Calculations of acoustic scattering from ellipsoidal voids: bends, krill and fish.

The T-matrix approach is used to calculate the scattering of sound waves by an ellipsoidal void in a fluid. Results are presented for the total cross-section of a sphere as a function of frequency; this is related to the detection of the onset of bends in divers. Results are also presented for the angular variation in scattered amplitude when a plane wave is incident on an ellipsoidal cavity in water; this is related to the target strength of euphausiids and teleostean. It is concluded that the model is a useful representation of the scattering from such marine organisms.