Follow-up studies of very low birth weight infants (1,250 grams or less) born and treated within a perinatal center.

The growth and development of inborn very low birth weight infants was evaluated in 50 of 60 survivors from 132 babies weighing less than or equal to 1,250 gm born July 1974 to December 1977. Mean +/- SE birth weight and gestation was 1,066 +/- 19.3 gm and 29.5 +/- 0.3 weeks, respectively, with 13 infants small-for-gestational age. Of the survivors, 26% weighed less than or equal to 1,000 gm. Male to female ratio was 1:1.4. Apgar scores less than or equal to 5 at five minutes occurred in 16% of the infants. Respiratory distress syndrome occurred in 56%, but only 10% (5/50) required mechanical ventilation. At 1 year, 46% small for gestational age (SGA) and 8% appropriate for gestational age (AGA) infants were less than the third percentile for weight. Major neurologic abnormality occurred in three infants (6%), one of whom is also blind. Grade V retrolental fibroplasia occurred in two others. Severe developmental delay (development quotient < 80, Gesell) occurred in these five infants and two other neurologically normal babies. Of 15 infants weighing less than or equal to 1,000 gm, two had major handicaps. Eight percent of the AGA infants and 30% of the SGA infants had major handicaps. These data indicate that infants born and treated in a perinatal center have a decreased incidence of asphyxia and severe respiratory distress syndrome and that the incidence of major handicaps is reduced, especially in the appropriate for gestational age baby.

Piezoelectric properties and temperature stability of poly(vinylidene fluoride-trifluorethylene) copolymers.

Piezoelectric measurements were made on several copolymers of vinylidene fluoride and trifluorethylene having a vinylidene fluoride concentration in the range of 65-70%. The hydrostatic g constant showed only a slight dependence on pressure, and pressures up to 35 MPa caused no apparent loss of the piezoelectric activity. A significant increase in the value of the hydrostatic g constant was observed both at temperatures above and considerably below the room temperature. The anomalous result obtained upon cooling below the room temperature can be attributed to the glass transition temperature of the trifluoroethylene comonomer. Temperature aging studies were performed at high temperatures using films of these copolymers. A significant loss of piezoelectric activity occurred after long-time exposure. Isothermal studies at various aging temperatures revealed that this decay continued over a long time span. The aging behavior characteristically followed a linear dependence on the logarithm of aging time.

Electroacoustic evaluations of 1-3 piezocomposite SonoPanel(TM ) materials.

An advanced configuration 1-3 piezocomposite, designated by its manufacturer as SonoPanel(TM), has been investigated for potential underwater acoustical applications. In-air electromechanical characteristics and in-water acoustical properties of the SonoPanel(TM) were experimentally examined. The in-air impedance measurement results showed the existence of parasitic modes in the composite panel in addition to the expected thickness mode. This modal behavior is identified to be related to the piezocomposite structure. In-water acoustical properties of the new 1-3 piezocomposite panels were investigated as a function of temperature, hydrostatic pressure, and frequency. The effect of underwater explosive shock on the acoustic responses showed no detrimental effects in mechanical structure or acoustical performance of the piezocomposite panel. Linearity with electrical drive level and hydrostatic pressure stability of the 1-3 piezocomposites also were established. These results suggest that the SonoPanel(TM) piezocomposite material is potentially useful for underwater acoustical applications, particularly in applications in which large area coverage is desired.

Unidimensional modeling of multi-layered piezoelectric transducer structures.

Multi-layered transducer structures offer the potential of improved performance in terms of increased transmit sensitivity, greater bandwidth, and enhanced reception characteristics. Unfortunately, the successful design of such devices is often difficult, owing to the complex interaction between the active piezoelectric layers and passive intermediate interface layers. Furthermore, in many practical applications, the loading effects imposed by the electrical drive circuitry often limit the performance improvements that may be physically realized. This paper describes the development of a comprehensive, unidimensional modeling approach. This model may be employed to facilitate the analysis and subsequent optimization of laminated transducer assemblies. The devices currently under consideration include both piezoceramic and piezopolymer configurations, as well as alternative piezocomposite designs. The effects of varying bondline thickness and the introduction of passive interface layers are examined, as is the influence of the electrical load circuitry on overall system response. The ability to accurately predict the response of stacked piezoelectric structures is demonstrated through extensive comparison of experimental and theoretical responses. This paper concludes by highlighting the important role that modeling plays in the design, fabrication, and optimization of complex multi-layered transducer assemblies.

Enzyme activity gel analysis of human immunodeficiency virus reverse transcriptase.

An activity gel analysis was performed in order to examine the catalytically active component of human immunodeficiency virus (HIV) reverse transcriptase in purified enzyme preparations and HIV-infected cell extracts. Immunoaffinity purified HIV reverse transcriptase contains two proteins with molecular weights 66,000 and 51,000 in approximately equal proportions. After denaturing polyacrylamide gel electrophoresis and removal of sodium dodecyl sulfate, the p66 component of reverse transcriptase was sufficient for both DNA- and RNA-directed DNA synthesis. No DNA synthetic activity of p51 was observed. Recovery of p66 catalytic activity was approximately 10% that of DNA polymerase beta, and the density of the autoradiographic band corresponding to p66 was linear with enzyme concentration. No additional HIV-specific DNA polymerases besides p66 were observed in HIV-infected H9 cell extracts.

Human immunodeficiency virus reverse transcriptase. General properties and its interactions with nucleoside triphosphate analogs.

Using affinity purified human immunodeficiency virus (HIV) reverse transcriptase the reaction assay conditions were determined. The optimum incorporation of dTMP into the (rA)n(dT)10 template with HIV reverse transcriptase required 6 mM MgCl2 and 80 mM KCl. The template specificity of HIV reverse transcriptase is quite different from those of the human gamma-polymerase-associated reverse transcriptase or avian virus reverse transcriptase. The preferential inhibition of HIV reverse transcriptase as compared to human gamma-reverse transcriptase was observed with several nucleoside analog triphosphates. The Ki values for thymidine triphosphate analogs with HIV reverse transcriptase ranged from 5 to 13 nM with decreasing effectiveness for 3'-fluoro greater than 3'-amino greater than 2',3'-dideoxy greater than 3'-azido groups. This study provides information on the structure activity relationships of the triphosphate analogs inhibitory effects on HIV reverse transcriptase versus human gamma-polymerase-associated reverse transcriptase, and the possible mechanisms of action of 3' azido thymidine and the 2',3'-dideoxynucleosides, and also identifies other nucleoside analogs for possible development as inhibitors of HIV.