Space shuttle external tank performance improvements: The challenge

The external tank (ET) has been actively involved in performance improvements since the inception of the space shuttle program, primarily by weight savings. Weight savings were realized on the first block of flight articles (standard weight tank). With a need for further performance improvements, the ET Program Office was requested to develop a program to reduce tank weight an additional 6000 lb and schedule delivery of the first lightweight ET (LWT) for June 1982. The weight savings program was accomplished by: (1) a unique approach to use of factors of safety; (2) design optimization; and (3) redesign of structures with large margins of safety which resulted in an actual weight savings of 7294 lb. Additional studies have identified further weight savings which are to be implemented at appropriate times in production flow. Examples are an improved thermal protection system for the LH2 tank aft dome and reduction of slosh baffles in the LO2 tank based on flight data. All performance improvements were compared and selected based on non-recurring and recurring cost and technical risk

Validating performance of automotive materials at high strain rate for improved crash design

This paper investigates sources of performance variability in high velocity testing of automotive crash structures. Sources of variability, or so called noise factors, present in a testing environment, arise from uncertainty in structural properties, joints, boundary conditions and measurement system. A box structure, which is representative of a crash component, is designed and fabricated from a high strength Dual Phase sheet steel. Crush tests are conducted at low and high speed. Such tests intend to validate a component model and material strain rate sensitivity data determined from high speed tensile testing. To support experimental investigations, stochastic modeling is used to investigate the effect of noise factors on crash structure performance variability, and to identify suitable performance measures to validate a component model and material strain rate sensitivity data. The results of the project will enable the measurement of more reliable strain rate sensitivity data for improved crashworthiness predictions of automotive structures

Interaction of laser generated ultrasonic waves with wedge-shaped samples

Wedge-shaped samples can be used as a model of acoustic interactions with samples ranging from ocean wedges, to angled defects such as rolling contact fatigue, to thickness measurements of samples with non-parallel faces. We present work on laser generated ultrasonic waves on metal samples; one can measure the dominant Rayleigh-wave mode, but longitudinal and shear waves are also generated. We present calculations, models, and measurements giving the dependence of the arrival times and amplitudes of these modes on the wedge apex angle and the separation of generation and detection points, and hence give a measure of the wedge characteristics

Superconductivity at 2.3 K in the misfit compound (PbSe)1.16(TiSe2)2

The structural misfit compound (PbSe)1.16(TiSe2)2 is reported. It is a superconductor with a Tc of 2.3 K. (PbSe)1.16(TiSe2)2 derives from a parent compound, TiSe2, which shows a charge density wave transition and no superconductivity. The crystal structure, characterized by high resolution electron microscopy and powder x-ray diffraction, consists of two layers of 1T-TiSe2 alternating with a double layer of (100) PbSe. Transport measurements suggest that the superconductivity is induced by charge transfer from the PbSe layers to the TiSe2 layers.Comment: 17 pages, 4 figures. To be published in Physical Review

CELLULAR EVENTS IN THE IMMUNE RESPONSE : ANALYSIS AND IN VITRO RESPONSE OF MOUSE SPLEEN CELL POPULATIONS SEPARATED BY DIFFERENTIAL FLOTATION IN ALBUMIN GRADIENTS

Cell suspensions from the spleens of normal mice or mice injected with sheep erythrocytes were separated on a discontinous bovine serum albumin density gradient. Four bands or subpopulations were obtained and were assayed for antibody-forming cells, and for antigen-sensitive precursor cells. The antibody-forming cells were assayed by the hemolytic plaque assay and the antigen-sensitive precursors were assayed by the number of plaque-forming cells which developed after 3 or 5 day's culture with antigen. It was found that both antibody-forming cells and their precursors were present in the denser region of the gradient when spleen cell suspensions were taken from unimmunized mice. In contrast, both antibody-forming cells and precursors floated to the top in cell suspensions from mice sacrificed 1, 2, or 3 days after antigen injection. The change in density was detectable as early as 12 hr and was complete by 18 hr. The cell which changed in density was specific for the antigen that brought about that change. The significance of these findings is discussed

Evaluating the Chinese Revised Controlling Behaviors Scale (C-CBS-R)

The present study evaluated the utility of the Chinese version of the Revised Controlling Behaviors Scale (C-CBS-R) as a measure of controlling behaviors in violent Chinese intimate relationships. Using a mixed-methods approach, in-depth, individual interviews were conducted with 200 Chinese women survivors to elicit qualitative data about their personal experiences of control in intimate relationships. The use of controlling behaviors was also assessed using the C-CBS-R. Interview accounts suggested that the experiences of 91 of the women were consistent with the description of coercive control according to Dutton and Goodman’s (2005) conceptualization of coercion. Using the split-half validation procedure, a receiver operating characteristics (ROC) curve analysis was conducted with the first half of the sample. The area under the curve (AUC) for using the C-CBS-R to identify high control was .99, and the cutoff score of 1.145 maximized both sensitivity and specificity. Applying the cutoff score to the second half gave a sensitivity of 96% and a specificity of 95%. Overall, the C-CBS-R has demonstrated utility as a measure of controlling behaviors with a cutoff score for distinguishing high from low levels of control in violent Chinese intimate relationships