Environmental stability graphite/PMR-15 composites

During the past few years the Boeing Company was screening graphite composites for use in hot areas of engine nacelle structure. Structural and thermal analyses have shown that there is the potential for a 25 to 30 percent weight savings by using a graphite polyimide (Gr/PI) composite material in this type of structure. Work conducted on the NASA CASTS program (Composites for Advanced Space Transportation Systems) amply demonstrated the capability of Graphite/PMR-15 for short term service (125 hours) at temperatures up to 589 K (600 F). In addition, the CASTS program demonstrated that large structures could be fabricated using Gr/PMR-15. In commercial applications, however, the requirement exists for long term service capability (tens of thousands of hours) at temperatures ranging upwards from 449 K (350 F). The results of Graphite/PMR-15 materials characterization efforts conducted at Boeing are presented with emphasis on materials properties after isothermal aging at temperatures of 449 K (350 F) and above

Perceptions of time in relation to climate change

Time is at the heart of understanding climate change, from the perspective of both natural and social scientists. This article selectively reviews research on time perception and temporal aspects of decision making in sociology and psychology. First we briefly describe the temporal dimensions that characterize the issue of climate change. Second, we review relevant theoretical approaches and empirical findings. Then we propose an integration of these insights for the problem of climate change and discuss mismatches between the human mind, surrounding social dynamics, and climate change. Finally, we discuss the implications of this article for understanding and responding to climate change, and make suggestions on how we can use the strengths of the human mind and social dynamics to communicate climate change in its temporal context.This article is categorized under: Climate, History, Society, Culture &gt; Ideas and Knowledge Perceptions, Behavior, and Communication of Climate Change &gt; Perceptions of Climate Change </jats:p

Fillers for improved graphite fiber retention by polymer matrix composites

The results of a program designed to determine the extent to which elemental boron and boron containing fillers added to the matrix resin of graphite/epoxy composites prevent the release of graphite fibers when the composites are exposed to fire and impact conditions are described. The fillers evaluated were boron, boron carbide and aluminum boride. The conditions evaluated were laboratory simulations of those that could exist in the event of an aircraft crash and burn situation. The baseline (i.e., unfilled) laminates evaluated were prepared from commercially available graphite/epoxy. The baseline and filled laminates' mechanical properties, before and after isothermal and humidity aging, also were compared. It was found that a small amount of graphite fiber was released from the baseline graphite/epoxy laminates during the burn and impact conditions used in this program. However, the extent to which the fibers were released is not considered a severe enough problem to preclude the use of graphite reinforced composites in civil aircraft structure. It also was found that the addition of boron and boron containing fillers to the resin matrix eliminated this fiber release. Mechanical properties of laminates containing the boron and boron containing fillers were lower than those of the baseline laminates. These property degradations for two systems: boron (5 micron) at 2.5 percent filler loading, and boron (5 micron) at 5.0 percent filler loading do not appear severe enough to preclude their use in structural composite applications

Capitalising the value of free schools : the impact of supply characteristics and uncertainty.

There has been a growing literature in both the US (for example Haurin and Brasington 1996, and Black 1999) and the UK (for example Gibbons & Machin, 2003) that estimates the way in which school quality is capitalised into house prices. Cheshire and Sheppard 1995 and 1999 estimated hedonic models in which the quality of the secondary school to which a household was assigned was a significant variable which provided evidence that secondary school quality was being capitalised into the price of houses. In contrast Gibbons and Machin concluded that primary schools were more significant. Each of these analyses is predicated on the assumption that the value of local schools should be reflected in the value of houses. We argue here that this is rather too simple. We should expect variation in the capitalised price of a given school quality at either primary or secondary level according to the elasticity of supply of ‘school quality’ in the local market, the certainty with which that quality can be expected to be maintained over time and the suitability of the dwelling to accommodate children. These factors will vary systematically between and perhaps within cities. This paper explores the sources and the impact of such variations as well as the impact of model specification. The results provide new evidence on the complex and subtle ways in which housing markets capitalise the value of local public goods such as school quality and perhaps most importantly suggest that this is highly non-linear: houses in the catchment areas of only the best state schools command substantial premiums but such capitalised values can be very substantial indeed.

Cryogenic/high temperature structural adhesives

Results are described of the work performed to develop a structural adhesive system which possesses useful properties over a 20K (-423 F) to 589 K (600 F) temperature range. Adhesives systems based on polyimide, polyphenylquinoxaline polyquinoxaline, polybenzothiazole and polybenzimidazole polymers first were screened for suitability. Detailed evaluation of two polyimide adhesive sytems, Br34/FM34 and P4/A5F or P4A/A5FA, and one polyphenylquinoxaline adhesive system, PPQ II (IMW), then was performed. Property information was generated over the full temperature range for shear strength, stressed and unstressed thermal aging, thermal shock and coefficient of thermal expansion. Both polyimide adhesive systems were identified as being capable of providing structural adhesive joints for cryogenic/high temperature service

The Effect of Medicaid Expansions for Low-Income Children on Medicaid Participation and Private Insurance Coverage : Evidence from the SIPP

We examine Medicaid enrollment and private coverage loss following expansions of Medicaid eligibility. We attempt to replicate Cutler and GruberÂ’s (1996) results using the Survey of Income and Program Participation, and find smaller rates of take-up and little evidence of crowding out. We find that some of the difference in results can be attributed to different samples and recall periods in the data sets used. Extending the previous literature, we find that take-up is slightly increased if a childÂ’s siblings are eligible and with time spent eligible. Focusing on children whose eligibility status changes during the sample, we estimate smaller take-up effects. We find little evidence of crowding out in any of our extensions.

Did Expanding Medicaid Affect Welfare Participation?

Using data from the 1988-1996 Current Population Surveys (CPS), we re-examine the evidence presented in Yelowitz (1995) showing that expansions in Medicaid eligibility for children were associated with increased labor force participation and reduced participation in Aid to Families with Dependent Children (AFDC) among single mothers. We find that Yelowitz's results were the result of two factors. First, he imposed a strong restriction on the parameter estimates that is not predicted by theory and is rejected in the CPS data. Second, he used only one of the two income tests that families must pass to be eligible for AFDC, resulting in higher imputed AFDC breakeven income levels for larger families. Once these problems are addressed, the Medicaid income limits have no significant effect on AFDC participation. The AFDC income limits, however, are significantly related to welfare and labor force participation in both his original sample and the entire 1988-1996 sample.

The Effect of Medicaid Expansions for Low-Income Children on Medicaid Participation and Insurance Coverage: Evidence from the SIPP

Increased availability of public health insurance for children has led to two potentially contradictory concerns for public policy: that expanded availability of public insurance may lead families to decline private insurance and that additional public coverage may not reach many uninsured children. We examine these two concerns using data from the 1987-1993 Surveys of Income and Program Participation. Using static models we find that the expansions resulted in increased Medicaid coverage, although the estimates of take-up are smaller than estimates from previous research. We find little evidence of a negative relationship of any significant magnitude between eligibility for Medicaid and private coverage. We also find that children who have been eligible for Medicaid longer are more likely to be enrolled in Medicaid but no more likely to have lost private coverage. Including individual fixed effects reduces the magnitude of the estimated take-up effect, while the fixed effects estimates for the private insurance regression become negative and marginally statistically significant in some specifications. Simple dynamic models of insurance choice show that insurance choice is quite persistent. The estimated long run impact of eligibility in the dynamic models is larger than the estimate from the static models, while the immediate impact of expanded Medicaid eligibility from the dynamic models is smaller than the estimated effect from the static models.

Cost practices and problems in the production of coke

The method of arriving at the cost of producing coke is practically the same in all plants. As suggested elsewhere in this paper, the method is not at all satisfactory. The problem is one which is the subject of considerable discussion among producers and their accounting departments. Referring again to the illustration given, the costs consist of the coal at cost price, the cost of carbonization (coking costs), and to these costs are credited the market or sale value of the by-products leaving the excess of these costs over the market value of the by-products as the cost of coke. It will readily be seen that this method of accounting is subject to criticism, especially in the conversion of coal where coke frequently becomes a by-product, and not the major product. Experience has shown us that the so-called by-products of coke are in many cases or localities considered as having decidedly a greater value than the coke, thus reducing the so-called main product to the class of by-products. A number of plants have been built for the primary purpose of manufacturing gas