Factors modifying the response of large animals to low-intensity radiation exposure

In assessing the biological response to space radiation, two of the most important modifying factors are dose protraction and dose distribution to the body. Studies are reported in which sheep and swine were used to compare the hematology and lethality response resulting from radiation exposure encountered in a variety of forms, including acute (high dose-rate), chronic (low dose-rate), combinations of acute and chronic, and whether received as a continuous or as fractionated exposure. While sheep and swine are basically similar in response to acute radiation, their sensitivity to chronic irradiation is markedly different. Sheep remain relatively sensitive as the radiation exposure is protracted while swine are more resistant and capable of surviving extremely large doses of chronic irradiation. This response to chronic irradiation correlated well with changes in radiosensitivity and recovery following an acute, sublethal exposure

Shock-induced separation of adiabatic turbulent boundary layers in supersonic axially symmetric internal flow

An experimental investigation at Mach 4 of shock-induced turbulent boundary layer separation at the walls of axially symmetric flow passages is discussed, with particular emphasis placed on determining the shock strengths required for incipient separation. The shock waves were produced by interchangeable sting-mounted cones placed on the axes of the flow passages and aligned with the freestream flow. The interactions under study simulate those encountered in axially symmetric engine inlets of supersonic aircraft. Knowledges of the shock strengths required for boundary layer separation in inlets is important since for shocks of somewhat greater strength rather drastic alterations in the inlet flow field may occur

Will You Miss Me When I Am Gone? The Economic Consequences of Absent Parents

This paper examines the effects of family structure on the economic resources available to children, using family fixed-effects to control for unobservable characteristics of the family. The effects of divorce on the income and consumption of children born to two-parent households, and the effects of marriage on children born into single-parent households are both considered. In the long-run (six or more years after the most recent divorce) family income falls by 40 to 45% after divorce, and food consumption is reduced by 17%. Six or more years after the most recent marriage, income of children born to single parents rises by 50 to 57%, but there is no statistically significant increase in food consumption. These estimates are substantially less than the difference in income implied by cross-sectional comparisons of different family types. When income changes are measured according to time since the parents first divorce, there is substantial recovery in income, virtually all of which is explained by subsequent remarriages. Similarly, when we look at income several years after a parent's first marriage, the gain is 28 to 33%, reflecting the short-lived nature of many of these marriages.

Multimode propagation in phononic crystals with overlapping Bragg and hybridization effects

Unusual dispersion properties are observed in a phononic crystal of nylon rods in water when the lattice constant is adjusted so that Bragg and hybridization gaps overlap in frequency. On the basis of experimental and numerical analyses of time-dependent transmission and spatial field maps, the presence of two coexisting propagation modes of similar amplitude is demonstrated near the resonance frequency. This phenomenon is attributed to the coupling of the rod resonances arranged in a triangular lattice, with phase shifts driven by the Bragg condition.Comment: 5 pages, 5 figure

Does Human Capital Transfer from Parent to Child? The Intergenerational Effects of Compulsory Schooling

The strong correlation between parents' economic status and that of their children has been well-documented, but little is known about the extent to which this is a causal phenomenon. This paper attempts to improve our understanding of the causal processes that contribute to intergenerational immobility by exploiting historical changes in compulsory schooling laws that affected the educational attainment of parents without affecting their innate abilities or endowments. We examine the influence of parental compulsory schooling on grade retention status for children aged 7 to 15 using the 1960, 1970 and 1980 U.S. Censuses. Our estimates indicate that a one-year increase in the education of either parent reduces the probability that a child repeats a grade by between two and seven percentage points. Among 15 to 16 year olds living at home, we also estimate that parental compulsory schooling significantly lowers the likelihood of dropping out. These findings suggest that education policies may be able to reduce part of the intergenerational transmission of inequality.

A practical experience with independent verification and validation

One approach to reducing software cost and increasing reliability is the use of an independent verification and validation (IV & V) methodology. The Software Engineering Laboratory (SEL) applied the IV & V methodology to two medium-size flight dynamics software development projects. Then, to measure the effectiveness of the IV & V approach, the SEL compared these two projects with two similar past projects, using measures like productivity, reliability, and maintain ablilty. Results indicated that the use of the IV & V methodology did not help the overall process nor improve the product in these cases

Control of rotordynamic instability in a typical gas turbine's power system

The effect of rotor internal friction on the system's stability was studied when operated above the first critical speed. This internal friction is commonly caused by sliding press fits or sliding splines. Under conditions of high speed and low bearing damping, these systems will occassionally whirl at a frequency less than the shaft's rotational speed. This subsynchronous precession is a self excited phenomenon and stress reversals are created. This phenomenon was observed during engine testing. The reduction of spline friction and/or the inclusion of squeeze film damping have controlled the instability. Case history and the detail design of the squeeze film dampers is discussed