Trends in Self-Employment Among White and Black Men: 1910-1990

We examine trends in self-employment among white and black men from 1910 to 1990 using Census and CPS microdata. Self-employment rates fell over most of the century and then started to rise after 1970. For white men, we find that the decline was due to declining rates within industries, but was counterbalanced somewhat by a shift in employment towards high self-employment industries. Recently, the increase in self-employment was caused by an end to the within industry decline and the continuing shift in employment towards high self-employment industries. We find that the trends in self-employment average returns do not easily explain the decline in self-employment from 1950 to 1970, nor the increase from 1970 to 1990. We also find that changes in tax rates, social security benefits, and immigration patterns do not explain the recent upturn in self-employment. For black men, we find that the self-employment rate remained at a level of roughly one-third the white rate from 1910 to 1990. The large and constant gap between the black and the white rates is not due to blacks being concentrated in low self-employment rate industries, but is consistent with job opportunities outside of self-employment increasing relative to those in self-employment. However, more recently the relative earnings of blacks in self-employment rose more than relative earnings for whites the near constancy of the relative self-employment rates more surprising. We also find that absent continuing forces holding down black self-employment, a simple inter-generational model of self-employment suggests that black and white rates would converge quickly.

Dissection of Nodule Development by Supplementation of \u3cem\u3eRhizobium leguminosarum\u3c/em\u3e biovar \u3cem\u3ephaseoli\u3c/em\u3e Purine Auxotrophs with 4-Aminoimidazole-5-Carboxamide Riboside

Purine auxotrophs of Rhizobium leguminosarum biovar phaseoli CFN42 elicit uninfected pseudonodules on bean (Phaseolus vulgaris L.). Addition of 4-aminoimidazole-5-carboxamide (AICA) riboside to the root medium during incubation of the plant with these mutants leads to enhanced nodule development, although nitrogenase activity is not detected. Nodules elicited in this manner had infection threads and anatomical features characteristic of normal nodules, such as peripheral vasculature rather than the central vasculature of the pseudonodules that were elicited without AICA riboside supplementation. Although 105 to 106 bacteria could be recovered from these nodules after full development, bacteria were not observed in the interior nodule cells. Instead, large cells with extensive internal membranes were present. Approximately 5% of the normal amount of leghemoglobin and 10% of the normal amount of uricase were detected in these nodules. To promote the development of true nodules rather than pseudonodules, AICA riboside was required no later than the second day through no more than the sixth day following inoculation. After this period, removal of AICA riboside from the root medium did not prevent the formation of true nodules. This observation suggests that there is a critical stage of infection, reached before nodule emergence, at which development becomes committed to forming a true nodule rather than a pseudonodule

Techniques for aerothermal tests of large, flightweight thermal protection panels in a Mach 7 wind tunnel

Thermal performance and structural integrity are experimentally evaluated in the Langley 8-ft high temperature structures tunnel, which uses a combustion products test medium to provide realistic combinations of aerodynamic heating and loading. Recently developed techniques provide independent control of rate and magnitude of surface heating and differential pressure, protection against adverse acoustics buffeting during facility starting and stopping, programed radiant heating before exposing test panels to the high energy stream, and infrared radiometry for detailed surface temperatures. These techniques were verified repeatedly by return of useful data on metallic and nonmetallic panel concepts of reusable surface insulation

PROCUREMENT STRATEGIES: IMPACTS OF QUALITY RISKS IN HARD WHEAT

Analytical models were developed in this paper to evaluate cost/risk tradeoffs of three alternative procurement strategies in the case of hard red spring (HRS) wheat. Results indicate a naive strategy has the lowest expected cost, but a high probability of not conforming to end-use requirements. Two alternative specifications for the constant share strategy result in higher probabilities of meeting requirements, but at higher costs. The opportunistic strategy results in a higher probability of meeting requirements than either of the other two alternative strategies at a comparable cost.Crop Production/Industries,

TRANSPARENCY AND BIDDING COMPETITION IN INTERNATIONAL WHEAT TRADE

One of the major trade policy problems identified by U.S. interests, including grower groups, traders, and policymakers, is that of pricing transparency. This has been a gnawing issue generally related to the pricing practices of competitor exporting countries with state trading enterprises (STEs). The transparency problem generally refers to the inability to observe rivals' terms of trade (including price, quality, credit, etc.) and is normally associated with commercial exporters competing against STE rivals. The perception being the less transparent competitors (STEs) would have a strategic advantage. A game theory model of bidding competition was developed to simulate the effects of information asymmetry amongst rivals. A Bayes-Nash equilibrium was used to derive equilibrium solutions. Several stylized examples were used to illustrate aspects of competition and to analyze effects on bidding strategies. Results indicate that: 1) anything that reduces uncertainties among rivals would reduce equilibrium bids and prices; 2) bidding situations in which there is less transparency have the effect of increasing bids and prices to buyers, and payoffs to sellers; and 3) increases in the number of rivals have the effect of reducing bids and mitigating the informational advantages of STEs. In all cases, less transparent sellers have an advantage in bidding competition relative to more transparent sellers. That advantage in our stylized case was in the area of 1-2$/mt. However, that advantage is mitigated with an increase in the number of transparent rivals and in the case where more transparent players have acted as agents for an STE and have more information about costs of an STE. Further, cessation of exports under U.S. EEP programs should have decreased the transparency of U.S. firms, increasing their competitiveness in the international grain trade.Price Transparency, Strategic Bidding, Game Theory, Bayesian-Nash, State Trading Enterprises, Export Enhancement Program, Wheat, International Relations/Trade,

PROCUREMENT STRATEGIES: IMPACTS OF QUALITY RISKS IN HARD WHEAT

Development and organization of procurement strategies have escalated in importance with maturity of the food processing industry, as well as with the prospect of greater choice attributable to variety development and information technology. Conventional alternatives for procurement range from spot purchases with specifications for easily measurable characteristics, to varying forms of strategies with pre-commitment. In the case of grains these choices are complicated by two factors. First, there is intrinsic uncertainty associated with end-use qualities that are not easily measurable. Second, grain prices and therefore procurement costs vary spatially due to competing market regions. Thus, shifting origins may involve higher cost due to having to bid grain away from its next best market. We posed three procurement strategies and developed analytical models to evaluate the risks and costs among these alternatives in the case of hard red spring (HRS) wheat. The first involves no commitment. The second involves some form of irrevocable commitment and the third entails less commitment. Stochastic simulation models were developed for each with an objective of cost minimization subject to different levels of risk. The results indicate that the naive strategy has the lowest expected cost, but a fairly high probability of not conforming to end-use requirements. The constant share strategies result in higher probabilities of meeting requirements, but at substantially higher costs. The opportunistic strategy results in a higher probability of meeting requirements than either of the other two alternative strategies at a comparable cost.Marketing, Agribusiness,

Grain Shipments on the Mississippi River System: A Long-Term Projection

The costs of delays for shipping commodities on the Mississippi River are important and adversely impact growth in shipments. Lock and dam expansion requires substantial capital investment and an extended time period to complete. This study analyzes delay costs and the competitive position of grain shipments on the Mississippi River system. A spatial optimization model of the world grain trade was developed. Results indicated that without expansion in barge capacity, delay costs in 2020 would increase on each reach, with some up to $1.08/mt. Expansion results in reduced delay costs. Barge demand is also impacted by rail capacity. Finally, expanding the locks would result in a re-allocation of shipments among modes, reaches, and ports, notwithstanding minor adjustments in production.Agribusiness, International Relations/Trade,