Abrasion by aeolian particles: Earth and Mars

Estimation of the rate of aeolian abrasion of rocks on Mars requires knowledge of: (1) particle flux, (2) susceptibilities to abrasion of various rocks, and (3) wind frequencies on Mars. Fluxes and susceptibilities for a wide range of conditions were obtained in the laboratory and combined with wind data from the Viking meteorology experiment. Assuming an abundant supply of sand-sized particles, estimated rates range up to 2.1 x 10 to the minus 2 power cm of abrasion per year in the vicinity of Viking Lander 1. This rate is orders of magnitude too great to be in agreement with the inferred age of the surface based on models of impact crater flux. The discrepancy in the estimated rate of abrasion and the presumed old age of the surface cannot be explained easily by changes in climate or exhumation of ancient surfaces. The primary reason is thought to be related to the agents of abrasion. At least some sand-sized (approx. 100 micrometers) grains appear to be present, as inferred from both lander and orbiter observations. High rates of abrasion occur for all experimental cases involving sands of quartz, basalt, or ash. However, previous studies have shown that sand is quickly comminuted to silt- and clay-sized grains in the martian aeolian regime. Experiments also show that these fine grains are electrostatically charged and bond together as sand-sized aggregates. Laboratory simulations of wind abrasion involving aggregates show that at impact velocities capable of destroying sand, aggregates from a protective veneer on the target surface and can give rise to extremely low abrasion rates

Results of the AFRSI Detailed-Environment Test of the 0.035-Scale SSV Pressure-Loads Model 84-0 in the Ames 11X11 Ft. TWT and the Lewis 8X6 Ft. and 10X10 Ft. SWT (OA-310A, B, C), Volume 2

In order to support analysis of the STS-6 advanced flexible reusable surface insulation (AFRSI) anomaly, data were obtained for aerodynamic and aeroacoustic environments in affected areas of the orbiter. Data are presented in tabular form

Microgravity studies of aggregation in particulate clouds

Aggregation in clouds of submillimeter quartz and volcanic ash particles was studied in microgravity. Particle clouds generated by pulses of air immediately formed electrostatic filamentary aggregates upon cessation of air turbulence. Manual agitation of experiment chambers produced cm-size loose grain clusters which voraciously scavenged free-floating material in their vicinity. A dipole model accounts for these observations. Experimental results have ramifications for the behavior of natural cloud systems and primary accretion of solids in the early solar nebula

Inverse Medea as a Novel Gene Drive System for Local Population Replacement: A Theoretical Analysis

One strategy to control mosquito-borne diseases, such as malaria and dengue fever, on a regional scale is to use gene drive systems to spread disease-refractory genes into wild mosquito populations. The development of a synthetic Medea element that has been shown to drive population replacement in laboratory Drosophila populations has provided encouragement for this strategy but has also been greeted with caution over the concern that transgenes may spread into countries without their consent. Here, we propose a novel gene drive system, inverse Medea, which is strong enough to bring about local population replacement but is unable to establish itself beyond an isolated release site. The system consists of 2 genetic components—a zygotic toxin and maternal antidote—which render heterozygous offspring of wild-type mothers unviable. Through population genetic analysis, we show that inverse Medea will only spread when it represents a majority of the alleles in a population. The element is best located on an autosome and will spread to fixation provided any associated fitness costs are dominant and to very high frequency otherwise. We suggest molecular tools that could be used to build the inverse Medea system and discuss its utility for a confined release of transgenic mosquitoes

The Effect of Risk on the Firm's Optimal Capital Stock: A Note

In this paper we extend the recent work on the choice of input mix under uncertainty. In particular, we demonstrate that the qualitative nature of the disturbance term, along with the decision sequence, is a crucial determinant of the overall effect of uncertainty on the optimal input mix of a firm. Using general demand and production functions in conjunction with a mean-variance framework for financial valuation, we demonstrate the differential effects of systematic and non-systematic risk on the firm's choice of an optimal input mix. Consistent with earlier work in economics, this analysis demonstrates that uncertainty, regardless of the source, has important implications for the firm's choice of technology.

Economic Value of the Oil and Gas Resources on the Outer Continential Shelf

A theoretical framework for estimating the economic value of the federal government's offshore oil and gas resources is developed. This framework is then applied to geological and economic data generated by the Minerals Management Service in support of their five-year leasing plan. With an 8 percent real discount rate and a 1 percent real price growth rate, the remaining economic rent as of 1987 on the reserves plus the undiscovered offshore oil and gas resources is estimated at $118.6 billion (1987 dollars). The present value of the government's receipts from cash bonus and royalty payments on these deposits is estimated at$37.2 billion. Over 80 percent of the remaining economic rent is derived from developed reserve deposits located in the Gulf of Mexico. The private sector has previously paid cash bonuses for the leases located on those deposits and financed the installation of the development platforms. Because of this, the government will collect only a small portion, approximately 22 percent, of the rent remaining on those reserves.Environmental Economics and Policy, Resource /Energy Economics and Policy,

Aeolian abrasion on Venus: Preliminary results from the Venus simulator

The role of atmospheric pressure on aeolian abrasion was examined in the Venus Simulator with a constant temperature of 737 K. Both the rock target and the impactor were fine-grained basalt. The impactor was a 3 mm diameter angular particle chosen to represent a size of material that is entrainable by the dense Venusian atmosphere and potentially abrasive by virtue of its mass. It was projected at the target 10 to the 5 power times at a velocity of 0.7 m/s. The impactor showed a weight loss of approximately 1.2 x 10 to the -9 power gm per impact with the attrition occurring only at the edges. Results from scanning electron microscope analysis, profilometry, and weight measurement are summarized. It is concluded that particles can incur abrasion at Venusian temperatures even with low impact velocities expected for Venus

Design and calibration of the carousel wind tunnel

In the study of planetary aeolian processes the effect of gravity is not readily modeled. Gravity appears in the equations of particle motion along with interparticle forces but the two terms are not separable. A wind tunnel that would permit variable gravity would allow separation of the forces and aid greatly in understanding planetary aeolian processes. The design Carousel Wind Tunnel (CWT) allows for a long flow distance in a small sized tunnel since the test section is a continuo us circuit and allows for a variable pseudo gravity. A prototype design was built and calibrated to gain some understanding of the characteristics of the design and the results presented