Impacts and atmospheric erosion on the early Earth

It was suggested that heating and/or vaporization of accreting carbonaceous-chondrite-type planetestimals could result in the release of their volatile components. Modeling of this process strongly suggests that substantial atmospheres/hydrospheres could develop this way. During most of the accretionary process, impact velocities generally differed from the escape velocity of the growing proto-planet because most of the collisions were between bodies in nearly matching orbits. Toward the end of accretion, however, collisions were rarer but more energetic, involving large planetestimals and higher impact velocities. Such impacts result in a net loss of atmosphere from a planet, and the cumulative effect impacts during the period of heavy bombardment might have dramatically depleted the original atmospheres. Models developed to study atmospheric erosion by impacts on Mars and the interaction of the vapor plume produced by KT impactor on Earth are applied to the case of the evolution of Earth's atmosphere

Jetting and the origin of tektites

The scientific consensus is that tektites were produced by impacts on the Earth, but the exact mechanism by impacts might form tektites is still unclear. The most widely cited mechanism is jetting, which results from the extremely high pressures generated at the intersection of two bodies whose surfaces converge obliquely at high speed. Theory of jetting for thin plates is extended to the case of the impact of the sphere onto a half-space. The calculations are done for the impact of a silicate sphere onto a silicate target for impact speeds of 15, 20, and 25 km/sec, spanning the range of reasonable impact speeds for asteroids. The angle of impact is varied from 0 to 75 deg. The mass jetted, the jet velocity, projectile fraction in the jet, azimuthal distribution of the jet, and the phase of the jetted material are calculated as functions of time. The total mass jetted and the overall mass-averages of jet velocity, etc. are also calculated

Melt droplet formation in energetic impacts

Impacts between rocky bodies at velocities exceeding about 15 km/sec are capable of melting or vaporizing both the impacting object and a portion of the target. Geological materials initially shocked to high pressure approach the liquid-vapor phase boundary from the liquid side as they decompress, breaking up into an expanding spray of liquid droplets. A simple theory is presented for estimating the sizes of these droplets as a function of impactor size and velocity. It is shown that these sizes are consistent with observations of microtektites and spherules found in the Cretaceous-Tertiary boundary layer, the Acraman impact structure, Archean beds in South Africa and lunar regolith. The model may also apply to the formation of chondrules

Production of impact melt in craters on Venus, Earth, and the moon

Impact craters imaged by Magellan clearly show large amounts of flow-like ejecta whose morphology suggests that the flows comprise low-viscosity material. It was suggested that this material may be either turbidity flows or very fine-grained ejecta, flows of ejecta plus magma, or impact melts. The last of these hypotheses is considered. If these flows are composed of impact melts, there is much more melt relative to the crater volume than is observed on the moon. The ANEOS equation of state program was used for dunite to estimate the shock pressures required for melting, with initial conditions appropriate for Venus, Earth, and the moon. A simple model was then developed, based on the Z-model for excavation flow and on crater scaling relations that allow to estimate the ratio of melt ejecta to total ejecta as a function of crater size on the three bodies

Application of Biotechnology to the Study of Filarial Parasites and Their Vectors

Over 200 species of filarial parasites have been described, although the life cycle and nature of their obligate intermediate arthropod vectors have been identified for only about a quarter of them. Traditional methods of studying phylogenetic relationships between closely related parasite species have utilized morphologic, biochemical and biologic characteristics, usually of the microfilarial stage. Identification of competent vectors from among complexes of sibling species, has employed similar techniques, despite the fact that differences between geographical isolates may reflect environmental rather than genetically controlled factors. Studies of the prevalence and transmission of animal, human and zoonotic filarids, so important for vector identification and control, has lead to the examination of filarial parasites at the genetic level. Genomic DNA libraries are being constructed and screened for clones which are species specific. From this work, DNA probes which can accurately enumerate larval stages in vector squash preparations, and monoclonal antibodies specific for defined filarial antigens, are being prepared. The nucleotide sequences of rRNA are also being defined. The application of these technologies to the study of filarial parasites and their vectors, promises to not only allow the construction of accurate phylogenetic trees, but also to provide the data necessary for the identification and control of the vectors of filarial pathogens of animals and man

Impostor Phenomenon, College-Going Knowledge, and Staff Expectations: Ramifications on First Time in College Students Enrollment

A lack of technically trained, skilled, and educated workforce has become a critical issue in Texas. Furthermore, an educated workforce improves communities and individuals with economic, health, and personal benefits. Community colleges not only provide open-access admissions and low-cost tuition but are specifically aligned with educating the technical and industrial skilled workforce. Although a post-high school education has never been more accessible or necessary for obtaining high-earning jobs, post-high school college enrollment is declining, and conventional reform strategies do not appear to be effecting change. Graduating high school students aspire to attend postsecondary training by applying and being accepted but are not following through to register and attend. Friction points occur between aspiring or applying to college and registering or attending school, leading to a phenomenon known as summer melt. Two identified possible friction points are impostor phenomenon (IP) and college-going knowledge. IP is a belief that one’s successes are not based on one’s abilities and aptitudes but instead on luck or other external forces, and therefore, the individual believes that he or she is a fake, living in fear of being discovered as an imposter. College-going knowledge is the knowledge regarding admissions, financial aid, housing, and other college jargon that makes up the students’ social capital easily transitioning to the higher education environment. IP is well documented in higher education and specifically in first-generation college students. Acting as institutional agents, student services staff may mediate high levels of IP feelings and low levels of college-going knowledge. The findings from this study indicated that many first-time in college students experience moderate to high levels of IP, with the majority frequently having occurrences of IP. There was no significant difference between first-generation college students and continuing-generation college students. Additionally, the college-going knowledge of the vi majority of students was high. New staff had higher expectations of students’ levels of college-going knowledge, while experienced staff held low expectations. Findings from this body of work can be used to influence curriculum development in higher education graduate programs and staff or faculty training on IP and how to assist students in redefining their academic identity

Land Application of Manure: Minnesota Livestock Producers\u27 Practices and Educational Needs

A combination of farmer focus groups and a pre-discussion survey was employed to determine adoption of recommended manure management practices and preferred Extension education methods. Eight focus groups followed a 2-year education program that addressed revised Minnesota feedlot rules and manure application practices. Constraints for practice adoption included uniformity of nutrient application with solid manure, access to spreader calibration scales and record keeping forms, and adequate spreading area away from water bodies. Preferred education topics included manure application related to phosphorus, environmentally sensitive areas, and equipment. Publication was the most preferred information delivery method

MBS Ratings and the Mortgage Credit Boom

We study credit ratings on subprime and Alt-A mortgage-backed securities (MBS) deals issued between 2001 and 2007, the period leading up to the subprime crisis. The fraction of highly-rated securities in each deal is decreasing in mortgage credit risk (measured either ex-ante or ex-post), suggesting ratings contain useful information for investors. However, we also find evidence of significant time-variation in risk-adjusted credit ratings, including a progressive decline in standards around the MBS market peak between the start of 2005 and mid-2007. Conditional on initial ratings, we observe underperformance (high mortgage defaults and losses, and large rating downgrades) amongst deals with observably higher-risk mortgages based on a simple ex-ante model, and deals with a high fraction of opaque low-documentation loans. These findings hold over the entire sample period, not just for deal cohorts most affected by the crisis.