On the disintegrating action of meteoritic impacts

Action on planets and asteroids of crater forming meteorite

Direct Visualization of Laser-Driven Focusing Shock Waves

Cylindrically or spherically focusing shock waves have been of keen interest for the past several decades. In addition to fundamental study of materials under extreme conditions, cavitation, and sonoluminescence, focusing shock waves enable myriad applications including hypervelocity launchers, synthesis of new materials, production of high-temperature and high-density plasma fields, and a variety of medical therapies. Applications in controlled thermonuclear fusion and in the study of the conditions reached in laser fusion are also of current interest. Here we report on a method for direct real-time visualization and measurement of laser-driven shock generation, propagation, and 2D focusing in a sample. The 2D focusing of the shock front is the consequence of spatial shaping of the laser shock generation pulse into a ring pattern. A substantial increase of the pressure at the convergence of the acoustic shock front is observed experimentally and simulated numerically. Single-shot acquisitions using a streak camera reveal that at the convergence of the shock wave in liquid water the supersonic speed reaches Mach 6, corresponding to the multiple gigapascal pressure range 30 GPa

The New White Flight

White charter school enclaves—defined as charter schools located in school districts that are thirty percent or less white, but that enroll a student body that is fifty percent or greater white— are emerging across the country. The emergence of white charter school enclaves is the result of a sobering and ugly truth: when given a choice, white parents as a collective tend to choose racially segregated, predominately white schools. Empirical research supports this claim. Empirical research also demonstrates that white parents as a collective will make that choice even when presented with the option of a more racially diverse school that is of good academic quality. Despite the connection between collective white parental choice and school segregation, greater choice continues to be injected into the school assignment process. School choice assignment policies, particularly charter schools, are proliferating at a substantial rate. As a result, parental choice rather than systemic design is creating new patterns of racial segregation and inequality in public schools. Yet the Supreme Court’s school desegregation jurisprudence insulates racial segregation in schools ostensibly caused by parental choice rather than systemic design from regulation. Consequently, the new patterns of racial segregation in public schools caused by collective white parental choice largely escapes regulation by courts. This article argues that the time has come to reconsider the legal and normative viability of regulating racial segregation in public schools caused by collective white parental choice. The article makes two important contributions to the legal literature on school desegregation. First, using white charter school enclaves as an example, it documents the ways in which school choice policies are being used to allow whites as a collective to satisfy their preference for segregated predominately white schools. Second, the article sets forth both constitutional and normative arguments for regulating the private choices that result in stark racial segregation patterns in public schools

Deep Impact Mission to Tempel 1 Favours New Explosive Cosmogony of Comets

The assumption that short-period (SP) comets are fragments of massive icy envelopes of Ganymede-like bodies saturated by products of ice electrolysis that underwent global explosions provides a plausible explanation of all known manifestations of comets, including the jet character of outflows, the presence of ions in the vicinity of the nucleus, the bursts and splitting of cometary nuclei, etc., with solar radiation initiating burning of the products of electrolysis in the nucleus. As shown persuasively by numerical simulation carried out in hydrodynamic approximation, the shock wave initiated by the Deep Impact (DI) impactor in the cometary ice saturated originally by the electrolysis products 2H2 + O2 is capable of activating under certain conditions exothermal reactions (of the type O2 + H2 + organics = H2O + CO + HCN + other products of incomplete burning of organics including its light and heavy pyrolyzed compounds, soot, etc.), which will slow down shock wave damping (forced detonation) and increase many times the energy release. As a result, the measured energetics of ejections and outflows from the crater have to exceed the DI energetics. Analysis of different clusters of the DI experiment data confirms these conclusions and expectations and thus it favours the planetary origin of comets.Comment: 21 pages incluging 3 figure