Dynamic compression of enstatite

New shock wave data for Bamle enstatite (Mg_(0.86),Fe_(0.14))SiO_3 in the range from 60–480 kb indicate a Hugoniot elastic limit of 67±10 kb and a possible phase-transition-produced shock front of 135±10 kb amplitude. Above the latter shock pressure, states in a mixed-phase regime are achieved up to ∼350 kb, above which the Hugoniot states are believed to represent the equation of state of a shock-induced phase, probably having the majorite (garnet) structure with a zero-pressure density of ∼3.67 g/cm^3. The present data, representing the high-pressure phase, agree closely with those of R. G. McQueen, S. P. Marsh, and J. N. Fritz above 610 kb for a Stillwater bronzitite of similar mineralogy. It is suggested that the formation of majorite from enstatite in naturally impacted rocks and meteorites requires dynamic pressures of at least ∼135 kb

Optical absorption spectra of ruby and periclase at high shock pressures

A spectrographic system is described that is capable of measuring optical absorption spectra in solids to shock pressures of several hundred kilobars. The system utilized light from a ‘point’ source at about 60,000°K. Spectra have a resolution of about 40 A and cover the visible range. With a streak camera, time resolution of about 75 nsec can be obtained. The spectrum of MgO is observed to remain featureless at 450 kb and upon unloading from this pressure. The color centers observed in shock-recovered material must result from either higher pressures or other processes. The optical absorption spectra of ruby under shock compressions of almost 15% have been measured in the range 375–600 nm. Below the elastic limit the large anisotropic strains are evident from the splitting of the ^4A_2 → ^4T_2 (F) absorption band by 3730 cm^(−1). Above the elastic limit this splitting is not resolved (but must be less than 800 cm^(−1)), indicating considerable loss of shear strength in such cases. Above the Hugoniot elastic limit up to pressures of 530 kb (15% volume compression) the measured value of the crystal field parameter agrees, within experimental error, with the value calculated from a point charge model (Dq α r^(−5)) if the local compressibility is equal to the bulk compressibility. This result agrees with Stephens and Prickamer's absorption data up to 150 kb and suggests that the point charge model is useful in predicting crystal field effects in mantle minerals, especially those having similar oxygen anion packings such as corundum

Identification of Ice VI on the Hugoniot of Ice I_h

Ice VI has been produced by shock compression of ice I_h to about 2 GPa. This is the second high-pressure polymorph of water observed in shock loading. These experiments point out the ease with which high-pressure phases can form when ice I_h is impacted. The new shock data, combined with previous static measurements, provide preliminary equation of state parameters for ice VI

Blade loss transient dynamics analysis, volume 2. Task 2: Theoretical and analytical development. Task 3: Experimental verification

The component element method was used to develop a transient dynamic analysis computer program which is essentially based on modal synthesis combined with a central, finite difference, numerical integration scheme. The methodology leads to a modular or building-block technique that is amenable to computer programming. To verify the analytical method, turbine engine transient response analysis (TETRA), was applied to two blade-out test vehicles that had been previously instrumented and tested. Comparison of the time dependent test data with those predicted by TETRA led to recommendations for refinement or extension of the analytical method to improve its accuracy and overcome its shortcomings. The development of working equations, their discretization, numerical solution scheme, the modular concept of engine modelling, the program logical structure and some illustrated results are discussed. The blade-loss test vehicles (rig full engine), the type of measured data, and the engine structural model are described

Experimental studies of QCD using flavour tagged jets with DELPHI

Identified $b\overline{b}g$ and $q\overline{q}\gamma$ events from DELPHI are used to measure the ratio of the mean charged particle multiplicity distribution between gluon and quark jets. The dependence of this ratio with the jet energy is established using about three million Z$^0$ decays. Results from all other detectors are discussed and compared. A nice agreement is found among all them. The ratio between the normalized total three-jet cross sections of $b\overline{b}g$ and $q\overline{q}g, q \equiv u,d,s$ events is also determined. The preliminary value obtained indicates that $b$ quarks are experimentaly seen to radiate less than light quarks due to their higher mass. The suggested experimental error is $\sim$300 MeV for the $b$ mass determination at the M$_Z$ scale.Comment: Latex, 5 pages, 3 figures,to appear in the Proceedings of the High Energy Physics International Euroconference on Quantum Chromodynamics (QCD '96), Montpellier, France, 4-12th July 1996. Ed. S. Narison, Nucl Phys. B (Proc. Suppl.

Characterization of Secondary Organic Aerosol (SOA) formed by the Reaction of β-caryophyllene, Soot and Ozone: Climate Impact

Diesel soot (black carbon, BC) is an important light absorbing aerosol component in atmosphere that can cause tropospheric heating. Laboratory studies have found it to be unreactive to ozone at ambient temperature. The low uptake coefficient i.e., γ 300 K = 2× 10-7 , of the soot-O3 reaction indicates a low probability of irreversible O3 loss from gas phase to surface-adsorbed product (Particle phase). This shows clearly that at low temperature soot is not reactive with atmospheric oxidants. In contrast, sesquiterpenes (SQT) such as β-caryophyllene (C15H24), which are produced primarily by plants, are extremely reactive with ozone. For example, the residence time of β- caryophyllene in the atmosphere is only 2 min in the presence of 60 ppb ozone. Thus, ozonolysis reaction of β-caryophyllene is expected to be a significant source of biogenic secondary organic aerosols. These oxidized products may condense onto soot particles, and a question arises as to how they will partition between the soot surface, vapor phase, and aqueous aerosol phases. Liquid chromatography- mass spectrometry (LC/MS), Fourier transform infrared (FTIR) and UVVis spectroscopies are being used to study the β- caryophyllene-dark ozonolysis reaction at low ozone levels (40-60 ppb). Products identified include low molecular weight highly volatile and water soluble products such as formaldehyde, acetaldehyde, acetone, and acetic acid. Also identified are high molecular weight components (~350 Dalton) with lower water solubility and vapor pressures. The SOA coatings of these SQTs on soot are being evaluated to determine their hygroscopicity. As these compounds absorb in the IR and UV-Vis they can add to radiative forcing by submicron aerosols and need to be better understood for climate modeling

Phylogeny, biogeography and diversification patterns of side-necked turtles (Testudines: Pleurodira)

Pleurodires or side-necked turtles are today restricted to freshwater environments of South America, Africa– Madagascar and Australia, but in the past they were distributed much more broadly, being found also on Eurasia, India and North America, and marine environments. Two hypotheses were proposed to explain this distribution; in the first, vicariance would have shaped the current geographical distribution and, in the second, extinctions constrained a previously widespread distribution. Here, we aim to reconstruct pleurodiran biogeographic history and diversification patterns based on a new phylogenetic hypothesis recovered from the analysis of the largest morphological dataset yet compiled for the lineage, testing which biogeographical process prevailed during its evolutionary history. The resulting topology generally agrees with previous hypotheses of the group and shows that most diversification shifts were related to the exploration of new niches, e.g. littoral or marine radiations. In addition, as other turtles, pleurodires do not seem to have been much affected by either the Cretaceous– Palaeogene or the Eocene–Oligocene mass extinctions. The biogeographic analyses highlight the predominance of both anagenetic and cladogenetic dispersal events and support the importance of transoceanic dispersals as a more common driver of area changes than previously thought, agreeing with previous studies with other non-turtle lineages.Fil: Ferreira, Gabriel S.. Universidade de Sao Paulo; Brasil. Senckenberg Centre For Human Evolution And Palaeoenvironment; Alemania. Universität Tübingen; AlemaniaFil: Bronzati Filho, Mario. Bayerische Staatssammlung für Paläontologie und Geologie; AlemaniaFil: Langer, Max C.. Universidade de Sao Paulo; BrasilFil: Sterli, Juliana. Museo Paleontológico Egidio Feruglio; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Divergences in the Effective Action for Acausal Spacetimes

The 1--loop effective Lagrangian for a massive scalar field on an arbitrary causality violating spacetime is calculated using the methods of Euclidean quantum field theory in curved spacetime. Fields of spin 1/2, spin 1 and twisted field configurations are also considered. In general, we find that the Lagrangian diverges to minus infinity at each of the nth polarised hypersurfaces of the spacetime with a structure governed by a DeWitt-Schwinger type expansion.Comment: 17 pages, Late