Shockwaves in converging geometries

Plate impact experiments are a powerful tool in equation of state (EOS) development, but are inherently limited by the range of impact velocities accessible to the gun. In an effort to dramatically increase the range of pressures which can be studied with available impact velocities, a new experimental technique is being developed. The possibility of using a confined converging target to focus Shockwaves and produce a large amplitude pressure pulse is examined. When the planar shock resulting from impact enters the converging target the impedance mismatch at the boundary of the confinement produces reflected Mach waves and the subsequent wave interactions produce a diffraction cycle resulting in increases in the shock strength with each cycle. Since this configuration is limited to relatively low impedance targets, a second technique is proposed in which the target is two concentric cylinders designed such that the inner cylinder will have a lower shock velocity than the much larger shock velocity in the outer cylinder. The resulting dispersion in the wave front creates converging shocks, which will interact and eventually result in a steady Mach configuration with an increase in pressure in the Mach disk. Numerical simulations indicate a significant increase in pressure for both methods and show promise for the proposed concepts

Advances in Shock Compression of Mantle Materials and Implications

Hugoniots of lower mantle mineral compositions are sensitive to the conditions where they cross phase boundaries including both polymorphic phase transitions and partial to complete melting. For SiO_2, the Hugoniot of fused silica passes from stishovite to partial melt (73 GPa, 4600 K) whereas the Hugoniot of crystal quartz passes from CaCi_2 structure to partial melt (116 GPa, 4900 K). For Mg_2SiO_4, the forsterite Hugoniot passes from the periclase +MgSiO_3 (perovskite) assemblage to melt before 152 GPa and 4300 K, whereas the wadsleyite Hugoniot transforms first to periclase +MgSiO_3 (post-perovskite) and then melts at 151 GPa and 4160 K. Shock states achieved from crystal enstatite are molten above 160 GPa. High-pressure Grüneisen parameters for molten states of MgSiO_3 and Mg_2SiO_4 increase markedly with compression, going from 0.5 to 1.6 over the 0 to 135 GPa range. This gives rise to a very large (>2000 K) isentropic rise in temperature with depth in thermal models of a primordial deep magma ocean within the Earth. These magma ocean isentropes lead to models that have crystallization initiating at mid-lower mantle depths. Such models are consistent with the suggestion that the present ultra-low velocity zones, at the base of the lowermost mantle, represent a dynamically stable, partially molten remnant of the primordial magma ocean. The new shock melting data for silicates support a model of the primordial magma ocean that is concordant with the Berkeley-Caltech iron core model [1] for the temperature at the center of the Earth

Shock temperatures of preheated MgO

Shock temperature measurements via optical pyrometry are being conducted on single-crystal MgO preheated before compression to 1905–1924 K. Planar shocks were generated by impacting hot Mo(driver plate)-MgO targets with Mo or Ta flyers launched by the Caltech two-stage light-gas gun up to 6.6 km/s. Quasi-brightness temperature was measured with 2–3% uncertainty by a 6-channel optical pyrometer with 3 ns time resolution, over 500–900 nm spectral range. A high-power, coiled irradiance standard lamp was adopted for spectral radiance calibration accurate to 5%. In our experiments, shock pressure in MgO ranged from 102 to 203 GPa and the corresponding temperature varied from 3.78 to 6.53 kK. For the same particle velocity, preheated MgO Hugoniot has about 3% lower shock velocity than the room temperature Hugoniot. Although model shock temperatures calculated for the solid phase exceeded our measurements by ~5 times the uncertainty, there was no clear evidence of MgO melting, up to the highest compression achieved

EXPERIMENTAL STUDIES OF MITIGATION MATERIALS FOR BLAST INDUCED TBI

The objective of this experimental study is to compare the effects of various materials obstructing the flow of a blast wave and the ability of the given material to reduce the damage caused by the blast. Several methods of energy transfer in blast wave flows are known or expected including: material interfaces with impedance mismatches, density changes in a given material, internal shearing, and particle fracture. The theory applied to this research is that the greatest energy transfer within the obstructing material will yield the greatest mitigation effects to the blast. Sample configurations of foam were varied to introduce material interfaces and filler materials with varying densities and impedances (liquids and powders). The samples were loaded according to a small scale blast produced by an explosive driven shock tube housing gram-range charges. The transmitted blast profiles were analyzed for variations in impulse characteristics and frequency components as compared to standard free field profiles. The results showed a rounding effect of the transmitted blast profile for all samples with the effects of the low density fillers surpassing all others tested.United States. Office of Naval Research (N00014-08-1-0261

Dietary Essential Amino Acids Affect the Reproduction of the Keystone Herbivore Daphnia pulex

Recent studies have indicated that nitrogen availability can be an important determinant of primary production in freshwater lakes and that herbivore growth can be limited by low dietary nitrogen availability. Furthermore, a lack of specific essential nitrogenous biochemicals (such as essential amino acids) might be another important constraint on the fitness of consumers. This might be of particular importance for cladoceran zooplankton, which can switch between two alternative reproductive strategies – the production of subitaneously developing and resting eggs. Here, we hypothesize that both the somatic growth and the type of reproduction of the aquatic keystone herbivore Daphnia is limited by the availability of specific essential amino acids in the diet. In laboratory experiments, we investigated this hypothesis by feeding a high quality phytoplankton organism (Cryptomonas) and a green alga of moderate nutritional quality (Chlamydomonas) to a clone of Daphnia pulex with and without the addition of essential amino acids. The somatic growth of D. pulex differed between the algae of different nutritional quality, but not dependent on the addition of dissolved amino acids. However, in reproduction experiments, where moderate crowding conditions at saturating food quantities were applied, addition of the essential amino acids arginine and histidine (but not lysine and threonine) increased the total number and the developmental stage of subitaneous eggs. While D. pulex did not produce resting eggs on Cryptomonas, relatively high numbers of resting eggs were released on Chlamydomonas. When arginine and histidine were added to the green algal diet, the production of resting eggs was effectively suppressed. This demonstrates the high, but previously overlooked importance of single essential amino acids for the reproductive strategy of the aquatic keystone herbivore Daphnia

Presence of depression and anxiety before and after coronary artery bypass graft surgery and their relationship to age

<p>Abstract</p> <p>Background</p> <p>Scientific literature on depression and anxiety in patients with coronary heart disease (CHD) consistently reports data of elevated anxiety and depression scores indicating clinically relevant quantities of these psychopathological conditions. Depression is considered to be a risk factor for the development of CHD and deteriorates the outcome after cardiac rehabilitation efforts. The aim of our study was to evaluate the presence of clinically relevant anxiety and depression in patients before and after coronary artery bypass grafting (CABG). Additionally we evaluated their relationship to age because of the increasing number of elderly patients undergoing CABG surgery.</p> <p>Methods</p> <p>One hundred and forty-two consecutive patients who underwent CABG in our hospital were asked to fill in the "Hospital Anxiety and Depression Scale – German Version (HADS)" to measure depression and anxiety scores two days before and ten days after CABG surgery. Differences between these pre- and post-surgical scores were then calculated as means for changes, and the amount of elevated scores were appraised. In order to investigate the relationship between age and anxiety and depression, respectively, Spearman correlations between age and the difference scores were calculated. In addition, ANOVA procedures with the factor "age group" and McNemar tests were calculated. Therefore the sample was divided into four equally sized age groups.</p> <p>Results</p> <p>25.8% of the patients were clinically depressed before and 17.5% after surgery; 34.0% of the patients were clinically anxious before and 24.7% after surgery. This overall change is not significant. We found a significant negative correlation between age and the difference between the two time points for anxiety (Spearman rho = -.218; p = 0.03), but not for depression (Spearman rho = -.128; p = 0.21). ANOVA and McNemar-Tests revealed that anxiety scores and the number of patients high in anxiety declined statistically meaningful only in the youngest patient group. Such a relationship could not be found for depression.</p> <p>Conclusion</p> <p>Our data show a relationship between age and anxiety. Younger patients are more anxious before CABG surgery than older ones and show a decline in symptoms while elderly patients show hardly any change.</p

Effects of an anionic surfactant (FFD-6) on the energy and information flow between a primary producer (Scenedesmus obliquus) and a consumer (Daphnia magna)

The effects of a commercially available anionic surfactant solution (FFD-6) on growth and morphology of a common green alga (Scenedesmus obliquus) and on survival and clearance rates of the water flea Daphnia magna were studied. The surfactant-solution elicited a morphological response (formation of colonies) in Scenedesmus at concentrations of 10–100 μl l−1 that were far below the No Observed Effect Concentration (NOEC) value of 1,000 μl l−1 for growth inhibition. The NOEC-value of FFD-6 for colony-induction was 3 μl l−1. Daphnia survival was strongly affected by FFD-6, yielding LC50–24h and LC50–48h of 148 and 26 μl l−1, respectively. In addition, clearance rates of Daphnia feeding on unicellular Scenedesmus were inhibited by FFD-6, yielding a 50% inhibition (EC50–1.5h) at 5.2 μl l−1 with a NOEC of 0.5 μl l−1. When Daphnia were offered FFD-6-induced food in which eight-celled colonies (43 × 29 μm) were most abundant, clearance rates (~0.14 ml ind.−1 h−1) were only 25% the rates of animals that were offered non-induced unicellular (15 × 5 μm) Scenedesmus (~0.56 ml ind.−1 h−1). As FFD-6 concentrations in the treated food used in the experiments were far below the NOEC for clearance rate inhibition, it is concluded that the feeding rate depression was caused by the altered morphology of the Scenedesmus moving them out of the feeding window of the daphnids. The surfactant evoked a response in Scenedesmus that is similar to the natural chemically induced defensive reaction against grazers and could disrupt the natural information conveyance between these plankton organisms