Optical and TEM study of shock metamorphism from the Sedan test site

Thus far, detailed petrologic studies of shock metamorphism have been performed on samples recovered from laboratory experiments and on a few natural impactites. The loading history of these samples is quite different: In particular, laboratory experiments spend only a short time (less than 1 microsec) at peak pressure, whereas natural impactites may have stress pulses from 0.1 - 1 ms. On the other hand, laboratory experiments have known stress histories; natural impactites do not. Natural samples are also subjected to thousands or millions of years of postshock annealing and/or weathering. A useful intermediate case is that of nuclear detonation. Stress pulses for these events can reach 0.1 ms or higher, and samples are obtained in pristine condition. All three types of loading produce stresses of hundreds of kilobars. Samples studied were taken from the Sedan nulcear test site, and consist of a coarse-grained granodiorite containing quartz, K-feldspar, cordierite, and hornblende. Samples were studied optically in this section, then were thinned with an ion mill and studied by transmission electron microscopy (TEM). Optically, quartz and K-feldspar displayed numerous sets of planar deformation features (PDF's) identical to the nondecorated PDF's seen in laboratory samples and many natural impactites. TEM study showed that the PDF's in quartz and feldspar corresponded to densely packed wide transformation lamellae identical to those described in laboratory studies. The transformation lamellae in both minerals were amorphous, with no sign of high-pressure phases. In the case of K-feldspar only, narrow sublamellae extended outward from some wide lamellae. Quartz, which was more abundant and studied more extensively, contained no shock-induced dislocations. Some planar features were also seen in cordierite, but could not be identified due to rapid beam damage. No shock defects were seen in hornblende in TEM. The shock-induced defects present at the Sedan site are very similar to those seen in shock recovery experiments, and also to those present at certain natural events (e.g., Meteor Crater). This suggests that shock deformation in quartz is not strongly dependent on shock pulse duration, and that laboratory recovery experiments are useful simulations of natural impact events

Simulated meteorite impacts and volcanic explosions: Ejecta analyses and planetary implications

Past cratering studies have focused primarily on crater morphology. However, important questions remain about the nature of crater deposits. Phenomena that need to be studied include the distribution of shock effects in crater deposits and crater walls; the origin of mono- and polymict breccia; differences between local and distal ejecta; deformation induced by explosive volcanism; and the production of unshocked, high-speed ejecta that could form the lunar and martian meteorites found on the Earth. To study these phenomena, one must characterize ejecta and crater wall materials from impacts produced under controlled conditions. New efforts at LLNL simulate impacts and volcanism and study resultant deformation. All experiments use the two-stage light-gas gun facility at LLNL to accelerate projectiles to velocities of 0.2 to 4.3 km/s, including shock pressures of 0.9 to 50 GPa. We use granite targets and novel experimental geometries to unravel cratering processes in crystalline rocks. We have thus far conducted three types of simulations: soft recovery of ejecta, 'frozen crater' experiments, and an 'artificial volcano. Our ejecta recovery experiments produced a useful separation of impactites. Material originally below the projectile remained trapped there, embedded in the soft metal of the flyer plate. In contrast, material directly adjacent to the projectile was jetted away from the impact, producing an ejecta cone that was trapped in the foam recovery fixture. We find that a significant component of crater ejecta shows no signs of strong shock; this material comes from the near-surface 'interference zone' surrounding the impact site. This phenomenon explains the existence of unshocked meteorites on the Earth of lunar and martian origin. Impact of a large bolide on neighboring planets will produce high-speed, weakly shocked ejecta, which may be trapped by the Earth's gravitational field. 'Frozen crater' experiments show that the interference zone is highly localized; indeed, disaggregation does not extend beyond approx. 1.5 crater radii. A cone-shaped region extending downward from the impact site is completely disaggregated, including powdered rock that escaped into the projectile tube. Petrographic analysis of crater ejecta and wall material will be presented. Finally, study of ejecta from 0.9- and 1.3-GPa simulations of volcanic explosions reveal a complete lack of shock metamorphism. The ejecta shows no evidence of PDF's, amorphization, high-pressure phases, or mosaicism. Instead, all deformation was brittle, with fractures irregular (not planar) and most intergranular. The extent of fracturing was remarkable, with the entire sample reduced to fragments of gravel size and smaller

Oceanographic influences on the sea ice cover in the Sea of Okhotsk

Sea ice conditions in the Sea of Okhotsk, as determined by satellite images from the electrically scanning microwave radiometer on board Nimbus 5, were analyzed in conjunction with the known oceanography. In particular, the sea ice coverage was compared with the bottom bathymetry and the surface currents, water temperatures, and salinity. It is found that ice forms first in cold, shallow, low salinity waters. Once formed, the ice seems to drift in a direction approximating the Okhotsk-Kuril current system. Two basic patterns of ice edge positioning which persist for significant periods were identified as a rectangular structure and a wedge structure. Each of these is strongly correlated with the bathymetry of the region and with the known current system, suggesting that convective depth and ocean currents play an important role in determining ice patterns

Observation of a temperature dependent electrical resistance minimum above the magnetic ordering temperature in Gd2_2PdSi3_3

Results on electrical resistivity, magnetoresistance, magnetic Results on electrical resistivity, magnetoresistance, magnetic susceptibility, heat capacity and Gd Mossbauer measurements on a Gd-based intermetallic compound, Gd$_{2}$PdSi$_{3}$ are reported. A finding of interest is that the resistivity unexpectedly shows a well-defined minimum at about 45 K, well above the long range magnetic ordering temperature (21 K), a feature which gets suppressed by the application of a magnetic field. This observation in a Gd alloy presents an interesting scenario. On the basis of our results, we propose electron localization induced by s-f (or d-f) exchange interaction prior to long range magnetic order as a mechanism for the electrical resistance minimum.Comment: 4 pages, 4 figure

Different types of soluble fermentable dietary fibre decrease food intake, body weight gain and adiposity in young adult male rats

We thank Donna Wallace and the Rowett Animal House staff for the daily care of experimental rats, body weight and food intake measurements and MRI scanning, Vivien Buchan and Donna Henderson of the Rowett Analytical Department for proximate analyses and SCFA GC, and Andrew Chappell for conducting the beta-glucan analysis. This research was funded by the Scottish Government’s Rural and Environment Science and Analytical Services Division.Peer reviewedPublisher PD

Across-Column Cracks and Axial Splits in S2 Saline Ice under Compression

Experiments on plate-like specimens have established that across-column cracks from within S2 (columnar) salt-water ice when compressed uniaxially along a direction inclined to the long axis of the grains. Wing cracks initiate from the across-column cracks and lengthen into axial splits when the ice is rapidly deformed; correspondingly; the macroscopic behavior changes from ductile to brittle. The across-column cracking is attributed to grain-boundary sliding, and the splitting to the suppression of crack-tip creep

Diagnosis and Interim Treatment Outcomes from the First Cohort of Multidrug-Resistant Tuberculosis Patients in Tanzania.

Kibong'oto National Tuberculosis Hospital (KNTH), Kilimanjaro, Tanzania. Characterize the diagnostic process and interim treatment outcomes from patients treated for multidrug-resistant tuberculosis (MDR-TB) in Tanzania. A retrospective cohort study was performed among all patients treated at KNTH for pulmonary MDR-TB between November 2009 and September 2011. Sixty-one culture-positive MDR-TB patients initiated therapy, 60 (98%) with a prior history of TB treatment. Forty-one (67%) were male and 9 (14%) were HIV infected with a mean CD4 count of 424 (±106) cells/µl. The median time from specimen collection to MDR-TB diagnosis and from diagnosis to initiation of MDR-TB treatment was 138 days (IQR 101-159) and 131 days (IQR 32-233), respectively. Following treatment initiation four (7%) patients died (all HIV negative), 3 (5%) defaulted, and the remaining 54 (89%) completed the intensive phase. Most adverse drug reactions were mild to moderate and did not require discontinuation of treatment. Median time to culture conversion was 2 months (IQR 1-3) and did not vary by HIV status. In 28 isolates available for additional second-line drug susceptibility testing, fluoroquinolone, aminoglycoside and para-aminosalicylic acid resistance was rare yet ethionamide resistance was present in 9 (32%). The majority of MDR-TB patients from this cohort had survived a prolonged referral process, had multiple episodes of prior TB treatment, but did not have advanced AIDS and converted to culture negative early while completing an intensive inpatient regimen without serious adverse event. Further study is required to determine the clinical impact of second-line drug susceptibility testing and the feasibility of alternatives to prolonged hospitalization

Quantitative Sequencing for the Determination of Kdr-type Resistance Allele (V419L,L925I, I936F) Frequencies in Common Bed Bug, Cimex lectularius L., (Hemiptera: Cimicidae) Populations Collected from Israel

Human bed bug infestations have dramatically increased worldwide since the mid-1990s. A similar phenomenon was also observed in Israel since 2005, when infestations were reported from all over the country. Two single nucleotide polymorphisms (V419L and L925I) in the bed bug voltage sensitive sodium channel confer kdr-type resistance to pyrethroids. Using quantitative sequencing (QS), the resistance allele frequencies of Israeli bed bug populations from across the country were determined. Genomic DNA was extracted from samples of 12 populations of bed bugs collected from Israel and DNA fragments containing the V419L or L925I and I936F mutations sites were PCR amplified. The PCR products were analyzed by QS and the nucleotide signal ratios calculated and used to predict the resistance allele frequencies of the unknown populations. Results of the genetic analysis show that resistant nucleotide signals are highly correlated to resistance allele frequencies for both mutations. Ten of the 12 tested populations had 100% of the L925I mutation and 0% of the V419L mutation. One population was heterogeneous for the L925I mutation and had 0% of the V419L mutation and another population was heterozygous for the V419L mutation and had 100% of the L925I mutation. I936F occurred only at low levels. These results indicate that bed bugs in Israel are genetically resistant to pyrethroids. Thus, pyrethroids should only be used for bed bug management with caution using effective application and careful monitoring procedures. Additionally, new and novel-acting insecticides and non-chemical means of controlling bed bugs should be explored