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Ices of CO2/H2O Mixtures. Reflection-Absorption IR Spectroscopy and Theoretical Calculations
No full textIce mixtures of CO2 and H2O are studied using Fourier transform reflection-absorption infrared (RAIR)
spectroscopy. Mixtures are prepared by sequential deposition or co-deposition of the two components from
the gas phase onto an Al plate kept at 87 K inside a low-pressure chamber. Two CO2 structures are found in
most experiments: a crystalline form similar to pure CO2, which evaporates when warming at 105 K, and a
noncrystalline species which remains embedded in amorphous water ice after warming. Significant spectral
variations are found depending on the deposition method and the thickness of the solid. Features characteristic
of the RAIR technique appear in the spectral regions of the normal modes of the bending and asymmetric
stretching CO2 vibrations. Simulations using Fresnel theory and Mie scattering are carried out with acceptable
agreement with the experimental spectra of solids of variable thickness, from 1 ím to the limit of
nanoparticles. Theoretical calculations of a pure CO2 crystal are performed. The relaxed geometry of the
solid and its vibrational spectrum are determined and compared to the experimental results
Size sorting in marine muds: Processes, pitfalls and prospects for palaeoflow-speed proxies
No full textThe basis for, and use of, fine grain size parameters for inference of paleoflow speeds is reviewed here. The basis resides in data on deposited sediment taken in conjunction with flow speed measurements in the field, experimental data on suspended sediment transport and deposition, and theoretical treatments of the generation of size distributions of deposits from suspension controlled by particle settling velocity and flow speed. In the deep sea, sorting events occur under resuspension/deposition events in benthic storms. At flow speeds below 10–15 cm s−1, size in the noncohesive “sortable silt” (10–63 μm) range is controlled by selective deposition, whereas above that range, removal of finer material by winnowing also plays a role. The best particle size instruments to measure a flow speed–related grain size employ the settling velocity method, while laser diffraction sizers can yield misleading results because of particle shape effects. Potential problems, including source effects, downslope supply on continental margins, spatial variability of flow over bedforms, and influence of ice‐rafted detritus, are examined. A number of studies using the sortable silt flow speed proxy are reviewed, and inverse modeling of grain size distributions is examined. Outstanding problems are that corroboration is sparse because almost no studies have yet used the full range of proxies for flow rate and water mass identification and that the sortable silt mean size is not yet properly calibrated in terms of flow speed
Predation Upon Mytilus Galloprovincialis (mollusca: Bivalvia: Mytilidae) by Juvenile Carcinus Maenas (crustacea: Decapoda) Using Mandibular Chipping
No full textField observations of small (<20 mm) individuals of Mytulus galloprovincialis at Littlehampton (West Sussex) on the south-eastern coast of England showed that many collected as recently dead shells had a distinctive pattern of damage around the posterior valve margins. Laboratory experiments confirmed that small Carcinus maenas (<22 mm carapace width) were capable of inflicting a similar style of damage. Small C. maenas fed successfully on a range of mussel sizes (5–20 mm shell length), positively correlated with carapace width. All used the same technique to access the bivalve prey, that is, by marginal mandibular chipping in order to achieve sufficient damage to allow insertion of a chelal dactyl between the valves. Mandibular chipping has previously been reported upon from non-chelate decapods and juvenile lobsters. The chelae of juvenile C. maenas are small and have a lower mechanical advantage than has been reported upon for adult conspecifics which, in any case, are not highly adapted for durophagy. We suggest that because of the poor mechanical performance and small gape of the chelae juvenile C. maenas behave as though they were achelate. As well as broadening our understanding of the repertoire of known feeding behaviours of C. maenas, our study may also provide an insight into the evolution of durophagy within the Decapoda
Combining InSAR and seismology to study the 2003 Siberian Altai earthquakes - dextral strike-slip and anticlockwise rotations in the northern India-Eurasia collision zone
No full textThe 2003 September 27 Mw 7.2 Siberian Altai earthquake was the largest to have struck the Altai mountains in more than seventy years, and was closely followed by two Mw 6.2 and 6.6 aftershocks. We use radar interferometry, seismic bodywaves and field investigations to examine the source processes of these earthquakes. The main shock of the initial earthquake ruptured a subvertical, ∼NW–SE striking dextral strike-slip fault. The fault was previously unrecognised; although it approximately follows the southwestern boundaries of two intermontane depressions within the interior northwestern Altai, it has very little topographic expression. A ∼NE-dipping Mw∼ 6.7 reverse subevent, possibly triggered by shear waves from the main shock, occurred ten seconds afterwards strike to the southeast. The later Mw 6.2 and 6.6 aftershocks were dextral strike-slip events which contributed further to deformation in the northwest part of the fault zone. However, interferometric and bodywave models disagree significantly on the source parameters of the earthquakes, in particular the total moment released and the dip of the fault planes. Trade-offs of fault dip with moment and centroid depth in the bodywave modelling can account for some, but not all, of these discrepancies. The interferometric data is unevenly distributed, containing many more data points on one side of the fault zone than the other; however, on the basis of calculations with synthetic data we rule this out as a reason for the discrepancies in fault parameters. The lower moment predicted by interferometry could be explained by the lack of coherent data close to the faulting, if slip was concentrated at very shallow depths. The dip yielded by the interferometric modelling might be influenced by lateral changes in elastic properties, although these would also affect the bodywave solutions. The earthquake sequence occurred close to recent palaeomagnetic measurements of late Cenozoic anticlockwise rotations. These suggest that the right-lateral strike-slip faulting that ruptured in the 2003 earthquakes accommodates regional ∼NNE–SSW shortening by rotating anticlockwise over time. The reverse subevent is a rare case of pure shortening perpendicular to the trend of the Altai range
The heartbeat of the oligocene climate system
No full textA 13-million-year continuous record of Oligocene climate from the equatorial Pacific reveals a
pronounced “heartbeat” in the global carbon cycle and periodicity of glaciations. This heartbeat
consists of 405,000-, 127,000-, and 96,000-year eccentricity cycles and 1.2-million-year obliquity
cycles in periodically recurring glacial and carbon cycle events. That climate system response to
intricate orbital variations suggests a fundamental interaction of the carbon cycle, solar forcing,
and glacial events. Box modeling shows that the interaction of the carbon cycle and solar forcing
modulates deep ocean acidity as well as the production and burial of global biomass. The
pronounced 405,000-year eccentricity cycle is amplified by the long residence time of carbon in
the oceans
Neutron diffraction study of the orientational order in filter cakes made of kaolinite under laminar and turbulent cross-flow
No full textThe orientational order of plate-like particles in filter cakes prepared under cross-flow conditions is determined using a neutron diffraction approach and the fluid flow through the filter cakes during their formation followed using volumetric studies. Data has been collected using an unusual cross-flow geometry, fixed volume filtration cell covering a wider range of flow fields than previously reported which allows the study of the transition from laminar to turbulent flow conditions. Interestingly, these results indicate that there is minimal additional orientational alignment when the cross-flow is laminar, compared to the static case, but that there is more extensive alignment when the imposed flow is turbulent. This behaviour is discussed in terms of several mechanisms including suspension and redeposition of particles in the imposed flow fields and the orienting effects of turbulent eddies adjacent to a boundary. In addition, we provide evidence that particle resuspension is not the dominant mechanism. During cross-flow filtration studies two dominant regimes have been identified. A ‘quasi-static’ regime where the filtrate mass goes as t1/2 under laminar conditions; and a flow rate dependent “dynamic-regime” where filtrate mass goes as tn, where n rises with increasing imposed shear rate until n is unity and the filtrate mass goes linearly with time, under turbulence
Annealing in a Natural Laboratory: an EBSD and Cl Study of Calcite and Quartz Growth from Volumes of Rock Heated by a Nearby Melt Intrusion
No full textAnnealing is an important mechanism of microstructural modification both in rocks and metals. In order to relate directly changes in crystallographic orientation to migrating boundaries the researcher has the option to investigate either samples where the grain boundary motion can be directly tracked or a series of samples exhibiting successively higher degrees of annealing. Here we present results from rock samples collected from two well characterised contact aureoles (a volume of rock heated by the intrusion of a melt in its vicinity): One quartz sample in which patterns revealed by Cathodoluminescence (CL) indicate the movement of grain boundaries and a series of calcite samples of known temperature history. Electron backscatter diffraction (EBSD) analysis is used to link the movement of grain, twin boundaries and substructures with the crystallographic orientation / misorientation of a respective boundary. Results from the quartz bearing rock show: (a) propagation of substructures and twin boundaries in swept areas both parallel and at an angle to the growth direction, (b) development of slightly different crystallographic orientations and new twin boundaries at both the growth interfaces and within the swept area, and (c) a gradual change in crystallographic orientation in the direction of growth. Observations are compatible with a growth mechanism where single atoms are attached and detached both at random and at preferential sites i.e. crystallographically controlled sites or kinks in boundary ledges. Strain fields caused by defects and/or trace element incorporation may facilitate nucleation sites for new crystallographic orientations at distinct growth interfaces but also at continuously migrating boundaries. Calcite samples show with increasing duration and temperature of annealing: (a) systematic decrease of the relative frequency of low angle grain boundaries (gbs), (b) decrease in lattice distortion within grains, (c) development of distinct subgrains with little internal lattice distortion, (d) change in lobateness of gbs and frequency of facet parallel gbs and (e) change in position of second phase particles. These observations point to an increasing influence of grain boundary anisotropy with increasing annealing temperature, while at the same time the influence of second phase particles and subtle driving-force variations decrease. This study illustrates the usefulness of using samples from natural laboratories and combining different analysis techniques in microprocess analysis
Ossification sequence in the mole Talpa occidentalis (Eulipotyphla, Talpidae) and comparison with other mammals
No full textThe skeleton of mammals has been the subject of detailed anatomical and functional studies for centuries, and investigations of its ontogeny enjoy a long tradition (Starck 1995). However, knowledge of the timing of ossification is restricted to few species. Most available data of this kind pertain to species used in the lab or domesticated animals (e.g., Curgy 1965). Here we report on the ossification timing in the Iberian mole Talpa occidentalis (Fig. 1), based on the study of a developmental series obtained in studies of reproductive biology and growth in this species (e.g., Barrionuevo et al., 2004 F.J. Barrionuevo, F. Zurita, M. Burgos and R. Jiménez, Developmental stages and growth rate of the mole Talpa occidentalis (Insectivora, Mammalia), J. Mammal. 85 (2004), pp. 120–125. Full Text via CrossRef | View Record in Scopus | Cited By in Scopus (5)Barrionuevo et al. 2004). This study complements those on the ossification patterns in the European mole Talpa europaea (Prochel 2006; Goswami and Prochel 2007) and in other eulipotyphlans (Prochel et al. 2004)
Electronic stopping power in LiF from first principles
No full textUsing time-dependent density-functional theory we calculate from first principles the rate of energy
transfer from a moving proton or antiproton to the electrons of an insulating material, LiF. The behavior of
the electronic stopping power versus projectile velocity displays an effective threshold velocity of
0:2 a:u: for the proton, consistent with recent experimental observations, and also for the antiproton.
The calculated proton/antiproton stopping-power ratio is 2:4 at velocities slightly above the threshold
(v 0:4 a:u:), as compared to the experimental value of 2.1. The projectile energy loss mechanism is
observed to be extremely local