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High-pressure synthesis and electrochemical behavior of layered (1-a)LiNi1-yAlyO2 center dot aLi[Li1/3Ni2/3]O-2 oxides.
No full textLayered ð1 aÞLiNi1yAlyO2 aLi½Li1=3Ni2=3O2 oxides, 0pao0:4, have been prepared by solid state reaction between NiO,
Al2O3 and Li2O2 under high pressure. The structural characterization of the layered oxides was performed using powder XRD, IR
spectroscopy and EPR spectroscopy at 9.23 and 115 GHz. It has been found that the high-pressure favors Al substitution for Ni in
the NiO2-layers of layered LiNiO2. A random Al/Ni distribution in the layer was found. The incorporation of extra Li in the
Ni1yAlyO2-layer starts at a precursor composition Li=ðNi þ AlÞ41:2. While pure NiO2-layers are able to incorporate under highpressure
up to 1/3Li, the appearance of Al in the NiO2-layers hinders Liþ dissolution ðLioð1 yÞ=3Þ. In addition, with increasing Al
content there is a strong cationic mixing between the layers. High-frequency EPR of Ni3þ indicates that the structural interaction of
LiAlyNi1yO2 with Li½Li1=3Ni2=3O2 proceeds via the formation of domains comprising different amount of Ni3þ ions. The use of
Li1:08Al0:09Ni0:83O2 as a cathode material in a lithium ion cells displays a first irreversible Li extraction at 4.8 V, after which a
reversible lithium insertion/extraction between 3.0 and 4.5V is observed on further cycling
Negligable temperature dependence of calcium isotope fractionation in twelve species of planktonic foraminifera.
No full textThe influence of temperature on calcium (Ca) isotope fractionation during biomineralization was investigated through the
paired analyses of d44/42Ca (via MC-ICP-MS) and d18O on the calcite tests of 12 species of planktonic foraminifera from coretop
sediments. Samples were collected from a suite of box-cores from sites between 608N and 308S in the North Atlantic and
West Indian oceans, spanning a range in sea surface temperature of 9–27 8C. The d44/42CaSRM915a of the samples ranged from
+0.21x to +0.81x over a range in the d18OVPDB of the foraminiferal calcite of between 2.3x and +2.1x. The bulk of the
species investigated produced calcite with an average calcite–seawater Ca enrichment factor (e) of 0.65F0.08x (n=45). The
globorotaliid species and a single Globigerina bulloides sample were confined to the upper 0.4x of the observed range in
d44/42Ca values, with the globorotaliids displaying a lesser degree of fractionation of 0.56F0.23x (n=15), possibly as a result
of physiological or metabolic processes such as the production of calcite crusts at depth, leading to the depletion of internal
stores of Ca. No significant correlation between temperature and Ca enrichment factor was observed in any of the 12 species of
foraminifera investigated. The influence of temperature on e was close to zero for the combined non-globorotaliid species,
0.07F0.10 K (e versus 1000/K; 0.0008F0.0012x 8C1). The results suggest that the theoretically expected relationship
between the Ca enrichment factor and temperature can be obscured by, as yet, unquantified metabolic and physiological
processes in nature. These processes are particularly relevant to the globorotaliid species and G. bulloides in this core-top study.
Consequently, their effects must be better understood before laboratory-determined temperature calibrations can be applied to
downcore material with confidence. Provided that the effects of metabolic and physiological processes on e remain constant
through time, Orbulina universa, Globigerinoides sacculifer, Neogloboquadrina pachyderma and Globigerinella aequilateralis
are suitable for the investigation of temporal changes in the calcium isotopic composition of seawater
Modern and Holocene hydrographic characteristics of the shallow Kara Sea shelf (Siberia) as reflected by stable isotopes of bivalves and benthic foraminifera.
No full textRiver discharge of Ob and Yenisei to the Kara Sea is highly variable on seasonal and interannual time scales.
River water dominates the shallow bottom water near the river mouths, making it warmer and less saline
but seasonally and interannually more changeable than bottom water on the deeper shelf. This hydrographic
pattern shows up in measurements and modelling, and in stable isotope records (d18O, d13C) along the
growth axis of bivalve shells and in multiple analyses of single benthic foraminiferal shells. Average isotope
ratios increase, but sample-internal variability decreases with water depth and distance from river mouths.
However, isotope records of bivalves and foraminifera of a sediment core from a former submarine channel of
Yenisei River reveal a different pattern. The retreat of the river mouth from this site due to early Holocene sea
level rise led to increasing average isotope values up core, but not to the expected decrease of the in-sample
isotope variability. Southward advection of cold saline water along the palaeo-river channel probably obscured
the hydrographic variability during the early Holocene. Later, when sediment filled the channel, the hydrographic
variability at the core location remained low, because the shallowing proceeded synchronously with the
retreat of the river mouth
Precipitate formation in a porous rock through evaporation of saline water.
No full textWe examine the motion of a high-pressure aqueous solution, through a lowpermeability
fracture, towards a low-pressure well. As the liquid decompresses in the
fractures it expands, and for sufficiently high initial temperature the liquid reaches
the boiling point. A vaporization front then develops, so that vapour issues from
the well. As the fluid evaporates near the well, the salt concentration of the residual
fluid increases. If the salt concentration increases beyond the saturation limit, then
the evaporation leads to precipitation of salt in the fracture. We find a new family
of self-similar solutions to describe the boiling and precipitation in a single idealized
fracture, which at long times remains approximately isothermal owing to the crossfracture
heat transfer. The solutions describe the mass of salt that precipitates as
a function of the initial salt concentration, the reservoir temperature and pressure,
and the well pressure. In fact, this family of self-similar solutions is multi-valued:
we identify a liquid-advection-dominated regime, in which the boiling front advances
slowly and the fracture porosity decreases significantly, and a boiling-dominated
regime, in which the boiling front advances more rapidly, and less precipitate forms
at each point in the fracture. As the pressure difference between the well and the far
field reservoir increases, these solutions converge, and eventually coincide. Beyond
this critical point, there is no similarity solution, since the advective flux of salt from
the far-field would produce more precipitate than can be taken up in the fracture
adjacent to the boiling front. Instead, the rock will become fully sealed through
precipitation, thereby suppressing flow into the well. We extend the model to show
that an analogous result also occurs within an extensive porous layer. However in that
case, the system is not isothermal; instead, the heat flux is supplied in the direction
of flow, while the cross-flow heat flux is small. We discuss the relevance of the work
to the natural venting of steam in high-temperature geothermal systems
Atomic scale modelling of the cores of dislocations in complex materials part 1: methodology.
No full textDislocations influence many properties of crystalline solids, including plastic deformation, growth and dissolution, diffusion and the formation of polytypes. Some of these processes can be described using continuum methods but this approach fails when a description of the structure of the core is required. To progress in these types of problems, an atomic scale model is essential. So far, atomic scale modelling of the cores of dislocations has been limited to systems with rather simple crystal structures. In this article, we describe modifications to current methodology, which have been used for strongly ionic materials with simple structures. These modifications permit the study of dislocation cores in more structurally complex materials
Crustal accretion at the Reykjanes Ridge, 61°–62°N
No full textWe report results of a seismic, gravity, and magnetic survey of the Reykjanes Ridge spreading center at 61°–62°N, about 600 km from the center of the Iceland mantle plume. Anomalously shallow water on the ridge crest enabled us to record seismic refractions on a 2.4 km hydrophone streamer. The velocity within layer 2A is 2.4 ± 0.3 km s−1, and its mean thickness is 400 ± 100 m. The velocity at the base of layer 2A is 3.3 ± 0.3 km s−1 on the ridge axis, increasing with crustal age to ∼4.0 km s−1 at 1.5 Ma and ∼4.5 km s−1 at 5 Ma. Assuming that seismic layer 2A on the ridge axis is also the extrusive layer, i.e., the magnetic source layer, we have successfully modeled the variations in amplitude of the magnetic field. The best magnetic model includes enhanced magnetization within layer 2A at the sites of recent volcanic activity as independently recognized in side-scan sonar data. We also present a full crustal seismic model, based on wide-angle seismic recordings on digital ocean bottom hydrophones and disposable sonobuoys. The seismic model is complemented by gravity modeling, which further suggests that the ridge crest is in isostatic equilibrium. The zero age crust is 10.0 km thick, while crust of age 5 Ma is 7.8 km thick. These crustal thicknesses are greater than those of normal oceanic crust, which we attribute to the presence of anomalously hot asthenospheric mantle beneath the spreading center. We suggest that the variation in thickness between 0 Ma and 5 Ma crust is caused by temporal variation in the plume-fed asthenospheric temperature beneath the Reykjanes Ridge
Preferential adsorption of solid monolayers of hydrocarbons over fluorocarbons at the solid/liquid interface
No full textA novel combination of sensitive calorimetry, neutron diffraction and NMR have been used to investigate the preferential adsorption and phase behaviour of the solid monolayers absorbed onto graphite from binary n-alkane/n-perfluoroalkane mixtures. The results indicate that the alkane preferentially adsorbs for essentially all mixture compositions to the complete exclusion of the fluoroalkane. The fluoroalkane monolayer is completely displaced from the graphite surface on addition of the equivalent of just 1 ML of alkane to the mixture. The hydrocarbon is preferentially adsorbed both as solid monolayer and as a liquid
Radiometric dates of uplifted marine fauna in Greece: Implications for the interpretation of recent earthquake and tectonic histories using lithophagid dates
No full textn AD 365 a great (Mw N 8) earthquake lifted up western Crete, exposing a shoreline encrusted by marine
organisms, and up to 10 m of marine substrate beneath it. Radiocarbon ages determined for corals and
bryozoans exposed between the paleo-shoreline and present sea level are consistent, within measurement
error, with each other and with the date of the earthquake. But radiocarbon ages determined for the boring
bivalve Lithophaga lithophaga found on the same substrate are at least 350 years, and up to 2000 years, older
than the date of the earthquake that lifted them above sea level. These observations reveal two important
effects that limit the use of radiocarbon lithophagid ages in tectonic and paleoseismological studies. The first
is that the exceptional preservation potential of lithophagids allows them to remain intact and in situ long
after natural death, while the substrate continues to be colonised until eventual uplift. The second, which we
confirm with radiocarbon analysis of museum specimens of known age, is the incorporation of old (14C-free)
carbon into lithophagid shells from the limestone host rock into which the lithophagids bored. The two
effects are both significant in Crete and central Greece, and can cause the radiocarbon lithophagid ages to be
up to 2000 years older than the uplift event which exposed them. Understanding these effects is important
because lithophagids are far more abundantly preserved, and used to date uplift, than most other marine
organisms. This study shows that they can rarely be used to distinguish uplift events, or date them to better
than 1000 years, or even to distinguish whether observed uplift occurred in a single or in multiple events.
After taking account of these uncertainties, the ages of the lithophagids are, however, consistent with the
hypothesis that the highest prominent marine notches and exposed lithophagid holes within a few metres of
sea level in Greece formed when sea level became relatively stable ~ 6000 years ago, following rapid rise after
the last glacial maximum
Methods for inexpensive, nonintrusive detection of skeletal elements in small zoological specimens using micro-computed tomography.
No full textSubducted seafloor relief stops rupture in South American great earthquakes: Implications for rupture behaviour in the 2010 Maule, Chile earthquake
No full textGreat subduction earthquakes cause destructive surface deformation and ground shaking over hundreds of kilometres. Their rupture length is limited by the characteristic strength of the subduction plate interface, and by lateral variations in its mechanical properties. It has been proposed that subduction of topographic features such as ridges and seamounts can affect these properties and stop rupture propagation, but the required relief and physical mechanisms of topographic rupture limitation are not well understood. Here, we show that the rupture limits of thirteen historic great earthquakes along the South America–Nazca plate margin are strongly correlated with subducted topography with relief > 1000 m, including the Juan Fernandez Ridge. The northern limit of rupture in the Mw 8.8 Maule, Chile earthquake of 27 February 2010 is located where this ridge subducts. Analysis of intermediate-magnitude earthquakes shows that in most places, the subduction of high seafloor relief creates weak, aseismic zones at the plate interface, which prevent rupture propagation, but that the Juan Fernandez Ridge is associated with a locally strong plate interface. The maximum rupture length, and thus magnitude, of great subduction earthquakes is therefore determined by the size and lateral spacing of topographic features where they are present on the subducting plate