7,556 research outputs found
The structural and diagenetic evolution of injected sandstones: examples from the Kimmeridgian of NE Scotland
Abstract: Injected sandstones occurring in the Kimmeridgian of NE Scotland along the bounding Great Glen
and Helmsdale faults formed when basinal fluids moved upward along the fault zones, fluidizing Oxfordian
sands encountered at shallow depth and injecting them into overlying Kimmeridgian strata. The orientation of
dykes, in addition to coeval faults and fractures, was controlled by a stress state related to dextral strike-slip
along the bounding fault zones. Diagenetic studies of cements allow the reconstruction of the fluid flow
history. The origin of deformation bands in sandstone dykes and sills was related to the contraction of the
host-rocks against dyke and sill walls following the initial stage of fluidized flow, and these deformation bands
are the earliest diagenetic imprint. Early non-ferroan calcite precipitated in injection structures at temperatures
between 70 and 100 8C, indicating that it precipitated from relatively hot basinal fluids that drove injection.
Coeval calcite-filled fractures show similar temperatures, suggesting that relatively hot fluids were responsible
for calcite precipitation in any permeable pathway created by dextral simple shear along the faults. During
progressive burial, percolating sea water was responsible for completely cementing the still relatively porous
injected sandstones with a second generation of ferroan calcite, which contains fluid inclusions with
homogenization temperatures below 50 8C. During this phase, depositional host sandstones were also
cemented
Bio-inspired swing leg control for spring-mass robots running on ground with unexpected height disturbance
We proposed three swing leg control policies for spring-mass running robots, inspired by experimental data from our recent collaborative work on ground running birds. Previous investigations suggest that animals may prioritize injury avoidance and/or efficiency as their objective function during running rather than maintaining limit-cycle stability. Therefore, in this study we targeted structural capacity (maximum leg force to avoid damage) and efficiency as the main goals for our control policies, since these objective functions are crucial to reduce motor size and structure weight. Each proposed policy controls the leg angle as a function of time during flight phase such that its objective function during the subsequent stance phase is regulated. The three objective functions that are regulated in the control policies are (i) the leg peak force, (ii) the axial impulse, and (iii) the leg actuator work. It should be noted that each control policy regulates one single objective function. Surprisingly, all three swing leg control policies result in nearly identical subsequent stance phase dynamics. This implies that the implementation of any of the proposed control policies would satisfy both goals (damage avoidance and efficiency) at once. Furthermore, all three control policies require a surprisingly simple leg angle adjustment: leg retraction with constant angular acceleration
Growth to early adulthood following extremely preterm birth: the EPICure study.
OBJECTIVE: To investigate growth trajectories from age 2.5 to 19 years in individuals born before 26 weeks of gestation (extremely preterm; EP) compared with term-born controls. METHODS: Multilevel modelling of growth data from the EPICure study, a prospective 1995 birth cohort of 315 EP participants born in the UK and Ireland and 160 term-born controls recruited at school age. Height, weight, head circumference and body mass index (BMI) z-scores were derived from UK standards at ages 2.5, 6, 11 and 19 years. RESULTS: 129 (42%) EP children were assessed at 19 years. EP individuals were on average 4.0 cm shorter and 6.8 kg lighter with a 1.5 cm smaller head circumference relative to controls at 19 years. Relative to controls, EP participants grew faster in weight by 0.06 SD per year (95% CI 0.05 to 0.07), in head circumference by 0.04 SD (95% CI 0.03 to 0.05), but with no catch-up in height. For the EP group, because of weight catch-up between 6 and 19 years, BMI was significantly elevated at 19 years to +0.32 SD; 23.4% had BMI >25 kg/m2 and 6.3% >30 kg/m2 but these proportions were similar to those in control subjects. EP and control participants showed similar pubertal development in early adolescence, which was not associated with height at 19 years in either study group. Growth through childhood was related to birth characteristics and to neonatal feeding practices. CONCLUSIONS: EP participants remained shorter and lighter and had smaller head circumferences than reference data or controls in adulthood but had elevated BMI
The Effect Of Antimony, Chloride Ion, And Glue On Copper Electrorefining
A study has been made to determine the effect of antimony, chloride ion, and glue on copper electrorefining. All deposits were made at a temperature of 65° C on a titanium cathode. Current densities of 398 A m-2 and 133 A m-2 were used. The deposits were analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD) to determine morphology and crystal orientation. Atomic absorption (AA) and Auger spectroscopy (AES) were used to study the chemical composition of the deposits and a simple bend test was used to determine structural integrity. It was found that when the antimony concentration in the electrolyte exceeded 300 ppm, brittle deposits were produced containing considerable amounts of antimony. Very small amounts of chloride ion (1.5 ppm or above) decreased the codeposition of antimony greatly and produced ductile deposits. However, at a chloride ion level of 15 ppm or above, the back side of the deposit had a very rough, powdery appearance. The effect of glue was to counteract this and to produce a mirror-like finish on the deposit back. © 1978 Chapman and Hall Ltd
First passage behaviour of fractional Brownian motion in two-dimensional wedge domains
We study the survival probability and the corresponding first passage time
density of fractional Brownian motion confined to a two-dimensional open wedge
domain with absorbing boundaries. By analytical arguments and numerical
simulation we show that in the long time limit the first passage time density
scales as t**{-1+pi*(2H-2)/(2*Theta)} in terms of the Hurst exponent H and the
wedge angle Theta. We discuss this scaling behaviour in connection with the
reaction kinetics of FBM particles in a one-dimensional domain.Comment: 6 pages, 4 figure
Extreme value statistics and return intervals in long-range correlated uniform deviates
We study extremal statistics and return intervals in stationary long-range
correlated sequences for which the underlying probability density function is
bounded and uniform. The extremal statistics we consider e.g., maximum relative
to minimum are such that the reference point from which the maximum is measured
is itself a random quantity. We analytically calculate the limiting
distributions for independent and identically distributed random variables, and
use these as a reference point for correlated cases. The distributions are
different from that of the maximum itself i.e., a Weibull distribution,
reflecting the fact that the distribution of the reference point either
dominates over or convolves with the distribution of the maximum. The
functional form of the limiting distributions is unaffected by correlations,
although the convergence is slower. We show that our findings can be directly
generalized to a wide class of stochastic processes. We also analyze return
interval distributions, and compare them to recent conjectures of their
functional form
Entropy of the Nordic electricity market: anomalous scaling, spikes, and mean-reversion
The electricity market is a very peculiar market due to the large variety of
phenomena that can affect the spot price. However, this market still shows many
typical features of other speculative (commodity) markets like, for instance,
data clustering and mean reversion. We apply the diffusion entropy analysis
(DEA) to the Nordic spot electricity market (Nord Pool). We study the waiting
time statistics between consecutive spot price spikes and find it to show
anomalous scaling characterized by a decaying power-law. The exponent observed
in data follows a quite robust relationship with the one implied by the DEA
analysis. We also in terms of the DEA revisit topics like clustering,
mean-reversion and periodicities. We finally propose a GARCH inspired model but
for the price itself. Models in the context of stochastic volatility processes
appear under this scope to have a feasible description.Comment: 16 pages, 7 figure
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