621 research outputs found
The origin of centennial- to millennial-scale chronological gaps in storm emplaced beach ridge plains
Recent studies of tropical cyclone surge and wave emplaced beach ridge plains have shown that these sequences often contain centennial to millennial scale gaps in their chronologies. Two explanations for the gaps exist — they are due to erosion, or alternatively a cessation or substantial slowing of depositional processes suggestive of a quieter phase in intense storm activity. Differentiating between the two is important for uncovering reliable long-term storm histories from these sequences. We use landform morphology, sediment texture and luminescence chronology to determine the origin of substantial chronological gaps in a plain containing more than 100 shore-parallel ridges composed of fine-grained sand located in northeast Australia. We identify and describe the characteristics associated with both erosional and non-erosional gaps. The erosional gaps are associated with changes in orientation between ridge sets and often a high ridge with hummocky topography that appears to have been disturbed by aeolian activity. River floods likely caused the partial erosion of ridge sets. Non-erosional gaps do not display these morphological characteristics and are likely associated with quiescence in severe tropical cyclone activity. These geomorphic and chronological signatures can be used to identify different sorts of gaps in other ridge plains and are an important tool in the reconstruction of long-term storm histories from these coastal landforms. The data also suggests that fine-grained ridges can, like their coarse-grained counterparts, be predominantly deposited by storm waves and surge and their texture need not necessarily be indicative of the processes responsible for ridge development
Pharmacokinetics of Octreotide in Patients With Cirrhosis and Portal Hypertension; Relationship Between the Plasma Levels of the Analogue and the Magnitude and Duration of the Reduction in Corrected Wedged Hepatic Venous Pressure
In healthy subjects octreotide is largely metabolised
by the liver suggesting that the plasma half-life of the
somatostatin analogue may be prolonged in patients
with hepatic dysfunction. The aim of this study was
therefore (a) to determine the pharmacokinetics of
octreotide following its subcutaneous injection in 6
patients with cirrhosis and portal hypertension and
(b) compare the magnitude and duration of the effects
of intravenous administration of 250 μg somatostatin
and 50 μg octreotide on corrected wedged hepatic
venous pressure (WHVP) and to relate the findings to
the plasma levels of the analogue 1h after administration
in 13 patients with cirrhosis and portal
hypertension. Following subcutaneous administration
of 50 μg octreotide the circulating half life (range
2.4 to 4.79 h) was prolonged whereas the clearance
(range 2.101 to 4.775 L/h) was decreased compared to
healthy controls. Intravenous bolus administration of
25 μg somatostatin or 50 μg octreotide resulted in a
reduction in WHVP of approximately the same
magnitude and duration despite appreciable quantities
of the analogue in the blood lh after administration
(1944 ± 226 pg/ml). These results indicate
that the circulating half-life of octreotide is prolonged
in cirrhotics suggesting that the dosage
regimens should be modified in such patients to
avoid accumulation of the analogue in the blood
which may result in undesirable side-effects or
toxicity. Furthermore, since the magnitude and
duration of the reduction in WHVP elicited by IV
octreotide is similar to that obseved with somatostatin,
the analogue, like the native hormone, must be
administered by continuous IV infusion to produce a
sustained response and hence a therapeutic effect in
the management of acute variceal bleeding
Transition to turbulence in particulate pipe flow
We investigate experimentally the influence of suspended particles on the
transition to turbulence. The particles are monodisperse and neutrally-buoyant
with the liquid. The role of the particles on the transition depends both upon
the pipe to particle diameter ratios and the concentration. For large
pipe-to-particle diameter ratios the transition is delayed while it is lowered
for small ratios. A scaling is proposed to collapse the departure from the
critical Reynolds number for pure fluid as a function of concentration into a
single master curve.Comment: 4 pages, 4 figure
A Novel Method of Determining Portal Systemic Shunting using Biodegradable 99TCm Labelled Albumin Microspheres
Portal systemic shunting (PSS) and portal pressure were measured in control rats and in animals
with portal hypertension induced by partial portal vein ligation (PPVL). The portal pressure in
rats with partial portal vein ligation (13.4 ± 0.5 mm.Hg.) was significantly higher (p < 0.005) than
in the control group (9.6 ± 0.6 mm.Hg.). Portal systemic shunting measured by consecutive
injections of radiolabelled methylene diphosphonate (MDP), a non-diffusable marker and
albumin microspheres directly into the splenic pulp was significantly increased (P < 0.005) in the
portal hypertensive animals (30.8 ± 2.5%) compared to sham operated rats (2.6 ± 1.5%). Similarly,
in portal hypertensive rats portal systemic shunting measured by intrasplenic injections of
radiolabelled cobalt microspheres (37.1 ± 3.9%) was significantly greater (p < 0.005) than in
control animals. There was a good correlation and agreement (r = 00.97) between the two
methods of measuring portal systemic shunting. However because the 99Tcm-albumin microspheres
are biodegradable the method allows portal systemic shunting to be measured in man.
Furthermore since the computer adjusts the baseline to zero after each determination of portal
systemic shunting the methodology allows repeated measurements to be made
Instability-induced ordering, universal unfolding and the role of gravity in granular Couette flow
Linear stability theory and bifurcation analysis are used to investigate the role of gravity in shear-band formation in granular Couette flow, considering a kinetic-theory rheological model. We show that the only possible state, at low shear rates, corresponds to a 'plug' near the bottom wall, in which the particles are densely packed and the shear rate is close to zero, and a uniformly sheared dilute region above it. The origin of such plugged states is shown to be tied to the spontaneous symmetry-breaking instabilities of the gravity-free uniform shear flow, leading to the formation of ordered bands of alternating dilute and dense regions in the transverse direction, via an infinite hierarchy of pitchfork bifurcations. Gravity plays the role of an 'imperfection', thus destroying the 'perfect' bifurcation structure of uniform shear. The present bifurcation problem admits universal unfolding of pitchfork bifurcations which subsequently leads to the formation of a sequence of a countably infinite number of 'isolas', with the solution structures being a modulated version of their gravity-free counterpart. While the solution with a plug near the bottom wall looks remarkably similar to the shear-banding phenomenon in dense slow granular Couette flows, a 'floating' plug near the top wall is also a solution of these equations at high shear rates. A two-dimensional linear stability analysis suggests that these floating plugged states are unstable to long-wave travelling disturbances.The unique solution having a bottom plug can also be unstable to long waves, but remains stable at sufficiently low shear rates. The implications and realizability of the present results are discussed in the light of shear-cell experiments under 'microgravity' conditions
Approximate Bayesian Computation via Regression Density Estimation
Approximate Bayesian computation (ABC) methods, which are applicable when the
likelihood is difficult or impossible to calculate, are an active topic of
current research. Most current ABC algorithms directly approximate the
posterior distribution, but an alternative, less common strategy is to
approximate the likelihood function. This has several advantages. First, in
some problems, it is easier to approximate the likelihood than to approximate
the posterior. Second, an approximation to the likelihood allows reference
analyses to be constructed based solely on the likelihood. Third, it is
straightforward to perform sensitivity analyses for several different choices
of prior once an approximation to the likelihood is constructed, which needs to
be done only once. The contribution of the present paper is to consider
regression density estimation techniques to approximate the likelihood in the
ABC setting. Our likelihood approximations build on recently developed marginal
adaptation density estimators by extending them for conditional density
estimation. Our approach facilitates reference Bayesian inference, as well as
frequentist inference. The method is demonstrated via a challenging problem of
inference for stereological extremes, where we perform both frequentist and
Bayesian inference
- …