Large amplitude folding in finely layered viscoelastic rock structures

We analyze folding phenomena in finely layered viscoelastic rock. Fine is meant in the sense that the thickness of each layer is considerably smaller than characteristic structural dimensions. For this purpose we derive constitutive relations and apply a computational simulation scheme (a finite-element based particle advection scheme; see MORESI et al., 2001) suitable for problems involving very large deformations of layered viscous and viscoelastic rocks. An algorithm for the time integration of the governing equations as well as details of the finite-element implementation is also given. We then consider buckling instabilities in a finite, rectangular domain. Embedded within this domain, parallel to the longer dimension we consider a stiff, layered plate. The domain is compressed along the layer axis by prescribing velocities along the sides. First, for the viscous limit we consider the response to a series of harmonic perturbations of the director orientation. The Fourier spectra of the initial folding velocity are compared for different viscosity ratios. Turning to the nonlinear regime we analyze viscoelastic folding histories up to 40% shortening. The effect of layering manifests itself in that appreciable buckling instabilities are obtained at much lower viscosity ratios (1:10) as is required for the buckling of isotropic plates (1:500). The wavelength induced by the initial harmonic perturbation of the director orientation seems to be persistent. In the section of the parameter space considered here elasticity seems to delay or inhibit the occurrence of a second, larger wavelength. Finally, in a linear instability analysis we undertake a brief excursion into the potential role of couple stresses on the folding process. The linear instability analysis also provides insight into the expected modes of deformation at the onset of instability, and the different regimes of behavior one might expect to observe.

Air Entrainment Processes in a Full-Scale Rectangular Dropshaft at Large Flows

Rectangular dropshafts, commonly used in sewers and storm water systems, are characterised by significant flow aeration. New detailed air-water flow measurements were conducted in a near-full-scale dropshaft at large discharges. In the shaft pool and outflow channel, the results demonstrated the complexity of different competitive air entrainment mechanisms. Bubble size measurements showed a broad range of entrained bubble sizes. Analysis of streamwise distributions of bubbles suggested further some clustering process in the bubbly flow although, in the outflow channel, bubble chords were in average smaller than in the shaft pool. A robust hydrophone was tested to measure bubble acoustic spectra and to assess its field application potential. The acoustic results characterised accurately the order of magnitude of entrained bubble sizes, but the transformation from acoustic frequencies to bubble radii did not predict correctly the probability distribution functions of bubble sizes.

Achromatic optical phase shifter/modulator

We propose and demonstrate, theoretically and experimentally, a novel achromatic optical phase shifter modulator based on a frequency-domain optical delay line configured to maintain zero group delay as variable phase delay is generated by means of tilting a mirror. Compared with previously reported phase shifter modulators, e.g., based on the Pancharatnam (geometric) phase, our device is high speed and polarization insensitive and produces a large, bounded phase delay that, uniquely, is one-to-one mapped to a measurable parameter, the tilt angle.

Clustering Process Analysis in a Large-Size Dropshaft and in a Hydraulic Jump

Recent efforts in the characterization of air-water flows properties have included some clustering process analysis. A cluster of bubbles is defined as a group of two or more bubbles, with a distinct separation from other bubbles before and after the cluster. The present paper compares the results of clustering processes two hydraulic structures. That is, a large-size dropshaft and a hydraulic jump in a rectangular horizontal channel. The comparison highlighted some significant differences in clustering production and structures. Both dropshaft and hydraulic jump flows are complex turbulent shear flows, and some clustering index may provide some measure of the bubble-turbulence interactions and associated energy dissipation.

Employee adjustment to large-scale organisational change

The present study was designed to test the utility of a stress-coping model of employee adjustment to organisational change. Specifically, it was proposed that employee adjustment to this type of work stress would be influenced by the characteristics of the change situation, employees' appraisals of the situation, their coping strategies, and the extent of their personal resources. Data were collected from 140 middle managers and supervisors involved in a large-scale public sector integration. The results of the research provided some support for the proposed model: high levels of psychological distress were related to a reliance on informal sources of information, high appraised stress, low appraised certainty, and the use of avoidant rather than problem-focused strategies, whereas poor social functioning was associated with low self-esteem, high levels or disruption across the period of change, a reliance on informal sources of information, and the use of avoidant coping strategies. There was no evidence that coping strategies mediated the effects of the event characteristics, situational appraisals, and personal resources on adjustment; however, there was some evidence linking these variables to coping strategies, in particular, problem-focused coping. There was also some evidence to indicate that the experience of organisational change was different for managers and supervisors: levels of threat were higher for the managers than the supervisors, but there was no difference between the groups of employees in terms of adjustment.

Experimentally tracking unstable steady states by large periodic modulation

Experimental suppression of chaos has been achieved in an optically pumped far-infrared (NH3)-N-15 laser which displays Lorenz-like chaos. The method of control involves the application of a large amplitude slow (i.e., nonresonant) modulation of the pump power. This may be related to a delayed bifurcation to chaos observed when the pump power is ramped at a constant late.

Electrical impedance particle size method (Coulter Counter) detects the large fat globules in poorly homogenised UHT processed milk

The large fat globules that can be present in UHT milk due to inadequate homogenisation cause a cream layer to form that limits the shelf life of UHT milk. Four different particle size measurement techniques were used to measure the size of fat globules in poorly homogenised UHT milk processed in a UHT pilot plant. The thickness of the cream layer that formed during storage was negatively correlated with homogenisation pressure. It was positively correlated with the mass mean diameter and the percentage volume of particles between 1.5 and 2 mu m diameter, as determined by laser light scattering using the Malvern Mastersizer. Also, the thickness of the cream layer was positively correlated with the volume mode diameter and the percentage volume of particles between 1.5 and 2 mu m diameter, as determined by electrical impedance using the Coulter Counter. The cream layer thickness did not correlate significantly with the Coulter Counter measurements of volume mean diameter, or volume percentages of particles between 2 and 5 mu m or 5 and 10 mu m diameter. Spectroturbidimetry (Emulsion Quality Analyser) and light microscopy analyses were found to be unsuitable for assessing the size of the fat particles. This study suggests that the fat globule size distribution as determined by the electrical impedance method (Coulter Counter) is the most useful for determining the efficiency of homogenisation and therefore for predicting the stability of the fat emulsion in UHT milk during storage.

Familial hyperaldosteronism type II: Description of a large kindred and exclusion of the aldosterone synthase (CYP11B2) gene

Familial hyperaldosteronism type II (FH-II) is characterized by autosomal dominant inheritance and hypersecretion of aldosterone due to adrenocortical hyperplasia or an aldosterone-producing adenoma; unlike FH type I (FH-I), hyperaldosteronism in FH-II is not suppressible by dexamethasone. Of a total of 17 FH-II families with 44 affected members, we studied a large kindred with 7 affected members that was informative for linkage analysis. Family members were screened with the aldosterone/PRA ratio test; patients with aldosterone/PRA ratio greater than 25 underwent fludrocortisone/salt suppression testing for confirmation of autonomous aldosterone secretion. Postural testing, adrenal gland imaging, and adrenal venous sampling were also performed. Individuals affected by FH-II demonstrated lack of suppression of plasma A levels after 4 days of dexamethasone treatment (0.5 mg every 6 h). All patients had neg ative genetic testing for the defect associated with FH-I, the CYP11B1/CYP11B2 hybrid gene. Genetic linkage was then examined between FH-II and aldosterone synthase (the CYP11B2 gene) on chromosome 8q. A polyadenylase repeat within the 5'-region of the CYP11B2 gene and 9 other markers covering an approximately 80-centimorgan area on chromosome 8q21-8qtel were genotyped and analyzed for linkage. Two-point logarithm of odds scores were negative and ranged from -12.6 for the CYP11B2 polymorphic marker to -0.98 for the D8S527 marker at a recombination distance (theta) of 0. Multipoint logarithm of odds score analysis confirmed the exclusion of the chromosome 8q21-8qtel area as a region harboring the candidate gene for FH-II in this family. We conclude that FH-II shares autosomal dominant inheritance and hyperaldosteronism with FH-I, but, as demonstrated by the large kindred investigated in this report, it is clinically and genetically distinct. Linkage analysis demonstrated that the CYP11B2 gene is not responsible for FH-II in this family; furthermore, chromosome 8q21-8qtel most likely does not harbor the genetic defect in this kindred.

A numerical study of large sparse matrix exponentials arising in Markov chains

Krylov subspace techniques have been shown to yield robust methods for the numerical computation of large sparse matrix exponentials and especially the transient solutions of Markov Chains. The attractiveness of these methods results from the fact that they allow us to compute the action of a matrix exponential operator on an operand vector without having to compute, explicitly, the matrix exponential in isolation. In this paper we compare a Krylov-based method with some of the current approaches used for computing transient solutions of Markov chains. After a brief synthesis of the features of the methods used, wide-ranging numerical comparisons are performed on a power challenge array supercomputer on three different models. (C) 1999 Elsevier Science B.V. All rights reserved.AMS Classification: 65F99; 65L05; 65U05.

Modelling the large deformations in stratified media - the Cosserat continuum approach

Methods employing continuum approximation in describing the deformation of layered materials possess a clear advantage over explicit models, However, the conventional implicit models based on the theory of anisotropic continua suffers from certain difficulties associated with interface slip and internal instabilities. These difficulties can be remedied by considering the bending stiffness of the layers. This implies the introduction of moment (couple) stresses and internal rotations, which leads to a Cosserat-type theory. In the present model, the behaviour of the layered material is assumed to be linearly elastic; the interfaces are assumed to be elastic perfectly plastic. Conditions of slip or no slip at the interfaces are detected by a Coulomb criterion with tension cut off at zero normal stress. The theory is valid for large deformation analysis. The model is incorporated into the finite element program AFENA and validated against analytical solutions of elementary buckling problems in layered medium. A problem associated with buckling of the roof and the floor of a rectangular excavation in jointed rock mass under high horizontal in situ stresses is considered as the main application of the theory. Copyright (C) 1999 John Wiley & Sons, Ltd.

Chemical synthesis and folding pathways of large cyclic polypeptide: Studies of the cystine knot polypeptide kalata B1

Kalata B1 is a member of a new family of polypeptides, isolated from. plants, which have a cystine knot structure embedded within an amide-cyclized backbone. This family of molecules are the largest known cyclic peptides, and thus, the mechanism of synthesis and folding is of great interest. To provide information about both these phenomena, we have synthesized kalata B1 using two distinct strategies. In the first, oxidation of the cysteine residues of a linear precursor peptide to form the correct disulfide bonds results in folding of the three-dimensional structure and preorganization of the termini in close proximity for subsequent cyclization. The second approach involved cyclization prior to oxidation. In the first method, the correctly folded peptide was produced only in the presence of partially hydrophobic solvent conditions. These conditions are presumably required to stabilize the surface-exposed hydrophobic residues. However,; in the synthesis,involving cyclization prior to oxidation, the cyclic reduced peptide folded to a significant degree in the absence of hydrophobic solvents and even more efficiently in the presence of hydrophobic solvents. Cyclization clearly has a major effect on the folding pathway and facilitates formation of the correctly disulfide-bonded form in aqueous solution; In addition to facilitating folding to a compact stable structure cyclization has an important effect on biological activity as assessed by hemolytic activity.

Identifying rate-limiting nodes in large-scale cortical networks for visuospatial processing: an illustration using fMRI

With the advent of functional neuroimaging techniques, in particular functional magnetic resonance imaging (fMRI), we have gained greater insight into the neural correlates of visuospatial function. However, it may not always be easy to identify the cerebral regions most specifically associated with performance on a given task. One approach is to examine the quantitative relationships between regional activation and behavioral performance measures. In the present study, we investigated the functional neuroanatomy of two different visuospatial processing tasks, judgement of line orientation and mental rotation. Twenty-four normal participants were scanned with fMRI using blocked periodic designs for experimental task presentation. Accuracy and reaction time (RT) to each trial of both activation and baseline conditions in each experiment was recorded. Both experiments activated dorsal and ventral visual cortical areas as well as dorsolateral prefrontal cortex. More regionally specific associations with task performance were identified by estimating the association between (sinusoidal) power of functional response and mean RT to the activation condition; a permutation test based on spatial statistics was used for inference. There was significant behavioral-physiological association in right ventral extrastriate cortex for the line orientation task and in bilateral (predominantly right) superior parietal lobule for the mental rotation task. Comparable associations were not found between power of response and RT to the baseline conditions of the tasks. These data suggest that one region in a neurocognitive network may be most strongly associated with behavioral performance and this may be regarded as the computationally least efficient or rate-limiting node of the network.

Large mitochondrial repeats multiplied during the polymerase chain reaction

The number of repeats in repetitive DNA like micro- and minisatellites is often determined by polymerase chain reaction (PCR). When we counted repeats in an array of mitochondrial repeats in the cattle tick (Boophilus microplus) we found that the number of repeats increased during PCR. Multiplication of the repeats was independent of the primers used to amplify the region, the PCR annealing temperature and the length of the PCR product. The use of PCR to determine the number of repeats in arrays needs to be reassessed. For long repeats, a subset of samples should always be analysed by Southern blot hybridization to confirm the PCR results.

The VITATOPS (vitamins to prevent stroke) Trial: Rationale and design of an international, large, simple, randomised trial of homocysteine-lowering multivitamin therapy in patients with recent transient ischaemic attack or stroke

Background: Epidemiological studies suggest that raised plasma concentrations of total homocysteine (tHcy) may be a common, causal and treatable risk factor for atherothromboembolic ischaemic stroke. Although tHcy can be lowered effectively with small doses of folic acid, vitamin B-12 and vitamin B-6, it is not known whether lowering tHcy, by means of multivitamin therapy, can prevent stroke and other major atherothromboembolic vascular events. Purpose: To determine whether vitamin supplements (folic acid 2 mg, B-6 25 Mg, B-12 500 mug) reduce the risk of stroke, and other serious vascular events, in patients with recent stroke or transient ischaemic attacks of the brain or eye (TIA). Methods: An international, multi-centre, randomised, double-blind, placebo-controlled clinical trial. Results: As of November 2001, more than 1,400 patients have been randomised from 10 countries in four continents. Conclusion: VITATOPS aims to recruit and follow up 8,000 patients between 2000 and 2004, and provide a reliable estimate of the safety and effectiveness of dietary supplementation with folic acid, vitamin B-12, and vitamin B-6 in reducing recurrent serious vascular events among a wide range of patients with TIA and stroke. Copyright (C) 2002 S. Karger AG, Basel.