The creep of concrete under the cyclic uniaxial compression

The thesis describes an investigation into the creep deformation of plain concrete subjected to a cyclic compressive loading. Under such loading considerably increased creep occurs, especially in the early stages, over that observed for a static stress equal to the mean of the cyclicstress. The increase is greater the greater the amplitude for a given mean stress, and greater the greater the mean stress for a given amplitude. The creep-stress-time relationship can be expressed in terms of a power function expression for early time intervals and a logarithmic expression for later stages, if a linear creep-stress relationship is assumed. The latter assumption is reasonable for amplitudes of less than 0.4 of ultimate as long as the maximum stress is less than 0.55* The increased creep in this linear range is explained in terms of the repeated stress reversals in the absorbed water layers between gel particles causing a breakdown in the structure of the layers and hence increased mobility of the gel particles. Activation energy calculations indicate that movement of gel particles rather than water movement is responsible for the creep process. At stresses outside the linear range there is a large increase in creep which is shown to be due to load oriented microcracking. Though causing increased creep, a cyclic stress below the fatigue limit has a beneficial effect on strength and modulus, the tendency being for concrete to achieve internal structural stability more rapidly than under a static stress

Applying systematic review methods in chemical risk assessment

Context : Chemical risk assessment has traditionally been dependent on “narrative” approaches for synthesising evidence about potential health harms from exposure to chemical substances. However, narrative reviews are recognised as being vulnerable to a range of methodological shortcomings which introduce bias and inconsistency into the summarisation of scientific evidence. This is likely to be a contributing factor in a number of controversies about the safety of chemical substances. The potential value of systematic review methods for improving the transparency and validity of chemical risk assessments was arguably first articulated in the mid-2000s. By 2015, the first major frameworks for conducting systematic reviews of environmental health evidence had been published. What was not well understood at the time was how systematic review, as a technically exacting methodology originally developed for evaluating the effectiveness of interventions in healthcare, might be adapted to the specific workflows and evidence streams of chemical risk assessment. Objectives : The aim of this Thesis is to investigate how systematic review methods can be applied to the conduct of chemical risk assessment. This overall aim is broken down into four specific objectives: to identify practical challenges and knowledge gaps which impede the implementation of systematic review methods in chemical risk assessment; to define a consensus view on key recommended practices for the planning and conduct of systematic reviews in the environmental health sciences; to examine how “biological plausibility” as a concept fundamental to risk assessment is accommodated in systematic review methodologies; and to describe the role of ontologies in making evidence accessible for use in systematic chemical assessments. Discussion : The use of systematic review methods should improve the validity, utility and transparency of chemical risk assessments. However, the successful implementation of systematic review methods hinges on addressing a number of challenges, including the development of guidance for their conduct in environmental health contexts, and the technical development of methods where systematic review approaches need to be adapted to the specific requirements of chemical risk assessment. In terms of developing guidance, a detailed set of recommendations for the conduct of systematic reviews in environmental health and toxicological research was developed. These “COSTER” recommendations identify 70 practices across eight performance domains that will help ensure consistent and high standards for the growing number systematic reviews on environmental health topics. In terms of technical development of methods, “biological plausibility” is a concept used by risk assessors to describe the extent to which an experimental surrogate or knowledge of relevant biological mechanisms are informative of a systematic review conclusion. Through examination of 12 case examples it is concluded that “biological plausibility” is in fact already accommodated in the systematic review process under the assessment of the indirectness or external validity of evidence; however, the considerations which risk assessors take into account when assessing biological plausibility should be absorbed into the assessment of external validity of studies. Finally, examination of the concept of biological plausibility demonstrates the extreme heterogeneity and volume of data which has to be accommodated in chemical risk assessments. The role of ontologies in Knowledge Organisation Systems is examined as a key enabler of scaling up of systematic review methods to handling the volume of evidence which needs to be analysed if tens of thousands of chemicals, covering potentially millions of studies, are to be reviewed systematically

Porous isotactic polypropylene from supercritical propane solution : synthesis and characterization.

Solid-supercritical fluid (S-SCF) and liquid-vapor equilibria (cloud-point pressures) for iPP/propane systems were determined. Liquid-vapor equilibria below S-SCF equilibria temperatures for iPP/propane were obtained by studying the atactic polypropylene (aPP)/propane system. Modeling of these systems by the Sanchez-Lacombe lattice fluid theory required empirical adjustment of mixing parameters. Cloud-point pressures for polyolefins of increasing branch length and some poly(ethylene-co-octene) copolymers in propane were also determined. They decrease with increasing percentage of carbon in the branches. Crystallization of iPP from single phase systems was achieved by controlling temperature and pressure. Under most conditions, crystallizations of unnucleated iPP resulted in large (100+ $\mu$m) microspheres having poor mechanical coherency. A highly effective nucleating agent, dibenzylidene-d-sorbitol (DBS), was added to promote nucleation and coherence, but requires a cosolvent for solubilization. S-SCF equilibria for DBS in propane/1-propanol mixtures were determined as well as changes in the phase behavior of aPP/propane with the addition of an alcohol and is summarized in terms of changes in critical behavior. Surface areas and pore size distributions (PSD) in the mesopore range (20 to $\sim$500 A) were determined by analysis of nitrogen adsorption-desorption isotherms. Surface areas ranged from 120-180 m\sp2/g with most probable pore sizes, based on a cylindrical pore model, of between 100-200 A. This pore size is supported by small angle x-ray scattering data analyzed by a model which treats the pores as a distribution of spherical aggregates. A more specific model is proposed in which the microsphere contains a dense core defined by a radius beyond which fibrillation and gas adsorption sets in. The high surface area of porous iPP is attributed to as yet unknown details of the organization of iPP lamellae on the nanoscale

Impedance Matching in Aural Prosthesis

Mechanical Engineerin

Effect of electron-nuclear spin interactions on electron-spin qubits localized in self-assembled quantum dots

The effect of electron-nuclear spin interactions on qubit operations is investigated for a qubit represented by the spin of an electron localized in a self-assembled quantum dot. The localized electron wave function is evaluated within the atomistic tight-binding model. The magnetic field generated by the nuclear spins is estimated in the presence of an inhomogeneous environment characterized by a random nuclear spin configuration, by the dot-size distribution, by alloy disorder, and by interface disorder. Due to these inhomogeneities, the magnitude of the nuclear magnetic field varies from one qubit to another by the order of 100 G, 100 G, 10 G, and 0.1 G, respectively. The fluctuation of the magnetic field causes errors in exchange operations due to the inequality of the Zeeman splitting between two qubits. We show that the errors can be made lower than the quantum error threshold if an exchange energy larger than 0.1 meV is used for the operation.Comment: 15 pages, 2 figure

The acceleration dilemma : can English law accommodate constructive acceleration?

Purpose – The aim of this paper is to explore the hypothesis that a contractor is entitled to payment for “constructive” acceleration implemented to avoid liquidated damages when denied a warranted time extension request by the employer or certifier under an English law construction contract. This claim is recognised in the US legal system, but not elsewhere. Design/methodology/approach – This paper adopts a “black letter” approach to reviewing the claim of constructive acceleration within the context of English and Commonwealth case law, from the perspective of a claimant contractor. Findings – The research presented in this paper concludes that whilst claims for constructive acceleration are unlikely to succeed in an English court on the basis of US law, a claim might be supportable on more orthodox common law grounds. These include implied instructions under the contract, breach of the contract based on the employer or certifier’s failure to operate the contract, mitigation of damages, unjust enrichment and tortious intimidation. Research limitations/implications – The focus of this paper is placed on English, Unites States, Canadian and Australasian case law. Practical implications – The range of potential legal grounds for constructive acceleration examined in this paper provides a toolkit for practitioners preparing to make or defend constructive acceleration claims. This paper also bring more clarity to a potential legal problem faced by practitioners in circumstances of significant tension and limited time. Originality/value – This paper provides a useful information source for practitioners faced with the prospect of advancing or defending constructive acceleration claims, and it provides a foundation for future related studies examining a wider scope of jurisdictions

Response to “Every ROSE has its thorns”

Abstract: Sharp et al. [1] raise a number of concerns about the development and communication of ROSES (RepOrting standards for Systematic Evidence Syntheses), and we welcome the opportunity to explain some of the underlying thinking behind development of the reporting standards for environmental evidence syntheses

Rubidium Chloride and Cesium Chloride Sprayed on Maize Plants and Evaluated for Marking \u3ci\u3eDiatraea grandiosella\u3c/i\u3e (Lepidoptera: Crambidae) in Mark–Recapture Dispersal Studies

Experiments were undertaken to determine the potential for using rubidium chloride (RbCl) or cesium chloride (CsCl) to mark southwestern corn borer, Diatraea grandiosella Dyar, for use in applied ecological studies. Maize, Zea mays L., plants were sprayed with aqueous solutions of RbCl or CsCl at rates of 100, 1000, or 10,000 µg/g and inoculated with D. grandiosella neonates. Rubidium and cesium were successfully absorbed and translocated in maize plants. There were only a few minor effects of the treatment on maize or on southwestern corn borers.Rb and Cs were detected in plants, but not in insects, by using Flame atomic absorption spectrophotometry. Graphite furnace-atomic absorption spectrophotometry (GF-AAS) and neutron activation analysis (NAA) allowed identification of Rb and Cs in adults. Rb and Cs were detected by GF-AAS in feral unmarked adults, and they contained higher levels of Rb than Cs. Males and females contained similar amounts of Rb, but Cs levels were higher in males than in females. Adults recovered from field maize treated with 1000 µg/g Cs had higher levels of Cs than did those from untreated plants. Using NAA, neither Rb nor Cs was detected in adults recovered from greenhouse-grown untreated maize. Males and females recovered from maize treated with 1000 µg/g RbCl and CsCl contained similar amounts of Rb, but females contained more Rb than Cs. We conclude that application of 1000 µg/g RbCl or CsCl on plants is effective in marking adults of D. grandiosella with Rb or Cs and would be useful for mark-recapture dispersal studies

Preregistration templates as a new addition to the evidence-based toxicology toolbox

In this editorial, we define the practice of “preregistration” of research and describe its motivations, explain why we believe preregistration templates should make preregistration more effective as an intervention for improving the quality of scientific research, and introduce Evidence-Based Toxicology’s Preregistration Templates Special Issue