Statistical thermodynamics of crystal lattices

This work is the development of a new approach to the theory of thermodynamical equilibrium in the ideal solid state, recently put forward by Professor Max Born (1951a, 1951b). His purpose was to overcome a fundamental expansion difficulty in the usual theory and to generalise it to include strongly anharmonic effects (such as exist in solid helium); it was also hoped to provide alternative solutions of the non -linear vibrational equations which might I indicate intrinsic imperfections ( "block -structure" -- see Born (1947), Pìzrth (1949)) in the equilibrium state. Such solutions have not been found; even in the non -linear case an ideal lattice configuration can be proposed as a solution (though perhaps not the only one), with some changes as discussed by Born (1951a), and the atoms can be taken to vibrate about this reference configuration with stable, fourth degree oscillations. By a method of adaptation independent harmonic modes of vibration can be chosen to be a close approximation to the atomic motion, whatever the reference configuration, and the corresponding thermodynamical formulae may be developed either for large anharmonic effects or by treating the third and fourth degree terms in the potential energy as a small perturbation.Instead of at the start taking the atoms to vibrate about the minimum -energy configuration, which leads to the fundamental difficulty that thei mean displacements increasingly diverge from these positions as the size of the specimen increases, owing to the anharmonicity, we keep the reference configuration free and fix its coordinates as the quantum mechanical average positions at a later stage of the calculation; in this way both zero - energy and temperature effects can be properly accounted for and the vibrations can always be regarded as (relatively) small compared to the atomic spacing. At the same time, new effective harmonic lattice frequencies are established which reduce in a continuous fashion to those of the ordinary quadratic theory when the vibrations are very small.The general theory will first be developed, then the theoretical example of a monatomic linear viii. chain will be worked out in full, both to illustratF the three dimensional theory and to provide approximations for later work, and finally an application of the non -linear results to the thermal behaviour of solid helium will be made

Integrating Escherichia coli Antimicrobial Susceptibility Data from Multiple Surveillance Programs

Collaboration between networks presents opportunities to increase analytical power and cross-validate findings. Multivariate analyses of 2 large, international datasets (MYSTIC and SENTRY) from the Global Advisory on Antibiotic Resistance Data program explored temporal, geographic, and demographic trends in Escherichia coli resistance from 1997 to 2001. Elevated rates of nonsusceptibility were seen in Latin America, southern Europe, and the western Pacific, and lower rates were seen in North America. For most antimicrobial drugs considered, nonsusceptibility was higher in isolates from men, older patients, and intensive care unit patients. Nonsusceptibility to ciprofloxacin was higher in younger patients, rose with time, and was not associated with intensive care unit status. In univariate analyses, estimates of nonsusceptibility from MYSTIC were consistently higher than those from SENTRY, but these differences disappeared in multivariate analyses, which supports the epidemiologic relevance of findings from the 2 programs, despite differences in surveillance strategies

Supplementary Cementitious Materials for Concrete: Characterization Needs

peer reviewedA wide variety of materials are currently used as supplementary cementitious materials (SCMs) for concrete, including natural materials and byproducts from various industries. Historically, natural SCMs, mostly derived from volcanic deposits, were common in concrete. In recent years, the dominant SCMs have been industrial by-products such as fly ash, ground granulated blast furnace slag (GGBFS), and silica fume. There is currently a resurgence of research into historic and natural SCMs, as well as other alternative SCMs for many reasons. The primary benefits of SCM use in improvement of long-term mechanical performance, durability, and sustainability are widely accepted, so local demand for these materials can exceed supply. This paper describes some of the SCMs that are attracting attention in the global research community and the properties and characteristics of these materials that affect their performance. Special attention is paid to the importance and demands of material characterization. Many SCMs do not necessarily lend themselves to characterization methods used in standardized test methods, which sometimes fail to describe the properties that are most important in predicting reactivity

The minor flagellin of Campylobacter jejuni (FlaB) confers defensive properties against bacteriophage infection

A screen of bacteriophages infecting a panel of Campylobacter jejuni PT14 gene knock-out mutants identified a role for the minor flagellin encoded by the flaB gene, in the defense of the host against CP8unalikevirus bacteriophage CP_F1 infection. Inactivation of the flaB gene resulted in an increase in the susceptibility of PT14 cultures to infection by CP_F1 and an increase in bacteriophage yields. Infection of wild type PT14 with CP_F1 produces turbid plaques in bacterial lawns, from which 78% of the resistant isolates recovered exhibit either attenuation or complete loss of motility. CP_F1 produces clear plaques on the flaB mutant with no regrowth in the lysis zones. Complementation of the mutant restored overgrowth and the development of resistance at the expense of motility. Further analyses revealed an increase in bacteriophage adsorption constant of nearly two-fold and burst-size three-fold, relative to the wild type. Motility analysis showed no major reduction in swarming motility in the flaB mutant. Thus we propose a new role for FlaB in the defense of campylobacters against bacteriophage infection

Host adaption to the bacteriophage carrier state of Campylobacter jejuni

The carrier state of the foodborne pathogen Campylobacter jejuni represents an alternative life cycle whereby virulent bacteriophage can persistent in association with host bacteria without commitment to lysogeny. Host bacteria exhibit significant phenotypic changes that improve their ability to survive extra-intestinal environments but exhibit growth phase dependent impairment in motility. We demonstrate that early-exponential phase cultures become synchronised with respect to the non-motile phenotype, which corresponds with a reduction in their ability adhere and invade intestinal epithelial cells. Comparative transcriptome analyses (RNA-seq) identify changes in gene expression that account for the observed phenotypes: down regulation of stress response genes hrcA, hspR and perR; and down regulation of the major flagellin flaA with the chemotactic response signalling genes cheV, cheA and cheW. These changes present mechanisms by which the host and bacteriophage can remain associated without lysis, and the cultures survive extra-intestinal transit. These data provide a basis for understanding a critical link in the ecology of Campylobacter bacteriophage

Reactivity tests for supplementary cementitious materials: RILEM TC 267-TRM phase 1

A primary aim of RILEM TC 267-TRM: “Tests for Reactivity of Supplementary Cementitious Materials (SCMs)” is to compare and evaluate the performance of conventional and novel SCM reactivity test methods across a wide range of SCMs. To this purpose, a round robin campaign was organized to investigate 10 different tests for reactivity and 11 SCMs covering the main classes of materials in use, such as granulated blast furnace slag, fly ash, natural pozzolan and calcined clays. The methods were evaluated based on the correlation to the 28 days relative compressive strength of standard mortar bars containing 30% of SCM as cement replacement and the interlaboratory reproducibility of the test results. It was found that only a few test methods showed acceptable correlation to the 28 days relative strength over the whole range of SCMs. The methods that showed the best reproducibility and gave good correlations used the R3 model system of the SCM and Ca(OH)2, supplemented with alkali sulfate/carbonate. The use of this simplified model system isolates the reaction of the SCM and the reactivity can be easily quantified from the heat release or bound water content. Later age (90 days) strength results also correlated well with the results of the IS 1727 (Indian standard) reactivity test, an accelerated strength test using an SCM/Ca(OH)2-based model system. The current standardized tests did not show acceptable correlations across all SCMs, although they performed better when latently hydraulic materials (blast furnace slag) were excluded. However, the Frattini test, Chapelle and modified Chapelle test showed poor interlaboratory reproducibility, demonstrating experimental difficulties. The TC 267-TRM will pursue the development of test protocols based on the R3 model systems. Acceleration and improvement of the reproducibility of the IS 1727 test will be attempted as well