Strain-induced structural instability in FeRh

We perform density functional calculations to investigate the structure of the intermetallic alloy FeRh under epitaxial strain. Bulk FeRh exhibits a metamagnetic transition from a low-temperature antiferromagnetic (AFM) phase to a ferromagnetic phase at 350 K, and its strain dependence is of interest for tuning the transition temperature to the room-temperature operating conditions of typical memory devices. We find an unusually strong dependence of the structural energetics on the choice of exchange-correlation functional, with the usual local density approximation yielding the wrong ground-state structure, and generalized gradient (GGA) extensions being in better agreement with the bulk experimental structure. Using the GGA we show the existence of a metastable face-centered-cubic-like AFM structure that is reached from the ground-state body-centered-cubic-like AFM structure by following the epitaxial Bain path. We show that the behavior is well described using nonlinear elasticity theory, which captures the softening and eventual sign change of the orthorhombic shear modulus under compressive strain, consistent with this structural instability. Finally, we predict the existence of an additional unit-cell-doubling lattice instability, which should be observable at low temperature.

Structural features in ODP Holes 128-794D and 128-799B

Numerous structural features occur in the Leg 128 cores from the Japan Sea. They include (1) gravity-induced structures such as slump folds, (2) dewatering structures comprising several sets of veins, and (3) larger faults and veins developed in the volcanic basement of the Yamato Basin as well as in the sedimentary rocks of the Oki Ridge and Kita-Yamato Trough. Gravity-induced structures, mainly slumps and associated faults, suggest the existence of paleoslopes and the dominance of gravitational tectonics during the early and middle Miocene, at the Pliocene/Pleistocene boundary, and during the Quaternary. Several types of mud-filled veins having various shapes were observed. These are especially abundant in the middle Miocene siliceous claystones and porcellanites from the Kita-Yamato Trough. They have been interpreted as dewatering conduits that formed preferentially in highly porous, water-saturated diatomaceous muds on a slope, because of episodic loss of sediment strength, collapse of the sediment framework, and consequent fluid migration. The central part of the vein serves once as a fluid conduit, whereas the transition between conduit-controlled and intergranular flow occurs at the branching extremities, with concentration of fines. The likely trigger responsible for the strength loss is seismic activity. Development of these veins, spatially and chronologically linked to small normal microfaults, implies an extensional regime having layer-parallel extension and a local bedding-parallel shear couple, probably the result of gravitational gliding. The brittle fractures found in Yamato Basin basement Hole 794D cores comprise joints, faults, and veins filled with chlorite-saponite, saponite, and calcite. They suggest a likely transpressive to transtensional regime around the early Miocene/ middle Miocene boundary, with a north-northeast-south-southwest compression alternating with a west-northwest-eastsoutheast extension. The faults from Site 799 cores on the Yamato Rise exhibit a prominent early Miocene-middle Miocene extensional environment, a late Miocene-early Pliocene phase of normal and strike-slip faulting, and a final phase that began during the latest Pliocene. Site 798, on the Oki Ridge, reveals faults that recorded a consistent extensional tectonic regime from Pliocene to the Holocene. These data support the pull-apart kinematic model for early Miocene-middle Miocene time, as regarding the stress regime deduced from the Yamato Basin basement fractures. The recent compression known in the eastern margin of the Japan Sea was not documented by compressive structures at any site. The late Miocene-early Pliocene faulting phase corresponds to a major and general reorganization of the stress distribution in the arc area. Evidence for rapid and main subsidence and synsedimentary extension of the Yamato Basin and Yamato Rise areas between 20 and 15 Ma, and the concomitant rotation of southwest Japan, raise the question of links between this opening and the Shimanto Belt collision in southwest Japan, between the arc and the Philippine Sea Plate.

An investigation of the effectiveness of existing bridge design methodology in providing adequate structural resistance to seismic disturbances : Phase III, Nonlinear soil-structure interaction of skew highway bridges : final report : prepared for Federal Highway Administration, Offices of Research and Development /

Bibliography: p. 46-48.

An independent sector assessment of the Job Training Partnership Act : phase I, the initial transition /

Cover title.

Global changes in gene expression observed at the transition from growth to stationary phase in Listeria monocytogenes ScottA batch culture

Listeria monocytogenes is a food-borne Gram-positive bacterium that is responsible for a variety of infections (worldwide) annually. The organism is able to survive a variety of environmental conditions and stresses, however, the mechanisms by which L. monocytogenes adapts to environmental change are yet to be fully elucidated. An understanding of the mechanism(s) by which L. monocytogenes survives unfavourable environmental conditions will aid in developing new food processing methods to control the organism in foodstuffs. We have utilized a proteomic approach to investigate the response of L. monocytogenes batch cultures to the transition from exponential to stationary growth phase. Proteomic analysis showed that batch cultures of L. monocytogenes perceived stress and began preparations for stationary phase much earlier (approximately A(600) = 0.75, mid-exponential) than predicted by growth characteristics alone. Global analysis of the proteome revealed that the expression levels of more than 50% of all proteins observed changed significantly over a 7-9 h period during this transition phase. We have highlighted ten proteins in particular whose expression levels appear to be important in the early onset of the stationary phase. The significance of these findings in terms of functionality and the mechanistic picture are discussed.

Structural change in macroeconomic time series: A complex systems perspective

We demonstrate that the process of generating smooth transitions Call be viewed as a natural result of the filtering operations implied in the generation of discrete-time series observations from the sampling of data from an underlying continuous time process that has undergone a process of structural change. In order to focus discussion, we utilize the problem of estimating the location of abrupt shifts in some simple time series models. This approach will permit its to address salient issues relating to distortions induced by the inherent aggregation associated with discrete-time sampling of continuous time processes experiencing structural change, We also address the issue of how time irreversible structures may be generated within the smooth transition processes. (c) 2005 Elsevier Inc. All rights reserved.

Deindustrialisation:lessons from the structural outcomes of post-Communist transition

Theoretical and empirical studies show that deindustrialisation, broadly observed in developed countries, is an inherent part of the economic development pattern. However, post-communist countries, while being only middle-income economies, have also experienced deindustrialisation. Building on the model developed by Rowthorn and Wells (1987) we explain this phenomenon and show that there is a strong negative relationship between the magnitude of deindustrialisation and the efficiency and consistency of market reforms. We also demonstrate that reforms of the agricultural sector play a significant role in placing a transition country on a development path that guarantees convergence to EU employment structures.

Deindustrialisation and structural change during the post-Communist transition

The aim of this paper is to model the evolution of employment structure in post-communist economies in the broader context of deindustrialisation. The paper builds on the model of structural change developed by Rowthorn and Wells (1987). We show that the starting point of high industry sector share in total employment and its direct fall when productivity of sectors changes in favour of services can be explained in terms of this framework. Moreover, the model can also describe the phenomenon of a further expansion of the agriculture, observed in countries classified as "less consistent" in the reforms implementation. Hence, we distinguish two development paths, the efficient one, called "horizontal", and the inefficient one called "vertical". We illustrate it with empirical data, using alternative measures of structural change and patterns of structural evolutions during transition. Finally, we discuss the link between the EBRD indicators of reforms and structural change. We show that the "quality" of reforms, not the initial GDP level determines a country's development path.

Structural Characterization of Metal Hydrides for Energy Applications

Hydrogen can be an unlimited source of clean energy for future because of its very high energy density compared to the conventional fuels like gasoline. An efficient and safer way of storing hydrogen is in metals and alloys as hydrides. Light metal hydrides, alanates and borohydrides have very good hydrogen storage capacity, but high operation temperatures hinder their application. Improvement of thermodynamic properties of these hydrides is important for their commercial use as a source of energy. Application of pressure on materials can have influence on their properties favoring hydrogen storage. Hydrogen desorption in many complex hydrides occurs above the transition temperature. Therefore, it is important to study the physical properties of the hydride compounds at ambient and high pressure and/or high temperature conditions, which can assist in the design of suitable storage materials with desired thermodynamic properties. ^ The high pressure-temperature phase diagram, thermal expansion and compressibility have only been evaluated for a limited number of hydrides so far. This situation serves as a main motivation for studying such properties of a number of technologically important hydrides. Focus of this dissertation was on X-ray diffraction and Raman spectroscopy studies of Mg2FeH6, Ca(BH4) 2, Mg(BH4)2, NaBH4, NaAlH4, LiAlH4, LiNH2BH3 and mixture of MgH 2 with AlH3 or Si, at different conditions of pressure and temperature, to obtain their bulk modulus and thermal expansion coefficient. These data are potential source of information regarding inter-atomic forces and also serve as a basis for developing theoretical models. Some high pressure phases were identified for the complex hydrides in this study which may have better hydrogen storage properties than the ambient phase. The results showed that the highly compressible B-H or Al-H bonds and the associated bond disordering under pressure is responsible for phase transitions observed in brorohydrides or alanates. Complex hydrides exhibited very high compressibility suggesting possibility to destabilize them with pressure. With high capacity and favorable thermodynamics, complex hydrides are suitable for reversible storage. Further studies are required to overcome the kinetic barriers in complex hydrides by catalytic addition. A comparative study of the hydride properties with that of the constituting metal, and their inter relationships were carried out with many interesting features.^

Origin of scale-free intermittency in structural first-order phase transitions

16 pages, 22 figures

The structural and piezoresponse properties of c-axis-oriented Aurivillius phase Bi5Ti3FeO15 thin films deposited by atomic vapor deposition

The deposition by atomic vapor deposition of highly c-axis-oriented Aurivillius phase Bi 5Ti 3FeO 15 (BTFO) thin films on (100) Si substrates is reported. Partially crystallized BTFO films with c-axis perpendicular to the substrate surface were first deposited at 610°C (8 excess Bi), and subsequently annealed at 820°C to get stoichiometric composition. After annealing, the films were highly c-axis-oriented, showing only (00l) peaks in x-ray diffraction (XRD), up to (0024). Transmission electron microscopy (TEM) confirms the BTFO film has a clear layered structure, and the bismuth oxide layer interleaves the four-block pseudoperovskite layer, indicating the n 4 Aurivillius phase structure. Piezoresponse force microscopy measurements indicate strong in-plane piezoelectric response, consistent with the c-axis layered structure, shown by XRD and TEM.

Physical and chemical kinetics of structural build-up of cement suspensions

Abstract : The structural build-up of fresh cement-based materials has a great impact on their structural performance after casting. Accordingly, the mixture design should be tailored to adapt the kinetics of build-up given the application on hand. The rate of structural build-up of cement-based suspensions at rest is a complex phenomenon affected by both physical and chemical structuration processes. The structuration kinetics are strongly dependent on the mixture’s composition, testing parameters, as well as the shear history. Accurate measurements of build-up rely on the efficiency of the applied pre-shear regime to achieve an initial well-dispersed state as well as the applied stress during the liquid-solid transition. Studying the physical and chemical mechanisms of build-up of cement suspensions at rest can enhance the fundamental understanding of this phenomenon. This can, therefore, allow a better control of the rheological and time-dependent properties of cement-based materials. The research focused on the use of dynamic rheology in investigating the kinetics of structural build-up of fresh cement pastes. The research program was conducted in three different phases. The first phase was devoted to evaluating the dispersing efficiency of various disruptive shear techniques. The investigated shearing profiles included rotational, oscillatory, and combination of both. The initial and final states of suspension’s structure, before and after disruption, were determined by applying a small-amplitude oscillatory shear (SAOS). The difference between the viscoelastic values before and after disruption was used to express the degree of dispersion. An efficient technique to disperse concentrated cement suspensions was developed. The second phase aimed to establish a rheometric approach to dissociate and monitor the individual physical and chemical mechanisms of build-up of cement paste. In this regard, the non-destructive dynamic rheometry was used to investigate the evolutions of both storage modulus and phase angle of inert calcium carbonate and cement suspensions. Two independent build-up indices were proposed. The structural build-up of various cement suspensions made with different cement contents, silica fume replacement percentages, and high-range water reducer dosages was evaluated using the proposed indices. These indices were then compared to the well-known thixotropic index (Athix.). Furthermore, the proposed indices were correlated to the decay in lateral pressure determined for various cement pastes cast in a pressure column. The proposed pre-shearing protocol and build-up indices (phases 1 and 2) were then used to investigate the effect of mixture’s parameters on the kinetics of structural build-up in phase 3. The investigated mixture’s parameters included cement content and fineness, alkali sulfate content, and temperature of cement suspension. Zeta potential, calorimetric, spectrometric measurements were performed to explore the corresponding microstructural changes in cement suspensions, such as inter-particle cohesion, rate of Brownian flocculation, and nucleation rate. A model linking the build-up indices and the microstructural characteristics was developed to predict the build-up behaviour of cement-based suspensions The obtained results showed that oscillatory shear may have a greater effect on dispersing concentrated cement suspension than the rotational shear. Furthermore, the increase in induced shear strain was found to enhance the breakdown of suspension’s structure until a critical point, after which thickening effects dominate. An effective dispersing method is then proposed. This consists of applying a rotational shear around the transitional value between the linear and non-linear variations of the apparent viscosity with shear rate, followed by an oscillatory shear at the crossover shear strain and high angular frequency of 100 rad/s. Investigating the evolutions of viscoelastic properties of inert calcite-based and cement suspensions and allowed establishing two independent build-up indices. The first one (the percolation time) can represent the rest time needed to form the elastic network. On the other hand, the second one (rigidification rate) can describe the increase in stress-bearing capacity of formed network due to cement hydration. In addition, results showed that combining the percolation time and the rigidification rate can provide deeper insight into the structuration process of cement suspensions. Furthermore, these indices were found to be well-correlated to the decay in the lateral pressure of cement suspensions. The variations of proposed build-up indices with mixture’s parameters showed that the percolation time is most likely controlled by the frequency of Brownian collisions, distance between dispersed particles, and intensity of cohesion between cement particles. On the other hand, a higher rigidification rate can be secured by increasing the number of contact points per unit volume of paste, nucleation rate of cement hydrates, and intensity of inter-particle cohesion.