Types Of Structural Changes Research Articles

Cation field strength effects on high pressure aluminosilicate glass structure: Multinuclear NMR and La XAFS results

We examined aluminosilicate glasses containing a variety of network modifying to intermediate cations (Li, La, Sc, and Fe), quenched from melts at 1 atm to 8 GPa, to further investigate the role of cation field strength in Al coordination changes and densification. 27Al Nuclear Magnetic Resonance Spectroscopy (NMR) reveals that the mean Al coordination increases with increasing pressure in the Li-containing glasses, which can be explained by a linear dependence of fractional change in Al coordination number on cation field strengths in similar K-, Na-, and Ca-containing aluminosilicate glasses (K < Na < Li < Ca). Measured recovered densities follow a similar linear trend. In contrast, the La-containing glasses have significantly lower mean Al coordination numbers at given pressures than the cation field strength of La and glass density would predict. La L 3 X-ray absorption fine structure (XAFS) spectroscopy results indicate a significant increase with pressure in average La–O bond distances, suggesting that La and Al may be “competing” for higher coordinated sites and hence that both play a significant role in the densification of these glasses, especially in the lower pressure range. However, in Na aluminosilicate glasses with small amounts of Sc, 45Sc NMR reveals only modest Sc coordination changes, which do not seem to significantly affect the mean Al coordination values. For a Li aluminosilicate glass, 17O MAS and multiple quantum magic angle spinning (3QMAS) NMR data are consistent with generation of more highly coordinated Al at the expense of non-bridging oxygen (NBO), whereas La aluminosilicate glasses have roughly constant O environments, even up to 8 GPa. Finally, we demonstrate that useful 23Na and 27Al MAS NMR spectra can be collected for Ca–Na aluminosilicate glasses containing up to 5 wt.% Fe oxide. We discuss the types of structural changes that may accompany density increases with pressure and how these structural changes are affected by the presence of different cations.

Statistical pattern recognition for Structural Health Monitoring using time series modeling: Theory and experimental verifications

Statistical pattern recognition methodologies have gained considerable attention for Structural Health Monitoring (SHM) applications to detect changes in a structure (e.g. damage). For most of such applications, outlier analysis of the damage sensitive features obtained from the SHM data is used to detect the changes in the structure. There are a number of different approaches used by different research groups and it is widely accepted that success of a certain methodology may depend on the structure and/or structural change to be identified. Therefore, it is very important that promising methodologies are verified by using different test structures and damage cases. The main objective of this study is to investigate statistical pattern recognition methods in the context of SHM using different laboratory structures. Time series modeling, i.e. auto-regressive models, is used in conjunction with Mahalanobis distance-based outlier detection algorithms to identify different types of structural changes on different test structures. Similar approaches were reported in the literature but here the methodology is modified by using random decrement functions to eliminate the effects of the exogenous input. Then a number of tests are conducted by using two different test structures in laboratory conditions in order to evaluate the results in a comparable fashion. The first test specimen is a simply supported steel beam where the second structure is a highly redundant steel grid structure. Various damage conditions are simulated by using these structures. The ambient vibration data is analyzed by using the methodology described and results are presented. Finally, the advantages and drawbacks of the methodology are discussed in the light of experimental results.

Productivity growth and structural change in Chinese manufacturing, 1980-2002

This article focuses on the contribution of structural change to aggregate manufacturing and industrial productivity in China. Using shift-share techniques, this article examines three types of structural change: changes in the sectoral structure of production, changes in the ownership structure, and changes in the regional structure of production. Overall productivity growth was slow in the 1980s, but accelerated dramatically from 1990 onwards. In 1980s, we found evidence of a structural change bonus, with sectoral shifts contributing 24% to overall productivity growth. However, when productivity growth accelerated in the 1990s, the contribution of the shift effect dropped to a mere 3.3%. In contrast to sectoral changes, changes in the ownership structure in the early 1980s contributed negatively to overall productivity growth. The contributions of ownership change turned positive after 1985, reaching 23% of productivity growth in the period 1992-1997. Shifts in ownership explain a substantial part of productivity growth during the productivity boom. Like shifts in ownership, regional shifts initially contributed negatively to productivity growth till 1992, and positively thereafter. However, the general contribution of regional shifts is lower than the contributions of sectoral and ownership shifts. Contrary to initial expectations, the regional analysis of productivity trends does not indicate regional divergence.

Effects of Acidification with and without Rennet on a Concentrated Casein System: A Kinetic NMR Probe Diffusion Study

The self-diffusion coefficients of 620 and 96 750 g/mol poly(ethylene glycol) (PEG) were measured by pulsed field gradient (PFG)-NMR throughout the coagulation processes of a concentrated casein suspension induced by acidification alone and with the concomitant action of chymosin. The diffusion of water molecules was also investigated during the acidification process. In all experiments, the diffusion coefficient of the molecule studied was modified nonlinearly, and the precise moments at which its evolution changed corresponded to key stages of both coagulation processes. These variations were not directly related to sol−gel transitions as revealed by rheological measurements but were caused by other types of structural changes in the sample whatever its viscoelastic state (solution or gel). The diffusion of the large PEG was very sensitive to variations in the size of the casein particles and the casein aggregates constituting the network before and after gelation, respectively. In contrast, the diffusi...

Transformation of gold by shearing at high pressure and at room temperature

Structures of solids sheared at high pressure are not always the same as those sheared at high-hydrostatic pressure. The structure of the former remains at atmospheric pressure. Therefore, there is a hope of making new materials that can be used at ambient conditions by shearing solids at high pressure. The main purpose of this paper is to present gold formed by shearing at high pressure and at room temperature. This gold has larger crystal lattices than those of usual gold. This phenomenon is against the accepted idea that crystal lattices contract at high pressure and that gold does not transform; interplanar spacings of many solids have been determined by comparing those of “untransformable” and unoxidizable gold. The only possible explanation for the enlarging of the crystal lattices is the embedding of gold atoms into usual gold crystal lattices. This type of structural change by deformation has not yet been reported.

The joint determination of the number and the type of structural changes

This note suggests the use of information criteria to jointly determine the number and the type of multiple structural changes. The simulation evidence shows that the Bayesian information criterion is consistent and has good finite sample performance for various model specifications.

The environmental impact of changing logistics structures

PurposeThis paper seeks to address how firms may contribute to environmental improvement through structural changes of their logistics systems.Design/methodology/approachA comprehensive literature review discloses the low interest that has been directed to environmental issues in logistics, and findings relevant for structural issues at a firm level are described. Three cases where firms have implemented different types of structural changes to their logistics systems support the analysis.FindingsA range of different measures to succeed in environmental as well as logistics performance are presented, comprising types of consolidation, logistics standardisation, and IS/IT solutions allowing a vast restructuring of logistics systems.Originality/valueThe discussion about logistics and the environment has mostly revolved around more environmental friendly technological solutions, concerning single firms as well as governmental support for technology development. The structural, more organisational issues, have been addressed on a societal level, where solutions concern infrastructure. There is a need to reduce the amount of transport in general. The paper discusses how logistics systems' environmental performance can be improved simultaneously with a non‐reduction of logistics performance in terms of costs and delivery service.

The Performance of Structural Change Tests

This paper provides analytical and Monte Carlo studies of the effect of different types of structural change (residual variance, process mean and process persistence) on the performance of the Chow/Wald stability test. We focus on the first-order autoregressive model, which has been used to estimate and assess changes in inflation persistence. Our results show that the autoregressive model is a difficult subject for the Chow test.

Molecular Dynamics Study on Microscopic Mechanism for Stress Induced Phase Transformation of Ni-Ti Alloy

Ni-Ti alloy, one of well-known shape memory alloys, attracts attention by their functional advantages in thin films or their nanostructures. Stress induced martensitic transformation (SIMT) is recognized as a principal deformation mechanism, while its atomistic view on nucleation or prematensitic transformation is left unrevealed. Therefore, we computationally investigate microscopic mechanism of SIMT in Ni-Ti alloy using molecular dynamics simulation (MDS) with embedded atom metod (EAM) potential function. The Ni-Ti simulation model consisted of 19 404 atoms and surrounded by free surfaces is subjected to loading and unloading with appropriate structural relaxations. To identifying crystalline phase changes from B 2 (parent) to B 19' (martensite) in the alloy under loading, we monitor lattice parameters, ratio of two lattice parameters, and their angles from instantaneous atomic positions. We define the martensite phase by specifying possible combination of the parameters according to literatures. In loading process, with rapid stress descent, the MDS model deforms and shows maximal ratio of martensite phase. We find that there are two major paths of atomic configurational change from B 2 to B 19' in these martensite structures and there is also another kind of long-range atomic migration whose distance is larger than single lattice constant. The separation into these multiple paths is caused by discrepancy in angles between interatomic connecting line in unitcell and the tensile direction. It is also find that each paths have characteristic activation energies during configurational change (i.e. during phase transformation). It is ensured that SIMT is microscopically constructed by various types of structural changes and their energetics.

Sub-picosecond ultraviolet laser filamentation-induced bulk modifications in fused silica

We present experiments with sub-picosecond ultraviolet laser pulses (248 nm, 450 fs) tightly focused in the bulk of fused-silica samples. The high laser intensities attained generate plasma through multi-photon absorption and electron avalanche processes in the bulk of the material. Depending on the initial experimental conditions three distinct types of structural changes in the material are observed, from small changes of the refractive index to birefringence, and even cracks and voids. We also observe the creation of micro-channels, up to 115 μm in length, inside the material due to self-guiding and filamentation of the laser pulses in the transparent material. The selective change of the refractive index is a promising method for the fabrication of photonic structures such as waveguides and three-dimensional integrated optical devices.

A Formal Representation of Hybrid Mobile Components

The Heterogeneous Flow System Specification (HFSS) is a modeling formalism that represents hybrid simulation components in a modular and hierarchical form. The HFSS formalism exploits the hierarchical aspects of modeling by permitting the representation of dynamic structure components. An important type of structural change involves the migration of a component between two models. This type of component is called a mobile component. Component mobility provides a natural representation for many complex systems composed of dynamic entities that move between places, providing a representation that structurally mimics the reality. The author identifies the key operations to support component mobility—namely, the ability to remove a component; transmit the component through a channel, possibly with some time delay; and restore the component at the destination. The author shows how mobile components can be used to represent mobile agents, a network technology that involves the migration of software units between computers through a computer network.

Spatio-temporal change-point modeling

There is by now a substantial literature on spatio-temporal modeling. However, to date, there exists essentially no literature which addresses the issue of process change from a certain time. In fact, if we look at change points for purely time series data, the customary form is to propose a model involving a mean or level shift. We see little attempting to capture a change in association structure. Part of the concern is how to specify flexible ways to bridge the association across the time point and still ensure that a proper joint distribution has been defined for all of the data. Introducing a spatial component evidently adds further complication. We want to allow for a change-point reflecting change in both temporal and spatial association. In this paper we propose a constructive, flexible model formulation through additive specifications. We also demonstrate how computational concerns benefit from the availability of temporal order. Finally, we illustrate with several simulated datasets to examine the capability of the model to detect different types of structural changes.

Distinguishing effects of structure and decay on attachment and repair: A cue-based parsing account of recovery from misanalyzed ambiguities

This paper presents the cue-based retrieval theory of parsing and reanalysis and illustrates how this account can accommodate a number of key results about parsing and reanalysis, including effects due to structure, distance, and type of structural change. Three offline experiments and one online experiment permit establishing the locus of these effects as due to properties of the initial parsing processes or to the repair mechanism. Specifically, the data reported here suggest that a structural factor specific to the operation of the parser, retrieval interference, affects attachment uniformly across ambiguous and unambiguous sentences and serves to create a limit on successful repair. In addition, these experiments suggest that distance of the head of an ambiguous phrase from its disambiguator affects repair processes—and not attachment processes—independently of the interference effect. These results are interpreted with respect to alternative models of reanalysis, which are contrasted with the cue-based retrieval account, which requires no distinct repair mechanism to account for the current results. A further contribution of this article is to suggest a statistical correction for individual variance in reading rates. Statistical analyses on individual subject data confirmed previous speculations regarding a possible increase in reading rates as subjects move through a sentence. While this individual variation limits fair comparisons of reading times in sentence regions that appear in non-identical serial positions, we demonstrate that such comparisons become meaningful when the appropriate regression analyses have been performed.

Effect of hydrogen charging on the microstructure of duplex stainless steel

The influence of hydrogen on the microstructure of austenitic–ferritic stainless steel was investigated. Thin foils of this steel subjected to cathodic hydrogen charging were examined using transmission electron microscopy. The effect of hydrogen charging time on the microstructure evolution was studied. The characteristic evolution of the α and γ phases microstructures were observed. The microstructural transformations in the γ phase consist of an increase of the number of stacking faults and dislocation density. Another specific type of structural changes was revealed in the α phase by electron diffraction. The hypothesis of ferrite strong grain refinement was considered. It is suggested that the character of the interphase boundary affects the mode of cracking. Possible explanations of the effects observed are discussed.

Basic Types of Structural Changes in the Leaf Mesophyll during Adaptation of Eastern Pamir Plants to Mountain Conditions

Quantitative characteristics of mesophyll structure were compared in leaves of eleven alpine plant species grown under natural conditions in the Eastern Pamirs at various altitudes, from 3800 to 4750 m. Basic types of changes in mesophyll structure, associated with plant adaptation to mountain conditions, were characterized. These changes manifested themselves in different numbers of cell layers and cell sizes in the palisade tissue and, as a consequence, in changed leaf thickness and cell number per unit of leaf area. Three plant groups were identified by the changes in the leaf structural characteristics depending on the type of mesophyll structure, ecological group of plant species, and altitude of plant habitat. The first group comprised alpine xerophytes with an isopalisade structure, in which the volume of palisade cells decreased and their number per unit of leaf area increased with the altitude of plant habitat. The number of mesophyll layers and leaf thickness decreased or did not change with altitude. The second group comprised subalpine plant species with a dorsoventral structure of mesophyll; these species occur below the line of continuous night frost. In these plant species, the number of mesophyll layers, leaf thickness, and cell number per unit of leaf area increased with altitude. The third group comprised mesophyte plants with a dorsoventral and homogenous mesophyll structure, which are encountered in a wide range of habitats, including the nival belt (from 4700 to 5000 m). In this group, cell volume increased and cell number per unit of leaf area decreased with altitude. We present a general scheme of leaf structural changes, which explains the changes in the quantitative characteristics of mesophyll as a function of altitude and highland environmental conditions.

Mg-nucleotides induced dissociation of liposome-bound creatine kinase: reversible changes in its secondary structure and in the fluidity of the bilayer.

MgADP binding to mitochondrial creatine kinase (mtCK) adsorbed on liposomes was induced by the photorelease of caged ADP. The nucleotide binding produced two types of structural changes. One was related to the well-established release of mtCK from the liposomes. The other corresponded to reversible structural changes induced by nucleotide binding to mtCK as demonstrated here. Infrared spectroscopy data show that the MgADP-induced desorption of mtCK from vesicles led to a slight increase in alpha-helix structures in mtCK at the expense of a small decrease in beta-sheet structures and a concomitant increase in the fluidity of the membranes. The desorption of mtCK induced by MgADP and MgATP was almost complete, as shown by centrifugation and enzymatic activity measurements. The photorelease of MgADP in a reactive medium containing phosphocreatine and mtCK associated with liposomes led to nucleotide binding and to the formation of MgATP and creatine. Addition of phosphocreatine also desorbed mtCK from liposomes, while addition of creatine did not. Interpretation of these results would suggest that ADP, ATP or phosphocreatine induce the release of mtCK from membranes, increase the phospholipid bilayer fluidity, and may also decrease the number of contact sites between inner and outer mitochondrial membranes, thus affecting the activity of other mitochondrial enzymes. It is tempting to propose that membrane mtCK binding regulation by nucleotide and PCr concentrations may serve as a physiological adaptation for energy supply.

Evidence of a Order-Disorder Transition in the Crystalline Phase of Cd6Yb, 1/1 cubic approximant of icosahedral Cd 5.7 Yb

ABSTRACTThe electrical and thermal transport properties (electrical resistivity, thermopower, heat capacity and thermal conductivity) of the crystalline phase of the binary Cd6Yb system has been measured over a temperature range from 10 K to 300 K. Evidence for a phase transition in Cd6Yb is observed in the electrical transport properties with distinct changes in the temperature dependence of the resistivity and thermopower around T ≈ 110K. An anomaly in the heat capacity and a thermal conductivity is also observed at this same temperature. Hysteretic behavior is not evident in the temperature dependence of any of the electrical and thermal transport properties. In addition, the elastic properties using resonant ultrasound (RUS) techniques have been investigated over a similar temperature range. A large “resonance dip” is observed in the RUS data at T ≈ 110K, which is indicative of some type of structural change in the crystalline material at this temperature. These data will be presented and discussed in context of the undergoes reversible order-disorder transition in the 1/1 cubic approximant at about 110 K, which makes the system very interesting compared to the quasicrystal phase Cd5.7Yb

Comparison of volatile emissions and structural changes of melt reprocessed polypropylene resins

AbstractPolypropylene (PP), as a commodity recyclable thermoplastic, was studied in this research to evaluate the potential environmental impact resulting from volatile organic compounds (VOCs) emitted during multiple melt reprocessing. Unstabilized PP (U‐PP) and stabilized PP (S‐PP) resins, simulating recycled materials prone to degradation, were evaluated for total VOC emissions generated during multiple melt reprocessing by injection molding and extrusion, respectively. Results show that the maximum amount of total VOCs from each cycle (up to six cycles for extrusion and up to ten for injection molding) did not significantly change, while the cumulative VOCs increased with increasing processing cycle for both materials. A good correlation between cumulative VOC increases and melt flow index increase for the U‐PP and weight‐average molecular weight Mw decrease for the S‐PP were obtained. Reprocessing in all cases was accompanied by decreases in Mw and melt viscosity as a result of thermooxidative degradation. FTIR data considering increases in carbonyl content and degree of unsaturation suggest that at equivalent cycle numbers, degradation appears to be more severe for the extruded material in spite of the longer oxidative induction time of the “as received” pellets used in extrusion. The onset and type of structural changes are shown to depend on cycle number and reprocessing method. © 2002 Wiley Periodicals, Inc. Adv Polym Techn 21: 235–242, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.10027

An assessment of the staffing structures of university libraries in Ghana

The nature of organisational structure is discussed. A survey is reported comparing the organisational structures of university libraries in Ghana with those of their counterparts in the UK. The discussion covers factors that make changes in present structures necessary and type of structural changes required. Problems are identified and current organisational processes and management style discussed.

Domino mechanisms in photoinduced phase transitions

Photoinduced structural phase transitions via excited electronic states are discussed theoretically using a one-dimensional model composed of localized electrons and lattices under the adiabatic or diabatic approximation. We show that the global structural change by photoexcitation only at a site is possible, and we clarify conditions for the occurrence of such phenomena. Spatiotemporal dynamics of nonequilibrium first-order phase transitions is also investigated in detail in terms of photoinduced nucleations and domino processes of the domain boundaries (domain walls), which are in striking contrast to the mean-field dynamics. In the adiabatic regime, after the spontaneous emission of a photon, an initial local structural change (i) remains locally, (ii) induces cooperatively a global structural change, or (iii) disappears and returns to the initial phase. Dynamical features of the case (ii) are characterized by the deterministic (semichaotic) domino process; domain walls between the two phases move determinis-tically at a constant velocity (with changing speed) without further spontaneous emissions in the case of strong (weak) dissipation. In the diabatic regime, similar three types of structural change exist. The domain-wall dynamics is described as the stochastic domino process, which is accompanied by the successive radiative transitions. A new theoretical treatment is also proposed to study crossover between the adiabatic and diabatic regimes.