Types Of Imperfections Research Articles

Discrete time quantum walks on percolation graphs

Randomly breaking connections in a graph alters its transport properties, a model used to describe percolation. In the case of quantum walks, dynamic percolation graphs represent a special type of imperfections, where the connections appear and disappear randomly in each step during the time evolution. The resulting open system dynamics is hard to treat numerically in general. We shortly review the literature on this problem. We then present our method to solve the evolution on finite percolation graphs in the long time limit, applying the asymptotic methods concerning random unitary maps. We work out the case of one dimensional chains in detail and provide a concrete, step by step numerical example in order to give more insight into the possible asymptotic behavior. The results about the case of the two-dimensional integer lattice are summarized, focusing on the Grover type coin operator.

Surface Defect on Hot Rolled Steel Sheet with Cu Content

Structural steel grades S235JRCCu+N and S355JRCCu+N with 0.25 – 0.35% copper content are intended for products with increased corrosion resistance. They are used for railcar and container bodies. The low copper alloying strongly increases the material life-time in the conditions of atmospheric corrosion. Sheets with fine sharp needle-type bodies on both sheet surfaces were delivered for the analysis. As per the customer information, they were present on almost whole length of on cast strips. Considering the steel copper content, it was assumed that the improper steel alloying was the reason of imperfection. Chemical composition results didn’t confirm this expectation. Metallographic analysis should determine the imperfection origin and decide if copper presence was the primary factor of it. The analyses using SEM coupled with EDS analyzer have shown that the sliver-type defects, few millimeters long bands of ductile iron oxides, were present in very small material depth of about 50 – 150 μm in the analyzed material The bands were formed in more layers parallel to the sheet surface; their thickness was similar to the thickness of surface scales. Oxidic material under the sliver had the same micro-morphology and chemical composition like the scales on the sheet surface. Very fine globular copper particles were randomly and very sporadically present in the layer of ductile oxides in slivers and also in surface scale. Besides this, the material in defect area was chemically homogeneous and no particles were found in the layer boundaries. Copper particles were not detected in the steel basic material; the copper was dissolved in the matrix. The nature of imperfection was typical for V-shaped slivers, caused by overheating sheet surface in reheat furnace. After revising technical conditions of reheat furnace operation, this imperfection type was suppressed.

Optimum design of hierarchical stiffened shells for low imperfection sensitivity

A concept of hierarchical stiffened shell is proposed in this study, aiming at reducing the imperfection sensitivity without adding additional weight. Hierarchical stiffened shell is composed of major stiffeners and minor stiffeners, and the minor stiffeners are generally distributed between adjacent major stiffeners. For various types of geometric imperfections, e.g., eigenmode-shape imperfections, hierarchical stiffened shell shows significantly low imperfection sensitivity compared to traditional stiffened shell. Furthermore, a surrogate-based optimization framework is proposed to search for the hierarchical optimum design. Then, two optimum designs based on two different optimization objectives (including the critical buckling load and the weighted sum of collapse loads of geometrically imperfect shells with small- and large-amplitude imperfections) are compared and discussed in detail. The illustrative example demonstrates the inherent superiority of hierarchical stiffened shells in resisting imperfections and the effectiveness of the proposed framework. Moreover, the decrease of imperfection sensitivity can finally be converted into a decrease of structural weight, which is particularly important in the development of large-diameter launch vehicles.

Robust Control, Informational Frictions, and International Consumption Correlations

In this paper we examine the effects of two types of information imperfections, robustness (RB) and finite information-processing capacity (called rational inattention or RI), on international consumption correlations in an otherwise standard small open economy model. We show that in the presence of capital mobility in financial markets, RB lowers the international consumption correlations by generating heterogeneous responses of consumption to income shocks across countries facing different macroeconomic uncertainty. However, the calibrated RB model cannot explain the observed consumption correlations quantitatively. We then show that introducing RI is capable of matching the behavior of international consumption quantitatively via two channels: (1) the gradual response to income shocks that increases the correlations and (2) the presence of the common noise shocks that reduce the correlations.

Satellite Image Classification and Content-Base Image Retrieval Using Type-2 Fuzzy Logic

The detection of oceanic structures, such as upwelling's or eddies, from satellite images has significance for marine environmental studies, coastal resource management, and ocean dynamics studies. There is a lack of tools that allow us to retrieve automatically relevant structures from large satellite image databases. This Paper focuses on the development and validation of a Content-Based Image Retrieval (CBIR) system to classify and retrieve oceanic structures from satellite images with improved accuracy. The image we obtain from http://oceancolor.gsfc.nasa.gov/, which give images from different satellite like Sea-viewing Wide Field-of-view Sensor (SeaWiFS), Moderate Resolution Imaging Spectroradiometer (MODIS), or MEdium Resolution Imaging Spectrometer (MERIS). During the processing of satellite images, different types of imperfection (uncertainties, ambiguities and vagueness) can occur. These imperfections can involve the gray-level intensities, the geometrical characteristics and relations among image objects, and the expert knowledge itself used to overcome these problems. The CBIR system includes several types of soft computing technologies, such as neural networks and fuzzy logic. An advantage of fuzzy logic approach is that the system can be more comprehensible to human users because fuzzy databases (DBs) manage a terminology close to natural languages. This system give retrieval of most relevant and typical oceanic structures, such as upwelling,

Functional Electron Microscopy for Electrochemistry Research: From the Atomic to the Micro Scale

The operation of batteries, fuel cells, and other energy storage and conversion devices is underpinned by the intricate synergy of ion transport, phase transformations, and electrochemical reactions. While electrochemical processes in well-defined molecular systems are amenable to classical chemical techniques including in situ optical spectroscopies and nuclear magnetic resonance (NMR), phase transformations and reactivity in solids and at solid interfaces remain largely an enigma. The presence of multiple types of structural defects and imperfections, competing electron and ion transport pathways, and multiple possible surface reconstruction types, combined with the directionality of ion flows and state of charge transformation fronts render these phenomena inaccessible to macroscopic interrogation techniques. At the same time, knowledge of the individual mechanisms involved in electrochemical reactivity of solids at the level of individual, atomic size structural elements is required for understanding the fundamental mechanisms of energy storage, factors controlling charge/discharge rates, degradation and failure processes, and ultimately knowledge-driven prediction and optimization of energy materials. 1-3

Construction of Microsatellite-Enriched Library and Isolation of Icrosatellite Markers in Stevia rebaudiana

Stevia is one of important special crops in China, but its genetic background about molcular markers is known a little so far. Based on the principle of the strong affinity between biotin and streptavidin, we used streptavidin paramagnetic particles to catch a synthetic oligonucletide probe(AG)15 during an indirect selection from the genomic microsatellite sequence of restriction fragments of DNA in Stevia rebaudiana. The enriched DNA fragments were ligated to the pUC-T vector to construct a S. rebaudiana microsatellite sequence enriched library. From a library of 354 cloned colonies, 158 were screened by PCR examination and the positive clones were sequenced, resulting in 134(84.81%) clones containing microsatellite sequences. Among these microsatellites, 85(64.34%) belonged to the perfect type, 15(11.19%) to the imperfect type and 34(25.38%) to the compound type. From the primers designed for the 71 microsatellite loci, 62 could amplify stable PCR products. An analysis of individual genetic diversity of the 62 pairs primers using 24 S. rebaudiana varieties showed 16 loci had polymorphism and the number of alleles at each locus ranged from two to eight. The average site amplified 4.5 alleles and the polymorphic information content ranged from 0.3163 to 0.7595. The observed heterozygosity(Ho) varied from 0.2174 to 0.9167 and the expected heterozygosity(He) varied from 0.3555 to 0.8076. By clustering analysis, S. rebaudiana were divided into two categories. The microsatellite markers developed at this study could provide useful genetic markers for molecular breeding of S. rebaudiana.

Metal-oxide surge arrester monitoring and diagnosis by self-organizing maps

The main metal-oxide surge arrester are usually monitored by measuring the total leakage current and decomposing it into a capacitive component and a resistive component. However, these techniques present some limitations which make their implementation in the field quite difficult. This paper describes a monitoring technique based on classifying the harmonic characteristics of the leakage current. Self-organizing maps have been used in the classification process. Several station classes arresters were tested in the laboratory and their leakage current signals were recorded. Six different types of artificial imperfections were created in the arresters in order to assess the technical capability to discriminate arresters operating under different field conditions. The self-organizing maps are able to identify defective arresters with certainty of almost 98%. The results show that the technique is feasible for monitoring the condition of metal-oxide surge arresters.

Non-linear Ultrasonic NDE of Titanium Diffusion Bonds

Diffusion bonding is an attractive solid-state welding technique that represents a valuable tool for reducing weight and improving performance in the aerospace industry. However, its full exploitation in titanium components is currently limited by a lack of robust NDE techniques capable of overcoming the crystallographic anisotropy of these important materials. Advanced ultrasonic techniques have been explored previously, but their sensitivity to imperfections is limited by the linear acoustic phenomena on which they depend. Non-linear ultrasonic methods have been shown to be significantly more sensitive than their linear counterparts to these types of imperfections, but suppressing extraneous contributions to the non-linear response of the interface is not trivial. An approach that succeeds in suppressing such contributions is presented here. The technique, which is based on the non-collinear mixing of ultrasonic waves to generate a spectrally, modally and spatially dissociable third wave, was used to reliably characterise a set of samples whose bond quality was indeterminable using conventional ultrasonic methods.

Distribution Characteristics of the Remaining Oil of Putaohua Oil Layer in Pubei Oil Field of Songliao Basin

A comprehensive analysis has been made for the remaining oil of Putaohua oil layer in Pubei oil field of Songliao basin by using core and logging and dynamic data. It is considered that it’s distribution is controlled by positive structures, lateral fault seal, sedimentary microfacies and pattern matching of ‘fault-sand’. The forward fault trap and the top of internal micro-structures on the edge of fault block control the position of the enrichment of remaining oil; lateral fault seal affects the level of the enrichment of the remaining oil; the underwater distributary channel of shallow water delta and the main sheet sand constitute the remaining oil reservoir unit; pattern matching of fault and sand determines the rich layer of remaining oil. On the basis of the above study, four types of remaining oil has been established: fault edge screened type, top of micro-structures type, injection-production imperfection type and anisotropism of sheet sand. Different programs for different situations are proposed: inclined well for fault edge screened type, infilled straight well for top of micro-structures type, horizontal well for injection-production imperfection type, well fracturing for anisotropism sheet sand.

Broadband Laser-Ultrasonic Spectroscopy for Quantitative Characterization of Porosity Effect on Acoustic Attenuation and Phase Velocity in CFRP Laminates

This work aims at applying the method of broadband laser-ultrasonic spectroscopy for quantitative evaluation of the effect of isolated dispersed voids and additional extended interply delaminations on the acoustic attenuation and on the phase velocity in CFRP laminates. This method is based on the laser thermoelastic generation of broadband reference pulses of longitudinal ultrasonic waves in the specially designed source of ultrasound. The high-sensitivity piezoelectric transducer is used to detect these pulses propagating normal to the fiber plies in composite specimens. The laminate specimens investigated have different total porosity levels up to 10.5 % determined by the X-ray computer tomography. The resonance peak of the attenuation coefficient and the corresponding jump of the phase velocity are observed governed by the periodic layered structure of the specimens. The absolute maximum and the frequency bandwidth of the resonance attenuation peak depend on the total porosity level formed by the predominant type of imperfections, either of isolated spheroidal voids entrapped in epoxy layers or of extended interply delaminations. With an increase of the specimen’s total porosity dispersion of the phase velocity becomes noticeable in the low-frequency band before the resonance jump. The derived empirical relations between the total porosity level and the parameters of the frequency dependencies of the ultrasonic attenuation coefficient and of the phase velocity can be used for rapid quantitative characterization of the structure of CFRP laminates subject to different fabrication conditions.

Failures in Urban Capital Markets and Consequences for Project Funding

Public authority interventions are a justified means to remedy market failures. We apply this idea in the context of urban development projects by analysing the three main market imperfections, namely external effects, imperfect competition and incomplete information. For (combinations of) the three types of imperfections, we derive whether funding is appropriate at all and which are suitable types of funding – either grants or success-dependent measures. Depending on the sensitivity to the respective imperfections, we categorise a range of urban development projects which are suggested to be chosen for Urban Development Funds under the JESSICA initiative. Finally, we suggest a procedure for the general screening of regions suitable for funding through Urban Development Funds.

Energy Absorption of Thin-Walled Square Tubes With a Prefolded Origami Pattern—Part I: Geometry and Numerical Simulation

Thin-walled tubes subjected to axial crushing have been extensively employed as energy absorption devices in transport vehicles. Conventionally, they have a square or rectangular section, either straight or tapered. Dents are sometimes added to the surface in order to reduce the initial buckling force. This paper presents a novel thin-walled energy absorption device known as the origami crash box that is made from a thin-walled tube of square cross section whose surface is prefolded according to a developable origami pattern. The prefolded surface serves both as a type of geometric imperfection to lower the initial buckling force and as a mode inducer to trigger a collapse mode that is more efficient in terms of energy absorption. It has been found out from quasi-static numerical simulation that a new collapse mode referred to as the completed diamond mode, which features doubled traveling plastic hinge lines compared with those in conventional square tubes, can be triggered, leading to higher energy absorption and lower peak force than those of conventional ones of identical weight. A parametric study indicates that for a wide range of geometric parameters the origami crash box exhibits predictable and stable collapse behavior, with an energy absorption increase of 92.1% being achieved in the optimum case. The origami crash box can be stamped out of a thin sheet of material like conventional energy absorption devices without incurring in-plane stretching due to the developable surface of the origami pattern. The manufacturing cost is comparable to that of existing thin-walled crash boxes, but it absorbs a great deal more energy during a collision.

Quantitative analysis of the influence of voids and delaminations on acoustic attenuation in CFRP composites by the laser-ultrasonic spectroscopy method

The aim of the present work is to develop the ultrasonic spectroscopy method using laser thermoelastic generation and piezoelectric detection of broadband acoustic pulses for quantitative evaluation of the influence on the ultrasonic attenuation coefficient of microscopic dispersed voids and interply delaminations in CFRP laminates. The specimens under study have different entire porosity values up to 10% determined by the X-ray computer tomography. The ultrasonic attenuation resonance is observed in all specimens governed by their periodic layered structure. The absolute maximum and the frequency bandwidth of the resonance peak depend on the total porosity level formed by the predominant type of imperfections, either of only microscopic spheroidal voids entrapped in the epoxy layers or of additional extended interply delaminations. The derived empirical relations between these parameters and the total porosity level can be used for rapid nondestructive evaluation of the structure of CFRP composite laminates subject to different manufacturing conditions.

Thermal conduction phenomena in carbon nanotubes and related nanostructured materials

The extremely high thermal conductivities of carbon nanotubes have motivated a wealth of research. Progress includes innovative conduction metrology based on microfabricated platforms and scanning thermal probes as well as simulations exploring phonon dispersion and scattering using both transport theory and molecular dynamics. This article highlights these advancements as part of a detailed review of heat conduction research on both individual carbon nanotubes and nanostructured films consisting of arrays of nanotubes or disordered nanotube mats. Nanotube length, diameter, and chirality strongly influence the thermal conductivities of individual nanotubes and the transition from primarily diffusive to ballistic heat transport with decreasing temperature. A key experimental challenge, for both individual nanotubes and aligned films, is the separation of intrinsic and contact resistances. Molecular dynamics simulations have studied the impacts of specific types of imperfections on the nanotube conductance and its variation with length and chirality. While the properties of aligned films fall short of predictions based on individual nanotube data, improvements in surface engagement and postfabrication nanotube quality are promising for a variety of applications including mechanically compliant thermal contacts.

The effect of morphological imperfections on damage in 3D FE analysis of open-cell metal foam core sandwich panels

A 3D FE model of an open-cell aluminium alloy metal foam core sandwich panel subject to uniform compression has been created in ABAQUS to study the effect of varying the foam strut aspect ratio on the elastic properties of the core. A continuum viscoplastic damage model, previously calibrated using microtensile test data for the aluminium alloy’s optimally aged condition in conjunction with X-ray micro-tomography scans of the undeformed struts, was implemented through the user defined subroutine VUMAT. In addition, FE models of the open-cell metal foam core sandwich panel subject to three point and four point bending were produced in accordance with ASTM C-393-00, hence providing a virtual standardised test to assess the foam core elastic properties. These FE models used a tabulated elastic–plastic material model and were employed to verify the implementation of the damage model in the uniform compression FE simulations. The effect of two different types of morphological imperfections – fractured cell walls and missing cells – on the mechanical properties of the foam core was studied for uniform compression. The effect of these imperfections on the extent of visible structural damage of the foam core was studied for indentation loading scenarios indicative of an accidental tool strike under ground repair conditions, which is one important design consideration for potential alternative airplane wing skin materials. The effect of varying the indenter radius on the extent of visible structural damage was also considered so as to capture the influence of varying angles of tool drop impact. The Young’s modulus and shear strength of the foam core experienced a significant knock-down effect under the presence of both fractured cell walls and missing cells. The extent of visible structural damage was largely unaffected by either type of defect or by varying the indenter radius.

A Unified Framework and Sparse Bayesian Perspective for Direction-of-Arrival Estimation in the Presence of Array Imperfections

Self-calibration methods play an important role in reducing the negative effects of array imperfections during direction-of-arrival (DOA) estimation. However, the dependence of most such methods on the eigenstructure techniques greatly degrades their adaptation to demanding scenarios, such as low signal-to-noise ratio (SNR) and limited snapshots. This paper aims at formulating a unified framework and sparse Bayesian perspective for array calibration and DOA estimation. A comprehensive model of the array output is presented first when a single type of array imperfection is considered, with mutual coupling, gain/phase uncertainty, and sensor location error treated as typical examples. The spatial sparsity of the incident signals is then exploited, and a Bayesian method is proposed to realize array calibration and source DOA estimation. The array perturbation magnitudes are assumed to be small according to most application scenarios, and the geometries of mutually coupled arrays are assumed to be uniform linear and those of arrays with sensor location errors are assumed to be linear. Cramer-Rao lower bounds (CRLBs) for the array calibration and DOA estimation precisions are also obtained. The sparse Bayesian method is finally extended to deal with the DOA estimation problem when more than one type of array perturbation coexists.

Locally imperfect conical shells under uniform external pressure

Conical shells are extensively used in numerous types of engineering structures with various types of geometric imperfections. Nonetheless, quite few are the studies investigating the effect of special types of imperfections on the buckling load of conical shells under external pressure. In the present study, depression type of imperfection which is found in the zone of longitudinal weld is in the center of attention. To this end, this paper reports on different simulations including finite element results and discusses the effect of this type of imperfection on the critical buckling load of such structures. Obtained results are compared with the previous corresponding test results, some theoretical predictions, recommendations and codes.

Importance of flexural mode shapes in dynamic analysis of high-speed trains traveling on bridges

The effects of railway car-body flexibility on the dynamic analysis of high-speed trains traveling on bridges are studied. The flexible car-body is modeled as a uniform beam supported by the primary and secondary suspensions. A parametric sensitivity study is carried out to examine the effects of different parameters, namely the track irregularity, rail joint, traveling speed and the wheel flat, on the dynamic responses of the car-body and bridge. The rail surface roughness is regenerated by its power spectral density. Different types of rail joint geometries and wheel imperfections are mathematically modeled and included in the numerical simulation. It is found that the flexural mode shapes of the body structure can remarkably affect the calculated ride comfort index especially in the low frequency range.

On lateral and upheaval buckling of subsea pipelines

The lateral and upheaval buckling of subsea pipelines is investigated in this paper. For lateral buckling, analytical and numerical studies are conducted and compared and a new interpretation of localisation is given based on an isolated half-wavelength model. For upheaval buckling, a tabulated analytical solution based on a long heavy elastic beam resting on a rigid frictional foundation is given and the response under three types of localised initial imperfection is compared. A comparison of the lateral and upheaval responses of a subsea pipeline is made and indicates that excessive bending stress can be induced, particularly under upheaval buckling. The paper also highlights some differences between the current and previously published results.