Engineering Commons^™

An Analysis Of The Barriers To And Drivers Of Green Public Procurement In Achieving A More Sustainable Construction Industry, Myles Keaveney, Paul Butler

Conference papers

The public sector in Ireland possesses enormous purchasing power which has the strength to affect production and consumption trends in all market sectors. Environmental purchasing tools such as Green Public Procurement (GPP) are seen by many as the solution to greener purchasing decisions in order to obtain and maintain not only a more sustainable construction sector but also a more sustainable economy. The purpose of this research is to determine and examine the key barriers to and drivers of implementing GPP in public procurement departments in order to reduce the effect construction works have on the environment. There was limited ...

Design Of Microwave Lowpass Filters Based On Metamaterial Components, Mushtaq Ahmed

Mushtaq A. Alqaisy

No abstract provided.

Impact Of Chain Architecture On The Thickness Dependence Of Physical Aging Rate Of Thin Polystyrene Films, Gregory Brown, Elizabeth Lewis, Bryan D. Vogt

Honors Research Projects

The dynamics of polymer thin films have been demonstrated to be significantly altered from the bulk, but the origins of such differences are not well defined. In this work, we seek to understand the differences in the structural dynamics (or physical aging) of polystyrene (PS) through branching and other well defined architectures (comb and centipede). The aging dynamics of ultrathin films (< 30 nm) differ from relatively thick films (100-150nm) with linear PS thin films aging more rapidly than the relatively “bulk-like” thick films. Ellipsometric measurements are used to characterize the physical aging rate of the films. The change in film thickness and refractive index as the films are held below the glass transition temperature (T_g) provides a simple measure of the physical aging. In this study, four different architectures (linear, comb, 4 arm star, and centipede) will be investigated. For each PS architecture, the aging rate will be determined for film thickness ranging ...

Stability Analysis Of A More General Class Of Systems With Delay-Dependent Coefficients, Chi Jin, Keqin Gu, Islam Boussaada, Silviu-Iulian Niculescu

SIUE Faculty Research, Scholarship, and Creative Activity

This paper presents a systematic method to analyse the stability of systems with single delay in which the coefficient polynomials of the characteristic equation depend on the delay. Such systems often arise in, for example, life science and engineering systems. A method to analyze such systems was presented by Beretta and Kuang in a 2002 paper, but with some very restrictive assumptions. This work extends their results to the general case with the exception of some degenerate cases. It is found that a much richer behavior is possible when the restrictive assumptions are removed. The interval of interest for the ...

Investigation Of Thermoplastic Polymers And Their Blends For Use In Hybrid Rocket Combustion, Spencer D. Mathias

All Graduate Theses and Dissertations

This thesis set out to find a blend of thermoplastics that had better combustion properties than the current ABS (acrylonitrile butadiene styrene) plastic or “Lego ^TM plastic” used by Utah State University. The current work is in an effort to eliminate toxic propellants from small space applications. High and low density polyethylene plastics were used because they are common plastic waste items. In this way rocket fuel can be made from these items to reduce the waste found in landfills. Three plastics were considered for replacement and as mixture components with the ABS plastic, namely low and high density polyethylene ...

Motion-Based Design Approach For A Novel Variable Friction Cladding Connection Used In Wind Hazard Mitigation, Yongqiang Gong, Liang Cao, Simon Laflamme, James Ricles, Spencer Quiel, Douglas Taylor

Civil, Construction and Environmental Engineering Publications

Cladding systems typically serve architectural purposes and protect occupants against the external environment. It is possible to leverage these systems to enhance structural resiliency. A common application is the use of blast resistant panels for enhanced protection against man-made hazards, whereas energy is dissipated through sacrificial elements. However, because these protection systems are passive, their mitigation capabilities are bandwidth limited, therefore targeting single types of hazards. The authors have recently proposed a novel variable friction cladding connection (VFCC), which enables the leveraging of cladding inertia for mitigating blast, wind, and seismic hazards. The variation in the friction force is generated ...

Agen Jual Obat Perangsang Liquid Sex Di Surabaya 085755475693 Obat Bius Di Surabaya, Toko Jakarta

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Slip Of Shuffle Screw Dislocations Through Tilt Grain Boundaries In Silicon, Hao Chen, Valery Levitas, Liming Xiong

Aerospace Engineering Publications

In this paper, molecular dynamics (MD) simulations of the interaction between tilt grain boundaries (GBs) and a shuffle screw dislocation in silicon are performed. Results show that dislocations transmit into the neighboring grain for all GBs in silicon. For Σ3, Σ9 and Σ19 GBs, when a dislocation interacts with a heptagon site, it transmits the GB directly. In contrast, when interacting with a pentagon site, it first cross slips to a plane on the heptagon site and then transmits the GB. The energy barrier is also quantified using the climbing image nudged elastic band (CINEB) method. Results show that Σ3 ...

Critical Analysis Of Case Law: Are Partnering Charters Binding?, Milagros Pinto Nunez, Douglas D. Gransberg

Civil, Construction and Environmental Engineering Publications

Construction project partnering in the United States has been used successfully for nearly 30 years in reducing disputes. Most partnered projects are characterized by the joint development of a nonbinding partnering charter between the owner and the contractor, which encapsulates the project’s goals and lays out the desired process for resolving issues at the lowest level. This paper explores the outcomes when partnered projects fail and the parties involved must turn to the courts to settle their disputes. The paper evaluates the case law for 16 partnered projects through content analysis and cross-case comparison. The paper explores the question ...

Data Evidencing Slow Anaerobic Digestion In Emergency Treatment And Disposal Of Infectious Animal Carcasses, Jacek A. Koziel, Heekwon Ahn, Thomas D. Glanville, Timothy S. Frana, J. (Hans) Van Leeuwen, Lam T. Nguyen

Agricultural and Biosystems Engineering Publications

Burial of infectious and potentially infectious livestock and poultry animals is the most common response to an emergency situation. The data set summarizes 22-week-long experiment that simulates the environment found within conventional burial trenches for emergency disposal of animal carcasses, worldwide, sometimes with a topical application of quicklime as it is required in the Republic of Korea. This data set shows the rarely presented evidence of the extremely slow decay of animal carcasses. Besides visual evidence of no visible breakdown of carcass material, i.e., carcass (or carcass quarters and coarse cuts) still resembled the initial material at the end ...

Stability Of The M2 Phase Of Vanadium Dioxide Induced By Coherent Epitaxial Strain, N. F. Quackenbush, Yijia Gu

Yijia Gu

Tensile strain along the cR axis in epitaxial VO₂ films raises the temperature of the metal insulator transition and is expected to stabilize the intermediate monoclinic M2 phase. We employ surface-sensitive x-ray spectroscopy to distinguish from the TiO₂ substrate and identify the phases of VO₂ as a function of temperature in epitaxial VO₂/TiO₂ thin films with well-defined biaxial strain. Although qualitatively similar to our Landau-Ginzburg theory predicted phase diagrams, the M2 phase is stabilized by nearly an order of magnitude more strain than expected for the measured temperature window. Our results reveal that the ...

Phenomenological Thermodynamic Potential For Catio₃ Single Crystals, Yijia Gu, Karin Rabe, Eric Bousquet, Venkatraman Gopalan, Long-Qing Chen

Yijia Gu

The antiferrodistortive (AFD) structural transitions of calcium titanate (CaTiO₃) at ambient pressure have been extensively studied during the last few years. It has been found that none of the AFD polymorphs is polar or ferroelectric. However, it was recently shown theoretically and later experimentally confirmed that a ferroelectric transition in CaTiO₃ can be induced by tensile strains. The ferroelectric instability is believed to be strongly coupled to the AFD soft modes. In this paper, we present a complete thermodynamic potential for describing the coupling between the AFD and ferroelectric phase transitions. We analyzed the dependence of transition temperatures ...

Universal Emergence Of Spatially Modulated Structures Induced By Flexoantiferrodistortive Coupling In Multiferroics, Eugene A. Eliseev, Sergei V. Kalinin, Yijia Gu, Maya D. Glinchuk, Victoria V. Khist

Yijia Gu

We proved the existence of a universal flexoantiferrodistortive coupling as a necessary complement to the well-known flexoelectric coupling. The coupling is universal for all antiferrodistortive systems and can lead to the formation of incommensurate, spatially modulated phases in multiferroics. Our analysis can provide a self-consistent mesoscopic explanation for a broad range of modulated domain structures observed experimentally in multiferroics.

Origin Of Interfacial Polar Order In Incipient Ferroelectrics, Yijia Gu, Nan Wang, Fei Xue, Long-Qing Chen

Yijia Gu

There are ample experimental evidences indicating that the ferroelastic domain walls of incipient ferroelectrics, such as SrTiO₃ and CaTiO₃, are polar. The emergence of such interfacial polar order at a domain wall is exciting and believed to arise from the coupling between a primary order parameter, such as a strain or an antiferrodistortive (AFD) order parameter, and polarization. There have been several mechanisms proposed to explain the emergence of interfacial polar order, including biquadratic coupling, AFD-antiferroelectric coupling, and flexoelectric coupling. Using CaTiO₃ as an example, we demonstrate, using both asymptotic analytics and numerical calculation, that the flexoelectric ...

Thermodynamics Of Strained Vanadium Dioxide Single Crystals, Yijia Gu, Jinbo Cao, Junqiao Wu, Long-Qing Chen

Yijia Gu

Vanadium dioxide undergoes a metal-insulator transition, in which the strain condition plays an important role. To investigate the strain contribution, a phenomenological thermodynamic potential for the vanadium dioxide single crystal was constructed. The transformations under the uniaxial stress, wire, and thin film boundary conditions were analyzed, and the corresponding phase diagrams were constructed. The calculated phase diagrams agree well with existing experimental data, and show that the transformation temperature (and Curie temperature) strongly depends on the strain condition.

Thermotropic Phase Boundaries In Classic Ferroelectrics, Tom T. A. Lummen, Yijia Gu, Jianjun Wang

Yijia Gu

High-performance piezoelectrics are lead-based solid solutions that exhibit a so-called morphotropic phase boundary, which separates two competing phases as a function of chemical composition; as a consequence, an intermediate low-symmetry phase with a strong piezoelectric effect arises. In search for environmentally sustainable lead-free alternatives that exhibit analogous characteristics, we use a network of competing domains to create similar conditions across thermal inter-ferroelectric transitions in simple, lead-free ferroelectrics such as BaTiO₃ and KNbO₃. Here we report the experimental observation of thermotropic phase boundaries in these classic ferroelectrics, through direct imaging of low-symmetry intermediate phases that exhibit large enhancements in ...

Orientations Of Low-Energy Domain Walls In Perovskites With Oxygen Octahedral Tilts, Fei Xue, Yijia Gu, Linyun Liang, Yi Wang, Long-Qing Chen

Yijia Gu

Many applications of ferroic materials, such as data storage and spintronics, are achieved through the control and manipulation of their domain wall (DW) orientations and configurations. Here we propose a rotational compatibility condition to identify low-energy DWs in perovskites with oxygen octahedral tilt instability. It is derived from the strong DW energy anisotropy arising from the rigidity and corner-sharing feature of the octahedral network. We analyze quantitatively the DWs in SrTiO₃ and explain successfully the unusual ferroelectric DW width and energy in BiFeO₃.

Nanoscale Mechanical Switching Of Ferroelectric Polarization Via Flexoelectricity, Yijia Gu, Zijian Hong, Jason Britson, Long-Qing Chen

Yijia Gu

Flexoelectric coefficient is a fourth-rank tensor arising from the coupling between strain gradient and electric polarization and thus exists in all crystals. It is generally ignored for macroscopic crystals due to its small magnitude. However, at the nanoscale, flexoelectric contributions may become significant and can potentially be utilized for device applications. Using the phase-field method, we study the mechanical switching of electric polarization in ferroelectric thin films by a strain gradient created via an atomic force microscope tip. Our simulation results show good agreement with existing experimental observations. We examine the competition between the piezoelectric and flexoelectric effects and provide ...

Monoclinic Phases Arising Across Thermal Inter-Ferroelectric Phase Transitions, Yijia Gu, Fei Xue, Shiming Lei, Tom T. A. Lummen, Jianjun Wang

Yijia Gu

Thermotropic phase boundaries (TPBs), as thermal analogs of morphotropic phase boundaries (MPBs), are associated with the thermal inter-ferroelectric phase transitions. Similar to an MPB, a TPB exhibits a characteristically flattened energy profile which favors polarization rotation, thus giving rise to a structurally bridging low-symmetry phase. We report on the kinetic process of thermal inter-ferroelectric phase transitions in BaTiO₃ and KNbO₃ using the phase-field method. The domain structures are found to play key roles in stabilizing the monoclinic phase. In simple domain structures, the monoclinic phase is a transient phase and cannot be stabilized into its neighboring phase regimes ...

Flexoelectricity And Ferroelectric Domain Wall Structures: Phase-Field Modeling And Dft Calculations, Yijia Gu, Menglei Li, Anna N. Morozovska, Yi Wang, Eugene A. Eliseev

Yijia Gu

We show that flexoelectric effect is responsible for the non-Ising character of a 180° ferroelectric domain wall. The wall, long considered being of Ising type, contains both Bloch- and Néel-type polarization components. Using the example of classic ferroelectric BaTiO3, and by incorporating the flexoelectric effect into a phase-field model, it is demonstrated that the flexoelectric effect arising from stress inhomogeneity around the domain wall leads to the additional Bloch and Néel polarization components. The magnitudes of these additional components are two or three magnitudes smaller than the Ising component, and they are determined by the competing depolarization and flexoelectric fields ...

Large Kinetic Asymmetry In The Metal-Insulator Transition Nucleated At Localized And Extended Defects, W. Fan, Jinbo Cao, J. Seidel, Yijia Gu, J. W. Yim

Yijia Gu

Superheating and supercooling effects are characteristic kinetic processes in first-order phase transitions, and asymmetry between them is widely observed. In materials where electronic and structural degrees of freedom are coupled, a wide, asymmetric hysteresis may occur in the transition between electronic phases. Structural defects are known to seed heterogeneous nucleation of the phase transition, hence reduce the degree of superheating and supercooling. Here we show that in the metal-insulator transition of single-crystal VO 2, a large kinetic asymmetry arises from the distinct spatial extension and distribution of two basic types of crystal defects: point defects and twin walls. Nanometer-thick twin ...

First-Principles Study Of 180⁰ Domain Walls In Batio₃: Mixed Bloch-Néel-Ising Character, Menglei Li, Yijia Gu, Yi Wang, Long-Qing Chen, Wenhui Duan

Yijia Gu

The 180⁰ ferroelectric domain walls (FDWs) have long been regarded as purely Ising type in ferroelectrics, but recent theoretical works suggested that they can also have Néel- and/or Bloch-like rotations. Using a combination of first-principles calculations with phase-field simulations, we studied the 180⁰ FDWs on different crystallographic planes in prototypical ferroelectric perovskite BaTiO₃. The polarization profiles of 180 FDWs on (100) and (410) planes revealed that the (100)- and (410)-FDWs both exhibit Néel-like character besides their intrinsic Ising character, while the (410)-FDW also simultaneously shows a Bloch-like oblique of ~6 nm, as a consequence of the ...

Low-Symmetry Monoclinic Ferroelectric Phase Stabilized By Oxygen Octahedra Rotations In Strained EuXSr1-XTio₃ Thin Films, Anna N. Morozovska, Yijia Gu, Victoria V. Khist, Maya D. Glinchuk, Long-Qing Chen

Yijia Gu

Using Landau-Ginzburg-Devonshire theory and phase-field modeling, we explore the complex interplay between a structural order parameter (oxygen octahedron rotation) and polarization in Eu_xSr_1-xTiO₃ thin films. Under a biaxially tensile strain, a low-symmetry monoclinic phase with in-plane ferroelectric polarization is found to be stabilized by antiferrodistortive oxygen octahedra tilts. The monoclinic phase is stable over a wide temperature range. It is characterized by a large number of energetically equivalent polar and structural twin domains. This work demonstrates the development of a spontaneous polarization and piezo- and pyroelectricity in a ferroelastic twin boundary arising from flexoelectric coupling ...

Erratum: Orientations Of Low-Energy Domain Walls In Perovskites With Oxygen Octahedral Tilts (Physical Review B - Condensed Matter And Materials Physics (2014) 90 (220101)), Fei Xue, Yijia Gu, Linyun Liang, Yi Wang, Long-Qing Chen

Yijia Gu

In the Acknowledgment of the original article, the Award No. DMR-0820404 should be replaced by DMR-1420620.

Electric Field-Induced Tetragonal To Orthorhombic Phase Transitions In [110]C-Oriented Batio₃ Single Crystals, D. J. Franzbach, Yijia Gu, Long-Qing Chen, K. G. Webber

Yijia Gu

Electric field-induced phase transitions in [110]_c-oriented BaTiO₃ single crystals were studied by macroscopic electrical measurements in the temperature range from 20 °C to 50 °C. Discontinuous, hysteretic jumps in the polarization and strain were observed, indicating a tetragonal ↔ orthorhombic phase transition. The critical electric field to induce the transition was found to shift to higher values with increasing temperature. The Landau-Devonshire theory was used to analyze the observed electric field-induced T ↔ O phase transitions.

Erratum: "Composition- And Pressure-Induced Ferroelectric To Antiferroelectric Phase Transitions In Sm-Doped Bifeo₃ System" [Appl. Phys. Lett. 106, 012903 (2015)], Fei Xue, Linyun Liang, Yijia Gu, Ichiro Takeuchi, Sergei V. Kalinin, Long-Qing Chen

Yijia Gu

In the acknowledgement of the original article,1 the Award No. DMR-0820404 should be replaced by DMR-1420620.

Electric-Field Induced Ferromagnetic Phase In Paraelectric Antiferromagnets, Maya D. Glinchuk, Eugene A. Eliseev, Yijia Gu, Long-Qing Chen, Venkatraman Gopalan, Anna N. Morozovska

Yijia Gu

The phase diagram of a quantum paraelectric antiferromagnet EuTiO₃3 under an external electric field is calculated using Landau-Ginzburg-Devonshire theory. The application of an electric field E in the absence of strain leads to the appearance of a ferromagnetic (FM) phase due to the magnetoelectric (ME) coupling. At an electric field greater than a critical field, E_cr, the antiferromagnetic (AFM) phase disappears for all considered temperatures, and FM becomes the only stable magnetic phase. The calculated value of the critical field is close to the values reported recently by Ryan et al. [Nat. Commun. 4, 1334 (2013)10 ...

Evolution Of The Statistical Distribution In A Topological Defect Network, Fei Xue, Xueyun Wang, Ion Socolenco, Yijia Gu, Longqing Chen, Sang-Wook Cheong

Yijia Gu

The complex networks of numerous topological defects in hexagonal manganites are highly relevant to vastly different phenomena from the birth of our cosmos to superfluidity transition. The topological defects in hexagonal manganites form two types of domain networks: type-I without and type-II with electric self-poling. A combined phase-field simulations and experimental study shows that the frequencies of domains with N-sides, i.e. of N-gons, in a type-I network are fitted by a lognormal distribution, whereas those in type-II display a scale-free power-law distribution with exponent ~ 2. A preferential attachment process that N-gons with a larger N have higher probability of ...

Erratum: "Impact Of Symmetry On The Ferroelectric Properties Of Catio₃ Thin Films" (Applied Physics Letters 106:162904 (2015)), Michael D. Biegalski, Liang Qiao, Yijia Gu, Apurva Mehta, Qian He

Yijia Gu

There is a typo of the space group. All the Pnmb should be Pbnm (or Pnma). So the Glazer notation should be changed to (a−a−c+) for Pbnm space group on page 4 of the article.1 We have also noticed that the thermodynamic analysis of CaTiO3 thin film is not correct.

Conductivity Of Twin-Domain-Wall/Surface Junctions In Ferroelastics: Interplay Of Deformation Potential, Octahedral Rotations, Improper Ferroelectricity, And Flexoelectric Coupling, Eugene A. Eliseev, Anna N. Morozovska, Yijia Gu, Albina Borisevich, Long-Qing Chen

Yijia Gu

Electronic and structural phenomena at the twin-domain-wall/surface junctions in the ferroelastic materials are analyzed. Carriers accumulation caused by the strain-induced band structure changes originated via the deformation potential mechanism, structural order parameter gradient, rotostriction, and flexoelectric coupling is explored. Approximate analytical results show that inhomogeneous elastic strains, which exist in the vicinity of the twin-domain-wall/surface junctions due to the rotostriction coupling, decrease the local band gap via the deformation potential and flexoelectric coupling mechanisms. This is the direct mechanism of the twin-wall static conductivity in ferroelastics and, by extension, in multiferroics and ferroelectrics. On the other hand, flexoelectric ...