Conference Programme

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K-05: Poster Session
Tuesday, 20/Jun/2017:
4:00pm - 6:15pm

Location: Foyer

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AlN Phononic Crystals Phenomena Results from Scattered and Locally Resonant Effects

Ying-Pin TSAI, Fu-Li HSIAO

Institute of Photonics, National Changhua University of Education, Taiwan

Phononic crystals (PnCs) are periodic arrays of materials with different elastic parameters; the properties of acoustic frequency band gap makes PnCs extensively used in acoustic devices. Recent years, PnCs with piezoelectric materials such as quartz (SiO2), lithium niobate (LiNbO3) and aluminum nitride (AlN) got lots of attention. We chose AlN as the material because of the great piezoelectric properties, and high electro-mechanical coupling coefficient, which can let us further study the acousto-optic coupling. We designed the two kinds of PnC consist of honeycomb lattice of air holes array and AlN pillars array on AlN plats. The main goal is to investigate and compare the properties of AlN PnCs based of scattered and locally resonant effects.

In this research, the honeycomb lattice PnCs with AlN as the host materials. We focus on two kinds of geometric structures, which are AlN plate with air holes array and AlN cylinder pillars array standing on the AlN plate, respectively. We show both band structures of two types of PnCs and investigate the band gap width and the central frequency of band gap varying as a function of geometry parameters.

The band structures show both of the air-hole type and the pillar-based type have complete band gaps. The air-hole type band gap opens at 1.76~2.06 GHz when r/a ratio is 0.45 and plate thickness is 0.5μm, and the band gap width increase with plate thickness increase. The pillar-based PnCs generate more than one complete band gaps at same r/a ratio, and the band gaps width decrease with the plate thickness. Due to the well optic properties of AlN, the AlN based PnC can be applied for acoustic-optics coupling devices. The air-hole type and pillar-based type PnCs offers more choose for further applications.


Carbon Ordering in Martensite Lattice Under External Stress: Molecular Dynamics Simulation

Alexander MIRZOEV, Pavel CHIRKOV

South Ural State University, Russian Federation

We performed molecular dynamics (MD) simulations of carbon ordering under action of external stress. In this study we employ EAM/FS interatomic potential T. Lau and C. J. F. Forst (2007) for Fe-C system and open-source LAMMPS code.It was previously shown that the potential correctly reproduce the concentration dependence of tetragonality c/a in Fe-C martensite. It should be noted that the potential does not describe the carbide formation thus we used molecular dynamic simulation at high temperatures for acceleration carbon diffusion processes because of computational resources limitation. All calculations were performed in Nose-Hoover isothermal-isobaric ensemble (NPT) with anisotropic pressure controller. This choice makes possible uniaxial cell deformations and reordering of carbon atoms. It was shown that external stress has strong influence on carbon order at octahedral sites and direction of tetrahedral distortion can change because of cell deformation. The phenomenon of martensite tetragonality axis changing under external stress is the similar to orientation of magnetic moments in external magnetic field. Formation of ordered state along new direction occurs only when threshold stress value is achieved. Dependences of critical stress on temperature and carbon content were obtained. When temperature is increased at fixed carbon content the critical stress is decreased to zero and is increased with concentration rise. The computer simulations results are consistent with theoretical data.The work was supported by the Russian Science Foundation, grant no. 16-19-10252.


Computational Simulation of the Elastic Vesicle Including Particles

Hibiki ITOGA1, Ryota MORIKAWA1, Tsuyoshi UETA2, Takeshi MIYAKAWA1, Yuno NATSUME3, Masako TAKASU1

1Tokyo University of Pharmacy and Life Sciences, Japan; 2The Jikei University, Japan; 3Japan Women's University, Japan

We study physics of the shape of vesicle including colloidal particles. Y. Natsume and H. Terasawa et al. reported that the vesicle containing polystyrene particles, polyethylene glycol or dextran transforms to the pearl necklace shape, at a high volume fraction of inner particles and rich excess area. The transformation is considered to be caused by the interaction between membrane and these inner particles, whereas its mechanism is not confirmed.

We constructed a model of vesicle including colloidal particles using triangular lattice and inner coarse-grained particles. Each grid point of the lattice of the membrane has a hard-core repulsion, and its tethering is fluid. This model is known as “fluid tether and bead membrane”. The membrane was closed to create vesicles, and the vesicle have energies of bending elasticity, area-difference elasticity, osmotic pressure and the other. The equilibrium shape of the vesicle including particles is obtained by using the Metropolis algorithm under constraints of constant surface area. The shape of the model membrane with particles is not significantly different from that of the one without particles.

The suppression of the pearl necklace shape including narrow neck is due to hardening of the membrane and to inhibition of the approach of the membranes. Both effects have the same origin, which is uneven surface of the tether and bead membrane. The strong repulsion between the next-nearest neighbor grid-points increases the effective bending elastic module. Therefore, we employed a fluid plaquette vesicle composed of flexible impenetrable triangles.

In the presentation, we discuss the probability distributions of the dihedral angle and the normal-normal correlation functions of different self-avoidance types of the membrane models. Then, we would like to discuss the shape transformations depending on the membrane model, the osmotic pressure and particles.


Development of Energy Efficient Control Strategies Based on Room Occupancy

Xiaoli ZHOU1, Hua LI1, Yengchai SOH2, Chaoyang JIANG2

1School of Mechanical and Aerospace Engineering, Nanyang Technological University, Singapore; 2School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore

The air-conditioned environment in buildings is responsible for significant portion of global energy demand. The rationalities of airflow pattern and thermal distribution significantly influence the energy cost of air-conditioning. In current control systems, the maximum occupancy is usually accounted for maintaining human comfort. However, in actual situations, there are areas that are heated or cooled needlessly. Therefore, it appeals to develop a control strategy based on room occupancy, in order to achieve the optimized thermal comfort with the minimized energy consumption. In this work, a novel model is developed by integrating a simplified CFD model into the model predictive control (MPC) algorithm to form a CFD-based MPC system, which significantly improves the performance of the control system with the superiority of CFD for highly-efficient prediction of the detailed airflow and temperature fields based on room occupancy. Preliminary case studies are conducted by the proposed CFD-based MPC system. It is demonstrated that the CFD-based MPC system can serve well as an energy-efficient platform with controllable accuracy, with regard to different occupancy estimates.

Acknowledgement—The work was supported by Singapore’s National Research Foundation under Grant NRF2011NRF-CRP001-090, and partially supported by the Energy Research Institute at NTU (ERI@N).


Effective Inhibition of Hydrogenase by Carbon Monoxide to Prevent Oxygen Damage

Kritika DIXIT1, Shailendra Kumar SINGH2, Vinod KANNAUJIYA3, Akhlaqur RAHMAN1, Ashish Kumar SRIVASTAVA1, Sujeet SINGH1, Rudi ETTRICH4, Shanthy SUNDARAM1

1University of Allahabad, India; 2Department of Biological Sciences, Birla Institute of Technology & Science, Pilani - Hyderabad, India; 3Department of Botany, Banaras Hindu University, India; 4Center for Nanobiology and Structural Biology, Institute of Microbiology Academy of Sciences of the Czech Republic Zamek, Czech Republic

Hydrogenases efficiently catalyze the production and cleavage of molecular hydrogen. Their use in biotechnological applications is anticipated to make a remarkable contribution to future renewable fuel production. There are three types of hydrogenases: Fe-Fe, Ni-Fe and Fe-only hydrogenases. In this study, the Fe-Fe hydrogenases are majorly focused. The Fe-Fe hydrogenases of green algae (Chlorophytes) are also called “Chlorophyta type” hydrogenases. Fe-Fe hydrogenases do not contain F-cluster. The presence of H-cluster at the active site is the main attribute of chlorophyte’s hydrogenase. Carbon monoxide (CO) is an effective inhibitor of Fe-Fe hydrogenases and so is oxygen (O2). Oxygen irreversibly destroys the enzyme active site causing potential loss of function. CrHydA1 is a substrate for hydrogenase enzyme and is important functionally for efficient enzyme activity. CO, being a competitive inhibitor of CrHydA1, binds to the iron atom of the 2Fe-H domain and is ordinarily, non-destructive, securing the Fe-S clusters to remain intact in the enzyme. CO has nearly two folds higher affinity for the active site of hydrogenase as compared to oxygen protecting the enzyme against damage from O2.

Here, we present a study of the mechanism by which O2 irreversibly attacks the H-cluster, by in-silico techniques with the reversible inhibitor CO as a complementary binding substrate. The enzyme kinetics was studied for oxygen, carbon monoxide and CrHydA1 and Km was calculated by the Hyper32 software. Km value 50μM, 22μM and 28 μM were recorded respectively for the inhibitors and the substrate suggesting CO as a potent non-destructive inhibitor, which can protect against oxygen damage. Identification of gas channels for studying structural and oxidation state changes was done using Yasara Simulation.


Electronic Properties, Mechanical Stability and Reduction Reaction Energies for Cubic Lanthanide Oxide Composites: A Computational Modelling Approach

Hussein A. MIRAN1,2, Mohammednoor ALTARAWNEH1, Zainab N. JAF1,2, Hantarto WIDJAJA1, Jean-Pierre VEDER3, Zhong-Tao JIANG1

1Surface Analysis and Materials Engineering Research Group School of Engineering and Information Technology, Murdoch University, Australia; 2Department of Physics, College of Education for Pure Sciences - Ibn Al-Haitham, University of Bagdad, Iraq; 3John de Laeter Centre, Curtin University, Australia

Lanthanide(Ln) oxides represent an array of materials which exhibit unique properties, such as, superior mechanical, thermal, optical and magnetic properties, derived by their unfilled semicore 4f orbitals. Two forms of cerium oxide(CeO2 and Ce2O3) for instance have been the subject of numerous studies aiming to elucidate chemical and physical characteristics of their bulk and thin film properties. Cerium oxides have been widely deployed as catalysts in the preparation of active metal nanoparticles, as electrolytes or anode support materials. On the theoretical side, density functional theory(DFT) investigation has elucidated structures and electronic properties by utilizing hybrid DFT methods. Studied compounds include the A-type hexagonal structure and CeO2 with the cubic fluorite structure (space group Fm-3m). This study presents a comprehensive DFT + U account into electronic structures, mechanical properties of C-type lanthanide sesquioxides and thermodynamic (redox) properties. The aim of this work is fourfold: (1) to evaluate the effects of the Hubbard U parameter on the electronic and structural properties of C-type lanthanide sesquioxides (Ln2O3), (2) to assess the mechanical stability of all C-type lanthanide sesquioxides, (3) to elucidate the thermodynamic feasibility of CeO2 to undergo a redox reaction at temperatures relevant to catalytic applications, and (4) to underpin the effect of adding Hf and Zr to CeOδ [ δ=2-1.5] on reduction energies. We find that a Ueff value of ~ 5 eV reproduces the analogous experimental band gap of Ce2O3. Bader’s charge distributions on the C-type Ln2O3 have verified the ionic bonding nature of these compounds. Our analysis for the reduction energy of CeO2, in a wide range of temperatures, demonstrates that transfer cerium oxide between the two + 4 and + 3 oxidation states exhibit a temperature independent behavior. Preliminary results indicate that CeO2 alloyed with Hf or Zr results in enhancing its redox characteristics by lowering reduction enthalpies.


Exploring the Structures and Phase Transitions of Hf3N4

Feng ZHENG, Jinchai LI, Shunqing WU

Collaborative Innovation Center for Optoelectronic Semiconductors and Efficient Devices, Department of Physics, Xiamen University, China

Understanding of phase behavior in early transition-metal nitrides (TMN) with the metal in maximum oxidation state is important due to the potential applications as visible light photocatalysts. Recently, cubic Hf3N4 and Zr3N4 have been successfully synthesized at pressures up to 18 GPa and high temperatures (~3000 K). Besides, an orthorhombic Eu3O4-type phase of Zr3N4 can be prepared at ambient pressure. In this work, we explore the structures of Hf3N4 using Adaptive Genetic Algorithm (AGA) crystal structure prediction method. At ambient pressure, we identify a new stable phase with C2/m space group for Hf3N4. The results of the phonon dispersions and elastic constants demonstrate that the C2/m phase is dynamically and mechanically stable. To understand the relative stabilities of Hf3N4 among different phases, we also study the pressure-temperature phase diagram for different Hf3N4 phases including the new-found C2/m phase, the orthorhombic Zr3N4-type (Pnam) and also the high-pressure I-43d phase. Phase transitions of Hf3N4 under different pressure/temperature conditions are investigated.


Modeling and Simulation of Crack Propagation through Different Materials and Interface

Giftson.P.H. SAM, Ni ZHANG, Zishun LIU

International Center for Applied Mechanics, State Key Laboratory for Strength and Vibration of Mechanical Structures, Xi’an Jiaotong University, China

In engineering, failures have occurred for many reasons, including uncertainties in the loading or environment, defects in the materials, inadequacies in design, and deficiencies in construction or maintenance. Design against failure or fracture has a technology of its own, and this is a very active area of current research. In this study we discuss about a specific aspect in this field, crack propagation through different materials of finite thickness and interface. This study was directed at the mechanics of such material system when there is a crack which is propagating through the interface, and sought to find parameters that govern the crack growth through different materials, such as the crack tip stress intensity factors and strain energy release rates. To simulate probable direction of the crack extension, we investigate crack propagation through different materials of finite thickness and interface using modeling and simulation method. In modeling and simulation, the extended finite element method (XFEM) is used to investigate the fracture propagation.


Moment Reconstruction of Grain Size Distributions from Nucleation and Growth

Yang Hao LAU, Siu Sin QUEK, David T. WU

Institute of High Performance Computing, Agency for Science, Technology and Research (A*STAR), Singapore

A polycrystalline material's grain size distribution is an important determinant of material properties – e.g., thermal stability, strength, and ductility. Typically this distribution depends on the nucleation and growth process during the material's formation. Therefore, modeling this processing-structure relation, in conjunction with structure-property relation, has important applications for material property optimization. An efficient model exploits the reconstruction of a grain size distribution from its moments, which may be computed for a given nucleation and growth schedule. A caveat of the method is the reconstruction's sensitivity to the choice of basis distribution, and the lack of fundamental principles favoring one basis over another. Presently, the question of which basis to use remains open, hindering the method's direct application. We therefore propose an answer, via comparative study of the fidelity of reconstructions using different bases to analytic and empirical distributions. We consider a large class of relevant distributions, so our results may extend to distributions from general nucleation and growth schedules.


Origins of Grain Boundary Resistance for Thermal Conduction in Bulk Si

Kohei FUNAI1, Susumu FUJII1, Tatsuya YOKOI1, Masatoshi TANEMURA1, Masato YOSHIYA1,2

1Department of Adaptive Machine Systems, Osaka University, Japan; 2Nanostructures Research Laboratory, Japan Fine Ceramics Center, Japan

Nanostructuring is one of the promising ways to suppress thermal conduction without deteriorating electronic conduction for better thermoelectric energy conversion. Extensive studies have been done to study the impact of nanostructures on resultant transport properties of Si which can also be a model material that represent many kinds of compounds having tetrahedral network structure. Attempts have been made to acquire structure-properties correlation though it is still challenging only by experiments. From the perspective of analytical theories, mean free path is the primary means to sort out the experimental findings. However, those transport phenomena are frequency or wavelength dependent and while only electrons near Fermi-level contribute electronic conduction whole range of phonons can contribute to lattice thermal conduction in principle, impeding in-depth understanding of the impact of the nanostructures.

In this study, perturbed molecular dynamics simulations have been done to calculate and analyze thermal conduction in grain boundary (GB)-containing Si and examined the dependence of thermal conduction at or in the vicinity of GB on characteristics of GB, namely misorientation angle between neighboring grains and rotation axis from the perspective of grains or modification in coordination number and bondlength in the vicinity of GB from atomistic perspective.

With the increase of misorientation angle, atomic arrangement on the GB plane is gradually changed. Grain boundary energy shows, however, non-linear dependence on the misorientation angle for a give orientation axis, which is presumably due to atomic relaxation to minimize the energy penalty of lattice discontinuity. Thermal conduction exhibits non-linear dependence, either, or there is no remarkable correlation with grain boundary energy. Further analyses revealed that the decrease in thermal conduction by the GBs can be understood in terms of local atomic coordinations, which would provide useful information as to how various nanostructures determine thermal conduction.


Phase Behavior of Colloids Coated with Mobile DNA-linkers

Hao HU, Pablo Sampedro RUIZ, Ran NI

Nanyang Technological University, Singapore

Single-stranded DNA (ssDNA) can bind selectively to complementary ssDNA. By coating colloids with complementary ssDNAs, we can design the interaction between them, leading to the efficient self-assembly of target structures. For example, recently Angioletti-Uberti, Varilly, Mognetti and Frenkel [PRL 113, 128303 (2014)] studied colloids coated with mobile DNA-linkers, and showed that one can control the coordination number by tuning the nonspecific repulsion between particles. In this work, we study the phase behavior of colloids coated with mobile DNA-linkers. In the strong binding region, as the density increases, we find that CsCl, CuAu, and tetragonal structures occur consecutively in three-dimensional space. Similarly, in two-dimensional space, the floppy binary square-lattice crystal appears before the compact hexagonal crystal. The presence of noncompact structures is related to the entropy arising from DNA binding. Finally, we present a new method to calculate the ground states of the system at infinitely strong binding, which confirms the entropy driven formation of open structures of mobile DNA coated colloids at the strong DNA binding limit.


Thermodynamic and Thermo-Mechanical Properties of Ytterbium Silicates for Environmental Barrier Coatings

Yusuke SUMI1, Arata IOKI1, Tatsuya YOKOI1, Masato YOSHIYA1,2

1Department of Adaptive Machine Systems, Osaka University, Japan; 2Nanostructures Research Laboratory, Japan Fine Ceramics Center, Japan

Wide spectrum of extensive studies have been done to increase operating temperature of jet-engines to further improve fuel-consumption, enabling longer distance travel, and to reduce CO2 emission, in order to meet with growing demand for massive transportation across the globe. For that purpose, attention has been paid to thermal barrier coatings (TBC) and environmental barrier coatings (EBC) that protect inner turbine blades from high temperature and corrosive gas species, respectively. Although ytterbium silicates attract attention for a prime candidate for future top-coat materials of the EBC, understanding of fundamental properties of the ytterbium silicates are limited, which impedes further optimize the properties of the EBC system or to solve problems including cracks during thermal-cycle exposure test.

In this study, first principles calculations have been carried out to evaluate thermodynamic, mechanical and thermal properties of the silicate materials to enable discussion their interplay upon thermal-cycle through in-depth understanding of the origins of the properties. Projector-augmented wave method is used to deal with inner-core electrons frozen in the course of the calculations with generalized gradient correction approximation formulated by Perdew, Burke and Ernzerhof (GGA-PBE) for exchange-correlation functional. Both lattice dynamics and molecular dynamics in combination with the first principles calculations are used to supplement shortcomings of each method using VASP code.

It is found that, while other rare-earth disilicates exhibit structure transformations accompanying volume change when temperature is increased, β-phase of Yb2Si2O7 remains stable over other phases, enabling to avoid crack-generation due to the volume change. Elastic constants and coefficient of thermal expansion show high anisotropy originating from its crystal structures. Further analyses revealed that SiO4 tetrahedral network in its crystal structure governs those properties. Further details of the analyses and the outlook of the ways to improve the EBC will be discussed in the presentation.


Modeling and Simulation of Hydraulic Fracture Propagation of the Shale Bedding

Ni ZHANG, Giftson.P.H. SAM, Zishun LIU

International Center for Applied Mechanics, State Key Laboratory for Strength and Vibration of Mechanical Structures, Xi’an Jiaotong University, China

The exploitation of shale gas has become a promising field of green energy development and the efficiency of exploitation can reduce the environmental pollution caused by coal and other fossil fuels. Although great success has been achieved in shale gas utilization with the technique of hydraulic fracturing, only 5%-15% of the stored oil and gas has been exploited. It will be imperatives to understand the hydraulic fracturing process and the effects of the geological condition of shale. In this study, the process of hydraulic fracturing of shale will be studied by using modeling and simulation method. In modeling and simulation, the extended finite element method is used to simulate the fracturing process of shale and the role of bedding planes. The mechanical properties of bedding planes, the approaching angle between the crack and the bedding plane, the fracture propagation behavior, as well as the fracture network features will be numerical investigated in details. Furthermore, geological discontinuities, such as joints, faults, and bedding planes which can affect the overall geometry of the hydraulic fractures will be analyzed. Additionally, a key factor to create a fracture network to get higher well productivity will be discussed.

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