bluuebunny/crossref_metadata_2025_split huggingface dataset:
Rheology of a granular column
Authors: Kolb Evelyne , Ovarlez Guillaume , Sausse Pascal , Clément Eric 
Published: June 2019

ABSTRACTWe study the rheology of a granular material in a confined geometry. The grains are stacked in a vertical cylinder and pushed at different driving velocities. The resistance force encountered by the bottom piston is monitored while the piston is pushing the granular column upwards. Above a critical velocity, the motion is characterized by a steady sliding and by a force level increasing rather slowly with the pushing velocity. For driving velocities under this threshold, the system undergoes a dynamic instability and then, a stick-slip motion occurs. The amplitude of the slipping events, and thus, the elastic energy release, increase strongly when the velocity decreases. The critical velocity depends on the stiffness of the driving system and on the height of the granular column. This transition can be shifted towards higher velocity values by increasing the friction at the walls of the cylinder. It is also very sensitive to the state of compaction of the grains. Moreover, the mean energy release during a stick-slip motion seems to increase as a power-law when the pushing velocity is decreased. We also show that the distribution of energy release is strongly dependent on the level of disorder in the grains (polydispersity, friction, etc.). We argue that this complex phenomenology characterizes confined granular packing in connection with arching and aging phenomena.
Flow of Granular Material through Rotating Cylinders: Modelling Transients
Authors: Spurling Richard J. , Davidson John F. , Scott David M. 
Published: June 2019

ABSTRACTGranular material, fed continuously into the top of a slowly rotating, slightly inclined cylinder, forms a moving bed. Much of the bed rotates with the cylinder in solid body motion. When particles reach the surface of the bed, they move rapidly down it, and are absorbed once more into the solid body motion. Such cylinders are used in calcining, pharmaceutical manufacture, and drying. A steady state transport model, applicable when the bed depth varies slowly along the cylinder, has existed for around 50 years. The bed surface is considered locally flat, and particles in it fall along the line of steepest descent, inclined to the horizontal at the angle of repose. There is reasonable agreement with experiment.We propose a quasi-steady state dynamical model, in which the steady state model is coupled with a volume balance across an axial element. The model takes the form of a nonlinear diffusion equation which was solved numerically. The parameters of the dynamic model are the dimensions of the cylinder and outlet dam, the inclination of the axis of the cylinder, its rotational speed, the angle of repose of the granular material and its feed volumetric flow rate: the dynamic model has no free parameters. Experiments were conducted using sand, mean particle size 490 μm, in a perspex tube of length 1 m, radius 0.0515 m, lined with sandpaper, with a feed end dam of height 0.029 m, and with no exit dam, or an exit dam of height 0.0105 m. With the system initially in steady state, step changes in feed flow rate, rotational speed or axis inclination were imposed, and the resulting discharge flow rate and bed depth axial profile measured as functions of time. Good agreement is found between model and experiment.
Dislocation Exhaustion During Plastic Deformation
Authors: Couteau Olivier , Charbonnier Corinne , Kruml Tomas , Martin Jean-Luc 
Published: June 2019

AbstractRepeated stress-relaxation experiments are used to characterize the deformation parameters in 3 types of single crystals (Cu, Ni3Al and Ge) in which different dislocation mechanisms are known to operate. Mobile dislocation exhaustion rates and the amplitude of the yield point at reloading after stress-relaxation are measured. These two parameters are discussed in terms of the work-hardening coefficient in monotonic tests.
New Line Model for Optimized Dislocation Dynamics Simulations
Authors: Madec Ronan , Devincre Benoit , Kubin Ladislas P. 
Published: June 2019

AbstractA new model for the discretisation of dislocation lines is presented, which is optimised for mesoscale simulations of dislocation dynamics. By comparison with the existing edge-screw model, the present one provides a better description of the stress field close to the dislocation lines. It simplifies the modelling of dislocation reactions and accelerates computations by allowing to make use of larger time steps. An application to attractive junctions and forest hardening is briefly sketched.
Coarse Slip Bands in a Single-Crystalline Aluminum Alloy
Authors: Yang Seung-Yong , Li Xianghong , Alloy Aluminum 
Published: June 2019

AbstractThe effect of crystal orientation on the discontinuous deformation and coarse slip bands in aluminum single crystals has been investigated by finite element simulation. The numerical analysis is based on a rate-dependent crystal plasticity model recently formulated by us with modifications made here that explicitly accounts for the three strain hardening stages and the effect of the interaction of dislocations and alloying elements on setting the hardening rules on the individual slip systems of the aluminum alloy crystal. The dependence of the magnitude of the serrations of tensile stress-strain curves on orientation and its evolution over the three strain hardening stages of Al-0.3%Mg single crystals observed experimentally has been successfully explained in this investigation.
Lattice Trapping of Cracks in Fe Using an Interatomic Potential Derived from Experimental Data and Ab Initio Calculations
Authors: Farkas D. , Mehl M. J. , Papaconstantopoulos D. A. 
Published: June 2019

AbstractA recent approach which combines first-principles and experimental data to produce highly accurate and reliable interatomic potentials is tested for the case of bcc and fcc Fe. The Embedded-Atom-like potential accurately reproduces the basic equilibrium properties of bcc Fe, including elastic constants, phonon properties, and vacancy formation energies, as well as the correct relative stability of structures with coordination numbers ranging from 12 to 4. This potential was used in a simulation study of lattice trapping effects during the cleavage fracture of bcc Fe. A strong directional anisotropy for crack propagation was observed due to lattice trapping effects. The strongest trapping effects were observed for cleavage along the {110} planes and it was found that lattice trapping strongly favors cleavage along the {100} planes.
Self-Affinity Analysis of the Fracture Surfaces of Polypropylene and Opal Glass.
Authors: Hinojosa M. , Reyes E. , Guerrero C. , Ortiz U. 
Published: June 2019

AbstractIn this work we report the self-affinity analysis of the fracture surfaces of a polymeric semicrystalline material and an opal glass. In the case of the plastic material, samples of isotactic polypropylene (i-PP) were prepared by varying the cooling rate from the melt; this resulted in different spherulite sizes. Samples were then broken in bend test after being immersed in liquid nitrogen. In the case of the opal glass, samples with different sizes of the opacifying particles, obtained by different thermal treatments, were broken in a punch test. In both cases the fracture surfaces were analyzed by both Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) in the contact mode. Self-affinity analysis was performed by the variable bandwidth method, covering a range of length scales spanning from a few nanometers up to ten micrometers. The roughness exponents are found to be of similar values close to ζ = 0.8 with the correlation length corresponding to the size of the spherulites in the plastic material and to the size of the opacifying particles in the opal glass. These results should be taken into account in the development of multiscale models and simulations of the fracture process of real heterogeneous materials.
Cosserat Modeling of Size Effects in Crystalline Solids
Authors: Forest Samuel 
Published: June 2019

AbstractThe mechanics of generalized continua provides an efficient way of introducing intrinsic length scales into continuum models of materials. A Cosserat framework is presented here to descrine the mechanical behavior of crystalline solids. The first application deals with the problem of the stress field at a crak tip in Cosserat single crystals. It is shown that the strain localization patterns developping at the crack tip differ from the classical picture : the Cosserat continuum acts as a bifurcation mode selector, whereby kink bands arising in the classical framework disappear in generalized single crystal plasticity. The problem of a Cosserat elastic inclusion embedded in an infinite matrix is then considered to show that the stress state inside the inclusion depends on its absolute size lc. Two saturation regimes are observed : when the size R of the inclusion is much larger than a characteristic size of the medium, the classical Eshelby solution is recovered. When R is much small than the inclusion, a much higher stress is reached (for an inclusion stiffer than the matrix) that does not depend on the size any more. There is a transition regime for which the stress state is not homogeneous inside the inclusion. Similar regimes are obtained in the study of grain size effects in polycrystalline aggregates of Cosserat grains.
Coupling of Length Scales: Hybrid Molecular Dynamics and Finite Element Approach for Multiscale Nanodevice Simulations
Authors: Lidorikis Elefterios , Bachlechner Martina E. , Kalia Rajiv K. , Voyiadjis George Z. , Nakano Aiichiro , Vashishta Priya 
Published: June 2019

AbstractA hybrid molecular-dynamics/finite-element simulation scheme is applied to describe multiscale phenomena in nanodevices. The quality of both static and dynamic coupling between atomistic and continuum regions is studied. The hybrid scheme is used for the Si/Si3N4 interface problem (static coupling), and for the projectile impact on Si problem (dynamic coupling). Excellent agreement is found between hybrid and full molecular dynamics simulation results in the static case, and no wave reflections are found at the atomistic/continuum hand-shake in the dynamic case. The hybrid scheme is thus validated a powerful and cost effective method for performing multiscale simulations of nanodevices.
Microstructure and optical properties of GaN films grown on porous SiC substrate by MBE
Authors: Yun F. , Reshchikov M. A. , He L. , King T. , Huang D. , Morkoç H. , Inoki C. K. , Kuan T. S. 
Published: June 2019

AbstractGaN thin films were grown on porous SiC substrates using reactive molecular beam epitaxy with ammonia as the nitrogen source. Microstructure analysis and optical characterization were performed to assess the quality of the effect of pores on the growth and the quality of the GaN films. Results indicate that the GaN films on porous SiC are slightly less defective and more strain-relaxed (some completely relaxed) when grown on porous SiC substrate, as compared to growth on standard 6H-SiC substrates. Rocking curve FWHMs of 3.3 arcmin for (0002) diffraction and 13.7 arcmin for (1012) diffraction were obtained for sub-micron thick GaN films. Excitonic transition with FWHM as narrow as 9.5 meV was observed at 15K on the GaN layer grown on porous SiC without a skin layer.
Influence of Be Doping on Material Properties of Low-Temperature-Grown GaAs
Authors: Marcinkevièius Saulius , Gaarder Andreas , Siegert Jörg , Roux Jean-Fraņois , Coutaz Jean-Louis , Wolos Agnieszka , Kaminska Maria , Adomavičius Ramūnas , Bertulis Klemensas , Krotkus Arunas 
Published: June 2019

AbstractA number of experimental techniques were used to characterize structural quality, ultrafast carrier dynamics and deep center properties of low-temperature-grown GaAs doped with Be. GaAs layers grown at 280 °C, doped with the Be concentration from 5×1017 cm-3 to 2×1019 cm-3 and annealed at temperatures between 500 and 800 °C were studied. Electron trapping times in these samples varied from hundreds of femtoseconds to several picoseconds. A non-monotonous electron trapping time dependence on Be doping level is explained by the influence of triple-charged gallium vacancies and single-charged Be-acceptors on the number of ionized As antisite defects.
Charges and Dipoles at Semiconductor Interfaces
Authors: Tung Raymond T. 
Published: June 2019

AbstractThe formation of the Schottky barrier height at metal-semiconductor interfaces has often been discussed in terms of interface states. This paper examines theoretical models that specifically relate defects and other interface states (such as MIGS) to the interface dipole. These models usually rely on the assumption, which is also invoked in most experimental determination of interface state distribution, that the interface dipole can be broken up into the product of an interface charge and an interface distance/width. Various inconsistencies associated with this assumption are discussed, suggesting that the formation of the interface dipole is an integral process which cannot be divided. It is shown that the inclusion of the bond polarization at semiconductor interfaces, proposed in recent work, gives quantitative account of experimental Fermi level pinning effect. In addition, the bond polarization concept can be extended to the theoretical description of band offsets at epitaxial semiconductor heterojunctions. These results underscore the importance of correctly handling the chemistry at semiconductor interfaces in order to understand their electronic properties.
Injection of point defects by oxidation of AlGaAs
Authors: Chamberlin Danielle R. , McHugo Scott A. , Burak Dariusz , Burke Deyon , Osentowski Tim , Rosner S. Jeffrey 
Published: June 2019

AbstractInjection of point defects into GaAs/AlxGa1-xAs heterostructures by oxidation of AlxGa1-xAs is investigated. The blueshift of the PL emission from GaAs quantum wells is measured as a function of rapid thermal annealing conditions in as-grown and thermally oxidized samples. Contrary to published data for point defect injection by oxidation of GaAs, oxidation of AlxGa1-xAs appears to reduce the interdiffusion of the quantum wells. The PL peak shifts after annealing have been fit assuming Al diffusion in the quantum wells and solving the singleparticle Schrödinger equation. These fits show a reduction in group-III diffusivity of over an order of magnitude with an oxidized layer of AlxGa1-xAs on the surface.
Laser Engineering of Barrier Structures Based on Solid Solution ZnCdHgTe.
Authors: Khlyap Galina 
Published: June 2019

AbstractRoom-temperature electric investigations carried out in CO2-laser irradiated ZnCdHgTe epifilms revealed current-voltage and capacitance-voltage dependencies typical for the metal-semiconductor barrier structure. The epilayer surface studies had demonstrated that the cell-like relief has replaced the initial tessellated structure observed on the as-grown samples. The detailed numerical analysis of the experimental measurements and morphological investigations of the film surface showed that the boundaries of the cells formed under the laser irradiation are appeared as the regions of accumulation of derived charged defects of different type of conductivity supplying free charge carriers under the applied electric field.
An Study of Influence of Imperfections on the Delamination of Diamond-Like Carbon Films
Authors: Moon Myoung-Woon , Lee Kyang-Ryel , Chung Jin-Won , Oh Kyu Hwan 
Published: June 2019

AbstractThe role of imperfections on the initiation and propagation of interface delaminations in compressed thin films has been analyzed using experiments with diamond-like carbon (DLC) films deposited onto glass substrates. The surface topologies and interface separations have been characterized by using the Atomic Force Microscope (AFM) and the Focused Ion Beam (FIB) imaging system. The lengths and amplitudes of numerous imperfections have been measured by AFM and the interface separations characterized on cross sections made with the FIB. Chemical analysis of several sites, performed using Auger Electron Spectroscopy (AES), has revealed the origin of the imperfections. The incidence of buckles has been correlated with the imperfection length.
First-Principles Simulation of Hydrogen Interaction in Amorphous Silicon Nitride
Authors: Kroll Peter 
Published: June 2019

AbstractStructure and properties of amorphous hydrogented silon nitride (a- SiNx:H) are studied using density functional methods. Models of a-SiNx:H were generated using a random network algorithm. In addition we investigarted the N-H terminated surfaces of β-Si3N4.A comparison between the vibrational spectra of the surface and of the bulk models shows that within the bulk the frequency of N-H bond stretching (≈ 3150 cm-1) is lower than at the surface (≈3300 cm-1). Both spectra show an asymmetric form of the principal peak tailing towards space of hydrogen with nearby atoms. Car-Parrinello moleculat dynamic simulations at elevated temperatures show hopping of bulk hydrogen between different two bonding sites. Moreover, hydrogen acts as network transformer releasing internal stresses.
Modeling Growth Directional Features of Silicon Nanowires Obtained Using SiO
Authors: Tan T. Y. , Lee S. T. , Gösele U. 
Published: June 2019

AbstractSilicon nanowires (SiNW) grown using Si monoxide source materials are mainly oriented in the <112> direction, and some in the <110> direction. These directional features may be understood by postulating that growth of the SiNW is governed by lateral advancement of {111} plane layers that are stepped, and the role of particular kinds of dislocations providing perpetuate steps.
Understanding the Formation Energy of Transition Metal Hydrides
Authors: Smithson Huw J. , Morgan Dane , Ven Anton Van der , Marianetti Chris , Pedith Ashley , Ceder Gerbrand 
Published: June 2019

AbstractA detailed analysis of the formation energies of transition metal hydrides is presented. The hydriding energies are computed for various crystal structures using Density Functional Theory. The process of hydride formation is broken down into three consecutive, hypothetical reactions in order to analyse the different energy contributions, and explain the observed trends. We find that the stability of the host metal is very significant in determining the formation energy, thereby providing a more fundamental justification for Miedema's “law of inverse stability” [1] (the more stable the metal, the less stable the hydride). The conversion of the host metal to the structure formed by the metal ions in the hydride (fcc in most cases) is only significant for metals with a strong bcc preference such as V and Cr - this lowers the driving force for hydride formation. The final contribution is the chemical bonding between the hydrogen and the metal. This is the only contribution that is negative, and hence favourable to hydride formation. We find that it is dominated by the position of the Fermi level in the host metal.
Electrical and Optical characteristics of ZnO:Al Thin Films
Authors: Keum M.J. , Yang J.S. , Son I.H. , Shin S.K. , Choi H.W. , Lee W.S. , Choi M.K. , Chu S.N. , Kim K.H. 
Published: June 2019

AbstractZnO with hexagonal wurzite structure is a wide band gap n-type semiconductor. ZnO films can be prepared to obtain high transparency in the visible range, low resistivity, chemical stability and stability in hydrogen plasma including many foreign materials such as Al, In. In this work, we prepared ZnO:Al thin film by Facing Targets Sputtering system with Zn metal target and ZnO:Al(Al2O3 2wt%, 4wt%) ceramic target at total working gas pressure 1mTorr, substrate temperature R.T.. We evaluated the crystallographic, electrical and optical characteristics of the ZnO:Al films.
A Grain Boundary Engineering Approach to Promote Special Boundaries in a Pb-base Alloy
Authors: Lee D.S. , Ryoo H.S. , Hwang S.K. 
Published: June 2019

AbstractA grain boundary engineering approach was employed to improve the microstructure of a commercial Pb-base alloy for better performance in automobile battery application. Through a combination of cold working, recrystallization and subsequent thermomechanical-processing, it was possible to increase the fraction of the low ∑ coincidence site lattice boundaries up to 91% in addition to the substantial grain refinement. A preliminary electrochemical evaluation indicated a better corrosion resistance in the experimental material laden with the special boundaries. The high frequency of the coincidence site lattice boundaries in the specimens was interpreted in terms of the '∑3 regeneration' model proposed in previous works.
Ultralight Amorphous Silicon Alloy Photovoltaic Modules For Space Applications
Authors: Beernink Kevin , Pietka Ginger , Noch Jeff , Younan Kais , Wolf David , Banerjee Arindam , Yang Jeffrey , Jones Scott , Guha Subhendu 
Published: June 2019

AbstractResults for solar cells with high specific power (W/kg) using amorphous silicon alloy technology are reported. Currently available roll-to-roll production technology capable of high volume has been used to form cells on thinned stainless steel with high specific power. Results of cells on thinned stainless steel formed in batch mode in research and development (R&D) machines are also presented. Cells on polyimide in the early R&D stage have also been formed and are described. An analysis of cell component material and dimension changes to increase specific power shows that specific power ∼2000 W/kg is possible as a long-term goal. Cells with specific power ranging from 300 to 400 W/kg for production cells with 8.5 % beginning of life AM0 efficiency to over 1200 W/kg for R&D cells on polyimide substrates are presented.