bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Density Functional Theory Study of the Catalytic role of Ti atoms in Reversible Hydrogen Storage in the Complex Metal Hydride, NaAlH4
Authors: Chaudhuri Santanu , Muckerman James T 
Published: June 2019

AbstractPresence of ∼2-4 % Ti is critical for reversible hydrogenation/rehydrogenation in NaAlH4. We have investigated the probable catalytic role of Ti in this complex multi-step process. The present part of our study concentrates on the rehydrogenation reaction, i.e., the reverse reaction that forms NaAlH4 from its constituent binary hydrides. First principles calculations using density functional theory (DFT) show that a particular arrangement of Ti atoms on the surface of Al metal promotes the chemisorption of molecular hydrogen. We also present comparisons with existing experimental data (EXAFS and TEM) to support the existence of such an arrangement on the surface.
Transmission Electron Microscopy Studies of 5-cycled Na Alanate with Ti Based Additive
Authors: Andrei Carmen M. , Walmsley John C. , Holmestad Randi , Botton Gianluigi A. , Srinivasan Sesha S. , Jensen Craig M. , Hauback Bjorn C. 
Published: June 2019

AbstractTi doped NaAlH4 hydride is proposed as a reversible hydrogen storage material. In this work, the microstructure of NaAlH4 with 2% TiCl3 additive was studied after 5 hydrogen cycles using a combination of transmission electron microscopy (TEM) techniques including energy dispersive spectroscopy (EDS) X-ray analysis. Selected area diffraction and high-resolution (HR) imaging confirmed the presence of the NaH phase in the material. Electron diffraction was dominated by Al. HRTEM showed the presence of edge dislocations, which might influence the hydrogen diffusivity process in these materials.
The Influence of Hydrogen on the Electrical and Photoelectric Properties of Photodiodes Based on Indium Monoselenide
Authors: Drapak S.I. , Kaminskii V.M. , Kovalyuk Z.D. , Netyaga V.V. 
Published: June 2019

AbstractInfluence of hydrogen intercalation on indium monoselenide is investigated measuring electrical properties of based on it such photosensitive structures as metal-insulator-semiconductor (MIS) and Mott diode (MD). It is established that intercalation of the basic semiconductor with hydrogen leads to the improvement of diodic properties of the MIS structures whereas those for the MD structure becomes worse. For the both structures charge transfer mechanisms are analyzed on the basis of their band diagrams.
Synthesis and Characterization of Nanoscale Transition Metal Complex for Hydrogen Storage
Authors: Srinivasan Sesha S. , Smith Matthew T. , Deshpande Deepak , Stefanakos Eias K. , Goswami Yogi , Jurczyk Michael , Kumar Arun , Kumar Ashok 
Published: June 2019

AbstractThe development of light weight hydrogen storage systems with high volumetric and gravimetric hydrogen densities is indeed essential for the on-board fuel cell vehicular applications [1]. Among the different hydrogen storage systems designed and developed so far, Ti- doped sodium aluminum hydrides exhibit potential promise of reversible hydrogen storage capacity (4-5 wt.%) at moderate temperatures [2,3]. However, the poor cyclic stability of these hydrides due to the partial reversibility of the two step reactions necessitates the development of exotic materials or tailoring the known hydride systems. On the other hand, transition metal complex hydrides, TMHx(T = Mg; M = Fe, Co, Ni) have also been identified as potential candidates for hydrogen storage [4-6] and/or analogous to alanates [7]. These hydrides especially Mg2FeH6, have shown excellent cyclic capacities (more than 500 cycles) even without a catalyst [8]. Besides, Mg2FeH6possesses the highest volumetric and gravimetric hydrogen densities of 150 kg/m3and 5.6 wt.% respectively [9]. However, at low temperatures, the rate of release of hydrogen and the effective reversible hydrogen capacity seems poor. Recent reports declared that the enhancement in the cycling kinetics and reduction in the operating temperature is very much possible by using a distorted nano-scale Mg structure [10, 11], doping the host lattice with Ti- species and/or lattice substitution [12]. Keeping these facts in view, the present investigation aims to improve the sorption kinetics and thermodynamics of Mg2FeH6, by 1) preparing nano-scale Mg-Fe-H system using mechano-chemical synthesis process, 2) surface localized catalyst (Ti- species) doping and 3) cationic substitution of Na+/Li+for Mg2+by incorporating NaH/LiH. The synergistic behavior of the tailored nano-scale transition metal complex for hydrogen storage is outlined.
Effect of Physical State of Carbon Nanocomposite on Hydrogen Adsorption and Desorption
Authors: Kumar Arun , Jurczyk Michael U. , Kumar Ashok , Stefanakos Elias 
Published: June 2019

AbstractThe inclusion of multiwalled carbon nanotubes in a conjugated polymer matrix results in extensive alterations in the polymer morphology. When the physical state of a substance is changed, heat is either absorbed or liberated but the temperature remains constant. The flexibility of chain molecules arises from rotation round the saturated chain bond moreover the potential energy barriers hindering this rotation. It is not surprising therefore that the flexibility of polymer chains is an important factor in determining their melting points and stability. If the substitution of carbon nanotube is random the primary effect is a decrease in the degree of crystallinity. These microstructures are governed by the balance of interactions between hydrodynamic forces (both viscous and elastic) and the forces working to retain the integrity of the disperse particles, such as interfacial tension or, in the case of solid filler and their mechanical strength. Carbon materials have long been shown to absorb as much as 60 wt% hydrogen due to their large surface areas as well as their high surface to volume ratios. In the present approach conducting polyaniline was doped with metal oxide, such as SnO2, as well as carbon nanotubes. The resulting carbon nanocomposite was made in both gel- and solid-state to study the effect of physical state on hydrogen adsorption and desorption by weight percentage. The morphology formation process and its impact on the rheological properties of complex polymer systems, i.e. polymer blends and composites are being studied. The materials are also compared with regard to their thermal stability using DSC, and further characterized using various techniques such as FTIR. Further experiments are in progress to better understand the nature of the hydrogen storage mechanism.
Group III-nitride Materials for High Efficiency Photoelectrochemical Cells
Authors: Ager J. W. , Walukiewicz W. , Yu K. M. , Shan W. , Denlinger J. , Wu J 
Published: June 2019

AbstractTwo ternary alloys based on III-nitride semiconductor alloys are explored as potential components of photoelectrochemical cells (PECs) for the direct generation of hydrogen using solar energy. For In1-xGaxN, it will be shown using prior measurements of band offsets that spontaneous water splitting can occur for x up to 0.2 and potentially higher. Flat band potential and photocurrent measurements from an n-type epilayer with x = 0.37 will be presented. This initial data appears to indicate that the flat band potential lies just below the H+/H2 from pH 0 – 14. In the case of GaAsxN1-x we will demonstrate that the replacement of a few percent of As in N sublattice drives the bandgap down from the GaN value (3.4 eV) into a range that is attractive for PEC cells [1]. This band gap reduction is explained by the valence band anticrossing that pushes the valence band maximum up initially by 0.5 eV. From the point of view of a PEC cell, this reduces the gap (desirable for efficiency) without compromising the desired H+/H2 overpotential.
Indentation to Probe Atelectasis in Mammalian Lung
Authors: Silva Maricris C. , Hoyos Melissa D , Rooney Jean E , Gouldstone Andrew 
Published: June 2019

ABSTRACTOf all the internal organs, mechanical behavior of the lung is arguably most closely related to physiologic function. In inflation and deflation, lung parenchyma may be treated as an elastic material with some viscous damping. However, quasi-plasticity is observed, in the form of atelectasis, which is the localized collapse of alveoli under different conditions. General anesthesia in lung is known to increase tendency for pulmonary atelectasis, and this condition is typically removed by mechanical inflation to high pressures, which can be hazardous. The specific mechanisms of atelectasis are not fully known, one reason for this being the difficulty in developing a direct characterization method to perform causal investigations. In a previous abstract, we described the potential for controlled indentation tests to probe atelectatic tendency in lung. In this talk, we present the first results of ‘hardness testing’ on dog and rabbit lung, using different inflation schemes. Specifically, we indented excised lungs at physiologic pressures, inflated with air, pure oxygen, and 0.2% isoflurane in oxygen. Between these three conditions, we found marked differences in ‘hardness’ of the lung, when indented with tip radii comparable to that of ribs. That is to say, large contrasts in residual impressions, as well as re-inflation behavior, were observed. In addition, effects of different inflation gases occurred within a much shorter time than previously reported in other surgical experiments, indicating perhaps different, faster mechanisms controlling atelectasis than previously considered.
Fracture and Energy Partitioning in Uncooked and Cooked Noodles
Authors: Sui Zhongquan , Corke Harold , Oyen Michelle L. , Lucas Peter W. 
Published: June 2019

ABSTRACTHumans perform fascinating science experiments at home on a daily basis when they undertake the modification of natural and naturally-derived materials by a cooking process prior to consumption. The material properties of such foods are of interest to food scientists (texture is often fundamental to food acceptability), oral biologists (foods modulate feeding behavior), anthropologists (cooking is probably as old as the genus Homo and distinguishes us from all other creatures) and dentists (foods interact with tooth and tooth replacement materials). Material scientists may be interested in the drastic changes in food properties observed over relatively short cooking times. In the current study, the mechanical properties of one of the most common (and oldest at 4,000+ years) foods on earth, the noodle, were examined as a function of cooking time. Two types of noodles, each made from natural materials (wheat flour, salt, alkali and water) by kneading dough and passing them through a pasta-making machine. These were boiled for between 2–14 min and tested at regular intervals from raw to an overcooked state. Cyclic tensile tests at small strain levels were used to examine energy dissipation characteristics. Energy dissipation was >50% per cycle in uncooked noodles, but decreased by an order of magnitude with cooking. Fractional dissipation values remained approximately constant at cooking times greater than 7 min. Overall, a greater effect of cooking was on viscoplastic dissipation characteristics rather than fracture resistance. The results of the current study plot the evolution of a viscoplastic mixture into an essentially elastic material in the space of 7 minutes and have broad implications for understanding what cooking does to food materials. In particular, they suggest that textural assessments by consumers of the optimally cooked state of food has a definite physical definition.
Load Carrying Mechanisms in Wood at Different Observation Scales: A Combined Random-Periodic Multistep Homogenization Scheme
Authors: Hofstetter Karin , Hellmich Christian , Eberhardsteiner Josef 
Published: June 2019

ABSTRACTWood exhibits a highly diversified microstructure. It appears as a solid-type composite material at a length scale of some micrometers, while it resembles an assembly of plate-like elements arranged in a honeycomb fashion at the length scale of some hundreds of micrometers. These structural features of wood result in different load carrying mechanisms at different observation scales and at different loading conditions. In this paper, we elucidate the main load carrying mechanisms by means of a micromechanical model for wood across different species, based on tissue-independent stiffness properties of cellulose, lignin, and water. The model comprises three homogenization steps, two based on continuum micromechanics and one on the unit cell method. The latter represents plate-like bending and shear of the cell walls, due to transverse shear loading and axial straining in the tangential direction Accurate representation of these deformation modes results in accurate (orthotropic) stiffness estimates, which deviate, on average, by less than 10 % from corresponding experimental results, across a variety of softwood species.
Effect of Water on Mechanical Properties of Mineralized Tissue Composites
Authors: Bembey Amanpreet Kaur , Oyen Michelle L , Ferguson Virginia L. , Bushby Andrew J. , Boyde Alan 
Published: June 2019

ABSTRACTIn the current study, the effects of polar solvents on tissue volume and mechanical properties are considered. Area shrinkage measurements are conducted for mineralized, bone tissue samples soaked in polar solvents. Area shrinkage is used to calculate approximate linear and volume shrinkage. Results are compared with viscoelastic mechanical parameters for bone in the same solvents (as measured previously) and with both shrinkage measurements and mechanical data for nonmineralized tissues, as taken from the existing literature. As expected, the shrinkage of mineralized tissues is minimal when compared with shrinkage of nonmineralized tissues immersed in the same polar solvents. The mechanical changes in bone are also substantially less than in nonmineralized tissues. The largest stiffness values are found in shrunken bone samples (immersed in acetone and ethanol). The mineral phase in bone thus resists tissue shrinkage that would otherwise occur in the pure soft tissue phase.
Nanomechanics of Knockout Mouse Bones
Authors: Kavukcuoglu N Beril , Mann Adrian B. 
Published: June 2019

ABSTRACTOsteocalcin (OC) and osteopontin (OPN) are among the most abundant non-collagenous bone matrix proteins. Both have drawn interest from investigators studying their function in osteoporosis and it is known that mutations of these proteins can also have dramatic effects on the properties of bone. Other proteins including fibrillin 1 and 2 (FBN2) have been less widely studied, but can be mutated in some individuals resulting in connective tissue disorders. It has been reported that abnormal fibrillin may play a role in decreased bone mass. In this study bones from osteopontin (OPN), osteocalcin (OC) and fibrillin-2 (FBN2) knockout mice have been investigated. The study has identified how these proteins affect the bone's nanomechanical properties (hardness and elastic modulus). Nanoindentation tests were performed on the radial axis of cortical femora bones from the knockout mice and their wildtype controls. The results showed that young (age< 12 weeks) OPN knock-out bones have significantly lower mechanical properties than wild-type bones indicate a crucial role for OPN in early bone mineralization. After 12 weeks of age, the OPN knockout and wild-type control bones did not show any statistical difference. In OC deficient mice the mechanical properties were found to increase in the cortical mid-shaft of femora from 1 year old mice, suggesting an increase in bone mineralization, but 3 month old FBN2 deficient mice bones showed a decrease in mechanical properties across the cortical radial axis of the mid- femora.
Multiscale Modeling of Carbon Nanotube Adhesion for Dry Adhesives
Authors: Xia Zhenhai , Liang Jianyu 
Published: June 2019

ABSTRACTGeckos have extraordinary ability to move on vertical surfaces and ceilings. The secret of the climbing ability stems from their foot pads, a special hierarchical hairy structure. Mimicking such structure would lead to dry adhesives for many applications. Recent experiments showed that the adhesion of multiwalled carbon nanotubes is larger than that of a gecko foot-hair. To explore the adhesive mechanisms of the nanotubes, we have developed a multiscale approach to simulate the adhesion process of carbon nanotubes. A molecular dynamics is used to simulate the deformation and damage of the nanotubes when contacting with a rough surface at atomic scale. A coarse graining method is developed to predict the interactions and adhesion of larger scale nanotube array. The parameters used in the coarse graining method are determined by the detailed molecular dynamics. The preliminary results show that the nanotube bending under pre-applied pressure increases the contact area and therefore enhances the adhesion. The nanotube breakage during pre-loading will reduce the adhesion in post cycles. These results are consistent with the experiments found in literature.
Atomistic Simulations of Strain Rate Dependent Deformation Behavior at Continuum Timescales
Authors: Tomar Vikas 
Published: June 2019

AbstractA majority of computational mechanical analyses of nanocrystalline materials or nanowires have been carried out using classical molecular dynamics (MD). Due to the fundamental reason that the MD simulations must resolve atomic level vibrations, they cannot be carried out at the timescale of the order of microseconds. Additionally, MD simulations have to be carried out at very high loading rates (∼108 s−1) rarely observed in experiments. In this investigation, a modified Hybrid Monte Carlo (HMC) method that can be used to analyze time-dependent (strain rate dependent) atomistic mechanical deformation of nanostructures at continuum timescales is established. In this method there is no restriction on the size of MD timestep except that it must be such that to ensure a reasonable acceptance rate between consecutive Monte-Carlo (MC) time-steps. For the purpose of comparison HMC analyses of Cu nanowires deformation at two different strain rates (108 s−1 and 109 s−1) (each with three different timesteps 2 fs, 4fs, and 8 fs) are compared with the analyses based on MD simulations at the same strain rates and a MD timestep of 2 fs. As expected, the defect formation is found to be strain rate dependent. In addition, HMC with timestep of 8 fs correctly reproduces defect formation and stress-strain response observed in the case of MD with 2 fs (for the interatomic potential used 2 fs is the highest MD timestep). Simulation time analyses show that by using HMC a saving of the order of 4 can be achieved bringing the atomistic analyses closer to the continuum timescales.
Grain Boundary Responses to Local and Applied Stress: An In Situ TEM Deformation Study
Authors: Miller Bryan , Fenske Jamey , Su Dong , Li Chung-Ming , Dougherty Lisa , Robertson Ian M. 
Published: June 2019

AbstractDeformation experiments at temperatures between 300 and 750 K have been performed in situ in the transmission electron microscope to investigate dislocation interactions and reactions with grain boundaries and other obstacles. Dislocations, both partial and perfect, as well as deformation twins have been observed being emitted from grain boundaries and, in some cases, even the same grain boundary. The ejection of dislocations from the grain boundary can result in its partial or total annihilation. In the latter case, the disintegration of the grain boundary was accompanied by grain growth and a change in misorientation.
On the Characterization of Thin Film-only Mechanical Property Based on the Indentation Image Analysis
Authors: Lee Yun-Hee , Kim Yong-Il , Jang Hoon-Sik , Nahm Seung-Hoon , Kim Ju-Young , Kwon Dongil , Jang Jae-il 
Published: June 2019

AbstractConventional nanoindentation testing generally uses a peak penetration depth of less than 10 % of thin-film thickness in order to measure film-only mechanical properties, without considering the critical depth for a given thin film-substrate system. The uncertainties in this testing condition make hardness measurement more difficult. We propose a new way to determine the critical relative depth for general thin-film/substrate systems; an impression volume analyzed from the remnant indent image is used here as a new parameter. Nanoindents made on soft Cu and Au thin films with various indentation loads were observed by atomic force microscope. The impression volume calculated from 3D remnant image was normalized by the indenter penetration volume. This indent volume ratio varied only slightly in the shallow regime but decreased significantly when the indenter penetration depth exceeded the targeted critical relative depth. Thus, we determined the critical relative depth by empirically fitting the trend of the indent volume ratio and determining the inflection point. The critical relative depths for Cu and Au films were determined as 0.170 and 0.173, respectively, values smaller than 0.249 and 0.183 determined from the hardness variation of the two thin films. Hence the proposed indent volume ratio is highly sensitive to the substrate constraint, and stricter control of the penetration depth is needed to measure film-only mechanical properties.
Size Effect in the Initiation of Plasticity for Ceramics in Nanoscale Contact Loading
Authors: Zhu Tingting , Hou X.D. , Walker C. J. , P'ng K. M.Y. , Dunstan D. J. , Bushby A. J. 
Published: June 2019

AbstractIn nanoindentation, the plasticity size effect has been observed for several years, where a higher hardness is measured as indenter size decreases. In this paper, we report the size effect on the initiation of plasticity in ceramics by using spherical indenters. Here, we show a clear method that is able to determine the details of the onset of plasticity in nanoindentation. This enables us to measure the yield pressure with a high degree of accuracy and over a large range of indenter radii (hundreds of nanometers to several tens of micrometers). Our data shows clearly that there is a significant yield strength enhancement, which is inversely proportional to the cube root of the indenter radius. Also after normalization by the bulk yield strength, the increase in yield strength with decreasing indenter radius is shown to follow a single relation for all the ceramics studied in agreement with recent results for metals [1], and consistent with critical thickness theory for the initiation of yielding over a finite volume.
Thermal Effects of Phase Transformations: A General Approach
Authors: Umantsev Alex 
Published: June 2019

AbstractAll stages of phase transformations in materials, nucleation, growth, and coarsening, are subjected to thermal effects that stem from the redistribution of energy in the system like, release of latent heat and heat conduction. The thermal effects change the rate and outcome of the transformation and may result in appearance of unusual states or phases, in particular in nanosystems. This paper is not a complete account of the theory of thermal effects; it is rather a guide through many seemingly unrelated effects in different phase transformations, which in fact have unified origin. Although the dynamical Ginzburg-Landau approach will be used for the analysis of the effects, they are robust and independent of the employed theoretical methods. Another purpose of this review is to bring these effects to the attention of experimenters and motivate them on conducting new experiments in the area of phase transitions.