Hierarchical multiscale model for biomechanics analysis of microfilament networks

The mechanisms of force generation and transference via microfilament networks are crucial to the understandings of mechanobiology of cellular processes in living cells. However, there exists an enormous challenge for all-atom physics simulation of real size microfilament networks due to scale limitation of molecular simulation techniques. Following biophysical investigations of constitutive relations between adjacent globular actin monomers on filamentous actin, a hierarchical multiscale model was developed to investigate the biomechanical properties of microfilament networks. This model was validated by previous experimental studies of axial tension and transverse vibration of single F-actin. The biomechanics of microfilament networks can be investigated at the scale of real eukaryotic cell size (10 μm). This multiscale approach provides a powerful modeling tool which can contribute to the understandings of actin-related cellular processes in living cells.

Shear capacity of reinforced concrete columns strengthened with CFRP sheet

This paper discusses the results of tests on the shear capacity of reinforced concrete columns strengthened with carbon fiber reinforced plastic (CFRP) sheet. The shear transfer mechanism of the specimens reinforced with CFRP sheet was studied. The factors affecting the shear capacity of reinforced concrete columns strengthened with CFRP sheet were analyzed. Several suggestions such as the number of layers, width and tensile strength of the CFRP sheet are proposed for this new strengthening technique. Finally, a simple and practical design method is presented in the paper. The calculated results of the suggested method are shown to be in good agreement with the test results. The suggested design method can be used in evaluating the shear capacity of reinforced concrete columns strengthened with CFRP sheet.

Half metallicity in finite-length zigzag single walled carbon nanotube : A first-principle prediction

We predict here from first-principle calculations that finite-length (n,0) single walled carbon nanotubes (SWCNTs) with H-termination at the open ends displaying antiferromagnetic coupling when n is greater than 6. An opposite local gating effect of the spin states, i.e., half metallicity, is found under the influence of an external electric field along the direction of tube axis. Remarkably, boron doping of unpassivated SWCNTs at both zigzag edges is found to favor a ferromagnetic ground state, with the B-doped tubes displaying half-metallic behavior even in the absence of an electric field. Aside of the intrinsic interest of these results, an important avenue for development of CNT-based spintronic is suggested.

Vacancy mediated desorption of hydrogen from a sodium alanate surface : An ab initio spin-polarized study

Ab initio spin-polarized density functional theory calculations are performed to explore the effect of single Na vacancy on NaAlH4(001) surface on the initial dehydrogenation kinetics. The authors found that two Al–H bond lengths become elongated and weakened due to the presence of a Na vacancy on the NaAlH4(001) surface. Spontaneous recombination from the surface to form molecular hydrogen is observed in the spin-polarized ab initio molecular dynamics simulation. The authors’ results indicate that surface Na vacancies play a critical role in accelerating the dehydrogenation kinetics in sodium alanate. The understanding gained here will aid in the rational design and development of complex hydride materials for hydrogen storage

The role of V2O5 on the dehydrogenation and hydrogenation in magnesium hydride : An ab initio study

Ab initio density functional theory calculations are performed to study the experimentally observed catalytic role of V2O5 in the recycling of hydrogen in magnesium hydride. We find that the Mg–H bond length becomes elongated when MgH2 clusters are positioned on single, two, and three coordinated oxygen sites (O1, O2, and O3) on the V2O5(001) surface. Molecular hydrogen is predicted to spontaneously form at the hole site on the V2O5(001) surface. Additionally, the activation barrier for the dissociation of hydrogen on V-doped Mg(0001) surface is 0.20 eV, which is only 1/5 of that on pure Mg(0001) surface. Our results indicate that oxygen sites on the V2O5(001)surface and the V dopant in Mg may be important facilitators for dehydrogenation and rehydrogenation, respectively. The understanding gained here will aid in the rational design and development of Mg-based hydrogen storage materials.

Graphene-based thin film supercapacitor with graphene oxide as dielectric spacer

Thin film supercapacitors are produced by using electrochemically exfoliated graphene (G) and wet-chemically produced graphene oxide (GO). Either G/GO/G stacked film or sole GO film are sandwiched by two Au films to make devices, where GO is the dielectric spacer. The addition of graphene film for charge storage can increase the capacitance about two times, compared to the simple Au electrode. It is found that the GO film has very high dielectric constant, accounting for the high capacitance of these devices. AC measurements reveal that the relative permittivity of GO is in the order of 104 within the frequency range of 0.1–70 Hz.

Diffusion tensor of water in partially aligned fibre networks

Monte Carlo simulations were used to investigate the relationship between the morphological characteristics and the diffusion tensor (DT) of partially aligned networks of cylindrical fibres. The orientation distributions of the fibres in each network were approximately uniform within a cone of a given semi-angle (θ0). This semi-angle was used to control the degree of alignment of the fibres. The networks studied ranged from perfectly aligned (θ0 = 0) to completely disordered (θ0 = 90°). Our results are qualitatively consistent with previous numerical models in the overall behaviour of the DT. However, we report a non-linear relationship between the fractional anisotropy (FA) of the DT and collagen volume fraction, which is different to the findings from previous work. We discuss our results in the context of diffusion tensor imaging of articular cartilage. We also demonstrate how appropriate diffusion models have the potential to enable quantitative interpretation of the experimentally measured diffusion-tensor FA in terms of collagen fibre alignment distributions.

Effects of substrate temperature on the microstructure of YBa2Cu3O7-δ films grown on (001) Y-ZrO2 substrates

High-quality YBa2Cu3O7-δ films grown on (001) single-crystal Y-ZrO2 substrates by pulsed laser deposition have been studied as a function of substrate temperature using transmission electron microscopy. A transition from epitaxial films to c-axis oriented polycrystalline films was observed at 740°C. An intermediate, polycrystalline, BaZrO3 layer was formed from a reaction between the film and the substrate. A dominant orientation relationship of [001] YBCO//[001]int. layer//[001]YSZ and [110] YBCO//[110]int. layer//[100]YSZ was observed. The formation of grain boundaries in the films resulted in an increased microwave surface resistance and a decreased critical-current density. The superconducting transition temperature remained fairly constant at about 90 K.

Early stages of growth of YBa2Cu3O7-δ high Tc superconducting films on (001) Y-ZrO2 substrates

The early stages of growth of high quality YBa2Cu 3O7-δ (YBCO) films grown on (001) Y-ZrO2 (YSZ) substrates by pulsed laser deposition have been studied using a combination of atomic force microscopy and transmission electron microscopy. A one unit cell thick YBCO layer and relatively large CuO particles formed in the initial stages. Additional YBCO grew on top of the first layer in the form of one or a few unit cell high c-axis oriented islands about 30 nm in diameter. The rounded islands subsequently coalesced into faceted domains. Elongated Y 2BaCuO5 particles nucleated after the first layer of YBCO. A highly textured BaZrO3 layer formed between the YSZ and the YBCO with a cube-on-cube dominant orientation relationship with respect to the YBCO film.

Growth and properties of a multilayer system based on Y1Ba 2Cu3Ox and amorphous Y-ZrO2

The growth of c-axis oriented Y1Ba2Cu 3Ox thin films on an amorphous buffer layer of Y-ZrO 2, deposited on sapphire substrates, was investigated. Both films were grown by a pulsed laser deposition technique. A strong correlation was observed between the properties of Y1Ba2Cu 3Ox and the thickness of the buffer layer. A Tc of 89 K was obtained for an optimal buffer layer thickness of 9 nm. A model that adequately describes the film growth process was developed. A multilayer system of Y1Ba2Cu3Ox and amorphous Y-ZrO2 was grown and a Tc of 87 K for the upper c-axis oriented layer was measured.

YBa2Cu3O7-x films on yttria-stabilized ZrO2 substrates : influence of the substrate morphology

c-axis-oriented YBa2Cu3O7-x (YBCO) thin films were laser deposited on (001) yttria-stabilized ZrO2 (YSZ) substrates with different surface morphologies. The in-plane orientation of the films on smooth substrates was sensitive to the deposition conditions, often resulting in mixed orientations. However, a strongly dominating [110] YBCO//[110]YSZ orientation was obtained at a deposition temperature of 770°C. Films on substrates with surface steps, induced by depositing a homoepitaxial buffer layer or by thermally annealing the substrate, had a [110]YBCO//[100]YSZ orientation when deposited at the same temperature. It was concluded that the [110]YBCO//[100] YSZ orientation was promoted by a graphoepitaxial mechanism. Films prepared under identical conditions on smooth and stepped substrates grew with extended c axes on the former. It is proposed that the extension can be induced by disorder, invoked by a low oxygen pressure and a low density of adsorption sites. The disorder may be eliminated by either an increase of the oxygen pressure or an increase of the density of adsorption sites in the form of steps. The film microstructure influenced the microwave surface resistance, which was similar for films with one exclusive in-plane orientation and higher for films with mixed orientations. The films on the stepped surfaces had superior superconducting properties; inductive measurements gave a Tc onset of 88 K, a ΔT(90%-10%) c of 0.2 K, and the transport jc was 1.5×106 A/cm2 at 83 K, for films on substrates with homoepitaxial buffer layers.

Weak links and dc SQUIDS on artificial nonsymmetric grain boundaries in YBa2Cu3O7-δ

We have studied weak links and dc-SQUIDs made from pulsed laser deposited YBa2Cu3O7-δ thin films on Y-ZrO 2 bicrystal substrates. The transport properties of the weak links were studied as a function of the misorientation angle (θ) between the two halves of the bicrystal and an exponential dependence of the weak link critical current density was observed for angles up to 40°at 77 K. Josephson effects with clear microwave and magnetic field responses were observed. An optimum dc-SQUID performance at 77 K was obtained for θ=32°. At this temperature, we achieved a periodic magnetic field response with a modulation depth of 12 μV.

YBa2Cu3O7/NdGaO3/YBa 2Cu3O7 trilayers by modified off-axis sputtering

High-quality epitaxial YBa2Cu3O7-δ (YBCO) thin films were achieved by a modified off-axis sputtering technique with high deposition rates (3.3 nm/min). The film quality and the deposition rate depended crucially on the target-to-substrate separation. Epitaxial YBCO/NdGaO3(NGO)/YBCO trilayers were successfully grown onto SrTiO3, Y-ZrO2, and LaAlO3 substrates by dc and rf sputtering. The epitaxial relations were found to be [001] YBCO//[001]NGO, [100]YBCO, or [010] YBCO//[110]NGO and [001]YBCO//[110] NGO, [100]YBCO, or [010]YBCO//[001] NGO, where the latter orientation relationship was dominating. Subsequent top YBCO layers grew c axis oriented independently of the two epitaxial orientations of the NGO. The orientation relationships between YBCO and NGO were the same. Auger electron depth profiles and transmission electron microscopy indicated that the interdiffusion at the interface between the YBCO and NGO layers was not strong even at 740°C. The superconducting transition temperatures of the top and bottom YBCO layers were about the same as that of YBCO single layers, i.e., 87-90 K. Scanning electron microscopy of the surface morphologies of the YBCO and the NGO showed that a smaller substrate-target distance resulted in smoother films.

Investigations of the physical origins of etching LiNbO3 during Ti in-diffusion

We investigate the physical origins of etching observed during Ti diffusion. The relationship between observed etch depth and water vapor content in the annealing environment is quantified. The dynamics of the etching process are also identified. It is discovered that water vapor content is essential for etching and that there is a characteristic delay before etching is observed. From these observations we can conclude that the process is electrochemical in nature with ionic defects diffusing into the Ti strip from the lithium niobate and these defects catalyzing the dissociation of water into reactive ions.

F-actin crosslinker : a key player for the mechanical stability of filopodial protrusion

Filopodial protrusion initiates cell migration, which decides the fate of cells in biological environments. In order to understand the structural stability of ultra-slender filopodial protrusion, we have developed an explicit modeling strategy that can study both static and dynamic characteristics of microfilament bundles. Our study reveals that the stability of filopodial protrusions is dependent on the density of F-actin crosslinkers. This cross-linkage strategy is a requirement for the optimization of cell structures, resulting in the provision and maintenance of adequate bending stiffness and buckling resistance while mediating the vibration. This cross-linkage strategy explains the mechanical stability of filopodial protrusion and helps understand the mechanisms of mechanically induced cellular activities.