Thermal vibration analysis of orthotropic nanoplates based on nonlocal continuum mechanics

This paper presents the thermal vibration analysis of orthotropic nanoplates such as graphene, using the two variable refined plate theory and nonlocal continuum mechanics for small scale effects. The nanoplate is modeled based on two variable refined plate theory and the axial stress caused by the thermal effects is also considered. The two variable refined plate theory takes account of transverse shear effects and parabolic distribution of the transverse shear strains through the thickness of the plate, hence it is unnecessary to use shear correction factors. Nonlocal governing equations of motion for the nanoplate are derived from the principle of virtual displacements. The closed form solution for thermal-vibration frequencies of a simply supported rectangular nanoplate has been obtained by using Navier's method of solution. Numerical results obtained by the present theory are compared with available solutions in the literature and the molecular dynamics results. The influences of the small scale coefficient, the room or low temperature, the high temparature, the half wave number and the aspect ratio of nanoplate on the natural frequencies are considered and discussed in detail. It can be concluded that the present theory, which does not require shear correction factor, is not only simple but also comparable to the first-order and higher order shear deformation theory. The present analysis results can be used for the design of the next generation of nanodevices that make use of the thermal vibration properties of the nanoplates. (C) 2012 Elsevier B.V. All rights reserved.

PIV study on the dimple mid-plane of a narrow rectangular channel with dimples applied to one wall

This paper presents an investigation of the fluid flow in the fully developed portion of a rectangular channel (Aspect Ratio of 2) with dimples applied to one wall at channel Reynolds numbers of 20,000, 30,000, and 40,000. The dimples are applied in a staggered-row, racetrack configuration. Results for three different dimple geometries are presented: a large dimple, small dimple, and double dimple. Heat transfer and aerodynamic results from preceding works are presented in Nusselt number and friction factor augmentation plots as determined experimentally. Using particle image velocimetry, the region near the dimple feature is studied in detail in the location of the entrainment and ejection of vortical packets into and out of the dimple; the downstream wake region behind each dimple is also studied to examine the effects of the local flow phenomenon that result in improved heat transfer in the areas of the channel wall not occupied by a feature. The focus of the paper is to examine the secondary flows in these dimpled channels in order to support the previously presented heat transfer trends. The flow visualization is also intended to improve the understanding of the flow disturbances in a dimpled channel; a better understanding of these effects would lead the development of more effective channel cooling designs. Copyright © 2011 by ASME.

Efficient field emission properties of ZnO (core)/graphite (shell) nanowires

In this work the field emission studies of a new type of field emitter, zinc oxide (ZnO) core/graphitic (g-C) shell nanowires are presented. The nanowires are synthesized by chemical vapor deposition of zinc acetate at 1300 degrees C Scanning and transmission electron microscopy characterization confirm high aspect ratio and novel core-shell morphology of the nanowires. Raman spectrum of the nanowires mat represents the characteristic Raman modes from g-C shell as well as from the ZnO core. A low turn on field of 2.75 V/mu m and a high current density of 1.0 mA/cm(2) at 4.5 V/mu m for ZnO/g-C nanowires ensure the superior field emission behavior compared to the bare ZnO nanowires. (C) 2012 Elsevier B.V. All rights reserved.

Natural convection in a series of thermally interacting cavities with wall mounted heaters

Laminar natural convection in a series of thermally interacting cavities is numerically studied. Each cavity consists of a conducting bottom wall with a surface mounted heater. The side walls of the cavities are isothermally cooled. Each cavity thermally interacts with its adjacent cavities through the conducting walls. Flow and heat transfer characteristics are studied in detail for various Rayleigh numbers. The convection characteristics in multiple cavities are compared with those in single independent cavity. The thermal interaction between the cavities results in lower temperatures compared with those in independent cavities. While heat is rejected into the adjacent upper cavity through some portion of the conducting wall, heat is received from the adjacent cavity through the remaining portion of the wall. The influence of substrate conductivity on heat exchange between adjacent cavities are examined. Substrate conductivity shows strong effect on temperature distribution. When cooling at both vertical sides is changed to one side cooling, the heat transfer characteristics are changed drastically and many interesting flow features are observed. Effects of cavity aspect ratio is studied and higher heat transfer rates are observed at higher aspect ratios. Correlations for dimensionless temperature maximum and average Nusselt number are presented in terms of Rayleigh number.

Size-dependent free flexural vibration behavior of functionally graded nanoplates

In this paper, size dependent linear free flexural vibration behavior of functionally graded (FG) nanoplates are investigated using the iso-geometric based finite element method. The field variables are approximated by non-uniform rational B-splines. The nonlocal constitutive relation is based on Eringen's differential form of nonlocal elasticity theory. The material properties are assumed to vary only in the thickness direction and the effective properties for the FG plate are computed using Mori-Tanaka homogenization scheme. The accuracy of the present formulation is demonstrated considering the problems for which solutions are available. A detailed numerical study is carried out to examine the effect of material gradient index, the characteristic internal length, the plate thickness, the plate aspect ratio and the boundary conditions on the global response of the FG nanoplate. From the detailed numerical study it is seen that the fundamental frequency decreases with increasing gradient index and characteristic internal length. (c) 2012 Elsevier B.V. All rights reserved.

Nanoparticle agglomeration in an evaporating levitated droplet for different acoustic amplitudes

Radiatively heated levitated functional droplets with nanosilica suspensions exhibit three distinct stages namely pure evaporation, agglomeration, and finally structure formation. The temporal history of the droplet surface temperature shows two inflection points. One inflection point corresponds to a local maximum and demarcates the end of transient heating of the droplet and domination of vaporization. The second inflection point is a local minimum and indicates slowing down of the evaporation rate due to surface accumulation of nanoparticles. Morphology and final precipitation structures of levitated droplets are due to competing mechanisms of particle agglomeration, evaporation, and shape deformation. In this work, we provide a detailed analysis for each process and propose two important timescales for evaporation and agglomeration that determine the final diameter of the structure formed. It is seen that both agglomeration and evaporation timescales are similar functions of acoustic amplitude (sound pressure level), droplet size, viscosity, and density. However, we show that while the agglomeration timescale decreases with initial particle concentration, the evaporation timescale shows the opposite trend. The final normalized diameter can be shown to be dependent solely on the ratio of agglomeration to evaporation timescales for all concentrations and acoustic amplitudes. The structures also exhibit various aspect ratios (bowls, rings, spheroids) which depend on the ratio of the deformation timescale (t(def)) and the agglomeration timescale (t(g)). For t(def) < t(g), a sharp peak in aspect ratio is seen at low concentrations of nanosilica which separates high aspect ratio structures like rings from the low aspect ratio structures like bowls and spheroids. (C) 2013 American Institute of Physics. http://dx.doi.org/10.1063/1.4775791]

Uninterrupted and reusable source for the controlled growth of nanowires

Generally, the length of the oxide nanowires grown by vapor phase transport is limited by the degradation of the source materials. Furthermore, the source material is used once for the nanowires growth. By exploiting the Si-Zn phase diagram, we have developed a simple methodology for the non-catalytic growth of ultralong ZnO nanowires in large area with controllable aspect ratio and branched structures. The insolubility of Zn in Si and the use of a Si cap on the Zn source to prevent local source oxidation of Zn (i.e. prevents the degradation of the source) are the keys to grow longer nanowires without limitations. It has been shown that the aspect ratio can be controlled by thermodynamically (temperature) and more importantly by kinetically (vapor flux). One of the interesting findings is that the same source material can be used for several depositions of oxide nanostructured materials.

Doping by diffusion of dopants from the substrate: synthesis of doped ZnO nanowires

We report on the substrate assisted doping of ZnO nanowires grown by a vapor transport technique. The nanowires were grown non-catalytically on multiwalled carbon nanotubes (MWCNTs) and soda lime glass (SLG). Carbon from MWCNTs and sodium from SLG diffuse into ZnO during the growth and are distributed uniformly and provide doping. An advantage associated with the technique is that no conventional external dopant source is required to obtain doped ZnO nanowires. The diameter, length and hence the aspect ratio can easily be varied by changing the growth conditions. The transport studies on both carbon and sodium doped ZnO support the p-type nature of ZnO. The p-type nature of carbon doped ZnO is stable for at least eight months.

Criteria for thermally induced atomization and catastrophic breakup of acoustically levitated droplet

We report thermally induced instability leading to catastrophic breakup in acoustically levitated vaporizing fuel droplets. Change in surface tension and viscosity with increase in droplet temperature causes wide fluctuations in droplet aspect ratio. If the viscous damping of aspect ratio oscillation is not strong enough, the droplet goes through unbounded stretching. If the droplet exceeds a critical Weber number locally, a bag type and capillary wave induced atomization can occur, which leads to catastrophic breakup. A stability criterion has been established based on the inhomogeneity of Bernoulli (acoustic) pressure and surface tension of the droplet in terms of a local Weber number and Ohnesorge number. This instability is thermally induced in a droplet which does not experience instabilities without heating. (C) 2012 Elsevier Ltd. All rights reserved.

Acto-myosin contractility rotates the cell nucleus

The nucleus of the eukaryotic cell functions amidst active cytoskeletal �laments, but its response to the stresses carried by these �laments is largely unexplored. We report here the results of studies of the translational and rotational dynamics of the nuclei of single �broblast cells, with the e�ects of cell migration suppressed by plating onto �bronectin-coated micro-fabricated patterns. Patterns of the same area but di�erent shapes and/or aspect ratio were used to study the e�ect of cell geometry on the dynamics. On circles, squares and equilateral triangles, the nucleus undergoes persistent rotational motion, while on high-aspect-ratio rectangles of the same area it moves only back and forth. The circle and the triangle showed respectively the largest and the smallest angular speed. We show that our observations can be understood through a hydrodynamic approach in which the nucleus is treated as a highly viscous inclusion residing in a less viscous uid of orientable �laments endowed with active stresses. Lowering actin contractility selectively by introducing blebbistatin at low concentrations drastically reduced the speed and persistence time of the angular motion of the nucleus. Time-lapse imaging of actin revealed a correlated hydrodynamic ow around the nucleus, with pro�le and magnitude consistent with the results of our theoretical approach. Coherent intracellular ows and consequent nuclear rotation thus appear to be a generic property that cells must balance by speci�c mechanisms in order to maintain nuclear homeostasis

OTCYMIST: Otsu-Canny minimal spanning tree for born-digital images

Text segmentation and localization algorithms are proposed for the born-digital image dataset. Binarization and edge detection are separately carried out on the three colour planes of the image. Connected components (CC's) obtained from the binarized image are thresholded based on their area and aspect ratio. CC's which contain sufficient edge pixels are retained. A novel approach is presented, where the text components are represented as nodes of a graph. Nodes correspond to the centroids of the individual CC's. Long edges are broken from the minimum spanning tree of the graph. Pair wise height ratio is also used to remove likely non-text components. A new minimum spanning tree is created from the remaining nodes. Horizontal grouping is performed on the CC's to generate bounding boxes of text strings. Overlapping bounding boxes are removed using an overlap area threshold. Non-overlapping and minimally overlapping bounding boxes are used for text segmentation. Vertical splitting is applied to generate bounding boxes at the word level. The proposed method is applied on all the images of the test dataset and values of precision, recall and H-mean are obtained using different approaches.

Thermal vibration analysis of monolayer graphene embedded in elastic medium based on nonlocal continuum mechanics

This paper presents the thermal vibration analysis of single-layer graphene sheet embedded in polymer elastic medium, using the plate theory and nonlocal continuum mechanics for small scale effects. The graphene is modeled based on continuum plate theory and axial stress caused by the thermal effects is also considered. Nonlocal governing equation of motion for this graphene sheet system is derived from the principle of virtual displacements. The closed form solution for thermal-vibration frequencies of a simply supported rectangular nanoplate has been obtained by using the Navier's method of solution. Numerical results obtained by the present theory are compared with available solutions in the literature and the molecular dynamics results. The influences of the small scale coefficient, the room or low temperature, the high temperature, the half wave number and the aspect ratio of nanoplate on the natural frequencies are considered and discussed in detail. The thermal vibration analysis of single- and double-layer graphene sheets are considered for the analysis. The mode shapes of the respective graphene system are also captured in this work. The present analysis results can be used for the design of the next generation of nanodevices that make use of the thermal vibration properties of the graphene.

Microstructure and texture evolution during sub-transus thermo-mechanical processing of Ti-6Al-4V-0.1B alloy: part II. static annealing in (alpha plus beta) regime

The first part of this study describes the evolution of microstructure and texture in Ti-6Al-4V-0.1B alloy during sub-transus rolling vis-A -vis the control alloy Ti-6Al-4V. In the second part, the static annealing response of the two alloys at self-same conditions is compared and the principal micromechanisms are analyzed. Faster globularization kinetics has been observed in the Ti-6Al-4V-0.1B alloy for equivalent annealing conditions. This is primarily attributed to the alpha colonies, which leads to easy boundary splitting via multiple slip activation in this alloy. The other mechanisms facilitating lamellar to equiaxed morphological transformations, e.g., termination migration and cylinderization, also start early in the boron-modified alloy due to small alpha colony size, small aspect ratio of the alpha lamellae, and the presence of TiB particles in the microstructure. Both the alloys exhibit weakening of basal fiber (ND||aOE (c) 0001 >) and strengthening of prism fiber (RD||aOE (c) aOE(a)) upon annealing. A close proximity between the orientations of fully globularized primary alpha and secondary alpha phases during alpha -> beta -> alpha transformation has accounted for such a texture modification.

Yield stress, thixotropy and shear banding in a dilute aqueous suspension of few layer graphene oxide platelets

We demonstrate a rigidity percolation transition and the onset of yield stress in a dilute aqueous dispersion of graphene oxide platelets (aspect ratio similar to 5000) above a critical volume fraction of 3.75 x 10(-4) with a percolation exponent of 2.4 +/- 0.1. The viscoelastic moduli of the gel at rest measured as a function of time indicate the absence of structural evolution of the 3D percolated network of disks. However a shear-induced aging giving rise to a compact jammed state and shear rejuvenation indicating a homogenous flow is observed when a steady shear stress (sigma) is imposed in creep experiments. We construct a shear diagram (sigma vs. volume fraction phi) and the critical stress above which shear rejuvenation occurs is identified as the yield stress sigma(y) of the gel. The minimum steady state shear rate (gamma) over dot(m) obtained from creep experiments agrees well with the end of the plateau region in a controlled shear rate flow curve, indicating a shear localization below (gamma) over dot(m). A steady state shear banding in the plateau region of the flow curve observed in particle velocimetry measurements in a Couette geometry confirms that the dilute suspensions of GO platelets form a thixotropic yield stress fluid.

Pulsed electric field mediated in vitro cellular response of fibroblast and osteoblast-like cells on conducting austenitic stainless steel substrate

This article reports the intermittent pulse electric field stimulus mediated in vitro cellular response of L929 mouse fibroblast/SaOS2 osteoblast-like cells on austenitic steel substrates in reference to the field strength dependent behavior. The cellular density and morphometric analyses revealed that the optimal electric (E) fields for the maximum cell density of adhered L929 (similar to 270 % to that of untreated sample) and SaOS2 (similar to 280 % to that of untreated sample) cells are 1 V (0.33 V/cm) and 2 V (0.67 V/cm), respectively. The trend in aspect ratio of elongated SaOS2 cells did not indicate any significant difference among the untreated and treated (up to 3.33 V/cm) cells. The average cell and nucleus areas (for SaOS2 cells) were increased with an increase in the applied voltage up to 8 V (2.67 V/cm) and reduced thereafter. However, the ratio of nucleus to total cell area was increased significantly on the application of higher voltages (2-10 V), indicating the possible influence of E-field on cell growth. Further, the cell density results were compared with earlier results obtained with sintered Hydroxyapatite (HA) and HA-BaTiO3 composites and such comparison revealed that the enhanced cell density on steel sample occurs upon application of much lower field strength and stimulation time. This indicates the possible role of substrate conductivity towards cell growth in pulsed E-field mediated culture conditions.