The transport mechanism of laminar combined convection flow of an incompressible viscous non-Newtonian nanofluid in a shear- and buoyancy-driven enclosure has been investigated in this article. The micropolar fluid model is used for the rheological behavior of the non-Newtonian fluid. A heat source with constant volumetric rate is attached in a part of the bottom wall and the remaining parts are thermally insulated. The vertical walls of the cavity are considered to be adiabatic, while the top wall is cooled and moves from left to right with uniform velocity. The thermal conductivity and the dynamic viscosity of the nanofluid are represented by different experimental correlations that are suitable to each nanoparticles. The finite volume method is applied to solve the dimensionless form of the governing equations. A discussion is provided for the effects of the governing parameters on the local Nusselt number and average Nusselt number along the heat source. It is found that an increase in the vortex-viscosity parameter causes a reduction in the local Nusselt number. As the vortex-viscosity parameter increases by 10 times from 0.5 to 5, the Nusselt number reduces by 15%. Additionally, as the nanoparticle volume fraction increases, the rate of heat transfer increases. As the volume fraction increases by 100% from 0.1 to 0.2, the Nusselt number increases by 86%.
This article reports synergetic effect of naturally available Indian bentonite nanoclay and fire retardants on the thermal and fire retardation behavior of vinylester. Indian bentonite nanoclay organically modified with hexadecyltrimethylammonium bromide by cation exchange capacity method, along with aluminum trihydroxide and magnesium hydroxide were dispersed in vinylester and tested. Addition of 30% aluminum trihydroxide and 4 wt% Indian bentonite increased the glass transition temperature of vinylester by 24.4%; decreased thermal degradation by 47%, vertical burning rate by 54% and horizontal burning rate by 72%; and increased limiting oxygen index by 56.6% and microhardness by 49.6%.
Wave propagation analysis of a functionally graded carbon nanotubes reinforced piezoelectric composite (FG-CNTRPC) microplate is the major main of the present research. In order to present a realistic model, the material properties of the system are assumed viscoelastic and the Kelvin–Voigt model is applied. The viscoelastic FG-CNTRPC microplate is subjected to longitudinal magnetic and three-dimensional electric fields. The distribution of carbon nanotubes in FG-CNTRPC microplate is supposed as uniform distribution and surrounding circumference is simulated as Visco-Pasternak foundation. The original formulation of the quasi-three-dimensional sinusoidal shear deformation plate theory is here extended to the wave propagation analysis and the size effects are considered based on Eringen’s nonlocal theory. In order to calculate the dimensionless frequency, cut-off and escape frequencies analytical solution is applied. In this article, the influences of the volume fraction of carbon nanotubes, electro-magnetic fields and elastic medium on the dimensionless frequency of viscoelastic FG-CNTRPC microplate are investigated. Furthermore, the effect of small-scale parameter on the cut-off and escape frequencies of the system will be studied. Results demonstrate that the dimensionless cut-off and escape frequencies decrease with increasing the magnitude of small-scale parameter. In addition, the imposed magnetic field and external voltage are significant parameters for controlling wave propagation of the viscoelastic FG-CNTRPC microplate. Results of this investigation can be helpful for the study and design of composite systems based on smart control and sensor applications.
The unsteady forced bioconvection boundary layer flow of a viscous incompressible micropolar nanofluid containing microorganisms over a stretching/shrinking sheet is studied numerically. A mathematical model, with the aid of appropriate transformations, is presented. The transformed non-linear ordinary differential equations are solved numerically by the Runge–Kutta–Fehlberg fourth- to fifth-order numerical method. The effect of the governing parameters on the dimensionless velocity, micro-rotation, temperature, nanoparticle volume fraction and microorganism as well as the local skin friction coefficient, the heat transfer rate and microorganisms transfer rate is thoroughly examined. The findings show that the value of skin friction and Nusselt number are decreased and microorganism number is increased as velocity slip, thermal slip and microorganism slip parameter are increased, respectively. Results from this investigation were compared with previous investigations demonstrating very good correlation. The present results are relevant to improving the performance of microbial fuel cells deploying nanofluids.
This article presents the synthesis and the structural, morphological, magnetic and spectroscopic characterisations of GaN-doped Fe2O3 nanoparticles prepared by the sol–gel method. The ‘Sci find’ software was unable to trace any of the references to point out the earlier knowledge and existence of this novel compound in the literature. We claim our contribution for the same. The structural analysis is done using the X-ray diffraction and energy-dispersive X-ray analysis, while the morphological analysis is done by the scanning electron microscope and the transmission electron microscope. The samples show a simple cubic crystalline structure. The morphological and energy-dispersive X-ray analysis and the infrared studies confirm the composition of the material and the particle sizes of the samples are found to be in the range of 9–27 nm (for x = 0.5) and 23–30 nm (for x = 0.75). The particle sizes, obtained from the histogram evaluations, the Debye–Scherrer formula in X-ray diffraction and the selected area electron diffraction measurements are all in good agreement. The room temperature magnetic measurements obtained using the vibration sample magnetometer for x = 0.5, 0.75,1 and 5 are presented as the hysteresis curves and their related plots. The discussion about the conclusions drawn therein infers that the coercivity increases with the concentration. The compound exhibits spinel structure and vivid changes from the super paramagnetic to the ferromagnetic state.
This article confirms experimental results by finite element analysis. The study includes meshing the specimen of size 40 x 12 x 6 mm3. The model is constructed in DesignModeler (ANSYS Workbench). Multi-walled carbon nanotubes are aligned in different angles to correlate the experimental results. The modelling method employed for analysis is based on weight ratio. The proportion of multi-walled carbon nanotubes is 0.25%, 0.5%, 0.75% and 1% by weight of polymer matrix (epoxy resin) for different specimens. Multi-walled carbon nanotubes are dispersed in epoxy matrix using ultrasonic energy. Composite beams were tested under flexure in order to evaluate their mechanical property such as load–deflection criteria by three-point bending test. Finite element method results were in close agreement with the experimental outcomes with different orientation of multi-walled carbon nanotubes into the matrix considered.
Ni-P composite coatings were prepared on cellulose fiber surface via a simple electroless Ni-P approach. The metal-coated extent, dispersion extent of micro or nano cellulose fibers and crystalline structure of Ni-P composite coatings were investigated. The homogeneous hollow composite coatings and metal-coated extent of micro or nano cellulose fibers were improved with the increase in ultrasonic power, and the ideal composite coatings were obtained as ultrasonic up to 960 W. The metallization for cellulose fibers enhanced the dispersion extent of micro or nano cellulose fibers. A uniform coating, consisting of the hollow coating on cellulose fibers surface, could be obtained. At the same time, metallization did not damage the original structure and surface functional groups of cellulose fibers. The concentration of cellulose fibers and ultrasonic power had a direct influence on the metal-coated extent of cellulose fiber surface. The metal-coated extent, dispersion extent of micro or nano cellulose fibers and crystalline structure of Ni-P composite coatings exhibited excellent properties as the concentration of cellulose fibers and ultrasonic power were 2 g/L and 960 W, respectively.
Surface texturing helps in reducing the reflectance of the surface and hence it improves the ultimate efficiency of the solar cell. In this article, rigorous coupled wave analysis was used to find out the effect of different nanohole parameters such as nanohole diameter (D), pitch (P) and nanohole depth (H) on the reflectance and the ultimate efficiency of a c-Si solar cell of 275 μm thickness. Response surface methodology was used for co-relating the nanohole geometry parameters with the ultimate efficiency. The developed relation was used for optimization using genetic algorithm implemented through MATLAB. The optimized parameters have resulted in a 17.81% improvement in ultimate efficiency as compared with bare substrate of same thickness. A comparative study was made on the effect of parameters on the ultimate efficiency of the solar cell and it was found that higher value of diameter yielded greater ultimate efficiency. Finally, the performance of structured Si was compared with that of bare Si and Si coated with anti-reflective coating in various configurations. A 50 nm deep hole filled with anti-reflective coating and with a top surface anti-reflective coating of 75 nm yielded the highest ultimate efficiency of 47.61%.
This article analyses the transient magnetohydrodynamic free convective flow in vertical micro-concentric annuli in the presence of velocity slip and temperature jump at the outer surface of the inner cylinder and the inner surface of the outer cylinder. The Laplace transform technique has been used to find the solutions for the velocity and temperature fields by solving the governing partial differential equations in Laplace domain. However, the Riemann-sum approximation method is used to invert the Laplace domain to the time domain. The solution derived is validated by assenting comparison with exact solutions derived for the steady state which has been derived separately. An excellent agreement was found for transient and steady state at large value of time. The solution obtained for the velocity has been used to compute the skin friction, while the temperature has been used to compute the Nusselt number. The effect of various flow parameters entering into the problem such as time, Prandtl number, curvature radius ratio, Hartmann number, rarefaction parameter, and fluid–wall interaction parameter are discussed with the aid of line graphs.
Several types of carbon nanotubes in their perfect and imperfect form were simulated, and their vibrational behavior was studied by performing computational examinations with fixed-free boundary conditions. Both computational and analytical results were compared in the case of perfect tubes. Afterward, three kinds of imperfections, that is, twisting angle, z-distortion along the longitudinal axis and xy-distortion along the radial axis, were introduced to the structure of perfect carbon nanotubes, and the natural frequencies of imperfect carbon nanotubes were numerically evaluated and compared with the behavior of the perfect ones. It was concluded that the existence of any type of imperfection in the structure of carbon nanotubes leads to a lower natural frequency and, as a result, lower vibrational stability. However, this trend was more visible for the carbon nanotubes with higher chirality.
This paper theoretically investigates the conjugate effects of viscous dissipation and non-uniform heat source/ sink on the double-diffusive boundary layer flow of a viscoelastic nanofluid over a stretching sheet. In this model, where binary nanofluid is used, the Brownian motion, thermophoresis and cross-diffusion are classified as the main mechanisms which are responsible for the enhancement of the convection features of the nanofluid. The boundary layer equations governed by the partial differential equations are transformed into a set of ordinary differential equations with the help of group theory transformations. Computations are made by the hp-Galerkin finite element method (FEM). The hp-FEM needs a smaller number of nodes and consequently, less computational time and less memory to achieve the same or even better accuracy than h-FEM. A detailed evaluation of the effects of the governing physical parameters on the velocity, temperature, solutal and nanoparticle concentration via graphical plots is conducted for two different cases, namely prescribed surface temperature (PST) and prescribed heat flux (PHF). The reduced Sherwood number (in PST-case) is observed to be increased with the effects of nanofluid and the modified Dufour parameter, whereas the contrary behaviour is computed for the surface solutal concentration in PHF-case. Heat transfer is increasing function of viscoelastic parameter and decreasing function of Brownian motion, thermophoresis, space and time dependent heat source/sink parameter and Eckert number. Mass transfer is increasing function of Eckert number, space and time dependent heat source/sink parameter and decreasing function of viscoelastic parameter.
In this article, using energy method, the effect of surface stress on the free vibration and bending analysis of single-layer graphene sheet embedded in an elastic medium based on nonlocal elasticity theory is studied. Surface stress plays a more important role due to the high surface-to-volume ratio in nanoscale materials. For this purpose, Gurtin–Murdoch continuum mechanics approach is used. The effects of surface properties including surface elasticity, surface residual stresses and surface mass density are considered. In this research, the effects of Winkler spring constant, Pasternak shear constant, aspect ratio, Young’s modulus of surface layer, surface residual stress, nonlocal parameter on the natural frequency ratio and deflection of single-layer graphene sheet are investigated. The results indicate that the natural frequency ratio decreases with an increase in the surface residual stress and vice versa for deflection of nonlocal single-layer graphene sheet. Also, the natural frequency ratio increases with an increase in Young’s modulus of surface layer and vice versa for deflection of nonlocal single-layer graphene sheet. Moreover, the elastic medium causes to stiffen the single-layer graphene sheet. The influence of the small-scale parameter on the natural frequency ratio and deflection of single-layer graphene sheet is more significant for lower values of foundation parameters and vice versa for higher values of foundation parameters.
A finite element analysis is performed to study the unsteady natural convection flow of a nanofluid past a vertical cone under the influence of applied magnetic field and thermal radiation. The governing two-dimensional momentum, energy and concentration are highly non-linear coupled partial differential equations. They are solved by finite element method based on Galerkin weighted residual approach. The investigations are conducted for the effects of various physical parameters such as magnetic parameter (M), Prandtl number (Pr), radiation parameter (Rd ), Lewis number (Le), Brownian motion parameter (Nb), thermophoresis parameter (Nt), ratio of Grashof numbers and index parameter (n). The results indicate that the velocity, temperature and concentration fields are significantly dependent on the above-mentioned flow parameters.
A reflective acoustic streaming micropump was designed in this study. After proposing the micropump structure model, the best driving frequency of 11,548,960 Hz was determined from modal analysis. Then the acoustic pressure field and the acoustic instantaneous intensity distribution were studied. The streaming velocity in the pump chamber was calculated and the maximum velocity reached 3 mm/s. The maximum velocity of the suspended microparticles was 1.0938 mm/s, and the influence factors on the microparticles movement were discussed. The microparticle movement was determined by acoustic streaming when microparticle diameter was less than 2 µm and the acoustic radiation force became dominated when microparticle diameter was more than 5 µm.
A boundary layer analysis is presented for the warm, laminar nanoliquid flow to a melting vertical plate surface in a moving non-Newtonian nanoliquid. We consider the natural convection boundary layer regime. Using the appropriate variables, the basic equations are transformed to non-similar form. These equations are solved numerically, employing the implicit finite difference method together with Keller box scheme. The rates of heat and mass transfer and the surface shear stress are presented graphically for parametric variations in the melting parameter M, buoyancy ratio parameter Nr , Brownian motion parameter Nb , thermophoresis parameter Nt , Lewis number Le and the power law exponent n.
Flexural sensitivity is a key parameter of atomic force microscopy. In order to improve the dynamic atomic force microscopy’s flexural sensitivity, a scanning method that drives the atomic force microscopy cantilever vibrating at its high resonant frequency is utilized. In this article, the operation principle of the high resonant atomic force microscopy is introduced and the factors that affect the sensitivity in the measurement of the displacement of the amplitude based on optical lever detection method are analyzed, and the flexural sensitivities of the cantilever vibrating at different resonant frequencies are compared theoretically and measured experimentally. The experimental results indicate that the flexural resolution of atomic force microscopy operated on the fundamental mode and the second mode is 0.30 and 0.13 nm, respectively. Both the theoretical and experimental results demonstrate that the flexural sensitivity of the high resonant cantilever is better than that of the fundamental mode cantilever. It is an effective method to improve the sensitivity of dynamic atomic force microscopy cantilever by working at higher resonant frequency.
With the increasing power densities of chip and diminishing size of semiconductor chips, thermal interface materials become a research emphasis to accelerate the development of semiconductor industry. Vertically aligned carbon nanotubes are good thermal interface materials because of high thermal conductance and excellent mechanical compliance. To reduce the thermal contact resistance between vertically aligned carbon nanotubes and silicon, thermocompression method in magnetic field was used to bond them in this work. The surface of vertically aligned carbon nanotubes was metallized with nickel and a vacuum chamber was used as bonding condition. The thermal contact resistance Rmc between vertically aligned carbon nanotubes and metallized Si of 12 sample groups were measured with a thermal transient tester. The result shows that the Rmc with magnetic field is 14% lower than the Rmc without magnetic field averagely. The magnetic field can be used to reduce the thermal contact resistance between vertically aligned carbon nanotubes and metallized Si.
In this article, the authors studied the effect of Cl– on the fluorescence of methyl orange solution containing silver nanoparticles by UV–visible absorption spectra, fluorescence spectra, and transmission electron microscopy. The results indicated that there is little change in the UV–visible absorption spectra of methyl orange after adding Cl– into the mixed solutions of the methyl orange and silver colloid. With the increase in Cl– content, the fluorescence of S1->S0 decreases first and then increases, and the fluorescence of S2->S0 increases, which almost has nothing to do with the pH value of methyl orange solution. The fluorescence enhancement ratio of S1->S0 in the solution of pH = 6.1 was higher than that in the solution of pH = 2.1. The authors discussed the mechanism of the effect of Cl– on the fluorescence of methyl orange solution containing silver nanoparticles in terms of interaction and energy transfer. The results indicated that the effect of Cl– on the fluorescence of methyl orange solution containing silver nanoparticles depends on the bridge role and the competitive adsorption between nanoparticles and methyl orange molecules, molecular adsorption mode, and so on.
Carbon nanotube fillers in polymers are quite effective compared to traditional carbon black micro particles, primarily due to their high aspect ratios. Increasing attention is being focused on the carbon nanotube surface, namely, the interface between the carbon nanotube and the surrounding polymer matrix. From micromechanics, it is through shear stress build-up at this interface that stress is transferred from the matrix to the carbon nanotube. Because of the dissimilarity in elastic properties of polymer matrix and carbon nanotube, there will usually be some asymmetry near the crack tip even if the geometry and loading are symmetric and interface cracks tend to be mixed mode. In this article, the effect of crack on the interface of polymer matrix and carbon nanotube is analysed using both analytical and extended finite element method. The delamination is modelled as an interface crack problem and stress intensity factor and energy release rate is calculated as a function of crack length and stiffness ratio of matrix and carbon nanotube.
Piezoelectric inchworm actuators have a wide application in the field of nano-positioning and ultra-precision detecting instruments. Ultra-precision positioning equipments are urgently needed in the field of precision optics. A new piezoelectric linear actuator, based on inchworm motion principle, with a symmetry lever displacement amplification mechanism has been designed in this article. The whole structure adopts uniaxial-type double-notch right circular flexible hinge as its main hinges, which offers the driving part a larger displacement and makes clamping part have enough clamping force at the same time. High-precision cross roller guide ways are utilized to improve the positioning accuracy of the actuator. Both theoretical analysis and finite element analysis of clamping mechanism and driving mechanism have been carried out. An experimental test platform has been built, and a controlling program of the actuator is compiled by LabVIEW. The experimental results show that the working stroke of the actuator is ± 25 mm, resolution is 60 nm, the clamping force is 17 N, and the bearing capacity is 11 N; the actuator has a highest speed of 1.259 mm/s at the driving voltage 150 V.
With the rapid development of terahertz radiation sources and detectors, there is also a great demand for terahertz filters. The quantitative studies on polarizer have been carried out in other spectral range, but the studies on terahertz wave polarizer are still very limited. Therefore, it is valuable to investigate the design of a polarizer in the terahertz range. In this article, tellurium and polystyrene thin film is used to compose a symmetrical structure, and then 10 periods of this structure are used in our design. A terahertz wave polarizer with micrometer scale is gained. Results of simulations show that the polarizer has a high performance in reflectivity for transverse-electric part polarized terahertz wave as well as low reflectivity for transverse-magnetic part polarized terahertz wave. The work frequency and incident angle of our design are 0.5 THz and 45°, respectively, and it has a reasonable incident angle range.
A biomimetic micro-pump model was constructed in this study based on the hydrodynamics of flagellated bacteria traveling-wave movement in a viscous fluid environment. In order to avoid the complicated force calculation, immersed boundary was introduced into lattice Boltzmann equation as velocity source. This method modified the traditional immersed boundary–lattice Boltzmann method in which immersed boundary was treated as force source. The present modified immersed boundary–lattice Boltzmann method was applied for solving the model, which can improve the computational efficiency and accuracy. The effect of the traveling field produced by the elastomer on the fluid flow was then probed. Numerical-simulation experiments were carried out to discuss the influences of traveling-wave deformations on the pressure distribution and velocity field and also to find out the effects of frequency, amplitude, elastomer’s length, wavelength, the thickness of the elastomer, and kinematic viscosity of the fluid on the flow rate.
In this research, Ni–P/nano-SiC composite coatings were prepared on wood surface by simple electroless plating approach. The flatness, porosity, and crystallinity of Ni–P/nano-SiC composite coatings were investigated. The flatness and porosity of the composite coatings enhanced with the increase in nano-SiC content of the coatings, and the composite coatings were obtained within the range of 0.5–1.5 g (1.8 g/L) nano-SiC in the solution bath. The full width at half maximum values of Ni X-ray diffraction peaks in the composite coatings broadened and strengthened with the increment of nano-SiC content in the coatings, which triggered preferred growth direction of diffraction peaks. The composite structure was characterized with scanning electron microscopy images. The uniformity of particles in the composite coatings could be improved obviously with the increase in the nano-SiC content of the coatings because an amorphous phase of SiC hindered the movement of dislocations and declined the size of Ni–P crystallite. Besides, the flatness, porosity, and crystallinity of composite coatings depended on the P content in the composite coatings. P content can be decreased by increasing SiC content of plating solutions. The flatness, porosity, crystallinity, and wear resistance of composite coatings exhibited excellent properties as the content of nano-SiC in the composite coatings reached 1.0 g (1.8 g/L).
A passive wireless pressure sensor based on low-temperature co-fired ceramic was investigated. The sensor is equivalent to a LC resonant circuit, which has a planar spiral inductor and an interdigital capacitor electrically connected. The inductor and capacitor are fabricated by screen printing technology. The working principle of the sensor is based on the pressure-sensitive resonant frequency of the LC circuit. Wireless detection can be realized by electromagnetic coupling with two inductor coils. The results show that the resonant frequency of sensor decreases with the increase in pressure, and sensitivity of the sensor is about 412.32 kHz/bar.
Generally, two spiral tool path generation methods are applied to ultra-precision three-axis turning of off-axis convex ellipsoidal surface, which are tool path generating by revolving around the axis of convex ellipsoidal surface and revolving around the axis of cylindrical surface. In this article, two different computed results of spiral tool path generation for off-axis convex ellipsoidal surface are analyzed, and several key technologies during tool path generation are analyzed in theory. The general procedure of generating the precision tool trajectory is also presented. The characteristics of two different turning trajectories for the surface manufacturing are compared and studied in some typical aspects in the end. The studies show that each of the two different tool path generation methods has its own suitable work environment, and a reasonable method should be chosen according to the processing requirement and work environment during the process of single-point diamond turning. The analysis and argument presented provide an effective choice of the accurate spiral tool path generation method in ultra-precision manufacturing of the off-axis convex ellipsoidal surface, and the method can be used in the accurate spiral tool path choice of any kind of off-axis surface.
K2Ti6O13 nanowires are excellent inorganic nanomaterials, which have high value and huge potential use in many fields. However, the biocompatibility of K2Ti6O13 nanowires will be directly related to its application. But the quantity of its hemocompatibility reports is limited. In this study, K2Ti6O13 nanowires were first synthesized by sol–gel/hydrothermal combined method. In view of its biosafety, the hemocompatibility of the novel nanomaterial was investigated by a hemolysis test. Fresh whole blood was drawn by venipuncture from a healthy human volunteer. The absorbance of free hemoglobin in the clear supernatant of the blood mixtures in contact with the test, positive and negative control groups was measured by ultraviolet–visible spectrophotometer for evaluating the hemolysis ratio. The hemolysis ratio of the test group is far lower than the standard of 5%. And the results indicate that the novel material has no hemolytic effect and has application prospects in the fields of biomedicine and biomaterials.
Static and continuous-flow micro-gap reactors have been designed for the sterilization of bacteria. Their performances were verified using some pulsed electric fields. Several parameters such as electric field strength, pulse number and width, as well as flow rate, which may impact the sterilization effect, have been experimentally evaluated on these devices. Experimental results showed that the strength and width of pulses had significant impacts on the sterilization. Stronger and wider pulses favored the sterilization. More pulses could also achieve better sterilization effect. Continuous-flow manipulation contributed to realize high-efficiency sterilization. However, flow rate should be lower than a critical value. Higher flow rate may reduce the residence time in the reactor and harm the sterilization effect. Micro-gap reactor between the two parallel plate electrodes can contain more solution and the sample can be manipulated in a continuous way to realize higher sterilization throughput, but it is sometimes difficult to form even gap between these plate electrodes. Rough surface or burrs on these electrodes may induce discharge and limit the electric field strength. Some coatings on their surface may decrease the discharge, but they also undermine the electric field.
Based on strain gradient theory with surface effect, this article discusses magneto-vibration of coupled double-layered visco-elastic graphene sheet systems embedded on elastic foundation. Graphene sheets were placed in uniform magnetic field and coupled with each other by an enclosing visco-Pasternak medium. Considering the Kirchhoff plate theory and Kelvin–Voigt model, the governing equation is derived using Hamilton’s principle. The equation is solved analytically to obtain the frequency of the coupled system. The parametric study is thoroughly performed, concentrating on the series effects of a magnetic field, visco-elastic damping structure coefficient, aspect ratio, surface layer, visco-Pasternak elastic medium, shear modulus, and mode number. In this system, in-phase and out-of-phase vibrations are investigated. The numerical results of this article show a perfect correspondence with those of the previous researches. The effect of magnetic field on the vibration of graphene sheet with different Winkler coefficients is exposed. Results from the model demonstrate that the magnetic field increases the natural frequencies.
Extrudate swell exerts a significant impact on the shape and dimensional accuracy of extruded products. It is one of the important factors to be considered when designing the extrusion die and controlling the quality of products. The die swell ratio (B) is used to evaluate the degree of extrudate swell. In this article, comparative experiments were performed in order to simulate and observe in a precise fashion the extrudate swell behavior of carboxymethyl cellulose solution at a microscale by means of a visualization device. We chose micro dies capillaries where the inner diameter was in the range of 0.1–0.5 mm. The effects of capillary geometry, entrance velocity, and shear rate (shear stress) on extrudate swell were investigated. The results indicated that shear rate (shear stress) increases and the value of B is enhanced with decreasing capillary diameter under the same capillary entrance velocity. At different entrance velocities, the die swell behavior from 0.3- to 0.5-mm-diameter capillaries was similar to that of conventional ones, and the value of B increased with increasing shear rate. Additionally, the extrudate swell from the 0.2-mm-diameter capillaries revealed a decline, whereas that from the 0.1-mm-diameter capillaries first diminished and then increased concomitantly with rising shear rate. We expect that this was due to wall slip that occurred analytically in our micro channel.
The influence of gravity on mass transport and micro direct methanol fuel cell performance is presented in this article. A multi-physics three-dimensional model calculated by COMSOL Multiphysics is established. The results show that gravity significantly affects the distribution of pressure and methanol concentration. To verify the simulation, a self-breathing transparent micro direct methanol fuel cell with horizontal orientation and vertical orientation is designed, fabricated and tested. The polarization curves of horizontal orientation exhibit the best performance with the power density of 25.57 mW cm–2. Moreover, the cell placed with horizontal orientation exhibits faster CO2 emission velocity than that of the cell with vertical orientation.
Bacterial cellulose/hyaluronic acid composites have been prepared by the nontoxic cross-linking agent 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide. The effects of hyaluronic acid concentration, temperature, and the 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide addition way on the performance of the composites have been discussed. Field emission scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, and thermogravimetric analyzer have been used to characterize the composite materials. The hyaluronic acid contents in the composites have been assayed by a colorimetric method. Hyaluronic acid concentration, the 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide addition way, and temperature have impacts on the hyaluronic acid content in composites. Fourier transform infrared spectra confirm the amide groups on the composites, which is attributed to hyaluronic acid molecules. The crystallinity indexes of composites decrease, in comparison with pristine bacterial cellulose, known from X-ray diffraction tests, possibly due to the integration of hyaluronic acid. The thermal decomposition temperatures of Composites A and B from Process 1 are lower than those of bacterial cellulose, which is ascribed to lower pyrolysis temperatures of hyaluronic acid compound in composite materials. However, Composites C and D from Process 2 do not undergo descent thermal stability. The novel nanocomposites have the potential to be used for biomedical and tissue engineering scaffold materials.
The etching characteristics of Si (1 0 0) in silicon deep wet etching with tetramethyl ammonium hydroxide solution, containing silicic acid and ammonium persulfate, were studied in this article. The phenomena associated with the addition of ammonium persulfate at intervals in tetramethyl ammonium hydroxide solution were analyzed, and the mechanism of interplay between ammonium persulfate and silicic acid for increasing etch rate was proposed. The influence of these phenomena on the etch rate and roughness of Si (1 0 0) was discussed. The addition of ammonium persulfate at a periodic interval of time to a tetramethyl ammonium hydroxide solution, especially at the temperature of 80 °C, resulted in remarkable ascending of silicon etch rate. The etch rate of Si (1 0 0) in tetramethyl ammonium hydroxide solution with adding ammonium persulfate at intervals was superior to the etch rate in tetramethyl ammonium hydroxide solution without adding ammonium persulfate at intervals. The highest etch rate of Si (1 0 0) (0.83 µm/min), calculated with the help of profiler, was achieved after etching in tetramethyl ammonium hydroxide solution with adding ammonium persulfate at an interval of 120 min. This method appears to be a good candidate in applications where high and stable etch rate is required in long-time etching.
The objective of this article is to simulate a piezoelectric cantilever beam generator with power harvesting from ambient vibration energy. This power device will act as the electrical energy supply of a micro-system, which can be used in inaccessible situations, to eliminate dependence on batteries. Optimization of the micro-silicon-based piezoelectric cantilever parameters was achieved by determining the most advantageous dimensions for the piezoelectric generator, while varying the beam length, width, thickness, proof mass weight and so on. The program also made sure that the piezoelectric cantilever beam structure’s natural frequency is equal to the desired input frequency from the ambient exciting vibration. In addition, a prototype miniature generator was fabricated with bulk silicon combined with etching.
We have calculated the density of the quantum state in the conduction band (N C) for series stress addition to GaAs thin film along [100], [010] and [001] direction. We present here the results of our investigation of the electronic parameter affected by the stress. Within the range of 0.02–0.2 GPa, we find that the value of N C decreases about 1.0 x 1021 cm–3 from the free status of films. The results reveal that the stresses on GaAs film are extremely important and impact its electronic properties.
Three-dimensional Ce-doped ZnO was synthesized via coprecipitation and roasting processes. The samples were characterized by X-ray diffraction, scanning electron microscopy, specific surface area (Brunauer–Emmett–Teller method), and photoluminescence spectra. Also, the photocatalytic activities of ZnO and Ce-doped ZnO were investigated in ultraviolet light for degradation of methylene blue solution. The results indicated that the concentration of NaOH and the doping amount of Ce showed great influence on morphology, structures, and properties of Ce-doped ZnO. When the (Ce3++Zn2+)/OH– was 1:2.5 and the concentration of Ce was 2 mol%, the morphology of the Ce-doped ZnO was microspheres with superstructures assembled by large amounts of interleaving nanosheets. The morphology transformed from microspheres with superstructures to amorphous by changing the ratio of (Ce3++Zn2+)/OH– from 1:2 to 1:3. The photoluminescence spectra indicated that the recombination rate of photogenerated electron–hole pairs of Ce-doped ZnO was suppressed. The prepared Ce-doped ZnO showed much enhanced photocatalytic property than pure ZnO. When the doping concentration of Ce was 2 mol%, the Ce-doped ZnO photocatalysts showed best photocatalytic activity with 99.10% degradation of methylene blue solution after 2 h.
In this article, the photoinduced anisotropy of a liquid crystal molecule doped into a polymer with photosensitive group was studied. The polymer with coumarin photosensitive group as side chain can generate a polarization axis-selective photoreaction and obtain anisotropy after being exposed at a certain wavelength of linearly polarized ultraviolet light, which occurs as [2+2] cycloaddition and form anchoring force. The thin film underwent subsequent annealing in the liquid crystal temperature range and it leads to a large optical anisotropic change in the polymer film for the self-assembly of molecule. The ultraviolet dynamic spectrum was used to evaluate the absorbance of the film, and the photoinduced optical anisotropy A and order parameter S were calculated. The result shows that when the exposure energy was increased to 1908 mJ/cm2, the value of the absorbance does not change with the increase in exposure energy. When annealing temperature changed from 120 °C to 240 °C, A changed from 0.07 to 0.11 and S changed from 0.02 to 0.04.
Nano-TiO2 was dispersed in water to study the influences of nanoparticles on the tribological properties of water-based rolling liquid for hot steel. The phase composition and microstructure of nano-TiO2 were investigated by X-ray diffraction and transmission electron microscopy methods. The friction reduction and antiwear properties were measured on a four-ball friction tester, and then hot rolling experiments with lubrication have been carried out. The rolling force and surface roughness were measured. Moreover, the surface elements of the steel lubricated by nano-TiO2 rolling liquid were analyzed by energy dispersive spectroscopy. The results showed that nano-TiO2 as water-based liquid additives can effectively improve the antiwear properties of steel–steel friction pair and reduce the friction coefficient. At the same time, nano-TiO2 shows good lubrication properties during hot rolling. It is inferred from the lubrication and repairing mechanism that TiO2 nanoparticles sediment on the surface of steel, and the lower surface film is formed under high temperature and high pressure. The film possesses excellent antiwear, friction-reducing and repair properties.
Silicon-functionalized graphene in its initial configuration, as anode materials for lithium-ion battery, will directly affect the battery’s reversible capacity, charge and discharge rate and service life. To present its optimal initial configuration, the relaxation and stretching properties of silicon-functionalized graphene were studied using molecular dynamics simulation with the Tersoff potential, the Lennard–Jones potential and the velocity Verlet time-stepping algorithm. In this study, many models of silicon-functionalized graphene with different arrangement of silicon atoms, different Si/C ratios, different vacancy defect ratios, different tension rates and different temperatures were primarily developed respectively to simulate the influence of different configurations on the volume, potential energy, elastic modulus, tensile strain, strength and other properties of the model, and we found that (1) the model with random arrangement of silicon atoms possessed biggest system potential energy, biggest volume and highest mechanics property among all models. (2) With the increasing amount of silicon atoms, the wavy corrugations and the peak became clearer, the potential energy decreased and volume increased. The model with Si/C ratio of 3.28% possessed highest mechanics property. (3) With the increasing vacancy, the system’s potential energy increased and volume decreased. The model with a vacancy defect ratio of 1% possessed highest mechanics property parameters. (4) Mechanics properties were the highest at the temperature of 300 K.
This article reports the organomodification of Indian bentonite clay with three modifiers and the fire behavior of organomodified Indian bentonite clay/vinylester/glass nanocomposites. Indian bentonite (Na-IB) clay was organomodified using hexadimethyl ammonium bromide (HDTMA-Br), tetra-n-butylammonium bromide (TBA-Br) and triphenyl methyl phosphonium bromide (TPP-Br) by varying the cation exchange capacity. Basal spacing of 34 Å was observed in Na-IB modified with HDTMA-Br (HDTMABr-IB) followed by 28 Å in Na-IB modified with TPP-Br (TPPBr-IB) and 26 Å in Na-IB modified with TBA-Br (TBABr-IB). Fourier transform infrared spectra of HDTMABr-IB confirmed the attachment of functional groups, its zeta potential increased from –36.34 to 5.35 mV indicating greater surface potential and thermogravimetric analysis showed greater weight loss confirming Na+ ion exchange with alkyl amines. Energy-dispersive X-ray analysis showed compositional changes between modified and unmodified clay with the presence of 37.03% carbon in the HDTMABr-IB. Horizontal and vertical burning rates of vinylester/glass composites decreased with the addition of HDTMABr-IB. Limiting oxygen index increased by 40% with the addition of 5 wt% HDTMABr-IB to vinylester/glass.
Ethylene propylene diene monomer and silicon rubber were blended in different ratios, and the physico-mechanical properties and the cure characteristics were studied. It was found that the ratio 60/40 phr (parts per hundred parts of rubber) of ethylene propylene diene monomer/silicon rubber exhibited the best value. Therefore, this ratio was loaded with the required concentration of each, unmodified clay and the two modified clays (one modified with distilled water and the other with anionic surfactant), to prepare rubber nanocomposites. The modified clays were characterized by X-ray diffraction and transmission electron microscopy. The properties of nanocomposites were investigated in terms of the cure characteristics, scanning electron microscopy, flammability and mechanical and thermal properties. It was noted that nanocomposites loaded with modified clays resulted in the highest cure and mechanical properties. The scanning electron microscopy and X-ray diffraction revealed the exfoliation of the nanoclay layers with uniform dispersion and good interaction between the nanoclay particles and rubber matrix. The thermal stability and flammability of nanocomposites were improved by the addition of different concentrations of Mg(OH)2.
In order to achieve a fast, high-efficiency analysis of platelet aggregation, a novel microfluidic chip was designed and fabricated based on the traditional measurement principle and method. The chip had a main channel and six branch channels, which were connected with their own inlets (outlets). The master of this chip was fabricated using the traditional photolithography methods. Polydimethylsiloxane chip was replica molded on the master. In the platelet aggregation assay, blood sample and coagulant were loaded from separate inlets on both sides of the chip. Due to the diffusion of analytes in the laminar flow, two analytes diffused and mixed with each other within the main channel and gradually aggregated. The distance from the mixing point to the aggregation point denoted the aggregation capacity of the blood sample. Compared with traditional measurement methods based on glass tubes, this microfluidic chip–based method is simple, highly efficient, rapid, low consuming, inexpensive, and has high repeatability. Furthermore, it may be made as a portable device for wide application in clinical analysis.
The gradient type of nonlocal stress field theory has been one of the most popular theoretical approaches to study some size-dependent mechanical properties of microstructures. In this work, the nonlocal elasticity field theory is employed to investigate transverse bending vibration of the microbeams subjected to a pair of initial axial tensions, and the dynamical responses of such microstructures are determined and discussed in detail. The governing equation of motion containing a small length–scale parameter is derived according to the mechanical model constructed at microscale. Subsequently, two different methods, including the method of separation of variables and the multiple-scales analysis, are applied in the equation of motion to reveal the nonlocal elastic effects in vibrational behaviors of microstructures. It shows that the results by the two methods are in good agreement. Furthermore, the critical axial tension is also obtained, and it is observed to decrease with an increase in microscale parameter, which means an increase in nonlocal elastic effects causes the critical axial tension to decrease. By comparing with the results provided by the classical continuum vibration theory, inherent frequencies of the microbeams are lower or the bending stiffness is weakened in such a nonlocal stress model presented in this article.
This study provides an analysis of the nanoparticle effects over the steady boundary layer flow and heat transfer of viscous fluid flowing over a vertical cylinder that is stretched along its axial direction. The system of nonlinear partial differential equations associated with the problem along with the appropriate boundary conditions is nondimensionalized by means of the boundary layer estimates and invoking a suitable similarity transformation. The resulting nonlinear coupled system of ordinary differential equations subject to the appropriate boundary conditions is solved through the Runge–Kutta–Fehlberg numerical scheme. A comparison of the obtained numerical results is also presented with the help of homotopy analysis method. At the end, effects of the allied physical features for the flow, heat transfer and nanoparticle concentration profiles are also discussed.
In all the process steps of manufacturing high-temperature pressure silicon carbide sensors, deep etching and ohmic contact are two crucial processes. Reactive ion etching is used for the deep etching of silicon carbide in our experiment, and the surface has a high quality after etching. Using nickel as the mask material on the C layer by electroplating, the depth of deep etching reaches about 81 µm and the thickness uniformity is fairly good, fluctuating within 200 nm or less. The Ti–TiN–Pt system is proposed for metallization, in which Ti, TiN and Pt are used as the contact layer, the diffusion impervious layer and the lead interaction layer, respectively. The Kelvin test shows that stable ohmic contact is achieved and a specific contact resistivity of 8.42 x 10–4 cm2 is detected. The etching depth of 81 µm meets the requirement of forming a sensitive circular membrane, and the metal system of Ti–TiN–Pt ensures reliable connection and stable ohmic contact between the metal and semiconductor at high temperatures.
In this article, the resonant behavior of a single-walled boron nitride nanotube (SWBNNT)-based mass sensor has been analyzed considering the chiral atomic structures and the presence of point defect along the length of the nanotube. The single atom vacancies and divacancy (BN divacancy) are considered as point defects. The resonant frequency-based analysis has been performed considering a finite element model of a cantilevered single-walled boron nitride nanotube, based on molecular structural mechanics. The analysis has been performed considering the different chiral atomic structures of a single-walled boron nitride nanotube, having a chiral angle of between 0° (zigzag) and 30° (armchair). Also, along with the effect of chirality, the presence of a point defect along the length of nanotube has been analyzed as a poor atomic structure of a single-walled boron nitride nanotube. The three different positions of point defect along the length of nanotube have been considered. The obtained results indicate that, for the particular size of nanotube, as the chiral angle decreases, the atomic structure of nanotube become more closely packed and ultimately effects the resonant behavior of nanotube. The presence of a point defect and its different positions along the length of nanotube effects the overall resonant behavior of a single-walled boron nitride nanotube, which is attributed due to change in the structural stiffness of the nanotube. The reported results can be used to identify the different types of considered point defects as well as its position along the length of nanotube. The present simulation approach is found to be very effectual, incorporates the different atomic structures of a single-walled boron nitride nanotube and simulates the different boundary conditions.
In this article, transport properties of a single-wall carbon nanotube having chirality (4, 0), connected to copper, gold and graphene electrodes, have been investigated. Electronic structures have been analyzed using the density functional theory calculator. Transport properties of the devices formed by interfacing of single-wall carbon nanotube and electrodes are computed using the nonequilibrium Green’s functional method coupled with density functional theory approach. Contact effects due to metal–carbon nanotube interface have significant impact on transport properties of charge carriers. Therefore, transport properties have been critically analyzed with the help of transmission spectra, differential conductance and conductance plots and I–V characteristics. From these results, it has been concluded that formulation of the electrode material is not the single-factor responsible for creating conduction problems. Along with the electrode material, interface position of metal–carbon nanotube configuration and heterostructure contacts are also responsible in influencing transport phenomenon. In this way, varying the contact geometry is found to play an important role in integrated circuit interconnect technologies for exploring the transport properties. Gold is best among all three simulated contact electrodes, and for low-power applications, graphene can be next choice over an applied bias range of –1 to +1 V. Atomistix software tool has been used to analyze transport properties of interconnect models.
Based on nonlocal piezoelasticity theory, dynamic stability of double-walled boron nitride nanotube conveying viscous fluid is investigated using Timoshenko beam theory. Double-walled boron nitride nanotube is surrounded in visco-Pasternak medium and conducts the internal fluid. Modified Navier–Stokes relation is used to evaluate fluid–double-walled boron nitride nanotube interaction considering the effects of bulk viscosity and slip boundary condition. Mechanical harmonic excitation and thermal loadings are exerted on double-walled boron nitride nanotube with zero electrical boundary condition. Nonlinear van der Waals forces between the inner and outer layers of double-walled boron nitride nanotube are taken into account. Hamilton’s principle is utilized to derive governing equations with regard to von Kármán geometric nonlinearity. Charge equation is used to consider the coupling of electric potential and mechanical displacement. Space and time domains are discretized using Galerkin and incremental harmonic balance approaches. Finally the eigenvalue equations are solved based on the iterative method to derive dynamic instability regions. The detailed parametric study is conducted, focusing on the combined effects of aspect ratio, nonlocal parameter, fluid velocity, Knudsen number, thermal changes, van der Waals forces and surrounding medium on dynamic instability regions of double-walled boron nitride nanotube.
We developed a simple and efficient micro-electromagnetic energy harvester based on micro-electro-mechanical systems technology. For processes of electromagnetic vibration energy harvesters in the presence of the magnet, the compatibility with the micro-electro-mechanical systems processing is not good. Therefore, we have adopted a method of micro-assembly production energy harvester. The energy harvester mainly consists of a resonator chip processed by micro-electro-mechanical systems and a winding coil. The total volume of the energy harvesters is 0.95 cm3. Test results show that the energy harvester generated a maximum load power of 116.64 µW across 400 load at 291.4 Hz for an acceleration of 0.5g (g = 9.8 m/s2) after the optimization of the parameters.
Highly ordered TiO2 nanotube arrays on Ti substrates were prepared by an electrochemical anodization process in a mixture of glycerol and water containing 0.5 wt% NH4F and then thermally annealed from 400 °C to 600 °C. The sample structures were characterized by scanning electron microscopy and X-ray diffraction measurements, where the nanotube pore diameter and length were found to increase with increasing anodization voltage and reaction time. Thermal annealing at 450 °C was found to lead to the generation of the largest anatase crystalline domains, and at higher annealing temperature, the anatase components started to convert into the rutile ones. The corresponding photocatalytic activity was then evaluated by the photodegradation of Alizarin Red S under ultraviolet light irradiation. The results showed that the nanotubes prepared by anodization at 25 V for 10 h and subsequently annealed at 450 °C exhibited the optimal photocatalytic activity with a rate constant of 2.70 x 10–3 min–1 and 39.2% of Alizarin Red S degraded after 180 min of photoirradiation. These results indicated that the photocatalytic activity was primarily determined by the crystalline properties of the TiO2 nanotubes, and additional improvement might be achieved by a deliberate manipulation of the nanotube dimensions as a combined contribution of light penetration and mass transport within the nanotube arrays.
The poly(ethylene terephthalate) waste was depolymerized using 1,4-butanediol, and diethylene glycol and the glycolyzed products were used in the preparation of the unsaturated polyester. The composition of the glycolyzed products and the prepared polyester (unsaturated polyester) were investigated in view of their infrared and 1H NMR spectra. Different samples of unsaturated polyester/nanocomposites containing various amounts (1, 3, and 5 wt%) of different nanofillers, namely Nanofil 116, Cloisite 30B, and Laponite RD, were also prepared. The effect of the nanofiller type and content on the morphological structure of the fractured surfaces, thermal, mechanical, and electrical properties was investigated.
The research of nanoscale contact problem has important significance for the micro-/nano-machinery, especially for micro-/nano-contact problem of material defects, from which deformation and failure mechanism of materials could be revealed. Molecular dynamics method is a valid approach that describes microscopic phenomenon. Taking the rigid hemispherical surface in contact and indentation process with the perfect and defective monocrystalline copper as the research object, the molecular dynamics model of nanoscale contact was established, after solving and simulating analysis. Results showed that the substrates above the square void collapse at contact depths of 0.20 and 0.37 nm when the depths of the square void (d) are 0.8 and 1.6 nm, respectively. The dislocations and glide band increase as the d increases; at the same time, a larger depth of square void results in a bigger contact force between the hemispherical surface and the substrate surface. In the process of disengagement, there is a sudden drop in the contact force, and unrecoverable plastic deformation of the copper material occurs. Moreover, with the increase in void depth, the number of high-stress atoms increases between the hemisphere and the surface of substrate. The stress is mainly distributed in the diagonal of the square void, and the contact area generates stress concentration.
In this article, an integrated thermopile vacuum gauge with an XeF2 dry-etching process is presented. The integrated thermopile vacuum gauge consists of an N-polysilicon heater and 38 N-polysilicon/Al thermocouples. By using XeF2 front-side isotropic post-etching technique, the integrated vacuum gauge structure was released, and a small size of the integrated thermopile vacuum gauge structure about 0.4 x 1.5 mm2 has been achieved. Compared with applying a constant voltage to the integrated thermopile vacuum gauge, applying a constant power to the gauge is more sensitive. The experimental results show that the dynamic pressure range of the integrated thermopile vacuum sensor is 10–2–105 Pa.
By introducing the working principle of the two-stage decoupled micro-machined gyroscope, the vibration equation of the driving mode is established. Using Laplace transform, the differential equation and the analytical solution are solved, and the amplitude–frequency characteristics of the driving mode are obtained. Moreover, this article introduces the hardware of the noncontact vibration measurement system and the algorithm. By experiments, the characteristic of vibration of the tested micro-machined gyroscope is obtained. Experimental results indicate that the precision of the amplitude is 0.1 µm, and the two-stage decoupled micro-machined gyroscope is immune to mechanical coupling and has high linearity inherently.
In this article, a novel cathode current collector with "cross" self-breathing configuration is proposed to improve the performance of self-breathing micro-direct methanol fuel cell. The simulation result shows that "cross" cathode micro-direct methanol fuel cell effectively improves the efficiency of oxygen mass transport and makes oxygen distribute uniformly which lead to high power density and temperature. The novel "cross" cathode structure and comparative high temperature promote rate of water evaporation which suspends flooding in the cathode, and the end of channel connects with atmosphere causing liquid state water on the gas diffusion layer to discharge outside directly. The self-breathing micro-direct methanol fuel cells with "cross" cathode structure are fabricated using micro-electro-mechanical systems technologies and are tested at room temperature. The experimental results show that the "cross" cathode micro-direct methanol fuel cell, whose peak power density is 17.1 mW cm–2, exhibits significantly higher performance than the conventional perforated cathode micro-direct methanol fuel cell. Moreover, during the long-term operation of the "cross" cathode micro-direct methanol fuel cell, there is no water flooding on the cathode surface.
This article introduces the implementation of a low-cost 4 x 5 pixel array uncooled infrared microbolometer together with its integrated readout circuit in a standard 0.5-µm CMOS technology and post-CMOS process. Each pixel, which has a size of 80 µm x 80 µm, is a novel structure of aluminum microbolometer fabricated by etching the surface sacrificial layer without any additional masking and lithography procedure. The aluminum microbolometer consists of an aluminum thermistor and a thermally isolated micromachined membrane suspended by two arms. The thermal conductance, thermal time constant, thermal capacitance, and responsivity of the aluminum microbolometer are experimentally measured.
Based on semiclassical theory, a model of the interaction between neutral atoms and the laser standing wave field has been established in this article. The trajectories and the deposition characteristics are analyzed with channel effect, and the full width at half maximum of nano-grating is 96.70, 0.532 and 12.16 nm when the divergence angle, spherical and chromatic aberration are discussed, respectively. The simulation results show that the contrast of the stripes decreases with the increasing divergence angle of the atomic beam. Also, the contrasts of the stripe are 85.2:1 and 5.33:1 when the divergence angles equal 0.1 and 0.3 mrad. Owing to the scission of the stripe, the quality of the deposition deteriorates with a divergence angle over 0.5 mrad.
This article presents the properties of the micro–nano sacle laser patterning system based on digital micromirror device. The introduction of the excellent spatial light modulator—digital micromirror device—provides a possibility for the patterning system to combine high resolution and accuracy with short writing time. The optical characteristics of the digital micromirror device–input imaging system are analyzed. An overlapping exposure method is proposed to obtain optical resolution enhancement and high fidelity of the input pattern. Based on this method, an optical synthetic-aperture effect is realized without increasing the system complexity or decreasing the process efficiency.
A boundary layer analysis has been presented for the natural convection flow of a non-Newtonian nanofluid past a sphere. Solutions of the set of nonsimilarity equations are obtained by employing the implicit finite difference method together with Keller box elimination method. Numerical results for friction factor, surface heat transfer rate and mass transfer rate have been presented for parametric variations of the material parameters, buoyancy ratio parameter T, Brownian motion parameter NB, thermophoresis parameter NT and Schmidt number Sc. The dependency of the surface heat transfer rate (Nusselt number) and mass transfer rate on these parameters has been discussed. It was found that the heat transfer rate decreases and mass transfer rates increase as Schmidt number increases. The friction factor and heat transfer rates decrease as the cross viscosity parameter R increases. The heat transfer rates increase and mass transfer rates decrease as the buoyancy ratio parameter N increases. As the thermophoresis parameter NT increases, the heat and mass transfer rates increase. As the Brownian parameter NB increases, the heat and mass transfer rates decrease. Brownian motion decelerates the flow in the nanofluid boundary layer. Brownian diffusion promotes heat conduction. The Brownian motion and thermophoresis of nanoparticles increase the effective thermal conductivity of the nanofluid. Both Brownian diffusion and thermophoresis give rise to cross diffusion terms that are similar to the familiar Soret and Dufour cross diffusion terms that arise with a binary fluid.
The electric resistance and transport properties of a carbon nanotube (5,5) adsorbed with a copper chain connected with two copper electrodes have been calculated by employing nonequilibrium Green’s functions and Density Functional Theory. The properties of the pure carbon nanotube (5,5) with the Cu junction electrodes have also been calculated as a reference. Both the equilibrium and nonequilibrium conditions have been investigated. The results show that the resistance of the metallic carbon nanotube (5,5) has been reduced by the adsorption of a Cu chain due to the interaction between the Cu and the carbon nanotube. The change of the current–voltage curve slope is also explained in terms of transmission spectrum.
In this study, an integrated polarization band-pass filter was designed; it consists of a bilayer nanowire-grid polarizer and a multilayer dielectric band-pass filter. The grating parameters were optimized by rigorous coupled-wave analysis theory and analyzed by effective medium theory. Transverse magnetic transmission higher than 81% and extinction ratio higher than 1000 were obtained at 400–500 nm, and extremely low transmission in the other spectrum was also realized.
This article demonstrates a novel chemical vapor deposition strategy of tin oxide (SnO2) by vapor phase material reaction at room temperature and presents the applications to hydrogen detection using this material. Tin chloride anhydrate was used as the precursor, and it reacted with NH3 to form Sn(OH)4 nanospheres. The samples with Sn(OH)4 nanospheres were subject to drying up at 80 °C, and then they transformed to polycrystalline SnO2 nanospheres. The X-ray diffraction measurement was carried out to investigate the structural properties of the SnO2 films annealed at various temperatures. The morphology of the samples was investigated by field-emission scanning electron microscopy. Micropellistor was fabricated based on the SnO2 catalyst for hydrogen detection. Compared with the traditional method to make SnO2 sensing material (hydrolysis of SnCl4·5H2O in basic solutions), the SnO2 nanospheres prepared by this method have a higher relative sensitivity and a good linearity for the concentration of H2 ranging from 0% v/v to 4% v/v. A short response time about 6 s was achieved.
Highly ordered TiO2 nanotube arrays were fabricated via electrochemical anodization, and CdS nanoparticles were deposited on TiO2 nanotube arrays through sequential chemical bath deposition technique. The influence of water content on the intertube space and length and pore size of TiO2 nanotubes were studied systematically. The uniformity of CdS nanoparticles deposited on the TiO2 nanotube arrays with different intertube spaces was also investigated. The results show that when the water content increased from 2 to 10 vol.%, the shape of TiO2 nanotubes changed from hexagon to round with the increasing intertube space, and CdS nanoparticles could be deposited uniformly both inside and outside of TiO2 nanotubes when the water content was 10 vol.%.
In this article, the anisotropy of the friction force with a variety of rotation angles between a silicon tip and a substrate was investigated using molecular dynamics simulations. When the silicon tip slides over the silicon substrate under incommensurate contacting surfaces, the results of the simulations illustrate that the sliding friction forces decrease with the increase of the rotation angle from 0° to 45° and increase with the increase of the rotation angle from 45° to 90°. Furthermore, an approximate symmetrical curve of the friction force for the 45° angle can be obtained, and the friction force is minimum and close to superlubricity at the 45° angle. However, at the same angle, the friction force stops decreasing with the increase of the temperature and its magnitude depends mainly on the degree of the commensurability of the contacting surfaces rather than the temperature.
Generation of mechanical force regulated by external electric field is studied both theoretically and by molecular dynamics simulations. The force arises in deformable bodies linked to the free end of a grafted polyelectrolyte chain, which is exposed to an electric field that favours its adsorption. We consider a few target bodies with different force–deformation relations including (1) linear and (2) cubic dependences as well as (3) Hertzian-like force. Such force–deformation relations mimic the behaviour of (1) coiled and (2) stretched polymer chains, respectively, or (3) that of a squeezed colloidal particle. The magnitude of the arising force varies over a wide interval although the electric field alters within a relatively narrow range only. The predictions of our theory agree quantitatively well with the results of numerical simulations. Both cases of zero and finite electrical current are investigated, and we do not obtain substantial differences in the force generated. The phenomenon studied could possibly be utilised to design, for example, vice-like devices to fix nano-sized objects.
Based on the embedded atom method potential, this article presents a molecular dynamics study of gold nanowires with three diameter sizes at a strain rate of 1.4 x 109 s–1 applied in <100> axial orientation. The mechanical properties including Young’s modulus, yielding stresses and yielding strains are computed and compared with available results. The atomic configuration stress–strain curves are given and analyzed in detail. The simulation results show that for the same-length gold nanowires, Young’s modulus and the yielding stress will decrease with the decrease in the diameter size of gold nanowires. Due to surface premelting at room temperature, Young’s modulus of the nanowires with the smallest diameter was about 28.6% smaller than the experimental value of 46.49 GPa. The nanowires displayed crystalline-ordered deformation governed by the formation of a main dislocation plane and the development of subplanes around the main plane. In case of diameters smaller than 5.84 nm, the nanowires experienced a double elastic periods and double plastic periods phenomenon subject to the strain rate and the characteristic size.
A boundary-layer analysis is presented for the mixed convection in an axisymmetric flow of a non-Newtonian nanofluid on a vertical cylinder. The micropolar model is chosen for the non-Newtonian fluid since the spinning motion of the nanoparticles as they move along the streamwise direction can be best described by the micropolar fluid model. Numerical results for friction factor, surface heat transfer rate and mass transfer rate have been presented for parametric variations of the micropolar material parameters, Brownian motion parameter Nb, thermophoresis parameter Nt and Lewis number Le. The dependency of the friction factor, surface heat transfer rate (Nusselt number) and mass transfer rate on these parameters has been discussed. Two flow regions, namely, the buoyancy-assisted and buoyancy-opposed cases, are considered.