Variational iteration method for the nanobeams-based N/MEMS system.

The nano/microelectromechanical system (N/MEMS) has triggered worldwide concern, and its applications have revolutionized technologies in various advanced fields from wearable sensors, 5 G communication technology, to energy harvesting, to aerospace. However, when the applied force is sufficiently large, the pull-in instability arises, and reliable operation is forbidden. Therefore, it is extremely important to insight fast and accurately into the periodic motion of the system to prevent the system from its pull-in motion. The basic aim of this study is to demonstrate the applicability of the well-known variational iteration method (VIM) for predicting the dynamic behavior of N/MEMS. For this, a nanobeam-based microstructure with van der Waals force for actuation is used as an example to reveal its periodic properties. The governing equation for the oscillation of the microsystem is obtained from the Euler-Bernoulli beam principle, considering the midplane stretching effect. We then employ the Galerkin technique to transform the governing partial differential equation into an ordinary differential equation, which is highly nonlinear, making it extremely difficult to solve by some traditional analytical methods, however, the VIM shows its ability to elucidate accurately the basic properties of the N/MEMS by simple calculation. This paper offers a new road for fast and accurate prediction of the microsystem's properties, and the result can be used for optimizing the N/MEMS.•A nanobeam-based N/MEMS system with van der Waals force is considered.•A strongly governing equation without a linear term is obtained.•The variational iteration method is applied to figure out the basic properties of the system.

Double Bubble Electrospinning: Patents and Nanoscale Interface.

BACKGROUND: Bipolymeric nanofibers have gained significant attention in various fields due to their enhanced functionality, improved mechanical properties, and controlled release capabilities. However, the fabrication of these composite fibers with a well-defined polymer-polymer interface remains a challenging task. METHODS: The double bubble electrospinning setup was developed and simulated using Maxwell 3D to analyze the electric field. PVP and PVA polymers were electrospun simultaneously to create bipolymer nanofibers with an interface. The resulting nanofibers were compared with nanofibers made from pure PVA, PVP, and a PVA/PVP blend. The characterization of the nanofibers was performed using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). RESULTS: The SEM images showed the formation of PVA/PVP interfacial nanofibers aligned side by side, with a diameter of a few thousand nanometers on each side. By increasing the voltage from 20 kV to 40 kV during electrospinning, the diameter of the nanofibers on the PVA and PVP sides was successfully reduced by 60.8% and 66.3%, respectively. FTIR analysis confirmed the presence of both PVA and PVP in the bipolymeric interfacial nanofibers. TGA analysis demonstrated a weight retention of 14.28% compared to PVA, PVP, and the PVA/PVP blend even after degradation at 500°C. The Maxwell simulation of double bubble electrospinning revealed a stronger and more uniform electric field pattern at 40 kV compared to 20 kV. CONCLUSION: The study has demonstrated the potential of double bubble electrospinning for the fabrication of bipolymer nanofibers with an interface, opening new avenues for the development of functional nanofibers.

Numerical analysis of multi-dimensional time-fractional diffusion problems under the Atangana-Baleanu Caputo derivative.

This paper presents the Elzaki homotopy perturbation transform scheme (EHPTS) to analyze the approximate solution of the multi-dimensional fractional diffusion equation. The Atangana-Baleanu derivative is considered in the Caputo sense. First, we apply Elzaki transform (ET) to obtain a recurrence relation without any assumption or restrictive variable. Then, this relation becomes very easy to handle for the implementation of the homotopy perturbation scheme (HPS). We observe that HPS produces the iterations in the form of convergence series that approaches the precise solution. We provide the graphical representation in 2D plot distribution and 3D surface solution. The error analysis shows that the solution derived by EHPTS is very close to the exact solution. The obtained series shows that EHPTS is a very simple, straightforward, and efficient tool for other problems of fractional derivatives.

Intelligent Nanomaterials for Solar Energy Harvesting: From Polar Bear Hairs to Unsmooth Nanofiber Fabrication.

Polar bears can live in an extremely cold environment due to their hairs which possess some remarkable properties. The hollow structure of the hair enables the bear to absorb energy from water, and the white and transparent hairs possess amazing optical properties. However, the surface morphology function of bear hairs has been little-studied. Herein, we demonstrate that the micro-structured scales distributed periodically along the hair can absorb maximal radiative flux from the Sun. This polar bear hair effect has the ability for the hair surface not to reflect radiation with a wavelength of about 500 nm. Mimicking the polar bears' solar performance in the fabrication of nanofibers will certainly stimulate intelligent nanomaterials for efficient solar energy absorption. Therefore, a new technology is discussed in this work for the fabrication of periodic unsmooth nanofibers toward solar energy harvesting.

Nanofiber template-induced preparation of ZnO nanocrystal and its application in photocatalysis.

Traditional preparation of ZnO nanocrystal requires heating zinc acetate to a temperature over 350 °C, whereas in this work, zinc acetate was first electrospun with PVDF to form a nanofiber, followed by thermal treatment at only 140 °C to give nanocrystalline ZnO. The much lower temperature required in thermal treatment is attributed to the high reactivity of zinc acetate at nano dimension. The as-prepared ZnO-doped PVDF nanofiber mat shows excellent effect in the photocatalytic degradation of Rhodamine B, comparable to ZnO particle thermally treated at 600 °C. Highly-oriented ZnO nanorods were obtained by further hydrothermal synthesis of the electrospun nanofiber mat, giving nanostructured ZnO of different morphologies well-aligned on the surface of organic nanofiber. Notably, the hydrothermal synthesis of the successful preparation of these nanostructured ZnO requires a processing temperature below 100 °C at atmospheric pressure, showing great potential to be scaled up for vast manufacturing.

Control of Macromolecule Chains Structure in a Nanofiber.

Mechanical property is one of the most important properties of nanofiber membranes. Electrospinning is widely used in the preparation of nanofibers due to its advantages such as good stability and easy operation. Compared with some nature silk, the mechanical properties of nanofibers prepared by electrospinning are poor. Based on the principle of vortex spinning and DNA structure, this paper designed an air vortex electrospinning device that can control the structure of macromolecular chains in nanofibers. When a weak air vortex is generated in the electrospinning process, the macromolecule chains will entangle with each other and form a DNA-like structure so as to improve the mechanical property. In addition, when a strong air vortex is generated during the electrospinning process, the nanofibers will adhere to each other, thereby enhancing the mechanical property and enlarging the pore size.

Electrospun Mussel-derived Silk Fibers.

BACKGROUND: Though there are many patents on silk, patents on sea silk are rare. Sea silk is one of the most coveted materials in the world, and the technology to make sea silk is at an extremely high risk of extinction. Unlike spider dragline silk and silkworm silk, this natural silk has been forgotten in the academic commune for millennia, though it has many fascinating properties: high strength, remarkable adhesion, extreme lightweight, and others. METHODS: Here we report that mussel-derived silk fibers can be fabricated by electrospinning. Instead of extracting proteins from byssus, we directly use the protein solution from alive blue mussels, which are intensely commercially used. The protein solution and the polyvinyl alcohol solution are mixed together to produce mussel-based silk fibers. RESULTS: The mussel-based silk fibers have many special properties like high mechanical strength, remarkable super-contraction and good wetting properties. CONCLUSION: The electrospinning mussel-based silk fibers have the potential for use as a replacement for the rarest sea silk and as a new bio-inspired material with multi-functions.

Bubble Electrospinning with an Auxiliary Electrode and an Auxiliary Air Flow.

BACKGROUND: The patented bubble electrospinning, which is a simple and effective technique for mass-production of polymer nanofibers, has been studying extensively, but it is still under development. In the bubble electrospinning, multiple jets move from the positive electrode to the receptor, a long distance between the two electrodes is needed to guarantee complete solvent evaporation, as a result a relative high voltage is needed. OBJECTIVE: The aim of the present study is to use an auxiliary electrode and an auxiliary air flow to improve bubble electrospinning with lower voltage and higher output than those by its traditional one. METHODS: The modification of the bubble electrospinning with an auxiliary electrode and an auxiliary airflow is used to fabricate nanofibers. The auxiliary electrode is close to the positive electrode. The experiment was carried out at room temperature with 8%PVA solution. The result was analyzed with a S4800 cold field scanning electron microscope (SEM, Hitachi S-4800, Tokyo, Japan). RESULTS: The auxiliary electrode can generate a strong induced electric field force. With the action of airflow, the jets will fly to the receptor instead of the auxiliary electrode. CONCLUSION: Both auxiliary electrode and auxiliary airflow are two important factors affecting the spinning process. It can reduce the spinning voltage and improve spinning efficiency.

Insight into the Wetting Property of a Nanofiber Membrane by the Geometrical Potential.

BACKGROUND: There are many patents on design of a material surface with special wetting property, however, theoretical methods are lacked. The wetting property of a nanofiber member has attracted much attention. A material with different sizes or with different structures possesses different wetting properties. No theory can explain the phenomenon. METHODS: The contact angle, fiber fineness, pore size and layer of the nanofiber membrane were tested. The contact angles were measured for membranes with different thicknesses. The geometrical potential is used to explain the experimental phenomenon. RESULTS: The wetting property of a nanofiber membrane mainly depends on fiber diameter and thickness. CONCLUSION: Wetting property of a PVA nanofiber membrane depends upon not only the hydrophilic groups, but also the geometrical structure of its surface, the latter prevails when the porous size of the membrane tends to a nanoscale, and the wetting property can be inverted from hydrophilicity to hydrophobicity.

Fabrication of Latex-based Nanofibers by Electrospinning.

BACKGROUND: Natural latex has been widely used in medical gloves, gas masks and nipples characterized by high elasticity, good film-forming performance and flexible film, but it is seldom used in nanomaterials. Electrospinning is an effective technology for manufacturing microfibrous or nanofibrous membranes. Latex-based nanofibers can be fabricated by electrospinning. Few relevant patents to the topic have been reviewed and cited. METHODS: The natural rubber latex and PVA solution were prepared for electrospinning in this study. RESULTS: When the rubber tends to nano scales, the flexibility of natural rubber gets enhanced. Additionally, the latex fluid can be used as an additive to improve mechanical property of nanofibers. CONCLUSION: The electrospinning rubber nanofibers shed a new light on rubber industry.

Macromolecule Orientation in Nanofibers.

Electrospinning is now commercially used for the fabrication of nano/micro fibers. Compared with spider dragline silk, artificial fibers have poor mechanical properties. Unlike natural silk, which has a hierarchical structure with an approximate 3-fold symmetry, the molecular structure of spun fiber has neither folding nor orientation. To date, it is almost impossible to control molecule orientation during the spinning process. Here, we show that macromolecule orientation can be easily controlled using the laminar flow of fluid mechanics. A lasting laminar flow in a long needle can order macromolecules. We find that the orientation of macromolecules can greatly affect the morphology and mechanical properties of fibers. We expect our technology to be helpful for more sophisticated fabrication of fibers with ordered macromolecules and DNA-like twists.

Fabrication of Beltlike Fibers by Electrospinning.

Electrospinning is always used to fabricate one-dimensional nanofibers. Cylindrical fibers are formed during the spinning process due to the minimal-surface principle. However, when the moving jet has high rigidity, which can counteract the surface tension for a minimal surface, beltlike fibers can be obtained. Using the Hall⁻Petch effect, the rigidity of the moving jet can be greatly enhanced by adding nanoparticles. Polyethylene glycol with a nanometric crystallite size of 4 nm and ZrO2 nanoparticles are used as additives in the experiment, a theoretical analysis is carried out, and the theoretical predictions are verified experimentally.

Variational iteration method for Bratu-like equation arising in electrospinning.

This paper points out that the so called enhanced variational iteration method (Colantoni & Boubaker, 2014) for a nonlinear equation arising in electrospinning and vibration-electrospinning process is the standard variational iteration method. An effective algorithm using the variational iteration algorithm-II is suggested for Bratu-like equation arising in electrospinning. A suitable choice of initial guess results in a relatively accurate solution by one or few iteration.

Fatalness of virus depends upon its cell fractal geometry.

Why do more complex viruses (e.g., HIV, AIDS-virus and SARS coronavirus) tend to be more fatal? The paper concludes that the cell fractal geometry of viruses is the key. This paper also suggests two possible new approaches using nanotechnology and temperature to cure or prevent virus infection.

On body size of infected mice.

Coutinho et al.'s experimental observation reveals that infected mice gain higher body weight. A theoretical analysis is given to explain the phenomenon, the result agrees remarkably well with Coutinho et al.'s experimental data (Acta Tropica 101, 2007, pp. 15-24).

The allometry of leaf form in early plant ontogeny.

A general allometric model between metabolic rate and body size has been derived for early plant ontogeny. The scaling exponent is (2+N/6)/3, where N is the cell's degree of freedom of motion. For early plant ontogeny N=2, our prediction agrees well with Sack et al.'s observation [Sack, L., Maranon, T., Grubb, P.J., 2002. Science 295, 1923].

Resistance in cell membrane and nerve fiber.

A mathematical model describing the resistance in cell membrane and nerve fiber is proposed, which is naturally different from that for metal conductors. An allometric scaling law between the resistance and the section area is obtained. In the derivation, He Chengtian's interpolation, which has millennia history, is applied. Most famous models, such as the Hodgkin-Huxley model, FitzHugh-Nagumo models, should be, therefore, revised.

Fifth dimension of life and the 4/5 allometric scaling law for human brain.

Brain cells are not spherical. The basal metabolic rate (B) of a spherical cell scales as B approximately r2, where r is the radius of the cell; that of a brain cell scales as B approximately r(d), where r is the characteristic radius of the cell and d is the fractal dimensionality of its contour. The fractal geometry of the cell leads to a 4/5 allometric scaling law for human brain, uniquely endowing humans with a 5th dimension and successfully explains why the scaling exponent varies during rest and exercise. A striking analogy between Kleiber's 3/4 law and Newton's second law is heuristically illustrated. A physical explanation is given for the 4th dimension of life for three-dimensional organisms and the 5th dimension for human brain.