A simple and accurate four-node quadrilateral element using stabilized nodal integration for laminated plates

This paper reports the development of a simple but efficient and accurate four-node quadrilateral element for models of laminated, anisotropic plate behaviour within the framework of the first-order shear deformation theory. The approach incorporates the strain smoothing method for mesh-free conforming nodal integration into the conventional finite element techniques. The membrane-bending part of the element stiffness matrix is calculated by the line integral on the boundaries of the smoothing elements while the shear part is performed using an independent interpolation field in the natural co-ordinate system. Numerical results show that the element offered here is locking-free for extremely thin laminates, reliable and accurate, and easy to implement. Its convergence properties are insensitive to mesh distortion, thickness-span ratios, lay-up sequence and degree of anisotropy.     

Synthesis and characterization of Pt-Pd alloy and core-shell bimetallic nanoparticles for direct methanol fuel cells (DMFCs): Enhanced electrocatalytic properties of well-shaped core-shell morphologies and nanostructures

In our research, we present the controlled synthesis of poly(vinylpyrrolidone) (PVP) protected Pt-Pd nanoparticles of various alloy and core-shell morphologies by modified polyol method with the assistance of AgNO₃. The Pt-Pd alloy and core-shell nanoparticles were characterized by transmission electron microscopy (TEM), high-resolution TEM, and electrochemical measurements. The comparison of electrocatalytic properties of Pd-Pt bimetallic nanoparticles was described to confirm their highest catalytic performance. Importantly, the catalytic activity of Pt-Pd alloy and core-shell nanoparticles was investigated to develop novel electrocatalysts in direct methanol fuel cells (DMFCs). The results showed that the core-shell nanoparticles with the thin nanoshells as monolayers exhibit as great nanocatalysts. The correlation among structure, size and morphology was presented in their catalytic characterization.     

New Representative Collective Signatures Based on the Discrete Logarithm Problem

The representative collective digital signature scheme allows the creation of a unique collective signature on document M that represents an entire signing community consisting of many individual signers and many different signing groups, each signing group is represented by a group leader. On document M, a collective signature can be created using the representative digital signature scheme that represents an entire community consisting of individual signers and signing groups, each of which is represented by a group leader. The characteristic of this type of letter is that it consists of three elements (U, E, S), one of which (U) is used to store the information of all the signers who participated in the formation of the collective signature on document M. While storing this information is necessary to identify the signer and resolve disputes later, it greatly increases the size of signatures. This is considered a limitation of the collective signature representing 3 elements. In this paper, we propose and build a new type of collective signature, a collective signature representing 2 elements (E, S). In this case, the signature has been reduced in size, but it contains all the information needed to identify the signer and resolve disputes if necessary. To construct the approved group signature scheme, which is the basic scheme for the proposed representative collective signature schemes, we use the discrete logarithm problem on the prime finite field. At the end of this paper, we present the security analysis of the AGDS scheme and a performance evaluation of the proposed collective signature schemes.     

Cu–Fe Incorporated Graphene-Oxide Nanocomposite as Highly Efficient Catalyst in the Degradation of Dichlorodiphenyltrichloroethane (DDT) from Aqueous Solution

Topics in Catalysis - Fe/graphene oxide and Cu–Fe/graphene oxide nanocomposite were synthesized by the atomic implantation method to study the photocatalytic degradation of...     

Thermal degradation of epoxy resin/carbon fiber composites: Influence of carbon fiber fraction on the fire reaction properties and on the gaseous species release

The thermal degradation of epoxy resin/carbon fiber composites has been performed in ISO 5660 standard cone calorimeter using a piloted ignition. Two kinds of composites that differ by their volume fractions in carbon fiber (56 and 59 vol.%) were tested in this study. The cone calorimeter irradiance level was increased up to 75 kW m^?2 to characterize the carbon fiber volume fraction influence on the composite thermal degradation. Thus, main flammability and combustibility parameters were determined and calculated such as mass loss, mass loss rate, ignition time, thermal response parameter, ignition temperature, thermal inertia, and heat of gasification. As a result, all the characteristic parameters for the thermal resistance of composites were decreased when the carbon fiber volume fraction increased. Moreover, the main gaseous products (such as NO, CO, CO₂, HCN, H₂O, and lightweight hydrocarbons) emitted as well as the oxygen consumption during the composite thermal decomposition were also quantified simultaneously with a portable gas analyzer and a Fourier transform infrared spectrometer. The main species emission yields calculated from the gas analysis results increased slightly when the carbon fiber volume fraction was increased in the initial sample. The epoxy composite was represented as a sooty material with a significant production of soot particles during the combustion process. Furthermore, heat release rate, total heat release, and effective heat of combustion were calculated by using the oxygen consumption calorimetry technique. The results obtained showed that a small increasing of composite carbon fiber amount induced a sharp decrease of heat release rate and total heat release. Copyright © 2014 John Wiley & Sons, Ltd.     

Infrared Aluminum Metamaterial Perfect Absorbers for Plasmon‐Enhanced Infrared Spectroscopy

Matured surface chemistry and excellent chemical stability have enabled gold to become the material‐of‐choice for plasmonic sensing in both visible and infrared wavelength range. Here, successful surface functionalization of metamaterials made from a low‐cost abundant plasmonic material, aluminum, with phosphonic acid and subsequent detection of the C?O vibration mode via surface‐enhanced infrared absorption spectroscopy is demonstrated. The metamaterial consists of infrared perfect absorbers fabricated by colloidal lithography. Near perfect absorption is achieved at resonance wavelengths, which can be readily tuned by changing the diameters of the Al disk resonators, enabling excellent overlapping with the molecular vibration. Separately, the detection of a physically adsorbed protein layer on the Al metamaterial is also demonstrated. Surface functionalization with phosphonic acid provides various functional groups to the Al surfaces. Combined with tunable metamaterials, the work herein opens up great opportunities for Al‐based plasmonic nanostructures for biochemical sensing applications.     

Ultrahigh Responsivity in Graphene–ZnO Nanorod Hybrid UV Photodetector

Ultraviolet (UV) photodetectors based on ZnO nanostructure/graphene (Gr) hybrid‐channel field‐effect transistors (FETs) are investigated under illumination at various incident photon intensities and wavelengths. The time‐dependent behaviors of hybrid‐channel FETs reveal a high sensitivity and selectivity toward the near‐UV region at the wavelength of 365 nm. The devices can operate at low voltage and show excellent selectivity, high responsivity (R_I ), and high photoconductive gain (G). The change in the transfer characteristics of hybrid‐channel FETs under UV light illumination allows to detect both photovoltage and photocurrent. The shift of the Dirac point (V _Dirac) observed during UV exposure leads to a clearer explanation of the response mechanism and carrier transport properties of Gr, and this phenomenon permits the calculation of electron concentration per UV power density transferred from ZnO nanorods and ZnO nanoparticles to Gr, which is 9 × 10¹⁰ and 4 × 10¹⁰ per mW, respectively. The maximum values of R_I and G infer from the fitted curves of R_I and G versus UV intensity are 3 × 10⁵ A W^?1 and 10⁶, respectively. Therefore, the hybrid‐channel FETs studied herein can be used as UV sensing devices with high performance and low power consumption, opening up new opportunities for future optoelectronic devices.     

Gradient Porous Elastic Hydrogels with Shape‐Memory Property and Anisotropic Responses for Programmable Locomotion

Programmable locomotion of responsive hydrogels has gained increasing attention for potential applications in soft robotics, microfluidic components, actuators, and artificial muscle. Modulation of hydrogel pore structures is essential for tailoring their mechanical strength, response speeds, and motion behaviors. Conventional methods forming hydrogels with homogeneous or stepwise‐distributed pore structures are limited by the required compromise to simultaneously optimize these aspects. Here, a heterobifunctional crosslinker enabled hydrothermal process is introduced to synthesize responsive hydrogels with well‐defined gradient pore construction. According to gradient porosity controls, the hydrogels simultaneously exhibit rapid responses to external stimuli, high elasticity/compressibility, and programmable locomotion capability. By incorporating polypyrrole nanoparticles as photothermal transducers, photo/thermal responsive composite hydrogels are formed to enable programmable control of locomotion such as bending, curving, twisting, and octopus‐like swimming under near‐infrared laser stimulation. The tunable pore structures, mechanical properties, and locomotion of this new class of materials make these gradient porous hydrogels potentially suitable for a variety of applications.