Secure Handover Authentication Protocol Based on Bilinear Pairings

Handover authentication protocol enables a mobile node to switch from one base station to another without loss or interruption of service when the node exits the transmission area of his or her current base station. This paper proposes a secure prime-order handover authentication protocol based on bilinear pairings. The proposed protocol adapts the concept of pseudonyms to provide user anonymity and user unlinkability. It withstands well-known security threats and achieves mutual authentication, user unlinkability. A batch signature verification mechanism to verify a mass of signatures is presented in our scheme. We also prove that our scheme is secure under random oracle.     

Improvement of the Nanoparticle Charging Efficiency of a Single-Wire Corona Unipolar Charger by Using Radial Sheath Airflow: Numerical Study

A single-wire corona unipolar charger with radial sheath air was proposed to enhance the nanoparticle charging efficiency. The charger consists of an insulated Teflon tube (inner diameter = 6.35 mm) with a 6 mm-long grounded porous metal tube placed at its center from which radial sheath air is introduced, and a discharge gold wire of 50 μm in the outer diameter and 6 mm in the effective length. The performance of the charger was evaluated and optimized numerically. The effect of the position of the sheath air opening on reducing charged particle loss was found to be important and two designs were studied. In design 1, both ends of the 6 mm wide sheath air opening are aligned with the ends of the 6 mm-long discharge wire, while in design 2 the sheath air opening is shifted 2 mm toward the left of the leading edge of the wire. At the same operating condition, design 2 was found to have less electrostatic loss than design 1 because of its smaller deposition region for charged particles. Compared to two unipolar chargers with the highest extrinsic charging efficiency for particles smaller than 10 nm in diameter, design 2 operated at the applied voltage of +3.5 kV, aerosol flow rate of 0.5 L/min, and sheath airflow rate of 0.7 L/min has a comparable extrinsic charging efficiency of 17.2%–70.5% based on particle number for particles ranging from 2.5 to 10 nm in diameter.

Copyright 2013 American Association for Aerosol Research     

A Study of Rheological Behavior and Compatibility of NR/BR Blends

In this study, we research the Mooney viscosity, curing rates, and processibility of natural rubber (NR) and polybutadiene rubber (BR) blends at different blending ratios. The changing values are measured during vulcanization processing and were tested by Mooney viscometer, Monsanto viscometer, etc. The results of scanning electron microscope (SEM) and dynamic mechanical analysis (DMA) experiments are used to explore the surface morphologies and molecular mobility of NR/BR blends.

The experimental results indicate that Mooney viscosity tends to decrease with increasing NR content of NR/BR blends, and this results in superior processibility of NR/BR blends with increasing NR content. NR/BR blends' curing rate improved with increasing NR content. The DMA experimental results show that the temperature is suitable to produce a character peak (T_αn) in molecular motions of NR/BR blends. There tends to a lower temperature range with decreasing NR content of NR/BR blends. In addition, T_αb would move to a lower temperature with decreasing BR content of NR/BR blends.     

Tribological Performance of Oil-Based Lubricants with Carbon-Fe Nanocapsules Additive

The present study investigates the tribological properties of carbon-Fe nanocapsules (CFNCs) under high contact loads. Block-on-ring wear tests are performed using mineral oil lubricants containing CFNC particles with concentrations ranging from 0.01 to 0.1 wt%. In addition, high-resolution electron transmission microscopy (HR-TEM) and scanning electron microscopy (SEM) analysis were conducted on the test samples. The results show that for a contact load of 650 N, a CFNC concentration of 0.07 wt% and a sliding velocity of 1.65 m/s enhance the surface permeability, fill-up properties, and microbearing lubrication mechanism and promote effective reduction in the wear at the surface contact interface.     

Tribological Performance of Engine Oil Blended with Various Diesel Fuels

In this study, petrodiesel (D100) and different concentrations of commercial biodiesels (B100, B50, B5) were blended with a commercial engine oil at a fixed volume ratio of 1:9 to investigate the tribological effect of the biodiesels on the antiwear performance of the engine oil. The antiwear performance of the blended oils was evaluated using a Plint TE77 reciprocating ball-on-flat tribometer at room temperature and 150°C. Results show that the antiwear performance of the engine oil blended with petrodiesel is worse than that of the other blended oils with biodiesels at both temperatures. At room temperature, the physical adsorption and local hydrodynamic effects of the blended oils dominate the tribological behavior; at 150°C, the biodiesel seems to promote the growth of a reaction film with the antiwear additives in engine oil and enhance the growth rate of chemical films. However, an excess concentration of biodiesels causes tribochemical wear, thus reducing antiwear performance.     

Modeling of transport phenomena in hybrid laser-MIG keyhole welding

Mathematical models and associated numerical techniques have been developed to investigate the complicated transport phenomena in spot hybrid laser-MIG keyhole welding. A continuum formulation is used to handle solid phase, liquid phase, and the mushy zone during the melting and solidification processes. The volume of fluid (VOF) method is employed to handle free surfaces, and the enthalpy method is used for latent heat. Dynamics of weld pool fluid flow, energy transfer in keyhole plasma and weld pool, and interactions between droplets and weld pool are calculated as a function of time. The effect of droplet size on mixing and solidification is investigated. It is found that weld pool dynamics, cooling rate, and final weld bead geometry are strongly affected by the impingement process of the droplets in hybrid laser-MIG welding. Also, compositional homogeneity of the weld pool is determined by the competition between the rate of mixing and the rate of solidification.     

Flow and heat transfer over an unsteady stretching surface with non-uniform heat source

The non-uniform heat source/sink effect on the flow and heat transfer from an unsteady stretching sheet through a quiescent fluid medium extending to infinity is studied. The boundary layer equations are transformed by using similarity analysis to be a set of ordinary differential equations containing three parameters: unsteadiness parameter (S), space-dependent parameter (A?) and temperature-dependent parameter (B?) for heat source/sink. The velocity and temperature fields are solved using the Chebyshev finite difference method (ChFD). Results showed that the heat transfer rate, − θ′(0) and the skin friction, − f″(0) increase as the unsteadiness parameter increases whereas decrease as the space-dependent and temperature-dependent parameters for heat source/sink increase.     

Preparation and properties of carbon nanotube/polypropylene nanocomposite bipolar plates for polymer electrolyte membrane fuel cells

This study aims at the fabrication of lightweight and high performance nanocomposite bipolar plates for the application in polymer electrode membrane fuel cells (PEMFCs). The thin nanocomposite bipolar plates (the thickness <1.2 mm) consisting of multiwalled carbon nanotubes (MWCNTs), graphite powder and PP were fabricated by means of compression molding. Three types of polypropylene (PP) with different crystallinities including high crystallinity PP (HC-PP), medium crystallinity PP (MC-PP), low crystallinity PP (LC-PP) were prepared to investigate the influence of crystallinity on the dispersion of MWCNTs in PP matrix. The optimum composition of original composite bipolar plates was determined at 80 wt.% graphite content and 20 wt.% PP content based on the measurements of electrical and mechanical properties with various graphite contents. Results also indicate that MWCNTs was dispersed better in LC-PP than other PP owing to enough dispersed regions in nanocomposite bipolar plates. This good MWCNT dispersion of LC-PP would cause better bulk electrical conductivity, mechanical properties and thermal stability of MWCNTs/PP nanocomposite bipolar plates. In the MWCNTs/LC-PP system, the bulk electrical conductivities with various MWCNT contents all exceed 100 S cm⁻¹. The flexural strength of the MWCNTs/LC-PP nanocomposite bipolar plate with 8 phr of MWCNTs was approximately 37% higher than that of the original nanocomposite bipolar plate and the unnotched Izod impact strength of MWCNTs/LC-PP nanocomposite bipolar plates was also increased from 68.32 J m⁻¹ (0 phr) to 81.40 J m⁻¹ (8 phr), increasing 19%. In addition, the coefficient of thermal expansion of MWCNTs/LC-PP nanocomposite bipolar plate was decreased from 32.91 μm m⁻¹ °C⁻¹ (0 phr) to 25.79 μm m⁻¹ °C⁻¹ (8 phr) with the increasing of MWCNT content. The polarization curve of MWCNTs/LC-PP nanocomposite bipolar plate compared with graphite bipolar plate was also evaluated. These results confirm that the addition of MWCNTs in LC-PP leads to a significant improvement on the cell performance of the nanocomposite bipolar plate.     

Investigation of Ag-bulk/glassy-phase/Si heterostructures of printed Ag contacts on crystalline Si solar cells

The interface structure of screen-printed silver contacts on a crystalline silicon solar cell has been studied by transmission electron microscopy (TEM). TEM results confirmed that the glassy-phase plays an important role in contact properties. There are at least three different microstructures present in optimal fired contacts. The location where silver-bulk directly contacts silicon is observed through SEM, and this is actually a very thin glass layer in between. In addition, high-density silver embryos on silicon were found for samples fired optimally. The results presented in this study suggest that Ag-bulk/thin-glass-layer/Si contact is the most decisive path for current transportation.     

Investigation of the microwave dielectric properties of Ca1−xMgxLa4Ti5O17 ceramics for application in coplanar patch antenna

In this paper, the dielectric properties of Ca_1−xMg_xLa₄Ti₅O₁₇ ceramics at microwave frequency have been studied. The diffraction peaks of Ca_(1−x)Mg_xLa₄Ti₅O₁₇ ceramics nearly unchanged with x increasing from 0 to 0.03. Similar X-ray diffraction peaks of Ca_0.99Mg_0.01La₄Ti₅O₁₇ ceramic were observed at different sintering temperatures. A maximum density of 5.3 g/cm³ can be obtained for Ca_0.99Mg_0.01La₄Ti₅O₁₇ ceramic sintered at 1500 °C for 4 h. A maximum dielectric constant (_r) and quality factor (Q × f) of Ca_0.99Mg_0.01La₄Ti₅O₁₇ ceramic sintered at 1500 °C for 4 h are 56.3 and 12,300 GHz (at 6.4 GHz), respectively. A near-zero temperature coefficient of resonant frequency (τ_f) of −9.6 ppm/°C can be obtained for Ca_0.99Mg_0.01La₄Ti₅O₁₇ ceramic sintered at 1500 °C for 4 h. The measurement results for the aperture-coupled coplanar patch antenna at 2.5 GHz are presented. With this technique, a 3.33% bandwidth (return loss <−10 dB) with a center frequency at approximately 2.5 GHz has been successfully achieved.