Effect of Reactive Graphitic Nanofibers (r-GNFs) on Tensile Behavior of UHMWPE Fiber/Nano-Epoxy Bundle Composites

Ultra-high molecular weight polyethylene (UHMWPE) fibers have good mechanical and physical properties and effective radiation shielding functions, which are significant for aerospace structures. In our previous work, nano-epoxy matrices were developed based on addition of reactive graphitic nanofibers (r-GNFs) in a diluent to form a blend. It is found that improved wettability and enhanced adhesion of the matrices to UHMWPE fibers can be obtained. In this study, a series of nano-epoxy matrices with different concentrations of r-GNFs (up to 0.8 wt%) and different weight ratios of r-GNFs to a reactive diluent (1:4, 1:6, 1:7, and 1:9) were prepared. Composite bundle specimens of UHMWPE fiber/nano-epoxy were fabricated and their tensile behavior was investigated. All load-displacement curves of the UHMWPE/nano-matrix bundle composites under tensile loading showed three regions corresponding to the three deformation and failure stages of the materials: 1) elastic deformation stage, 2) plateau stage, and 3) UHMWPE fiber failure stage. The nano-epoxy with 0.3 wt% of r-GNFs and with 1:6 ratio of r-GNFs to the diluent proved to be the best matrix for UHMWPE fiber composites with enhanced tensile properties. For the resulting composite, the load level and consumed energy in the plateau stage were increased by 8% and 30% over the UHMWPE fiber/pure-epoxy specimens, respectively. This UHMWPE fiber composite with the optimized nano-epoxy matrix also possesses the highest initial stiffness and ultimate tensile strength among all the resulting UHMWPE fiber composites. These results laid a foundation for us to fabricate UHMWPE fiber reinforced composite laminates in the near future.     

A fundamental study on electrowetting by traditional and multifunctional ionic liquids: possible use in electrowetting on dielectric-based microfluidic applications

Water or aqueous electrolytes are the dominant components in electrowetting on dielectric (EWOD)-based microfluidic devices. Low thermal stability, evaporation, and a propensity to facilitate corrosion of the metal parts of integrated circuits or electronics are drawbacks of aqueous solutions. The alternative use of ionic liquids (ILs) as electrowetting agents in EWOD-based applications or devices could overcome these limitations. Efficient EWOD devices could be developed using task-specific ILs. In this regard, a fundamental study on the electrowetting properties of ILs is essential. Therefore electrowetting properties of 19 different ionic liquids, including mono-, di-, and tricationic, plus mono- and dianionic ILs were examined. All tested ILs showed electrowetting of various magnitudes on an amorphous flouropolymer layer. The effects of IL structure, functionality, and charge density on the electrowetting properties were studied. The enhanced stability of ILs in electrowetting on dielectric at higher voltages was studied in comparison with water. Deviations from classical electrowetting theory were confirmed. The physical properties of ILs and their electrowetting properties were tabulated. These data can be used as references to engineer task-specific electrowetting agents (ILs) for future electrowetting-based applications.     

Anionomeric waterborne poly(urethane semicarbazide) dispersions and their adhesive properties

Aqueous polyurethane dispersions were prepared from isocyanate‐terminated ionic polyurethane prepolymers by chain extension with dihydrazides. These water‐borne dispersions had excellent adhesive properties and were used to bond leather and canvas. The base polymers were varied with respect to (1) the ionic content with the same chain extender and (2) the nature of the chain extender with the ionic content kept constant. Studies on the particle size and viscosity revealed that the ionic content had an influence on the aforementioned properties: the particle size decreased and the viscosity increased with increasing ionic content. The polarity of the films cast from the dispersions were determined with contact‐angle measurements: hydrophilic character was exhibited by all the compositions. X‐ray studies revealed that the increase in the ionic content led to increasing intensities of the diffraction peaks due to increased secondary forces of bonding. The tensile strength measurements showed that the films were highly elastomeric and had good mechanical strength, which varied with the composition. A shear strength and peel strength analysis of specimens obtained through the bonding of leather to leather, leather to canvas, and canvas to canvas revealed that the waterborne dispersions were excellent adhesives for bonding leather surfaces. Thus, a very efficient, ecofriendly waterborne dispersion of polyurethane that could find applications in bonding leather in the footwear industry was prepared successfully. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Wear Behavior of Disk Shape Spray Formed Al-Si-Pb Alloys

Wear behavior of spray formed Al-Si-Pb alloys was investigated using a pin on disk type wear testing machine. Wear rate behavior with applied load was observed to depict three stages, in the second stage rate of increase in wear rate was the lowest and in the third stage it was the highest. The wear rate decreased with the increase in distance from center to periphery of the spray deposit. It decreased linearly with the increase in lead content and it was lower for 12% Si as compared to that of 6% Si in Al-Si-Pb alloys. The coefficient of friction decreased rapidly up to the load of 40 N and beyond this load the friction coefficient was almost constant. The coefficient of friction was lower for higher lead content.     

Free Vibration Analysis of Thin Circular Cylindrical Shell with Closure Using Finite Element Method

Vibration analysis of a thin circular cylindrical shell with closure is conducted using finite element method (FEM). Theoretically, shell vibrates in different axial modes, m; circumferential modes, n; and any of their combinations with corresponding modal frequencies. The present FEM results are verified by the results reported in the literature using various shell theories. The eigenvalues of the shell are extracted using block Lanczos and subspace iteration methods, in order to investigate their computational efficacy. Further, the effect of adding various types of closures at one end of the circular cylindrical shell such as flat, cone, and dome, on the modal frequencies are investigated. The two aspect ratios (length to radius ratio) of shell with closure, broad, and slender are considered for this study. The effect of the ratio of the thickness of the closure to the thickness of shell wall on the frequency is also investigated. For the shell with the closure, the vibration modes can be cylinder, closure, or combined cylinder and closure. The modal frequency of the cylindrical shell is significantly affected by the closure. The lowest frequency is observed in the flat type of closure in both the broad and slender cylindrical shells in comparison to the non-closure, dome, and cone type of the closures.     

EMUNE: Architecture for Mobile Data Transfer Scheduling with Network Availability Predictions

With the mobile communication market increasingly moving towards value-added services, the network cost will need to be included in the service offering itself. This will lead service providers to optimize network usage based on real cost rather than simplified network plans sold to consumers traditionally. Meanwhile, today’s mobile devices are increasingly containing multiple radios, enabling users on the move to take advantage of the heterogeneous wireless network environment. In addition, we observe that many bandwidth intensive services such as video on demand and software updates are essentially non real-time and buffers in mobile devices are effectively unlimited. We therefore propose EMUNE, a new transfer service which leverages these aspects. It supports opportunistic bulk transfers in high bandwidth networks while adapting to device power concerns, application requirements and user preferences of cost and quality. Our proposed architecture consists of an API, a transport service and two main functional units. The well defined API hides all internal complexities from a programmer and provides easy access to the functionalities. The prediction engine infers future network and bandwidth availability. The scheduling engine takes the output of the prediction engine as well as the power and monetary costs, application requirements and user preferences into account and determines which interface to use, when and for how long for all outstanding data transfer requests. The transport service accordingly executes the inferred data transfer schedule. The results from the implementation of EMUNE’s and of the prediction and scheduling engines evaluated against real user data show the effectiveness of the proposed architecture for better utilization of multiple network interfaces in mobile devices.     

Assessment of the nutritional status of preschool-age children during the second Intifada in Palestine

BACKGROUND: The Palestinian economy has dramatically deteriorated at all levels since the Al-Aqsa Intifada (uprising) began in 2000, resulting in an unprecedented catastrophe to the livelihoods of the Palestinians residing in the West Bank and Gaza. It was also marked by lack of household physical and financial access to food and health care, which placed children at increased risk of malnutrition and poor health. This prompted a significant increase in food aid from 2002 until the summer of 2003. OBJECTIVES: To assess the nutritional status of children 6 to 59 months of age after 1 year of food assistance. METHODS: In the West Bank and Gaza, a nationally representative sample of children 6 to 59 months of age was randomly selected with a validated multistage clustered design, with the Health Survey 1999 sample used as the sampling frame. The sample was stratified according to governorate, place of residence (urban, nonurban, or refugee camp), locality, and size of locality (number of households). A cross-sectional survey of nutritional status was carried out. Data were collected by interviews with the primary caregivers of the children. Measurements were made of children's weight and height or length. Food-intake data were collected by the 24-hour food-recall method with the use of a booklet of photographs of foods commonly eaten in Palestine. RESULTS: A total of 3,089 children were assessed, of whom 3.1% in the West Bank and 3.9% in the Gaza Strip were suffering from acute malnutrition; the prevalence of chronic malnutrition was 9.2% in the West Bank and 12.7% in the Gaza Strip (p = .02). Sex, refugee status, locality, and maternal education were not significantly associated with acute malnutrition by logistic regression analysis, whereas infants 6 to 23 months of age were significantly at risk. Calorie and protein intakes were generally lower than recommended dietary allowances. CONCLUSIONS: The prevalence rates of both acute and chronic malnutrition among children in the West Bank and Gaza are significantly higher than the national Palestinian averages. There is a need to establish nutritional surveillance systems to monitor the nutritional status of children in conflict areas.     

A finite element modeling-based approach to predict vibrations transmitted through different body segments of the operator within the workspace of a small tractor

Agricultural tractor drivers are subjected to high levels of whole-body vibrations and hand arm vibrations during most part of the farm activities due to unevenness of field surface, uneasy posture, improper workplace design, moving parts of the tractor, and other unavoidable circumstances. The comfort level of the operator inside a dynamic tractor is dependent on the level of vibration generated inside the different human body segments. In the present study, a finite element modeling was proposed to predict vertical vibrations (Z-axis) and frequencies at the different body segments of the seated small tractor operator. The forces required for different controls of the tractor were measured to be used as input parameters in the finite element modeling. The maximum mean forces of the brake (172.8 N) and clutch (153.2 N) were used as the input parameters for the simulation study. The simulated results were validated with the field measured values of vertical accelerations at selected body segments of the operator. The simulation could successfully predict vertical vibrations at selected points of interest (i.e., foot, leg, thigh, lower arm, upper arm, back, and head) except the chest of the body, as the buttock of the operator model was fixed (degree of freedom is equal to zero) in the simulation. The obtained results were compared with the international standards ISO 2631-1 (1985/1997) and ISO 5349-1 (2001) to assess the vibration characteristics at the different body segments of the operator. The foot, leg, lower arm, and upper arm of the operator were subjected to vertical vibration frequencies from 10 to 200 Hz. Most of the resonance of vertical accelerations occurred in one-third octave bands of 20–80 Hz frequencies. The thigh, chest, back, and head of the operator were exposed to vibration frequencies below 40 Hz during field operation. At these parts of the body, the vertical acceleration resonated at lower frequencies, between 2 and 8 Hz.     

Microstructure and Polarization Studies on Interlayer Free La0.65Sr0.3Co0.2Fe0.8O3–δ Cathodes Fabricated on Yttria Stabilized Zirconia by Solution Precursor Plasma Spraying

Nano‐structured cathodes of La_0.65Sr_0.3Co_0.2Fe_0.8O_3–δ (LSCF) are fabricated by solution precursor plasma spraying (SPPS) on yttria stabilized zirconia (YSZ) electrolytes (LSCF‐SPPS‐YSZ). Phase pure LSCF is obtained at all plasma power. Performances of LSCF‐SPPS‐YSZ cathodes are compared with conventionally prepared LSCF cathodes on YSZ (LSCF‐C‐YSZ) and gadolinium doped ceria (GDC) (LSCF‐C‐GDC) electrolytes. High R_p is observed in the LSCF‐C‐YSZ (∼42 Ohm cm² at 700 °C) followed by LSCF‐C‐GDC (R_p ∼ 1.5 Ohm cm² at 700 °C) cathodes. Performance of the LSCF‐SPPS‐YSZ cathodes (R_p ∼ 0.1 Ohm cm² at 700 °C) is found to be even superior to the performance of LSCF‐C‐GDC cathodes. High performance in LSCF‐SPPS‐YSZ cathodes is attributed to its nano‐structure and absence of any interfacial insulating phase which may be attributed to the low temperature at the interaction point of LSCF and YSZ and low interaction time between LSCF and YSZ during SPPS process. In the time scale of 100 h, no change in the polarization resistances is observed at 750 °C. Based on the literature and from the present studies it can be stated that SOFC with YSZ electrolyte and LSCF‐SPPS‐YSZ cathode can be operated at 750 °C for a longer duration of time and good performance can probably be achieved.