High-Frequency Fatigue Behavior of Woven-Fiber-Fabric-Reinforced Polymer-Derived Ceramic-Matrix Composites

The monotonic and high-frequency (100 Hz) fatigue behavior of two Nicalon-fabric-reinforced SiCON matrix composites was investigated at room temperature. The matrix composition was varied by the addition of BN and SiC particulate fillers, to contain shrinkage from processing by polymer infiltration and pyrolysis (PIP). The composites had strong fiber/matrix bonding, which resulted in substantially less frictional heating than observed with weakly bonded composites. Both composites exhibited fatigue runout at 10⁷ cycles at ∼80% of the monotonic strength. Comparison with existing fatigue data in the literature (for the same composites) at 1 Hz shows no change in fatigue life; i.e., no frequency effect was observed. Most of the stiffness reduction in the composites occurred in the first fatigue cycle, whereas subsequent decreases in moduli were attributed to limited fiber cracking. The major driving force for failure was the localized debonding of transverse and longitudinal plies at the crossover points in the fabric, which, when linked, resulted in interlaminar damage and failure in the composite.     

Charge-Programmable Photopolymers for 3D Electronics via Additive Manufacturing

Charge-programmed 3D printing enables the fabrication of 3D electronics with lightweight and high precision via selective patterning of metals. This selective metal deposition is catalyzed by Pd nanoparticles that are specifically immobilized onto the charged surface and promises to fabricate a myriad of complex electronic devices with self-sensing, actuation, and structural elements assembled in a designed 3D layout. However, the achievable property space and the material-performance correlation of the charge-programmed printing remain unexplored. Herein, a series of photo-curable resins are designed for unveiling how the charge and crosslink densities synergistically impact the nanocatalyst-guided selective deposition in catalytic efficiency and properties of the 3D printed charge-programmed architectures, leading to high-quality 3D patterning of solid and liquid metals. The findings offer a wide tunability of the structural properties of the printed electronics, ranging from stiff to extreme flexibility. Capitalizing on these results, the printing and successful application of an ultralight-weight and deployable 3D multi-layer antenna system operating at an ultrahigh-frequency of 19 GHz are demonstrated.     

In vivo evaluation of a mucoadhesive polymeric caplet for intravaginal anti-HIV-1 delivery and development of a molecular mechanistic model for thermochemical characterization

Context and objective: The aim of this study was to develop, characterize and evaluate a mucoadhesive caplet resulting from a polymeric blend (polymeric caplet) for intravaginal anti-HIV-1 delivery.

Materials and methods: Poly(lactic-co-glycolic) acid, ethylcellulose, poly(vinylalcohol), polyacrylic acid and modified polyamide 6, 10 polymers were blended and compressed to a caplet-shaped device, with and without two model drugs 3′-azido-3′-deoxythymidine (AZT) and polystyrene sulfonate (PSS). Thermal analysis, infrared spectroscopy and microscopic analysis were carried out on the caplets employing temperature-modulated DSC (TMDSC), Fourier transform infra-red (FTIR) spectrometer and scanning electron microscope, respectively. In vitro and in vivo drug release analyses as well as the histopathological toxicity studies were carried out on the drug-loaded caplets. Furthermore, molecular mechanics (MM) simulations were carried out on the drug-loaded caplets to corroborate the experimental findings.

Results and discussion: There was a big deviation between the T_g of the polymeric caplet from the T_g's of the constituent polymers indicating a strong interaction between constituent polymers. FTIR spectroscopy confirmed the presence of specific ionic and non-ionic interactions within the caplet. A controlled near zero-order drug release was obtained for AZT (20 d) and PSS (28 d). In vivo results, i.e. the drug concentration in plasma ranged between 0.012–0.332?mg/mL and 0.009–0.256?mg/mL for AZT and PSS over 1–28 d.

Conclusion: The obtained results, which were corroborated by MM simulations, attested that the developed system has the potential for effective delivery of anti-HIV-agents.     

Ultrasonic Anomaly Near the Charge Ordering Transition in Sr-Doped Nd0.3La0.2Ca0.5−x Sr x MnO3 Manganites

Sr doping in the charge-ordered compound Nd_0.3La_0.2Ca_0.5?x Sr _x MnO₃ has been systematically studied to examine its effect on ultrasonic velocity and elastic moduli as well as magnetic and electrical transport properties. DC electrical resistivity, ρ and AC susceptibility, χ′ measurements showed all samples exhibit metal-insulator (MI) behavior accompanied by ferromagnetic-paramagnetic (FM-PM) transition where the MI transition temperature, T _MI and FM-PM transition temperature, T _C increased with Sr content indicating the enhancement of double-exchange mechanism. Analysis of the resistivity change with respect to temperature, dlnρ/dT ^?1 versus T indicates onset of charge-ordering (CO) state where its CO transition temperature, T _CO decreased with Sr content indicating weakening of the CO state. On the other hand, both absolute longitudinal and shear velocities as well as elastic moduli measured at 80 K increased significantly with Sr doping indicating improvement in elastic properties, which is suggested to be due to the increase in formation of ferromagnetic domains. A longitudinal velocity anomaly characterized by a slope change around the vicinity of T _CO was observed for all samples. The longitudinal elastic anomaly is attributed to the Jahn–Teller (JT) effect of Mn³⁺ ions where analysis of the anomaly using the mean-field theory suggests involvement of the JT effect in the samples, which transforms from dynamic to static type with decreasing temperature. The elastic anomaly shifted down from 222 K (x=0) to 205 K (x=0.05) indicating that the static JT effect was weakened with Sr content.     

Ordered Semantic Hyper Tableaux

A family of tableau methods, called ordered semantic hyper (OSH) tableau methods for first-order theories with function symbols, is presented. These methods permit semantic information to guide the search for a proof. They also may make use of orderings on literals, clauses, and interpretations to guide the search. In a typical tableau, the branches represent conjunctions of literals, and the tableau represents the disjunction of the branches. An OSH tableau is as usual except that each branch B has an interpretation I ₀[B] associated with it, where I ₀ is an interpretation supplied at the beginning and I ₀[B] is the interpretation most like I ₀ that satisfies B. Only clauses that I ₀[B] falsifies may be used to expand the branch B, thus restricting the kinds of tableau that can be constructed. This restriction guarantees the goal sensitivity of these methods if I ₀ is properly chosen. Certain choices of I ₀ may produce a purely bottom-up tableau construction, while others may result in goal-oriented evaluation for a given query. The choices of which branch is selected for expansion and which clause is used to expand this branch are examined and their effects on the OSH tableau methods considered. A branch reordering method is also studied, as well as a branch pruning technique called complement modification, that adds additional literals to branches in a soundness-preserving manner. All members of the family of OSH tableaux are shown to be sound, complete, and proof convergent for refutations. Proof convergence means that any allowable sequence of operations will eventually find a proof, if one exists. OSH tableaux are powerful enough to be treated as a generalization of several classes of tableau discussed in the literature, including forward chaining and backward chaining procedures. Therefore, they can be used for efficient query processing.     

Towards a classification of energy aware MAC protocols for wireless sensor networks

Power management is an important issue in wireless sensor networks (WSNs) because wireless sensor nodes are usually battery powered, and an efficient use of the available battery power becomes an important concern specially for those applications where the system is expected to operate for long durations. This necessity for energy efficient operation of a WSN has prompted the development of new protocols in all layers of the communication stack. Provided that, the radio transceiver is the most power consuming component of a typical sensor node, large gains can be achieved at the link layer where the medium access control (MAC) protocol controls the usage of the radio transceiver unit. MAC protocols for sensor networks differ greatly from typical wireless networks access protocols in many issues. MAC protocols for sensor networks must have built‐in power conservation, mobility management, and failure recovery strategies. Furthermore, sensor MAC protocols should make performance trade‐off between latency and throughput for a reduction in energy consumption to maximize the lifetime of the network. This is in general achieved through duty cycling the radio transceiver. Many MAC protocols with different objectives were proposed for wireless sensor networks in the literature. Most of these protocols take into account the energy efficiency as a main objective. There is much more innovative work should be done at the MAC layer to address the hard unsolved problems. In this paper, we first outline and discuss the specific requirements and design trade‐offs of a typical wireless sensor MAC protocol by describing the properties of WSN that affect the design of MAC layer protocols. Then, a typical collection of wireless sensor MAC protocols presented in the literature are surveyed, classified, and described emphasizing their advantages and disadvantages whenever possible. Finally, we present research directions and identify open issues for future medium access research. Copyright © 2009 John Wiley & Sons, Ltd.