Synthesis and characterization of open‐cell foams for sound absorption with rotational molding method

Foams with open‐cell structures have improved sound absorption abilities over conventional closed‐cell foams. One technique to optimize the acoustic abilities of open‐cell foams is to control their cellular properties through the manipulation of processing parameters. This article presents a novel process to synthesize open‐cell polymeric foams for acoustic applications. The process combined rotational foam molding and particulate leaching to produce foams with open‐cell networks that are desirable for acoustic absorption. Open‐cell foams with open‐porosity of about 0.90 were successfully fabricated with this combined foaming process. Effects of processing parameters on the cellular and acoustic properties of the foam samples were examined and discussed. On the basis of the results from the study, the cellular and acoustic properties of the foam fabricated from the proposed method can be controlled through the use of different salt particle sizes in the process. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Thermal buckling analysis of laminated composite beams using hyperbolic refined shear deformation theory

In this article, thermal buckling of laminated composite beams, based on hyperbolic refined shear deformation theory, presented for the first time, is formulated using the principle of minimum total potential energy. Navier’s analytical solution is derived to analytically solve the differential equations and the thermal critical buckling is presented in closed-form solution. The effects of temperature distribution, length to thickness ratio, modulus ratio, and thermal expansion coefficient ratio on thermal buckling of isotropic, orthotropic and laminated composite beams are investigated. The accuracy of the numerical model is verified by comparison with the available results in the literature.     

Low-temperature processing and characterization of single-phase PZT powders by sol-gel method

A new sol-gel system using acetoin was developed and employed for the fabrication of PZT powders and films with compositions near the morphotropic phase boundary Pb(Zr_0.52Ti_0.48)O₃. Acetoin was used as chelating agent to replace the highly toxic methoxyethanol used in previous formulations. This route simplified the chemical processing of PZT-based solutions. Powders were completely crystallized by about 450 °C and contained the ferroelectric perovskite single phase. The firing temperature and time were to be the most important variables. Metallic lead formed only when excess Pb was incorporated. The precursor and the heat-treated powders have been characterized by using thermal analysis and X-ray diffractometry (XRD) studies. The average particle size, as measured from X-ray line broadening, was ∼35 nm.     

Intrusion detection and tolerance: A global scheme

Protecting implemented security mechanisms and trusting their output (e.g. log files) when the host, under which they are deployed, is compromised, is among the major challenges that have to be faced. To fulfil this need, recent advances in security have considered the design of storage-based intrusion detection system, which detect intrusions by looking at the low-level disk requests patterns. However, these systems neither tolerate intrusions, nor do they distinguish whether the disk requests are generated by legitimate or malicious processes; and consequently, they generate a lot of false negative and positive alerts. In this paper, we present a Cooperative Intrusion Detection and Tolerance System, called CIDTS, which takes advantage of the information that are available at the network, host operating system, and storage level to better detect intrusion attempts in their early stages, even when the host is compromised. To allow cooperation, the disk communication interface that transports requests between the storage level and the host level is extended to forward information about the processes that generate the request. The paper also provides intrusion tolerance capabilities and provides techniques to support investigation activities. Copyright © 2007 John Wiley & Sons, Ltd.     

Adsorption property and affinity chromatography of polystyrene derivative sorbent towards cow's milk xanthine oxidase

On the basis of the biospecific molecular recognition between complementary chemical groups of xanthine oxidase (XO) and their ligands particularly sulphated glycoaminoglycans and heparin. Poly (styrene chlorosulfonyl) particles modified by sulfonate sodium groups was synthesized and its adsorption property towards cow's milk XO was established. The adsorption of XO onto this functional polymer was performed in batch at 4 °C and at pH 6.0 during 30 min. of incubation. The adsorbed XO content at the interface allows establishing the chemisorption isotherm curve. The affinity association estimated from this adsorption isotherm according to the Langmuir equation was found to be significantly high in the magnitude of 1.25 × 10⁶ M^? 1. Affinity chromatography on column using this functional polymer as a stationary phase confirms its high ability to adsorb XO at low ionic strength. In fact, the xanthine oxidase of the crude extract is strongly adsorbed onto the sorbent and is eluted at high ionic strength with out any significant loss of its biological activity. The purified enzyme possesses a protein flavin ratio (PFR) of 6.05 with a specific activity of 1.78 UI/mg. On the other hand, the electrophoresis of XO fraction showed a single band with a molecular weight of about 150 kDa. Thus, the synthesized beads functionalized by sulfonate group could be used efficiently and advantageously in the purification of XO instead of other conventional chromatographic methods which need several steps.     

Efficient Realization of Large Size Two’s Complement Multipliers Using Embedded Blocks in FPGAs

This paper presents an optimized design approach for two’s complement large size multipliers using smaller size embedded multiplier blocks available as resources in field programmable gate arrays (FPGAs). The realization is based on the Baugh–Wooley algorithm, which segments the multiplication into unsigned and signed components. To achieve efficient implementation results, a set of optimized schemes for the realization of the additions required for the unsigned multipliers and for combining the unsigned and signed components is proposed. The implementations of the multipliers have been carried out for operands with sizes ranging from 20 to 128 bits. The designs are synthesized and implemented on Xilinx’s Spartan-3 in the ISE 8.1 design platform and compared with three other realizations using the following approaches: (1) conventional sign-extension approach, (2) Xilinx’s IP-Core generator, and (3) sign-and-magnitude-based approach. The experimental results indicate that our proposed method outperforms the other techniques.     

On cavitation and macroscopic behaviour of amorphous polymer-rubber blends

The macroscopic behaviour of rubber-modified polymethyl methacrylate (PMMA) was investigated by taking into account the microdeformation mechanisms of rubber cavitation. The dependence of the macroscopic stress–strain behaviour of matrix deformation on the cavitation of rubber particles was discussed. A phenomenological elastic-viscoplastic model was used to model the behaviour of the matrix material, while the rubber particles were modelled with the hyperelasticity theory. A two-phase composite material with a periodic arrangement of reinforcing particles of a circular unit cell section was considered. Finite-element analysis was used to determine the local stresses and strains in the two-phase composite. In order to describe the cavitation of the rubber particles, a criterion of void nucleation is implemented in the finite-element (FE) code. A comparison of the numerically predicted response with experimental result indicates that the numerical homogenisation analysis gives satisfactory prediction results.     

Synthesis and characterization of new pyrochlore solid solution Bi1.5Sb1.5Cu1−xMnxO7

A new pyrochlore solid solution with formula Bi_1.5Sb_1.5Cu_1−xMn_xO₇ has been synthesized using ceramic method at 1000 °C. The cell parameter decreases linearly with increasing manganese concentration. Rietveld refinements for (B_1.5Mn_0.5)(Sb_1.5Mn_0.5)O₇ compound using X-ray powder diffraction data confirmed an overall A₂B₂O₇ cubic pyrochlore structure with a = 10.42749 (4) Å and Fd-3m symmetry. The reliability factors are R_wp = 3.48%; R_p = 2.37%; R_exp = 1.65% and R_Bragg = 1.58%. The magnetic susceptibility measurements achieved between 4 and 300 K indicate a paramagnetic behaviour with an oxidation state “2+” of the manganese ion. The electric resistance measured using complex impedance spectroscopy method put in evidence a decrease of the electric resistance with the temperature, which reached 5 × 10² Ω at 675 K. Dielectric properties depend on the variation of frequency and temperature, results indicate a conductive compound.     

WHOMoVeS: An optimized broadband sensor network for military vehicle tracking

With the advance of sensing technologies and their applications, advanced sensor networks are gaining increasing interest. For certain sensitive applications, heterogeneous sensors can be deployed in the monitored space to ensure scalability, high-speed communication, and long network lifetime. Hybrid sensor networks have capabilities to combine the use of both resource-rich and resource-impoverished sensor nodes. This paper proposes a heterogeneous broadband sensor network architecture for military vehicle tracking. Powerful sensor devices with good bandwidth and energy capabilities are used as a communication backbone while energy sensors are used to track moving targets. Copyright © 2007 John Wiley & Sons, Ltd.     

Development of polylactide open‐cell foams with bimodal structure for high‐acoustic absorption

In this study, a highly porous and interconnected foam structure was fabricated using compression molding combined with particulate‐leaching technique. The foamed structures were fabricated with polylactide (PLA) and polyethylene glycol (PEG) with salt as the particulate. The pore size of the foam structure is controlled by the particulates size and higher interconnectivity is achieved by the co‐continuous blending morphology of the PLA matrix with the water‐soluble PEG. PLA is a fully bio‐based thermoplastic polymer and is derived from renewable resources, such as cornstarch or sugarcanes. PEG is also fully biodegradable polymer produced from ethylene. Fabricated foams were characterized for cellular, acoustic, and mechanical properties. The acoustic performance of the foams was studied by measuring the normal incident absorption coefficient in accordance with the ASTM E1050 standard. The results show open porosity as high as 88% was achieved and the effect of water‐soluble polymer on cellular properties and acoustic and mechanical performance of the foams was studied. As a result of the secondary porous structure formed into cell walls by water soluble polymer, the overall absorption of fabricated PLA foams was increased to above 90% while the average absorption of the foams remained unchanged. In addition, the resulting acoustic foams are benign and environmentally friendly. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39518.