Structural Control of Phase Formation in Low-Tem perature AIPO4—Sio2 Reactions

The phase relation along the binary join of AIPO₄-SiO₂ were investigated up to 400°C using starting materials made by a solution route. Precursor structures used were boehmite (AIOOH), H₃PO₄, noncrystalline silica, and quartz. The silica precursors acted as structural seeds for the epitaxial growth of AIPO₄. Studies showed that SiO₂ and AIPO₄ were the only crystalline and noncrystalline phases present along the binary join, and no substantial crystalline solution or any ternary phase was observed. Three polymorphic forms of AIPO₄, i.e., berlinite, tridymite, and cristobalite, coexisted as low as 200°C. The nature of the silica precursor greatly influenced the development of the polymorphic phases of AIPO₄. The low-quartz precursor suppressed the formation of the cristobalite form of AIPO₄ and favored berlinite (AIPO₄ quartz) production. On the other hand, noncrystallin silica with a cristobalite-like broad XRD peak suppressed the formation of berlinite and enhaned that of the cristobalite form of AIPO₄. These precursor effects indicate that heteroepitaxy is very significant during the nucleation and growth of AIPO₄ phases on the surface of SiO₂ particles even in these low-temperature reactions.     

Enzymatic Synthesis of Tyrosol-Based Phenolipids: Characterization and Effect of Alkyl Chain Unsaturation on the Antioxidant Activities in Bulk Oil and Oil-in-Water Emulsion

Oxidative stability of lipids is one of the most important parameters affecting their quality. Lipase‐catalyzed lipophilic tyrosyl esters with an equivalent carbon alkyl chain but different degrees of unsaturation (C18:0 to C18:4n3) were prepared, characterized, and used as antioxidants. Free fatty acids and fatty acid ethyl esters (substrate molar ratio tyrosol: acyl donor, 1:10) were used as acyl donors and immobilized lipase from Candida antarctica was the biocatalyst (10 %). The phenolipids were isolated and characterized using ESI–MS, ¹H‐NMR, and ¹³C‐NMR. Peroxide value (PV) and para‐anisidine value (p‐AV) were measured to evaluate their antioxidant activities in bulk oil structured lipid (SL) and in an oil‐in‐water emulsion (SL‐based infant formula). No significant difference was found in yield and reaction time between the two types of acyl donors. However, as the unsaturation of the fatty acids increased the reaction time also increased. In SL, tyrosyl esters exhibited lower antioxidant activity than tyrosol whereas the addition of an alkyl chain enhanced the antioxidant efficiency of tyrosol in infant formula. Tyrosyl oleate was the most efficient antioxidant in the emulsion system followed by tyrosyl stearate and tyrosyl linoleate. These results suggest that the synthesized phenolipids may be used as potential antioxidants in lipid‐based products.     

Detection of blackhole attack in a Wireless Mesh Network using intelligent honeypot agents

A Wireless Mesh Network (WMN) is a promising way of providing low-cost broadband Internet access. The underlying routing protocol naively assumes that all the nodes in the network are non-malicious. The open architecture of WMN, multi-hop nature of communication, different management styles, and wireless communication paves way to malicious attackers. The attackers can exploit hidden loopholes in the multipath mesh routing protocol to have a suction attack called the blackhole attack. The attacker can falsify routing metrics such as the shortest transmission time to reach any destination and thereby suck the network traffic. We propose a novel strategy by employing mobile honeypot agents that utilize their topological knowledge and detect such spurious route advertisements. They are deployed as roaming software agents that tour the network and lure attackers by sending route request advertisements. We collect valuable information on attacker’s strategy from the intrusion logs gathered at a given honeypot. We finally evaluate the effectiveness of the proposed architecture using simulation in ns-2.     

Exploiting sequential access when declustering data over disks and MEMS-based storage

Due to the large difference between seek time and transfer time in current disk technology, it is advantageous to perform large I/O using a single sequential access rather than multiple small random I/O accesses. However, prior optimal cost and data placement approaches for processing range queries over two-dimensional datasets do not consider this property. In particular, these techniques do not consider the issue of sequential data placement when multiple I/O blocks need to be retrieved from a single device. In this paper, we reevaluate the optimal cost of range queries by declustering two-dimensional datasets over multiple devices, and prove that, in general, it is impossible to achieve the new optimal cost. This is because disks cannot facilitate two-dimensional sequential access which is required by the new optimal cost. Then we revisit the existing data allocation schemes under the new optimal cost, and show that none of them can achieve the new optimal cost. Fortunately, MEMS-based storage is being developed to reduce I/O cost. We first show that the two-dimensional sequential access requirement can not be satisfied by simply modeling MEMS-based storage as conventional disks. Then we propose a new placement scheme that exploits the physical properties of MEMS-based storage to solve this problem. Our theoretical analysis and experimental results show that the new scheme achieves almost optimal I/O costs. Recommended by: Sunil Prabhakar This research is supported by the NSF grants under IIS-0220152 and CNF-0423336.     

Measuring Domain Sizes and Compositional Heterogeneities in P3HT‐PCBM Bulk Heterojunction Thin Films with 1H Spin Diffusion NMR Spectroscopy

The application of ¹H spin diffusion nuclear magnetic resonance (NMR) is expanded to polymer‐fullerene blends for bulk heterojunction (BHJ) organic photovoltaics (OPV) by developing a new experimental methodology for measuring the thin films used in poly‐3‐hexylthiophene–phenyl C61‐butyric acid methyl ester (P3HT‐PCBM) OPV devices and by creating an analysis framework for estimating domain size distributions. It is shown that variations in common P3HT‐PCBM BHJ processing parameters such as spin‐coating speed and thermal annealing can significantly affect domain size distributions, which in turn affect power conversion efficiency. ¹H spin diffusion NMR analysis reveals that films spin‐cast at fast speeds in dichlorobenzene are primarily composed of small (<10 nm) domains of each component; these devices exhibit low power conversion efficiencies (η = 0.4%). Fast‐cast films improve substantially by thermal annealing, which causes nanometer‐scale coarsening leading to higher efficiency (η = 2.2%). Films spin‐cast at slow speeds and then slowly dried exhibit larger domains and even higher efficiencies (η = 2.6%), but do not benefit from thermal annealing. The ¹H spin diffusion NMR results show that a significant population of domains tens of nanometers in size is a common characteristic of samples with higher efficiencies.     

Decentralized key generation scheme for cellular-based heterogeneous wireless ad hoc networks

With the support of cellular system a cellular-based mobile ad hoc network (MANET) offers promising communication scenarios while entails secure data exchange as other wireless systems. In this paper, we propose a novel decentralized key generation mechanism using shared symmetric polynomials in which the base stations (BSs) carry out an initial key generation by a symmetric polynomial in a distributed manner and then pass on the key material to mobile stations (MSs). Thereafter, our proposed key generation scheme enables each pair of MSs to establish a pairwise key without any intervention from the BS, thus reducing the management cost for the BS. The shared key between two MSs is computed without any interaction between them. In addition, the trust among MSs is derived from the cellular infrastructure, thus enjoying an equal security level as provided in the underlying cellular network. Simulations are done to observe the system performance and the results are very encouraging.     

Seismic response of shear‐core with sliding support to bi‐directional ground excitation

To study the effectiveness of a sliding support for the isolation of structures from damaging ground motion, the model of a shear‐core supported on a sliding foundation and subjected to random ground motion in two orthogonal directions is considered here. A fictitious spring model is adopted to deal with the discontinuous nature of the sliding structural system. The rigid friction force deformation characteristics of the sliding support are modelled as elasto‐plastic with high elastic stiffness. The sliding support is assumed to remain in the elastic state during non‐sliding and is treated as plastic during the sliding state. An incremental numerical scheme for the solution of a multi‐degree‐of‐freedom system is used for solving the time history responses. The responses (the absolute value of the acceleration of the top of the wall, and the bending moment at the base of the wall), are calculated under various important parametric variations. The result presented here are of interest in the area of the vibration isolation of important structural systems. Copyright © 1999 John Wiley & Sons, Ltd.     

Block Copolymer Nanostructures and Their Applications: A Review

Block copolymer nanostructures are smart, intelligent, and environment sensitive nanostructures designed to respond in a controlled manner to an external stimulus. Block copolymer nanostructures are being extensively utilized in pharmaceutical field, nanotechnology, and inforensics. Upon micellization, the hydrophobic core of block copolymer nanostructures region serves as a reservoir for hydrophobic medication, which can be loaded by chemical, physical, or electrostatic means. DNA combined with synthetic block copolymer nanostructure enhances the chemical and biological behaviors of biomacromolecule and at the same time completely suppress undesirable properties. Novel Nanoelectromechanical Systems/Microelectromechanical Systems (NEMS/MEMS) devices are being realized using block copolymer nanostructures and DNA combined with inorganic material nanoparticles and small organic moieties.     

Decrystallizing Solid Crystalline Titania, Without Melting, Using Microwave Magnetic Fields

TiO₂—a prototype ceramic—was decrystallized in a 2.45 GHz AC magnetic field in a single mode TE₁₀₃ applicator. The titania powders were synthesized by a sol–gel process and pressed into circular pellets. The pellets were very slightly reduced at 1273 K in a reducing atmosphere. The reduced pellets were introduced into the single mode microwave cavity and placed at the magnetic field maximum node and exposed for 10–30 s in a forming gas atmosphere. The reacted samples were then characterized by XRD, SEM, Raman, and TEM. The data presented in this note demonstrate that a very short treatment in the AC magnetic field at 2.45 GHz can transform rutile structure oxides to a noncrystalline state.