Tiered bandwidth reservation scheme for multimedia wireless networks

It is important to provide quality of service (QoS) guarantees if we want to support multimedia applications over wireless networks. In this paper, considering the features of tiering in sectored cellular networks, we propose a novel scheme for bandwidth reservation to approach QoS provisioning. By predicting the movement of each connection, the reserving of bandwidth is only required in needful neighboring cells instead of in all neighboring cells. In addition, an admission control mechanism incorporated with bandwidth borrowing assists in distributing scarce wireless bandwidth in more adaptive way. Through mathematical analysis, we proof the advantages of tier‐based approach and the bound for the selection of tiered boundary. The simulation results also verify that our scheme can achieve superior performance than traditional schemes regarding no bandwidth reserving, fixed bandwidth reserving, and bandwidth borrowing in sectored cellular networks when performance metrics are measured in terms of the connection dropping probability (CDP), connection blocking probability (CBP), and bandwidth utilization (BU). Copyright © 2008 John Wiley & Sons, Ltd.     

Surface‐Enhanced Raman Scattering Using Microstructured Optical Fiber Substrates

Microstructured optical fibers (MOFs) represent a promising platform technology for fully integrated next generation surface enhanced Raman scattering (SERS) sensors and plasmonic devices. In this paper we demonstrate silver nanoparticle substrates for SERS detection within MOF templates with exceptional temporal and mechanical stability, using organometallic precursors and a high‐pressure chemical deposition technique. These 3D substrates offer significant benefits over conventional planar detection geometries, with the long electromagnetic interaction lengths of the optical guided fiber modes exciting multiple plasmon resonances along the fiber. The large Raman response detected when analyte molecules are infiltrated within the structures can be directly related to the deposition profile of the nanoparticles within the MOFs via electrical characterization.     

Encapsulation of Nanoparticles Using Nitrilotriacetic Acid End‐Functionalized Polystyrenes and Their Application for the Separation of Proteins

The use of nitrilotriacetic acid end‐functionalized polystyrenes (NTA‐PS) as a multifunctional nanocarrier for the aqueous dispersion of CdSe, γ‐Fe₂O₃ and gold nanoparticles (NPs) is described. When the amphiphilic end‐ functionalized polystyrenes and NPs are dissolved together in tetrahydrofuran, the addition of water causes the spontaneous formation of micellar aggregates, resulting in the successful encapsulation and aqueous dispersion of NPs. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), photoluminescence (PL) spectroscopy, and vibrating sample magnetometer (VSM) are used to characterize the structure and properties of the NPs‐containing micellar aggregates (nanocarrier). After complexation of Ni²⁺ with NTA on the surface of the nanocarrier containing γ‐Fe₂O₃, specific binding between Ni‐NTA complex and histidine‐tagged (His‐tagged) proteins enables selective separation of His‐tagged proteins using a magnet.     

Cold isostatic pressing technique for producing highly efficient flexible dye‐sensitised solar cells on plastic substrates

One of the biggest challenges for making dye‐sensitised solar cells (DSCs) on plastic substrates is the difficulty in making good quality nanoporous TiO₂ films with both good mechanical stability and high electrical conductivity. Cold isostatic pressing (CIP) is a powder compaction technique that applies an isostatic pressure to a powder sample in all directions. It is particularly suitable for making thin films on plastic substrates, including non‐flat surfaces. Cold isostatically pressed nanocrystalline TiO₂ electrodes with excellent mechanical robustness were prepared on indium tin oxide (ITO)‐coated polyethylene naphthalate (PEN) substrates in the absence of organic binders and without heat treatment. The morphology and the physical properties of the TiO₂ films prepared by the CIP method were found to be very compatible with requirements for flexible DSCs on plastics. This room‐temperature processing technique has led to an important technical breakthrough in producing high efficiency flexible DSCs. Devices fabricated on ITO/PEN films by this method using standard P‐25 TiO₂ films with a Ru‐complex sensitiser yielded a maximum incident photon‐to‐current conversion efficiency of 72% at the wavelength of 530 nm and showed high conversion efficiencies of 6.3% and 7.4% for incident light intensities of 100 and 15 mW cm⁻², respectively, which are the highest power conversion efficiencies achieved so far for any DSC on a polymer substrate using the widely used, commercially available P‐25 TiO₂ powder. Copyright © 2011 John Wiley & Sons, Ltd.     

Theoretical studies of CO hydrogenation to methanol over Cu, Pd, and Pt metals

Theoretical studies of CO hydrogenation to methanol over Cu, Pd, and Pt metals have been carried out using a quasi‐relativistic density‐functional method. The metal surface is simulated by a M₁₀ cluster model. Reaction energies for the elementary steps involved are determined. The activation energies are estimated by the analytic BOC‐MP formula. The results support that these metals are active in CO hydrogenation to methanol. The rate‐determining steps are shown to be different for the metals. The highest activation energies of reaction on the metals fall in the order Cu < Pd < Pt, which corresponds to the order of the catalytic activities of the metals in CO hydrogenation. This revised version was published online in July 2006 with corrections to the Cover Date.     

Photo‐induced Charge Transfer and Relaxation of Persistent Charge Carriers in Polymer/Nanocrystal Composites for Applications in Hybrid Solar Cells

The photo‐induced charge transfer and the dynamics of persistent charge carriers in blends of semiconducting polymers and nanocrystals are investigated. Regioregular poly(3‐hexylthiophene) (P3HT) is used as the electron donor material, while the acceptor moiety is established by CdSe nanocrystals (nc‐CdSe) prepared via colloidal synthesis. As a reference system, organic blends of P3HT and [6,6]‐phenyl C₆₁‐butyric acid methyl ester (PCBM) are studied as well. The light‐induced charge transfer between P3HT and the acceptor materials is studied by photoluminescence (PL), photo‐induced absorption (PIA) and light‐induced electron spin resonance spectroscopy (LESR). Compared to neat P3HT samples, both systems show an intensified formation of polarons in the polymer upon photo‐excitation, pointing out successful separation of photogenerated charge carriers. Additionally, relaxation of the persistent charge carriers is investigated, and significant differences are found between the hybrid composite and the purely organic system. While relaxation, reflected in the transient signal decay of the polaron signal, is fast in the organic system, the hybrid blends exhibit long‐term persistence. The appearance of a second, slow recombination channel indicates the existence of deep trap states in the hybrid system, which leads to the capture of a large fraction of charge carriers. A change of polymer conformation due to the presence of nc‐CdSe is revealed by low temperature LESR measurements and microwave saturation techniques. The impact of the different recombination behavior on the photovoltaic efficiency of both systems is discussed.     

Lipid oxidation products of heated soybeans as a possible cause of protection from ruminal biohydrogenation

Heating oilseeds has been shown to improve the milk fatty acid profile when given to dairy cows, compared to raw oilseeds. However, results from published studies are conflicting. The conditions of heating and storage of the oilseeds could be responsible for these differences, probably partly through their effects on lipid oxidation, the products of which could act on ruminal biohydrogenation (BH). Thus, 15 different treatments were applied to ground soybeans: three levels of heating (no heating, 30 min at 110 or 150°C) × 5 ambient storage durations (0, 1, 2, 4, or 6 months). Soybeans were incubated in vitro with ruminal fluid for 6 h. Triacylglycerol (TAG) polymers, hydroperoxides and hydroxyacids (HOA), aldehydes, and fatty acids were assayed in soybeans and ruminal culture. No TAG polymer was detected in any treatment. Soybeans stored for a long time had a high content of HOA, whereas those heated at 150°C, whatever the storage duration, had high aldehyde contents. The percentage disappearance of cis‐9,cis‐12 18:2 and cis‐9,cis‐12,cis‐15 18:3 in incubates decreased significantly in cultures with heated soybeans, especially at 150°C, suggesting that this partial protection of polyunsaturated fatty acids (PUFA) from BH was at least in part linked to the aldehyde content of the heated soybeans. Practical applications: Oilseeds given to ruminants are often heated, and heat treatment is known to generate oxidation products. Knowing what oxidation products influence ruminal biohydrogenation of unsaturated fatty acids could result in technological processes allowing a better transfer of unsaturated fatty acids from oilseeds to ruminant products.