ZCZ‐CDMA and OFDMA using M‐QAM for broadband wireless communications

This paper considers direct‐sequence code‐division multiple‐access with zero‐correlation zone sequences (ZCZ‐CDMA) and orthogonal frequency‐division multiple‐access (OFDMA) schemes using M‐ary QAM signaling for broadband wireless communications. Their system structures, complexities and performances in both AWGN and multipath frequency‐selective fading channels are evaluated and compared. For ZCZ‐CDMA, joint suppression of the multipath fading interference and multiple‐access interference can be achieved with a reduced family‐size of the spreading sequences. For OFDMA, analytical and simulation results indicate that it has the same performance as ZCZ‐CDMA in fast time‐varying multipath fading channels. In time‐invariant or slowly time‐varying channels, where the channel information can be made available to transmitters, OFDMA outperforms ZCZ‐CDMA, offers a higher capacity and is more flexible for system reconfiguration with a comparable computational complexity. Copyright © 2004 John Wiley & Sons, Ltd.     

REGIONAL 3D MODELLING OF THE PERMO‐CARBONIFEROUS AL KHLATA FORMATION IN THE RIMA AREA,EASTERN FLANK OF THE SOUTH OMAN SALT BASIN

The glaciogenic Al Khlata Formation (Late Carboniferous – Early Permian) contains important reservoir and seal intervals in oil fields in southern Oman. Here we describe a 3D regional geological model of the Al Khlata Formation and the underlying Misfar Group in a 1750 km² area in the Eastern Flank of the South Oman Salt Basin. The Misfar Group (Devonian‐Carboniferous?) was included in the model because it also contains glaciogenic facies in the study area. The 3D model is based on wireline logs from 42 wells, palynological zonation in 31 wells, cores from three wells, and a 2011 3D seismic dataset from which three horizons (top‐Huqf, top‐Rahab Shale and top‐Gharif) were interpreted throughout the study area. The combined Al Khlata and Misfar interval varies in thickness in the area from 20 to 730 m over relatively short distances. These large variations in thickness were due to the creation of accommodation in mini‐basins resulting from the removal of underlying Infracambrian salt at the basin margin. In places, some of the available accommodation was occupied by Cambrian sandstones of the Nimr Group and Haima Supergroup, influencing the location and thickness of the Al Khlata mini‐basins. These local depocentres vary in scale, shape and orientation relative to the present‐day salt edge: some are ovoid in plan‐view, others more linear and parallel to the salt edge, and one takes the form of a narrow graben almost perpendicular to the salt edge. By the Early Permian, towards the end of Al Khlata time, deposits become more blanket‐like and uniform, indicating an external or more regional control on base level. Four key lithofacies have been distinguished from wireline logs and were populated zone‐by‐zone through the geological model: sandstone (reservoir), shale (seal), and sandy and silty diamictite. Sandstones are most common towards the base of the Misfar – Al Khlata interval and shales towards the top. The Rahab Shale (Early Permian) at the top of the Al Khlata Formation forms an important seal for oil fields in South Oman, often in combination with seals in overlying intervals. The Rahab Shale was the first widespread seal to be deposited which may have trapped oil migrating from the South Oman Salt Basin during the Palaeozoic. The most common lithofacies in the Misfar – Al Khlata interval in the modelled area is diamictite (60%), which is normally considered to be a waste‐rock lithology. However thick silty diamictites of sufficient extent can seal hydrocarbon accumulations, and some sandy diamictites have the potential to be unconventional reservoir rocks. Even after 50 years of exploration and production of oil from the Al Khlata Formation, there remains potential for further discoveries and overlooked pay zones due to its heterogeneous character and the occurrence of intra‐formational seals.     

Optimized Preparation of Elastically Soft,Highly Piezoelectric,Cellular Ferroelectrets from Nonvoided Poly(ethylene Terephthalate) Films

Electrically charged cellular polymer films can exhibit very high piezoelectric activity and are therefore more and more often employed in advanced electromechanical and electro‐acoustical transducers. In this paper, we report an optimized sequence of steps for preparing such ferroelectrets from commercial nonvoided poly(ethylene terephthalate) (PETP) films by means of foaming with CO₂, biaxial mechanical stretching, controlled void inflation, and bipolar electric charging. The nonvoided PETP films were foamed with supercritical CO₂ at a suitably high pressure and subsequently annealed for stabilization. The cellular foam structure was further optimized by means of well‐controlled biaxial stretching in a commercial stretcher and sometimes subsequent inflation in a pressure chamber. Bipolar electric charging of the internal voids was achieved through the application of high electric fields in an SF₆ atmosphere. The new optimized PETP ferroelectrets exhibit quite large piezoelectric coefficients up to almost 500 pC N^–1, for which unusually low elastic stiffnesses of only around 0.3 MPa are essential. The PETP‐foam ferroelectrets possess unclamped thickness‐extension resonance frequencies between approximately 120 and 250 kHz, and are thus highly suitable for several established as well as novel ultrasonic‐transducer applications.     

Photoresponse Properties of CdSe Single‐Nanoribbon Photodetectors

Photodetectors are fabricated from individual single‐crystal CdSe nanoribbons, and the photoresponse properties of the devices are studied systematically. The photodetector shows a high sensitivity towards excitation wavelength with a sharp cut‐off at 710 nm, corresponding to the bandgap of CdSe. The device exhibits a high photo‐to‐dark current ratio of five orders of magnitude at 650 nm, and can function with excellent stability, reproducibility, and high response speed (< 1 ms) in a wide range of switching frequency (up to 300 Hz). The photocurrent of the device shows a power‐law dependence on light intensity. This finding together with the analysis of the light intensity‐dependent response speed reveals the existence of various traps at different energy levels (shallow and deep) in the bandgap. Coating with a thin SiO₂ isolating layer increases the photocurrent but decreases the response speed of the CdSe nanoribbon, which is attributed to reduction of recombination centers on ribbon surface.     

Highly Efficient Orange and Green Solid‐State Light‐Emitting Electrochemical Cells Based on Cationic IrIII Complexes with Enhanced Steric Hindrance

Highly efficient orange and green emission from single‐layered solid‐state light‐emitting electrochemical cells based on cationic transition‐metal complexes [Ir(ppy)₂sb]PF₆ and [Ir(dFppy)₂sb]PF₆ (where ppy is 2‐phenylpyridine, dFppy is 2‐(2,4‐difluorophenyl)pyridine, and sb is 4,5‐diaza‐9,9′‐spirobifluorene) is reported. Photoluminescence measurements show highly retained quantum yields for [Ir(ppy)₂sb]PF₆ and [Ir(dFppy)₂ sb]PF₆ in neat films (compared with quantum yields of these complexes dispersed in m‐bis(N‐carbazolyl)benzene films). The spiroconfigured sb ligands effectively enhance the steric hindrance of the complexes and reduce the self‐quenching effect. The devices that use single‐layered neat films of [Ir(ppy)₂sb]PF₆ and [Ir(dFppy)₂sb]PF₆ achieve high peak external quantum efficiencies and power efficiencies of 7.1 % and 22.6 lm W^–1) at 2.5 V, and 7.1 % and 26.2 lm W^–1 at 2.8 V, respectively. These efficiencies are among the highest reported for solid‐state light‐emitting electrochemical cells, and indicate that cationic transition‐metal complexes containing ligands with good steric hindrance are excellent candidates for highly efficient solid‐state electrochemical cells.     

Mechanical Reinforcement of Polyethylene Using Polyethylene‐Grafted Multiwalled Carbon Nanotubes

The incorporation of carbon nanotubes to a polymer generally improves the stiffness and strength of the polymer, but the ductility and toughness of the polymer are compromised in most cases. Here we report the mechanical reinforcement of polyethylene (PE) using polyethylene‐grafted multiwalled carbon nanotubes (PE‐g‐MWNTs). The stiffness, strength, ductility and toughness of PE are all improved by the addition of PE‐g‐MWNTs. The grafting of PE onto MWNTs enables the well‐dispersion of nanotubes in the PE matrix and improves MWNT/PE interfacial adhesion. The grafting was achieved by a reactive blending process through melt blending of PE containing 0.85 wt % of maleic anhydride and amine‐functionalized MWNTs. The reaction between maleic anhydride and amine groups, as evidenced by X‐ray photoelectron spectroscopy and Raman spectroscopy, leads to the grafting of PE onto the nanotubes.     

Solution‐Processible Multi‐component Cyclometalated Iridium Phosphors for High‐Efficiency Orange‐Emitting OLEDs and Their Potential Use as White Light Sources

The synthesis and photophysical studies of several multifunctional phosphorescent iridium(III) cyclometalated complexes consisting of the hole‐transporting carbazole and fluorene‐based 2‐phenylpyridine moieties are reported. All of them are isolated as thermally and morphological stable amorphous solids. Extension of the π‐conjugation through incorporation of electron‐pushing carbazole units to the fluorene fragment leads to bathochromic shifts in the emission profile, increases the highest occupied molecular orbital levels and improves the charge balance in the resulting complexes because of the propensity of the carbazole unit to facilitate hole transport. These iridium‐based triplet emitters give a strong orange phosphorescence light at room temperature with relatively short lifetimes in the solution phase. The photo‐ and electroluminescence properties of these phosphorescent carbazolylfluorene‐functionalized metalated complexes have been studied in terms of the coordinating position of carbazole to the fluorene unit. Organic light‐emitting diodes (OLEDs) using these complexes as the solution‐processed emissive layers have been fabricated which show very high efficiencies even without the need for the typical hole‐transporting layer. These orange‐emitting devices can produce a maximum current efficiency of ～ 30 cd A^–1 corresponding to an external quantum efficiency of ～ 10 % ph/el (photons per electron) and a power efficiency of ～ 14 lm W^–1. The homoleptic iridium phosphors generally outperform the heteroleptic counterparts in device performance. The potential of exploiting these orange phosphor dyes in the realization of white OLEDs is also discussed.     

A location‐aware peer‐to‐peer overlay network

This work describes a novel location‐aware, self‐organizing, fault‐tolerant peer‐to‐peer (P2P) overlay network, referred to as Laptop. Network locality‐aware considerations are a very important metric for designing a P2P overlay network. Several network proximity schemes have been proposed to enhance the routing efficiency of existing DHT‐based overlay networks. However, these schemes have some drawbacks such as high overlay network and routing table maintenance overhead, or not being completely self‐organizing. As a result, they may result in poor scalability as the number of nodes in the system grows. Laptop constructs a location‐aware overlay network without pre‐determined landmarks and adopts a routing cache scheme to avoid maintaining the routing table periodically. In addition, Laptop significantly reduces the overlay maintenance overhead by making each node maintain only the connectivity between parent and itself. Mathematical analysis and simulations are conducted to evaluate the efficiency, scalability, and robustness of Laptop. Our mathematical analysis shows that the routing path length is bounded by log_d N, and the joining and leaving overhead is bounded by d log_d N, where N is the number of nodes in the system, and d is the maximum degree of each node on the overlay tree. Our simulation results show that the average latency stretch is 1.6 and the average routing path length is only about three in 10 000 Laptop nodes, and the maximum degree of a node is bounded by 32. Copyright © 2006 John Wiley & Sons, Ltd.     

A Novel and Efficient Feature Extraction Method for Iris Recognition

With a growing emphasis on human identification, iris recognition has recently received increasing attention. Iris recognition includes eye imaging, iris segmentation, verification, and so on. In this letter, we propose a novel and efficient iris recognition method which employs a cumulative‐sum‐based grey change analysis. Experimental results demonstrate that the proposed method can be used for human identification in efficient manner.     

A Temperature‐Controllable Microelectrode and Its Application to Protein Immobilization

This letter presents a smart integrated microfluidic device which can be applied to actively immobilize proteins on demand. The active component in the device is a temperature‐controllable microelectrode array with a smart polymer film, poly(N‐isopropylacrylamide) (PNIPAAm) which can be thermally switched between hydrophilic and hydrophobic states. It is integrated into a micro hot diaphragm having an integrated micro heater and temperature sensors on a 2‐micrometer‐thick silicon oxide/silicon nitride/silicon oxide (O/N/O) template. Only 36 mW is required to heat the large template area of 2 mm×16 mm to 40°C within 1 second. To relay the stimulus‐response activity to the microelectrode surface, the interface is modified with a smart polymer. For a model biomolecular affinity test, an anti‐6‐(2, 4‐dinitrophenyl) aminohexanoic acid (DNP) antibody protein immobilization on the microelectrodes is demonstrated by fluorescence patterns.