A computationally efficient selected mapping technique for reducing PAPR of OFDM

In orthogonal frequency division multiplexing (OFDM) system, high value of peak-to-average power ratio (PAPR) is an operational problem that may cause non-linear distortion resulting in high bit error rate. Selected mapping (SLM) is a well known technique that shows good PAPR reduction capability but inflicts added computational overhead. In this paper, using Riemann sequence based SLM method, we applied reverse searching technique to find out low PAPR yielding phase sequences with significant reduction in computational complexity. Additionally, we explored side-information free transmission that achieves higher throughput but sacrifices PAPR reduction. Finally, to overcome this loss in PAPR reduction, we proposed application of Square-rooting companding technique over the output OFDM transmitted signal. Simulation results show that the proposed method is able to compensate the sacrifice in PAPR and achieved PAPR reduction of 8.9 dB with very low computational overhead.     

A Complete Separation of Hexane Isomers by a Functionalized Flexible Metal Organic Framework

The separation ability of branched alkane isomers (nHEX, 3MP, 22DMB) of the flexible and functionalized microporous iron(III) dicarboxylate MIL‐53(Fe)‐(CF₃)₂ solid is evaluated through a combination of breakthrough experiments (binary or ternary mixtures), adsorption isotherms, X‐ray diffraction temperature analysis, quasi‐elastic neutron scattering measurements and molecular dynamics simulations. A kinetically controlled molecular sieve separation between the di‐branched isomer of hexane 22DMB from a mixture of paraffins is achieved. The reported total separation between mono‐ and di‐branched alkanes which was neither predicted nor observed so far in any class of porous solids is spectacular and paves the way towards a potential unprecedented upgrading of the RON of gasoline.     

Constellation constrained multiuser multiple‐input multiple‐output for high capacity and error performance over correlated fading channels

Channels' correlation has direct impact to degrade the capacity and reliability of multiple‐input multiple‐output (MIMO) systems considerably. In this paper, new signal constellation designs are investigated to mitigate fading correlation and maximize the capacity and error performance of multiuser MIMO (MU‐MIMO) over correlated channels, which is a major research challenge. Two methods are studied in a novel constellation constrained MU‐MIMO approach, namely, unequal power allocation and rotated constellation. Based on principles of maximizing the minimum Euclidean distance (d_min) of composite received signals, users' data can be recovered using maximum likelihood joint detection irrespective of correlation values. Compared with the identical constellation scenario in conventional MU‐MIMO, it is shown that constellation rearrangement of transmitted signals has direct impact to resolve the detection ambiguity when the channel difference is not sufficient, particularly in moderate to high correlations. Extensive analysis and simulation results demonstrate the superiority of proposed technique to capture most of the promised gains of multiantenna systems and application for future wireless communications. Copyright © 2014 John Wiley & Sons, Ltd.     

Amorphous Boron Nitride: A Universal,Ultrathin Dielectric For 2D Nanoelectronics

Next‐generation nanoelectronics based on 2D materials ideally will require reliable, flexible, transparent, and versatile dielectrics for transistor gate barriers, environmental passivation layers, capacitor spacers, and other device elements. Ultrathin amorphous boron nitride of thicknesses from 2 to 17 nm, described in this work, may offer these attributes, as the material is demonstrated to be universal in structure and stoichiometric chemistry on numerous substrates including flexible polydimethylsiloxane, amorphous silicon dioxide, crystalline Al₂O₃, other 2D materials including graphene, 2D MoS₂, and conducting metals and metal foils. The versatile, large area pulsed laser deposition growth technique is performed at temperatures less than 200 °C and without modifying processing conditions, allowing for seamless integration into 2D device architectures. A device‐scale dielectric constant of 5.9 ± 0.65 at 1 kHz, breakdown voltage of 9.8 ± 1.0 MV cm^?1, and bandgap of 4.5 eV were measured for various thicknesses of the ultrathin a‐BN material, representing values higher than previously reported chemical vapor deposited h‐BN and nearing single crystal h‐BN.     

Effect of CO<Subscript>2</Subscript> on the oxidation of cyclohexene by H<Subscript>2</Subscript>O<Subscript>2</Subscript> using Co<Subscript>1.5</Subscript>PW<Subscript>12</Subscript>O<Subscript>40</Subscript> catalyst

Oxidation of cyclohexene by cheap and environmentally friendly oxidants, namely H₂O₂ and CO₂ has been catalyzed by Co_1.5PW₁₂O₄₀. It has been found that the main products of the oxidation are 2-cyclohexen-l-one (enone), 2-cyclohexen-l-ol (enol) and 1, 2-cyclohexanediol (diol) with the enone as the major product. Oxidation by CO₂ along with H₂O₂ remarkably increased the conversion compared to that by CO₂ and H₂O₂ separately. This might be due to the fact that CO₂ increases the percarbonate species (HCO₄ ^?) responsible of the oxidation by oxygen transfer, which indicated that the CO₂/H₂O₂ mixture is a useful reagent system. The decrease of both the selectivity of the enone and epoxide in favor of that of diol at higher conversions indicated that the diol was formed from the epoxide by consecutive reaction and/or directly from cyclohexene.     

DEPOSITIONAL AND DIAGENETIC BARRIERS,BAFFLES AND CONDUITS: PERMIAN – CARBONIFEROUS UNAYZAH RESERVOIR,NUAYYIM FIELD,CENTRAL SAUDI ARABIA

The Unayzah Formation is one of the most important Palaeozoic reservoir systems in Saudi Arabia. In the Nuayyim field, Central Saudi Arabia, it produces light, sweet crude oil and consists of three main reservoir units, in descending stratigraphic order: Unayzah A, B and C. These reservoir units include a wide range of depositional facies deposited under a variety of climatic conditions, from high‐latitude glacio‐fluvial to more temperate playa/lacustrine, floodplain and braided‐fluvial to hot‐arid aeolian environments. Together with the diagenetic changes superimposed on the various depositional facies, this has produced complex reservoir heterogeneity. The effects of this diagenetic and sedimentologic complexity on reservoir quality and compartmentalization are the subject of this paper. Approximately 816 ft of core and 611 core plug samples were examined from three wells which penetrate, completely or in part, the Unayzah reservoir. We combine petrographic and scanning electron microscope analysis with porosity and permeability data and calculated pore throat dimensions to identify fluid conduits, barriers and baffles to fluid flow. A rock classification scheme is proposed which takes into account whether the pore‐level control on fluid flow is due to depositional or diagenetic processes and the composition of depositional or diagenetic phases within the pores. Distinguishing depositional versus diagenetic controls on fluid flow is important for predicting the three‐dimensional geometry of conduits, barriers and baffles, and a priori knowledge of potential reactions between injected fluids and reservoir rocks is important for designing enhanced oil recovery fluids. In the three wells studied, it appears that the Unayzah reservoir is compartmentalized vertically due to the occurrence of diagenetic and depositional barriers and baffles. There is insufficient data to assess the lateral or areal extent of the barriers, baffles and fluid conduits, but the understanding of pore‐level controls on reservoir quality and the rock classification schemes introduced here will provide a starting point for future studies. These studies should combine well logs, seismic and engineering data with data presented here to assist mapping conduits, barriers and baffles across the field. The proposed classification schemes may also prove to be useful for assessing reservoirs in other fields both within Saudi Arabia and elsewhere.     

An improved light attenuation technique for measuring large interfacial areas

A laser-based light attenuation technique was successfully used to measure interfacial areas as high as 5832 m²/m³ and Sauter mean bubble diameter varying between 50 and 5600 μm. Good agreement between this approach and the photographic technique was obtained particularly at low gas holdups.     

Organic solvent pretreatment to enhance enzymic saccharification of straw

Enzymic saccharification of wheat straw in the absence of any pretreatment was only about 20 %. Acid hydrolysis did not improve the overall cellulose enzymic breakdown, nor did pretreatment by flash autohydrolysis under pressure or sodium chlorite delignification. When wheat straw was treated with N-methyl-morpholine-N-oxide (MMNO) at J20°C for 20–30 min, this treatment and subsequent enzymic hydrolysis produced carbohydrate conversion of 73%. Similar results could be obtained by treating straw with 0·1 M sodium hydroxide. When MMNO treatment was combined with any other pretreatment, the saccharification yield was greatly enhanced. Nearly quantitative conversion was obtained by swelling straw in 0·1 M sodium hydroxide followed by MMNO treatment. The results show that lignin content of plant material does not represent the limiting factor to enzymic saccharification.