Efficient rate-power allocation for OFDM in a realistic fading environment

The implementation of practical adaptive resource allocation scheme remains a key criterion to be satisfied for realising spectrally efficient multitone wireless communications. The ever-increasing demand for spectrally efficient broadband wireless transmission technologies has spurred intensive research leading towards the implementation of adaptive OFDM and adaptive MIMO systems. Efforts in this direction have been frustrated however by the lack of a clear and accurate description of the fading behaviour typically encountered in the broadband wireless transmission environment. This has been partially been overcome by the use of mathematical modelling which captures certain large-scale characteristics of the channel and facilitates theoretical research. The “average” channel parameters gleaned from these processes is typically then used to inform the design and configuration of wireless networking equipment after the broad application of generous safety margins. The resulting solu�tion is therefore quite robust to certain transient channel quality degradation yet the generous safety tolerances render it unable to exploit other transient transmission quality improvements We seek to overcome the problems associated with this ap�proach by applying a theoretically sound novel adaptive resource allocation framework to actual broadband wireless channel development data. The allocation framework is derived from the optimal OFDM allocation scheme for a known channel [1]: the channel development data is obtained from actual measurement of a broadband wireless mobile environment [2]. Prediction tech�niques are employed to overcome the time lag between channel assessment and symbol transmission. We present the details of the predictive resource allocation scheme used and include a broad characterisation of the transmission environment in terms of the time-varying fading processes observed. We provide some results of the application of this scheme as typical performance levels that may be achieved in an actual transmission environment

Photochemistry of Mycolactone A/B, the Causative Toxin of Buruli Ulcer

Photochemistry of mycolactone A/B and related unsaturated fatty acid esters is reported. On exposure to visible light, mycolactone A/B gave a mixture of four photomycolactones. Pentaenoates and tetraenoates, representing the unsaturated fatty acid portion of mycolactone A/B, were found to show the reactivity profile parallel with that of mycolactone A/B. The structure of the four photomycolactones was elucidated via (1) structure determination of the four photoproducts in the tetraenoate series; (2) their transformation to the photoproducts in the pentaenoate and then mycolactone series. Triplet quenchers did not affect the photochemical transformation, thereby indicating an event at the singlet state. A concerted, photochemically allowed [4πs + 2πa] cycloaddition was suggested to account for the observed result. This study provided the structurally defined and homogeneous material, which allowed demonstration that photomycolactones exhibit significantly reduced cytotoxicity, compared with mycolactone A/B

MnO Nanoparticles Interdispersed in 3D Porous Carbon Framework for High Performance Lithium-Ion Batteries

Interdispersed MnO nanoparticles that are anchored and encapsulated in a three-dimensional (3D) porous carbon framework (MnO@CF) have been constructed, which display nanosphere architecture with rich porosity, well-defined carbon framework configuration, and excellent structure stability. When evaluated as an anode material, the MnO@CF exhibits relatively high specific capacity of 939 mA h g^–1 at current rate of 0.2 A g^–1 over 200 cycles and excellent rate capability of 560.2 mA h g^–1 at 4 A g^–1. By virtue of its mechanical stability and desirable ionic/electronic conductivity, the specific design can be a promising approach to fabricate high-performance lithium-ion batteries

Simple Synthesis of Mesoporous Carbon Nanofibers with Hierarchical Nanostructure for Ultrahigh Lithium Storage

In this study, a simple and reproducible synthesis strategy was developed to fabricate mesoporous carbon nanofibers (MCNFs) by using dual hard templates, a porous anodic aluminum oxide (AAO) membrane, and colloidal silica (Ludox TM-40). By using commercial templates, and removing AAO and the silica simultaneously, the synthesis procedures for MCNFs are greatly simplified without the need for separate preparation or the removal of templates in sequence. With phenol resin as a carbon precursor, the as-prepared MCNFs material reveals not only high surface area and mesoporous volume but also hierarchical nanostructure composed of hollow macrochannels derived from the AAO template, large mesopores (ca. 22 nm) from the removal of silica particles and micropores from the carbonization of phenol resin. Such unique surface and structural characteristics could provide a large quantity of active sites for Li storage and facilitate fast mass transport. Moreover, a one-dimensional (1D) carbon nanofiber (CNF) nanostructure favors fast electron transfer. The as-prepared MCNF anode demonstrates ultrahigh lithium storage capacity particularly at high rates, which is much higher than that reported for the commercial graphite and also significantly higher than other nanostructured carbon materials, such as ordered mesoporous carbon CMK-3 and ordered multimodal porous carbon (OMPC)

Hierarchical CuO–TiO₂ Hollow Microspheres for Highly Efficient Photodriven Reduction of CO₂ to CH₄

In this study, a scalable one-pot template-free synthesis strategy was employed to fabricate CuO-incorporated TiO₂ hollow microspheres in large scale. The as-prepared hollow spherical TiO₂ nanoparticles possess unique structural characteristics, namely, large surface area and a hierarchical nanoarchitecture composed of a hollow macroporous core connected with large mesopores in the shell. The large surface area provides a great number of surface active sites for the reactant adsorption and reaction whereas the hierarchical nanoarchitecture enables fast mass transport of reactant and product molecules within the porous framework. In addition, the hollow macroporous core–mesoporous shell nanostructure favors multilight scattering/reflection, resulting in enhanced harvesting of exciting light. Furthermore, the incorporated CuO clusters work efficiently as a cocatalyst to improve the photocatalytic activity. As a result, the CuO-incorporated TiO₂ hollow microsphere catalyst demonstrates much higher photocatalytic activity toward photodriven reduction of CO₂ with H₂O into CH₄ compared with the state-of-the-art photocatalyst, commercial Degussa P25 TiO₂. Also, the simple synthesis strategy would enable large-scale industrial production of CuO–TiO₂ hollow microspheres

Large-Scale Synthesis of TiO₂ Microspheres with Hierarchical Nanostructure for Highly Efficient Photodriven Reduction of CO₂ to CH₄

In this study, a simple and reproducible synthesis strategy was employed to fabricate TiO₂ microspheres with hierarchical nanostructure. The microspheres are macroscopic in the bulk particle size (several hundreds to more than 1000 μm), but they are actually composed of P25 nanoparticles as the building units. Although it is simple in the assembly of P25 nanoparticles, the structure of the as-prepared TiO₂ microspheres becomes unique because a hierarchical porosity composed of macropores, larger mesopores (ca. 12.4 nm), and smaller mesopores (ca. 2.3 nm) has been developed. The interconnected macropores and larger mesopores can be utilized as fast paths for mass transport. In addition, this hierarchical nanostructure may also contribute to some extent to the enhanced photocatalytic activity due to increased multilight reflection/scattering. Compared with the state-of-the-art photocatalyst, commercial Degussa P25 TiO₂, the as-prepared TiO₂ microsphere catalyst has demonstrated significant enhancement in photodriven conversion of CO₂ into the end product CH₄. Further enhancement in photodriven conversion of CO₂ into CH₄ can be easily achieved by the incorporation of metals such as Pt. The preliminary experiments with Pt loading reveal that there is still much potential for considerable improvement in TiO₂ microsphere based photocatalysts. Most interestingly and significantly, the synthesis strategy is simple and large quantity of TiO₂ microspheres (i.e., several hundred grams) can be easily prepared at one time in the lab, which makes large-scale industrial synthesis of TiO₂ microspheres feasible and less expensive

Copper/Manganese Cocatalyzed Oxidative Coupling of Vinylarenes with Ketones

A novel copper/manganese cocatalyzed direct oxidative coupling of terminal vinylarenes with ketones via C­(sp³)–H bond functionalization following C–C bond formation has been developed using <i>tert</i>-butyl hydroperoxide as the radical initiator. Various ketones underwent a free-radical addition of terminal vinylarenes to give the corresponding 1,4-dicarbonyl products with excellent regioselectivity and efficiency through one step. A possible reaction mechanism has been proposed

Unactivated C(sp³)–H Bond Functionalization of Alkyl Nitriles with Vinylarenes and Mechanistic Studies

The first example of a metal-free unactivated C­(sp³)–H bond functionalization of alkyl nitriles with terminal vinylarenes to provide γ-ketonitrile derivatives is described. This protocol features simple operations, a broad substrate scope, and atom and step economy. In addition, Cu-catalyzed C­(sp³)–H bond functionalization of azodi­isobutyro­nitrile (AIBN) and analogues with terminal vinylarenes to generate γ-ketonitriles was also studied. A preliminary free-radical pathway was confirmed by capturing an alkyl radical, and a conjugate system was found that can stabilize radical intermediates and be in favor of this transformation. Density functional theory (DFT) calculations also provide important evidence of the free-radical pathway

<i>De Novo</i> Asymmetric Synthesis of Phoracantholide J

A <i>de novo</i> asymmetric total synthesis of the macrolide natural product (<i>S</i>)-phoracantholide J has been achieved in 10 steps from the commodity chemicals (1-pentyne, ethyl acrylate, acetaldehyde, and hydrogen). The asymmetry of the route was introduced by a Noyori reduction of a 3-yn-2-one, which makes the route equally amenable to the synthesis of either enantiomer. In addition, this route relies upon an alkyne zipper, a hydroalkynylation, and a macrolactonization to complete the synthesis

Efficacy of Rifampin Plus Clofazimine in a Murine Model of <i>Mycobacterium ulcerans</i> Disease

<div><p>Treatment of Buruli ulcer, or <i>Mycobacterium ulcerans</i> disease, has shifted from surgical excision and skin grafting to antibiotic therapy usually with 8 weeks of daily rifampin (RIF) and streptomycin (STR). Although the results have been highly favorable, administration of STR requires intramuscular injection and carries the risk of side effects, such as hearing loss. Therefore, an all-oral, potentially less toxic, treatment regimen has been sought and encouraged by the World Health Organization. A combination of RIF plus clarithromycin (CLR) has been successful in patients first administered RIF+STR for 2 or 4 weeks. Based on evidence of efficacy of clofazimine (CFZ) in humans and mice with tuberculosis, we hypothesized that the combination of RIF+CFZ would be effective against <i>M</i>. <i>ulcerans</i> in the mouse footpad model of <i>M</i>. <i>ulcerans</i> disease because CFZ has similar MIC against <i>M</i>. <i>tuberculosis</i> and <i>M</i>. <i>ulcerans</i>. For comparison, mice were also treated with the gold standard of RIF+STR, the proposed RIF+CLR alternative regimen, or CFZ alone. Treatment was initiated after development of footpad swelling, when the bacterial burden was 4.64±0.14log₁₀ CFU. At week 2 of treatment, the CFU counts had increased in untreated mice, remained essentially unchanged in mice treated with CFZ alone, decreased modestly with either RIF+CLR or RIF+CFZ, and decreased substantially with RIF+STR. At week 4, on the basis of footpad CFU counts, the combination regimens were ranked as follows: RIF+STR>RIF+CLR>RIF+CFZ. At weeks 6 and 8, none of the mice treated with these regimens had detectable CFU. Footpad swelling declined comparably with all of the combination regimens, as did the levels of detectable mycolactone A/B. In mice treated for only 6 weeks and followed up for 24 weeks, there were no relapses in RIF+STR treated mice, one (5%) relapse in RIF+CFZ-treated mice, but >50% in RIF+CLR treated mice. On the basis of these results, RIF+CFZ has potential as a continuation phase regimen for treatment of <i>M</i>. <i>ulcerans</i> disease.</p></div