An efficient indium-mediated 2-bromoallylation of aldehydes at low temperature in aqueous DMF

An efficient synthesis of 2-bromohomoallylic alcohols was carried out via an indium-mediated Barbier-type 2-bromoallylation of aldehydes in moderate yields. The reaction was performed at low temperature (−20 °C) in aqueous DMF in order to minimize decomposition of 2-bromoallylindium reagent to allene.     

Characterization of the Core Oligosaccharide and the O‐Antigen Biological Repeating Unit from Halomonas stevensii Lipopolysaccharide: The First Case of O‐Antigen Linked to the Inner Core

A novel core structure among bacterial lipopolysaccharides (LPS) that belong to the genus Halomonas has been characterized. H. stevensii is a moderately halophilic microorganism, as are the majority of the Halomonadaceae. It brought to light the pathogenic potential of this genus. On account of their role in immune system elicitation, elucidation of LPS structure is the mandatory starting point for a deeper understanding of the interaction mechanisms between host and pathogen. In this paper we report the structure of the complete saccharidic portion of the LPS from H. stevensii. In contrast to the finding that the O‐antigen is usually covalently linked to the outer core oligosaccharide, we could demonstrate that the O‐polysaccharide of H. stevensii is linked to the inner core of an LPS. By means of high‐performance anion‐exchange chromatography with pulsed amperometric detection we were able to isolate the core decasaccharide as well as a tridecasaccharide constituted by the core region plus one O‐repeating unit after alkaline degradation of the LPS. The structure was elucidated by one‐ and two‐dimensional NMR spectroscopy, ESI Fourier transform ion cyclotron resonance (FT‐ICR) mass spectrometry, and chemical analysis.     

Capacity and Energy Efficiency of Multi-User Spectrum Sharing Systems with Opportunistic Scheduling

This paper investigates the capacity and energy efficiency of spectrum sharing systems with opportunistic user selection where a secondary network utilizes spectrum bands licensed to a primary network under interference regulation. In spectrum sharing systems, secondary users consume a fraction of their resources in sensing the channels to the primary users to comply with the interference constraints. Although more resources for sensing improve reliability and performance, the throughput loss due to time overhead and energy loss due to power overhead should be properly incorporated in performance evaluation. In this context, we define and derive a new metric ? average capacity normalized by the total energy consumption ? reflecting time and power overhead for spectrum sensing. Based on the developed framework, the optimal normalizedcapacity is investigated. We also propose a simple and practical suboptimal best-n scheme motivated by the infeasibility and high computational complexity of the optimal strategy, where n denotes the number of sensing secondary users. Our analytical and simulation results show that the proposed best-1 scheme is an energy-efficient technique with near optimality in terms of the capacity normalized by the energy consumption.     

Relaxation-free harmonically mode-locked semiconductor-fiber ringlaser

A 10-Gb/s semiconductor-fiber ring laser is proposed and demonstrated. The performance of a harmonically mode-locked semiconductor-fiber ring laser was described in detail. A long cavity length configuration in semiconductor optical amplifier is found to eliminate the relaxation oscillation, and improved short-term amplitude stability. The laser output has a pulsewidth of 18.4 ps and a spectral width of 0.3 nm     

Multi-user diversity in a spectrum sharing system

We investigate the effects of multi-user diversity in a spectrum sharing system where secondary users restrictively utilize a spectrum licensed to primary users only if interference perceived at primary users is regulated below a predetermined level. This interference regulation affects the characteristics of multiuser diversity gains previously known in non-spectrum sharing systems. Our numerical and analytical results show that the multiuser diversity gain in a spectrum sharing system increases differently according to conditions given by the transmit power of secondary users, P, and a predetermined interference temperature, Q - if P is sufficiently larger than Q, the multiuser diversity gain in terms of capacity scales like log2 (W (Ns)) similarly to a previously known scaling law in the non-spectrum sharing systems, where W(·) and Ns denote a Lambert W function and the number of secondary transmitters, respectively. However, the scaling law of multiuser diversity gain becomes log2(Ns) as P becomes sufficiently larger such that P ≫ QNs.     

Solvent Effects on Aza‐anionic Cycloaromatization of 2‐(2‐Substituted‐ethynyl)benzonitriles

The methanolysis of 2‐(2‐aryl ethynyl)benzonitriles is accelerated when the polar aprotic solvents are added, which could enhance the 6‐endo pathway and give isoquinolones, though the 5‐exo pathway is occupied mostly. The yields of products would also be in creased.     

Reinvestigation of Ge4Se9 based on single‐crystal data

Tetra­germanium nona­selenide, Ge₄Se₉, adopts a two‐dimensional layered structure. The layer is made up of infinite chains of corner‐sharing GeSe₄ tetra­hedra and the chains are connected via the Ge₂Se₇ unit to form the two‐dimensional layer. These layers are stacked to form the three‐dimensional structure with a van der Waals gap. A previous structure report on Ge₄Se₉ based on powder diffraction data [Fjellvåg, Kongshaug & Stølen (2001). J. Chem. Soc. Dalton Trans. pp. 1043–1045] is comparable with our results except for the absolute structure determination.