Detection of viable antibiotic‐resistant/sensitive Acinetobacter baumannii in indoor air by propidium monoazide quantitative polymerase chain reaction

Acinetobacter baumannii represents a significant cause of nosocomial infections. Therefore, we combined real‐time quantitative polymerase chain reaction (PCR) with the propidium monoazide (PMA‐qPCR) to assess the feasibility of detecting viable, airborne A. baumannii. The biological collection efficiencies of three samplers for collecting airborne A. baumannii were evaluated by PMA‐qPCR in a chamber study. After sampling, the effects of storage in collection fluid on A. baumannii were evaluated. The results showed that the culturable ratio of A. baumannii measured using the culture method was significantly correlated with the viable ratio measured using PMA‐qPCR, but was not significantly correlated with the qPCR results. It was indicated that the AGI‐30 impinger and the BioSampler were much more effective than the Nuclepore filter sampler for collecting airborne A. baumannii. The storage temperature was critical for aerosol samples, as the loss of viable A. baumannii was minimized when the PMA‐bound DNA was stored at ?20°C or if the collected cells were stored at 4°C and subsequently processed by PMA‐qPCR within 1 month. The PMA‐qPCR method was also to distinguish between colistin‐sensitive and colistin‐resistant A. baumannii, and no colistin‐sensitive A. baumannii was detected by PMA‐qPCR upon treatment of the BioSampler collection medium with 2 μg/ml colistin for 5 min.     

Mechanical characterization of nanoindented graphene via molecular dynamics simulations

The mechanical behavior of graphene under various indentation depths, velocities, and temperatures is studied using molecular dynamics analysis. The results show that the load, elastic and plastic energies, and relaxation force increased with increasing indentation depth and velocity. Nanoindentation induced pile ups and corrugations of the graphene. Resistance to deformation decreased at higher temperature. Strong adhesion caused topological defects and vacancies during the unloading process.     

A miniature generator using piezoelectric bender with elastic base

Nowadays green energy devices such as vibration generators attempt to harvest energy from environment. A lot of studies dealing with vibration generators put emphasis on mechanism designs or power generation methods, but few on lowering the resonant frequency of power generation systems. This study proposes that elastic bases attached to vibration generators can lower natural frequencies, so as to make natural frequencies closer to ambient vibration frequency. Therefore, this study investigates miniature electric generators consisting of piezoelectric benders and elastic bases. To install the elastic base, this work uses a spring with prescribed stiffness and a board with given mass between the piezoelectric bender and a vibration source to make the resonant frequency of piezoelectric benders close to the frequency of ambient vibration. Analytical derivation is carried out to obtain optimal mass and stiffness. Accordingly, more electric power can be generated from piezoelectric generators using an elastic base with appropriate mass and stiffness. According to experimental results, using an elastic base increases 376 times generated power compared with no elastic base. In the presence of the elastic base, the power increases 132% when a point mass is added.     

Spectrum sensing scheduling for group spectrum sharing in cognitive radio networks

This paper addresses the issues on spectrum sharing in a cognitive radio network consisting of a primary user and a group of cognitive users. Each cognitive user may occupy a non‐overlapped sub‐band of the primary spectrum, but it needs to perform spectrum sensing independently before accessing the sub‐band. To reduce the complexity of spectrum sensing and thus energy consumption, this paper proposes a scheduled spectrum sensing scheme. First, we consider a single spectrum sensing scenario where only one cognitive user is elected to perform spectrum sensing, and then it broadcasts its sensing results to the other cognitive users. The scheduled spectrum sensing scheme works in both network‐centric and user‐centric ways. Next, the scheduled spectrum sensing scheme is further generalized to work in a multiple spectrum sensing scenario. The results show the effectiveness of the proposed schemes compared with the traditional schemes where all cognitive users may perform spectrum sensing at the same time. Copyright © 2010 John Wiley & Sons, Ltd.     

Photoluminescent properties of LiInO2 nanocrystals

Synthesis and luminescence properties of LiInO₂ nanocrystals by the sol–gel process were investigated. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), photoluminescence spectroscopy and absorption spectra. The well-crystallized tetragonal LiInO₂ can be obtained by heat treatment above 600 °C from XRD. The excitation wavelengths at about 246 nm were associated with charge transfer between In and O with In³⁺ ions in octahedral coordination. The PL spectra excited at 246 nm have a broad and strong emission band maximum at 391 nm, corresponding to the self-activated luminescence. The optical absorption spectra of the 600 °C sample exhibited the band gap energies of 3.7 eV.     

Experimental study of the flow rectification performance of conical diffuser valves

Flow rectification performance of conical diffuser valves has been investigated experimentally. In order to quantify the valving capability of the diffuser, a diffuser performance test cell is designed. The main feature of the test cell is that the volume change of the pumping chamber is independent of the diffuser geometry and actuation frequency. Experiments have been carried out over a range of diffuser angles varying from 10° to 35° and Roshko numbers (based on diffuser throat diameter and actuation frequency) from 25 to 300. Results show that the valving performance of the diffuser is significantly affected by the tapered angle and Roshko number. The diffuser valve with diverging angle of 10° exhibits the best performance. This is consistent with our recent simulations. The maximum flow rectification efficiency that has been attained at condition of zero backpressure is around 48%. In addition, we have simultaneously measured the time-dependent pressure inside the actuation chamber. It is found that the variations of the pressure amplitude with the Roshko number are qualitatively similar to those of the valving efficiency; high rectification efficiencies are always associated with large actuation pressures. However, for a large actuation volume, the valve performance declines, even though the actuation pressure increases. A possible explanation for this phenomenon is also provided.     

Photoluminescence and preparation of ZnNb2O6 doped with Eu and Tm nanocrystals for solar cell

Synthesis and luminescence properties of Eu³⁺ and Tm³⁺-doped ZnNb₂O₆ nanocrystals by the sol–gel process were investigated. The products were characterized by differential thermal analysis (DTA), scanning electron microscopy (SEM), and photoluminescence spectroscopy (PL). ZnNb₂O₆:Eu³⁺ shows bright red luminescence with maximum peak at 613 nm attributed to ⁵D₀ → ⁷F₂ transition. The major blue emission peak of ZnNb₂O₆:Tm³⁺ was at 483 nm, corresponding to the transitions ¹G₄ → ³H₆. The optimum concentration of Eu³⁺ and Tm³⁺ showing the maximum PL intensity was 4 mol% and 1 mol%, respectively.     

复杂功能超高层建筑的结构设计挑战

0引言 总部位于美国纽约的宋腾添玛沙帝工程顾问有限公司(Thornton Tomasetti lnc.,简称TT),是一个专长大型复杂结构设计的公司,其凭借专业实力,参与了世界前20个超高层建筑中近一半项目的结构设计,包括已建成的中国台湾台北市的世界金融中心(即台北101)、马来西亚吉隆坡的双子石油大厦、上海的恒隆广场和正在建设中的上海中心、芝加哥螺旋塔、平安国际金融中心等。     

Electrochemical Performance of PrBaCo2O5+δ and Sm0.5Sr0.5CoO3−δ Infiltrated Ce0.9Gd0.1O1.95 Cathodes

Cathodes with PrBaCo₂O_5+δ (PBC) and Sm_0.5Sr_0.5CoO_3−δ (SSC) infiltrated on Ce_0.9Gd_0.1O_1.95 (CGO) backbones are prepared using metal nitrates as precursors and ethanol as wetting agent. Electrochemical impedance spectra (EIS) are measured from cathode/CGO/cathode symmetrical cells in 400–650 °C under humidified air. The results indicate that interfacial area specific resistance (ASR) value decreases and then increases with infiltrate loading and minimum values occur at 50 wt.% loading (relative to sum of infiltrate and backbone) for both PBC and SSC infiltrates. ASR values of PBC infiltrated cathodes are lower than that of corresponding SSC infiltrated cathodes in general, and in particular ASR values as low as 1.36 × 10⁻² and 2.27 × 10⁻² Ω cm² are obtained at 650 °C in air for 50 wt.% PBC and 50 wt.% SSC infiltrated cathodes, respectively. Conductivity values of CGO electrolyte increase with infiltrate loading and agree with the reported values when the loading reaches 50 wt.%.