OFDM系统中最大似然调制识别算法研究

对观测样本进行非线形变换,提出了基于子载波和子载波组的OFDM系统最大似然调制识别算法,解决了载波频偏引起最大似然调制识别算法性能急剧下降的问题.仿真结果表明,当归一化频偏小于0.15时,该算法具有良好的识别性能.     

肾小管上皮细胞损伤及其诱导草酸钙晶体成核

肾上皮细胞损伤可促进肾结石形成.本文采用过氧化氢(H2O2)对人类肾小管上皮细胞(HKC)进行了氧化损伤,采用扫描电子显微镜(SEM)、X射线衍射分析(XRD)和倒置显微镜观察了HKC损伤前后的形态变化及其调控草酸钙(CaOxa)晶体成核、生长的差异;采用zeta电位分析仪检测了损伤前后HKC表面的zeta电位变化.结果表明,H2O2能明显地损伤HKC,降低细胞活性,且在H2O2浓度范围0.1～0.5mmol/L、作用时间0.5～1.5h内具有明显的剂量和时间的依赖性;使用0.5mmol/LH2O2作用1.5h可使HKC损伤达到饱和状态.HKC损伤程度增加后,其诱导的晶体数量显著增加,但晶体尺寸增加不明显(P0.05),表明损伤细胞诱导尿石症形成主要是增加晶体的成核位点而非促进晶体的生长.本文所建立的HKC氧化损伤的模型有助于进一步阐明CaOxa结石形成的细胞机制.     

Synthesis and applications of a chiral-oxygenated 3-chloro-3,6-dihydro-2H-pyran obtained under Overman rearrangement conditions

A chlorinated side product was formed under Overman rearrangement conditions from a trichloroacetimidate along with the expected allylic amide. The chlorinated product derived from a hex-2-enopyranoside was obtained in a totally stereoselective manner, and it can be a useful synthetic intermediate for chlorinated sugars. In order to improve the isolated yields of either the expected Overman rearrangement product or the chlorinated compound, we carried out a thorough study on the experimental conditions. The application of the latter for the synthesis of potential calpain inhibitors is also reported.     

A Soluble Dynamic Complex Strategy for the Solution‐Processed Fabrication of Organic Thin‐Film Transistors of a Boron‐Containing Polycyclic Aromatic Hydrocarbon

The solution‐processed fabrication of thin films of organic semiconductors enables the production of cost‐effective, large‐area organic electronic devices under mild conditions. The formation/dissociation of a dynamic B?N coordination bond can be used for the solution‐processed fabrication of semiconducting films of polycyclic aromatic hydrocarbon (PAH) materials. The poor solubility of a boron‐containing PAH in chloroform, toluene, and chlorobenzene was significantly improved by addition of minor amounts (1 wt % of solvent) of pyridine derivatives, as their coordination to the boron atom suppresses the inherent propensity of the PAHs to form π‐stacks. Spin‐coating solutions of the thus formed Lewis acid–base complexes resulted in the formation of amorphous thin films, which could be converted into polycrystalline films of the boron‐containing PAH upon thermal annealing. Organic thin‐film transistors prepared by this solution process displayed typical p‐type characteristics.     

Chemically-modified nanopores for sensing

Sensing with chemically-modified nanopores is an emerging field that is expected to have major impact on bioanalysis and fundamental understanding of nanoscale chemical interactions down to the single-molecule level. The main strength of nanopore sensing is that it implies the prospect of label-free single-molecule detection by taking advantage of the built-in transport-modulation-based amplification mechanism. At present, fabrication and application of solid-state nanopores are becoming the focus of attention because, compared with their biological counterparts, they offer greater flexibility in terms of shape, size, and surface properties, as well as superior robustness. A breakthrough in label-free nanopore sensing for real-world applications is therefore expected from implementing solid-state nanopores, an area that is still developing. Without claiming comprehensiveness, the focus of this review comprises recent results and trends in nanopore-based sensing (i.e. emerging technologies for fabricating solid-state nanopores, their chemical functionalization, and detection methods for quantitative analysis).     

含时调制的Jaynes-Cummings模型的Pancharatnam相位

基于含时调制的Jaynes-Cummings模型的SU(2)群结构,求得它的Pancharatnam相位,并分析 了该模型从绝热开启直到关闭原子与场的相互作用的整个过程的相位变化.讨论了该模型在 半经典近似条件下的情况. 关键词： 含时调制的Jaynes-Cummings模型 Pancharatnam相位 SU(2)群     

Thinking machines

We propose that a sufficiently advanced civilisation may employ Cepheid variable stars as beacons to transmit all-call information throughout the galaxy and beyond. They might employ a pulsed neutrino beam to trigger the expansion of a Cepheid at an earlier than normal time, generating a binary signature of normal period or artificially shortened period. One can construct many scenarios wherein it would be desirable for such a civilisation of star ticklers to transmit data to anyone else within viewing range. The beauty of employing Cepheids is that these stars can be seen from afar (we monitor them out through the Virgo cluster), and any developing technological society would seem to be likely to closely observe them as distance markers. Records exist of Cepheids for well over 100 years. We propose that these (and other regularly variable types of stars) be searched for signs of phase modulation (in the regime of short pulse duration) and patterns, which could be indicative of intentional signalling.     

Direct modulation and optical confinement factor modulation of semiconductor lasers

Abstract

A method for modulation of semiconductor lasers is demonstrated. The method is based on the modulation of the optical confinement factor. Using this method an enhanced—3-dB bandwidth is observed in agreement with the small signal rate equation analysis. A modulation response that drops at high frequencies slower than the conventional direct current modulation response is achieved. This supports the theoretical predictions, showing an intrinsic 1/f decay rate for the optical confinement factor modulation scheme versus an intrinsic 1/f² decay for direct modulation.     

A Novel Approach to All-Optical Generation of Ultra-Wideband Signals

Abstract

The generation of ultra-wideband signals in the optical domain is highly desirable for ultra-wideband-over-fiber systems, which has recently become a topic of interest. In this article, a novel and simple approach to achieve all-optical generation of ultra-wideband signals is proposed, which is based on delaying and superimposing optical Gaussian pulses with opposite polarities. The proposed system is capable of generating both ultra-wideband monocycle and doublet pulses, and the polarity of the generated ultra-wideband monocycle pulses can be fast-switched to implement pulse polarity modulation with the required bit pattern. A model to describe the proposed system is developed, and the generation of ultra-wideband signals is demonstrated with simulations and a proof-of-concept experiment.