QoS enhancement in OFDM based systems under transceiver impairments

Broadband wireless systems generally use orthogonal frequency division multiplexing (OFDM) with link adaptation (LA) to achieve high throughput while meeting bit error rate (BER) constraint. OFDM systems are known to be affected by non-linearity of high power amplifier (HPA) at transmitter, carrier frequency offset (CFO), symbol timing offset (STO) and channel estimation error at the receiver. The delay in feedback of channel state information (CSI) further affects the performance of LA procedures. The focus of this work is on performance analysis in presence of simultaneous affect of all these impairments on LA based OFDM systems. The results are found to be useful for threshold readjustment which is essential for successful implementation of LA scheme to counter the effects of change in operating conditions from ideal to as listed above.     

活性炭负载杂多酸催化剂的研究进展

介绍了以活性炭为载体的负载型杂多酸催化剂的研究进展,包括制备方法、影响负载量的因素、负载催化剂的性质、吸附模型和脱附作用。总结了杂多酸在活性炭上的吸附形态研究以及杂多酸与活性炭表面含氧基团的化学键合作用的研究成果,展望了该催化剂未来的研究方向。     

Environmentally friendly and highly efficient synthesis of benzoxazepine and malonamide derivatives using HPA/TPI‐Fe3O4 nanoparticles as recoverable catalyst in aqueous media

A magnetic inorganic–organic nanohybrid material (HPA/TPI‐Fe₃O₄ NPs) was produced as an efficient, highly recyclable and eco‐friendly catalyst for the one‐pot multi‐component synthesis of malonamide and 2,3,4,5‐tetrahydrobenzo[b ][1,4]oxazepine derivatives with high yields in short reaction times (25–35 min) in aqueous media at room temperature. The nanohybrid catalyst was prepared by the chemical anchoring of H₆P₂W₁₈O₆₂ onto the surface of modified Fe₃O₄ nanoparticles (NPs) with N ‐[3‐(triethoxysilyl)propyl]isonicotinamide (TPI) linker. The magnetic recoverable catalyst was easily recycled at least ten times without any loss of catalytic activity.     

Determination of marker pteridins and biopterin reduced forms, tetrahydrobiopterin and dihydrobiopterin, in human urine, using a post-column photoinduced fluorescence liquid chromatographic derivatization method

A liquid chromatographic method for the simultaneous analysis of marker pteridins and biopterin reduced forms, in urine samples is proposed. A Zorbax Eclipse XDB-C18 column was used for the chromatographic separation, using a 98/2 (v/v), citrate buffer (pH 5.5)-acetonitrile mobile phase, in isocratic mode. A post-column photoderivatization was carried out with an on-line photoreactor, located between a diode array detector (DAD) and a fast scanning fluorescence detector (FSFD). Neopterin (NEO), biopterin (BIO), pterin (PT) and dihydrobiopterin (BH2) were determined by measuring native fluorescence, using the photoreactor in OFF-mode, and tetrahydrobiopterin (BH4) was determined by measuring of the induced fluorescence of the generated photoproducts, using the photoreactor in ON-mode. In addition, Creatinine (CREA), as a reference of metabolites excrection in urine, was simultaneously determined using the DAD detector. Detection limits were 0.2, 13.0, 0.3, 0.3 and 3.5 ng mL⁻¹, for NEO, BH2, BIO, PT and BH4, respectively, and 0.4 μg mL⁻¹ for CREA. Ratio values for NEO/CREA, PT/CREA, BH4/CREA, BH2/CREA, NEO/BIO and BIO_total/CREA, in urine samples, of healthy children and adults, phenylketonuric children and infected mononucleosis children, are reported. A comparative study, about the mean values obtained for each of the compounds, by the present procedure and by the classical iodine oxidation method (Fukushimás method), has been performed, in urine samples belonging to healthy volunteers. The values obtained were BH4/CREA: 0.41, BH2/CREA: 0.31 and BIO_total/CREA: 0.73, by the proposed method, and BH4/CREA: 0.35, BH2/CREA: 0.20 and BIO_total/CREA: 0.48, by iodine oxidation method.     

Autocatalator as the source of instability in the complex non-linear neuroendocrine model

The mathematical analogy between properties of simple and complex models of non-linear reactions was used to determine reaction steps in the complex model, necessary to generate instability region and appropriate type of bifurcations on the border between stable and unstable non-equilibrium stationary state. The autocatalator was recognized as the simple prototype two-variable non-linear model practical for examination of the complex four-variable non-linear neuroendocrine system known as the Hypothalamic-Pituitary-Adrenal (HPA) axis. In both cases, we derived the instability criteria by stoichiometric network analysis (SNA), determine conditions under which dynamic transitions, i.e. bifurcations occur, and identify the type of bifurcation. The supercritical Andronov–Hopf bifurcation was found in both cases whereas saddle-node bifurcation was detected only in the model for HPA axis.Thus, by stoichiometric network analysis, the mathematical analogy is found between two different models with same autocatalytic steps, that is, between two models with easily recognizable qualitative analogy.     

SiO2负载磷钨杂多酸催化的甲苯与乙酸酐酰化反应

以SiO2负载12-磷钨酸（PW）为催化剂,对甲苯与乙酸酐(AA)的酰化反应进行了研究。采用XRD、BET、TGA和NH3-TPD等对PW/SiO2催化剂进行了表征。结果表明,PW负载量及焙烧温度对PW/SiO2的酸性、PW在SiO2上的分散状态以及酰化催化活性有明显的影响。PW的负载量40%（按质量计）、焙烧温度300℃制备的PW(40%)/SiO2催化剂,其PW在载体表面的分散度好,酸量及酸强度适宜,对甲苯与乙酸酐的酰化反应具有较高的催化活性。在130℃,催化剂/乙酸酐（质量比）2.2时,催化反应效果最佳。     

Heteropoly acids-catalyzed organic reactions in water: doubly green reactions

The organic reactions in water, as the most significant green solvent, have attracted much attention due to their unique properties over conventional organic ones. In the catalytic area, heteropoly acids (HPAs) are also promising green solid acids to replace environmentally harmful liquid acid catalysts. Herein, we wish to report the organic reactions catalyzed by HPAs, their salt, and polyoxometalates (POMs) in aqueous systems.     

多金属氧酸盐对聚乙烯醇在水中溶胀性能的影响

制备了含不同结构多金属氧酸盐(HPA)和含量不同多金属氧酸盐的聚乙烯醇(PVA)纤维材料,并用IR、XRD光谱和扫描电镜(SEM)对其进行了表征.针对PVA在水中的溶胀性能,系统地研究了多金属氧酸盐的种类、含量、交联温度和时间对PVA纤维材料的水溶性的影响.     

一种基于泰勒级数的HPA失真模型的非线性校正方法

本文提出一种高功率放大器非线性校正方法.它采用预失真技术,消除HPA失真模型的Taylor表达式中产生非线性的奇次方项,实现HPA的非线性校正.仿真结果表明,较好地补偿了HPA的非线性失真.     

基于非线性压扩的降低OFDM信号PAPR的算法

本文在分析高PAPR形成的原因及常用的解决方法的基础上,提出了一种新的基于信号压扩的算法.通过处理后的信号与原信号在时域和频域的对比证明了本文提出的算法的正确性,并通过与其它方法的比较体现了本文算法的优势.