Sol-gel chemistry approach in the preparation of precursors for the substituted superconducting oxides

Sol-gel processing of ceramic materials for advanced applications involves several steps starting from precursor synthesis and ending up with multicomponent metal oxides. A simple sol-gel synthesis technique has been refined to prepare the precursors for the superconducting (Y_1−xSc_x)Ba₂Cu₄O₈ and (Y_1−xGa_x)Ba₂Cu₄O₈ compounds. The amorphous gel powders were characterized by powder X-ray diffraction, infrared spectroscopy, thermal analysis and elemental analysis. A systematic characterization of precursor gels led us to predict the approximate composition and the chemical reactions involved during gelation. The stability and high level of homogeneity obtained for the gels make them suitable as processable precursors to substituted (Y_1−xSc_x)Ba₂Cu₄O₈ and (Y_1−xGa_x)Ba₂Cu₄O₈ superconducting compounds.     

Characterisation of porosity and sensor response times of sol-gel-derived thin films for oxygen sensor applications

In recent years, sol-gel-derived films have played a significant role in optical sensor development. This paper focuses on the characterisation of oxygen-sensitive tetraethoxysilane (TEOS) and methyltriethoxysilane (MTEOS)-based films. Film porosity and sensor response times are reported for a range of films fabricated under different conditions. Porosity data are correlated with predicted film behaviour and also with previous characterisation studies. Oxygen diffusion coefficients are estimated from the response times. The enhanced diffusion coefficient of MTEOS films compared to TEOS films is discussed in terms of the relative oxygen solubility of the films. Comparisons are made with data for oxygen-sensitive polymer films, indicating an enhanced solubility for sol-gel films compared with typical polymer films.     

Novel Convolutional Neural Network with Variational Information Bottleneck for P300 Detection

In the area of brain-computer interfaces (BCI), the detection of P300 is a very important technique and has a lot of applications. Although this problem has been studied for decades, it is still a tough problem in electroencephalography (EEG) signal processing owing to its high dimension features and low signal-to-noise ratio (SNR). Recently, neural networks, like conventional neural networks (CNN), has shown excellent performance on many applications. However, standard convolutional neural networks suffer from performance degradation on dealing with noisy data or data with too many redundant information. In this paper, we proposed a novel convolutional neural network with variational information bottleneck for P300 detection. Wiht the CNN architecture and information bottleneck, the proposed network termed P300-VIB-Net could remove the redundant information in data effectively. The experimental results on BCI competition data sets show that P300-VIB-Net achieves cutting-edge character recognition performance. Furthermore, the proposed model is capable of restricting the flow of irrelevant information adaptively in the network from perspective of information theory. The experimental results show that P300-VIB-Net is a promising tool for P300 detection.     

The Resolvent Problem and $${{H^{\infty}}}$$ -calculus of the Stokes Operator in Unbounded Cylinders with Several Exits to Infinity

It is proved that the Stokes operator in L^q -space on an infinite cylindrical domain of 300_TeX2GIFIEq2.gif" alt=" $${{\mathbb{R}^{n}}}$$ " align="middle" border="0"> , 300_TeX2GIFIEq3.gif" alt=" $${{n \geq 3}}$$ " align="middle" border="0"> , with several exits to infinity generates a bounded and exponentially decaying analytic semigroup and admits a bounded 300_TeX2GIFIEq4.gif" alt=" $${{H^{\infty}}}$$ " align="middle" border="0"> -calculus. For the resolvent estimates, the Stokes resolvent system with a prescribed divergence in an infinite straight cylinder with bounded cross-section 300_TeX2GIFIEq5.gif" alt=" $${{\Sigma}}$$ " align="middle" border="0"> is studied in L ^q 300_TeX2GIFIEq6.gif" alt=" $${{(\mathbb{R}; L^{r}_{\omega} (\Sigma))}}$$ " align="middle" border="0"> where 300_TeX2GIFIEq7.gif" alt=" $${{1 < q,r < \infty}}$$ " align="middle" border="0"> and 300_TeX2GIFIEq8.gif" alt=" $${{\omega \, \epsilon \, A_{r}(\mathbb{R}^{n-1})}}$$ " align="middle" border="0"> is an arbitrary Muckenhoupt weight. The proofs use cut-off techniques and the theory of Schauder decomposition of UMD spaces based on 300_TeX2GIFIEq9.gif" alt=" $${{\mathcal{R}}}$$ " align="middle" border="0"> -boundedness of operator families and on square function estimates involving Muckenhoupt weights.     

高温热裂解电催化剂Ketjen Black EC300J碳黑负载钴卟啉的氧还原性能

选用具有高介孔表面积和高导电性能的碳黑Ketjen Black EC 300J(简称KB)作为载体,制备了碳黑负载钴卟啉(CoTMPP/KB),经过900℃热处理后得到电催化剂,用于燃料电池阴极氧还原反应.利用循环伏安法(CV)研究了碳载体不同预处理方法以及高温热处理对碳黑负载钴卟啉电催化剂的氧还原催化性能的影响.结果表明,6 mol/L HNO3预处理可以很好地改善KB性能,碳黑负载钴卟啉经过900℃热处理得到的电催化剂,虽然其中钴卟啉的结构发生了裂解,但催化剂具有较好的氧还原催化性能,阴极峰值电位(Ep)及最大电容电流(Ip)均为最佳.采用IR、XRD、TEM和氮吸附/脱附等手段对KB碳黑以及电催化剂表面性质及微观结构进行了分析,经6 mol/L HNO3预处理的KB碳黑表面羟基(—OH)等含氧基团增多,团聚不明显,平均粒径约30 nm;孔结构主要由孔径分布较窄的中孔组成,是一种较好的电催化剂载体;经900℃热处理后,电催化剂结构中有CoC3(101)和金属态Co(111)结构出现,钴离子在碳黑表面的分散较好,平均孔径为8.2 nm,比表面积为463.4 m2/g.     

Analytical Methods for the Determination of Traces of Cr(VI) in Water Samples with Suppressed Ion Chromatography

A rapid and sensitive method for the direct determination of hexavalent chromium in natural waters has been developed. Anion exchange chromatography was used for the fast separation of chromates from matrix anions, within 15 minutes, using a 35 mM KOH eluant. Mobile phase suppression was employed prior to direct conductivity (CD) detection, comparing two different electrolytic suppressor models and achieving a 10 times lower detection limit. Post column derivatization of Cr(VI) with diphenylcarbazide was used for further selective diode array (PDA) detection. Possible Cr(III) interference was evaluated with the addition of concentrations up to 10 mg/L of Cr(III) in a Cr(VI) positive natural water sample resulting in negligible interference. Both detection techniques gave instrumental LOD of 0.05 µg/L and method LOD of 0.08 µg/L for CD and 0.05 µg/L for PDA detection in underground water. Average repeatability and reproducibility (%RSD) was 1.3% and 5.4% for CD and 1.3% and 6.1% for PDA detection for two concentration levels. Recovery ranged from 70% to 103% for CD and from 90% to 100% for PDA. Method accuracy was additionally confirmed by analyzing positive samples with LC-ICP-MS. The method was successfully applied to the determination of Cr(VI) in several tap, spring and groundwater samples from the wider area of Asopos River, Greece. High concentrations where confirmed to the majority of the analyzed samples, revealing the serious and expanded problem of industrial pollution.     

Price–volume cross-correlation analysis of CSI300 index futures

We investigate the cross-correlation between price returns and trading volumes for the China Securities Index 300 (CSI300) index futures, which are the only stock index futures traded on the China Financial Futures Exchange (CFFEX). The basic statistics suggest that distributions of these two time series are not normal but exhibit fat tails. Based on the detrended cross-correlation analysis (DCCA), we obtain that returns and trading volumes are long-range cross-correlated. The existence of multifractality in the cross-correlation between returns and trading volumes has been proven with the multifractal detrended cross-correlation analysis (MFDCCA) algorithm. The multifractal analysis also confirms that returns and trading volumes have different degrees of multifractality. We further perform a cross-correlation statistic to verify whether the cross-correlation significantly exists between returns and trading volumes for CSI300 index futures. In addition, results of the test for lead-lag effect demonstrate that contemporaneous cross-correlation of return and trading volume series is stronger than cross-correlations of leaded or lagged series.     

Fatigue life assessment of a high strength steel 300 M in the gigacycle regime

The fatigue behavior of a high strength steel 300 M in the gigacycle regime was investigated. Fully reversed tension — compression fatigue tests at ambient temperature were performed using an ultrasonic fatigue system operating at 20 kHz. The staircase test method was employed to obtain accurate values of the mean fatigue strength corresponding to fixed numbers of cycles up to 10⁹. These results were compared to the curve which is estimated by the data tested in the mid-long life regime on conventional servo hydraulic test machine at 20 Hz. Results indicate that the fatigue strength determined from ultrasonic fatigue testing is lightly higher than conventional testing in the range of 10⁶–10⁷ cycles. It is obvious that nucleations of fractures tend to occur below the surface, if fractures happen after more than 10⁷ cycles. All the fractured specimens fails from internal SiO₂ inclusions or smaller carbides and carbide clusters.     

Investigation of alpha particle induced reactions on thulium

Alpha particle induced reactions on the target element thulium were investigated up to 75 MeV, using foil-stack activation technique and Ge(Li) gamma ray spectroscopy method. Excitation functions for eight reactions of the type¹⁶⁹Tm(α, xn),x=1 − 4;¹⁶⁹Tm(α, pxn),x=3; and¹⁶⁹Tm(α, αxn),x=1, 2, 4 were investigated. Of these, four reactions¹⁶⁹Tm(α, p3n),¹⁶⁹Tm(α, αn),¹⁶⁹Tm(α, α2n)¹⁶⁹Tm(α, α4n), were studied for the first time and in the remaining four reactions, some 19 new energy-point cross-sections were measured for the first time. The experimental cross-sections were compared with the predictions of pre-equilibrium hybrid model, as well as the more recent index model, using the initial excition number,n ₀=4 (4p0h). Both the models show better agreement in respect of (α, xnyp) type of reactions. However they are equally bad for (α, αxn) type of reactions which involve theα-particle in the exit channels, and for which some direct reaction contributions are indicated.     

The fatigue of high-strength fused silica optical fibers in low humidity

The strength and dynamic fatigue of UV-acrylate coated silica optical fibers were measured as a function of relative humidity in the range ∼0.025-13% at 25 °C. The degradation kinetics of silica in low humidities was investigated and it was found that the reaction order was approximately first-order with respect to humidity. In our previous work, a second-order reaction was found in the humidity range 20-95% RH at 25 °C and the process for obtaining this reaction order was found to be independent of the mathematical form of the kinetic models used. The change in reaction order observed here verifies some earlier results based on the power law which implied a change in the reaction order from ∼2 (15-100% RH) to ∼1 at low humidity (<0.01%).