AMS-02超导磁体300K-80K受控冷却系统的工艺流程设计

300K-80K受控冷却系统是AMS-02探测器的低温地面支持设备(CGSE)系统中的重要子系统,其主要作用是实现AMS-02磁体从常温(约300K)到接近液氮温度(约80K)的冷却。对该系统进行了工艺流程设计,在恒温器内设置多个调节阀和温度、压力、流量检测元件,通过自动调节手段控制经该系统冷却后前往磁体的氦气的温度和流量。同时介绍了该系统的组成及低温恒温器、HX1、HX2和HX3的结构和特点。     

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.     

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.     

The preparation of carbon aerogels based upon the gelation of resorcinol-furfural in isopropanol with organic base catalyst

Carbon aerogels with high BET surface area were developed by sol-gel polycondensation of resorcinol and furfural in isopropanol using hexamethylenetetramine (HMTA) as a catalyst, and then directly drying the organic gels under isopropanol supercritical conditions, followed by carbonization under a nitrogen atmosphere. The preparation conditions of carbon aerogels were explored by changing the mole ratio of resorcinol to basic catalyst HMTA (R/C), the ratio of resorcinol to isopropanol (R/I), and the mole ratio of resorcinol to furfural (R/F). The effect of these preparation conditions on the porous structure of the carbon aerogels obtained was studied by nitrogen adsorption isotherms. According to the characterizations of TEM, SEM and nitrogen adsorption, the carbon aerogels obtained have a three-dimensional network that consists of carbon nano-particles with size from 20 to 30 nm, which define numerous micropores, mesopores and macropores. HMTA reacts not only as a catalyst but also as a reagent in the gelation polymerization. XRD characterization indicates that carbon aerogels have disordered nanocrystalline structures similar to activated carbon.     

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.