金属材料高频电磁波响应研究

不同频率的电磁波在金属材料中,有着不同的导电极限频率。各种金属材料都有各自的高频极限,高频极限是区分材料作为导电体与电介质的分界线。通过建立理想化的金属晶格模型,导出了金属材料的高频极限关系式,从而明确了电介质材料与金属材料的高频频率分界,对于研究电磁波与金属材料的作用机理有着实际意义。

高频电凝下金属夹内镜下结肠黏膜切除术,氩等离子凝固术在结肠息肉中的治疗价值

目的 对比高频电凝下金属夹内镜下结肠黏膜切除术和氩等离子凝固术对结直肠息肉的治疗效果。方法 纳入2020年2月—2022年2月无锡虹桥医院消化内科收治的200例结肠息肉患者为研究对象,经随机数表法平均分组,每组100例。对照组接受高频电凝下金属夹内镜下结肠黏膜切除术,观察组给予氩等离子凝固术,对比两组临床疗效、血脂水平和生存质量。结果 观察组总有效率为96.00%,与对照组的91.00%比较,差异无统计学意义(χ^(2)=2.057,P=0.152);两组术前血脂水平和生存质量对比,差异无统计学意义(P>0.05)。复查时,观察组总胆固醇(5.12±0.72)mmol/L,三酰甘油(1.44±0.28)mmol/L,低密度脂蛋白胆固醇(4.12±1.24)mmol/L,均低于对照组,高密度脂蛋白胆固醇水平和生存质量总分高于对照组,差异有统计学意义(P<0.05)。结论 高频电凝下金属夹内镜下结肠黏膜切除术和氩等离子凝固术均可有效治疗结肠息肉,相比而言,后者在调节血脂水平,改善生存质量方面的作用更明显。

浅淡高频铝基板孔金属化加工工艺

孔金属化高频铝基板是一种特种印制板,其具有高频印制板频带宽、信息量大,传输速度快和铝基印制板强度高、散热性好等优点,近年在混合集成电器、大功率电气设备、电源设备等领域得到了广泛应用,本文就孔金属化高频铝基板的生产加工进行交流。

多功能电离子治疗机治疗慢性肥厚性鼻炎54例报告

慢性肥厚性鼻炎是耳鼻喉科临床常见的疾病。我科自1994年4月引进国产GX—Ⅲ型多功能电离子治疗机,利用其短火高频金属电极对肥厚性的鼻甲粘膜行局部烧灼技术,在治疗慢性肥厚性鼻炎方面取得较满意的临床效果。现报告如下: 1 资料与方法 1.1 一般资料:本组54例,诊断标准依据武汉第一医院附属医院1978年编著的耳鼻咽喉科学中关于慢性肥厚性鼻炎诊断。其中男30例,女24例;

Prediction of metal futures price volatility and empirical analysis based on symbolic time series of high-frequency

The metal futures price fluctuation prediction model was constructed based on symbolic high-frequency time series using high-frequency data on the Shanghai Copper Futures Exchange from July 2014 to September 2018,and the sample was divided into 194 histogram time series employing symbolic time series.The next cycle was then predicted using the K-NN algorithm and exponential smoothing,respectively.The results show that the trend of the histogram of the copper futures earnings prediction is gentler than that of the actual histogram,the overall situation of the prediction results is better,and the overall fluctuation of the one-week earnings of the copper futures predicted and the actual volatility are largely the same.This shows that the results predicted by the K-NN algorithm are more accurate than those predicted by the exponential smoothing method.Based on the predicted one-week price fluctuations of copper futures,regulators and investors in China’s copper futures market can timely adjust their regulatory policies and investment strategies to control risks.

Volatility forecasting in Chinese nonferrous metals futures market

This paper seeks to model and forecast the Chinese nonferrous metals futures market volatility and allows new insights into the time-varying volatility of realized volatility and leverage effects using high-frequency data.The LHAR-CJ model is extended and the empirical research on copper and aluminum futures in Shanghai Futures Exchange suggests the dynamic dependencies and time-varying volatility of realized volatility,which are captured by long memory HAR-GARCH model.Besides,the findings also show the significant weekly leverage effects in Chinese nonferrous metals futures market volatility.Finally,in-sample and out-of-sample forecasts are investigated,and the results show that the LHAR-CJ-G model,considering time-varyingvolatility of realized volatility and leverage effects,effectively improves the explanatory power as well as out-of sample predictive performance.

Volatility-volume relationship of Chinese copper and aluminum futures market

Following Bessembinder and Seguins,trading volume is separated into expected and unexpected components.Meanwhile,realized volatility is divided into continuous and discontinuous jump components.We make the empirical research to investigate the relationship between trading volume components and various realized volatility using1min high frequency data of Shanghai copper and aluminum futures.Moreover,the asymmetry of volatility-volume relationship is investigated.The results show that there is strong positive correlation between volatility and trading volume when realized volatility and its continuous component are considered.The relationship between trading volume and discontinuous jump component is ambiguous.The expected and unexpected trading volumes have positive influence on volatility.Furthermore,the unexpected trading volume,which is caused by arrival of new information,has a larger influence on price volatility.The findings also show that an asymmetric volatility-volume relationship indeed exists,which can be interpreted by the fact that trading volume has more explanatory power in positive realized semi-variance than negative realized semi-variance.The influence of positive trading volume shock on volatility is larger than that of negative trading volume shock,which reflects strong arbitrage in Chinese copper and aluminum futures markets.

Spillovers among China’s precious and industrial metals markets:Evidence from higher moments and jumps

This study reveals the time-varying spillover effects of higher moments(realized volatility,realized skewness and realized kurtosis)and jumps between China’s precious metals and industrial metals markets.Using 5-min high-frequency data from May 10,2012 to October 21,2021,the dynamic effects of spillovers are uncovered using the time-frequency domain spillover index framework.The results show that the system connectedness weakens as the moment order gets higher whereas the total jumps connectedness is the smallest,and the spillovers of all estimators are more evident in the short term.The overall information spillovers are time-varying and influenced by major market events.Specifically,for realized volatility,copper is the largest net transmitter and silver is always a net transmitter,while zinc is the largest net receiver.For realized skewness,copper is the largest net transmitter and silver is always a net transmitter,while lead is the largest net receiver.For realized kurtosis and jumps,copper is the largest net transmitter,while aluminum is the largest net receiver.Overall,copper and silver play dominant roles in China’s precious and industrial metals markets system.

Interfacial characteristics of high frequency induction brazed Cu and pre-metalized graphite joints

Oxygen-free copper and pre-metalized graphite were brazed using CuNiSnP braze alloy by high frequency induction heating method. Interracial microstructures and reaction phases were analyzed by scanning electron microscopy （SEM） and energy dispersive X-ray spectroscopy （EDS）. The strength and resistance of the joints were tested. It is found that when the brazing parameters are optimized, the structures of the joints are graphite/（Cu,Ni）/Ni（s.s）＋NixPy/Cu3P＋Cu（s.s） （including Sn）＋eutectic structures （Cu3P＋Ni3P＋Cu（s.s）/Cu （s.s）/Cu）. When the temperature increases to 750℃ or the holding time prolongs to 300 s, the eutectie structures disappear and the amount of Cu3P increases. The maximum shear strength of the joints is 5.2 MPa, which fracture at the interface of graphite and metallization. The resistance of the joints is no more than 5 mΩ.

Metamorphic AlInAs/GaInAs HEMTs on silicon substrates by MOCVD

Metamorphic Al0.50In0.50As/Ga0.47In0.53As high electron mobility transistors (mHEMTs) grown by Metal Organic ChemicalVapor Deposition (MOCVD) on n-type silicon substrates with introduction of a novel multi-stage buffering stack scheme havebeen fabricated for the first time. 1.0- m-gate-length depletion-mode mHEMTs with maximum transconductance up to 613mS/mm are achieved. The unity current gain cut-off frequency (fT) and the maximum oscillation frequency (fmax) are 36.9 and55.6 GHz, respectively. This device has the highest fTyet reported for 1.0- m-gate-length HEMTs grown on silicon byMOCVD. Also, this performance is comparable to that of similar GaAs-based mHEMTs. These are encouraging initial resultsleading to the manufacturing potential of integrated high-speed metamorphic devices for logic applications on silicon sub-strates by MOCVD.

Analysis of dipole-like ultra high frequency RFID tags close to metallic surfaces

It is a challenge for passive RFID tags to be mounted on the surface of metal because the parameters of tag antennas,such as the impedance matching,the radiation efficiency and the radiation pattern,are seriously affected by the metallic surface.This paper presents the characteristics of the dipole-like antennas of ultra high frequency(UHF) radio frequency identification(RFID) tags that are placed close to metallic surfaces.The finite element method(FEM) and method of moment(MoM) were used to simulate the changes of the antenna parameters near the metallic surface.Two typical dipole-like antennas close to the metallic surface,a closed loop antenna and a loaded meander antenna,were modeled,and the performance was evaluated.Experiment was carried out and the results were in good agreement with the simulation,showing that a distance of 0.05λ～0.1λ(λ is the free space wavelength) from the metallic surface could make the dipole-like UHF RFID tag performance be acceptable.