Effects of sapphire substrates surface treatment on epitaxial ZnO thin films grown by MOCVD

The surface treatment effects of sapphire substrate on the quality of epitaxial ZnO thin films grown by metal-organic chemical vapor deposition (MOCVD) were studied. The sapphire substrates have been investigated by means of atomic force microscopy (AFM) and X-ray diffraction rocking curves (XRCs). The results show that sapphire substrate surfaces have the best-quality by CMP with subsequent chemical etching. The surface treatment effects of sapphire substrate on the ZnO thin films were examined by X-ray diffraction (XRD), atomic force microscopy (AFM) and photoluminescence (PL) measurements. Results show that the intensity of (002) diffraction peak of ZnO thin films on sapphire substrates treated by CMP with subsequent chemical etching is strongest. FWHM of (002) diffraction peak is narrowest and the intensity of UV peak of PL spectrum is strongest, indicating surface treatment on sapphire substrate preparation may improve ZnO thin films crystal quality and photoluminescent property.     

The effect of transglutaminase on some physicochemical and sensory properties of the Turkish drinking yoghurt Ayran

This article presents research on the effect of microbial transglutaminase on the properties of Turkish drinking yoghurt Ayran. Transglutaminase (TGase) enzyme was added to Ayran milk at different production steps, after pasteurisation and together with starter culture addition, and two different incubation times (10 min and 1 h) were used. Three TGase‐treated Ayran samples and control sample were analysed on 1st, 10th and 20th days of storage. TGase addition did not cause significant changes on chemical properties of Ayran (P > 0.05). However, physical properties of Ayran were improved by TGase throughout the storage period. Compared to the untreated control sample, pretreatment of milk with enzyme increased the viscosity dramatically (P < 0.05) and prevented serum separation. Scanning electron microscopic studies revealed that transglutaminase treatment of milk led to more regular distribution of proteins in Ayran gel and decreased gel permeability. TGase treatment did not show any unfavourable effect on the sensory properties of the final product.     

Luminescence and electrical properties of Eu-modified Bi0.5Na0.5TiO3 multifunctional ceramics

The Eu³⁺-modified Bi_0.5Na_0.5TiO₃ (BNT) ceramics have been fabricated by the solid-state reaction method. The impact of Eu³⁺ doping on the structure, photoluminescence, and electrical properties has been studied by XRD, SEM, PL spectra, and LCR meter. X-ray diffraction analysis reveals that the crystal structure of the samples is well matched with the trigonal perovskite, and the optimal temperature of presintering is 880°C. The Eu³⁺-doped BNT ceramics show excellent red fluorescence at 614 nm corresponding to the ⁵D₀→⁷F₂ transition of Eu³⁺ under 466 nm excitation and relatively long fluorescence lifetime. The BNT-0.02Eu ceramic density is up to 5.68 g/cm³ and the relative density is up to 94.6% with sintering temperature 1075°C. The piezoelectric constant (d₃₃) of samples has been significantly improved up to 110 pC/N by Eu³⁺ doping. The BNT-0.03Eu ceramic presintered at 880°C and sintered at 1050°C has good dielectric properties and excellent luminescence properties. Eu³⁺-doped BNT ceramics make it potential applications for novel integrated electro-optical and multifunctional devices.     

微纳结构超疏水表面参数影响含不凝气蒸汽冷凝传热的理论分析

超疏水表面结构参数对滴状冷凝传热性能、液滴生长和分布均会产生影响。首先利用竖直壁面液滴的受力平衡确定了不凝气条件下蒸汽冷凝过程中液滴的脱落半径,随后建立了含不凝气蒸汽滴状冷凝的传热模型,研究了不同不凝气浓度和过冷度下超疏水表面微柱的柱间距对滴状冷凝传热性能的影响,得到了使超疏水表面冷凝传热性能达到最佳的柱间距值,并对其随不凝气浓度和过冷度的变化规律进行了分析。结果表明在所研究的过冷度范围内,当不凝气浓度较低时（<20%）,最佳柱间距随不凝气浓度升高而增大;而当不凝气浓度高于20%时,最佳柱间距随不凝气浓度升高而减小。为驱动含不凝气蒸汽冷凝传热性能的超疏水微纳结构参数的优化提供了必要的基础数据。     

Biomechanical and microbiological changes in natural hog casings treated with ozone

The objective of this study was to determine the biomechanical and microbiological effects of exposing natural hog casings to ozonated water ≈7 mg/l for 0, 2 or 4 h at 16 °C. A total of 450 casing segments representing 10 hanks were used over five testing days and arranged in a randomized block split-plot design. For each treatment, pH, temperature, actual ozone concentration, bursting strength, maximum rupture force, and L^∗, a^∗ and b^∗ color space values were determined. The bursting strength and the maximum rupture force values suggested that casings can be treated by ozone up to 2 h without deterioration. After ozone treatments, changes in L^∗, a^∗ and b^∗ color space values made the casings appear lighter than the control samples. Microbiological studies showed that 1 and 2 h ozonation reduced counts of Escherichia coli biotype I, which expressed green fluorescent protein, by 0.4 and 0.6 log₁₀ CFU/25.4 cm casing, respectively.     

干涉型光纤传感器中的双重降噪方法

基于马赫-曾德尔(Mach-Zehnder)干涉仪结构,构造了全保偏光纤传感系统,以单频窄线宽保偏光纤激光器作为光源,采用了光源光电负反馈和双光路平衡检测双重降噪方法,降低了光源的附加强度噪声,使系统信噪比(SNR)提高了约15 dB,达到60 dB。     

改进的DFIG与VSC-HVDC协调控制改善风电场 低电压穿越能力

经VSC-HVDC并网风电系统在风电场侧故障时,风电机组出口母线电压过低,极易引起风力机脱网。而双馈风力发电机(DFIG)传统的Crowbar技术在故障时将转子侧变流器(RSC)短接,使发电机定子侧失去了为电网提供无功的能力,风力机的低电压穿越能力较低。提出一种改进的DFIG模型,加入了主动式DC-Chopper,与传统的Crowbar相配合,降低Crowbar动作的概率,使得DFIG转子侧变流器可以控制定子侧在故障时期继续提供无功功率。并利用此改进的DFIG与VSC-HVDC协调控制,改善风电场侧母线电压水平。通过算例仿真表明,在严重故障时采用改进式DFIG的Crowbar仍未动作。从而大大降低Crowbar动作的概率,双馈风电机组RSC故障期间可以继续投入运行并为电网提供无功支持。完成故障期间DFIG两侧变流器与VSC-HVDC风电场侧变流器(WFVSC)之间的无功协调,使风电场具有更好的低电压穿越能力(Low Voltage Ride Though, LVRT)。     

BEM for Diffraction of Elastic Wave and Dynamic Stress Concentrations in Thin Plate with a Circular Hole

oroThinplateS.arewidelyusedinengineering.DifferentholesaresomthesInadeinplatestosatisfyvariousneeds,therebycausingrvtricaldiscontinuahon.Dy-nndcstressconcentIationoccursamundtheholeinaplateonload.TheloadbearingcaPaityoftheplateisthereforeloweredanditSservicelifeisshortened-ThisisthereasonwhymanyexpeItShathhomeandabtalnmthcoreticalanalysis,calculationandexperiInntalreserehonthisasPectinrecentyere['-'].ForstalcsbessconcentIationamundaholeinaplateonbendingload,muchstudyhasbeenunderwayforyear…     

六流小方坯中间包内型优化数模研究

利用数模对新设计的六流小方坯连铸机中间包三维流场、浓度场、温度场进行研究，设计了一种新型的挡墙结构，使中间包钢水流动合理，温度分布均匀。６个水口的钢水测量平均停留时间和钢水温度的计算值分别是４８０ｓ、３７８ｓ、４１７ｓ和１５４９℃、１５４７℃、１５４２℃，与实际使用后的测量值非常接近。解决了六流中间包浇注过程中１、６流温度偏低，容易堵塞水口的问题。