Effects of magnesium and copper additions on tensile properties of Al-Si-Cr die casting alloy under as-cast and T5 conditions

Aluminum high pressure die casting(HPDC)technology has evolved in the past decades,enabling stronger and larger one-piece casting with significant part consolidation.It also offers a higher design freedom for more mass-efficient thin-walled body structures.For body structures that require excellent ductility and fracture toughness to be joined with steel sheet via self-piercing riveting(for instance,shock towers and hinge pillars,etc.),a costly T7 heat treatment comprising a solution heat treatment at elevated temperatures(450℃-500℃)followed by an over-ageing heat treatment is needed to optimize microstructure for meeting product requirement.To enable cost-efficient mass production of HPDC body structures,it is important to eliminate the expensive T7 heat treatment without sacrificing mechanical properties.Optimizing die cast alloy chemistry is a potential solution to improve fracture toughness and ductility of the HPDC components.The present study intends to tailor the Mg and Cu additions for a new Al-Si-Cr type die casting alloy(registered as A379 with The Aluminum Association,USA)to achieve the desired tensile properties without using T7 heat treatment.It was found that Cu addition should be avoided,as it is not effective in enhancing strength while degrades tensile ductility.Mg addition is very effective in improving strength and has minor impact on tensile ductility.The investigated Al-Si-Cr alloy with a nominal composition of Al-8.5wt.%Si-0.3wt.%Cr-0.2wt.%Fe shows comparable tensile properties with the T7 treated AlSi10MnMg alloy which is currently used for manufacturing shock towers and hinge pillars.

Non-symmetric distributions of solids deposition for solid-water stratified flow in deviated tubing strings

Dynamic performance on solids flow with water in deviated tubing is essential for the reliability of pump and normal operation of horizontal and directional wells.Compared with coal-water flow in vertical tubing and sand-oil flow with high production in deviated tubing,solids deposition with water shows obvious non-symmetric distributions in deviated tubing from simulations and experiments.The mathematical model of two phase flow was developed under coupling conditions of deviated tubing,low flow rate and viscosity based on the kinetic theory of granular flow and first-order discrete scheme.The results show that solid-water stratified flow in deviated tubing can be divided into two zones of suspension bed and the moving bed throughout the flow field.The solid flowing velocity with water is negative and particles slide down at the bottom of moving bed zone.The process of solids flow with water in deviated tubing will produce pressure loss and consume the kinetic energy.The thickness of deposited layer and the flowing velocity of solids flow downward with water at the moving bed zone enhance with the decreased inlet flow rate and the increased particle size,tubing inside diameter(ID)and inclination angle.Solids are easier into suspension from the upper part of moving bed zone to suspension bed zone and more solid particles flow with water towards the tubing outlet with the increase of inlet flowing velocity.The decision is made to reduce the screen width,tubing ID and inclination angle to maintain to be greater than critical deposition velocity in order to prevent solids settling.And it provides the theoretical basis and technical reserves for solid control and offers an effective approach to enhance tubing cleaning in deviated strings.

Bcl-2、Bax、Ki67在原发性翼状胬肉组织中的表达研究

目的:观察Bcl-2、Bax、Ki67在原发性翼状胬肉和正常球结膜组织中的表达。方法:将手术切除的原发性翼状胬肉和正常球结膜组织进行固定、石蜡包埋、切片,利用免疫组织化学染色方法分析Bcl-2(B细胞淋巴瘤-2)、Bax(与Bcl-2相关的X蛋白)、Ki67(细胞核相关抗原)在其中的表达情况。结果:Bcl-2、Bax、Ki67在原发性翼状胬肉组织中的阳性表达率分别为14.73%、7.00%、12.73%,在正常球结膜组织阳性表达率分别为4.00%、6.00%、0,其中Bcl-2、Ki67在原发性翼状胬肉组织头部上皮中的表达明显高于颈部和体部。结论:Bcl-2、Ki67在原发性翼状胬肉组织中呈高表达,且在胬肉头部表达最高,在正常球结膜组织中呈低表达;Bax在原发性翼状胬肉和正常球结膜组织中表达无明显差异,提示细胞凋亡失衡和异常增殖可能是原发性翼状胬肉发生发展的机制之一。

手术治疗高度近视合并白内障的研究进展

高度近视的全球发病率逐年上升,高度近视与白内障密切相关,而高度近视合并特殊病理变化,使得高度近视合并白内障的手术难度及术后并发症远高于普通白内障手术,而随着屈光性白内障时代的到来,患者术后的视觉质量要求更高,对眼科医生的挑战也更大,因此对于高度近视合并白内障手术患者的管理需要得到我们的重视。本文对高度近视合并白内障的手术方式、术前生物学测量、术中术后常见的并发症做一综述。

高度近视并发性白内障术后屈光误差影响因素的研究进展

高度近视是我国乃至全世界主要致盲性疾病之一,而高度近视并发性白内障更是一种高致盲风险的复杂性白内障,目前手术是唯一的治疗手段,由于高度近视可导致眼内一系列复杂改变,相比正常眼轴眼而言,术后更易产生屈光误差以及屈光漂移,本文就术前生物学测量准确性、人工晶状体计算公式的选择、有效人工晶状体位置变化等几部分对高度近视并发性白内障术后屈光误差的影响因素作一综述。

Fabrication and characterization of one-port surface acoustic wave resonators on semi-insulating GaN substrates

One-port surface acoustic wave resonators(SAWRs) are fabricated on semi-insulating high-quality bulk GaN and GaN film substrates, respectively. The semi-insulating GaN substrates are grown by hydride vapor phase epitaxy(HVPE)and doped with Fe. The anisotropy of Rayleigh propagation and the electromechanical coupling coefficient in Fe-doped GaN are investigated. The difference in resonance frequency between the SAWs between [1120] GaN and [1100] GaN is about 0.25% for the Rayleigh propagation mode, which is smaller than that of non-intentionally doped GaN film(~1%)reported in the literature. The electromechanical coupling coefficient of Fe-doped GaN is about 3.03%, which is higher than that of non-intentionally doped GaN film. The one-port SAWR fabricated on an 8-μm Fe-doped GaN/sapphire substrate has a quality factor of 2050, and that fabricated on Fe-doped bulk GaN has a quality factor as high as 3650. All of our results indicate that high-quality bulk GaN is a very promising material for application in SAW devices.

Metastatic suppressor genes inactivated by aberrant methylation in gastric cancer

AIM: To screen out the differentially methylated DNA sequences between gastric primary tumor and metastatic lymph nodes, test the methylation difference of gene PTPRG between primary gastric tumor and metastatic lymph nodes, and test the regulatory function of 5-aza- 2-deoxycytidine which is an agent with suppression on methylation and the level of methylation in gastric cancer cell line. METHODS: Methylated DNA sequences in genome were enriched with methylated CpG islands amplification (MCA) to undergo representational difference analysis (RDA), with MCA production of metastatic lymph nodes as tester and that of primary tumor as driver. The obtained differentially methylated fragments were cloned and sequenced to acquire the base sequence, which was analyzed with bioinformatics. With methylation-specific PCR (MSP) and RT-PCR, methylation difference of gene PTPRG was detected between primary tumor and metastatic lymph nodes in 36 cases of gastric cancer. Methylation of gene PTPRG and its regulated expression were observed in gastric cancer cell line before and after being treated with methylation-suppressive agent. RESULTS: Nineteen differentially methylated sequences were obtained and located at 5' end, exons, introns and 3' end, in which KL59 was observed to be located at 9p21 as the first exon of gene p16 and KL22 to be located at promoter region of PRPRG . KL22, as the probes, was hybridized with driver, tester and 3-round RDA products respectively with all positive signals except with the driver. Significant difference was observed in both methylation rate of gene PTPRG and PTPRG mRNA expression rate between primary tumor and metastatic lymph nodes. Demethylation of gene PTPRG, with recovered expression of PTPRG mRNA, was observed after gastric cancer cell line being treated with methylation-suppressive agent. CONCLUSION: Difference exists in DNA methylation between primary tumor and metastatic lymph nodes of gastric cancer, with MCA-RDA as one of the good analytical methods. Significant difference exists in methylation of gene PTPRG between primary tumor and metastatic lymph nodes of gastric cancer. Methylation level in gastric cancer cell line can be decreased by 5-aza-2'-deoxycytidine, which is the methylation- suppressive agent, with PTPRG expression being recovered.

Increased Levels of p53 and PARP-1 in EL-4 Cells Probably Related with the Immune Adaptive Response Induced by Low Dose Ionizing Radiation in vitro

Objective This paper is to explore the DNA repair mechanism of immune adaptive response （AR） induced by low dose radiation （LDR）, the changes of mRNA levels and protein expressions of p53, ATM, DNA-PK catalytic subunit （DNA-PKcs） and PARP-1 genes in the LDR-induced AR in EL-4 cells. Methods The apoptosis and cell cycle progression of EL-4 cells were detected by flow cytometry in 12 h after the cells received the pre-exposure of 0.075 Gy X-rays （inductive dose, D 1） and the succeeding high dose irradiation （challenge dose, D2; 1.0, 1.5, and 2.0 Gy X-rays, respectively） with or without wortmannin （inhibitor of ATM and DNA-PK） and 3-aminobenzamid （inhibitor of PARP-1）. And the protein expressions and mRNA levels related to these genes were detected with flow cytometry and reverse transcription-polymerase chain reaction in 12 h after irradiation with D2. Results The mRNA and protein expressions of p53 and PARP-1 in EL-4 cells in the D1 ＋ D2 groups were much lower than those in the D2 groups, and those of PARP-1 in the 3-AB ＋ D2 and the 3-AB ＋ D1 ＋ D2 groups were much lower than those in the D2 and the D1 ＋ D2 groups. The percentage of apoptotic EL-4 cells in the 3-AB ＋ D1 ＋ D2 groups was much higher than that in the D1 ＋ D2 groups, that in the G0/G1 and the G2 ＋ M phases was much higher, and that in the S phase were much lower. Although the ATM and DNA-PKcs mRNA and protein expressions in wortmannin ＋ D1 ＋ D2 groups were much lower than those in the D1 ＋ D2 groups, there were no significant changes in the apoptosis and cell cycle progression between the wortmannin ＋ D1 ＋ D2 and the D1 ＋ D2 groups. Conclusion PARP-1 and p53 might play important roles in AR induced by LDR.

Fabrication and characterization of vertical GaN Schottky barrier diodes with boron-implanted termination

The vertical GaN-on-GaN Schottky barrier diode with boron-implanted termination was fabricated and characterized.Compared with the Schottky barrier diode(SBD)without boron-implanted termination,this SBD effectively improved the breakdown voltage from 189 V to 585 V and significantly reduced the reverse leakage current by 10^5 times.In addition,a high Ion/Ioff ratio of ~10^8 was achieved by the boron-implanted technology.We used Technology Computer Aided Design(TCAD)to analyze reasons for the improved performance of the SBD with boron-implanted termination.The improved performance of diodes may be attributed to that B+could confine free carriers to suppress electron field crowding at the edge of the diode,which could improve the breakdown voltage and suppress the reverse leakage current.

Potential role of the compound Eucommia bone tonic granules in patients with osteoarthritis and osteonecrosis: A retrospective study

BACKGROUND Osteoarthritis is a major source of pain,disability,and socioeconomic cost worldwide.Osteonecrosis is a disabling disorder that frequently occurs in the younger population aged from 20-50 years.The compound Eucommia bone tonic granules,a traditional Chinese medicine,can alleviate the damage of osteoarthritis and osteonecrosis.AIM To investigate the potential role of the compound Eucommia bone tonic granules(Eucommia)in the treatment of patients with osteoarthritis and osteonecrosis.METHODS One-hundred forty osteoarthritis and osteonecrosis cases admitted to our hospital from January 2013 to December 2017 were selected.Patients were divided into two groups:Eucommia-meloxicam group and meloxicam group.Clinical efficacy and the Western Ontario and McMaster Universities Arthritis Index(WOMAC)score were evaluated according to the evaluation criteria of orthopedic diseases.The levels of bone-GLA protein,interleukin-17,recombinant human S100 calcium binding protein A12,sphingosine 1-phosphate,cystatin C,creatinine,and hemoglobin in peripheral blood were determined.RESULTS The total effective rate in the two osteoarthritis groups was not different,but the total effective rate in the two osteonecrosis groups was significantly different.The overall efficacy of Eucommia-meloxicam group was superior to that of the meloxicam group.WOMAC showed that pain,stiffness,and dysfunction in the two groups of osteoarthritis and osteonecrosis before and after treatment were significantly different.The concentration of recombinant human S100 calcium binding protein A12,sphingosine 1-phosphate,cystatin C,creatinine,and hemoglobin before and after treatment in the Eucommia-meloxicam group and meloxicam group of osteoarthritis and osteonecrosis were significantly different,and the two treatment groups were significantly different from each other for osteoarthritis.CONCLUSION Our findings indicate that Eucommia can effectively enhance the curative effect of meloxicam,and the combination of Eucommia and meloxicam is superior to meloxicam alone.

Site-testing at Muztagh-ata site Ⅰ:ground meteorology and sky brightness

Site-testing is crucial for achieving the goal of scientific research and analysis of meteorological and optical observing conditions,one of the associated basic tasks.As one of three potential sites to host the 12-meter Large Optical/infrared Telescope(LOT),the Muztagh-ata site,which is located on the Pamir Plateau in Xinjiang,in west China,began its site-testing task in the spring of 2017.In this paper,we firstly start with an introduction to the site and then present a statistical analysis of the ground-level meteorological properties such as air temperature,barometric pressure,relative humidity,and wind speed and direction,recorded by an automatic weather station with standard meteorological sensors for a two-year duration.We also show the monitoring results of sky brightness during this period.

Stray light analysis of the Xinglong 2.16-m telescope

An effort towards understanding the problems associated with stray light related to the Xinglong2.16-m telescope is presented to estimate the stray light performance of the telescope itself and provide a method for improving stray light suppression.Stray light analysis for the 2.16-m telescope model,which consists of an onion shaped dome,telescope structure,equatorial mount and telescope optics,has been developed in two cases(1)pointing to 60?and(2)pointing to zenith,in both azimuth and elevation directions.The Point Source Normalized Irradiance Transmittance(PSNIT),which is generally used for assessing stray light and is uncorrelated to entrance aperture,is calculated with a series of off-axis angles.It shows that the PSNIT values are less than 10-7 when off-axis angles are larger than±20?.The dominant contributors to stray light(primary and secondary mirror,telescope structure and dome)are identified to guide performance improvement.The analyses indicate that significant benefit can be realized by adding only five vanes inside the bottom portion of the secondary baffle.In the case of pointing to zenith,the PSNIT values will decrease about 40%on average.

Research on performances of back-illuminated scientific CMOS for astronomical observations

To evaluate performances of a back-illuminated scientific CMOS(sCMOS)camera for astronomical observations,comparison tests between Andor Marana s CMOS and Andor iKon-L 936 CCD cameras were conducted in a laboratory and on a telescope.The laboratory tests showed that the readout noise of the sCMOS camera is about half lower,the dark current is about 17 times higher,the dynamic range is lower in the 12-bit setting and higher in the 16-bit setting,and the linearity and bias stability are comparable relative to those of the CCD camera.In field tests,we observed the open cluster M67 with the sCMOS and CCD cameras on a 60 cm telescope.Unlike the CCD camera,the sCMOS camera has a dual-amplifier architecture.Since a 16-bit image of the sCMOS camera is composed of two 12-bit images sampled with 12-bit high gain and low gain amplifiers simultaneously,it is not real 16-bit output data.The evaluation tests indicated that the dual-amplifier architecture of the s CMOS camera leads to a decline of photometric stability by about six times around specific pixel counts.For photometry of bright objects with similar magnitudes that require high frame rates,the s CMOS camera under 12-bit setting is a good choice.Therefore,the sCMOS camera is fitted with survey observations of variable objects requiring short exposure times,mostly less than 1 s,and high frame rates.It also satisfies the requirements for an offset guiding instrument owing to its high sensitivity,high temporal resolution and high stability.

Growth and doping of bulk GaN by hydride vapor phase epitaxy

Doping is essential in the growth of bulk GaN substrates,which could help control the electrical properties to meet the requirements of various types of GaN-based devices.The progresses in the growth of undoped,Si-doped,Ge-doped,Fedoped,and highly pure GaN by hydride vapor phase epitaxy(HVPE) are reviewed in this article.The growth technology and precursors of each type of doping are introduced.Besides,the influence of doping on the optical and electrical properties of GaN are presented in detail.Furthermore,the problems caused by doping,as well as the methods to solve them are also discussed.At last,highly pure GaN is briefly introduced,which points out a new way to realize high-purity semi-insulating(HPSI) GaN.

Site testing campaign for the Large Optical/infrared Telescope of China:overview

The Large Optical/infrared Telescope(LOT)is a ground-based 12 m diameter optical/infrared telescope which is proposed to be built in the western part of China in the next decade.Based on satellite remote sensing data,along with geographical,logistical and political considerations,three candidate sites were chosen for ground-based astronomical performance monitoring.These sites include:Ali in Tibet,Daocheng in Sichuan and Muztagh-ata in Xinjiang.Up until now,all three sites have continuously collected data for two years.In this paper,we will introduce this site testing campaign,and present its monitoring results obtained during the period between March 2017 and March 2019.

A 3-channel CCD photometer at the Xinglong Observatory

We describe the design and construction of a new rapid 3-channel CCD photometer, dedicated to simultaneous multicolor photometric observations of rapidly variable objects. This photometer is equipped on the 1-meter telescope at the Xinglong Observatory. It allows simultaneous imaging within fields of view of 18.81′×18.8′, 18.2′×17.6′ and 9.2′×9.2′ in the Sloan Digital Sky Survey＇s g′, r′ and i′ bands, respectively. The results of its calibration and performance are reported.

Long-term analysis of clear nights using satellite data considering astronomical sites in western China

A large ground-based optical/infrared telescope is being planned for a world-class astronomical site in China.The cloud-free night percentage is the primary meteorological consideration for evaluating candidate sites.The data from GMS and NOAA satellites and the MODIS instrument were utilized in this research,covering the period from 1996 to 2015.Our data analysis benefits from overlapping results from different independent teams as well as a uniform analysis of selected sites using GMS+NOAA data.Although significant ground-based monitoring is needed to validate these findings,we identify three different geographical regions with a high percentage of cloud-free conditions(~83%on average),which is slightly lower than at Mauna Kea and Cerro Armazones(~85%on average)and were chosen for the large international projects TMT and ELT respectively.Our study finds evidence that cloud distributions and the seasonal changes affected by the prevailing westerly winds and summer monsoons reduce the cloud cover in areas influenced by the westerlies.This is consistent with the expectations from climate change models and is suggestive that most of the identified sites will have reduced cloud cover in the future.

Dislocation slip behaviors in high-quality bulk GaN investigated by nanoindentation

The dislocation slip behaviors in GaN bulk crystal are investigated by nanoindentation, the dislocation distribution patterns formed around an impress are observed by cathodoluminescence(CL) and cross-sectional transmission electron microscope(TEM). Dislocation loops, vacancy luminescence, and cross-slips show hexagonal symmetry around the 11-20 and 1-100 direction on c-plane. It is found that the slip planes of dislocation in GaN crystal are dominated in {0001}basal plane and {10-11} pyramid plane. According to the dislocation intersection theory, we come up with the dislocation formation process and the related mechanisms are discussed.

Electrochemical liftoff of freestanding GaN by a thick highly conductive sacrificial layer grown by HVPE

Separation technology is an indispensable step in the preparation of freestanding GaN substrate. In this paper, a largearea freestanding GaN layer was separated from the substrate by an electrochemical liftoff process on a sandwich structure composed of an Fe-doped GaN substrate, a highly conductive Si-doped sacrificial layer and a top Fe-doped layer grown by hydride vapor phase epitaxy(HVPE). The large difference between the resistivity in the Si-doped layer and Fe-doped layer resulted in a sharp interface between the etched and unetched layer. It was found that the etching rate increased linearly with the applied voltage, while it continuously decreased with the electrochemical etching process as a result of the mass transport limitation. Flaky GaN pieces and nitrogen gas generated from the sacrificial layer by electrochemical etching were recognized as the main factors responsible for the blocking of the etching channel. Hence, a thick Si-doped layer grown by HVPE was used as the sacrificial layer to alleviate this problem. Moreover, high temperature and ultrasonic oscillation were also found to increase the etching rate. Based on the results above, we succeeded in the liftoff of ~ 1.5 inch GaN layer. This work could help reduce the cost of freestanding GaN substrate and identifies a new way for mass production.

Introduction to the environmental monitoring instruments for LOT

The Large Optical/infrared Telescope(LOT)is a ground-based 12 m diameter optical/infrared telescope,which is proposed to be built in the western part of China in the next decade.To select the best site which satisfies the construction and future operation of LOT,data monitoring and comparing are required for all the candidate sites.The comparison of most of the instruments was done at Xinglong Observatory.These instruments include weather station,all sky camera,sky background meter and differential image motion monitor(DIMM).This paper introduces the instruments used in LOT site monitoring and the instruments comparisons.The results show that the instrument is stable and the data uniformity of the identical instruments is good.This paper provides a fundamental description of LOT site monitoring.