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Research on the Performance of Supercritical CO2 Dry Gas Seal with Different Deep Spiral Groove
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作者 DU Qiuwan ZHANG Di 《热科学学报:英文版》 SCIE EI CAS CSCD 2019年第3期547-558,共12页
The performance of supercritical CO2(SCO2)dry gas seal(DGS)with different deep spiral groove is investigated with the thermal-fluid-solid coupling method.The performance parameters of DGSs with five different kinds of... The performance of supercritical CO2(SCO2)dry gas seal(DGS)with different deep spiral groove is investigated with the thermal-fluid-solid coupling method.The performance parameters of DGSs with five different kinds of grooves are obtained.The influence of inlet temperature,inlet pressure,velocity and film thickness on performance is analyzed compared with air DGS.The average film pressure,open force and leakage decrease while the average face temperature and flow velocity increase as the spiral groove number increases.The average film pressure,average face temperature,open force and leakage of DGS with radial different deep groove are higher than those of DGS with circumferential different deep groove respectively under the same spiral groove number while the average flow velocity is the opposite.SCO2 DGS can generate larger average film pressure,open force and leakage with lower average face temperature than air DGS.SCO2 DGS could maintain better sealing performance despite larger leakage with the variations of inlet temperature,inlet pressure,velocity and film thickness.The variables hold a more remarkable influence on SCO2 DGS compared with air DGS. 展开更多
关键词 SUPERCRITICAL carbon dioxide DIFFERENT DEEP SPIRAL GROOVE dry gas SEAL thermal-fluid-solid coupling method
High gain multiband planar spiral slot rectenna with dipole arms
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作者 Tan Lirong Zhao Feng +2 位作者 Cai Lingxiang Sun Youming Poo Yin 《中国邮电高校学报:英文版》 EI CSCD 2019年第3期91-97,共7页
A novel low profile multiband rectenna was proposed for harvesting the 2 nd generation(2 G), the 3 rd generation(3 G), the 4 th generation(4 G), wireless local area networks(WLANs) etc., electromagnetic wave energy. T... A novel low profile multiband rectenna was proposed for harvesting the 2 nd generation(2 G), the 3 rd generation(3 G), the 4 th generation(4 G), wireless local area networks(WLANs) etc., electromagnetic wave energy. The proposed rectenna consists of a novel multiband antenna and a rectifier. The multiband antenna includes a radiating element on one side of a single layer dielectric substrate and a feeding spiral balun on the other side of the substrate. A conductive via is connected between the balun and the radiating element. In the radiating element, a deformed dipole structure is connected with an equiangular spiral slot structure and is used to generate a low frequency radiation around 900 MHz. The multiband antenna can work simultaneously at 0.869 GHz~0.948 GHz, 1.432 GHz~2.173 GHz, and 2.273 GHz~2.465 GHz with its peak gains of 7.1 dBi at 903 MHz, 4.1 dBi at 1 800 MHz, 5.2 dBi at 2 430 MHz. The radio frequency to direct current(RF-to-DC) conversion efficiencies of the rectifier are 58%~62% at these three frequencies for an input power of 0 dBm. The overall measurement results validate that the rectenna suits for energy harvesting and exhibits approximate maximum efficiencies of 58% at 0.9 GHz, 56% at 1.8 GHz, and 55% at 2.4 GHz with a low incident power density of 8 μW/cm^2. 展开更多
关键词 energy harvesting deformed DIPOLE planar equiangular SPIRAL ANTENNA MULTIBAND ANTENNA SLOT ANTENNA RECTENNA
Mathematical Model and Machining Method for Spiral Flute Rake Faces of Hourglass Worm Gear Hob 预览
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作者 YANG Jie LI Haitao +2 位作者 RUI Chengjie HUANG Yi ZHANG Xiaodi 《南京航空航天大学学报:英文版》 EI CSCD 2019年第3期401-412,共12页
To improve the cutting performance of an hourglass worm gear hob and the accuracy of the resulting worm gear,the rake angles of the teeth on the pitch circle should be reduced.A method of forming the spiral flutes by ... To improve the cutting performance of an hourglass worm gear hob and the accuracy of the resulting worm gear,the rake angles of the teeth on the pitch circle should be reduced.A method of forming the spiral flutes by using a variable transmission ratio was developed.This method ensures that the rake angles on the indexing torus of each tooth are approximately 0°.Based on the gear meshing theory and the hourglass worm forming method,the discretization mathematical model of the rake face of a planar double enveloping worm gear hob was established by using cylindrical generating surface,and the feed parameters for machining the rake face for a variable transmission ratio were obtained.The spiral flute was simulated and the hob was machined on a four axis CNC milling machine.A contourgraph was used to measure the rake angle.The measurement results showed that the proposed method can reduce the absolute value of the rake angle on both sides of the cutting teeth,which can be used for machining the spiral flute rake face of an hourglass worm gear hob. 展开更多
关键词 HOURGLASS WORM gear HOB cylindrical generating surface SPIRAL FLUTE RAKE face RAKE angle
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Zn-Mg合金中两种不同共晶组织竞争生长机理的分析
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作者 唐玲 刘文义 夏鹏举 《热加工工艺》 北大核心 2019年第10期70-75,共6页
通过OM、SEM、XRD研究了Zn-Mg合金在3种成分不同冷却条件(薄壁、厚壁)下的凝固组织,探讨了Zn-Mg合金中两种共晶组织的形成机理。结果表明:Zn-2%Mg,Zn-3%Mg和Zn-5%Mg合金中均存在两种共晶结构的竞争生长,分别是非平衡态的EU1(α-Zn/γ-Mg... 通过OM、SEM、XRD研究了Zn-Mg合金在3种成分不同冷却条件(薄壁、厚壁)下的凝固组织,探讨了Zn-Mg合金中两种共晶组织的形成机理。结果表明:Zn-2%Mg,Zn-3%Mg和Zn-5%Mg合金中均存在两种共晶结构的竞争生长,分别是非平衡态的EU1(α-Zn/γ-Mg Zn2)和平衡态的EU2(α-Zn/β-Mg2Zn11)。当冷却速率较大时,倾向于析出平衡态EU2(α-Zn/β-Mg2Zn11)的共晶组织,且平衡态EU2的共晶组织为层片(棒状)的规则的共晶胞形态,宏观下的结构为台阶柱状式;当冷却速率较小时,倾向于析出非平衡态EU1(α-Zn/γ-Mg Zn2)的共晶组织,且非平衡态EU1的共晶组织为螺旋线型的非规则共晶形态。 展开更多
关键词 Zn-Mg合金 平衡态共晶EU2 非平衡态共晶EU1 竞争生长 螺旋型 台阶柱状
螺旋式混凝土布料机关键技术研究 预览
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作者 欧阳周全 《河南科技》 2019年第16期70-72,共3页
在现有技术基础之上,对螺旋式混凝土布料机的关键技术进行了分析研究,并针对现有产品存在的不足,提出了改进方法和结构的优化设计,对螺旋式混凝土布料机关键运动部件选型计算,并对主要承载结构件进行有限元分析,为螺旋式混凝土布料机的... 在现有技术基础之上,对螺旋式混凝土布料机的关键技术进行了分析研究,并针对现有产品存在的不足,提出了改进方法和结构的优化设计,对螺旋式混凝土布料机关键运动部件选型计算,并对主要承载结构件进行有限元分析,为螺旋式混凝土布料机的开发提供理论基础和技术依据,最后对螺旋式混凝土布料机的发展方向进行了预判。 展开更多
关键词 螺旋式 混凝土布料机 关键技术
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职业院校“螺旋式”课程体系编排探析 预览
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作者 焦丽君 王争 汤梦玲 《邢台职业技术学院学报》 2019年第2期1-3,共3页
在课程体系编排方式中,有直线式和螺旋式两种。文章站在教学围墙外,着眼于职业能力发展规律,秉承传统学徒制理念,探索"以工作关系为主、学科知识穿插其中"的工程造价专业螺旋式课程体系编排,让学生的学习过程循序渐进,像剥洋... 在课程体系编排方式中,有直线式和螺旋式两种。文章站在教学围墙外,着眼于职业能力发展规律,秉承传统学徒制理念,探索"以工作关系为主、学科知识穿插其中"的工程造价专业螺旋式课程体系编排,让学生的学习过程循序渐进,像剥洋葱一样从外到内,从易到难,完成专业理论知识及专业实操知识的学习。 展开更多
关键词 螺旋式 剥洋葱 学徒制 职业能力发展规律
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SIMULATED FINE STRUCTURES OF SPIRAL RAINBANDS IN TYPHOON CHANCHU(2006)
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作者 王咏青 蔡敏敏 葛旭阳 《热带气象学报:英文版》 SCIE 2019年第2期141-152,共12页
In this study, fine structures of spiral rainbands in super Typhoon Chanchu(2006) are examined using an Advanced Research Weather Research and Forecast(WRF-ARW) model simulation with the finest grid size of 2 km.Resul... In this study, fine structures of spiral rainbands in super Typhoon Chanchu(2006) are examined using an Advanced Research Weather Research and Forecast(WRF-ARW) model simulation with the finest grid size of 2 km.Results show that the simulation reproduces well Typhoon Chanchu’s track, intensity and basic structures. According to their locations and features, spiral rainbands are classified into principal, secondary, inner and distant rainbands, and their dynamic and thermodynamic features are investigated. The principal rainbands remain quasi-stationary with respect to Chanchu’s center and exhibit a wavenumber-1 feature with their outer edges separated by dry air. The secondary rainbands that occur on the radially inward side of the principal rainbands move around Chanchu’s center. The inner rainbands are closest to the center. They propagate both radially outward and azimuthally with time. The distant rainbands are located outside the inner-core region, and have stronger and continuous updrafts compared to the other rainbands. Distant rainbands are inward-sloping with height along the radial direction and have a cold pool in the low layers, whereas the principal and secondary rainbands lean radially outward with height. The inner rainbands do not show tilting with height along the radial direction. However, there are few vertical tilting cells along the azimuthal orientation among the four types of rainbands. The simulated radar reflectivity cores in all rainbands are collocated with the maxima of updrafts and equivalent potential temperatures in the low layer, indicating the important roles of energy supply in the boundary layer in determining the development of the rainband convection. 展开更多
关键词 TYPHOON SPIRAL RAINBANDS FINE STRUCTURES
原位螺旋构型回肠新膀胱尿流动力学及感染分析 预览
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作者 沈悦凡 钟欢 +1 位作者 王伟高 李辉 《中国现代手术学杂志》 2019年第3期228-231,共4页
目的 探讨根治性膀胱全切+原位螺旋构型回肠新膀胱术后患者尿流动力学及感染情况。方法 回顾性分析1998年1月~2012年12月在我院行膀胱全切+原位螺旋构型回肠新膀胱术治疗的54例膀胱癌患者的临床资料,其中尿路上皮癌50例,腺癌2例,鳞癌2... 目的 探讨根治性膀胱全切+原位螺旋构型回肠新膀胱术后患者尿流动力学及感染情况。方法 回顾性分析1998年1月~2012年12月在我院行膀胱全切+原位螺旋构型回肠新膀胱术治疗的54例膀胱癌患者的临床资料,其中尿路上皮癌50例,腺癌2例,鳞癌2例。临床病理T分期:T1 6例,T2 20例,T3 17例,T4 11例;病理N分期:N0 46例,N1 6例,N2 2例。分析其尿流动力学资料及术后感染情况。结果 本组随访时间36~152个月,平均(65.46±18.25)个月,术后早期(3月内)无失访病例。29例患者尿流动力学检查结果:最大膀胱容量平均(500±71)ml,最大充盈压力(23±5)cmH 2O,最大尿流率(16±5)ml/s,最大尿流率时逼尿肌压力(79±11)ml/cmH 2O,残余尿量(50±44)ml。术后早期(3个月内)6例(11.1%)出现肾盂肾炎,其中3例尿培养为大肠埃希菌,1例为绿脓杆菌,另2例尿培养阴性;尿道狭窄1例。术后晚期(3个月后)15例(27.8%)出现有症状的泌尿道感染,其中8例为泌尿道感染反复发作,7人为肾盂肾炎;尿道狭窄5例,UVJ狭窄10例。3例患者术后尿道狭窄行尿道切开术,2例术后因残余尿增多行清洁导尿;7例肾盂肾炎患者中,4例发现输尿管新膀胱连接部狭窄,其中3例行开放输尿管膀胱再植术。结论 螺旋构型折叠回肠能达到术后新膀胱低压、高容量的要求,输尿管“插入式再植”后膀胱输尿管连接部狭窄发生率高可能是引起远期泌尿道感染患病率增加的原因。 展开更多
关键词 回肠新膀胱 螺旋构型 尿流动力学 尿道感染 膀胱肿瘤
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Experimental Study on Thermal Performance of FLNG Spiral Wound Heat Exchanger under Sloshing Conditions
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作者 YAN Yan SUN Chongzheng +1 位作者 HAN Hui LI Yuxing 《热科学学报:英文版》 SCIE EI CAS CSCD 2019年第5期1042-1053,共12页
The FLNG spiral wound heat exchanger(SWHE) is affected by the sea conditions, which leads to more complex flow process and decrease the heat transfer performance of the heat exchanger. In order to study the thermal pe... The FLNG spiral wound heat exchanger(SWHE) is affected by the sea conditions, which leads to more complex flow process and decrease the heat transfer performance of the heat exchanger. In order to study the thermal performance of FLNG SWHE under heaving and swaying conditions, the experimental devices of FLNG SWHE and six-DOF(degree of freedom) sloshing platform were built. The effects of heaving and swaying motions on the pressure drop and heat transfer characteristics were analyzed at different sloshing amplitudes. The results showed that the heaving and swaying motions can cause the temperature rise and pressure fluctuation of SWHE, especially for swaying. The effect of sloshing on the heat transfer performance at the top of SWHE was greater than bottom. The pressure fluctuation percentage was within 7% and the amount of temperature change was less than 2℃, under the sloshing displacement among 120–255 mm. 展开更多
关键词 SPIRAL WOUND heat EXCHANGER FLNG EXPERIMENTAL SLOSHING
金属陶瓷螺旋立铣刀槽型优选及应用研究 预览
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作者 王羽中 尹兵 倪高明 《工具技术》 2019年第9期58-61,共4页
通过NAK80模具钢的铣削试验,运用全面试验方法研究金属陶瓷螺旋立铣刀螺旋角和径向前角对切削性能的影响,优化了其结构参数,对比研究了涂层和非涂层金属陶瓷立铣刀切削性能、涂层金属陶瓷立铣刀在气冷和水冷条件下切削性能。利用扫描电... 通过NAK80模具钢的铣削试验,运用全面试验方法研究金属陶瓷螺旋立铣刀螺旋角和径向前角对切削性能的影响,优化了其结构参数,对比研究了涂层和非涂层金属陶瓷立铣刀切削性能、涂层金属陶瓷立铣刀在气冷和水冷条件下切削性能。利用扫描电镜(SEM)、X射线能谱仪(EDS)对主切削刃进行观察,研究了两种刀片的磨损形态及磨损机理。试验结果表明:优选金属陶瓷螺旋立铣刀螺旋角为45°,径向前角为0°;非涂层金属陶瓷螺旋立铣刀不适合加工P类材料,AlTiN涂层金属陶瓷螺旋立铣刀加工P类材料时磨损形式为粘结磨损和化学磨损;气冷有利于减小刀具磨损,延长刀具寿命;水冷有利于提高零件表面质量,表面粗糙度值可稳定在Ra0.05以下,但因热冲击作用,其金属陶瓷基体易出现热裂纹,导致出现刀具微崩和涂层不规则脱落现象。 展开更多
关键词 金属陶瓷 立铣刀 螺旋 磨损
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煤用螺旋分选机的应用现状及优化设计方向 预览
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作者 孙吉鹏 马志国 +5 位作者 王治帅 葛家君 公绪文 王世兰 马运广 张歌 《煤炭加工与综合利用》 CAS 2019年第4期8-11,19,I0001共6页
介绍了螺旋分选机近年来在选煤厂粗煤泥分选工艺中的使用情况,同时对影响螺旋分选机分选效果的诸多因素从理论上进行了简要分析与总结;结合螺旋分选机引入国内后演变而来的诸多类型螺旋分选设备,提出了优化设计的方向,并希望相关机构加... 介绍了螺旋分选机近年来在选煤厂粗煤泥分选工艺中的使用情况,同时对影响螺旋分选机分选效果的诸多因素从理论上进行了简要分析与总结;结合螺旋分选机引入国内后演变而来的诸多类型螺旋分选设备,提出了优化设计的方向,并希望相关机构加大研发工作,解决螺旋分选机存在的处理量小、分选精度低等问题。 展开更多
关键词 选煤 螺旋分选机 粗煤泥 分选效果 结构优化
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Spacelike Mobius Hypersurfaces in Four Dimensional Lorentzian Space Form
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作者 Yan Bin LIN Ying LU Chang Ping WANG 《数学学报:英文版》 SCIE CSCD 2019年第4期519-536,共18页
In this paper, we first set up an alternative fundamental theory of Mobius geometry for any umbilic-free spacelike hypersurfaces in four dimensional Lorentzian space form, and prove the hypersurfaces can be determined... In this paper, we first set up an alternative fundamental theory of Mobius geometry for any umbilic-free spacelike hypersurfaces in four dimensional Lorentzian space form, and prove the hypersurfaces can be determined completely by a system consisting of a function W and a tangent frame {Ei}. Then we give a complete classification for spacelike Mobius homogeneous hypersurfaces in four dimensional Lorentzian space form. They are either M?bius equivalent to spacelike Dupin hypersurfaces or to some cylinders constructed from logarithmic curves and hyperbolic logarithmic spirals. Some of them have parallel para-Blaschke tensors with non-vanishing Mobius form. 展开更多
关键词 MOBIUS metric para-Blaschke tensor MOBIUS homogeneous HYPERSURFACE hyperbolic logarithmic spiral Dupin HYPERSURFACE
Diagnostic Value of 128-slice Spiral CT Combined with Virtual Colonoscopy for Colorectal Cancer 预览
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作者 Wen-juan TANG Zhuang NIE +3 位作者 Wen-liang FAN Lan CHENG Zi-qiao LEI Ming YANG 《当代医学科学(英文)》 SCIE CAS 2019年第1期146-152,共7页
The objective of this study was to evaluate the diagnostic value of 128-slice spiral CT combined with virtual colonoscopy in diagnosis of colorectal cancer.We retrospectively analyzed 45 patients of colorectal disease... The objective of this study was to evaluate the diagnostic value of 128-slice spiral CT combined with virtual colonoscopy in diagnosis of colorectal cancer.We retrospectively analyzed 45 patients of colorectal diseases who underwent definition AS+128-slice spiral CT combined with virtual colonoscopy after bowel preparation and gas injection to evaluate the clinical diagnostic value of this technology.All the patients received electronic colonoscopy and were confirmed by pathology.In total,colorectal cancer was confirmed in 42 cases and inflammation in 3 cases.Diagnostic results shows:there were 17 cases of lump,10 cases of infiltration,6 cases of ulcer,9 cases of mixed type,4 cases of liver metastases,and 36 cases of lymph node metastasis.There was no significant difference between 128-slice spiral CT combined with virtual colonoscopy and electronic colonoscopy in detection,localization and characterization of colorectal tumors.CT virtual endoscopy has great advantages in observing the invasion around the lesion and the presence or absence of metastasis in distant organs and lymph node metastasis.It is also possible to understand the shape of the lesion in the intestinal lumen and the length of the lesion involving the lumen of the intestine. 展开更多
关键词 128-slice SPIRAL CT VIRTUAL ENDOSCOPY COLORECTAL cancer
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Characterization of focusing performance of spiral zone plates with fractal structure
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作者 臧华平 郑程龙 +10 位作者 吉子雯 范全平 魏来 李永杰 牧凯军 陈述 王传珂 朱效力 谢常青 曹磊峰 梁二军 《中国物理B:英文版》 SCIE EI CAS CSCD 2019年第6期184-188,共5页
We propose an efficient method of generating a vortex beam with multi-foci by using a fractal spiral zone plate(FSZP), which is designed by combining fractal structure with a spiral zone plate(SZP) in the squared radi... We propose an efficient method of generating a vortex beam with multi-foci by using a fractal spiral zone plate(FSZP), which is designed by combining fractal structure with a spiral zone plate(SZP) in the squared radial coordinate.The theoretical analysis reveals that the number of foci that embed vortices is significantly increased as compared with that obtained by using a conventional SZP. Furthermore, the influence of topological charge on the intensity distribution in focal plane is also discussed in detail. For experimental investigation, an FSZP with topological charge p = 1 and 6.4 mm diameter is fabricated by using a photo-etching technique. The calibration indicates that the focusing performances of such a kind of zone plane(ZP) accord well with simulations, thereby providing its potential applications in multi-dimensional optical manipulation and optical imaging technology. 展开更多
关键词 OPTICAL VORTICES SPIRAL ZONE PLATE DIFFRACTIVE OPTICAL elements
Slow Quasi-Periodic Curves and Spiral Cracks in Chalcogenide Glass Thin Films 预览
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作者 Myroslav Kozak Vladimir Zhikharev +1 位作者 Vasyl Loya Vasyl Fedelesh 《材料科学与工程:中英文A版》 2019年第3期109-115,共7页
In the paper,thin films(1.5÷2.5μm thick)of As2S3 and As2Se3 chalcogenide glasses were investigated.The propagation of slow curves cracks in real time was observed,as well as circular Hertz cracks,the growth of w... In the paper,thin films(1.5÷2.5μm thick)of As2S3 and As2Se3 chalcogenide glasses were investigated.The propagation of slow curves cracks in real time was observed,as well as circular Hertz cracks,the growth of which is an increase in the diameter of the crack in time.All crack patterns known in the literature were observed.Research shows the spiral crack is a consequence of the superposition of the Hertz crack and the straight crack.The principle of coordination of stress relieving during the formation of patterns is formulated.Authors have done a lot of research work.And authors have drawn some meaningful conclusions. 展开更多
关键词 CHALCOGENIDE glasses CRACK patterns SPIRAL CRACK Hertz CRACK
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Increased levels of miR-124 in human dental pulp stem cells alter the expression of neural markers 预览
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作者 Ameneh Mehri-Ghahfarrokhi Zahra Pourteymourfard-Tabrizi +2 位作者 Effat Farrokhi Morteza Hashemzadeh Chaleshtori Mohammad-Saeid Jami 《中华耳科学杂志:英文版》 CSCD 2019年第4期121-127,共7页
Auditory neuropathy is the particular form of deafness in humans which cannot be treated by replacement therapy.Human dental pulp stem cells(hDPSCs)are derived from an ectomesenchymal neural crest cell population.Ther... Auditory neuropathy is the particular form of deafness in humans which cannot be treated by replacement therapy.Human dental pulp stem cells(hDPSCs)are derived from an ectomesenchymal neural crest cell population.Therefore,they possess a promising capacity for neuronal differentiation and repair.miR-124,a key regulator of neuronal development in the inner ear,is expressed at high levels in auditory and vestibular neurons.Here,we evaluated the possible effect of miR-124 in alteration of neural protein markers expression.Using quantitative reverse transcription-PCR(qRT-PCR)analyses and immunofluorescence staining,we studied the expression patterns of neural progenitor markers(Nestin,NOTCH1,and SOX2)and neural markers(b-tubulin Ⅲ,GATA-3,and peripherin)upon transfection of hDPSCs with miR-124.The qRT-PCR results showed that Nestin was upregulated 6 h post-transfection.In contrast,Nestin expression exhibited a decreasing trend 24 h and 48 h post-transfection.Higher levels of b-tubulin Ⅲ,6 h and 16 h post transfection in RNA level as compared with control cells,were determined in transfected DPSCs.However,b-tubulin-Ⅲ expression decreased 48 h post-transfection.The immunoflourescence results indicated that transfection of hDPSCs with miR-124,only affected Nestin among the studied neural progenitor and neural marker expression in protein level. 展开更多
关键词 Sensorineural hearing loss miR-124 Spiral ganglion neurons NESTIN DPSCs
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Reconciling the Earth's stratigraphic record with the structure of our galaxy 预览
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作者 Michael Gillman Hilary Erenler 《地学前缘:英文版》 CAS CSCD 2019年第6期2147-2151,共5页
The passage of our Solar System through the spiral arms has been implicated as a contributor to global environmental perturbations.The suggestion of a consistent structure within the arms,informed by density wave theo... The passage of our Solar System through the spiral arms has been implicated as a contributor to global environmental perturbations.The suggestion of a consistent structure within the arms,informed by density wave theory,raises the possibility of repeating patterns of events at each arm crossing.Here we test the hypothesis that the structure of the arms of our galaxy influences the stratigraphic record on Earth.We construct independent structural and temporal models and colbine these to compare the timings of arm tracers,materials from the earliest Solar System and events on Earth,including the largest extinctions.We find that a recurring sequence of events across the four arms emerges with an average arm-passing time of 188 million years.We suggest that the multiple temporal overlaps of events across arms,and their alignment with arm tracers and the earliest Solar System,presents an opportunity for a greater understanding of both Earth-based phenomena and galactic structure. 展开更多
关键词 SPIRAL ARMS STRATIGRAPHY Superchron Earliest Solar System EXTINCTIONS GLACIATIONS
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A 3D analytical model for vortex velocity field based on spiral streamline pattern 预览
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作者 Maryam Azarpira Amir Reza Zarrati 《水科学与水工程:英文版》 EI CAS CSCD 2019年第3期244-252,共9页
Vortices that develop over intakes are a hazardous hydraulic phenomenon.In this study, a 3D model was developed to study the flow field in air-core vortices.This model is based on the spiral pattern of streamlines and... Vortices that develop over intakes are a hazardous hydraulic phenomenon.In this study, a 3D model was developed to study the flow field in air-core vortices.This model is based on the spiral pattern of streamlines and the analytical solution of the momentum and continuity equations for deriving the three components of velocity.The model provides equations for free surface profiles and 3D patterns of the streamlines.Moreover, a new relationship was suggested for calculating effective viscosity and its distribution across the vortex flow field.The performance of the proposed analytical model was compared with existing experimental data and the results of previous analytical models.The outcomes indicated that the proposed model could predict characteristics of the vortex flow with good accuracy. 展开更多
关键词 Air-core VORTICES ANALYTICAL model Velocity distribution SPIRAL STREAMLINES Free surface profile
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Interaction of Wave Trains with Defects
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作者 陈贤伟 李鹏飞 +3 位作者 袁晓平 赵叶华 马军 陈江星 《理论物理通讯:英文版》 SCIE CAS CSCD 2019年第3期334-338,共5页
The evolution and transition of planar wave trains propagating through defects(obstacles) in an excitable medium are studied. When the frequency of the planar wave trains is increased, three different dynamical regime... The evolution and transition of planar wave trains propagating through defects(obstacles) in an excitable medium are studied. When the frequency of the planar wave trains is increased, three different dynamical regimes,namely fusion,"V" waves, and spiral waves, are observed in turn and the underlying mechanism is discussed. The dynamics is concerned with the shapes of the defects. Circle, triangle, and rectangle defects with different sizes are considered. The increase of pacing frequency broadens the fan-shaped broken region in the behind of a rectangle defect.The increase of width of a triangle defect leads to breakup of wave trains easier while the change of height shows opposite effect, which is presented in a phase diagram. Dynamical comparison on defects with different shapes indicates that the decrease of the defect width along the propagation of wave trains makes the fan-shaped region and the minimal frequency for breakup of spiral both increased. 展开更多
关键词 PLANAR WAVE TRAINS defects FUSION “V” pattern SPIRAL WAVE
The Distribution and Uncertainty Quantification of Wind Profile in the Stochastic General Ekman Momentum Approximation Model
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作者 Bing YAN Sixun HUANG +1 位作者 Jing FENG Yu WANG 《气象学报:英文版》 SCIE CSCD 2019年第2期336-348,共13页
The general Ekman momentum approximation boundary-layer model(GEM) can be effectively used to describe the physical processes of the boundary layer. However, eddy viscosity, which is an approximated value, can lead to... The general Ekman momentum approximation boundary-layer model(GEM) can be effectively used to describe the physical processes of the boundary layer. However, eddy viscosity, which is an approximated value, can lead to uncertainty in the solutions. In this paper, stochastic eddy viscosity is taken into consideration in the GEM, and generalized polynomial chaos is used to quantify the uncertainty. The goal of uncertainty quantification is to investigate the effects of uncertainty in the eddy viscosity on the model and to subsequently provide reliable distribution of simulation results. The performances of the stochastic eddy viscosity and generalized polynomial chaos method are validated based on three different types of eddy viscosities, and the results are compared based on the Monte Carlo method. The results indicate that the generalized polynomial chaos method can be accurately and efficiently used in uncertainty quantification for the GEM with stochastic eddy viscosity. 展开更多
关键词 generalized POLYNOMIAL CHAOS Monte Carlo method GENERAL EKMAN MOMENTUM approximation model EKMAN SPIRAL
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