Mechanism of improving forward and reverse blocking voltages in AlGaN/GaN HEMTs by using Schottky drain

In this paper, we demonstrate that a Schottky drain can improve the forward and reverse blocking voltages （BVs） simultaneously in A1GaN/GaN high-electron mobility transistors （HEMTs）. The mechanism of improving the two BVs is investigated by analysing the leakage current components and by software simulation. The forward BV increases from 72 V to 149 V due to the good Schottky contact morphology. During the reverse bias, the buffer leakage in the Ohmic- drain HEMT increases significantly with the increase of the negative drain bias. For the Schottky-drain HEMT, the buffer leakage is suppressed effectively by the formation of the depletion region at the drain terminal. As a result, the reverse BV is enhanced from -5 V to -49 V by using a Schottky drain. Experiments and the simulation indicate that a Schottky drain is desirable for power electronic applications.

Influence of a drain field plate on the forward blocking characteristics of an AlGaN/GaN high electron mobility transistor

In this paper, the influence of a drain field plate （FP） on the forward blocking characteristics of an AlGaN/GaN high electron mobility transistor （HEMT） is investigated. The HEMT with only a gate FP is optimized, and breakdown voltage VBR is saturated at 1085 V for gate–drain spacing LGD ≥ 8 μm. On the basis of the HEMT with a gate FP, a drain FP is added with LGD=10 μm. For the length of the drain FP LDF ≤ 2 μm, VBR is almost kept at 1085 V, showing no degradation. When LDF exceeds 2 μm, VBR decreases obviously as LDF increases. Moreover, the larger the LDF, the larger the decrease of VBR. It is concluded that the distance between the gate edge and the drain FP edge should be larger than a certain value to prevent the drain FP from affecting the forward blocking voltage and the value should be equal to the LGD at which VBR begins to saturate in the first structure. The electric field and potential distribution are simulated and analyzed to account for the decrease of VBR.

Reverse blocking enhancement of drain field plate in Schottky-drain AlGaN/GaN high-electron mobility transistors

In this paper, we present the combination of drain field plate （FP） and Schottky drain to improve the reverse blocking capability, and investigate the reverse blocking enhancement of drain FP in Schottky-drain AlGaN/GaN high-electron mobility transistors （HEMTs）. Drain FP and gate FP were employed in a two-dimensional simulation to improve the reverse blocking voltage （VRB） and the forward blocking voltage （VFB）. The drain-FP length, the gate-FP length and the passivation layer thickness were optimized. VRB and VFB were improved from -67 V and 134 V to -653 V and 868 V respectively after optimization. Simulation results suggest that the combination of drain FP and Schottky drain can enhance the reverse blocking capability significantly.

Improvement of reverse blocking performance in vertical power MOSFETs with Schottky–drain-connected semisuperjunctions

To enhance the reverse blocking capability with low specific on-resistance,a novel vertical metal-oxidesemiconductor field-effect transistor（MOSFET） with a Schottky-drian（SD） and SD-connected semisuperjunctions（SDD-semi-SJ）,named as SD-D-semi-SJ MOSFET is proposed and demonstrated by two-dimensional（2D） numerical simulations.The SD contacted with the n-pillar exhibits the Schottky-contact property,and that with the p-pillar the Ohmic-contact property.Based on these features,the SD-D-semi-SJ MOSFET could obviously overcome the great obstacle of the ineffectivity of the conventional superjunctions（SJ） or semisuperjunctions（semi-SJ） for the reverse applications and achieve a satisfactory trade-off between the reverse breakdown voltage（BV） and the specific on-resistance（R_（on）A）.For a given pillar width and n-drift thickness,there exists a proper range of n-drift concentration（N）,in which the SD-D-semi-SJ MOSFET could exhibit a better trade-off of R_（on）A-BV compared to the predication of SJ MOSFET in the forward applications.And what is much valuable,in this proper range of N,the desired BV and good trade-off could be achieved only by determining the pillar thickness,with the top assist layer thickness unchanged.Detailed analyses have been carried out to get physical insights into the intrinsic mechanism of R_（on）A-BV improvement in SD-D-semi-SJ MOSFET.These results demonstrate a great potential of SD-D-semi-SJ MOSFET in reverse applications.

基于坐封受力模型的暂堵球封堵效果影响因素与参数优化

暂堵球在射孔孔眼及压裂裂缝中的坐封状态影响其封堵稳定性,暂堵球封堵效果决定暂堵转向压裂技术的成败。通过建立暂堵球坐封受力计算模型,研究了压裂液排量、密度、暂堵球及孔眼参数对暂堵球坐封受力状态及其封堵效率的影响,实验模拟了不同射孔参数、压裂排量及暂堵球/压裂液性能对封堵效果的影响。结果表明:暂堵球受拖拽力、脱离力及持球力随压裂液排量的增加而增大,暂堵球更易坐封;压裂液及暂堵球密度对暂堵球坐封封堵效率影响不大;暂堵球粒径大于孔眼直径时,暂堵球坐封封堵效率随粒径增加而增大,当暂堵球直径小于孔眼直径时,暂堵球不容易坐封;射孔孔眼数增加影响暂堵球坐封封堵效率。实验评价暂堵球最佳直径为9.0 mm,最佳泵送排量大于4.0 m^(3)/min时,有助于提高暂堵球坐封成功率,增强暂堵压裂设计的可靠性。

Dynamic simulation and optimization approach to construction diversion of hydraulic and hydroelectric projects

To solve the engineering and scientific problems in construction diversion and its simulation analysis, a complete scheme is presented. Firstly, the complex constraint relationship was analyzed among main buildings, diversion buildings and flow control. Secondly, the time-space relationship model of construction diversion system and the general block diagram-oriented simulation model of diversion process were set up. Then, the corresponding numerical simulation method and 3D dynamic visual simulation method were put forward. Further, the simulation and optimization platform of construction diversion control process was developed, integrated with simulation modeling, computation and visualization. Finally, these methods were applied to a practical project successfully, showing that the modeling process is convenient, the computation and the visual analysis can be coupled effectively, and the results conform to practical state. They provide new theoretical principles and technical measures for analyzing the control problems encountered in construction diversion of hydraulic and hydroelectric engineering under complex conditions.

新疆油田深层致密砂岩气藏增产改造工艺技术研究

新疆油田深层非常规致密砂岩储层具有埋藏深、异常高压、储层破裂压力高、地温高、低孔低渗、非均质性强、横向储层厚度变化大、纵向分布多等特点,储层压开成功率低、加砂困难,增产改造工艺技术面临极大挑战。针对该区块致密砂岩储层改造难点,优化形成了不同储层类型的针对性改造工艺技术:Ⅰ类储层采用“重晶石解除+酸化”工艺,解除重晶石污染堵塞、溶解裂缝内钙质,疏通天然裂缝系统;天然裂缝不同程度发育的Ⅱ、Ⅲ类储层采用缝网压裂工艺,前置液降低储层温度并激活天然裂缝系统、主体压裂液携砂形成高导流能力的主裂缝网络系统。对于储层厚度大、笼统改造无法实现巨厚储层的纵向均匀改造,则采用分层改造工艺。针对层间应力差为2~5 MPa的井,优选暂堵软分层工艺,缝网压裂采用“粉末+陶粒”不同粒径组合的暂堵软分层工艺;针对层间应力差大于5 MPa,采用机械分层改造工艺,若2个封隔器之间的跨度大于60 m,采用机械分层+软分层复合分层工艺。配套完善了以超级瓜尔胶稠化剂为主的基础压裂液体系,支撑剂选取40~70目粒径的陶粒,配套暂堵转向材料主要有可降解纤维、纤维粉末及颗粒暂堵剂等。形成的深层致密砂岩气藏的针对性储层改造工艺技术对探索非常规致密砂岩气藏储层改造技术具有重要借鉴意义。

历史文化街区空间活力测度与作用机制分析——以广州市荔湾区为例

为探究广州市历史文化街区空间活力特点与机制,对荔湾区不同类型历史文化街区的人口活动、交通区位、空间形态、功能特性、历史文化资源分布进行定量分析,以人口活动作为空间活力的外在表征,探究历史文化街区的空间活力影响因素。结果表明历史文化街区的空间活力主要与街道类型、功能密度、街道布局形态、交通区位、功能混合度密切相关,但与历史文化资源分布未表现出显著相关,提示仍需进一步发掘传统街巷的历史文化价值。

Bird Habitats in Urban Environments: A Case from an Urban Landfill in and around Tayba Al Hasanab Landfill, Khartoum, Sudan

Managed open landfill sites can serve as crucial feeding grounds for birds. Studies have demonstrated that garbage dumps offer favorable feeding habitats for various trophic generalist species, including storks and scavenger raptors. This study aimed to assess bird diversity and abundance in and around Tayba Al Hasanab Landfill, Khartoum. A bird census was conducted using block counts in January 2021. A questionnaire complemented field observations, and interviews were conducted with landfill authorities and waste collectors to gather information on bird availability, numbers, and diversity. During the block counts, 23 bird species were recorded inside and around the landfill. These species directly relied on food resources available at and around the landfill, belonging to 8 orders and 11 families. The four most abundant species foraging at the landfill were Sparrow House (Passer domesticus) with 97 individuals, Black kite (Milvus migrans) with 67 individuals, cattle egret (Bubulcus ibis) with 42 individuals, and Laughing Dove (Spilopelia senegalensis) with 36 individuals. This suggests that these species are the primary exploiters of food resources at the landfill. The results indicate that all species are considered least concerned except the Egyptian Vulture (Neophron percnopterus), which is classified as endangered. Most of the interviewed individuals reported seeing birds in the study area. The study recorded instances of dead birds, such as a white stork colliding and being electrocuted with a transition line observed at different sites along transmission lines near the landfill. Surveys around Tayba landfill need to be conducted to identify deadly power lines for replacement or implement possible mitigation measures on power lines running parallel and close to the Tayba landfills. The avian community foraging at the landfill displayed fluctuations in abundance and interspecific interactions across seasons. Given that the substantial influx of birds to landfills can pose various environmental challenges in urban settings, this study underscores the significance of examining the seasonal dynamics of bird communities concerning the location and management of landfills.

综掘工作面风幕阻尘效果影响因素研究

目前综掘工作面粉尘污染的研究多集中于单一因素对综掘工作面风幕阻尘效果的影响,而未充分考虑各因素间的交互作用,使得压风分流技术的工程应用效果欠佳。为明确附壁风筒径向出风距离、径向出风比及轴向出风距离对风幕阻尘效果的影响,以潘三矿810西翼机巷综掘工作面为研究对象,运用Fluent软件对径向出风距离为10~25 m、径向出风比为0.6~0.9及轴向出风距离为6~12 m条件下的风流分布和粉尘扩散情况进行数值模拟。结果表明:(1)随着径向出风距离增大,径向涡流风幕在巷道内的转变更充分,综掘机司机前端的风流分布越均匀,更有利于形成风速方向均指向工作面的轴向阻尘风幕。当径向出风距离为10 m时,距工作面7 m断面内涡流特性明显,风速方向紊乱;当径向出风距离为25 m时,距工作面7 m断面内,风流分布趋于均匀,风速方向均指向工作面,形成了能够覆盖全断面的轴向阻尘风幕。(2)随着径向出风比增大,整流风筒轴向风流风量减小,轴向风流风速和射流强度降低,轴向风流对综掘工作面前端气流的扰动减弱;径向出风比越大,越有利于形成风流方向指向工作面且能覆盖全断面的轴向阻尘流场,即轴向阻尘风幕。(3)径向涡流风幕的阻尘能力随径向出风比的增大先增强后减弱,轴向阻尘风幕的阻尘能力随径向出风比的增大而不断增强。(4)在采取压风分流风幕阻尘技术后,当压风总量为300 m^(3)/min,吸风量为400 m^(3)/min,附壁风筒径向出风距离为20 m,径向出风比为0.9,整流风筒轴向出风距离为8~10 m时,能很好地将粉尘聚集在吸尘口附近,达到高效控尘除尘的目的。在810西翼机巷综掘工作面进行现场测试,测点风速和粉尘质量浓度实测值与模拟值基本一致,高浓度粉尘被有效阻控于工作面前端,隔尘效果较为明显,验证了数值模拟的有效性。

基于马尔可夫等效模块化的核电厂DAS系统可靠性分析

核电厂多样性驱动系统(DAS)是当保护系统发生共因失效时,用于抵御核电厂发生的设计基准事件的系统,对DAS进行可靠性分析至关重要。针对马尔可夫方法的组合爆炸问题,本文提出了一种等效模块化的分析方法,能够将DAS的隐马尔可夫模型分解成若干的部分,并对这些复杂度相对低的部分进行定量分析,根据计算的结果将每个部分再等效为一个设备或模块,最后整合所有部分等效的设备来组成一个等效系统,构建该等效系统的马尔可夫模型,以替代原系统的马尔可夫模型进行定量分析。然后用于对核电厂DAS系统平台进行了定量计算,并采用动态可靠性框图法(DRBD)对结果进行验证,结果显示了其有效性。

四川盆地渝西大安区块龙潭组深层煤岩气压裂技术探索

据多轮次煤层气资源评价结果,沉积于海陆交互环境的四川盆地上二叠统龙潭组也是重要的产煤层系,其中作为南方首个浅层山地煤层气代表的川南地区筠连煤层气田已成功实现商业开发,而深层煤岩气勘探评价仍处于探索试验阶段,亟需结合深层煤岩的构造和储层特征,建立一套适用于深层煤岩气的压裂技术体系。为此,从储层物性、岩石力学、顶底板特征3个方面,对比分析了四川盆地渝西区块龙潭组19号煤岩与其他深层煤岩气的地质工程差异,通过正交试验优化压裂参数,形成了“小簇间距布缝(15~23 m)+单段多簇射孔(4簇)+大排量大规模造缝(施工排量18~20 m^(3)/min、用液强度32~35 m^(3)/m)+高强度加砂支撑(6.5~7.0 t/m)”的压裂工艺技术,成功实施了四川盆地首口深层煤岩气水平井的压裂作业。研究结果表明:①龙潭组深层煤岩煤质呈软塑性,割理和裂缝发育,需通过小簇间距布缝、大排量大规模造缝、高强度加砂支撑的压裂工艺思路以提高缝网复杂程度和支撑裂缝导流能力;②微注入压降测试(DFIT)获取的地质参数与测井资料预测的数据吻合度好,在深层煤岩具有良好的适用性;③针对深层煤岩具有高孔隙度、发育割理和裂隙的地质特征,停泵30 min+投球暂堵的方式可以有效提高改造范围和效果。结论认为,在四川盆地渝西大安区块深层煤岩气的探索实践,有助于形成深层煤岩气压裂改造技术体系,对加快推进四川盆地超压、超饱和深层龙潭组煤岩气高效规模开发具有重要的指导意义。

一种关于楔形封堵体承载能力计算方法研究

导流洞作为水电工程中高水头的有压隧洞,其封堵措施是保证水电工程蓄水及正常运行的重要一环,其结构设计内容至关重要。目前关于封堵体的计算方法多针对于柱状封堵体,关于工程实用性较大及应用较多的楔形封堵体的计算方法较少。因此,基于规范推荐的柱状封堵体抗滑稳定计算公式,从楔形封堵体的受力分析出发,推导出适用于楔形封堵体承载力计算方法。将其计算结果与柱状封堵体计算结果对比,结果表明:相较于柱状封堵体,楔形封堵体更好地利用了围岩的特性,在泊松效应的加持下,极大程度地增强了封堵体对于水压的承载能力,该公式对于楔形封堵体的设计具有一定的参考作用。

基于集体记忆的城市历史文化街区景观重塑策略——以北海老街为例

目前中国历史文化街区的商业化发展迅速,但人们往往容易忽视其历史与文化和谐发展的需求。街区中的人文环境与集体记忆受到一定程度的冲击与破坏,原本丰富多样的文化与生活元素面临消逝的困境。文章以北海老街为例,将集体记忆作为切入点,分别从文化记忆、空间记忆以及生活记忆3个方面进行研究,提出在地文化与地理特征的有效结合以及“市井生活”的场景再现等设计策略,以此促进老街街巷空间的景观特色发展,并实现历史文化街区集体记忆的有效延续。

长大引水隧洞富水段综合灌浆防水技术

结合引绰济辽输水工程引水隧洞富水段工程案例,介绍了掌子面超前高压灌浆、地表高压灌浆和新型聚氨酯灌浆材料(OPU)封堵隧洞出水点等综合阻水方式,对涌水点进行封堵后,掌子面前方及洞身围岩实现有效固结,达到了隧洞涌水治理的目的,阻水、固结效果良好。

新沂河入海泓道分流比变化与海口枢纽下游减淤措施初步研究

针对新沂河海口滩地植被密布、闸上泓道复杂多分汊、口外含沙量大等特点,分析了江苏沿海建闸多分汊河口分流比变化特点及成因,表明南、北深泓分流比较设计值均偏大,中深泓反之,分流比偏离的主要原因是中深泓闸下泓道回淤严重加上芦苇“锚固”作用致使行洪断面面积锐减50%以上,严重限制了中深泓的行洪能力,加之闸上引河及中深泓底高程远高于南深泓和北深泓,导致中深泓汇流阻力大。建立了新沂河二维潮流泥沙数学模型,在水动力和泥沙回淤验证的基础上,预测了泥沙回淤过程,研究了分流比优化措施及闸下减淤效果,可为海口枢纽除险加固与运维提供参考。

踝周神经阻滞麻醉联合“牛鼻子”引流术在糖尿病足清创中的应用效果

目的:研究踝周神经阻滞麻醉联合“牛鼻子”引流术在糖尿病足清创中的应用效果。方法:选取我院收治的糖尿病足患者104例,分为常规清创组(GG组)53例,微创清创组(MG组)51例,比较两组间糖尿病足类型分布以及大、小截肢发生率的差异,比较两组间多个时点在溃疡面积、创面渗出量、VAS疼痛评分及心理量表评分的差别。比较两组间不同时点空腹血糖、白细胞计数(WBC)、高敏C反应蛋白(hs-CRP)、肿瘤坏死因子-α(TNF-α)水平的差异。结果:两组的糖尿病足类型分布均包括缺血型、神经型及混合型,无统计学差异(P>0.05);GG组大截肢发生率高于MG组,差异有统计学意义(P<0.05),而两组小截肢发生率间无明显差别(P>0.05);随着时间推移,MG组创面渗出量、VAS疼痛评分、心理量表评分优于GG组,差异有统计学意义(P<0.05);两组间空腹血糖、WBC、hs-CRP水平,差异无统计学意义(P>0.05),MG组TNF-α水平低于GG组,差异有统计学意义(P<0.05)。结论:采用踝周神经阻滞麻醉方式进行清创术后行“牛鼻子”引流术治疗糖尿病足感染的临床效果良好,值得临床推广应用。

装配式建筑外墙防水设计与施工技术研究

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