Effects of the initiation position on the damage and fracture characteristics of linear-charge blasting in rock

To study the effects of the initiation position on the damage and fracture characteristics of linear-charge blasting, blasting model experiments were conducted in this study using computed tomography scanning and three-dimensional reconstruction methods. The fractal damage theory was used to quantify the crack distribution and damage degree of sandstone specimens after blasting. The results showed that regardless of an inverse or top initiation, due to compression deformation and sliding frictional resistance, the plugging medium of the borehole is effective. The energy of the explosive gas near the top of the borehole is consumed. This affects the effective crushing of rocks near the top of the borehole, where the extent of damage to Sections Ⅰ and Ⅱ is less than that of Sections Ⅲ and Ⅳ. In addition, the analysis revealed that under conditions of top initiation, the reflected tensile damage of the rock at the free face of the top of the borehole and the compression deformation of the plug and friction consume more blasting energy, resulting in lower blasting energy efficiency for top initiation. As a result, the overall damage degree of the specimens in the top-initiation group was significantly smaller than that in the inverse-initiation group. Under conditions of inverse initiation, the blasting energy efficiency is greater, causing the specimen to experience greater damage. Therefore, in the engineering practice of rock tunnel cut blasting, to utilize blasting energy effectively and enhance the effects of rock fragmentation, using the inverse-initiation method is recommended. In addition, in three-dimensional(3D) rock blasting, the bottom of the borehole has obvious end effects under the conditions of inverse initiation, and the crack distribution at the bottom of the borehole is trumpet-shaped. The occurrence of an end effect in the 3D linear-charge blasting model experiment is related to the initiation position and the blocking condition.

Three-dimensional positions of scattering centers reconstruction from multiple SAR images based on radargrammetry

A method and procedure is presented to reconstruct three-dimensional(3D) positions of scattering centers from multiple synthetic aperture radar(SAR) images. Firstly, two-dimensional(2D) attribute scattering centers of targets are extracted from 2D SAR images. Secondly, similarity measure is developed based on 2D attributed scatter centers' location, type, and radargrammetry principle between multiple SAR images. By this similarity, we can associate 2D scatter centers and then obtain candidate 3D scattering centers. Thirdly, these candidate scattering centers are clustered in 3D space to reconstruct final 3D positions. Compared with presented methods, the proposed method has a capability of describing distributed scattering center, reduces false and missing 3D scattering centers, and has fewer restrictionson modeling data. Finally, results of experiments have demonstrated the effectiveness of the proposed method.

New Three-Dimensional Assessment Model and Optimization of Acoustic Positioning System

This paper addresses the problem of assessing and optimizing the acoustic positioning system for underwater target localization with range measurement.We present a new three-dimensional assessment model to evaluate the optimal geometric beacon formation whether meets user requirements.For mathematical tractability,it is assumed that the measurements of the range between the target and beacons are corrupted with white Gaussian noise with variance,which is distance-dependent.Then,the relationship between DOP parameters and positioning accuracy can be derived by adopting dilution of precision(DOP)parameters in the assessment model.In addition,the optimal geometric beacon formation yielding the best performance can be achieved via minimizing the values of geometric dilution of precision(GDOP)in the case where the target position is known and fixed.Next,in order to ensure that the estimated positioning accuracy on the region of interest satisfies the precision required by the user,geometric positioning accuracy(GPA),horizontal positioning accuracy(HPA)and vertical positioning accuracy(VPA)are utilized to assess the optimal geometric beacon formation.Simulation examples are designed to illustrate the exactness of the conclusion.Unlike other work that only uses GDOP to optimize the formation and cannot assess the performance of the specified size,this new three-dimensional assessment model can evaluate the optimal geometric beacon formation for each dimension of any point in three-dimensional space,which can provide guidance to optimize the performance of each specified dimension.

HY-PC:Enabling Consistent Positioning and Communication Using Visible Light

Visible light(VL)plays an important role in achieving high-precision positioning and low bit error radio(BER)data communication.However,most VL-based systems can not achieve positioning and communication,simultaneously.There are two problems:1)the hybrid systems are difficult to extract distinguishable positioning beacon features without affecting communication performance,2)in the hybrid systems,the lost data bits in the inter-frame gap(IFG)are hard to recover,which affects positioning and communication performance.Therefore,in this article,we propose a novel VL-based hybrid positioning and communication system,named HY-PC system,to solve the above problems.First,we propose the robust T-W mapping for recognizing specific Light Emitting Diodes(LEDs),which can provide stable LED recognition accuracy without adding extra beacon data and does not decrease the communication rate.Furthermore,we also propose the novel linear block coding and bit interleaving mechanism,which can recover the lost data bits in the IFG and improve data communication performance.Finally,we use commercial off-the-shelf devices to implement our HY-PC system,extensive experimental results show that our HY-PC system can achieve consistent high-precision positioning and low-BER data communication,simultaneously.

Integration system research and development for three-dimensional laser scanning information visualization in goaf

An integration processing system of three-dimensional laser scanning information visualization in goaf was developed. It is provided with multiple functions, such as laser scanning information management for goaf, cloud data de-noising optimization, construction, display and operation of three-dimensional model, model editing, profile generation, calculation of goaf volume and roof area, Boolean calculation among models and interaction with the third party soft ware. Concerning this system with a concise interface, plentiful data input/output interfaces, it is featured with high integration, simple and convenient operations of applications. According to practice, in addition to being well-adapted, this system is favorably reliable and stable.

Undrained Stability Analysis of Three-Dimensional Rectangular Trapdoor in Clay

A new collapse model of the trapdoors,three-dimensional rectangular trapdoor(3DRT),is presented for ground surface collapse.Undrained stability of 3DRT is examined with the upper bound method of plasticity limit analysis theory.The soil where the trapdoors are located is assumed to be a perfectly plastic model with a Tresca yield criterion.Block analysis technique is employed to investigate the collapse of 3DRT.The model is divided into five different block types and added up to ten rigid blocks.According to the law of conservation of energy,the critical stability ratios of 3DRT are obtained through a search proceeding.The results of upper bound solution for 3DRT are given,and three trapdoor models with depth various are discussed during the application in the stability analysis of square trapdoors.The critical stability ratios can be used in the design of underground excavation and support force.

改良Twin-block矫治器对恒牙早期安氏Ⅱ类1分类错[牙合]髁突位置的影响

目的:探讨改良Twin-block矫治器对恒牙早期安氏Ⅱ类1分类错[牙合]患者颞下颌关节位置及形态结构变化的影响。方法:临床选择30例恒牙早期安氏Ⅱ类1分类错[牙合]患者,男女各15例,平均年龄12.2岁,均采用改良Twin-block矫治器进行Ⅰ期矫形治疗,所有患者矫治前后行CBCT扫描,利用QR-NNT软件对原始影像进行3D重建,测量矢状向、冠状向关节间隙大小,分析髁突位置变化;测量髁突内外径、前后径,关节窝宽度、深度,髁突长度,分析关节形态变化。结果:矫治后上颌牙弓宽度增加,改良Twin-block矫治器刺激下颌骨生长,患者双侧磨牙达中性关系,覆[牙合]覆盖明显改善,侧貌趋于直面型。导下颌向前后关节前间隙减小(0.50±0.19)mm(P<0.01),关节上间隙和后间隙分别增大(1.25±1.84)mm(P<0.01)和(1.48±1.60)mm(P<0.01),冠状向关节内间隙增大(0.91±1.92)mm(P<0.05),关节上间隙增大(0.85±1.25)mm(P<0.01),差异有统计学意义;髁突内外径、前后径,髁突长度,关节窝宽度均有所增加,差异有统计学意义,关节窝深度减小,差异无统计学意义。结论:改良Twin-block矫治器矫治安氏Ⅱ类1分类患者解除了上颌牙弓狭窄对下颌的限制,髁突在关节窝内向前向下移位,充分利用了恒牙早期生长潜力,促进下颌骨生长发育,随着髁突生长,颞下颌关节发生适应性改建,软硬组织改变,面部比例更加趋于协调,可快速、高效改善面部外形。

Twin-block联合上颌扩弓器矫治下颌后缩儿童前后舌位的改变及上气道的三维变化

目的:观察有口呼吸病史的下颌骨后缩儿童使用Twin-block联合上颌扩弓器矫治后上气道容积的三维变化及舌位改变。方法:选择安氏Ⅱ类伴下颌骨后缩的儿童患者20例,使用Twin-block联合上颌扩弓器进行矫治,将治疗前后的锥形束CT(CBCT)导入Mimics 21.0软件,测量治疗前后上气道(鼻咽段+口咽段)总容积以及鼻咽段、舌咽段、口咽段分段气道容积,舌咽段腭垂尖端处的气道横截面积、最大矢状径,上颌骨宽度。观察治疗前后舌位的高低改变。采用SPSS 26.0软件包对数据进行统计学分析。结果:矫治后,患者上气道总容积及鼻咽、口咽、舌咽段气道容积显著增加(P<0.05);舌咽段腭垂尖端处的气道横截面积及最大矢状径、上颌骨宽度显著增大(P<0.05),舌位升高且前移。结论:Twin-block联合上颌扩弓器可以使安氏Ⅱ类下颌骨后缩儿童鼻咽段、口咽段、舌咽段及上气道总容积增加,对口咽部的前后向深度有扩张作用,使上颌骨宽度增加、舌位趋于正常,有助于气道通畅性提高。

Three-dimensional Information Decoupling System Based on PSD and Deviation Correction

Three-dimensional Information Decoupling System Based on PSD were designed based on LabVIEW, in order to achieve precision, timeliness, reliability require-ments of the PSD used in the ATP system of Satellite Earth quantum communication. Firstly, the laser light source was driven by a stepper motor to scan on the PSD photosensitive surface, and the voltage value was collected and calculated to get the spot position. Analyzing the cause of nonlinear, a mathematical model was built between the actual value and the measured value by using binary quadratic polynomial method, PSD nonlinear correction function would be got. Then, the object micro displacement and angle offset were measured by combining optical triangulation method, and the error of the measurement results was corrected. Experimental results showed that, after the correction, the measuring deviation could be significantly reduced, the PSD performance calibration requirements was achieved, the efficiency of the system was developed greatly by using LabVIEW.

Twin-block矫治器与无托槽隐形矫治器对下颌后缩患者舌骨位置及上气道矢状径的影响比较

目的:探讨Twin-block矫治器与无托槽隐形矫治器对下颌后缩患者舌骨位置及上气道矢状径的影响。方法:采用随机抽样法,选取2018年5月-2020年5月笔者医院80例安氏Ⅱ类1分类错牙合下颌后缩患者。按照随机数字表法分为对照组与研究组,各40例。对照组给予无托槽隐形矫治器治疗,研究组给予Twin-block矫治器治疗。比较两组矫治时间及治疗前后舌骨位置、上气道矢状径及上下颌形态指标变化。结果:研究组矫治时间(8.36±1.13)个月,长于对照组的(7.12±1.02)个月(P<0.05);治疗后,研究组与对照组舌骨位置指标H-NP、H-CVP、H-Or、H-PP、H-MP、H-FH、H-PNS大于治疗前,上气道矢状径指标PNS-Ba、SPP-SPPW、Mc1-Mc2、U-MPW、V-LPW大于治疗前,上下颌形态指标ANB小于治疗前,且SNB、Go-Gn、Ar-Go、髁突内外径大于治疗前(P<0.05);治疗后,研究组H-FH、PNS-Ba、Go-Gn、Ar-Go大于对照组(P<0.05)。结论:安氏Ⅱ类1分类错牙合下颌后缩患者采用Twin-block矫治器、无托槽隐形矫治器治疗均有一定效果,前者改善舌骨位置、上气道矢状径效果更明显,但矫治时间稍长。

不同镇痛方法用于髋部或股骨干骨折患者椎管内麻醉摆放体位时镇痛效果的网状Meta分析

目的采用网状Meta分析系统评价不同镇痛方法用于髋部或股骨干骨折患者椎管内麻醉摆放体位时的镇痛效果。方法计算机检索PubMed、Cochrane Library、Web of Science、EMbase、中国生物医学文献数据库(CBM)、中国知网、维普、万方,检索时间为建库至2022年8月,纳入髋部或股骨干骨折患者摆放体位和椎管内麻醉时实施镇痛的随机对照研究。由两名研究员独立进行文献筛选、资料提取和偏倚风险评价,采用Stata 17.0和RevMan 5.3软件进行统计分析。结果共纳入28篇文献,患者1773例。累计排序概率曲线下面积(SUCRA)显示,降低摆放体位时VAS疼痛评分PENG阻滞(94.4%)效果最佳,其次是FIB联合IVA(83.8%)和FIB(71.1%);降低椎管内麻醉时VAS疼痛评分PENG阻滞(98.2%)效果最佳,其次是FIB(71.1%)和FNB(55.6%);缩短椎管内麻醉操作时间PENG阻滞(84.1%)效果最佳,其次是FNB(70.7%)和FIB(68.5%);升高体位摆放质量评分PENG阻滞(99.1%)效果最佳,其次是FIB(73.1%)和FNB(52.9%)。结论神经阻滞或神经阻滞联合IVA可降低髋部或股骨干骨折患者体位摆放和椎管内麻醉时VAS疼痛评分、缩短麻醉操作时间和升高体位摆放质量评分。PENG阻滞对髋部或股骨干骨折患者摆放体位和椎管内麻醉时实施镇痛的效果最佳。

面向超分辨率重建的层次间局部特征增强网络

基于卷积神经网络的超分辨率重建模型以单项传播为主,层次越靠后感知信息的能力越微弱,导致层次间局部特征部分丢失,难以实质提升网络的特征表达能力。针对此问题,提出层次间局部特征增强网络。该方法由级联残差模块、层次间特征增强块和特征感知注意力机制组成。级联残差模块通过有效残差连接增加对残差分支信息的利用;层次间特征增强块提取不同深度特征的依赖关系,自适应调整中间层特征权值增强捕获关键信息的能力;特征感知注意力机制采用方向感知和位置判断的方式准确定位和识别感兴趣对象。多项标准数据集的实验结果表明,该方法能改善超分辨率的视觉重建效果,整体性能优于现有方法。

艾司氯胺酮对急诊下肢骨折手术患者麻醉前摆放体位时的镇痛效果

目的观察艾司氯胺酮对急诊下肢骨折手术患者麻醉前摆放体位时的镇痛效果。方法选取2021年11月至2022年12月滨州医学院烟台附属医院收治的70例急诊下肢骨折手术患者为研究对象,在组间基线特征可比的原则上,采用随机数字表法分为观察组(麻醉前摆放体位时给予0.25 mg/kg艾司氯胺酮镇痛)和对照组(麻醉前摆放体位时不进行镇痛,给予0.25 mg/kg生理盐水),每组35例。比较分析两组患者进入手术室时(T_(1))、艾司氯胺酮静脉推注10 min后(T_(2))、摆放体位时(T_(3))的疼痛程度以及T_(1)、T_(2)、T_(3)、麻醉平面稳定后5 min(T_(4))的镇静情况。比较分析两组患者的麻醉操作时间、麻醉满意度评分、镇痛泵按压次数以及术后48 h的不良反应发生率。结果T_(1)时刻,两组患者的视觉模拟评分法评分、Ramsay镇静评分比较差异均无统计学意义(P>0.05);T_(2)、T_(3)时刻,观察组患者的视觉模拟评分法评分低于对照组,差异均有统计学意义(P<0.05);T_(2)、T_(3)、T_(4)时刻,观察组患者的Ramsay镇静评分高于对照组,差异均有统计学意义(P<0.05)。观察组患者的麻醉操作时间、镇痛泵按压次数均短于或少于对照组,麻醉满意度评分高于对照组,差异均有统计学意义(P<0.05)。两组患者术后48 h的不良反应发生率比较差异无统计学意义(χ^(2)=0.159,P=0.690)。结论术前应用艾司氯胺酮蛛网膜下腔阻滞可显著减轻急诊下肢骨折手术患者麻醉前摆放体位时的疼痛程度,缩短麻醉操作时间,明显提高患者的麻醉满意度,且安全性较好。

改良Twin-block 治疗颞下颌关节盘可复性前移位

目的探讨改良Twin-block治疗颞下颌关节盘可复性前移位前后关节盘形态和位置的变化。方法将2015年7月~2016年6月就诊于深圳市第二人民医院口腔科,经临床及MRI检查诊断为单侧或双侧颞下颌关节盘可复性前移位,并接受改良Twin-block矫治器进行治疗者19例,共28侧关节纳入研究,治疗前后均拍摄MRI,测量治疗前后关节盘前后径、盘髁距离、盘髁角度并进行配对t检验,对治疗前后的关节盘形态进行Wilcoxon符号秩和检验,P<0.01为差异具有统计学意义。结果 19例患者28侧关节盘均存在可复性前移位,经过改良Twin-block治疗后,24侧关节盘位置恢复正常,4侧关节盘在闭口时仍处于前移位状态。治疗后关节盘前后径增加,盘髁距离、盘髁角度减小,差异均具有统计学意义(P<0.01)。关节盘形态治疗前以V形最多(16侧),其次为双面平滑形(9侧);治疗后以双凹形(16侧)和双面平滑形(10侧)为主;治疗后关节盘形变程度减小,且差异有统计学意义(P<0.01)。4侧关节盘复位失败者,治疗前盘髁距离及盘髁角度相对较大,关节盘形变相对较重。结论改良Twin-block是治疗颞下颌关节盘可复性前移位的一种有效手段,可以使发生移位的关节盘前后径及位置恢复,使关节盘形变减小。但对于关节盘移位及形变程度较重者,其治疗效果可能不理想,还需进一步扩大样本量进行分层研究,并延长随访时间。

REFINEMENTS OF THE NORM OF TWO ORTHOGONAL PROJECTIONS

In this paper,some refinements of norm equalities and inequalities of combination of two orthogonal projections are established.We use certain norm inequalities for positive contraction operator to establish norm inequalities for combination of orthogonal projections on a Hilbert space.Furthermore,we give necessary and sufficient conditions under which the norm of the above combination of o`rthogonal projections attains its optimal value.

钢管半浸装置及输送机构的研究

介绍了半浸式钢管淬火设备中的关键核心部件半浸装置的组成及技术特点,分析了半浸式钢管淬火设备与“旋转+内喷+外淋”淬火设备钢管输送淬火位的区别,提出了半浸装置钢管输送到淬火位过程中存在的问题,在对以往技术经验总结的基础上对半浸装置进行了设计改进,主要是翻料装置由2个工作位增加至4个工作位即淬火位(最低位)、接料位、挡料位和翻料位(最高位),并对接料小斜台的倾斜角度进行重新设计。这样的设计避免了原来从接料小斜台高速滚落的热钢管与旋转装置的支撑轮间的直接撞击,经过翻料装置的缓冲挡料后再被轻轻放至旋转装置的支撑轮上,既减少了热钢管淬火前的表面磕碰伤,又延长了旋转支撑轮的使用寿命,取得了良好的应用效果。

联合自适应LASSO与块稀疏贝叶斯直接定位方法

无源定位中,直接定位方法优势在于适用低信噪比、参数独立等。然而,当辐射源距无源侦测系统较远时,受低信噪比的影响,接收信号模型中存在的部分未知参数会大幅降低算法对于辐射源的定位性能。为了有效地解决该难题,给出了一种联合自适应LASSO先验与块稀疏贝叶斯的辐射源直接定位方法。经由贝叶斯理论构建分层稀疏模型,联合不同的先验分布以赋予信号中元素独立的自适应LASSO,同时探索信号的块结构和块内相关性,联合具有共享稀疏性的不同基站的字典重建过完备字典,实现远距离辐射源定位。仿真结果表明:在远距离下,当快拍数设置较少,信噪比设定较低时,在辐射源定位效果上所提算法显著优于如MUSIC等传统直接定位算法、Laplace先验方法以及块稀疏贝叶斯方法。

彩色多普勒超声显像评估收肌管阻滞导管位置的效果

目的 观察利用彩色多普勒超声显像快速、准确定位收肌管导管位置在全膝关节置换术(TKA)术后恢复中的应用。方法 选择初次进行全身麻醉下单侧TKA的患者60例,男26例,女34例,年龄50~80岁,BMI 18~30 kg/m^(2),ASAⅠ—Ⅲ级。采用随机数字表法将患者分为两组:彩色多普勒超声显像组(CFD组)和水分离技术组(CUG组),每组30例。术后CFD组采用彩色多普勒超声显像确认导管位置,CUG组采用传统局麻药扩散的“水分离”技术判断导管位置。记录收肌管置管时间、置管期间使用局麻药总量,术后4、8、24、48、72 h静息和活动时VAS疼痛评分,镇痛泵总按压次数、补救镇痛情况、术后首次下床活动时间、术后住院时间,穿刺部位水肿、血肿、院内跌倒等术后不良事件发生情况和患者术后满意度评分。结果 与CUG组比较,CFD组置管时间明显缩短、置管期间使用局麻药总量明显减少(P<0.05),术后首次下床活动时间、术后住院时间明显缩短(P<0.05),术后穿刺部位水肿等不良事件发生率明显降低(P<0.05),患者术后满意度评分明显升高(P<0.05)。两组术后不同时点VAS疼痛评分、镇痛泵总按压次数和补救镇痛率、穿刺部位血肿和院内跌倒发生率差异均无统计学意义。结论 在TKA中应用彩色多普勒超声显像准确判断收肌管导管位置,能够实现快速准确放置导管,利于患者早期下床活动,缩短患者术后住院时间,提高患者满意度,促进早期康复。

GPS Block IIF卫星频间钟差偏差分析

使用37个IGS站的实测数据解算了4颗在轨Block IIF卫星(PRN01、PRN24、PRN25、PRN27)的IFCB值并进行特性分析。结果表明,目前所有GPS Blcok IIF卫星三频信号间存在的IFCB量级在cm到dm级;快速解算方法比非差估计方法更加省时高效;12、6、8、4 h的周期组合模型能较好地描述IFCB的变化,精度可达cm级;现有的IFCB计算方法、模型也适用于所有的Block IIF卫星。

2023年欧洲重症医学学会与美国胸科协会急性呼吸窘迫综合征新指南之异同

随着科学研究和临床实践的进展,近5年急性呼吸窘迫综合征(ARDS)的诊治策略取得了长足发展。基于此,2023年欧洲重症医学学会(ESICM)和美国胸科协会(ATS)在2017年ARDS临床实践指南(CPG)的基础上,分别对ARDS治疗策略进行了更新和修订。ESICM新指南从ARDS定义、表型和呼吸支持策略3大主题的9个关键领域提出了21项推荐意见。ATS新指南则在2017 CPG的基础上,纳入了关于糖皮质激素、静脉-静脉体外膜氧合、神经肌肉阻断剂以及呼气末正压应用的新证据,并进行了条件限制性推荐。在特定临床问题的推荐意见上存在差异除外,两者总体上保持一致。该文对ESICM新指南和ATS新指南进行比较分析,以期为在临床实践中进行合理的循证决策提供可靠依据。