Effect of proximal femur nail anti-rotation on unstable intertrochanteric fractures: A prospective observational study

Objective:To assess the effect of proximal femur nail anti-rotation on the functional and radiological outcome of unstable intertrochanteric fractures.Methods:This prospective observational study was conducted in the orthopedic department of a tertiary care hospital.Altogether 86 patients with unstable intertrochanteric fractures treated with proximal femur nail anti-rotation between January 2010 and January 2015 were included.Patients were followed in the outpatient clinic at regular intervals after discharge to assess the radiological union of fractures and complications.The functional outcomes were evaluated after 2 years by Harris hip score.Results:All patients achieved a radiological union of fractures after a mean duration of 24.6 weeks.The follow up showed 23 complications(systemic and local).Eight patients developed urinary tract infections,and three patients developed chest infections,two patients had screw cut-out,one patient had knee stiffness,one patient developed superficial surgical site infection,and four patients developed varus collapse and shortening subsequently.The two year follow up showed that 69(80.2%)patients had an excellent and good functional outcome according to Harris hip score.Conclusions:With lower complication rates,proximal femur nail is a valid and reasonable option especially in treating unstable intertrochanteric fractures.

Comparative efficacy of proximal femoral nail vs dynamic condylar screw in treating unstable intertrochanteric fractures

BACKGROUND Among the most frequent hip fractures are trochanteric fractures,which usually occur from low-energy trauma like minor falls,especially in older people with osteoporotic bones.AIM To evaluate the treatment efficacy of dynamic condylar screws(DCS)and proximal femoral nails(PFN)for unstable intertrochanteric fractures.METHODS To find pertinent randomized controlled trials and retrospective observational studies comparing PFN with DCS for the management of unstable femoral intertrochanteric fractures,a thorough search was carried out.For research studies published between January 1996 and April 2024,PubMed,EMBASE,Scopus,Web of Science,Cochrane Library,and Google Scholar were all searched.The complete texts of the papers were retrieved,vetted,and independently examined by two investigators.Disputes were settled by consensus,and any disagreements that persisted were arbitrated by a third author.RESULTS This study included six articles,comprising a total of 173 patients.Compared to the DCS,the PFN had a shorter operation time[mean difference(MD):-41.7 min,95%confidence interval(95%CI):-63.04 to-20.35,P=0.0001],higher success rates with closed reduction techniques[risk ratio(RR):34.05,95%CI:11.12-104.31,P<0.00001],and required less intraoperative blood transfusion(MD:-1.4 units,95%CI:-1.80 to-1.00,P<0.00001).Additionally,the PFN showed shorter fracture union time(MD:-6.92 wk,95%CI:-10.27 to-3.57,P<0.0001)and a lower incidence of reoperation(RR:0.37,95%CI:0.17-0.82,P=0.01).However,there was no discernible variation regarding hospital stay,implant-related complications,and infections.CONCLUSION Compared to DCS,PFN offers shorter operative times,reduces the blood transfusions requirements,achieves higher closed reduction success,enables faster fracture healing,and lowers reoperation incidence.

Additive manufactured osseointegrated screws with hierarchical design

Bone screws are devices used to fix implants or bones to bones.However,conventional screws are mechanically fixed with thread and often face long-term failure due to poor osseointegration.To improve osseointegration,screws are evolving from solid and smooth to porous and rough.Additive manufacturing(AM)offers a high degree of manufacturing freedom,enabling the preparation of predesigned screws that are porous and rough.This paper provides an overview of the problems currently faced by bone screws:long-term loosening and screw breakage.Next,advances in osseointegrated screws are summarized hierarchically(sub-micro,micro,and macro).At the sub-microscale level,we describe surface-modification techniques for enhancing osseointegration.At the micro level,we summarize the micro-design parameters that affect the mechanical and biological properties of porous osseointegrated screws,including porosity,pore size,and pore shape.In addition,we highlight three promising pore shapes:triply periodic minimal surface,auxetic structure with negative Poisson ratio,and the Voronoi structure.At the macro level,we outline the strategies of graded design,gradient design,and topology optimization design to improve the mechanical strength of porous osseointegrated screws.Simultaneously,this paper outlines advances in AM technology for enhancing the mechanical properties of porous osseointegrated screws.AM osseointegrated screws with hierarchical design are expected to provide excellent long-term fixation and the required mechanical strength.

Biomechanical effects of posterior lumbar interbody fusion with vertical placement of pedicle screws compared to traditional placement

BACKGROUND The pedicle screw technique is widely employed for vertebral body fixation in the treatment of spinal disorders.However,traditional screw placement methods require the dissection of paraspinal muscles and the insertion of pedicle screws at specific transverse section angles(TSA).Larger TSA angles require more force to pull the muscle tissue,which can increase the risk of surgical trauma and ischemic injury to the lumbar muscles.AIM To study the feasibility of zero-degree TSA vertical pedicle screw technique in the lumbosacral segment.METHODS Finite element models of vertebral bodies and pedicle screw-rod systems were established for the L4-S1 spinal segments.A standard axial load of 500 N and a rotational torque of 10 N/m were applied.Simulated screw pull-out experiment was conducted to observe pedicle screw resistance to pull-out,maximum stress,load-displacement ratio,maximum stress in vertebral bodies,load-displacement ratio in vertebral bodies,and the stress distribution in pedicle screws and vertebral bodies.Differences between the 0-degree and 17-degree TSA were compared.RESULTS At 0-degree TSA,the screw pull-out force decreased by 11.35%compared to that at 17-degree TSA(P<0.05).At 0-degree and 17-degree TSA,the stress range in the screw-rod system was 335.1-657.5 MPa and 242.8-648.5 MPa,separately,which were below the fracture threshold for the screw-rod system(924 MPa).At 0-degree and 17-degree TSA,the stress range in the vertebral bodies was 68.45-78.91 MPa and 39.08-72.73 MPa,separately,which were below the typical bone yield stress range for vertebral bodies(110-125 MPa).At 0-degree TSA,the load-displacement ratio for the vertebral bodies and pedicle screws was slightly lower compared to that at 17-degree TSA,indicating slightly lower stability(P<0.05).CONCLUSION The safety and stability of 0-degree TSA are slightly lower,but the risks of screw-rod system fracture,vertebral body fracture,and rupture are within acceptable limits.

Experimental Study on Horizontal Bearing Characteristics of Screw Pile

The horizontal bearing capacity of the screw pile and monopile was analyzed by model tests.Results showed that the horizontal bearing capacity of the screw pile was significantly greater than that of the monopile under the same loading conditions.With the increase in horizontal loading speed,the ultimate horizontal bearing capacity of the two piles also increases,and the difference decreases gradually.Moreover,the influence of vertical loading on the horizontal bearing capacity of screw pile and monopile is studied at the horizontal loading speed of 2 mm s-1.The findings indicate that vertical load evidently affects the horizontal bearing capacity of common piles,but slightly influences the horizontal bearing capacity of screw piles.

Revised in-depth meta-analysis on the efficacy of robot-assisted versus traditional free-hand pedicle screw insertion

Objective:Robot-assisted pedicle screw insertion has recently emerged as an alternative to the traditional free-hand technique.However,discrepancies in the accuracy of screw placement between the 2 methods have been highlighted by some comparative studies.This meta-analysis was conducted to synthesize evidence comparing these techniques.Methods:Searches were conducted in 5 electronic databases adhering to specific eligibility criteria for randomized and observational studies.The data were analyzed using RevMan software and the results are presented as odds ratios(ORs),mean differences,or standard mean differences(SMDs)with 95%confidence intervals(CIs).Our analysis included 12 studies(7 randomized trials and 5 observational studies,involving 883 patients and 4903 screws).Results:The results demonstrated a higher rate of Grade A Gertzbein and Robbins pedicle placement score(OR:1.77;95%CI:1.10e2.87),a lower rate of revision surgeries(OR:0.21;95%CI:0.09e0.52),and a shorter radiation exposure duration(SMD?1.38,95%CI:2.32 to0.44)in the robot-assisted group compared with the free-hand group.Nonetheless,the length of hospital stay,volume of intraoperative blood loss,postoperative visual analogue scale scores for back pain,and rate of wound infection were similar between the 2 groups.Significant heterogeneity was observed in some outcomes.Conclusion:Compared with the free-hand method,the robot-assisted technique provides greater accuracy and reduced radiation exposure.The efficacy of the robot-assisted technique is expected to improve further as experience with its use in surgery grows.

Treatment of long-segment fracture in middle-up part of femoral shaft with long proximal femoral nail anti-rotation of AO/ASIF

Objective To investigate the operative method and evaluate the clinical outcomes of long proximal femoral nail anti-rotation (PFNA-long) in treating long-segment fracture in middle-up part of femoral bone.Methods From June 2006 to

Roller Screw and Threaded Chain Speed Reducer: An Experimental Evaluation

We are developing a speed reducer that can be considered a transformation of a worm gear reducer: the worm is replaced by an inverted roller screw, and the gear is replaced by a threaded chain drive. This configuration lessens wear, increases load capacity, and improves efficiency. The threaded chain consists of nut-shaped links. This paper presents the results of tests carried out on a prototype with a reduction ratio of 46.

Clinical Effectiveness of the Plate Screw Internal Fixation Technique in the Treatment of Patients with Traumatic Fractures of Long Bones in the Lower Extremities

Objective: To investigate the effectiveness of the plate screw internal fixation technique on the clinical outcomes of patients with traumatic fractures of long bones in the lower extremities. Methods: From January 2022 to December 2023, 70 patients with traumatic fractures of long bones in the lower extremities were admitted to the hospital and randomly divided into two groups: the control group and the observation group, each consisting of 35 cases. The control group underwent traditional closed interlocking intramedullary nailing, while the observation group received internal fixation with steel plates and screws. Relevant surgical indicators, treatment effectiveness, and postoperative complication rates were compared between the two groups. Results: The observation group exhibited significantly short surgical duration (80.65 ± 5.01 vs. 88.36 ± 5.26 minutes), fracture healing time (13.27 ± 0.32 vs. 15.52 ± 0.48 weeks), and hospitalization days (10.49 ± 1.13 vs. 16.57 ± 1.15 days) compared to the control group (P = 0.000). The effective treatment rate was significantly higher in the observation group (29/82.86%) than in the control group (21/60.00%), with a significant difference observed (χ2 = 4.480, P = 0.034). Additionally, the complication rate in the observation group (2/5.71%) was significantly lower than that in the control group (8/22.86%), with a correlated difference (χ2 = 4.200, P = 0.040). Conclusion: The plate screw internal fixation technique demonstrates significant clinical efficacy in treating traumatic fractures of long bones in the lower extremities. It improves the healing rate, reduces complications, and represents a safe and effective treatment strategy worthy of widespread use and application.

基于麻雀算法优化神经网络的螺杆砂带磨削去除深度预测

目的准确获得螺杆转子砂带磨削材料去除深度,探究工艺参数对材料去除深度的影响。方法通过分析螺杆转子砂带磨削去除机理,确定材料去除深度影响因素。提出一种基于麻雀算法优化长短时记忆网络-卷积神经网络模型(SSA-CNN-LSTM),对螺杆转子砂带磨削加工中的材料去除深度进行预测。以磨削中影响材料去除深度的因素为输入,磨削深度为输出,构建利用SSA对CNN-LSTM超参数进行寻优的预测模型,并且与CNN-LSTM、LSTM、PSO-BP、RBF以及随机森林预测方法进行对比。结果所提预测方法平均绝对百分比误差MAPE可达0.0461,均方根差RMSE为9.261,平均绝对误差MAE达7.836,确定系数R^(2)为0.9974,相比于未优化CNN-LSTM网络和其他经典网络模型,预测精度更高,能够有效预测螺杆转子磨削材料去除深度。利用提出的模型探究了磨削工艺参数对材料去除深度MRD和材料去除一致性的影响。由预测结果可知,螺杆转子砂带磨削材料去除深度随法向压力、砂带线速度增加而增大,随进给速度、砂带目数增加而减小,且受法向压力影响最明显。通过对磨削前后工件廓形进行分析可知,材料去除深度随磨削区域受到的法向压力呈现中间磨削深度大、两侧逐渐减小的趋势。结论提出的预测模型预测效果显著,分析了工艺参数对磨削材料去除深度和去除一致性的影响规律,可为其他类型的加工轮廓预测提供参考。

钉合木-混凝土组合楼板浅槽型连接件抗剪性能试验

钉合木(NLT)是一种不使用胶黏剂的结构材,具有环保、加工快捷等优点,可用于木结构建筑的楼板、屋面板等。将混凝土板设置在钉合木楼板上方,并通过剪力连接件将二者组合,可以提高原钉合木楼板的结构性能。本文提出适用于钉合木-混凝土组合楼板的浅槽型连接件,并基于推出试验开展浅槽型连接的抗剪性能研究。试验参数主要包括开槽宽度、螺钉倾斜角度和螺钉尺寸,其中,开槽宽度设置为100和200 mm;螺钉倾斜角度设置为垂直和交叉45°;螺钉尺寸主要考虑螺钉直径和锚固深度的影响。基于试验结果分析上述因素对浅槽型连接承载力、抗剪刚度和延性的影响。结果表明:采用交叉斜螺钉代替垂直螺钉、增大螺钉的直径和锚固深度均可提高浅槽型连接的抗剪性能;开槽宽度对浅槽型连接的抗剪承载力和滑移刚度影响较为显著。

开口式移动螺旋输送关键参数的研究

封闭式螺旋输送设备产量计算公式不适应于开口式移动螺旋输送机,因此,针对螺旋输送的机壳开口角度、移速、螺旋直径和转速等关键参数进行研究。首先从原理着手分析开口式移动螺旋的输送机理,后用EDEM对开口式移动螺旋输送的过程进行了离散元仿真,从而验证理论是否可靠。由原理获得开口式螺旋输送产量与机壳开口角度、移速、螺旋直径以及转速等参数的数值关系,分析得到几个关键参数对开口螺旋输送量的显著性和影响趋势。从理论与仿真结果的对比来看,两者较为吻合,理论结果较为可靠,研究为开口螺旋输送的设计提供理论依据。

股骨颈骨折空心螺钉内固定术后供养血管注射富血小板血浆效果分析

目的分析股骨颈骨折空心螺钉内固定术后供养血管注射富血小板血浆(PRP)的临床效果。方法选取2019年6月至2021年6月郑州人民医院收治的106例股骨颈骨折患者作为研究对象,按照空心螺钉内固定术后供养血管是否注射PRP将其分为试验组(53例)和对照组(53例)。试验组患者空心螺钉内固定术后于供养血管注射PRP,对照组患者空心螺钉内固定术后不做处理,对比观察两组患者围手术期指标、骨折愈合时间、髋关节功能、骨痂生长情况以及不良事件发生情况。结果试验组患者手术时间明显长于对照组(t=16.915,P<0.001),完全负重所需时间、骨折愈合时间均明显短于对照组(t=12.610、8.213,P均<0.001),术中出血量与对照组无明显差异(t=1.685,P=0.095);术后1、3、6个月,试验组患者Harris评分、Fernandez-Esteve骨痂评分均明显高于对照组(术后1个月:t=8.919、6.118,P均<0.001;术后3个月:t=10.951、9.217,P均<0.001;术后6个月:t=7.024、6.937,P均<0.001);试验组患者术后不良事件发生率为9.43%,明显低于对照组患者的不良事件发生率30.19%(χ^(2)=7.185,P=0.007)。结论与单纯采用空心螺钉内固定治疗相比,于空心螺钉内固定术后给予供养血管注射PRP治疗股骨颈骨折,能够有效促进骨痂生长,明显缩短完全负重所需时间及骨折愈合时间,改善髋关节功能,减少股骨头坏死等不良事件的发生,临床应用价值更高。

股骨颈动力交叉钉联合空心钉治疗Pauwels Ⅱ型中青年股骨颈骨折的有限元分析

背景:股骨颈骨折是一种还未被解决的骨折,虽然涌现了空心螺钉、动力髋螺钉及股骨颈动力交叉钉等效果较好的植入物,但对于Pauwels角和剪切力较大的股骨颈骨折的最佳内固定方案尚无定论。目的:采用有限元分析法研究不同置钉位置的股骨颈动力交叉钉联合空心螺钉治疗PauwelsⅡ型中青年股骨颈骨折的生物力学特性。方法:根据提取的志愿者股骨CT数据建立Pauwels角为50°的股骨颈骨折模型,将股骨颈均分为3等分,构建4组模型:A组股骨颈动力交叉钉主钉位于股骨颈中间1/3;B组股骨颈动力交叉钉主钉位于股骨颈下1/3;C组股骨颈动力交叉钉主钉位于股骨颈下1/3+空心螺钉位于股骨颈上1/3;D组股骨颈动力交叉钉主钉位于股骨颈中间偏前内侧1/3+空心螺钉位于股骨颈中间偏后内侧1/3。在1200 N的载荷下测量4组股骨、内固定模型的应力分布及峰值、最大变形情况和骨折断面的应力分布。结果与结论:①通过有限元分析可知,C组的股骨及内固定模型的应力分布及峰值、最大变形情况和骨折断面的应力均小于其余3组;②B组相较于A组有着更小的股骨骨质、内固定物和骨折断面应力和位移,说明股骨颈动力交叉钉头钉放置于股骨颈下1/3比中1/3更稳定;③结果表明,股骨颈动力交叉钉头钉位于股骨颈下1/3联合股骨颈上1/3平行放置螺钉对青壮年PauwelsⅡ型股骨颈骨折具有更好的稳定性,是治疗该类型骨折的有效选择。

Numerical Simulations of Polymer Melt Conveying in Co-Rotating Twin Screw Extruder

The 3 D non isothermal flow of non Newtonian viscous polymer melt in a co rotating twin screw extruder is modeled. The distributions of the velocity, temperature, pressure and the viscous dissipation in the flow domain are presented by using a fluid dynamics analysis package (Polyflow). The numerical results show that the temperatures are high in the intermeshing region and on the screw surface, the maximum pressure and the minimum pressure occur in the intermeshing region, and the flow rate is almost proportional to the screw speed.

颈前路减压融合ROI-C^(TM)自锁系统治疗退行性颈椎病的Meta分析

目的:颈前路减压融合术是治疗退行性颈椎病的经典手术方式,钉板的使用增加了融合率及稳定性的同时,间接导致了邻近椎体退变和术后吞咽困难的发生。文章通过Meta分析方法比较ROI-C^(TM)自锁系统和传统融合器联合钉板内固定治疗退行性颈椎病患者的临床结果和并发症情况,为颈前路减压融合术中内固定方式的选择提供循证学支持。方法:检索中国知网、万方、维普、PubMed、Cochrane Library、Web of Science和Embase数据库,检索关于颈前路减压融合术中应用ROI-C^(TM)自锁系统与融合器联合钉板内固定治疗退行性颈椎病的中英文文献。检索时间范围为各数据库建库至2023年7月。由2名研究者严格按照纳入与排除标准选择文献,采用Cochrane偏倚风险工具对随机对照试验进行质量评价,NOS量表对队列研究进行质量评价。采用RevMan 5.4软件进行Meta分析。结局指标包括手术时间、术中出血量、日本骨科协会(Japanese Orthopaedic Association Scores,JOA)评分、颈椎功能障碍指数、C_(2)-C_(7)Cobb角、融合率、邻近椎体退变发生率、融合器沉降率和吞咽困难发生率。结果:共纳入13项研究,其中回顾性队列研究11项,随机对照试验2项,共1136例患者,ROI-C组569例,融合器联合钉板组567例。Meta分析结果显示:ROI-C组与融合器联合钉板组在手术时间(MD=-15.52,95%CI:-18.62至-12.42,P<0.00001),术中出血量(MD=-24.53,95%CI:-32.46至-16.61,P<0.00001),术后邻近节段退变率(RR=0.40,95%CI:0.27-0.60,P<0.00001)和术后总吞咽困难发生率(RR=0.18,95%CI:0.13-0.26,P<0.00001)均具有显著性差异。两者在术后JOA评分、颈椎功能障碍指数、C_(2)-C_(7)Cobb角、融合率和融合器沉降率方面无显著性差异(P≥0.05)。结论:在颈椎前路减压融合术中应用ROI-C^(TM)自锁系统与传统融合器联合钉板内固定治疗退行性颈椎病均可达到满意的临床效果,ROI-C^(TM)自锁系统操作更加简单,相比融合器联合钉板内固定能明显减少手术时间及术中出血量,在减少术后吞咽困难及邻近节段退变发生率等方面具有明显优势,对于跳跃型颈椎病及邻椎病翻修患者,更加推荐使用ROI-C^(TM)自锁系统。但鉴于其可能存在较高的沉降率,对于多节段且合并融合器沉降高危因素如骨质疏松、椎体终板破损的退行性颈椎病患者,仍建议使用融合器联合钉板内固定。

机器学习预测肱骨近端骨折钢板内固定后继发性螺钉切出的风险

背景:继发性螺钉切出关节面是肱骨近端骨折锁定钢板内固定术后的主要并发症之一,切出的螺钉会磨损关节盂和引起肩峰撞击,影响肩关节功能。因此,准确的风险预测有积极的临床意义。目的:通过机器学习方法筛选肱骨近端骨折钢板内固定后继发性螺钉切出的风险因素,开发并验证风险预测模型,便于临床医生早期甄别并干预高风险患者。方法:收集2013年6月至2022年6月接受锁定钢板内固定治疗的214例肱骨近端骨折患者的临床资料作为训练组建立模型,将同一时间段另一医院收治的同类患者61例纳入外部验证组。按照患者术后是否出现继发性螺钉切出,分为螺钉切出组和螺钉维持组。训练组利用随机森林、支持向量机、逻辑回归3种机器学习算法构建预测模型;采用递归特征消除法、10折交叉验证重抽样作为变量的筛选方法,并将3种模型准确度最高时纳入变量的交集作为与螺钉切出高度相关的可靠风险变量。通过R语言软件构建动态预测模型,以网页计算器形式展示,并对模型进行内、外部验证。模型内部检验采用Bootstrap法重抽样1000次,使用受试者工作特征曲线下面积、校准曲线、临床决策曲线评价模型的区分度、校准能力及临床应用价值。通过Youden指数确定预测模型的最佳风险分界值,据此将外部验证组患者分为高、低风险组,根据模型风险预测能力的准确度来评价其稳定性和外延性。结果与结论:①机器学习算法筛选出继发性螺钉切出高度相关的4个风险变量,分别为肱骨近端内侧柱皮质支撑、三角肌结节指数、骨折类型及术后复位情况;②构建的风险预测模型表现出良好的区分度和准确度[曲线下面积=0.874,95%置信区间(0.827,0.922)],校准曲线显示模型预测风险和实际发生风险有较好的一致性;③临床决策曲线提示风险阈值概率在0.1-0.75范围内时,模型具有较好的临床适用性;④风险概率为26%是模型风险分层的最佳阈值,外部验证组利用模型风险分层预测螺钉切出的总正确率为84%;⑤结果说明该风险预测模型准确度和外延性较好,可为指导临床治疗提供依据。

斜外侧腰椎椎间融合联合经皮椎弓根钉内固定后前凸角与融合器沉降的关系

背景:随着医疗技术的不断进步,斜外侧腰椎椎间融合联合经皮椎弓根钉内固定已成为治疗腰椎退行性疾病的一种常用方法,然而关于术后不同节段前凸角变化与融合器沉降之间的关系尚缺乏深入研究。目的:探究斜外侧腰椎椎间融合联合经皮椎弓根钉固定后不同节段前凸角变化与融合器沉降的关系。方法:选择2019年2月至2023年4月于潍坊市中医院行斜外侧腰椎椎间融合联合经皮椎弓根钉固定治疗的腰椎退行性疾病患者93例为研究对象,根据术后椎间隙高度丢失值,分为融合器沉降组(25例,≥2 mm)和非融合器沉降组(68例,<2 mm)。采用多因素Logistic回归法分析融合器沉降的危险因素,应用逐步回归法评估各危险因素与融合器沉降的关系,构建风险预测模型并评价。结果与结论:①最终校正混杂因素后,腰椎前凸角丢失值和节段前凸角改善值均与融合器沉降风险仍存在独立相关性(P<0.05);②年龄、Oswestry功能障碍指数、椎间隙高度改善值、节段前凸角改善值以及腰椎前凸角丢失值,均是融合器沉降发生的独立影响因素(P<0.05),其中年龄、腰椎前凸角丢失值、椎间隙高度改善值和节段前凸角改善值与融合器沉降关联最紧密;③多元Logistic回归模型分析结果显示,当P=0.80时,约登指数最高,预测效果最好,准确度为89.27%,灵敏度为86.67%,特异度为89.89%;模型评价结果显示,其区分度较好、准确度较高;④随着腰椎前凸角丢失值和节段前凸角改善值升高,融合器沉降风险增加,影响临床疗效;⑤提示年龄、腰椎前凸角丢失值、椎间隙高度改善值和节段前凸角改善值与融合器沉降关联最紧密,临床医生应多加关注。

螺牙高度对螺纹桩竖向承载特性的影响

为探明竖向荷载作用下螺牙高度对螺纹桩承载特性及桩周土体的影响,通过室内半面模型桩试验,结合数字图像相关技术(DIC),研究了不同螺牙高度、不同荷载条件对桩身承载性能、桩周土体破坏特征、桩周土体位移场的影响。采用ABAQUS数值模拟方法对模型试验的结果进行验证,并扩展了螺牙高度的取值范围,分析螺纹桩桩身极限承载力与材料利用率、桩周土体应力场分布随螺牙高度变化的规律。结果表明:增加螺牙高度能提升桩身承载力,增大桩周土体位移影响范围,延缓桩侧土体剪切破坏的发展;随着桩身沉降量增加,桩顶荷载以桩侧阻力承受为主,逐渐演变为以桩端阻力承受为主;螺牙高度的增加虽然能提升桩身极限承载力,但桩身材料利用率存在峰值。

双螺杆捏合方式制备的三基发射药的流变性研究

为掌握三基发射药连续化捏合工艺中药料的流变特性,提高工艺模型的准确性,按照三基发射药代料配方制备了预混药料,使用双螺杆挤出机对预混药料进行捏合,并通过专用双料筒毛细管流变仪测试捏合后药料的流变特性。分别改变双螺杆挤出机的螺杆转速和捏合温度、药料的固含量和溶剂比,分析以上变量对三基发射药流变学参数的影响规律。结果表明:双螺杆捏合后,药料的本构方程与Carreau-Yasuda本构模型拟合程度较高;一定范围内,螺杆转速或捏合温度的提高会使捏合后的药料的剪切黏度降低;同时,螺杆转速的提高会使药料的停留时间减少,而过短的停留时间会导致捏合后的药料的黏度上升;固含量的增加或溶剂比的减小会使捏合后的药料的剪切黏度增大,而黏度增大会使药料的停留时间增长,一定程度上使药料受到更充分的捏合作用。