Spiral effect of helical carbon nanorods boosting electrocatalysis of oxygen reduction reaction

Helical metal-organic frameworks(MOFs)were used as templates or precursors to fabricate helical carbon nanorods(HCNRs)for the first time.Helical carbon contains many topological defects such as pentagonal or heptagonal carbons,which have the potential to facilitate oxygen reduction reactions(ORR).HCNRs show more positive onset/halfwave reduction potentials and higher limited current density than straight carbon nanorods(SCNRs).They also exhibit four-electron oxygen reduction in tests of ORR,while the alternative SCNRs prefer a two-electron reduction mechanism.Experimental and theoretical studies reveal that these enhanced ORR activities can be attributed to pentagon/heptagon defects in HCNRs.This work provides an effective strategy to synthesize helical,defect-rich carbon materials and opens up a new perspective for utilization of a spiral effect for the development of more effective electrocatalysts.

Numerical Analysis of a Spiral-groove Dry-gas Seal Considering Micro-scale Effects

A dry-gas seal system is a non-contact seal technology that is widely used in different industrial applications.Spiral-groove dry-gas seal utilizes fluid dynamic pressure effects to realize the seal and lubrication processes,while forming a high pressure gas film between two sealing faces due to the deceleration of the gas pumped in or out.There is little research into the effects and the influence on seal performance,if the grooves and the gas film are at the micro-scale.This paper investigates the micro-scale effects on spiral-groove dry-gas seal performance in a numerical solution of a corrected Reynolds equation.The Reynolds equation is discretized by means of the finite difference method with the second order scheme and solved by the successive-over-relaxation（SOR） iterative method.The Knudsen number of the flow in the sealing gas film is changed from 0.005 to 0.120 with a variation of film depth and sealing pressure.The numerical results show that the average pressure in the gas film and the sealed gas leakage increase due to micro-scale effects.The open force is enlarged,while the gas film stiffness is significantly decreased due to micro-scale effects.The friction torque and power consumption remain constant,even in low sealing pressure and spin speed conditions.In this paper,the seal performance at different rotor face spin speeds is also described.The proposed research clarifies the micro-scale effects in a spiral-groove dry-gas seal and their influence on seal performance,which is expected to be useful for the improvement of the design of dry-gas seal systems operating in the slip flow regime.

CONTRACTED EFFECT OF BELL-SHADE SHAPE WELDING ARC AND ACCOMPANIED MAGNETIC FIELD WITH SPIRAL PIPE SHAPE

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Effects of Strong Turbulence on the Spiral Plane Mode of Whittaker-Gaussian Beam through Terrene-Atmosphere

The analytic formulae of probability distribution of spiral plane modes for the Whittaker-Gaussian （WG） beams with orbital angular momentum （OAM） in strong turbulence regime are modeled based on the modified Rytov approximation. Numerical results show that the erosstalk range of OAM modes in the vicinity of signal mode increases with the increasing refractive-index construction parameter. However, effects of change of the width of the Gaussian envelope and the parameter Wo of WG beams on normalization energy weight of signal mode can be ignored. We find theoretically that signal spiral plane mode of WG beams at each OAM level approximatively has the same normalization energy weight, implying that the channels with WG （pseudo non-diffraction） beam have higher channel capacity than the channels with the Laguerre-Gaussian beam.

The coupling effect of air-bridges on broadband spiral inductors in SiC-based MMIC technology

The coupling effect of air-bridges on broadband spiral inductors in SiC-based MMIC technology has been investigated deeply. The fabricated 1-nH spiral inductor on SiC substrate demonstrates a self-resonant frequency of 51.6 GHz, with a peak Q-fact of 12.14 at 22.1 GHz. From the S-parameters measurements, the exponential decay phenomenon is observed for L, Q-factor, and SRF with the air-bridge height decreasing, and an analytic expression is concluded to exactly fit the measured data which can be used to predict the performance of the spiral inductor. All the coefficients in the formula have specific meaning. By means of establishing the lumped model, the parasitic coupling capacitance of the air-bridge has been extracted and presents the exponential decay with the air-bridge heights decreasing which indicates that this capacitor is directly related to the coupling effect of the air-bridge. Through the electromagnetic field distribution simulation, the details of the electric field around the air-bridge have been presented which demonstrate the formation and the variation principles of the coupling effect.

Finite element synthesized analysis of the forming process of spiral welded pipe

Numerical simulation concerning the forming and welding process of spiral welded pipe was conducted, which included three steps ： the first step was the stress analysis when the spiral was formed, and then the stress was regarded as initial condition of melding during the temperature field analysis in the process of welding, the last step was the thermal stress analysis of the weld seam after the welding was over. Moreover, when the steel strip was pushed, the stress was also calculated by non-linearity contact technology using Abaqus Software. By finite element modeling and calculating of the forming and welding process of the spiral welded pipe, the key points of the multi-fields synthetic simulating were studied and discussed.

Simplified Model of a Layer of Interconnects under a Spiral Inductor

An empirical effective medium approximation that provides a homogeneous equivalent for a layer of interconnects un-derneath a spiral inductor is presented. When used as part of a numerical 3D model of the inductor, this approach yields a faster simulation that uses less memory, yet still predicts the quality factor and inductance to within 1%. We expect this technique to find use in the electromagnetic modeling of System-on-Chip.

Flow Dynamics of a Spiral-groove Dry-gas Seal

The dry-gas seal has been widely used in different industries. With increased spin speed of the rotator shaft, turbulence occurs in the gas film between the stator and rotor seal faces. For the micro-scale flow in the gas film and grooves, turbulence can change the pressure distribution of the gas film. Hence, the seal performance is influenced. However, turbulence effects and methods for their evaluation are not considered in the existing industrial designs of dry-gas seal. The present paper numerically obtains the turbulent flow fields of a spiral-groove dry-gas seal to analyze turbulence effects on seal performance. The direct numerical simulation （DNS） and Reynolds-averaged Navier-Stokes （RANS） methods are utilized to predict the velocity field properties in the grooves and gas film. The key performance parameter, open force, is obtained by integrating the pressure distribution, and the obtained result is in good agreement with the experimental data of other researchers. Very large velocity gradients are found in the sealing gas film because of the geometrical effects of the grooves. Considering turbulence effects, the calculation results show that both the gas film pressure and open force decrease. The RANS method underestimates the performance, compared with the DNS. The solution of the conventional Reynolds lubrication equation without turbulence effects suffers from significant calculation errors and a small application scope. The present study helps elucidate the physical mechanism of the hydrodynamic effects of grooves for improving and optimizing the industrial design or seal face pattern of a dry-gas seal.

Experimental Study &Heat Transfer Analysis on Copper Spiral Heat Exchanger Using Water Based SiO₂Nanofluid as Coolant

Heat exchangers have its major application in automobile, air condition, refrigerator, power plants, and many others. Heat transfer characteristics and performance of Copper spiral heat exchanger are investigated and compared with pure water. Nanofluid can enhance thermos-physical properties. Experiment is carried out for water based SiO2 Nanofluid with 15 nm average sized nanoparticle at varying air velocity and mass flow rate of fluid to investigate its effect on heat transfer coefficient. From the experimental data, a closed form solution for Nusselt number has been calculated using ∈-NTU method. A new correlation has been proposed as a function of Reynolds number and Prandtl number. The heat transfer rate, effectiveness, has been significantly higher compared to pure water and with increasing volume fraction of nanoparticles.

Geostrophic Spirals Generated by the Horizontal Diffusion of Vortex Stretching in the Yellow Sea

Horizontal velocity spirals with a clockwise rotation(downward looking) rate of 1.7?m^(-1), on average, were observed in the western and northern Yellow Sea from December 2006 to February 2007. With the observed thermal wind relation,the beta-spiral theory was used to explain the dynamics of spirals. It was found that the horizontal diffusion of geostrophic vortex stretching is likely to be a major mechanism for generating geostrophic spirals. Vertical advection associated with surface/bottom Ekman pumping and topography-induced upwelling is too weak to support these spirals. Strong wind stirring and large heat loss in wintertime lead to weak stratification and diminish the effects of vertical advection. The cooling effect and vertical diffusion are offset by an overwhelming contribution of horizontal diffusion in connection with vortex stretching. The Richardson number-dependent vertical eddy diffusivity reaches a magnitude of 10^(-4) m^2 s^(-1) on average. An eddy diffusivity of 2870 m^2 s^(-1) is required for dynamic balance by estimating the residual term. This obtained value of 10-4 m^2 s^(-1) is in good agreement with the estimation in terms of observed eddy activities. The suppressed and unsuppressed diffusivities in the observation region are 2752 and 2881 m^2 s^(-1), respectively, which supports a closed budget for velocity rotation.

早期矫治在青少年下颌后缩畸形中的效果观察及对美学效果的影响研究

目的探讨螺旋扩弓器联合Twin-block矫治器早期矫治在青少年下颌后缩畸形中的效果观察及对美学效果的影响研究。方法将河南大学赛思口腔医院2021年1月至2022年1月收治的65例青少年下颌后缩畸形患者,按照随机数字表法分为两组,对照组33例、观察组32例,对照组早期给予Twin-block矫治器治疗,观察组早期给予螺旋扩弓器联合Twin-block矫治器矫治治疗,比较两组颌面部形态指标、面部美容指标、牙齿咬合力及咀嚼能力。结果矫治后3个月,观察组蝶胺中心-鼻根点-上牙槽座点角(SNA)、蝶鞍中心-鼻根点-下牙槽座点角(SNB)、上牙槽座点-鼻根点-下牙槽座点角(ANB)、下面高(ANS-Me)、上面高(N-ANS)、全面高(N-Me)改善情况均优于对照组(P<0.05);矫治后3个月,观察组上唇角(ALs-FH)、面突角(G-Sn-Pg)、颌沟倾角(Pg B-FH)、颌唇沟角(Li-b-Pos)的改善情况均优于对照组(P<0.05);矫治后3个月,观察组牙齿咬合力、咀嚼能力均优于对照组(P<0.05)。结论螺旋扩弓器联合Twin-block矫治器早期矫治可以有效改善青少年下颌后缩畸形患者的面部形态,提高面部美学效果,改善牙齿咬合力和咀嚼功能。

基于涡旋高斯光束的自成像效应数值实验

涡旋光束的传输动力学行为是光学领域研究的热点之一。该文采用理论分析与数值模拟相结合的方法,研究了经典光学涡旋、非对称幂指数光学涡旋和对称幂指数光学涡旋三类不同涡旋高斯光束的传输行为。结果表明,在自由空间中三类光学涡旋高斯光束均可产生整数、分数自成像效应,其自成像距离与无光学涡旋高斯光束产生的自成像现象的复现距离一致。自成像平面上光场结构由一系列周期性阵列光束构成,其光强分布与涡旋相位的拓扑荷数和幂指数阶数密切相关。对于所施加的三类光学涡旋,阵列波束表现出了圆环、螺旋及花瓣型三类不同的光场分布,但是其相位分布基本保持不变。该研究为系统认识周期性涡旋光束的演化动力学行为,以及获得新颖的结构光束提供了新的思路和方法。

基于DEM的旋钻深松过程仿真及机理研究

为研究旋钻深松机理,提出了土壤颗粒运动速度、颗粒混合度、堆积角、土壤耕作阻力及波动系数及深松功耗等评价指标。结合旋钻三维模型和土壤离散元模型,建立基于离散元的旋钻-土壤模型;选取合理的运动参数,对旋钻深松土壤的过程进行离散元仿真,并分析其深松效果及旋钻对土壤的影响;基于控制变量法设计不同耕作深度和不同耕作速度下的9组正交仿真试验,全面评价了深松效果,总结了耕作深度和耕作速度对深松效果的影响规律。研究结果表明:耕作速度对深松效果影响较大,实际工况中在保证打破土壤犁底层的前提下,应尽量选择较低的耕作速度,研究结果可为旋钻深松土壤提供理论依据。

多层螺旋CT与数字化X线摄影对多发肋骨骨折患者的诊断效果分析

目的:探讨多层螺旋CT三维成像(MSCT)与数字化X线摄影(DR)检查对多发肋骨骨折患者的诊断价值。方法:选择2022年1月-2023年11月苏州市中医医院100例疑似多发肋骨骨折患者为研究对象,均实施MSCT、DR检查,以临床诊断结果为对照,分析MSCT、DR的诊断效能。结果:100例疑似患者通过临床综合诊断,其中88例证实为多发肋骨骨折,以此结果作为对照,DR检查真阳、真阴、假阳、假阴例数分别为78、7、5、10例;MSCT检查分别为86、11、1、2例。MSCT的诊断敏感度、准确度分别为97.73%、97.00%,均高于DR的88.64%、85.00%,差异均有统计学意义(P<0.05);两种检查方式的特异度分别为58.33%、91.67%,差异无统计学意义(P>0.05)。结论:多发性肋骨骨折诊断中应用MSCT技术,诊断准确率较高,可得到清晰的影像学图像,且无创安全,方便快捷,为疾病诊治提供可靠依据。

截齿对采煤机装煤效果的影响研究

采煤机螺旋滚筒是截煤和装煤的主要工具,现有装煤效果的研究大多基于滚筒结构参数、运动参数等影响因素进行研究,忽略了截齿对装煤效果的影响。针对该问题,利用离散元分析软件EDEM构建采煤机螺旋滚筒截割煤壁耦合模型,对安装不同截齿的采煤机滚筒的装煤性能进行数值模拟,获取不同截齿下的采煤机滚筒装煤性能差异,以期为提高井下采煤机采煤效率提供必要的技术参考。

块煤防破碎螺旋溜槽技术在新田煤矿的应用

新田煤矿由于井底煤仓内原煤落差大,易导致块煤破碎,造成块煤损失率高。针对新田煤矿煤质特性以及井底煤仓的结构特点,提出在井底煤仓加装防破碎螺旋溜槽的方案,介绍了螺旋溜槽防破碎原理及在新田煤矿的应用效果和取得的技术经济效益。

对比分析MSCT与MR对患者膝关节交叉韧带损伤的诊断效果

目的:探讨分析对膝关节交叉韧带损伤患者采用MR(MR)及多层螺旋CT(MSCT)进行诊断的临床应用效果。方法:选取本院2019年9月-2020年12月收治的90例膝关节较韧带损伤患者为研究对象,全部患者均接受关节镜检查得到确诊,并将确诊结果设为金标准。同时,对患者分别采用MR及MSCT进行诊断,将诊断结果与金标准进行对比,从而确认对患者的诊断准确率。结果:MSCT的诊断准确率与金标准进行对比,差异无统计学意义(P>0.05);MR的诊断准确率与金标准进行对比,差异无统计学意义(P>0.05);MSCT的诊断结果与MR的诊断结果对比,差异无统计学意义(P>0.05);MSCT与MR获取的患者膝关节前交叉韧带相关解剖数据比较,差异无统计学意义(P>0.05);MSCT与MR获取的患者膝关节后交叉韧带相关解剖数据比较,差异无统计学意义(P>0.05)。结论:根据本次研究的结果,可以确认对膝关节交叉韧带损伤患者采用MR及MSCT进行诊断的效果均比较理想,可以根据患者的实际情况,选择合适的诊断方式。

膝关节损伤诊断中磁共振成像及多层螺旋CT的诊断比较分析

目的探讨磁共振成像(magnetic resonance imaging,MRI)与多层螺旋CT在膝关节损伤诊断中的效果。方法选择2020年1月—2023年10月丹阳市第三人民医院收治的76例疑似膝关节损伤患者为研究对象,均开展MRI与多层螺旋CT检查,以关节镜检查结果为金标准,评估MRI与多层螺旋CT的诊断效能以及对不同类型损伤的诊断符合率。结果经关节镜检查,76例患者确诊阳性59例、阴性17例。MRI对膝关节损伤诊断的准确度为97.37%(74/76)、灵敏度为98.30%(58/59),均高于多层螺旋CT的84.21%(64/76)、84.74%(50/59),差异有统计学意义(χ^(2)=10.000、6.125,P均<0.05)。两种检查方法的特异度比较,差异无统计学意义(P>0.05)。两种检查方法对关节腔积液、骨折诊断符合率比较,差异无统计学意义(P均>0.05)。MRI对半月板损伤及韧带损伤诊断符合率高于多层螺旋CT%,差异有统计学意义(P均<0.05)。结论MRI检查对膝关节损伤的诊断效能高于多层螺旋CT,且在半月板损伤及韧带损伤的诊断上,MRI更具有优势。

超高速干气密封微织构气膜润滑特性研究

针对航天航空领域,设备超高速、高压运转,干气密封稳定性问题,依据槽型织构优化设计,提出一种槽底微织构螺旋槽干气密封结构,以解决密封在超高速旋转过程中气膜稳定性问题。基于气体润滑理论,建模、划分网格,再导入FLUENT软件对流场进行仿真模拟;改变工况参数和槽型结构参数后,在超高速、高压工况下,相比于普通螺旋槽,槽底微织构螺旋槽干气密封的动压效果有显著提升。结果表明,槽深h_(g)=6μm,膜厚h_(0)=2μm,微织构槽深δ=2μm、微织构槽宽取3.97 mm,微织构槽位于螺旋槽底中间位置时,槽底微织构螺旋槽相比于普通螺旋槽可产生明显的动压效应。

脑梗死出血性转化的多层螺旋CT表现及相关危险因素分析

目的研究脑梗死出血性转化的多层螺旋CT表现并针对出血转化的相关危险因素进行分析。方法选取2021年10月—2023年6月在本院接受治疗的脑梗死患者97例,根据是否出血将所有患者分为出血转化组(n=23)和非出血转化组(n=74)。本研究对所有患者均实施多层螺旋CT检查,分析CT诊断效能、影像学表现及脑梗死出血转化性危险因素。结果多层螺旋CT在脑梗死出血性转化中的诊断敏感度为86.96%、特异度为86.49%、准确度为86.60%,阳性预测值为66.67%,阴性预测值为95.52%。脑梗死出血性转化组与非出血转化组患者在性别、BMI、缺血再灌注时间以及高血压、冠心病、糖尿病、高血脂、脑卒中史、吸烟构成比方面的差异不明显,无统计学意义(P>0.05);两组患者在年龄、NIHSS评分及梗死面积方面的差异显著,具有统计学意义(P<0.05)。多因素Logistic回归分析结果表明年龄、NIHSS评分及梗死面积为脑梗死出血性转化的危险因素(P<0.05),年龄>60岁患者、NIHSS评分≥21分及梗死面积≥40mm^(2)可使脑梗死患者出血转化的风险升高。结论多层螺旋CT在脑梗死出血性转化中的诊断效能较高,可为临床诊断脑梗死出血性转化提供指导,年龄、NIHSS及梗死面积为脑梗死出血性转化危险因素。