基于智能优化的3D mesh微调算法

3D mesh简化是计算机图形学中的关键技术。大多数简化算法旨在权衡被简化3D mesh的占用内存和近似误差,因此很难找到最优的简化3D mesh。为了解决这一问题,文章提出了一种新的3D mesh微调算法。该算法通过调整被简化的3D mesh的点坐标,以搜索具有最小近似误差的简化3D mesh。实验结果表明,设计的微调算法可以进一步减小被简化的3D mesh的近似误差,并缩小被简化3D mesh与原始3D mesh之间的外观差距。

Face recognition using SIFT features under 3D meshes

Expression, occlusion, and pose variations are three main challenges for 3D face recognition. A novel method is presented to address 3D face recognition using scale-invariant feature transform(SIFT) features on 3D meshes. After preprocessing, shape index extrema on the 3D facial surface are selected as keypoints in the difference scale space and the unstable keypoints are removed after two screening steps. Then, a local coordinate system for each keypoint is established by principal component analysis(PCA).Next, two local geometric features are extracted around each keypoint through the local coordinate system. Additionally, the features are augmented by the symmetrization according to the approximate left-right symmetry in human face. The proposed method is evaluated on the Bosphorus, BU-3DFE, and Gavab databases, respectively. Good results are achieved on these three datasets. As a result, the proposed method proves robust to facial expression variations, partial external occlusions and large pose changes.

An Eigen-Normal Approach for 3D Mesh Watermarking Using Support Vector Machines

The use of support vector machines （SVM） for watermarking of 3D mesh models is investigated. SVMs have been widely explored for images, audio, and video watermarking but to date the potential of SVMs has not been explored in the 3D watermarking domain. The proposed approach utilizes SVM as a binary classifier for the selection of vertices for watermark embedding. The SVM is trained with feature vectors derived from the angular difference between the eigen normal and surface normals of a 1-ring neighborhood of vertices taken from normalized 3D mesh models. The SVM learns to classify vertices as appropriate or inappropriate candidates for modification in order to accommodate the watermark. Experimental results verify that the proposed algorithm is imperceptible and robust against attacks such as mesh smoothing, cropping and noise addition.

基于3D Mesh结构的一种静态路由算法

3D NoC在同构多核系统中相比2D NoC具有更为优越的性能。本文在研究3DMesh结构的基础上,对拓扑结构中的平均延时和理想吞吐量进行了理论上的评估,并提出了一种基于3DMesh的新的静态路由算法,最后运用NS2网络仿真软件对其进行仿真和比较。实验结果显示,新的路由算法可以有效地提高吞吐量,并在大规模数据传输时不容易造成阻塞,表现了较好的性能。

Fast ion diffusion alloy layer facilitating 3D mesh substrate for dendrite-free zinc-ion hybrid capacitors

Although aqueous zinc ion hybrid capacitors have advantageous integration of batteries and supercapacitors,they still suffer from the inherent problems of dendrite growth and interfacial side reactions on Zn anodes.Herein,a universal fast zinc-ion diffusion layer on a three-dimensional(3 D)mesh structure model is demonstrated to effectively improve Zn plating/stripping reversibility.The fast ion diffusion alloy layer accelerates the Zn^(2+)migration in an orderly manner to homogenize Zn^(2+)flux and overcomes the defects of the commercial mesh substrate,effectively avoiding dendrite growth and side reactions.Consequently,the proof-of-concept silver-zinc alloy modified stainless steel mesh delivers superb reversibility with the high coulombic efficiency over 99.4%at 4 mA cm^(-2)after 1600 cycles and excellent reliability of over 830 h at 1 mA cm^(-2),Its feasibility is also evidenced in commercial zinc ion hybrid capacitors with activated carbon as the cathode.This work enriches the fundamental comprehension of fast zinc-ion diffusion layer combined with a 3 D substrate on the Zn deposition and opens a universal approach to design advanced host for Zn electrodes in zinc ion hybrid capacitors.

High Efficiency Crypto-Watermarking System Based on Clifford-Multiwavelet for 3D Meshes Security

Since 3D mesh security has become intellectual property,3D watermarking algorithms have continued to appear to secure 3D meshes shared by remote users and saved in distant multimedia databases.The novelty of our approach is that it uses a new Clifford-multiwavelet transform to insert copyright data in a multiresolution domain,allowing us to greatly expand the size of the watermark.After that,our method does two rounds of insertion,each applying a different type of Clifford-wavelet transform.Before being placed into the Clifford-multiwavelet coefficients,the watermark,which is a mixture of the mesh description,source mesh signature(produced using SHA512),and a logo encrypted using the RSA(Ronald Shamir Adleman)technique,is encoded using Turbo-code.Using the Least Significant Bit method steps,data embedding involves modulation and insertion processes.Finally,the watermarked mesh is reconstructed using the inverse Cliffordmultiwavelet transform.Due to the utilization of a hybrid insertion domain,our technique has demonstrated a very high insertion rate while retaining mesh quality.The mesh is watermarked,and the extracted data is acquired in real-time.Our approach is also resistant to the most common types of attacks.Our findings reveal that the current approach improves on previous efforts.

An Experience of Short-Term Results of Laparoscopic Inguinal Hernioplasty Using 3D Mesh in a Developing Country

Background: The experience of short term results of laparoscopic inguinal hernia repair using 3D mesh in a developing country is reviewed. Methods: From January 2012 to February 2014, 53 patients underwent laparoscopic inguinal hernioplasty. A retrospective case series of 53 consecutive patients undergoing TEP/TAPP by a single surgical team was followed prospectively with a focused physical examination and interview. 4 out of 53 patients had recurrent hernia following open repairs and 49 had primary hernias. Data collected included operative time, intraoperative bleeding, intraoperative difficulties, immediate postoperative pain, chronic groin pain, recurrence, sensory disturbance, activity or occupational limitation and personal satisfaction. Results: All the patients were male aged 32 to 75 years with a mean age of 53.5 years. Mean operative time was 37.4 minutes;intraoperative dissection, blood loss were less;and immediate postoperative pain was negligible as assessed by VAS. There was no mortality or major morbidity. Mean follow-up was 12 months (2 to 18 months). Follow-up was completed by interview and physical examination. Hernia was not found to recur during the follow up period. Chronic pain occurred in 2 patients (3.7%), which was mild in nature. Ninety-seven percent of patients were satisfied with their repair and would or had recommended TEP/TAPP to others using 3D Mesh. Conclusions: Short-term results of TEP/TAPP hernia repair using 3D mesh demonstrated to be an effective and safe procedure with low prevalence of chronic pain that is generally of a mild, infrequent nature. It was also concurred that there is decrease in operative time. Manipulation of mesh was significantly reduced. Intraoperative bleeding and use of post operative analgesia was reduced considerably. There was no recurrence, however the cost of the mesh increased the overall cost of the procedure acting as a limiting factor in a developing country.

Securing 3D Point and Mesh Fog Data Using Novel Chaotic Cat Map

With the rapid evolution of Internet technology,fog computing has taken a major role in managing large amounts of data.The major concerns in this domain are security and privacy.Therefore,attaining a reliable level of confidentiality in the fog computing environment is a pivotal task.Among different types of data stored in the fog,the 3D point and mesh fog data are increasingly popular in recent days,due to the growth of 3D modelling and 3D printing technologies.Hence,in this research,we propose a novel scheme for preserving the privacy of 3D point and mesh fog data.Chaotic Cat mapbased data encryption is a recently trending research area due to its unique properties like pseudo-randomness,deterministic nature,sensitivity to initial conditions,ergodicity,etc.To boost encryption efficiency significantly,in this work,we propose a novel Chaotic Cat map.The sequence generated by this map is used to transform the coordinates of the fog data.The improved range of the proposed map is depicted using bifurcation analysis.The quality of the proposed Chaotic Cat map is also analyzed using metrics like Lyapunov exponent and approximate entropy.We also demonstrate the performance of the proposed encryption framework using attacks like brute-force attack and statistical attack.The experimental results clearly depict that the proposed framework produces the best results compared to the previous works in the literature.

Deep 3D mesh watermarking with self-adaptive robustness

Robust 3D mesh watermarking is a traditional research topic in computer graphics,which provides an efficient solution to the copyright protection for 3D meshes.Traditionally,researchers need manually design watermarking algorithms to achieve suffcient robustness for the actual application scenarios.In this paper,we propose the first deep learning-based 3D mesh watermarking network,which can provide a more general framework for this problem.In detail,we propose an end-to-end network,consisting of a watermark embedding sub-network,a watermark extracting sub-network and attack layers.We employ the topology-agnostic graph convolutional network(GCN)as the basic convolution operation,therefore our network is not limited by registered meshes(which share a fixed topology).For the specific application scenario,we can integrate the corresponding attack layers to guarantee adaptive robustness against possible attacks.To ensure the visual quality of watermarked 3D meshes,we design the curvature consistency loss function to constrain the local geometry smoothness of watermarked meshes.Experimental results show that the proposed method can achieve more universal robustness while guaranteeing comparable visual quality.

网孔结构3D打印面料的制备及力学性能研究

为提升3D打印面料的服用性能,探究3D打印面料的组织结构和力学性能的关系,以柔性聚乳酸为材料,通过熔融沉积成形技术制备出3种网孔结构3D打印面料,并对打印面料的拉伸性能、撕破性能及顶破性能进行测试表征。结果表明:3种网孔结构3D打印面料表面平整,无疵点,网孔效果明显,表面无焦黄现象,无脱散现象。3种网孔结构3D打印面料的拉伸性能、撕破性能及顶破性能均与面料网孔中的网格宽度呈正比。当网格宽度相同时,对于纵向断裂强力,菱形组织最小,仿纬平针组织最大;对于横向断裂强力,仿纬平针组织最小,仿平纹组织最大;对于纵向撕破强力,菱形组织最小,仿平纹组织最大;对于横向撕破强力,菱形组织最小,仿纬平针组织最大;对于顶破强力,菱形组织最小,仿纬平针组织最大。

3D网布包覆仪表板乘客侧气囊静态点爆与外观质量的控制措施

3D网布包覆仪表板以其产品轻量化、零件开发周期短、表皮颜色纹理切换自由度高等自身优势,近年来被新能源汽车所青睐,并广泛应用。对这一兴起的新型热压包覆仪表板,进行外观质量的有效控制来满足客户对内饰质量越来越高的需要,便显得尤为重要。

基于3D几何特征深度表达学习的物理系统仿真

针对现有深度学习方法在物理系统仿真中无法处理几何边界与初始条件同时变化的场景的问题,提出将几何边界约束的表达与物理系统仿真解耦的技术思路,设计了几何特征表达学习和物理系统仿真双步骤的技术路线。在构建与外部物理条件无关的几何特征提取模块之后,融合提取的几何特征与物理特征,最后设计基于神经网络的物理系统仿真方法。在应力场预测实验中,所提方法的预测时间为2.63 ms,远低于有限元法(FEM)的0.6 s,且平均绝对误差(MAE)仅为MeshNet的0.389倍。实验结果表明,所提方法能够保持较高仿真精度,同时能够较好地适应不同的几何边界与初始条件。

探讨汽车仪表台3D-Mesh包覆工艺与设计

仪表台是汽车内饰的重要零件,运用3D-Mesh包覆设计可以达到比传统软质仪表台工艺更低的成本和更高的设计自由度。

碳纳米管修饰3D纤维网基压力传感器的制备及性能

为改善纤维基传感器灵敏度低和响应范围窄等问题,提出了一种以3D纤维网为基材,采用超声辅助浸渍碳纳米管修饰纤维表面,构建出了3D纤维网络结构的压阻式压力传感器。介绍了3D纤维网传感器的制备过程,并对所制备的传感器形貌结构、力学传感性能及应用进行了测试与表征。结果表明:碳纳米管修饰3D纤维网的传感器灵敏度为3.53×10^(-3)kPa^(-1),具有较好的线性度和较高的灵敏度;检测范围达到200 kPa;响应时间和回复时间分别为153 ms和226 ms;经过2000次循环施加压力测试表现出较好的稳定性和耐久性。该传感器能够用于监测人体的运动,如手指弯曲、手腕弯曲、手指点击和脚跟压力等,在可穿戴电子织物领域具有广阔的应用前景。

3D打印金属椎体替代物力学性能评价

目的 对钛网及3D打印金属椎体替代物力学性能进行研究,为临床中人工椎体选择与结构优化设计提供指导。方法 通过压缩力学测试,对钛网及3D打印多孔型、桁架型与拓扑型椎体替代物的等效力学属性与结构破坏形式进行系统研究。结果 钛网等效弹性模量[(2 908.73±287.39) MPa]仅次于拓扑型椎体替代物,但其结构强度与稳定性较差,等效屈服强度[(46.61±4.85) MPa]高于多孔型椎体替代物,且在压缩中率先屈服;多孔型椎体替代物结构强度[(18.14±0.17)~(25.79±0.40) MPa]不足,难以满足脊柱重建力学要求;桁架型椎体替代物等效弹性模量[(2 477.86±55.19)~(2 620.08±194.36)MPa]与等效屈服强度[(77.61±0.50)~(88.42±1.07) MPa]良好但稳定性不足,在压缩过程中容易出现失稳现象;拓扑型椎体替代物具有最高的等效弹性模量[(3 746.28±183.80) MPa]与等效屈服强度[(177.43±3.82) MPa],可为人工椎体在体服役安全稳定提供更强保障。结论 拓扑优化方法可实现椎体替代物高强度、高稳定性设计,提供更大的设计空间与安全余量,为人工椎体轻量化与新材料设计提供更多可能。

3D打印个性化钛网辅助下的引导骨再生与块状自体骨移植在复杂牙槽骨缺损重建中的临床回顾性研究

目的拟采用临床回顾性研究的方法,对比3D打印个性化钛网(3D-PITM)辅助下的引导骨再生(guided bone regeneration,GBR)与块状自体骨移植在复杂牙槽骨缺损重建中的骨增量效果。方法纳入2018年5月至2022年1月就诊于重庆医科大学附属口腔医院种植科的39名牙槽骨缺损种植患者,根据其骨增量术式不同分为3D-PITM+GBR组(19名)和自体骨Onlay组(20名)。术前拍摄CBCT影像导入Mimics-Research和3-Matic软件进行三维重建与数字化设计,采用计算机辅助设计(CAD)/激光选区熔融(SLM)技术制作3D-PITM。术中固定3D-PITM或自体骨块完成相应的骨增量手术。收集患者术前、植骨术后、术后6~9个月、种植体植入后的CBCT影像资料。基于CBCT数字影像资料,分别测量两组患者在种植体中轴线上牙槽骨增加的高度,以及在种植体平台下方0 mm、2 mm、4 mm处牙槽骨增加的宽度,并计算其成骨率。结果3D-PITM+GBR组在骨增量前后和种植前后的垂直骨增量[2.68 mm(0.45,4.23)、2.27 mm(0.49,3.27)]均高于块状自体骨移植[1.60 mm(0.33,1.62)、1.74 mm(0.53,1.60)]。3D-PITM+GBR组在骨增量前后牙槽嵴顶下方0 mm、2 mm、4 mm平均骨宽度增量[(1.97±0.97)mm、(2.59±1.22)mm、(2.94±1.50)mm]高于块状自体骨移植[(1.06±0.99)mm、(1.45±1.25)mm、(2.32±1.23)mm]。3D-PITM+GBR组在种植前后种植体平台下方0 mm、2 mm、4mm平均骨宽度增量[(2.34±1.09)mm、(2.53±1.48)mm、(2.85±2.20)mm]反低于块状自体骨移植[(2.51±1.34)mm、(3.04±1.73)mm、(3.38±1.94)mm]。3D-PITM+GBR组在水平方向和垂直方向的成骨率(66.8%,68.8%)均高于块状自体骨Onlay移植组(64.6%,62.6%)。3D-PITM用于重建复杂牙槽骨缺损能够较块状自体骨移植明显提高牙槽骨重建的高度和宽度,但植入物暴露率(21%)仍高于自体骨Onlay组(5%)。结论3D-PITM+GBR技术可代替块状自体骨移植用于重建复杂牙槽骨缺损,获得理想的骨增量效果和稳定的骨轮廓,但钛网暴露仍是其应用的常见并发症。

具有表面微孔的3D打印PCL网状支架的制备及性能

为制备表面具有微孔结构、粗糙度可控、力学性能高的骨组织工程支架,采用不同反应参数组合的NaOH蚀刻处理改善聚己内酯(PCL)网状支架的表面微形貌,解决3D打印PCL网状支架因亲水性差而不利于细胞生长的问题。NaOH处理反应参数组合包括NaOH溶液浓度和处理时间,浓度为0.5,1,5,10,15 mol/L,处理时间为1,6,12,24,48 h。采用扫描电子显微镜、能量色散X射线光谱仪、接触角测量仪、电动液压伺服机械测试机等手段对NaOH处理后支架进行了表征。结果表明,处理后支架主要产生了3种类型的表面形貌:一是温和处理条件下形成的褶皱表面,二是较强处理形成的粗糙表面,三是处理强度进一步增加时形成的凹坑和孔洞。蚀刻后支架表面接触角均显著降低,同时压缩强度下降,但NaOH处理参数组合为5 mol/L-24 h,10 mol/L-6 h的蚀刻支架,其压缩强度与未处理支架对比,差异没有统计学意义。蚀刻支架上细胞数目增多,单个细胞铺展面积大,黏附细胞伸出的突触变多。处理参数组合为10 mol/L-6 h的NaOH处理3D打印PCL网状支架可有效改善支架表面形貌和细胞反应,有利于增加湿润性和细胞黏附。

双曲抛物面形态和传统近似牙槽嵴形态3D打印钛网的力学性能研究

目的探究双曲抛物面空间结构对个性化钛网的力学性能影响。方法使用3-Matic 15软件为牙槽嵴吸收患者的下颌骨三维模型进行虚拟骨增量,分别增量为双曲抛物面结构和近似牙槽嵴结构,并制作孔隙为圆形、三角形、四边形和六边形,厚度为0.2 mm、0.3 mm、0.4 mm的个性化钛网,构建有限元分析模型,施加力和约束,分析各组钛网的应力和位移。结果同一厚度下,不同孔隙结构的双曲抛物面钛网应力和位移均明显低于近似牙槽嵴形态的钛网;随厚度减小,各组钛网的应力和位移显著增加。结论双曲抛物面这一空间结构可以均匀的分散应力,减少个性化钛网的应力集中,减少钛网受力后的位移,使钛网兼具了良好的力学性能和较薄的厚度,降低了对软组织的刺激,减少钛网暴露的可能。

在3D-Mesh网络中的两种路由研究

在研究并行计算机系统容错时,路由算法是一个极为重要的研究课题。主要研究的是自适应路由算法和确定性路由算法在3D-Mesh网络上的性能。在每个结点具有独立的出错概率的模型下,提出的方法使得能够严格地推导出路由算法的成功概率,从而能够对算法进行分析和比较。研究结果表明,自适应路由算法具有明显的优势。一方面,自适应路由算法基于局部信息而变得高效;另一方面,自适应路由算法对于结点出错和网络规模具有更好的健壮性,而使其具有更高的成功概率。

3D打印人工椎体在颈椎脊索瘤全脊椎切除术中的应用

目的:通过比较颈椎脊索瘤全脊椎切除术后3D打印人工椎体和钛网下沉率的差异,探讨3D打印人工椎体重建前方椎体能否减少术后内植物的下沉。方法:回顾性分析2005年3月至2019年9月在北京大学第三医院行全脊椎切除术的24例颈椎脊索瘤患者资料,其中采用3D打印人工椎体重建颈椎前方椎体(3D椎体组)有9例,采用钛网重建(钛网组)有15例。收集患者的年龄、性别、椎体CT值、手术信息(手术节段、手术时间、出血量及围手术期并发症)和术后内植物下沉等随访资料,采用SPSS 22.0进行数据分析。结果:比较两组患者的性别、年龄、椎体CT值、手术节段、手术时间、出血量及围手术期并发症,差异无统计学意义。术后3个月随访内植物下沉显示,3D椎体组有8例椎体高度下降<1 mm(无内植物下沉),1例椎体高度下降>1 mm(轻度内植物下沉);钛网组有5例椎体高度下降<1 mm(无内植物下沉),8例椎体高度下沉>1 mm(轻度内植物下沉),2例缺失术后3个月的影像学资料,两组3个月内植物下沉率的比较差异有统计学意义(P<0.05)。术后12个月随访内植物下沉显示,3D椎体组有8例椎体高度下降<1 mm(无内植物下沉),1例椎体高度下沉>3 mm(重度内植物下沉);钛网组有4例椎体高度下降<1 mm(无内植物下沉),2例椎体高度下沉>1 mm(轻度内植物下沉),9例椎体高度下沉>3 mm(重度内植物下沉),两组12个月内植物下沉率的比较差异有统计学意义(P<0.01),且两组的重度内植物下沉率(椎体高度下沉>3 mm)比较差异有统计学意义(P<0.05)。术后24个月随访内植物下沉显示,3D椎体组死亡1例,7例椎体高度下降<1 mm(无内植物下沉),1例椎体高度下沉>3 mm(重度内植物下沉);钛网组死亡1例,失访1例,1例椎体高度下降<1 mm(无内植物下沉),1例椎体高度下沉>1 mm(轻度内植物下沉),11例椎体高度下沉>3 mm(重度内植物下沉),两组24个月内植物下沉率比较差异有统计学意义(P<0.01),且两组的重度内植物下沉率比较差异有统计学意义(P<0.01)。结论:在颈椎脊索瘤的全脊椎切除术中,3D打印人工椎体可提供可靠的即刻和中远期的颈椎稳定性,与钛网重建相比,能够减少术后内植物下沉的发生率。