The geometric characteristics of fractures within a rock mass can be inferred by the data sampling from boreholes or exposed surfaces.Recently,the universal elliptical disc(UED)model was developed to represent natural...The geometric characteristics of fractures within a rock mass can be inferred by the data sampling from boreholes or exposed surfaces.Recently,the universal elliptical disc(UED)model was developed to represent natural fractures,where the fracture is assumed to be an elliptical disc and the fracture orientation,rotation angle,length of the long axis and ratio of short-long axis lengths are considered as variables.This paper aims to estimate the fracture size-and azimuth-related parameters in the UED model based on the trace information from sampling windows.The stereological relationship between the trace length,size-and azimuth-related parameters of the UED model was established,and the formulae of the mean value and standard deviation of trace length were proposed.The proposed formulae were validated via the Monte Carlo simulations with less than 5%of error rate between the calculated and true values.With respect to the estimation of the size-and azimuth-related parameters using the trace length,an optimization method was developed based on the pre-assumed size and azimuth distribution forms.A hypothetical case study was designed to illustrate and verify the parameter estimation method,where three combinations of the sampling windows were used to estimate the parameters,and the results showed that the estimated values could agree well with the true values.Furthermore,a hypothetical three-dimensional(3D)elliptical fracture network was constructed,and the circular disc,non-UED and UED models were used to represent it.The simulated trace information from different models was compared,and the results clearly illustrated the superiority of the proposed UED model over the existing circular disc and non-UED models。展开更多
Since natural fractures are often non-equidimensional,the circular disc model still has great limitations.By contrast,the elliptical disc model is more applicable to representing natural fractures,especially for slend...Since natural fractures are often non-equidimensional,the circular disc model still has great limitations.By contrast,the elliptical disc model is more applicable to representing natural fractures,especially for slender ones.This paper developed a universal elliptical disc(UED)model by incorporating the center point,size,and azimuth of fractures as variables.Specifically,with respect to the azimuth of elliptical fractures in three-dimensional(3D)space,we proposed a paradigm to construct its probability density function(PDF)by coupling the orientation and rotation angle of long axis based on three coordinate transformations.To illustrate the construction process of the PDF of the fracture azimuth,we took the orientation following the Fisher distribution and the rotation angle following Von Mises distribution as an example.A rock slope is used to show the use of the developed UED model,and the 3D DFNs for the slope rock mass are generated by Monte Carlo simulation.In addition,the DFNs for the rock mass are also generated based on the existing circular disc model and non-universal elliptical disc model.The comparison results from the three models clearly illustrate the superiority of the UED model over the existing circular and non-universal elliptical disc models.展开更多
To study the rock deformation with three- dimensional model under rolling forces of disc cutter, by car- rying out the circular-grooving test with disc cutter rolling around on the rock, the rock mechanical behavior u...To study the rock deformation with three- dimensional model under rolling forces of disc cutter, by car- rying out the circular-grooving test with disc cutter rolling around on the rock, the rock mechanical behavior under rolling disc cutter is studied, the mechanical model of disc cutter rolling around the groove is established, and the the- ory of single-point and double-angle variables is proposed. Based on this theory, the physics equations and geometric equations of rock mechanical behavior under disc cutters of tunnel boring machine （TBM） are studied, and then the bal- ance equations of interactive forces between disc cutter and rock are established. Accordingly, formulas about normal force, rolling force and side force of a disc cutter are de- rived, and their validity is studied by tests. Therefore, a new method and theory is proposed to study rock- breaking mech- anism of disc cutters.展开更多
This paper presents a dynamic model for a disc subjected to two sliders rotating in the circumferential direction over the top and bottom surfaces of the disc.The two sliders are vertically misaligned and each is a ma...This paper presents a dynamic model for a disc subjected to two sliders rotating in the circumferential direction over the top and bottom surfaces of the disc.The two sliders are vertically misaligned and each is a mass-spring-damper system with friction between the slider and the disc. The moving loads produced by misaligned sliders can destabilise the whole system.Stability analysis is carried out in a simulated example.This model is meant to explain the friction mechanism for generating unstable vibration in many applications involving rotating discs.展开更多
The Brazilian test is a widely used method for determining the tensile strength of rocks and for calibrating parameters in bondedparticle models（BPMs）. In previous studies, the Brazilian disc has typically been trim...The Brazilian test is a widely used method for determining the tensile strength of rocks and for calibrating parameters in bondedparticle models（BPMs）. In previous studies, the Brazilian disc has typically been trimmed from a compacted rectangular specimen. The present study shows that different tensile strength values are obtained depending on the compressive loading direction. Several measures are proposed to reduce the anisotropy of the disc. The results reveal that the anisotropy of the disc is significantly influenced by the compactibility of the specimen from which it is trimmed. A new method is proposed in which the Brazilian disc is directly generated with a particle boundary, effectively reducing the anisotropy. The stiffness（particle and bond） and strength（bond） of the boundary are set at less than and greater than those of the disc assembly, respectively,which significantly decreases the stress concentration at the boundary contacts and prevents breakage of the boundary particle bonds. This leads to a significant reduction in the anisotropy of the disc and the discreteness of the tensile strength. This method is more suitable for carrying out a realistic Brazilian test for homogeneous rock-like material in the BPM.展开更多
Objectives： To develop a rabbit model of intervertebral disc degeneration that more exactly simulates the pathological changes of human intervertebral disc degeneration. Methods： Twelve New Zealand white rabbits wer...Objectives： To develop a rabbit model of intervertebral disc degeneration that more exactly simulates the pathological changes of human intervertebral disc degeneration. Methods： Twelve New Zealand white rabbits were utilized to establish three different disc injury models according to the following protocol; group A： anulus punctures were done with a 18-gauge needle at L2-L3 and L5-L6; Group B： intradiscal injection of interleukin-1 IL-1β with a 23-gauge needle at L3-L4; and Group C： intradiscal injection of phosphate buffer saline（PBS） with a 23-gauge needle at L4-LS. The L1-L2 level was used as a control. Rabbits were killed after 24 weeks. The intervertebral disc height was measured by lateral plain radiographs. After the radiographic measurements were obtained, the intervertebral discs were removed and analyzed for DNA, sulfated glycosaminoglycan（s-GAG） and water contents of nucleus pulposus. Results： The intervertebral disc height, s-GAG, and water contents in anulus needle punctures were significantly decreased in Group A, but the DNA content in the nucleus pulposus was significantly increased when compared to the control. The significant decrease of disc height and water contents were demonstrated, only the s-GAG and DNA contents did not show a significant difference in Group B when compared to the control. The significant decrease of disc height, s-GAG, water, and DNA contents did not show in Group C when compared to the control. Conclusion： The 18-gauge puncture models produced the most consistent disc degeneration in the rabbit lumbar spine.展开更多
Background: Degeneration of the intervertebral disc is one of the causes of kyphosis. Several biomechanical studies have investigated the mechanisms of development of spinal deformity using simulation models. Realisti...Background: Degeneration of the intervertebral disc is one of the causes of kyphosis. Several biomechanical studies have investigated the mechanisms of development of spinal deformity using simulation models. Realistic musculoskeletal models are helpful for investigating the pathophysiology and changes in internal forces in patients with kyphosis. However, the association between intervertebral disc pressure and kyphosis has not been fully elucidated to date. Purpose: To calculate intervertebral disc pressure in elderly women with kyphosis using a novel and precise thoracolumbar three-dimensional musculoskeletal model. Materials and Method: Ten female patients with a mean age of 80.0 ± 6.5 years who visited our hospital for medical examination of osteoporosis were included. The subjects were divided into the normal and kyphosis groups depending on their sagittal vertical axis. Intervertebral disc pressures in the thoracic and lumbar spines of subjects were analyzed by inverse dynamics analysis using a novel three-dimensional musculoskeletal model, and were compared between the groups. Result: Significant differences in lumbar lordosis (LL) were observed between the two groups. Furthermore, the kyphosis group was older and shorter. In the kyphosis group, the upper thoracic vertebrae (T1 - T6) showed significantly higher intervertebral pressure than the normal group. Conclusion: Intervertebral disc pressure in the thoracic and lumbar spines of patients with spinal deformities was evaluated using a novel thoracolumbar three-dimensional musculoskeletal model. Using this novel model with separated thoracic spine and modified muscle path reflecting actual physiological curvature, disc pressure closer to the realistic condition was obtained. Intervertebral disc pressure in the upper thoracic spine in the kyphosis group was significantly increased compared with that in the normal group. Moreover, intervertebral disc pressures in the upper thoracic spine correlated negatively with LL.展开更多
One of the key problems in the concept of planetary systems origin and early evolution is solid bodies formation in the protoplanetary gas-dust disc around young stars. Dust particles interactions inside the original ...One of the key problems in the concept of planetary systems origin and early evolution is solid bodies formation in the protoplanetary gas-dust disc around young stars. Dust particles interactions inside the original fluffy dust clusters of fractal nature resulted from gravitational instability and fragmentation in the disc’s central plane areassumed as the most plausible mechanism of primary bodies set up owing to particles integration within the clusters. Follow upcollisions are regarded to be responsible for eventual growth of primary bodies to the size of planetesimals. We discuss this scenario including chemical nature of particles depending on the disc’s radial temperature distribution and phase transitions. The mathematical model is developed based on the method of penetrating particles with the account for internal structure/properties of bodies involved, complicated patterns of their interaction, and phenomenological approach to describe energy distribution in the contact zone. The model is mainly addressed to the stage of formed solid bodies collisions. The results of numerical evaluation of the model are described involving some constraints for complete or partial destruction of colliding bodies followed by either scattering of collisional fragments orpartial back accumulation.展开更多
为探究混凝土的拉伸断裂特性和裂纹演化规律,开展了巴西圆盘的准静态劈裂试验和落锤冲击动态劈裂试验,结合有限元-黏聚单元耦合法(finite-cohesive element method,FCEM)模拟分析裂纹扩展过程及力学响应。试验结果表明:准静态加载时,混...为探究混凝土的拉伸断裂特性和裂纹演化规律,开展了巴西圆盘的准静态劈裂试验和落锤冲击动态劈裂试验,结合有限元-黏聚单元耦合法(finite-cohesive element method,FCEM)模拟分析裂纹扩展过程及力学响应。试验结果表明:准静态加载时,混凝土圆盘试件发生拉伸断裂,圆盘中心形成一条沿加载方向贯穿的主裂纹和少量与其平行的次裂纹,裂纹主要在砂浆内部及骨料-砂浆界面扩展;三维圆盘试件的拉伸性能随厚径比的增大而增强。在动态冲击载荷作用下,试件仍为中心起裂模式,即圆盘中心形成一条沿加载方向的主裂纹,边缘则产生三角状破碎区域。随着落锤释放高度的增加,试件的破坏形态依次表现为:未起裂、起裂未贯穿、起裂贯穿和严重破碎。通过高速摄影获得的不同时刻裂纹长度的结果表明,随着落锤释放高度的降低,裂纹扩展时间延长。数值模拟结果显示,试件的起裂时间随落锤释放高度的增加呈非线性递减,并给出了起裂时间与落锤释放高度关系的经验公式。展开更多
目的:基于机器学习的不同算法,开展腰椎间盘突出症的预测模型研究已成为目前精准化医学发展的趋势和热点。但目前使用机器学习进行腰椎间盘突出症预后预测模型的报告质量和方法学质量的证据有限。通过全面的文献检索,全面整合分析基于...目的:基于机器学习的不同算法,开展腰椎间盘突出症的预测模型研究已成为目前精准化医学发展的趋势和热点。但目前使用机器学习进行腰椎间盘突出症预后预测模型的报告质量和方法学质量的证据有限。通过全面的文献检索,全面整合分析基于机器学习开发和验证腰椎间盘突出症预后预测模型的既往研究报告质量和偏倚风险,以探索机器学习算法在预测腰椎间盘突出症预后方面的性能。方法:计算机检索中国知网、万方数据库、维普数据库、中国生物医学文献服务系统、PubMed、Web of Science、Embase和The Cochrane Library数据库,搜集关于机器学习用于开发(和/或验证)腰椎间盘突出症预后预测模型的相关研究,检索时限为各数据库建立至2023-12-31。由2名研究者独立筛选文献、提取资料并评估纳入研究的偏倚风险。通过多变量预测模型透明报告(TRIPOD)声明和预测模型偏倚风险评估工具(PROBAST)来评估纳入研究的报告质量和偏倚风险。对于评价的结果使用描述性统计和可视化图表进行分析。结果:①共纳入23项研究,每项研究的TRIPOD遵循度在11%-87%之间,中位遵循度为54%;标题、治疗措施的详细说明、预测因素的盲法、缺失数据的处理方法、危险分层的细节、研究对象纳入的具体流程、模型解释以及模型性能的报告质量大多较差,TRIPOD遵循率在4%-35%之间;②所有纳入的研究中,61%具有高偏倚风险,39%具有不明确的整体偏倚风险;3项研究主要使用曲线下面积、准确度、敏感度及特异性指标评估模型性能;20个模型报道了模型的曲线下面积,范围为0.561-0.999;3个模型报道了模型的准确率,范围为82.07%-89.65%;③在所有纳入的研究中,统计分析领域最常被评估为高偏倚风险,主要是由于有效样本数量较小、根据单变量分析选择预测因素和缺乏研究中模型的校准度、区分度评估所致。结论:结果表明,在腰椎间盘突出症的预后模型开发及验证分析中,机器学习能取得良好的预测能力;常用的算法有回归算法、支持向量机、决策树、随机森林、人工神经网络、朴素贝叶斯等算法,合理的算法结合临床实践可以提高腰椎间盘突出症预后预测的准确性;但基于机器学习的预后预测模型的报告和方法学质量较差,不同模型间的预测性能差异较大,研究模型的普适性和外推性不明确,迫切需要改进此类研究的设计、实施和报告;对于模型开发研究,建模前需全面考虑与疾病预后相关的各类预测因素,建模时严格遵循PROBAST工具的相关标准开展研究,以推动机器学习在腰椎间盘突出症预测模型临床实践中的应用。展开更多
目的:术后复发是经皮内镜腰椎间盘切除治疗腰椎间盘突出症的常见并发症,可显著增加再手术风险。性能良好的风险预测模型有助于早期识别高危人群,预防术后复发。此次研究系统评价经皮内镜腰椎间盘切除术后复发风险预测模型,为手术决策提...目的:术后复发是经皮内镜腰椎间盘切除治疗腰椎间盘突出症的常见并发症,可显著增加再手术风险。性能良好的风险预测模型有助于早期识别高危人群,预防术后复发。此次研究系统评价经皮内镜腰椎间盘切除术后复发风险预测模型,为手术决策提供借鉴。方法:检索PubMed、Embase、Web of Science、中国知网、万方、维普和生物医学文献数据库,搜集关于经皮内镜腰椎间盘切除后复发风险预测模型的相关研究,检索时限从各数据库建立至2024-07-01。由2名研究者独立筛选文献和提取资料,并采用偏倚风险评价工具和个体预后与诊断多变量预测模型报告规范(TRIPOD)清单分别对模型进行偏倚风险、适用性和报告质量评价。应用Revman 5.4软件对经皮内镜腰椎间盘切除术后复发率和相关预测因子进行Meta分析。结果:①共纳入15项研究,均为回顾性研究,包括24个经皮内镜腰椎间盘切除后复发风险预测模型;②偏倚风险评价工具评价结果显示,15项研究均为高偏倚风险;在适用性方面,2项研究为低适用性风险,13项研究为高适用性风险;③在TRIPOD报告质量方面,15项研究整体报告质量较低,主要原因包括未报告盲法、未说明样本量计算方法、缺乏对缺失数据处理方法的详细描述,同时也缺少对所使用模型的介绍等信息;④此外,纳入模型的受试者工作特征曲线下面积在0.684-0.972之间,潜在预测变量数量范围为15-28个;⑤Meta分析结果显示,通过经皮内镜腰椎间盘切除治疗的腰椎间盘突出症患者术后复发率为12%(95%CI=9.0%-15.0%),Modic改变(OR=6.72,95%CI=3.90-11.59)、体质量指数(OR=1.28,95%CI=1.10-1.49)、工作强度(OR=3.22,95%CI=1.85-5.59)、年龄(OR=2.28,95%CI=1.50-3.48)和吸烟史(OR=2.65,95%CI=1.75-4.00)是经皮内镜腰椎间盘切除术后复发的独立影响因素(均P<0.05)。结论:经皮内镜腰椎间盘切除术后复发风险预测模型整体预测性能较好,但模型总体偏倚风险和适用性风险较高,报告质量较低,且缺乏前瞻性研究和外部验证,未来风险预测模型的建立可重点关注Modic改变、体质量指数、工作强度、年龄和吸烟史等预测因子。展开更多
The frequency of any periodic event can be defined in terms of units of Time. Planck constructed a unit of time called the Plank time from other physical constants. Vyasa defined a natural unit of time, kshana, or mom...The frequency of any periodic event can be defined in terms of units of Time. Planck constructed a unit of time called the Plank time from other physical constants. Vyasa defined a natural unit of time, kshana, or moment based on the motion of a fundamental particle. It is the time taken by an elementary particle, to change its direction from east to north. According to Vyasa, kshana is discrete, exceedingly small, indivisible, and is a constant time quantum. When the intrinsic spin angular momentum of an electron was related to the angular momentum of a simple thin circular plate, spherical shell, and solid sphere model of an electron, we found that the value of kshana in seconds was equal to ten to a power of minus twenty-one second. The disc model for the spinning electron provides an accurate value of the number of kshanas per second as determined previously and compared with other spinning models of electrons. These results indicate that the disk-like model of spinning electrons is the correct model for electrons. Vyasa’s definition of kshana opens the possibility of a new foundation for the theory of physical time, and perspectives in theoretical and philosophical research.展开更多
Objective: To assess the effects of axial vibrations on gene expression and lumbar intervertebral disc degeneration in vivo. Methods: A modified bipedal rat model was established using a brachial plexus rhizotomy appr...Objective: To assess the effects of axial vibrations on gene expression and lumbar intervertebral disc degeneration in vivo. Methods: A modified bipedal rat model was established using a brachial plexus rhizotomy approach to imitate human upright posture. The experimental animals were randomly divided into three groups: control, vertical vibration, and whole-body vibration. Gene expression in degeneration of the intervertebral discs was assessed by reverse transcription-quantitative polymerase chain reaction. Results: The expression of aggrecan, Col1α1, Col2α1, and decorin were shown to be up-regulated in 14-week-old rats in the vertical vibration and whole-body vibration groups, whereas biglycan and versican expression was down-regulated in 14-week-old rats of the two experimental groups. Furthermore, biglycan and versican expression levels were shown to be lower in the whole-body vibration group than in the vertical vibration group(P<0.05). Conclusions: This in-vivo study demonstrated that vibrations can influence the expression of anabolic genes. Furthermore, whole-body vibrations seem to have a greater effect in this regard than vertical vibrations. A new method is expected to relieve the low back pain of the patients through our research.展开更多
基金funded by National Natural Science Foundation of China(Grant No.41972264)Zhejiang Provincial Natural Science Foundation of China(Grant No.LR22E080002)the Observation and Research Station of Geohazards in Zhejiang,Ministry of Natural Resources,China(Grant No.ZJDZGCZ-2021).
文摘The geometric characteristics of fractures within a rock mass can be inferred by the data sampling from boreholes or exposed surfaces.Recently,the universal elliptical disc(UED)model was developed to represent natural fractures,where the fracture is assumed to be an elliptical disc and the fracture orientation,rotation angle,length of the long axis and ratio of short-long axis lengths are considered as variables.This paper aims to estimate the fracture size-and azimuth-related parameters in the UED model based on the trace information from sampling windows.The stereological relationship between the trace length,size-and azimuth-related parameters of the UED model was established,and the formulae of the mean value and standard deviation of trace length were proposed.The proposed formulae were validated via the Monte Carlo simulations with less than 5%of error rate between the calculated and true values.With respect to the estimation of the size-and azimuth-related parameters using the trace length,an optimization method was developed based on the pre-assumed size and azimuth distribution forms.A hypothetical case study was designed to illustrate and verify the parameter estimation method,where three combinations of the sampling windows were used to estimate the parameters,and the results showed that the estimated values could agree well with the true values.Furthermore,a hypothetical three-dimensional(3D)elliptical fracture network was constructed,and the circular disc,non-UED and UED models were used to represent it.The simulated trace information from different models was compared,and the results clearly illustrated the superiority of the proposed UED model over the existing circular disc and non-UED models。
基金funded by the National Natural Science s of China(No.41972264)the Key R&D Project of Zhejiang Province(No.2021C03159)the Field Scientific Observation&Research Station of Geological Hazard in Zhejiang,Ministry of Natural Resources,China(No.ZJDZGCZ-2021)。
文摘Since natural fractures are often non-equidimensional,the circular disc model still has great limitations.By contrast,the elliptical disc model is more applicable to representing natural fractures,especially for slender ones.This paper developed a universal elliptical disc(UED)model by incorporating the center point,size,and azimuth of fractures as variables.Specifically,with respect to the azimuth of elliptical fractures in three-dimensional(3D)space,we proposed a paradigm to construct its probability density function(PDF)by coupling the orientation and rotation angle of long axis based on three coordinate transformations.To illustrate the construction process of the PDF of the fracture azimuth,we took the orientation following the Fisher distribution and the rotation angle following Von Mises distribution as an example.A rock slope is used to show the use of the developed UED model,and the 3D DFNs for the slope rock mass are generated by Monte Carlo simulation.In addition,the DFNs for the rock mass are also generated based on the existing circular disc model and non-universal elliptical disc model.The comparison results from the three models clearly illustrate the superiority of the UED model over the existing circular and non-universal elliptical disc models.
基金supported by the National Natural Science Foundation of China (51075147)
文摘To study the rock deformation with three- dimensional model under rolling forces of disc cutter, by car- rying out the circular-grooving test with disc cutter rolling around on the rock, the rock mechanical behavior under rolling disc cutter is studied, the mechanical model of disc cutter rolling around the groove is established, and the the- ory of single-point and double-angle variables is proposed. Based on this theory, the physics equations and geometric equations of rock mechanical behavior under disc cutters of tunnel boring machine （TBM） are studied, and then the bal- ance equations of interactive forces between disc cutter and rock are established. Accordingly, formulas about normal force, rolling force and side force of a disc cutter are de- rived, and their validity is studied by tests. Therefore, a new method and theory is proposed to study rock- breaking mech- anism of disc cutters.
文摘This paper presents a dynamic model for a disc subjected to two sliders rotating in the circumferential direction over the top and bottom surfaces of the disc.The two sliders are vertically misaligned and each is a mass-spring-damper system with friction between the slider and the disc. The moving loads produced by misaligned sliders can destabilise the whole system.Stability analysis is carried out in a simulated example.This model is meant to explain the friction mechanism for generating unstable vibration in many applications involving rotating discs.
基金Support provided by the National Basic Research Program of China (2015CB258500, 2015CB058102, 2014CB046904)
文摘The Brazilian test is a widely used method for determining the tensile strength of rocks and for calibrating parameters in bondedparticle models（BPMs）. In previous studies, the Brazilian disc has typically been trimmed from a compacted rectangular specimen. The present study shows that different tensile strength values are obtained depending on the compressive loading direction. Several measures are proposed to reduce the anisotropy of the disc. The results reveal that the anisotropy of the disc is significantly influenced by the compactibility of the specimen from which it is trimmed. A new method is proposed in which the Brazilian disc is directly generated with a particle boundary, effectively reducing the anisotropy. The stiffness（particle and bond） and strength（bond） of the boundary are set at less than and greater than those of the disc assembly, respectively,which significantly decreases the stress concentration at the boundary contacts and prevents breakage of the boundary particle bonds. This leads to a significant reduction in the anisotropy of the disc and the discreteness of the tensile strength. This method is more suitable for carrying out a realistic Brazilian test for homogeneous rock-like material in the BPM.
基金National Natural Science Foundation ofChina(30400163)
文摘Objectives： To develop a rabbit model of intervertebral disc degeneration that more exactly simulates the pathological changes of human intervertebral disc degeneration. Methods： Twelve New Zealand white rabbits were utilized to establish three different disc injury models according to the following protocol; group A： anulus punctures were done with a 18-gauge needle at L2-L3 and L5-L6; Group B： intradiscal injection of interleukin-1 IL-1β with a 23-gauge needle at L3-L4; and Group C： intradiscal injection of phosphate buffer saline（PBS） with a 23-gauge needle at L4-LS. The L1-L2 level was used as a control. Rabbits were killed after 24 weeks. The intervertebral disc height was measured by lateral plain radiographs. After the radiographic measurements were obtained, the intervertebral discs were removed and analyzed for DNA, sulfated glycosaminoglycan（s-GAG） and water contents of nucleus pulposus. Results： The intervertebral disc height, s-GAG, and water contents in anulus needle punctures were significantly decreased in Group A, but the DNA content in the nucleus pulposus was significantly increased when compared to the control. The significant decrease of disc height and water contents were demonstrated, only the s-GAG and DNA contents did not show a significant difference in Group B when compared to the control. The significant decrease of disc height, s-GAG, water, and DNA contents did not show in Group C when compared to the control. Conclusion： The 18-gauge puncture models produced the most consistent disc degeneration in the rabbit lumbar spine.
文摘Background: Degeneration of the intervertebral disc is one of the causes of kyphosis. Several biomechanical studies have investigated the mechanisms of development of spinal deformity using simulation models. Realistic musculoskeletal models are helpful for investigating the pathophysiology and changes in internal forces in patients with kyphosis. However, the association between intervertebral disc pressure and kyphosis has not been fully elucidated to date. Purpose: To calculate intervertebral disc pressure in elderly women with kyphosis using a novel and precise thoracolumbar three-dimensional musculoskeletal model. Materials and Method: Ten female patients with a mean age of 80.0 ± 6.5 years who visited our hospital for medical examination of osteoporosis were included. The subjects were divided into the normal and kyphosis groups depending on their sagittal vertical axis. Intervertebral disc pressures in the thoracic and lumbar spines of subjects were analyzed by inverse dynamics analysis using a novel three-dimensional musculoskeletal model, and were compared between the groups. Result: Significant differences in lumbar lordosis (LL) were observed between the two groups. Furthermore, the kyphosis group was older and shorter. In the kyphosis group, the upper thoracic vertebrae (T1 - T6) showed significantly higher intervertebral pressure than the normal group. Conclusion: Intervertebral disc pressure in the thoracic and lumbar spines of patients with spinal deformities was evaluated using a novel thoracolumbar three-dimensional musculoskeletal model. Using this novel model with separated thoracic spine and modified muscle path reflecting actual physiological curvature, disc pressure closer to the realistic condition was obtained. Intervertebral disc pressure in the upper thoracic spine in the kyphosis group was significantly increased compared with that in the normal group. Moreover, intervertebral disc pressures in the upper thoracic spine correlated negatively with LL.
文摘One of the key problems in the concept of planetary systems origin and early evolution is solid bodies formation in the protoplanetary gas-dust disc around young stars. Dust particles interactions inside the original fluffy dust clusters of fractal nature resulted from gravitational instability and fragmentation in the disc’s central plane areassumed as the most plausible mechanism of primary bodies set up owing to particles integration within the clusters. Follow upcollisions are regarded to be responsible for eventual growth of primary bodies to the size of planetesimals. We discuss this scenario including chemical nature of particles depending on the disc’s radial temperature distribution and phase transitions. The mathematical model is developed based on the method of penetrating particles with the account for internal structure/properties of bodies involved, complicated patterns of their interaction, and phenomenological approach to describe energy distribution in the contact zone. The model is mainly addressed to the stage of formed solid bodies collisions. The results of numerical evaluation of the model are described involving some constraints for complete or partial destruction of colliding bodies followed by either scattering of collisional fragments orpartial back accumulation.
文摘为探究混凝土的拉伸断裂特性和裂纹演化规律,开展了巴西圆盘的准静态劈裂试验和落锤冲击动态劈裂试验,结合有限元-黏聚单元耦合法(finite-cohesive element method,FCEM)模拟分析裂纹扩展过程及力学响应。试验结果表明:准静态加载时,混凝土圆盘试件发生拉伸断裂,圆盘中心形成一条沿加载方向贯穿的主裂纹和少量与其平行的次裂纹,裂纹主要在砂浆内部及骨料-砂浆界面扩展;三维圆盘试件的拉伸性能随厚径比的增大而增强。在动态冲击载荷作用下,试件仍为中心起裂模式,即圆盘中心形成一条沿加载方向的主裂纹,边缘则产生三角状破碎区域。随着落锤释放高度的增加,试件的破坏形态依次表现为:未起裂、起裂未贯穿、起裂贯穿和严重破碎。通过高速摄影获得的不同时刻裂纹长度的结果表明,随着落锤释放高度的降低,裂纹扩展时间延长。数值模拟结果显示,试件的起裂时间随落锤释放高度的增加呈非线性递减,并给出了起裂时间与落锤释放高度关系的经验公式。
文摘目的:基于机器学习的不同算法,开展腰椎间盘突出症的预测模型研究已成为目前精准化医学发展的趋势和热点。但目前使用机器学习进行腰椎间盘突出症预后预测模型的报告质量和方法学质量的证据有限。通过全面的文献检索,全面整合分析基于机器学习开发和验证腰椎间盘突出症预后预测模型的既往研究报告质量和偏倚风险,以探索机器学习算法在预测腰椎间盘突出症预后方面的性能。方法:计算机检索中国知网、万方数据库、维普数据库、中国生物医学文献服务系统、PubMed、Web of Science、Embase和The Cochrane Library数据库,搜集关于机器学习用于开发(和/或验证)腰椎间盘突出症预后预测模型的相关研究,检索时限为各数据库建立至2023-12-31。由2名研究者独立筛选文献、提取资料并评估纳入研究的偏倚风险。通过多变量预测模型透明报告(TRIPOD)声明和预测模型偏倚风险评估工具(PROBAST)来评估纳入研究的报告质量和偏倚风险。对于评价的结果使用描述性统计和可视化图表进行分析。结果:①共纳入23项研究,每项研究的TRIPOD遵循度在11%-87%之间,中位遵循度为54%;标题、治疗措施的详细说明、预测因素的盲法、缺失数据的处理方法、危险分层的细节、研究对象纳入的具体流程、模型解释以及模型性能的报告质量大多较差,TRIPOD遵循率在4%-35%之间;②所有纳入的研究中,61%具有高偏倚风险,39%具有不明确的整体偏倚风险;3项研究主要使用曲线下面积、准确度、敏感度及特异性指标评估模型性能;20个模型报道了模型的曲线下面积,范围为0.561-0.999;3个模型报道了模型的准确率,范围为82.07%-89.65%;③在所有纳入的研究中,统计分析领域最常被评估为高偏倚风险,主要是由于有效样本数量较小、根据单变量分析选择预测因素和缺乏研究中模型的校准度、区分度评估所致。结论:结果表明,在腰椎间盘突出症的预后模型开发及验证分析中,机器学习能取得良好的预测能力;常用的算法有回归算法、支持向量机、决策树、随机森林、人工神经网络、朴素贝叶斯等算法,合理的算法结合临床实践可以提高腰椎间盘突出症预后预测的准确性;但基于机器学习的预后预测模型的报告和方法学质量较差,不同模型间的预测性能差异较大,研究模型的普适性和外推性不明确,迫切需要改进此类研究的设计、实施和报告;对于模型开发研究,建模前需全面考虑与疾病预后相关的各类预测因素,建模时严格遵循PROBAST工具的相关标准开展研究,以推动机器学习在腰椎间盘突出症预测模型临床实践中的应用。
文摘目的:术后复发是经皮内镜腰椎间盘切除治疗腰椎间盘突出症的常见并发症,可显著增加再手术风险。性能良好的风险预测模型有助于早期识别高危人群,预防术后复发。此次研究系统评价经皮内镜腰椎间盘切除术后复发风险预测模型,为手术决策提供借鉴。方法:检索PubMed、Embase、Web of Science、中国知网、万方、维普和生物医学文献数据库,搜集关于经皮内镜腰椎间盘切除后复发风险预测模型的相关研究,检索时限从各数据库建立至2024-07-01。由2名研究者独立筛选文献和提取资料,并采用偏倚风险评价工具和个体预后与诊断多变量预测模型报告规范(TRIPOD)清单分别对模型进行偏倚风险、适用性和报告质量评价。应用Revman 5.4软件对经皮内镜腰椎间盘切除术后复发率和相关预测因子进行Meta分析。结果:①共纳入15项研究,均为回顾性研究,包括24个经皮内镜腰椎间盘切除后复发风险预测模型;②偏倚风险评价工具评价结果显示,15项研究均为高偏倚风险;在适用性方面,2项研究为低适用性风险,13项研究为高适用性风险;③在TRIPOD报告质量方面,15项研究整体报告质量较低,主要原因包括未报告盲法、未说明样本量计算方法、缺乏对缺失数据处理方法的详细描述,同时也缺少对所使用模型的介绍等信息;④此外,纳入模型的受试者工作特征曲线下面积在0.684-0.972之间,潜在预测变量数量范围为15-28个;⑤Meta分析结果显示,通过经皮内镜腰椎间盘切除治疗的腰椎间盘突出症患者术后复发率为12%(95%CI=9.0%-15.0%),Modic改变(OR=6.72,95%CI=3.90-11.59)、体质量指数(OR=1.28,95%CI=1.10-1.49)、工作强度(OR=3.22,95%CI=1.85-5.59)、年龄(OR=2.28,95%CI=1.50-3.48)和吸烟史(OR=2.65,95%CI=1.75-4.00)是经皮内镜腰椎间盘切除术后复发的独立影响因素(均P<0.05)。结论:经皮内镜腰椎间盘切除术后复发风险预测模型整体预测性能较好,但模型总体偏倚风险和适用性风险较高,报告质量较低,且缺乏前瞻性研究和外部验证,未来风险预测模型的建立可重点关注Modic改变、体质量指数、工作强度、年龄和吸烟史等预测因子。
文摘The frequency of any periodic event can be defined in terms of units of Time. Planck constructed a unit of time called the Plank time from other physical constants. Vyasa defined a natural unit of time, kshana, or moment based on the motion of a fundamental particle. It is the time taken by an elementary particle, to change its direction from east to north. According to Vyasa, kshana is discrete, exceedingly small, indivisible, and is a constant time quantum. When the intrinsic spin angular momentum of an electron was related to the angular momentum of a simple thin circular plate, spherical shell, and solid sphere model of an electron, we found that the value of kshana in seconds was equal to ten to a power of minus twenty-one second. The disc model for the spinning electron provides an accurate value of the number of kshanas per second as determined previously and compared with other spinning models of electrons. These results indicate that the disk-like model of spinning electrons is the correct model for electrons. Vyasa’s definition of kshana opens the possibility of a new foundation for the theory of physical time, and perspectives in theoretical and philosophical research.
基金supported by the National Natural Science Foundation of China(Grant No.81401768,81301646)the Natural Science Foundation of Jiangsu Province(Grant No.BK20140289)+1 种基金the Specialized Research Fund for the Doctoral Program of Higher Education of China(Grant No.20123201120018)China Postdoctoral Science Foundation on the 53rd general program(Grant No.2013M531404)
文摘Objective: To assess the effects of axial vibrations on gene expression and lumbar intervertebral disc degeneration in vivo. Methods: A modified bipedal rat model was established using a brachial plexus rhizotomy approach to imitate human upright posture. The experimental animals were randomly divided into three groups: control, vertical vibration, and whole-body vibration. Gene expression in degeneration of the intervertebral discs was assessed by reverse transcription-quantitative polymerase chain reaction. Results: The expression of aggrecan, Col1α1, Col2α1, and decorin were shown to be up-regulated in 14-week-old rats in the vertical vibration and whole-body vibration groups, whereas biglycan and versican expression was down-regulated in 14-week-old rats of the two experimental groups. Furthermore, biglycan and versican expression levels were shown to be lower in the whole-body vibration group than in the vertical vibration group(P<0.05). Conclusions: This in-vivo study demonstrated that vibrations can influence the expression of anabolic genes. Furthermore, whole-body vibrations seem to have a greater effect in this regard than vertical vibrations. A new method is expected to relieve the low back pain of the patients through our research.
