共查询到20条相似文献，搜索用时 359 毫秒
1.
Rate-dependent constitutive model of poly（ethylene terephthalate） for dynamic analysis 总被引：1，自引：0，他引：1
Uniaxial tensile testing at strain rates ranging from 10-3 to 10-1 s-1 was carried out to study the rate-dependent me-chanical behavior for poly（ethylene terephthalate） （PET） used in the packaging industry. The experimental results show that a rate-dependent plastic behavior exists for PET material. The value of the yield strength was found to increase with the increasing strain rate. A new constitutive model based on the improved Cowper-Symonds rate-dependent constitutive model is proposed to describe the mechanical behavior of PET material in the strain rate ranging from 10-3 to 10-1 s-1, providing more accurate material data for the subsequent simulation analysis of drop test and dynamic buckling. The predictions obtained using the proposed model are compared with experimental results of the improved Cowper-Symonds model. The simulating results of the proposed model agree well with the experimental data. For a low strain rate, the predictions of this model are more precise than those obtained using the improved Cowper-Symonds model. This confirms that the new constitutive model is suitable for describing the me-chanical behavior of PET material at a low strain rate and modeling impact problem. 相似文献
2.
Kazumoto Tanaka 《美中教育评论》2010,7(7):107-113
It is said that improving movement habits is effective way to solve the problem of obesity. However, there are many people who are unable to form a habit of exercising for reasons, such as ＂feeling troublesome to go to the gym＂ and ＂getting sick of exercise at home due to the monotony＂. Previous researches have proposed systems that provide virtual reality environment for enjoying interactive exercising. In this paper, the authors describe a virtual tennis system that can control a game mode to let a user maintain an appropriate exercise load based on an estimation of the user＇s heart rate state. The author has created a Bayesian network model for heart rate state estimation. The probabilities of heart rate states can be calculated by using the model, and then the heart rate state which has the highest probability is selected as an estimation result. The author has evaluated the virtual tennis system experimentally and ascertained the effectiveness of the system to appropriate exercise load maintenance. 相似文献
3.
Thermoporometry （TPM） is a calorimetric-based technique for characterizing pore structure according to the freezing and melting point depression of liquid confined in pores which attributes to a varying phase-transition free energy by interface curvature. TPM has demonstrated an emerging success in applications for determining the mesopores of cement-based materials in recent decades. To improve its resolution and accuracy, this paper discussed these factors which show a great influence on the baseline heat flow and the derived pore structure using two molecular sieves with discontinuous size for calibration, referring to the sample handling, the mass of sample and the varying temperature. The pore size distributions of ordinary and high-strength concrete by TPM were favorably compared to the results taken by nitrogen adsorption/desorption （NAD） and mercury intrusion porosimetry （MIP）. The results illustrated that both the accuracy and resolution improve with the decreasing cooling/heating rate until 1 ℃/rain; however, if the rate is too slow, it can lead to an unstable result. The mass of the sample tested has much less an effect on the accuracy when it increases to more than 30 mg. TPM is demonstrated to be more accurate to characterize the mesopores with the size bigger than 4 nm as compared to NAD and MIP. 相似文献
4.
Numerous experiments have shown that the water flow in fine-grained soils can obey an exponential relationship at small gradients and a linear relationship when the hydraulic gradient exceeds a certain limit. Based on the non-Darcian flow described by exponent and threshold gradient, the theory of 1D consolidation is modified in this paper to consider a linear variation in the vertical total stress with depth and the effect of ramp loading. The numerical solutions were derived in detail by the finite difference method for excess pore water pressure and the average degree of consolidation. Finally, the influence of various parameters on consolidation behavior was investigated. The results show that the rate of consolidation is reduced when non-Darcian flow described by exponent and threshold gradient is adopted in the theory of 1D consolidation. As well the distribution of vertical total stress has a great influence on the dissipation of excess pore water pressure, either for pervious top and pervious bottom （PTPB） or for pervious top and impervious bottom （PTIB）. For the case of PTIB, the distribution of vertical total stress in a foundation has a great influence on the rate of consolidation; however, for the case of PTPB, the rate of consolidation is independent of the distribution of vertical total stress. The rate of consolidation is dependent on the ratio of the thickness of a soil layer to the equivalent head of the final average vertical total stress; the greater the value of this ratio, the slower the rate of consolidation. Finally, an increase in construction time reduces the consolidation rate of a foundation. Thus, consolidation behavior of 1D consolidation with non-Darcian flow has been thoroughly acquainted in this paper. 相似文献
5.
Jun Li Nan Gao Guang-yi Cao Heng-yong Tu Ming-ruo Hu Xin-jian Zhu Jian Li 《浙江大学学报(A卷英文版)》2010,11(1):61-70
In this paper, an application of a nonlinear predictive controller based on a self recurrent wavelet network （SRWN） model for a direct internal reforming solid oxide fuel cell （DIR-SOFC） is presented. As operating temperature and fuel utilization are two important parameters, the SOFC is identified using an SRWN with inlet fuel flow rate, inlet air flow rate and current as inputs, and temperature and fuel utilization as outputs. To improve the operating performance of the DIR-SOFC and guarantee proper operating conditions, the nonlinear predictive control is implemented using the off-line trained and on-line modified SRWN model, to manipulate the inlet flow rates to keep the temperature and the fuel utilization at desired levels. Simulation results show satisfactory predictive accuracy of the SRWN model, and demonstrate the excellence of the SRWN-based predictive controller for the DIR-SOFC. 相似文献
6.
RAMAKRISHNAN S. SELVAN S. 《浙江大学学报(A卷英文版)》2007,8(4):538-549
A new approach based on multiwavelets transformation and singular value decomposition (SVD) is proposed for the classification of image textures. Lower singular values are truncated based on its energy distribution to classify the textures in the presence of additive white Gaussian noise (AWGN). The proposed approach extracts features such as energy, entropy, local homogeneity and max-min ratio from the selected singular values of multiwavelets transformation coefficients of image textures. The classification was carried out using probabilistic neural network (PNN). Performance of the proposed approach was compared with conventional wavelet domain gray level co-occurrence matrix (GLCM) based features, discrete multiwavelets transformation energy based approach, and HMM based approach. Experimental results showed the superiority of the proposed algorithms when compared with existing algorithms. 相似文献
7.
《浙江大学学报(A卷英文版)》2013,(11):834-834
Hydrogen is starting to be mentioned as an alternative fuel to replace the fossil fuel in future transportation applications due to its characteristics of zero greenhouse gas emission and high energy effi- ciency. Before hydrogen fuel and its facilities can be introduced to the public, relevant safety issues and its hazards must be assessed in order to avoid any chance of injury or loss. While a traditional risk assessment has difficulty in prioritizing the risk of failure modes, this paper proposes a new fuzzy-based risk evaluation tech- nique which uses fuzzy value to prioritize the risk of various scenarios. In this study, the final risk of each failure modes was prioritized by using the MATLAB fuzzy logic tool box with a combination of two assess- ments. The first assessment was concerned with the criteria which affected the actual probability of occurrence. This assessment considered the availability of the standard that was applied to prevent the likelihood of the scenario occurring. On the other hand, the second assessment was focused on evaluating the consequence of the failure by taking into account the availability of detection and the complexity of the failure rather than only the severity of the scenarios. A total of 87 failure scenarios were identified using failure modes and effect analysis （FMEA） procedures on hydrogen refueling station models. Fuzzy-based assessments were performed through risk prioritizing various failure scenarios with a fuzzy value （0 to 1） and risk level （low, medium, and high） while a traditional risk assessment approach presented the risks only in forms of level （low, medium, and/or high）. Availability of the fuzzy value enabled further prioritizing on the risk results that fell in the same level of risk. This study concluded that fuzzy-based risk evaluation is able to further prioritize the decisions when compared with a traditional risk assessment method. 相似文献
8.
Carbon fiber reinforced polymer （CFRP） bars were prestressed for the structural strengthening of 8 T-shaped reinforced concrete （RC） beams of a 21-year-old bridge in China. The ultimate bearing capacity of the existing bridge after retrofit was discussed on the basis of concrete structures theory. The flexural strengths of RC beams strengthened with CFRP bars were controlled by the failure of concrete in compression and a prestressing method was applied in the retrofit. The field construction processes of strengthening with CFRP bars including grouting cracks, cutting groove, grouting epoxy and embedding CFRP bars, surface treating, banding with the U-type CFRP sheets, releasing external prestressed steel tendons-were introduced in detail. In order to evaluate the effectiveness of this strengthening method, field tests using vehicles as live load were applied before and after the retrofit. The test results of deflection and concrete strain of the T-shaped beams with and without strengthening show that the capacity of the repaired bridge, including the bending strength and stiffness, is enhanced. The measurements of crack width also indicate that this strengthening method can enhance the durability of bridges. Therefore, the proposed strengthening technology is feasible and effective. 相似文献
9.
Hydrogen is starting to be mentioned as an alternative fuel to replace the fossil fuel in future transportation applica- tions due to its characteristics of zero greenhouse gas emission and high energy efficiency. Before hydrogen fuel and its facilities can be introduced to the public, relevant safety issues and its hazards must be assessed in order to avoid any chance of injury or loss. While a traditional risk assessment has difficulty in prioritizing the risk of failure modes, this paper proposes a new fuzzy-based risk evaluation technique which uses fuzzy value to prioritize the risk of various scenarios. In this study, the final risk of each failure modes was prioritized by using the MATLAB fuzzy logic tool box with a combination of two assessments. The first assessment was concerned with the criteria which affected the actual probability of occurrence. This assessment considered the availability of the standard that was applied to prevent the likelihood of the scenario occurring. On the other hand, the second assessment was focused on evaluating the consequence of the failure by taking into account the availability of detection and the complexity of the failure rather than only the severity of the scenarios. A total of 87 failure scenarios were identified using failure modes and effect analysis （FMEA） procedures on hydrogen refueling station models. Fuzzy-based assessments were performed through risk prioritizing various failure scenarios with a fuzzy value （0 to 1） and risk level （low, medium, and high） while a tra- ditional risk assessment approach presented the risks only in forms of level （low, medium, and/or high）. Availability of the fuzzy value enabled further prioritizing on the risk results that fell in the same level of risk. This study concluded that fuzzy-based risk evaluation is able to further prioritize the decisions when compared with a traditional risk assessment method. 相似文献
10.
Researchers in P. R. China commonly create triangulate irregular networks （TINs） from contours and then convert TINs into digital elevation models （DEMs）. However, the DEM produced by this method can not precisely describe and simulate key hydrological features such as rivers and drainage borders. Taking a hilly region in southwestern China as a research area and using ArcGISTM software, we analyzed the errors of different interpolations to obtain distributions of the errors and precisions of different algorithms and to provide references for DEM productions. The results show that different interpolation errors satisfy normal distributions, and large error exists near the structure line of the terrain. Furthermore, the results also show that the precision of a DEM interpolated with the Australian National University digital elevation model （ANUDEM） is higher than that interpolated with TIN. The DEM interpolated with TIN is acceptable for generating DEMs in the hilly region of southwestern China. 相似文献
11.
Heart rate variability (HRV) analysis is affected by ectopic beats. An efficient method was proposed to deal with the ectopic
beats. The method was based on trend correlation of the heart timing signal. Predictor of R-R interval (RRI) value at ectopic
beat time was constructed by the weight calculation and the slope estimation of preceding normal RRI. The type of ectopic
beat was detected and replaced by the predictor of RRI. The performance of the simulated signal after ectopic correction was
tested by the standard value using power spectrum density (PSD) estimation, whereas the results of clinical data with ectopic
beats were compared with the adjacent ectopic-free data. The result showed the frequency indexes after ectopy corrected had
less error than other methods with the test of simulated signal and clinical data. It indicated our method could improve the
PSD estimation in HRV analysis. The method had advantages of high accuracy and real time properties to recover the sinus node
modulation. 相似文献
12.
为对心脏疾病患者进行实时心率监测,提出一种心率检测方法。采用 STM32 单片机作为控制芯片,传感器采用 SON1205 心率传感器。首先将心率信号输出成对应的方波,将此方波输入到单片机处理,然后通过设计的心率检测算法得出心率,再经过滤波算法处理,得到准确的心率,最后通过 LabVIEW 软件进行仿真实验,得到心率波形。实验结果表明,与高精度测量仪器相比,该方法误差值最多不超过 3,准确率达到 96%以 上。基于 STM32 的心率检测方法性能稳定,数据可靠,可用于日常心率检测。 相似文献
13.
14.
Derek R. Becker Sybil Carrère Chelsea Siler Stephanie Jones Bonnie Bowie Cheryl Cooke 《Mind, Brain, and Education》2012,6(1):10-18
In this study we examined high frequency heart rate variability (HF‐HRV, a parasympathetic index) both at rest and during challenge, to assess if variations in cardiovascular activity measured during a Stroop task could be used to predict reading achievement in typically developing children. Reading achievement was examined using the Peabody Individual Achievement Test–Revised. Results showed that greater HF‐HRV suppression during both the Stroop word and Stroop word–color conflict tasks was associated with better reading achievement. Higher basal levels of HF‐HRV did not predict better reading scores. These results are among the first to show a link between HF‐HRV and reading achievement in a normative school age population, and offer new insight into the association between cognitive activity and autonomic regulation of the heart. 相似文献
15.
无创正压通气治疗急性左心衰的临床研究 总被引：1，自引：0，他引：1
目的：观察机械通气治疗急性左心衰的疗效。方法：60例急性左心衰患者,随机分为常规治疗组和无创通气组,无创通气组在常规治疗基础上加用机械通气治疗,观察通气前后心率（HR）、呼吸频率（RR）,平均动脉压（MAP）及血气分析（pH、PaO2、SaO2、PaCO2）的变化及临床症状的改善情况。结果：机械通气治疗后,患者呼吸困难明显改善,生命体征很快稳定,血气分析指标明显好转。结论：对各种不同原因引起的急性左心衰,机械通气能及时有效的改善患者的临床症状及低氧血症,是抢救急性左心衰的有效措施。 相似文献
16.
Yong MAO Xin HUANG Ke YU Hai-bin QU Chang-xiao LIU Yi-yu CHENG 《Journal of Zhejiang University. Science. B》2008,9(6):474-481
Hepatitis B virus (HBV)-induced liver failure is an emergent liver disease leading to high mortality. The severity of liver failure may be reflected by the profile of some metabolites. This study assessed the potential of using metabolites as biomarkers for liver failure by identifying metabolites with good discriminative performance for its phenotype. The serum samples from 24 HBV-induced liver failure patients and 23 healthy volunteers were collected and analyzed by gas chromatography-mass spectrometry (GC-MS) to generate metabolite profiles. The 24 patients were further grouped into two classes according to the severity of liver failure. Twenty-five commensal peaks in all metabolite profiles were extracted, and the relative area values of these peaks were used as features for each sample. Three algorithms, F-test, k-nearest neighbor (KNN) and fuzzy support vector machine (FSVM) combined with exhaustive search (ES), were employed to identify a subset of metabolites (biomarkers) that best predict liver failure. Based on the achieved experimental dataset, 93.62% predictive accuracy by 6 features was selected with FSVM-ES and three key metabolites, glyceric acid, cis-aconitic acid and citric acid, are identified as potential diagnostic biomarkers. 相似文献
17.
目的 探讨血清IL-6和NT-proBNP在慢性心力衰竭患者中的临床诊断价值.方法 选择80例慢性心力衰竭患者为CHF组,60例健康人群作为对照组.采用双抗体夹心免疫法检测两组人群的血清IL-6和NT-proBNP浓度,并对检测结果进行统计学分析.结果 CHF组患者的血清IL-6和NT-proBNP浓度均明显高于对照组,且随心衰严重程度的加重而增高,两组间差异有统计学意义（P＜0.01）.冠心病组IL-6浓度明显高于其他原发病因组,组间差异有统计学意义（P＜0.01）,CHF患者不同原发病因组NT-proBNP浓度差异无统计学意义（P＞0.05）.结论 IL-6和NT-proBNP参数均与CHF的发生及严重程度密切相关,联合检测可用于对CHF的早期诊断. 相似文献
18.
姚素萍 《襄樊职业技术学院学报》2011,10(3):32+37-32,37
目的通过典型慢性肺心病心衰治疗时加用硝酸甘油,探索硝酸甘油作为血管扩张剂治疗慢性肺心病心衰的疗效。方法在抗感染、氧疗、纠正酸碱平衡及电解质紊乱、纠正心率失常、利尿的基础治疗上加用硝酸甘油微泵推注。结果 2例慢性肺心病心衰患者在常规综合治疗基础上加用硝酸甘油,咳嗽、呼吸困难、胸闷、心慌症状得以缓解,紫绀、水肿消退,肺部啰音减轻或消失,心功能也得以改善。结论硝酸甘油能有效控制心衰,改善症状。 相似文献
19.
首先分析了基于小波变换和奇异值分解方法对同幅图像拼接篡改检测的缺点,结合相关重要的思想,构建了一种改进算法,该算法运用SVD提取图像块特征,并采用偏移频率的直方图来确定阈值。在仿真实验中,通过运用三种算法对图像篡改进行检测,对比结果表明,文章所提算法对同幅图像单次篡改和多次篡改均有更好的检测效果,而且通过修改图像的质量因子的实验进一步证实了该算法具有一定的鲁棒性。 相似文献
20.
顾彬 《泰州职业技术学院学报》2005,5(6):45-46
目的探讨老年慢性肺心病伴发急性心肌梗死(AMI)的临床特点.方法对66例老年慢性肺心病伴发AMI的病人(A组)进行分析,并与老年单纯冠心病AMI152例(B组)作比较.结果A组疼痛发生率(45.4%)显著低于B组(83.9%)(p＜0.01),A组急性左心衰、心源性休克发生率显著高于B组,分别为53.1%与25.0%,48.4%与21.7%(p＜0.05),A组病死率(42.4%)显著高于B组(15.7%),肺心病对其伴发AMI的发生部位无影响.结论对老年肺心病患者突然发生的急性左心衰和/或心源性休克应高度警惕伴发AMI的可能. 相似文献