Response Statistics Of Shell Structures With Geometrical And Material Nonlinearities

The investigation in this thesis is concerned with response statistics of shell structures with geometrical and material nonlinearities under stationary and non-stationary Gaussian random excitations.;A series of hybrid strain based three node flat triangular shell elements is developed for linear and nonlinear shell structural analyses. In the former the Hellinger-Reissner variational principle is employed. The elements are obtained by combining a triangular bending element and a plane stress element, and incorporating the drilling degrees-of-freedom. For the nonlinear analysis the updated Lagrangian formulation and the incremental Hellinger-Reissner variational principle are applied, with incremental displacements and strains being the independently assumed fields. Accordingly, the incremental second Piola-Kirchhoff stress and the incremental Washizu strain are selected as the incremental stress and strain measures. Schemes to transform the second Piola-Kirchhoff stresses to Cauchy stresses are included. The director and simplified versions of the stiffness and consistent mass matrices are derived. Material nonlinearity is of elasto-plastic type with isotropic hardening which is formulated by the J{dollar}\sb2{dollar} flow theory with Ilyushin\u27s yield criterion. In all cases, explicit expressions for the stiffness and consistent mass matrices are obtained. Various shell structures studied in this thesis show that the element formulations are accurate, effective, flexible, and applicable to thin to moderately thick shells with geometrical and material nonlinearities.;In parallel, the stochastic central difference (SCD) method and its associated computational strategies are applied to determine response statistics of general structures. The strategies include the time coordinate transformation (TCT) and adaptive time schemes (ATS). The SCD method with the strategies has excellent accuracy and effectiveness, and does not cause computational instability.;The SCD method is subsequently extended to include a relatively general non-stationary random excitation that consists of a deterministic and stochastic components. In conjunction with the TCT and ATS, it is applied to compute the random responses of general nonlinear shell structures that are discretized by the derived shell elements. Numerical results employing the proposed methodologies are presented and the effectiveness of the methodologies addressed.;The thesis concludes with recommendations for further investigations

AN IMPROVED CYCLING HELMET TECHNOLOGY TO MITIGATE HEAD INJURIES

This study examined the extent to which cycling helmet paddings made of thermoplastic polyurethane (TPU) material mitigated impact accelerations in a cycling helmet to reduce the likelihood of concussions. The results of this study indicate that the TPU paddings mitigate peak linear acceleration between 8.37% and 25.48%, and reduce the risk of head injury, as measured by the Gadd Severity Index (GSI) scores, ranging 20.97% to 27.62% across helmet impact locations. This information becomes useful for researchers, cyclist and helmet designers because it provides an avenue to improve cycling helmet capabilities in minimizing the risk of traumatic brain injuries due to a head impact

INVESTIGATING THE PERFORMANCE OF CYCLING AND HOCKEY HELMET LINER MATERIALS IN MITIGATING IMPACTS AT LOWER SPEEDS DURING FREE FALLS

This study examined the performance of helmets made of expanded polystyrene (EPS) and expanded propylene (EPP) in mitigating linear impacts over three consecutive drop trials at 16 impact speeds ranging from 0.93 to 3.96 m/s. It was found that EPS, a liner material used in cycling helmets, had lower capacity of mitigating linear impact acceleration and captured a larger compressed area of impact than the EPPs, liner materials used for hockey helmets. EPS and EPPs all experienced some degrees of loss in their capacities to mitigate acceleration after the initial impact. All tested materials had no statistically significant difference in their peak resultant linear acceleration (PRLA) between the first and third impacts, and the second and third impacts. This study also found strong and positive correlations between ellipse area and PRLA

EFFECT OF SPRING CANE TIPS ON MEASURES OF PEAK VERTICAL GROUND REACTION FORCES DURING WALKING

This study examined the effect of different spring cane tips on measures of peak vertical ground reaction forces (GRFs) transferred to the cane and foot during walking. Thirty-three participants were fitted with a T-Scope Knee Brace® to simulate a knee flexion contracture. Participants performed cane-aided walking tests under four different spring cane conditions. Each participant walked five trials for each cane tip over two force plates to measure GRFs for the cane and foot respectively. Four (spring cane tip conditions) x two (cane and foot) repeated measures ANOVA was conducted on measures of vertical GRFs. This analysis revealed a significant main effect on measures of vertical GRFs between the cane and foot, F(1,32) = 225.79,p \u3c .05, η2 = .876. This outcome has implications for cane tip designs to prevent upper extremity injuries occurring due to cane use

THE EFFECTIVENESS OF BOXING HEADGUARDS WITH THERMOPLASTIC POLYURETHANE INSERTS IN MITIGATING LINEAR AND ANGULAR IMPACT ACCELERATIONS TO THE HEAD USING A DYNAMIC HEAD MODEL

The purpose of this study was to examine the capacity of commercial boxing headguards and an experimental thermoplastic polyurethane (TPU) liner to mitigate the risk of concussions. Headguards were tested dynamically across a range of impact locations using simulated head impacts with a pneumatic horizontal impactor to explore the behavior of the headguards. This study showed differences between headguard types in mitigating concussion risk resulting from linear and angular accelerations of the head. The results demonstrated that introducing TPU into a headguard reduces concussion risk most prominently by decreasing peak resultant linear acceleration (PRLA) and peak resultant rotational acceleration (PRRA) of the head. This study provides information about the performance of commercial headguards and suggests an avenue for further TPU research

A study of adaptive thermal comfort in a well-controlled climate chamber

This paper aims to critically examine the application of Predicted Mean Vote (PMV) in an air-conditioned environment in the hot-humid climate region. Experimental studies have been conducted in a climate chamber in Chongqing, China, from 2008 to 2010. A total of 440 thermal responses from participants were obtained. Data analysis reveals that the PMV overestimates occupants' mean thermal sensation in the warm environment (PMV > 0) with a mean bias of 0.296 in accordance with the ASHRAE thermal sensation scales. The Bland–Altman method has been applied to assess the agreement of the PMV and Actual Mean Vote (AMV) and reveals a lack of agreement between them. It is identified that habituation due to the past thermal experience of a long-term living in a specific region could stimulate psychological adaptation. The psychological adaptation can neutralize occupants’ actual thermal sensation by moderating the thermal sensibility of the skin. A thermal sensation empirical model and a PMV-revised index are introduced for air-conditioned indoor environments in hot-humid regions. As a result of habituation, the upper limit effective thermal comfort temperature SET* can be increased by 1.6 °C in a warm season based on the existing international standard. As a result, a great potential for energy saving from the air-conditioning system in summer could be achieved

EVALUATING THE COMBINED EFFECT OF NECK MUSCLE STRENGTH AND HOCKEY GOALTENDER HELMET LINERS IN MITIGATING CONCUSSION RISK DURING SIMULATED HORIZONTAL HEAD IMPACTS

Concussions represent the second most common injury for ice hockey goaltenders. This study examined the combined effect of neck strength level and helmet liner type in mitigating concussion risk for ice hockey goaltenders. The researchers tested each helmet liner material statically for energy absorption capacity of the liner material, and dynamically by recreating concussion-causing events via head impact simulations for the risk of head injury criterion (HIC). The thermoplastic polyurethane (TPU) liner outperformed the standard vinyl nitrite (VN) liner during static testing and significantly reduced the HIC for high levels of neck strength (in newtons) during the repeated impact testing at the front, side, and back locations of the helmet. This information may facilitate the development of helmet liners composed of TPU and VN material across a range of neck strength levels to mitigate concussion risk for goaltenders

A modified method of evaluating the impact of air humidity on human acceptable air temperatures in hot-humid environments

This research aims to investigate human thermal responses to air humidity in warm and hot environments and to evaluate the effect of humidity on human thermal comfort. 20 subjects were involved in 12 exposure experiments in a well-controlled climate chamber at three relative humidity levels (40%, 60%, 80%) and four air temperature levels (26 °C, 28 °C, 30 °C, 32 °C) with little indoor airflow. The physical environmental and physiological parameters, as well as subjective questionnaires, were collected simultaneously with the on-going experiments. The results show that in hot environments, particularly when the air temperature exceeds 30 °C, the relative humidity has a significant effect on human thermal responses both physiologically and subjectively. The Standard Effective Temperature (SET) is biased when evaluating human thermal comfort in hot-humid environments without considering human thermal adaptation to humidity. Hence, a humidity correction coefficient eRH is proposed to modify the deviation of the SET under different relative humidity levels, and to quantify the effect of humidity on human acceptable air temperatures. The modified acceptable temperature-humidity zone has been obtained using the modified method

Protective Efficacy of Vitamins C and E on p,p′-DDT-Induced Cytotoxicity via the ROS-Mediated Mitochondrial Pathway and NF-κB/FasL Pathway

Dichlorodiphenoxytrichloroethane (DDT) is a known persistent organic pollutant and liver damage toxicant. However, there has been little emphasis on the mechanism underlying liver damage toxicity of DDT and the relevant effective inhibitors. Hence, the present study was conducted to explore the protective effects of vitamin C (VC) and vitamin E (VE) on the cytotoxicity of DDT in HL-7702 cells and elaborate the specific molecular mechanisms. The results demonstrated that p,p′-DDT exposure at over 10 µM depleted cell viability of HL-7702 cells and led to cell apoptotic. p,p′-DDT treatment elevated the level of reactive oxygen species (ROS) generation, induced mitochondrial membrane potential, and released cytochrome c into the cytosol, with subsequent elevations of Bax and p53, along with suppression of Bcl-2. In addition, the activations of caspase-3 and -8 were triggered. Furthermore, p,p′-DDT promoted the expressions of NF-κB and FasL. When the cells were exposed to the NF-κB inhibitor (PDTC), the up-regulated expression of FasL was attenuated. Strikingly, these alterations caused by DDT treatment were prevented or reversed by the addition of VC or VE, and the protective effects of co-treatment with VC and VE were higher than the single supplement with p,p′-DDT. Taken together, these findings provide novel experimental evidences supporting that VC or/and VE could reduce p,p′-DDT-induced cytotoxicity of HL-7702 cells via the ROS-mediated mitochondrial pathway and NF-κB/FasL pathway

A Smac-mimetic sensitizes prostate cancer cells to TRAIL-induced apoptosis via modulating both IAPs and NF-kappaB

<p>Abstract</p> <p>Background</p> <p>Although tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a promising agent for human cancer therapy, prostate cancer still remains resistant to TRAIL. Both X-linked inhibitor of apoptosis (XIAP) and nuclear factor-kappaB function as key negative regulators of TRAIL signaling. In this study, we evaluated the effect of SH122, a small molecule mimetic of the second mitochondria-derived activator of caspases (Smac), on TRAIL-induced apoptosis in prostate cancer cells.</p> <p>Methods</p> <p>The potential of Smac-mimetics to bind XIAP or cIAP-1 was examined by pull-down assay. Cytotoxicity of TRAIL and/or Smac-mimetics was determined by a standard cell growth assay. Silencing of XIAP or cIAP-1 was achieved by transient transfection of short hairpin RNA. Apoptosis was detected by Annexin V-PI staining followed by flow cytometry and by Western Blot analysis of caspases, PARP and Bid. NF-kappaB activation was determined by subcellular fractionation, real time RT-PCR and reporter assay.</p> <p>Results</p> <p>SH122, but not its inactive analog, binds to XIAP and cIAP-1. SH122 significantly sensitized prostate cancer cells to TRAIL-mediated cell death. Moreover, SH122 enhanced TRAIL-induced apoptosis via both the death receptor and the mitochondrial pathway. Knockdown of both XIAP and cIAP-1 sensitized cellular response to TRAIL. XIAP-knockdown attenuated sensitivity of SH122 to TRAIL-induced cytotoxicity, confirming that XIAP is an important target for IAP-inhibitor-mediated TRAIL sensitization. SH122 also suppressed TRAIL-induced NF-kappaB activation by preventing cytosolic IkappaB-alpha degradation and RelA nuclear translocation, as well as by suppressing NF-kappaB target gene expression.</p> <p>Conclusion</p> <p>These results demonstrate that SH122 sensitizes human prostate cancer cells to TRAIL-induced apoptosis by mimicking Smac and blocking both IAPs and NF-kappaB. Modulating IAPs may represent a promising approach to overcoming TRAIL-resistance in human prostate cancer with constitutively active NF-kappaB signaling.</p