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排序方式: 共有3299条查询结果,搜索用时 15 毫秒
91.
《Ergonomics》2012,55(1):65-73
Shearing is a rural occupation developing considerable spinal loads and carrying a high risk of low back pain (LBP). Although the workforce has a skill structure, interaction between skill, spinal loads and LBP is unknown. We examined whether skill and LBP influenced trunk postures and loads within a sample of 80 shearers representing shear skill levels. A progression from junior to open class demonstrated a 100% increase in productivity, less time in severe flexion, more time in neutral lateral bend, and more time in axially twisted postures, with no increase in cumulative compressive and anterior shear forces. LBP prevalence increased linearly from 10% for junior through to 76% for open class shearers. Shearers with a history of LBP generated greater cumulative right medio-lateral shear forces, greater left lateral bend and left axial twist moments. Skill-based training that reduces asymmetric forces may help reduce such high prevalence levels of LBP. Statement of Relevance: Shearing is an important and physically demanding rural occupation. It requires sustained flexed postures that generate considerable spinal loads and a high risk of LBP. This research examines how skill and a history of LBP it carries interact to influence trunk postures and spinal loads within a sample of shearers. 相似文献
92.
结合具体工程实例,对现浇剪力墙结构转换层模板设计进行了探讨,并对梁侧模板、梁模板扣件的钢管支撑进行了计算说明,阐述了混凝土的浇筑顺序,提出了施工质量控制目标,以供类似工程参考应用。 相似文献
93.
Reduced graphene oxide (rGO) sheets have received great attention as a key element for thin barrier films that block the permeation of water vapor and other gases. However, it remains a challenge to prepare the rGO-based barrier films on plastic substrates through a chemically benign and low temperature fabrication route. Toxic chemicals or high temperature thermal treatments that are widely used for preparing rGO need to be avoided because they can damage the underlying plastic substrates. In this study, we report the fabrication of rGO/TiO2 composite films via an eco-friendly and low temperature ultraviolet (UV) photoreduction process and demonstrate their enhanced gas barrier properties by measuring water vapor transmission rates (WVTRs). When photocatalytic TiO2 nanoparticles are employed, UV exposure reduces the GO/TiO2 composite solution to form rGO/TiO2, which is subsequently deposited on plastic substrates. The rGO/TiO2 composites become resistant to water absorption because the UV photoreduction of GO/TiO2 effectively removes most polar groups on the GO sheets. We confirmed that rGO/TiO2 composites were successfully deposited onto the plastic substrate through a solution process and the barrier films led to a substantial reduction in WVTRs of the substrate. Our strategy for preparing graphene-based thin barrier films by using a UV photoreduction process enables the fabrication of solution-processed graphene-based encapsulation layers on plastic substrates with an eco-friendly and low temperature fabrication method. 相似文献
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A. RashidE.T. White T. HowesJ.D. Litster I. Marziano 《Chemical Engineering Research and Design》2012,90(1):158-161
To quantify the crystallization of racemic ibuprofen [2-(4-isobutyl-phenyl)-propionic acid] from aqueous ethanol it is necessary to know the growth rate kinetics. Growth rates were measured by adding SPG (size proportional growth) seed crystals to an isothermal non-nucleating batch crystallization and sampling during the batch. The supersaturation was measured by refractive index and the crystal size by laser light scattering (Malvern). To ensure the batch was non-nucleating the supersaturation was kept within the narrow secondary MZ (metastable zone). Measurements were made at three temperatures, 10, 25 and 40 °C. The growth rate was proportional (first order kinetics) to the solution supersaturation, expressed in mass ratio of ibuprofen to ethanol units. Despite the narrow MZ, the initial growth rates were substantial (up to 1 μm/min). Temperature has a large effect on growth rate with an activation energy of 13.7 kJ/mol. The water content affects the growth rate coefficient differently depending on the temperature. 相似文献
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In recent years advanced high strength steels (AHSS) received increased interest for light structures with improved performance, but they are often sensitive to edge cracking during sheet metal forming. In this study mechanically sheared edges were characterized for three dual phase steels (DP600, DP780 and DP980), sheared with three die clearances (5%t, 10%t, 15%t) and along rolling and transverse directions. Microstructures of the materials were provided first, and then the sheared edges were examined by optical microscopy and scanning electron microscopy that reveal the morphology and random feature of the sheared edges. A factorial analysis was performed to reveal the general trends of the processing parameters on four edge zones. A new strain measurement method was used for characterizing strain distribution in the sheared region, which shows the peak strain to be higher than 3. The strain quickly decreases from sheared edge to interior, leaving a shear-affected zone of about 500 μm or 31% of the thickness. The fracture processes and involved mechanisms were discussed. 相似文献
100.
Muhammad Atiqullah Mohammad M Hossain Sagir Adamu Anwar Hossaen 《Polymer International》2014,63(10):1824-1834
The melting and crystallization behaviours of a polyethylene‐block‐poly(methyl methacrylate) (PE‐b‐PMMA) diblock copolymer and a PE homopolymer were investigated using multiple heating and cooling rate differential scanning calorimetry (DSC) experiments, and modelling of the crystallization kinetics and lamellar thickness distribution. This new model was first validated applying literature and experimental data. The model‐predicted morphology (n = 3.2) closely matched the spherulitic morphology (n = 3), which was determined using polarized optical microscopy. For each experimental cooling rate, the model predicted diblock copolymer crystallinity that well matched the entire DSC crystallinity curve, notably for an Avrami–Erofeev index of n = 2; and apparent crystallization activation energy that hardly varied with the cooling rates used, relative crystallinity (α), and crystallization temperature or time. This disfavours the concept of variable activation energy. The use of the right crystallization model and parameter estimation algorithm is important for addressing the mathematical artefact. Under non‐isothermal cooling, the PE‐b‐PMMA diblock copolymer, as per the model prediction, crystallized without confinement (n ≠ 1), preserving the cylindrical structure. From the characteristic shapes of the crystallization function f(α(T)) versus 1/T and crystallization rate versus α plots, the resulting Tcmax and narrow αmax range can guide the search for an appropriate crystallization model. The overall treatment illustrated in this study is not restricted to a PE homopolymer and a PE‐b‐isotactic PMMA block copolymer. It can be generally applied to crystalline homopolymers and copolymers (alternating, random and block), as well as their blends. The block copolymers and blends can be crystalline–amorphous as well as crystalline–crystalline. © 2014 Society of Chemical Industry 相似文献