玻璃离子水门汀加入二氧化钛纳米颗粒后的机械与抑菌性能

背景:玻璃离子水门汀已被逐渐应用于口腔临床的诸多方面,但其机械强度较低、抑菌作用不明显,限制了其进一步广泛应用。目的:考察加入不同比例二氧化钛纳米颗粒对玻璃离子水门汀机械性能和抑菌作用的提升效果。方法:实验分4组,低、中、高质量分数二氧化钛组玻璃离子水门汀中分别含3%,6%,9%二氧化钛纳米颗粒,对照组不含二氧化钛纳米颗粒。利用万能材料试验机和硬度测试仪考察各组试件的抗弯强度、抗压强度和表面硬度。将试样浸没在人工唾液中,采用氟离子选择性电极测定氟释放量累积量,利用直接接触法考察试样对变形链球菌的抑菌效果。结果与结论:与对照组相比,低、中质量分数二氧化钛组高玻璃离子水门汀的抗弯强度、抗压强度和表面硬度显著提高(P<0.05),高质量分数二氧化钛组显著下降(P<0.05)。各组玻璃离子水门汀的氟释放累积量随时间变化均表现为平滑递增曲线。低质量分数二氧化钛组变形链球菌的吸光度值最低。说明二氧化钛纳米颗粒的加入对玻璃离子水门汀的氟释放行为影响不显著,可显著提高对变形链球菌的抑菌效果。

New criterion for rock joints based on three-dimensional roughness parameters

The shear behavior of rock joints is important in solving practical problems of rock mechanics. Three group rock joints with different morphologies are made by cement mortar material and a series of CNL(constant normal loading) shear tests are performed. The influences of the applied normal stress and joint morphology to its shear strength are analyzed. According to the experimental results, the peak dilatancy angle of rock joint decreases with increasing normal stress, but increases with increasing roughness. The shear strength increases with the increasing normal stress and the roughness of rock joint. It is observed that the modes of failure of asperities are tensile, pure shear, or a combination of both. It is suggested that the three-dimensional roughness parameters and the tensile strength are the appropriate parameter for describing the shear strength criterion. A new peak shear criterion is proposed which can be used to predict peak shear strength of rock joints. All the used parameters can be easily obtained by performing tests.

Bonding between Aggregates and Cement Pastes in Concrete

This investigation was carried out to study the effect of aggregate roughness on ITZ （interfacial transition zone） at same water/cement ratio and the influence of silica fume on the bond strength. On the experimental side, two types of aggregates （limestone and granite） were used, which were prepared with broken surface. Cement （Type I） was used with same w/c ratio for all batches. In order to study the effect of silica fume on the bond, the same mixes were produced with 8% silica fume. Three different tests were performed： ＂pull a part＂, Brazilian test and compressive strength test. The specimens for Brazilian and compressive strength were tested after 28 days, while the ＂pull a part＂ specimens were tested after 29 days. The result showed that the bond strength is influenced by the surface roughness of aggregate. For the same mix, limestone recorded higher bond strength than granite. Moreover, the bond strength is increased by adding the silica fume.

Fatigue behavior of press hardened Al-Si coated high strength steel

The fatigue behavior of press hardened Al-Si coated high strength steel has been investigated,and the fatigue strength turns out to be about 1 000 MPa.Surface morphology of fractured and non-fractured specimen has been observed,and the coating shows significant influence on the fatigue behavior.The difference of elastic modulus between coating and substrate led to the main cracks perpendicular to the loading direction.The coating close to fracture exfoliated thinly,while the coating far away from the fracture kept integrated.Though the specimen was polished to obtain high surface quality,3 types of cracks occurred during the fatigue test.What’s more,inclusion particles were proved to play a crucial role in causing these cracks.

Surface enhanced fluorescence by porous alumina with nanohole arrays

The fluorescence enhancement of Rhodanfine 6G （Rh6G） fluorophore in the close vicinity of porous alumina film with ordered nanohole arrays is investigated. Experimental observations show that the nonmetallic substrate with hole arrays enhances the fluorescence intensity. By comparing the fluorescence emissions that are excited with 325 nm and 532 nm, better fluorescence enhancement is obtained with excitation at a shorter wavelength. The study suggests that higher fluorescence excitation effi- ciency due to the energy transfer from oxygen vacancies to Rh6G fluorophore molecules is responsible for better fluorescence enhancement. The contribution of the scattering of nanohole arrays to the fluorescence enhancement is also proposed based on the intensity increase and reduced lifetime when the energy transfer from oxygen vacancy is absent. The result of the current study is useful for developing non-metal substrates in the study of spectroscopic enhancement, and is expected to advance the applications of porous alumina to microanalysis.