Abstract:Objectives: Polymerization shrinkage of dental composites remains a major concern in restorative dentistry because it can lead to micro-cracking of the tooth and debonding at the tooth-restoration interface. The aim of this study was to measure the full-field polymerization shrinkage of dental composites using the optical digital image correlation (DIC) method and to evaluate how the measurement is influenced by the factors in experiment setup and image analysis. Methods: Four commercial dental composites, Premise Dentine, Z100, Z250 and Tetric EvoCeram, were tested. Composite was first placed into a slot mould to form a bar specimen with rectangular-section of 4 mm×2 mm, followed by the surface painting to create irregular speckles. Curing was then applied at one end of the specimen while the other part were covered against curing light for simulating the clinical curing condition of composite in dental cavity. The painted surface was recorded by a charge-coupled device (CCD) camera before and after curing. Subsequently, the volumetric shrinkage of the specimen was calculated with specialist DIC software based on image cross correlation. In addition, a few factors that may influence the measuring accuracy, including the subset window size, speckle size, illumination light and specimen length, were also evaluated. Results: The volumetric shrinkage of the specimen generally decreases with increasing distance from the irradiated surface with a conspicuous exception being the composite Premise Dentine as its maximum shrinkage occurred at a subsurface distance of about 1 mm instead of the irradiated surface. Z100 had the greatest maximum shrinkage strain, followed by Z250, Tetric EvoCeram and then Premise Dentine. Larger subset window size made the shrinkage strain contour smoother. But the cost was that some details in the heterogeneity of the material were lost. Very small subset window size resulted in a lot of noise in the data, making it difficult to discern the general pattern in the strain distribution. Speckle size did not seem to have obvious effect on the volumetric shrinkage strain along specimen length; however, larger speckles resulted in higher level of noise or heterogeneity in the shrinkage distribution. Compared with bright illumination, dimmer lighting produced larger standard deviations in the measured shrinkage, indicating a higher level of noise. The longer the specimen, the greater was the rate of reduction with distance from the irradiated surface, especially for the longitudinal strain. Significance: The image correlation method is capable of producing full-field polymerization shrinkage of dental composites. The accuracy of the measurements relies on selection of optimal parameters in experimental setup and DIC analysis.

The model of flow press servo valve is built in this paper, during building the model, the author emphatically analyses the flow equation and force (torque) balance equation of every part of the valve, at the same time, all levels sub-models are organic combined according to power flow direction, signal flow direction of elements and causality, then we get the bond graph model of the flow press servo from this way. Adapting flow press servo valve and flow servo valve to concurrently control load system has its great advantage in restraining the superfluous force of the electro-hydraulic load simulator system, the performance such as load precision of system is enhanced greatly according to this method. Based on the system bond graph model, and by comparing the simulation curves and experiment curves, we can know that the simulation curves basically tally with the experiment curves, the bond graph models are validated right, which are flow press servo valve bond graph model and double valves concurrently control the electro-hydraulic load simulator system bond graph model. Simultaneity, the bond graph models in this paper take on generality, they are can be used on other aspects, such as other valve controlling cylinder system simulation, design and control strategy theory research.

It is very hard to fabricate nano-strctures on PEDOT:PSS film by conventional Nanoimprint Lithography for its non-thermoplastic property. Here we demonstrated a new nanoimprint process to pattern the PEDOT:PSS film at low temperature and low pressure by adding proper amount of Glycerol into PEDOT:PSS solution and pressing the Si-mold into Glycerol-PEDOT:PSS film under a pressure of 6.2Mpa for 45min at 80°C. We also compared our result to L. Tan and co-workers’. They found that positive replica was left on PEDOT:PSS film after pressing the Si-mold into Glycerol-PEDOT:PSS film under a pressure of 10Kpa for 5min at 80°C, but our work showed negative replica formed. Pressing time maybe is the critical reason to explain the different results. Holding the pressure longer gave the PEDOT:PSS enough time to flow into Si-mold and also gave Glycerol enough time to evaporate so that PEDOT:PSS became strong enough when separated the Si-mold from the PEDOT:PSS film. At last, Roman spectra was measured to confirm adding glycerol to PEDOT:PSS will not influence its molecular structure.

The thesis describes the feature and system principle of a new type automatic solar tracker in the Solar Radiation Observing System. The new type automatic solar tracker is absolutely automatic、all-weather and with high precision. The system plans two control modes: orbit tracking mode and sensor tracking mode. In the paper the rationale and the project of the two control modes in the system is elaborated and the smooth switch between the two control modes is discussed.

In order to suppress the friction and leakage interference of continuous rotary electro-hydraulic servo motor, make the motor tracking the periodic signals with high accuracy, and improve the high frequency response performance of continuous rotary electro-hydraulic servo motor, this paper established the mathematic model of the electro-hydraulic position servo system of the continuous rotary motor, and adopted the controlling method based on the zero phase error tracking controller to suppress the interference. Through the simulation, the result confirms that the zero phase error tracking control method decreases the tracking error of the system, increases the robust performance of the system and improves the frequency response performance of continuous rotary electro-hydraulic servo motor. This method is simple and feasible.