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Polyurethane polishing pads are often used for polishing hard and brittle materials such as optical glass. The morphology and the wear of polishing pads directly influence the polishing accuracy and efficiency. Experimental studies were conducted on the micro-morphology and wear behavior of polyurethane polishing pads during different polishing time and their effects on material removal rate and surface roughness were analyzed. The results showed that the material removal rate and surface roughness are 0.977μm/min and 153.67nm respectively when the spindle speed is 8000r/min， the feed speed is 0.0150mm/s and the axial ultrasonic amplitude is 5μm. Polyurethane polishing pads have relatively little wear in the first 30 min， the surface of the polishing pads is filled with abrasive particles and optical glass debris， as the polishing time increases， damaging the porous structure of polishing pads. The surface of the polishing pads gradually hardens and loses its elasticity. Meanwhile， the abrasive particles and the debris invading the surface of the polishing pads will prevent the renewal of the abrasive particles in the contact area during the polishing， resulting in a reduction in the polishing quality. [ABSTRACT FROM AUTHOR]

BACKGROUND: Totally 60%-70% of hospital-acquired infections are related to medical devices of different materials, and bacterial biofilm cells play an important role in chronic infections. Bacterial adhesion and biofilm formation are affected by the characteristics of biological materials, such as surface charge, hydrophobicity, hardness, and surface chemistry. OBJECTIVE: To study the phagocytosis of macrophages on the early biofilm cells of E. coli on polydimethylsiloxane, a biomaterial with different surface hardness. METHODS: Hard (5:1), medium (20:1) and soft (40:1) polydimethylsiloxane with three surface hardness was prepared by controlling the mass ratio of base material and curing agent. (1) E. coli were inoculated on the surface of three kinds of hard materials to incubate bacterial biofilm cells. Activated macrophages were dropped onto the surface of each material. CFU cell counting, flow cytometry and inverted fluorescence microscope were used to detect the difference in macrophages Phagocytosis of E. coli biofilm cells on surface hardness materials. (2) Macrophages were inoculated on the surface of three hard materials, and then E. coli was added. CFU cell count was applied to detect macrophages phagocytosis of E. coli biofilm cells on materials with different surface hardness. RESULTS AND CONCLUSION: (1) Bacteria were inoculated first and then macrophages were added to the experiment: CFU cell count, flow cytometry technology and inverted fluorescence microscope detection showed that as the surface hardness of the material increased, the phagocytosis of macrophages increased and the number of E. coli biofilm cells decreased. The difference in the phagocytic rate of bacterial biofilm cells among the three groups was significant (P < 0.001). (2) Macrophages were inoculated first and then bacteria were added to the experiment: CFU cell count test showed that as the surface hardness of the material increased, the phagocytosis of macrophages increased and the number of bacterial cells decreased. It could be seen under the microscope that the macrophages were on the hard surface material more spread, with higher activity, and visible extension of pseudopods. (3) The results show that with the increase of the hardness of polydimethylsiloxane, the efficiency of macrophages phagocytosis of E. coli biofilm cells is higher. It is speculated that by optimizing the hardness of biological materials, endophyte-related infections can be better controlled. [ABSTRACT FROM AUTHOR]

The grinding experiment of soda-lime glass was carried out to study the effects of grinding parameters on the surface roughness and morphology of the glass. The surface morphology was compared after grinded by different coated micro-grinding tools and surface roughness under different cooling conditions were also analyzed. The results show that when the grinding speed increases and the grinding depth and feed rate decrease, the surface roughness decreases and the surface morphology becomes smoother and better. Under different cooling conditions, the level of surface roughness after wet grinding is lower and the surface quality is better. In comparison with the CBN-coated micro-grinding with the same granularity, the diamond-coated micro-grinding can perform a better surface quality and more suitable for hard and brittle materials, such as glass. [ABSTRACT FROM AUTHOR]

As polydimethylsiloxane (PDMS) is a high elastic material rather than a hard and brittle material at room temperature, the processing efficiency is very low or even zero by using micro-abrasive air jet to process it, and a large number of abrasive particles will be embedded into the surface of PDMS. When the cooling of PDMS is incomplete, that is, in the transition state between the high elastic state and the glass state, the machining of PDMS using cryogenic micro-abrasive air jet will still have a very serious abrasive embedding phenomenon, resulting in poor processing effect. To solve this problem, this paper uses ANSYS Fluent software to conduct heat transfer simulation analysis on PDMS to obtain the internal temperature change of PDMS, so as to calculate the cooling rate in the depth direction of PDMS. At the same time, the same process parameters are used to process micro holes on the surface of PDMS, and the maximum average erosion processing rate in the depth direction of PDMS can be calculated. Finally, it is found that the cooling rate is much faster than the erosion processing rate. According to the analysis results of heat transfer simulation, single-factor experiments are carried out to explore the effect of feed speed v, processing distance D, erosion angle α, and processing pressure p on the processing performance of PDMS, which provides an important reference for further research. [ABSTRACT FROM AUTHOR]

High surface temperature can easily cause heat stress in dairy cows in most tropic areas of China in summer. Heat stress can negatively affect the production and reproductive performance, as well as the immune capacity of cows. Mild and moderate heat stress has also gradually become a key factor constraining the healthy production of dairy cows in recent years, with the improvement of large-scale breeding. However, the current cowshed cooling technology is limited by environmental conditions or high energy consumption. It is highly demanding for the local cooling system in the whole bed suitable for a low-temperature cooling source. In this study, a local cooling system of water pipes was designed to improve the bed environment and alleviate heat stress of dairy cows, according to the heat dissipation of thermal sensitive areas. The experiment was carried out in Datong Experimental Station of the National Dairy Industry Technology System. DN40 galvanized water pipes were laid in front of and behind the breastplate positions of two-bed rows in a naturally ventilated cowshed. The water pipes were covered with a cushion layer about 3 cm thick to meet the safety and comfort needs of cows. A floor heating radiation film of 0.6 m wide was laid below to reduce cooling loss of the system, particularly for heat preservation and insulation. Water pipes were arranged in a single serpentine coil suitable for the narrow rectangle bed, with 2 tubes at the height of mouth and nose of cow, while 4 tubes at the contact position of chest and abdomen of cow, where the space between tubes was 60 mm. The cooling water of the system was first from 200 m deep groundwater in the milking hall, and then flowed through the treated beds in the cowshed to cool down, finally back to the storage tank in the milking hall for washing. The flow rate was 0.3 m/s in pipes. Performance indexes were selected to evaluate the system operation, such as the temperature of the water pipe wall and bed surface. The results showed that the pipe wall temperature varied between 18oC and 22oC under the pipe flow of 0.38 kg/s and flow rate of 0.3 m/s, indicating a positive linear correlation between the pipe wall temperature and the distance of water inlet (P<0.01). The surface temperature of the no-load bed decreased by 2.1oC in the treated group, compared with the control. Besides, the application of the system was tested in different core body temperatures, respiration rates, milk yields, and lying behaviors of cows. Specifically, the cows were detected in the moderate heat stress for 50.7% of the day, while the mild heat stress for 17.4% during phase one. The average core body temperature in the treated group was 0.3oC lower than that in the control group, indicating an extremely significant difference (P<0.01). The respiratory rate in the treated group was at most 9times/min lower than that in the control group. There was no significant decrease in the milk yield of cows in the treated group. Correspondingly, a similar trend was achieved in the daily changes of core body temperature and respiratory rate of cows for the treated and control groups. Specifically, the cooling system performed better, as the temperature increased. Furthermore, there was no significant difference in the lying-down time between the two groups, even though the local bed environment in the treated group was significantly better than that of the control group. More importantly, a 3 cm thick pad was laid on water pipes to improve the bed comfort, which was installed after the chest plate position to ensure that the region of the udder was not squeezed when cows laid down. Nevertheless, there was an inevitable impact on the bedrest comfort, where the single lying time fluctuated greatly in the initial operation of the system, because the galvanized water pipe was made of hard material, while the cushion was often opened by hooves. The lying time in the treated group gradually approached that in the control group, as the experiment went on. Anyway, the water-cooled bed system can widely be expected to effectively improve the local bed environment in the cowshed, further alleviating the heat stress of cows. [ABSTRACT FROM AUTHOR]

The variations in the constitutive characteristics of hard and brittle materials processed under ultrasonic vibration are researched based on the nonlocal theory in order to explore the high efficiency and ductility of ultrasonic vibration processing. The kernel function formula is deduced by analyzing the kernel parameters. The effects of internal and external characteristic variables, such as grain space, amplitude and frequency of ultrasonic vibration, on the nonlocal kernel function are systematically studied through numerical simulation. The theoretic results about the influence of ultrasonic vibration on the kernel function are verified in uniaxial tensile experiments. The research results show that, in terms of the effects of amplitudes and frequencies on the kernel function, there appears a shape of the downward parabola and there exists a critical value. In the experiment of tensile rupture, the practical influences of amplitudes and frequencies agree with the theoretic results deduced by numerical simulation. The fracture stress is minimal when the amplitude is 14.94 µm and the frequency is 35 kHz. This study of the nonlocal elastic kernel function under ultrasonic vibration ensures an accurate understanding of the influences of ultrasonic vibration on the constitutive characteristics of materials, and provides the optimal parameters for ultrasonic vibration processing. [ABSTRACT FROM AUTHOR]