高频振动筛代替击振细筛在铁矿选厂的应用

高频振动筛代替击振细筛在铁矿选厂的应用张永昌，孙子建，郭瑞珍（冶金部邯邢冶金矿山管理局）高频振动筛用于选矿二段分级代替旋流器、击振细筛在符山铁矿选厂经过工业性试验，于１９９２年９月投入使用。由于高频振动筛效率高，减少了二段磨矿负荷，从而减少了设备，简...

Evaluation of ultra-fine grained tungsten under transient high heat flux by high-intensity pulsed ion beam

Pure tungsten, oxide dispersion strengthened tungsten and carbide dispersion strengthened tungsten were fabricated by high-energy ball milling and spark plasma sintering process. In order to evaluate the properties of the tungsten alloys under transient high heat flues, four tungsten samples with different grain sizes were tested by high-intensity pulsed ion beam with a heat flux as high as 160 MW/（m^2·s^-1/2）. Compared with the commercial tungsten, the surface modification of the oxide dispersion strengthened tungsten by high-intensity pulsed ion beam is completely different. The oxide dispersion strengthened tungsten shows inferior thermal shock response due to the low melting point second phase of Ti and Y2O3, which results in the surface melting, boiling bubbles and cracking. While the carbide dispersion strengthened tungsten shows better thermal shock response than the commercial tungsten.

Constitutive model for concrete subjected to impact loading

To better design and analyze concrete structures, the mechanical properties of concrete subjected to impact loadings are investigated. Concrete is considered to be a two-phase composite made up of micro-cracks and solid parts which consist of coarse aggregate particles and a cement mortar matrix. The cement mortar matrix is assumed to be elastic, homogeneous and isotropic. Based on the Moil-Tanaka concept of average stress and the Eshelby equivalent inclusion theory, a dynamic constitutive model is developed to simulate the impact responses of concrete. The impact compression experiments of concrete and cement mortar are also carried out. Experimental results show that concrete and cement mortar are rate-dependent. Under the same impact velocity, the load-carrying capacity of concrete is higher than that of cement mortar. Whereas, the maximum strain of concrete is lower than that of cement mortar. Regardless of whether it is concrete or cement mortar, with the increase in the impact velocity, the fragment size of specimens after experiment decreases.

Effect of various melt and heat treatment conditions on impact toughness of A356 aluminum alloy

The microstructure and impact behavior of A356 aluminum alloy were studied after melt treatment processes of grain refinement and modification under both non-heat treated and T6 heat treated conditions. The modification and grain refinement were done with the addition of Al-10%Sr and Al-5Ti-1B master alloys, respectively. All casting parameters were kept constant in order to focus on the influence of mentioned treatments. The results indicate that the eutectic silicon morphology is the main parameter to control the impact behavior of alloy. Consequently, the individual grain refinement of as-cast alloy does not improve the impact toughness as the modification does. While, simultaneous grain refinement and modification provide higher impact toughness in comparison with individual treatments. T6 heat treatment of the alloy improves the impact toughness under all melt-treated conditions. This is related to the further modification of eutectic silicon particles. To verify the results and clarify the mechanisms, three-point bending test and fractography were used to interpret the improvement of impact toughness of the alloy.

Atomic force microscopy imaging and mechanical properties measurement of red blood cells and aggressive cancer cells

Mechanical properties play an important role in regulating cellular activities and are critical for unlocking the mysteries of life. Atomic force microscopy (AFM) enables researchers to measure mechanical properties of single living cells under physiological conditions. Here, AFM was used to investigate the topography and mechanical properties of red blood cells (RBCs) and three types of aggressive cancer cells (Burkitt's lymphoma Raji, cutaneous lymphoma Hut, and chronic myeloid leukemia K562). The surface topography of the RBCs and the three cancer cells was mapped with a conventional AFM probe, while mechanical properties were investigated with a microsphere glued onto a tip-less cantilever. The diameters of RBCs are significantly smaller than those of the cancer cells, and mechanical measurements indicated that Young's modulus of RBCs is smaller than those of the cancer cells. Aggressive cancer cells have a lower Young's modulus than that of indolent cancer cells, which may improve our understanding of metastasis.

Spatial and temporal profile of apoptosis following lateral fluid percussion brain injury

Objective: To investigate the spatial and temporal profile of neural cell apoptosis following traumatic brain injury (TBI). Methods: In addition to morphological evidence of apoptosis, TUNEL histochemistry assay was used to identify DNA fragmentation in situ at both light and electron microscopic levels, whereas characteristic internucleosomal DNA fragmentation of apoptosis was demonstrated by DNA gel electrophoresis. Results: Using TUNEL method, we detected massive cells with extensive DNA fragmentation in different regions of the brains of rats subjected to experimental traumatic brain injury. Compared with the sham controls, in the injured cortex, the apoptotic cells were detectable for up to 24 h and reached a peak at 1 week after injury. The number of apoptotic cells in the white matter had a significant increase as early as 12 h after injury and peaked at 1 week. The number of apoptotic cells increased in the hippocampus at 72 h, whereas in the thalamus, the peak of apoptotic cells was at 2 weeks after injury. The number of apoptotic cells in most regions returned to sham values 2 months after injury. Gel electrophoresis of DNA extracted from affected areas of the injured brain revealed only internucleosomal fragmentation at 185-bp intervals, a feature originally described in apoptotic cell death. And no DNA ladder was detectable in the cortex and hippocampus contralateral to the injured hemisphere.Conclusions: These data suggest that in addition to the well described necrotic cell death, a temporal course of apoptotic cell death is initiated after brain trauma in selected brain regions.