对于破碎骨料的过碎率研究

本文对骨料在破碎时的过碎率,进行了定量性的研究和描述。确定了测算值时的装置与取值基准;同时,还应用实际经验和数理统计的方法,提出了测定批数和批量的建议。这将是制胶工业考核碎骨机械装备优劣的一项统一标准。

发展农村商品经济问题及其对策——大同市新荣区新荣镇的调查

山西省大同市新荣区新荣镇位于万里长城脚下,地处塞北高原的丘岭地带,与内蒙接壤;可谓土地辽阔、资源丰富、交通方便,具有发展商品经济的天然优势。 一 党的十一届三中全会以后,农村普遍推行了以家庭为中心的联产承包经营责任制,改革对粮、棉、油等重要农副产品的购销体制,大幅度提高了农副产品收购价格,逐步减少了统购派购任务,扩大了生产经营自主权,调动了农民的生产积极性,新荣镇农村经济取得了突破性的进展。

语文教师如何避免无效提问

1.课堂提问存在诸多问题。比如课堂设置的问题过多、过于简单、缺乏新意、问题过大、问点不准、随意性强、问题过碎过细、提问急于求成、提问对象过于集中等。2.课堂提问如何避免无效提问。(1)问题要有一定的开放性。(2)多提些理解型和应用型的问题。(3)提问目的要明确。(4)提问要有针对性。

Pre-treatment of rocks prior to comminution--A critical review of present practices

It has been an established fact that comminution processes, crushing and grinding, are most energy intensive processes which account for more than half of the total energy consumed in mineral industries.Various alternative pre-treatment methods have been tried by experts around the globe. Although these methods yielded positive results in terms of reduction in energy consumption in crushing and particularly, in grinding operations at laboratory scale, their industrial application still remains an unresolved issue and challenge. Present review paper describes each one of these methods along with outcome of earlier studies and issues that need to be addressed through further rigorous experimental investigation.It also suggests the direction in which future studies can be carried out to meet the primary objective of making comminution processes more energy efficient than today they are.

Breaking process and mining stress evolution characteristics of a high-position hard and thick stratum

Based on the boundary support conditions of overlying high-position,hard and thick strata,a Winkler foundation beam mechanical model was built.Computational expressions for the characteristics and position of the bending moment for high-position,hard and thick strata were constructed by theoretical analysis,and the initial breaking position of high-position,hard and thick strata was also analyzed.The breaking process and evolution law of mining stress in high-position,hard and thick strata were studied by similar material simulation tests.Studies show that:due to the foundation deformation effect of the lower strata,the initial break position in high-position,hard thick layers is in the middle of goaf;vertical tension fractures first occur under the middle surface,then tilt tension fractures form at both sides and a non-uniform thickness of the fracture structure forms and produces subsidence deformation;behind the coal wall tilt fractures extend and eventually complete the migration.Mining stress produces obvious changes before and after the breakage of the high,hard and thick stratum;high stress concentration forms in front of the coal wall before breakage and fracture stress concentration significantly reduces after migration.Coal seam mining under high-position,hard thick strata can easily induce dynamic phenomena.

A novel wastewater cleaning system for the stone-crushing and sand-making process

The nature of the slurry from the stone-crushing and sand-making processes is analyzed to develop a novel separation process.The process comprises hydro-cyclone separation followed by screening of the fines,clarification,and filtration.Recovering fine sand and clean wastewater for recycle is demonstrated.The +0.045 mm fine sand fraction and à0.045 mm ultra-fine clay in the slurry are separated and recovered.Fine sand that was previously lost and wasted is now recoverable.The cleaned and reused water is as much as 94% of the total.

A New Attempt of Using Crushed Plastic Solid Wastes in Water Filtration

The aim of this new study is to investigate the ability of using crushed plastic solid wastes in water filtration by using a pilot plant. Two sets of filters were used. The first set represents mono media filters. The first filter is a sand media with effective size of 0.65 mm and the others three are plastic media with different grain sizes. The second set represents dual media filters with different depths, the filters were made to operate with the same effective size （0.6-1.0 mm）. These filters were subjected to the same operating conditions of filtration rates and infiuent turbidity. The filters were operated at rates of 5, 7.5, 10, and 12.5 m/h in order to find the optimum filtration velocity with influent turbidity ranged between 7 and l0 NTU （nephelometric turbidity unit）. The results indicated that the single plastic filters and the dual filters produced water of the same high quality as the sand filter. Plastic filters were slower in the development of head losses by about of 8%-78% less and they have longer running time than the sand filter, while the dual filters were slower in the development of head losses by about of 14%-16% and they have longer running time by about of 12%-40% than the sand filter.

Energy dissipation through wind-generated breaking waves

Wave breaking is an important process that controls turbulence properties and fluxes of heat and mass in the upper oceanic layer.A model is described for energy dissipation per unit area at the ocean surface attributed to wind-generated breaking waves,in terms of ratio of energy dissipation to energy input,windgenerated wave spectrum,and wave growth rate.Also advanced is a vertical distribution model of turbulent kinetic energy,based on an exponential distribution method.The result shows that energy dissipation rate depends heavily on wind speed and sea state.Our results agree well with predictions of previous works.

Influence of the Hydriding Cycles on U-IOMo Alloy Comminution Process

Hydriding-dehydriding process has been widely employed to comminute uranium alloys. Developments have been made to improve this process because it is a cheaper way to obtain powder of uranium alloys compared to the other methods, such as atomization. This work presented an innovative comminution process of U-10Mo alloy in laboratory scale where a Sievert type equipment was utilized and only hydriding cycles were employed without repetition of the dehydriding procedure. Experiments of comminution of the U-10Mo alloy were carried out by employing alloy samples which were submitted to different heat treatment conditions and, subsequently, to different hydriding cycles. The heat treatments considered were hot rolled at 800 ℃, homogenization at 900 ℃ or 1,000 ℃ and aging at 520℃. It was observed that the number of hydriding cycles and heat treatment conditions have influenced the particle size distributions. Samples that were hot-rolled, homogenized at 1,000 ℃ and aged, and comminuted with five cycles of hydriding have produced powders with particle size distribution more uniform with the major quantity of particles in the range from 50μm to 200 μm while the other conditions have obtained a great quantity above 200 μm.

A constitutive model for granular materials considering grain breakage

A particle breakage has a significant impact on the mechanical behavior of granular materials. In this paper, we present an elasto-plastic model with two yield surfaces to which the influence of particle breakage has been introduced. The main feature of this model is to incorporate the change in the critical state line (CSL) consequent to the grain breakage induced by isotropic and deviatoric stresses during loading. For this purpose we propose a breakage function which connects the evolution of the CSL to the energy consumed. Results from earlier studies on drained and undrained compression and extension triaxial tests were used to calibrate and validate the model. Comparison between earlier results and our simulations indicates that the model can reproduce with good accuracy the mechanical behavior of crushable granular materials and predict the evolution of the grain size distribution during loading.

Modeling on effervescent atomization:A review

The study and modeling process of effervescent atomization are reviewed. The mechanism of droplet events and the treatment of liquid fragmentation process and dispersed particles are systematically presented, which includes the primary atomization of Newtonian and non-Newtonian fluid, instability analysis, turbulence treatment, particle tracking, secondary atomization and droplets collision. The review on the sub-models involved in the simulation of effervescence is followed by a summary of the achievements of modeling. First is the validation of models; then the parametric study is summarized; the third part introduces the fitting formula of droplet mean size and impinging factors, and finally the scope of future study is indicated.

Bubble breakup in a microfluidic T-junction

We conduct a computational fluid dynamics simulation to investigate the behaviors of bubble breakup in a microfluidic T-junction using volume-of-fluid method to represent the interface. The evolution of bubble mor- phology and the distributions of velocity and pressure in flow field are analyzed, and the effect of width ratio between main channel and branch on the bubble mor- phology are evaluated. The results indicate that, the ＂tun- nel＂ breakup, obstructed breakup, combined breakup and non-breakup are observed during the bubble flows through the T-junctions under different condition. The whole bub- ble breakup process undergoes the extension, squeeze and pinch-off stages, while the non-breakup process experi- ences extension and pushing stages. We find that, in the squeeze stage, a local vortex flow forms at the front edge of the bubble for the ＂tunnel＂ breakup while the velocity inside the bubble is of a parabolic distribution for the obstructed breakup. Irrespective of non-breakup regimes, there is a sudden pressure drop occurring at the gas-liquid interface of the bubble in the squeeze stage, and the pres- sure drop at the front interface is far larger than that at the depression region. The transition of the bubble breakup regime through the T-junction occurs with an increase in width ratio of main channel to the branch, which sequen- tially experiences the non-breakup regime, ＂tunnel＂ breakup regime and obstructed breakup regime. The flow regime diagrams are plotted with a power-law correlation to distinguish the bubble/droplet breakup and non-breakup regimes, which also characterize the difference between bubble and droplet breakup through a T-junction.

On the Theory of Fragmentation Process with Initial Particle Volume

The problem of fragmentation(disintegration) process is theoretically studied with allowance for the initial particle volume. An exact analytical solution of integro-differential model governing the fragmentation phenomenon is obtained. The key role of a finite initial volume of particles leading to substantial changes of the particle-size distribution function is demonstrated.

Soil and climate equally contribute to changes in the species compositions of Brazilian dry forests across 300 km

Aims Understanding the factors that control biodiversity distributions at different spatial scales has been a key challenge for conservation efforts.That biodiversity,reflected in differences in species compositions among sites(beta diversity),can be derived from species replacement(turnover)and is driven by multiple factors.Here,we sought to tackle this issue through two questions related to threatened Brazilian seasonally dry forests:(i)what is the contribution of species turnover to beta diversity?and(ii)which factors drive variations in species compositions among forest patches?Methods We sampled tree species and environmental variables(soils and climate)in 17 dry forest patches spaced almost 300 km apart.We used the beta diversity partitioning framework to determine the contribution of turnover.We used redundancy analysis,with properly controlled spatial structure,to assess the contributions of the environmental and spatial factors to the variations of the species composition.Important Findings Beta diversity among the patches was mainly represented by the turnover component(98.2%),with Simpson dissimilarity superior to other regions of the country(means of 0.89 and 0.71 in multiple site and pairwise measures,respectively).The environmental factors measured explained more than space,representing 30.3%of the variation of the species composition,of which 28.1%was nonspatially structured.We suggest that 300 km represents a threshold at which edaphic and climatic predictors have similar effects in determining community turnover(14.9%and 12.6%,respectively,without spatial structure).Thus,conservation strategies should be considered across landscapes to effectively protect tropical forest diversity,as even considering the different climatic aspects covered by the scale,landscaped edaphic varieties are important drivers of species turnover.

Removal of a broken guide wire entrapped in a fractured femoral neck

Guide wire plays an important role in the fixation of femoral neck fracture with dynamic hip screw （DHS）. Breakage of a guide wire during operation is a very rare condition. We met such a dilemma in DHS fixation of a 54-year-old male patient who sustained Garden type IV frac- ture of the right femoral neck. The distal end of the guide wire broke and was entrapped in the fractured femoral neck. We tried to get the broken part out by a cannulated drill. Reaming was started with the cannulated drill slowly rotat- ing arotmd the guide K-wire until the reamer fully contained the target under fluoroscope. A bone curette was used to get the broken wire out but failed, so we had to use the cannuated drill to dredge this bone tunnel. Finally the bro-ken wire end was taken out, mixed with blood and bone fragments. Through the existing drilling channel, DHS fixa- tion was easily finished. The patient had an uneventful re- covery without avascular necrosis of femoral head or non- union of the fracture at one year＇s follow-up. A few methods can be adopted to deal with the broken guide wire. The way used in our case is less invasive but technically challenging. When the guide wire is properly positioned, this method is very practical and useful.