Large-scale flame structures in ultra-lean hydrogen-air mixtures

The paper discusses the peculiarities of flame propagation in the ultra-lean hydrogen-air mixture. Numerical analysis of the problem shows the possibility of the stable self-sustained flame ball existence in unconfined space on sufficiently large spatial scales. The structure of the flame ball is determined by the convection processes related to the hot products rising in the terrestrial gravity field. It is shown that the structure of the flame ball corresponds to the axisymmetric structures of the gaseous bubble in the liquid. In addition to the stable flame core, there are satellite burning kernels separated from the original flameball and developing inside the thermal wake behind the propagating flame ball. The effective area of burning expands with time due to flame ball and satellite kernels development. Both stable flame ball existence in the ultra-lean mixture and increase in the burning area indicate the possibility of transition to rapid deflagrative combustion as soon as the flame ball enters the region filled with hydrogen-air mixture of the richer composition. Such a scenario is intrinsic to the natural spatial distribution of hydrogen in the conditions of terrestrial gravity and therefore it is crucial to take it into account in elaborating risk assessments techniques and prevention measures.     

Self-arrangement of solder balls by using the surface wettability difference

This letter describes a simple and efficient method of the solder ball placement for electronic packaging. For self-arranging solder balls by using the surface wettability difference, the substrate surface was patterned into the hydrophilic Au solder ball land array with the hydrophobic Teflon passivation layer. Water droplets were formed only on the solder ball lands after dipping the patterned substrate into water. Then, the solder balls were placed on each of the wetted solder ball lands. After soldering two plates with 3 × 3, 4 × 4, and 5 × 5 arrayed solder balls, their average shear strengths were as high as 195, 220, and 251 MPa, respectively.     

Use of soybean isolate in coated foods: simulation study employing glass balls and substantiation with extruded products

Simulation studies on coating using glass balls as ideal solid and soy flour isolate dispersions of different concentrations (10–25%) and at different temperatures (20–50 °C) were conducted. A few coating parameters such as total uptake of dispersion, solid uptake, dimensionless uptake (DU) and uptake per unit area were determined. Further, the study was extended by using corn‐soy extrudates in place of glass balls while using soy flour isolate dispersion of same concentrations and maintained temperature ranges. Rheological characteristics of the dispersions like flow behaviour index, consistency index, apparent viscosity and yield stress were determined to relate them with coating behaviour. The dispersions behaved like a non‐Newtonian shear‐thinning fluid and exhibited yield stress between 0.75 and 1.72 Pa. An increase in concentration of solids in the dispersion increased yield stress, consistency index and apparent viscosity while the flow behaviour index decreased from 0.67 and 0.39. Inter‐relationships between various rheological and coating characteristics were determined; simulation studies on coating by employing glass balls can provide a good interrelation of |r| ≥ 0.88–0.99 that is comparable with |r| ≥ 0.69–0.99 (P ≤ 0.01) obtained with actual experimentation using corn‐soy extrudates.     

Improved pruning of large data sets for the minimum enclosing ball problem

Minimum enclosing ball algorithms are studied extensively as a tool in approximation and classification of multidimensional data. We present pruning techniques that can accelerate several existing algorithms by continuously removing interior points from the input. By recognizing a key property shared by these algorithms, we derive tighter bounds than have previously been presented, resulting in twice the effect on performance. Furthermore, only minor modifications are required to incorporate the pruning procedure. The presented bounds are independent of the dimension, and empirical evidence shows that the pruning procedure remains effective in dimensions up to at least 200. In some cases, performance improvements of two orders of magnitude are observed for large data sets.     

利用排列组合解决多种“分球入盒”问题

将重复排列数、重复组合数、（广义）第二类Stirling数等排列组合的知识巧妙用来解决概率论中的几类＂分球入盒＂问题,其中涉及到球是否可辨、盒是否可辨等多种情况,并举出一些实例对模型加以应用。     

工具基准球在汽车模具加工检测上的应用

针对汽车注射模型芯的外形和结构特点及加工和检测中找正的难点,分析讨论了如何使用工具球,使加工和检测的找正速度方便、快捷、准确。提高模具制造的效率和质量。     

立方排列球体层渗流特性数值模拟研究

在多年冻土区块石夹层和块石护坡路基温度场的计算中,可以将块石层看作为多孔介质,但是块石的不规则给其渗透特性的研究带来了很大的麻烦,通过对立方排列球体层渗透特性的研究以期能为块石层的渗透特性研究做出铺垫。基于连续性方程、动量方程以及RNG湍流模型对直径为0.20 m、0.24 m和0.30 m立方排列球体层渗透特性进行模拟研究。对比和分析计算结果发现:球体层内部空气压力梯度与渗流速度之间呈良好的非线性幂函数关系;球体层的阻力系数与球体直径也显现出幂函数关系,球体直径越大,阻力系数越小。     

响应面法分析影响芹菜牛肉丸质地的因素

传统肉丸质构特性已有不少研究,但对于蔬菜类肉丸质构特性的研究却不多。以芹菜牛肉丸为研究对象,采用响应面分析法对其质构特性进行研究分析。结果表明,加工芹菜牛肉丸较好品质的条件是:淀粉添加量13%、卡拉胶添加量1.5%、芹菜汁添加量57%。     

Enhanced removal of ultrafine particles from kerosene combustion using a dielectric barrier discharge reactor packed with porous alumina balls

Ultrafine particles(UFPs) are harmful to human beings, and their effective removal from the environment is an urgent necessity. In this study, a dielectric barrier discharge(DBD) reactor packed with porous alumina(PA) balls driven by a pulse power supply was developed to remove the UFPs(ranging from 20 to 100 nm) from the exhaust gases of kerosene combustion. Five types of DBD reactors were established to evaluate the effect of plasma catalysis on the removal efficiency of UFPs. The influences of gas flow rate, peak voltage and pulse frequency of different reactors on UFPs removal were investigated. It was found that a high total UFP removal of91.4% can be achieved in the DBD reactor entirely packed with PA balls. The results can be attributed to the enhanced charge effect of the UFPs with PA balls in the discharge space. The UFP removals by diffusion deposition and electrostatic attraction were further calculated,indicating that particle charging is vital to achieve high removal efficiency for UFPs.