基于多周期同步测量的频率计设计

针对工程实践中发现的频率计存在1字节误差以及待测信号幅度过大的问题。基于多周期同步测量计数理论,提出了一种以C8051F020与FPGA为最小系统的频率计制作方案,实现对待测信号频率及脉宽的精确测量。系统主要包括3部分：信号整形部分、频率计算部分、液晶显示部分。待测信号经过信号处理后和标准信号一同输入FPGA内部,单片机协同FPGA对信号进行频率测量并读取测频数据,然后将读取到的数据经过运算处理后显示。经实验验证,该系统测频范围可达0.1 Hz~10 MHz,有效消除了1个字节的误差且具有一定的抗干扰能力。     

内蒙古翁牛特旗二台营子银多金属矿成矿地质特征及找矿标志

二台营子银多金属矿位于内蒙古大兴安岭成矿省,突泉-林西海西、燕山期铁(锡)、铜、铅、锌、银、铌(钽)Ⅲ级成矿带之次级成矿带的结合部位。区内岩浆活动频繁,褶皱、断裂发育,具有良好的形成银、金多金属矿床的成矿条件,但多年来一直没有投入系统的勘查工作,限制了本区的找矿突破。本文通过调查研究,论述了二台营子银多金属矿床的主要成矿地质特征,分析了其找矿标志,为本区开展进一步找矿工作提供了参考。     

对非相干光纤激光组束耦合效率的仿真研究

为了提高非相干光纤激光组束系统的耦合效率,需要分析影响耦合效率的各参数.理论分析及仿真研究结果表明,较小的高斯模场纵向偏移、离焦度和透镜焦距,较大的光栅周期对提高耦合效率是有利的,并且还存在最佳的光斑半径.在优化的系统参数基础上,系统的平均耦合效率可以达到58.1%.     

Supplementing Holstein cows with low doses of bovine somatotropin prepartum and postpartum reduces calving-related diseases

The objective of this study was to evaluate whether supplementing Holstein cows with bovine somatotropin (bST; 142.8 mg/14 d), beginning at 21 d (±3 d) before expected calving and continuing through 42 d in milk (±3 d), affected the incidence rates of retained fetal membranes (RFM), metritis (MET), clinical mastitis (MAS), digestive problems (DIG), ketosis (KET), milk fever (MF), displaced abomasum (DA, left or right), lameness (LAM), or number of sick cows during the first 60 d in milk. Data for multiparous Holstein cows from 3 separate trials were merged for analyses (n = 437). Cows in the bST-supplemented group (n = 162) received biweekly subcutaneous injections of Posilac, whereas control cows (n = 166) and a group of cohorts (n = 109) were not supplemented. Incidences of disease were collected from the herd health records. Across all treatment groups, the incidence rates (number of diseased cows divided by the total number of cows) for RFM, MET, MAS, DIG, KET, MF, DA, and LAM were 8.47, 18.31, 16.02, 4.35, 4.35, 3.66, 3.20, and 3.66%, respectively. The incidence rates of RFM, MET, MAS, DIG, KET, MF, DA, and LAM for cows in the bST-supplemented, control, and cohort groups were 6.79, 7.83, and 11.93%; 16.05, 7.47, and 22.94%; 10.49, 18.07, and 21.10%; 1.23, 5.42, and 7.34%; 1.23, 6.02, and 6.42%; 2.47, 4.22, and 4.59%; 2.47, 3.61, and 3.67%; and 3.70, 3.61, and 3.67%, respectively. The percentages of sick cows (number of cows having one or more cases of disease divided by the total number of cows) in the bST-supplemented, control, and cohort groups were 33.95, 43.37, and 49.54%, respectively. Significant chi-squared values were detected between the bST-supplemented and control groups for MAS, DIG, and KET, with a greater number of healthy cows in the bST-supplemented group. No differences in incidences of diseases or sick cows were detected between the control and cohort groups. Results indicated that a low dose of bST supplemented to Holstein cows for 3 wk prepartum through 60 d in milk reduced the incidences of some calving-related diseases compared with nonsupplemented controls or cohorts. Importantly, no negative effects of bST supplementation on postpartum calving diseases were detected compared with nonsupplemented cows.     

Environmental factors for phage-induced fermentation problems: replication and adsorption of the Lactococcus lactis phage P008 as influenced by temperature and pH

The lactococcal phage P008 was investigated for its growth characteristics under certain environmental conditions. Phage growth was characterized by the latency period, the average burst size (determined in one-step growth experiments) and by the percentage of adsorption to the host cells after 1, 5, 10 and 15 min (determined in modified one-step growth experiments). The incubation conditions studied were temperatures from 20 to 40 degrees C and pH values of 4.8 and 6.4. The growth medium was ultrafiltration permeate of skim milk, which forms the water phase of milk. Both, the temperature and the pH influenced the growth parameters: Increased temperature as well as low pH led to a faster latency along with a higher average burst size. The percentage of adsorption was at maximum when the standard conditions of 30 degrees C and pH 6.4 were applied. Below pH 5, adsorption was reduced to below 10%. A decrease of temperature slightly reduced phage multiplication. Data were incorporated into a model to simulate phage multiplication under certain conditions, taking the percentage adsorption into account. The cell destruction of the host culture was calculated accordingly. The simulation (extrapolation) was validated by experimental growth curves of phages and phage-infected host cultures.     

提高2500m3高炉热风温度的实践

高风温是高炉提高喷煤比、节能降耗、降本增效的有效措施.不锈钢分公司炼铁厂2500m3高炉在采用提高热风炉拱顶温度、提高废气温度、助燃空气与煤气双预热、富氧烧炉、全关混风闸阀等多项技术外,近年来.采取热风炉富氧烧炉、掺烧高热值转炉煤气、增加换炉次数缩短烧炉送风周期等措施提高风温.近几年高炉风温不断提高,2006年2500m3高炉月平均风温达到1158℃,最高达到1195℃.     

皮卫星星间高精度载波测距系统研究

高精度微波测距系统依赖于周期大于载波在星间传输时间的长期时钟误差影响的消除,需要超稳晶振源和精确的定时系统作为保障.微小型皮卫星体积小、功耗低的特点无法满足这些要求.我们提出一种基于双向载波测距的系统,同样能够消除长期的时钟误差,但是不需要复杂的定时系统.理论分析和试验表明,利用皮卫星S波段的双向载波测距,其精度可以达到亚毫米级.     

Research on the fracture behavior of PBX under static tension

The fracture behavior of polymer-bonded explosive （PBX） seriously affects the safety and reliability of weapon system. The effects of interface debonding and initial meso-damage on the fracture behavior of PBX under quasi-static tension are studied using numerical method. A two- dimensional representative volume element （RVE） is established based on Voronoi model in which the component contents could be regulated and the particles are randomly distributed. A nonlinear damage model of polymer matrix relative to matrix depth between particles is constructed. The results show that the simulated strain-stress relation is coincident with experiment data. It is found that interface debonding leads to the nucleation and propagation of meso-cracks, and a main crack approximately perpendicular to the loading direction is generated finally. The interface debonding tends to occur in the interface perpendicular to the loading direction. There seems to be a phenomenon that strain softening and hardening alternatively appear around peak stress of stress and strain curve. It is shown that the initial damages of intragranular and interfacial cracks both decrease the modulus and failure stress, and the main crack tends to propagate toward the initial meso-cracks.     

基于拟平稳分布的随机服务系统k 阶繁忙期研究

为深入研究随机服务系统的"繁忙期",基于拟平稳分布对其进行探讨。利用生灭过程的拟平稳分布概率特性,得到某个确定初始状态下生灭过程的平均灭绝时间,依据它和随机服务系统平均k阶繁忙期概率分布的相似,得到结果,并以实例进行模拟验证。结果表明:该模型进一步拓展了拟平稳分布的应用空间,能为深入研究随机服务系统的"繁忙期"提供参考。     

煤与瓦斯突出过程中能量耗散规律的研究

对煤与瓦斯突出过程中煤体质点内的能量耗散过程用热力学定律进行了分析；论证了由地应力引起的弹性潜能最先消耗在煤体的破碎上，为谋体内瓦斯能的释放创造了条件；在突出过程中起决定作用的是煤体本身释放的初始释放瓦斯膨胀能．通过突出模拟及测定表明，受地应力破坏后的含瓦斯煤体在卸压初始时刻确实有一个释放瓦斯膨胀能的能量峰，并且该能量峰的大小与揭煤时的动力现象显著与否密切相关．