Queue length‐based load balancing in data center networks

Traffic load balancing in data centers is an important requirement. Traffic dynamics and possibilities of changes in the topology (e.g., failures and asymmetries) make load balancing a challenging task. Existing end‐host–based schemes either employ the predominantly used ECN or combine it with RTT to get congestion information of paths. Both congestion signals, ECN and RTT, have limitations; ECN only tells whether the queue length is above or below a threshold value but does not inform about the extent of congestion; similarly, RTT in data center networks is on the scale of up to few hundreds of microseconds, and current data center operating systems lack fine‐grained microsecond‐level timers. Therefore, there is a need of a new congestion signal which should give accurate information of congestion along the path. Furthermore, in end‐host–based schemes, detecting asymmetries in the topology is challenging due to the inability to accurately measure RTT on the scale of microseconds. This paper presents QLLB, an end‐host–based, queue length–based load balancing scheme. QLLB employs a new queue length–based congestion signal that gives an exact measure of congestion along the paths. Furthermore, QLLB uses relative‐RTT to detect asymmetries in the topology. QLLB is implemented in ns‐3 and compared with ECMP, CONGA, and Hermes. The results show that QLLB significantly improves performance of short flows over the other schemes and performs within acceptable level, of CONGA and Hermes, for long flows. In addition, QLLB effectively detects asymmetric paths and performs better than Hermes under high loads.     

激光激发下拉曼光谱相对辐射定标模型研究

为了提高变压器油中气体检测性能,提出基于激光激发下拉曼光谱的相对辐射定标模型,采用激光成像技术进行拉曼光谱图像成像处理,提取拉曼光谱图像的边缘轮廓特征量,采用多尺度小波降噪方法进行激光激发下拉曼光谱图像降噪滤波,在邻域内采用颜色梯度分解方法进行拉曼光谱图像区域融合性增强处理,根据激光激发下拉曼光谱图像RGB值与邻域均值实现拉曼光谱相对辐射标定和检测,提高拉曼光谱图像的相对辐射定标能力。仿真结果表明,采用该方法进行激光激发下拉曼光谱相对辐射定标的准确性较高,识别精度较高,图像信息增强性能较好。     

地基沉降对BCCP接口力学性能影响的试验研究

BCCP是一种具有广泛应用前景的输水用大口径新型复合管道,其管道接口结构的稳定对整条管线的运营至关重要。为研究地基沉降对管道接口力学性能的影响,设计了BCCP地基沉降试验,分析地基沉降值与相对转角之间的关系以及接口应变分布和变化规律,最后给出接口结构失效判别标准。试验结果表明:当接口相对转角的绝对值达到极限值附近时,接口结构发生破坏,在工程应用中该极限值可以作为判断接口结构完整性的下限值。     

Comparison of the relative stability of pharmaceutical cocrystals consisting of paracetamol and dicarboxylic acids

Objective: The aim of this study is to evaluate the relative stability of pharmaceutical cocrystals consisting of paracetamol (APAP) and oxalic acid (OXA) or maleic acid (MLA).

Significance: These observations of cocrystal stability under various conditions are useful coformer criteria when cocrystals are selected as the active pharmaceutical ingredient in drug development.

Method: The relative stability was determined from the preferentially formed cocrystals under various conditions.

Result: Cocrystal of APAP–OXA was more stable than that of APAP–MLA in a ternary cogrinding system and possessed thermodynamical stability. On the other hand, when grinding with moisture or maintaining at high temperatures and relative humidity conditions, APAP–MLA was more stable, and OXA converted to OXA dihydrate. In the slurry method, APAP–OXA was more stable in aprotic solvents because the APAP–OXA with low-solubility product precipitated.

Conclusions: The relative stability order was affected by preparing conditions of presence of moisture. This order might attribute to the small difference of crystal structure in the extension of the hydrogen bond network.     

多档位行星变速传动系统动力学参数优化修改

针对多档位行星变速传动系统因为参数选取不当致使多个档位存在扭转共振的问题,提出以系统固有频率对参数相对灵敏度为约束条件,采用相对初始参数变化率最小的动态优化目标函数和动态约束边界的多步遗传优化算法,对系统进行了多档位动力学参数优化修改。对采用不同优化步长情况下以基于相对初始参数最优和基于单步最优为目标函数进行了对比研究,并对行星传动系统固有频率对参数灵敏度用于传动系统多档位和单个档位参数优化修改的特点进行了分析。结果表明:以相对初始参数最优的多步遗传优化算法可以获得相比以单步最优的多步遗传优化算法更好的优化结果;行星变速传动系统单个档位固有频率对参数的灵敏度不能直接作为多个档位同时进行参数优化修改的参考。参数优化修改后系统所有档位在工作转速范围内都不会发生扭振共振,可为多档位行星变速传动系统设计提供一定的指导。     

碳纳米管对激光选区熔化成形Al基复合材料的影响

基于激光选区熔化（SLM）方式,通过改变扫描速度,制备不同碳纳米管（CNTs,质量分数分别为0、0.5wt%、1.0wt%、1.5wt%、2.0wt%）含量的CNTs/Al复合材料试件,探究不同CNTs含量与激光扫描速度对试件性能的影响。结果表明,CNTs含量小于1.0wt%时,分散效果较好,大部分CNTs以单根状态黏附于Al粉表面;含量大于1.0wt%时,CNTs团聚尺寸增大、数量增多。相同SLM成形工艺下,低CNTs含量的CNTs/Al复合材料试件内部孔隙较少,致密度较高;高CNTs含量的CNTs/Al复合材料试件内部孔隙逐渐增多,致密度降低。激光扫描速度为1 300 mm/s工艺下,随着CNTs质量分数的增加,CNTs/Al复合材料试件硬度呈先上升后下降趋势,在CNTs含量为1.0wt%显微硬度达到最高。CNTs/Al复合材料试件平均晶粒尺寸相对于铝合金试件更加细化,在CNTs含量大于1.0wt%时,尽管晶粒依然细化,但试件致密度降低造成显微硬度下降明显。     

Absolute Measurement and Relative Measurement of Ultrasonic Nonlinear Parameters

The ultrasonic nonlinear parameter is measured from the amplitudes of the harmonic frequency components generated during the propagation of ultrasonic waves in a material. There are two definitions for this parameter: absolute and relative. The absolute parameter is defined by the displacement amplitude; however, it is difficult to measure because of the very small displacement amplitude of the harmonic components. Conversely, the relative parameter is defined by the amplitude of the detected signal, regardless of displacement. Many researchers use the relative parameter because it is easier to measure, although it is only available for a relative comparison of different materials. However, it has not yet been verified that the ratio of the relative parameters between two materials is identical to that of the absolute parameters. In this study, we make it clear that the ratio of the relative parameters is inherently not identical to that of the absolute parameters, but that they can be identical to each other by compensating for material-dependent differences, such as detection-sensitivity and wavenumber. For verification, the absolute and relative parameters were measured for two different materials. The results showed that the ratios of absolute and relative parameters were in good agreement after compensation.     

6 种典型流场中超声流量计校准系数随企业污染源烟气排放量变化研究

采用计算流体力学方法,对6种典型流场中超声流量计校准系数随企业污染源烟气不同流速变化的规律进行研究。分析不同负荷下超声流量计校准系数相对标准偏差在不同声道角度、管道直径、声道布置形式、上游直管段长度、管道形式时的变化规律。通过国家烟道流量计量标准装置进行实验验证,验证结果表明:不同负荷下校准系数相对标准偏差均未超过1%,且可以通过单负荷校准实现对烟道超声流量计的校准。     

核电厂基础开挖爆破振动监测与数据分析

结合福建漳州核电厂一期工程场地平整土石方工程施工实例,为取得厂区岩体爆破施工时的振动能量分布,优化核电站二期工程爆破技术方案设计,对爆破振动数据进行采集,应用小波变换方法对具有短时非平稳特点的爆破振动信号进行了特征分析。基于小波变换的时-频特性和分层分解分析对比可知,爆破振动持续时间在不同方向上存在差异,且振动持续时间表现出与频率的反相关关系;振动信号的频率分布在不同振动方向上也呈现差异性;由于地形及岩性的因素作用,核电厂区爆破振动的能量分布主要集中在10~50 Hz范围内。     

基于ANP和TOPSIS优化方法的专业性购物网站评价研究

目的针对专业性购物网站设计的评价排序问题,提出一种基于用户体验的评价方法,并对评价结果数据的处理方法进行研究。方法基于用户体验对专业性购物网站建立评价体系,采用优化的层次分析法(AHP),即网络分析法(ANP)对评价体系的权重进行确立,并引入相对熵优化的TOPSIS方法对网站的评价结果数据进行排序。结论通过样例证明,该评价体系考虑全面,数据处理方法稳定,可以确定专业性购物网站设计和改进中需要优先考虑的问题,并有效且正确地反映市场的实际竞争情况。