Numerical simulation of bistatic scattering from a target at low altitude above rough sea surface under an EM wave incidence at low grazing angle by using the finite element method

Astudyofscatteringfromavolumetrictargetaboverandomroughsurfaceisofgreatsignificanceintargetdetectioninterrainandoceanicclutters.Mostofanalyticalapproachestoroughsurfacescatteringarebasedonsomeapproximations,suchastheKirchhofftangentplaneapproximation,smallperturbationapproximation,two-scalemodelandothers[1].Analyticalstudyofscatteringfromanobjectabovethesurfacehasbeenlimitedtothemodelofasphereoracylinderaboveaplanarconductingsurface[2,3].Numericalmodelforsimulationofscatteringfromcomplextarget…     

LGA器件焊点缺陷分析及解决

文章针对LGA器件回流焊后常见的空洞和锡珠等缺陷,对其产生的原因进行了分析.通过对LGA器件采用预上锡回流工艺和印制板钢网一字架桥开口的方式,提升回流焊过程中焊膏中挥发气体的逸出,并通过对比试验,找到合适的预上锡钢网尺寸,解决了生产中LGA器件焊接常见的空洞大等缺陷.     

Interaction between Metformin,Folate and Vitamin B12 and the Potential Impact on Fetal Growth and Long-Term Metabolic Health in Diabetic Pregnancies

Metformin is the first-line treatment for many people with type 2 diabetes mellitus (T2DM) and gestational diabetes mellitus (GDM) to maintain glycaemic control. Recent evidence suggests metformin can cross the placenta during pregnancy, thereby exposing the fetus to high concentrations of metformin and potentially restricting placental and fetal growth. Offspring exposed to metformin during gestation are at increased risk of being born small for gestational age (SGA) and show signs of ‘catch up’ growth and obesity during childhood which increases their risk of future cardiometabolic diseases. The mechanisms by which metformin impacts on the fetal growth and long-term health of the offspring remain to be established. Metformin is associated with maternal vitamin B₁₂ deficiency and antifolate like activity. Vitamin B₁₂ and folate balance is vital for one carbon metabolism, which is essential for DNA methylation and purine/pyrimidine synthesis of nucleic acids. Folate:vitamin B₁₂ imbalance induced by metformin may lead to genomic instability and aberrant gene expression, thus promoting fetal programming. Mitochondrial aerobic respiration may also be affected, thereby inhibiting placental and fetal growth, and suppressing mammalian target of rapamycin (mTOR) activity for cellular nutrient transport. Vitamin supplementation, before or during metformin treatment in pregnancy, could be a promising strategy to improve maternal vitamin B₁₂ and folate levels and reduce the incidence of SGA births and childhood obesity. Heterogeneous diagnostic and screening criteria for GDM and the transient nature of nutrient biomarkers have led to inconsistencies in clinical study designs to investigate the effects of metformin on folate:vitamin B₁₂ balance and child development. As rates of diabetes in pregnancy continue to escalate, more women are likely to be prescribed metformin; thus, it is of paramount importance to improve our understanding of metformin’s transgenerational effects to develop prophylactic strategies for the prevention of adverse fetal outcomes.     

Ti表面脉冲激光氮化成膜温度场的数值模拟

本文用有限差分法对金属钛表面脉冲激光生成氮化钛薄膜过程的温度场进行了三维数值模拟计算。模型主要考虑了入射的脉冲激光在时间与空间上的Gauss分布特性 ,以及工件的有限尺寸 ,工件材料热物理性质的温度依赖关系 ,对流辐射造成的表面热损失。此外还从理论上计算了激光脉冲在脉冲宽度加宽后的温度场变化。     

LGA焊点形态对焊点寿命影响的有限元分析

通过Surface Evolver软件对LGA焊点进行了三维形态预测,利用有限元数值模拟对LGA焊点在热循环条件下寿命进行了分析。研究了热循环条件下LGA焊点的应力应变分布规律,随着焊点远离元件的中心位置焊点所受到的等效应力、等效应变和塑性应变能密度逐渐增大,从而得出处于外面拐角的焊点最先发生失效的结论。基于塑性应变范围和Coffin-Manson公式计算了焊点热疲劳寿命;找出了LGA焊点形态对焊点寿命的影响规律,模板厚度一定时PCB焊盘尺寸小于上焊盘时LGA焊点的热疲劳寿命与PCB焊盘尺寸成正比,大于上焊盘时成反比,大约相等时焊点寿命最大。当PCB焊盘和模板开孔尺寸固定时,通过增大模板厚度来增加焊料体积在一定程度上可提高LGA焊点的热疲劳寿命,但是模板厚度增大到一定值时LGA焊点寿命会逐渐降低。     

全最小一乘准则下的LGA新算法

为克服传统提取数据集中线性结构的LGA对噪声数据比较敏感的缺陷,提出了两种基于稳健的全最小一乘准则下的LGA新算法。首先证明了全最小一乘准则下数据集最优划分的存在性,并据此给出一种有限步终止算法。其次为提高计算速度,根据k-means算法、全最小一乘准则和重抽样方法给出另一种快速收敛算法。通过与传统的LGA和基于Trimmed k-means思想的稳健LGA的比较,仿真结果表明提出的算法具有较好的稳健性,可以在离群数据较多的情形下,同时找出数据集合中的所有强线性结构。     

脉冲激光钼表面氮化处理温度场的数值模拟

本文用有限差分法对金属钼表面脉冲激光生成氮化钼薄膜过程的温度场进行了三维数值模拟计算,计算模型在能量平衡方程的基础上,将入射的脉冲激光在时间与空间上的分布以Gauss分布考虑,同时考虑工件尺寸、工件材料热物理性质及对流辐射造成的表面热损失等对温度场的影响,此外还从理论上计算了激光脉冲在脉冲宽度加宽后的温度场变化,分析了利用长脉冲激光进行材料表面相变硬化和激光重熔的可行性。     

Data collection and assessment of commonly consumed foods and recipes in six geo-political zones in Nigeria: Important for the development of a National Food Composition Database and Dietary Assessment

A cross-sectional study was undertaken to collect and assess commonly consumed foods/recipes from the six geopolitical zones in Nigeria for the production of food composition database (FCDB) for dietary assessment. Communities used were selected using a multi-stage sampling plan. Focus group discussions, interviews, recipe documentation, food preparations and literature reviews were employed. Qualitative methods were used to analyse and present data. SWOT (strengths, weaknesses, opportunities, and threats) analysis was used to evaluate the project. A total of 322 recipes were collected out of which 110 were soups. Food consumption patterns across the geographical zones were found to be changing. Variations in recipes and methods of preparation of similar foods were observed. Factors to be considered in the development of a country-specific FCDB were identified. There were challenges with the use of values reported in literature for Nigerian foods. The study justifies the need for a country-specific FCDB that will include traditional recipes.     

基于深度神经网络的电液伺服泵控系统健康评估研究

电液伺服泵控系统具备功重比高、响应快等优点,在多领域得到广泛应用,但如何针对该系统开展更有效健康评估,进一步保障系统的安全性和可靠性成为必须面对的问题。按照明确原理、建立数学模型、建立仿真模型、仿真分析的思路针对健康评估方法开展研究,提出油液体积含气量、气隙磁密、泄漏系数3个健康评估指标并确定阈值,构建了LGA（LSTM-GRNN-ANN）深度神经网络健康评估方法并进行仿真分析,结果显示该方法准确率约为97.48%,比LSTM、GRNN健康评估方法具有更高的准确率,为继续深入开展电液伺服泵控系统健康评估的研究提供了理论支持。     

Exploring the Role of Different Neonatal Nutrition Regimens during the First Week of Life by Urinary GC-MS Metabolomics

In this study, a gas-chromatography mass spectrometry (GC-MS) metabolomics study was applied to examine urine metabolite profiles of different classes of neonates under different nutrition regimens. The study population included 35 neonates, exclusively either breastfed or formula milk fed, in a seven-day timeframe. Urine samples were collected from intrauterine growth restriction (IUGR), large for gestational age (LGA), and appropriate gestational age (AGA) neonates. At birth, IUGR and LGA neonates showed similarities in their urine metabolite profiles that differed from AGA. When neonates started milk feeding, their metabolite excretion profile was strongly characterized by the different diet regimens. After three days of formula milk nutrition, urine had higher levels of glucose, galactose, glycine and myo-inositol, while up-regulated aconitic acid, aminomalonic acid and adipic acid were found in breast milk fed neonates. At seven days, neonates fed with formula milk shared higher levels of pseudouridine with IUGR and LGA at birth. Breastfed neonates shared up-regulated pyroglutamic acid, citric acid, and homoserine, with AGA at birth. The role of most important metabolites is herein discussed.