Effect of Nozzle Inclination Angle on Fuel-Air Mixing and Combustion in a Heavy Fuel Engine

Heavy-fuel engines are widely used in UAVs(Unmanned Autonomous Vehicles)because of their reliability and high-power density.In this study,a combustion model for an in-cylinder direct injection engine has been imple-mented using the AVL FIRE software.The effects of the angle of nozzle inclination on fuel evaporation,mixture distribution,and combustion in the engine cylinder have been systematically studied at 5500 r/min and consider-ing full load cruise conditions.According to the results,as the angle of nozzle inclination increases,the maximum combustion explosion pressure in the cylinderfirst increases and then it decreases.When the angle of nozzle incli-nation is less than 45°,the quality of the mixture in the cylinder and the combustion performance can be improved by increasing the angle.When the angle of nozzle inclination is greater than 45°,however,the mixture unevenness increases slightly with the angle,leading to a deterioration of the combustion performances.When the angle of nozzle inclination is between 35°and 55°,the overall combustion performance of the engine is rela-tively good.When the angle of nozzle inclination is 45°,the combustion chamber’s geometry and the cylinder’s airflow are well matched with the fuel spray,and the mixture quality is the best.Compared with 25°,the peak heat release rate increases by 20%,and the maximum combustion burst pressure increases by 5.5%.

局部聚类分析的FCN-CNN云图分割方法

空气中的尘埃、污染物及气溶胶粒子的存在严重影响了大气预测的有效性,毫米波雷达云图的有效分割成为解决这一问题的关键.提出了一种基于超像素分析的全卷积神经网路FCN和深度卷积神经网络CNN(FCNCNN)的云图分割方法.首先通过超像素分析对云图每个像素点的近邻域实现相应的聚类,同时将云图输入到不同步长的全卷积神经网络FCN 32s和FCN 8s中实现云图的预分割;FCN 32s预测结果中的"非云"区域一定是云图中的部分"非云"区域,FCN 8s预测结果中的"云"区域一定是云图中的部分"云"区域;余下的不确定的区域通过深度卷积神经网络CNN进行进一步分析.为提高效率,FCN-CNN选取了不确定区域中超像素的几个关键像素来代表超像素区域的特征,通过CNN网络来判断关键像素是"云"或者是"非云".实验结果表明,FCN-CNN的精度与MR-CNN、SP-CNN相当,但是速度相比于MR-CNN提高了880倍,相比于SP-CNN提高了1.657倍.

一种面向人脸活体检测的对抗样本生成算法

近年来,基于深度卷积神经网络的人脸活体检测技术取得了较好的性能.然而,深度神经网络被证明容易受到对抗样本的攻击,影响了人脸系统的安全性.为了建立更好的防范机制,需充分研究活体检测任务对抗样本的生成机理.相对于普通分类问题,活体检测任务具有类间距离小,且扰动操作难度大等特性.在此基础上,提出了基于最小扰动维度和人眼视觉特性的活体检测对抗样本生成算法,将扰动集中在少数几个维度上,并充分考虑人眼的视觉连带集中特性,加入扰动点的间距约束,以便最后生成的对抗样本更不易被人类察觉.该方法只需平均改变输入向量总维度的1.36%,即可成功地欺骗网络,使网络输出想要的分类结果.通过志愿者的辨认,该方法的人眼感知率比DeepFool方法降低了20%.

慢性鼻-鼻窦炎伴鼻息肉鼻内窥镜手术后应用不同中效糖皮质激素的临床效果

目的探讨慢性鼻-鼻窦炎伴鼻息肉(CRSwNP)鼻内窥镜手术(ESS)后应用甲泼尼龙、泼尼松两种不同中效糖皮质激素对患者术后出血及鼻粘膜功能恢复的影响。方法回顾性分析攀枝花市妇幼保健院2013年4月~2017年10月76例行ESS手术的CRSwNP患者的临床资料,按治疗方法分为观察组和对照组,每组38例。观察组给予甲泼尼龙治疗,对照组给予泼尼松治疗。比较两组术前1d及术后8周鼻粘膜功能(鼻粘液纤毛清除率、鼻粘液纤毛清除速度)、鼻粘膜重塑情况[组织转化生长因子-β1(TGF-β1)、血管内皮生长因子(VEGF)]的差异,并记录两组鼻粘膜上皮化时间及术后出血情况。结果术后8周时,两组鼻粘液纤毛清除率、鼻粘液纤毛清除速度均较术前升高(P<0.05);鼻息肉组织TGF-β1、VEGF检测A值水平较术前降低,且观察组变化幅度大于对照组(均P<0.05)。观察组术后鼻粘膜上皮化时间及出血事件发生率均低于对照组(均P<0.05)。结论甲泼尼龙、泼尼松均能改善CRSwNP患者ESS术后鼻粘膜功能,但甲泼尼龙能更有效地减少术腔重塑,促进鼻粘膜修复,还可减少术后出血事件,有利于促进鼻粘膜功能的恢复。

级联手工特征与深度特征的视频关键帧检测方法

关键帧检测是有效的视频内容分析的关键环节。常用的基于手工特征的方法运行效率高但很难有效表征关键帧特征,因而性能不好。基于深度特征的方法因为网络结构复杂,导致效率不高。在体育比赛类视频中,关键帧常为比赛转播中镜头变化的最后一帧。但广播视频中除了包含比赛视频还包括很多其他类型的镜头如中场休息、渐变镜头等。因此检测最后一帧包含很多比赛无关内容。针对这一问题,本文提出了一种手工特征与深度特征相结合的视频关键帧检测方法。首先基于颜色直方图特征进行镜头边界检测获取最后一帧。进一步基于直方图相似性提出一种类似聚类的方法得到候选关键帧。最后,基于深度神经网络对候选关键帧进行分类,得到真正的关键帧。在冰壶比赛视频和篮球比赛视频上的对比实验结果表明,相对于传统的背景差分法、光流法等,本文提出方法能够快速、可靠地提取关键帧。

Modifying microstructures and tensile properties of Mg-Sm based alloy via extrusion ratio

Microstructure and tensile properties of a Mg-Sm-Zn-Zr alloy with various extrusion ratios(ERs)of 6.9,10.4 and 17.6 were systematically investigated.It was identified that,greater ER increased dynamic recrystallization(DRX)fraction and coarsened DRX grains,which further suggests weakened basal fiber texture for the studied alloy.This is mainly due to the rising temperature from massive deformation heat when hot-extrusion.As a result,greater ER corresponds to a decreased strength but improved ductility.Finally,transmission electron microscopy(TEM)observations reveal that the dominant intermetallic phase,Mg_(3)Sm,is metastable,and it will transform into Mg_(41)Sm_(5)during extrusion with high-ER.This transformation leads to the accumulation of surplus Sm and Zn atoms,which induces the precipitation of Sm Zn_(3)phase at the surface of Mg_(41)Sm_(5)matrix.

Savitzky-Golay滤波和L1范数优化相结合的视频稳像算法

近年来,越来越多的人利用手持设备拍摄视频表达自己或社会问题等,这类视频常存在抖动现象,如何消除视频序列中的随机抖动成为近年来的研究热点。本文面向视频去抖动应用场景,提出了一种Savitzky-Golay滤波和L1范数优化相结合的视频稳像算法。首先基于帧间配对特征点进行运动估计;然后利用Savitzky-Golay滤波算法进行路径平滑处理,去除运动路径中的高频抖动分量,避免了噪声对后续生成稳定路径的影响;进一步,对平滑后的有效路径信息进行基于优化的L1范数优化算法拟合,得到最终的稳定路径;最后对原始视频图像序列进行运动补偿,生成稳定的图像序列。对比实验结果表明,本文方法稳像效果优于原始L1范数优化算法和最近较好的方法,算法速度快于目前效果较好的二维稳像算法。

Early Aerobic Exercise Promotes Neurological Function Recovery of Rats after Cerebral Ischemia/Reperfusion by Upregulating the Expression of Heat Shock Protein A5

Objective The neuroprotective function of heat shock protein A5(HSPA5)in ischemic stroke has been confirmed.This study aimed to investigate the effects of early aerobic exercise on neurological function recovery from cerebral ischemia/reperfusion and to determine whether these effects are associated with the expression level of HSPA5 in the ischemic penumbra.Methods A total of 72 male Sprague-Dawley rats were randomly assigned to the ischemia and exercise group[middle cerebral artery occlusion(MCAO)-Ex,n=18],ischemia and sedentary group(MCAO-St,n=18),sham-surgery and exercise group(Sham-Ex,n=18),or sham-surgery and sedentary group(Sham-St,n=18).The MCAO-Ex and MCAO-St groups were subjected to MCAO for 60 min,whereas the Sham-Ex and Sham-St groups were subjected to an identical operation without MCAO.Rats in the MCAO-Ex and Sham-Ex groups then ran on a treadmill for 30 min once a day for 5 consecutive days.After reperfusion,the motor function of the rats was scored by the Bederson neurological function test,balance beam test,and screen test.Nissl staining was conducted to assess morphological and structural change of nerve cells in the ischemic penumbra.The reverse transcription-quantitative polymerase chain reaction was applied to detect the mRNA expression of HSPA5.Western blot analysis was conducted to determine the protein expression of HSPA5.Terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling(TUNEL)staining was carried out in the ischemic penumbra after MCAO.Results Rats receiving early treadmill exercise had lower Bederson neurological function,balance beam,and screen test scores on the 3rd,7th,and 14th days after MCAO;in addition,more neurons survived in the ischemic penumbra after MCAO,and higher mRNA and protein expression of HSPA5 and fewer TUNEL-positive stained cells were observed.Conclusion Our study demonstrated that early aerobic exercise can improve neurological function recovery after ischemia/reperfusion.Furthermore,the increased level of HSPA5 in the ischemic penumbra might be one of the mechanisms of enhanced neurological function recovery.

Multiplex intermetallic phases in a gravity die-cast Mg-6.0Zn-1.5Nd-0.5Zr(wt%) alloy

Components and crystal structures of the intermetallic phases in a gravity die-cast Mg-6.0Zn-1.5Nd-0.5Zr(wt%)alloy were investigated using transmission electron microscopy.The results indicate that this alloy has multiple intermetallic phases and various inner faults.Totally,six eutectoid intermetallic phases,namely W(Mg Nd Zn_(3)),T(Mg_(39)Zn_(55)Nd_(6)),(Mg,Zr)Zn_(2),Z(Mg_(28)Zn_(65)Nd_(7)),H_(2)(Mg_(15)Zn_(70)Nd_(15)),and H1(Mg_(24)Zn_(64)Nd_(11)),were simultaneously observed at grain boundaries,and six precipitates(Z,Mg_(7)Zn_(3),T,Mg_(4)Zn_(7),β_(1)-Mg Zn_(2) and β_(2)-Mg Zn_(2))were found inα-Mg grains.Furthermore,faults like sub-grain boundaries,orientation domains(coherent with the same matching plane but with different orientations),stacking faults and twins were observed in the eutectoid intermetallic phases.Finally,some new orientation relationships between the known intermetallic phases were revealed.This paper can provide new insight into alloy design for Mg-Zn-RE(RE:rare earth)based alloys.

Long-term potentiation-based screening identifies neuronal PYGM as a synaptic plasticity regulator participating in Alzheimer's disease

Synaptic dysfunction is an important pathological hallmark and cause of Alzheimer's disease(AD).High-frequency stimulation(HFS)-induced long-term potentiation(LTP)has been widely used to study synaptic plasticity,with impaired LTP found to be associated with AD.However,the exact molecular mechanism underlying synaptic plasticity has yet to be completely elucidated.Whether genes regulating synaptic plasticity are altered in AD and contribute to disease onset also remains unclear.Herein,we induced LTP in the hippocampal CA1 region of wildtype(WT)and AD model mice by administering HFS to the CA3 region and then studied transcriptome changes in the CA1 region.We identified 89 genes that may participate in normal synaptic plasticity by screening HFS-induced differentially expressed genes(DEGs)in mice with normal LTP,and 43 genes that may contribute to synaptic dysfunction in AD by comparing HFS-induced DEGs in mice with normal LTP and AD mice with impaired LTP.We further refined the 43 genes down to 14 by screening for genes with altered expression in pathological-stage AD mice without HFS induction.Among them,we found that the expression of Pygm,which catabolizes glycogen,was also decreased in AD patients.We further demonstrated that down-regulation of PYGM in neurons impaired synaptic plasticity and cognition in WT mice,while its overexpression attenuated synaptic dysfunction and cognitive deficits in AD mice.Moreover,we showed that PYGM directly regulated energy generation in neurons.Our study not only indicates that PYGM-mediated energy production in neurons plays an important role in synaptic function,but also provides a novel LTP-based strategy to systematically identify genes regulating synaptic plasticity under physiological and pathological conditions.

一种基于多示例学习的运动员检测方法

体育视频包含大量不同类型的人体,其中运动员的行为与比赛进程和视频内容直接相关,因此运动员检测是体育视频分析的关键环节。现有人体目标检测算法在通用人体检测任务上取得了良好的性能,但是无法有效区分运动员和非运动员。专门训练一个运动员检测模型需要标注大量的运动员位置,成本较高。本文提出了一种基于多示例学习的人体目标检测方法。在通用人体检测的基础上,引入多示例学习模块,基于图像级标注,通过弱监督方式自动学习获取特征映射矩阵,将人体特征映射到运动员特征空间,最后通过度量人体特征与运动员特征之间的相似度,实现运动员与非运动员的区分。对比实验结果表明,本文方法充分利用通用人体检测框架,以极小的标注数据量达到了专门训练运动员检测模型的精度。

Characterizations on the instantaneously formed Ni-containing intermetallics in magnesium alloys

Instantaneous reactions of Al,Mn,Zn,Zr and Y with Ni by mixing the prepared Mg-8Al-0.4Mn,Mg-6Zn-2Y-0.5Zr and Mg-0.6Ni melts were investigated in this work to reveal the underlying mechanisms of their effects on the removal of Ni impurity.The results indicate three Ni-containing intermetallics,namely Al_(4)NiY,Al_(4)Ni(Y,Zr)and Al_(31)Ni_(2)Mn_(6).The former two phases present lath-like and have a relatively larger size(>20μm in length)than the latest one which is granular with the diameter of∼120 nm.This illustrates that Al and Y(/Zr)can efficiently remove Ni by forming Al_(4)NiY or Al_(4)Ni(Y,Zr)which would precipitate to the bottom of the melt.Furthermore,adding Y into Mg-Al based alloys can simultaneously remove Fe and Ni,which contributes their excellent corrosion resistance.Finally,this paper proposes two methods helped to efficiently remove Ni for both Mg-Al based alloys and Al-free Mg alloys,and both of them are also benefit to improve alloys’strength.

Microstructures and mechanical properties of as-cast Mg-Sm-Zn-Zr alloys with varying Gd contents

The effect of Gd content on the microstructure and tensile properties of as-cast Mg-Sm-Zn-Zr alloy has been systematically investigated.In the Mg-3Sm-0.5Zn-0.5Zr alloy, the intermetallic compounds with multiple morphologies are identified as Mg_(3)Sm phase. In addition to Mg_(3)RE phase, Mg_(5)RE phase originated from Gd addition is observed in Gd-modified alloys. It should be noted that the lattice parameters of all the observed intermetallic compounds are significantly reduced by Zn segregation. The segregation behavior of Zn in Mg_(3)Sm phase is inhibited to some extent by Gd addition due to the electronegativity difference between Sm/Gd and Zn elements. In addition, the increased Gd content effectively leads to much more accumulation of solute atoms in front of the liquid-solid interface during solidification, which can prominently promote nucleation in liquid region and then refine grains. The tensile yield stress of the present alloys is thus improved with increasing Gd addition. Finally, Gd-modified alloys exhibit significantly age-hardening effect, which can be mainly attributed to the high-volume fraction and high density nano-scale precipitates.

HALL EFFECT IN NIOBIUM DOPED YBa_2Cu_3O_(7-y) SUPERCONDUCTOR

YBa_2Cu_(3-x)Nb_xO_(7-y) superconductors have been prepared. XRD shows that the system remains orthorhombic for all composition. Substitution of Nb^(5+) for Cu^(2+) occurs in the Cu(2) sites. The introduction of the Nb^(5+) ions produces some extra free-electrons. These electrons recombine with the carriers of the system. It makes the mobility and the Hall number of YBa_2Cu_(3-x)Nb_xO_(7-y) decrease and also result in a depression in Tc.

2023年可解释人工智能技术主要发展动向分析

可解释人工智能与当下人工智能研究与应用所重点关注的可信赖性和鲁棒性等问题密切相关。对2023年可解释人工智能技术领域的主要发展动向进行了综合评述。首先介绍可解释人工智能的概念内涵和实现途径,然后介绍可解释人工智能技术的当前最新进展,最后概述可解释人工智能技术的未来发展趋势。综述表明,针对当下热门的生成式人工智能模型的解释研究,已经成为当前可解释人工智能领域的重要研究热点;针对传统人工智能模型的解释研究主要聚焦于探索多视角融合的解释途径、强化无监督学习框架的可解释性;此外,可解释人工智能开源社区建设提速,助力打开模型“黑盒”的开源工具不断丰富。综述认为,突破微观神经元行为层面的可解释性瓶颈、构建兼具内在常识与外在环境交互能力的“心智系统”等研究方向,正在成为未来可解释人工智能技术的重要发展趋势。

木葡聚糖及其在植物抗逆过程中的功能研究进展

木葡聚糖(XyG)是一种存在于所有陆生植物细胞壁中的基质多糖,是双子叶植物初生细胞壁中含量(20%–25%,w/w)最丰富的半纤维素成分。作为细胞壁的组分,XyG不仅与植物的生长发育密切相关,还在植物抵抗各种生物和非生物逆境过程中发挥重要作用。XyG代谢相关基因主要通过改变植物细胞壁的组成以及对细胞壁进行重排进而改变细胞壁的弹性/硬度等特性,影响植物的抗逆性。XyG及其寡糖也可能作为信号分子,或与其它信号分子协同作用应对逆境胁迫。该文概述了XyG的结构与类型及参与XyG生物合成与降解的相关基因,重点阐述XyG相关基因应答生物和非生物胁迫的作用机制。

ECMO氧合器膜丝阵列多相流动数值模拟与分析

为分析体外膜肺氧合技术(extracorporeal membrane oxygenation,ECMO)氧合器内膜丝排列方式对血液流动和气体输运的影响,该文选取某商用氧合器的轴截面为简化模型,采用基于沉浸边界(immersed boundary,IB)法的自编软件进行了稳态血液流动与多气体组分耦合输运的数值模拟。通过与商业计算流体动力学(computational fluid dynamics, CFD)软件Fluent计算结果、已有文献结果进行比较,验证了所采用的数值方法和自编软件具有适用性。计算结果表明:在一定的孔隙率下改变膜丝排列方式和膜丝倾斜角将影响轴向和径向渗透率,会明显改变血液流动和气体输运的性能;具有径向交错和大倾斜角的膜丝排列能避免出口段大尺度旋涡,降低血液损伤风险。进一步分析可知,ECMO气体输运性能主要受膜丝排列方式的影响,且增大倾斜角有利于提升交错阵列的气体输运效率。该文研究可为实际工程中广泛存在的三维孔隙尺度多相流动数值模拟提供一定参考,为ECMO结构优化、临床运行中参数调整提供科学依据。

ECMO氧合器血液流动数值模拟及损伤评估

为准确获得ECMO氧合器内血液流动细节,本文以交错排布的120根中空纤维束构成的简化氧合器为对象,采用基于沉浸边界法(IB)的自编程序对二维稳态血液层流进行数值模拟。结果表明,中空纤维束区域血液运动黏度变动范围在3.37~7.04×10^(-6)m^(2)/s,模拟时需要考虑血液的流变特性。通过对比IB自编程序与商业CFD软件Fluent的计算结果可知,最大壁面切应力和压降的最大相对误差分别为3.38%和2.9%,验证了IB自编程序计算氧合器微间隙流道内血液流动的准确性。与基于多孔介质假设的一维半经验公式相比,IB自编程序能够反映沿程粘性损失和惯性损失的变化,并可依据切应力累积值、溶血指数、血细胞停留时间三个指标对氧合器血液损伤风险进行综合评估。研究结果可为ECMO的性能预测、临床运行参数调节提供科学依据。

Effects of samarium content on microstructure and mechanical properties of Mg–0.5Zn–0.5Zr alloy

Effects of samarium (Sm) content (0, 2.0, 3.5, 5.0, 6.5 wt%) on microstructure and mechanical proper-ties of Mg-0.5Zn-0.5 Zr alloy under as-cast and as-extruded states were thoroughly investigated. Results indicate that grains of the as-cast alloys are gradually refined as Sm content increases. The dominant intermetallic ph^se changes from Mg3Sm to Mg4iSm5 till Sm content exceeds 5.0 wt%. The dynami-cally precipitated intermetallic phase during hot-extrusion in dll Sm-containing alloys is Mg3Sm. The intermetallic particles induced by Sm addition could act as heterogeneous nucleation sites for dynamic recrystallization during hot extrusion. They promoted dynamic recrystallization via the particle stim-ulated nucleation mechanism, and resulted in weakening the basal texture in the as-extruded alloys. Sm addition can significantly enhance the strength of the as-extruded Mg-0.5Zn-0.5Zr alloy at room temperature, with the optimal dosage of 3.5 wt%. The optimal yield strength (YS) and ultimate tensile strength (UTS) are 368 MPa and 383 MPa, which were enhanced by approximately 23.1% and 20.8% com-pared with the Sm-free alloy, respectively. Based on microstructural analysis, the dominant strengthening mechanisms are revealed to be grain boundary strengthening and dispersion strengthening.

Microstructures and tensile properties of Mg-Zn-(Gd)-Zr alloys extruded at various temperatures

The microstructures and tensile properties of Mg-6.0 Zn-0.6 Zr(ZK60) and ZK60 + 1.8 Gd(ZEK620(RE = Gd)) alloys extruded at 290, 305, 320, 340 and360 ℃ were investigated. The results indicate that Gd addition can refine the microstructures of ZK60 alloy and the extrusion parameters such as the extrusion temperature will influence the tensile properties of both as-extruded ZK60 and ZEK620 alloys, although it is much slighter for ZK60 alloy. And the sensitivity is closely related to the textures developed during extrusion. In addition, Gd addition will also clearly improve the tensile strength at room temperature(24 ℃) and particularly at high temperatures(150 and 200 ℃), due to the much finer grains and smaller intermetallic particles. The highest strength is achieved in the as-extruded ZEK620 alloy with extrusion temperature of 320 ℃, with ultimate tensile strength(UTS) and tensile yield strength(TYS) of 405 and375 MPa, respectively, which are improved by approximately 9% and 11% than those of the as-extruded ZK60 alloy which owns the highest strength at extrusion temperature of 290 ℃.