国产软铝材料失稳时的应力应变分析

本文利用金属薄膜试验求出的软铝塑性应力应变关系．分析了国产软铝材料在简单拉伸、柱形薄壳和球形薄壳失稳时的应力和应变．     

应力生长FeCoSiB非晶薄膜的磁各向异性研究

采用应力生长方法，制备出受压应力和张应力作用的FeCoSiB非晶磁弹性薄膜，研究了薄膜中的应变大小对FeCoSiB薄膜的磁滞回线、剩磁、应力诱导各向异性场等磁特性的影响．结果表明，无应变薄膜在薄膜面内呈现各向同性，而有应变的薄膜呈现出明显的各向异性。张应力诱导的各向异性与应力方向平行，而压应力形成垂直于应力方向的磁各向异性。各向异性场随应变的增大而线性增大。     

预应变法调整芳纶－铝层板的残余应力

采用预应变法能有效地调整芳纶-铝层板的层间残余应力[1]。本文分析了3/2铺层的芳纶-铝层板的残余应力与所施加的预应变的关系;并用腐蚀法测定了几种不同的预应变层板中铝层的残余应力;研究了施加预应变对层板的拉伸性能和疲劳性能的影响。     

预应变法调整芳纶－铝层板的残余应力

采用预应变法能有效地调整芳纶－铝层板的层间残余应力［１］。本文分析了３／２铺层的芳纶－铝层板的残余应力与所施加的预应变的关系；并用腐蚀法测定了几种不同的预应变层板中铝层的残余应力；研究了施加预应变对层板的拉伸性能和疲劳性能的影响。     

中等应变率下泡沫铝的吸能特性

进行了不同密度、高度和压缩方向下泡沫铝的准静态压缩试验和中等应变率下(＜100 s-1)的冲击试验,研究了具有不同密度的闭孔泡沫铝在准静态压缩和冲击工况下的吸能特性.结果表明,泡沫铝是一种近似的各向同性结构,具有较高的单位质量吸能特性,是一种较好的吸能材料.在准静态和中等应变率冲击条件下,泡沫铝对应变率不敏感,其应力应变关系与应变率关系不大.不同的泡沫铝,其平台应力与密度之间的关系不同,在研究其性能时,必须测量应力-应变关系.泡沫铝的致密区对其吸能特性有很大的影响.     

真空镀Al/PVC膜残余应力的研究

利用X射线衍射研究了在塑料表面真空生成的铝膜残余应力.结果表明,残余应力在研究范围内为压应力,初步认识了铝薄膜的附着机理.     

闭孔泡沫铝在动态加载下的压缩力学行为研究

为研究闭孔泡沫铝的动态压缩力学响应过程,基于典型泡沫铝试样的孔型和分布情况构建了Voronoi模型,根据实验结果验证了模型的准确性。基于LS-DYNA分析了目前泡沫铝常用的Kelvin模型和Voronoi模型之间的差异性,研究了加载速度、基体应变率效应和压缩惯性效应对闭孔泡沫铝变形模式和应力水平的影响规律。研究结果表明:Voronoi模型应力-应变水平和变形模式与实验结果拟合较好,内部结构比单胞阵列的Kelvin模型更趋真实合理;在低速压缩下,泡沫铝惯性效应基本上可以被忽略,而高速压缩下,受压缩惯性效应影响,泡沫铝平台应力随着加载速度的增大而增大;当考虑泡沫铝基体应变率效应时,泡沫铝平台应力水平会得到有效的改善,且泡沫铝整体呈现应变率效应。     

液相基底上铝薄膜的开裂与折叠行为研究

利用真空蒸发方法在液相基底(硅油)上成功制备出具有自由支撑边界和界面条件的金属铝薄膜系统,研究了薄膜的开裂和折叠行为。结果表明:沉积过程中,硅油基底的受热膨胀使铝薄膜处于较大张应力状态,伴随着张应力的释放,薄膜中出现开裂形貌。沉积完成之后,系统的逐渐冷却促使硅油基底收缩,并使得铝薄膜处于较大压应力状态,伴随着压应力的释放,薄膜中出现特征的折叠形貌。基于液相基底上金属薄膜的特殊力学行为,对此类开裂和折叠形貌进行了深入阐述。     

织构对CVD自支撑金刚石薄膜残余应变的影响

计算了薄膜试样不同方向的弹性模量,研究了织构和甲烷浓度对CVD自支撑金刚石薄膜的宏观残余应变的影响.结果表明,织构使CVD金刚石薄膜的弹性模量和宏观残余应变呈现各向异性.甲烷浓度的升高导致织构组分密度水平变化,使薄膜的弹性模量增大,从而降低残余应变;另一方面,杂质浓度的升高增大宏观残余应变.改变薄膜沉积工艺参数可调整织构,从而调节薄膜的残余应力.     

聚氨酯泡沫铝复合材料动态力学实验

通过在开孔泡沫铝中填充聚氨酯得到了聚氨酯泡沫铝,利用Hopkinson杆对泡沫铝与泡沫聚氨酯组成的三维连续网络增强复合材料进行了在不同相对密度、应变率和聚氨酯含量下的动态压缩实验.结果表明,在相同应变率和相对密度下,与泡沫纯铝相比,聚氨酯泡沫铝屈服强度和压缩应变量显著增加,而且应力-应变曲线出现明显的抖动.随着应变的不...     

穿越非均匀土体埋地管道地震离心实验研究

穿越非均匀土体经历不同地震作用的埋地管线的变形和残余强度严重影响着管道的安全。该文采用离心振动台分别平行于埋地管道长度方向输入0.6 g和0.3 g峰值地面加速度地震波,研究了埋地管道在一系列地震作用和不均匀土体变形共同作用下的响应,得到了PVC和铝合金两种埋地管道穿越软土/硬土土体的地震响应规律。地震引起不均匀土体的瞬时变形,导致埋地管道最大应变发生在土体分界面和软土中,管道拉伸应变幅值软土要大于硬土,而压缩应变幅值正好相反,硬土中管道拉伸应变幅值小于压缩应变幅值,硬土中管道压缩应变幅值受地震烈度影响比软土大。地震引起的土体永久变形对埋地管道残余变形影响很大,硬土中的管道残余应变为压应变,软土中管道的残余应变为拉压应变交替分布。     

Fast projected gradient method for support vector machines

We present an algorithm for training dual soft margin support vector machines (SVMs) based on an augmented Lagrangian (AL) that uses a modification of the fast projected gradient method (FPGM) with a projection on a box set. The FPGM requires only first derivatives, which for the dual soft margin SVM means computing mainly a matrix-vector product. Therefore, AL-FPGM being computationally inexpensive may complement existing quadratic programming solvers for training large SVMs. We report numerical results for training the SVM with the AL-FPGM on data up to tens of thousands of data points from the UC Irvine Machine Learning Repository.     

Numerical investigation of axial crushing behavior of a tailor welded tube

This study aimed to determine numerically the crashworthiness performances of tubular members made of aluminum (AL6061-T6), high strength steels (AISI1018, HSLA350, DP600, DP800) and tailor-welded tubes (TWTs), which are composed of aluminum and high strength steels (AL6061-T6&AISI1018, AL6061-T6&HSLA350, AL6061-T6&DP600, AL6061-T6&DP800). Numerical analyses were carried out to investigate the effects of material type, thickness and aspect ratio (tube length to diameter ratio) of tube using the commercially available finite element analysis package Ls-Dyna. Absorbed energy and crushing force variations against the crushing displacement were obtained to determine the axial crushing performance of TWTs. Results showed that the absorbed energy and crushing force can be favorably adjusted by choosing the TWTs with different materials and thickness.     

Analysis of C-reactive protein on amide-linked N-hydroxysuccinimide-dextran arrays with a spectral surface plasmon resonance biosensor for serodiagnosis

A new label-free array system using amide-linked (AL) NHS-dextran and a spectral SPR biosensor are presented for the high-throughput analysis of C-reactive protein (CRP) in human sera. The AL NHS-dextran layer on the surface of gold arrays was composed of an amide linkage between NHS-modified carboxymethyl-dextran and amine-modified 11-mercaptoundecanoic acid. The topology of the AL NHS-dextran layer was analyzed by atomic force microscopy, and it was found to be superior to the previously used epoxide-linked carboxymethyl-dextran layer in its immobilization of proteins. Specific immunoreactions and a dose-dependent increase of SPR signals were demonstrated on the AL NHS-dextran layer. Then, the label-free array system was successfully applied to the rapid analysis of CRP in 120 human sera. CRP levels in human sera determined by the array-based spectral SPR biosensor showed a good correlation with those determined by the latex-enhanced turbidimetry immunoassay (n = 120, r = 0.945, p < 0.0001). Thus, the array-based spectral SPR biosensor based on the AL NHS-dextran surface is a potential system for rapid and label-free serodiagnosis of human diseases.     

Biomechanics of the optic nerve head and peripapillary sclera in a mouse model of glaucoma

The deformation of the mouse astrocytic lamina (AL) and adjacent peripapillary sclera (PPS) was measured in response to elevated intraocular pressure. We subjected explanted mouse eyes to inflation testing, comparing control eyes to those 3 days and 6 weeks after induction of ocular hypertension (OHT) via ocular microbead injection. Laser scanning microscopy was used with second harmonic generation to image the collagenous PPS and two-photon fluorescence to image transgenic fluorescent astrocytes in the AL. Digital volume correlation was applied to calculate strains in the PPS and AL. The specimen-averaged strains were biaxial in the AL and PPS, with greater strain overall in the x- than y-direction in the AL and greater strain in the θ- than the r-direction in the PPS. Strains increased after 3-day OHT, with greater strain overall in the 3-day AL than control AL, and greater circumferential strain in the 3-day PPS than control PPS. In the 6-week OHT eyes, AL and PPS strains were similar overall to controls. This experimental glaucoma model demonstrated a dynamic change in the mechanical behaviour of the AL and PPS over time at the site of neuronal injury and remodelling in glaucoma.     

Use of AL307 light-emitting diodes as photodetectors for diagnostics of femtosecond light pulses

A nonlinear electrical response has been observed for the first time from AL307 light-emitting diodes exposed to femtosecond light pulses. When used in an unconventional fashion as unbiased photodiodes, these AL307 light-emitting diodes give an electrical response proportional to the square of the recorded radiation intensity of ultrashort light pulses. Autocorrelation functions are given for femtosecond pulses obtained using AL307 light-emitting diodes in the autocorrelator instead of the conventional photodetector and nonlinear crystal system. Pis’ma Zh. Tekh. Fiz. 24, 62–65 (January 12, 1998)     

PH- and calcium ion-dependent release from egg phosphatidylcholine liposomes incorporating hydrophobically modified alginate

Liposomes, which release their contents in response to change in environmental pH and Ca2+ concentration, were prepared by modifying the surface of egg phosphatidylcholine (EPC) liposome with hydrophobically modified alginate (Hm AL). The liposomes prepared using the ratio of 1:7 (Hm AL:EPC) was stable when the pH of release medium was higher than 6.5. They started to release at pH 6.0, and the degree of release in 300 sec was more than 80% at pH 4.5. The collapse of Hm AL chains, caused by the lack of intramolecular electrostatic repulsion, would impose a mechanical energy on the liposomal membrane, promoting a release from the liposomes. Liposomes bearing less amount of Hm AL exhibited less degree of release, but the release profiles were found similar whatever Hm AL to EPC ratio was. On the other hand, the liposomes bearing Hm AL released calcein significantly (10-30%) in 300 sec when Ca2+ was contained in the release medium (5 mM and 10 mM). The collapse or the gellation of Hm AL, caused by an electrostatic interaction between Ca2+ and the polysaccharide, would be responsible for the release.     

Synthesis, characterization and osteoconductivity properties of bone fillers based on alendronate-loaded poly(ε-caprolactone)/hydroxyapatite microspheres

A superior drug controlled release system capable of achieving efficient osteogenesis is in imperative demand because of limited bone substitute tissue for the treatment of bone defect. In the present study, we investigated the potential of using poly(ε-caprolactone)–hydroxyapatite (PCL–HA) composite microspheres as an injectable bone repair vehicle by controlled release of alendronate (AL), a medicine that belongs to the bisphosphonates family. The PCL/HA–AL microspheres were prepared with solid/oil/water emulsion technique, which included two processes: (1) AL was loaded on the hydroxyapatite nanoparticles; (2) the HA–AL complex was built in the PCL matrix. The spherical PCL/HA–AL microspheres were characterized with its significantly improved encapsulation efficiency of hydrophilic AL and better sustained release. Human bone mesenchymal stem cells (hMSCs) were cultured on the surface of these microspheres and exhibited high proliferative profile. Specifically, in osteogenic medium, hMSCs on the surface of PCL/HA–AL microspheres displayed superior osteogenic differentiation which was verified by alkaline phosphatase activity assay. In conclusion, by presenting strong osteogenic commitment of hMSCs in vitro, the PCL/HA–AL microspheres have the potential to be used as an injectable vehicle for local therapy of bone defect.     

不同阻隔性包装材料对茶叶儿茶素含量的影响研究

选择了LDPE,BOPP/PE,BOPP/PET/PE,PT/AL/PE和BOPP/AL/PE等5种典型具有代表性的包装材料进行了茶叶贮藏试验,从儿茶素的角度比较了它们的处理效果。结果表明:不同阻隔性(阻气、阻湿、阻光)的包装材料对茶叶的儿茶素含量的影响存在极显著差异(P<0.01),从儿茶素角度来讲,包装材料的处理效果优劣依次为BOPP/AL/PE,BOPP/PET/PE,PT/AL/PE,BOPP/PE和LDPE;同时,茶叶需贮藏在常温或低温、干燥、避光、与氧隔绝的环境下,儿茶素才会相对比较稳定。