连载一洋兰

在中国，兰花的栽培有悠久的历史，中国在《易经》中已有“同心之言，其臭如兰”的说法。孔子在过隐谷时，见幽兰独茂，叹曰：“夫兰当为王者香，今乃与众草为伍；譬贤者不逢时？鄙夫为伦也。”以兰花的幽香来比喻人之高雅。     

A Study of Melt Flow Analysis of an ABS-Iron Composite in Fused Deposition Modelling Process

Fused deposition modelling (FDM) is a filament based rapid prototyping system which offers the possibility of introducing new composite material for the FDM process as long as the new material can be made in feedstock filament form. Swinburne has been undertaking extensive research in development of new composite materials involving acrylonitrile-butadiene-styrene (ABS) and other materials including metals. In order to predict the behaviour of new ABS based composite materials in the course of FDM process, it is necessary to investigate the flow of the composite material in liquefier head. No such study is available considering the geometry of the liquefier head. This paper presents 2-D and 3-D numerical analysis of melt flow behaviour of a representative ABS-iron composite through the 90-degree bent tube of the liquefier head of the fused deposition modelling process using ANSYS FLOTRAN and CFX finite element packages. Main flow parameters including temperature, velocity, and pressure drop have been investigated. Filaments of the filled ABS have been fabricated and characterized to verify the possibility of prototyping using the new material on the current FDM machine. Results provide promising information in developing the melt flow modelling of metal-plastic composites and in optimising the FDM parameters for better part quality with such composites.     

臭氧对小白鼠生长及学习行为影响的初步研究

本实验用0.50——1.00ppm 浓度的臭氧处理小白鼠66小时。实验结果初步表明:小白鼠在接受臭氧处理后,体重增长较缓,条件反射活动不易建立,学习能力明显地低于对照组。     

洋葱性状的回归分析

本文就洋葱鳞茎的颈粗、横径、纵径、生物产量、叶数与鳞茎鲜重进行了回归分析,结果表明:洋葱鳞茎的横径、纵径、单株生物产量与洋葱鲜重之间的回归关系显著,横径的作用大于纵径。     

Graphene/SrTiO3 hetero interface studied by X-ray photoelectron spectroscopy

The present paper focuses on study of graphene and strontium titanate(SrTiO_3 or STO) interface. An ambient pressure chemical vapour deposition(AP-CVD) setup is used to grow graphene on STO(110)substrates in the presence of methane, argon and hydrogen gases at 1000 °C for 4 h. Raman spectroscopy measurements confirm the presence of graphene on STO substrates due to the existence of typical D and G peaks referring to graphene. These characteristic peaks are missing in the spectrum for bare substrates.X-ray photoelectron spectroscopy(XPS) is carried out for elemental analysis of samples, and study their bonding with STO substrates. We employed the valence band spectrum to calculate the valence band offset(VBO) and conduction band offset(CBO) at the G-STO interface. Also, we present an energy band diagram for Bi-layer and ABC(arranging pattern of carbon layers) stacked graphene layers.     

子结构法解三维稳定渗流问题的数学原理

在本文中,我们论述了结构分析中的子结构法用于三维稳定渗流计算的数学原理及其有效性。     

The finished DNA sequence of human chromosome 12

Human chromosome 12 contains more than 1,400 coding genes and 487 loci that have been directly implicated in human disease. The q arm of chromosome 12 contains one of the largest blocks of linkage disequilibrium found in the human genome. Here we present the finished sequence of human chromosome 12, which has been finished to high quality and spans approximately 132 megabases, representing approximately 4.5% of the human genome. Alignment of the human chromosome 12 sequence across vertebrates reveals the origin of individual segments in chicken, and a unique history of rearrangement through rodent and primate lineages. The rate of base substitutions in recent evolutionary history shows an overall slowing in hominids compared with primates and rodents.     

MARSIS radar sounder evidence of buried basins in the northern lowlands of Mars

A hemispheric dichotomy on Mars is marked by the sharp contrast between the sparsely cratered northern lowland plains and the heavily cratered southern highlands. Mechanisms proposed to remove ancient crust or form younger lowland crust include one or more giant impacts, subcrustal transport by mantle convection, the generation of thinner crust by plate tectonics, and mantle overturn following solidification of an early magma ocean. The age of the northern lowland crust is a significant constraint on these models. The Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) instrument on the European Space Agency's Mars Express spacecraft is providing new constraints on the martian subsurface. Here we show evidence of buried impact basins ranging in diameter from about 130 km to 470 km found over approximately 14 per cent of the northern lowlands. The number of detected buried basins >200 km in diameter indicates that the lowland crust is ancient, dating back to the Early Noachian epoch. This crater density is a lower limit because of the likelihood that not all buried basins in the area surveyed by MARSIS have been detected. An Early Noachian age for the lowland crust has been previously suggested on the basis of a large number of quasi-circular topographic depressions interpreted to be evidence of buried basins. Only a few of these depressions in the area surveyed by MARSIS, however, correlate with the detected subsurface echoes. On the basis of the MARSIS data, we conclude that the northern lowland crust is at least as old as the oldest exposed highland crust. This suggests that the crustal dichotomy formed early in the geologic evolution of Mars.     

悬空轨枕对轨道结构动力响应的影响

首先建立了带有悬空轨枕的铁路轨道数学模型,在此基础上推导了车—轨系统运动方程,其中考虑了轮轨非线性接触力引起的非线性问题,然后利用逐步积分法解方程重点分析了悬空轨枕对轨道各个组成部分动力响应的影响,结果表明如果在悬空部分存在轨道不平顺,会引起很大的轨枕加速度和轮轨接触力