The DFS-heuristic for orthogonal graph drawing

In this paper, we present a new heuristic for orthogonal graph drawings, which creates drawings by performing a depth-first search and placing the nodes in the order they are encountered. This DFS-heuristic works for graphs with arbitrarily high degrees, and particularly well for graphs with maximum degree 3. It yields drawings with at most one bend per edge, and a total number of m−n+1 bends for a graph with n nodes and m edges; this improves significantly on the best previous bound of m−2 bends.     

In‐plane birefringence and elongation behavior of uniaxially drawn aromatic polyimide films

Six kinds of aromatic poly(amic acid) films, the precursor of polyimides, were uniaxially drawn by constant loads during thermal curing with varying the final curing temperature and the load. The in‐plane birefringence (Δn) generated by uniaxial orientation of polyimide molecules in the film plane was investigated in relation with their molecular structures and the elongation behavior of polyimide films. The polyimides derived from pyromellitic dianhydride (PMDA) showed much larger values of Δn than the polyimides derived from dianhydrides having rotatable diphenyl linkages. The Δn of the former polyimides increases with increasing the final curing temperature and the elongation between the most shrunken and the most elongated states during curing. In particular, the polyimides having rod‐like structures show the largest value of Δn. In contrast, the latter polyimides take maximal values of Δn at much lower temperatures. The introduction of hexafluroisopropiridene (? C(CF₃)₂? ) group into the main chain effectively lowers the values of Δn. This result can be related to the inherent low polarizability anisotropy and the decreased molecular packing constant that are characteristic of highly fluorinated groups. These experimental results are qualitatively explained by the calculations of polarizability anisotropies of model compounds using FPT‐MNDO‐PM3 theory. Copyright © 2001 John Wiley & Sons, Ltd.     

丙类谐振功率放大器动态线作法与应用探讨

基于晶体三极管在共射组态的大电流和大集－射电压的电特性,提出了适于丙类谐振功率放大器动态线的近似作法,讨论了各有电压和负载的变化对动态线的影响,并运用该动态线对丙类谐振功率放大器的工作状态和性能进行了定性分析。     

PLC提高性实验的实验教学改革探索

介绍PLC即可编程序控制器在实验教学中进行的提高性实验,提高性实验之一是PLC对三台鼠笼异步电动机的自动与手动控制,PLC指令的灵活应用及实现。     

Poly(ethylene terephthalate) Nanofibers Made by Sea–Island‐Type Conjugated Melt Spinning and Laser‐Heated Flow Drawing

Nylon‐6/poly(ethylene terephthalate) (PET) ultra‐multi‐island sea–island conjugated melt‐spun fibers are flow‐drawn at a draw ratio of 174 with heating by CO₂ laser irradiation. Continuous PET nanofibers that have a diameter of 39 nm could be obtained from the flow‐drawn fiber with further drawing and removal of the sea component. In addition, the drawn fiber has a strength of 0.54 GPa. This result shows that a PET nanofiber having a strength almost equal to that of a conventional PET fiber can be obtained by the combination of conjugate‐melt‐spinning and laser‐heated flow‐drawing.

     

摸彩决策的数学模型

生活中 ,摸彩的人们总以为越先摸 ,中彩的可能性越大 ,其实不然 !为此本文从概率角度建立了数学模型 ,证明了每个摸彩者中彩的机会均等 ,与先后摸彩顺序无关 .同时 ,通过分析在中彩时 ,已摸过的彩票数目的数学期望 ,向彩票发行者提出了几点建议 .     

三段加热系统对大尺寸MPOF预制棒一步拉伸工艺

采用自行设计的微结构聚合物光纤专用拉丝系统对大尺寸微结构聚合物光纤预制棒的一步拉伸工艺进行了研究.该微结构聚合物光纤加热系统采用三段式梯度加热,可保持炉内温度的控制准确度在±2℃以内.在保持送料速度与牵引速度恒定、协调的条件下,通过对温度场温度梯度控制优化,确定了最佳拉丝温度组合,并得到了直径规格310 μm、标准偏差为±20 μm的较高质量的微结构聚合物光纤.     

Numerical solution of fractional order differential equations by extrapolation

We present an extrapolation type algorithm for the numerical solution of fractional order differential equations. It is based on the new result that the sequence of approximate solutions of these equations, computed by means of a recently published algorithm by Diethelm [6], possesses an asymptotic expansion with respect to the stepsize. From this we conclude that the application of extrapolation is justified, and we obtain a very efficient differential equation solver with practically no additional numerical costs. This is also illustrated by a number of numerical examples. This revised version was published online in August 2006 with corrections to the Cover Date.     

On the Crossing Number of Circular Graphs

1.IntroductionInVLSIchipdesign,thetwo-layerroutingofgraphGplayanimportantrole.Thatis,theupperlayercanonlybeusedforverticalwiringandthesecondlaer,theloweroneonlyforhorizontalwiring.Soweconsidertheplanarprojectionofth.etwolayers,i.e.,consideratwodimensionalgridasapropergraphmodel.ThenoneobviousconditiontoberequiredisthateveryvertexofGhasitsdegreeatmost4.Withoutlossofgeneralitylweonlyconsider4regUlargraphs.IfGisaplanargraphwitha(G)S4,alinearalgorithmhadbeenprovidedforfindingarectilineajrrout…     

Effects of the drawing form and draw ratio on the fiber structure and mechanical properties of CO2-laser-heated-drawn poly(ethylene terephthalate) fibers

The structure, mechanical properties, and thermomechanical properties of poly(ethylene terephthalate) (PET) fibers obtained by laser-heated drawing were investigated in terms of their dependence on the draw ratio and feed speed and the differences between neck-drawn fibers and flow-drawn fibers. The long period at a draw ratio of 6.0 reached 19.0 nm, notably larger than at lower ratios, whereas the tilting angle of the laminar structure was constant at about 60°, regardless of the draw ratio. A maximum value of 15.0 GPa was attained for the initial modulus, and 1.07 GPa was attained for the tensile strength. A higher tensile strength orientation-induced crystallized fiber at the same initial modulus was obtained from higher molecular weight PET. The relationship between the compliance and molecular orientation of the amorphous phase was studied with a series model of crystalline and amorphous phases. The results revealed that, in the high-draw-ratio fibers, the compliance of the amorphous phase decreased with the draw ratio at a higher rate than indicated by extrapolation to intrinsic values. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 79–90, 2004