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As a type of transmission tower with excellent mechanical properties, steel tubular tower is widely used in engineering. However, when the length of steel tubular tower is relatively large and tends to be arranged horizontally, the steel tubular rod is prone to vortex-induced vibration at low wind speed. In the long run, the continuous and repeated vibration may cause fatigue damage to the steel tubular tower members. Once the tower structure is damaged, it will directly threaten the stable operation of the power grid. In order to solve this problem, two vortic-induced vibration pneumatic control measures of spiral turbulence and passive blowing sleeve are studied by using large size true steel pipe and rod through wind tunnel test. The influence law of different spiral number and pitch on vortex vibration control effect is analyzed. The influence of different orifice thickness and orifice shape on vortex vibration control is analyzed. The results show that the effect of single-helix control is not so good. The three-helix control can reduce the vortex vibration by 97.7% at most, and the hollow-loop control can reduce the vortex vibration by 75.5% at most. In this paper, a full-size model is used to meet the Reynolds number demand and realize the study closer to the real environment of steel pipe in transmission tower, providing reference for the vorticity vibration suppression of steel pipe in practical engineering. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Jilin University (Science Edition) / Jilin Daxue Xuebao (Lixue Ban) is the property of Zhongguo Xue shu qi Kan (Guang Pan Ban) Dian zi Za zhi She and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of the Chinese Society of Rare Earths is the property of Editorial Department of Journal of the Chinese Society of Rare Earths and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Toroids have attracted widespread attention due to their unique structures and properties. Chiral structures are ubiquitous in nature and chiral materials display excellent performance in diverse fields. Polymer self-assembly is an efficient way toward various nanostructures including nanotoroids and chiral nanostructures. However, currently, there is no report regarding chiral toroidal nanostructures by self-assembly of polymers. Recently, the group of Prof. Lin Jiaping and Prof. Cai Chunhua from East China University of Science and Technology has reported that a binary system containing polypeptide homopolymer and its block copolymer can self-assemble into uniform chiral nanotoroids in solution. In such a unique structure, the homopolymers aggregate into fibrils and then convolve into a toroidal template, resembling the toroidal condensation of DNA. While the block copolymers self-assemble on the homopolymer toroids forming helical surface nanopatterns, the chirality and width of the surface helical patterns can be varied by the chirality and molecular weight of the polypeptide block copolymers. Their work not only proposes a novel route toward uniform nanotoroids, but also provides a new strategy constructing chiral nanopatterns on the surface of toroids. [ABSTRACT FROM AUTHOR]

A new approacli was developed for regulating the morphology and mesopore structure of mesoporous materials. A variety of mesoporous silica with complex architectures have been successfully fabricated in mixed F127 ( EO106 PO70 EO106 ) -CTAB systems by the hydrolysis of TEOS in aqueous HC1 solutions, such as nanofiber, gyroids, spheres and curved shells. By the investigation of the concentration effect of the reactants and the temperature effect, it has been observed that helical structures of mesoporous silica can only be obtained within a relatively narrow concentration ranges under room temperature. In these mixed systems, CTAB acts as the pore-induced agent, and F127 can tune the sample morphology only when the concentration of FI27 is below the cmc. Based on the research results, detailed mechanism for the helical mesoporous silica synthesized in non ionic surfactants and cationic surfactants mixed systems were discussed innovativelv. [ABSTRACT FROM AUTHOR]

The ring milling tool has higher cutting efficiency than ball-end milling tool in finish-milling of hardened steel molds. Also , it has better processing technology and quality of machined surface compared with the flat end milling tool. In order to machine ring milling tool accurately, the theory of edge line of ring milling tool is analyzed. According to the geometrical characteristics of rotary cutting tool and the forming principle of spiral, a continuous cutter edge curve model with equal helix angle for ring milling cutter is derived. The blade edge equation mathematical model can reflect the geometric features of circumferential blade curve and fillet curve. Combined with the established model of cutting line, the ring milling tool is grinded by Saacke five-axis grinding machine. The test results for tool geometric parameters indicate that the tool has high grinding precision. [ABSTRACT FROM AUTHOR]

The equation of the helix on hyperboloid of one sheet is given. The coordinate transformation such as rotating , moving, and so on, are used to draw a circle at the start point of the helix. The plane of the circle and the tangent of the start point of the helix are vertical. The command "extrude" in AutoCAD is used to move the circle on the spiral helix for making the helical spring on hyperboloid of one sheet. The relations about the lead of the helical spring, the parameters of the hyperboloid of one sheet and the radius of the circle are analyzed, and the approximate equation of theirs is given. It is proved that the approximate equation is a feasible method in computer modeling. Finally, the forming principle and the modeling method of which the section of the helical body on hyperboloid of one sheet is not circular are studied. [ABSTRACT FROM AUTHOR]

We have investigated theoretical conformational feature of an isolated poly(lactic acid) (PLA) chain involving a racemic unit at the central position. Two polymers were employed, one with the sequence of 25 units of L-lactic acid (1) and one in which the 13th position is substituted by the D-isomer (1-D). In both PLAs, several initial conformers were geometry-optimized with the semi-empirical molecular orbital method. The energy value of each converged structure was re-evaluated with DFT single-point computation. In the optimization of 1 from eight periodic conformers, a "g-t"-helical conformer was found to be the most stable. In the case of 1-D, most of the corresponding eight structures were energetically destabilized or deformed at around the central position. The D-isomer incorporated into the most stable "g-t'-helical conformer of 1 led the whole chain to a triangle-like shape that reduced the edge-to-edge distance by ca. 25%. The present simulation reveals that the introduction of a single heterochiral unit into a long homochiral PLA chain generates large con formational flexibility to vary its physicochemical properties. [ABSTRACT FROM AUTHOR]