A numerical study on local buckling and energy dissipation of CHS seismic bracing

Seismic provisions for steel buildings present limiting width-thickness and slenderness ratios for bracing members, most of which were established based on experimental observations. A finite element study has been undertaken to evaluate these limits for pin-ended circular hollow section (CHS) steel braces. Uncertainties in modeling and quantification arise in the simulation of cyclic brace buckling. A finite element modeling procedure was developed and calibrated using existing experimental data. Sensitivity of the finite element analysis results to the uncertainties in modeling and quantification methods were studied in detail. A parametric study was conducted utilizing the calibrated modeling technique. Fifty four CHS brace models possessing different diameter-to-thickness ratios varying from 5 to 30 and slenderness ratios varying from 40 to 200 were analyzed. The effect of cyclic hardening modulus on the response of braces was explored. In all analysis, the models were subjected to reversed cyclic displacements up to ten times the yield displacement. In this paper, the results are presented in terms of the ductility level attained by the member at the onset of local buckling. It is shown that local buckling of the section is not only a function of the diameter-to-thickness ratio but is also influenced by the slenderness ratio of the member. Moreover, the amount of hardening modulus was found to affect the local buckling response significantly. The need to include this material property into seismic provisions is demonstrated. Finally, the hysteretic energy dissipated by the member was quantified for each displacement excursion.     

磁链受力分析在磁选回收率计算中的应用

计算了钛磁铁矿颗粒在磁场中形成磁链所需要的时间,得出了钛磁铁矿的磁选回收本质上是磁链的磁选回收的结论。通过详细分析磁链在磁场中的受力,得出了适合于由强磁性物料形成磁链的磁选回收计算的通用公式。     

300 mm硅片双面抛光运动轨迹模拟和优化

通过建立300 mm硅片双面化学机械抛光中硅片上定点相对于上下抛光垫的运动轨迹方程,分析了内外齿轮转速、抛光布转速对运动轨迹分布的影响,调整三者大小使得运动轨迹分布较均匀。实验证明运动轨迹路径长度与抛光去除厚度成正比关系,计算运动轨迹路径长度确定抛光垫的转速以达到上下表面具有相同的抛光速率。研究结果为300 mm硅片双面化学机械抛光找出优化工艺参数、提高硅片抛光后表面质量提供了理论依据。     

The bacterial battery and the effect of different exposure conditions on biofilm properties

A galvanic cell with pure copper and Al 2024 and Shewanella oneidensis MR-1 in Luria Bertani (LB) medium and a control cell, which did not contain the bacteria, have been tested. Potentiodynamic polarization experiments were used to determine cell voltage (V)-current (i) and power (P)-i curves as a function of time. The results for the cell without bacteria demonstrated that the maximum power output was obtained in the first day and dropped drastically in the following days. For the cell with MR-1 the power output of the cell increased slowly with time for around 100 days and remained at similar values for another 100 days. For pure Cu significant changes of the impedance spectra were found in the presence of MR-1. The impedance spectra resembled those usually observed for polymer-coated metals. In order to investigate this phenomenon in more detail, the effects of the different exposure conditions on the electrochemical behavior of copper were evaluated in LB containing MR-1. A second time constant was observed in the impedance spectra of copper that was partially immersed in the test solution (cell B). Complete immersion of copper in the electrolyte (no air/liquid interface) or deaeration of cell B resulted in one-time-constant spectra that are typical of those found for passive metals. Excellent corrosion protection was provided by MR-1 regardless of exposure condition. The corrosion potential increased with time for the Cu electrode exposed in cell B, while it decreased for the other two exposure conditions.     

Access control to two multiserver loss queues in series

We consider admission policies to two multiserver loss queues in series with two types of traffic. Both are generated according to independent Poisson processes with constant arrival rates. The first type requires service at the first queue and with a positive probability enters the second queue; the second type requires service at only the second queue. The service time distribution is exponential at either station. We show that under appropriate conditions the optimal admission policy that maximizes the expected total discounted reward over an infinite horizon is given by a switching curve. We characterize the form and shape of this curve and its variation with system parameters     

Der Schutz von Fichten gegen Schälen durch Rotwild und der Einfluß der Schutzmaßnahmen auf die Güte des Stammholzes

Zusammenfassung Vor 25 bis 30 Jahren wurde an einigen Standorten in der ČSSR die Rinde von 25 bis 30 Jahre alten Fichten mit besonderen Ger?ten zum Schutz vor dem Sch?len durch das Wild verwundet. Die Fichten bildeten durch den Austritt und die Oxydation von Harz an der Stammoberfl?che einen eigenen chemisch-mechanischen Schutz. Bei Durchforstungen konnten keine Unterschiede zwischen verwundeten und nichtverwundeten Fichten hinsichtlich des Befalles durch holzzerst?rende Pilze oder durch Insekten festgestellt werden. Es sollte nun ermittelt werden, ob sich die Qualit?t des Holzes ge?ndert hatte. Zu diesem Zweck wurden aus den erw?hnten Best?nden verwundete und nichtverwundete Probest?mme entnommen. Nach den gültigen tschechischen Normen wurde geprüft, ob Unterschiede in den mechanisch-physikalischen Eigenschaften zwischen den verwundeten und den nichtverwundeten Fichten auftraten. Nach den Ergebnissen der Signifikanzprüfung kann bei 95% Sicherheitsniveau ausgesagt werden, da? die mechanisch-physikalishchen Eigenschaften des Holzes der verwundeten und der nichtverwundeten Fichten sich nicht voneinander unterscheiden und den mitteleurop?ischen Verh?ltnissen entsprechen. Ebenso konnte nachgewiesen werden, da? die Rindenverwundung der Fichten praktisch keine nachteilige Wirkung auf das in der Zellstoff- und Papierindustrie verwendete Holz ausübt, da sie im Holz selbst keine erh?hte Harzbildung hervorruft.

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The protection of spruce against bark damage caused by game and the influence of the protective measures upon the quality of the wood

Summary 25 to 30 years ago on various sites of the ČSSR the bark of 25 to 30 years old spruces was ripped with special tools to protect the trees from barking damage caused by game. By reason of the exudation and oxidation of resin, the trees formed a specific chemo-mechanical protection on the stem surface. Selective thinning showed no difference between ripped and non-ripped spruces as to the wood-destroying attacks by fungi and insects. It now had to be investigated whether the quality of their wood had changed. For this purpose samples were taken from ripped and nonripped trees. According to the valid Czeck standards the differences of the mechano-physical properties between ripped and nonripped stems were investigated. With a level of significance of 95%, the results of the investigation showed no difference in the mechano-physical properties of the wood between ripped and non-ripped spruce stems, yet an equivalence with central European conditions. Equally, it could be proved that the bark rippings of the spruces had no negative effect on the wood for the pulp and paper industries, since no increased resin formation was caused in the wood itself.

     

Obstacle avoidance in person following for vision-based autonomousland vehicle guidance using vehicle location estimation and quadraticpattern classifier

An obstacle avoidance method for use in person following for vision-based autonomous land vehicle (ALV) guidance is proposed. This method is based on the use of vehicle location estimation and a quadratic pattern classifier, and aims to guide the ALV to follow a walking person in front by navigating along a derived collision-free path. Before generating the collision-free path, the person's location is obtained from extracted objects in the image by a person detection method. The object closest to a predicted person location is regarded as the followed person and the remaining objects are regarded as obstacles. The collision-free navigation path is designed for ALV guidance in such a way that the ALV not only can keep following the person but also can avoid collision with nearby obstacles. The navigation path results from a quadratic classifier that uses the vehicle and all of the objects in the image as input patterns. A turn angle is then computed to drive the ALV to follow the navigation path. Successful navigation sessions confirm the feasibility of the approach     

Evolutionary shape optimization of thermoelastic bodies exchanging heat by convection and radiation

Shape optimization of heat conducting, elastic bodies subjected to thermal and standard loads is considered. Interaction of stress and temperature fields is modelled using the formulation of steady state thermoelasticity. The presence of heat radiation with mutual irradiation of the boundaries and the presence of shadow zones is taken into account. Evolutionary algorithm is used to evaluate the optimal shape. The boundary element method is applied to discretize the thermoelasticity, conduction and radiation problems.     

Inhibition of telomerase activity by PKC inhibitors in human nasopharyngeal cancer cells in culture

Telomerase is a specialized ribonucleoprotein polymerase that adds hexanucleotides (TTAGGG) onto human chromosomal ends. The expression of telomerase activity has been associated with cell immortalization and the malignant phenotype in most cancers. How the telomerase activity is regulated in cancer cells is presently not known. In this work, the effects of cell cycle blockers, DNA damaging agents, TopII inhibitors and proteins kinase inhibitors on the telomerase activity were examined in cultured nasopharyngeal carcinoma cells NPC-076. Agents which interfere with tubulin assembly (Taxol and vinblastine) and agents which arrest cells at S phase (methotrexate and 5-fluorouracil) did not inhibit telomerase activity of treated cells. Agents which damage DNA (cisplatin, methyl methanesulfonate, and UV radiation) and TopII inhibitors (etoposide and daunorubicin) also did not inhibit telomerase activity of treated cells. Among the protein kinase inhibitors examined, no significant inhibition of telomerase activity was observed with cells treated with quercetin, H-89, or herbimycin A. On the other hand, two protein kinase C (PKC) inhibitors (bisindolylmaleimide I and H-7) were found to produce a big inhibition of telomerase activity in treated cells. Staurosporine produced a moderate inhibition, and sphingosine had a small inhibitory effect. The inhibition of telomerase activity by PKC inhibitors appears to be specific since the treated cells were mostly viable (i.e., greater than 75%) and still retained significant levels of protein synthesis capability. These results implicate that protein kinase C is involved in the regulation of telomerase activity in vivo.     

Fast image thresholding by finding the zero(s) of the first derivative of between-class variance

Among many thresholding methods, Otsu's method is an attractive one due to its simplicity in computation. In Otsu's paper, the between-class variance (BCV) is defined, and the gray level at the BCV maximum determines an optimal threshold. However, Otsu's method could fail to apply in cases of images with multiple BCV peaks, where a BCV peak rather than the BCV overall maximum can be a better choice as an optimal threshold. This paper presents new thresholding methods by solving a nonlinear equation that was derived based on searching for the zero derivative of image BCV. The study of finding the BCV maximum (or peaks) is treated as solving for the root(s) of the nonlinear equation, using a numerical root finder with good convergence property. From our analytical derivation, the relationship between Otsu's method and Ridler's algorithm (Trussell's equation) can be built. The proposed methods are applicable for thresholding images with single BCV peak as well as multiple BCV peaks.. One of the proposed methods is equivalent to Ridler's algorithm in the total computational cost, but it is three times faster than Otsu's method. For images with a single BCV peak, the convergence and uniqueness in searching for the peak using the bisection method are always guaranteed as long as the BCV slope is continuous. But due to the round-off error, Ridler's algorithm could prematurely converge, and the uniqueness of convergence may not be guaranteed. The adequacy of the proposed methods has been proven through extensive tests, and some examples are included for illustration. Received: 25 June 2000 / Accepted: 3 January 2002