Nonlinear Dynamic Response of Tension Leg Platform

Tension Leg Platform (TLP) is a typical compliant offshore structure for oil exploitation in deep water. Most of the existing mathematical models for analyzing the dynamic response of TLP are based on explicit or implicit assumptions that displacements (translations and rotations) are small magnitude. Herein a theoretical method for analyzing the nonlinear dynamic behavior of TLP with finite displacement is developed, in which multifold nonlinearities are taken into account, i.e. finite displacement, coupling of the six degrees of freedom, instantaneous position, instantaneous wet surface, free surface effects and viscous drag force. Using this theoretical model, we perform the numerical analysis of dynamic response of a representative TLP. The comparison between the degenerative linear solution of the proposed nonlinear model and the published one shows good agreements. Furthermore, numerical results are presented which illustrate that nonlinearities exert a distinct influence on the dynamic responses of the TLP.

Short-Term Nonlinear Response of Tension Leg Platform in Random Sea Waves

Most of the existing mathematical models for analyzing the dynamic response of TLP are based on explicit or implicit assumptions that motions (translations and rotations) are small magnitude. However, when TLP works in severe adverse conditions, the a priori assumption on small displacements may be inadequate. In such situation, the motions should be regarded as finite magnitude. This paper will study stochastic nonlinear dynamic responses of TLP with finite displacements in random waves. The nonlinearities considered are: large amplitude motions, coupling the six degrees-of-freedom, instantaneous position, instantaneous wet surface, free surface effects and viscous drag force. The nonlinear dynamic responses are calculated by using numerical integration procedure in the time domain. After the time histories of the dynamic responses are obtained, we carry out cycle counting of the stress histories of the tethers with rain-flow counting method to get the stress range distribution.

Electronic states of InAs/GaAs quantum ring

In the framework of effective mass envelope function theory, the electronic states of the InAs/GaAs quantum ring are studied. Our model can be used to calculate the electronic states of quantum wells, quantum wires, and quantum dots. In calculations, the effects due to the different effective masses of electrons in rings and out rings are included. The energy levels of the electron are calculated in the different shapes of rings. The results indicate that the inner radius of rings sensitively changes the electronic states. The energy levels of the electron are not sensitively dependent on the outer radius for large rings. If decreasing the inner and outer radii simultaneously, one may increase the energy spacing between energy levels and keep the ground state energy level unchanged. If changing one of two radii (inner or outer radius), the ground state energy level and the energy spacing will change simultaneously. These results are useful for designing and fabricating the double colors detector by intraband and interband translations. The single electron states are useful for studying the electron correlations and the effects of magnetic fields in quantum rings. Our calculated results are consistent with the recent experimental data of nanoscopic semiconductor rings. (C) 2001 American Institute of Physics.

Simulations to design an online motion compensation system for scanned particle beams

Respiration-induced target motion is a major problem in intensity-modulated radiation therapy. Beam segments are delivered serially to form the total dose distribution. In the presence of motion, the spatial relation between dose deposition from different segments will be lost. Usually, this results in over-and underdosage. Besides such interplay effects between target motion and dynamic beam delivery as known from photon therapy, changes in internal density have an impact on delivered dose for intensity-modulated charged particle therapy. In this study, we have analysed interplay effects between raster scanned carbon ion beams and target motion. Furthermore, the potential of an online motion strategy was assessed in several simulations. An extended version of the clinical treatment planning software was used to calculate dose distributions to moving targets with and without motion compensation. For motion compensation, each individual ion pencil beam tracked the planned target position in the lateral aswell as longitudinal direction. Target translations and rotations, including changes in internal density, were simulated. Target motion simulating breathing resulted in severe degradation of delivered dose distributions. For example, for motion amplitudes of +/- 15 mm, only 47% of the target volume received 80% of the planned dose. Unpredictability of resulting dose distributions was demonstrated by varying motion parameters. On the other hand, motion compensation allowed for dose distributions for moving targets comparable to those for static targets. Even limited compensation precision (standard deviation similar to 2 mm), introduced to simulate possible limitations of real-time target tracking, resulted in less than 3% loss in dose homogeneity.

胸苷酸合成酶和二氢叶酸还原酶mRNA亲和肽的发现及mRNA体外展示技术的优化

胸苷酸合成酶（thymidylate synthase，简称TS）和二氢叶酸还原酶（dihydrofolate reductase, 简称DHFR）都是叶酸依赖性酶，在维持DNA合成和DNA修复上发挥关键作用，并且多年来一直是肿瘤研究和化疗的重要靶点。我们前期的研究发现，TS和DHFR在翻译水平上存在负反馈调控机制。人TS和DHFR可以与其自身的mRNA结合，从而抑制mRNA的表达，化疗药物可以与TS或者DHFR相互作用，形成的复合物不能与TS mRNA结合， 使负反馈机制丧失。因此深入研究TS和DHFR的翻译调控机理，对阐明肿瘤抗药性机制，对发现新的抗肿瘤药物和肿瘤的治疗都具有十分重要的意义。 本论文利用mRNA体外展示技术，构建多肽库（约10万亿种多肽分子），利用多种实验手段将mRNA体外展示技术进行优化，提高了多肽库融合肽的产量，提高了mRNA体外展示技术筛选的特异性。将TS mRNA分子上的顺式因子TS30 RNA固定于磁珠上，将融合肽库与顺式因子作用，经过6轮循环，由多肽库中获得了与TS mRNA高度亲和的多肽序列，体外结合实验证明亲和肽可以与TS全长mRNA结合，体外翻译实验证明多肽可以抑制TS mRNA的翻译。并且利用phage display技术由噬菌体肽库（12个氨基酸随机肽库）经过四轮筛选，分别筛选到TS和DHFR的亲和肽，凝胶阻滞实验证明它们分别能与TS和DHFR mRNA结合。 本论文利用的展示技术可以广泛应用于特异靶点的蛋白质筛选，并且本论文筛选到的TS和DHFR亲和肽可以作为TS和DHFR的抑制剂，从而为获得新型的抗肿瘤药物奠定基础。