残基突变对P53-DNA结合域肽段构象影响的分子动力学模拟

基于分子动力学模拟方法研究了R249S、R248W 和G245S 突变对P53-DNA 结合域肽段(残基230-258)结构的影响. 采用GROMACS 软件包和GROMOS 43A1分子力场, 分别对野生型wtP53肽段、单点突变型P53-R249S肽段、两点突变型P53-R249S/R248W肽段和三点突变型P53-R249S/R248W/G245S肽段进行了4组独立的分子动力学模拟, 每组体系模拟时间为500 ns. 研究结果表明: R249S单残基突变影响肽段残基形成二级结构的情况, 但不改变肽段三维结构的模式, 同时使该肽段结构相对稳定; R249S和R248W两残基同时突变会加剧R249S突变对肽段的影响, 同时导致三维结构发生较大变化, 构象弯曲呈现双turn 结构, 肽段稳定性进一步增大; G245S突变对肽段的影响与R249S和R248W同时突变对其结构的影响相反, 在两残基突变的基础上, G245S突变会使原突变引起的变化减弱甚至消失, 同时使得该肽段结构稳定性减小. 该研究对认识肿瘤致病分子机制和设计新药物有重要意义.     

Basin of attraction of a cusp–fold singularity in 3D piecewise smooth vector fields

Generic one-parameter families of piecewise smooth vector fields on R³${\mathbb{R}}^3$ presenting the so-called cusp–fold singularity are studied. The bifurcation diagrams are exhibited and the asymptotic and structural stabilities are discussed.     

A mathematical model for horizontal axis wind turbine blades

A mathematical model describing the nonlinear vibration of horizontal axis wind turbine (HAWT) blades is proposed in this paper. The system consists of a rotating blade and four components of deformation including longitudinal vibration (named axial extension), out-of-plane bend (named flap), in-plane/edgewise bend (named lead/lag) and torsion (named feather). It is assumed that the center of mass, shear center and aerodynamic center of a cross section all lie on the chord line, and do not coincide with each other. The structural damping of the blade, which is brought about by materials and fillers is taken into account based on the Kelvin–Voigt theory of composite materials approximately. The equivalent viscosity factor can be determined from empirical data, theoretical computation and experimental test. Gravitational loading and aerodynamic loading are considered as distributed forces and moments acting on blade sections. A set of partial differential equations governing the coupled, nonlinear vibration is established by applying the generalized Hamiltonian principle, and the current model is verified by previous models. The solution of equations is discussed, and examples concerning the static deformation, aeroelastic stability and dynamics of the blade are given.     

An analysis of the structural complexity of supply chain networks

Each enterprise in a supply chain network needs quantitative indicators to analyze and manage its interactions with different business partners in the network. Supply chains exhibit the characteristics of complex systems. In a supply chain network, a large number of firms cooperate simultaneously with many suppliers and customers, and interact through a variety of information and material flows to achieve a balance between supply and demand. However, the complexity of a supply chain is not a simple linear structure where a small change often results in a chain reaction. When supply chain complexity increases, monitoring and managing the interaction between different elements of the chain becomes more difficult. An entropy model based on information theory provides an appropriate means of quantifying the complexity of a supply chain system by delivering information required to describe the state of the system. The entropy measure links uncertainty and complexity so that, as a system grows in uncertainty, it becomes more complex and more information is required to describe and monitor it. In this paper, we propose an entropy-based measure for analyzing the structural complexity in relation to the structure and system uncertainty. The method provides guidelines for estimating the complexity throughout the supply chain structure.     

Diseño óptimo robusto utilizando modelos Kriging: aplicación al diseño óptimo robusto de estructuras articuladas

Conventional methods addressing the robust design optimization problem of structures usually require high computational requirements due to the nesting of uncertainty quantification within the optimization process. In order to address such a problem, this work proposes a methodology, based on Kriging models, to efficiently assess the uncertainty quantification in the optimization process. The Kriging model approximates the structural performance both in the design domain and in the stochastic domain, which allows to decouple the uncertainty quantification process and the optimization process. In addition, an infill criterion based on the variance of the Kriging prediction is included to update the Kriging model towards the global Pareto front. Three numerical examples show the applicability and the accuracy of the proposed methodology. The results show that the proposed method is appropriate to solve the robust design optimization problem with reasonable accuracy and a considerably lower number of function calls than required by conventional methods.     

Preparation and characterization of transparent TiO2 thin films coated on fused-silica substrates

The transparent TiO₂ thin films coated on fused-SiO₂ substrates were prepared by the sol–gel method and spin-coating technique. Effects of calcination temperature on crystal structure, grain size, surface texture, and light transmittance of the films were investigated. After calcining at 600–1,200 °C, the thicknesses of the TiO₂ films were all around 80 nm and the molecular structures of the films were anatase, even at 1,200 °C. The calcined TiO₂ films had the ultraviolet light (wavelength 200–400 nm) transmittances of ≤29% and the visible light (wavelength 400–800 nm) transmittance of ≥72%. By photocatalytically decomposing the methylene blue (MB) in water, the photocatalytic activities of the TiO₂ thin films were measured and represented using the characteristic time constant (τ) for the MB degradation. While the films prepared at 1,000 and 1,200 °C photodecomposed about 54 mol% of the MB in water (the corresponding τ ≈ 14.8 h) after exposing to 365-nm UV light for 12 h, the films prepared at 600 and 800 °C had smaller τ (≈9.0 h) and photodecomposed about 74 mol% of the MB in water at the same testing conditions.     

Heating effects on morphological and textural characteristics of individual and composite nanooxides

Morphological, structural and adsorption characteristics of nanooxides (fumed individual silica, alumina and titania, and composite silica/alumina, silica/titania and alumina/silica/titania) were compared after different treatments (wetting/drying, ball-milling, suspending/drying, heating) at different temperatures (373–1173 K) using low-temperature nitrogen adsorption data. The structural characteristics such as specific surface area (S _BET), pore volume (V _p), pore (PSD) and particle (PaSD) size distributions (calculated using self-consisting regularization procedure with respect to both PSD and PaSD), fractality, adsorption energy distributions depend differently on heating temperature because desorption of water molecularly and dissociatively adsorbed at a surface and in bulk of primary nanoparticles occurs over a wide temperature range at different rates. These processes affect both structural and energetic characteristics of nanooxides.     

“Through-space” nuclear spin–spin couplings in ferrocenyl polyphosphanes and diphosphino cavitands: A new way of gathering structural information in constrained P(III) ligands by NMR

Nuclear magnetic resonance is an invaluable technique for investigating a variety of important issues ranging from the determination of molecular structure to therapeutic medical imaging. In this respect, the indirect nuclear spin–spin coupling involving common nuclei such as ¹H, ¹³C or ³¹P provides, via the J constant, conclusive data for compound characterization in solution. This electron-mediated nuclear spin coupling is usually regarded as being transmitted by covalently bonded magnetic atoms. However, several experimental and theoretical studies, first focused on constrained organofluorides, and more recently devoted to phosphane ligands highlighted the existence of very intense J-couplings operating “through-space”. Herein, the intramolecular “through-space” ³¹P³¹P and ³¹P¹³C couplings are discussed in the light of recent examples found in constrained phosphorus-containing ligands such as phosphinocalixarenes, phosphinocyclodextrins and ferrocenyl phosphanes. The emphasis is put on the origin and transmitting mode of these nonbonded spin–spin couplings as well as on the relevant structural information they provide in solution.     

V2.38Nb10.7O32.7: A V2O5-Nb2O5 mixed oxide tunnel structure related to the tetragonal tungsten bronzes

A crystal structural model for the orthorhombic compound V_2.38Nb_10.7O_32.7, which is known as “V₂Nb₉O_27.5”, was developed by means of selected area electron diffraction (SAED), Rietveld refinement and high resolution electron microscopy (HREM). The metastable compound is obtained by thermal decomposition of freeze-dried precursors as chain-like agglomerated nanoparticles or by reaction of V₂O₅ with fresh-precipitated Nb₂O₅ as more compact micro-scaled crystals. With the latter, it was possible to identify its structure for the first time (space group Cmmm). The tetragonal tungsten bronze (TTB)-type structure shows high potential for ionic intercalation, since easily reducible [V⁵⁺₂O²⁻] units are implemented in the tunnels of a rigid niobium oxide framework.     

Geometric parameterization of the YBaCo4O7 structure type: Implications for stability of the hexagonal form and oxygen uptake

We explore the stability of the hexagonal form of MBaCo₄O₇ cobaltites in terms of geometric characteristics of the crystal structure and Global Instability Index (GII) based on the bond-valence considerations. Mismatch between an M^3+/2+ and the three-dimensional network of CoO₄ tetrahedra, whether expressed using an M ionic radii or GII, is shown to essentially determine both the temperature of structural transition to an orthorhombic modification and oxygen storage properties. A number of M cations not reported in the literature are identified to be suitable for the octahedral sites in an MBaCo₄O₇ structure.