关键词： RNA polymerase II   transcription   mRNA degradation   m6A   CCR4-Not complex   IRES   poly(A) tails   gene expression buffering   mRNA buffering   m6A methyltransferase complex  

摘要： Gene expression is regulated by the rates of synthesis and degradation of mRNAs, but how these processes are coordinated is poorly understood. Here, we show that reduced transcription dynamics of specific genes leads to enhanced m(6)A deposition, preferential activity of the CCR4-Not complex, shortened poly(A) tails, and reduced stability of the respective mRNAs. These effects are also exerted by internal ribosome entry site (IRES) elements, which we found to be transcriptional pause sites. However, when transcription dynamics, and subsequently poly(A) tails, are globally altered, cells buffer mRNA levels by adjusting the expression of mRNA degradation machinery. Stress-provoked global impediment of transcription elongation leads to a dramatic inhibition of the mRNA degradation machinery and massive mRNA stabilization. Accordingly, globally enhanced transcription, such as following B cell activation or glucose stimulation, has the opposite effects. This study uncovers two molecular pathways that maintain balanced gene expression in mammalian cells by linking transcription to mRNA stability.

关键词： Molecules  

摘要： C-60 fullerene has been utilized in various applications, including low friction and wear coatings, due to its unique molecular structure. In this work, molecular dynamics simulations were conducted to assess the nano-mechanical behaviour of a single C-60 fullerene and its crystallized structure. A single C-60 model and a model of a face-centred cubic structured C-60 crystal with a one-unit-cell thickness were prepared for compression and unloading simulations based on the adaptive intermolecular reactive empirical bond-order potential for carbon. Force-displacement curves and molecule-averaged virial stresses were obtained during the simulation. The models applied during the compression and unloading processes were visualized to confirm the deformation behaviour. Both the single and crystal C-60 models showed a perfectly reversible deformation before the point of force decrease that occurred during compression. In particular, the face-centred cubic structure of the crystal C-60 model was severely altered during compression before the individual C-60 molecules experienced permanent deformation. The maximum values of the normal virial stress in the compression direction before the permanent deformation of the molecules were almost same for both the single and crystallized models.

关键词： Hydrogels  

摘要： Understanding the three-dimensional (3D) mechanical and chemical properties of distinctly different, adjacent biological tissues is crucial to mimicking their complex properties with materials. 3D printing is a technique often employed to spatially control the distribution of the biomaterials, such as hydrogels, of interest, but it is difficult to print both mechanically robust (high modulus and toughness) and biocompatible (low modulus) hydrogels in a single structure. Moreover, due to the fast diffusion of mobile species during printing and nonequilibrium swelling conditions of low-solids-content hydrogels, it is challenging to form the high-fidelity structures required to mimic tissues. Here a predictive transport and swelling model is presented to model these effects and then is used to compensate for these effects during printing. This model is validated experimentally by photopatterning spatially distinct hydrogel elastic moduli using a single photo-tunable poly(ethylene glycol) (PEG) pre-polymer solution by sequentially patterning and in-diffusing fresh pre-polymer for further polymerization.

关键词： Hydrogen   Desorption   Solutions   Composites   Indium  

摘要： Improving desorption kinetics and achieving thermodynamic destabilization of MgH2 is of great importance for its practical applications. In the present study, a MgH2-In composite was synthesized through high-energy ball milling of MgH2 and In, and microstructures;hydrogen ab/desorption properties of the composite were carefully investigated with respect to the identically processed pure MgH2. The thermodynamic destabilization of MgH2 was achieved through reversible phase transformation of Mg(In) solid solution due to the partial solubility of In in Mg lattice (11 atom %), which resulted in lower enthalpy values and reduced desorption temperatures. X-ray diffraction peak analysis revealed the presence of internal stress/strain fields caused by the lattice mismatch between Mg and indium, which could play an important role in improving the desorption properties of the composite. Hydrogen evolution of the MgH2-In composite was directly observed via an in situ highresolution transmission electron microscope (TEM), which shows the "hydrogen pump" effect of a Mg3In phase which is stable only under a hydrogen environment. The formation mechanism of the Mg3In phase and its role as "hydrogen pump" in the improvements of desorption kinetics are thoroughly discussed based on the TEM observations and density functional theory (DFT) calculations.

关键词： 运动力学   机械结构设计   应用  

摘要： 现阶段,随着社会的发展也有了进步。机械结构设计过程中,会运用很多原理,其中运动力学原理发挥着非常重要的理论指导作用.在物理学的很多力学实验中,运动力学也是受到很多研究人员重视和关注的.可以说,运动力学作为机械科学与物理学科的一种连接纽带,通过科学合理的应用运动动力学,对于机械结构设计的改良和优化,具有十分有价值的指导意义。

关键词： energy transfer   luminescence   luminescence decay dynamics   phosphor   rare earths  

摘要： Green‐to‐red color tunability was achieved by controlling the Tb³⁺/Eu³⁺ doping ratio in Na₄CaSi₃O₉ upon UV excitation. The Tb³⁺→Eu³⁺ energy‐transfer pathway was systematically investigated in the vacuum ultraviolet (VUV)/UV/Vis region, by employing luminescence decay dynamics analysis in combination with the appropriate model simulation. A prototype white‐light‐emitting diode (WLED) device was successfully fabricated by using this phosphor. More information can be found in the Full Paper by Z.‐Q. Liu et al. on page 5619 ff. by S. P. de Visser.

关键词： energy transfer   luminescence   luminescence decay dynamics   phosphor   rare earths  

摘要： In this work, a latent energy-transfer process in traditional Eu3+,Tb3+-doped phosphors is proposed and a new class of Eu3+,Tb3+-doped Na4CaSi3O9 (NCSO) phosphors is presented which is enabled by luminescence decay dynamics that optimize the electron-transfer energy process. Relative to other Eu3+,Tb3+-doped phosphors, the as-synthesized Eu3+,Tb3+-doped NCSO phosphors show improved large-scale tunable emission color from green to red upon UV excitation, controlled by the Tb3+/Eu3+ doping ratio. Detailed spectroscopic measurements in the vacuum ultraviolet (VUV)/UV/Vis region were used to determine the Eu3+-O2- charge-transfer energy, 4f-5d transition energies, and the energies of 4f excited multiplets of Eu3+ and Tb3+ with different 4f(N) electronic configurations. The Tb3+-> Eu3+ energy-transfer pathway in the co-doped sample was systematically investigated, by employing luminescence decay dynamics analysis to elucidate the relevant energy-transfer mechanism in combination with the appropriate model simulation. To demonstrate their application potential, a prototype white-light-emitting diode (WLED) device was successfully fabricated by using the yellow luminescence NCSO:0.03Tb(3+), 0.05Eu(3+) phosphor with high thermal stability and a BaMgAl10O17:Eu2+ phosphor in combination with a near-UV chip. These findings open up a new avenue to realize and develop multifunctional high-performance phosphors by manipulating the energy-transfer process for practical applications.

关键词： 运动力学   机械结构   设计   应用  

摘要： 随着我国经济水平的提升,机械制造行业正处于快速发展阶段。当前机械制造业,是我国工业领域以及制造业发展的基石。为应对社会经济结构的改变,机械领域相关企业或单位应该重视机械制造技术的创新以及升级。结合运动学力学原理,提升机械产品的科技感。本文主要介绍运动力学相关原理在机械结构设计中的应用,以期为相关工作人员提供有价值的参考内容。

关键词： Metallic glasses   Molecular dynamics   Mechanical behavior   Atomic structure   Hydrogen  

摘要： Comparative studies on Zr35Cu65and Zr65Cu35amorphous systems were performed using molecular dynamic simulations to explore whether their hydrogenated mechanical behavior depends on the content of hydride-forming *** both of them present an increased strength and ductility after hydrogen microalloying,we observe the improved mechanical behavior for Zr35Cu65is more pronounced than that for *** these two samples,the distribution of configurational potential energy and flexibility volume respectively follows a similar H-induced variation tendency;all of the hydrogenated alloys not just have more stable atoms with smaller flexibility volume,but possess a larger fraction of readily activated ***,the atomic-scale details,based on the local"gradient atomic packing structure"model,indicate minor additions of hydrogen can promote more"soft spots"along with more strengthened"backbones"in the low-Zr alloy than that in the high-Zr sample,which endows the former with much higher strength and deformability after hydrogen *** regard this finding as a further step forward to distilling the tell-tale metrics of the H-dependent mechanical behavior observed in Zr-based metallic glasses.

关键词： 运动力学   机械结构   设计  

摘要： 在当下制造业发展迅速,基础设施建设发展火热的状况下,对于机械结构设计的研究变得尤为重要.本文就针对运动力学在机械结构设计之中的应用进行了一定的探讨,供有关部门进行参考.