Unfolding events of Chymotrypsin Inhibitor 2 (CI2) revealed by Monte Carlo (MC) simulations and their consistency from structure-based analysis of conformations

We investigated the behavior of the conformations of Chymotrypsin Inhibitor (CI2) from the native to the denatured states, obtained in Monte Carlo (MC)/Metropolis simulations, where a low-resolution model is used together with knowledge-based potentials. New conformations starting from the X-ray native structure are generated by random perturbations along with a constraint to increase the radius of gyration. Unfolding is also simulated by unrestrained simulations at a higher temperature. All simulations yield a similar sequence of unfolding events. The preferred pathway starts with loss of native contacts between (N-terminal)-β₃ and continues with β₂-β₃. The persistence of the contacts between β₁ and β₂ at intermediate values of the fraction of native contacts (Q); whereas, highly unfolded conformations with only some helical contacts persisting at low values of Q, are observed. Structure-based analysis of the fluctuations of the unfolded conformations by Gaussian Network Model (GNM) reveals that the termini of the chain—C terminus being more mobile—depict relatively higher flexibility with a native-like hinge near β₂ that divides the structure into two domains. The fluctuations of the two domains are negatively correlated, with partly folded α-helix and a small hydrophobic cluster in the middle of the chain displaying positively correlated fluctuations. The most persistent short-range rotational bond correlations are observed between the residues of α-helix, C terminus of the β₁-part of the reactive site loop, and around the C terminus of the β₂. The latter regions also appear as hot spots; i.e. high frequency fluctuating regions, of the structure surviving in unfolded conformations. The results imply that the unfolded CI2 has an intrinsic ability to undergo correlated fluctuations along with some residual native structure specifically induced by its sequence, consisting at the lowest level of a single hinge.     

Evaluation of a polyolefin coated urea (Meister) as a fertilizer for irrigated cotton

The effectiveness of two polyolefin coated products, ‘Meister 70’ and ‘Meister 270’, as slow-release sources of nitrogen (N) for irrigated cotton, and uncoated calcium carbide as a source of acetylene to inhibit nitrification of urea-N and reduce losses by denitrification were studied. The crop was grown on a grey clay in the Namoi Valley of north western New South Wales. The fertilisers were applied at 50 and 150 kg N/ha, combined factorialy with two application times, either pre- or post-sowing. Meister 270 did not release N fast enough to supply the plant’s requirements, and is not recommended as a source of N for cotton. Meister 70 was worthy of further study as a pre-sowing source of N because it maintained a higher concentration of ammonium in the soil for longer than urea, resulted in lower soil nitrate concentrations at all times, and increased the apparent recovery efficiency of fertilizer N. The uncoated calcium carbide was not as effective as the wax-coated material tested in previous studies.     

山地城市慢行交通规划初探——以左权县城市总体规划为例

本文基于对慢行交通的认识,分析了山地城市发展慢行交通的必要性,并以左权县城市慢行交通规划为例,对山地城市慢行交通系统规划做出初步探索。     

周期慢波结构高频特性的仿真研究

由于理论方法数值计算量大以及与实际复杂结构差别大,同时实验测试方法误差大、且高次模难激励。针对这些算法的缺点,采用理论和数值模拟结合方法从而克服上述方法不足,仿真研究了圆柱载膜波导慢波结构的色散特性,其结果和理论计算结果模拟比较,二者吻合。研究表明圆柱载膜波导慢波结构的谐振频率(同一模式下)与载膜半径成正比、与周期成反比;同时表明上述方法计算简单,省去了繁琐的求解方程过程。最后给出各个模式电场分布,对研究分析束波互作用提供依据。     

Singularity and Slow Convergence of the EM algorithm for Gaussian Mixtures

Singularities in the parameter spaces of hierarchical learning machines are known to be a main cause of slow convergence of gradient descent learning. The EM algorithm, which is another learning algorithm giving a maximum likelihood estimator, is also suffering from its slow convergence, which often appears when the component overlap is large. We analyze the dynamics of the EM algorithm for Gaussian mixtures around singularities and show that there exists a slow manifold caused by a singular structure, which is closely related to the slow convergence of the EM algorithm. We also conduct numerical simulations to confirm the theoretical analysis. Through the simulations, we compare the dynamics of the EM algorithm with that of the gradient descent algorithm, and show that their slow dynamics are caused by the same singular structure, and thus they have the same behaviors around singularities.     

Slow flow across macroscopically semi-circular fibre lattices and a free-flow region of variable width—visualisation by magnetic resonance imaging

Slow flow of an incompressible Newtonian fluid across a fibrous porous medium bounded by a free-flow region of variable width was studied experimentally by magnetic resonance imaging velocimetry. The fibrous porous medium (fibre lattice) comprised of aligned rows of cylindrical rods, which were macroscopically arranged in a semi-circular fashion in a Hele-Shaw cell. The local aspects of the flow in the interior of and exterior to the fibre lattices were studied for (i) three individual semi-circular fibre lattices of different porosity and/or cylinder size, with each lattice bounded by an open channel and (ii) an assembly of five fibre lattices with the interstitial space between them forming a free-flow region. The symmetry (in a practical sense) of slow flow over symmetrical lattice-channel arrangements is demonstrated. The subtle characteristics of the flow within the lattices are seen as considerable local velocity enhancements (LVE) transverse to and in the direction of superficial flow. These LVE within the lattices strongly depend on the interface configuration of the lattice-channel arrangement, the gap size between the cylinders and the lattice porosity. The penetration depth of the LVE may even extend to the lattice centre. When a fibre lattice is a part of an assembly, the surface irregularities of neighbouring lattices create more complex tortuous flow pathways in the free-flow region. These pathways produce recurrent LVE within the fibre lattice. The implications that the above findings have for the flow, heat transfer and mass transfer in conceptually similar heterogeneous porous media used in, for example, liquid composite moulding processes and filtration processes are discussed.     

Monitoring extremely slow rolling element bearings: part II

The most established technique for monitoring the integrity of rolling element bearings is vibration analysis. However, at extremely slow rotational speeds monitoring the health of rolling element bearings is fraught with difficulty. Part I of this work details difficulties with monitoring rolling element bearings rotating at speeds of less than 2 rpm. Furthermore, it presents a study of the high frequency acoustic emission (AE) technique as a means of monitoring low-speed rolling element bearings. The application of AEs to monitor operational slow-speed bearings with bore diameters of 120 mm is presented. It is concluded that the mechanism of AE generation was the relative movement between bearing elements experiencing loss of mechanical integrity, for example, the rolling/sliding action of a roller on a defective outer race.     

振动压路机液压马达动态压力测试及分析

本文简要论述了齿轮马达在振动压路机液压系统中的动态压力测试过程,分析了造成马达裂体、漏油的原因及改进措施     

基于变化载荷下孔口出流的扭矩缓慢输出装置

扭矩缓慢输出装置通过齿轮齿条以及压簧良好的储能特性产生扭矩,通过液压缸、单向阀和流量阀的组合应用,实现扭矩的缓慢输出。针对液压缸非恒定出流缺少变化载荷下的计算公式,无法进行量化分析,建立了受变化载荷下的孔口非恒定出流的流速和流量的数学模型,得到了扭矩缓慢输出的时间。经过理论分析和实验验证可以将大扭矩缓慢输出,验证了建立的数学模型的正确性。该装置具有结构简单、传动效率高、输出扭矩大等特点,同时可以有效地防止其在零件失效的情况下因扭矩快速输出造成危害。     

一种快速瞬态响应的无片外电容LDO

设计了一种快速瞬态响应的无片外电容低压差线性稳压器(LDO)。采用具有摆率增强作用的缓冲级电路,可以在不额外增加静态电流的同时检测输出端电压,在负载瞬间变化时增大功率器件栅极电容的充放电电流。缓冲级电路还引入了简单的负反馈技术,增加了环路的相位裕度。采用SMIC 180 nm的CMOS工艺进行设计和仿真。仿真结果表明,当输入电压为1.4~5 V时,该LDO的输出电压为1.2 V,最大负载电流为300 mA; 负载电流在1 mA和300 mA间变化时,最大过冲电压为76.5 mV,响应时间仅为1.5 μs。