The crystal chemistry of L-Ta2O5 and related structures

Single crystals of a new form of L-Ta₂O₅ with a 19×b superstructure have been synthesised by flux growth. The phase is most likely stabilised by the incorporation of a small amount of lithium (0.14 wt% Li) from the flux. The phase has C-centred monoclinic symmetry with , (), , γ=90.00(1)°. The structure was refined in space group C112/m to R₁=0.044 for 814 unique reflections with F>4σ(F). The structure can be described as comprising chains of edge-shared TaO₇ pentagonal bipyramids that are regularly folded at (010) planes to give sinusoidal chains along [010]. These chains are interconnected along [100] and [001] by corner sharing, creating inter-chain regions that are occupied by isolated TaO₆ octahedra and pairs of corner-shared octahedra. A comparison with published data for high-quality refinements of related structures has led to the development of a general model that can explain the structural chemistry variations in the known L-Ta₂O₅-related structures. A shorthand notation is presented for representing the structures, based on the sequence along [010] of the interchain octahedra.     

Empirical scoring functions: I. The development of a fast empirical scoring function to estimate the binding affinity of ligands in receptor complexes

This paper describes the development of a simple empirical scoringfunction designed to estimate the free energy of binding for aprotein–ligand complex when the 3D structure of the complex is knownor can be approximated. The function uses simple contact terms to estimatelipophilic and metal–ligand binding contributions, a simple explicitform for hydrogen bonds and a term which penalises flexibility. Thecoefficients of each term are obtained using a regression based on 82ligand–receptor complexes for which the binding affinity is known. Thefunction reproduces the binding affinity of the complexes with across-validated error of 8.68 kJ/mol. Tests on internal consistency indicatethat the coefficients obtained are stable to changes in the composition ofthe training set. The function is also tested on two test sets containing afurther 20 and 10 complexes, respectively. The deficiencies of this type offunction are discussed and it is compared to approaches by other workers.     

Thermodynamic and19F NMR studies of antimony trifluoride in water

Densities, specific heat capacities per unit volume and enthalpies of dilution at 25°C and osmotic coefficients at 37°C were measured for antimony trifluoride in water as functions of concentration. From the first three properties the apparent and partial molar volumes, heat capacities and relative enthalpies were derived. As well, pH measurements in water at 25°C and¹⁹F NMR spectra in water and methanol at 33°C were also carried out. All the thermodynamic properties together with the chemical shifts abruptly change in the very dilute concentration region (<0.1m) and, then, tend to a constant value. These trends have been rationalized through a simple model based on an equilibrium of dissociation of SbF₃ into two ionic species. From the simulation of all the data it is derived that two concomitant equilibria are present in solution: the hydrolysis process of SbF₃ which explains the pH values and the ionic dissociation of SbF₃ which accounts for the¹⁹F NMR data.     

基于Expectile和Realized GARCH模型的波动率预测

Realized GARCH模型是预测波动率的经典模型之一,最小化非对称二次损失函数的Expectile对收益率尾部分布更加敏感,我们在Realized GARCH模型的基础上引入Expectile提出Expectile-Realized GARCH模型。以沪深300指数的高频收益率为例建模分析,对比不同模型下的波动率预测效果,发现Expectile-Realized GARCH模型较Realized GARCH模型对波动率预测能力更好。其中,当风险水平为95%时,对应的Expectile-Realized GARCH波动率预测能力最好。     

基于轮轨蠕滑机理的货车车轮磨耗寿命预测

为对货车车轮磨耗寿命进行预测,在SIMPACK中建立车辆-轨道多体动力学模型,基于轮轨半赫兹接触理论和Zobory车轮磨耗模型编制车轮磨耗数值仿真程序.对C80型货车等在环形线和大秦线上运行时的车轮磨耗行为进行仿真,并根据实测结果和仿真结果对Zobory车轮磨耗模型进行修正,最后利用修正后的Zobory模型对C80型货车在国内某重载线路上运行时的车轮磨耗寿命进行预测.结果表明:车辆在环形线和大秦线上运行时,仿真得到的车轮磨耗分布范围以及圆周磨耗深度和轮缘厚度随运行里程的变化趋势均与现场实测结果较为接近,但车轮圆周磨耗率分别为实测结果的1.394 ～1.842倍和2.172 ～3.658倍,主要原因是仿真中采用了轮轨半赫兹接触理论,考虑了弹性剪切变形对滑动速度的影响,并且国内货车采用的CL60钢的硬度大于国外BSll钢的硬度;C80型货车在国内某重载线路上运行时,利用修正后的Zobory模型仿真得到的车轮段修磨耗寿命为39×105 km,运用磨耗寿命为65×105 km,与现场统计结果较为吻合.     

Potential polymorphs of aspirin

Aspirin is only found experimentally in one crystal structure. In this article, the method of Karfunkel and Gdanitz is used to predict potential polymorphs of aspirin. The known structure, containing a nonplanar conformer is found, along with a number of other low energy structures, many of which are based on a planar conformer. Semiempirical and ab initio calculations show that the planar conformer is less stable than the experimentally known one. Force field calculations suggest that the planar conformer is more stable. The lattice energy of the experimentally known crystal structure is 1.4 kcal/mol lower than any of the potential crystal structures, even though there are a number of structures with lower total (lattice+intramolecular) energies. Conformational maps indicate that another stable conformation occurs within a few kilocalories per mole of the known structure. Polymorphs are predicted for this conformer, but it is found to pack poorly. It is proposed that routes to producing polymorphs of aspirin might be found if consideration is given to promoting the stability of the planar conformer with appropriate solvents or additives. ©1999 John Wiley & Sons, Inc. J Comput Chem 20: 262–273, 1999     

A novel approach toward the prediction of the glass transition temperature: Application of the EVM model,a designer QSPR equation for the prediction of acrylate and methacrylate polymers

We describe an original QSPR model called the EVM model (Energy, Volume, Mass) to calculate the glass transition temperature (T_g) of aliphatic acrylate and methacrylate homopolymers using classical molecular mechanics and dynamics. The latter was used to calculate an energy density function related to the cylindrical volume of a 20 monomer unit polymer segment (TSSV, Total Space around a Standard deviation Volume). We then calculated the T_g as a function of this density function and the repeat unit molecular weight, although no interchain interactions were taken into account. For linear and branched aliphatic acrylate and methacrylate polymers, the standard deviation from linear regression was 12 K, and the r² was 0.96. The model allows calculation of the T_g with an average absolute error of error of 10% for linear and branched derivatives not included in the original linear regression analysis. The results obtained with the EVM model are compared with those obtained with Bicerano's model. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 2579–2590, 1997     

Interactive System for Similarity-Based Inspection and Assessment of the Well-Being of mHealth Users

Recent digitization technologies empower mHealth users to conveniently record their Ecological Momentary Assessments (EMA) through web applications, smartphones, and wearable devices. These recordings can help clinicians understand how the users’ condition changes, but appropriate learning and visualization mechanisms are required for this purpose. We propose a web-based visual analytics tool, which processes clinical data as well as EMAs that were recorded through a mHealth application. The goals we pursue are (1) to predict the condition of the user in the near and the far future, while also identifying the clinical data that mostly contribute to EMA predictions, (2) to identify users with outlier EMA, and (3) to show to what extent the EMAs of a user are in line with or diverge from those users similar to him/her. We report our findings based on a pilot study on patient empowerment, involving tinnitus patients who recorded EMAs with the mHealth app TinnitusTips. To validate our method, we also derived synthetic data from the same pilot study. Based on this setting, results for different use cases are reported.     

Reservoir Computing with Delayed Input for Fast and Easy Optimisation

Reservoir computing is a machine learning method that solves tasks using the response of a dynamical system to a certain input. As the training scheme only involves optimising the weights of the responses of the dynamical system, this method is particularly suited for hardware implementation. Furthermore, the inherent memory of dynamical systems which are suitable for use as reservoirs mean that this method has the potential to perform well on time series prediction tasks, as well as other tasks with time dependence. However, reservoir computing still requires extensive task-dependent parameter optimisation in order to achieve good performance. We demonstrate that by including a time-delayed version of the input for various time series prediction tasks, good performance can be achieved with an unoptimised reservoir. Furthermore, we show that by including the appropriate time-delayed input, one unaltered reservoir can perform well on six different time series prediction tasks at a very low computational expense. Our approach is of particular relevance to hardware implemented reservoirs, as one does not necessarily have access to pertinent optimisation parameters in physical systems but the inclusion of an additional input is generally possible.     

Crystal structure predictions for acetic acid

Possible crystal structures of acetic acid were generated, considering eight space groups and assuming one molecule in the asymmetric unit. Our grid-search method was compared with a Monte Carlo approach as implemented in the Biosym/MSI Polymorph Predictor. This revealed no sampling deficiencies. A large number of possible crystal structures were found (∼100 within only 5 kJ/mol), including the experimental structure. Energy minimizations were done with a united-atoms force field (GROMOS), an all-atoms force field (AMBER), and a potential that describes the electrostatic interactions with distributed multipoles (DMA). In all cases, the experimental structure had a low lattice energy. The number of hypothetical crystal structures was reduced considerably by removing space-group symmetry constraints, or by a primitive molecular dynamics shake-up. Nevertheless, sufficient structures of equal or lower energy compared with the experimental structure remained to suggest that other factors need to be considered for genuine structure prediction. © 1998 John Wiley & Sons, Inc. J Comput Chem 19: 459–474, 1998