GOS+MU:一种查询对象选择新方法

在分析单一MU(Most Uncertainty)采样缺陷的基础上,提出一种"全局最优搜寻"方法 GOS(Global Optimal Search),并结合MU共同完成查询选择。GOS+MU方法中,GOS着眼全局寻找目标,在应用环境能提供的训练样本数量有限、分类器受训不充分时,该方法选择的对象学习价值高,能快速推进分类器学习进程;MU则能够在GOS采样失效情形下,利用分类器当前训练成果,选择查询不确定性最强的样本补充训练集。通过对网络商品的用户评论进行分类仿真,并比较其他采样学习方法的效果,证明了GOS+MU方法在压缩学习成本、提高训练效率方面的有效性。     

Influence of Bridgman solidification on microstructures and magnetic behaviors of a non-equiatomic FeCoNiAlSi high-entropy alloy

The non-equiatomic FeCoNiAlSi alloy is prepared by the Bridgman solidification (BS) technique at different withdrawal velocities (V = 30, 100, and 200 μm/s). Various characterization techniques have been used to study the microstructure and crystal orientation. The morphological evolutions accompanying the crystal growth of the alloy prepared at different withdrawal velocities are nearly the same, from equiaxed grains to columnar crystals. The transition of coercivity is closely related to the local microstructure, while the saturation magnetization changes little at different sites. The coercivity can be significantly reduced from the equiaxed grain area to the columnar crystal area when the applied magnetic field direction is parallel to the crystal growth direction, no matter what is the withdrawal velocity. In addition, the alloy possesses magnetic anisotropy when the applied magnetic field is in different directions.     

Study on the hydrogen storage properties of a TiZrNbTa high entropy alloy

High-entropy alloys (HEAs), as a new class of metallic materials, have received more and more attention due to its excellent mechanical properties. In this study, the hydrogen absorption properties, such as hydrogen absorption capacity, thermodynamics, kinetics and cyclic properties, as well as the hydride structure of a newly designed TiZrNbTa HEA were investigated. The results showed that multiple hydrides including ε-ZrH₂, ε-TiH₂ and β-(Nb,Ta)H were found in the TiZrNbTa HEA after hydrogenation. With the increase of temperature from 293 K to 493 K, the maximum hydrogen absorption capacity decreased from 1.67 wt% to 1.25 wt% and the plateau pressure related with β-(Nb,Ta)H hydrides increased from 1.6 kPa to 14.8 kPa. The formation enthalpy of β-(Nb,Ta)H hydride was determined to be −6.4 kJ/mol, which was less stable than that of NbH and TaH hydrides. The results also showed that the TiZrNbTa HEA exhibited a rapid hydrogen absorption kinetic even at the room temperature with a short incubation time, and the hydrogen absorption mechanism was determined to be the nucleation and growth mechanism. Moreover, the hydrogen absorption capacity at 293 K decreased slowly with the cycle numbers, and remained 86% capacity after 10 cycles. Cracking occurred after hydrogen absorption and became worse with cycles.     

Formation and properties of high entropy oxides in Co-Cr-Fe-Mg-Mn-Ni-O system: Novel (Cr,Fe,Mg,Mn,Ni)3O4 and (Co,Cr,Fe,Mg,Mn)3O4 high entropy spinels

Possibility of formation of quinary and senary equimolar high entropy oxides from the Co-Cr-Fe-Mg-Mn-Ni-O system is presented. Different proposed compositions are synthesized using the solid-state reaction route at high temperatures (900−1100 °C) and quenched to room temperature. Phase composition of the samples is studied, showing tendency toward formation of two main phases: rock salt-structured Fm-3 m and spinel-structured Fd-3 m. It is documented that the annealing temperature has a profound effect on stability of both structures, and at 1100 °C usually the highest content of Fm-3 m phase is usually observed. Three different oxides, namely, (Co,Cr,Fe,Mn,Ni)₃O₄, (Co,Cr,Fe,Mg,Mn)₃O₄ and (Cr,Fe,Mg,Mn,Ni)₃O₄ are obtained as single-phase materials, which structure can be described as the high entropy Fd-3 m spinel one. The latter two compounds have not been previously reported in the literature. Activated character of the electrical conductivity dependence on temperature is observed, with relatively high total conductivity at high temperatures and corresponding high absolute values of Seebeck coefficient.     

Boiling: Size Distribution of Bubbles as Demanded by the Principle of Maximum Information

The principle of maximum informational entropy is used to find the probability density function for the departure radius of a bubble in boiling on a solid surface. A general relation is derived, which leads to particular expressions.     

最大熵重建的迭代凸I投影算法

本文探讨了用迭代凸Ｉ投影（ＩｔｅｒａｔｉｖｅＣｏｎｖｅｘＩ－Ｐｒｏｊｅｃｔｉｏｎ，ＩＣＩＰ）算法求解最大熵Ｘ－ＣＴ重建问题．其思路是将这个复杂问题转化为多个简单子问题，然后迭代地求解这种单约束子问题．理论证明，这种算法收敛并能收敛到问题的最大熵解．这种算法形式优美，仿真结果表明算法同时也是有效的．     

基于小波变换的医学图象压缩编码

本文研究了医学图象小波变换系数的统计特征。根据医学图象的特点，提出了基于小波变换的医学图象编码方法。实验表明，这种方法具有较好的压缩编码性能，优于JPEG标准。同时，它支持逐次浮现式传输，从而能满足医学图象存储、通信、检索的需要。     

Hydrolysis of Fe(OH)SO4 in the presence of metallic iron

Hydrolysis of Fe(OH)SO₄ was carried out in the presence of metallic iron in order to prevent the formation of iron(III) oxides with strongly bonded sulphate. Under the conditions of the experiment, the products were found to be mixtures of ?-Fe₂O₃ and α-FeOOH. The occluded sulphate, if any, could be easily washed out with water. The hydrolysis reaction passes through an equilibrium state before coming to completion. The entropy with enthalpy of the hydrolysis corresponding to the equilibrium state were found to be 4 e.u. and 0·5 kJ/mol, respectively. The activation energy of the hydrolysis reaction was found to be 21 kJ/mol.     

A method to estimate entropies and heat capacities applied to alkali oxides

We present a method that is useful in the estimate and assessment of heat capacity data. The approach is based on an analysis of the logarithmic average of the phonon frequencies. In this quantity, that may be easily derived from experimental data on the vibrational entropy, the influence of atomic masses can be exactly accounted for even in polyatomic solids. Our method is applied to Li₂O, Na₂O, K₂O, Rb₂O, and Cs₂O. In particular, literature data for K₂O are critically examined.