Modeling of quantitative relationships between physicochemical properties of active pharmaceutical ingredients and tensile strength of tablets using a boosted tree

Objectives: The aim of this study was to explore the potential of boosted tree (BT) to develop a correlation model between active pharmaceutical ingredient (API) characteristics and a tensile strength (TS) of tablets as critical quality attributes.

Methods: First, we evaluated 81 kinds of API characteristics, such as particle size distribution, bulk density, tapped density, Hausner ratio, moisture content, elastic recovery, molecular weight, and partition coefficient. Next, we prepared tablets containing 50% API, 49% microcrystalline cellulose, and 1% magnesium stearate using direct compression at 6, 8, and 10?kN, and measured TS. Then, we applied BT to our dataset to develop a correlation model. Finally, the constructed BT model was validated using k-fold cross-validation.

Results: Results showed that the BT model achieved high-performance statistics, whereas multiple regression analysis resulted in poor estimations. Sensitivity analysis of the BT model revealed that diameter of powder particles at the 10th percentile of the cumulative percentage size distribution was the most crucial factor for TS. In addition, the influences of moisture content, partition coefficients, and modal diameter were appreciably meaningful factors.

Conclusions: This study demonstrates that BT model could provide comprehensive understanding of the latent structure underlying APIs and TS of tablets.     

碳纳米管改性水泥石力学性能研究

随着非常规油气的勘探开发，超深井、复杂井、页岩气井等对固井质量的要求越来越高，现有水泥基材料性能已经不能满足要求，需要探索新型材料在水泥基材料中的应用以及对水泥石的性能改造。从碳纳米管自身的特点出发，制备稳定性较好的碳纳米管分散液，通过水泥石抗压强度、抗折强度测试、单轴三轴力学性能实验以及微观结构测试对碳纳米管的加量范围、分散效果进行了讨论，分析碳纳米管对水泥石力学性能的影响规律。实验结果表明，0.05%~0.1%碳纳米管加量能够提高水泥石的抗压、抗折性能，并且随着龄期的增长其增强效果更加明显；碳纳米管能够降低水泥石的弹性模量，同时增大塑性形变，使水泥石韧性增加；碳纳米管对微观结构的增强增韧机理表现为拨出、桥联、纳米诱导效应和网状填充效应，经过分散的碳纳米管与基体的相容性较好。      

Dielectric Properties of Ultrathin CaF2 Ionic Crystals

Mechanically exfoliated 2D hexagonal boron nitride (h-BN) is currently the preferred dielectric material to interact with graphene and 2D transition metal dichalcogenides in nanoelectronic devices, as they form a clean van der Waals interface. However, h-BN has a low dielectric constant (≈3.9), which in ultrascaled devices results in high leakage current and premature dielectric breakdown. Furthermore, the synthesis of h-BN using scalable methods, such as chemical vapor deposition, requires very high temperatures (>900 °C) , and the resulting h-BN stacks contain abundant few-atoms-wide amorphous regions that decrease its homogeneity and dielectric strength. Here it is shown that ultrathin calcium fluoride (CaF₂) ionic crystals could be an excellent solution to mitigate these problems. By applying >3000 ramped voltage stresses and several current maps at different locations of the samples via conductive atomic force microscopy, it is statistically demonstrated that ultrathin CaF₂ shows much better dielectric performance (i.e., homogeneity, leakage current, and dielectric strength) than SiO₂, TiO₂, and h-BN. The main reason behind this behavior is that the cubic crystalline structure of CaF₂ is continuous and free of defects over large regions, which prevents the formation of electrically weak spots.     

基于同轴线相位法的两相流含气率测量研究

为了准确测量气液两相流含气率,提出一种同轴线相位差测量方法。利用同轴线传感器,通过测量电磁波经过在同轴线内分布状况不同的气液混合介质后相位差的变化,得到混合介质的含气率。完成了同轴线测量电路及测量传感器的设计,建立了一种含气率测量模型。以气液两相做了室内静态实验,并对垂直管状态下传感器响应和实验结果进行了误差分析。结果表明:相位差输出与含气率呈线性关系;同时,在不同频率下,预测结果和实验结果的相对误差在±5%范围内,说明预测模型准确度较好。     

缓冷出口温度对连续退火SPCC冷轧薄板屈服强度的影响

研究了缓冷出口温度对连续退火SPCC冷轧薄板组织和屈服强度的影响。结果表明:连续退火SPCC冷轧薄板的组织由等轴的铁素体晶粒和晶界处的块状渗碳体及晶粒内的颗粒状渗碳体组成。随着缓冷出口温度从680 ℃提高至700 ℃,平均晶粒尺寸从10.1 μm增加至12.5 μm;此外,提高缓冷出口温度还能够抑制晶界处块状渗碳体的形成,促进晶粒内细小渗碳体更加细小弥散的析出。当缓冷出口温度从680 ℃提高至700 ℃时,冷轧薄板的屈服强度约降低了28 MPa。     

硅渣和玻璃粉直接烧结制备多孔材料的气孔结构与力学性能

以硅渣和玻璃粉为原料,采用粉体直接烧结法制备多孔材料,研究了烧结温度(700~900℃)、烧结时间(15~120min)和升温速率(10~100℃·min^-1)对多孔材料表观密度、气孔率、物相组成、抗压强度的影响。结果表明:气孔结构均匀性随烧结温度的升高而降低;表观密度随烧结温度的升高先减小后增大,随保温时间的延长而增大,随升温速率的增大而减小,气孔率的变化趋势与表观密度的相反;多孔材料的主要物相为玻璃相和硅、SiC、SiO2、Ca2Al2SiO7等结晶相,且结晶度随烧结温度的升高而降低;抗压强度随烧结温度的升高呈先增大后减小的趋势;当烧结温度为750℃,升温速率为30℃·min^-1,烧结时间为30 min时,多孔材料的主晶相为硅和Ca2Al2SiO7,抗压强度最大(1.60MPa),表观密度为0.43g·cm^-3,气孔率为80%。     

Comparison of mechanical properties of ground corn stover,switchgrass, and willow and their pellet qualities

Mechanical and physical properties of ground corn stover, switchgrass, and willow were measured and compared in addition to the quality of pellets. Biomass was size-reduced with two different screen sizes (3.175 and 6.35?mm) and conditioned to obtain samples at two different moisture contents (17.5 and 20% on wet basis). Ground switchgrass had the smallest and willow had the highest D₅₀ when size-reduced with the same screen size. Hydrostatic triaxial compression tests were performed using the cubical triaxial tester to determine the bulk modulus, compression index, and spring-back index at specific unloading pressures (20, 45, 70, and 95?kPa). The trends of pressure vs. volumetric strain and void ratio vs. natural log of pressure were similar for all three materials; however, the magnitudes were different. Willow, size-reduced with 3.175?mm screen size at 17.5% wet basis, had the highest bulk modulus among different conditions of all the three biomass. Pellet durability values for all the three materials were higher than 80%. Corn stover pellets formed with 3.175?mm screen size at 20% wet basis had the highest diametral tensile and axial compressive strengths among different conditions for all the three biomass, however the values were not significantly different (p?>?0.05).     

Dynamic tensile mechanical properties and failure mode of zirconium diboride-silicon carbide ceramic composites

Dynamic indirect tension experiments were performed on zirconium diboride-silicon carbide (ZrB₂−20%SiC) ceramic. Flattened Brazilian disc specimens of ZrB₂−20%SiC were prepared to conduct dynamic tensile tests using the modified Split Hopkinson pressure bar system. The tensile experiments were completed at the range of loading rates from 7.53 to 74.71 GP s⁻¹. The tensile experimental results revealed that the zirconium diboride-silicon carbide ceramic composite is rate-sensitive in terms of the tensile strength and failure mode. The dynamic tensile strength increases linearly with the loading rate and changes from 195 MPa at 7.53 GP s⁻¹ to 654 MPa at 74.71 GP s⁻¹. Moreover, the dynamic tensile strength decreases with the increase in critical fracture time, which conforms to Tuler and Butcher's fracture criterion. In dynamic experiments, a high-speed camera was used to examine the tensile failure process, and fragments were collected to analyze the dynamic tensile failure mechanism. The tensile fracture mode of ZrB₂−20%SiC obviously showed the sensitivity of the loading rate. The fragment size of ZrB₂−20%SiC ceramic decreased but the quantity of fragments increased as the loading rate increased.     

Fabrication of improved flexural strength C/SiC composites via LA-CVI method using optimized spacing of mass transfer channels

The traditional chemical vapor infiltration (CVI) method still faces massive challenge in improving the densification owing to its unavoidable bottleneck effect. Herein, laser assisted-chemical vapor infiltration (LA-CVI) was introduced to fabricate C/SiC composites with mass transfer channels. As a result, the densities of the C/SiC composites were improved due to the dense band formed during the LA-CVI process. Also, with different spacing of mass transfer channels, C/SiC composites exhibited enhanced degree of densification varying from 2.10 to 2.23 g/cm³. When the spacing of channels was 3 mm, the maximum value of flexural strength reached 528 ± 12 MPa. Additionally, micro-CT and finite element analysis were empolyed to investigate dense band and density gradient in detail. The results show that C/SiC composites prepared via LA-CVI method with suitable spacing of channels had improved density and great flexural strength. The proposed method provides a novel route for the preparation of ceramic matrix composites with high density.