A Numerical Analysis of Turbulent Compressible Radial Channel Flow with Particular Reference to Pneumatic Controllers

A numerical analysis of turbulent axisymmetric radial compressible channel flow between a nozzle and a flat plate is presented in this paper. In particular, the application of this type of flow situation in pneumatic dimensional control systems is considered. The Spalart-Allmaras one-equation turbulence model is used. The resulting highly coupled PDE system has been solved using the control volume based numerical approach where the power-law scheme was used extensively to compute the diffusive and convective fluxes of momentum. Results show that local Mach numbers can easily achieve and surpass unity for typical industrial configurations. Also, in the case of a standard industrial nozzle geometry, the presence of a toroidal recirculation zone that moves radially outward is clearly identified in most cases. Separated flow areas are of particular concern as it has been shown previously that they can cause nozzle fouling in industrial applications. It has been shown that the size of this region is dependant on feed pressure. Considerable differences between results obtained using the Spalart-Allmaras and standard k- εturbulence models have also been noticed.     

Do zebra mussels (Dreissena polymorpha) alter lake water chemistry in a way that favours Microcystis growth?

This study examined possible relationships between the presence of zebra mussels (Dreissena polymorpha) and Microcystis spp. abundance. Experiments were conducted in 12 microcosms designed to mimic shallow lake ecosystems. Fresh, aerated water with phytoplankton (pseudokirchneriella spp. and Microcystis spp.) was pumped into each microcosm daily to ensure zebra mussels were exposed to oxygen and food. Microcosms containing zebra mussels experienced significantly higher fluxes of nitrate (p=0.019) and lower fluxes of ortho-phosphate (p=0.047) into sediments. In a second experiment, water column nutrient concentrations were compared in microcosms with and without live zebra mussels. Consistent with results of the previous experiment, microcosms with zebra mussels had significantly less nitrate (p=0.023) and organic nitrogen (p=0.003) in the water column, while ammonium (p=0.074), phosphate (p=0.491), and dissolved organic carbon (p=0.820) in the water column were not different between microcosms with or without zebra mussels. Microcosms with zebra mussels also experienced a reduction in green algae (pseudokirchneriella) (p<0.001) and an increase in abundance of Microcystis (p<0.001) relative to microcosms without zebra mussels. In an experiment without zebra mussels, nutrient ratios (N/P) were manipulated to determine potential links between N/P and relative abundance of each phytoplankton. Manipulation of N/P was intended to mimic differences observed in microcosms with and without zebra mussels in the previous experiment. Low N/P (mimicking microcosms with zebra mussels) was related to an increase in Microcystis (p<0.001) and Microcystis/Pseudokirchneriella biovolume (p<0.001). It is this shift in N/P, and possibly some level of selective feeding, that is believed to have driven changes in the relative abundance of Microcystis. In lakes invaded by zebra mussels, alterations in the processing of nitrogen and phosphorus could contribute to the re-emergence of Microcystis blooms.     

Mixed-mode crack growth in bonded composite joints under standard and impact-fatigue loading

Carbon fibre reinforced polymers (CFRPs) are now well established in many high-performance applications and look set to see increased usage in the future, especially if lower cost manufacturing and solutions to certain technical issues, such as poor out-of-plane strength, can be achieved. A significant question when manufacturing with CFRP is the best joining technique to use, with adhesive bonding and mechanical fastening currently the two most popular methods. It is a common view that mechanical fastening is preferred for thicker sections and adhesive bonding for thinner ones; however, advances in the technology and better understanding of ways to design joints have lead to increasing consideration of adhesive bonding for traditionally mechanically fastened joints. In high-performance applications fatigue loading is likely and in some cases repetitive low-energy impacts, or impact fatigue, can appear in the load spectrum. This article looks at mixed-mode crack growth in epoxy bonded CFRP joints in standard and impact fatigue. It is shown that the back-face strain technique can be used to monitor cracking in lap-strap joints (LSJs) and piezo strain gauges can be used to measure the strain response of impacted samples. It is seen that there is significant variation in the failure modes seen in the samples and that the crack propagation rate is highly dependent on the fracture mode. Furthermore, it is found that the crack propagation rate is higher in impact fatigue than in standard fatigue even when the maximum load is significantly lower.     

视觉深度伪造检测技术综述

随着生成式深度学习算法的发展,深度伪造技术发展并应用于各个领域。深度伪造技术的滥用使人们逐渐意识到其带来的威胁,伪造检测技术随之而生。本文基于视觉深度伪造技术研究进行综述。1)简要介绍了视觉深度伪造技术的发展历程及技术原理,包括生成对抗网络在深度伪造制品中的应用;2)对现有的视觉深度伪造数据集进行汇总并归类;3)对目前的视觉深度伪造检测技术进行了分类,将现有的检测方法归纳为基于具体伪影的、基于数据驱动的、基于信息不一致和其他类型视觉深度伪造检测等4种分类。其中,基于伪影的检测方法着重于寻找伪造制品与真实图像之间的像素级差异,通过机器学习识别深度伪造制品中的人工伪影痕迹,基于信息不一致的方法则着重于寻找伪造制品与真实图像或视频之间的信息级差异,这两种方法都具有识别效率高、训练便捷等优点;基于数据驱动的方法通过大量的数据集和机器学习训练,直接使用神经网络本身对深度伪造制品进行训练,并通过改善网络架构增进模型以提高训练效率,因为其模型的多变和高精确率成为目前深度伪造检测的热门方向。同时,本文分析了4种方法的具体优缺点,并进一步给出了未来视觉深度伪造检测研究的重点和难点。     

Synthesis and characterization of the ternary metal diboride solid-solution nanopowders

The synthesis of the multi-component transition-metal diboride (MeB₂) solid-solution powders has been recently attracting considerable attentions. However, the synthesis of the ternary or more component MeB₂ solid-solution powders has rarely been reported until now. To fabricate the ternary MeB₂ solid-solution powders, herein we utilized two kinds of the ternary MeB₂ solid solutions as prototypes, namely (Hf_1/3Zr_1/3Ti_1/3)B₂ (HZTB) and (Ta_1/3Nb_1/3Ti_1/3)B₂ (TNTB). The formation possibility of HZTB and TNTB was first analyzed by the first-principles calculations and then we attempted of fabricated them by a simple molten salt synthesis technique. The first-principles calculations results showed that the mixing Gibbs free energy at room temperature and lattice size difference at 0 K of HZTB and TNTB were (1.666 kJ/mol and 3.146%) and (−3.030 kJ/mol and 1.254%), respectively. This suggested that TNTB solid solution was more prone to being fabricated than HZTB solid solution. The experimental results showed the high purity TNTB solid-solution nanopowders were successfully synthesized by the molten salt synthesis technique at 1373 K with 30% excessive B as precursors while the HZTB solid solution was not able to be synthesized by the molten salt synthesis technique. The as-synthesized TNTB solid-solution nanopowders exhibited the distinguished nanorod morphology with the diameters of 20-40 nm and lengths of 100-200 nm. Meanwhile, they possessed the good single-crystal hexagonal structure and high compositional uniformity from nanoscale to microscale. In addition, their formation mechanism associated to the possible chemical reactions was well interpreted by the thermodynamics analysis.     

Synthesis of high-purity high-entropy metal diboride powders by boro/carbothermal reduction

Synthesis of high-purity high-entropy metal diboride powders is critical to implementing their extensive applications. However, the related studies are rarely reported. Herein we first theoretically studied the synthesis possibility of high-purity high-entropy diboride powders, namely (Hf_0.25Ta_0.25Nb_0.25Ti_0.25)B₂ (HTNTB), via boro/carbothermal reduction by analyzing the thermodynamics of the possible chemical reactions and then successfully synthesized the high-purity and superfine HTNTB powders via boro/carbothermal reduction for the first time. The as-prepared powders exhibited low-oxygen impurity content of 0.49 wt% and small average particle size of 260 nm. Meanwhile, they possessed good single-crystal hexagonal structure of metal diborides and high-compositional uniformity from nanoscale to microscale. This work will open up a new research field on the synthesis of high-purity high-entropy metal diboride powders.     

Thermal properties and degradation of polytetrafluoroethylene low‐molecular fractions

The present article describes the results of studies of the peculiarities of thermal behavior and degradation of low‐molecular fractions obtained by sublimation of the powder ultradispersed polytetrafluoroethylene under isothermal conditions at 50°C–100°C. The peculiarities of fractions transition into the gas phase at heating were studied with IR spectroscopy method and interpreted based on the quantum‐chemical calculations of the model fluorocarboned molecules. The calculation and spectroscopic data provide grounds to assume the presence of small molecules and radical structures in gas phase. The radical fragments formed in the gas phase as a result of the polymer chains thermal destruction provide the structure recovery during the subsequent condensation of the sample. A new averaged powder fraction is formed during condensation. POLYM. ENG. SCI., 59:2413–2417, 2019. © 2019 Society of Plastics Engineers     

OSCILLATORY EXTRACTION OF URANIUM

ABSTRACT

The kinetics of U and Ce extraction by tri-n-butyl-phosphate ( TBP) and the redox potential behavior in the aqueous phase have been investigated in an oscillatory extraction system. The extraction has been followed continuously by UV-visible spectroscopy, potentiometry, and radioactive counting methods. Data collected showed the changes of Ce⁴⁺ and U0²⁺ concentrations in organic and aqueous phases with time. Uranium actively responded to the redox potential fluctuations. The uranium distribution coefficient changed repeatedly and was out-of-phase with Ce( IV) fluctuations.     

Pyrazolopyrimidines: Potent Inhibitors Targeting the Capsid of Rhino‐ and Enteroviruses

There are currently no drugs available for the treatment of enterovirus (EV)‐induced acute and chronic diseases such as the common cold, meningitis, encephalitis, pneumonia, and myocarditis with or without consecutive dilated cardiomyopathy. Here, we report the discovery and characterization of pyrazolopyrimidines, a well‐tolerated and potent class of novel EV inhibitors. The compounds inhibit the replication of a broad spectrum of EV in vitro with IC₅₀ values between 0.04 and 0.64 μM for viruses resistant to pleconaril, a known capsid‐binding inhibitor, without affecting cytochrome P450 enzyme activity. Using virological and genetics methods, the viral capsid was identified as the target of the most promising, orally bioavailable compound 3‐(4‐trifluoromethylphenyl)amino‐6‐phenylpyrazolo[3,4‐d]pyrimidine‐4‐amine (OBR‐5‐340). Its prophylactic as well as therapeutic application was proved for coxsackievirus B3‐induced chronic myocarditis in mice. The favorable pharmacokinetic, toxicological, and pharmacodynamics profile in mice renders OBR‐5‐340 a highly promising drug candidate, and the regulatory nonclinical program is ongoing.     

One-pot synthesis of mesoporous SBA-15 containing protonated 3-aminopropyl groups

A new technique of synthesis of mesoporous silica with protonated amino groups avoiding microwave treatment of mesophase was developed using a template method. The block-copolymer P123 was used as a template and sodium meta-silicate with 3-aminopropyltriethoxysilane as precursors. After the removal of template from mesophase with boiling ethanol, the obtained sample displayed highly ordered hexagonal structure with attractive textural parameters: S_BET = 460 m² g^?1, V_total = 0.79 cm³g^?1 and d = 7.1 nm. FTIR and ¹³C CP/MAS NMR spectroscopy revealed the presence of alkyl ammonium groups (0.7 mmol g^?1) that were able to attach anions of molybdophosphoric acid to the surface of the synthesized mesoporous material. The resulting anion-ion exchange phase can find applications in many areas (adsorption, catalysis, etc.).