磁性石墨烯/聚氨酯柔性复合材料的制备及自修复效能

为了提高复合材料的导电、导热及自修复性能，在传统共混法的基础上采用化学沉积法将四氧化三铁（Fe₃O₄）修饰到石墨烯上，得到磁性石墨烯，并将其与聚氨酯、碳纳米管共混后经磁场干预控制石墨烯片层的排列得到磁性石墨烯/聚氨酯柔性复合材料。采用SEM、Raman、FTIR对柔性复合材料的微观形貌、分子结构进行表征，并通过激光导热仪、四探针电阻率测定仪和万能试验机分析磁场调控对复合材料电、热、力学以及修复性能的影响。结果表明：磁场下柔性复合材料中的石墨烯片层排列规则，且层次分明，轮廓清晰可见；其热扩散系数相比于未加磁场提高了10 %~12 %，且在高温下具有稳定性，缺陷修复时间减少了50 %；对比出现缺陷前及修复后的复合材料发现，表面电阻率和抗拉强度分别相差0.006Ω·cm和2.4MPa，而无磁场环境下的变化量是其 3～4倍。     

基于摄动法的表贴式永磁电机转子偏心空载气隙磁场计算

采用摄动法解析计算表贴式永磁电机转子偏心空载气隙磁场,以无量纲的偏心扰动量作为摄动变量,可解决表贴式永磁电机内转子结构和外转子结构的转子偏心磁场解析问题。根据气隙区域及永磁体区域的边界条件求解拉普拉斯方程和泊松方程,通过矢量磁位推导出气隙磁通密度的解析表达式,进而应用麦克斯韦应力张量法计算不平衡磁拉力,并将解析法结果与有限元法结果进行比较,发现二者一致性较好,验证了该方法的正确性和有效性。     

Detailed Insight into the Interaction of Bicyclic Somatostatin Analogue with Cu(II) Ions

Somatostatin analogues are useful pharmaceuticals in peptide receptor radionuclide therapy. In previous studies, we analyzed a new bicyclic somatostatin analogue (BCS) in connection with Cu(II) ions. Two characteristic sites were present in the peptide chain: the receptor- and the metal-binding site. We have already shown that this ligand can form very stable imidazole complexes with the metal ion. In this work, our aim was to characterize the intramolecular interaction that occurs in the peptide molecule. Therefore, we analyzed the coordination abilities of two cyclic ligands, i.e., P1 only with the metal binding site and P2 with both sites, but without the disulfide bond. Furthermore, we used magnetic circular dichroism (MCD) spectroscopy to better understand the coordination process. We applied this method to analyze spectra of P1, P2, and BCS, which we have described previously. Additionally, we analyzed the MCD spectra of P3 ligand, which has only the receptor binding site in its structure. We have unequivocally shown that the presence of the Phe-Trp-Lys-Thr motif and the disulfide bond significantly increases the metal binding efficiency.     

Effects of Newtonian heating and thermal radiation on micropolar ferrofluid flow past a stretching surface: Spectral quasi‐linearization method

This study article addressesthe flow and heat transfer characteristics of a magnetite Fe₃O₄ micropolar ferrofluid flow past a stretching sheet. For practical interest, thermal radiation, Newtonian heating, and a heat source or sink are considered in this investigation. A useful Tiwari‐Das nanofluid model is considered to analyze the microstructure and inertial characteristics of the water‐based nanofluids containing iron oxide. The dimensionless nonlinear ordinary differential equations are solved by employing suitable similarity variables. The resulting nonlinear system is solved by the spectral quasi‐linearization method. The effects of different nondimensional parameters on various profiles are shown graphically and explored in detail. It is found that the micropolar ferrofluid exhibits a higher energy distribution than that of a classical micropolar fluid. Compared to the classical micropolar liquid, local skin‐friction is more significant for the micropolar magnetite ferrofluid. In the presence of Newtonian heating, the thermal behavior of the micropolar nanofluid is remarkably better than that of the classical micropolar fluid.     

Reduction in Microsegregation in Al-Cu Alloy by Alternating Magnetic Field

The microsegregation behavior of the Al-4.5 wt%Cu alloy solidified at different cooling rates under the alternating magnetic field(AMF) was investigated.The experimental results showed that the amount of non-equilibrium eutectics in the interdendritic region decreased upon applying the AMF at the same cooling rate.The change in microsegregation could be explained quantificationally by the modifications of dendritic coarsening,solid-state back diffusion and convection in the AMF.The enhanced diffusivity in the solid owing to the AMF was beneficial for the improvement in microsegregation compared to the cases without an AMF.In contrast,the enhanced dendritic coarsening and forced convection in the AMF were found to aggravate the microsegregation level.Considering the contributions of the changes in above factors,an increase in solid diffusivity was found to be primarily responsible for the reduced microsegregation in the AMF.In addition,the microsegregation in the AMF was modeled using the analytical model developed by Voller.The calculated and experimental results were in reasonable agreement.     

Experimental investigation of a new thermal energy storage system using thermo‐sensitive magnetic fluid and porous medium

In this paper, a novel thermal energy storage (TES) system based on a thermo‐sensitive magnetic fluid (MF) in a porous medium is proposed to store low‐temperature thermal energy. In order to have a better understanding about the fluid flow and heat‐transfer mechanism in the TES system, four different configurations, using ferrofluid as the basic fluid and either copper foam or porous carbon with different porosity (90 and 100 PPI, respectively) as the packed bed, are investigated experimentally. Furthermore, two thermal performance parameters are evaluated during the heat charging cycle, which are thermal storage velocity and thermal storage capacity of the materials under a range of magnetic field strength. It is shown that heat conduction is the primary heat‐transfer mechanism in copper foam TES system, while magnetic thermal convection of the magnetic fluid is the dominating heat‐transfer mechanism in the porous carbon TES. In practical applications in small‐scale systems, the 90‐PPI copper foam should be selected among the four porous materials because of its cost efficiency, while porous carbon should be used in industrial scale systems because of its sensitivity to magnetic field and cost efficiency.     

BX型强磁选机分选白云鄂博低品位铁矿石试验研究

针对白云鄂博低品位铁矿石资源利用率低、选矿成本高等问题,在系统研究其矿石性质的基础上,采用BX型强磁选机进行磁选工艺试验研究。结果表明,原矿石TFe品位16.52%,通过干磁抛尾—两段磨矿—三段选别的工艺流程,可获得产率16.54%、TFe品位65.31%、TFe回收率65.39%、S、P含量分别为0.36%和0.07%的铁精矿。研究结果可为该低品位铁矿石的高效利用提供技术支持。     

Experimental and mathematical modelling of magnetically labelled mesenchymal stromal cell delivery

A key challenge for stem cell therapies is the delivery of therapeutic cells to the repair site. Magnetic targeting has been proposed as a platform for defining clinical sites of delivery more effectively. In this paper, we use a combined in vitro experimental and mathematical modelling approach to explore the magnetic targeting of mesenchymal stromal cells (MSCs) labelled with magnetic nanoparticles using an external magnet. This study aims to (i) demonstrate the potential of magnetic tagging for MSC delivery, (ii) examine the effect of red blood cells (RBCs) on MSC capture efficacy and (iii) highlight how mathematical models can provide both insight into mechanics of therapy and predictions about cell targeting in vivo. In vitro MSCs are cultured with magnetic nanoparticles and circulated with RBCs over an external magnet. Cell capture efficacy is measured for varying magnetic field strengths and RBC percentages. We use a 2D continuum mathematical model to represent the flow of magnetically tagged MSCs with RBCs. Numerical simulations demonstrate qualitative agreement with experimental results showing better capture with stronger magnetic fields and lower levels of RBCs. We additionally exploit the mathematical model to make hypotheses about the role of extravasation and identify future in vitro experiments to quantify this effect.     

Experimental investigation on bubble growth and detachment characteristics on vertical microelectrode surface under electrode-normal magnetic field in water electrolysis

The effects of current density and electrode-normal magnetic fields on the growth and detachment characteristics of a single bubble on vertical microelectrode surface have been investigated. A high-speed camera was used to capture the bubble evolution behavior and the bubble contact characteristic parameters were extracted and analyzed with OpenCV-Python program. The results reveal that an apparent bubble coalescence behavior occurs at low current densities and can be gradually inhibited with increasing current density. With the increase of current density, the bubble growth rate, departure diameter, working electrode potential and potential fluctuations increase, while the bubble growth time first increases and then decreases continuously. The upper microelectrode surface is more easily covered than the lower microelectrode surface. The whole microelectrode can be completely covered when the current density exceeds a certain limit with and without magnetic fields. The external magnetic fields can obviously promote the bubble detachment behavior within a relatively large current density range.