Weak acid leaching of uranium ore from a high carbonate uranium deposit

Journal of Radioanalytical and Nuclear Chemistry - Mineralogical study showed that the Yuejin uranium ore is from a low grade, high carbonate and high pyrite sandstone type uranium deposit. Uranium...     

基于混合溶剂有机电解液的超低温孔洞石墨烯超级电容

适用于极低温环境的石墨烯超级电容具有广阔的应用前景。然而,由于片层间严重的堆叠团聚,目前石墨烯超级电容的低温储能性能并不理想。本文使用H₂O₂氧化刻蚀法制备了孔洞石墨烯(rHGO),将传统有机溶剂碳酸丙烯酯(PC)和低凝固点溶剂甲酸甲酯(MF)混合制备了混合溶剂有机电解液,组装获得了能够在-60 ℃极低温环境下稳定工作的超级电容。结果表明,该超级电容在-60 ℃下的比电容为106.2 F·g^-1,相对于常温电容(150.5 F·g^-1)的性能保持率高达70.6%,显著优于未做处理的石墨烯(52.3%)以及文献中的其他石墨烯材料。得益于孔洞化形貌中丰富的介孔和大孔所形成的离子传输通道和缩短的离子传输路径,孔洞石墨烯内的离子扩散阻抗远小于普通石墨烯,且受温度降低的影响更小。在-60 ℃的极低温条件下,该超级电容表现出26.9 Wh·kg^-1的最大能量密度和18.7 kW·kg^-1的最大功率密度,优于传统碳材料的低温超级电容性能。-60 ℃时在5 A·g^-1电流密度下循环充放电10000次后电容保持率达89.1%,具有良好的低温循环稳定性。     

三维MXene多孔结构的构建与应用研究进展

MXene作为一种新型二维（2D）纳米材料以其独特的高导电性、高电化学表面活性等特性在多个领域引起了广泛关注。然而,MXene纳米片在自组装过程中出现的紧密堆叠现象导致比表面积急剧下降,降低了活性表面积,从而严重阻碍了它们在能源储存、电磁屏蔽、吸附等领域的潜在应用。构建三维多孔结构是解决MXene组装过程中自堆叠问题的一种有效途径,而且通过不同的组装方法可以实现对多孔宏观结构组成成分、孔径分布以及孔径大小的调控,使得MXene多孔材料在机械性能、电学性能以及光热转换性能等方面得到更好的调整,从而满足不同应用领域的需求。本综述以Ti₃C₂T_x MXene为主要研究材料总结了各种多孔MXene宏观结构的制备方法,讨论了其在电池/超级电容器、电磁屏蔽与吸收、海水淡化、光催化以及传感和环境修复等方面的应用,阐述了MXene多孔结构在各种应用中的贡献与意义,并针对MXene多孔结构的制备、结构调控和应用等方面的机遇和挑战作了论述。     

Construction of lamellar morphology by side-chain crystalline comb-like polymers for gas barrier

A comb-like polymer containing crystallized alkyl side chains and the intermolecular hydrogen bonds between the linking groups was fabricated by grafting long-chain fatty amine onto poly(styrene-co-acrylic acid)_n (P(S-AA)_n, wherein “n” denoted AA feed ratio). The chemical structures and crystallization behaviors of the comb-like polymer P(S-AA)_n-g(p) (wherein “p” denoted the number of side-chain carbon atoms) were analyzed by Fourier transform infrared, gel permeation chromatography, X-ray photoelectron spectroscopy, and X-ray diffractometer, differential scanning calorimetry, atomic force microscopy, respectively. It was found that the lamellar morphology could be generated by controlling the grafting density and side chain length of P(S-AA)_n-g(p). Moreover, it was identified that the hydrogen bonds between amide groups could enhance the crystallinity and then adjust the interlamellar spacing of lamellar phase. As a result, P(S-AA)₇₀-g(18) with the highest degree of crystallinity and closely packed lamellar morphology showed a good gas-barrier performance, and the nitrogen permeability reached 1.78 × 10^?14 cm³·cm/cm²·s·Pa. Furthermore, the permeation switch of the obtained comb-like polymer could reach 500 times traversing the melting point.     

Sierpinski 地毯上S4模型的临界特性

通过键移动重整化群的方法, 分析了Sierpinski 地毯上S⁴模型的临界行为, 得到了系统的临界点. 由得到的结果可知, 本系统不仅有一个高斯不动点, 而且还存在着一个Wilson Fisher不动点, 把它与Sierpinski 地毯上的高斯模型相互对比, 发现本系统的临界点变化很大. 这说明这两个系统隶属于两个不同的普适类.     

基于XML的故障诊断虚拟训练描述模型研究

随着科学技术的迅猛发展,传统故障诊断训练存在的问题日益突出,越来越难以满足维修人员的故障诊断训练需求。提出了通过虚拟方式进行辅助训练,来提高维修人员的故障诊断能力和掌握故障诊断相关知识,满足故障诊断训练需求。为实现故障诊断虚拟训练,分析了故障诊断虚拟训练模型的描述要素和描述语言。运用诊断树分析方法,基于XML建立了故障诊断虚拟训练描述模型,为实现故障诊断虚拟训练提供模型支撑。最后,基于此模型对液压千斤顶回收不到位的故障进行了描述,验证了描述模型的正确性与实用性。     

带喷流超声速后台阶流场精细结构及其运动特性研究

采用基于纳米示踪的平面激光散射技术(NPLS)对带超声速喷流的后台阶流动精细结构进行了研究. 来流马赫数为3.4, 喷流实测马赫数为2.45, 而名义马赫数为2.5. 结果清晰地揭示了激波、剪切层、混合层、Kelvin-Helmholtz涡、羊角涡及湍流大尺度结构等大量典型流场结构. 基于大量流场精细结构图像, 对典型位置处的结构进行了空间两点相关性分析, 在喷流混合层前端涡结构小于湍流充分发展的尾端, 结构角相对也小. 喷流工作时, 模型台阶下游表面由一薄层气膜覆盖. 获得了模型流向和不同高度展向平面内的流场结构, 对照纹影试验结果, 分析了流动特点及时间演化规律. 采用微型压力扫描系统测试了模型表面的压力系数分布, 靠近喷流下游处压力系数区域0.0146. 针对NPLS图像做了流动的分形维数的分析, 发现在流动初始阶段分形维数接近于1, 越靠下游分形维数越高.     

Effects of pressure and/or magnetism on superconductivity of δ-MoN single crystal

Effects of pressure and/or magnetism on the critical superconducting temperature(Tc)ofδ-Mo N single crystal were investigated using a Maglab system.Theδ-Mo N single crystal was synthesized at extreme conditions of high pressure and high temperature.The carrier density ofδ-Mo N single crystal as a function of applied pressure was determined using Hall coefficient measurement.     

First-principles study of structure and nonlinear optical properties of CdHg(SCN)4 crystal

The geometric structure,electronic structure,and optical properties of CdHg(SCN)4 crystal are calculated by using the density functional perturbation theory and Green function screening Coulomb interaction approximation.The band gap of CdHg(SCN)4 crystal is calculated to be 3.198 eV,which is in good agreement with the experimental value 3.265 eV.The calculated second-order nonlinear optical coefficients are d_(14) = 1.2906 pm/V and d_(15) = 5.0928 pm/V,which are in agreement with the experimental results(d_(14)=(1.4 ±0.6) pm/V and d_(15)=(6.0 ±0.9) pm/V).Moreover,it is found that the contribution to the valence band mainly comes from Cd-4d,Hg-5d states,and the contributions to the valence band top and the conduction band bottom predominantly come from C-2p,N-2p,and S-3p states.The second-order nonlinear optical effect of CdHg(SCN)_4 crystal results mainly from the internal electronic transition of(SCN)~-.     

Baseline optimization of SQUID gradiometer for magnetocardiography

SQUID gradiometer techniques are widely used in noise cancellation for biomagnetic measurements.An appropriate gradiometer baseline is very important for the biomagnetic detection with high performance.By placing several magnetometers at different heights along the vertical direction,we could simultaneously obtain the synthetic gradiometers with different baselines.By using the traditional signal-to-noise ratio(SNR) as a performance index,we successfully obtain an optimal baseline for the magnetocardiography(MCG) measurement in a magnetically shielded room(MSR).Finally,we obtain an optimal baseline of 7 cm and use it for the practical MCG measurement in our MSR.The SNR about 38 dB is obtained in the recorded MCG signal.