Tensile Properties and Fracture Behavior of Aluminum Alloy Foam Fabricated from Die Castings without Using Blowing Agent by Friction Stir Processing Route

Al foam has been used in a wide range of applications owing to its light weight, high energy absorption and high sound insulation. One of the promising processes for fabricating Al foam involves the use of a foamable precursor. In this study, ADC12 Al foams with porosities of 67%–78% were fabricated from Al alloy die castings without using a blowing agent by the friction stir processing route. The pore structure and tensile properties of the ADC12 foams were investigated and compared with those of commercially available ALPORAS. From X-ray computed tomography (X-ray CT) observations of the pore structure of ADC12 foams, it was found that they have smaller pores with a narrower distribution than those in ALPORAS. Tensile tests on the ADC12 foams indicated that as their porosity increased, the tensile strength and tensile strain decreased, with strong relation between the porosity, tensile strength, and tensile strain. ADC12 foams exhibited brittle fracture, whereas ALPORAS exhibited ductile fracture, which is due to the nature of the Al alloy used as the base material of the foams. By image-based finite element (FE) analysis using X-ray CT images corresponding to the tensile tests on ADC12 foams, it was shown that the fracture path of ADC12 foams observed in tensile tests and the regions of high stress obtained from FE analysis correspond to each other. Therefore, it is considered that the fracture behavior of ADC12 foams in relation to their pore structure distribution can be investigated by image-based FE analysis.     

A Study of Crystalline Mechanism of Penetration Sealer Materials

It is quite common to dispense a topping material like crystalline penetration sealer materials (CPSM) onto the surface of a plastic substance such as concrete to extend its service life span by surface protections from outside breakthrough. The CPSM can penetrate into the existing pores or possible cracks in such a way that it may form crystals to block the potential paths which provide breakthrough for any unknown materials. This study investigated the crystalline mechanism formed in the part of concrete penetrated by the CPSM. We analyzed the chemical composites, in order to identify the mechanism of CPSM and to evaluate the penetrated depth. As shown in the results, SEM observes the acicular-structured crystals filling capillary pores for mortar substrate of the internal microstructure beneath the concrete surface; meanwhile, XRD and FT-IR showed the main hydration products of CPSM to be C-S-H gel and CaCO₃. Besides, MIP also shows CPSM with the ability to clog capillary pores of mortar substrate; thus, it reduces porosity, and appears to benefit in sealing pores or cracks. The depth of CPSM penetration capability indicated by TGA shows 0–10 mm of sealer layer beneath the concrete surface.     

不同材料固定义齿修复后牙连续缺损的效果及对口腔生物膜的影响

目的 研究不同材质义齿与修复材料对口腔生物膜的影响。方法 选择自2018年5月～2019年5月我院收治的120例2颗后牙连续缺损患者进行研究。将选取的120例牙体缺损患者平均分为三组,分别通过二氧化锆全瓷冠、钴铬合金烤瓷冠和银钯合金烤瓷冠进行修复。修复后三组患者均通过构建口腔生物膜体外模型对口腔生物膜形成情况进行分析;通过涂布等平板计数法对口腔生物膜平板菌落计数和口腔生物膜变形链球菌代谢产物进行分析。结果 三组患者口腔生物膜的形成、平板菌落计数和变形链球菌代谢产物的终pH值和ΔpH之间存在显著差异。其中二氧化锆组患者生物膜形成量较其他两组患者多,而平板菌落计数和变形链球菌代谢产物的pH值变化较小,三个指标的变化规律一致。结论 不同材质义齿与修复材料对口腔生物膜的影响不同。二氧化锆对患者口腔生物膜影响效果较其他两种材质与修复材料好,可进行临床推广。     

iRoot SP的特性及根管封闭剂超充的研究进展

根管治疗效果与根管封闭剂密切相关,而在充填过程中,很可能存在根管封闭剂超充填的情况。商品化的根管封闭剂种类众多,iRoot SP作为一种新型生物陶瓷类根管封闭剂,因具有良好的生物相容性、封闭性和抗菌性而逐渐被重视,其超充是否会影响患牙的预后也引起了关注。本文总结了iRoot SP理化及生物学性能,以及根管封闭剂超充填的研究进展,结合随访病例分析iRoot SP超充的预后情况。     

Photoinduced transformations of stiff-stilbene-based discrete metallacycles to metallosupramolecular polymers

Control over structural transformations in supramolecular entities by external stimuli is critical for the development of adaptable and functional soft materials. Herein, we have designed and synthesized a dipyridyl donor containing a central Z-configured stiff-stilbene unit that self-assembles in the presence of two 180° di-Pt(II) acceptors to produce size-controllable discrete organoplatinum(II) metallacycles with high efficiency by means of the directional-bonding approach. These discrete metallacycles undergo transformation into extended metallosupramolecular polymers upon the conformational switching of the dipyridyl ligand from Z-configured (0°) to E-configured (180°) when photoirradiated. This transformation is accompanied by interesting morphological changes at nanoscopic length scales. The discrete metallacycles aggregate to spherical nanoparticles that evolve into long nanofibers upon polymer formation. These fibers can be reversibly converted to cyclic oligomers by changing the wavelength of irradiation, which reintroduces Z-configured building blocks owing to the reversible nature of stiff-stilbene photoisomerization. The design strategy defined here represents a novel self-assembly pathway to deliver advanced supramolecular assemblies by means of photocontrol.Natural systems provide many examples of self-assembled biosupramolecules that respond to external stimuli through conformational changes that ultimately play a role in carrying out their various biological functions. Mimicking this stimuli-responsive behavior in artificial systems is a promising route toward obtaining sophisticated molecular-based architectures with functional and structural tunability (1–3). Using the absorption of photons as a trigger is particularly attractive in that light-induced transformations maintain high spatial and temporal resolution without producing waste products even during multiple reversible switching sequences (4). In materials science, one of the most appealing characteristics of photochromic molecules is the direct conversion of light into mechanical energy based on their photo-reversible structural transformations (5). Among such chromophores, a stiff-stilbene moiety (1,1′-biindane) is useful owing to its unique characteristics (6). First, stiff stilbene can adopt either a cis or trans configuration with respect to its central double bond. Second, the high activation barrier between the two isomers (∼43 kcal⋅mol⁻¹, corresponding to a half-life of ∼10⁹ y at 300 K) makes thermal E/Z isomerization negligible at temperatures of 420 K and lower. Third, the quantum yield for the photoisomerization of either isomer is high (50%). Fourth, the stiff-stilbene core is readily substituted using well-established synthetic methods. Owing to these promising characteristics, Boulatov and coworkers (7) constructed a molecular force probe by integrating the moiety into a stretched polymer to mimic the strain generated in diverse functional groups. Yang and coworkers (8) reported hydrogen-bonded supramolecular polymers and studied their polymerization mechanisms and physical properties based on the photoisomerization of the stiff-stilbene units. Nevertheless, stiff-stilbene-based supramolecular entities are underexplored despite exhibiting properties that make the functionality potentially useful in the construction of photoresponsive supramolecular materials.Coordination-driven self-assembly is a powerful method of constructing supramolecular coordination complexes (SCCs) by the spontaneous formation of metal–ligand bonds that draws inspiration from the design principles of natural systems (9–20). This approach organizes metal acceptors and organic donors to prepare well-defined cavity-cored 2D metallacycles and 3D metallacages, which can be functionalized on their interior or exterior vertices for applications in host–guest chemistry (21, 22), catalysis (23), molecular flasks (24), bioengineering (25), amphiphilic self-assembly (26), and so on. The versatility of coordination-driven self-assembly can be enhanced by designs that allow for post-self-assembly modifications that in some cases result in complete structural transformations. For example, the Stang group previously demonstrated the transformation of self-assembled polygons by changing the angle between the bonding sites of a ligand from 180° to 120° upon treatment of Co₂(CO)₆ with an acetylene moiety (27). Yang and coworkers (28) reported the construction of multibisthienylethene hexagons capable of reversible supramolecule-to-supramolecule conversions induced by ring-open and ring-closed conformational changes of the bisthienylethene units. Herein we expand upon the transformations established by the systems described above designing SCCs capable of evolving from discrete metallacycles into infinite constructs using external stimuli.Supramolecular polymers can be defined as dynamically reversible polymeric arrays (29–37) that form from the explicit manipulation of noncovalent forces between monomeric units (38–43). Supramolecular polymer chemistry can readily complement coordination-driven self-assembly, as exemplified by our efforts to design hierarchical supramolecular polymerizations of discrete organoplatinum(II) metallacycles, thus accessing novel supramolecular polymeric materials, such as macroscopic hexagonal supramolecular polymer fibers (44), dendronized organoplatinum(II) metallacyclic polymers (45), and a responsive, cavity-cored supramolecular polymer network metallogel (46). Herein, we report photoresponsive supramolecular transformations between discrete organoplatinum(II) metallacycles and infinite metallosupramolecular polymers induced by a cis/trans conformational transition of a stiff-stilbene-based dipyridyl ligand. The self-assembly behaviors, physical properties, topologies, and morphologies of these SCCs can be regulated by photoisomerization, demonstrating this powerful approach to prepare advanced supramolecular coordination complexes.     

Direct evidence for a magnetic f-electron–mediated pairing mechanism of heavy-fermion superconductivity in CeCoIn5

To identify the microscopic mechanism of heavy-fermion Cooper pairing is an unresolved challenge in quantum matter studies; it may also relate closely to finding the pairing mechanism of high-temperature superconductivity. Magnetically mediated Cooper pairing has long been the conjectured basis of heavy-fermion superconductivity but no direct verification of this hypothesis was achievable. Here, we use a novel approach based on precision measurements of the heavy-fermion band structure using quasiparticle interference imaging to reveal quantitatively the momentum space (k-space) structure of the f-electron magnetic interactions of CeCoIn₅. Then, by solving the superconducting gap equations on the two heavy-fermion bands Ekα,β with these magnetic interactions as mediators of the Cooper pairing, we derive a series of quantitative predictions about the superconductive state. The agreement found between these diverse predictions and the measured characteristics of superconducting CeCoIn₅ then provides direct evidence that the heavy-fermion Cooper pairing is indeed mediated by f-electron magnetism.Superconductivity of heavy fermions is of abiding interest, both in its own right (1–7) and because it could exemplify the unconventional Cooper pairing mechanism of high-temperature superconductors (8–11). Heavy-fermion compounds are intermetallics containing magnetic ions in the 4f- or 5f-electronic state within each unit cell. At high temperatures, each f-electron is localized at a magnetic ion (Fig. 1A). At low temperatures, interactions between f-electron spins (red arrows Fig. 1A) lead to the formation of a narrow but the subtly curved f-electron band εkf near the chemical potential (red curve, Fig. 1B), and Kondo screening hybridizes this band with the conventional c-electron band εkc of the metal (black curve, Fig. 1B). As a result, two new heavy-fermion bands Ekα,β (Fig. 1C) appear within a few millielectron volts of the Fermi energy. Their electronic structure is controlled by the hybridization matrix element s_k for interconversion of conduction c-electrons to f-electrons and vice-versa, such thatEkα,β=εkc+εkf2±(εkc−εkf2)2+sk2.[1]The momentum structure of the narrow bands of hybridized electronic states (Eq. 1 and Fig. 1C, blue curves at left) near the Fermi surface then directly reflects the form of magnetic interactions encoded within the parent f-electron band εkf. It is these interactions that are conjectured to drive the Cooper pairing (1–5) and thus the opening up of a superconducting energy gap (Fig. 1C, yellow curves at right).Open in a separate windowFig. 1.Effects of f-electron magnetism in a heavy-fermion material. (A) The magnetic subsystem of CeCoIn₅ consists of almost localized magnetic f-electrons (red arrows) with a weak hopping matrix element yielding a very narrow band with strong magnetic interactions between the f-electron spins. (B) The heavy f-electron band is shown schematically in red and the light c-electron band in black. (C) On the left, schematic of the result of hybridizing the c- and f-electrons in B into new composite electronic states referred to as heavy fermions (blue). On the right, the opening of a superconducting energy gap is schematically shown by back-bending bands near the chemical potential. The microscopic interactions driving Cooper pairing of these states, and thus of heavy-fermion superconductivity, have not been identified unambiguously for any heavy-fermion compound.     

Importance of the DNA “bond” in programmable nanoparticle crystallization

If a solution of DNA-coated nanoparticles is allowed to crystallize, the thermodynamic structure can be predicted by a set of structural design rules analogous to Pauling’s rules for ionic crystallization. The details of the crystallization process, however, have proved more difficult to characterize as they depend on a complex interplay of many factors. Here, we report that this crystallization process is dictated by the individual DNA bonds and that the effect of changing structural or environmental conditions can be understood by considering the effect of these parameters on free oligonucleotides. Specifically, we observed the reorganization of nanoparticle superlattices using time-resolved synchrotron small-angle X-ray scattering in systems with different DNA sequences, salt concentrations, and densities of DNA linkers on the surface of the nanoparticles. The agreement between bulk crystallization and the behavior of free oligonucleotides may bear important consequences for constructing novel classes of crystals and incorporating new interparticle bonds in a rational manner.Materials scientists have accomplished much by studying the way atoms and molecules crystallize. In these systems, however, the identity of the atom and its bonding behavior cannot be independently controlled, limiting our ability to tune material properties at will. In contrast, when a nanoparticle is modified with a dense shell of upright, oriented DNA, it can behave as a programmable atom equivalent (PAE) (1, 2) that can be used to synthesize diverse crystal structures with independent control over composition, scale, and lattice symmetry (3–14). The thermodynamic product of this crystallization process has been extensively studied by both experimental and theoretical means, and thus a series of design rules has been proposed and validated with a simple geometric model known as the complementary contact model (CCM). These rules allow one to predict the thermodynamically favored structure as the arrangement of particles that maximizes complementary contacts and therefore DNA hybridization (2, 6). These efforts have been very successful in predicting the thermodynamically favored product; recent studies have even demonstrated that PAEs can form single-crystal Wulff polyhedra that are analogous to those formed in atomic systems with the same crystallographic symmetry (15). However, the fact that there is a crystalline thermodynamic product does not mean that any choice of DNA and nanoparticles will result in crystalline systems in practice (3, 4). For example, crystallization has been observed for a relatively narrow class of PAEs (16) and in a manner that is primarily dependent upon the length of the DNA linker and temperature at which assembly occurs (8). Thus, absent from our understanding of these systems is a connection between the crystallization process and the properties of the DNA bonds that form the foundation of these structures.Here, we study the crystallization process and find that the complexity of the polyvalent DNA interactions can be simply understood by considering the behavior of a single DNA bond. By systematically studying the roles of nucleobase sequence, solution ionic strength, DNA density, and temperature on crystallization, we find that the effects of these factors are mirrored by the rates of hybridization and dehybridization of free DNA. In addition to examining steady-state structures, we evaluate the formation and reorganization of these crystals in a time-resolved manner using small-angle X-ray scattering (SAXS) to study how crystallization dynamics are affected by each design variable. Finally, we develop a predictive model that allows one to compare the range of temperatures over which crystallization will occur for different conditions. In addition to providing an avenue for improving PAE crystallization and realizing new architectures, the effectiveness of this reductionist model suggests that this approach can be applied to study crystallization in a broader class of systems, thus making an impact in the materials by design community.     

Silane influence on bonding to CAD-CAM composites: An interfacial fracture toughness study

ObjectivesTo evaluate silane influence on the interfacial fracture toughness (IFT) of composite cement, with the two sub-classes of CAD-CAM composites, polymer-infiltrated ceramic networks (PICN) and dispersed fillers (DF), after hydrofluoric acid etching (HF) or airborne-particle abrasion (AB). A secondary objective was to correlate results with developed interfacial area ratio (Sdr) and surface wettability.MethodsExperimental PICN and DF blocks were cut into equilateral half-prisms, which were treated with HF or AB, then treated with an experimental silane or not and bonded to their counterparts with an experimental light-cure resin cement. After thermocycling, samples (n = 30 per group) were tested for IFT using the notchless triangular prism test in a water bath at 36 °C. Moreover, profilometry and contact angle measurement were performed on rectangular samples of each group. Finally, bonding interface was analysed by SEM.ResultsPICN-HF treated with silane showed the highest IFT significantly. Three-way ANOVA revealed the influence of silane, material class and surface pre-treatment (HF or AB) on IFT (p < 0.05). When silane was used, IFT was correlated with Sdr, while surface wettability was increased. Silane application significantly increased IFT for PICN but not for DF, while PICN performed better with HF and DF with AB.SignificanceSilane increases IFT of composite cement with PICNs, but not with DF materials. Results suggest that silane increases the micromechanical bond by promoting resin cement spreading and penetration in surface roughness. This roughness is significantly higher for pre-treated PICNs than for DF due to their specific honeycomb microstructure when etched, which explains their better bonding properties.     

前胡类药材的化学成分及质量控制方法研究

目的：概述前胡类药材化学成分及其相关成方制剂的质量控制标准的研究现状,为前胡类药材及成药的标准研究提供参考。方法：检索并查阅前胡类药材相关研究文献及标准记载情况,归纳其主要化学成分及制剂的质量控制方法。结果：以“前胡”为药材名的药用植物较多,其所含化学成分主要有香豆素类、黄酮类、萜类及挥发油类;质量标准除《中华人民共和国药典》收载前胡及紫花前胡外,尚有多省份地方药材标准收载以前胡的近缘种作为地方习用品使用。质量控制方法主要涉及性状鉴别、显微鉴别、薄层鉴别、指纹图谱、含量测定等方法。结论：前胡为常用传统中药,应用广泛,前胡及其中成药的质量标准参差不齐,有待进一步提升。     

发展监管科学，促进中药产业传承创新

2008年新药创制重大专项启动实施以来的10多年间,紧密围绕构建国家药物创新技术体系目标,为我国新药研发和公众用药安全提供了重要的保障,获得重大进展。药品监管科学是近十几年发展形成的前沿学科,受到世界科学界和管理界的重视。本文秉着中药监管科学发展与现实存在问题,需要理论创新、药物创新、技术创新、方法创新和应用创新。中药监管科学研究计划是国家推进的9个监管科学行动计划之一。启动以中药临床为导向的中药安全性评价研究,构建中药安全性和质量控制体系。作者认为通过监管科学研究,制定科学规范的中药质量标准和评价指导原则和技术指南,推进中药材、中药饮片和中成药,特别是经典名方制剂品种示范研究,有利于中药产业健康科学发展。在本文中还结合当前的中药监管科学问题,加强药材和饮片的基础研究、中药注射剂质量疗效的再评价研究、经典名方的开发和简化申请的监管科学研究,提出监管科学研究顶层设计建议,制定技术原则与技术指南,有利于药典品种和市场产品的质量和临床有效性再评价。