Yield-Point Phenomenon and Plastic Bands in Ferrite–Pearlite Steels

Lüders deformation is one type of discontinuous yielding in ferrite–pearlite steel. The yield-point phenomenon and localized plastic bands are two features of the Lüders phenomenon. It is believed that the yield-point phenomenon is related to the formation of plastic bands, but the correlation between them is unclear. In this study, this correlation was investigated by examining the global and local deformation behaviors in the tension processes of four ferrite–pearlite steels (carbon content, 0.05–0.3%; pearlite fraction, 1.2–32%) via an extensometer and digital image correlation (DIC) technique. The main obtained results are as follows: (1) the degree of yield drop decreased with an increase in the pearlite fraction (the magnitude of the yield stress drop was 8.6–0 MPa), and (2) a plastic band was formed at a certain stress level smaller than the upper yield stress; when the stress level was larger than 92% of the upper yield stress, the upper yield point disappeared.     

正交试验优选复方参芪软胶囊的醇沉工艺

优选复方参芪软胶囊的醇沉工艺。方法：采用正交试验设计,以药液中总多糖的含量和干膏得率为指标,考察浓缩液的相对密度、醇沉浓度、静置时间、醇沉温度对醇沉效果的影响。结果：最佳醇沉工艺为药液浓缩至相对密度1.10,加95％乙醇至含醇量为60％,室温下静置48h。结论：优选的复方参芪软胶囊醇沉工艺简便易行,适用于实际生产配制。     

Investigation of factors affecting loosening of Ilizarov ring-wire external fixator systems at the bone-wire interface

The potential for peri-implant bone yielding and subsequent loosening of Ilizarov ring-wire external fixation systems was investigated using non-linear finite element (FE) analyses. A strain-based plasticity model was employed to simulate bone yielding. FE models also incorporated contact behavior at the wire-bone interface, orthotropic elasticity, and periosteal-endosteal variation of bone properties. These simulations were used to determine the extent and location of yielding with change in age-related bone structure and properties for the bone-Ilizarov construct at the tibial midshaft. At critical wire-bone interfaces, the predicted volume of yielded bone with four wires (on either side of the fracture) was ～40% of that with two wires. Old-aged cases showed considerably greater bone yielding at the wire-bone interface than young cases (1.7-2.2 times greater volumes of yielded bone). The volume of yielded bone at all wire-bone interfaces decreased with an increase in wire pre-tension. The absence of continuous through-thickness yielding offers an explanation for the clinical observation that Ilizarov ring-wire fixation can provide stable fracture fixation even in bone with high porosity.     

白头翁汤提取工艺试验研究

目的：筛选最佳白头翁汤提取工艺条件.方法：观察白头翁汤不同水提液中的沉淀量.采用正交设计法,以得膏率、小檗碱含量为指标,考察加水倍数,浸提时间,浸提次数,对该方提取的影响.结果：浸提次数是影响最大的因素.结论：白头翁汤提取工艺最优条件是浸提次数为3次,浸提时间为0.5小时,加水量为9倍药材量.     

正交试验优选中药祛白颗粒的水提工艺

摘 要 目的：优化中药祛白颗粒的水提工艺。 方法: 采用正交试验法,对影响水提工艺的因素加水倍数、浸泡时间、提取时间及提取次数进行考察,以干浸膏得率及阿魏酸含量为考察指标。结果: 最佳提取工艺为：A₂B₁C₂D₂,即加入10倍水,无需提前浸泡,提取2次,每次2 h。 结论:该工艺简便、稳定,重复性好,可为大生产提供依据。     

Structure-activity relationship,selectivity and mode of inhibition of terminal deoxyribonucleotidyltransferaseby streptolydigin analogs

Three of thirty-one streptolydigin analogs resembled the parent compound in selectively inhibiting terminal deoxyribonucleotidyltransferase (terminal transferase) when compared with cellular DNA polymerases α, β and γ, simian sarcoma virus DNA polymerase, herpes simplex virus-induced DNA polymerase and cellular RNA polvmerase II. The other twenty-eight compounds either did not inhibit any of these enzymes or inhibited all of these enzymes without selectivity for terminal transferase. Two analogs that selectively inhibited terminal transferase (K_i = 0.12mM) were 2- to 3-fold more potent than streptolydigin (K_i = 0.32mM). All the selective inhibitors of termininal transferase are 3-acylte-tramic acids with various substituent groups at the 1-, 3- and 5-positions. One of these, a less potent inhibitor of terminal transferase than streptolydigin, lacks the 3- and 5-substituents of streptolydigin but has virtually the same 1-substituent. The substituent groups of the other two selective inhibitors are structurally different from those of streptolydigin but essentally identical to each other. The mode of inhibition of terminal transferase by selective inhibitors was the same as for streptolydigin, but different from an analog which non-selectively inhibited terminal transferase. Evidence suggested that the selective inhibitors specifically interacted with terminal transferase and not with initiator (oligo- or polydeoxyribonucleotide), substrate (deoxyribonucleoside 5'-triphosphates) or the divalent cation (Mn ²⁺) required for enzyme activity. The data also implied that these compounds bind to the enzyme at a site(s) other than the initiator or substrate binding sites. In contrast, an analog which non-selectively inhibited terminal transferase apparently interacted with many proteins and polydeoxyribonucleotides non-specifically.     

The role of annealing in determining the yielding behavior of glasses under cyclic shear deformation

Yielding behavior in amorphous solids has been investigated in computer simulations using uniform and cyclic shear deformation. Recent results characterize yielding as a discontinuous transition, with the degree of annealing of glasses being a significant parameter. Under uniform shear, discontinuous changes in stresses at yielding occur in the high annealing regime, separated from the poor annealing regime in which yielding is gradual. In cyclic shear simulations, relatively poorly annealed glasses become progressively better annealed as the yielding point is approached, with a relatively modest but clear discontinuous change at yielding. To understand better the role of annealing on yielding characteristics, we perform athermal quasistatic cyclic shear simulations of glasses prepared with a wide range of annealing in two qualitatively different systems—a model of silica (a network glass) and an atomic binary mixture glass. Two strikingly different regimes of behavior emerge. Energies of poorly annealed samples evolve toward a unique threshold energy as the strain amplitude increases, before yielding takes place. Well-annealed samples, in contrast, show no significant energy change with strain amplitude until they yield, accompanied by discontinuous energy changes that increase with the degree of annealing. Significantly, the threshold energy for both systems corresponds to dynamical cross-over temperatures associated with changes in the character of the energy landscape sampled by glass-forming liquids.

The response of structural materials to applied stresses is of fundamental importance in determining their utility. Many structural materials are amorphous solids, with molecular glasses being a predominant example. In addition to specific types of molecular glasses, many other amorphous solids are the subject of ongoing fundamental and applied research investigations, such as colloidal suspensions, foams, emulsions, and granular packings (1–4). Upon increasing deformation or applied stresses, the mechanical response of such amorphous solids generically changes from elastic solid-like response at small deformations to elastoplastic flow at large deformations. However, the transition between these two regimes occurs in diverse ways. For many molecular glasses, yielding is a sudden, sharp event (often followed by brittle fracture, as in window glass or silica) or strong localization of strain (as in metallic glasses), features which we refer to as characterizing brittle behavior in what follows. For many soft solids, the transition between the elastic and plastic flow regimes is gradual (ductile), with no sharply defined transition point between them. Prominent among the challenges in understanding yielding is the rationalization of this diversity. A number of theoretical and computational investigations have recently addressed the nature of the yielding transition (5–23), many of which support the notion that yielding must be understood as a spinodal limit, at which system-spanning plastic deformation occurs discontinuously. The nature of such a limit (whether it is critical or not and whether correlated plastic rearrangements or avalanches diverge upon approaching it, etc.) is a matter of ongoing debate. Computational investigations have typically focused on the limit of athermal quasistatic (AQS) deformation of atomistic models, using both uniform (12–15, 20, 24–26) or cyclic (8, 9, 16, 17, 19, 22) shear deformation and simulations of elastoplastic models (7, 20, 21, 27, 28). Although the role of the degree of annealing in determining the mechanical response of glasses has been studied from early on (1, 24–26, 29), the focus has been on features such as strain localization and not the nature of the yielding transition itself. Recently, Ozawa et al. (20) investigated the dependence on annealing of the nature of yielding by considering uniform shear simulations of glasses prepared over a wide range of temperatures. Based on their numerical results and accompanying theoretical analysis, they identified two distinct regimes of annealing, one of high annealing in which yielding is discontinuous and the other of poor annealing where it is gradual, and argued that a random critical point (of the class described by the random-field Ising model) separates the two regimes at a critical value of annealing (or disorder). Investigations using cyclic shear deformation, with both poorly annealed and moderately well-annealed glasses (17, 22), reveal an apparently different picture. For amplitudes of strain below a critical value, repeated cyclic shear results in annealing the glasses, with the degree of annealing increasing with an increase in the strain amplitude. Yielding occurs discontinuously at a critical strain value, with a jump in the peak stress, the emergence of diffusive motion of particles, and shear banding (9, 16, 17, 19, 22).An important question raised by the above results is whether uniform and cyclic shear protocols lead to qualitatively different manifestations of yielding behavior. Additionally, one may ask how general the results in earlier work (17, 20, 22) are since the studied systems have all been models of atomic glasses. Finally, if a threshold degree of annealing or disorder does robustly separate brittle and ductile yielding behaviors, one may ask whether we can attribute any physical significance to the threshold annealing. We address these questions in the present work. We consider cyclic shear simulations of a model atomic glass studied earlier (the Kob–Andersen binary mixture Lennard–Jones model [KA BMLJ]) (17, 22) but over a much broader degree of annealing. As an important example of a distinct class of glasses with which to study the generality of the aforementioned results, we study silica, a network-forming glass. From the analysis of these two models, we conclude that cyclic shear indeed reveals the transition from ductile to brittle behavior, consistently with uniform shear investigations, revealing additional interesting characteristics of the transition. Finally, our results reveal an interesting physical significance to the threshold degree of annealing—we find that the threshold degree of annealing corresponds to well-studied dynamical cross-overs in the studied systems, the fragile–strong cross-over in silica, and the mode coupling temperature in the KA BMLJ model.For both the model systems we study, the glasses we subject to AQS deformation are generated by local energy minimization of simulated instantaneous liquid configurations. Based on the well-studied relationship between temperature and energies of typical minima or inherent structures (ISs) (e.g., ref. 30) (SI Appendix, Fig. S1), the degree of annealing of the glasses is equivalently specified by the potential energy of the ISs or the temperature of the equilibrium liquid from which they are obtained.We simulate the van Beest-Kramer-van Santen (BKS) model (31) of silica as implemented in Saika-Voivod et al. (32) for a temperature range from T=2,500 to 6,000 K, at density ρ=2.8gm/cm3 using N=1728 ions. Arising from its tetrahedral local geometry, silica exhibits a liquid–liquid phase transition (33, 34) and an associated fragile to strong cross-over (32, 35–37), which occurs around T=3,100 K for ρ=2.8 gm/cm3, inside the range of temperatures we simulate.The KA BMLJ is simulated at reduced density ρ=1.2, for N=4,000, for IS energies from EIS=−6.89 to −7.07, which correspond to T=1.5 to T≈0.35, the lower-energy configurations obtained from the procedure outlined in ref. 38 [to be compared with the extrapolated Kauzmann energy of EISK=−7.15 (38)]. We use the same procedure for system sizes N=2,000,8,000,16,000,32,000,64,000 to obtain glasses with lowest energy EIS=−7.05, for performing a system size analysis.These initial ISs are subjected to AQS shearing protocol involving 1) affine transformation by small strain increments of dγ=2×10−4 in the xz plane (x′→x+dγ z, y′→y, z′→z) and 2) energy minimization. The strain γ is varied cyclically: 0→γmax→−γmax→0 (or uniformly, for part of the study). Repeated deformation cycles for a given γmax result in the glasses reaching steady states wherein the properties on average do not change. Further details regarding simulations may be found in Materials and Methods.     

正交试验设计优选甲芪肝纤颗粒提取工艺的研究

目的以黄芪甲苷、干膏得率为含量指标 ,研究甲芪肝纤颗粒的水提工艺。方法采用正交试验设计进行优选 ,薄层色谱扫描测定黄芪甲苷含量 ,干燥失重法测定干膏得率。结果提取时间对黄芪甲苷和干膏得率的影响有显著性差异 (P <0 .0 5 ) ;加水量对黄芪甲苷和干膏得率的影响不具显著性 (P >0 .0 5 )。结论最佳提取工艺为水煮提 2次 ,第 1次 1 .5h ,第 2次 1h,加水量分别为药材量的 1 0倍和 8倍。