The chemistry of deformation: how solutes soften pure metals

Solutes have been added to strengthen elemental metals, generating usable materials for millennia; in the 1960s, solutes were found to also soften metals. Despite the empirical correlation between the "electron number" of the solute and the change in strength of the material to which it is added, the mechanism responsible for softening is poorly understood. Using state-of-the-art quantum-mechanical methods, we studied the direct interaction of transition-metal solutes with dislocations in molybdenum. The interaction increases dramatically with increasing electron number and strongly influences the mechanisms responsible for plasticity in these materials. Our quantitative model explains solution softening of metals by using changes in energy and stress scales of plasticity from solutes.     

Optimization by simulated annealing

There is a deep and useful connection between statistical mechanics (the behavior of systems with many degrees of freedom in thermal equilibrium at a finite temperature) and multivariate or combinatorial optimization (finding the minimum of a given function depending on many parameters). A detailed analogy with annealing in solids provides a framework for optimization of the properties of very large and complex systems. This connection to statistical mechanics exposes new information and provides an unfamiliar perspective on traditional optimization problems and methods.     

重组竹方材增湿软化工艺

针对重组竹方材含水率低、密度大且难刨切的现状,采用不同压力的加压浸注和不同温度的水煮软化工艺对重组竹方材进行增湿软化处理,研究增湿软化后重组竹方材的增重率、传热及硬度的变化情况。研究结果表明:随着压力的增大和时间的延续,重组竹方材的增重率逐步增大,压力1.2 MPa以后增重率增加不明显;随着水煮软化温度的升高和时间的延续,重组竹方材的增重率变化率呈增大的趋势,36.0 h后增大趋势变缓;重组竹内部温度在8.0 h时已趋于稳定。硬度测试结果表明,经过加压浸渍和水煮软化后,重组竹材的硬度下降明显,和未处理材相比下降了36.2%,而重组竹表面的裂纹长度和宽度有所增加,和未处理材相比裂纹平均长度增加了21.1%,平均宽度增加了16.7%。说明采用加压浸注和水煮软化的生产工艺能对重组竹方材起到较好的软化效果,但也在一定程度上影响了其表面的裂纹长度和宽度。图4表2参16     

Drosophila BLM in double-strand break repair by synthesis-dependent strand annealing

Bloom syndrome, characterized by a predisposition to cancer, is caused by mutation of the RecQ DNA helicase gene BLM. The precise function of BLM remains unclear. Previous research suggested that Drosophila BLM functions in the repair of DNA double-strand breaks. Most double-strand breaks in flies are repaired by homologous recombination through the synthesis-dependent strand-annealing pathway. Here, we demonstrate that Drosophila BLM mutants are severely impaired in their ability to carry out repair DNA synthesis during synthesis-dependent strand annealing. Consequently, repair in the mutants is completed by error-prone pathways that create large deletions. These results suggest a model in which BLM maintains genomic stability by promoting efficient repair DNA synthesis and thereby prevents double-strand break repair by less precise pathways.     

Beating crystallization in glass-forming metals by millisecond heating and processing

The development of metal alloys that form glasses at modest cooling rates has stimulated broad scientific and technological interest. However, intervening crystallization of the liquid in even the most robust bulk metallic glass-formers is orders of magnitude faster than in many common polymers and silicate glass-forming liquids. Crystallization limits experimental studies of the undercooled liquid and hampers efforts to plastically process metallic glasses. We have developed a method to rapidly and uniformly heat a metallic glass at rates of 10(6) kelvin per second to temperatures spanning the undercooled liquid region. Liquid properties are subsequently measured on millisecond time scales at previously inaccessible temperatures under near-adiabatic conditions. Rapid thermoplastic forming of the undercooled liquid into complex net shapes is implemented under rheological conditions typically used in molding of plastics. By operating in the millisecond regime, we are able to "beat" the intervening crystallization and successfully process even marginal glass-forming alloys with very limited stability against crystallization that are not processable by conventional heating.     

Quartz: extreme preferred orientation produced by annealing

Annealing of samples of flint under high pressure, after hot-working in the beta-quartz stability field, produced an exceedingly strong concentration of c-axes parallel to the direction of compression. A specimen deformed under identical conditions, but not annealed, exhibited a much weaker orientation. The strength of the annealed orientation rivals that of the remarkable "cube texture" produced by annealing some face-centered cubic metals after extreme reduction by rolling.     

凹凸棒土对生活污泥中重金属的钝化作用

生活污泥中重金属是影响其农用的主要因素之一.为研究凹凸棒土对生活污泥中重金属的钝化作用,通过在生活污泥中添加干基质量6％、12％、18％的凹凸棒土,利用粘土矿物的吸附特性,研究其对污泥中Pb、Cd、Cu、Ni、Cr、Zn等重金属的吸附钝化效果.试验结果表明:凹凸棒土对6种重金属在初始时均表现出钝化效果,至试验结束(30d)时凹凸棒土对Pb、Cd、Ni、Zn的钝化量减小或被活化,Cr始终保持被钝化状态,而对Cu的钝化效果则有所加强.     

果实软化的细胞壁降解酶及其调控研究进展

软化是果实成熟的一个重要标志,果实软化是由细胞壁降解酶促进细胞壁物质的降解,从而引起细胞壁超微结构发生变化所致.细胞壁降解酶活性的升高受基因的调控,采后生物技术为研究果实成熟软化提供了新的途径.反义基因技术证明,细胞壁降解酶基因的任何一种表达被抑制,果实都能够正常软化,表明果实的软化有其它因子的参与.文章就细胞壁降解酶在果实软化过程中的作用及其调控的研究进展进行了综述.     

乙烯对树莓果实成熟软化的影响

采收不同成熟期"哈瑞太兹"树莓果实,成熟期果实室温放置16、30、44、56 h,乙烯利和1-MCP处理白果期果实1、2、3、4、5 d,测定呼吸速率、乙烯生成速率、乙烯相关酶基因RiACO1和RiACS1转录水平以及相关生理指标。发现果实自然成熟过程中未出现呼吸峰和乙烯峰,且采后短时间内呼吸速率及乙烯生成速率无明显变化,乙烯利处理可暂时提高呼吸速率和乙烯生成速率,提高RiACO1和RiACS1转录水平,加速果实变红,降低硬度、可溶性固形物和花青素积累以及可滴定酸和叶绿素含量,而1-MCP处理延缓此过程。据此,树莓可能具有跃变型和非跃变型果实两种呼吸类型的特点。     

Plastic and moldable metals by self-assembly of sticky nanoparticle aggregates

Deformable, spherical aggregates of metal nanoparticles connected by long-chain dithiol ligands self-assemble into nanostructured materials of macroscopic dimensions. These materials are plastic and moldable against arbitrarily shaped masters and can be thermally hardened into polycrystalline metal structures of controllable porosity. In addition, in both plastic and hardened states, the assemblies are electrically conductive and exhibit Ohmic characteristics down to approximately 20 volts per meter. The self-assembly method leading to such materials is applicable both to pure metals and to bimetallic structures of various elemental compositions.     

城市园林土壤板结机理及改良研究

为了改良城市园林板结土壤的质量,促进城市绿地持续、健康发展,对重庆市主城9区园林绿化板结土壤的容重、粗骨物质、有机质、碱解氮、有效磷、速效钾、微生物种群数量、植物配置等理化及生物学性质进行了研究。结果表明,城市园林绿化土壤板结的主要原因是:(1)人为压实严重,土壤容重总平均值为(1.47±0.05)g/cm3,最高的可达1.72g/cm3;(2)粗骨物质多,各区含量总平均值为(40.2±4.43)%;(3)有机质含量低,总平均值为(27.2±1.1)g/kg;碱解氮、速效钾等有效养分含量偏低,总平均值分别为(39.4±1.1)mg/kg和(87.3±1.9)mg/kg;(4)植物配置不合理;(5)土壤微生物种群数量少,细菌数量、真菌数量和放线菌数量的总平均值分别为(29.71±7.8)×105cfu/g、(9.98±1.55)×103cfu/g和(7.6±1.64)×105cfu/g。基于城市园林土壤的板结机理,结合景观生态学、共生生物学原理,提出了改良城市园林板结土壤的综合配套改良技术。     

细胞壁代谢与‘富有’甜柿采后果实软化的相关性

将3种成熟度的‘富有’甜柿果实贮藏于4℃的冰箱中,定期测定细胞壁成分和相关代谢酶活性的变化,探讨果实采后贮藏期间细胞壁代谢与果实软化的关系.结果表明:果实细胞壁组分中的原果胶和纤维素含量与硬度呈显著相关,可溶性果胶含量则相反;纤维素酶活性在果实初期软化中起作用,多聚半乳糖醛酸酶和β-半乳糖苷酶活性在整个贮藏期间对果实的软化起重要作用.     

Catalysis by transition metals: metal-carbon double and triple bonds

Several well-characterized transition metal catalysts contain a metal-carbon double bond or a metal-carbon triple bond. In other homogeneous (or heterogeneous) catalyst systems in which the metal is likely to be in a relatively high oxidation state, such as molybdenum(VI) or tungsten(VI), metal-carbon multiple bonds may play an important role. Some recent results suggest that even supposedly well understood reactions such as ethylene polymerization may actually involve catalysts that behave as if they contained a metal-carbon double bond instead of a metal-carbon single bond. The chemistry of metal-carbon double and triple bonds should eventually complement and perhaps. overlap the known chemistry of complexes containing metal-oxygen double bonds or metal-nitrogen triple bonds, respectively; unique catalytic reactions involving carbon, nitrogen, and oxygen ligands multiply bonded to transition metals are therefore possible.     

钝化剂对重金属的吸附及其吸附机理的研究

试验探讨了静态条件下沸石和草炭对重金属离子的吸附特性和吸附热力学性质。结果表明,重金属钝化剂沸石和草炭中加入重金属溶液(Cu2+、Mn2+、Zn2+、Pb2+、Cd2+)的浓度越大,钝化剂对重金属离子的吸附量越多;不同钝化剂对重金属离子的吸附能力略有不同,草炭>沸石;草炭对重金属的吸附亲和力顺序为Zn2+>Mn2+>Cu2+>Cd2+>Pb2+;沸石的为Zn2+>Cu2+>Mn2+>Cd2+>Pb2+;两种钝化剂对重金属的吸附等温线与Freundlich和Temkin方程均有较好的拟合性,Langmuir方程不适宜描述两种钝化剂对重金属的等温吸附过程,其等温线符合Freundlich吸附等温模型。     

Formation and subdivision of deformation structures during plastic deformation

During plastic deformation of metals and alloys, dislocations arrange in ordered patterns. How and when these self-organization processes take place have remained elusive, because in situ observations have not been feasible. We present an x-ray diffraction method that provided data on the dynamics of individual, deeply embedded dislocation structures. During tensile deformation of pure copper, dislocation-free regions were identified. They showed an unexpected intermittent dynamics, for example, appearing and disappearing with proceeding deformation and even displaying transient splitting behavior. Insight into these processes is relevant for an understanding of the strength and work-hardening of deformed materials.     

重金属污染土壤的有机-中性化修复技术试验

通过田间定位试验,采用石灰、钙镁磷肥、泥炭、猪粪、石灰+泥炭、石灰+猪粪、钙镁磷肥+泥炭、钙镁磷肥+猪粪等处理对污染田进行改良.试验表明,大部分处理能提高土壤的pH值、有机质含量、碱解氮及速效磷含量;各处理pH值大小顺序为,钙镁磷肥+泥炭、钙镁磷肥、钙镁磷肥+猪粪>石灰+猪粪、石灰+泥炭、石灰>泥炭、猪粪.经统计分析,土壤pH值与土壤有效镉、有效铅、有效铜含量之间呈显著负相关.说明通过提高土壤pH值,降低土壤重金属活性是有机-中性化改良技术的主要机理.     

Roton-type mode softening in a quantum gas with cavity-mediated long-range interactions

Long-range interactions in quantum gases are predicted to give rise to an excitation spectrum of roton character, similar to that observed in superfluid helium. We investigated the excitation spectrum of a Bose-Einstein condensate with cavity-mediated long-range interactions, which couple all particles to each other. Increasing the strength of the interaction leads to a softening of an excitation mode at a finite momentum, preceding a superfluid-to-supersolid phase transition. We used a variant of Bragg spectroscopy to study the mode softening across the phase transition. The measured spectrum was in very good agreement with ab initio calculations and, at the phase transition, a diverging susceptibility was observed. The work paves the way toward quantum simulation of long-range interacting many-body systems.     

碱-偏高岭土胶凝材料的凝结硬化性能研究

对碱 偏高岭土胶凝材料的凝结硬化性能进行了研究.研究方法是将碱激发剂∶偏高岭土∶砂=0.7∶1∶1(质量比)混合并成型为3cm×3cm×3cm的试块,在规定的条件下养护到规定的时间,根据试块的抗压强度来评价凝结硬化性能.试验结果表明:碱 偏高岭土胶凝材料的胶砂强度随碱的浓度增加而加快;随养护温度升高和养护时间延长而加快;与水玻璃的模数有关.当水玻璃模数为0.75～1时,胶砂强度发展速率迅速;当水玻璃模数≥2时,砂浆在80℃养护24h不能脱模;当水玻璃模数为0.5时,砂浆拌合时发生闪凝.由此可以推断:当水玻璃模数为0.75～1时,水玻璃中SiO2初始状态有利于反应产物的形成以及(或者)偏高岭土在该水玻璃的碱浓度中的溶解度可能与反应物的形成速度相匹配.     

硒阻控作物吸收重金属机制研究进展

重金属污染对粮食安全及人体健康造成巨大威胁,目前已开发出许多农田重金属污染修复方法。硒的补充显著降低作物对重金属的吸收,同时促进作物在重金属污染土壤中的生长,施硒已成为阻控作物吸收重金属的新途径。本文对施硒阻控作物吸收重金属的5种机制即硒改变土壤重金属的生物有效性、硒与重金属竞争植物摄取通道、硒促进植物根系铁膜形成、硒诱导植物根系形态及结构变化、硒调控植物重金属螯合和转运基因表达等研究进展进行了综述,同时对施硒阻控作物吸收重金属潜在风险及未来研究重点进行展望,以期为将来利用硒作为重金属阻控剂提供参考。     

拱棚盘秧打孔炼苗及机插配套技术

水稻机插秧作业的关键在于与之配套的育秧方式。目前,广泛采用旱育拱棚盘秧,但这种育秧方式易发生水稻秧苗立枯病。防治秧苗立枯病的核心技术是床土调酸培育壮秧,盘育壮秧依赖于科学的床土配方和合理的通风炼苗等措施的落实。通过采用打孔通风炼苗的创新技术,实现拱棚昼夜自然通风,可较好地解决这一问题。