Multi-scale homogenization-based modeling of semi-crystalline polymers

This paper presents a finite-strain, multi-scale constitutive model for semi-crystalline polymers, accounting explicitly for the current state and evolution of the underlying crystallographic, lamellar and morphological texture. Specifically, a semi-crystalline polymer is modeled as a two-scale composite, assumed to be, at the larger length scale, an aggregate of randomly distributed grains that, at the smaller length scale, are made up of alternating layers of an amorphous and a crystalline phase. The model incorporates finite elasticity for the amorphous phase and crystallographic hardening for the crystalline phase. The instantaneous effective response of this composite is determined by means of multi-scale homogenization methods, consisting in the use of a “linear comparison composite” (LCC) with the same internal structure as the actual nonlinear composite, with local properties that are optimally chosen via suitably designed variational principles. The effective properties of the resulting two-scale LCC are obtained through a “sequential” homogenization procedure, involving the exact solution for the effective behavior of the lamellar grains and a self-consistent estimate for the aggregate. The latter results are also used to establish evolution laws for the appropriate internal variables in the material. The predictions of the model for the macroscopic response and texture evolution in high-density polyethylene are confronted with available experimental results and compared with those of earlier models.     

中国共产党党章的百年变迁—主题与变奏

作为依规治党的根本大法和依法治国的价值担纲,党章构成了“中国之治”的基础规范。党章内含的“社会主义”“民族主义”“发展主义”三项根本法,是理解党章百年变迁的内在线索。党章中的“社会主义”,经历了从“社会革命”到新民主主义革命,再到社会主义初级阶段的转换,克服了时序上的盲动主义和内涵上的教条主义,进入了用“中国特色”探索和定义社会主义的新阶段;党章中的“民族主义”有着民族先锋队和民族共同体的双重内涵,并呈现出构成性民族主义和超越性民族主义的双重面向;党章中的“发展主义”在阶段上经历了从救亡图存到伟大复兴的重大转换,在理念上正在实现从传统发展主义到新发展主义的历史跨越。党创制了党章,党章也在塑造着党。正确处理党章三项根本性议程及其内在张力,是“通过党章的治理”之关键所在。     

壳管相变蓄热器强化传热实验研究

为了强化相变蓄热器传热性能,本文设计了三种新型壳管相变蓄热器结构,并对其换热性能进行实验研究.结果表明:在蓄热器内部添加分层结构和斜翅片换热性能最高,内部温度达到均匀化的时间随换热单元数增加而增大;换热管道间翅片的添加可有效地强化换热效果,改善蓄热器内部出现的温度严重分层现象,温度分布更加均匀;在研究范围内,换热流体温...     

一次人工触发闪电上行正先导的传输特征

利用山东一次人工触发闪电的高速摄像和30 m, 60 m和480 m的同步电场测量, 清晰显示了人工触发闪电上行正先导的传输特征.上行正先导头部光强相对较强, 二维发展速度变化波动较大并呈现明显不规则性,表明上行正先导发展具有明显的梯级特征. 在先导开始阶段从340 m到705 m高度之间上行正先导平均发展速度为9.8×10⁴ m/s,起始速度是 3.8×10⁴ m/s,局部速度总体上随高度呈现增加趋势.电场变化在近距离产生有规律的梯级状 变化,记录到的28个梯级相邻梯级间隔变化从14 μs 到 39 μs,几何平均值为25.1 μs. 估计的先导梯级长度分布在0.9 m到3.7 m,几何平均值为1.7 m.先导电场变化由慢的正向梯级状变化和 脉冲变化组成,结合光学和电场变化测量结果,得出正先导头部通道发生弯曲可使其电场变化的梯级特征减弱 或消失;正负先导梯级形成机制可能类似,均由其先导头部前端的双向流光发展而来.     

PrNi$lt;sub$gt;2$lt;/sub$gt;的磁和磁热性能研究

在一些磁性材料内, 磁性离子间交换作用和磁性离子的自旋涨落对材料磁性有影响. 本文根据磁比热实验值确定了晶场参数后, 利用包含自旋涨落的交换作用有效场H_m= n₀ (1 + γ T + β e^{ω T})M, 计算了PrNi₂晶体晶场能级的Zeeman劈裂. 在温度为3.8 K ≤T≤ 30 K范围内, 计算了该晶体多晶磁矩随外磁场的变化, 以及外磁场H=5000 Oe时磁化率倒数随温度的变化, 计算结果和实验值符合较好. 当外磁场在0–50000 Oe时, 计算的该晶体的磁熵变与已有文献的理论结果相似. 计算结果说明, 提出的包含自旋涨落的交换作用有效场不仅适合亚铁磁性晶体, 而且也适合顺磁性晶体. 关键词： 2')" href="#">PrNi₂ 磁比热 交换作用有效场 磁矩 磁熵变     

Cu对用于高速相变存储器的Sb2Te薄膜的结构及相变的影响研究

采用原位X射线衍射仪、拉曼光谱仪和X射线反射仪分别研究了Cu-Sb₂Te 薄膜的微结构、成键结构和结晶前后的密度变化. Sb₂Te薄膜的结晶温度随着Cu含量的增加而增大. 在10 at.%和14 at.% Cu的Sb₂Te薄膜中, Cu与 Te 成键, 结晶相由六方相的Cu₇Te₄、菱形相的Sb及六方相的Sb₂Te构成. 10 at.% 和14 at.% Cu 的Sb₂Te薄膜在结晶前后的厚度变化分别约为3.2%和 4.0%, 均小于传统的Ge₂Sb₂Te₅ (GST)薄膜. 制备了基于Cu-Sb₂Te薄膜的相变存储单元, 并测试了其器件性能. Cu-Sb₂Te器件均能在10 ns的电脉冲下实现可逆SET-RESET操作. SET和RESET操作电压随着Cu含量的增加而减小. 疲劳测试结果显示, Cu 含量为10 at.%和14 at.%的PCRAM单元的循环操作次数分别达到1.3×10⁴和1.5×10⁵, RESET和SET态的电阻比值约为100. Cu-Sb₂Te可以作为应用于高速相变存储器(PCRAM)的候选材料.     

Si1Sb2Te3 phase change material for chalcogenide random access memory

This paper investigated phase change Si1Sb2Te3 material for application of chalcogenide random access memory. Current-voltage performance was conducted to determine threshold current of phase change from amorphous phase to polycrystalline phase. The film holds a threshold current about 0.155 mA, which is smaller than the value 0.31 mA of Ge2Sb2Te5 film. Amorphous Si1Sb2Te3 changes to face-centred-cubic structure at ~ 180℃ and changes to hexagonal structure at ~ 270℃. Annealing temperature dependent electric resistivity of Si1Sb2Te3 film was studied by four-point probe method. Data retention of the films was characterized as well.     

Back to the future: A retrospective assessment of model‐based scenarios for the management of the shrimp fishery in French Guiana facing global change

While the number of models dedicated to predicting the consequences of alternative resource management strategies has increased, instances in which authors look back at past predictions to learn from discrepancies between these and observed developments are scarce. In the past decades, the French Guiana shrimp fishery has experienced shrimp market globalization and decreasing levels of shrimp recruitment due to environmental changes. In 2006, a bio‐economic model of this fishery was developed to simulate its possible responses to economic and environmental scenarios up to 2016. Here, we compare here these predictions to the observed trajectories. While the number of active vessels corresponds to that which was predicted, the estimated shrimp stock does not. Important driving factors had not been anticipated, including a general strike, natural disasters, and the end of the global financial crisis. These results show the importance of participative approaches involving stakeholders in the co‐construction and shared representation of scenarios. Recommendations for resource managers

• Effective fisheries resources management and a fortiori, the capacity of the fisheries to adapt to global change, requires understanding of both ecological and economics dynamics.
• The temporal trajectory of the trawling shrimp fisheries has been well monitored, and the decline of both stock and fleet is understood regarding ecological and economic changes: Changes in the environmental conditions of shrimp recruitment, and oil price increase and selling price decrease.
• However, our bio‐economic modeling work showed that, even with a good understanding of the dynamics explaining past trajectories, unpredictable events (strike, natural disasters…) have acted as other key driving factors altering the capacity of the model to represent possible futures.
• These results led us to recommend a better integration of the expertise of social and political scientists in developing models of bio‐economic systems to increase the quality of scenario predictions, and to argue for more participative approaches involving the stakeholders.

     

THE CRYSTAL STRUCTURE OF 2-[(N,N-DIMETHYLAMINO)METHYL]BENZENETELLURENYL CHLORIDE

The crystal structure of 2-[N,N-dimethylamino)methyl]benzenetel-lurenyl chloride (2), a compound previously formulated as bis[[2-(N,N-dimethylamino)methyl]phenyl] ditelluride bis hydrochloride (1a), was determined. In the molecule 2, tellurium is bonded to the carbon of the phenyl group [2.120(3) Å], the nitrogen of the ortho dimethylamino substituent [2.362(3) Å], and the chlorine atom [2.536(1) Å]. There also is an intermolecular interaction of the tellurium atom with the phenyl ring of a neighbouring molecule [3.655(1) Å], resulting in the formation of zigzag chains along the b axis. The noncentrosymmetric space group of the crystal can be explained by the chiral surrounding of tellurium.     

Solvatochromic Determination of Second-order Polarizabilities of Chromophore-functionalized Dextran and Amylose Derivatives

Linear dextran and helix amylose were covalently bonded with nonlinear optical (NLO) chromophores. The influence of the conformation of the polymer matrix on the NLO behavior of the supramolecular structure has been studied. The second order hyperpolarizability depends not only on the secondary structure of the biopolymer, but also on the position of the chromophore towards the polymeric backbone. Functionalization of NLO-phores with biopolymers led to increased thermo- and photostability.