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1.
This study investigates the recovery of electric resistivity in pure iron, Fe–0.6Ni and Fe–1.5Mn as related to isochronal annealing following 1 MeV proton irradiation at lower temperature than 70 K, focusing on the relationship between solute atoms and irradiation defects. Both nickel and manganese prevent stage ID recovery, which corresponds to correlated recombination. Stage II recovery is also changed by the addition of a solute, which corresponds to the migration of small interstitial clusters. In both pure iron and Fe–0.6Ni, no evident difference was observed in the stage III region, which corresponds to the migration of vacancies. In contrast, two substages appeared in the Fe–1.5Mn at a higher temperature than stage IIIB appeared in pure iron. These substages are considered to represent the release of irradiation-induced defects, which was trapped by manganese.  相似文献   
2.
Zeolite crystals can be used as seeds or aluminosilicate sources in syntheses to control polymorphs and/or reduce the quantity of organics used as structure-directing agents. A frequently invoked hypothesis for interzeolite transformations is that zeolites share some underlying similarity in structure, most notably in cases pertaining to organic-free syntheses. Herein, we show for the first time that ZSM-5 (MFI) can be directly obtained from USY (FAU) through an interzeolite transformation between parent–daughter structures lacking common building units in the absence of a structure-directing agent and seeds. We show that interzeolite transformation leads to a crystalline product with fewer defects. Our findings also reveal that ZSM-5 is a metastable intermediate that undergoes further transformation to mordenite (MOR) and quartz. The MFI-to-MOR transition is counter to reported trends for which transformations lead to structures with reduced molar volume. Herein, we propose mechanistic arguments that suggest the driving force for interzeolite transformation is more complex than guidelines posited in the literature.  相似文献   
3.
冬小麦不同生育时期叶面积指数反演方法   总被引:20,自引:0,他引:20  
针对当前作物叶面积指数遥感反演过程中,在不同生育时期采用相同的植被指数进行反演存在叶面积指数反演精度较低的问题。以冬小麦为研究对象,选取了对冬小麦覆盖度响应程度不同的六种宽带和四种窄带共10种植被指数,分析比较了在冬小麦整个生育期选用当前广泛使用的归一化植被指数(NDVI)反演冬小麦的LAI和在冬小麦不同生长阶段选用不同的植被指数反演冬小麦LAI的结果差异。在冬小麦整个生育期内使用NDVI反演小麦LAI得到的LAI反演值和真实值之间的R2=0.558 5,RMSE=0.320 9。改进的比值植被指数(mSR)适合于反演冬小麦生长前期(拔节期之前)的LAI,得到的LAI反演值和真实值之间的相关系数r=0.728 7,均方根误差RMSE=0.297 1;比值植被指数(SR)适于反演冬小麦生长中期(拔节到抽穗前),得到的LAI反演值和真实值之间的R2=0.654 6,RMSE=0.306 1;NDVI适于反演冬小麦生长后期(抽穗到成熟期)的LAI,得到的LAI反演值和真实值之间的R2=0.679 4,均方根误差RMSE=0.316 4。研究表明:在冬小麦的不同生育时期,根据地表作物覆盖度的变化和反射率的变化,选择不同的植被指数建立冬小麦LAI的反演模型获得的反演精度均高于在冬小麦整个生育期使用NDVI获得的反演结果。说明在冬小麦的不同生育时期选择不同的植被指数构建LAI的分段反演模型可以改善冬小麦LAI的反演精度。  相似文献   
4.
A rotational stage is a key component of every X‐ray instrument capable of providing tomographic or diffraction measurements. To perform accurate three‐dimensional reconstructions, runout errors due to imperfect rotation (e.g. circle of confusion) must be quantified and corrected. A dedicated instrument capable of full characterization and circle of confusion mapping in rotary stages down to the sub‐10 nm level has been developed. A high‐stability design, with an array of five capacitive sensors, allows simultaneous measurements of wobble, radial and axial displacements. The developed instrument has been used for characterization of two mechanical stages which are part of an X‐ray microscope.  相似文献   
5.
Crystallization of organic molecules is quite complicated because the crystallization process is governed by weak intermolecular interactions. By exploiting aggregation‐induced emission (AIE), we attempted to realize the selective detection of phase transformation during the evaporative crystallization of hexaphenylsilole (HPS), which shows different fluorescent colors in the amorphous and crystalline phases. No fluorescence emission was observed in the HPS solution immediately after dropping on the glass substrate due to the non‐radiative deactivation induced by intramolecular rotational or vibrational motion, suggesting that HPS exists as a monomer in solution. As time elapsed after dropping, green emission first appeared, which changed to blue after solvent evaporation, because of phase transformation from the amorphous state to the crystalline state. This phenomenon supports not only the two‐step nucleation model involving an intermediate such as a liquid‐like cluster prior to nucleation but also the real‐time detection of Ostwald's rule of stages during evaporative crystallization.  相似文献   
6.
In this paper, we establish a mathematical model of online game addiction with two stages to research the dynamic properties of it. The existence of all equilibria is obtained, and the basic reproduction number is calculated by the method of next-generation matrix. The global asymptotic stability of disease-free equilibrium (DFE) is proved by comparison principle, and the global asymptotic stability of endemic equilibrium (EE) is proved by constructing an appropriate Lyapunov function. Then we use the Pontryagin's maximum principle to find the optimal solution of the model, so that the number of infected people can be minimized. In numerical simulation, firstly, we validate the global stability of DFE and EE. Secondly, we consider three kind of control measures (treatment, isolation, and education) and divide them into four cases. The models with control and without control are solved numerically by using forward and backward sweep Runge-Kutta method. In order to achieve the best control effect, we suggest that three kind of measures should be used simultaneously according to the optimal control strategy.  相似文献   
7.
按胸径将浙江省桐庐县白云源森林公园长叶榧群体划分为成体、小树、幼苗3个年龄级,利用RAPD和ISSR分子标记对不同年龄级的遗传多样性及遗传分化进行分析.12个RAPD引物和12个ISSR引物分别扩增出199和180个条带,总多态位点百分率分别为44.72%和56.11%.RAPD和ISSR分析均显示3个年龄级的多态位点百分率、Shannon信息指数、Nei指数以成体最高,小树次之,幼苗最低,表明长叶榧群体遗传变异呈衰退趋势.分子方差分析(AMOVA)表明长叶榧群体不同年龄级内、年龄级间均存在遗传变异,但遗传变异主要存在于年龄级内.RAPD和ISSR分析显示,长叶榧群体不同年龄级间的遗传分化系数(Gst)分别为0.2869、0.3077,基因流(Nm)分别为1.2412、1.1231.长叶榧群体不同年龄级间的遗传相似度以幼苗与小树最高,遗传距离以幼苗与小树间最小.在长叶榧群体不同年龄级中,ISSR能检测到比RAPD更多的遗传变异,经Mantel检验,两种分子标记的分析结果相关性极显著.  相似文献   
8.
This study is based on the stance that Pólya's “Look Back,” though understudied, remains relevant to Mathematics curricula that place emphasis on problem solving. Although the Singapore Mathematics curriculum adopts the goal of teaching Look Back, research about how it is carried out in actual classroom practice is rare. In our project, we focus on a redesign of a teacher development programme that is targeted to help teachers realize Pólya's original vision of Look Back in the classroom. We report the cases of two teachers who have participated in the teacher development programme: their thinking about Look Back (through interview records) and their interpretation of Look Back in their classroom practice (through video records). By bringing these two spheres of data together, we discuss their degree of ‘buy-in’ to Look Back in the overall problem solving enterprise.  相似文献   
9.
A fixed topology of stages and/or a fixed branching scheme are common assumptions for applications and numerical solution of scenario based multistage stochastic programs. Using contamination technique to test this structure, we extend the results of Dupačová (Contamination for multistage stochastic programs. In: Hušková M, Janžura M (eds) Prague stochastics. Matfyzpress, Praha, pp 91–101, 2006a) to stochastic programs with multistage polyhedral risk objectives. The ideas are exemplified by bond portfolio management problems and complemented by illustrative numerical results.  相似文献   
10.
In a production system, rework process plays an important role in eliminating waste and effectively controlling the cost of manufacturing. Determining the optimal batch size in a system that allows for rework is, therefore, a worthwhile objective to minimize the inventory cost of work-in-processes and the finished goods. In this paper, models for the optimum batch quantity in a multi-stage system with rework process have been developed for two different operational policies. Policy 1 deals with the rework within the same cycle with no shortage and policy 2 deals with the rework done after N cycles, incurring shortages in each cycle. The major components that play a role in minimizing this cost of the system are manufacturing setups, work-in-processes, storage of finished goods, rework processing, waiting-time, and penalty costs to discourage the generation of defectives. The mathematical structure of this rework processing model falls under a nonlinear convex programming problems for which a closed-form solution has been proposed and results are demonstrated through numerical examples, followed by sensitivity analyses of different important parameters. It is concluded that the total cost in policy 2 tends to be smaller than that in policy 1 at lower proportion of defectives if the in-process carrying cost is low. Policy 2 may be preferred when the work-in-process carrying cost is low and the penalty cost is negligible.  相似文献   
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