A Study on the Microstructure Characteristic of the Cold-Rolled Deformed Nanocrystalline Nickel

In this paper the microstructure characteristic of the cold-rolled deformed nanocrystalline Nickel metal has been studied by transmission electron microscopy (TEM). The results show that there were step structures near by grain boundary (GB), and the contrast of stress field in front of the step corresponds to the step in the shape. It indicates that the interaction between twins and dislocations is not a necessary condition to realizing the deformation. In the later stage of the deformation when the grain size became about 100 nm, the deformation occurs only depend upon the moving of the boundary of the stack faults (SFs) which result from the imperfection dislocations emitted from GBs. In the other word, the movement of the boundary dislocations of SFs results to growing-up of the size of the SFs, therefore realizes deformation. However, when the size of stack faults grows up, the local internal stress which is in front of the step gradually becomes higher. When this stress reach a critical value stopping the gliding of the partial dislocations, the SFs will stop growing up and leave a step structure behind.

重金属对小麦根干重和在不同培肥条件下对土壤铵态氮的影响

笔者的研究目的在于了解土壤重金属污染对小麦根部生长发育的影响以及在不同培肥条件下土壤重金属的生物活性的变化情况。通过盆栽试验研究了重金属铬、镉和铅三种重金属对小麦根重的影响,利用室内培养试验研究了氮磷化肥、氮磷化肥+低秸、氮磷化肥+中秸、氮磷化肥+高秸、氮磷肥+厩肥、氮磷肥+低秸(休闲田)以及无肥对照区等7种不同培肥条件下重金属铬、镉和铅对土壤铵态氮含量的影响。研究结果表明,重金属铬对小麦的根重影响较大,这3种重金属的复合污染对小麦根重的影响要比单因素条件下的影响要明显;在不同肥料条件下重金属对土壤环境内的铵态氮的影响作用存在差异,氮磷肥料条件下,重金属对土壤铵态氮的抑制作用明显增强;氮磷+低秸(休闲田)条件下,重金属铬、镉与铅对土壤铵态氮的抑制性显著降低,铵态氮总量基本影响较小。通过研究表明,不同培肥条件能够影响土壤重金属的生物活性,可以通过控制土壤培肥条件达到降低土壤重金属生物活性,减轻对重金属污染土壤的程度。

幼儿绘画表征的发展－－发展过程及其影响因素

Two major questions in this study are the development of children's representative drawing and the influence of semantic representation and image representation on it. Children aged from 3 and a half to 7 participated the experiments. Two-dimension and three-dimension displays were used in four experiments. The results show that: The development of children's representational drawing can be divided into stages. They become maturer in selecting the strategies of the representational drawing, which are different in nature across different ages. There is a development from feature processing to integrative processing in children's drawing. At the feature processing stage, the typological features are represented easily. No matter global or partial. They tend to use unconnected parts to represent, which is called the strategy of distributed representation, those displays without prominent features. In integrative processing stage, the features of two-dimension display are integrated according to its gestalt. And the features of three-dimension display are integrated by its prototypical view across the main axis of the display. Cubic representations were found in some of the children's drawings, but none of them can do it from a perspective view before 7 years old. The semantic processing of the display, both global and partial meaning, can influence the development of the representational drawing. The structural features of the display influence the development of drawing representation. Semantic principles and structural features influence the representational drawings together. For three-dimension display, the semantic face and structural face coexist and work together. Children's ability to draw the display according to the right perspective rather than the prototypical view increase along with them growing up.

Characterizing CO2 fluxes for growing and non-growing seasons in a shrub ecosystem on the Qinghai-Tibet Plateau

To assess carbon budget for shrub ecosystems on the Qinghai-Tibet Plateau, CO2 flux was measured with an open-path eddy covariance system for an alpine shrub ecosystem during growing and non-growing seasons. CO2 flux dynamics was distinct between the two seasons. During the growing season from May to September, the ecosystem exhibited net CO2 uptake from 08:00 to 19:00 (Beijing Standard Time), but net CO2 emission from 19:00 to 08:00. Maximum CO2 uptake appeared around 12:00 with values of 0.71, 1,19, 1.46 and 0.67 g CO2 m(-2) h(-1) for June, July, August and September, respectively. Diurnal fluctuation Of CO2 flux showed higher correlation with photosynthetic photon flux density than temperature. The maximum net CO2 influx occurred in August with a value of 247 g CO2 m(-2). The total CO2 uptake by the ecosystem was up to 583 g CO2 m(-2) for the growing season. During the non-growing season from January to April and from October to December, CO2 flux showed small fluctuation with the largest net CO2 efflux of 0.30 g CO2 m(-2) h(-1) in April. The diurnal CO2 flux was close to zero during most time of the day, but showed a small net CO2 eff lux from 11:00 to 18:00. Diurnal CO2 flux, is significantly correlated to diurnal temperature in the non-growing season. The maximum monthly net CO2 eff lux appeared in April, with a value of 105 g CO2 m(-2). The total net CO2 eff lux for the whole non-growing season was 356 g CO2 m(-2).

Liquid phase epitaxy growth of AlxGayIn1-x-yPzAs1-zGaAs with direct band gap up to 2.0 eV

III-V pentenary semiconductor AlGaInPAs with a direct band gap of up to 2.0 eV has been grown successfully on GaAs substrates by liquid phase epitaxy;(LPE). With the introduction of the energy bowing parameters of quaternaries, the theoretical calculations agree well with the measured PL peak energy data from pentenary samples.

Effects of 'sinking in' and 'piling up' on estimating the contact area under load in indentation

The phenomena of the 'piling up' and 'sinking-in' of surface profiles in conical indentation in elastic-plastic solids with work hardening are studied using dimensional and finite-element analysis. The degree of sinking in and piling up is shown to depend on the ratio of the initial yield strength Y to Young's modulus E and on the work-hardening exponent n. The widely used procedure proposed by Oliver and Pharr for estimating contact depth is then evaluated systematically. By comparing the contact depth obtained directly from finite-element calculations with that obtained from the initial unloading slope using the Oliver-Pharr procedure, the applicability of the procedure is discussed.

Refractive index and thickness analysis of natural silicon dioxide film growing on silicon with variable-angle spectroscopic ellipsometry

The refractive index and thickness of SiO2 thin films naturally grown on Si substrates were determined simultaneously within the wavelength range of 220-1100 nm with variable-angle spectroscopic ellipsometry. Different angles of incidence and wavelength ranges were chosen to enhance the analysis sensitivity for more accurate results. Several optical models describing the practical SiO2-Si system were investigated, and best results were obtained with the optical model, including an interface layer between SiO2 and Si, which proved the existence of the interface layer in this work as described in other publications.

A New Modified Expanding Cavity Model for Characterizing the Spherical Indentation Behaviour of Bulk Metallic Glass with Pile-up

Spherical nanoindentation tests were performed on Zr41.2Ti13.8Cu12.5Ni10Be22.5 bulk metallic glass and pile-ups were observed around the indenter. A new modified expanding cavity model was developed to characterize the indentation deformation behavior of strain-hardening and pressure-dependent materials. By using this model, the representative stress-strain response of this bulk metallic glass to hardness and indentation in the elastic-plastic regime were obtained taking into consideration the effect of pile-up.

Numerical Study Of Pile-Up In Bulk Metallic Glass During Spherical Indentation

Pile-up around indenter is usually observed during instrumented indentation tests on bulk metallic glass. Neglecting the pile-up effect may lead to errors in evaluating hardness, Young's modulus, stress-strain response, etc. Finite element analysis was employed to implement numerical simulation of spherical indentation tests on bulk metallic glass. A new model was proposed to describe the pile-up effect. By using this new model, the contact radius and hardness of Zr41.2Ti13.8Cu12.5Ni10Be22.5 bulk metallic glass were obtained under several different indenter loads with pile-up, and the results agree well with the data generated by numerical simulation.

Plane strain problem of growing crack for a perfectly plastic solid

In this paper, fundamental equations of the plane strain problem based on the 3-dimensional plastic flow theory are presented for a perfectly-plastic solid The complete governing equations for the growing crack problem are developed. The formulae for determining the velocity field are derived.The asymptotic equation consists of the premise equation and the zero-order governing equation. It is proved that the Prandtl centered-fan sector satisfies asymptotic equation but does not meet the needs of hlgher-order governing equations.

Transient Flows in Low Permeability Porous Media with Composite Start-Up Pressure Gradient

A new mathematical model for the transient flow in the composite low permeability is established. It is solved by FEM with different boundary conditions such as infinite, circular closed and constant pressure boundary conditions. The typical curves for transient wellbore pressure have been presented. It is shown that the pressure and pressure derivative curves with composite start-up pressure gradients have different slopes which are depended on the start-up pressure gradients and the mobility radios in different regions. The boundary effects are the same as the normal reservoirs without start-up pressure gradients. The study provides a new tool to analyze the transient pressure test data in the low permeability reservoir.

Coherent enhancement of broadband frequency up-conversion in BBO crystal by shaping femtosecond laser pulses

An optimal feedback control of broadband frequency up-conversion in BBO crystal is experimentally demonstrated by shaping femto-second laser pulses based on genetic algorithm, and the frequency up-conversion efficiency can be enhanced by similar to 16%. SPIDER results show that the optimal laser pulses have shorter pulse-width with the little negative chirp than the original pulse with the little positive chirp. By modulating the fundamental spectral phase with periodic square distribution on SLM-256, the frequency up-conversion can be effectively controlled by the factor of about 17%. The experimental results indicate that the broadband frequency up-conversion efficiency is related to both of second harmonic generation (SHG) and sum frequency generation (SFG), where the former depends on the fundamental pulse intensity, and the latter depends on not only the fundamental pulse intensity but also the fundamental pulse spectral phase. (c) 2006 Elsevier B.V. All rights reserved.

Fast growing mode of stimulated Raman scattering in a pure three-wave process

Stimulated Raman scattering (SRS) of a relativistic laser in plasmas is studied in the framework of the standard equation set of a three-wave process. As far as every wave involved in the process is concerned, its evolution has two aspects: time-dependent amplitude and time-dependent frequency. These two aspects affect each other. Strict analysis and numerical experiment on the full three-wave equation set reveal that a fast growing mode of the instability, which could reach a balance or saturation point during a period far shorter than an estimation based on conventional analysis, could take place in a standard three-wave process without coupling with a fourth wave. This fast growing mode is found to stem from the constraint set by the background density on the amplitude of the driven Langmuir wave. The effect of various parameters on the development of the SRS instability is studied by numerical calculation of the history of the instability in different cases. (c) 2007 American Institute of Physics.