Effects of Rain Events on Carbon Fluxes from Biological Soil Crusts

In dry ecosystems, biological soil crusts (BSCs) have been suggested as one of the factors responsible for the large rate of annual CO2 net uptake (Xie et al. 2009). However, most studies carried out on carbon (C) fluxes in arid and semi-arid ecosystems, such as soil respiration, have neglected the carbon fluxes from BSCs. Although BSCs are a vital component of the dry-land soil C cycle, few studies have parameterized the conditions required for photosynthesis in BSCs or determined BSCs respiration (Elbert et al. 2009, Castillo-Monroy et al. 2011). Precipitation in dry land is dominated by small events (Lauenroth and Bradford 2009). Even the smallest events will influence the carbon fluxes of BSCs, while intermediate pulses might wet the subsurface biotic community, and typically only larger events are used by plants for carbon gain or growth of roots or shoots (Belnap et al. 2005). As BSCs dry quickly and are hence very responsive to moisture pulses, the pulsed nature of precipitation can lead to highly variable carbon fluxes from BSCs (Bowling et al. 2011). Therefore, it is very important to study the effect of rain events upon carbon fluxes through BSCs in the dry ecosystem

Movement characteristic of a circuit breaker with repulsion force compensated contact system

This article proposes a new structure of contact system to improve short-time withstand capacity of direct current circuit breaker. With this new contact system, the electrodynamic repulsion force is compensated. The principle of compensation is illustrated at the beginning. Then the electrodynamic force of the contact system is quantified by analyzing the Lorentz force in conductive loop and the Holm force between contacts. The factors and their influences on electrodynamic force are also investigated. Subsequently, based on multibody dynamics, the movement characteristic model is established. The opening and closing characteristics of breaker and the dynamic stress distribution of closing putters are investigated. The results are verified by experiments. It is indicated that this contact system can improve the short-time withstand capacity. The research could provide theoretical references to large-capacity medium-voltage air direct current circuit breaker development

Numerical simulation of side intake flow of a gas turbine

[Objectives] This paper studies the influence of wind direction on the stability,evenness and loss of flow resistance of the side intake flow of a gas turbine.[Methods] CFX is applied to make numerical simulation of the intake flow of the gas turbine. Through setting of the intake angle and comparison of the flow line distribution of the intake system under different intake status,the total pressure distribution of the fore intake louver,the side intake louver and the outlet of the intake system,and the cross-sectional velocity distribution of the fore and side intake filters,the intake evenness of the gas turbine with intake flow in different directions is studied.[Results] It is shown that,the mixing intensity of fore and side intake air varies with the intake angle. Thanks to the intake system,the unevenness of air flow due to difference between fore and side intake angles is greatly improved after the air flows through the intake pressure stabilizing chamber,making the downstream airflow more even.[Conclusions] The findings are meaningful for guiding the design of the side intake system of the gas turbine

Effect of Annealing on Structural and Magnetic Properties of a Thick (Ga,Mn)As Layer

We investigate effects of annealing on magnetic properties of a thick (Ga,Mn)As layer, and find a dramatic increase of the Curie temperature from 65 to 115 K by postgrowth annealing for a 500-nm (Ga,Mn)As layer. Auger electron spectroscopy measurements suggest that the increase of the Curie temperature is mainly due to diffusion of Mn interstitial to the free surface. The double-crystal x-ray diffraction patterns show that the lattice constant of (Ga,Mn)As decreases with increasing annealing temperature. As a result, the annealing induced reduction of the lattice constant is mainly attributed to removal of Mn interstitial

A new model for Thomson-type actuator including the pressure buffer

The motion characteristics and flow field variation of Thomson-type actuator have been investigated in this article, in which a two-dimensional axisymmetric cylindrical coordinate model is constructed and described by a set of multi-physical equations reflecting the flow field, transient electromagnetic field, electric circuit, and mechanical motion. The motion performance of the actuator and the pressure drag caused by the high-speed movement of metal plate are analyzed under different opening speeds. It shows that the pressure drag has a strong buffer effect on the actuator. The influence of the laminar and standard k − ε models on the pressure distribution, velocity distribution, and motion characteristics is focused on. In comparison with the laminar model, the pressure drag of the turbulence model is much higher than the laminar model and is more beneficial for the buffer design of the mechanism