6,147 research outputs found

    Poverty, Food Insecurity and Nutritional Deprivation in Rural China: Implications for Children\u27s Literacy Achievement

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    Globally, food insecurity is a significant contextual aspect of childhood. About 850 million people were undernourished worldwide during the period 2006 to 2008, including 129.6 million people, or 10 percent of the population, in China (FAO 2011:45‐46). Implications of food insecurity for children\u27s schooling in developing country contexts are poorly understood. Analyses of a survey of children from 100 villages in northwest China show that long‐term undernourishment and food insecurity strike the poorest disproportionately, but not exclusively; long‐term undernourishment matters for literacy via early achievement; and, after adjusting for socioeconomic status, long‐term undernourishment, and prior achievement, food insecure children have significantly lower literacy scores

    In-situ Lock-in Thermographic Measurement Of Powder Layer Thermal Diffusivity And Thickness In Laser Powder Bed Fusion

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    The thermal transport properties of the powder layer play a crucial role in the process of laser powder bed fusion (LPBF). This paper introduces an in-situ measurement method utilizing active lock-in infrared thermography (LIT) to determine the thermal diffusivity and thickness of the powder layer. The proposed method exhibits great potential for accurate powder property and thickness measurements and real-time process monitoring. In this lock-in thermographic technique, the LPBF laser beam is directed through an optical diffuser and modulated into a square thermal wave. This thermal wave serves as an active heat source to heat the surface of the powder bed. The surface temperature response is captured using a long-wave infrared (LWIR) camera. A one-dimensional thermal model is employed to provide insights into heat transfer in the frequency domain. The frequency-dependent phase response of temperature is influenced by the effective thermal diffusivity and thickness of the powder layer. This model is validated experimentally first and then utilized to measure the thermal diffusivity of different powder layers created using various particle sizes and wiper spreading speeds. Larger particle size and slower wiper spreading speed are shown to produce higher thermal diffusivity. Finally, the paper shows how this technique can be used to measure the powder layer thickness over printed geometries. This capability enables the detection of deviations in the fused part surface or errors in the wiper through analysis of resulting variations in the powder. These findings highlight the potential of the lock-in thermographic technique for rapid in-situ inspection of the new powder layer in laser powder bed fusion (LPBF) processes

    Tunable Low Density Palladium Nanowire Foams

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    Nanostructured palladium foams offer exciting potential for applications in diverse fields such as catalyst, fuel cell, and particularly hydrogen storage technologies. We have fabricated palladium nanowire foams using a cross-linking and freeze-drying technique. These foams have a tunable density down to 0.1% of the bulk, and a surface area to volume ratio of up to 1,540,000:1. They exhibit highly attractive characteristics for hydrogen storage, in terms of loading capacity, rate of absorption and heat of absorption. The hydrogen absorption/desorption process is hysteretic in nature, accompanied by substantial lattice expansion/contraction as the foam converts between Pd and PdHx.Comment: 17 pages, 4 figure
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