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Selective laser sintering has become one of the most popular additive manufacturing technologies owing to its great capability of fabricating complex structures with reduced or even eliminated need for the support structure. Meanwhile, an average of 50% to 70% of the consumed powder materials is not directly used for part fabrication. To reduce material waste and enhance material usage efficiency, research studies have been conducted to facilitate the recycling and/or reusing of the waste powder in selective laser sintering. In this research, polyamide 12 powders are studied including virgin powder, waste powder, recycled powder, and mixed powder (with a 30% refresh rate) in terms of their microscopic morphology and material properties. In addition, the location of the powder sampled from the build chamber is also studied for its impact on the powder size and shape. Experimental results show that the average particle size does not change much in different samples, but the standard deviation increases in waste powder. Furthermore, the averaged ultimate tensile strength of test specimens fabricated with virgin powder is around 25% higher than specimens made with mixed powder (30% virgin powder and 70% recycled powder), showing a clear mechanical degradation.

Metamaterials have emerged as a group of promising materials with potential applications in a wide range of industries such as aerospace and automobile, owing to their unconventional properties. The state-of-the-art suggests that lattice metamaterials offer lightweight structures while ensuring good mechanical properties, and hollow lattices can be leveraged to achieve ultra-lightweight metamaterials to further broaden the application horizons. In this research, hollow cross-sections are designed for lattice-based metamaterials in order to achieve a high stiffness/strength-to-weight ratio. The Mechanics of Structure Genome method is adopted to perform the beam cross-section analysis, leading to three cross-sections studied including solid, elliptical, and rectangular cross-sections. The designed metamaterials with hollow cross-sections have complex structures and therefore they are fabricated using the Selective Laser Sintering process. The compressive tests suggest that metamaterials with hollow cross-sections have a higher stiffness-to-weight ratio of 25% to 30% in comparison with solid cross-sections. In addition, hollow lattice metamaterials demonstrate better energy absorption capability compared to solid lattices of the same density, which is a critical characteristic to avoid catastrophic mechanical failure. It is observed from the compressive tests that the nodes in the unit cells tend to break first, indicating possible future research to further enhance the strength of hollow lattice metamaterials.

The present study was undertaken with a view to finding out the carps poly-culture technique, pond management and cost analysis in Mohanpur, Rajshahi region of Bangladesh. The study was conducted for a period of four months (October 2010 to February 2011). It provides an overview on the guiding principles, aspects and tasks, and presents the applicable production techniques and patterns of carp polyculture. It is expected that this publication will help identify resources and contribute to the successful planning and realization of fish production by those fish pond owners and operators who need to strengthen and improve their knowledge on the subject. Asian Australas. J. Biosci. Biotechnol. 2017, 2 (1), 100-105