Nitrogen Flow Effects on Part Bed Surface Temperature during Laser Sintering

The role of nitrogen flow rate was invested as it affects the surface temperature of a polymer laser sintering part bin. A SinterStation 2500® was used for this study. The effect of nitrogen chamber flow rates between 0.5 and 2.5 m3/hr was observed and compared to the results of a computational fluids dynamics model. Increasing convective flow generates a uniform reduction in the surface temperature, but it does not meaningfully reduce surface temperature gradients. The part bin piston was modified to allow down drafting of nitrogen through the part bin. Down drafting, while once considered to be effective in accelerating cooling at the end of builds, did not have a significant effect on the surface temperature profile.Mechanical Engineerin

Thermal Conductivity Measurements of Polyamide 12

An important component in understanding the laser sintering process is knowledge of the thermal properties of the processed material. Thermal conductivity measurements of pure polyamide 12 were conducted based on transient plane source technology using a Hot Disk® TPS500 conductivity measurement device. Polyamide samples were packed to three different densities in nitrogen at steady state. Thermal diffusivity and conductivity were measured from 40°C to 170°C for both fresh powder and previously heated (“recycled”) powder. The fresh powder tests revealed that thermal conductivity increased linearly with temperature while for previously heated powder, more constant and higher thermal conductivity was observed as it formed a powder cake. Tests were also performed on fully dense polyamide 12 to establish a baseline. Polyamide 12 powder had a room-temperature thermal conductivity of approximately 0.1 W/mK which increased with temperature, whereas the bulk laser sintered polyamide 12 room-temperature value was 0.26 W/mK and generally decreased with increasing temperature.Mechanical Engineerin

Do skilled immigrants affect the wage rate of Australian workers?

We hypothesise that skilled immigration increases the wage rate in Australia. Our alternative hypothesis is that skilled immigration decreases the wage rate in Australia. The data used for this research comes from the Australian Bureau of Statistics and Department of Immigration andCitizenship. Based on our analysis, we find that there is positive relationship between high-skilled immigration and employee earnings per hour.We also find that low-skilled immigrants have a negative effect on employee earnings per hour. We believe that low-skilled workers are easily replaced such that low-skilled immigrants are substitutes to Australian low-skilled workers. However, there are some limitations of our research. Notably, our result are restricted to three occupations

A Sinorhizobium meliloti-specific N-acyl homoserine lactone quorum-sensing signal increases nodule numbers in Medicago truncatula independent of autoregulation

N-acyl homoserine lactones (AHLs) act as quorum sensing signals that regulate cell-density dependent behaviors in many gram-negative bacteria, in particular those important for plant-microbe interactions. AHLs can also be recognized by plants, and this may influence their interactions with bacteria. Here we tested whether the exposure to AHLs affects the nodule-forming symbiosis between legume hosts and rhizobia. We treated roots of the model legume, Medicago truncatula, with a range of AHLs either from its specific symbiont, Sinorhizobium meliloti, or from the potential pathogens, Pseudomonas aeruginosa and Agrobacterium vitis. We found increased numbers of nodules formed on root systems treated with the S. meliloti-specific AHL, 3-oxo-C14-homoserine lactone, at a concentration of 1 μM, while the other AHLs did not result in significant changes to nodule numbers. We did not find any evidence for altered nodule invasion by the rhizobia. Quantification of flavonoids that could act as nod gene inducers in S. meliloti did not show any correlation with increased nodule numbers. The effects of AHLs were specific for an increase in nodule numbers, but not lateral root numbers or root length. Increased nodule numbers following 3-oxo-C14-homoserine lactone treatment were under control of autoregulation of nodulation and were still observed in the autoregulation mutant, sunn4 (super numeric nodules4). However, increases in nodule numbers by 3-oxo-C14-homoserine lactone were not found in the ethylene-insensitive sickle mutant. A comparison between M. truncatula with M. sativa (alfalfa) and Trifolium repens (white clover) showed that the observed effects of AHLs on nodule numbers were specific to M. truncatula, despite M. sativa nodulating with the same symbiont. We conclude that plant perception of the S. meliloti-specific 3-oxo-C14-homoserine lactone influences nodule numbers in M. truncatula via an ethylene-dependent, but autoregulation-independent mechanism.Debora F. Veliz-Vallejos was supported by a PhD scholarship from Becas Chile; Ulrike Mathesius was supported by a Future Fellowship (FT100100669) from the Australian Research Council

A Sinorhizobium meliloti-specific N-acyl homoserine lactone quorum-sensing signal increases nodule numbers in Medicago truncatula independent of autoregulation

N-acyl homoserine lactones (AHLs) act as quorum sensing signals that regulate cell-density dependent behaviors in many gram-negative bacteria, in particular those important for plant-microbe interactions. AHLs can also be recognized by plants, and this may influence their interactions with bacteria. Here we tested whether the exposure to AHLs affects the nodule-forming symbiosis between legume hosts and rhizobia. We treated roots of the model legume, Medicago truncatula, with a range of AHLs either from its specific symbiont, Sinorhizobium meliloti, or from the potential pathogens, Pseudomonas aeruginosa and Agrobacterium vitis. We found increased numbers of nodules formed on root systems treated with the S. meliloti-specific AHL, 3-oxo-C14-homoserine lactone, at a concentration of 1 μM, while the other AHLs did not result in significant changes to nodule numbers. We did not find any evidence for altered nodule invasion by the rhizobia. Quantification of flavonoids that could act as nod gene inducers in S. meliloti did not show any correlation with increased nodule numbers. The effects of AHLs were specific for an increase in nodule numbers, but not lateral root numbers or root length. Increased nodule numbers following 3-oxo-C14-homoserine lactone treatment were under control of autoregulation of nodulation and were still observed in the autoregulation mutant, sunn4 (super numeric nodules4). However, increases in nodule numbers by 3-oxo-C14-homoserine lactone were not found in the ethylene-insensitive sickle mutant. A comparison between M. truncatula with M. sativa (alfalfa) and Trifolium repens (white clover) showed that the observed effects of AHLs on nodule numbers were specific to M. truncatula, despite M. sativa nodulating with the same symbiont. We conclude that plant perception of the S. meliloti-specific 3-oxo-C14-homoserine lactone influences nodule numbers in M. truncatula via an ethylene-dependent, but autoregulation-independent mechanism

Exploring the effect of stakeholder relationship quality on technological innovation in off-site construction: the mediating role of the knowledge sharing

Off-site construction (OSC) is generally propagated as a sustainable and green construction method in the global construction industry. Over the past few decades, OSC has become famous worldwide for its numerous benefits. Technological innovation can speed up the development of OSC and has attracted a lot of attention from stakeholders who are promoting technological innovation by seeking collaborations. OSC is different from traditional manufacturing, and little effort has been spent on how the stakeholder relationship quality affects technological innovation. This study therefore makes efforts to explore the mechanism of how stakeholder relationship quality influences the OSC technological innovation and to explain the stakeholder relationship quality in terms of communication, trust, and commitment. This paper constructs a multidimensional hypothesis model consisting of five concepts: communication, trust, commitment, knowledge sharing, and technological innovation. A valid sample of 125 was collected through a questionnaire survey in mainland China. The sample data were dealt with and analyzed using partial least squares structural equation modeling (PLSSEM) to validate the proposed hypothesis model. The results reveal that trust and knowledge sharing affect technological innovation directly. Communication and commitment are not identified to have statistically significant influences on technological innovation in OSC. Communication, trust, and commitment positively contribute to knowledge sharing. Last, knowledge sharing completely and partially mediates between relationship quality and technological innovation. This study explores the impact of stakeholder relationship quality on OSC technological innovation and verifies the mediating role of knowledge sharing. These findings provide valuable theoretical guidance for OSC technological innovation and practical insights for stakeholders to promote technological innovation by enhancing relationship quality and knowledge sharing. First published online 13 December 202

High-mobility graphene on liquid p-block elements by ultra-low-loss CVD growth

The high-quality and low-cost of the graphene preparation method decide whether graphene is put into the applications finally. Enormous efforts have been devoted to understand and optimize the CVD process of graphene over various d-block transition metals (e.g. Cu, Ni and Pt). Here we report the growth of uniform high-quality single-layer, single-crystalline graphene flakes and their continuous films over p-block elements (e.g. Ga) liquid films using ambient-pressure chemical vapor deposition. The graphene shows high crystalline quality with electron mobility reaching levels as high as 7400 cm2 V−1s−1 under ambient conditions. Our employed growth strategy is ultra-low-loss. Only trace amounts of Ga are consumed in the production and transfer of the graphene and expensive film deposition or vacuum systems are not needed. We believe that our research will open up new territory in the field of graphene growth and thus promote its practical application

Analysis of differential colostrum metabolism in high and low yielding Guanzhong dairy goats

In order to identify and analyze the metabolites of colostrum differences between high yielding and low yielding Guanzhong dairy goats from metabolomics point of view. Six high-yielding (milk yield (3.68 ± 0.57) kg/d) and six low-yielding (milk yield (1.17 ± 0.64) kg/d) Guanzhong dairy goats of similar age, litter size, body weight, and days of lactation (2nd day postpartum) were selected. The colostrum samples were examined by liquid chromatography-tandem mass spectrometry (LC-MS/MS), and the results were combined with orthogonal partial least squares discriminant analysis (OPLS-DA) and Student’s t-test. The metabolites were screened for differential metabolites based on the principle of variable importance in the projection (VIP) > 1, P < 0.05, and the differential metabolites were subjected to cluster analysis, significant difference screening, and enrichment of Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. The results showed that 95 differential metabolites were screened from the colostrum of Guanzhong dairy goats in the two groups, and the clustering heatmap showed that 9 of the top 50 differential metabolites were the most abundant in relative terms. The metabolites with significantly increased content in the colostrum of Guanzhong dairy goats in the high-yield group were D-alanine-D-serine, α-lactose, isoflavoprotein 2”-(6’-p-coumaroylglucoside), D-maltose, pravastatin, and diketoglucuronic acid, whereas the differential metabolites with relatively decreased content were taurocholate, L-carnitine, and thiamphenicol A. KEGG pathways enrichment analysis identified 8 potential metabolic pathways The results of this experiment provide a theoretical basis for the subsequent analysis of the mechanism of milk production traits in dairy livestock and the selection and breeding of high-yielding dairy goats