Topic
Urea
About: Urea is a research topic. Over the lifetime, 21394 publications have been published within this topic receiving 382444 citations. The topic is also known as: carbamide & carbonic acid diamide.
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TL;DR: In this article, the results revealed that pH played a crucial role in the Mg-Al hydrotalcite precipitation by controlling [urea]/[NO] molar ratio in reaction solution at 378 K.
Abstract: Layered double hydroxides based on the structure (Mg6Al2(OH)16CO3·4H2O) were synthesized by urea hydrolysis method and characterized by XRD, FTIR, SEM, and EDS. The results revealed that pH played a crucial role in the Mg-Al hydrotalcite precipitation by controlling [urea]/[NO] molar ratio in reaction solution at 378 K and the optimized [urea]/[NO] molar ratio was 4.0. The sample calcined at 773 K was used as a solid catalyst for biodiesel synthesis. The catalyst was found to have a high catalytic activity in transesterification of rape oil to methanol with about 94% oil conversion at 338 K for 3 h. The water content of the oil could be kept below 2.0 wt % and free fatty acid content of the oil could be kept below 3.0 mg KOH·g[oil]−1 in order to get the best conversion. So, the solid catalyst was more tolerant to free fatty acid and water in rape oil than homogeneous basic-catalysts. Moreover, the catalyst could be reused, but catalytic activity decreased on reuse of the catalyst although it remained highly active for the five uses. © 2009 American Institute of Chemical Engineers AIChE J, 2009
98 citations
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TL;DR: Methionine was shown to be the first limiting essential amino acid when non specific amino nitrogen needs were supplied by glutamic acid and may provide an index of amino acid status in the growing lamb.
Abstract: The qualitative amino acid adequacy of ruminally synthesized protein for growing lambs was evaluated by nitrogen retention responses to abomasal infusions of amino acids. The experimental animals were fed a controlled level of semipurified diet containing urea as the sole nitrogen source. Methionine alone con sistently increased nitrogen retention above isonitrogenous urea-infused controls. Lysine produced a positive nitrogen retention response only after supplemental methionine was provided. Threonine increased nitrogen retention only when infused concurrently with methionine and lysine. The data suggested that the limiting order of essential amino acids for growing lambs fed urea as the sole nitrogen source was: 1) methio nine, 2) lysine and 3) threonine. An abomasal supplement of the combination of methionine, lysine and threonine increased nitrogen retention 60% above the urea infusion control values. Tryptophan, histidine or leucine did not significantly in fluence nitrogen retention when infused with methionine, lysine and threonine. Methionine was also shown to be the first limiting essential amino acid when non specific amino nitrogen needs were supplied by glutamic acid. Plasma amino acid patterns appeared responsive to infusions and may provide an index of amino acid status in the growing lamb.
98 citations
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TL;DR: Depending on the concentrations used, ammonia exposure may enhance subsequent fish appetite and growth rate and have a similar effect on growth performances as restricting feeding level and no detrimental effect on the metabolic capacity of the fish was recorded.
98 citations
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98 citations
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TL;DR: It appears that the reate of endogenous catabolism of urea depends mainly on the activity of the gut flora which may be affected by dietary intake and clinical status of the subject.
98 citations