13 research outputs found
Assessment of the stability, sorption, and exchangeability of marine dissolved and colloidal metals
The size partitioning of dissolved trace metals is an important factor for determining reactivity and bioavailability of metals in marine environments. This, alongside the advent of more routine shipboard ultrafiltration procedures, has led to increased attention in determining the colloidal phase of metals such as Fe in seawater. While clean and efficient filtration, prompt acidification, and proper storage have long been tenets of trace metal biogeochemistry, few studies aim to quantify the kinetics of colloidal exchange and metal adsorption to bottle walls during storage and acidification. This study evaluates the effect of storage conditions on colloidal size partitioning, the kinetics of colloid exchange over time, and the timescale of bottle wall adsorption and desorption for dissolved Fe, Cu, Ni, Zn, Cd, Pb, Mn and Co. We report that preservation of dissolved size partitioning is possible only for Fe and only under frozen conditions. All metals except Mn and Cd show regeneration of the colloidal phase following its removal in as short as 14 h, validating the importance of prompt ultrafiltration. Adsorption of metals to bottle walls is a well-known sampling artifact often cited for Fe and assumed to be potentially significant for other metals as well. However, only Fe and Co showed significant proclivity to adsorption onto low density polyethylene bottle walls, sorbing a maximum of 91 and 72% over 40 months, respectively. After 20 weeks of acidification neither Fe nor Co desorbed to their original concentrations, leading to an acidified storage recommendation of 30 weeks prior to analyses following storage of unacidified samples for long periods of time. This study provides empirical recommendations for colloidal and dissolved trace metal methodology while also paving the way for much-needed future methods testing
ExigĂȘncias de lisina digestĂvel para juvenis de tilĂĄpia-do-nilo Digestible lysine requirements of Nile tilapia juveniles
Este estudo foi realizado com o objetivo de determinar a exigĂȘncia de lisina digestĂvel para juvenis de tilĂĄpia-do-nilo. Noventa e seis peixes revertidos sexualmente e com peso vivo inicial de 5,72 ± 0,10 g foram alimentados por 42 dias com quatro raçÔes (29.51% de PB e 3.235 kcal de energia digestĂvel/kg) contendo diferentes nĂveis de L-lisina HCl (0,1; 0,3; 0,5 e 0,7%, correspondendo a raçÔes com 1,04; 1,27; 1,51 e 1,741% de lisina digestĂvel, respectivamente). Os peixes foram distribuĂdos em 16 tanques com capacidade de 1.000 L cada um, em um delineamento inteiramente casualizado, com quatro tratamentos, trĂȘs repetiçÔes e seis peixes por unidade experimental. NĂŁo foi observado efeito dos nĂveis de lisina sobre o Ăndice hepato-somĂĄtico, a gordura visceral, a sobrevivĂȘncia e os teores de ĂĄgua e extrato etĂ©reo na carcaça. A anĂĄlise de Linear Response Plateau do ganho de peso e da conversĂŁo alimentar versus nĂveis de lisina digestĂvel demonstrou estimativa de exigĂȘncia de 1,56 e 1,44% de lisina digestĂvel, respectivamente. Foi observado efeito quadrĂĄtico sobre o rendimento de carcaça, que aumentou atĂ© o nĂvel de 1,61% de lisina digestĂvel. Considerando o desempenho, recomenda-se que dietas para juvenis de tilĂĄpia-do-nilo devem conter 1,44% de lisina digestĂvel (5,23% da proteĂna da dieta).<br>This trial was carried out to determine the digestible lysine requirements of Nile tilapia juveniles. Ninety- six reverted fishes averaging initial weight of 5.72 ± 0.10 g were fed four diets (29.51% of crude protein and 3,235 kcal/kg of digestible energy) containing increasing levels of L-lysine HCl (0.1, 0.3, 0.5, and 0.7%), during 42 days. The following treatments were evaluated: dietary lysine levels of 1.04; 1.27; 1.51 and 1.741%. Fishes were allotted to 1000-L 16 tanks, as a completely randomized design with four treatments, three replicates and eight fishes per experimental unit. No treatment effects on hepatosomatic index, visceral fat, survival rate and water ether extract in the carcass were observed. The Linear Response Plateau analysis of weight gain and feed:gain ratio versus digestible lysine level yielded an estimated digestible lysine requirement of 1.56 and 1.44% for Nile tilapia juveniles, respectively. Quadratic effect of treatments on carcass yield that increased up to 1.61% of digestible lysine was observed. Considering the performance, it is recommended diets containing up to 1.44% of digestible lysine (5.23% of protein) for Nile tilapia juveniles
Use of ideal protein concept for precision formulation of amino acid levels in fish-meal-free diets for juvenile Nile tilapia (Oreochromis niloticus L.)
Farinha de resĂduos da filetagem de tilĂĄpias na alimentação de tilĂĄpia-do-nilo (Oreochromis niloticus) na fase de reversĂŁo sexual
Team attributes and performance of operational service teams: An empirical taxonomy development
Teams have been regarded as an integral element of a number of operations management (OM) strategies and many of their related concepts such as group dynamics and people issues are considered important for knowledge of behavioral operations. In practice, the management of operational service teams is challenging for OM managers because of its potential problems such as unstructured tasks and negative member behavior. In this study, operational service teams' attribute patterns and their associated performance levels were examined using a configuration approach. Based on the data collected from 201 operational service teams in Hong Kong and Macao (China), an empirical taxonomy was developed, comprising team attributes including team use, organizational support, clear goals, collaborative climate, coercive influence and adaptation difficulty. The taxonomy indicated that there were three attribute patterns among the sample teams. The analyzed results indicated that the sample teams of different attribute patterns achieved markedly different levels of team performance. The study contributes to the literature by providing empirical evidence that team attributes and their combined patterns are determinants of operational service teams' performance. It also contributes to practitioners by reporting the current status of operational service team management and offering guidelines on enhancement of team performance.Department of Logistics and Maritime Studie