烤烟叶片发育过程中氨基酸含量变化的研究

对烤烟不同叶片发育过程中总氨基酸及游离氨基酸含量的变化进行了研究。结果表明,随着叶龄的增长,烟叶中总氨基酸含量下降,通过相关分析表明,叶龄与总氨基酸含量呈显著的负相关,其相关系数分别为-0.9900(下)、-0.9895(中)、-0.9600(上);至烟叶成熟时,总氨基酸含量降至最低,烤后有所增加。随叶龄增长,烟叶中组成蛋白质的大多数氨基酸组分是降低的,尤以天冬氨酸和谷氨酸降幅最大,而色氨酸、胱氨酸变化很小。分析结果表明,烟叶中游离氨基酸总量随叶龄增长变化较为复杂,但总的变化趋势是:幼叶含量高,进入成熟期其含量明显下降。      

Quantification of heterocyclic amines from thermally processed meats selected from a small-scale population-based study

Heterocyclic amines (HAs) are potent mutagens that form at high temperatures in cooked, protein-rich food. Due to their frequent intake, these compounds are considered a risk factor for human cancer. Cooking conditions and eating habits strongly influence the level of HA exposure. Thus, it is difficult to assess the intake of HAs in a large population. Food-frequency questionnaires (FFQs), designed to provide data on parameters that affect HA formation, were used to survey a small population (459 persons) from Barcelona (NE Spain). Subsequently, the most-consumed food items named were cooked according to the preferences of the population surveyed and analyzed for HAs using SPE and LC-MS/MS. In the population studied, the estimated intake via consumption of 13 meat dishes was 285.6 ng of mutagenic HAs per capita and day. PhIP (2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine) was the HA to which the population was most exposed, mainly from fried chicken and griddled beef. When the co-mutagens norharman and harman are included, the mean daily intake of HAs rises to 475.6 ng per capita and day. A novel putative DMIP regioisomer was detected in the cooked meats, which was analyzed in the present study by multistage MS.     

Conservation Properties of Unstructured Finite-Volume Mesh Schemes for the Navier-Stokes Equations

The Navier-Stokes equations describe fluid flow by conserving mass and momentum. There are two main mesh discretizations for the computation of these equations, the collocated and staggered schemes. Collocated schemes locate the velocity field at the same grid points as the pressure one, while staggered discretizations locate variables at different points within the mesh. One of the most important characteristic of the discretization schemes, aside from accuracy, is their capacity to discretely conserve kinetic energy, specially when solving turbulent flow. Hence, this work analyzes the accuracy and conservation properties of two particular collocated and staggered schemes by solving various problems.     

海上移动式钻井平台的强度分析与补强设计

通过对某海上移动式钻井平台进行的有限元法强度分析，找到了平台发生局部损坏的原因，由分析结果发现，在极端工况条件下，对该平台悬臂梁的改造导致弯矩剧增，使局部应力超过许用应力而造成损坏。通过补强设计，可以使其完全满足有关安全作业的要求，实验结果与计算结果吻合良好。     

Materials with Giant Mechanocaloric Effects: Cooling by Strength

The search for materials with large caloric effects has become a major challenge in material science due to their potential in developing near room‐temperature solid‐state cooling devices, which are both efficient and clean, and that can successfully replace present refrigeration technologies. There are three main families of caloric materials: magnetocaloric, electrocaloric, and mechanocaloric. While magnetocaloric and electrocaloric materials have been studied intensively in the last few decades, mechanocaloric materials are only very recently receiving a great deal of attention. The mechanocaloric effect refers to the reversible thermal response of a solid when subjected to an external mechanical field, and encompasses both the elastocaloric effect, corresponding to a uniaxial force, and the barocaloric effect, which corresponds to the response to hydrostatic pressure. Here, the state of the art in giant mechanocaloric effects is reviewed and a critical analysis of the thermodynamic quantities that characterize the major families of barocaloric and elastocaloric materials is provided. Finally perspectives for further development in this area are given.     

A Taxonomy of Recommender Agents on the Internet

Recently, Artificial Intelligence techniques have proved useful inhelping users to handle the large amount of information on the Internet.The idea of personalized search engines, intelligent software agents,and recommender systems has been widely accepted among users who requireassistance in searching, sorting, classifying, filtering and sharingthis vast quantity of information. In this paper, we present astate-of-the-art taxonomy of intelligent recommender agents on theInternet. We have analyzed 37 different systems and their references andhave sorted them into a list of 8 basic dimensions. These dimensions arethen used to establish a taxonomy under which the systems analyzed areclassified. Finally, we conclude this paper with a cross-dimensionalanalysis with the aim of providing a starting point for researchers toconstruct their own recommender system.     

Bibliometric Analysis of Physics in Catalonia: Towards Quality Consolidation?

This paper studies the main bibliometric figures in order to analyse the "states of the art" and the evolution of research in physics in Catalonia (Spain) between 1981 and 1998 via the National Citation Report (NCR) for Catalonia elaborated by ISI (Institute for Scientific Information). The main indicators and parameters used are: bibliometric size, rate of citation, citedness of papers, concentration of scientific categories, journals and types of paper, index of immediacy, international collaboration, and papers and citation distribution by research centres and universities.     

Preservation of the endogenous antioxidant system of fish muscle by grape polyphenols during frozen storage

The capacity of a phenolic extract, OW, obtained from grape (Vitis vinifera) by-products, and of a purified fraction of procyanidins from OW, fraction IV, for preservation of endogenous antioxidants of fatty fish was investigated during frozen storage. They were used in muscle concentrations of 0.01% (w/w). Grape polyphenols were compared with propyl gallate, a synthetic antioxidant. The exogenous compounds were added to minced mackerel (Scomber scombrus) muscle and horse mackerel (Trauchurus trauchurus) fillets, before freezing at –10 °C. The results demonstrated that grape polyphenols and propyl gallate inhibit the depletion of endogenous -tocopherol, ubiquinone-10 and total glutathione. Grape polyphenols and propyl gallate showed similar efficiency for preservation of ubiquinone, in both minced and filleted muscle, and total glutathione, in minced muscle. Total glutathione in the fillets was better maintained by propyl gallate than grape polyphenols. The endogenous antioxidant more efficiently preserved by grape polyphenols and propyl gallate was -tocopherol. Its loss elapsed faster in the order control> OW>fraction IV>propyl gallate. The depletion of -tocopherol was highly correlated with the evolution of lipid oxidation. The development of lipid oxidation was repressed, while the concentration of -tocopherol was not reduced up to critical levels.