Effect of structure on the glass transition temperatures of linear and crosslinked poly(isobornylacrylate-co-isobutylacrylate)

A series of linear acrylic copolymers based on Isobornyl acrylate (IBOA) and isobutyl acrylate (IsoBA) were elaborated by radical photopolymerization. In addition, several photochemically crosslinked poly(IBOA-co-IsoBA) were prepared by introducing small amounts of 1,6-hexanedioldiacrylate as crosslinking agent. The evolution of the glass transition temperature was determined experimentally by differential scanning calorimetry as a function of composition for both linear and crosslinked poly(IBOA-co-IsoBA), yielding T_g values ranging from (~249) to (~315 K). Theoretical modeling was performed applying Fox, Gordon-Taylor and Couchman-Karasz models by simple calculations using experimental data, leading to only fair agreement between theoretical and experimental values, or by applying fitting procedures involving one or two adjustable parameters. Likewise, the Kwei model, known to take into account hydrogen bonding interactions between monomers, could not describe well the evolution of T_g, indicating the existence of other factors influencing T_g. Finally, a thermodynamic approach based on entropy considerations allowed to attribute an explanation of the evolution of T_g.     

Anelastic Stokes Eigenmodes in Infinite Channel

The anelastic Stokes eigenmodes are computed for a fluid confined, in presence of gravity, between two horizontally infinite plates. These eigenmodes are described by one horizontal wave number k. The eigenvalues λ(k ²) are proved to be all negative. They depend monotonically upon k, behaving like k ² for very large k. Two particular values of k are considered, i.e., k=2?π and k=0, and the stratification parameter of the equilibrium state is taken between 0 (incompressible approximation) and 10 (upper limit of the anelastic configuration). The k=2?π eigenvalue problem is solved numerically while the k=0 is solved both numerically and analytically. Two physical configurations are analyzed, one with no-slip boundary conditions imposed on both horizontal walls, and one with no-stress, while imposing no flow through these boundaries in both cases. The main results are: (i) the smaller the stratification, the larger the decay rate, (ii) the eigenmodes are localized in the lower part of the channel, their vertical extension increasing with the eigenmode spatial frequency, (iii) the Neumann eigenmode decay rates are smaller than their Dirichlet counterparts, except for k=0, where it is just the reverse, (iv) a general trend seems to emerge from the present study, regarding the way the numerical eigenvalues of an elliptic operator compare with the analytical ones, viz., the numerical spectrum overestimates (in absolute value) the analytical spectrum, slightly in the low frequency part of the spectrum and more and more strongly in the upper part.     

Effect of protein hydrolysates from sardinelle (Sardinella aurita) on the oxidative status and blood lipid profile of cholesterol-fed rats

This study was designed to test the hypolipidemic properties and antioxidative activities of sardinelle (Sardinella aurita) protein hydrolysates (SPHs) obtained by treatment with crude enzyme preparations from Bacillus pumilus A1(SPHA1), Bacillus mojavensis A21(SPHA21) and crude enzyme extract from sardinelle viscera (SPHEE).Wistar rats were fed during 7 weeks a standard laboratory diet, a cholesterol-enriched diet (1%) or a cholesterol SPH-enriched diet. The hypercholesterolemic diet induced the elevation of total cholesterol (TC), triglycerides (TG), and low-density lipoprotein cholesterol (LDL-C). Supplementing cholesterol-enriched diet with SPHs or whole sardinelle protein (WSP) at a concentration of 5% (w/w) increased the serum level of high-density lipoprotein cholesterol (HDL-C) and HDL-C/TC ratio and decreased the serum levels of TC, TG, LDL-C and LDL-C/HDL-C ratio significantly.The thiobarbituric acid-reactive substances (TBARS) level, as an indicator of lipid peroxidation, and the activity of superoxide dismutase (SOD), glutathione peroxidase (GPx) and catalase (CAT) were examined. The hepatic antioxidant enzymes activities were significantly decreased and the malondialdehyde (MDA) level was increased in rats fed a cholesterol-enriched diet compared to those fed a standard diet. The treatment of hypercholesterolemic (HCD) diet rats with SPHs reduced the MDA concentration and increased the antioxidant enzyme activities.These results suggested that the hypolipidemic effect of SPHs might be due to their abilities to lower serum TC, TG, and LDL-C levels as well as to their antioxidant activities preventing the lipid peroxidation process.     

Correlative metabolite profiling approach to understand antioxidant and antimicrobial activities from citrus essential oils

The objective of this study was to investigate the chemical composition of the essential oils from citrus species, as well as their antioxidant and antimicrobial activities. By gas chromatography-mass spectrometry, we identified thirty-seven metabolites and a range of unique compounds, contributing to the discrimination of the species. Different biological potentialities were detected depending on the species supported the significant effect of the genetic factor. C. aurantium and C. limon exhibited the highest antioxidant activities which make them a potential source of natural preservative. C. limon exhibited the highest antibacterial activities and C. reticulata the highest antifungal activities. Essential oils extracted from these agro-wastes could serve as natural food preservatives to prevent food pathogens and then extending the shelf life. A set of potential metabolites could be implicated in the observed biological activity, underlying that the antimicrobial activity is a complex trait.     

Alginate grafted with poly(ε‐caprolactone): effect of enzymatic degradation on physicochemical properties

The paper discusses the enzymatic behaviour of a series of copolymers composed of alginate grafted with poly(ε‐caprolactone) (PCL) of various lengths and degrees of substitution. The study is focused on viscosity measurements and pyrene probe fluorescence with or without two enzymes: alginate lyase, which breaks the alginate backbone; and esterase, which breaks PCL pendent groups. Alginate lyase is inactive at pH = 3.8 and degrades quickly all copolymers at pH = 6.3. The degradation is not complete and is slowed down by the presence of PCL. Esterase degrades only copolymers with long pendent PCL groups. It has no effect on copolymers when PCL has a length of 530 g mol^?1. These systems are good candidates for controlled release of drugs using an enzymatic method. Copyright © 2012 Society of Chemical Industry     

钢-混凝土粘结预测的人工神经网络模型

提出人工神经网络模型来模拟传统的带肋钢筋和混凝土之间的粘结性能,目的是预测钢筋从混凝土混合物中拔出的极限荷载(第一神经网络模型)或抗压强度(第二神经网络)以及根据RILEM试验设计的不同钢筋直径的拔出极限荷载。采用112个带肋钢筋(直径为10mm、12mm)以及三种不同混凝土配合比的拔出试验结果数据库,对神经网络模型进行训练。根据反向传播算法,进行多层感知器训练。第一个模型(ANN-6)有6个输入:钢筋直径、水灰比、砂石比、级配、水泥种类和混凝土龄期。第二个模型(ANN-2)有2个输入:钢筋直径、混凝土抗压强度,两个模型的输出均为极限拔出荷载。研究结果显示:所采用的模型预测精度高、误差低、具有鲁棒性。从鲁棒性方面,第一个模型(ANN-6)比第二个模型(ANN-2)更精确。将混凝土的成分作为输入参数,而不是混凝土的强度,对于带肋钢筋-混凝土界面的局部现象更具代表性。     

SAFT-VNDN: A Socially-Aware Forwarding Technique in Vehicular Named Data Networking

Vehicular Social Networks (VSNs) is the bridge of social networks and Vehicular Ad-Hoc Networks (VANETs). VSNs are promising as they allow the exchange of various types of contents in large-scale through Vehicle-to-Vehicle (V2V) and Vehicle-to-Infrastructure (V2I) communication protocols. Vehicular Named Data Networking (VNDN) is an auspicious communication paradigm for the challenging VSN environment since it can optimize content dissemination by decoupling contents from their physical locations. However, content dissemination and caching represent crucial challenges in VSNs due to short link lifetime and intermittent connectivity caused by vehicles’ high mobility. Our aim with this paper is to improve content delivery and cache hit ratio, as well as decrease the transmission delay between end-users. In this regard, we propose a novel hybrid VNDN-VSN forwarding technique based on social communities, which allows requester vehicles to easily find the most suitable forwarder or producer among the community members in their neighborhood area. Furthermore, we introduce an effective caching mechanism by dividing the content store into two parts, one for community private contents and the second one for public contents. Simulation results show that our proposed forwarding technique can achieve a favorable performance compared with traditional VNDN, in terms of data delivery ratio, average data delivery delay, and cache hit ratio.