Evaluation of antioxidants for cod liver oil by chemiluminescence and the rancimat method

Commercial blends of natural antioxidants,viz., tocopherol concentrates, rosemary extracts, sage extracts, and lecithins, were tested for their ability to stabilize cod liver oil. The antioxidants were tested by using the Rancimat apparatus at 80°C and by a method based on hypochlorite-activated chemiluminescence analysis of samples stored at 35°C for 24 h in light. In addition, a stability study at 5°C in the dark for 8 wk, under conditions realistic for normal consumption of cod liver oil was carried out. A low correlation (r=0.339) was found between Rancimat induction times and chemiluminescence data for the sixteen antioxidant systems tested, probably due to temperature differences, and different ways of detecting oxidation products. Based on Rancimat induction times, δ-tocopherol-rich antioxidants and lecithin had the best stabilizing effect. However, based on the chemiluminescence method, the tocopherols acted as prooxidants, while tocopherols with lecithin increased the stability. Both Racimat and chemiluminescence data showed stabilizing effects with rosemary and sage extracts, but no synergistic effect between the herbal extracts and lecithin or tocopherol was observed. Analyses of oil aged at 5°C for 8 wk showed the highest stability for cod liver oil containing rose-mary extracts. The tocopherol mixtures showed only a minor effect on the stability. Ranking of antioxidants varied considerably depending on the method used, and increasing the temperature seemed to decrease the usefulness of the method. Antioxidant evaluation has to be done by using as many evaluation methods as possible under conditions relevant for normal storage and use.     

Comparison of near‐infrared emission spectroscopy and the Rancimat method for the determination of oxidative stability

This work presents a comparison between a new method for the determination of the oxidative stability of edible oils at frying temperatures, based on near‐infrared emission spectroscopy (NIRES), and the Rancimat method at 110 °C. In the NIRES‐based method, the induction time (IT) is determined by means of the variation of the emission band at 2900 nm during heating at 160 °C. The comparison between the IT values obtained with the two methods for 12 samples of edible oils shows some correlation for samples of the same type once there is an agreement on the sequence of highest to lowest IT values between the methods, but a poor correlation considering all samples (correlation coefficient of 0.78). This lack of correlation demonstrates that the results obtained with the Rancimat method cannot be used as an indication of the oxidative stability, or the resistance to degradation, of edible oils at frying temperatures. The difference in the heating temperatures used in the two methods leads to 20–36 times higher IT values for the Rancimat method in relation to the NIRES‐based method, but with similar repeatabilities (2.0 and 2.8%, respectively).     

Comparison of four analytical methods for the determination of peroxide value in oxidized soybean oils

Previous work in our laboratory demonstrated that soybean oil oxidation, expressed as PV, can be determined using NIR transmission spectroscopy as an alternative to the official AOCS iodometric titration method. In the present study, a comparison of four peroxide analytical methods was conducted using oxidized soybean oil. The methods included the official AOCS iodometric titration, the newly developed NIR method, the PeroxySafe^™ kit, and a ferrous xylenol orange (FOX) method, the latter two being colorimetric methods based on oxidation of iron. Five different commercially available soybean oils were exposed to fluorescent light to obtain PV levels of 0–20 meq/kg; periodic sampling was done to ensure having representative samples throughout the designated range. A total of 46 oil samples were analyzed. Statistical analysis of the data showed that the correlation coefficient (r) and standard deviation of differences (SDD) between the standard titration and NIR methods were r=0.991, SDD=0.72 meq/kg; between titration and the PeroxySafe^™ kit were r=0.993, SDD=0.56 meq/kg; and between the standard titration and FOX method were r=0.975, SDD=2.3 meq/kg. The high correlations between the titration, NIR, and PeroxySafe^™ kit data indicated that these methods were equivalent.     

Comparison of finite volume and lattice Boltzmann methods for multicomponent flow simulations

In pseudopotential lattice Boltzmann (LB) models for simulating multicomponent flows, interaction forces between the components of a mixture lead to phase separation and interfacial tension. At the macroscopic scale, such LB models solve an advection-diffusion equation for each component and the Navier-Stokes equations for the fluid mixture. In this paper, the computational efficiency of the LB method is compared with a finite volume (FV) solver for the same macroscopic-scale equations for a binary system in a two dimensional domain. The FV implementation replicates the phase separation of the LB model. Differences in the interfacial tension are due to truncation of the Taylor series expansion of the LB interaction force in the FV version. While the computations required to update the domain for each timestep can be completed faster with the FV approach, a smaller timestep is required to achieve stability, which negates the improvement in processing speed. The FV implementation, however, allows independent variation of model parameters, which is not possible in LB. For example, the viscosity can be changed without affecting interfacial tension or the extent of phase separation. Furthermore, it is possible to obtain low interfacial tensions without suppressing phase separation with the FV formulation. The significance of changing the diffusion rate of components on the deformation of a droplet in shear is also demonstrated. For three-dimensional simulations, the finite volume approach is expected to be faster than LB and would benefit from the demonstrated flexibility in specifying model parameters.     

Study of fire retardancy and thermal stability of vinyl acetate-2-ethylhexyl acrylate copolymer by blending with amino resin in aqueous medium

Trimethoxymethyl melamine (TMMM) and hexamethoxymethyl melamine (HMMM) were blended with the widely used acrylic medium, the copolymer of vinyl acetate and 2-ethylhexyl acrylate (VAc-EHA), for preparing water-based blends having improved fire retardancy. The weight fraction of the VAc-EHA copolymer was varied from 40 to 95%, at the pH value of 7 and a solid content of 50% was kept in all cases. The limiting oxygen index (LOI) and char yield of the blends were evaluated and the surface morphology of TMMM, HMMM, and the VAc-EHA copolymer at room temperature and at 110, 340, and 550°C was also studied to explain the improvement in the fire-retardancy behavior of the blends. The LOI and char yield of the VAc-EHA copolymer was found to improve substantially on incorporation of both TMMM and HMMM. But due to the limited stability of TMMM in aqueous medium, HMMM is more suitable for blending with VAc-EHA, to give a water-based coating having good fire-retardancy properties. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 985–990, 1997     

Comparison of finite difference and control volume methods for solving differential equations

Comparisons are made between the finite difference method (FDM) and the control volume formulation (CVF). An analysis of truncation errors for the two methods is presented. Some rules-of-thumb related to the accuracy of the methods are included. It is shown that the truncation error is the same for both methods when the boundary conditions are of the Dirichlet type, the system equations are linear and represented in Cartesian coordinates. A technique to analyze the accuracy of the methods is presented. Two examples representing different physical situations are solved using the methods. The FDM failed to conserve mass for a small number of nodes when both boundary conditions include a derivative term (i.e. either a Robin or Neumann type boundary condition) whereas the CVF method did conserve mass for these cases. The FDM is more accurate than the CVF for problems with interfaces between adjacent regions. The CVF is (ΔX) order of accuracy for a Neumann type boundary condition whereas the FDM is (ΔX)² order.     

Performance of symmetric polygonal fins with and without tip loss — A comparison of different methods of prediction

No analytical solution exists for estimating the efficiency of symmetric polygonal fins (SPFs) circumscribing circular tubes. Performance of such fins is conventionally determined from either of the two approximate techniques, namely, the equivalent annulus method and the sector method. The present work aims to judge the relative merits and applicability of these two methods critically. To this end, the results obtained from the approximate techniques have compared with those obtained from a semi‐analytical technique. It has been noted that, with the increase of the tip heat loss, the accuracy of prediction from any of the approximate methods decreases. For the sector method, a modification has been suggested. The prediction from the modified version of the sector method is always more accurate than that from the equivalent annulus method. It has been further illustrated that though the approximate techniques can be employed for the prediction of efficiency, they cannot be used to predict the tip temperatures accurately.     

中欧钢结构规范受弯构件整体稳定性计算方法比较

结合我国钢结构设计规范(GB 50017—2003)及欧洲钢结构设计规范(EN1993-1-1:2005),从计算公式、临界弯距和整体稳定系数三方面,对两本规范的受弯构件整体稳定性计算方法进行了分析对比,并通过计算实例得到了两本规范之间的一些差异。     

Comparison of different methods for lignin determination as a basis for calibration of near-infrared reflectance spectroscopy and implications of lignoproteins

Three commonly employed methods for lignin determination, i.e., the thioglycolic acid (TGA), the acetylbromide (AB), and the acid detergent fiber (ADF) method, were compared using leaves and xylem tissue from five species (Nicotiana tabacum, Populus x canescens, Fagus sylvatica. Quercus robur, and Picea abies). In each case, cell walls were isolated before lignin determination. Each of the three methods estimated a different lignin concentration in a given tissue, except for spruce wood. The lignin concentration determined with the AB method was strongly dependent on whether or not the cell walls were subjected to alkaline hydrolysis to remove covalently bound aromatic nonligneous components before lignin determination. Lignin concentrations determined in hydrolyzed cell walls of different tissues and species by the AB method showed a good correlation with those obtained by the TGA method and, thus, were convertible. In contrast, gravimetrically estimated ADF lignins did not or only moderately correlate with lignins measured with methods based on the UV absorbance of the solubilized lignin degradation products. Leaves of a given species generally contained higher ADF-lignin concentrations than the corresponding stem tissue. Both ADF and TGA lignin data of beech were used to calibrate near-infrared reflectance spectra (NIRS) for lignin prediction. Both NIRS calibration procedures gave good statistical fits with correlation coefficients close to 1, indicating that TGA and ADF lignin concentrations of beech can be estimated by NIRS with high accuracy. However, the two calibrations were based on different empirical terms, showing that TGA and ADF lignins did not share the same physical basis for calibration. C/N analysis revealed the presence of 3.1 and 1.4% nitrogen in ADF lignins of beech leaves and wood, respectively. The major fraction of this nitrogen was recovered in amino acids, which corresponded to 14% and 3% protein in ADF lignins of leaves and wood, respectively. These results show that ADF lignins contain significant concentrations of lignin-bound proteins, which renders this method unsuitable to determine genuine lignin.     

高硬度低碱度深井水药剂软化预处理方法比较

针对一种高硬度低碱度深井水,比较了不同药剂的软化预处理效果。CaO除硬为负效应;Na2CO3除硬效率较低,投加过量38%￣314%时,总硬去除率为49%￣60%;Na3PO4除硬效率较高,过量12%的总硬去除率达96.3%,但沉淀速度较慢,成本较高。采用石灰-纯碱法,使CaO投加量>理论量,三种Na2CO3投加量下除硬效果不同。当Na2CO3投加量小于理论量时,Na2CO3用量是影响硬度去除的主要因素,总硬最佳去除率为67.4%;当Na2CO3用量接近理论量时,CaO用量是影响硬度去除的主要因素,总硬最佳去除率为78.9%;当Na2CO3过剩12%时,在钙硬去除率最大的CaO用量下,投加少量的NaOH,总硬去除率可达99%。     

Accuracy, temporal performance and stability comparisons of discretization methods for the numerical solution of Partial Differential Equations (PDEs) in the presence of steep moving fronts

In this paper, several competitive spatial discretization methods recently developed for the convection term are reviewed and analyzed in terms of accuracy, temporal performance, and stability. This analysis was performed using a prediction–correction DAE integrator within the framework of the MOL (Method Of Lines). The discretization methods are classified by Fixed Stencil (FS), Adaptive Stencil (AS) and Weighted Stencil (WS) approaches and their main characteristics are demonstrated via a number of bench marking tests. Of the 14 discretization methods tested, four have been shown to be the most reliable, when we consider the accuracy of the calculation and the computational time required. Application of commonly-used FS methods to convection-dominated problems containing a moving shock results in a relatively short calculation time. However, almost of the FS methods, except for the first-order upwind FS method, are unstable, providing spurious oscillatory profiles (termed the Gibbs phenomena) near the shock. Employing AS methods such as ENO (Essentially Non-Oscillatory) schemes, this Gibbs phenomena disappears. Therefore, AS methods enhance stability and accuracy but are somewhat prohibitive. WS methods (i.e. Weighted ENO schemes), which use a convex combination of candidate stencils weighted by the ENO idea, can reduce the calculation time, and are inheriting of the non-oscillation nature inherent in the AS methods. The ENO and WENO methods are efficient to track a shock and steep moving front and these methods are essential for numerical schemes which use relatively small number of mesh points.     

应用于圆筒径向开孔接管结构应力分析的极限载荷法和应力分类法之比较

依据受压圆筒爆破实验得到的数据,对极限载荷法、应力分类法的结果进行了分析,并对两种方法的相对安全性进行了比较。同时,对于应力分类法中的一次局部薄膜应力以及薄膜应力加弯曲应力的强度条件进行了讨论。     

固相萃取与热脱附GC-MS对硫化胶中有机助剂分析的比较研究

本文分别采用溶剂抽提法和热脱附两种前处理方法对硫化胶中的有机助剂成分进行提取,并利用气相色谱-质谱联用仪(GC-MS)进行了研究分析。通过一系列不同胶种中有机助剂的分析效果的比较,以及综合两种方法各自的优缺点,对于一般的橡胶,可采用热脱附GC-MS法进行分析,而遇到含大量矿物油、烷烃油或(氯化)石蜡的橡胶时,建议采用抽提法经固相萃取提取分离后再进行GC-MS分析。     

Comparison of Cu1.3Mn1.7O4 spinels doped with Ni or Fe and synthesized via wet chemistry and solid-state reaction methods,designed as potential coating materials for metallic interconnects

The influence of the method applied to synthesize Cu-Mn-O spinel was evaluated. The methods selected for the investigation were EDTA gel processes and solid-state reaction synthesis. From the obtained powders, sinters were prepared and assessed in terms of their properties as potential coating materials. Additionally, the influence of Ni and Fe dopants was evaluated. The results show that the EDTA gel processes method seems to be more suitable for spinel synthesis. This method yields spinels that exhibit electrical conductivity above the required threshold (>50 S/cm) over a temperature range of 400–850 °C, and it also ensures continuous spinel matrices and high spinel content. Spinels obtained via solid-state reactions exhibit inferior properties. A higher concentration of Ni allows electrical conductivity to be improved further, while the opposite tendency is observed for Fe. Finally, it was shown that spinels obtained via EDTA gel processes are promising protective-conducting coating materials for SOEC/SOFCs steel interconnects.