Internal stress of epoxy resin modified with acrylic polymers having crosslinks produced byin situ UV radiation polymerization

In order to reduce the internal stress of cured epoxy resin generated by shrinkage in the cooling process from cure temperature to room temperature, two kinds of acrylic polymers were introduced byin situ UV radiation polymerization prior to curing. Polybutyl acrylate (A) and butyl acrylate-monoethylene glycol dimethacrylate copolymer (molar ratio 955) (B) were used as the acrylic polymer. In the A-modified resin, a heterogeneous structure with spherical submicrometre domains were formed. In the B-modified resin, irregularly shaped submicrometre domains in which the microphase separation occurred were observed. The modulus of cured epoxy resin decreased as a result of the modifications, and was lower in the B-modified resin than in the A-modified resin. Therefore the internal stress decreased more effectively in the B-modified resin.     

Heat and mass transfer in calcination of limestone particles

The heat and mass‐transfer phenomena occurring during the calcination of limestone particles was studied by means of modeling. The applicability of two modeling methods for calcination was compared under different conditions. An unsteady numerical particle model with mass, momentum, energy balance, and shrinking core models were chosen for the study. The influence of different phenomena (chemical kinetics, advective and diffusive mass transfer, and heat transfer) in different conditions was evaluated with the aid of dimensionless parameters, and their relative importance was shown in a regime chart. Especially, the significance of advection was studied and its importance in high CO₂ concentration was observed. Local temperatures inside the particle were obtained by solving a dynamic energy balance in each particle layer including calcination reaction energy and conduction heat transfer. Noticeable temperature differences between constant ambient conditions and the particle were observed. © 2011 American Institute of Chemical Engineers AIChE J, 58: 2563–2572, 2012     

Up-conversion luminescence properties of Y2O2S:Yb,Er nanophosphors

Up-converting yttrium oxysulfide nanomaterials doped with ytterbium and erbium (Y₂O₂S:Yb³⁺,Er³⁺) were prepared with the flux method. The precursor oxide materials were prepared using the combustion synthesis. The morphology of the oxysulfides was characterized with transmission electron microscopy (TEM). The particle size distribution was 10–110 nm, depending on the heating temperature. According to the X-ray powder diffraction (XPD), the crystal structure was found hexagonal and the particle sizes estimated with the Scherrer equation agreeded with the TEM images. Upon the 970 nm infrared (IR) laser excitation, the materials yield moderate green ((²H_11/2, ⁴S_3/2) → ⁴I_15/2 transition) and strong red (⁴F_9/2 → ⁴I_15/2) luminescence. The green luminescence was enhanced with respect to the red one by an increase in both the crystallite size and erbium concentration due to the cross-relaxation (CR) processes. The most intense up-conversion luminescence was achieved with x_Yb and x_Er equal to 0.10 and 0.005, respectively. Above these concentrations, concentration quenching occurred.     

SIMULATION OF BUBBLE FORMATION AND HEAPING IN A VIBRATING GRANULAR BED

The Eulerian-Eulerian approach is used to simulate flow in a dense granular bed subjected to a slight, vertical, sinusoidal vibration. The bottom of the bed was subjected to a vertical vibration, ASin(ω _v t)J ₀(k _m x), where J represents the profile of the bottom wall and is the first kind of Bessel function. The governing equations of the gas phase and particle phase are described and the results of the model with different vibration frequencies and amplitudes are presented. Bubble formation and upward and downward heaping were observed at different amplitudes and frequencies. The results of the model confirm that there is a change from upward to downward heaps according to the strength of the vibration. In addition, the location of the bubble and the shape of the heaping at the interface of the bed depend on the strength of the vibration and the profile of the bottom of the container.     

Internal stress of epoxy resin modified with acrylic polymers produced by in situ UV radiation polymerization

A cured epoxy resin is modified with polybutyl acrylate (A) and polyethyl acrylate (B) produced by in situ ultraviolet radiation polymerizations of their corresponding monomers in the epoxy resin, respectively, to reduce the internal stress. In the A system, a heterogeneous structure with submicron domains was formed. In the B system, however, the B mixed well with the epoxy matrix. In both systems, the internal stress was decreased by the modification. The glass transition temperature of the epoxy matrix decreased in the B system more than in the A system. The A-modified resin was superior to the B-modified resin in reducing the internal stress without decreasing the thermal resistance of epoxy resin.     

Computer science research articles: the locations of different section types,and a proposal for standardization in the structure

This paper presents an analysis of the structure of computer science research articles published in the Lecture Notes of Computer Science series. While it is clear that most articles start with an Introduction and end with a Conclusion, the structure of text between these two sections is rather diverse. We studied the positions of different section types, and analysed dependencies between them. As a result, we present a number of common patterns used by writers, and make suggestions on how to improve the presentation of research in computer science.     

Ligand Enabling Visible Wavelength Excitation of Europium(III) for Fluoroimmunoassays in Aqueous Micellar Solutions

Fluorescent reporters based on lanthanide ions, such as europium chelates, enable highly sensitive detection in immunoassays and other ligand binding assays. Unfortunately they normally require UV-excitation produced by a xenon flash or nitrogen laser light source. In order to use modern solid state excitation sources such as light emitting diodes (LEDs), these reporters need to be excited at wavelengths longer than 365 nm, where high-powered ultraviolet LEDs are available. A novel ligand, 9-ethyl-3,6-bis(5',5',5',4',4'-pentafluoro-1',3'-dioxopentyl)carbazole (bdc), was synthesized to efficiently excite europium(III) at wavelengths up to 450 nm in micellar solutions, and its performance was compared to a commercially available DELFIA enhancement solution. The detection limit of Eu(III) with the bdc-ligand using 365 nm excitation was determined to be 63 fM, which is 3 times lower than with the DELFIA solution. The bdc-ligand enabled sensitive detection of europium(III) ions in solution using 365 nm excitation and displayed similar sensitivity and functionality as commercially available DELFIA enhancement solution. Therefore, this novel enhancement solution might be a feasible alternative in producing time-resolved fluorescence under LED-excitation.     

Solving uncapacitated multilevel lot-sizing problems using a particle swarm optimization with flexible inertial weight

The multilevel lot-sizing (MLLS) problem is a key production planning problem in materials requirements planning (MRP) system. The MLLS problem deals with determining the production lot-sizes of various items appearing in the product structure over a given finite planning horizon to minimize the production cost, the inventory carrying cost, the back ordering cost and etc. This paper proposed a particle swarm optimization (PSO) algorithm for solving the uncapacitated MLLS problem with assembly structure. All the mathematical operators in our algorithm are redefined and the inertial weight parameter can be either a negative real number or a positive one. The feasibility and effectiveness of our algorithm are investigated by comparing the experimental results with those of a genetic algorithm (GA).     

Dynamics of water in agar gels studied using low and high resolution 1H NMR spectroscopy

The aim of this work was to determine whether the decreased motion of water in agar gels (2.5–12.5% agar) resulted not only from the chemical interaction of the water molecules with the agar macromolecules but also from obstruction by the gel networks. Relaxation experiments were conducted using a 500‐MHz nuclear magnetic resonance (NMR) spectrometer. Diffusion experiments were conducted using a 23‐MHz NMR spectrometer with diffusion times ranging between 15 and 200 ms and a 500‐MHz NMR spectrometer with a fixed diffusion time of 10 ms. This study shows that the interaction of water with hydroxyl groups of agar macromolecules resulted in faster relaxation and slower self‐diffusion of water. The time‐dependent self‐diffusion coefficient of water provides clear evidence of the obstructive effects of the agar gel network on diffusion. This work is the first report on restricted diffusion of water in agar gel systems.     

Polycyclic aromatic hydrocarbons contamination of traditionally grilled pork marketed in South Benin and health risk assessment for the Beninese consumer

ABSTRACT

Polycyclic aromatic hydrocarbons (PAHs) contamination was monitored in grilled pork sold in Beninese street restaurants, as well as in grilled pork from a well-controlled experiment replicating traditional grilling using Acacia auriculiformis wood as fuel. Fifteen PAHs were analysed using a high-performance liquid chromatography method coupled with fluorescence detection. To assess the risk for the consumer, the margins of exposure (MOEs) were calculated, as the ratio between benchmark PAHs levels and consumer intakes. A MOE below 10,000 indicates a concern for human health for carcinogenic compounds such as PAHs. Benzo(a)pyrene (BaP) levels up to 17.9 and 53.6 µg/kg were found in grilled pork sampled in restaurants and from the controlled experiment, respectively. When considering both median estimated daily intake and median PAHs contamination levels, MOEs calculated for Benzo(a)pyrene (BaP) alone, or for the sum of 2, 4 or 8 PAHs were above 10,000, meaning no risk in these cases. However, for the same PAHs contamination level, MOE for consumers having large amounts of grilled pork (97.5th percentile and maximum level of pork consumption) were well below 10,000. When considering the maximum level of PAHs contamination, MOEs ranged between 257 and 2,757 for the high and median levels of consumption, indicating a safety concern for these consumers. This study reveals that Beninese grilled pork consumers from South Benin can be exposed to high levels of PAHs, which might result in public health issues.