Experiment and Simulation of Breakage of Particle Compounds under Compressive Loading

ABSTRACT

Two-dimensional finite element (FE) compressive stress analyses were carried out on the particle compound material to understand the stress pattern distributions before cracking. FE analysis was followed by discrete element (DE) simulation. A study of the crack propagating mechanism in a particle was represented by a model material that typifies pellets of high-strength pressed agglomerate building materials. For this, concrete spheres of strength category B35 (compressive strength 35 N/mm²) were used. It was observed that the ring tensile stress is responsible for the crack initiation in the spherical particle compounds.     

Temperature dependence of cohesive laws for an epoxy adhesive in Mode I and Mode II loading

The influence of the temperature on the cohesive laws for an epoxy adhesive is studied in the glassy region, i.e. below the glass transition temperature. Cohesive laws are derived in both Mode I and Mode II under quasi-static loading conditions in the temperature range $-30\le T \le 80^{\,\circ }$ C. Three parameters of the cohesive laws are studied in detail: the elastic stiffness, the peak stress and the fracture energy. Methods for determining the elastic stiffness in Mode I and Mode II are derived and evaluated. Simplified bi-linear cohesive laws to be used at any temperature within the studied temperature range are derived for each loading mode. All parameters of the cohesive laws are measured experimentally using only two types of specimens. The adhesive has a nominal layer thickness of 0.3 mm and the crack tip opening displacement is measured over the adhesive thickness. The derived cohesive laws thus represent the entire adhesive layer as having the present layer thickness. It is shown that all parameters, except the Mode I fracture energy, decrease with an increasing temperature in both loading modes. The Mode I fracture energy is shown to be independent of the temperature within the evaluated temperature span. At $80^{\,\circ }$ C the Mode II fracture energy is decreased to about 2/3 of the fracture energy at $-30^{\,\circ }$ C. The experimental results are verified by finite element analyses.     

A microfluidic electrocapture device in sample preparation for protein analysis by MALDI mass spectrometry

The design and operation of a microfluidic device for sample preparation in MALDI mass spectrometry of peptides and proteins is described. It is particularly useful for proteomics applications and for mass determination of proteins in salt- and detergent-containing solutions. The system consists of a flow channel with two conductive areas or electrical junctions where proteins and peptides are retained by means of an electric field. The microfluidic device is made of PEEK tubing, and the junctions are covered with a conductive polymeric membrane. A syringe pump connected to the device produces a flow stream, and injection of sample is carried out manually via hydrodynamic pressure. Proteolytic peptides and intact proteins in salt- and detergent-containing acidic media were captured at the cathode junction followed by exchange of the original solution to a solvent suitable for subsequent mass spectrometry. Using this principle, a significant desalting effect was obtained for tryptic peptides in mass-mapping experiments. Protein sequence coverages were high (up to 40%) at subpicomole levels with results better than those obtained using reversed-phase solid-phase extraction. In contrast to the latter technique, the microfluidic device has the capacity to efficiently remove detergents such as CHAPS before peptide mapping and protein analysis.     

Carbon nanotube-based nanocarriers: the importance of keeping it clean

Nanotechnology-introduced materials have promising applications as nanocarriers for drugs, peptides, proteins and nucleic acids. Several studies showed that the geometry (shape and size) and chemical properties of nanoparticles affect the kinetics and pathways of cellular uptake and their intracellular trafficking and signaling. Accurate physico-chemical characterization of nanoparticles customarily precedes their use in cell biology and in vivo experiments. However, a fact that is easily overlooked is that nanomaterials decorated with organic matter or resuspended in aqueous buffers can be theoretically contaminated by fungal and bacterial microorganisms. While investigating the effects of extensively characterized PEGylated carbon nanotubes (PNTs) on T lymphocyte activation, we demonstrated bacterial contamination of PNTs, which correlated with low reproducibility and artifacts in cell signaling assays. Contamination and artifacts were easily eliminated by preparing the materials in sterile conditions. We propose that simple sterile preparation procedures should be adopted and sterility evaluation of nanoparticles should be customarily performed, prior to assessing nanoparticle intracellular internalization, trafficking and their effects on cells and entire organisms.     

Energy absorption during compression and impact of dry elastic-plastic spherical granules

The discrete modelling and understanding of the particle dynamics in fluidized bed apparatuses, mixers, mills and others are based on the knowledge about the physical properties of particles and their mechanical behaviour during slow, fast and repeated stressing. In this paper model parameters (modulus of elasticity, stiffness, yield pressure, restitution coefficient and strength) of spherical granules (γ-Al₂O₃, zeolites 4A and 13X, sodium benzoate) with different mechanical behaviour have been measured by single particle compression and impact tests. Starting with the elastic compression behaviour of granules as described by Hertz theory, a new contact model was developed to describe the force-displacement behaviour of elastic-plastic granules. The aim of this work is to understand the energy absorption during compression (slow stressing velocity of 0.02 mm/s) and impact (the impact velocity of 0.5–4.5 m/s) of granules. For all examined granules the estimated energy absorption during the impact is found to be far lower than that during compression. Moreover, the measured restitution coefficient is independent of the impact velocity in the examined range and independent of the load intensity by compression (i.e. maximum compressive load). In the case of repeated loading with a constant load amplitude, the granules show cyclic hardening with increasing restitution coefficient up to a certain saturation in the plastic deformation. A model was proposed to describe the increase of the contact stiffness with the number of cycles. When the load amplitude is subsequently increased, further plastic deformation takes place and the restitution coefficient strongly decreases.     

Switching between negative and positive electrorheological effect of g-C3N4 by copper ions doping

Investigation of pristine g-C₃N₄ and copper ions doped g-C₃N₄ as dispersed phases in silicone-oil based electrorheological (ER) fluids is reported for the first time. Pristine g-C₃N₄ was prepared via standard thermal polycondensation of urea. Introduction of Cu ions into g-C₃N₄ polymeric network was performed by treatment of pristine powder by a solution containing tetraammoniumdiaquacopper(II) complex ions followed by annealing. The structure and properties of products were revealed with the aid of XRD, FTIR, UV–Vis and XPS, and complemented by SEM investigation of morphology, pycnometry, BET analysis, and conductivity measurements. The response of prepared ER fluids to an external electric field was examined by rheometry and the effects visualized with optical microscopy. While ER fluids based on g-C₃N₄ exhibited negative ER effect (decrease in viscosity when the field is switched-on), ER fluids based on a g-C₃N₄/Cu-doped analogue exhibited positive ER effect. Dielectric spectroscopy using Havriliak-Negami model revealed that introduction of the dopant almost doubled the dielectric relaxation strength while the relaxation time was halved. The ability of g-C₃N₄/Cu as a candidate for further studies necessary to increase the ER effect was demonstrated. Thereto, described modification of g-C₃N₄ by copper ions shall be applicable also for other metals forming ammonia complexes.     

Analysis of Amadori compounds by high-performance cation exchange chromatography coupled to tandem mass spectrometry

High-performance cation exchange chromatography coupled to tandem mass spectrometry or electrochemical detection was found to be an efficient tool for analyzing Amadori compounds derived from hexose and pentose sugars. The method allows rapid separation and identification of Amadori compounds, while benefiting from the well-known advantages of mass spectrometry, such as specificity and sensitivity. Glucose- and xylose-derived Amadori compounds of several amino acids, such as glycine, alanine, valine, leucine/isoleucine, methionine, proline, phenylalanine, and glutamic acid, were separated or discriminated using this new method. The method is suitable for the analysis of both model reaction mixtures and food products. Fructosylglutamate was found to be the major Amadori compound in dried tomatoes (approximately 1.5 g/100 g) and fructosylproline in dried apricots (approximately 0.2 g/100 g). Reaction of xylose and glycine at 90 degrees C (pH 6) for 2 h showed rapid formation of xylulosylglycine (approximately 12 mol %, 15 min) followed by slow decrease over time. Analysis of pentose-derived Amadori compounds is shown for the first time, which represents a major breakthrough in studying occurrence, formation, and decomposition of these labile Maillard intermediates.     

Scatter correction of transmission near-infrared spectra by photon migration data: quantitative analysis of solids

The scope of this work is a new methodology to correct conventional near-infrared (NIR) data for scattering effects. The technique aims at measuring the absorption coefficient of the samples rather than the total attenuation measured in conventional NIR spectroscopy. The main advantage of this is that the absorption coefficient is independent of the path length of the light inside the sample and therefore independent of the scattering effects. The method is based on time-resolved spectroscopy and modeling of light transport by diffusion theory. This provides an independent measure of the scattering properties of the samples and therefore of the path length of light. This yields a clear advantage over other preprocessing techniques, where scattering effects are estimated and corrected for by using the shape of the measured spectrum only. Partial least squares (PLS) calibration models show that, by using the proposed evaluation scheme, the predictive ability is improved by 50% as compared to a model based on conventional NIR data alone. The method also makes it possible to predict the concentration of active substance in samples with other physical properties than the samples included in the calibration model.