Temperature-dependent Raman spectroscopic study of the nematic liquid crystal 4-n-pentyl-4'-cyanobiphenyl

The spectral behaviors of 4-n-pentyl-4'-cyanobiphenyl (5 CB) have been studied by means of temperature-dependent Raman spectros-copy in the range between --70 and 70 degrees C. The nu(C identical with N) bands in the Raman spectra were found splitting below the transition temperature from the solid to the nematic liquid crystalline phase at approximately 24 degrees C, suggesting the existence of solid crystalline polymorphism. The interfacial structures of 5 CB on metal plate surfaces have been reexamined by surface-enhanced Raman scattering (SERS) at different temperatures. On Ag and Au, the asymmetric shapes of the nu(C identical with N) bands suggest that there should exist different binding schemes for 5 CB on metal surfaces. These asymmetric bands in the nu(C identical with N) stretching region were found to vary in changing temperature.     

Osteoradionecrosis (ORN) of the mandible: a laser Raman spectroscopic study

Laser Raman spectroscopy has been used in this study to characterize mandibular bone samples from patients who had undergone radiation therapy for oral cancer. The paper discusses spectral changes resulting in osteoradionecrosis (ORN) of the mandibular bone, a serious complication that may occur after radiation therapy. Histopathological studies normally reveal the radiation damage on vascular canals and loss in bone cells, but will not reveal any structural or biochemical changes. All radiation-induced side effects are attributed to this hypovascularity and hypocellularity caused by early- and/or late-delayed effects. Our Raman studies on normal and ORN bone and on bone exposed to radiation, but not in the ORN state, show that irradiation produces immediate structural changes in the inorganic bone matrix with a slight loss in cells. ORN bone, in addition to the structural changes that had already occurred on radiation exposure, shows almost complete loss of cellular components. Since bone tissue is continuously being remodeled (dissolved and rebuilt) under normal conditions, our results suggest that the immediate structural changes in the calcium hydroxy apatite mineral part is not repaired in ORN, due to loss of the highly transient osteoblasts and osteoclasts resulting from destruction of stem cells. The spectral studies also show changes in the organic matrix, which is mostly type I collagen.     

Fibre/matrix stress transfer through a discrete interphase. Part 1: single-fibre model composites

This paper reports a study of the effect of an interphase on strain development in fibre-fragments. In order to form an interphase, an epoxy resin with known properties was applied to the surface of unsized reinforcing fibres and cured. These were then embedded in a matrix resin coupon, prior to fragmentation testing. The study included an examination of the effect of interphase thickness, by applying multiple coats of one of the resins, and the effect of the interphase properties, by varying the coating resins. It was found that the average fragment lengths at saturation were difficult to distinguish, as a result of the scatter introduced by the statistical distribution of fibre strengths. However, the strain interval between onset of fragmentation and saturation was found to be more sensitive to variations in the interphase properties.A finite element model was used to examine the strain development in the fragments in more detail. The mechanical properties of the fibre, interphase and matrix were accurately incorporated into the model, providing a realistic representation of the state of strain in the experimental samples. The predicted deformations around the fibre-break provided an explanation for the experimental observations.     

The influence of the temperature dependence of the yield stress on the stress distribution in a thermally assembled elastic-plastic shrink fit

Summary The subject of the investigation is the thermal assembly of an elastic-plastic shrink fit with hollow inner component. Based on Tresca's yield condition and the flow rule associated with it, the transient stress distribution is studied. Special attention is paid to the influence of the reduction of the yield stress at elevated temperatures on the interface pressure. However, it turns out that this influence is not significant.Dedicated to Prof. Dr. Kurt Desoyer on the occasion of the 70^th anniversary of his birthday     

Toward a spectroscopic hemogram: Raman spectroscopic differentiation of the two most abundant leukocytes from peripheral blood

The first response to infection in the blood is mediated by leukocytes. As a result crucial information can be gained from a hemogram. Conventional methods such as blood smears and automated sorting procedures are not capable of recording detailed biochemical information of the different leukocytes. In this study, Raman spectroscopy has been applied to investigate the differences between the leukocyte subtypes which have been obtained from healthy donors. Raman imaging was able to visualize the same morphological features as standard staining methods without the need of any label. Unsupervised statistical methods such as principal component analysis and hierarchical cluster analysis were able to separate Raman spectra of the two most abundant leukocytes, the neutrophils and lymphocytes (with a special focus on CD4(+) T-lymphocytes). For the same cells a classification model was built to allow an automated Raman-based differentiation of the cell type in the future. The classification model could achieve an accuracy of 94% in the validation step and could predict the identity of unknown cells from a completely different donor with an accuracy of 81% when using single spectra and with an accuracy of 97% when using the majority vote from all individual spectra of the cell. This marks a promising step toward automated Raman spectroscopic blood analysis which holds the potential not only to assign the numbers of the cells but also to yield important biochemical information.     

A study on the yield stress of perlite-filled high-density polyethylenes

Four different types of high-density polyethylenes were blended with expanded perlite at different compositions. -aminopropyltriethoxysilane was applied to perlite (2 wt%) from ether and water solutions to enhance the interfacial adhesion between the polymer and the filler. It was shown that silane treatment advances the yield stress with improving dispersion and increasing the interfacial adhesion of the filler with the polymer matrix. The experimental results were then checked with the expression of Turcsanyiet al.'s.     

Crystal quality of a 6H-SiC layer grown over macrodefects by liquid-phase epitaxy: a Raman spectroscopic study

Liquid-phase epitaxial (LPE) growth on silicon carbide simultaneously covers macroscale defects, e.g. micropipes, and improves the quality of the crystal. In this study, an epi-layer grown over a macrodefect was evaluated by micro-Raman scattering spectroscopy. Before the growth process, the density of the stacking fault was high and the carrier density spatially inhomogeneous in the vicinity of the macrodefects. On the other hand, after growth, the layer over the macrodefect displayed good quality; the density of the stacking fault was less than that before growth and the homogeneity of the carrier density improved.     

Effects of inter-fibre spacing and matrix cracks on stress amplification factors in carbon-fibre/epoxy matrix composites. Part I: planar array of fibres

When the loading on a composite is sufficient to cause fracture of an individual fibre, the resulting stress amplification in the adjacent intact fibres may be large enough to cause failure of these fibres. In this work, 3D elasto-plastic finite element analysis was used to investigate the effect of inter-fibre spacing on the stress amplification factor in a composite comprising a planar array of fibres. A Progressional Approach was used in the FE analysis to simulate the constituent non-linear processes associated with the generation of thermal residual stresses from fabrication, the fibre fracture event and the subsequent initiation and propagation of conical matrix cracks induced with incremental tensile loading. As the inter-fibre spacing increases, the effect of fibre fracture on the stress distribution in the neighbouring intact fibres is reduced, whereas the effect on the matrix material is increased, thereby inducing localised yielding. The presence of a conical-shaped matrix crack was found to increase both the stress amplification factor and the positively affected length in neighbouring fibres. For a large inter-fibre spacing, a longer matrix crack is required to obtain good agreement with LRS measurements of fibre stress.     

A DEM-based analysis of the influence of aggregate structure on suspension shear yield stress

This study theoretically examined the effect of aggregate structure on the suspension shear yield stress. The aggregation process of colloidal particles was simulated using the discrete element model (DEM) combined with the well-known DLVO theory. The predicted aggregate structural characteristics, namely the coordination number and inter-particle forces were then used in a modified version of the Flatt and Bowen mechanistic model [6] to calculate the corresponding suspension yield stress. The effect of key parameters such as solid volume fraction, suspension pH and ionic strength on the aggregate structure and hence the yield stress of the suspension was investigated.The results showed that the yield stress increased significantly under conditions that were favourable for formation of complex net-like aggregate structures, such as high solid volume fractions, pH values near the iso-electric point, and high ionic strengths. In such cases, the mean coordination number reached a maximum value which was considered to be dependent on the particle size and size distribution. The suspension yield stress exhibited a power law dependency on the solid volume fraction. The interconnected network structure developed at high solid volume fractions was found to be the major contributing factor to the observed high suspension yield stress. As the particle–particle repulsion became significant, a decrease in both the number of bonds and the mechanical bonding strength of the aggregate structure was observed. That was considered to be responsible for the reduction in the suspension yield stress. The suspension yield stress became independent of the suspension ionic strength when the ionic strength exceeded the critical coagulation concentration. Satisfactory agreements were obtained between simulation results and the published experimental data.     

The influence of Poisson contraction on matrix cracking stress in fiber reinforced ceramics

The influence of Poisson contraction on the stresses for propagating a semi-infinite fiber-bridged crack in unidirectional fiber reinforced ceramics is studied in this paper. The situation of bonded fibers that is subjected to compressive pressure due to thermal expansion mismatch between the fiber and the matrix is considered in the present analysis. The results show that the Poisson contraction has profound effects on the matrix cracking stress predictions in the ceramic matrix composites, especially for the composites with high coefficient of friction. The Poisson contraction effects can be evidenced by the comparison of the present analysis with the Aveston, Cooper and Kelly (ACK) model. The roles played by the interfacial properties of the interfacial bonding energy and the coefficient of friction on the stresses for matrix cracking are discussed.     

A study of fastener pull-through failure of composite laminates. Part 2: Failure prediction

The experimental study of fastener pull-through failure in composite laminates reported in Part 1 of this paper found pull-through failure to be characterised by substantial internal damage similar to that observed for low-velocity impacted composite panels. Damage is manifested in the form of a conically distributed network of matrix cracking and delaminations extending through-the-thickness from the fastener head outer edge, directed away from the fastener hole. Analysis is conducted in this paper to identify the mechanisms responsible for failure. Finite element analysis indicated high shear stresses at the fastener head outer edge to be responsible for the matrix cracking in this region. Tensile in-plane stresses are the cause of flexural failures found elsewhere in laminates of reduced bending stiffness. Fastener pull-through failure results from the tensile strength of the resin being exceeded. Matrix cracking was found to be the initial mode of failure with cracks aligning themselves perpendicular to the direction of principal stresses. Interply delamination is a secondary mode of failure and represents a propagation of cracking along the path of least resistance. Delaminations are induced due to excessive interlaminar shear and peel strains in the laminate due to through-thickness deformation and matrix cracking respectively. A numerical procedure for the prediction of failure was developed based upon a progressive damage model and a maximum principal strain criterion. Very good correlation between experimental and predicted pull-through failure loads, failure location and failure sequence were achieved. This research constitutes work performed as part of the Cooperative Research Centre for Advanced Composite Structures (CRC-ACS) task on highly loaded joints.     

Effects of sterilization on an extracellular matrix scaffold: Part II. Bioactivity and matrix interaction

Small intestinal submucosa (SIS) has been successfully used to treat a variety of damaged or diseased tissues in human patients. As a biologic scaffold, SIS stimulates repair of damaged or diseased tissues and organs with tissue that is similar in structure and function to the material it was meant to replace. To meet clinical safety requirements, biologic materials from animal tissues must undergo processing treatments to minimize host immune response and to eliminate the possibility of disease transmission. The effect of peracetic acid disinfection, lyophilization, and ethylene oxide sterilization on the in vitro bioactivity of the processed SIS was therefore examined in murine fibroblasts and pheochromocytoma (PC12) cells. Specifically, the ability of processed SIS to support fibroblast attachment, to stimulate PC12 cell differentiation, and to upregulate fibroblast VEGF secretion was examined. Fibroblasts attach to the sterilized SIS, remain viable, and more than double their secretion of VEGF as a result of interacting with the SIS matrix components. Additionally, PC12 cells exhibit increased neurite outgrowth following stimulation by SIS matrix proteins versus controls. We conclude that a biologic scaffold can be prepared for human use and still retain significant bioactivity.     

Effects of sterilization on an extracellular matrix scaffold: Part I. Composition and matrix architecture

The impact of peracetic acid (PAA), lyophilization, and ethylene oxide (EO) sterilization on the composition and three dimensional matrix structure of small intestinal submucosa (SIS), a biologic scaffold used to stimulate the repair of damaged tissues and organs, was examined. Fibronectin and glycosaminoglycans are retained in SIS following oxidation by peracetic acid and alkylation using ethylene oxide gas. Significant amounts of FGF-2 are also retained, but VEGF is susceptible to the effects of PAA and is dramatically reduced following processing. Further, matrix oxidation, lyophilization, and sterilization with EO can be performed without irreversibly collapsing the three dimensional structure of the native SIS. These structural features and growth promoting extracellular matrix constituents are likely to be important variables underlying cellular attachment, infiltration and eventual incorporation of SIS into healing host tissues.