Rich Matrices Research Articles

Magnetic moments of Fe clusters embedded in an Fe-Co alloy

Motivated by the search for high moment materials, we present first-principles calculations of the magnetic moments for Fe clusters embedded in an Fe-Co alloy as well as in a pure Co matrix. Both spin and orbital contributions have been calculated with the use of a real-space linear muffin-tin orbital method within the atomic sphere approximation. The cluster sizes considered range from 1 to 51 atoms. We find an enhancement of the spin moments of the atoms close to the interface between the cluster and the embedding matrix. The spin moment enhancement is decreasing with increasing Fe content in the surrounding matrix. The slightly lower magnetic moments for the Fe clusters embedded in the Fe rich matrices can nevertheless result in a material with an enhanced saturation magnetization due to the higher moments in the matrix. We argue that the largest average magnetic moments for embedded Fe clusters are obtained for an ${\mathrm{Fe}}_{0.5}{\mathrm{Co}}_{0.5}$ alloy in the matrix surrounding the clusters.

Modifications on Collagen Structures Promoted by 1,4-Dioxane Improve Thermal and Biological Properties of Bovine Pericardium as a Biomaterial

Collagen is a widely used raw material for biomaterial manufacture, which generally depends on chemical modifications of this fibrillar protein with cross-linking agents to improve biocompatibility and mechanical properties. However, cross-linking reduces the natural properties of collagen, such as low immune response, low toxicity as well as the ability to promote cellular growth and attachment. In this work, the modifications promoted by 1,4-dioxane solvent on the collagen present in native bovine pericardium (NBP) matrix routinely used in bioprosthesis manufacture, with or without subsequent cross-linking by glutaraldehyde, has been studied. The structural changes of NBP evaluated by scanning electron microscopy show that 1,4-dioxane induces a more homogeneous material by increasing aggregation of collagen fibers, while transmission scanning electron microscopy shows that natural collagen fibril arrangement, integrity, and the D-periodicity pattern are maintained by solvent treatments. Measurements of thermal stability and resistance to collagenase enzymatic digestion of NBP matrices treated with 1,4-dioxane show an increase in melting temperature and decrease in biodegradability, as compared to native pericardium. Cross-linking with glutaraldehyde improves all the analyzed NBP properties, which are not impaired by previous treatment with 1,4-dioxane. Histological evaluation of NBP submitted to 1,4-dioxane treatment shows lower lipid and cell contents and improvement in other morphologic characteristics compared to native pericardium. Altogether, these results suggest the use of 1,4-dioxane organic solvent as an alternative non-cross-linking treatment for direct utilization on rich collagen matrices, resulting in materials with improved biocompatibility and physicochemical properties suitable for tissue engineering.

Neurocan-GFP fusion protein: a new approach to detect hyaluronan on tissue sections and living cells.

Hyaluronan is an unsulfated glycosaminoglycan (GAG) that is ubiquitously expressed in the extracellular matrix (ECM) of all vertebrates, where hyaluronan rich matrices constitute a particular permissive environment for the development of complex biological structures and also for tumor progression. Because of its conserved structure and ubiquitous expression, antibodies for its histochemical detection cannot be produced. We have engineered a fusion protein, neurocan-GFP, and expressed it as a secreted molecule in mammalian cells. Neurocan-GFP fusion protein specifically binds to hyaluronan and directly visualizes hyaluronan on tissue sections, revealing a very detailed picture of hyaluronan distribution. The fluorescent fusion protein can be used in combination with antibodies and nuclear markers for double or triple staining. In addition, it is suitable to visualize hyaluronan on living cells by time-lapse video microscopy. The successful production and application of the neurocan-GFP fusion protein opens up new perspectives for using GFP fusion proteins as detection tools in histological and cytological studies complementing conventional antibody and biotin/avidin techniques.

Determination of nutrients in the presence of high chloride concentrations by column-switching ion chromatography

Determination of inorganic anions in waters of high salinity is one of the most difficult task in analytical chemistry. A simple column-switching method, based on an original chromatographic set-up, for the determination of nutrients (nitrate, nitrite and phosphate) in chloride rich aqueous matrices is presented. A pre-separation system (made of two in line pre-columns, Dionex AG9-HC 4 mm) connected to an analytical column (Dionex AS9-HC 4 mm) by a four way pneumatic valve, allows chloride to be eluted off into the waste and nutrients to be separated and detected by a conductimeter and/or a UV spectrophotometer. Neither chemical pre-treatment nor sample dilution are required; sample matrices presenting a large range of chloride concentrations can be investigated. Moreover by using this technology, automation for routine analysis, low analysis time and low costs can be achieved. LODs of 100, 300, 1000 μg/l for nitrate, nitrite and phosphate, respectively, have been obtained by spiking a synthetic sea water sample containing 20 000 mg/l of chloride and 3000 mg/l of sulphate. Analyte calibration curves of analytes are linear ( r>0.99) in the range between the LODs and 60 mg/l. This method was applied to nutrients determination in sea water samples collected near a river outlet.

Morphology/behavior relationship and recyclability of composites based on PP/EPDM blends and short aramid fibers

AbstractThe effect of short aramid fibers on the mechanical behavior of polypropylene (PP) and ethylene‐propylene‐diene (EPDM) and their blends has been investigated by means of an experimental design. The results have shown that aramid fibers are very effective reinforcing agents for composites when the continuous phase of the matrix is constituted by PP, so sensible increments in tensile modulus and strength are obtained as fiber content in the composites increases. An optimal matrix composition and fiber content has been observed that produced high abrasion resistance compounds. However, the abrasion resistance of very rich EPDM matrices is hardly affected by fibers content. The addition of fibers to EPDM rich (>50%) matrices gives rise to a sensible decrease of the impact strength of this polymer. However, at PP contents above 50% in the polymer matrix, an increase of impact strength is observed at fiber percentages in the composites above 10%. The different behavior of the fibers depending on matrix type can be attributed to a better affinity of these fibers for PP matrix. Morphological studies of the composites have been carried out by scanning electron microscopy. Finally, the price and recyclability of these materials have been analyzed. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2474–2484, 2002

Melanoma cell-derived factors stimulate glycosaminoglycan synthesis by fibroblasts cultured as monolayers and within contracted collagen lattices.

Various tumours exhibit glycosaminoglycan rich, and in particular hyaluronan rich matrices surrounding them that facilitate tumour growth and invasion. In many tumours, this matrix is predominantly synthesized by fibroblasts following stimulation by tumour cell-derived factors. To determine what effect tumour cell-conditioned medium has upon fibroblast glycosaminoglycan synthesis when cells were cultured as monolayers and within contracted collagen lattices. Serum-free conditioned medium from melanoma cell lines (C8161, MV3, A375 and Hs294T) was examined for its ability to stimulate the incorporation of 3H-glucosamine and 35SO4 into glycosaminoglycans synthesized by fibroblasts. Conditioned medium from all four melanoma cell lines exhibited potent glycosaminoglycan-stimulating activity. In monolayer culture, C8161-conditioned medium stimulated a 4.2-fold increase in fibroblast hyaluronan, and a 9.9-fold increase in sulphated glycosaminoglycan synthesis, while 35SO4 incorporation was increased only 2.1-fold. In collagen lattice cultures, C8161-conditioned medium stimulated a 4.9-fold increase in hyaluronan synthesis, a 5.4-fold increase in sulphated glycosaminoglycans, and a 1.3-fold increase in 35SO4 incorporation. Melanoma cells produce factors that are potent stimulators of fibroblast glycosaminoglycan synthesis, in both monolayer culture and within contracted collagen lattices. Synthesis of both hyaluronan and sulphated glycosaminoglycans with a reduced degree of polymer sulphation is stimulated. Such changes are likely to promote tumour cell proliferation and migration.

Changes in the liver parenchyma after proton beam radiotherapy: evaluation with MR imaging

The objective of this study was to describe magnetic resonance (MR) findings with a 1.5T imager for hepatic parenchymal changes after proton beam radiotherapy. Thirty-two patients who received proton radiotherapy with doses of 50–87 Gy underwent MR imaging 1–75 months (mean 22 months) after the start of irradiation. Axial T 2, T 1-weighted imaging, and a dynamic study after a gadolinium injection were performed. The irradiated areas showed hypointense in T 1-weighted images, hyperintense in T 2-weighted images, and intense and prolonged enhancement on the dynamic study (maximum relative enhancement 441.8% ± 263.3 vs. surrounding liver 145.6% ± 67.7, p < 0.0001). T 2 values of the irradiated areas were 50.6 to 65.8 msec greater than in the surrounding liver ( p < 0.005). The values increased with time, being significantly greater 13 months or longer after the beginning of the therapy than after a period of less than 3 months ( p < 0.05). Pathologic examinations ( n = 3) indicated that the irradiated areas were composed of collapsed lobules with hepatic small vein occlusions, and rich extracellular matrices which retained extracellular fluid. MR imaging can demonstrate hepatic parenchymal changes after proton beam radiotherapy, and show the changes are irreversible.

Determination of Impurities in Uranium and Plutonium Dioxides by Laser-Induced Breakdown Spectroscopy

Laser-induced breakdown spectroscopy (LIBS), a spectrochemical technique in which a laser beam is used as the excitation source, was applied to detect trace elements contained in uranium and plutonium dioxides. Partial spectra of plasmas, generated by focusing the second harmonic (Λ = 532 nm) of a pulsed Nd:YAG laser on UO2 and PuO2 targets at atmospheric pressure, were recorded. Eighteen impurities at concentrations of about 500 ppm (μg/g) and twelve at concentrations of about 100 ppm, respectively, were observed in the rich emission matrices UO2 and PuO2. The possibility of quantifying impurities in such matrices is discussed.

Processing of laminin-5 and its functional consequences: role of plasmin and tissue-type plasminogen activator.

The laminin-5 component of the extracellular matrices of certain cultured cells such as the rat epithelial cell line 804G and the human breast epithelial cell MCF-10A is capable of nucleating assembly of cell- matrix adhesive devices called hemidesmosomes when other cells are plated upon them. These matrices also impede cell motility. In contrast, cells plated onto the laminin-5-rich matrices of pp126 epithelial cells fail to assemble hemidesmosomes and are motile. To understand these contradictory phenomena, we have compared the forms of heterotrimeric laminin-5 secreted by 804G and MCF-10A cells with those secreted by pp126 cells, using a panel of laminin-5 subunit-specific antibodies. The alpha3 subunit of laminin-5 secreted by pp126 cells migrates at 190 kD, whereas that secreted by 804G and MCF-10A cells migrates at 160 kD. The pp126 cell 190-kD alpha3 chain of laminin-5 can be specifically proteolyzed by plasmin to a 160-kD species at enzyme concentrations that do not apparently effect the laminin-5 beta and gamma chains. After plasmin treatment, pp126 cell laminin-5 not only impedes cell motility but also becomes competent to nucleate assembly of hemidesmosomes. The possibility that plasmin may play an important role in processing laminin-5 subunits is supported by immunofluorescence analyses that demonstrate colocalization of laminin-5 and plasminogen in the extracellular matrix of MCF-10A and pp126 cells. Whereas tissue-type plasminogen activator (tPA), which converts plasminogen to plasmin, codistributes with laminin-5 in MCF-10A matrix, tPA is not present in pp126 extracellular matrix. Treatment of pp126 laminin-5-rich extracellular matrix with exogenous tPA results in proteolysis of the laminin-5 alpha3 chain from 190 to 160 kD. In addition, plasminogen and tPA bind laminin-5 in vitro. In summary, we provide evidence that laminin-5 is a multifunctional protein that can act under certain circumstances as a motility and at other times as an adhesive factor. In cells in culture, this functional conversion appears dependent upon and is regulated by tPA and plasminogen.

Separation and determination of gold from iron rich matrices by an off/on-line preconcentration system coupled to ICP-AES

A preconcentration/separation method has been developed for the off/on-line determination by ICP-AES of gold in complex matrices, containing iron and manganese which cause severe spectral interferences on the two most sensitive Au-lines. The available automated preconcentration apparatus was modified using as absorbent the highly selective, for precious metals, chelating anion exchanger SRAFION NMRR. From the elution of this resin with 5% thiourea a nearly quantitative recovery of gold and its separation from iron, existing in percent range in the matrix, and from manganese was obtained. The validity of the developed method was tested by the determination of gold in standard reference materials from BCR, such as sewage sludge of domestic and mainly industrial origin and in a calcareous loam soil. The preconcentration procedure was synchronized with the ICP operating parameters in order to get an optimised on-line coupling of these two systems. The described process has been successfully applied to the determination of low gold contents in dissolved iron rich sediments using for the gold prospection.

Interaction between synoviocytes and extracellular matrix in vitro.

Synoviocyte adhesion, migration, and proliferation are essential in the growth of pannus and the subsequent invasion of cartilage in inflammatory arthritis. These cellular functions are regulated by the extracellular matrix.' In vitro studies of synoviocytes have previously demonstrated that they display abnormal phenotypic properties, including a transformation-like morphology manifested by cell overlapping and focus formation.2 3 Abnormal synoviocyte phenotype has been shown to be strongly influenced by extracellular matrix; synoviocytes exhibit extensive focus formation when plated on exogenous fibronectin rich matrices or when primed to switch endogenous matrix production from a collagen enriched to a fibronectin enriched type.3 To determine if the influence of matrix on synoviocyte morphology is associated with effects on synoviocyte adhesion and growth, we studied the effect of purified matrix components and a cell free matrix preparation isolated from human synovium on the attachment, spreading, and proliferation of human synoviocytes in vitro.

Direct determination of landthanides, yttrium and scandium in bauxites and red mud from alumina production

An analytical procedure for the rapid, accurate and reproducible determination of lanthanides, yttrium and scandium in iron-aluminum rich matrices as bauxites and red mud from alumina production was developed. After a suitable dissolution, the samples were directly analysed for these elements by inductively coupled plasma atomic emission spectroscopy (ICP-AES), without using any separation or preconcentration step. Some of the investigated elements were also directly determined in the solid samples by x-ray fluorescence analysis (XRF). The optimum conditions and analytical wavelengths were selected by both methods for each investigated element, after detailed studying of the spectral interferences from the major elements from the matrix and the interlanthanide-interferences. In the unique reference bauxitic material BX-N, for which only some proposed values exist, the concentration of nearly all lanthanides, yttrium and scandium Sc could be determined. The precision and accuracy of the described ICP-AES and XRF methods for these elements were tested on the geological standard materials SY-2, SY-3 (Canadian syenites) and the proposed values of BX-N. In this study the enrichment factor of the above mentioned elements in red mud were also determined in comparison to the feed bauxites and the constancy of the concentration level in productions samples, followed up over three years. The obtained results for the lanthanides were evaluated on the basis of chondrite normalized distribution patterns.

On reduced polynomial-based split algorithms

In this work we analyze the mathematical structure associated with the split algorithms for computing the reflection coefficients for a given real, symmetric, positive-definite Toeplitz matrix. A new form of three-term recurrence relation is derived and computationally efficient alternatives to the Levinson-Durbin, Schur, lattice, and normalized lattice algorithms are obtained. The computational complexity of the new algorithms is the same as those of the split algorithms described in the recent literature. The relationships between the various algorithms are also established. These algorithms also provide further insight into the mathematical properties of the structurally rich Toeplitz matrices.

Computationally Efficient Reduced Polynomial Based Algorithms for Hermitian Toeplitz Matrices

In this work, the mathematical structure is analyzed that is associated with the fast order-recursive algorithms for computing the reflection coefficients, and the Levinson polynomial associated with a hermitian, positive-definite Toeplitz matrix. A new form of three-term recurrence relation is derived anda computationally efficient alternative to the classical Levinson–Durbin algorithm is obtained. The computational complexity of the new algorithm is the same as those of the split algorithms described in the recent literature. The new algorithm also provides further insight into the mathematical properties of the structurally rich Toeplitz matrices.

The Levinson recurrence and fast algorithms for solving Toeplitz systems of linear equations

This work brings together classical polynomial theory as it relates to the Levinson recurrence for a Hermitian Toeplitz operator and matrix theory as it relates to the class of Hermitian centro-Hermitian matrices. A new computationally efficient alternative is presented to the Levinson recurrence on either the Hermitian or skew-Hermitian polynomial spaces. This approach also leads to an entirely new algorithm for solving systems of linear equations when the coefficient matrix is Hermitian Toeplitz or real symmetric Toeplitz. Analysis of the computational complexity of the algorithms presented is also performed, and it is shown that these algorithms lead to significant improvements in the computational complexity as compared to the previously best-known recursive algorithms. They also provide further insight into the mathematical properties of the structurally rich Toeplitz matrices.

Electrical conductivity of carbon black filled ethylene-vinyl acetate copolymer as a function of vinyl acetate content

The electrical conductivity of carbon black filled ethylene-vinyl acetate copolymer was measured as a function of carbon and vinyl acetate (VAc) content. For the composites whose matrices contain less than 32 wt% ofVAc content, a sharp break point of the relation between carbon content and conductivity was observed. The conductivity jumps as much as ten orders of magnitude at the break point. The critical carbon content corresponding to the break point can essentially be predicted by our previous model. This model was derived under certain assumptions, the most important of which is that when the interfacial excess energy introduced by carbon particles into the polymer matrix reaches a “universal value”,Δg*, the carbon particles begin to coagulate so as to avoid any further increase of energy and to form networks which facilitate electrical conduction. On the other hand, for the composites whose matrices contain more than 32 wt% ofVAc content, a sharp break of the relation between the carbon content and conductivity cannot be observed and conductivity increases continuously with increasingVAc content. In this region ofVAc content, carbon particles were dispersed well in theVAc rich matrices. This is because the presence of polar groups in aVAc component enhances its bonding to conductive fillers. In this case, the interfacial excess energy,Δg, seems to be the caseΔg≤0. Better dispersibility of fillers in this region ofVAc content can be shown from an electron micrograph (TEM).

Larn experience in nondestructive analysis of gold artifacts

Performances of PIXE for the accurate determination of bulk composition of major elements in gold rich matrices are illustrated. Topographical composition of elements in solders of artifacts obtained in a completely nondestructive microprobe arrangement allows to bring light on the workmanship of ancient goldsmiths. The purpose is illustrated for an Iranian pendant of the 4th century B.C. (Musée du Louvre) on which four different kinds of solders have been discovered in a region extending over less than 6 mm.