The maximum multiplicity of an eigenvalue in a matrix whose graph is a tree

We study the maximum possible multiplicity of an eigenvalue of a matrix whose graph is a tree, expressing that maximum multiplicity in terms of certain parameters associated with the tree.     

Mechanical, rheological, fatigue, and degradation behavior of PLLA, PGLA and PDGLA as materials for vascular implants

The biggest challenge in the treatment of arterial stenosis remains the issue of optimization of stent design. Despite continuous improvement in surgical techniques and use of intensive pharmacotherapy, the results of stent coronary interventions may be unsatisfactory, and long-term interaction of a metal implant with a blood vessel results in complications such as recurrent stenosis and thrombosis. Therefore, it is necessary to search for new materials and stent designs to obtain a stent capable of restoring flow in the vessel and disappearing after fulfilling its function. Such stent must also be compatible with the vessel wall to enable regeneration of new structure of endothelium and deeper artery layers damaged during implantation. Consequently, there is ongoing search for functional solutions with minimum effects of long-term implant-tissue interaction. In light of the above, the team investigated the possibility of using biodegradable polymers already mentioned in the literature as a construction material for vascular stent. The study used three polyhydroxyacids based on lactic acid and glycolic acid: poly(l-lactide), poly(lactide-co-glycolide) and poly(d,l-lactide-co-glycolide). The research focused on assessing changes in mechanical, thermomechanical, rheological, and fatigue properties during the process of hydrolytic degradation. The analysis also covered the rate of release of degradation products. The results of the conducted tests indicate the possibility of developing a vascular stent with biodegradable polymers.     

Comparison of two posthydrolysis processes of Brewery's spent grain autohydrolysis liquor to produce a pentose-containing culture medium

A readily fermentable pentose-containing hydrolysate was obtained from Brewery's spent grain by a two-step process consisting of an auto-hydrolysis (converting the hemicelluloses into oligosaccharides) followed by an enzymatic or sulfuric acid-catalyzed posthydrolysis (converting the oligosaccharides into monosaccharides). Enzymatic hydrolyses were performed with several commercial enzymes with xylanolytic and cellulolytic activities. Acid-catalyzed hydrolyses were carried out at 121°C under various sulfuric acid concentrations and reaction times, and the effects of treatments were interpreted by means of a corrected combined severity factor (CS ¹), which varied in the range of 0.80–2.01. Under the tested conditions, chemicalhydrolysis allowed higher pentose yields than enzymatic hydrolysis. Optimized conditions (defined by CS ¹=1.10) allowed both complete monosaccharide recovery and low content of inhibitors. Liquors subjected to posthydrolysis under optimal conditions were easily fermented by Debaryomyces hansenii CCMI 941 in semiaerobic shake-flask experiments, leading to xylitol and arabitol as major fermentation products. The bioconversion process was improved by hydrolysate concentration and supplementation of fermentation media with casamino acids. The authors wish it to be known that the first two authors should be regarded as joint First Authors.     

Electrochemistry of lanthanum and uranium chlorides in organic media: Deposition of lanthanum and uranium

Molten salts have been widely used for the electrochemical preparation of lanthanum and uranium metals at high temperature. In this paper we demonstrate the feasibility of a similar process in dimethylformamide (DMF) and in the mixture g-butyrolactone/tetrahydrofuran (g-BL/THF). The best conditions for the preparation were deduced from preliminary transient electrochemistry experiments and from secondary ions mass spectrometry (SIMS) measurements involving SIMS mappings and SIMS depth profile analyses.     

A survey on inborn errors of metabolism in 323 neonates from the state of Rio de Janeiro, Brazil

Inborn errors of metabolism (IEM) are a relevant cause of morbidity and death among children, and neonates in particular. However, little is known about the prevalence of these disorders in Brazilian newborns. Our laboratory of IEM (LABEIM) at the Department of Biochemistry, Institute of Chemistry, Federal University of Rio de Janeiro (UFRJ), has been working on the diagnosis of IEM since 1988. Out of 3,300 patients (90% children), screened and evaluated from 1989 to 2,000 because of a high clinical suspicion of having an IEM, 323 (9.8%) were neonates. Patients came from different regions of the state of Rio de Janeiro, in which lives approximately 8.5% of the total Brazilian population. Chemical tests, various chromatographic techniques and enzyme assays were performed in urine, plasma and in some cases, cerebrospinal fluid (CSF). This study describes our laboratory and the experience with the 323 investigated neonates, among which 28 cases (8.7%) of IEM were identified and 18 (5.6%), strongly suspected. All these cases were related mainly to the metabolism of amino acids, organic acids, lysosomal enzymes and carbohydrates. Furthermore, data on population, community and health services are presented.     

Specific Features of the Properties of Co–Cu Granular Media Caused by the Structure of the Material

A comparative analysis of rapidly quenched strips and thin films prepared from Co–Cu alloys with giant reluctance is performed. It is established that their microstructure and phase composition differ strongly. Precipitates of Co-enriched phase of two types that differ in their origin and sizes are present in strips. Large particles (100 nm) having the fcc structure determine the magnetic properties, and small particles ( 5 nm) determine the reluctance. In films, Co particles of only one type are detected. They have hexagonal close-packed lattice, can be in superparamagnetic and ferromagnetic states, and yield the corresponding contributions to the giant reluctance. The above-indicated specific features in the microstructure lead to different magnetic and reluctance properties of strips and films.     

Critical assessment of the parameters that affect the selection of coating compounds for piezoelectric quartz crystal microbalances

The selection of the compound to be used as a coating for a piezoelectric quartz crystal is of utmost importance in the development of a chemical sensor. The relevant parameters to be evaluated (stability, sensitivity, reversibility, response time, reproducibility, and selectivity), and the main variables affecting the results and influencing the choice of coatings are discussed and illustrated with experiments performed during the evaluation of coatings to detect carbon dioxide.     

Tunable solid-state lasers incorporating dye-doped, polymer-nanoparticle gain media

Tunable laser action in the visible spectrum has been established for what is believed to be the first time by use of dye-doped, polymer-silica nanoparticle gain media. The silica nanoparticles, ranging from 9 to 12 nm in diameter, appear to be uniformly dispersed in the poly(methyl methacrylate) matrix because the optical homogeneity of the gain medium is maintained. With Rhodamine 6G dye and 30% weight-by-weight silica nanoparticles, laser action was established in the 567-603-nm range. At the peak wavelength (lambda approximately 580 nm), laser conversion efficiency is approximately 63% at a beam divergence of 1.9 mrad (approximately 1.3 times the diffraction limit). The new solid-state gain medium also exhibits a reduction in /deltan/deltaT/.     

Direction coherence in scale-free lattices of chaotic maps

We considered a coupled chaotic logistic map lattice exhibiting the scale-free property: the outreach connectivity of each node obeys a power-law distribution. We analyzed a weak form of coherent spatio-temporal behavior (direction coherence) which presents features common to completely synchronized states, like a transitional behavior with intermittent bursting. We studied such phenomena and their dependence on the parameters of the coupled scale-free lattice. Prospective applications in neuronal networks are emphasized.