Free-standing urethane/urea elastomer films undoped and doped with ferro-nano-particles

We report on an experimental study of the structures presented by urethane/urea elastomeric films without and with ferromagnetic nanoparticles incorporated. The study is made by using the X-ray diffraction, nuclear magnetic resonance (NMR), optical, atomic and magnetic force (MFM) microscopy techniques, and mechanical assays. The structure of the elastomeric matrix is characterized by a distance of 0.46nm between neighboring molecular segments, almost independent on the stretching applied. The shear casting performed in order to obtain the elastomeric films tends to orient the molecules parallel to the flow direction thus introducing anisotropy in the molecular network which is reflected on the values obtained for the orientational order parameter and its increase for the stretched films. In the case of nanoparticles-doped samples, the structure remains nearly unchanged although the local order parameter is clearly larger for the undoped films. NMR experiments evidence modifications in the molecular network local ordering. Micrometer size clusters were observed by MFM for even small concentration of magnetic particles.     

The maximum balanced subgraph of a signed graph: Applications and solution approaches

The Maximum Balanced Subgraph Problem (MBSP) is the problem of finding a subgraph of a signed graph that is balanced and maximizes the cardinality of its vertex set. This paper is the first one to discuss applications of the MBSP arising in three different research areas: the detection of embedded structures, portfolio analysis in risk management and community structure. The efficient solution of the MBSP is also in the focus of this paper. We discuss pre-processing routines and heuristic solution approaches to the problem. a GRASP metaheuristic is developed and improved versions of a greedy heuristic are discussed. Extensive computational experiments are carried out on a set of instances from the applications previously mentioned as well as on a set of random instances.     

Existence and Multiplicity of Radial Positive Solutions for a Quasilinear Elliptic Equation with Sign-Changing Nonlinearity

In this paper we will be concerned with questions of existence and multiplicity of radial nonnegative solutions of the quasilinear elliptic equation We will use variational methods in order to prove the existence of multiple solutions in case f is a sign-changing nonlinearity.     

Electrochemical permeability of GCO: Estimation of overpotentials

The basic relationships required to analyse permeability data of fluorite-based solid electrolytes are rewritten in order to account for an overpotential term related to slow surface exchange. Results of a gadolinia doped ceria solid electrolyte suggest that surface exchange might limit the permeability especially at low Po₂ and temperature. However, the analysis of the data with different relationships leads to somewhat different estimates of the electron and hole conductivity and overpotential values. Paper presented at the 5th Euroconference on Solid State Ionics, Benalmádena, Spain, Sept. 13–20, 1998     

Cadmium determination in biological samples by direct solid sampling flame atomic absorption spectrometry

A direct solid sampling flame atomic absorption spectrometric procedure for trace determination of cadmium in biological samples has been developed. Test samples (0.05–2.00 mg) were ground and weighed into small polyethylene vials, which were connected to the device for solid sample introduction into a conventional air/acetylene flame. Test samples were carried as a dry aerosol to a quartz cell, placed between the burner and the optical path, which had a perpendicular entrance and a slit in the upper part. The atomic vapor generated in the flame produced a transient signal that was totally integrated within 1 s. The effect of operating conditions and the extent of grinding on the analytical signal were evaluated. Background signals were always low and a characteristic mass of 0.29 ng Cd was obtained. Calibration was performed using different masses of solid certified reference materials. Results obtained for certified and in-house reference materials were typically within the 95% confidence interval of the certified and/or reference value, and the precision, expressed as relative standard deviation, was between 3.8 and 6.7%. The proposed system is simple and it might be adapted to conventional atomic absorption spectrometers allowing the determination of Cd in more than 80 test samples per hour, excluding weighing.     

On an inequality by N. Trudinger and J. Moser and related elliptic equations

It has been shown by Trudinger and Moser that for normalized functions u of the Sobolev space ??^{1, N} (Ω), where Ω is a bounded domain in ?^N, one has ∫_Ω exp(α_N|u|^{N/(N ? 1)})dx ≤ C_N, where α_N is an explicit constant depending only on N, and C_N is a constant depending only on N and Ω. Carleson and Chang proved that there exists a corresponding extremal function in the case that Ω is the unit ball in ?^N. In this paper we give a new proof, a generalization, and a new interpretation of this result. In particular, we give an explicit sequence that is maximizing for the above integral among all normalized “concentrating sequences.” As an application, the existence of a nontrivial solution for a related elliptic equation with “Trudinger‐Moser” growth is proved. © 2002 John Wiley & Sons, Inc.     

Ein Mehrfluidmodell für die turbulente Gas- und Flüssigkeitsfilm-Strömung

Zusammenfassung Zur Berechnung des Impulstransports in einer abwärts gerichteten, turbulenten Zweiphasenströmung, bestehend aus einer Gasphase und einem Flüssigkeitsfilm (Kern/Film-Strömung) mit welliger Phasengrenzfläche, wird ein Mehrfluidmodell eingeführt. Das Strömungsfeld wird in einen Grundfilm-, einen Wellen- und einen Kernbereich eingeteilt.Die Phasenverteilung im Strömungsfeld wird durch die unvollständige Gamma-Funktion dargestellt, die Reibung zwischen den Phasen durch einen Reibungsbeiwert, welcher von einem dimensionslosen Druckgradienten abhängig ist.Durch Lösung des Gleichungssystems ergibt sich der Druckabfall der Kern/Film-Strömung als Funktion der Reynolds-Zahl des Films und des Kerns. Der berechnete Druckabfall stimmt mit dem aus empirischen Korrelationen gut überein.

---

A multifluid-model for turbulent gas- and liquid-film flow

A multifluid-model is introduced for the momentum transport of a downwards directed turbulent two-phase-flow consisting of a gaseous core and a liquid film (core-film-flow) with wavy interface. The flow field is subdivided into a basic film region, a wavy region and the gaseous core.The phase distribution is represented by the incomplete Gamma-function, and the friction between the phases is given by a friction factor depending on a dimensionsless pressure gradient.From the solution of the governing equations the pressure drop of the core-film-flow is obtained as a function of the liquid- and the core-Reynolds-number. The calculated pressure drop is in good agreement with that obtained from empirical correlations.

     

X-ray powder diffraction and57Fe Mössbauer spectroscopy study of the thermal breakdown of vivianite,Fe3(PO4)2.8H2O

Ferric phosphates resulting from the thermal breakdown of natural Fe₃(PO₄)₂.₈H₂O are studied by X-ray powder diffraction and Mössbauer spectroscopy. Total iron oxidation and water release give rise to an amorphous material. During heating, a transitional cristobalite-type ferric orthophosphate recrystallizes prior to the stable berlinite-type. The main additional final product is a poorly characterized “Fe₃PO₇” phase with iron in octahedral coordination.     

Use of thermal neutrons to perform clinical analyses in blood and urine samples

Summary In this study we show that the NAA technique can be used to perform clinical analyses of blood and urine, with many advantages towards the conventional methods. From the knowledge of the neutron flux and the induced activity, the concentration ofelements were obtained. In comparison to the conventional techniques, this methodology uses smaller quantities of biological material and allows the simultaneous evaluation of the concentrations of several elements in biological samples at once, something not always possible in the conventional clinical analysis. Another important advantage is that it eliminates the use of standard materials, thus making the analyzing process practical and economic.