Mo–Si–B alloys for ultra-high-temperature space and ground applications: liquid-assisted fabrication under various temperature and time conditions

Journal of Materials Science - Boron-doped molybdenum silicides have been already recognized as attractive candidates for space and ground ultra-high-temperature applications far beyond limits of...     

Hydrogen Evolution on Binary and Ternary Cobalt Alloys Deposited With Superimposed Magnetic Field

The article presents results of electrodeposition of Co-Mo Co-Mo-C alloys in a magnetic field characterized by low overvoltage of hydrogen evolution.Addition of molybdenum and carbon was to lower the values of overvoltage of hydrogen evolution on cobalt.The influence of bath pH,bath composite,current density and magnetic field with different orientation on the deposits composition,structure and overpotential for hydrogen evolution reaction(HER)was determined.Electrocatalytic properties of the obtained alloy coatings within the range of hydrogen evolution were tested in a concentrated NaOH solution.The comparison of electrocatalytic properties of Co-Mo alloys with properties of Co-Mo-C ones enabled determining the influence of carbon presence in cathodic deposits on the overpotential values for hydrogen evolution.     

The influence of oxidizing agents on water extracts of rye flour

The main constituents of rye flour extracts are proteins and pentosans. After cross-linking under the action of oxidizing agents those components are able to bind much more water than in their native (prior to modifications) state. As a consequence rheological properties of extract are changed.It was observed that kinematic viscosity of water extract of rye flour decreases rapidly with time. The reason for this behavior could be high enzymatic activity of flour extract.It was also found that the addition of hydrogen peroxide in the absence of additional peroxidase (which is naturally present in 1:9 or 1:1 water extracts of flour) causes the greatest increase in viscosity, due to the cross-linking of soluble polymers. Moreover after the addition of H₂O₂ to water extracts strong gels were obtained, which were characterized by tan δ = 0.5 (tan δ < 1). Moreover G′ was independent of frequency, which also suggests cross-linking of the pentosans.The addition of ascorbic acid, which is known to act preferably on gluten proteins, to 1:9 or 1:1 flour extracts had only a little effect on viscosity. In this case the values of tan δ = 0.9 were close to 1, which is typical for a weak gel.The application of inactivated rye flour extract, containing mainly proteins and pentosans, proved stronger effect of H₂O₂ in comparison to ascorbic acid on polymer cross-linking, but only after the addition of peroxidase. The gel obtained with H₂O₂ and peroxidase was also characterized by low tan δ = 0.4.The results indicate, that pentosans are the main subject of cross-linking reactions in rye flour water extracts.     

Parameter estimation of the electrothermal model of the ferromagnetic core

The paper presents a new form of the electrothermal model of the ferromagnetic core for SPICE and the way, in which the parameters of the model are determined. The manner of determining magnetic, geometric and thermal parameters of this model is described. The correctness of the proposed model and the manner of determining the values of the parameters are verified by comparing the calculated and measured characteristics of the selected ferromagnetic cores.     

Analysis of Experimental Grain Boundary Distributions Based on Boundary-Space Metrics

Grain boundary distributions in the space of macroscopic boundary parameters are basic statistical characteristics of boundary networks. To avoid artifacts caused by the currently used computation method, it is proposed to utilize the kernel density estimation technique and to determine boundary distributions based on metric functions defined in the boundary space. A distribution is calculated at points of interest by summing areas of boundaries that fall within specified distances from these points. The new method is illustrated on experimental data of a nickel-based superalloy.     

ANN–supported control strategy for a solid oxide fuel cell working on demand for a public utility building

The idea of control strategy of SOFC operating to meet demand of a public utility building was presented. The strategy was formulated with the support of Artificial Neural Network. The network was used to predict the demand for electricity. The calculations were carried out on the example of a building of the Institute of Heat Engineering Warsaw University of Technology. The control strategy is influenced by various factors depending on changes in market conditions and operating characteristics of the cell. We can define different objective functions eg: working for own needs, for maximum profit and maximum service life. The article presents a simulation of SOFC operation for demand profile of the IHE building from the selected time period.     

Modification of Fe and Al elemental powders’ sintering with addition of magnesium and magnesium hydride

An attempt to modify sintering of iron and aluminium elemental powders with use of small additions of Mg and MgH₂ was presented in this paper. The kinetics of such modified sintering was investigated using DSC technique, XRD analysis and SEM observations. Significant changes in the mechanism of exothermal formation reaction of Fe–Al intermetallic phases in compositions doped with magnesium and its hydride was observed. Initiation temperature of Self-propagating High-temperature Synthesis (SHS) reaction was pronouncedly shifted to lower value as compared with undoped composition. Influence of additions on the SHS reaction kinetics parameters was also calculated with use of the JMA model and changes of the Avrami exponent value of specific phase formation was noticed. Positive effect of MgH₂ addition on partial homogeneity of final product was also studied.     

Constrained pseudo‐transient continuation

This paper addresses the problem of finding a stationary point of a nonlinear dynamical system whose state variables are under inequality constraints. Systems of this type often arise from the discretization of PDEs that model physical phenomena (e.g., fluid dynamics) in which the state variables are under realizability constraints (e.g., positive pressure and density). We start from the popular pseudo‐transient continuation method and augment it with nonlinear inequality constraints. The constraint handling technique does not help in situations where no steady‐state solution exists, for example, because of an under‐resolved discretization of PDEs. However, an often overlooked situation is one in which the steady‐state solution exists but cannot be reached by the solver, which typically fails because of the violation of constraints, that is, a non‐physical state error during state iterations. This is the shortcoming that we address by incorporating physical realizability constraints into the solution path from the initial condition to steady state. Although we focus on the DG method applied to fluid dynamics, our technique relies only on implicit time marching and hence can be extended to other spatial discretizations and other physics problems. We analyze the sensitivity of the method to a range of input parameters and present results for compressible turbulent flows that show that the constrained method is significantly more robust than a standard unconstrained method while on par in terms of cost. Copyright © 2015 John Wiley & Sons, Ltd.     

Polyurethane/Polylactide-Based Electrospun Nonwovens as Carriers for Human Adipose-Derived Stromal Stem Cells and Chondrogenic Progenitor Cells

Articular cartilage dysfunctions are major cause of pain and disability and lead to serious health complications. Cell-based therapies are proposed as treatment methods for cartilage regeneration. In this study, we proposed polyurethane/poly(L-lactide-co-D, L-lactide)-based electrospun nonwovens as carriers for the delivery of human adipose-derived stromal stem cells. We found that 6:4 and 8:2 polyurethane/poly(L-lactide-co-D, L-lactide) initially enhance proliferative rate of human adipose-derived stromal stem cells, shorten their population doubling time, promote creation of functional chondrogenic nodules during chondrogenic differentiation, improve the collagen-2-to-collagen-1 protein ratio, and upregulate the expression of collagen-2 and aggrecan genes.