Three-dimensional fundamental solution of wave propagation and transient heat transfer in non-homogenous media

The main purpose of this paper is developing fundamental solutions of three-dimensional wave and transient heat conduction in non-homogenous media. A variable transformation method is used to change the basic equations into a simple standard Helmholtz form. First, two different ways, i.e. harmonic excitation method and Laplace transform are used to eliminate time expression, and final solutions are expressed in the time-space domain. In addition, FE approach is applied to solve transient heat conduction in functionally graded material (FGM) domain. Different numerical examples are used to validate the proposed methodology by comparing the results with others and FE method. Fundamental solutions are found for both homogenous and non-homogenous media separately. For each example, appropriate graphs are provided to show the differences between the results of homogenous and non-homogenous media.     

Highly selective ratiometric fluorescence determination of Eu3+ ion based on (4E)-4-(2-phenyldiazenyl)-2-((E)-(2-aminoethylimino)methyl)phenol

(4E)-4-(2-phenyldiazenyl)-2-((E)-(2-aminoethylimino)methyl)phenol (PAMP) was synthesized for the first time and used as a ratiometric fluorescent chemosensor for recognition of Eu³⁺ ions in acetonitrile solution. PAMP shows a fluorescent emission at 536 nm. When it forms a complex with Eu³⁺ ion, two new fluorescent enhancements at 418 and 496 nm appeared. In acetonitrile solution, the blue shift of fluorescent emission upon europium binding is due to the formation of a 1:1 metal ligand complex. The chemosensor shows a linear response toward Eu³⁺ in the range of 8.3 × 10^? 8 M to 8.3 × 10^? 6 M. The new fluorescent probe exhibits high selectivity toward Eu³⁺ ions over a large number of interfering cations.     

Fuel cell energy generation and recovery cycle analysis for residential application

Today’s concern regarding limited fossil fuel resources and their contribution to environmental pollution have changed the general trend to utilization of high efficiency power generation facilities like fuel cells. According to annual reducing capital cost of these utilities, their entrance to commercial level is completely expected. Hot exhaust gases of Solid Oxide Fuel Cells (SOFC) are potentially applicable in heat recovery systems. In the present research, a SOFC with the capacity of 215 kW has been combined with a recovery cycle for the sake of simultaneous of electric power, cooling load and domestic hot water demand of a hotel with 4600 m² area. This case study has been evaluated by energy and exergy analysis regarding exergy loss and second law efficiency in each component. The effect of fuel and air flow rate and also current density as controlling parameters of fuel cell performance have been studied and visual software for energy-exergy analysis and parametric study has been developed. At the end, an economic study of simultaneous energy generation and recovery cycle in comparison with common residential power and energy systems has been done. General results show that based on fuel lower heating value, the maximum efficiency of 83 percent for simultaneous energy generation and heat recovery cycle can be achieved. This efficiency is related to typical climate condition of July in the afternoon, while all the electrical energy, cooling load and 40 percent of hot water demand could be provided by this cycle. About 49 percent of input exergy can be efficiently recovered for energy requirements of building. Generator in absorption chiller and SOFC are the most destructive components of exergy in this system.     

Polyester-polyether block copolymers. I. Wide-angle X-ray diffraction studies of poly(hexamethylene terephthalate)/poly(oxytetramethylene) and related block polymers

The crystallisation and orientation of the individual structural components of poly(hexamethylene terephthalate)/poly(oxytetramethylene) block copolymers have been studied by wide-angle X-ray diffraction. The crystallisation behaviour in the unstretched state is determined by the proportions and molecular weights of the polyether blocks. For copolymers containing less than 60 wt% of polyether of m. w. ≯ 2000, only the polyester segments crystallise spontaneously, but with polyether m. w > 2000 two crystalline phases are formed. Similar behaviour was found in block polymers from other readily crystallising polyesters, but with non-crystallising polyesters the polyether segments crystallised spontaneously. Moderate tensile deformation of the block copolymers from polyether of m. w. 2000 leads to the stress-reversible highly oriented crystallisation of the polyether whilst the polyester remains undeformed. At higher extensions, irreversible orientation of the polyester segments occurs. The observations suggest that the polyester and polyether segments form discrete regions since otherwise homogeneous crystallisation should occur.     

Kinetics and Mechanism of Potassium Persulphate/L-Serine Initiated Polymerization of Methylmethacrylate

The polymerization kinetics of methyl methacrylate with K₂S₂O₈/L-serine redox system has been investigated volumetrically at 35±0.1°C under nitrogen atmosphere acidic aqueous medium in DMF/H₂O mixture (50% v/v). The rates of polymerization were measured varying concentrations of the monomer, initiator, L-serine as well as temperature; and it was found to increase with increasing of both temperature and concentrations of monomer, initiator, and L-serine. The overall energy of activation (E _a ) has been calculated to be 29.48 kJ/mol from the Arrhenius plot in temperature range 25–50°C. The molecular weight of the polymer was determined by gel permeation chromatography (GPC). Based on kinetic studies and depending on the results obtained, a suitable reaction mechanism has been suggested and the rates of polymerization found to obey the following equation: V _p [methyl methacrylate]^1.09[L-serine]^1.03[K₂S₂O₈]^0.96.     

Ceramic electrolytes and electrochemical sensors

The electrochemical method involving solid electrolytes has been known as a selective and an accurate way of sensing chemical species in the environment and even in liquid metal for some time. The most successful among the electrochemical sensors are the emission control sensor (-sensor) for the automobile engine and the oxygen sensor used in steelmaking, both made of stabilized zirconia. This article presents an overview of basic principles of various types of electrochemical sensors including active (potentiometric) and passive (amperometric) sensors. Recent advances in oxygen (O₂), carbon dioxide (CO₂) and hydrogen (H₂) sensors are also presented.     

Stochastic behavior of a two-unit cold standby redundant system subject to random failure

The present paper deals with a stochastic model of a two-unit cold standby redundant system subject to random failure. The random failure occurs at random times which follow an exponential distribution. Using a regenerative point technique in the Markov-renewal process, several reliability characteristics are obtained. The mean time to system failure function is studied graphically.