The coefficient of performance for a solar absorption dual cycle

The traditional definition of the coefficient of performance (COP) can create misleading results because this definition does not define the heat input base to be used for estimating the COP. Furthermore, such one-dimensional definitions do not consider other important factors which may affect the system selection.

A new selection criterion for a solar powered dual absorption system will be presented in this paper. The dual cycle, which has the advantage of not using a cooling tower, has often been ignored because of the misleading definition of the COP.

The present paper also describes a lithium bromide dual absorption cycle.     

A solar-powered LiBr dual cycle

The absorption system is one of the most suitable techniques for utilising solar energy for air-conditioning purposes. Although it uses solar energy directly with minimum conversion, it consumes considerable quantities of water for the cooling tower. This is a serious disadvantage where solar energy is available whilst water is scarce.The main purpose of this paper is to introduce the lithium bromide (LiBr) absorption cycle which avoids the use of a wet cooling tower. The characteristics of this dual cycle will be examined and new selection criteria for such solar-powered dual absorption systems will be introduced.     

Development of electrically conductive hybrid nanofibers based on CNT‐polyurethane nanocomposite for cardiac tissue engineering

Conductive nanofibers have been considered as one of the most interesting and promising candidate scaffolds for cardiac patch applications with capability to improve cell–cell communication. Here, we successfully fabricated electroconductive nanofibrous patches by simultaneous electrospray of multiwalled carbon nanotubes (MWCNTs) on polyurethane nanofibers. A series of CNT/PU nanocomposites with different weight ratios (2:10, 3:10, and 6:10wt%) were obtained. Scanning electron microscopy, conductivity analysis, water contact angle measurements, and tensile tests were used to characterize the scaffolds. FESEM showed that CNTs were adhered on PU nanofibers and created an interconnected web‐like structures. The SEM images also revealed that the diameters of nanofibers were decreased by increasing CNTs. The electrical conductivity, tensile strength, Young's modulus, and hydrophilicity of CNT/PU nanocomposites also enhanced after adding CNTs. The scaffolds revealed suitable cytocompatibility for H9c2 cells and human umbilical vein endothelial cells (HUVECs). This study indicated that simultaneous electrospinning and electrospray can be used to fabricate conductive CNT/PUnanofibers, resulting in better cytocompatibility and improved interactions between the scaffold and cardiomyoblasts.     

Characterization of the structural,magnetic and magnetocaloric properties of double perovskite La<Subscript>1.95</Subscript>Sr<Subscript>0.05</Subscript>BMnO<Subscript>6</Subscript> (B = Ni and Co)

An exhaustive study of structural, magnetic and magnetocaloric properties on La_1.95Sr_0.05BMnO₆ (B?=?Ni and Co) double perovskite were performed. The samples were prepared by the sol–gel method. The crystallographic structure was studied by the X-ray diffraction patterns and Rietveld refinement which revealed that all samples crystallize in a monoclinic structure with P2₁/n space group. The magnetic behaviors of these double perovskite have been studied in detail. For La_1.95Sr_0.05NiMnO₆, the M(T) curves exhibit double magnetization transition temperature at 68 K and 266 K which can be ascribed to Ni³⁺–O–Mn³⁺ and Ni²⁺–O–Mn⁴⁺ superexchange interaction, respectively. However, unique magnetic transition has been observed for the La_1.95Sr_0.05CoMnO₆ double perovskite at 210 K due to Co²⁺–O–Mn⁴⁺ superexchange interaction. A deep investigation based on the Landau Theory and Arrot analysis confirmed a second order ferromagnetic phase transition for both samples. Besides, the magnetocaloric behaviors of these new samples have been studied by analysis the magnetic entropy change. This latter reached maximum values of 1.01 and 1.35 J/kg/K for La_1.95Sr_0.05NiMnO₆ and La_1.95Sr_0.05CoMnO₆, respectively, under µ₀H?=?5 T. Moreover, the relative cooling power values for La_1.95Sr_0.05NiMnO₆ and La_1.95Sr_0.05CoMnO₆ are found to be 94 J/kg and 116 J/kg, respectively, under µ₀H?=?5 T. Based on the obtained ΔS_M data, we have also described the universal master curve for (ΔS_M/\(\Delta S_{M}^{{\hbox{max} }}\)) versus rescaled temperature to confirm the order magnetic phase transition. Interestingly, all the ΔS_M(T, H) data points are collapsed into a universal curve in the whole temperature range. The significant values of relative cooling power for both samples suggest that they might be an interesting candidate for exploring a new kind of magnetic refrigerants.     

Phenomenological model of the magnetocaloric effect and its correlation with critical behavior near room temperature in La<Subscript>0.7</Subscript>Ca<Subscript>0.2</Subscript>Sr<Subscript>0.1</Subscript>MnO<Subscript>3</Subscript> manganite

In this paper, we investigate the field dependence of the magnetocaloric properties of La_0.7Ca_0.2Sr_0.1MnO₃ powder sample using a phenomenological model. Our compound was elaborated by the conventional solid state reaction. The model parameters were determined from the magnetization data and were used to give better fits to magnetic transition and to calculate the magnetocaloric quantities. The magnetocaloric parameters such as the maximum of the magnetic entropy change \(\Delta S_M^{max}\) and the relative cooling power RCP, have been determined from the calculation of the magnetization as a function of temperature under several magnetic applied field. Thus, from the magnetocaloric results, such as RCP?≈?b(μ₀H)^1+1/δ and T_peak???T_C ≈ b (µ₀H)^1/Δ, the critical exponents values related to the magnetic transition have been determined. The estimated results are close to those expected by the tricritical mean-field model. Furthermore, the values of the ferromagnetic transition temperature T_C, as well as the critical exponents β, γ and δ obtained by the theoretical model, are compared with those obtained by other various techniques (such as the modified Arrott plots, the Kouvel–Fisher method and the critical isotherm analysis). A good agreement has been found in the vicinity of the Curie temperature.     

Cutset enumeration of network systems with link and node failures

Network reliability analysis has received considerable attention and is thus widely studied to predict and prevent any network failure. However, most of such works presume perfectly reliable nodes. Although a few studies have considered both link and node failures, none of these methods has utilized the minimal paths or cuts, which are considered as fundamental approaches in the network reliability evaluation. An efficient method for deducing the minimal cutsets of a system subject to both link and node failures from the minimal cutsets of the system, which assumes perfect node reliability, is presented. The proposed method does not require re-enumeration of minimal cutsets for the additional consideration of the node failures. For a simple extension of such a method, the proposed approach can be embedded in any exact or approximate algorithm to account for link failures as well as node failures. As a result, the application of this method would be more realistic and valuable in practice for the reliability evaluation of networks with unreliable nodes.     

A newly synthesized single crystal zinc complex as molecular electrocatalyst for efficient hydrogen generation from neutral aqueous solutions

A new chlorobis(2-aminomethylbenzimidazole)zinc(II) perchlorate complex [Zn(AMB)₂Cl](ClO₄) 1 has been synthesized and characterized. Spectral and X-ray structural features led to the conclusion that the zinc(II) complex has a square-pyramidal environment around zinc(II) center with coordination chromophore ZnN₄Cl. Different amounts of complex 1 were supported on glassy carbon (GC) electrode yielding three GC-supported complex 1 electrodes with different loading densities (0.2, 0.4, and 0.8 mg cm^?2). These electrodes were tested as molecular electrocatalysts for the hydrogen evolution reaction (HER) in phosphate buffer aqueous solutions (pH 7), employing linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS). Results showed that GC-complex 1 catalysts are highly active for the HER, and this catalytic activity enhances with the loading density. The one with the highest loading density (0.8 mg cm^?2) exhibited high HER catalytic activity with low onset potential of ?140 mV vs. RHE and a high exchange current density of 0.22 mA cm^?2. It required an overpotential of 240 mV to achieve a current density of 10 mA cm^?2. It also recorded a turnover frequency (TOF) of 1722 mol of hydrogen per mole of catalyst per hour at overpotential 500 mV, which is comparable with the most active molecular electrocatalysts reported in the literature for H₂ generation from aqueous neutral solutions. A catalytic cycle is proposed for the generation of hydrogen by complex 1 and the mechanism of the HER is discussed based on the measured Tafel slope (140 mV dec^?1).     

Cycloadditions of 1-Aza-2-azoniaallene Salts derived from coumarin and camphor

The 1-aza-2-azoniaallene salt 8 prepared from 3-acetyl coumarin via the hydrazone 6 and the (chloroalkyl)azo derivative 7 reacts with nitriles to afford the 3-(3-chromenyl)-1,2,4-triazolium salts 11a–d . With diisopropylcarbodiimide the triazolium salt 13 and with norborene a tricyclic pyrazolium salt 14 are obtained. Concurrent to these cycloadditions the by-product 12 is formed by intramolecular cyclization of the cumulene 8 . Similarly, the intramolecular cyclization product 18 is isolated as the sole product when the 1-aza-2-azoniaallene salt 17a (prepared from the ethyl carbazone of camphor by chlorination and treatment of the product 16a with SbCl₅) was treated with nitriles, carbodiimides or alkenes. In contrast, 1,2,4-triazolium salts 20a–c , 23c , respectively pyrazolium salts 20d–f , and 1,3,4-thiadiazolium salts 23a,b are obtained by reaction of the 1-aza-2-azoniaallene salt 17b with nitriles, respectively alkenes, alkynes, diisopropylcarbodiimide, and isothiocyanates. The constitutions of two of these products ( 20e, 23a ) were secured by X-ray structural analysis.     

Software‐defined networking approach for enhanced evolved packet core network

The evolved packet core (EPC) network is the mobile network standardized by the 3rd Generation Partnership Project and represents the recent evolution of mobile networks providing high‐speed data rates and on‐demand connectivity services. Software‐defined networking (SDN) is recently gaining momentum in network research as a new generation networking technique. An SDN‐based EPC is expected to introduce gains to the EPC control plane architecture in terms of simplified, and perhaps even software‐based, vendor independent infrastructure nodes. In this paper, we propose a novel SDN‐based EPC architecture along with the protocol‐level detailed implementation and provide a mechanism for identifying information fields exchanged between SDN‐EPC entities that maintains correct functionality with minimal impact on the conventional design. Furthermore, we present the first comprehensive network performance evaluation for the SDN‐based EPC versus the conventional EPC and provide a comparative analysis of 2 networks performances identifying potential bottlenecks and performance issues. The evaluation focuses on 2 network control operations, namely, the S1‐handover and registration operations, taking into account several factors, and assessing performance metrics such as end‐to‐end delay (E2ED) for completion of the respective control operation, and EPC nodes utilization figures.