Microstructural characterization of transparent conducting aluminium doped zinc oxide films prepared by spray pyrolysis

X-ray diffraction patterns of pyrolytically sprayed aluminium doped zinc oxide films have been recorded and X-ray line profile analysis studies have been carried out after correcting for instrumental broadening. Different microstructural parameters such as crystallite size, r.m.s. strain and dislocation density have been determined from the variance analysis of X-ray line profiles. Texture coefficient, the degree of preferred orientation of the crystallites and stacking fault have been estimated from the X-ray diffraction data. It is observed that the figure of merit as a transparent conductor depends on the dopant concentration and microstructural parameters of the films deposited under identical growth conditions.     

Photoluminescence properties of sesquioxide doped ceria synthesized by modified sol-gel route

Highly crystalline and porous sesquioxide (Sm₂O₃, La₂O₃) doped ceria with different molar ratio is successfully synthesized by a simple modified sol-gel route. X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDAX) are used to investigate their phase, microstructure and composition. XRD analysis confirmed the formation of highly crystalline cubic fluorite phase in all samples. The Raman spectroscopy revealed a single triple degenerated F_2g mode as the attestation of the oxygen vacancy in the doped and undoped samples. Strong photoluminescence lines due to interconfigurational transition and vacancy mediated transition were observed in doped CeO₂. The oxygen vacancy induced luminescence of CeO₂ was strongly enhanced due to La doping. The effect of rare earth dopant on the photoluminescence properties has been studied in details.     

A model for optimal repair-effort decision for standby redundant systems with common-cause failures and its application to pulverizer systems

This paper presents a model to allocate the repair efforts optimally between the individual unit and the subsystem contributing to the common cause failure of the system with a view to improving the overall system availability. It describes a general model to solve repair-effort decision problem for a redundant system with common-cause failures and three types of repair. The application of this model to a pulverizer system is also presented in this paper.     

Structural basis for the recognition of carbohydrates by human galectin-7

Knowledge about carbohydrate recognition domains of galectins, formerly known as S-type animal lectins, is important in understanding their role(s) in cell-cell interactions. Here we report the crystal structure of human galectin-7 (hGal-7), in free form and in the presence of galactose, galactosamine, lactose, and N-acetyl-lactosamine at high resolution. This is the first structure of a galectin determined in both free and carbohydrate-bound forms. The structure shows a fold similar to that of the prototype galectins -1 and -2, but has greater similarity to a related galectin molecule, Gal-10. Even though the carbohydrate-binding residues are conserved, there are significant changes in this pocket due to shortening of a loop structure. The monomeric hGal-7 molecule exists as a dimer in the crystals, but adopts a packing arrangement considerably different from that of Gal-1 and Gal-2, which has implications for carbohydrate recognition.     

Periodicity and bifurcations in capillary tube boiling with a concentric heating wire

Nucleate boiling from a vertical glass capillary in a pool of water is investigated here. Electrical heating is provided with a wire passing concentrically through the center of the capillary, and a fast-response thermocouple at the lip of the capillary records the instants of bubble departure. Different lengths and diameters of capillaries are used in the experiments. The average frequency of bubbling is seen to increase with applied heat flux, the relation being linear in the initial stages. With the heat flux used as a bifurcation parameter, one-dimensional return maps of the time interval between successive bubble emission events are used to study the transitions from the periodic state. The first bifurcation from the periodic to a two-period state is observed to be due to lateral instability of the liquid film adhering to the capillary wall. Further bifurcations to period two and then to period three bubbling are also observed. Simplified analysis of the different phases of the boiling process yields solutions which show close agreement with the experimental data.     

Low-temperature preparation of polycrystalline silicon from silicon tetrachloride

Polycrystalline silicon has been prepared by zinc reduction of silicon tetrachloride at a low temperature (≈550° C) in a vertical vapour phase reactor. Characterisation of the remelted polycrystalline ingot by X-ray, SEM and electrical methods shows that the material is p-type with an average grain size of 0.5 μm having a room-temperature resistivity in the range 1.0–1.5 Ω cm suitable for solar cell fabrication.     

A Heuristic Approach to the Railroad Track Maintenance Scheduling Problem

Abstract: Every year, billions of dollars are spent on rail track maintenance to keep the serviceability of the railroad network. These maintenance projects (of different types) must be performed by suitable maintenance teams within a planning horizon. This article presents a time‐space network model to solve the track maintenance scheduling problem (TMSP). The objective is to minimize the total travel costs of the maintenance teams as well as the impact of maintenance projects on railroad operation, which are formulated by three types of side constraints: mutually exclusive, time window, and precedence constraints. An iterative heuristic solution approach is proposed to solve the large‐scale TMSP model with a large number of side constraints. The proposed model and solution approach are applied to a large‐scale real‐world problem. Compared to the current industry practice the model outcome eliminated all hard side‐constraint violations and reduced the total objective value (travel costs and soft side‐constraint violation penalties) by 66.8%.     

Analysis and characterization of wind-solar-constant torque spring hybridized model

Solar and wind are the most promising renewable energy resources. But their unpredictable and varying nature prevents them from being used as the sole resource for power generation. This paper presents a model of wind and solar thermal hybrid power plant with a spring storage system which is expected to play an efficient role in combating with the drawbacks related to renewable power generation. In the proposed scheme, wind energy is harnessed by a hybrid vertical axis wind turbine, solar energy is utilized by a Stirling engine, and the surplus energy is stored in a winding spring. The paper discusses the working methodologies and analyses the performance of such 2.6 kW hybrid power plant model. It has been observed that the plant is capable of consistently generating 50% of its rated capacity irrespective of limitations in solar and wind resources.     

Refrigerants as working fluid in a CPC collector system for electric power generation

Compound parabolic concentrators (CPC) achieve highest possible concentration for any acceptance angle. One of the simplest methods of utilizing the energy of the sun to generate electric power is to use a CPC collector system. A truncated CPC can be used without much loss in concentration. Compared with a full CPC the cost of construction of a truncated CPC is much less. A CPC requires only seasonal adjustments. This further reduces the cost of tracking which is required for other types of concentrators. In this paper it has been shown that the refrigerants R11, R12, R113 and R114 can be satisfactorily used as working fluids in CPC collector systems. By using these working fluids, overall conversion efficiency of 9% can be achieved. Other refrigerants R12, B1, R22, R500, R502, R115 and C318 are found not to be suitable as they produce very low overall conversion efficiencies. In order to produce 20 kW of electricity at 1000 W/m² insolation about 920 truncated CPC collectors (2 m length, 0.15 m aperture) with a concentration ratio of 8 are required. This minimum number of collectors would be required at an overall conversion efficiency of 9%.