Influence of Al doping in LaCoO3 on structural,electrical and magnetic properties

We report investigations on polycrystalline LaCo_1?x Al _x O₃ (x = 0–0.9) bulk samples. The solid state synthesized samples showed a coexistence of rhombohedral and monoclinic phases in the intermediate concentrations (0.2 ≤ x ≤ 0.5) and pure rhombohedral phase otherwise. The observed effect of Al doping on dc transport has been analysed on the basis of small polaron hopping mechanism. The magnetisation results presented give evidence of weak ferromagnetism and anomalous temperature dependence of coercivity which we associate to the canting of the localised high-spin Co(III) and anti-symmetric exchange interactions at low temperatures.     

Multiple insights call for revision of modern thermodynamic models to account for structural fluctuations in water

Modern thermodynamic models incorporate the concept of association (hydrogen bonding) and they can describe very satisfactorily many properties of water containing mixtures. They have not been successful in representing water's anomalous properties and this work provides a possible explanation. We have analyzed and interpreted recent experimental data, molecular simulation results, and two-state theory approaches and compared against the predictions from thermodynamic models. We show that the dominance of the tetrahedral structure implemented in modern thermodynamic models may be the reason for their failure for describing water systems. While this study does not prove the two-state theories for water, it indicates that a high level of tetrahedral structure of water is not in agreement with water's anomalous properties when used in thermodynamic models.     

Nd:YAG激光焊接中装夹预紧力对焊缝的影响

由于在焊缝处热影响区会产生较小的力的作用,预夹持力的大小在焊接过程中会不断变化.热膨胀、冷却过程中的收缩以及工件宽度的微小减少都会通过焊点影响夹持力的变化.试样的拉伸试验结果表明,加裁在试样上的夹持力一般会提高焊缝的断裂力,更重要的是可以得到优化后的焊接夹持力.     

Forbidden pitches in sub-wavelength lithography and their implications on design

Moore’s Law has been the most important benchmark for microelectronics development over the past four decades. It has been interpreted to mean that critical dimensions (CD) of a design must shrink geometrically over time. The chip-level integration of devices has been possible through concurrent improvement in lithographic resolution. The lithographic resolution was primarily improved by moving deeper into ultraviolet spectrum of light. However, the wavelength of the optical source used for lithography has not improved for nearly a decade. This has lead to the development of sub-wavelength lithography. The diffraction effects of sub-wavelength lithography were offset by optical proximity correction (OPC), phase shift masking (PSM) and impending move to immersion lithography. Unfortunately, one time benefits from each of these resolution enhancement techniques (RET) have nearly exhausted. In this paper, we explore one important diffraction aspect of sub-wavelength lithography viz. the forbidden pitch phenomenon and its implication on future designs. We studied Forbidden pitches in context of 65 and 45 nm technologies using aerial imaging simulation. Aerial imaging simulation is computationally expensive and is not possible to perform on entire layout structures. Based on results from our simulations on selected patterns, we observe that in absence of any other resolution enhancement technique, many of the current layout patterns will be disallowed in 45 nm technology. Such restrictions significantly mitigate the benefit of migration to 45 nm technology in terms of area, power and performance of a design. We further show that even structured gate array based designs are not immune to this problem.     

Efficient Generation of Electricity from Methane using High Temperature Fuel Cells – Status,Challenges and Prospects

High temperature fuel cells (HTFCs), comprising solid oxide fuel cells and molten carbonate fuel cells, present efficient means for generating electricity from methane and natural gas. The high quality heat generated by HTFCs allows operation in the combined heat and power mode (CHP) to further enhance efficiency. The overall fuel-to-electricity conversion efficiency of an HTFC system operating in CHP mode can approach up to 80 %. Despite the high operating efficiency of HTFCs, high capital costs and durability issues have hindered their widespread commercialization. This article provides an overview of the operating principles, technical challenges, commercialization status of HTFCs, and outlines the strategies being adopted to lower capital costs and increase durability.     

The polarization behavior of the anode in a microbial fuel cell

Microbial fuel cell (MFC) systems are unique electrochemical devices that employ the catalytic action of bacteria to drive the oxidation of organic compounds. These systems have been suggested as renewable energy sources for small remote devices; however, questions remain about how MFCs can be efficiently optimized for this purpose. Several electrochemical techniques have been employed in this study to elucidate the limiting factors in power production by MFCs. Impedance spectra were collected for the anode and cathode at their open-circuit potential (OCP) before and after all other electrochemical tests. Cell voltage-current curves were obtained using a potential sweep technique and used to determine the maximum power available from the system. Potentiodynamic polarization in two different potential regions was used to determine the exchange current for the reaction occurring at the anode at its OCP and to explore the polarization behavior of the anode and the cathode in a wide potential range. Cyclic voltammetry was used to evaluate the redox activity of the anode. These techniques used in combination showed that the microorganism Shewanella oneidensis MR-1 is solely responsible for the observed decrease of the OCP of the anode, the increased rate of oxidation of lactate, the larger cell voltage and the increased maximum power output of the MFC.     

Identification of complex nonlinear processes based on fuzzy decomposition of the steady state space

A methodology for identification and control of complex nonlinear plants using multi-model approach is presented in this paper. The proposed methodology is based on fuzzy decomposition of the steady state map. It is shown that such a decomposition strategy facilitates the design of input perturbation signals and helps in identifying linear or simple nonlinear models for each local region. A composition strategy to aggregate the local model predictions is proposed and shown to give excellent cross validation as well as to facilitate smooth switching between the local models. A novel control scheme that is based on the multi model strategy is proposed. The practicality of the identification and control scheme presented here is demonstrated by application to the continuous fermenter of Henson and Seborg (M.A. Henson, D.E. Seborg, Nonlinear control strategies for continuous fermenter, in: Proceedings of 1990 American Control Conference, San Diego, 1990), which exhibits severe nonlinearities and gain directionality changes.     

Simultaneous Path Planning and Topological Mapping (SP2ATM) for environment exploration and goal oriented navigation

In this paper, a novel approach, Simultaneous Path Planning and Topological Mapping (SP²ATM), is presented to address the problem of path planning in unknown environments by concurrent and incremental construction of a map, which strictly exploits only the topology rather than grid representation. For local topological information representation, a new concept, Admissible Space Tree (AST), is presented to describe the admissible free space in the environment as a group of nodes and graphs. The global map of the explored environment is encoded in a Hierarchical Topological Map (HTM), which by embedding the AST, serves as the least information to facilitate path planning. For simplicity, the algorithm is implemented in a planar space on our differentially driven mobile robot X1, based on its range sensing and self-localization capabilities. Experiments’ results show that SP²ATM is effective and globally convergent in complex and dynamic environments.