Series Expansion based Efficient Architectures for Double Precision Floating Point Division

Floating point division is a complex operation among all floating point arithmetic; it is also an area and a performance dominating unit. This paper presents double precision floating point division architectures on FPGA platforms. The designs are area optimized, running at higher clock speed, with less latency, and are fully pipelined. Proposed architectures are based on the well-known Taylor series expansion, using relatively smaller amount of hardware in terms of memory (initial look-up table), multiplier blocks, and slices. Two architectures have been presented with various trade-offs among area, memory and accuracy. Designs are based on the use of the partial block multipliers, in order to reduce hardware usage while minimizing the loss of accuracy. All the implementations have been targeted and optimized separately for different Xilinx FPGAs to exploit their specific resources efficiently. Compared to previously reported literature, the proposed architectures require less area, reduced latency, with the advantage of higher performance gain. The accuracy of the designs has been both theoretically analyzed and validated using random test cases.     

Flexible ZnO-cellulose nanocomposite for multisource energy conversion

Materials with the ability to harness multiple sources of energy from the ambient environment could lead to new types of energy-harvesting systems. It is demonstrated that nanocomposite films consisting of zinc oxide nanostructures embedded in a common paper matrix can be directly used as energy-conversion devices to transform mechanical and thermal energies to electric power. These mechanically robust and flexible devices can be fabricated over large areas and are capable of producing an output voltage and power up to 80 mV and 50 nW cm(-2) , respectively. Furthermore, it is shown that by integrating a certain number of devices (in series and parallel) the output voltage and the concomitant output power can be significantly increased. Also, the output voltage and power can be enhanced by scaling the size of the device. This multisource energy-harvesting system based on ZnO nanostructures embedded in a flexible paper matrix provides a simplified and cost-effective platform for capturing trace amounts of energy for practical applications.     

Advanced Pd-based nanomaterials for electro-catalytic oxygen reduction in fuel cells: A review

Devising cost-effective and high-performance nanocatalysts for the inherently slow oxygen reduction reaction (ORR) represents a critical hurdle in the commercial improvement of fuel cells for energy conversion. Recently, considerable attempts have concentrated on exploring Pd-based nanocatalysts with advanced stability to utilize as substitutes for Pt. In this review, we first describe ORR mechanisms and summarize research conducted with Pd electro-catalysts, including single and alloyed Pd nanostructures on different substrates. The application of Pd catalysts as cathode nanomaterials in proton exchange membrane fuel cells (PEMFCs), direct methanol fuel cells (DMFCs), and anion exchange membrane fuel cells (AEMFCs) is also reviewed. The insights into the connections between catalytic performance, structure, and preparation process are addressed. In particular, approaches for fabricating efficient Pd electro-catalysts, such as increasing the number of reactive centers and modifying nanoparticle-support interactions, are discussed. Challenges and prospects for upcoming investigations in developing desirable ORR nanocatalysts are highlighted.     

Post-CHF heat transfer during two-phase upflow boiling of R-407C in a vertical pipe

This paper reports a study of heat transfer in the post-critical heat flux (post-CHF) regime under forced convective upflow conditions in a uniformly heated vertical tube of 12.7 mm internal diameter and 3 m length. Experiments were conducted with non-azeotropic ternary refrigerant mixture R-407C for reduced pressures ranging from 0.37 to 0.75, mass flux values from 1200 to 2000 kg/m² s and heat flux from 50 to 80 kW/m². Data shows a considerable effect of system pressure on the post-CHF heat transfer coefficient for specified mass and heat fluxes. The post-CHF heat transfer coefficients for R-407C are compared with three existing correlations which are found to over predict the current data. A modified correlation to represent the experimental data for R-407C is presented.     

Variable Time Impulse System Optimization with Continuous Control and Impulse Control

Optimal control of a variable time impulse system is considered in this study. Besides impulse control, the system is assumed to operate with continuous control also. Necessary conditions for the optimization of such system are derived using the calculus of variations. A reinforcement based solution technique called a single network adaptive critic (SNAC) method is developed in this paper to obtain an optimal solution. Details of the SNAC‐based algorithm are presented. Simulation examples are also presented for illustrative purposes.     

Integrated approach for assembly tolerance analysis

In mechanical design, tolerance assignment is a critical but complex task since the designer will not only have to consider the associated cost to achieve a certain tolerance level, but also the cost due to failure in assembling task. These associated tolerance costs as well as the failure rate are fuzzy in nature. This paper presents an integrated approach to incorporate manufacturing costs of certain tolerance specifications into design stages for automatic tolerance assignment and design. Tolerance design is interdisciplinary in nature and is characterized by a highly uncertain environment. In recent years, fuzzy logic has appeared as a credible alternative for tolerance design. A fuzzy based tolerance representation scheme is presented to model three dimensional (3D) tolerances. With this representation, relative assembly tolerance constraints can be expressed. A fuzzy tolerance generation and assignment process for assembly is discussed. Fuzzy tolerance equations are generated for 3D assembly considerations. Manufacturing process information, along with uncertain cost information modelled in fuzzy terms, is added to the system to arrive at a cost-optimal tolerance assignment.