Temporal clustering for order reduction of nonlinear parabolic PDE systems with time‐dependent spatial domains: Application to a hydraulic fracturing process

A temporally‐local model order‐reduction technique for nonlinear parabolic partial differential equation (PDE) systems with time‐dependent spatial domains is presented. In lieu of approximating the solution of interest using global (with respect to the time domain) empirical eigenfunctions, low‐dimensional models are derived by constructing appropriate temporally‐local eigenfunctions. Within this context, first of all, the time domain is partitioned into multiple clusters (i.e., subdomains) by using the framework known as global optimum search. This approach, a variant of Generalized Benders Decomposition, formulates clustering as a Mixed‐Integer Nonlinear Programming problem and involves the iterative solution of a Linear Programming problem (primal problem) and a Mixed‐Integer Linear Programming problem (master problem). Following the cluster generation, local (with respect to time) eigenfunctions are constructed by applying the proper orthogonal decomposition method to the snapshots contained within each cluster. Then, the Galerkin's projection method is employed to derive low‐dimensional ordinary differential equation (ODE) systems for each cluster. The local ODE systems are subsequently used to compute approximate solutions to the original PDE system. The proposed local model order‐reduction technique is applied to a hydraulic fracturing process described by a nonlinear parabolic PDE system with the time‐dependent spatial domain. It is shown to be more accurate and computationally efficient in approximating the original nonlinear system with fewer eigenfunctions, compared to the model order‐reduction technique with temporally‐global eigenfunctions. © 2017 American Institute of Chemical Engineers AIChE J, 63: 3818–3831, 2017     

Stealth modification versus nuisance attacks in the LOCKSS peer-to-peer digital preservation system

The LOCKSS system is a world-wide peer-to-peer system for the preservation of academic journals and other archival information published on the Web. The system is deployed at over 200 libraries around the world and currently preserving titles of publishers representing more than 2000 academic titles. It consists of a large number of independent, low-cost, persistent Web caches that cooperate to detect and repair damage to their content by voting in “opinion polls.” Based on our experience working with the LOCKSS system, in this paper, we identify and characterize a fundamental tradeoff in the system’s ability to defend against adversaries with competing goals. In particular, the techniques used to defend against adversaries attempting stealth modification of content being preserved in the system are at odds with those used to identify nuisance adversaries simply trying to disrupt system procedures. We show that with a simple change to the design of the system’s preservation protocol we are able to create moderately strong defense against both of these competing adversaries simultaneously.     

Nanoparticle scanning and detection on flat and structured surfaces using fluorescence microscopy

A new technique is proposed for the scanning and detection of nanoparticles on flat substrates and three-dimensional structures using fluorescence microscopy. This technique is utilized for particle removal measurements especially in semiconductor and hard disk manufacturing. This fluorescent particle scanning technique enables nanoscale particle detection. The technique shows that single particles down to 63 nm could be detected and counted. The technique is also capable of detecting particles in trenches that are as deep as 500 microm.     

Market development at the bottom of the pyramid: examining the role of information and communication technologies

This paper addresses the research question, “How can the use of information and communication technology (ICT) enable development of markets at the bottom of the pyramid (BOP)?” Integrating ideas centered on the threefold role of ICT (automate–informate–transform), market mechanisms, and agency freedom aspects of ICT-enabled development, we examine how (1) ICT facilitate development of market mechanisms at the BOP, (2) market mechanisms enable economic and social benefit outcomes for BOP markets and members, and (3) complementary conditions facilitate or hinder ICT-enabled market development. The findings are based on qualitative primary data from interviews with 27 BOP individuals from India, and from published and secondary examples. Theoretical contributions and implications for practice and further research are discussed.     

Analysis and Simulation of Schottky Tunneling Using Schottky Barrier FET with 2-D Analytical Modeling

Silicon - A novel analytical model of surface potential for a double metal gate schottky barrier tunnelling (SBT) FET using schottky tunnelling with HfO2 as gate dielectric is proposed. The...     

Electrochemically active and robust cobalt doped copper phosphosulfide electro-catalysts for hydrogen evolution reaction in electrolytic and photoelectrochemical water splitting

The area of non-noble metals based electro-catalysts with electrochemical activity and stability similar or superior to that of noble metal electro-catalyst for efficient hydrogen production from electrolytic and photoelectrochemical (PEC) water splitting is a subject of intense research. In the current study, exploiting theoretical first principles study involving determination of hydrogen binding energy to the surface of the electro-catalyst, we have identified the (Cu_0.83Co_0.17)₃P: x at. % S system displaying excellent electrochemical activity for hydrogen evolution reaction (HER). Accordingly, we have experimentally synthesized (Cu_0.83Co_0.17)₃P: x at. % S (x = 10, 20, 30) demonstrating excellent electrochemical activity with an onset overpotential for HER similar to Pt/C in acidic, neutral as well as basic media. The highest electrochemical activity is exhibited by (Cu_0.83Co_0.17)₃P:30 at. % S nanoparticles (NPs) displaying overpotential to reach 100 mA cm^?2 in acidic, neutral and basic media similar to Pt/C. The (Cu_0.83Co_0.17)₃P:30 at. % S NPs also display excellent electrochemical stability in acidic media for long term electrolytic and PEC water splitting process [using our previously reported (Sn_0.95Nb_0.05) O₂: N-600 nanotubes (NTs) as the photoanode]. The applied bias photon-to-current efficiency obtained using (Cu_0.83Co_0.17)₃P:30 at. % S NPs as the cathode electro-catalyst for HER in an H-type PEC water splitting cell (～4%) is similar to that obtained using Pt/C (～4.1%) attesting to the promise of this exciting non-noble metal containing system.     

Active and robust novel bilayer photoanode architectures for hydrogen generation via direct non-electric bias induced photo-electrochemical water splitting

Photo-electrochemical (PEC) water splitting is a promising and environmentally benign approach for generation of hydrogen using solar energy with minimum greenhouse gas emissions. The development of semiconductor materials for photoanode with superior optoelectronic properties combined with excellent photoelectrochemical activity and stability is vital for the realization of viable commercial development of PEC water splitting systems. Herein, we report for the very first time, the study of nanoscale bilayer architecture of WO₃ and Nb and N co-doped SnO₂ nanotubes (NTs), wherein WO₃ NTs are coated with (Sn_0.95Nb_0.05)O₂:N-600 (annealed in NH₃ at 600 °C) layer of different thicknesses, as a potential semiconductor photoanode material for PEC water splitting. An excellent long term photoelectrochemical stability under illumination in the acidic electrolyte solution combined with a solar-to-hydrogen efficiency (STH) of ～3.83% (under zero applied potential) is obtained for the bilayer NTs, which is the highest STH obtained thus far, to the best of our knowledge compared to the other well studied semiconductor materials, such as TiO₂, ZnO and Fe₂O₃. These promising results demonstrate the excellent potential of bilayer NTs as a viable and promising photoanode in PEC water splitting.     

Enhancement of Boiling Heat Transfer Using Surface Vibration

An experimental investigation of the effect of mechanical vibrations of a copper flat circular surface on the pool boiling heat transfer coefficient of water at atmospheric pressure are presented in this paper. A vibration exciter was used to vibrate this copper test surface vertically. Effect of frequency and amplitude of vibration on the boiling heat transfer coefficient was studied. An increase in the heat transfer coefficient was observed at low frequency and amplitudes, at higher amplitude and frequency heat transfer deteriorates. Heat transfer coefficient increases up to 26% with vibration intensity, represented by vibrational Reynolds number.     

Highly active robust oxide solid solution electro-catalysts for oxygen reduction reaction for proton exchange membrane fuel cell and direct methanol fuel cell cathodes

The identification and development of novel non-noble metals based electro-catalyst exhibiting excellent electrochemical activity and stability than noble metal electro-catalyst is important for commercial development of proton exchange membrane fuel cells (PEMFCs). Such non-noble electro-catalyst with unique electronic structure and superior electrochemical performance will immensely contribute to lowering the capital cost of PEMFCs. Herein, we have identified solid solution electro-catalysts of WO₃ and IrO₂ for oxygen reduction reaction (ORR) in PEMFCs exploiting theoretical first principles approaches. The theoretical results were experimentally validated by generation of nanostructured (W_1-xIr_x)O_y (x = 0.2, 0.3; y = 2.7–2.8) electro-catalysts for ORR. (W_0.7Ir_0.3)O_y demonstrated ～43% improved electrochemical activity than Pt/C with similar loading at 0.9 V (vs RHE), respectively. Moreover, single full cell PEMFC study revealed an acceptable ～81% improved maximum power density for (W_0.7Ir_0.3)O_y than Pt/C combined with excellent long term stability. These results thus, show the potential of (W_0.7Ir_0.3)O_y as ORR electro-catalyst for replacing of Pt/C in PEMFCs and direct methanol fuel cells on the additional grounds of superior methanol tolerance.     

Mechanical properties of Al-based metal matrix composites reinforced with Zr-based glassy particles produced by powder metallurgy

Al-based metal matrix composites consisting of pure Al reinforced with different amounts of mechanically alloyed Zr₅₇Ti₈Nb_2.5Cu_13.9Ni_11.1Al_7.5 glassy powder were produced by powder metallurgy, and their mechanical properties were investigated by room temperature compression tests. The samples were consolidated into highly dense bulk specimens at temperatures within the supercooled liquid region in order to take advantage of the viscous flow behavior of the glassy powder. Compression tests show that the addition of the glass reinforcement increases the strength of pure Al from 155 to 250 MPa, while retaining appreciable plastic deformation with a fracture strain ranging between 70% and 40%. The yield strength and the elastoplastic deformation of such composites containing a high volume fraction of glassy particles were accurately modeled using a shear lag model and a self-consistent effective medium approach. Finally, the fracture characteristics of the reinforcing particles were rationalized using a proposed fracture criterion.