An Efficient Noninteractive Zero-Knowledge Proof System for NP with General Assumptions

We consider noninteractive zero-knowledge proofs in the shared random string model proposed by Blum et al. [5]. Until recently there was a sizable polynomial gap between the most efficient noninteractive proofs for NP based on general complexity assumptions [11] versus those based on specific algebraic assumptions [7]. Recently, this gap was reduced to a polylogarithmic factor [17]; we further reduce the gap to a constant factor. Our proof system relies on the existence of one-way permutations (or trapdoor permutations for bounded provers). Our protocol is stated in the hidden bit model introduced by Feige et al. [11]. We show how to prove that an n -gate circuit is satisfiable, with error probability 1/n ^O(1) , using only O(n lg n) random committed bits. For this error probability, this result matches to within a constant factor the number of committed bits required by the most efficient known interactive proof systems. Received 20 November 1995 and revised 7 October 1996     

Platinum-plated nanoporous gold: An efficient,low Pt loading electrocatalyst for PEM fuel cells

Platinum-plated nanoporous gold leaf (Pt-NPGL) is made by coating a conformal, atomically thin skin of platinum over the high surface area pores of a thin membrane of nanoporous gold. Because Pt loading in Pt-NPGL can be controlled down to 0.01 mg cm⁻² using only simple benchtop chemistry, the material holds promise as a low Pt loading, carbon-free electrocatalyst. Here, we report successful use of Pt-NPGL as a catalyst in proton exchange membrane (PEM) fuel cells. Stable and high performance Pt-NPGL/Nafion membrane electrode assemblies (MEAs) were made using a stamping technique. The performance of Pt-NPGL MEAs is comparable to conventional carbon-supported nanoparticles-based MEAs with much higher loading, generating an output power density of up to 4.5 kW g⁻¹ Pt in our non-optimized test configuration. Correlations between the performance of Pt-NPGL MEAs, the electrochemically accessible surface area, and material microstructure are discussed. Our success in using Pt-NPGL as a fuel cell catalyst suggests that creating precious metals skins over nanoporous metal supports is a viable strategy for designing new catalysts for PEM fuel cells. This promising approach allows tailoring catalytic activity by engineering precious metal/substrate interactions, employs materials with dual functionality acting both as current collector and catalyst, and may avoid the sintering problems plaguing conventional nanoparticle-based catalysts.     

Performance of a concentrating photovoltaic/thermal solar collector

The performance of a parabolic trough photovoltaic/thermal collector with a geometric concentration ratio of 37× is described. Measured results under typical operating conditions show thermal efficiency around 58% and electrical efficiency around 11%, therefore a combined efficiency of 69%. The impact of non-uniform illumination on the solar cells is investigated using purpose built equipment that moves a calibrated solar cell along the line of the receiver and measures short circuit current. The measured illumination flux profile along the length shows significant variation, despite the mirror shape error being less than 1 mm for most of the mirror area. The impact of the illumination non-uniformities due to the shape error, receiver support post shading and gaps between the mirrors is shown to have a significant effect on the overall electrical performance. The flux profile transverse to the receiver length is also investigated. Peak flux intensities are shown to be around 100 suns. The impact on efficiency due to open circuit voltage reduction is discussed.     

Long-term trends and opportunities for managing regional water supply and wastewater greenhouse gas emissions

Greenhouse gas emissions are likely to rise faster than growth in population and more than double for water supply and wastewater services over the next 50 years in South East Queensland (SEQ), Australia. New sources of water supply such as rainwater tanks, recycled water, and desalination currently have greater energy intensity than traditional sources. In addition, direct greenhouse gas emissions from reservoirs and wastewater treatment and handling have potentially the same magnitude as emissions from the use of energy. Centralized and decentralized water supply and wastewater systems are considered for a scenario based upon a government water supply strategy for the next 50 years. Many sources of data have large uncertainties which are estimated following the IPCC Good Practice Guidelines. Important sources of emissions with large uncertainties such as rainwater tanks and direct emissions were identified for further research and potential mitigation of greenhouse gas emissions.     

One-dimensional pattern of Au nanodots by ion-beam sputtering: formation and mechanism

Highly ordered one-dimensional arrays of nanodots, or nanobeads, are fabricated by forming nanoripples and nanodots in sequence, entirely by ion-beam sputtering (IBS) of Au(001). This demonstrates the capability of IBS for the fabrication of sophisticated nanostructures via hierarchical self-assembly. The intricate nanobead pattern ideally serves to identify the governing mechanisms for the pattern formation: nonlinear effects, especially local redeposition and surface-confined transport, are essential both for the formation and the preservation of the one-dimensional order of the nanobead pattern.     

Wind energy for the 1990s and beyond

Electrical power must be available to the consumer in any amount upon demand. Conventional methods of power generation, such as the burning of fossil fuels, hydroelectric plants, and nuclear power plants, have considerable shortcomings. Governmental regulations have increased in quantity and have raised the already rigid standards of producing electric power without further damage to the environment. Electrical power produced by wind energy conversion systems are undergoing extensive research and revitalization as a viable solution to clean air power generation. The basic challenge to scientists and engineers is to develop wind energy conversion systems that produce adequate amounts of power, but at a cost comparable to present conventional methods. This article discusses the background and impact of the modern wind energy conversion system on future power generation.     

Novel,Robust, and Versatile Bijels of Nitromethane,Ethanediol, and Colloidal Silica: Capsules,Sub‐Ten‐Micrometer Domains,and Mechanical Properties

Bicontinuous, interfacially jammed emulsion gels (bijels) are a class of soft solid materials in which interpenetrating domains of two immiscible fluids are stabilized by an interfacial colloidal monolayer. Such structures form through the arrest of the spinodal decomposition of an initially single‐phase liquid mixture containing a colloidal suspension. With the use of hexalmethyldisilazane, the wetting character of silica colloids, ranging in size and dye content, can be modified for fabricating a novel bijel system comprising the binary liquid ethanediol–nitromethane. Unlike the preceding water‐lutidine based system, this bijel is stable at room temperature and its fabrication and resultant manipulation are comparatively straightforward. The new system has facilitated three advancements: firstly, we use sub 100 nm silica particles to stabilize the first bijel made from low molecular weight liquids that has domains smaller than ten micrometers. Secondly, our new and robust bijel permits qualitative rheological work which reveals the bijel to be significantly elastic and self healing whilst its domains are able to break, reform and locally rearrange. Thirdly, we encapsulate the ethanediol–nitromethane bijel in Pickering drops to form novel particle‐stabilized bicontinuous multiple emulsions that we christen bijel capsules. These emulsions are stimuli responsive – they liberate their contained materials in response to changes in temperature and solvency, and hence they show potential for controlled release applications.     

Improving the measurement performance for a self-mixing interferometry-based displacement sensing system

Approaches that are, to our knowledge, novel, are proposed in this paper to improve the accuracy performance of self-mixing interferometry (SMI) for displacement measurement. First, the characteristics associated with signals observed in SMI systems are studied, based on which a new procedure is proposed for achieving accurate estimation of the laser phase. The studies also revealed the reasons for the inherent errors associated with the existing SMI-based techniques for displacement measurement. Then, this paper presents a new method for estimating the optical feedback level factor (denoted by C) in real time. Combining the new algorithms for estimating the laser phase and updating C value, the paper finally presents a novel technique for displacement measurement with improved accuracy performance in contrast to existing techniques. The proposed technique is verified by both simulation and experimental data.     

Development of a fiber-optic laser delivery system capable of delivering 213 and 266 nm pulsed Nd:YAG laser radiation for tissue ablation in a fluid environment

Ultraviolet (UV) lasers have the capability to precisely remove tissue via ablation; however, due to strong absorption of the applicable portion the UV spectrum, their surgical use is currently limited to extraocular applications at the air/tissue boundary. Here we report the development and characterization of a fiber-optic laser delivery system capable of outputting high-fluence UV laser pulses to internal tissue surfaces. The system has been developed with a view to intraocular surgical applications and has been demonstrated to ablate ocular tissue at the fluid/tissue boundary. The fifth (213?nm) and fourth(266?nm) harmonics of a Nd:YAG laser were launched into optical fibers using a hollow glass taper to concentrate the beam. Standard and modified silica/silica optical fibers were used, all commercially available. The available energy and fluence as a function of optical fiber length was evaluated and maximized. The maximum fluence available to ablate tissue was affected by the wavelength dependence of the fiber transmission; this maximum fluence was greater for 266?nm pulses (8.4?J/cm2) than for 213?nm pulses (1.4?J/cm2). The type of silica/silica optical fiber used did not affect the transmission efficiency of 266?nm pulses, but transmission of 213?nm pulses was significantly greater through modified silica/silica optical fiber. The optical fiber transmission efficiency of 213?nm pulses decreased as a function of number of pulses transmitted, whereas the transmission efficiency of 266?nm radiation was unchanged. Single pulses have been used to ablate fresh porcine ocular tissue. In summary, we report a method for delivering the fifth (213?nm) and fourth (266?nm) harmonics of a Nd:YAG laser to the surface of immersed tissue, the reliability and stability of the system has been characterized, and proof of concept via tissue ablation of porcine ocular tissue demonstrates the potential for the intraocular surgical application of this technique.