Cancellation of acoustic scattering from an elastic sphere

Recent research has suggested the possibility of creating acoustic cloaks using metamaterial layers to eliminate the acoustic field scattered from an elastic object. This paper explores the possibility of applying the scattering cancellation cloaking technique to acoustic waves and the use of this method to investigate its effectiveness in cloaking elastic and fluid spheres using only a single isotropic elastic layer. Parametric studies showing the influence of cloak stiffness and geometry on the frequency dependent scattering cross-section of spheres have been developed to explore the design space of the cloaking layer. This analysis shows that an appropriately designed single isotropic elastic cloaking layer can provide up to 30 dB of scattering reduction for ka values up to 1.6. This work also illustrates the importance of accounting for the elasticity of the object and the relevant limitations of simplistic quasi-static analyses proposed in recent papers.     

Sound speed in water-saturated glass beads as a function of frequency and porosity

Sound propagation in water-saturated granular sediments is known to depend on the sediment porosity, but few data in the literature address both the frequency and porosity dependency. To begin to address this deficiency, a fluidized bed technique was used to control the porosity of an artificial sediment composed of glass spheres of 265 μm diameter. Time-of-flight measurements and the Fourier phase technique were utilized to determine the sound speed for frequencies from 300 to 800 kHz and porosities from 0.37 to 0.43. A Biot-based model qualitatively describes the porosity dependence.     

Comparison of fuzzy sets on the same decision space

Some methods of making fuzzy decisions include a comparison of fuzzy sets on the same space. Methods have been published which suffer from lack of discrimination between alternatives and occasional conflict with intuitive choice. These methods are reviewed in this paper and then a new approach is described which overcomes their drawbacks. Methods of evaluating the parameter used in decision-making are given which can be varied to incorporate different utility functions.     

One-pot synthesis of new iso-DPP derivatives from terminal alkynes and isocyanates

The reaction of phenyl acetylide anion with aryl isocyanates followed by quenching with water is shown to produce pyrrolopyrrole (iso-DPP) derivatives in addition to the isomeric cyclopentadienone imines previously reported. If the reaction is quenched with dilute HCl, 5-ylidenepyrrol-2(5H)-ones, formed by a Meyer-Schuster rearrangement, can be isolated instead. A possible mechanism for this reaction is suggested.     

Rapid drug detection in oral samples by porous silicon assisted laser desorption/ionization mass spectrometry

The demand for analysis of oral fluid for illicit drugs has arisen with the increased adoption of roadside testing, particularly in countries where changes in legislation allow random roadside testing of drivers for the presence of a palette of illicit drugs such as methamphetamine (MA), 3,4‐methylenedioxymethamphetamine (MDMA) and Δ⁹‐tetrahydrocannabinol (THC). Oral samples are currently tested for such drugs at the roadside using an immunoassay‐based commercial test kit. Positive roadside tests are sent for confirmatory laboratory analysis, traditionally by means of gas chromatography/mass spectrometry (GC/MS). We present here an alternative rapid analysis technique, porous silicon assisted laser desorption/ionization time‐of‐flight mass spectrometry (pSi LDI‐MS), for the high‐throughput analysis of oral fluids. This technique alleviates the need for sample derivatization, requires only sub‐microliter sample volumes and allows fast analysis (of the order of seconds). In this study, the application of the technique is demonstrated with real samples from actual roadside testing. The analysis of oral samples resulted in detection of MA and MDMA with no extraction and analysis of THC after ethyl acetate extraction. We propose that, subject to miniaturization of a suitable mass spectrometer, this technique is well suited to underpin the deployment of oral fluid testing in the clinic, workplace and on the roadside. Copyright © 2009 John Wiley & Sons, Ltd.     

Understanding the Role of Gold Nanoparticles in Enhancing the Catalytic Activity of Manganese Oxides in Water Oxidation Reactions

The Earth‐abundant and inexpensive manganese oxides (MnO_x) have emerged as an intriguing type of catalysts for the water oxidation reaction. However, the overall turnover frequencies of MnO_x catalysts are still much lower than that of nanostructured IrO₂ and RuO₂ catalysts. Herein, we demonstrate that doping MnO_x polymorphs with gold nanoparticles (AuNPs) can result in a strong enhancement of catalytic activity for the water oxidation reaction. It is observed that, for the first time, the catalytic activity of MnO_x/AuNPs catalysts correlates strongly with the initial valence of the Mn centers. By promoting the formation of Mn³⁺ species, a small amount of AuNPs (<5 %) in α‐MnO₂/AuNP catalysts significantly improved the catalytic activity up to 8.2 times in the photochemical and 6 times in the electrochemical system, compared with the activity of pure α‐MnO₂.     

Feasible algorithms for approximate reasoning using fuzzy logic

Deductive reasoning with classical logic is hampered when imprecision is present in the variables, although human reasoning can cope quite adequately with vague concepts. A new approach to reasoning which allows imprecise conclusions to be drawn consistently from imprecise premises was introduced by Baldwin [2]. This method is economical in calculation as it avoids the high dimensionality that fuzzy set representations often involve.This paper briefly reviews the method from an operational viewpoint, isolating the individual processes that are used in the method. A feasible algorithm for computing each process is then presented.It is assumed that the reader is familiar with the concept of, and operations on, fuzzy sets introduced by Zadeh [14].