Transonic flow in a converging-diverging nozzle Final report

Transonic equations of motion for convergent-divergent nozzl

High frequency asymptotics of antenna/structure interactions

This thesis is motivated by the need to calculate the electromagnetic fields produced by sources radiating in the presence of conductors. We begin by reviewing existing theory concerning sources in the presence of flat structures. Various extensions to the canonical Sommerfeld problem are considered. In particular we investigate the asymptotic solution for a finite source that focusses its energy at a point. In chapter 5 we review and extend the asymptotic results concerning illumination of a convex perfect conductor by an incident plane wave and outline the procedure for decoupling the electromagnetic surface field into two scalar modes. In chapter 6 we place a source on a perfect conductor and obtain a complete asymptotic solution for the fields. Special attention is paid to the asymptotic structure that smoothly matches between the leading order lit and shadow regions. We also investigate the degenerate case where one of the curvatures of the perfect conductor is zero. The case where the source is just off the surface is also investigated. In chapter 8 we use the Euler-Maclaurin summation formula to cheaply calculate the fields due to complicated arrays of point dipoles. The final chapter combines many earlier results to consider more general sources on the surface of a perfect conductor. In particular we must introduce new asymptotic regions for open sources. This then enables us to consider the focussing of the surface field due to a finite source. The nature of the surface and geometrical optics fields depends on the size of the source in comparison to the curvatures of the surface on which they lie. We discuss this in detail and conclude with the practical example of a spiral antenna

The Effect of Explicit Instruction on the Perception of Spanish Stops by Speakers of Korean

Many studies have been conducted on the influence of explicit phonetic instruction on speech perception and production of English as a second (L2) and foreign (FL) language (e.g. Bradlow, Pisoni, Akahane-Yamada & Tohkura, 1997; Derwing, Munro & Wiebe, 1998), some of which have focused on Spanish as a FL learned by American students whose first or native language (L1) is English (e.g. Elliot, 1997; Lord, 2005). Nonetheless, research has only recently been carried out on third language (L3) perception, with an even greater scarcity of studies that have focused on non-native speakers of English (e.g. Llama, Cardoso & Collins, 2008; Llisterri, & Poch, 1987). As Spanish is the most studied FL in the U.S. and its classrooms often contain non-native English students, it is important to take into account how these individuals’ perception may affect their acquisition of L3 phonology and strive to discover efficient and effective ways of instruction for these linguistic minorities. This study concentrates on Korean L1 speakers and the influence of explicit phonetic instruction on their perception of word-initial consonant stops in Spanish. Consonant stops in both Spanish and English are defined by voicing, differing only somewhat in Voice Onset Time (VOT) (Abramson & Lisker, 1973). In Korean, however, consonant stops are not defined by voicing, but rather by two features: tenseness and aspiration (Kim, C. W., 1965; Kim, N., 1990). It has been shown that this Korean system greatly influences the perception of systems whose elements are distinguished by voicing (Kang, Kyoung-Ho & Susan Guion, 2006). The participants in this study were 13 native speakers of Korean studying in the U.S. The experiment tested the effect of explicit instruction on participants’ perception by having participants listen to 36 voice recordings of Spanish syllables and choose the syllable (written in Latin characters) which best represented the one they heard. The experimental group completed a pre-test before receiving instruction in the form of a video, after which they took an immediate post-test, with a delayed post-test the following week. Based on previous research, it was hypothesized that L1 Korean speakers would parse the voiced stops with more accuracy than the voiceless ones, but that explicit phonetic instruction would improve participants’ perception of the latter. The results of the present study support this conclusion

Comparison of NASA and contractor results from aeroacoustic tests of QCSEE OTW engine

The aerodynamics and acoustics of the over-the-wing (OTW) Quiet, Clean, Short Haul Experimental Engine (QCSEE) were tested. A boilerplate (nonflight weight), high-throat Mach number, acoustically treated inlet and a D-shaped OTW exhaust nozzle with variable position side doors were used. Some acoustic directivity results for the type "D" nozzle and acoustic effects of variations in the nozzle side door positions are included. It was found that the results are in agreement with those previously obtained

Effect of duct shape, Mach number, and lining construction on measured suppressor attenuation and comparison with theory

Noise attenuation was measured for several types of cylindrical suppressors that use a duct lining composed of honeycomb cells covered with a perforated plate. The experimental technique used gave attenuation data that were repeatable and free of noise floors and other sources of error. The suppressor length, the effective acoustic diameter, suppressor shape and flow velocity were varied. The agreement among the attenuation data and two widely used analytical models was generally satisfactory. Changes were also made in the construction of the acoustic lining to measure their effect on attenuation. One of these produced a very broadband muffler

Acoustic properties of a supersonic fan

Acoustic properties of supersonic fan with short blade spa

Technology‐assisted clinical care

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Plant essential oils synergize various pyrethroid insecticides and antagonize malathion in Aedes aegypti

Pyrethroid resistance is a significant threat to agricultural, urban and public health pest control activities. Because economic incentives for the production of novel active ingredients for the control of public health pests are lacking, this field is particularly affected by the potential failure of pyrethroid‐based insecticides brought about by increasing pyrethroid resistance. As a result, innovative approaches are desperately needed to overcome insecticide resistance, particularly in mosquitoes that transmit deadly and debilitating pathogens. Numerous studies have demonstrated the potential of plant essential oils to enhance the efficacy of pyrethroids. The toxicity of pyrethroids combined with plant oils is significantly greater than the baseline toxicity of either oils or pyrethroids applied alone, which suggests there are synergistic interactions between components of these mixtures. The present study examined the potential of eight plant essential oils applied in one of two concentrations (1% and 5%) to enhance the toxicity of various pyrethroids (permethrin, natural pyrethrins, deltamethrin and β‐cyfluthrin). The various plant essential oils enhanced the pyrethroids to differing degrees. The levels of enhancement provided by combinations of plant essential oils and pyrethroids in comparison with pyrethroids alone were calculated and synergistic outcomes characterized. Numerous plant essential oils significantly synergized a variety of pyrethroids; type I pyrethroids were synergized to a greater degree than type II pyrethroids. Eight plant essential oils significantly enhanced 24‐h mortality rates provided by permethrin and six plant essential oils enhanced 24‐h mortality rates obtained with natural pyrethrins. By contrast, only three plant essential plants significantly enhanced the toxicity of deltamethrin and β‐cyfluthrin. Of the plant essential oils that enhanced the toxicity of these pyrethroids, some produced varying levels of synergism and antagonism. Geranium, patchouli and Texas cedarwood oils produced the highest levels of synergism, displaying co‐toxicity factors of \u3e 100 in some combinations. To assess the levels of enhancement and synergism of other classes of insecticide, malathion was also applied in combination with the plant oils. Significant antagonism was provided by a majority of the plant essential oils applied in combination with this insecticide, which suggests that plant essential oils may act to inhibit the oxidative activation processes within exposed adult mosquitoes