18,865 research outputs found
Analytical investigation of synchrophasing as a means of reducing aircraft interior noise
The noise control characteristics of synchrophasing are investigated using a simplified model of an aircraft fuselage. The analysis presented here includes directivity effects of the noise sources and solves in closed form the coupled motion between the interior and exterior acoustic fields and the shell vibrational response. The variation in sound pressure level at various locations inside the shell is studied for various synchrophase angles as well as the shell vibrational response and input power flow in order to uncover the principal mechanisms behind the transmission phenomena
Public health applications of remote sensing
Remote infrared and multispectral photography were used to identify coastal salt water-fresh water interfaces conducive to encephalitis vector mosquito breeding in Florida, and to determine the environmental conditions that caused an explosive outbreak of anthrax in Louisiana. Multiband photographic inventories were obtained by simultaneously processing three photographic negatives of the same view which record different wavelength portions of the same light. The process enhances differentiation of vegetative communities and sharply delineates edge effects by assigning false colors to differentiate subtle density differences
Information technology professionals and the new-rich middle class in Chennai (Madras)
Since 1991, when the policy of economic liberalisation began in earnest, the size and prosperity of India's middle class have grown considerably. Yet sound sociological and ethnographic information about its social structure and cultural values is still sparse, and as AndrĂ© BĂ©teille comments: âEverything or nearly everything that is written about the Indian middle class is written by middle-class IndiansâŠ[who] tend to oscillate between self-recrimination and self-congratulationâ. The former is exemplified by Pavan Varma's The Great Indian Middle Class (1998), which excoriates this class for its selfish materialism and the âretreat from idealismâ that was manifest in the smaller, âtraditional middle classâ of the earlier, post-independence period. A good example of the opposite tendency is Gurcharan Das's India Unbound (2002), which celebrates âthe rise of a confident new middle classâDas's diagnosis of what has changed is actually very similar to Varma's, but he insists that the new middle class is no âgreedierâ than the old one, and the âchief difference is that there is less hypocrisy and more self-confidence
Traditional vocations and modern professions among Tamil Brahmans in colonial and post-colonial south India
Since the nineteenth century, Tamil Brahmans have been very well represented in the educated professions, especially law and administration, medicine, engineering and nowadays, information technology. This is partly a continuation of the Brahmansâ role as literate service people, owing to their traditions of education, learning and literacy, but the range of professions shows that any direct continuity is more apparent than real. Genealogical data are particularly used as evidence about changing patterns of employment, education and migration. Caste traditionalism was not a determining constraint, for Tamil Brahmans were predominant in medicine and engineering as well as law and administration in the colonial period, even though medicine is ritually polluting and engineering resembles low-status artisansâ work. Crucially though, as modern, English-language, credential-based professions that are wellpaid and prestigious, law, medicine and engineering were and are all deemed eminently suitable for Tamil Brahmans, who typically regard their professional success as a sign of their caste superiority in the modern world. In reality, though, it is mainly a product of how their old social and cultural capital and their economic capital in land were transformed as they seized new educational and employment opportunities by flexibly deploying their traditional, inherited skills and advantages
Quantification of channel planform change on the lower Rangitikei River, New Zealand, 1949-2007: response to management?
The Rangitikei River, a large gravelâbed wandering river located in the North Island of New Zealand, has outstanding scenic characteristics, recreational, fisheries and wildlife habitat features. Recently concerns
have been raised over the potential negative impact that perceived channel changes in the latter part of the 20th century may be having on the Rangitikei River recreational fishery. This study describes and quantifies the largeâscale morphological changes that have occurred in selected reaches of the lower
Rangitikei River between 1949 and 2007.
This research utilised historical aerial photography and analysis in ArcGISÂź to quantify channel planform change in three reaches, encompassing ~18 km of the lower Rangitikei River. This showed that the
lower Rangitikei was transformed from a multiâchannelled planform to a predominantly singleâthread wandering planform, with an associated reduction in morphological complexity and active channel width of up to 74%, between 1949 and 2007. Bank protection measures instigated under the Rangitikei
River Scheme have primarily driven these changes. Gravel extraction has also contributed by enhancing channelâfloodplain disconnection and exacerbating sediment deficits. The findings of this study have
implications for future management of the Rangitikei. Previous lower Rangitikei River management schemes have taken a reachâbased engineering approach with a focus on bank erosion protection and flood mitigation. This study has confirmed the lower river has responded geomorphologically to these
goals of river control. However questions as to the economic and ecological sustainability of this management style may encourage river managers to consider the benefits of promoting a selfâadjusting fluvial system within a catchmentâframed management approach
Morphological budgeting in the Motueka River: an analysis of technique
Morphological budgeting is a key method for monitoring and studying sediment transfers within gravelly rivers. We assess the utility of traditional crossâsection approaches to budgeting using Digital Elevation Model (DEM) analysis. DEMs give a more accurate volume calculation within the
constraint of sampling frequency compared with cross sections, since a greater area of river bed is sampled. DEM volume calculation within the 1.7 km âThree Beachesâ reach in the upper Motueka revealed a net loss of 3219 m3 in this reach between 2008â2009. Comparisons of this value with cross sectionâbased volume calculations at a range of section spacing using (i) Mean Bed Level (MBL) analysis and (ii) DEMs generated from cross section data, suggest accuracy of the budget is maximised at a critical cross section spacing not exceeding 90 m. Careful positioning of cross sections could lengthen this distance further and is essential to accurately represent river channel morphology. MBL analysis using crossâsections in the reach monumented by Tasman District Council (TDC) for river monitoring underestimates the magnitude of net sediment transfers by c. 30%
Prospects for Detecting Supernova Neutrino Flavor Oscillations
The neutrinos from a Type II supernova provide perhaps our best opportunity
to probe cosmologically interesting muon and/or tauon neutrino masses. This is
because matter enhanced neutrino oscillations can lead to an anomalously hot
nu_e spectrum, and thus to enhanced charged current cross sections in
terrestrial detectors. Two recently proposed supernova neutrino observatories,
OMNIS and LAND, will detect neutrons spalled from target nuclei by neutral and
charged current neutrino interactions. As this signal is not flavor specific,
it is not immediately clear whether a convincing neutrino oscillation signal
can be extracted from such experiments. To address this issue we examine the
responses of a series of possible light and heavy mass targets, 9Be, 23Na,
35Cl, and 208Pb. We find that strategies for detecting oscillations which use
only neutron count rates are problematic at best, even if cross sections are
determined by ancillary experiments. Plausible uncertainties in supernova
neutrino spectra tend to obscure rate enhancements due to oscillations.
However, in the case of 208Pb, a signal emerges that is largely flavor specific
and extraordinarily sensitive to the nu_e temperature, the emission of two
neutrons. This signal and its flavor specificity are associated with the
strength and location of the first-forbidden responses for neutral and charge
current reactions, aspects of the 208Pb neutrino cross section that have not
been discussed previously. Hadronic spin transfer experiments might be helpful
in confirming some of the nuclear structure physics underlying our conclusions.Comment: 27 pages, RevTeX, 2 figure
Bearing detection in the presence of two sources of varying coherence using the complex cepstrum
The effect of the presence of two acoustic sources (one, the primary, whose location is to be detected) of varying coherence on a cepstral bearing finding procedure is experimentally studied. The coherence between the acoustic sources was altered by adding random noise of various SNR (signal-to-noise ratio) to the input signal of the primary source; the same base signal being fed to both sources. The results demonstrate that, when block liftering is used, the primary source bearing is reliably estimated for coherences as low as gamma sup 2 greater than or approx equal to 0.5. The results also imply that background noise (unreflected) of SNR greater than or approx equal to 10 dB will not markedly affect the accuracy of the bearing estimation algorithm
An experimental investigation of the interior noise control effects of propeller synchrophasing
A simplified cylindrical model of an aircraft fuselage is used to investigate the mechanisms of interior noise suppression using synchrophasing techniques. This investigation allows isolation of important parameters to define the characteristics of synchrophasing. The optimum synchrophase angle for maximum noise reduction is found for several interior microphone positions with pure tone source excitation. Noise reductions of up to 30 dB are shown for some microphone positions, however, overall reductions are less. A computer algorithm is developed to decompose the cylinder vibration into modal components over a wide range of synchrophase angles. The circumferential modal response of the shell vibration is shown to govern the transmission of sound into the cylinder rather than localized transmission. As well as investigating synchrophasing, the interior sound field due to sources typical of propellers has been measured and discussed
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