361 research outputs found

    Towards the prediction of supersonic jet noise predictions using a unified asymptotic approximation for the adjoint vector Green's function

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    In this paper we continue efforts aimed at modeling jet noise using self-consistent analytical approaches within the generalized acoustic analogy (GAA) formulation. The GAA equations show that the far-field pressure fluctuation is given by a convolution product between a propagator tensor that depends on the (true) non-parallel jet mean flow and a generalized fluctuating stress tensor that is a stationary random function of time and includes the usual fluctuating Reynolds’ stress tensor as well as enthalpy fluctuation components. Here, we focus on approximating the propagator tensor by determining an appropriate asymptotic solution to the adjoint vector Green’s function that it depends on by using an asymptotic approach at all frequencies of interest for jet noise prediction. The Green’s function is then rationally approximated by a composite formula in which the GSA (Goldstein-Sescu-Afsar, J. Fluid Mech., vol. 695, pp. 199-234, 2012) non-parallel flow Green’s function asymptotic solution is used at low frequencies and the O(1) frequency parallel flow Green’s function is used for all frequencies thereafter. The former solution uses the fact that non-parallelism will have a leading order effect on the Green’s function everywhere in the jet under a distinguished scaling in which the jet spread rate is of the same order as the Strouhal number for a slowly-diverging mean flow expansion. Since this solution, however, is expected to apply up to the peak frequency, the latter O(1) frequency Green’s function in a parallel flow must be used at frequencies thereafter. We investigate the predictive capability of the composite Green’s function for the prediction of supersonic axi-symmetric round jets at fixed jet Mach number of 1.5 and two different temperature ratios (isothermal & heated) using Large-eddy simulation data. Our results show that, in the first instance, excellent jet noise predictions are obtained using the non-parallel flow asymptotic approach, remarkably, up to a Strouhal number of 0.5. This is true for both heated and un-heated jets. Furthermore, we develop the analytical approach required to extend this solution by appropriate asymptotic approximation to O(1) frequencies

    Polymethylhydrosiloxane-modified gas-diffusion cathode for more efficient and durable H2O2 electrosynthesis in the context of water treatment

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    On-site H2O2 electrosynthesis via two-electron oxygen reduction reaction (ORR) is attracting great interest forwater treatment. The use of carbon black-based gas-diffusion electrodes (GDEs) is especially appealing, but theiractivity, selectivity and long-term stability must be improved. Here, a facile GDEs modification strategy usingtrace polymethylhydrosiloxane (PMHS) allowed reaching a outstanding H2O2 production, outperforming theconventional polytetrafluoroethylene (PTFE)-GDE (1874.8 vs 1087.4 mg L-1 at 360 min). The superhydrophobicityconferred by PMHS endowed the catalytic layer with high faradaic efficiencies (76.2%-89.7%)during long-term operation for 60 h. The electrochemical tests confirmed the high activity and selectivity of thePMHS-modified GDE. Moreover, the efficient degradation of several micropollutants by the electro-Fentonprocess demonstrated the great potential of the new GDE. An in-depth understanding of the roles of PMHSfunctional groups is provided from DFT calculations: the -CH3 groups contribute to form a superhydrophobicinterface, whereas Si-H and as-formed Si-O-C sites modulate the coordination environment of active carboncenters

    Monorail/Foxa2 regulates floorplate differentiation and specification of oligodendrocytes, serotonergic raphe neurones and cranial motoneurones

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    In this study, we elucidate the roles of the winged-helix transcription factor Foxa2 in ventral CNS development in zebrafish. Through cloning of monorail (mol), which we find encodes the transcription factor Foxa2, and phenotypic analysis of mol(-/-) embryos, we show that floorplate is induced in the absence of Foxa2 function but fails to further differentiate. In mol(-/-) mutants, expression of Foxa and Hh family genes is not maintained in floorplate cells and lateral expansion of the floorplate fails to occur. Our results suggest that this is due to defects both in the regulation of Hh activity in medial floorplate cells as well as cell-autonomous requirements for Foxa2 in the prospective laterally positioned floorplate cells themselves. Foxa2 is also required for induction and/or patterning of several distinct cell types in the ventral CNS. Serotonergic neurones of the raphe nucleus and the trochlear motor nucleus are absent in mol(-/-) embryos, and oculomotor and facial motoneurones ectopically occupy ventral CNS midline positions in the midbrain and hindbrain. There is also a severe reduction of prospective oligodendrocytes in the midbrain and hindbrain. Finally, in the absence of Foxa2, at least two likely Hh pathway target genes are ectopically expressed in more dorsal regions of the midbrain and hindbrain ventricular neuroepithelium, raising the possibility that Foxa2 activity may normally be required to limit the range of action of secreted Hh proteins

    Parameterization of subgrid plume dilution for use in large-scale atmospheric simulations

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    A new model of plume dynamics has been developed for use as a subgrid model of plume dilution in a large-scale atmospheric simulation. The model uses mean wind, shear, and diffusion parameters derived from the local large-scale variables to advance the plume cross-sectional shape and area in time. Comparisons with a large eddy simulation of aircraft emission plume dynamics, with an analytical solution to the dynamics of a sheared Gaussian plume, and with measurements of aircraft exhaust plume dilution at cruise altitude show good agreement with these previous studies. We argue that the model also provides a reasonable approximation of line-shaped contrail dilution and give an example of how it can be applied in a global climate model

    Land Use Patterns and the Scale of Adoption of Agroforestry in the Rural Landscapes of Padma Floodplain in Bangladesh

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    This research was conducted in six typical villages of Northern Bangladesh. A sample of 170 farmers was selected. Research indicates that the farmers practising agroforestry own small farms and the income of agroforestry helps them to reduce their poverty, maintain their socio-economic needs and sustain their livelihoods. Agroforestry is not a new concept in the study area. The people have been practicing agroforestry traditionally in the form of home gardens, hedgerows and alley cropping. Homestead agroforestry is an age old practice. Alley cropping and hedgerow agroforestry systems are comparatively new. Yet alley cropping is now most popular and is widely accepted in the study area because of its socio-economic advantages and environmental sustainability

    Kinetic Energy Decay Rates of Supersonic and Super-Alfvenic Turbulence in Star-Forming Clouds

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    We present numerical studies of compressible, decaying turbulence, with and without magnetic fields, with initial rms Alfven and Mach numbers ranging up to five, and apply the results to the question of the support of star-forming interstellar clouds of molecular gas. We find that, in 1D, magnetized turbulence actually decays faster than unmagnetized turbulence. In all the regimes that we have studied 3D turbulence-super-Alfvenic, supersonic, sub-Alfvenic, and subsonic-the kinetic energy decays as (t-t0)^(-x), with 0.85 < x < 1.2. We compared results from two entirely different algorithms in the unmagnetized case, and have performed extensive resolution studies in all cases, reaching resolutions of 256^3 zones or 350,000 particles. We conclude that the observed long lifetimes and supersonic motions in molecular clouds must be due to external driving, as undriven turbulence decays far too fast to explain the observations.Comment: Submitted to Phys. Rev. Letters, 29 Nov. 1997. 10 pages, 2 figures, also available from http://www.mpia-hd.mpg.de/theory/preprints.html#maclo

    Direct peptide bioconjugation/PEGylation at tyrosine with linear and branched polymeric diazonium salts

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    Direct polymer conjugation at peptide tyrosine residues is described. In this study Tyr residues of both leucine enkephalin and salmon calcitonin (sCT) were targeted using appropriate diazonium salt-terminated linear monomethoxy poly(ethylene glycol)s (mPEGs) and poly(mPEG) methacrylate prepared by atom transfer radical polymerization. Judicious choice of the reaction conditions-pH, stoichiometry, and chemical structure of diazonium salt-led to a high degree of site-specificity in the conjugation reaction, even in the presence of competitive peptide amino acid targets such as histidine, lysines, and N-terminal amine. In vitro studies showed that conjugation of mPEG 2000 to sCT did not affect the peptide's ability to increase intracellular cAMP induced in T47D human breast cancer cells bearing sCT receptors. Preliminary in vivo investigation showed preserved ability to reduce [Ca 2+] plasma levels by mPEG 2000-sCT conjugate in rat animal models. © 2012 American Chemical Society
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