A Parabolised Stability Equation based Broadband Shock-Associated Noise Model

International audienceWavepacket models have been used extensively to predict the noise produced from turbulent subsonic and supersonic jets. Such wavepackets, which represent the organised structures of the flow, are solutions to the linearised Navier-Stokes equations. Using a kinematic two-point model, Wong et al. [1] have indicated the importance of incorporating coherence decay in modelling broadband shock-associated noise (BBSAN) in supersonic jets. In this work, we aim to improve the model by using solutions from linear parabolised stability equations (PSE) to model the wavepacket part of the BBSAN source. The two-point coherence of the wavepackets is obtained from large-eddy simulation (LES) data of a M j = 1.5 fully-expanded isothermal supersonic jet [2]. The aim is to build a dynamic sound-source model for BBSAN that would improve on the simplified line-source model proposed by Wong et al. [3]. We find that a frequency dependent coherence decay length scale is important in order to suppress the higher-order harmonic peaks [4] and to obtain the correct BBSAN peak shape. Moderate agreement up to St = 1 was found between the current noise predictions and those from experimental data. I. Nomenclature ω = wavepacket frequency θ = azimuthal coordinate c s n = amplitude coefficient of the shock cells G = Green's function k s = shock-cell wavenumber k h = hydrodynamic wavenumber L = longitudinal extent of wavepacket L c = coherence length of wavepacket m = azimuthal mode number M j = ideally-expanded Mach number r = radial coordinate u s = shock cell velocity fluctuation u t = wavepacket fluctuationŝ u * ω = velocity fluctuations at a frequency ω x = axial coordinat

Impact of gonadectomy on blood pressure regulation in ageing male and female rats

Sexual dimorphism in blood pressure has been associated with differential expression of the angiotensin II (AII) receptors and with activity of the nervous system. It is generally accepted that aging affects kidney function as well as autonomic nervous system and hormonal balance. Given that hypertension is more prevalent in men than women until women reach their seventh decade we hypothesised that females would be relatively protected from adverse effects of ageing compared to males, and that this would be mediated by the protective effect of ovarian steroids. Intact and gonadectomised male and female normotensive Wistar rats aged 6, 12 and 18 months were used to study renal function, blood pressure, heart rate and blood pressure variability. We observed that intact females had lower levels of proteinuria and higher (12.5%) creatinine clearance compared to intact males, and that this difference was abolished by castration but not by ovariectomy. Ovariectomy resulted in a change by 9% in heart rate, resulting in similar cardiovascular parameters to those observed in males or gonadectomised males. Spectral analysis of systolic blood pressure revealed that high frequency power spectra were significantly elevated in the females vs. males and were reduced by ovariectomy. Taken altogether the results show that females are protected from age-related declining renal function and to a lesser extent from rising blood pressure in comparison to males. Whilst ovariectomy had some deleterious effects in females, the strongest effects were associated with gonadectomy in males, suggesting a damaging effect of male hormones

The Genetic Structure of Leishmania infantum Populations in Brazil and Its Possible Association with the Transmission Cycle of Visceral Leishmaniasis

Leishmania infantum is the etiologic agent of visceral leishmaniasis (VL) in the Americas, Mediterranean basin and West and Central Asia. Although the geographic structure of L. infantum populations from the Old World have been described, few studies have addressed the population structure of this parasite in the Neotropical region. We employed 14 microsatellites to analyze the population structure of the L. infantum strains isolated from humans and dogs from most of the Brazilian states endemic for VL and from Paraguay. The results indicate a low genetic diversity, high inbreeding estimates and a depletion of heterozygotes, which together indicate a predominantly clonal breeding system, but signs of sexual events are also present. Three populations were identified from the clustering analysis, and they were well supported by F statistics inferences and partially corroborated by distance-based. POP1 (111 strains) was observed in all but one endemic area. POP2 (31 strains) is also well-dispersed, but it was the predominant population in Mato Grosso (MT). POP3 (31 strains) was less dispersed, and it was observed primarily in Mato Grosso do Sul (MS). Strains originated from an outbreak of canine VL in Southern Brazil were grouped in POP1 with those from Paraguay, which corroborates the hypothesis of dispersal from Northeastern Argentina and Paraguay. The distribution of VL in MS seems to follow the west-east construction of the Bolivia-Brazil pipeline from Corumbá municipality. This may have resulted in a strong association of POP3 and Lutzomyia cruzi, which is the main VL vector in Corumbá, and a dispersion of this population in this region that was shaped by human interference. This vector also occurs in MT and may influence the structure of POP2. This paper presents significant advances in the understanding of the population structure of L. infantum in Brazil and its association with eco-epidemiological aspects of VL

Tool life and tool wear in taper turning of a nickel-based superalloy

Due to their high ductility and strain hardening coefficient, high mechanical strength and hardness even in high temperatures, chemical affinity with almost every tool material, and low thermal conductivity, nickel-based superalloys are known to present very low machinability. Some researchers point out that taper turning may prolong tool life as ramping may distribute tool wear along tool edge, avoiding the presence of notch wear in the end of the depth of cut, which usually occurs in the tools used in turning of these alloys. In this work, tool life, tool wear, and resulting surface roughness of Inconel 625 were evaluated for taper turning in comparison with straight turning. In taper turning, double feed was tested to compensate metal removal rate reduction (since in this operation, the feed length is doubled), and in order to avoid roughness increase caused by the higher feed, a wiper tool was used. Results show that taper turning was not successful in terms of tool life, although the furrowing mechanism of the tool coating caused by the hard burr formed, that leads to notch wear, was avoided. This mechanism was replaced by strong adhesion that promoted rapid and wide flank wear. Feed increase has also produced microchipping due to the extra load on the tool edge. Although wiper tool had provided better finishing when high feed was employed, conventional tool seems to be more suitable for tapering considering tool life875-82023203