Secondary threshold amplitudes for sinuous streak breakdown

The nonlinear stability of laminar sinuously bent streaks is studied for the plane Couette flow at Re=500 in a nearly minimal box and for the Blasius boundary layer at Re_d*= 700. The initial perturbations are nonlinearly saturated streamwise streaks of amplitude AU perturbed with sinuous perturbations of amplitude AW. The local boundary of the basin of attraction of the linearly stable laminar flow is computed by bisection and projected in the AU – AW plane providing a well defined critical curve. Different streak transition scenarios are seen to correspond to different regions of the critical curve. The modal instability of the streaks is responsible for transition for AU ~ 25%–27% for the considered flows, where sinuous perturbations of amplitude below AW ~ 1%–2% are sufficient to counteract the streak viscous dissipation and induce breakdown. The critical amplitude of the sinuous perturbations increases when the streamwise streak amplitude is decreased. With secondary perturbations amplitude AW ~ 4%, breakdown is induced on stable streamwise streaks with AU ~ 13%, following the secondary transient growth scenario first examined by Schoppa and Hussain [J. Fluid Mech. 453, 57 (2002)]. A cross-over, where the critical amplitude of the sinuous perturbation becomes larger than the amplitude of streamwise streaks, is observed for streaks of small amplitude AU < 5%–6%. In this case, the transition is induced by an initial transient amplification of streamwise vortices, forced by the decaying sinuous mode. This is followed by the growth of the streaks and final breakdown. The shape of the critical AU – AW curve is very similar for Couette and boundary layer flows and seems to be relatively insensitive to the nature of the edge states on the basin boundary. The shape of this critical curve indicates that the stability of streamwise streaks should always be assessed in terms of both the streak amplitude and the amplitude of spanwise velocity perturbations

Bioreactors landfills: comparison and kinetics of the different systems

The need for more sustainable landfilling has increased interest in bioreactor landfills as a suitable tool for optimising degradation processes. Bioreactors can be categorised as follows: anaerobic, aerobic, semi aerobic and hybrid. The choice of a specific bioreactor can be strongly influenced by the desired treatment objectives (i.e., energy recovery, increased rate of waste stabilisation, washing) as well as by the specific site conditions (e.g., waste characteristics, climate and social/economic situation, regulations). However, the increased rate of waste stabilisation should be the primary driving principle in the bioreactor landfill design (Cossu, 2010). Full-scale bioreactor landfills are still uncommon and one of the reasons is the perception that the effectiveness of this technology is not well demonstrated. This paper aims to contribute to filling this knowledge gap by analysing and comparing the lab scale applications of different types of bioreactors available in the literature and providing a survey of the different methods by considering their respective advantages and disadvantages. Qualitative analysis of the main types of bioreactor landfills is provided according to a few selected characteristics (i.e. energy recovery, biochemical kinetics, technological complexity, costs). Considering landfill sustainability, the discussion is primarily focused on the quantification of the stabilisation capability of the different bioreactors which is calculated in terms of COD and ammonia removal kinetics. The results demonstrate that the optimisation of COD removal kinetics is the highest in aerated bioreactors, while ammonia removal kinetics is maximum in hybrid bioreactors (i.e., 6 and 10 times higher, respectively, compared to the anaerobic bioreactors)

A discussion on cell therapy in Manchester

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Marine benthic forms of the Marine Protected Area Capo Caccia-Isola Piana (Sardinia, Italy)

The great ecological and economic value of the biocenoses of Marine Protected Area 'Capo Caccia-Isola Piana' (MPA) requires a constant monitoring. For this reason, a continuous study of the area producing overlapping maps useful to control in real time the evolution of the biocenoses is necessary. The integrated use of several methodologies, such as Side Scan Sonar, Remote Operating Vehicle and Drone, has allowed us to realize a very detailed map. This paper presents the marine benthic map of the MPA and compares the present situation with that recorded in 2008

Analysis of fouling development under dynamic membrane filtration operation

This research is a contribution towards evaluating the appropriate fouling mechanism responsible for the flux decline under dynamic membrane (DM) filtration and its formation mechanism by using gravity-driven filtration in a specifically designed experimental setup. Series of extended short term filtration experiments were performed at varying operating conditions of mixed liquor suspended solids (MLSS) concentrations, trans-membrane pressures (TMP) and mesh pore sizes. Blocking models were applied to identify the fouling mechanisms occurring in DM development. The results demonstrated that cake filtration model can adequately describe fouling mechanisms during DM filtration. According to the analysis of variance, DM development, as described by flux (J) trends during filtration, was significantly affected only by MLSS concentration while effluent turbidity was significantly affected by MLSS concentration and TMP. On the contrary, J and effluent turbidity trends during filtration were not significantly influenced by mesh pore size, at least in the range used in this study (10–200 μm)

Mitochondrial DNA reveals genetic structuring of <i>Pinna nobilis</i> across the Mediterranean Sea

Pinna nobilis is the largest endemic Mediterranean marine bivalve. During past centuries, various human activities have promoted the regression of its populations. As a consequence of stringent standards of protection, demographic expansions are currently reported in many sites. The aim of this study was to provide the first large broad-scale insight into the genetic variability of P. nobilis in the area that encompasses the western Mediterranean, Ionian Sea, and Adriatic Sea marine ecoregions. To accomplish this objective twenty-five populations from this area were surveyed using two mitochondrial DNA markers (COI and 16S). Our dataset was then merged with those obtained in other studies for the Aegean and Tunisian populations (eastern Mediterranean), and statistical analyses (Bayesian model-based clustering, median-joining network, AMOVA, mismatch distribution, Tajima’s and Fu’s neutrality tests and Bayesian skyline plots) were performed. The results revealed genetic divergence among three distinguishable areas: (1) western Mediterranean and Ionian Sea; (2) Adriatic Sea; and (3) Aegean Sea and Tunisian coastal areas. From a conservational point of view, populations from the three genetically divergent groups found may be considered as different management units

Mendelian breeding units <i>versus</i> standard sampling strategies: mitochondrial DNA variation in southwest Sardinia

We report a sampling strategy based on Mendelian Breeding Units (MBUs), representing an interbreeding group of individuals sharing a common gene pool. The identification of MBUs is crucial for case-control experimental design in association studies. The aim of this work was to evaluate the possible existence of bias in terms of genetic variability and haplogroup frequencies in the MBU sample, due to severe sample selection. In order to reach this goal, the MBU sampling strategy was compared to a standard selection of individuals according to their surname and place of birth. We analysed mitochondrial DNA variation (first hypervariable segment and coding region) in unrelated healthy subjects from two different areas of Sardinia: the area around the town of Cabras and the western Campidano area. No statistically significant differences were observed when the two sampling methods were compared, indicating that the stringent sample selection needed to establish a MBU does not alter original genetic variability and haplogroup distribution. Therefore, the MBU sampling strategy can be considered a useful tool in association studies of complex traits