The paper presents a numerical study where a hybrid CFD-Chemical Reactor Network (CRN) approach is used to predict pollutant emissions in a tubular combustor for aero-engine applications. A ...fully-automated clustering of the simulated flow field with the generation of a reactor network representative of the main flow features is exploited. Similar cells are detected and grouped using a two step approach, the first one based only on aerodynamic criteria for turbulent flows followed by a chemical refinement based on mixture fraction. A formulation for turbulent diffusion fluxes is introduced in the reactor code to model species and energy exchanges between reactors. Three different operating conditions are studied for which measured NOx and CO are available. Results highlight the importance of including turbulent diffusion in the network solution. The accurate prediction of pollutant emissions at different load points confirms that CFD-CRN is a valid and flexible approach for preliminary assessment of aero-engine combustor emissions in the design phase.
Inertial particles in turbulent flows are characterised by preferential concentration and segregation and, at sufficient mass loading, dense particle clusters may spontaneously arise due to momentum ...coupling between the phases. These clusters, in turn, can generate and sustain turbulence in the fluid phase, which we refer to as cluster-induced turbulence (CIT). In the present work, we tackle the problem of developing a framework for the stochastic modelling of moderately dense particle-laden flows, based on a Lagrangian probability-density-function formalism. This framework includes the Eulerian approach, and hence can be useful also for the development of two-fluid models. A rigorous formalism and a general model have been put forward focusing, in particular, on the two ingredients that are key in moderately dense flows, namely, two-way coupling in the carrier phase, and the decomposition of the particle-phase velocity into its spatially correlated and uncorrelated components. Specifically, this last contribution allows us to identify in the stochastic model the contributions due to the correlated fluctuating energy and to the granular temperature of the particle phase, which determine the time scale for particle–particle collisions. The model is then validated and assessed against direct-numerical-simulation data for homogeneous configurations of increasing difficulty: (i) homogeneous isotropic turbulence, (ii) decaying and shear turbulence and (iii) CIT.
In railway applications, the estimation of wear at the wheel–rail interface is an important field of study, mainly correlated to the planning of maintenance interventions, vehicle stability and the ...possibility of carrying out specific strategies for the wheel profile optimization. In this work the authors present a model for the evaluation of wheel and rail profile evolution due to wear specifically developed for complex railway networks. The model layout is made up of two mutually interactive but separate units: a vehicle model (composed of the multibody model and the global contact model) for the dynamical analysis and a model for the wear evaluation (composed of the local contact model, the wear evaluation procedure and the profile update strategy).
The authors propose a statistical approach for the railway track description to study complex railway lines in order to achieve general significant accuracy results in a reasonable time: in fact the exhaustive simulation of the vehicle dynamics and of wear evolution on all the railway network turn out to be too expensive in terms of computational effort for each practical purpose.
The wear model has been validated in collaboration with Trenitalia S.P.A and RFI, which have provided the technical documentation and the experimental data relating to some tests performed on a scenario that exhibits serious problems in terms of wear: the vehicle ALn 501 “Minuetto” circulating on the Aosta-Pre Saint Didier Italian line.
•Development of a new wheel and rail wear model for complex railway networks.•The railway network has been described through innovative statistical techniques.•Multibody models and a new wheel–rail contact model have been used to study the dynamics of the vehicles.•The wear model has been validated and tested in terms of accuracy and computational load.
Several studies have shown that physical activity has positive effects on cognition in healthy older adults without cognitive complains but lesser is known about the effectiveness of aerobic exercise ...in patients suffering from Mild Cognitive Impairment (MCI). The aim of the present study was to systematically review the evidence from randomized controlled trials (RCTs) about the effects of aerobic exercise upon cognition in MCI patients. To this end, PubMed, Cochrane and Web of Science databases were analytically searched for RCTs including aerobic exercise interventions for MCI patients. There is evidence that aerobic exercise improves cognition in MCI patients. Overall research reported moderate effects for global cognition, logical memory, inhibitory control and divided attention. Due to methodological limitations of the investigated studies, findings should be interpreted with caution. Standardized training protocols, larger scale interventions and follow-ups may also provide better insight into the preventive effects of aerobic exercise on cognitive deterioration in MCI and its conversion into dementia.
Accumulating evidence suggests that pregnancy does not protect women from mental illness. The aim of this study was to assess the prevalence, sociodemographic correlates, and the risks factors for ...perinatal depression and anxiety. Five hundred ninety women between 28th and the 32nd gestational weeks were recruited and submitted to a sociodemographic, obstetric, and psychological interview. The Edinburgh Postnatal Depression Scale (EPDS) and the state-trait anxiety inventory (STAI-Y) were also administered in antenatal period and 3 months postnatally. The Structured Clinical Interview for DSM-IV (SCID-I) was used to diagnose mood and anxiety disorders. Three months after delivery, EPDS was administered by telephone interview. Women with an EPDS score ≥10 were 129 in antenatal period (21.9%) and 78 in postnatal period (13.2%). During pregnancy 121 women (20.5%) were positive for STAI-Y state and 149 women (25.3%) for STAI-Y trait. The most important risk factors for antenatal depression are: foreign nationality, conflictual relationship with family and partner, and lifetime psychiatric disorders. The principal risk factors for postnatal depression are: psychiatric disorders during pregnancy and artificial reproductive techniques. Psychiatric disorders, during and preceding pregnancy, are the strongest risk factors for antenatal state and trait anxiety. Antenatal depressive and anxiety symptoms appear to be as common as postnatal symptoms. These results provide clinical direction suggesting that early identification and treatment of perinatal affective disorders is particularly relevant to avoid more serious consequences for mothers and child.
Abstract Aim of the study The aim of this study was to retrospectively analyse early and late results of surgical management of internal carotid artery (ICA) true and false aneurysms in a ...single-centre experience. Materials and methods From January 1988 to December 2011, 50 consecutive interventions for ICA aneurismal disease were performed; interventions were performed for true ICA aneurysm in 19 cases (group 1) and for ICA post-carotid endarterectomy (CEA) pseudo-aneurysm in the remaining 31 (group 2). Early results (<30 days) were evaluated in terms of mortality, stroke and cranial nerves' injury and compared between the two groups with χ2 test. Follow-up results (stroke free-survival, freedom from ICA thrombosis and reintervention) were analysed with Kaplan–Meier curves and compared with log-rank test. Results All the patients in group 1 had open repair of their ICA aneurysm; in group 2 open repair was performed in 30 cases, while three patients with post-CEA aneurysm without signs of infection had a covered stent placed. There were no perioperative deaths. Two major strokes occurred in group 1 and one major stroke occurred in group 2 ( p = 0.1). The rates of postoperative cranial nerve injuries were 10.5% in group 1 and 13% in group 2 ( p = 0.8). Median duration of follow-up was 60 months (range 1–276). Estimated 10-year stroke-free survival rates were 64% in group 1 and 37% in group 2 ( p = 0.4, log rank 0.5); thrombosis-free survival at 10 years was 66% in group 1 and 34% in group 2 ( p = 0.2, log rank 1.2), while the corresponding figures in terms of reintervention-free survival were 68% and 33%, respectively ( p = 0.2, log rank 1.8). Conclusions Surgical treatment of ICA aneurismal disease provided in our experience satisfactory early and long-term results, without significant differences between true and false aneurysms. In carefully selected patients with non-infected false aneurysm, the endovascular option seems to be feasible.
Smooth cordgrass (Spartina alterniflora) was introduced to China in December 1979 to buffer against tides and to accelerate coastal wetland accretion. Since then, its propagation and natural ...dispersal have allowed this exotic plant to rapidly expand throughout coastal China with generally negative ecological effects. In 2003 S. alterniflora was labeled as an invasive plant in China, and it now covers ~50,000 ha. In this review, we first summarize the mechanisms of spread and spatial distribution of S. alterniflora, and how its physiological characteristics and strong adaptability to the available niche space in China's wetlands have enabled its spread and competition with native plants. Then we review the effects of S. alterniflora on ecosystem function in terms of habitat conversion and the alteration of biodiversity, soil carbon flux and sequestration, and various processes of nutrient regulation. We conclude that we need a long-term and context-dependent perspective, in order to maximize the benefits and minimize the costs of S. alterniflora within each of China's unique provinces.
Objectives
Spinal dural arteriovenous fistulas (SDAVFs) are acquired diseases that represent the majority of all arteriovenous spinal shunts, leading to progressive and disabling myelopathy. ...Treatment is focused on accurately disconnecting the fistula point. We present our experience with the double-cone-beam CT fusion technique successfully applied to evaluate treatment results in a series of SDAVFs.
Methods
Between November 2011 and December 2015 we performed double-DynaCT acquisition (pre- and post-embolisation) in 12 cases of SDAVF.
Results
A successful DynaCT fusion technique was only achieved in the group of patients with pre- and post-treatment images acquired at the same time as the treatment session, under general anaesthesia (4/12). DynaCT performed on different days proved to be inadequate for the automated fusion technique because of changes in the body position (8/12).
Conclusions
A pre-treatment flat-panel cone-beam CT with contrast, at the time of diagnostic angiography, can be very helpful to detect the correct level of the fistula and the relationship between the fistula and the surrounding structures. In case of the endovascular approach, additional post-treatment native acquisition merged with the pre-treatment acquisition (double-cone-beam CT fusion technique) permits to immediately evaluate the distribution of the glue cast and to confirm the success of the procedure.
Key Points
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SDAVF treatment must be aimed to occlude the fistula point shunt.
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Native post-operative cone-beam CT permits high-spatial-resolution imaging of the embolic cast.
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The automated double-cone-beam CT fusion technique (pre/post) accurately demonstrates intravascular glue distribution after embolisation.
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Patient movements should be avoided to obtain good technical results.
The Mediterranean Sea is a two‐basin system, with the boundary zone restricted to the Strait of Sicily and the narrow Strait of Messina. Two main population groups are recognized in the Mediterranean ...endemic seagrass Posidonia oceanica, corresponding to the Western and the Eastern basins. To address the nature of the East–West cleavage in P. oceanica, the main aims of this study were: (i) to define the genetic structure within the potential contact zone (i.e. the Strait of Sicily) and clarify the extent of gene flow between the two population groups, and (ii) to investigate the role of present water circulation patterns vs. past evolutionary events on the observed genetic pattern. To achieve these goals, we utilized SSR markers and we simulated, with respect to current regime, the possible present‐day dispersal pattern of Posidonia floating fruits using 28‐day numerical Lagrangian trajectories. The results obtained confirm the presence of the two main population groups, without any indices of reproductive isolation, with the break zone located at the level of the Southern tip of Calabria. The populations in the Strait of Sicily showed higher affinity with Western than with Eastern populations. This pattern of genetic structure probably reflects historical avenues of recolonization from relict glacial areas and past vicariance events, but seems to persist as a result of the low connectivity among populations via marine currents, as suggested by our dispersal simulation analysis.
The modelling and the reduction of wear due to wheel-rail interaction is a fundamental aspect in the railway field, mainly correlated to safety, maintenance interventions and costs. In this work, the ...authors present two innovative wheel profiles, specifically designed with the aim of improving the wear and stability behaviour of the standard ORE S1002 wheel profile matched with the UIC60 rail profile canted at 1/20 rad, which represents the wheel-rail combination adopted in the Italian railway line. The two wheel profiles, conventionally named CD1 and DR2, have been developed by the authors in collaboration with Trenitalia S.p.A. The CD1 profile has been designed with the purpose of spreading the contact points in the flange zone on a larger area in order to reduce wear phenomena and having a constant equivalent conicity for small lateral displacements of the wheelset with respect to the centred position in the track. The DR2 wheel profile is instead designed to guarantee the same kinematic characteristics of the matching formed by ORE S1002 wheel profile and UIC60 rail profile with laying angle α
p
equal to 1/40 rad, widely common in European railways and characterised by good performances in both wear and kinematic behaviour. The evolution of wheel profiles due to wear has been evaluated through a wear model developed and validated by the authors in previous works. The wear model comprises two mutually interactive units: a vehicle model for the dynamic simulations and a model for the wear assessment. The whole model is based on a discrete process: each discrete step consists in one dynamic simulation and one profile update by means of the wear model while, within the discrete step, the profiles are supposed to be constant. The choice of an appropriate step is crucial in terms of precision and computational effort: the particular strategy adopted in the current work has been chosen for its capacity in representing the nonlinear wear evolution and for the low computational time required. In the present research, the investigated trainset is the passenger vehicle ALSTOM ALn 501 'Minuetto', which is usually equipped with the standard ORE S1002 wheel profile in Italian railways. The entire model has been simulated on a virtual track specifically developed to represent a statistical description of the whole Italian line. The data necessary to build the virtual track and the vehicle model were provided by Trenitalia S.p.A. and Rete Ferroviaria Italiana. The CD1 and DR2 wheel profiles, matched to the UIC60 rail with cant 1/20 rad, have shown a good behaviour in terms of wear resistance if compared with the old ORE S1002 wheel profile, consequently assuring a more uniform distribution of the removed material and a prolongation of the mean time between two subsequent re-profiling interventions.
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