1,356,225 research outputs found
High Speed Marine Vehicles With Aerodynamic Surfaces: Development of a Dynamic Model for a Novel Configuration.
No full textA research programme on high speed marine vehicles fitted with aerodynamic
surfaces started in Cranfield University in 2005. One of the configurations
analyzed is a high speed prismatic planing hull with one or more aerodynamic
surfaces; it is called a hybrid vehicle (HV). Two mathematical models have been
developed for the dynamic behavior which is a combination of the very different
behaviors of aircraft and ships. The first model estimates the equilibrium
attitude of the HV at a certain speed. A parametric analysis for the influence
of the configuration on the performance of the HV has been conducted (1). With
the second model, the authors propose a set of ordinary differential equations
of motion, derived in the frame of small-disturbance stability theory which has
been used to investigate the longitudinal dynamic stability of the HV (2). Ref.
(1) and (2) present a complete description of the mathematical models, while
this article summarizes the methodology adopted to develop these dynamic models
and gives a brief summary of the results. (1) COLLU, M., PATEL, M. H., TRARIEUX,
F., A Mathematical Model to analyze the Static Stability of Hybrid (Aero-
hydrodynamically supported) vehicles., 8th Symposium on High Speed Marine
Vehicles 2008 (HSMV08), Naples, Italy, 2008. (2) COLLU, M., PATEL, M. H.,
TRARIEUX, F., A Unified Mathematical Model for High Speed Hybrid (Air and Water-
borne) Vehicles., 2nd International Conference on Marine Research and
Transportation, 2007
The inverse prosthesis as a revision prosthesis in failures of shoulder hemiarthroplasty
No full textThe authors describe their series of seven cases of complications and failures of shoulder hemiarthroplasty that were submitted to revision surgery involving an inverse prosthesis. This prosthesis has for some time now been indicated in elderly patients with arthropathy caused by rupture of the cuff. In our cases this prosthesis was implanted in patients who had undergone shoulder hemiarthroplasty for fracture and for arthrosis. The Constant score was used for pre- and postoperative evaluation. Results at mid-term, from 2 to 4 years, indicate evident improvement in Constant score that rose from a mean of 23.14 preoperatively to a mean of 49.14 postoperatively. Despite the limited follow-up the authors suggest the use of the inverse prosthesis as an effective alternative solution in shoulder arthroplasty revision surgery
3D URANS analysis of a vertical axis wind turbine in skewed flows
No full textThe paper demonstrates the potential of an unsteady RANS 3D approach to predict the effects of skewed winds on the performance of an H-type vertical-axis wind turbine (VAWT). The approach is validated through a comparison between numerical and experimental results for a full-scale Darrieus turbine, demonstrating an improved prediction ability of 3D CFD with respect to both 2D CFD and semi-empirical models based on the double multiple stream tubes method. A 3D URANS approach is then adopted to investigate the power increase observed for a straight-bladed small-scale turbine in a wind tunnel when the rotational axis is inclined from 0° to 15° from the vertical. The main advantage of this approach is a more realistic description of complex three-dimensional flow characteristics, such as dynamic stall, and the opportunity to derive local blade flow conditions on any blade portion during upwind and downwind paths. Consequently, in addition to deriving the turbine overall performance in terms of power coefficient, a better insight into the temporal and spatial evolution of the physical mechanisms is obtained. Our principal finding is that the power gain in skewed flows is obtained during the downwind phase of the revolution as the end part of the blade is less disturbed by the wake generated during the upwind phase
Functional Rotation of the Transporter AcrB: The Essentials of Peristaltic Motion and Subsequent Substrate Extrusion
No full textBacteria, such as E. coli, use multidrug efflux pumps to export toxic substrates through their cell membranes, including antibiotics. The RND transporter of the AcrAB-TolC efflux pump is able to export structurally and chemically different substrates via a functional rotation. The three major states of this rotation cycle were found in several asymmetric crystal structures. After initially analyzing the basic mechanisms of opening of the TolC channel [1] and of substrate extrusion by AcrB [2] separately, we have continued the analysis of the latter one. Thereby, we have focused both on the local interactions between substrate and protein, the properties of the extrusion pathway, as well as the principal subdomain movements which lead to the peristaltic motion. Furthermore, we have investigated the possibility to pull the substrate from the final state of the previous simulations out of the exit gate to estimate whether the substrate is already free to leave the protein via diffusion, which is usually beyond the time scale of computer simulations.
[1] R. Schulz, U. Kleinekathöfer, Biophys. J. 96, 3116 (2009)
[2] R. Schulz, A. Vargiu, F. Collu, U. Kleinekathöfer, P. Ruggerone, submitte
A Molecular Approach to Ligand-Receptor Interaction
No full textWe have studied a human delta-opioid receptor interacting with two agonists, Clozapine and Desmethylclozapine. Delta-opioid receptors belong to the family of G protein-coupled receptors, that transduce an intracellular biological signal upon activation via interaction with a ligand in the transmembrane domain. Although Clozapine and Desmethylclozapine only differ by a methyl group, experimental data have evidenced a more efficient action of Desmethylclozapine in the treatment of refractory schizophrenia. A molecular analysis may help to clarify issues related this difference. Molecular Dynamics simulations help to elucidate the microscopic mechanism of the interactions between the ligand and the receptor identifying features barely seen in experiments. However, as in our case, the time scale of the processes of interest is often too long to be approached by standard MD techniques. Thus, for our study we have used a recent technique, the metadynamics, that accelerates MD runs extending simulation times. Our results pointed out different routes of the drugs inside the receptor: Clozapine touches a larger number of competing minima far from the putative receptor active zone than Desmethylclozapine. This latter spends most of its time inside the receptor close to the residues of the active zone, inducing noticeable structural modifications. Additionally, the simulation of the entrance has provided evidence of a stronger interaction with the receptor of Desmethylclozapine than Clozapine, resulting in a more frequent entrance of the former. Clozapine exhibits a preferential interaction with the membrane because of its enhanced hydrophobicity. The free energy surfaces extracted from the simulations have been used for kinetic Monte Carlo simulations to obtain reliable residence times of the drugs inside the receptor. The whole results helps to understand how microscopic details can remarkably affect efficiency and activity of compounds, supporting the idea of a bottom-up strategy in the drug design
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Floating Spar-Type Offshore Wind Turbine Hydrodynamic Response Characterisation: A Computational Cost Aware Approach
No full textThe hydromechanics analysis of floating offshore wind turbines is a fundamental and time consuming part of the design process, traditionally analysed with methods of computational fluid dynamics. In this work, an alternative computational framework is suggested, able to significantly accelerate the design process with minimal accuracy loss. Through the use of a state-of-the-art potential-flow code, a surrogate model is developed with the aim to approximate the Response Amplitude Operators of any arbitrary floating offshore wind turbine of the spar buoy type. The results, measured in terms of accuracy and computational effort, demonstrate that this approach is able to approximate the potential-flow solver with very high accuracy at a fraction of the computational cost
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