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A Alexakis

Publications and source records attributed to A Alexakis.

8 recordsLinked to original sources
PubMed2006

Large-scale flow effects, energy transfer, and self-similarity on turbulence.

The effect of large scales on the statistics and dynamics of turbulent fluctuations is studied using data from high resolution direct numerical simulations. Three different kinds of forcing, and spatial resolutions ranging from 256(3) to 1024(3), are being used. The study is carried out by investigating the nonlinear triadic interactions in Fourier space, transfer functions, structure functions, and probability density functions. Our results show that the large scale flow plays an important role in the development and the statistical properties of the small scale turbulence. The role of helicity is also investigated. We discuss the link between these findings and intermittency, deviations from universality, and possible origins of the bottleneck effect. Finally, we briefly describe the consequences of our results for the subgrid modeling of turbulent flows.

Journal Article↗
PubMed2005

Imprint of large-scale flows on turbulence.

We investigate the locality of interactions in hydrodynamic turbulence using data from a direct numerical simulation on a grid of 1024(3) points; the flow is forced with the Taylor-Green vortex. An inertial range for the energy is obtained in which the flux is constant and the spectrum follows an approximate Kolmogorov law. Nonlinear triadic interactions are dominated by their nonlocal components, involving widely separated scales. The resulting nonlinear transfer itself is local at each scale but the step in the energy cascade is independent of that scale and directly related to the integral scale of the flow. Interactions with large scales represent 20% of the total energy flux. Possible explanations for the deviation from self-similar models, the link between these findings and intermittency, and their consequences for modeling of turbulent flows are briefly discussed.

Journal Article↗
PubMed2002

Dramatic improvement of the enantiomeric excess in the asymmetric conjugate addition reaction using new experimental conditions.

The asymmetric conjugate addition of dialkylzincs is usually performed with Cu(OTf)(2) in toluene. We show that by using a copper carboxylate in Et(2)O, THF, or EtOAc, we strongly improve the enantioselectivity with a given ligand. Ee values up to 99.1% could be reached with new ligands based on the induced atropisomerism of a simple biphenol unit. In addition, we show that the Lewis acid effect of Cu(OTf)(2) is not a significant.

Journal Article↗
PubMed2002

Shear instability of fluid interfaces: stability analysis.

We examine the linear stability of fluid interfaces subjected to a shear flow. Our main object is to generalize previous work to an arbitrary Atwood number, and to allow for surface tension and weak compressibility. The motivation derives from instances in astrophysical systems where mixing across material interfaces driven by shear flows may significantly affect the dynamical evolution of these systems.

Journal Article↗
PubMed2000

A regulated telemedicine system for day to day application in remote areas.

The NIVEMES project creates an international network of Health Service providers which offer Telemedicine-Teleconsultation services to Remote, Isolated places and to ship vessels for both routine and emergency situations. The base of the system is the powerful Multimedia Health Record, with the ability to manage conventional data, images, videos and biosignals, acquired directly from the medical device. National and international medical codification schemata are employed such as ICD-X and WHO standards. Telemedicine and Computing in Health Care are rapidly covering a pending gap, not fulfilled by current bureaucratic and telematic procedures. However even from the first test fields conducted during the past year, it is obvious that a variety of new training needs has arisen. The users of such systems need to be instructed new ways of conducting their business, of taking advantage of the services, even a new way of perceiving health care provision. The user interface of the software is kept simple, thus getting acquainted with it requires minimum effort; however there are other issues on which training is required to best exploit the advantages the system offers. The telemedical networks spawned in each country must be co-ordinated, and the user needs to know where and how he/she will acquire the necessary support. Home-cared patients will have to operate medical devices and telemedical software, a task which although made easy from today's technology, it still requires some basic training, specially as far as elderly users are concerned. The NIVEMES system uncovers a set of new training needs, but it offers at the same time a vehicle for educating the professional health-carers. The Health Record comprises a multimedia, explicit account of the patient history, which can be used for detailed and integrated study from trainee health carers of all levels (as well as from officers on board, people taking care of home-confined patients and others), on real data or in a simulated environment. At the same time the telemedicine facilities may increase the effectiveness of junior doctors working in remote areas and enhance the confidence residents have about their local health centres. Systems like NIVEMES prove that new user needs arise nowadays and employment of modern tools requires training in modern methods and in a new way of thinking.

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