854 research outputs found
A heuristic for optimum allocation of real-time service workflows
No full textIn this paper, the problem of optimum allocation of real-time service workflows over a set of heterogeneous resources is tackled. In previous works, this problem was formally stated in terms of a Mixed-Integer Non-Linear Programming optimization program, that could be solved by recurring to commercial solvers. However, due to the big dimension of the solution space to be searched, finding the absolutely optimum solution: might take too much time in order to be concretely useful; it may preclude the use of these techniques in large-scale infrastructures; it makes the technique hardly usable adaptively in response to corrective actions that may be needed when some bad event occurs while the services are running (e.g., hardware-level failures). Therefore, in this paper a heuristic algorithm based on graph-matching is introduced that may find very efficiently a reasonably good, albeit non-necessarily optimum, solution. The algorithm is described, and its performance assessed by a set of synthetic experiments
Heavy Ion Carcinogenesis and Human Space Exploration
No full textPrior to the human exploration of Mars or long duration stays on the Earth s moon, the risk of cancer and other diseases from space radiation must be accurately estimated and mitigated. Space radiation, comprised of energetic protons and heavy nuclei, has been show to produce distinct biological damage compared to radiation on Earth, leading to large uncertainties in the projection of cancer and other health risks, while obscuring evaluation of the effectiveness of possible countermeasures. Here, we describe how research in cancer radiobiology can support human missions to Mars and other planets
A Topology Optimization Method for Stochastic Lattice Structures
No full textStochastic lattice structures are very powerful solutions for filling three-dimensional spaces using a generative algorithm. They are suitable for 3D printing and are well appropriate to structural optimization and mass distribution, allowing for high-performance and low-weight structures. The paper shows a method, developed in the Rhino-Grasshopper environment, to distribute lattice structures until a goal is achieved, e.g. the reduction of the weight, the harmonization of the stresses or the limitation of the strain. As case study, a cantilever beam made of Titan alloy, by means of SLS technology has been optimized. The results of the work show the potentiality of the methodology, with a very performing structure and low computational efforts
Cosmic Rays: Hurdles on the Road to Mars
No full textSpace radiation has long been recognized as a major health hazard for human space exploration. Unlike terrestrial radiation, space radiation comprises high energy protons and high charge and energy (HZE) nuclei, which produce distinct forms of biological damage to biomolecules, cells, and tissue compared to terrestrial radiation, making risk predictions highly uncertain [1]. While the crews in low Earth orbit (LEO), such as the International Space Station (ISS), are partially protected by the Earth's magnetic field, for interplanetary missions in deep space the risk of acute effects caused by solar particle events (SPE) and late effects induced by protons and HZE nuclei in the galactic cosmic rays (GCR) is significant. Intense SPE can be lethal for unprotected crews, but shielding is effective against solar protons. Chronic exposure to GCR represents instead a very serious risk of carcinogenesis [2]. It is not clear if the health risks associated with long-term exposure to HZE nuclei can be adequately estimated by epidemiological studies, as done for radiation protection on Earth, due to both quantitative and qualitative differences in biological damage. Therefore, risk estimates, mostly based on ground-based cell or animal studies, are affected by large uncertainties. Moreover, shielding from very energetic CGR nuclei tends to be poor given the weight constraints of spacecraft
Sail Plan Parametric CAD Model for an A-Class Catamaran Numerical Optimization Procedure Using Open Source Tools
No full textA geometric tool for a catamarans sail plan and appendages optimization procedure is descripted. The method integrates a parametric CAD model, an automatic computational domain generator and a Velocity Prediction Program (VPP) based on a combination of sail RANS computations and analytical models. The boat performance is obtained, in an iterative process, solving the forces and moment equilibrium system of equations. Hull and appendages forces are modelled by analytical formulations. The closure of the equilibrium system is provided by the CFD solution of the sail plan. The procedure permits to find the combination of appendages configuration, rudders setting, sail planfonn, shape and trim that maximize the VMG (Velocity Made Good). A significant effort was addressed to the selection and evaluation of open-source tools to be adopted in the implementation of the method. The geometric parametric model, which is the core of the procedure, was object of particular attention. The FreeCAD geometric modeller was selected for this task. The sail shapes candidates are automatically generated, within the optimization procedure, by Python scripts that drive FreeCAD to update the geometry according to the variables combination A very flexible model, able to offer a very wide space of variables, was implemented. This paper describes the implemented geometric model and the environment in which is included
Chromosomes lacking telomeres are present in the progeny of human lymphocytes exposed to heavy ions.
No full textCancer risk from exposure to galactic cosmic rays: implications for space exploration by human beings.
No full textSpace programmes are shifting toward planetary exploration, and in particular towards missions by human beings to the moon and Mars. However, exposure to space radiation is an important barrier to exploration of the solar system by human beings because of the biological effects of high-energy heavy ions. These ions have a high charge and energy, are the main contributors to radiation risk in deep space, and their biological effects are understood poorly. Predictions of the nature and magnitude of risks posed by exposure to radiation in space are subject to many uncertainties. In recent years, worldwide efforts have focussed on an increased understanding of the oncogenic potential of galactic cosmic rays. A review of the new results in this specialty will be presented here
Analysis and Optimization of Dysprosium-Doped Yellow Fiber Lasers for Ophthalmology Applications
No full textIn this paper, a Forward Time Centered Space (FTCS) method and an analytical method have been developed to fully investigate the to lasing transition of a dysprosium Dydoped ZBLAN fiber which provides the potential of highly efficient yellow laser direct generation. This light source is of significant interest for treating diabetic retinopathy, which can cause blindness. The developed method's validity is confirmed through the comparison with experimental investigations of Dydoped ZBLAN fiber lasers in other valid research. A full analysis of Dydoped fiber laser including the population of the energy levels, power evolution of the laser and pump signals, amplified spontaneous emission (ASE), excited state absorption (ESA), radiative and non-radiative time transition rates are presented. The developed numerical method gives a better understanding of the impact of ASE and ESA on laser performance. The influence of overlap integrals, output mirror reflectivity, and active fiber length on laser performance is investigated. The optimization criteria based on the different robust configurations of laser cavities are found which predict the slope efficiencies higher than half of the Stokes limit
The effect of longitudinal rails on an air cavity stepped planing hull
No full textThe use of ventilated hulls is rapidly expanding. However, experimental and numerical analyses are still very limited, particularly for high-speed vessels and for stepped planing hulls. In this work, the authors present a comparison between towing tank tests and CFD analyses carried out on a single-stepped planing hull provided with forced ventilation on the bottom. The boat has identical geometries to those presented by the authors in other works, but with the addition of longitudinal rails. In particular, the study addresses the effect of the rails on the bottom of the hull, in terms of drag, and the wetted surface assessment. The computational methodology is based on URANS equation with multiphase models for high-resolution interface capture between air and water. The tests have been performed varying seven velocities and six airflow rates and the no-air injection condition. Compared to flat-bottomed hulls, a higher incidence of numerical ventilation and air–water mixing effects was observed. At the same time, no major differences were noted in terms of the ability to drag the flow aft at low speeds. Results in terms of drag reduction, wetted surface, and its shape are discussed
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