PGD-Based Computational Vademecum for Efficient Design, Optimization and Control

In this paper we are addressing a new paradigm in the field of simulation-based engineering sciences (SBES) to face the challenges posed by current ICT technologies. Despite the impressive progress attained by simulation capabilities and techniques, some challenging problems remain today intractable. These problems, that are common to many branches of science and engineering, are of different nature. Among them, we can cite those related to high-dimensional problems, which do not admit mesh-based approaches due to the exponential increase of degrees of freedom. We developed in recent years a novel technique, called Proper Generalized Decomposition (PGD). It is based on the assumption of a separated form of the unknown field and it has demonstrated its capabilities in dealing with high-dimensional problems overcoming the strong limitations of classical approaches. But the main opportunity given by this technique is that it allows for a completely new approach for classic problems, not necessarily high dimensional. Many challenging problems can be efficiently cast into a multidimensional framework and this opens new possibilities to solve old and new problems with strategies not envisioned until now. For instance, parameters in a model can be set as additional extra-coordinates of the model. In a PGD framework, the resulting model is solved once for life, in order to obtain a general solution that includes all the solutions for every possible value of the parameters, that is, a sort of computational vademecum. Under this rationale, optimization of complex problems, uncertainty quantification, simulation-based control and real-time simulation are now at hand, even in highly complex scenarios, by combining an off-line stage in which the general PGD solution, the vademecum, is computed, and an on-line phase in which, even on deployed, handheld, platforms such as smartphones or tablets, real-time response is obtained as a result of our queries.     

Hierarchical power management in disruption tolerant networks using traffic-aware optimization

Recent efforts in Disruption Tolerant Networks (DTNs) have shown that mobility can be a powerful means for delivering messages in highly-challenged environments. DTNs are wireless mobile networks that are particularly useful in sparse environments where the density of nodes is insufficient to support direct end-to-end communication. Unfortunately, many mobility scenarios depend on untethered devices with limited energy supplies. Without careful management, depleted energy supplies will degrade network connectivity and counteract the robustness gained by mobility. A primary concern is the energy consumed by wireless communication, and in particular the energy consumed in searching for other nodes to communicate with. In this paper we examine a hierarchical radio architecture in which nodes are equipped with two complementary radios: a long-range, high-power radio and a short-range, low-power radio. In this architecture energy can be conserved by using the low-power radio to discover communication opportunities with other nodes and waking the high-power radio to undertake data transmission. We develop a generalized power management framework for controlling the wake-up intervals of the two radios. In addition, we show how to incorporate knowledge of the traffic load, and we devise approximation algorithms to control the sleep/wake-up cycling to provide maximum energy conservation while discovering enough communication opportunities to handle that load. We evaluate our schemes through simulation under various mobility scenarios. Our results show that our generalized power management scheme can tune wake-up intervals of the two radios to balance energy efficiency and delivery performance. Also, when traffic load can be predicted, our approximation algorithms reduce energy consumption from 60% to 99% compared to no power management.     

Spin-lattice relaxation in gadolinium-doped calcium tungstate

The spin-lattice relaxation of the S-state ion Gd³⁺ in a calcium tungstate host lattice has been examined at 37.5 GHz over the temperature range 1.5 to 30 K. The gadolinium concentrations in the doped single crystals used were about 50 ppm. Single exponential recovery was observed and the spin-lattice relaxation time (T ₁) varied from about 14 msec at 1.5 K to 0.03 msec at 30 K, measured with =90° and =8°. It was found that T ₁ varied with temperature (T) as T ₁ T ^–1 below 8 K and as T ₁ T ^–3 between 8 and 30 K. The experimental data was fitted by the expressions T ₁ ^–1 =35 T+0.5 T ³ and T ₁ ^–1 =35T+0.1 T ^3.6 for crystals of nominal gadolinium concentrations 0.005 wt % and 0.05 wt % respectively. The difference between the observed dependence and the T ^–5 variation predicted in the Raman region for an S-state ion in a perfect lattice is attributed to defects. Measurements in the -plane at 4.2 K showed that T ₁ was anisotropic with a maximum value at =25° about three times greater than the minimum value obtained at =55°. The angular positions at which these features occur show a remarkable coincidence with the acoustic axes of symmetry of the crystal, which have recently been determined by ultrasonic methods.     

Architectural-level risk analysis using UML

Risk assessment is an essential part in managing software development. Performing risk assessment during the early development phases enhances resource allocation decisions. In order to improve the software development process and the quality of software products, we need to be able to build risk analysis models based on data that can be collected early in the development process. These models will help identify the high-risk components and connectors of the product architecture, so that remedial actions may be taken in order to control and optimize the development process and improve the quality of the product. In this paper, we present a risk assessment methodology which can be used in the early phases of the software life cycle. We use the Unified Modeling Language (UML) and commercial modeling environment Rational Rose Real Time (RoseRT) to obtain UML model statistics. First, for each component and connector in software architecture, a dynamic heuristic risk factor is obtained and severity is assessed based on hazard analysis. Then, a Markov model is constructed to obtain scenarios risk factors. The risk factors of use cases and the overall system risk factor are estimated using the scenarios risk factors. Within our methodology, we also identify critical components and connectors that would require careful analysis, design, implementation, and more testing effort. The risk assessment methodology is applied on a pacemaker case study.     

Permutation flowshop scheduling problems with maximal and minimal time lags

In this paper, we study permutation flowshop problems with minimal and/or maximal time lags, where the time lags are defined between couples of successive operations of jobs. Such constraints may be used to model various industrial situations, for instance the production of perishable products. We present theoretical results concerning two-machine cases, we prove that the two-machine permutation flowshop with constant maximal time lags is strongly NP-hard. We develop an optimal branch and bound procedure to solve the m$m$-machine permutation flowshop problem with minimal and maximal time lags. We test several lower bounds and heuristics providing upper bounds on different classes of benchmarks, and we carry out a performance analysis.     

Design,Synthesis, Characterization,Swelling and in Vitro Drug Release Behavior of Composite Hydrogel Beads Based on Methotrexate and Chitosan Incorporating Antipyrine Moiety

Novel biodégradable pH and thermal-responsive hydrogels were prepared for controlled drug delivery studies via reaction of chitosan with 4-chloroacetylantipyrine in DMF/H₂O, followed by heating of the formed poly [acetylantipyrine-chitosan] with glutaraldehyde as a crosslinking agent to give the hydrogels. These hydrogels were subjected to equilibrium swelling studies at different temperatures (25°C, 37°C and 45°C) in solutions of pH 2.1 and 7.4. Methotrexate (MTX) was entrapped in the hydrogels, and drug release studies were carried out at 37 °C in solutions at pH 2.1 and 7.4.     

Spin-lattice relaxation of Fe3+ in iron doped magnesium oxide

Spin-lattice relaxation measurements for Fe³⁺/MgO were carried out in the temperature range from 4.2 to 27 K at 37.5 Hz utilizing the pulse saturation method. This revealed a close agreement with the theoretical predictions, demonstrating aT ^–1 behaviour at low temperatures as a direct process and aT ^–4.6 variation as a raman process at higher temperatures, with a transition temperature near 20 K between these two regimes. Measurements oft ₁ were carried out for samples with iron concentrations of 140, 310 and 110 ppm and gave the values of 1.0, 0.8 and 0.1 msec, respectively, at 4.2 K. This confirms that the inverse proportionality oft ₁ with concentration holds over this range of samples. Variation of relaxation timet ₁ with crystal orientation for the central transition of Fe³⁺/MgO revealed two minima that were explained as due to crossrelaxation mechanisms. Comparison of our results with both those computed by Shiren at 10 GHz and the experimental results of Castle and Feldman at the same frequency showed that at ₁ (frequency)^–4 law was obeyed. The present data has provided another example of anS-state ion behaving in the manner predicted by the present theories of relaxation.ESR = election spin resonance.     

Écoulement de Taylor‐Couette en géométrie finie et à surface libre

The reactors of Taylor‐Couette type are relatively recent application in the engineering processes field. The stability and the flow structure in this device are examined under the effect combined of the free surface and the fluid's height in annular space. The exploitation of the flow regimes is carried out according to the number of Taylor for various values of aspect ration Γ. By means of ultrasonic velocimetry (UPV) we determine axial average velocity profile and the axial wavelength. We also carry out the spectral analysis by Fourier's fast transform of the fluctuations associated with the average velocity values in order to analyze the flow structure. We particularly aim for checking the presence or the absence of the azimuth wave according to the filling height and the rotational velocity imposed. We highlight the effects of free surface and aspect ratio on the conditions of appearance of the second instability ( wavy mode). The analysis of the fluctuation shows that the appearance of the azimuth wave regime (Wavy mode) is delayed when the aspect ration decreases. Below a critical value noted Γc = 10, the azimuth wave regime is not observed any more.     

Video multicast over the Internet

Multicast distribution of video is an important component of many existing and future networked services. The Internet lacks support for quality of service (QoS) assurance, which makes the transmission of real-time traffic challenging. In addition, the heterogeneity of the Internet's transmission resources and end-systems makes it extremely difficult, if not impossible, to agree on acceptable traffic characteristics among multiple receivers of the same video stream. We survey techniques that have been proposed for transmitting video in this environment. These generally involve adaptation of video traffic carried over the network to match receiver requirements and network conditions. In addition to their applicability to the near-term capabilities of the Internet, they also are of relevance to a future, QoS-aware Internet environment. We first consider source-based techniques in which the source adjusts the video stream traffic to match some consensus among the receivers about its desired characteristics. These techniques can result in an unfair treatment for receivers, especially those whose capability is significantly above or below the group consensus. We then consider techniques that aim to improve the fairness among the receivers by sending the video in multiple (layered or replicated) streams. We also discuss several error control mechanisms, using timely retransmission of missing data to further improve the quality of the received video. Finally, we discuss some of the issues in the development of Internet video multicast protocols