N-dimensional error control multiresolution algorithms for the point value discretization

Decision makers tend to define their optimization problems as multi-objective optimization problems. Generating the whole nondominated set is often unrealistic due to its size but also because most of these points are irrelevant to the decision maker. Another approach consists in obtaining preference information and integrating it a priori, in order to reduce the size of the nondominated set and have a gain in computation time. In this work we focus on a partial preference relation based on requirement and tolerance thresholds that translate the Pareto dominance cone. After introducing this preference relation, we present adaptations to use it in existing discrete multi-objective optimization algorithms. Numerical experiments on multi-objective combinatorial optimization problems show the applicabiliy of our approach.

This article reviewed how to enhance safety rules through human error and behavioural control strategies. To understand what strategies could be applied safety rules, types of safety rules, safety violations, organisational factors, and behavioural types were explored. To complete this article twelve peer-reviewed articles and three statistical data sets were used based on the Fast-Moving Consumer Goods (FMCG) industry. The importance of safety is undisputed and the need for a holistic approach to enhance safety rules through human error and behavioural control strategies is required. Five key strategies to enhance safety rules through human error and behavioural control strategies include 1. Reducing the number and complexity of safety rules, 2. Consultation, 3. Data Banks, 4. Feedback 5. Proactive and Positive Leadership.

The extension of the known source angular biasing technique by individual targeting for each of the source neutrons on a given arbitrary rectangular target on the reactor first wall, indicating the area of interest in the problem, is considered in search of the possibilities to reduce the time of Monte Carlo calculation for bulky ITER models. The technique is tested in the source unit of the 3D code BLANK implementing the direct Monte Carlo method. A simple cylindrical model of ITER with a rectangular generatrix and a thickness of the side wall of the shielding material (80% stainless steel + 20% H2O) of 50 cm is calculated. The rectangular target matches the input hole of the equatorial port (2 × 2 m). The model calculations showed that the application of the technique did not result in a noticeable reduction of statistical uncertainty for the total neutron flux and its energy components in the first wall zone in the entire range of the targeting probability owing to the prevailing contributions of albedo neutrons. The error at the back surface of the model side wall was ~0.75 of the reference uncertainty (without targeting) in a targeting probability range of 0.2–0.4, which corresponds to a potential gain in computation time of up to ~2 times. These results yielded general empirical conclusions: the neutron flux estimated using this technique is unbiased, and a certain gain in the computer time, as compared to the calculation without targeting, is possible. The technique is expected to be more efficient in calculation of the neutron flux functionals in the depth of the shielding compositions, where the contribution of albedo neutrons from the first wall is insignificant, and the result is mainly determined by the intensity of the leading group of source neutrons. Since the considered technique is universal, it can be implemented as a useful option in any Monte Carlo code.

Since wireless channel is always band-limited with multi-path fading and highly burst errors, flexible error control is needed in wireless asynchronous transfer mode (WATM) networks. This paper proposes a hybrid automatic repeat request (HARQ) architecture which has on-demand quality of services (QoS). By choosing different options in the architecture, we get different error control schemes. In this paper, we investigate the performance of three different error control schemes, namely HARQ, HARQ with different redundancy, and adaptive HARQ with traffic-type-dependent redundancy. The simulation results show that the HARQ with FEC adaptation offers the best performance.

Wireless links are known to suffer location-dependent, time-varying, and bursty errors. This paper considers a class of adaptive error-control schemes in the data link layer for reliable communication over wireless links in which the error-control code and the frame length are chosen adaptively, based on the estimated channel state/condition. Three error-control schemes are considered according to: (1) the number of Reed Solomon code segments a packet is divided into and (2) the way a lost packet is retransmitted. Through throughput performance and computation complexity analyses, these three schemes are compared, and then one of them is claimed to be the most attractive in terms of computation complexity and practicality even though its throughput performance is not the best. The simulation results also verify that this scheme works well over a time-varying fading channel. Error control for the medium access control (MAC) header and its effect on the performance of each error-control scheme are also considered since, without proper error protection for the header, it would be futile to exercise error control on the user data.

Very high resolution optical remote sensing images (RSI) are often corrupted by noise. Among popular denoising methods in the state of the art, nonlocal Bayes (NLB) has led to successful results on real datasets, with high quality and reasonable computation time. However, its computation time remains prohibitive with respect to requirements of operational RSI pipelines, such as Pleiades one. In this paper, we tackle such an issue and introduce several optimizations aiming to significantly reduce the computation time required by NLB while keeping the best denoising quality (i.e., preserving edges, textures, and homogeneous areas). More precisely, our improvements consist of reducing multiple estimations of a same pixel with a masking technique and modifying the spatial extent of the similar patch search area (i.e., one of the main parts of nonlocal algorithms, such as NLB). We report several experiments and discuss optimal settings for these parameters, allowing a gain in computation time of 50% (resp. 15%) with optimized masking strategy (resp. spatial extent of the search area). When both contributions are combined, we achieve the same denoising quality as standard NLB while doubling the computation efficiency, the latter being increased fivefold if we accept a very small (lower than 0.1%) loss in quality.

We study the interaction between error control and media synchronization. We approach the problem by considering a virtual application data unit (ADU) network with error control within the network boundary and media synchronization outside the network boundary. We introduce the concept of cumulative inter-ADU jitter, which is the running total of the differences between inter-ADU spacings at the receiver and at the sender, to model the ADU departure process from the network observed at the entry of the playback buffer. We investigate how different error control schemes, network and source characteristics influence the process on one hand and how the process affects the choice of playback delay in order to minimize ADU losses on the other hand. Our numerical results, obtained through simulation, verify the analysis and reveals that jitter control within the network is not as important as controlling the bandwidth and the delay, especially in the presence of error control and variable bit rate source.

This paper presents a new hybridization between MoM-GEC and some asymptotic methods. In fact, a new hybrid current function based on Physical Optic (PO) and a modal method is developed. The approach consists in approximating the total current on an invariant metallic pattern on two parts; the inside of metal is governed by PO method; however, the edges are modeled by infinite cylinders and described by Hankel functions (modal method). The considered single test function is required then by MoM method to replace a lot of sinusoidal or triangular test functions, in order to get a rapid convergence and less computational time. For validation purposes, the new developed hybrid approach is applied to compute scattering in different structures. The obtained input impedances, currents and fields distributions are in agreement with those obtained by MoM method. Considerable gain in computational time and memory resources is achieved.

This paper presents an adaptive rate error control scheme for digital communication over time-varying channels. The cyclic code with majority-logic decoding is used in a cascaded way as an inner code to create a simple and powerful hybrid-ARQ error control scheme. Inner code is used only for error correction and the outer code is used for both error correction and error detection. When an error is detected, retransmission is required. The unsuccessful packets are not discarded as with conventional schemes, but are combined with their retransmitted copies. Approximations for the throughput efficiency and the undetectable error probability are given. A high reliability coupled with a simple high-speed implementation makes it suitable for high data rate error control over both stationary and non-stationary channels. Adaptive error control scheme becomes the best solution for time-varying channels when the optimum code is selected according to the actual channel conditions to enhance the system performance. The main feature of this system is that the basic structure of the encoder and decoder need not be modified while the error-correction capability of the code increases. Results of a comparative analysis show that the proposed scheme outperforms other similar ARQ protocols. >

In this paper, we present a novel analytical framework for the study of a multiple access scheme for an ad hoc CDMA network with HARQ error control and MF-LSIC receivers. We focus on a scenario where users access the channel simultaneously, fully exploiting the PHY layer multiuser potential. To improve efficiency and reliability we consider a rate controlled system where nodes adapt their transmission rate to the channel conditions in terms of both fading and interference. We compare ARQ and type I-II HARQ error control schemes. We show that in this scenario the error control scheme used to ensure reliability is of particular importance, since it not only determines the average interference level in the network, but also heavily conditions the channel predictability since it affects the interference statistics.

Observing the threshold effect of CDMA systems, this paper proposes a simple, fair protocol suitable for the CDMA environment, which does not need the additional feedback channel but can still achieve the goal of error control. Based on the same rationale as the CSMA/CD protocol, this protocol is designed to avoid collision or congestion of traffic before formal transmission of a packet. By the handshake procedure, the intended transmitter is able to test the channel quality and the receiver's status using a very short handshake packet. Therefore, channel traffic can be controlled to avoid overload. The throughput and reliability are analyzed based on the underlying Markovian models. Numerical results are compared to other error control schemes and show that with a reasonably short handshake time compared to the packet transmission time, this handshake protocol with simple forward error correction offers an excellent alternative for error control and can even improve the throughput performance.

The paper proposes an error control scheme that dynamically adjusts the polling schedule so that more corrupted messages can be manipulated within their deadlines for real-time communication on IEEE 802.11 wireless LAN. Monitoring the current traffic in the CFP (collision free period) interval as well as inspecting whether a node is executing an error control procedure, the AP (access point) terminates CFP, if possible, to extend the duration of the next CP (collision period). With the enlarged time, the AP gives more polls to the node in need to increase the number of timely recovered messages. Simulation result performed via SMPL shows that this adaptation scheme can reduce the message discard due to transmission error by 5.5%, compared with the existing error controls method for real-time communication on WLAN.

A Shape memory alloy (SMA) actuators have great potential in advanced technology applications where space, weight and cost are crucial design factors. They are known for the shape memory effect which is the ability to recover an initial configuration by simple heating after deformation. SMAs also exhibit a behavior called "pseudoelasticity" also known as "superelasticity" which is the shape recovery associated with mechanical loading and unloading at temperatures above specific values. The key characteristic of SMAs is the martensitic phase transformation, brought about by temperature change and/or by application of stress. Martensitic transformation is usually accompanied by significant changes in mechanical, electrical and thermal properties that render them as prime candidates for the development of smart structures and devices. This work is a contribution to the study of the influence of parameters such as operating temperature and the mode of heat transfer (natural or forced convection) on the pseudoelastic response of SMA used as actuators. Based on the mathematical formalism of the Müller, Achenbach and Seelecke model known as the "MAS model", we develop through a new mathematical formalism a new iterative resolution methodology of the coupled equations. The new approach provides very significant results and allows a significant gain in computation time.

We consider the flow and transport of chemically reactive substances (precursors) in a channel over substrates having complex geometry. In particular, these substrates are in the form of trenches forming oscillating boundaries. The precursors react at the boundaries and get deposited. The deposited layers lead to changes in the geometry and are explicitly taken into account. Consequently, the system forms a free boundary problem. Using formal asymptotic techniques, we obtain the upscaled equations for the system where these equations are defined on a domain with flat boundaries. This provides a huge gain in computational time. Numerical experiments show the effectiveness of the upscaling process.

Finite mixtures of multivariate skew t (MST) distributions have proven to be useful in modelling heterogeneous data with asymmetric and heavy tail behaviour. Recently, they have been exploited as an effective tool for modelling flow cytometric data. A number of algorithms for the computation of the maximum likelihood (ML) estimates for the model parameters of mixtures of MST distributions have been put forward in recent years. These implementations use various characterizations of the MST distribution, which are similar but not identical. While exact implementation of the expectation-maximization (EM) algorithm can be achieved for `restricted' characterizations of the component skew t-distributions, Monte Carlo (MC) methods have been used to fit the `unrestricted' models. In this paper, we review several recent fitting algorithms for finite mixtures of multivariate skew t-distributions, at the same time clarifying some of the connections between the various existing proposals. In particular, recent results have shown that the EM algorithm can be implemented exactly for faster computation of ML estimates for mixtures with unrestricted MST components. The gain in computational time is effected by noting that the semi-infinite integrals on the E-step of the EM algorithm can be put in the form of moments of the truncated multivariate non-central t-distribution, similar to the restricted case, which subsequently can be expressed in terms of the non-truncated form of the central t-distribution function for which fast algorithms are available. We present comparisons to illustrate the relative performance of the restricted and unrestricted models, and demonstrate the usefulness of the recently proposed methodology for the unrestricted MST mixture, by some applications to three real datasets.