A GRASP×ELS for the vehicle routing problem with basic three-dimensional loading constraints

This paper addresses an extension of the capacitated vehicle routing problem where the client demand consists of three-dimensional weighted items (3L-CVRP). The objective is to design a set of trips for a homogeneous fleet of vehicles based at a depot node which minimizes the total transportation cost. Items in each vehicle trip must satisfy the three-dimensional orthogonal packing constraints. This problem is strongly connected to real-life transportation systems where the packing of items to be delivered by each vehicle can have a significant impact on the routes. We propose a new way to solve the packing sub-problem. It consists of a two-step procedure in which the z-constraints are first relaxed to get a (x,y) positioning of the items. Then, a compatible z-coordinate is computed to get a packing solution. Items can be rotated but additional constraints such as item fragility, support and LIFO are not considered. This method is included in a GRASP×ELS hybrid algorithm dedicated to the computation of VRP routes. The route optimization alternates between two search spaces: the space of VRP routes and the space of giant trips. The projection from one to the other is done by dedicated procedures (namely the Split and the concatenation algorithms). Moreover, a Local Search is defined on each search space. Furthermore, hash tables are used to store the result of the packing checks and thus save a substantial amount of CPU time. The effectiveness of our approach is illustrated by computational experiments on 3L-CVRP instances from the literature. A new set of realistic instances based on the 96 French districts are also proposed. They range from 19 nodes for the small instances to 255 nodes for the large instances and they can be stated as realistic since they are based on true travel distances in kilometers between French cities. The impact of the hash tables is illustrated as well.     

Polymer chain dynamics in solution probed with a fluorescence blob model

This Account describes a new fluorescence tool that characterizes the chain dynamics of polymers in solution. This new tool, coined the fluorescence blob model (FBM), is employed to analyze the fluorescence decays of polymers randomly labeled with pyrene. The FBM yields the number of monomers making up a blob (Nblob) where a blob is the volume probed by an excited pyrene. By establishing a relationship between Nblob and the lifetime of pyrene used as an internal clock, the FBM provides previously unavailable information about polymer chain dynamics and opens new venues of research, which are described in this Account.     

Models and hybrid methods for the onshore wells maintenance problem

Workover rigs are used in onshore basins but they are often in limited number and they may not attend all the maintenance requests. We consider here the problem of scheduling the rigs over a time horizon in order to minimize the total oil loss due to the idle production states. Three mixed integer linear models are proposed. The first one improves an existing scheduling-based formulation. The second one uses an open vehicle routing approach and the third one is an extended model for which a column generation strategy is developed. Several improvements are presented as well as two heuristics coupled with column generation. To our knowledge, the first optimal values for medium-size instances of the problem are presented in this paper. The results show the potential of the column generation and its interest in a practical context.     

Decision-Feedback Equalization for Pulse-Position Modulation

In this paper, we propose a minimum mean squared error (MMSE) decision feedback equalizer (DFE) for pulse position modulated (PPM) signals in the presence of intersymbol interference (ISI). While traditional uses of PPM may not have had ISI, PPM is increasingly being considered for use in situations where ISI is an issue, such as high-performance optical communication systems and ultrawideband communications. First, we review previous work on the subject which used the zero-forcing criterion under strict assumptions about the channel and equalizer lengths. Then, we derive a computationally efficient MMSE equalizer which removes these restrictions, and is suitable for use with training-based stochastic gradient-descent algorithms. Finally, we demonstrate the performance of the proposed equalizer with simulations.     

On Blind Equalization of Biorthogonal Signaling

Motivated by increasing interest in energy efficient modulations, we provide the first look at adaptive equalization of biorthogonal signaling. While this modulation has historically been considered only for use in narrowband systems without intersymbol interference (ISI), recent attention has been given to its use in ISI channels. Due to the fact that biorthogonal modulation (BOM) results in a source that is not i.i.d., however, classical blind adaptive equalization techniques cannot be directly applied to equalization of BOM signals. We first examine minimum mean-squared error (MMSE) and least mean squares (LMS)-based equalizers, and identify some peculiarities that arise in equalization of BOM signals when compared to more traditional modulations like binary phase shift keying (BPSK). Next, we present two novel blind algorithms for the adaptive equalization of BOM signals: LTBOMB and TROMBONE. We discuss the convergence properties of these algorithms, and demonstrate their performance with numerical simulations     

A fast exact least mean square adaptive algorithm

A general block formulation of the least-mean-square (LMS) algorithm for adaptive filtering is presented. This formulation has an exact equivalence with the original LMS algorithm; hence it retains its convergence properties, while allowing a reduction in arithmetic complexity, even for very small block lengths. Working with small block lengths is interesting from an implementation point of view (large blocks result in large memory and large system delay) and allows a significant reduction in the number of operations. Tradeoffs between a number of operations and a convergence rate are obtainable by applying certain approximations to a matrix involved in the algorithm. Hence, the usual block LMS appears as a special case, which explains its convergence behavior according to the type of input signal (correlated or uncorrelated)     

Adaptive solution for blind identification/equalization usingdeterministic maximum likelihood

A deterministic maximum likelihood (DML) approach is presented for the blind channel estimation problem. It is first proposed in a block version, which consists of iterating two steps, each one solving a least-squares problem either in the channel or in the symbols. In the noiseless case and under certain conditions, this algorithm gives the exact channel and the exact symbol vector with a finite number of samples. It is shown that even if the DML method has a single global minimum, the proposed iterative procedure can converge to spurious local minima. This problem can be detected (under some channel diversity conditions) by using a numerical test that is proposed in the paper. Based on these considerations, we extend the maximum likelihood block algorithm (MLBA) to recursive implementations [maximum likelihood recursive algorithm (MLRA)]. The MLRA is able to track variations of the system by the introduction of an exponential forgetting factor in the DML criterion. The link between the adaptive algorithm and a soft decision feedback equalizer (SDFE) is emphasized. Low-complexity versions of the recursive and adaptive algorithm are presented     

Band-edge phenomena and spontaneous polarisation above and below Tc FOR BaTiO3 and KNbO3

The band-edge phenomena and the polarisation induced effects are analysed through the Bloch orbital interactions above and below T_c.     

An asymmetric watermarking method

This paper presents an asymmetric watermarking method as an alternative to classical direct sequence spread spectrum and watermarking Costa (1983) schemes techniques. This new method provides a higher security level against malicious attacks threatening watermarking techniques used for a copy protection purpose. This application, which is quite different from the classical copyright enforcement issue, is extremely challenging as no public algorithm is yet known to be secure enough, and some proposed proprietary techniques have been already hacked. Our method is thus an attempt toward the proof that the Kerckhoff's (1883) principle can be stated in the copy protection framework.