CIGI2011: A heuristic method for resource-constrained project scheduling with activity overlapping

The overlapping of activities is a common practice to accelerate the execution of engineering projects. This technique consists in executing in parallel two activities, normally executed in a sequential way, by allowing the downstream activity to start before the end of the upstream activity based on preliminary information. In this paper, we propose a constructive heuristic for the resource-constrained project scheduling problem with overlapping modes (RCPSP-OM). Given a set of activities to execute, the RCPSP-OM consists in determining the order of execution in time of a set of activities so as to minimize the total project duration, while respecting precedence relations, resource constraints and overlapping possibilities. The heuristic implies that rework tasks related to overlapping are added to downstream activities and that the consumption of the resources is constant throughout the execution of the project (including rework). The method also considers that the possible overlapping modes for every couple of activities and the duration of rework tasks associated with every mode are known in advance. Results show that, when the objective consists in minimizing the project duration, the consideration of the costs associated to activity overlapping allows to significantly reducing the cost of reworks. On the other hand, when the objective consists in maximizing the gains related to the project execution, the search for the best trade-off between acceleration and increase of project costs enables to avoid losses.     

A physical explanation of the gas flow diode effect

Gas flow properties in channels with slightly varying cross section have a dependency on the direction of channel perfusion when the gas is in the slip and transitional flow regimes. In the past, it was observed that the flow rate in converging direction is higher compared to the case where the channel diverges alongside. This gas flow diode effect does neither exist in the continuum regime nor in the free molecular regime, and it has its maximum at the same level of gaseous rarefaction as the well-known Knudsen minimum. However, no comprehensive study on the physics of this diode effect is carried out yet. In order to overcome this knowledge gap, the current paper proceeds our previous works by an appropriate experimental study. Here we can show that the diode effect crucially depends on the proportion of inclined walls to the overall channel inner surface. Also the inclination of the wall itself determines the strength of the diode effect meaning that the diodicity increases with the opening angle. Furthermore, we found indication that the diodicity also depends on the molar mass and the internal structure of the impinging gas molecules. Finally, we propose an explanation of the diode effect that is mainly based on the tangential reflection process of gas molecules colliding with the inclined walls of a tapered channel.     

Temporal variations of radon concentration in the saturated soil of Alpine grassland: The role of groundwater flow

Radon concentration has been monitored from 1995 to 1999 in the soil of the Sur-Frêtes ridge (French Alps), covered with snow from November to April. Measurements were performed at 70 cm depth, with a sampling time of 1 h, at two points: the summit of the ridge, at an altitude of 1792 m, and the bottom of the ridge, at an altitude of 1590 m. On the summit, radon concentration shows a moderate seasonal variation, with a high value from October to April (winter), and a low value from May to September (summer). At the bottom of the ridge, a large and opposite seasonal variation is observed, with a low value in winter and a high value in summer. Fluctuations of the radon concentration seem to be associated with temperature variations, an effect which is largely delusory. Indeed, these variations are actually due to water infiltration. A simplified mixing model is used to show that, at the summit of the ridge, two effects compete in the radon response: a slow infiltration response, rich in radon, with a typical time scale of days, and a fast infiltration of radon-poor rainwater. At the bottom of the ridge, similarly, two groundwater contributions compete: one slow infiltration response, similar to the response seen at the summit, and an additional slower response, with a typical time scale of about a month. This second slower response can be interpreted as the aquifer discharge in response to snow melt. This study shows that, while caution is necessary to properly interpret the various effects, the temporal variations of the radon concentration in soil can be understood reasonably well, and appear to be a sensitive tool to study the subtle interplay of near surface transfer processes of groundwater with different transit times.     

A comparison of biological activities of a new soya biopeptide studied in an in vitro skin equivalent model and human volunteers

During aging, the epidermis and dermis become thin and an efficient anti-aging product should be able to stimulate the metabolism of senescent fibroblast and keratinocytes, in order to increase the quantity of extra-cellular matrix components such as collagen and glycosaminoglycans. A study performed in parallel on an in vitro skin equivalent model, and in vivo, with human volunteers, demonstrated the efficacy of one specific soya biopeptide for anti-aging properties. Such a biopeptide induces a significant increase of glycosaminoglycans synthesis in vitro and in vivo after a one-month treatment. We also showed that this new cosmetic ingredient is able to stimulate favourably the collagen synthesis in vitro and in vivo. This study provided the proof for anti-aging properties of a new soya biopeptide and also validated the skin equivalent model developed for this experimentation as an alternative method to animal or human testing for some cosmetic efficacy evaluations.     

Properties of carboxymethylated cotton prepared in nonaqueous media

Mercerized cotton printcloth was converted to sodium cellulosates of various degrees of substitution by reaction with sodium methoxide in methanol. These sodium cellulosates were reacted with sodium monochloroacetate in dimethyl sulfoxide at room temperature. The sodium hydroxide pretreatment affected not only the yield of the sodium cellulosate but also the degree of conversion of cellulosate to carboxymethyl (CM) cellulose. The nonaqueously prepared CM cottons had fabric properties that differed from the properties of CM cottons prepared by conventional aqueous methods. By the nonaqueous method, CM cottons of increased capacity, or degree of substitution (D.S.), were obtained by a one-treatment procedure. These CM cottons in the sodium salt or acid form were insoluble in water and in 23% NaOH. Those of D.S. of about 0.3, when in the acid form, possessed improved wrinkle recovery angles. The salt form of CM cotton acts as a built-in catalyst for the reactions of cotton with methylolated ureas such as dimethylolurea (DMU) and dimethylolethyleneurea (DMEU). However, only DMU was effective in imparting improved conditioned and wet wrinkle recovery to CM cotton. Initial replacement of Na⁺ ions of CM cotton by H⁺ was easily accomplished. After replacement of approximately half of the Na⁺ ions, it was more difficult to replace the remaining half of Na⁺ from CM cottons that had been prepared in nonaqueous media. Affinity of carboxylate ions in CM cottons prepared nonaqueously for cations did not decrease with size of cation even though affinity for H⁺ ions was greatest.     

Interplay Between Normal Phase Nucleation and Energy Transport in Superconducting Superheated Sn Grains

We report a study of the response of Superconducting Superheated Sn Grains (SSG) dispersions to energy depositions from particle radiation. SSG dispersions, with volume filling factors up to 8.3% are cooled at 70mK and irradiated by a ¹⁰⁹Cd radioactive source. Irradiation produces magnetic field gaps in the superheating transition curves whose width is found to be independent of the magnetostatic inter-grain interactions. We elaborate, on this basis, a model whose main assumptions are: (i) the width of the gaps originates in the dispersion of the local transition fields of the individual grains and (ii) normal state nucleation occurs when the initial energy deposition is fully shared among quasiparticles and phonons which are homogeneously dispersed within the grain volume. This model is used to correlate the width of the magnetic field gaps to the deposited energies and is verified experimentally without any adjustable parameter. Normal state nucleations occurring before homogenization of the grain temperature are subsequently highlighted and interpreted as resulting from the competition between the energy transport through the grain volume and the penetration of the magnetic flux across the thickness of the superheating surface barrier.     

A survey of models and algorithms for emergency response logistics in electric distribution systems. Part I: Reliability planning with fault considerations

Emergency response operations in electric distribution systems involve a host of decision-making problems at the reliability and contingency planning levels. Those operations include fault diagnosis, fault location, fault isolation, restoration, and repair. As the first of a two-part survey, this paper reviews optimization models and solution methodologies for reliability planning problems with fault considerations related to electric distribution operations. Contingency planning problems of emergency distribution response are discussed in the second part. The present paper surveys research on determining a distribution substation single-fault capacity, reallocating excess load, configuring distribution systems, partitioning a geographical area into service territories, and locating material stores and depots.