Stochastic control in manpower planning

Our concern is with control problems which arise in connection wi th a discrete time Markov chain model for a graded manpower system. In this model, the members of an organisation are classified into distinct classes. As time passes, they move from one class to another, or to the outside world, in a random way governed by fixed transition probabilities. The emphasis is, then, placed on examining means of reaching and then retaining the structure best adapted to the aims of the organisation, with the assumption that only the recruitment flows are subject to control. Attainability and maintainability have received a great deal of attention in recent years. However, much of the work has been concerned with deterministic analysis, in the sense that average values are used in place of random variables. We adopt, instead, a stochastic approach to the study of these forms of control. We present some of the problems encountered when evaluating probabilities related to the distribution of stock numbers at different steps and we give a detailed numerical comparison of different recruitment strategies. An iterative method is developed to compute exact values of the probabilities of attaining and maintaining a structure in one step. It is designed for the special but very important case of systems in which promotion is only possible to the next highest grade. Its efficiency makes possible the use of exact results in the comparison of the recruitment strategies, which was formerly accomplished by means of simulation techniques only. As to the comparison itself, it emerges that the strategy which, at each step, steers the system as far as possible towards the goal is superior to all deterministic strategies. Also, this strategy is shown to come close to providing the highest level of control that is possible

Effects of timing of adjunctive systemic antibiotics on the clinical outcome of periodontal therapy : a systematic review

Many systematic reviews and meta-analysis have indicated beneficial effects of adjunctive systemic antibiotics in periodontal therapy in specific situations. However, some essential issues such as the ideal time of their administration during periodontal therapy remain unanswered. This systematic review aimed to determine at which phase of periodontal treatment would adjunctive systemic antibiotics lead to the best clinical outcomes, during the active phase or in the reevaluation phase. Searches in the databases Medline, Scopus and Cochrane Library were conducted. The randomized clinical trials and retrospective cohort studies comparing the clinical benefits of adjunctive systemic antibiotic administration in the active phase of periodontal treatment versus their administration in the reevaluation phase were included. The primary outcomes assessed were differences in clinical changes in periodontal pocket depth and clinical attachment loss at all post-treatment phases. Of the 6209 records identified, two randomized clinical trials and two retrospective cohort studies were eligible according to inclusion criteria. Two studies suggested there were greater clinical benefits when systemic antibiotics were prescribed during the active phase of periodontal therapy than in the reevaluation phase while two other studies showed no significant difference in clinical outcomes at 6 months between these two different timing of administration. The evidence available and evaluated in this systematic review is of heterogeneous quality and limited by the restricted number of studies and their dissimilarities in their study design and outcome reporting. Despite insufficient evidence to determine the ideal time to the adjunctive systemic antibiotic administration in the periodontal therapy, it seems that prescription of systemic antibiotic at the active phase of periodontal therapy leads to better clinical outcomes

Multi-thin layers as electrodes for organic solar cell:Elaboration and numerical modeling.

In this work, the conventional and inverse organic solar cells (OSC and IOSC) were studied and improved using the GPVDM software. The initial studied two cells (OSC and IOSC) consist a of photoactive layer (PAL), an electron transporting layer (ETL) and a hole transporting layer (HTL). The PAL was a blend of the poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61-butyric acid methylester (PCBM) organic semiconductor (P3HT:PCBM). The initial ETL was Tittanium Oxide (TiOx) while the ETL was a poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) with a thickness of 50 nm in OSC and IOSC. The effect of the active layer thickness was systematically investigated, then the ETL and HTL thicknesses effect were studied. Also, a group of candidate materials were proposed as ETL and HTL. It was found that the best ETL and HTL were TiOx and Cu2O respectively for the conventional cell while they were PEDOT:PSS and ZnO for the inverse cell. The optimised efficiency for normal and reverse cells were 4.77% and 5.35% for both Al/ TiOx (50 nm)/ P3HT:PCBM (150 nm)/ Cu2O (10 nm)/ITO and Ag/ PEDOT:PSS (20 nm)/ P3HT:PCBM (200 nm)/ ZnO (30nm)/ ITO for normal and reverse cells. Multilayer electrodes of the form TCO / Ag / TCO were also proposed and improved within GPVDM. It was found that AZO (40 nm) / Ag (6 nm) / AZO (40 nm) is the best alternative to ITO with efficiencies improved to 4.96% and 5.29% for the normal and inverse cells respectively. The same study was carried out using the SILVACO ATLAS software. The results showed that the best efficiency for the normal cell reached 4.73% for the structure Al / ZnO (10 nm) /P3HT:PCBM (100 nm) / PEDOT:PSS (10 nm) / ITO OSC, while it reached 4.77% for an Ag/ NiO (10 nm)/ P3HT:PCBM (300 nm)/ TiO2 (60nm)/ITO IOSC. The TCO/Ag/TCO multilayer electrode was also studied and improved using a developed MATLAB program, where it was found that the transmittances of all studied electrodes exceeded 97%, which is better than what is obtained for ITO. When the developed electrodes applied in the two improved organic solar cells, it was found that the results were improved, and the best performances reached 4.78% and 4.91% for OSC and IOSC, respectively. The optimized multilayer electrode was MoO3(50nm)/Ag(7nm)/MoO3(50nm). As expected, the results are close, but not completely identical, and this difference is due to the nature of the program, the applied physical equations, and the parameters used

Contribution à l'étude de la relation entre les différentes formes du phosphore dans les sédiments d'une retenue de barrage eutrophe en climat méditerranéen (El Kansera, Maroc)

Le présent travail porte sur l'évaluation des différentes formes de phosphore, dans les sédiments d'un réservoir eutrophe en climat méditerranéen (El Kansera, Maroc) et la détermination des relations entre ces formes. L'application d'un schéma de fractionnement chimique du phosphore a permis de déterminer les proportions de quatre formes différentes : le phosphore lié au fer Fe(OOH)-P, le phosphore lié au calcium CaCO3-P, le phosphore organique soluble dans l'acide POSA et le phosphore organique résiduel POR. La forme biodisponible a été déterminée par ailleurs, par des bioessais en utilisant une Chlorophycée (Scenedesmus crassus) isolée à partir des eaux de la retenue du barrage étudié.Une étude par analyse factorielle des correspondances a mis en évidence l'influence de la nature des sédiments étudiés et de leurs propriétés physico-chimiques sur la répartition des formes du phosphore dans les sédiments. En période de basses eaux, les sédiments sont caractérisés par la prédominance des formes inorganiques ; alors qu'en période de hautes eaux, la forme POSA est la plus abondante. La confrontation des résultats obtenus par la méthode des bioessais avec ceux relatifs aux extractions chimiques séquentielles de phosphore a montré par ailleurs, que la forme biodisponible du phosphore est fortement corrélée aux formes inorganiques {Fe(OOH)-P et CaCO3-P} et indépendante vis à vis des formes organiques {POSA et POR}.We have studied in this work the different forms of phosphorus in the sediments of a eutrophic reservoir in a Mediterranean climate (El Kansera – Morocco). The studied sediments have been collected at eight sampling stations located at different points in the middle of the lake during two sampling sessions in contrasting weather conditions: the first sampling occurred in November 1992, a period of autumn mixing and low water levels, whereas the second took place in January 1994 during a high water level period, just after the first winter floods of the Beht river whose waters are retained in the studied reservoir.The evaluation of the different forms of phosphorus was carried out using both a chemical extraction method and a bioassay method. The application of the chosen chemical extraction scheme allowed the determination of the proportions of four different phosphorus forms: iron-bound {Fe(OOH)-P}, calcium-bound {CaCO3-P}, acid-soluble organic {POSA} and residual organic {POR}. The bioavailable form {Pbio}, representing less than 32 % of the total sediment phosphorus content, has been evaluated using a Scenedesmus crassus algal strain isolated from El Kansera reservoir waters.According to the results of our analyses, the concentrations of iron-bound phosphorus are higher overall than those of calcium-bound phosphorus. The sediments collected during the low water period contain spatially stable values of POSA (0.03 – 0.09 mg.g-1). These values are lower than those determined in the sediments collected during the high water period (0.24 – 0.42 mg.g-1). This form represents less than 11% of the total phosphorus in the low water period whereas it represents more than 25% and up to 56% of the total phosphorus in the filling period. This result can be explained by the freshness of the organic matter supplied by the continuous water flow in the high water period and the degradation of this organic matter during the low water period. Moreover, the anaerobic conditions of the hypolimnetic layers and the low external supply during the low water period favour organic phosphorus mineralisation.A Factorial Correspondence analysis study has shown the influence of the nature and the physico-chemical properties of the studied sediments on the distribution of the different phosphorus forms. In the low level period, the predominance of the inorganic forms is obvious while POSA is the most abundant form in the period of rising water levels. This differentiation can be explained by the different transport dynamics of suspended organic or inorganic particles according to the water level and also to the external or internal supply of the organic matter.We have also determined the statistical relations among the estimated different forms of phosphorus in El Kansera reservoir sediments. This statistical analysis was carried out to establish the correlation between the bioavailable phosphorus determined by the bioassay method and the phosphorus forms determined by chemical speciation. The goal of the study was to determine, according to statistically significant correlations, the chemical forms of the bioavailable phosphorus contained in the studied sediments.The comparison between the results we have obtained by the bioassay method and those obtained by sequential chemical extraction has shown that the bioavailable form of phosphorus is strongly correlated with the inorganic forms {Fe(OOH)-P} and {CaCO3-P}. The high correlation found between the iron-bound form of phosphorus and the bioavailable one is in good agreement with previous work described in the literature that has shown that an important part of the iron-bound and aluminium- bound phosphorus is bioavailable, whatever the extraction method may be.It has also been demonstrated that the forms {Pbio}, {Fe(OOH)-P}, {CaCO3-P} and {Pinorg}are notably independent from the {POSA} and {Porg} forms, the correlation coefficients being relatively low. The residual organic form of phosphorus {POR} does not seem to be linked to any variable. Therefore, we can say that this form is not bioavailable for the Scenedesmus crassus species

Development of mathematical models for predicting the iron concentrations of Lake Oubeira waters (ne Algerian)

Facing the increase of surface water samples contaminated by ETMs, usually from the geochemical background, the emergence of new human diseases is worrying. To solve this problem, we have developed several models based on different learning algorithms qualified by high performance, using different transfer functions. We have shown that all the Neural Models presented more or less important performance  compared to the one based on multiple linear regressions. The best revealed model ANN in the current work is a MLP type that uses the Levenberg-Marquardt algorithm as a learning algorithm, with Tansig and Purelin as transfer functions, respectively in the hidden layer and the output layer. This successful model can be considered as an important tool of great effectiveness in the context of environmental prediction and especially in anticipation of the iron contents of the Oubeira Lake water.Keywords: Prediction, heavy metals, Linear multiple regression, artificial neural  networks, Oubéira Lake