Optimal joint selective imperfect maintenance and multiple repairpersons assignment strategy for complex multicomponent systems

This paper addresses the joint selective maintenance and repairperson assignment problem (JSM–RAP) for complex multicomponent systems. The systems perform consecutive missions separated by scheduled finite duration breaks and are imperfectly maintained during the breaks. Current selective maintenance (SM) models usually assume that only one repair channel is available or that the repairperson assignment optimisation can be done at a subsequent stage. Using a generalised reliability function for k-out-of-n systems, we formulate the JSM–RAP for multicomponent systems more complex than the series-parallel systems commonly used in previous SM models. Two nonlinear formulations and their corresponding binary integer programming models are then proposed and optimally solved. Numerical experiments show the added value of the proposed approach and highlight the benefit of jointly carrying out the selection of the components to be maintained, the maintenance level to be performed and the assignment of the maintenance tasks to repairpersons. It is also shown that the flexibility provided by mixed skill cohorts of repairpersons over uniform cohorts can yield higher performance levels when the skillsets are significantly different.     

Dendritic anion hosts: perchlorate uptake by G5-NH2 poly(propyleneimine) dendrimer in water and model electrolyte solutions

Perchlorate (ClO4-) has emerged as a major groundwater and surface water contaminant in the United States. Ion exchange (IX) is the most widely used technology for treating water containing lower concentrations of perchlorate (<100 ppb). However, a major drawback of IX is the need for frequent regeneration or disposal of the perchlorate-laden resins. As a first step toward the development of high-capacity, selective and recyclable dendritic ligandsforthe recovery of perchloratefrom aqueous solutions by dendrimer filtration, we tested the hypothesis that dendrimers with hydrophobic cavities and positively charged internal groups should selectively bind ClO4- over more hydrophilic anions such as Cl-, NO3-, SO4(2-), and HCO3-. We measured the uptake of ClO4- by the fifth generation (G5-NH2) poly(propyleneimine) (PPI) dendrimer with a diaminobutane core and terminal NH2 groups in deonized water and model electrolyte solutions as a function of (i) anion-dendrimer loading, (ii) solution pH, (iii) background electrolyte concentration, and (iv) reaction time. The ClO4- binding capacity of this dendrimer is comparable to those of perchlorate-selective IX resins. However, its ClO4- binding kinetics is faster and reaches equilibrium in approximately 1 h. Note also that only a high pH (approximately 9.0) aqueous solution is needed to release more than 90% of the bound ClO4- anions by deprotonation of the dendrimer tertiary amine groups. The overall results of this study suggest that dendritic macromolecules such as the G5-PPI NH2 dendrimer provide ideal building blocks for the development of high-capacity, selective and recyclable ligands for the recovery of anions such as perchlorate from aqueous solutions by dendrimer enhanced filtration.     

The Quest for Bose-Einstein Condensation in Solid 4He

Ever since the seminal torsional oscillator (TO) measurements of Kim and Chan which suggested the existence of a phase transition in solid ⁴He, from normal to a ??supersolid?? state below a critical temperature T _c = 200 mK, there has been an unprecedented amount of excitement and research activity aimed at better understanding this phase. Despite much work, this remarkable phase has yet to be independently confirmed by conventional scattering techniques, such as neutron scattering. We have carried out a series of neutron scattering measurements, which we here review, aimed at observing Bose-Einstein condensation (BEC) in solid ⁴He at temperatures below T _c . In bulk liquid ⁴He, the appearance of BEC below T _?? signals the onset of superfluidity. The observation of a condensate fraction in the solid would provide an unambiguous confirmation for ??supersolidity??. Although, our measurements have not yet revealed a non-zero condensate fraction or algebraic off diagonal long-range order n ₀ in solid ⁴He down to 65 mK, i.e. n ₀=(0±0.3)%, our search for BEC and its corollaries continues with improved instrumentation.     

Spray Drying, Freeze Drying, or Freezing of Three Different Lactic Acid Bacteria Species

Lactococcus lactis ssp. cremoris D11, Lactobacillus casei ssp. pseudo-plantarum UL137, and Streptococcus thermophilus CH3TH, were separately frozen, freeze dried or spray dried, and tested for survival and lactic acid production before and after processing. Virtually all cells survived freezing. Of the survivors, 60 to 70% survived the dehydration step of freeze drying. In contrast to freezing and freeze drying, spray drying caused considerable delay in lactic acid production and reduction in survival. After spray drying, survival was greatest for S. thermophilus and lowest for Lc. cremoris.     

Infection risk assessment of diarrhea-related pathogens in a tropical canal network

A quantitative microbial risk assessment (QMRA) of Cryptosporidium, Giardia and diarrhegenic Escherichia coli (DEC) infection was performed using Monte Carlo simulations to estimate the human health risks associated with the use of canal water for recreational purposes, unrestricted and restricted irrigation in a tropical peri-urban area. Three canals receiving municipal, agricultural, and, predominantly, industrial wastewater were investigated. Identification of pathogenic protozoans revealed the major presence of Cryptosporidium hominis and both assemblages A and B of Giardia lamblia. The highest individual infection risk estimate was found to be for Giardia in an exposure scenario involving the accidental ingestion of water when swimming during the rainy season, particularly in the most polluted section, downstream of a large wholesale market. The estimated annual risks of diarrheal disease due to infection by the protozoan parasites were up to 120-fold greater than the reported disease incidence in the vicinity of the studied district and the entire Thailand, suggesting a significant host resistance to disease beyond our model's assumptions. In contrast, annual disease risk estimates for DEC were in agreement with actual cases of diarrhea in the study area.     

Survival of Brevibacterium linens (ATCC 9174) after Spray Drying, Freeze Drying, or Freezing

The objectives of this work were to: (1) contrast spray drying, freeze drying and freezing for large-scale preservation of B. linens, (2) determine the thermal resistance curves, and (3) measure the storage stability. When B. linens was freeze-dried and frozen in feed suspensions containing 3% (w/v) cell paste and 25% (w/w) total solids, survival was 100%. During spray drying, lethal thermal injury was the main cause of loss of viability. Accordingly, by extrapolation, 100% viability would be possible at an outlet-air temperature of 57°C. Spray-dried and freeze-dried cells were stable during storage at 4°C in the absence of oxygen and moisture.     

Dendritic chelating agents. 2. U(VI) binding to poly(amidoamine) and poly(propyleneimine) dendrimers in aqueous solutions

Chelating agents are widely employed in many separation processes used to recover uranyl [U(VI)] from contaminated aqueous solutions. This article describes an experimental investigation of the binding of U(VI) to poly(amidoamine) [PAMAM] and poly(propyleneimine) [PPI] dendrimers in aqueous solutions. We combine fluorescence spectroscopy with bench scale ultrafiltration experiments to measure the extent of binding and fractional binding of U(VI) in aqueous solutions of these dendrimers as a function of (i) metal-ion dendrimer loading, (ii) dendrimer generation, (iii) dendrimer core and terminal group chemistry, and (iv) solution pH and competing ligands (NO3-, PO4(3-), CO3(2-), and Cl-). The overall results of this study suggest that uranyl binding to PAMAM and PPI dendrimers in aqueous solutions involves the coordination of the UO2(2+) ions with the dendrimer amine, amide, and carboxylic groups. We find significant binding of U(VI) to PAMAM dendrimers in (i) acidic solutions containing up to 1.0 M HNO3 and H3PO4 and (ii) in basic solutions containing up to 0.5 M Na2CO3. However, no binding of U(VI) by PAMAM dendrimers is observed in aqueous solutions containing 1.0 M NaCl at pH 3.0. These results strongly suggest that PAMAM and PPI dendrimers can serve as high capacity and selective chelating ligands for U(VI) in aqueous solutions.     

RadA,a Key Gene of the Circadian Rhythm of Escherichia coli

Circadian rhythms are present in almost all living organisms, and their activity relies on molecular clocks. In prokaryotes, a functional molecular clock has been defined only in cyanobacteria. Here, we investigated the presence of circadian rhythms in non-cyanobacterial prokaryotes. The bioinformatic approach was used to identify a homologue of KaiC (circadian gene in cyanobacteria) in Escherichia coli. Then, strains of E. coli (wild type and mutants) were grown on blood agar, and sampling was made every 3 h for 24 h at constant conditions. Gene expression was determined by qRT-PCR, and the rhythmicity was analyzed using the Cosinor model. We identified RadA as a KaiC homologue in E. coli. Expression of radA showed a circadian rhythm persisting at least 3 days, with a peak in the morning. The circadian expression of other E. coli genes was also observed. Gene circadian oscillations were lost in radA mutants of E. coli. This study provides evidence of molecular clock gene expression in E. coli with a circadian rhythm. Such a finding paves the way for new perspectives in antibacterial treatment.     

Permeability measurement and flow simulation through fiber reinforcement

Continuous fiber reinforced polymer composites can be produced by the injection of a reactive fluid into a mold with preplaced reinforcement. Mold filling modeling softwares such as our RTMFLOT software are being developed to help design and production engineers meet their requirements for part production. The utilization of accurate permeability values is an absolute necessity for relevant mold filling simulation. This paper presents permeability results for several reinforcements. Experimental techniques being used to measure the permeability are also discussed. Several points are highlighted and suggestions are made to help the investigator in the search for reliable permeability data.