Operational flexibility quantification in a make-to-order assembly system

Manufacturing flexibility is becoming a fundamental production objective, along with cost, quality, and delivery time. Current production systems face quick changes in market conditions and they need to adapt in this environment. The supply chain and industrial globalization give an important role for assembly systems. Placed at the end of the value chain, assembly systems must face those quick changes successfully to reach the expected performance. The key performance indicators are normally based on cost, quality, and delivery time objectives. Reducing costs and improving quality are almost universal goals. Delivery time is typically determined by customer demand in the supply chain, planning from make-to-stock to make-to-order, and aspiring to reach a just-in-time manufacturing system. In this context, flexibility could be the differential advantage to tackle uncertainty. Closely related to the rest of production objectives and the overall performance of the system, flexibility must be integrated in the system for successful decision-making in operations. This work presents this approach of flexibility. A brief review of flexibility concepts and measurements in the literature precedes an introduction to flexibility, defined based on the function of utility. This function represents the expectations of system performance. This approach allows the formulation of the taxonomy of operational flexibility in agreement with the classical types identified in former works. Next, an integer model is programmed to simulate the basic behavior of task planning in a make-to-order assembly system. This first application illustrates flexibility quantification based on utility evolution. The use of common industrial parameters to quantify operational flexibility will finally facilitate an integrated interpretation of system performance trends.     

Long-range effect of cyanide on mercury methylation in a gold mining area in southern Ecuador

Small-scale gold mining in Portovelo-Zaruma, Southern Equador, performed by mercury amalgamation and cyanidation, yields 9-10 t of gold/annum, resulting in annual releases of around 0.65 t of inorganic mercury and 6000 t of sodium cyanide in the local river system. The release of sediments, cyanide, mercury, and other metals present in the ore such as lead, manganese and arsenic significantly reduces biodiversity downstream the processing plants and enriches metals in bottom sediments and biota. However, methylmercury concentrations in sediments downstream the mining area were recently found to be one order of magnitude lower than upstream or in small tributaries. In this study we investigated cyanide, bacterial activity in water and sediment and mercury methylation potentials in sediments along the Puyango river watershed, measured respectively by in-situ spectrophotometry and incubation with ³H-leucine and ²⁰³Hg²⁺.Free cyanide was undetectable (< 1 μg·L^− 1) upstream mining activities, reached 280 μg·L^− 1 a few km downstream the processing plants area and was still detectable about 100 km downstream. At stations with detectable free cyanide in unfiltered water, 50% of it was dissolved and 50% associated to suspended particles. Bacterial activity and mercury methylation in sediment showed a similar spatial pattern, inverse to the one found for free cyanide in water, i.e. with significant values in pristine upstream sampling points (respectively 6.4 to 22 μgC·mg wet weight^− 1·h^− 1 and 1.2 to 19% of total ²⁰³Hg·g dry weight^− 1·day^− 1) and undetectable downstream the processing plants, returning to upstream values only in the most distant downstream stations. The data suggest that free cyanide oxidation was slower than would be expected from the high water turbulence, resulting in a long-range inhibition of bacterial activity and hence mercury methylation. The important mercury fluxes resultant from mining activities raise concerns about its biomethylation in coastal areas where many mangrove areas have been converted to shrimp farming.     

Robust h-index

Scientometrics - The h-index is the most used measurement of impact for researchers. Sites such as Web of Science, Google Scholar, Microsoft Academic, and Scopus leverage it to show and compare the...     

Cortical variations of the dimension of correlation in children with attention deficit hyperactivity syndrome

INTRODUCTION AND OBJECTIVE: The syndrome of deficient attention and hyperactivity affects approximately 5% of children of school age. Clinically it is characterized by deficient attention, impulsiveness and excessive motor activity. Developments in nonlinear dynamic theory have made it possible to think of modelling cerebral activity as a dynamic system of chaotic type. One the most widely standardized measurements is the dimension of correlation (D2). In this paper we study the electroencephalographic traces of a control group of 9 healthy children and another group of 19 children with the syndrome of deficient attention, at rest and whilst carrying out a visuomotor task (Test of perception of differences). MATERIAL AND METHODS: The dimension of correlation was estimated for both groups. Statistical comparison was made between the cortical distributions of the D2 between both types of recordings and between both groups. RESULTS: The children with lack of attention showed a larger number of activated cortical areas than those of the control group when carrying out the same task. However, during the resting state there were no differences in the D2 between the control children and the children with deficient attention. The indicates that both groups have the same basal level of activation. CONCLUSION: The dimension of correlation is a method which permits the demonstration of an increase in neuronal activity in the stimulated areas, in this case in the occipital region.     

Septicemia associated with central venous catheterization in a children's hospital. A multivariate study

BACKGROUND: The blood stream infections (BSI) are the principal nosocomial infection in the child hospitals. In this study we estimate the incidence of BSI associated with central venous catheterization, and estimate different risk and protective factors, through a multivariate study. MATERIAL AND METHODS: The study have followed in a prospective way during 6 months all the children with central venous catheterization (489 catheters), from the moment of insertion until withdrawal, collecting various data previous to the development of the infection: place of insert, type of catheter, duration, clinic information, microbiology, and the treatments administered through the catheter. In was accomplished an multivariate analysis with logistic regression, for two principal effect variables, the catheter colonization and the catheter related BSI. RESULTS: The incidence of catheter related BSI was 5.5% and for local infection 11.2%. The density of incidence was 3.15 and 6.42 for each 1,000 catheters-day, respectively. The logistic regression model included: colonization of the skin in the insertion point > 15 colonies, days with antibiotics through catheter, use of lipidic parenteral solutions and fever, previous to the infection. The area under the ROC curve was 0.72. CONCLUSIONS: In children with septicemias associated with central catheterization the predictors or sentry criterion for the decision on when to withdraw a catheter are colonization (> 15 colonies) of the insert point, together with the use of lipidic parenteral solutions or extended antibiotic treatment.     

Maximum entropy pdfs and the moment problem under near-Gaussian conditions

This paper focuses on a class of continuous probability density functions (pdfs) that are generated by the maximum entropy method (mem), which are of potential interest in fluid dynamics. It discusses their properties and presents a method for obtaining approximate solutions to the moment problem that is associated with this class of pdfs. The method allows one to express pdf parameters in terms of constrained moments, alone. The results thus obtained hold for pdfs that represent small perturbations from a known pdf within this class. On combining these results with exact moment equations, one obtains successful approximations to the closure relations that are associated with these pdfs. The Gaussian pdf belongs in this class, and the method can be used to explore the near-Gaussian region.     

Effects of phoneme repertoire on phoneme decision

In three experiments, listeners detected vowel or consonant targets in lists of CV syllables constructed from five vowels and five consonants. Responses were faster in a predictable context (e.g., listening for a vowel target in a list of syllables all beginning with the same consonant) than in an unpredictable context (e.g., listening for a vowel target in a list of syllables beginning with different consonants). In Experiment 1, the listeners' native language was Dutch, in which vowel and consonant repertoires are similar in size. The difference between predictable and unpredictable contexts was comparable for vowel and consonant targets. In Experiments 2 and 3, the listeners' native language was Spanish, which has four times as many consonants as vowels; here effects of an unpredictable consonant context on vowel detection were significantly greater than effects of an unpredictable vowel context on consonant detection. This finding suggests that listeners' processing of phonemes takes into account the constitution of their language's phonemic repertoire and the implications that this has for contextual variability.     

On the high affinity binding site for [3H]-1,3-dipropyl-8-cyclopentylxanthine in frog brain membranes

1. Radioligand binding properties of the adenosine receptor ligands, [3H]-1,3-dipropyl-8-cyclopentylxanthine ([3H]-DPCPX), and [3H]-R-phenylisopropyladenosine ([3H]-R-PIA) were investigated in frog brain membranes. 2. The specific binding of the adenosine antagonist, [3H]-DPCPX to frog brain membranes showed one binding site with Kd and Bmax values of 43.8 nM and 0.238 +/- 0.016 pmol mg-1 protein, respectively. Guanosine 5'-triphosphate (GTP, 100 microM) decreased to 72 +/- 7% and Mg2+ (8 mM) increased to 121 +/- 3% [3H]-DPCPX (40 nM) binding to frog brain membranes. 3. [3H]-DPCPX saturation binding experiments performed in the presence of Mg2+ (8 mM), or in the presence of GTP showed that Mg2+ ions decreased the Kd value of [3H]-DPCPX to 14 nM, and GTP increased this value to 65.6 nM. Bmax values were not significantly (P > 0.05) modified (0.261 +/- 0.018 pmol mg-1 protein, with Mg2+, and 0.266 +/- 0.026 pmol mg-1 protein, in presence of GTP) by the presence of Mg2+ or GTP. 4. The specific binding of [3H]-R-PIA (15 nM) was decreased to 37 +/- 6% by GTP (100 microM) and increased to 123 +/- 4% by Mg2+ (8 mM). [3H]-R-PIA saturation binding experiments performed in the presence of Mg2+ (8 mM) showed one binding site with Kd and Bmax values of 0.9 nM and 0.229 +/- 0.008 pmol mg-1 of protein, respectively. 5. The concentration-inhibition curves of adenosine agonists and antagonists versus [3H]-DPCPX binding showed the following order of potencies: CPA> R-PIA~ NECA> S-PIA> > CGS 21680, for the agonists, and XAC ~-DPCPX> > XCC> PACPX, for the antagonists.6. The present results suggest that the adenosine binding site in the frog brain membranes is G-protein coupled, but that the antagonist affinities and the pharmacological profile is different from the Al or A2 adenosine receptors.