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.     

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.     

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.     

Microscopic images of intraspheroidal pH by 1H magnetic resonance chemical shift imaging of pH sensitive indicators

Objective We investigate microscopic pH heterogeneity within tumor spheroids using a novel ¹H NMR methodology that provides high resolution measurements of intraspheroidal pH. Material and Methods: High resolution microscopic images of intraspheroidal pH were obtained by ¹H NMR using chemical shift selective excitation of the H2 resonance of imidazole added to the incubation medium. Imidazole accumulated in the intraspheroidal space in a pH dependent manner. Maps of intraspheroidal pH could be obtained by transforming pixel by pixel (32 × 32$) the regional variation of imidazole H2 intensity into a relative pH scale. Results: Our analysis revealed drastic intraspheroidal pH alterations depending on the size of the spheroid, ca. 0.6 pH units more acidic in the necrotic core than in the periphery, for spheroids of 600 μm diameter. The presence of concentric regions having similar intraspheroidal pH was consistently observed. The thickness of these regions decreased from pH 7.2 to pH 6.8 and increased below the latter pH value. Conclusion: Our observations are compatible with the general model of spheroid growth where the more external layers of cells are in active growth and depict more alkaline pH values while the inner layers remain quiescent or evolve to a necrotic core, depicting more acidic pH values.     

Sinus aspergillosis after an endodontic treatment. Presentation of a clinical case

Aspergillosis is an opportunistic deep mycosis that occurs in immunocompromised patients, often in the paranasal sinuses. However, it sometimes occurs in healthy subjects, producing symptoms similar to those of a chronic sinusitis that is unresponsive to conventional treatment. A possible entry point for Aspergillus is the oroantral communication originated by perforation of the dental root cavity during root canal of a molar with penetration of material. We report the clinical case of a patient with symptoms of chronic sinusitis who was diagnosed as sinus aspergillosis after radiological and histological study. The origin may have been a third upper molar in which a root canal was performed.     

Gold Stabilized with Iridium on Ceria–Niobia Catalyst: Activity and Stability for CO Oxidation

Topics in Catalysis - Monometallic gold and iridium, and bimetallic gold–iridium on ceria–niobia (Nb2O5–CeO2) catalysts were synthesized by deposition–precipitation with...