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A Córdoba

Publications and source records attributed to A Córdoba.

At least 19 recordsLinked to original sources
PubMed2006

Stabilization from chaotic to periodical states in a model of cellular automaton for oxidation of CO.

The chaotic behavior of a chemical reaction can be controlled perturbing periodically some of the parameters externally governing the reaction. Based on the resonance phenomenon, the method of external forcing can convert chaotic behavior into a periodical one through the application of a sinusoidal modulation. In this paper we analyze the effect of a periodical perturbation on room temperature in a model of cellular automaton that studies catalytic oxidation of CO. This model considers the reaction of carbon monoxide and oxygen adsorbed on a surface allowing the variation of the surface temperature and analyzing the time oscillations in the reaction. The results of simulations of this model show quasiperiodical and chaotic behaviors. Then the strategy of control through periodical forcing is able to remove the chaotic dynamics by means of the stabilization of periodical solutions, there being enough of a perturbing harmonic function with only one frequency to transform a chaotic state of the system into a periodical state with periodicity 1.

Journal Article↗
PubMed2006

Periodical forcing for the control of chaos in a chemical reaction.

Control of the chaotic behavior of a chemical system can be achieved perturbing periodically some control parameters of the system. This procedure based on external forcing, which is based on the phenomenon of resonance, can change a chaotic behavior into a periodical one by means of the application of a sinusoidal perturbation. In this paper, the influence of a periodical modulation added to the parameter controlling the oxygen adsorption rate in a cellular automaton (CA) model studying CO oxidation is analyzed. This CA model considers the oxidation reaction of CO on a catalytic surface, taking into account the catalyst temperature variation in order to analyze the reaction time oscillatory behavior. Simulations of the CA model exhibit chaotic and quasiperiodical behaviors, and it can be shown that the periodical forcing strategy can suppress the chaotic dynamics by means of the stabilization of periodical solutions.

Journal Article↗
PubMed2000

Screening of the municipal water system of La Plata, Argentina, for human intestinal parasites.

The La Plata River, though severely contaminated by intestinal parasites through the discharge of tons of crude fecal material from a main sewage channel, nevertheless provides drinking water to two-thirds of La Plata, Argentina, after conventional purification at a processing plant. With intestinal parasitosis being endemic here, we investigated the importance of this water in transmitting such pathogens to the city's populace by means of standard methodology for sample acquisition and processing involving filter-concentration of waterborne particulates. Of 14 tap-water samples collected from the distribution network, 12 pertained to four zones (A-D) within the city center; while the remaining 2 were obtained near the processing plant, 15 kilometers outside the city. Although parasites were found within the samples derived from the four urban zones, none were detected in the specimens obtained near the plant. The four downtown areas differed from each other as to the quantity and nature of the parasites present in their water: whereas zones A and B registered similar lower levels of contaminants, C and D exhibited higher values significantly different from the former two and from each other. Given an average parasite count/l citywide of 0.38 and a probability of encountering a parasite within 11 of water of 0.32, the municipal network is seen to contribute to the transmission of intestinal parasites. A routine system of water-quality control is therefore needed throughout the city along with the establishment of infrastructures for locating and eliminating peripheral sources of contamination.

Animals↗
PubMed1998

Granular-cell tumor of the esophagus: report of a case with a cytologic diagnosis based on esophageal brushing.

We report a case of granular-cell tumor (GCT) in the esophagus. This is a rare location for this tumor and only 80 cases have been described. The tumor was diagnosed in a 24-yr-old woman with epigastralgia. Endoscopic examination revealed a submucosal ulcerated lesion. The smears derived from esophageal brushings contained clusters of granular cells. Histologic examination of the endoscopic biopsy provided diagnostic confirmation of GCT. To our knowledge, this is the first reported case of esophageal GCT in which the characteristic tumor cells were seen in the endoscopic brushing material. This case demonstrates that a cytologic diagnosis of GCT is possible if the lesion is ulcerated and/or brushing is subsequent to taking the biopsy. Although rare in the esophagus, GCT should be considered in the differential diagnosis of esophageal neoplasms.

Adult↗
PubMed1998

Plasma homocysteine is related to albumin excretion rate in patients with diabetes mellitus: a new link between diabetic nephropathy and cardiovascular disease?

The high risk of cardiovascular disease in patients with diabetes mellitus, particularly in those with nephropathy, is not completely explained by classical risk factors. A high plasma homocysteine concentration is an independent risk factor for cardiovascular disease but information on its association with diabetes is limited. Fasting homocysteine concentrations were measured in the plasma of 165 diabetic patients (75 with insulin-dependent [IDDM]; 90 with non-insulin-dependent diabetes [NIDDM]) and 56 non-diabetic control subjects. Other measurements included the prevalence of diabetic complications, glycaemic control, lipid and lipoprotein levels, vitamin status and renal function tests. Patients with NIDDM had higher homocysteine levels than control subjects, whereas IDDM patients did not (9.2 +/- 4.5 vs 7.7 +/- 2 micromol/l, p < 0.01; and 7.0 +/- 3 vs 7.4 +/- 2 micromol/l, NS). Univariate correlations and multiple regression analysis showed albumin excretion rate to be the parameter with the strongest independent association with homocysteine. Patients with both types of diabetes and nephropathy had higher plasma homocysteine concentrations than those without nephropathy. Increases of homocysteine in plasma were related to increases in the severity of the nephropathy. Fasting hyperhomocysteinaemia was considered as the mean of the plasma homocysteine for all control subjects (7.5 +/- 2.1 micromol/l) + 2 SD (cut-off = 11.7 micromol/l). Nephropathy was present in 80 % of diabetic patients with fasting hyperhomocysteinaemia. In conclusion, increases in fasting homocysteine in diabetic patients are associated with increased albumin excretion rate, especially in those with NIDDM, thus providing a potential new link between microalbuminuria, diabetic nephropathy and cardiovascular disease.

Adult↗
PubMed1998

Moderate hyperhomocysteinemia is a highly prevalent defect in Spanish patients with venous thromboembolic disease.

Recent studies suggest that mild hyperhomocysteinemia may be a risk factor for venous thromboembolic disease (VTED). In this work we evaluated the prevalence of moderate hyperhomocysteinemia in patients with VTED in our area. We found hyperhomocysteinemia in 23.4% of 64 patients studied compared with 7.35% of 68 healthy controls (p = 0.014). Our results suggest that moderate hyperhomocysteinemia is one of the most prevalent abnormalities associated with VTED.

Aged↗
PubMed1996

[Dendriform diffuse pulmonary ossification. Report of 2 cases].

Two cases of diffuse dendriform pulmonary ossification are reported which was diagnosed postmorten. Both patients had a previous history of chronic obstructive pulmonary disease with pneumonic complications. The radiological study was interpreted as pulmonary fibrosis in the first case, an entity which ranks first in the differential diagnosis. In some cases the obtention of highly contrasted X-ray films can be useful for recognizing this are entity.

Aged↗
PubMed1994

A trigonometric sum relevant to the nonrelativistic theory of atoms.

We extend Van der Corput's method for exponential sums to study an oscillatory term appearing in the quantum theory of large atoms. We obtain an interpretation in terms of classical dynamics and we produce sharp asymptotic upper and lower bounds for the oscillations.

Journal Article↗
PubMed1993

Deep intramuscular leiomyoma of the lower limb.

The authors present a case of intramuscular leiomyoma of the lower limb. Its location was the internal gastrocnemius muscle of the right leg. The treatment consisted in ablation of the tumor, which was well delimited and had well-defined edges. The evolution after surgery was entirely satisfactory, with no complications or recurrences in the 24 months following the procedure.

Adult↗