Showing papers by "National University of La Plata published in 1995"

The Behavior of the Stahel-Donoho Robust Multivariate Estimator

Abstract: The Stahel-Donoho estimators (t, V) of multivariate location and scatter are defined as a weighted mean and a weighted covariance matrix with weights of the form w(r), where w is a weight function and r is a measure of “outlyingness,” obtained by considering all univariate projections of the data. It has a high breakdown point for all dimensions and order √n consistency. The asymptotic bias of V for point mass contamination for suitable weight functions is compared with that of Rousseeuw's minimum volume ellipsoid (MVE) estimator. A simulation shows that for a suitable w, t and V exhibit high efficiency for both normal and Cauchy distributions and are better than their competitors for normal data with point-mass contamination. The performances of the estimators for detecting outliers are compared for both a real and a synthetic data set.

pHi Regulation in Myocardium of the Spontaneously Hypertensive Rat : Compensated Enhanced Activity of the Na+-H+ Exchanger

Abstract: To elucidate the mechanisms controlling pHi in myocardium of the spontaneously hypertensive rat (SHR), experiments were performed in papillary muscles (isometrically contracting at 0.2 Hz) from SHR and age-matched normotensive Wistar-Kyoto (WKY) rats loaded with the pH-sensitive fluorescent probe BCECF-AM. An enhanced activity of the Na(+)-H+ exchanger was detected in the hypertrophic myocardium of SHR. This conclusion was based on the following: (1) The myocardial pHi was more alkaline in SHR (7.23 +/- 0.03) than in WKY rats (7.10 +/- 0.03) (P < .05) in HEPES buffer. (2) SITS (0.1 mmol/L in HEPES buffer) did not alter pHi in the SHR (pHi 7.26 +/- 0.03 and 7.28 +/- 0.03 before and after SITS, respectively). (3) The fall in pHi observed after 20 minutes of Na(+)-H+ exchanger inhibition [5 mumol/L 5-(N-ethyl-N-isopropyl)amiloride (EIPA)] was greater in SHR (-0.16 +/- 0.01) than in WKY rats (-0.09 +/- 0.02, P < 0.05). (4) The velocity of pHi recovery from an intracellular acid load was faster in SHR than in WKY rats (0.068 +/- 0.02 versus 0.014 +/- 0.002 pH units/min at pHi 6.99, P < .05). (5) After EIPA inhibition, the rate of pHi recovery from the same acid load decreased to a similar value in both rat strains (0.0032 +/- 0.002 pH units/min in SHR and 0.0032 +/- 0.002 pH units/min in WKY rats). Under the more physiological HCO3(-)-CO2 buffer, no significant difference in steady state myocardial pHi was detected between rat strains (7.15 +/- 0.03 in SHR and 7.11 +/- 0.05 in WKY rats).(ABSTRACT TRUNCATED AT 250 WORDS)

Vanadium derivatives act as growth factor--mimetic compounds upon differentiation and proliferation of osteoblast-like UMR106 cells.

Abstract: The effect of different vanadium compounds on proliferation and differentiation was examined in osteoblast-like UMR106 cells. Vanadate increased the cell growth in a biphasic manner, the higher doses inhibiting cell progression. Vanadyl stimulated cell proliferation in a dose-responsive manner. Similar to vanadate, pervanadate increased osteoblast-like cell proliferation in a biphasic manner but no inhibition of growth was observed. Vanadyl and pervanadate were stronger stimulators of cell growth than vanadate. Only vanadate was able to regulate the cell differentiation as measured by cell alkaline phosphatase activity. These results suggest that vanadium derivatives behave like growth factors on osteoblast-like cells and are potential pharmacological tools in the control of cell growth.

Strange matter equation of state in the quark mass-density-dependent model.

Abstract: We study the properties and stability of strange matter at [ital T]=0 in the quark mass-density-dependent model for noninteracting quarks. We found a wide stability window'' for the values of the parameters ([ital C],[ital M][sub [ital s]0]) and the resulting equation of state at low densities is stiffer than that of the MIT bag model. At high densities it tends to the ultrarelativistic behavior expected because of the asymptotic freedom of quarks. The density of zero pressure is near the one predicted by the bag model and [ital not] shifted away as stated before; nevertheless, at these densities the velocity of sound is [approx]50% larger in this model than in the bag model. We have integrated the equations of stellar structure for strange stars with the present equation of state. We found that the mass-radius relation is very much the same as in the bag model, although it extends to more massive objects, due to the stiffening of the equation of state at low densities.

Disturbance torque estimation in a sensorless DC drive

Abstract: The estimation of the disturbance torque in a sensorless DC motor drive is carried out by extending the classical observer theory. Three estimation schemes are formulated according to the representation of the disturbance torque and the processing of the observer states. In addition to the disturbance torque, all the schemes deliver an estimation of the motor speed. Steady-state accuracy and dynamics of the schemes are first determined in nominal conditions, identifying the scheme with the best performance. The effects of variations in the motor parameters are then analyzed, with the finding that a proper modeling of the motor makes the steady-state estimation of the disturbance torque insensitive to any variation. As a test, the schemes are applied to a sensorless DC motor drive for both compensating for the disturbance torque and closing the speed loop. The responses obtained with the best-performance scheme are reported. >

Comunidades vegetales de la Sierra de la Ventana, Provincia de Buenos Aires, Argentina

Abstract: Se describen las comunidades vegetales de la porcion central (38o- 38° 10' S, 61° 45 - 62° 8' W) de las Sierras Australes (1243 m sm de altura maxima).

Detection of Bacillus larvae spores in Argentinian honeys by using a semi-selective medium.

Abstract: A semi-selective medium for the detection in Argentinian honeys of spores of Bacillus larvae, a pathogen of American foulbrood, was developed. The technique involves dilution of samples (1:2) in phosphate buffer, concentration of spores by centrifugation and heat treatment prior to inoculation. Two media (JNxPa and JNxPb) were prepared from J-agar, to which nalidixic acid and pipemidic acid were added. Both JNxP media were reliable for the isolation of B. larvae colonies and, at the same time, prevented the development of other Bacillus species which normally develop on the plates before B. larvae spores can germinate.

Evaluation of the effectiveness of an ambulatory teaching/treatment programme for non-insulin dependent (type 2) diabetic patients

Abstract: The aim of this study was to evaluate the effect of a structured teaching/treatment programme on the clinical and metabolic control of non-insulin-dependent (type 2) diabetic patients. The programme was aimed at improving the overall treatment quality in these patients through measures involving self-care, diet, exercise and weight reduction. Four theoretical-practical teaching units were given once a week to group of 5–8 ambulatory patients by previously trained general practitioners. Clinical and biochemical parameters were recorded at the beginning of the course and 1 year after its completion in 40 patients attending the programme and in 39 patients of similar clinical characteristics under conventional diabetes treatment, but receiving no structured teaching before or during the survey period (control group). The drop-out percentage in the intervention group (25%) was significantly lower than in the control group (45%),P<0.05, suggesting an incentive toward greater compliance in the former. At the end of the 1-year follow-up, the mean differences observed in the control and in the intervention groups were: body weight loss −2.4±0.5 kg vs −0.4±0.5 (P<0.001); haemoglobin HbA1 −0.2%±0.4% vs +0.8±0.4% (NS); number of daily oral hypoglycaemic agent intake −1.4±0.2 vs +0.9±0.2 tablets (P<0.001). Our results strongly suggest that this programme, applied through family doctors, may constitute an efficient tool to improve the compliance and clinico-metabolic control of type 2 patients at the primary health care level.

Strange matter equation of state and the combustion of nuclear matter into strange matter in the quark mass-density-dependent model at T>0.

Abstract: We study the properties and stability of strange matter in the mass-density-dependent model at Tg0 We find the temperature dependence of the strange matter stability window and the critical temperature above which there is no stable strange matter It occurs at ${\mathit{T}}_{\mathit{c}}$=34 MeV Also, the resulting equation of state in this approach is presented We also study the combustion of nuclear matter into strange matter We employ for strange matter the equation of state of this paper and for nuclear matter a set of equations of state (free neutrons, Bethe-Johnson, Lattimer-Ravenhall, and Walecka) It is shown the the results are very similar to the ones found employing the MIT bag model However, the only equation of state which shows a noticeable dependence with temperature is the Walecka one Moreover, contrary to the former case, the Walecka equation of state is flammable in the present model It is found that, also at finite temperatures, the properties of strange quark matter in the quark mass-density-dependent model and in the MIT bag model are very similar

Optimization of a competitive ELISA with polyclonal antibodies for quantification of prolamins in foods

Abstract: The optimization of a sequential competitive ELISA for the quantification of prolamins in foods is described in this article. The assay was developed using polyclonal antibodies obtained by the hyper‐immunization of rabbits with commercial gliadin. The ELISA developed in this way showed a very high degree of detectability (detection limit, 1 ng ml‐1), as well as the ability to discriminate between prolamins harmful to coeliac individuals from non‐toxic prolamins. The influence of the solvent used for extraction of the samples on the detection capability of the test was also studied. The assay proved to be useful for the evaluation of gliadins in processed foods including meat products. The assay was applied to many types of foods and was compared with a commercial kit approved by the Association of Official Analytical Chemists.

Robe's restricted three-body problem revisited

Abstract: Robe's restricted three-body problem is reanalyzed with a view to incorporate a new assumption, namely that the configuration of the fluid body is that described by an hydrostatic equilibrium figure (Roche's ellipsoid). In the concomitant gravitational field a full treatment of the buoyancy force is given. The pertinent equations of motion are derived, the linear stability of the equilibrium solution is studied and the connection between the effect of the buoyancy forces and a perturbation of the Coriolis force is pointed out.

The euclidean traveling salesman problem and a space-filling curve

Abstract: We elucidate the relationship between space-fillling curves and the Euclidean Traveling 2

Spreading analysis and finite-size scaling study of the critical behavior of a forest fire model with immune trees

Abstract: In a forest fire model with immune trees (FFMIT) recently proposed by Drossel and Schwabl (Physica A 199 (1993) 183), the sites of the lattice are either empty, a tree or a burning tree, and at each time step the system is updated in parallel according to the following rules: (i) A burning tree becomes an empty site, (ii) trees grow with probability p from empty sites, and (iii) a green tree becomes a burning tree with probability (1-g) if at least one next neighbor is burning. Fixing an arbitrary grow probability (p) and starting with a small immunity (g), increments of g causes the fire density of the steady state to decrease until the fire becomes irreversibly extinguished at a certain critical point of coordinates {pc, gc}. The set of critical points defines a critical curve gc (p) which, in the L = ∞ limit, divides the {p, g}-plane in two regions: a steady state with fire fronts for g

Los estratotipos de los pisos montehermosense y chapadmalalense [Plioceno] del esquema cronológico sudamericano

Abstract: The stratigraphic section at the Baliza Monte Hermoso (near Punta Tejada, 17 km to the west of Pehuen-co, provincia de Buenos Aires, Argentina) has been known since Darwin 's voyage. The section is remarkable because the typic Montehermosan and the lower par! of Chapadmalalan crop out there and abundant mammals are recorded. Recently, Zavala (1993) and Zavala and Navarro (1993) revised the geology of the area. We disagree in several points with the conclusions of those authors: 1) we accept the biostratigraphy as a base for chronostratigraphic units, and 2) we found a clear biostratigraphic pattern at the section of Baliza Monte Hermoso with two Pliocene zones. These biostratigraphic units are the material basis for the Montehennosan and possibly for the lower Chapadmalalan. We also discuss the correlation of the Monte Hermoso Formation with other units in Buenos Aires province.

The mite Varroa jacobsoni does not transmit American foulbrood from infected to healthy colonies

Abstract: The present study was conducted to determine whether Varroa jacobsoni can transmit American foulbrood (AFB), caused by the bacterium Paenibacillus larvae to healthy colonies by the surface transport of spores. Five two-storey Langstroth colonies of Apis mellifera ligustica were infested by placing a sealed brood comb, with 10% Varroa prevalence, between the central brood combs of each colony. Two months later the colonies were inoculated with P. larvae by adding brood comb pieces with clinical signs of AFB (45±5 scales per colony). After 60 days the brood area was completely uncapped by means of dissecting needles and tweezers, separating the Varroa mites from the larvae and the collected mites were introduced at a rate of 51 per colony into four recipient hives placed in an isolated apiary. Twenty female Varroa specimens were separated at random and observed by SEM. Paenibacillus larvae spores were found on the dorsal shield surface and on idiosomal setae. All colonies died after 4–5 months due to a high incidence of varroosis. No clinical AFB symptoms or P. larvae spores were observed in microscopic preparations. It is concluded that Varroa jacobsoni does not transmit AFB from infected to healthy colonies; it does, however transport P. larvae spores on its surface.