Showing papers by "National University of La Plata published in 1981"
539 citations
TL;DR: In this paper, the consistency and asymptotic normality of the general M-estimators are proved assuming general regularity conditions on Φ and χ and assuming the joint distribution of (x, y) and (y, y ) to fulfill the model (*) only approximately.
Abstract: Let (xini, y
i
be a sequence of independent identically distributed random variables, where x
i
∃R
p
and y
i
∃R, and let θ∃R
p
be an unknown vector such that y
i
=x′
i
θ+u
i
(*), where u
i
is independent of x
i
and has distribution function F(u/σ), where σ>0 is an unknown parameter. This paper deals with a general class of M-estimates of regression and scale, (θ
*,σ*), defined as solutions of the system:
$$\sum\limits_i \phi ({\text{x}}_i ,r_i )x_i = 0,\sum\limits_i \chi (|r_i |) = 0,$$
, where r= (y
i
−x
i
1θ*/σ)*, with Φ∶ R
p
×R→R and χ∶ R→R. This class contains estimators of (θ, σ) proposed by Huber, Mallows and Krasker and Welsch. The consistency and asymptotic normality of the general M-estimators are proved assuming general regularity conditions on Φ and χ and assuming the joint distribution of (x
i
, y
i
) to fulfill the model (*) only approximately.
125 citations
TL;DR: Fujikawa's analysis of the noninvariance of the fermion pathintegral measure under axial gauge transformations was used to derive the solution of the Schwinger model as mentioned in this paper.
Abstract: Fujikawa's analysis of the noninvariance of the fermion path-integral measure under axial gauge transformations is used to derive the solution of the Schwinger model. Subtleties in proceeding from infinitesimal to finite axial gauge transformations are presented in the Appendix.
93 citations
TL;DR: Craniofacial development in the rat seems to be a process more complex than what has been generally accepted and a nutritional stress may alter the relative growth between the facial functional components to a greater extent than that between the major functional components; viz. the neurocranium and the splanchnocranium.
Abstract: Weanling male Holtzman rats were subjected to each of the following nutritional treatments: malnutrition; malnutrition–recuperation; undernutrition; and undernutrition–recuperation. The rats were sacrificed when they were 49 days old, and dimensions of each one of the neurocranial, respiratory, and masticatory components were measured. Each component was compared with its counterpart in control rats (21, 28, 35, 42, and 49 day-old) by means of Mahalanobis D2 distances. The same functional components of 49 day-old control skulls were compared with their counterparts in younger control skulls. The means of the chosen cranial dimensions were compared by Tukey tests. Two periods of craniofacial development were identified. In the first, both facial components showed a similar growth that was greater than the neurocranial growth. In teh second period, the growth of the masticatory component was greater than that of the respiratory component, which in turn, was greater than that of the neurocranial component. Nutritional deficiencies delayed the growth of the masticatory component more than that of the neurocranial component, which, in turn, was delayed more than that of the respiratory one. About 7% of the dimensions measured were insensitive to both growth and nutrition; 31% were insensitive to nutrition; and 62% were modified by nutrition. Craniofacial development in the rat seems to be a process more complex than what has been generally accepted. A nutritional stress may alter the relative growth between the facial functional components to a greater extent than that between the major functional components; viz. the neurocranium and the splanchnocranium. The cranial dimensions studied were classified according to their sensitivity to growth and/or nutrition into invariable, nutritionally stable, and nutritionally unstable traits.
50 citations
TL;DR: In this article, the thermal decomposition of (NH4)2[Mo3S(S2)6] · nH2O was studied by DTA/TG, infrared spectroscopy, X-ray diffraction, determination of specific surfaces and temperature programmed desorption measurements.
Abstract: The thermal decomposition of (NH4)2[Mo3S(S2)6] · nH2O was studied by DTA/TG, infrared spectroscopy, X-ray diffraction, determination of specific surfaces and temperature programmed desorption measurements. The results are reported and discussed with respect to the stability of the MoIV-triangle system which is retained during the thermal treatment up to the formation of hexagonal MoS2, which can be understood nicely from a mechanistic point of view.
Thermische Zersetzung von (NH4)2[Mo3S(S2)6] · nH2O
Die thermische Zersetzung von (NH4)2[Mo3S(S2)6] · nH2O wurde mit DTA/TG, Infrarotspektren, Rontgenbeugung, Bestimmungen der spezifischen Oberflache und temperatur-programmierte Desorptionsexperimente verfolgt. Die Ergebnisse werden mitgeteilt und im Hinblick auf die Stabilitat des MoIV-Dreiecks, welches bei der thermischen Behandlung bis hin zur Bildung von hexagonalem MoS2 erhalten bleibt, diskutiert.
42 citations
TL;DR: The fatty acid composition and the ω6/ω3 acid ratio were constant during the whole year, suggesting a very stable diet, rich in vegetal detritus and poor in diatoms.
Abstract: Diplodom patagonicus is a freshwater bivalve mollusk living in lakes of the patagonian Andes mountains in Argentina. Lipid composition and seasonal changes in the mollusk were studied in the natural habitat. In addition to common nonpolar and polar lipids, small amounts of alk-1-enyldiacylglycerol ethers and significant quantities of ceramide aminoethyl phosphonate were present. Total lipid content changed during the year, primarily because of decreased triacylglycerols in winter. The fatty acid composition of the lipids, remarkably different from that of marine bivalves, and even from other fresh water animals, was especially rich in the ω6 fatty acids, linoleic and arachidonic (ca. 25%), and poor in the ω3 acids, 20∶5 and 22∶6. The ω6/ω3 acid ratio was ca. 2, which is very high compared to marine bivalves. The fatty acid composition and the ω6/ω3 acid ratio were constant during the whole year, suggesting a very stable diet, rich in vegetal detritus and poor in diatoms. The influence of environmental temperature fluctuation with season on fatty acid composition also was negible. Modest proportions of 22∶2 nonmethylene-interrupted (NMI) acids were detected and confirmed by mass spectrometry. It was shown that 20∶2 NMI acids were absent.
37 citations
TL;DR: An association between viral antigens, cytopathic effect (CPE) and viral titers in blood and lymphoid tissues suggests a direct CPE of Junin virus on the lymphopoietic organs of guinea pigs infected with 10(3) 50% lethal doses of the XJ prototype strain.
Abstract: An association between viral antigens, cytopathic effect (CPE), and viral titers in blood and lymphoid tissues suggests a direct CPE of Junin virus on the lymphopoietic organs of guinea pigs infected with 103 50070 lethal doses of the XJ prototype strain. After seven days of infection, all lymphoreticular organs had infectivity titers higher than those for blood. Virus was recovered from bone marrow and lymph nodes at day 5 after infection; peak titers were obtained from bone marrow, spleen, and lymph nodes after day 10. Granular specific fluorescence was detected in the cytoplasm of reticular monocytes after day 7; megakaryocytes showed positive fluorescence, but specific staining of other lymphoid cells was not observed. Necrosis of bone marrow, lymph nodes, and spleen was observed after day 9. CPE consisted of overdevelopment of reticuloendoplasmic cisternae of reticulomonocytes and myeloblasts. Typical Junin virus particles were observed. Reticular cells were gradually destroyed, and simultaneous necrosis of surrounding lymphoid cells was observed. Argentine hemorrhagic fever (AHF) is an endemic epidemic disease of the Pampean area of Argentina caused by Junin virus, a member of the arenavirus group. This disease mainly affects rural workers involved in corn harvesting. The major clinical characteristics are malaise, fever, central nervous system involvement, and a pronounced leukopenia and thrombocytopenia with hemorrhagic diathesis [1].
36 citations
TL;DR: In this paper, pure samples of the monoclinic (monazite-like) form of PrCrO 4 have been obtained for the first time and some of its properties are reported.
26 citations
TL;DR: The hypothesis that the alterations in the sensitivity to catecholamines induced by the changes in pH are not due to a release of endogenous noradrenaline nor to alterations of the mechanisms which remove catechlamines from the biophase is supported.
Abstract: The influence of “respiratory” and “metabolic” acid-base alterations on the myocardial sensitivity to catecholamines was studied in the isolated rat atria. The ability of noradrenaline for increasing the atrial rate was enhanced during alkalosis and conversely, it was decreased by acidosis. These changes in sensitivity shifted the concentration-effect curve for noradrenaline to the right by about 0.5 log unit when the pH was lowered from 7.60 to 7.00. No changes in the maximum attainable response were detected. Essentially the same shifts of the concentration-effect curves were obtained with changes in pH brought about by altering the pCO2 or at constant pCO2. The decrease in the pH produced a similar shift to the right of the concentration-effect curve for isoprenaline, after the extraneuronal uptake inhibition by hydrocortisone and also in atria tissue with low content of endogenous noradrenaline (reserpine-pretreated and newborn rats). The ability of isoprenaline for increasing cyclic AMP levels in atrial tissue was also enhanced by alkalosis and decreased by acidosis. However, the shift to the right of the concentration-effect curve for cyclic AMP induced by the decrease in the pH was greater than the shift detected in the chronotropic-effect curve. In addition a decrease in the maximum increment of cyclic AMP was detected under acidosis, in spite of equal maximal chronotropic response.
23 citations
TL;DR: In this article, the applicability of perturbed angular correlation to the study of the internal oxidation process is proved through the time differential perturbation angular correlation investigation of the system in Ag, and an unusually high electric quadrupole interaction was found.
23 citations
TL;DR: D. patagonicus is highly sensitive to food composition and varies little with temperature and seasonal changes, but a change of habitat from lake to estuary changed very significantly the fatty acid composition of the animal.
Abstract: Some effects of food, habitat and temperature on the lipid composition of a freshwater mollusk,Diplodom patagonicus, were studied. Animals kept and fasted up to 60 days in an aquarium at 9 C and 20 C showed a decrease of the total lipid content that corresponded to a decrease of triacylglycerols and diacylglycerol ethers. This decrease evoked an increase of polar-to-nonpolar lipid ratio. However, no significant change in the total fatty acid composition was shown. Moreover, a decrease of temperature from 20 C to 9 C decreased the incorporation of labeled linoleic and α-linolenic acid into the lipids, but did not modify the unsaturated: saturated acid ratio of the mollusk lipids during this period. A change of habitat from lake to estuary changed very significantly the fatty acid composition of the animal. The ω6 acids, linoleic and arachidonic, typical ofD. patagonicus living in the lake, were partially replaced by ω3 acids. That this change was due to a change of food composition was indicated by the fatty acids of corresponding sediments. Therefore, the fatty acid composition ofD. patagonicus is highly sensitive to food composition and varies little with temperature and seasonal changes.
TL;DR: In this article, a series of rare earth decavanadates of the type Ln2V10O28·nH2O have been obtained from monocrystals by precession and Weissenberg measurements.
TL;DR: In this article, cold fission phenomena are explained in the framework of the maximal entropy condition, subject to only one constraint, the mass number A, where A is the maximum number of atoms in the system.
TL;DR: In this article, the authors compare the IR and Raman spectra of α-Te2MoO7 with those of telluromolybdates of the type MIITeMoO6 and propose a structural model for these phases.
Abstract: Die IR- und Raman-Spektren von α-Te2MoO7 wurden aufgenommen und an Hand der bekannten kristallographischen Daten zugeordnet. Durch Vergleich dieser Spektren mit demjenigen einiger Telluromolybdate des Typs MIITeMoO6 kann fur diese Phasen ein Strukturvorschlag gegeben werden, der sich durch die spektroskopischen Daten einwandfrei rechtfertigen last.
Vibrational Spectrum of α-Te2MoO7 and a Proposal for the Structure of Telluromolybdates of Divalent Cations
Infrared and Raman spectra of α-Te2MoO7 have been recorded and discussed in relation to their known crystalline structure. The comparison of these spectra with those of telluromolybdates of the type MIITeMoO6, allows us to propose a structural model for these phases, which is totally consistent with the spectroscopic findings.
01 Jan 1981
01 Jan 1981
01 Jan 1981
01 Jan 1981
TL;DR: In this paper, the authors studied the kinetics of the hydrolytic degradation of cellulose and revealed that the degradation of native cellulose takes place by two simultaneously occurring kinetic mechanisms.
Abstract: The kinetics of the hydrolytic degradation of celluloses the molecular properties of which still correspond largely to those of the native state are studied. The hydrolytic agent has been 0,5 mol/l aqueous solution of KHSO4. The degrees of polymerization were determined viscosimetrically in copper ethylene diamine (CuEn) as solvent under standard conditions. In order to convert viscosity-average and weight-average degrees of polymerization DPη and DPw in the corresponding number-average DPn, a DPw/DPn calibration curve had been elaborated using polymer analogeous nitrates of a series of samples degraded under the same conditions. The results reveal that hydrolytic degradation of native cellulose takes place by two simultaneously occurring kinetic mechanisms, for which the following rate constants were derived: k1 = 0,12 h−1, k2 = 3,88·10−6 h−1, and k1 = 0,79 h−1; k2 = 38,35 · 10−6 h−1, corresponding to a degradation temperature of 40°C and 60°C, respectively, and related to an initial degree of polymerization DP0 = 13 000. The number of faster cleaving bonds per molecule (β1) and the number average of normally splitting bonds being between two “weak links” (β2) resulted in β1 ≈ 3,5 and β2 ≈ 3 600. The activation energies of the rapid and the slower reaction were found to be 20 kcal/mol (83,7 kJ/mol) and 24 kcal/mol (100,4 kJ/mol), respectively. Additional degradation experiments on the same, but pre-swollen or pre-reduced samples did not provoke any variations in the results. It can be excluded, therefore, that the simultaneous occurrence of two kinteic mechanisms is a consequence either of facts which involve diffusion control, or the existence of “stressed” bonds. The found relatively high activation energies rather permit to assume native modifications in the chemical structure of the cellulose molecule as the most probable reason for the faster bond splitting reaction.
TL;DR: In this paper, structural, lithological and geochronological data of metamorphic and granitoid rocks of the El Cristo area, southern part of Tandilia Range, are considered in terms of structural, geochemical, and meteorological data.
Abstract: Metamorphic and granitoid rocks of the El Cristo area, southern part of Tandilia Range, are considered in terms of structural, lithological and geochronological data.
TL;DR: In this paper, the infrared and Raman spectra of Ba3V10O28·19 H2O has been recorded and an assignement for the internal vibrations of the V10O 28 − 6− 19 H 2O anion is given.
Abstract: The infrared andRaman spectra of Ba3V10O28·19 H2O has been recorded and an assignement for the internal vibrations of the V10O
28
6−
anion is given. Infrared data of the hydrated decavanadates of silver, cadmium, magnesium and lanthanum are also reported and briefly discussed.
01 Jan 1981
01 Jan 1981
TL;DR: The presente trabajo trata sobre las especies de Lycopodium agrupadas en the Seccion Crassistachys Herter (Herter, 1909).
Abstract: El genero Lycopodium es una entidad altamente diversificada, cuya sistematica es confusa y contradictoria. Es posible encontrar tantos sistemas como autores. Los sistemas propuestos son, en su mayoria, discutibles, y no siempre estan basados en informacion concluyente. El presente trabajo trata sobre las especies de Lycopodium agrupadas en la Seccion Crassistachys Herter (Herter, 1909) y sus principales objetivos son:presentar una lista de las especies de esta seccion, comentarios criticos sobre los limites de las mismas, sus relaciones, afinidades y posicion sistematica, agregando, ademas, datos sobre su distribucion geografica y ecologia. Finalmente se incluye una clave para la identificacion de las especies. El ordenamiento presentado en esta sinopsis se ve justificado por la confusion reinante en trabajos anteriores sobre esta misma seccion, los cuales llevaron a la proliferacion de nombres sin el apoyo suficiente de estudios morfologicos cuidadosos.
TL;DR: In this article, a time resolution of 2τ = 0.75 ns, achieved with a conventional TDPAC setup with FCs detectors, allowed a determination of the very high electric field gradient at Hf impurity sites in K2ZrF6.
Abstract: A time resolution of 2τ=0.75 ns, achieved with a conventional TDPAC setup with FCs detectors, allowed a determination of the very high electric field gradient at Hf impurity sites in K2ZrF6. Simple theoretical calculations seem to indicate that nearest neighbours are responsible for the interaction observed.
TL;DR: In this article, the Ising model in a magnetic field was studied in its quantum version, and the particular realization of the renormalization group proposed gives both the ferromagnetic and antiferromagnetic fixed points.
Abstract: The Ising model in a magnetic field is studied in its quantum version. The particular realization of the renormalization group proposed gives both the ferromagnetic and antiferromagnetic fixed points. The critical exponents are obtained in a very simple analytical way.
TL;DR: Sn 3 PO 4 F 3, one of the main products of the reaction between stannous fluoride and dental enamel, was further characterized through its infrared and 119 Sn-Mossbauer spectra, highlighting the usefulness of Mossb Bauer spectroscopy in the investigation of dental surfaces or reactions involving dental tissues.
01 Jan 1981
TL;DR: In this article, the charge exchange resonances in 90 Zr are discussed within the framework of a simple model and the experimental results are confronted with the corresponding theoretical estimates, and the results are presented in terms of charge exchange resonance.
TL;DR: Mean amplitudes of vibration of SeF4 and TeF4 have been calculated from known spectroscopic data in a wide temperature range as discussed by the authors, and some comparisons with related species are made.
Abstract: Mean amplitudes of vibration of SeF4 and TeF4 have been calculated from known spectroscopic data in a wide temperature range. The results are briefly discussed and some comparisons with related species are made.