Evaluación estadística de la densidad electrónica máxima a -120 de latitud dip

Se estudia la distribución de la densidad electrónica máxima de la región F2 de la ionosfera a -12° de latitud dip. En este trabajo se comparan datos experimentales obtenidos por sondadores con valores proporcionados por el SLIM (Modelo Ionosférico Se- miempírico para Bajas Latitudes). El modelo nuestra las densidades electrónicas como una función de la altura, la latitud dip y el tiempo local, resolviendo numéricamente la ecuación de continuidad del O*. No se tiene en cuenta el efecto longitudinal. Los datos experimentales que se analizan provienen de Tucumán y Vanimo. Se ha trabajado con las medianas mensuales de la frecuencia crítica máxima para ambos sois ticios y el equinoccio, realizando un promedio de los meses correspondientes. Se han calculado los coeficientes de correlación p y de regresión y también se han construido rectas de regresión entre los valores experimentales y los determinados por el mcdelo. Para ambas estaciones, existe un buen acuerdo en el equinoccio mientras que en el solsticio de diciembre es cuando se manifiesta el mayor apartamien to entre los valores medidos y los calculados.The ionospheric F2 region maximum electronic density distribution at -12® dip latitude is studied. In this paper sounders experimental data are compared with SLIM ("Semi Empirical Low-Latitude Ionospheric Medel") values. In this model, electron densities as a function of altitude, latitude and local time are calculated by solving the time dependent ion (O+) continuity equation numerically. The longitudinal effect is not taken into account. Experimental data analyzed are from Tucumán and Vanirno. Average maximum critical frequency monthly medians were used for both solsticies and equinox. Correlation and regression coefficients were computed and the regression lines, between experimen tai and inc del data were plotted. There is a good agreement during equinox in both stations while in december solstice an important distance between computed and measured data is observed.Asociación Argentina de Geofísicos y Geodesta

Incidencia de las tormentas geomagnéticas sobre el comportamiento tranquilo de la ionosfera

Se realiza un estudio del comportamiento tranquilo de la Ionosfera para poder poner de manifiesto las deformaciones que ella sufre durante el desarrollo de las tormentas geomagnéticas. Este análisis se efectúa para la cadena australiano-japonesa de sondadores, habiéndose seleccionado los que están a una longitud aproximadamente constante. Se consideran los meses de verano del año 1975 y tres tormentas que tienen lugar en esos meses. Se estudia la variación de la concentración electrónica máxima en función de la latitud geomagnética. Se concluye que: a) se encuentran presentes los mecanismos que dan origen a la formación y existencia de la anomalía ecuatorial y b) las tormentas magnéticas afectan severamente la ionosfera, produciendo en ella cambios significativos; en particular alteran notablemente la estructura de la anomalía ecuatorial.A study of the ionosphere during quiet conditions has been made in order to make evident the deformations ocurring during the development of geomagnetic storms. This analysis is performed for the Australian-Japanese ionosonde network, having been selected those located around the same longitude. The 1975 summer months and three storms ocurring during those months have been considered. The maximum electron concentration variation as a function of the geomagnetic latitude is studied. The conclusions are: a) the mechanisms responsible for the equatorial anomaly formation and existence are present; b) the magnetic storms affect severely the ionosphere producing significative changes; particulary they notably alter the equatorial anomaly structure.Asociación Argentina de Geofísicos y Geodesta

Painleve-Gullstrand Coordinates for the Kerr Solution

We construct a coordinate system for the Kerr solution, based on the zero angular momentum observers dropped from infinity, which generalizes the Painleve-Gullstrand coordinate system for the Schwarzschild solution. The Kerr metric can then be interpreted as describing space flowing on a (curved) Riemannian 3-manifold. The stationary limit arises as the set of points on this manifold where the speed of the flow equals the speed of light, and the horizons as the set of points where the radial speed equals the speed of light. A deeper analysis of what is meant by the flow of space reveals that the acceleration of free-falling objects is generally not in the direction of this flow. Finally, we compare the new coordinate system with the closely related Doran coordinate system.Comment: 6 pages; v2: new section, matches final published version; v3: sign error in the expression of the function delta correcte

Tetrads in SU(3) X SU(2) X U(1) Yang-Mills geometrodynamics

The relationship between gauge and gravity amounts to understanding underlying new geometrical local structures. These structures are new tetrads specially devised for Yang-Mills theories, Abelian and Non-Abelian in four-dimensional Lorentzian spacetimes. In the present manuscript a new tetrad is introduced for the Yang-Mills SU(3) X SU(2) X U(1) formulation. These new tetrads establish a link between local groups of gauge transformations and local groups of spacetime transformations. New theorems are proved regarding isomorphisms between local internal SU(3) X SU(2) X U(1) groups and local tensor products of spacetime LB1 and LB2 groups of transformations. The new tetrads and the stress-energy tensor allow for the introduction of three new local gauge invariant objects. Using these new gauge invariant objects and in addition a new general local duality transformation, a new algorithm for the gauge invariant diagonalization of the Yang-Mills stress-energy tensor is developed.Comment: There is a new appendix. The unitary transformations by local SU(2) subgroup elements of a local group coset representative is proved to be a new local group coset representative. This proof is relevant to the study of the memory of the local tetrad SU(3) generated gauge transformations. Therefore, it is also relevant to the group theorems proved in the paper. arXiv admin note: substantial text overlap with arXiv:gr-qc/060204

Respuesta hemisférica de la ionosfera a las fuertes perturbaciones magnéticas de agosto de 1972

Se conoce perfectamente que la ionosfera y en especial la región F, sufren notables apartamientos de su comportamiento normal durante el desarrollo de tormentas geomagnéticas fuertes. El presente trabajo consiste en el estudio del comportamiento de los parámetros foF2, h’F y hpF2 para las redes sudamericana, africana y australiana de sondadores para el período que se extiende desde el 3 al 6 de agosto de 1972 , caracterizado por tres comienzos súbitos (SC) de tormentas magnéticas. Es evidente de los resultados, que las perturbaciones son consistentes con procesos TID (perturbaciones ionosféricas viajeras), con propagación tanto en latitud como en longitud y velocidades que van desde los 400 a los 1.000 m/seg.Large departure from normal behavior of the .ionosphere and specially F-region during the development of strong geomagnetic storms is well known. The present paper studies the foF2, h’F and hpF2 parameters behavior for the South American, African and Australian ionosonde networks for the august 3-6 period characterized by three magnetic storm sudden commencements (SC). It is evident from the results that the disturbances are consistent with the TID’s processes that propagate both in latitude and longitude with speeds of 400 to 1.000 m/seg.Asociación Argentina de Geofísicos y Geodesta

Présence de métaux lourds et de résidus médicamenteux dans les effluents des établissements de santé de Dakar (Sénégal)

L’objectif de cette étude est de quantifier les concentrations en métaux lourds et de rechercher la présence de résidus de molécules médicamenteuses des effluents de trois hôpitaux de Dakar (Sénégal). C’est ainsi que la collecte des effluents a été réalisée chaque jour sur une période de trois semaines à l’entrée du déversoir des services de radiologie, de médecine interne et d’odontologie. Ensuite, des échantillons composites par semaine ont été constitués pour rechercher leur composition en métaux lourds et en résidus médicamenteux. Le transport a été effectué à +4 °C et à l'obscurité pour assurer une conservation satisfaisante. Les métaux lourds ont été dosés par ICP-MS et les résidus de médicaments ont été recherchés par UPLCMS/ MS. Les médicaments identifiés dans les effluents sont essentiellement des analgésiques et des psychotropes. La concentration en métaux lourds des effluents des trois hôpitaux est inférieure aux normes sénégalaises et de celles de L’OMS fixant les conditions de rejet de métaux dans les eaux usées. Cependant, bien que les taux retrouvés soient tolérables, leur introduction continuelle en milieu aquatique pourrait être à l’origine d’effets néfastes sur les organismes marins par des phénomènes de bioaccumulation et de biomagnification. D’où l’importance et la nécessité des stations d’épuration pour une bonne gestion et une réduction des risques écotoxicologiques liés aux effluents liquides hospitaliers.Mots clés : Effluents hospitaliers, métaux lourds, résidus médicamenteux, toxicité

Initial data for two Kerr-like black holes

We prove the existence of a family of initial data for the Einstein vacuum equation which can be interpreted as the data for two Kerr-like black holes in arbitrary location and with spin in arbitrary direction. When the mass parameter of one of them is zero, this family reduces exactly to the Kerr initial data. The existence proof is based on a general property of the Kerr metric which can be used in other constructions as well. Further generalizations are also discussed.Comment: revtex, 5 pages, no figure

Can Schwarzschildean gravitational fields suppress gravitational waves?

Gravitational waves in the linear approximation propagate in the Schwarzschild spacetime similarly as electromagnetic waves. A fraction of the radiation scatters off the curvature of the geometry. The energy of the backscattered part of an initially outgoing pulse of the quadrupole gravitational radiation is estimated by compact formulas depending on the initial energy, the Schwarzschild radius, and the location and width of the pulse. The backscatter becomes negligible in the short wavelength regime.Comment: 18 pages, Revtex. Added three references; a new comment in Sec. 7; several misprints corrected. To appear in the Phys. Rev.

The Trypanosoma cruzi nucleic acid binding protein Tc38 presents changes in the intramitochondrial distribution during the cell cycle

Background: Tc38 of Trypanosoma cruzi has been isolated as a single stranded DNA binding protein with high specificity for the poly [dT-dG] sequence. It is present only in Kinetoplastidae protozoa and its sequence lacks homology to known functional domains. Tc38 orthologues present in Trypanosoma brucei and Leishmania were proposed to participate in quite different cellular processes. To further understand the function of this protein in Trypanosoma cruzi, we examined its in vitro binding to biologically relevant [dT-dG] enriched sequences, its expression and subcellular localization during the cell cycle and through the parasite life stages.Results: By using specific antibodies, we found that Tc38 protein from epimastigote extracts participates in complexes with the poly [dT-dG] probe as well as with the universal minicircle sequence (UMS), a related repeated sequence found in maxicircle DNA, and the telomeric repeat. However, we found that Tc38 predominantly localizes into the mitochondrion. Though Tc38 is constitutively expressed through non-replicating and replicating life stages of T. cruzi, its subcellular localization in the unique parasite mitochondrion changes according to the cell cycle stage. in epimastigotes, Tc38 is found only in association with kDNA in G1 phase. From the S to G2 phase the protein localizes in two defined and connected spots flanking the kDNA. These spots disappear in late G2 turning into a diffuse dotted signal which extends beyond the kinetoplast. This later pattern is more evident in mitosis and cytokinesis. Finally, late in cytokinesis Tc38 reacquires its association with the kinetoplast. in non-replicating parasite stages such as trypomastigotes, the protein is found only surrounding the entire kinetoplast structure.Conclusions: the dynamics of Tc38 subcellular localization observed during the cell cycle and life stages support a major role for Tc38 related to kDNA replication and maintenance.FIRCAFondo Clemente Estable (DICyT)FAPESConselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)PROSULPEDECIBAAMSUD-PasteurFac Ciencias, Lab Interacc Mol, Montevideo, UruguayFac Med, Dept Genet, Montevideo, UruguayFac Ciencias, Dept Biol Celular & Mol, Montevideo, UruguayInst Invest Biol Clemente Estable Montevideo Urug, Dept Neurobiol Celular & Mol, Montevideo, UruguayUniv Nacl Gen San Martin, CONICET, INTECH, Inst Invest Biotecnol, Buenos Aires, DF, ArgentinaUniversidade Federal de São Paulo, Dept Microbiol Imunol & Parasitol, São Paulo, BrazilSUNY Buffalo, Dept Microbiol & Immunol, Buffalo, NY 14260 USAInst Biol Mol Parana, Curitiba, Parana, BrazilUniversidade Federal de São Paulo, Dept Microbiol Imunol & Parasitol, São Paulo, BrazilFIRCA: R03 TW05665-01Fondo Clemente Estable (DICyT): 7109Web of Scienc