Rocas volcánicas de la Patagonia: su comportamiento frente a la RAS

En la Patagonia (Argentina) existen gran cantidad de rocas volcánicas que se utilizan como agregados para hormigón. Muchas son potencialmente reactivas frente a los álcalis por contener vidrio volcánico y otras variedades de sílice lábil. En el presente trabajo se estudiaron rocas basálticas y riolíticas de las Prov. de Río Negro y Chubut. Se identificaron como basaltos Huala y Facundo, riolitas Albistur y Camarones (Chubut) y basaltos Pillahuincó compacto y poroso, Meseta de Somún Curá, Ruca Choroi, Cerro Medina, Ing. Jacobacci, Cabecera del Salado, riolita Bienvenida y traquita El Cain (Río Negro). Se aplicó la norma IRAM 1649 para el análisis petrográfico y el método acelerado de la barra de mortero (IRAM 1674). Se concluyó acerca de su potencial reactividad frente a la RAS y se vincularon las causas del comportamiento deletéreo, correlacionando la petrografía, la expansión en las barras de mortero y la incidencia de la sílice disuelta

Aplicación de un modelo estadístico para evaluar la reactividad alcalina potencial en rocas basálticas

Samples of basaltic rocks from differenlocations of Río Negro and Neuquén provinces were studied by means of the the petrographic method (ASTM C-295), the mortar bars method (ASTM C-1260) and the chemical test method (ASTM C-289). Besides, an aliquot of the solution was analyzed by ICP, to determine the contents of Al$latex ^{_{2}}$and MnO. The obtained results were statistically treated by the Principal Components method and compared with the results obtained in a previous work. lt is concluded that expansion is closely related to the dissolved silica contributed by volcanic glass and its alteration products, and by poorly crystallized silica. lts propases a prompt method to establish the reactivity potential using the Principal Components statistical method

Detection of nonpregnant cows and potential embryo losses by color Doppler ultrasound and interferon-stimulated gene expression in grazing dairy cows

Many studies have been conducted to estimate pregnancy losses between 19 and 34 d after artificial insemination (AI) in dairy cows managed under confinement-based systems, but few studies have examined embryo mortality during this interval in dairy cows managed under gazing systems. The objectives of this prospective cohort study were (1) to assess the diagnostic value of the corpus luteum (CL) blood perfusion (BP) evaluation by Doppler ultrasound (US) to detect nonpregnant cows at 19 to 20 d post-AI, and (2) to assess the rate of potential embryo mortality between 19 to 34 d post-AI. The CL-BP of all cows included in the study (n = 131) was examined on farm by power and color mode of Doppler US and later using an image processing software by a second evaluator. The endometrium thickness and echotexture were evaluated by B-mode US at the same visit to assess if the nonpregnancy diagnosis could be improved at 19 to 20 d post-AI by this additional diagnostic tool. Blood samples were obtained at 19 to 20 d post-AI for progesterone (P4) measurement by chemiluminescence and to determine the mRNA expression of ISG by real-time PCR. Pregnancy diagnosis based on embryo visualization was performed at 33 to 34 d post-AI by US B-mode. In parallel interpretation, ISG15 and MX2 mRNA expression in leukocytes [sensitivity (Se), 100%] were regarded as suitable biomarkers for early pregnancy and were selected for molecular characterization of pregnancy at 19 to 20 d post-AI. At 19 to 20 d post-AI, 61.1% of the cows had positive CL-BP by Doppler US (Se, 98.0%), 62.7% had ISG mRNA expression in leukocytes over the cutoff point (Se, 95.7%), and 50.8% were positive, based on the combination of ISG mRNA expression, CL-BP by Doppler US, and P4 concentration (Se, 100%), and were considered as possible pregnant. At 33 to 34 d, the pregnancy rate was 37.4% diagnosed by the B-mode US. Based on the expression of the selected biomarkers in cows with active CL, we found that 28.1% of the cows could have potentially lost their pregnancy between 19 and 34 d post-AI. The Doppler US color mode showed similar accuracy and a higher negative predictive value than the genes selected as biomarkers. The additional B-mode ultrasound evaluation of the uterine stratum vasculare and the endometrium thickness improved the diagnostic accuracy. Therefore, assessing the CL-BP by Doppler US allowed early detection of nonpregnant cows at 19 to 20 d post-AI. The combination of early CL-BP by Doppler US (d 19 to 20) with early embryo detection by B-mode US (d 33–34) could be used to facilitate earlier rebreeding of dairy cows

Ayenia mansfeldiana (Herter) Herter ex Cristóbal

15Km al N de CuruzúpublishedVersio

Pecluma singeri (de la Sota) M.G. Price

LoretopublishedVersio

Chaos in Static Axisymmetric Spacetimes I : Vacuum Case

We study the motion of test particle in static axisymmetric vacuum spacetimes and discuss two criteria for strong chaos to occur: (1) a local instability measured by the Weyl curvature, and (2) a tangle of a homoclinic orbit, which is closely related to an unstable periodic orbit in general relativity. We analyze several static axisymmetric spacetimes and find that the first criterion is a sufficient condition for chaos, at least qualitatively. Although some test particles which do not satisfy the first criterion show chaotic behavior in some spacetimes, these can be accounted for the second criterion.Comment: More comments for the quantitative estimation of chaos are added, and some inappropriate terms are changed. This will appear on Class. Quant. Gra

Chaos in black holes surrounded by gravitational waves

The occurrence of chaos for test particles moving around Schwarzschild black holes perturbed by a special class of gravitational waves is studied in the context of the Melnikov method. The explicit integration of the equations of motion for the homoclinic orbit is used to reduce the application of this method to the study of simple graphics.Comment: 15 pages, LaTex

Ayenia praecipua Cristóbal

LoretopublishedVersio

Perfil sérico hormonal de un dispositivo intravaginal liberador de progesterona en ovejas

Los dispositivos intravaginales (DIV) con 300 mg de progesterona (P4) pueden reutilizarse en los protocolos de sincronización en ovinos con una duración de hasta 7 días. La reutilización de DIV con menor concentración hormonal, así como estudios far- maco-cinéticos a través del análisis no compartimental de las concentraciones hormonales luego de la colocación de dispositivos de 1° o 2° uso no han sido descriptos previamente. El objetivo del presente trabajo fue evaluar la utilización y reutilización de dispositivos intrava- ginales con una concentración inicial de 160 mg de P4. Para ello se utilizaron 20 ovejas que conformaron cinco grupos: control (sin DIV), CIDN (DIV 300 mg P4 1° uso), CIDU (DIV 300 mg P4 2° uso), CRON (DIV 160 mg P4 1° uso) y CROU (DIV 300 mg P4 2° uso). Las valoraciones séricas hormonales se realizaron a través de radioinmunoensayo. La concentración máxima y el tiempo medio de residencia fueron similares entre CIDN Y CRON, en cambio CIDU presentó una concentración máxima y un tiempo medio de residencia mayor que CROU. Además, CROU presentó concentraciones séricas sub-luteales a partir de las 48 h de colocado y liberó un 68,5% menos de P4 que CIDU y un 72,5% menos que CRON. En base a los resultados obtenidos, la reutilización de DIV con menor concentración hormonal provocaría niveles sub-luteales que posiblemente afectarían la fertilidad

Tasa de preñez en búfalas sometidas a distintos protocolos de inseminación artificial a tiempo fijo en el nordeste argentino

El objetivo del trabajo fue comparar las tasas de preñez obtenidas con dos diferentes protocolos de inseminación artificial a tiempo fijo (IATF) en búfalas de raza Mediterránea, en el norte de Corrientes, Argentina. Se utilizaron 93 búfalas pluríparas, con crías, divididas en dos grupos. En el Grupo 1 (G1, n=34)se ensayó el protocolo Ovsynch: sincronización (día 0): 8 ug de buserelina (GnRH); día 7:150 mg de cloprostenol (PGF2α); día 9: 8 ug de GnRH; día 10: IATF. Resincronización (día28: 8 ug de GnRH); día 35: diagnóstico de gestación por ultrasonografía y 150 ug de PGF2αa los animales diagnosticados vacíos; día 37: 8 ug de GnRH; día 38: IATF. En el Grupo 2(G2, n=41) se empleó un protocolo con dispositivos intravaginales (DIV) de progestágenos:sincronización (día 0): 2 mg de benzoato de estradiol (BE) y 1 DIV de primer uso durante7 días; día 7: 150 mg de PGF2α; día 8: 1 mg de BE; día 9: IATF. Resincronización (día 28): 1mg de BE y DIV de segundo uso durante 7 días; día 35: diagnóstico de gestación medianteultrasonografía y 150 ug de PGF2α a los animales diagnosticados vacíos; día 36: 1 mg de BE;día 37: IATF. Entre los días 55 y 75 se realizó repaso con toros y el día 100 se efectuó ecografíapara determinar preñez final. Los resultados para primo inseminación, resincronizacióny preñez final en G1 y G2 fueron respectivamente de 44 y 68% (p> 0,03), 75 y 80% y 83 y87%. Se resalta la más alta tasa de preñez obtenida por el grupo sometido al protocolo condispositivos intravaginales de progestágenos