Comments on : diet, physiology and ecology of fossil mammals as inferred from stable carbon and nitrogen isotope biogeochemistry: implications for Pleistocene bears

A detailed study of isotopic relationships in European Pleistocene ursid teeth have been presented by Bocherens et al. (1994). We agree with the resu1ts and broad conclusions derived from the stable carbon isotope relationships. These are findings that confirm the previous hypothesis relating to the diets of Ursus deningeri and Ursus spelaeu

Pleistocene paleoenvironmental evolution at continental middle latitude inferred from carbon and oxygen stable isotope analysis of ostracodes from the Guadix-Baza Basin (Granada, SE Spain)

A representative paleoenvironmental reconstruction of continental middle latitude from ca. 2my to the upper part of Middle Pleistocene (279±77ky) was obtained from the carbon and oxygen stable isotopes analyzed in ostracode shells (Cyprideis torosa) recovered in the Guadix-Baza Basin (SE Spain), an intramontaneous closed depression filled by alluvial and lacustrine sediments. This study was performed along a 356-m-thick composite section, dated previously by paleomagnetism and the amino acid racemization method. 013C and 0180 profiles reflected changes in temperature, the evaporationJinfill ratio in the water bodies and the amount of rain. 013C is also affected by changes in plant biomass: periods with high 013C and 0180 values are associated with warm and dry regimes, and with less vegetation, which, in some cases, coincide with the development of displacive gypsum crystals, whereas low 013C and 0180 values correlate with cold and humid episodes, which cause more vegetation biomass and, therefore, increasing the input of isotopically light carbon. Intermediate 0180 values are linked to temperate dry or humid episodes when they coincide with high or low 013C values, respectively. 86 paleoclimatic events were distinguished in the Pleistocene record from the 013C and 0180 profiles. From both the statistical analysis of the geochemical data and the geological observations, four Cold and Humid Long Periods (low 0180) and four Warm and Dry Long Periods (high 0180) were defined. This differs with respect to the paleoclimatological behavior established for the Northern Hemisphere where during cold periods (glacial), no water was available while permafrost conditions persisted, whereas in warm episodes (interglacial), higher precipitation rates occurred. Good correspondences between the Guadix-Baza Basin paleoclimatic record and a marine oxygen-isotope sequence, two continental cores and other long Mediterranean paleoenvironmental records (pollen sequences from Israel) were found, which suggested that climate changes in the Guadix-Baza Basin were in tune with global climatic changes

Scale and structure of time-averaging (age mixing) in terrestrial gastropod assemblages from Quaternary eolian deposits of the eastern Canary Islands

Quantitative estimates of time-averaging (age mixing) in gastropod shell accumulations from Quaternary (the late Pleistocene and Holocene) eolian deposits of Canary Islands were obtained by direct dating of individual gastropods obtained from exceptionally well-preserved dune and paleosol shell assemblages. A total of 203 shells of the gastropods Theba geminata and T. arinagae, representing 44 samples (= strati graphic horizons) from 14 sections, were dated using amino acid (isoleucine) epimerization ratios calibrated with 12 radiocarbon dates. Most samples reveal a substantial variation in shell age that exceeds the error that could be generated by dating imprecision, with the mean within-sample shell age range of 6670 years and the mean standard deviation of 2920 years. Even the most conservative approach (Monte Carlo simulations with a non-sequential Bonferroni correction) indicates that at least 25% of samples must have undergone substantial time-averaging (e.g., age variations within those samples cannot be explained by dating imprecision alone). Samples vary in shell age structure, including both left-skewed (17 out of 44) and right-skewed distributions (26 out of 44) as well as age distributions with a highly variable kurtosis. Dispersion and shape of age distributions of samples do not show any notable correlation with the stratigraphic age of samples, suggesting that the structure and scale of temporal mixing is time invariant. The statistically significant multi-millennial time-averaging observed here is consistent with previous studies of shell accumulations from various depositional settings and reinforces the importance of dating numerous specimens per horizon in geochrono logical studies. Unlike in the case of marine samples, typified by right-skewed age distributions (attributed to an exponential-like shell loss from older age classes), many of the samples analyzed here displayed leftskewed distributions, suggestive of different dynamics of age mixing in marine versus terrestrial shell accumulations

Universal diagrams for te waves guided by thin films bounded by saturable nonlinear media

It is shown that universal V-b diagrams provide a powerful tool when analyzing the stationary waveguiding properties of the TE waves guided by a thin film bounded by a saturable nonlinear substrate or cladding. For a wide class of nonlinearities, the allowed and forbidden regions of these diagrams, for a stationary guided propagation to occur, display a universal pattern, the marginal loci separating different allowed regions from the forbidden ones being simple functions of only the asymmetry measure of the waveguide and the saturation value of the nonlinear permittivity. Relevant information for device design purposes is summarized on a few diagrams, so general waveguiding properties can be immediately read-off from them, and threshold power-independent values of the normalized thickness of the waveguide for a particular kind of guided wave to be allowed are obtained. Qualitative information concerning both the guided power and the stability of guided waves is also included in the diagrams.Peer ReviewedPostprint (published version

Similarity rules for nonlinear Kerr-like slab optical waveguides

It is shown that the stationary waveguiding properties of TE guided waves in a slab optical waveguide with a nonlinear Kerr-like bounding medium can be described in a compact way by means of the usual normalized effective modal index (b) and a set of only four independent normalized parameters: the well-known normalized thickness (V) and asymmetry measure (a) of the waveguide, the generalized aspect ratio between film and substrate refractive indexes, and a guided power measure. From an analysis starting on Buckingham's II-theorem, the similarity rules existing between the above waveguiding structures have been investigated. Allowed and forbidden regions in (b,V,a)-space in order that a guided solution exists have been recognized and classified, with the marginal loci separating different regions being a function of only V and a.Peer ReviewedPostprint (published version

New type of guided waves in birefringent media

The existence of waves guided by thin dielectric films deposited over a positive birefringent crystal for waveguide parameters below usual cutoff is discussed. This additional kind of guided wave has a hybrid nature and occurs in properly tailored waveguides when a suitable orientation of the crystal optical axis, relative to the waveguide axis, is taken. The dependence of the allowed orientations on various waveguide parameters has been analyzed. Noticeable fast variations, with potential interest for switching applications, have been found.Peer ReviewedPostprint (published version

Radio emission of SN1993J. The complete picture: II. Simultaneous fit of expansion and radio light curves

We report on a simultaneous modelling of the expansion and radio light curves of SN1993J. We have developed a simulation code capable of generating synthetic expansion and radio light curves of supernovae by taking into consideration the evolution of the expanding shock, magnetic fields, and relativistic electrons, as well as the finite sensitivity of the interferometric arrays used in the observations. Our software successfully fits all the available radio data of SN 1993J with an standard emission model for supernovae extended with some physical considerations, as an evolution in the opacity of the ejecta material, a radial drop of the magnetic fields inside the radiating region, and a changing radial density profile of the circumstellar medium beyond day 3100 after explosion.Comment: 12 pages, 12 figures, accepted for publication in A&

Estandarización del presupuesto plurianual de costos de mantenimiento y sus determinantes en la industria del Oil & Gas

El presupuesto de mantenimiento y de operación de los ductos y estaciones en el sector del Oil & Gas es una de las variables más relevantes para cualquier organización ya que esta infraestructura hace posible el transporte de los productos, especialmente cuando dichos activos afrontan la topografía colombiana -- La necesidad de evacuar la creciente producción de crudos y refinados ha aumentado la infraestructura de forma importante y por ende ha hecho que la industria pase de una vista fragmentada de plantas y ductos a una de procesos empresariales interrelacionados entre las compañías del sector, de tal forma que las técnicas del ejercicio presupuestario han cambiado en parte las técnicas del ejercicio presupuestario -- El objetivo de este artículo es investigar cuáles son los aspectos metodológicos que se tienen para generar el presupuesto y de este modo estandarizar los procesos al interior de la organización -- Una vez se recopile la información de costos de mantenimiento con la calidad deseada, se podrán realizar cálculos de indicadores más acertados y puede llegarse a obtener un modelo econométrico que permita determinar el impacto en costos y la generación de valor, visibilizando aquellos procesos empresariales que requieren un replanteamiento en su esquema de operación, o la aplicación de transferencias cruzadas, como por ejemplo,subsidio

Viability study of sailing propulsion combined with a conventional system

For many years now, sails have been used as a propulsion system. At present, they are restricted to recreational/sport crafts since the appearance of the first steam vessels in the beginning of the 19 th century. But in the last years, due to the increase of fuel price and the pollution of the environment, it is being studied the possibility to introduce again the sail as a propulsive method combined with other conventional systems. In this paper, it is studied the viability of using a sail as a propellant with other conventional systems of propulsion. After considering the concept of apparent wind, the range of use of this complementary propulsion is presented. The calculation methodology, the numerical simulations and the wind inputs from a specific route are also included