957 resultados para Tucídides, ca. 460-ca. 400 a. C.
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Cretaceous-Tertiaty (K-T) boundary (ca. 65 Ma) sections on a Southwest Pacific island containing dinosaurs were unknown until March 2003 when theropod bones were recovered from the Takatika Grit on the remote Chatham Islands (latitude 44 degrees S, longitude 176 degrees W), along the Chatham Rise. Tectonic and palaeontologic evidence support the eastward extension of a ca. 900 km land bridge that connected the islands to what is now New Zealand prior to the K-T boundary. The Chathams terrestrial fauna inhabited coastal, temperate environments along a low-lying, narrow, crustal extension of the New Zealand subcontinent, characterised by a tectonically dynamic, volcanic landscape with eroding hills (horsts) adjacent to flood plains and deltas, all sediments accumulating in grabens. This finger-like tract was blanketed with a conifer and clubmoss (Lycopodiopsida) dominated forest. The Chatham Islands region would have, along with New Zealand, provided a dinosaur island sanctuary after separating from the Gondwana margin ca. 80 Ma. (c) 2005 Elsevier B.V. All rights reserved.
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Growth, Condition Index (CI) and survival of the pearl oysters, Pinctada maxima and R margaritifera, were measured in three size groups of oysters over 14 months at two dissimilar environments in the Great Barrier Reef lagoon. These were the Australian Institute of Marine Science (AIMS) in a mainland bay and Orpheus Island Research Station (OIRS) in coral reef waters. Temperature, suspended particulate matter (SPM) and particulate organic matter (POM) were monitored during the study. Temperature at AIMS fluctuated more widely than at OIRS both daily and seasonally, with annual ranges 20-31 degrees C and 22-30 degrees C, respectively. Mean SPM concentration at AIMS (11.1 mg l(-1)) was much higher than at OIRS (1.4 mg l(-1)) and fluctuated widely (2-60 mg l(-1)). Mean POM level was also substantially higher at AIMS, being 2.1 mg l(-1) compared with 0.56 mg l(-1) at OIRS. Von Bertalatiffy growth curve analyses showed that P. maxima grew more rapidly and to larger sizes than P. margaritifera at both sites. For the shell height (SH) of R maxima, growth index phi'=4.31 and 4.24, asymptotic size SHinfinity = 229 and 205 mm, and time to reach 120 mm SH (T-(120))= 1.9 and 2.1 years at AIMS and OIRS, respectively. While for P margaritifera, phi'=4.00 and 4.15, SHinfinity = 136 and 157 mm, and T-(120) = 2.5 and 3.9 years at AIMS and OIRS, respectively. R maxima had significantly lower growth rates and lower survival of small oysters during winter compared with summer. There were, however, no significant differences between the two sites in growth rates of P. maxima and final Cl values. In contrast, P. margaritifiera showed significant differences between sites and not seasons, with lower growth rates, survival of small oysters, final Cl values and asymptotic sizes at AIMS. The winter low temperatures, but not high SPM at AIMS, adversely affected P. maxima. Conversely, the high SPM levels at AIMS, but not temperature, adversely affected P. margaritifera. This was in accordance with earlier laboratory-based energetics studies of the effects of temperature and SPM on these two species. P maxima has potential to be commercially cultured in ca. > 25 degrees C waters with a wide range of SPM levels, including oligotrophic coral reef waters with appropriate particle sizes. It is possible to culture R margaritifera in turbid conditions, but its poor performance in these conditions makes commercial culture unlikely. (c) 2005 Elsevier B.V. All rights reserved.
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Accurate dating of lagoon sediments has been a difficult problem, although lagoon profiles, usually with high deposition rates, have a great potential for high-resolution climate reconstruction. We report 26 high-precision TIMS U-series dates (on 25 coral branches) and five AMS C-14 dates (on foraminifera) for a 15.4-m long lagoon core from Yongshu Reef, Nansha area, southern South China Sea. All the dates are in the correct stratigraphical sequence, providing the best chronology so far reported for lagoon deposits. The results reveal a similar to 4000-a continuous depositional history, with sedimentation rates varying from 0.8 to 24.6 mm a(-1), with an average of 3.85 mm a(-1), which corresponds to an average net carbonate accumulation rate of similar to 2700 g CaCO3 m(-2) a(-1), significantly higher than the mean value (800 +/- 400 g CaCO3 m(-2) a(-1)) used for lagoons in general in previous studies of global carbonate budget. Episodes of accelerated depositions within the last 1000 years correlate well with strong storm events identified by U-series dates of storm-transported coral blocks in the area. However, in the longer term, the sedimentation rates during the past 1000 years were much higher than earlier on, probably due to more vigorous wave-reef interaction as a result of relative sea-level fall since 500 AD and expansion of reef flat area, supplying more sediments. The coral TIMS U-series ages and foraminifera AMS 14C dates reveal intriguing apparent radiocarbon reservoir ages (R) from 572 to 1052 years, which are much higher than global mean values of similar to 400 years. (c) 2006 Elsevier Ltd. All rights reserved.
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The fatigue-crack propagation and threshold behaviour of a C-Mn steel containing boron has been investigated at a range of strength levels suitable for mining chain applications. The heat-treatment variables examined include two austenitizing temperatures (900 degree C and 1250 degree C) and a range of tempering treatments from the as-quenched condition to tempering at 400 degree C. In mining applications the haulage chains undergo a 'calibration' process which has the effect of imposing a tensile prestrain on the chain links before they go into service. Prestrain is shown to reduce threshold values in these steels and this behaviour is related to its effects on the residual stress distribution in the test specimens.
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Ocean acidification is predicted to have widespread implications for marine bivalve mollusks. While our understanding of its impact on their physiological and behavioral responses is increasing, little is known about their reproductive responses under future scenarios of anthropogenic climate change. In this study, we examined the physiological energetics of the Manila clam Ruditapes philippinarum exposed to CO2-induced seawater acidification during gonadal maturation. Three recirculating systems filled with 600 L of seawater were manipulated to three pH levels (8.0, 7.7, and 7.4) corresponding to control and projected pH levels for 2100 and 2300. In each system, temperature was gradually increased ca. 0.3 °C per day from 10 to 20 °C for 30 days and maintained at 20 °C for the following 40 days. Irrespective of seawater pH levels, clearance rate (CR), respiration rate (RR), ammonia excretion rate (ER), and scope for growth (SFG) increased after a 30-day stepwise warming protocol. When seawater pH was reduced, CR, ratio of oxygen to nitrogen, and SFG significantly decreased concurrently, whereas ammonia ER increased. RR was virtually unaffected under acidified conditions. Neither temperature nor acidification showed a significant effect on food absorption efficiency. Our findings indicate that energy is allocated away from reproduction under reduced seawater pH, potentially resulting in an impaired or suppressed reproductive function. This interpretation is based on the fact that spawning was induced in only 56% of the clams grown at pH 7.4. Seawater acidification can therefore potentially impair the physiological energetics and spawning capacity of R. philippinarum.
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a) In der horizontalen Verbreitung sind die vorwiegend kalkschaligen Benthos-Foraminiferen im Untersuchungsgebiet auf zwei Faciesbereiche verteilt: 1. Eine sandige Facies mit stärkeren Temperatur- und Salzgehaltschwankungen; Wasseroberfläche t = 2O-17°C, Salzgehalt nie über 32 per mil, Meerestiefe 30 bis 92 m. 2. Schlick-Facies mit zum Teil feinsandigen Beimengungen. Temperatur- und Salzgehaltschwankungen sind geringer; Wasseroberfläche t = ca. 4O-15° C, Salzgehalt bis 34 per mil, Meerestiefe 135-548 m. b) Einige Stoßröhren-Proben (Station 18, 21, 27, 28) zeigen in ihrer vertikalen Verbreitung auffallende Faunenunterschiede. c) Im Profil des Lotkerns wechseln in der Foraminiferenfauna Bolivinen- und Cassidulinen-Nonioninen-Provinzen miteinander ab. Die Profile der beiden tiefsten Stoßröhren-Kerne (Station 23, 26; s. Tab. I) stimmen in ihrer Mikrofauna mit der des oberen Teils des Lotkerns (s. Tab. 4) überein. d) Die unter b und C angefuührten Faunenwechsel werden auf langperiodische Klimaerwärmungen im skandinavischen Raum und den damit verbundenen Anstieg des Meeresspiegels zurückgeführt. e) Der Lotkern kann mit Hilfe von Untersuchungsergebnissen aus seiner näheren Umgebung (Bohuslän, Oslofjord) nur bedingt in ein stratigraphisches, durch Megafossilien belegtes Schema eingefügt werden, da er nach unten durch die Mikrofauna keine echte Begrenzung aufweist. Durch die Einwanderung mehrerer Foraminiferenarten mit boreal-lusitanischer Verbreitung in die Untersuchungsgebiete wird der Lotkern in die Isocardia-Absätze (Atlanticum-oberes Subboreal) eingegliedert. f) Aus einer Tabelle von PRATJE(1940) kann entnommen werden, da dieser Zeitabschnitt nach DE GEER etwa um 5000 v.Chr. beginnt. Danach beträgt die geringste Sedimentation, die in dem Kerngebiet nach dieser Zeitrechnung möglich ist, bei einer Eindringtiefe des Lots von 10 m ungefähr 1,40 m pro Jahrtausend. Wahrscheinlich wird dieses Ma etwas größer sein.
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Chironomid headcapsules were used to reconstruct late glacial and early-Holocene summer temperatures at Lago Piccolo di Avigliana (LPA). Two training sets (northern Sweden, North America) were used to infer temperatures. The reconstructed patterns of temperature change agreed well with the GRIP and NGRIP d18O records. Inferred temperatures were high during the Bølling (ca 19 °C), slowly decreased to ca 17.5 °C during the Allerød, reached lowest temperatures (ca 16 °C) during the Younger Dryas, and increased to ca. 18.5 °C during the Preboreal. The amplitudes of change at climate transitions (i.e. Oldest Dryas/Bølling: 3 °C, Allerød/Younger Dryas: 1.5 °C, and Younger Dryas/Preboreal: 2.5 °C) were smaller than in the northern Alps but similar to those recorded at another site in northeastern Italy. Our results suggest that (1) Allerød temperatures were higher in the southern Alps and (2) higher during the Preboreal (1 °C) than during the Allerød. These differences might provide an explanation for the different responses of terrestrial-vegetation to late glacial and early-Holocene climatic changes in the two regions. Other sites on both sides of the Alps should be studied to confirm these two hypotheses.
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Analysis of the word lancea, of Hispanic origin after Varro, and of place names, people´s names and personal names derived from it. It confirms that the spear was the most important weapon in the Bronze Age, belonging to the iuventus and used as heroic and divine symbol. This analysis confirms also the personality of the Lusitanians, a people related to the Celts but with more archaic archaeological, linguistic and cultural characteristics originated in the tradition of the Atlantic Bronze in the II millennium BC. It is also relevant to better know the organisation of Broze and Iron Age societies and the origin of Indo-Europeans peoples in Western Europe and of pre-Roman peoples of Iberia.
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En el presente artículo analizamos los desplazamientos de cultos indígenas hispanos desde distintas áreas de la Península Ibérica hacia los principales lugares de inmigración en Hispania: las áreas mineras y las ciudades. Proponemos que estos grupos de emigrantes rendían culto en su nueva residencia a las deidades que veneraban en sus regiones de procedencia como un medio de preservar su cohesión social y su identidad cultural. La dureza de la vida laboral en las áreas mineras reforzaba la necesidad de fortalecer los lazos culturales.
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The governance of climate adaptation involves the collective efforts of multiple societal actors to address problems, or to reap the benefits, associated with impacts of climate change. Governing involves the creation of institutions, rules and organizations, and the selection of normative principles to guide problem solution and institution building. We argue that actors involved in governing climate change adaptation, as climate change governance regimes evolve, inevitably must engage in making choices, for instance on problem definitions, jurisdictional levels, on modes of governance and policy instruments, and on the timing of interventions. Yet little is known about how and why these choices are made in practice, and how such choices affect the outcomes of our efforts to govern adaptation. In this introduction we review the current state of evidence and the specific contribution of the articles published in this Special Feature, which are aimed at bringing greater clarity in these matters, and thereby informing both governance theory and practice. Collectively, the contributing papers suggest that the way issues are defined has important consequences for the support for governance interventions, and their effectiveness. The articles suggest that currently the emphasis in adaptation governance is on the local and regional levels, while underscoring the benefits of interventions and governance at higher jurisdictional levels in terms of visioning and scaling-up effective approaches. The articles suggest that there is a central role of government agencies in leading governance interventions to address spillover effects, to provide public goods, and to promote the long-term perspectives for planning. They highlight the issue of justice in the governance of adaptation showing how governance measures have wide distributional consequences, including the potential to amplify existing inequalities, access to resources, or generating new injustices through distribution of risks. For several of these findings, future research directions are suggested.
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The Hainholz quarry in the Osterwald hills of NW-Germany is the most impressive outcrop in the Lower Saxony Basin exposing Late Jurassic (Korallenoolith, Oxfordian) coral buildups. The Korallenoolith deposits in the quarry commence with a oolitic sequence about 20 m thick which is limited by a distinctive hardground at its top. This sequence is overlain by the so called “Obere Korallenbank”-Member about 13 m in thickness which is mainly build up by coral reef complexes. Throughout a lateral extend of about 400 m exposed in the quarry, the Obere Korallenbank Member shows numerous pillar-shaped reefal build ups which are flanked by a reefal debris limestone. The coral fauna of the in situ reefal bioconstructions comprises not less than 37 taxa most of which have been described from the Lower Saxony Basin for the first time. Probably, the pillar-shaped reefs formed a small positive relief of only a few dm against the debris deposits during deposition. The interreef debris limestones in the lower and middle part of the Obere Korallenbank Member show three intercalated biostromal coral layers. In the upper part of the member, the interreef facies is represented by a mikritic peloidal limestone rich in sponge remains and, unusual in such a depositional environment, ammonites (Dichotomo-sphinctes bifurcatoides, D. sp.). Additionaly, at the top of of the peloidal limestone a layer enriched in nerineids and other gastropods limits the reefal constructions of the Obere Korallenbank Member against the overlying “humeralis-Oolith” sequence. On the basis of the facies development of this depositional sequence the reef formation in relation to sealevel changes is discussed.
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Académico - Licenciaturas
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La tuberculosis TB es una de las principales causas de muerte en el mundo en individuos con infección por VIH. En Colombia esta coinfección soporta una carga importante en la población general convirtiéndose en un problema de salud pública. En estos pacientes las pruebas diagnósticas tienen sensibilidad inferior y la enfermedad evoluciona con mayor frecuencia hacia formas diseminadas y rápidamente progresivas y su diagnóstico oportuno representa un reto en Salud. El objetivo de este proyecto es evaluar el desempeño de las pruebas diagnósticas convencionales y moleculares, para la detección de TB latente y activa pacientes con VIH, en dos hospitales públicos de Bogotá. Para TB latente se evaluó la concordancia entre las pruebas QuantiFERON-TB (QTF) y Tuberculina (PPD), sugiriendo superioridad del QTF sobre la PPD. Se evaluaron tres pruebas diagnósticas por su sensibilidad y especificidad, baciloscopia (BK), GenoType®MTBDR plus (Genotype) y PCR IS6110 teniendo como estándar de oro el cultivo. Los resultados de sensibilidad (S) y especificidad (E) de cada prueba con una prevalencia del 19,4 % de TB pulmonar y extrapulmonar en los pacientes que participaron del estudio fue: BK S: 64% E: 99,1%; Genotype S: 77,8% E: 94,5%; PCRIS6110 S: 73% E: 95,5%, de la misma forma se determinaron los valores predictivos positivos y negativos (VPP y VPN) BK: 88,9% y 94,8%, Genotype S: 77,8% E: 94,5%; PCRIS6110 S: 90% y 95,7%. Se concluyó bajo análisis de curva ROC que las pruebas muestran un rendimiento diagnóstico similar por separado en el diagnóstico de TB en pacientes con VIH, aumentando su rendimiento diagnostico cuando se combinan