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Temperature Oscillations (temperature + oscillation)
Selected AbstractsHistorical changes in the phenology of British Odonata are related to climateGLOBAL CHANGE BIOLOGY, Issue 5 2007CHRISTOPHER HASSALL Abstract Responses of biota to climate change take a number of forms including distributional shifts, behavioural changes and life history changes. This study examined an extensive set of biological records to investigate changes in the timing of life history transitions (specifically emergence) in British Odonata between 1960 and 2004. The results show that there has been a significant, consistent advance in phenology in the taxon as a whole over the period of warming that is mediated by life history traits. British odonates significantly advanced the leading edge (first quartile date) of the flight period by a mean of 1.51 ±0.060 (SEM, n=17) days per decade or 3.08±1.16 (SEM, n=17) days per degree rise in temperature when phylogeny is controlled for. This study represents the first review of changes in odonate phenology in relation to climate change. The results suggest that the damped temperature oscillations experienced by aquatic organisms compared with terrestrial organisms are sufficient to evoke phenological responses similar to those of purely terrestrial taxa. [source] Thermal reservoir modeling in petroleum geomechanicsINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 4 2009Shunde Yin Abstract Thermal oil recovery processes involve high pressures and temperatures, leading to large volume changes and induced stresses. These cannot be handled by traditional reservoir simulation because it does not consider coupled geomechanics effects. In this paper we present a fully coupled, thermal half-space model using a hybrid DDFEM method. A finite element method (FEM) solution is adopted for the reservoir and the surrounding thermally affected zone, and a displacement discontinuity method is used for the surrounding elastic, non-thermal zone. This approach analyzes stress, pressure, temperature and volume change in the reservoir; it also provides stresses and displacements around the reservoir (including transient ground surface movements) in a natural manner without introducing extra spatial discretization outside the FEM zone. To overcome spurious spatial temperature oscillations in the convection-dominated thermal advection,diffusion problem, we place the transient problem into an advection,diffusion,reaction problem framework, which is then efficiently addressed by a stabilized finite element approach, the subgrid-scale/gradient subgrid-scale method. Copyright © 2008 John Wiley & Sons, Ltd. [source] Investigation of the temperature oscillations in the cylinder walls of a diesel engine with special reference to the limited cooled caseINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 11 2004C. D. Rakopoulos Abstract This work investigates the interesting phenomenon of the temperature (cyclic) oscillations in the combustion chamber walls of a diesel engine. For this purpose, a comprehensive simulation code of the thermodynamic cycle of the engine is developed taking into account both the closed and the open parts of it. The energy and state equations are applied, with appropriate combustion, gas heat transfer, and mass exchange with the atmosphere sub-models, to yield cylinder pressure, local temperatures and heat release histories as well as various performance parameters of the engine. The model is appropriately coupled to a wall periodic conduction model, which uses the gas temperature variation as boundary condition throughout the engine cycle after being treated by Fourier analysis techniques. It is calibrated against measurements, at various load and speed conditions, from an experimental work carried out on a direct injection (DI), naturally aspirated, four-stroke, diesel engine located at the authors' laboratory, which has been reported in detail previously. After gaining confidence into the predictive capabilities of the model, it is used to investigate the phenomenon further, thus providing insight into many interesting aspects of transient engine heat transfer, as far as the influence that engine wall material properties have on the values of cyclic temperature swings. These swings can take prohibitive values causing high wall thermal fatigue, when materials of specific technological interest such as thermal insulators (ceramics) are used, and may lead to deterioration in engine performance. Copyright © 2004 John Wiley & Sons, Ltd. [source] Did ciguatera prompt the late Holocene Polynesian voyages of discovery?JOURNAL OF BIOGEOGRAPHY, Issue 8 2009Teina Rongo Abstract The famous Polynesian voyages characterized an intensive network of cultural exchange and colonization that was particularly active from ad 1000 to 1450. But, why would large groups of people leave their homelands to voyage into the unknown? Oceanic voyages are risky, albeit less so today than in the past. Landfalls were not guaranteed improvements over ports of departure. Taking the Cook Islands as an example, we ask whether harmful algal blooms that result in ciguatera fish poisoning in humans prompted past and present emigration pulses of peoples from within Polynesia. We take a multipronged approach to examine our hypothesis, involving: (1) archaeological evidence, (2) ciguatera fish poisoning reports since the 1940s, and (3) climate and temperature oscillations using palaeodatasets. The archaeological records of fish bones and hooks show abrupt changes in fishing practices in post- ad 1450 records. Sudden dietary shifts are not linked to overfishing, but may be a sign of ciguatera fish poisoning and adjustment of fishing preference. While fishes form the staple diet of Polynesians, such poisoning renders fishes unusable. We show that ciguatera fish poisoning events coincide with Pacific Decadal Oscillations and suggest that the celebrated Polynesian voyages across the Pacific Ocean may not have been random episodes of discovery to colonize new lands, but rather voyages of necessity. A modern analogue (in the 1990s) was the shift towards processed foods in the Cook Islands during ciguatera fish poisoning events, and mass emigration of islanders to New Zealand and Australia. [source] Holocene vegetation and land-use changes in response to climatic changes in the forelands of the southwestern Alps, Italy,JOURNAL OF QUATERNARY SCIENCE, Issue 3 2006Walter Finsinger Abstract The Holocene sediment of Lago Piccolo di Avigliana (Piedmont, Italy, 356,m,a.s.l.) was dated by 14C and analysed for pollen to reconstruct the vegetation history of the area. The early- and mid-Holocene pollen record shows environmental responses to centennial-scale climatic changes as evidenced by independent palaeoclimatic proxies. When human impact was low or negligible, continental mixed-oak forests decreased at ca. 9300 BC in response to the early-Holocene Preboreal climatic oscillation. Abies alba expanded in two phases, probably in response to higher moisture availability at ca. 6000 and ca. 4000 BC, while Fagus expanded later, possibly in response to a climatic change at 3300 BC. During and after the Bronze Age five distinct phases of intensified land use were detected. The near synchroneity with the land-use phases detected in wetter regions in northern and southern Switzerland points to a common forcing factor in spite of cultural differences. Increasing minerogenic input to the lake since 1000 BC coincided with Late Bronze,Iron Age technical innovations and probably indicate soil erosion as a consequence of deforestation in the lake catchment. The highest values for cultural indicators occurred at 700,450 and at 300,50 BC, coinciding with periods of high solar activity (inferred from ,14C). This suggests that Iron Age land use was enhanced by high solar activity, while re-occupation of partly abandoned areas after crises in earlier periods match better with the GRIP stable isotope record. On the basis of our data and comparison with independent palaeoclimatic proxies we suggest that precipitation variation was much more important than temperature oscillations in driving vegetation and societal changes throughout the Holocene. Copyright © 2006 John Wiley & Sons, Ltd. [source] Palaeovegetational and palaeoenvironmental trends in the summit of the Guaiquinima massif (Venezuelan Guayana) during the Holocene,JOURNAL OF QUATERNARY SCIENCE, Issue 2 2005Valentí Rull Abstract The summits of the table mountains (tepuis) from the Neotropical Guayana region are remote environments suitable for palaeoecological studies with evolutionary, biogeographical and palaeoclimatic implications. Here, using palynological analyses of two radiocarbon-dated peat bogs from a tepui summit, the Holocene palaeovegetational trends are reconstructed, and related to possible forcing factors. Because of the pristine character of the Guaiquinima summit, the recorded palaeoenvironmental changes are probably due to natural causes, which makes them valuable archives of the natural component of climatic change at a millennial time scale. The sequence begins with pioneer communities or meadows similar to present-day ones, between about 8.4 and 4.5,ky BP. After this date, and until about 2,kyr BP the expansion of gallery forests suggests an increase in precipitation, documented also at regional (Neotropical) level. Between ca. 2,kyr BP and the last century, gallery forests are replaced by forests characteristic of the upper Guaiquinima altitudes, coinciding with a regional phase of reduced moisture. The present-day meadows, established relatively quickly during the last century, substituted the former upland forests. In the locality studied, the main controlling factor of the vegetation during the Holocene seems to have been the moisture balance. In contrast to other tepui summits, there is no clear evidence for changes linked to temperature oscillations. This could be due to the elevation of the site, far from any characteristic ecological boundary, that makes it insensitive to this parameter. Copyright © 2005 John Wiley & Sons, Ltd. [source] | |||||||||||||