150 research outputs found
Comparative analysis and optimization of technical and weight parameters of turbo-electric propulsion systems
According to Flightpath 2050, the aviation industry is aiming to substantially reduce emissions over the coming decades. One possible solution to meet these ambitious goals is by moving to hybrid-electric drivetrain architectures which require the electric components to be extremely lightweight and efficient at the same time. It has been claimed in several publications that cryogenic and in particular superconducting components can help to fulfill such requirements that potentially cannot be achieved with non-cryogenic components. The purpose of this work was to make a fair comparison between a cryogenic turbo-electric propulsion system (CEPS) and a non-cryogenic turbo-electric propulsion system (TEPS) on a quantitative level. The results on the CEPS were presented in detail in a previous publication. The focus of this publication is to present the study on the TEPS, which in conclusion allows a direct comparison. For both systems the same top-level aircraft requirements were used that were derived within the project TELOS based on an exemplary mission profile and the physical measures of a 220-passenger aircraft. Our study concludes that a CEPS could be 10% to 40% lighter than a TEPS. Furthermore, a CEPS could have a total efficiency gain of up to 18% compared to a similar TEPS
Decadal-centennial scale monsoon variations in the Arabian Sea during the Early Holocene
An essential prerequisite for the prediction of future climate change due to anthropogenic input is an understanding of the natural processes that control Earth's climate on timescales comparable to human-lifespan. The Early Holocene period was chosen to study the natural climate variability in a warm interval when solar insolation was at its maximum. The monsoonal system of the Tropics is highly sensitive to seasonal variations in solar insolation, and consequently marine sediments from the region are a potential monitor of past climate change. Here we show that during the Early Holocene period rapid
Brownian markets
Financial market dynamics is rigorously studied via the exact generalized
Langevin equation. Assuming market Brownian self-similarity, the market return
rate memory and autocorrelation functions are derived, which exhibit an
oscillatory-decaying behavior with a long-time tail, similar to empirical
observations. Individual stocks are also described via the generalized Langevin
equation. They are classified by their relation to the market memory as heavy,
neutral and light stocks, possessing different kinds of autocorrelation
functions
Coupled sea surface temperature-seawater delta O-18 reconstructions in the Arabian Sea at the millennial scale for the last 35 ka
Two sediment cores from the western (905; 10.46°9′N, 51.56°4′E, water depth 1586 m) and eastern (SK17; 15°15′N, 72°58′E, water depth 840 m) Arabian Sea were used to study past sea surface temperatures (SST) and seawater δ 18O (δ 18Ow) variations for the past 35 ka. We used coupled Mg/Ca-δ 18O calcite variability in two planktonic foraminiferal species: Globigerinoides ruber, which thrives throughout the year, and Globigerina bulloides, which occurs mainly when surface waters contain high nutrients during upwelling or convective mixing. SSTs in both areas based on Mg/Ca in G. ruber were ∼3 to 4°C lower during the Last Glacial Maximum (LGM; ∼21 ka) than today and the Holocene period. The SST records based on G. bulloides also indicate general cooling, down to 18°C in both areas. SSTs in the western Arabian Sea based on G. bulloides were always lower than those based on G. ruber, indicating the presence of strong seasonal temperature contrast during the Holocene and LGM. We interpret the consistent presence of this seasonal temperature contrast to reflect a combination of seasonal summer upwelling (SW monsoon) and winter convective mixing (NE monsoon) in the western Arabian Sea. In the eastern Arabian Sea, G. bulloides-based SSTs were slightly lower (about 1°C) than G. ruber-based SSTs during the Holocene, indicating the almost absence of a seasonal temperature gradient, similar to today. However, a large seasonal temperature contrast occurred during the LGM which favors the assumption that strong NE monsoon winds forced winter upwelling or convective mixing offshore Goa. SST and δ 18Ow reconstructions reveal evidence of millennial-scale cycles, particularly in the eastern Arabian Sea. Here, the stadial periods (Northern Hemisphere cold periods such as Younger Dryas and Heinrich events) are marked by increasing SSTs and salty sea surface conditions relative to those during the interstadial periods. Indeed, the δ 18Ow record shows evidence of low-saline surface waters during interstadial periods, indicating increased freshwater runoff from the Western Ghats as a consequence of enhanced SW monsoon intensity
Precision of the current methods to measure the alkenone proxy UK'37 and absolute alkenone abundance in sediments : results of an interlaboratory comparison study
Measurements of the UK'37 index and the absolute abundance of alkenones in marine sediments are increasingly used in paleoceanographic research as proxies of past sea surface temperature and haptophyte (mainly coccolith-bearing species) primary productivity, respectively. An important aspect of these studies is to be able to compare reliably data obtained by different laboratories from a wide variety of locations. Hence the intercomparability of data produced by the research community is essential. Here we report results from an anonymous interlaboratory comparison study involving 24 of the leading laboratories that carry out alkenone measurements worldwide. The majority of laboratories produce data that are intercomparable within the considered confidence limits. For the measurement of alkenone concentrations, however, there are systematic biases between laboratories, which might be related to the techniques employed to quantify the components. The maximum difference between any two laboratories for any two single measurements of UK'37 in sediments is estimated, with a probability of 95%, to be <2.18C. In addition, the overall within-laboratory precision for the UK'37 temperature estimates is estimated to be <1.68C (95% probability). Similarly, from the analyses of alkenone concentrations the interlaboratory reproducibility is estimated at 32%, and the repeatability is estimated at 24%. The former is compared to a theoretical estimate of reproducibility and found to be excessively high. Hence there is certainly scope and a demonstrable need to improve reproducibility and repeatability of UK'37 and especially alkenone quantification data across the community of scientists involved in alkenone research
Sea surface temperatures of the western Arabian Sea during the last deglaciation.
In this study we present a sea surface temperature (SST) record from the western Arabian Sea for the last\ud
20,000 years. We produced centennial-scale d18O and Mg/Ca SST time series of core NIOP929 with focus on\ud
the glacial-interglacial transition. The western Arabian Sea is influenced by the seasonal NE and SW monsoon\ud
wind systems. Lowest SSTs occur during the SW monsoon season because of upwelling of cold water, and\ud
highest SSTs can be found in the low-productivity intermonsoon season. The Mg/Ca-based temperature record\ud
reflects the integrated SST of the SW and NE monsoon seasons. The results show a glacial-interglacial SST\ud
difference of 2C, which is corroborated by findings from other Arabian Sea cores. At 19 ka B.P. a yet\ud
undescribed warm event of several hundred years duration is found, which is also reflected in the d18O record. A\ud
second centennial-scale high SST/low d18O event is observed at 17 ka B.P. This event forms the onset of the\ud
stepwise yet persistent trend toward Holocene temperatures. Highest Mg/Ca-derived SSTs in the NIOP929\ud
record occurred between 13 and 10 ka B.P. Interglacial SST is 24C, indicating influence of upwelling. The\ud
onset of Arabian Sea warming occurs when the North Atlantic is experiencing minimum temperatures. The rapid\ud
temperature variations at 19, 17, and 13 ka B.P. are difficult to explain with monsoon changes alone and are\ud
most likely also linked to regional hydrographic changes, such as trade wind induced variations in warm water\ud
advection
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Precision of the current methods to measure the alkenone proxy U₃₇ K’ and absolute alkenone abundance in sediments: results of an interlaboratory comparison study
Measurements of the U₃₇ K’ index and the absolute abundance of alkenones in marine sediments are increasingly used in paleoceanographic research as proxies of past sea surface
temperature and haptophyte (mainly coccolith-bearing species) primary productivity, respectively. An
important aspect of these studies is to be able to compare reliably data obtained by different laboratories
from a wide variety of locations. Hence the intercomparability of data produced by the research
community is essential. Here we report results from an anonymous interlaboratory comparison study
involving 24 of the leading laboratories that carry out alkenone measurements worldwide. The majority
of laboratories produce data that are intercomparable within the considered confidence limits. For the measurement of alkenone concentrations, however, there are systematic biases between laboratories,
which might be related to the techniques employed to quantify the components. The maximum
difference between any two laboratories for any two single measurements of U₃₇ K’ in sediments is
estimated, with a probability of 95%, to be <2.1°C. In addition, the overall within-laboratory precision
for the U₃₇ K’ temperature estimates is estimated to be <1.6°C (95% probability). Similarly, from the
analyses of alkenone concentrations the interlaboratory reproducibility is estimated at 32%, and the
repeatability is estimated at 24%. The former is compared to a theoretical estimate of reproducibility
and found to be excessively high. Hence there is certainly scope and a demonstrable need to improve
reproducibility and repeatability of U₃₇ K’ and especially alkenone quantification data across the
community of scientists involved in alkenone research
Testing the alkenone D/H ratio as a paleo indicator of sea surface salinity in a coastal ocean margin (Mozambique Channel)
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