120 research outputs found
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
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
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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
Quaternary climate modulation of Pb isotopes in the deep Indian Ocean linked to the Himalayan chemical weathering
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