| 421. |
|
|
| 422. |
|
|
| 423. |
- Rosenberg, Philip D., et al.
(författare)
-
Quantifying particle size and turbulent scale dependence of dust flux in the Sahara using aircraft measurements
- 2014
-
Ingår i: Journal of Geophysical Research - Atmospheres. - 2169-897X .- 2169-8996. ; 119:12, s. 7577-7598
-
Tidskriftsartikel (refereegranskat)abstract
- The first size-resolved airborne measurements of dust fluxes and the first dust flux measurements from the central Sahara are presented and compared with a parameterization by Kok (2011a). High-frequency measurements of dust size distribution were obtained from 0.16 to 300 mu m diameter, and eddy covariance fluxes were derived. This is more than an order of magnitude larger size range than previous flux estimates. Links to surface emission are provided by analysis of particle drift velocities. Number flux is described by a -2 power law between 1 and 144 mu m diameter, significantly larger than the 12 mu m upper limit suggested by Kok (2011a). For small particles, the deviation from a power law varies with terrain type and the large size cutoff is correlated with atmospheric vertical turbulent kinetic energy, suggesting control by vertical transport rather than emission processes. The measured mass flux mode is in the range 30-100 mu m. The turbulent scales important for dust flux are from 0.1 km to 1-10 km. The upper scale increases during the morning as boundary layer depth and eddy size increase. All locations where large dust fluxes were measured had large topographical variations. These features are often linked with highly erodible surface features, such as wadis or dunes. We also hypothesize that upslope flow and flow separation over such features enhance the dust flux by transporting large particles out of the saltation layer. The tendency to locate surface flux measurements in open, flat terrain means these favored dust sources have been neglected in previous studies.
|
|
| 424. |
- Rosenberg, T. M., et al.
(författare)
-
Humid periods in southern Arabia : Windows of opportunity for modern human dispersal
- 2011
-
Ingår i: Geology. - 0091-7613 .- 1943-2682. ; 39:12, s. 1115-1118
-
Tidskriftsartikel (refereegranskat)abstract
- Arabia is a key area for the dispersal of anatomically modern humans (AMH, Homo sapiens) out of Africa. Given its modern hostile environment, the question of the timing of dispersal is also a question of climatic conditions. Fresh water and food were crucial factors facilitating AMH expansions into Arabia. By dating relict lake deposits, four periods of lake formation were identified: one during the early Holocene and three during the late Pleistocene centered ca. 80, ca. 100, and ca. 125 ka. Favorable environmental conditions during these periods allowed AMH to migrate across southern Arabia. Between ca. 75 and 10.5 ka, arid conditions prevailed and turned southern Arabia into a natural barrier for human dispersal. Thus, expansion of AMH through the southern corridor into Asia must have taken place before 75 ka, possibly in multiple dispersals.
|
|
| 425. |
|
|
| 426. |
- Schroeder, Kari B., et al.
(författare)
-
Haplotypic background of a private allele at high frequency in the Americas
- 2009
-
Ingår i: Molecular biology and evolution. - : Oxford University Press (OUP). - 0737-4038 .- 1537-1719. ; 26:5, s. 995-1016
-
Forskningsöversikt (refereegranskat)abstract
- Recently, the observation of a high-frequency private allele,the 9-repeat allele at microsatellite D9S1120, in all sampledNative American and Western Beringian populations has been interpretedas evidence that all modern Native Americans descend primarilyfrom a single founding population. However, this inference assumedthat all copies of the 9-repeat allele were identical by descentand that the geographic distribution of this allele had notbeen influenced by natural selection. To investigate whetherthese assumptions are satisfied, we genotyped 34 single nucleotidepolymorphisms across 500 kilobases (kb) around D9S1120 in 21Native American and Western Beringian populations and 54 otherworldwide populations. All chromosomes with the 9-repeat alleleshare the same haplotypic background in the vicinity of D9S1120,suggesting that all sampled copies of the 9-repeat allele areidentical by descent. Ninety-one percent of these chromosomesshare the same 76.26 kb haplotype, which we call the "AmericanModal Haplotype" (AMH). Three observations lead us to concludethat the high frequency and widespread distribution of the 9-repeatallele are unlikely to be the result of positive selection:1) aside from its association with the 9-repeat allele, theAMH does not have a high frequency in the Americas, 2) the AMHis not unusually long for its frequency compared with otherhaplotypes in the Americas, and 3) in Latin American mestizopopulations, the proportion of Native American ancestry at D9S1120is not unusual compared with that observed at other genomewidemicrosatellites. Using a new method for estimating the timeto the most recent common ancestor (MRCA) of all sampled copiesof an allele on the basis of an estimate of the length of thegenealogy descended from the MRCA, we calculate the mean timeto the MRCA of the 9-repeat allele to be between 7,325 and 39,900years, depending on the demographic model used. The resultssupport the hypothesis that all modern Native Americans andWestern Beringians trace a large portion of their ancestry toa single founding population that may have been isolated fromother Asian populations prior to expanding into the Americas.
|
|
| 427. |
- Schweinsberg, Martin, et al.
(författare)
-
Same data, different conclusions : Radical dispersion in empirical results when independent analysts operationalize and test the same hypothesis
- 2021
-
Ingår i: Organizational Behavior and Human Decision Processes. - : Elsevier BV. - 0749-5978 .- 1095-9920. ; 165, s. 228-249
-
Tidskriftsartikel (refereegranskat)abstract
- In this crowdsourced initiative, independent analysts used the same dataset to test two hypotheses regarding the effects of scientists' gender and professional status on verbosity during group meetings. Not only the analytic approach but also the operationalizations of key variables were left unconstrained and up to individual analysts. For instance, analysts could choose to operationalize status as job title, institutional ranking, citation counts, or some combination. To maximize transparency regarding the process by which analytic choices are made, the analysts used a platform we developed called DataExplained to justify both preferred and rejected analytic paths in real time. Analyses lacking sufficient detail, reproducible code, or with statistical errors were excluded, resulting in 29 analyses in the final sample. Researchers reported radically different analyses and dispersed empirical outcomes, in a number of cases obtaining significant effects in opposite directions for the same research question. A Boba multiverse analysis demonstrates that decisions about how to operationalize variables explain variability in outcomes above and beyond statistical choices (e.g., covariates). Subjective researcher decisions play a critical role in driving the reported empirical results, underscoring the need for open data, systematic robustness checks, and transparency regarding both analytic paths taken and not taken. Implications for orga-nizations and leaders, whose decision making relies in part on scientific findings, consulting reports, and internal analyses by data scientists, are discussed.
|
|
| 428. |
|
|
| 429. |
- Skei, J, et al.
(författare)
-
Eutrophication and contaminants in aquatic ecosystems
- 2000
-
Ingår i: Ambio: a Journal of Human Environment. - 0044-7447. ; 29:4-5, s. 184-194
-
Tidskriftsartikel (refereegranskat)abstract
- Eutrophication and persistent pollutants are two of the main environmental problems in European marine and freshwater ecosystems. As they tend to co-occur, interactive processes between eutrophication and contaminants are suggested, that may lead to environmental effects that cannot be predicted from each process alone. In order to predict the consequences of remedial measures (changing the input of organic matter, nutrients and contaminants) it is important to understand mechanisms that alter the bioavailability and fate of contaminants. The environmental risks will depend on the speciation of contaminants and their association to media and matter and by that means affect exposure. Furthermore, the risks will depend on the mobility of the substances and their pathways in food chains. In 1995, the Swedish Environmental Protection Agency initiated a 5-year research program Interactions between EUtrophication and CONtaminants (EUCON). A background document was prepared listing a number of relevant questions and hypotheses. On the basis of this document a program was launched, addressing the problems related to the interaction between eutrophication and contaminants (persistent organic compounds and trace metals) in the marine environment, with focus on the Baltic Sea, and in lakes. This paper summarizes the state-of-the-art, hypotheses and highlights from the research program with emphasis on the implications and applications of the results.
|
|
| 430. |
|
|
