662 research outputs found
Reach-scale river dynamics moderate the impact of rapid Holocene climate change on floodwater farming in the desert Nile
Full text linkThe relationship between climate change and the development of Old World riverine civilizations is poorly understood because inadequate dating control has hindered effective integration of archaeological, fluvial, and climate records. This paper presents the most comprehensive and robustly dated archaeological and paleoenvironmental data sets yet compiled for the desert Nile. It focuses on the valley floor hinterland of the Kingdom of Kerma (2400-1450 B.C.) in northern Sudan. Kerma emerged as a rival to Egypt during Africa's first "Dark Age" drought. In contrast to other irrigation-based agriculturists in Egypt and Asia, Kerma flourished during the environmental crisis ca. 2200 B.C. We have studied the stratigraphy and archaeological records of paleochannels across an 80 km reach of the Nile upstream of Kerma using optically stimulated luminescence to date when channels flowed and when they dried up. The dynamics of the local alluvial environment were critical in determining whether climatic fluctuations and changes in river flow represented an opportunity for floodwater farmers (5000-3500 B.C.), a hazard that could be managed (2400-1300 B.C.), or an environmental catastrophe that resulted in settlement abandonment (after 1300 B.C.). © 2013 Geological Society of America.Mark G. Macklin, Jamie C. Woodward, Derek A. Welsby, Geoff A.T. Duller, Frances M. Williams, and Martin A.J. William
Computation of electromagnetic fields in inhomogeneous media: Scattering and guiding properties
No full textElectrical Engineering, Mathematics and Computer Scienc
Efficient implementation of the domain-integrated field relations method for quasi-static magnetic fields
No full textAuthor accepted manuscript of the 17th Annual Review of Progress in Applied Computational Electromagnetics, Monterey, pp. 337-344, 19 Mar 2001 → 23 Mar 2001Electrical Engineering, Mathematics and Computer Scienc
Generation of acoustic waves in piezo-electric devices
No full textElectrical Engineering, Mathematics and Computer Scienc
Chasing snails:Automating the processing of EMCCD images of luminescence from opercula
Full text linkOpercula of the gastropod Bithynia tentaculata are composed of calcite, and are typically 2–4 mm in length. They emit a thermoluminescence (TL) signal that can be used for dose reconstruction, and spatially resolved TL data from them can be obtained using an electron multiplying charge coupled device (EMCCD). However, when multiple measurements are made of the same sample with imaging detectors such as the EMCCD, registering the different images is crucial so that when regions of interest (ROI) are defined they consistently relate to the same part of the specimen. Previous work on opercula has undertaken this registration by hand, but this is prohibitively time consuming and is also potentially prone to human error. An automated registration process is described, and its use is illustrated using a dose recovery experiment. Without registration more than half of the regions of interest defined across the operculum failed the recycling test, and for those ROIs which did pass recycling the dose recovery ratio varied from 0.7 to 1.2. After registration more than 97% of ROIs passed recycling and all these ROIs gave dose recovery ratios within two sigma of unity. The automated registration process described here has potential for application to other types of solid sample such as rock slices provided they are not perfectly circular.</p
Evaluation of the 5mg-g liver iron concentration threshold and its association with morbidity in patients with β-thalassemia intermedia
No full textIron overload may still occur in transfusion-independent patients with β-thalassemia intermedia due to increased intestinal iron absorption. In this study, we evaluated the association between iron overload, using a liver iron concentration threshold of therapeutic significance (≥. 5. mg-g), and morbidity in 168 chelation naive patients with β-thalassemia intermedia. We demonstrated that patients with a liver iron concentration ≥. 5. mg-g have a significantly higher prevalence of several serious vascular and endocrine-bone morbidities than do patients with . 5. mg-g, and we established absolute morbidity risk values differentiating both groups. We also demonstrated that the association between iron overload and morbidity in such patients is independent of the effects of advancing age and disease severity. These findings suggest that treating iron burden in β-thalassemia intermedia may be associated with reduction in serious morbidity risk. © 2013 Elsevier Inc.Belhoul KM, 2012, ANN HEMATOL, V91, P1107, DOI 10.1007-s00277-012-1412-7; Haidar R, 2011, BONE, V48, P425, DOI 10.1016-j.bone.2010.10.173; Kell DB, 2009, BMC MED GENOMICS, V2, DOI 10.1186-1755-8794-2-2; Musallam KM, 2011, HEMOGLOBIN, V35, P503, DOI 10.3109-03630269.2011.605499; Musallam KM, 2012, BLOOD CELL MOL DIS, V49, P136, DOI 10.1016-j.bcmd.2012.06.001; Musallam KM, 2011, HAEMATOL-HEMATOL J, V96, P1605, DOI 10.3324-haematol.2011.047852; Musallam KM, 2012, BLOOD REV, V26, pS16, DOI 10.1016-S0268-960X(12)70006-1; Musallam KM, 2012, THROMB RES, V130, P695, DOI 10.1016-j.thromres.2012.07.013; Pootrakul P, 2003, BRIT J HAEMATOL, V122, P305, DOI 10.1046-j.1365-2141.2003.04412.x; Rivella S, 2012, BLOOD REV, V26, pS12, DOI 10.1016-S0268-960X(12)70005-X; St Pierre TG, 2005, BLOOD, V105, P855, DOI 10.1182-blood-2004-01-0177; Taher A, 2008, HAEMATOL-HEMATOL J, V93, P1584, DOI 10.3324-haematol.13098; Taher AT, 2012, BLOOD, V120, P970, DOI 10.1182-blood-2012-02-412692; Taher AT, 2010, BLOOD, V115, P1886, DOI 10.1182-blood-2009-09-243154; Wood JC, 2005, BLOOD, V106, P1460, DOI 10.1182-blood-2004-10-39825101
The Euler charateristic of the generalized Kummer scheme of an Abelian threefold
No full textLet X be an Abelian threefold. We prove a formula, conjectured by the first author, expressing the Euler characteristic of the generalized Kummer schemes KnX of X in terms of the number of plane partitions. This computes the Donaldson–Thomas invariant of the moduli stack [ KnX/ Xn]
Structure and chronology of a star dune at Erg Chebbi, Morocco, reveals why star dunes are rarely recognised in the rock record
Full text linkStar dunes are the tallest dunes on Earth and are amongst the larger and more spectacular aeolian landforms. Although they are widespread in modern sandy deserts, star dunes are rarely recognised in the rock record probably due to a lack of suitable sedimentary models. This paper presents a new sedimentary model for the structure of a star dune at Erg Chebbi in Morocco (Sahara Desert) on the basis of ground-penetrating radar (GPR) surveys. Individual sedimentary structures in star dunes are
similar to those in linear or barchanoid dunes, likely leading to misidentification in the rock record. However, the suite of features described in this paper will permit identification of star dunes in future studies of the rock record. Optically stimulated luminescence (OSL) dating shows that accumulation of the Erg Chebbi star dune post-dates the end of the African Humid Period (AHP). At the base of the dune, there is an ~8000-year hiatus in the record. Since then, the dune has grown rapidly to create a 100 m high dune within the past 1000 years and is migrating towards the west. Changes in the cross-strata support the idea that star dune construction was accompanied by a change in the wind directions
Government expenditures as a citizens'evaluation of public output : public choice and the benefit principle of taxation
Full text linkCombining elements from the theories of public choice and benefit taxation, the author develops a framework in which private citizens can evaluate public activities. Why, and under what circumstances, do bureaucrats increase the size of the public sector and the amount of public spending in their own self interest? What does the private sector think public output should be, what is actual public output, and how does the private sector evaluate that output? The author applies the theoretical results of an attempt to answer these questions in four Central European countries (Czechoslovakia, Hungary, Poland, and Slovenia), using actual data for 1989-91 and projections for 1992. Interpreting indirect evidence, he shows that the private sector would prefer less government activity in all countries, from a low of 5 percent less public spending (in Poland) to a high of one-third less (in Slovenia). If those governments were to follow those guidelines, their spending-to-GDP ratios would more closely resemble the 1987-89 average for a selected group of European market economies. The author also introduces a more rigorous, if not necessarily more objective, approach to determining optimal government spending. This approach requires little information, but uses a static model and requires faith in the direction of causality for some key variables. To the extent that one can accept those limitations, the model may be a useful operational tool in public spending evaluation.Public Sector Economics&Finance,National Governance,Economic Theory&Research,Environmental Economics&Policies,Fiscal&Monetary Policy
Characterising and correcting for a previously unconsidered source of scatter in measurements of equivalent dose
Full text linkSingle aliquot methods make it feasible to routinely determine multiple estimates of equivalent dose (De) for a sample. The scatter in De values observed within a sample has been used previously to make inferences about the resetting of the luminescence signal being measured prior to the event dated, about post-depositional processes that may have affected the sample, and about spatial variations in environmental dose rate on a small (millimetre) scale. However, in addition to processes associated with deposition and burial, scatter in the De values generated may also arise if the dose rate from the beta source used as part of the De determination method varies between grains or aliquots. Spatial variation in the beta dose arising from 90Sr plaque beta sources has been known for more than 20 years. What has not previously been described is variation in beta dose rate between different sample positions on the Risø TL/OSL instruments, one of the most widely used commercial systems used for luminescence dating. The variation arises from misalignment of the carousel used to hold samples with respect to the lid upon which the beta source is mounted. For one instrument in this study, this misalignment led to variations in apparent dose between different carousel positions of 14%. For most instruments the variability was lower (0.15–∼2%), but still detectable. A method for assessing the severity of this problem for individual instruments is described, along with a procedure for correcting for the effect and thus reducing the impact of this hitherto undescribed source of scatter in De.</p
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