title: Robust radiocarbon dating of wood samples by high-sensitivity liquid scintillation spectroscopy in the 50–70 kyr age range

authors: Hogg, Alan G.

subjects: liquid scintillation

abstract: Although high-sensitivity liquid scintillation (LS) spectroscopy is theoretically capable of producing finite radiocarbon ages in the 50,000- to 70,000-yr range, there is little evidence in the literature that meaningful dates in this time period have been obtained. The pressing need to undertake calibration beyond 26 kyr has resulted in the regular publication of ¹⁴C results in excess of 50 kyr, yet very little effort has been made to demonstrate their accuracy or precision. There is a paucity of systematic studies of the techniques required to produce reliable dates close to background and the methods needed to assess contamination from either in situ sources or laboratory handling and processing. We have studied the requirements for producing accurate and reliable dates beyond 50 kyr. Laboratory procedures include optimization of LS spectrometers to obtain low and stable non-¹⁴C background count rates, use of low-background counting vials, large benzene volumes, long counting times, and preconditioning of vacuum lines. We also discuss the need for multiple analyses of a suitable material containing no original ¹⁴C (background blank) and the application of an appropriate statistical model to compensate for variability in background contamination beyond counting statistics. Accurate and reproducible finite ages >60 kyr are indeed possible by high-sensitivity LS spectroscopy, but require corroborating background blank data to be defensible.

text: Robust radiocarbon dating of wood samples by high-sensitivity liquid scintillation spectroscopy in the 50–70 kyr age range Although high-sensitivity liquid scintillation (LS) spectroscopy is theoretically capable of producing finite radiocarbon ages in the 50,000- to 70,000-yr range, there is little evidence in the literature that meaningful dates in this time period have been obtained. The pressing need to undertake calibration beyond 26 kyr has resulted in the regular publication of ¹⁴C results in excess of 50 kyr, yet very little effort has been made to demonstrate their accuracy or precision. There is a paucity of systematic studies of the techniques required to produce reliable dates close to background and the methods needed to assess contamination from either in situ sources or laboratory handling and processing. We have studied the requirements for producing accurate and reliable dates beyond 50 kyr. Laboratory procedures include optimization of LS spectrometers to obtain low and stable non-¹⁴C background count rates, use of low-background counting vials, large benzene volumes, long counting times, and preconditioning of vacuum lines. We also discuss the need for multiple analyses of a suitable material containing no original ¹⁴C (background blank) and the application of an appropriate statistical model to compensate for variability in background contamination beyond counting statistics. Accurate and reproducible finite ages >60 kyr are indeed possible by high-sensitivity LS spectroscopy, but require corroborating background blank data to be defensible.

year: 2007

title: Bipenalty method from a frequency domain perspective

authors: Ilanko, Sinniah

subjects: bipenalty method

abstract: In a recent paper, it was shown that for time domain analysis, the simultaneous use of inertial and stiffness type penalty parameters to enforce constraints was found to yield accurate and converging results without causing any stability problems. From a frequency domain perspective, this is somewhat unexpected because the solution converges from below when stiffness penalty parameters are used to model constraints, and the convergence is from above when inertial penalty parameters are used. The purpose of this paper is to explain the effect of the simultaneous use of stiffness and inertial penalty parameters on the natural frequencies of constrained systems. In this work, it is shown that if suitably tuned, the bipenalty approach works well for frequency domain analysis also, and that with two different tuned set of stiffness and inertial penalty parameters, bounded solutions to the natural frequencies of constrained systems may be obtained. The method is applicable for any linear eigenvalue problem.

text: Bipenalty method from a frequency domain perspective In a recent paper, it was shown that for time domain analysis, the simultaneous use of inertial and stiffness type penalty parameters to enforce constraints was found to yield accurate and converging results without causing any stability problems. From a frequency domain perspective, this is somewhat unexpected because the solution converges from below when stiffness penalty parameters are used to model constraints, and the convergence is from above when inertial penalty parameters are used. The purpose of this paper is to explain the effect of the simultaneous use of stiffness and inertial penalty parameters on the natural frequencies of constrained systems. In this work, it is shown that if suitably tuned, the bipenalty approach works well for frequency domain analysis also, and that with two different tuned set of stiffness and inertial penalty parameters, bounded solutions to the natural frequencies of constrained systems may be obtained. The method is applicable for any linear eigenvalue problem.

year: 2013

title: ‘Inside Out’: The politics of enumerating the nation by ethnicity

authors: Kukutai, Tahu

abstract: Since the 1990s, state practices of counting and classifying populations by ethnicity have come under increased scrutiny within the social sciences (Arel 2002 ; Kertzer and Arel 2002 ; Nobles 2000 ; Perlmann and Waters 2002 ; Petersen 1997 ; Statistics Canada and U.S. Census Bureau 1993 ). A number of excellent case studies have provided critical insights into how and why ethnic enumeration is pursued in particular times and places. ¹ However, with some notable exceptions (Morning 2008 ; Rallu
et al. 2006 ), little attention has been given to theorizing or empirically testing a global
model of ethnic classifi cation and counting. Consequently, there is a limited understanding
about the general conditions that impede or encourage state recognition of ethnicity in the national census and the forms that such recognition takes.

text: ‘Inside Out’: The politics of enumerating the nation by ethnicity Since the 1990s, state practices of counting and classifying populations by ethnicity have come under increased scrutiny within the social sciences (Arel 2002 ; Kertzer and Arel 2002 ; Nobles 2000 ; Perlmann and Waters 2002 ; Petersen 1997 ; Statistics Canada and U.S. Census Bureau 1993 ). A number of excellent case studies have provided critical insights into how and why ethnic enumeration is pursued in particular times and places. ¹ However, with some notable exceptions (Morning 2008 ; Rallu
et al. 2006 ), little attention has been given to theorizing or empirically testing a global
model of ethnic classifi cation and counting. Consequently, there is a limited understanding
about the general conditions that impede or encourage state recognition of ethnicity in the national census and the forms that such recognition takes.

year: 2015