Time scale, calibration

One important line of investigation which has supported the radical rebound hypothesis is the use of radical clock substrate probes. These probes rearrange in a diagnostic way on a very rapid and calibrated time scale when a hydrocarbon radical is formed. In the case of P450, rearranged products have been isolated after oxidation and have been used as evidence of an intermediate substrate radical. In this way, even though the lifetime of the radical is too short for it to be observed directly, its character can be explored by the judicious choice of substrate analogues. 

Bard E, Hamelin B, Fairbanks RG, Zindler A, Mathieu G, Arnold M (1990) U/Th and ages of corals from Barbados and their use for calibrating the time scale beyond 9000 years BP. Nucl lustrum Methods Phys Res Sect B 52 461-468... 

Schramm A, Stein M, Goldstein SL (2000) Calibration of the ""C time scale to 50 kyr by " U- °Th dating of sediments from Lake Lisan (the paleo-Dead Sea). Earth Planet Sci Lett 175 27-40 Schwarcz HP (1986) Geochronology and isotope geochemistry of speleothems. In ... 

Pearson, G. W. and M. Stuiver (1993), High-precision bidecadal calibration of the radiocarbon time scale 500-2500 BC, Radiocarbon 35, 25-33. 

The reflection calibration method with the specialized filter block has the advantage that it does not require the sample to be moved to recalibrate. As a result it might be particularly useful for long time scale time series data. 

It is necessary to calibrate the 14C time scale for greater dating accuracy. However, the second-order variations are at least as important as the first-order constancy of atmospheric 14C. For example, they provide a record of prehistoric solar variations, changes in the Earth s dipole moment and an insight into the fate of C02 from fossil fuel combustion. Improved techniques are needed that will enable the precise measurement of small cellulose samples from single tree rings. The tandem accelerator mass spectrometer (TAMS) may fill this need. 

Calibration of the Radiocarbon Dating Time Scale, Radiocarbon. 22(3), 947-949 (1980). 

Cooper, R. A. 1999. The Ordovician time scale - calibration of graptolite and conodont zones. Acta Universitatis Carolinae -Geologica, 43 (1/2), 1-4. 

In some cases the equilibration rate is very slow compared to the time scale of the analytical separation. The pre-equilibrated reaction mixture behaves indeed as a mixture of inert components and can be separated by capillary electrophoresis. The concentrations are directly derived from the peak areas or peak heights after calibration. This method is suitable if ligand and substrate are separable and the migration time does not exceed 1% of the half-life of complex decomposition. 

The time scales of modem oscilloscopes are highly accurate. Furthermore, they carry internal standards for time calibrations to check their timing accuracy. Cole (Ref 1, Chapt 5) devotes... 

The constant /3 contains a partitioning coefficient of the analyte between the solution and the modifying layer, as well as the constants related to the bulk electrolysis in a small volume (i.e., thin) cell (Bard and Faulkner, 2001). If the electroactive species are confined to the electrode, if the couple is perfectly reversible, and if the extraction is fast on the time scale of the experiment, the peaks in the cyclic voltammogram occur at the same potential and the areas (charge) below the cathodic and anodic branches are equal, as is the case in Fig. 7.12. Obviously, any deviations from these conditions are reflected in the shape of the CV curve. Nevertheless, even then the relationship between the peak current iv and the bulk concentration of the electroactive species can be reproducible. In the determination of Fe2+ using the above procedure, the linear calibration between 5 x 10 8 and 5 x 10-6 M concentration has been obtained. 

Fig. 9. (i) Fluorescence decay curve (solid lines) for Rhodamine B (1 X 10 6 M, room temperature) (a) linear (b) semi-log. (ii) fluorescence decay curves (solid lines) for Rhodamine B (1 X 1CT6 M, room temperature) in the presence of 1.2 M KI (a) linear, (b) semi-log. The laser excitation pulse profile is shown by the broken lines. The time scale calibration of 64.1 ps per channel was derived from the 13.020 ns spacing between the mode-locked laser pulses. (After ref. 54.)... 

The time scale of the MCA spectrum has to be calibrated. In analogue systems this can be done by (a) using a commercially available time calibrator (b) stopping the TAC-MCA clock with a delayed start pulse, then introducing an extra known delay and measuring the change in channel... 

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