Density-viscosity product of small-volume ionic liquid samples using quartz crystal impedance analysis

Quartz crystal impedance analysis has been developed as a technique to assess whether room-temperature ionic liquids are Newtonian fluids and as a small-volume method for determining the values of their viscosity-density product, rho eta. Changes in the impedance spectrum of a 5-MHz fundamental frequency quartz crystal induced by a water-miscible room-temperature ionic liquid, 1-butyl-3-methylimidazolium. trifluoromethylsulfonate ([C(4)mim][OTf]), were measured. From coupled frequency shift and bandwidth changes as the concentration was varied from 0 to 100% ionic liquid, it was determined that this liquid provided a Newtonian response. A second water-immiscible ionic liquid, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide [C(4)mim][NTf2], with concentration varied using methanol, was tested and also found to provide a Newtonian response. In both cases, the values of the square root of the viscosity-density product deduced from the small-volume quartz crystal technique were consistent with those measured using a viscometer and density meter. The third harmonic of the crystal was found to provide the closest agreement between the two measurement methods; the pure ionic liquids had the largest difference of similar to 10%. In addition, 18 pure ionic liquids were tested, and for 11 of these, good-quality frequency shift and bandwidth data were obtained; these 12 all had a Newtonian response. The frequency shift of the third harmonic was found to vary linearly with square root of viscosity-density product of the pure ionic liquids up to a value of root(rho eta) approximate to 18 kg m(-2) s(-1/2), but with a slope 10% smaller than that predicted by the Kanazawa and Gordon equation. It is envisaged that the quartz crystal technique could be used in a high-throughput microfluidic system for characterizing ionic liquids.

Radiocarbon wiggle-match dating of proglacial lake sediments - Implications for the 8.2 ka event

The problem of insufficient age-control limits the utilisation of the 8.2 ka BP event for modelling freshwater forcing in climate change studies. High-resolution radiocarbon dates, magnetic susceptibility and lithostratigraphic evidence from a lake sediment core from Nedre Hervavatnet located at Sygnefjell in western Norway provide a record of the early Holocene. We use the method of radiocarbon wiggle-match dating of the lake sediments using the non-linear relationship between the C-14 calibration curve and the consecutive accumulation order of the sample series in order to build a high-resolution age-model. The timing and duration of Holocene environmental changes is estimated using 38 AMS radiocarbon dates on terrestrial macrofossils, insects and chironomids covering the time period from 9750 to 1180 cal BP. Chironomids, Salix and Betula leaves produce the most consistent results. Sedimentological and physical properties of the core suggest that three meltwater events with high sedimentation rates are superimposed on a long-term trend with glacier retreat between 9750 and 8000 cal BP. The lake sediment sequence of Nedre Hervavatnet demonstrates the following: only a reliable high-resolution geochronology based on carefully selected terrestrial macrofossils allows the reconstruction of a more refined and complex environmental change history before and during the 8.2 ka event. (C) 2009 Elsevier Ltd. All rights reserved.

High precision C-14 dating of Holocene peat deposits: A comparison of Bayesian calibration and wiggle-matching approaches

The chronologies of five northern European ombrotrophic peat bogs subjected to a large ANIS C-14 dating effort (32-44 dates/site) are presented here. The results of Bayesian calibration (BCal) of dates with a prior assumption of chronological ordering were compared with a Bayesian wiggle-match approach (Bpeat) which assumes constant linear accumulation over sections of the peat profile. Interpolation of BCal age estimates of dense sequences of C-14 dates showed variable patterns of peat accumulation with time, with changes in accumulation occurring at intervals ranging from 20 to 50 cm. Within these intervals, peat accumulation appeared to be relatively linear. Close analysis suggests that some of the inferred variations in accumulation rate were related to the plant macrofossil composition of the peat. The wiggle-matched age-depth models had relatively high chronological uncertainty within intervals of closely spaced 14 C dates, suggesting that the premise of constant linear accumulation over large sections of the peat profile is unrealistic. Age models based on the assumption of linear accumulation over large parts of a peat core (and therefore only effective over millennial timescales), are not compatible with studies examining environmental change during the Holocene, where variability often occurs at decadal to centennial time-scales. Ideally, future wiggle-match age models should be constrained, with boundaries between sections based on the plant macrofossil composition of the peat and physical-chemical parameters such as the degree of decomposition. Strategies for the selection of material for dating should be designed so that there should be enough C-14 dates to accurately reconstruct the peat accumulation rate of each homogeneous stratigraphic unit. (c) 2006 Elsevier Ltd. All rights reserved.

Radiocarbon dating of bulk peat samples from raised bogs: nonexistence of a previously reported 'reservoir effect'?

In 1995. an unexpected reservoir effect was reported in sequences of bulk C-14 dates of raised bog peat. In most peat Studies bulk C-14 dates are used for obtaining chronologies. Therefore it is important to confirm and quantify such a C-14 reservoir effect. Five bulk peat samples from the raised bog Engbertsdijksveen were conventionally C-14 dated. The same core had previously been precisely dated by C-14 AMS dates of carefully selected above-ground plant remains. The existence of a reservoir effect in bulk peat C-14 samples could not be confirmed. Other explanations for the reported reservoir effect are discussed. (C) 2004 Elsevier Ltd. All rights reserved.

Small volume laboratory on a chip measurements incorporating the quartz crystal microbalance to measure the viscosity-density product of room temperature ionic liquids

A microfluidic glass chip system incorporating a quartz crystal microbalance (QCM) to measure the square root of the viscosity-density product of room temperature ionic liquids (RTILs) is presented. The QCM covers a central recess on a glass chip, with a seal formed by tightly clamping from above outside the sensing region. The change in resonant frequency of the QCM allows for the determination of the square root viscosity-density product of RTILs to a limit of similar to 10 kg m(-2) s(-0.5). This method has reduced the sample size needed for characterization from 1.5 ml to only 30 mu l and allows the measurement to be made in an enclosed system.

Dating peat profiles using tephra: stratigraphy, geochemistry and chronology

In this article we provide a brief overview of the protocols for dating peat profiles using tephrochronology. A standardised methodology for the detection, extraction and analysis of tephras is presented and the relevant problems and limitations are discussed.

High-resolution 14C dating of a 25,000-year lake-sediment record from equatorial East Africa

We dated a continuous, ~22-m long sediment sequence from Lake Challa (Mt. Kilimanjaro area, Kenya/Tanzania) to produce a solid chronological framework for multi-proxy reconstructions of climate and environmental change in equatorial East Africa over the past 25,000 years. The age model is based on a total of 168 AMS 14C dates on bulk-organic matter, combined with a 210Pb chronology for recent sediments and corrected for a variable old-carbon age offset. This offset was estimated by i) pairing bulk-organic 14C dates with either 210Pb-derived time markers or 14C dates on grass charcoal, and ii) wiggle-matching high-density series of bulk-organic 14C dates. Variation in the old-carbon age offset through time is relatively modest, ranging from ~450 yr during glacial and late glacial time to ~200 yr during the early and mid-Holocene, and increasing again to ~250 yr today. The screened and corrected 14C dates were calibrated sequentially, statistically constrained by their stratigraphical order. As a result their constrained calendar-age distributions are much narrower, and the calibrated dates more precise, than if each 14C date had been calibrated on its own. The smooth-spline age-depth model has 95% age uncertainty ranges of ~50–230 yr during the Holocene and ~250–550 yr in the glacial section of the record. The d13C values of paired bulk-organic and grass-charcoal samples, and additional 14C dating on selected turbidite horizons, indicates that the old-carbon age offset in Lake Challa is caused by a variable contribution of old terrestrial organic matter eroded from soils, and controlled mainly by changes in vegetation cover within the crater basin.

‘Old wood’ effect in radiocarbon dating of prehistoric cremated bones?

Numerous reports of successful radiocarbon dating of cremated bones have emerged during the last decade. The success of radiocarbon dating cremated bones depends on the temperature during burning and the degree of recrystallisation of the inorganic bone matrix. During cremation bones undergo major morphological and mineralogical changes which have raised some interesting questions and discussion on the origin of the carbon source in archaeologically cremated bones. Recent laboratory experiments reveal that the properties of the combustion atmosphere play a significant role regarding the source carbon in cremated bones. Thus radiocarbon dating cremated bones is potentially dating the wood used for the cremation fire. Here we compare a high precision radiocarbon dated human bone with an associated dendrochronological age from an oak coffin. We find that the age discrepancy between the dendrochronological age and the cremated bone of 73 ± 26 14C yr is best accounted for by the so called ‘old wood’ effect.

Carbon-14 wiggle-match dating of peat deposits: advantages and limitations

Carbon-14 wiggle-match dating (WMD) of peat deposits uses the non-linear relationship between 14C age and calendar age to match the shape of a series of closely spaced peat 14C dates with the 14C calibration curve. The method of WMD is discussed, and its advantages and limitations are compared with calibration of individual dates. A numerical approach to WMD is introduced that makes it possible to assess the precision of WMD chronologies. During several intervals of the Holocene, the 14C calibration curve shows less pronounced fluctuations. We assess whether wiggle-matching is also a feasible strategy for these parts of the 14C calibration curve. High-precision chronologies, such as obtainable with WMD, are needed for studies of rapid climate changes and their possible causes during the Holocene.

Cobalt-doped ZnO nanowires on quartz: Synthesis by simple chemical method and characterization

The synthesis of cobalt-doped ZnO nanowires is achieved using a simple, metal salt decomposition growth technique. A sequence of drop casting on a quartz substrate held at 100 degrees C and annealing results in the growth of nanowires of average (modal) length similar to 200 nm and diameter of 15 +/- 4 nm and consequently an aspect ratio of similar to 13. A variation in the synthesis process, where the solution of mixed salts is deposited on the substrate at 25 degrees C, yields a grainy film structure which constitutes a useful comparator case. X-ray diffraction shows a preferred [0001] growth direction for the nanowires while a small unit cell volume contraction for Co-doped samples and data from Raman spectroscopy indicate incorporation of the Co dopant into the lattice; neither technique shows explicit evidence of cobalt oxides. Also the nanowire samples display excellent optical transmission across the entire visible range, as well as strong photoluminescence (exciton emission) in the near UV, centered at 3.25 eV. (C) 2012 Elsevier B.V. All rights reserved.