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Carotid Plaque Age Is a Feature of Plaque Stability Inversely Related to Levels of Plasma Insulin

C-declination curve (a result of the atomic bomb tests in the 1950s and 1960s) to determine the average biological age of carotid plaques.C content by accelerator mass spectrometry. The average plaque age (i.e. formation time) was 9.6±3.3 years. All but two plaques had formed within 5–15 years before surgery. Plaque age was not associated with the chronological ages of the patients but was inversely related to plasma insulin levels (p = 0.0014). Most plaques were echo-lucent rather than echo-rich (2.24±0.97, range 1–5). However, plaques in the lowest tercile of plaque age (most recently formed) were characterized by further instability with a higher content of lipids and macrophages (67.8±12.4 vs. 50.4±6.2, p = 0.00005; 57.6±26.1 vs. 39.8±25.7, p<0.0005, respectively), less collagen (45.3±6.1 vs. 51.1±9.8, p<0.05), and fewer smooth muscle cells (130±31 vs. 141±21, p<0.05) than plaques in the highest tercile. Microarray analysis of plaques in the lowest tercile also showed increased activity of genes involved in immune responses and oxidative phosphorylation.C, can improve our understanding of carotid plaque stability and therefore risk for clinical complications. Our results also suggest that levels of plasma insulin might be involved in determining carotid plaque age

Comment on “Intracavity OptoGalvanic Spectroscopy Not Suitable for Ambient Level Radiocarbon Detection"

Every new discovery must undergo thorough scientific scrutiny before being recognized. One important step in the process is confirmation by independent experiments. The case at hand is intracavity optogalvanic spectroscopy (ICOGS), which was first published by Murnick et al. in 2008, and claimed to have the potential to revolutionize rare-isotope measurements in general and those of radiocarbon in particular. Since then, no data has been reported in any shape or form to support it. On the contrary, in spite of extensive efforts at five different sites around the world – apart from Murnick’s group at Rutgers University, Professor Meijer’s group at the Energy and Sustainability Research Institute Groningen at University of Groningen, Professor Lackner’s group at the Department of Earth and Environmental Engineering at Columbia University, our group at the Department of Physics and Astronomy at Uppsala University, and the company Planetary Emission Management Inc. – the original data still remains unconfirmed, and a number of publications have seriously questioned the scientific validity of the original report

Intracavity optogalvanic spectroscopy: Is there any evidence of a radiocarbon signal?

In 2008, the first report of an ultrasensitive method for ro-vibrational spectrometry of radiocarbon dioxide was published. The method, called intracavity optogalvanic spectroscopy (ICOGS), claimed a sensitivity and limit-of-detection comparable to accelerator mass spectroscopy. ICOGS was claimed to utilize the isotope-dependent ro-vibrational absorption lines of carbon dioxide in the infrared spectrum. In order to facilitate unambiguous detection of radiocarbon, the sample was placed inside the cavity of a radiocarbon dioxide laser. This intracavity approach was claimed to increase the sensitivity by seven orders of magnitude compared with traditional optogalvanic methods. However, despite the methodical and thorough efforts of several research groups worldwide, these claims have not been possible to reproduce. Instead, we have previously reported serious deviations from the original results, where we found that ICOGS suffers from considerable problems with the stability and reproducibility of the optogalvanic signal, and that misinterpretations of these uncertainties likely are the explanation for the claimed sensitivity in the first reports. Having identified the stability and reproducibility of the detection as major concerns, we decided to improve the setup by with state-of-the-art plasma source technology. Deploying a custom-made stripline split-ring resonator optogalvanic detector, we have now investigated the applicability of ICOGS to radiocarbon detection even further. Measurements have been made with a wide range of parameters including different gas mixtures at various pressures and wavelengths. We have also conducted measurements with gas flowing through the sample cell to investigate the effect of plasma induced decomposition of the sample. Still, we have seen no indications of a significant radiocarbon signal in a concentration range between 0.29 Modern and 9.7 Modern, i.e., the range of interest to the radiocarbon community. Hence, our conclusions after four years of working in this field, is that ICOGS is not a viable method for radiocarbon detection.

Intracavity optogalvanic spectroscopy: Is there any evidence of a radiocarbon signal?

In 2008, the first report of an ultrasensitive method for ro-vibrational spectrometry of radiocarbon dioxide was published. The method, called intracavity optogalvanic spectroscopy (ICOGS), claimed a sensitivity and limit-of-detection comparable to accelerator mass spectroscopy. ICOGS was claimed to utilize the isotope-dependent ro-vibrational absorption lines of carbon dioxide in the infrared spectrum. In order to facilitate unambiguous detection of radiocarbon, the sample was placed inside the cavity of a radiocarbon dioxide laser. This intracavity approach was claimed to increase the sensitivity by seven orders of magnitude compared with traditional optogalvanic methods. However, despite the methodical and thorough efforts of several research groups worldwide, these claims have not been possible to reproduce. Instead, we have previously reported serious deviations from the original results, where we found that ICOGS suffers from considerable problems with the stability and reproducibility of the optogalvanic signal, and that misinterpretations of these uncertainties likely are the explanation for the claimed sensitivity in the first reports. Having identified the stability and reproducibility of the detection as major concerns, we decided to improve the setup by with state-of-the-art plasma source technology. Deploying a custom-made stripline split-ring resonator optogalvanic detector, we have now investigated the applicability of ICOGS to radiocarbon detection even further. Measurements have been made with a wide range of parameters including different gas mixtures at various pressures and wavelengths. We have also conducted measurements with gas flowing through the sample cell to investigate the effect of plasma induced decomposition of the sample. Still, we have seen no indications of a significant radiocarbon signal in a concentration range between 0.29 Modern and 9.7 Modern, i.e., the range of interest to the radiocarbon community. Hence, our conclusions after four years of working in this field, is that ICOGS is not a viable method for radiocarbon detection.

Improved optogalvanic detection with voltage biased Langmuir probes

Optogalvanic detectors show great potential for infrared spectroscopy, especially in cavity enhanced techniques where they, in contrast to ordinary absorption detectors, can perform intracavity measurements. This enables them to utilize the signal-to-noise ratio improvement gained from the extended effective path length inside an optical cavity, without losing signal strength due to the limited amount of light exiting through the rear mirror. However, if optogalvanic detectors are to become truly competitive, their intrinsic sensitivity and stability has to be improved. This, in turn, requires a better understanding of the mechanisms behind the generation of the optogalvanic signal. The study presented here focuses on an optogalvanic detector based on a miniaturized stripline split-ring resonator plasma source equipped with Langmuir probes for detecting the optogalvanic signal. In particular, the effect of applying a constant bias voltage to one of the probes is investigated, both with respect to the sensitivity and stability, and to the mechanism behind the generation of the signal. Experiments with different bias voltages at different pressures and gas composition have been conducted. In particular, two different gas compositions (pure CO2 and 0.25% CO2 in 99.75% N-2) at six different pressures (100 Pa to 600 Pa) have been studied. It has been shown that probe biasing effectively improves the performance of the detector, by increasing the amplitude of the signal linearly over one order of magnitude, and the stability by about 40% compared with previous studies. Furthermore, it has been shown that relatively straightforward plasma theory can be applied to interpret the mechanism behind the generation of the signal, although additional mechanisms, such as rovibrational excitation from electron-molecule collisions, become apparent in CO2 plasmas with electron energies in the 1-6 eV range. With the achieved performance improvement and the more solid theoretical framework presented here, stripline split-ring resonator optogalvanic detectors can evolve into a compact, inexpensive, and easy-to-operate alternative for future infrared spectrometers. (C) 2014 AIP Publishing LLC

State of the art Intracavity Optogalvanic Spectroscopy at Uppsala University

About five years ago, the first reports of a novel and ultrasensitive method for ro-vibrational spectroscopy of isotope ratios were published [1-3]. The method was called intracavity optogalvanic spectroscopy (ICOGS), and claimed a sensitivity and limit-of-detection (LOD) for detection of radiocarbon in the 10-15range. Applied to measuring the isotopic composition of carbon samples, ICOGS utilizes the narrow linewidth ro-vibrational absorption lines of CO2 in the long-wavelength IR spectrum, typically between 10 - 13 µm [4]. These absorption lines are strongly dependent on the isotopic composition of the CO2 molecule, where a 14CO2 line typically is separated by several hundred linewidths form the nearest 12CO2 and 13CO2 lines. In order to facilitate unambiguous detection of radiocarbon, which is typically 1010-1012 times less abundant than the isotopes 12C and 13C, the sample is moved inside the laser cavity of a 14CO2 laser. This intracavity approach has been claimed to increase the sensitivity of the detection by almost seven orders of magnitude as compared to traditional ‘extracavity’ optogalvanic spectroscopy [3]. However, despite the methodical and thorough efforts of at least five research groups worldwide, the exceptional claims regarding the sensitivity and LOD of ICOGS have not been possible to confirm.       As the first research group to properly repeat the original experiments, we recently reported [5] serious deficiencies in the reproducibility of the original results [1-3]. We found that ICOGS in its original embodiment suffers from considerable problems with the stability and reproducibility of the optogalvanic signal, and that these uncertainties, together with mix-ups and mistakes, likely are the explanation for the extraordinary sensitivity in the original reports. An example of the irreproducibility of the original results can be seen in Fig. 1 (a) where the shape of the P20 line of 14C16O2 with different 14C concentrations is shown. As can be seen, the previously reported Voight profile-like line shape, indicating resonant absorption [3], was not found for 14C concentrations in the 10-13 ‒10-11 range, but only for samples with much higher 14C concentration. The problems with stability and reproducibility can be traced back to instabilities in the plasma source, in which the sample is partially ionized in order to extract the optogalvanic signal. The plasma sources currently used in ICOGS are based on 30 years old technology and suffer from problems with both electromagnetic interference and reproducibility in terms of the discharge conditions (pressure, temperature, etc.).       In order to overcome these problems, we aim to deploy a completely novel kind of plasma source, based on a stripline split-ring resonator (SSRR), for ICOGS, Fig. 1 (b). We have recently published a report on the applicability of such a plasma source for ordinary optogalvanic spectroscopy [6], and now intend to optimize it for ICOGS. Based on its intrinsic properties, an SSRR could not only improve the stability of the signal, but also reduce the non-resonant background in the spectrum, and facilitate analysis of smaller samples. The latter is due to its extremely small size, with an analyzed volume in the order of 10 µl, Fig. 1 (c). In this report, we summarize our criticism towards the original publications on ICOGS, and report on the latest development regarding our efforts in the deployment of the SSRR plasma source