Quantitative evaluation of polymer gel dosimeters by broadband ultrasound attenuation

Ultrasound has been examined previously as an alternative readout method for irradiated polymer gel dosimeters, with authors reporting varying dose response to ultrasound transmission measurements. In this current work we extend previous work to measure the broadband ultrasound attenuation (BUA) response of irradiated PAGAT gel dosimeters, using a novel ultrasound computed tomography system

Reconstructing 3D x-ray CT images of polymer gel dosimeters using the zero-scan method

In this study x-ray CT has been used to produce a 3D image of an irradiated PAGAT gel sample, with noise-reduction achieved using the ‘zero-scan’ method. The gel was repeatedly CT scanned and a linear fit to the varying Hounsfield unit of each pixel in the 3D volume was evaluated across the repeated scans, allowing a zero-scan extrapolation of the image to be obtained. To minimise heating of the CT scanner’s x-ray tube, this study used a large slice thickness (1 cm), to provide image slices across the irradiated region of the gel, and a relatively small number of CT scans (63), to extrapolate the zero-scan image. The resulting set of transverse images shows reduced noise compared to images from the initial CT scan of the gel, without being degraded by the additional radiation dose delivered to the gel during the repeated scanning. The full, 3D image of the gel has a low spatial resolution in the longitudinal direction, due to the selected scan parameters. Nonetheless, important features of the dose distribution are apparent in the 3D x-ray CT scan of the gel. The results of this study demonstrate that the zero-scan extrapolation method can be applied to the reconstruction of multiple x-ray CT slices, to provide useful 2D and 3D images of irradiated dosimetry gels

Germinação de Eragrostis plana Nees sob efeito do extrato de Achyrocline satureioides (Lam.) DC.

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Iron biogeochemistry across marine systems progress from the past decade

Based on an international workshop (Gothenburg, 14–16 May 2008), this review article aims to combine interdisciplinary knowledge from coastal and open ocean research on iron biogeochemistry. The major scientific findings of the past decade are structured into sections on natural and artificial iron fertilization, iron inputs into coastal and estuarine systems, colloidal iron and organic matter, and biological processes. Potential effects of global climate change, particularly ocean acidification, on iron biogeochemistry are discussed. The findings are synthesized into recommendations for future research areas

Preproglucagon neurons in the hindbrain have IL-6 Receptor α (IL-6Rα) and show Ca 2+ influx in response to IL-6

Neuronal circuits in the hypothalamus and hindbrain are of importance for control of food intake, energy expenditure, and fat mass. We have recently shown that treatment with exendin-4 (Ex-4), an analog of the proglucagon-derived molecule glucagon-like peptide 1 (GLP-1), markedly increases mRNA expression of the cytokine interleukin-6 (IL-6) in the hypothalamus and hindbrain and that this increase partly mediates the suppression of food intake and body weight by Ex-4. Endogenous GLP-1 in the central nervous system (CNS) is produced by preproglucagon (PPG) neurons of the nucleus of the solitary tract (NTS) in the hindbrain. These neurons project to various parts of the brain, including the hypothalamus. Outside the brain, IL-6 stimulates GLP-1 secretion from the gut and pancreas. In this study, we aim to investigate whether IL-6 can affect GLP-1-producing PPG neurons in the nucleus of the solitary tract (NTS) in mouse hindbrain via the ligand binding part of the IL-6 receptor, IL-6 receptor-α (IL-6Rα). Using immunohistochemistry, we found that IL-6Rα was localized on PPG neurons of the NTS. Recordings of these neurons in GCaMP3/GLP-1 reporter mice showed that IL-6 enhances cytosolic Ca2+ concentration in neurons capable of expressing PPG. We also show that the Ca2+ increase originates from the extracellular space. Furthermore, we found that IL-6Rα was localized on cells in the caudal hindbrain expressing immunoreactive NeuN (a neuronal marker) or CNP:ase (an oligodendrocyte marker). In summary, IL-6Rα is present on PPG neurons in the NTS, and IL-6 can stimulate these cells by increasing influx of Ca2+ to the cytosol from the extracellular space

Respiratory responses to hypercapnia and hypoxia in mice with genetic ablation of Kir5.1 (Kcnj16)

Inward rectifier (Kir) potassium channels contribute to the control of electrical activity in excitable tissues and their activity is modulated by many biochemical factors, including protons. Heteromeric Kir4.1–Kir5.1 channels are highly pH sensitive within the physiological range of pH changes and are strongly expressed by the peripheral chemosensors as well as in the brainstem pH-sensitive areas which mediate respiratory responses to changes in blood and brain levels of /[H+]. In the present study, Kir5.1 knockout mice (Kir5.1−/−) were used to determine the role of these channels in the chemosensory control of breathing. We found that Kir5.1−/− mice presented with persistent metabolic acidosis and a clear respiratory phenotype. Despite metabolic acidosis, ventilation at rest and in hyperoxic hypercapnia were similar in wild-type and Kir5.1−/− mice. Ventilatory responses to hypoxia and normoxic hypercapnia were significantly reduced in Kir5.1−/− mice; however, carotid body chemoafferent responses to hypoxia and CO2 were not affected. In the in situ brainstem–spinal cord preparations with denervated peripheral chemoreceptors, resting phrenic nerve activity and phrenic nerve responses to respiratory acidosis or isohydric hypercapnia were also similar in Kir5.1−/− and wild-type mice. In in situ preparations of Kir5.1−/− mice with intact peripheral chemoreceptors, application of CN− resulted in a significantly reduced phrenic nerve response, suggesting that the relay of peripheral chemosensory information to the CNS is compromised. We suggest that this compensatory modulation of the peripheral chemosensory inputs develops in Kir5.1−/− mice in order to counteract the effect of continuing metabolic acidosis on the activity of the peripheral chemoreceptors. These results therefore suggest that despite their intrinsic pH sensitivity, Kir4.1–Kir5.1 channels are dispensable for functional central and peripheral respiratory chemosensitivity

A hybrid radiation detector for simultaneous spatial and temporal dosimetry

In this feasibility study an organic plastic scintillator is calibrated against ionisation chamber measurements and then embedded in a polymer gel dosimeter to obtain a quasi-4D experimental measurement of a radiation field. This hybrid dosimeter was irradiated with a linear accelerator, with temporal measurements of the dose rate being acquired by the scintillator and spatial measurements acquired with the gel dosimeter. The detectors employed in this work are radiologically equivalent; and we show that neither detector perturbs the intensity of the radiation field of the other. By employing these detectors in concert, spatial and temporal variations in the radiation intensity can now be detected and gel dosimeters can be calibrated for absolute dose from a single irradiation

Ground Vibrational State SiO Emission in the VLA BAaDE Survey

Using a subsample of the Bulge Asymmetries and Dynamical Evolution (BAaDE) survey of stellar SiO masers, we explore the prevalence and characteristics of $^{28}$SiO $J=1-0, v=0$ emission. We identify 90 detections of maser, thermal, or composite $^{28}$SiO $J=1-0, v=0$ emission out of approximately 13,000 candidate spectra from the NSF's Karl G. Jansky Very Large Array (VLA). We find that the detected sources are likely asymptotic giant branch (AGB) stars belonging to a bright, foreground Milky Way stellar disk population. For the 32 sources showing thermal components, we extract values for outflow velocity by fitting thermal line profiles. We find a range of circumstellar envelope expansion velocities, and compare to previously recorded OH and CO expansion velocities. This preliminary survey is already the largest study of stellar ground-vibrational-state SiO masers to date, and will be expanded to include the entire VLA BAaDE dataset when data reduction for the 18,988 target sources is completed.Comment: 23 pages, 8 figures, to be published in The Astronomical Journa