Radioactivity concentration measurements in fish and shellfish samples from the west coast of Canada after the Fukushima nuclear accident (2011-2018).

Radioactive contamination of the Pacific Ocean following the Fukushima nuclear accident has raised public concern about seafood safety, particularly in coastal Indigenous communities. To address this, Health Canada and partners have collected and analyzed a total of 621 samples of commonly consumed salmon, ground fish, and shellfish from the Canadian west coast from 2011 to 2018. While the vast majority of the 137Cs and 134Cs levels were below the Minimum Detectable Concentration (MDC, typically 0.7-1.0 Bq kg-1 fw for a 6 h counting), further examination of 19 fish samples revealed 137Cs concentrations of 0.17-0.53 Bq kg-1 fw with an average value and uncertainty (k = 1) of 0.29 ± 0.02 Bq kg-1 fw. Of these, only two samples were found to have trace levels of 134Cs likely derived from the Fukushima accident. The global fallout contribution from atmospheric nuclear weapons testing to the observed 137Cs in these two samples was determined to be 0.26 ± 0.08 Bq kg-1 fw (49 ± 14%) and 0.12 ± 0.02 Bq kg-1 fw (24 ± 4%) for collection years 2015 and 2016, respectively. The annual average level of 137Cs in fish and shellfish was also determined by spectral summation for collection years 2014-2018. In fish, 137Cs levels determined through spectral summation were relatively constant (0.18-0.25 Bq kg-1 fw) with an average value and uncertainty of 0.21 ± 0.02 Bq kg-1 fw. By contrast, 38 shellfish samples (bivalves) were measured and revealed no radiocesium or other anomalies in either tissue or shell. In all, measurements over eight years showed that the radioactivity in fish and shellfish was dominated by natural radionuclides and that the level of anthropogenic radionuclides, as indicated by the radioactive cesium content, remained small. An upper bound for ingested dose from 137Cs was determined to be approximately 0.26 µSv per year, far below the worldwide average annual effective dose of 2400 µSv from exposure to natural background radiation. We can therefore conclude that fish, such as salmon, ground fish, and shellfish from the Canadian west coast are of no radiological health concern despite the Fukushima Dai-ichi nuclear accident of 2011.

A stable, unified model for resonant Faraday cages.

We study some effective transmission conditions able to reproduce the effect of a periodic array of Dirichlet wires on wave propagation, in particular when the array delimits an acoustic Faraday cage able to resonate. In the study of Hewett & Hewitt (2016 Proc. R. Soc. A 472, 20160062 (doi:10.1098/rspa.2016.0062)) different transmission conditions emerge from the asymptotic analysis whose validity depends on the frequency, specifically the distance to a resonance frequency of the cage. In practice, dealing with such conditions is difficult, especially if the problem is set in the time domain. In the present study, we demonstrate the validity of a simpler unified model derived in Marigo & Maurel (2016 Proc. R. Soc. A 472, 20160068 (doi:10.1098/rspa.2016.0068)), where unified means valid whatever the distance to the resonance frequencies. The effectiveness of the model is discussed in the harmonic regime owing to explicit solutions. It is also exemplified in the time domain, where a formulation guaranteeing the stability of the numerical scheme has been implemented.

Enhanced resonance of sparse arrays of Helmholtz resonators-Application to perfect absorption.

The influence of the spacing on the resonance of a periodic arrangement of Helmholtz resonators is inspected. An effective problem is used which accurately captures the properties of the resonant array within a large range of frequencies, and whose simplified version leaves an impedance condition. It is shown that the strength of the resonance is enhanced when the array becomes sparser. This degree of freedom on the radiative damping is of particular interest since it does not affect the resonance frequency nor the damping due to losses within each resonator; in addition, it does not affect the total thickness of the array. It is shown that it can be used for the design of a perfect absorbing wall.

210Po in Pacific Salmon from the West Coast of Canada and its Contribution to Dose by Ingestion.

In response to public concern in Canada regarding health impacts attributable to the Fukushima Daiichi nuclear accident, oceanic seawater samples from the north Pacific and Arctic oceans, coastal seawater samples from 16 locations along the British Columbia coastline, and seafood samples (salmon, steelhead trout, and shellfish) from British Columbia coastal waters were collected and analyzed. This paper reports radiological analysis results of Pacific salmon samples (Oncorhynchus species) obtained from summer 2013 to fall 2016. While radioactive cesium from the Fukushima disaster was not detectable in most salmon samples, naturally occurring Po was measured in almost all individual samples in varying activity concentrations, from below the detection limit of 0.2 Bq kg fresh weight up to 4.7 Bq kg fresh weight. The average Po concentration among 297 salmon samples was 0.73 Bq kg fresh weight. The average ingested radiation dose per kilogram of salmon from Po is estimated to be 0.88 µSv, and the average dose from Cs is estimated to be 0.0026 µSv. The annual dose from ingested salmon would be only a fraction of the worldwide average annual effective dose from exposure to natural background radiation (2,400 µSv y) (). The measurement results showed clearly that radiation doses to people consuming fish (such as salmon) from the Canadian west coast pose no health concern.

Measurements of cesium in Arctic beluga and caribou before and after the Fukushima accident of 2011.

Concern from northern communities following the Fukushima Daiichi nuclear accident of March 2011 has prompted a reassessment of the safety of their traditional foods with respect to radioactivity levels. To this end, a study was conducted to measure the levels of radionuclides in Arctic caribou (Rangifer tarandus) and beluga (Delphinapterus leucas). The main radionuclide of concern is cesium-137, which is easily transferred through the lichen-caribou food chain. Previous studies have been conducted on the cesium-137 levels in Canadian caribou herds from 1958 to 2000, allowing researchers to determine the amount of cesium-137 in caribou specifically attributable to atmospheric weapons testing and the Chernobyl nuclear accident in 1986. In this study, samples of lichens, mushrooms, caribou, beluga and beluga prey collected before and after the Fukushima accident were analyzed for radioactivity levels. Samples were processed and measured using gamma ray spectroscopy to identify the radionuclides present and determine the radioactivity concentration. Both calibration standards and Monte Carlo simulations were used to determine the efficiency of the detectors for the samples, taking into account differences in individual sample sizes as well as matrices. In particular, a careful analysis of the atomic composition of lichens and mushrooms was performed to ensure the efficiencies for these sample types were correct. A comparison of the concentrations from before and after the accident indicated that there was no increase in radioactivity as a result of the atmospheric plume from the Fukushima accident. Some cesium-137, likely attributable to fallout from atmospheric weapons testing of the 1950s and 1960s (since there was no cesium-134 measured in the samples), was measured in the post Fukushima caribou and beluga whale samples; however, this amount was determined to be insignificant for any radiological concern (9.1 ± 1.8 and 0.63 ± 0.23 Bq kg-1 ww respectively). The activity concentrations of cesium-137 was about 200 times smaller than that of natural radioactive potassium in the beluga samples. Both the caribou and beluga results showed that these foods continue to be a healthy food choice for northern Canadians with respect to radioactivity, and this result has been communicated to the nearby northern communities and stakeholders.

Preoperative prognostic value of dynamic contrast-enhanced MRI-derived contrast transfer coefficient and plasma volume in patients with cerebral gliomas.

BACKGROUND AND PURPOSE: The prognostic value of dynamic contrast-enhanced MR imaging-derived plasma volume obtained in tumor and the contrast transfer coefficient has not been well-established in patients with gliomas. We determined whether plasma volume and contrast transfer coefficient in tumor correlated with survival in patients with gliomas in addition to other factors such as age, type of surgery, preoperative Karnofsky score, contrast enhancement, and histopathologic grade. MATERIALS AND METHODS: This prospective study included 46 patients with a new pathologically confirmed diagnosis of glioma. The contrast transfer coefficient and plasma volume obtained in tumor maps were calculated directly from the signal-intensity curve without T1 measurements, and values were obtained from multiple small ROIs placed within tumors. Survival curve analysis was performed by dichotomizing patients into groups of high and low contrast transfer coefficient and plasma volume. Univariate analysis was performed by using dynamic contrast-enhanced parameters and clinical factors. Factors that were significant on univariate analysis were entered into multivariate analysis. RESULTS: For all patients with gliomas, survival was worse for groups of patients with high contrast transfer coefficient and plasma volume obtained in tumor (P < .05). In subgroups of high- and low-grade gliomas, survival was worse for groups of patients with high contrast transfer coefficient and plasma volume obtained in tumor (P < .05). Univariate analysis showed that factors associated with lower survival were age older than 50 years, low Karnofsky score, biopsy-only versus resection, marked contrast enhancement versus no/mild enhancement, high contrast transfer coefficient, and high plasma volume obtained in tumor (P < .05). In multivariate analysis, a low Karnofsky score, biopsy versus resection in combination with marked contrast enhancement, and a high contrast transfer coefficient were associated with lower survival rates (P < .05). CONCLUSIONS: In patients with glioma, those with a high contrast transfer coefficient have lower survival than those with low parameters.

Generalized method for retrieving effective parameters of anisotropic metamaterials.

Electromagnetic or acoustic metamaterials can be described in terms of equivalent effective, in general anisotropic, media and several techniques exist to determine the effective permeability and permittivity (or effective mass density and bulk modulus in the context of acoustics). Among these techniques, retrieval methods use the measured reflection and transmission coefficients (or scattering coefficients) for waves incident on a metamaterial slab containing few unit cells. Until now, anisotropic effective slabs have been considered in the literature but they are limited to the case where one of the axes of anisotropy is aligned with the slab interface. We propose an extension to arbitrary orientations of the principal axes of anisotropy and oblique incidence. The retrieval method is illustrated in the electromagnetic case for layered media, and in the acoustic case for array of tilted elliptical particles.

Diagnostic accuracy of dynamic contrast-enhanced MR imaging using a phase-derived vascular input function in the preoperative grading of gliomas.

BACKGROUND AND PURPOSE: The accuracy of tumor plasma volume and K(trans) estimates obtained with DCE MR imaging may have inaccuracies introduced by a poor estimation of the VIF. In this study, we evaluated the diagnostic accuracy of a novel technique by using a phase-derived VIF and "bookend" T1 measurements in the preoperative grading of patients with suspected gliomas. MATERIALS AND METHODS: This prospective study included 46 patients with a new pathologically confirmed diagnosis of glioma. Both magnitude and phase images were acquired during DCE MR imaging for estimates of K(trans)_φ and V(p_)φ (calculated from a phase-derived VIF and bookend T1 measurements) as well as K(trans)_SI and V(p_)SI (calculated from a magnitude-derived VIF without T1 measurements). RESULTS: Median K(trans)_φ values were 0.0041 minutes(-1) (95 CI, 0.00062-0.033), 0.031 minutes(-1) (0.011-0.150), and 0.088 minutes(-1) (0.069-0.110) for grade II, III, and IV gliomas, respectively (P ≤ .05 for each). Median V(p_)φ values were 0.64 mL/100 g (0.06-1.40), 0.98 mL/100 g (0.34-2.20), and 2.16 mL/100 g (1.8-3.1) with P = .15 between grade II and III gliomas and P = .015 between grade III and IV gliomas. In differentiating low-grade from high-grade gliomas, AUCs for K(trans)_φ, V(p_φ), K(trans)_SI, and V(p_)SI were 0.87 (0.73-1), 0.84 (0.69-0.98), 0.81 (0.59-1), and 0.84 (0.66-0.91). The differences between the AUCs were not statistically significant. CONCLUSIONS: K(trans)_φ and V(p_)φ are parameters that can help in differentiating low-grade from high-grade gliomas.

Increased environmental gamma-ray dose rate during precipitation: a strong correlation with contributing air mass.

It has long been observed that the environmental gamma-ray dose rate increases noticeably during precipitation intervals. This increase, due to the presence of radon progeny in the rain droplets (or snow flakes), can affect the reliability of the monitoring of artificial radioactivity and long term estimates of exposure to ambient natural radionuclides in surveillance network. Predicting the amplitude of the dose increase has been shown to be surprisingly challenging. In this work, standard air mass back trajectory analysis is used to show that the amplitude of the increase can be quantitatively linked to the history of the air mass where the precipitation is occurring. Furthermore, we show how back trajectory analysis, environmental gamma and rain data can be used to obtain estimations of relative radon emanation rates for locations far from the actual point of detection.

Derivation of semiconductor laser mean-field and Swift-Hohenberg equations.

Bulk and quantum well semiconductor lasers by nature display fundamentally different physical characteristics relative to multilevel gas and solid state lasers. In particular, the refractive index is nonzero at peak gain and the peak gain can shift strongly with varying carrier density or temperature. Moreover, a quantum well laser gain may be strongly asymmetric if more than the lowest subband is populated. Rigorously computed and experimentally validated, gain and refractive index spectra are now available for a variety of quantum well structures emitting from the infrared to the visible. Active devices can be designed and grown such that the gain spectrum remains approximately parabolic for carrier density variations typically encountered in above threshold pumped broad area edge-emitting semiconductor lasers. Under this assumption, we derive a robust optical propagation model that tracks the important peak gain shifts and broadening as long as the gain remains approximately parabolic over the relevant energy range in a running laser. We next derive a multimode model where the longitudinal modes are projected out of the total field. The next stage is to derive a mean-field single longitudinal mode model for a wide aperture semiconductor laser. The mean-field model allows for significant cavity losses and widely different facet reflectivities such as occurs with antireflection- and high-reflectivity-coated facets. The single mode mean-field model is further reduced using an asymptotic expansion of the relevant physical fields with respect to a small parameter. The end result is a complex semiconductor Swift-Hohenberg description of a single longitudinal mode wide aperture laser. The latter should provide a useful model for studying scientifically and technologically important lasers such as vertical cavity surface emitting semiconductor lasers.

An exactly solvable Ogston model of gel electrophoresis: VIII. Nonconducting gel fibers, curved field lines, and the Nernst-Einstein relation.

In this article, we examine the low-field electrophoretic migration of infinitely small analytes in dilute sieving media made of nonconducting gel fibers. Using an Ogston obstruction model, we show that the electrophoretic mobility is not affected by the presence of curved field lines. In other words, the Nernst-Einstein relation between the mobility and the diffusion coefficient is valid regardless of the electrical properties of the gel fibers. Although this finding may greatly simplify the development of obstruction models of electrophoretic sieving, it also represents a critical test for any analytical or computational approach.

An exactly solvable Ogston model of gel electrophoresis. V. Attractive gel-analyte interactions and their effects on the Ferguson plot.

We examine the effect of attractive analyte-gel interactions within the framework of our recently developed lattice model of gel electrophoresis. We show that it is possible to take into account such interactions and still calculate exact mobilities for various analytes and gel structures. Our study then focuses on two main issues: (i) the effect of these interactions on the separation efficiency of the Ogston regime; and (ii) the presence of inflection points (changes of curvature) in Ferguson plots. We establish some general principles, and we describe the results for selected two- and three-dimensional model systems. Numerous practical problems, such as chiral separations and affinity electrophoresis, can be treated using this approach.

Theory of DNA electrophoresis: a look at some current challenges.

Although electrophoresis is one of the basic methods of the modern molecular biology laboratory, new ideas are being suggested at an accelerated rate, in large part because of the pressing demands of the biomedical community. Although we now have, at least for some methods, a fairly good theoretical understanding of the physical mechanisms that lead to the observed peak spacings, widths and shapes, this knowledge is often too qualitative to be used to guide further technical developments and improvements. In this article, we review some selected elements of the current state of our theoretical ignorance, focusing mostly on DNA electrophoresis, and we offer several suggestions for further theoretical investigations.

An exactly solvable Ogston model of gel electrophoresis IV: sieving through periodic three-dimensional gels.

In this article, we extend our recently developed lattice model of gel electrophoresis to periodic three-dimensional gels made of either isolated obstacles or infinitely long fibers. Exact mobilities are calculated using a much improved numerical method that allows us to treat very large systems. A comparison of the exact mobilities and free available volumes indicates that the main assumption of the Ogston-Morris-Rodbard-Chrambach model (OMRCM), which postulates that the mobility (mu) of charged particles is directly related to the fractional gel volume available to them, is not valid. However, a study of the gel concentration and analyte size dependence of the zero-field mobility indicates that the OMRCM and the Ferguson plots can indeed be used to obtain useful, semi-quantitative information about the gel properties. A procedure to study more realistic three-dimensional gel systems is discussed.

[Radiology in the medicolegal identification of cadavers. A new technique of radiography of the maxilla]. / Apports de la radiologie pour l'identification médico-légale des corps. Une technique nouvelle de radiographie des maxillaires.

After removal, the maxilla and the mandible are placed on a standard radiologic cassette and a X-ray is performed with a low energy beam. Different views can be obtained if required. These radiographic images provide a complete, permanent and detailed record of dental anatomy and restorations, for comparison with antemortem radiographies. Two examples are provided. Moreover, this technique enables the determination of the dental age of children.

[The role of the radiologist in the medicolegal procedure after an aviation accident]. / Rôle du radiologiste dans l'enquête médico-légale après une catastrophe aérienne.

The role of radiologic imaging studies in the forensic medical procedure following an airborne disaster is now well established. This report summarizes the experience and the results acquired with a recent air crash, and insists on three suggestions: the necessity of a prepared identification team consisting of specialist in forensic medicine, in forensic odontology and specialist in forensic radiology, and the usefulness of a suitable structure for the study and the storage of the dead bodies, the need for a compilation of radiological informations, notably dental X-Ray examinations for the flying personnel.

Renal kallikrein excretion as a distal nephrotoxicity marker during cadmium exposure in rats.

Cadmium exposure is known to induce hypertension, but development of hypertension is not universal in exposed animals. However, the cellular uptake of cadmium could also exert renal cytotoxic effects which have been, until now, essentially only studied at the proximal tubule level. Kallikrein is an enzyme synthetized in renal cortex and excreted in the urine in the distal tubule. Therefore, to evaluate the distal renal effect of cadmium, we studied the daily urinary kallikrein excretion (UKE) in conscious unrestrained female Brown Norway rats during long-term chronic exposure to 2 dosages of cadmium given subcutaneously 3 times a week, a low dose (LD): 0.25 mg/kg and a high dose (HD): 1 mg/kg. Neither dose of cadmium was able to induce significant hypertension in the treated animals. HD administration for 24 weeks resulted in a decreased UKE associated with an increase in plasma renin activity and sodium and potassium excretions. LD administration had no significant effect on UKE. Twenty weeks after stopping cadmium administration, a persistent reduction in UKE was still observed; furthermore, the group which had been previously administered a LD of cadmium, now also exhibited a reduced UKE. During this re-examination period in both groups, the UKE reductions were associated with normal systolic blood pressure, glycosuria, natriuresis. Our data show that cadmium administration can influence UKE, plasma renin activity, plasma aldosterone concentration and electrolyte excretion without inducing any variation of blood pressure. This may reflect a nephrotoxic, non-hypertensive effect. Since this effect persisted after stopping cadmium administration, it may indicate a prolonged irreversible nephrotoxic effect at the distal nephron level. Thus, UKE may be a useful non-invasive index to evaluate distal nephrotoxicity.