Omega-3 canola oil effectively replaces fish oil as a new safe dietary source of docosahexaenoic acid (DHA) in feed for juvenile Atlantic salmon

Limited availability of fish oils (FO), rich in n-3 long-chain (≥C20) PUFA, is a major constraint for further growth of the aquaculture industry. Long-chain n-3 rich oils from crops GM with algal genes are promising new sources for the industry. This project studied the use of a newly developed n-3 canola oil (DHA-CA) in diets of Atlantic salmon fingerlings in freshwater. The DHA-CA oil has high proportions of the n-3 fatty acids (FA) 18 : 3n-3 and DHA and lower proportions of n-6 FA than conventional plant oils. Levels of phytosterols, vitamin E and minerals in the DHA-CA were within the natural variation of commercial canola oils. Pesticides, mycotoxins, polyaromatic hydrocarbons and heavy metals were below lowest qualifiable concentration. Two feeding trials were conducted to evaluate effects of two dietary levels of DHA-CA compared with two dietary levels of FO at two water temperatures. Fish increased their weight approximately 20-fold at 16°C and 12-fold at 12°C during the experimental periods, with equal growth in salmon fed the FO diets compared with DHA-CA diets. Salmon fed DHA-CA diets had approximately the same EPA+DHA content in whole body as salmon fed FO diets. Gene expression, lipid composition and oxidative stress-related enzyme activities showed only minor differences between the dietary groups, and the effects were mostly a result of dietary oil level, rather than the oil source. The results demonstrated that DHA-CA is a safe and effective replacement for FO in diets of Atlantic salmon during the sensitive fingerling life-stage.acceptedVersio

Calathus: A sample-return mission to Ceres

Ceres, as revealed by NASA's Dawn spacecraft, is an ancient, crater-saturated body dominated by low-albedo clays. Yet, localised sites display a bright, carbonate mineralogy that may be as young as 2 Myr. The largest of these bright regions (faculae) are found in the 92 km Occator Crater, and would have formed by the eruption of alkaline brines from a subsurface reservoir of fluids. The internal structure and surface chemistry suggest that Ceres is an extant host for a number of the known prerequisites for terrestrial biota, and as such, represents an accessible insight into a potentially habitable “ocean world”. In this paper, the case and the means for a return mission to Ceres are outlined, presenting the Calathus mission to return to Earth a sample of the Occator Crater faculae for high-precision laboratory analyses. Calathus consists of an orbiter and a lander with an ascent module: the orbiter is equipped with a high-resolution camera, a thermal imager, and a radar; the lander contains a sampling arm, a camera, and an on-board gas chromatograph mass spectrometer; and the ascent module contains vessels for four cerean samples, collectively amounting to a maximum 40 g. Upon return to Earth, the samples would be characterised via high-precision analyses to understand the salt and organic composition of the Occator faculae, and from there to assess both the habitability and the evolution of a relict ocean world from the dawn of the Solar System.The attached document is the authors’ final accepted version of the journal article provided here with a Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0) Creative Commons Licence. You are advised to consult the publisher’s version if you wish to cite from it.

Flashs Gamma Terrestres et émissions électromagnétiques associées ; des rayonnements radio aux rayonnements gamma

Les flashs gamma terrestres (TGF) sont d’intenses bouffées de rayonnement gamma, de durées inférieures à la milliseconde, produits dans les champs électriques des nuages d’orage. Les TGF sont déclenchés par un processus connu sous le nom d’Avalanche d’Électrons Runaway Relativistes (RREA), mais le mécanisme exact de production et le contexte général derrière ce processus fait encore débat. Dans cette thèse, nous utilisons différents outils de modélisation afin d’explorer les divers aspects des TGF ainsi que des émissions électromagnétiques qui leur sont associées. Ce faisant, nous abordons un des sujets de recherche les plus récents dans le domaine de la physique atmosphérique des hautes énergies. Lors de la propagation des RREA, des électrons de basse énergie ainsi que des ions positifs et négatifs sont produits. Ces particules chargées produisent des courants lors de leur mouvement dans le champ électrique de l’orage. Nous modélisons les espèces chargées produites par les RREA, et les émissions radio qui en résultent dans le contexte d’électrons runaway thermiques injectés par un leader d’éclair. Nous trouvons que pour certaines conditions initiales, ces émissions radio correspondent aux ``slow LF pulses'' qui ont été précédemment observés simultanément avec des TGF. Cela confirme que les slow LF pulses sont en fait générés directement par la source du TGF elle-même, comme cela a été précédemment suggéré. Les slow LF pulses pourront ainsi être utilisés pour déterminer les propriétés caractéristiques des sources de TGF. Depuis que le Telescope Array (Utah, États-Unis) commence à détecter de particules de haute énergie corrélées avec des éclairs, le nombre de détection depuis le sol a considérablement augmenté. Les observations de TGF depuis le sol représentent un outil complémentaire aux observations satellites. La proximité avec l’évènement et la possibilité d’observer un évènement avec plusieurs détecteurs pourraient révéler de nouvelles informations sur la production des TGF. Nous nous intéressons aux TGF inversés (dirigés vers le sol) en utilisant un modèle Monte Carlo de transport de photon dans l’atmosphère. Les pulses de rayonnement gamma détectés par le Telescope Array s’étendent sur des périodes de quelques centaines de microsecondes, avec des structures temporelles inférieure à 10 µs. Nous prédisons que de telles structures seraient observables aux altitudes de satellites, en supposant une résolution temporelle suffisante. D’autre part, nous démontrons comment différents spectres de sources de TGF mèneraient à différent nombres de photons atteignant le sol, ce qui impacte les conclusions qu’on peut tirer en utilisant les données observationnelles. Lors de la propagation d’un TGF, le rayonnement gamma qui ionise l’air environnant, produit ainsi des électrons libres. Ces électrons émettent un rayonnement bremsstrahlung (ici appelé photons secondaires), principalement dû aux collisions avec les noyaux des molécules de l’air. Une partie de ce rayonnement bremsstrahlung sera d’énergie suffisante pour atteindre l’altitude des satellites. Le spectre de ces photons secondaires dépend des propriétés initiales du TGF, et peut être utilisé pour caractériser ces dernières à partir des observations. Les photons secondaires sont également une signature directe de l’énergie déposée dans l’atmosphère par les TGF. Parce qu’ils ne sont pas facilement distinguables des photons du TGF, nous proposons trois mesures pour analyser les résultats liés aux spectres des photons secondaires. De cette façon, nous sommes capables de quantifier les propriétés de TGF de différents spectres initiaux et différentes géométrie de faisceaux. Dans cette thèse, nous démontrons que la combinaison de divers effets de différentes natures liés aux TGF peut être un outil puissant pour résoudre nombre de questions ouvertes dans le domaine de la physique de l’atmosphère des hautes énergies.Terrestrial Gamma-ray Flashes (TGFs) are bright, sub-millisecond bursts of gamma rays originating in the electric fields of thunderstorms. TGFs are thought to be initiated by a process known as a Relativistic Runaway Electron Avalanche (RREA), but the exact seeding mechanism and general context behind the process remain debated. In this thesis, we use a range of modeling tools to explore several different aspects of TGFs and associated electromagnetic emissions. In doing so, we address some of the most recent research in the field of high-energy atmospheric physics.As RREAs propagate, they leave a trail of low-energy electrons and positive and negative ions behind. These populations of charged particles will carry currents as they move in the thunderstorm electric field. We model the charged species left behind by the propagating RREA, and the resulting radio emissions in the context of injection of thermal runaway seed electrons by a lightning leader. We find that for certain initial conditions, these radio emissions match slow LF pulses that have previously been observed concurrently with TGFs. This confirms that the slow LF pulses are generated directly by the TGF source itself, as has been previously suggested. Slow LF pulses may therefore be used to infer characteristic properties of TGF sources.Until recently, there were only a few ground-based observations of TGFs. Since the Telescope Array in Utah, USA, started reporting detections of high-energy particles correlated with lightning, their number has greatly increased. Ground observations of TGFs represent a valuable addition to space-borne detectors. The proximity to the event and the ability to observe an event with several detectors may reveal new information about the production of TGFs. We study downward directed TGFs using Monte Carlo modeling of photon transport through the atmosphere. The Telescope Array-observed pulses of gamma rays spread over periods of a few hundred microseconds, with time structures of less than 10 µs. We predict such structures to be observable at satellite altitude, given sufficient time resolution. Additionally, we demonstrate how various source spectra would lead to different number of photons reaching ground, which impacts the conclusions one can draw using observational data.As a TGF propagates, gamma rays will knock electrons free as they interact with the surrounding air. These electrons emit bremsstrahlung (here referred to as secondary photons), mainly due to collisions with the nuclei of air molecules. Some of this bremsstrahlung has sufficient energy to reach satellite altitude. The spectrum of secondary photons is dependent on the initial TGF’s properties, and can be used to infer these from observations. Secondary photons are also a direct signature of the energy deposited into the atmosphere by TGFs. Because they are not easily separated from the photons of the TGF, we propose three measures to analyze results relating to secondary photon spectra. In this way, we are able to quantify properties of TGFs with different initial energy spectra and beaming geometry.In this thesis, we demonstrate that the combination of multiple TGF-related effects of different nature can be a powerful tool to solve many of the open questions in high-energy atmospheric physics

Constraining Downward Terrestrial Gamma Ray Flashes Using Ground‐Based Particle Detector Arrays

International audienceUntil recently, there were only a few ground‐based observations of terrestrial gamma ray flashes (TGFs). Since the Telescope Array in Utah, USA, started reporting detections of high‐energy particles correlated with lightning, their number has greatly increased. Ground observations of TGFs represent a valuable addition to space‐borne detectors. The proximity to the event and the ability to observe an event with several detectors may reveal new information about the production of TGFs. In this paper, we study downward directed TGFs using Monte Carlo modeling of photon transport through the atmosphere. The Telescope Array‐observed pulses of gamma rays spread over periods of a few hundred microseconds. We predict such structures to be observable at satellite altitude, given sufficient time resolution. Additionally, we demonstrate how various source spectra would lead to different number of photons reaching ground, which impacts the conclusions one can draw using observational data.Plain Language SummaryTerrestrial gamma ray flashes (TGFs) are bursts of high‐energy photons that originate in thunderstorms. TGFs have been routinely observed from space since their discovery. Until recently, there were only a few ground‐based observations of TGFs. Their number has increased since the Telescope Array started reporting detections of high‐energy particles at the same time as lightning. Ground observations of TGFs represent a valuable addition to detectors in space. They are closer to the source of the event, and it is possible to observe a single event with several detectors. Because of this, ground observations may reveal new information about the production mechanisms of TGFs. We study downward TGFs by modeling photons moving through the atmosphere. The Telescope Array‐observed pulses of gamma rays. We predict that similar pulses should be observable by satellites, given sufficient time resolution. TGFs are thought to start out as photons moving in a cone‐shaped beam. We want to find the shape of this beam from ground observations, but photons interacting with the atmosphere changes how the beam looks. We determine the beam shape by the photons' positions on ground. We also find that the number of photons reaching ground is dependent on the photons' initial energies

Secondary bremsstrahlung X-rays emitted during TGF propagation

International audienceTerrestrial gamma ray flashes (TGFs) are high-energy bursts of photons bright enough to be routinely observed from space. They originate in thunderstorms in association with lightning activity. As the gamma rays propagate through the atmosphere, interactions of photons with air molecules produce secondary electrons. When trapped around geomagnetic field lines, some of these electrons can be observed as terrestrial electron beams (TEBs) at satellite altitude. Most of secondary electrons do not make it as far as space; rather they lose their energy through interactions with the atmosphere. Through bremsstrahlung, the secondary electrons also produce another population of photons in the X-ray energy range. The satellite Taranis (CNES) and the observatory ASIM (ESA) have been specifically designed to study TGFs and other lightning-related phenomena, and will have X- and gamma ray detection capabilities. Through Monte Carlo simulations of particle propagation and interaction with the atmosphere, we model the production and properties of secondary electrons and the induced second generation of photons. We aim to predict how secondary X-rays might be detected by space-based instruments. We find that especially at the lower end of the TGF energy range, the secondary X-rays make a noticeable contribution to the spectrum

Secondary bremsstrahlung X-rays emitted during TGF propagation

International audienceTerrestrial gamma ray flashes (TGFs) are high-energy bursts of photons bright enough to be routinely observed from space. They originate in thunderstorms in association with lightning activity. As the gamma rays propagate through the atmosphere, interactions of photons with air molecules produce secondary electrons. When trapped around geomagnetic field lines, some of these electrons can be observed as terrestrial electron beams (TEBs) at satellite altitude. Most of secondary electrons do not make it as far as space; rather they lose their energy through interactions with the atmosphere. Through bremsstrahlung, the secondary electrons also produce another population of photons in the X-ray energy range. The satellite Taranis (CNES) and the observatory ASIM (ESA) have been specifically designed to study TGFs and other lightning-related phenomena, and will have X- and gamma ray detection capabilities. Through Monte Carlo simulations of particle propagation and interaction with the atmosphere, we model the production and properties of secondary electrons and the induced second generation of photons. We aim to predict how secondary X-rays might be detected by space-based instruments. We find that especially at the lower end of the TGF energy range, the secondary X-rays make a noticeable contribution to the spectrum

A new population of Terrestrial Gamma-ray Flashes

Terrestrial Gamma-ray Flashes (TGFs) consist of large numbers of highenergy photons produced in thunderstorms in connection with the lightning flash, and are the most energetic photon phenomenon naturally occurring on Earth. The satellite RHESSI, originally designed for observing solar flares, is also able to register gamma-rays from Earth. Algorithms for finding TGFs in the RHESSI data have been purposefully conservative, but Østgaard et al. [2015] presented a method to identify TGFs that were not part of previous RHESSI TGF catalogs. By superposing RHESSI data intervals for each lightning detection by the World Wide Lightning Location Network (WWLLN) within RHESSI’s field-of-view, they showed that there exists a group of weak signal TGFs. Expanding on this work we here provide a statistical analysis comparing the signal strength to both background levels and to a Poisson distribution. We seek to optimize the range of the search parameters in order to minimize the chance of including background events. The geographical distribution of the TGFs will also be investigated. As many of the TGFs we work with have a weak signal, they can be difficult to distinguish from the background level. Because of this the factors that cause variation of the incoming background radiation levels are of interest to us, and we have identify several such factors

Observationally weak TGFs in the RHESSI data

International audienceTerrestrial gamma‐ray Flashes (TGFs) are sub‐millisecond bursts of high energetic gamma radiation associated with intracloud flashes in thunderstorms. In this paper we use the simultaneity of lightning detections by WWLLN to find TGFs in the RHESSI data that are too faint to be identified by standard search algorithms. A similar approach has been used in an earlier paper, but here we expand the dataset to include all years of RHESSI+WWLLN data, and show that there is a population of observationally weak TGFs all the way down to 0.22 of the RHESSI detection threshold (3 counts in the detector). One should note that the majority of these are “normal” TGFs that are produced further away from the sub‐satellite point (and experience a 1/r2 effect) or produced at higher latitudes with a lower tropoause, and thus experience increased atmospheric attenuation. This supports the idea that the TGF production rate is higher than currently reported. We also show that, compared to lightning flashes, TGFs are more partial to ocean and coastal regions than over land

Geomagnetic Deviation of Relativistic Electron Beams Producing Terrestrial Gamma Ray Flashes

International audienceIn this work, we investigate the effect of the geomagnetic field on terrestrial gamma ray flashes (TGFs). Although this effect should be relatively weak for a single event, for example compared to the effect of the electric field orientation in the source region, it must be systematically present. Indeed, we show that a statistically significant excess of TGFs is detected to the east of their presumed lightning source by Fermi-Gamma-ray Burst Monitor (GBM). The corresponding eastward deviation is found to be likely greater than 0.1° in longitude, which is consistent with the expected effect of the geomagnetic field on relativistic runaway electron beams producing TGFs. Using analytical and numerical means, we show that the geomagnetic deviation can be used to estimate the magnitude of the electric field in TGF source regions. The electric field magnitudes we obtain are consistent with those necessary to drive relativistic runaway electron avalanches (RREAs)

Modeling Low‐Frequency Radio Emissions From Terrestrial Gamma Ray Flash Sources

International audienceRelativistic runaway electron avalanches (RREAs) occur when electrons in electric fields in air reach energies above which they gain more energy from the electric field than they lose to collisions with the surrounding atmosphere. RREAs are known to happen in the electric fields in thunderstorms, and are considered to be the mechanism responsible for producing Terrestrial Gamma-ray Flashes (TGFs). As RREAs propagate, they leave a trail of low-energy electrons and positive and negative ions behind. These populations of charged particles will carry currents as they move in the thunderstorm electric field. In the present work, we model the charged species left behind by the propagating RREA, and the resulting radio emissions in the context of injection of thermal runaway seed electrons by a leader. We find that for certain initial conditions, these radio emissions match the slow low-frequency (LF) pulses that have previously been observed concurrently with TGFs. This confirms that the slow LF pulses are likely generated directly by the TGF source itself, as has been previously suggested using a different TGF production model. Slow LF pulses may therefore potentially be used to infer characteristic properties of TGF sources