| 1. |
- Aminalragia-Giamini, Sigiava, et al.
(författare)
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Solar Energetic Particle Event occurrence prediction using Solar Flare Soft X-ray measurements and Machine Learning
- 2021
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Ingår i: Journal of Space Weather and Space Climate. - : EDP Sciences. - 2115-7251. ; 11
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Tidskriftsartikel (refereegranskat)abstract
- The prediction of the occurrence of Solar Energetic Particle (SEP) events has been investigated over many years, and multiple works have presented significant advances in this problem. The accurate and timely prediction of SEPs is of interest to the scientific community as well as mission designers, operators, and industrial partners due to the threat SEPs pose to satellites, spacecrafts, and crewed missions. In this work, we present a methodology for the prediction of SEPs from the soft X-rays of solar flares associated with SEPs that were measured in 1 AU. We use an expansive dataset covering 25 years of solar activity, 1988-2013, which includes thousands of flares and more than two hundred identified and catalogued SEPs. Neural networks are employed as the predictors in the model, providing probabilities for the occurrence or not of a SEP, which are converted to yes/no predictions. The neural networks are designed using current and state-of-the-art tools integrating recent advances in the machine learning field. The results of the methodology are extensively evaluated and validated using all the available data, and it is shown that we achieve very good levels of accuracy with correct SEP occurrence prediction higher than 85% and correct no-SEP predictions higher than 92%. Finally, we discuss further work towards potential improvements and the applicability of our model in real-life conditions.
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| 2. |
- Fan, Bo-Guang, et al.
(författare)
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Total parenteral nutrition influences both endocrine and exocrine function of rat pancreas
- 1997
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Ingår i: Pancreas. - 0885-3177. ; 15:2, s. 147-153
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this study was to examine the effect of total parenteral nutrition (TPN) on the endocrine and exocine function of the pancreas. Endocrine function was investigated using an intravenous glucose tolerance test (IGTT) in rats with TPN for 7 or 14 days. Exocrine function was evaluated by measuring amylase secretion from isolated acini as well as pancreatic weight, water content, protein, and enzymes after 7 days of TPN. When the TPN rats were compared with the controls, the glucose tolerance curve after an IGTT was unchanged, the basal plasma insulin levels were slightly lower and the insulin secretory response to intravenous glucose was markedly impaired. No differences could be seen between the insulin response after 7 days and that after 14 days of TPN. The weight of pancreas, the total content and concentration of pancreatic protein, and the total amylase content of the pancreas were lower, whereas the total content of both chymotrypsin and trypsin was higher. The concentration of DNA remained intact, whereas the total DNA content decreased. The levels of lipolytic enzymes, except for carboxylesterlipase, were unaffected. After TPN treatment, the insulin secretory response to glucose is impaired, the exocrine pancreas is hypoplastic and the storage pattern of pancreatic exocrine enzymes is altered.
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| 3. |
- Sandberg, Ingmar, 1974-
(författare)
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Drift and Mirror Modes in Magnetized Plasmas
- 2002
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Low frequency plasma instabilities driven by plasma inhomogeneity and velocity anisotropies are major candidates for the explanation of various phenomena observed in fusion and space plasmas. For low-β fusion plasma, the influence of plasma rotation and finite ion temperature on the structure and the type of toroidal drift eigenmodes in tokamaks is investigated rigorously, including the effects induced by the toroidal geometry such as the coupling mode, the radial variation of plasma rotation velocity and the magnetic shear. The conditions at which global or propagating drift modes are formed and the analytical dispersion relations are obtained for various cases. For high-β space plasma, a unified theory of the mirror instability based on a quasi-hydrodynamic approach and a unified fully kinetic theory of the drift mirror instabilities have been developed. The obtained results are applicable for arbitrary distribution functions and can be used to determine whether mirror and drift mirror modes are stable or unstable in a multi-component plasma, including electron temperature effects and electron pressure anisotropies. A major outcome of the theory of drift mirror instabilities, is the prediction of a hydrodynamic drift mirror instability with threshold lower than the classic ion drift mirror instability.
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| 4. |
- Sandberg, Ingmar, et al.
(författare)
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Finite Larmor radius effects on the coupled trapped electron and ion temperature gradient modes
- 2007
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1070-664X .- 1089-7674. ; 14:9, s. 092504-
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Tidskriftsartikel (refereegranskat)abstract
- The properties of the coupled trapped electron and toroidal ion temperature gradient modes are investigated using the standard reactive fluid model and taking rigorously into account the effects attributed to the ion polarization drift and to the drifts associated with the lowest-order finite ion Larmor radius effects. In the flat density regime, where the coupling between the modes is relatively weak, the properties of the unstable modes are slightly modified through these effects. For the peak density regions, where the coupling of the modes is rather strong, these second-order drifts determine the spectra of the unstable modes near the marginal conditions.
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| 5. |
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| 6. |
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| 7. |
- Sandberg, Ingmar, et al.
(författare)
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Zonal flow in toroidal ion temperature gradient mode turbulence
- 2007
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Ingår i: Journal of Plasma Physics. - 0022-3778 .- 1469-7807. ; 73:4, s. 565-573
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Tidskriftsartikel (refereegranskat)abstract
- The properties of zonal flows in the toroidal ion temperature gradient mode turbulence are investigated taking into account the polarization drift effects. The stability criterion and the characteristic oscillation frequency of the zonal flow are determined in terms of the spectra of turbulent fluctuations. The nonlinear evolution of zonal flows may lead to the formation of stationary long-lived coherent structures supporting stationary shear layers. These results indicate the existence of regions with reduced levels of anomalous transport attributed to zonal flows generalizing previous findings regarding zonal flows in electron drift turbulence.
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| 8. |
- Sarris, Theodoros E., et al.
(författare)
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Daedalus : a low-flying spacecraft for in situ exploration of the lower thermosphere-ionosphere
- 2020
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Ingår i: Geoscientific Instrumentation, Methods and Data Systems. - : COPERNICUS GESELLSCHAFT MBH. - 2193-0856 .- 2193-0864. ; 9:1, s. 153-191
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Tidskriftsartikel (refereegranskat)abstract
- The Daedalus mission has been proposed to the European Space Agency (ESA) in response to the call for ideas for the Earth Observation program's 10th Earth Explorer. It was selected in 2018 as one of three candidates for a phase-0 feasibility study. The goal of the mission is to quantify the key electrodynamic processes that determine the structure and composition of the upper atmosphere, the gateway between the Earth's atmosphere and space. An innovative preliminary mission design allows Daedalus to access electrodynamics processes down to altitudes of 150 km and below. Daedalus will perform in situ measurements of plasma density and temperature, ion drift, neutral density and wind, ion and neutral composition, electric and magnetic fields, and precipitating particles. These measurements will unambiguously quantify the amount of energy deposited in the upper atmosphere during active and quiet geomagnetic times via Joule heating and energetic particle precipitation, estimates of which currently vary by orders of magnitude between models and observation methods. An innovation of the Daedalus preliminary mission concept is that it includes the release of subsatellites at low altitudes: combined with the main spacecraft, these subsatellites will provide multipoint measurements throughout the lower thermosphereionosphere (LTI) region, down to altitudes below 120 km, in the heart of the most under-explored region in the Earth's atmosphere. This paper describes Daedalus as originally proposed to the ESA.
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| 9. |
- Sarris, Theodore E., et al.
(författare)
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Daedalus MASE (mission assessment through simulation exercise): A toolset for analysis of in situ missions and for processing global circulation model outputs in the lower thermosphere-ionosphere
- 2023
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Ingår i: Frontiers in Astronomy and Space Sciences. - : Frontiers Media SA. - 2296-987X. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- Daedalus MASE (Mission Assessment through Simulation Exercise) is an open-source package of scientific analysis tools aimed at research in the Lower Thermosphere-Ionosphere (LTI). It was created with the purpose to assess the performance and demonstrate closure of the mission objectives of Daedalus, a mission concept targeting to perform in-situ measurements in the LTI. However, through its successful usage as a mission-simulator toolset, Daedalus MASE has evolved to encompass numerous capabilities related to LTI science and modeling. Inputs are geophysical observables in the LTI, which can be obtained either through in-situ measurements from spacecraft and rockets, or through Global Circulation Models (GCM). These include ion, neutral and electron densities, ion and neutral composition, ion, electron and neutral temperatures, ion drifts, neutral winds, electric field, and magnetic field. In the examples presented, these geophysical observables are obtained through NCAR’s Thermosphere-Ionosphere-Electrodynamics General Circulation Model. Capabilities of Daedalus MASE include: 1) Calculations of products that are derived from the above geophysical observables, such as Joule heating, energy transfer rates between species, electrical currents, electrical conductivity, ion-neutral collision frequencies between all combinations of species, as well as height-integrations of derived products. 2) Calculation and cross-comparison of collision frequencies and estimates of the effect of using different models of collision frequencies into derived products. 3) Calculation of the uncertainties of derived products based on the uncertainties of the geophysical observables, due to instrument errors or to uncertainties in measurement techniques. 4) Routines for the along-orbit interpolation within gridded datasets of GCMs. 5) Routines for the calculation of the global coverage of an in situ mission in regions of interest and for various conditions of solar and geomagnetic activity. 6) Calculations of the statistical significance of obtaining the primary and derived products throughout an in situ mission’s lifetime. 7) Routines for the visualization of 3D datasets of GCMs and of measurements along orbit. Daedalus MASE code is accompanied by a set of Jupyter Notebooks, incorporating all required theory, references, codes and plotting in a user-friendly environment. Daedalus MASE is developed and maintained at the Department for Electrical and Computer Engineering of the Democritus University of Thrace, with key contributions from several partner institutions.
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