| 1. |
- Korablev, O., et al.
(författare)
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The Atmospheric Chemistry Suite (ACS) of Three Spectrometers for the ExoMars 2016 Trace Gas Orbiter
- 2018
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Ingår i: Space Science Reviews. - : Springer. - 0038-6308 .- 1572-9672. ; 214:1
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Tidskriftsartikel (refereegranskat)abstract
- The Atmospheric Chemistry Suite (ACS) package is an element of the Russian contribution to the ESA-Roscosmos ExoMars 2016 Trace Gas Orbiter (TGO) mission. ACS consists of three separate infrared spectrometers, sharing common mechanical, electrical, and thermal interfaces. This ensemble of spectrometers has been designed and developed in response to the Trace Gas Orbiter mission objectives that specifically address the requirement of high sensitivity instruments to enable the unambiguous detection of trace gases of potential geophysical or biological interest. For this reason, ACS embarks a set of instruments achieving simultaneously very high accuracy (ppt level), very high resolving power (>10,000) and large spectral coverage (0.7 to 17 μm—the visible to thermal infrared range). The near-infrared (NIR) channel is a versatile spectrometer covering the 0.7–1.6 μm spectral range with a resolving power of ∼20,000. NIR employs the combination of an echelle grating with an AOTF (Acousto-Optical Tunable Filter) as diffraction order selector. This channel will be mainly operated in solar occultation and nadir, and can also perform limb observations. The scientific goals of NIR are the measurements of water vapor, aerosols, and dayside or night side airglows. The mid-infrared (MIR) channel is a cross-dispersion echelle instrument dedicated to solar occultation measurements in the 2.2–4.4 μm range. MIR achieves a resolving power of >50,000. It has been designed to accomplish the most sensitive measurements ever of the trace gases present in the Martian atmosphere. The thermal-infrared channel (TIRVIM) is a 2-inch double pendulum Fourier-transform spectrometer encompassing the spectral range of 1.7–17 μm with apodized resolution varying from 0.2 to 1.3 cm−1. TIRVIM is primarily dedicated to profiling temperature from the surface up to ∼60 km and to monitor aerosol abundance in nadir. TIRVIM also has a limb and solar occultation capability. The technical concept of the instrument, its accommodation on the spacecraft, the optical designs as well as some of the calibrations, and the expected performances for its three channels are described.
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| 2. |
- Mikhaylova, Maria, et al.
(författare)
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The effect of biocompatible coating layers on magnetic properties of superparamagnetic iron oxide nanoparticles
- 2004
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Ingår i: Hyperfine Interactions. - 0304-3843 .- 1572-9540. ; 156:1, s. 257-263:156/157, s. 257-263
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Tidskriftsartikel (refereegranskat)abstract
- The effect of the surface coating on the magnetic properties of superparamagnetic iron oxide nanoparticles (SPION) with 8 nm in size has been studied. Four different biocompatible coating layers are considered: poly L,L-lactic acid (PLLA), poly epsilon-caprolactone (PCL), bovine serum albumin (BSA) and gold. The presence of coating layer on the surface of SPION is confirmed by FT-IR spectroscopy. Mossbauer spectroscopy and magnetic susceptibility measurements show that for uncoated SPION and Au@SPION the superparamagnetic fraction is retained. The formation of clusters in the case of BSA@SPION and chain-like structure for PCL@SPION and PLLA@SPION increase the inter-particle interactions resulting in hyperfine magnetic structure observed in the Mossbauer spectra at ambient temperature.
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| 3. |
- Korovinskiy, D., et al.
(författare)
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MHD Modeling of the Kink "Double-gradient" Branch of the Ballooning Instability in the Magnetotail
- 2014
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Ingår i: NUMERICAL MODELING OF SPACE PLASMA FLOWS. - : ASTRONOMICAL SOC PACIFIC. - 9781583818602 ; , s. 149-154
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Konferensbidrag (refereegranskat)abstract
- We present a numerical investigation of the double-gradient mode, which is believed to be responsible for the magnetotail flapping oscillations the fast vertical oscillations of the Earth's magnetotail plasma sheet (quasiperiod similar to 100 - 200 s). It is known that this mode has an unstable solution in the region of the tailward-growing normal magnetic field component. The kink branch of the mode is the focus of our study. The instability is studied using the magnetotail near-equilibrium configuration, fixed by the approximate solution of the Grad-Shafranov equation. The linear three-dimensional numerical analysis is complemented with full 3-D MUD simulations. The results of our linearized MHD code agree with the theory, and the growth rate is found to be close to the peak value provided by an analytical estimate. Also, the eigenfunctions, calculated analytically, are very similar to the perturbations obtained numerically. The full 3D MHD simulations are initialized with the numerically relaxed magnetotail equilibrium, similar to the linear code initial condition. The calculations show that the double-gradient mode is excited in a region of small radii of the magnetic field lines curvature, which is in accordance with the analytical predictions. In contrast to the linearized MHD simulations, non-local interactions are involved; hence, the overall growth rate turns out to be close to the theoretical estimate averaged over the computational domain.
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| 4. |
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| 5. |
- Mader, P., et al.
(författare)
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Experimental validation of fringing field effects for the multipactor phenomenon
- 2012
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Ingår i: 15th International Symposium on Antenna Technology and Applied Electromagnetics, ANTEM 2012, Toulouse, 25-28 June 2012. - 9781467302913
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Konferensbidrag (refereegranskat)abstract
- The multipactor effect is a constraining phenomenon in the design of RF components. Due to an increasing number of channels and power levels for multicarrier signals, specific requirements of design must be taken into account in order to prevent the multipactor effect. The current methods of analysis are based on the Hatch and Williams diagrams, which provide the multipaction threshold voltage for a parallel plate geometry as a function of the frequency gap product. However, whereas experimental results have shown good correlation with the theoretical charts for the parallel plate geometry, discrepancies have been found for complex geometries such as irises.
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| 6. |
- Mikhaylova, Maria, et al.
(författare)
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Superparamagnetism of magnetite nanoparticles : Dependence on surface modification
- 2004
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 20:6, s. 2472-2477
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Tidskriftsartikel (refereegranskat)abstract
- Superparamagnetic iron oxide nanoparticles (SPION) with an average particle diameter of 6 nm are prepared by controlled chemical coprecipitations. Colloidal suspensions of noninteracting SPION, where the surface has been modified with three different types of biocompatible substances, namely, starch, gold (An), and methoxypoly(ethylene glycol) (MPEG) have been fabricated via three different techniques. Starch-coated SPION are prepared by coprecipitation in a polymeric matrix, Au-coated SPION are fabricated by the microemulsion method, and MPEG-coated SPION are prepared using the self-assembly approach. The magnetic nanoparticles form a core-shell structure, and the magnetic dipole-dipole interactions are screened by a layer of coating agents. The amounts of coating agents and SPION are indirectly calculated from the thermogravinietric analysis and superconducting quantum interference device measurements by assuming passive oxidation on the surface of the SPION, and the other conditions do not influence the measurements. The dependency of the spectral characteristics of Mossbauer spectroscopy as a function of an external magnetic field H-ext is measured to investigate the effect of dipole-dipole screening of the different coating layers on the SPION. Uncoated SPION show a stable magnetic moment under H-etx and the superparamagnetic (SPM) fraction transforms to a ferrimagnetic state. Starch and Au-coated SPION retain the SPM fraction according to Mossbauer spectroscopy and magnetization measurements. MPEG-coated SPION show hyperfine magnetic structure without the quadrupole effect with increasing the value of the blocking temperature.
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| 7. |
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| 8. |
- Tournier, P-H, et al.
(författare)
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Microwave tomographic imaging of cerebrovascular accidents by using high-performance computing
- 2019
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Ingår i: Parallel Computing. - : ELSEVIER SCIENCE BV. - 0167-8191 .- 1872-7336. ; 85, s. 88-97
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Tidskriftsartikel (refereegranskat)abstract
- The motivation of this work is the detection of cerebrovascular accidents by microwave tomographic imaging. This requires the solution of an inverse problem relying on a minimization algorithm (for example, gradient-based), where successive iterations consist in repeated solutions of a direct problem. The reconstruction algorithm is extremely computationally intensive and makes use of efficient parallel algorithms and high-performance computing. The feasibility of this type of imaging is conditioned on one hand by an accurate reconstruction of the material properties of the propagation medium and on the other hand by a considerable reduction in simulation time. Fulfilling these two requirements will enable a very rapid and accurate diagnosis. From the mathematical and numerical point of view, this means solving Maxwell's equations in time-harmonic regime by appropriate domain decomposition methods, which are naturally adapted to parallel architectures.
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| 9. |
- Akperov, Mirseid, et al.
(författare)
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Future projections of wind energy potentials in the arctic for the 21st century under the RCP8.5 scenario from regional climate models (Arctic-CORDEX)
- 2023
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Ingår i: Anthropocene. - 2213-3054. ; 44
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Tidskriftsartikel (refereegranskat)abstract
- The Arctic has warmed more than twice the rate of the entire globe. To quantify possible climate change effects, we calculate wind energy potentials from a multi-model ensemble of Arctic-CORDEX. For this, we analyze future changes of wind power density (WPD) using an eleven-member multi-model ensemble. Impacts are estimated for two periods (2020-2049 and 2070-2099) of the 21st century under a high emission scenario (RCP8.5). The multi-model mean reveals an increase of seasonal WPD over the Arctic in the future decades. WPD variability across a range of temporal scales is projected to increase over the Arctic. The signal amplifies by the end of 21st century. Future changes in the frequency of wind speeds at 100 m not useable for wind energy production (wind speeds below 4 m/s or above 25 m/s) has been analyzed. The RCM ensemble simulates a more frequent occurrence of 100 m non-usable wind speeds for the wind-turbines over Scandinavia and selected land areas in Alaska, northern Russia and Canada. In contrast, non-usable wind speeds decrease over large parts of Eastern Siberia and in northern Alaska. Thus, our results indicate increased potential of the Arctic for the development and production of wind energy. Bias corrected and not corrected near-surface wind speed and WPD changes have been compared with each other. It has been found that both show the same sign of future change, but differ in magnitude of these changes. The role of sea-ice retreat and vegetation expansion in the Arctic in future on near-surface wind speed variability has been also assessed. Surface roughness through sea-ice and vegetation changes may significantly impact on WPD variability in the Arctic.
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| 10. |
- Semenov, V. E., et al.
(författare)
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General Study of Multipactor Between Curved Metal Surfaces
- 2014
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Ingår i: IEEE Transactions on Plasma Science. - 0093-3813 .- 1939-9375. ; 42:3, s. 721-728
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Tidskriftsartikel (refereegranskat)abstract
- An analytical study of the electron trajectories between two opposite electrodes having curved surfaces is undertaken for the case when the electron transit time exceeds the RF period. The analysis is based on a statistical approach, which makes it possible to calculate the width of an electron bunch after a number of electron transits taking into account the spread of electron emission velocity, and the spatial nonuniformity of the RF field using the concept of the ponderomotive force. The results are used to estimate the multipactor threshold in terms of a value of the secondary emission yield, which is necessary to balance electron losses. Based on the model, it is predicted that multipactor is impossible inside the realistic configuration of a helix antenna where four electrodes are placed on the same cylindrical surface
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