| 1. |
- Richter, I., et al.
(författare)
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Observation of a new type of low-frequency waves at comet 67P/Churyumov-Gerasimenko
- 2015
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Ingår i: Annales Geophysicae. - : Copernicus GmbH. - 0992-7689 .- 1432-0576. ; 33:8, s. 1031-1036
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Tidskriftsartikel (refereegranskat)abstract
- We report on magnetic field measurements made in the innermost coma of 67P/Churyumov-Gerasimenko in its low-activity state. Quasi-coherent, large-amplitude (delta B/B similar to 1), compressional magnetic field oscillations at similar to 40 mHz dominate the immediate plasma environment of the nucleus. This differs from previously studied cometary interaction regions where waves at the cometary ion gyro-frequencies are the main feature. Thus classical pickup-ion-driven instabilities are unable to explain the observations. We propose a cross-field current instability associated with newborn cometary ion currents as a possible source mechanism.
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| 2. |
- Brain, D., et al.
(författare)
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A comparison of global models for the solar wind interaction with Mars
- 2010
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Ingår i: Icarus. - : Elsevier BV. - 0019-1035 .- 1090-2643. ; 206:1, s. 139-151
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Tidskriftsartikel (refereegranskat)abstract
- We present initial results from the first community-wide effort to compare global plasma interaction model results for Mars. Seven modeling groups participated in this activity, using MHD, multi-fluid, and hybrid assumptions in their simulations. Moderate solar wind and solar EUV conditions were chosen, and the conditions were implemented in the models and run to steady state. Model output was compared in three ways to determine how pressure was partitioned and conserved in each model, the location and asymmetry of plasma boundaries and pathways for planetary ion escape, and the total escape flux of planetary oxygen ions. The two participating MHD models provided similar results, while the five sets of multi-fluid and hybrid results were different in many ways. All hybrid results, however, showed two main channels for oxygen ion escape (a pickup ion 'plume' in the hemisphere toward which the solar wind convection electric field is directed, and a channel in the opposite hemisphere of the central magnetotail), while the MHD models showed one (a roughly symmetric channel in the central magnetotail). Most models showed a transition from an upstream region dominated by plasma dynamic pressure to a magnetosheath region dominated by thermal pressure to a low altitude region dominated by magnetic pressure. However, calculated escape rates for a single ion species varied by roughly an order of magnitude for similar input conditions, suggesting that the uncertainties in both the current and integrated escape over martian history as determined by models are large. These uncertainties are in addition to those associated with the evolution of the Sun, the martian dynamo, and the early atmosphere, highlighting the challenges we face in constructing Mars' past using models.
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| 3. |
- Fazio, V. S. U., et al.
(författare)
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Enhanced phase-matched second-harmonic generation in a ferroelectric liquid crystal waveguide
- 2001
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Ingår i: Molecular Crystals and Liquid Crystals Science and Technology. - 1058-725X. ; 368, s. 4061-4070
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Tidskriftsartikel (refereegranskat)abstract
- A binary mixture of crosslinkable ferroelectric liquid crystals (FLCs) was used for the design of a channel waveguide. The liquid crystal was aligned in layers parallel to the glass plates (homeotropic) in a sandwich geometry and then the arrangement was permanently fixed by photopolymerization which yielded a polar network possessing a high thermal and mechanical stability. The linear and nonlinear optical properties have been measured and all four independent components of the nonlinear susceptibility tensor d have been determined. The off-resonant d-coefficients are remarkably high and comparable to those of the best known inorganic materials. Phase-matching was achieved by taking advantage of the modal dispersion of the waveguide. A reversal of sign of chi ((2)) at the nodal plane of the electric field distribution of the first-order mode was needed to maximize the overlap. integral between the fundamental and the second-harmonic (SH) light. In samples with chi ((2)) inversion the SH Signal was 1000 larger that in samples without chi ((2)) inversion.
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| 4. |
- Fazio, V. S. U., et al.
(författare)
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Nonlinear optical properties of a channel waveguide produced with crosslinkable ferroelectric liquid crystals
- 2000
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Ingår i: The European Physical Journal E Soft matter. - : Springer Science and Business Media LLC. - 1292-8941 .- 1292-895X. ; 3:3, s. 245-251
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Tidskriftsartikel (refereegranskat)abstract
- A binary mixture of ferroelectric liquid crystals (FLCs) was used for the design of a channel waveguide. The FLCs possess two important functionalities: a chromophore with a high hyperpolarizability beta and photoreactive groups. The smectic liquid crystal is aligned in layers parallel to the glass plates in a sandwich geometry. This alignment offers several advantages, such as that moderate electric fields are sufficient to achieve a high degree of polar order. The arrangement was then permanently fixed by photopolymerization which yielded a polar network possessing a high thermal and mechanical stability which did not show any sign of degradation within the monitored period of several months. The linear and nonlinear optical properties have been measured and all four independent components of the nonlinear susceptibility tensor (d) over bar have been determined. The off-resonant d-coefficients are remarkably high and comparable to those of the best known inorganic materials. The alignment led to an inherent channel waveguide for p-polarized light without additional preparation steps. The photopolymerization did not induce scattering sites in the waveguide and the normalized losses were less than 2 dB/cm. The material offers a great potential for the design of nonlinear optical devices such as frequency doublers of low-power laser diodes.
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| 5. |
- Fazio, V. S. U., et al.
(författare)
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Phase-matched second-harmonic generation in a ferroelectric liquid crystal waveguide
- 2000
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 77:3, s. 319-321
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Tidskriftsartikel (refereegranskat)abstract
- True phase-matched second-harmonic generation in a waveguide of crosslinkable ferroelectric liquid crystals is demonstrated. These materials allow the formation of macroscopically polar structures whose order can be frozen by photopolymerization. Homeotropic alignment was chosen which offers decisive advantages compared to other geometries. All parameters contributing to the conversion efficiency are maximized by deliberately controlling the supramolecular arrangement. The system has the potential to achieve practical level of performances as a frequency doubler for low power laser-diodes.
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| 6. |
- Lammer, H., et al.
(författare)
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Geophysical and Atmospheric Evolution of Habitable Planets
- 2010
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Ingår i: Astrobiology. - : Mary Ann Liebert Inc. - 1531-1074 .- 1557-8070. ; 10:1, s. 45-68
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Tidskriftsartikel (refereegranskat)abstract
- The evolution of Earth-like habitable planets is a complex process that depends on the geodynamical and geophysical environments. In particular, it is necessary that plate tectonics remain active over billions of years. These geophysically active environments are strongly coupled to a planet's host star parameters, such as mass, luminosity and activity, orbit location of the habitable zone, and the planet's initial water inventory. Depending on the host star's radiation and particle flux evolution, the composition in the thermosphere, and the availability of an active magnetic dynamo, the atmospheres of Earth-like planets within their habitable zones are differently affected due to thermal and nonthermal escape processes. For some planets, strong atmospheric escape could even effect the stability of the atmosphere.
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