Earth's Inner Core dynamics induced by the Lorentz force

Seismic studies indicate that the Earth's inner core has a complex structure and exhibits a strong elastic anisotropy with a cylindrical symmetry. Among the various models which have been proposed to explain this anisotropy, one class of models considers the effect of the Lorentz force associated with the magnetic field diffused within the inner core. In this paper we extend previous studies and use analytical calculations and numerical simulations to predict the geometry and strength of the flow induced by the poloidal component of the Lorentz force in a neutrally or stably stratified growing inner core, exploring also the effect of different types of boundary conditions at the inner core boundary (ICB). Unlike previous studies, we show that the boundary condition that is most likely to produce a significant deformation and seismic anisotropy is impermeable, with negligible radial flow through the boundary. Exact analytical solutions are found in the case of a negligible effect of buoyancy forces in the inner core (neutral stratification), while numerical simulations are used to investigate the case of stable stratification. In this situation, the flow induced by the Lorentz force is found to be localized in a shear layer below the ICB, which thickness depends on the strength of the stratification, but not on the magnetic field strength. We obtain scaling laws for the thickness of this layer, as well as for the flow velocity and strain rate in this shear layer as a function of the control parameters, which include the magnitude of the magnetic field, the strength of the density stratification, the viscosity of the inner core, and the growth rate of the inner core. We find that the resulting strain rate is probably too small to produce significant texturing unless the inner core viscosity is smaller than about $10^{12}$ Pa.s.Comment: submitted to Geophysical Journal Internationa

Intervention to Increase Knowledge and Consumption of Folate-rich Foods Based on the Health Belief Model

Folate is important in the prevention of birth defects and in the maintenance of general health. Even after mandatory fortification, many people are still not consuming the RDA of 400 mcg/day. Consuming a diet rich in naturally high-folate foods, as opposed to supplementation, may offer additional health benefits and promote an overall healthy diet. The purpose of this pilot study was to test the hypothesis that a learner-centered educational intervention based on the Health Belief Model (HBM) will successfully increase knowledge and consumption of folate-rich foods, while increasing positive beliefs about folate and health. A two group parallel control trial was conducted at two schools in Nebraska. Pre- and post- study questionnaires included a folate-based food frequency questionnaire, a HBM questionnaire, and a folate knowledge test. Participants in the intervention group also completed a post-study evaluation. The intervention consisted of three 30-minute lessons followed by participant creation of podcasts. One podcast was viewed each week for eight weeks following the lessons. Data were entered into SPSS. T-tests measured simple effects within the intervention and control groups, and ANOVA measured within-subject effects between the groups. Folate consumption decreased in both the intervention and control groups, with a greater decrease occurring in the control group. These differences were not significant (p \u3e 0.05). Significant increases (p= 0.000) in folate knowledge occurred in the intervention group. This difference remained significant (p= 0.001) when compared to the control group. Average HBM rankings significantly decreased (p \u3c 0.05) toward “strongly agree” (likert scale of 1-6) in the intervention group (p \u3c 0.05) for all constructs except cues to action. However, when compared to the control group these differences were only significant for self efficacy and perceived susceptibility. Creating and viewing podcasts may be helpful for the retention of knowledge over time, but did not appear to be an effective cue to action. Advisor: Julie A. Albrech

Intervention to Increase Knowledge and Consumption of Folate-rich Foods Based on the Health Belief Model

Folate is important in the prevention of birth defects and in the maintenance of general health. Even after mandatory fortification, many people are still not consuming the RDA of 400 mcg/day. Consuming a diet rich in naturally high-folate foods, as opposed to supplementation, may offer additional health benefits and promote an overall healthy diet. The purpose of this pilot study was to test the hypothesis that a learner-centered educational intervention based on the Health Belief Model (HBM) will successfully increase knowledge and consumption of folate-rich foods, while increasing positive beliefs about folate and health. A two group parallel control trial was conducted at two schools in Nebraska. Pre- and post- study questionnaires included a folate-based food frequency questionnaire, a HBM questionnaire, and a folate knowledge test. Participants in the intervention group also completed a post-study evaluation. The intervention consisted of three 30-minute lessons followed by participant creation of podcasts. One podcast was viewed each week for eight weeks following the lessons. Data were entered into SPSS. T-tests measured simple effects within the intervention and control groups, and ANOVA measured within-subject effects between the groups. Folate consumption decreased in both the intervention and control groups, with a greater decrease occurring in the control group. These differences were not significant (p \u3e 0.05). Significant increases (p= 0.000) in folate knowledge occurred in the intervention group. This difference remained significant (p= 0.001) when compared to the control group. Average HBM rankings significantly decreased (p \u3c 0.05) toward “strongly agree” (likert scale of 1-6) in the intervention group (p \u3c 0.05) for all constructs except cues to action. However, when compared to the control group these differences were only significant for self efficacy and perceived susceptibility. Creating and viewing podcasts may be helpful for the retention of knowledge over time, but did not appear to be an effective cue to action. Advisor: Julie A. Albrech

Formation of helium lines in solar prominences

We summarize the results on the formation of the helium spectrum in solar prominences obtained over recent years. The radiative transfer problem under non-LTE conditions is solved to compute the profiles of the lines of He I and He II. The structure of the prominence-to-corona transition region (PCTR) has a major influence on the resulting spectrum of the resonance lines since they are formed mostly in this part of the prominence. However, subordinate lines are also affected by the structure of the PCTR. We pay particular attention to the formation of the He II 304 Å resonance line which is routinely observed from space, but yet not fully understood. Future steps in the modelling will be addressed

Length-weight relationship of fishes from coral reefs and lagoons of New Caledonia: an update

Length-weight relationships of 316 reef and lagoon fish from New Caledonia (SW Pacific Ocean) belonging to 68 families are computed. A total of 43,750 individuals was used for this purpose. Fish were sampled by different techniques such as rotenone poisoning, handline and bottom longline fishing, gill and trammel nets, and trawling in various isotopes (coral reefs, lagoon bottoms and mangroves)

Numerical Evaluation of the Accuracy and Stability Properties of High-order Direct Stokes Solvers with or without Temporal Splitting

The temporal stability and effective order of two different direct high-order Stokes solvers are examined. Both solvers start from the primitive variables formulation of the Stokes problem, but are distinct by the numerical uncoupling they apply on the Stokes operator. One of these solvers introduces an intermediate divergence free velocity for performing a temporal splitting (J. Comput. Phys. [1991] 97, 414-443) while the other treats the whole Stokes problem through the evaluation of a divergence free acceleration field (C.R. Acad. Sci. Paris [1994] 319 Serie I, 1455-1461; SIAM J. Scient. Comput. [2000] 22(4), 1386-1410). The second uncoupling is known to be consistent with the harmonicity of the pressure field (SIAM J. Scient. Comput. [2000] 22(4), 1386-1410). Both solvers proceed by two steps, a pressure evaluation based on an extrapolated in time (of theoretical order Je) Neumann condition, and a time implicit (of theoretical order Ji) diffusion step for the final velocity. These solvers are implemented with a Chebyshev mono-domain and a Legendre spectral element collocation schemes. The numerical stability of these four options is investigated for the sixteen combinations of (Je,Ji), 1 ≤ Je, Ji ≤

Behaviour of molecular hydrogen emission in three solar flares

We have systematically investigated ultraviolet (UV) emission from molecular hydrogen (H$_{2}$) using the Interface Region Imaging Spectrometer (IRIS), during three X-ray flares of C5.1, C9.7 and X1.0 classes on Oct. 25, 2014. Significant emission from five H$_{2}$ spectral lines appeared in the flare ribbons, interpreted as photo-excitation (fluorescence) due to the absorption of UV radiation from two Si IV spectral lines. The H$_{2}$ profiles were broad and consisted of two non-stationary components in red and in the blue wings of the line in addition to the stationary component. The red (blue) wing components showed small redshifts (blue shifts) of ~5-15 km s$^{-1}$ (~5-10 km s$^{-1}$). The nonthermal velocities were found to be ~5-15 km s$^{-1}$. The interrelation between intensities of H$_{2}$ lines and their branching ratios confirmed that H$_{2}$ emission formed under optically thin plasma conditions. There is a strong spatial and temporal correlation between Si IV and H$_{2}$ emission, but the H$_{2}$ emission is more extended and diffuse, further suggesting H$_{2}$ fluorescence, and - by analogy with flare ''back-warming'' providing a means to estimate the depth from which the H$_{2}$ emission originates. We find that this is 1871$\pm$157 km and 1207$\pm$112 km below the source of the Si IV emission, in two different ribbon locations.Comment: 14 pages, 12 figures, accepted for publication in MNRA

Exploration of long-period oscillations in an Hα prominence

Context. In previous work, we studied a prominence which appeared like a tornado in a movie made from 193 Å filtergrams obtained with the Atmospheric Imaging Assembly (AIA) imager aboard the Solar Dynamics Observatory (SDO). The observations in Hα obtained simultaneously during two consecutive sequences of one hour with the Multi-channel Subtractive Double Pass Spectrograph (MSDP) operating at the solar tower in Meudon showed that the cool plasma inside the tornado was not rotating around its vertical axis. Furthermore, the evolution of the Dopplershift pattern suggested the existence of oscillations of periods close to the time-span of each sequence. Aims. The aim of the present work is to assemble the two sequences of Hα observations as a full data set lasting two hours to confirm the existence of oscillations, and determine their nature. Methods. After having coaligned the Doppler maps of the two sequences, we use a Scargle periodogram analysis and cosine fitting to compute the periods and the phase of the oscillations in the full data set. Results. Our analysis confirms the existence of oscillations with periods between 40 and 80 min. In the Dopplershift maps, we identify large areas with strong spectral power. In two of them, the oscillations of individual pixels are in phase. However, in the top area of the prominence, the phase is varying slowly, suggesting wave propagation. Conclusions. We conclude that the prominence does not oscillate as a whole structure but exhibits different areas with their own oscillation periods and characteristics: standing or propagating waves. We discuss the nature of the standing oscillations and the propagating waves. These can be interpreted in terms of gravito-acoustic modes and magnetosonic waves, respectively