Mass and charge transport in alcohol and ketone solvents and electrolyte solutions

Experimental data show there is a distinct relationship between the molal conductivity and concentration for electrolyte solutions with low dielectric constants. The molal conductivity decreases with the square root of the concentration to a minimum in the area referred to as "region I", and then increases to a maximum over the concentration range referred to as "region II". This behavior has been attributed to changes in ionic association in the electrolyte. The electrolyte systems used in this study, however, show this behavior but exhibit no spectroscopic evidence of ionic association. Molecular level properties are determined using the compensated Arrhenius Formalism (CAF) that add valuable insight in describing the qualitative behavior of the molal conductivity with concentration. The CAF assumes that transport is a thermally activated process, and uses the dielectric constant as a measure of changes in the intermolecular interactions. This formalism makes it possible to measure the energy of activation for mass and charge transport. Hydrodynamic models that use the solution viscosity as a characteristic system property in describing transport do not paint any picture of these transport mechanisms at the molecular level. Modeling mass and charge transport as a thermally activated process through the use of the CAF agrees with the experimental data. This work uses the dielectric constant as a key component in describing transport. The CAF is applied to mass transport in hydrogen-bonded 1- and 3-alcohol liquids and non-associating 2-ketone liquids, and the differences observed between the systems are explained using the CAF results. The CAF is also applied to a range of concentrations of tetrabutylammonium trifluoromethanesulfonate (TbaTf) dissolved in 1- and 3-alcohol and 2-ketone solvents. The results offer a new interpretation for the qualitative behavior of the molal conductivity with concentration. This work will show that the increase in region II is a complicated relationship between the concentration dependence of the energy of activation and the concentration dependence of the dielectric constant, consistent with the data from multiple electrolyte systems

Online Education: Transferring Personal Experiences to Professional Development

In this paper, we discuss how one candidate’s experience as she participated an online mathematics specialist program bolstered her confidence and ability to provide online professional development for her teachers. We include personal accounts by the mathematics specialist program instructors, the mathematics specialist candidate, and an elementary school teacher to illustrate how the experience of completing online graduate courses led to the candidate providing online learning opportunities for teachers. In particular, we highlight the importance of building relationships and using high-quality mathematical tasks in both the online preparation program and the online professional development. This case study provides evidence that exposure to online learning environments as a learner can help lower the barrier of entry for planning and providing online learning experiences as a teacher

Characterizing the limitations to the coupling between Saturn's ionosphere and middle magnetosphere

Observations of Saturn's ultraviolet and infrared aurora show structures that, when traced along the planetary magnetic field, map to the inner, middle, and outer magnetosphere. From low to high latitudes the structures seen in the UV are the Enceladus footprint, which maps to an equatorial radius of 4 R S (Saturn radii); a diffuse emission that maps to a broad equatorial region from 4-11 RS on the nightside; and a bright ring of emission that maps to ∼15 RS. With the exception of the Enceladus spot, the magnetospheric drivers for these auroral emissions are not yet fully understood. We apply a 1D spatial, 2D velocity space Vlasov solver to flux tubes mapping from equatorial radii of 4, 6, 9, and 13 RS to Saturn's southern atmosphere. The aim is to globally characterize the field-aligned potential structure and plasma density profiles. The ionospheric properties - the field-aligned current densities at the ionospheric boundary, energy intensity profiles and fluxes of the electrons precipitating into the ionosphere - are also determined. We then couple our results to an ionospheric model to calculate the Pedersen conductances at the foot of the relevant flux tubes. We find that for a zero net potential drop between the ionosphere and magnetosphere, there exists a sharp potential drop at ∼1.5 RS along the magnetic field line as measured from the planetary center. The strength of this potential drop is approximately equal to that of the ambipolar potential resulting from the centrifugal confinement of the heavy, cold magnetospheric ion population. We also find that the ionospheric properties respond to changes in the magnetospheric plasma population, which are reflected in the nature of the precipitating electron population. For the flux tube mapping to 9 RS (-70), the incident electron energy flux into the ionosphere resulting from a magnetospheric plasma population with a small fraction of hot electrons is an order of magnitude less than that inferred from observations, implying that significant high-latitude field-aligned potentials (up to 1.5 keV) may exist in the saturnian magnetosphere. Calculated ionospheric Pedersen conductances range from 3.0-18.9 mho, and are thus not expected to limit the currents flowing between the ionosphere and magnetosphere

Current-voltage relation for the Saturnian system

Saturn's magnetosphere is populated by plasma created from neutrals ejected by the moon Enceladus. These neutrals are ionized and picked up by the planetary magnetic field requiring large amounts of angular momentum to be transferred from Saturn's upper atmosphere to the magnetospheric plasma. The resulting upward currents that supply this angular momentum are associated with electrons, which travel toward the planetary atmosphere. At high magnetic latitudes along the flux tube, parallel electric fields may develop to enhance the field-aligned current density flowing between the two regions. We show that, similar to the Jovian system, the current-voltage relation in the Saturnian system must be evaluated at the top of the acceleration region, which occurs at ~1.5 RS along the magnetic field line as measured from the center of the planet. Owing to the large abundance of protons in the Saturnian system, cold electrons carry the majority of the field-aligned current for net potential drops less than 500 V. For the flux tube intersecting the equatorial plane at 4 RS, field-aligned potentials of 50-130 V are consistent with the energy fluxes inferred from the Enceladus emission. In the middle magnetosphere, field-aligned potentials of ∼1.5 kV produce ionospheric electron energy fluxes of 0.3 mW/m2 when hot electrons comprise 0.3% of the magnetospheric electron population. Key Points Current-voltage relation must be evaluated at high magnetic latitudes. Cold electrons contribute strongly to field-aligned current density. Full Knight (1973) current-voltage relation must be applied to Saturnian system

Determinants of parents' reticence toward vaccination in urban areas in Benin (West Africa)

Analysis of the data reveals those who are vaccination-reticent say it goes against the will of God, that it is a poison from the “white witch doctor,” and a sin. Members of the control group argued against this, but without conviction. They adhere to the principle of obedience to authority, a biblical precept invoked when the vaccinators oblige them to vaccinate their children. To limit the spread of this phenomenon among the religious population of the cities like Parakou and Cotonou in Benin, more detailed information and negotiation between health authorities and pastors of the churches are essential

Malnutrition Has No Effect on the Timing of Human Tooth Formation

The effect of nutrition on the timing of human tooth formation is poorly understood. Delays and advancements in dental maturation have all been reported as well as no effect. We investigated the effect of severe malnutrition on the timing of human tooth formation in a large representative sample of North Sudanese children. The sample (1102 males, 1013 females) consisted of stratified randomly selected healthy individuals in Khartoum, Sudan, aged 2-22 years using a cross-sectional design following the STROBE statement. Nutritional status was defined using WHO criteria of height and weight. Body mass index Z-scores and height for age Z-scores of ≤-2 (cut-off) were used to identify the malnourished group (N = 474) while the normal was defined by Z-scores of ≥0 (N = 799). Clinical and radiographic examination of individuals, with known ages of birth was performed including height and weight measurements. Mandibular left permanent teeth were assessed using eight crown and seven root established tooth formation stages. Mean age at entry and mean age within tooth stages were calculated for each available tooth stage in each group and compared using a t-test. Results show the mean age at entry and mean age within tooth stages were not significantly different between groups affected by severe malnutrition and normal children (p>0.05). This remarkable finding was evident across the span of dental development. We demonstrate that there is little measurable effect of sustained malnutrition on the average timing of tooth formation. This noteworthy finding supports the notion that teeth have substantial biological stability and are insulated from extreme nutritional conditions compared to other maturing body systems