Dynamos with weakly convecting outer layers: implications for core-mantle boundary interaction

Convection in the Earth's core is driven much harder at the bottom than the top. This is partly because the adiabatic gradient steepens towards the top, partly because the spherical geometry means the area involved increases towards the top, and partly because compositional convection is driven by light material released at the lower boundary and remixed uniformly throughout the outer core, providing a volumetric sink of buoyancy. We have therefore investigated dynamo action of thermal convection in a Boussinesq fluid contained within a rotating spherical shell driven by a combination of bottom and internal heating or cooling. We first apply a homogeneous temperature on the outer boundary in order to explore the effects of heat sinks on dynamo action; we then impose an inhomogeneous temperature proportional to a single spherical harmonic Y2² in order to explore core-mantle interactions. With homogeneous boundary conditions and moderate Rayleigh numbers, a heat sink reduces the generated magnetic field appreciably; the magnetic Reynolds number remains high because the dominant toroidal component of flow is not reduced significantly. The dipolar structure of the field becomes more pronounced as found by other authors. Increasing the Rayleigh number yields a regime in which convection inside the tangent cylinder is strongly affected by the magnetic field. With inhomogeneous boundary conditions, a heat sink promotes boundary effects and locking of the magnetic field to boundary anomalies. We show that boundary locking is inhibited by advection of heat in the outer regions. With uniform heating, the boundary effects are only significant at low Rayleigh numbers, when dynamo action is only possible for artificially low magnetic diffusivity. With heat sinks, the boundary effects remain significant at higher Rayleigh numbers provided the convection remains weak or the fluid is stably stratified at the top. Dynamo action is driven by vigorous convection at depth while boundary thermal anomalies dominate in the upper regions. This is a likely regime for the Earth's core

TB13: The Use of Aerial Photographs in Studies of Marsh Vegetation

This publication describes a study using aerial photographs of marsh habitat in Merrymeeting Bay, Maine, to determine the kind of information relative to marsh vegetation that could be obtained from them, and also to determine the accuracy of the photographic interpretation.https://digitalcommons.library.umaine.edu/aes_techbulletin/1175/thumbnail.jp

No well-defined remnant Fermi surface in Sr2CuO2Cl2

In angle-resolved photoelectron spectra of the antiferromagnetic insulators Ca2CuO2Cl2 and Sr2CuO2Cl2 a sharp drop of the spectral intensity of the lowest-lying band is observed along a line in k space equivalent to the Fermi surface of the optimally doped high-temperature superconductors. This was interpreted as a signature of the existence of a remnant Fermi surface in the insulating phase of the high-temperature superconductors. In this paper it is shown that the drop of the spectral intensity is not related to the spectral function but is a consequence of the electron-photon matrix elementComment: 4 pages, 3 figure

Intravitreal Aflibercept Outcomes in Patients with Persistent Macular Exudate Previously Treated with Bevacizumab and/or Ranibizumab for Neovascular Age-Related Macular Degeneration

Purpose. To assess whether intravitreal aflibercept (2.0mg) can effectively reduce persistent macular exudate and enhance visual acuity in ranibizumab (0.5mg) and/or bevacizumab (1.25 mg) treatment resistant patients with neovascular age-related macular degeneration. Methods. This retrospective study included 47 treatment resistant eyes from 47 patients switched to intravitreal aflibercept injections after receiving a minimum of 3 injections with either ranibizumab or bevacizumab. Snellen visual acuity and optical coherence tomography were assessed just prior to the first injection (baseline) and prior to the fourth injection (final). Additionally, anatomical regions of persistent macular exudate were tracked to determine if these areas yielded varying responses to aflibercept. Results. At baseline, patients had received an average of 11.3 injections with any prior anti-VEGF drug (SD 5.96). For whole group analysis, baseline and final central retinal thickness were 370.57 mu m and 295.7 mu m (P \u3c =.001), respectively. Baseline and final retinal fluid volumes were 4.81 mm(3) and 4.37 mm(3) (P \u3c =.001), respectively. Baseline and final logMAR were 0.56 and 0.53 (P = 0.301), respectively. Anatomic location of persistent exudate did not appreciably alter treatment outcome. Conclusion. Central retinal thickness and total retinal fluid volume were reduced in ranibizumab and/or bevacizumab treatment resistant patients following three aflibercept injections. No appreciable change in visual acuity was noted

Band dispersion in C60(111): An angle-resolved photoemission study

Angle-resolved photoemission studies of single-crystal C60(111) films grown on GeS(001) reveal changes in valence feature line shape with emission angle and photon energy that are indicative of band dispersion. For an excitation energy (hν) of 10 eV, normal emission spectra show four sharp structures within the ∼1.1-eV-wide valence feature derived from the second highest molecular orbital (HOMO-1) of C60. For hν=8.1 eV, the 1-eV-wide HOMO-derived feature exhibits changes with emission angle mainly due to dispersion of 0.6 eV in the unoccupied bands. The distribution of electronic states underlying HOMO and HOMO-1 indicates that vibronic loss structures are not necessary to explain the width of these valence features

Light attenuation characteristics of glacially-fed lakes

Transparency is a fundamental characteristic of aquatic ecosystems and is highly responsive to changes in climate and land use. The transparency of glacially-fed lakes may be a particularly sensitive sentinel characteristic of these changes. However, little is known about the relative contributions of glacial flour versus other factors affecting light attenuation in these lakes. We sampled 18 glacially-fed lakes in Chile, New Zealand, and the U.S. and Canadian Rocky Mountains to characterize how dissolved absorption, algal biomass (approximated by chlorophyll a), water, and glacial flour contributed to attenuation of ultraviolet radiation (UVR) and photosynthetically active radiation (PAR, 400–700 nm). Variation in attenuation across lakes was related to turbidity, which we used as a proxy for the concentration of glacial flour. Turbidity-specific diffuse attenuation coefficients increased with decreasing wavelength and distance from glaciers. Regional differences in turbidity-specific diffuse attenuation coefficients were observed in short UVR wavelengths (305 and 320 nm) but not at longer UVR wavelengths (380 nm) or PAR. Dissolved absorption coefficients, which are closely correlated with diffuse attenuation coefficients in most non-glacially-fed lakes, represented only about one quarter of diffuse attenuation coefficients in study lakes here, whereas glacial flour contributed about two thirds across UVR and PAR. Understanding the optical characteristics of substances that regulate light attenuation in glacially-fed lakes will help elucidate the signals that these systems provide of broader environmental changes and forecast the effects of climate change on these aquatic ecosystems

Habitat Standardization of CPUE Indices: Research Needs

Habitat standardization for billfish CPUE offers a potentially useful alternative to the statistical procedures used in the past. However, most of the assumptions of the current habitatstandardization methodology remain untested and some are not consistent with current knowledge about the behavior of billfish. This paper outlines research required to ensure the methods for habitat standardization produce robust estimates of CPUE

Alpha‐melanocyte stimulating hormone increases the activity of melanocortin‐3 receptor‐expressing neurons in the ventral tegmental area

The mesocorticolimbic dopamine system, the brain’s reward system, regulates multiple behaviours, including food intake and food reward. There is substantial evidence that the melanocortin system of the hypothalamus, an important neural circuit controlling feeding and body weight, interacts with the mesocorticolimbic dopamine system to affect feeding, food reward and body weight. For example, melanocortin‐3 receptors (MC3Rs) are expressed in the ventral tegmental area (VTA) and our laboratory previously showed that intra‐VTA injection of the MC3R agonist, MTII, decreases home‐cage food intake and operant responding for sucrose pellets. However, the cellular mechanisms underlying the effects of intra‐VTA alpha‐melanocyte stimulating hormone (α‐MSH) on feeding and food reward are unknown. To determine how α‐MSH acts in the VTA to affect feeding, we performed electrophysiological recordings in acute brain slices from mice expressing enhanced yellow fluorescent protein in MC3R neurons to test how α‐MSH affects the activity of VTA MC3R neurons. α‐MSH significantly increased the firing rate of VTA MC3R neurons without altering the activity of non‐MC3R expressing VTA neurons. In addition, the α‐MSH‐induced increase in MC3R neuron activity was independent of fast synaptic transmission and intracellular Ca2+ levels. Finally, we show that the effect of α‐MSH on MC3R neuron firing rate is probably activity‐dependent. Overall, these studies provide an important advancement in the understanding of how α‐MSH acts in the VTA to affect feeding and food reward.Key pointsAlpha‐melanocyte stimulating hormone (α‐MSH) is an anorexigenic peptide. Injection of the α‐MSH analog MTII into the ventral tegmental area (VTA) decreases food and sucrose intake and food reward.Melanocortin‐3 receptors (MC3R) are highly expressed in the VTA, suggesting that the effects of intra‐VTA α‐MSH may be mediated by α‐MSH changing the activity of MC3R‐expressing VTA neurons.α‐MSH increased the firing rate of MC3R VTA neurons in acute brain slices from mice, although it did not affect the firing rate of non‐MC3R VTA neurons.The α‐MSH induced increase in MC3R neuron firing rate is probably activity‐dependent, and was independent of fast synaptic transmission and intracellular Ca2+ levels.These results help us to better understand how α‐MSH acts in the VTA to affect feeding and other dopamine‐dependent behaviours.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/149572/1/tjp13547.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/149572/2/tjp13547_am.pd

Shifts in Southern Wisconsin Forest Canopy and Understory Richness, Composition, and Heterogeneity

We resurveyed the under- and overstory species composition of 94 upland forest stands in southern Wisconsin in 2002–2004 to assess shifts in canopy and understory richness, composition, and heterogeneity relative to the original surveys in 1949–1950. The canopy has shifted from mostly oaks (Quercus spp.) toward more mesic and shade-tolerant trees (primarily Acer spp.). Oak-dominated early-successional stands and those on coarse, nutrient-poor soils changed the most in canopy composition. Understories at most sites (80%) lost native species, with mean species density declining 25% at the 1-m2 scale and 23.1% at the 20-m2 scale. Woody species have increased 15% relative to herbaceous species in the understory despite declining in absolute abundance. Initial canopy composition, particularly the abundance of red oaks (Quercus rubra and Q. velutina), predicted understory changes better than the changes observed in the overstory. Overall rates of native species loss were greater in later-successional stands, a pattern driven by differential immigration rather than differential extirpation. However, understory species initially found in early-successional habitats declined the most, particularly remnant savanna taxa with narrow or thick leaves. These losses have yet to be offset by compensating increases in native shade-adapted species. Exotic species have proliferated in prevalence (from 13 to 76 stands) and relative abundance (from 1.2% to 8.4%), but these increases appear unrelated to the declines in native species richness and heterogeneity observed. Although canopy succession has clearly influenced shifts in understory composition and diversity, the magnitude of native species declines and failure to recruit more shade-adapted species suggest that other factors now act to limit the richness, heterogeneity, and composition of these communities