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Current sea-level rise partly stems from increased surface melting and meltwater runoff from the Greenland ice sheet. Multi-year snow, also known as firn, covers about 80% of the ice sheet and retains part of the surface meltwater. Since the firn cold content integrates its physical and thermal characteristics, it is a valuable tool for determining the meltwater-retention potential of firn. We use gap-filled climatological data from nine automatic weather stations in the ice-sheet accumulation area to drive a surface-energy-budget and firn model, validated against firn density and temperature observations, over the 1998–2017 period. Our results show a stable top 20 m firn cold content (CC20) at most sites. Only at the lower-elevation Dye-2 site did CC20 decrease, by 24% in 2012, before recovering to its original value by 2017. Heat conduction towards the surface is the main process feeding CC20 at all nine sites, while CC20 reduction occurs through low-cold-content fresh-snow addition at the surface during snowfall and latent-heat release when meltwater refreezes. Our simulations suggest that firn densification, while reducing pore space for meltwater retention, increases the firn cold content, enhances near-surface meltwater refreezing and potentially sets favourable conditions for ice-slab formation.
The new compound (4R)-methyl-3-(1-(4-chlorophenyl)-1H-1,2,3-triazole-4-carbonyl)thiazolidin-4-carboxylate was synthesized by the 1,3-dipolar cycloaddition reaction between (4R)-methyl-3-propionyl-thiazolidin-4-carboxylate (1) and 4-chlorophenylazide using the click chemistry approach. Molecular characterization was carried out by infrared spectroscopy and mass spectrometry. The X-ray powder diffraction study determined that the title compound crystallized in an orthorhombic system with unit-cell parameters a = 20.876 (2) Å, b = 12.111 (1) Å, and c = 6.288 (9) Å. The volume of the unit cell is V = 1589.7 (2) Å3. All measured diffraction maxima were indexed and are consistent with the P2221 space group (No. 17). No detectable impurities were observed.
Firestone & Scholl (F&S) rely on three problematic assumptions about the mind (modularity, reflexiveness, and context-insensitivity) to argue cognition does not fundamentally influence perception. We highlight evidence indicating that perception, cognition, and emotion are constructed through overlapping, distributed brain networks characterized by top-down activity and context-sensitivity. This evidence undermines F&S's ability to generalize from case studies to the nature of perception.
Recent advances in dynamo theory have been made by examining the competition between small- and large-scale dynamos at high magnetic Reynolds number
. Small-scale dynamos rely on the presence of chaotic stretching whilst the generation of large-scale fields occurs in flows lacking reflectional symmetry via a systematic electromotive force (EMF). In this paper we discuss how the statistics of the EMF (at high
) depend on the properties of the multi-scale velocity that is generating it. In particular, we determine that different scales of flow have different contributions to the statistics of the EMF, with smaller scales contributing to the mean without increasing the variance. Moreover, we determine when scales in such a flow act independently in their contribution to the EMF. We further examine the role of large-scale shear in modifying the EMF. We conjecture that the distribution of the EMF, and not simply the mean, largely determines the dominant scale of the magnetic field generated by the flow.
This study evaluated the influence of tubular density of different dentin depths and location on the bond strength of high-viscosity glass ionomer cements (GIC). A total of 20 molars were selected and assigned into six experimental groups, considering two different high-viscosity GICs—Fuji IX (FIX) or Ketac Molar (KM), and dentin location—proximal, occlusal superficial, or occlusal deep dentin (n=10). Teeth were cut and a topographical analysis of four sections per group was performed to obtain data about the tubular density of each different dentin location and depths by laser scanning confocal microscopy (100×). Polyethylene tubes were placed over the pretreated surfaces and filled with one of the GICs. Microshear bond strength (µSBS) test was performed after storage in distilled water (24 h at 37°C). Failure modes were evaluated using a stereomicroscope (400×). Multilevel regression analysis was performed to compare the results at a significance level set at 5%. The tubule density was inversely proportional to the bond strength for both GICs (p<0.05). Adhesive/mixed failure prevailed in all experimental groups. Proximal (30036.5±3433.3) and occlusal superficial 29665.3±1434.04 dentin shows lower tubule density, resulting in a better GIC bonding performance (proximal: FIX–3.61±1.05; KM–3.40±1.62; occlusal superficial: FIX–4.70±1.85; KM–4.97±1.25). Thus, we can concluded that the lowest tubule density in proximal and occlusal superficial dentin results in a better GIC bond strength performance.
In order better to understand how dynamo systems saturate, we study the kinematic dynamo properties of velocity fields that arise from nonlinearly saturated dynamos. The technique is implemented by solving concurrently, in addition to the momentum equation, two induction equations, one for the actual magnetic field and one for an independent passive vector field. We apply this technique to two illustrative examples: convectively driven turbulence and turbulence represented by a shell model. In all cases we find that the velocity remains an efficient kinematic dynamo even after nonlinear saturation occurs. We discuss the implications to the process of dynamo saturation.
We consider the kinematic dynamo problem for a velocity field consisting of a mixture of turbulence and coherent structures. For these flows the dynamo growth rate is determined by a competition between the large flow structures that have large magnetic Reynolds number but long turnover times and the small ones that have low magnetic Reynolds number but short turnover times. We introduce the concept of a quick dynamo as one that reaches its maximum growth rate in some (small) neighbourhood of its critical magnetic Reynolds number. We argue that if the coherent structures are quick dynamos, the overall dynamo growth rate can be predicted by looking at those flow structures that have spatial and temporal scales such that their magnetic Reynolds number is just above critical. We test this idea numerically by studying 2.5-dimensional dynamo action which allows extreme parameter values to be considered. The required velocities, consisting of a mixture of turbulence with a given spectrum and long-lived vortices (coherent structures), are obtained by solving the active scalar equations. By using spectral filtering we demonstrate that the scales responsible for dynamo action are consistent with those predicted by the theory.
The eggshells of Sergentomyia minuta, S. schwetzi and S. ingrami are studied by scanning (SEM) and transmission (TEM) electron microscopy. In all three species the surface sculpturing is characterized by a polygonal pattern due to intersecting ridges. Each ridge is formed by columns arranged in palisade and resting on a reticular basal layer. TEM shows that the columns represent the outer chorion and the basal layer the intermediated one. Under these layers an inner chorion and a vitelline envelope are present. The eggshell structures of the three species are compared with those of other Phlebotominae and their taxonomic value is discussed.
Various types of polymeric materials with enhanced electrical properties have been characterized recently. Many of these conducting polymers are of specific interest in solid state electrochemistry and in solid state ionics since they act as novel electrode and electrolyte materials. Indeed, these materials are currently used as improved polymer electrolytes and polymer electrodes for the development of advanced-design electrochemical devices. However, there are still some problems which prevent the wide utilization of these conductors. In this paper we attempt to identify the nature of these problems and discuss their possible solutions.
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