On Warm and Moist Air Intrusions into Winter Arctic

In this study, warm and moist air intrusions (WaMAI) over the Arctic Ocean sectors of Barents, Kara, Laptev, East Siberian, Chukchi and Beaufort Seas in recent 40 winters (from 1979 to 2018) are identified from ERA5 reanalysis using both Eulerian and Lagrangian views. The analysis shows that WaMAIs, fuelled by Arctic blockings, causes a relative surface warming and hence a sea ice reduction by exerting positive anomalies of net thermal irradiances and turbulent fluxes to the surface. Over Arctic Ocean sectors with land-locked sea ice in winter, such as Laptev, East Siberian, Chukchi and Beaufort Seas, total surface energy budget is dominated by net thermal irradiance. From a Lagrangian perspective, total water path (TWP) increases linearly with the downstream distance from the sea ice edge over the completely ice-covered sectors, inducing almost linearly increasing net thermal irradiance and total surface energy-budget. However, over the Barents Sea, with an open ocean to the south, total net surface energy-budget is dominated by the surface turbulent flux. With the energy in the warm-and-moist air continuously transported to the surface, net surface turbulent flux gradually decreases with distance, especially within the first 2 degrees north of the ice edge, inducing a decreasing but still positive total surface energy budget. The boundary-layer energy-budget patterns over the Barents Sea can be categorized into three classes: radiation-dominated, turbulence-dominated and turbulence-dominated with cold dome, comprising about 52 %, 40 % and 8 % of all WaMAIs, respectively. Statistically, turbulence-dominated cases with or without cold dome occur along with one order of magnitude larger large-scale subsidence than the radiation-dominated cases. For the turbulence-dominated category, larger turbulent fluxes are exerted to the surface, probably because of stronger wind shear. In radiation-dominated WaMAIs, stratocumulus develops more strongly and triggers intensive cloud-top radiative cooling and related buoyant mixing that extends from cloud top to the surface, inducing a thicker well-mixed layer under the cloud. With the existence of cold dome, fewer liquid water clouds were formed and less or even negative turbulent fluxes could reach the surface.

Influence of a bark-filler on the properties of PLA biocomposites

In this study, wood plastic composites (WPC) made of poly(lactic acid) PLA and a bark-filler were manufactured. Two degrees of bark comminution (10–35 mesh and over 35 mesh) and varied content of bark (40, 50 and 60%) were investigated. The studied panels were compared with analogically manufactured HDPE boards. The manufacture of composites involved two stages: at first, WPC granules with the appropriate formulation were produced using the extruder (temperatures in individual extruder sections were 170–180 °C) and crushing using a hammer mill after cooling the extruded composite; secondly, the obtained granulate was used to produce boards with nominal dimensions of 300 × 300 × 2.5 mm3 by flat pressing in a mold, using a single daylight press at a temperature 200 °C. The study proved that comminuted bark can be applied as a filler in PLA composites. However, an increase in bark content decreased mechanical properties (MOR, MOE) and deteriorated humidity resistance (high TS and WA) of the panels. Along with the increase in bark content, an increase in the contact angle of the composite surfaces and a decrease in the total surface energy were noted. It was also found that PLA composites have higher strength parameters and lower moisture resistance compared to HDPE composites with the same bark content. Graphical abstract

Synthesis, crystal structure, Hirshfeld surface analysis and energy framework calculations of trans-3,7,9,9-tetramethyl-10-(prop-2-yn-1-yl)-1,2,3,4,4a,9,9a,10-octahydroacridine

The title heterocyclic compound, C20H27N, has been prepared in good yield (72%) via a BiCl3-catalyzed cationic Povarov reaction between N-propargyl-4-methylaniline and (±)-citronellal. The X-ray single-crystal study indicates that the structure consists of molecules connected by C—H...π contacts to produce chains, which pack in a sandwich–herringbone fashion along the b-axis direction. Hirshfeld surface analysis indicates that H...H interactions dominate by contributing 79.1% to the total surface. Energy frameworks and DFT calculations indicate a major contribution of dispersive forces to the total interaction energy.

Applications of an Updated Atmospheric Energetics Formulation

As observations and atmospheric reanalyses have improved, the diagnostics that can be computed with confidence also increase. Accordingly, a new formulation of the energetics of the atmosphere is laid out, with a view to advancing diagnostic studies of Earth’s energy budget and flows. It is utilized to produce assessments of the vertically integrated divergences in both the atmosphere and ocean. Careful conservation of mass is required, with special attention given to the hydrological cycle and redistribution of mass associated with precipitation and evaporation, and a new method for ensuring this is developed. It guarantees that the atmospheric divergence is associated with moisture and precipitation, unlike previous methods. A new term, identified as associated with the enthalpy of precipitation, is included in a preliminary way. It is sensitive to the formulation, and the use of temperature in degrees Celsius instead of Kelvin greatly reduces errors and produces the extra term with values up to about ±5 W m−2. New results for 2000 to 2016 are presented for the vertical-mean and annual-mean diabatic atmospheric heating, atmospheric moistening, and total atmospheric energy divergence. Results for the atmospheric divergence are combined with top-of-atmosphere radiation observations to deduce total surface energy fluxes. Along with estimates of changes in ocean heat content, the Atlantic Ocean meridional heat transports are recomputed for March 2000 through 2013. The new results are compared with previous estimates and an assessment is made of the effects of the new mass balance, change in temperature scale, and the extra precipitation enthalpy term.

Textural equilibrium melt geometries around tetrakaidecahedral grains

In textural equilibrium, partially molten materials minimize the total surface energy bound up in grain boundaries and grain–melt interfaces. Here, numerical calculations of such textural equilibrium geometries are presented for a space-filling tessellation of grains with a tetrakaidecahedral (truncated octahedral) unit cell. Two parameters determine the nature of the geometries: the porosity and the dihedral angle. A variety of distinct melt topologies occur for different combinations of these two parameters, and the boundaries between different topologies have been determined. For small dihedral angles, wetting of grain boundaries occurs once the porosity has exceeded 11%. An exhaustive account is given of the main properties of the geometries: their energy, pressure, mean curvature, contiguity and areas on cross sections and faces. Their effective permeabilities have been calculated, and demonstrate a transition between a quadratic variation with porosity at low porosities to a cubic variation at high porosities.

Mechanisms of void shrinkage in aluminium

Voids can significantly affect the performance of materials and a key question is how voids form and evolve. Voids also provide a rare opportunity to study the fundamental interplay between surface crystallography and atomic diffusion at the nanoscale. In the present work, the shrinkage of voids in aluminium from 20 to 1 nm in diameter throughin situannealing is imaged in a transmission electron microscope. It is found that voids first shrink anisotropically from a non-equilibrium to an equilibrium shape and then shrink while maintaining their equilibrium shape until they collapse. It is revealed that this process maximizes the reduction in total surface energy per vacancy emitted. It is also observed that shrinkage is quantized, taking place one atomic layer and one void facet at a time. By taking the quantization and electron irradiation into account, the measured void shrinkage rates can be modelled satisfactorily for voids down to 5 nm using bulk diffusion kinetics. Continuous electron irradiation accelerates the shrinkage kinetics significantly; however, it does not affect the energetics, which control void shape.