A Structural Comparison of A1n Layers Grown on Basal Plane Sapphire and SiC Substrates by MOCVD
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Hybrid FEA/SEA Assessment for an Orthogrid Cylindrical Panel Section and Periodic Subsystem Modeling Evaluation
In the lower frequency range, where particular boundary conditions can make a significant difference to panel response characteristics Statistical Energy Analysis (SEA) has never been the analytical tool of choice. In addition to boundary condition effects, SEA is not well suited in frequency bands where no modes or less than a few modes exist. The advent of the Hybrid Module has enabled integration of Finite Element Analysis to expand and enhance the capability for response calculations within VA One into the lower frequency range. Exploration of several additional modeling approaches was completed for the cylindrical orthogrid panel test article that was examined in Reference 1. Comparison of the new analytical response predictions with the measured response data from ground test and the pure SEA results from the reference will be presented. One approach that is considered promising is the periodic subsystem capability. Initially, a detailed FEM of just one region of the test article is defined. After evaluating this small region using symmetric boundary conditions, the FEM may be expanded to determine the properties of the entire system using similar connected regions that map over the entire test article. Another approach is the direct use of a very detailed finite element model of the entire panel, explicitly modeling pocket and rib details of the structure. A third approach is to approximate localized structure geometry details with a smeared property generalization using a PCOMP (NASTRAN card used to define layered composite structures) to define skin layer and ribbed layer for the orthogrid panel. The authors expect to demonstrate that the integrated Hybrid/FEM approach increases confidence in response prediction in the lower frequency range (for example from 20-300 Hz for the test article under consideration). In addition the strength and weakness of each additional approach will be highlighted and compared to those reported with those reported in an earlier paper
Smith, Andrew M.↗
Vertical Structure of Ice Cloud Layers From CloudSat and CALIPSO Measurements and Comparison to NICAM Simulations
The shape of the vertical profile of ice cloud layers is examined using 4 months of CloudSat and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) global measurements taken on January, April, July, and October 2007. Ice clouds are selected using temperature profiles when the cloud base is located above the 253K temperature level. The obtained ice water content (IWC), effective radius, or extinction coefficient profiles are normalized by their layer mean values and are expressed in the normalized vertical coordinate, which is defined as 0 and 1 at the cloud base and top heights, respectively. Both CloudSat and CALIPSO observations show that the maximum in the IWC and extinction profiles shifts toward the cloud bottom, as the cloud depth increases. In addition, clouds with a base reaching the surface in a high-latitude region show that the maximum peak of the IWC and extinction profiles occurs near the surface, which is presumably due to snow precipitation. CloudSat measurements show that the seasonal difference in normalized cloud vertical profiles is not significant, whereas the normalized cloud vertical profile significantly varies depending on the cloud type and the presence of precipitation. It is further examined if the 7 day Nonhydrostatic Icosahedral Atmospheric Model (NICAM) simulation results from 25 December 2006 to 1 January 2007 generate similar cloud profile shapes. NICAM IWC profiles also show maximum peaks near the cloud bottom for thick cloud layers and maximum peaks at the cloud bottom for low-level clouds near the surface. It is inferred that oversized snow particles in the NICAM cloud scheme produce a more vertically inhomogeneous IWC profile than observations due to quick sedimentation.
Ham, Seung-Hee↗
Detail Enhancement of AIRS/AMSU Temperature and Moisture Profiles Using a 3D Deep Neural Network
In recent decades, spaceborne microwave and hyperspectral infrared sounding instruments have significantly benefited weather forecasting and climate science. However, existing retrievals of lower troposphere temperature and humidity profiles have limitations in vertical resolution, and often cannot accurately represent key features such as the mixed layer thermodynamic structure and the inversion at the planetary boundary layer (PBL) top. Because of the existing limitations in PBL remote sensing from space, there is a compelling need to improve routine, global observations of the PBL and enable advances in scientific understanding and weather and climate prediction. To address this, we have developed a new 3D deep neural network (DNN) which enhances detail and reduces noise in Level 2 granules of temperature and humidity profiles from the Atmospheric Infrared Sounder (AIRS)/Advanced Microwave Sounding Unit (AMSU) sounder instruments aboard NASA’s Aqua spacecraft. We show that the enhancement improves accuracy and detail including key features such as capping inversions at the top of the PBL over land, resulting in improved accuracy in estimations of PBL height.
Adam B Milstein↗
Direct observation of electrothermal instability structures in the skin layer of an intensely Ohmically heated conductor.
Abstract not provided.
Awe, Thomas James↗
Methods of forming structures and fissile fuel materials by additive manufacturing
A method of forming one or more structures by additive manufacturing comprises introducing a first layer of a powder mixture comprising graphite and a fuel on a surface of a substrate. The first layer is at least partially compacted and then exposed to laser radiation to form a first layer of material comprising the fuel dispersed within a graphite matrix material. At least a second layer of the powder mixture is provided over the first layer of material and exposed to laser radiation to form inter-granular bonds between the second layer and the first layer. Related structures and methods of forming one or more structures are also disclosed.
36 MATERIALS SCIENCE↗
Methods of additively manufacturing a structure
A method of forming one or more structures by additive manufacturing comprises introducing a first layer of a powder mixture comprising graphite and a fuel on a surface of a substrate. The first layer is at least partially compacted and then exposed to laser radiation to form a first layer of material comprising the fuel dispersed within a graphite matrix material. At least a second layer of the powder mixture is provided over the first layer of material and exposed to laser radiation to form inter-granular bonds between the second layer and the first layer. Related structures and methods of forming one or more structures are also disclosed.
van Rooyen, Isabella J.↗
An experimental study of changes in the structure of a turbulent boundary layer due to surface geometry changes
This investigation attempts to observe changes in the flow structure of a nominally zero pressure gradient turbulent boundary layer by altering the surface of a smooth plate with small triangular riblets oriented in the direction of flow and protruding just above the viscous sublayer. Hot-wire measurements show a reduction in the local skin friction over the riblet valleys by about 40% compared to the smooth surface near the end of the plate. Local skin friction increases by about 10% over the riblet peaks. Results showing the effects of the riblets on the mean, root-mean-square and skewness factor distributions of the streamwise velocity are presented. The mean profile displays characteristics similar to those of drag reducing additives; the streamwise turbulence intensity is reduced by approximately 10-15% near the surface by the riblets; the skewness factor distribution is virtually unchanged. A comparison of results from an application of the VITA 'burst' detection technique to smooth and riblet surface data is also presented although the results are rather inconclusive. Flow visualization of 'bursting' over both surfaces, while dramatically revealing the structure, reveals little difference resulting from the presence of the riblet.
Source record↗
Quinary Defect-Rich Ultrathin Bimetal Hydroxide Nanosheets for Water Oxidation
The electronic structure of layered double hydroxides (LDHs) can be modulated by heteroatom doping and creating vacancies. The number of exposed active sites can be enriched by exfoliating the bulk structure into fewer layers. Herein, we successfully achieved multielement doping and exfoliation for Co 3 Fe LDHs by one SF 6 -plasma etching step at room temperature (named as Co 3 Fe LDHs-SF 6 ). The obtained Co 3 Fe LDHs-SF 6 ultrathin nanosheets display outstanding oxygen evolution reaction (OER) activity, which only needs 268 mV overpotential to reach 10 mA cm –2 . Tafel slope and charge transfer resistance are dramatically decreased indicating a faster reaction kinetic rate. Lastly, the excellent OER activity can be attributed to an increased number of active sites and an optimized electronic structure modulated by the incorporation of electron-withdrawing F, electron-donating S, and abundant vacancies resulting in proper adsorption energy to oxygen species.
77 NANOSCIENCE AND NANOTECHNOLOGY↗
Imitating Architectural Mortise‐Tenon Structure for Stable Ni‐Rich Layered Cathodes
Ni-rich layered oxides are the most promising cathodes for Li-ion batteries, but chemo-mechanical failures during cycling and large first-cycle capacity loss hinder their applications in high-energy batteries. Herein, by introducing spinel-like mortise-tenon structures into the layered phase of LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811), the adverse volume variations in cathode materials can be significantly suppressed. Meanwhile, these mortise-tenon structures play the role of the expressway for fast lithium-ion transport, which is substantiated by experiments and calculations. Moreover, the particles with mortise-tenon structures usually terminate with the most stable (003) facet. The new cathode exhibits a discharge capacity of 215 mAh g –1 at 0.1 C with an initial Coulombic efficiency of 97.5%, and capacity retention of 82.2% after 1200 cycles at 1 C. Importantly, this work offers a viable lattice engineering to address the stability and low initial Coulombic efficiency of the Ni-rich layered oxides, and facilitates the implementation of Li-ion batteries with high-energy density and long durability.
25 ENERGY STORAGE↗
A microstructural analysis of aluminum buildup during thermomechanical processing
Highlights: • Microstructure of roll coating developed on a ground steel work roll was examined. • Roll coating was formed during the 20 pass hot rolling schedule of an Al-Mg alloy. • The roll coating had a complex layered nanocrystalline and amorphous structure. • The roll coating layers were composed of metallic Al, porous MgO and C. • Work roll debris, Fe and Cr, were observed embedded within the roll coating. - Abstract: The microstructure and composition of a roll coating built-up on an AISI M2 steel work roll during a 20 pass hot rolling schedule using a laboratory rolling tribo-simulator with a roll-on-block configuration was examined. The AISI M2 steel work roll was characterized by grinding grooves and possessed a surface roughness (R{sub a}) of 0.17 μm. The roll coating developed under these lubricated conditions was discontinuous, patchy and streaked out in the rolling direction. The microstructure and chemical composition of the material transfer that made up the roll coating was analysed and revealed to possess a complex composite microstructure consisting of nanocrystalline aluminum, nanocrystalline/amorphous MgO and amorphous carbon layers. The nanocrystalline MgO layers were porous structures lying between the solid metallic aluminum layers. Debris particles from the wear of the work roll were detected embedded within the carbon layer and at the base of the roll coating. The microstructure of the roll coating appear to be determined by the deformation conditions experienced during the rolling process, while its composition is dependent on the composition of the rolled alloy, the work roll and the lubrication conditions employed.
77 NANOSCIENCE AND NANOTECHNOLOGY↗
Large-Eddy Simulation in Planetary Boundary-Layer Research
The structure and dynamics of the convective boundary layer are discussed. The vertical transport of a conservative, passive scalar was simulated. Also studied were the statistics by top-down and bottom-up scalar fields. Substantial differences were found between them due, presumably, to the asymmetry in the convective boundary layer. A generalization of mixed-layer scaling was developed which allows one to include the effects of top-down diffusion.
Wyngaard, J. C.↗
Synthesis, structure and canted antiferromagnetism of layered cobalt hydroxide sorbate
Layered hybrid organic–inorganic compounds of the transition metal hydroxides, in which part of the hydroxide ions are exchanged for organic ligands that act as spacers of the 2-dimensional inorganic layers, elicit new or enhanced properties. The interlayer ligands enable fine-tuning of the physicochemical properties of the metal hydroxide layers, including their magnetism. Specifically, within the Co(OH) 2 family of transition ion hydroxides, this approach has been leveraged to stabilize antiferromagnetic and ferrimagnetic ground states for pillared and layered complexes, respectively. Here, in this work, we further investigate the effects of changing dimensionality, local Co coordination, and interlayer spacing on the magnetic ground state of brucite-like β-Co(OH) layered complexes. We report the hydrothermal synthesis of a new crystalline material, Co(OH)(sorb), where the inorganic layers are spaced by monotopic, doubly unsaturated sorbate ligands (sorb = [C 6 H 7 O 2 ] – ). The material was structurally characterized using powder X-ray and neutron diffraction measurements and the crystal structure was solved ab initio from powder diffraction data and refined using the Rietveld method. The magnetic susceptibility and magnetization measurements reveal canted antiferromagnetic ordering with T N = 41.7 K. This report augments our understanding of tuning magnetism through dimensionality in layered complexes and represents a step forward in the design of new 2D layered hybrid compounds.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Crystal structure and dielectric properties of layered perovskite-like solid solutions Bi{sub 3–x}Y{sub x}TiNbO{sub 9} (x = 0, 0.1, 0.2, 0.3) with high Curie temperature
The structural and electrophysical characteristics of a number of solid solutions of layered perovskite-like oxides Bi{sub 3–x}Y{sub x}TiNbO{sub 9} (x = 0, 0.1, 0.2, 0.3) have been studied. According to the data of powder X-ray diffraction, all the compounds are single-phase with the structures of two-layer Aurivillius phases (m = 2) with the orthorhombic crystal lattice (space group A2{sub 1}am). The temperature dependence of the relative permittivity ε/ε0(T) compounds have been measured and showed that the Curie temperature of the perovskite-like oxides Bi{sub 3–x}YxTiNbO{sub 9} linearly increases with the substituting parameter x up to T{sub C} = 965°C.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Layer-resolved magnetic proximity effect in van der Waals heterostructures
Magnetic proximity effects are integral to manipulating spintronic, superconducting, excitonic and topological phenomena in heterostructures. These effects are highly sensitive to the interfacial electronic properties, such as electron wavefunction overlap and band alignment. The recent emergence of magnetic two-dimensional materials opens new possibilities for exploring proximity effects in van der Waals heterostructures. In particular, atomically thin CrI 3 exhibits layered antiferromagnetism, in which adjacent ferromagnetic monolayers are antiferromagnetically coupled. In this paper, we report a layer-resolved magnetic proximity effect in heterostructures formed by monolayer WSe 2 and bi/trilayer CrI 3 . By controlling the individual layer magnetization in CrI 3 with a magnetic field, we show that the spin-dependent charge transfer between WSe 2 and CrI 3 is dominated by the interfacial CrI 3 layer, while the proximity exchange field is highly sensitive to the layered magnetic structure as a whole. In combination with reflective magnetic circular dichroism measurements, these properties allow the use of monolayer WSe 2 as a spatially sensitive magnetic sensor to map out layered antiferromagnetic domain structures at zero magnetic field as well as antiferromagnetic/ferromagnetic domains at finite magnetic fields. Our work reveals a way to control proximity effects and probe interfacial magnetic order via van der Waals engineering.
36 MATERIALS SCIENCE↗
An experimental study of combustion: The turbulent structure of a reacting shear layer formed at a rearward-facing step
A premixed propane-air flame is stabilized in a turbulent free shear layer formed at a rearward-facing step. The mean and rms averages of the turbulent velocity flow field were determined by LDV for both reacting and non-reacting flows. The reaching flow was visualized by high speed schlieren photography. Large scale structures dominate the reacting shear layer. The growth of the large scale structures is tied to the propagation of the flame. The linear growth rate of the reacting shear layer defined by the mean velocity profiles is unchanged by combustion but the virtual origin is shifted downstream. The reacting shear layer based on the mean velocity profiles is shifted toward the recirculation zone and the reattachments lengths are shortened by 30%.
Pitz, R. W.↗
Layered topological semimetal GaGeTe: New polytype with non-centrosymmetric structure
GaGeTe is a layered van der Waals material composed of germanene and GaTe sublayers that has been recently predicted to be a basic Z 2 topological semimetal. To date, only one polytype of GaGeTe is known with trigonal centrosymmetric structure (α phase, space group R-3m, No. 166). Here we show that as-grown samples of GaGeTe show traces of at least another polytype with hexagonal non-centrosymmetric structure (β phase, space group P6 3 mc, No. 186). Moreover, we suggest that another bulk hexagonal polytype (γ phase, space group P-3m1, No. 164) could also be found near room conditions. Both α and β polytypes have been identified and characterized by means of X-ray diffraction and Raman scattering measurements with the support of ab initio calculations. We provide the vibrational properties of both polytypes and show that the Raman spectrum reported for GaGeTe almost forty years ago and attributed to the α phase, was, in fact, that of the secondary β phase. Additionally, we show that a Fermi resonance occurs in α-GaGeTe under non-resonant excitation conditions, but not under resonant excitation conditions. Theoretical calculations show that bulk β-GaGeTe is a non-centrosymmetric weak topological semimetal with even smaller lattice thermal conductivity than centrosymmetric bulk α-GaGeTe. In perspective, our work paves the way for the control and engineering of GaGeTe polytypes to design and implement complex van der Waals heterostructures formed by a combination of centrosymmetric and non-centrosymmetric layers of up to three different polytypes in a single material, suitable for a number of fundamental studies and technological applications.
36 MATERIALS SCIENCE↗
Structural modification and photoluminescence studies of Eu in lamellar fluorphlogopite by the adjustment of layer charge
Highlights: • The structure of fluorphlogopite was modified by the decrease of layer charge. • Characteristic emission of Eu{sup 3+} was greatly enhanced as doped to the modified clay. • The emitting color changed from orange-red to red in respect to the original host. • This is a new strategy to enhance the luminescence of inorganic layered materials. - Abstract: In this paper, the lamellar fluorphlogopite was structurally modified by the adjustment of layer charge and the rare earth Eu{sup 3+} was doped to fluorphlogopite with a subsequent high temperature solid state reaction process. The structural modification involved a preliminary treatment of fluorphlogopite with HNO{sub 3} and oxalic acid to reduce the layer charge density, and part of the charge-reduced fluorphlogopite was converted to a homoionic Na form by ion exchange with NaCl or NaB(C{sub 6}H{sub 5}){sub 4}. It has been noticed that the interlayer spacing of modified fluorphlogopite is decreased as compared with the original fluorphlogopite due to the ionic radius difference between K{sup +} and Na{sup +}. The photoluminescence study suggests that adjustment of layer charge of fluorphlogopite is beneficial to enhance the luminescence intensity excited with near UV light, and the layered system may be a potential red light component for the use of solid-state lighting and other optoelectronic fields.
36 MATERIALS SCIENCE↗