337 research outputs found
Language of Lullabies: The Russification and De-Russification of the Baltic States
This article argues that the laws for promotion of the national languages are a legitimate means for the Baltic states to establish their cultural independence from Russia and the former Soviet Union
Frequency Domain Measurements of Melt Pool Recoil Force using Modal Analysis
Recoil pressure is a critical factor affecting the melt pool dynamics during Laser Powder Bed Fusion (LPBF) processes. Recoil pressure depresses the melt pool. When the recoil pressure is low, thermal conduction and capillary forces may be inadequate to provide proper fusion between layers. However, excessive recoil pressure can produce a keyhole inside the melt pool, which is associated with gas porosity. Direct recoil pressure measurements are challenging because it is localized over an area proportionate to the laser spot size producing a force in the mN range. This paper reports a vibration-based approach to quantify the recoil force exerted on a part in a commercial LPBF machine. The measured recoil force is consistent with estimates from high speed synchrotron imaging of entrained particles, and the results show that the recoil force scales with applied laser power and is inversely related to the laser scan speed. These results facilitate further studies of melt pool dynamics and have the potential to aid process development for new materials
Understanding the role of crystallographic shear on the electrochemical behavior of niobium oxyfluorides
The effects of shear planes in perovskite materials have been studied in order to identify their role in the electrochemical behavior of Liāŗ intercalation hosts. These planes modulate the structural stability and ionic transport pathways and therefore play an intimate role in the characteristics and performance of shear compounds. Herein, two Nb-based compounds, NbOāF and NbāOāF, were chosen as representative perovskite and shear derivatives respectively to investigate the role of crystallographic shear. A series of operando measurements, including X-ray diffraction and X-ray absorption spectroscopy, in conjunction with structural analysis, Raman spectroscopy, and detailed electrochemical studies identified the effect of shear planes. It was found that shear planes led to increased structural stability during Liāŗ (de)intercalation with shear layers being maintained, while perovskite layers were seen to degrade rapidly. However, disordering in the shear plane stacking introduced during delithiation ultimately led to poor capacity retention despite structural maintenance as Liāŗ diffusion channels are disrupted
Constitutional Pluralism and Democratic Politics: Reflections on the Interpretive Approach of Baker v. Carr
Multielectron, Cation and Anion Redox in Lithium-Rich Iron Sulfide Cathodes
Conventional Li-ion cathodes store charge by reversible intercalation of Li coupled to metal cation redox. There has been increasing interest in new materials capable of accommodating more than one Li per transition-metal center, thereby yielding higher charge storage capacities. We demonstrate here that the lithium-rich layered iron sulfide LiāFeSā as well as a new structural analogue, LiNaFeSā, reversibly store ā„1.5 electrons per formula unit and support extended cycling. Ex situ and operando structural and spectroscopic data indicate that delithiation results in reversible oxidation of FeĀ²āŗ concurrent with an increase in the covalency of the FeāS interactions, followed by reversible anion redox: 2 SĀ²ā»/(Sā)Ā²ā». S K-edge spectroscopy unequivocally proves the contribution of the anions to the redox processes. The structural response to the oxidation processes is found to be different in LiāFeSā in contrast to that in LiNaFeSā, which we suggest is the cause for capacity fade in the early cycles of LiNaFeSā. The materials presented here have the added benefit of avoiding resource-sensitive transition metals such as Co and Ni. In contrast to Li-rich oxide materials that have been the subject of so much recent study and that suffer capacity fade and electrolyte degradation issues, the materials presented here operate within the stable potential window of the electrolyte, permitting a clearer understanding of the underlying processes
A Tale of Prosecutorial Indiscretion: Ramsey Clark and the Selective Non-Prosecution of Stokely Carmichael
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