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"Kang, J."
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Isostructural metal-insulator transition in VO2
Separating structure and electrons in VO2Above 341 kelvin—not far from room temperature—bulk vanadium dioxide (VO2) is a metal. But as soon as the material is cooled below 341 kelvin, VO2 turns into an insulator and, at the same time, changes its crystal structure from rutile to monoclinic. Lee et al. studied the peculiar behavior of a heterostructure consisting of a layer of VO2 placed underneath a layer of the same material that has a bit less oxygen. In the VO2 layer, the structural transition occurred at a higher temperature than the metal-insulator transition. In between those two temperatures, VO2 was a metal with a monoclinic structure—a combination that does not occur in the absence of the adjoining oxygen-poor layer.Science, this issue p. 1037The metal-insulator transition in correlated materials is usually coupled to a symmetry-lowering structural phase transition. This coupling not only complicates the understanding of the basic mechanism of this phenomenon but also limits the speed and endurance of prospective electronic devices. We demonstrate an isostructural, purely electronically driven metal-insulator transition in epitaxial heterostructures of an archetypal correlated material, vanadium dioxide. A combination of thin-film synthesis, structural and electrical characterizations, and theoretical modeling reveals that an interface interaction suppresses the electronic correlations without changing the crystal structure in this otherwise correlated insulator. This interaction stabilizes a nonequilibrium metallic phase and leads to an isostructural metal-insulator transition. This discovery will provide insights into phase transitions of correlated materials and may aid the design of device functionalities.
Journal Article
Sintering - Densification, Grain Growth, and Microstructure
Sintering is the process of forming materials and components from a powder under the action of thermal energy. It is a key materials science subject; most ceramic materials and many specialist metal powder products for use in key industries such as electronics, automotive and aerospace are formed this way. Written by one of the leading experts in the field, this book offers an unrivalled introduction to sintering and sintering processes for students of materials science and engineering, and practicing engineers in industry. The book is unique in providing a complete grounding in the principles of sintering and equal coverage of the three key sintering processes: densification, grain growth and microstructure. Students and professional engineers alike will be attracted by the emphasis on developing a detailed understanding of the theory and practical processes of sintering, the balanced coverage of ceramic and metal sintering, and the accompanying examination questions with selected solutions.
eBook
The vulnerability of teaching and learning in a selfie society
This book explores the generative power of vulnerabilities facing individuals who inhabit educational spaces. We argue that vulnerability can be an asset in developing understandings of others, and in interrogating the self. Explorations of vulnerability offer a path to building empathy and creating engaged generosity within a community of dissensus. This kind of self-examination is essential in a selfie society in which democratic participation often devolves into neoliberal silos of discourse and marginalization of others who look, think, and believe differently.
Book
A sustained high-temperature fusion plasma regime facilitated by fast ions
Nuclear fusion is one of the most attractive alternatives to carbon-dependent energy sources
1
. Harnessing energy from nuclear fusion in a large reactor scale, however, still presents many scientific challenges despite the many years of research and steady advances in magnetic confinement approaches. State-of-the-art magnetic fusion devices cannot yet achieve a sustainable fusion performance, which requires a high temperature above 100 million kelvin and sufficient control of instabilities to ensure steady-state operation on the order of tens of seconds
2
,
3
. Here we report experiments at the Korea Superconducting Tokamak Advanced Research
4
device producing a plasma fusion regime that satisfies most of the above requirements: thanks to abundant fast ions stabilizing the core plasma turbulence, we generate plasmas at a temperature of 100 million kelvin lasting up to 20 seconds without plasma edge instabilities or impurity accumulation. A low plasma density combined with a moderate input power for operation is key to establishing this regime by preserving a high fraction of fast ions. This regime is rarely subject to disruption and can be sustained reliably even without a sophisticated control, and thus represents a promising path towards commercial fusion reactors.
A magnetic confinement regime established at the Korea Superconducting Tokamak Advanced Research device enables the generation of plasmas over 10
8
kelvin for 20 seconds with the aid of fast ions without plasma edge instabilities or impurity accumulation.
Journal Article
The prognostic impact of the neutrophil-to-lymphocyte ratio in patients with small-cell lung cancer
Background:
The neutrophil-to-lymphocyte ratio (NLR) and platelet-to-lymphocyte ratio (PLR) are prognostic factors for various types of cancer. In this study, we assessed the association of NLR and PLR with the prognosis of small-cell lung cancer (SCLC) in patients who received the standard treatment.
Methods:
We retrospectively reviewed patients who were diagnosed with SCLC and treated with platinum-based chemotherapy between July 2006 and October 2013 in Gyeongsang National University Hospital Regional Cancer Center and Changwon Samsung Hospital.
Results:
In total, 187 patients were evaluated. Compared with low NLR (<4), high NLR (⩾4) at diagnosis was associated with poor performance status, advanced stage, and lower response rate. Median overall survival (OS) and progression-free survival (PFS) were worse in the high-NLR group (high
vs
low, 11.17
vs
9.20 months,
P
=0.019 and 6.90
vs
5.49 months,
P
=0.005, respectively). In contrast, PLR at diagnosis was not associated with OS or PFS (
P
=0.467 and
P
=0.205, respectively). In multivariate analysis, stage, lactate dehydrogenase, and NLR at diagnosis were independent prognostic factors for OS and PFS.
Conclusions:
NLR is easily measurable and reflects the SCLC prognosis. A future prospective study is warranted to confirm our results.
Journal Article
Greenland records of aerosol source and atmospheric lifetime changes from the Eemian to the Holocene
The Northern Hemisphere experienced dramatic changes during the last glacial, featuring vast ice sheets and abrupt climate events, while high northern latitudes during the last interglacial (Eemian) were warmer than today. Here we use high-resolution aerosol records from the Greenland NEEM ice core to reconstruct the environmental alterations in aerosol source regions accompanying these changes. Separating source and transport effects, we find strongly reduced terrestrial biogenic emissions during glacial times reflecting net loss of vegetated area in North America. Rapid climate changes during the glacial have little effect on terrestrial biogenic aerosol emissions. A strong increase in terrestrial dust emissions during the coldest intervals indicates higher aridity and dust storm activity in East Asian deserts. Glacial sea salt aerosol emissions in the North Atlantic region increase only moderately (50%), likely due to sea ice expansion. Lower aerosol concentrations in Eemian ice compared to the Holocene are mainly due to shortened atmospheric residence time, while emissions changed little.
Past climate changes in Greenland ice were accompanied by large aerosol concentration changes. Here, the authors show that by correcting for transport effects, reliable source changes for biogenic aerosol from North America, sea salt aerosol from the North Atlantic, and dust from East Asian deserts can be derived.
Journal Article
Automation and control of laser wakefield accelerators using Bayesian optimization
Laser wakefield accelerators promise to revolutionize many areas of accelerator science. However, one of the greatest challenges to their widespread adoption is the difficulty in control and optimization of the accelerator outputs due to coupling between input parameters and the dynamic evolution of the accelerating structure. Here, we use machine learning techniques to automate a 100 MeV-scale accelerator, which optimized its outputs by simultaneously varying up to six parameters including the spectral and spatial phase of the laser and the plasma density and length. Most notably, the model built by the algorithm enabled optimization of the laser evolution that might otherwise have been missed in single-variable scans. Subtle tuning of the laser pulse shape caused an 80% increase in electron beam charge, despite the pulse length changing by just 1%.
Laser wakefield accelerators are compact sources of ultra-relativistic electrons which are highly sensitive to many control parameters. Here the authors present an automated machine learning based method for the efficient multi-dimensional optimization of these plasma-based particle accelerators.
Journal Article
Olaparib for Metastatic Castration-Resistant Prostate Cancer
Up to 30% of patients with metastatic castration-resistant prostate cancer have deleterious mutations in genes involved in homologous recombination repair of DNA damage. The use of the PARP inhibitor olaparib in such patients was associated with longer progression-free survival and a longer time to pain progression than control therapy.
Journal Article