Matching Items (152)
Description
The story of graphene truly began in what was simply a stub in the journal Physical Review not two years after the end of World War II. In 1947, McGill University physicist P.R. Wallace authored “The Band Theory of Graphite” and attempted to develop a foundation on which the structure-property relationship of graphite could be explored; he calculates the number of free electrons and conductivity of what he describes as “a single hexagonal layer” and “suppos[es] that conduction takes place only in layers” in bulk graphite to predict wave functions, energies at specific atomic sites in the hexagonal lattice, and energy contours using a tight binding approximation for a hypothesized version of what we now call ‘armchair-style’ graphene. While Wallace was the first to explore the band structure and Brillouin Zones of single-layer graphite, the concept of two-dimensional materials was not new. In fact, for years, it was dismissed as a thermodynamic impossibility.
Everything seemed poised against any proposed physical and experimental stability of a structure like graphene. “Thermodynamically impossible”– a not uncommon shutdown to proposed novel physical or chemical concepts– was once used to describe the entire field of proposed two-dimensional crystals functioning separately from a three-dimensional base or crystalline structure. Rudolf Peierls and Lev Davoidovich Landau, both very accomplished physicists respectively known for the Manhattan Project and for developing a mathematical theory of helium superfluidity, rejected the possibility of isolated monolayer to few-layered crystal lattices. Their reasoning was that diverging thermodynamic-based crystal lattice fluctuations would render the material unstable regardless of controlled temperature. This logic is flawed, but not necessarily inaccurate– diamond, for instance, is thermodynamically metastable at room temperature and pressure in that there exists a slow (i.e. slow on the scale of millions of years) but continuous transformation to graphite. However, this logic was used to support an explanation of thermodynamic impossibility that was provided for graphene’s lack of isolation as late as 1979 by Cornell solid-state physicist Nathaniel David Mermin. These physicists’ claims had clear and consistent grounding in experimental data: as thin films become thinner, there exists a trend of a decreasing melting temperature and increasing instability that renders the films into islands at somewhere around ten to twenty atomic layers. This is driven by the thermodynamically-favorable minimization of surface energy.
Everything seemed poised against any proposed physical and experimental stability of a structure like graphene. “Thermodynamically impossible”– a not uncommon shutdown to proposed novel physical or chemical concepts– was once used to describe the entire field of proposed two-dimensional crystals functioning separately from a three-dimensional base or crystalline structure. Rudolf Peierls and Lev Davoidovich Landau, both very accomplished physicists respectively known for the Manhattan Project and for developing a mathematical theory of helium superfluidity, rejected the possibility of isolated monolayer to few-layered crystal lattices. Their reasoning was that diverging thermodynamic-based crystal lattice fluctuations would render the material unstable regardless of controlled temperature. This logic is flawed, but not necessarily inaccurate– diamond, for instance, is thermodynamically metastable at room temperature and pressure in that there exists a slow (i.e. slow on the scale of millions of years) but continuous transformation to graphite. However, this logic was used to support an explanation of thermodynamic impossibility that was provided for graphene’s lack of isolation as late as 1979 by Cornell solid-state physicist Nathaniel David Mermin. These physicists’ claims had clear and consistent grounding in experimental data: as thin films become thinner, there exists a trend of a decreasing melting temperature and increasing instability that renders the films into islands at somewhere around ten to twenty atomic layers. This is driven by the thermodynamically-favorable minimization of surface energy.
ContributorsShulman, Neal Arthur (Author) / Adams, James (Thesis director) / Islam, Rafiqul (Committee member) / Materials Science and Engineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2018-05
Description
Autism Spectrum Disorder (ASD) is a complex neurodevelopmental condition characterized by a wide range of symptoms and severities, affecting communication, behavior, and social interactions. With the prevalence of ASD rising to affect nearly 1 in 36 children in the United States, understanding and addressing the multifaceted needs of those with ASD is increasingly critical. This review explores the interplay between genetic, environmental, and immune factors in the onset of ASD, focusing on metabolic dysfunctions and the role of the gut-brain axis. Emerging research highlights the significance of abnormal metabolites and gut microbiota imbalances in contributing to the pathophysiology of ASD, suggesting that these factors may influence neurological function and behavior through modulating immune responses.
Recent analyses have uncovered metabolic disturbances in ASD, affecting amino acid metabolism, glutathione metabolism, glycolysis and the TCA cycle, homocysteine metabolism, ketone body synthesis, and lipid metabolism. These disturbances offer insights into how metabolic dysfunctions may contribute to the neurological and behavioral features of ASD. Furthermore, the gut microbiota's role in immune responses and the controversial impact of antibiotic use on gut flora composition is important to the complexity of ASD and the need for a nuanced understanding of treatment effects.
This review delves into the current understanding of metabolic dysfunctions in children with ASD, emphasizing the critical role of gut microbiota and the impact of antibiotic use. Specifically, this review discusses SCFAs, para-cresol, amino acid metabolites, and glutathione and their respective specific treatments. It also explores the potential of vitamin/mineral supplementation as a therapeutic strategy, highlighting significant improvements in metabolic markers and behavioral symptoms associated with ASD. The findings from key studies, including those by Adams et al., suggest that targeted nutritional interventions and careful management of gut health could offer promising avenues for improving the quality of life for individuals with ASD. The review also acknowledges the need for further research to confirm the long-term effects of these interventions and to develop personalized treatment approaches that consider the unique needs in individuals with ASD.
ContributorsNandakumar, Keshav (Author) / Adams, James (Thesis director) / Flynn, Christina (Committee member) / Barrett, The Honors College (Contributor) / Department of Psychology (Contributor)
Created2024-05