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"Rowe, C. J"
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Theaetetus and Sophist
\"Plato's Theaetetus and Sophist are two of his most important dialogues, and are widely read and discussed by philosophers for what they reveal about his epistemology and particularly his accounts of belief and knowledge. Although they form part of a single Platonic project, these dialogues are not usually presented as a pair, as they are in this new and lively translation. Offering a high standard of accuracy and readability, the translation reveals the continuity between these dialogues and others in the Platonic corpus, especially the Republic. Christopher Rowe's supporting introduction and notes help the reader to follow the arguments as they develop, explaining their structure, context and interpretation. This new edition challenges current scholarly approaches to Plato's work and will pave the way for fresh interpretations both of Theaetetus and Sophist and of Plato's writings in general\"-- Provided by publisher.
BOOK
Gut microbiota promoting propionic acid production accompanies caloric restriction-induced intentional weight loss in cats
Rodent models and human clinical studies have shown gut microbiota-derived short-chain fatty acids (SCFAs) play roles in obesity and insulin resistance. These roles have been minimally explored in cats, where in the USA an estimated 60% of cats are overweight or obese. Overweight/obese research cats (n = 7) were transitioned from a maintenance diet to a reduced calorie diet fed ad libitum for 7 days, then calories were restricted to achieve 1–2% weight loss per week for an additional 77 days. Cats then received their original maintenance diet again for 14 days. Significant intentional weight loss was noted after calorie restriction (adjusted p < 0.0001). 16S rRNA gene amplicon sequencing and targeted SCFA metabolomics were performed on fecal samples. Fecal microbial community structure significantly differed between the four study phases (PERMANOVA p = 0.011). Fecal propionic acid was significantly higher during caloric restriction-induced weight loss (adjusted p < 0.05). Repeated measures correlation revealed the relative abundances of
Prevotella 9 copri
(correlation coefficient = 0.532, 95% CI (0.275, 0.717), p = 0.0002) significantly correlated with propionic acid composition. Like humans, obese cats experienced an altered microbial community structure and function, favoring propionic acid production, during caloric restriction-induced weight loss.
Journal Article
Killing Socrates: Plato's later thoughts on democracy
The paper has two main aims, one larger and one slightly narrower. The larger aim is to undermine further a tendency that has dogged the interpretation of Platonic political philosophy in modern times, despite some dissenting voices: the tendency to begin from the assumption that Plato's thinking changed and developed over time, as if we already had privileged access to his biography. The slightly narrower aim is to reply to two charges of intellectual parricide made against Plato. The first is explicit and well known: that he recommended political structures of a sort that would exclude the free-ranging philosophical inquiry sponsored by Socrates. The second is implicit in the standard reading of the Politicus, and says that Plato actually came to approve (however reluctantly) of Athens' execution of his teacher. I argue that the relevant passage (Plt. 297C - 302B) has been misunderstood, and that it is in fact fully consistent with the blanket criticism we find in the Republic of all existing forms of constitution. The Athenian democracy still got it wrong, both in general, and in making the particular decision to kill off old Socrates. I also argue that so far from proposing to abolish Socratic inquiry, Plato's political works as a whole (Republic, Politicus and Laws included) are actually designed to show the need for it.
Journal Article
Mechanistic study of the formation of ring-retaining and ring-opening products from the oxidation of aromatic compounds under urban atmospheric conditions
Aromatic hydrocarbons make up a large fraction of anthropogenic volatile organic compounds and contribute significantly to the production of tropospheric ozone and secondary organic aerosol (SOA). Four toluene and four 1,2,4-trimethylbenzene (1,2,4-TMB) photooxidation experiments were performed in an environmental chamber under relevant polluted conditions (NOx∼10 ppb). An extensive suite of instrumentation including two proton-transfer-reaction mass spectrometers (PTR-MS) and two chemical ionisation mass spectrometers (NH4+ CIMS and I− CIMS) allowed for quantification of reactive carbon in multiple generations of hydroxyl radical (OH)-initiated oxidation. Oxidation of both species produces ring-retaining products such as cresols, benzaldehydes, and bicyclic intermediate compounds, as well as ring-scission products such as epoxides and dicarbonyls. We show that the oxidation of bicyclic intermediate products leads to the formation of compounds with high oxygen content (an O:C ratio of up to 1.1). These compounds, previously identified as highly oxygenated molecules (HOMs), are produced by more than one pathway with differing numbers of reaction steps with OH, including both auto-oxidation and phenolic pathways. We report the elemental composition of these compounds formed under relevant urban high-NO conditions. We show that ring-retaining products for these two precursors are more diverse and abundant than predicted by current mechanisms. We present the speciated elemental composition of SOA for both precursors and confirm that highly oxygenated products make up a significant fraction of SOA. Ring-scission products are also detected in both the gas and particle phases, and their yields and speciation generally agree with the kinetic model prediction.
Journal Article
Dimensionality-reduction techniques for complex mass spectrometric datasets: application to laboratory atmospheric organic oxidation experiments
Oxidation of organic compounds in the atmosphere produces an immensely complex mixture of product species, posing a challenge for both their measurement in laboratory studies and their inclusion in air quality and climate models. Mass spectrometry techniques can measure thousands of these species, giving insight into these chemical processes, but the datasets themselves are highly complex. Data reduction techniques that group compounds in a chemically and kinetically meaningful way provide a route to simplify the chemistry of these systems but have not been systematically investigated. Here we evaluate three approaches to reducing the dimensionality of oxidation systems measured in an environmental chamber: positive matrix factorization (PMF), hierarchical clustering analysis (HCA), and a parameterization to describe kinetics in terms of multigenerational chemistry (gamma kinetics parameterization, GKP). The evaluation is implemented by means of two datasets: synthetic data consisting of a three-generation oxidation system with known rate constants, generation numbers, and chemical pathways; and the measured products of OH-initiated oxidation of a substituted aromatic compound in a chamber experiment. We find that PMF accounts for changes in the average composition of all products during specific periods of time but does not sort compounds into generations or by another reproducible chemical process. HCA, on the other hand, can identify major groups of ions and patterns of behavior and maintains bulk chemical properties like carbon oxidation state that can be useful for modeling. The continuum of kinetic behavior observed in a typical chamber experiment can be parameterized by fitting species' time traces to the GKP, which approximates the chemistry as a linear, first-order kinetic system. The fitted parameters for each species are the number of reaction steps with OH needed to produce the species (the generation) and an effective kinetic rate constant that describes the formation and loss rates of the species. The thousands of species detected in a typical laboratory chamber experiment can be organized into a much smaller number (10–30) of groups, each of which has a characteristic chemical composition and kinetic behavior. This quantitative relationship between chemical and kinetic characteristics, and the significant reduction in the complexity of the system, provides an approach to understanding broad patterns of behavior in oxidation systems and could be exploited for mechanism development and atmospheric chemistry modeling.
Journal Article
Using collision-induced dissociation to constrain sensitivity of ammonia chemical ionization mass spectrometry (NH 4 + CIMS) to oxygenated volatile organic compounds
Chemical ionization mass spectrometry (CIMS) instruments routinely detect hundreds of oxidized organic compounds in the atmosphere. A major limitation of these instruments is the uncertainty in their sensitivity to many of the detected ions. We describe the development of a new high-resolution time-of-flight chemical ionization mass spectrometer that operates in one of two ionization modes: using either ammonium ion ligand-switching reactions such as for NH4+ CIMS or proton transfer reactions such as for proton-transfer-reaction mass spectrometer (PTR-MS). Switching between the modes can be done within 2 min. The NH4+ CIMS mode of the new instrument has sensitivities of up to 67 000 dcps ppbv−1 (duty-cycle-corrected ion counts per second per part per billion by volume) and detection limits between 1 and 60 pptv at 2σ for a 1 s integration time for numerous oxygenated volatile organic compounds. We present a mass spectrometric voltage scanning procedure based on collision-induced dissociation that allows us to determine the stability of ammonium-organic ions detected by the NH4+ CIMS instrument. Using this procedure, we can effectively constrain the sensitivity of the ammonia chemical ionization mass spectrometer to a wide range of detected oxidized volatile organic compounds for which no calibration standards exist. We demonstrate the application of this procedure by quantifying the composition of secondary organic aerosols in a series of laboratory experiments.
Journal Article
Below-ground interactions in tropical agroecosystems: concepts and models with multiple plant components
This book provides a synthesis of plant-soil-plant interactions in agroforestry, intercropping and grass-legume interactions. It focuses on the process level, which is relevant to many types of multi-species agroecosystem. It also links basic research to practical applications in a wide range of systems with or without trees, and considers effects of global change on below-ground interactions. The contents include soil biodiversity and food webs, phosphorus dynamics and mobilization by plants, and crop and tree root-system dynamics. The book will be of significant interest to researchers in plant, crop and soil sciences as well as agroforestry.
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