Dynamics of light propagation in spatiotemporal dielectric structures

Propagation, transmission and reflection properties of linearly polarized plane waves and arbitrarily short electromagnetic pulses in one-dimensional dispersionless dielectric media possessing an arbitrary space-time dependence of the refractive index are studied by using a two-component, highly symmetric version of Maxwell's equations. The use of any slow varying amplitude approximation is avoided. Transfer matrices of sharp nonstationary interfaces are calculated explicitly, together with the amplitudes of all secondary waves produced in the scattering. Time-varying multilayer structures and spatiotemporal lenses in various configurations are investigated analytically and numerically in a unified approach. Several new effects are reported, such as pulse compression, broadening and spectral manipulation of pulses by a spatiotemporal lens, and the closure of the forbidden frequency gaps with the subsequent opening of wavenumber bandgaps in a generalized Bragg reflector

Gait speed characteristics and Its spatiotemporal determinants in nursing home residents: A cross-sectional study

Fien, S ORCiD: 0000-0003-0181-5458BACKGROUND AND PURPOSE: Low and slowing gait speeds among nursing home residents are linked to a higher risk of disability, cognitive impairment, falls, and mortality. A better understanding of the spatiotemporal parameters of gait that influence declining mobility could lead to effective rehabilitation and preventative intervention. The aims of this study were to objectively quantify the spatiotemporal characteristics of gait in the nursing home setting and define the relationship between these parameters and gait speed. METHODS: One hundred nursing home residents were enrolled into the study and completed 3 habitual gait speed trials over a distance of 3.66 m. Trials were performed using an instrumented gait analysis. The manner in which the spatiotemporal parameters predicted gait speed was examined by univariate and multivariable regression modeling. RESULTS: The nursing home residents had a habitual mean (SD) gait speed of 0.63 (0.19) m/s, a stride length of 0.83 (0.15) m, a support base of 0.15 (0.06) m, and step time of 0.66 (0.12) seconds. Multivariable linear regression revealed stride length, support base, and step time predicted gait speed (R = 0.89, P < .05). Step time had the greatest influence on gait speed, with each 0.1-second decrease in step time resulting in a 0.09 m/s (95% confidence interval, 0.08-0.10) increase in habitual gait speed. CONCLUSIONS: This study revealed step time, stride length, and support base are the strongest predictors of gait speed among nursing home residents. Future research should concentrate on developing and evaluating intervention programs that were specifically designed to focus on the strong predictors of gait speed in nursing home residents. We would also suggest that routine assessments of gait speed, and if possible their spatiotemporal characteristics, be done on all nursing home residents in an attempt to identify residents with low or slowing gait speed

Capacitively-coupled rf discharge with a large amount of microparticles: spatiotemporal emission pattern and microparticle arrangement

The effect of micron-sized particles on a low-pressure capacitively-coupled rf discharge is studied both experimentally and using numerical simulations. In the laboratory experiments, microparticle clouds occupying a considerable fraction of the discharge volume are supported against gravity with the help of the thermophoretic force. The spatiotemporally resolved optical emission measurements are performed with different arrangements of microparticles. The numerical simulations are carried out on the basis of a one-dimensional hybrid (fluid-kinetic) discharge model describing the interaction between plasma and microparticles in a self-consistent way. The study is focused on the role of microparticle arrangement in interpreting the spatiotemporal emission measurements. We show that it is not possible to reproduce simultaneously the observed microparticle arrangement and emission pattern in the framework of the considered one-dimensional model. This disagreement is discussed and attributed to two-dimensional effects, e.g., radial diffusion of the plasma components

Expansive evolution of the TREHALOSE-6-PHOSPHATE PHOSPHATASE gene family in Arabidopsis

Trehalose is a nonreducing sugar used as a reserve carbohydrate and stress protectant in a variety of organisms. While higher plants typically do not accumulate high levels of trehalose, they encode large families of putative trehalose biosynthesis genes. Trehalose biosynthesis in plants involves a two-step reaction in which trehalose-6-phosphate (T6P) is synthesized from UDPglucose and glucose-6-phosphate (catalyzed by T6P synthase [TPS]), and subsequently dephosphorylated to produce the disaccharide trehalose (catalyzed by T6P phosphatase [TPP]). In Arabidopsis (Arabidopsis thaliana), 11 genes encode proteins with both TPS- and TPP-like domains but only one of these (AtTPS1) appears to be an active (TPS) enzyme. In addition, plants contain a large family of smaller proteins with a conserved TPP domain. Here, we present an in-depth analysis of the 10 TPP genes and gene products in Arabidopsis (TPPA-TPPJ). Collinearity analysis revealed that all of these genes originate from whole-genome duplication events. Heterologous expression in yeast (Saccharomyces cerevisiae) showed that all encode active TPP enzymes with an essential role for some conserved residues in the catalytic domain. These results suggest that the TPP genes function in the regulation of T6P levels, with T6P emerging as a novel key regulator of growth and development in higher plants. Extensive gene expression analyses using a complete set of promoter-beta-glucuronidase/green fluorescent protein reporter lines further uncovered cell- and tissue-specific expression patterns, conferring spatiotemporal control of trehalose metabolism. Consistently, phenotypic characterization of knockdown and overexpression lines of a single TPP, AtTPPG, points to unique properties of individual TPPs in Arabidopsis, and underlines the intimate connection between trehalose metabolism and abscisic acid signaling

Modelling the spatial behaviour of a tropical tuna purse seine fleet.

Industrial tuna fisheries operate in the Indian, Atlantic and Pacific Oceans, but concerns over sustainability and environmental impacts of these fisheries have resulted in increased scrutiny of how they are managed. An important but often overlooked factor in the success or failure of tuna fisheries management is the behaviour of fishers and fishing fleets. Uncertainty in how a fishing fleet will respond to management or other influences can be reduced by anticipating fleet behaviour, although to date there has been little research directed at understanding and anticipating the human dimension of tuna fisheries. The aim of this study was to address gaps in knowledge of the behaviour of tuna fleets, using the Indian Ocean tropical tuna purse seine fishery as a case study. We use statistical modelling to examine the factors that influence the spatial behaviour of the purse seine fleet at broad spatiotemporal scales. This analysis reveals very high consistency between years in the use of seasonal fishing grounds by the fleet, as well as a forcing influence of biophysical ocean conditions on the distribution of fishing effort. These findings suggest strong inertia in the spatial behaviour of the fleet, which has important implications for predicting the response of the fleet to natural events or management measures (e.g., spatial closures)

Variational multiscale reinforcement learning for discovering reduced order closure models of nonlinear spatiotemporal transport systems

A central challenge in the computational modeling and simulation of a multitude of science applications is to achieve robust and accurate closures for their coarse-grained representations due to underlying highly nonlinear multiscale interactions. These closure models are common in many nonlinear spatiotemporal systems to account for losses due to reduced order representations, including many transport phenomena in fluids. Previous data-driven closure modeling efforts have mostly focused on supervised learning approaches using high fidelity simulation data. On the other hand, reinforcement learning (RL) is a powerful yet relatively uncharted method in spatiotemporally extended systems. In this study, we put forth a modular dynamic closure modeling and discovery framework to stabilize the Galerkin projection based reduced order models that may arise in many nonlinear spatiotemporal dynamical systems with quadratic nonlinearity. However, a key element in creating a robust RL agent is to introduce a feasible reward function, which can be constituted of any difference metrics between the RL model and high fidelity simulation data. First, we introduce a multi-modal RL to discover mode-dependant closure policies that utilize the high fidelity data in rewarding our RL agent. We then formulate a variational multiscale RL (VMRL) approach to discover closure models without requiring access to the high fidelity data in designing the reward function. Specifically, our chief innovation is to leverage variational multiscale formalism to quantify the difference between modal interactions in Galerkin systems. Our results in simulating the viscous Burgers equation indicate that the proposed VMRL method leads to robust and accurate closure parameterizations, and it may potentially be used to discover scale-aware closure models for complex dynamical systems.publishedVersio

Against a Davidsonian analysis of copula sentences

Semantic research over the past three decades has provided impressive confirmation of Donald Davidsons famous claim that “there is a lot of language we can make systematic sense of if we suppose events exist” (Davidson 1980:137). Nowadays, Davidsonian event arguments are no longer reserved only for action verbs (as Davidson originally proposed) or even only for the category of verbs, but instead are widely assumed to be associated with any kind of predicate (e.g. Higginbotham 2000, Parsons 2000).1 The following quotation from Higginbotham and Ramchand (1997) illustrates the reasoning that motivates this move: "Once we assume that predicates (or their verbal, etc. heads) have a position for events, taking the many consequences that stem therefrom, as outlined in publications originating with Donald Davidson (1967), and further applied in Higginbotham (1985, 1989), and Terence Parsons (1990), we are not in a position to deny an event-position to any predicate; for the evidence for, and applications of, the assumption are the same for all predicates. (Higginbotham and Ramchand 1997:54)" In fact, since Davidson’s original proposal the burden of proof for postulating event arguments seems to have shifted completely, leading Raposo and Uriagereka (1995), for example, to the following verdict: "it is unclear what it means for a predicate not to have a Davidsonian argument (Raposo and Uriagereka 1995:182)" That is, Davidsonian eventuality arguments apparently have become something like a trademark for predicates in general. The goal of the present paper is to subject this view of the relationship between predicates and events to real scrutiny. By taking a closer look at the simplest independent predicational structure – viz. copula sentences – I will argue that current Davidsonian approaches tend to stretch the notion of events too far, thereby giving up much of its linguistic and ontological usefulness. More specifically, the paper will tackle the following three questions: 1. Do copula sentences support the current view of the inherent event-relatedness of predicates? 2. If not, what is a possible alternative to an event-based analysis of copula sentences? 3. What does this tell us about Davidsonian events? The paper is organized as follows: Section 2 first reviews current event-based analyses of copula sentences and then gives a brief summary of the Davidsonian notion of events. Section 3 examines the behavior of copula sentences with respect to some standard (as well as some new) eventuality diagnostics. Copula expressions will turn out to fail all eventuality tests. They differ sharply from state verbs like stand, sit, sleep in this respect. (The latter pass all eventuality tests and therefore qualify as true “Davidsonian state” expressions.) On the basis of these observations, section 4 provides an alternative account of copula sentences that combines Kim’s (1969, 1976) notion of property exemplifications with Ashers (1993, 2000) conception of abstract objects. Specifically, I will argue that the copula introduces a referential argument for a temporally bound property exemplification (= “Kimian state”). The proposal is implemented within a DRT framework. Finally, section 5 offers some concluding remarks and suggests that supplementing Davidsonian eventualities by Kimian states not only yields a more adequate analysis for copula expressions and the like but may also improve our treatment of events