The six-phase two-circuit synchronous generator and its associated transformer

Imperial Users onl

Diffusion and bulk flow in phloem loading - a theoretical analysis of the polymer trap mechanism in plants

Plants create sugar in the mesophyll cells of their leaves by photosynthesis. This sugar, mostly sucrose, has to be loaded via the bundle sheath into the phloem vascular system (the sieve elements), where it is distributed to growing parts of the plant. We analyze the feasibility of a particular loading mechanism, active symplasmic loading, also called the polymer trap mechanism, where sucrose is transformed into heavier sugars, such as raffinose and stachyose, in the intermediary-type companion cells bordering the sieve elements in the minor veins of the phloem. Keeping the heavier sugars from diffusing back requires that the plasmodesmata connecting the bundle sheath with the intermediary cell act as extremely precise filters, which are able to distinguish between molecules that differ by less than 20% in size. In our modeling, we take into account the coupled water and sugar movement across the relevant interfaces, without explicitly considering the chemical reactions transforming the sucrose into the heavier sugars. Based on the available data for plasmodesmata geometry, sugar concentrations and flux rates, we conclude that this mechanism can in principle function. We find that the water flow through the plasmodesmata, which has not been quantified before, contributes only 10-20% to the sucrose flux into the intermediary cells, while the main part is transported by diffusion. On the other hand, the subsequent sugar translocation into the sieve elements would very likely be carried predominantly by bulk water flow through the plasmodesmata. Thus, in contrast to apoplasmic loaders, all the necessary water for phloem translocation would be supplied in this way with no need for additional water uptake across the plasma membranes of the phloem.Comment: 29 pages with 5 figure

Stochastic Parameter Estimation of Poroelastic Processes Using Geomechanical Measurements

Understanding the structure and material properties of hydrologic systems is important for a number of applications, including carbon dioxide injection for geological carbon storage or enhanced oil recovery, monitoring of hydraulic fracturing projects, mine dewatering, environmental remediation and managing geothermal reservoirs. These applications require a detailed knowledge of the geologic systems being impacted, in order to optimize their operation and safety. In order to evaluate, monitor and manage such hydrologic systems, a stochastic estimation framework was developed which is capable of characterizing the structure and physical parameters of the subsurface. This software framework uses a set of stochastic optimization algorithms to calibrate a heterogeneous subsurface flow model to available field data, and to construct an ensemble of models which represent the range of system states that would explain this data. Many of these systems, such as oil reservoirs, are deep and hydraulically isolted from the shallow subsurface making near-surface fluid pressure measurements uninformative. Near-surface strainmeter, tiltmeter and extensometer signals were therefore evaluated in terms of their potential information content for calibrating poroelastic flow models. Such geomechanical signals are caused by mechanical deformation, and therefore travel through hydraulically impermeable rock much more quickly. A numerical geomechanics model was therefore developed using Geocentric, which couples subsurface flow and elastic deformation equations to simulate geomechanical signals (e.g. pressure, strain, tilt and displacement) given a set of model parameters. A high-performance cluster computer performs this computationally expensive simulation for each set of parameters, and compares the simulation results to measured data in order to evaluate the likelihood of each model. The set of data-model comparisons are then used to estimate each unknown parameter, as well as the uncertainty of each parameter estimate. This uncertainty can be inuenced by limitations in the measured dataset such as random noise, instrument drift, and the number and location of sensors, as well as by conceptual model errors and false underlying assumptions. In this study we find that strain measurements taken from the shallow subsurface can be used to estimate the structure and material parameters of geologic layers much deeper in the subsurface. This can signicantly mitigate drilling and installation costs of monitoring wells, as well as reduce the risk of puncturing or fracturing a target reservoir. These parameter estimates were also used to develop an ensemble of calibrated hydromechanical models which can predict the range of system behavior and inform decision-making on the management of an aquifer or reservoir

Combining Sentiment Lexica with a Multi-View Variational Autoencoder

When assigning quantitative labels to a dataset, different methodologies may rely on different scales. In particular, when assigning polarities to words in a sentiment lexicon, annotators may use binary, categorical, or continuous labels. Naturally, it is of interest to unify these labels from disparate scales to both achieve maximal coverage over words and to create a single, more robust sentiment lexicon while retaining scale coherence. We introduce a generative model of sentiment lexica to combine disparate scales into a common latent representation. We realize this model with a novel multi-view variational autoencoder (VAE), called SentiVAE. We evaluate our approach via a downstream text classification task involving nine English-Language sentiment analysis datasets; our representation outperforms six individual sentiment lexica, as well as a straightforward combination thereof.Comment: To appear in NAACL-HLT 201

Classics, crisis and the Soviet experiment to 1939

Postprin

On a Generalization of the Frobenius Number

We consider a generalization of the Frobenius Problem where the object of interest is the greatest integer which has exactly $j$ representations by a collection of positive relatively prime integers. We prove an analogue of a theorem of Brauer and Shockley and show how it can be used for computation.Comment: 5 page

Synthetic X-ray and radio maps for two different models of Stephan's Quintet

We present simulations of the compact galaxy group Stephan's Quintet (SQ) including magnetic fields, performed with the N-body/smoothed particle hydrodynamics (SPH) code \textsc{Gadget}. The simulations include radiative cooling, star formation and supernova feedback. Magnetohydrodynamics (MHD) is implemented using the standard smoothed particle magnetohydrodynamics (SPMHD) method. We adapt two different initial models for SQ based on Renaud et al. and Hwang et al., both including four galaxies (NGC 7319, NGC 7320c, NGC 7318a and NGC 7318b). Additionally, the galaxies are embedded in a magnetized, low density intergalactic medium (IGM). The ambient IGM has an initial magnetic field of $10^{-9}$ G and the four progenitor discs have initial magnetic fields of $10^{-9} - 10^{-7}$ G. We investigate the morphology, regions of star formation, temperature, X-ray emission, magnetic field structure and radio emission within the two different SQ models. In general, the enhancement and propagation of the studied gaseous properties (temperature, X-ray emission, magnetic field strength and synchrotron intensity) is more efficient for the SQ model based on Renaud et al., whose galaxies are more massive, whereas the less massive SQ model based on Hwang et al. shows generally similar effects but with smaller efficiency. We show that the large shock found in observations of SQ is most likely the result of a collision of the galaxy NGC 7318b with the IGM. This large group-wide shock is clearly visible in the X-ray emission and synchrotron intensity within the simulations of both SQ models. The order of magnitude of the observed synchrotron emission within the shock front is slightly better reproduced by the SQ model based on Renaud et al., whereas the distribution and structure of the synchrotron emission is better reproduced by the SQ model based on Hwang et al..Comment: 20 pages, 15 figures, accepted to MNRA

Gel phantom data for dynamic X-ray tomography

This is the documentation for dynamic X-ray tomography measurements of a gel phantom diffused with potassium iodide contrast agent. The measured data and additional materials are available at http://www.fips.fi/dataset.php and Zenodo (https://doi.org/10.5281/zenodo.3696817) for open use by the scientific community, as long as the data and this documentation at arXiv are appropriately referenced. The files contain: (1) 17 consecutive measurements of the gel phantom organized into sinograms at two different resolutions (binning levels) and some additional metadata which can be used to create matrix-free forward operators and filtered back-projection reconstructions; (2) the first measurement using a greater number of projections, and an additional measurement of an 18th time step using very dense angular sampling, for example to be used for reference reconstructions; (3) short example codes to showcase how the data could be used to test and validate reconstruction algorithms.Comment: Actual data can be found at https://doi.org/10.5281/zenodo.369681

Giellariššu: Indigenous language revitalisation in the city

Source at https://multiethnica.org/About 10% of all pupils in grades 1–10 who learn Sámi in Norwegian schools live in the city of Tromsø in Northern Norway. This group totalled 232 pupils in the school year 2020/2021, and the pupils went to over 20 different schools. All but one were pupils of North Sámi, and a handful also received instruction in South Sámi. In Umeå in Sweden, 42 pupils attended mother tongue classes in Sámi in the winter of 2021, divided among four different varieties of Sámi, reflecting the diverse composition of the Sámi population in the area. In neither city, the Sámi pupils exceed 3 percent of their municipal peer group and they are embedded in local communities fully dominated by the Norwegian and Swed- ish majority language, respectively.We discuss the challenges and opportunities that Sámi children who grow up in two urban environments face when reclaiming, maintaining, and developing their indigenous heritage language, and we report from piloted language (re)vitalisation activities. Giellariššu gathers pupils from different schools regularly for activities in Sámi, led by adult proficient speakers with the goal to strengthen the pupils’ language skills and the social bonds between children who otherwise do not meet on a regular basis