948 research outputs found
Balancing the books ? a statistical theory of prospective budgets in Earth System science
International audienceAn honest declaration of the error in a mass, momentum or energy balance, ?, simply raises the question of its acceptability: "At what value of ? is the attempted balance to be rejected?" Answering this question requires a reference quantity against which to compare ?. This quantity must be a mathematical function of all the data used in making the balance. To deliver this function, a theory grounded in a workable definition of acceptability is essential. A distinction must be drawn between a retrospective balance and a prospective budget in relation to any natural space-filling body. Balances look to the past; budgets look to the future. The theory is built on the application of classical sampling theory to the measurement and closure of a prospective budget. It satisfies R.A. Fisher's "vital requirement that the actual and physical conduct of experiments should govern the statistical procedure of their interpretation". It provides a test, which rejects, or fails to reject, the hypothesis that the closing error on the budget, when realised, was due to sampling error only. By increasing the number of measurements, the discrimination of the test can be improved, controlling both the precision and accuracy of the budget and its components. The cost-effective design of such measurement campaigns is discussed briefly. This analysis may also show when campaigns to close a budget on a particular space-filling body are not worth the effort for either scientific or economic reasons. Other approaches, such as those based on stochastic processes, lack this finality, because they fail to distinguish between different types of error in the mismatch between a set of realisations of the process and the measured data. Keywords: balance, budget, sampling, hypothesis test, closing error, Earth Syste
Isaiah 28-33 : a literary and contextual analysis.
Available from British Library Document Supply Centre- DSC:D90368 / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo
A tractable inhomogeneous closure theory for flow over mean topography
The quasi-diagonal direct interaction approximation (QDIA) is shown to be a computationally tractable closure theory for inhomogeneous two-dimensional turbulent flow over mean (single-realization) topography. In this paper numerical results for the QDIA are compared to direct numerical simulation (DNS) at moderate Reynolds number for two cases with quite different topographic and mean field amplitudes. The QDIA is found to be in excellent agreement with DNS for cases where the small-scale topographic amplitude is significant. For cases where the small-scale topography is weak, the QDIA closely reproduces the evolving mean field and large-scale energy containing transients but under represents the amplitudes of the small-scale transients in a similar way to the homogeneous DIA. We discuss the prospects of ameliorating the small-scale deficiencies using a regularization of the interaction coefficients
Thresholds, switches and hysteresis in hydrology from the pedon to the catchment scale: a non-linear systems theory
International audienceHysteresis is a rate-independent non-linearity that is expressed through thresholds, switches, and branches. Exceedance of a threshold, or the occurrence of a turning point in the input, switches the output onto a particular output branch. Rate-independent branching on a very large set of switches with non-local memory is the central concept in the new definition of hysteresis. Hysteretic loops are a special case. A self-consistent mathematical description of hydrological systems with hysteresis demands a new non-linear systems theory of adequate generality. The goal of this paper is to establish this and to show how this may be done. Two results are presented: a conceptual model for the hysteretic soil-moisture characteristic at the pedon scale and a hysteretic linear reservoir at the catchment scale. Both are based on the Preisach model. A result of particular significance is the demonstration that the independent domain model of the soil moisture characteristic due to Childs, Poulavassilis, Mualem and others, is equivalent to the Preisach hysteresis model of non-linear systems theory, a result reminiscent of the reduction of the theory of the unit hydrograph to linear systems theory in the 1950s. A significant reduction in the number of model parameters is also achieved. The new theory implies a change in modelling paradigm
Systematic derivation of a surface polarization model for planar perovskite solar cells
Increasing evidence suggests that the presence of mobile ions in perovskite
solar cells can cause a current-voltage curve hysteresis. Steady state and
transient current-voltage characteristics of a planar metal halide
CHNHPbI perovskite solar cell are analysed with a drift-diffusion
model that accounts for both charge transport and ion vacancy motion. The high
ion vacancy density within the perovskite layer gives rise to narrow Debye
layers (typical width 2nm), adjacent to the interfaces with the transport
layers, over which large drops in the electric potential occur and in which
significant charge is stored. Large disparities between (I) the width of the
Debye layers and that of the perovskite layer (600nm) and (II) the ion
vacancy density and the charge carrier densities motivate an asymptotic
approach to solving the model, while the stiffness of the equations renders
standard solution methods unreliable. We derive a simplified surface
polarisation model in which the slow ion dynamic are replaced by interfacial
(nonlinear) capacitances at the perovskite interfaces. Favourable comparison is
made between the results of the asymptotic approach and numerical solutions for
a realistic cell over a wide range of operating conditions of practical
interest.Comment: 32 pages, 7 figure
Balancing the books – a statistical theory of prospective budgets in Earth System science
An honest declaration of the error in a mass, momentum or energy balance, ε, simply raises the question of its acceptability: 'At what value of ε is the attempted balance to be rejected?' Answering this question requires a reference quantity against which to compare ε. This quantity must be a mathematical function of all the data used in making the balance. To deliver this function, a theory grounded in a workable definition of acceptability is essential. A distinction must be drawn between a retrospective balance and a prospective budget in relation to any natural space-filling body. Balances look to the past; budgets look to the future. The theory is built on the application of classical sampling theory to the measurement and closure of a prospective budget. It satisfies R.A. Fisher's 'vital requirement that the actual and physical conduct of experiments should govern the statistical procedure of their interpretation'. It provides a test, which rejects, or fails to reject, the hypothesis that the closing error on the budget, when realised, was due to sampling error only. By increasing the number of measurements, the discrimination of the test can be improved, controlling both the precision and accuracy of the budget and its components. The cost-effective design of such measurement campaigns is discussed briefly. This analysis may also show when campaigns to close a budget on a particular space-filling body are not worth the effort for either scientific or economic reasons. Other approaches, such as those based on stochastic processes, lack this finality, because they fail to distinguish between different types of error in the mismatch between a set of realisations of the process and the measured data. Keywords: balance, budget, sampling, hypothesis test, closing error, Earth Syste
GAL4 Drivers Specific for Type Ib and Type Is Motor Neurons in Drosophila.
The Drosophila melanogaster larval neuromuscular system is extensively used by researchers to study neuronal cell biology, and Drosophila glutamatergic motor neurons have become a major model system. There are two main Types of glutamatergic motor neurons, Ib and Is, with different structural and physiological properties at synaptic level at the neuromuscular junction. To generate genetic tools to identify and manipulate motor neurons of each Type, we screened for GAL4 driver lines for this purpose. Here we describe GAL4 drivers specific for examples of neurons within each Type, Ib or Is. These drivers showed high expression levels and were expressed in only few motor neurons, making them amenable tools for specific studies of both axonal and synapse biology in identified Type I motor neurons.This work was supported by grant BB/L021706/1 from the UK Biotechnology and Biological Sciences Research Council to CJO’K, and Marie Sklodowska-Curie 19 fellowship 745007 from the European Union Horizon 2020 research and innovation programme to JJPM
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