Modelling the permeability of polymers: a neural network approach

In this short communication, the prediction of the permeability of carbon dioxide through different polymers using a neural network is studied. A neural network is a numeric-mathematical construction that can model complex non-linear relationships. Here it is used to correlate the IR spectrum of a polymer to its permeability. The underlying assumption is that the chemical information hidden in the IR spectrum is sufficient for the prediction. The best neural network investigated so far does indeed show predictive capabilities

Normal mere exposure effect with impaired recognition in Alzheimer’s disease.

We investigated the mere exposure effect and the explicit memory in Alzheimer’s disease (AD) patients and elderly control subjects, using unfamiliar faces. During the exposure phase, the subjects estimated the age of briefly flashed faces. The mere exposure effect was examined by presenting pairs of faces (old and new) and asking participants to select the face they liked. The participants were then presented with a forced-choice explicit recognition task. Controls subjects exhibited above-chance preference and recognition scores for old faces. The AD patients also showed the mere exposure effect but no explicit recognition. These results suggest that the processes involved in the mere exposure effect are preserved in AD patients despite their impaired explicit recognition. The results are discussed in terms of Seamon et al.’s proposal (1995) that processes involved in the mere exposure effect are equivalent to those subserving perceptual priming. These processes would depend on extrastriate areas which are relatively preserved in AD patients

Processing of signals from an ion-elective electrode array by a neural network

Neural network software is described for processing the signals of arrays of ion-selective electrodes. The performance of the software was tested in the simultaneous determination of calcium and copper(II) ions in binary mixtures of copper(II) nitrate and calcium chloride and the simultaneous determination of potassium, calcium, nitrate and chloride in mixtures of potassium and calcium chlorides and ammonium nitrate. The measurements for the Ca2+/Cu2+ determinations were done with a pH-glass electrode and calcium and copper ion-selective electrodes; results were accurate to ±8%. For the K+/Ca2+NO−3/Cl− determinations, the measurements were made with the relevant ion-selective electrodes and a glass electrode; the mean relative error was ±6%, and for the worst cases the error did not exceed 20%

Artificial neural networks as a multivariate calibration tool: modelling the Fe-Cr-Ni system in X-ray fluorescence spectroscopy

The performance of artificial neural networks (ANNs) for modeling the Cr---Ni---Fe system in quantitative x-ray fluorescence spectroscopy was compared with the classical Rasberry-Heinrich model and a previously published method applying the linear learning machine in combination with singular value decomposition. Apart from determining if ANNs were capable of modeling the desired non-linear relationships, also the effects of using non-ideal and noisy data were studied. For this goal, more than a hundred steel samples with large variations in composition were measured at their primary and secondary K¿ and Kß lines. The optimal calibration parameters for the Rasberry-Heinrich model were found from this dataset by use of a genetic algorithm. ANNs were found to be robust and to perform generally better than the other two methods in calibrating over large ranges

Why current-carrying magnetic flux tubes gobble up plasma and become thin as a result

It is shown that if a current-carrying magnetic flux tube is bulged at its axial midpoint z=0 and constricted at its axial endpoints z=+h,-h, then plasma will be accelerated from z=+h,-h towards z=0 resulting in a situation similar to two water jets pointed at each other. The ingested plasma convects embedded, frozen-in toroidal magnetic flux from z=+h,-h to z=0. The counter-directed flows collide and stagnate at z=0 and in so doing (i) convert their translational kinetic energy into heat, (ii) increase the plasma density at z~0, and (iii) increase the embedded toroidal flux density at z~0. The increase in toroidal flux density at z~0 increases the toroidal field Bphi and hence increases the magnetic pinch force at z~0 and so causes a reduction of the flux tube radius at z~0. Thus, the flux tube develops an axially uniform cross-section, a decreased volume, an increased density, and an increased temperature. This model is proposed as a likely hypothesis for the long-standing mystery of why solar coronal loops are observed to be axially uniform, hot, and bright.Comment: to appear in Physics of Plasmas 24 pages, 5 figure

Unstable coronal loops : numerical simulations with predicted observational signatures

We present numerical studies of the nonlinear, resistive magnetohydrodynamic (MHD) evolution of coronal loops. For these simulations we assume that the loops carry no net current, as might be expected if the loop had evolved due to vortex flows. Furthermore the initial equilibrium is taken to be a cylindrical flux tube with line-tied ends. For a given amount of twist in the magnetic field it is well known that once such a loop exceeds a critical length it becomes unstableto ideal MHD instabilities. The early evolution of these instabilities generates large current concentrations. Firstly we show that these current concentrations are consistent with the formation of a current sheet. Magnetic reconnection can only occur in the vicinity of these current concentrations and we therefore couple the resistivity to the local current density. This has the advantage of avoiding resistive diffusion in regions where it should be negligible. We demonstrate the importance of this procedure by comparison with simulations based on a uniform resistivity. From our numerical experiments we are able to estimate some observational signatures for unstable coronal loops. These signatures include: the timescale of the loop brightening; the temperature increase; the energy released and the predicted observable flow speeds. Finally we discuss to what extent these observational signatures are consistent with the properties of transient brightening loops.Comment: 13 pages, 9 figure

Maatregelen bij mogelijke vestiging van tomatenmineermot Tuta absoluta

Het optreden van Tuta absoluta kan worden vastgesteld door middel van feromoonvallen. Het is minstens zo belangrijk om gewaswaarnemingen te doen. De jonge mijnen onderscheiden zich niet eenvoudig van mijnen van mineervliegen. In oudere mijnen is duidelijk plaatselijke ophoping van uitwerpselen te zien. In mijnen van mineervliegen is dat alleen een onderbroken zwarte streep. Rupsen van Tuta absoluta kunnen worden bestreden met abametine (Vertimec) en spinosad (Tracer). Bij aanvang van de teelt of al in de opkweek wordt Macrolophus melanotoma (= M. caliginosus) loslaten, zodat er zo snel mogelijk voldoende roofwantsen in het gewas zitten

Onderzoek aan de tomatenmineermot Tuta absoluta in 2010: Testen van chemische middelen en inventarisatie van natuurlijke vijanden

Referaat Er zijn ook in 2010 verschillende behandelingen met middelen uitgevoerd tegen de tomatenmineermot Tuta absoluta. Middelen met een snelle werking tegen rupsen zijn flubendiamide (Fame), abamectine (Vertimec), emamectin benzoaat (Proclaim) en spinosad (Tracer). Ook indoxacarb heeft een effect. De rupsen stoppen met eten, maar het duurt langere tijd voordat ze dood zijn. Buiten werden tomatenplanten belegd met eieren van Tuta absoluta bij het natuurgebied van Kinderdijk neergezet, met als doel natuurlijke vijanden te verzamelen. Het bleek dat Tuta absoluta door twee soorten inheemse sluipwespen werd geparsiteerd: Elachertus inunctus en Pnigalio soemius. Ook werd de roofwants Dicyphus errans op de tomatenplanten met Tuta absoluta gevonden. De beheersstratgie (monitoring, herkenning, bestrijding) blijft voorlopig als volgt: Het optreden van Tuta absoluta kan worden vastgesteld doormiddel van feromoonvallen. Maar omdat op deze wijze alleen mannetjes worden gevangen, is het ook belangrijk om te letten op aantasting in het gewas. De jonge mijnen zijn vrij moeilijk van mijnen van mineervliegen te onderscheiden. In de oude mijnen van Tuta absoluta zijn de uitwerpselen gemakkelijk te zien. Voor de praktijk blijft het belangrijk de aantallen van de roofwants Macrolophus zo snel mogelijk op een hoog niveau te krijgen. Abstract Different chemical and a biological agents were tested against the tomato leaf miner Tuta absoluta in 2010. Agents with a quick action were flubendiamide (Fame), abamectin (Vertimec), emamectin benzoaat (Proclaim) and spinosad (Tracer). Idoxacarb was also effective. The caterpillars stopped eating, but it took more time before they died. Tomato plants with eggs of Tuta absoluta were placed outside in the nature reserve of Kinderdijk, far away from the greenhouse areas. The aim was to find natural enemies. Two indigenous parasitoids parasitized caterpilars of Tuta absoluta: Elachertus inunctus and Pnigalio soemius. The predatory bug Dicyphus errans was also active on the tomato plants with Tuta absoluta. The current strategy (monitoring, recognition, control) remains as follows: Pheromone traps are useful to discover Tuta absoluta in greenhouses. Only males are being trapped, which means that it is also important to search for mines in the crops. Young mines of Tuta absoluta and other leaf miners are difficult to distinguish. Older mines of Tuta absoluta are recognized by large amounts of frass. It is important to establish high numbers of Macrolophus in the tomato crop as soon as possible

PEARL model for pesticide behaviour and emissions in soil-plant systems : description of the processes in FOCUS PEARL v 1.1.1

The use of pesticides in agriculture presents risks to the environment, which are increasingly evaluated by using computation models. The new PEARL model simulates the behaviour of pesticides in soil-plant systems and their emissions to the environment. The pesticide model is used in combination with the hydrological model SWAP. Various agricultural situations and ways of applying the pesticides can be simulated. The model accounts for different sorption mechanisms, in equilibrium and non-equilibriumdomains of the soil. Pesticide transport in the liquid and gas phases is described by the convection-dispersion-diffusion type equation, which is supplemented with sink terms. Comprehensive reaction schemes are processed in matrix form. The rate in first-order transformation kinetics is dependent on temperature, soil moisture content and depth in the soil. Besides computing persistence and distribution of the pesticidal compounds in soil, the model computes volatilization into the air, lateral drainage to water courses and leaching to groundwater