Results 1 - 10 of 1499
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[en] The aim of this study was to find a model able to extract the net time per unit of net worked area from different agricultural field basic shapes (square, circle, rectangle and triangle) considering the following variables: field gross area, working speed, number of turnings (these depending on the effective working width), side length parallel and orthogonal to working direction, and working direction type. Being this a non-linear problem, an approach based on artificial neural networks is proposed. The model was trained using an artificial dataset calculated for the various shapes (internal test) and then tested on 47 different agricultural operations extracted by a real field dataset for the estimation of the net time (external test). The net time records obtained from both, the trained model and the external test, were correlated and the performance parameter r was extracted. Both regression coefficients (r), for the training and internal test, appear to be excellent being equal to 0.98 with respect to traditional linear approach (0.13). The variable “number of turnings” scored the highest impact, with a value equal to 44.34% for the net time estimation. Finally, the r correlation parameter for the external test resulted to be very high (0.80). This information is very valuable of the use of information management system for precision agriculture.
[en] In the present study, differential interferometry and shadowgraphy are combined to determine cavitation-induced pressure fields and corresponding bubble dynamics during laser-induced single-bubble cavitation. An evaluation method is presented that allows to reconstruct the pressure distribution from interference images with high accuracy. The minimum reconstruction accuracy of the pressure amplitudes with the presented method is determined from synthetic data sets for an angular range of to be . On the basis of statistically evaluated data, the energy budget of single cavitation bubbles and the corresponding pressure wave energy could be determined also for weak pressure wave amplitudes in the order of . Graphical abstract: .
[en] In this paper, we generalize the formalism of gravity's rainbow to complex space-time. The resulting geometry depends on the energy of the probe in such a way that the usual real manifold is the low energy approximation of the Planck scale geometry of space-time. So, our formalism agrees with all the observational data about our space-time being real, as at the scale these experiments are preformed, the imaginary part of the geometry is suppressed by Planck energy. However, the imaginary part of the geometry becomes important near the Planck energy, and so it cannot be neglected near the Planck scale. So, the Planck scale geometry of space-time is described by a complex manifold. (author)
[en] The article Experimental investigation of the axial strength of glued-in rods in cross laminated timber, written by Boris Azinović, Erik Serrano, Miha Kramar, Tomaž Pazlar, was originally published online without Open Access.
[en] From the perspective of quantum thermodynamics, realisable measurements cost work and result in measurement devices that are not perfectly correlated with the measured systems. We investigate the consequences for the estimation of work in non-equilibrium processes and for the fundamental structure of the work fluctuations when one assumes that the measurements are non-ideal. We show that obtaining work estimates and their statistical moments at finite work cost implies an imperfection of the estimates themselves: more accurate estimates incur higher costs. Our results provide a qualitative relation between the cost of obtaining information about work and the trustworthiness of this information. Moreover, we show that Jarzynski’s equality can be maintained exactly at the expense of a correction that depends only on the system’s energy scale, while the more general fluctuation relation due to Crooks no longer holds when the cost of the work estimation procedure is finite. We show that precise links between dissipation and irreversibility can be extended to the non-ideal situation. (paper)
[en] Capillary tubes with straight, spiral, and helically coiled shapes have been widely used as expansion devices in small refrigeration systems. Many physical models are required to evaluate the refrigerant flow rate through a helically coiled capillary tube because of the complicated flow behavior in such tube. In this study, a numerical model was developed to evaluate refrigerant flow through a helically coiled capillary tube. The mass flow rates predicted using various combinations of empirical correlations were compared with the experimental data available in the open literature, including R22, R134a, R407C, R410A and LPG. On the basis of these comparisons, a recommended set of correlations was selected to calculate the mass flow rates through a helically coiled capillary tube. The present numerical model exhibited good agreement with the experimental data.
[en] A longstanding question on the mechanically forced Faraday instability in rectangular geometries arises from a disparity between theory and experiments (Craik and Armitage in Fluid Dyn Res 15:129–143, 1995). It can be stated as: do corners in a rectangular geometry Faraday experiment cause the disparity between prediction and experiment? This study is an attempt to settle this question by comparing the Faraday instability for two fluids in rectangular geometries where corners must be present with equivalent annular geometries where such corners are necessarily absent. Non-idealities, i.e., damping, arising from a slight meniscus wave motion and induced sidewall damping are observed for thin gaps, causing discrepancies between the predicted instability thresholds and those determined experimentally. However, even for thin-gap geometries, experimental agreement between the tested rectangular geometry and its corresponding annular geometry remains excellent. This suggests that corner effects on the system stability are negligible for rectangular geometries and thus any disparity between theory and experiment is due principally to the damping caused by proximity of the lateral walls. Graphical abstract: .
[en] We have considered basic theoretical models describing various aspects of the formation and acceleration of plasma in pulsed accelerators. The discharge current, magnetic field, and plasma bunch velocity have been determined experimentally at different initial gas pressures in the accelerator chamber. We have considered the correspondence of some theoretical models of plasma acceleration to experimental data obtained in a KPU-30 coaxial accelerator. It is shown that the formation of the plasma in the coaxial accelerator depends on the plasma density, and acceleration processes at densities higher and lower than a certain transient density value on the order of 1011–1012 cm–3 are different. At a density higher than this critical value, the plasma is accelerated by a magnetic force. At the same time, at a low plasma density, plasma can be accelerated by an internal electric field.
[en] We investigate estimation of fluctuating channels and its effect on security of continuous-variable quantum key distribution. We propose a novel estimation scheme which is based on the clusterization of the estimated transmittance data. We show that uncertainty about whether the transmittance is fixed or not results in a lower key rate. However, if the total number of measurements is large, one can obtain using our method a key rate similar to the non-fluctuating channel even for highly fluctuating channels. We also verify our theoretical assumptions using experimental data from an atmospheric quantum channel. Our method is therefore promising for secure quantum communication over strongly fluctuating turbulent atmospheric channels. (paper)