Lessons learned from longitudinal modeling of mobile-equipped visitors in a complex museum

Neural Computing and Applications - Cultural sites are evolving toward smart environments, including the notion of hyper-connected museums. In this context, stakeholders of cultural assets need...     

The numerical solution of fractional differential equations using the Volterra integral equation method based on thin plate splines

Finding the approximate solution of differential equations, including non-integer order derivatives, is one of the most important problems in numerical fractional calculus. The main idea of the current paper is to obtain a numerical scheme for solving fractional differential equations of the second order. To handle the method, we first convert these types of differential equations to linear fractional Volterra integral equations of the second kind. Afterward, the solutions of the mentioned Volterra integral equations are estimated using the discrete collocation method together with thin plate splines as a type of free-shape parameter radial basis functions. Since the scheme does not need any background meshes, it can be recognized as a meshless method. The proposed approach has a simple and computationally attractive algorithm. Error analysis is also studied for the presented method. Finally, the reliability and efficiency of the new technique are tested over several fractional differential equations and obtained results confirm the theoretical error estimates.

     

Bias extension test for pantographic sheets: numerical simulations based on second gradient shear energies

We consider a bi-dimensional sheet consisting of two orthogonal families of inextensible fibres. Using the representation due to Rivlin and Pipkin for admissible placements, i.e. placements preserving the lengths of the inextensible fibres, we numerically simulate a standard bias extension test on the sheet, solving a non-linear constrained optimization problem. Several first and second gradient deformation energy models are considered, depending on the shear angle between the fibres and on its gradient, and the results obtained are compared. The proposed numerical simulations will be helpful in designing a systematic experimental campaign aimed at characterizing the internal energy for physical realizations of the ideal pantographic structure presented in this paper.     

Nonlinear Galerkin methods for a system of PDEs with Turing instabilities

We address and discuss the application of nonlinear Galerkin methods for the model reduction and numerical solution of partial differential equations (PDE) with Turing instabilities in comparison with standard (linear) Galerkin methods. The model considered is a system of PDEs modelling the pattern formation in vegetation dynamics. In particular, by constructing the approximate inertial manifold on the basis of the spectral decomposition of the solution, we implement the so-called Euler–Galerkin method and we compare its efficiency and accuracy versus the linear Galerkin methods. We compare the efficiency of the methods by (a) the accuracy of the computed bifurcation points, and, (b) by the computation of the Hausdorff distance between the limit sets obtained by the Galerkin methods and the ones obtained with a reference finite difference scheme. The efficiency with respect to the required CPU time is also accessed. For our illustrations we used three different ODE time integrators, from the Matlab ODE suite. Our results indicate that the performance of the Euler–Galerkin method is superior compared to the linear Galerkin method when either explicit or linearly implicit time integration scheme are adopted. For the particular problem considered, we found that the dimension of approximate inertial manifold is strongly affected by the lenght of the spatial domain. Indeeed, we show that the number of modes required to accurately describe the long time Turing pattern forming solutions increases as the domain increases.     

Aluminum Nitride Thin Films on an LTCC Substrate

Aluminum nitride thin films deposited on a low-temperature co-fired ceramics substrate by reactive magnetron sputtering were investigated with regard to their crystal orientation and microstructural characteristics. Strong c -axis orientations of AlN thin films were observed when either a higher deposition temperature or an RF bias was adopted. This orientation was believed to be responsible for the high thermal conductivity of 26 W/mK for the AlN films deposited at 700°C under 25-W bias. Photoluminescence spectrum in the wavelength range of 350–650 nm was analyzed to prove the involvement of potential oxygen-related defects in the thin films.     

Temperature dependence of calcium and magnesium induced caseinate precipitation in H2O and D2O

Casein is a well-known and highly studied protein present in milk found in the form of large colloidal particles called casein micelles. Here we assessed the influence of two solvents, H₂O and D₂O, on the precipitation temperatures of sodium caseinate induced by calcium and magnesium ions. The intrinsic fluorescence of casein was correlated with the suspended and precipitated protein fractions in order to extrapolate the precipitation temperature. The precipitation temperature values were determined for several calcium and magnesium concentrations in H₂O, demonstrating the strong differences in the association behaviour induced by the two divalent cations. The precipitation temperatures of caseinate, in the presence of calcium induced by heating the samples in D₂O, were significantly lower compared with the one performed in H₂O. On the contrary, the precipitation temperatures of casein in the presence of magnesium were very close to those obtained in the samples tested in H₂O. Thus, calcium interaction with the protein depends on temperature and solvents, two parameters that modify the accessibility of the binding site of the cation. Conversely, the interaction of the divalent magnesium ion with casein was shown to depend only upon the temperature. Remarkably, this evidence indicates that the two ions have different binding sites on the protein, suggesting that the D₂O solvent plays an important role in the detection of the different binding sites for calcium and magnesium. Additionally, the results obtained with the simultaneous presence of both cations suggest the existence of a cooperative mechanism between the two ions, in which the presence of calcium makes more sites available for the binding of magnesium.     

Performance analysis of IEEE 802.15.4 wireless sensor networks: An insight into the topology formation process

Topology formation is an important issue in a wireless sensor network. Performance parameters such as energy consumption, network lifetime, data delivery delay, sensor field coverage depend on the network topology. In this paper, we analyze the process of formation of a wireless sensor network according to the IEEE 802.15.4/ZigBee standards. We focus on both single-sink scenarios and multi-sink ones where: (i) we characterize the topology in terms of network depth and nodes distribution at different network levels; (ii) we analyze some network performance as a function of the number of sinks; (iii) we investigate the effects of some topology constraints on network performance; (iv) we study the effects of nodes mobility on the network formation. The whole study is performed by taking into account the specific features and recommendations of the IEEE 802.15.4/ZigBee standards; thus, our results can be used to configure IEEE 802.15.4/ZigBee procedures and set the related parameters, as a function of the desired application requirements.     

In place merging of satellite based atmospheric water vapour measurements

Atmospheric water vapour plays a key role in the climatology of the Earth. It has traditionally been measured using radiosondes for reasons of instrumental simplicity but these offer limited opportunities for spatial and continuous measurements of dynamic water vapour changes over large areas of the Earth's atmosphere. Efforts have recently turned to using satellite remote sensing instruments with different spectral and spatial capabilities to derive measurements of total water vapour content in atmospheric columns or simply precipitable water. The merging of remote sensing data with different spectral and spatial capabilities can result in large biases when independent measurements are not nested correctly to produce the final product. Consequently, such merging of data must take into account the intrinsic time dynamics of measured parameters. In this paper, the impact of atmospheric water vapour dynamics on the merging of satellite-based retrieval of precipitable water estimates is investigated by comparing independent measurements obtained at different spatial resolutions from the High Resolution Infrared Sounder (HIRS) and the Advanced Very High Resolution Radiometer (AVHRR). Correlations are used to infer optimal merging parameters depending on the observational conditions. The authors conclude that the merging technique reproduces HIRS-based retrievals in cloud-free and partly cloudy locations from AVHRR soundings.     

Effect of Ar+ ion beam in the process of plasma surface modification of PET films

In general, plasma modified polymer surfaces tend to show short aging time and rapid hydrophobic recovery after treatment. To prevent reorientation from the surface to the bulk, appropriate crosslinking is necessary among the polymer chains. In this work, an Ar⁺ ion beam was used to provide crosslinking to the surface. Crosslinking was shown by spectroscopic ellipsometry, AFM, and FTIR. Contact angle measurements were performed to see the aging of the modified surfaces. The surface modified with Ar⁺ ion beam followed by RF plasma treatment exhibited reduced chain mobility and a highly stable hydrophilic surface. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1679–1683, 2000