Real-time Quantum evolution in the Classical approximation and beyond

With the goal in mind of deriving a method to compute quantum corrections for the real-time evolution in quantum field theory, we analyze the problem from the perspective of the Wigner function. We argue that this provides the most natural way to justify and extend the classical approximation. A simple proposal is presented that can allow to give systematic quantum corrections to the evolution of expectation values and/or an estimate of the errors committed when using the classical approximation. The method is applied to the case of a few degrees of freedom and compared with other methods and with the exact quantum results. An analysis of the dependence of the numerical effort involved as a function of the number of variables is given, which allow us to be optimistic about its applicability in a quantum field theoretical context.Comment: 32 pages, 6 figure

Selection of AGN candidates in the GOODS-South Field through SPITZER/MIPS 24 μ\mum variability

We present a study of galaxies showing mid-infrared variability in data taken in the deepest Spitzer/MIPS 24 $\mu$m surveys in the GOODS-South field. We divide the dataset in epochs and subepochs to study the long-term (months-years) and the short-term (days) variability. We use a $\chi^2$-statistics method to select AGN candidates with a probability $\leq$ 1% that the observed variability is due to statistical errors alone. We find 39 (1.7% of the parent sample) sources that show long-term variability and 55 (2.2% of the parent sample) showing short-term variability. That is, 0.03 sources $\times$ arcmin$^{-2}$ for both, long-term and short-term variable sources. After removing the expected number of false positives inherent to the method, the estimated percentages are 1.0% and 1.4% of the parent sample for the long-term and short-term respectively. We compare our candidates with AGN selected in the X-ray and radio bands, and AGN candidates selected by their IR emission. Approximately, 50% of the MIPS 24 $\mu$m variable sources would be identified as AGN with these other methods. Therefore, MIPS 24 $\mu$m variability is a new method to identify AGN candidates, possibly dust obscured and low luminosity AGN, that might be missed by other methods. However, the contribution of the MIPS 24 $\mu$m variable identified AGN to the general AGN population is small ($\leq$ 13%) in GOODS-South.Comment: Accepted for publication in MNRA

Lime amendment effects on physico-chemical and chemical fluctuations of flooded soils

Rice growth in wetlands or paddy soils is economically important in Latin America.Lime amendment is becoming a conventional practice for rice production in this area. A field study was conducted to compare changes induced by liming paddy soils in Corrientes (Argentina). Three different treatments were considered: a control plot, with no lime addition, and two amended plots with 625 kg/ha and 1250 kg/ha rates of dolomite application. Before flooding and at two week intervals during ten weeks after flooding, the following soil physico-chemical and chemical parameters were measured in each of the treatments: Eh, pH, NH 4+-N, extractable Mn and Fe and P. In all the three treatments two weeks after flooding a sharply Eh fall and simultaneously a sharply pH rise was observed. Lime addition showed a clear trend to lower Eh values, all over the waterlogging study period. However, the initial differences in pH between the control plot and plots amended with dolomite vanished at the end of the ten weeks experience. Before flooding, high NH4+-N differences between treatments were also observed. In the control plot, the trend during anaerobiosis was to increase the low initial NH 4+- N level, whereas the high NH4+-N content at the beginning of the experience in the amended plots was somewhat reduced. Extractable Mn and Fe increased as a function of flooding duration and lime addition increased the extractability of these two elements, so that at the end of the experience Mn and Fe levels were much higher in dolomite amended plots than in control. Olsen- extractable P was also initially higher in the amended plots than in the control plot and after flooding no unique fluctuation trend was observed

Stiffness map of the grasping contact areas of the human hand

The elasticity and damping of the soft tissues of the hand contribute to dexterity while grasping and also help to stabilise the objects in manipulation tasks. Although some previous works have studied the force-displacement response of the fingertips, the responses in all other regions of the hand that usually participate in grasping have not been analysed to date. In this work we performed experimental measurements in 20 subjects to obtain a stiffness map of the different grasping contact areas of the human hand. A force-displacement apparatus was used to simultaneously measure force and displacement at 39 different points on the hand at six levels of force ranging from 1 N to 6 N. A non-linear force-displacement response was found for all points, with stiffness increasing with the amount of force applied. Mean stiffness for the different points and force levels was within the range from 0.2 N/mm to 7.7 N/mm. However, the stiffness range and variation with level of force were found to be different from point to point. A total of 13 regions with similar stiffness behaviours were identified. The stiffness in the fingertips increased linearly with the amount of force applied, while in the palm it remained more constant for the range of forces considered. It is hypothesised that the differences in the stiffness behaviour from one region to another allow these regions to play different roles during grasping.

Mechanical performance of endodontic restorations with prefabricated posts: sensitivity analysis of parameters with a 3D finite element model

Many studies have investigated the effect of different parameters of the endodontically restored tooth on its final strength, using in vitro tests and model simulations. However, the differences in the experimental set-up or modelling conditions and the limited number of parameters studied in each case prevent us from obtaining clear conclusions about the relative importance of each parameter. In this study, a validated 3D biomechanical model of the restored tooth was used for an exhaustive sensitivity analysis. The individual influence of 20 different parameters on the mechanical performance of an endodontic restoration with prefabricated posts was studied. The results bring up the remarkable importance of the loading angle on the final restoration strength. Flexural loads are more critical than compressive or tensile loads. Young’s modulus of the post and its length and diameter are the most influential parameters for strength, whereas other parameters such as ferrule geometry or core and crown characteristics are less significant

Hand posture prediction using neural networks within a biomechanical model

This paper proposes the use of artificial neural networks (ANNs) in the framework of a biomechanical hand model for grasping. ANNs enhance the model capabilities as they substitute estimated data for the experimental inputs required by the grasping algorithm used. These inputs are the tentative grasping posture and the most open posture during grasping. As a consequence, more realistic grasping postures are predicted by the grasping algorithm, along with the contact information required by the dynamic biomechanical model (contact points and normals). Several neural network architectures are tested and compared in terms of prediction errors, leading to encouraging results. The performance of the overall proposal is also shown through simulation, where a grasping experiment is replicated and compared to the real grasping data collected by a data glove device.