Full experimental modelling of a liver tissue mimicking phantom for medical ultrasound studies employing different hydrogels

Tissue mimicking phantoms have been widely reported to be an important tool for development, optimisation and performance testing of ultrasound-based diagnostic techniques. In particular, modern applications of tissue mimicking phantoms often include characterisation of the nonlinear behaviour of experimental ultrasound contrast agents. In such cases, the tissue-mimicking materials should be chosen not only based on the values of their density, speed of sound and attenuation coefficient, but also considering their effect on the appearance of “native harmonics” due to nonlinear distortion of ultrasound signal during propagation. In a previous paper it was demonstrated that a cellulose-based hydrogel is suitable to simulate nonlinear acoustical behaviour of liver tissue for thicknesses up to 8 cm. In this paper we present the experimental characterisation of the nonlinear acoustical behaviour of a different polyethylene glycol diacrylate (PEGDA)-based hydrogel, in order to assess whether and how it can improve the performances and overcome some limitations of the cellulose-based hydrogel as liver tissue-mimicking material. Samples of pig liver tissue, cellulose-based hydrogel and PEGDA-based hydrogel were insonified in a through-transmission set-up, employing 2.25-MHz pulses with different mechanical index (MI) values. Second harmonic and first harmonic amplitudes were extracted from the spectra of received signals and their difference was then used to compare sample behaviours. Obtained results show how a new more accurate and combined experimental model of linear and nonlinear acoustical behaviour of liver tissue is feasible. In fact, a further confirmation of the cellulose-based hydrogel effectiveness to precisely simulate the liver tissue for penetration depths up to 8 cm was provided, and it was also shown that the employment of the PEGDA-based hydrogel can extend the range of useful tissue-mimicking material thicknesses up to 11 cm, moreover allowing a considerable improvement of the time stability and behaviour reliability of the corresponding manufactured phantoms.     

The effect of pulsed electric fields,ultraviolet light or high intensity light pulses in combination with manothermosonication on selected physico-chemical and sensory attributes of an orange and carrot juice blend

A blend of orange and carrot juice was processed by three selected treatments combining pulsed electric fields (PEF) (24 kV/cm, 18 Hz, 93 μs), ultraviolet light (UV) (10.6 J/cm²) or high intensity light pulses (HILP) (3.3 J/cm²), in each case, with manothermosonication (MTS) technology (400 kPa, 35 °C, 1000 W, 20 kHz). Treatment effects on selected physico-chemical and sensory properties of the juice were evaluated. No significant changes were found in non-enzymatic browning (NEBI) or antioxidant activity compared to an untreated control. However, the treatments increased all the Hunter Lab colour values, while total phenolics were significantly decreased. Each combination achieved on average 78% inactivation of pectin methyl esterase (PME). Sensory analysis showed that the colour of the product processed by hurdle combinations was preferred to that of a pasteurised sample (72 °C, 26 s), while the flavour was adversely affected by all of the non-thermal treatments. Panellists did not perceive differences in the odour, sweetness or acidity of the product. Results indicate that, under the current experimental conditions, the application of the selected combinations of non-thermal technologies resulted in a product in which certain quality attributes were somewhat inferior to those of a lightly pasteurised control juice.     

An AGM-style belief revision mechanism for probabilistic spatio-temporal logics

There is now extensive interest in reasoning about moving objects. A probabilistic spatio-temporal (PST) knowledge base (KB) contains atomic statements of the form “Object o is/was/will be in region r at time t with probability in the interval [?,u]”. In this paper, we study mechanisms for belief revision in PST KBs. We propose multiple methods for revising PST KBs. These methods involve finding maximally consistent subsets and maximal cardinality consistent subsets. In addition, there may be applications where the user has doubts about the accuracy of the spatial information, or the temporal aspects, or about the ability to recognize objects in such statements. We study belief revision mechanisms that allow changes to the KB in each of these three components. Finally, there may be doubts about the assignment of probabilities in the KB. Allowing changes to the probability of statements in the KB yields another belief revision mechanism. Each of these belief revision methods may be epistemically desirable for some applications, but not for others. We show that some of these approaches cannot satisfy AGM-style axioms for belief revision under certain conditions. We also perform a detailed complexity analysis of each of these approaches. Simply put, all belief revision methods proposed that satisfy AGM-style axioms turn out to be intractable with the exception of the method that revises beliefs by changing the probabilities (minimally) in the KB. We also propose two hybrids of these basic approaches to revision and analyze the complexity of these hybrid methods.     

Allocating data for broadcasting over wireless channels subject to transmission errors

Broadcasting is an efficient and scalable way of transmitting data over wireless channels to an unlimited number of clients. In this paper the problem of allocating data to multiple channels is studied, assuming flat data scheduling per channel and the presence of unrecoverable channel transmission errors. The objective is that of minimizing the average expected delay experienced by the clients. Two different channel error models are considered: the Bernoulli model and the simplified Gilbert–Elliot one. In the former model, each packet transmission has the same probability to fail and each transmission error is independent from the others. In the latter one, bursts of erroneous or error-free packet transmissions due to wireless fading channels are modeled. Particular cases are detected where optimal solutions can be found in polynomial time. For general cases, simulations show that good sub-optimal solutions can be found on benchmarks whose item popularities follow Zipf distributions.     

Coupling system dynamics and contact behaviour: Modelling bearings subjected to environmental induced vibrations and ‘false brinelling’ degradation

During the last decades the increase in power of mechanical systems and the demand for increasing service life leads mechanical components of a system to work in extreme conditions. Moreover, actual mechanical systems include surfaces in sliding contact that are subjected to wear if exposed to high vibration. In fact, the vibration of components in contact results in large oscillations of the local contact stresses, due to the local deformation of the components at the contact interfaces. To approach correctly tribological problems, the coupling between the scale of the mechanism (system dynamics) and the scale of the contact needs to be accounted for.This paper presents an analysis concerning the influence of the vibrations induced by aircraft engines on the contact stresses of rolling bearings of the bleed system valves. To study the wear, resulting from false brinelling at the contact surfaces between balls and races of the bearings, it is then necessary to determine the forces due to the system vibrations and acting at the bearing connections with the structure. In order to perform a numerical transient analysis of the system dynamics a nonlinear simplified model of the valve (mechanism scale) is developed. The model is validated by comparing the numerical results with experimental tests. The time behaviour of the global forces on the bearings, and the respective displacements between the contact surfaces, are then used as inputs for a finite element model of the bearings (contact scale). The model is used to calculate and analyze the behaviour in time of the local contact constraints between race and balls. This analysis, developed in the framework of a European project, is an example of the proposed general approach to contact problems, by coupling the analysis of the mechanism and contact scales.