1,720,965 research outputs found
Heat transfer modeling in soil microwave heating
No full textThe agricultural neediness of cost-effective, environmental friendly and chemical-free methods for farmlands disinfection led to the development of microwave-based solutions, an efficient way of directly conveying energy to the target. Harmful agents such as weeds pests, fungi and bacteria can be suppressed heating the contaminated soil up to pasteurization or sterilization temperatures by irradiating electromagnetic energy by an antenna. The treatment can be carefully devised and designed optimizing the temperature distribution and calibrating the exposure time depending on the soil characteristics, and on the environmental and boundary conditions. In this work a computational model to solve the non-linear multi-physic dielectric heating phenomenon is presented, so taking into account the temperature dependence of the dielectric and thermal soil properties, in order to demonstrate the possibility of properly tuning the microwave application depending on the external heat transfer conditions. It was found that, in the specific conditions here analyzed, an increase of the external convection heat transfer coefficient up to 50 W∙m-2∙K-1, despite being a possible critic condition for the surface, brings to the possibility of treating a soil layer of higher thickness, up to 20 cm. On the other hand, doubling the microwave power from 12 to 24 kW∙m-2 generally reduces the treatment time to less than half, with overall energy savings
Permittivity measurements of mixtures as a function of their composition for microwave heating improving
No full textMicrowave heating is a more efficient alternative to conventional heating in the chemical reactions field due to its positive effects on conversion and reaction kinetics. Dielectric properties of substances and mixtures are important for the optimization of microwave heating processes; notwithstanding this, specific databases are poor and far from being complete, and in the scientific literature only a few data regarding these properties can be found. Dielectric properties are represented by permittivity, which is a complex measure of a substance behaviour in the presence of an electromagnetic field and depends on the field frequency, as well as on the temperature and composition of the chemical system under study. In this work, some real and imaginary parts of permittivity measurements were carried out using a specially designed measurement system. The apparatus was tested in the estimation of permittivity values in water-ethanol mixtures, varying their composition. The results were compared to literature data and fitted with available literature models to verify their trend as a function of composition. The permittivity real part values increase with reducing the molar fraction of ethanol, whereas the imaginary part decreases, according to the values of water and ethanol permittivity reported in the literature. The regressions carried out to describe the permittivity dependence on composition prove that the measured values can be well described by the models taken into account
Microwave heating improvement: permittivity characterization of water–ethanol and water–NaCl binary mixtures
Full text linkMicrowave heating offers a lot of advantages compared to conventional heating methods in the chemical reactions field due to its positive effects on reaction time and selectivity. Dielectric properties, and in particular permittivity, of substances and mixtures, are important for the optimization of microwave heating processes; notwithstanding this, specific databases are poor and far from being complete, and in the scientific literature very little data regarding these properties can be found. In this work, impedance measurements were carried out using a specially designed system to get the real and imaginary parts of the dielectric constant. The apparatus was tested in the estimation of permittivity of water–ethanol and water–NaCl mixtures, varying their composition to obtain a wide range of permittivity values. The results were compared to literature data and fitted with available literature models to verify the correspondence between them, finding that permittivity dependence on mixture composition can be effectively described by the models
Permittivity Measurements of Simulated Biological Tissues for Hyperthermia Applications
No full textHyperthermia is one of the most promising cancer therapies but, to be effective, it needs a preliminary study phase of the area under treatment. For this reason, over the years, the research focused on the development of phantoms, substances or materials able to simulate biological tissues and useful to test the treatment, as well as calibrate the operative parameters and conditions. One of the most important characteristics that phantoms have to simulate is the dielectric permittivity. In this paper are reported some permittivity measurements performed for the realization of phantom for biomedical applications. Different mixtures of substances have been prepared and subjected to measurement with the purpose of realization of an aqueous phantom
Microwave Tomography of the Neck with ANNs: Preliminary Results with Simplified Numerical Phantoms
No full textA microwave imaging approach based on artificial neural networks (ANNs) for the reconstruction of the properties of a cross section of the neck is proposed in this paper. The aim of this work is to retrieve the distribution maps of the neck dielectric properties starting from electromagnetic scattered fields. Possible applications include the diagnosis of cervical diseases. To this end, simplified neck phantoms were developed to test the feasibility of the proposed method. The developed network presents four fully-connected layers with a last regression layer. Several numerical tests were performed to evaluate the performance of the ANN. The preliminary findings indicate a quite good reconstruction of dielectric properties and the possibility to evaluate the spinal canal dimension
Application of MRI, fMRI and Cognitive Data for Alzheimer's Disease detection
No full textMagnetic resonance imaging (MRI) has the clinical potential of helping diagnosis in providing to doctors structural and functional information of several neurological disorders. In this study, we proposed a new method based on the elaboration of MR-Images and functional Magnetic Resonace Images (fMRI), combined with the explotation of Mini Mental Score Examination (MMSE) to discriminate Alzheimer's Disease (AD) by control subjects using Support Vector Machine (SVM) classification. 69 subjects from the Alzheimer's disease Neuroimaging Initiative (ADNI) open database, 33 AD patients and 36 healthy controls (HC), were analyzed. The use of a unimodal approach led to unsatisfactory results, whereas the multimodal approach, i.e., the combination of MRI, fMRI, and MMSE features, provided an accuracy of 95.65%, a specificity of 97.22%, and a sensibility of 93.39%
Microwave Imaging of Cervical Myelopathy: A Preliminary Feasibility Assessment
No full textMicrowave imaging is acquiring a growing importance in several biomedical applications, such as breast and brain stroke diagnosis and monitoring. In this work, a preliminary feasibility analysis concerning the application of such a technique to the monitoring of cervical myelopathy is reported. In particular, suitable working conditions are defined on the basis of a simplified multilayer model of the neck and a first inversion result, aimed at assessing the possibility of retrieving the spinal cord size, is shown
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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