1,721,102 research outputs found
NMR applications for the diagnosis of female pathologies
No full textNuclear magnetic resonance (NMR) imaging (MRI) and spectroscopy (MRS) are powerful techniques that can be used to study the in-vivo human body and diseases. MRS allows for the quantification of metabolites and a chemical analysis of the analyzed sample, whereas MRI is a multi-parametric technique that provides detailed cross-sectional images of the body’s internal structures using non-ionizing radiation. In particular, Diffusion-Weighted imaging (DWI) allows the evaluation of the diffusion properties of water in biological tissues without requiring contrast agents and with excellent resolution dependent on diffusion length. These techniques applied in the brain studies have been revolutionizing the neuroimaging field, leading to important information related to the microstructure and function of the brain. To extract this information, the development of mathematical models has been the topic of greatest interest over the last 20 years. Indeed, in DWI the NMR signal is the Fourier transform of the motion propagator, which is easily calculated for free water, but it is more complex in biological tissues leading to the development of models such as the Intravoxel incoherent motion (IVIM) model and the Kurtosis representation. All these models were first applied and optimized for neurological application; hence the body application should be carried out considering these limitations (related to the structural and physiological differences between cerebral and ex cranial tissues) and adapting the models to the specific analyzed tissues to avoid the evaluation of parameters without physical sense. Sometimes, clinical NMR images are affected by high level of noise which imply the wrong evaluation of the NMR parameters. Hence, it is necessary to know the signal to noise ratio (SNR) of each image and perform a denoising if the SNR is too low.
In this thesis, a biophysical model with two perfusion compartments was adapted for placental tissues analysis to study the diffusion and perfusion properties of water in the placenta which is characterized by three main compartments: the fastest perfusion compartment due to the fetal villous-trees, a slower perfusion compartment related to the trophoblastic activity and a diffusion compartment linked to the maternal blood in the intra-villous space. The model was applied to evaluate the characteristics of the normal placental tissues and to find any differences between normal placentas and those affected by two specific pathologies: the fetal growth restriction disease (FGR) and the placental accretism. The application of this new model allowed the identification of new biomarkers non-obtainable applying the more known and used IVIM model, which nevertheless is able to highlight important perfusion features. Indeed, the IVIM model was used to study the differences between normal placentas and those belonging to women with SARS-CoV-2 infection, pinpointing substantial differences in the values of the diffusion coeffcient due to a damage to the microstructure of the tissue.
DWI also has important applications in the oncology field. In fact, it has been widely used to study the complexity of tumor tissues in the brain. In this work, DWI was adopted to study the cervical cancer and the endometrial cancer in particular. Generally, the diagnosis of these kinds of pathologies is performed by the histology which is an invasive technique and it is limited by the size of the taken tissue. In this thesis, tissue complexity and tumor grade were evaluated using the kurtosis representation combined with a clusterization based on the tissue differences in the same region of interest obtaining a higher variance of the kurtosis parameters in tumor tissues than in the healthy endometrium. Since the kurtosis representation is sensitive to image noise, a denoising was performed before applying the model and the non-dependence of the parameter to the noise was verified.
MRS was used to pinpoint early biomarkers in bone marrow and muscles to study the osteoporosis and osteoarthritis diseases, highlighting interesting differences in the fat lipid content and in the level of unsaturated fatty-acids in both bones and muscles, corroborating the hypothesis that these pathologies involve the whole musculoskeletal system.
Although the promising results, new perspectives should be considered for the diffusion model’s selection. Indeed, the dynamics underlying the studied system is crucial for the model selection since the application of the wrong model would bring the evaluation of physically no-sense parameters. In this work a preliminary experimental study was conducted on PEG to evaluate its true dynamics and then choose the right diffusion model applying a particular “recipe” conceived and developed in the NMR laboratory of the CNR-ISC & Sapienza where I carried out my PhD work. These last results underline the importance of the knowledge of the tissue diffusion properties a priori to perform more precise and faithful quantification of diffusion parameters indispensable for more precise and early clinical diagnostic
Preface to Special Issue on Building Integrated Renewable Energy Systems (BIRES)
No full textSpecial Issue on Building Integrated Renewable Energy
Systems (BIRES
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
SDEWES 2018 - 13th Conference on Sustainable Development of Energy, Water and Environment Systems
No full textSolar heating and cooling systems by absorption and adsorption chillers driven by stationary and concentrating photovoltaic/thermal solar collectors: Modelling and simulation
No full textSolar heating and cooling systems are a promising technology which may significantly contribute to the reduction of greenhouse gas emissions, the enhancement of energy efficiency, and the increase of renewables share in the building sector. The available literature show a high number of papers aiming at investigating solar heating and cooling systems based on heat driven and solar technologies, configurations, operating strategies, and financing issues. Nevertheless, none of the papers available in literature investigates the possibility to replace conventional solar thermal collectors by flat plat and concentrating photovoltaic/thermal systems, also producing renewable electricity. To cover this lack of knowledge, in this paper a dynamic simulation model of novel solar polygeneration heating and cooling systems is presented. Such dynamic simulation model is developed and implemented in a computer code, written in MatLab, and allows investigating the energy, economic and environmental performance of such novel solar polygeneration systems, based on both adsorption and absorption chiller technologies fed by dish-shaped concentrating and flat photovoltaic/thermal collectors. In order to show the potentiality of the presented tool, a comprehensive parametric case study is carried out to find out the optimal system configurations, as a function of crucial design and operating parameters and of weather conditions. The presented case study analysis refers to a small cluster of four buildings, including office and residential spaces, located in different European weather zones. The modelled solar polygeneration systems simultaneously produce electricity, space heating and cooling, and domestic hot water; electricity is self-consumed or delivered to the electrical grid. For comparative purposes, two different back-up system configurations, based on an electric chiller and a condensing gas-fired heater are also taken into account as conventional reference building-plant systems. By means of this systematic parametric analysis, comprehensive guidelines for system designers, practitioners and/or researchers focused on the development and use of solar heating and cooling systems are provided
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
Maximization of primary energy savings of solar heating and cooling systems by transient simulations and computer design of experiments
No full textIn this paper, the simulation of the performance of solar-assisted heating and cooling systems is analyzed. Three different plant layouts are considered: (i) the first one consists of evacuated solar collectors and a single-stage LiBr-H2O absorption chiller; here in order to integrate the system in case of insufficient solar radiation, an electric water-cooled chiller is activated; (ii) configuration of the secondly considered system is similar to the first one, but the absorption chiller and the solar collector area are sized for balancing about 30% of the building cooling load only; (iii) the layout of the thirdly considered system differs from the first one since the auxiliary electric chiller is replaced by a gas-fired heater. Such system configurations also include: circulation pumps, storage tanks, feedback controllers, mixers, diverters and on/off hysteresis controllers. All such devices are modelled for maximizing the system energy efficiency. In order to simulate the systems' performance for dynamic heating/cooling loads, a single-lumped capacitance building is also modelled and implemented in the computer code. A cost model is also developed in order to calculate the systems' operating and capital costs. All the models and the relative simulations are carried out by TRNSYS. A design of experiment procedure is also included. By such tool the effects of the system operating parameters' variation on the relative energy efficiency are analyzed. In addition, the set of synthesis/design variables maximizing the system's energetic performance can be also identified. The annual primary energy saving is chosen as the optimization objective function, whereas collector slope, pump flows, set-point temperatures and tank volume are selected as optimizing system design variables. A case study was developed for an office building located in South Italy. Here, the energetic and the economic analysis for all the three considered system layouts are carried out. The simulations' results are referred to both the initial and the optimized systems configurations. The highest primary energy saving vs. the reference traditional HVAC system is reached by the first considered system layout. The economic performance of the investigated solar heating/cooling systems is still unsatisfactory. The economical profitability of the considered solar heating and cooling systems can be improved only by significant public finding. From this point of view, the best results were achieved by the second above mentioned system configuration
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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