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Phys Chem Chem Phys ; 2020 Nov 26.
Artigo em Inglês | MEDLINE | ID: mdl-33242036


Mineral transformations of the gypsum-anhydrite system under microwave heating have been studied using in situ dielectric thermal analysis (MW-DETA) and Raman spectroscopy simultaneously. The dielectric properties of samples that were measured under microwave heating provided thorough information about the dynamics of the gypsum-anhydrite system transformations and its significance from the mineralogical point of view. In particular, the MW-DETA technique revealed a new intermediate phase with a γ-anhydrite structure. This phase corresponds to the soluble stage of γ-anhydrite, and it is characterized by a high ionic charge inside the crystal channels. The complete sequence is gypsum → 0.625-subhydrate → bassanite → hydro γ-anhydrite → anhydrous γ-anhydrite → ß-anhydrite. The transformations were also assessed using DSC, TG, DTA and dielectric measurements at room temperature, as well as other techniques including X-ray powder diffraction (XRPD) and high-temperature XRD (HT-XRD). Correlations between the dielectric properties with temperature and the rest of the techniques elucidated the heating mechanisms of this material under microwave energy during the different stages. The in situ combination of the MW-DETA and the Raman analysis appears to be a powerful technique, providing new insights about the mechanisms which govern the volumetric heating of this and other materials.

Eur J Intern Med ; 81: 78-82, 2020 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-32553586


INTRODUCTION: There is scarce information about the clinical profile and prognosis of acute heart failure (AHF) at the extreme ranges of age. We aimed to evaluate the 1-year death (all-cause mortality and HF-death) and HF-rehospitalizations of patients ≥85 years admitted for AHF. METHODS: We prospectively evaluated a cohort of 3054 patients admitted with AHF from 2007 to 2018 in a third-level center. Age was categorized per 10-year categories (<65 years; 65-74 years, 75-84 years, and ≥85 years). The risk of mortality and HF-rehospitalizations across age categories was evaluated with Cox regression analysis and Cox regression adapted for competing events as appropriate. RESULTS: The mean age was 73.6 ± 11.2 years, 48.9% were female, and 52.8% had preserved left ventricular ejection fraction (HFpEF). A total of 414 (13.6%) patients were ≥85 years. Among this group of age, female sex and HFpEF phenotype were more frequent. At 1-year follow-up 667 all-cause deaths (22,1%), 311 HF-deaths (10.1%) and 693 HF-hospitalizations (22,7%) were recorded. After multivariable adjustment, and compared to patients <65 years, a stepwise increased risk of all-cause mortality and HF-death was found for each decade increase in age, especially for patients ≥85 years (HR=3.47; 95% CI: 2.49 - 4.84, p<0.001, HR=3.31; 95% CI: 1.95 - 5.63; p<0.001, respectively). This subgroup of patients also showed an increased risk of HF-rehospitalization (HR=1.58; 95% CI: 1.16 - 2.16, p=0.004). CONCLUSIONS: Super elderly patients admitted with AHF showed a dramatically increased risk of 1-year death. This subset of patients also shown an increased risk of 1-year HF-readmission.

Materials (Basel) ; 9(5)2016 May 07.
Artigo em Inglês | MEDLINE | ID: mdl-28773471


Microwave-assisted processes have recognized advantages over more conventional heating techniques. However, the effects on the materials' microstructure are still a matter of study, due to the complexity of the interaction between microwaves and matter, especially at high temperatures. Recently developed advanced microwave instrumentation allows the study of high temperature microwave heating processes in a way that was not possible before. In this paper, different materials and thermal processes induced by microwaves have been studied through the in situ characterization of their dielectric properties with temperature. This knowledge is crucial in several aspects: to analyze the effects of the microwave field on the reaction pathways; to design and optimize microwave-assisted processes, and to predict the behavior of materials leading to repeatable and reliable heating processes, etc.

Phys Chem Chem Phys ; 17(9): 6212-6, 2015 Mar 07.
Artigo em Inglês | MEDLINE | ID: mdl-25650128


An open coaxial re-entrant microwave sensor has been used for the non-invasive and continuous monitoring of the sol-gel transition of physical gels characterized by different gelation mechanisms, solvents, compositions, and stabilities. Comparison of measurements by differential scanning calorimetry allowed the identification of the phase transition by a change in the dielectric properties of the material over time.

Géis , Micro-Ondas , Varredura Diferencial de Calorimetria
Artigo em Inglês | MEDLINE | ID: mdl-19227069


The palm oil mills extraction process requires the separation of oil-water-sludge emulsions. For this purpose, the use of sedimentation and/or centrifugation techniques have been required until now. However, significant losses persist in different process flows and new methods are needed to further decrease them, such as methods based on electromagnetic waves application. In the study, emulsions obtained from two flow processes, namely press liquor stream (PL) and recovered stream of the centrifugal step (RC), were exposed to microwave radiation with different exposure times. In the case of the press liquor stream, different oil/water dilution ratios were also studied. The sedimentation speed and efficiency were studied for the irradiated samples and compared to those obtained for the same fluids with no radiation. Also, chromatographic tests were performed on the recovered oil to determine the effect on the oil quality after microwave radiation. The obtained results allow us to conclude that microwave exposure during periods below 1 minute lead to better sedimentation speed and efficiency. It was observed that microwaves facilitate the break of the charges and polarities balances in the emulsions at considerably lower temperatures than the corresponding in the conventional process, without affecting the recovered oil quality.

Micro-Ondas , Óleos Vegetais/isolamento & purificação , Água/química , Emulsões , Resíduos Industriais , Óleo de Palmeira , Transição de Fase , Óleos Vegetais/química , Esgotos
Artigo em Inglês | MEDLINE | ID: mdl-18557397


Waveguide structures are very popular in the microwave power industry due to their power handling capabilities. Modal expansion of the waveguide fields and application of the circuit theory allow for the division of a complex device into several simpler sections which can be analyzed separately with the best suited method. The modal techniques can be divided into two groups--those which analyze junctions or discontinuities and those which examine propagation characteristics. In this paper, a review of modal techniques for high power applications is given. Modal expansion of the fields in the waveguides is then performed and applied to modeling of k-furcated waveguides. The modal analysis based on the Coupled Mode Method is described for the waveguides partially filled with isotropic materials. A hybrid modal analysis coupled with Finite Element Method suitable for more complex waveguide structures is also described. Computational results obtained for some real-life microwave devices are presented. Excellent agreement was found when comparing the results with those generated with a commercial FDTD simulator demonstrates the validity and reliability of the proposed method.

Desenho Assistido por Computador , Eletrônica/instrumentação , Desenho de Equipamento/métodos , Micro-Ondas , Modelos Teóricos , Simulação por Computador , Análise de Falha de Equipamento/métodos , Teste de Materiais