Synthesis by a solid state reaction of the Sr4Al6O12SO4 compound

J.A. Rodríguez-García,E. Rocha-Rangel,J. Torres-Torres,J. M. Almanza-Robles 한양대학교 세라믹연구소 2011 Journal of Ceramic Processing Research Vol.12 No.3

The synthesis and formation of Sr4Al6O12SO4 in the system SrCO3-Al2O3-SrSO4 has been studied in the range of temperatures from 800 oC to 1400 oC using X-ray diffraction, thermo gravimetric, differential thermal and scanning electron microscopy analysis. Pellets of a mixture of 3 : 3 : 1 molar ratio of reactive grade Al2O3, SrCO3 and SrSO4 respectively were prepared, by solid state sintering, the reactive powders were thoroughly mixed under high energy ball-milling, uniaxially pressed into cylindrical samples and pressureless-sintered. Additionally the densities of some samples that were heat treated for 10 h at 1200, 1300 and 1400 oC were determined by the Archimedes method. The powder mixture was analyzed by TGA and DTA from room temperature to 1200 oC. XRD patterns indicated the formation of Sr3Al2O6 and SrAl2O4 as intermediate phases that nearly at the end of the process reacted with SrSO4 to form Sr4Al6O12SO4. The formation of Sr4Al6O12SO4 was complete at 1150 oC as XRD and DTA analysis indicated. An increase in the heat treatment time promotes the formation of Sr4Al6O12SO4at lower temperatures. The Sr4Al6O12SO4 powders were composed of spherical particles of small agglomerates. Results of density measurement indicated that only 80% of the theoretical density was reached for a treatment at 1400 oC of 10 h, which indicated the difficulty to obtain a dense material.

<i>δ</i> Sct-type pulsations in eclipsing binary systems: Y Cam

Rodrí,guez, E.,Garcí,a, J. M.,Costa, V.,Lampens, P.,van Cauteren, P.,Mkrtichian, D. E.,Olson, E. C.,Amado, P. J.,Daszyń,ska-Daszkiewicz, J.,Turcu, V.,Kim, S.-L.,Zhou, A. Y.,Ló,p Blackwell Publishing Ltd 2010 MONTHLY NOTICES- ROYAL ASTRONOMICAL SOCIETY Vol.408 No.4

<P>ABSTRACT</P><P>We present the results of a three-continent multisite photometric campaign carried out on the Algol-type eclipsing binary system Y Cam, in which the primary component is a multiperiodic δ Sct-type pulsator. The observations consist of 86 nights and more than 450 h of useful data collected mainly during the Northern winter 2002–2003. This means that this is the most extensive time series for such kind of systems obtained so far. These observations were collected mostly in the Johnson V filter, but they also include, for the first time, nearly complete binary light curves in simultaneous Strömgren <I>uvby</I> filters together with a few Crawford Hβ data obtained around the orbital phase of the first quadrature. A detailed photometric analysis is presented for both binarity and pulsation. The results indicate a semidetached system with the secondary filling its Roche lobe. No significant contribution from a third body is found. The residuals from the computed binary solution were then used to investigate the pulsational content of the primary component. The frequency analysis of the out-of-primary-eclipse data leads to a set of eight significant and independent pulsational peaks in a well-defined region of the frequency domain. This means that this is the largest set of excited modes discovered so far in the pulsating component of such kind of systems. The possibility of aliasing problems during the present run or short-term time-scale amplitude variations in some of them was investigated with null results. Indeed the results indicate that <I>f</I><SUB>1</SUB> and <I>f</I><SUB>3</SUB> form a frequency doublet with a beat period of <I>P</I><SUB>beat</SUB>= 17.065 d. Our results confirm the frequencies already detected by earlier authors and show the presence of some additional significant peaks. The observed amplitudes during the present run are also consistent with those derived from older data sets. We perform a preliminary mode identification for most of the frequencies on the basis of the collected multicolour photometry, the observed frequency spacings and the mode visibility in eclipsing binaries.</P>

Physical Properties of the Sr4Al6O12SO4 Ceramic Compound

J.A. Rodríguez-García,E. Rocha-Rangel,J. López Hernández,C.A. Hernández Bocanegra,A.L. Leal Cruz,J.M. Almanza Robles,J. Torres Torres 한양대학교 세라믹연구소 2017 Journal of Ceramic Processing Research Vol.18 No.11

The Sr4Al6O12SO4 ceramic compound was synthesized by a solid state reaction starting from stoichiometric mixtures of 3 : 3 : 1 molar ratio of reactive grade of SrCO3, Al2O3 and SrSO4, respectively. Cylindrical samples were confirmed by uniaxial pressing at 100 MPa and were heat treated at 1400 oC during 4 hrs. Subsequently, the samples were ground and re-conformed in cylindrical shape samples by uniaxial pressing at 300 MPa. The new samples were heat treated at 1400 oC during 24 hrs. This process was done in order to increase density of the samples. The Sr4Al6O12SO4 ceramic compound was characterized by the study of its physical properties such as: density, micro-hardness, thermal expansion and stability, enthalpy of formation, magnetic properties and electrical conductivity. Experimental results show that the maximum density obtained for the Sr4Al6O12SO4 ceramic compound was 2.913 grcm−3, with thermal expansion coefficient of 10.12E−06(oC−1); it also presents an enthalpy of 2.3 KJmol-1 and an excellent thermal stability at elevated temperatures in different atmospheres. In addition, the Sr4Al6O12SO4 ceramic compound is neither electrically conductive nor magnetic.

A pH/Temperature-Sensitive s-IPN Based on Poly(vinyl alcohol), Poly(vinyl methyl ether-alt-maleic acid) and Poly(vinyl methyl ether) Prepared by Autoclaving

Karla F. García-Verdugo,Andya J. Ramírez-Irigoyen,Mónica Castillo-Ortega,Dora E. Rodríguez-Félix,Jesús M. Quiroz-Castillo,Judith Tánori-Córdova,Francisco Rodríguez-Félix,Antonio Ledezma-Pérez,Teresa d 한국고분자학회 2022 Macromolecular Research Vol.30 No.6

A novel semi-interpenetrating polymer network (s-IPN) based on the entrapment of a thermosensitive polymer, the poly(vinyl methyl ether) (PVME), within a crosslinked 3D structure of poly(vinyl alcohol) (PVA) and poly(vinyl methyl etheralt- maleic acid) (COP) was synthesized by an autoclaving process. The preparation method avoids the use of toxic crosslinkers and allows the simultaneous sterilization of material. The PVA/COP/PVME hydrogel were characterized by Fourier transform infrared spectroscopy, thermal techniques, swelling kinetic measurements, scanning electron microscopy, and rheological analysis. The entrapment of PVME within the hydrated polymer framework significantly modified its transition temperature at pH 7.4 and pH 3 conditions. The swelling kinetics of the s-IPN were dependent on pH (7.4, 3 and 1), and temperature (25 and 37℃). The interpenetrated polymer chains reduced the internal pore sizes of crosslinked network without altering its elastic, solid-like behavior. The loading and in vitro release of 5-fluorouracil, a chemotherapeutic agent, from hydrogel systems were studied at different temperature and pH values. The hydrogels showed a sustained drug release up to 5 h at 37℃, in different pH media. The s-IPN exhibited a promising performance for a range of biomedical applications, in particular, for the controlled drug delivery in response to the pH and temperature conditions.

The medium-term consequences of COVID-19 lockdown on lifestyle among Spanish older people with hypertension, pulmonary, cardiovascular, and musculoskeletal-diseases, depression, and cancer

Rodríguez-Gómez Irene,Sánchez-Martín Coral,García-García Francisco J.,García-Esquinas Esther,Miret Marta,Vicente-Rodriguez Germán,Gusi Narcís,Mañas Asier,Carnicero José A.,Gonzalez-Gross Marcela,Ayuso 한국역학회 2022 Epidemiology and Health Vol.44 No.-

OBJECTIVES: This study investigated the associations of chronic diseases with changes in lifestyle and health behaviours in older people following the coronavirus disease 2019 (COVID-19) lockdown in Spain and compared the differences in changes over time. METHODS: 1,092 participants (80.3± 5.6 years; 66.5% female) from 2 Spanish cohorts were included. Telephone-based questionnaires were conducted to evaluate lifestyle and health risk behaviours at the end of lockdown and 7 months post-lockdown. Participants were classified as having physician-diagnosed chronic diseases based on self-reported data. Cox proportional models adjusted for major confounders were used. RESULTS: Compared to those without the corresponding chronic diseases, older people with hypertension were less likely to report increased alcohol consumption (hazard ratio [HR], 0.73; 95% confidence interval [CI], 0.55 to 0.99). Pulmonary diseases were associated with lower risks of increased sedentary time (HR, 0.58; 95% CI, 0.39 to 0.86) and worsened sleep quality (HR, 0.56; 95% CI, 0.36 to 0.87), while cardiovascular diseases were associated with a lower risk of decreased sedentary time (HR, 0.58; 95% CI, 0.38 to 0.88). Depression was linked to a higher likelihood of improved diet quality (HR, 1.53; 95% CI, 1.00 to 2.36). Cancer pacients were less likely to have worsened sleep quality (HR, 0.44; 95% CI, 0.22 to 0.89) but more likely to have reduced their frequency of social contact (HR, 2.05; 95% CI, 1.05 to 3.99). CONCLUSIONS: Older people with chronic diseases showed beneficial changes in lifestyle and health risk behaviours after the COVID-19 lockdown. In particular, older people with hypertension, pulmonary disease, and cancer tended to make beneficial lifestyle and health behaviour changes. However, older people with cardiovascular disease and depression engaged in more health risk behaviours.

Dielectric properties of strontium titanate synthesized by means of solid state reactions activated mechanically

Enrique Rocha-Rangel,Juan López-Hernández,José A. Rodríguez-García,Eddie N. Armendáriz-Mireles,Carlos A. Calles-Arriaga,W. J. Pech-Rodríguez,José A. Castillo-Robles 한양대학교 세라믹연구소 2017 Journal of Ceramic Processing Research Vol.18 No.8

In this work, strontium titanate samples were prepared starting from SrCO3 and TiO2 powders mixture. Raw materials wereactivated mechanically in a planetary mill and then calcined at different temperatures (900 to 1300 oC). Powders after grindingwere analyzed by differential thermal analysis in order to follow the carbonate decomposition. On the other hand, samplesresulting from heat treatment were characterized by XRD, SEM and electrical measurements. XRD analysis determines thatSrTiO3 synthetized presents the cubic structure of perovskite. Complete reaction for SrTiO3 compound formation occurs at1200 oC. SEM observations indicate the presence of a microstructure with very small gran size and consequently a largenumber of grain boundaries. Electrical measurements suggest the formation of a material with high insulating capacity. Withthis evidence, it can be concluded that solid state reactions activated mechanically, proved to be an effective way to fabricatestrontium titanate compound with very fine microstructure and high insulating behavior.

Eco-friendly Production of Metallic Nanoparticles in Polymeric Solutions and Their Processing into Biocompatible Composites

Alejandra Pérez-Nava,Josué D. Mota-Morales,Zaira Y. García-Carvajal,Sara E. Herrera-Rodríguez,Gerardo Arrevillaga-Boni,Cristy L. Azanza-Ricardo,Milton O. Vazquez-Lepe,J. Betzabe Gonzalez-Campos 한국섬유공학회 2018 Fibers and polymers Vol.19 No.1

Silver and gold nanoparticles were produced and embedded in poly(vinyl alcohol) (PVA) and chitosan (CTS) solutions by the photoreduction of metallic salt precursors triggered by direct sunlight irradiation, in which the polymers acted as reducing, dispersing and stabilizing agents. Sunlight photoreduction can be standardized using a constant UV index regardless of the season. This strategy was found to be an improvement over other common energy sources used to trigger the reduction of metal ions, including UV light irradiation and high-temperature reduction with mechanical stirring. The resulting PVA/metal nanoparticle and CTS/metal nanoparticle composite solutions were processed into thin films and nanofiber composites. In vitro testing of the cytotoxicity and biocompatibility demonstrates that the film composites are non-toxic andbiocompatible with the HT-29 human colon cancer cell line. Promotion of HT-29 cell growth using our hybrid composites was observed, in contrast to other studies in which colloidal NPs were tested. Therefore, a sustainable approach for the onestep preparation of biocompatible polymer/metallic nanoparticle composites is reported.