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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.
Welchen, Elina,Viola, Ivana L.,Kim, Hye Jin,Prendes, Luciana P.,Comelli, Raú,l N.,Hong, Jong Chan,Gonzalez, Daniel H. Oxford University Press 2009 Journal of experimental botany Vol.60 No.3
<P>Sequences required for the expression of Cytc-2 (At4g10040), one of two cytochrome c genes from Arabidopsis thaliana, were characterized using plants transformed with deleted and mutagenized promoter fragments fused to gus. These studies indicated that a region containing a G-box and an ACGT motif is essential for expression. Mutation of the ACGT motif causes a complete loss of expression, while mutation of the G-box causes decreased expression in aerial parts and abolishes expression in roots and induction by environmental factors. Upstream located site II elements are required for maximal expression, mainly in reproductive tissues, and maximal induction by different factors. One-hybrid screenings allowed the identification of transcription factors from the bZIP and bHLH families that interact mainly with the G-box. Four of these factors were able to bind to the Cytc-2 promoter in vitro and in transactivation assays in Arabidopsis. Analysis of available microarray data indicated that the bZIP transcription factors share expression characteristics with the Cytc-2 gene, suggesting that they act as mediators of its response to tissue-specific, environmental, and metabolic conditions. Site II elements interact with a TCP family protein and may co-ordinate the expression of the Cytc-2 gene with that of other respiratory chain components. A model is proposed for the evolution of the Cytc-2 gene through the incorporation of a segment containing a G-box and an ACGT motif into an ancestral gene that contained site II elements. This may have reduced the importance of site II elements for basal expression and conferred new responses to environmental factors.</P>
Gonzalez-Herrera, A.L.,Salgado-Bernabe, M.,Velazquez-Velazquez, C.K.,Salcedo-Vargas, M.,Andrade-Manzano, A.,Avila-Moreno, F.,Pina-Sanchez, P. Asian Pacific Journal of Cancer Prevention 2015 Asian Pacific journal of cancer prevention Vol.16 No.4
Background: Cervical cancer (CeCa) is the second most common cancer in women in developing countries, and human papilloma virus (HPV) is the primary etiological factor. Aberrant expression of HOX transcription factors has been observed in several types of cancer. To date, however, no reports exist on the expression of HOXB2 and HOXB13 proteins during neoplastic progression in CeCa and its correlation with HPV infection. Materials and Methods: Expression of HOXB2 and HOXB13 proteins was assessed in tissue microarrays from normal cervical epithelium, cervical intraepithelial neoplasias grade 1-3, and CeCa. HPV was detected by PCR and sequencing. Expression of HOX-positive cells was determined in each diagnostic group. Results: Percentage of HOXB2- and HOXB13-positive cells gradually increased from means of 10.9% and 16.7%, respectively, in samples from healthy women, to 75.2% and 88.6% in those from CeCa patients. Frequency of HPV infection also increased from 13% in healthy tissue samples to 92.3% in CeCa. Both HOXB2 and HOXB13 proteins were preferentially expressed in HPV+ samples. Conclusions: The present study represents the first report on the expression of both HOXB2 and HOXB13 proteins through cervix tumorigenesis, providing evidence that increased expression of such proteins is a common event during progression to CeCa.
Analysis of Power Device Failure Under Avalanche Mode Conduction
P. Alexakis,O. Alatise,J. Hu,S. Jahdi,J. Ortiz Gonzalez,L. Ran,P. A. Mawby 전력전자학회 2015 ICPE(ISPE)논문집 Vol.2015 No.6
This paper investigates the physics of device failure during avalanche for 1.2 kV SiC MOSFETs, silicon MOSFETs and silicon IGBTs. The impact of ambient temperature, initial conditions of the device prior to avalanche breakdown and the avalanche duration is explored for the different technologies. Two types of tests were conducted namely (i) constant avalanche duration with different peak avalanche currents and (ii) constant peak avalanche current with different avalanche durations. SiC MOSFETs are shown to be the most rugged technology followed by the silicon IGBT and the silicon MOSFET. The material properties of SiC suppress the triggering of the parasitic BJT that causes thermal runaway during avalanche.
Tunable room-temperature magnetic skyrmions in Ir/Fe/Co/Pt multilayers
Soumyanarayanan, Anjan,Raju, M.,Gonzalez Oyarce, A. L.,Tan, Anthony K. C.,Im, Mi-Young,Petrović,, A. ,P.,Ho, Pin,Khoo, K. H.,Tran, M.,Gan, C. K.,Ernult, F.,Panagopoulos, C. Nature Publishing Group 2017 Nature Materials Vol.16 No.9
Magnetic skyrmions are nanoscale topological spin structures offering great promise for next-generation information storage technologies. The recent discovery of sub-100-nm room-temperature (RT) skyrmions in several multilayer films has triggered vigorous efforts to modulate their physical properties for their use in devices. Here we present a tunable RT skyrmion platform based on multilayer stacks of Ir/Fe/Co/Pt, which we study using X-ray microscopy, magnetic force microscopy and Hall transport techniques. By varying the ferromagnetic layer composition, we can tailor the magnetic interactions governing skyrmion properties, thereby tuning their thermodynamic stability parameter by an order of magnitude. The skyrmions exhibit a smooth crossover between isolated (metastable) and disordered lattice configurations across samples, while their size and density can be tuned by factors of two and ten, respectively. We thus establish a platform for investigating functional sub-50-nm RT skyrmions, pointing towards the development of skyrmion-based memory devices.
Reactivity of hydroxyl radicals with neonicotinoid insecticides: mechanism and changes in toxicity
Dell'Arciprete, Maria L.,Santos-Juanes, Lucas,Sanz, Antonio Arques,Vicente, Rafael,Amat, Ana M.,Furlong, Jorge P.,Martirea, Daniel O.,Gonzalez, Monica C. Korean Society of Photoscience 2009 Photochemical & photobiological sciences Vol.8 No.7
The reactivity of hydroxyl radicals ($HO^{\cdot}$) towards three neonicotonoid insecticides, namely imidacloprid, thiacloprid and acetamiprid was investigated. These radicals were generated by photolysis of $H_2O_2$ solutions. Flash photolysis experiments were used to determine the rate constants of $5.5{\times}10^{10}M^{-1}s{-1}$, $6{\times}10^{10}M^{-1}s^{-1}$, and $7.5{\times}10^{10}M^{-1}s^{-1}$, for the reactions of $HO^{\cdot}$ with acetamiprid, imidacloprid, and thiacloprid, respectively. Continuous irradiation experiments in the absence and presence of $H_2O_2$ allowed the identification and toxicity evaluation of the primary photo- and oxidation products of the insecticides. In all cases, the less toxic 6-chloronicotinic acid was found to be the major product at higher degrees of oxidation. The results reported here indicate that the half life of the insecticides due to their reaction with $HO^{\cdot}$ radicals in natural aquatic reservoirs may vary between 5 h and 19 days, and therefore the hydroxyl radical-mediated oxidation may be a significant abiotic elimination route. However, elimination of the insecticide under such conditions might not improve the quality of the contaminated water, as the primary products of degradation still show considerable toxicity to Vibrio fischeri assays.
Negative magnetoresistance in sputtered niobium thin films grown on silicon substrates
T.C. Freitas,J.L. Gonzalez,V.P. Nascimento,A.Y. Takeuchi,E.C. Passamani 한국물리학회 2017 Current Applied Physics Vol.17 No.11
Nb-films (thicknesses of 20 nm, 50 nm and 100 nm), directly grown on orientated Si substrates by DC sputtering, have shown reduced superconducting critical temperatures TC as compared to the bulk value; an effect associated with their disordered granular character (the disorder phenomenon of the Nb-films depresses the density of states at the Fermi level, consequently shifts the TC value towards low temperatures). The disorder effect was also correlated to the semiconducting-like behavior observed in the RðTÞ measurements. At the normal state, while the 100 nm Nb-film is dominated by a metallic-like behavior, the thinner Nb-films (20 nm and 50 nm thick) show significant negative magnetoresistances in a small temperature range about TC. This behavior was also explained assuming their granular characters, where the applied magnetic field first destroys the global superconducting character of the Nb-films, leaving Cooper pairs localized inside Nb-grains. A further increase of the applied field strength affects the superconductivity inside Nb-grains, enhancing the normal intergranular electric transport channel, which decreases the whole resistance of the Nb-films. The present study suggests that the microscopic disorder, at the grain surfaces/interfaces, seems to be an essential point to comprehend the negative magnetoresistance effect observed in some superconducting granular systems.
Optical and Electrical Properties of Bulk-grown Ternary In_xGa_(1−x)As
Y. K. Yeo,A. C. Bergstrom,R. L. Hengehold,J. W. Wei,S. Guha,L. P. Gonzalez,G. Rajagopalan,류미이 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.58 No.51
Bulk ternary In_xGa_(1−x)As polycrystals were grown using the vertical Bridgman technique. The optical and electrical properties of these bulk In_xGa_(1−x)As were investigated as a function of indium mole fraction from 0.75 to 0.99 by using photoluminescence (PL) and Hall-effect measurements. All samples showed good infrared transmission. A free exciton (FX) transition peak was observed from all bulk In_xGa_(1−x)As samples, and it redshifted from 0.568 to 0.412 eV as the indium mole fraction increased from 0.75 to 0.99. Bandgaps estimated from the indium compositionand temperature-dependent FX peaks generally followed the theoretically calculated bandgaps. All as-grown In_xGa_(1−x)As samples showed n-type conductivity. Although all bulk In_xGa_(1−x)As samples showed good optical transmissions and PL transitions, as well as high carrier mobilitites, they exhibited some random compositional fluctuations across the sample area.
Modeling of Temperature Dependent Parasitic Gate Turn-On in Silicon IGBTs
R. Bonyadi,O. Alatise,S. Jahdi,J. Ortiz Gonzalez,L. Ran,P. A. Mawby 전력전자학회 2015 ICPE(ISPE)논문집 Vol.2015 No.6
Parasitic turn-on can cause unintentional triggering of the IGBTs since the discharge current of the Miller capacitance coupled with high dV/dt can activate a device that should be off. The short circuit current resulting from parasitic turn-on coupled with the high voltage causes significant power dissipation which can be a reliability issue. This issue is exacerbated by higher ambient temperatures since the negative temperature coefficient of the IGBT’s threshold voltage as well as the positive temperature coefficient of the minority carrier lifetime will increase the peak and duration of the short circuit current. Accurate modeling of the shoot-through power and its temperature dependency is important for circuit designers when designing mitigation techniques like multiple resistive paths and bipolar gate drivers. The physics-based model proposed in this paper can produce accurate results with good matching over temperature. The model improves on compact circuit models based on lumped parameters.