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M. I. Pech-Canul,M. Rodríguez-Reyes3,M. A. Pech-Canul,J. C. Rendón-Angeles 대한금속·재료학회 2011 METALS AND MATERIALS International Vol.17 No.6
In this work, SiC_P and SiC_P/SiO_2 porous preforms were infiltrated without assistance in Ar→N_2 atmosphere with the alloy Al-10.3 Mg-12.04 Si (wt.%) at 1050 and 1100 °C, for 20, 40 and 60 min. It was found that a decrease in residual porosity and an increase in elastic modulus by about 22 % with respect to composites produced without SiO_2 additions to the preforms are associated with the formation of magnesium aluminate spinel (MgAl_2O_4). A concurrent increase of the matrix hardness is ascribed to a strengthening mechanism by MgAl_2O_4 formation, similar to the strengthening observed with Mg_2Si in aluminum alloys. Therefore, the spinel can be considered as a co-reinforcement of SiC_p in the aluminum matrix composites. Reactions for spinel formation and possible mechanisms for hardness enhancement are outlined.
Reyes-Salazar, Alfredo,Soto-Lopez, Manuel Ernesto,Bojorquez-Mora, Eden,Lopez-Barraza, Arturo Techno-Press 2012 Structural Engineering and Mechanics, An Int'l Jou Vol.41 No.2
Several issues regarding the structural idealization of steel buildings with perimeter moment resisting steel frames (MRSFs) and interior gravity frames (GFs) are studied. Results indicate that the contribution of GFs to the lateral structural resistance may be significant. The contribution increases when the stiffness of the connection of the GFs is considered and is larger for inelastic than for elastic behavior. The interstory shears generally increase when the connections stiffness is taken into account. Resultant stresses at some base columns of MRSFs also increase in some cases but to a lesser degree. For columns of the GFs, however, the increment is significant. Results also indicate that modeling the building as planes frames may result in larger interstory shears and displacements and resultant stresses than those obtained from the more realistic 3-D formulation. These differences may be much larger when semi-rigid (SR) connections are considered. The conservativism is more for resultant stresses. The differences observed in the behaviour of each structural representation are mainly due to a) the elements that contribute to strength and stiffness and b) the dynamics characteristics of each structural representation. It is concluded that, if the structural system under consideration is used, the three-dimensional model should be used in seismic analysis, the GFs should be considered as part of the lateral resistance system, and the stiffness of the connections should be included in the design of the GFs. Otherwise, the capacity of gravity frames may be overestimated while that of MRSFs may be underestimated.
Ductility and ductility reduction factor for MDOF systems
Reyes-Salazar, Alfredo Techno-Press 2002 Structural Engineering and Mechanics, An Int'l Jou Vol.13 No.4
Ductility capacity is comprehensively studied for steel moment-resisting frames. Local, story and global ductility are being considered. An appropriate measure of global ductility is suggested. A time domain nonlinear seismic response algorithm is used to evaluate several definitions of ductility. It is observed that for one-story structures, resembling a single degree of freedom (SDOF) system, all definitions of global ductility seem to give reasonable values. However, for complex structures it may give unreasonable values. It indicates that using SDOF systems to estimate the ductility capacity may be a very crude approximation. For multi degree of freedom (MDOF) systems some definitions may not be appropriate, even though they are used in the profession. Results also indicate that the structural global ductility of 4, commonly used for moment-resisting steel frames, cannot be justified based on this study. The ductility of MDOF structural systems and the corresponding equivalent SDOF systems is studied. The global ductility values are very different for the two representations. The ductility reduction factor $F_{\mu}$ is also estimated. For a given frame, the values of the $F_{\mu}$ parameter significantly vary from one earthquake to another, even though the maximum deformation in terms of the interstory displacement is roughly the same for all earthquakes. This is because the $F_{\mu}$ values depend on the amount of dissipated energy, which in turn depends on the plastic mechanism, formed in the frames as well as on the loading, unloading and reloading process at plastic hinges. Based on the results of this study, the Newmark and Hall procedure to relate the ductility reduction factor and the ductility parameter cannot be justified. The reason for this is that SDOF systems were used to model real frames in these studies. Higher mode effects were neglected and energy dissipation was not explicitly considered. In addition, it is not possible to observe the formation of a collapse mechanism in the equivalent SDOF systems. Therefore, the ductility parameter and the force reduction factor should be estimated by using the MDOF representation.
Evolution pathway of CZTSe nanoparticles synthesized by microwave-assisted chemical synthesis
Reyes, Odin,Sanchez, Monica F.,Pal, Mou,Llorca, Jordi,Sebastian, P.J. Techno-Press 2017 Advances in nano research Vol.5 No.3
In this study we present the reaction mechanism of $Cu_2ZnSnSe_4$ (CZTSe) nanoparticles synthesized by microwave-assisted chemical synthesis. We performed reactions every 10 minutes in order to identify different phases during quaternary CZTSe formation. The powder samples were analyzed by x-ray diffraction (XRD), Raman spectroscopy, energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The results showed that in the first minutes copper phases are predominant, then copper and tin secondary phases react to form ternary phase. The quaternary phase is formed at 50 minutes while ternary and secondary phases are consumed. At 60 minutes pure quaternary CZTSe phase is present. After 60 minutes the quaternary phase decomposes in the previous ternary and secondary phases, which indicates that 60 minutes is ideal reaction time. The EDS analysis of pure quaternary nanocrystals (CZTSe) showed stoichiometric relations similar to the reported research in the literature, which falls in the range of Cu/(Zn+Sn): 0.8-1.0, Zn/Sn: 1.0-1.20. In conclusion, the evolution pathway of CZTSe synthesized by this novel method is similar to other synthesis methods reported before. Nanoparticles synthesized in this study present desirable properties in order to use them in solar cell and photoelectrochemical cell applications.
Reyes, Alisha Wehdnesday Bernardo,Arayan, Lauren Togonon,Hop, Huynh Tan,Ngoc Huy, Tran Xuan,Vu, Son Hai,Min, WonGi,Lee, Hu Jang,Kim, Suk Elsevier 2018 Microbial pathogenesis Vol.119 No.-
<P><B>Abstract</B></P> <P>In this study, we investigated the effects of gallic acid (GA) in intracellular signaling within murine macrophages and its contribution to host immunity during <I>Brucella</I> infection<I>. In vitro</I> analysis revealed that GA treatment decreased F-actin content and suppressed p38α phosphorylation level. <I>In vivo</I> analysis showed that GA treatment reduced inflammation and proliferation of <I>Brucella</I> in spleens of mice in comparison to PBS treatment yielding a significant protection unit. For the analysis of immune response, the uninfected GA-treated mice showed increased production of IFN-γ and MCP-1, and the <I>Brucella-</I>infected GA-treated mice showed elevated levels of IL-12p70, TNF, IFN-γ, MCP-1, IL-10 and IL-6 in comparison to negative and positive control groups, respectively. These findings demonstrate the therapeutic effects of GA against <I>Brucella</I> infection through interference on intracellular signaling pathway, induction of cytokine production and protection from bacterial proliferation in spleens of mice.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Gallic acid (GA) decreased F-actin content and p38α phosphorylation level in RAW 264.7 cells. </LI> <LI> GA reduced inflammation and proliferation of <I>Brucella</I> in the spleens of mice. </LI> <LI> GA-treated mice showed increased production of IFN-γ and MCP-1. </LI> <LI> <I>Brucella</I>-infected GA-treated mice showed elevated levels of IL-12p70, TNF, IFN-γ, MCP-1, IL-10 and IL-6. </LI> <LI> GA treatment revealed potential therapeutic effects against <I>Brucella</I> infection in animals. </LI> </UL> </P>