Mechanics of the slaking of shales

Vallejo, Luis E. Techno-Press 2011 Geomechanics & engineering Vol.3 No.3

Waste fills resulting from coal mining should consist of large, free-draining sedimentary rocks fragments. The successful performance of these fills is related to the strength and durability of the individual rock fragments. When fills are made of shale fragments, some fragments will be durable and some will degrade into soil particles resulting from slaking and inter-particle point loads. The degraded material fills the voids between the intact fragments, and results in settlement. A laboratory program with point load and slake durability tests as well as thin section examination of sixty-eight shale samples from the Appalachian region of the United States revealed that pore micro-geometry has a major influence on degradation. Under saturated and unsaturated conditions, the shales absorb water, and the air in their pores is compressed, breaking the shales. This breakage was more pronounced in shales with smooth pore boundaries and having a diameter equal to or smaller than 0.060 mm. If the pore walls were rough, the air-pressure breaking mechanism was not effective. However, pore roughness (measured by the fractal dimension) had a detrimental effect on point load resistance. This study indicated that the optimum shales to resist both slaking as well as point loads are those that have pores with a fractal dimension equal to 1.425 and a diameter equal to or smaller than 0.06 mm.

Fractal and laboratory analyses of the crushing and abrasion of granular materials

Vallejo, Luis E.,Chik, Zamri Techno-Press 2009 Geomechanics & engineering Vol.1 No.4

Gravels forming part of the base of flexible pavements experience abrasion and crushing as a result of static and dynamic loads. Abrasion takes place when the sharp corners of the particles of gravel are removed as a result of compressive and shear loads. As a result of abrasion, the particles change in shape. Crushing is caused by the fragmentation of the particles into a mixture of many small particles of varying sizes. In this study, the abrasion and crushing of gravels are evaluated experimentally and analytically. The laboratory component of this study involves gravels that were subjected to abrasion and dynamic compression tests. The evaluation of the abrasion and crushing experienced by the gravel was carried out using fractals. In this study, the fractal dimension concept from fractal theory is used to evaluate: (a) the changes in shape, and (b) the crushing (fragmentation) of the original particles of gravel. It was determined that the fractal dimension of the profile of the particles decreased as a result of abrasion. With respect to crushing, the fragmentation fractal dimension was found to increase with the degree of breakage of the gravel. To understand the influence of crushing on the permeability of the gravels, the hydraulic conductivity of the gravels was measured before and after crushing. The hydraulic conductivity of the gravels was found to decrease with an increase in their level of crushing. Also, changes in the angle of friction of the granular materials as a result of abrasion was calculated using the Krumbein's roundness chart. The angle of friction of the granular materials was found to decrease as a result of abrasion.

An hydrogen adsorption study on graphene-based surfaces with core–shell type catalysts

Vallejo Emmanuel 한국탄소학회 2023 Carbon Letters Vol.33 No.3

An hydrogen adsorption study on graphene-based surfaces consisting of nitrogen-doped graphene and core–shell type catalysts of initially Pd13 , Pt13 , PdPt12 and PtPd12 core–shells, is presented in this work. Density functional theory results indicate correlation between charge transfer and structural properties, hydrogen adsorption energies, magnetic behavior and electronic properties. Reduction of hydrogen, together with higher values of charge transfer was observed for high hydrogen dissociation, compared to the case of non-hydrogen dissociation. In some cases, these values may be almost an order of magnitude larger than that of non-hydrogen dissociation. Hydrogen dissociation is also related to oxidation of the surface and correlates with a non-core shell-type structure, high adsorption energies and low magnetic moments, in general. Besides, core shell-type structure dramatically changes the magnetic and electronic properties of charge transfer. The results obtained in this work may provide important information for storing hydrogen.

Fractal evaluation of the level of alligator cracking in pavements

Vallejo, Luis E. Techno-Press 2012 Geomechanics & engineering Vol.4 No.3

Pavement management systems require systematic monitoring of pavement surfaces to determine preventive and corrective maintenance. The process involves the accumulation of large amounts of visual data, typically obtained from site visitation. The pavement surface condition is then correlated to a pavement distress index that is based on a scoring system previously established by state or federal agencies. The scoring system determines if the pavement section requires maintenance, overlay or reconstruction. One of the surface distresses forming part of the overall pavement distress index is the Alligator Crack Index (AC Index). The AC Index involves the visual evaluation of the crack severity of a section of a pavement as being low, medium, or high. This evaluation is then integrated into a formula in order to obtain the AC Index. In this study a quantification of the visual evaluation of the severity of alligator cracking is carried out using photographs and the fractal dimension concept from fractal theory. Pavements with low levels of cracking were found to have a fractal dimension equal to 1.051. Pavements with moderate levels of cracking had a fractal dimension equal to 1.1754. Pavements with high degrees of cracking had a fractal dimension that varied between 1.5037 (high) and 1.7111 (very high). Pavements with a level of cracking equal to 1.8976 represented pavements that disintegrated and developed potholes. Thus, the visual evaluation of the state of cracking of a pavement (the AC Index) could be enhanced with the use of the fractal dimension concept from fractal theory.

Production of elastin-like recombinamer-based nanoparticles for docetaxel encapsulation and use as smart drug-delivery systems using a supercritical anti-solvent process

R. Vallejo,J. Gonzalez-Valdivieso,M. Santos,S. Rodriguez-Rojoa,F.J. Ariasb 한국공업화학회 2021 Journal of Industrial and Engineering Chemistry Vol.93 No.-

This study presents a new groundbreaking methodology for integrating innovative concepts todevelop novel drug-delivery strategies. This methodology combines genetically engineered elastin-likerecombinamers (ELRs) with supercriticalfluid (SCF) techniques to encapsulate a poorly water-solubledrug in a one-step process. The chemotherapeutic agent docetaxel (DTX) is encapsulated with a blockcopolymer ELR containing the RGD peptide, a specific target sequence for cancer cells, using thesupercritical anti-solvent (SAS) technique in a high process yield of up to 70%. SEM studies showspherical microparticles of 10 mm after encapsulation. After dispersion under physiological conditions,microparticles disaggregate into stable monodisperse nanoparticles of 40 nm size and30 mVz-potential. This protects the drug, as confirmed by NMR analysis, thereby increasing the watersolubility of DTX up tofifty orders of magnitude. The delivery process is governed by the Fick diffusionmechanism and indicates that the presence of DTX on the particles surface is practically negligible. Cellular assays showed that, due to the presence of the cancer target sequence RGD, breast cancer cellswere more affected than human endothelial cells, thus meaning that the strategy developed in thiswork opens the way to new controlled release systems more precise than non-selectivechemotherapeutic drugs.

Role of the transforming growth factor (TGF)-β1 and TGF-β1 signaling pathway on the pathophysiology of respiratory pneumococcal infections

ANDRADE VALLEJO MAR IA JOSE,임재향 영남대학교 의과대학 2017 Yeungnam University Journal of Medicine Vol.34 No.2

Streptococcus pneumoniae, pneumococcus, is the most common cause of community-acquired pneumonia (CAP). CAP is an important infectious disease with high morbidity and mortality, and it is still one of the leading causes of death worldwide. Many genetic factors of the host and various environmental factors surrounding it have been studied as important determinants of the pathophysiology and outcomes of pneumococcal infections. Various cytokines, including transforming growth factor (TGF)-β1, are involved in different stages of the progression of pneumococcal infection. TGF-β1 is a cytokine that regulates a wide range of cellular and physiological functions, including immune and inflammatory responses. This cytokine has long been known as an anti-inflammatory cytokine that is critical to preventing the progression of an acute infection to a chronic condition. On the other hand, recent studies have unveiled the diverse roles of TGF-β1 on different stages of pneumococcal infections other than mitigating inflammation. This review summarizes the recent findings of the role of TGF-β1 on the pathophysiology of pneumococcal infections, which is fundamental to developing novel therapeutic strategies for such infections in immune-compromised patients

THE OVERSEAS KOREAN FOUNDATION AND CULTURAL CONVENTIONS

Gabriel Vallejo 한국서비스경영학회 2016 한국서비스경영학회 학술대회 Vol.2016 No.5

Photoluminescence and Thermoluminescence of Phosphate Glasses Doped with Dy3+ and Containing Silver Nanoparticles

M. A. Vallejo,M. Perez,P. V. Ceron,R. Navarro,C. Villaseñor,T. Cordova,M. Sosa 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2017 NANO Vol.12 No.12

Phosphate glasses doped with Dy3+ ions and containing silver nanoparticles (SNPs) were synthesized in the present work. We report photoluminescence characterization by absorption and emission spectra. The effect of Ag concentration on the thermoluminescence (TL) glow curves was studied. The scanning electron microscopy (SEM) shows the formation of SNP. Absorption spectra of the samples show the influence of the SNP in the bands 350 nm at 425 nm associated with the Dy3+, in the same spectra we can see the bands 750, 800, 875, 1098, 1278 nm and 1675 nm belonging to the Dy3+. Emission spectra show two prominent bands at 480 nm and 574 nm and one faint band at 665 nm corresponding to 4 F 9/2 → 6 H 15/2, 4 F 9/2 → 6 H13/2 and 4 F 9/2 → 6 H 11/2 transitions, respectively. All bands under 364 nm pumping, and the fluorescence in the 550 nm and 590 nm spectral range enhanced four times. The Commission Internationale de 1'Eclairage (CIE) color coordinates were evaluated from the emission spectra to simulate white light emission from the phosphate glasses. The photostability of the samples was also studied in the UVA (315–403 nm) and UVB (280–315 nm) ranges. TL due to ultraviolet radiation (UVR) was studied; the glow curves show significant dependence of the TL intensity with the increment of SNPs in the samples. These results show the phosphate glasses doped with Dy3+ and containing SNP as a potential candidate have to be used in solid-state illumination and retrospective dosimetry.

Effect of Crystal Size and Ag Concentration on the Thermoluminescent Response of Pure and Ag-Doped LiF Cubes

Miguel A. Vallejo,Modesto A. Sosa,Esteban Rivera,Juan C. Azorin,Jesus Bernal,Ricardo Navarro,Emma K. Encarnacion,Luis A. Diaz-Torres 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2016 NANO Vol.11 No.4

In this paper, the co-precipitation method was used to synthesize pure and Ag-doped LiF crystals and the effect of crystalline cube sizes and Ag concentration on the thermoluminescent (TL) response is reported. The synthesized materials were characterized by scanning electron microscopy and their morphology and size distributions were determined. Crystal sizes were found to be strongly dependent on the ethanol:water ratio, varying from 4.1 µm to 150 nm for pure LiF crystals. For Ag-doped samples, the best ethanol : water ratio was found to be 9:1, giving crystals from 0.50 µm to 1.21 µm. A single cubic crystalline phase was determined by XRD for all synthesized samples. The photoluminescence spectra as well as UV-Vis absorbance were also analyzed. The TL response to X-ray irradiation was studied for an exposition of 43 R. Two effects were observed in the TL response. The first concerns with a significant dependence of the TL intensity on the size of the crystals, being larger for the smallest crystals for pure LiF, and second, for Ag-doped samples the TL intensity augmented almost linearly with the Ag concentration.

Detection of Clavibacter michiganensis subsp. michiganensis Assisted by Micro-Raman Spectroscopy under Laboratory Conditions

Perez, Moises Roberto Vallejo,Contreras, Hugo Ricardo Navarro,Herrera, Jesus A. Sosa,Avila, Jose Pablo Lara,Tobias, Hugo Magdaleno Ramirez,Martinez, Fernando Diaz-Barriga,Ramirez, Rogelio Flores,Vazqu The Korean Society of Plant Pathology 2018 Plant Pathology Journal Vol.34 No.5

Clavibacter michiganensis subsp. michiganesis (Cmm) is a quarantine-worthy pest in $M{\acute{e}}xico$. The implementation and validation of new technologies is necessary to reduce the time for bacterial detection in laboratory conditions and Raman spectroscopy is an ambitious technology that has all of the features needed to characterize and identify bacteria. Under controlled conditions a contagion process was induced with Cmm, the disease epidemiology was monitored. Micro-Raman spectroscopy ($532nm\;{\lambda}$ laser) technique was evaluated its performance at assisting on Cmm detection through its characteristic Raman spectrum fingerprint. Our experiment was conducted with tomato plants in a completely randomized block experimental design (13 plants ${\times}$ 4 rows). The Cmm infection was confirmed by 16S rDNA and plants showed symptoms from 48 to 72 h after inoculation, the evolution of the incidence and severity on plant population varied over time and it kept an aggregated spatial pattern. The contagion process reached 79% just 24 days after the epidemic was induced. Micro-Raman spectroscopy proved its speed, efficiency and usefulness as a non-destructive method for the preliminary detection of Cmm. Carotenoid specific bands with wavelengths at 1146 and $1510cm^{-1}$ were the distinguishable markers. Chemometric analyses showed the best performance by the implementation of PCA-LDA supervised classification algorithms applied over Raman spectrum data with 100% of performance in metrics of classifiers (sensitivity, specificity, accuracy, negative and positive predictive value) that allowed us to differentiate Cmm from other endophytic bacteria (Bacillus and Pantoea). The unsupervised KMeans algorithm showed good performance (100, 96, 98, 91 y 100%, respectively).