bluuebunny/crossref_metadata_2025 huggingface dataset:
Melting properties of sodium halides: molecular dynamics simulation
Authors: Zakiryanov D O , Kobelev M A , Tkachev N K
Published: November 2019

Molecular dynamics was used to calculate the melting phase transition properties in classical ionic systems. A simplified model of pair potential is considered, with only two terms the Born-Mayer repulsion and the Coulomb interaction. Preliminary ab initio calculation of the potential parameters was carried out for sodium halides. Regularities in changes of temperature, enthalpy and entropy of melting have been analyzed by direct heating method. It was found that the calculated values of the enthalpy of melting differ from the experimental data less than 5%.
Phase transitions and critical properties of 1-propanol–n-hexane system
Authors: Bazaev E A , Bazaev A R
Published: November 2019

By using experimental data on p, T, x and p, T, ρ, x - relations of 1-propanol- n-hexane mixtures (0.2, 0.5, 0.8 and 0.9 mol. fraction of n-hexane x) and the method of isochore fracture p = f (T)
ρ,x
at two-phase (liquid-gas), one-phase (liquid, gas), near-critical and supercritical region liquid ↔ gas (ps
, ρs
, Ts
) phase transition parameters are determined. And parameters of critical points (pc
, ρs
, Tc
) are determined by the grapho-analytical method combining with scaling behavior. The dependence of pressure from temperature, density and composition along the phase coexistence curve is described by three parameter polynomial represented by expansion of the compressibility factor Z = p/RTρ into a power series of density ω = ρ/ρk
and temperature

τ
=
T
/

T
k

:
Z
=

p

R
T

ρ
m

=
1
+

∑

i
=
1

m

∑

j
=
0

n

∑

k
=
0

a

a

i
j
k

ω
i

x
k

/

τ
j

, and

p
=
R
T

ρ
m

[

1
+

∑

i
=
1

m

∑

j
=
0

n

∑

k
=
0

a

a

i
j
k

ω
i

x
k

/

τ
j

]

.

The average relative deviation of calculated values of pressure from experimental ones is 1%. The dependence of temperature from density along the liquid ↔ gas phase coexistence curve is described by equations: far from critical points ρ = ρk
(1 ± B
0
τ

β
0
+ B
1
τ

β
1
± B
2
τ
β2
+ …), and in the symmetrical part of equilibrium curve (ρf – ρg)/2ρk
= B
0
τ

β
0
+ B
2
τ

β
2
+ B
4
τ

β
4
+ …, where τ = (T – Tk
)/Tk
and ω = (ρ – ρk
)/ρk
. Average relative error is 1.47%.
Features of heat transfer to hydrocarbon fuel at bubble and film boiling
Authors: Zhukov S A , Yanovskiy L S , Molokanov A A
Published: November 2019

The article presents the results of a study of heat transfer from a heater to a RT grade hydrocarbon fuel. A number of features of heat transfer during boiling of hydrocarbon fuel in bubble and film modes were discovered. The presence of self-oscillations occurring during heat transfer is noted.
The effect of water traces on heat transfer in liquid hydrocarbons under pulse heating mode
Authors: Lukianov K V , Kotov A N , Starostin A A , Skripov P V
Published: November 2019

The peculiarities of heat transfer and spontaneous boiling-up of pure hydrocarbons (n-hexane, n-decane, and n-hexadecane) and those with water traces have been studied under the pulse heating mode. The pulse lengths were from 5 to 25 ms; the pressure was elevated up to the critical one. The phenomenon of strong sensitivity of heat transfer intensity to the presence of water traces has been revealed in the vicinity of spontaneous boiling-up temperature. The hypothesis on the initiating action of water traces on macroscopic phase transitions is assumed.
Thermodynamic fundamentals of extraction of hydrocarbons from oil sludge with the use of supercritical propane-butane mixture
Authors: Khairutdinov V F , Gumerov F M , Zaripov Z I , Farakhov M I
Published: November 2019

Current paper represents the results of the study on phase equilibrium characteristics and thermal conductivity of some thermodynamic systems involved in the extraction of hydrocarbons from oil sludge with the use of propane-butane mixture in both liquid and supercritical (SC) states. Phase equilibria have been studied for such previously unexplored binary systems as: “naphthalene – propane/butane”, “sulfur – propane/butane”, “water – propane/butane”. The studies have been carried out with the traditional version of the static method, as well as by using an optical cell for phase equilibrium studies, designed for high pressures. Thermal conductivity of water-oil emulsion at a pressure of 0.098 MPa in the temperature range of 290 – 360 K has been investigated using the hot-wire method.
Desalination of seawater using an electrode modified with poly(3,4-ethylenedioxythiophene)
Authors: Salgado R , Arteaga G C , Romero M , Martínez J , Ramos A , Burgos R , García C
Published: November 2019

The procedure for obtaining electrodes modified with poly(3,4-ethylenedioxythiophene) has been widely studied for its multiple applications. This study evaluates the potential contribution of electrodes modified with poly(3,4-ethylenedioxythiophene) for desalination of seawater. Potentiostatic electropolymerization of 3,4-ethylenedioxythiophene was conducted on 6 cm2steel electrodes by using a supporting electrolyte consisting of lithium perchlorate in acetonitrile. This modified electrode was used in the extraction of anions and cations from samples of synthetic seawater by means of 20 extraction cycles (optimal cycles) and using a combination of p-type and n-type doping. A total of 140 extractions (number of optimal extractions) were carried out, which led to desalination of synthetic seawater by about 80-90%, as evidenced by the decrease in the conductivity of the solution containing the ions. Therefore, this procedure could become an alternative for seawater desalination.
Graphene deposit in direct current abnormal glow discharge
Authors: Alvarez B , Sarmiento-Santos A , Hernández Y
Published: November 2019

With the advent of nanotechnology, graphene has gained relevance in the last two decades, due to its exceptional mechanical, electrical and thermal properties. This material being one of the thinnest existing, has at the same time great mechanical strength, flexibility, is transparent, in addition to very good conductor of electricity, much better than copper or any other known material. These properties are due to its structure constituted by a flat monoatomic sheet of carbon atoms arranged cyclically with the same structure of benzene. Several layers (>10) of superimposed graphene constitute the well-known graphite structure. To obtain it, among other methods, plasma enhanced chemical vapor deposition has been used, which uses electric discharges in the radiofrequency regime. In this work, the formation of graphene in the plasma of the abnormal glow discharge of direct current is reported. For this purpose, a mixture of 60% Ar, 5% C2H2 and 35% H2 is used as gas atmosphere, at a pressure of 2.0 torr. Electrolytic copper sheets were used as substrate. Temperature of the process was 600 °C and the formation time was 5 s. Deposits characterization was made by infrared spectroscopy and Raman spectroscopy.
Corrosion resistance hydroxyapatite assessment and tricalcium beta phosphate coating, deposited on stainless steel low carbon vacuum melted
Authors: Rojas C , Vera E , Aperador W
Published: November 2019

316 stainless steel low carbon vacuum melted, used for surgical implants, has good corrosion resistance, but it is degraded in the body fluids presence, generating problems for the receiver, therefore it is necessary to apply coatings that improve their biocompatibility. In the current work hydroxyapatite and tricalcium beta phosphate coatings were applied on 316 stainless steel substrates, by the radio frequency magnetron sputtering technique, with a 2 m thickness for possible biomedical applications. The coatings characterization was performed, using scanning electron microscopy, found the Ca/P ratio of 1.639 for hydroxyapatite and 1.515 for phosphate, the friction coefficient was additionally evaluated by pin on disk tribometer, with a lower coefficient of beta tricalcium phosphate in relation to hydroxyapatite. The corrosion evaluation was carried out using the electrochemical polarization technique Tafel, in Ringer lactate, as simulated biological fluid. It was observed that the coatings improve the steel electrochemical behavior and between the two coatings the one that best behaves is the tricalcium beta phosphate, with a corrosion low rate.
Effects of increasing the concentration of Cr in the alloys Nb1-xCrxN
Authors: Ortega López C , Murillo G J F , Espitia Rico M J
Published: November 2019

We investigate the effects of increasing in the concentration of Cr atoms on the structural and electronic properties of Nb1-xCrxN alloys in the concentrations (x = 0.0,0.125,0.25,0.50,0.75 and 1.0) in the NiAs phase. For NbN and CrN in all concentrations, the calculations were carried out using the Quantum ESPRESSO code through the pseudopotential method within the framework of density functional theory. Regarding the structural properties, it was found that the lattice constant of the alloys decreases while the concentration of Cr increases. The bulk modulus of the alloys changes slightly compared to the bulk modulus of the binary NbN compound. Furthermore, the density of states calculations shows that the incorporation of Cr into the NbN matrix gives magnetic properties to the NbN. All the alloys have a metallic-ferromagnetic character.
Mechanical response to tensile stress of a composite material reinforced with sugar cane fibers
Authors: Vega H F , Bohórquez O , Pertuz A , Sánchez Acevedo H G , González-Estrada O A
Published: November 2019

Composite materials reinforced with organic fibers have attracted great interest in the area of mechanical engineering in recent decades due to the wide variety of industrial applications where these materials can be used, and the low impact on the environment, compared with traditional materials. In this work, experimental and numerical tests are carried out to investigate the mechanical response to a tensile load of a composite material with an epoxy matrix, reinforced with sugar cane fibers. Mechanical tests under the ASTM standard for tensile loads were performed. Then, a numerical model to investigate the mechanical response of the composite is done by finite element analysis. Results indicate that this composite material has good performance under axial loading conditions, and can be used for structural applications.
Adsorbent materials obtained from palm waste and its potential use for contaminants removal from aqueous solutions
Authors: Giraldo S , Ramirez A P , Flórez E , Acelas N Y
Published: November 2019

This work reports the production of an adsorbent material obtained by H3PO4 chemical activation of oil palm waste (fiber). The experiments were carried out to explore methylene blue uptake by this adsorbent. The influence of initial dye concentration and adsorbent dosage was investigated. The adsorption equilibrium data of methylene blue onto the adsorbent material were best fitted to the Langmuir model. The maximum adsorption capacity monolayer was of 20.85 mg g−1, which showed to be high compared to other adsorbent materials reported in the literature. Adsorption of methylene blue onto adsorbent material followed pseudo-second order model. The structural and chemical characterization of the adsorbent material was carried out by using various analytical techniques. FTIR showed the formation of oxygenated functional groups on the surface, which are very important for adsorption applications because they act as active sites capable of interacting with dye molecules.
Removal of rhodamine B in wastewater from the textile industry using geopolymeric material
Authors: Pinto L F , Montaño A M , González C P , Barón G C
Published: November 2019

In this work a geopolymeric material was synthesized by alkaline activation of calcined coal gangue at 700 °C using a solution 1:9 of NaOH:Na2SiO3, as a sorbent to remove rhodamine B from aqueous solutions. X-ray diffraction, fourier-transform infrared spectroscopy and scanning electron microscopy were used to characterize the material structurally and morphologically; removal efficiency and rhodamine B sorption capacity were evaluated by using ultraviolet-visible spectrophotometry. Sorption tests were performed to evaluate the effect of the dose of geopolymeric material and the contact time of this material with rhodamine B solution in a range from 0.5 to 30 hours, interval in which the best sorption was observed. Removal efficiencies and sorption capacity to 80.4% and 1.035 mg/g respectively were found, these values show the usefulness of the material for the removal of rhodamine B in aqueous solution, making it an interesting alternative for water decontamination and object of study for future works. Removal efficiency increased by increasing geopolymer dosage and contact time.
Sintering of a metal matrix composite Cu-Ti-TiC assisted by abnormal glow discharge
Authors: Bohórquez C D , Pérez S , Sarmiento A , Mendoza M
Published: November 2019

A metal matrix composite based copper with ceramic reinforcement at 1% w/w of titanium carbide had been studied under variable titanium at 10%, 15% and 20%, in order to evaluate the microstructure and tribological properties (coefficient of friction and wear rate) in the composite material after abnormal glow discharge sintering. The metal matrix composite was manufactured by powder metallurgy process that included: mechanical and ultrasonic mixing in a suspension of 2-propanol, compaction at 200 MPa and sintering by abnormal glow discharge in an atmosphere of 10% nitrogen and 90% argon. As a result, a differentiation in the morphology and properties had been found due to the temperature, this effect was related with diffusion phenomena and energy provide by the plasma process. The final porosity of the samples at 750 °C decreases with titanium increments, reach to 2.6% with 20%. Additionally, in the grain limits of the titanium particles were detected CuTi and CuTi2 phases. On the other hand, at 850 °C the porosity increased with concentration of titanium, a value of 16.8% was shown at 20%. Furthermore, intermetallic phases as Cu3Ti, Cu4Ti, CuTi2 had been identified in the sintered at 850°C. Tribological properties had evidenced that the samples at 750 °C with Ti contents of 20% presented a wear rate value of 7.2x10−8 mm3.N−1.m−1, despite the porous morphology of the compound at 850 °C was estimated in 2.0x10−8 mm3.N−1.m−1 with concentration of 20%.
Carbides formation in weld metal produced by recycling of titanium machining swarf
Authors: Fagundes J G , Ventrella V A , Gallego J , Moreno A M , Jácome J L , Bracarense A Q
Published: November 2019

Application of titanium alloys for orthodontic implants have increase in last years and it has generated a great amount of titanium chips which are disposed as metal scrap. Titanium carbide has high hardness and can be applied as coating reinforcement against wear. Chips of titanium alloys were processed and used in the fabrication of experimental hardfacing consumables for improving the resistance of wear of mechanical components. Coatings were produced in cast steel specimens using the gas tungsten arc welding process. Microstructure was investigated by means of scanning electron microscopy. Microhardness of the coatings was analyzed by a dynamic ultra-micro hardness tester. The microstructure of the welding metal was composed of circular particles of titanium carbide surrounded by a ferritic matrix. The measures made by electron dispersive spectroscopy showed a variation in titanium amount trough the weld, where larger contents of titanium were found, and the matrix. The crystallographic analyses reinforced the formation of titanium carbides embedded in a ferrite matrix into welding metal.
Technological characterization of Colombian clay during the stages of the production process
Authors: García-León R A , Quintero-Quintero W , Espinel-Blanco E
Published: November 2019

Clays are of great importance at the industrial level because they can be used to make masonry products such as blocks, roof tiles, bricks, and tiles, among others. Currently, many companies in the ceramic sector get a lot of waste due to the lack of technical analysis of the raw material to forecast the behavior of the ceramic mixtures and to improve the quality of the final product. In this paper, the physical and chemical characterization of the clay used in one of the companies dedicated to the manufacture of masonry products for construction in Ocaña, Norte de Santander, Colombia was conducted. The development of the investigation was achieved by means of the execution of physical and chemical tests to the sample of selected clay from different points of the production process with which the granulometry, index of plasticity and the mineralogical composition were determined. The results obtained show that the clays currently used by the company are at a low level for masonry products for construction. This is why the addition of other clays is considered, with which an optimum mixture is achieved with which can meet the requirements of the current regulations in force. It is essential to technologically characterize the clays to optimize the mix and thus avoid defective products. It will obviously improve the company’s environmental and economic resources.
Use of musa paradisiaca fibers for the preparation and chemical, physical and mechanical characterization of a biodegradable composite material
Authors: Martínez C , Ruiz W , Lesmes S , Laverde D , Pertuz A
Published: November 2019

Composite materials with comparable properties and low environmental impact have been at the forefront of research. In the present work, the mechanical, physics and chemical properties that allow knowing the potential applications of Musa Paradisiaca fibers are evaluated, through an experimental process that starts from the selection of the binder and its fiber/binder ratio through tensile tests. The finally formed material is composed of a matrix of gelatin type C and glycerin and a reinforcement of banana fibers. The compound obtained was characterized by infrared spectroscopy by the Fourier transform, thermogravimetry, scanning electron microscopy and mechanical tensile and hardness tests. The results obtained from this study allowed confirming the presence of lignin and hemicellulose and evidencing the presence of good mechanical properties with a modulus of elasticity equivalent to 0.57 MPa, a percentage of elongation of 56%, an ultimate tensile strength of 3.5 MPa and a hardness of 82 Shore A, which allows us to consider a biodegradable composite material for applications in which soft gums and elastomers perform. The results obtained allow us to consider other alternatives for the use of Colombian banana fibers, in addition to their use as a biodegradable compound.
Thixotropic behaviour study of clayey soils from the lacustrine deposits of Bogotá high plateau
Authors: Ruge J C , Molina-Gómez F , Rojas J P
Published: November 2019

Thixotropy is a distinctively rheological (time-dependent) phenomenon, which is found in many complex materials, especially colloidal systems as fine-grained soils. Clays are materials that can recover their initial strength after remoulding. The estimation of such recovering allows optimising the designs of geotechnical structures and then reducing the construction costs. This paper presents the results of a study that evaluates the thixotropy phenomenon of clayey soils. The work methodology involved an experimental plan composed of five phases: (i) extraction of samples; (ii) physical and mechanical characterisation of the undisturbed samples; (iii) remoulding of samples after testing; (iv) storage of remoulded samples; and (v) evaluation of undrained shear strength recovering for 0, 15, 30, and 60 days after remoulding. Undisturbed samples were collected using Shelby tube from the municipality of Madrid, near Bogotá, in Colombia. Results were analysed in terms of sensitivity degree because this parameter allows estimating the shear strength recovering. Findings show that clayey soils from lacustrine deposits of Bogota high plateau do not loss completely all of their original mechanical properties after remoulding and exhibit a medium sensitive behaviour. Conclusions indicate there is a recovering of undrained shear strength along the time, in which the samples will recover their original state about one year after remoulding.
Characterization of smart materials requirements for actuation in the robotic applications
Authors: Ramirez J L , Rubiano A , Cogollo J G
Published: November 2019

This paper presents the requirements specification of artificial muscles based on smart materials for a robotic finger prosthesis. The first part introduces the robotic finger, designed to mimic human precision grasping. A methodology to determine three critical parameters (strain, frequency and force) is presented. The methodology uses experimental data combined with kinematics and dynamics. Obtained values are calculated using the developed finger; as a result, we define that main requirements are: (i) Minimum active strain 5.5% for extension-based actuation or 60% bending-based actuation, (ii) Frequency (8.89 Hz, 22.2 Hz), and (iii) Force (4.80 N, 6.74 N) for bending-based actuation or force (17.81 N, 25.11 N) for extension-based actuation. Finally, a review of smart materials is presented with the aim of choosing the group of materials that can be used as artificial muscles for robotic hands. We show that shape memory Alloys can fulfill the established specifications. We also stand out Ionic polymer metal composites as a very promising actuation solution for robotic hands, due to their active strain and settling time, even though the blocking force is below the requirements.
Synthesis and size evolution of 1D hydroxyapatite crystals under surfactant-free hydrothermal conditions
Authors: García-Negrete C , Goméz R , Brun L , Barrera M , Arteaga G , Beltrán A , Fernández A
Published: November 2019

Hydroxyapatite nanoparticulate materials have received a great deal of scientific attention due to their dental and orthopedic applications but simple strategies to control particle characteristics (e.g., surface area, shape and size distribution) are still needed. Among several hydroxyapatite structures, one-dimensional nanoscale materials such as nanowires, nanorods and nanobelts can be synthesized in the presence of specific surfactants added during synthesis in order to alter the particle growth. This contribution is aim to explore strategies to obtain one dimensional hydroxyapatite crystals without the use of surfactants. Particularly, we study the effect of several variables such as temperature, reaction time and pH on shape and size of hydroxyapatite crystals produced under hydrothermal conditions. The results obtained show the formation of hydroxyapatite nanorods as well as some interesting insights about how to control particle sizes in samples obtained at temperatures between 180 °C and 220 °C. These results have potential benefits at the time of producing one dimensional hydroxyapatite crystals in a simple and not expensive way.
Evaluation of the effect of a hyperbranched polyester on the thermal, rheological, morphological and mechanical properties of polyvinyl chloride/hemp fiber blends
Authors: Tolosa R , Acevedo C , Murillo E A
Published: November 2019

The aim of this study was to investigate the effect of the hyperbranched polyester polyol from second generation content on the structural, thermal, rheological, morphological and mechanical properties of recycled polyvinyl chloride/hemp fiber/hyperbranched polyester polyol obtained from second generation blends. In all blends, the amounts of recycled polyvinyl chloride and hemp fiber were 70 wt% and 30 wt% respectively. The blends were obtained in a torque rheometer. The proportions of hyperbranched polyester polyol regards to those of the polyvinyl chloride and hemp fibers were 5 wt%, 10 wt%, 15 wt% and 20 wt%. Additionally, a recycled polyvinyl chloride/hemp fiber blend was prepared to be used as control blend. Infrared analysis was then used to evidence the interaction between components of the blends. The thermal stability of the recycled polyvinyl chloride/hemp fiber/hyperbranched polyester polyol blends was lower than that of the polyvinyl chloride. Furthermore, it was not observed a trend in the thermal behavior of the recycled polyvinyl chloride blends. Hyperbranched polyester polyol increased the glass transition temperature of the blends. Additionally, rheological analysis results indicated that the hyperbranched polyester polyol reduced the viscosity of the blends.
Methodology for simulating the process of microbiologically induced degradation of concrete by chemical exposure of specimens under controlled laboratory conditions
Authors: Cortés M , Vera E
Published: November 2019

Research studies on the kinetics of the corrosion process that attacks concrete coincide in the amount of variables that interfere with the process, such as the impact of the pH levels of the corrosive environment and the surface of the concrete and the concentrations of biogenic sulfuric acid at the site. For this reason, it is vitally important to know the resistance of concrete to this attack in controlled laboratory conditions, defining a methodology that contributes to the development of new research related, for example, to the degradation of concrete in component elements of a sewer system.
All-glass vacuum tube heat transfer simplified model
Authors: Ardila O , Quiroga J , Martínez O
Published: November 2019

This paper addresses the design of an algorithm that estimates the irradiance and the selective layer temperature of the all-glass vacuum tube as a function of the ambient temperature in Bucaramanga, Northern Colombia. A Matlab code to meteorological National Aeronautics and Space Administration data processing and to find a linear relationship between the irradiance and ambient temperature on the location of study, was developed. The behavior of this relationship for several hours of the day was studied, and it was found that it is possible to use this relationship as a reliable preliminary approach in water heating systems design using all-glass vacuum tube. This facilitates the design calculations and would encourage the use of solar energy in water heating systems in Colombia.
Synthesis of Cu2ZnSnSe4 from nitrate and selenite inks for use as an absorbent layer in the design of solar cells
Authors: Torres-Barahona E A , Castellanos-Báez Y , Gómez-Cuaspud J A , Vera-López E , Carda J B , Pineda-Triana Y
Published: November 2019

This research was conducted to identify two acceptable precursors and methods of synthesis for the manufacture of photovoltaic cells. The kesterite Cu2ZnSnSe4, a promising material for solar cell applications, was synthesized from metal salts of Cu, Zn, Sn, and Se, by two low-cost routes: the direct dissolution of metal nitrates, and coprecipitation of selenites. In both cases, inks were obtained and deposited as thin-films by the Doctor Blade technique on glass substrates coated with molybdenum. The films were annealed in an oven at 550 °C by 30 minutes. The phases of each thin film were analyzed by X-ray diffraction and Raman scattering. The morphology and the thickness of the layers were observed using a scanning electron microscope. The optical band gap was determined by ultraviolet-visible spectroscopy and the Tauc equation. The results confirmed the main phase of kesterite material, consistent with a tetragonal crystalline system oriented along the plane (112). These values are consistent with those found by Raman spectroscopy, where the main vibrational mode was identified at 173 cm−1 and 196 cm−1, characteristic of mode A vibration, and 243 cm−1 of mode B vibration; typical of kesterite. Simultaneously, a band gap of 0.89 eV was identified. These results demonstrate the effectiveness of the selenite’s coprecipitation method for synthesis of kesterite, without evidence of secondary phases. This determines the possibility of using this material in solar cell applications.
Design and characterization of a magneto-dielectric composite in high frequency with aligned magnetite powders
Authors: Lara L A , Mancipe D L , Pineda Y , Moreno J J , Peña-Rodríguez G
Published: November 2019

A magneto-dielectric material composed of a polyester resin-based microstrip (P115A), copper sheets and magnetite powders was designed in concentrations of 10, 20 and 30% Wt and with filters of 200, 325 and 500. The particles were aligned vertically and horizontally during the curing process using 300 mT magnetic fields. From a complete factorial design of 33, 27 microstrip-type circuits of 4 mm width, 70 mm length and 0.93 mm thickness were manufactured, characterized by scanning electron microscopy and vector network analysis. The cross-matrix analysis determined an optimal circuit response from the magneto-dielectric material with a concentration of 20% magnetite and an average particle size of 21.48 μm in horizontal alignment to the applied magnetic field and to the transmission line, obtaining a relative dielectric constant of Er 3.88 with a low dielectric loss of 0.054, within an operating range of 150 KHz to 4 GHz.
Characterization of biodeteriorating microorganisms in buildings in Bucaramanga, Colombia
Authors: Mantilla K , Suárez-Barrera M , Rueda-Forero N J , Guarín O D , Gómez F R , Durán S M , Tiria L C
Published: November 2019

The action of the microorganisms upon the integrity of the constructing material is termed Biodeterioration, concrete resistance to the action of the microorganisms is considered an indirect measurement of its durability and could be used as a marker of the integrity of the structure. In Colombia, the studies considering this parameter are rare. The objective of this study was to isolate and characterize the microbial communities present in areas with evident deterioration in the selected buildings. To accomplish this, isolation, culturing and molecular identification of the isolates was performed. Results showed that Cladosporium spp, Aspergillus spp, Mucor spp, Penicillium spp, Penicillium spp, Rhizopus spp, Fusarium spp, Geotrichum spp, and bacterial genera such as Bacillus spp and Amphibacillus spp, coexist within the biofilms sampled. This study is a description and a starting point to deepen the characterization of these communities and to understand the role they perform in the integrity of the building materials considering the climatic and environmental conditions.
Estimation of multiple parameters using algorithms expectation maximization
Authors: Ospina R , Correa G , Cárdenas P P
Published: November 2019

In this paper the strategy of the expectation maximization algorithm is developed in order to solve the problem of maximization of the likelihood which becomes a complex problem when it is expected to estimate multiple parameters at the same time. All this will be achieved with the introduction of basic concepts of statistical estimators and will be verified by simulations carried out in the MATLAB software.
Embedded quantum dots in semiconductor nanostructures
Authors: Paredes Gutiérrez H , Pérez Merchancano S T
Published: November 2019

In this work, we report the behavior of the tunneling current in a semiconductor nanostructure of (Ga, Al)As/GaAs which takes into account the behavior of the electrons and the Rashba’s spin orbit interaction in the presence of embedded quantum dots of different geometries (lens, pyramid and ring) in voltage function, magnetic field, and the different values of the interaction spin orbit (π/2, π/4 and 3π/4). The results that were obtained show, that the intensity of the current presents appreciable changes when is changed the configuration of the quantum dot as the intensities of external fields and spin polarization as well. All these internal and external effects that are studied in our model, significantly modify the transport of information of the semiconductor nanostructure, our results show that the spin effects and the quantum dot configuration contribute to the quantum memories efficiency and the spin filter devices of actual use on nanoscience and nanotechnology.
Structural study of hydrogen absorption properties using Thermocalc software for application in energy storage
Authors: Bellon D , Martínez-Amariz A , Montes E
Published: November 2019

The interest in developing experiments and processes in general through mathematical modelling or simulation, has been growing considerably in recent decades; the previous, insofar as it offers highly reliable results that have an impact on advantages such as reduction of the risk associated with the execution of costly or difficult to reproduce experiments since they handle many variables or even the elimination of times associated with the execution of said experiments. For its part, the study of hydrogen storage alloys represents a fundamental element in the so-called hydrogen economy, which seeks the integration of hydrogen as an alternative solution to dependence on fossil fuels, due that this energy vector has a high energy density when is compared to the gasoline and the only residue of this process is water vapor that will undoubtedly reduce CO2 emissions. Thus, in this study a simulation of the evolution of the microstructure of hydrogen storage alloys based on TiCrV is developed, using ternary systems at different temperatures; this evolution is the result of the phase change when the elements are subjected from high temperatures to room temperature, obtaining a body-centered cubic structure. Likewise, the solidification process of the components present in the alloy is studied to corroborate the final structure with experimental data. In preliminary results, it is observed that the simulation throws a body centered structure, and in the solidification process, a remnant of a compact hexagonal structure is observed. This Ti-Cr-V system is widely studied due to its large hydrogen storage capacity, which can be used for technological purposes.
Numerical modelling of guided waves dispersion curves in an aluminium flat plate by finite element analysis
Authors: Galvis L , Quiroga J , González-Estrada O A
Published: November 2019

This work presents a practical approach to obtain the dispersion curves for a plate via numerical modelling using the commercial software ANSYS. The method is based on the dynamic analysis of the waveguide to extract the mode shapes (eigenvectors) for each resonant frequency (eigenvalue) from the natural frequency response without damping. Each eigenvalue provides a frequency and the dimensions of the model (wavelength), which are the basis of the dispersion curves. Then, an algorithm is developed in MATLAB to stack the different mode solutions with its respective frequencies using the modal assurance criterion. The data obtained is compared with the dispersion curves provided by the GUIGW software.
Numerical simulation of electron cyclotron resonance phenomenon using an axisymmetric transverse electric field
Authors: Otero O , Orozco E A
Published: November 2019

As a contribution to the study of the resonant interaction between of an electron and the transverse electric field of a stationary electromagnetic wave in the presence of a static homogeneous magnetic field in this work we develop a numerical study of the acceleration of electrons by cylindrical mode TE011. In order to get a better understanding of the particle-wave interaction, the electric field of the microwave mode is decompose as the superposition of a left-and a right-hand circularly polarized standing wave because electrons interact effectively only with right-handed circular polarized wave. The trajectory, energy and phase-shift between the electron transverse velocity and the electric field are determined by the numerical solution of the relativistic Newton-Lorentz equation using a finite difference scheme. For an electron injected longitudinally with an energy of 5 keV and that starts at the radial midpoint of the cavity, it is accelerated up to an energy of about 90 keV using an electric field amplitude of 14 kV/cm and a frequency of 2.45 GHz. These results are compared with those obtained for another two points of injection located in different radial positions. This levels of energy can be used to produce soft X-ray which has some important medical applications like imageology. The results suggest that the particle-wave interaction using the cylindrical mode TE011 could be optimized through the application of a external magnetic field which is gradually growing in time to preserve the resonance condition and sustain the phase stability.
Modelling the effect of temperature on the physical and mechanical properties of ceramic composites filled with foundry sand waste
Authors: Roa KL , Paredes RA , Trejo F , Castro HF , Vera E , Peña G
Published: November 2019

The aim of this research is to describe the temperature effect on the water absorption, linear shrinkage, density and compressive strength of ceramic composites produced by mixing clay with additions of foundry sand waste from 20% to 40% wt. Previous studies have shown that foundry sands can be recycled due to the high content of SiO2 on its chemical composition, therefore, in this research is proposed as an alternative raw material in ceramic bodies. Prototypes were shaped by uniaxial pressing method and fired at three different temperatures (850°C, 950°C and 1,050°C) in order to promote the formation of the ceramic phases. Physical and mechanical properties were measured based on the procedures specified by standard ASTM C373 and ASTM C773-88. It was found that at 1,050°C properties such as mechanical strength and density reach its maximum values, effect that might be associated to the reduction in pore size inside the microstructure during calcination. The main merit of the models obtained is offer a valuable tool to set up a proper thermal process in order to obtain eco-friendly ceramic samples with physical and mechanical properties at its optimum values, reducing environmental problems related to landfill disposal and minimizing costs of manufacturing.
Design and simulation of an alternative aqueduct network for urban population
Authors: Orjuela Abril M S , Rojas Suárez J P , Prada Botia G C
Published: November 2019

Aqueduct systems help to record water consumption, being a connection between nature and the population, allowing water to be transported continuously; a good design of aqueduct networks is necessary to meet the purpose of providing the community with a technical report that can serve as a starting point to carry out a construction of the aqueduct for the public battery. This research presents the simulation of an aqueduct system by means of the epanet software according to the daily maximum flow, pressure, velocities of the distribution network, pumping time, with respect to the different pressures and diameters, diagnosing the routes, nodes, forms of access, restrictions and limitations that may affect the proper functioning of the system; In this way, the advantages and the magnitude of beneficiaries who will have this new access and improved service to meet the needs of the inhabitants are evident, according to the technical requirements of drinking water and sanitation of the technical regulation of the drinking water and basic sanitation sector, where it can be implemented by any public company in the country.
Fractal analysis in rural domestic wastewater quality under dissolved oxygen stability in wetlands planted with Chrysopogon zizanioides
Authors: Prada D A , Reátiga A , Correa S N , Acevedo A , Mantilla J , Florville T , Nuñez J
Published: November 2019

Chrysopogon zizanioides is a plant with adaptability characteristics in a variety of soils and climatic conditions, improves quality of wastewater and industrial water, due to the root system, allows the consumption of organic matter and capture pollutants. One of the water quality indicators is the amount of dissolved oxygen present. To analyze the recovery behavior of dissolved oxygen in wastewater, an artificial subsurface flow wetland was designed with stone as a filter material with dimensions 0.9 m wide, 2.5 m long and 0.60 m deep and 30 Vetiver plants. These dimensions and quantity of plants were considered appropriate in terms of space and low cost in order to replicate in rural and semi-urban areas, because in some of these they do not have an appropriate aqueduct, then this strategy becomes an option for people residing in these places. The water treated in this wetland is domestic wastewater from a rural house in the municipality of Floridablanca, Colombia. For 4 weeks the data of the dissolved oxygen present in said water was recorded using a multiparameter probe, to observe how effective the process is in a shorter time and using fractal dimension the volatility of this time series was observed.
Study for the dispersion of particulate matter emissions from a steel industry using Gaussian Plume equation through computational modeling
Authors: Maués C S , Guimarães C S , Martinez-Amariz A
Published: November 2019

Mathematical models allow evaluating air pollutants effects to the environment, being a relevant tool for planning and regulatory purposes. The present study aims to evaluate the air quality of Volta Redonda, Brazil, due to particulate matter emitted by stationary point sources of a large steel plant using meteorological data from three monitoring stations. A mathematical model was developed linking Matlab® and RStudio®, using the Gaussian dispersion equation and Google Maps to visualize the results. Observed data revealed southern, north-western and northern light prevailing winds that were used to simulate stable and unstable atmosphere conditions according Pasquill-Guifford classification. Results have exposed elevated concentrations of particulate matter in ambient air, reaching particularly Santa Cecilia neighbourhood. National air quality standards recently updated were partially met however numerous violations were indicated, considerably higher in Santa Cecilia station (47.98%), followed by Belmonte (6.69%) and Retiro (4.17%), indicating a forthcoming need for an update of the technologies and processes that emit particulate matter to improve the city air quality, preventing from environmental and human health effects.
Virtual laboratory for measuring of elastic modulus with stress and strain for different metals
Authors: Acevedo J C , Trejos J G , Celis D M , Herrera J R , Cristiano K L , Triana D A
Published: November 2019

The Colombian ministry of information and communications technologies is leading a digital revolution to bring computer and internet equipment to rural areas, taking into account that in these areas there are educational establishments that do not have equipment and materials for the performance of laboratories or experimental demonstrations. Therefore, this project proposed the development of a virtual learning laboratory for the study of the elastic modulus, obtained from real tensile-compression tests. It is important to clarify that there is not theoretical procedure to obtain stress-strain curves out of their linear regime. The virtual laboratory was developed in python language. The simulation allows the students to manipulate tensile-compression test for different materials. Also, they can visualization of the procedure, the stress-strain curve, and the Young modulus, all with the aim of transferring the conceptual and procedural knowledge of the physical phenomenon to the student.
Collaborative work as a learning strategy to teach mathematics incorporating robotics using led godt education system and fischertechnik in seventh graders at the school Isidro Caballero Delgado in Floridablanca Santander Colombia
Authors: Rico-Bautista N A , Rico-Bautista D W , Medina-Cárdenas Y C
Published: November 2019

This article describes the impact of collaborative work to teach Mathematics in Seventh graders (70 students) at the school Isidro Caballero Delgado, Ocaña, Colombia. Led godt education system and fischertechnik allowed a great interaction and participation and provided the tools to incorporate robotics in the classroom. Moreover, these tools are used as a learning strategy to achieve understanding and analysis in the solving problems teaching math. Students became more critical and responsible facing daily solutions and a better understanding of basic problems of geometry, math and statistics. Students also learnt about and improved interpersonal abilities and improved social interaction. It also allowed making learning effective creating a better environment to improve the acquisition of mathematical concepts.
Usable rainwater volume; results of a hydrological study conducted at the Universidad de Santander, Bucaramanga, Colombia
Authors: Tiria L C , Duran L M , Ardila D F
Published: November 2019

This study was carried out at the “Universidad de Santander”, in Bucaramanga, Colombia, to calculate the volume of rainwater capturable from the roofs of five campus buildings, as the blueprints for these surfaces were available to obtain their areas. Roof areas were first obtained for the Guane, Motilón, Arhuaco, Chibcha and Yariguíes buildings, from which rainwater can be captured. Intensity, duration, and frequency curves from the “Instituto de Hidrología, Meteorología y Estudios Ambientales” were then used to calculate a design flow, yielding the diameter of the pipe necessary to evacuate the water captured. In addition, data from the “Universidad de Santander” meteorological station was evaluated to obtain monthly rainfall figures. The highest-yielding structure was the Motilón building, with approximately 80 m3 in the months of May and November, 2018, as this structure has the largest roof area, and the area experienced its greatest quantity of rain during these months. The total accumulation predicted by the study was 1837.96 m3 annually, sufficient to suggest the possibility of its use in restrooms, gardens, and floor washing at the “Universidad de Santander”, Bucaramanga, Colombia. The volume of water calculated is variable on a yearly basis, and was estimated by means of one year of rainfall readings from the university’s meteorological station. Hydraulic structures designed for the purpose of capturing this water would require a specific study, taking into account the records of other nearby meteorological stations, and making necessary provision for the storage of water in excess of expected volumes.
Energetics of domain wall in magnetic nanowire
Authors: Trushin Oleg , Barabanova Natalia
Published: November 2019

Micromagnetic modeling is used to study the energetics of magnetic switching of single-layer permalloy nanowire. The energy landscape of the system is studied using Nudged Elastic Band method. It has been shown that presence of rectangular shape defects on long side and inside nanowire leads to the appearance of local maxima and minima on the energy profile. Thus artificially created imperfections can be used for effective DW pinning.
Ordering and frustrations in generalized Ising chain
Authors: Tsuvarev E S , Kassan-Ogly F A , Proshkin A I
Published: November 2019

The Ising model on a one-dimensional monoatomic equidistant lattice with different nearest-neighbour and second-neighbour exchange interactions is researched. Generalized Kramers-Wannier transfer-matrix with translation on two periods of a lattice is introduced. A property similar to supercooling and superheating is detected. At the triple points phases are not individualized, but completely frustrated which corresponds to the phenomenon of critical opalescence. Exact analytical expressions for free energy, heat capacity and entropy including zero-temperature entropy are obtained. Various new special cases were analyzed and compared with all known results. All frustration fields for magnetization, frustration values for the zero-temperature entropy and magnetization are found.
Monte Carlo simulations of Heisenberg magnets by the Wang-Landau method
Authors: Lozhnikov V E , Prudnikov P V , Mamonova M V , Sorokin A V , Baksheev G G
Published: November 2019

In this work, we investigate the critical behavior of the three dimensional Heisenberg model by parallel Wang-Landau algorithm developed with using of the OpenMP technology.