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A. Neira-Carrillo,M. S. Fernández,J. L. Arias,S. Navarrete G,M. Paz Díaz,M. Yazdani-Pedram 한국고분자학회 2011 Macromolecular Research Vol.19 No.11
Based on polypropylene (PP) grafted with different percentages of maleic anhydride (PP-g-MA) or monomethylitaconate (PP-g-MMI) a new porous scaffold was prepared with porosities in the range of 50-200 μm. The swelling capacity was analyzed, and morphological, mechanical, and elemental analyses of these scaffolds were carried out. In vitro swelling in the simulated body fluid (SBF), chitosan (CHI) of low (70 kDa) and high (350 kDa)molecular weight, and chitosan-hydroxyapatite solutions were assayed at 37 ℃ from 24 h to 4 weeks. The swelling degree (SD) of these scaffolds was in the range of 25%-125%. The highest SD value was found in the low-molecular weight (LMW) chitosan solution. The PP-g-MMI and PP-g-MA with 0.7% and 1% of grafting, respectively, showed the highest SD values in the CHI solution. The in vitro treatment of the scaffold was performed by immersion in LMW chitosan and/or the double ionic diffusion (DID) method. The pore structure of the scaffolds was unaltered after these treatments, as revealed by scanning electron microscopy (SEM). Mechanical properties, that is, fracture resistance and deformation of the porous scaffolds depended on the percentage of grafting. Scaffolds with a smaller pore size showed higher mechanical properties. Energy Dispersive Spectroscopy (EDS) measurements of PP-g-MMI with 0.7% of grafting after in vitro treatment revealed the formation of hydroxyapatite (HA) crystals with different morphologies on the porous scaffold. It was concluded that the porous scaffold based on PP-g-MMI could be used as a potential prototype bone graft.
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Analysis of body sliding along cable
Kozar, Ivica,Malic, Neira Toric Techno-Press 2014 Coupled systems mechanics Vol.3 No.3
Paper discusess a dynamic engineering problem of a mass attached to a pendulum sliding along a cable. In this problem the pendulum mass and the cable are coupled together in a model described by a system of differential algebraic equations (DAE). In the paper we have presented formulation of the system of differential equations that models the problem and determination of the initial conditions. The developed model is general in a sense of free choice of support location, elastic cable properties, pendulum length and inclusion of braking forces. Examples illustrate and validate the model.
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Establishing non-linear convective heat transfer coefficient
Cuculic, Marijana,Malic, Neira Toric,Kozar, Ivica,Tibljas, Aleksandra Deluka Techno-Press 2022 Coupled systems mechanics Vol.11 No.2
The aim of the work presented in this paper is development of numerical model for prediction of temperature distribution in pavement according to the measured meteorological parameters, with introduction of non-linear heat transfer coefficient which is a function of temerature difference between the air and the pavement. Developed model calculates heat radiated from the pavement back in the air, which is an important part of the heat trasfer process in the open air surfaces. Temperature of the pavement surface, heat radiation together with many meteorological parameters were measured in series during two years in order to validate the model and calibrate model parameters. Special finite element method for temperature heat transfer towards the soil together with the time integration scheme are used to solve the governing equation. It is proved that non-linear heat transfer coefficient, which is a function of time and temperature difference between the air and the pavement, is required to decribe this phenomena. Proposed model includes heat tranfer coefficient callibration for specific climate region, through the iterative inverse procedure.
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Inverse model for pullout determination of steel fibers
Kozar, Ivica,Malic, Neira Toric,Rukavina, Tea Techno-Press 2018 Coupled systems mechanics Vol.7 No.2
Fiber-reinforced concrete (FRC) is a material with increasing application in civil engineering. Here it is assumed that the material consists of a great number of rather small fibers embedded into the concrete matrix. It would be advantageous to predict the mechanical properties of FRC using nondestructive testing; unfortunately, many testing methods for concrete are not applicable to FRC. In addition, design methods for FRC are either inaccurate or complicated. In three-point bending tests of FRC prisms, it has been observed that fiber reinforcement does not break but simply pulls out during specimen failure. Following that observation, this work is based on an assumption that the main components of a simple and rather accurate FRC model are mechanical properties of the concrete matrix and fiber pullout force. Properties of the concrete matrix could be determined from measurements on samples taken during concrete production, and fiber pullout force could be measured on samples with individual fibers embedded into concrete. However, there is no clear relationship between measurements on individual samples of concrete matrix with a single fiber and properties of the produced FRC. This work presents an inverse model for FRC that establishes a relation between parameters measured on individual material samples and properties of a structure made of the composite material. However, a deterministic relationship is clearly not possible since only a single beam specimen of 60 cm could easily contain over 100000 fibers. Our inverse model assumes that the probability density function of individual fiber properties is known, and that the global sample load-displacement curve is obtained from the experiment. Thus, each fiber is stochastically characterized and accordingly parameterized. A relationship between fiber parameters and global load-displacement response, the so-called forward model, is established. From the forward model, based on Levenberg-Marquardt procedure, the inverse model is formulated and successfully applied.
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Simple factor analysis of measured data
Kozar, Ivica,Kozar, Danila Lozzi,Malic, Neira Toric Techno-Press 2022 Coupled systems mechanics Vol.11 No.1
Quite often we have a lot of measurement data and would like to find some relation between them. One common task is to see whether some measured data or a curve of known shape fit into the cumulative measured data. The problem can be visualized since data could generally be presented as curves or planes in Cartesian coordinates where each curve could be represented as a vector. In most cases we have measured the cumulative 'curve', we know shapes of other 'curves' and would like to determine unknown coefficients that multiply the known shapes in order to match the measured cumulative 'curve'. This problem could be presented in more complex variants, e.g., a constant could be added, some missing (unknown) data vector could be added to the measured summary vector, and instead of constant factors we could have polynomials, etc. All of them could be solved with slightly extended version of the procedure presented in the sequel. Solution procedure could be devised by reformulating the problem as a measurement problem and applying the generalized inverse of the measurement matrix. Measurement problem often has some errors involved in the measurement data but the least squares method that is comprised in the formulation quite successfully addresses the problem. Numerical examples illustrate the solution procedure.
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Yussef Esparza,Alejandro Huaiquil,Luz Neira,Allison Leyton,Mónica Rubilar,Luis Salazar,Carolina Shene 한국식품과학회 2011 Food Science and Biotechnology Vol.20 No.5
The effect of 8 factors [(with/without) daily mixing and moisture control, incubation time (t), temperature,ratio between dry substrate mass and bed’s cross section area (MA), inoculum size (spores/g), wheat germ content (WG), initial pH, and moisture content (M)] in the production of a prolyl endopeptidase (PEP) by Aspergillus niger ATCC 11414 in solid state fermentation (SSF) was tested. Contribution of all the factors was significant (p<0.05); main effects were those of MA, t, and M. The 4interactions that presented high interaction severity indexes involved the WG. Under optimized conditions PEP and protease activity were 9.76±0.06 and 3.6×10^6±1.5×10^5 U/kg,respectively. The enzyme was partially purified (ammonium sulfate precipitation, dialysis, DEAE-Sepharose ionexchange);it has a molecular weight of 66 kDa (SDSPAGE),and maximum activity was exhibited at pH 4 and 50°C. The enzyme is stable in a wide pH range (2.2-10)and at temperatures lower than 70^oC.
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Delay Tracking in Spaceborne GNSS-R Ocean Altimetry
Park, Hyuk,Valencia, Enric,Camps, Adriano,Rius, Antonio,Ribo, Serni,Martin-Neira, Manuel IEEE 2013 IEEE geoscience and remote sensing letters Vol.10 No.1
<P>Tracking, in radar altimetry, is the positioning of the waveforms in the correlation window. This letter presents a tracking strategy in spaceborne altimetry using global navigation satellite system reflectometry. First, the tracking procedure is illustrated, and the tracking parameters are discussed one by one: the determination of the correlation window, the accuracy of specular delay guess, and the tracking-refresh period. Based on the results, the proposed European Space Agency Passive Reflectometry and Interferometry System In-Orbit Demonstrator tracking case study is examined.</P>
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