Quadratic optimal controller to stabilise symmetrical systems

In this paper, we design a controller for stabilising a control system. The technique used for designing the controller includes a linear regulator and an asymptotical observer which form the controller. The linear regulator designed is a feedback of estimated states and also it must minimise a quadratic performance index. The gain matrix of optimal feedback is obtained by solving the Riccati equation, whilst the gain observer matrix is computed by making use of symmetrical systems properties. The properties of symmetrical systems allow us to find the optimal gain matrix of the observer without solving the dual Riccati equation, we only need to compute the matrices of controllability and observability. Having calculated the gain matrices of regulator and of observer, we proceeded to compute the transfer function of the observer-based controller.     

Standsicherheitsuntersuchung für ein räumliches Böschungssystem – Berechnung mit einem zusammengesetzten dreidimensionalen Bruchmechanismus und Modellversuch im Gelände – Teil 3: Modellversuch und Schlußfolgerungen

Stability analysis for a three‐dimensional slope system – calculation with a composed rigid body failure mechanism and model test in an open site. Part 3: Model test. In Part 1 and 2 of this paper a movable three‐dimensional composed rigid body failure mechanism for the graben‐like rupture of a high three‐dimensional slope system in open‐cast lignite mines during working in small windows is developed. For various geometrical proportions the safety factor is calculated. In the Part 3, a model test is described performed in an open site in the scale 1:50 to verify the assumed kinematics of failure. The slope bodies were formed from a medium sand, the deep sliding clay layer from a highly plastic clay prepared with a high water content. The movements were measured by means of photogrammetry of the surface and by embedded columns of coloured sand. The failure took place approximately under the predicted width of the window. The slip surfaces which had to be expected in case of the corresponding plane strain situation developed as thin plane shear bands in the predicted position and inclination. However, the slip surfaces assumed and predicted additionally because of the three‐dimensionality in the calculation were observed as not sharply bounded spatial shear zones. The rigid body motions were superimposed by continuous strain fields. The average directions of the displacements corresponded to the assumed failure mechanism. At the end the conclusions of the complete investigation are presented.     

Standsicherheitsuntersuchung für ein räumliches Böschungssystem – Berechnung mit einem zusammengesetzten dreidimensionalen Bruchmechanismus und Modellversuch im Gelände – Teil 2: Durchführung der Berechnung und Ergebnisse

Stability analysis for a three‐dimensional slope system – calculation with a composed rigid body failure mechanism and model test in an open site. Part2: Execution of the calculation and results. To determine the safety factor against a three‐dimensional graben rupture on a high rim slope of an open‐cast lignite mine a three‐dimensional composed rigid body failure mechanism is outlined and calculated. The basic relations and equations are presented in part 1 of this paper. In the part 2 the execution of calculation, the optimization of the failure mechanism and typical results are described.     

Some contributions to mechanical behaviors of lacustrine deposit in Bogota,Colombia

This paper presents the mechanical behaviors of the lacustrine deposit,a representative soil in Bogota,Colombia.Initially,the physical characterization of the deposit is performed via laboratory tests(grain size distribution,scanning electron microscopy,Atterberg limits and water content).This characterization intends to explain the special characteristics of the mechanical behaviors of this soil.Then,various triaxial tests are carried out with controlled loading path,strain rate change,relaxation,extensile stress,and cyclic loading.The test results reveal the shape of the yield curve for Bogota soil(in a natural state),and also show that an increasing effect of the strain rate depends on the liquid limit.This effect is also preserved with extensile stresses(which are poorly studied in soil mechanics).Finally,other effects,such as the loss of structure in the reconstituted samples and the effect of shear modulus at low strains,are studied for Bogota soil.     

Antioxidant activity and polyphenol content of aqueous extracts from Colombian Amazonian plants with medicinal use

The total phenol and flavonoid contents of 19 Amazonian plants and their related antioxidant activities were determined. The extracts from the plant leaf, bark, root, fruit and/or stem were prepared as infusions, as are traditionally used in popular medicine. Total phenols ranged from 0.8 to 22.2 mg gallic acid equivalents/g and flavonoids from 0.0 to 10.2 mg catechin equivalents/g, by using Folin–Ciocalteau and aluminium chloride colourimetric methods. Differences were observed in phenol and flavonoid contents at the organic level, the leaf presenting greater values than the stem. All the extracts showed different degrees of antioxidant activity with TEAC, 1.1 up to 117.4 and ORAC, 7.8 up to 359.1 μmol Trolox equivalents/g. These values correlated with total phenol content (r² = 0.90) and flavonoid content (r² = 0.70 for TEAC; r² = 0.76 for ORAC). Piper putumayoense, Piper glandulosissimum, Piper krukoffii and Senna reticulata leaves and Brownea rosademonte bark showed elevated antioxidant activities, thus representing promising plant-sources of medicine.     

Mechanical properties of sodium and potassium activated metakaolin-based geopolymers

In this study, a set of mechanical properties of geopolymers, synthesized by alkali (NaOH or KOH) activation of metakaolin and SiO₂ mixture, were characterized at ambient temperature. Samples with K/Al or Na/Al atomic ratios equal to 1, Si/Al atomic ratios in the 1.25–2.5 range and H₂O/Al₂O₃ molar ratios of 11 or 13 are cured at 80 °C for 24 and 48 h before characterization, to determine effect of Si/Al ratio and curing time on the structure and mechanical properties of geopolymers. The structure of synthesized geopolymers characterized using XRD, NMR, SEM, and density measurements was correlated to their mechanical properties, including compressive strength, Young’s modulus, hardness, and fracture toughness. The results of this study suggest a strong effect of Si/Al ratios (in the 1.5–2 range), density, and microstructure on the maximum strength, Young’s modulus, and hardness of geopolymers. There were also notable differences in strength between samples cured for 24 and 48 h, suggesting that the degree of geopolymerization reaction also plays important role in mechanical properties of this new class of inorganic polymers.     

Prediction of Permanent Deformations in Pavements Using a High-Cycle Accumulation Model

The present paper discusses the application of a high-cycle accumulation (HCA) model originally developed for sand for the prediction of permanent deformations in an unbound granular material (UGM) used for base and subbase layers in pavements. Cyclic triaxial tests on precompacted samples of an UGM have been performed in order to validate and calibrate the model. The stress amplitude, the initial density, and the average stress were varied. The test results are compared to those of air-pluviated samples of sand (subgrade material). Some significant differences in the behavior of both materials under cyclic loading are outlined. It is demonstrated that the functions describing the intensity of accumulation can be maintained for an UGM with different material constants, but that the flow rule must be generalized in order to describe the anisotropy. Recalculations of the laboratory tests show a good prediction of the modified HCA model.     

Attention to instruction directed to another by U.S. Mexican-heritage children of varying cultural backgrounds.

Children commonly observe and pitch in to ongoing activities in Indigenous communities of Mexico, according to ethnographic research. The present study examines the generality of this approach to learning by comparing its use among Mexican immigrants of two cultural backgrounds in the United States. Results showed more sustained attention to (and learning from) instruction directed to another person by 22 U.S. Mexican-heritage 6- to 11-year-old children whose families likely have experience with Indigenous practices (and limited involvement in Western schooling), compared with 16 U.S. Mexican-heritage children whose families have extensive involvement in Western schooling (and related practices). (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Stearic acid as interface modifier and lubricant agent of the system: Polypropylene/calcium carbonate nanoparticles

The toughness and the rheology of polypropylene (PP)‐calcium carbonate (CaCO₃) nanocompounds using stearic acid as an interface modifier were studied in this work. Compounding of the nanocomposites was carried out with a twin‐screw extruder. The benchmark samples (untreated) and stearic acid‐treated CaCO₃ nanoparticles were characterized by Fourier transform infrared (FTIR) spectroscopy. The nanocompounds were characterized by impact test, tensile test, scanning electron microscopy (SEM), rheological analysis, and differential scanning calorimetry (DSC). The elongation‐at‐break and impact resistance were increased in nanocompounds with interface modifier (stearic acid in hopper of the extruder). Nanocompounds with stearic acid showed the best dispersion state. Stearic acid helps to reduce complex viscosity acting as a lubricant, reducing frictional forces between nanoparticles of calcium carbonate (NCC) and PP chains. Nanocompounds with better dispersion state had crystallization temperatures very similar to the PP homopolymer. POLYM. ENG. SCI., 59:E279–E285, 2019. © 2019 Society of Plastics Engineers