Stabilizing effects of Ag doping on structure and thermal stability of FeN thin films

In this work, we investigated the effect of Ag doping (2-20 at.%) on the phase formation of iron mononitride (FeN) thin films. Together with deposition of FeN using reactive dc magnetron sputtering, Ag was also co-sputtered at various doping levels between 2-20 at.%. We found that doping of Ag around 5 at.% is optimum to not only improve the thermal stability of FeN but also to reduce intrinsic defects that are invariably present in (even in epitaxial) FeN. Conversion electron Mössbauer spectroscopy and N K-edge x-ray near edge absorption measurements clearly reveal a reduction of defects in Ag doped FeN samples. Moreover, Fe self-diffusion measurements carried out using secondary ion mass spectroscopy depth-profiling and polarized neutron reflectivity in 57Fe enriched samples exhibit an appreciable reduction in Fe self-diffusion in Ag doped FeN samples. Ag being immiscible with Fe and non-reactive with N, occupies grain-boundary positions as nanoparticles and prohibits the fast Fe self-diffusion in FeN.

THE STRENGTH OF NANOCOMPOSITES POLYMER / 2D-NANOFILLER WITH ULTRASMALL FILLER CONTENTS

The theoretical model, using the notions of fractal analysis is proposed for description of strength of nanocomposites polymer/2D-nanofiller on the example of nanocomposites polyvinylalcohol/boron nitride. For correct description of strength of these two-phase nanomaterial the knowledge of initial characteristics of matrix polymer (stress of fracture), geometrical parameters of nanofiller and level of interfacial adhesion polymer matrix-nanofiller is necessary. The indicated level, characterizing by shear interfacial strength, was determined theoretically within the framework of fractal conception of adhesion. Its absolute values found high enough – they are comparable with this characteristic in systems polymer-carbon nanotubes and are higher essentially than in systems polymer-microfiber (glassy and carbon fibers). This factor defines high enough strength of the considered nanocomposites. The important factor for fracture process of nanomaterials is aggregation of initial platelets of nanofiller, which forms “packets” (tactoids) of such platelets. The relatively small aggregation degree of nanofiller gives appreciable reduction of strength of nanocomposites polymer/2D-nanofiller. The indicated reduction is connected with transition of 2D-nanofiller structure from exfoliated to intercalated one, i.e. from separate platelets to their tactoids.

SEASONAL PATTERNS OF SPRING DISCHARGE AT SILVER FALLS, CROSBY COUNTY, TEXAS

Beneath the high plains of the Llano Estacado lies the southern extension of the Ogallala aquifer, which provides a key source of groundwater for the region. Along the eastern fringes of the Llano Estacado one can find numerous natural springs that discharge from the Ogallala formation and provide a valuable source of freshwater. Large-scale irrigation has altered hydrological conditions, which has influenced the flow of springs along the eastern escarpment. In late 2012, the author began a study of one such spring located at Silver Falls in Blanco Canyon, east of Crosbyton, Texas. The goal was to monitor the discharge of this naturally flowing spring over a period of many years to establish temporal patterns. Measurements of spring flow rates over a seven-year period did not show an appreciable reduction associated with the depletion of the Ogallala aquifer; however, discharge was found to follow a seasonal pattern of declining flow during the summer followed by a recovery starting in late fall and reaching maximum discharge during winter and early spring. Whereas seasonal variations of spring discharge can be measured precisely, the cause of these seasonal patterns is less certain. It is likely that the combined effects of seasonal groundwater extraction for irrigation and the growth and transpiration of natural vegetation contribute to the observed seasonal patterns of groundwater discharge at Silver Falls.

ZnS/CuFe2O4: Magnetic Hybrid Nanocomposite to Catalyze the Synthesis of 2,4,5-triaryl-1H-imidazole Derivatives

Integration of nanomaterials is an entirely new method to synthesis efficient catalysts. These compounds provided new characteristics and distinctive application which is not accessible in the single-particle nanostuctures. Although there is little catalytic activity in each component of the hybrid material, their hybrid displays much higher activity. Indeed, the presence of intermediate metal and their oxides in the framework of hybrid catalyst caused a synergistic effect, thus facilitate the organic reaction more effectively. The extensive biochemical and pharmacological activities of imidazole-containing compounds have required the development of efficient methods for synthesizing these compounds, which is a significant topic in organic chemistry. The imidazole nucleus function as a main scaffold for constructing of biologically important molecules. The ZnS/CuFe2O4 magnetic hybrid nanocatalyst was synthesized by a simple co precipitation and characterized by conventional analyses successfully. Synthesized nanocomposite was utilized as a magnetic and heterogeneous catalyst for the one-pot synthesis of 2,4,5-triaryl-1H-imidazole derivatives with condensation of various aromatic aldehydes, benzil and ammonium acetate. The presented method shows some advantages such as mild conditions, good yields, and simple separation of products from the reaction mixture and cost-effective catalyst. The experimental data showed ZnS/CuFe2O4 nanocatalyst were easily separated from the reaction mixture using an external magnetic field and use again five times in subsequent reactions without appreciable reduction in catalytic activity.

Smallholder Farmers’ Market Participation: Concepts and Methodological Approach from Sub-Saharan Africa

This paper reviews the empirical evidence on smallholder farmers’ market participation focusing on cash/food crops and livestock in Sub-Saharan Africa (SSA) with special attention on the methodological approaches employed in this region in an attempt to x-ray these methods, identifying their advantages and limitations and possible means smallholder farmers would be able to transit from subsistence to commercialised agriculture capable of lifting them out of poverty trap that seems to have engulfed many rural SSA. This paper recommends interventions geared towards improving smallholder farmers’ organisation, producers’ association and ensuring appreciable reduction in transaction costs and also improving farmers’ access to productive assets and improved technologies capable of stimulating profitable smallholders’ market participation.

Effects of Electromagnetic Field Use on Jaw Bone Densification

The working hypothesis started from the premise of the benefits of the electromagnetic field therapy (EMFT) benefits in order to densify the periodontal bone tissues. The objective of this study was to quantify the results of using this therapy with the Electronic Doctor Stem Generator (EDSG) in the densification of affected alveolar bone tissues by clinical and radiological examinations. The study was performed on 30 patients, who benefited from adjuvant therapy in the electromagnetic field (EMF) with the EDSG device after performing the specific dental treatments. We applied these very low-frequency EMF bioactivation treatment delivered by EDSG device, 30 daily exposures for a 2-hour interval. The results proved the appreciable reduction of teeth mobility, the reduction of periodontal pockets depth and the bone regeneration in the regions exposed to the EMF produced by EDSG device. EMF adjuvant therapy with EDSG device is an innovative, atraumatic and non-invasive therapy.

Experimental evaluation of selective laser melting process for optimized lattice structures

Lattice structures fabricated with micromelting of metal powders are promising solutions for lightweight applications. Additive manufacturing processes as selective laser melting are largely used to build bulk components, but the influence of laser settings on lattice struts morphology is not jet fully investigated. Previous studies demonstrate the effect of laser speed and layers thickness on the material density and lattice struts dimensions. In this paper, the effects of the laser volume energy density associated with the process setup parameters are analyzed in relation to the dimensional accuracy of lattice struts. The statistical approach based on design of experiments used in this paper allows getting appreciable reduction of the average errors of struts dimensions (from 48% to 16% and from 22% to 7% in horizontal and vertical orientations, respectively).

FACILE FUNCTIONALIZATION OF sp2 CARBON ALLOTROPES WITH A BIOBASED JANUS MOLECULE

ABSTRACT A simple, versatile, sustainable, not expensive method for the functionalization of sp2 carbon allotropes, both nano-sized and nano-structured, without altering their bulk crystalline organization, is presented. Carbon materials available at the commercial scale were used: furnace carbon black (CB), nano-sized graphite with high surface area, and multiwalled carbon nanotubes. A bio-sourced molecule, 2-(2,5-dimethyl-1H-pyrrol-1-yl)-1,3-propanediol (serinol pyrrole), was used for the functionalization. Serinol pyrrole (SP) was obtained from serinol through a reaction with atomic efficiency of about 82%, performed in the absence of solvents or catalysts. Synthesis of serinol pyrrole was performed as well on carbon allotropes as the solid support. Adducts of serinol pyrrole with a carbon allotrope were prepared with the help of either thermal or mechanical energy. Functionalization yield was in all cases larger than 90%. With such adducts, stable dispersions in water and in NR latex were prepared. A few layers of graphene were isolated from the water dispersions, and NR-based composites precipitated from the latex revealed very even distribution of fine graphitic particles. Composites were prepared, based on NR, IR, and BR as the rubbers and CB and silica as the fillers, with different amounts of CB–SP adduct, and were cross-linked with a sulfur-based system without observing appreciable effect of functionalization on vulcanization kinetics. The CB–SP adduct led to appreciable reduction of the Payne effect.

Influencia de la proporción de ácido esteárico en las propiedades de almidón modificado con ácido esteárico

Antecedentes: Usualmente se han realizado modificaciones de almidón (Alm) con ácido esteárico (AE) en solución y empleando como catalizador persulfato de potasio. Objetivo: En este estudio se evaluó la influencia de la proporción de AE en las propiedades estructurales, térmicas, reológicas y morfológicas de muestras de Alm-AE obtenidas empleando el ácido p-toluensulfónico (p-TAS) como catalizador. Metodología: Las muestras de Alm-AE fueron preparadas usando un reómetro de torque. Las respectivas cantidades de Alm, AE y p-TAS (4 %), fueron llevadas al reómetro y mantenidas a 100 °C y una velocidad de agitación de 50 rpm. En todos los casos el tiempo de mezclado fue de 20 min. Las relaciones en peso de Alm:AE empleadas para obtener los materiales, fueron las siguientes: 70:30 (AE30), 60:40 (AE40) y 50:50 (AE50). Resultados: Se observó que después del incremento en el torque debido a la fusión del AE, se presentó otro aumento en éste, lo cual se atribuyó a la reacción de esterificación entre el Alm y el AE. El grado de esterificación incrementó con la cantidad de AE empleada en la preparación de los materiales. La modificación del Alm con el AE, causó una apreciable reducción de la cristalinidad de las muestras de Alm-AE. La muestra AE40, mostró el mayor comportamiento elástico. La muestra AE30 presentó el comportamiento más viscoso. Conclusión: Este estudio permitió obtener muestras de Alm-AE por un proceso en fundido y sin el uso de solventes orgánicos. La modificación del Alm con el AE, afecta las propiedades estructurales, térmicas y morfológicas de Alm.Palabras clave: Almidón, ácido esteárico, propiedades. AbstractBackground: usually have been realized modifications of starch (Alm) with stearic acid (AE) in solution and by employing as catalyzer potassium persulfate. Objective: In this study was evaluated the influence of the proportion of AE on the structural, thermal, rheological and morphological properties of the samples Alm-AE obtained employing p-toluenesulfonic acid as catalyzer. Methods: the samples Alm-AE were prepared by using a torque rheometer trade mark Thermo Scientific. The respective amounts of Alm, AE and p-TAS (4 wt%), were carried out to the rheometer and kept at 100 °C and to stirring rate of 50 rpm. In all cases the mix time was 20 min. The weight ratio ofAlm-AE employed for obtaining the materials were the following: 70:30 (AE30), 60:40 (AE40) y 50:50 (AE50). Results: It was observed that after of the increasing on torque due to melting of AE, was presented another enhance in this, which was attributed to the esterification reaction between Alm and AE. Esterification degree increased with the AE amount employed in the preparation of the materials. The modification of the Alm with AE, caused an appreciable reduction of the crytallinity of the samples Alm-AE. The sample AE40, showed highest elastic behavior. The sample AE30 presented highest viscous behavior. Conclusions: this study allowed to obtain samples of Alm-AE by a molten process without use of organic solvents. The modification of Alm with AE, affect the structural, thermal and morphological properties of the Alm.Keywords: starch, stearic acid, properties.

Vibration Control by Time Delayed Linear and Non-Linear Acceleration Feedback

The forced Duffing oscillator is investigated by time-delayed linear and nonlinear acceleration feedbacks. The method of Slowly Varying Parameter (SVP) can efficiently develop frequency response curves with stability of solutions. Appreciable reduction in peak value of response and gradual reduction in the skew-ness in frequency response curve is observed with the introduction of gain and delay. For some values of control parameters the entrainment phenomena are also observed. Appropriate choice of gain and delay parameters are made from the primary stability zone of linear stability analysis graph. The results obtained by this method are compared with numerical integration (NI) method and they are in good agreement.