Search

Copyright of Journal of Central European Agriculture is the property of Journal of Central European Agriculture and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Composites consisting of iron aluminide and iron silicide phases were studied in this work. Powders of iron aluminide and iron silicide were prepared by mechanical alloying separately. Subsequently, they were blended in three different proportions and sintered by the SPS method under various conditions. After sintering, the composites are composed of FeAl and amounts of other silicides (Fe5Si3 and Fe3Si). Ternary Fe–Al–Si phases were not determined, even though their presence was predicted by DFT calculations. This disagreement was explained by steric factors, i.e., by differences in the space lattice of the present phases. Hardness and tribological properties were measured on composites with various weight ratios of iron aluminide and iron silicide. The results show that sintered silicides with the matrix composed of iron aluminide reach comparable hardness to tool steels. The composites with higher mass ratios of iron aluminide than silicide have higher hardness and better tribological properties. [ABSTRACT FROM AUTHOR]

Questions: What are the main vegetation types of forest and shrubland vegetation in central and eastern Euxine Turkey and SW Georgia? What are the main environmental factors affecting their diversity? What is their syntaxonomic position? Can we integrate them into the European vegetation classification system? Location: Central and eastern Euxine Turkey and SW Georgia. Methods: We collected 3104 vegetation plots of forest and shrubland vegetation in the study region and performed Two‐Way Indicator Species Analysis (TWINSPAN) classification. We described vegetation types based on the classification results, expert knowledge and information from literature sources. We defined diagnostic species and prepared distribution maps for each vegetation type. To determine the most significant environmental variables on floristic differentiation, we used canonical correspondence analysis. Detrended correspondence analysis with passive projection of most significant environmental variables was run to interpret the environmental variation of vegetation types. Results: The studied vegetation was divided into 29 vegetation types related to seven main vegetation groups: relict Mediterranean forests and shrubland (mainly along the coastline, beside some inland localities), lowland to submontane forests, central Euxine mountain forests, eastern Euxine (Colchic) mountain forests, subeuxine forests, azonal riparian forests and subalpine and alpine shrubland. Elevation is the most important factor causing the differentiation in vegetation. It is followed by longitude and latitude. Among climatic variables, temperature seasonality, annual precipitation and precipitation of the wettest quarter are the most significant factors for vegetation differentiation. These factors correlate with the reduction of maritime climate and geomorphological features. Conclusions: Vegetation types mostly correspond to the syntaxa accepted in the EuroVegChecklist. However, some of them do not appear in the EuroVegChecklist since they appear only beyond Europe. We described three syntaxa as new: Abietion equi‐trojani, Querco cerridis‐Carpinion orientalis and Piceo orientalis‐Fagenion orientalis. The study revealed high vegetation diversity of the region that should be taken into consideration in ecosystem management and used as a reference in restoration and mitigation of the effects of global changes. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Central European Agriculture is the property of Journal of Central European Agriculture and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This work presents the possibilities of producing a substitute for a commercial matrix material for sintered metal–diamond tools which is characterized by increased tribological properties required in machining natural stones and concrete. In this study, the improvement in wear behavior of sintered pre-alloyed matrix caused by a thermal treatment was investigated. Several mixtures made of commercially available powders were homogenized by ball milling and consolidated at 900 °C using the spark plasma sintering (SPS) method. During cooling down, the specimens were subjected to isothermal holding at 350 or 250 °C for 1 h. After consolidation, all specimens were tested for density and hardness, whereas selected specimens were characterized by scanning electron microscopy (SEM) and flexural strength tests. The specimens made of BDCM50 powder (a mixture of the base and pre-alloyed powders in 50:50 proportion) shows excellent properties including σ0.2 = 1045 MPa in the three-point bending test and HV10 ≈ 380. Resistance to abrasive wear evaluated in both three-body and two-body conditions in the MWT abrasion test was estimated at A i 3 = 18.1 ± 3.9 μm/20 m and   A i 2 = 95.9 ± 11.8 μm/20 m, respectively. A series of diamond-impregnated specimens (segments) was also produced and tested for wear rate on abrasive concrete. The potential graphitization of the diamond grits was investigated using Raman spectroscopy and X-ray diffraction. As a reference, both the base Fe-Mn-Cu-Sn-C and commercially available Co+20%WC alloy were used to compare selected properties of the investigated materials. It has been proved that heat-treated specimens made of the base mixture modified with pre-alloyed powders are characterized by increased hardness and resistance to abrasive wear. The BDCM50 matrix has a negligible effect on diamond graphitization and shows excellent field performance, which makes it a good potential substitute for replacing Co+20%WC in sintered diamond-impregnated tools. [ABSTRACT FROM AUTHOR]

This article discusses methods for selecting criteria used for stopping iterative regularization methods applied to solving continuation of gravity observed at or outside the Earth's surface down to the geoid. This computational step is required for determination of the gravimetric geoid by the Stokes approach. For surface gravity data measured with spatial resolutions at the kilometer level and higher, their downward continuation becomes ill posed and its solution numerically unstable. Two iterative methods often used for solving this problem, namely the Landweber and conjugate gradient least-squares (CGLS) methods, are investigated using a sample of surface gravity data synthesized from a global gravitational model over a mountainous test area in Colorado, USA. Five different commonly used stopping criteria are applied to both iterative methods and neither of them, except L-curve, succeed to stop the iterative process at the reasonable solution. A simple approach is proposed to stop the iterative methods exploiting stochastic properties of surface gravity data. Results of numerical tests suggest that a rather simple stopping criterion based on stochastics parameters of surface gravity data estimated using a leave-one-out cross-validation procedure yields results superior to those based on the L-curve approach which is best performing among the five standard methods for selecting the stopping criterion. Results based on the Landweber method outperform those based on the CGLS method. Iterative methods based on optimum numbers of iterations represent an alternative to commonly used regularization techniques for solving ill-posed inverse problems, such as Tikhonov, that require optimal estimates of regularization parameters. L'article examine les approches de sélection de critères utilisés pour arrêter les méthodes de régularisation itératives appliquées à la résolution du prolongement jusqu'au géoïde de la gravité observée à la surface de la Terre ou en dehors de celle-ci. Cette étape computationnelle est nécessaire pour la détermination du géoïde gravimétrique par l'approche de Stokes. Pour les données de gravité de surface mesurées à des résolutions spatiales kilométriques ou supérieures, leur prolongement vers le bas devient mal posé et sa solution, numériquement instable. Deux méthodes itératives souvent utilisées pour résoudre ce problème, les méthodes de Landweber et des moindres carrées du gradient conjugué (MCGC), sont examinées en utilisant un échantillon de données de gravité de surface synthétisées à partir d'un modèle gravitationnel planétaire sur une région montagneuse expérimentale au Colorado (États-Unis). Cinq critères d'arrêt couramment utilisés sont appliqués aux deux méthodes itératives et aucun d'entre eux, sauf la << L-curve >>, n'arrive à arrêter le processus itératif sur une solution raisonnable. Une approche simple est proposée pour arrêter les méthodes itératives, qui exploite les propriétés stochastiques des données de gravité de surface. Les résultats d'essais numériques portent à croire qu'un critère d'arrêt assez simple reposant sur des paramètres stochastiques des données de gravité de surface estimés en utilisant une procédure de validation croisée de type << leave-one-out >> donne de meilleurs résultats que les critères basés sur l'approche L-curve, la méthode qui, des cinq méthodes standards, performe le mieux pour lasélection de critères d'arrêt. Les résultats basés sur la méthodede Landweber sont meilleurs que ceux basés sur la méthode MCGC. Les méthodes itératives reposant sur des nombres optimaux d'itérations représentent une solutionderechange aux techniquesde régularisation couramment employées pour résoudre des problèmes inverses mal posés, comme celle de Tikhonov, qui requièrent des estimations optimales des paramètres de régularisation. [Traduit par la Rédaction], 1. Introduction Stokes's solution of the gravimetric geoid from surface gravity data requires gravity anomalies to be known on the geoid. Thus, surface gravity values observed at the topography must [...]