Experimental evaluation and modelling of the boronizing kinetics of AISI H13 hot work tool steel

In the study for this contribution, the AISI H13 hot work steel was pack-boronized between 2 and 6 h of exposure time within the temperature range of 800 – 1000 °C. The boriding agent was composed of a powder mixture containing (in weight percent): 90 % of boron carbide (B4C) and 10 % of sodium tetrafluoroborate (NaBF4). The SEM observations showed a less pronounced jagged interface between the boronized layer and the transient zone. A double phase boride layer (FeB and Fe2B) was identified over the surface of AISI H13 steel with the presence of metallic borides inside this compound layer. The mean diffusion coefficient (MDC) method was applied to analyze the growth of iron borides (FeB and Fe2B) as compact layers over the surfaces of AISI H13 steel. The boron activation energies in the two iron borides were also assessed from the present kinetic approach by assuming the Arrhenius relationships. Afterwards, the kinetic model was checked experimentally by considering two extra boriding conditions (925 °C for 1 and 3 h). Finally, the predicted layer thicknesses are in accordance with experimental measurements.

EpCAM promotes endosomal modulation of the cortical RhoA zone for epithelial organization

At the basis of cell shape and behavior, the organization of actomyosin and its ability to generate forces are widely studied. However, the precise regulation of this contractile network in space and time is unclear. Here, we study the role of the epithelial-specific protein EpCAM, a contractility modulator, in cell shape and motility. We show that EpCAM is required for stress fiber generation and front-rear polarity acquisition at the single cell level. In fact, EpCAM participates in the remodeling of a transient zone of active RhoA at the cortex of spreading epithelial cells. EpCAM and RhoA route together through the Rab35/EHD1 fast recycling pathway. This endosomal pathway spatially organizes GTP-RhoA to fine tune the activity of actomyosin resulting in polarized cell shape and development of intracellular stiffness and traction forces. Impairment of GTP-RhoA endosomal trafficking either by silencing EpCAM or by expressing Rab35/EHD1 mutants prevents proper myosin-II activity, stress fiber formation and ultimately cell polarization. Collectively, this work shows that the coupling between co-trafficking of EpCAM and RhoA, and actomyosin rearrangement is pivotal for cell spreading, and advances our understanding of how biochemical and mechanical properties promote cell plasticity.

Investigation of the formability behaviour of optimized tufted and un-tufted multi-layer carbon preforms during the stamping process

The originality of this work consists of studying the stamping behaviour of tufted and un-tufted multi-layer carbon preforms. Several tufted preforms with different stratifications have been manufactured. The stamping test was carried out using a hemispherical punch and conducted at two blank-holder pressures (0.05 and 0.2 MPa). The experimental data show that the addition of tufting yarn, the number of layers and the blank-holder pressure significantly affected the forming behaviour: the tufted preform presents a higher punch force, lower material drawin and shear angles with significant structural defects than the un-tufted preform. The increase of the blank-holder pressure increases all these characteristics and emphasizes the structural defects on the fibrous reinforcements. Similarly, the transition from two layers to four layers lamination at the same blank-holder pressure is followed by an increase of the punch force, reducing the material draw-in and the shear angles especially those measured at the transient zone, and causes more structural defects on all stamped preforms. Therefore, two localized tufting configurations, Right Localized Tufted and Inclined Localized Tufted, at the stamping transition area have been proposed. The results show that these two configurations present a minimum punch force and a maximum material draw-in similar to those measured on the un-tufted structure. The shear angles are much greater than those recorded on the conventionally (fully) tufted preform. Thus, the localized tufting in the most stressed areas proves to be the most suitable solution for the stamped preforms.

A new molecular method for the exploration of hybrid zones between two toad species of conservation interest

Analyzing hybrid zones between previously isolated lineages allows insight into processes determining the fate of re-encounter of these taxa. The distributions of Fire-bellied (Bombina bombina) and Yellow-bellied toads (B. variegata) meet in the Carpathian Basin resulting in a narrow contact zone in the foothill regions, where hybrids often appear. Our aim was to explore a transient zone between B. bombina and B. variegata within the Carpathian Basin along a transect including the Börzsöny Hills in Hungary and Krupinská Planina in Slovakia. We visited 28 locations in these areas and collected altogether 230 specimens, photographed and sampled them using buccal swabs. In order to distinguish between the two species and determine hybrid individuals, we used mitochondrial markers and designed a novel technique based on the restriction of the Ncx-1 gene. The geographical distribution pattern of these two species delivered unexpected results, as Börzsöny Hills was completely colonised by B. bombina including locations which can be classified as typical habitats of B. variegata. Moreover, in Krupinská Planina many locations were also colonised by B. bombina, including high altitude ponds. The most remote sites still harbour B. variegata populations, but seven of these were found with hybrid individuals. This pattern may indicate the northward and altitudinal range expansion of B. bombina and the colonisation of habitats of its sister species in these areas. Our results warrant enhanced attention to hybrid zones, where introgression and changes in population composition may reflect recent rapid environmental alterations and redirect conservation focus.

Diatomic compounds in the soils of bee-farm and nearby territories in Samarskaya oblast

This article sheds light on the role diatomic algae in soils play in the assessment of bee farm and nearby territories in four soil and landscape zones in Samarskaya Oblast. The community of diatomic algae is characterized by low species diversity, of which 23 taxons were found. The most often found species are represented by Hantzschia amphioxys (Ehrenberg) Grunow in Cleve & Grunow and Luticola mutica (Kützing) D.G.Mann in Round et al. The maximum of phyla (18) were found in the buffer (transient) zone; in the wooded steppe zone, 11 species were recorded; in the steppe – 2 species, and in the dry steppe zone no species of diatomic algae were found. The qualitative and quantitative characteristics of diatomic algae communities in various biotopes depend on the natural and climate features of a territory and the degree of the anthropogenic impact on the soil and vegetation, which is proved by the fact that high species wealth signifies that the ecosystem is stable and resilient to the changing conditions in the environment, while poor algal flora is less resilient due to the lower degree of diversity.

Effect of Shear Overloads on Crack Propagation in Al-7075 Under In-Plane Biaxial Fatigue Loading

A cruciform specimen of Al 7075-T651 is used to study crack propagation behavior in an in-plane biaxial fatigue loading subjected to shear overloads of different magnitudes, which were applied at different crack lengths. The microscale fracture features of the specimen were identified and compared for the pre-overload region, overload region, and post-overload region at two different values of crack lengths, using scanning electron microscopy (SEM). It was observed that the transient region, created by the application of the shear overload, improved the fatigue life of the specimen. The overload also displayed an instant upsurge in the fatigue crack growth rate, which was immediately followed by a sharp crack retardation. The crack growth rate was restored once it came out of the transient zone and traveled a distance equal to the value of recovery distance. Both, the magnitude of the applied shear overload and the location of overload with respect to crack length seemed to affect the size of the transient zone, fatigue life, crack growth rate, and recovery distance. Investigations made on the fracture surfaces revealed that there is no significant change in the microscale fracture features when the overload was applied at different values of crack lengths; however, a clear and significant difference in the fracture features appear when the surfaces of the pre-overload region, overload region, and post-overload region are compared.

Influence of Subflux Turbulence Controller and Ladle Shroud Asymmetric Using on Hydrodynamic Conditions in One Strand Slab Tundish

The tundish plays a key role in the process of continuous steel casting (CSC), as it ensures a stable flow of steel to the mould. Therefore, particular attention is paid to the behavior of liquid steel in the tundish. A wedge-shape tundish with a nominal capacity of 30 tons was tested. The present study has examined different variants of subflux turbulence controller (STC) and ladle shroud (LS) positions relative to one another. For the designed continuous casting variants with the modified tundish pouring zones, numerical simulations of liquid steel behavior were performed. From the computer simulations results, motion, velocity magnitude, and temperature of liquid steel were obtained. Moreover the shares of stagnant volume flow, dispersed plug flow, well-mixed volume flow and transient zone were calculated. It is possible to effectively modify the hydrodynamic conditions by appropriate selection the position of the STC and LS.

Investigation of Flux-Less Soldering of Metal Matrix Composite and Ceramics by Use of Zn Solder

The work was dealing with direct soldering of Al2O3 ceramics and a metal/ceramic composite (MMC) with Al matrix. The joints were fabricated by application of flux-less process by use of a hot plate at the assistance of ultrasound with frequency of 40 kHz. The experiments were performed by use of Zn6Al6Ag solder. Wetting was attained on both substrates. The joints of a good quality were fabricated. The soldering temperature was 420 °C. The microstructural studies of interface have revealed a transient zone of Al dissolving on the side of MMC and formation of Zn oxides on the side of ceramics, which were responsible for bond formation.

New explicit correlations for turbulent flow friction factor

Two new correlations of single-phase friction factor for turbulent pipe flow are shown in this paper. These two formulas are actually explicit approximations of iterative Colebrook's relation for calculation of flow friction factor. Calculated friction factors are valid for whole turbulent flow including hydraulically smooth and rough pipes with special attention on transient zone of turbulence between them. Hydraulically smooth regime of turbulence does not occur only in total absence of roughness of inner pipe surface, but also, four new relations for this theoretical regime are presented. Some recent formulas for turbulent flow friction calculation are also commented.

Evolutionary Optimization of Colebrook’s Turbulent Flow Friction Approximations

This paper presents evolutionary optimization of explicit approximations of the empirical Colebrook’s equation that is used for the calculation of the turbulent friction factor (λ), i.e., for the calculation of turbulent hydraulic resistance in hydraulically smooth and rough pipes including the transient zone between them. The empirical Colebrook’s equation relates the unknown flow friction factor (λ) with the known Reynolds number (R) and the known relative roughness of the inner pipe surface (ε/D). It is implicit in the unknown friction factor (λ). The implicit Colebrook’s equation cannot be rearranged to derive the friction factor (λ) directly, and therefore, it can be solved only iteratively [λ = f(λ, R, ε/D)] or using its explicit approximations [λ ≈ f(R, ε/D)], which introduce certain error compared with the iterative solution. The optimization of explicit approximations of Colebrook’s equation is performed with the aim to improve their accuracy, and the proposed optimization strategy is demonstrated on a large number of explicit approximations published up to date where numerical values of the parameters in various existing approximations are changed (optimized) using genetic algorithms to reduce maximal relative error. After that improvement, the computational burden stays unchanged while the accuracy of approximations increases in some of the cases very significantly.