Comparison of abrasive wear behavior of ductile iron with different dual matrix structures

Abrasive wear behavior of ductile irons with different dual matrix structures has been investigated. In order to obtain ductile irons with different dual matrix structures an unalloyed ductile iron specimens were austenitized in the two-phase region (α + γ) at various temperature (795 °C and 815 °C) and then rapidly transferred to a salt bath held at the 365 °C for austempering for 30, 90 and 120 min. Some specimens were quenched from same intercritical austenitizing temperatures and tempered at 550 °C for 60 and 300 min. Some specimens were also conventionally austempered and/or quenched from 900 °C for comparison. Experimental results showed that, the tensile strength increased and ductility decreased with increasing martensite volume fraction in the specimen with martensite dual matrix structure. By increasing the tempering time, the yield and UTS decreased and ductility increased. In addition, the specimens with ausferrite dual matrix structures exhibited much greater ductility than conventionally austempered ones. The tensile strength increased while ductility decreased with increasing ausferrite volume fraction. Furthermore in all austenitized specimens, the abrasive weight loss of austempered specimens (A series) was lower than those of quenched specimens (Q series) irrespective of all loads due to increased AFVFs and total elongation. It was shown that wear loss of both tested materials in abrasive wear was proportional to the applied load. However, there was a decreasing trend in the weight loss of the A795 with dual matrix structure austempered for 30 and 90 min with increasing load. The reason was because of the fact that the specimen surface was work hardened with cutting efficiency of the abrasive reduced through clogging, and attrition jointly leading to less weight loss. Moreover, increasing the austempering time caused more ductile ausferritic structure to displace hard martensite. In all austempered samples, the abrasive weight loss increased with increasing the austempering time. As for the case of Q samples, the abrasive weight loss increased more or less linearly with load since an increase in the applied load might increase the contact stress. Among the Q samples, the highest weight loss was obtained for the Q795-300, Q815-300 sample because of lower martensite volume fraction, but the lowest weight loss was observed for the Q900 sample due to the highest martensite volume fraction. For Q900 samples, the amount of fracture of the abrasives was found to be increase with the harder specimen, and it may have contributed somewhat to the increased wear.Furthermore, microchips were dominant wear mechanism by cutting mode for higher ductile materials while micro-ploughing was predominant wear for harder materials, but wear also occurred by combinations of ploughing and embedding particles into the surface for Q samples. Cross-section examination by SEM through the wear surfaces revealed that a more smoother surface was observed for the A795 sample than that of the Q795 sample. However, a more rougher surface was observed for the A900-120 sample than that of the Q900 sample.     

Chromatin-unstable boar spermatozoa have little chance of reaching oocytes in vivo

In the present study, the prevalence of chromatin instability in the fertilizing-competent sperm population in the porcine oviduct in vivo was examined through qualitative analysis of the chromatin structure status of accessory boar sperm found in in vivo-derived embryos. The binding of chromatin-unstable sperm to oviductal epithelium in vitro was also studied. To examine the sperm chromatin state, a modified fluorescence microscopic sperm chromatin structure assay was used. Among a population of 173 fertile boars, individuals were selected for according to their chromatin status: 25 animals showed more than 5% of chromatin-unstable sperm in their ejaculates, and 7 showed consistently elevated percentages of chromatin-unstable sperm in three successively collected semen samples. A positive correlation was found between incidence of chromatin instability and attached cytoplasmic droplets (r=0.44, P<0.01). Analyses of accessory spermatozoa from in vivo-derived embryos demonstrated that the proportion of chromatin-unstable sperm was significantly (P<0.05) reduced in the population of fertilizing-competent sperm in the oviduct compared with the inseminated sperm. Populations of sperm bound to the oviduct in vitro had significantly (P<0.05) lower percentages of chromatin instability than in the original diluted semen sample. In conclusion, numbers of sperm with unstable chromatin are reduced in the oviductal sperm reservoir, possibly because of associated changes in the plasma membrane that prevent sperm from binding to the oviductal epithelium. We conclude that in vivo the likelihood that sperm with unstable chromatin will reach the egg and fertilize it is low.     

Control of Aspergillus flavus with essential oil and methanol extract of Satureja hortensis

The essential oil and methanol extract of Satureja hortensis were tested for antifungal activity against Aspergillus flavus in vitro on Petri plates and liquid culture, and under storage conditions. The oil showed strong antifungal activity based on the inhibition zone and minimal inhibitory concentration values against the pathogen on Petri plates assays. The very low concentrations of them also reduced wet and dry mycelium weight of pathogen fungus in liquid culture. When the oils at 25, 12.5 and 6.25 microl/mL concentrations were applied to lemon fruits before seven days of pathogen inoculation on storage conditions, the decay on fruits caused by the pathogen could be prevented completely. The results in this study showed that the essential oil of S. hortensis had strong antifungal activity against pathogen fungi tested. So, the essential oil of S. hortensis could be used for management of this pathogen as a potential source of sustainable eco-friendly botanical fungicides.     

Assessment of gas radiative property models in the presence of nongray particles

In this study, a radiation code based on the method of lines solution of the discrete ordinates method for the prediction of radiative heat transfer in nongray gaseous media is developed by incorporation of two different spectral gas radiative property models, banded spectral line-based weighted sum of gray gases (banded SLW) and gray wide band (GWB) approximation in the presence of nongray absorbing–emitting–scattering particles. The aim is to introduce an accurate and CPU efficient spectral gas radiation model, which is compatible with spectral fuel/ash particle property models. Input data required for the radiation code and its validation are provided from two combustion tests previously performed in a 300 kWt atmospheric bubbling fluidized bed combustor test rig burning low calorific value Turkish lignite with high volatile matter/fixed carbon (VM/FC) ratio in its own ash. The agreement between wall heat fluxes and source term predictions obtained by global and banded SLW models reveal that global SLW model can be converted to an accurate wide band gas model (banded SLW) which can directly be coupled with spectral particle radiation. Furthermore, assessment of GWB approximation by benchmarking its predictions against banded SLW model shows that GWB gives reasonable agreement with a higher CPU efficiency when the particle absorption coefficient is at least in the same order of magnitude with the gas absorption coefficient.     

Determination of the Junction Recombination Velocity Initiating the Short Circuit Situation Sfsc of a Bifacial Silicon Solar Cell Irradiated Under Magnetic Field in Dynamic Frequency Regime

The object of this work, a study of the junction recombination velocity limiting the short circuit (Sfsc) of a silicon solar cell under magnetic field in the dynamic frequency regime is presented. From the continuity equation, the density of minority Charge carrier’s in the base and the photocurrent are determined. The study of this photocurrent, according to the junction recombination velocity, allows us to determine the junction recombination velocity limiting the short circuit. The photocurrent density is studied as a function of the junction recombination velocity for different modulation frequencies. From the variation profile of the photocurrent density as a function of the junction recombination velocity, a technique for determining junction recombination velocity initiating the short-circuit situation is presented.

     

Face-Specific Data Augmentation for Unconstrained Face Recognition

International Journal of Computer Vision - We identify two issues as key to developing effective face recognition systems: maximizing the appearance variations of training images and minimizing...     

Activity and stability of TiO2 samples with different phase compositions in the decomposition of formaldehyde in SCW

TiO₂ samples with different crystal sizes and compositions were synthesized using a sol-gel method at different calcination temperatures (350–900 °C). The activity and stability of TiO₂ samples were determined by the gasification of formaldehyde in supercritical water (SCW) and by treatment in SCW. Increasing calcination temperature and SCW gasification (SCWG)/SCW treatment decreased the surface area of anatase TiO₂ samples due to growing crystallite size via agglomeration and sintering. Among anatase TiO₂ samples, the TiO₂ calcinated at 450 °C was found as the most suitable material under SCW conditions. However, the surface area of rutile TiO₂ slightly increased from 17.2 m² g^?1 to 19.8 m² g^?1 with the weakly crumbling of particles during SCWG. The highest hydrogen formation (63%) from formaldehyde in the SCW was obtained in the presence of anatase TiO₂ calcined at 350 °C and rutile TiO₂ calcined at 800 °C. CO₂ formation in the presence of anatase TiO₂ is higher than rutile TiO₂ because of the presence of active lattice oxygen species (O^?, O^2?) based on O₂-TPD.     

A two-dimensional material for high capacity supercapacitors: S-doped graphene

In this work, sulfur-doped graphene-coated electrodes are prepared by cyclic voltammetry in different potential ranges and different cycles (from 10 to 50) for selective modification of electrodes by different functional groups. The prepared electrodes are characterized by spectroscopic, microscopic and electrochemical methods. In scanning electron microscopic analysis, formation of graphene layers and their porous structure have been determined. Electrochemical impedance spectroscopic and cyclic voltammetric analyses are also used in electrochemical characterization of the electrodes. Then, the prepared sulfur-doped graphene-coated electrodes by using cyclic voltammetry in one-step and low cost are used as electrode materials of supercapacitor for the first time in the literature. Since the mesoporous structure of the electrodes prepared in lower potential ranges increases, specific capacitance of the electrodes increases from 74 to 1833 mF cm⁻² with 10 mA cm⁻² current density. This result shows that specific capacitances of prepared electrodes are higher than those of the electrodes prepared with metal-doped in the literature.     

Suppression of asymmetric flow behavior downstream of two side-by-side circular cylinders with a splitter plate in shallow water

The flow downstream of a pair of circular cylinder in a side-by-side arrangement normal to the free stream is known to exhibit intermittently bistable structure for the range of G/D = 1.2–2.2 where G is the center-to-center distance between the cylinders and D is the diameter of the cylinder. Eventually, the wake downstream of one of the two cylinders can be wider or narrower than the one downstream of the other cylinder depending on the direction of gap-flow deflection. In the present study, such an asymmetric flow behavior downstream of two side-by-side cylinders, which were vertically located in shallow water, was passively controlled with a splitter plate with a length of L   (1?L/D?5$1?L/D?5$). The center of splitter plate was just coincided with the mid-height of the gap between centers of the cylinders. The investigations were carried out in a water channel using dye visualization and particle image velocimetry, PIV for qualitative and quantitative measurements, respectively. The diameter of the cylinder, D was 40 mm while the depth of water was 20 mm so that the shallow flow condition was provided through the experiments. The Reynolds number, Re based on D was 5000 and the cylinder’s center to center spacing to the cylinder diameter ratio (G/D  ) was equal to 1.25. The results demonstrated that the deflection of the wake and thereby the bistability of the wake was considerably prevented with the presence of the splitter plate for L/D?3$L/D?3$ which resulted in two well symmetric, stable wakes having approximately the same order of magnitudes of vortex shedding frequencies around the cylinders.