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    Effects of long-term heat stress and dietary restriction on the expression of genes of steroidogenic pathway and small heat-shock proteins in rat testicular tissue
    (Wiley, 2017) Bozkaya, F.; Atli, M. O.; Guzeloglu, A.; Kayis, S. A.; Yildirim, M. E.; Kurar, E.; Yilmaz, R.
    The aim was to investigate the effects of long-term heat stress and dietary restriction on the expression of certain genes involving in steroidogenic pathway and small heat-shock proteins (sHSPs) in rat testis. Sprague Dawley rats (n = 24) were equally divided into four groups. Group I and II were kept at an ambient temperature of 22 degrees C, while Groups III and IV were reared at 38 degrees C for 9 weeks. Feed was freely available for Group I and Group III, while Group II and Group IV were fed 60% of the diet consumed by their ad libitum counterparts. At the end of 9 weeks, testicles were collected under euthanasia. Total RNA was isolated from testis tissue samples. Expression profiles of the genes encoding androgen-binding protein, follicle-stimulating hormone receptor, androgen receptor, luteinising hormone receptor, steroidogenic acute regulatory protein (StAR), cyclooxygenase-2 and sHSP genes were assessed at mRNA levels using qPCR. Long-term heat stress decreased the expression of StAR and HspB10 genes while dietary restriction upregulated StAR gene expression. The results suggested that long-term heat stress negatively affected the expression of StAR and HspB10 genes and the dietary restriction was able to reverse negative effect of heat stress on the expression of StAR gene in rat testis.
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    The effects of retrogression parameters in RRA treatment on tensile strength of 7075 aluminium alloys
    (2012) Özyürek, D.; Yilmaz, R.; Kibar, E.
    In this study retrogression and re-aging (RRA) treatments has been applied on 7075 aluminium alloys after T6 treatment. The alloys were retrogressed at various temperatures and times in the retrogression stage of RRA treatment. The effects of the parameters mentioned above on tensile strengths and % elongations were investigated. Besides fracture surfaces were examined by scanning electron microscopy (SEM) for determination of the effects of retrogression temperatures and times on fracture mechanism. The alloy retrogressed at 220°C for 60 minutes showed the highest tensile strength values, on the other hand, the lowest elongation values. Strong relationship has been seen between hardness and tensile strength; however, no effective relationship for elongation was available. Retrogression temperatures and times affects on microstructure of the alloys, therefore, it has also great influence on the hardness and tensile strength, elongation and fracture mechanism.
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    The effects of retrogression parameters on hardness and wear behaviours of 7075 aluminium alloys
    (2012) Yilmaz, R.; Özyürek, D.; Kibar, E.
    In this study, retrogression and re-aging (RRA) treatments on 7075 aluminium alloys has been carried out. 7075 aluminium alloys that were already T6 temper applied were retrogressed at the range of 180-260°C for durations between 15-75 minutes and later re-aged in T6 aging condition of 120°C for 24 hours. The effects of retrogression temperature and times on the hardness and wear properties were investigated. Wear tests were carried out by using machine that is for pin on disc technique. Worn surfaces of the samples after tests were also examined by scanning electron microscopy (SEM) for better understanding of wear mechanism. Experimental studies show that retrogression treatments parameters such as temperatures and times have great effects on wear resistance of 7075 aluminium alloys. Close relationship between the hardness and wear resistance values were seen in those alloys. Variations in hardness values were all depend on retrogression temperatures and times. The alloy retrogressed at 220°C for 60 minutes showed the highest hardness values and wear resistance.
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    Exchange of experience the effect of synthesis time on the wear behavior of Al-8%Ti alloy produced by mechanical alloying
    (Springer, 2012) Ozyurek, D.; Tekeli, S.; Tuncay, T.; Yilmaz, R.
    In this study, Al-8%Ti alloy was produced by mechanical alloying. The produced powders were cold pressed at 630 MPa and synthesized at 600A degrees C for 12 and 24 h under argon gas atmosphere. After synthesis processes, the specimens were examined by SEM, XRD, and hardness tests. Wear tests were carried out under dry sliding conditions using a pin-on-disk type machine at a constant load of 30 N and a sliding speed of 1 m/sec. Total sliding distances were selected as 500, 1000, 1500, and 2000 m. The experimental results showed that the hardness and density of Al-%8Ti alloy increased with increasing synthesis time. It was also observed that volume reduction increased with increasing sliding distance and decreased with increasing synthesis time.