Sung-Whan Cho

Zearalenone induces male germ cell apoptosis in rats

Zearalenone (ZEA), a nonsteroidal estrogenic mycotoxin, is known to cause toxicity of testis in male rats. To investigate whether apoptosis is involved in ZEA-induced testicular toxicity and to identify the stage and target germ cell type, 10-week-old Sprague-Dawley male rats were treated with a single intraperitoneal (i.p.) dose of ZEA (5 mg/kg) and euthanized at 3, 6, 12, 24, or 48 h subsequently. Histopathologically, germ cell degeneration was found at stages I-VI 12 h after dosing. Degenerating germ cells were shown to undergo apoptosis as revealed by in situ terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL). The frequency of TUNEL-labeled germ cells increased in a stage-specific manner, the peak frequency gradually progressing at stages I-VI of seminiferous tubules with time after dosing, suggesting that the damaged germ cells, especially spermatogonia and spermatocytes, gradually underwent the processes leading to apoptosis. DNA laddering on gel electrophoresis was apparent 12 h after dosing. The results demonstrated that a single dose of ZEA induces testicular germ cell apoptosis in a time-dependent and stage-specific pattern. This study has established that apoptosis is the principal mechanism contributing to germ cell depletion and testicular atrophy following ZEA exposure.

The effects of processing parameters on the microstructure and mechanical properties of modified B390 alloy in direct squeeze casting

Abstract The direct squeeze casting of B390 has been investigated as a function of melt temperature and applied pressure. Commercial finite volume method (FVM) computer code for heat transfer analysis, MAGMAsoft, was used to simulate cooling curves obtained from the direct squeeze casting process. The experimental and modeling results are discussed, and the correlation between cooling rate and microstructure is studied. The effects of applied pressures and melt temperature on the formation of primary Si and Chinese scripts are also discussed in connection with mechanical properties such as hardness and tensile strength.

Somatostatin and Substance P Induced in vivo by Lipopolysaccharide and in Peritoneal Macrophages Stimulated with Lipopolysaccharide or Interferon-Gamma Have Differential Effects on Murine Cytokine Production

We have investigated whether lipopolysaccharide (LPS) induces substance P (SP) and somatostatin (SOM) in popliteal lymph nodes in vivo and whether macrophages are a source of SP and SOM in vitro. We have also investigated the effect of SP and SOM treatment on the production of cytokines. SP reached a maximum 3 days after injection of LPS (100 μg/footpad) and then declined. SOM expression after LPS injection reached a maximum at 5–7 days. Stimulation of thioglycolate-elicited peritoneal macrophages with LPS (20 μg/ml), recombinant interferon-γ (rIFN-γ, 100 U/ml), and LPS plus rIFN-γ induced SOM and SP. Thioglycolate-elicited, unstimulated peritoneal macrophages also synthesized these peptides. SOM (10–12–10–8 M) significantly inhibited IL-6 and IFN-γ production, whereas SP at those concentrations enhanced cytokine production by activated lymphocytes and macrophages. These findings suggest that neuropeptides which originate from macrophages and nerve fibers act as immunomodulators to mediate changes in the pattern of cytokine production.

Characteristics of Al2O3–SiC composite powder prepared by the self-propagating high-temperature synthesis process and its sintering behavior

Abstract Al 2 O 3 –SiC composite powder was prepared by the self-propagating high-temperature synthesis (SHS) process, using SiO 2 , Al, and C powders as raw materials. The effects of keeping the SiO 2 :Al molar ratio fixed at 3:4 while varying the relative carbon amount, compaction pressure, initial temperature of reactants, and combustion process on the products were studied. SHS of the SiO 2 /Al/C system required preheating above 400°C, because of the low combustion temperature. It was found that, as a result of the combustion reaction, the purity of the final product was better than that of the reactants. The optimum molar ratio of SiO 2 :Al:C in the system was found to be 3:4:6. The free carbon was removed by roasting at 650°C for 30 min. Pressureless sintering was found to be very effective in hindering the disintegration of the specimen with a Al 2 O 3 –SiC powder bed and obtaining a dense sintered body at 1700°C. The sintered body produced by hot-pressing was about 98% of the relative density.

Synthesis of Al2O3-WC composite powder by SHS process

Al2O3-WC composite powder was synthesized by self-propagating high-temperature synthesis using Al powder as a reducing agent. WC, W2C and Al2O3 were concurrently formed in WO3-Al-C system. It was found that the complete reaction was achieved with excessive addition of carbon and appropriate processing parameters such as degree of dilution, particle size of aluminum, pellet compaction pressure and carbon source. The final product which was leached by 50% 1 : 4 HNO3 + HF diluted solution was consisted of Al2O3-55wt%WC having 2–3 μm of mean particle size.

Effects of melt flow and temperature on the macro and microstructure of scroll compressor in direct squeeze casting

Orbiting scroll compressors were successfully manufactured by direct squeeze casting. Solidification and melt flow of B390 alloy in an orbiting scroll compressor die has been simulated using a 3D-FVM code which takes full account of coupled heat and melt flow. Defect formation of the orbiting scroll compressor during squeeze casting has been investigated. Experimental results give a critical melt temperature of 600°C for sound castings, whereas this critical temperature is even below the liquidus temperature. These abnormal filling behaviors were attributed to complicated die geometry in conjunction with time delay prior to pressurization. This melt flow phenomena could be explained by the calculation results. The effect of the melt temperature on the microstructures and mechanical properties of the orbiting scroll compressor are also discussed.

Foaming behaviour of Al–Si–Cu–Mg alloys

Abstract The powder metallurgical route was utilised to obtain the Al–5Si–4Cu–4Mg (alloy 544) and Al–3Si–2Cu–2Mg (alloy 322) foams. Various steps such as centrifugal atomisation, mixing alloy powder and foaming agent (1 wt-%TiH2), cold compaction of mixture, hot extrusion and foaming in a preheated furnace were performed. Foaming behaviour of the alloys was investigated by digital microscopy, image analysis, scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) mapping in this study. It was found that alloy 544 takes a shorter period of time to initiate pore nucleation than alloy 322. Alloy 544 had a higher pore growth rate than alloy 322 at the same pre-set furnace temperature. In both alloys, crack-like pore nucleation occurred between aluminium alloy powders elongated in a direction parallel to the extrusion direction. Both alloys showed the same foaming sequence of crack-like pore nucleation, spherical pore growth, coalescence of neighbouring pores and collapse of pores adjacent to the free surface of specimen. The time required to start pore nucleation decreased with the increase of foaming temperature. The cell walls of both alloys consisted of α-Al phase and eutectic phase.

Microstructure and mechanical properties of rapidly solidified Al-20Si-xFe-3Cu-lMg (x=0 and 5 wt.%) Extradates

The effects of Fe addition and initial powder size distribution on mechanical properties of Al-20Si-3Cu-lMg alloy, prepared by gas atomization and followed by hot consolidation, were studied by using optical microscopy, transmission electron microscopy, X-ray diffractometry, tensile and wear test. The Al-20Si-xFe-3Cu-lMg (x=0, 5) alloys showed homogeneous and refined microstructure. Addition of Cu and Mg to Al-20Si alloy showed increased tensile property due to precipitation hardening. Addition of Fe to Al-20Si-3Cu-lMg increased tensile strength further due to the formation of spherical Al-Si-Fe compound during hot consolidation and phase transformed from the metastable phase. Alloy bars prepared from powder with wide-size distribution showed low tensile strength and wear resistance.

THE SELF-PROPAGATION HIGH-TEMPERATURE SYNTHESIS OF ULTRAFINE HIGH PURITY TUNGSTEN POWDER FROM SCHEELITE

High-purity tungsten was prepared by self-propagating high-temperature synthesis (SHS) process from a mixture of CaO{center_dot}WO{sub 3} and Mg. The complete reduction of CaO{center_dot}WO{sub 3} required a 33{percent} excess of magnesium over the stoichiometric molar ratio Mg/CaO{center_dot}WO{sub 3} of 3:1. The MgO and CaO in the product was leached with an HCl solution. The product tungsten had a purity of 99.980{percent} which was higher than that of the reactants. The high purity results because the non tungsten reactants and products are volatilized by the high temperatures generated during the rapid exothermic SHS reaction and are dissolved during HCl leaching of the product. {copyright} {ital 1996 Materials Research Society.}

Extrusion behavior of RQ Al composite powder manufactured by a stone mill type crusher

Abstract The aim of the present investigation is to predict surface cracking and reinforcement distribution during hot extrusion in Al 6061 and 5083 composite powder reinforced by hybrid TiC–Al 2 O 3 particles. The composite powders were manufactured by crushing in the newly developed stone mill crusher using twin rolled flakes. With increasing initial billet temperature, surface cracking occurred during extrusion due to a decrease in damage criterion. It was enlightened to obtain an optimal distribution of ceramic particles in Al alloy matrix as a function of milling cycles. Optimal distribution of the reinforcement in the matrix was taken into consolidation with milling cycles.