Calculation of temperature and heat flux in quenched cylinders for different wetting processes

The cooling of pieces being quenched in evapourable fluids is mainly determined by the process of wetting, which is defined as the sequence of the three known cooling stages film boiling, nucleate boiling and convective heat transfer. All these determine the properties of the finished product. The effect of different wetting processes and heat transfer coefficients on the time-dependent distribution of temperature and heat flux in quenched cylinders was examined using numerical methods. Only transformation-free quenching was considered. When the three cooling stages simultaneouly take place on the sample's surface the radial heat fluxes are superimposed by high axial heat fluxes, which could not be pointed out experimentally before. The consequences may be great axial differences of structure and hardness, especially for steels with low hardenability, as well as residual stresses. The axial temperature gradients can be reduced by producing high wetting velocities. An optimum wetting process involves a very fast breakdown of the vapour envelope on the whole surface of the quenched piece.     

Low body temperature affects associative processes in long-trace conditioned flavor aversion

Meliacine (MA), a peptide isolated from leaves of the high plant Melia azedarach L inhibited the multiplication of foot and mouth disease virus (FMDV) in BHK-21 cells. In this report, we establish that the MA-inhibitable process takes place within the first hour of the viral reproductive cycle. MA had no virucidal effect and did not affect adsorption and penetration of the virus in cells. In experiments with neutral red-labeled virus, it was found that MA significantly suppressed the development of photoresistance of the virus in infected cells. In untreated cultures nearly all virus which adsorbed to cells was uncoated within 1 h at 37 degrees C, whereas in treated cultures, even after 3 h only 3% of the virus was uncoated. Labeling of BHK-21 cells with acridine orange showed that MA affects the pH of intracellular acidic vesicles. Therefore, it is concluded that MA prevents the process of uncoating of FMDV in BHK-21 cells by inhibiting vacuolar acidification.     

Irreversible lithium neurotoxicity: an overview

Lithium is widely used, and most of its side effects are well established and recognized. Persistent neurologic sequelae or dysfunctions are not common, but they are serious side effects. They usually persist after acute toxicity following accidental or suicidal overdose or during maintenance therapy, when toxicity is more insidious. The irreversible neurologic sequelae are generally cerebellar signs, especially ataxia and dysarthria. Risk factors are sometimes present and recognizable, but more often they are not well identified. Persistent neurologic handicaps greatly reduce the quality of life and are difficult to manage. Lithium toxicity can be avoided by conservative prescribing, care in combining drug therapies, and, above all, educating the patient and caregivers to recognize early signs of the condition. A review of the literature is presented, together with vignettes of a further seven cases.     

电渣重熔过程中焦耳热与温度场的有限元分析

建立了电渣重熔过程中的电磁场与温度场的耦合数学模型,利用商业软件ANSYS对包括电极、渣池和钢锭的一体化电渣重熔系统电磁场、焦耳热场和温度场进行有限元计算,并分析冷却水温对重熔系统温度的影响.结果表明:重熔系统中的焦耳热主要分布在渣池中,其最大值出现在渣池与电极端口接触处,即电流密度最大处;重熔系统的最高温度出现在电极...     

Irreversible inactivation of protein kinase C by glutathione

The tripeptide glutathione (GSH) is the predominant low molecular weight thiol reductant in mammalian cells. In this report, we show that at concentrations at which GSH is typically present in the intracellular milieu, GSH and the oxidized GSH derivatives GSH disulfide (GSSG) and glutathione sulfonate each irreversibly inactivate up to 100% of the activity of purified Ca2+- and phosphatidylserine (PS)-dependent protein kinase C (PKC) isozymes in a concentration-dependent manner by a novel nonredox mechanism that requires neither glutathiolation of PKC nor the reduction, formation, or isomerization of disulfide bridges within PKC. Our evidence for a nonredox mechanism of PKC inactivation can be summarized as follows. GSSG antagonized the Ca2+- and PS-dependent activity of purified rat brain PKC with the same efficacy (IC50 = 3 mM) whether or not the reductant dithiothreitol was present. Glutathione sulfonate, which is distinguished from GSSG and GSH by its inability to undergo disulfide/thiol exchange reactions, was as effective as GSSG in antagonizing Ca2+- and PS-dependent PKC catalysis. The irreversibility of the inactivation mechanism was indicated by the stability of the inactivated form of PKC to dilution and extensive dialysis. The inactivation mechanism did not involve the nonspecific phenomena of denaturation and aggregation of PKC because it obeyed pseudo-first order kinetics and because the hinge region of PKC-alpha remained a preferential target of tryptic attack following GSH inactivation. The selectivity of GSH in the inactivation of PKC was also indicated by the lack of effect of the tripeptides Tyr-Gly-Gly and Gly-Ala-Gly on the activity of PKC. Furthermore, GSH antagonism of the Ser/Thr kinase casein kinase 2 was by comparison weak (<25%). Inactivation of PKC-alpha was not accompanied by covalent modification of the isozyme by GSH or other irreversible binding interactions between PKC-alpha and the tripeptide, but it was associated with an increase in the susceptibility of PKC-alpha to trypsinolysis. Treatment of cultured rat fibroblast and human breast cancer cell lines with N-acetylcysteine resulted in a substantial loss of Ca2+- and PS- dependent PKC activity in the cells within 30 min. These results suggest that GSH exerts negative regulation over cellular PKC isozymes that may be lost when oxidative stress depletes the cellular GSH pool.     

Influence of time and temperature dependent processes on strain controlled low cycle fatigue behavior of alloy 617

Strain controlled low cycle fatigue tests have been conducted in air to ascertain the influence of strain rate(ε = 4 × 10^-6'to 4 × 10^-3 s^-1) and temperature(T = 750/850/950 °C) on LCF behavior of Alloy 617. A strain range of 0.6 pct and a symmetrical triangular wave form were employed for all the tests. Crack initiation and propagation modes were studied. Microstructural changes that occurred during fatigue deformation were evaluated and compared with the results obtained on isothermal aging. Deformation and damage mechanisms which influence the endurance have been identified. A reduction in fatigue life was observed with decreasing ε at 850 °C and with increasing temperature at ε = 4 × 10^-5 s^-1. Cyclic stress response varied as a complex function of temperature and strain rate. Fatigue deformation was found to induce cellular precipitation of carbides at 750 and 850 ‡. Dynamic strain aging characterized by serrated flow was observed at 750 °C (ε = 4 × 10^-5 s^-1) and in the tests at higher ε at 850 °C. Strengthening of the matrix due to dynamic strain aging of matrix dislocations by precipitation of M₂₃C₆ carbides led to fracture of grain boundary carbide films formed at 750 °C, producing brittle intergranular crack propagation. At 850 °C transgranular crack propagation was observed at the higher strain rates ε≥4× 10^-4 s^-1. At 850 and 950 °C even at strain rates of 4 × 10^-5 s^-1 or lower, life was not governed by intergranular creep rupture damage mechanisms under the symmetrical, continuous cycling conditions employed. Reduction of endurance at lower strain rates is caused by increased inelastic strain and intergranular crack initiation due to oxidation of surface connected grain boundaries. formerly Guest Scientist at the De-partment for Reactor Materials of the Nuclear Research Centre, Juelich (IRW/KFA),     

螺旋管内传热过程的不可逆损失分析

以水为工作介质,给出了表征不可逆损失的无因次熵产数Ns的计算式;并应用最小熵产原理分析了各种参数对不可逆损失的影响.结果表明:层流状态下存在一个最佳Re数使Ns 值最小,影响不可逆损失和最佳Re 数的主要因素是无因次入口温差r、定义的无因次数U2及半径比S.这对确定螺旋管合理的流动工况、结构参数和减小传热过程中的不可逆损失有重要意义.     

Irreversible cataract as a possible side effect of isoretinoin

BACKGROUND: Isoretinoin, a drug used in the treatment of severe cystic acne, is known for its numerous adverse ocular side effects, among others. Generally these side effects are benign in nature and reversible on cessation of drug therapy, as for instance transient acute myopia. However, two cases of irreversible cataract possibly related to isotretinoin have been described up till now. PATIENT: We examined a 37-year-old woman with acute unilateral cataract that occurred after a treatment with isotretinoin for four months, terminated a few days previously. A clear etiological relation could not be established. CONCLUSION: The time relation, the acute onset and the absence of other factors nevertheless suggest an influence of isotretinoin therapy to the occurrence of the cataract.