椭圆齿旋流口平带传热管内自动清洗及其传热强化

介绍了一种特殊结构的旋流口椭圆齿平带的研制。平带上的每个椭圆齿都是使平带自转的流体动力结构元素,平带两侧的旋流口结构能够使管内的部分液体形成螺旋线流,因而具有近似斜齿纽带那样能够在较低流速下自转实现管内污垢在线自动清洗的宝贵性能。由于椭圆齿后的大量涡流、管内部分液体流线转变为螺旋线流股以及螺旋线流股与轴向流股分合交错这样3方面的作用,管内的对流传热强化的幅度由此远远高于光滑纽带。试验结果表明,这种平带不仅容易制造,并且综合性能好,在管内流速0.5m/s左右就可运行;管内侧的传热系数提高170%,流体阻力在一般工程许可的范围内,因此具有较高的工程应用价值。     

Protein kinase C switches the Raf kinase inhibitor from Raf-1 to GRK-2

Feedback inhibition is a fundamental principle in signal transduction allowing rapid adaptation to different stimuli. In mammalian cells, the major feedback inhibitor for G-protein-coupled receptors (GPCR) is G-protein-coupled receptor kinase 2 (GRK-2), which phosphorylates activated receptors, uncouples them from G proteins and initiates their internalization. The functions of GRK-2 are indispensable and need to be tightly controlled. Dysregulation promotes disorders such as hypertension or heart failure. In our search for a control mechanism for this vital kinase, here we show that the Raf kinase inhibitor protein (RKIP) is a physiological inhibitor of GRK-2. After stimulation of GPCR, RKIP dissociates from its known target, Raf-1 (refs 6-8), to associate with GRK-2 and block its activity. This switch is triggered by protein kinase C (PKC)-dependent phosphorylation of the RKIP on serine 153. The data delineate a new principle in signal transduction: by activating PKC, the incoming receptor signal is enhanced both by removing an inhibitor from Raf-1 and by blocking receptor internalization. A physiological role for this mechanism is shown in cardiomyocytes in which the downregulation of RKIP restrains beta-adrenergic signalling and contractile activity.     

Prolonged vibration of cutaneous artery: absence of persisting aftereffects

1-3 h after prolonged (3-16 h) vibration (120 Hz, 0.2-0.3 mm amplitude) of rings of canine saphenous arteries there was no significant change in the contractile response to electrical stimulation, exogenous norepinephrine or of neuronal uptake of tritium labeled norepinephrine. These results did not provide evidence for persistent aftereffects of prolonged vibration.     

Structure of the catalytic domain of the hepatitis C virus NS2-3 protease

Hepatitis C virus is a major global health problem affecting an estimated 170 million people worldwide. Chronic infection is common and can lead to cirrhosis and liver cancer. There is no vaccine available and current therapies have met with limited success. The viral RNA genome encodes a polyprotein that includes two proteases essential for virus replication. The NS2-3 protease mediates a single cleavage at the NS2/NS3 junction, whereas the NS3-4A protease cleaves at four downstream sites in the polyprotein. NS3-4A is characterized as a serine protease with a chymotrypsin-like fold, but the enzymatic mechanism of the NS2-3 protease remains unresolved. Here we report the crystal structure of the catalytic domain of the NS2-3 protease at 2.3 A resolution. The structure reveals a dimeric cysteine protease with two composite active sites. For each active site, the catalytic histidine and glutamate residues are contributed by one monomer, and the nucleophilic cysteine by the other. The carboxy-terminal residues remain coordinated in the two active sites, predicting an inactive post-cleavage form. Proteolysis through formation of a composite active site occurs in the context of the viral polyprotein expressed in mammalian cells. These features offer unexpected insights into polyprotein processing by hepatitis C virus and new opportunities for antiviral drug design.