拉西瓦水电站进水塔混凝土及竖井开挖技术

拉西瓦水电站引水系统工程在1-6号拦污栅墩和5、6号进水塔混凝土浇筑中采用了滑模施工技术;在进水塔场地狭小、混凝土垂直入仓布置困难的情况下,采用了搭设钢栈桥、皮带机配合BOX溜管输送三级料垂直入仓的施工方法;在引水洞竖井开挖中采用了反井钻机技术,取得了良好的效果。     

浸染状矿石破碎的选择性

目前浸染状矿石,特别是铜矿石和铜锌矿石,由于矿物嵌布复杂且不均匀,用传统方法(棒磨机和球磨机)磨矿的选择性欠佳,导致浮选时有用组分以连生体和细泥形式大量损失。本文评论改善磨矿选择性的可能性和在此基础上改进选矿工艺的远景。     

A technique for assessment of torso kinesiology

A technique is described for monitoring and analysis of the angular displacement of the human torso. The technique is based on the use of miniature electromechanical inclinometers and video recording. The system was developed for continuous measurement of the angular displacement of spinal segments in the sagittal plane during all stages of lifting. Angular displacements of the cervical, thoracic and lumbar regions were obtained from a dynamic lifting case study using a digital processing system. The geometrical changes of the torso during five prescribed stages were measured. The system revealed good accuracy with high correlation coefficient scores for a wide range of lifting tasks in a comparative laboratory study. This paper describes the monitoring technique; the system's advantages, disadvantages and measuring accuracy are discussed.     

The minimum quantity of nitrite required to stain sliced and homogenised cooked pork

The levels of nitrite used in curing pork are in excess of those required to produce an adequate cured colour, but the minimum level for pink coloration to be visible has not been established experimentally. This paper demonstrates the effect of low nitrite levels from local surface application to pork muscle, simulating inadvertent contamination from work surfaces. An homogenate is used for comparison in which the nitrite was evenly distributed throughout the product. The results indicate that surface contact with nitrite produces essentially the same pattern of colour change as in the homogenate. Visible pink coloration was evident from 1-2 mg kg(-1) sodium nitrite absorbed.     

Structural and kinetic studies on ligand binding in wild-type and active-site mutants of penicillin acylase

Penicillin acylase catalyses the condensation of Calpha-substituted phenylacetic acids with beta-lactam nucleophiles, producing semi-synthetic beta-lactam antibiotics. For efficient synthesis a low affinity for phenylacetic acid and a high affinity for Calpha-substituted phenylacetic acid derivatives is desirable. We made three active site mutants, alphaF146Y, betaF24A and alphaF146Y/betaF24A, which all had a 2- to 10-fold higher affinity for Calpha-substituted compounds than wild-type enzyme. In addition, betaF24A had a 20-fold reduced affinity for phenylacetic acid. The molecular basis of the improved properties was investigated by X-ray crystallography. These studies showed that the higher affinity of alphaF146Y for (R)-alpha-methylphenylacetic acid can be explained by van der Waals interactions between alphaY146:OH and the Calpha-substituent. The betaF24A mutation causes an opening of the phenylacetic acid binding site. Only (R)-alpha-methylphenylacetic acid, but not phenylacetic acid, induces a conformation with the ligand tightly bound, explaining the weak binding of phenylacetic acid. A comparison of the betaF24A structure with other open conformations of penicillin acylase showed that betaF24 has a fixed position, whereas alphaF146 acts as a flexible lid on the binding site and reorients its position to achieve optimal substrate binding.     

Note: The intermodulation lockin analyzer

Nonlinear systems can be probed by driving them with two or more pure tones while measuring the intermodulation products of the drive tones in the response. We describe a digital lockin analyzer which is designed explicitly for this purpose. The analyzer is implemented on a field-programmable gate array, providing speed in analysis, real-time feedback, and stability in operation. The use of the analyzer is demonstrated for intermodulation atomic force microscopy. A generalization of the intermodulation spectral technique to arbitrary drive waveforms is discussed.     

The effect of handle friction and inward or outward torque on maximum axial push force

OBJECTIVE: To investigate the relationship among friction, applied torque, and axial push force on cylindrical handles. BACKGROUND: We have earlier demonstrated that participants can exert greater contact force and torque in an "inward" movement of the hand about the long axis of a gripped cylinder (wrist flexion/forearm supination) than they can in an "outward" hand movement. METHOD: Twelve healthy participants exerted anteriorly directed maximum push forces along the long axis of aluminum and rubber handles while applying deliberate inward or outward torques, no torque (straight), and an unspecified (preferred) torque. RESULTS: Axial push force was 12% greater for the rubber handle than for the aluminum handle. Participants exerted mean torques of 1.1, 0.3, 2.5, and -2.0 Nm and axial push forces of 94, 85, 75, and 65 N for the preferred, straight, inward, and outward trials, respectively. Left to decide for themselves, participants tended to apply inward torques, which were associated with increased axial push forces. CONCLUSION: Axial push force was limited by hand-handle coupling--not the whole body's push strength. Participants appeared to intuitively know that the application of an inward torque would improve their maximum axial push force. Axial push forces were least when a deliberate torque was requested, probably because high levels of torque exertions interfered with the push. APPLICATION: A low-friction handle decreases maximum axial push force. It should be anticipated that people will apply inward torque during maximum axial push.