原子力显微镜评价奥氏体不锈钢晶间腐蚀敏感性的研究

由13Cr可焊马氏体不锈钢(WMSGSS)制造的油气管线由于价格便宜,相对于昂贵的耐腐蚀合金来说是一个很有竞争力的选择。但是实验室试验和现场经历表明,13Cr马氏体不锈钢焊接接头热影响区发生了沿晶应力腐蚀开裂(IGSCC)。对于低等级的马氏体不锈钢来说,沿晶应力腐蚀开裂机理被认为是在晶界的碳化物附近存在贫铬区。对于中等级和高等级马氏体不锈钢来说,只在实验室试验发现有应力腐蚀开裂。它们的应力腐蚀开裂机理还没有明确,虽然最可能的应力腐蚀开裂机理也被认为和低等级马氏体不锈钢的应力腐蚀开裂机理类似。原子力显微镜(AFM)已开始广泛用于材料显微组织和环境敏感断裂的研究中。高等级马氏体不锈钢焊接接头对晶间腐蚀/应力腐蚀开裂敏感性很有希望由原子力显微镜检测到。在原子力显微镜技术应用于这项研究之前,用由304不锈钢准备的不同敏化度的试样来确定它的适用性是十分有益的。本文用原子力显微镜研究了不同敏化程度的304不锈钢的晶间腐蚀敏感性并和SEM和EDS结果进行了对比。     

REQUISITE VARIETY IN THE SYSTEMS AND CONTROL SCIENCES†

Trends in the systems and control sciences are discussed in relation to certain results in cybernetics. In particular, optimal control theory is reviewed in the light of practical engineering requirements and servomechanism theory is considered in the light of Ashby's law of requisite variety.     

REACHABILITY AND CONTROLLABILITY OF DISCRETE-TIME LINEAR DYNAMICAL SYSTEMS

The concepts of reachability and controllability do not coincide but reflect a fundamental difference between the dynamical characteristics of different classes of multi-variable systems. This difference is discussed in relation to discrete-time linear dynamical systems and is illustrated by a simple numerical example.     

An evaluation of digitized APT data from the TIROS-N/NOAA-A, -J series of meteorological satellites

The TIROS-N/NOAA-A, -J series of meteorological satellites transmit imagery data to the Earth in both digital and analogue formats. The analogue data are a processed subset of the digital data and have lower resolution. A quantitative evaluation of a post-reception digitized version of this is made using the corresponding digital data as a standard. In nine comparisons the calibration of the infrared sensor on board was within 001°C. Sea surface temperature estimates from APT data were 0.3°C below the corresponding digitally transmitted data. The albedo estimates were within 0.2 per cent. Processed APT data are adequate for many mesoscale measurements in the fields of oceanography and meteorology and are more readily accessible than the digitally transmitted data.     

HIGH PRESSURE–HIGH TEMPERATURE STERILIZATION: FROM KINETIC ANALYSIS TO PROCESS VERIFICATION†

The inactivation of Clostridium sporogenes PA 3679 spores by high pressure at high temperatures (HP–HT) in phosphate buffer was investigated in a lab‐scale temperature‐controlled HP system (QFP‐6) with an internal heater to maintain the sample temperature. Some inactivation of spores occurred during the pressurization come‐up time (CUT) and depressurization time. The inactivation of PA 3679 was found to be exponential during the adiabatic holding period of the HP cycle at constant pressures and temperatures. The inactivation rate increased with both pressure and temperature. The kinetic parameters – such as D‐values at tested temperatures and pressures that are necessary for the design of process parameters of HP sterilization process – were determined. Within the pressure range of 600–800 MPa, the calculated D‐values ranged from 270.3 to 357.4 and 49.0 to 67.6 s at 91 and 108C, respectively. These studies provided basic data on the effects of pressure and temperature on the inactivation of PA 3679 spores under conditions applicable to the development of preservation specifications for commercial HP–HT processing of low acid foods. The spore strips of C. sporogenes were used as indicators for microbiological verification of delivered lethality of HP–HT sterilization process at different processing conditions in a pilot scale HP vessel.     

THE STIMULATION OF PHENOLICS AND ANTIOXIDANT ACTIVITY IN PEA (PISUM SATIVUM) ELICITED BY GENETICALLY TRANSFORMED ANISE ROOT EXTRACT

A series of dark germination experiments demonstrate the potential of an Agrobacterium rhizogenes‐transformed, high cytokinin root extract of anise (Pimpinella anisum), to stimulate phytophenolic and enhance antioxidant activity in pea (Pisum sativum) seedlings. Average shoot weight increased 40–60% after imbibing seeds for 24 h in a 1.5 to 2.0% extract of the anise root clone AR‐10. Phenolic concentration was positively correlated with shoot weight, suggesting that the total phenolic content was related to seedling vigor. Antioxidant protection factor in pea shoots was also stimulated by AR‐10 extracts. Free proline concentrations were 2–3 times higher in shoots collected from AR‐10 treated peas versus controls. However, proline content also increased as shoot weight declined after being subjected to an overdose of AR‐10 extract in 25% ethanol. G6PDH specific activity, the first committed step of the pentose phosphate pathway, was negatively associated with shoot growth and proline concentrations.     

USE OF ABLATION TO DETERMINE THE CONVECTIVE HEAT TRANSFER COEFFICIENT IN TWO-PHASE FLOW

The fluid to particle convective heat transfer coefficient (h_fp) is an essential design parameter in the development of an aseptic processing system. The convective heat transfer coefficient was determined using a new method based on ablation heat transfer. The amount of solid lost (ablated) was shown to be directly proportional to the energy flux across the fluid‐solid interface with the constant of proportionality being h_fp. Change in mass of an ice sphere was used as an ablation probe to study h_fp in straight, round conduit. Values of h_fp ranged from 1,369 to 2,749 W/m²K over a Reynolds number range of 2,766 to 17,081.