做好钨极气体弧焊的几点建议

为了获得始终如一的优质钨极气体弧焊缝，必须遵守焊接程序技术规范(WPS)上所列举的重要焊接参数，此外，焊接设备必须运作正常，焊接工具和夹具也必须工作正常，最后，焊工即焊接作业人员必须胜任特定的焊接作业，而且必须正常施焊。事实上对于手工钨极气体弧焊(GTAW)来说，焊工的人工熟练程度、手—眼协调性、自律性连同正确的焊接程序是成功的关健。图1为CTAW设备的典型配置。     

A Comparison of Alternative Intervention Strategies for Unintended Roadway Departure (URD) Control

This paper investigates the use of several different inputs for the control of a vehicle, in the context of URD. In this investigation, the goal of the URD controller is to provide an intervention in the event of the vehicle leaving the road. The types of inputs that will be considered are (i) Four Wheel Steering, (ii) Front Wheel Steering, (iii) Four Wheel Brake Steering, (iv) Front Wheel Brake Steering, and (v) Rear Wheel Brake Steering. The controller design is an LQ controller based on the simplified dynamics of a 2 degree of freedom bicycle model. However, the analysis of the different strategies are performed on a 7 degree-of-freedom nonlinear vehicle model. The key contribution of this paper is the quantitative evaluation of the relative efficiencies of each of these input strategies being examined. Unlike most control schemes, the performance measure to be used will not be the output tracking error of the system. Instead, the metric of performance is the ratio of peak tire force used versus available tire force or, in other words, the actuator response relative to the maximum available actuator capability.     

Are urban bus services natural monopolies?

Although Britain's local bus services have been open to free competition for more than three years, most have continued to be operated as monopolies by the original incumbents. Some competition has occurred, but the incumbents have usually driven off entrants. This paper uses findings from case-studies of competition and from deregulation generally to consider whether monopoly operation has inherent advantages over competitive operation. If so, urban bus routes would be natural monopolies. The evidence suggests that they may be, because single-operator services are more convenient for users.     

Alternatives in assigning short‐term counts to seasonal adjustment factor groupings

The precise estimation of the annual average daily traffic (AADT) is a task of significant interest for many transportation authorities and Departments of Transportation. In this study, three methods are developed to improve the assignment of short‐term counts to seasonal adjustment factor (SAF) groupings: the traditional functional classification, a discriminant analysis (DA), and a new statistical approach based on a weighted coefficient of variation (WCV). The data analyzed within this study are generated from all available continuous counters within the State of Ohio between 2002 and 2006. The analysis is conducted using SAFs that are separately calculated for the total volume and the directional specific volumes of a site. The results show that the directionally based assignment errors are statistically lower at a 95% confidence interval when compared with those generated by the total volume analysis. It is also found that the hourly time‐of‐day factors are more important in the assignment process than the average daily traffic. The directionally based WCV produces a decline in the average mean absolute percentage error (MAPE) over the roadway functional classification by 58% and in the standard deviation of the absolute error (SDAE) by 70%. On the contrary, the directionally based DA lowers the MAPE and the SDAE by 35% and 60%, respectively. Copyright © 2012 John Wiley & Sons, Ltd.     

临床致病性不动杆菌的分子生物学鉴定

目的对临床致病性不动杆菌进行种属鉴定,并比较3种方法(44℃生长试验、特异性引物PCR扩增和16SrRNA测序)对鲍曼不动杆菌鉴定的特异性、准确性及应用价值。方法收集临床致病不动杆菌56株,首先接种在胰蛋白胨大豆肉汤中44℃进行培养,观察是否可以生长;其次,提取56株不动杆菌基因组DNA,用两组不同的特异性引物进行PCR扩增鉴定;最后,用通用引物对56株不动杆菌的16SrRNA进行测序鉴定。结果 56株不动杆菌中有17株可在44℃生长。经特异性引物PCR扩增鉴定,发现8株鲍曼不动杆菌和3株13TU型不动杆菌均可在44℃中较早较快生长。金标准16SrRNA测序确定56株不动杆菌中含有9个种,其中鲍曼不动杆菌和13TU型不动杆菌的鉴定结果与特异性引物PCR扩增法相同。结论应用分子生物学方法鉴定鲍曼不动杆菌具有准确、高效且可重复性高的优点,尤其是特异性PCR扩增法,可作为较难诊断的鲍曼不动杆菌的首选鉴定方法。     

Perspectives on the commercial development of landing gear health monitoring systems

The development of health monitoring technologies for aerospace systems creates a number of challenges for the community of engineers and technical specialists as they seek to integrate the technology into well defined working practices. These challenges do not just extend to the technical, but require a number of commercial questions to be addressed. It is of vital importance, that there is a clearly identified need for aerospace health monitoring, both from a technological and commercial viewpoint. If these needs cannot be identified, then any attempt for marketing health monitoring as a necessary future technological requirement is doomed for failure. Health monitoring technology will need to either deliver significant cost saving benefits to the aircraft operator or demonstrated increases in aircraft safety. The objective of the paper is to provide an assessment of the commercial benefits and development of aircraft landing gear health monitoring. The commercial need and challenges for health monitoring systems are explored in this paper within the context of a changing aerospace maintenance industry and the role in which new systems technology will play. The key findings of the research study are that within the aerospace industry there is a desired paradigm shift within aircraft maintenance towards offering maintenance systems with predictive capabilities. This maintenance revolution will not just incorporate new technologies, but will result in aircraft maintenance packages tailored towards individual customer requirements. The study illustrates the state-of-the-art in health monitoring currently restricts aerospace integration and a number of key technical and commercial issues need to be addressed. Predictive health monitoring offers a variety of commercial benefits for maintenance providers, aircraft operators and manufacturers. However, in order for these benefits to be realised increased transparency in maintenance related information is required between these key players.     

Impact of information technology on the methods and working systems of the freight forwarding industry

Freight forwarding fulfils the role of information processor. The past decade has seen considerable change in the information industry. Combine these two facts and we can begin to explain why freight forwarders have a vested interest in using computer based information systems to their full. Many organizations have tried, some with considerable success, but in others a lack of real commitment and professionalism has cost considerable sums. In this paper the background to the industry is reviewed together with an analysis of the reasons for the poor implementation of successful systems.     

The spatial distribution of journey-to-work trips in Greater London

Although a great deal is known about the distribution of homes and the distribution of workplaces in Greater London, the spatial relationship between them is less well understood. Using 1966 census data, the authors try to give a simple visual picture of this relationship, and to assess the relative travel intensities which would arise at different points in London from commuter trips, assuming straight line routing.The results show firstly that a large proportion of the population work quite close to their homes, with radial travel towards the city centre being only slightly more prominent than other directions of movement. The remainder tend to work near the city centre and to travel much longer distances. Secondly, relative to various annuli at 2 km increments centred on Charing Cross, the amounts of through traffic expressed as a proportion of the totals are roughly constant for radii between 4 and 14 km. Thirdly, people's choice of home in relation to their workplace is, on the whole, quite efficient, since it gives rise to a total amount of travel which is much closer to the theoretical minimum than it is to the amount corresponding to a random choice of homes from the available stock.     

Potential port responses to new information systems on ships

Innovations in information technology, satellite navigation and hydrography are making it technically possible for commercial ships, run by very small crews, to be navigated in the world's seas and oceans with positional accuracies measured in tens of metres. If shipping lines do make the necessary investment in technological hardware, training, operational readjustments and data acquisition, and are also allowed to exploit the full potential of GPS, it will not be surprising if they then expect the ports to provide levels of information that allow the ships to exploit their new capabilities right up to the berth. Ports wishing to hold or improve their perceived service quality in the competitive port league will need to consider whether, and how, they can meet the shipping lines' requirements.

The introduction of strict product liability law adds a new dimension to the assessment of commercial risk in the various technological possibilities available to the ports. The possible costs involved in cases where third party data processors, software producers and electronic chart hardware manufacturers all stand between the port's data output and the user's perception and use of it, in a completely ephemeral form on a screen, need to be considered carefully. Simpler forms of data transmission, such as via traffic advice broadcast or by pilots in person may be seen as the more prudent choice in the five to ten year horizon.     

Car-deficit households: determinants and implications for household travel in the U.S.

Transportation - In the U.S., households with less than one car per driver (auto-deficit households) are more than twice as common as zero-vehicle households. Yet we know very little about these...