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Demand Levels (demand + level)

Distribution by Scientific Domains
Engineering50%

Selected Abstracts

The China rheumatology workforce: a status report

INTERNATIONAL JOURNAL OF RHEUMATIC DISEASES, Issue 4 2009
Fengchun ZHANG
Abstract This article aims to provide an accurate database of the rheumatology workforce in mainland China. A face-to-face survey was conducted in 2007 using a custom-designed questionnaire that included demographic information, educational background, training history, professional rank, years of working experience within the specialty, and workload. Potential rheumatology practitioners were identified by provincial rheumatology associations. The survey identified a total of 2216 rheumatologists. Seventy percent of the entire workforce had , 10 years of working experience. The number of male and female rheumatologists was equal, at ages of 41 years and above. At , 40 years of age, female rheumatologists predominated at 63%. The national rheumatologist density was 1.67 per million population. The rheumatology workforce in China is relatively young, indicating a rapid expansion. However, the supply of rheumatologists is still significantly below the demand level. [source]

Probabilistic evaluation of seismic performance of 3-story 3D one- and two-way steel moment-frame structures

EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 5 2008
Hiroyuki Tagawa
Abstract This paper presents the results of a probabilistic evaluation of the seismic performance of 3D steel moment-frame structures. Two types of framing system are considered: one-way frames typical of construction in the United States and two-way frames typical of construction in Japan. For each framing system, four types of beam,column connections are considered: pre-Northridge welded-flange bolted-web, post-Northridge welded-flange welded-web, reduced-beam-section, and bolted-flange-plate connections. A suite of earthquake ground motions is used to compute the annual probability of exceedence (APE) for a series of drift demand levels and for member plastic-rotation capacity. Results are compared for the different framing systems and connection details. It is found that the two-way frames, which have a larger initial stiffness and strength than the one-way frames for the same beam and column volumes, have a smaller APE for small drift demands for which members exhibit no or minimal yielding, but have a larger APE for large drift demands for which members exhibit large plastic rotations. However, the one-way frames, which typically comprise a few seismic frames with large-sized members that have relatively small rotation capacities, may have a larger APE for member failure. The probabilistic approach presented in this study may be used to determine the most appropriate frame configuration to meet an owner's performance objectives. Copyright © 2008 John Wiley & Sons, Ltd. [source]

A risk-averse user equilibrium model for route choice problem in signal-controlled networks

JOURNAL OF ADVANCED TRANSPORTATION, Issue 4 2010
William H.K. Lam
Abstract This paper proposes a new risk-averse user equilibrium (RAUE) model to estimate the distribution of traffic flows over road networks with taking account the effects of accident risks due to the conflicting traffic flows (left- and right-turning and through traffic flows) at signalized intersections. It is assumed in the proposed model that drivers consider simultaneously both the travel time and accident risk in their route choices. The accident risk of a route is measured by the potential accident rate on that route. The RAUE conditions are formulated as an equivalent path-based variational inequality problem which can be solved by a path-based solution algorithm. It is shown that the traditional user equilibrium (UE) model is in fact a special case of the proposed model. A numerical example on a grid network is used to illustrate the application of the proposed model and to compare the results with the conventional UE traffic assignment. Numerical results show that the traditional UE model may underestimate the total system travel time and overestimate the system accident rate. Sensitivity tests are also carried out to assess the effects of drivers' preferences, signal control parameters (i.e., green time proportions), and various network demand levels on the route choice problem. Copyright © 2010 John Wiley & Sons, Ltd. [source]

Designing man-portable power generation systems for varying power demand

AICHE JOURNAL, Issue 5 2008
Mehmet Yunt
Abstract Portable electronic devices operate at varying power demand levels. This variability of power demand must be considered explicitly in the design of man-portable power generation systems for acceptable performance and portability. In this regard, a mathematical programming based design method is proposed. The method transcribes optimal operation of the system at a given power demand into a mathematical program. The power demand specific programs are incorporated into another upper level mathematical program encoding design requirements to form a final two-stage formulation. The design and operational parameters of the power generation system comprise a solution of the formulation. Unlike designs, based on a nominal power demand, the design guarantees that each power demand and all operational requirements can be satisfied. A detailed study of a microfabricated fuel-cell based system is performed. The proposed method produces smaller designs with significantly better performances than nominal power demand based approaches. © 2008 American Institute of Chemical Engineers AIChE J, 2008 [source]