845,961 research outputs found

    Opposition at the Water Cooler: The Treatment of Non-Purposive Conduct Under Title VIIā€™s Anti-Retaliation Clause

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    A well-functioning, energy-efficient ventilation system is of vital importance to offices, not only to provide the kind of comfortable, healthy indoor environment necessary for the well-being and productive work performance of occupants, but also to reduce energy use in buildings and the associated impact of CO2 emissions on the environment. To achieve these goals impinging jet ventilation has been developed as an innovative ventilation concept. In an impinging jet ventilation system, a high momentum of air jet is discharged downwards, strikes the floor and spreads over it, thus distributing the fresh air along the floor in the form of a very thin shear layer. This system retains advantages of mixing and stratification from conventional air distribution methods, while capable of overcoming their shortcomings. The aim of this thesis is to reach a thorough understanding of impinging jet ventilation for providing a good thermal environment for an office, by using Computational Fluid Dynamics (CFD) supported by detailed measurements. The full-field measurements were carried out in two test rooms located in a large enclosure giving relatively stable climate conditions. This study has been divided into three parts where the first focuses on validation of numerical investigations against measurements, the second addresses impacts of a number of design parameters on the impinging jet flow field and thermal comfort level, and the third compares ventilation performance of the impinging jet supply device with other air supply devices intended for mixing, wall confluent jets and displacement ventilation, under specific room conditions. In the first part, velocity and temperature distributions of the impinging jet flow field predicted by different turbulence models are compared with detailed measurements. Results from the non-isothermal validation studies show that the accuracy of the simulation results is to a great extent dependent on the complexity of the turbulence models, due to complicated flow phenomena related to jet impingement, such as recirculation, curvature and instability. The v2-f turbulence model shows the best performance with measurements, which is slightly better than the SST k-Ļ‰ model but much better than the RNG k-Īµ model. The difference is assumed to be essentially related to the magnitude of turbulent kinetic energy predicted in the vicinity of the stagnation region. Results from the isothermal study show that both the SST k-Ļ‰ and RNG k-Īµ models predict similar wall jet behaviours of the impinging jet flow. In the second part, three sets of parametric studies were carried out by using validated CFD models. The first parametric study shows that the geometry of the air supply system has the most significant impact on the flow field. The rectangular air supply device, especially the one with larger aspect ratio, provides a longer penetration distance to the room, which is suitable for industrial ventilation. The second study reveals that the interaction effect of cooling ceiling, heat sources and impinging jet ventilation results in complex flow phenomena but with a notable feature of air circulation, which consequently decreases thermal stratification in the room and increases draught discomfort at the foot level. The third study demonstrates the advantage of using response surface methodology to study simultaneous effects on changes in four parameters, i.e. shape of air supply device, jet discharge height, supply airflow rate and supply air temperature. Analysis of the flow field reveals that at a low discharge height, the shape of air supply device has a major impact on the flow pattern in the vicinity of the supply device. Correlations between the studied parameters and local thermal discomfort indices were derived. Supply airflow rates and temperatures are shown to be the most important parameter for draught and stratification discomfort, respectively. In the third part, the impinging jet supply device was shown to provide a better overall performance than other air supply devices used for mixing, wall confluent jets and displacement ventilation, with respect to thermal comfort, heat removal effectiveness, air exchange efficiency and energy-saving potential related to fan power

    Modeling IS Activities for Business Process Reengineering : A Colored Petri Net Approach

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    The day to day functioning of any organization involves many business processes. Each business process is comprised of different activities. The identification of activities and their cost drivers is a critical factor for successful Business Process Reengineering. Since the resources used by the activities form an integral part of the model, the identification of the cost drivers is also simplified. This paper details the following : 1. It proposesthe use of colored Petri nets for process modeling. Brimson(1991) identifies the process modeling approach to activity analysis as useful since it graphically links the inputs and outputs among activities and identifies the information flow in the processes. However, use of process flow charts, which is most commonly used in activity analysis cannot capture some of the aspects of office processes, like supervision, general management, etc. In addition, representing the complex business logic associated with activities would be difficult in such flow models. The use of colored Petri nets overcomes this limitation, as business logic and various office processes can be easily represented. In addition, the complexity of the system is handled by resorting to hierarchical representation of the processes. 2. The paper applies the concept of activity based costing to the management of the IS processes in firms. The cost structure of these processes, to our knowledge, has not been studied from the activity based costing perspective. The article proposes the use of activity based costing for IS processes. Such analysis could help the organization in making operational as well as strategic decisions as related to its IS processe

    Salt marsh nitrogen analysis : fertilization and the allocation of biological productivity

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    A five compartment schematic model of the flow of nitrogen through Great Sippewissett Marsh is presented. Flows are described in terms of annual inputs, outputs and intercompartmental transfers of nitrogen. The nitrogen in all forms occurring in the marsh is considered, though dissolved organic nitrogen is disaggregated from the total flow. A computer aided input - output analysis is performed on the model to assess the degree to which nitrogen inputs to the marsh surface are linked to nitrogen outputs in the form of net growth in marsh shellfish. In this way the effects of both direct and indirect flows linking the two compartments involved are considered. The analysis is done to assess the likelihood that a large scale application of fertilizer to the marsh surface will signjficantly enhance shellfish growth in marsh tidal creeks. While no definitive answer to this question can be given, it is argued that the present level of understanding of the marsh nitrogen cycle does not support an expectation that shellfish growth will be enhanced. This argument is supported by a comparative analysis which shows a strong likelihood that Spartina growth is enhanced by fertilization, an effect which has already been observed.Prepared with funds from the Pew Memorial Trust and by the Department of Commerce, NOAA Office of Sea Grant under Grant #04-8- M01-149 and the Institution's Marine Policy and Ocean Management Program

    Laboratory experiments on eddy generation by a buoyant coastal current flowing over variable bathymetry

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    Author Posting. Ā© American Meteorological Society, 2006. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 36 (2006): 395-411, doi:10.1175/JPO2857.1.Irminger rings are warm-core eddies formed off the west coast of Greenland. Recent studies suggest that these eddies, which are implicated in the rapid springtime restratification of the Labrador Sea, are formed by an internal instability of the West Greenland Current (WGC), triggered by bathymetric variations. This study seeks to explore the effect of the magnitude and downstream length scale of bathymetric variations on the stability of a simple model of the WGC in a series of laboratory experiments in which a buoyant coastal current was allowed to flow over bathymetry consisting of piecewise constant slopes of varying magnitude. The currents did not form eddies over gently sloping bathymetry and only formed eddies over steep bathymetry if the current width exceeded the width of the sloping bathymetry. Eddying currents were immediately stabilized if they flowed onto gently sloping topography. Bathymetric variations that persisted only a short distance downstream perturbed the flow locally but did not lead to eddy formation. Eddies formed only once the downstream length of the bathymetric variations exceeded a critical scale of about 8 Rossby radii. These results are consistent with the observed behavior of the WGC, which begins to form Irminger rings after entering a region where the continental slope abruptly steepens and becomes narrower than the WGC itself in a region spanning about 20ā€“80 Rossby radii of downstream distance.The authors gratefully acknowledge the National Science Foundation (Grant OCE- 9810657) and the Office of Naval Research (Grant N00014-97-1-0934) for their support of the 2003 WHOI Geophysical Fluid Dynamics Summer School where much of the research presented in this paper was performed. CLW received additional support from the Office of Naval Research Grant N00014-98-1-0813

    Integrating power flow modelling with building simulation

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    The inclusion of photovoltaic facades and other local sources of both heat and power within building designs has given rise to the concept of embedded generation: where some or all of the heat and power demands are produced close to the point of use. This paper describes recent work to simulate the heat and power flows associated with both an embedded generation system and the building it serves. This is achieved through the development of an electrical power flow model and its integration within the ESP-r simulation program

    Probabilistic Hybrid Action Models for Predicting Concurrent Percept-driven Robot Behavior

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    This article develops Probabilistic Hybrid Action Models (PHAMs), a realistic causal model for predicting the behavior generated by modern percept-driven robot plans. PHAMs represent aspects of robot behavior that cannot be represented by most action models used in AI planning: the temporal structure of continuous control processes, their non-deterministic effects, several modes of their interferences, and the achievement of triggering conditions in closed-loop robot plans. The main contributions of this article are: (1) PHAMs, a model of concurrent percept-driven behavior, its formalization, and proofs that the model generates probably, qualitatively accurate predictions; and (2) a resource-efficient inference method for PHAMs based on sampling projections from probabilistic action models and state descriptions. We show how PHAMs can be applied to planning the course of action of an autonomous robot office courier based on analytical and experimental results

    An Approximate Numerical Scheme for the Theory of Cavity Flows Past Obstacles of Arbitrary Profile

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    Recently an exact theory for the cavity flow past an obstacle of arbitrary profile at an arbitrary cavitation number has been developed by adopting a free-streamline wake model. The analysis in this general case leads to a set of two functional equations for which several numerical methods have been devised; some of these methods have already been successfully carried out for several typical cases on a high speed electronic computer. In this paper an approximate numerical scheme, somewhat like an engineering principle, is introduced which greatly shortens the computation of the dual functional equations while still retaining a high degree of accuracy of the numerical result. With such drastic simplification, it becomes feasible to carry out this approximate mrmerical scheme even with a hand computing machine

    Consistency in Multi-Viewpoint Architectural Design of Enterprise Information Systems

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    Different stakeholders in the design of an enterprise information system have their own view on that design. To help produce a coherent design this paper presents a framework that aids in specifying relations between such views. To help produce a consistent design the framework also aids in specifying consistency rules that apply to the view relations and in checking the consistency according to those rules. The framework focuses on the higher levels of abstraction in a design, we refer to design at those levels of abstraction as architectural design. The highest level of abstraction that we consider is that of business process design and the lowest level is that of software component design. The contribution of our framework is that it provides a collection of basic concepts that is common to viewpoints in the area of enterprise information systems. These basic concepts aid in relating viewpoints by providing: (i) a common terminology that helps stakeholders to understand each others concepts; and (ii) a basis for defining re-usable consistency rules. In particular we define re-usable rules to check consistency between behavioural views that overlap or are a refinement of each other. We also present an architecture for a tool suite that supports our framework. We show that our framework can be applied, by performing a case study in which we specify the relations and consistency rules between the RM-ODP enterprise, computational and information viewpoints
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