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  • Springer  (34)
  • American Association for the Advancement of Science  (2)
  • 1995-1999  (16)
  • 1990-1994  (20)
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Year
  • 1
    Electronic Resource
    Electronic Resource
    Estimating the throughput of an exponential CONWIP assembly system (1993)
    Springer
    Queueing systems 14 (1993), S. 135-157 
    Details
    ISSN: 1572-9443
    Keywords: Assembly-like queues ; approximations ; throughput, design issues
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract We consider a production system consisting of several fabrication lines feeding an assembly station where both fabrication and assembly lines consist of multiple machine exponential workstations and the CONWIP (CONstant Work-In-Process) mechanism is used to regulate work releases. We model this system as an assembly-like queue and develop approximations for the throughput and average number of jobs in queue. These approximations use an estimate of the time that jobs from each line spend waiting for jobs from other lines before being assembled. We use our approximations to gain insight into the related problems of capacity allocation, bottleneck placement and WIP setting.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01153531
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  • 2
    Electronic Resource
    Electronic Resource
    Estimating variance of output from cyclic exponential queueing systems (1990)
    Springer
    Queueing systems 7 (1990), S. 337-353 
    Details
    ISSN: 1572-9443
    Keywords: Closed queueing networks ; cyclic queues ; approximations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract Production systems, particularly those making use of a “pull” production control mechanism, are well-modeled as closed queueing networks. Average throughput is clearly one important performance measure for these systems. However, many control decisions require information concerning the variability of the output process as well as throughput. Because of this, the standard deviation of the number of outputs during a specified interval is a practical performance measure for production systems. In this paper, we consider the standard deviation of the number of outputs during a time interval from a closed queueing network consisting ofM single server exponential queues. Because computing this quantity exactly is extremely cumbersome, we introduce a simple approximation that makes use of (1) known results for the variance of the time a marked job takes to complete a round trip and (2) an approximate correction term for the covariance between successive round trips. We show through comparisons with simulation that our method is quite accurate under a variety of conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01154550
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  • 3
    Electronic Resource
    Electronic Resource
    Forecast horizons and dynamic facility location planning (1992)
    Springer
    Annals of operations research 40 (1992), S. 125-151 
    Details
    ISSN: 1572-9338
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Economics
    Notes: Abstract We consider a dynamic facility location model in which the objective is to find a planning horizon, τ*, and a first period decision,X 1*, such thatX 1* is a first period decision for at least one optimal policy for all problems with planning horizons equal to or longer than τ*. In other words, we seek a planning horizon, τ*, such that conditions after τ* do not influence the choice of the optimal initial decision,X 1*. We call τ* aforecast horizon andX 1* anoptimal initial decision. For the dynamic uncapacitated fixed charge location problem, we show that simple conditions exist such that the initial decision depends on the length of the planning horizon. Thus, a strictly optimal forecast horizon and initial policy may not exist. We therefore introduce the concepts ofe-optimal forecast horizons and ε-optimal initial solutions. Our computational experience inicates that such solutions can be found for practical problems. Although computing ε-optimal forecast horizons and initial decisions can be cumbersome, this approach offers the potential for making significantly better decisions than those generated by other approaches. To illustrate this, we show that the use of the scenario planning approach can lead to the adoption of the worst possible initial decision under conditions of future uncertainty. On the basis of our results, it appears that the forecast horizon approach offers an attractive tool for making dynamic location decisions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02060473
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  • 4
    Electronic Resource
    Electronic Resource
    Influence of forbs and shrubs on intake, digestibility, and nitrogen and energy balance in sheep fed low-quality straw (1993)
    Springer
    Agroforestry systems 24 (1993), S. 95-104 
    Details
    ISSN: 1572-9680
    Keywords: barley straw ; alfalfa ; forbs ; shrubs ; wethers ; supplementation ; intake ; digestibility ; nitrogen balance ; metabolizable energy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract A 4×4 Latin square experiment (Exp) was conducted using eight Debouillet yearling wethers with two wethers/cell to compare the effects of forbs and shrubs supplementation to a low-quality barley straw with alfalfa hay (ALF) supplementation in terms of nutrient digestion and balance. Diets studied in the Exp were barley straw (0.56% N) and straw plus either 42% ALF, 63% forbs (a 50:50 mixture of scarlet globemallow and leatherleaf croton) or 62% shrubs (mixture of 50% fourwing saltbush and 50% mountain mahogany). Diets containing ALF, forbs and shrubs were isonitrogenous (1.68% N). Periods of each Latin square were 15 days with total fecal and urine collections obtained on the last 5 days of each period. Dry matter intake of ALF and shrub-containing diets was similar and higher (P〈0.05) than straw alone or straw plus forb diets. Nitrogen (N) retention was improved, but NDF digestibility was reduced (P〈0.05), in diets containing ALF and shrubs compared with straw only. No difference in N retention among diets were detected (P〉0.05) when N intake was used as a covariate. Metabolizable energy (ME) content of all the diets was similar except the shrub containing diet that was lower than the straw plus forbs or straw plus ALF but similar to the straw diet. Forbs had little influence on digestion and N utilization in the Exp presumably because of their reduced acceptability in the dried and ground form by sheep. Results suggest that native shrubs used in the study influenced intake and N utilization in a manner similar to ALF; and forbs used were similar in ME to ALF.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00705270
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  • 5
    Electronic Resource
    Electronic Resource
    Influence of forbs and shrubs on ruminal fermentation and digesta kinetics in sheep fed a grass hay/straw diet (1993)
    Springer
    Agroforestry systems 24 (1993), S. 145-156 
    Details
    ISSN: 1572-9680
    Keywords: blue grama ; barley straw ; alfalfa ; forbs ; shrubs ; wethers ; supplementation ; pH ; ammonia-concentrations ; ruminal fermentation digesta kinetics ; in situ digestibility
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Four ruminally cannulated, Debouillet wethers were used in a 4×4 latin square experiment to evaluate the influence of a forb mix, a shrub mix and alfalfa (ALF) hay on ruminal fermentation characteristics and digesta kinetics of a basal grass hay/straw (GH/S; 1.04% N) diet. The grass hay was mostly blue grama (Bouteloua gracilis) mixed with barley (Hordeum vulgare) straw. Wethers were fed either the GH/S mix (70∶30), GH/S∶ALF (29∶58∶13), GH/S∶forbs (26∶54∶20), or GH/S∶shrubs (26∶54∶20). The forb component consisted of equal parts of scarlet globemallow (Sphaeralcea coccinea) and leatherleaf croton (Croton corymbulosus) while shrubs were composed of equal parts of fourwing saltbush (Atriplex canescens) and mountain mahogany (Cercocarpus montanus). Ruminal pH, ammonia-N, as well as total VFA concentrations and molar proportions of individual VFA did not differ among diets. Particulate passage rates tended (P〉0.10) to be greater for diets containing ALF, forbs or shrubs (2.8, 2.9 and 2.8% h−1) than the GH/S diet (2.5% h−1). In situ DM and NDF disappearance of a GH/straw (50∶50) mix did not differ among treatments at most incubation times, except at 96 h when extent of both DM and NDF disappearance were greater (P〈0.05) in sheep fed either forbs or shrubs than in those fed other diets.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00706888
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  • 6
    Electronic Resource
    Electronic Resource
    HAPEX-Sahel: a large-scale study of land-atmosphere interactions in the semi-arid tropics (1994)
    Springer
    Annales geophysicae 12 (1994), S. 53-64 
    Details
    ISSN: 0992-7689
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The Hydrologic Atmospheric Pilot EXperiment in the Sahel (HAPEX-Sahel) was carried out in Niger, West Africa, during 1991 - 1992, with an intensive observation period (IOP) in August - October 1992. It aims at improving the parameterization of land surface atmosphere interactions at the Global Circulation Model (GCM) gridbox scale. The experiment combines remote sensing and ground based measurements with hydrological and meteorological modelling to develop aggregation techniques for use in large scale estimates of the hydrological and meteorological behaviour of large areas in the Sahel. The experimental strategy consisted of a period of intensive measurements during the transition period of the rainy to the dry season, backed up by a series of long term measurements in a 1^ by 1^ square in Niger. Three “supersites” were instrumented with a variety of hydrological and (micro) meteorological equipment to provide detailed information on the surface energy exchange at the local scale. Boundary layer measurements and aircraft measurements were used to provide information at scales of 100 - 500 km2. All relevant remote sensing images were obtained for this period. This programme of measurements is now being analyzed and an extensive modelling programme is under way to aggregate the information at all scales up to the GCM grid box scale. The experimental strategy and some preliminary results of the IOP are described.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-994-0053-0
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  • 7
    Electronic Resource
    Electronic Resource
    A calibration technique for multiple-sensor hot-wire probes and its application to vorticity measurements in the wake of a circular cylinder (1993)
    Springer
    Experiments in fluids 15 (1993), S. 209-218 
    Details
    ISSN: 1432-1114
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A calibration technique for multiple-sensor hot-wire probes is presented. The technique, which requires minimal information about the probe geometry, is tested using a four-sensor and a twelve-sensor probe. Two data reduction algorithms are introduced. The first one assumes a uniform velocity over the probe sensing-volume and is applied to the four-sensor probe measurements. The second one assumes a uniform velocity gradient over the sensing volume of the probe. The procedure, when applied to the twelve-sensor probe, is shown to measure the velocity gradient components successfully. In both algorithms, the unknowns (velocity and velocity gradient components) are obtained by solving the resulting systems of nonlinear algebraic equations in a least-squares sense. The performances of the probes and the algorithms are tested with measurements in the wake of a circular cylinder. The statistics and spectra show that the twelve-sensor probe is successful in the simultaneous measurement of all three components of the velocity and all three components of the vorticity vectors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00189888
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  • 8
    Electronic Resource
    Electronic Resource
    Turbulence averaging within spark ignition engines (1999)
    Springer
    Experiments in fluids 27 (1999), S. 92-101 
    Details
    ISSN: 1432-1114
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract  This paper examines velocity averaging within Spark-Ignition (SI) engines, a non-stationary system. Comparison is made between the mean and turbulence velocities found from (a) Ensemble, (b) Cyclic and (c) Wavelet-based averaging. The various methods of extracting turbulence within this flow system result in qualitatively similar average velocities; however, there are significant differences in the turbulence velocities and spectral content of the flow field based on the definition used. The differing interpretation of turbulence results in a subjectivity to the physical understanding of the flows. The experience in extracting coherent structures in stationary turbulence suggests that wavelet analysis offers a unique insight that has applicability for engine studies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003480050333
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  • 9
    Electronic Resource
    Electronic Resource
    Investigations into the effect of LDV seed particles on the operating characteristics of a spark ignition engine (1999)
    Springer
    Experiments in fluids 27 (1999), S. 175-180 
    Details
    ISSN: 1432-1114
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract  LDV measurements are commonly made in spark ignition engines to investigate the interaction between the flow field and the combustion process. To achieve high LDV data rates relatively large quantities of seed particles must be introduced into the engine intake flow. Based on the measurement of the characteristic engine operating parameters, it was determined that the introduction of TiO2 seed particles into an optical L-head research engine fuelled by natural gas at stoichiometric and lean conditions did not significantly influence the combustion process.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003480050342
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  • 10
    Electronic Resource
    Electronic Resource
    The velocity field of the turbulent very near wake of a circular cylinder (1996)
    Springer
    Experiments in fluids 20 (1996), S. 441-453 
    Details
    ISSN: 1432-1114
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Hot-wire measurements were conducted in the very near wake (x/d⩽10) of a circular cylinder at a Reynolds number based on cylinder diameter, Re d of 3900. Measurements of the streamwise velocity component with the use of single sensor hot-wire probes were found to be inaccurate for such flowfields where high flow angles are present. An X-array probe provided detailed streamwise and lateral velocity component statistics. Frequency spectra of these two velocity components are also presented. Measurements with a 4-sensor hot-wire probe confirmed that the very near wake region is dominantly two-dimensional, thus validating the accuracy of the present X-array data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00189383
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