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One-dimensional Models (one-dimensional + models)

Distribution by Scientific Domains

Engineering	50%

Selected Abstracts

Mobile radio bi-dimensional large-scale fading modelling with site-to-site cross-correlation

EUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 1 2008
Rubén Fraile
Wireless communication simulations are generally conducted using one-dimensional models for large-scale fading. While simple and with low computational costs, these models cannot produce correlated fading values for mobiles that are in nearby positions. To overcome this limitation, this paper presents a novel bi-dimensional large-scale fading model which introduces the spatial correlation present in real systems. Besides, it is also able to model the non-negligible cross-correlation among signals coming from different sites. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Using Temperature to Test Models of Flow Near Yucca Mountain, Nevada

GROUND WATER, Issue 5 2003
Scott Painter
Ground water temperatures in the fractured volcanic aquifer near Yucca Mountain, Nevada, have previously been shown to have significant spatial variability with regions of elevated temperatures coinciding roughly with near-vertical north-south trending faults. Using insights gained from one-dimensional models, previous investigators have suggested upwelling along faults from an underlying aquifer as a likely explanation for this ground water temperature pattern. Using a three-dimensional coupled flow and heat-transport model, we show that the thermal high coinciding with the Paintbrush fault zone can be explained without significant upwelling from the underlying aquifer. Instead, the thermal anomaly is consistent with thermal conduction enhanced slightly by vertical ground water movement within the volcanic aquifer sequence. If more than -400 m3/day of water enters the volcanic aquifer from below along a 10 km fault zone, the calculated temperatures at the water table are significantly greater than the measured temperatures. These results illustrate the potential limitations in using one-dimensional models to interpret ground water temperature data, and underscore the value in combining temperature data with fully coupled three-dimensional simulations. [source]

One-Dimensional Rabbit Sinoatrial Node Models:

JOURNAL OF CARDIOVASCULAR ELECTROPHYSIOLOGY, Issue 2003
Benefits, Limitations
Introduction: Cardiac multicellular modeling has traditionally focused on ventricular electromechanics. More recently, models of the atria have started to emerge, and there is much interest in addressing sinoatrial node structure and function. Methods and Results: We implemented a variety of one-dimensional sinoatrial models consisting of descriptions of central, transitional, and peripheral sinoatrial node cells, as well as rabbit or human atrial cells. These one-dimensional models were implemented using CMISS on an SGI® Origin® 2000 supercomputer. Intercellular coupling parameters recorded in experimental studies on sinoatrial node and atrial cell-pairs under-represent the electrotonic interactions that any cardiomyocyte would have in a multidimensional setting. Unsurprisingly, cell-to-cell coupling had to be scaled-up (by a factor of 5) in order to obtain a stable leading pacemaker site in the sinoatrial node center. Further critical parameters include the gradual increase in intercellular coupling from sinoatrial node center to periphery, and the presence of electrotonic interaction with atrial cells. Interestingly, the electrotonic effect of the atrium on sinoatrial node periphery is best described as opposing depolarization, rather than necessarily hyperpolarizing, as often assumed. Conclusion: Multicellular one-dimensional models of sinoatrial node and atrium can provide useful insight into the origin and spread of normal cardiac excitation. They require larger than "physiologic" intercellular conductivities in order to make up for a lack of "anatomical" spatial scaling. Multicellular models for more in-depth quantitative studies will require more realistic anatomico-physiologic properties. (J Cardiovasc Electrophysiol, Vol. 14, pp. S121-S132, October 2003, Suppl.) [source]

Explanation of high solar cell diode factors by nonuniform contact resistance

PROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 1 2005
A. S. H. van der Heide
Abstract The current density,voltage (J,V) curve that characterises the performance of a solar cell is often extra rounded, resulting in reduced efficiency. When fitting to the standard one-dimensional models, it is often found that the rounding cannot be fitted by the series resistance only. In these cases, the diode factor m or the depletion region saturation current density J0DR (depending on the model used) is increased. This behaviour could not be explained so far; this paper discusses if a nonuniform contact resistance of the front side metallisation leads to an increase of m or J0DR. The theoretical part of the investigation is the simulation of the curve for a cell with two regions with different contact resistance. It was found indeed that m or J0DR is increased, while the series resistance is not increased as much as expected. The experimental part was the calculation of the J,V curve of a high- m solar cell with local contact resistances measured with the so-called Corescan and the cell's resistanceless J,V curve as measured with the so-called Suns- Voc method. The calculated curve approximated the actual curve quite well, demonstrating in practice that high diode factors can be explained by nonuniform contact resistance. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Models of Change Agency: a Fourfold Classification

BRITISH JOURNAL OF MANAGEMENT, Issue 2 2003
Raymond Caldwell
Change agents often play significant roles in initiating, managing or implementing change in organizations. Yet these roles are invariably exaggerated or misrepresented by one-dimensional models that ignore the full complexity and scope of change agent roles. Following a review and theoretical clarification of some of the literature and empirical research on change agency, a new fourfold classification of change agents is proposed, covering leadership, management, consultancy, and team models. The four models reaffirm the significance of the multifaceted and complex roles change agents perform in organizational change, while underlining the importance of conceiving change interventions within organizations as processes that need to be coordinated and effectively managed. [source]