| 11. |
- Chen, Ming, 1972, et al.
(author)
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New Approaches for Channel Prediction Based on Sinusoidal Modeling
- 2007
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In: Eurasip Journal on Applied Signal Processing. - : Springer Science and Business Media LLC. - 1110-8657 .- 1687-0433. ; 2007
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Journal article (peer-reviewed)abstract
- Long-range channel prediction is considered to be one of the most important enabling technologies to future wireless communication systems. The prediction of Rayleigh fading channels is studied in the frame of sinusoidal modeling in this paper. A stochastic sinusoidal model to represent a Rayleigh fading channel is proposed. Three different predictors based on the statistical sinusoidal model are proposed. These methods outperform the standard linear predictor (LP) in Monte Carlo simulations, but underperform with real measurement data, probably due to nonstationary model parameters. To mitigate these modeling errors, a joint moving average and sinusoidal (JMAS) prediction model and the associated joint least-squares (LS) predictor are proposed. It combines the sinusoidal model with an LP to handle unmodeled dynamics in the signal. The joint LS predictor outperforms all the other sinusoidal LMMSE predictors in suburban environments, but still performs slightly worse than the standard LP in urban environments.
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| 12. |
- Ekman, Bertil, et al.
(author)
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A dose titration model for recombinant GH substitution aiming at normal plasma concentrations of IGF-I in hypopituitary adults
- 2002
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In: European Journal of Endocrinology. - : Oxford University Press (OUP). - 0804-4643 .- 1479-683X. ; 147:1, s. 49-57
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Journal article (peer-reviewed)abstract
- OBJECTIVE: To evaluate a dose titration model for recombinant human GH substitution in adult patients with GH deficiency, aiming at normal plasma levels of IGF-I.DESIGN AND METHODS: Eighteen patients participated and a start dose of 0.17 mg GH/day was used except by two men who started with 0.33 mg/day. To demonstrate a clear GH effect the patients were first titrated, with steps of 0.17 mg GH/day every 6-8 weeks, to IGF-I levels in the upper range of age-adjusted reference values. The GH dose was then reduced 1 dose step and kept for a further 6 months. For comparison we investigated 17 healthy control subjects.RESULTS: Plasma IGF-I was increased after 2 weeks on the start dose and did not increase further for up to 8 weeks. Women had significantly lower GH sensitivity than men measured as net increment of IGF-I on the start dose of GH. GH sensitivity was not changed by age. The plasma IGF-I levels increased from 76.3+/-47.0 (s.d.) to 237+/-97 microg/l at the end of the study (P<0.001), and similar IGF-I levels were obtained in both sexes. The maintenance median GH dose was 0.33 mg/day in males and 0.83 mg/day in females (P=0.017). The GH dose correlated negatively with age in both sexes. Body weight, very low density triglycerides, lipoprotein(a) (Lp(a)), and fasting insulin increased, whereas insulin sensitivity index (QUICKI) decreased significantly. In comparison with the controls, the patients had lower fasting blood glucose, fasting insulin and Lp(a) levels at baseline, but these differences disappeared after GH substitution. The two groups had equal insulin sensitivity (QUICKI), but 2 h oral glucose tolerance test values of blood glucose and insulin were significantly higher in the patients at the end of the study.CONCLUSIONS: In conclusion our data suggest that the starting dose of GH substitution and the dose titration steps should be individualised according to GH sensitivity (gender) and the IGF-I level aimed for (age). The reduced insulin sensitivity induced by GH substitution could be viewed as a normalisation if compared with control subjects.
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| 13. |
- Ekman, Bertil, et al.
(author)
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A randomised double blind crossover study comparing two and four dose hydrocortisone regimen with regard to quality for life, cortisol and ACTH profiles in patients with primary adrenal insufficiency
- 2012
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In: Clinical Endocrinology. - : Wiley-Blackwell. - 0300-0664 .- 1365-2265. ; 77:1, s. 18-25
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Journal article (peer-reviewed)abstract
- ContextCurrent guidelines on how to divide the daily cortisol substitution dose in patients with primary adrenal insufficiency (PAI) are controversial and mainly based on empirical data.ObjectiveTo assess how an equal dose of hydrocortisone given either four times daily or twice daily influence diurnal profiles of cortisol and ACTH, patient preferences and health related quality of life (HRQoL).DesignDouble blind, crossover.MethodsFifteen patients with PAI (6 women) were included. Capsules of hydrocortisone or placebo were given at 07:00, 12:00, 16:00 and 22:00 h in 4-week treatment periods: either one period with four doses (10+10+5+5 mg) or one period with two doses (20+0+10+0 mg). Diurnal profiles of cortisol and ACTH were collected and area under the curve (AUC) was calculated. Questionnaires were used to evaluate patient preferences and HRQoL.ResultsThe four-dose regimen gave a higher serum cortisol before tablet intake in the morning (P = 0.027) and a higher 24-h-cortisolAUC (P < 0.0001) compared with the two-dose period. In contrast a lower median plasma ACTH in the morning before tablet intake (P = 0.003) and a lower 24-h-ln(ACTHAUC) were found during the four-dose period. The patients preferred the four-dose regimen (P = 0.03), and the HRQoL scores tended to be higher (high score indicates better HRQoL) for the four-dose period.In summary a four-dose regimen gives increased availability of cortisol and an enhanced effect with a less elevated ACTH in the morning in comparison with a two-dose regimen but the effect on HRQoL remains inconclusive.
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| 14. |
- Ekman, Bertil, et al.
(author)
-
Individualized growth hormone substitution with normalized IGF-I levels does not stimulate the renin–angiotensin–aldosterone system
- 2002
-
In: Clinical Endocrinology. - : Wiley. - 0300-0664 .- 1365-2265. ; 57:4, s. 473-479
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Journal article (peer-reviewed)abstract
- objective To study the effects of individualized recombinant GH substitution, aiming at normal circulating IGF-I levels, in GH-deficient adults on blood pressure, the renin–angiotensin–aldosterone system (RAAS), natriuretic peptides and urine free cortisol.study design Open study with control group. The patients were titrated in dose steps of 0·17 mg GH/day every 6–8 weeks until an IGF-I level around the mean + 1 SD was attained (Tmax). After another month the dose was reduced by 0·17 mg (minimum dose 0·17 mg/day) to produce IGF-I levels at or slightly below the age-related mean (Tend), and this maintenance dose was held constant for 6 months.subjects Eighteen patients (11 males and seven females) with GH deficiency participated. For comparison we also prospectively evaluated 17 matched control subjects.measurements Blood pressure and heart rate, circulating levels of IGF-I, plasma renin activity (PRA), immunoreactive active renin (IRR), angiotensin II, aldosterone, atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP) and 24-h urine aldosterone and urine free cortisol levels.results Blood pressure was unchanged by GH substitution but heart rate increased significantly (P < 0·03). PRA was elevated on the highest GH dose (Tmax) compared to baseline (P < 0·01), but returned to baseline and levels of controls at Tend. Four patients developed transient oedema and tended to have higher PRA levels than the rest of the subjects (P = 0·09). The circulating levels of IRR, angiotensin II, aldosterone, BNP and 24-h urine aldosterone and urine free cortisol levels were unchanged by GH substitution, and did not differ from the levels in the control subjects. Baseline ANP levels in the patients were lower than in the controls (P < 0·01), but increased after GH substitution (P < 0·01) to levels found in with the controls.conclusions We found no major changes of the variables in the circulating renin–angiotensin–aldosterone system and a normalization of atrial natriuretic peptide when an individualized dose of GH was titrated to near-normal IGF-I levels.
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| 15. |
- Ekman, Maria, et al.
(author)
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Inte så smakfullt
- 1997
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In: Dagens Nyheter. ; :27 februari
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Journal article (pop. science, debate, etc.)
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| 16. |
- Ekman, Petter, 1988-, et al.
(author)
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Aerodynamic Drag Reduction - from Conceptual Design on a Simplified Generic Model to Full-Scale Road Tests
- 2015
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In: SAE 2015 World Congress & Exhibition. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International.
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Conference paper (peer-reviewed)abstract
- Road transportation by trucks is the major part of the goods transportations system in the European Union (EU), and there is a need for increased fuel efficiency. While truck manufacturers already spend significant resources in order to reduce the emissions from their vehicles, most truck manufacturers do not control the shape of the trailer and/or swap bodies. These devices are usually manufactured by different companies that cannot consider the overall aerodynamics around the complete vehicle.By use of Computational Fluid Dynamics (CFD) and previous wind tunnel experiments, the flow around a simplified generic tractor-trailer model has been investigated. With better understanding of the flow features around the tractor with attached trailer or swap bodies, an improved design of the trailer and swap body can be achieved, which is the aim for the project. Special emphasis is put on achieving simple, easy to install or implement drag-reducing geometrical modifications to the trailer or swap bodies that can be mounted on existing trucks.Reynolds-Averaged Navier-Stokes (RANS) simulations were used for the conceptual development phase where trends in drag reduction due to the modified geometries were studied using a parameter study, while more advanced scale resolving simulations (SRS) were used in order to investigate the details of the flow fields.The investigation indicates that aerodynamic drag reduction is possible with quite simple geometrical modifications. Some of the results have also been verified through road tests of vehicles in commercial use, which has shown reduced fuel consumption of up to 5%.
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| 17. |
- Ekman, Peter, 1969-, et al.
(author)
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Extending the ERP system : considering the business relationship portfolio
- 2014
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In: Business Process Management Journal. - : Emerald Group Publishing Limited. - 1463-7154 .- 1758-4116. ; 20:3, s. 480-501
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Journal article (peer-reviewed)abstract
- Purpose – Research has shown that companies focus their internal processes when they adopt enterprise resource planning (ERP) systems. However, the ERP systems need to expand their functionality to include customers and suppliers (with e-commerce functionality) to reach their full potential. The purpose of this paper is to consider business relationships as a resource but also a limitation when companies strive to get an extended ERP system.Design/Methodology/approach – The paper presents an illustrative case study of an industrial company’s process of developing an extended ERP and how the company’s portfolio of business relationships has affected the solution. The analysis is supported by the markets-as-networks theory.Findings – The process of developing an extended ERP system needs to incorporate the company’s business partners (customers and suppliers). It is a simultaneously bottom-up and top-down process given that the operative frontline staff hold the knowledge about the company’s business relationships while the corporate management has the means of extending the ERP system functionality and align it with the focal company’s strategy.Research implications – Companies need to consider the fact that the technological and financial status of their customers and suppliers differ. Thus, an effective and flexible extended ERP system needs to include both a high-end and low-end solution as well as understand that a full interorganizational integration might not be realistic.Originality/value – The paper puts forth business relationship portfolios as an important factor to consider when extending the ERP system functionality in the supply chain and towards customers.
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| 18. |
- Ekman, Petter, 1988-, et al.
(author)
-
Importance of Sub-Grid Scale Modeling for Accurate Aerodynamic Simulations
- 2021
-
In: Journal of Fluids Engineering. - : ASME. - 0098-2202 .- 1528-901X. ; 143:1
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Journal article (peer-reviewed)abstract
- The Ahmed body is one of the most well-investigated vehicle bodies for aerodynamic purposes. Despite its simple geometry, the flow around the body, especially at the rear, is very complex as it is dominated by a large wake with strong interaction between vortical structures. In this study, the flow around the 25 deg Ahmed body has been investigated using large eddy simulations and compared to high-resolution particle image velocimetry (PIV) measurements. Special emphasis was put on studying three commonly used sub-grid scale (SGS) models and their ability to capture vortical structures around the Ahmed body. The ability of the SGS models to capture the near-wall behavior and small-scale dissipation is crucial for capturing the correct flow field. Very good agreement between simulations and PIV measurements were seen when using the dynamic Smagorinsky-Lilly and the wall-adopting local eddy-viscosity SGS models, respectively. However, the standard Smagorinsky-Lilly model was not able to capture the flow patterns when compared to the PIV measurements due to shortcomings in the near-wall modeling in the standard Smagorinsky-Lilly model, resulting in overpredicted separation.
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| 19. |
- Ekman, Petter, 1988-
(author)
-
Important Factors for Accurate Scale-Resolving Simulations of Automotive Aerodynamics
- 2020
-
Doctoral thesis (other academic/artistic)abstract
- Road transports are responsible for almost 18 % of the greenhouse gas emission in Europe and are today the leading cause of air pollution in cities. Aerodynamic resistance has a significant effect on fuel consumption and hence the emission of vehicles. For electric vehicles, emissions are not affected by the aerodynamics as such but instead have a significant effect on the effective range of the vehicle.In 2017, a new measurement procedure was introduced, Worldwide Harmonized Light Vehicles Test Procedure (WLTP), for measuring emissions, fuel consumption, and range. This procedure includes a new test cycle with increased average driving speed compared to the former procedure, which thereby increases the importance of the aerodynamic resistance, as it drastically increases with speed. A second effect is that the exact car configuration sold to the customer needs to be certified in terms of fuel consumption and emissions. The result is that every possible combination of optional extras, which might affect the aerodynamic resistance, needs to be aerodynamically analyzed and possibly improved. From 2021, the European Commission will introduce stricter emission regulations for new passenger cars, with the fleet-wide average lowered to 95 grams CO2=km, which puts an even higher demand on achieving efficient aerodynamics.Virtual development of the aerodynamics of road vehicles is today used to a great extent, using Computational Fluid Dynamics, as it enables faster and cheaper development. However, achieving high accuracy for the prediction of the flow field and aerodynamic forces is challenging, especially given the complexity of both the vehicle geometry in itself and the surrounding flow field. Even for a simplified generic bluff body, accurately predicting the flow field and aerodynamic forces is a challenge. The main reason for this challenge of achieving results with high accuracy is the prediction of the complex behavior of turbulence. Scale-resolving simulation (SRS) methods, such as Large Eddy Simulation (LES), where most of the turbulent structures are resolved has in many studies shown high accuracy but unfortunately to a very high computational cost. It is primarily the small turbulent structures within the near-wall region that requires a _ne resolution in both space (the mesh) and in time. This fine resolution is the reason for the very high computational cost and makes LES unfeasible for practical use in industrial aerodynamic development at present and in the near future. By modeling the turbulent structures within the near-wall region using a Reynolds-Averaged Navier-Stokes (RANS) model, and resolving the turbulence outside the region with a LES model, a coarser resolution is possible to use, resulting in significantly lower computational cost. Which used RANS model is of high importance, and especially how much turbulent viscosity the model generates, as too high values can result in suppression of the resolved turbulence.The transitioning between the RANS and LES regions have a significant effect on the results. Faster transition enables more resolved turbulence, favorable for higher accuracy, but needs to be balanced with sufficient shielding of the RANS region. If resolving the turbulence occurs within the near-wall region, and the mesh is not sufficiently fine, it can result in poor accuracy.By increasing the time-step size and disregarding best-practice guides, the computational cost can be significantly reduced. The accuracy is reasonably insensitive to the larger time step sizes until a certain degree, thereby enabling computationally cheaper SRS to achieve high accuracy of aerodynamic predictions needed to meet present and future emission regulations.
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| 20. |
- Ekman, Stefan, et al.
(author)
-
Skånes lavar
- 2003
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In: Floran i Skåne. Vegetation och utflyktsmål.. - 9197102148 ; , s. 125-132
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Book chapter (pop. science, debate, etc.)
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