Alborg University

Aalborg, Denmark

Alborg University

Aalborg, Denmark
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Skaaby T.,Glostrup Hospital | Husemoen L.L.N.,Glostrup Hospital | Borglykke A.,Glostrup Hospital | Jorgensen T.,Glostrup Hospital | And 6 more authors.
Endocrine | Year: 2014

Vitamin D deficiency is common among patients with liver diseases. Both cholestatic and non-cholestatic liver diseases can cause vitamin D deficiency. Whether vitamin D status can also affect liver function is poorly understood. To investigate the association between vitamin D status, liver enzymes, and incident liver disease, we included a total of 2,649 individuals from the Monica10 study conducted in 1993-1994. Vitamin D status as assessed by serum 25-hydroxyvitamin, serum alanine transaminase (ALT), aspartate transaminase (AST), and gamma glutamyl transferase (GGT) were measured at baseline. Information on fatal and non-fatal liver disease was obtained from the Danish National Patient Register and The Danish Registry of Causes of Death, respectively. Median follow-up time was 16.5 years, and there were 62 incident cases of fatal and non-fatal liver disease. Multivariable Cox regression analyses with age as underlying time axis and delayed entry showed a statistically significant inverse association between vitamin D status and incident liver disease with a hazard ratio = 0.88 (95 % confidence interval 0.79-0.99) per 10 nmol/l higher vitamin D status at baseline (adjusted for gender, season, alcohol consumption, smoking, physical activity, dietary habits, education, body mass index, and ALT). The risk of having a high level of ALT, AST, or GGT tended to be higher for lower vitamin D levels, although not statistically significant. In this general population study, vitamin D status was inversely associated with incident liver disease. Further studies are needed to determine whether patients in risk of developing impaired liver function should be screened for vitamin D deficiency for preventive purposes. © 2013 Springer Science+Business Media.

Skaaby T.,Glostrup University Hospital | Husemoen L.L.N.,Glostrup University Hospital | Thuesen B.H.,Glostrup University Hospital | Pisinger C.,Glostrup University Hospital | And 7 more authors.
Cancer Epidemiology Biomarkers and Prevention | Year: 2014

Background: Observational studies have suggested an inverse association between vitamin D status and cancer.Weinvestigated the prospective associations between vitaminDstatus and the total and specific type of cancer in three cohorts from the general Danish population. Methods: A total of 12,204 individuals 18 to 71 years old were included. The level of 25-hydroxyvitamin D was measured at baseline, and information about cancer was obtained from the Danish Cancer Registry. Results: During the 11.3-year median follow-up time, there were 1,248 incident cancers.HRs [95%confidence intervals (CI)] per 10nmol/L higher baseline vitaminDlevel were: for all cancers (HR=1.02; 95%CI, 0.99-1.04), all cancers excluding non-melanoma skin cancer, NMSC (HR = 1.00; 95% CI, 0.97-1.03), head and neck cancer (HR = 0.97; 95% CI, 0.84-1.12), colorectal cancer (HR = 0.95; 95% CI, 0.88-1.02), cancer of bronchus and lung (HR= 0.98; 95%CI, 0.91-1.05), breast cancer (HR= 1.02; 95%CI, 0.96-1.09), cancer of the uterus (HR= 1.10; 95% CI, 0.95-1.27), prostate cancer (HR = 1.00; 95% CI, 0.93-1.08), cancer of the urinary organs (HR = 1.01; 95% CI, 0.90-1.14), NMSC (HR = 1.06; 95% CI, 1.02-1.10), and malignant melanoma (HR = 1.06; 95% CI, 0.95-1.17). Conclusions: Apart from a significantly higher risk for NMSC with higher vitamin D status, we found no statistically significant associations between vitamin D status and total or specific cancers. Impact: Our results do not indicate that there is an impact of vitamin D on total cancer incidence. © 2014 American Association for Cancer Research.

Skaaby T.,Glostrup Hospital | Husemoen L.L.N.,Glostrup Hospital | Pisinger C.,Glostrup Hospital | Jorgensen T.,Glostrup Hospital | And 5 more authors.
PLoS ONE | Year: 2012

Background: Vitamin D deficiency is associated with an increased risk of all-cause mortality in observational studies. The specific causes of death underlying this association lack clarity. We investigated the association between vitamin D status and cause-specific mortality. Methods: We included a total of 9,146 individuals from the two population-based studies, Monica10 and Inter99, conducted in 1993-94 and 1999-2001, respectively. Vitamin D status was assessed as serum 25-hydroxyvitamin D. Information on causes of death was obtained from The Danish Register of Causes of Death until 31 December 2009. There were a total of 832 deaths (median follow-up 10.3 years). Results: Multivariable Cox regression analyses with age as underlying time axis and vitamin D quartiles showed significant associations between vitamin D status and death caused by diseases of the respiratory system, the digestive system, and endocrine, nutritional and metabolic diseases with hazard ratios (HRs) 0.26 (ptrend = 0.0042), 0.28 (ptrend = 0.0040), and 0.21 (ptrend = 0.035), respectively, for the fourth vitamin D quartile compared to the first. We found non-significantly lower HRs for death caused by mental and behavioural diseases and diseases of the nervous system, but no association between vitamin D status and death caused by neoplasms or diseases of the circulatory system. Conclusion: The associations of vitamin D status and cause-specific mortality suggest that we also look elsewhere (than to cardiovascular disease and cancer) to explain the inverse association between vitamin D status and mortality. © 2012 Skaaby et al.

Nielsen P.H.,Technical University of Denmark | Hattel J.,Technical University of Denmark | Leban K.,Alborg University | Svendsen H.,Sintef | Berthelsen P.A.,Norwegian Marine Technology Research Institute
Energy Procedia | Year: 2014

The DeepWind concept has been described previously on challenges and potentials, this new offshore floating technology can offer to the wind industry [1]. The paper describes state of the art design improvements, new simulation results of the DeepWind floating vertical axis wind turbine concept, which implies a high potential for cost saving. The most critical aspects of the concept are addressed in proving feasibility, and if it can be scaled up to 20 MW. Applying structural mechanics, generator, floater and mooring system, control system design, and rotor design using detailed integrated models, results have evolved to a 5 MW baseline design. This important outcome will be used as a reference for further improvements. Emphasis in this paper is made on the interplay between different components and some trade-offs. One such example is the rotational speed which largely influences the design of both the generator and the aerodynamic rotor. Another example is aerofoil design affecting energy capture, stall behaviour, structural dynamics and control design. Finally, the potential for up-scaling to 20 MW is discussed. © 2014 Elsevier Ltd. This is an open access article under the CC BY-NC-ND license.

Paulsen U.S.,Technical University of Denmark | Vita L.,Technical University of Denmark | Madsen H.A.,Technical University of Denmark | Hattel J.,Technical University of Denmark | And 4 more authors.
Energy Procedia | Year: 2012

The first 5MW baseline design of the DeepWind concept is presented for a Darrieus type floating wind turbine system for water depths of more than 150 m. This design will be used as design reference to test the next technological improvements of subcomponent level, being based as much as possible on existing technology. The iterative design process involves all sub-components and the potential constraints, and the most important dependencies are highlighted and the selected design presented. The blades are designed with constraints to minimize the gravitational loads and to be produced in a controlled pultrusion process. The floating platform is a slender cylindrical structure (i.e. spar buoy) rotating along with the rotor. The stability of the platform is achieved by adding counter weight at the bottom of the structure. During operations, the rotor is tilted and acts as a gyro, describing an elliptical trajectory on the water plane. The generator is placed at the bottom of the platform and uses 5MW direct drive technology. The conceptual design is evaluated with numerical simulations in the time domain using the aero-elastic code HAWC2. In order to investigate the concept, a double-disc blade element momentum (BEM) code for VAWTs has been included in the numerical solver through a dll. The analysis of the design is carried out in two different steps: 1) to estimate natural frequencies of the platform in order to avoid major resonance problems, 2) to evaluate the baseline concept for certain load cases. A site has been chosen for the floating turbine off Norway as representative for external conditions. The structure is verified according to an ultimate strength analysis, including loads from wind, waves and currents. The stability of the platform is investigated, considering the displacements of the spar buoy and the maximum inclination angle, which is kept lower than 15 degrees. © 2012 Published by Elsevier Ltd.

Kanthe A.M.,University of Zagreb | Simunic D.,University of Zagreb | Prasad R.,Alborg University
2012 IEEE International Conference on Computational Intelligence and Computing Research, ICCIC 2012 | Year: 2012

The mobile ad-hoc networks (MANET) are an emerging research area with applications. It has features like working as a router, dynamic topology and autonomous. In MANET, nodes have limited resources like battery power, storage space and bandwidth. There is a need to do more research for Denial of Service (DoS) attacks in MANET as compared to wire line DoS attacks. MANET is vulnerable to different types of DoS attack in which packets are drop. Black hole attack, packet drop attack and gray hole attack are an event that eliminates a network's capacity to perform its expected function. These attacks are type of DoS attack which we examine in this paper. This paper shows the effects of black hole attack, packet drop attack and gray hole attack on AODV protocol under different performance metrics throughput, packet drop rate and end-to-end delay. The simulation is done in Network Simulator (NS) 2. © 2012 IEEE.

Shafiee Q.,Alborg University | Nasirian V.,University of Texas at Arlington | Guerrero J.M.,Alborg University | Lewis F.L.,University of Texas at Arlington | Davoudi A.,University of Texas at Arlington
Proceedings, IECON 2014 - 40th Annual Conference of the IEEE Industrial Electronics Society | Year: 2014

This paper proposes a distributed control strategy for voltage and reactive power regulation in ac Microgrids. First, the control module introduces a voltage regulator that maintains the average voltage of the system on the rated value, keeping all bus voltages within an acceptable range. Dynamic consensus protocol is used to estimate the average voltage across the Microgrid. This estimation is further utilized by the voltage regulator to elevate/lower the voltage-reactive power (Q-E) droop characteristic, compensating the drop caused by the droop mechanism. The second module, the reactive power regulator, dynamically fine-tunes the Q-E coefficients to handle the proportional reactive power sharing. Accordingly, locally supplied reactive power of any source is compared with neighbor sources and the local droop coefficient is adjusted to mitigate and, ultimately, eliminate the load mismatch. The proposed controllers are fully distributed; i.e., each source requires information exchange with only a few other sources, those in direct contact through the communication infrastructure. A Microgrid test bench is used to verify the proposed control methodology, where different test scenarios such as load change, link failure, and inverter outage are carried out. © 2014 IEEE.

Elmitwally A.,Mansoura University | Elsaid M.,Mansoura University | Elgamal M.,Mansoura University | Chen Z.,Alborg University
IEEE Transactions on Sustainable Energy | Year: 2015

This paper proposes a new multiagent control system (MACS) for service restoration in distribution systems with integrated distributed generation (DG) units. First, the MACS detects and locates faults, then decides the optimal reconfiguration of the network for restoring de-energized loads, and finally regulates the nodes voltages. Unintentional islanding operation of DG units is avoided and different postfault response modes of DG unit are addressed in the MACS design. The MACS has a hybrid centralizeddecentralized structure where agents are arranged in two layers with different responsibilities and communication capabilities. Agents at load buses in the first layer can only communicate directly with its next neighbor load agents on the same feeder and to its feeder agent, whereas the higher level agents in the second layer can communicate directly with each other. This MACS structure reduces the possibilities of control system failures for a moderate communication network infrastructure. Full dynamic simulation model for evaluating the MACS is implemented. © 2010-2012 IEEE.

Elmitwally A.,Mansoura University | Elsaid M.,Mansoura University | Elgamal M.,Mansoura University | Chen Z.,Alborg University
IEEE Transactions on Power Systems | Year: 2015

In this paper, a new multi-agent control system (MACS) is proposed for smart distribution networks. It can: 1) eliminate the feeders' congestion, 2) globally correct voltage violations, and 3) coordinate the operation of reactive power control devices. In performing its functions, the MACS must prevent overstress on the substation voltage regulator tap changer under all operating conditions, and avoid selective active power curtailment from DG units. This can help to improve reliability, economic revenue, and power quality. A fuzzy rule-based system is employed for decision-making support in MACS. The proposed MACS can achieve the self-healing requirement of smart distribution network. It eliminates feeders' congestion by properly reconfiguring the distribution network. Meanwhile, it amends most of voltage violation problems by coordinated operation of voltage control devices in the distribution system. The MACS overcomes the severe voltage violation problems via distribution network reconfiguration. It is applied to the IEEE 33-bus test feeder. A full dynamic model is constructed using a parallel MATLAB-JADE simulation arrangement. Comparative performance evaluations of the MACS and other schemes are presented under various conditions. © 1969-2012 IEEE.

Martinez J.,Vestas Inc. | Kjar P.C.,Vestas Inc. | Rodriguez P.,Alborg University | Teodorescu R.,Alborg University
Wind Energy | Year: 2010

Modern wind power plants are required and designed to ride through faults in electrical networks, subject to fault clearing. Wind turbine fault current contribution is required from most countries with a high amount of wind power penetration. In order to comply with such grid code requirements, wind turbines usually have solutions that enable the turbines to control the generation of reactive power during faults. This paper addresses the importance of using an optimal injection of active current during faults in order to fulfil these grid codes. This is of relevant importance for severe faults, causing low voltages at the point of common coupling. As a consequence, a new wind turbine current controller for operation during faults is proposed. It is shown that to achieve the maximum transfer of reactive current at the point of common coupling, a strategy for optimal setting of the active current is needed. Copyright © 2010 John Wiley & Sons, Ltd.

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