Showing papers by "Aalborg University published in 2008"

General and abdominal adiposity and risk of death in Europe.

Abstract: Background Previous studies have relied predominantly on the body-mass index (BMI, the weight in kilograms divided by the square of the height in meters) to assess the association of adiposity with the risk of death, but few have examined whether the distribution of body fat contributes to the prediction of death. Methods We examined the association of BMI, waist circumference, and waist-to-hip ratio with the risk of death among 359,387 participants from nine countries in the European Prospective Investigation into Cancer and Nutrition (EPIC). We used a Cox regression analysis, with age as the time variable, and stratified the models according to study center and age at recruitment, with further adjustment for educational level, smoking status, alcohol consumption, physical activity, and height. Results During a mean follow-up of 9.7 years, 14,723 participants died. The lowest risks of death related to BMI were observed at a BMI of 25.3 for men and 24.3 for women. After adjustment for BMI, waist circumfer...

Overview of different wind generator systems and their comparisons

Abstract: With rapid development of wind power technologies and significant growth of wind power capacity installed worldwide, various wind turbine concepts have been developed. The wind energy conversion system is demanded to be more cost-competitive, so that comparisons of different wind generator systems are necessary. An overview of different wind generator systems and their comparisons are presented. First, the contemporary wind turbines are classified with respect to both their control features and drive train types, and their strengths and weaknesses are described. The promising permanent magnet generator types are also investigated. Then, the quantitative comparison and market penetration of different wind generator systems are presented. Finally, the developing trends of wind generator systems and appropriate comparison criteria are discussed. It is shown that variable speed concepts with power electronics will continue to dominate and be very promising technologies for large wind farms. The future success of different wind turbine concepts may strongly depend on their ability of complying with both market expectations and the requirements of grid utility companies.

Weighted sum-rate maximization using weighted MMSE for MIMO-BC beamforming design

Abstract: This paper studies linear transmit filter design for Weighted Sum-Rate (WSR) maximization in the multiple input multiple output broadcast channel (MIMO-BC). The problem of finding the optimal transmit filter is non-convex and intractable to solve using low complexity methods. Motivated by recent results highlighting the relationship between mutual information and minimum mean square error (MMSE), this paper establishes a relationship between weighted sum-rate and weighted MMSE in the MIMO-BC. The relationship is used to propose two low complexity algorithms for finding a local weighted sum-rate optimum based on alternating optimization. Numerical results studying sum-rate show that the proposed algorithms achieve high performance with few iterations.

Production of phycocyanin : a pigment with applications in biology, biotechnology, foods and medicine

Abstract: C-phycocyanin (C-PC) is a blue pigment in cyanobacteria, rhodophytes and cryptophytes with fluorescent and antioxidative properties. C-PC is presently extracted from open pond cultures of the cyanobacterium Arthrospira platensis although these cultures are not very productive and open for contaminating organisms. C-PC is considered a healthy ingredient in cyanobacterial-based foods and health foods while its colouring, fluorescent or antioxidant properties are utilised only to a minor extent. However, recent research and developments in C-PC synthesis and functionality have expanded the potential applications of C-PC in biotechnology, diagnostics, foods and medicine: The productivity of C-PC has been increased in heterotrophic, high cell density cultures of the rhodophyte Galdieria sulphuraria that are grown under well-controlled and axenic conditions. C-PC purification protocols based on various chromatographic principles or novel two-phase aqueous extraction methods have expanded in numbers and improved in performance. The functionality of C-PC as a fluorescent dye has been improved by chemical stabilisation of C-PC complexes, while protein engineering has also introduced increased stability and novel biospecific binding sites into C-PC fusion proteins. Finally, our understanding of the physiological functions of C-PC in humans has been improved by a mechanistic hypothesis that links the chemical properties of the phycocyanobilin chromophores of C-PC to the natural antioxidant, bilirubin, and may explain the observed health benefits of C-PC intake. This review outlines how C-PC is produced and utilised and discusses the novel C-PC synthesis procedures and applications.

Reliability Issues in Photovoltaic Power Processing Systems

Abstract: Power processing systems will be a key factor of future photovoltaic (PV) applications. They will play a central role in transferring, to the load and/or to the grid, the electric power produced by the high-efficiency PV cells of the next generation. In order to come up the expectations related to the use of solar energy for producing electrical energy, such systems must ensure high efficiency, modularity, and, particularly, high reliability. The goal of this paper is to provide an overview of the open problems related to PV power processing systems and to focus the attention of researchers and industries on present and future challenges in this field.

Graphene antidot lattices: designed defects and spin qubits.

Abstract: Antidot lattices, defined on a two-dimensional electron gas at a semiconductor heterostructure, are a well-studied class of man-made structures with intriguing physical properties. We point out that a closely related system, graphene sheets with regularly spaced holes ("antidots"), should display similar phenomenology, but within a much more favorable energy scale, a consequence of the Dirac fermion nature of the states around the Fermi level. Further, by leaving out some of the holes one can create defect states, or pairs of coupled defect states, which can function as hosts for electron spin qubits. We present a detailed study of the energetics of periodic graphene antidot lattices, analyze the level structure of a single defect, calculate the exchange coupling between a pair of spin qubits, and identify possible avenues for further developments.

Discovery of convoys in trajectory databases

Abstract: As mobile devices with positioning capabilities continue to proliferate, data management for so-called trajectory databases that capture the historical movements of populations of moving objects becomes important. This paper considers the querying of such databases for convoys, a convoy being a group of objects that have traveled together for some time.More specifically, this paper formalizes the concept of a convoy query using density-based notions, in order to capture groups of arbitrary extents and shapes. Convoy discovery is relevant for real-life applications in throughput planning of trucks and carpooling of vehicles. Although there has been extensive research on trajectories in the literature, none of this can be applied to retrieve correctly exact convoy result sets. Motivated by this, we develop three efficient algorithms for convoy discovery that adopt the well-known filter-refinement framework. In the filter step, we apply line-simplification techniques on the trajectories and establish distance bounds between the simplified trajectories. This permits efficient convoy discovery over the simplified trajectories without missing any actual convoys. In the refinement step, the candidate convoys are further processed to obtain the actual convoys. Our comprehensive empirical study offers insight into the properties of the paper's proposals and demonstrates that the proposals are effective and efficient on real-world trajectory data.

Arabidopsis MAP kinase 4 regulates gene expression through transcription factor release in the nucleus

Abstract: Plant and animal perception of microbes through pathogen surveillance proteins leads to MAP kinase signalling and the expression of defence genes. However, little is known about how plant MAP kinases regulate specific gene expression. We report that, in the absence of pathogens, Arabidopsis MAP kinase 4 (MPK4) exists in nuclear complexes with the WRKY33 transcription factor. This complex depends on the MPK4 substrate MKS1. Challenge with Pseudomonas syringae or flagellin leads to the activation of MPK4 and phosphorylation of MKS1. Subsequently, complexes with MKS1 and WRKY33 are released from MPK4, and WRKY33 targets the promoter of PHYTOALEXIN DEFICIENT3 (PAD3) encoding an enzyme required for the synthesis of antimicrobial camalexin. Hence, wrky33 mutants are impaired in the accumulation of PAD3 mRNA and camalexin production upon infection. That WRKY33 is an effector of MPK4 is further supported by the suppression of PAD3 expression in mpk4–wrky33 double mutant backgrounds. Our data establish direct links between MPK4 and innate immunity and provide an example of how a plant MAP kinase can regulate gene expression by releasing transcription factors in the nucleus upon activation.

Optimized Maximum Power Point Tracker for Fast-Changing Environmental Conditions

Abstract: This paper presents a high-performance maximum power point tracker (MPPT) optimized for fast cloudy conditions, e.g., rapidly changing irradiation on the photovoltaic panels. The rapidly changing conditions are tracked by an optimized hill-climbing MPPT method called dP-P&O. This algorithm separates the effects of the irradiation change from the effect of the tracker's perturbation and uses this information to optimize the tracking according to the irradiation change. The knowledge of the direction of the irradiation change enables the MPPT to use different optimized tracking schemes for the different cases of increasing, decreasing, or steady irradiance. When the irradiance is changing rapidly this strategy leads to faster and better tracking, while in steady-state conditions it leads to lower oscillations around the MPP. The simulations and experimental results show that the proposed dP-P&O MPPT provides a quick and accurate tracking even in very fast changing environmental conditions.

Comparing the Expressiveness of Timed Automata and Timed Extensions of Petri Nets

Abstract: Time dependant models have been intensively studied for many reasons, among others because of their applications in software verification and due to the development of embedded platforms where reliability and safety depend to a large extent on the time features. Many of the time dependant models were suggested as real-time extensions of several well-known untimed models. The most studied formalisms include Networks of Timed Automata which extend the model of communicating finite-state machines with a finite number of real-valued clocks, and timed extensions of Petri nets where the added time constructs include e.g. time intervals that are assigned to the transitions (Time Petri Nets) or to the arcs (Timed-Arc Petri Nets). In this paper, we shall semi-formally introduce these models, discuss their strengths and weaknesses, and provide an overview of the known results about the relationships among the models.

Shunt Active-Power-Filter Topology Based on Parallel Interleaved Inverters

Abstract: In this paper, an interleaved active-power-filter concept with reduced size of passive components is discussed. The topology is composed of two pulsewidth-modulation interleaved voltage-source inverters connected together on the ac line and sharing the same dc-link capacitor. The advantages of the proposed approach are as follows: 1. significant reduction in the linkage inductors' size by decreasing the line-current ripple due to the interleaving; 2. reduction of the switching stress in the dc-link capacitor, due to the shared connection; and 3. more accurate compensation for high-power applications, because the power sharing allows one to use a higher switching frequency in each inverter. This paper analyzes the design of the passive components and gives a practical and low-cost solution for the minimization of the circulation currents between the inverters, by using common-mode coils. Several simulation results are discussed, and experimental results with a three-phase 10-kVA 400-V unit are obtained to validate the theoretical analysis.

SpaceTwist: Managing the Trade-Offs Among Location Privacy, Query Performance, and Query Accuracy in Mobile Services

Abstract: In a mobile service scenario, users query a server for nearby points of interest but they may not want to disclose their locations to the service. Intuitively, location privacy may be obtained at the cost of query performance and query accuracy. The challenge addressed is how to obtain the best possible performance, subjected to given requirements for location privacy and query accuracy. Existing privacy solutions that use spatial cloaking employ complex server query processing techniques and entail the transmission of large quantities of intermediate result. Solutions that use transformation-based matching generally fall short in offering practical query accuracy guarantees. Our proposed framework, called SpaceTwist, rectifies these shortcomings for k nearest neighbor (kNN) queries. Starting with a location different from the user's actual location, nearest neighbors are retrieved incrementally until the query is answered correctly by the mobile terminal. This approach is flexible, needs no trusted middleware, and requires only well-known incremental NN query processing on the server. The framework also includes a server-side granular search technique that exploits relaxed query accuracy guarantees for obtaining better performance. The paper reports on empirical studies that elicit key properties of SpaceTwist and suggest that the framework offers very good performance and high privacy, at low communication cost.

LCA of soybean meal

Abstract: Background, Aim and Scope Soybean meal is an important protein input to the European livestock production, with Argentina being an important supplier. The area cultivated with soybeans is still increasing globally, and so are the number of LCAs where the production of soybean meal forms part of the product chain. In recent years there has been increasing focus on how soybean production affects the environment. The purpose of the study was to estimate the environmental consequences of soybean meal consumption using a consequential LCA approach. The functional unit is ‘one kg of soybean meal produced in Argentina and delivered to Rotterdam Harbor’.

The effects of improvisational music therapy on joint attention behaviors in autistic children: a randomized controlled study.

Abstract: The purpose of this study was to investigate the effects of improvisational music therapy on joint attention behaviors in pre-school children with autism. It was a randomized controlled study employing a single subject comparison design in two different conditions, improvisational music therapy and play sessions with toys, and using standardized tools and DVD analysis of sessions to evaluate behavioral changes in children with autism. The overall results indicated that improvisational music therapy was more effective at facilitating joint attention behaviors and non-verbal social communication skills in children than play. Session analysis showed significantly more and lengthier events of eye contact and turn-taking in improvisational music therapy than play sessions. The implications of these findings are discussed further.

Guiding and focusing of electromagnetic fields with wedge plasmon polaritons.

Abstract: We study theoretically electromagnetic modes guided by metallic wedges at telecom wavelengths. These modes are found to exhibit superior confinement while showing similar propagation loss as compared to other subwavelength guiding configurations. It is also shown that mode focusing can be realized by gradual modification of the wedge geometry along the mode propagation direction.

The technology of microalgal culturing

Abstract: This review outlines the current status and recent developments in the technology of microalgal culturing in enclosed photobioreactors. Light distribution and mixing are the primary variables that affect productivities of photoautotrophic cultures and have strong impacts on photobioreactor designs. Process monitoring and control, physiological engineering, and heterotrophic microalgae are additional aspects of microalgal culturing, which have gained considerable attention in recent years.

Review of islanding detection methods for distributed generation

Abstract: This paper presents an overview of power system islanding and islanding detection techniques. Islanding detection techniques, for a distribution system with distributed generation (DG), can broadly be divided into remote and local techniques. A remote islanding detection technique is associated with islanding detection on the utility side, whereas a local technique is associated with islanding detection on the DG side. Local techniques can further be divided into passive techniques, active techniques and hybrid techniques. These islanding detection techniques for DG are described and analyzed.

Problem-Oriented and Project-Based Learning (POPBL) as an Innovative Learning Strategy for Sustainable Development in Engineering Education.

Abstract: In a world where systems are increasingly larger, where their boundaries are often difficult to identify, and where societal rather than technical issues play increasingly bigger roles, problems cannot be solved by applying a technical solution alone It thus becomes important for engineers to be skilled not only in terms of their particular technical field but also their ability to identify non-technical aspects of problems, the interaction between these aspects and possible solutions Introducing and integrating these aspects into engineering education is certainly not an easy task and requires innovative approaches In this article, focus is placed on the so-called Aalborg Model, a problem-oriented and project-based learning paradigm utilised at Aalborg University (Denmark), and the mutual benefits that this particular learning strategy provides for students, faculty and communities The article discusses the concept of sustainable development; accounts for the general capabilities of engineer

An Improved Control Strategy of Limiting the DC-Link Voltage Fluctuation for a Doubly Fed Induction Wind Generator

Abstract: The paper presents to develop a new control strategy of limiting the dc-link voltage fluctuation for a back-to-back pulsewidth modulation converter in a doubly fed induction generator (DFIG) for wind turbine systems. The reasons of dc-link voltage fluctuation are analyzed. An improved control strategy with the instantaneous rotor power feedback is proposed to limit the fluctuation range of the dc-link voltage. An experimental rig is set up to valid the proposed strategy, and the dynamic performances of the DFIG are compared with the traditional control method under a constant grid voltage. Furthermore, the capabilities of keeping the dc-link voltage stable are also compared in the ride-through control of DFIG during a three-phase grid fault, by using a developed 2 MW DFIG wind power system model. Both the experimental and simulation results have shown that the proposed control strategy is more effective, and the fluctuation of the dc-link voltage may be successfully limited in a small range under a constant grid voltage and a non-serious grid voltage dip.

Finding question-answer pairs from online forums

Abstract: Online forums contain a huge amount of valuable user generated content. In this paper we address the problem of extracting question-answer pairs from forums. Question-answer pairs extracted from forums can be used to help Question Answering services (e.g. Yahoo! Answers) among other applications. We propose a sequential patterns based classification method to detect questions in a forum thread, and a graph based propagation method to detect answers for questions in the same thread. Experimental results show that our techniques are very promising.

Performance of Uplink Fractional Power Control in UTRAN LTE

Abstract: UTRAN long term evolution is currently being standardized in 3GPP with the aim of more than twice the capacity over high-speed packet access. The chosen multiple access for uplink is single carrier FDMA, which avoids the intra-cell interference typical of CDMA systems, but it is still sensitive to inter-cell interference. As a result, the role of the power control becomes decisive to provide the required SINR, while controlling at the same time the interference caused to neighboring cells. This is the target of the fractional power control (FPC) algorithm lately approved in 3GPP. This paper evaluates in detail the impact of a FPC scheme on the SINR and interference distributions in order to provide a sub-optimal configuration tuned for both interference- and noise-limited scenarios.

PAD: privacy-area aware, dummy-based location privacy in mobile services

Abstract: Location privacy in mobile services has the potential to become a serious concern for service providers and users. Existing privacy protection techniques that use k-anonymity convert an original query into an anonymous query that contains the locations of multiple users. Such techniques, however, generally fail in offering guaranteed large privacy regions at reasonable query processing costs. In this paper, we propose the PAD approach that is capable of offering privacy-region guarantees. To achieve this, PAD uses so-called dummy locations that are deliberately generated according to either a virtual grid or circle. These cover a user's actual location, and their spatial extents are controlled by the generation algorithms. The PAD approach only requires a lightweight server-side front-end in order for it to be integrated into an existing client/server mobile service system. In addition, query results are organized according to a compact format on the server, which not only reduces communication cost, but also facilitates the result refinement on the client side. An empirical study shows that our proposal is effective in terms of offering location privacy, and efficient in terms of computation and communication costs.

In-Band Interference Effects on UTRA LTE Uplink Resource Block Allocation

Abstract: In this paper we investigate the impact of in-band interference on the uplink multiple access of UMTS Terrestrial Radio Access, long term evolution (UTRA LTE). In- band and out-of-band interference arise as a result of transmitter imperfections. Out-of- band, or adjacent channel, interference can be controlled by a spectral shaping filter. However, the shaping filter cannot control the leakage within the system bandwidth, and the resulting leakage can interfere with other users' transmission in the uplink multiple access. The situation is emphasized when the resource block allocation size is small, and when the interfering signal is received at higher power spectral density (PSD). The effect of frequency offset and different PSD level from the UE interferers to a victim UE is studied. The impact on different UE resource block size allocation is also investigated. The results are obtained from an LTE uplink link level simulation. It is shown that a significant SNR degradation is observed at the victim UE with smaller resource block size, when evaluated in a realistic channel. Considering that the frequency offset can be maintained below 200 Hz and PSD level offset below 10 dB, the SNR loss at 10% BLER target is less than 1 dB.