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  • Resultat 1-10 av 35547
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  • Läthén, Gunnar, et al. (författare)
  • Non-ring Filters for Robust Detection of Linear Structures
  • 2010
  • Ingår i: Proceedings of the 20th International Conference on Pattern Recognition. - Los Alamitos, CA, USA : IEEE Computer Society. - 978-1-4244-7542-1 ; s. 233-236
  • Konferensbidrag (refereegranskat)abstract
    • Many applications in image analysis include the problem of linear structure detection, e.g. segmentation of blood vessels in medical images, roads in satellite images, etc. A simple and efficient solution is to apply linear filters tuned to the structures of interest and extract line and edge positions from the filter output. However, if the filter is not carefully designed, artifacts such as ringing can distort the results and hinder a robust detection. In this paper, we study the ringing effects using a common Gabor filter for linear structure detection, and suggest a method for generating non-ring filters in 2D and 3D. The benefits of the non-ring design are motivated by results on both synthetic and natural images.
  • Fredenberg, Erik, 1979- (författare)
  • Spectral Mammography with X-Ray Optics and a Photon-Counting Detector
  • 2009
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • Early detection is vital to successfully treating breast cancer, and mammography screening is the most efficient and wide-spread method to reach this goal. Imaging low-contrast targets, while minimizing the radiation exposure to a large population is, however, a major challenge. Optimizing the image quality per unit radiation dose is therefore essential. In this thesis, two optimization schemes with respect to x-ray photon energy have been investigated: filtering the incident spectrum with refractive x-ray optics (spectral shaping), and utilizing the transmitted spectrum with energy-resolved photon-counting detectors (spectral imaging).Two types of x-ray lenses were experimentally characterized, and modeled using ray tracing, field propagation, and geometrical optics. Spectral shaping reduced dose approximately 20% compared to an absorption-filtered reference system with the same signal-to-noise ratio, scan time, and spatial resolution. In addition, a focusing pre-object collimator based on the same type of optics reduced divergence of the radiation and improved photon economy by about 50%.A photon-counting silicon detector was investigated in terms of energy resolution and its feasibility for spectral imaging. Contrast-enhanced tumor imaging with a system based on the detector was characterized and optimized with a model that took anatomical noise into account. Improvement in an ideal-observer detectability index by a factor of 2 to 8 over that obtained by conventional absorption imaging was found for different levels of anatomical noise and breast density. Increased conspicuity was confirmed by experiment. Further, the model was extended to include imaging of unenhanced lesions. Detectability of microcalcifications increased no more than a few percent, whereas the ability to detect large tumors might improve on the order of 50% despite the low attenuation difference between glandular and cancerous tissue. It is clear that inclusion of anatomical noise and imaging task in spectral optimization may yield completely different results than an analysis based solely on quantum noise.
  • Selén, Yngve, et al. (författare)
  • Empirical Bayes linear regression with unknown model order
  • 2008
  • Ingår i: Digital signal processing (Print). - 1051-2004 .- 1095-4333. ; 18:2, s. 236-248
  • Tidskriftsartikel (refereegranskat)abstract
    • We study maximum a posteriori probability model order selection for linear regression models, assuming Gaussian distributed noise and coefficient vectors. For the same data model, we also derive the minimum mean-square error coefficient vector estimate. The approaches are denoted BOSS (Bayesian order selection strategy) and BPM (Bayesian parameter estimation method), respectively. In their simplest form, both BOSS and BPM require a priori knowledge of the distribution of the coefficients. However, under the assumption that the coefficient variance profile is smooth, we derive "empirical Bayesian" versions of our algorithms which estimate the coefficient variance profile from the observations and thus require little or no information from the user. We show in numerical examples that the estimators can outperform several classical methods, including the well-known AICc and BIC for model order selection.
  • Överstam, Henrik, 1975- (författare)
  • The interdependence of plastic behaviour and final properties of steel wire, analysed by the finite element method
  • 2004
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • The finite element method (FEM) has been used in order to study the interdependence of plastic behaviour and final properties in steel wire. Three processes metal forming have been studied: billet forging, wire rod rolling, and cold drawing.The forging study focuses on the possibilities to eliminate voids, pores and pipes by altering the bite ratio in open die forging. Forging is used in wire manufacturing when dealing with materials that are difficult or impossible to roll, e.g. tool steels like high-speed steels, and powder metallurgically manufactured materials like tungsten-molybdenum filament wire. The elimination of inner defects by forging were successfully simulated by the FEM.The rolling study focuses on the problems due of the extreme finish rolling velocities in modern wire rod mills and modern technologies such as thermo-mechanical rolling and sizing. A design for a high-speed laboratory mill for studies of material behaviour at extreme strain rates was made. With a combination of two-high stands and three-roll units is it possible to obtain a smoother temperature distribution in the bar cross section.Two studies of the cold drawing process were made. The first describes the distribution of the plastic deformation due to the die geometry. It was found that the influence of the die angle on the amount of inhomogeneous deformation decreases with increasing area reduction. The frictional behaviour was also studied.The second study describes how the bearing geometry affects the residual stress-state in the wire. It was found that a small taper could change the residual stress state in the surface immensely. This was shown with FE simulations and verified by X-ray diffraction measurements. The results in this paper gives a tool for control of the residual stress-state in the wire. This gives a possibility to increase e.g. the fatigue strength in the final product.
  • Ahmed, Rehan M., 1978-, et al. (författare)
  • Compliant motion control for safe human robot interaction
  • 2009
  • Ingår i: Robot motion and control 2009. - Berlin : Springer. - 978-1-84882-984-8 ; s. 265-274
  • Konferensbidrag (refereegranskat)abstract
    • Robots have recently been foreseen to work side by side and share workspace with humans in assisting them in tasks that include physical human-robot (HR) interaction. The physical contact with human tasks under uncertainty has to be performed in a stable and safe manner [6]. However, current industrial robot manipulators are still very far from HR coexisting environments, because of their unreliable safety, rigidity and heavy structure. Besides this, the industrial norms separate the two spaces occupied by a human and a robot by means of physical fence or wall [9]. Therefore, the success of such physical HR interaction is possible if the robot is enabled to handle this interaction in a smart way to prevent injuries and damages.
  • Ahmed, Rehan M., et al. (författare)
  • Safe robot with reconfigurable compliance/stiffness actuation
  • 2009
  • Ingår i: Proceedings of ASME/IFToMM International Conference on Reconfigurable Mechanisms and Robots. ReMAR'2009. - IEEE. - 978-88-89007-37-2 ; s. 633-638
  • Konferensbidrag (refereegranskat)abstract
    • Human robot interaction (HRI) in constrained motion tasks requires robots to have safe sharing of work space and to demonstrate adaptable compliant behavior Compliance control of industrial robots, normally can be achieved by using active compliance control of actuators based on various sensor data. Alternatively, passive devices allow controllable compliance motion but usually are mechanically complex. We present a unique method using a novel actuation mechanism based on magneto-rheological fluid (MRF) that incorporates reconfigurable compliance directly into the robot joints. This brings much simple interaction control strategy compared to other antagonistic methods. In this studies, we have described three essential modes of motions required for physical human system interaction. Then we have discussed their respective control disciplines. Finally, we have presented functional performance of reconfigurable MRF actuation mechanism in constrained motion tasks by simulating various HRI scenarios.
  • Andersson, Carina, 1970- (författare)
  • Informationsdesign i tillståndsövervakning En studie av ett bildskärmsbaserat användargränssnitt för tillståndsövervakning och tillståndsbaserat underhåll
  • 2010
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • This research concerns the information design and visual design of graphical user interfaces (GUI) in the condition monitoring and condition-based maintenance (CBM) of production equipment. It also concerns various communicative aspects of a GUI, which is used to monitor the condition of assets. It applies to one Swedish vendor and its intentions to design information. In addition, it applies to the interaction between the GUI and its individual visual elements, as well as the communication between the GUI and the users (in four Swedish paper mills).The research is performed as a single case study. Interviews and observations have been the main methods for data collection. Empirical data is analyzed with methods inferred to semiotics, rhetoric and narratology. Theories in information science and regarding remediation are used to interpret the user interface design.The key conclusion is that there are no less than five different forms of information, all important when determining the conditions of assets. These information forms include the words, images and shapes in the GUI, the machine components and peripherals equipment, the information that takes form when personnel communicate machine conditions, the personnel’s subjective associations, and the information forms that relate to the personnel's actions and interactions.Preventive technicians interpret the GUI-information individually and collectively in relation to these information forms, which influence their interpretation and understanding of the GUI information. Social media in the GUI makes it possible to represent essential information that takes form when employees communicate a machine’s condition. Photographs may represent information forms as a machine’s components, peripherals, and local environment change over time. Moreover, preventative technicians may use diagrams and photographs in the GUI to change attitudes among the personnel at the mills and convince them, for example, of a machine’s condition or the effectiveness of CBM as maintenance policy.
  • Andreasson, Henrik, 1977-, et al. (författare)
  • A Minimalistic Approach to Appearance-Based Visual SLAM
  • 2008
  • Ingår i: IEEE Transactions on Robotics. - New York, NY, USA : IEEE. - 1552-3098. ; 24:5, s. 991-1001
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper presents a vision-based approach to SLAM in indoor / outdoor environments with minimalistic sensing and computational requirements. The approach is based on a graph representation of robot poses, using a relaxation algorithm to obtain a globally consistent map. Each link corresponds to a relative measurement of the spatial relation between the two nodes it connects. The links describe the likelihood distribution of the relative pose as a Gaussian distribution. To estimate the covariance matrix for links obtained from an omni-directional vision sensor, a novel method is introduced based on the relative similarity of neighbouring images. This new method does not require determining distances to image features using multiple view geometry, for example. Combined indoor and outdoor experiments demonstrate that the approach can handle qualitatively different environments (without modification of the parameters), that it can cope with violations of the “flat floor assumption” to some degree, and that it scales well with increasing size of the environment, producing topologically correct and geometrically accurate maps at low computational cost. Further experiments demonstrate that the approach is also suitable for combining multiple overlapping maps, e.g. for solving the multi-robot SLAM problem with unknown initial poses.
  • Bazzan, Ana L. C., et al. (författare)
  • Re-routing agents in an abstract traffic scenario
  • 2008
  • Ingår i: Advances in artificial intelligence : SBIA 2008. - Berlin : Springer. - 978-3-540-88189-6 ; s. 63-72
  • Konferensbidrag (refereegranskat)abstract
    • Human drivers may perform replanning when facing traffic jams or when informed that there are expected delays on their planned routes. In this paper, we address the effects of drivers re-routing, an issue that has been ignored so far. We tackle re-routing scenarios, also considering traffic lights that are adaptive, in order to test whether such a form of co-adaptation may result in interferences or positive cumulative effects. An abstract route choice scenario is used which resembles many features of real world networks. Results of our experiments show that re-routing indeed pays off from a global perspective as the overall load of the network is balanced. Besides, re-routing is useful to compensate an eventual lack of adaptivity regarding traffic management.
  • Bazzan, Ana L. C., et al. (författare)
  • To adapt or not to adapt : consequences of adapting driver and traffic light agents
  • 2008
  • Ingår i: Adaptive agents and multi-agent systems III : adaptation and multi-agent learning : 5th, 6th, and 7th European Symposium,ALAMAS 2005-2007on Adaptive and Learning Agents and Multi-Agent Systems : revised selected papers. - New York : Springer. - 978-3-540-77947-6 ; s. 1-14
  • Konferensbidrag (refereegranskat)abstract
    • One way to cope with the increasing traffic demand is to integrate standard solutions with more intelligent control measures. However, the result of possible interferences between intelligent control or information provision tools and other components of the overall traffic system is not easily predictable. This paper discusses the effects of integrating co-adaptive decision-making regarding route choices (by drivers) and control measures (by traffic lights). The motivation behind this is that optimization of traffic light control is starting to be integrated with navigation support for drivers. We use microscopic, agent-based modelling and simulation, in opposition to the classical network analysis, as this work focuses on the effect of local adaptation. In a scenario that exhibits features comparable to real-world networks, we evaluate different types of adaptation by drivers and by traffic lights, based on local perceptions. In order to compare the performance, we have also used a global level optimization method based on genetic algorithms.
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