Mårten Sjöström

Technical and economical assessment of HTS cables

Besides the option of HTS cables as retrofit elements in densely populated areas, the technically most attractive aspect of HTS is the possibility of high power transmission at reduced voltage. In this paper, the authors concentrate on this second aspect. High power/low voltage HTS lines are analysed from the technical and economical point of view in two case studies: (i) a 110 kV/1 GVA transalpine line replacing a 380 kV overhead line; and (ii) a 30 km/600 MVA line connecting a nuclear power plant with a densely populated area. The technical analysis shows that high power cables at reduced voltages (>20 kV) and with acceptable electrical properties (losses, dimensions, reactive power) are technically feasible. In the economical analysis, the life cycle costs of the different scenarios are calculated including the investment and operation costs of the cable, the undergrounding costs and the costs of secondary equipment (fault current limiter, converter, cooling). The analysis shows that the DC HTS line can be interesting, whereas the AC HTS cable systems can hardly compete economically with conventional AC cable installations.

Scalable Coding of Plenoptic Images by Using a Sparse Set and Disparities

One of the light field capturing techniques is the focused plenoptic capturing. By placing a microlens array in front of the photosensor, the focused plenoptic cameras capture both spatial and angular information of a scene in each microlens image and across microlens images. The capturing results in a significant amount of redundant information, and the captured image is usually of a large resolution. A coding scheme that removes the redundancy before coding can be of advantage for efficient compression, transmission, and rendering. In this paper, we propose a lossy coding scheme to efficiently represent plenoptic images. The format contains a sparse image set and its associated disparities. The reconstruction is performed by disparity-based interpolation and inpainting, and the reconstructed image is later employed as a prediction reference for the coding of the full plenoptic image. As an outcome of the representation, the proposed scheme inherits a scalable structure with three layers. The results show that plenoptic images are compressed efficiently with over 60 percent bit rate reduction compared with High Efficiency Video Coding intra coding, and with over 20 percent compared with an High Efficiency Video Coding block copying mode.

Bi(2223) Ag sheathed tape Ic and exponent n characterization and modelling under DC applied magnetic field

We use a dual channel digital lock-in to perform electrical measurement of AC losses at power frequencies. A DC magnetic field between 2 and 400 mT is applied with a varying angle from parallel to perpendicular to the tape surface, thus having a complete view of the loss behavior under DC applied field. Furthermore, the same experimental layout is used to acquire time series of current and voltage across the sample. Using a triangular input current, we measure and average the voltage, which then is fitted to a power law (I/I/sub c/)/sup 11/. The measurements are repeated for the mentioned magnetic field and angle domain to give the dependencies of I/sub c/ and n with magnetic field and angle. For device modeling purposes, we can then express a phenomenological law giving I/sub c/ and n as a function of the applied magnetic fields intensity and direction.

Region-of-Interest 3D Video Coding Based on Depth Images

Three dimensional (3D) TV is becoming a mature technology due to the progress within areas such as display and network technology among others. However, 3D video demands a higher bandwidth in order to transmit the information needed to render or directly display several different views at the receiver. The 2D plus depth representation requires less bit rate than most 3D video representations, although the necessary views have to be rendered at the receiver. In this paper we propose to combine the 2D plus depth representation with region-of-interest (ROI) video coding to ensure a higher quality at parts of the sequence that are of interest to the viewer. These include objects close to the viewer as well as faces. This allows either the bit rate to be reduced by 12-28 % or the quality within the ROI to be increased by 0.57 - 1.5 dB, when a fixed bit rate is applied.

Improved ROI video coding using variable Gaussian pre-filters and variance in intensity

In applications involving video over mobile phones or Internet, the limited quality depending on the transmission rate can be further improved by region-of-interest (ROI) coding. In this paper we present a preprocessing method using variable Gaussian filters controlled by a quality map indicating the distance to the ROI border. The border effects are reduced introducing a small improvement of the PSNR of the intensity component within the ROI after compression, compared to using only one low pass filter. With the compressed original sequence as a reference, the average PSNR was increased by 1.25 dB and 2.3 dB for 100 kbit/s and 150 kbit/s, respectively. A modified quality map is introduced using variance to exclude pixels, which are not visibly affected by the Gaussian filters, reducing computational complexity. Using less than 76% of the pixels gives no noticeable change in quality.

Coding of Focused Plenoptic Contents by Displacement Intra Prediction

A light field is commonly described by a two-plane representation with four dimensions. Refocused 3D contents can be rendered from light field images. A method for capturing these images is using cameras with microlens arrays. A dense sampling of the light field results in large amounts of redundant data. Therefore, an efficient compression is vital for a practical use of these data. In this paper, we propose a displacement intra prediction scheme with a maximum of two hypotheses for the compression of plenoptic contents from focused plenoptic cameras. The proposed scheme is further implemented into High Efficiency Video Coding (HEVC). The work is aiming at efficiently coding plenoptic captured contents without knowing underlying camera geometries. In addition, the theoretical analysis of the displacement intra prediction for plenoptic images is explained; the relationship between the compressed captured images and their rendered quality is also analyzed. Evaluation results show that plenoptic contents can be efficiently compressed by the proposed scheme. Bit rate reduction up to 60% over HEVC is obtained for plenoptic images, and more than 30% is achieved for the tested video sequences.

Technical and economical impacts on a power system by introducing an HTS FCL

Fault current limiters (FCLs) can be considered as key elements in power systems using high temperature superconductors. This analysis takes into account the system benefits provided by the introduction of FCLs in various network configurations. New meshing possibilities, alternative grounding method and increase of power transmission are highlighted. It is the desire of most power system utilities to maximize transferred power and to reduce system losses to a minimum in their systems. These goals could be achieved if the system impedance could be reduced. However, such measures would increase short-circuit currents enormously and endanger equipment and safety. This problem could be circumvented by the installation of an IFCL. FCLs are often implemented in combination with transformers but the transformer itself could also be designed having an integrated current limiting functionality.

Adaptive depth filtering for HEVC 3D video coding

Consumer interest in 3D television (3DTV) is growing steadily, but current available 3D displays still need additional eye-wear and suffer from the limitation of a single stereo view pair. So it can be assumed that autostereoscopic multiview displays are the next step in 3D-at-home entertainment, since these displays can utilize the Multiview Video plus Depth (MVD) format to synthesize numerous viewing angles from only a small set of given input views. This motivates efficient MVD compression as an important keystone for commercial success of 3DTV. In this paper we concentrate on the compression of depth information in an MVD scenario. There have been several publications suggesting depth down- and upsampling to increase coding efficiency. We follow this path, using our recently introduced Edge Weighted Optimization Concept (EWOC) for depth upscaling. EWOC uses edge information from the video frame in the upscaling process and allows the use of sparse, non-uniformly distributed depth values. We exploit this fact to expand the depth down-/upsampling idea with an adaptive low-pass filter, reducing high energy parts in the original depth map prior to subsampling and compression. Objective results show the viability of our approach for depth map compression with up-to-date High-Efficiency Video Coding (HEVC). For the same Y-PSNR in synthesized views we achieve up to 18.5% bit rate decrease compared to full-scale depth and around 10% compared to competing depth down-/upsampling solutions. These results were confirmed by a subjective quality assessment, showing a statistical significant preference for 87.5% of the test cases.

A Weighted Optimization Approach to Time-of-Flight Sensor Fusion

Acquiring scenery depth is a fundamental task in computer vision, with many applications in manufacturing, surveillance, or robotics relying on accurate scenery information. Time-of-flight cameras can provide depth information in real-time and overcome short-comings of traditional stereo analysis. However, they provide limited spatial resolution and sophisticated upscaling algorithms are sought after. In this paper, we present a sensor fusion approach to time-of-flight super resolution, based on the combination of depth and texture sources. Unlike other texture guided approaches, we interpret the depth upscaling process as a weighted energy optimization problem. Three different weights are introduced, employing different available sensor data. The individual weights address object boundaries in depth, depth sensor noise, and temporal consistency. Applied in consecutive order, they form three weighting strategies for time-of-flight super resolution. Objective evaluations show advantages in depth accuracy and for depth image based rendering compared with state-of-the-art depth upscaling. Subjective view synthesis evaluation shows a significant increase in viewer preference by a factor of four in stereoscopic viewing conditions. To the best of our knowledge, this is the first extensive subjective test performed on time-of-flight depth upscaling. Objective and subjective results proof the suitability of our approach to time-of-flight super resolution approach for depth scenery capture.

A Combined Pre-Processing and H.264-Compression Scheme for 3D Integral Images

The next evolutionary step in enhancing video communication fidelity is taken by adding scene depth. 3D video using integral imaging (II) is widely considered as the technique able to take this step. However, an increase in spatial resolution of several orders of magnitude from todays 2D video is required to provide a sufficient depth fidelity, which includes motion parallax. In this paper we propose a pre-processing and compression scheme that aims to enhance the compression efficiency of integral images. We first transform a still integral image into a pseudo video sequence consisting of sub-images, which is then compressed using an H.264 video encoder. The improvement in compression efficiency of using this scheme is evaluated and presented. An average PSNR increase of 5.7 dB or more, compared to JPEG 2000, is observed on a set of reference images.