A theorem on “localized” self-adjointness of Shrödinger operators with L

We prove a result which concludes the self-adjointness of a Schrödinger operator from the self-adjointness of the associated localized Schrödinger operators having LLOC1-Potentials

A Distributed Multimedia Communication System and its Applications to E-Learning

In this paper we report on a multimedia communication system including a VCoIP (Video Conferencing over IP) software with a distributed architecture and its applications for teaching scenarios. It is a simple, ready-to-use scheme for distributed presenting, recording and streaming multimedia content. We also introduce and investigate concepts and experiments to IPv6 user and session mobility, with the special focus on real-time video group communication.Comment: Including 6 figure

A THEOREM ON "LOCALIZED" SELF-ADJOINTNESS OF SCHRÖDINGER OPERATORS WITH L 1 Loc-POTENTIALS

We prove a result which concludes the self-adjointness of a Schrödinger operator from the self-adjointness of the associated "localized" Schrödinger oper

Efficient Pre-Coding Techniques for Wavelet-Based Image Compression

In this paper we introduce a novel framework for the design of effective compression schemes using the discrete wavelet transform (DWT). Wavelet-based image compression schemes combine transform coding with subband coding techniques. Usually they consist of three modules: first and main part is an invertible transformation which decomposes the signal into dyadic structured subbands by convolution-decimation operations. It decorrelates mutually dependent parts and performs an energy compaction. The second module is a quantizer which annihilates visually non-relevant information, and the third and final part in this three-stage process consists of an entropy coder which removes redundancies in the stream of symbols generated by the quantizer. Many (very effective) research activities intend to optimize the transformation and/or the quantization in order to increase the compression performance of the coder [2] [4] [8]. In this paper, however, we use a non-sophisticated fast wavelet trans..

Very Low Bit Rate Video Coding Using Wavelet-Based Techniques

In this paper, we propose a very low bit rate video coding scheme based on a discrete wavelet transform (DWT), block-matching motion estimation (BME) and overlapped block motion compensation (OBMC). Our approach reveals that the coding process works more efficiently if the quantized wavelet coefficients will be pre-processed by a mechanism exploiting the redundancies in the wavelet subband structure. Thus, we introduce a new framework of pre-coding techniques based on the concepts of partitioning, aggregation and conditional coding (PACC). Our experimental results show that our PACC coder outperforms the VM (Version 5.1) of MPEG4 both for coding of intra-frames (1--2 dB PSNR) and residual frames (up to 1.5 dB PSNR) of typical MPEG4 test sequences. The subjective quality of reconstructed video is in general superior to that obtained from the VM implementation. In addition, when restricted to intra-frame mode, the proposed coding algorithm produces results which are among the best report..

Mobile Serverless Video Communication

Voice and video conferencing have well established as regular communication services within the wired Internet. Facing the paradigm of ubiquitous computing and mobile communication, they are on the spot to be launched within a wireless Internet infrastructure. Following an 802.11, 802.16 or 3G standard, wireless networks provide enough bandwidth to support data intensive communication services such as videoconferencing. The vision of nomadic users at roaming devices performing synchronous communication, such as voice or videoconferencing over IP (VoIP/VCoIP), is around, but raises new challenges for the Internet infrastructure. In conferencing scenarios addressability raises the first major issues. To globally call a device, a routable IP address must be in use. On a large scale such address space is only provided by IPv6. To identify a communication partner’s current device, a supplementary global user locating scheme is needed. In wireless infrastructures, where users share limited bandwidth from a restricted frequency space, multicasting is needed to enable group conferencing compliant to transmission resources and without placing the burden of dedicated group-server infrastructure. At the same time, synchronous real-time applications s. a. VoIP and VCoIP place new demands on the quality of IP mobility services: Packet loss, delay and delay variation (jitter) in a constant bit rate scenario need careful simultaneous control. A spoken syllable is about the payload of 100 ms continuous voice traffic. Each individual occurrence of packet loss above 1 %, latencies over 100 ms or jitter exceeding 50 ms will clearly alienate or even distract the user. Audio and visual streams in video conferencing additionally require tight synchronization. Inter-stream latencies should remain below 30 ms for audio arriving ahead, 40 ms for audio being behind. While uni-directional distribution may compensate quality deficits by buffers, available techniques of hiding packet loss at the cost of delay and jitter or vice versa are of limited use in conferencing. Their requirements impose strong challenges on a mobile Internet scenario. Challenges are even tightened by multicast-based group communication, since in conferencing scenarios each member commonly operates as receiver and as sender. Real-time requirements consequently are a major driving force for the development of a seamless mobile Internet layer. In concordance with communication capabilities video coding techniques have evolved, as well. The latest standard for video coding H.264/AVC (ITU H.264, 2005), although designed as a generic standard, is predestined for applications like mobile video communications (Stockhammer, Hannuksela & Wiegand, 2003). Besides enhanced compression efficiency it delivers also network friendly video representation for interactive (video telephony) and non-interactive applications (broadcast, streaming, storage, and video on demand). H.264/AVC provides gains in compression efficiency of up to 50% over a wide range of bit rates and video resolutions compared to previous standards. While H.264/AVC decoding software has been successfully deployed on handhelds, high computational complexity still prevents pure software encoders in current mobile systems. There are however also fast hardware implementations available (see a list in Wikipedia, H.264, 2006). Next generation codecs like Scalable Video Coding (SVC) are already in a design state (Reichel, Schwarz, & Wien, 2005, Schwarz et.al., 2004). The main new feature, scalability, addresses schemes for delivery of video to diverse clients over heterogeneous networks, particularly in scenarios where the downstream conditions are not known in advance. The basic idea is that one encoded stream can serve networks with varying bandwidths or clients with different display resolutions or systems with different storage resources, which is an obvious advantage in heterogeneous networks prevalent in mobile applications