Based on the means–end chains (MECs) and push–pull–mooring (PPM) model, this study aims to reveal the functional attributes of Facebook (FB) and Instagram (IG), classify them into the PPM model (i.e. push, pull, and mooring effect) and integrate the nature of MECs (i.e. attribute–consequence–value linkages) to examine young people’s perceptions of FB and IG and their switching intentions. Mixed methods, including qualitative and quantitative approaches are employed to gather data in Taiwan. Sixty-two one-on-one in-depth interviews were content-analysed to design the survey questionnaire. A total of 457 valid samples were collected to establish a hybrid hierarchical value map (HVM) for MEC and PPM analyses. The hybrid HVM shows that ‘privacy protection’ and ‘information collection’ are push effects, which are the unfavourable factors of FB that push users to migrate to IG. By contrast, ‘visual interaction’, ‘relationship maintenance’, and ‘expanding friendship ties’ are pull effects favourable to IG that encourage FB users to migrate. Moreover, ‘self-expression’ and ‘message seeding’ belonging to mooring effects are factors that discourage FB users from migrating. Valuable insights may be provided for the design and improvement of social networking sites by understanding the hybrid HVM.

In this paper, we propose a direct mapping (DM) orthogonal frequency division multiplexing (OFDM) based transmission scheme for underwater acoustic multimedia (UAM). We adopt DM multi-input multi-output (MIMO), power assignment mechanism, OFDM, adaptive modulation, and unequal error protection in the UAM system. The proposed underwater acoustic multimedia system employs high power, low speed modulation, and schemes providing significant error protection for the transmission of sensor data messages requiring a stringent bit-error rate (BER). In contrast, low power, high speed modulation, and less capable error protection schemes are provided for messages that can tolerate a high BER. Simulation results show that the proposed scheme can not only fulfill the quality of services (QoS) required by a UAM system, but also achieve the mission of maximum transmission bit rates or minimum transmission power.

In this paper, we have developed a two-dimensional (2D) chaos-based encryption scheme that can be applied to electroencephalography (EEG) signals, and mobile telemedicine. Compared with the one-dimensional (1D) chaos-based encryption scheme, the proposed 2D schemes uses the concept of parallel processing is to increase the encryption speed. An essential feature of the proposed scheme is that signals mapping of a 2D chaotic scrambler and a permutation scheme are used to obtain EEG information that requires higher-level encryption. Simulation results show that when correct deciphering parameters are inputted, EEG signals are completely recovered. However, these signals will not be recovered if there is an error in the input parameters, for example, an initial point error of 0.00000001%.

In this paper we present an efficient data compression scheme, the template run-length encoding (TRLE) scheme, for image composition of parallel volume rendering systems. Given an image with 2n/spl times/2n pixels, in the TRLE scheme, the image is treated as n/spl times/n blocks and each block has 2/spl times/2 pixels. Since a pixel can be a blank or non-blank pixel, there are 16 templates in a block. To compress an image, the TRLE scheme uses the templates to encode blocks row by row. Blocks in the same row are encoded as a TRLE-sequence. By packing all TRLE-sequences in a packet, the packet is the compressed partial image that can be sent/received among processors. To evaluate the performance of the TRLE scheme, we compare the proposed scheme with the BR, the RLE, and the BRLC schemes. Since a data compression scheme needs to cooperate with some data communication schemes, in the implementation, the binary-swap (BS), the parallel-pipelined (PP), and the rotate-tiling (RT) data communication schemes are used. By combining the four data compression schemes with the three data communication schemes, we have twelve image composition methods. These twelve methods are implemented on a PC cluster The data computation time and the data communication time are measured. The experimental results show that the TRLE data compression scheme with the RT data communication scheme outperforms other eleven image composition methods.

The marching cubes method is a well-known surface extraction method by using the surface configurations of cubes for surface rendering of volume data. The marching cubes method has three main disadvantages: it is time consuming, ambiguous, and holes are generated. All these disadvantages come from the use of the surface configurations of cubes. We propose an efficient surface extraction method, the marching voxels method, for surface rendering of volume data. Instead of using the surface configurations of cubes, the marching voxels method first generates triangles for inner voxels. Then it combines the triangles of inner voxels to produce the surface of an object. Finally, the surface of an object is projected to a plane to form the final image. Since the marching voxels method considers the combination of triangles of voxels not cubes and the combination of triangles is performed in a deterministic way, there is neither ambiguous case of a combination nor holes for the generated surface. The experimental results show that the marching voxels method saves about 30% of the surface rendering time compared to the marching cubes method for test samples.

The binary-swap and the parallel-pipelined methods are two popular image composition methods for volume rendering on distributed memory multicomputers. However, these methods either restrict the number of processors to a power of two or require many steps to transform image data that results in high communication overheads. In this paper, we present an efficient image composition method, the rotate-tiling (RT), for parallel volume rendering on distributed memory multicomputers. The RT method can fully utilize all available processors and minimize the communication overheads. In addition, we provide data compression method, the template run-length encoding (TRLE), to further reduce the communication data size. To evaluate the performance of the RT method, we compare the proposed method with the binary-swap method and the parallel-pipelined method. Both theoretical analysis and experimental test are conducted. In the theoretical analysis, we analyze the best performance bound of the RT method in terms of the startup time, the data transmission time, the number of processors, and the number of initial block of a sub-image. In the experimental test, we have implemented these three methods on an SP2 parallel machine. Three volume datasets are used as test samples. The experimental results show that our method outperforms the binary-swap and the parallel-pipelined methods for all test samples and match the results analyzed in the theoretical analysis. For the TRLE method, the experimental results show that the TRLE method can further reduce the composition time for these three methods.

We investigate a new application of the well-known spread spectrum code division multiple access (SS-CDMA) techniques to multimedia services related to the development of the next-generation wireless mobile networks interconnecting with a wireline ATM-based broadband network. Such services allow users to share novel multimedia applications without any geographical restrictions. However, since the mobile radio channel has a fixed limited bandwidth, the traditional SS-CDMA system may not be sufficient to accommodate the variable bit rate (VBR) multimedia services requested by multiple mobile users simultaneously. Moreover, the traffic load at the base station can change dynamically due to the time-varying throughput requirement of these requested multimedia services. To tackle this difficulty, a multicode CDMA (MC-CDMA) technique is proposed to provide multirate multimedia services by varying the number of spreading codes assigned to each user in order to meet its throughput requirement. In MC-CDMA, a spreading code can be used to transmit information at a basic bit rate. Users (video or data) who need higher transmission rates can use multiple codes in parallel. Meanwhile, the maximum available number of codes in the MC-CDMA system is still limited. Hence, a cost-effective dynamic code allocation scheme has then been proposed to dynamically assign an appropriate number of codes to each user for achieving the maximum resource utilization for multiuser multimedia services via the mobile radio channel. Finally, a number of real multimedia titles generated from the well-known MacroMind Director are conducted to evaluate performance.

We present a generic ATM-based multicode code division multiple access (CDMA) transport architecture for the Motion Picture Experts Group phase 2 (MPEG-2) compressed video services over a bandlimited mobile channel with the emphasis of wireless asynchronous transfer mode (ATM) cell design, spreading code management, and the impact of CDMA systems on the video services. Such services allow users to share novel MPEG-2 video applications without any geographical restrictions. The ATM technique is especially well suited for variable bit rate (VBR) MPEG-2 video because of its ability to allocate bandwidth on demand to these services. However, since the mobile radio has a limited channel capacity, the overall capacity of the traditional ATM-based CDMA system may not be sufficient to accommodate the MPEG-2 video services requested by the multiple mobile users simultaneously. To tackle this difficulty, a multicode CDMA technique is proposed to provide multiple VBR MPEG-2 video services by varying the number of spreading codes assigned to each MPEG-2 video in order to meet its dynamic throughput requirement. Moreover, both the multipath fading and interference on CDMA radio channels tend to cause significant transmission error and MPEG-2 bit streams are very vulnerable to these errors. Powerful forward error connection (FEC) codes are therefore necessary to protect the video data so that it can be successfully transmitted at acceptable signal power level. Two separate FEC code schemes are applied to the header and payload of an ATM cell containing MPEG-2 video data, respectively. The ATM cell header is protected by a relatively powerful FEC code to ensure the low average cell loss rate (CLR). On the other hand, the ATM cell payload is encoded for varying degrees of error protection according to both the priority and statistical behavior of the payload data in MPEG-2 videos. An adaptive FEC code combining scheme is proposed to provide good protection cell payload data with the maximization of its code rate in order to minimize the extra bandwidth for FEC overhead. Two typical MPEG2 test sequences are conducted to evaluate the effectiveness of our system.