On holomorphic isometric embeddings of the unit n-ball into products of two unit m-balls

We study holomorphic isometric embeddings of the complex unit n-ball into products of two complex unit m-balls with respect to their Bergman metrics up to normalization constants (the isometric constant). There are two trivial holomorphic isometric embeddings for m ≥ n, given by F1(z) = (0, In;m(z)) with the isometric constant equal to (m + 1)/(n + 1) and F2(z) = (In;m(z), In;m(z)) with the isometric constant equal to 2(m + 1)/(n + 1). Here In;m: ℂn → ℂm is the canonical embedding. We prove that when m < 2n, these are the only holomorphic isometric embeddings up to unitary transformations. © 2010 Springer-Verlag.postprin

Effect of blood's velocity on blood resistivity

Blood resistivity is an important quantity whose value influences the results of various methods used in the study of heart and circulation. In this paper, the relationship between blood resistivity and velocity of blood flow was evaluated and analyzed based upon a probe using six-ring electrodes and a circulatory model. The experimental results indicated that the change in blood resistivity was only ±1.1% when the velocity of blood flow changed from 2.83 to 40 cm/s and it rose to 23% when the velocity was lower than 2.83 cm/s

A multiresolution two-layer video codec for networking applications

We propose an improved multiresolution two-layer video codec that can operate at a base layer of 64 kbps and a variable bit rate second layer (VBR). The basic idea is to use a multiresolution technique to reduce the original CIF format video to the QCIF format. The low-resolution video is then encoded with an improved H.261 codec. To reduce the bit rate of the second layer, the residuals are encoded with the discrete cosine transform (DCT) using perceptually weighted quantization step sizes. Simulation results show that the Miss America sequence can be transmitted at 64 kbps in the CIF format with a reasonably good picture quality. For a good picture quality, the second layer would typically require 190 kbps.published_or_final_versio

Buffer control algorithm for low bit-rate video compression

In this paper, a new buffer control algorithm for motion-compensated hybrid DPCM/DCT coding (like H.261 and MPEG-1 I pictures) is presented. The algorithm uses the bit allocation algorithm to determine the quantization scale factor of each macroblock under a given target bit rate. An important advantage of the algorithm is that it has precise control of the buffer and avoids buffer overflow events which is a severe problem in low bit rate video coder. Furthermore, the coder is able to allocate bits to the picture as a whole, resulting in better rate-distortion trade-off. Simulation results show that the H.261 coder, using the proposed algorithm, can achieve a higher PSNR and better visual quality than codec using conventional buffer control algorithm.published_or_final_versio

An adaptive multiresolution modification of the H.263 video coding algorithm

An adaptive multiresolution approach for video coding is presented. The algorithm uses the information content to determine the resolution of the video to be encoded. An important advantage of the algorithm is that the codec can maintain a very stable frame rate with reasonable image quality during scene change and provide better quality video when the motion is less rapid. Simulation results show that the modified H.263 coder, using the proposed algorithm, can maintaining better image quality and a more steady frame rate than the TMN 5 algorithm at low bit-rate.published_or_final_versio

A modified H.263 algorithm using bit allocation buffer control algorithm

Buffer control is an important problem in very low bitrate video coding. In a recent work [ 111, the authors had proposed a new buffer control algorithm for motion-compensated hybrid DPCMiDCT coding. The algorithm is based on the use of bit allocation algorithm to determine the quantization scale factors in such coder to meet a given target bit rate. Simulation results showed that, using the proposed algorithm, the H.261 coder can achieve a higher PSNR and better visual quality than the coder using traditional buffer control algorithm. In this paper, we apply this buffer control algorithm to a modified version of the H.263 algorithm for very low bit-rate video coding. Comparing the performance of the modified H.263 codec with the TMN5 model also shows that better visual quality can be obtained at comparable PSNR values.published_or_final_versio

不受歡迎的生物多樣性：香港的外來植物物種

The flora of Hong Kong has been well-surveyed since the mid nineteenth century and has had a long history of alien plant invasions. To the present day, more than 2130 wild plant species have been recorded, including 238 species that are probably naturalized alien species. Among them, Mikania micrantha, Ipomoea cairica, Eupatorium catarium, and Panicum maximum are most abundant. Naturalized alien plants are most prominent in human-disturbed habitats, such as abandoned farmland, wasteland and roadsides, and are rarely important in relatively undisturbed forest habitats, or in fire-maintained impoverished shrubland and grassland. Impacts of naturalized alien plants on local ecosystems are so far limited to lowland habitats, including wetlands and forest margins, where they form monospecific thickets, out-compete native plant species, and reduce local habitat and animal diversity. The biggest impact on the local flora by an alien species, however, was caused by the Pinewood Nematode introduced in the 1970s. Introduction of alien vertebrates may also have an impact on Hong Kong' s vegetation. As the biggest port on the southern coast of China, Hong Kong has probably been an important entry point for alien species to China. Among Hong Kong' s naturalized alien plants, some have only recently been noticed, and have few or no records from the mainland. The potential for these species to invade the mainland should not be neglected. Appropriate measures to control spread of these plants, both locally and regionally, are essential.published_or_final_versio

A robust M-estimate adaptive equaliser for impulse noise suppression

In this paper, a FIR adaptive equaliser for impulse noise suppression is proposed. It is based on the minimization of an M-estimate objective function which has the ability to ignore or down-weight a large error signal when it exceeds certain thresholds. An advantage of the proposed method is that its solution is governed by a system of linear equations, called the M-estimate normal equation. Therefore, traditional fast algorithms like the recursive least squares algorithm can be applied. Using a robust estimation of the thresholds and the recursive least square algorithm, an M-estimate RLS (M-RLS) algorithm is developed. Simulation results show that the proposed algorithm has better convergence performance than the N-RLS and MN-LMS algorithms when the input signal of the equaliser is corrupted by individually or consecutive impulse noises. It also shares the low steady state error of the traditional RLS algorithm.published_or_final_versio

Generalized lapped transform (GLT) based high-speed for transmissionfor wireless mobile communications

In this paper, we describe a generalized lapped transform (GLT) based high-speed transmission technique for wireless mobile communications over Rayleigh fading channels. In this technique, the high-rate data bits are serial-to-parallel converted into low-rate data streams which are then modulated by the GLT based signature sequences. Numerical results show that the GLT based system gives better results than the Walsh code, PN concatenated sequence based system (Letaief et al., 1995)published_or_final_versio

Post-processing of transform coded images using selective filtering and fuzzy-based enhancement

Transform coding often leads to artifacts called blocking when the image or video is compressed to low bit-rate. In this paper, a new post-processing scheme using selective low-pass filtering and fuzzy-based enhancement is proposed. The merit of the scheme is that it can remove most of the blocking artifacts found in image or video coding while preserving most of the fine details. Simulation results demonstrated that the proposed algorithm can significantly improve the visual quality of the decoded image.published_or_final_versio