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Abstract-This paper describes a hybrid motion-compensated wavelet transform coder designed for encoding video at very low bit rates. The coder and its components have been submitted to MPEG-4 to support the functionalities of compression efficiency and scalability. Novel features of this coder are the use of overlapping block motion compensation in combination with a discrete wavelet transform followed by adaptive quantization and zerotree entropy coding, plus rate control. The coder outperforms the VM of MPEG-4 for coding of I-frames and matches the performance of the VM for P-frames while providing a path to spatial scalability, object scalability, and bitstream scalability.

The surface chemistry and band bending of the ammonium sulfide-treated GaAs (100) surface has been studied using surface-sensitive synchrotron radiation photoemission spectroscopy. We find that the treatment leaves the GaAs surface terminated with roughly a monolayer of sulfur bonded to both As and Ga atoms. An n-type barrier height of 0.8 eV is measured. The thermal stability of the various chemical components is studied and various issues of the passivating mechanism are discussed.

%e report a systematic study of the early oxidation process in a wide temperature range (20 -700'C) for the Si(111)-(7&7) annealed surface. Oxygen uptake data obtained by Auger-electron spectroscopy indicate that the surface oxygen uptake increases and then gradually saturates with 02 exposure at 20 C. At intermediate temperatures, there is no saturation and the oxygen uptake rate is enhanced. At 700'C, the uptake rate is enhanced in the high-exposure (or high-02-pressure} region, but is significantly reduced in the low-exposure region, presumably because of oxygen desorption as volatile SiO. Low-energy electron diffraction pattern transition from 7X7 to no pattern through a 1X1 intermediate pattern seems to be governed only by the amount of surface oxygen at any temperature, Using photoelectron spectroscopy we found that 02 exposures corresponding to this 1X1 pattern result in the disappearance of surface states centered about 0.6 eV below the valence-band maximum. A chemical-shift study of the Si 2p core level shows that not only the oxygen uptake rate, but also the way oxygen bonds to Si is strongly dependent on temperature. Our results show that at room temperature (20'C) all the Si atoms are oxidized at more or less the same rate, so that the adsorbed oxygen atoms are spread out uniformly over the entire Si surface. At high temperatures, certain Si atoms are being oxidized faster (i.e. , have more oxygen atoms bonded to them) than others, so that the distribution of adsorbed oxygen atoms is highly nonuniform; we find microscopic regions of Si02-like material interdispersed with regions of Si-like material. Therefore, in the early stage of oxidation, heating the substrate causes nonuniform oxidation with microscopic phase separation of Si02 and Si in the oxide film. Tight-binding calculations reported in the literature predict the oxygen 2p orbital to produce these valence states: 0 m (nonbonding}, 0 o (0 bonding), and 0 i (intermediate nature between nonbonding and 0 bonding). By studying the Oi -Op eak height ratio as a function of oxidation temperature and referring to theoretical calculations, we again come to the conclusion of nonuniform oxidation at high temperatures.

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