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Reversible watermarking methods have drawn attention of many researchers in recent years because original cover objects can be completely restored upon extraction of embedded information. The prediction error expansion (PEE) embedding proposed by Thodi and Rodriguez can embed one information bit into one cover pixel and achieve good visual quality of watermarked images. However, the PEE method is not a generalised scheme and its embedding capacity measured by bit per pixel (bpp) and visual quality measured by peak signal-to-noise ratio (PSNR) can be improved. Thus, we propose two novel schemes based on the PEE method by using pixel partition strategies to improve embedding capacity and/or visual quality. The first proposed scheme makes the PEE method be generalised and the second proposed scheme can embed more than 1 bpp. Experimental results show that the proposed schemes can significantly improve visual quality of the watermarked images produced by the PEE method when embedding capacity falls within the...

We use the Pad\'e-Z$_2$ stochastic estimator for calculating Tr log M to compute quark loop corrections to quenched QCD. We examine the main source of error in this technique and look at a way of controlling it., Comment: 5 pages, 6 Postscript figures, Lattice 2000 (Algorithms)

It is argued that the gauge anomalies are only the artefacts of quantum field theory when certain subtleties are not taken into account. With the Berry's phase needed to satisfy certain boundary conditions of the generating path integral, the gauge anomalies associated with homotopically nontrivial gauge transformations are shown explicitly to be eliminated, without any extra quantum fields introduced. This is in contra-distinction to other quantisations of `anomalous' gauge theory where extra, new fields are introduced to explicitly cancel the anomalies.

Current algorithms used to put a lattice gauge configuration into Landau gauge either suffer from the problem of critical slowing-down or involve an additional computational expense to overcome it. Evolutionary Algorithms (EAs), which have been widely applied to other global optimisation problems, may be of use in gauge fixing. Also, being global, they should not suffer from critical slowing-down as do local gradient based algorithms. We apply EA's and also a Steepest Descent (SD) based method to the problem of Landau Gauge Fixing and compare their performance., Comment: LATTICE98(algorithms), 3 pages, 6 figures

The path-integral functional of chiral gauge theories with background gauge potentials are derived in the holomorphic representation. Justification is provided, from first quantum mechanical principles, for the appearance of a functional phase factor of the gauge fields in order to maintain the gauge invariance. This term is shown to originate either from the Berry phase of the first-quantized hamiltonians or from the normal ordering of the second-quantized hamiltonian with respect to the Dirac in-vacuum. The quantization of the chiral Schwinger model is taken as an example.

Several fundamental problems and restrictions for universal quantum computers are pointed out. Firstly, it is shown that the halting of universal quantum computers is incompatible with the constraint of unitarity of the quantum dynamics. Secondly, the consequences of the second law of thermodynamics and the existence of time constants associated with the generation of initial states of quantum systems are shown to impose severe limits on the capabilities of quantum computers.

A simulation method based on the RG blocking is shown to yield statistical errors smaller than that of the crude MC using absolute values of the original measures. The new method is particularly suitable to apply to the sign problem of indefinite or complex-valued measures. We demonstrate the many advantages of this method in the simulation of 2D Ising model with complex-valued temperature.

Random-lattice fermions have been shown to be free of the doubling problem if there are no interactions or interactions of a non-gauge nature. However, gauge interactions impose stringent constraints as expressed by the Ward-Takahashi identities which could revive the free-field suppressed doubler modes in loop diagrams. After introducing a formulation for fermions on a new kind of random lattice, we compare random, naive and Wilson fermions in two dimensional Abelian background gauge theory. We show that the doublers are revived for random lattices in the continuum limit, while demonstrating that gauge invariance plays the critical role in this revival. Some implications of the persistent doubling phenomenon on random lattices are also discussed., 16 A4 pages, UM-P-93/05

Random-lattice fermions have been shown to be free of the doubling problem if there are no interactions or interactions of a non-gauge nature. On the other hand, gauge interactions impose stringent constraints as expressed by the Ward-Takahashi identities which could revive the free-field suppressed doubler modes in loop diagrams. Comparing random lattice, naive and Wilson fermions in two dimensional abelian background gauge theory, we show that indeed the doublers are revived for random lattices in the continuum limit. Some implications of the persistent doubling phenomenon on random lattices are also discussed., 7 A4 pages, 3 figures in postcript are included

The chiral Schwinger model is studied on the lattice with use of Wilson fermions. The arbitrary mass term for the gauge boson is shown to originate from the arbitrariness of the Wilson parameter, which is required to avoid the doubling phenomenon on the lattice. The necessity for such a term is thus demonstrated in contrast to the mere admissibility as indicated by previous continuum calculations.

The relationship between the phenomenon of species doubling on the lattice and the Abelian anomaly is generalized to the case of the non-Abelian anomaly. It is shown that each species individually gives the correct consistent anomaly. In total, however, the anomaly is canceled by opposite-handed species. It is thus demonstrated that a wide class of lattice fermions can reproduce the non-Abelian anomaly by decoupling the doublers.

The conditions for the experimental observation of new types of eigenmodes in a typical laboratory magnetized plasma with two ion species are discussed. It is shown that the most favourable condition occurs during the current carrying phase of the discharge, with an appropriately chosen mixture of ions.