Unsupervised Image Segmentation Using Hierarchical Clustering

In the analysis of a medical image database aimed at formulating useful knowledge for image diagnosis requires an unsupervised image processing technique without preconceived knowledge. In this paper, we propose a method for unsupervised image segmentation, which is suitable for finding the features contained in an image. A small region around each pixel is considered as a pattern vector, and the set of pattern vectors acquired from the whole image is classified using the hierarchical clustering technique. In hierarchical clustering, the classification of pattern vectors is divided into two clusters at each node according to the statistical criterion based on the entropy in thermodynamics. Results of the test image generated by the Markov random field (MRF) model and real medical images photomicrographs of a colon tumor are shown.     

Bright optical lattices in a longitudinal magnetic field. Experimental study of the oscillating and jumping regimes

All the bright optical lattices studied so far have been designed to obtain a circularly polarized light at the bottom of the optical potential wells. This condition minimizes the departure rate of the atoms from the fundamental adiabatic surface and permits an oscillating regime in a large range of parameters. We present here an experimental study of cesium atoms in a three-dimensional optical lattice, where the light is linearly polarized at the bottom of the potential wells. Temperature measurements and pump-probe spectroscopy give similar results for this lattice and for the conventional lin lin lattice (which have circular polarizations at the bottom of the wells) despite the fact that one lattice operates in the jumping regime and the other in the oscillating regime. We study the behaviour of the two types of lattices in a longitudinal magnetic field, with particular emphasis on the zero field and strong field regimes. The strong field situation is very simple because the eigenstates are then almost pure Zeeman substates and the adiabatic and diabatic potential surfaces are identical. The comparison between the zero-field and the high-field situations shows that the diabatic potentials are more appropriate to account for experimental observations in the novel lattice. Received: 9 October 1997 / Accepted: 6 November 1997     

Swollen-collapsed transition in random hetero-polymers

A lattice model of a hetero-polymer with random hydrophilic-hydrophobic charges interacting with the solvent is introduced, whose continuum counterpart has been proposed by Garel, Leibler and Orland [#!GLO!#]. The transfer matrix technique is used to study various constrained annealed systems which approximate at various degrees of accuracy the original quenched model. For highly hydrophobic chains an ordinary -point transition is found from a high temperature swollen phase to a low temperature compact phase. Depending on the type of constrained averages, at very low temperatures a swollen phase or a coexistence between compact and swollen phases are found. The results are carefully compared with the corresponding ones obtained in the continuum limit, and various improvements in the original calculations are discussed. Received: 10 April 1998 / Revised: 4 June 1998 / Accepted: 1st July 1998     

New aspects of critical sound attenuation in magnetic systems with spin-lattice relaxation

A general theory of critical sound propagation, including phonon-spin-energy coupling, is studied in anisotropic magnets above their transition temperature. The Kawasaki weak singularity in the ultrasonic attenuation is found as a nonasymptotic effect. A new nonasymptotic regime similar to the one in the binary mixture is also determined. The role of coupling constants and the bare relaxation times in establishing the dominance region of particular terms, is discussed. Received: 9 December 1997 / Accepted: 24 February 1998     

Ionic diffusion on a lattice: Effects of the order-disorder transition on the dynamics of non-equilibrium systems

We examine the behaviour of the concentration profiles of particles with repulsive interactions diffusing on a host lattice. At low temperature, the diffusion process is strongly influenced by the presence of ordered domains. We use mean field equations and Monte-Carlo simulations to describe the various effects which influence the kinetic behaviour. An effective diffusion coefficient is determined analytically and is compared with the simulations. Finite gradient effects on the ordered domains and on the diffusion are discussed. The kinetics studied is relevant for superionic conductors, for intercalation and also for the diffusion of particles adsorbed on a substrate. Received: 26 June 1997 / Revised: 18 September 1997 / Accepted: 10 November 1997     

激光辐射功率量值传递和量程扩展新方法探讨

简述传统激光辐射功率量值传递和量程扩展方法,用经典理论和量子光学理论对传统方法进行了简要分析。提出一种新的光电结合型激光辐射功率量值传递和量程扩展方法,它更接近实际测试工作状态,从而可望提高激光辐射功率测量的准确性及其量值传递的唯一性。     

Characterization and magnetic properties of Fe–Co ultrafine particles

Characterization and magnetic properties of Fe–Co ultrafine particles were investigated systematically by means of X-ray diffraction, Mössbauer spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, energy disperse spectroscopy analysis, chemical analysis, oxygen determination and magnetization measurement. In comparison with bulk iron–cobalt alloys, the corresponding Fe–Co ultrafine particles have significant difference in the phase structure and magnetic properties, depending on the condition of evaporating and subsequent quenching. The mechanism for the formation of the ultrafine particles as well as the origin of ferromagnetism and paramagnetism (or superparamagnetism) were discussed.     

光纤光栅反射谱的放缩特性

利用介质光波导耦合模理论,证明了弱扰动的光纤光栅具有一个重要特性--放缩特性;即如果光纤光栅的折射率扰动分布沿光纤轴放大α倍,同时扰动强度缩小α倍,那么光栅的反射谱就以共振波长为中心在波长轴上缩小α倍.     

Electron-phonon scattering in an asymmetric double barrier resonant tunneling structure

We calculate the electron-phonon scattering rate for an asymmetric double barrier resonant tunneling structure based on dielectric continuum theory, including all phonon modes, and show that interface phonons contribute much more to the scattering rate than do bulk-like LO phonons for incident energies which are approximately within an order of magnitude of the Fermi energy. The maximum scattering rate occurs for incident electron energies near the quantum well resonance. Subband nonparabolicity has a significant influence on electron-phonon scattering in these structures. We show that the relaxation time is comparable to the dwell time of electrons in the quantum well for a typical resonant tunneling structure. Received: 23 December 1997 / Revised: 24 March 1998 / Accepted: 9 March 1998