Aspects of nucleon Compton scattering

We consider the spin-averaged nucleon forward Compton scattering amplitude in heavy baryon chiral perturbation theory including all terms to order . The chiral prediction for the spin-averaged forward Compton scattering amplitude is in good agreement with the data for photon energies110 MeV. We also evaluate the nucleon electric and magnetic Compton polarizabilities to this order and discuss the uncertainties of the various counter terms entering the chiral expansion of these quantities.     

Cluster description of water-in-oil microemulsions near the critical and percolation points

The three-component ionic microemulsion system consisting of AOT/water/decane shows an unusual phase behavior in the vicinity of room temperature. The phase diagram in the temperature-volume fraction (of the dispersed phase) plane exhibits a lower consolute critical point at about 40 degrees centigrades and 10% volume fraction. A percolation line, starting from the vicinity of the critical point, cuts across the plane, extending to high volume fraction side at progressively lower temperatures. In this paper we review the evidence that allows to interpret the phase behavior of our system in terms of interacting spherical droplets. We also investigate the dynamics of droplets, below and approaching the critical point by dynamic light scattering. The first cumulant and time evolution of the droplet density correlation function can be quantitatively calculated by assuming the existence of polydispersed fractal clusters formed by the microemulsion droplets due to attraction. The relaxation phenomena observed in an extensive set of measurements of electrical conductivity and permittivity close to percolation is also reviewed and interpreted through the same cluster-forming mechanism, which reproduces the most relevant features of the frequency-dependent complex dielectric constant of this system. Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Copanello, Italy, July 4–8, 1994.     

Spatial dependence of meson correlation functions at high temperature

The spatial dependence of meson correlation functions at high temperature is studied in perturbative QCD, keeping only the lowest order term. We obtain analytic results for the static correlation function in this approximation. Problems connected with the regularization of the divergent expressions are discussed in detail. The meson screening mass is determined from the form of the correlation function at large distances. We obtain , which agrees with the results of Eletskii and Ioffe, for massless quarks (M=0). Finally, the correlation function in the temporal direction is briefly discussed. For massless quarks, we find the corresponding screening massm _scr=2T.Research supported in part by the Polish State Committee for Scientific Research under Grant No. 2.0204.91.01     

Density and momentum dependence of the coupling strengths for scalar and vector fields

The collision term has been deduced based on the effective Lagrangian in addition to the mean-field. We propose the momentum- and density-dependent coupling strengths for scalar and vector fields. The saturation properties of nuclear matter, the experimental data of the energy-dependent optical potential and the mean free path in the nuclei can be reproduced simultaneously. The in-mediumn–n cross section has also been calculated for different densities and energies, our results are consistent with Dirac-Brueckner-Hartree-Fock calculations.Supported by National Natural Science Foundation of China     

C60/PMMA复合材料的反饱和吸收与光限幅特性研究

本文报导C₆₀/PMMA复合材料的制备方法,并采用调QNd:YAG倍频脉冲激光照射C₆₀/PMMA夏合材料,研究了其反饱和吸收与光限幅将性。在线性透射率为46%条件下,光限幅阈值能量密度为65mJ/cm²,材料破坏能量密度阈值为600mJ/cm².与C₆₀甲苯溶液相比具有一定的优点。     

固体C60/PMMA的激发态吸收光限幅研究

应用五能级模型计算了C₆₀/PMMA的激发态吸收光限幅特性;采用调Q倍频Nd:YAG脉冲激光测量了C₆₀/PMMA的激发态吸收光限幅效应。理论和实验结果基本符合。     

A strange pigeon-hole principle

Using Ramsey theory, we establish the following pigeon-hole type principle: From a large number of random variables (functions, vectors, etc.) one can always select two, X and Y, such that P(X < Y) 1/2. We apply the principle for a poset problem.     

On a question of H. Kraljević

In this paper, assuming a certain set-theoretic hypothesis, a positive answer is given to a question of H. Kraljevi, namely it is shown that there exists a Lebesgue measurable subsetA of the real line such that the set {c R: A + cA contains an interval} is nonmeasurable. Here the setA + cA = {a + ca: a, a A}. Two other results about sets of the formA + cA are presented.     

A new Pythagorean functional equation

The purpose of this paper is to solve the following Pythagorean functional equation:(e ^p(x,y) ) ² ) = q(x,y) ² + r(x, y) ², where each ofp(x,y), q(x, y) andr(x, y) is a real-valued unknown harmonic function of the real variablesx, y on the wholexy-planeR ².The result is as follows.