Resonant coupling of small size-controlled lead clusters with an intense laser field

We exposed small size-controlled lead clusters with a few hundreds of atoms to laser pulses with peak intensities up to 10¹⁵ W cm^-2 and durations between 60 fs to 2.5 ps. We measured kinetic energies and ionic charge of fragments as a function of the laser intensity and pulse duration. Highly charged Pbⁿ⁺ ions up to n = 26 have been detected presenting kinetic energies up to 15 keV. For comparison with our experimental results, we have performed simulations of the laser coupling with a cluster-sized lead nanoplasma using a qualitative model that was initially proposed by Ditmire and co-workers at LLNL for the case of rare gas clusters. From these simulations we conclude that two mechanisms are responsible for the explosion dynamics of small lead clusters. As already observed for large rare gas clusters (n = 10⁶), fragments with charge states below +10 are driven by Coulomb forces, whereas the higher charged fragments are accelerated by hydrodynamic forces. The latter mechanism is a direct consequence of the strong laser heating of the electron cloud in the nanoplasma arising from a plasmon-like resonance occurring at n _e = 3n _c. In order to obtain an optimized laser-nanoplasma coupling, our results suggest that the plasma resonance should occur at the peak intensity of the laser pulse. Due to inertial effects, even for such small-sized clusters, the observed optimum pulse duration is in the order of 1 ps which is in good agreement with our theoretical results. Received 18 March 2002 Published online 19 July 2002     

Rigorous entropy-energy arguments

We present a method for making rigorous various arguments which predict that certain situations are unstable because of a balance of energy vs. entropy. As applications, we give yet another proof that the two-dimensional plane rotor has no spontaneous magnetization and we make rigorous Thouless' arguments on the one-dimensional Ising model with couplingJ/n ².on leave from Departments of Mathematics and Physics, Princeton University. Research partially supported by U.S.N.S.F. under grant No. MCS-78-01885.Danforth Fellow. Research partially supported by U.S.N.S.F. under grant No. PHY 78-23952.     

Fluxes and the elimination of fast-relaxing variables

The behavior of fluxes under elimination of fast-relaxing variables from linear dynamical evolution equations is investigated. It is found that the fluxes corresponding to evolution equations which result from eliminations do not in general yield an adequate representation of the fluxes corresponding to the evolution equations from which the variables have been eliminated. In all examples considered, a discrepancy occurs when the eliminations reduce a cycle with nonzero thermodynamic force to a single state. The entropy production corresponding to the evolution equations resulting from the eliminations lacks terms corresponding to such cycles.     

Recent progress in plant cell culture

Conclusions Commercial application of plant cell cultures for the production of useful metabolites on a large scale has not yet been realized. However, some recently published papers and patents seem very attractive for industrial use because their results and techniques are apparently applicable to a large-scale production of metabolites. The author believes that commercial success using plant tissue cultures will be realized in the near future with advanced techniques if product selection is determined by economic and political principles. In 1982, the 5th International Congress of Plant Tissue and Cell Culture will be held in Japan and this undoubtedly will encourage research activity in our country.     

Approximate cores of replica games and economies: Part II: Set-up costs and firm formation in coalition production economies

A model of a coalition production economy allowing set-up costs, indivisibilities,and nonconvexities is developed. It is shown that for all sufficiently large replications, approximate cores of the economy are nonempty.     

Cluster validity for fuzzy clustering algorithms

The proportion exponent is introduced as a measure of the validity of the clustering obtained for a data set using a fuzzy clustering algorithm. It is assumed that the output of an algorithm includes a fuzzy nembership function for each data point. We show how to compute the proportion of possible memberships whose maximum entry exceeds the maximum entry of a given membership function, and use these proportions to define the proportion exponent. Its use as a validity functional is illustrated with four numerical examples and its effectiveness compared to other validity functionals, namely, classification entropy and partition coefficient.     

推拉并行模式的生产优化研究

本文提出一种推拉并行的生产模式 ,并分析了其优点 .该模式规定设备在完成普通订单的空闲时间补充库存但不许超过库房容量 ;如果加急订单到达时的库存量大于 0 ,则直接交货 ,并收取附加费用 ,否则与普通订单一道排队 .文章一方面给出了各种参数下加急订单的利润平衡点 ,另一方面展示出随着库存容量的增加 ,普通订单的交货时间接近于加急订单不存在时的数值 .     

Transverse momenta of secondaries from 200 GeV/c proton-nucleus interactions

A study of 100 interactions, produced by secondary particles from 200 GeV/c proton interactions in nuclear emulsions, has been made to estimate the transverse momenta of the secondary particles. The data have been analysed by different methods of energy estimation and the weighted average values ofp _t have been compared as estimated from various methods. An average value ofp _t equal to 0.38 ± 0.03 GeV/c, in proton-nucleus interactions at 200 GeV/c, has been obtained from the production mechanism method.     

Open quasi-free systems

We compute the time evolution of an infinitely extended, open, quasi-free system in the weak coupling limit followed by the thermodynamic limit, and we derive the Onsager relations and the properties of entropy production.On leave of absence from Istituto di Fisica dell'Università, Milan, Italy