Influence of ambient gas ionization on the deposition of clusters formed in an ablation plume

The effect of inert gas ionization on the dynamics of a laser ablation plume expanding through a background inert gas is studied. Charge transfer reactions between ablated ions and neutral background gas atoms yield to the formation of a charged layer on the plume expansion front. The energy lost by ablated ions when the plume is slowed down is calculated. The observed microstructure differences between carbon films prepared by pulsed laser deposition in helium, where the ionization mechanism is absent and respectively in argon, where it is present, are well correlated to model predictions.     

An investigation of finite-size scaling for systems with long-range interaction: The spherical model

A method is suggested for the derivation of finite-size corrections in the thermodynamic functions of systems with pair interaction potential decaying at large distancesr asr ^{–d –v3746m425nt/xxlarge963.gif" alt="sgr" align="BASELINE" BORDER="0">} , whered is the space dimensionality andv3746m425nt/xxlarge963.gif" alt="sgr" align="BASELINE" BORDER="0">>0. It allows for a unified treatment of short-range (v3746m425nt/xxlarge963.gif" alt="sgr" align="BASELINE" BORDER="0">=2) and long-range (v3746m425nt/xxlarge963.gif" alt="sgr" align="BASELINE" BORDER="0"><2) interaction. The asymptotic analysis is illustrated by the mean spherical model of general geometryL ^{d–dv3746m425nt/xxlarge8242.gif" alt="prime" align="BASELINE" BORDER="0">}×v3746m425nt/xxlarge8734.gif" alt="infin" align="MIDDLE" BORDER="0"> ^{dv3746m425nt/xxlarge8242.gif" alt="prime" align="BASELINE" BORDER="0">} subject to periodic boundary conditions. The Fisher-Privman equation of state is generalized to arbitrary real values ofdv3746m425nt/xxlarge10878.gif" alt="ges" align="MIDDLE" BORDER="0">v3746m425nt/xxlarge963.gif" alt="sgr" align="BASELINE" BORDER="0">, 0v3746m425nt/xxlarge10877.gif" alt="les" align="MIDDLE" BORDER="0">dv3746m425nt/xxlarge8242.gif" alt="prime" align="BASELINE" BORDER="0">v3746m425nt/xxlarge10877.gif" alt="les" align="MIDDLE" BORDER="0">v3746m425nt/xxlarge963.gif" alt="sgr" align="BASELINE" BORDER="0">. It is shown that thev3746m425nt/xxlarge949.gif" alt="epsi" align="BASELINE" BORDER="0">-expansion may be used to study the breakdown of standard finite-size scaling at the borderline dimensionalities.     

Photothermal determination of vertical crack lengths in silicon nitride

In this paper we describe the use of thermal microscopes in measuring the lengths of vertical cracks in silicon nitride. Results of theoretical calculations for temperature profiles in samples near the end of the cracks are demonstrated. These calculations showed that the effect of the crack decreases to a non-measurable level at distances of about 10 m from the end of the crack. Experimental measurements showed that thermally obtained crack lengths were at least 34% longer than those that were optically measured. The obtained crack length was independent of the heat modulation frequency used.     

Likelihood estimation of soft-core interaction potentials for Gibbsian point patterns

The likelihood method is developed for the analysis of socalled regular point patterns. Approximating the normalizing factor of Gibbs canonical distribution, we simultaneously estimate two parameters, one for the scale and the other which measures the softness (or hardness), of repulsive interactions between points. The approximations are useful up to a considerably high density. Some real data are analyzed to illustrate the utility of the parameters for characterizing the regular point pattern.     

MNDO study of reaction paths: Diboration of acetylene

The reaction of B₂H₄ with acetylene has been studied by the MNDO method. It is shown that the reaction is exothermic and proceeds in two steps. The first step is the formation of a three-center v26q1j5561597mv2/xxlarge960.gif" alt="pgr" align="BASELINE" BORDER="0">-complex and this is the rate-determining step of the reaction. The second step is the rearrangement of the v26q1j5561597mv2/xxlarge960.gif" alt="pgr" align="BASELINE" BORDER="0">-complex to the product and this step requires a very small amount of activation energy. The activation barrier for the diboration reaction is 12.8 kcal/mol.The proposed mechanism is significantly different from those proposed earlier and explains all experimental data relating to this reaction.     

The search for a new model structure of β-Factor XIIa

We present the search for a new model of v402700310m6450q/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-factor XIIa, a blood coagulation enzyme, with an unknown experimental 3D-structure. We decided to build not one but three different models using different homologous proteins as well as different techniques and different modellers. Additional studies, including extensive molecular dynamics simulations on the solvated state, allowed us to draw several conclusions concerning homology modelling, in general, and v402700310m6450q/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-factor XIIa, in particular.     

Fields as Kolmogzrov flows

It is widely recognized that for highly unstable dynamical systems there exists a fundamental limitation on predictability and determinism. An important class of such highly unstable systems is the class of K-flow, which is further characterized by the existence of time-asymmetric objects in the form of K-partition. Our recent approach to the problem of irreversibility has shown that when the implications of the limitation on determinism arising from strong form of instability and those of the existence of K-partition are consistently taken into account, one is naturally led from the physically unrealizable deterministic evolution of phase points to an entropy-increasing stochastic Markovian evolution. Furthermore, this transition is not the result of extraneously imposed coarse graining and/or approximation schemes, but can be brought about by an invertible transformation whose existence and construction are determined by the nature of the instability of the dynamical system itself. After a brief review of this theory which also contains some relatively new remarks, we prove that classical Klein-Gordon field (both massive and massless) possess the structure of K-flow. This seems to provide the first examples of relativistic systems that are K-flows. Some of the implications of this result are briefly discussed. From a mathematical point of view, this seems to be a first step toward an ergodic theory of partial differential equations. In the process, we also provide an independant group-theoretic proof of the existence of incoming and outgoing subspaces of the scattering theory of Lax and Phillips for the wave equation.     

Infrared asymptotic freedom of a hierarchical φ 3 6 lattice theory

For the weakly coupled latticev1mtr38388788j4w/xxlarge966.gif" alt="phgr" align="MIDDLE" BORDER="0"> ₃ ⁶ theory in a hierarchical model approximation a nonperturbative renormalization group analysis in the spirit of Gawedzki and Kupiainen is performed to study the flow of the effective actions. We deduce a domain of attraction to the tricritical (Gaussian) fixed point. The two relevant coupling constants of the problem are controlled by analytic continuation to complex domains, tracing their images under the renormalization group iterations.     

Synthesis and Characterization of Tetraosmium Carbonyl Complexes Containing a Bridging CO2 Ligand

Treatment of (thd)H (thd=2,2,6,6-tetramethyl-3,5-heptandionate) with excess Os₃(CO)₁₂ in an autoclave at 180°C gives the formation of a brown metal chain complex [Os₂(CO)₅(thd)₂]₂ (1) and a yellow CO₂ cluster complex [Os₄(v9kk208g5/xxlarge956.gif" alt="mgr" align="MIDDLE" BORDER="0">-H)(v9kk208g5/xxlarge956.gif" alt="mgr" align="MIDDLE" BORDER="0">-CO₂)(thd)(CO)₁₃] (2) in low yields. Complex 2 was fully identified by a combination of spectroscopic methods and X-ray diffraction study, showing a unique CO₂ ligand bridging a triosmium metal fragment, Os₃(v9kk208g5/xxlarge956.gif" alt="mgr" align="MIDDLE" BORDER="0">-H)(CO)₁₀ and a monometallic osmium fragment, Os(CO)₃(thd). Upon treatment of 1 with Me₃NO at an elevated temperature, oxidation of the CO ligand occurred at the position trans to the unique CO₂ ligand on the Os(CO)₃(thd) fragment, giving the formation of a second CO₂ cluster [Os₄(v9kk208g5/xxlarge956.gif" alt="mgr" align="MIDDLE" BORDER="0">-H)(v9kk208g5/xxlarge956.gif" alt="mgr" align="MIDDLE" BORDER="0">-CO₂)(thd)(CO)₁₂(NCMe)] (3), which is stabilized by a weakly coordinated acetonitrile molecule.