Searching for optimal configurations by simulated tunneling

Optimization theory deals with algorithms finding the lowest cost (energy) configuration in a minimal number of steps. When the cost function has many local minima, the deterministic algorithms become easily trapped in suboptimal solutions. The simulated annealing method tries to overcome this difficulty by introducting thermal noise in the problem. Here we explore the possibility of implementing search procedures analogous to the quantum tunneling effect. The suggested dynamics is a guided diffusion process of an interactingpopulation of configurations. Different dynamical aspects of the search process are formulated first in a simple one-dimensional tight-binding model with a hierarchical potential. The new algorithm is then applied to the Traveling Salesman Problem. It is demonstrated that the use of interacting, evolving populations of tours representing our wave packet leads to systematic improvements and possibly, to the optimal tour. In addition, the structure of the cost function landscape for a given instance becomes locally accessible. The performance of the algorithm and its implications for parallel computing and genetic programming are briefly discussed.     

Picosecond third-harmonic light generation inβ-BaB2O4

The type-II phase-matched third-harmonic light generation in a -BaB₂O₄ crystal is studied experimentally. A passively mode-locked Nd: phosphate glass laser is used as a pump source. At a pump pulse peak intensity ofI ₁₀=5×10¹⁰W/cm² a third-harmonic conversion efficiency of a percent is obtained. A theoretical discussion of phase-matched third-harmonic generation in crystals of the symmetry group of -BaB₂O₄ (trigonal class 3) is given. The effective nonlinear susceptibility _eff for type-II phase-matching is determined.On leave from the Shanghai Institute of Optics and Fine Mechanics, Academia Sinica, Shanghai, P.R. China     

Two-dimensional visualization of the flame front in an internal combustion engine by laser-induced fluorescence of OH radicals

Two-dimensional laser-induced fluorescence (2D-LIF) imaging of OH radicals, excited at 308 nm, has been employed to visualize the flame front in an internal combustion engine burning air/propane mixtures. Light sheet thicknesses down to 70 m have been attained for excitation. Hydroxyl radicals were detected up to pressures of 7.5 bar at engine speeds of 500 rpm. An upper limit of 300 m for the flame front thickness was obtained from line intensity profiles.     

The magnetic moment of the 10+ isomer in140Ce andE1 transitions inN=82 isotones caused by outer subshell configurations

Using the reaction¹³⁸Ba(α,2n)¹⁴⁰Ce the magnetic moment of the 10 ₁ ⁺ isomer atE _x =3714.7 keV in theN=82 nucleus¹⁴⁰Ce has been determined by means of the TDPAD method toμ=+10.3(4)μ _N . Measuredg-factors in¹⁴⁰Ce are compared to calculations within the shell model with configuration mixing. For the 10 ₁ ⁺ isomer in¹⁴⁰Ce the four proton configuration π(1g ₇ ^2/2 ,2d ₅ ^2/2 ) has been found to be dominant. From theg-factor measurement strong contributions of multiparticle excitations to thegp2d _3/2,π3s ₁ ² or π1h ₁₁ ² shells and admixtures of neutron excitations to the wave function of the 10 ₁ ⁺ state could be excluded. The strongE1γ-branch of the deexcitation of the 10 ₁ ⁺ isomer in¹⁴⁰Ce can be explained by means of small admixtures of configurations which contain the outer subshell excitationsπ2f _7/2 andπ1h _9/2. On this basisE1 transitions experimentally observed in theN=82 nuclei¹⁴⁰Ce,¹⁴¹Pr and¹⁴⁵Eu may be understood.     

Behavior of large nucleic acids in reversed-phase high-performance liquid chromatography.

Large nucleic acids can be separated by reversed-phase high-performance liquid chromatography. Analysis shows that the retention time depends not only on the chain length but also on the base composition and the secondary structure of the molecule. A model is proposed to interpret their behavior. This model, called "multiple-point interaction theory" is based on the observation that macromolecules are flexible and very large compared to the hydrophobic phase (octadecylsilane) of the column. It explains the behavior of large nucleic acids in terms of an equilibrium of the macromolecule between the two phases through a multiple-point attachment to the chromatographic matrix, the parameters of the equilibrium being both the hydrophobicity of the base and the number of attachment points. This model fits the experimental data and can be applied to all types of flexible macromolecules, especially proteins and nucleic acids, when they are chromatographed on reversed-phase columns. The model is used to explain the separation of nucleic acids of importance in molecular biology.     

Base-atom recognition in protein adsorption to alkyl agaroses.

The three proteins phosphorylase b, calmodulin and fibrinogen are adsorbed onto thioalkyl derivatives of Sepharose much more strongly than onto gels carrying the same alkyl residue coupled via a carbamate linkage. This enhancement of binding onto alkyl-S-Sepharoses compared with alkyl-N-agaroses is not primarily due to an increase in the extent of conformational changes of the proteins occurring on the gel surface. This can be shown in experiments with the tripeptide Trp-Trp-Trp. The Trp tripeptide is also adsorbed with a much higher affinity to butyl-S-Sepharose than to butyl-N-Sepharose, showing that the primary interaction between the immobilized alkyl residue and the amino acids of the protein is decisive for adsorption. A model stressing the strong influence of an atom or a group of atoms at the base of an immobilized alkyl residue is described as "base-atom recognition".     

Determination of gallium by anodic stripping square-wave voltammetry Detection of a GaZn intermetallic compound and its destruction by Sb in an NaSCNNaClO(4) supporting electrolyte

Reproducibility for successive determinations with a hanging mercury drop electrode is assessed in relation to solution stirring, drop size and back-diffusion to the mercury thread. The effect of experimental parameters such as drop size, deposition time and gallium concentration on the observed stripping current is investigated. The interference of zinc present in a 0.5M NaSCN + 4.2M NaClO(4) supporting electrolyte on the gallium detection limit and calibration plots is described. Formation of an intermetallic compound with a Zn:Ga ratio of 2:3 and its destruction by co-deposition of zinc with Sb are reported. A detection limit of 10(-8)M gallium was obtained in the presence of 10(-5)M Sb(III).     

On the occurrence and role of SnO2, SnS and FeSn2 in coal hydroliquefaction experiments using tin-based catalysts

Mössbauer Spectroscopy, X-Ray Diffraction and Electron Microscopy were applied to the study of solid residues of coal hydroliquefaction, for which tin-based catalysts were used. In the general case hydroliquefaction runs were performed in the presence of added sulphur and of finely dispersed SnO₂ as a catalyst precursor. The only observed tin species were SnO₂ and SnS, the former with percentages higher than expected from XRD, due to its large f factor, the latter as a symmetric doublet, which suggests that any asymmetry should be ascribed to small particle sizes rather than to structure. When the S content was only that of coal and the catalyst precursor β-Sn, FeSn₂ occurred together with Sn sulfides and oxides, while no β-Sn was detected. The main catalytic role is ascribed to SnS.     

Magnetic resonance in amorphous metals based on Fe in the millimeter radiowave range

The research technique of amorphous magnetics is described. The paper gives the experimental data obtained by a multifunctional low-temperature radiospectrometer Buran in the mm radiowave range and presents their analysis.     

Multiplicity distributions at 250 GeV/c,a comparison of fits

The multiplicity distribution of all charged particles, as well as that of negatives and positives taken separately have been fitted by a number of recently proposed parametrizations. The negative binomial (2 parameters) and Laguerre distribution (3 parameters), in general, give good and very similar fits, but one of the parameters of the Laguerre distribution remains undetermined by the fit. The Krasznovszky-Wagner distribution (3 parameters) is better than the two first ones for full phase space, but slightly worse in intermediate rapidity intervals. Its disadvantage is the behaviour atn=0. The Branching distribution does not fit at an energy of \(\sqrt s = 22\) GeV.