Multicanonical MCMC for sampling rare events: an illustrative review

Multicanonical MCMC (Multicanonical Markov Chain Monte Carlo; Multicanonical Monte Carlo) is discussed as a method of rare event sampling. Starting from a review of the generic framework of importance sampling, multicanonical MCMC is introduced, followed by applications in random matrices, random graphs, and chaotic dynamical systems. Replica exchange MCMC (also known as parallel tempering or Metropolis-coupled MCMC) is also explained as an alternative to multicanonical MCMC. In the last section, multicanonical MCMC is applied to data surrogation; a successful implementation in surrogating time series is shown. In the appendix, calculation of averages and normalizing constant in an exponential family, phase coexistence, simulated tempering, parallelization, and multivariate extensions are discussed.     

First-principles calculations of magnetic and electronic structures around surfaces and interfaces of magnetic multi-layered structure

Electronic and magnetic structures of ferromagnetic (FM)/non-magnetic (NM) and FM/antiferromagnetic (AF) bi-layer systems are calculated by the first principles approach. For the FM/NM system, we focus on the Co/Cu multi-layered structure whose interfacial layer is assumed to have a mixed composition of Co and Cu atoms, and show a possibility that Co atoms at the interface play a significant role as the spin-dependent scattering potentials. In the FM/AF system, we consider Fe or Co monolayer as FM layer and MnNi as AF layers. It is predicted that the Mn moments adjacent to FM layer are forced to align the FM moments, and those of under layer go gradually to anti-parallel alignment as in the bulk MnNi.     

Electrical activities of stacking faults and partial dislocations in 4H-SiC homoepitaxial films

The electrical activities of stacking faults (SFs) and partial dislocations in 4H-SiC homoepitaxial films were investigated by using the electron-beam-induced current (EBIC) technique. The basal plane dislocation was dissociated into Si_(g) 30^° and C_(g) 30^° partials under electron-beam irradiation, with a SF formed in between. The SF shows bright contrast at RT and dark contrast at 50 K in EBIC images. The reasons were discussed according to the quantum-well state of SF. C_(g) 30^° partial is always more electrically active than Si_(g) 30^° partial at each specific accelerating voltage. The EBIC contrasts of those two partials were discussed with the number of recombination centers.     

Enantiomeric Excess Determination for Monosaccharides Using Chiral Transmission to Cold Gas-Phase Tryptophan in Ultraviolet Photodissociation

Chiral transmission between monosaccharides and amino acids via photodissociation in the gas phase was examined using a tandem mass spectrometer fitted with an electrospray ionization source and a cold ion trap in order to investigate the origin of the homochirality of biomolecules in molecular clouds. Ultraviolet photodissociation mass spectra of cold gas-phase noncovalent complexes of the monosaccharide enantiomers glucose (Glc) and galactose (Gal) with protonated l-tryptophan H⁺(l-Trp) were obtained by photoexcitation of the indole ring of l-Trp. l-Trp dissociated via C_α–C_β bond cleavage when noncovalently complexed with d-Glc; however, no dissociation of l-Trp occurred in the homochiral H⁺(l-Trp)(l-Glc) noncovalent complex, where the energy absorbed by l-Trp was released through the evaporation of l-Glc. This enantioselective photodissociation of Trp was due to the transmission of chirality from Glc to Trp via photodissociation in the gas-phase noncovalent complexes, and was applied to the quantitative chiral analysis of monosaccharides. The enantiomeric excess of monosaccharides in solution could be determined by measuring the relative abundance of the two product ions in a single photodissociation mass spectrum of the cold gas-phase noncovalent complex with H⁺(l-Trp), and by referring to the linear relationships derived in this work.

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Preparation of functionally gradient fluorocarbon polymer films by plasma polymerization of NF3 and propylene

Fluorocarbon polymer films were prepared by plasma polymerization using nitrogen trifluoride (NF₃) and propylene as starting materials. To improve their adhesiveness to substrates, a novel functionally gradient film in which the content of fluorine decreased continuously from the surface to the interior was prepared by changing source gas composition during deposition. This film had a smooth and pinhole-free surface, and had a high contact angle (110°) for water drop. In addition, it showed good adhesion to a glass substrate. © 1996 John Wiley & Sons, Inc.     

Me3SiCl-promoted intramolecular cyclization of aromatic compounds tethered with N,O-acetals leading to the facile preparation of 1,4-benzodiazepine skeletons

The Me₃SiCl-promoted intramolecular aminomethylation of a novel type of N,O-acetals, which were prepared via a facile three-step synthesis from N-alkylaniline derivatives and N-alkyl-2-oxazolidinones that leads to the production of pharmaceutically useful 1,4-benzodiazepine skeletons with a variety of functional groups is described. This method was successfully applied to the facile preparation of both tricyclic benzodiazepine derivatives and a 1,4-benzoxazepine derivative via 7-exo-trig cyclization.     

Peroxidase-like catalytic activity of Mn- and Fe-tetrakis(4-carboxyphenyl)porphines bound to aminopropyl-glass bead in oxidative reaction of heterocyclic amines

Fe- or Mn-tetrakis(4-carboxyphenyl)porphine (Fe- and Mn-TCPP) bound to aminopropyl-glass bead (Fe- and Mn-TCPP_gs) was examined for the peroxidase (POD)-like function in order to develop a solid catalyst which can exhibit POD-like activity without adsorbing heterocyclic amines (HCAs). Mn-TCPP in aqueous solution had only a slight POD-like catalytic activity on HCAs (IQ and MeIQ). As for Fe-TCPP, it was impossible to examine the POD-like activity since it reacted with hydrogen peroxide in a liquid reaction system. However, both Fe- and Mn-TCPP when immobilized on aminopropyl-glass bead via peptide bond (Fe- and Mn-TCPP_gs), catalyzed the oxidative reaction of mutagenic HCAs with hydrogen peroxide. The catalytic activity of Fe- and Mn-TCPP_gs was investigated in more detail using as a substrate IQ and MeIQ which were oxidized more rapidly among the tested HCAs. Consequently, the optimal conditions for the oxidative reaction catalyzed by Fe- and Mn-TCPP_gs were determined. In addition, ESI-mass and absorption spectra of oxidation products of IQ and MeIQ showed that they are dimers. Thus, it was demonstrated that a solid catalyst with POD-like activity can be obtained by immobilizing Fe- and Mn-TCPPs on aminopropyl-glass beads.