Maximum-cover source location problems with objective edge-connectivity three

Given a graph G = (V, E), a set of vertices covers a vertex if the edge-connectivity between S and v is at least a given number k. Vertices in S are called sources. The maximum-cover source location problem, which is a variation of the source location problem, is to find a source set S with a given size at most p, maximizing the sum of the weight of vertices covered by S. In this paper, we show a polynomial-time algorithm for this problem in the case of k = 3 for a given undirected graph with a vertex weight function and an edge capacity function. Moreover, we show that this problem is NP-hard even if vertex weights and edge capacities are both uniform for general k.     

Theoretical study on the photochromic cycloreversion reactions of dithienylethenes; on the role of the conical intersections

The mechanism of the photochromic cycloreversion reactions is theoretically examined in a model system of dithienylethenes by means of the CASSCF and CASPT2 methods. The structures of its conical intersections (CIs), which are the branching points of the internal conversions, were obtained. The analyses of the minimum energy paths from the Franck-Condon states and the CI points suggest that the cycloreversion reaction occurs during the intramolecular vibrational energy redistribution (IVR) toward the quasi-equilibrium on the 2A state. The current study of the model system will provide a basic insight for the photochromic molecular design.     

Valence transition of YbInCu4 observed in hard X-ray photoemission spectra

Yb 3d and valence-band photoemission spectra of the first-order valence-transition compound YbInCu4 have been measured with hard x ray at an excitation energy of 5.95 keV. Abrupt changes are clearly observed in both spectra around the transition temperature T(V)=42 K, in comparison with ultraviolet and soft x-ray photoemission (VUV-PES and SX-PES) spectra. From the Yb 3d spectra, the Yb valence has been estimated to be approximately 2.90 from 220 down to 50 K and approximately 2.74 at 30-10 K. We propose that Yb 3d hard x-ray photoemission spectroscopy is a very powerful method to estimate the valence of Yb with high accuracy. On the other hand, the Yb2+ 4f-derived peaks in the valence-band spectra exhibit a remarkable enhancement below T(V). The shape of the valence-band spectra is different from those of the VUV-PES and SX-PES spectra above T(V), reflecting the In 5s and 5p contributions.     

Lanthanide organometallic sandwich nanowires: formation mechanism

A molecular beam of europium-cyclooctatetraene sandwich nanowires Eu(n)()(COT)(m)() was produced by a laser vaporization synthesis method. The formation mechanism of the nanowires was quantitatively revealed by photoelectron and photoionization spectroscopies of the Eu-COT species, together with supporting theoretical calculations. From these results, it is confirmed that growth processes extending the length of Eu-COT nanowires involve a series of elementary reactions in which efficient charge transfer occurs at the terminal reaction sites. In every elementary step, the reaction proceeds between one reactant having low ionization energy and the other reactant having high electron affinity, probably via a "harpoon" mechanism.     

Hydrogen atom formation from the photodissociation of water ice at 193 nm

The TOF spectra of photofragment hydrogen atoms from the 193 nm photodissociation of amorphous ice at 90-140 K have been measured. The spectra consist of both a fast and a slow components that are characterized by average translational energies of 2k(B)T(trans)=0.39+/-0.04 eV (2300+/-200 K) and 0.02 eV (120+/-20 K), respectively. The incident laser power dependency of the hydrogen atom production suggests one-photon process. The electronic excitation energy of a branched cluster, (H(2)O)(6+1), has been theoretically calculated, where (H(2)O)(6+1) is a (H(2)O)(6) cyclic cluster attached by a water molecule with the hydrogen bond. The photoabsorption of this branched cluster is expected to appear at around 200 nm. The source of the hydrogen atoms is attributed to the photodissociation of the ice surface that is attached by water molecules with the hydrogen bond. Atmospheric implications are estimated for the photodissociation of the ice particles (Noctilucent clouds) at 190-230 nm in the region between 80 and 85 km altitude.     

Geometry optimization of the ring-opened oxirane diradical: mechanism of the addition reaction of the triplet oxygen atom to olefins

Geometry optimizations of several low-lying diradical states of the ring-opened oxirane (·CH₂CH₂O·) were performed by using the energy gradients of the UHF MINDO/3, STO-3G and 4-31G solutions. Both the STO-3G and 4-3 IG methods predict that the most stable form is the triplet state of the non-twisted σπ conformation in which the unpaired spins localized on the terminal carbon and oxygen atoms are oriented perpendicularly to each other. The singlet σσ diradical state in which both the radical-site p orbitals are coplanar with the molecular framework is only 2.3 (STO-3G) and 1.2 (4-31G) kcal/mol less stable than the triplet σπ diradical state. It is found that the geometry of the singlet σσ diradical is unique in that the C-C-O angle is noticeably small as compared with various other diradical states. Implications of these results to the mechanism of the oxirane-forming O(³P) + C₂H₄ reaction are discussed.     

COMPLEX AMPHIPHILIC HYPERBRANCHED FLUOROPOLYMERS BY ATOM TRANSFER RADICAL SELF-CONDENSING VINYL (CO)POLYMERIZATION

Amphiphilic hyperbranched fluorohomopolymer (M(n) = 9.06 kDa, M(w)/M(n)= 1.90) and fluorocopolymer (M(n) = 17.2 kDa, M(w)/M(n)= 2.50) with tri(ethylene glycol) units incorporated at the molecular level were synthesized by atom transfer radical self-condensing vinyl homopolymerization of an inimer, 4-[oxy(tri(ethylene glycol))bromoisobutyryl]-2,3,5,6-tetrafluorostyrene, and copolymerization of the inimer with 2,3,4,5,6-pentafluorostyrene (1:3, inimer:monomer), using 2,2'-bipyridine together with CuCl/CuCl(2) as the ligand/catalyst/deactivator system. The structure and composition of the fluoropolymers were characterized by (1)H, (13)C, and (19)F NMR spectroscopies. As detected by thermogravimetric analyses, the homopolymer and the copolymer had thermal stability up to 175 °C and 210 °C, respectively. Differential scanning calorimetry revealed a glass transition temperature of -19 °C for the homopolymer and 20 °C for the copolymer. Solubility tests indicated that both polymers were soluble in a broad range of organic solvents, and the presence of tri(ethylene glycol) units resulted in the formation of water dispersible micelles from each of the polymers.     

Direct observation of OH radicals ejected from water ice surface in the photoirradiation of nitrate adsorbed on ice at 100 K

Production of gaseous OH radicals in the 248-350 nm photoirradiation of NO3(-) doped on amorphous ice at 100 K was monitored directly by using resonance-enhanced multiphoton ionization. The translational energy distribution of the OH product was represented by a Maxwell-Boltzmann energy distribution with the translational temperature of 3250 +/- 250 K. The rotational temperature was estimated to be 175 +/- 25 K. We have confirmed that the OH production should be attributed to the secondary photolysis of H2O2 produced on ice surface on the basis of the results of controlled photolysis experiments for H2O2 doped on ice surface.     

Finite-Difference-Time-Domain Analysis for Electro-Magnetic Field Distribution on Near-Field Optical Recording Probe Head

In recent years there has been a strong trend and movement towards digitalism and high memory capacity in the multi-media field including digital movies. It is expected that new kinds of high density data storage to match this environment will be developed. The optical disk system using near-field optics and technology is considered to be a strong candidate for ultra-high density optical memory. In order to realize a new optical recording system we have focused on the writing head with high optical efficiency and resolution. We evaluated the properties of pyramidal probe heads using the FDTD (finite difference time domain) method and obtained simulation results in order to find the best structure and design for new near-field optical probes. From these results, we understood that a novel probe structure having metal layers on just 3 side planes (scoop type) shows the best performance in optical power density and beam size. We believe that optical enhancement and beam confinement arise from the effect of surface plasmon on a metal layer and the beam blocking of metal, respectively. Using this scoop-type probe having a tip size of 55 nm, we can get a very small spot size of 33 #x00D7; 60 nm² in FWHM (full with half maximum), which allows us to realize the recording density of 300 Gb/in².