Morphological and crystallographic features of γ-γ′ Ni-Al and Ni-Al-Ti two-phase bicrystals

Several- Ni-Al and Ni-Al-Ti two-phase bicrystals were made by the solid-state diffusion couple method. Each couple consisted of a-phase single crystal and a pure-Ni polycrystal, and was annealed at 1473 K in an Ar gas atmosphere. Single crystal layers of-phase with uniform thickness always grow into the parent-phase single crystals. The resultant/ interface has no voids or facets regardless of the orientation of interface and the chemical composition of the-phase. Porosity formation due to the Kirkendall effect is observed in the diffused region. Concentration profiles exhibit nearly constant gradients in-phase. The orientation relationship between both phases is found to be 001//001, that is, the-phase grows epitaxially along the crystal orientation of-phase.     

Importance of multiple-phonon interactions in molecular dissociation and nanofabrication using optical near fields

A quasi-particle (exciton-phonon polariton) model, as a simple model of an optical near-field probe, is proposed to investigate an unresolved problem in photochemical processes, i.e., why a vapor molecule can be dissociated by an incident photon with less energy than the dissociation energy only if, not a propagating far field, but an optical near field is used, and what is the mechanism leading to the photon flux dependence of the deposition rates. Incident photon energy and intensity dependences of Zn deposition rates are analyzed, and good agreement between the theoretical and experimental results is obtained. It suggests that the probe system plays an important role in vibrational transitions as well as electronic transitions in photodissociation processes, and that the couplings between the optical near field and molecular vibrations are enhanced to permit a nonresonant photodissociation inherent in the optical near field.     

Demonstrating nanophotonic switching using near-field pump–probe photoluminescence spectroscopy of CuCl quantum cubes

We demonstrated a novel optical switching operation using three CuCl quantum cubes with a size ratio of . Their quantized excitonic energy levels resonate with one another, and the switching mechanism was based on the resonant near‐field energy transfer between the quantum cubes. Using near‐field pump–probe photoluminescence spectroscopy, we succeeded in controlling the near‐field energy transfer and obtained a controlled (i.e. switched) signal in a differential photoluminescence spectrum with and without a pump beam. The internal quantum efficiency of the switching operation was close to 1. These results suggest the possibility of making a nanophotonic switching device smaller than 30 nm.     

Simulation of a chemical reaction, 2LiH→Li2+H2, driven by doubly excitation

A direct computer simulation of reaction dynamics at the electronic excited states is not easy to perform, because nonadiabatic equations must be solved as a function of time. Here we present a simple simulation to integrate directly the time-dependent Schrödinger equation within the framework of the time-dependent density functional theory (for electrons) coupled with the Newtonian equation of motion (for nuclei). We find that a chemical reaction, 2LiH→Li₂+H₂, takes place by the doubly excitation. Along the reaction, a level crossing occurs automatically between the highest occupied and lowest unoccupied levels. The simulation demonstrates a mechanism for relaxation for the reactions driven by doubly excitation: electronic excited state changes smoothly into the electronic ground state leaving a kinetic energy of the atoms.     

Hydrogen storage in TiO2 functionalized (10, 10) single walled carbon nanotube (SWCNT) – First principles study

Hydrogen storage in titanium dioxide (TiO₂) functionalized (10, 10) armchair single walled carbon nanotube (SWCNT) is investigated through first principle calculations using density functional theory (DFT). This first principles study uses Vienna Ab-initio Simulation Package (VASP) with ultrasoft pseudopotentials and local density approximation (LDA). The necessary benchmark and other systematic calculations were carried out to project the hydrogen storage capability of the designed system. Interestingly, the TiO₂ molecules functionalized on the outer surface of SWCNT do not undergo any dimerization/clustering thus giving excellent stability and usable gravimetric hydrogen storage capacity of 5.7 wt.% and the value nearly fulfills the US DOE target (i.e. 6 wt.%). The band structure and density of states (DOS) plots suggest that the functionalization can lead a way to transform the nature (metallic → semiconducting) of the pristine SWCNT. The nominal values of H₂ storage capacity and binding energies give much hope for using CNT functionalized with TiO₂ as a practical and reversible hydrogen storage medium (HSM).     

Effects of rotating magnetic fields on thermocapillary flow: Comparison of the infinite and the Φ1–Φ2 models

Convection control of three-dimensional thermocapillary flow by a rotating magnetic field (RMF) was simulated numerically, and the RMF infinite and RMF Φ₁–Φ₂ models were compared. The results of using both RMF models demonstrate that the transverse RMF stirs convection in an azimuthal direction and suppresses convection in the axial direction, which is helpful for the three-dimensional melt convection to become axisymmetric. Compared to the RMF Φ₁–Φ₂ model, however, the over-simplified RMF infinite model leads to a relatively large deviation. With the same magnetic field (7 mT, 50 Hz), the RMF infinite model results in a larger azimuthal velocity and a smaller axial velocity.     

Optimal Online Algorithms for an Electronic Commerce Money Distribution System

Abstract. We consider the money distribution problem for a micro-payment scheme using a distributed server system; in particular, for an automatic charging scheme named PayPerClick that allows Internet users to view Web pages for which access charges are levied without tedious payment procedures. A major bottleneck in the scheme is the network traffic caused by the distribution of electronic money to many different servers. We propose a simple online algorithm for distributing electronic money to servers so that the network traffic is minimized. The algorithm achieves the optimal online competitive ratio. We also consider a weighted version, for which we give an asymptotically optimal online algorithm within a constant factor.     

A novel ATP regeneration system using polyphosphate-AMP phosphotransferase and polyphosphate kinase

Polyphosphate-AMP phosphotransferase (PAP) and polyphosphate kinase (PPK) were used for designing a novel ATP regeneration system, named the PAP-PPK ATP regeneration system. PAP is an enzyme that catalyzes the phospho-conversion of AMP to ADP, and PPK catalyzes ATP formation from ADP. Both enzymes use inorganic polyphosphate [poly(P)] as a phosphate donor. In the PAP-PPK ATP regeneration system, ATP was continuously synthesized from AMP by the coupling reaction of PAP and PPK using poly(P). Poly(P) is a cheap material compared to acetyl phosphate, phosphoenol pyruvate and creatine phosphate, which are phosphate donors used for conventional ATP regeneration systems. To achieve efficient synthesis of ATP from AMP, an excessive amount of poly(P) should be added to the reaction solution because both PAP and PPK consume poly(P) as a phosphate donor. Using this ATP generation reaction, we constructed the PAP-PPK ATP regeneration system with acetyl-CoA synthase and succeeded in synthesizing acetyl-CoA from CoA, acetate and AMP. Since too much poly(P) may chelate MG2+ and inhibit enzyme activity, the Mg2+ concentration was optimized to 24 mM in the presence of 30 mM poly(P) in the reaction. In this reaction, ATP was regenerated 39.8 times from AMP, and 99.5% of CoA was converted to acetyl-CoA. In addition, since the PAP-PPK ATP regeneration system can regenerate GTP from GMP, it could also be used as a GTP regeneration system.     

Geometrical indications of adsorbed hydrogen atoms on graphite producing star and ellipsoidal like features in scanning tunneling microscopy images: Ab initio study

Recent scanning tunneling microscopy (STM) experiments display images with star and ellipsoidal like features resulting from unique geometrical arrangements of a few adsorbed hydrogen atoms on graphite. Based on first-principles STM simulations, we have found that the model with three hydrogen atoms, in which the hydrogen atoms are symmetrically placed on the graphene sheet in an equilateral triangle, encompassing a complete hexagon ring of carbon atoms, reproduces the experimentally observed starlike STM patterns. Additionally, we confirm that an ortho-hydrogen pair is the configuration corresponding to the ellipsoidal images. These calculations reveal that when the hydrogen pairs are in the same orientation, they are energetically more stable.