A probabilistic simulator for population dynamics of quasispecies

We constructed a probabilistic simulator that allows all the events in population dynamics such as death, birth, mutation, and suppression/stimulation to be described by probabilistic rules. The simulator also facilitates a lattice used for expressing distribution and diversity (number of distinct strains) of quasispecies. The simulator is used to investigate the diversity threshold in HIV and T-cell interaction. This work was presented in part at the 13th International Symposium on Artificial Life and Robotics, Oita, Japan, January 31–February 2, 2008     

Effects of support and additive on oxidation state and activity of Pt catalyst in propane combustion

The effects of support and additive on the oxidation state and catalytic activity of Pt catalyst in the low temperature propane combustion were systematically investigated on Pt/MgO, Pt/Al₂O₃ and Pt/SiO₂–Al₂O₃. The catalytic activity varied much with both support materials and additives. The catalyst on the more acidic support showed higher activity, and the catalytic activity on every support materials increased as the electronegativity of additives increased, while some additives decreased the activity. The oxidation state of platinum, estimated by white line intensity of Pt L_III-edge XANES spectrum, also varied with the support and additives, and additives with higher electronegativity greatly prevented the platinum from its oxidation under oxidising atmosphere. Among almost all the catalysts with various supports and various additives, a clear relationship was observed between the oxidation state of platinum and the catalytic activity; the more metallic platinum showed higher activity. Thus, it was concluded that the total electrophilic/electrophobic property derived from those of the support and additive controls the oxidation state of platinum, which intensively affects the catalytic activity; i.e. higher electrophilic property provides less oxidised platinum, resulting in high catalytic activity. The mechanism of this effect was also discussed on the basis of thermochemical data, and it was proposed that the electrophobic materials promote the noble metal oxidation since the noble metal oxo-anion such as PtO^δ− is more stabilised with electrophobic cation.     

Structural instabilities and superconductivity in La-214 compounds

In La_2–x Ba _x CuO₄ (LBCO) the transition to a low-temperature tetragonal phase and the suppression of superconductivity occur at the carrier concentration p 1/8 per copper. We will discuss the roles of various material parameters that control this instability. An unusual lattice softening has been found by ultrasonic measurement on La_2–x Sr _x CuO₄ (LSCO). This softening is present only in an in-plane shearing mode and is ascribed to the growth of structural fluctuations in the normal state.These phenomena are closely related because both the structural change in LBCO and the applied strain in LSCO lift the degeneracy of in-plane oxygen sites. They clarify the importance of strong coupling between the normal-state electronic system and the lattice by a Peierls-type mechanism.     

Crossover from 3D to 2D metallic conduction in Sr2RuO4

We have investigated the normal-state conduction of superconducting Sr₂RuO₄ (T_c 1K), which is isostructural to La_2–xSr_xCuO₄. The resistivity of single crystals shows a crossover at T_M130K from 3D metallic conduction at lower temperatures to 2D one at higher temperatures. Concerning the temperature dependence of the out-of-plane resistivity, we present a systematic interpretation based on competition between the life time of the quasiparticles and the time for the quasiparticles to travel between the adjacent RuO₂ planes.     

Antibody-based computing: an application to the stable marriage problem

Antibodies, among other things, are important components of the immune system. This paper proposes using the specific recognition capability exhibited by antibodies for computation, in particular, for solving the stable marriage problem, which has been studied as a combinatorial computational problem. Antibody-based computation is proposed by integrating the recognition capabilities of antibodies. The computation is carried out on an array form that is suitable not only for expressing stable marriage problems, but also for further integration to antibody microarrays. This work was presented in part at the 12th International Symposium on Artificial Life and Robotics, Oita, Japan, January 25–27, 2007     

Time-dependent thermal convection in dilute solutions of 3He in superfluid 4He

Time-dependent thermal convection can occur in a unity-aspect-ratio Rayleigh-Beard convection cell containing a dilute solution of ³He in superfluid ⁴He when the fluid is heated from above. Results are presented primarily for a 0.24 mole % He solution at 0.925 K. Means is provided for introducing heat at the top and separately for a central plug and an outer ring such that both are at a constant temperature gDT above the bottom. A critical temperature difference T _cfor convection can be defined above which both steady and time-dependent convection occur. The time-dependent effects include a region of T. near T _cand characterized only by excessive noise, a region of somewhat higher T where there are intermittent major changes in the plug heating rate with a time distribution like that for random events, and a region at still higher T where periodic but nonsinusoidal variation of the heat flow is observed. When a long enough time, several months, has elapsed after cooling down the apparatus, time-dependent states no longer occur, and the heat flow above T _cis limited to steady convection. Briefly raising the temperature of the apparatus to 77 K is sufficient to restore the possibility of time-dependent states.     

Portable space charge measurement system using the pulsed electrostatic method

The pulsed electroacoustic (PEA) method is used to measure space charge distributions in insulating materials. A high-resolution PEA measurement system and signal procedure has been discussed in previous papers. Since the signal procedure is necessary for high-resolution measurement, the system must include a computer. In this paper, a new PEA system without signal processing is introduced. In order to eliminate the inevitable signal distortion of the conventional PEA method, the new system employs a new voltage waveform generator, one that is different from the very narrow pulse generator used in conventional PEA systems. Using the new waveform, designed based on the impulse response of the measurement system; the output signal can show the space charge distribution directly, without the need to conduct deconvolution. Thus, space charge distributions can be measured on site, such as in a factory, with a portable oscilloscope. The spatial resolution of the space charge measurement of the system is 10 /spl mu/m, which is the same as that of conventional PEA systems. Such a portable PEA system can contribute to various industrial applications.     

Three-dimensional space charge observation of ion migration in a metal-base printed circuit board

Internal space charge measurement has been mainly applied to investigate insulating materials used in RV apparatus, such as HVDC cables. We have observed the space charge profiles to monitor copper ion migration occurring in an insulation layer of a metal-base printed circuit board and found that the space charge distribution along the thickness direction corresponds to the progress of ion migration in insulation. The migration, however, can proceed in any direction in the specimen simultaneously; therefore, it should be measured in three dimensions. We measured metal-base epoxy resin insulated printed circuit boards by a newly developed three-dimensional pulsed electroacoustic method. The results show that the space charge density varies in the lateral direction when ion migration occurs in the specimen.