Off-resonant fifth-order response function for two-dimensional Raman spectroscopy of liquids CS2 and H2O

The off-resonant fifth-order response functions for two-dimensional (2D) Raman spectroscopy of molecular liquids CS2 and H2O are investigated by using molecular dynamics calculation. This spectroscopy, able to deal with a phase space dynamics, shows the existence of nodal lines in several polarization tensor elements [see L. Kaufman et al., Phys. Rev. Lett. 88, 207402 (2002) for experimental results]. The nodal property is found to arise from the dynamical couplings among rotational modes, not accounted for in a normal mode picture. The effects of anharmonicities and "mode coupling through polarizability" are also investigated by comparing the 2D Raman signal with a constant temperature velocity reassignment echo method.     

Achievement of a 920-MHz high resolution NMR

We have developed a 920-MHz NMR system and performed the proton NMR measurement of H(2)O and ethylbenzene using the superconducting magnet operating at 21.6 T (920 MHz for proton), which is the highest field produced by a superconducting NMR magnet in the persistent mode. From the NMR measurements, it is verified that both homogeneity and stability of the magnet have a specification sufficient for a high resolution NMR.     

A study on ac and dc conductivity characteristics of Y-doped BaCeO3 modified by Ar+ ion beam

The effects of surface modification on electrical characteristics in bulk, grain boundary and interface (electrolyte/electrode) of BaCe_0.9Y_0.1O_3-δ were investigated. The surface modification was performed by means of two processes: specimen was firstly irradiated by 10 keV Ar⁺ ion with dose of 1 × 10¹⁸ ions/cm² and then exposed to air. The modified surface was investigated by elastic recoil detection analysis (ERDA) for quantitative analysis of hydrogen concentration on the surface and alternating current (AC) and direct current (DC) conductivity measurements, respectively. The ERDA results showed that hydrogen concentration and reaction rate on the modified surface increased. The increase of hydrogen concentration was explained in terms of the increase of proton due to interaction between oxygen vacancy formed by modification and H₂O. In AC and DC electrical conductivity measurements, it concluded that the proton and electronic carrier generated on the surface by modification attributed to the increase of bulk, grain boundary and interface conductivity.     

Magnetism in singlet ground states

The spin‐gap phenomenon is a key characteristic of high T_c superconducting cuprates, whose experimental results are summarized and discussed in the context of the slave‐boson mean field theory of the extended t–J model. It is seen that there exists satisfactory agreement between theory and experiments in bilayer cuprates. As regards the apparent absence of the spin‐gap in single layer La_2-xSr_xCuO₄ (LSCO), the possible roles played by disorder have been pointed out in view of the recent neutron scattering experiment on other spin singlet systems, the spin‐Peierls CuGeO₃ and two‐leg ladders. This revised version was published online in July 2006 with corrections to the Cover Date.     

Nanoparticles in Emissions and Atmospheric Environment: Now and Future

Journal of Nanoparticle Research -     

Combustion behaviors of isolated n-decane and ethanol droplets in carbon dioxide-rich ambience under microgravity

The burning and sooting behaviors of isolated fuel droplets for ethanol and n-decane are examined in high concentration of the ambient carbon dioxide under microgravity. A quartz fiber with the diameter of 50 μm maintains the droplet in the center of the combustion chamber and the range in the initial droplet diameter is from 0.30 to 0.80 mm. The ambience consists of oxygen, nitrogen and carbon dioxide. The concentration of oxygen is 21% in volume, and that of carbon dioxide is varied from 0% to 60% in volume. Detail measurements of the projected image of the droplet are conducted by using a high speed video camera and the effective droplet diameter squared are calculated from the surface area of the rotating body of the projected object. From evolutions of the droplet diameter squared, the instantaneous burning rates are calculated. Time history of the instantaneous burning rate clearly represents the droplet combustion events, such as the initial thermal expansion, ignition and following combustion. The instantaneous burning rate for n-decane shows an increasing trend during combustion, while that for non-sooting ethanol remains almost constant or shows a decreasing trend. A slight stepwise increase in the instantaneous burning rate is observed for larger n-decane droplets in air, which may be attributed to soot accumulation. However, this behavior of the burning rate disappears in higher concentration of carbon dioxide. Direct observation of the droplet flame indicates suppression of soot production in higher concentration of carbon dioxide and the suppression is enhanced for smaller droplet.     

Passively mode-locked lasers with 17.2-GHz fundamental-mode repetition rate pulsed by carbon nanotubes

17.2 GHz, the highest fundamental-mode repetition rate to our knowledge, of a carbon nanotube-based passively mode-locked laser is realized at 1570 nm by employing purified single-walled carbon nanotubes as saturable absorbers. The ultrashort linear laser cavity configured with a approximately 9 mm length is designed and demonstrated with our extremely miniaturized nanotube mode locker and a mirror-coated semiconductor optical amplifier as gain medium. The demonstrated pulsed laser has the inferred temporal pulse width of 14 ps and a 3 dB spectral bandwidth of 0.73 nm.     

Phase-locked laser system for a metastable states qubit in 40 Ca+

We describe the development of a phase-locked laser system tailored to an ion-trap-based quantum information processor with (40)Ca(+). Laser outputs from an extended cavity diode laser and a Ti:sapphire laser with output laser wavelengths of approximately 850 and 854 nm, respectively, were phase locked and used to excite a Raman transition between the D(3/2) and D(5/2) metastable states qubit. Development and the performance of the laser system are described. We also compare the characteristics and the benefits of the developed qubit coupling with those in the conventional approaches.     

Oxygen isotope effect of superconducting (Nd1−xCex)2CuO4−δ system

The effect of oxygen isotope substitution on the transition temperature T_c of a superconducting (Nd_1−xCe_x)₂CuO_4−δ system was studied, where the special synthetic method was taken to minimize ambiguous factors on the oxygen concentration and to guarantee the complete substitution of ¹⁶O by ¹⁸O. The isotope exponent in the relationship of T_c∝1/M was estimated to be less than 0.15 by magnetic susceptibility measurements.     

Ergodic properties and thermodynamic behavior of elementary reversible cellular automata. I. Basic properties

This is the first part of a series devoted to the study of thermodynamic behavior of large dynamical systems with the use of a family of fully-discrete and conservative models named elementary reversible cellular automata (ERCAs). In this paper, basic properties such as conservation laws and phase space structure are investigated in preparation for the later studies. ERCAs are a family of one-dimensional reversible cellular automata having two Boolean variables on each site. Reflection and Boolean conjugation symmetries divide them into 88 equivalence classes. For each rule, additive conserved quantities written in a certain form are regarded as a kind of energy, if they exist. By the aid of the discreteness of the variables, every ERCA satisfies the Liouville theorem or the preservation of phase space volume. Thus, if an energy exists in the above sense, statistical mechanics of the model can formally be constructed. If a locally defined quantity is conserved, however, it prevents the realization of statistical mechanics. The existence of such a quantity is examined for each class and a number of rules which have at least one energy but no local conservation laws are selected as hopeful candidates for the realization of thermodynamic behavior. In addition, the phase space structure of ERCAs is analyzed by enumerating cycles exactly in the phase space for systems of comparatively small sizes. As a result, it is revealed that a finite ERCA is not ergodic, that is, a large number of orbits coexist on an energy surface. It is argued that this fact does not necessarily mean the failure of thermodynamic behavior on the basis of an analogy with the ergodic nature of infinite systems.