Wide-area remote-sensing system of pollution and gas dispersal by near-infrared absorption based on low-loss optical fiber network

An all optical remote sensing system utilizing long distance, ultralow loss optical fiber networks is studied and discussed for near infrared absorption measurements of combustible and/or explosive gases such as CH4 and C3H8 in our environment, including experimental results achieved in a diameter more than 20 km. The use of a near infrared wavelength range is emphasized

Current-feedback-stabilized laser system for quantum simulation experiments using Yb clock transition at 578 nm

We developed a laser system for the spectroscopy of the clock transition in ytterbium (Yb) atoms at 578 nm based on an interference-filter stabilized external-cavity diode laser (IFDL) emitting at 1156 nm. Owing to the improved frequency-to-current response of the laser-diode chip and the less sensitivity of the IFDL to mechanical perturbations, we succeeded in stabilizing the frequency to a high-finesse ultra-low-expansion glass cavity with a simple current feedback system. Using this laser system, we performed high-resolution clock spectroscopy of Yb and found that the linewidth of the stabilized laser was less than 320 Hz.Comment: 5 pages, 7 figure

N\'eel and singlet RVB orders in the t-J model

The N\'eel and the singlet RVB orders of the {\it t-J} model in a 2D square lattice are studied in the slave-boson mean-field approximation. It is shown that the N\'eel order parameter takes the maximum value at the finite temperature and disappear at the lower temperature for a certain range of doping. It is also shown that the N\'eel and the singlet RVB orders coexist at low temperature. This suggests the possibility of the coexistence of the N\'eel and the superconducting orders.Comment: RevTeX, 8 pages, 1 postscript figure. To appear in Physica C, Volume 257, issue 38

Electronic Structure of Charge- and Spin-controlled Sr_{1-(x+y)}La_{x+y}Ti_{1-x}Cr_{x}O_{3}

We present the electronic structure of Sr_{1-(x+y)}La_{x+y}Ti_{1-x}Cr_{x}O_{3} investigated by high-resolution photoemission spectroscopy. In the vicinity of Fermi level, it was found that the electronic structure were composed of a Cr 3d local state with the t_{2g}^{3} configuration and a Ti 3d itinerant state. The energy levels of these Cr and Ti 3d states are well interpreted by the difference of the charge-transfer energy of both ions. The spectral weight of the Cr 3d state is completely proportional to the spin concentration x irrespective of the carrier concentration y, indicating that the spin density can be controlled by x as desired. In contrast, the spectral weight of the Ti 3d state is not proportional to y, depending on the amount of Cr doping.Comment: 4 pages, 3 figures. Accepted for publication in Phys. Rev. Let

A debris-flow monitoring devices and methods bibliography

International audienceDebris-flow monitoring has two functions, warning and modeling. The warning function includes the following parameters: occurrence prediction and detection, proximity sensing, and discharge-estimation. The parameters obtained from debris-flow measurements can deduce a numerical model for creating a hazard map and designing various types of control structures to mitigate the hazards. Many devices and methods of monitoring are tabulated here for comparative study. Some of them are in operation. Advanced comparative studies lead to an improvement in debris-flow monitoring, an integrated system that can be applied to any torrent, and a breakthrough in future developments

Activation volumes in CoPtCr-SiO2 perpendicular recording media

CoPtCr-SiO2 perpendicular recording media with varying levels of SiO2 were examined by two different methods to determine the activation volume. The first is based on the sweep-rate dependence of the remanence coercivity using Sharrock's equation. The second is based on the measurement of the fluctuation field from time-dependence data, determined using a magneto-optical Kerr effect (MOKE) magnetometer. The values of V-act measured at the coercivity for both methods are almost the same, with the fluctuation field and activation volumes increasing with the SiO2 content. The difference between V-act and the grain volume measured directly from bright-field TEM images decreases as the SiO2 content increases due to the reduction of intergranular exchange coupling. The experimental results indicate that values of V-act obtained from single- and double-layered media are consistent. It was also found that the coercivity and normalized hysteresis loop slope at coercivity varied with SiO2 content, with the coercivity peaking at 8 at % SiO2 (nearly 26 vol% SiO2)

Finite-temperature Mott transitions in multi-orbital Hubbard model

We investigate the Mott transitions in the multi-orbital Hubbard model at half-filling by means of the self-energy functional approach. The phase diagrams are obtained at finite temperatures for the Hubbard model with up to four-fold degenerate bands. We discuss how the first-order Mott transition points $U_{c1}$ and $U_{c2}$ as well as the critical temperature $T_c$ depend on the orbital degeneracy. It is elucidated that enhanced orbital fluctuations play a key role to control the Mott transitions in the multi-orbital Hubbard model.Comment: 8 pages, 7 figure

The effect of gas drag on the growth of protoplanets -- Analytical expressions for the accretion of small bodies in laminar disks

Planetary bodies form by accretion of smaller bodies. It has been suggested that a very efficient way to grow protoplanets is by accreting particles of size <<km (e.g., chondrules, boulders, or fragments of larger bodies) as they can be kept dynamically cold. We investigate the effects of gas drag on the impact radii and the accretion rates of these particles. As simplifying assumptions we restrict our analysis to 2D settings, a gas drag law linear in velocity, and a laminar disk characterized by a smooth (global) pressure gradient that causes particles to drift in radially. These approximations, however, enable us to cover an arbitrary large parameter space. The framework of the circularly restricted three body problem is used to numerically integrate particle trajectories and to derive their impact parameters. Three accretion modes can be distinguished: hyperbolic encounters, where the 2-body gravitational focusing enhances the impact parameter; three-body encounters, where gas drag enhances the capture probability; and settling encounters, where particles settle towards the protoplanet. An analysis of the observed behavior is presented; and we provide a recipe to analytically calculate the impact radius, which confirms the numerical findings. We apply our results to the sweepup of fragments by a protoplanet at a distance of 5 AU. Accretion of debris on small protoplanets (<50 km) is found to be slow, because the fragments are distributed over a rather thick layer. However, the newly found settling mechanism, which is characterized by much larger impact radii, becomes relevant for protoplanets of ~10^3 km in size and provides a much faster channel for growth.Comment: accepted for publication in Astronomy & Astrophysic

Electronic states around a vortex core in high-Tc superconductors based on the t-J model

Electronic states around vortex cores in high-Tc superconductors are studied using the two-dimensional t-J model in order to treat the d-wave superconductivity with short coherence length and the antiferromagnetic (AF) instability within the same framework. We focus on the disappearance of the large zero-energy peak in the local density of states observed in high-Tc superconductors. When the system is near the optimum doping, we find that the local AF correlation develops inside the vortex cores. However, the detailed doping dependence calculations confirm that the experimentally observed reduction of the zero-energy peak is more reasonably attributed to the smallness of the core size rather than to the AF correlation developed inside the core. The correlation between the spatial dependence of the core states and the core radius is discussed.Comment: 4 pages, 4 figure