Fiber Inline Core-cladding-mode Mach-Zehnder Interferometer Fabricated by Two-point CO2 Laser Irradiations

We report a fiber inline Mach-Zehnder-type core-cladding-mode interferometer fabricated by two-point CO2 laser irradiations on a single-mode fiber. the laser irradiations caused efficient light coupling from the core mode to the lower order cladding modes and vice versa. High-quality interference spectra with a fringe visibility of about 20 dB were observed for four different interferometer lengths (5, 10, 20, and 40 mm). the temperature sensitivity of the device with a length of 5 mm was measured to be 0.0817 nm/°C. the sensitivity for refractive index measurement of the device was comparable with a long-period fiber grating of LP04 cladding mode. © 2009 IEEE

Geometric curvatures of plane symmetry black hole

In this paper, we study the properties and thermodynamic stability of the plane symmetry black hole from the viewpoint of geometry. Weinhold metric and Ruppeiner metric are obtained, respectively. The Weinhold curvature gives phase transition points, which correspond to the first-order phase transition only at N=1, where $N$ is a parameter in the plane symmetry black hole. While the Ruppeiner one shows first-order phase transition points for arbitrary $N\neq 1$. Both of which give no any information about the second-order phase transition. Considering the Legendre invariant proposed by Quevedo et. al., we obtain a unified geometry metric, which gives a correctly the behavior of the thermodynamic interactions and phase transitions. The geometry is also found to be curved and the scalar curvature goes to negative infinity at the Davies' phase transition points when the logarithmic correction is included.Comment: 16 pages, 6 figure

Atomistic Mechanisms Underlying Selectivities in C_1 and C_2 Products from Electrochemical Reduction of CO on Cu(111)

Practical environmental and energy applications of the electrochemical reduction of CO_2 to chemicals and fuels require far more efficient and selective electrocatalysts beyond the only working material Cu, but the wealth of experimental data on Cu can serve to validate any proposed mechanisms. To provide design guidelines, we use quantum mechanics to predict the detailed atomistic mechanisms responsible for C_1 and C_2 products on Cu. Thus, we report the pH dependent routes to the major products, methane and ethylene, and identify the key intermediates where branches to methanol, ketene, ethanol, acetylene and ethane are kinetically blocked. We discovered that surface water on Cu plays a key role in the selectivity for hydrocarbon products over the oxygen-containing alcohol products by serving as a strong proton donor for electrochemical dehydration reductions. We suggest new experiments to validate our predicted mechanisms

Nature of the active sites for CO reduction on copper nanoparticles; suggestions for optimizing performance

Recent experiments show that the grain boundaries (GBs) of copper nanoparticles (NP) lead to outstanding performance in reducing CO_2 and CO to alcohol products. We report here multiscale simulations that mimic experimental synthesis conditions to predict the structure of a 10nm Cu NP (158,555 atoms). To identify active sites, we first predict the CO binding at a large number of sites and select 4 exhibiting CO binding stronger than the (211) step surface. Then, we predict the formation energy of *OCCOH intermediate as a descriptor for C-C coupling, identifying two active sites, both of which have an undercoordinated surface square site adjacent to a subsurface stacking fault. We then propose a periodic Cu surface (4 by 4 supercell) with a similar site that substantially decreases the formation energy of *OCCOH, by 0.14 eV

Free-Energy Barriers and Reaction Mechanisms for the Electrochemical Reduction of CO on the Cu(100) Surface, Including Multiple Layers of Explicit Solvent at pH 0

The great interest in the photochemical reduction from CO_2 to fuels and chemicals has focused attention on Cu because of its unique ability to catalyze formation of carbon-containing fuels and chemicals. A particular goal is to learn how to modify the Cu catalysts to enhance the production selectivity while reducing the energy requirements (overpotential). To enable such developments, we report here the free-energy reaction barriers and mechanistic pathways on the Cu(100) surface, which produces only CH_4 (not C_2H_4 or CH_3OH) in acid (pH 0). We predict a threshold potential for CH_4 formation of −0.52 V, which compares well to experiments at low pH, −0.45 to −0.50 V. These quantum molecular dynamics simulations included ∼5 layers of explicit water at the water/electrode interface using enhanced sampling methodology to obtain the free energies. We find that that chemisorbed hydroxyl-methylene (CH–OH) is the key intermediate determining the selectivity for methane over methanol

Optical Fiber Harsh Environment Sensors

Various optical fiber harsh environment sensors were reported, including the miniaturized inline Fabry-Perot interferometer sensor by femtosecond laser micromachining, the long period fiber grating sensor and the inline core-cladding mode interferometer by CO2 laser irradiations