We experimentally demonstrate the efficient channeling of fluorescence photons from single q dots on optical nanofiber into the guided modes by measuring the photon-count rates through the guided and ...radiation modes simultaneously. We obtain the maximum channeling efficiency to be 22.0(±4.8)% at a fiber diameter of 350 nm for the emission wavelength of 780 nm. The results may open new possibilities in quantum information technologies for generating single photons into single-mode optical fibers.
We experimentally demonstrate efficient coupling of atomic fluorescence to the guided mode of a subwavelength-diameter silica fiber, an optical nanofiber. We show that fluorescence of a very small ...number of atoms, around the nanofiber can be readily observed through a single-mode optical fiber. We also show that such a technique enables us to probe the van der Waals interaction between atoms and surface with high precision by observing the fluorescence excitation spectrum through the nanofiber.
Local strain is introduced into the lattice around solute atom due to the size mismatch between solute and solvent atoms in alloy. In this study, local lattice strains are calculated for the first ...time in titanium alloys, using the plane-wave pseudopotential method. As an extreme case, the local lattice strain around a vacancy is also calculated in various bcc, fcc and hcp metals. It is found that the local strain energy is very high in both bcc Ti and bcc Fe, where the martensitic transformation takes place. From a series of calculations, it is shown that the magnitude of the strain energy stored in the local lattice is comparable to the thermal energy,
k
B
T
, where
k
B
is the Boltzmann constant and
T
is the absolute temperature. Therefore, the presence of local lattice strains in alloy could influence the phase stability that varies largely depending on temperatures. For example, the local lattice strain correlates with the martensitic transformation start temperature,
Ms
, in binary titanium alloys.
Crystallographically anisotropic platelet iron particles were successfully prepared using a conventional ball mill with addition of graphite (Gp) particles. The morphological and structural changes ...resulting from the milling were investigated using scanning electron microscopy and X-ray diffraction. The spherical iron particles were plastically deformed into platelet shapes during the milling. Simultaneously, it is suggested that the size of the Gp particles decreased and adhered as nanoparticles on the surface of the iron particles. The adhered Gp particles affected the plastic deformation behavior of the iron particles: the {001} planes of α-iron were oriented parallel to the particle face, and no preferred in-plane orientation was observed. This study not only details the preparation of soft magnetic metal particles that crystallographically oriented to enhance their magnetic properties but also provides new insight into the activities of the well-established and extensively studied mechanical milling method.
The alloying effects of ruthenium and tungsten on the hydrogen solubility, the resistance to hydrogen embrittlement and the hydrogen permeability are investigated for Nb–M (M
=
Ru and W) alloys. The ...hydrogen solubility decreases by alloying and also by increasing the temperature of the alloy. As a result, the resistance to hydrogen embrittlement is improved owing to the low hydrogen content in the alloy. On the other hand, the hydrogen flux increases with increasing hydrogen concentration difference, Δ
C, between the inlet and outlet sides of the alloy membrane. It is found that Nb–5
mol%X (X
=
Ru and W) alloys possess excellent hydrogen permeability without showing any hydrogen embrittlement when used under the appropriate permeation conditions of the temperatures and hydrogen pressures.
The effects of dopants on the electrical conductivity of ZnO were investigated through the ac impedance spectroscopy. The doping of Al increased the electrical conductivity of ZnO greatly, whereas ...the doping of Li decreased it both in the grain and in the grain boundary. The doping of the 3d transition metals (Co, Mn, and Cu) made the grain boundary more resistive, but the doping effect on the electrical conductivity inside the grain was varied depending on the doping elements. The doping of Co had no significant effects on the electrical conductivity of the grain, and the doping of Mn made the grain a little more resistive. The doping of Cu made the grain much more resistive. In addition, hydrogen was introduced into ZnO by the ion implantation method. The electrical conductivity in the hydrogen-implanted ZnO layer increased by four orders of magnitude. The mechanisms for the doping effects were discussed in this investigation.
The hydrogen permeability have been measured for pure niobium and Nb-5
mol%X (
X = Ru and W) alloys in order to investigate the alloying effects of ruthenium and tungsten on the hydrogen diffusivity ...during hydrogen permeation. The hydrogen diffusion coefficient during hydrogen permeation is estimated from a linear relationship between the normalized hydrogen flux,
J·
d, and the difference of hydrogen concentration, Δ
C, between the inlet and the outlet sides of the membrane. It is found that the addition of ruthenium or tungsten into niobium increases the hydrogen diffusion coefficient during the hydrogen permeation. On the other hand, the activation energy for hydrogen diffusion in pure niobium under the practical permeation condition is much higher than the reported values measured for dilute hydrogen solid solutions. It is interesting that the activation energy for hydrogen diffusion is decreased by alloying of ruthenium or tungsten into niobium.
The perovskite-type hydrides, MMgH3 (M=Na, K, Rb) were synthesized by ball-milling. They decomposed at the temperatures of 673–723K in several ways depending on M. Namely, NaMgH3 decomposed in the ...two-step reactions, NaMgH3→NaH+Mg+H2 and NaH→Na+(1/2)H2, whereas KMgH3 decomposed in the single-step reaction, KMgH3→K+Mg+(3/2)H2. However, RbMgH3 decomposed in the two-step reactions, but each reaction still remained uncertain. Judging from the experimental value of ΔH for MMgH3 (M=Na, K, Rb), the phase stability was found to change in the order, RbMgH3>KMgH3>NaMgH3, so that NaMgH3 is the most unstable among them.
The hydrogen solubility and the hydrogen permeability of Nb-based hydrogen permeable membranes are investigated in order to examine the hydrogen diffusion coefficient during the hydrogen permeation ...at high temperatures. It is shown that the hydrogen dissolution reaction into niobium and its alloys does not follow the Sieverts’ law at the pressure conditions of the practical hydrogen permeation, in contrast to the case of Pd-based alloys. The hydrogen diffusion coefficients during the hydrogen permeation are evaluated from a linear relationship between the normalized hydrogen flux,
J·
d, and the hydrogen concentration difference, Δ
C between the inlet and outlet sides of the membrane with the thickness of
d. It is found that the hydrogen diffusion coefficient for pure niobium is much lower than the reported values measured for dilute hydrogen solid solutions. Surprisingly, the hydrogen diffusion is found to be faster in Pd–Ag alloy with face-centered cubic (fcc) crystal structure than in pure niobium with body-centered cubic (bcc) crystal structure at 773
K during the hydrogen permeation. It is also found that the addition of Ru or W into niobium increases the hydrogen diffusion coefficient under the practical conditions.
We show that the fluorescence emission spectrum of few atoms can be measured by using an optical nanofiber combined with the optical heterodyne and photon correlation spectroscopy. The observed ...fluorescence spectrum of the atoms near the nanofiber shows negligible effects of the atom-surface interaction and agrees well with the Mollow triplet spectrum of free-space atoms at high excitation intensity.
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