Long distance fiber Bragg grating strain sensor interrogation using a high speed Raman-based Fourier domain mode-locked fiber laser with recycled residual Raman pump

We propose a novel fiber Bragg grating (FBG) sensor interrogation using a Raman-based Fourier-domain mode locking (FDML) fiber laser for a high speed and long distance measurement. A residual Raman pump after the generation of the Raman-based FDML fiber laser is recycled for secondary signal amplification in a 2-m erbium-doped fiber (EDF) to further enhance the output power. The chromatic dispersion is precisely controlled to suppress the phase noise in the FDML laser cavity, resulting in the improvement of an R-number of 1.43 mm/dB. After recycling residual pump, we achieve the 40-km round trip transmission of the sensing probe signal with a high scan rate of 30.8 kHz. With 205-mW residual pump power, the bandwidth and the maximum gain are measured to be more than 50 nm, 10.3 dB at 1550 nm, respectively. The sensitivity of the proposed Raman-based FDML fiber laser to strain is also measured, which are 0.81 pm/μstrain in the spectral domain and 0.19 ns/μstrain in the time domain, respectively

Perfect Basis Theory for Quantum Borcherds-Bozec Algebras

In this paper, we develop the perfect basis theory for quantum Borcherds-Bozec algebras $U_{q}(\mathfrak g)$ and their irreducible highest weight modules $V(\lambda)$. We show that the perfect graph (resp. dual perfect graph) of every perfect basis (resp. dual perfect basis) of $U_{q}^{-}(\mathfrak g)$ (resp. $V(\lambda)$) is isomorphic to $B(\infty)$ (resp. $B(\lambda)$). For this purpose, we define a new class of Kashiwara operators which is different from the one given by Bozec and prove all the interlocking inductive statements in Kashiwara's grand loop argument, which shows the existence and the uniqueness of crystal bases for quantum Borcherds-Bozec algebras

Influence of the waist diameters on transmission characteristics and strain sensitivity of microtapered long-period fiber gratings

Transmission characteristics of microtapered long-period fiber gratings (MTLPGs) and their strain and temperature sensitivities with variations in the waist diameters are investigated theoretically and experimentally. Transmission characteristics of MTLPGs strongly depend on the waist diameter of the tapered optical fiber (TOF) because of the modification of the effective index difference between the core and the cladding modes. Based on the photoelastic effect, the resonant wavelengths of MTLPGs with variations in strain shift to shorter wavelengths. The strain sensitivity of the MTLPG with a waist diameter of 25 μm is improved by a factor of 20 compared with that of a 125 μm long-period fiber grating. The temperature sensitivities of MTLPGs are also enhanced by reducing the waist diameter of the TOF

Nanopores of carbon nanotubes as practical hydrogen storage media

We report on hydrogen desorption mechanisms in the nanopores of multiwalled carbon nanotubes (MWCNTs). The as-grown MWCNTs show continuous walls that do not provide sites for hydrogen storage under ambient conditions. However, after treating the nanotubes with oxygen plasma to create nanopores in the MWCNTs, we observed the appearance of a new hydrogen desorption peak in the 300–350 K range. Furthermore, the calculations of density functional theory and molecular dynamics simulations confirmed that this peak could be attributed to the hydrogen that is physically adsorbed inside nanopores whose diameter is approximately 1 nm. Thus, we demonstrated that 1 nm nanopores in MWCNTs offer a promising route to hydrogen storage media for onboard practical applications

Two distinct red giant branch populations in the globular cluster NGC 2419 as tracers of a merger event in the Milky Way

Recent spectroscopic observations of the outer halo globular cluster (GC) NGC 2419 show that it is unique among GCs, in terms of chemical abundance patterns, and some suggest that it was originated in the nucleus of a dwarf galaxy. Here we show, from the Subaru narrow-band photometry employing a calcium filter, that the red giant-branch (RGB) of this GC is split into two distinct subpopulations. Comparison with spectroscopy has confirmed that the redder RGB stars in the $hk$[=(Ca$-b)-(b-y)$] index are enhanced in [Ca/H] by $\sim$0.2 dex compared to the bluer RGB stars. Our population model further indicates that the calcium-rich second generation stars are also enhanced in helium abundance by a large amount ($\Delta$Y = 0.19). Our photometry, together with the results for other massive GCs (e.g., $\omega$ Cen, M22, and NGC 1851), suggests that the discrete distribution of RGB stars in the $hk$ index might be a universal characteristic of this growing group of peculiar GCs. The planned narrow-band calcium photometry for the Local Group dwarf galaxies would help to establish an empirical connection between these GCs and the primordial building blocks in the hierarchical merging paradigm of galaxy formation.Comment: 4 pages, 4 figures, 1 table, accepted for the publication in ApJ

Molecular epidemiology of Japanese encephalitis virus circulating in South Korea, 1983-2005

We sequenced the envelope (E) gene of 17 strains of the Japanese encephalitis virus (JEV) isolated in South Korea in 1983-2005 and compared the sequences with those from previously reported strains. Our results show the remarkable genetic stability of the E gene sequence in Korean JEV strains. Five pairs of E gene sequences from 10 Korean strains were identical, despite geographical differences and a maximum five-year time span. Sequence comparisons with other Asian strains revealed that the Korean strains are closely related to those from China, Japan, and Vietnam. Genotype 3 strains were predominant in Korea before 1993, when genotype 1 strain K93A07 was first isolated. The two genotypes were detected simultaneously in 1994 but since then, only genotype 1 has been isolated in South Korea. Thus, the genotype change occurred according to the year of isolation rather than the geographical origin