Measurements and numerical analysis for femtosecond pulse deformations after propagation of hundreds of meters in air with water-vapor absorption lines

We have clarified the influences of water-vapor absorption lines in air on femtosecond pulse propagations from experimental and theoretical points of view. Precise measurements for the femtosecond pulse shapes after propagation of as much as 300 m through air have been made in a semiunderground optical testing tunnel. We observed the pulse splitting and the enhancement of the pulse broadening due to the 100-m propagation in air. The experimental results are in good agreement with the theoretical analysis by use of the HITRAN database at the edge and the center of the water-vapor absorption regions in air. Measured autocorrelation traces are mostly reproduced by those calculated with only the real part (dispersion) of the refractive index modulated by water-vapor absorption lines in air. This fact enables us to conclude that the pulse deformations due to water absorption lines in air are caused mainly by the real part (dispersion), not by the imaginary part (absorption), of the refractive index of air.     

Efficient Photocarrier Transfer and Effective Photoluminescence Enhancement in Type I Monolayer MoTe2/WSe2 Heterostructure

Artificial van der Waals heterostructures of 2D layered materials are attractive from the viewpoint of the possible discovery of new physics together with improved functionalities. Stacking various combinations of atomically thin semiconducting transition metal dichalcogenides, MX₂ (M = Mo, W; X = S, Se, Te) with a hexagonal crystal structure, typically leads to the formation of a staggered Type II band alignment in the heterostructure, where electrons and holes are confined in different layers. Here, the comprehensive studies are performed on heterostructures prepared from monolayers of WSe₂ and MoTe₂ using differential reflectance, photoluminescence (PL), and PL excitation spectroscopy. The MoTe₂/WSe₂ heterostructure shows strong PL from the MoTe₂ layer at ≈1.1 eV, which is different from the quenched PL from the WSe₂ layer. Moreover, enhancement of PL intensity from the MoTe₂ layer is observed because of the near‐unity highly efficient photocarrier transfer from WSe₂ to MoTe₂. These experimental results suggest that the MoTe₂/WSe₂ heterostructure has a Type I band alignment where electrons and holes are confined in the MoTe₂ layer. The findings extend the diversity and usefulness of ultrathin layered heterostructures based on transition metal dichalcogenides, leading to possibilities toward future optoelectronic applications.     

Characteristics of germanium avalanche photodiodes in the wavelength region of 1-1.6 µm

Dark current, quantum efficiency, multiplication noise, and pulse response of germanium avalanche photodiodes with n+-p junction were studied to find an optimum structure. The dark current can be separated by graphical means into a leakage current component and a multiplied component which flows through the junction. The dark current components are also evaluated by using diodes with various diameters. The quantum efficiency and the multiplication noise are shown to be strongly affected by the n+ layer thickness. An n+ layer thickness optimized for signal-to-noise ratio is estimated from experimental and calculated results, using a figure of merit for avalanche photodiodes. The response waveform for mode-locked Nd:YAG laser shows a rise time of 100 ps and a half pulsewidth of less than 200 ps.     

Experimental fluid dynamics of particles in a dielectric barrier discharge plasma-enhanced spouted bed

This study proposed the fluidized particles with dielectric barrier discharge (DBD) plasma in a slot-rectangular divergent-base spouted bed and focused on the dynamics of solid particles with the plasma irradiation. Two bed materials (Polypropylene (PP) particles and Polyamide (PA) particles) with same diameter (3 mm) were fluidized in this study. Fluidization parameters included gas velocity (7.4–14.9 m/s), particle amount (100–500), and plasma parameter (apply voltage, 0 and 7 kV) as the applied voltage were investigated here. Particle velocity profiles were analyzed through the methods of particle image velocimetry (PIV) and particle tracking velocimetry (PTV). Results show that the particle velocity was increased with the plasma irradiation, mainly by the enhancement in the vertical direction. The location of the highest particle velocity area related to the fluidization behavior of particles. With the increase of superficial gas velocity, the location of the highest particle velocity area raised along the central line but not reached the top of the solid bed. While the electron temperature of Ar plasma decreased with the addition of particles. Two electric fields (external electric field and surface charge electric field) presenting in the system were assumed to give the reason for the changes of the particle fluid dynamics.     

Behaviour of cobalt infiltration and abnormal grain growth during sintering of diamond on cobalt substrate

The infiltration behaviour of molten cobalt into a diamond powder compact was examined when the latter was placed on a cobalt disc and held at high pressure of 5.8 GPa and high temperature of 1350 to 1500° C. The larger the grain size of the starting diamond powder and the higher the holding temperature, the more easily cobalt infiltrated into the diamond compact. The infiltration is considered to occur because of the negative pressure in the voids formed between diamond grains. Although diamond powder was consolidated in this process of cobalt infiltration, abnormal grain growth was also observed in the boundary between cobalt and diamond compact because of the dissolution and precipitation process of the compact into molten cobalt.On leave from Chengdu University of Science and Technology, Chengdu, China.     

Variants of the 3' region of the cagA gene in Helicobacter pylori isolates from patients with different H. pylori-associated diseases

The CagA protein of Helicobacter pylori is an immunogenic antigen of variable size and unknown function that has been associated with increased virulence as well as two mutually exclusive diseases, duodenal ulcer and gastric carcinoma. The 3' region of the cagA gene contains repeated sequences. To determine whether there are structural changes in the 3' region of cagA that predict outcome of H. pylori infection, we examined 155 cagA gene-positive H. pylori isolates from Japanese patients including 50 patients with simple gastritis, 40 with gastric ulcer, 35 with duodenal ulcer, and 30 with gastric cancer. The 3' region of the cagA gene was amplified by PCR followed by sequencing. CagA proteins were detected by immunoblotting using a polyclonal antibody against recombinant CagA. One hundred forty-five strains yielded PCR products of 642 to 651 bp; 10 strains had products of 756 to 813 bp. The sequence of the 3' region of the cagA gene in Japan differs markedly from the primary sequence of cagA genes from Western isolates. Sequence analysis of the PCR products showed four types of primary gene structure (designated types A, B, C, and D) depending on the type and number of repeats. Six of the seven type C strains were found in patients with gastric cancer (P < 0.01 in comparison to noncancer patients). Comparison of type A and type C strains from patients with gastric cancer showed that type C was associated with higher levels of CagA antibody and more severe degrees of atrophy. Differences in cagA genotype may be useful for molecular epidemiology and may provide a marker for differences in virulence among cagA-positive H. pylori strains.     

The assessment of fracture of the mandibular condyle by use of computerized tomography. Incidence of sagittal split fracture

A survey was carried out to clarify the incidence of sagittal splitting fracture of the mandibular condyle using computerized tomography. There were 33 patients, between 11 and 67 years of age, with displaced or dislocated mandibular condylar process fractures (41 cases), seen at our clinic between 1986 and 1992. The incidence of no displacement was 4.9%; deviation and displacement, 34.1%; dislocation, 46.3%; and complete avulsion, 4.9%. A sagittal splitting fracture of condyle occurred with an incidence of 9.8%. Conservative treatment was effective in the treatment of sagittal splitting fracture. Therefore, classification of fracture of mandibular condyle should include the sagittal split fracture, and investigations should include computerized tomography.     

Hemolytic reaction due to graft-versus-host (GVH) antibody production after liver transplantation from living donors: report of two cases

Among 27 patients who received minor ABO-incompatible partial liver transplantations and 19 who received major ABO-incompatible partial liver transplantations from living donors, 2 developed hemolytic anemia within 2 weeks after transplantation. These 2 patients had received livers from their living fathers whose blood type was ABO-incompatible. B-to-A transplantation was performed in patient 1 and O-to-B transplantation was performed in patient 2. Anti-A IgM and IgG were detected in the serum of patient 1, and anti-B IgM and IgG were detected in the serum of patient 2. These antibodies were eluted from the red blood cells of the patients. The coexistence of donor-specific DNA in the peripheral blood of the patients proved that they had chimerism, and graft-versus-host antibody production due to passenger B lymphocytes in the donor's liver was subsequently confirmed.