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Laser–plasma interaction and hot electrons have been characterized in detail in laser irradiation conditions relevant for direct-drive inertial confinement fusion. The experiment was carried out at the Gekko XII laser facility in multibeam planar target geometry at an intensity of approximately
W/cm2. Experimental data suggest that high-energy electrons, with temperatures of 20–50 keV and conversion efficiencies of
, were mainly produced by the damping of electron plasma waves driven by two-plasmon decay (TPD). Stimulated Raman scattering (SRS) is observed in a near-threshold growth regime, producing a reflectivity of approximately
, and is well described by an analytical model accounting for the convective growth in independent speckles. The experiment reveals that both TPD and SRS are collectively driven by multiple beams, resulting in a more vigorous growth than that driven by single-beam laser intensity.
This study investigated a new effective method for controlling the capsalid monogenean Neobenedenia girellae. We examined in vitro and in vivo the effect on the percentage survival of N. girellae in buffers containing different metallic ions. Decreased survival was observed in buffer solutions lacking two ions. In particular, the percentage survival of N. girellae was significantly decreased after 10 min exposure to buffer containing neither Ca2+ nor Mg2+. Transmission electron microscopic observations showed that treatment with this buffer disrupted intercellular junctions. This significant effect on percentage survival of N. girellae using Ca2+/Mg2+-free buffer was confirmed in an in vivo assay. Ca2+/Mg2+-free buffer had no effect on the condition of the host, spotted halibut Verasper variegates (Pleuronectidae). These results suggest that treatment with Ca2+/Mg2+-free buffer is a new effective control method, which could replace existing control methods.
This paper describes supersonic flows of a gas-particle mixture around a sphere. The Euler equations for a gas-phase interacting with a particle one are solved by using a TVD (Total Variation Diminishing) scheme developed by Chakravarthy & Osher, and the particle phase is solved by applying a discrete particle-cloud model. First, steady two-phase flows with a finite loading ratio are simulated. By comparing in detail the dusty results with the dust-free ones, the effects of the presence of particles on the flow field in the shock layer are clarified. Also an attempt to correlate the particle behaviours is made with universal parameters such as the Stokes number and the particle loading ratio. Next, non-steady two-phase flows are treated. Impingement of a large particle-cloud on a shock layer of a dust-free gas in front of a sphere is numerically simulated. The effect of particles rebounded from the sphere is taken into account. It is shown that a temporal reverse flow region of the gas is induced near the body axis in the shock layer, which is responsible for the appearance of the gas flow region where the pressure gradient becomes negative along the body surface. These phenomena are consistent with the previous experimental observations. It will be shown that the present results support a flow model for the particle-induced flow field postulated in connection with ‘heating augmentation’ found in the heat transfer measurement in hypersonic particle erosion environments. The particle behaviour in such flows is so complicated that it is almost impossible to treat the particle phase as an ordinary continuum medium.
This paper is concerned with a numerical analysis of axisymmetric gas-particle two-phase flows. Underexpanded supersonic free-jet flows and supersonic flows around a truncated cylinder of gas-particle mixtures are solved numerically on the super computer Fujitsu VP-400. The gas phase is treated as a continuum medium, and the particle phase is treated partly as a discrete one. The particle cloud is divided into a large number of small clouds. In each cloud, the particles are approximated to have the same velocity and temperature. The particle flow field is obtained by following these individual clouds separately in the whole computational domain. In estimating the momentum and heat transfer rates from the particle phase to the gas phase, the contributions from these clouds are averaged over some volume whose characteristic length is small compared with the characteristic length of the flow field but large compared with that of the clouds. The results so obtained reveal that the flow characteristics of the gas-particle mixtures are widely different from those of the dust-free gas at many points.
Process-induced defects are a serious issue for modern sub-micron
Si LSIs. To characterize such defects, two different techniques
are useful: electrically detected magnetic resonance (EDMR) and
transmission electron microscope (TEM), which can detect small
(point) and extended defects, respectively. We applied EDMR and
TEM to the issue of defect-induced leakage currents in
dynamic-random-access memory (DRAM) cells. For our DRAM samples
(a 0.25-μm-rule series), although TEM showed no extended defects,
EDMR successfully detected two types of point defects:
V2+Ox (Si divacancy-oxygen complexes) and larger Si vacancies
(at least larger than V6). We confirmed that these defects are the
source of DRAM leakage currents. The observed defects were formed by ion
implantation processes, but were more thermally stable than those in bulk
Si crystals. The origins of this enhanced stability are attributed to the
presence of oxygen atoms and a strong mechanical strain in LSIs. To clarify
the origin of the complicated strain in LSI structures, we can directly
measure the local-strain distribution in DRAM samples by means of
convergent-beam electron diffraction (CBED) using TEM, which provides us
with a valuable hint for understanding the formation mechanism of
Non-steady-state solidification of YBa2Cu3O6+δ (Y-123) superconducting oxides was observed by the isothermal undercooling experiment. A sudden decrease in crystal growth rate was found for all the Y-123 samples processed at the different temperatures and from the different Y2BaCuO5 (Y-211) contents in the initial composition. Quantitative analysis revealed that the Y-211 particles are pushed by the Y-123 crystal and accumulate in the liquid during solidification. It is also found that the particle volume fraction increased and reached a constant value of about 0.6, when the growth rate decreased abruptly, regardless of a variety of growth conditions. A simple solidification model is developed to interpret the experimental observation. This model shows that particle accumulation, as a result of the particle-pushing behavior, causes less connectivity of the liquid and thereby decreases the liquid diffusion flux, which is responsible for the non-steady-state solidification of Y-123.
Unsteady circular jets are treated experimentally and numerically. The time evolution
of circular pulse jets is investigated systematically for a wide range of jet strength,
with the focus on the jet evolution, in particular the formation processes of Mach
disks in the middle stage and of shock-cell structures in the later stage. It is shown
that unsteady second shocks are realized for all sonic underexpanded jets and they
either breed conical shocks for lower pressure ratios or truncated cones (Mach disk
and reflected shock) for higher pressure ratios. The vortex ring produced near the
nozzle lip plays an important role in the formation of the shock-cell structure. In
particular, interactions between the vortex ring and the Mach disk connected with a
strong second shock affect remarkably the formation process of the first shock cell.
Different formation processes of the first cell structure are found. It is also made clear
that the Kelvin–Helmholtz instability along slip surfaces originating from the triple
point at the outer edge of the Mach disk is responsible for the generation of large
second vortices which entrain the first vortex. This results in strong mixing between
the primary jet and surrounding gas for higher pressure ratios. Numerical simulations
with a TVD-scheme for the Euler equations are also performed and the numerical
results are compared with the experimental ones to understand and predict the flow
characteristics of the pulse jets.
Application of negative heavy ions, alleviating surface charging on insulators, enables us to conduct low-energy and high-flux implantation, and leads to a well-defined tool to fabricate near-surface nanostructures. Negative Cu ions of 60 keV, at high doses, have generated nanocrystals in amorphous(a-)SiO2 with a size (∼10 nm) suitable for nonlinear optical devices. The kinetic processes, inside the solid and at the surface, are studied by cross-sectional TEM and tapping AFM, respectively. In a-SiO2, nanoparticles spontaneously grow with dose rate, being controlled by the surface tension and radiation-induced diffusion. Furthermore, the nanospheres give rise to a two-dimensional (2D) arrangement around a given dose rate. The 2D-distribution occurs in coincidence with enhanced sputtering where a considerable Cu fraction sublimates from the surface. The dose-rate dependence of nanoparticles indicates that the surface-sputtering process influences the intra-solid process and contributes to the 2D-distribution. A self-assembling mechanism for 2D-arrangement of nanospheres is discussed taking into account contribution of the surface sputtering.
New piezoelectric power devices -such as ultrasonic motors, piezoelectric actuators and piezoelectric transformers- have been studied intensively in recent years. The piezoelectric ceramics in these devices are often subjected to a high level of vibration, and the electromechanical characteristics of piezoelectric ceramics at high vibration levels vary when changes in vibration level are accompanied by changes in temperature. The effects of temperature and of vibration level on specific electromechanical characteristics of typical piezoelectric ceramics were therefore separated by using two measurement methods: the continuous-voltage-wave method, which results in an increased temperature; and the burst-voltage-wave method, which does not. The elastic, dielectric and piezoelectric constants were found to be sensitive to temperature but comparatively insensitive to vibration level. Mechanical loss, however, was found to be a function of both temperature and vibration level.
Microstructure control of SmBCO superconductor was carried out using the floating zone partial melting and solidification method under 0.01 atm oxygen partial pressure which is a preferable atmosphere to obtain a crystal with stoichiometric SmBCO. The growth rate, initial composition, and addition of small amount of platinum dependences on the microstructure formations of the (Sm211 + L) mixture during melting and the Sm123 or Sm123/211 during solidification were investigated. Furthermore, superconductive properties of the solidified Sm123/211 were measured by SQUID after appropriate oxygen annealing. Estimated critical current density of the single crystalline Sm123/211 was 3.6 × 104 A/cm at 77 K, 1 T.
Negative Cu ions of 60 keV have been applied to generate metal nanocrystals embedded in insulators. Crystalline (c-), amorphous (a-)SiO2 and a spinel oxide, MgO·2(Al2O3), were irradiated at various dose rates up to about 100 µA/cm2, at a total dose of 3.O×1016 ions/cm2. In a-Sio2, morphology of nanoparticles and the resultant optical property changed with dose rate and, at a critical condition, showed in-plane arrangement of nanocrystals. The optical property of c-Si0 2 (a-quartz) was qualitatively similar to that of a-SiO2, but the implanted region of c-SiO2 showed different irradiation responses. The c-SiO2 was susceptible to radiation-induced amorphization but the nanoparticle morphology was still different from a-SiO2, suggesting a stronger depth-oriented driving force. Unlike SiO2, the spinel oxide showed good structural stability against the implantation and no tendency of the long-range atomic rearrangement. The results indicate that the crystallinity and the relevant interactions may play an important role in the nanoparticle growth during the implantation.
Microstructure in melt-textured bulk RE1Ba2Cu3O6+d crystals (RE123; RE = Sm, Nd) was investigated, changing the initial composition from the tie-line composition of RE123–Sm2Ba1Cu1O5 (Sm211)/Nd4Ba2Cu2O10 (Nd422) to the Ba-enriched side. It was found that the Sm211/Nd422 particle size decreased in the liquid with increasing the Ba/Cu ratio of the initial composition, and this tendency was also found in the grown Sm123 crystals. Composition of the Sm123 grown crystal could be controlled by selecting the Ba-enriched initial composition to obtain an almost stoichiometric compound, which resulted in higher Tc values. Furthermore, the Jc values also increased under low magnetic fields due to the significant decrease of Sm211 particle size. Therefore, changing the initial composition toward the Ba-enriched side was found to be a new process to enhance both Jc and Tc values simultaneously.
Nd1+xBa2−xCu3O6+d (Nd123) single crystals have been successfully grown by the top-seeded solution-growth method. Compositions of Nd123 could be controlled by applying two different methods: control of the oxygen partial pressure of the atmosphere and control of the liquid composition in air. The critical temperatures of Nd123 obtained by these two methods were 96 K (oxygen control) and 95 K (liquid composition control), respectively. The relationship between the peak effect in the Jc-H curve and heat treatment was investigated. The peak effect was found not to be an intrinsic property of Nd123; consequently it could be controlled by heat treatment.
Microstructure control of the SmBCO superconductor was carried out using the floating zone partial melting and solidification method. It is generally recognized that finely and uniformly dispersed nonsuperconductive high temperature stable phase (Sm211) particles included in the superconductive Sm123 matrix act as effective pinning centers. Microstructure formation of the partial molten mixture (Sm211 particles and BaO–CuO liquid) by decomposition of the precursor Sm123 on melting and solidification of Sm123 from the mixture have to be controlled concurrently to fabricate the 123/211 composite fiber with the optimum microstructure. During unidirectional solidification, planar crystal growth which provides the single crystal growth of Sm123 becomes unstable with increased growth rate. During unidirectional melting, the mean diameter of aligned Sm211 particles behind the melting interface decreases with increased growth rate and with decreased temperature gradient at the melting interface. Initial composition of the precursor significantly affects the formation behavior of Sm211 particles. The contribution of process parameters to the microstructure formation is also briefly discussed.
Nanoparticles of Cu were fabricated by negative-ion implantation, leading to spontaneous formation at high beam fluxes. Negative ions, alleviating surface charging, exhibit significant merits in carrying out low-energy implantation at high dose rates. The kinetic processes were studied by measuring dose-rate dependence of colloid formation and resultant optical properties. Negative-Cu ions of 60 keV were implanted into silica glasses at high-current densities, up to 260 μA/cm2, fixing the total dose at 3.0 × 1016 ions/cm2. Spherical nanocrystals of Cu atoms formed within a narrow region, near the projectile range of Cu ions. Simultaneously, much smaller particles spread out beyond a depleted zone, deeper than the projectile range. The nanocrystal growth and optical properties were greatly dependent on the dose rate and the specimen boundary condition. The growth process is explained by a droplet-model based on surface tension and radiation-induced diffusion. Beam-surface interactions also play an important role in the mass transport from the beam flux to the interior solid.
A simple model is proposed to analyze the interface stability of the RE123 superconductor in accordance with the constitutional supercooling criterion. As the single crystal growth of the 123 phase is largely dependent on the growth interface stability, a quantitative analysis has been required. From the numerical analysis for the case of peritectically solidified Sm123, it was clarified that the constitutional supercooling must exist in the liquid when the 123 growth interface comes close to a 211 particle. It could also predict that larger 211 particle radius, smaller volume fraction of the 211 particles, larger growth rate, or smaller imposed temperature gradient cause easy occurrence of the constitutional supercooling. The growth rate and a 211 particle radius are determining parameters. Further consideration of the nucleation at the L/211 interface just ahead of the 123 growth front could describe the 123 growth morphological transition from with the planar interface to the equiaxed blocky.
A rare case of pharyngeal cyst arising from the second branchial cleft in a 14-year-old boy is described. A cyst located in the right posterolateral wall of the oropharynx was completely removed by an intraoral approach. Histopathological examination revealed that the cyst was lined with columnar (respiratory type) epithelium.
An extremely rare case of intravagal parathyroid adenoma is presented. The tumour caused fusiform swelling of the left vagus nerve was shelled out. Post-operatively the left recurrent nerve palsy was recovered in the two months. Serum calcium level returned to normal on the tenth day after the surgical operation without symptoms of hypocalcaemia.
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