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891.
Takeo Tomita Mamoru Takahashi Masaki Sasaki Hiroshi Sakamoto Masahiro Takahashi Hiroshi Tamura 《Shock Waves》2009,19(3):213-228
During development tests of the LE-7A prototype engine, severe side-loads were observed. The side-load peaks appeared only
in certain limited conditions during start-up and shut-down transients. To investigate phenomena causing those severe side-loads
observed in the LE-7A prototype engine nozzle, series of cold-flow tests and hot-firing tests as well as CFD analyses were
conducted. As a result of the hot-firing tests, two different phenomena were found to cause severe side-loads in the LE-7A
prototype engine nozzle. One was a restricted shock separation (RSS) flow structure and the other was a phenomenon termed
“separation jump,” the rapid movement of the separation location in the vicinity of the step. A step was installed in the
LE-7A prototype to supply film-cooling gas. Hot-firing test results showed that RSS can occur for a limited mixture ratio.
Detailed flow structure of RSS on the nozzle surface was revealed by the cold-flow tests. Measured pressures and visualized
images of cold-flow tests clarified the mechanism causing the separation jump. The key phenomenon ruling the separation jump
was found to be the base flow behind the step. Based on the results of the present study, the latest LE-7A engine nozzle design
has been changed to eliminate the severe side-load.
相似文献
相似文献
892.
Rheological investigation and X-ray analysis of silicone resins have been performed to get a fundamental understanding of the relationship between melt rheology and structure. Rheological properties of the melts of silicone resins were characterized by dynamic shear measurements. Samples were a series of silicone resins having different side groups, such as methyl, phenyl, methylphenyl, and propylphenyl. A time-temperature superposition based on the WLF rule was successfully applicable. The free volume fraction at the glass transition temperature and the free volume expansion coefficient were estimated from the C1 and C2 values of the WLF-equation. The loss modulus G′′ was found to be proportional to the angular frequency in a double-logarithmic plot over a wide frequency range. However, the storage modulus G′ exhibited a bending in a intermediate frequency region for all silicone resins. The shape of the G′ curve is unexpected from the results of gel permeation chromatography (GPC) and differential scanning calorimeter (DSC), which demonstrate that the silicone resins are amorphous polymers of relatively low molecular weight. To get more insight into the rheological properties of the silicone resins which indicate a heterogeneous structure, X-ray analysis was carried out. The X-ray measurement displayed two peaks, one broad peak around 4.5?Å of d-spacing which corresponds to a random amorphous structure, and the other higher intensity peak from 8.5?Å to 12?Å. This peak strongly depends on the size of organic side groups. From the rheological characterization and the X-ray analysis, it can be concluded that the silicone resins consist of two components; one of them shows a random amorphous and the other a regular structure even in the molten stage. 相似文献
893.
Akinari Minegishi Akihiro Nishioka Tatsuhiro Takahashi Yuichi Masubuchi Jun-ichi Takimoto Kiyohito Koyama 《Rheologica Acta》2001,40(4):329-338
A series of polystyrene (PS) and a small amount of ultra high molecular weight (UHMW) PS blends have been prepared by using
tetrahydrofuran (THF). Matrix PS has an Mw of 423,000 (Mw/Mn= 2.36) and UHMW-PS has either an Mw of 3,220,000 (Mw/Mn= 1.05) or 15,400,000 (Mw/Mn=1.30) in the range of concentration from 0 wt% to 1.5 wt%. The influence of a small amount of UHMW on dynamic viscoelasticity
was investigated. At the frequency lower than 0.001 rad/s, the enhancement of G′ was observed by the incorporation of a small
amount of UHMW. And the degree of enhancement was in the order of Mw of UHMW and its concentration. The measurement of uniaxial elongational viscosity for the blends was performed and the effects
of UHMW on strain-hardening properties were analyzed at equal strain-rate conditions. The concentration of UHMW where the
strain-hardening becomes substantially stronger was determined. To get more insight into the cause of enhancement of strain-hardening
at a certain concentration, the damping function from step-shear stress relaxation was measured. The influence of a small
amount of UHMW on the damping function was found to be small. It was interpreted, from time- and strain-dependency points,
that the enhancement of strain-hardening by a small amount of UHMW was governed by the long relaxation time.
Received: 6 September 2000 Accepted: 11 January 2001 相似文献
894.
Hiroshi Takahashi 《Hyperfine Interactions》2001,138(1-4):365-371
A high-intensity neutron source that is highly correlated spatially and with time and will be used for neutron scattering
experiments can be obtained by dt m catalyzed fusion by enhancing the formation rate of dtμ molecules using a high-intensity
pulsed laser to dtμ gas. This paper considers the use of dtμ fusion for fast ignition of inertial confinement fusion, and
the possibility of ensuring energy balance in energy production. dt fusion can be quickly ignited by depositing dtμ fusion
energy into a smaller space than is done in other methods, such as Z-pinch or heavy-ion fusion. Space propulsion can be obtained
with a light fuel mass rather than by a fission repulsion system using the muons produced by annihilation of the anti-protons
stored in liquid superfluid of condensed He. Using an extremely highly compressed target can create a source of high luminosity
muons for muon–muon collider- and neutrino-oscillation experiments. This approach can eliminate the need for a super-conducting
solenoidal for capturing the beam of pions and muons generated in a large target, and then these pions and muons can be manipulated
by a laser beam instead of by employing RF manipulation.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
895.
The electron spin resonance spectra of Mn2+ ions have been studied in GexTe100?x with x = 15, 17.5 and 20, and Ge20?xTe80Six with 0 ?x? 20. All samples are found to exhibit six hyperfine lines centered at g = 4.3 with hyperfine interaction constant A = 56 × 10?4cm?1. The g = 4.3 line is interpreted as being caused by Mn2+ ions incorporated in the amorphous network and surrounded by four Te atoms in an arrangement of orthorhombic symmetry. Some of the samples of GeTe show a g = 2.0 line. This line also appears after heat treatment in air at temperatures above the glass transition temperature. It is concluded that the g = 2.0 line is caused by Mn2+ ions in phase separated microcrystalline or concentrated regions of MnO in the glass. 相似文献
896.
This article proposes a new approximation scheme for quadratic-growth BSDEs in a Markovian setting by connecting a series of semi-analytic asymptotic expansions applied to short-time intervals. Although there remains a condition which needs to be checked a posteriori, one can avoid altogether time-consuming Monte Carlo simulation and other numerical integrations for estimating conditional expectations at each space–time node. Numerical examples of quadratic-growth as well as Lipschitz BSDEs suggest that the scheme works well even for large quadratic coefficients, and a fortiori for large Lipschitz constants. 相似文献
897.
A new method based on dispersive microsolid phase extraction using graphene oxide (GO) as a solid adsorbent and total reflection X-ray fluorescence (TXRF) spectrometry is proposed for trace determination of uranium. In the developed methodology, a suspension of GO was injected into uranium-spiked multielement solutions including rubidium; after filtration, the membrane filter with collected GO was placed in a small volume of internal standard acid solution and the eluent containing uranium was deposited onto a fluorine resin-coated slide glass, which is a disposable sample stage. Using GO was effective for removal of rubidium from the measurement solution to avoid interference between Rb Kα peak and U Lα peak. The high enrichment factor of 150 enables obtaining uranium detection limits of 0.042, 0.087, and 0.12 μg L−1 for ionic strength of 0.01, 0.1, and 1 mol L−1, respectively. Such low detection limits were obtained by using a benchtop TXRF spectrometer with 5-min measurement. The proposed method is suitable for trace uranium determination in water, including high salinity samples. 相似文献
898.
899.
We consider the heat equation with a superlinear absorption term in and study the existence of nonnegative solutions with an m-dimensional time-dependent singular set, where . We prove that if , then there are two types of singular solutions. Moreover, we show the uniqueness of the solutions and specify the exact behavior of the solutions near the singular set. 相似文献
900.
Kojiro Kawada Yuya Uchida Ikuo Takahashi Takahito Nomura Yasuyuki Sasaki Tadao Asami Shunsuke Yajima Shinsaku Ito 《Molecules (Basel, Switzerland)》2020,25(23)
Strigolactones (SLs) are carotenoid-derived plant hormones involved in the development of various plants. SLs also stimulate seed germination of the root parasitic plants, Striga spp. and Orobanche spp., which reduce crop yield. Therefore, regulating SL biosynthesis may lessen the damage of root parasitic plants. Biosynthetic inhibitors effectively control biological processes by targeted regulation of biologically active compounds. In addition, biosynthetic inhibitors regulate endogenous levels in developmental stage- and tissue-specific manners. To date, although some chemicals have been found as SL biosynthesis inhibitor, these are derived from only three lead chemicals. In this study, to find a novel lead chemical for SL biosynthesis inhibitor, 27 nitrogen-containing heterocyclic derivatives were screened for inhibition of SL biosynthesis. Triflumizole most effectively reduced the levels of rice SL, 4-deoxyorobanchol (4DO), in root exudates. In addition, triflumizole inhibited endogenous 4DO biosynthesis in rice roots by inhibiting the enzymatic activity of Os900, a rice enzyme that converts the SL intermediate carlactone to 4DO. A Striga germination assay revealed that triflumizole-treated rice displayed a reduced level of germination stimulation for Striga. These results identify triflumizole as a novel lead compound for inhibition of SL biosynthesis. 相似文献