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111.
This study focuses on the self-sustained oscillatory flow characteristics between two tandem circular cylinders of equal diameter
placed in a uniform inflow. The Reynolds number (Re
D
), based on the cylinder diameter, was around 1,000 and all experiments were performed in a recirculating water channel. The
streamwise distance between two tandem cylinders ranged within 1.5 ≤ X
c/D ≤ 7.0. Here X
c denotes the center-to-center distance between two tandem cylinders. For all experiments studied herein, quantitative velocity
measurements were performed using hot-film anemometer and the LDV system. The laser sheet technique was employed for qualitative
flow visualization. The wavelet transform was applied to elucidate the temporal variation and phase difference between two
spectral components of the velocity signals detected in the flow field. The remarkable finding was that when two tandem circular
cylinders were spaced at a distance within 4.5 ≤ X
c/D ≤ 5.5, two symmetrical unstable shear layers with a certain wavelength were observed to impinge onto the downstream cylinder.
The responding frequency (f
u
), measured between these two cylinders, was much higher than the natural shedding frequency behind a single isolated cylinder
at the same Re
D
. This responding frequency decreased as the distance X
c/D increased. Not until X
c/D ≥ 6.0, did it recover to the natural shedding frequency behind a single isolated cylinder. Between two tandem cylinders,
the Strouhal numbers (St
c = f
u
X
c/Uc) maintained a nearly constant value of 3, indicating the self-sustained oscillating flow characteristics with a wavelength X
c/3. Here U
c is the convection speed of the unstable shear layers between two tandem cylinders. At Re
D
= 1,000, the self-sustained oscillating characteristics between two tandem circular cylinders were proven to exhibit a sustained
flow pattern, not just a sporadic phenomenon. 相似文献
112.
Synthesis and thermotropic behaviour of liquid crystals containing tolane-based mesogenic units 总被引:3,自引:0,他引:3
Tolane-based liquid crystal materials with three different terminal groups: trifluoromethyltolanes, cyanotolanes, and nitrotolanes, and with different chain lengths of alkenyloxy groups, have been synthesized. The phase behaviour of these liquid crystal materials has been characterized by differential scanning calorimetry, optical polarized light microscopy and X-ray diffraction. The mesophase behaviour of the materials was shown to be significantly influenced by the polarity of the terminal groups. The trifluoromethyltolanes exhibit an enantiotropic smectic E mesophase and the cyanotolanes exhibit a monotropic nematic mesophase. The most polar among the three types of liquid crystal material; the nitrotolanes do not display any liquid crystalline phases, except for the homologue with an eleven methylene unit chain. 相似文献
113.
Tom H.H. Hsieh 《Tetrahedron》2009,65(16):3062-7210
Nitroalkenes have been called ‘chemical chameleons’ due to their versatility in numerous synthetic transformations. Herein, we describe the first transition metal-catalyzed transformation of conjugated nitroalkenes into indoles. Under mild reaction conditions (1 atm carbon monoxide, 110 °C), palladium catalyzes the reductive cyclization of nitroalkenes to form a putative nitrosoalkene intermediate, which then rearranges to provide 3-arylindoles in high yields. Notably, this novel C-H bond amination takes advantage of carbon monoxide as an inexpensive stoichiometric reductant and produces carbon dioxide as the major byproduct. 相似文献
114.
Theory of water waves in an elastic vessel 总被引:3,自引:0,他引:3
D. Y. Hsieh 《Acta Mechanica Sinica》2000,16(2):97-112
Recent experiments related to the Dragon Wash phenomena showed that axisymmetric capillary waves appear first from excitation,
and circumferential capillary waves appear after increase of the excitation strength. Based on this new finding, a theory
of parametric resonance is developed in detail to explain the on-set of the prominent circumferential capillary waves. Numerical
computation is also carried out and the results agree generally with the experiments. Analysis and numerical computation are
also presented to explain the generation of axisymmetric low-frequency gravity waves by the high-frequency external excitation. 相似文献
115.
The various oblique shock wave reflection patterns generated by a moving incident shock on a planar wedge using an ideal quantum
gas model are numerically studied using a novel high resolution quantum kinetic flux splitting scheme. With different incident
shock Mach numbers and wedge angles as flow parameters, four different types of reflection patterns, namely, the regular reflection,
simple Mach reflection, complex Mach reflection and the double Mach reflection as in the classical gas can be classified and
observed. Both Bose–Einstein and Fermi–Dirac gases are considered.
相似文献
116.
Jeng-Jong Hwang Tzu-Chen Yen Bor-Tsung Hsieh Gann Ting 《Journal of Radioanalytical and Nuclear Chemistry》1999,241(3):581-587
The evaluation of the pharmacokinetics of pure, beta radiopharmaceuticals is not possible with scintigraphy. Both whole-body
autoradiography (WBAR) and Packard Instantimager, a device for rapid imaging, were used to study the whole body distribution
of γ- and β-emitting radionuclides (99mTc-MDP,99mTc-sulfur colloid, or188Re-HEDP), and results obtained from both methods were compared. The biodistribution of99mTc-MDP and188Re-HEDP were seen mainly in bones including skull, spine, and vertebrae of spine and cardiac and skeletal muscles. The99mTc-sulfur colloid localized in liver, bone marrow, and spleen. The resolution of WBAR is superior than that of Packard Instantimager.
However, the advantage of Packard Instantimager is that rapid imaging within few minutes is possible with it, while WBAR imaging
requires several hours to days. 相似文献
117.
Y Hsieh M Chintala H Mei J Agans J M Brisson K Ng W A Korfmacher 《Rapid communications in mass spectrometry : RCM》2001,15(24):2481-2487
A higher-throughput bioanalytical method based on fast-gradient (1 min run time) high-performance liquid chromatography (HPLC) coupled with tandem mass spectrometry (MS/MS) was developed for screen-type analyses of plasma samples from early drug discovery studies in support of exploratory pharmacodynamic studies. The HPLC system equipped with minibore column was interfaced with either atmospheric pressure chemical ionization (APCI) or electrospray (ESI) ionization techniques. The matrix ion suppression effect of both quantitative HPLC/MS/MS analyses was compared using the post-column infusion system. The use of the described methods provided advantages such as a shorter chromatographic region of ion suppression, less solvent consumption and shorter run times in comparison with standard analytical column HPLC/MS/MS methods. The analytical results obtained by both HPLC/MS/MS methods were in good agreement (within 15% of error) and displayed a good correlation with the pharmacodynamic outcome. 相似文献
118.
(WO3)0.15(BiO1.5)0.85 exhibits a tetragonal structure derived from the fluorite subcell. The electrical conductivity of (WO3)0.15(BiO1.5)0.85 is lower than that of Y2O3-doped Bi2O3. The structure and electrical conductivity of samples formulated as (YO1.5)
x
(WO3)0.15(BiO1.5)0.85-
x
(x = 0.1, 0.2, 0.3, and 0.4) were investigated. The as-sintered (YO1.5)0.1(WO3)0.15(BiO1.5)0.75 exhibited a single cubic structure that is isostructural with δ-Bi2O3. For x = 0.2, 0.3, and 0.4, the as-sintered samples consisted of a cubic fluorite structure and rhombohedral Y6WO12. After heat treatment at 600 °C for 200 h, the cubic structures are stable for x = 0.1, 0.3, and 0.4. A transformation from cubic to rhombohedral phase after heat treatment at 600 °C for 200 h was observed
in the sample originally formulated as (YO1.5)0.2(WO3)0.15(BiO1.5)0.65. 相似文献
119.
The methanolysis of 2‐(2‐aryl ethynyl)benzonitriles is accelerated when the polar aprotic solvents are added, which could enhance the 6‐endo pathway and give isoquinolones, though the 5‐exo pathway is occupied mostly. The yields of products would also be in creased. 相似文献
120.
Polyurethanes (PU) based on poly(butylene adipate) [PU(PBA)] and poly(oxypropylene) [PU(PPG)] polyols have bean introduced into the diglycidyl ether of bisphenol A (epoxy) to form interpenetrating polymer networks (IPNs) with a PU-grafted epoxy structure (graft-IPNs). The tensile strength in both PU(PPG)/epoxy and PU(PBA)/epoxy systems increases with increasing PU content. Maximum values emerge at PU/epoxy ratios between 19/81 and 27/73. This is explained as a result of the presence of the graft structure, which leads to more intimate interpenetration between the PU and epoxy in the graft-IPNs. Dynamic mechanical analysis (DMA) indicates that the PU introduced can be incorporated in either the α or β transition domain of the epoxy. The tensile strength of the resulting graft-IPNs shows a significant improvement as the PU is incorporated in the α transition domain of the epoxy. It is also noted that suitable amounts of PU incorporated in both the α and β transition domains of epoxy can increase the tensile strength of the IPNs, while excessive amounts of PU introduced into both α or β transition domains tend to decrease the tensile strength of the graft-IPNs. 相似文献