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981.
The development of steady, turbulent flow in a 90° section of a curved square duct was studied at a Reynolds number of 4 × 104 by hot-wire anemometer. The curved duct has a cross-section measuring 80 × 80 mm and a curvature radius ratio of 4 and is
connected with a long, straight duct at its both ends. The longitudinal and lateral components of mean and fluctuating velocities,
and the Reynolds stresses were measured by the method of rotating a probe with an inclined hot-wire. The velocity fields of
the primary and secondary flows, and the Reynolds stress distributions in the cross-section were illustrated in the form of
contour map. The development of the primary flow was found to be connected with a strong pressure gradient near the outer
and inner wall and a secondary flow induced in the cross-section of the bend by a pressure difference between the outer and
inner wall and a centrifugal force acting on the fluid; the fluid is accelerated near the inner wall and decelerated near
the outer wall between the bend angle ϕ ≅ 0° and ϕ ≅ 30°, but an increase and decrease of the fluid velocity are reversed between ϕ ≅ 30° and ϕ ≅ 90°. The fluctuating velocity correlations, i.e. the Reynolds stresses follow a complicated progress according to the complex
development of the primary flow. The results obtained can be available to verify various types of turbulence models and to
develop new models.
Received: 10 May 1999/Accepted: 15 March 2000 相似文献
982.
A comparison of the stereochemistry of liver microsomal γ-hydroxylation of some cyclic α, β-unsaturated ketones with that of electrochemical γ-acetoxylation of the corresponding dienol esters and with that of peracid oxidation of the dienol esters has been carried out. 相似文献
983.
Kuniaki Tatsuta Yoshikazu Suzuki Tatsuya Toriumi Yoshiaki Furuya Seijiro Hosokawa 《Tetrahedron letters》2007,48(45):8018-8021
The first total synthesis and structural determination of (+)-BE-52440A have been achieved by enantiodivergent synthesis. S-Bridging dimerization including SN2 epoxy-opening reaction of tetrasubstituted epoxide 2 with sodium sulfide has been achieved in excellent yield with high regioselectivity. The structure of (+)-BE-52440A was determined to be the dimer of kalafungin type pyranonaphthoquinone. 相似文献
984.
Yasuhiro Sawai Masahiro Mizuno Tatsuya Ito Jun-ichi Kawakami Mitsuhisa Yamano 《Tetrahedron》2009,65(34):7122-687
A practical synthesis of (2R,3S)- and (2S,3R)-β-methyltryptophan ethyl ester (β-MeTrp-OEt) has been developed. Racemic threo-β-MeTrp-OEt was diastereoselectively prepared via crystallization-induced diastereomer transformation (CIDT) of the α-nitro equivalent of β-MeTrp-OEt. The enantiomers were resolved via diastereomeric salt formation using a half equivalent of (R)-2-(4-hydroxyphenoxy)propionic acid. The process allowed a diabetes drug candidate N-[(1R,2S)-1-({5-[(dimethylamino)methyl]-2-ethoxyphenyl}aminocarbonyl)-2-(1H-indol-3-yl)propyl]-4-phenyl-1-piperidinecarboxamide to be prepared in good yield with high quality. 相似文献
985.
Tatsuya Toga 《Tetrahedron letters》2009,50(6):723-726
Oxidation of (5R,6S)-5,6-dihydro-5,6-dihydroxythymidine (thymidine glycol) with sodium periodate efficiently produced N-(2-deoxy-β-d-erythro-pentofuranosyl)formamide, a hydroxyl radical-induced decomposition product of pyrimidine bases in DNA, and this method was successfully applied to the conversion of thymine glycol in oligonucleotides into the formamide lesion. 相似文献
986.
Phy3-LOV2 is the chromophore domain of a blue-light photoreceptor for tropic responses of plants. FMN is noncovalently bound to phy3-LOV2, and the protein structure is characteristic of the LOV (light-oxygen-voltage) domain. Primary photoreaction is considered to be adduct formation between FMN and a cysteine, while deprotonation of the cysteine S-H group was suggested. On the basis of the infrared spectral analysis, however, we have shown that the cysteine of phy3-LOV2 is in the protonated S-H form, and not in the thiolate form in the ground state. Upon formation of S390, the S-H group disappears, presumably forming the adduct between FMN and Cys966. S390 can be trapped at 150 K, and the protein structure of S390 may not be changed drastically at 295 K. 相似文献
987.
Imada T Ota S Nagamochi H Akutsu T 《Journal of chemical information and modeling》2011,51(11):2788-2807
Exhaustive and nonredundant generation of stereoisomers of a chemical compound with a specified constitution is an important tool for molecular structure elucidation and molecular design. It is known that many chemical compounds have outerplanar graph structures. In this paper we deal with chemical compounds composed of carbon, hydrogen, oxygen, and nitrogen atoms whose graphical structures are outerplanar and consider stereoisomers caused only by asymmetry around carbon atoms. Based on dynamic programming, we propose an algorithm of generating all stereoisomers without duplication. We treat a given outerplanar graph as a graph rooted at its structural center. Our algorithm first recursively computes the number of stereoisomers of the subgraph induced by the descendants of each vertex and then constructs each stereoisomer by backtracking the process of computing the numbers of stereoisomers. Our algorithm correctly counts the number of stereoisomers in O(n) time and space and correctly enumerates all of the stereoisomers in O(n3) time per stereoisomer on average and in O(n) space, where n is the number of atoms in a given structure. 相似文献
988.
Tatsuya Shigehiro Shigeyuki Yagi Takeshi Maeda Hiroyuki Nakazumi Hideki Fujiwara Yoshiaki Sakurai 《Tetrahedron letters》2014
Novel donor–acceptor–donor (D–A–D) π-conjugated molecules based on a dipyrido[3,2-a:2′,3′-c]phenazine (dppz) skeleton were synthesized, and their luminescent properties were investigated. Introduction of various aryl substituents to the 10- and 13-positions of dppz allowed us to tune the emission properties through modulation of the intramolecular charge transfer (ICT) character on the D–A–D chromophores. Coordination of platinum(II) to the diimine site of dppz also gave rise to facilitation of the ICT to induce a significant red shift of the emission. 相似文献
989.
Yuki Shinno Dr. Kenta Iyoki Dr. Koji Ohara Yutaka Yanaba Dr. Yusuke Naraki Prof. Dr. Tatsuya Okubo Prof. Dr. Toru Wakihara 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(45):20274-20278
The STW-type zeolite is attractive for developing novel enantioselective syntheses/separation of chiral compounds because it is the only chiral zeolitic microporous material whose enantioenriched synthesis has been achieved. In addition to the conventional industries in which zeolites are used, STW should have diverse industrial applications in the pharmaceutical and food industries. However, the toxic and caustic fluoride required for synthesizing STW severely hinders its commercialization by mass production. Herein, we report the first example of fluoride-free STW synthesis, in which the two roles of fluoride—formation of a zeolitic framework rich in tetravalent T-atoms and promotion of double 4-membered ring unit formation—were substituted by dry gel conversion and Ge addition, respectively. The STW obtained was highly crystalline, with a similar micropore volume and thermal stability as those of original fluoride-based STW. Our approach is promising not only for the fluoride-free synthesis of enantiomeric STW but also for general fluoride-free syntheses. 相似文献
990.
This paper reports the synthesis, structure, and hydrogen adsorption property of Li-doped mesoporous silica (MPS) with a 2D
hexagonal structure. The Li-doping is achieved by impregnation of the cylindrical mesopores with an ethanol solution of lithium
chloride followed by heat treatment. Detailed characterization by solid-state NMR, TG-MS, and FT-IR suggests that, during
the heat treatment, lithium chloride reacts with surface ethoxy groups (≡Si-OEt) to form ≡SiOLi groups, while ethyl chloride
is released into the gas phase. The hydrogen uptake at 77 K and 1 atm increases from 0.68 wt% for the undoped MPS to 0.81 wt%
for Li-doped MPS (Li-MPS). The isosteric heat of adsorption is 4.8 kJ mol−1, which is consistent with the quantum chemistry calculation result (5.12 kJ mol−1). The specific hydrogen adsorption on Li-MPS would be explained by the frontier orbital interaction between HOMO of hydrogen
molecules and LUMO of ≡SiOLi. These findings provide an important insight into the development of hydrogen storage materials
with specific adsorption sites. 相似文献