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Chatchawan Panraksa John E. Wetzel Wacharin Wichiramala 《Discrete and Computational Geometry》2007,37(2):297-299
In 1974 Gerriets and Poole conjectured for n = 3 that a convex set in the plane which contains a congruent copy of every n-segment
polygonal arc of unit length must be a cover for the family of all unit arcs. We disprove this general conjecture by describing
for each positive integer n a convex region Rn that contains a ongruent copy of every n-segment unit arc but not a congruent copy of every unit arc. 相似文献
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Total synthesis of isagarin (2) has been accomplished in five steps with 24.1% overall yield from 2‐bromonaphthoquinone (6). The key step is a palladium‐catalyzed cyclization to form a bicyclic ketal ring. 相似文献
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Prathumpai W Kocharin K Phimmakong K Wongsa P 《Applied biochemistry and biotechnology》2007,136(2):223-232
The production of six naphthoquinone derivatives, erythrostominone, deoxyerythrostominone, 4-O-methyl erythrostominone, epierythrostominol, deoxyerythrostominol, and 3,5,8-trihydroxy-6-methoxy-2-(5-oxohexa- 1,3-dienyl)-1,4-naphthoquinone, was examined during the growth of Cordyceps unilateralis BCC 1869 on different carbon and nitrogen sources. Erythrostominone production by the fungus accounted for more than 50% of total naphthoquinones, but production of each of the other five derivatives accounted for less than 20% of total naphthoquinones. The highest volumetric production rate of erythrostominone and overall naphthoquinone production rate were obtained on mannose as a sole carbon source and ammonium sulfate as a sole nitrogen source (4922.4 +/- 118.8 mg/[L.d] and 5.03 g/[L.d], respectively). The highest growth rate was obtained on arabinose (0.043 h-1), whereas the maximum overall naphthoquinone concentration was obtained on lactose (2 g/L) at 237 h. These naphthoquinones were produced with no pH control and were first detected at a pH of about 3.0 to 4.0. These results suggest that carbon and nitrogen influenced directly the production of naphthoquinones. 相似文献
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Rabinowitz constructed a parametric curve of constant width and expressed it as a plane algebraic curve; however, the algebraic curve also contains isolated points separate from the original curve. We show how to modify his example in order to produce a curve with no isolated points. We then conjecture a method for producing a family of such curves and prove the conjecture in several cases. 相似文献
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Chatchawan Panraksa John E. Wetzel Wacharin Wichiramala 《Periodica Mathematica Hungarica》2007,55(2):157-168
We describe the broadest three-segment unit arc in the plane, and we conclude with some conjectures about the broadest n-segment unit arc for n > 3.
Communicated by Imre Bárány 相似文献
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[structure: see text] Hirsutellone F (7), a novel alkaloid dimer, was isolated together with known monomers, hirsutellones A (1), B (2), and C (3), from the seed fungus Trichoderma sp. BCC 7579. The structure of 7 was elucidated by spectroscopic analysis. Studies on biomimetic chemistry, using the dimer 7, suggested that compound 8 (17,1'-dehydrohirsutellone B) should be the precursor for all hirsutellones. 相似文献
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Priyapan Posri Jittra Suthiwong Pitchayakarn Takomthong Chatchawan Wongsa Chindawadee Chuenban Chantana Boonyarat 《Natural product research》2019,33(8):1115-1121
A new flavonoid, atalantraflavone (1) as well as eight known compounds including atalantoflavone (2), racemoflavone (3), 5,4′-dihydroxy-(3″,4″-dihydro-3″,4″-dihydroxy)-2″,2″-dimethylpyrano-(5″,6″:7,8)-flavone (4), lupalbigenin (5), anabellamide (6), citrusinine I (7), p-hydroxybenzaldehyde (8), and frideline (9), were isolated from the leaves of Atalantia monophylla (L.) DC. Focusing on Alzheimer’s disease, acetylcholine esterase (AChE) inhibition and antioxidant activity were evaluated using the modified Ellman’s method and the ABTS scavenging assay, respectively. It was found that isoflavonoid 5, lupalbigenin, showed 79% inhibition to AChE and was 1.4-fold stronger than the tacrine standard. In addition, acridone 7, citrusinine I, displayed 90.68% antioxidant activity. 相似文献
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Chatchawan Changtam Boon-ek Yingyongnarongkul Apichart Suksamrarn 《Tetrahedron》2008,64(11):2626-2633
Microbial transformation of ecdysteroids with 3-hydroxy-2-mesyloxy functional group by the fungus Curvularia lunata NRRL 2178 furnished 3-dehydro-2-deoxy analogues. The metabolites included 3-dehydro-2-deoxy analogues of 20-hydroxyecdysone, pterosterone, ponasterone A, 20-hydroxyecdysone 20,22-acetonide, shidasterone, and poststerone. The mild biotransformation conditions prevented the metabolites from C-5 epimerization. 相似文献
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Periodica Mathematica Hungarica - We settle J. Wetzel’s 1970’s conjecture and show that a $$30^{\circ }$$ circular sector of unit radius can accommodate every planar arc of unit length.... 相似文献
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