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排序方式: 共有608条查询结果,搜索用时 15 毫秒
81.
New polyurethane cationomers synthesized by a two‐step substitution postreaction of urethane hydrogen atoms with nitroazobenzene groups were studied. As a starting polymer, a polyurethane based on poly(tetramethylene oxide)diol, isophorone diisocyanate, and 2,6‐bis(hydroximethyl)pyridine was used. After a preliminary metalation of the above polymer with natrium hydride, by reaction of polyurethane N‐sodate with 4‐nitro‐4′(β–iodoethylurethane)azobenzene, chromophoric groups between 2.85 and 10.53 wt % could be incorporated instead of hydrogen. Such polymers partially functionalized with azobenzene and further quaternized with methyl iodide led to the formation of pyridinium polyurethane cationomers N‐modified with nitroazo groups. The photosensible properties of the azobenzene chromophore in a polymer solution and film state indicated important differences in their photoresponse. In the polymer solution, the trans–cis photoisomerization of the chromophore is accompanied by an irreversible photobleaching effect, while under the same UV irradiation conditions, the ionomeric films exhibited an enhanced photostability. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1240–1247, 2002 相似文献
82.
William S. Oates Christopher S. Lynch Doru C. Lupascu Alain B. Kounga Njiwa Emil Aulbach Jürgen Rödel 《Journal of the American Ceramic Society》2004,87(7):1362-1364
Subcritical crack growth in terms of velocity–stress intensity factor ( v – K ) curves in lead zirconate titanate (PZT) were experimentally characterized on poled and unpoled compact tension specimens. The poled specimens were tested under open- and short-circuit electrical boundary conditions, which resulted in an increase in fracture toughness by 0.2 MPa·m1/2 for the accessible velocity range ( v = 10−9 to 10−4 m/s) in the open-circuit case. Subcritical crack growth of unpoled specimens was obtained under ambient (relative humidity = 35%) and dry (relative humidity ∼ 0.02%) conditions over a regime in stress intensity factor of 0.5 MPa·m1/2 . 相似文献
83.
Biological Evaluation and X‐ray Co‐crystal Structures of Cyclohexylpyrrolidine Ligands for Trypanothione Reductase,an Enzyme from the Redox Metabolism of Trypanosoma
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Raoul De Gasparo Dr. Elke Brodbeck‐Persch Dr. Steve Bryson Nina B. Hentzen Dr. Marcel Kaiser Prof. Dr. Emil F. Pai Prof. Dr. R. Luise Krauth‐Siegel Prof. Dr. François Diederich 《ChemMedChem》2018,13(9):957-967
The tropical diseases human African trypanosomiasis, Chagas disease, and the various forms of leishmaniasis are caused by parasites of the family of trypanosomatids. These protozoa possess a unique redox metabolism based on trypanothione and trypanothione reductase (TR), making TR a promising drug target. We report the optimization of properties and potency of cyclohexylpyrrolidine inhibitors of TR by structure‐based design. The best inhibitors were freely soluble and showed competitive inhibition constants (Ki) against Trypanosoma (T.) brucei TR and T. cruzi TR and in vitro activities (half‐maximal inhibitory concentration, IC50) against these parasites in the low micromolar range, with high selectivity against human glutathione reductase. X‐ray co‐crystal structures confirmed the binding of the ligands to the hydrophobic wall of the “mepacrine binding site” with the new, solubility‐providing vectors oriented toward the surface of the large active site. 相似文献
84.
The submitted work discussed the possibility of using two of the most problematic wastes to formulate an added‐value hard wood‐composite (HWC). The lignocellulosic rice straws (RS) fibers (as reinforced filler) and recycled expanded polystyrene foam (PS) wastes (as dispersed polymer matrix), were used to formulated the hard wood product applying the hot press technique. The air dried RS was added to the molten PS at increasing ratios (30–70% mass:mass), and the reached HWC sheet was subjected to tensile strength, water absorption and acoustic resistance characterizations. Based on the experimental data, it was found that increasing the RS contents accompanied with a diminish in the tensile strength value by about 50% at 70% RS compare to that at 30% RS. To improve the adhesion between the hydrophilic filler RS and the hydrophobic PS matrix, maleated PS graft (PS‐g‐MA) was prepared and added at the expanse of the PS content, to formulate an additional wood‐composite (HWCg) aiming to have better mechanical and dimensional stability features. Results obtained indicated that increasing the coupling agent content, keeping the RS added constant, enhance the tensile strength feature in addition, reduced the water absorption for the final products by more than 45%. The data obtained suggested that, it can create added‐value hard wood composites entirely from the two nominated problematic wastes. In addition to the value gained by the environment, the reached hard wood products record acceptable mechanical characterization, dimensional stability and sound resistance properties that qualified it to replace the natural wood in many daily applications. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44770. 相似文献
85.
Daniel F. Schafer II Peter T. Wolczanski Emil B. Lobkovsky Samantha N. MacMillan 《Israel journal of chemistry》2017,57(10-11):982-989
Treatment of (tBu3SiNH)(tBu3SiN=)2WH ( 1 -H) with small alkyl anions (RM) afforded tungsten alkyl hydride anions [(tBu3SiNH)(tBu3SiN=)2HWR)]M ( 3 -(R)M: R=CH3, M=Li; R=nBu, M=Li; R=neoPe, M=Li; R=CH2Ph (Bn), M=K (two isomers); R=CCH, M=Na; R=CH=CH2 (Vy), M=Li). The saturated alkyl anions 3 -(R)M ( 3 -(R)M: R=CH3, M=Li; R=nBu, M=Li; R=neoPe, M=Li; R=CH2Ph (Bn), M=K) degraded via apparent 1,2-RH-elimination to produce the known [(tBu3SiN=)3WH]M ( 2 -HM), but the acetylide ( 3 -(C2H)Na) and vinyl ( 3 -(Vy)Li) anions converted to their hydrogenated isomers, [(tBu3SiN=)3WVy]Na ( 2 -VyNa) and [(tBu3SiN=)3WEt]Li ( 2 -EtLi), respectively. The structure of 3 -(nBu)Li is reported, and a discussion of tungsten-hydride coupling constants in tBu3SiX-ligated (X=O, NH, N) systems is given. 相似文献
86.
We study the issue of whether the wind load factors specified in the ASCE 7–95 Standard for hurricane- prone regions on the one hand and extratropical storm regions on the other are mutually consistent with respect to risk. We consider structures or elements whose design is governed by wind loads and for which wind directionality effects are not significant. We present estimates according to which ASCE 7–95 Standard provisions for wind loads inducing the design strength result in (1) safety levels that are considerably lower for hurricane-prone than for extratropical storm regions, and (2) estimates of mean recurrence intervals of hurricane wind loads inducing the design strength of about 500 y if epistemic uncertainties are neglected, and significantly lower than 500 years otherwise. 相似文献
87.
Anastasio MA Zou Y Sidky EY Pan X 《Journal of the Optical Society of America. A, Optics, image science, and vision》2007,24(6):1569-1579
We develop reconstruction algorithms for local cone-beam tomography for use with generalized scanning trajectories. The algorithms are grounded theoretically in a recently developed chord-based theory for exact image reconstruction and principles of lambda tomography. Being chord based, they are distinct mathematically and conceptually from conventional local tomography reconstruction algorithms. The salient feature of our algorithms is that they permit reconstruction of discontinuities in the profiles of the object function along chords. By consideration of all possible chords, a 3D image that describes the locations of object discontinuities can be reconstructed. Results from microlocal analysis are applied for understanding the object features that can be reconstructed stably by use of the algorithms. A computer-simulation study is conducted to demonstrate the algorithms and compare their performance with an existing algorithm. 相似文献
88.
Leschkies KS Divakar R Basu J Enache-Pommer E Boercker JE Carter CB Kortshagen UR Norris DJ Aydil ES 《Nano letters》2007,7(6):1793-1798
We combine CdSe semiconductor nanocrystals (or quantum dots) and single-crystal ZnO nanowires to demonstrate a new type of quantum-dot-sensitized solar cell. An array of ZnO nanowires was grown vertically from a fluorine-doped tin oxide conducting substrate. CdSe quantum dots, capped with mercaptopropionic acid, were attached to the surface of the nanowires. When illuminated with visible light, the excited CdSe quantum dots injected electrons across the quantum dot-nanowire interface. The morphology of the nanowires then provided the photoinjected electrons with a direct electrical pathway to the photoanode. With a liquid electrolyte as the hole transport medium, quantum-dot-sensitized nanowire solar cells exhibited short-circuit currents ranging from 1 to 2 mA/cm2 and open-circuit voltages of 0.5-0.6 V when illuminated with 100 mW/cm2 simulated AM1.5 spectrum. Internal quantum efficiencies as high as 50-60% were also obtained. 相似文献
89.
Tindale R. Scott; Heath Linda; Edwards John; Posavac Emil J.; Bryant Fred B.; Suarez-Balcazar Yolanda; Henderson-King Eaaron; Myers Judith 《Canadian Metallurgical Quarterly》1999,3(4):313
Review of book: R. Scott Tindale et. al (Eds.) Theory and Research on Small Groups. New York: Plenum Press. 1998, 277 pp. Reviewed by Mark F. Stasson, Michael J. Markus, and Jason W. Hart. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
90.
Rodolfa Emil R.; Vieille Richard; Russell Peter; Nijjer Sukhvender; Nguyen Dao Q.; Mendoza Mary; Perrin Lori 《Canadian Metallurgical Quarterly》1999,30(4):415
As an internship applicant, do you know what internship agencies look for to select or exclude you from further consideration? In a survey, the authors examined exclusion and inclusion criteria used at 402 internship sites accredited by the American Psychological Association (APA). The 249 respondents (62%) rated fit between applicant goals and site opportunities as the most important inclusion criteria. Four exclusion criteria (lack of completion of orals, lack of APA status of doctoral program, poor fit between applicant goals and site opportunities, and incomplete doctoral course work) were most commonly used to eliminate applicants from consideration. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献