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101.
Guo J Erickson GA Fitzgerald RN Matsuoka RT Rafferty SW Sharp MJ Sickles BR Wisowaty JC 《The Journal of organic chemistry》2006,71(21):8302-8305
An efficient synthesis of 2-{4-[({4-{[4-(4-methoxyphenyl)piperazin-1-yl]methyl}-2-[4-(trifluoromethyl)phenyl]-1,3-thiazol-5-yl}methyl)thio]phenoxy}-2-methylpropanoic acid (1), a potent PPARpan agonist, is described. The seven-step synthesis, which afforded 1 in 30% overall yield, includes a highly regioselective carbon-sulfur bond formation via coupling of a bishydroxymethylthiazole (3) with 4-hydroxythiophenol, displacement of the remaining alcohol through a three-step telescoped sequence involving an efficient cleavage of an aryl mesylate, and an efficient and practical method of introducing an isobutyric acid fragment. 相似文献
102.
On the Least Median Square Problem 总被引:1,自引:0,他引:1
Jeff Erickson Sariel Har-Peled David M. Mount 《Discrete and Computational Geometry》2006,36(4):593-607
We consider the exact and approximate computational complexity of the multivariate least median-of-squares (LMS) linear regression
estimator. The LMS estimator is among the most widely used robust linear statistical estimators. Given a set of n points in
and a parameter k, the problem is equivalent to computing the narrowest slab bounded by two parallel hyperplanes that contains
k of the points. We present algorithms for the exact and approximate versions of the multivariate LMS problem. We also provide
nearly matching lower bounds for these problems. These lower bounds hold under the assumptions that k is Ω(n) and that deciding
whether n given points in
are affinely non-degenerate requires Ω(nd) time. 相似文献
103.
The unusual base-induced ring-enlargement of halomethylenecyclobutanes to 1-halocyclopentenes was examined with unsymmetrical and (13)C-labeled substrates to study regio- and stereochemical characteristics. Migration of a ring carbon atom (single migration) or simultaneous migration of a ring carbon atom and the halide (double migration) gives the ring-enlarged products. (13)C-labeling experiments established that both rearrangements occur with retention of configuration at the migrating center. These systems are suggested as models for the Fritsch-Buttenberg-Wiechell (FBW) rearrangement. 相似文献
104.
105.
Nice Point Sets Can Have Nasty Delaunay Triangulations 总被引:1,自引:1,他引:0
Erickson 《Discrete and Computational Geometry》2003,30(1):109-132
Abstract. We consider the complexity of Delaunay triangulations of sets of points in R
3
under certain practical geometric constraints. The spread of a set of points is the ratio between the longest and shortest pairwise distances. We show that in the worst case, the
Delaunay triangulation of n points in R
3
with spread Δ has complexity Ω(min{ Δ3, nΔ, n2 }) and O(min{ Δ4, n
2 }). For the case
, our lower bound construction consists of a grid-like sample of a right circular cylinder with constant height and radius.
We also construct a family of smooth connected surfaces such that the Delaunay triangulation of any good point sample has
near-quadratic complexity. 相似文献
106.
The movement of a particular component along an HPLC column is studied on the ba-sis of equilibrium equations. Numerical simulation of multi--step gradient elution HPLC isperformed by means o? a personal computer program. The location x, as a fraction of thecolumn length, for a given time t o? each compound is calculated, the velocity and corre-sponding acceleration are given as well. Diagrams for x,dx/dt and d~2x/dt~2 versus t display themovement process of the different components along the HPLC column during gradient elu-tion. The prediction of the retention time and peak width, and the optimization for the multi-step gradient elution HPLC are all based on such simulation and the molecular structure ofthe. components is separated as well. 相似文献
107.
P. F. Goldsmith H. R. Fetterman B. J. Clifton C. D. Parker N. R. Erickson 《International Journal of Infrared and Millimeter Waves》1981,2(5):915-924
We report here the first results obtained by cooling a submillimeter quasioptical mixer, utilizing a Schottky diode in a corner reflector mixer structure. Measurements have been carried out at a wavelength of 434 microns. The diode inverse slope parameter Vo at low current decreases by a factor of 3 upon cooling to 50 K while the minimum system noise temperature of 5600 K (SSB), including the IF contribution, demonstrates a reduction of approximately 40% from the ambient temperature value. We also report improved system noise temperatures at 184 m and 119 m wavelengths of 38000 K and 64000 K (SSB), respectively.This work was supported by the Army Research Office and the Air Force Office of Scientific Research 相似文献
108.
John G. Erickson 《Journal of polymer science. Part A, Polymer chemistry》1966,4(3):519-528
This paper describes polyesters and polyamides obtained by the base-catalyzed additions of hydrogen sulfide to α,β-unsaturated diesters and diamides. The compounds employed were ethylene diacrylate, the diacrylate of trans-1,4-bis(hydroxymethyl)cyclohexane, p-xylylene diacrylate, hydroquinone diacrylate, the diacrylate of 1,4-butanedithiol, tetraethylene glycol dimethacrylate, 1,4-butylene dicrotonate, 1,4-butylene dicinnamate, methylene bisacrylamide, and m-xylylene bisacrylamide. The polymers posses the general formula, , wherein R1 is hydrogen, methyl, or phenyl, R2 is hydrogen or methyl, R3 is an alkylene, aralkylene, or oxyalkylene group, and X is oxygen, sulfur, or the imino group. Polymers with as many as several hundred repeating units were obtained. Depending upon the structure, the products are liquids, rubbers, or solids, the polymers are obtained with vinyl or sulfhydryl termination and the efficiency of this termination is very high, as was shown by chain extension of a sulfhydryl-terminated polymer through oxidation to a polydisulfide, $$ \rlap{‐‐} ({\rm RSS\rlap{‐‐} )}_n $$, having a molecular weight 30 times as great as that of the parent dimercaptan. The syntheses of several new monomers are described. 相似文献
109.
Margret J. Geselbracht Ann S. Erickson John E. Greedan Matthew W. Stoltzfus Patrick M. Woodward 《Journal of solid state chemistry》2006,179(11):3489-3499
Reduced titanates in the ATi2O4 (A=Li, Mg) spinel family exhibit a variety of interesting electronic and magnetic properties, most notably superconductivity in the mixed-valence spinel, Li1+xTi2−xO4. The sodium and calcium analogs, NaTi2O4 and CaTi2O4, each differ in structure, the main features of which are double rutile-type chains composed of edge-sharing TiO6 octahedra. We report for the first time, the properties and band structures of these two materials. XANES spectroscopy at the Ti K-edge was used to probe the titanium valence. The absorption edge position and the pre-edge spectral features observed in the XANES data confirm the assignment of Ti3+ in CaTi2O4 and mixed-valence Ti3+/Ti4+ in NaTi2O4. Temperature-dependent resistivity and magnetic susceptibility studies are consistent with the classification of both NaTi2O4 and CaTi2O4 as small band-gap semiconductors, although changes in the high-temperature magnetic susceptibility of CaTi2O4 suggest a possible insulator-metal transition near 700 K. Band structure calculations agree with the observed electronic properties of these materials and indicate that while Ti-Ti bonding is of minimal importance in NaTi2O4, the titanium atoms in CaTi2O4 are weakly dimerized at room temperature. 相似文献
110.
Frost RL Erickson KL Weier ML Carmody O 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2005,61(5):829-834
Raman and infrared spectroscopy has been used to study the structure of selected vanadates including pascoite, huemulite, barnesite, hewettite, metahewettite, hummerite. Pascoite, rauvite and huemulite are examples of simple salts involving the decavanadates anion (V10O28)6-. Decavanadate consists of four distinct VO6 units which are reflected in Raman bands at the higher wavenumbers. The Raman spectra of these minerals are characterised by two intense bands at 991 and 965 cm(-1). Four pascoite Raman bands are observed at 991, 965, 958 and 905 cm(-1) and originate from four distinct VO6 sites. The other minerals namely barnesite, hewettite, metahewettite and hummerite have similar layered structures to the decavanadates but are based upon (V5O14)3- units. Barnesite is characterised by a single Raman band at 1010 cm(-1), whilst hummerite has Raman bands at 999 and 962 cm(-1). The absence of four distinct bands indicates the overlap of the vibrational modes from two of the VO6 sites. Metarossite is characterised by a strong band at 953 cm(-1). These bands are assigned to nu1 symmetric stretching modes of (V6O16)2- units and terminal VO3 units. In the infrared spectra of these minerals, bands are observed in the 837-860 cm(-1) and in the 803-833 cm(-1) region. In some of the Raman spectra bands are observed for pascoite, hummerite and metahewettite in similar positions. These bands are assigned to nu3 antisymmetric stretching of (V10O28)6- units or (V5O14)3- units. Because of the complexity of the spectra in the low wavenumber region assignment of bands is difficult. Bands are observed in the 404-458 cm(-1) region and are assigned to the nu2 bending modes of (V10O28)6- units or (V5O14)3- units. Raman bands are observed in the 530-620 cm(-1) region and are assigned to the nu4 bending modes of (V10O28)6- units or (V5O14)3- units. The Raman spectra of the vanadates in the low wavenumber region are complex with multiple overlapping bands which are probably due to VO subunits and MO bonds. 相似文献