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排序方式: 共有262条查询结果,搜索用时 15 毫秒
151.
Jairo R. Montoya-Torres 《Journal of Global Optimization》2003,27(1):97-103
We consider the problem of scheduling jobs on-line on a single machine with the objective of minimizing total completion time. We assume that jobs arrive over time and that release dates are known in advance, but not the processing times. The most important result we are given in this paper is the competitive analysis of a new clairvoyant on-line algorithm for this scheduling problem. We are proving that this deterministic semi-online algorithm, called ST-, is
-competitive, which beats the existing lower bound for non-clairvoyant online algorithms. 相似文献
152.
In this Letter we address the nature of broken ergodicity in the low temperature phase of Ising spin glasses by examining spectral properties of spin correlation functions C(ij) identical with. We argue that more than one extensive [i.e., O(N)] eigenvalue in this matrix signals replica symmetry breaking. Monte Carlo simulations of the infinite-range Ising spin-glass model, above and below the Almeida-Thouless line, support this conclusion. Exchange Monte Carlo simulations for the short-range model in four dimensions find a single extensive eigenvalue and a large subdominant eigenvalue consistent with droplet model expectations. 相似文献
153.
Addition of Hydrogen Peroxide to Groundwater with Natural Iron Induces Water Disinfection by Photo‐Fenton at Circumneutral pH and other Photochemical Events
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Héctor Mario Gutiérrez‐Zapata John Jairo Alvear‐Daza Julián Andrés Rengifo‐Herrera Janeth Sanabria 《Photochemistry and photobiology》2017,93(5):1224-1231
Samples of natural groundwater (with low turbidity, neutral pH and 0.3 mg L?1 iron concentration) inoculated with Escherichia coli K‐12 were exposed to simulated solar light both in the presence and in the absence 10 mg L?1 of H2O2. Results demonstrated that the viability of E. coli (by DVC–FISH) was grounded to zero after 360 min of irradiation. This abatement could be caused by the oxidative stress induced by radicals or another photo‐induced reactive oxygen species. Two 23 factorial experimental designs enabled the evaluation of the effects of chemical factors on the inactivation of E. coli. The first experimental design considered the pH, iron and H2O2, while the second evaluated the ions fluoride, carbonate and phosphate found in groundwater. pH was found to play a key role in the inactivation of E. coli. The best reduction in viability was obtained at the lower pH (6.75), while a nonsignificant effect was observed when iron or H2O2 concentrations were raised. At higher concentrations, anions, such as carbonate and phosphate, negatively affected the E. coli abatement. However, a higher concentration of fluoride accelerated it. In all experiments, the pH was observed to rise to values higher than 8.0 units after 360 min of treatment. 相似文献
154.
Jairo Quiroga Jaime Portilla Rodrigo Abonía Manuel Nogueras 《Tetrahedron letters》2007,48(11):1987-1990
New 6,8-dihydro-5H-benzo[f]pyrazolo[3,4-b]quinolines 6 have been obtained in a novel solvent-free three-component reaction involving β-tetralone along with 5-aminopyrazoles 1 and benzaldehydes 2. The isomeric 6,10-dihydro-5H-benzo[h]pyrazolo[3,4-b]quinolines 9 could not be prepared in a similar fashion directly from α-tetralone, but were obtained by the reaction of amines 1 with benzylidene-derivative 10 of α-tetralone in similar conditions. The yields of quinolines obtained via this novel protocol were good and the reaction times varied from few minutes to just few seconds. 相似文献
155.
Jairo Quiroga GermN Viveros Braulio Insuasty Manuel Nogueras Adolfo Snchez Justo Cobo 《Journal of heterocyclic chemistry》1999,36(2):501-504
The synthesis of 6-dimethylaminomethylenaminopyrimidin-4(3H)-ones 2 and its reaction with β-dimethyl-aminopropiophenone hydrochloride 3 is discussed in this work. The reaction of 6-aminopyrimidin-4(3H)-ones 1 with an excess of dimethylformamide dimethyl acetal gives rise to the formation of 6-dimethylaminomethyleneaminopyrimidines 2. The heating of equimolecular quantities of 2 and 3 in dimethylformamide leads to the 6-aroylpyrido[2,3-d]pyrimidines derivatives 4. The structures of compounds 2 and 4 were determined on the basis of nmr measurements. 相似文献
156.
Rodrigo Abonia Christopher Glidewell John N. Low Manuel Nogueras Jairo Quiroga 《Acta Crystallographica. Section C, Structural Chemistry》2003,59(5):o237-o239
Molecules of the title compound, C14H17N5O4, exhibit a highly polarized molecular–electronic structure. The molecules are linked into sheets by two N—H⋯O hydrogen bonds [H⋯O = 2.03 and 2.02 Å, N⋯O = 2.836 (2) and 2.887 (2) Å, and N—H⋯O = 153 and 168°], augmented by a single C—H⋯O hydrogen bond [H⋯O = 2.47 Å, C⋯O = 3.403 (2) Å and C—H⋯O = 166°]. Pairs of sheets, related by inversion, form bilayers with interdigitated dimethoxybenzyl substituents, weakly linked by a further C—H⋯O interaction [H⋯O = 2.50 Å, C⋯O = 3.350 (2) Å and C—H⋯O = 146°]. 相似文献
157.
Laura Gamboa-Carvajal Carlos Jara-Gutirrez Joan Villena Lautaro Taborga Jairo Ren Martínez Luis Espinoza Elena E. Stashenko 《Molecules (Basel, Switzerland)》2022,27(13)
In this work, the antioxidant activity of the hydro-ethanolic extracts of the leaves, flowers, and aerial parts of Steiractinia aspera Cuatrec, both fresh and post-distillation, was evaluated by ABTS+·, FRAP, H2O2 and DPPH assays. The cytotoxic activity was evaluated in MCF-7, MCF-10A and HT-29 cell lines. The hydro-ethanolic extracts were obtained by matrix solid-phase dispersion (MSPD) and ultrasound-assisted solvent extraction (SE). The fresh-leaf MSPD extract had the highest antioxidant activity, and the post-distillation leaf ultrasound-assisted SE extract had the highest cytotoxicity in the MCF-7 breast cancer cell line, although not selective, which was evaluated by sulforhodamine B assay. On the other hand, ROS was evaluated by flow cytometry which showed that post-distillation leaf extract is pro-oxidant. Chlorogenic acid, kaempferol-3-glucoside and quercetin were found in the fresh leaves’ extracts, according to HPLC-DAD. PLC-DAD permitted the isolation of p-coumaric acid, E-3-(4-(((E)-3-(3,4-dihydroxyphenyl) acryloyl) oxy)-3-hydroxyphenyl) acrylic acid and a diglucosylated derivative of ursolic acid, which were analyzed by 1H and 13C NMR. Our results suggest that the fresh leaf extract of Steiractinia aspera Cuatrec has potential use for antioxidant applications. 相似文献
158.
In this paper, we deal with one-parameter families of real cellular automata in R2. We prove that for a wide class of block functions from R2 to R, the corresponding real cellular automaton is expanding when the value of the parameter is large enough. 相似文献
159.
Jairo Quiroga Jaime Portilla Michael B. Hursthouse Justo Cobo Christopher Glidewell 《Acta Crystallographica. Section C, Structural Chemistry》2010,66(4):o159-o162
Molecules of the title compound [systematic name: (5‐amino‐3‐methylpyrazol‐1‐yl)(phenyl)methanone], C11H11N3O, contain an intramolecular hydrogen bond. The molecules are linked into sheets by a combination of N—H...N, C—H...O and C—H...π(arene) hydrogen bonds. Comparisons are made with the hydrogen‐bonded structures of some related compounds. 相似文献
160.
Jairo Quiroga Jorge Trilleras Dayana Pantoja Braulio Insuasty Justo Cobo 《Tetrahedron letters》2010,51(36):4717-2666
New pyrazolo[3,4-b]pyridine-5-spirocycloalkanedione derivatives were prepared via three-component reaction between 5-(4-R-benzylamino)pyrazoles, cyclic β-diketones and paraformaldehyde. The use of indandione as β-diketone resulted in the formation of two products, the pyrazolo[3,4-b]pyridine-5-spiroindanediones and 3-tert-butyl-1-phenylindeno[2,3-e]pyrazolo[3,4-b]pyridine. The structures of the pyrazolo[3,4-b]pyridine-5-spirocycloalkanedione were confirmed by single-crystal X-ray diffraction. This protocol provides a simple one-step synthetic methodology with the advantages of easy work-up, mild reaction conditions and environmentally benign. 相似文献