In this paper we discuss farthest-point problems in which a set or sequence S of n points in the plane is given in advance and can be preprocessed to answer various queries efficiently. First, we give a data structure that can be used to compute the point farthest from a query line segment in O(log2n) time. Our data structure needs O(nlogn) space and preprocessing time. To the best of our knowledge no solution to this problem has been suggested yet. Second, we show how to use this data structure to obtain an output-sensitive query-based algorithm for polygonal path simplification. Both results are based on a series of data structures for fundamental farthest-point queries that can be reduced to each other. 相似文献
A new kinetic approach to flowing chemical system is introduced, based on the elimination of reaction extents attached to linearly dependent reactions. The method is applied to analyze the propagation of acoustic waves in a reacting chemical mixture.
Coupling of diarylacetylenes with alkenes in the presence of dichlorobis(benzonitrile)palladium gives chloro(syn-1-chloro-anti-1-aryl-syn-3-alkyl)-π-allylpalladium complexes. 相似文献
A high-precision exact-matching quadruple isotope dilution method (ID4MS) was employed for the quantitation of nitrate in an air-dried spinach powder Certified Reference Material (CRM). The analyte was extracted in hot water following addition of 15NO\({}_{3}^{-}\) internal standard. The blend was then treated with sulfamic acid to remove nitrite and with triethyloxonium tetrafluoroborate to promote aqueous conversion of nitrate into volatile EtONO2. The derivative was analyzed by headspace GC–MS with 3-min elution time. The method performance was validated with a series of tests which demonstrated adequate selectivity and ruggedness. This method supported the development of novel SPIN-1 CRM giving a modest contribution to its uncertainty (uchar = 0.85%). With respect to previous attempts, the SPIN-1 was proven stable, homogeneous (uhom = 0.44%), and suitable for spinach monitoring under EU regulations. On dried basis, the nitrate content of SPIN-1 was found to be 22.53 ± 0.43 mg/g (Uc = 1.9%, k = 2). The material was also used in an inter-laboratory study where four laboratories employed a total of ten measurement methods.
Reactions of (norbornadiene)Cr(CO)4 or cis-(piperidine)2Mo(CO)4 with R2Sb-SbR2, and cyclo-(R′Sb)n (R′ = Et, n-Pr; n = 4, 5) give the complexes cyclo-[M(CO)4(R2Sb-SbR′- SbR′-SbR2)] (1: M = Cr, R = Me, R′= Et; 2: M = Mo, R = Et, R′ = Et; 3: M = Mo, R = Et, R′ = n-Pr). Not accessible to established characterization methods, the oily, extremely reactive unpurified mixture of 3 with scrambled ligands was characterized by mass spectrometry using liquid injection field desorption ionization (LIFDI). 相似文献
Thermostable heterocyclic polymers containing benzimidazole and imide rings, as well as flexible ester groups, have been synthesized by solution polycondensation of diaminobenzimidazoles with dianhydrides incorporating preformed ester linkages. The thermal stability and the electrical insulating properties of these products are discussed and compared with related heterocyclic polymers. 相似文献
Human biomonitoring (HBM) is a scientific technique that allows us to assess whether and to what extent environmental pollutants enter humans. We review here the current HBM efforts for organophosphate esters, emerging flame retardants, perfluoroalkyl substances, and phthalate esters. Use of some of these chemicals has already been banned or restricted; they are regularly detected in the environment, wildlife, and human matrices. Traditionally, blood and urine collection have been widely used as sampling methods. New non-invasive approaches (e.g., saliva, hair, nails) are emerging as valid alternatives since they offer advantages with respect to sampling, handling, and ethical aspects, while ensuring similar reliability and sensitivity. Nevertheless, the identification of biomarkers of exposure is often difficult because chemicals may be metabolized in the human body. For many of the above-mentioned compounds, the mechanisms of the favorable metabolization pathways have not been unraveled, but research on important metabolites that could be used as biomarkers of exposure is growing. This review summarizes the state of the art regarding human exposure to, (non-invasive) HBM of, and metabolism of major organophosphate esters, emerging flame retardants, perfluoroalkyl substances, and phthalate esters currently detected in the environment.
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Human biomonitoring of emerging contaminants-non-invasive versus invasive matrices 相似文献