Estimation of a quantile in some nonstandard cases

A necessary condition for the asymptotic normality of the sample quantile estimator isf(Q(p))=F(Q(p))>0, whereQ(p) is thep-th quantile of the distribution functionF(x). In this paper, we estimate a quantile by a kernel quantile estimator when this condition is violated. We have shown that the kernel quantile estimator is asymptotically normal in some nonstandard cases. The optimal convergence rate of the mean squared error for the kernel estimator is obtained with respect to the asymptotically optimal bandwidth. A law of the iterated logarithm is also established.This research was partially supported by the new faculty award from the University of Oregon.     

Polynitro-substitutedN-alkylalkaneimidoyl chlorides

The reaction of -fluorosubstituted polynitroalkylaldimines with HCl results in replacement of the fluorine atom by a chlorine atom. The hitherto unknown -chlorosubstituted polynitroalkylaldimines have been obtained, and their X-ray structural investigation has been performed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 440–443, March, 1994.     

At-column injector for capillary GC — design and evaluation

The present paper describes constructional details and evaluations of an at-column injector for capillary GC. Injections were made via a sample loop on a 0.32 mm i.d. capillary column. Two rotary valves were employed to allow a wash of the sample loop and a backflush of the transfer line. Repeatability, calculated from absolute area counts for n-alkanes was between 0.3–1% RSD, for injected sample volumes between 5 and 100 μl. Promising results were also obtained with syringe-based injections on narrow bore (100 μ i.d.) columns. Repeatability on the basis of normalized area counts was in the order of 0.1–0.2% RSD, while solvent tailing was practically absent.     

Coupling of thermal desorption in modified closeable sampling columns with wide-bore capillary gas chromatography and mass spectrometric detection

In contrast to usability of Curie-point pyrolysis at 700°C directly attached to gas chromatography-mass spectrometry (GC-MS) for determination of organic wood preservatives in waste wood samples the investigation method reported here consists of thermal desorption at temperatures about 260°C in connection with GC-MS for peak identification or GC with flame ionization detection for quantitative analyses. So-called “modified closeable sampling columns” are used as batch-reactor in thermal desorption experiments. Desorbed vapours can be introduced on capillary columns without sample discrimination and without a disturbing lost of resolution. In this manner a lot of individual polycyclic aromatic hydrocarbons were determinated in waste wood samples, especially in railway sleepers.     

A new procedure for bovine milk digestion in a focused microwave oven: gradual sample addition to pre-heated acid

Milk samples can be efficiently digested using a focused microwave oven, however the conventional procedure of addition of concentrated acids to the liquid sample leads to digestates with elevated acidity and residual carbon concentrations. In this work a focused microwave oven was applied for acid digestion of bovine milk samples using a conventional and an alternative procedure based on gradual sample addition to hot and concentrated acids. A two-level 2³ full factorial design experiment with eight runs was carried out to evaluate the optimum experimental conditions for reducing both the residual carbon and the final acidity of digestates. The three studied parameters were: temperature of the digestion medium for sample addition, addition of sulfuric acid before the sample or during the first step, and number of aliquots of the sample gradually added. The best conditions were attained by adding small aliquots of milk (ten-fold a volume of 0.5 ml added during 5.0 min) to a digestion mixture containing 3.0 ml nitric acid plus 1.0 ml sulfuric acid heated at 105 °C. It was demonstrated that the digestion efficiency of the alternative procedure was better than the conventional procedure, i.e. 98 and 80%, respectively. The alternative procedure was applied for determination of Ba, Ca, Cu, K, Mg, Na, P, and Zn in whole and non-fat bovine milk. The accuracy was proved using two certified reference materials (whole and non-fat milk powder).     

Thiourea to bicyclic scaffolds: highly regio- and stereoselective routes to dithiazolopyrimidines

Microwave-activated solvent-free Michael addition of 3-imino-1,4,2-dithiazoles to 4-arylidene-5(4H)-oxazolones furnished isolable adducts regio- and diastereoselectively, which underwent ring transformation to yield the target dithiazolopyrimidines. Alternatively, the similar conjugate addition of methanesulfinylmethylisothioureas to 4-arylidene-5(4H)-oxazolones diastereoselectively afforded Michael adducts, which underwent ring transformation followed by heterocyclization via deoxygenative demethylation with thionyl chloride to yield the same products dithiazolopyrimidines regio- and diastereoselectively.     

Nucleophilic Addition of Thiaproline to Electrochemically Derived o‐Quinone,Application to the Sensitive Voltammetric Detection of Thiaproline

The mechanism of electrochemical behavior of catechol in the presence of thiaproline is investigated by cyclic voltammetry, controlled‐potential coulometry and spectrophotometric tracing of the reaction coordinate. The results indicate that thiaproline participate in with an ECEC mechanism in a nucleophilic (Michael) addition to o‐quinone. Effect of pH of buffer solution on reaction pathway is studied and showed that addition of thiaproline to the o‐quinone is performed only in solutions with pHs higher than 5. These results indicate that the addition of thiaproline is occurred first from amine functional group. In the second step, the addition of carboxylate group of thiaproline to C‐5 of catechol results the final product with a lactone ring in its structure. Observation of two isosbestic point in absorption spectrum during the progress of the electrolysis together with the FT‐IR results for final product can be presented as evidence for two step addition of thiaproline to catechol. Final product, due to the electron donor property of thiaproline, more easily oxidized respect to the former catechol and as a result, a new redox couple is obtained for this compound in lower potentials. The easier anodic oxidation of addition product (relative to catechol) caused to an increase in anodic current for catechol, which is proportional to the thiaproline concentration. The differential pulse voltammetry (DPV) is applied as a sensitive voltammetric method for the detection of thiaproline. A linear range from 5×10^?8 to 5×10^?6 M with a detection limit of 1×10^?8 M is resulted for thiaproline. With respect to the reversibility of the electrochemical reactions in the mechanism, and also more facile oxidation of the addition products, the square‐wave voltammetry is presented as a method with considerably more sensitivity for the detection of sub‐micromolar amounts of thiaproline. The advantageous properties of the voltammetric method for thiaproline detection lie in its excellent catalytic activity, sensitivity and simplicity.     

Formation of sol-gel nanostructured mullite by additions of fluoride ion

Summary The subject of this study was to investigate the effect of fluoride ions addition on the temperature of sol gel mullite formation based on the hypotheses that the presence of fluoride ions can decrease the temperature of mullite formation (in respect to common 980°C, in sol-gel processing). Polymeric sols were prepared by mixing TEOS and aluminum nitrate nanohydrate and by adding fluoride ions (from 2 to 5 mass%). DTA, TG, XRD and SEM were used for characterisation of mullite gel and crystalline mullite. The experimental results confirmed that the addition of fluoride ions decrease the temperature of mullite formation up to 890°C for the fluorine concentration of 3.5 mass%. Experimental results showed that the temperature of mullite formation is not a simple function of the fluoride ion content. The mechanism of fluorine effect was discussed in terms of the gelling process, gel structure and the phase separation before the mullite formation.     

Reactions of Diethyl [(3-Bromomethyl-2-Thienyl)-Methylene]Propanedioate with Hydrazines: Syntheses of Dihydropyridazines,Pyridazines and O-Dimethylaminomethylarenecarbonitriles

Facile syntheses of dihydropyridazines, pyridazines, and o-dimethylaminomethylarenecarbonitriles have been achieved by the retro-malonate addition reaction. Bromoalkylidenemalonates 1,7, and 10 were treated with hydrazine to give dihydropyridazines 4, 8, and 11 in quantitative yields. DDQ or air oxidation of 4, 8, and 11 gave pyridazines 5, 9, and 12, Alternatively, treatment of 1, 7, and 10 with 1,1-dimethylhydrazine afforded o-dimethylaminomethylarenecarbonitriles 6,13, and 14 in good yields.     

Synthesis and molecular structure of [Re2(μ:η-C24H18N4)(CO)6] containing the rtct-tetrakis(2-pyridyl)cyclobutandiyl ligand, derived from the reaction of [Re2(CO)8(MeCN)2] and 1,2-bis(2-pyridyl)ethene

The reaction of the labile compound [Re₂(CO)₈(CH₃CN)₂] with trans-1,2-bis(2-pyridyl)ethene (C₁₂H₁₀N₂) at room temperature in tetrahydrofuran affords the compounds [Re₂(μ:η³-C₁₂H₁₀N₂)(CO)₈] (1) and the oxidative addition product [Re₂(μ-H)(μ:η³-C₁₂H₉N₂)(CO)₇] (2). When the reaction is carried out at temperatures of refluxing tetrahydrofuran, besides compounds 1 and 2, the oxidative addition product [Re₂(μ-H)(μ:η⁴-C₁₂H₉N₂)(CO)₆] (3), the insertion product [Re₂(μ:η⁴-C₁₂H₁₀N₂)(CO)₈] (4) and [Re₂(μ:η⁶-C₂₄H₁₈N₄)(CO)₆] (5) are obtained. Compound 5 contains the organic ligand rtct-tetrakis(2-pyridyl)cyclobutandiyl which is derived from a [2 + 2] cycloaddition of 1,2-bis(2-pyridyl)ethene mediated by its coordination to the bimetallic framework. The molecular structures of 1, 2, 4 and 5 were confirmed by X-ray crystallographic studies.