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261.
The goal of this article is to present a local exact controllability result for the two- and three-dimensional compressible Navier–Stokes equations on a constant target trajectory when the controls act on the whole boundary. Our study is then based on the observability of the adjoint system of some linearized version of the system, which is analyzed using a subsystem for which the coupling terms are somewhat weaker. In this step, we strongly use Carleman estimates in negative Sobolev spaces. 相似文献
262.
Development of a stir bar sorptive extraction method for the determination of volatile compounds in orange juices
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Carla Herrera Remedios Castro Carmelo García‐Barroso Enrique Durán‐Guerrero 《Journal of separation science》2016,39(18):3586-3593
A stir bar sorptive extraction method for the determination of volatile compounds in orange juices was developed. The extraction variables were optimized using a reduced two‐level factorial screening design (25‐1), and the most suitable analytical conditions for the extraction of the studied compounds were: sample volume 10 mL, extraction time 60 min, stirring speed 1800 rpm, NaCl amount 30% (weight/volume), and twister length 10 mm. The optimized method was further validated, obtaining good linearity and detection and quantification limits low enough to correctly determine the studied compounds. As well, for most of the studied compounds precision and recovery values were good. Several orange juice samples (squeezed and commercial) were extracted following the optimized extraction method and analyzed by gas chromatography coupled to mass spectrometry detection. The method has proven to be suitable for the determination of the aroma of orange juice, of which limonene was the major volatile compound in all the studied samples. 相似文献
263.
In this paper, we demonstrate under some general assumptions, that a generator of any uniformly bounded composition operator, mapping spaces of bounded variation (Waterman) functions into other spaces of this type, must be an affine function in the functional variable.
相似文献264.
Miguel A. Guerrero 《Tetrahedron letters》2006,47(15):2517-2520
An efficient Et3B-mediated oxidative radical substitution of substituted pyrroles and indoles using xanthate based radical chemistry in the presence of iron(II) sulfate is described. Unsubstituted indole gave only low yield or failed in the process. 2-Cyanofuran and 2-benzoylthiophene did not afford the corresponding alkylated products under these conditions. 相似文献
265.
R Juanola L Guerrero V Salvadó J.A Garcia Regueiro E Anticó 《Analytica chimica acta》2004,513(1):291-297
The effect of different corks stoppers on the sensory and instrumental determination of 2,4,6-trichloroanisole (TCA) was studied in wine and cork. A relationship between both measurements was also established.Four types of cork were used to seal white wine bottles for 8 months. The stoppers were from different raw material: a high quality commercial batch (C), slabs with yellow stain (YS) and slabs with a high musty and mouldy taint (T). Spiked samples (S) were prepared from C batch by injecting 1002 ng of TCA into the cork stoppers.TCA was determined by gas chromatography with electron capture detection after headspace solid phase microextraction in bottled wine (12 per group) and after extraction with pentane in the case of corks (six per group). Seven semi-trained assessors evaluated the different samples using a ranking test in 12 and six sessions for wine and cork stoppers, respectively.Wines and corks from S samples showed the highest TCA values in both sensory and instrumental measurements, the lowest values being for C samples. YS and T corks had intermediate values, although in general TCA concentration was higher in T. A slight tendency to increase the TCA content in stoppers with yellow stain compared to C samples was observed in wine. A high correlation coefficient (r=0.82) was found between sensory and instrumental analysis for wine, whereas this coefficient was much lower (r=0.56) for cork stoppers. Some hypotheses are given in order to explain these differences. 相似文献
266.
Non-linear regression methods in NIRS quantitative analysis 总被引:1,自引:0,他引:1
Due to its speed and precision, near-infrared reflectance spectroscopy (NIRS) has become a widely used analytical technique in many industries. It offers, moreover, a number of other advantages which make it ideal for meeting current demands in terms of control and traceability: low cost per sample analysed; little or no need for sample preparation; ability to analyse a wide range of products and parameters; a high degree of reproducibility and repeatability. NIRS can be built into in-line processes, and - since no reagents are required - produces no waste. However, the major drawback to the use of NIRS for its most traditional application (the generation of prediction equations) is that it is a secondary method, and as such needs to be calibrated using a conventional reference method. For quantitative applications, calibration involves ascertaining the optimum mathematical relationship between spectral data and data provided by the reference method. The model may be fairly complex, since the NIRS spectrum is highly variable and contains physical/chemical information for the sample which may be redundant. As a result, multivariate calibration is required, based on a set of absorption values from several wavelengths. Since the relationship to be modelled is often non-linear, classical regression methods are unsuitable, and more complex strategies and algorithms must be sought in order to model this non-linearity. This overview addresses the most widely used non-linear algorithms in the management of NIRS data. 相似文献
267.
SINGLET OXYGEN INDUCES FRANK STRAND BREAKS AS WELL AS ALKALI- AND PIPERIDINE-LABILE SITES IN SUPERCOILED PLASMID DNA 总被引:6,自引:0,他引:6
ED ROBERT BLAZEK JENNIFER G. PEAK MEYRICK J. PEAK 《Photochemistry and photobiology》1989,49(5):607-613
A covalently closed, circular, supercoiled plasmid was exposed to singlet oxygen by a separated-surface sensitizer. For each exposure, the quantity of single oxygen entering the DNA target solution was estimated by its oxidation of histidine. After singlet oxygen exposure, some DNA samples were treated to disclose occult lesions. Agarose gel electrophoresis was then used to resolve the unrelaxed supercoils from the relaxed circular and linear species, and all bands were quantitated fluorometrically. Exposure of supercoiled plasmid DNA to singlet oxygen induced frank DNA strand breaks, alkali-labile sites (pH 12.5, 90 degrees C, 30 min), and piperidine-labile sites (0.4 M, 60 degrees C, 30 min), all in a dose-dependent manner. Yields of alkali-labile and piperidine-labile sites ranged from one to four times the frank strand break yield. Replacement of buffered H2O by buffered D2O as the DNA solvent for singlet oxygen exposures increased DNA lesion yields by a factor of 2.6 (averaged over lesion classes). Our data for the detection of frank strand breaks is at variance with published results from studies in which singlet oxygen was derived from a thermolabile endoperoxide dissolved in the DNA solution. 相似文献
268.
[reaction: see text] Long-chain 2,2-difluoro-3-hydroxyacids have been synthesized in a new, straightforward manner by treatment of 4-hydroxy-1,1,1,3,3-pentafluoroalkyl ketones, easily obtained by reaction of pentafluoroenolate 2 with aldehydes and ketones, with base under mild conditions. The reaction sequence is marked by the selective cleavage of the CO-CF3 bond, as well as the absence of products arising from the alternative CO-CF2R bond cleavage. The process represents a convenient approach for the synthesis of 2,2-difluoro-3-hydroxyacids, as it is short, provides good to excellent yields under mild conditions, and uses hexafluoro-2-propanol, a very cheap reagent, as the fluorine source. 相似文献
269.
Olivella S Solé A Jiménez O Bosch MP Guerrero A 《Journal of the American Chemical Society》2005,127(8):2620-2627
Experimental results of an unprecedented haloform-type reaction in which 4-alkyl-4-hydroxy-3,3-difluoromethyl trifluoromethyl ketones undergo base-promoted selective cleavage of the CO-CF(3) bond, yielding 3-hydroxy-2,2-difluoroacids and fluoroform, are rationalized using DFT (B3LYP) calculations. The gas-phase addition of hydroxide ion to 1,1,1,3,3-pentafluoro-4-hydroxypentan-2-one (R) is found to be a barrierless process, yielding a tetrahedral intermediate (INT), involving a DeltaG(r)(298 K) of -61.4 kcal/mol. The CO-CF(3) bond cleavage in INT leads to a hydrogen-bonded [CH(3)CHOHCF(2)CO(2)H...CF(3)](-) complex by passage through a transition structure (TS1) with a DeltaG()(298 K) of 20.8 kcal/mol and a DeltaG(r)(298 K) of 9.8 kcal/mol. This complex undergoes a proton transfer between its components, yielding a hydrogen-bonded [CH(3)CHOHCF(2)CO(2)...CHF(3)](-) complex. This process has associated with it a DeltaG()(298 K) of only 3.1 kcal/mol and a DeltaG(r)(298 K) of -43.3 kcal/mol. The CO-CF(2) bond cleavage in INT leads to a hydrogen-bonded [CH(3)CHOHCF(2)...CF(3)CO(2)H](-) complex by passage through a transition structure (TS3) with a DeltaG()(298 K) of 29.2 kcal/mol and a DeltaG(r)(298 K) of 25.1 kcal/mol. The lower energy barrier found for CO-CF(3) bond cleavage in INT is ascribed to the larger number of fluorine atoms stabilizing the negative charge accumulated on the CF(3) moiety of TS1, as compared to the number of fluorine atoms stabilizing the negative charge on the CH(3)CHOHCF(2) moiety of TS3. The solvent-induced effects on the two pathways, introduced within the SCRF formalism through PCM calculations, do not reverse the predicted preference of the CO-CF(3) over the CO-CF(2) bond cleavage of R in the gas phase. 相似文献
270.
Ricardo Ernst Jose-Luis Guerrero Alan Roshwalb 《The Journal of the Operational Research Society》1993,44(11):1115-1127
In this paper we develop a new approach to monitor the accuracy of an inventory management system. A recorded stock level is considered accurate when the recorded level agrees with the actual stock level, otherwise there is an error. In practice, management relies on methods to measure or assure inventory accuracy not necessarily developed for this purpose. Our methodology is based on the average absolute relative difference as a simple analytical measure for inventory accuracy (AC N ). The approach captures the status of accuracy in an inventory and allows for greater understanding of what affects inaccuracy since the theoretical measure of accuracy is composed of several parameters representing the incidence and proportion of both overstock and understock. The implementation of the methodology is constrained because complete inspection of the inventory is very expensive in most situations, so we develop the sample analogue of the accuracy measure (AC n ) and discuss sampling strategies. The accuracy of the inventory system is monitored by incorporating AC n into a univariate control chart. 相似文献