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101.
Patrik Lundstr?m 《Algebras and Representation Theory》2012,15(1):119-135
We show a version of Hilbert 90 that is valid for a large class of algebras many of which are not commutative, distributive
or associative. This class contains the nth iteration of the Conway–Smith doubling procedure. We use our version of Hilbert 90 to parametrize all solutions in ordered
fields to the norm one equation for such algebras. 相似文献
102.
Most statistical machine translation systems are combinations of various models and tuning scaling factors is an important step. However, this optimisation problem is hard because the objective function has many local minima and the available algorithms cannot achieve a global optimum. Consequently, optimisations starting from different initial settings can converge to fairly different solutions. We present tuning experiments with the Simultaneous Perturbation Stochastic Approximation (SPSA) algorithm, and compare them with the widely used downhill simplex method. With IWSLT 2005 Chinese-English data, both methods showed similar performance, but SPSA was more robust to the choice of initial settings. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
103.
104.
105.
Ek. Todorova 《Journal of Thermal Analysis and Calorimetry》1996,46(1):187-192
To improve the separation of the dihydrate and hemihydrate phases, different sample masses, heating rates and crucibles were used. A TG-DTA method was developed for the determination of water evolved from CaSO4·xH2O. The new crucible introduced for the Q-1500D MOM derivatograph gives a possibility for the evolved water to be determined independently from the TG and DTA curves.I am very grateful to Prof. Pelovski for the opportunity to use the Gypsum & Lime collection. This study was supported by the National Fund Science Research-Bulgaria. 相似文献
106.
Direct coupling of micellar electrokinetic chromatography (MEKC) to mass spectrometry (MS) without employing partial filling is considered to be a challenge. One way of solving the problem would be the use of an MS-compatible surfactant. In the present study, the applicability of a series of surfactants (sodium dodecyl sulfate (SDS), lauric acid, cholic acid and perfluorated carboxylic acids) have been investigated both in terms of separation performance and MS compatibility. It was found that a MEKC system based on perfluorooctanoic acid (PFOA) and ammonia gave excellent results. The separation performance of the suggested system is comparable to the one obtained with standard systems based on SDS and sodium borate buffer although the selectivity is different. The electrospray ionization MS signal of the analytes is not seriously suppressed even at a PFOA concentration of 100 mM. Clusters are formed but their intensities are relatively low and comparable to those obtained with acetic acid. PFOA is volatile enough to allow long-term use, 30 h of continuous use has been recorded without any signs of decreasing performance. After use residual PFOA is easily removed from the ion-source (no memory effects). Furthermore, quantitation of trace impurities is possible at 25 ppb level when employing selected ion monitoring. 相似文献
107.
Spanel P Diskin AM Abbott SM Wang T Smith D 《Rapid communications in mass spectrometry : RCM》2002,16(22):2148-2153
We describe a method by which the concentrations of volatile compounds in the headspace of their dilute aqueous solutions in sealed containers can be determined using on-line selected ion flow tube mass spectrometry (SIFT-MS). Thus, the changing number density of the molecules of the volatile compound in the carrier gas of the SIFT-MS instrument is described in terms of its changing flow rate as the pressure in the sealed container decreases during the sampling procedure. It is shown that the best analytical procedure is to determine the mean concentration of the trace gas in the liquid headspace over a given sampling time and relate this to the required concentration, which is the initial equilibrium concentration established before the pressure in the sealed container reduces significantly. To test the validity of this analytical approach, the headspace concentrations of acetaldehyde, ethanol and acetone above aqueous solutions of known concentrations have been determined. Hence, the Henry's Law constants for these compounds have been determined and found to agree with the published values. The confirmation of the quality of this sampling methodology combined with SIFT-MS for the analysis of volatile compounds in liquid headspace paves the way for the rapid analyses of biological liquids such as urine and serum for clinical diagnosis and physiological monitoring. 相似文献
108.
Following our recent observation that Pseudomonas bacteria in vitro emit hydrogen cyanide, we have found it necessary to investigate the ion chemistry of this compound and to extend the kinetics database for selected ion flow tube mass spectrometry (SIFT-MS) to allow the accurate quantification of HCN in moist air samples, including exhaled breath. Because of the proximity of the proton affinities of HCN and H2O molecules, the presence of water vapour can significantly distort HCN analysis in the presence of water vapour and a more sophisticated analytical procedure has to be developed. Thus, the reactions of H3O+(H2O)0,1,2,3 ions with HCN molecules have been studied in the presence of varying concentrations of water vapour, reactions on which SIFT-MS analysis of HCN relies. The results of these experiments have allowed an analytical procedure to be developed which has extended the kinetics database of SIFT-MS, such that HCN can now be quantified in humid air and in exhaled breath. 相似文献
109.
Hiroaki Tsuchiya Jan M. Macak Luciano Taveira Patrik Schmuki 《Chemical physics letters》2005,410(4-6):188-191
In the present work, we report formation of high aspect ratio zirconia nanotubes by electrochemical anodization of zirconium in a 1 M (NH4)2SO4 electrolyte containing 0.5 wt% NH4F. Highly self-organized zirconia nanotubes can be formed with a diameter of ≈50 nm and a length of ≈17 μm, i.e. with an aspect ratio of more than 300. The nanotubes show a distinct smooth and straight morphology. XRD investigation reveals that the nanotubes have a cubic crystalline structure directly after anodization, that is, without any further annealing. 相似文献
110.
It is shown that covalent bonding between high density polyethylene (HDPE) and glass spheres can have a significant influence on the stress relaxation behaviour and the creep properties of the corresponding composites at room temperature. The bonding is obtained by reacting the glass spheres with an azide functional alkoxysilane which is capable of bonding to the HDPE-chain. The internal stress, evaluated from relaxation experiments, increased markedly as a result of this treatment, and it is suggested that the internal stress level reflects the properties of the interphase region between the filler and the bulk matrix and its effect on the viscoelastic properties. 相似文献