Parametric estimation of time-varying components using orthogonal bases

For nonstationary processes, classical frequency estimation methods are incapable of describing and showing the information embedded in the process. That is, because the statistical characteristics (SC) of the nonstationary processes are changing with time, estimation methods based on the stationarity assumption do not reflect this variation. Therefore, the idea of the time-frequency (TF) distribution has been introduced in the literature. Different methods for estimating the TF distribution (TFD) of a nonstationary process have also been proposed in the literature. All of these methods, however, depend on the degree of nonstationarity (DON) of the process, which, although of utmost importance, has not been yet addressed in the literature. In this paper, an algorithm for estimating the time-varying components (TVCs), and hence the TF kernel, of a non-stationary process by using orthogonal projection is proposed. The process is carried out by projecting each component of the process onto an expanding orthogonal basis. The TF kernel is then estimated with an order based on the dimensionality of the expanding orthogonal basis. Some experimental results are presented when the process has either single or multiple TVCs. This revised version was published online in June 2006 with corrections to the Cover Date.     

SPE-GC-MS for the Determination of Halogenated Acetic Acids in Drinking Water

The development and optimization of analytical methods for the better monitoring of disinfection by-products especially haloacetic acids in water are key step in order to estimate human exposure to such products after chlorination. A reliable and accurate analytical method is needed in order to reach the levels of concentration required by United States Environmental Protection Agency regulations. In this study a method was developed for determining halogenated acetic acids in drinking water, involving solid phase extraction, methylation derivatization, and GC-MS. The new SPE-GC-MS-SIM method is capable of analyzing all nine acids at extremely low μg L^–1 level. Run time is significantly reduced without compromising analytical results. The major advantages of the method are the simplicity of the chromatography, short run time and low detection limits. The method performance, limits of detection and spiking recovery were evaluated and the results proved that the accuracy and precision were good. This method outperforms previous GC-MS methods especially for the determination of dibromoacetic, dibromochloroacetic, dichlorobromoacetic and tribromoacetic acids. The method has been used to analyse domestic tap water and water samples collected at a local water treatment plant.

     

On the Fitting height of a soluble group that is generated by a conjugacy class of 3-elements (II)

Let G be a fnite group and P a subgroup of order 3. In this paper we proved some results about the soluble subgroups generated by three conjugates of P and we use these results to produce some properties of the group G.     

Thermodynamic properties of ethanol solution of chiral camphors and its derivatives

Enthalpies of mixing and the densities of ethanol solution of R- and S-enantiomers of camphor, 10-camphorsulfonamide, 10-camphorsulfonic acid, camphorquinone, and 10-camphorsulfonyl chloride have been measured for a wide range of mole fractions of heterochiral components at 298.15 K. Enthalpies of mixing were exothermic for all concentrations and heterochiral solutions were more stable than each of the homochiral solutions. Enthalpic stabilization of mixing of heterochiral solutions was increased with a decreasing concentration of all the camphor derivatives measured. The sequence of enthalpic stabilization on mixing was 10-camphorsulfonyl chloride, 10-camphorsulfonic acid, 10-camphorsulfonamide, camphor, and camphorquinone. Apparent molar volumes were determined and excess volumes of mixing of heterochiral solutions were small and negative. Enthalpic stabilizations were found to be dependent on dipole–dipole interaction between solutes and solvents.     

POOL — Listing service in game theory no. 17

POOL — Listing service in game theory no. 17     

Three-stage auto-ignition of n-heptane and methyl-cyclohexane mixtures at lean conditions in a flat piston rapid compression machine

One approach to enhancing the thermal efficiency of combustion systems is to burn fuels at ultra-lean conditions (equivalence ratio below 0.5). It has been recently reported that the auto-ignition of some hydrocarbon fuels, under specific temperature, pressure, and mixture conditions, releases heat in three distinctive stages. The three auto-ignition stages can be divided as a first low-temperature auto-ignition stage with conventional low temperature, and a high-temperature stage separated into two sub-stages. This study presents ignition delay time measurements of n-heptane and methyl-cyclohexane (MCH) mixtures in a flat piston rapid compression machine (RCM) under ultra-lean conditions. It provides experimental evidence of three-stage auto-ignition. This phenomenon of delayed high-temperature heat release is seldom reported in the literature and this is the first time to be reported for these types of fuels. The experiments cover two binary n-heptane/MCH mixtures of 15/85 and 70/30 by volume, pressures of 11 bar and 16 bar, temperature range of 700 to 900 K, and equivalence ratio of 0.4. The RCM optical access was utilized for high-speed chemiluminescence imaging. Detailed chemical kinetic simulations in a homogenous batch reactor with variable volume were conducted to further interrogate the three-stage auto-ignition phenomenon. Chemiluminescence shows that three-stage auto-ignition occurs in the adiabatically compressed end-gas, which indicates that this phenomenon is chemically-driven and is not induced by a thermal stratification in the RCM experiments. The model predicts the features of three-stage auto-ignition, which were experimentally observed at temperatures approximately below 750 K. As expected, significant discrepancies are observed in the ignition delays of experiment and simulation in the negative temperature coefficient (NTC) region. The simulation of the n-heptane/MCH 70/30 mixture shows better agreement with experiments in the Positive Temperature Coefficient (PTC) region compared to the 15/85 mixture.     

The influence of distal substitution on the base-induced isomerization of long-chain terminal alkynes

When compared to a long-straight chain terminal alkyne, a long chain terminal alkyne with a distal isopropyl unit (isobranched) isomerizes about two times faster when treated with strong base under identical conditions, and appears to follow pseudo first order kinetics. In both cases, equilibration to a 95–97:5–3 mixture of terminal:internal alkyne accompanies isomerization. The difference in rate may be due to an unusual folding of both long-chain alkynes, bringing the distal substituent close to the carbon-carbon-triple bond moiety. The distal isopropyl moiety may provide unanticipated steric hindrance that disrupts such folding, making the propargylic proton more available for reaction with base.     

THE DYNAMIC BUCKLING OF AN ORTHOTROPIC CYLINDRICAL THIN SHELL UNDER TORSION VARYING AS A POWER FUNCTION OF TIME

The subject of this investigation is to study the buckling of orthotropic cylindricalthin shells under torsion,which is a power function of time.The dynamic stability and compati-bility equations are obtained first.These equations are subsequently reduced to a time dependentdifferential equation with variable coefficient by using Galerkin's method.Finally,the critical dy-namic and static loading,the corresponding wave numbers,the dynamic factors,critical time andcritical impulse are found analytically by applying the Ritz type variational method.Using thoseresults,the effects of the variations of the power of time in the torsion load expression,of theloading parameter,the ratio of the Young's moduli and the ratio of the radius to thickness onthe critical parameters are studied numerically.It is observed that these factors have appreciableeffects on the critical parameters of the problem in the heading.