Fractal models of the shrinkage compensation mechanism for unsaturated polyesters

The shrinkage compensation mechanism in sheet molding compounds is governed by the morphology resulting from phase separation and microvoids formation. The observed microvoid morphology is quantified by using fractal geometry, in 2D and 3D spaces. The correlation between the morphologies of the matrix with phase separation and those of the microvoids is demonstrated by simulation. The pressure effect is studied. The fact that the shrinkage compensation has a pressure dependent optimum is explained by a model for the compensated volume. Thus, the “fractal pillar effect” is a model that represents properly speaking the compromise between pressure and volume creation shown by such a smart material.     

Development of high-temperature pulsed slit nozzle and its application to supersonic jet absorption spectrometry

A high-temperature pulsed slit nozzle, consisting of a circular pulsed nozzle and an interface to convert a circular flow into a slit flow has been constructed. The absorption spectrum is measured by scanning the wavelength of the monochromator equipped with a xenon arc lamp and by detecting the transmitted light through a jet with a photomultiplier. A rotationally cooled spectrum is clearly observed for aniline only when a long slit nozzle is employed. The absorptivity increases proportionally to the slit length at least up to 6 cm. The time for recording a spectrum is 3.5 min, which is reduced to several seconds by transmitting a white light through a jet and by measuring the spectrum with an optical multichannel analyzer. The detection limit is estimated to a partial vapor pressure of 0.4 torr for aniline. The present system can be conveniently used in routine analysis, because of a wide spectral coverage of the lamp source.     

A theory of measurement with applications to spectrometry

An analytic function operating on experimental data is optimized for making the most accurate measurement of a parameter of the expected data, under the conditions of non-stationary shot noise. The value of the parameter is obtained by equating the operation on experimental data with the same operation on the expected data which contains the parameter as an unknown value. If the operation is represented by a weighting function, the form of the optimum weighting function depends on the initial transformation of the experimental data by the measuring instrument. The optimum weighting function always contains the derivative of the expected signal with respect to the unknown parameter, divided by the time-dependent variance of the received signal. Weighting functions for the logarithmic output of a spectrophotometer are described. The superiority over least-squares curve-matching is shown. A method for determination of peak position by optimum slope measurement is derived. In general, the optimum weighting function is not a matched filter. The optimum result is the same for center-of-gravity measurements. The optimum parameter measurement is equivalent to a least-squares error minimization weighted by the inverse variance or mean-square noise level. This variance weighting is significant in photometric measurements limited by shot noise or other measurements described by Poisson statistics, such that the mean-square noise level varies with time. The form of the optimum filter, for non-white, non-stationary noise is derived.     

An automated submicrogram determination of selenium in vegetation by quartz-tube furnace atomic-absorption spectrophotometry

An automated method for the determination of submicrogram amounts of selenium in vegetation is described. A weighed sample of vegetation is digested with a 4:1 nitric-perchloric acid mixture, and made up to a known volume. The digested sample is placed in a Technicon sampler and reacted with sodium borohydride solution. The selenium converted into the gaseous hydride is swept by an argon stream into a gas-liquid separator. The mixed gas stream is passed through a heated quartz cell, positioned in the light-path of an atomic-absorption spectrophotometer. The absorption by the atomized selenium is recorded. The method is capable of analysing 50 samples a day by the use of a calibration curve or 25 a day by the standard addition technique. A relative standard deviation of better than 10% and a detection limit of 0.025 microg/g were obtained.     

Spontaneous curvature induced shape transformations of tubular polymersomes

The behavior of tubular polymersomes is investigated within the framework of the elastic energy model. The transition from a cylindrical tube to a chain of beads connected by small necks is studied in detail. The evolution of a polymersome shape, resulting from a change of the temperature is modeled by the shape transformations caused by a change of the spontaneous curvature. Good agreement between the experiments and the theoretical calculations is found.     

Prediction of chemical structure of aromatic hydrocarbons by pattern recognition of spectral lines obtained by fluorescence spectrometry in a supersonic jet

A technique based on pattern recognition of data obtained by supersonic jet spectrometry is employed for the prediction of chemical structure. The degree of similarity is evaluated quantitatively by calculating a cross correlation factor between sample and reference molecules. A probability density function is determined by fitting the data to a specified equation. The functional group and its position are also predicted by a similar technique. The pattern recognition provides a method for prediction of the chemical structure and is applicable to samples that have not been examined by supersonic jet spectrometry.     

Calculation and optimization of sample identification by laser induced breakdown spectroscopy via correlation analysis

Linear correlation analysis may be used as a technique for the identification of samples with a very similar chemical composition by laser induced breakdown spectroscopy. The spectrum of the “unknown” sample is correlated with a library of reference spectra. The probability of identification by single shot analysis can be estimated by the method described in this paper. When a right identification is not obtained by single shot correlation analysis the accuracy can be increased by averaging spectra or by averaging the correlation coefficients. The number of spectra or correlation coefficients to be averaged to obtain a 99.9% right identification is evaluated. We found out that the number of spectra to be averaged is equal to the number of correlation coefficients to be averaged. The benefit of using averaged spectra over averaging correlation coefficients is a faster calculation.     

Influence of spontaneous curvature and microtubules on the conformations of lipid vesicles

The conformations of vesicles deformed by microtubules are studied within the framework of the curvature energy. The phenomenon in which the destruction of a microtubule is followed by the formation of peristaltic shapes on a protrusion created by the microtubule is investigated. The influence of the spontaneous curvature on the conformations of vesicles is examined, and the results are compared to existing experiments. The elastic properties of a vesicle deformed by the microtubule are studied.     

Thermocrystallization flow of nonfreezing water films on the surface of capillaries

The rates of mass transfer under the influence of a temperature gradient between the menisci of ice in a thin quartz capillary are measured. The mass transfer rate is determined by the diffusion of vapor and by the flow of a nonfrozen polymolecular adsorption film over the capillary surface. It is shown that the flow of the film is attributable neither to the thermoosmotic nor to the thermocapillary flow. The flow rate of a nonfrozen film is well described by a thermocrystallization transfer equation derived earlier, the thermocrystallization transfer being controlled by the water-ice phase transition heat.     

Optimal control simulation of the Deutsch-Jozsa algorithm in a two-dimensional double well coupled to an environment

The quantum Deutsch-Jozsa algorithm is implemented by using vibrational modes of a two-dimensional double well. The laser fields realizing the different gates (NOT, CNOT, and HADAMARD) on the two-qubit space are computed by the multitarget optimal control theory. The stability of the performance index is checked by coupling the system to an environment. Firstly, the two-dimensional subspace is coupled to a small number Nb of oscillators in order to simulate intramolecular vibrational energy redistribution. The complete (2+Nb)D problem is solved by the coupled harmonic adiabatic channel method which allows including coupled modes up to Nb=5. Secondly, the computational subspace is coupled to a continuous bath of oscillators in order to simulate a confined environment expected to be favorable to achieve molecular computing, for instance, molecules confined in matrices or in a fullerene. The spectral density of the bath is approximated by an Ohmic law with a cutoff for some hundreds of cm(-1). The time scale of the bath dynamics (of the order of 10 fs) is then smaller than the relaxation time and the controlled dynamics (2 ps) so that Markovian dissipative dynamics is used.     

The propagation of radiation through a medium containing a component that absorbs the radiation and is steadily destroyed by it

The Beer–Lambert law is inadequate to describe the absorption of radiation by a medium if the absorbing component is being simultaneously destroyed by the radiation. A replacement law is derived and solved in terms of a family of polynomials. The solution is confirmed numerically and by simulation.     

Modeling the Electrochemical Response of Mesoporous Materials Toward Its Application to Biomolecular Detection

The performance of an electrochemical sensor based on the ability of a probe to cross a mesoporous membrane partially blocked by an analyte is predicted using a numerical model. The system comprehends a membrane placed close to the working electrode and the signal is generated by applying square wave voltammetry. The digital simulation allows comparing the responses for different situations regarding the way in which the membrane is blocked by the sample. The developed model is compared with experimental results. The effect of the sizes of the pore, analyte and probe on the system response is evaluated.     

天然水中硫酸根的交流示波极谱滴定

在NH_4Ac溶液中加入标准Ba~(2+)溶液沉淀SO_4~(2-)用标准K_2CrO_4溶液滴定过量Ba~(2+)。过量的CrO_4~(2-)在交流示波极谱图上出现切口指示终点,间接求出天然水中SO_4~(2-)含量。     

The Role of Viscoelastic Adhesive Contact in the Sintering of Polymeric Particles

The sintering of polymeric particles is analyzed by considering the growth of contact between viscoelastic spheres driven by adhesive intersurface forces. This process is dominant during the initial phase of sintering and is succeeded by a viscous sintering step that is driven by surface tension and accommodated by viscous flow. The intersurface forces in this work are described by a cohesive zone model. A new formulation of adhesive contact that does not require the cohesive zone to be smaller than the contact radius, together with finite element simulations is used to study the growth of contact. The results of this paper establish conditions that determine the dominant mechanism of contact growth during sintering. These conditions are described using a "deformation map". For a Maxwell material, if particle radius R(max),相似文献   

Baseline correction method for second-harmonic detection with tunable diode lasers

To measure small absorbances in tunable diode laser infrared spectrometry, second-harmonic detection is often used. The spectrum obtained is often used. The spectrum obtained is the sum of the desired molecular line profile, a contribution of the laser emission profile and various types of noise. It is shown that the undesired contributions can be reduced significantly by subtracting a least-squares fitted low-degree polynomial from the spectrum, followed by applying a digital low-pass filter to the remainder. A theory is developed for estimating the systematic error introduced by this procedure. The method is applied in a calibration experiment for nitrogen dioxide in air at low part-per-billion by volume levels.     

Atomabsorptionsspektrometrie durch Laserverdampfung mit nachfolgender elektrothermischer Atomisierung

The determination of trace elements in solid samples by the combination of laser-evaporation and flameless AAS is used. A ruby laser with passive Q-switch vaporizes microamounts of solids in a chamber. The solid aerosol is transported by an Ar gas flow into a hot graphite furnace, where the solid particles are atomized for the AA-measurement. The influence of the parameters of the laser and the flow rate of Ar is exemplified by a silver determination. Several problems connected with the use of standard powders in laser-AAS are discussed. The vaporization of solids by the laser is the reason for the poor standard deviation of the absorbance values. The analytical results reported here were obtained by the standard addition-technique.     

Specific determination of cysteine and penicillamine through cyclization to 2-thioxothiazolidine-4-carboxylic acids

A very simple and highly specific method for the determination of cysteine and penicillamine is presented. Treatment with 1,1'-thiocarbonyldiimidazole in slightly basic solutions converts cysteine rapidly and quantitatively to a very stable derivative, 2-thioxothiazolidine-4-carboxylic acid, which is not formed by thiols or amines. The cyclic derivative has a characteristic UV spectrum with a maximum at 272 nm and it can be quantified by one of two ways. (1) When only inorganic ions and common additives are present, a spectrophotometer or a plate reader capable of handling multiple samples is sufficient to estimate cysteine in the concentration range of 2-150 muM. Penicillamine is determined similarly by cyclization to 5,5-dimethyl-2-thioxothiazolidine-4-carboxylic acid. The method is also applicable to derivatives of cysteine modified only at the carboxyl group. (2) To determine cysteine in complex mixtures, a liquid chromatograph connected to a UV detector is used. The elution is rapid with well-separated peaks for the thiazolidine derivatives. The detection limit is 2 pmole of cysteine or penicillamine per injection and the detector response is linear up to 1 nmole. The usefulness of the method is demonstrated by determining cysteine and penicillamine in capsules and by measuring cysteine in a dietary supplement.     

A Total Synthesis of FK-506(1)

A total synthesis of FK-506 (1) is presented. The synthesis features a highly convergent approach utilizing a block coupling strategy. Top and bottom half sections of the molecule are coupled by addition of a vinyl cuprate with a spiroenone. The alpha-allyl aldol functionality is revealed by a reductive opening of the spiroenone system. The labile alpha,beta-diketoamide hemiketal portion of the molecule is prepared by a late stage generation and oxidation of a masked enediol. Top and bottom half segments are themselves derived by coupling of smaller subunits, resulting in a very convergent route.     

A novel study on CHEMCAD simulation of isopropyl alcohol dehydrogenation process development

Acetone is a product which is obtained via several processes. It is produced mainly by cumene hydroperoxide process. As an alternative process, acetone is obtained by isopropyl alcohol (IPA) dehydrogenation. The conversion of IPA to acetone is an endothermic gas-phase reaction which produces hydrogen as a byproduct. The process consists of an equilibrium reactor or kinetic reactor (EREA), a distillation column (SCDS), and a flash tank. As the fresh feed, liquid-phase IPA, combined with a recycle stream which contains slight amount of unseparated acetone, is vaporized and given into the equilibrium reactor. Reactor effluent is then cooled by two heat exchangers and pressurized by a compressor until unreacted IPA and formed acetone are liquidised. This stream is fed to a flash tank in order to separate the gas-phase hydrogen, which contains slight amount of acetone. The distillation column distinguishes the acetone from unreacted IPA. The distillate stream has an acetone purity over 99%. The bottoms stream, which consists of residual IPA and slight amount of acetone, is recycled back into the mixer. The purpose of this study is to improve the simulation of isopropyl alcohol (IPA) dehydrogenation process by using the ChemCad program in terms of industrial applications.