Improving the performance of the two-rate parameter by use of the integrating ratemeter and temporal optimization

The integrating ratemeter is used in concert with the two-rate parameter to form the integrating ratemeter two-rate parameter. Propagation of error theory is applied to the integrating ratemeter two-rate parameter to yield expressions for the precision of rates calculated from the integrating ratemeter two-rate parameter in terms of the precision of the rates measured with the integrating ratemeter. Simulations and experimental results show that in cases where the standard deviation of the rate is relatively constant, the optimum time to make a rate measurement using the integrating ratemeter is also the optimum time to measure either of the rates in the two-rate parameter. If either of the two rates comprising the two-rate parameter is measured at the optimum time, then the precision and accuracy of concentrations measured with this technique are optimized.     

Evaluation of ratemeters: application to an improved fixed-time instrument

Procedures and instrumentation for the evaluation of reaction ratemeters are discussed and applied to an improved fixed-time reaction ratemeter which employs digital integration. The improved ratemeter is compared with similar systems described previously. A procedure which allows evaluation of the computation circuitry with real noise from the reaction monitor is developed; this new procedure provides a much better evaluation of how the ratemeter will perform in real rate measurement situations. Results presented for synthetic slopes with and without artificial noise show typical relative standard deviations and relative errors of less than 0.3 %. However, with a significant amount of real noise, the precision of rate measurements is reduced.     

Investigation of leaching of an antifouling agent from marine paint formulations using radiotracer technique

A radiotracer technique was used to investigate the leaching of an antifouling agent from different marine paint formulations with an objective to select the best paint formulation for bulk production. The antifouling agent (Diuron) itself was labeled with carbon-14 (half-life: 5,730?years, ??-energy: 156?keV) and used as a radiotracer. The different paint formulations added with radiolabeled Diuron were applied onto suitably selected substrates and measured for initial intensity of ??-radiation using a Geiger-Muller detector connected to a ratemeter. The painted substrates were subjected to shower tests for a pre-decided time and subsequently measured for ??-radiations. The comparison of intensity of ??-radiations in substrates prior and post shower tests provides information about leaching of antifouling agent Diuron from the paint formulation. The high leaching percentage of antifouling agent Diuron post shower tests indicates non-suitability of paint formulation for marine and civil structures. However, low leaching rate of Diuron will make a paint formulation more efficient and suitable. Based on the results of investigation, a paint formulation with minimum leaching rate was identified and selected for bulk production by a paint company.     

Design and fabrication of an ultraviolet photoelectron spectrometer for the study of free molecules

An ultraviolet photoelectron spectrometer for the study of free atoms and molecules has been designed and fabricated with indigeneous components. The spectrometer consists of a 100 mA HeI discharge lamp, 180° hemispherical electron energy analyser (127 mm mean dia) and electron multiplier ratemeter electron detection systems. The resolution of the spectrometer is 90 meV/and the intensity of N₂ (5σ) band is 10⁵ c/sec. The sample inlet and the collision chamber can be heated to 500 K so that solids of low vapour pressure can be studied. Typical spectra of molecules recorded with the instrument are shown. Contribution No. 373 from the Solid State and Structural Chemistry Unit.     

Molecular dynamics at low time resolution

The internal dynamics of macromolecular systems is characterized by widely separated time scales, ranging from fraction of picoseconds to nanoseconds. In ordinary molecular dynamics simulations, the elementary time step Δt used to integrate the equation of motion needs to be chosen much smaller of the shortest time scale in order not to cut-off physical effects. We show that in systems obeying the overdamped Langevin equation, it is possible to systematically correct for such discretization errors. This is done by analytically averaging out the fast molecular dynamics which occurs at time scales smaller than Δt, using a renormalization group based technique. Such a procedure gives raise to a time-dependent calculable correction to the diffusion coefficient. The resulting effective Langevin equation describes by construction the same long-time dynamics, but has a lower time resolution power, hence it can be integrated using larger time steps Δt. We illustrate and validate this method by studying the diffusion of a point-particle in a one-dimensional toy model and the denaturation of a protein.     

Optical Study of Interactions of Glass Beads ER Particles

The amount of ER effect is determined by the difference of dielectric constants of ER particles base liquid.The intensity of ER fluids can be characterized by the interaction of two particles. A double optical tweezers system suitable to study particle interaction is used to measure the particle aggregation time, and it is found that the particle aggregation time is proportional to the square of the electric field. This is the first time to directly measure the interaction of the electric dipoles of ER particles. A method is developed to use high speed CCD in measuring diffusing-wave spectroscopy (DWS), and, for the first time, the auto-correlation functions of nonegordic system of particle structure are measured to study the ER mechanism. Structure response time and force response time are obtained for glass beads ER fluid, and the time variation of characteristic decay times of system correlation functions under different electric fields is also measured. Diffusing coefficients under different fields imply that the interaction is proportional to the square of fields.     

Electronic decoherence time for non-Born-Oppenheimer trajectories

An expression is obtained for the electronic decoherence time of the reduced density electronic matrix in mixed quantum-classical molecular-dynamics simulations. The result is obtained by assuming that decoherence is dominated by the time dependence of the overlap of minimum-uncertainty packets and then maximizing the rate with respect to the parameters of the wave packets. The expression for the decay time involves quantities readily available in non-Born-Oppenheimer molecular-dynamics simulations, and it is shown to have a reasonable form when compared with two other formulas for the decay time that have been previously proposed.     

Rupture of thin stagnant films on a solid surface due to random thermal and mechanical perturbations

A generalized formalism for the rupture of a nondraining thin film on a solid support due to imposed random thermal and mechanical perturbations, modeled as a Gaussian white noise, is presented. The evolution of amplitude of perturbation is described by a stochastic differential equation. The average film rupture time is the average time for the amplitude of perturbation to equal to the film thickness and is calculated by employing a first passage time analysis for different amplitudes of imposed perturbations, wavenumbers, film thickness, van der Waals and electrostatic interactions and surface tensions. The results indicate the existence of an optimum wavenumber at which the rupture time is minimum. A critical film thickness is identified based on the sign of the disjoining pressure gradient, below which the film is unstable in that the rupture time is very small. The calculated values of rupture time as well as the optimum wavenumber in the present analysis agree well with the results of linear stability analysis for immobile as well as completely mobile gas-liquid film interfaces. For stable films, the rupture time is found to increase dramatically with film thickness near the critical film thickness. As expected, the average rupture time was found to be higher for smaller amplitudes of imposed perturbations, larger surface potentials, larger surface tensions and smaller Hamaker constants.     

Aerosol deposition in furnace atomization

A novel approach to sample deposition in furnace atomization is suggested, which obviates the need for skilled application of microvolumes by syringe. The analyte in aerosol form is deposited under controlled conditions on the internal surface areas of graphite furnaces. Precision approaching that of flame atomization systems is achieved and at the same time, concentrational sensitivity may be increased simply by extending the deposition time. The amount of analyte deposited in the furnace is restricted only by the sample volume available and the matrix concentration. A single standard can be used to construct a calibration curve by simply varying the aerosol deposition time.     

Numerical simulation of phase separation of immiscible polymer blends on a heterogeneously functionalized substrate

The spinodal phase decomposition of an immiscible binary polymer blend system is investigated with numerical models in two-dimensional and three-dimensional (3D). The effect of the elastic energy is included. The mechanism of the evolution of the phase separation is studied and the characteristic length R(t) is shown to be proportional to t(13). In the case when the phase separation is directed by a heterogeneously functionalized substrate, the increase in the characteristic length is divided into two stages by a critical time. The R(t) approximately t(13) diagram can be fitted with a straight line in both the first and second stages. The slope of the fitting line significantly decreases after the critical time. The compatibility of the resulting pattern to the substrate pattern is also measured by a factor C(S). It is observed that there is also a critical time in the evolution of the compatibility for the cases with and without elastic energy. The critical time of C(S) is identical with the respective critical time of R(t). The lateral and vertical composition profiles functionalized substrate is observed with the 3D model. The difference mechanism of the cases with and without elastic energy is discussed.     

Retention time and effective separation factor in series-coupled columns with different stationary phases

Basic expressions are derived for both the retention time and the effective separation factor in serially coupled GC columns. The retention time is determined by two main parameters. The first is the fractional time spent by an unretarded solute in each column which, in turn, is determined by the relative column lengths and flow velocities through each column. The second parameter is the relative mass distribution coefficient of a particular solute in each column; a variable that can be adjusted by changing the relative temperatures of the columns. The expression for the effective separation factor relates the measured separation factor for the series combination to the separation factors on the individual columns, the fractional time spent by an unretarded peak in each column, as well as the relative values of the mass distribution coefficients of a particular solute on the different columns.     

Formulation approach for nicorandil pulsatile release tablet

The purpose of this study was to obtain a nicorandil pulsatile release tablet that has a well-regulated release lag time. When nicorandil is used as an antiangina drug, administration time control is important. A pulsatile release tablet is one of the effective approaches to modified release to reduce daily administration frequency. In this study, a pulsatile release tablet of nicorandil was formulated by fumaric acid dry coating around the core tablet including nicorandil. The model tablets, which had different content ratios of excipients in the dry-coating layer, were characterized by a dissolution test. The results showed that the release lag time was generated with fast release profiles. Various lag time controls of tablets were achieved, from 60 to 310 min on average, by variation of outer layer composition. From an analysis of the relation between lag times and outer layer composition, the key ingredient for prolongation of lag time was found to be fumaric acid. To analyze the lag time generation mechanism, water penetration for tablet was measured. The results indicated that the penetration depth was proportionate to the square root of time and the lag time formation mechanism was simple water penetration through the matrix of fumaric acid to the tablet core. The results also showed that the Washburn equation could be used to design the lag time of the pulsatile release tablet in this study. In conclusion, novel release control technology using fumaric acid was appropriate to obtain a nicorandil pulsatile release tablet that has well regulated lag time.     

Transient and athermal effects in the crystallization of polymers. I. Isothermal crystallization

The isothermal crystallization of poly(propylene) and poly(ethylene terephthalate) was investigated with differential scanning calorimetry and optical microscopy. It was found that the induction time depends on the cooling rate to a constant temperature. The isothermal crystallization of the investigated polymers is a complex process and cannot be adequately described by the simple Avrami equation with time‐independent parameters. The results indicate that crystallization is composed of several nucleation mechanisms. The homogeneous nucleation occurring from thermal fluctuations is preceded by the nucleation on not completely melted crystalline residues that can become stable by an athermal mechanism as well as nucleation on heterogeneities. The nucleation rate depends on time, with the maximum shortly after the start of crystallization attributed to nucleation on crystalline residues (possible athermal nucleation) and on heterogeneities. However, the spherulitic growth rate and the exponent n do not change with the time of crystallization. The time dependence of the crystallization rate corresponds to the changes in the nucleation rate with time. The steady‐state crystallization rate in thermal nucleation is lower than the rate determined in a classical way from the half‐time of crystallization. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1835–1849, 2002     

Observation of slow charge redistribution preceding excited-state proton transfer

The photoacid 8-hydroxy-N,N,N',N',N',N'-hexamethylpyrene-1,3,6-trisulfonamide (HPTA) and related compounds are used to investigate the steps involved in excited-state deprotonation in polar solvents using pump-probe spectroscopy and time correlated single photon counting fluorescence spectroscopy. The dynamics show a clear two-step process leading to excited-state proton transfer. The first step after electronic excitation is charge redistribution occurring on a tens of picoseconds time scale followed by proton transfer on a nanosecond time scale. The three states observed in the experiments (initial excited state, charge redistributed state, and proton transfer state) are recognized by distinct features in the time dependence of the pump-probe spectrum and fluorescence spectra. In the charge redistributed state, charge density has transferred from the hydroxyl oxygen to the pyrene ring, but the OH sigma bond is still intact. The experiments indicate that the charge redistribution step is controlled by a specific hydrogen bond donation from HPTA to the accepting base molecule. The second step is the full deprotonation of the photoacid. The full deprotonation is clearly marked by the growth of stimulated emission spectral band in the pump-probe spectrum that is identical to the fluorescence spectrum of the anion.     

Particle tracking microrheology of lyotropic liquid crystals

We present comprehensive results on the microrheological study of lyotropic liquid crystalline phases of various space groups constituted by water-monoglyceride (Dimodan) mixtures. In order to explore the viscoelastic properties of these systems, we use particle tracking of probe colloidal particles suitably dispersed in the liquid crystals and monitored by diffusing wave spectroscopy. The identification of the various liquid crystalline phases was separately carried out by small-angle X-ray scattering. The restricted motion of the particles was monitored and identified by the decay time of intensity autocorrelation function and the corresponding time-dependent mean square displacement (MSD), which revealed space group-dependent behavior. The characteristic time extracted by the intersection of the slopes of the MSD at short and long time scales, provided a characteristic time which could be directly compared with the relaxation time obtained by microrheology. Further direct comparison of microrheology and bulk rheology measurements was gained via the Laplace transform of the generalized time-dependent MSD, yielding the microrheology storage and loss moduli, G'(ω) and G'(ω), in the frequency domain ω. The general picture emerging from the microrheology data is that all liquid crystals exhibit viscoelastic properties in line with results from bulk rheology and the transition regime (elastic to viscous) differs according to the specific liquid crystal considered. In the case of the lamellar phase, a plastic fluid is measured by bulk rheology, while microrheology indicates viscoelastic behavior. Although we generally find good qualitative agreement between the two techniques, all liquid crystalline systems are found to relax faster when studied with microrheology. The most plausible explanation for this difference is due to the different length scales probed by the two techniques: that is, microscopical relaxation on these structured fluids, is likely to occur at shorter time scales which are more suitably probed by microrheology, whereas bulk, macroscopic relaxations occurring at longer time scales can only be probed by bulk rheology.     

Determination of ageing time of spirits in oak barrels using a headspace–mass spectrometry (HS-MS) electronic nose system and multivariate calibration

The aromatic composition of sugar cane spirits and, in general, of alcoholic beverages, is mainly influenced by the ageing process in wood barrels. There are several factors that affect the quality of the final aged product, but the time of the storage in the barrel is perhaps the most important one. Ageing time must therefore be controlled in order to detect counterfeits; however, this parameter is very difficult to control and, at present, there is no analytical method available to determine it. We propose a quantitative method for determining the ageing time of sugar cane spirits in oak barrels by using an electronic nose based on coupling directly a headspace sampler to a mass spectrometer (HS-MS), and multivariate calibration. The method developed is simple and provides, in 5 min, the ageing time of spirits with an accuracy of about 1 month.     

Transient response of a Brownian particle with general damping

We study the transient response of a Brownian particle with general damping in a system of metastable potential well. The escape rate is evaluated as a function of time after an infinite wall is removed from the potential barrier. It takes a relaxation time for the rate to reach its limit value and this rate relaxation time differs from the relaxation time of the majority of the probability around the bottom of the potential well. The rate relaxation time is found to depend on the temperature as well as the damping constant. It involves the diffusion time and the instanton time, in general agreement with recent studies of the overdamped case by Bier et al. [Phys. Rev. E 59, 6422 (1999)].     

Change in infrared dichroism during and following high-speed elongation of polyethylene

Use of a new apparatus is described which enables infrared dichroism to be followed as a function of time following the rapid stretching of a sample. The apparatus is double beam in dichroism, in that the infrared beam is alternately polarized parallel and perpendicular to the stretching direction and the transmitted intensity is observed on an oscilloscope. Results are presented for the stretching of a low-density polyethylene sample by approximately 28% in a time of approximately 0.1 sec. The infrared dichroism is observed to change in times of the order of 50 to 100 msec after stretching, confirming the observation made by other techniques that crystal orientation changes during this time.     

High-speed peak matching algorithm for retention time alignment of gas chromatographic data for chemometric analysis

A rapid retention time alignment algorithm was developed as a preprocessing utility to be used prior to chemometric analysis of large datasets of diesel fuel profiles obtained using gas chromatography (GC). Retention time variation from chromatogram-to-chromatogram has been a significant impediment against the use of chemometric techniques in the analysis of chromatographic data due to the inability of current chemometric techniques to correctly model information that shifts from variable to variable within a dataset. The alignment algorithm developed is shown to increase the efficacy of pattern recognition methods applied to diesel fuel chromatograms by retaining chemical selectivity while reducing chromatogram-to-chromatogram retention time variations and to do so on a time scale that makes analysis of large sets of chromatographic data practical. Two sets of diesel fuel gas chromatograms were studied using the novel alignment algorithm followed by principal component analysis (PCA). In the first study, retention times for corresponding chromatographic peaks in 60 chromatograms varied by as much as 300 ms between chromatograms before alignment. In the second study of 42 chromatograms, the retention time shifting exhibited was on the order of 10 s between corresponding chromatographic peaks, and required a coarse retention time correction prior to alignment with the algorithm. In both cases, an increase in retention time precision afforded by the algorithm was clearly visible in plots of overlaid chromatograms before and then after applying the retention time alignment algorithm. Using the alignment algorithm, the standard deviation for corresponding peak retention times following alignment was 17 ms throughout a given chromatogram, corresponding to a relative standard deviation of 0.003% at an average retention time of 8 min. This level of retention time precision is a 5-fold improvement over the retention time precision initially provided by a state-of-the-art GC instrument equipped with electronic pressure control and was critical to the performance of the chemometric analysis. This increase in retention time precision does not come at the expense of chemical selectivity, since the PCA results suggest that essentially all of the chemical selectivity is preserved. Cluster resolution between dissimilar groups of diesel fuel chromatograms in a two-dimensional scores space generated with PCA is shown to substantially increase after alignment. The alignment method is robust against missing or extra peaks relative to a target chromatogram used in the alignment, and operates at high speed, requiring roughly 1 s of computation time per GC chromatogram.     

Light-scattering studies of phase-demixing of polystyrene/poly(o-chlorostyrene) blends

The phase separation of blends of polystyrene and poly(o-chlorostyrene) has been studied by observing the changing small-angle light-scattering profile with time. As a blend is heated to a temperature at which it undergoes phase separation, a light-scattering maximum is observed which grows in intensity and moves to smaller angles with time. This maximum is associated with a characteristic spacing which increases at a rate which becomes greater at higher temperature or with lower molecular weight. This spacing varies with a power of time as might be expected for domain growth occurring by a viscous flow mechanism. The integrated scattering intensity (invariant) is found to increase initially with time and then remain constant, as is characteristic of phase separation followed by phase ripening.