Embedded diagonally implicit Runge–Kutta–Nystrom 4(3) pair for solving special second-order IVPs

In this paper, third-order 3-stage diagonally implicit Runge–Kutta–Nystrom method embedded in fourth-order 4-stage for solving special second-order initial value problems is constructed. The method has the property of minimized local truncation error as well as the last row of the coefficient matrix is equal to the vector output. The stability of the method is investigated and a standard set of test problems are tested upon and comparisons on the numerical results are made when the same set of test problems are reduced to first-order system and solved using existing Runge–Kutta method. The results clearly shown the advantage and the efficiency of the new method.     

Ab initio and variational transition state approach to beta-C3N4 formation: kinetics for the reaction of CH3NH2 with H

The CH3NH2 molecule has been considered as either an important intermediate in methane and ammonia mixtures or a precursor in methylamine and hydrogen mixtures in the synthesis of carbon nitride thin films. The fast Hydrogen (H) abstraction from CH3NH2 is an important process involved in the formation of HCN or CNH in the chemical vapor deposition (CVD) of carbon nitride thin films. The energetic and kinetic characteristics of the H abstraction reaction from CH3NH2 by atomic H used in CVD of beta-C3N4 were studied using ab initio direct dynamics methods for the first time. Two primary processes were identified for this reaction: H abstraction from the CH3 group and H abstraction from the NH2 group. On the basis of ab initio data, the rate constants of each channel have been deduced by canonical variational transition state theory with small-curvature tunneling correction over a wide temperature range of 200 to approximately 3000 K. The theoretical results were compared with available experimental data.     

热致型液晶聚合物的等温和非等温晶化动力学

利用等温和非等温方法详细研究了芳香族聚酯──热致型聚合物对，对’－联苯二甲酸二辛酯的结晶相和液晶相形成机理，并计算了相变过程中的表面自由能与温度系数，研究结果表明：从介晶相开始的结晶过程是二维异相成核、三维线性增长的，而从各向同性液相开始的液晶相形成过程则是二维异相成核二维线性增长的．对两个晶化过程的表面自由能的研究表明，该聚合物液晶相形成过程的相转变表面自由能比结晶过程小得多，预示了它将具有更大的晶化速率．研究还发现，该聚合物的液晶相形成过程具有比结晶过程大得多的温度敏感性．     

Cohesive energy densities of polyethers: Poly(hexamethylene oxide)

The solubility parameter of poly(hexamethylene oxide) has been estimated by measuring solution viscosities and by turbidimetric titrations in a series of solvents. From both experimental methods, a value of $\text{δ}{}_{\mathrm{<mtext>p</mtext>}}\text{= 33.9}\text{J}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{cm}{}^{\mathrm{<mtext>?3</mtext><mtext>2</mtext>}}$ ($\text{8.1}\text{cal}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{cm}{}^{\mathrm{<mtext>?3</mtext><mtext>2</mtext>}}$) was obtained, whence the cohesive energy density is 274.5 J cm^?3 (65.6 cal cm^?3). These experimental values are compared with those calculated by empirical methods.     

Crystallization kinetics of the monoclinic modification of poly(3,3-dimethyl oxetane)

Poly(3,3-dimethyl oxetane) fractions ranging in number average molecular weights from 18500 to 130000 have been isothermally crystallized from the relaxed melt state in the temperature range from 12 to 44 °C, where only the monoclinic modification is formed. The influence of molecular weight and undercooling in crystallization kinetics has been analyzed. The level of crystallinity is very slightly dependent on molecular weight but the influence of this parameter on the time scale of the crystallization is relatively pronounced. The crystallization temperature coefficient was determined and it was found a constant value of the product of the interfacial energies in the range of molecular weights which has been analyzed. Growth rate measurements were carried out for fraction ¯M _n=130000 and it was found that the temperature coefficients for overall and growth rates are equal. Finally, the comparison of the experimental results for this polymer with those reported for poly(oxetane) shows two main differences: first, the crystallization rate is slower for poly(3,3-dimethyl oxetane) and second, the temperature coefficient is smaller for this polymer.     

A coated piezoelectric crystal detector for phosgene

A piezoelectric quartz crystal coated with methyltrioctylphosphonium dimethylphosphate was found to be a good detector for phosgene in air. The coating is sensitive to phosgene in the μg 1^?1 range and has a reasonably long lifetime. The response curve is linear over the concentration range 5–140 μg 1^?1. The coated crystal can be used for more than six weeks without significant loss in sensitivity, provided that high ammonia concentrations are not encountered.     

Steady-state heat transfer and thermal zone spreading in gel isoelectric focusing.

The zone spreading caused by a transverse pH profile due to a temperature gradient through the thickness of a gel slab is estimated. The temperature difference (delta T) between the upper and lower gel surfaces can be calculated as a function of the electric power dissipated in the gel and the gel dimensions. It is found that when delta T is only 1 degree C the zone spreading due to this thermal excursion is as high as 0.5 mm. Thus, an admissible delta T is found to be equal to 0.2 degrees C, since this corresponds to a thermal zone spreading of only 0.1 mm, i.e. the same order of magnitude as the spatial resolution of a laser scanner. A thermal zone spreading of 0.1 mm is compatible with a resolving power of 0.01 pH unit, the current limit of conventional isoelectric focusing in amphoteric buffers. A requirement for the thickness of a gel slab is formulated: e.g., at 40 W applied power (over a gel surface area of 25 x 11 cm), a thermal zone spreading limited to 0.1 mm can only be obtained with a gel thickness of approximately 170 microns.     

A piezoelectric immunosensor for the detection of cortisol

A piezoelectric crystal immunosensor has been developed for the detection and determination of cortisol. Cortisol antibody was layered onto the gold electrodes of a 10 MHz piezoelectric crystal which was pre-coated with either protein A or gluteraldehyde. Crystals pre-coated with protein A showed the best results with respect to stability and sensitivity. The sensor was successfully used for the determination of cortisol in standard solutions from 36-3628 micrograms/L (part per billion). The advantages of the proposed sensor include simplicity, short analysis time, cost effectiveness and selectivity. The results demonstrate the feasibility of cortisol assay in clinical testing and in drug monitoring.     

Stability-indicating high-performance liquid chromatographic assay for the determination of metoclopramide hydrochloride in pharmaceutical dosage forms

A simple, reliable and selective high-performance liquid chromatographic method for the determination of metoclopramide hydrochloride in pharmaceutical dosage forms has been developed and evaluated. The drug and the internal standard (phenobarbitone) were eluted from a 5-micron C8 reversed-phase column at ambient temperature with a mobile phase consisting of phosphate buffer (10 mM)-methanol-acetonitrile (50 + 28 + 22) adjusted to pH 4.8 with orthophosphoric acid. The mobile phase was pumped at a flow-rate of 1.5 ml min-1 and the effluent was monitored spectrophotometrically at 214 nm. The retention times of the internal standard and metoclopramide hydrochloride were 3.0 and 7.5 min, respectively. Quantification was achieved by measuring the peak-height ratio of the drug to the internal standard. A linear relationship was found over the range 1-10 micrograms ml-1. Within-day coefficients of variation (CVs) ranged from 0.50 to 1.70% and between-day CVs from 0.68 to 4.07% at three different concentrations. The developed procedure was compared with the current BP method for the assay of metoclopramide hydrochloride in tablets. The proposed method was also used to study the stability of metoclopramide hydrochloride.     

Nanometer-sized zirconium dioxide microcolumn separation/preconcentration of trace metals and their determination by ICP-OES in environmental and biological samples

A new method is proposed using a microcolumn (20 mm × 2.0 mm) packed with nanometer-sized zirconia as solid-phase extractor for the separation/preconcentration of Mn, Cu, Cr, Zn, Ni and Co prior to their determination by inductively coupled plasma optical emission spectrometer (ICP-OES) in environmental samples. The factors affecting the separation and preconcentration of analytes such as pH, sample flow rate and volume, eluent concentration and volume were determined, interfering ions were studied, and the optimal experimental conditions were established. The adsorption capacity of nanometer-sized ZrO₂ for Mn, Cu, Cr, Zn, Ni and Co was found to be 1.3, 1.3, 1.7, 2.0, 3.9 and 1.5 mg g⁻¹, respectively. The detection limits of the method were 12, 58, 24, 2, 7 and 36 ng L⁻¹, respectively, with a preconcentration factor of 25. The precision of this method was 1.7% (Mn), 2.9% (Cu), 5.9% (Mn), 3.8% (Mn), 6.2% (Mn) and 4.3% (Mn) with 9 determinations of 10 ng mL⁻¹ of target analytes, respectively. The method was successfully applied to the determination of trace metals in lake water, dried fish samples, certified reference materials of human hair and milk, and provided satisfactory results.