High strain rate fragmentation of liquid systems at atmospheric pressure

The fragmentation characteristics of liquid systems at atmospheric pressure has been investigated experimentally and compared to hydrodynamic calculations as well as theoretical predictions. The geometry is a one-dimensional (1-D) nylon flat plate impacting a flat plate liquid system at velocities of approximately 0.3 km/s. The experiments were conducted at the Marquette University's gas gun facility. Hydrocodes calculations were used to investigate early time shock evolution, material deformation and strain rate. High-speed photography and witness cards were used to capture the impact and fragmentation event as well as drop distributions. The experimental drop distributions are compared to distributions obtained from a Grady–Kipp (GK) fragmentation model. The liquid spall GK fragmentation model predicted the correct median drop size while the flow stress spall over predicted the median drop size. The standard GK Poisson drop distribution superimposed over the median drop size produces a distribution which is wider than the data obtained.     

Biopharmaceutical evaluation of diclofenac sodium controlled release tablets prepared from gum karaya--chitosan polyelectrolyte complexes

The phenomena of polymer interactions and formation of polyelectrolyte complexes (PECs) of oppositely charged polymers have been the focus of interest in fundamental and applied research. Such PECs may possess unique properties that are different from those of individual polymers. In the present study, attempts were made to prepare PECs of negative colloid gum karaya (GK) and positively charged polysaccharide chitosan (CH). The association and factors affecting the interactions between GK and CH were studied by pH and conductivity studies. The dried complexes were characterized by X-ray diffraction, Fourier transformed Infrared (FTIR) Spectroscopy, Scanning Electron Microscopy. The PECs were utilized for encapsulation of diclofenac sodium. Selected polyelectrolyte microparticles were compressed into tablets and were compared with commercial sustained release product Voveran SR?. Positive results of the study indicated the applicability of PECs in the design of oral controlled release drug delivery systems.     

可穿戴石墨烯复合材料压阻传感性能计算方法及其参数分析

随机堆叠石墨烯制成的石墨烯复合材料(GC)的不均匀性,使得GC的压阻传感性能与其细观单元的尺寸密切相关.根据GC的微观结构特点,发展了一种GC压阻传感性能计算方法,依次计算了GC的电子渗流概率、初始方阻和相对电阻-应变关系.结果 表明:GC的电子渗流概率随着石墨烯面分比的增大而增大,大长宽比石墨烯组成的GC的渗流阈值更...     

A unified set of resequencing algorithms

A general algorithm for resequencing equations and finite element meshes is presented. This algorithm incorporates, in a unified form, the most successful resequencing schemes, namely: the Sloan, Gibbs–King (GK) and Gibbs–Poole–Stockmeyer (GPS) algorithms. As well it provides a context within which the development of new algorithms may take place with a minimum of change. It is easily programmed and has been shown to speed up the execution of the original GK algorithm.     

Picogram level quantitation of 2,3,7,8-tetrachlorodibenzo-p-dioxin in fish extracts by capillary gas chromatography/matrix isolation/Fourier transform infrared spectrometry

For the first time, gas chromatography/matrix isolation/Fourier transform infrared spectrometry (GC/MI/FTIR) has been reported to confirm the identity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (2378-TCDD) and to quantify its level in fish extracts in the 170-220 pg range "on disk". When expressed on a fish tissue basis, analyte levels ranged from 15 to 45 pg/g. Spectroscopic identification was based on the position and relative intensity of seven absorption bands. Optical alignment as well as performance evaluation and optimization of the GC/MI/FTIR system are described. The use of [13C12]2378-TCDD as an internal standard was essential for quantitation, and quality assurance controls were used to verify system performance. GC/MI/FTIR quantitation of 2378-TCDD was compared with that independently found by GC with electron capture detection. Recovery of 2378-TCDD averaged 52% (n = 8, 30% relative standard deviation) for fish extracts.     

Generalized K entropy and Gibbs entropy of a system of point vortices

A generalization of the Kolmogorov-Sinay entropy (K entropy) is proposed and applied to a polygonal system of point vortices. It is demonstrated that the generalized K entropy (GK entropy) not only characterizes the local instability and mixing in a dynamical system, but also describes its structural rearrangements, in particular, a transition of the vortex system from one stationary state to another according to some scenario of vortex combination. The Gibbs entropy is constructed, its relation to the GK entropy is established, and it is demonstrated that both describe the transition of a dynamical system to equilibrium.     

Simultaneous derivatization and quantification of the nitric oxide metabolites nitrite and nitrate in biological fluids by gas chromatography/mass spectrometry

Simultaneous quantification of nitrite and nitrate, the major oxidative metabolites of L-arginine-derived nitric oxide (NO), in biological fluids by GC or GC/MS methods is currently impossible. The separate analysis of these anions is associated with severe methodological problems. Therefore, a GC/MS method was developed which allows, for the first time, simultaneous quantification of nitrite and nitrate in various biological fluids. The method involves a single derivatization procedure, by which endogenous nitrite and nitrate and their externally added 15N-labeled analogues are simultaneously converted in aqueous acetone by pentafluorobenzyl bromide to the nitro and nitric acid ester pentafluorobenzyl derivatives, respectively, and a single GC/MS analysis. Nitrite and nitrate concentrations measured in plasma and urine of humans by this method correlated excellently with those from quantification of nitrite and nitrate in these matrixes using a previously reported GC/MS method that, however, requires reduction of nitrate to nitrite. Also, the present method enables discrimination between S-nitro- and S-nitroso-glutathione, which have identical chromatographic and spectrophotometric properties. The method is very useful to routinely study metabolism and reactions of NO and its metabolites in vitro and in vivo. It is accurate, interference-free, sensitive-50 fmol of [15N]-nitrite and [15N]nitrate were detected at signal-to-noise ratios of 870:1 and 95:1, respectively-and should be a reference method for nitrite and nitrate measurements.     

Fast gas chromatography combustion isotope ratio mass spectrometry

We report here the first coupling of fast GC to IRMS, in a system capable of 250 ms peak widths (fwhm) at 1 mL/min flow rates, one-fifth as narrow as any previously reported GCC-IRMS system. We developed an optimized postcolumn interface that results in minimal peak broadening, using a programmable temperature vaporization injector in place of a rotary valve or backflush system to divert solvent, a narrow capillary combustion reactor followed by a cryogenic water trap with narrow-bore (<0.20 mm i.d.) transfer lines, and a narrow i.d. open split to the IRMS directly inserted into the column effluent. Quantitative combustion was demonstrated with CH4 injections. A comparison of CO2 injections with different fwhm peak widths (250, 2500, and 7500 ms) showed similar precisions, SD(delta13C)=0.2-0.3 per thousand, for injections of >600 pmol C on column; precision for the narrow peaks (250 ms) was considerably better for injections<150 pmol C on column. SD(delta13C)<1 per thousand was achievable for injections of 5-15 pmol on column for 250 ms wide peaks, 10-fold better precision than 2500 ms wide peaks, and within a factor of 3 of the counting statistics limit. For a mixture of 15 fatty acid methyl esters (FAME), 1.5 nmol C of each on column yielded typical SD(delta13Cpdb)=0.4 per thousand for fast GC and 0.5 per thousand for conventional GC. For 14 of the 15 FAME, delta13C values between the two systems were within+/-1.5 per thousand and not significantly different. Fast GCC-IRMS required one-third the run time (450 s vs 1400 s) to achieve comparable resolution. Mean peak widths for fast GCC-IRMS of the FAME were 720 ms, compared to 650 ms by fast GC with flame ionization detection. At a 15-fold dilution (100 pmol C on column for each FAME), fast GCC-IRMS achieved approximately 2-fold better precision and accuracy than similar injections on conventional GCC-IRMS. Finally, a mixture of 10 steroids (approximately 7 nmol C (100 ng) each on column) was analyzed with mean precision of SD(delta13C)=0.2 per thousand in 620 s by fast GCC-IRMS, while conventional GCC-IRMS required 1200 s and achieved poorer resolution. delta13C values for the two system were similar (Deltadelta13C1 nmol C) and achieves modest precision (approximately 1 per thousand) near the counting statistics limit on low level components.     

Gas chromatography/electron ionization-mass spectrometry-selected ion monitoring screening method for a thorough investigation of polyhalogenated compounds in passive sampler extracts with quadrupole systems

Nontarget analysis and identification of unknown polyhalogenated compounds is important in acquiring a thorough picture of the present pollution status as well as for identifying emerging environmental problems. Such analyses usually require the application of electron ionization mass spectrometry because the resulting mass spectra frequently allow for compound identification. When quadrupoles are used as mass separators, the full scan technique often suffers from low sensitivity along with nonspecificity for polyhalogenated trace compounds which often result in interference by matrix compounds. We have developed a novel nontarget gas chromatography/electron ionization-mass spectrometry-selected ion monitoring (GC/EI-MS-SIM) method that overcomes these sensitivity and selectivity issues. Our method is based on the fact that the molecular ions and isotope patterns of polyhalogenated compounds involve the most relevant primary information with regard to the structure of polyhalogenated compounds. Additionally, the retention times of polyhalogenated compounds generally increase with increasing molecular weight. The retention time range of polyhalogenated compounds was divided in three partly overlapping segments of 112 u (segment A: m/z 300-412; segment B: m/z 350-462; segment C: m/z 450-562) that were screened in eight GC runs consisting of 15 consecutive SIM ions. This method was tested with a passive water sampler extract known to contain over 30 polyhalogenated compounds according to the sensitive analysis by GC/electron capture negative ion (ECNI)-MS. While none of these polyhalogenated compounds could be detected by GC/EI-MS in full scan mode, our nontarget GC/EI-MS-SIM method allowed for the detection of 38 polyhalogenated compounds. Only seven could be identified by means of reference standards while more than 15 of the unknowns could be traced back to at least the class of compounds based on the mass spectrometric data from the nontarget SIM runs. All compounds identified originated from halogenated natural products. The nontarget GC/EI-MS-SIM method combines the high sensitivity obtainable with quadrupole systems for trace analysis with the structural information essential for the identification of unknown pollutants.     

Biopolymer-based trimetallic nanocomposite synthesis,characterization and its application in the catalytic degradation of 4-nitrophenol

Journal of Materials Science: Materials in Electronics - Gum kondagogu (GK), a natural biopolymer was successfully employed in the synthesis of trimetallic (AgAuPd) nanocomposites and characterized...     

Comprehensive two-dimensional gas chromatography combustion isotope ratio mass spectrometry

We report the first coupling of comprehensive two-dimensional gas chromatography (GC x GC) to online combustion isotope ratio mass spectrometry (C-IRMS). A GC x GC system, equipped with a longitudinally modulated cryogenic system (LMCS), was interfaced to an optimized low dead volume combustion interface to preserve <300 ms full width at half-maximum (fwhm) fast GC peaks generated on the second GC column (GC2). The IRMS detector amplifiers were modified by configuration of resistors and capacitors to enable fast response, and a home-built system acquired data at 25 Hz. Software was home-written to handle isotopic time shifts of less than one bin (40 ms) and to integrate peak slices to recover isotope ratios from cryogenically sliced peaks. The performance of the GC x GCC-IRMS system was evaluated by isotopic analysis of urinary steroid standards. Steroids were separated by a nonpolar GC1 column (30 m x 0.25 mm, 5% phenyl), modulated into multiple 4- or 8-s cryogenic slices by the LMCS, and then separated on a polar GC2 column (1 or 2 m x 0.1 mm, 50% phenyl). GC2 peak widths from a 1-m column averaged 276 ms fwhm. Steroid standard sliced peaks were successfully reconstructed to yield delta(13)C VPDB values with average precisions of SD(delta(13)C) = 0.30 per thousand and average accuracies within 0.34 per thousand, at 8 ng on column. Two steroids, coeluting in GC1, were baseline separated in GC2 and resulted in delta(13)C VPDB values with average precisions of SD(delta(13)C) = 0.86 per thousand and average accuracies within 0.26 per thousand, at 3 ng on column. Results from this prototype system demonstrate that the enhanced peak capacity and signal available in GC x GC is compatible with high-precision carbon isotope analysis.     

Development of N-acetyl methyl ester derivatives for the determination of delta13C values of amino acids using gas chromatography-combustion- isotope ratio mass spectrometry

A novel derivatization procedure, N-acetyl methyl (NACME) esterification, was developed to improve the accuracy and precision of amino acid delta13C value determination using gas chromatography-combustion-isotope ratio mass spectrometry (GC/C/IRMS). Standard mixtures of 15 protein amino acids were converted to NACME and N-acetyl-isopropyl (NAIP) esters; the latter established derivative was employed for comparison purposes. Both procedures yielded baseline-resolved peaks for all 15 amino acids when GC columns coated with polar stationary phases were employed. For NACME esters, the methylation conditions governed reaction yields, with highest yields observed when a 1 h, 70 degrees C methylation procedure (anhydrous MeOH/acetyl chloride, 25:4, v/v) was performed. The mean derivatization yields expressed relative to an underivatized coinjected standard (n-nonadecane) for both NACME and NAIP esters were identical. Likewise, the mean kinetic isotope effects (KIEs) were not significantly different (KIE(NACME) = 1.036; KIE(NAIP) = 1.038) and were shown in both cases to be reproducible. The mean reproducibility obtained from 15 replicates (3 x batches of 5) of both derivatives was strong (mean STDV(NACME) = 0.3 per thousand and STDV(NAIP) = 0.4 per thousand). The isotopic robustness of both derivatization procedures was observed over a concentration range of 52,500 microg of amino acid. NACME esters displayed low errors (+/-0.6 per thousand for phenylalanine to +/-1.1 per thousand for serine) due to the higher sample-to-derivative carbon ratio of this derivative. Finally, the integrity of the new NACME procedure was confirmed through analysis of diet and bone collagen amino acids of rats reared on C3 or C4 diets, which indicated the high degree of both accuracy and precision of the delta13C values obtained for individual amino acids.     

Generating multiple independent retention index data in dual-secondary column comprehensive two-dimensional gas chromatography

A method producing simultaneously three retention indexes for compounds has been developed for comprehensive two-dimensional gas chromatography by using a dual secondary column approach (GC x 2GC). For this purpose, the primary flow of the first dimension column was equally diverted into two secondary microbore columns of identical geometry by means of a three-way flow splitter positioned after the longitudinally modulated cryogenic system. This configuration produced a pair of comprehensive two-dimensional chromatograms and generated retention data on three different stationary phases in a single run. First dimension retention indexes were determined on a polar SolGel-Wax column under linear programmed-temperature conditions according to the van den Dool approach using primary alcohol homologues as the reference scale. Calculation of pseudoisothermal retention indexes in both second dimensions was performed on low-polarity 5% phenyl equivalent polysilphenylene/siloxane (BPX5) and 14% cyanopropylphenyl/86% dimethylpolysiloxane (BP10) columns. To construct a retention correlation map in the second dimension separation space upon which KovAts indexes can be derived, two methods exploiting "isovolatility" relationships of alkanes were developed. The first involved 15 sequential headspace samplings of selected n-alkanes by solid-phase microextraction (SPME), with each sampling followed by their injection into the GC at predetermined times during the chromatographic run. The second method extended the second dimension retention map and consisted of repetitive introduction of SPME-sampled alkane mixtures at various isothermal conditions incremented over the temperature program range. Calculated second dimension retention indexes were compared with experimental values obtained in conventional one-dimensional GC. A case study mixture including 24 suspected allergens (i.e., fragrance ingredients) was used to demonstrate the feasibility and potential of retention index information in comprehensive 2D-GC.     

Cadmium-induced functional and ultrastructural alterations in roots of two transgenic cotton cultivars

The toxic effect of cadmium (Cd) at increasing concentrations was studied with special attention being given to the root morphological and ultrastructural changes in two transgenic cotton cultivars viz. BR001 and GK30 and their wild relative viz. Coker 312. In comparison to their respective controls, low concentration (10 and 100microM) of Cd greatly stimulated seed germination, while it was inhibited by highest concentration of Cd (1000microM) in case of two transgenic cultivars. However, in Coker 312 the seed germination percentage progressively decreased over the control at all Cd levels. Various physiological and morphological parameters of the root and whole plant in both transgenic cotton cultivars and their relative wild cotton genotype respond differently towards the Cd toxicity. Bioavailability of Cd was concentration-dependent where seedling root captured more Cd as compared to shoot. BR001 accumulated more Cd followed by GK30, while Coker 312 was less Cd accumulator. The ultrastructural modifications in the root tip cells of both the transgenic cotton cultivars and their wild relative were also dose-dependent. With the increase in Cd levels, the fine structures of their root cells also invariably changed. Increase in plasmolysis of the plasma membrane, greater number of nucleoli and vacuoles and enlarged vacuoles could be observed in both transgenic cotton cultivars. In comparison to them, Coker 312 showed relatively well developed ultrastructures of the root tips except enlarged vacuoles and greater number of mitochondria. Moreover, the accumulation of Cd in the form of electron dense granules and crystals both in vacuoles and attached to cell walls were visible in both transgenic cotton cultivars and their wild relative. These results suggest that both transgenic cotton cultivars and their wild relative cotton genotype responded positively towards Cd stress at seedling stage, the internal Cd-detoxification might be through apoplastic and symplastic binding. Moreover, as a whole BR001 proved to be sensitive whereas; GK30 and Coker 312 were found as tolerant.     

基于EEMD模糊熵和GK聚类的信号特征提取方法及应用

提出了一种基于集合经验模态分解模糊熵和GK聚类相结合的方法,应用于滚动轴承的故障诊断中。首先,利用EEMD方法将故障信号分解成多个本征模态分量来消除模态混叠影响;其次,通过相关性对IMF分量进行筛选,并求取其模糊熵作为特征向量进行GK聚类分析进行模式识别。在实验分析中,通过模糊熵、样本熵、近似熵3种特征参数的对比,和GK聚类与FCM聚类的对比,证明了该方法的有效性和优越性。     

Development of a solid-phase microextraction GC-NPD procedure for the determination of free volatile amines in wastewater and sewage-polluted waters.

An analytical procedure for the determination of free volatile C1-C6 amines in aqueous matrixes has been developed and applied to their determination in waste-water, primary and secondary effluents, and sewage-polluted river samples. The developed analytical procedure involves headspace sampling using solid-phase microextraction with a poly(dimethylpolysiloxane) coating (100 microns) followed by GC-NPD determination and GC/MS confirmation using a tailor-made PoraPLOT amines capillary GC column for volatile amines. Procedural detection limits were compound dependent but ranged from 3 to 56 micrograms L-1, being close to or lower than the odor threshold concentration, and the reproducibility was ca. 15% (N = 5) in real water samples. The developed analytical procedure is solvent free, cost-effective (no cryogenic trap needed), and faster than existing methods because no derivatization step is involved in the determination. Linearity was compound dependent but ranged at least from 50 to 600 micrograms L-1.     

Preparation of Nanoporous Carbonaceous Promoters for Enhanced CO2 Absorption in Tertiary Amines

Aqueous solutions of tertiary amines are promising absorbents for CO₂ capture, as they are typically characterized by a high absorption capacity, low heat of reaction, and low corrosivity. However, tertiary amines also exhibit very low kinetics of CO₂ absorption, which has made them unattractive options for large-scale utilization. Here, a series of novel nanoporous carbonaceous promoters (NCPs) with different properties were synthesized, characterized, and used as rate promoters for CO₂ absorption in aqueous N, N-diethylethanolamine (DEEA) solutions. To prepare a DEEA–NCP nanofluid, NCPs were dispersed into aqueous 3 mol·L⁻¹ DEEA solution using ultrasonication. The results revealed that among microporous (GC) and mesoporous (GS) carbonaceous structures functionalized with ethylenediamine (EDA) and polyethyleneimine (PEI) molecules, the GC–EDA promoter exhibited the best performance. A comparison between DEEA–GC–EDA nanofluid and typical aqueous DEEA solutions highlighted that the GC-EDA promoter enhances the rate of CO₂ absorption at 40 °C by 38.6% (36.8–50.7 kPa·min⁻¹) and improves the equilibrium CO₂ absorption capacity (15 kPa; 40 °C) by 13.2% (0.69–0.78 mol of CO₂ per mole of DEEA). Moreover, the recyclability of DEEA–GC–EDA nanofluid was determined and a promotion mechanism is suggested. The outcomes demonstrate that NCP–GC–EDA in tertiary amines is a promising strategy to enhance the rate of CO₂ absorption and facilitate their large-scale deployment.     

Enzymatic decarboxylation of tyrosine and phenylalanine to enhance volatility for high-precision isotopic analysis

We present a rapid and selective method to increase the volatility of tyrosine and phenylalanine without adding derivative C for high-precision gas chromatography-continuous-flow isotope ratio mass spectrometry (GCC-IRMS) based on enzymatic decarboxylation to yield alkylamines and evaluated for 15N isotopic integrity. Purified tyrosine and phenylalanine were converted to tyramine and phenethylamine by tyrosine and phenylalanine decarboxylases, respectively. GC separation was achieved using a thick stationary phase (5-microm) capillary column. Recoveries were 95 +/- 2%. The reproducibility of delta15N of tyramine and phenethylamine measured by GCC-IRMS averaged SD(delta15N) = 0.33 per thousand. The absolute differences between delta15N of amino acids measured by elemental analyzer-IRMS and the alkylamines measured by GCC-IRMS was not significant. Phenethylamine and tyramine prepared from a mixture of 18 amino acids were extracted by ethanol with 95% recovery, and analysis yielded clean chromatograms and equivalent precision. These data indicate that enzymatic decarboxylation of phenylalanine and tyrosine is a convenient method to increase their volatility for continuous-flow isotopic analysis without introducing extraneous C or significant isotopic fractionation.     

Compound-specific chlorine isotope analysis: a comparison of gas chromatography/isotope ratio mass spectrometry and gas chromatography/quadrupole mass spectrometry methods in an interlaboratory study

Chlorine isotope analysis of chlorinated hydrocarbons like trichloroethylene (TCE) is of emerging demand because these species are important environmental pollutants. Continuous flow analysis of noncombusted TCE molecules, either by gas chromatography/isotope ratio mass spectrometry (GC/IRMS) or by GC/quadrupole mass spectrometry (GC/qMS), was recently brought forward as innovative analytical solution. Despite early implementations, a benchmark for routine applications has been missing. This study systematically compared the performance of GC/qMS versus GC/IRMS in six laboratories involving eight different instruments (GC/IRMS, Isoprime and Thermo MAT-253; GC/qMS, Agilent 5973N, two Agilent 5975C, two Thermo DSQII, and one Thermo DSQI). Calibrations of (37)Cl/(35)Cl instrument data against the international SMOC scale (Standard Mean Ocean Chloride) deviated between instruments and over time. Therefore, at least two calibration standards are required to obtain true differences between samples. Amount dependency of δ(37)Cl was pronounced for some instruments, but could be eliminated by corrections, or by adjusting amplitudes of standards and samples. Precision decreased in the order GC/IRMS (1σ ≈ 0.1‰), to GC/qMS (1σ ≈ 0.2-0.5‰ for Agilent GC/qMS and 1σ ≈ 0.2-0.9‰ for Thermo GC/qMS). Nonetheless, δ(37)Cl values between laboratories showed good agreement when the same external standards were used. These results lend confidence to the methods and may serve as a benchmark for future applications.     

GOD/PPy/GC电极的电化学性能研究

采用电沉积法在玻碳(GC)电极表面合成纳米级聚吡咯(PPy),通过扫描电镜得到PPy的形貌。以PPy为载体,通过吸附法固定葡萄糖氧化酶(GOD),得到GOD/PPy/GC电极。利用循环伏安法对GOD/PPy/GC电极的电化学行为进行分析,结果表明,以PPy为载体可以很好地固定GOD并保持其生物活性。在0.1mol/L磷酸盐缓冲溶液中,无任何电子媒介体存在时,GOD/PPy/GC电极显示了很好的电催化性能。