FLOW-PIPE-SEEPAGE COUPLING ANALYSIS OF SPANNING INITIATION OF A PARTIALLY-EMBEDDED PIPELINE

The initiation of pipeline spanning involves the coupling between the flow over the pipeline and the seepage-flow in the soil underneath the pipeline. The pipeline spanning initiation is experimentally observed and discussed in this article. It is qualitatively indicated that the pressure-drop induced soil seepage failure is the predominant cause for pipeline spanning initiation. A flow-pipe-seepage sequential coupling Finite Element Method (FEM) model is proposed to simulate the coupling between the water flow-field and the soil seepage-field. A critical hydraulic gradient is obtained for oblique seepage failure of the sand in the direction tangent to the pipe. Parametric study is performed to investigate the effects of inflow velocity, pipe embedment on the pressure-drop, and the effects of soil internal friction angle and pipe embedment-to-diameter ratio on the critical flow velocity for pipeline spanning initiation. It is indicated that the dimensionless critical flow velocity changes approximately linearly with the soil internal friction angle for the submarine pipeline partially-embedded in a sandy seabed.

Double electron processes in collisions of partially stripped ions Cq+ (q=1-4) with helium

The multi-electron processes are investigated for 17.9-120keV/u C1+, 30-323 keV/u C2+, 120-438 keV/u C3+, 287-480keV/u C4+ incident on a helium target. The cross-section ratios of double electron (DE) process to the total of the single electron (SE) and the double electron process (i.e. SE+DE), the direct double electron (DDI) to the direct single ionization (DSI) as well as the contributions of DDI to DE and of TI to DE are measured using coincidence techniques. The energy and charge state dependences of the measured cross-section ratios are studied and discussed.

Preparation of monolithic column and its application in p-CEC

A novel monolithic stationary phase having long alkyl chain ligands was introduced and evaluated in pressurized-capillary electrochromatography of small neutral and charged compounds. The monolithic column was prepared by the in situ copolymerization of ethylene dimethacrylate, 1-hexadecene, allyl alcohol and 2-acrylamido-2-methyl-1-propanesulfonic acid in a quaternary porogenic solvent mixture consisting of 1,4-butanediol, cyclohexanol, dodecanol and water.

Prediction of soil organic carbon partition coefficients by soil column liquid chromatography

To avoid the limitation of the widely used prediction methods of soil organic carbon partition coefficients (K-OC) from hydrophobic parameters, e.g., the n-octanol/water partition coefficients (K-OW) and the reversed phase high performance liquid chromatographic (RP-HPLC) retention factors, the soil column liquid chromatographic (SCLC) method was developed for K-OC prediction. The real soils were used as the packing materials of RP-HPLC columns, and the correlations between the retention factors of organic compounds on soil columns (k(soil)) and K-OC measured by batch equilibrium method were studied. Good correlations were achieved between k(soil) and K-OC for three types of soils with different properties. All the square of the correlation coefficients (R-2) of the linear regression between log k(soi) and log K-OC were higher than 0.89 with standard deviations of less than 0.21. In addition, the prediction of K-OC from K-OW and the RP-HPLC retention factors on cyanopropyl (CN) stationary phase (k(CN)) was comparatively evaluated for the three types of soils. The results show that the prediction of K-OC from k(CN) and K-OW is only applicable to some specific types of soils. The results obtained in the present study proved that the SCLC method is appropriate for the K-OC prediction for different types of soils, however the applicability of using hydrophobic parameters to predict K-OC largely depends on the properties of soil concerned. (C) 2004 Elsevier B.V. All rights reserved.

Repeatedly usable immobilized pH gradient in a monolithic capillary column

Glycidyl methacrylate (GMA) and ethylene dimethacrylate (EDMA) were used to synthesize a monolithic capillary column containing reactive epoxy groups. Glutaraldehyde was introduced and linked to the monolith after a process of amination. An aqueous solution of commercial carrier ampholytes (CAs, Ampholine) was focused in such a polymer column. The primary amino groups of CAs reacted with glutaraldehyde along the capillary. CAs were immobilized at different positions in the column according to their isoelectric points (pl), resulting in a monolithic immobilized pH gradient (M-IPG). Isoelectric focusing (IEF) was performed without CAs in such an M-IPG column. Due to the covalent attachment of the CAs this M-IPG can be repeatedly used after its preparation. Good stability, linearity, and reproducibility were obtained.

Investigation on the influence of methanol on adsorption and leaching of pesticides with soil column liquid chromatography

The effect of methanol of low concentration on adsorption and leaching of atrazine and tebuconazole was studied in this paper. The adsorption coefficients and the retardation factors (R-m) of pesticides on EUROSOIL 3# log-linearly decreased as volumetric fraction of methanol (f(c)) was increased in the binary solvent mixtures of methanol and water. These data are consistent with solvophobic theory formerly outlined for describing the adsorption and transport of hydrophobic organic chemicals from mixed solvents. Nevertheless, the adsorption of these pesticides in soil-water system slightly increased when the soil was pre-washed with methanol in comparison with that pre-washed with water (pure water system). Furthermore, their adsorption coefficients were still higher in binary solvent systems with methanol of very low concentrations, i.e. f(c) < 0.03 for atrazine and f(c) < 0.01 for tebuconazole, than those in pure water system. The adsorption coefficients (logK(w)) of atrazine and tebuconazole predicted by solvophobic theory were 0.5792 and 1.6525, respectively, and their experimental logK(w) were 0.3701 and 1.6275 in pure water system. Obviously, the predicted log K-w of the two pesticides was higher than the experimental log K-w in pure water system. The predicted K-w and the retardation factor (R-w) in pure water system by solvophobic theory are thus possibly inaccurate. (C) 2004 Elsevier Ltd. All rights reserved.

Study of an electroosmotic pump for liquid delivery and its application in capillary column liquid chromatography

A packed-bed electroosmotic pump (EOP) was constructed and evaluated. The EOP consisted of three capillary columns packed in parallel, a gas-releasing device, Pt electrodes and a high-voltage power supply. The EOP could generate output pressure above 5.0 MPa and constant flow rate in the range of nl/min to a few mul/min for pure water, pure methanol, 2 mM potassium dihydrogenphosphate buffer, the buffer-methanol mixture and the pure water-methanol mixture at applied potentials less than 20 W The composition of solvent before/after pumping was quantitatively determined by using a gas chromatograph equipped with both flame ionization detector and thermal conductivity detector. It was found that there were no apparent changes in composition and relative concentrations after pumping process for a methanol-ethanol-acetonitrile mixture and a methanol-water mixture. Theoretical aspect of the EOP was discussed in detail. An capillary HPLC system consisting of the EOP, an injection valve, a 15 cm x 320 mum i.d., 5 mum Spherigel C(18) stainless steel analytical column, and an on-column UV detector was connected to evaluate the performance of the EOP. A comparative study was also carried out with a mechanical capillary HPLC pump on the same system. The results demonstrated that the reproducibility of flow rate and the pulsation-free flow property of the EOP are superior to that of mechanical pump in capillary HPLC application. (C) 2004 Elsevier B.V. All rights reserved.

Preparation and characterization of long methacrylate monolithic column for capillary liquid chromatography

Long methacrylate monolithic columns (100 cm x 320 mum i.d.) were prepared from silanized fused-silica capillaries of 320 mum i.d. by in situ copolymerization of butyl methacrylate (BMA) with ethylene dimethacrylate (EDMA) in the presence of a suitable porogen. The separation performance and selectivity of the column were evaluated and compared with a 25 cm x 320 mum i.d. column prepared in the same way by capillary high-performance liquid chromatography (mu-HPLC) The results showed that the 1 m long monolithic column can generate 33 x 10(3) plate number and exhibited good permeability, higher sample loadability, and separation capability. (C) 2004 Elsevier B.V. All rights reserved.

Monolithic column with zwitterionic stationary phase for capillary electrochromatography

A capillary electrochromatography (CEC) monolithic column with zwitterionic stationary phases was prepared by in situ polymerization of butyl methacrylate, ethylene dimethacrylate, methacrylic acid, and 2-(dimethyl amino) ethyl methacrylate in the presence of porogens. The stationary phases have zwitterionic functional groups, that is, both tertiary amine and acrylic acid groups, so the ionization of those groups on the zwitterionic stationary phase was affected by the pH values of the mobile phase, and further affects the strength and direction of the electroosmotic flow (EOF). Separations of alkylbenzenes and polycylic aromatic hydrocarbons based on the hydrophobic mechanism were obtained. Separation of various types of polar compounds, including phenols, anilines, and peptides, on the prepared column were performed under CEC mode with anodic and cathodic EOF, and different separation selectivities of those polar analytes were observed on the monolithic capillary column by using mobile phases with different pH values.

Capillary electrochromatographic separation of ionizable compounds with a molecular imprinted monolithic cationic exchange column

A polymer-based monolithic capillary column imprinted with 4-aminopyridine (4-AP) was prepared by a thermally-initiated polymerization process; and its performance as a capillary electrochromatographic medium was evaluated in separating 4-AP and 2-AP isomers. The effects of experimental parameters, such as pH value and ionic strength of the buffer, the acetonitrile content in the mobile phase, and the applied voltage, on the resolution of these isomers had been carefully investigated. It was found that in the retention process there were interplays of multiple mechanisms of ion-exchange, molecular imprinting, and electrophoresis. These mechanisms allowed more sophisticated control of experimental parameters in the separation of ionizable compounds.

Separation of peptides on mixed mode of reversed-phase and ion-exchange capillary electrochromatography with a monolithic column

The mixed mode of reversed phase (RP) and strong canon-exchange (SCX) capillary electrochromatography (CEC) based on a monolithic capillary column has been developed. The capillary monolithic column was prepared by in situ copolymerization of 2-(sulfooxy)ethyl methacrylate (SEMA) and ethylene dimethacrylate (EDMA) in the presence of porogens. The sulfate group provided by the monomer SEMA on the monolithic bed is used for the generation of the electroosmotic flow (EOF) from the anode to the cathode, but at the same time serves as a SCX stationary phase. A mixed-mode (RP/SCX) mechanism for separation of peptides was observed in the monolithic column, comprising hydrophobic and electrostatic interaction as well as electrophoretic migration at a low pH value of mobile phase. A column efficiency of more than 280000 plates/m for the unretained compound has been obtained on the prepared monoliths. The relative standard deviations observed for to and retention factors of peptides were about 0.32% and less than 0.71% for ten consecutive runs, respectively. Effects of mobile phase compositions on the EOF of the monolithic column and on the separation of peptides were investigated. The selectivity on separation of peptides in the monolithic capillary column could be easily manipulated by varying the mobile phase composition.