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At least 883 records · Page 49Linked to original sources
PubMed2006

Phase locking and in-phase supermode selection in monolithic multicore fiber lasers.

We report a compact multicore fiber laser that utilizes an all-fiber approach for phase locking and in-phase supermode selection. By splicing passive coreless fibers of controlled lengths to both ends of an active 19-core fiber, we demonstrate that the fundamental in-phase supermode can be selectively excited with a completely monolithic fiber device, instead of conventional free-space and bulk optics, to achieve phase-locked operation for a multiemitter laser device.

Journal Article↗
PubMed2004

Phase resetting and phase locking in hybrid circuits of one model and one biological neuron.

To determine why elements of central pattern generators phase lock in a particular pattern under some conditions but not others, we tested a theoretical pattern prediction method. The method is based on the tabulated open loop pulsatile interactions of bursting neurons on a cycle-by-cycle basis and was tested in closed loop hybrid circuits composed of one bursting biological neuron and one bursting model neuron coupled using the dynamic clamp. A total of 164 hybrid networks were formed by varying the synaptic conductances. The prediction of 1:1 phase locking agreed qualitatively with the experimental observations, except in three hybrid circuits in which 1:1 locking was predicted but not observed. Correct predictions sometimes required consideration of the second order phase resetting, which measures the change in the timing of the second burst after the perturbation. The method was robust to offsets between the initiation of bursting in the presynaptic neuron and the activation of the synaptic coupling with the postsynaptic neuron. The quantitative accuracy of the predictions fell within the variability (10%) in the experimentally observed intrinsic period and phase resetting curve (PRC), despite changes in the burst duration of the neurons between open and closed loop conditions.

Action Potentials↗
PubMed2002

A simple preparation of stationary phase of alkylamide reversed-phase liquid chromatograph for the separation of basic substances.

A simple preparation process of alkylamide phase for reversed-phase HPLC (RP-HPLC) is described. The process includes aminopropyltrimethoxysilane firstly reacted with octanoyl chloride, then the intermediate was coupled onto porous silica. The resultant bonded silica has a reproducible ligand surface concentration and homogenous bonded ligand distribution on the porous silica. Characterization of prepared packing was carried out with elemental analysis, solid-state 13C NMR and Fourier transform infrared (FT-IR). Chromatographic evaluations were carried out by using a mixture of organic compounds including acidic, basic and neutral analytes under methanol/water as binary mobile phase. The results showed that the stationary phase have excellent chromatographic properties and can be efficiently used for the separation of basic compounds.

Amides↗
PubMed2003

Chiral separation of organic phosphonate compounds on cellulose CSP (chiral stationary phase) under reversed phase mode.

The enantiomers of fourteen O,O-dialkyl-2-benzyloxycarbonyl-aminoarylmethyl-phosphonates are directly separated on the tris(3,5-dimethylphenylcarbamate) cellulose column (Chiralcel OD-R) under reversed phase mode. The results of the chiral separation are different from the results obtained in the normal phase mode. The mobile phase plays an essential role in chiral discrimination when using Chiralcel OD-R. The influences of the mobile phase composition on the retention and the enantioselectivity are investigated. The influences on chiral separation of the length and steric hindrance of alkoxy groups of the phosphonate ester and of the nature of the substituent on the benzene ring that is attached to the chiral carbon atom are also discussed.

Journal Article↗
PubMed2005

Normal-phase HPLC enantioseparation of novel chiral metal tetrahedrane-type clusters on an amylose-based chiral stationary phase.

In the present work, an amylose tris(3,5-dimethylphenylcarbamate) (ADMPC) chiral stationary phase (CSP) was prepared by coating ADMPC on small-particle silica gel. This ADMPC-CSP was for the first time successfully applied to separate a series of novel chiral metal tetrahedrane-type clusters. Furthermore, the influence of a mobile-phase modifier (various alcohols added in the mobile phase), including its concentration and structure, and the structures of the clusters on the chiral separation and retention was investigated. The results suggest that not only the structure and concentration of alcohol in the mobile phase, but also the subtle structural differences in racemate can have a pronounced effect on the enantiomeric separation and retention.

Journal Article↗
PubMed1997

Dual-phase helical CT of the kidney: value of the corticomedullary and nephrographic phase for evaluation of renal lesions and preoperative staging of renal cell carcinoma.

OBJECTIVE: Our objective was to evaluate early-phase unenhanced and late-phase contrast-enhanced helical CT in revealing renal lesions and staging renal cell carcinomas. SUBJECTS AND METHODS: Contrast-enhanced helical CT of the kidneys was performed in 145 patients who also underwent unenhanced CT. Contrast-enhanced CT was performed in the corticomedullary phase (CMP) and nephrographic phase (NP). A total of 173 lesions in 96 patients were proven histologically or cytologically. The performance of helical CT in the three study groups was compared: unenhanced and CMP enhancement, group 1; unenhanced and NP enhancement, group 2; unenhanced, CMP enhancement, and NP enhancement, group 3. Among the parameters evaluated were the sensitivity for helical CT of all 173 renal lesions and the sensitivity and specificity for the 90 malignant tumors. Also, the preoperative CT staging of the 76 renal cell carcinomas was correlated with the pathologic specimens. RESULTS: The sensitivity for detection of all renal lesions in group 1 (84%) was significantly less than in groups 2 and 3 (97% and 100%). The specificity and accuracy of helical CT in revealing renal cell carcinomas were significantly higher (p < .05) in group 3 (95% and 95%, respectively) than in groups 1 (93% and 92%, respectively) and 2 (89% and 91%, respectively). Two renal cell carcinomas were overlooked by the interpreters of the helical scans in group 1. The accuracy of preoperative CT staging of renal cell carcinomas was significantly better (p < .05) in group 3 (91%) than in groups 1 (82%) and 2 (86%). CONCLUSION: When patients underwent unenhanced helical CT, CMP helical CT, and NP helical CT, we achieved a better rate of detection and characterization of renal lesions and better preoperative staging of renal cell carcinomas than when we used either CMP helical CT or NP helical CT alone.

Adult↗
PubMedDate not supplied

Optimum excitation of phases and amplitudes in a phased array hyperthermia system.

In order to achieve a desired temperature distribution inside and outside of malignant tissues, optimization techniques could be used in phased array hyperthermia systems to control effectively the amplitude and phase of the radiating elements. The optimization of a four-element phased array hyperthermia system operating at 432 MHz is examined theoretically. The proposed technique is based on a detailed physical model of the tissue medium to be heated in terms of both electromagnetic and thermal properties. A penalty function technique using a Newton method is applied to determine the optimum phases and amplitudes of the array. Several array geometries have been studied and numerical results are presented.

Algorithms↗
PubMed1998

Effects of drug concentration in inner aqueous phase and additives in oleaginous phase on release and bioavailability of isoniazid from multiple emulsion.

The effects of drug concentration in internal aqueous phase of stabilized w/o/w emulsion and additives in oleaginous phase on release characteristics of isoniazid were investigated. The release was significantly effected by both of the formulation variables. The release was enhanced initially with increasing concentration of drug in internal aqueous phase followed by a steady release at high concentration of isoniazid. The release declined substantially in the presence of aluminum tristearate, cetostearyl alcohol, and cholesterol, and it increased with egg lecithin and oleic acid in oily phase. The bioavailability was increased with a multiple-emulsion formulation.

Administration, Oral↗
PubMed1984

High-performance liquid chromatographic determination of vitamin D in foods, feeds and pharmaceuticals by successive use of reversed-phase and straight-phase columns.

A simplified and accurate method for the determination of vitamin D in foods, feeds and pharmaceuticals was established by high-performance liquid chromatography (HPLC) using successively reversed-phase and straight-phase columns. About 1-2 g of a sample was accurately weighed and directly saponified. The extracted unsaponifiable matter was subjected to preparative HPLC using a reversed-phase column and a vitamin D fraction was collected. The fraction was subsequently subjected to analytical HPLC using a straight-phase column and vitamin D was assayed by estimating the peak height. The proposed method was applied to various kinds of samples, e.g., fishery products, fish meals, mixed feeds for fish farming and chicken farming, egg yolk, milk products, cattle liver, Shiitake, fortified foods and multivitamin preparations. The results showed that the proposed method was useful for the determination of vitamin D in such samples, because the peak of vitamin D in the profile of the second HPLC was always clearly separated from other concomitants and good recovery was obtained. Therefore, we think that the method is useful as a routine one for the determination of vitamin D in foods, feeds and pharmaceuticals.

Animal Feed↗
PubMedDate not supplied

Reversed-phase thin-layer chromatography with different stationary phases in studies of quantitative structure-biological activity relationship of new antimycotic compounds.

Reversed-phase thin-layer chromatography with RP-8, RP-18, and RP-18W stationary phases was used in quantitative structure-activity relationship (QSAR) studies of new antimycotic compounds. The retention behavior of 10 dihydroxythiobenzanilides was examined for acquisition of log k' data. With water-acetone mixtures as the mobile phases, the concentration range for which the correlation between log k' and acetone concentration is linear was established for each stationary phase and used to determine hydrophobicity parameters log k'w by linear extrapolation. The effect of substituents on retention constants was quantitated by using the group contribution parameters tau W. On the basis of QSAR equations obtained from these studies, log k'w data can be used to predict antifungal activities of dihydroxythiobenzanilides with satisfactory accuracy.

Antifungal Agents↗
PubMed2002

Dynamic equilibrium dissolution of complex nonaqueous phase liquid mixtures into the aqueous phase.

Human health risks posed by hazardous substances seeping from a pool of nonaqueous phase liquids (NAPLs) into groundwater change over time because the more soluble compounds such as benzene, toluene, ethylbenzene, and xylene (BTEX) dissolve faster into the aqueous phase than less soluble compounds such as polycyclic aromatic hydrocarbons (PAH). Long-term dissolution from diesel fuel into the aqueous phase was determined experimentally in a continuous flow-through system using the slow-stirring method. The data obtained are interpreted using a dynamic equilibrium dissolution model based on Raoult's law. The predicted temporal development of aqueous concentrations are in good agreement with the experimental results. When a compound in the NAPL approaches complete depletion, a tailing behavior is observed, which is assigned to nonequilibrium effects, such as mass transfer limitations in the NAPL phase. The model predicted an increase of the mean molar mass of the diesel fuel of 1.5% over the entire experimental period. It should be noted that, if the dissolution process were to proceed further, the change in the mean molar mass could become significant and render the simple model inaccurate. Yet the simple model supports the assessment of initial action after a contamination event as well as the planning of long-term remedial strategies.

Gasoline↗
PubMed2001

[Preparation and evaluation of alkyl ether-bonded phase for reversed-phase high performance liquid chromatography].

A new silane coupling agent, beta-(3,4-epoxycyclohexyl)ethyltrimethoxy silane, was for the firsty time used to react with octanol, then the intermediate product was coupled onto porous silica to obtain a novel bonded phase for reversed-phase high performance liquid chromatography (RP-HPLC). Characterization of prepared packing was carried out with elemental analysis, solid-state 13C nuclear magnetic resonance spectrometry (NMR), Fourier transform infrared(FT-IR) spectroscopy. Chromatographic evaluations were carried out by using a mixture of organic compounds and methanol-water as the binary mobile phase. The results showed that the stationary phase has excellent chromatographic properties and resist to hydrolysis at a pH value between 2.5 and 7.5. The silanophilic activity of the OEBP was weakened because of the existence of the cyclohexyl group in the packing. It can be efficiently used for the separation of basic compounds.

Aminophylline↗
PubMed2001

[Preparation and evaluation of amide-octyl-bonded phase for the separation of basic substances in reversed-phase liquid chromatography].

A new bonded-phase, amide-octyl-bonded phase (AOBP), with an internal polar functional group-amide was firstly prepared in domestic by two-step reaction process. The amino phase was formed in the first step and further modified in the second step by attaching an alkyl chain via reaction of an acid chloride with the amino ligand. Characterization of prepared packing was carried out with elemental analysis and Fourier transform infrared (FTIR) spectrometry. Hydrophobicity, selectivity and silanophilic activity of AOBP were evaluated by using organic components including acidic, bascic and neutral analytes and methanol-water as binary mobile phase. The applicable ranges of pH and stability of AOBP were also evaluated. The results showed that AOBP has excellent chromatographic properties and resistance to hydrolysis between pH = 2.5-7.5, It can be used for the separation of basic solutes efficiently.

1-Octanol↗
PubMed1999

[The study of ethanol-water used as reversed-phase high performance liquid chromatographic mobile phase].

The viscosity of ethanol-water at various temperatures was determined. The physicochemical properties and characters of the solvents used as the mobile phase of reversed-phase high performance liquid chromatography(RP-HPLC) were compared between methanol and ethanol. The components of several Chinese medicines have been determined by RP-HPLC with ethanol-water used as mobile phase, and the results were compared with those obtained with methanol-water or acetonitrile-water. It showed that ethanol can be used as RP-HPLC mobile phase by increasing the column temperature moderately.

Chromatography, High Pressure Liquid↗
PubMed1990

Statistical thermodynamics of phase separation and ion partitioning in aqueous two-phase systems.

A general model for the phase behavior of polymer-polymer aqueous two-phase systems containing small amounts of added inorganic salts has been developed from statistical thermodynamics. The model is based on the solution theory of Hill and new electrolyte solution model based on Fluctuation Solution Theory. It includes the effect of polymer molecular weight with scaling expressions from the Renormalization Group theory of polymer solutions. The model has been used to calculate the phase diagram and the partitioning of salt for an aqueous two-phase system containing polyethylene glycol (MW = 8000) and dextran (MW = 28,700) with 0.1 mole/kg of added Na2SO4. The calculations have been compared to experimental results with good agreement.

Ions↗
PubMedDate not supplied

Sample preparation for determination of macrocyclic lactone mycotoxins in fish tissue, based on on-line matrix solid-phase dispersion and solid-phase extraction cleanup followed by liquid chromatography/tandem mass spectrometry.

A new method based on matrix solid-phase dispersion (MSPD) on-line with a solid-phase extraction (SPE) cleanup process followed by liquid chromatography with tandem mass spectrometry (LC/MS/MS) is presented for the determination of 3 macrocyclic lactone mycotoxins in fish tissues: zearalenone, alpha-zearalenol, and beta-zearalenol. The sample was prepared in a device that used a reversed-phase material (C18) or a normal-phase material (neutral alumina) as a matrix dispersing agent, and a graphitized carbon black cartridge was used for sequential cleanup by SPE. LC/MS/MS was used for selective determination. Isocratic elution with acetonitrile-methanol-water was used for LC separation; for MS/MS, 2 types of interfaces (a pneumatically assisted electrospray ionization interface or an atmospheric pressure chemical ionization interface) were evaluated and compared in terms of the intensity of the total ion current produced by each analyte. The use of highly selective MSPD on-line with SPE for sample preparation before analysis allowed the removal of interfering matrix compounds present in tissue extracts that would otherwise cause severe ionization suppression of zearalenone and its metabolites during the ionization process. Average recoveries at 100 ng/g were between 83 and 103% with C18 and > or = 67% with neutral alumina; the relative standard deviations were < 11% with C18 and < 18% with alumina. The limits of detection ranged from 0.1 to 1.0 ng/g. Sample preparation is simple to perform, no special technical equipment is required, and solvent volumes are minimal.

Animals↗
PubMed2004

Development of some stationary phases for reversed-phase high-performance liquid chromatography.

The availability of a variety of stable organic stationary phases for columns has been a key factor in the development of HPLC as a major scientific tool. This paper explores the history and rationale used in the development of some important stationary phases and attempts to identify some of the strengths and limitations of these materials. Some of the author's experiences in stationary phase development illustrate approaches leading to present-day columns that exhibit a broad range of selectivity coupled with a high degree of reproducibility. Suggestions also are made for additional stationary phases that may be needed to complete column selectivity potential for HPLC separations.

Chromatography, High Pressure Liquid↗
PubMed2004

Investigation of retention on bare silica using reversed-phase mobile phases at elevated temperatures.

The use of unbonded silica as a stationary phase in reversed-phase HPLC is described as a useful alternative to bonded phase columns for polar, lipophilic amines. Using four lipophilic amines, the role of temperature is shown to favorably impact both efficiency and selectivity, which is not universally seen when using bonded phases. As temperature is raised, retention drops on the silica column. The temperature behavior appears to support the hypothesis that retention is dependant upon electrostatic and adsorptive forces.

Chromatography, High Pressure Liquid↗