Derivation of the RPA (Random Phase Approximation) Equation of ATDDFT (Adiabatic Time Dependent Density Functional Ground State Response Theory) from an Excited State Variational Approach Based on the Ground State Functional.

PubMed

Ziegler, Tom; Krykunov, Mykhaylo; Autschbach, Jochen

2014-09-09

The random phase approximation (RPA) equation of adiabatic time dependent density functional ground state response theory (ATDDFT) has been used extensively in studies of excited states. It extracts information about excited states from frequency dependent ground state response properties and avoids, thus, in an elegant way, direct Kohn-Sham calculations on excited states in accordance with the status of DFT as a ground state theory. Thus, excitation energies can be found as resonance poles of frequency dependent ground state polarizability from the eigenvalues of the RPA equation. ATDDFT is approximate in that it makes use of a frequency independent energy kernel derived from the ground state functional. It is shown in this study that one can derive the RPA equation of ATDDFT from a purely variational approach in which stationary states above the ground state are located using our constricted variational DFT (CV-DFT) method and the ground state functional. Thus, locating stationary states above the ground state due to one-electron excitations with a ground state functional is completely equivalent to solving the RPA equation of TDDFT employing the same functional. The present study is an extension of a previous work in which we demonstrated the equivalence between ATDDFT and CV-DFT within the Tamm-Dancoff approximation.

A polyacrylamide-based silica stationary phase for the separation of carbohydrates using alcohols as the weak eluent in hydrophilic interaction liquid chromatography.

PubMed

Cai, Jianfeng; Cheng, Lingping; Zhao, Jianchao; Fu, Qing; Jin, Yu; Ke, Yanxiong; Liang, Xinmiao

2017-11-17

A hydrophilic interaction liquid chromatography (HILIC) stationary phase was prepared by a two-step synthesis method, immobilizing polyacrylamide on silica sphere particles. The stationary phase (named PA, 5μm dia) was evaluated using a mixture of carbohydrates in HILIC mode and the column efficiency reached 121,000Nm -1 . The retention behavior of carbohydrates on PA stationary phase was investigated with three different organic solvents (acetonitrile, ethanol and methanol) employed as the weak eluent. The strongest hydrophilicity of PA stationary phase was observed in both acetonitrile and methanol as the weak eluent, when compared with another two amide stationary phases. Attributing to its high hydrophilicity, three oligosaccharides (xylooligosaccharide, fructooligosaccharide and chitooligosaccharides) presented good retention on PA stationary phase using alcohols/water as mobile phase. Finally, PA stationary phase was successfully applied for the purification of galactooligosaccharides and saponins of Paris polyphylla. It is feasible to use safer and cheaper alcohols to replace acetonitrile as the weak eluent for green analysis and purification of polar compounds on PA stationary phase. Copyright © 2017. Published by Elsevier B.V.

Retention properties of novel beta-CD bonded stationary phases in reversed-phase HPLC mode.

PubMed

Zhao, Yanyan; Guo, Zhimou; Zhang, Yongping; Xue, Xingya; Xu, Qing; Li, Xiuling; Liang, Xinmiao; Zhang, Yukui

2009-05-15

With the given special structures, the CD bonded stationary phases are expected to have complementary retention properties with conventional C18 stationary phase, which will be helpful to enhance the polar selectivity in RP mode separation. In this work, two beta-cyclodextrin (beta-CD) bonded stationary phases for reversed-phase HPLC, including 1, 12-dodecyldiol linked beta-CD stationary phase (CD1) and olio (ethylene glycol) (OEG) linked beta-CD stationary phase (CD2), have been synthesized via click chemistry. The resulting materials were characterized with FT-IR and elemental analysis, which proved the successful immobilization of ligands. The similarities and differences in retention characteristics between the CD and C18 stationary phases have been elucidated by using comparative linear solvation energy relationships (LSERs). The force related to solute McGowan volume has no significant difference, while the hydrogen bonding and dipolar interactions between solutes and CD stationary phases are stronger than between solutes and C18, which is attributed to the special structures (CD and triazole groups) of CD stationary phases. Chemical origins are interpreted by comparison between CD1 and CD2. Similar dispersive interactions of CD1 and CD2 are attributed to their similar length of spacer arms. CD2 which contains OEG spacer arm has relative weaker HBD acidity but stronger HBA basicity. CD stationary phases display no serious different methylene selectivity and higher polar selectivity than in the case of C18. Higher acid selectivity and lower basic selectivity are observed on CD2 than on CD1. Distinctive retention properties and good complementary separation selectivity to C18 make the novel CD bonded stationary phases available for more application in RPLC.

[Characteristics of electroosmotic flow in open-tubular capillary electrochromatography with magnetic nanoparticle coating as mixed-mode stationary phase].

PubMed

Qin, Sasa; Zhou, Chaoran; Zhu, Yaxian; Ren, Zhiyu; Zhang, Lingyi; Fu, Honggang; Zhang, Weibing

2011-09-01

A novel open-tubular capillary electrochromatography (OT-CEC) column with magnetic nanoparticle coating as mixed-mode stationary phase was prepared. The mixed-mode stationary phases were obtained by mixing C18 and amino modified magnetic nanoparticles with different ratios. The mixed modified magnetic nanoparticles as stationary phase were introduced into the capillary by using external magnetic force. The magnetic nanoparticle coating can be easily regenerated by removing the external magnetic field, and applied to other separation modes. The characteristics of electroosmotic flow (EOF) were theoretically investigated through the effect of physicochemical properties of different stationary phases on EOF. The experiment was conducted under different ratios of mixed-mode stationary phases and coating lengths, and it was verified that the theoretical conclusions accorded with the experimental results. It was shown that the EOF can be easily adjusted by changing the ratio of stationary phases or the number of permanent magnets.

Ubiquinone Function in Neurospora crassa

PubMed Central

Drabikowska, Alicja K.; Kruszewska, Anna

1972-01-01

Mitochondria of cytoplasmic respiratory mutants [mi-1] (poky) and [mi-4] contain about a fourfold molar excess of ubiquinone as compared to the wild-type strain of Neurospora crassa. In the wild type and [mi-1] cultures the concentration of ubiquinone remains constant during the exponential and stationary phase of growth. In [mi-4] cultures it markedly decreases in the stationary phase. The reduction of ubiquinone by substrates is approximately the same in the three strains tested and amounts 60 to 70% of total ubiquinone present in mitochondria, independent of its absolute amount. The reduction of ubiquinone on addition of substrates is accompanied by the similar reduction of cytochrome c. These indicate that mitochondrial ubiquinone and cytochrome c are involved in processes of oxidation in Neurospora and that ubiquinone belongs mainly if not entirely to the cytochrome system of electron transport in these strains. PMID:4344917

Modelling of Hydrophilic Interaction Liquid Chromatography Stationary Phases Using Chemometric Approaches

PubMed Central

Ortiz-Villanueva, Elena; Tauler, Romà

2017-01-01

Metabolomics is a powerful and widely used approach that aims to screen endogenous small molecules (metabolites) of different families present in biological samples. The large variety of compounds to be determined and their wide diversity of physical and chemical properties have promoted the development of different types of hydrophilic interaction liquid chromatography (HILIC) stationary phases. However, the selection of the most suitable HILIC stationary phase is not straightforward. In this work, four different HILIC stationary phases have been compared to evaluate their potential application for the analysis of a complex mixture of metabolites, a situation similar to that found in non-targeted metabolomics studies. The obtained chromatographic data were analyzed by different chemometric methods to explore the behavior of the considered stationary phases. ANOVA-simultaneous component analysis (ASCA), principal component analysis (PCA) and partial least squares regression (PLS) were used to explore the experimental factors affecting the stationary phase performance, the main similarities and differences among chromatographic conditions used (stationary phase and pH) and the molecular descriptors most useful to understand the behavior of each stationary phase. PMID:29064436

Liquid toroidal drop under uniform electric field

NASA Astrophysics Data System (ADS)

Zabarankin, Michael

2017-06-01

The problem of a stationary liquid toroidal drop freely suspended in another fluid and subjected to an electric field uniform at infinity is addressed analytically. Taylor's discriminating function implies that, when the phases have equal viscosities and are assumed to be slightly conducting (leaky dielectrics), a spherical drop is stationary when Q=(2R2+3R+2)/(7R2), where R and Q are ratios of the phases' electric conductivities and dielectric constants, respectively. This condition holds for any electric capillary number, CaE, that defines the ratio of electric stress to surface tension. Pairam and Fernández-Nieves showed experimentally that, in the absence of external forces (CaE=0), a toroidal drop shrinks towards its centre, and, consequently, the drop can be stationary only for some CaE>0. This work finds Q and CaE such that, under the presence of an electric field and with equal viscosities of the phases, a toroidal drop having major radius ρ and volume 4π/3 is qualitatively stationary-the normal velocity of the drop's interface is minute and the interface coincides visually with a streamline. The found Q and CaE depend on R and ρ, and for large ρ, e.g. ρ≥3, they have simple approximations: Q˜(R2+R+1)/(3R2) and CaE∼3 √{3 π ρ / 2 } (6 ln ⁡ρ +2 ln ⁡[96 π ]-9 )/ (12 ln ⁡ρ +4 ln ⁡[96 π ]-17 ) (R+1 ) 2/ (R-1 ) 2.

Changes of trehalose content and expression of relative genes during the bioethanol fermentation by Saccharomyces cerevisiae.

PubMed

Yi, Chenfeng; Wang, Fenglian; Dong, Shijun; Li, Hao

2016-10-01

Traditionally, trehalose is considered as a protectant to improve the ethanol tolerance of Saccharomyces cerevisiae. In this study, to clarify the changes and roles of trehalose during the bioethanol fermentation, trehalose content and expression of related genes at lag, exponential, and stationary phases (i.e., 2, 8, and 16 h of batch fermentation process) were determined. Although yeast cells at exponential and stationary phase had higher trehalose content than cells at lag phase (P < 0.01), there was no significant difference in trehalose content between exponential and stationary phases (P > 0.05). Moreover, expression of the trehalose degradation-related genes NTH1 and NTH2 decreased at exponential phase in comparison with that at lag phase; compared with cells at lag phase, cells at stationary phase had higher expression of TPS1, ATH1, NTH1, and NTH2 but lower expression of TPS2. During the lag-exponential phase transition, downregulation of NTH1 and NTH2 promoted accumulation of trehalose, and to some extent, trehalose might confer ethanol tolerance to S. cerevisiae before stationary phase. During the exponential-stationary phase transition, upregulation of TPS1 contributed to accumulation of trehalose, and Tps1 protein might be indispensable in yeast cells to withstand ethanol stress at the stationary phase. Moreover, trehalose would be degraded to supply carbon source at stationary phase.

Production and Reutilization of Fluorescent Dissolved Organic Matter by a Marine Bacterial Strain, Alteromonas macleodii

PubMed Central

Goto, Shuji; Tada, Yuya; Suzuki, Koji; Yamashita, Youhei

2017-01-01

The recalcitrant fraction of marine dissolved organic matter (DOM) plays an important role in carbon storage on the earth’s surface. Bacterial production of recalcitrant DOM (RDOM) has been proposed as a carbon sequestration process. It is still unclear whether bacterial physiology can affect RDOM production. In this study, we conducted a batch culture using the marine bacterial isolate Alteromonas macleodii, a ubiquitous gammaproteobacterium, to evaluate the linkage between bacterial growth and DOM production. Glucose (1 mmol C L-1) was used as the sole carbon source, and the bacterial number, the DOM concentration in terms of carbon, and the excitation–emission matrices (EEMs) of DOM were monitored during the 168-h incubation. The incubation period was partitioned into the exponential growth (0–24 h) and stationary phases (24–168 h) based on the growth curve. Although the DOM concentration decreased during the exponential growth phase due to glucose consumption, it remained stable during the stationary phase, corresponding to approximately 4% of the initial glucose in terms of carbon. Distinct fluorophores were not evident in the EEMs at the beginning of the incubation, but DOM produced by the strain exhibited five fluorescent peaks during exponential growth. Two fluorescent peaks were similar to protein-like fluorophores, while the others could be categorized as humic-like fluorophores. All fluorophores increased during the exponential growth phase. The tryptophan-like fluorophore decreased during the stationary phase, suggesting that the strain reused the large exopolymer. The tyrosine-like fluorophore seemed to be stable during the stationary phase, implying that the production of tyrosine-containing small peptides through the degradation of exopolymers was correlated with the reutilization of the tyrosine-like fluorophore. Two humic-like fluorophores that showed emission maxima at the longer wavelength (525 nm) increased during the stationary phase, while the other humic-like fluorophore, which had a shorter emission wavelength (400 nm) and was categorized as recalcitrant, was stable. These humic-like fluorophore behaviors during incubation indicated that the composition of bacterial humic-like fluorophores, which were unavailable to the strain, differed between growth phases. Our results suggest that bacterial physiology can affect RDOM production and accumulation in the ocean interior. PMID:28400762

Profiling of polar metabolites in biological extracts using diamond hydride-based aqueous normal phase chromatography.

PubMed

Callahan, Damien L; De Souza, David; Bacic, Antony; Roessner, Ute

2009-07-01

Highly polar metabolites, such as sugars and most amino acids are not retained by conventional RP LC columns. Without sufficient retention low concentration compounds are not detected due ion suppression and structural isomers are not resolved. In contrast, hydrophilic interaction chromatography (HILIC) and aqueous normal phase chromatography (ANP) retain compounds based on their hydrophilicity and therefore provides a means of separating highly polar compounds. Here, an ANP method based on the diamond hydride stationary phase is presented for profiling biological small molecules by LC. A rapid separation system based upon a fast gradient that delivers reproducible chromatography is presented. Approximately 1000 compounds were reproducibly detected in human urine samples and clear differences between these samples were identified. This chromatography was also applied to xylem fluid from soyabean (Glycine max) plants to which 400 compounds were detected. This method greatly increases the metabolite coverage over RP-only metabolite profiling in biological samples. We show that both forms of chromatography are necessary for untargeted comprehensive metabolite profiling and that the diamond hydride stationary phase provides a good option for polar metabolite analysis.

Mobile, stationary and mixed phase tracers: consequences to sea ice biogeochemistry

NASA Astrophysics Data System (ADS)

Jeffery, N.; Elliott, S.; Hunke, E. C.; Deal, C.; Jin, M.

2016-02-01

Models of brine motion in sea ice have offered mechanisms for transporting biogeochemical compounds vertically within the ice and between the ice-ocean interface. In these models, sea ice microstructure and/or gross physical properties determine the resupply of nitrate, for example, to sympagic algae and that resupply, in large part, constrains sea ice primary production. The assumption of brine transport models is that the transported matter exists in a purely mobile phase within the ice brine channels. As a result, non-reacting, mobile phase tracers evolve like salinity in dynamic sea ice. Field and laboratory observations indicate that this is a good approximation for the primary algal macronutrients - nitrate, silicate and phosphate, but clear deviations are evident for ammonium, micronutrients such as iron, humic substances, algal bi-products such as gels and extracellular polysaccharides, and the algae themselves. This wide range of biogeochemical matter resists brine motion and is present in both the mobile and stationary phases, i.e. these tracers are "mixed" with respect to their transport phases. Although the precise mechanism for this resistance may be due to attachment by frustules, "stickiness" of the material surface, adsorption, or, in the case of microorganisms, active motility, a key common element in all cases is the presence of the ice matrix. In this presentation we investigate the consequences of mixed phase tracers in sea ice on algal concentrations, vertical distributions, and the potential accumulation of biogeochemical matter within the ice. We assume that sea ice growth promotes retention to the stationary phase, while melt and the disintegration of the ice matrix promotes release into the mobile phase. By varying the retention and release timescales of this formulation, we retrieve the purely mobile and maximal accumulation limits.

Stability of semidiscrete approximations for hyperbolic initial-boundary-value problems: Stationary modes

NASA Technical Reports Server (NTRS)

Warming, Robert F.; Beam, Richard M.

1988-01-01

Spatially discrete difference approximations for hyperbolic initial-boundary-value problems (IBVPs) require numerical boundary conditions in addition to the analytical boundary conditions specified for the differential equations. Improper treatment of a numerical boundary condition can cause instability of the discrete IBVP even though the approximation is stable for the pure initial-value or Cauchy problem. In the discrete IBVP stability literature there exists a small class of discrete approximations called borderline cases. For nondissipative approximations, borderline cases are unstable according to the theory of the Gustafsson, Kreiss, and Sundstrom (GKS) but they may be Lax-Richtmyer stable or unstable in the L sub 2 norm on a finite domain. It is shown that borderline approximation can be characterized by the presence of a stationary mode for the finite-domain problem. A stationary mode has the property that it does not decay with time and a nontrivial stationary mode leads to algebraic growth of the solution norm with mesh refinement. An analytical condition is given which makes it easy to detect a stationary mode; several examples of numerical boundary conditions are investigated corresponding to borderline cases.

Simulated molecular-scale interaction of supercritical fluid mobile and stationary phases.

PubMed

Siders, Paul D

2017-12-08

In supercritical fluid chromatography, molecules from the mobile phase adsorb on the stationary phase. Stationary-phase alkylsilane-terminated silica surfaces might adsorb molecules at the silica, among the silanes, on a silane layer, or in pore space between surfaces. Mobile phases of carbon dioxide, pure and modified with methanol, and stationary phases were simulated at the molecular scale. Classical atomistic force fields were used in Gibbs-ensemble hybrid Monte Carlo calculations. Excess adsorption of pure carbon dioxide mobile phase peaked at fluid densities of 0.002-0.003Å -3 . Mobile phase adsorption from 7% methanol in carbon dioxide peaked at lower fluid density. Methanol was preferentially adsorbed from the mixed fluid. Surface silanes prevented direct interaction of fluid-phase molecules with silica. Some adsorbed molecules mixed with tails of bonded silanes; some formed layers above the silanes. Much adsorption occurred by filling the space between surfaces in the stationary-phase model. The distribution in the stationary phase of methanol molecules from a modified fluid phase varied with pressure. Copyright © 2017 Elsevier B.V. All rights reserved.

Novel stationary phases based on asphaltenes for gas chromatography.

PubMed

Boczkaj, Grzegorz; Momotko, Malwina; Chruszczyk, Dorota; Przyjazny, Andrzej; Kamiński, Marian

2016-07-01

We present the results of investigations on the possibility of the application of the asphaltene fraction isolated from the oxidized residue from vacuum distillation of crude oil as a stationary phase for gas chromatography. The results of the investigation revealed that the asphaltene stationary phases can find use for the separation of a wide range of volatile organic compounds. The experimental values of Rohrschneider/McReynolds constants characterize the asphaltenes as stationary phases of medium polarity and selectivity similar to commercially available phases based on alkyl phthalates. Isolation of asphaltenes from the material obtained under controlled process conditions allows the production of a stationary phase having reproducible sorption properties and chromatographic columns having the same selectivity. Unique selectivity and high thermal stability make asphaltenes attractive as a material for stationary phases for gas chromatography. A low production cost from a readily available raw material (oxidized petroleum bitumens) is an important economic factor in case of application of the asphaltene stationary phases for preparative and process separations. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Competitive fitness during feast and famine: how SOS DNA polymerases influence physiology and evolution in Escherichia coli.

PubMed

Corzett, Christopher H; Goodman, Myron F; Finkel, Steven E

2013-06-01

Escherichia coli DNA polymerases (Pol) II, IV, and V serve dual roles by facilitating efficient translesion DNA synthesis while simultaneously introducing genetic variation that can promote adaptive evolution. Here we show that these alternative polymerases are induced as cells transition from exponential to long-term stationary-phase growth in the absence of induction of the SOS regulon by external agents that damage DNA. By monitoring the relative fitness of isogenic mutant strains expressing only one alternative polymerase over time, spanning hours to weeks, we establish distinct growth phase-dependent hierarchies of polymerase mutant strain competitiveness. Pol II confers a significant physiological advantage by facilitating efficient replication and creating genetic diversity during periods of rapid growth. Pol IV and Pol V make the largest contributions to evolutionary fitness during long-term stationary phase. Consistent with their roles providing both a physiological and an adaptive advantage during stationary phase, the expression patterns of all three SOS polymerases change during the transition from log phase to long-term stationary phase. Compared to the alternative polymerases, Pol III transcription dominates during mid-exponential phase; however, its abundance decreases to <20% during long-term stationary phase. Pol IV transcription dominates as cells transition out of exponential phase into stationary phase and a burst of Pol V transcription is observed as cells transition from death phase to long-term stationary phase. These changes in alternative DNA polymerase transcription occur in the absence of SOS induction by exogenous agents and indicate that cell populations require appropriate expression of all three alternative DNA polymerases during exponential, stationary, and long-term stationary phases to attain optimal fitness and undergo adaptive evolution.

Multiple scattering in the high-frequency limit with second-order shadowing function from 2D anisotropic rough dielectric surfaces: I. Theoretical study

NASA Astrophysics Data System (ADS)

Bourlier, C.; Berginc, G.

2004-07-01

In this paper the first- and second-order Kirchhoff approximation is applied to study the backscattering enhancement phenomenon, which appears when the surface rms slope is greater than 0.5. The formulation is reduced to the geometric optics approximation in which the second-order illumination function is taken into account. This study is developed for a two-dimensional (2D) anisotropic stationary rough dielectric surface and for any surface slope and height distributions assumed to be statistically even. Using the Weyl representation of the Green function (which introduces an absolute value over the surface elevation in the phase term), the incoherent scattering coefficient under the stationary phase assumption is expressed as the sum of three terms. The incoherent scattering coefficient then requires the numerical computation of a ten- dimensional integral. To reduce the number of numerical integrations, the geometric optics approximation is applied, which assumes that the correlation between two adjacent points is very strong. The model is then proportional to two surface slope probabilities, for which the slopes would specularly reflect the beams in the double scattering process. In addition, the slope distributions are related with each other by a propagating function, which accounts for the second-order illumination function. The companion paper is devoted to the simulation of this model and comparisons with an 'exact' numerical method.

Crosslinked structurally-tuned polymeric ionic liquids as stationary phases for the analysis of hydrocarbons in kerosene and diesel fuels by comprehensive two-dimensional gas chromatography.

PubMed

Zhang, Cheng; Park, Rodney A; Anderson, Jared L

2016-04-01

Structurally-tuned ionic liquids (ILs) have been previously applied as the second dimension column in comprehensive two-dimensional gas chromatography (GC×GC) and have demonstrated high selectivity in the separation of individual aliphatic hydrocarbons from other aliphatic hydrocarbons. However, the maximum operating temperatures of these stationary phases limit the separation of analytes with high boiling points. In order to address this issue, a series of polymeric ionic liquid (PIL)-based stationary phases were prepared in this study using imidazolium-based IL monomers via in-column free radical polymerization. The IL monomers were functionalized with long alkyl chain substituents to provide the needed selectivity for the separation of aliphatic hydrocarbons. Columns were prepared with different film thicknesses to identify the best performing stationary phase for the separation of kerosene. The bis[(trifluoromethyl)sulfonyl]imide ([NTf2](-))-based PIL stationary phase with larger film thickness (0.28μm) exhibited higher selectivity for aliphatic hydrocarbons and showed a maximum allowable operating temperature of 300°C. PIL-based stationary phases containing varied amount of IL-based crosslinker were prepared to study the effect of the crosslinker on the selectivity and thermal stability of the resulting stationary phase. The optimal resolution of aliphatic hydrocarbons was achieved when 50% (w/w) of crosslinker was incorporated into the PIL-based stationary phase. The resulting stationary phase exhibited good selectivity for different groups of aliphatic hydrocarbons even after being conditioned at 325°C. Finally, the crosslinked PIL-based stationary phase was compared with SUPELCOWAX 10 and DB-17 columns for the separation of aliphatic hydrocarbons in diesel fuel. Better resolution of aliphatic hydrocarbons was obtained when employing the crosslinked PIL-based stationary phase as the second dimension column. Copyright © 2016 Elsevier B.V. All rights reserved.

Liquid Crystals in Chromatography

NASA Astrophysics Data System (ADS)

Witkiewicz, Zygfryd

The following sections are included: * INTRODUCTION * LIQUID CRYSTALS SUITABLE FOR GAS CHROMATOGRAPHY * Monomeric Liquid Crystal Stationary Phases * Polymeric Liquid Crystal Stationary Phases * Polymeric Liquid Crystal Stationary Phases * Conventional Analytical Columns * Capillary Columns * FACTORS AFFECTING THE CHROMATOGRAPHIC SEPARATIONS ON LIQUID CRYSTAL STATIONARY PHASES * Kind of Mesophase of the Liquid Crystal * Molecular Structure of the Liquid Crystals and of the Chromatographed Substances * Substrate on which the Liquid Crystal is Deposited * ANALYTICAL APPLICATIONS OF LIQUID CRYSTAL STATIONARY PHASES IN GAS CHROMATOGRAPHY * Separation of Isomers of Benzene and Naphthalene Derivatives * Separation of Alkane and Alkene Isomers * Separation of Mixtures of Benzene and Aliphatic Hydrocarbon Derivatives Containing Heteroatoms * Separation of Polynuclear Hydrocarbons * INVESTIGATION OF THE PROPERTIES OF LIQUID CRYSTALS BY GAS CHROMATOGRAPHY * APPLICATION OF LIQUID CRYSTALS IN LIQUID CHROMATOGRAPHY * Column Chromatography * Thin-Layer Chromatography * APPLICATION OF LIQUID CRYSTAL STATIONARY PHASES IN SUPERCRITICAL FLUID CHROMATOGRAPHY * FINAL REMARKS * References

Retention characteristics of a new butylimidazolium-based stationary phase. Part II: anion exchange and partitioning.

PubMed

Van Meter, David S; Sun, Yaqin; Parker, Kevin M; Stalcup, Apryll M

2008-02-01

A surface-confined ionic liquid (SCIL) and a commercial quaternary amine silica-based stationary phase were characterized employing the linear solvation energy relationship (LSER) method in binary methanol/water mobile phases. The retention properties of the stationary phases were evaluated in terms of intermolecular interactions between 28 test solutes and the stationary phases. The comparison reveals a difference in the hydrophobic and hydrogen bond acceptance interaction properties between the two phases. The anion exchange retention mechanism of the SCIL phase was demonstrated using nucleotides. The utility of the SCIL phase in predicting logk (IL/water) values by chromatographic methods is also discussed.

Selectivity assessment of DB-200 and DB-VRX open-tubular capillary columns.

PubMed

Kiridena, W; Koziola, W W; Poole, C F

2001-10-12

The solvation parameter model is used to study the influence of composition and temperature on the selectivity of two poly(siloxane) stationary phases used for open-tubular capillary column gas chromatography. The poly(methyltrifluoropropyldimethylsiloxane) stationary phase, DB-200, has low cohesion, intermediate dipolarity/polarizability, low hydrogen-bond basicity, no hydrogen-bond acidity, and repulsive electron lone pair interactions. The DB-VRX stationary phase has low cohesion, low dipolarity/polarizability, low hydrogen-bond basicity and no hydrogen-bond acidity and no capacity for electron lone pair interactions. The selectivity of the two stationary phases is complementary to those in a database of 11 stationary phase chemistries determined under the same experimental conditions.

The Nonstationary Dynamics of Fitness Distributions: Asexual Model with Epistasis and Standing Variation

PubMed Central

Martin, Guillaume; Roques, Lionel

2016-01-01

Various models describe asexual evolution by mutation, selection, and drift. Some focus directly on fitness, typically modeling drift but ignoring or simplifying both epistasis and the distribution of mutation effects (traveling wave models). Others follow the dynamics of quantitative traits determining fitness (Fisher’s geometric model), imposing a complex but fixed form of mutation effects and epistasis, and often ignoring drift. In all cases, predictions are typically obtained in high or low mutation rate limits and for long-term stationary regimes, thus losing information on transient behaviors and the effect of initial conditions. Here, we connect fitness-based and trait-based models into a single framework, and seek explicit solutions even away from stationarity. The expected fitness distribution is followed over time via its cumulant generating function, using a deterministic approximation that neglects drift. In several cases, explicit trajectories for the full fitness distribution are obtained for arbitrary mutation rates and standing variance. For nonepistatic mutations, especially with beneficial mutations, this approximation fails over the long term but captures the early dynamics, thus complementing stationary stochastic predictions. The approximation also handles several diminishing returns epistasis models (e.g., with an optimal genotype); it can be applied at and away from equilibrium. General results arise at equilibrium, where fitness distributions display a “phase transition” with mutation rate. Beyond this phase transition, in Fisher’s geometric model, the full trajectory of fitness and trait distributions takes a simple form; robust to the details of the mutant phenotype distribution. Analytical arguments are explored regarding why and when the deterministic approximation applies. PMID:27770037

Characteristic of laser diode beam propagation through a collimating lens.

PubMed

Xu, Qiang; Han, Yiping; Cui, Zhiwei

2010-01-20

A mathematical model of a laser diode beam propagating through a collimating lens is presented. Wave propagation beyond the paraxial approximation is studied. The phase delay of the laser diode wave in passing through the lens is analyzed in detail. The propagation optical field after the lens is obtained from the diffraction integral by the stationary phase method. The model is employed to predict the light intensity at various beam cross sections, and the computed intensity distributions are in a good agreement with the corresponding measurements.

Use of ionic liquids as stationary phases in hyphenated gas chromatography techniques.

PubMed

Ragonese, Carla; Sciarrone, Danilo; Tranchida, Peter Quinto; Dugo, Paola; Mondello, Luigi

2012-09-14

In the past decades a consistent number of ionic liquids have been specifically synthesized and evaluated as stationary phase in gas chromatography. Ionic liquid, also defined as "molten salts", are a class of organic non-molecular solvents liquid at room temperature (RTILs) that satisfy most of the requirements of a GC stationary phase, among which a high viscosity, the possibility to tune the selectivity (by changing the cation-anion combination) and a high thermal stability. The choice of the proper stationary phase plays a key role in the improvement/optimization of a GC method, and although the use of IL as stationary phases is still not well-established, the general interest in their applications has greatly increased, thanks to their particular properties. The present contribution provides an overview on recent evaluations and applications of IL stationary phases, focusing in particular on the use of these novel tools in hyphenated GC-based techniques. Copyright © 2012 Elsevier B.V. All rights reserved.

Polar stationary phases based on poly(oligo ethylene glycol)diacrylates for capillary gas chromatography

NASA Astrophysics Data System (ADS)

Shiryaeva, V. E.; Popova, T. P.; Korolev, A. A.; Kanat'eva, A. Yu.; Kurganov, A. A.

2017-08-01

New stationary phases for capillary columns in GC are synthesized and studied. The phases are prepared by depositing oligo(ethylene glycol)diacrylates on the column walls and subsequent polymerization (crosslinking) in the presence of peroxide initiators. It is shown that stationary phases based on monomers with molecular weights of 10 kDa or higher exhibit separation properties similar to those of conventional stationary phases based on polyethylene glycol (PEG); however, their thermal stability is higher because they have a higher degree of crosslinking and a more ordered structure of the crosslinked polymers than the respective parameters of phases based on native PEG.

A unified classification of stationary phases for packed column supercritical fluid chromatography.

PubMed

West, C; Lesellier, E

2008-05-16

The use of supercritical fluids as chromatographic mobile phases allows to obtain rapid separations with high efficiency on packed columns, which could favour the replacement of numerous HPLC methods by supercritical fluid chromatography (SFC) ones. Moreover, despite some unexpected chromatographic behaviours, general retention rules are now well understood, and mainly depend on the nature of the stationary phase. The use of polar stationary phases improves the retention of polar compounds, when C18-bonded silica favours the retention of hydrocarbonaceous compounds. In this sense, reversed-phase and normal-phase chromatography can be achieved in SFC, as in HPLC. However, these two domains are clearly separated in HPLC due to the opposite polarity of the mobile phases used for each method. In SFC, the same mobile phase can be used with both polar and non-polar stationary phases. Consequently, the need for a novel classification of stationary phases in SFC appears, allowing a unification of the classical reversed- and normal-phase domains. In this objective, the paper presents the development of a five-dimensional classification based on retention data for 94-111 solutes, using 28 commercially available columns representative of three major types of stationary phases. This classification diagram is based on a linear solvation energy relationship, on the use of solvation vectors and the calculation of similarity factors between the different chromatographic systems. This classification will be of great help in the choice of the well-suited stationary phase, either in regards of a particular separation or to improve the coupling of columns with complementary properties.

Survival of Campylobacter jejuni during Stationary Phase: Evidence for the Absence of a Phenotypic Stationary-Phase Response

PubMed Central

Kelly, Alison F.; Park, Simon F.; Bovill, Richard; Mackey, Bernard M.

2001-01-01

When Campylobacter jejuni NCTC 11351 was grown microaerobically in rich medium at 39°C, entry into stationary phase was followed by a rapid decline in viable numbers to leave a residual population of 1% of the maximum number or less. Loss of viability was preceded by sublethal injury, which was seen as a loss of the ability to grow on media containing 0.1% sodium deoxycholate or 1% sodium chloride. Resistance of cells to mild heat stress (50°C) or aeration was greatest in exponential phase and declined during early stationary phase. These results show that C. jejuni does not mount the normal phenotypic stationary-phase response which results in enhanced stress resistance. This conclusion is consistent with the absence of rpoS homologues in the recently reported genome sequence of this species and their probable absence from strain NCTC 11351. During prolonged incubation of C. jejuni NCTC 11351 in stationary phase, an unusual pattern of decreasing and increasing heat resistance was observed that coincided with fluctuations in the viable count. During stationary phase of Campylobacter coli UA585, nonmotile variants and those with impaired ability to form coccoid cells were isolated at high frequency. Taken together, these observations suggest that stationary-phase cultures of campylobacters are dynamic populations and that this may be a strategy to promote survival in at least some strains. Investigation of two spontaneously arising variants (NM3 and SC4) of C. coli UA585 showed that a reduced ability to form coccoid cells did not affect survival under nongrowth conditions. PMID:11319108

Growth phase-dependent induction of stationary-phase promoters of Escherichia coli in different gram-negative bacteria.

PubMed Central

Miksch, G; Dobrowolski, P

1995-01-01

RSF1010-derived plasmids carrying a fusion of a promoterless lacZ gene with the sigma s-dependent growth phase-regulated promoters of Escherichia coli, bolAp1 and fic, were constructed. The plasmids were mobilized into the gram-negative bacterial species Acetobacter methanolicus, Xanthomonas campestris, Pseudomonas putida, and Rhizobium meliloti. The beta-galactosidase activities of bacterial cultures were determined during exponential and stationary growth phases. Transcriptional activation of the fic promoter in the different bacteria was growth phase dependent as in E. coli and was initiated generally during the transition to stationary phase. The induction of the bolA promoter was also growth phase dependent in the bacteria tested. While the expression in E. coli and R. meliloti was initiated during the transition from exponential to stationary phase, the induction in A. methanolicus, P. putida, and X. campestris started some hours after stationary growth phase was reached. In all the species tested, DNA fragments hybridizing with the rpoS gene of E. coli were detected. The results show that in different gram-negative bacteria, stationary-phase-specific sigma factors which are structurally and functionally homologous to sigma s and are able to recognize the promoter sequences of both bolA and fic exist. PMID:7665531

Enantioselective potential of polysaccharide-based chiral stationary phases in supercritical fluid chromatography.

PubMed

Kucerova, Gabriela; Kalikova, Kveta; Tesarova, Eva

2017-06-01

The enantioselective potential of two polysaccharide-based chiral stationary phases for analysis of chiral structurally diverse biologically active compounds was evaluated in supercritical fluid chromatography using a set of 52 analytes. The chiral selectors immobilized on 2.5 μm silica particles were tris-(3,5-dimethylphenylcarmabate) derivatives of cellulose or amylose. The influence of the polysaccharide backbone, different organic modifiers, and different mobile phase additives on retention and enantioseparation was monitored. Conditions for fast baseline enantioseparation were found for the majority of the compounds. The success rate of baseline and partial enantioseparation with cellulose-based chiral stationary phase was 51.9% and 15.4%, respectively. Using amylose-based chiral stationary phase we obtained 76.9% of baseline enantioseparations and 9.6% of partial enantioseparations of the tested compounds. The best results on cellulose-based chiral stationary phase were achieved particularly with propane-2-ol and a mixture of isopropylamine and trifluoroacetic acid as organic modifier and additive to CO 2 , respectively. Methanol and basic additive isopropylamine were preferred on amylose-based chiral stationary phase. The complementary enantioselectivity of the cellulose- and amylose-based chiral stationary phases allows separation of the majority of the tested structurally different compounds. Separation systems were found to be directly applicable for analyses of biologically active compounds of interest. © 2017 Wiley Periodicals, Inc.

Preparation and evaluation of a silica-based 1-alkyl-3-(propyl-3-sulfonate) imidazolium zwitterionic stationary phase for high-performance liquid chromatography.

PubMed

Qiu, Hongdeng; Jiang, Qiong; Wei, Zheng; Wang, Xusheng; Liu, Xia; Jiang, Shengxiang

2007-09-07

A new zwitterionic stationary phase based on silica bonded with 1-alkyl-3-(propyl-3-sulfonate) imidazolium was synthesized and characterized in this paper. The materials have been confirmed and evaluated by elemental analysis, thermogravimetric analysis and X-ray photoelectron spectroscopy. Potassium and calcium were separated simultaneously with several common inorganic anions including an iodate, chloride, bromide, nitrate and iodide on the phase. The effects of the concentration, organic solvent and pH of the eluent on the separation of anions were studied. Operated in the anion-exchange mode, this new stationary phase shows considerable promise for the separation of anions. Bases, vitamins and three imidazolium ionic liquids with different alkyl chains are also separated successfully on this column. The stationary phase has multiple retention mechanisms, such as anion-exchange, electrostatic attraction and repulsion interactions, and hydrophobic interaction between the zwitterionic stationary phase and specimens.

A novel octadecylsilane functionalized graphene oxide/silica composite stationary phase for high performance liquid chromatography.

PubMed

Liang, Xiaojing; Wang, Shuai; Liu, Shujuan; Liu, Xia; Jiang, Shengxiang

2012-08-01

An octadecylsilane functionalized graphene oxide/silica stationary phase was fabricated by assembling graphene oxide onto the silica particles through an amide bond and subsequent immobilization of octadecylsilane. The chromatographic properties of the stationary phase were investigated by reversed-phase chromatography with alkylbenzenes, polycyclic aromatic hydrocarbons, amines, and phenolic compounds as the analytes. All the compounds achieved good separation on the column. The comparison between a C18 commercial column and the new stationary phase indicated that the existence of π-electron system of graphene oxide allows π-π interaction between analyte and octadecylsilane functionalized graphene oxide/silica stationary phase except for hydrophobic interaction, while only hydrophobic interaction presented between analyte and C18 commercial column. This suggests that some analytes can be better separated on the octadecylsilane functionalized graphene oxide/silica column. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The stability of two-phase flow over a swept-wing

NASA Technical Reports Server (NTRS)

Coward, Adrian; Hall, Philip

1994-01-01

We use numerical and asymptotic techniques to study the stability of a two-phase air/water flow above a flat porous plate. This flow is a model of the boundary layer which forms on a yawed cylinder and can be used as a useful approximation to the air flow over swept wings during heavy rainfall. We show that the interface between the water and air layers can significantly destabilize the flow, leading to traveling wave disturbances which move along the attachment line. This instability occurs for lower Reynolds numbers than in the case of the absence of a water layer. We also investigate the instability of inviscid stationary modes. We calculate the effective wavenumber and orientation of the stationary disturbance when the fluids have identical physical properties. Using perturbation methods we obtain corrections due to a small stratification in viscosity, thus quantifying the interfacial effects. Our analytical results are in agreement with the numerical solution which we obtain for arbitrary fluid properties.

Separation performance of cucurbit[7]uril in ionic liquid-based sol-gel coating as stationary phase for capillary gas chromatography.

PubMed

Wang, Xiaogang; Qi, Meiling; Fu, Ruonong

2014-12-05

Here we report the separation performance of a new stationary phase of cucurbit[7]uril (CB7) incorporated into an ionic liquid-based sol-gel coating (CB7-SG) for capillary gas chromatography (GC). The CB7-SG stationary phase showed an average polarity of 455, suggesting its polar nature. Abraham system constants revealed that its major interactions with analytes include H-bond basicity (a), dipole-dipole (s) and dispersive (l) interactions. The CB7-SG stationary phase achieved baseline separation for a wide range of analytes with symmetrical peak shapes and showed advantages over the conventional polar stationary phase that failed to resolve some critical analytes. Also, it exhibited different retention behaviors from the conventional stationary phase in terms of retention times and elution order. Most interestingly, in contrast to the conventional polar phase, the CB7-SG stationary phase exhibited longer retentions for analytes of lower polarity but relatively comparable retentions for polar analytes such as alcohols and phenols. The high resolving ability and unique retention behaviors of the CB7-SG stationary phase may stem from the comprehensive interactions of the aforementioned interactions and shape selectivity. Moreover, the CB7-SG column showed good peak shapes for analytes prone to peak tailing, good thermal stability up to 280°C and separation repeatability with RSD values in the range of 0.01-0.11% for intra-day, 0.04-0.41% for inter-day and 2.5-6.0% for column-to-column, respectively. As demonstrated, the proposed coating method can simultaneously address the solubility problem with CBs for the intended purpose and achieve outstanding GC separation performance. Copyright © 2014 Elsevier B.V. All rights reserved.

Surface-bonded ionic liquid stationary phases in high-performance liquid chromatography--a review.

PubMed

Pino, Verónica; Afonso, Ana M

2012-02-10

Ionic liquids (ILs) are a class of ionic, nonmolecular solvents which remain in liquid state at temperatures below 100°C. ILs possess a variety of properties including low to negligible vapor pressure, high thermal stability, miscibility with water or a variety of organic solvents, and variable viscosity. IL-modified silica as novel high-performance liquid chromatography (HPLC) stationary phases have attracted considerable attention for their differential behavior and low free-silanol activity. Indeed, around 21 surface-confined ionic liquids (SCIL) stationary phases have been developed in the last six years. Their chromatographic behavior has been studied, and, despite the presence of a positive charge on the stationary phase, they showed considerable promise for the separation of neutral solutes (not only basic analytes), when operated in reversed phase mode. This aspect points to the potential for truly multimodal stationary phases. This review attempts to summarize the state-of-the-art about SCIL phases including their preparation, chromatographic behavior, and analytical performance. Copyright © 2011 Elsevier B.V. All rights reserved.

Versatile ligands for high-performance liquid chromatography: An overview of ionic liquid-functionalized stationary phases.

PubMed

Zhang, Mingliang; Mallik, Abul K; Takafuji, Makoto; Ihara, Hirotaka; Qiu, Hongdeng

2015-08-05

Ionic liquids (ILs), a class of unique substances composed purely by cation and anions, are renowned for their fascinating physical and chemical properties, such as negligible volatility, high dissolution power, high thermal stability, tunable structure and miscibility. They are enjoying ever-growing applications in a great diversity of disciplines. IL-modified silica, transforming the merits of ILs into chromatographic advantages, has endowed the development of high-performance liquid chromatography (HPLC) stationary phase with considerable vitality. In the last decade, IL-functionalized silica stationary phases have evolved into a series of branches to accommodate to different HPLC modes. An up-to-date overview of IL-immobilized stationary phases is presented in this review, and divided into five parts according to application mode, i.e., ion-exchange, normal-phase, reversed-phase, hydrophilic interaction and chiral recognition. Specific attention is channeled to synthetic strategies, chromatographic behavior and separation performance of IL-functionalized silica stationary phases. Copyright © 2015 Elsevier B.V. All rights reserved.

Chaotic oscillations and noise transformations in a simple dissipative system with delayed feedback

NASA Astrophysics Data System (ADS)

Zverev, V. V.; Rubinstein, B. Ya.

1991-04-01

We analyze the statistical behavior of signals in nonlinear circuits with delayed feedback in the presence of external Markovian noise. For the special class of circuits with intense phase mixing we develop an approach for the computation of the probability distributions and multitime correlation functions based on the random phase approximation. Both Gaussian and Kubo-Andersen models of external noise statistics are analyzed and the existence of the stationary (asymptotic) random process in the long-time limit is shown. We demonstrate that a nonlinear system with chaotic behavior becomes a noise amplifier with specific statistical transformation properties.

Adsorption of water from aqueous acetonitrile on silica-based stationary phases in aqueous normal-phase liquid chromatography.

PubMed

Soukup, Jan; Jandera, Pavel

2014-12-29

Excess adsorption of water from aqueous acetonitrile mobile phases was investigated on 16 stationary phases using the frontal analysis method and coulometric Karl-Fischer titration. The stationary phases include silica gel and silica-bonded phases with different polarities, octadecyl and cholesterol, phenyl, nitrile, pentafluorophenylpropyl, diol and zwitterionic sulfobetaine and phosphorylcholine ligands bonded on silica, hybrid organic-silica and hydrosilated matrices. Both fully porous and core-shell column types were included. Preferential uptake of water by the columns can be described by Langmuir isotherms. Even though a diffuse rather than a compact adsorbed discrete layer of water on the adsorbent surface can be formed because of the unlimited miscibility of water with acetonitrile, for convenience, the preferentially adsorbed water was expressed in terms of a hypothetical monomolecular water layer equivalent in the inner pores. The uptake of water strongly depends on the polarity and type of the column. Less than one monomolecular water layer equivalent was adsorbed on moderate polar silica hydride-based stationary phases, Ascentis Express F5 and Ascentis Express CN column at the saturation capacity, while on more polar stationary phases, several water layer equivalents were up-taken from the mobile phase. The strongest affinity to water was observed on the ZIC cHILIC stationary phases, where more than nine water layer equivalents were adsorbed onto its surface at its saturation capacity. Columns with bonded hydroxyl and diol ligands show stronger water adsorption in comparison to bare silica. Columns based on hydrosilated silica generally show significantly decreased water uptake in comparison to stationary phases bonded on ordinary silica. Significant correlations were found between the water uptake and the separation selectivity for compounds with strong polarity differences. Copyright © 2014 Elsevier B.V. All rights reserved.

Transition operators in electromagnetic-wave diffraction theory. II - Applications to optics

NASA Technical Reports Server (NTRS)

Hahne, G. E.

1993-01-01

The theory developed by Hahne (1992) for the diffraction of time-harmonic electromagnetic waves from fixed obstacles is briefly summarized and extended. Applications of the theory are considered which comprise, first, a spherical harmonic expansion of the so-called radiation impedance operator in the theory, for a spherical surface, and second, a reconsideration of familiar short-wavelength approximation from the new standpoint, including a derivation of the so-called physical optics method on the basis of quasi-planar approximation to the radiation impedance operator, augmented by the method of stationary phase. The latter includes a rederivation of the geometrical optics approximation for the complete Green's function for the electromagnetic field in the presence of a smooth- and a convex-surfaced perfectly electrically conductive obstacle.

Haemophilus ducreyi Hfq contributes to virulence gene regulation as cells enter stationary phase.

PubMed

Gangaiah, Dharanesh; Labandeira-Rey, Maria; Zhang, Xinjun; Fortney, Kate R; Ellinger, Sheila; Zwickl, Beth; Baker, Beth; Liu, Yunlong; Janowicz, Diane M; Katz, Barry P; Brautigam, Chad A; Munson, Robert S; Hansen, Eric J; Spinola, Stanley M

2014-02-11

To adapt to stresses encountered in stationary phase, Gram-negative bacteria utilize the alternative sigma factor RpoS. However, some species lack RpoS; thus, it is unclear how stationary-phase adaptation is regulated in these organisms. Here we defined the growth-phase-dependent transcriptomes of Haemophilus ducreyi, which lacks an RpoS homolog. Compared to mid-log-phase organisms, cells harvested from the stationary phase upregulated genes encoding several virulence determinants and a homolog of hfq. Insertional inactivation of hfq altered the expression of ~16% of the H. ducreyi genes. Importantly, there were a significant overlap and an inverse correlation in the transcript levels of genes differentially expressed in the hfq inactivation mutant relative to its parent and the genes differentially expressed in stationary phase relative to mid-log phase in the parent. Inactivation of hfq downregulated genes in the flp-tad and lspB-lspA2 operons, which encode several virulence determinants. To comply with FDA guidelines for human inoculation experiments, an unmarked hfq deletion mutant was constructed and was fully attenuated for virulence in humans. Inactivation or deletion of hfq downregulated Flp1 and impaired the ability of H. ducreyi to form microcolonies, downregulated DsrA and rendered H. ducreyi serum susceptible, and downregulated LspB and LspA2, which allow H. ducreyi to resist phagocytosis. We propose that, in the absence of an RpoS homolog, Hfq serves as a major contributor of H. ducreyi stationary-phase and virulence gene regulation. The contribution of Hfq to stationary-phase gene regulation may have broad implications for other organisms that lack an RpoS homolog. Pathogenic bacteria encounter a wide range of stresses in their hosts, including nutrient limitation; the ability to sense and respond to such stresses is crucial for bacterial pathogens to successfully establish an infection. Gram-negative bacteria frequently utilize the alternative sigma factor RpoS to adapt to stresses and stationary phase. However, homologs of RpoS are absent in some bacterial pathogens, including Haemophilus ducreyi, which causes chancroid and facilitates the acquisition and transmission of HIV-1. Here, we provide evidence that, in the absence of an RpoS homolog, Hfq serves as a major contributor of stationary-phase gene regulation and that Hfq is required for H. ducreyi to infect humans. To our knowledge, this is the first study describing Hfq as a major contributor of stationary-phase gene regulation in bacteria and the requirement of Hfq for the virulence of a bacterial pathogen in humans.

Study of surface-bonded dicationic ionic liquids as stationary phases for hydrophilic interaction chromatography.

PubMed

Qiao, Lizhen; Li, Hua; Shan, Yuanhong; Wang, Shuangyuan; Shi, Xianzhe; Lu, Xin; Xu, Guowang

2014-02-21

In the present study, several geminal dicationic ionic liquids based on 1,4-bis(3-allylimidazolium)butane and 1,8-bis(3-allylimidazolium)octane in combination with different anions bromide and bis(trifluoromethanesulphonyl)imide were prepared and then bonded to the surface of 3-mercaptopropyl modified silica materials through the "thiol-ene" click chemistry as stationary phases for hydrophilic interaction chromatography (HILIC). Compared with their monocationic analogues, the dicationic ionic liquids stationary phases presented effective retention and good selectivity for typical hydrophilic compounds under HILIC mode with the column efficiency as high as 130,000 plates/m. Moreover, the influence of different alkyl chain spacer between dications and combined anions on the retention behavior and selectivity of the dicationic ionic liquids stationary phases under HILIC mode was displayed. The results indicated that the longer linkage chain would decrease the hydrophilicity and retention on the dicationic ionic liquid stationary phase, and while differently combined anions had no difference due to the exchangeability under the common HILIC mobile phase with buffer salt. Finally, the retention mechanism was investigated by evaluating the effect of chromatographic factors on retention, including the water content in the mobile phase, the mobile phase pH and buffer salt concentration. The results showed that the dicationic ionic liquids stationary phases presented a mixed-mode retention behavior with HILIC mechanism and anion exchange. Copyright © 2014 Elsevier B.V. All rights reserved.

Stereo Particle Image Velocimetry Measurements of Transition Downstream of a Forward-Facing Step in a Swept-Wing Boundary Layer

NASA Technical Reports Server (NTRS)

Eppink, Jenna L.

2017-01-01

Stereo particle image velocimetry measurements were performed downstream of a forward-facing step in a stationary-crossflow dominated flow. Three different step heights were studied with the same leading-edge roughness configuration to determine the effect of the step on the evolution of the stationary-crossflow. Above the critical step height, which is approximately 68% of the boundary-layer thickness at the step, the step caused a significant increase in the growth of the stationary crossflow. For the largest step height studied (68%), premature transition occurred shortly downstream of the step. The stationary crossflow amplitude only reached approximately 7% of U(sub e) in this case, which suggests that transition does not occur via the high-frequency secondary instabilities typically associated with stationary crossflow transition. The next largest step of 60% delta still caused a significant impact on the growth of the stationary crossflow downstream of the step, but the amplitude eventually returned to that of the baseline case, and the transition front remained the same. The smallest step height (56%) only caused a small increase in the stationary crossflow amplitude and no change in the transition front. A final case was studied in which the roughness on the leading edge of the model was enhanced for the lowest step height case to determine the impact of the stationary crossflow amplitude on transition. The stationary crossflow amplitude was increased by approximately four times, which resulted in premature transition for this step height. However, some notable differences were observed in the behavior of the stationary crossflow mode, which indicate that the interaction mechanism which results in the increased growth of the stationary crossflow downstream of the step may be different in this case compared to the larger step heights.

Silica, hybrid silica, hydride silica and non-silica stationary phases for liquid chromatography.

PubMed

Borges, Endler M

2015-04-01

Free silanols on the surface of silica are the "villains", which are responsible for detrimental interactions of those compounds and the stationary phase (i.e., bad peak shape, low efficiency) as well as low thermal and chemical stability. For these reasons, we began this review describing new silica and hybrid silica stationary phases, which have reduced and/or shielded silanols. At present, in liquid chromatography for the majority of analyses, reversed-phase liquid chromatography is the separation mode of choice. However, the needs for increased selectivity and increased retention of hydrophilic bases have substantially increased the interest in hydrophilic interaction chromatography (HILIC). Therefore, stationary phases and this mode of separation are discussed. Then, non-silica stationary phases (i.e., zirconium oxide, titanium oxide, alumina and porous graphitized carbon), which afford increased thermal and chemical stability and also selectivity different from those obtained with silica and hybrid silica, are discussed. In addition, the use of these materials in HILIC is also reviewed. © Crown copyright 2014.

Stationary phase deposition based on onium salts

DOEpatents

Wheeler, David R [Albuquerque, NM; Lewis, Patrick R [Albuquerque, NM; Dirk, Shawn M [Albuquerque, NM; Trudell, Daniel E [Albuquerque, NM

2008-01-01

Onium salt chemistry can be used to deposit very uniform thickness stationary phases on the wall of a gas chromatography column. In particular, the stationary phase can be bonded to non-silicon based columns, especially microfabricated metal columns. Non-silicon microfabricated columns may be manufactured and processed at a fraction of the cost of silicon-based columns. In addition, the method can be used to phase-coat conventional capillary columns or silicon-based microfabricated columns.

Direct HPLC separation of beta-aminoester enantiomers on totally synthetic chiral stationary phases.

PubMed

Gasparrini, F; D'Acquarica, I; Villani, C; Cimarelli, C; Palmieri, G

1997-01-01

The direct separation of beta-aminoester enantiomers by HPLC on synthetic chiral stationary phases based on a pi-acidic derivative of trans 1,2-diaminocyclohexane as selector is described. The application of different columns containing the stationary phase with opposite configurations and in the racemic form to the determination of enantiomeric excess in chemically impure samples is demonstrated.

The Proteome and Lipidome of Thermococcus kodakarensis across the Stationary Phase

PubMed Central

Yoshinaga, Marcos Y.; Garcia Prado, Franka; Hinrichs, Kai-Uwe; Thomm, Michael

2016-01-01

The majority of cells in nature probably exist in a stationary-phase-like state, due to nutrient limitation in most environments. Studies on bacteria and yeast reveal morphological and physiological changes throughout the stationary phase, which lead to an increased ability to survive prolonged nutrient limitation. However, there is little information on archaeal stationary phase responses. We investigated protein- and lipid-level changes in Thermococcus kodakarensis with extended time in the stationary phase. Adaptations to time in stationary phase included increased proportion of membrane lipids with a tetraether backbone, synthesis of proteins that ensure translational fidelity, specific regulation of ABC transporters (upregulation of some, downregulation of others), and upregulation of proteins involved in coenzyme production. Given that the biological mechanism of tetraether synthesis is unknown, we also considered whether any of the protein-level changes in T. kodakarensis might shed light on the production of tetraether lipids across the same period. A putative carbon-nitrogen hydrolase, a TldE (a protease in Escherichia coli) homologue, and a membrane bound hydrogenase complex subunit were candidates for possible involvement in tetraether-related reactions, while upregulation of adenosylcobalamin synthesis proteins might lend support to a possible radical mechanism as a trigger for tetraether synthesis. PMID:27274708

The Proteome and Lipidome of Thermococcus kodakarensis across the Stationary Phase.

PubMed

Gagen, Emma J; Yoshinaga, Marcos Y; Garcia Prado, Franka; Hinrichs, Kai-Uwe; Thomm, Michael

2016-01-01

The majority of cells in nature probably exist in a stationary-phase-like state, due to nutrient limitation in most environments. Studies on bacteria and yeast reveal morphological and physiological changes throughout the stationary phase, which lead to an increased ability to survive prolonged nutrient limitation. However, there is little information on archaeal stationary phase responses. We investigated protein- and lipid-level changes in Thermococcus kodakarensis with extended time in the stationary phase. Adaptations to time in stationary phase included increased proportion of membrane lipids with a tetraether backbone, synthesis of proteins that ensure translational fidelity, specific regulation of ABC transporters (upregulation of some, downregulation of others), and upregulation of proteins involved in coenzyme production. Given that the biological mechanism of tetraether synthesis is unknown, we also considered whether any of the protein-level changes in T. kodakarensis might shed light on the production of tetraether lipids across the same period. A putative carbon-nitrogen hydrolase, a TldE (a protease in Escherichia coli) homologue, and a membrane bound hydrogenase complex subunit were candidates for possible involvement in tetraether-related reactions, while upregulation of adenosylcobalamin synthesis proteins might lend support to a possible radical mechanism as a trigger for tetraether synthesis.

Preparation and evaluation of diblock copolymer-grafted silica by sequential surface initiated-atom transfer radical polymerization for reverse-phase/ion-exchange mixed-mode chromatography.

PubMed

Bo, Chun Miao; Wang, Chaozhan; Wei, Yin Mao

2017-12-01

A novel approach that involved the grafting of diblock copolymer with two types of monomer onto substrate by sequential surface initiated-atom transfer radical polymerization was proposed to prepare a mixed-mode chromatographic stationary phase. The distinguishing feature of this method is that it can be applied in the preparation of various mixed-mode stationary phases. In this study, a new reverse-phase/ion-exchange stationary phase was prepared by grafting hydrophobic styrene and cationic sodium 4-styrenesulfonate by the proposed approach onto silica surface. The chromatographic properties of the prepared stationary phase were evaluated by the separation of benzene derivatives, anilines, and β-agonists, and by the effect of pH values and acetonitrile content on the retention. Compared with typical RP columns, the prepared stationary phase achieved the better resolution and higher selectivity at a shorter separation time and lower organic content. Moreover, the application of the prepared column was proved by separating widely distributed polar and charged compounds simultaneously. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Gas chromatographic retention behavior of polycyclic aromatic hydrocarbons (PAHs) and alkyl-substituted PAHs on two stationary phases of different selectivity.

PubMed

Nalin, Federica; Sander, Lane C; Wilson, Walter B; Wise, Stephen A

2018-01-01

Retention indices (I) for 45 polycyclic aromatic hydrocarbons (PAHs) and 63 methyl-substituted PAHs were determined by gas chromatography - mass spectrometry (GC-MS) using two different stationary phases: a Rxi-PAH phase (a "higher phenyl-content stationary phase") and a 50% (mole fraction) liquid crystalline dimethylpolysiloxane phase. Retention data were obtained for parent PAHs from molecular mass (MM) 128 g/mol (naphthalene) to 328 g/mol (benzo[c]picene) and for 12 sets of methyl-PAHs (methylfluorenes, methylanthracenes, methylphenanthrenes, methylfluoranthenes, methylpyrenes, methylbenz[a]anthracenes, methylbenzo[c]phenanthrenes, methylchrysenes, methyltriphenylenes, methylbenzo[a]pyrenes, methylperylenes, and methylpicenes). Molecular shape descriptors such as length-to-breath ratio (L/B) and thickness (T) were determined for all the PAHs studied. Correlation between I and L/B ratio was evaluated for both stationary phases with a better correlation observed for the 50% liquid crystalline phase (correlation coefficients ranging from 0.22 to 1.00). Graphical Abstract GC separation of six methylchrysene isomers (m/z 242) on two different stationary phases: 50 % phenyl-like methylpolysiloxane phase and 50 % liquid crystalline phase. Retention indices (I) are plotted as a function of L/B for both phases. The data marker numbers identify each isomer based on methyl-substitution position.

New method for evaluating irreversible adsorption and stationary phase bleed in gas chromatographic capillary columns.

PubMed

Wright, Bob W; Wright, Cherylyn W

2012-10-26

A novel method is described for the evaluation of irreversible adsorption and column bleed in gas chromatographic (GC) columns using a tandem GC approach. This work specifically determined the degree of irreversible adsorption behavior of specific sulfur and phosphorous containing test probe compounds at levels ranging from approximately 50 picograms (pg) to 1 nanogram (ng) on selected gas chromatographic columns. This method does not replace existing evaluation methods that characterize reversible adsorption but provides an additional tool. The test compounds were selected due to their ease of adsorption and their importance in the specific trace analytical detection methodology being developed. Replicate chromatographic columns with 5% phenylmethylpolysiloxane (PMS), polyethylene glycol (wax), trifluoropropylpolysiloxane (TFP), or 78% cyanopropylpolysiloxane stationary phases from a variety of vendors were evaluated. As expected, the results demonstrate that the different chromatographic phases exhibit differing degrees of irreversible adsorption behavior. The results also indicate that all manufacturers do not produce equally inert columns nor are columns from a given manufacturer identical. The wax-coated columns for the test probes used were more inert as a group than 5% PMS coated columns, and they were more reproducibly manufactured. Both TFP and 78% cyanopropylpolysiloxane columns displayed superior inertness to the test compounds compared to either 5% PMS- or wax-coated columns. Irreversible adsorption behavior was characterized for a limited range of stationary phase film thicknesses. In addition, the method was shown effective for characterizing column bleed and methods to remove bleed components. This method is useful in screening columns for demanding applications and to obtain diagnostic information related to improved preparation methods. Copyright © 2012 Elsevier B.V. All rights reserved.

Shotgun proteomic monitoring of Clostridium acetobutylicum during stationary phase of butanol fermentation using xylose and comparison with the exponential phase

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sivagnanam, Kumaran; Raghavan, Vijaya G. S.; Shah, Manesh B

2012-01-01

Economically viable production of solvents through acetone butanol ethanol (ABE) fermentation requires a detailed understanding of Clostridium acetobutylicum. This study focuses on the proteomic profiling of C. acetobutylicum ATCC 824 from the stationary phase of ABE fermentation using xylose and compares with the exponential growth by shotgun proteomics approach. Comparative proteomic analysis revealed 22.9% of the C. acetobutylicum genome and 18.6% was found to be common in both exponential and stationary phases. The proteomic profile of C. acetobutylicum changed during the ABE fermentation such that 17 proteins were significantly differentially expressed between the two phases. Specifically, the expression of fivemore » proteins namely, CAC2873, CAP0164, CAP0165, CAC3298, and CAC1742 involved in the solvent production pathway were found to be significantly lower in the stationary phase compared to the exponential growth. Similarly, the expression of fucose isomerase (CAC2610), xylulose kinase (CAC2612), and a putative uncharacterized protein (CAC2611) involved in the xylose utilization pathway were also significantly lower in the stationary phase. These findings provide an insight into the metabolic behavior of C. acetobutylicum between different phases of ABE fermentation using xylose.« less

Evaluation of ODS-AQ stationary phase for use in capillary electrochromatography.

PubMed

Djordjevic, N M; Fitzpatrick, F; Houdiere, F

2001-04-01

The aim of this study was to evaluate the applicability of ODS-AQ packing material as a stationary phase in capillary electrochromatography (CEC). The electroosmotic flow created on an ODS-AQ stationary phase was measured at different mobile phase compositions and at different column temperatures. It was observed that the electroosmotic flow generated in the column increased by 50% when the temperature of the system was raised from 20 degrees C to 60 degrees C, while all other conditions were kept constant. The electroosmotic flow produced by the ODS-AQ stationary phase was found to be comparable to the flow generated in a column packed with Nucleosil bare-silica material. In addition, a set of polar compounds (D-lysergic acid diethylamide derivatives) was utilized to determine the influence of temperature and mobile phase composition on their chromatographic behavior on an ODS-AQ stationary phase in a CEC mode. A linear relationship between the solute retention factor and column temperatures was seen over the temperature range studied (20 degrees C to 60 degrees C). A quadratic function was used to describe the changes in the solute retention factors with variation of acetonitrile concentration in the mobile phase.

An assessment of the retention behaviour of polycyclic aromatic hydrocarbons on reversed phase stationary phases: selectivity and retention on C18 and phenyl-type surfaces.

PubMed

Kayillo, Sindy; Dennis, Gary R; Shalliker, R Andrew

2006-09-08

In this manuscript the retention and selectivity of a set of linear and non-linear PAHs were evaluated on five different reversed-phase columns. These phases included C18 and C18 Aqua stationary phases, as well as three phenyl phases: Propyl-phenyl, Synergi polar-RP and Cosmosil 5PBB phase. Overall, the results revealed that the phenyl-type columns offered better separation performance for the linear PAHs, while the separation of the structural isomer PAHs was enhanced on the C18 columns. The Propyl-phenyl column was found to have the highest molecular-stationary phase interactions, as evidenced by the greatest rate of change in 'S' (0.71) as a function of the molecular weight in the PAH homologous series, despite having the lowest surface coverage (3% carbon load) (where S is the slope of a plot of logk versus the solvent composition). In contrast, the C18 Aqua column, having the highest surface coverage (15% carbon load) was found to have the second lowest molecular-stationary phase interactions (rate of change in S=0.61). Interestingly, the Synergi polar-RP column, which also is a phenyl stationary phase behaved more 'C18-like' than 'phenyl-like' in many of the tests undertaken. This is probably not unexpected since all five phases were reversed phase.

Comparison of the peak resolution and the stationary phase retention between the satellite and the planetary motions using the coil satellite centrifuge with counter-current chromatographic separation of 4-methylumbelliferyl sugar derivatives.

PubMed

Shinomiya, Kazufusa; Zaima, Kazumasa; Harada, Yukina; Yasue, Miho; Harikai, Naoki; Tokura, Koji; Ito, Yoichiro

2017-01-20

Coil satellite centrifuge (CSC) produces the complex satellite motion consisting of the triplicate rotation of the coiled column around three axes including the sun axis (the angular velocity, ω 1 ), the planet axis (ω 2 ) and the satellite axis (the central axis of the column) (ω 3 ) according to the following formula: ω 1 =ω 2 +ω 3 . Improved peak resolution in the separation of 4-methylumbelliferyl sugar derivatives was achieved using the conventional multilayer coiled columns with ethyl acetate/1-butanol/water (3: 2: 5, v/v) for the lower mobile phase at the combination of the rotation speeds (ω 1 , ω 2 , ω 3 )=(300, 150, 150rpm), and (1:4:5, v/v) for the upper mobile phase at (300:100:200rpm). The effect of the satellite motion on the peak resolution and the stationary phase retention was evaluated by each CSC separation with the different rotation speeds of ω 2 and ω 3 under the constant revolution speed at ω 1 =300rpm. With the lower mobile phase, almost constant peak resolution and stationary phase retention were yielded regardless of the change of ω 2 and ω 3 , while with the upper mobile phase these two values were sensitively varied according to the different combination of ω 2 and ω 3 . For example, when ω 2 =147 or 200rpm is used, no stationary phase was retained in the coiled column while ω 2 =150rpm could retain enough volume of stationary phase for separation. On the other hand, the combined rotation speeds at (ω 1 , ω 2 , ω 3 )=(300, 300, 0rpm) or (300, 0, 300rpm) produced insufficient peak resolution regardless of the choice of the mobile phase apparently due to the lack of rotation speed except at (300, 0, 300rpm) with the upper mobile phase. At lower rotation speed of ω 1 =300rpm, better peak resolution and stationary phase retention were obtained by the satellite motion (ω 3 ) than by the planetary motion (ω 2 ), or ω 3 >ω 2 . The effect of the hydrophobicity of the two-phase solvent systems on the stationary phase retention was further examined using the n-hexane/ethyl acetate/1-butanol/methanol/water system at different volume ratios. In the satellite motion at (ω 1 , ω 2 , ω 3 )=(300, 150, 150rpm), almost constant stationary phase retention was obtained with the lower mobile phase regardless of the hydrophobicity of the solvent system whereas the stationary phase retention varied according to the volume ratio of the two-phase solvent system for the upper mobile phase. However, stable stationary phase retention was observed with either phase used as the mobile phase. In order to analyze the acceleration acting on the coiled column, an acceleration sensor was set on the column holder by displacing the multilayer column. The combination of the rotation speeds at (300, 100, 200rpm) showed double loops in the acceleration track, whereas (300, 150, 150rpm) showed a single loop, and all other combinations showed, complex tracks. The overall results indicate that the satellite motion is seriously affected by the combination of rotation speeds and the hydrophobicity of the two-phase solvent system when the upper phase was used as the mobile phase for separation. Copyright © 2016 Elsevier B.V. All rights reserved.

Comparison of the peak resolution and the stationary phase retention between the satellite and the planetary motions using the coil satellite centrifuge with counter-current chromatographic separation of 4-methylumbelliferyl sugar derivatives

PubMed Central

Shinomiya, Kazufusa; Zaima, Kazumasa; Harada, Yukina; Yasue, Miho; Harikai, Naoki; Tokura, Koji; Ito, Yoichiro

2016-01-01

Coil satellite centrifuge (CSC) produces the complex satellite motion consisting of the triplicate rotation of the coiled column around three axes including the sun axis (the angular velocity, ω1), the planet axis (ω2) and the satellite axis (the central axis of the column) (ω3) according to the following formula: ω1 = ω2 + ω3. Improved peak resolution in the separation of 4-methylumbelliferyl sugar derivatives was achieved using the conventional multilayer coiled columns with ethyl acetate/1-butanol/water (3 : 2 : 5, v/v) for the lower mobile phase at the combination of the rotation speeds (ω1, ω2, ω3) = (300, 150, 150 rpm), and (1 : 4 : 5, v/v) for the upper mobile phase at (300 : 100 : 200 rpm). The effect of the satellite motion on the peak resolution and the stationary phase retention was evaluated by each CSC separation with the different rotation speeds of ω2 and ω3 under the constant revolution speed at ω1 = 300 rpm. With the lower mobile phase, almost constant peak resolution and stationary phase retention were yielded regardless of the change of ω2 and ω3, while with the upper mobile phase these two values were sensitively varied according to the different combination of ω2 and ω3. For example, when ω2 = 147 or 200 rpm is used, no stationary phase was retained in the coiled column while ω2 = 150 rpm could retain enough volume of stationary phase for separation. On the other hand, the combined rotation speeds at (ω1, ω2, ω3) = (300, 300, 0 rpm) or (300, 0, 300 rpm) produced insufficient peak resolution regardless of the choice of the mobile phase apparently due to the lack of rotation speed except at (300, 0, 300 rpm) with the upper mobile phase. At lower rotation speed of ω1 = 300 rpm, better peak resolution and stationary phase retention were obtained by the satellite motion (ω3) than by the planetary motion (ω2), or ω3 > ω2. The effect of the hydrophobicity of the two-phase solvent systems on the stationary phase retention was further examined using the n-hexane/ethyl acetate/1-butanol/methanol/water system at different volume ratios. In the satellite motion at (ω1, ω2, ω3) = (300, 150, 150 rpm), almost constant stationary phase retention was obtained with the lower mobile phase regardless of the hydrophobicity of the solvent system whereas the stationary phase retention varied according to the volume ratio of the two-phase solvent system for the upper mobile phase. However, stable stationary phase retention was observed with either phase used as the mobile phase. In order to analyze the acceleration acting on the coiled column, an acceleration sensor was set on the column holder by displacing the multilayer column. The combination of the rotation speeds at (300, 100, 200 rpm) showed double loops in the acceleration track, whereas (300, 150, 150 rpm) showed a single loop, and all other combinations showed, complex tracks. The overall results indicate that the satellite motion is seriously affected by the combination of rotation speeds and the hydrophobicity of the two-phase solvent system when the upper phase was used as the mobile phase for separation. PMID:28040269

Approximating SIR-B response characteristics and estimating wave height and wavelength for ocean imagery

NASA Technical Reports Server (NTRS)

Tilley, David G.

1987-01-01

NASA Space Shuttle Challenger SIR-B ocean scenes are used to derive directional wave spectra for which speckle noise is modeled as a function of Rayleigh random phase coherence downrange and Poisson random amplitude errors inherent in the Doppler measurement of along-track position. A Fourier filter that preserves SIR-B image phase relations is used to correct the stationary and dynamic response characteristics of the remote sensor and scene correlator, as well as to subtract an estimate of the speckle noise component. A two-dimensional map of sea surface elevation is obtained after the filtered image is corrected for both random and deterministic motions.

Cold-stress response during the stationary-growth phase of Antarctic and temperate-climate Penicillium strains.

PubMed

Miteva-Staleva, Jeni G; Krumova, Ekaterina T; Vassilev, Spassen V; Angelova, Maria B

2017-07-01

Cold-induced oxidative stress during the aging of three Penicillium strains (two Antarctic and one from a temperate region) in stationary culture was documented and demonstrated a significant increase in the protein carbonyl content, the accumulation of glycogen and trehalose, and an increase in the activities of antioxidant enzymes (superoxide dismutase and catalase). The cell response to a temperature downshift depends on the degree of stress and the temperature characteristics of the strains. Our data give further support for the role of oxidative stress in the aging of fungi in stationary cultures. Comparing the present results for the stationary growth phase with our previous results for the exponential growth phase was informative concerning the relationship between the cold-stress response and age-related changes in the tested strains. Unlike the young cells, stationary-phase cultures demonstrated a more pronounced level of oxidative damage, as well as decreased antioxidant defence.

Preparation of hydrophilic interaction/ion-exchange mixed-mode chromatographic stationary phase with adjustable selectivity by controlling different ratios of the co-monomers.

PubMed

Bo, Chunmiao; Wang, Xiaomeng; Wang, Chaozhan; Wei, Yinmao

2017-03-03

Development of mixed-mode chromatography (MMC) stationary phase with adjustable selectivity is beneficial to meet the needs of complex samples. In this work, surface-initiated atom transfer radical polymerization (SI-ATRP) using the mixture of two functional monomers was proposed as a new preparation strategy for MMC stationary phase with adjustable selectivity. The mixture of sodium 4-styrenesulfonate (NASS) and dimethylaminoethyl methacrylate (DMAEMA) underwent SI-ATRP to bond poly(NASS-co-DMAEMA) on the surface of silica to prepare hydrophilic interaction/ion-exchange mixed-mode stationary phase. Various analytes (neutral, acidic, basic analytes and strong polar nucleosides) were employed to investigate the retention behaviors. The influences of water content and pH of the mobile phase on the retention validated the mixed-mode retention mechanisms of HILIC and ion-exchange. The charge and polarity of stationary phase as well as the separation selectivity were conveniently manipulated by the ratio of NASS to DMAEMA monomer, and the use of DMAEMA in the mixture additionally endowed the column with the temperature-responsive characteristics. Moreover, the application of the developed column was demonstrated by the successful separation of nucleosides, β-agonists and safflower injection. In a word, the proposed strategy can be potentially applied in the controllable preparation of MMC stationary phase with adjustable selectivity. Copyright © 2017 Elsevier B.V. All rights reserved.

Excretion of extracellular lipids by Streptococcus mutans BHT and FA-1.

PubMed Central

Cabacungan, E; Pieringer, R A

1980-01-01

Streptococcus mutans BHT and FA-1, when grown to log phase on chemically defined medium containing [14C]glycerol, excreted 15% of the total biosynthesized 14C-lipid into the medium. When grown to early stationary phase, 28 to 33% of the 14C-lipid was found in the medium. The radioactive lipids of these varieties of S. mutans were identified as diacylglycerol, diglucosyl diacylglycerol (DGD), monoglucosyl diacylglycerol, diphosphatidylglycerol, phosphatidylglycerol (PG), and smaller amounts of two other lipids tentatively were identified as amino acyl-PG and glycerol phosphoryl-DGD. All lipids were found as extracellular and intracellular components from cells grown to either log or stationary phase. However, there were some shifts in the relative percentage of these lipids as the cells changed from log to stationary phase. For example, the intracellular lipid content of log-phase S. mutans BHT was composed of 49% PG and 19% DGD, but these percents shifted to 18% PG and 57% DGD when the cells were grown to stationary phase. However, the extracellular lipids of this organism contained 50 to 60% PG and 20% DGD in both log and stationary phases. PMID:7380539

Effects of solvent composition in the normal-phase liquid chromatography of alkylphenols and naphthols

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hurtubise, R.J.; Hussain, A.; Silver, H.F.

1981-11-01

The normal-phase liquid chromatographic models of Scott, Snyder, and Soczewinski were considered for a ..mu..-Bondapak NH/sub 2/ stationary phase. n-Heptane:2-propanol and n-heptane:ethyl acetate mobile phases of different compositions were used. Linear relationships were obtained from graphs of log K' vs. log mole fraction of the strong solvent for both n-heptane:2-propanol and n-heptane:ethyl acetate mobile phases. A linear relationship was obtained between the reciprocal of corrected retention volume and % wt/v of 2-propanol but not between the reciprocal of corrected retention volume and % wt/v of ethyl acetate. The slopes and intercept terms from the Snyder and Soczewinski models were foundmore » to approximately describe interactions with ..mu..-Bondapak NH/sub 2/. Capacity factors can be predicted for the compounds by using the equations obtained from mobile phase composition variation experiments.« less

Evaluation of ionic liquid stationary phases for one dimensional gas chromatography-mass spectrometry and comprehensive two dimensional gas chromatographic analyses of fatty acids in marine biota.

PubMed

Gu, Qun; David, Frank; Lynen, Frédéric; Vanormelingen, Pieter; Vyverman, Wim; Rumpel, Klaus; Xu, Guowang; Sandra, Pat

2011-05-20

Ionic liquid stationary phases were tested for one dimensional gas chromatography-mass spectrometry (GC-MS) and comprehensive two dimensional gas chromatography (GC×GC) of fatty acid methyl esters from algae. In comparison with polyethylene glycol and cyanopropyl substituted polar stationary phases, ionic liquid stationary phases SLB-IL 82 and SLB-IL 100 showed comparable resolution, but lower column bleeding with MS detection, resulting in better sensitivity. The selectivity and polarity of the ionic liquid phases are similar to a highly polar biscyanopropyl-silicone phase (e.g. HP-88). In GC×GC, using an apolar polydimethyl siloxane×polar ionic liquid column combination, an excellent group-type separation of fatty acids with different carbon numbers and number of unsaturations was obtained, providing information that is complementary to GC-MS identification. Copyright © 2011 Elsevier B.V. All rights reserved.

Characterization of a new stationary phase based on microwave immobilized polybutadiene on titanium oxide-modified silica.

PubMed

Morais, Lais S R; Jardim, Isabel C S F

2005-05-06

Titanium oxide-modified silica was prepared by reaction of silica with titanium tetrabutoxide and then was used as support in the preparation of stationary phases with self-immobilized polybutadiene (PBD) and PBD immobilized through microwave radiation. Chromatographic performance of the stationary phases was evaluated in terms of the efficiency (plates/m), asymmetry (A(s)), retention factor (k) and resolution (R(s)) of two standard sample mixtures, one of then containing the basic compound N,N-dimethylaniline. A microwave irradiation of 30 min at 520 W gave the best efficiency (86,500 N m(-1)), greater than that of a 6-day self immobilized phase (69,500 N m(-1)). Self-immobilized stationary phases prepared with bare silica were also studied for comparison. These resulted in lower chromatographic performance, 43,800 N m(-1), when compared to the self-immobilized phase prepared with titanized silica.

Distinction of synthetic dl-α-tocopherol from natural vitamin E (d-α-tocopherol) by reversed-phase liquid chromatography. Enhanced selectivity of a polymeric C18 stationary phase at low temperature and/or at high pressure.

PubMed

Yui, Yuko; Miyazaki, Shota; Ma, Yan; Ohira, Masayoshi; Fiehn, Oliver; Ikegami, Tohru; McCalley, David V; Tanaka, Nobuo

2016-06-10

Separation of diastereomers of dl-α-tocopherol was studied by reversed-phase liquid chromatography using three types of stationary phases, polymeric ODS, polymeric C30, and monomeric ODS. Polymeric ODS stationary phase (Inertsil ODS-P, 3mmID, 20cm) was effective for the separation of the isomers created by the presence of three chiral centers on the alkyl chain of synthetic dl-α-tocopherol. Considerable improvement of the separation of isomers was observed on ODS-P phase at high pressure and at low temperature. Complete separation of four pairs of diastereomers was achieved at 12.0°C, 536bar, while three peaks were observed when the separation was carried out either at 12.0°C at low pressure or at 20°C at 488bar. Higher temperature (30.0°C) with the ODS-P phase resulted in only partial separation of the diastereomers even at high pressure. Only slight resolution was observed for the mixture of diastereomers with the C30 stationary phase (Inertsil C30) at 12.0°C and 441bar, although the stationary phase afforded greater resolution for β- and γ-tocopherol than ODS-P. A monomeric C18 stationary phase did not show any separation at 12.0°C and 463bar. The results suggest that the binding site of the polymeric ODS-P phase is selective for flexible alkyl chains that provided the longest retention for the natural form, (R,R,R) form, and the enantiomer, (S,S,S) form, of dl-α-tocopherol. Copyright © 2016. Published by Elsevier B.V.

Method of filling a microchannel separation column

DOEpatents

Arnold, Don W.

2002-01-01

A method for packing a stationary phase into a small diameter fluid passageway or flow channel. Capillary action is employed to distribute a stationary phase uniformly along both the length and diameter of the flow channel. The method disclosed here: 1) eliminates the need for high pressure pumps and fittings and the safety hazards associated therewith; 2) allows the use of readily available commercial microparticles, either coated or uncoated, as the stationary phase; 3) provides for different types of particles, different particle sizes, and different particle size distributions to be packed in sequence, or simultaneously; 4) eliminates the need for plugging the flow channel prior to adding the stationary phase to retain the packing particles; and 5) many capillaries can be filled simultaneously.

Highly stabilized, polymer-lipid membranes prepared on silica microparticles as stationary phases for capillary chromatography

PubMed Central

Gallagher, Elyssia S.; Adem, Seid M.; Baker, Christopher A.; Ratnayaka, Saliya N.; Jones, Ian W.; Hall, Henry K.; Saavedra, S. Scott; Aspinwall, Craig A.

2015-01-01

The ability to rapidly screen complex libraries of pharmacological modulators is paramount to modern drug discovery efforts. This task is particularly challenging for agents that interact with lipid bilayers or membrane proteins due to the limited chemical, physical, and temporal stability of conventional lipid-based chromatographic stationary phases. Here, we describe the preparation and characterization of a novel stationary phase material composed of highly stable, polymeric-phospholipid bilayers self-assembled onto silica microparticles. Polymer lipid membranes were prepared by photochemical or redox initiated polymerization of 1,2-bis[10-(2′,4′-hexadieoyloxy)decanoyl]-sn-glycero-2-phosphocholine (bis-SorbPC), a synthetic, polymerizable lipid. The resulting polymerized bis-SorbPC (poly(bis-SorbPC)) stationary phases exhibited enhanced stability compared to particles coated with 1,2-dioleoyl-sn-glycero-phosphocholine (unpolymerized) phospholipid bilayers when exposed to chemical (50mM triton X-100 or 50% acetonitrile) and physical (15 min sonication) insults after 30 days of storage. Further, poly(bis-SorbPC)-coated particles survived slurry packing into fused silica capillaries, compared to unpolymerized lipid membranes, where the lipid bilayer was destroyed during packing. Frontal chromatographic analyses of the lipophilic small molecules acetylsalicylic acid, benzoic acid, and salicylic acid showed > 44% increase in retention times (P < 0.0001) for all analytes on poly(bis-SorbPC)-functionalized stationary phase compared to bare silica microspheres, suggesting a lipophilic retention mechanism. Phospholipid membrane-functionalized stationary phases that withstand the chemical and physical rigors of capillary LC conditions can substantially increase the efficacy of lipid membrane affinity chromatography, and represents a key advance towards the development of robust membrane protein-functionalized chromatographic stationary phases. PMID:25670414

Mechanisms of Mutation in Non-Dividing Cells

DTIC Science & Technology

2003-05-01

which cells with a lac +1 frameshift allele on an F’ plasmid generate Lac+ mutants upon starvation on lactose medium (3). The stationary-phase mutations...starved on lactose . The accumulation of ampD mutants requires RecA, and is promoted at a greater frequency in RecG-deficient cells, similar to Lac...stationary-phase cells after they are starved in the presence of lactose . In studies performed to date by our lab and others, mutation in stationary-phase

The Stationary-Phase Cells of Saccharomyces cerevisiae Display Dynamic Actin Filaments Required for Processes Extending Chronological Life Span.

PubMed

Vasicova, Pavla; Lejskova, Renata; Malcova, Ivana; Hasek, Jiri

2015-11-01

Stationary-growth-phase Saccharomyces cerevisiae yeast cultures consist of nondividing cells that undergo chronological aging. For their successful survival, the turnover of proteins and organelles, ensured by autophagy and the activation of mitochondria, is performed. Some of these processes are engaged in by the actin cytoskeleton. In S. cerevisiae stationary-phase cells, F actin has been shown to form static aggregates named actin bodies, subsequently cited to be markers of quiescence. Our in vivo analyses revealed that stationary-phase cultures contain cells with dynamic actin filaments, besides the cells with static actin bodies. The cells with dynamic actin displayed active endocytosis and autophagy and well-developed mitochondrial networks. Even more, stationary-phase cell cultures grown under calorie restriction predominantly contained cells with actin cables, confirming that the presence of actin cables is linked to successful adaptation to stationary phase. Cells with actin bodies were inactive in endocytosis and autophagy and displayed aberrations in mitochondrial networks. Notably, cells of the respiratory activity-deficient cox4Δ strain displayed the same mitochondrial aberrations and actin bodies only. Additionally, our results indicate that mitochondrial dysfunction precedes the formation of actin bodies and the appearance of actin bodies corresponds to decreased cell fitness. We conclude that the F-actin status reflects the extent of damage that arises from exponential growth. Copyright © 2015, American Society for Microbiology. All Rights Reserved.

The Stationary-Phase Cells of Saccharomyces cerevisiae Display Dynamic Actin Filaments Required for Processes Extending Chronological Life Span

PubMed Central

Lejskova, Renata; Malcova, Ivana

2015-01-01

Stationary-growth-phase Saccharomyces cerevisiae yeast cultures consist of nondividing cells that undergo chronological aging. For their successful survival, the turnover of proteins and organelles, ensured by autophagy and the activation of mitochondria, is performed. Some of these processes are engaged in by the actin cytoskeleton. In S. cerevisiae stationary-phase cells, F actin has been shown to form static aggregates named actin bodies, subsequently cited to be markers of quiescence. Our in vivo analyses revealed that stationary-phase cultures contain cells with dynamic actin filaments, besides the cells with static actin bodies. The cells with dynamic actin displayed active endocytosis and autophagy and well-developed mitochondrial networks. Even more, stationary-phase cell cultures grown under calorie restriction predominantly contained cells with actin cables, confirming that the presence of actin cables is linked to successful adaptation to stationary phase. Cells with actin bodies were inactive in endocytosis and autophagy and displayed aberrations in mitochondrial networks. Notably, cells of the respiratory activity-deficient cox4Δ strain displayed the same mitochondrial aberrations and actin bodies only. Additionally, our results indicate that mitochondrial dysfunction precedes the formation of actin bodies and the appearance of actin bodies corresponds to decreased cell fitness. We conclude that the F-actin status reflects the extent of damage that arises from exponential growth. PMID:26351139

Synthesis of a mixed-model stationary phase derived from glutamine for HPLC separation of structurally different biologically active compounds: HILIC and reversed-phase applications.

PubMed

Aral, Tarık; Aral, Hayriye; Ziyadanoğulları, Berrin; Ziyadanoğulları, Recep

2015-01-01

A novel mixed-mode stationary phase was synthesised starting from N-Boc-glutamine, aniline and spherical silica gel (4 µm, 60 Å). The prepared stationary phase was characterized by IR and elemental analysis. The new stationary phase bears an embedded amide group into phenyl ring, highly polar a terminal amide group and non-polar groups (phenyl and alkyl groups). At first, this new mixed-mode stationary phase was used for HILIC separation of four nucleotides and five nucleosides. The effects of different separation conditions, such as pH value, mobile phase and temperature, on the separation process were investigated. The optimum separation for nucleotides was achieved using HILIC isocratic elution with aqueous mobile phase and acetonitrile with 20°C column temperature. Under these conditions, the four nucleotides could be separated and detected at 265 nm within 14 min. Five nucleosides were separated under HILIC isocratic elution with aqueous mobile phase containing pH=3.25 phosphate buffer (10mM) and acetonitrile with 20°C column temperature and detected at 265 nm within 14 min. Chromatographic parameters as retention factor, selectivity, theoretical plate number and peak asymmetry factor were calculated for the effect of temperature and water content in mobile phase on the separation process. The new column was also tested for nucleotides and nucleosides mixture and six analytes were separated in 10min. The chromatographic behaviours of these polar analytes on the new mixed-model stationary phase were compared with those of HILIC columns under similar conditions. Further, phytohormones and phenolic compounds were separated in order to see influence of the new stationary phase in reverse phase conditions. Eleven plant phytohormones were separated within 13 min using RP-HPLC gradient elution with aqueous mobile phase containing pH=2.5 phosphate buffer (10mM) and acetonitrile with 20°C column temperature and detected at 230 or 278 nm. The best separation conditions for seven phenolic compounds was also achieved using reversed-phase HPLC gradient elution with aqueous mobile phase containing pH=2.5 phosphate buffer (10mM) and acetonitrile with 20°C column temperature and seven phenolic compounds could be separated and detected at 230 nm within 16 min. Copyright © 2014 Elsevier B.V. All rights reserved.

Characterization of bonded stationary phase performance as a function of qualitative and quantitative chromatographic factors in chaotropic chromatography with risperidone and its impurities as model substances.

PubMed

Čolović, Jelena; Rmandić, Milena; Malenović, Anđelija

2018-05-17

Numerous stationary phases have been developed with the aim to provide desired performances during chromatographic analysis of the basic solutes in their protonated form. In this work, the procedure for the characterization of bonded stationary phase performance, when both qualitative and quantitative chromatographic factors were varied in chaotropic chromatography, was proposed. Risperidone and its three impurities were selected as model substances, while acetonitrile content in the mobile phase (20-30%), the pH of the aqueous phase (3.00-5.00), the content of chaotropic agents in the aqueous phase (10-100 mM), type of chaotropic agent (NaClO 4 , CF 3 COONa), and stationary phase type (Zorbax Eclipse XDB, Zorbax Extend) were studied as chromatographic factors. The proposed procedure implies the combination of D-optimal experimental design, indirect modeling, and polynomial-modified Gaussian model, while grid point search method was selected for the final choice of the experimental conditions which lead to the best possible stationary phase performance for basic solutes. Good agreement between experimentally obtained chromatogram and simulated chromatogram for chosen experimental conditions (25% acetonitrile, 75 mM of NaClO 4 , pH 4.00 on Zorbax Eclipse XDB column) confirmed the applicability of the proposed procedure. The additional point was selected for the verification of proposed procedure ability to distinguish changes in solutes' elution order. Simulated chromatogram for 21.5% acetonitrile, 85 mM of NaClO 4 , pH 5.00 on Zorbax Eclipse XDB column was in line with experimental data. Furthermore, the values of left and right peak half-widths obtained from indirect modeling were used in order to evaluate performances of differently modified stationary phases applying a half-width plots approach. The results from half-width plot approach as well as from the proposed procedure indicate higher efficiency and better separation performance of the stationary phase extra densely bonded and double end-capped with trimethylsilyl group than the stationary phase with the combination of end-capping and bidentate silane bonding for chromatographic analysis of basic solutes in RP-HPLC systems with chaotropic agents. Graphical abstract ᅟ.

Assessment of the chromatographic lipophilicity of eight cephalosporins on different stationary phases.

PubMed

Dąbrowska, Monika; Starek, Małgorzata; Komsta, Łukasz; Szafrański, Przemysław; Stasiewicz-Urban, Anna; Opoka, Włodzimierz

2017-04-01

The retention behaviors were investigated for a series of eight cephalosporins in thin-layer chromatography (TLC) using stationary phases of RP-2, RP-8, RP-18, NH 2 , DIOL, and CN chemically bonded silica gel. Additionally, various binary mobile phases (water/methanol and water/acetone) were used in different volume proportions. The retention behavior of the analyzed molecules was defined by R M0 constant. In addition, reversed phase high performance liquid chromatography (RP-HPLC) was performed in lipophilicity studies by using immobilized artificial membrane (IAM) stationary phase. Obtained chromatographic data (R M0 and logk' IAM ) were correlated with the lipophilicity, expressed as values of the log calculated (logP calc ) and experimental (logP exp(shake-flask) ) partition coefficient. Principal component analysis (PCA) was applied in order to obtain an overview of similarity or dissimilarity among the analyzed compounds. Hierarchical cluster analysis (HCA) was performed to compare the separation characteristics of the applied stationary phases. This study was undertaken to identify the best chromatographic system and chromatographic data processing method to enable the prediction of logP values. A comprehensive chromatographic investigation into the retention of the analyzed cephalosporins revealed a similar behavior on RP-18, RP-8 and CN stationary phases. The weak correlations obtained between experimental and certain computed lipophilicity indices revealed that R M0 and PC1/RM are relevant lipophilicity parameters and the RP-8, CN and RP-18 plates are appropriate stationary phases for lipophilicity investigation, whereas computational approaches still cannot fully replace experimentation. Copyright © 2017 Elsevier B.V. All rights reserved.

Anion-exchange behavior of several alkylsilica reversed-phase columns.

PubMed

Marchand, D H; Snyder, L R

2008-10-31

Some alkylsilica columns carry a positive charge at low pH, as determined by anion-exchange with nitrate ion. In the present study, the relative positive charge for 14 alkylsilica columns was measured for a mobile-phase pH 3.0. All but 3 of these columns were found to carry a significant positive charge under these conditions. The relative positive charge on these columns was found to correlate approximately with two other column characteristics: relative cation-exchange behavior as measured by the hydrophobic-subtraction model (values of C-2.8), and slow equilibration of the column to changes in the mobile-phase-as evidenced by a slow change in the retention of anionic and cationic solutes with time. The origin of this positive charge may arise from the bonding process, with incorporation of some cationic entity into the stationary phase.

Recent development of ionic liquid stationary phases for liquid chromatography.

PubMed

Shi, Xianzhe; Qiao, Lizhen; Xu, Guowang

2015-11-13

Based on their particular physicochemical characteristics, ionic liquids have been widely applied in many fields of analytical chemistry. Many types of ionic liquids were immobilized on a support like silica or monolith as stationary phases for liquid chromatography. Moreover, different approaches were developed to bond covalently ionic liquids onto the supporting materials. The obtained ionic liquid stationary phases show multi-mode mechanism including hydrophobic, hydrophilic, hydrogen bond, anion exchange, π-π, and dipole-dipole interactions. Therefore, they could be used in different chromatographic modes including ion-exchange, RPLC, NPLC and HILIC to separate various classes of compounds. This review mainly summarizes the immobilized patterns and types of ionic liquid stationary phases, their retention mechanisms and applications in the recent five years. Copyright © 2015 Elsevier B.V. All rights reserved.

Recent progress of chiral stationary phases for separation of enantiomers in gas chromatography.

PubMed

Xie, Sheng-Ming; Yuan, Li-Ming

2017-01-01

Chromatography techniques based on chiral stationary phases are widely used for the separation of enantiomers. In particular, gas chromatography has developed rapidly in recent years due to its merits such as fast analysis speed, lower consumption of stationary phases and analytes, higher column efficiency, making it a better choice for chiral separation in diverse industries. This article summarizes recent progress of novel chiral stationary phases based on cyclofructan derivatives and chiral porous materials including chiral metal-organic frameworks, chiral porous organic frameworks, chiral inorganic mesoporous materials, and chiral porous organic cages in gas chromatography, covering original research papers published since 2010. The chiral recognition properties and mechanisms of separation toward enantiomers are also introduced. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Tingting; Kirchhoff, Helmut; Gargouri, Mahmoud

Mixotrophic growth of microalgae offers great potential as an efficient strategy for biofuel production. In this study, photosynthetic regulation of mixotrophically cultured Chlorella sorokiniana cells was systematically evaluated. Mixotrophic cells in the exponential growth phase showed the highest photosynthetic activity, where maximum photosynthetic O 2 evolution was approximately 3- and 4-fold higher than cells in the same phase grown photoautotrophically in 1% CO 2 (in air) and air, respectively. Additionally, characteristic chlorophyll fluorescence parameters demonstrated that no limitation in electron transport downstream of PSII was detected in mixotrophic cells. Up-regulation of photosynthetic activity was associated with high total ribulose-1, 5-bisphosphatemore » carboxylase/oxygenase (Rubisco) carboxylase activity and expression level of phosphoribulokinase (PRK). After 3 days, photosynthetic O 2 evolution of mixotrophic cells that went to the stationary phase, was strongly reduced, with reduced photochemical efficiency and reorganization of the PSII complex. Simultaneously, enzymatic activity for Rubisco carboxylase and mRNA levels of Rubisco and PRK diminished. Importantly, there was almost no non-photochemical quenching for mixotrophic cells, whether grown in log or stationary phase. A decline in the quantum efficiency of PSII and an oxidized plastoquinone pool (PQ pool) was observed under N-depleted conditions during mixotrophic growth. Finally, these results demonstrate that photosynthesis is regulated differently in mixotrophically cultured C. sorokiniana cells than in cells grown under photoautotrophic conditions, with a particularly strong impact by nitrogen levels in the cells.« less

Transcriptional Characterization of Salmonella TAl00 in Growth and Stationary Phase: Mutagenesis of MX in Both Types of Cells

EPA Science Inventory

The Salmonella (Ames) mutagenicity assay can be performed using cells that are in different growth phases. Thus, the plate-incorporation assay involves plating stationary-phase cells with the mutagen, after which the cells undergo a brief lag phase and, consequently, are exposed ...

Predictions of spray combustion interactions

NASA Technical Reports Server (NTRS)

Shuen, J. S.; Solomon, A. S. P.; Faeth, G. M.

1984-01-01

Mean and fluctuating phase velocities; mean particle mass flux; particle size; and mean gas-phase Reynolds stress, composition and temperature were measured in stationary, turbulent, axisymmetric, and flows which conform to the boundary layer approximations while having well-defined initial and boundary conditions in dilute particle-laden jets, nonevaporating sprays, and evaporating sprays injected into a still air environment. Three models of the processes, typical of current practice, were evaluated. The local homogeneous flow and deterministic separated flow models did not provide very satisfactory predictions over the present data base. In contrast, the stochastic separated flow model generally provided good predictions and appears to be an attractive approach for treating nonlinear interphase transport processes in turbulent flows containing particles (drops).

Gradient stationary phase optimized selectivity liquid chromatography with conventional columns.

PubMed

Chen, Kai; Lynen, Frédéric; Szucs, Roman; Hanna-Brown, Melissa; Sandra, Pat

2013-05-21

Stationary phase optimized selectivity liquid chromatography (SOSLC) is a promising technique to optimize the selectivity of a given separation. By combination of different stationary phases, SOSLC offers excellent possibilities for method development under both isocratic and gradient conditions. The so far available commercial SOSLC protocol utilizes dedicated column cartridges and corresponding cartridge holders to build up the combined column of different stationary phases. The present work is aimed at developing and extending the gradient SOSLC approach towards coupling conventional columns. Generic tubing was used to connect short commercially available LC columns. Fast and base-line separation of a mixture of 12 compounds containing phenones, benzoic acids and hydroxybenzoates under both isocratic and linear gradient conditions was selected to demonstrate the potential of SOSLC. The influence of the connecting tubing on the deviation of predictions is also discussed.

Reverberation effects on directionality and response of stationary monopole and dipole sources in a wind tunnel

NASA Technical Reports Server (NTRS)

Baumeister, K. J.

1985-01-01

Analytical solutions for the three dimensional inhomogeneous wave equation with flow in a hardwall rectangular wind tunnel and in the free field are presented for a stationary monopole noise source. Dipole noise sources are calculated by combining two monopoles 180 deg out of phase. Numerical calculations for the modal content, spectral response and directivity for both monopole and dipole sources are presented. In addition, the effect of tunnel alterations, such as the addition of a mounting plate, on the tunnels reverberant response are considered. In the frequency range of practical importance for the turboprop response, important features of the free field directivity can be approximated in a hardwall wind tunnel with flow if the major lobe of the noise source is not directed upstream. However, for an omnidirectional source, such as a monopole, the hardwall wind tunnel and free field response are not comparable.

Development of a novel amide-silica stationary phase for the reversed-phase HPLC separation of different classes of phytohormones.

PubMed

Aral, Hayriye; Aral, Tarık; Ziyadanoğulları, Berrin; Ziyadanoğulları, Recep

2013-11-15

A novel amide-bonded silica stationary phase was prepared starting from N-Boc-phenylalanine, cyclohexylamine and spherical silica gel (4 µm, 60 Å). The amide ligand was synthesised with high yield. The resulting amide bonded stationary phase was characterised by SEM, IR and elemental analysis. The resulting selector bearing a polar amide group is used for the reversed-phase chromatography separation of different classes of thirteen phytohormones (plant hormones). The chromatographic behaviours of these analytes on the amide-silica stationary phase were compared with those of RP-C18 column under same conditions. The effects of different separation conditions, such as mobile phase, pH value, flow rate and temperature, on the separation and retention behaviours of the 13 phytohormones in this system were studied. The optimum separation was achieved using reversed-phase HPLC gradient elution with an aqueous mobile phase containing pH=6.85 potassium phosphate buffer (20 mM) and acetonitrile with a 22 °C column temperature. Under these experimental conditions, the 12 phytohormones could be separated and detected at 230 or 270 nm within 26 min. Copyright © 2013 Elsevier B.V. All rights reserved.

Simultaneous determination of inorganic anions and cations by supercritical fluid chromatography using evaporative light scattering detection.

PubMed

Foulon, Catherine; Di Giulio, Pauline; Lecoeur, Marie

2018-01-26

Supercritical fluid chromatography (SFC) is commonly used for the analysis of non-polar compounds, but remains poorly explored for the separation of polar and ionized molecules. In this paper, SFC has been investigated for the separation of 14 inorganic ions sampled in aqueous solutions. Four polar stationary phases were first screened using CO 2 -methanol-based mobile phases containing water or different acidic or basic additives, in order to select the most efficient conditions for the simultaneous retention of inorganic cations and anions and to favor their detection using evaporative light scattering detector (ELSD). Orthogonal selectivity was obtained depending on the stationary phase used: whereas anions are less retained on HILIC stationary phase, 2-ethylpyridine (2-EP) stationary phase exhibits strong interaction for anions. Best results were obtained under gradient elution mode using a 2-EP stationary phase and by adding 0.2% triethylamine in the CO 2 -methanol-based mobile phase. The composition of the injection solvent was also investigated. The results showed that a methanolic sample containing a percentage of water not exceeding 20% does not affect the analytical performances obtained on 2-EP. Moreover, the presence of triethylamine in the injection solvent contributes to eliminate peaks shoulders. Among the 14 inorganic ions tested, three cations (Li + , Ca 2+ and Mg 2+ ) and five anions (Cl - , Br - , NO 3 - , I - , SCN - ) were totally resolved in 15 min. NO 3 - and NO 2 - still coeluted in the final optimized conditions. The other investigated ions were either strongly retained on the stationary phase or not detected by the ELSD. Copyright © 2017 Elsevier B.V. All rights reserved.

Surface characteristics of Bacillus cereus and its adhesion to stainless steel.

PubMed

Peng, J S; Tsai, W C; Chou, C C

2001-04-11

The ability of a Bacillus cereus strain, isolated from spoiled milk, to adhere to the surface of stainless steel chips was evaluated during its growth in diluted tryptic soy broth (DTSB). The number of cells that adhered to the surface increased markedly as the culture reached the end of the log phase and entered stationary phase, and continued to increase with further incubation. The surface properties of cells from the log, stationary, and late stationary phases were measured by hydrophobic interaction chromatography (HIC) and electrostatic interaction chromatography (ESIC). It was found that surface hydrophobicity of B. cereus vegetative cells from the late stationary phase was the highest followed by those from the stationary phase and the log phase cultures. While the vegetative cells prepared from stationary phase and log phase cultures, respectively, had the highest and the lowest surface charges. Adhesion of B. cereus vegetative cells to stainless steel was positively correlated with the cell surface hydrophobicity (R = 0.979). Surface hydrophobicity and surface positive charge noted on the spores harvested from diluted tryptic soy agar (DTSA) and Mn2+-tryptone glucose extract agar were higher than those harvested from the sucrose or lactose-added DTSA. A wide variation in the surface charge values was noted on the surface of various spores prepared from cultures grown on the four different media tested, while their ability to adhere to stainless steel chips in phosphate buffered saline (PBS) showed no significant difference (p > 0.05). Similarly, the number of spores or vegetative cells adhering to stainless steel suspended in PBS, milk or diluted milk (1000 x) did not differ significantly (p > 0.05).

A 2H nuclear magnetic resonance study of the state of water in neat silica and zwitterionic stationary phases and its influence on the chromatographic retention characteristics in hydrophilic interaction high-performance liquid chromatography.

PubMed

Wikberg, Erika; Sparrman, Tobias; Viklund, Camilla; Jonsson, Tobias; Irgum, Knut

2011-09-23

2H NMR has been used as a tool for probing the state of water in hydrophilic stationary phases for liquid chromatography at temperatures between -80 and +4 °C. The fraction of water that remained unfrozen in four different neat silicas with nominal pore sizes between 60 and 300 Å, and in silicas with polymeric sulfobetaine zwitterionic functionalities prepared in different ways, could be determined by measurements of the line widths and temperature-corrected integrals of the 2H signals. The phase transitions detected during thawing made it possible to estimate the amount of non-freezable water in each phase. A distinct difference was seen between the neat and modified silicas tested. For the neat silicas, the relationship between the freezing point depression and their pore size followed the expected Gibbs-Thomson relationship. The polymeric stationary phases were found to contain considerably higher amounts of non-freezable water compared to the neat silica, which is attributed to the structural effect that the sulfobetaine polymers have on the water layer close to the stationary phase surface. The sulfobetaine stationary phases were used alongside the 100 Å silica to separate a number of polar compounds in hydrophilic interaction (HILIC) mode, and the retention characteristics could be explained in terms of the surface water structure, as well as by the porous properties of the stationary phases. This provides solid evidence supporting a partitioning mechanism, or at least of the existence of an immobilized layer of water into which partitioning could be occurring. Copyright © 2011 Elsevier B.V. All rights reserved.

[Preparation of L-phenylalanine chiral ligand-exchange chromatographic stationary phase by atom transfer radical polymerization and resolution of racemates].

PubMed

Sun, Yang; Xu, Fei; Gong, Bolin

2011-09-01

A novel stationary phase was synthesized for chiral ligand-exchange chromatography via atom transfer radical polymerization (ATRP). Glycidyl methacrylate (GMA) was grafted onto the surface of the silica by ATRP using bromoisobutyryl bromide as an initiator, and the organic metal compound formed in the CuCl/2,2'-bipyridine(Bpy) system as a catalyst at room temperature. The chiral stationary phase was then synthesized by grafting L-phenylalanine on the surface of the silica. The stationary phase was characterized by means of elementary analysis and evaluated in detail to determine its separability. The amount of L-phenylalanine on the surface of silica was calculated to be 4.32 mg/m2. The results showed that the good enantioseparations of some DL-amino acids were obtained using ligand-exchange chromatography on the synthesized chiral stationary phase (50 degrees C) with 0.05 mol/L KH2PO4 and 0.1 mmol/L Cu(Ac)2 solution (pH 4.5) as the mobile phase at a flow rate of 1.0 mL/min and a wavelength of 223 nm. The influences of the mobile phase pH, concentration of Cu (II), and temperature of column on the resolution of DL-amino acids by ligand-exchange chromatography were investigated. The results showed that these conditions could affect the resolution of racemates. Compared with the column prepared by radical method using L-phenylalanine directly bonded onto the surface of the silica, the synthesized stationary phase showed a better separation ability, and the DL-aspartic acids and DL-asparagines could be separated at baseline.

Effect of growth phase on harvesting characteristics, autoflocculation and lipid content of Ettlia texensis for microalgal biodiesel production.

PubMed

Salim, S; Shi, Z; Vermuë, M H; Wijffels, R H

2013-06-01

The effect of growth phase on the recovery of the autoflocculating microalgae Ettlia texensis was studied. In the stationary phase, 90% recovery was achieved after 3h settling. Scanning electron microscopic pictures revealed that extracellular polymeric substances (EPS) on the cell surface were involved in autoflocculation. During the stationary phase an increase of the protein fraction in the EPS was observed while the total fatty acids content increased. The autoflocculating properties of E. texensis combined with favourite fatty acid content and composition make this microalgae an excellent candidate for biodiesel production if harvested at the end of the stationary phase. Copyright © 2013 Elsevier Ltd. All rights reserved.

Proteomic Analysis of Stationary Phase in the Marine Bacterium 'Candidatus Pelagibacter ubique'

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sowell, Sarah M.; Norbeck, Angela D.; Lipton, Mary S.

2008-05-01

Candidatus Pelagibacter ubique, an abundant marine alphaproteobacterium, subsists in nature at low ambient nutrient concentrations and may often be exposed to nutrient limitation, but its genome revealed no evidence of global regulatory adaptations to stationary phase. We used high-resolution capillary liquid chromatography (LC) coupled online to an LTQ mass spectrometer to build an Accurate Mass and Time (AMT) tag library, and employed the AMT tag approach to quantitatively examine proteome differences between exponentially growing and stationary phase Cand. P. ubique cells cultivated in a seawater medium. The AMT tag library represented 72% of the predicted protein coding genes. Stationary phasemore » protein abundance increased for OsmC, which mitigates oxidative damage, and for molecular chaperones, enzymes involved in methionine and cysteine biosynthesis, proteins involved in rho-dependent transcription termination, and the signal transduction enzymes CheY-FisH and ChvG. Our findings indicate that Cand. P. ubique responds adaptively to stationary phase by increasing the abundance of a suite of proteins that contribute to homeostasis, but does not undergo major proteome remodeling. We speculate that this limited response may enable Cand. P. ubique to cope with ambient conditions in which nutrients are often insufficient for short periods, and the ability to resume growth overrides the capacity for long term survival afforded by more comprehensive global stationary phase responses.« less

ADVANCED COMBUSTION SYSTEMS FOR STATIONARY GAS TURBINE ENGINES: VOLUME I. REVIEW AND PRELIMINARY EVALUATION

EPA Science Inventory

The reports describe an exploratory development program to identify, evaluate, and demonstrate dry techniques for significantly reducing NOx from thermal and fuel-bound sources in stationary gas turbine engines. Volume 1 covers Phase I of the four-phase effort. In Phase I, duty c...

Preparation of a silica stationary phase co-functionalized with Wulff-type phenylboronate and C12 for mixed-mode liquid chromatography.

PubMed

Li, Hengye; Zhang, Xuemeng; Zhang, Lin; Wang, Xiaojin; Kong, Fenying; Fan, Dahe; Li, Lei; Wang, Wei

2017-04-15

A silica stationary phase was designed and synthesized through the co-functionalization of silica with Wulff-type phenylboronate and C12 for mixed-mode liquid chromatography applications. The as-synthesized stationary phase was characterized by elemental analysis and Fourier Transform-InfraRed Spectroscopy (FT-IR). Retention mechanisms, including boronate affinity (BA), reversed-phase (RP) and anion-exchange (AE), were involved. Retention mechanism switching was easily realized by adjustment of the mobile phase constitution. Cis-diol compounds could be selectively captured under neutral conditions in BA mode and off-line separated in RP mode. Neutral, basic, acidic and amphiprotic compounds were chromatographed on the column in RP chromatography, while inorganic anions were chromatographed in AE chromatography to characterize the mixed-mode nature of the prepared stationary phase. In addition, the RP performance was compared with an octadecyl silica column in terms of column efficiency (N/m), asymmetry factor (A f ), retention factor (k) and resolution (Rs). The prepared stationary phase offered multiple interactions with analytes in addition to hydrophobic interactions under RP elution conditions. Based on the mixed-mode properties, off-line 2D-LC, for selective capture and separation of urinary nucleosides, was successfully realized on a single column, demonstrating its powerful application potential for complex samples. Copyright © 2017 Elsevier B.V. All rights reserved.

Effect of pressure on the selectivity of polymeric C18 and C30 stationary phases in reversed-phase liquid chromatography. Increased separation of isomeric fatty acid methyl esters, triacylglycerols, and tocopherols at high pressure.

PubMed

Okusa, Kensuke; Iwasaki, Yuki; Kuroda, Ikuma; Miwa, Shohei; Ohira, Masayoshi; Nagai, Toshiharu; Mizobe, Hoyo; Gotoh, Naohiro; Ikegami, Tohru; McCalley, David V; Tanaka, Nobuo

2014-04-25

A high-density, polymeric C18 stationary phase (Inertsil ODS-P) or a polymeric C30 phase (Inertsil C30) provided improved resolution of the isomeric fatty acids (FAs), FA methyl esters (FAMEs), triacylglycerols (TAGs), and tocopherols with an increase in pressure of 20-70MPa in reversed-phase HPLC. With respect to isomeric C18 FAMEs with one cis-double bond, ODS-P phase was effective for recognizing the position of a double bond among petroselinic (methyl 6Z-octadecenoate), oleic (methyl 9Z-octadecenoate), and cis-vaccenic (methyl 11Z-octadecenoate), especially at high pressure, but the differentiation between oleic and cis-vaccenic was not achieved by C30 phase regardless of the pressure. A monomeric C18 phase (InertSustain C18) was not effective for recognizing the position of the double bond in monounsaturated FAME, while the separation of cis- and trans-isomers was achieved by any of the stationary phases. The ODS-P and C30 phases provided increased separation for TAGs and β- and γ-tocopherols at high pressure. The transfer of FA, FAME, or TAG molecules from the mobile phase to the ODS-P stationary phase was accompanied by large volume reduction (-30∼-90mL/mol) resulting in a large increase in retention (up to 100% for an increase of 50MPa) and improved isomer separation at high pressure. For some isomer pairs, the ODS-P and C30 provided the opposite elution order, and in each case higher pressure improved the separation. The two stationary phases showed selectivity for the isomers having rigid structures, but only the ODS-P was effective for differentiating the position of a double bond in monounsaturated FAMEs. The results indicate that the improved isomer separation was provided by the increased dispersion interactions between the solute and the binding site of the stationary phase at high pressure. Copyright © 2014 Elsevier B.V. All rights reserved.

A new thermally immobilized fluorinated stationary phase for RP-HPLC.

PubMed

Maldaner, Liane; Jardim, Isabel C S F

2010-02-01

A new fluorinated stationary phase was prepared through thermal immobilization of poly(methyl-3,3,3-trifluoropropylsiloxane) onto 5 microm Kromasil silica particles. The best conditions of immobilization time and temperature were determined through a central composite design and response surface methodologies. Physical-chemical characterization using solid-state (29)Si NMR measurements, infrared spectroscopy and elemental analysis showed that the immobilization process was effective to promote a coating of the support that corresponds to a monolayer of polymer. The stationary phase presents selectivity for positional isomers and good peak shape for basic compounds.

Semiclassical approximations in the coherent-state representation

NASA Technical Reports Server (NTRS)

Kurchan, J.; Leboeuf, P.; Saraceno, M.

1989-01-01

The semiclassical limit of the stationary Schroedinger equation in the coherent-state representation is analyzed simultaneously for the groups W1, SU(2), and SU(1,1). A simple expression for the first two orders for the wave function and the associated semiclassical quantization rule is obtained if a definite choice for the classical Hamiltonian and expansion parameter is made. The behavior of the modulus of the wave function, which is a distribution function in a curved phase space, is studied for the three groups. The results are applied to the quantum triaxial rotor.

Quantum noise of a Bose-Einstein condensate in an optical cavity, correlations, and entanglement

NASA Astrophysics Data System (ADS)

Szirmai, G.; Nagy, D.; Domokos, P.

2010-04-01

A Bose-Einstein condensate of ultracold atoms inside the field of a laser-driven optical cavity exhibits dispersive optical bistability. We describe this system by using mean-field approximation and by analyzing the correlation functions of the linearized quantum fluctuations around the mean-field solution. The entanglement and the statistics of the atom-field quadratures are given in the stationary state. It is shown that the mean-field solution, that is, the Bose-Einstein condensate, is robust against entanglement generation for most of the phase diagram.

Comparison of GC stationary phases for the separation of fatty acid methyl esters in biodiesel fuels.

PubMed

Goding, Julian C; Ragon, Dorisanne Y; O'Connor, Jack B; Boehm, Sarah J; Hupp, Amber M

2013-07-01

The fatty acid methyl ester (FAME) content of biodiesel fuels has traditionally been determined using gas chromatography with a polar stationary phase. In this study, a direct comparison of the separation of FAMEs present in various biodiesel samples on three polar stationary phases and one moderately polar stationary phase (with comparable column dimensions) was performed. Retention on each column was based on solubility in and polarity of the phase. Quantitative metrics describing the resolution of important FAME pairs indicate high resolution on all polar columns, yet the best resolution, particularly of geometric isomers, is achieved on the cyanopropyl column. In addition, the separation of four C18 monounsaturated isomers was optimized and the elution order determined on each column. FAME composition of various biodiesel fuel types was determined on each column to illustrate (1) chemical differences in biodiesels produced from different feedstocks and (2) chemical similarities in biodiesels of the same feedstock type produced in different locations and harvest seasons.

Selectivity optimization in green chromatography by gradient stationary phase optimized selectivity liquid chromatography.

PubMed

Chen, Kai; Lynen, Frédéric; De Beer, Maarten; Hitzel, Laure; Ferguson, Paul; Hanna-Brown, Melissa; Sandra, Pat

2010-11-12

Stationary phase optimized selectivity liquid chromatography (SOSLC) is a promising technique to optimize the selectivity of a given separation by using a combination of different stationary phases. Previous work has shown that SOSLC offers excellent possibilities for method development, especially after the recent modification towards linear gradient SOSLC. The present work is aimed at developing and extending the SOSLC approach towards selectivity optimization and method development for green chromatography. Contrary to current LC practices, a green mobile phase (water/ethanol/formic acid) is hereby preselected and the composition of the stationary phase is optimized under a given gradient profile to obtain baseline resolution of all target solutes in the shortest possible analysis time. With the algorithm adapted to the high viscosity property of ethanol, the principle is illustrated with a fast, full baseline resolution for a randomly selected mixture composed of sulphonamides, xanthine alkaloids and steroids. Copyright © 2010 Elsevier B.V. All rights reserved.

Iptycene-based stationary phase with three-dimensional aromatic structure for highly selective separation of H-bonding analytes and aromatic isomers.

PubMed

Yang, Xiaohong; Han, Ying; Qi, Meiling; Chen, Chuanfeng

2016-05-06

Unique structures and molecular recognition ability endow iptycene derivatives with great potential as stationary phases in chromatography, which, however, has not been explored yet. Herein, we report the first example of utilizing a pentiptycene quinone (PQ) for gas chromatographic (GC) separations. Remarkably, the statically coated capillary column with the stationary phase achieved extremely high column efficiency of 4800 plates/m. It exhibited preferential retention and high resolving capability for H-bonding and aromatic analytes and positional isomers, showing advantages over the ordinary polysiloxane phase. Moreover, the fabricated iptycene column showed excellent separation repeatability with RSD values of 0.02-0.06% for intra-day, 0.20-0.35% for inter-day and 3.1-5.5% for between-column, respectively. In conclusion, iptycene derivatives as a new class of stationary phases show promising future for their use in GC separations. Copyright © 2016 Elsevier B.V. All rights reserved.

The PaPsr1 and PaWhi2 genes are members of the regulatory network that connect stationary phase to mycelium differentiation and reproduction in Podospora anserina.

PubMed

Timpano, Hélène; Chan Ho Tong, Laetitia; Gautier, Valérie; Lalucque, Hervé; Silar, Philippe

2016-09-01

In filamentous fungi, entrance into stationary phase is complex as it is accompanied by several differentiation and developmental processes, including the synthesis of pigments, aerial hyphae, anastomoses and sporophores. The regulatory networks that control these processes are still incompletely known. The analysis of the "Impaired in the development of Crippled Growth (IDC)" mutants of the model filamentous ascomycete Podospora anserina has already yielded important information regarding the pathway regulating entrance into stationary phase. Here, the genes affected in two additional IDC mutants are identified as orthologues of the Saccharomyces cerevisiae WHI2 and PSR1 genes, known to regulate stationary phase in this yeast, arguing for a conserved role of these proteins throughout the evolution of ascomycetes. Copyright © 2016 Elsevier Inc. All rights reserved.

Morphological and quantitative changes in mitochondria, plastids, and peroxisomes during the log-to-stationary transition of the growth phase in cultured tobacco BY-2 cells.

PubMed

Toyooka, Kiminori; Sato, Mayuko; Wakazaki, Mayumi; Matsuoka, Ken

2016-01-01

We developed a wide-range and high-resolution transmission electron microscope acquisition system and obtained giga-pixel images of tobacco BY-2 cells during the log and stationary phases of cell growth. We demonstrated that the distribution and ultrastructure of compartments involved in membrane traffic (i.e., Golgi apparatus, multivesicular body, and vesicle cluster) change during the log-to-stationary transition. Mitochondria, peroxisomes, and plastids were also enumerated. Electron densities of mitochondria and peroxisomes were altered during the growth-phase shift, while their numbers were reduced by nearly half. Plastid structure dramatically changed from atypical to spherical with starch granules. Nearly the same number of plastids was observed in both log and stationary phases. These results indicate that mechanisms regulating organelle populations differ from organelle to organelle.

Kinetic modeling of sporulation and product formation in stationary phase by Bacillus coagulans RK-02 vis-à-vis other Bacilli.

PubMed

Das, Subhasish; Sen, Ramkrishna

2011-10-01

A logistic kinetic model was derived and validated to characterize the dynamics of a sporogenous bacterium in stationary phase with respect to sporulation and product formation. The kinetic constants as determined using this model are particularly important for describing intrinsic properties of a sporogenous bacterial culture in stationary phase. Non-linear curve fitting of the experimental data into the mathematical model showed very good correlation with the predicted values for sporulation and lipase production by Bacillus coagulans RK-02 culture in minimal media. Model fitting of literature data of sporulation and product (protease and amylase) formation in the stationary phase by some other Bacilli and comparison of the results of model fitting with those of Bacillus coagulans helped validate the significance and robustness of the developed kinetic model. Copyright © 2011 Elsevier Ltd. All rights reserved.

Winner-take-all in a phase oscillator system with adaptation.

PubMed

Burylko, Oleksandr; Kazanovich, Yakov; Borisyuk, Roman

2018-01-11

We consider a system of generalized phase oscillators with a central element and radial connections. In contrast to conventional phase oscillators of the Kuramoto type, the dynamic variables in our system include not only the phase of each oscillator but also the natural frequency of the central oscillator, and the connection strengths from the peripheral oscillators to the central oscillator. With appropriate parameter values the system demonstrates winner-take-all behavior in terms of the competition between peripheral oscillators for the synchronization with the central oscillator. Conditions for the winner-take-all regime are derived for stationary and non-stationary types of system dynamics. Bifurcation analysis of the transition from stationary to non-stationary winner-take-all dynamics is presented. A new bifurcation type called a Saddle Node on Invariant Torus (SNIT) bifurcation was observed and is described in detail. Computer simulations of the system allow an optimal choice of parameters for winner-take-all implementation.

Methodology for modeling the microbial contamination of air filters.

PubMed

Joe, Yun Haeng; Yoon, Ki Young; Hwang, Jungho

2014-01-01

In this paper, we propose a theoretical model to simulate microbial growth on contaminated air filters and entrainment of bioaerosols from the filters to an indoor environment. Air filter filtration and antimicrobial efficiencies, and effects of dust particles on these efficiencies, were evaluated. The number of bioaerosols downstream of the filter could be characterized according to three phases: initial, transitional, and stationary. In the initial phase, the number was determined by filtration efficiency, the concentration of dust particles entering the filter, and the flow rate. During the transitional phase, the number of bioaerosols gradually increased up to the stationary phase, at which point no further increase was observed. The antimicrobial efficiency and flow rate were the dominant parameters affecting the number of bioaerosols downstream of the filter in the transitional and stationary phase, respectively. It was found that the nutrient fraction of dust particles entering the filter caused a significant change in the number of bioaerosols in both the transitional and stationary phases. The proposed model would be a solution for predicting the air filter life cycle in terms of microbiological activity by simulating the microbial contamination of the filter.

Propagation of coherent light pulses with PHASE

NASA Astrophysics Data System (ADS)

Bahrdt, J.; Flechsig, U.; Grizzoli, W.; Siewert, F.

2014-09-01

The current status of the software package PHASE for the propagation of coherent light pulses along a synchrotron radiation beamline is presented. PHASE is based on an asymptotic expansion of the Fresnel-Kirchhoff integral (stationary phase approximation) which is usually truncated at the 2nd order. The limits of this approximation as well as possible extensions to higher orders are discussed. The accuracy is benchmarked against a direct integration of the Fresnel-Kirchhoff integral. Long range slope errors of optical elements can be included by means of 8th order polynomials in the optical element coordinates w and l. Only recently, a method for the description of short range slope errors has been implemented. The accuracy of this method is evaluated and examples for realistic slope errors are given. PHASE can be run either from a built-in graphical user interface or from any script language. The latter method provides substantial flexibility. Optical elements including apertures can be combined. Complete wave packages can be propagated, as well. Fourier propagators are included in the package, thus, the user may choose between a variety of propagators. Several means to speed up the computation time were tested - among them are the parallelization in a multi core environment and the parallelization on a cluster.

Adsorption of ibuprofen enantiomers on a chiral stationary phase with a grafted antibiotic eremomycin

NASA Astrophysics Data System (ADS)

Reshetova, E. N.; Asnin, L. D.

2015-02-01

The adsorption of ibuprofen enantiomers on a chiral stationary phase Nautilus-E with a grafted antibiotic eremomycin from aqueous ethanol acetate buffer solutions was studied by chromatography. The ethanol concentration in the mobile phase was varied from 40 to 60 vol %. The adsorption isotherms of both enantiomers had a complex shape characterized by non-Langmuir type curvature and the presence of an inflection point. This is explained by two factors: the energy heterogeneity of the surface of the stationary phase and the dissociation of ibuprofen in the liquid phase. The effect of the system peak on the shape of the chromatograms of the target component was investigated. The temperature effect on the adsorption equilibrium was discussed.

Aerial hawking and landing: approach behaviour in Natterer's bats, Myotis nattereri (Kuhl 1818).

PubMed

Melcón, Mariana L; Denzinger, Annette; Schnitzler, Hans-Ulrich

2007-12-01

We compared the flight and echolocation behaviour of a vespertilionid bat (Myotis nattereri) approaching a large stationary or a small moving target. Bats were trained to either land on a landing grid or to catch a moving tethered mealworm. When closing in on these two targets, the bats emitted groups of sounds with increasing number of signals and decreasing pulse interval and duration. When pursuing the mealworm, the approach phase always ended with a terminal group consisting of buzz I and buzz II. When landing, the bats emitted either a terminal group consisting of buzz I alone, with one or two extra pulses, or a group consisting of buzz I and buzz II. In all situations, buzz I ended on average between 47-63 ms prior to contact with the target of interest, which is approximately the reaction time of bats. Therefore, the information collected in buzz II does not guide the bats to the target. The relevant part of the approach phase to reach the target ends with buzz I. The basic sound pattern of this part is rather similar and independent of whether the bats approach the large stationary or the small moving target.

Inhibition of initial adhesion of uropathogenic Enterococcus faecalis by biosurfactants from Lactobacillus isolates.

PubMed

Velraeds, M M; van der Mei, H C; Reid, G; Busscher, H J

1996-06-01

In this study, 15 Lactobacillus isolates were found to produce biosurfactants in the mid-exponential and stationary growth phases. The stationary-phase biosurfactants from lactobacillus casei subsp. rhamnosus 36 and ATCC 7469, Lactobacillus fermentum B54, and Lactobacillus acidophilus RC14 were investigated further to determine their capacity to inhibit the initial adhesion of uropathogenic Enterococcus faecalis 1131 to glass in a parallel-plate flow chamber. The initial deposition rate of E. faecalis to glass with an adsorbed biosurfactant layer from L. acidophilus RC14 or L. fermentum B54 was significantly decreased by approximately 70%, while the number of adhering enterococci after 4 h of adhesion was reduced by an average of 77%. The surface activity of the biosurfactants and their activity inhibiting the initial adhesion of E. faecalis 1131 were retained after dialysis (molecular weight cutoff, 6,000 to 8,000) and freeze-drying. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy revealed that the freeze-dried biosurfactants from L. acidophilus RC14 and L. fermentum B54 were richest in protein, while those from L. casei subsp. rhamnosus 36 and ATCC 7469 had relatively high polysaccharide and phosphate contents.

Inhibition of initial adhesion of uropathogenic Enterococcus faecalis by biosurfactants from Lactobacillus isolates.

PubMed Central

Velraeds, M M; van der Mei, H C; Reid, G; Busscher, H J

1996-01-01

In this study, 15 Lactobacillus isolates were found to produce biosurfactants in the mid-exponential and stationary growth phases. The stationary-phase biosurfactants from lactobacillus casei subsp. rhamnosus 36 and ATCC 7469, Lactobacillus fermentum B54, and Lactobacillus acidophilus RC14 were investigated further to determine their capacity to inhibit the initial adhesion of uropathogenic Enterococcus faecalis 1131 to glass in a parallel-plate flow chamber. The initial deposition rate of E. faecalis to glass with an adsorbed biosurfactant layer from L. acidophilus RC14 or L. fermentum B54 was significantly decreased by approximately 70%, while the number of adhering enterococci after 4 h of adhesion was reduced by an average of 77%. The surface activity of the biosurfactants and their activity inhibiting the initial adhesion of E. faecalis 1131 were retained after dialysis (molecular weight cutoff, 6,000 to 8,000) and freeze-drying. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy revealed that the freeze-dried biosurfactants from L. acidophilus RC14 and L. fermentum B54 were richest in protein, while those from L. casei subsp. rhamnosus 36 and ATCC 7469 had relatively high polysaccharide and phosphate contents. PMID:8787394

Cancellation of spurious arrivals in Green's function extraction and the generalized optical theorem

USGS Publications Warehouse

Snieder, R.; Van Wijk, K.; Haney, M.; Calvert, R.

2008-01-01

The extraction of the Green's function by cross correlation of waves recorded at two receivers nowadays finds much application. We show that for an arbitrary small scatterer, the cross terms of scattered waves give an unphysical wave with an arrival time that is independent of the source position. This constitutes an apparent inconsistency because theory predicts that such spurious arrivals do not arise, after integration over a complete source aperture. This puzzling inconsistency can be resolved for an arbitrary scatterer by integrating the contribution of all sources in the stationary phase approximation to show that the stationary phase contributions to the source integral cancel the spurious arrival by virtue of the generalized optical theorem. This work constitutes an alternative derivation of this theorem. When the source aperture is incomplete, the spurious arrival is not canceled and could be misinterpreted to be part of the Green's function. We give an example of how spurious arrivals provide information about the medium complementary to that given by the direct and scattered waves; the spurious waves can thus potentially be used to better constrain the medium. ?? 2008 The American Physical Society.

Pressure resistance of cold-shocked Escherichia coli O157:H7 in ground beef, beef gravy and peptone water.

PubMed

Baccus-Taylor, G S H; Falloon, O C; Henry, N

2015-06-01

(i) To study the effects of cold shock on Escherichia coli O157:H7 cells. (ii) To determine if cold-shocked E. coli O157:H7 cells at stationary and exponential phases are more pressure-resistant than their non-cold-shocked counterparts. (iii) To investigate the baro-protective role of growth media (0·1% peptone water, beef gravy and ground beef). Quantitative estimates of lethality and sublethal injury were made using the differential plating method. There were no significant differences (P > 0·05) in the number of cells killed; cold-shocked or non-cold-shocked. Cells grown in ground beef (stationary and exponential phases) experienced lowest death compared with peptone water and beef gravy. Cold-shock treatment increased the sublethal injury to cells cultured in peptone water (stationary and exponential phases) and ground beef (exponential phase), but decreased the sublethal injury to cells in beef gravy (stationary phase). Cold shock did not confer greater resistance to stationary or exponential phase cells pressurized in peptone water, beef gravy or ground beef. Ground beef had the greatest baro-protective effect. Real food systems should be used in establishing food safety parameters for high-pressure treatments; micro-organisms are less resistant in model food systems, the use of which may underestimate the organisms' resistance. © 2015 The Society for Applied Microbiology.

Assessment of photosynthesis regulation in mixotrophically cultured microalga Chlorella sorokiniana

DOE PAGES

Li, Tingting; Kirchhoff, Helmut; Gargouri, Mahmoud; ...

2016-07-19

Mixotrophic growth of microalgae offers great potential as an efficient strategy for biofuel production. In this study, photosynthetic regulation of mixotrophically cultured Chlorella sorokiniana cells was systematically evaluated. Mixotrophic cells in the exponential growth phase showed the highest photosynthetic activity, where maximum photosynthetic O 2 evolution was approximately 3- and 4-fold higher than cells in the same phase grown photoautotrophically in 1% CO 2 (in air) and air, respectively. Additionally, characteristic chlorophyll fluorescence parameters demonstrated that no limitation in electron transport downstream of PSII was detected in mixotrophic cells. Up-regulation of photosynthetic activity was associated with high total ribulose-1, 5-bisphosphatemore » carboxylase/oxygenase (Rubisco) carboxylase activity and expression level of phosphoribulokinase (PRK). After 3 days, photosynthetic O 2 evolution of mixotrophic cells that went to the stationary phase, was strongly reduced, with reduced photochemical efficiency and reorganization of the PSII complex. Simultaneously, enzymatic activity for Rubisco carboxylase and mRNA levels of Rubisco and PRK diminished. Importantly, there was almost no non-photochemical quenching for mixotrophic cells, whether grown in log or stationary phase. A decline in the quantum efficiency of PSII and an oxidized plastoquinone pool (PQ pool) was observed under N-depleted conditions during mixotrophic growth. Finally, these results demonstrate that photosynthesis is regulated differently in mixotrophically cultured C. sorokiniana cells than in cells grown under photoautotrophic conditions, with a particularly strong impact by nitrogen levels in the cells.« less

Radiation resistance of lactobacilli isolated from radurized meat relative to growth and environment.

PubMed

Hastings, J W; Holzapfel, W H; Niemand, J G

1986-10-01

Of 113 lactobacilli isolated from radurized (5 kGy) minced meat, 7 Lactobacillus sake strains, 1 L. curvatus strain, and 1 L. farciminis strain were used for radiation resistance studies in a semisynthetic substrate (i.e., modified MRS broth). Five reference Lactobacillus spp., one Staphylococcus aureus strain, and one Salmonella typhimurium strain were used for comparative purposes. All L. sake isolates exhibited the phenomenon of being more resistant to gamma-irradiation in the exponential (log) phase than in the stationary phase of their growth cycles by a factor of 28%. Four references strains also exhibited this phenomenon, with L. sake (DSM 20017) showing a 68% increase in resistance in the log phase over the stationary phase. This phenomenon was not common to all bacteria tested and is not common to all strains with high radiation resistance. Four L. sake isolates and three reference strains were used in radiation sensitivity testing in a natural food system (i.e., meat). The bacteria were irradiated in minced meat and packaged under four different conditions (air, vacuum, CO2, and N2). Organisms exhibited the highest death rate (lowest D10 values [doses required to reduce the logarithm of the bacterial population by 1] ) under CO2 packaging conditions, but resistance to irradiation was increased under N2. The D10 values of the isolates were generally greater than those of the reference strains. The D10 values were also higher (approximately two times) in meat than in semisynthetic growth medium.

Radiation resistance of lactobacilli isolated from radurized meat relative to growth and environment.

PubMed Central

Hastings, J W; Holzapfel, W H; Niemand, J G

1986-01-01

Of 113 lactobacilli isolated from radurized (5 kGy) minced meat, 7 Lactobacillus sake strains, 1 L. curvatus strain, and 1 L. farciminis strain were used for radiation resistance studies in a semisynthetic substrate (i.e., modified MRS broth). Five reference Lactobacillus spp., one Staphylococcus aureus strain, and one Salmonella typhimurium strain were used for comparative purposes. All L. sake isolates exhibited the phenomenon of being more resistant to gamma-irradiation in the exponential (log) phase than in the stationary phase of their growth cycles by a factor of 28%. Four references strains also exhibited this phenomenon, with L. sake (DSM 20017) showing a 68% increase in resistance in the log phase over the stationary phase. This phenomenon was not common to all bacteria tested and is not common to all strains with high radiation resistance. Four L. sake isolates and three reference strains were used in radiation sensitivity testing in a natural food system (i.e., meat). The bacteria were irradiated in minced meat and packaged under four different conditions (air, vacuum, CO2, and N2). Organisms exhibited the highest death rate (lowest D10 values [doses required to reduce the logarithm of the bacterial population by 1] ) under CO2 packaging conditions, but resistance to irradiation was increased under N2. The D10 values of the isolates were generally greater than those of the reference strains. The D10 values were also higher (approximately two times) in meat than in semisynthetic growth medium. PMID:3096207

Increments to chiral recognition facilitating enantiomer separations of chiral acids, bases, and ampholytes using Cinchona-based zwitterion exchanger chiral stationary phases.

PubMed

Wernisch, Stefanie; Pell, Reinhard; Lindner, Wolfgang

2012-07-01

The intramolecular distances of anion and cation exchanger sites of zwitterionic chiral stationary phases represent potential tuning sites for enantiomer selectivity. In this contribution, we investigate the influence of alkanesulfonic acid chain length and flexibility on enantiomer separations of chiral acids, bases, and amphoteric molecules for six Cinchona alkaloid-based chiral stationary phases in comparison with structurally related anion and cation exchangers. Employing polar-organic elution conditions, we observed an intramolecular counterion effect for acidic analytes which led to reduced retention times but did not impair enantiomer selectivities. Retention of amphoteric analytes is based on simultaneous double ion pairing of their charged functional groups with the acidic and basic sites of the zwitterionic selectors. A chiral center in the vicinity of the strong cation exchanger site is vital for chiral separations of bases. Sterically demanding side chains are beneficial for separations of free amino acids. Enantioseparations of free (un-derivatized) peptides were particularly successful in stationary phases with straight-chain alkanesulfonic acid sites, pointing to a beneficial influence of more flexible moieties. In addition, we observed pseudo-enantiomeric behavior of quinine and quinidine-derived chiral stationary phases facilitating reversal of elution orders for all analytes. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Comparison of core-shell and totally porous ultra high performance liquid chromatographic stationary phases based on their selectivity towards alfuzosin compounds.

PubMed

Szulfer, Jarosław; Plenis, Alina; Bączek, Tomasz

2014-06-13

This paper focuses on the application of a column classification system based on the Katholieke Universiteit Leuven for the characterization of physicochemical properties of core-shell and ultra-high performance liquid chromatographic stationary phases, followed by the verification of the reliability of the obtained column classification in pharmaceutical practice. In the study, 7 stationary phases produced in core-shell technology and 18 ultra-high performance liquid chromatographic columns were chromatographically tested, and ranking lists were built on the FKUL-values calculated against two selected reference columns. In the column performance test, an analysis of alfuzosin in the presence of related substances was carried out using the brands of the stationary phases with the highest ranking positions. Next, a system suitability test as described by the European Pharmacopoeia monograph was performed. Moreover, a study was also performed to achieve a purposeful shortening of the analysis time of the compounds of interest using the selected stationary phases. Finally, it was checked whether methods using core-shell and ultra-high performance liquid chromatographic columns can be an interesting alternative to the high-performance liquid chromatographic method for the analysis of alfuzosin in pharmaceutical practice. Copyright © 2014 Elsevier B.V. All rights reserved.

Dynamics of amino acid utilization in Phaeobacter inhibens DSM 17395.

PubMed

Zech, Hajo; Hensler, Michael; Koßmehl, Sebastian; Drüppel, Katharina; Wöhlbrand, Lars; Trautwein, Kathleen; Colby, Thomas; Schmidt, Jürgen; Reinhardt, Richard; Schmidt-Hohagen, Kerstin; Schomburg, Dietmar; Rabus, Ralf

2013-10-01

Time-resolved utilization of multiple amino acids by Phaeobacter inhibens DSM 17395 was studied during growth with casamino acids. The 15 detected amino acids could be grouped according to depletion rate into four different categories, i.e. from rapid (category I) to nondepletion (category IV). Upon entry into stationary growth phase, amino acids of category I (e.g. glutamate) were (almost) completely depleted, while those of categories II (e.g. leucine) and III (e.g. serine) were further consumed at varying rates and to different extents. Thus, cultures entered stationary growth phase despite the ample presence of organic nutrients, i.e. under nonlimiting conditions. Integrated proteomic and metabolomic analysis identified 1747 proteins and 94 intracellular metabolites. Of these, 180 proteins and 86 metabolites displayed altered abundance levels during growth. Most strikingly, abundance and activity profiles of alanine dehydrogenase concomitantly increased with the onset of enhanced alanine utilization during transition into stationary growth phase. Most enzymes of amino acid and central metabolism, however, displayed unaltered abundances across exponential and stationary growth phases. In contrast, metabolites of the Entner-Doudoroff pathway and gluconeogenesis as well as cellular fatty acids increased markedly in abundance in early stationary growth phase. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Method developments approaches in supercritical fluid chromatography applied to the analysis of cosmetics.

PubMed

Lesellier, E; Mith, D; Dubrulle, I

2015-12-04

Analyses of complex samples of cosmetics, such as creams or lotions, are generally achieved by HPLC. These analyses are often multistep gradients, due to the presence of compounds with a large range of polarity. For instance, the bioactive compounds may be polar, while the matrix contains lipid components that are rather non-polar, thus cosmetic formulations are usually oil-water emulsions. Supercritical fluid chromatography (SFC) uses mobile phases composed of carbon dioxide and organic co-solvents, allowing for good solubility of both the active compounds and the matrix excipients. Moreover, the classical and well-known properties of these mobile phases yield fast analyses and ensure rapid method development. However, due to the large number of stationary phases available for SFC and to the varied additional parameters acting both on retention and separation factors (co-solvent nature and percentage, temperature, backpressure, flow rate, column dimensions and particle size), a simplified approach can be followed to ensure a fast method development. First, suited stationary phases should be carefully selected for an initial screening, and then the other operating parameters can be limited to the co-solvent nature and percentage, maintaining the oven temperature and back-pressure constant. To describe simple method development guidelines in SFC, three sample applications are discussed in this paper: UV-filters (sunscreens) in sunscreen cream, glyceryl caprylate in eye liner and caffeine in eye serum. Firstly, five stationary phases (ACQUITY UPC(2)) are screened with isocratic elution conditions (10% methanol in carbon dioxide). Complementary of the stationary phases is assessed based on our spider diagram classification which compares a large number of stationary phases based on five molecular interactions. Secondly, the one or two best stationary phases are retained for further optimization of mobile phase composition, with isocratic elution conditions or, when necessary, two-step gradient elution. The developed methods were then applied to real cosmetic samples to assess the method specificity, with regards to matrix interferences, and calibration curves were plotted to evaluate quantification. Besides, depending on the matrix and on the studied compounds, the importance of the detector type, UV or ELSD (evaporative light-scattering detection), and of the particle size of the stationary phase is discussed. Copyright © 2015 Elsevier B.V. All rights reserved.

Characterization, production, and purification of carnocin H, a bacteriocin produced by Carnobacterium 377.

PubMed

Blom, H; Katla, T; Nissen, H; Holo, H

2001-10-01

Carnocin H, a bacteriocin produced by a Carnobacterium sp., inhibited lactic acid bacteria, clostridia, enterococci, and some Staphylococcus aureus strains. Some strains of Listeria and Pediococcus were also sensitive to carnocin H. The bacteriocin was produced during the late stationary growth phase. Carnocin H was purified by cation exchange chromatography and reverse phase chromatography. Amino acid sequence and composition indicate that carnocin H is a novel bacteriocin belonging to the class II bacteriocins. The bacteriocin consists of approximately 75 amino acid residues with a highly cationic N-terminal containing six succeeding lysines. Activity, as measured by agar diffusion zones, was reduced at increased pH values, levels of indicator bacteria, NaCl, agar, and soy oil.

A family of approximate solutions and explicit error estimates for the nonlinear stationary Navier-Stokes problem

NASA Technical Reports Server (NTRS)

Gabrielsen, R. E.; Karel, S.

1975-01-01

An algorithm for solving the nonlinear stationary Navier-Stokes problem is developed. Explicit error estimates are given. This mathematical technique is potentially adaptable to the separation problem.

Bulk water phase and biofilm growth in drinking water at low nutrient conditions.

PubMed

Boe-Hansen, Rasmus; Albrechtsen, Hans-Jørgen; Arvin, Erik; Jørgensen, Claus

2002-11-01

In this study, the bacterial growth dynamics of a drinking water distribution system at low nutrient conditions was studied in order to determine bacterial growth rates by a range of methods, and to compare growth rates in the bulk water phase and the biofilm. A model distribution system was used to quantify the effect of retention times at hydraulic conditions similar to those in drinking water distribution networks. Water and pipe wall samples were taken and examined during the experiment. The pipes had been exposed to drinking water at approximately 13 degrees C, for at least 385 days to allow the formation of a mature quasi-stationary biofilm. At retention times of 12 h, total bacterial counts increased equivalent to a net bacterial growth rate of 0.048 day(-1). The bulk water phase bacteria exhibited a higher activity than the biofilm bacteria in terms of culturability, cell-specific ATP content, and cell-specific leucine incorporation rate. Bacteria in the bulk water phase incubated without the presence of biofilm exhibited a bacterial growth rate of 0.30 day(-1). The biofilm was radioactively labelled by the addition of 14C-benzoic acid. Subsequently, a biofilm detachment rate of 0.013 day(-1) was determined by measuring the release of 14C-labelled bacteria of the biofilm. For the quasi-stationary phase biofilm, the detachment rate was equivalent to the net growth rate. The growth rates determined in this study by different independent experimental approaches were comparable and within the range of values reported in the literature.

Retention behavior of isomeric polycyclic aromatic sulfur heterocycles in gas chromatography on stationary phases of different selectivity

PubMed Central

Wilson, Walter B.; Sander, Lane C.; Oña-Ruales, Jorge O.; Mössner, Stephanie G.; Sidisky, Leonard M.; Lee, Milton L.; Wise, Stephen A.

2017-01-01

Retention indices for 48 polycyclic aromatic sulfur heterocycles (PASHs) were determined using gas chromatography with three different stationary phases: a 50% phenyl phase, a 50% liquid crystalline dimethylpolysiloxane (LC-DMPS) phase, and an ionic liquid (IL) phase. Correlations between the retention behavior on the three stationary phases and PASH geometry (L/B and T, i.e., length-to-breadth ratio and thickness, respectively) were investigated for the following four isomer sets: (1) 4 three-ring molecular mass (MM) 184 Da PASHs, (2) 13 four-ring MM 234 Da PASHs, (3) 10 five-ring MM 258 Da PASHs, and (4) 20 five-ring MM 284 Da PASHs. Correlation coefficients for retention on the 50% LC-DMPS vs L/B ranged from r = 0.50 (MM 284 Da) to r = 0.77 (MM 234 Da). Correlation coefficients for retention on the IL phase vs L/B ranged from r = 0.31 (MM 234 Da) to r = 0.54 (MM 284 Da). Correlation coefficients for retention on the 50% phenyl vs L/B ranged from r = 0.14 (MM 258 Da) to r = 0.59 (MM 284 Da). Several correlation trends are discussed in detail for the retention behavior of PASH on the three stationary phases. PMID:28089272

Retention behavior of isomeric polycyclic aromatic sulfur heterocycles in gas chromatography on stationary phases of different selectivity.

PubMed

Wilson, Walter B; Sander, Lane C; Oña-Ruales, Jorge O; Mössner, Stephanie G; Sidisky, Leonard M; Lee, Milton L; Wise, Stephen A

2017-02-17

Retention indices for 48 polycyclic aromatic sulfur heterocycles (PASHs) were determined using gas chromatography with three different stationary phases: a 50% phenyl phase, a 50% liquid crystalline dimethylpolysiloxane (LC-DMPS) phase, and an ionic liquid (IL) phase. Correlations between the retention behavior on the three stationary phases and PASH geometry (L/B and T, i.e., length-to-breadth ratio and thickness, respectively) were investigated for the following four isomer sets: (1) 4 three-ring molecular mass (MM) 184Da PASHs, (2) 13 four-ring MM 234Da PASHs, (3) 10 five-ring MM 258Da PASHs, and (4) 20 five-ring MM 284Da PASHs. Correlation coefficients for retention on the 50% LC-DMPS vs L/B ranged from r=0.50 (MM 284Da) to r=0.77 (MM 234Da). Correlation coefficients for retention on the IL phase vs L/B ranged from r=0.31 (MM 234Da) to r=0.54 (MM 284Da). Correlation coefficients for retention on the 50% phenyl vs L/B ranged from r=0.14 (MM 258Da) to r=0.59 (MM 284Da). Several correlation trends are discussed in detail for the retention behavior of PASH on the three stationary phases. Published by Elsevier B.V.

Temporal scaling of the growth dependent optical properties of microalgae

NASA Astrophysics Data System (ADS)

Zhao, J. M.; Ma, C. Y.; Liu, L. H.

2018-07-01

The optical properties of microalgae are basic parameters for analyzing light field distribution in photobioreactors (PBRs). With the growth of microalgae cell, their optical properties will vary with growth time due to accumulation of pigment and lipid, cell division and metabolism. In this work, we report a temporal scaling behavior of the growth dependent optical properties of microalgae cell suspensions with both experimental and theoretical evidence presented. A new concept, the temporal scaling function (TSF), defined as the ratio of absorption or scattering cross-sections at growth phase to that at stationary phase, is introduced to characterize the temporal scaling behavior. The temporal evolution and temporal scaling characteristics of the absorption and scattering cross-sections of three example microalgae species, Chlorella vulgaris, Chlorella pyrenoidosa, and Chlorella protothecoides, were experimentally studied at spectral range 380-850 nm. It is shown that the TSFs of the absorption and scattering cross-sections for different microalgae species are approximately constant at different wavelength, which confirms theoretical predictions very well. With the aid of the temporal scaling relation, the optical properties at any growth time can be calculated based on those measured at stationary phase, hence opens a new way to determine the time-dependent optical properties of microalgae. The findings of this work will help the understanding of time dependent optical properties of microalgae and facilitate their applications in light field analysis in PBRs design.

Gas-liquid chromatography with a volatile "stationary" liquid phase.

PubMed

Wells, P S; Zhou, S; Parcher, J F

2002-05-01

A unique type of gas-liquid chromatography is described in which both mobile and "stationary" phases are composed of synthetic mixtures of helium and carbon dioxide. At temperatures below the critical point of the binary mixture and pressures above the vapor pressure of pure liquid carbon dioxide, helium and carbon dioxide can form two immiscible phases over extended composition ranges. A binary vapor phase enriched in helium can act as the mobile phase for chromatographic separations, whereas a CO2-rich liquid in equilibrium with the vapor phase, but condensed on the column wall, can act as a pseudostationary phase. Several examples of chromatographic separations obtained in "empty" capillary columns with no ordinary stationary liquid phase illustrate the range of conditions that produce such separations. In addition, several experiments are reported that confirm the proposed two-phase hypothesis. The possible consequences of the observed chromatographic phenomenon in the field of supercritical fluid chromatography with helium headspace carbon dioxide are discussed.

Surface radical chain-transfer reaction in deep eutectic solvents for preparation of silica-grafted stationary phases in hydrophilic interaction chromatography.

PubMed

Yang, Beibei; Cai, Tianpei; Li, Zhan; Guan, Ming; Qiu, Hongdeng

2017-12-01

In this paper, deep eutectic solvents (DESs) were firstly used as new and green solvents for the preparation of polymer-grafted silica stationary phases. 1-Vinylimidazole and acrylic acid were homopolymerized and copolymerized on silica via surface radical chain-transfer reaction in the DESs. Three stationary phases including poly(1-vinylimidazole)-, poly(acrylic acid)-, poly(1-vinylimidazole-co-acrylic acid)-grafted silica were obtained and characterized by elemental analysis and Fourier transform infrared spectroscopy. Their hydrophilic interaction chromatographic properties were investigated for separation of nucleosides, nucleobases, saccharides and amino acids. The retention changes of nucleosides and nucleobases on these columns were investigated under different chromatographic conditions including acetonitrile content, salt concentration, pH of mobile phase and column temperature. The repeatability of these columns was also investigated. The results demonstrate that DESs can be used as new media for the synthesis of silica-based stationary phases by homopolymerization and copolymerization on the surface of porous silica particles. Copyright © 2017 Elsevier B.V. All rights reserved.

Procedure 5 Quality Assurance Requirements For Vapor Phase Mercury Continuous Emissions Monitoring Systems And Sorbent Trap Monitoring Systems Used For Compliance Determination At Stationary Sources

EPA Pesticide Factsheets

Promulgated quality assurance Procedure 5 Quality Assurance Requirements For Vapor Phase Mercury Continuous Emissions Monitoring Systems And Sorbent Trap Monitoring Systems Used For Compliance Determination At Stationary Sources

Development of the first sphingomyelin biomimetic stationary phase for immobilized artificial membrane (IAM) chromatography.

PubMed

Verzele, Dieter; Lynen, Frédéric; De Vrieze, Mike; Wright, Adrian G; Hanna-Brown, Melissa; Sandra, Pat

2012-01-28

A prototype sphingomyelin stationary phase for Immobilized Artificial Membrane (IAM) chromatography was synthesized by an ultra-short, solid-phase inspired methodology, in which an oxidative release monitoring strategy played a vital role. Evaluated in a proof-of-concept model for blood-brain barrier passage, partial least squares regression demonstrated its potential as an in vitro prediction tool.

MUTATIONAL AND TRANSCRIPTIONAL RESPONSES OF STATIONARY- AND LOGARITHMIC-PHASE SALMONELLA TO MX: CORRELATION OF MUTATIONAL RESPONSE TO CHANGES IN GENE EXPRESSION

EPA Science Inventory

We measured the mutational and transcriptional response of stationary-phase and logarithmic-phase S. typhimurium TA100 to 3 concentrations of the drinking water mutagen 3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX). The mutagenicity of MX in strain TA100 was evaluated...

Hierarchical CaCO3 chromatography: a stationary phase based on biominerals.

PubMed

Sato, Kosuke; Oaki, Yuya; Takahashi, Daisuke; Toshima, Kazunobu; Imai, Hiroaki

2015-03-23

In biomineralization, acidic macromolecules play important roles for the growth control of crystals through a specific interaction. Inspired by this interaction, we report on an application of the hierarchical structures in CaCO3 biominerals to a stationary phase of chromatography. The separation and purification of acidic small organic molecules are achieved by thin-layer chromatography and flash chromatography using the powder of biominerals as the stationary phase. The unit nanocrystals and their oriented assembly, the hierarchical structure, are suitable for the adsorption site of the target organic molecules and the flow path of the elution solvents, respectively. The separation mode is ascribed to the specific adsorption of the acidic molecules on the crystal face and the coordination of the functional groups to the calcium ions. The results imply that a new family of stationary phase of chromatography can be developed by the fine tuning of hierarchical structures in CaCO3 materials. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

[Evaluation of chromatographic performance of polymerized ionic liquid stationary phase for capillary gas chromatography].

PubMed

Chen, Xiaoyan; Lu, Kai; Qi, Meiling; Fu, Ruonong

2009-11-01

The selectivity and thermal stability of ionic liquids as the stationary phases for capillary gas chromatography (CGC) have attracted much attention of researchers in recent years. In this study, 1-vinyl-3-benzyl imidazolium-bis(trifluoromethane-sulphonyl)imidate (VBIm-NTf2) was synthesized and polymerized (PVBIm-NTf2) in a CGC column. In comparison with VBIm-NTf2, PVBIm-NTf2 exhibits much better thermal stability and chromatographic selectivity, and achieves satisfactory resolution for Grob test mixture, alcohols mixture, esters mixture and aromatics mixture with narrow and symmetric peak shapes. The satisfactory resolution and selectivity of the polymerized column still remain after conditioned at 250 degrees C for 6 h. Additionally, the Abraham solvation parameters of PVBIm-NTf2 were determined and the interactions between the stationary phase and solutes were elucidated. The present work demonstrates that the polymerization is an effective way to improve the selectivity and thermal stability of common ionic liquids as CGC stationary phases.

A stationary phase solution for mountain waves with application to mesospheric mountain waves generated by Auckland Island

NASA Astrophysics Data System (ADS)

Broutman, Dave; Eckermann, Stephen D.; Knight, Harold; Ma, Jun

2017-01-01

A relatively general stationary phase solution is derived for mountain waves from localized topography. It applies to hydrostatic, nonhydrostatic, or anelastic dispersion relations, to arbitrary localized topography, and to arbitrary smooth vertically varying background temperature and vector wind profiles. A simple method is introduced to compute the ray Jacobian that quantifies the effects of horizontal geometrical spreading in the stationary phase solution. The stationary phase solution is applied to mesospheric mountain waves generated by Auckland Island during the Deep Propagating Gravity Wave Experiment. The results are compared to a Fourier solution. The emphasis is on interpretations involving horizontal geometrical spreading. The results show larger horizontal geometrical spreading for nonhydrostatic waves than for hydrostatic waves in the region directly above the island; the dominant effect of horizontal geometrical spreading in the lower ˜30 km of the atmosphere, compared to the effects of refraction and background density variation; and the enhanced geometrical spreading due to directional wind in the approach to a critical layer in the mesosphere.

Approaches for enantioselective resolution of pharmaceuticals by miniaturised separation techniques with new chiral phases based on nanoparticles and monolithis.

PubMed

Sierra, Isabel; Marina, Maria Luisa; Pérez-Quintanilla, Damián; Morante-Zarcero, Sonia; Silva, Mariana

2016-10-01

This article discusses new developments in the preparation of nanoparticles and monoliths with emphasis upon their application as the stationary and pseudo-stationary phases for miniaturised liquid phase separation techniques, which have occurred in the last 10 years (from 2006 to the actuality). References included in this review represent current trends and state of the art in the application of these materials to the analysis, by EKC, CEC and miniaturised chromatography, of chiral compounds with environmental interest such as pharmaceuticals. Due to their extraordinary properties, columns prepared with these new chiral stationary or pseudo-stationary phases, based on materials such as gold nanoparticles, metal-organic frameworks, ordered mesoporous silicas, carbonaceous materials, polymeric-based and silica-based monoliths or molecularly imprinted materials, can usually show some improvements in the separation selectivity, column efficiency and chemical stability in comparison with conventional chiral columns available commercially. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Evaluation of an amide-based stationary phase for supercritical fluid chromatography

PubMed Central

Borges-Muñoz, Amaris C.; Colón, Luis A.

2017-01-01

A relatively new stationary phase containing a polar group embedded in a hydrophobic backbone (i.e., ACE® C18-amide) was evaluated for use in supercritical fluid chromatography. The amide-based column was compared with columns packed with bare silica, C18 silica, and a terminal-amide silica phase. The system was held at supercritical pressure and temperature with a mobile phase composition of CO2 and methanol as cosolvent. The linear solvation energy relationship model was used to evaluate the behavior of these stationary phases, relating the retention factor of selected probes to specific chromatographic interactions. A five-component test mixture, consisting of a group of drug-like molecules was separated isocratically. The results show that the C18-amide stationary phase provided a combination of interactions contributing to the retention of the probe compounds. The hydrophobic interactions are favorable; however, the electron donating ability of the embedded amide group shows a large positive interaction. Under the chromatographic conditions used, the C18-amide column was able to provide baseline resolution of all the drug-like probe compounds in a text mixture, while the other columns tested did not. PMID:27396487

Spiral Countercurrent Chromatography

PubMed Central

Ito, Yoichiro; Knight, Martha; Finn, Thomas M.

2013-01-01

For many years, high-speed countercurrent chromatography conducted in open tubing coils has been widely used for the separation of natural and synthetic compounds. In this method, the retention of the stationary phase is solely provided by the Archimedean screw effect by rotating the coiled column in the centrifugal force field. However, the system fails to retain enough of the stationary phase for polar solvent systems such as the aqueous–aqueous polymer phase systems. To address this problem, the geometry of the coiled channel was modified to a spiral configuration so that the system could utilize the radially acting centrifugal force. This successfully improved the retention of the stationary phase. Two different types of spiral columns were fabricated: the spiral disk assembly, made by stacking multiple plastic disks with single or four interwoven spiral channels connected in series, and the spiral tube assembly, made by inserting the tetrafluoroethylene tubing into a spiral frame (spiral tube support). The capabilities of these column assemblies were successfully demonstrated by separations of peptides and proteins with polar two-phase solvent systems whose stationary phases had not been well retained in the earlier multilayer coil separation column for high-speed countercurrent chromatography. PMID:23833207

Methodology for Modeling the Microbial Contamination of Air Filters

PubMed Central

Joe, Yun Haeng; Yoon, Ki Young; Hwang, Jungho

2014-01-01

In this paper, we propose a theoretical model to simulate microbial growth on contaminated air filters and entrainment of bioaerosols from the filters to an indoor environment. Air filter filtration and antimicrobial efficiencies, and effects of dust particles on these efficiencies, were evaluated. The number of bioaerosols downstream of the filter could be characterized according to three phases: initial, transitional, and stationary. In the initial phase, the number was determined by filtration efficiency, the concentration of dust particles entering the filter, and the flow rate. During the transitional phase, the number of bioaerosols gradually increased up to the stationary phase, at which point no further increase was observed. The antimicrobial efficiency and flow rate were the dominant parameters affecting the number of bioaerosols downstream of the filter in the transitional and stationary phase, respectively. It was found that the nutrient fraction of dust particles entering the filter caused a significant change in the number of bioaerosols in both the transitional and stationary phases. The proposed model would be a solution for predicting the air filter life cycle in terms of microbiological activity by simulating the microbial contamination of the filter. PMID:24523908

The separation of flavonoids from Pongamia pinnata using combination columns in high-speed counter-current chromatography with a three-phase solvent system.

PubMed

Yin, Hao; Zhang, Si; Long, Lijuan; Yin, Hang; Tian, Xinpeng; Luo, Xiongming; Nan, Haihan; He, Sha

2013-11-08

The mangrove plant Pongamia pinnata (Leguminosae) is well known as a plant pesticide. Previous studies have indicated that the flavonoids are responsible of the biological activities of the plant. A new high-speed counter-current chromatography (HSCCC) method for the separation of three flavonoids, karanjin (1), pinnatin (2), and pongaflavone (3), from P. pinnata was developed in the present study. The lower and intermediate phase (LP and IP) of a new three-phase solvent system, n-hexane-acetonitrile-dichloromethane-water, at a volume ratio of 5:5:1:5, were used as the stationary phases, while the upper phase (UP) was used as the mobile phase, and the volume ratio between the stationary phases in the CCC column could be tuned by varying the initial pumped volume ratio of the stationary phases. The CCC columns containing all three phases of the solvent system were considered combination columns. According to the theories of combination column, it is possible to optimize the retention time of the target compounds by varying the volume ratio of the stationary phases in the HSCCC combination columns, as well as the suitable volume ratios of the stationary phases for the separation of the target compounds were predicted from the partition coefficients of the compounds in the three-phase solvent system. Then, three HSCCC separations using the combination columns with initial pumped LP:IP volume ratios of 1:0, 0.9:0.1, and 0.7:0.3 were performed separately based on the prediction. Three target compounds were prepared with high purity when the initial pumped volume ratio of the stationary phases was 0.9:0.1. The baseline separation of compounds 2 and 3 was achieved on the combination column with an initial pumped volume ratio of 0.7:0.3. Furthermore, the three experiments clearly demonstrated that the retentions and resolutions of the target compounds increased with an increasing volume ratio of IP, which is consistent with the prediction for the retention times for the solutes on combination columns. The method proposed here reduces the need for solvent selection compared with the conventional method and may have broad potential applicability in the preparation of natural products. Copyright © 2013 Elsevier B.V. All rights reserved.

Poly(1-allylimidazole)-grafted silica, a new specific stationary phase for reversed-phase and anion-exchange liquid chromatography.

PubMed

Sun, Min; Qiu, Hongdeng; Wang, Licheng; Liu, Xia; Jiang, Shengxiang

2009-05-01

A new specific stationary phase based on poly(1-allylimidazole)-grafted silica has been synthesized and characterized, by infrared spectra, elemental analysis, thermogravimetric analysis and X-ray photoelectron spectroscopy. The results of test showed that poly(1-allylimidazole) can effectively mask the residual silanol groups and reduce the adverse effect of residual silanol. Using this stationary phase, phenol compounds, aniline compounds, and polycyclic aromatic hydrocarbons were successfully separated with symmetric peak shapes in the reversed-phase chromatography. Inorganic anions (IO(3)(-), BrO(3)(-), Br(-), NO(3)(-), I(-), SCN(-)) were also separated completely in the anion-exchange chromatography using sodium chloride solution as the mobile phase. The effects of pH and the concentration of eluent on the separation of inorganic anions were studied. The separation mechanism appears to involve the mixed interactions of hydrogen bonding, hydrophobic, pi-pi, electrostatic, and anion-exchange interactions.

Expanding the term "Design Space" in high performance liquid chromatography (I).

PubMed

Monks, K E; Rieger, H-J; Molnár, I

2011-12-15

The current article presents a novel approach to applying Quality by Design (QbD) principles to the development of high pressure reversed phase liquid chromatography (HPLC) methods. Four common critical parameters in HPLC--gradient time, temperature, pH of the aqueous eluent, and stationary phase--are evaluated within the Quality by Design framework by the means of computer modeling software and a column database, to a satisfactory degree. This work proposes the establishment of two mutually complimentary Design Spaces to fully depict a chromatographic method; one Column Design Space (CDS) and one Eluent Design Space (EDS) to describe the influence of the stationary phase and of the mobile phase on the separation selectivity, respectively. The merge of both Design Spaces into one is founded on the continuous nature of the mobile phase influence on retention and the great variety of the stationary phases available. Copyright © 2011 Elsevier B.V. All rights reserved.

Time dependent semiclassical tunneling through one dimensional barriers using only real valued trajectories

DOE Office of Scientific and Technical Information (OSTI.GOV)

Herman, Michael F.

2015-10-28

The time independent semiclassical treatment of barrier tunneling has been understood for a very long time. Several semiclassical approaches to time dependent tunneling through barriers have also been presented. These typically involve trajectories for which the position variable is a complex function of time. In this paper, a method is presented that uses only real valued trajectories, thus avoiding the complications that can arise when complex trajectories are employed. This is accomplished by expressing the time dependent wave packet as an integration over momentum. The action function in the exponent in this expression is expanded to second order in themore » momentum. The expansion is around the momentum, p{sub 0{sup *}}, at which the derivative of the real part of the action is zero. The resulting Gaussian integral is then taken. The stationary phase approximation requires that the derivative of the full action is zero at the expansion point, and this leads to a complex initial momentum and complex tunneling trajectories. The “pseudo-stationary phase” approximation employed in this work results in real values for the initial momentum and real valued trajectories. The transmission probabilities obtained are found to be in good agreement with exact quantum results.« less

Separations of corticosteroids using electrochemically modulated liquid chromatography: Selectivity enhancements at a porous graphitic carbon stationary phase

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ting, E.Y.; Porter, M.D.

Electrochemically modulated liquid chromatography has been applied to the separation of a mixture of structurally similar corticosteroids (i.e., prednisone, prednisolone, cortisone, and hydrocortisone) using a porous graphitic carbon stationary phase. Changes in the voltage applied to the column markedly affected the efficiency as well as the elution order of the separation, with the mixture fully resolved at large negative values of applied potential. Mechanistic aspects in terms of the influence of changes in the applied voltage on the extent of the interactions between these analytes and the stationary phase are briefly discussed. 19 refs., 2 figs.

A simple subcritical chromatographic test for an extended ODS high performance liquid chromatography column classification.

PubMed

Lesellier, Eric; Tchapla, Alain

2005-12-23

This paper describes a new test designed in subcritical fluid chromatography (SFC) to compare the commercial C18 stationary phase properties. This test provides, from a single analysis of carotenoid pigments, the absolute hydrophobicity, the silanol activity and the steric separation factor of the ODS stationary phases. Both the choice of the analytical conditions and the validation of the information obtained from the chromatographic measurements are detailed. Correlations of the carotenoid test results with results obtained from other tests (Tanaka, Engelhard, Sander and Wise) performed both in SFC and HPLC are discussed. Two separation factors, calculated from the retention of carotenoid pigments used as probe, allowed to draw a first classification diagram. Columns, which present identical chromatographic behaviors are located in the same area on this diagram. This location can be related to the stationary phase properties: endcapping treatments, bonding density, linkage functionality, specific area or silica pore diameter. From the first classification, eight groups of columns are distinguished. One group of polymer coated silica, three groups of polymeric octadecyl phases, depending on the pore size and the endcapping treatment, and four groups of monomeric stationary phases. An additional classification of the four monomeric groups allows the comparison of these stationary phases inside each group by using the total hydrophobicity. One hundred and twenty-nine columns were analysed by this simple and rapid test, which allows a comparison of columns with the aim of helping along their choice in HPLC.

Electrochromatographic retention of peptides on strong cation-exchange stationary phases.

PubMed

Nischang, Ivo; Höltzel, Alexandra; Tallarek, Ulrich

2010-03-01

We analyze the systematic and substantial electrical field-dependence of electrochromatographic retention for four counterionic peptides ([Met5]enkephalin, oxytocin, [Arg8]vasopressin, and luteinizing hormone releasing hormone (LHRH) ) on a strong cation-exchange (SCX) stationary phase. Our experiments show that retention behavior in the studied system depends on the charge-selectivity of the stationary phase particles, the applied voltage, and the peptides' net charge. Retention factors of twice positively charged peptides ([Arg8]vasopressin and LHRH at pH 2.7) decrease with increasing applied voltage, whereas lower charged peptides (oxytocin and [Met5]enkephalin at pH 2.7, [Arg8]vasopressin and LHRH at pH 7.0) show a concomitant increase in their retention factors. The observed behavior is explained on the basis of electrical field-induced concentration polarization (CP) that develops around the SCX particles of the packing. The intraparticle concentration of charged species (buffer ions, peptides) increases with increasing applied voltage due to diffusive backflux from the enriched CP zone associated with each SCX particle. For twice charged and on the SCX phase strongly retained peptides the local increase in mobile phase ionic strength reduces the electrostatic interactions with the stationary phase, which explains the decrease of retention factors with increasing applied voltage and CP intensity. Lower charged and weaker retained peptides experience a much stronger relative intraparticle enrichment than the twice-charged peptides, which results in a net increase of retention factors with increasing applied voltage. The CP-related contribution to electrochromatographic retention of peptides on the SCX stationary phase is modulated by the applied voltage, the mobile phase ionic strength, and the peptides' net charge and could be used for selectivity tuning in difficult separations.

Two-Camera Acquisition and Tracking of a Flying Target

NASA Technical Reports Server (NTRS)

Biswas, Abhijit; Assad, Christopher; Kovalik, Joseph M.; Pain, Bedabrata; Wrigley, Chris J.; Twiss, Peter

2008-01-01

A method and apparatus have been developed to solve the problem of automated acquisition and tracking, from a location on the ground, of a luminous moving target in the sky. The method involves the use of two electronic cameras: (1) a stationary camera having a wide field of view, positioned and oriented to image the entire sky; and (2) a camera that has a much narrower field of view (a few degrees wide) and is mounted on a two-axis gimbal. The wide-field-of-view stationary camera is used to initially identify the target against the background sky. So that the approximate position of the target can be determined, pixel locations on the image-detector plane in the stationary camera are calibrated with respect to azimuth and elevation. The approximate target position is used to initially aim the gimballed narrow-field-of-view camera in the approximate direction of the target. Next, the narrow-field-of view camera locks onto the target image, and thereafter the gimbals are actuated as needed to maintain lock and thereby track the target with precision greater than that attainable by use of the stationary camera.

Directed intermittent search for a hidden target on a dendritic tree

NASA Astrophysics Data System (ADS)

Newby, Jay M.; Bressloff, Paul C.

2009-08-01

Motivated by experimental observations of active (motor-driven) intracellular transport in neuronal dendrites, we analyze a stochastic model of directed intermittent search on a tree network. A particle injected from the cell body or soma into the primary branch of the dendritic tree randomly switches between a stationary search phase and a mobile nonsearch phase that is biased in the forward direction. A (synaptic) target is presented somewhere within the tree, which the particle can locate if it is within a certain range and in the searching phase. We approximate the moment generating function using Green’s function methods. The moment generating function is then used to compute the hitting probability and conditional mean first passage time to the target. We show that in contrast to a previously explored finite interval case, there is a range of parameters for which a bidirectional search strategy is more efficient than a unidirectional one in finding the target.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Flechsig, U.; Follath, R.; Reiche, S.

PHASE is a software tool for physical optics simulation based on the stationary phase approximation method. The code is under continuous development since about 20 years and has been used for instance for fundamental studies and ray tracing of various beamlines at the Swiss Light Source. Along with the planning for SwissFEL a new hard X-ray free electron laser under construction, new features have been added to permit practical performance predictions including diffraction effects which emerge with the fully coherent source. We present the application of the package on the example of the ARAMIS 1 beamline at SwissFEL. The X-raymore » pulse calculated with GENESIS and given as an electrical field distribution has been propagated through the beamline to the sample position. We demonstrate the new features of PHASE like the treatment of measured figure errors, apertures and coatings of the mirrors and the application of Fourier optics propagators for free space propagation.« less

Molecular-level comparison of alkylsilane and polar-embedded reversed-phase liquid chromatography systems.

PubMed

Rafferty, Jake L; Siepmann, J Ilja; Schure, Mark R

2008-08-15

Stationary phases with embedded polar groups possess several advantages over conventional alkylsilane phases, such as reduced peak tailing, enhanced selectivity for specific functional groups, and the ability to use a highly aqueous mobile phase. To gain a deeper understanding of the retentive properties of these reversed-phase packings, molecular simulations were carried out for three different stationary phases in contact with mobile phases of various water/methanol ratios. Two polar-embedded phases were modeled, namely, amide and ether containing, and compared to a conventional octadecylsilane phase. The simulations show that, due to specific hydrogen bond interactions, the polar-embedded phases take up significantly more solvent and are more ordered than their alkyl counterparts. Alkane and alcohol probe solutes indicate that the polar-embedded phases are less retentive than alkyl phases for nonpolar species, whereas polar species are more retained by them due to hydrogen bonding with the embedded groups and the increased amount of solvent within the stationary phase. This leads to a significant reduction of the free-energy barrier for the transfer of polar species from the mobile phase to residual silanols, and this reduced barrier provides a possible explanation for reduced peak tailing.

Identifying excessive vehicle idling and opportunities for off-road fuel tax credits for stationary operations in the Caltrans fleet, phase 1

DOT National Transportation Integrated Search

2011-01-01

This report documents the research project Identifying Excessive Vehicle Idling and Opportunities for Off-Road Fuel Tax Credits for : Stationary Operations in the Caltrans Fleet - Phase 1, performed in response to a California Department of Tra...

Preparation, characterization and application of a reversed phase liquid chromatography/hydrophilic interaction chromatography mixed-mode C18-DTT stationary phase.

PubMed

Wang, Qing; Long, Yao; Yao, Lin; Xu, Li; Shi, Zhi-Guo; Xu, Lanying

2016-01-01

A mixed-mode chromatographic stationary phase, C18-DTT (dithiothreitol) silica (SiO2) was prepared through "thiol-ene" click chemistry. The obtained material was characterized by fourier transform infrared spectroscope, nitrogen adsorption analysis and contact angle analysis. Chromatographic performance of the C18-DTT was systemically evaluated by studying the effect of acetonitrile content, pH, buffer concentration of the mobile phase and column temperature. It was demonstrated that the novel stationary phase possessed reversed phase liquid chromatography (RPLC)/hydrophilic interaction liquid chromatography (HILIC) mixed-mode property. The stop-flow test revealed that C18-DTT exhibited excellent compatibility with 100% aqueous mobile phase. Additionally, the stability and column-to-column reproducibility of the C18-DTT material were satisfactory, with relative standard deviations of retention factor of the tested analytes (verapamil, fenbufen, guanine, tetrandrine and nicotinic acid) in the range of 1.82-3.72% and 0.85-1.93%, respectively. Finally, the application of C18-DTT column was demonstrated in the separation of non-steroidal anti-inflammatory drugs, aromatic carboxylic acids, alkaloids, nucleo-analytes and polycyclic aromatic hydrocarbons. It had great resolving power in the analysis of various compounds in HILIC and RPLC chromatographic conditions and was a promising RPLC/HILIC mixed-mode stationary phase. Copyright © 2015 Elsevier B.V. All rights reserved.

The effect of barriers on wave propagation phenomena: With application for aircraft noise shielding

NASA Technical Reports Server (NTRS)

Mgana, C. V. M.; Chang, I. D.

1982-01-01

The frequency spectrum was divided into high and low frequency regimes and two separate methods were developed and applied to account for physical factors associated with flight conditions. For long wave propagation, the acoustic filed due to a point source near a solid obstacle was treated in terms of an inner region which where the fluid motion is essentially incompressible, and an outer region which is a linear acoustic field generated by hydrodynamic disturbances in the inner region. This method was applied to a case of a finite slotted plate modelled to represent a wing extended flap for both stationary and moving media. Ray acoustics, the Kirchhoff integral formulation, and the stationary phase approximation were combined to study short wave length propagation in many limiting cases as well as in the case of a semi-infinite plate in a uniform flow velocity with a point source above the plate and embedded in a different flow velocity to simulate an engine exhaust jet stream surrounding the source.

Use of vancomycin silica stationary phase in packed capillary electrochromatography: III. enantiomeric separation of basic compounds with the polar organic mobile phase.

PubMed

Fanali, Salvatore; Catarcini, Paolo; Quaglia, Maria Giovanna

2002-02-01

The separation of basic compounds into their enantiomers was achieved using capillary electrochromatography in 50 or 75 microm inner diameter (ID) fused-silica capillaries packed with silica a stationary phase derivatized with vancomycin and mobile phases composed of mixtures of polar organic solvents containing 13 mM ammonium acetate. Enantiomer resolution, electroosmotic flow, and the number of theoretical plates were strongly influenced by the type and concentration of the organic solvent. Mobile phases composed of 13 mM ammonium acetate dissolved in mixtures of acetonitrile/methanol, ethanol, n-propanol, or isopropanol were tested and the highest enantioresolutions were achieved using the first mobile phase, allowing the separation of almost all investigated enantiomers (9 from 11 basic compounds). The use of capillaries with different ID (50 and 75 microm ID) packed with the same chiral stationary phase revealed that a higher number of theoretical plates and higher enantioresolution was achieved with the tube with lowest ID.

Recent development in liquid chromatography stationary phases for separation of Traditional Chinese Medicine components.

PubMed

Jin, Hongli; Liu, Yanfang; Guo, Zhimou; Wang, Jixia; Zhang, Xiuli; Wang, Chaoran; Liang, Xinmiao

2016-10-25

Traditional Chinese Medicine (TCM) is an ancient medical practice which has been used to prevent and cure diseases for thousands of years. TCMs are frequently multi-component systems with mainly unidentified constituents. The study of the chemical compositions of TCMs remains a hotspot of research. Different strategies have been developed to manage the significant complexity of TCMs, in an attempt to determine their constituents. Reversed-phase liquid chromatography (RPLC) is still the method of choice for the separation of TCMs, but has many problems related to limited selectivity. Recently, enormous efforts have been concentrated on the development of efficient liquid chromatography (LC) methods for TCMs, based on selective stationary phases. This can improve the resolution and peak capacity considerably. In addition, high-efficiency stationary phases have been applied in the analysis of TCMs since the invention of ultra high-performance liquid chromatography (UHPLC). This review describes the advances in LC methods in TCM research from 2010 to date, and focuses on novel stationary phases. Their potential in the separation of TCMs using relevant applications is also demonstrated. Copyright © 2016 Elsevier B.V. All rights reserved.

Indications for an inducible component of error-prone DNA repair in yeast.

PubMed

Siede, W; Eckardt, F

1984-01-01

In a thermoconditional mutant of mutagenic DNA repair (rev 2ts = rad 5-8) of Saccharomyces cerevisiae recovery of survival and mutation frequencies can be monitored by incubating UV-irradiated cells in growth medium at a permissive temperature (23 degrees C) before plating and a shift to restrictive temperature (36 degrees C). Inhibition of protein synthesis with cycloheximide during incubation at permissive conditions blocks this REV 2 dependent recovery process in stationary phase rev 2ts cells, whereas it can be reduced but not totally abolished in exponentially growing cells. These results indicate a strict dependence on post-irradiation protein synthesis in stationary phase cells and argue for a considerable constitutive level and only limited inducibility in logarithmic phase cells. The UV inducibility of the REV 2 coded function in stationary phase cells could be confirmed by analysis of the dose-response pattern of the his 5-2 reversion: in stationary phase rev 2ts cells, the quadratic component of the biphasic linear-quadratic induction kinetics found at 23 degrees C, which is interpreted as the consequence of induction of mutagenic repair, is eliminated at 36 degrees C.

On the Structure and Stabilization Mechanisms of Planar and Cylindrical Premixed Flames

NASA Technical Reports Server (NTRS)

Eng, James A.; Zhu, Delin; Law, Chung K.

1993-01-01

The configurational simplicity of the stationary one-dimensional flames renders them intrinsically attractive for fundamental flame structure studies. The possibility and fidelity of studies of such flames on earth, however, have been severely restricted by the unidirectional nature of the gravity vector. To demonstrate these complications, let us first consider the premixed flame. Here a stationary, one-dimensional flame can be established by using the flat-flame burner. We next consider nonpremixed flames. First it may be noted that in an unbounded gravity-free environment, the only stationary one-dimensional flame is the spherical flame. Indeed, this is a major motivation for the study of microgravity droplet combustion, in which the gas-phase processes can be approximated to be quasi-steady because of the significant disparity between the gas and liquid densities for subcritical combustion. In view of the above considerations, an experimental and theoretical program on cylindrical and spherical premixed and nonpremixed flames in microgravity has been initiated. For premixed flames, we are interested in: (1) assessing the heat loss versus flow divergence as the dominant stabilization mechanism; (2) determining the laminar flame speed by using this configuration; and (3) understanding the development of flamefront instability and the effects of the flame curvature on the burning intensity.

Pitch angle scattering of relativistic electrons from stationary magnetic waves: Continuous Markov process and quasilinear theory

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lemons, Don S.

2012-01-15

We develop a Markov process theory of charged particle scattering from stationary, transverse, magnetic waves. We examine approximations that lead to quasilinear theory, in particular the resonant diffusion approximation. We find that, when appropriate, the resonant diffusion approximation simplifies the result of the weak turbulence approximation without significant further restricting the regime of applicability. We also explore a theory generated by expanding drift and diffusion rates in terms of a presumed small correlation time. This small correlation time expansion leads to results valid for relatively small pitch angle and large wave energy density - a regime that may govern pitchmore » angle scattering of high-energy electrons into the geomagnetic loss cone.« less

[Influence of mobile phase composition on chiral separation of organic selenium racemates].

PubMed

Han, Xiao-qian; Qi, Bang-feng; Dun, Hui-juan; Zhu, Xin-yi; Na, Peng-jun; Jiang, Sheng-xiang; Chen, Li-ren

2002-05-01

The chiral separation of some chiral compounds with similar structure on the cellulose tris (3,5-dimethylphenylcarbamate) chiral stationary phase prepared by us was obtained. Ternary mobile phases influencing chiral recognition were investigated. A mode of interaction between the structural character of samples and chiral stationary phase is discussed. The results indicated that the retention and chiral separation of the analytes had a bigger change with minute addition of alcohols or acetonitrile as modifier in n-hexane/2-propanol (80/20, volume ratio) binary mobile phase.

[Is it possible to "cancel" aging process of cell cultures under optimal conditions for cultivation?].

PubMed

Bozhkov, A I; Kovaleva, M K; Menzianova, N G

2011-01-01

The characteristics of the cells epigenotypes Dunaliella viridis Teod. in the process of chronological and replicative aging were investigated. By 40th day of accumulative cultivation (which coincided with the stationary growth phase) DNA content in the cells of Dunaliella viridis increased 2 times, triacylglycerides 3 times, beta-carotene and carbonyl proteins 2 times, RNA content decreased in comparison with cells in exponential growth phase, i. e., the 40th day of growth of culture forms the age-related epigenotype. 4 received subcultures were being transplanted during 2 years in mid-logarithmic growth phase (subculture-10), early stationary phase of growth (subculture-20), in the mid-stationary growth phase (subculture-30), and late stationary growth phase (subculture-40). It is shown that epigenotype of subculture-10 remained unchanged over 2 years of cultivation, i. e., it does not manifest replicative aging. At the same time, the subculture-20, although long enough (at least 40 passages), maintained epigenotype characteristic of young cultures, and showed age-related changes. Pronounced age-dependent changes of epigenotype in the course of cultivation were identified for subculture-30, and subculture-40 was characterized by unstable epigenotype. Thus, cultivation conditions determine the intensity of replicative aging in Dunaliella viridis.

[High-performance liquid-liquid chromatography in beverage analysis].

PubMed

Bricout, J; Koziet, Y; de Carpentrie, B

1978-01-01

Liquid liquid chromatography was performed with columns packed with stationary phases chemically bonded to silica microparticules. These columns show a high efficiency and are used very easily. Flavouring compounds like aromatic aldehydes which have a low volatility were analyzed in brandy using a polar phase alkylnitrile. Sapid substances like amarogentin in Gentiana lutea or glyryrrhizin in Glycyrrhiza glabra were determined by reversed phase chromatography. Finally ionizable substances like synthetic dyes can be analyzed by paired ion chromatography witha non polar stationary phase.

Dynamic least-squares kernel density modeling of Fokker-Planck equations with application to neural population.

PubMed

Shotorban, Babak

2010-04-01

The dynamic least-squares kernel density (LSQKD) model [C. Pantano and B. Shotorban, Phys. Rev. E 76, 066705 (2007)] is used to solve the Fokker-Planck equations. In this model the probability density function (PDF) is approximated by a linear combination of basis functions with unknown parameters whose governing equations are determined by a global least-squares approximation of the PDF in the phase space. In this work basis functions are set to be Gaussian for which the mean, variance, and covariances are governed by a set of partial differential equations (PDEs) or ordinary differential equations (ODEs) depending on what phase-space variables are approximated by Gaussian functions. Three sample problems of univariate double-well potential, bivariate bistable neurodynamical system [G. Deco and D. Martí, Phys. Rev. E 75, 031913 (2007)], and bivariate Brownian particles in a nonuniform gas are studied. The LSQKD is verified for these problems as its results are compared against the results of the method of characteristics in nondiffusive cases and the stochastic particle method in diffusive cases. For the double-well potential problem it is observed that for low to moderate diffusivity the dynamic LSQKD well predicts the stationary PDF for which there is an exact solution. A similar observation is made for the bistable neurodynamical system. In both these problems least-squares approximation is made on all phase-space variables resulting in a set of ODEs with time as the independent variable for the Gaussian function parameters. In the problem of Brownian particles in a nonuniform gas, this approximation is made only for the particle velocity variable leading to a set of PDEs with time and particle position as independent variables. Solving these PDEs, a very good performance by LSQKD is observed for a wide range of diffusivities.

HPLC imprinted-stationary phase prepared by precipitation polymerisation for the determination of thiabendazole in fruit.

PubMed

Turiel, E; Tadeo, J L; Cormack, P A G; Martin-Esteban, A

2005-12-01

A molecularly imprinted polymer (MIP) tailored for the HPLC determination of the fungicide thiabendazole (TBZ) has been synthesised in one single preparative step by precipitation polymerisation in an acetonitrile/toluene co-solvent, using TBZ as template molecule, methacrylic acid as functional monomer and divinylbenzene-80 as crosslinker. The imprinted polymer particulates obtained were characterised by scanning electron microscopy and nitrogen sorption porosimetry. These analyses showed clearly that spherical polymer particulates (polymer microspheres) with narrow size distributions (average particle diameter approximately 3.5 microm) and well-developed pore structures had been produced. The imprinted microspheres were packed into a stainless steel HPLC column (50 x 4.6 mm id) and evaluated as an imprinted stationary phase. The imprinting effect was demonstrated clearly, i.e., the column was observed to bind TBZ selectively, and the effect of different chromatographic parameters (e.g., temperature, flow-rate and elution solvents) on TBZ retention/elution studied. Under optimised conditions, the TBZ-imprinted column was used for the HPLC-fluorescence (HPLC-F) determination of TBZ directly from orange (both whole fruit and juice), lemon, grape and strawberry extracts at low concentration levels in less than 15 min, without any need for a clean-up step in the analytical protocol.

Spiral counter-current chromatography of small molecules, peptides and proteins using the spiral tubing support rotor.

PubMed

Knight, Martha; Finn, Thomas M; Zehmer, John; Clayton, Adam; Pilon, Aprile

2011-09-09

An important advance in countercurrent chromatography (CCC) carried out in open flow-tubing coils, rotated in planetary centrifuges, is the new design to spread out the tubing in spirals. More spacing between the tubing was found to significantly increase the stationary phase retention, such that now all types of two-phase solvent systems can be used for liquid-liquid partition chromatography in the J-type planetary centrifuges. A spiral tubing support (STS) frame with circular channels was constructed by laser sintering technology into which FEP tubing was placed in 4 spiral loops per layer from the bottom to the top and a cover affixed allowing the tubing to connect to flow-tubing of the planetary centrifuge. The rotor was mounted and run in a P.C. Inc. type instrument. Examples of compounds of molecular weights ranging from <300 to approximately 15,000 were chromatographed in appropriate two-phase solvent systems to assess the capability for separation and purification. A mixture of small molecules including aspirin was completely separated in hexane-ethyl acetate-methanol-water. Synthetic peptides including a very hydrophobic peptide were each purified to a very high purity level in a sec-butanol solvent system. In the STS rotor high stationary phase retention was possible with the aqueous sec-butanol solvent system at a normal flow rate. Finally, the two-phase aqueous polyethylene glycol-potassium phosphate solvent system was applied to separate a protein from a lysate of an Escherichia coli expression system. These experiments demonstrate the versatility of spiral CCC using the STS rotor. Copyright © 2011 Elsevier B.V. All rights reserved.

A finite state projection algorithm for the stationary solution of the chemical master equation.

PubMed

Gupta, Ankit; Mikelson, Jan; Khammash, Mustafa

2017-10-21

The chemical master equation (CME) is frequently used in systems biology to quantify the effects of stochastic fluctuations that arise due to biomolecular species with low copy numbers. The CME is a system of ordinary differential equations that describes the evolution of probability density for each population vector in the state-space of the stochastic reaction dynamics. For many examples of interest, this state-space is infinite, making it difficult to obtain exact solutions of the CME. To deal with this problem, the Finite State Projection (FSP) algorithm was developed by Munsky and Khammash [J. Chem. Phys. 124(4), 044104 (2006)], to provide approximate solutions to the CME by truncating the state-space. The FSP works well for finite time-periods but it cannot be used for estimating the stationary solutions of CMEs, which are often of interest in systems biology. The aim of this paper is to develop a version of FSP which we refer to as the stationary FSP (sFSP) that allows one to obtain accurate approximations of the stationary solutions of a CME by solving a finite linear-algebraic system that yields the stationary distribution of a continuous-time Markov chain over the truncated state-space. We derive bounds for the approximation error incurred by sFSP and we establish that under certain stability conditions, these errors can be made arbitrarily small by appropriately expanding the truncated state-space. We provide several examples to illustrate our sFSP method and demonstrate its efficiency in estimating the stationary distributions. In particular, we show that using a quantized tensor-train implementation of our sFSP method, problems admitting more than 100 × 10 6 states can be efficiently solved.

A finite state projection algorithm for the stationary solution of the chemical master equation

NASA Astrophysics Data System (ADS)

Gupta, Ankit; Mikelson, Jan; Khammash, Mustafa

2017-10-01

The chemical master equation (CME) is frequently used in systems biology to quantify the effects of stochastic fluctuations that arise due to biomolecular species with low copy numbers. The CME is a system of ordinary differential equations that describes the evolution of probability density for each population vector in the state-space of the stochastic reaction dynamics. For many examples of interest, this state-space is infinite, making it difficult to obtain exact solutions of the CME. To deal with this problem, the Finite State Projection (FSP) algorithm was developed by Munsky and Khammash [J. Chem. Phys. 124(4), 044104 (2006)], to provide approximate solutions to the CME by truncating the state-space. The FSP works well for finite time-periods but it cannot be used for estimating the stationary solutions of CMEs, which are often of interest in systems biology. The aim of this paper is to develop a version of FSP which we refer to as the stationary FSP (sFSP) that allows one to obtain accurate approximations of the stationary solutions of a CME by solving a finite linear-algebraic system that yields the stationary distribution of a continuous-time Markov chain over the truncated state-space. We derive bounds for the approximation error incurred by sFSP and we establish that under certain stability conditions, these errors can be made arbitrarily small by appropriately expanding the truncated state-space. We provide several examples to illustrate our sFSP method and demonstrate its efficiency in estimating the stationary distributions. In particular, we show that using a quantized tensor-train implementation of our sFSP method, problems admitting more than 100 × 106 states can be efficiently solved.

Breathing multichimera states in nonlocally coupled phase oscillators

NASA Astrophysics Data System (ADS)

Suda, Yusuke; Okuda, Koji

2018-04-01

Chimera states for the one-dimensional array of nonlocally coupled phase oscillators in the continuum limit are assumed to be stationary states in most studies, but a few studies report the existence of breathing chimera states. We focus on multichimera states with two coherent and incoherent regions and numerically demonstrate that breathing multichimera states, whose global order parameter oscillates temporally, can appear. Moreover, we show that the system exhibits a Hopf bifurcation from a stationary multichimera to a breathing one by the linear stability analysis for the stationary multichimera.

Electrochemically modulated liquid chromatography using a boron-doped diamond particle stationary phase

PubMed Central

Muna, Grace W.; Swope, Vernon M.; Swain, Greg M.; Porter, Marc D.

2011-01-01

This paper reports on preliminary tests of the performance of boron-doped diamond powder (BDDP) as a stationary phase in electrochemically modulated liquid chromatography (EMLC). EMLC manipulates retention through changes in the potential applied (Eappl) to a conductive packing. Porous graphitic carbon (PGC) has routinely been utilized as a material in EMLC separations. Herein the utility of BDDP as a stationary phase in EMLC was investigated and its stability, both compositionally and microstructurally, relative to PGC was compared. The results show that BDDP is stable over a wide range of Eappl values (i.e., −1.2 to +1.2 V vs. Ag/AgCl, sat’d NaCl). The data also reveal that electrostatics play a key role in the adsorption of the aromatic sulfonates on the BDDP stationary phase, and that these analytes are more weakly retained in comparison to the PGC support. The potential for this methodology to provide a means to advance the understanding of molecular adsorption and retention mechanisms on carbonaceous materials is briefly discussed. PMID:18922535

Photoemission studies of fluorine functionalized porous graphitic carbon

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ganegoda, Hasitha; Olive, Daniel; Cheng, Lidens

2012-03-01

Porous graphitic carbon (PGC) has unique properties desirable for liquid chromatography applications when used as a stationary phase. The polar retention effect on graphite (PREG) allows efficient separation of polar and non-polar solutes. Perfluorinated hydrocarbons however lack polarizabilty and display strong lipo- and hydrophobicity, hence common lipophilic and hydrophilic analytes have low partition coefficiency in fluorinated stationary phases. Attractive interaction between fluorinated stationary phase and fluorinated analytes results in strong retention compared to non-fluorinated analytes. In order to change the selectivities of PGC, it is necessary to develop a bonded PGC stationary phase. In this study, we have synthesized perfluorinated,more » PGC using hepatadecafluoro-1-iodooctane, under different temperature conditions. Surface functionalization of the raw material was studied using photoelectron spectroscopy (PES). Results indicate the existence of fluorine containing functional groups, -CF, -CF{sub 2} along with an intercalated electron donor species. Multiple oxygen functional groups were also observed, likely due to the presence of oxygen in the starting material. These oxygen species may be responsible for significant modifications to planer and tetrahedral carbon ratios.« less

Synthesis and Purification of Iodoaziridines Involving Quantitative Selection of the Optimal Stationary Phase for Chromatography

PubMed Central

Boultwood, Tom; Affron, Dominic P.; Bull, James A.

2014-01-01

The highly diastereoselective preparation of cis-N-Ts-iodoaziridines through reaction of diiodomethyllithium with N-Ts aldimines is described. Diiodomethyllithium is prepared by the deprotonation of diiodomethane with LiHMDS, in a THF/diethyl ether mixture, at -78 °Cin the dark. These conditions are essential for the stability of the LiCHI2 reagent generated. The subsequent dropwise addition of N-Ts aldimines to the preformed diiodomethyllithium solution affords an amino-diiodide intermediate, which is not isolated. Rapid warming of the reaction mixture to 0 °C promotes cyclization to afford iodoaziridines with exclusive cis-diastereoselectivity. The addition and cyclization stages of the reaction are mediated in one reaction flask by careful temperature control. Due to the sensitivity of the iodoaziridines to purification, assessment of suitable methods of purification is required. A protocol to assess the stability of sensitive compounds to stationary phases for column chromatography is described. This method is suitable to apply to new iodoaziridines, or other potentially sensitive novel compounds. Consequently this method may find application in range of synthetic projects. The procedure involves firstly the assessment of the reaction yield, prior to purification, by 1H NMR spectroscopy with comparison to an internal standard. Portions of impure product mixture are then exposed to slurries of various stationary phases appropriate for chromatography, in a solvent system suitable as the eluent in flash chromatography. After stirring for 30 min to mimic chromatography, followed by filtering, the samples are analyzed by 1H NMR spectroscopy. Calculated yields for each stationary phase are then compared to that initially obtained from the crude reaction mixture. The results obtained provide a quantitative assessment of the stability of the compound to the different stationary phases; hence the optimal can be selected. The choice of basic alumina, modified to activity IV, as a suitable stationary phase has allowed isolation of certain iodoaziridines in excellent yield and purity. PMID:24893769

Solid-phase extraction sorbent consisting of alkyltrimethylammonium surfactants immobilized onto strong cation-exchange polystyrene resin.

PubMed

Reid, Kendra R; Kennedy, Lonnie J; Crick, Eric W; Conte, Eric D

2002-10-25

Presented is a solid-phase extraction sorbent material composed of cationic alkyltrimethylammonium surfactants attached to a strong cation-exchange resin via ion-exchange. The original hydrophilic cation-exchange resin is made hydrophobic by covering the surface with alkyl chains from the hydrophobic portion of the surfactant. The sorbent material now has a better ability to extract hydrophobic molecules from aqueous samples. The entire stationary phase (alkyltrimethylammonium surfactant) is removed along with the analyte during the elution step. The elution step requires a mild elution solvent consisting of 0.25 M Mg2+ in a 50% 2-propanol solution. The main advantage of using a removable stationary phase is that traditionally utilized toxic elution solvents such as methylene chloride, which are necessary to efficiently release strongly hydrophobic species from SPE stationary phases, may now be avoided. Also, the final extract is directly compatible with reversed-phase liquid chromatography. The performance of this procedure is presented using pyrene as a test molecule.

Preparation and chromatographic evaluation of zwitterionic stationary phases with controllable ratio of positively and negatively charged groups.

PubMed

Cheng, Xiao-Dong; Hao, Yan-Hong; Peng, Xi-Tian; Yuan, Bi-Feng; Shi, Zhi-Guo; Feng, Yu-Qi

2015-08-15

The present study described the preparation and application of zwitterionic stationary phases (ACS) with controllable ratio of positively charged tertiary amine groups and negatively charged carboxyl groups. Various parameters, including water content, pH values and ionic strength of the mobile phase, were investigated to study the chromatographic characteristics of ACS columns. The prepared ACS columns demonstrated a mix-mode retention mechanism composed of surface adsorption, partitioning and electrostatic interactions. The elemental analysis of different batches of the ACS phases demonstrated good reproducibility of the preparation strategy. Additionally, various categories of compounds, including nucleosides, water-soluble vitamins, benzoic acid derivatives and basic compounds were successively employed to evaluate the separation selectivity of the prepared ACS stationary phases. These ACS phases exhibited entirely different selectivity and retention behavior from each other for various polar analytes, demonstrating the excellent application potential in the analysis of polar compounds in HILIC. Copyright © 2015 Elsevier B.V. All rights reserved.

Yeast Pah1p Phosphatidate Phosphatase Is Regulated by Proteasome-mediated Degradation*

PubMed Central

Pascual, Florencia; Hsieh, Lu-Sheng; Soto-Cardalda, Aníbal; Carman, George M.

2014-01-01

Yeast PAH1-encoded phosphatidate phosphatase is the enzyme responsible for the production of the diacylglycerol used for the synthesis of triacylglycerol that accumulates in the stationary phase of growth. Paradoxically, the growth phase-mediated inductions of PAH1 and phosphatidate phosphatase activity do not correlate with the amount of Pah1p; enzyme abundance declined in a growth phase-dependent manner. Pah1p from exponential phase cells was a relatively stable protein, and its abundance was not affected by incubation with an extract from stationary phase cells. Recombinant Pah1p was degraded upon incubation with the 100,000 × g pellet fraction of stationary phase cells, although the enzyme was stable when incubated with the same fraction of exponential phase cells. MG132, an inhibitor of proteasome function, prevented degradation of the recombinant enzyme. Endogenously expressed and plasmid-mediated overexpressed levels of Pah1p were more abundant in the stationary phase of cells treated with MG132. Pah1p was stabilized in mutants with impaired proteasome (rpn4Δ, blm10Δ, ump1Δ, and pre1 pre2) and ubiquitination (hrd1Δ, ubc4Δ, ubc7Δ, ubc8Δ, and doa4Δ) functions. The pre1 pre2 mutations that eliminate nearly all chymotrypsin-like activity of the 20 S proteasome had the greatest stabilizing effect on enzyme levels. Taken together, these results supported the conclusion that Pah1p is subject to proteasome-mediated degradation in the stationary phase. That Pah1p abundance was stabilized in pah1Δ mutant cells expressing catalytically inactive forms of Pah1p and dgk1Δ mutant cells with induced expression of DGK1-encoded diacylglycerol kinase indicated that alteration in phosphatidate and/or diacylglycerol levels might be the signal that triggers Pah1p degradation. PMID:24563465

Tubing modifications for countercurrent chromatography (CCC): Stationary phase retention and separation efficiency.

PubMed

Englert, Michael; Vetter, Walter

2015-07-16

Countercurrent chromatography (CCC) is a separation technique in which two immiscible liquid phases are used for the preparative purification of synthetic and natural products. In CCC the number of repetitive mixing and de-mixing processes, the retention of the stationary phase and the mass transfer between the liquid phases are significant parameters that influence the resolution and separation efficiency. Limited mass transfer is the main reason for peak broadening and a low number of theoretical plates along with impaired peak resolution in CCC. Hence, technical improvements with regard to column design and tubing modifications is an important aspect to enhance mixing and mass transfer. In this study we constructed a crimping tool which allowed us to make reproducible, semi-automated modifications of conventional round-shaped tubing. Six crimped tubing modifications were prepared, mounted onto multilayer coils which were subsequently installed in the CCC system. The stationary phase retention of the tubing modifications were compared to the conventional system with unmodified tubing in a hydrophobic, an intermediate and a hydrophilic two-phase solvent system. Generally, the tubing modifications provided higher capabilities to retain the stationary phase depending on the solvent system and flow rates. In the intermediate solvent system the separation efficiency was evaluated with a mixture of six alkyl p-hydroxybenzoates. The peak resolution could be increased up to 50% with one of the tubing modifications compared to the unmodified tubing. Using the most convincing tubing modification at fixed values for the stationary phase retention, a reasonable comparison to the unmodified tubing was achieved. The peak width could be reduced up to 49% and a strong positive impact at increased flow rates regarding peak resolution and theoretical plate number was observed compared to unmodified tubing. It could be concluded that the tubing modification enhanced the interphase mixing and mass transfer of the two phases by additional and more vigorous agitation. Copyright © 2015 Elsevier B.V. All rights reserved.

Sound propagation in water containing large tethered spherical encapsulated gas bubbles with resonance frequencies in the 50 Hz to 100 Hz range.

PubMed

Lee, Kevin M; Hinojosa, Kevin T; Wochner, Mark S; Argo, Theodore F; Wilson, Preston S; Mercier, Richard S

2011-11-01

The efficacy of large tethered encapsulated gas bubbles for the mitigation of low frequency underwater noise was investigated with an acoustic resonator technique. Tethered latex balloons were used as the bubbles, which had radii of approximately 5 cm. Phase speeds were inferred from the resonances of a water and balloon-filled waveguide approximately 1.8 m in length. The Commander and Prosperetti effective-medium model [J. Acoust. Soc. Am. 85, 732-746 (1989)] quantitatively described the observed dispersion from well below to just below the individual bubble resonance frequency, and it qualitatively predicted the frequency range of high attenuation for void fractions between 2% and 5% for collections of stationary balloons within the waveguide. A finite-element model was used to investigate the sensitivity of the waveguide resonance frequencies, and hence the inferred phase speeds, to changes in individual bubble size and position. The results indicate that large tethered encapsulated bubbles could be used mitigate low frequency underwater noise and that the Commander and Prosperetti model would be useful in the design of such a system.

Stationary-phase optimized selectivity liquid chromatography: development of a linear gradient prediction algorithm.

PubMed

De Beer, Maarten; Lynen, Fréderic; Chen, Kai; Ferguson, Paul; Hanna-Brown, Melissa; Sandra, Pat

2010-03-01

Stationary-phase optimized selectivity liquid chromatography (SOS-LC) is a tool in reversed-phase LC (RP-LC) to optimize the selectivity for a given separation by combining stationary phases in a multisegment column. The presently (commercially) available SOS-LC optimization procedure and algorithm are only applicable to isocratic analyses. Step gradient SOS-LC has been developed, but this is still not very elegant for the analysis of complex mixtures composed of components covering a broad hydrophobicity range. A linear gradient prediction algorithm has been developed allowing one to apply SOS-LC as a generic RP-LC optimization method. The algorithm allows operation in isocratic, stepwise, and linear gradient run modes. The features of SOS-LC in the linear gradient mode are demonstrated by means of a mixture of 13 steroids, whereby baseline separation is predicted and experimentally demonstrated.

Different Spectrophotometric and Chromatographic Methods for Determination of Mepivacaine and Its Toxic Impurity.

PubMed

Abdelwahab, Nada S; Fared, Nehal F; Elagawany, Mohamed; Abdelmomen, Esraa H

2017-09-01

Stability-indicating spectrophotometric, TLC-densitometric, and ultra-performance LC (UPLC) methods were developed for the determination of mepivacaine HCl (MEP) in the presence of its toxic impurity, 2,6-dimethylanaline (DMA). Different spectrophotometric methods were developed for the determination of MEP and DMA. In a dual-wavelength method combined with direct spectrophotometric measurement, the absorbance difference between 221.4 and 240 nm was used for MEP measurements, whereas the absorbance at 283 nm was used for measuring DMA in the binary mixture. In the second-derivative method, amplitudes at 272.2 and 232.6 nm were recorded and used for the determination of MEP and DMA, respectively. The developed TLC-densitometric method depended on chromatographic separation using silica gel 60 F254 TLC plates as a stationary phase and methanol-water-acetic acid (9 + 1 + 0.1, v/v/v) as a developing system, with UV scanning at 230 nm. The developed UPLC method depended on separation using a C18 column (250 × 4.6 mm id, 5 μm particle size) as a stationary phase and acetonitrile-water (40 + 60, v/v; pH 4 with phosphoric acid) as a mobile phase at a flow rate of 0.4 mL/min, with UV detection at 215 nm. The chromatographic run time was approximately 1 min. The proposed methods were validated with respect to International Conference on Harmonization guidelines regarding precision, accuracy, ruggedness, robustness, and specificity.

Quantitation of anticonvulsant drugs in serum by gas-chromatography on the stationary phase SP-2510.

PubMed

Godolphin, W; Thoma, J

1978-03-01

A new column packing, SP-2510 DA (Supelco, Inc., Bellefonte, Pa. 16823), is an excellent stationary phase for the determination of a wide variety of anticonvulsant drugs by gas--liquid chromatography without derivatization. However, when uncomplicated extraction procedures are used, serum cholesterol interferes with the determination of primidone. By the simple expedient of adding a short "pre-column" containing another phase (SP-2250 DA) the problem is overcome.

Characterization of adsorption on the stationary phase using high-performance immunoaffinity chromatography.

PubMed

Nielsen, R G; Wilson, G S

1987-12-25

Low-level adsorption on the stationary phase has been studied using immunochemical reagents. An immunoaffinity column has been evaluated using affinity-purified radioisotope-labeled monoclonal antibodies. Recovery experiments including continuous immunosorbent monitoring have been performed. Proper characterization of an immunoaffinity separation can result in the recovery of immunologically active material in high yield.

Prebifurcation periodic ghost orbits in semiclassical quantization

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kus, M.; Haake, F.; Delande, D.

1993-10-04

Classical periodic orbits are stationary-phase points in path integral representations of quantum propagators. We show that complex solutions of the stationary-phase equation, not corresponding to real classical periodic orbits, give additional contributions to the propagator which can be important, especially near bifurcations. We reveal the existence and relevance of such periodic ghost orbits for a kicked top.

Experimental comparison of chiral metal-organic framework used as stationary phase in chromatography.

PubMed

Xie, Sheng-Ming; Zhang, Mei; Fei, Zhi-Xin; Yuan, Li-Ming

2014-10-10

Chiral metal-organic frameworks (MOFs) are a new class of multifunctional material, which possess diverse structures and unusual properties such as high surface area, uniform and permanent cavities, as well as good chemical and thermal stability. Their chiral functionality makes them attractive as novel enantioselective adsorbents and stationary phases in separation science. In this paper, the experimental comparison of a chiral MOF [In₃O(obb)₃(HCO₂)(H₂O)] solvent used as a stationary phase was investigated in gas chromatography (GC), high-performance liquid chromatography (HPLC) and capillary electrochromatography (CEC). The potential relationship between the structure and components of chiral MOFs with their chiral recognition ability and selectivity are presented. Copyright © 2014 Elsevier B.V. All rights reserved.

Topology of Collisionless Relaxation

NASA Astrophysics Data System (ADS)

Pakter, Renato; Levin, Yan

2013-04-01

Using extensive molecular dynamics simulations we explore the fine-grained phase space structure of systems with long-range interactions. We find that if the initial phase space particle distribution has no holes, the final stationary distribution will also contain a compact simply connected region. The microscopic holes created by the filamentation of the initial distribution function are always restricted to the outer regions of the phase space. In general, for complex multilevel distributions it is very difficult to a priori predict the final stationary state without solving the full dynamical evolution. However, we show that, for multilevel initial distributions satisfying a generalized virial condition, it is possible to predict the particle distribution in the final stationary state using Casimir invariants of the Vlasov dynamics.

Evaluation of a new polymeric stationary phase with reversed-phase properties for high temperature liquid chromatography.

PubMed

Vanhoenacker, Gerd; Dos Santos Pereira, Alberto; Kotsuka, Takashi; Cabooter, Deirdre; Desmet, Gert; Sandra, Pat

2010-05-07

The performance of a polymeric stationary phase with reversed-phase properties (ET-RP1) was evaluated for LC separations at elevated temperature. The most significant observation was that the reduced plate height (h) decreased from 3.4 at 25 degrees C (optimal flow 0.5 mL/min) to 2.4 at 150 degrees C (optimal flow 2.5 mL/min) which is comparable to the efficiency obtained with silica-based reversed-phase columns of 4.6mm ID operated at 0.8 mL/min. The phase showed no deterioration after long use at 150 degrees C within the pH range 1-9. Catalytic activity originating from the stationary phase material, e.g. as experienced on zirconium columns operated at elevated temperature, was absent. The performance of ET-RP1 is illustrated with the analysis of some pharmaceutical samples by LC and LC-MS. Operation at elevated temperature also allows to reduce the amount of organic modifier or to replace acetonitrile and methanol by the biodegradable ethanol. Copyright (c) 2009 Elsevier B.V. All rights reserved.

Preparation and characterization of a new microwave immobilized poly(2-phenylpropyl)methylsiloxane stationary phase for reversed phase high-performance liquid chromatography.

PubMed

Begnini, Fernanda R; Jardim, Isabel C S F

2013-07-05

A new reversed phase high-performance liquid chromatography (RP-HPLC) stationary phase was prepared and its chromatographic and physical-chemical properties were evaluated. The new stationary phase was prepared with a silica support and poly(2-phenylpropyl)methylsiloxane (PPPMS), a phenyl type polysiloxane copolymer. Since this is a new copolymer and there is little information in the literature, it was submitted to physical-chemical characterization by infrared spectroscopy and thermogravimetry. The chromatographic phase was prepared through sorption and microwave immobilization of the copolymer onto a silica support. The chromatographic performance was evaluated by employing test procedures suggested by Engelhardt and Jungheim, Tanaka and co-workers, Neue, and Szabó and Csató. These test mixtures provide information about the hydrophobic selectivity, silanophilic activity, ion-exchange capacity, shape selectivity and interaction with polar analytes of the new Si-PPPMS reversed phase. Stability tests were developed using accelerated aging tests under both basic and acidic conditions to provide information about the lifetime of the packed columns. Copyright © 2013 Elsevier B.V. All rights reserved.

Using the liquid nature of the stationary phase in countercurrent chromatography. IV. The cocurrent CCC method.

PubMed

Berthod, Alain; Hassoun, Mahmoud

2006-05-26

The retention volumes of solutes in countercurrent chromatography (CCC) are directly proportional to their distribution coefficients, K(D) in the biphasic liquid system used as mobile and stationary phase in the CCC column. The cocurrent CCC method consists in putting the liquid "stationary" phase in slow motion in the same direction as the mobile phase. A mixture of five steroid compounds of widely differing polarities was used as a test mixture to evaluate the capabilities of the method with the biphasic liquid system made of water/methanol/ethyl acetate/heptane 6/5/6/5 (v/v) and a 53 mL CCC column of the coil planet centrifuge type. It is shown that the chromatographic resolution obtained in cocurrent CCC is very good because the solute band broadening is minimized as long as the solute is located inside the "stationary" phase. Pushing the method at its limits, it is demonstrated that the five steroids can still be (partly) separated when the flow rate of the two liquid phases is the same (2 mL/min). This is due to the higher volume of upper phase (72% of the column volume) contained inside the CCC column producing a lower linear speed compared to the aqueous lower phase linear speed. The capabilities of the cocurrent CCC method compare well with those of the gradient elution method in HPLC. Continuous detection is a problem due to the fact that two immiscible liquid phases elute from the column. It was partly solved using an evaporative light scattering detector.

Retention behavior of alkyl-substituted polycyclic aromatic sulfur heterocycle isomers in gas chromatography on stationary phases of different selectivity.

PubMed

Wilson, Walter B; Sander, Lane C; Oña-Ruales, Jorge O; Mössner, Stephanie G; Sidisky, Leonard M; Lee, Milton L; Wise, Stephen A

2017-02-10

Retention indices for 10 sets of alkyl-substituted polycyclic aromatic sulfur heterocycles (PASHs) isomers (total of 80 PASHs) were determined using gas chromatography with three different stationary phases: a 50% phenyl phase, a 50% liquid crystalline dimethylpolysiloxane (LC-DMPS) phase, and an ionic liquid (IL) phase. Correlations between the retention behavior on the three stationary phases and PASH geometry [length-to-breadth (L/B) and thickness (T)] were investigated for the following PASHs: 4 methyl-substituted dibenzothiophenes (DBTs), 3 ethyl-substituted DBTs, 15 dimethyl-substituted DBTs, 8 trimethyl-substituted DBTs, 15 methyl-substituted naphthothiophenes, 30 methyl-substituted benzonaphthothiophenes, and 5 methyl-substituted tetrapheno[1,12-bcd]thiophene. Correlation coefficients for retention on the 50% phenyl phase vs L/B ranged from r=-0.28 (MeBbN23Ts) to r=0.92 (EtDBTs). Correlation coefficients for retention on the IL phase vs L/B ranged from r=0.13 (MeN12Ts) to r=0.83 (EtDBTs). Correlation coefficients for retention on the 50% LC-DMPS phase vs L/B ranged from r=0.22 (MeDBTs) to r=0.84 (TriMeDBTs). Published by Elsevier B.V.

Separation of piracetam derivatives on polysaccharide-based chiral stationary phases.

PubMed

Kažoka, H; Koliškina, O; Veinberg, G; Vorona, M

2013-03-15

High-performance liquid chromatography was used for the enantiomeric separation of two chiral piracetam derivatives. The suitability of six commercially available polysaccharide-based chiral stationary phases (CSPs) under normal phase mode for direct enantioseparation has been investigated. The influence of the CSPs as well the nature and content of an alcoholic modifier in the mobile phase on separation and elution order was studied. It was established that CSP Lux Amylose-2 shows high chiral recognition ability towards 4-phenylsubstituted piracetam derivatives. Copyright © 2013 Elsevier B.V. All rights reserved.

Chemically bonded stationary phases that use synthetic hosts containing aromatic binding clefts: HPLC analysis of nitro-substituted polycyclic aromatic hydrocarbons.

PubMed Central

Zimmerman, S C; Saionz, K W; Zeng, Z

1993-01-01

The synthesis of hosts with improved binding affinities for nitroaromatic guests is described. Association constants for several host-guest complexes were measured in chloroform solution and ranged over three orders of magnitude. Two hosts were covalently linked to silica gel to produce chemically bonded stationary phases for HPLC. The use of these phases for HPLC analysis of nitro-substituted polycyclic aromatic hydrocarbons is discussed. PMID:8433981

Effect of a crystal-melt interface on Taylor-vortex flow

NASA Technical Reports Server (NTRS)

Mcfadden, G. B.; Coriell, S. R.; Murray, B. T.; Glicksman, M. E.; Selleck, M. E.

1990-01-01

The linear stability of circular Couette flow between concentric infinite cylinders is considered for the case that the stationary outer cylinder is a crystal-melt interface rather than a rigid surface. A radial temperature difference is maintained across the liquid gap, and equations for heat transport in the crystal and melt phases are included to extend the ordinary formulation of this problem. The stability of this two-phase system depends on the Prandtl number. For small Prandtl number the linear stability of the two-phase system is given by the classical results for a rigid-walled system. For increasing values of the Prandtl number, convective heat transport becomes significant and the system becomes increasingly less stable. Previous results in a narrow-gap approximation are extended to the case of a finite gap, and both axisymmetric and nonaxisymmetric disturbance modes are considered. The two-phase system becomes less stable as the finite gap tends to the narrow-gap limit. The two-phase system is more stable to nonaxisymmetric modes with azimuthal wavenumber n = 1; the stability of these n = 1 modes is sensitive to the latent heat of fusion.

Berry phase dependent quantum trajectories of electron-hole pairs in semiconductors under intense terahertz fields

NASA Astrophysics Data System (ADS)

Yang, Fan; Liu, Ren-Bao

2013-03-01

Quantum evolution of particles under strong fields can be approximated by the quantum trajectories that satisfy the stationary phase condition in the Dirac-Feynmann path integrals. The quantum trajectories are the key concept to understand strong-field optics phenomena, such as high-order harmonic generation (HHG), above-threshold ionization (ATI), and high-order terahertz siedeband generation (HSG). The HSG in semiconductors may have a wealth of physics due to the possible nontrivial ``vacuum'' states of band materials. We find that in a spin-orbit-coupled semiconductor, the cyclic quantum trajectories of an electron-hole pair under a strong terahertz field accumulates nontrivial Berry phases. We study the monolayer MoS2 as a model system and find that the Berry phases are given by the Faraday rotation angles of the pulse emission from the material under short-pulse excitation. This result demonstrates an interesting Berry phase dependent effect in the extremely nonlinear optics of semiconductors. This work is supported by Hong Kong RGC/GRF 401512 and the CUHK Focused Investments Scheme.

Polar silica-based stationary phases. Part II- Neutral silica stationary phases with surface bound maltose and sorbitol for hydrophilic interaction liquid chromatography.

PubMed

Rathnasekara, Renuka; El Rassi, Ziad

2017-07-28

Two neutral polyhydroxylated silica bonded stationary phases, namely maltose-silica (MALT-silica) and sorbitol-silica (SOR-silica), have been introduced and chromatographically characterized in hydrophilic interaction liquid chromatography (HILIC) for a wide range of polar compounds. The bonding of the maltose and sorbitol to the silica surface was brought about by first converting bare silica to an epoxy-activated silica surface via reaction with γ-glycidoxypropyltrimethoxysilane (GPTMS) followed by attaching maltose and sorbitol to the epoxy surface in the presence of the Lewis acid catalyst BF 3 .ethereate. Both silica based columns offered the expected retention characteristics usually encountered for neutral polar surface. The retention mechanism is majorly based on solute' differential partitioning between an organic rich hydro-organic mobile phase (e.g., ACN rich mobile phase) and an adsorbed water layer on the surface of the stationary phase although additional hydrogen bonding was also responsible in some cases for solute retention. The MALT-silica column proved to be more hydrophilic and offered higher retention, separation efficiency and resolution than the SOR-silica column among the tested polar solutes such as derivatized mono- and oligosaccharides, weak phenolic acids, cyclic nucleotide monophosphate and nucleotide-5'-monophosphates, and weak bases, e.g., nucleobases and nucleosides. Copyright © 2017 Elsevier B.V. All rights reserved.

Immunoassay of paralytic shellfish toxins by moving magnetic particles in a stationary liquid-phase lab-on-a-chip.

PubMed

Kim, Myoung-Ho; Choi, Suk-Jung

2015-04-15

In this study, we devised a stationary liquid-phase lab-on-a-chip (SLP LOC), which was operated by moving solid-phase magnetic particles in the stationary liquid phase. The SLP LOC consisted of a sample chamber to which a sample and reactants were added, a detection chamber containing enzyme substrate solution, and a narrow channel connecting the two chambers and filled with buffer. As a model system, competitive immunoassays of saxitoxin (STX), a paralytic shellfish toxin, were conducted in the SLP LOC using protein G-coupled magnetic particles (G-MPs) as the solid phase. Anti-STX antibodies, STX-horseradish peroxidase conjugate, G-MPs, and a STX sample were added to the sample chamber and reacted by shaking. While liquids were in the stationary state, G-MPs were transported from the sample chamber to the detection chamber by moving a magnet below the LOC. After incubation to allow the enzymatic reaction to occur, the absorbance of the detection chamber solution was found to be reciprocally related to the STX concentration of the sample. Thus, the SLP LOC may represent a novel, simple format for point-of-care testing applications of enzyme-linked immunosorbent assays by eliminating complicated liquid handling steps. Copyright © 2014 Elsevier B.V. All rights reserved.

[Changes in the rates of glucose consumption and lactate release by cells in perfused and nonperfused cultures].

PubMed

Berestovskaia, N G; Akatov, V S; Lavrovskaia, V P

1993-01-01

The energetic state of Chinese hamster fibroblasts was investigated under stationary cultural conditions and under condition of culture medium perfusion immediately above the cells. Specific rates of glucose utilization and lactate formation under the former conditions (1.88 +/- 0.2) x 10(-13) and (4.3 +/- 0.56) x 10(-13) Mole/cell/h at the logarithmic growth phase, and (0.21 +/- 0.08) x 10(-13) and (0.58 +/- 0.06) x 10(-13) Mole/cell/h at the stationary phase, respectively. In the perfused culture, specific rates of glucose utilization and formation of lactate are (4.86 +/- 0.56) x 10(-13) and (11.0 +/- 1.8) x 10(-13) Mole/cell/h at the logarithmic growth phase, and (1.57 +/- 0.14) x 10(-13) and (4.11 +/- 0.5) x 10(-13) Mole/cell/h at the stationary phase, respectively. It has been proposed that under conditions of stationary culture the fall of the rates, as the culture reaches the survival phase, is due to diffusion-dependent limitations of mass transfer between the medium and the culture. Under perfusion conditions, the fall of the rates can be explained by some deficiency of necessary components and by excessive amounts of metabolic products in the multilayer structure.

Synthesis of a stationary phase based on silica modified with branched octadecyl groups by Michael addition and photoinduced thiol-yne click chemistry for the separation of basic compounds.

PubMed

Huang, Guang; Ou, Junjie; Wang, Hongwei; Ji, Yongsheng; Wan, Hao; Zhang, Zhang; Peng, Xiaojun; Zou, Hanfa

2016-04-01

A novel silica-based stationary phase with branched octadecyl groups was prepared by the sequential employment of the Michael addition reaction and photoinduced thiol-yne click chemistry with 3-aminopropyl-functionalized silica microspheres as the initial material. The resulting stationary phase denoted as SiO2 -N(C18)4 was characterized by elemental analysis, FTIR spectroscopy and Raman spectroscopy, demonstrating the existence of branched octadecyl groups in silica microspheres. The separations of benzene homologous compounds, acid compounds and amine analogues were conducted, demonstrating mixed-mode separation mechanism on SiO2 -N(C18)4 . Baseline separation of basic drugs mixture was acquired with the mobile phase of acetonitrile/H2 O (5%, v/v). SiO2 -N(C18)4 was further applied to separate Corydalis yanhusuo Wang water extracts, and more baseline separation peaks were obtained for SiO2 -N(C18)4 than those on Atlantis dC18 column. It can be expected that this new silica-based stationary phase will exhibit great potential in the analysis of basic compounds. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Effect of curvature on the backscattering from leaves

NASA Technical Reports Server (NTRS)

Sarabandi, K.; Senior, T. B. A.; Ulaby, F. T.

1988-01-01

Using a model previously developed for the backscattering cross section of a planar leaf at X-band frequencies and above, the effect of leaf curvature is examined. For normal incidence on a rectangular section of a leaf curved in one and two dimensions, an integral expression for the backscattered field is evaluated numerically and by a stationary phase approximation, leading to a simple analytical expression for the cross section reduction produced by the curvature. Numerical results based on the two methods are virtually identical, and in excellent agreement with measured data for rectangular sections of coleus leaves applied to the surfaces of styrofoam cylinders and spheres of different radii.

Effect of curvature on the backscattering from a leaf

NASA Technical Reports Server (NTRS)

Sarabandi, K.; Senior, T. B. A.; Ulaby, F. T.

1988-01-01

Using a model previously developed for the backscattering cross section of a planar leaf at X-band frequencies and above, the effect of leaf curvature is examined. For normal incidence on a rectangular section of a leaf curved in one and two dimensions, an integral expression for the backscattered field is evaluated numerically and by a stationary phase approximation, leading to a simple analytical expression for the cross-section reduction produced by the curvature. Numerical results based on the two methods are virtually identical, and in excellent agreement with measured data for rectangular sections of coleus leaves applied to the surfaces of styrofoam cylinders and spheres of different radii.

Revisiting resolution in hydrodynamic countercurrent chromatography: tubing bore effect.

PubMed

Berthod, A; Faure, K

2015-04-17

A major challenge in countercurrent chromatography (CCC), the technique that works with a support-free biphasic liquid system, is to retain the liquid stationary phase inside the CCC column (Sf parameter). Two solutions are commercially available: the hydrostatic CCC columns, also called centrifugal partition chromatographs (CPC), with disks of interconnected channels and rotary seals, and the hydrodynamic CCC columns with bobbins of coiled open tube and no rotary seals. It was demonstrated that the amount of liquid stationary phase retained by a coiled tube was higher with larger bore tubing than with small bore tubes. At constant column volume, small bore tubing will be longer producing more efficiency than larger bore tube that will better retain the liquid stationary phase. Since the resolution equation in CCC is depending on both column efficiency and stationary phase retention ratio, the influence of the tubing bore should be studied. This theoretical work showed that there is an optimum tubing bore size depending on solute partition coefficient and mobile phase flow rate. The interesting result of the theoretical study is that larger tubing bores allow for dramatically reduced experiment durations for all solutes: in reversed phase CCC (polar mobile phase), hydrophobic solutes are usually highly retained. These apolar solutes can be separated by the same coil at high flow rates and reduced Sf with similar retention times as polar solutes separated at smaller flow rates and much higher Sf. Copyright © 2015 Elsevier B.V. All rights reserved.

Inviscid spatial stability of a compressible mixing layer. II - The flame sheet model

NASA Technical Reports Server (NTRS)

Jackson, T. L.; Grosch, C. E.

1990-01-01

The results of an inviscid spatial calculation for a compressible reacting mixing layer are reported. The limit of infinitive activation energy is taken and the diffusion flame is approximated by a flame sheet. Results are reported for the phase speeds of the neutral waves and maximum growth rates of the unstable waves as a function of the parameters of the problem: the ratio of the temperature of the stationary stream to that of the moving stream, the Mach number of the moving streams, the heat release per unit mass fraction of the reactant, the equivalence ratio of the reaction, and the frequency of the disturbance. These results are compared to the phase speeds and growth rates of the corresponding nonreacting mixing layer. We show that the addition of combustion has important and complex effects on the flow stability.

Use of Long-Term E. Coli Cultures: To Study Generation of Genetic Diversity & Teach General Microbiology Laboratory Skills

ERIC Educational Resources Information Center

Petrie, Angela; Finkel, Steven E.; Erbe, Jarrod

2005-01-01

A novel method of studying the generation of genetic diversity in an undergraduate microbiology laboratory is described. The basis of this approach is the accumulation of mutations that confer a competitive advantage, or growth advantage in stationary phase (GASP) phenotype, to E. coli grown in stationary phase for extended periods of time.

Selectivity of hexaphenylbenzene-based hydrocarbon stationary phase with propeller-like conformation for aromatic and aliphatic isomers.

PubMed

Yang, Yinhui; Chang, Zhengfeng; Yang, Xiaohong; Qi, Meiling; Wang, Jinliang

2018-08-03

Herein we report a propeller-like hexaphenylbenzene-based hydrocarbon material (denoted as BT) as the stationary phase for capillary gas chromatography (GC). The statically-coated BT capillary column showed a high column efficiency of 4340 plates m -1 and weak polarity. Owing to its unique conformation, π-electron toroidal delocalization and intrinsic microporosity, the BT stationary phase exhibited interesting selectivity for aromatic compounds over alkanes. Compared with the graphene (G) column, the BT column showed much prolonged retention and high selectivity for aromatic isomers, especially methylnaphthalenes, dimethylnaphthalenes and phenanthrene/anthracene, mainly because of its propeller-like conformation with rich intercalation effects. Moreover, it exhibited good column repeatability (intra-day, inter-day) and reproducibility (between-column) with RSD values on the retention times less than 0.08% for intra-day, 0.32% for inter-day and 3.8% for between-column, respectively. Also, it showed good potential for determination of minor isomer impurities in real samples. To the best of our knowledge, this work presents the first example of employing an neat aromatic hydrocarbon material as the GC stationary phase with high selectivity for analytes of a wide ranging polarity. Copyright © 2018 Elsevier B.V. All rights reserved.

Probing Gamma-ray Emission of Geminga and Vela with Non-stationary Models

NASA Astrophysics Data System (ADS)

Chai, Yating; Cheng, Kwong-Sang; Takata, Jumpei

2016-06-01

It is generally believed that the high energy emissions from isolated pulsars are emitted from relativistic electrons/positrons accelerated in outer magnetospheric accelerators (outergaps) via a curvature radiation mechanism, which has a simple exponential cut-off spectrum. However, many gamma-ray pulsars detected by the Fermi LAT (Large Area Telescope) cannot be fitted by simple exponential cut-off spectrum, and instead a sub-exponential is more appropriate. It is proposed that the realistic outergaps are non-stationary, and that the observed spectrum is a superposition of different stationary states that are controlled by the currents injected from the inner and outer boundaries. The Vela and Geminga pulsars have the largest fluxes among all targets observed, which allows us to carry out very detailed phase-resolved spectral analysis. We have divided the Vela and Geminga pulsars into 19 (the off pulse of Vela was not included) and 33 phase bins, respectively. We find that most phase resolved spectra still cannot be fitted by a simple exponential spectrum: in fact, a sub-exponential spectrum is necessary. We conclude that non-stationary states exist even down to the very fine phase bins.

Green chromatography separation of analytes of greatly differing properties using a polyethylene glycol stationary phase and a low-toxic water-based mobile phase.

PubMed

Šatínský, Dalibor; Brabcová, Ivana; Maroušková, Alena; Chocholouš, Petr; Solich, Petr

2013-07-01

A simple, rapid, and environmentally friendly HPLC method was developed and validated for the separation of four compounds (4-aminophenol, caffeine, paracetamol, and propyphenazone) with different chemical properties. A "green" mobile phase, employing water as the major eluent, was proposed and applied to the separation of analytes with different polarity on polyethylene glycol (PEG) stationary phase. The chromatography separation of all compounds and internal standard benzoic acid was performed using isocratic elution with a low-toxicity mobile phase consisting of 0.04% (v/v) triethylamine and water. HPLC separation was carried out using a PEG reversed-phase stationary phase Supelco Discovery HS PEG column (15 × 4 mm; particle size 3 μm) at a temperature of 30 °C and flow rate at 1.0 mL min(-1). The UV detector was set at 210 nm. In this study, a PEG stationary phase was shown to be suitable for the efficient isocratic separation of compounds that differ widely in hydrophobicity and acid-base properties, particularly 4-aminophenol (log P, 0.30), caffeine (log P, -0.25), and propyphenazone (log P, 2.27). A polar PEG stationary phase provided specific selectivity which allowed traditional chromatographic problems related to the separation of analytes with different polarities to be solved. The retention properties of the group of structurally similar substances (aromatic amines, phenolic compounds, and xanthine derivatives) were tested with different mobile phases. The proposed green chromatography method was successfully applied to the analysis of active substances and one degradation impurity (4-aminophenol) in commercial preparation. Under the optimum chromatographic conditions, standard calibration was carried out with good linearity correlation coefficients for all compounds in the range (0.99914-0.99997, n = 6) between the peak areas and concentration of compounds. Recovery of the sample preparation was in the range 100 ± 5% for all compounds. The intraday method precision was determined as RSD, and the values were lower than 1.00%.

A Dancing Black Hole

NASA Astrophysics Data System (ADS)

Shoemaker, Deirdre; Smith, Kenneth; Schnetter, Erik; Fiske, David; Laguna, Pablo; Pullin, Jorge

2002-04-01

Recently, stationary black holes have been successfully simulated for up to times of approximately 600-1000M, where M is the mass of the black hole. Considering that the expected burst of gravitational radiation from a binary black hole merger would last approximately 200-500M, black hole codes are approaching the point where simulations of mergers may be feasible. We will present two types of simulations of single black holes obtained with a code based on the Baumgarte-Shapiro-Shibata-Nakamura formulation of the Einstein evolution equations. One type of simulations addresses the stability properties of stationary black hole evolutions. The second type of simulations demonstrates the ability of our code to move a black hole through the computational domain. This is accomplished by shifting the stationary black hole solution to a coordinate system in which the location of the black hole is time dependent.

Imaginary geometric phases of quantum trajectories in high-order terahertz sideband generation

NASA Astrophysics Data System (ADS)

Yang, Fan; Liu, Ren-Bao

2014-03-01

Quantum evolution of particles under strong fields can be described by a small number of quantum trajectories that satisfy the stationary phase condition in the Dirac-Feynmann path integral. The quantum trajectories are the key concept to understand the high-order terahertz siedeband generation (HSG) in semiconductors. Due to the nontrivial ``vacuum'' states of band materials, the quantum trajectories of optically excited electron-hole pairs in semiconductors can accumulate geometric phases under the driving of an elliptically polarized THz field. We find that the geometric phase of the stationary trajectory is generally complex with both real and imaginary parts. In monolayer MoS2, the imaginary parts of the geometric phase leads to a changing of the polarization ellipticity of the sideband. We further show that the imaginary part originates from the quantum interference of many trajectories with different phases. Thus the observation of the polarization ellipticity of the sideband shall be a good indication of the quantum nature of the stationary trajectory. This work is supported by Hong Kong RGC/GRF 401512 and the CUHK Focused Investments Scheme.

Mathematical Simulation of Perturbations of Attack Angle of Asymmetric Nanosatellite Passing through Resonance

NASA Astrophysics Data System (ADS)

Lyubimov, V. V.; Kurkina, E. V.

2018-05-01

The authors consider the problem of a dynamic system passing through a low-order resonance, describing an uncontrolled atmospheric descent of an asymmetric nanosatellite in the Earth's atmosphere. The authors perform mathematical and numerical modeling of the motion of the nanosatellite with a small mass-aerodynamic asymmetry relative to the center of mass. The aim of the study is to obtain new reliable approximate analytical estimates of perturbations of the angle of attack of a nanosatellite passing through resonance at angles of attack of not more than 0.5π. By using the stationary phase method, the authors were able to investigate a discontinuous perturbation in the angle of attack of a nanosatellite passing through a resonance with two different nanosatellite designs. Comparison of the results of the numerical modeling and new approximate analytical estimates of the perturbation of the angle of attack confirms the reliability of the said estimates.

Radiation resistance of lactobacilli isolated from radurized meat relative to growth and environment. [Lactobacillus sake; Lactobacillus curvatus; Lactobacillus farciminis; Staphylococcus aureus; Salmonella typimurium

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hastings, J.W.; Holzapfel, W.H.; Niemand, J.G.

1986-10-01

Of 113 lactobacilli isolated from radurized (5 kGy) minced meat, 7 Lactobacillus sake strains, 1 L. curvatus strain, and 1 L. farciminis strain were used for radiation resistance studies in a semisynthetic substrate (i.e., modified MRS broth). Five reference Lactobacillus spp. one Staphylococcus aureus strain, and one Salmonella typhimurium strain were used for comparative purposes. All L. sake isolates exhibited the phenomenon of being more resistant to gamma-irradiation in the exponential (log) phase than in the stationary phase of their growth cycles by a factor of 28%. Four reference strains also exhibited this phenomenon, with L. sake (DSM 20017) showingmore » a 68% increase in resistance in the log phase over the stationary phase. This phenomenon was not common to all bacteria tested and is not common to all strains with high radiation resistance. Four L. sake isolates and three reference strains were used in radiation sensitivity testing in a natural food system (i.e., meat). The bacteria were irradiated in minced meat and packaged under four different conditions (air, vacuum, CO/sub 2/, and N/sub 2/). Organisms exhibited the highest death rate (lowest D/sub 10/ values (doses required to reduce the logarithm of the bacterial population by 1) under CO/sub 2/ packaging conditions, but resistance to irradiation was increased under N/sub 2/. The D/sup 10/ values of the isolates were generally greater than those of the reference strains. The D/sup 10/ values were also higher (approximately two times) in meat than in a semisynthetic growth medium.« less

Cyclohexylamine additives for enhanced peptide separations in reversed phase liquid chromatography.

PubMed

Cole, S R; Dorsey, J G

1997-01-01

While the choice of stationary phase, organic modifier, and gradient strength can have significant effects on biomolecule separations, mobile phase additives can also have a significant effect on the chromatographic selectivity, recovery, efficiency and resolution. Given the importance of stationary phase coverage, the beneficial, silanol-masking properties of amines, and the potential for selectivity modification through ion-pair interactions, cyclohexylamine was examined as a mobile phase additive and compared with triethylamine and trifluoroacetic acid. Greatly improved separation was possible when cyclohexylamine was used as compared with phosphate buffer, and cyclohexylamine did not require purification before use, while triethylamine required distillation before 'clean' chromatograms were obtained.

Wiener filter preprocessing for OFDM systems in the presence of both nonstationary and stationary phase noises

NASA Astrophysics Data System (ADS)

Zhong, Ke; Lei, Xia; Li, Shaoqian

2013-12-01

Statistics-based intercarrier interference (ICI) mitigation algorithm is proposed for orthogonal frequency division multiplexing systems in presence of both nonstationary and stationary phase noises. By utilizing the statistics of phase noise, which can be obtained from measurements or data sheets, a Wiener filter preprocessing algorithm for ICI mitigation is proposed. The proposed algorithm can be regarded as a performance-improving technique for the previous researches on phase noise cancelation. Simulation results show that the proposed algorithm can effectively mitigate ICI and lower the error floor, and therefore significantly improve the performances of previous researches on phase noise cancelation, especially in the presence of severe phase noise.

Hilbert and Blaschke phases in the temporal coherence function of stationary broadband light.

PubMed

Fernández-Pousa, Carlos R; Maestre, Haroldo; Torregrosa, Adrián J; Capmany, Juan

2008-10-27

We show that the minimal phase of the temporal coherence function gamma (tau) of stationary light having a partially-coherent symmetric spectral peak can be computed as a relative logarithmic Hilbert transform of its amplitude with respect to its asymptotic behavior. The procedure is applied to experimental data from amplified spontaneous emission broadband sources in the 1.55 microm band with subpicosecond coherence times, providing examples of degrees of coherence with both minimal and non-minimal phase. In the latter case, the Blaschke phase is retrieved and the position of the Blaschke zeros determined.

Preparation of a polybutadiene stationary phase immobilized by gamma radiation for reversed-phase high-performance liquid chromatography.

PubMed

Lopes, Nilva P; Collins, Kenneth E; Jardim, Isabel C S F

2003-02-14

Polybutadiene (PBD) has been immobilized on HPLC silica by gamma radiation doses in the range from 5 to 180 kGy. Columns prepared from these reversed-phase materials, as well as from similar non-irradiated materials, were tested with standard sample mixtures and characterized by elemental analysis (% C) and infrared spectroscopy. A low dose of 5 kGy is sufficient to produce a layer of immobilized PBD which functions as an efficient and stable stationary phase. Higher doses give thicker immobilized layers having less favorable chromatographic properties.

Integrated reactor and centrifugal separator and uses thereof

DOEpatents

Birdwell, Jr., Joseph F; Jennings, Harold L [Clinton, TN; McFarlane, Joanna [Oak Ridge, TN; Tsouris, Constantino [Oak Ridge, TN

2012-01-17

An apparatus for providing reaction of fluids and separation of products with increased residence time. The apparatus includes a stationary shell, a rotating hollow cylindrical component disposed in the stationary shell, a residence-time increasing device external to the stationary shell, a standpipe for introducing fluid into an interior cavity of the hollow cylindrical component from the residence-time increasing device, a first outlet in fluid flow communication with the interior cavity of the hollow cylindrical component for a less dense phase fluid, and a second outlet in fluid flow communication with the interior cavity of the hollow cylindrical component for a more dense phase fluid.

Stationary states in quantum walk search

NASA Astrophysics Data System (ADS)

PrÅ«sis, Krišjānis; Vihrovs, Jevgěnijs; Wong, Thomas G.

2016-09-01

When classically searching a database, having additional correct answers makes the search easier. For a discrete-time quantum walk searching a graph for a marked vertex, however, additional marked vertices can make the search harder by causing the system to approximately begin in a stationary state, so the system fails to evolve. In this paper, we completely characterize the stationary states, or 1-eigenvectors, of the quantum walk search operator for general graphs and configurations of marked vertices by decomposing their amplitudes into uniform and flip states. This infinitely expands the number of known stationary states and gives an optimization procedure to find the stationary state closest to the initial uniform state of the walk. We further prove theorems on the existence of stationary states, with them conditionally existing if the marked vertices form a bipartite connected component and always existing if nonbipartite. These results utilize the standard oracle in Grover's algorithm, but we show that a different type of oracle prevents stationary states from interfering with the search algorithm.

Induction motors airgap-eccentricity detection through the discrete wavelet transform of the apparent power signal under non-stationary operating conditions.

PubMed

Yahia, K; Cardoso, A J M; Ghoggal, A; Zouzou, S E

2014-03-01

Fast Fourier transform (FFT) analysis has been successfully used for fault diagnosis in induction machines. However, this method does not always provide good results for the cases of load torque, speed and voltages variation, leading to a variation of the motor-slip and the consequent FFT problems that appear due to the non-stationary nature of the involved signals. In this paper, the discrete wavelet transform (DWT) of the apparent-power signal for the airgap-eccentricity fault detection in three-phase induction motors is presented in order to overcome the above FFT problems. The proposed method is based on the decomposition of the apparent-power signal from which wavelet approximation and detail coefficients are extracted. The energy evaluation of a known bandwidth permits to define a fault severity factor (FSF). Simulation as well as experimental results are provided to illustrate the effectiveness and accuracy of the proposed method presented even for the case of load torque variations. Copyright © 2013 ISA. Published by Elsevier Ltd. All rights reserved.

A new mathematical model and control of a three-phase AC-DC voltage source converter

DOE Office of Scientific and Technical Information (OSTI.GOV)

Blasko, V.; Kaura, V.

1997-01-01

A new mathematical model of the power circuit of a three-phase voltage source converter (VSC) was developed in the stationary and synchronous reference frames. The mathematical model was then used to analyze and synthesize the voltage and current control loops for the VSC. Analytical expressions were derived for calculating the gains and time constants of the current and voltage regulators. The mathematical model was used to control a 140-kW regenerative VSC. The synchronous reference frame model was used to define feedforward signals in the current regulators to eliminate the cross coupling between the d and q phases. It allowed themore » reduction of the current control loop to first-order plants and improved their tracking capability. The bandwidths of the current and voltage-control loops were found to be approximately 20 and 60 times (respectively) smaller than the sampling frequency. All control algorithms were implemented in a digital-signal processor. All results of the analysis were experimentally verified.« less

Stochastic Computations in Cortical Microcircuit Models

PubMed Central

Maass, Wolfgang

2013-01-01

Experimental data from neuroscience suggest that a substantial amount of knowledge is stored in the brain in the form of probability distributions over network states and trajectories of network states. We provide a theoretical foundation for this hypothesis by showing that even very detailed models for cortical microcircuits, with data-based diverse nonlinear neurons and synapses, have a stationary distribution of network states and trajectories of network states to which they converge exponentially fast from any initial state. We demonstrate that this convergence holds in spite of the non-reversibility of the stochastic dynamics of cortical microcircuits. We further show that, in the presence of background network oscillations, separate stationary distributions emerge for different phases of the oscillation, in accordance with experimentally reported phase-specific codes. We complement these theoretical results by computer simulations that investigate resulting computation times for typical probabilistic inference tasks on these internally stored distributions, such as marginalization or marginal maximum-a-posteriori estimation. Furthermore, we show that the inherent stochastic dynamics of generic cortical microcircuits enables them to quickly generate approximate solutions to difficult constraint satisfaction problems, where stored knowledge and current inputs jointly constrain possible solutions. This provides a powerful new computing paradigm for networks of spiking neurons, that also throws new light on how networks of neurons in the brain could carry out complex computational tasks such as prediction, imagination, memory recall and problem solving. PMID:24244126

Selectivity differences of water-soluble vitamins separated on hydrophilic interaction stationary phases.

PubMed

Yang, Yuanzhong; Boysen, Reinhard I; Hearn, Milton T W

2013-06-01

In this study, the retention behavior and selectivity differences of water-soluble vitamins were evaluated with three types of polar stationary phases (i.e. an underivatized silica phase, an amide phase, and an amino phase) operated in the hydrophilic interaction chromatographic mode with ESI mass spectrometric detection. The effects of mobile phase composition, including buffer pH and concentration, on the retention and selectivity of the vitamins were investigated. In all stationary phases, the neutral or weakly charged vitamins exhibited very weak retention under each of the pH conditions, while the acidic and more basic vitamins showed diverse retention behaviors. With the underivatized silica phase, increasing the salt concentration of the mobile phase resulted in enhanced retention of the acidic vitamins, but decreased retention of the basic vitamins. These observations thus signify the involvement of secondary mechanisms, such as electrostatic interaction in the retention of these analytes. Under optimized conditions, a baseline separation of all vitamins was achieved with excellent peak efficiency. In addition, the effects of water content in the sample on retention and peak efficiency were examined, with sample stacking effects observed when the injected sample contained a high amount of water. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Acridine orange staining reaction as an index of physiological activity in Escherichia coli

NASA Technical Reports Server (NTRS)

McFeters, G. A.; Singh, A.; Byun, S.; Callis, P. R.; Williams, S.

1991-01-01

The assumption that the acridine orange (AO) color reaction may be used as an index of physiological activity was investigated in laboratory grown Escherichia coli. Spectrofluorometric observations of purified nucleic acids, ribosomes and the microscopic color of bacteriophage-infected cells stained with AO confirmed the theory that single-stranded nucleic acids emit orange to red fluorescence while those that are double-stranded fluoresce green in vivo. Bacteria growing actively in a rich medium could be distinguished from cells in stationary phase by the AO reaction. Cells from log phase appeared red, whereas those in stationary phase were green. However, this differentiation was not seen when the bacteria were grown in a minimal medium or when a variation of the staining method was used. Also, shifting bacteria in stationary phase to starvation conditions rapidly changed their AO staining reaction. Boiling and exposure to lethal concentrations of azide and formalin resulted in stationary-phase cells that appeared red after staining but bacteria killed with chlorine remained green. These findings indicate that the AO staining reaction may be suggestive of physiological activity under defined conditions. However, variables in staining and fixation procedures as well as uncertainties associated with mixed bacterial populations in environmental samples may produce results that are not consistent with the classical interpretation of this reaction. The importance of validating the putative physiological implications of this staining reaction is stressed.

The Global Regulators GacA and ςS Form Part of a Cascade That Controls Alginate Production in Azotobacter vinelandii

PubMed Central

Castañeda, Miguel; Sánchez, Judith; Moreno, Soledad; Núñez, Cinthia; Espín, Guadalupe

2001-01-01

Transcription of the Azotobacter vinelandii algD gene, which encodes GDP-mannose dehydrogenase (the rate-limiting enzyme of alginate synthesis), starts from three sites: p1, p2, and p3. The sensor kinase GacS, a member of the two-component regulatory system, is required for transcription of algD from its three sites during the stationary phase. Here we show that algD is expressed constitutively throughout the growth cycle from the p2 and p3 sites and that transcription from p1 started at the transition between the exponential growth phase and stationary phase. We constructed A. vinelandii strains that carried mutations in gacA encoding the cognate response regulator of GacS and in rpoS coding for the stationary-phase ςS factor. The gacA mutation impaired alginate production and transcription of algD from its three promoters. Transcription of rpoS was also abolished by the gacA mutation. The rpoS mutation impaired transcription of algD from the p1 promoter and increased it from the p2 ςE promoter. The results of this study provide evidence for the predominant role of GacA in a regulatory cascade controlling alginate production and gene expression during the stationary phase in A. vinelandii. PMID:11698366

Construction of a hydrazone-linked chiral covalent organic framework-silica composite as the stationary phase for high performance liquid chromatography.

PubMed

Zhang, Kai; Cai, Song-Liang; Yan, Yi-Lun; He, Zi-Hao; Lin, Hui-Mei; Huang, Xiao-Ling; Zheng, Sheng-Run; Fan, Jun; Zhang, Wei-Guang

2017-10-13

Covalent organic frameworks (COFs), as an emerging class of crystalline porous organic polymers, have great potential for applications in chromatographic separation owning to their fascinating crystalline structures and outstanding properties. However, development of COF materials as novel stationary phases in high performance liquid chromatography (HPLC) is just in its infancy. Herein, we report the design and construction of a new hydrazone-linked chiral COF, termed BtaMth COF, from a chiral hydrazide building block (Mth) and present a one-pot synthetic method for the fabrication of BtaMth@SiO 2 composite for HPLC separation of isomers. The as-synthesized BtaMth chiral COF displays good crystallinity, high porosity, as well as excellent chemical stability. Meanwhile, the fabricated HPLC column by using BtaMth@SiO 2 composite as the new stationary phase exhibits high resolution performances for the separation of positional isomers including nitrotoluene and nitrochlorobenzene, as well as cis-trans isomers including beta-cypermethrin and metconazole. Additionally, some effects such as the composition of the mobile phase and column temperature for HPLC separations on the BtaMth@SiO 2 packed column also have been studied in detail. The successful applications indicate the great potentials of hydrazone-linked chiral COF-silica composite as novel stationary phase for the efficient HPLC separation. Copyright © 2017 Elsevier B.V. All rights reserved.

Monolithic poly[(trimethylsilyl-4-methylstyrene)-co- bis(4-vinylbenzyl)dimethylsilane] stationary phases for the fast separation of proteins and oligonucleotides.

PubMed

Jakschitz, Thomas A E; Huck, Christian W; Lubbad, Said; Bonn, Günther K

2007-04-13

In this paper the synthesis, optimisation and application of a silane based monolithic copolymer for the rapid separation of proteins and oligonucleotides is described. The monolith was prepared by thermal initiated in situ copolymerisation of trimethylsilyl-4-methylstyrene (TMSiMS) and bis(4-vinylbenzyl)dimethylsilane (BVBDMSi) in a silanised 200 microm I.D. fused silica column. Different ratios of monomer and crosslinker, as well as different ratios of micro- (toluene) and macro-porogen (2-propanol) were used for optimising the physical properties of the stationary phase regarding separation efficiency. The prepared monolithic stationary phases were characterised by measurement of permeability with different solvents, determination of pore size distribution by mercury intrusion porosimetry (MIP). Morphology was studied by scanning electron microscopy (SEM). Applying optimised conditions, a mixture comprised of five standard proteins ribunuclease A, cytochrome c, alpha-lactalbumine, myoglobine and ovalbumine was separated within 1 min by ion-pair reversed-phase liquid chromatography (IP-RPLC) obtaining half-height peak widths between 1.8 and 2.4 s. Baseline separation of oligonucleotides d(pT)(12-18) was achieved within 1.8 min obtaining half-height peak widths between 3.6 and 5.4 s. The results demonstrate the high potential of this stationary phase for fast separation of high-molecular weight biomolecules such as oligonucleotides and proteins.

SpxB is a suicide gene of Streptococcus pneumoniae and confers a selective advantage in an in vivo competitive colonization model.

PubMed

Regev-Yochay, Gili; Trzcinski, Krzysztof; Thompson, Claudette M; Lipsitch, Marc; Malley, Richard

2007-09-01

The human bacterial pathogen Streptococcus pneumoniae dies spontaneously upon reaching stationary phase. The extent of S. pneumoniae death at stationary phase is unusual in bacteria and has been conventionally attributed to autolysis by the LytA amidase. In this study, we show that spontaneous pneumococcal death is due to hydrogen peroxide (H(2)O(2)), not LytA, and that the gene responsible for H(2)O(2) production (spxB) also confers a survival advantage in colonization. Survival of S. pneumoniae in stationary phase was significantly prolonged by eliminating H(2)O(2) in any of three ways: chemically by supplementing the media with catalase, metabolically by growing the bacteria under anaerobic conditions, or genetically by constructing DeltaspxB mutants that do not produce H(2)O(2). Likewise, addition of H(2)O(2) to exponentially growing S. pneumoniae resulted in a death rate similar to that of cells in stationary phase. While DeltalytA mutants did not lyse at stationary phase, they died at a rate similar to that of the wild-type strain. Furthermore, we show that the death process induced by H(2)O(2) has features of apoptosis, as evidenced by increased annexin V staining, decreased DNA content, and appearance as assessed by transmission electron microscopy. Finally, in an in vivo rat model of competitive colonization, the presence of spxB conferred a selective advantage over the DeltaspxB mutant, suggesting an explanation for the persistence of this gene. We conclude that a suicide gene of pneumococcus is spxB, which induces an apoptosis-like death in pneumococci and confers a selective advantage in nasopharyngeal cocolonization.

SpxB Is a Suicide Gene of Streptococcus pneumoniae and Confers a Selective Advantage in an In Vivo Competitive Colonization Model▿

PubMed Central

Regev-Yochay, Gili; Trzcinski, Krzysztof; Thompson, Claudette M.; Lipsitch, Marc; Malley, Richard

2007-01-01

The human bacterial pathogen Streptococcus pneumoniae dies spontaneously upon reaching stationary phase. The extent of S. pneumoniae death at stationary phase is unusual in bacteria and has been conventionally attributed to autolysis by the LytA amidase. In this study, we show that spontaneous pneumococcal death is due to hydrogen peroxide (H2O2), not LytA, and that the gene responsible for H2O2 production (spxB) also confers a survival advantage in colonization. Survival of S. pneumoniae in stationary phase was significantly prolonged by eliminating H2O2 in any of three ways: chemically by supplementing the media with catalase, metabolically by growing the bacteria under anaerobic conditions, or genetically by constructing ΔspxB mutants that do not produce H2O2. Likewise, addition of H2O2 to exponentially growing S. pneumoniae resulted in a death rate similar to that of cells in stationary phase. While ΔlytA mutants did not lyse at stationary phase, they died at a rate similar to that of the wild-type strain. Furthermore, we show that the death process induced by H2O2 has features of apoptosis, as evidenced by increased annexin V staining, decreased DNA content, and appearance as assessed by transmission electron microscopy. Finally, in an in vivo rat model of competitive colonization, the presence of spxB conferred a selective advantage over the ΔspxB mutant, suggesting an explanation for the persistence of this gene. We conclude that a suicide gene of pneumococcus is spxB, which induces an apoptosis-like death in pneumococci and confers a selective advantage in nasopharyngeal cocolonization. PMID:17631628

Nutrient control for stationary phase cellulase production in Trichoderma reesei Rut C-30.

PubMed

Callow, Nicholas V; Ray, Christopher S; Kelbly, Matthew A; Ju, Lu-Kwang

2016-01-01

This work describes the use of nutrient limitations with Trichoderma reesei Rut C-30 to obtain a prolonged stationary phase cellulase production. This period of non-growth may allow for dependable cellulase production, extended fermentation periods, and the possibility to use pellet morphology for easy product separation. Phosphorus limitation was successful in halting growth and had a corresponding specific cellulase production of 5±2 FPU/g-h. Combined with the addition of Triton X-100 for fungal pellet formation and low shear conditions, a stationary phase cellulase production period in excess of 300 h was achieved, with a constant enzyme production rate of 7±1 FPU/g-h. While nitrogen limitation was also effective as a growth limiter, it, however, also prevented cellulase production. Copyright © 2015 Elsevier Inc. All rights reserved.

Method for making a non-extractable stationary phase of polymer within a capillary column

DOEpatents

Springston, Stephen R.

1990-01-01

A method for coating interior capillary column surfaces, or packing material of a packed column, used for gas chromatography, with a stationary polymer phase that is cross-linked by exposing it to a low-temperature plasma that is uniformly distributed over the column or packing material for a predetermined period of time to effect the desired degree of cross-linking of the coating.

Antagonistic Potential of Native Trichoderma viride Strain against Potent Tea Fungal Pathogens in North East India.

PubMed

Naglot, A; Goswami, S; Rahman, I; Shrimali, D D; Yadav, Kamlesh K; Gupta, Vikas K; Rabha, Aprana Jyoti; Gogoi, H K; Veer, Vijay

2015-09-01

Indigenous strains of Trichoderma species isolated from rhizosphere soils of Tea gardens of Assam, north eastern state of India were assessed for in vitro antagonism against two important tea fungal pathogens namely Pestalotia theae and Fusarium solani. A potent antagonist against both tea pathogenic fungi, designated as SDRLIN1, was selected and identified as Trichoderma viride. The strain also showed substantial antifungal activity against five standard phytopathogenic fungi. Culture filtrate collected from stationary growth phase of the antagonist demonstrated a significantly higher degree of inhibitory activity against all the test fungi, demonstrating the presence of an optimal blend of extracellular antifungal metabolites. Moreover, quantitative enzyme assay of exponential and stationary culture filtrates revealed that the activity of cellulase, β-1,3-glucanase, pectinase, and amylase was highest in the exponential phase, whereas the activity of proteases and chitinase was noted highest in the stationary phase. Morphological changes such as hyphal swelling and distortion were also observed in the fungal pathogen grown on potato dextrose agar containing stationary phase culture filtrate. Moreover, the antifungal activity of the filtrate was significantly reduced but not entirely after heat or proteinase K treatment, demonstrating substantial role of certain unknown thermostable antifungal compound(s) in the inhibitory activity.

Nanostructured pillars based on vertically aligned carbon nanotubes as the stationary phase in micro-CEC.

PubMed

Wu, Ren-Guei; Yang, Chung-Shi; Wang, Pen-Cheng; Tseng, Fan-Gang

2009-06-01

We present a micro-CEC chip carrying out a highly efficient separation of dsDNA fragments through vertically aligned multi-wall carbon nanotubes (MWCNTs) in a microchannel. The vertically aligned MWCNTs were grown directly in the microchannel to form straight nanopillar arrays as ordered and directional chromatographic supports. 1-Pyrenedodecanoic acid was employed for the surface modification of the MWCNTs' stationary phase to adsorb analytes by hydrophobic interactions. This device was used for separating dsDNA fragments of three different lengths (254, 360, and 572 bp), and fluorescence detection was employed to verify the electrokinetic transport in the MWCNT array. The micro-CEC separation of the three compounds was achieved in less than 300 s at a field strength of 66 V/cm due to superior laminar flow patterns and a lower flow resistance resulting from the vertically aligned MWCNTs being used as the stationary phase medium. In addition, a fivefold reduction of band broadening was obtained when the analyte was separated by the chromatographic MWCNT array channel instead of the CE channel. From all of the results, we suggest that an in situ grown and directional MWCNT array can potentially be useful for preparing more diversified forms of stationary phases for vertically efficient chip-based electrochromatography.

Antagonistic Potential of Native Trichoderma viride Strain against Potent Tea Fungal Pathogens in North East India

PubMed Central

Naglot, A.; Goswami, S.; Rahman, I.; Shrimali, D. D.; Yadav, Kamlesh K.; Gupta, Vikas K.; Rabha, Aprana Jyoti; Gogoi, H. K.; Veer, Vijay

2015-01-01

Indigenous strains of Trichoderma species isolated from rhizosphere soils of Tea gardens of Assam, north eastern state of India were assessed for in vitro antagonism against two important tea fungal pathogens namely Pestalotia theae and Fusarium solani. A potent antagonist against both tea pathogenic fungi, designated as SDRLIN1, was selected and identified as Trichoderma viride. The strain also showed substantial antifungal activity against five standard phytopathogenic fungi. Culture filtrate collected from stationary growth phase of the antagonist demonstrated a significantly higher degree of inhibitory activity against all the test fungi, demonstrating the presence of an optimal blend of extracellular antifungal metabolites. Moreover, quantitative enzyme assay of exponential and stationary culture filtrates revealed that the activity of cellulase, β-1,3-glucanase, pectinase, and amylase was highest in the exponential phase, whereas the activity of proteases and chitinase was noted highest in the stationary phase. Morphological changes such as hyphal swelling and distortion were also observed in the fungal pathogen grown on potato dextrose agar containing stationary phase culture filtrate. Moreover, the antifungal activity of the filtrate was significantly reduced but not entirely after heat or proteinase K treatment, demonstrating substantial role of certain unknown thermostable antifungal compound(s) in the inhibitory activity. PMID:26361476

Enantioseparation of Six Antihistamines with Immobilized Cellulose Chiral Stationary Phase by HPLC

PubMed Central

Zhou, Jie; Luo, Pei; Chen, Shanshan; Meng, Lingchang; Sun, Chong; Du, Qiuzheng; Sun, Fang

2016-01-01

A stereoselective high performance liquid chromatography method has been developed for the chiral separation of the enantiomers of six antihistamines, doxylamine, carbinoxamine, dioxopromethazine, oxomemazine, cetirizine and hydroxyzine. The effects of mobile phase additive, column temperature and flow rate on the retention time and resolution were studied. Enantiomeric separation of cetirizine, doxylamine and hydroxyzine were achieved on cellulose tris-(3,5-dichlorophenylcarbamate) immobilized on silica gel chiral stationary phase known as Chiralpak IC (RS = 3.74, RS = 1.85 and RS = 1.74, respectively). PMID:26657408

Simultaneous separation of inorganic anions and metal-citrate complexes on a zwitterionic stationary phase with on-column complexation.

PubMed

Nesterenko, Ekaterina P; Nesterenko, Pavel N; Paull, Brett

2008-12-05

The retention and separation selectivity of inorganic anions and on-column derivatised negatively charged citrate or oxalate metal complexes on reversed-phase stationary phases dynamically coated with N-(dodecyl-N,N-dimethylammonio)undecanoate (DDMAU) has been investigated. The retention mechanism for the metal-citrate complexes was predominantly anion exchange, although the amphoteric/zwitterionic nature of the stationary phase coating undoubtedly also contributed to the unusual separation selectivity shown. A mixture of 10 inorganic anions and metal cations was achieved using a 20 cm monolithic DDMAU modified column and a 1 mM citrate eluent, pH 4.0, flow rate equal to 0.8 mL/min. Selectivity was found to be strongly pH dependent, allowing additional scope for manipulation of solute retention, and thus application to complex samples. This is illustrated with the analysis of an acidic mine drainage sample with a range of inorganic anions and transition metal cations, varying significantly in their concentrations levels.

Effects of Surotomycin on Clostridium difficile Viability and Toxin Production In Vitro

PubMed Central

Bouillaut, Laurent; McBride, Shonna; Schmidt, Diane J.; Suarez, José M.; Tzipori, Saul; Mascio, Carmela; Chesnel, Laurent

2015-01-01

The increasing incidence and severity of infection by Clostridium difficile have stimulated attempts to develop new antimicrobial therapies. We report here the relative abilities of two antibiotics (metronidazole and vancomycin) in current use for treating C. difficile infection and of a third antimicrobial, surotomycin, to kill C. difficile cells at various stages of development and to inhibit the production of the toxin proteins that are the major virulence factors. The results indicate that none of the drugs affects the viability of spores at 8× MIC or 80× MIC and that all of the drugs kill exponential-phase cells when provided at 8× MIC. In contrast, none of the drugs killed stationary-phase cells or inhibited toxin production when provided at 8× MIC and neither vancomycin nor metronidazole killed stationary-phase cells when provided at 80× MIC. Surotomycin, on the other hand, did kill stationary-phase cells when provided at 80× MIC but did so without inducing lysis. PMID:25941230

Synthesis and evaluation of a maltose-bonded silica gel stationary phase for hydrophilic interaction chromatography and its application in Ginkgo Biloba extract separation in two-dimensional systems.

PubMed

Sheng, Qianying; Yang, Kaiya; Ke, Yanxiong; Liang, Xinmiao; Lan, Minbo

2016-09-01

Maltose covalently bonded to silica was prepared by using carbonyl diimidazole as a cross-linker and employed as a stationary phase for hydrophilic interaction liquid chromatography. The column efficiency and the effect of water content, buffer concentration, and pH value influenced on retention were investigated. The separation or enrichment selectivity was also studied with nucleosides, saccharides, amino acids, peptides, and glycopeptides. The results indicated that the stationary phase processed good separation efficiency and separation selectivity in hydrophilic interaction liquid chromatography mode. Moreover, a two-dimensional hydrophilic interaction liquid chromatography× reversed-phase liquid chromatography method with high orthogonality was developed to analyze the Ginkgo Biloba extract fractions. The development of this two-dimensional chromatographic system would be an effective tool for the separation of complex samples of different polarities and contents. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

'Click Chemistry' in the preparation of porous polymer-basedparticulate stationary phases for mu-HPLC separation of peptides andproteins

DOE Office of Scientific and Technical Information (OSTI.GOV)

Slater, Michael; Snauko, Marian; Svec, Frantisek

With the use of the copper(I)-catalyzed (3 + 2) azide-alkynecycloaddition, an element of "click chemistry," stationary phasescarrying long alkyl chains or soybean trypsin inhibitor have beenprepared for use in HPLC separations in the reversed-phase and affinitymodes, respectively. The ligands were attached via a triazole ring tosize monodisperse porous beads containing either alkyne or azide pendantfunctionalities. Alkyne-containing beads prepared by directcopolymerization of propargyl acrylate with ethylene dimethacrylate wereallowed to react with azidooctadecane to give a reversed-phase sorbent.Azide-functionalized beads were prepared by chemical modification ofglycidyl methacrylate particles. Subsequent reaction with a terminalaliphatic alkyne produced a reversed-phase sorbent similar to thatobtained from themore » alkyne beads. Soybean trypsin inhibitor wasfunctionalized with N-(4-pentynoyloxy) succinimide to carry alkyne groupsand then allowed to react with the azide-containing beads to produce anaffinity sorbent for trypsin. The performance of these stationary phaseswas demonstrated with the HPLC separations of a variety of peptides andproteins.« less

Metabolic activity of permafrost bacteria below the freezing point

NASA Technical Reports Server (NTRS)

Rivkina, E. M.; Friedmann, E. I.; McKay, C. P.; Gilichinsky, D. A.

2000-01-01

Metabolic activity was measured in the laboratory at temperatures between 5 and -20 degrees C on the basis of incorporation of (14)C-labeled acetate into lipids by samples of a natural population of bacteria from Siberian permafrost (permanently frozen soil). Incorporation followed a sigmoidal pattern similar to growth curves. At all temperatures, the log phase was followed, within 200 to 350 days, by a stationary phase, which was monitored until the 550th day of activity. The minimum doubling times ranged from 1 day (5 degrees C) to 20 days (-10 degrees C) to ca. 160 days (-20 degrees C). The curves reached the stationary phase at different levels, depending on the incubation temperature. We suggest that the stationary phase, which is generally considered to be reached when the availability of nutrients becomes limiting, was brought on under our conditions by the formation of diffusion barriers in the thin layers of unfrozen water known to be present in permafrost soils, the thickness of which depends on temperature.

Growth phase-dependent proteomes of the Malaysian isolated Lactococcus lactis dairy strain M4 using label-free qualitative shotgun proteomics analysis.

PubMed

Yap, Theresa Wan Chen; Rabu, Amir; Abu Bakar, Farah Diba; Rahim, Raha Abdul; Mahadi, Nor Muhammad; Illias, Rosli Md; Murad, Abdul Munir Abdul

2014-01-01

Lactococcus lactis is the most studied mesophilic fermentative lactic acid bacterium. It is used extensively in the food industry and plays a pivotal role as a cell factory and also as vaccine delivery platforms. The proteome of the Malaysian isolated L. lactis M4 dairy strain, obtained from the milk of locally bred cows, was studied to elucidate the physiological changes occurring between the growth phases of this bacterium. In this study, ultraperformance liquid chromatography nanoflow electrospray ionization tandem mass spectrometry (UPLC- nano-ESI-MS(E)) approach was used for qualitative proteomic analysis. A total of 100 and 121 proteins were identified from the midexponential and early stationary growth phases, respectively, of the L. lactis strain M4. During the exponential phase, the most important reaction was the generation of sufficient energy, whereas, in the early stationary phase, the metabolic energy pathways decreased and the biosynthesis of proteins became more important. Thus, the metabolism of the cells shifted from energy production in the exponential phase to the synthesis of macromolecules in the stationary phase. The resultant proteomes are essential in providing an improved view of the cellular machinery of L. lactis during the transition of growth phases and hence provide insight into various biotechnological applications.

Preparation and evaluation of surface-bonded tricationic ionic liquid silica as stationary phases for high-performance liquid chromatography.

PubMed

Qiao, Lizhen; Shi, Xianzhe; Lu, Xin; Xu, Guowang

2015-05-29

Two tricationic ionic liquids were prepared and then bonded onto the surface of supporting silica materials through "thiol-ene" click chemistry as new stationary phases for high-performance liquid chromatography. The obtained columns of tricationic ionic liquids were evaluated respectively in the reversed-phase liquid chromatography (RPLC) mode and hydrophilic interaction liquid chromatography (HILIC) mode, and possess ideal column efficiency of 80,000 plates/m in the RPLC mode with naphthalene as the test solute. The tricationic ionic liquid stationary phases exhibit good hydrophobic and shape selectivity to hydrophobic compounds, and RPLC retention behavior with multiple interactions. In the HILIC mode, the retention and selectivity were evaluated through the efficient separation of nucleosides and bases as well as flavonoids, and the typical HILIC retention behavior was demonstrated by investigating retention changes of hydrophilic solutes with water volume fraction in mobile phase. The results show that the tricationic ionic liquid columns possess great prospect for applications in analysis of hydrophobic and hydrophilic samples. Copyright © 2015 Elsevier B.V. All rights reserved.

Inviscid spatial stability of a compressible mixing layer. Part 2: The flame sheet model

NASA Technical Reports Server (NTRS)

Jackson, T. L.; Grosch, C. E.

1989-01-01

The results of an inviscid spatial calculation for a compressible reacting mixing layer are reported. The limit of infinitive activation energy is taken and the diffusion flame is approximated by a flame sheet. Results are reported for the phase speeds of the neutral waves and maximum growth rates of the unstable waves as a function of the parameters of the problem: the ratio of the temperature of the stationary stream to that of the moving stream, the Mach number of the moving streams, the heat release per unit mass fraction of the reactant, the equivalence ratio of the reaction, and the frequency of the disturbance. These results are compared to the phase speeds and growth rates of the corresponding nonreacting mixing layer. We show that the addition of combustion has important, and complex effects on the flow stability.

Prediction and mechanism elucidation of analyte retention on phospholipid stationary phases (IAM-HPLC) by in silico calculated physico-chemical descriptors.

PubMed

Russo, Giacomo; Grumetto, Lucia; Barbato, Francesco; Vistoli, Giulio; Pedretti, Alessandro

2017-03-01

The present study proposes a method for an in silico calculation of phospholipophilicity. Phospholipophilicity is intended as the measure of analyte affinity for phospholipids; it is currently assessed by HPLC measures of analyte retention on phosphatidylcholine-like stationary phases (IAM - Immobilized Artificial Membrane) resulting in log k W IAM values. Due to the amphipathic and electrically charged nature of phospholipids, retention on these stationary phases results from complex mechanisms, being affected not only by lipophilicity (as measured by n-octanol/aqueous phase partition coefficients, log P) but also by the occurrence of polar and/or electrostatic intermolecular interaction forces. Differently from log P, to date no method has been proposed for in silico calculation of log k W IAM . The study is aimed both at shedding new light into the retention mechanism on IAM stationary phases and at offering a high-throughput method to achieve such values. A wide set of physico-chemical and topological properties were taken into account, yielding a robust final model including four in silico calculated parameters (lipophilicity, hydrophilic/lipophilic balance, molecular size, and molecule flexibility). The here presented model was based on the analysis of 205 experimentally determined values, taken from the literature and measured by a single research group to minimize the interlaboratory variability; such model is able to predict phospholipophilicity values on both the two IAM stationary phases to date marketed, i.e. IAM.PC.MG and IAM.PC.DD2, with a fairly good degree (r 2 =0.85) of accuracy. The present work allowed the development of a free on-line service aimed at calculating log k W IAM values of any molecule included in the PubChem database, which is freely available at http://nova.disfarm.unimi.it/logkwiam.htm. Copyright © 2016 Elsevier B.V. All rights reserved.

Characterization of high hydrostatic pressure-injured Bacillus subtilis cells.

PubMed

Inaoka, Takashi; Kimura, Keitarou; Morimatsu, Kazuya; Yamamoto, Kazutaka

2017-06-01

High hydrostatic pressure (HHP) affects various cellular processes. Using a sporulation-deficient Bacillus subtilis strain, we characterized the properties of vegetative cells subjected to HHP. When stationary-phase cells were exposed to 250 MPa of HHP for 10 min at 25 °C, approximately 50% of cells were viable, although they exhibited a prolonged growth lag. The HHP-injured cells autolyzed in the presence of NaCl or KCl (at concentrations ≥100 mM). Superoxide dismutase slightly protected the viability of HHP-treated cells, whereas vegetative catalases had no effect. Thus, unlike HHP-injured Escherichia coli, oxidative stress only slightly affected vegetative B. subtilis subjected to HHP.

Distribution or adsorption: the major dilemma in reversed-phase HPLC

NASA Astrophysics Data System (ADS)

Deineka, V. I.

2008-06-01

A method is suggested for analyzing the dependences obtained for different compositions of mobile eluent system phases, their slopes and intercepts, log k( i, B) = a + b log k ( i, A), where a is the intercept for the A and B stationary phases and b is the proportionality factor. An analysis requires parallel investigation of sorbate retention on at least three stationary phases with different lengths of grafted hydrocarbon radicals. The dependence of correlation parameters on the sorbate retention mechanism is discussed. It is shown that the hypothetical dependences coincide with the experimental dependences for surface sorption of resveratrol and volume distribution of triglycerides.

Testing for nonlinearity in non-stationary physiological time series.

PubMed

Guarín, Diego; Delgado, Edilson; Orozco, Álvaro

2011-01-01

Testing for nonlinearity is one of the most important preprocessing steps in nonlinear time series analysis. Typically, this is done by means of the linear surrogate data methods. But it is a known fact that the validity of the results heavily depends on the stationarity of the time series. Since most physiological signals are non-stationary, it is easy to falsely detect nonlinearity using the linear surrogate data methods. In this document, we propose a methodology to extend the procedure for generating constrained surrogate time series in order to assess nonlinearity in non-stationary data. The method is based on the band-phase-randomized surrogates, which consists (contrary to the linear surrogate data methods) in randomizing only a portion of the Fourier phases in the high frequency domain. Analysis of simulated time series showed that in comparison to the linear surrogate data method, our method is able to discriminate between linear stationarity, linear non-stationary and nonlinear time series. Applying our methodology to heart rate variability (HRV) records of five healthy patients, we encountered that nonlinear correlations are present in this non-stationary physiological signals.

Nonconscious memory for motion activates MT+.

PubMed

Thakral, Preston P; Slotnick, Scott D

2014-11-12

Extrastriate region MT+ is widely thought to reflect conscious motion processing. The primary aim of the present functional MRI study was to assess whether MT+ is activated during nonconscious memory for motion. During the encoding phase, moving and stationary abstract shapes were presented to the left or right of fixation. During the retrieval phase, the same shapes were presented at fixation and participants classified each shape as 'moving-left', 'moving-right', 'stationary-left', or 'stationary-right'. The contrast of moving>stationary shapes at encoding was used to identify the location of MT+. Event-related activity was then extracted from MT+ within each hemisphere. MT+ activity was significantly greater for moving-misses than for stationary-misses, which indicates that nonconscious memory for motion activates MT+. Furthermore, nonconscious memory activity (moving-misses) had an earlier temporal onset than conscious memory activity (moving-hits). The present results are the first, to our knowledge, to demonstrate that MT+ is associated with nonconscious motion processing. Therefore, activity in this region or in other visual-sensory regions should not be assumed to reflect conscious processing.

Separation of alkylphenols by normal-phase and reversed-phase high-performance liquid chromatography

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schabron, J.F.; Hurtubise, R.J.; Silver, H.F.

1978-11-01

Empirical correlation factors were developed which relate log k' values for alkylphenols, the naphthols, and two phenylphenols to structural features. Both normal-phase and reversed-phase chromatographic systems were studied. The stationary phases employed in the normal-phase work were ..mu..-Bondapak CN, ..mu..-Bondapak NH/sub 2/, and ..mu..-Porasil. The structural features which affect retention in the normal-phase chromatographic systems are the number of ortho substituents, the number of aliphatic carbons, and the number of aromatic rings. The stationary phases employed in the reversed-phase work were ..mu..-Bondapak C/sub 18/ and ..mu..-Bondapak CN. The structural features which affect retention in the reversed-phase chromatographic systems are themore » number of aliphatic carbons and the number of aromatic double bonds. On ..mu..-Bondapak C/sub 18/, the presence or absence of a nonaromatic ring is of added importance.« less

Method for making a non-extractable stationary phase of polymer within a capillary column

DOEpatents

Springston, S.R.

1990-10-30

A method is described for coating interior capillary column surfaces, or packing material of a packed column, used for gas chromatography, with a stationary polymer phase that is cross-linked by exposing it to a low-temperature plasma that is uniformly distributed over the column or packing material for a predetermined period of time to effect the desired degree of cross-linking of the coating. 7 figs.

Two-phase vesicles: a study on evolutionary and stationary models.

PubMed

Sahebifard, MohammadMahdi; Shahidi, Alireza; Ziaei-Rad, Saeed

2017-05-01

In the current article, the dynamic evolution of two-phase vesicles is presented as an extension to a previous stationary model and based on an equilibrium of local forces. In the simplified model, ignoring the effects of membrane inertia, a dynamic equilibrium between the membrane bending potential and local fluid friction is considered in each phase. The equilibrium equations at the domain borders are completed by extended introduction of membrane section reactions. We show that in some cases, the results of stationary and evolutionary models are in agreement with each other and also with experimental observations, while in others the two models differ markedly. The value of our approach is that we can account for unresponsive points of uncertainty using our equations with the local velocity of the lipid membranes and calculating the intermediate states (shapes) in the consequent evolutionary, or response, path.

Classification of LC columns based on the QSRR method and selectivity toward moclobemide and its metabolites.

PubMed

Plenis, Alina; Olędzka, Ilona; Bączek, Tomasz

2013-05-05

This paper focuses on a comparative study of the column classification system based on the quantitative structure-retention relationships (QSRR method) and column performance in real biomedical analysis. The assay was carried out for the LC separation of moclobemide and its metabolites in human plasma, using a set of 24 stationary phases. The QSRR models established for the studied stationary phases were compared with the column test performance results under two chemometric techniques - the principal component analysis (PCA) and the hierarchical clustering analysis (HCA). The study confirmed that the stationary phase classes found closely related by the QSRR approach yielded comparable separation for moclobemide and its metabolites. Therefore, the QSRR method could be considered supportive in the selection of a suitable column for the biomedical analysis offering the selection of similar or dissimilar columns with a relatively higher certainty. Copyright © 2013 Elsevier B.V. All rights reserved.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Read, Douglas; Sillerud, Colin Halliday

The overarching goal of this project is to integrate Sandia's microfabricated gas-chromatography ( GC) columns with a stationary phase material that is capable of retaining high-volatility chemicals and permanent gases. The successful integration of such a material with GCs would dramatically expand the repertoire of detectable compounds for Sandia's various microanalysis systems. One such promising class of candidate materials is metal-organic frameworks (MOFs). In this report we detail our methods for controlled deposition of HKUST-1 MOF stationary phases within GC columns. We demonstrate: the chromatographic separation of natural gas; a method for determining MOF film thickness from chromatography alone; andmore » the first-reported GC x GC separation of natural gas -- in general -- let alone for two disparate MOF stationary phases. In addition we determine the fundamental thermodynamic constant for mass sorption, the partition coefficient, for HKUST-1 and several light hydrocarbons and select toxic industrial chemicals.« less

Green roofs'retention performances in different climates

NASA Astrophysics Data System (ADS)

Viola, Francesco; Hellies, Matteo; Deidda, Roberto

2017-04-01

The ongoing process of global urbanization contributes to increasing stormwater runoff from impervious surfaces, threatening also water quality. Green roofs have been proved to be an innovative stormwater management tool to partially restore natural state, enhancing interception, infiltration and evapotranspiration fluxes. The amount of water that is retained within green roofs depends mainly on both soil properties and climate. The evaluation of the retained water is not trivial since it depends on the stochastic soil moisture dynamics. The aim of this work is to explore performances of green roofs, in terms of water retention, as a function of their depth considering different climate regimes. The role of climate in driving water retention has been mainly represented by rainfall and potential evapotranspiration dynamics, which are simulated by a simple conceptual weather generator at daily time scale. The model is able to describe seasonal (in-phase and counter-phase) and stationary behaviors of climatic forcings. Model parameters have been estimated on more than 20,000 historical time series retrieved worldwide. Exemplifying cases are discussed for five different climate scenarios, changing the amplitude and/or the phase of daily mean rainfall and evapotranspiration forcings. The first scenario represents stationary climates, in two other cases the daily mean rainfall or the potential evapotranspiration evolve sinusoidally. In the latter two cases, we simulated the in-phase or in counter-phase conditions. Stochastic forcings have been then used as an input to a simple conceptual hydrological model which simulate soil moisture dynamics, evapotranspiration fluxes, runoff and leakage from soil pack at daily time scale. For several combinations of annual rainfall and potential evapotranspiration, the analysis allowed assessing green roofs' retaining capabilities, at annual time scale. Provided abacus allows a first approximation of possible hydrological benefits deriving from the implementation of intensive or extensive green roofs in different world areas, i.e. less input to sewer systems.

Description and Evaluation of Chiral Interactive Sites on Bonded Cyclodextrin Stationary Phases for Liquid Chromatography

NASA Astrophysics Data System (ADS)

Beesley, Thomas E.

Development of chiral separations has been essential to the drug discovery and development process. The solubility requirements for a number of methods and/or the mobile phase requirements for application of certain detection systems have opened up many opportunities for cyclodextrin-based CSPs for liquid chromatography. Even though a few chiral stationary phases cover a wide area of enantioselectivity, they do not meet the entire needs of the industry. Cyclodextrin phases offer some unique mechanisms and opportunities to resolve chiral separation problems especially in the aqueous reversed-phase and non-aqueous polar organic modes. This chapter addresses the need to understand the chiral stationary phase structure, the mechanisms at work, and the role mobile phase composition plays in driving those mechanisms to produce enantioselectivity. In addition, the development of certain derivatives has played an essential part in expanding that basic role for certain chiral separations. What these derivatives contribute in concert with the basic structure is a critical part of the understanding to the effective use of these phases. During this study it was determined that the role of steric hindrance has been vastly underestimated, both to the extent that it has occurred and to its effectiveness for obtaining enantioselectivity. References to the entire 20-year history of the cyclodextrin phase development and application literature up to this current date have been reviewed and incorporated.

The use of Whatman-31ET paper for an efficient method for radiochemical purity test of 131I-Hippuran

NASA Astrophysics Data System (ADS)

Rezka Putra, Amal; Maskur; Sugiharto, Yono; Chairuman; Hardi Gunawan, Adang; Awaludin, Rohadi

2018-01-01

Current chromatography methods used for radiochemical purity test of 131I-Hippuran is time consuming. Therefore, in this study we explored several static and mobile phases in order to have a chromatography method which is accurate and efficient or less time consuming. In this study, stationary phases (Whatman-1, 31ET, and 3MM papers) and several mobile phases were explored to separate 131I-Hippuran from its impurity (131I iodide ion). The results of this study showed that the most efficient chromatography system for measurement of radiochemical purity of 131I-Hippuran was by using Whatman-31ET paper and n-butanol: acetic acid: water (4:1:1) as a static phase and mobile phase respectively. Developing time for this method was of approximately 75.7 ± 2.7 minutes. The result of radiochemical purity (%RCP) of 131I-Hippuran measured with this chromatography system either using Whatman-1 or Whatman-31ET paper strips was 98.7%. The short size of Whatman-31ET paper strip (1 x 8 cm) was found to have shorter developing time compared to that of long size paper. This system showed a good separation of 131I-Hippuran from its impurities and gave %RCP of 98.1% ± 0.04% with developing time approximately 44.3 ± 9.4 minutes. The short size of Whatman-31ET paper strips was found to be more efficient compared to that of Whatman-1 and Whatman-3MM paper strips in term of developing time.

A new method for the radiochemical purity measurement of ¹¹¹In-pentetreotide.

PubMed

Salgado-Garcia, Carlos; Montoza-Aguado, Manuel; Luna-Alcaide, Ana B; Segovia-Gonzalez, Maria M; de Mora, Elena Sanchez; Lopez-Martin, Juana; Ramos-Font, Carlos; Jimenez-Heffernan, Amelia

2011-12-01

The recommended method for the measurement of radiochemical purity (RCP) of ¹¹¹In-labelled pentetreotide is thin-layer chromatography with a silica gel as the stationary phase and a 0.1 N sodium citrate solution (pH 5) as the mobile phase. According to the supplier's instructions, the mobile phase must be prepared before the test is carried out, and the recommended stationary phase is off-market. We propose a new method for RCP measurement in which the mobile phase is acid citrate dextrose, solution A, which does not need to be prepared beforehand, and thin-layer chromatography is performed with a silica gel-impregnated glass fibre sheet as the stationary phase. We used both methods to measure the percentages of radiopharmaceutical and impurities. The range of RCP values obtained was 98.0-99.9% (mean=99.3%) by the standard method and 98.1-99.9% (mean=99.2%) by the new method. We observed no differences between the RCP values of both methods (P=0.070). The proposed method is suitable for RCP testing because it yields results that are in good agreement with those of the standard method and because it is easier to perform as the mobile-phase solution need not be prepared in advance.

Numerical Study of Nonlinear Structures of Locally Excited Marangoni Convection in the Long-Wave Approximation

NASA Astrophysics Data System (ADS)

Wertgeim, Igor I.

2018-02-01

We investigate stationary and non-stationary solutions of nonlinear equations of the long-wave approximation for the Marangoni convection caused by a localized source of heat or a surface active impurity (surfactant) in a thin horizontal layer of a viscous incompressible fluid with a free surface. The distribution of heat or concentration flux is determined by the uniform vertical gradient of temperature or impurity concentration, distorted by the imposition of a slightly inhomogeneous heating or of surfactant, localized in the horizontal plane. The lower boundary of the layer is considered thermally insulated or impermeable, whereas the upper boundary is free and deformable. The equations obtained in the long-wave approximation are formulated in terms of the amplitudes of the temperature distribution or impurity concentration, deformation of the surface, and vorticity. For a simplification of the problem, a sequence of nonlinear equations is obtained, which in the simplest form leads to a nonlinear Schrödinger equation with a localized potential. The basic state of the system, its dependence on the parameters and stability are investigated. For stationary solutions localized in the region of the surface tension inhomogeneity, domains of parameters corresponding to different spatial patterns are delineated.

Stability of Bifurcating Stationary Solutions of the Artificial Compressible System

NASA Astrophysics Data System (ADS)

Teramoto, Yuka

2018-02-01

The artificial compressible system gives a compressible approximation of the incompressible Navier-Stokes system. The latter system is obtained from the former one in the zero limit of the artificial Mach number ɛ which is a singular limit. The sets of stationary solutions of both systems coincide with each other. It is known that if a stationary solution of the incompressible system is asymptotically stable and the velocity field of the stationary solution satisfies an energy-type stability criterion, then it is also stable as a solution of the artificial compressible one for sufficiently small ɛ . In general, the range of ɛ shrinks when the spectrum of the linearized operator for the incompressible system approaches to the imaginary axis. This can happen when a stationary bifurcation occurs. It is proved that when a stationary bifurcation from a simple eigenvalue occurs, the range of ɛ can be taken uniformly near the bifurcation point to conclude the stability of the bifurcating solution as a solution of the artificial compressible system.

Reversed phase liquid chromatography with UV absorbance and flame ionization detection using a water mobile phase and a cyano propyl stationary phase Analysis of alcohols and chlorinated hydrocarbons.

PubMed

Quigley, W W; Ecker, S T; Vahey, P G; Synovec, R E

1999-10-01

The development of liquid chromatography with a commercially available cyano propyl stationary phase and a 100% water mobile phase is reported. Separations were performed at ambient temperature, simplifying instrumental requirements. Excellent separation efficiency using a water mobile phase was achieved, for example N=18 800, or 75 200 m(-1), was obtained for resorcinol, at a retention factor of k'=4.88 (retention time of 9.55 min at 1 ml min(-1) for a 25 cmx4.6 mm i.d. column, packed with 5 mum diameter particles with the cyano propyl stationary phase). A separation via reversed phase liquid chromatography (RP-LC) with a 100% water mobile phase of six phenols and related compounds was compared to a separation of the same compounds by traditional RP-LC, using octadecylsilane (ODS), i.e. C18, bound to silica and an aqueous mobile phase modified with acetonitrile. Nearly identical analysis time was achieved for the separation of six phenols and related compounds using the cyano propyl stationary phase with a 100% water mobile phase, as compared to traditional RP-LC requiring a relatively large fraction of organic solvent modifier in the mobile phase (25% acetonitrile:75% water). Additional understanding of the retention mechanism with the 100% water mobile phase was obtained by relating measured retention factors of aliphatic alcohols, phenols and related compounds, and chlorinated hydrocarbons to their octanol:water partition coefficients. The retention mechanism is found to be consistent with a RP-LC mechanism coupled with an additional retention effect due to residual hydroxyl groups on the cyano propyl stationary phase. Advantages due to a 100% water mobile phase for the chemical analysis of alcohol mixtures and chlorinated hydrocarbons are reported. By placing an absorbance detector in-series and preceding a novel drop interface to a flame ionization detector (FID), selective detection of a separated mixture of phenols and related compounds and aliphatic alcohols is achieved. The compound class of aliphatic alcohols is selectively and sensitively detected by the drop interface/FID, and the phenols and related compounds are selectively and sensitively detected by absorbance detection at 200 nm. The separation and detection of chlorinated hydrocarbons in a water sample matrix further illustrated the advantages of this methodology. The sensitivity and selectivity of the FID signal for the chlorinated hydrocarbons are significantly better than absorbance detection, even at 200 nm. This methodology is well suited to continuous and automated monitoring of water samples. The applicability of samples initially in an organic solvent matrix is explored, since an organic sample matrix may effect retention and efficiency. Separations in acetonitrile and isopropyl alcohol sample matrices compared well to separations with a water sample matrix.

Chromatographic evaluation of self-immobilized stationary phases for reversed-phase liquid chromatography.

PubMed

Bottoli, Carla B G; Collins, Kenneth E; Collins, Carol H

2003-02-14

The preparation of stationary phases for HPLC using polymers deposited on silica usually includes an immobilization step involving cross-linking by free radicals induced by ionizing radiation or by other radical initiators. The present paper reports changes which occur at ambient temperature in the character of poly(methyloctylsiloxane) deposited on porous silica particles as a function of the time interval between particle loading and column packing. Column performance and retention factors increase with time and these changes are attributed to rearrangement (self-assembly) which result in "self-immobilization" of the polymer molecules on the silica surface.

Proteomics Analysis of Lactobacillus casei Zhang, a New Probiotic Bacterium Isolated from Traditional Home-made Koumiss in Inner Mongolia of China*

PubMed Central

Wu, Rina; Wang, Weiwei; Yu, Dongliang; Zhang, Wenyi; Li, Yan; Sun, Zhihong; Wu, Junrui; Meng, He; Zhang, Heping

2009-01-01

Lactobacillus casei Zhang, isolated from traditional home-made koumiss in Inner Mongolia of China, was considered as a new probiotic bacterium by probiotic selection tests. We carried out a proteomics study to identify and characterize proteins expressed by L. casei Zhang in the exponential phase and stationary phase. Cytosolic proteins of the strain cultivated in de Man, Rogosa, and Sharpe broth were resolved by two-dimensional gel electrophoresis using pH 4–7 linear gradients. The number of protein spots quantified from the gels was 487 ± 21 (exponential phase) and 494 ± 13 (stationary phase) among which a total of 131 spots were identified by MALDI-TOF/MS and/or MALDI-TOF/TOF according to significant growth phase-related differences or high expression intensity proteins. Accompanied by the cluster of orthologous groups (COG), codon adaptation index (CAI), and GRAVY value analysis, the study provided a very first insight into the profile of protein expression as a reference map of L. casei. Forty-seven spots were also found in the study that showed statistically significant differences between exponential phase and stationary phase. Thirty-three of the spots increased at least 2.5-fold in the stationary phase in comparison with the exponential phase, including 19 protein spots (e.g. Hsp20, DnaK, GroEL, LuxS, pyruvate kinase, and GalU) whose intensity up-shifted above 3.0-fold. Transcriptional profiles were conducted to confirm several important differentially expressed proteins by using real time quantitative PCR. The analysis suggests that the differentially expressed proteins were mainly categorized as stress response proteins and key components of central and intermediary metabolism, indicating that these proteins might play a potential important role for the adaptation to the surroundings, especially the accumulation of lactic acid in the course of growth, and the physiological processes in bacteria cell. PMID:19508964

Growth Substrate- and Phase-Specific Expression of Biphenyl, Benzoate, and C1 Metabolic Pathways in Burkholderia xenovorans LB400

PubMed Central

Denef, V. J.; Patrauchan, M. A.; Florizone, C.; Park, J.; Tsoi, T. V.; Verstraete, W.; Tiedje, J. M.; Eltis, L. D.

2005-01-01

Recent microarray experiments suggested that Burkholderia xenovorans LB400, a potent polychlorinated biphenyl (PCB)-degrading bacterium, utilizes up to three apparently redundant benzoate pathways and a C1 metabolic pathway during biphenyl and benzoate metabolism. To better characterize the roles of these pathways, we performed quantitative proteome profiling of cells grown on succinate, benzoate, or biphenyl and harvested during either mid-logarithmic growth or the transition between the logarithmic and stationary growth phases. The Bph enzymes, catabolizing biphenyl, were ∼16-fold more abundant in biphenyl- versus succinate-grown cells. Moreover, the upper and lower bph pathways were independently regulated. Expression of each benzoate pathway depended on growth substrate and phase. Proteins specifying catabolism via benzoate dihydroxylation and catechol ortho-cleavage (ben-cat pathway) were approximately an order of magnitude more abundant in benzoate- versus biphenyl-grown cells at the same growth phase. The chromosomal copy of the benzoyl-coenzyme A (CoA) (boxC) pathway was also expressed during growth on biphenyl: BoxC proteins were approximately twice as abundant as Ben and Cat proteins under these conditions. By contrast, proteins of the megaplasmid copy of the benzoyl-CoA (boxM) pathway were only detected in transition-phase benzoate-grown cells. Other proteins detected at increased levels in benzoate- and biphenyl-grown cells included general stress response proteins potentially induced by reactive oxygen species formed during aerobic aromatic catabolism. Finally, C1 metabolic enzymes were present in biphenyl-grown cells during transition phase. This study provides insights into the physiological roles and integration of apparently redundant catabolic pathways in large-genome bacteria and establishes a basis for investigating the PCB-degrading abilities of this strain. PMID:16291673

Enantioseparations by capillary electrochromatography.

PubMed

Fanali, S; Catarcini, P; Blaschke, G; Chankvetadze, B

2001-09-01

The review summarizes recent developments in enantioseparations by capillary electrochromatography (CEC). Selected fundamental aspects of CEC are discussed in order to stress those features which may allow the success of this technique in the competitive field of enantioseparations. In addition, the comparative characteristics of the different modes of chiral CEC and the stationary phases are presented. The effects of the characteristics of the stationary and liquid phases and operational conditions on the separation results are discussed. Finally, some future trends are briefly addressed.

Freeze drying for gas chromatography stationary phase deposition

DOEpatents

Sylwester, Alan P [Livermore, CA

2007-01-02

The present disclosure relates to methods for deposition of gas chromatography (GC) stationary phases into chromatography columns, for example gas chromatography columns. A chromatographic medium is dissolved or suspended in a solvent to form a composition. The composition may be inserted into a chromatographic column. Alternatively, portions of the chromatographic column may be exposed or filled with the composition. The composition is permitted to solidify, and at least a portion of the solvent is removed by vacuum sublimation.

Cellular Metabolic Activity and the Oxygen and Hydrogen Stable Isotope Composition of Intracellular Water and Metabolites

NASA Astrophysics Data System (ADS)

Kreuzer-Martin, H. W.; Hegg, E. L.

2008-12-01

Intracellular water is an important pool of oxygen and hydrogen atoms for biosynthesis. Intracellular water is usually assumed to be isotopically identical to extracellular water, but an unexpected experimental result caused us to question this assumption. Heme O isolated from Escherichia coli cells grown in 95% H218O contained only a fraction of the theoretical value of labeled oxygen at a position where the O atom was known to be derived from water. In fact, fewer than half of the oxygen atoms were labeled. In an effort to explain this surprising result, we developed a method to determine the isotope ratios of intracellular water in cultured cells. The results of our experiments showed that during active growth, up to 70% of the oxygen atoms and 50% of the hydrogen atoms in the intracellular water of E. coli are generated during metabolism and can be isotopically distinct from extracellular water. The fraction of isotopically distinct atoms was substantially less in stationary phase and chilled cells, consistent with our hypothesis that less metabolically-generated water would be present in cells with lower metabolic activity. Our results were consistent with and explained the result of the heme O labeling experiment. Only about 40% of the O atoms on the heme O molecule were labeled because, presumably, only about 40% of the water inside the cells was 18O water that had diffused in from the culture medium. The rest of the intracellular water contained 16O atoms derived from either nutrients or atmospheric oxygen. To test whether we could also detect metabolically-derived hydrogen atoms in cellular constituents, we isolated fatty acids from log-phase and stationary phase E. coli and determined the H isotope ratios of individual fatty acids. The results of these experiments showed that environmental water contributed more H atoms to fatty acids isolated in stationary phase than to the same fatty acids isolated from log-phase cells. Stable isotope analyses of biomass of Bacillus subtilis, a Gram-positive bacterium, showed the same pattern. Rapidly-dividing cells derived fewer of their O and H atoms from environmental water than did more slowly-growing cells and spores. To test whether a eukaryotic cell, surrounded by only a membrane, would also maintain an isotopic gradient and a detectable percentage of metabolic water, we applied our approach to cultured rat fibroblasts. Preliminary results showed that approximately 50% of the O and H atoms in exponentially growing cells were derived from metabolic activity. In quiescent cells, metabolic activity generated approximately 25% of the O and H atoms in intracellular water. Thus far, the data we have obtained is consistent with the following model: (1) Intracellular water is composed of water that diffuses in from the extracellular environment and water that is created as a result of metabolic activity. (2) The relative amounts of environmental and metabolic water inside a cell are a function of the cell's metabolic activity. (3) The oxygen and hydrogen isotope ratios of cellular metabolites are a function of those of intracellular water, and therefore reflect the metabolic activity of the cell at the time of biosynthesis.

Penetrable silica microspheres for immobilization of bovine serum albumin and their application to the study of the interaction between imatinib mesylate and protein by frontal affinity chromatography.

PubMed

Ma, Liyun; Li, Jing; Zhao, Juan; Liao, Han; Xu, Li; Shi, Zhi-guo

2016-01-01

In the current study, novel featured silica, named penetrable silica, simultaneously containing macropores and mesopores, was immobilized with bovine serum albumin (BSA) via Schiff base method. The obtained BSA-SiO2 was employed as the high-performance liquid chromatographic (HPLC) stationary phase. Firstly, D- and L-tryptophan were used as probes to investigate the chiral separation ability of the BSA-SiO2 stationary phase. An excellent enantioseparation factor was obtained up to 4.3 with acceptable stability within at least 1 month. Next, the BSA-SiO2 stationary phase was applied to study the interaction between imatinib mesylate (IM) and BSA by frontal affinity chromatography. A single type of binding site was found for IM with the immobilized BSA, and the hydrogen-bonding and van der Waals interactions were expected to be contributing interactions based on the thermodynamic studies, and this was a spontaneous process. Compared to the traditional silica for HPLC stationary phase, the proposed penetrable silica microsphere possessed a larger capacity to bond more BSA, minimizing column overloading effects and enhancing enantioseparation ability. In addition, the lower running column back pressure and fast mass transfer were meaningful for the column stability and lifetime. It was a good substrate to immobilize biomolecules for fast chiral resolution and screening drug-protein interactions.

Preferential Ty1 retromobility in mother cells and nonquiescent stationary phase cells is associated with increased concentrations of total Gag or processed Gag and is inhibited by exposure to a high concentration of calcium.

PubMed

Peifer, Andrew C; Maxwell, Patrick H

2018-03-21

Retrotransposons are abundant mobile DNA elements in eukaryotic genomes that are more active with age in diverse species. Details of the regulation and consequences of retrotransposon activity during aging remain to be determined. Ty1 retromobility in Saccharomyces cerevisiae is more frequent in mother cells compared to daughter cells, and we found that Ty1 was more mobile in nonquiescent compared to quiescent subpopulations of stationary phase cells. This retromobility asymmetry was absent in mutant strains lacking BRP1 that have reduced expression of the essential Pma1p plasma membrane proton pump, lacking the mRNA decay gene LSM1 , and in cells exposed to a high concentration of calcium. Mother cells had higher levels of Ty1 Gag protein than daughters. The proportion of protease-processed Gag decreased as cells transitioned to stationary phase, processed Gag was the dominant form in nonquiescent cells, but was virtually absent from quiescent cells. Treatment with calcium reduced total Gag levels and the proportion of processed Gag, particularly in mother cells. We also found that Ty1 reduced the fitness of proliferating but not stationary phase cells. These findings may be relevant to understanding regulation and consequences of retrotransposons during aging in other organisms, due to conserved impacts and regulation of retrotransposons.

Preferential Ty1 retromobility in mother cells and nonquiescent stationary phase cells is associated with increased concentrations of total Gag or processed Gag and is inhibited by exposure to a high concentration of calcium

PubMed Central

Peifer, Andrew C.

2018-01-01

Retrotransposons are abundant mobile DNA elements in eukaryotic genomes that are more active with age in diverse species. Details of the regulation and consequences of retrotransposon activity during aging remain to be determined. Ty1 retromobility in Saccharomyces cerevisiae is more frequent in mother cells compared to daughter cells, and we found that Ty1 was more mobile in nonquiescent compared to quiescent subpopulations of stationary phase cells. This retromobility asymmetry was absent in mutant strains lacking BRP1 that have reduced expression of the essential Pma1p plasma membrane proton pump, lacking the mRNA decay gene LSM1, and in cells exposed to a high concentration of calcium. Mother cells had higher levels of Ty1 Gag protein than daughters. The proportion of protease-processed Gag decreased as cells transitioned to stationary phase, processed Gag was the dominant form in nonquiescent cells, but was virtually absent from quiescent cells. Treatment with calcium reduced total Gag levels and the proportion of processed Gag, particularly in mother cells. We also found that Ty1 reduced the fitness of proliferating but not stationary phase cells. These findings may be relevant to understanding regulation and consequences of retrotransposons during aging in other organisms, due to conserved impacts and regulation of retrotransposons. PMID:29562219

Normal and polar-organic-phase high-performance liquid chromatographic enantioresolution of omeprazole, rabeprazole, lansoprazole and pantoprazole using monochloro-methylated cellulose-based chiral stationary phase and determination of dexrabeprazole.

PubMed

Dixit, Shuchi; Dubey, Rituraj; Bhushan, Ravi

2014-01-01

Enantioresolution of four anti-ulcer drugs (chiral sulfoxides), namely, omeprazole, rabeprazole, lansoprazole and pantoprazole, was carried out by high-performance liquid chromatography using a polysaccharide-based chiral stationary phase consisting of monochloromethylated cellulose (Lux cellulose-2) under normal and polar-organic-phase conditions with ultraviolet detection at 285 nm. The method was validated for linearity, accuracy, precision, robustness and limit of detection. The optimized enantioresolution method was compared for both the elution modes. The optimized method was further utilized to check the enantiomeric purity of dexrabeprazole. Copyright © 2013 John Wiley & Sons, Ltd.

Nano-particle modified stationary phases for high-performance liquid chromatography.

PubMed

Nesterenko, Ekaterina P; Nesterenko, Pavel N; Connolly, Damian; He, Xiaoyun; Floris, Patrick; Duffy, Emer; Paull, Brett

2013-08-07

This review covers the latest developments and applications of nano-materials in stationary phase development for various modes of high-performance liquid chromatography. Specific attention is placed upon the development of new composite phases, including the synthetic and immobilisation strategies used, to produce either encapsulated nano-particles, or surface attached nano-particles, layers, coatings and other structures. The resultant chromatographic applications, where applicable, are discussed with comment upon enhanced selectivity and/or efficiency of the nano-particle modified phases, where such effects have been identified. In the main this review covers developments over the past five years and is structured according to the nature of the nano-particles themselves, including carbonaceous, metallic, inorganic, and organopolymer based materials.

Linear Reconstruction of Non-Stationary Image Ensembles Incorporating Blur and Noise Models

DTIC Science & Technology

1998-03-01

for phase distortions due to noise which leads to less deblurring as noise increases [41]. In contrast, the vector Wiener filter incorporates some a...AFIT/DS/ENG/98- 06 Linear Reconstruction of Non-Stationary Image Ensembles Incorporating Blur and Noise Models DISSERTATION Stephen D. Ford Captain...Dissertation 4. TITLE AND SUBTITLE 5. FUNDING NUMBERS LINEAR RECONSTRUCTION OF NON-STATIONARY IMAGE ENSEMBLES INCORPORATING BLUR AND NOISE MODELS 6. AUTHOR(S

Stationary plasma thruster evaluation in Russia

NASA Technical Reports Server (NTRS)

Brophy, John R.

1992-01-01

A team of electric propulsion specialists from U.S. government laboratories experimentally evaluated the performance of a 1.35-kW Stationary Plasma Thruster (SPT) at the Scientific Research Institute of Thermal Processes in Moscow and at 'Fakel' Enterprise in Kaliningrad, Russia. The evaluation was performed using a combination of U.S. and Russian instrumentation and indicated that the actual performance of the thruster appears to be close to the claimed performance. The claimed performance was a specific impulse of 16,000 m/s, an overall efficiency of 50 percent, and an input power of 1.35 kW, and is superior to the performance of western electric thrusters at this specific impulse. The unique performance capabilities of the stationary plasma thruster, along with claims that more than fifty of the 660-W thrusters have been flown in space on Russian spacecraft, attracted the interest of western spacecraft propulsion specialists. A two-phase program was initiated to evaluate the stationary plasma thruster performance and technology. The first phase of this program, to experimentally evaluate the performance of the thruster with U.S. instrumentation in Russia, is described in this report. The second phase objective is to determine the suitability of the stationary plasma thruster technology for use on western spacecraft. This will be accomplished by bringing stationary plasma thrusters to the U.S. for quantification of thruster erosion rates, measurements of the performance variation as a function of long-duration operation, quantification of the exhaust beam divergence angle, and determination of the non-propellant efflux from the thruster. These issues require quantification in order to maximize the probability for user application of the SPT technology and significantly increase the propulsion capabilities of U.S. spacecraft.

New stationary phase for hydrophilic interaction chromatography to separate chito-oligosaccharides with degree of polymerization 2-6.

PubMed

Zhai, Xingchen; Zhao, Haitian; Zhang, Min; Yang, Xin; Sun, Jingming; She, Yongxin; Dong, Aijun; Zhang, Hua; Yao, Lei; Wang, Jing

2018-04-01

A new 3‑aminophenylboronic acid-functionalized stationary phase based on silica for hydrophilic interaction liquid chromatography (HILIC) was developed and showed great HILIC characteristics on separation for chito‑oligosaccharides. The material was synthesized by grafting 3‑aminophenylboronic acid group to silica, and it was characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), elemental analysis and thermal gravimetric analysis (TGA). Nucleobases and nucleosides were used to evaluate the retention property and to investigate retention mechanism by the models designed for description of partitioning and surface adsorption through adjusting ratio of water in the mobile phase. Parameters affecting chromatography behavior such as ionic strength, buffer pH and column temperature were also investigated. Results have indicated that the retention mechanism was a combination of partitioning and surface adsorption, and the hydrogen bond seemed to be the main force for the retention behavior. Finally, the new 3‑aminophenylboronic acid-functionalized based on silica stationary phase was applied to separate chito-oligosaccharide samples with optimized mobile phase conditions and showed acceptable chromatograms. Copyright © 2018 Elsevier B.V. All rights reserved.

Optimising reversed-phase liquid chromatographic separation of an acidic mixture on a monolithic stationary phase with the aid of response surface methodology and experimental design.

PubMed

Wang, Y; Harrison, M; Clark, B J

2006-02-10

An optimization strategy for the separation of an acidic mixture by employing a monolithic stationary phase is presented, with the aid of experimental design and response surface methodology (RSM). An orthogonal array design (OAD) OA(16) (2(15)) was used to choose the significant parameters for the optimization. The significant factors were optimized by using a central composite design (CCD) and the quadratic models between the dependent and the independent parameters were built. The mathematical models were tested on a number of simulated data set and had a coefficient of R(2) > 0.97 (n = 16). On applying the optimization strategy, the factor effects were visualized as three-dimensional (3D) response surfaces and contour plots. The optimal condition was achieved in less than 40 min by using the monolithic packing with the mobile phase of methanol/20 mM phosphate buffer pH 2.7 (25.5/74.5, v/v). The method showed good agreement between the experimental data and predictive value throughout the studied parameter space and were suitable for optimization studies on the monolithic stationary phase for acidic compounds.

Thin-layer chromatography with stationary phase gradient as a method for separation of water-soluble vitamins.

PubMed

Cimpoiu, Claudia; Hosu, Anamaria; Puscas, Anitta

2012-02-03

The group of hydrophilic vitamins play an important role in human health, and their lack or excess produces specific diseases. Therefore, the analysis of these compounds is indispensable for monitoring their content in pharmaceuticals and food in order to prevent some human diseases. TLC was successfully applied in the analysis of hydrophilic vitamins, but the most difficult problem in the simultaneous analysis of all these compounds is to find an optimum stationary phase-mobile phase system due to different chemical characteristics of analytes. Unfortunately structural analogues are difficult to separate in one chromatographic run, and this is the case in hydrophilic vitamins investigations. TLC gives the possibility to perform two-dimensional separations by using stationary phase gradient achieving the highest resolution by combining two systems with different selectivity. The goal of this work was to develop a method of analysis enabling separation of hydrophilic vitamins using TLC with adsorbent gradient. The developed method was used for identifying the water-soluble vitamins in alcoholic extracts of Hippophae rhamnoides and of Ribes nigrum. Copyright © 2011 Elsevier B.V. All rights reserved.

Liquid chromatographic separation and thermodynamic investigation of lorcaserin hydrochloride enantiomers on immobilized amylose-based chiral stationary phase.

PubMed

Wani, Dattatraya V; Rane, Vipul P; Mokale, Santosh N

2018-03-01

A novel liquid chromatographic method was developed for enantiomeric separation of lorcaserin hydrochloride on Chiralpak IA column containing chiral stationary phase immobilized with amylose tris (3.5-dimethylphenylcarbamate) as chiral selector. Baseline separation with resolution greater than 4 was achieved using mobile phase containing mixture of n-hexane/ethanol/methanol/diethylamine (95:2.5:2.5:0.1, v/v/v/v) at a flow rate of 1.2 mL/min. The limit of detection and limit of quantification of the S-enantiomer were found to be 0.45 and 1.5 μg/mL, respectively; the developed method was validated as per ICH guideline. The influence of column oven temperatures studied in the range of 20°C to 50°C on separation was studied; from this, retention, separation, and resolution were investigated. The thermodynamic parameters ΔH°, ΔS°, and ΔG° were evaluated from van't Hoff plots,(Ink' versus 1/T) and used to explain the strength of interaction between enantiomers and immobilized amylose-based chiral stationary phase. © 2017 Wiley Periodicals, Inc.

Protein synthesis and the recovery of both survival and cytoplasmic "petite" mutation in ultraviolet-treated yeast cells. II. Mitochondrial protein synthesis.

PubMed

Heude, M; Chanet, R

1975-04-01

The contribution of mitochondrial proteins in the repair of UV-induced lethal and cytoplasmic genetic damages was studied in dark liquid held exponential and stationary phase yeast cells. This was performed by using the specific inhibitors, erythromycin (ER) anc chloramphenicol (CAP). It was shown that mitochondrial proteins are involved in the recovery of stationary phase cells. Mitochondrial proteins are partly implicated in the mechanisms leading to the restoration of the (see article) genotype in UV-irradiated dark liquid held exponential phase cells. Here again, in stationary phase cells, mitochondrial enzymes do not seem to participate in the negative liquid holding (NLH) process for the (see article) induction, as shown by inhibiting mitochondrial protein synthesis or both mitochondrial and nuclear protein synthesis. When cells are grown in glycerol, the response after dark liquid holding of UV-treated cells in the different growth stages are similar to that found for glucose-grown cells. In other words, the fate of cytoplasmic genetic damage, in particular, is not correlated with the repressed or derepressed state of the mitochondria.

Deteriorated Stress Response in Stationary-Phase Yeast: Sir2 and Yap1 Are Essential for Hsf1 Activation by Heat Shock and Oxidative Stress, Respectively

PubMed Central

Cohen, Aviv; Bar-Nun, Shoshana

2014-01-01

Stationary-phase cultures have been used as an important model of aging, a complex process involving multiple pathways and signaling networks. However, the molecular processes underlying stress response of non-dividing cells are poorly understood, although deteriorated stress response is one of the hallmarks of aging. The budding yeast Saccharomyces cerevisiae is a valuable model organism to study the genetics of aging, because yeast ages within days and are amenable to genetic manipulations. As a unicellular organism, yeast has evolved robust systems to respond to environmental challenges. This response is orchestrated largely by the conserved transcription factor Hsf1, which in S. cerevisiae regulates expression of multiple genes in response to diverse stresses. Here we demonstrate that Hsf1 response to heat shock and oxidative stress deteriorates during yeast transition from exponential growth to stationary-phase, whereas Hsf1 activation by glucose starvation is maintained. Overexpressing Hsf1 does not significantly improve heat shock response, indicating that Hsf1 dwindling is not the major cause for Hsf1 attenuated response in stationary-phase yeast. Rather, factors that participate in Hsf1 activation appear to be compromised. We uncover two factors, Yap1 and Sir2, which discretely function in Hsf1 activation by oxidative stress and heat shock. In Δyap1 mutant, Hsf1 does not respond to oxidative stress, while in Δsir2 mutant, Hsf1 does not respond to heat shock. Moreover, excess Sir2 mimics the heat shock response. This role of the NAD+-dependent Sir2 is supported by our finding that supplementing NAD+ precursors improves Hsf1 heat shock response in stationary-phase yeast, especially when combined with expression of excess Sir2. Finally, the combination of excess Hsf1, excess Sir2 and NAD+ precursors rejuvenates the heat shock response. PMID:25356557

Deteriorated stress response in stationary-phase yeast: Sir2 and Yap1 are essential for Hsf1 activation by heat shock and oxidative stress, respectively.

PubMed

Nussbaum, Inbal; Weindling, Esther; Jubran, Ritta; Cohen, Aviv; Bar-Nun, Shoshana

2014-01-01

Stationary-phase cultures have been used as an important model of aging, a complex process involving multiple pathways and signaling networks. However, the molecular processes underlying stress response of non-dividing cells are poorly understood, although deteriorated stress response is one of the hallmarks of aging. The budding yeast Saccharomyces cerevisiae is a valuable model organism to study the genetics of aging, because yeast ages within days and are amenable to genetic manipulations. As a unicellular organism, yeast has evolved robust systems to respond to environmental challenges. This response is orchestrated largely by the conserved transcription factor Hsf1, which in S. cerevisiae regulates expression of multiple genes in response to diverse stresses. Here we demonstrate that Hsf1 response to heat shock and oxidative stress deteriorates during yeast transition from exponential growth to stationary-phase, whereas Hsf1 activation by glucose starvation is maintained. Overexpressing Hsf1 does not significantly improve heat shock response, indicating that Hsf1 dwindling is not the major cause for Hsf1 attenuated response in stationary-phase yeast. Rather, factors that participate in Hsf1 activation appear to be compromised. We uncover two factors, Yap1 and Sir2, which discretely function in Hsf1 activation by oxidative stress and heat shock. In Δyap1 mutant, Hsf1 does not respond to oxidative stress, while in Δsir2 mutant, Hsf1 does not respond to heat shock. Moreover, excess Sir2 mimics the heat shock response. This role of the NAD+-dependent Sir2 is supported by our finding that supplementing NAD+ precursors improves Hsf1 heat shock response in stationary-phase yeast, especially when combined with expression of excess Sir2. Finally, the combination of excess Hsf1, excess Sir2 and NAD+ precursors rejuvenates the heat shock response.

Physiological Response of Crocosphaera watsonii to Enhanced and Fluctuating Carbon Dioxide Conditions

PubMed Central

Gradoville, Mary R.; White, Angelicque E.; Letelier, Ricardo M.

2014-01-01

We investigated the effects of elevated pCO2 on cultures of the unicellular N2-fixing cyanobacterium Crocosphaera watsonii WH8501. Using CO2-enriched air, cultures grown in batch mode under high light intensity were exposed to initial conditions approximating current atmospheric CO2 concentrations (∼400 ppm) as well as CO2 levels corresponding to low- and high-end predictions for the year 2100 (∼750 and 1000 ppm). Following acclimation to CO2 levels, the concentrations of particulate carbon (PC), particulate nitrogen (PN), and cells were measured over the diurnal cycle for a six-day period spanning exponential and early stationary growth phases. High rates of photosynthesis and respiration resulted in biologically induced pCO2 fluctuations in all treatments. Despite this observed pCO2 variability, and consistent with previous experiments conducted under stable pCO2 conditions, we observed that elevated mean pCO2 enhanced rates of PC production, PN production, and growth. During exponential growth phase, rates of PC and PN production increased by ∼1.2- and ∼1.5-fold in the mid- and high-CO2 treatments, respectively, when compared to the low-CO2 treatment. Elevated pCO2 also enhanced PC and PN production rates during early stationary growth phase. In all treatments, PC and PN cellular content displayed a strong diurnal rhythm, with particulate C:N molar ratios reaching a high of 22∶1 in the light and a low of 5.5∶1 in the dark. The pCO2 enhancement of metabolic rates persisted despite pCO2 variability, suggesting a consistent positive response of Crocosphaera to elevated and fluctuating pCO2 conditions. PMID:25343645

Imaging of Lipids in Microalgae with Coherent Anti-Stokes Raman Scattering Microscopy1[OPEN

PubMed Central

Cavonius, Lillie; Fink, Helen; Kiskis, Juris; Albers, Eva; Undeland, Ingrid; Enejder, Annika

2015-01-01

Microalgae have great prospects as a sustainable resource of lipids for refinement into nutraceuticals and biodiesel, which increases the need for detailed insights into their intracellular lipid synthesis/storage mechanisms. As an alternative strategy to solvent- and label-based lipid quantification techniques, we introduce time-gated coherent anti-Stokes Raman scattering (CARS) microscopy for monitoring lipid contents in living algae, despite strong autofluorescence from the chloroplasts, at approximately picogram and subcellular levels by probing inherent molecular vibrations. Intracellular lipid droplet synthesis was followed in Phaeodactylum tricornutum algae grown under (1) light/nutrient-replete (control [Ctrl]), (2) light-limited (LL), and (3) nitrogen-starved (NS) conditions. Good correlation (r2 = 0.924) was found between lipid volume data yielded by CARS microscopy and total fatty acid content obtained from gas chromatography-mass spectrometry analysis. In Ctrl and LL cells, micron-sized lipid droplets were found to increase in number throughout the growth phases, particularly in the stationary phase. During more excessive lipid accumulation, as observed in NS cells, promising commercial harvest as biofuels and nutritional lipids, several micron-sized droplets were present already initially during cultivation, which then fused into a single giant droplet toward stationary phase alongside with new droplets emerging. CARS microspectroscopy further indicated lower lipid fluidity in NS cells than in Ctrl and LL cells, potentially due to higher fatty acid saturation. This agreed with the fatty acid profiles gathered by gas chromatography-mass spectrometry. CARS microscopy could thus provide quantitative and semiqualitative data at the single-cell level along with important insights into lipid-accumulating mechanisms, here revealing two different modes for normal and excessive lipid accumulation. PMID:25583924

Production, secretion, and stability of human secreted alkaline phosphatase in tobacco NT1 cell suspension cultures.

PubMed

Becerra-Arteaga, Alejandro; Mason, Hugh S; Shuler, Michael L

2006-01-01

Tobacco NT1 cell suspension cultures secreting active human secreted alkaline phosphatase (SEAP) were generated for the first time as a model system to study recombinant protein production, secretion, and stability in plant cell cultures. The SEAP gene encodes a secreted form of the human placental alkaline phosphatase (PLAP). During batch culture, the highest level of active SEAP in the culture medium (0.4 U/mL, corresponding to approximately 27 mg/L) was observed at the end of the exponential growth phase. Although the level of active SEAP decreased during the stationary phase, the activity loss did not appear to be due to SEAP degradation (based on Western blots) but due to SEAP denaturation. The protein-stabilizing agents polyvinylpirrolidone (PVP) and bacitracin were added extracellularly to test for their ability to reduce the loss of SEAP activity during the stationary phase. Bacitracin (100 mg/L) was the most effective treatment at sustaining activity levels for up to 17 days post-subculture. Commercially available human placental alkaline phosphatase (PLAP) was used to probe the mechanism of SEAP deactivation. Experiments with PLAP in sterile and conditioned medium corroborated the denaturation of SEAP by factors generated by cell growth and not due to simple proteolysis. We also show for the first time that the factors promoting activity loss are heat labile at 95 degrees C but not at 70 degrees C, and they are not inactivated after a 5 day incubation period under normal culture conditions (27 degrees C). In addition, there were no significant changes in pH or redox potential when comparing sterile and cell-free conditioned medium during PLAP incubation, indicating that these factors were unimportant.

Gordonia (nocardia) amarae foaming due to biosurfactant production.

PubMed

Pagilla, K R; Sood, A; Kim, H

2002-01-01

Gordonia amarae, a filamentous actinomycete, commonly found in foaming activated sludge wastewater treatment plants was investigated for its biosurfactant production capability. Soluble acetate and paringly soluble hexadecane were used as carbon sources for G. amarae growth and biosurfactant production in laboratory scale batch reactors. The lowest surface tension (critical micelle concentration, CMC) of the cell-free culture broth was 55 dynes/cm when 1,900 mg/L acetate was used as the sole carbon source. The lowest surface tension was less than 40 dynes/cm when either 1% (v/v) hexadecane or a mixture of 1% (v/v) hexadecane and 0.5% (w/v) acetate was used as the carbon source. The maximum biomass concentration (the stationary phase) was achieved after 4 days when acetate was used along with hexadecane, whereas it took about 8 days to achieve the stationary phase with hexadecane alone. The maximum biosurfactant production was 3 x CMC with hexadecane as the sole carbon source, and it was 5 x CMC with the mixture of hexadecane and acetate. Longer term growth studies (approximately 35 days of culture growth) indicated that G. amarae produces biosurfactant in order to solubilize hexadecane, and that adding acetate improves its biosurfactant production by providing readily degradable substrate for initial biomass growth. This research confirms that the foaming problems in activated sludge containing G. amarae in the activated sludge are due to the biosurfactant production by G. amarae when hydrophobic substrates such as hexadecane are present.

Experimental Evaluation of an Invasive Medical Instrument Based on a Displacement Measurement System.

PubMed

Fotiadis, Dimitris A; Astaras, Alexandros; Bamidis, Panagiotis D; Papathanasiou, Kostas; Kalfas, Anestis

2015-09-01

This paper presents a novel method for tracking the position of a medical instrument's tip. The system is based on phase locking a high frequency signal transmitted from the medical instrument's tip to a reference signal. Displacement measurement is established having the loop open, in order to get a low frequency voltage representing the medical instrument's movement; therefore, positioning is established by means of conventional measuring techniques. The voltage-controlled oscillator stage of the phase-locked loop (PLL), combined to an appropriate antenna, comprises the associated transmitter located inside the medical instrument tip. All the other low frequency PLL components, low noise amplifier and mixer, are located outside the human body, forming the receiver part of the system. The operating details of the proposed system were coded in Verilog-AMS. Simulation results indicate robust medical instrument tracking in 1-D. Experimental evaluation of the proposed position tracking system is also presented. The experiments described in this paper are based on a transmitter moving opposite a stationary receiver performing either constant velocity or uniformly accelerated movement, and also together with two stationary receivers performing constant velocity movement again. This latter setup is implemented in order to demonstrate the prototype's accuracy for planar (2-D) motion measurements. Error analysis and time-domain analysis are presented for system performance characterization. Furthermore, preliminary experimental assessment using a saline solution container to more closely approximate the human body as a radio frequency wave transmission medium has proved the system's capability of operating underneath the skin.

Polyphosphate and Orthophosphate Content of Nitrosomonas europaea as a Function of Growth

PubMed Central

Terry, K. R.; Hooper, A. B.

1970-01-01

After inoculation of a stationary-phase culture of Nitrosomonas europaea into fresh growth solution, the cell-associated orthophosphate increased rapidly to 800 μmoles/g (wet weight), whereas the acid-insoluble long-chain polyphosphate content decreased rapidly to 22 μmoles/g. As growth proceeded, the orthophosphate content decreased rapidly to a level of 15 μmoles/g and the long-chain polyphosphate content gradually increased to 60 to 90 μmoles/g. When the pH of a culture of Nitrosomonas decreased during growth below approximately 7.4, the rate of nitrite and polyphosphate synthesis increased and the ratio of change in protein to change in nitrite decreased. When the pH of the culture was maintained above 7.6 throughout growth, polyphosphate accumulation, an increased rate of nitrite and polyphosphate synthesis, and a decreased ratio of change in protein to change in nitrite were not observed. Cells of Nitrosomonas apparently accumulated polyphosphate when adenosine triphosphate generated during the oxidation of ammonia to nitrite was not efficiently used to promote an increase in cell mass. The rapid hydrolysis of polyphosphate after the transfer of stationary-phase cells into fresh growth solution was found to be triggered primarily by the higher pH of the fresh growth solution. The efflux of orthophosphate during culture growth was not associated with a decrease in the pH of the growth solution. Data on the chemical composition of Nitrosomonas are presented. PMID:5423370

Fiber-based monolithic columns for liquid chromatography.

PubMed

Ladisch, Michael; Zhang, Leyu

2016-10-01

Fiber-based monoliths for use in liquid chromatographic separations are defined by columns packed with aligned fibers, woven matrices, or contiguous fiber structures capable of achieving rapid separations of proteins, macromolecules, and low molecular weight components. A common denominator and motivating driver for this approach, first initiated 25 years ago, was reducing the cost of bioseparations in a manner that also reduced residence time of retained components while achieving a high ratio of mass to momentum transfer. This type of medium, when packed into a liquid chromatography column, minimized the fraction of stagnant liquid and resulted in a constant plate height for non-adsorbing species. The uncoupling of dispersion from eluent flow rate enabled the surface chemistry of the stationary phase to be considered separately from fluid transport phenomena and pointed to new ways to apply chemistry for the engineering of rapid bioseparations. This paper addresses developments and current research on fiber-based monoliths and explains how the various forms of this type of chromatographic stationary phase have potential to provide new tools for analytical and preparative scale separations. The different stationary phases are discussed, and a model that captures the observed constant plate height as a function of mobile phase velocity is reviewed. Methods that enable hydrodynamically stable fiber columns to be packed and operated over a range of mobile phase flow rates, together with the development of new fiber chemistries, are shown to provide columns that extend the versatility of liquid chromatography using monoliths, particularly at the preparative scale. Graphical Abstract Schematic representation of a sample mixture being separated by a rolled-stationary phase column, resulting separated peaks shown in the chromatogram.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Karamatskos, E. T.; Stockhofe, J.; Kevrekidis, P. G.

In this study, we consider a binary repulsive Bose-Einstein condensate in a harmonic trap in one spatial dimension and investigate particular solutions consisting of two dark-bright solitons. There are two different stationary solutions characterized by the phase difference in the bright component, in-phase and out-of-phase states. We show that above a critical particle number in the bright component, a symmetry-breaking bifurcation of the pitchfork type occurs that leads to a new asymmetric solution whereas the parental branch, i.e., the out-of-phase state, becomes unstable. These three different states support different small amplitude oscillations, characterized by an almost stationary density of themore » dark component and a tunneling of the bright component between the two dark solitons. Within a suitable effective double-well picture, these can be understood as the characteristic features of a bosonic Josephson junction (BJJ), and we show within a two-mode approach that all characteristic features of the BJJ phase space are recovered. For larger deviations from the stationary states, the simplifying double-well description breaks down due to the feedback of the bright component onto the dark one, causing the solitons to move. In this regime we observe intricate anharmonic and aperiodic dynamics, exhibiting remnants of the BJJ phase space.« less

Stability and tunneling dynamics of a dark-bright soliton pair in a harmonic trap

DOE PAGES

Karamatskos, E. T.; Stockhofe, J.; Kevrekidis, P. G.; ...

2015-04-30

In this study, we consider a binary repulsive Bose-Einstein condensate in a harmonic trap in one spatial dimension and investigate particular solutions consisting of two dark-bright solitons. There are two different stationary solutions characterized by the phase difference in the bright component, in-phase and out-of-phase states. We show that above a critical particle number in the bright component, a symmetry-breaking bifurcation of the pitchfork type occurs that leads to a new asymmetric solution whereas the parental branch, i.e., the out-of-phase state, becomes unstable. These three different states support different small amplitude oscillations, characterized by an almost stationary density of themore » dark component and a tunneling of the bright component between the two dark solitons. Within a suitable effective double-well picture, these can be understood as the characteristic features of a bosonic Josephson junction (BJJ), and we show within a two-mode approach that all characteristic features of the BJJ phase space are recovered. For larger deviations from the stationary states, the simplifying double-well description breaks down due to the feedback of the bright component onto the dark one, causing the solitons to move. In this regime we observe intricate anharmonic and aperiodic dynamics, exhibiting remnants of the BJJ phase space.« less

Effects of the dynamic modification of stationary phases by sorbates in gas chromatography: The possibility of separating enantiomers in achiral systems

NASA Astrophysics Data System (ADS)

Zenkevich, I. G.; Pavlovskii, A. A.

2016-10-01

It is shown that the gas chromatographic separation of enantiomers on columns with achiral nonpolar stationary phases is principally possible as a result of the dynamic modification of stationary phases by sorbates under analysis. It is found that a number of key characteristic features is intrinsic to such separation: it can be only partial, it does not occur for all chromatographic columns, and it is observed only for some compounds and only within narrow ranges of quantities of sorbates that are close to the limits of mass overload of chromatographic systems. These characteristic features are illustrated by the examples of separating (1 R,5 R)-(+)- and (1 S,5 S)-(-)-α-pinenes on a WCOT column with an RTX-5 phase. The main characteristic feature of the separation of enantiomers as a result of the dynamic modification of stationary phases is the nonconformity of peaks in chromatograms with two individual enantiomers, compared to other ways and means for their separation; the first eluting peak belongs to the enantiomer that predominates in a mixture irrespective of its configuration, while the second peak corresponds to the racemic mixture of enantiomers; i.e., the ratio of peak areas in chromatograms does not correspond to the actual ratio of enantiomers in samples under analysis and is strongly distorted as a result of their incomplete separation. It is concluded that the separation of racemic mixtures in achiral systems is fundamentally impossible under any conditions, and this is one of the key criteria of the validity of the considered concept as a whole.

Inhibition of free radical scavenging enzymes affects mitochondrial membrane permeability transition during growth and aging of yeast cells.

PubMed

Deryabina, Yulia; Isakova, Elena; Sekova, Varvara; Antipov, Alexey; Saris, Nils-Erik L

2014-12-01

In this study, we investigated the change in the antioxidant enzymes activity, cell respiration, reactive oxygen species (ROS), and impairment of membrane mitochondria permeability in the Endomyces magnusii yeasts during culture growth and aging. We showed that the transition into stationary phase is the key tool to understanding interaction of these processes. This growth stage is distinguished by two-fold increase in ROS production and respiration rate as compared to those in the logarithmic phase. It results in induction of alternative oxidase (AO) in the stationary phase, decline of the main antioxidant enzymes activities, ROS-production, and mitochondria membrane permeability. Significant increase in the share of mitochondrial isoform of superoxide dismutase (SOD2) occurred in the stationary phase from 51.8% (24 h of cultivation) to 68.6% (48 h of cultivation). Upon blocking the essential ROS-scavenging enzymes, SODs and catalases (CATs) some heterogeneity of cell population was observed: 80-90% of cells displayed evident signs of early apoptosis (such as disorientation of mitochondria cristae, mitochondrial fragmentation and deformation of nuclear chromatine). However, 10-20% of the population were definitely healthy. It allowed to draw the conclusion that a complete system of cell antioxidant protection underlies normal mitochondria functioning while the E. magnusii yeasts grow and age. Moreover, this system provides unimpaired cell physiology under oxidative stress during culture aging in the stationary phase. Failures in mitochondria functions due to inhibition of ROS-scavenging enzymes of CATs and SODs could lead to damage of the cells and some signs of early apoptosis.

A finite difference Davidson procedure to sidestep full ab initio hessian calculation: Application to characterization of stationary points and transition state searches

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sharada, Shaama Mallikarjun; Bell, Alexis T., E-mail: mhg@bastille.cchem.berkeley.edu, E-mail: bell@cchem.berkeley.edu; Head-Gordon, Martin, E-mail: mhg@bastille.cchem.berkeley.edu, E-mail: bell@cchem.berkeley.edu

2014-04-28

The cost of calculating nuclear hessians, either analytically or by finite difference methods, during the course of quantum chemical analyses can be prohibitive for systems containing hundreds of atoms. In many applications, though, only a few eigenvalues and eigenvectors, and not the full hessian, are required. For instance, the lowest one or two eigenvalues of the full hessian are sufficient to characterize a stationary point as a minimum or a transition state (TS), respectively. We describe here a method that can eliminate the need for hessian calculations for both the characterization of stationary points as well as searches for saddlemore » points. A finite differences implementation of the Davidson method that uses only first derivatives of the energy to calculate the lowest eigenvalues and eigenvectors of the hessian is discussed. This method can be implemented in conjunction with geometry optimization methods such as partitioned-rational function optimization (P-RFO) to characterize stationary points on the potential energy surface. With equal ease, it can be combined with interpolation methods that determine TS guess structures, such as the freezing string method, to generate approximate hessian matrices in lieu of full hessians as input to P-RFO for TS optimization. This approach is shown to achieve significant cost savings relative to exact hessian calculation when applied to both stationary point characterization as well as TS optimization. The basic reason is that the present approach scales one power of system size lower since the rate of convergence is approximately independent of the size of the system. Therefore, the finite-difference Davidson method is a viable alternative to full hessian calculation for stationary point characterization and TS search particularly when analytical hessians are not available or require substantial computational effort.« less

Modeling non-stationary, non-axisymmetric heat patterns in DIII-D tokamak

DOE PAGES

Ciro, D.; Evans, T. E.; Caldas, I. L.

2016-10-27

Non-axisymmetric stationary magnetic perturbations lead to the formation of homoclinic tangles near the divertor magnetic saddle in tokamak discharges. These tangles intersect the divertor plates in static helical structures that delimit the regions reached by open magnetic field lines reaching the plasma column and leading the charged particles to the strike surfaces by parallel transport. In this article we introduce a non-axisymmetric rotating magnetic perturbation to model the time evolution of the three-dimensional magnetic field of a singlenull DIII-D tokamak discharge developing a rotating tearing mode. The non-axiymmetric field is modeled using the magnetic signals to adjust the phases andmore » currents of a set of internal filamentary currents that approximate the magnetic field in the plasma edge region. The stable and unstable manifolds of the asymmetric magnetic saddle are obtained through an adaptive calculation providing the cuts at a given poloidal plane and the strike surfaces. Lastly, for the modeled shot, the experimental heat pattern and its time development are well described by the rotating unstable manifold, indicating the emergence of homoclinic lobes in a rotating frame due to the plasma instabilities.« less

The effect of sampling rate on observed statistics in a correlated random walk

PubMed Central

Rosser, G.; Fletcher, A. G.; Maini, P. K.; Baker, R. E.

2013-01-01

Tracking the movement of individual cells or animals can provide important information about their motile behaviour, with key examples including migrating birds, foraging mammals and bacterial chemotaxis. In many experimental protocols, observations are recorded with a fixed sampling interval and the continuous underlying motion is approximated as a series of discrete steps. The size of the sampling interval significantly affects the tracking measurements, the statistics computed from observed trajectories, and the inferences drawn. Despite the widespread use of tracking data to investigate motile behaviour, many open questions remain about these effects. We use a correlated random walk model to study the variation with sampling interval of two key quantities of interest: apparent speed and angle change. Two variants of the model are considered, in which reorientations occur instantaneously and with a stationary pause, respectively. We employ stochastic simulations to study the effect of sampling on the distributions of apparent speeds and angle changes, and present novel mathematical analysis in the case of rapid sampling. Our investigation elucidates the complex nature of sampling effects for sampling intervals ranging over many orders of magnitude. Results show that inclusion of a stationary phase significantly alters the observed distributions of both quantities. PMID:23740484

Modeling non-stationary, non-axisymmetric heat patterns in DIII-D tokamak

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ciro, D.; Evans, T. E.; Caldas, I. L.

Non-axisymmetric stationary magnetic perturbations lead to the formation of homoclinic tangles near the divertor magnetic saddle in tokamak discharges. These tangles intersect the divertor plates in static helical structures that delimit the regions reached by open magnetic field lines reaching the plasma column and leading the charged particles to the strike surfaces by parallel transport. In this article we introduce a non-axisymmetric rotating magnetic perturbation to model the time evolution of the three-dimensional magnetic field of a singlenull DIII-D tokamak discharge developing a rotating tearing mode. The non-axiymmetric field is modeled using the magnetic signals to adjust the phases andmore » currents of a set of internal filamentary currents that approximate the magnetic field in the plasma edge region. The stable and unstable manifolds of the asymmetric magnetic saddle are obtained through an adaptive calculation providing the cuts at a given poloidal plane and the strike surfaces. Lastly, for the modeled shot, the experimental heat pattern and its time development are well described by the rotating unstable manifold, indicating the emergence of homoclinic lobes in a rotating frame due to the plasma instabilities.« less

Carboxylate modified porous graphitic carbon: a new class of hydrophilic interaction liquid chromatography phases.

PubMed

Wahab, M Farooq; Ibrahim, Mohammed E A; Lucy, Charles A

2013-06-18

Stationary phases for hydrophilic interaction liquid chromatography (HILIC) are predominantly based on silica and polymer supports. We present porous graphitic carbon particles with covalently attached carboxylic acid groups (carboxylate-PGC) as a new HILIC stationary phase. PGC particles were modified by adsorbing the diazonium salt of 4-aminobenzoic acid onto the PGC, followed by reduction of the adsorbed salt with sodium borohydride. The newly developed carboxylate-PGC phase exhibits different selectivity than that of 35 HPLC columns, including bare silica, zwitterionic, amine, reversed, and unmodified PGC phases. Carboxylate-PGC is stable from pH 2.0 to 12.6, yielding reproducible retention even at pH 12.6. Characterization of the new phase is presented by X-ray photoelectron spectroscopy, thermogravimetry, zeta potentials, and elemental analysis. The chromatographic performance of carboxylate-PGC as a HILIC phase is illustrated by separations of carboxylic acids, nucleotides, phenols, and amino acids.

Influence of physical properties and operating parameters on hydrodynamics in Centrifugal Partition Chromatography.

PubMed

Adelmann, S; Schembecker, G

2011-08-12

Besides the selection of a suitable biphasic solvent system the separation efficiency in Centrifugal Partition Chromatography (CPC) is mainly influenced by the hydrodynamics in the chambers. The flow pattern, the stationary phase retention and the interfacial area for mass transfer strongly depend on physical properties of the solvent system and operating parameters. In order to measure these parameters we visualized the hydrodynamics in a FCPC-chamber for five different solvent systems with an optical measurement system and calculated the stationary phase retention, interfacial area and the distribution of mobile phase thickness in the chamber. Although inclined chambers were used we found that the Coriolis force always deflected the mobile phase towards the chamber wall reducing the interfacial area. This effect increased for systems with low density difference. We also have shown that the stability of phase systems (stationary phase retention) and its tendency to disperse increased for smaller values of the ratio of interfacial tension and density difference. But also the viscosity ratio and the flow pattern itself had a significant effect on retention and dispersion of the mobile phase. As a result operating parameters should be chosen carefully with respect to physical properties for a CPC system. In order to reduce the effect of the Coriolis force CPC devices with greater rotor radius are desirable. Copyright © 2011 Elsevier B.V. All rights reserved.

Preparation of stationary phases for reversed-phase high-performance liquid chromatography using thermal treatments at high temperature.

PubMed

Vigna, Camila R M; Bottoli, Carla B G; Collins, Kenneth E; Collins, Carol H

2007-07-13

Batches of poly(methyloctylsiloxane) (PMOS)-loaded silica were prepared by deposition from a solution of PMOS into the pores of HPLC silica. Portions of PMOS-loaded silica were subjected to a thermal treatment at 100 degrees C for 24h (condition 1) in a tube furnace under a nitrogen atmosphere. After that, the material was heated for 4h at higher temperatures (150-400 degrees C) (condition 2). Heating at higher temperatures produces polymer bilayers. Non-immobilized and thermally treated stationary phases were characterized by percent carbon, (29)Si cross-polarization magic angle spinning nuclear magnetic resonance spectroscopy and reversed-phase chromatographic performance. The results show that thermal treatment between 150 and 300 degrees C accelerates the immobilization process, possibly due to some bond breaking of the polysiloxane, with formation of strong linkages to the surface of the support, resulting in more complete coverage of the silica. The chromatographic results show an improvement of efficiency with the increase of the temperature of condition 2 up to 300 degrees C and an increase in the resolution of the components, mainly for the phase heated at 300 degrees C. Such results demonstrate that a two-step thermal treatment (100 degrees C then 150-300 degrees C) produces stationary phases with good properties for use in reversed-phase high-performance liquid chromatography.

Multi-mode application of graphene quantum dots bonded silica stationary phase for high performance liquid chromatography.

PubMed

Wu, Qi; Sun, Yaming; Zhang, Xiaoli; Zhang, Xia; Dong, Shuqing; Qiu, Hongdeng; Wang, Litao; Zhao, Liang

2017-04-07

Graphene quantum dots (GQDs), which possess hydrophobic, hydrophilic, π-π stacking and hydrogen bonding properties, have great prospect in HPLC. In this study, a novel GQDs bonded silica stationary phase was prepared and applied in multiple separation modes including normal phase, reversed phase and hydrophilic chromatography mode. Alkaloids, nucleosides and nucleobases were chosen as test compounds to evaluate the separation performance of this column in hydrophilic chromatographic mode. The tested polar compounds achieved baseline separation and the resolutions reached 2.32, 4.62, 7.79, 1.68 for thymidine, uridine, adenosine, cytidine and guanosine. This new column showed satisfactory chromatographic performance for anilines, phenols and polycyclic aromatic hydrocarbons in normal and reversed phase mode. Five anilines were completely separated within 10min under the condition of mobile phase containing only 10% methanol. The effect of water content, buffer concentration and pH on chromatographic separation was further investigated, founding that this new stationary phase showed a complex retention mechanism of partitioning, adsorption and electrostatic interaction in hydrophilic chromatography mode, and the multiple retention interactions such as π-π stacking and π-π electron-donor-acceptor interaction played an important role during the separation process. This GQDs bonded column, which allows us to adjust appropriate chromatography mode according to the properties of analytes, has possibility in actual application after further research. Copyright © 2017 Elsevier B.V. All rights reserved.

Ionic liquids as stationary phases for fatty acid analysis by gas chromatography.

PubMed

Fanali, C; Micalizzi, G; Dugo, P; Mondello, L

2017-12-04

The present paper provides an overview of the application of ionic liquid (IL) columns for GC analysis of fatty acid methyl esters (FAMEs). Although their separation can be carried out utilizing GC columns containing polar stationary phases, some ILs have been employed as stationary phases, either commercial or laboratory made, in GC analysis. Monodimensional and bidimensional GC methods have been optimized in order to achieve the best separation especially considering the geometric and positional isomers of unsaturated fatty acids. Several methods for the analysis of trans-fatty acids have also been reported. The use of GC-GC, using either the same IL columns or different columns in the first and second dimensions, allowed the separation of a large number of FAMEs. The application of the IL columns for GC analysis of FAMEs in different types of real samples is described, e.g., oil of different nature (fish, flaxseed, and olive), margarine and butter, biodiesel, milk, bacteria etc.

Ionic liquid stationary phases for gas chromatography.

PubMed

Poole, Colin F; Poole, Salwa K

2011-04-01

This article provides a summary of the development of ionic liquids as stationary phases for gas chromatography beginning with early work on packed columns that established details of the retention mechanism and established working methods to characterize selectivity differences compared with molecular stationary phases through the modern development of multi-centered cation and cross-linked ionic liquids for high-temperature applications in capillary gas chromatography. Since there are many reviews on ionic liquids dealing with all aspects of their chemical and physical properties, the emphasis in this article is placed on the role of gas chromatography played in the design of ionic liquids of low melting point, high thermal stability, high viscosity, and variable selectivity for separations. Ionic liquids provide unprecedented opportunities for extending the selectivity range and temperature-operating range of columns for gas chromatography, an area of separation science that has otherwise been almost stagnant for over a decade. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Sake yeast strains have difficulty in entering a quiescent state after cell growth cessation.

PubMed

Urbanczyk, Henryk; Noguchi, Chiemi; Wu, Hong; Watanabe, Daisuke; Akao, Takeshi; Takagi, Hiroshi; Shimoi, Hitoshi

2011-07-01

Sake yeast strains produce a high concentration of ethanol during sake brewing compared to laboratory yeast strains. As ethanol fermentation by yeast cells continues even after cell growth stops, analysis of the physiological state of the stationary phase cells is very important for understanding the mechanism of producing higher concentrations of ethanol. We compared the physiological characteristics of stationary phase cells of both sake and laboratory yeast strains in an aerobic batch culture and under sake brewing conditions. We unexpectedly found that sake yeast cells in the stationary phase had a lower buoyant density and stress tolerance than did the laboratory yeast cells under both experimental conditions. These results suggest that it is difficult for sake yeast cells to enter a quiescent state after cell growth has stopped, which may be one reason for the higher fermentation rate of sake yeast compared to laboratory yeast strains. Copyright © 2011 The Society for Biotechnology, Japan. Published by Elsevier B.V. All rights reserved.

The glyoxylate shunt is essential for desiccation tolerance in C. elegans and budding yeast

PubMed Central

Erkut, Cihan; Gade, Vamshidhar R; Laxman, Sunil; Kurzchalia, Teymuras V

2016-01-01

Many organisms, including species from all kingdoms of life, can survive desiccation by entering a state with no detectable metabolism. To survive, C. elegans dauer larvae and stationary phase S. cerevisiae require elevated amounts of the disaccharide trehalose. We found that dauer larvae and stationary phase yeast switched into a gluconeogenic mode in which metabolism was reoriented toward production of sugars from non-carbohydrate sources. This mode depended on full activity of the glyoxylate shunt (GS), which enables synthesis of trehalose from acetate. The GS was especially critical during preparation of worms for harsh desiccation (preconditioning) and during the entry of yeast into stationary phase. Loss of the GS dramatically decreased desiccation tolerance in both organisms. Our results reveal a novel physiological role for the GS and elucidate a conserved metabolic rewiring that confers desiccation tolerance on organisms as diverse as worm and yeast. DOI: http://dx.doi.org/10.7554/eLife.13614.001 PMID:27090086

Two Synthetic Methods for Preparation of Chiral Stationary Phases Using Crystalline Degradation Products of Vancomycin: Column Performance for Enantioseparation of Acidic and Basic Drugs.

PubMed

Abdollahpour, Assem; Heydari, Rouhollah; Shamsipur, Mojtaba

2017-07-01

Two chiral stationary phases (CSPs) based on crystalline degradation products (CDPs) of vancomycin by using different synthetic methods were prepared and compared. Crystalline degradation products of vancomycin were produced by hydrolytic loss of ammonia from vancomycin molecules. Performances of two chiral columns prepared with these degradation products were investigated using several acidic and basic drugs as model analytes. Retention and resolution of these analytes on the prepared columns, as two main parameters, in enantioseparation were studied. The results demonstrated that the stationary phase preparation procedure has a significant effect on the column performance. The resolving powers of prepared columns for enantiomers resolution were changed with the variation in vancomycin-CDP coverage on the silica support. Elemental analysis was used to monitor the surface coverage of silica support by vancomycin-CDP. The results showed that both columns can be successfully applied to chiral separation studies.

A standardized method for the calibration of thermodynamic data for the prediction of gas chromatographic retention times.

PubMed

McGinitie, Teague M; Ebrahimi-Najafabadi, Heshmatollah; Harynuk, James J

2014-02-21

A new method for calibrating thermodynamic data to be used in the prediction of analyte retention times is presented. The method allows thermodynamic data collected on one column to be used in making predictions across columns of the same stationary phase but with varying geometries. This calibration is essential as slight variances in the column inner diameter and stationary phase film thickness between columns or as a column ages will adversely affect the accuracy of predictions. The calibration technique uses a Grob standard mixture along with a Nelder-Mead simplex algorithm and a previously developed model of GC retention times based on a three-parameter thermodynamic model to estimate both inner diameter and stationary phase film thickness. The calibration method is highly successful with the predicted retention times for a set of alkanes, ketones and alcohols having an average error of 1.6s across three columns. Copyright © 2014 Elsevier B.V. All rights reserved.

Surface confined ionic liquid as a stationary phase for HPLC

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Qian; Baker, Gary A; Baker, Sheila N

Trimethoxysilane ionosilane derivatives of room temperature ionic liquids based on alkylimidazolium bromides were synthesized for attachment to silica support material. The derivatives 1-methyl-3-(trimethoxysilylpropyl)imidazolium bromide and 1-butyl-3-(trimethoxysilylpropyl)imidazolium bromide were used to modify the surface of 3 {micro}m diameter silica particles to act as the stationary phase for HPLC. The modified particles were characterized by thermogravimetric analysis (TGA) and {sup 13}C and {sup 29}Si NMR spectroscopies. The surface modification procedure rendered particles with a surface coverage of 0.84 {micro}mol m{sup -2} for the alkylimidazolium bromide. The ionic liquid moiety was predominantly attached to the silica surface through two siloxane bonds of themore » ionosilane derivative (63%). Columns packed with the modified silica material were tested under HPLC conditions. Preliminary evaluation of the stationary phase for HPLC was performed using aromatic carboxylic acids as model compounds. The separation mechanism appears to involve multiple interactions including ion exchange, hydrophobic interaction, and other electrostatic interactions.« less

T7 phage factor required for managing RpoS in Escherichia coli.

PubMed

Tabib-Salazar, Aline; Liu, Bing; Barker, Declan; Burchell, Lynn; Qimron, Udi; Matthews, Steve J; Wigneshweraraj, Sivaramesh

2018-06-05

T7 development in Escherichia coli requires the inhibition of the housekeeping form of the bacterial RNA polymerase (RNAP), Eσ 70 , by two T7 proteins: Gp2 and Gp5.7. Although the biological role of Gp2 is well understood, that of Gp5.7 remains to be fully deciphered. Here, we present results from functional and structural analyses to reveal that Gp5.7 primarily serves to inhibit Eσ S , the predominant form of the RNAP in the stationary phase of growth, which accumulates in exponentially growing E. coli as a consequence of the buildup of guanosine pentaphosphate [(p)ppGpp] during T7 development. We further demonstrate a requirement of Gp5.7 for T7 development in E. coli cells in the stationary phase of growth. Our finding represents a paradigm for how some lytic phages have evolved distinct mechanisms to inhibit the bacterial transcription machinery to facilitate phage development in bacteria in the exponential and stationary phases of growth.

Capillary electrochromatography of inorganic cations in open tubular columns with a controllable capacity multilayered stationary phase architecture.

PubMed

Kubán, Pavel; Kubán, Petr; Kubán, Vlastimil; Hauser, Peter C; Bocek, Petr

2008-05-09

In this paper capillary electrochromatography of alkali and alkaline-earth metal cations in open tubular capillary columns is described. Capillary columns are prepared by coating fused silica capillaries of 75 microm I.D. with poly(butadiene-maleic acid) copolymer (PBMA) in multiple layers. Thermally initiated radical polymerization is used to crosslink the stationary phase. Capillary columns with different number of stationary phase layers can be prepared and allow for the adjustment of separation selectivity in the electrochromatographic mode. Fast and sensitive separations of common inorganic cations are achieved in less than 6 min in a 60 cm capillary column with on-column capacitively coupled contactless conductivity detector. Limits of detection (S/N=3) for the determination of alkali and alkaline-earth metal cations range from 0.3 to 2.5 microM and repeatability is better than 0.5, 4.5 and 6.1% for migration times, peak heights and peak areas, respectively.

Adaptive feedforward control of non-minimum phase structural systems

NASA Astrophysics Data System (ADS)

Vipperman, J. S.; Burdisso, R. A.

1995-06-01

Adaptive feedforward control algorithms have been effectively applied to stationary disturbance rejection. For structural systems, the ideal feedforward compensator is a recursive filter which is a function of the transfer functions between the disturbance and control inputs and the error sensor output. Unfortunately, most control configurations result in a non-minimum phase control path; even a collocated control actuator and error sensor will not necessarily produce a minimum phase control path in the discrete domain. Therefore, the common practice is to choose a suitable approximation of the ideal compensator. In particular, all-zero finite impulse response (FIR) filters are desirable because of their inherent stability for adaptive control approaches. However, for highly resonant systems, large order filters are required for broadband applications. In this work, a control configuration is investigated for controlling non-minimum phase lightly damped structural systems. The control approach uses low order FIR filters as feedforward compensators in a configuration that has one more control actuator than error sensors. The performance of the controller was experimentally evaluated on a simply supported plate under white noise excitation for a two-input, one-output (2I1O) system. The results show excellent error signal reduction, attesting to the effectiveness of the method.

Effects of supercritical fluid chromatography conditions on enantioselectivity and performance of polyproline-derived chiral stationary phases.

PubMed

Novell, Arnau; Méndez, Alberto; Minguillón, Cristina

2015-07-17

The chromatographic behaviour and performance of four polyproline-derived chiral stationary phases (CSPs) were tested using supercritical fluid chromatography (SFC). A series of structurally related racemic compounds, whose enantioseparation was proved to be sensitive to the type of mobile phase used in NP-HPLC, were chosen to be tested in the SFC conditions. Good enantioselection ability was shown by the CSPs for the analytes tested in the new conditions. Resolution, efficiency and analysis time, were considerably improved with respect to NP-HPLC when CO2/alcohol mobile phases were used. Monolithic columns clearly show enhanced chromatographic parameters and improved performance respect to their bead-based counterparts. Copyright © 2015 Elsevier B.V. All rights reserved.

SU-G-JeP3-14: Positioning and Dosimetric Uncertainties in Image-Guided Radiation Therapy with Respiratory Gating

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ali, I; Hossain, S; Algan, O

Purpose: To investigate quantitatively positioning and dosimetric uncertainties due to 4D-CT intra-phase motion in the internal-target-volume (ITV) associated with radiation therapy using respiratory-gating for patients setup with image-guidance-radiation-therapy (IGRT) using free-breathing or average-phase CT-images. Methods: A lung phantom with an embedded tissue-equivalent target is imaged with CT while it is stationary and moving. Four-sets of structures are outlined: (a) the actual target on CT-images of the stationary-target, (b) ITV on CT-images for the free-moving phantom, (c) ITV’s from the ten different phases (10–100%) and (d) ITV on the CT-images generated from combining 3 phases: 40%–50%–60%. The variations in volume, lengthmore » and center-position of the ITV’s and their effects on dosimetry during dose delivery for patients setup with image-guidance are investigated. Results: Intra-phase motion due to breathing affects the volume, center position and length of the ITVs from different respiratory-phases. The ITV’s vary by about 10% from one phase to another. The largest ITV is measured on the free breathing CT images and the smallest is on the stationary CT-images. The ITV lengths vary by about 4mm where it may shrink or elongated depending on the motion-phase. The center position of the ITV varies between the different motion-phases which shifts upto 10mm from the stationary-position which is nearly equal to motion-amplitude. This causes systematic shifts during dose delivery with beam gating using certain phases (40%–50%–60%) for patients setup with IGRT using free-breathing or average-phase CT-images. The dose coverage of the ITV depends on the margins used for treatment-planning-volume where margins larger than the motion-amplitudes are needed to ensure dose coverage of the ITV. Conclusion: Volume, length, and center position of the ITV’s change between the different motion phases. Large systematic shifts are induced by respiratory-gating with ITVs on certain phases when patients are setup with IGRT using free-breathing or average-phase CT-images.« less

Preparative enantiomer separation of dichlorprop with a cinchona-derived chiral selector employing centrifugal partition chromatography and high-performance liquid chromatography: a comparative study.

PubMed

Gavioli, Elena; Maier, Norbert M; Minguillón, Cristina; Lindner, Wolfgang

2004-10-01

A countercurrent chromatography protocol for support-free preparative enantiomer separation of the herbicidal agent 2-(2,4-dichlorphenoxy)propionic acid (dichlorprop) was developed utilizing a purposefully designed, highly enantioselective chiral stationary-phase additive (CSPA) derived from bis-1,4-(dihydroquinidinyl)phthalazine. Guided by liquid-liquid extraction experiments, a solvent system consisting of 10 mM CSPA in methyl tert-butyl ether and 100 mM sodium phosphate buffer (pH 8.0) was identified as a suitable stationary/mobile-phase combination. This solvent system provided an ideal compromise among stationary-phase retention, enantioselectivity, and well-balanced analyte distribution behavior. Using a commercial centrifugal partition chromatography instrument, complete enantiomer separations of up to 366 mg of racemic dichlorprop could be achieved, corresponding to a sample load being equivalent to the molar amount of CSPA employed. Comparison of the preparative performance characteristics of the CPC protocol with that of a HPLC separation using a silica-supported bis-1,4-(dihydroquinidinyl)phthalazine chiral stationary phase CSP revealed comparable loading capacities for both techniques but a significantly lower solvent consumption for CPC. With respect to productivity, HPLC was found to be superior, mainly due to inherent flow rate restrictions of the CPC instrument. Given that further progress in instrumental design and engineering of dedicated, highly enantioselective CSPAs can be achieved, CPC may offer a viable alternative to CSP-based HPLC for preparative-scale enantiomer separation.

REVIEW AND EVALUATION OF CURRENT METHODS AND USER NEEDS FOR OTHER STATIONARY COMBUSTION SOURCES

EPA Science Inventory

The report gives results of Phase 1 of an effort to develop improved methodologies for estimating area source emissions of air pollutants from stationary combustion sources. The report (1) evaluates Area and Mobile Source (AMS) subsystem methodologies; (2) compares AMS results w...

Aqueous Biphasic Systems for the Synthesis of Formates by Catalytic CO2 Hydrogenation: Integrated Reaction and Catalyst Separation for CO2 -Scrubbing Solutions.

PubMed

Scott, Martin; Blas Molinos, Beatriz; Westhues, Christian; Franciò, Giancarlo; Leitner, Walter

2017-03-22

Aqueous biphasic systems were investigated for the production of formate-amine adducts by metal-catalyzed CO 2 hydrogenation, including typical scrubbing solutions as feedstocks. Different hydrophobic organic solvents and ionic liquids could be employed as the stationary phase for cis-[Ru(dppm) 2 Cl 2 ] (dppm=bis-diphenylphosphinomethane) as prototypical catalyst without any modification or tagging of the complex. The amines were found to partition between the two phases depending on their structure, whereas the formate-amine adducts were nearly quantitatively extracted into the aqueous phase, providing a favorable phase behavior for the envisaged integrated reaction/separation sequence. The solvent pair of methyl isobutyl carbinol (MIBC) and water led to the most practical and productive system and repeated use of the catalyst phase was demonstrated. The highest single batch activity with a TOF av of approximately 35 000 h -1 and an initial TOF of approximately 180 000 h -1 was achieved in the presence of NEt 3 . Owing to higher stability, the highest productivities were obtained with methyl diethanolamine (Aminosol CST 115) and monoethanolamine (MEA), which are used in commercial scale CO 2 -scrubbing processes. Saturated aqueous solutions (CO 2 overpressure 5-10 bar) of MEA could be converted into the corresponding formate adducts with average turnover frequencies up to 14×10 3  h -1 with an overall yield of 70 % based on the amine, corresponding to a total turnover number of 150 000 over eleven recycling experiments. This opens the possibility for integrated approaches to carbon capture and utilization. © 2017 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

Aqueous Biphasic Systems for the Synthesis of Formates by Catalytic CO2 Hydrogenation: Integrated Reaction and Catalyst Separation for CO2‐Scrubbing Solutions

PubMed Central

Scott, Martin; Blas Molinos, Beatriz; Westhues, Christian

2017-01-01

Abstract Aqueous biphasic systems were investigated for the production of formate–amine adducts by metal‐catalyzed CO2 hydrogenation, including typical scrubbing solutions as feedstocks. Different hydrophobic organic solvents and ionic liquids could be employed as the stationary phase for cis‐[Ru(dppm)2Cl2] (dppm=bis‐diphenylphosphinomethane) as prototypical catalyst without any modification or tagging of the complex. The amines were found to partition between the two phases depending on their structure, whereas the formate–amine adducts were nearly quantitatively extracted into the aqueous phase, providing a favorable phase behavior for the envisaged integrated reaction/separation sequence. The solvent pair of methyl isobutyl carbinol (MIBC) and water led to the most practical and productive system and repeated use of the catalyst phase was demonstrated. The highest single batch activity with a TOFav of approximately 35 000 h−1 and an initial TOF of approximately 180 000 h−1 was achieved in the presence of NEt3. Owing to higher stability, the highest productivities were obtained with methyl diethanolamine (Aminosol CST 115) and monoethanolamine (MEA), which are used in commercial scale CO2‐scrubbing processes. Saturated aqueous solutions (CO2 overpressure 5–10 bar) of MEA could be converted into the corresponding formate adducts with average turnover frequencies up to 14×103 h−1 with an overall yield of 70 % based on the amine, corresponding to a total turnover number of 150 000 over eleven recycling experiments. This opens the possibility for integrated approaches to carbon capture and utilization. PMID:28103428

Marine sources of ice nucleating particles: results from phytoplankton cultures and samples collected at sea

NASA Astrophysics Data System (ADS)

Wilbourn, E.; Thornton, D.; Brooks, S. D.; Graff, J.

2016-12-01

The role of marine aerosols as ice nucleating particles is currently poorly understood. Despite growing interest, there are remarkably few ice nucleation measurements on representative marine samples. Here we present results of heterogeneous ice nucleation from laboratory studies and in-situ air and sea water samples collected during NAAMES (North Atlantic Aerosol and Marine Ecosystems Study). Thalassiosira weissflogii (CCMP 1051) was grown under controlled conditions in batch cultures and the ice nucleating activity depended on the growth phase of the cultures. Immersion freezing temperatures of the lab-grown diatoms were determined daily using a custom ice nucleation apparatus cooled at a set rate. Our results show that the age of the culture had a significant impact on ice nucleation temperature, with samples in stationary phase causing nucleation at -19.9 °C, approximately nine degrees warmer than the freezing temperature during exponential growth phase. Field samples gathered during the NAAMES II cruise in May 2016 were also tested for ice nucleating ability. Two types of samples were gathered. Firstly, whole cells were fractionated by size from surface seawater using a BD Biosciences Influx Cell Sorter (BD BS ISD). Secondly, aerosols were generated using the SeaSweep and subsequently size-selected using a PIXE Cascade Impactor. Samples were tested for the presence of ice nucleating particles (INP) using the technique described above. There were significant differences in the freezing temperature of the different samples; of the three sample types the lab-grown cultures tested during stationary phase froze at the warmest temperatures, followed by the SeaSweep samples (-25.6 °C) and the size-fractionated cell samples (-31.3 °C). Differences in ice nucleation ability may be due to size differences between the INP, differences in chemical composition of the sample, or some combination of these two factors. Results will be presented and atmospheric implications discussed.

Preparation of a novel dual-function strong cation exchange/hydrophobic interaction chromatography stationary phase for protein separation.

PubMed

Zhao, Kailou; Yang, Li; Wang, Xuejiao; Bai, Quan; Yang, Fan; Wang, Fei

2012-08-30

We have explored a novel dual-function stationary phase which combines both strong cation exchange (SCX) and hydrophobic interaction chromatography (HIC) characteristics. The novel dual-function stationary phase is based on porous and spherical silica gel functionalized with ligand containing sulfonic and benzyl groups capable of electrostatic and hydrophobic interaction functionalities, which displays HIC character in a high salt concentration, and IEC character in a low salt concentration in mobile phase employed. As a result, it can be employed to separate proteins with SCX and HIC modes, respectively. The resolution and selectivity of the dual-function stationary phase were evaluated under both HIC and SCX modes with standard proteins and can be comparable to that of conventional IEC and HIC columns. More than 96% of mass and bioactivity recoveries of proteins can be achieved in both HIC and SCX modes, respectively. The results indicated that the novel dual-function column could replace two individual SCX and HIC columns for protein separation. Mixed retention mechanism of proteins on this dual-function column based on stoichiometric displacement theory (SDT) in LC was investigated to find the optimal balance of the magnitude of electrostatic and hydrophobic interactions between protein and the ligand on the silica surface in order to obtain high resolution and selectivity for protein separation. In addition, the effects of the hydrophobicity of the ligand of the dual-function packings and pH of the mobile phase used on protein separation were also investigated in detail. The results show that the ligand with suitable hydrophobicity to match the electrostatic interaction is very important to prepare the dual-function stationary phase, and a better resolution and selectivity can be obtained at pH 6.5 in SCX mode. Therefore, the dual-function column can replace two individual SCX and HIC columns for protein separation and be used to set up two-dimensional liquid chromatography with a single column (2DLC-1C), which can also be employed to separate three kinds of active proteins completely, such as lysozyme, ovotransferrin and ovalbumin from egg white. The result is very important not only to the development of new 2DLC technology with a single column for proteomics, but also to recombinant protein drug production for saving column expense and simplifying the process in biotechnology. Copyright © 2012 Elsevier B.V. All rights reserved.

Features of the adsoprtion of naproxen on the chiral stationary phase (S,S)-Whelk-O1 under reversed-phase conditions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Asnin, Leonid; Gritti, Fabrice; Kaczmarski, Krzysztof

Using elution chromatography, we studied the adsorption mechanism of the Naproxen enantiomers on the chiral stationary phase (S,S)-Whelk-O1, from buffered methanol-water solutions. We propose an adsorption mechanism that assumes monolayer adsorption of the more retained enantiomer and the associative adsorption of the less retained one. The effects of the mobile phase composition on the adsorption of Naproxen are discussed. The combination of an elevated column temperature and of the use of an acidic mobile phase led to the degradation of the column and caused a major loss of its separation ability. The use of a moderately acidic mobile phase atmore » temperature slightly above ambient did not produce rapid severe damages but, nevertheless, hampered the experiments and caused a slow gradual deterioration of the column.« less

Experimental observations of the hydrodynamic behavior of solvent systems in high-speed counter-current chromatography. I. Hydrodynamic distribution of two solvent phases in a helical column subjected to two types of synchronous planetary motion.

PubMed

Ito, Y

1984-10-05

Hydrodynamic distribution of two-phase solvent systems in a rotating helical column subjected to centrifugal fields produced by two different types of synchronous planetary motion has been studied by the use of the combined horizontal flow-through coil planet centrifuge. With continuous elution of the mobile phase, the simpler type of motion resulted in low retention of the stationary phase in the column whereas a more complex motion, which produces a quasi-radial centrifugal field varying in both intensity and direction, yielded high stationary phase retention for commonly used solvent systems having a wide range of hydrophobicity. These solvent systems display highly complex modes of hydrodynamic interaction in the coil according to their particular physical properties.

Poly(alkylmethylsiloxanes) thermally immobilized on silica as stationary phases for high-performance liquid chromatography.

PubMed

Bottoli, Carla B G; Chaudhry, Zahra F; Fonseca, Dania A; Collins, Kenneth E; Collins, Carol H

2002-03-01

Poly(methyloctylsiloxane) (PMOS) and poly(methyloctadecylsiloxane) (PMODS) were sorbed onto porous HPLC silica and thermally immobilized, in the absence of radical initiators, at temperatures in the range of 80 to 180 degrees C. Following extraction of non-immobilized polymer the materials were packed into columns and their chromatographic properties evaluated. The shorter chain (PMOS) stationary phase showed good HPLC characteristics after thermal immobilizations up to 120 degrees C while the longer chain (PMODS) phase gave satisfactory HPLC phases following thermal immobilizations at 80 and 100 degrees C. Stability evaluation for the PMOS and PMODS columns immobilized at 100 degrees C required 250 ml of pH 8.5 mobile phase at 60 degrees C to significantly decrease efficiency, suggesting a long useful life time at neutral pH and ambient temperature.

Effect of non-stationary climate on infectious gastroenteritis transmission in Japan.

PubMed

Onozuka, Daisuke

2014-06-03

Local weather factors are widely considered to influence the transmission of infectious gastroenteritis. Few studies, however, have examined the non-stationary relationships between global climatic factors and transmission of infectious gastroenteritis. We analyzed monthly data for cases of infectious gastroenteritis in Fukuoka, Japan from 2000 to 2012 using cross-wavelet coherency analysis to assess the pattern of associations between indices for the Indian Ocean Dipole (IOD) and El Niño Southern Oscillation (ENSO). Infectious gastroenteritis cases were non-stationary and significantly associated with the IOD and ENSO (Multivariate ENSO Index [MEI], Niño 1 + 2, Niño 3, Niño 4, and Niño 3.4) for a period of approximately 1 to 2 years. This association was non-stationary and appeared to have a major influence on the synchrony of infectious gastroenteritis transmission. Our results suggest that non-stationary patterns of association between global climate factors and incidence of infectious gastroenteritis should be considered when developing early warning systems for epidemics of infectious gastroenteritis.

The Bacterial Growth Curve.

ERIC Educational Resources Information Center

Paulton, Richard J. L.

1991-01-01

A procedure that allows students to view an entire bacterial growth curve during a two- to three-hour student laboratory period is described. Observations of the lag phase, logarithmic phase, maximum stationary phase, and phase of decline are possible. A nonpathogenic, marine bacterium is used in the investigation. (KR)

Temperature-responsive chromatography for the separation of biomolecules.

PubMed

Kanazawa, Hideko; Okano, Teruo

2011-12-09

Temperature-responsive chromatography for the separation of biomolecules utilizing poly(N-isopropylacrylamide) (PNIPAAm) and its copolymer-modified stationary phase is performed with an aqueous mobile phase without using organic solvent. The surface properties and function of the stationary phase are controlled by external temperature changes without changing the mobile-phase composition. This analytical system is based on nonspecific adsorption by the reversible transition of a hydrophilic-hydrophobic PNIPAAm-grafted surface. The driving force for retention is hydrophobic interaction between the solute molecules and the hydrophobized polymer chains on the stationary phase surface. The separation of the biomolecules, such as nucleotides and proteins was achieved by a dual temperature- and pH-responsive chromatography system. The electrostatic and hydrophobic interactions could be modulated simultaneously with the temperature in an aqueous mobile phase, thus the separation system would have potential applications in the separation of biomolecules. Additionally, chromatographic matrices prepared by a surface-initiated atom transfer radical polymerization (ATRP) exhibit a strong interaction with analytes, because the polymerization procedure forms a densely packed polymer, called a polymer brush, on the surfaces. The copolymer brush grafted surfaces prepared by ATRP was an effective tool for separating basic biomolecules by modulating the electrostatic and hydrophobic interactions. Applications of thermally responsive columns for the separations of biomolecules are reviewed here. Copyright © 2011 Elsevier B.V. All rights reserved.

Application of a cholesterol stationary phase in the analysis of phosphorothioate oligonucleotides by means of ion pair chromatography coupled with tandem mass spectrometry.

PubMed

Studzińska, Sylwia; Krzemińska, Katarzyna; Szumski, Michał; Buszewski, Bogusław

2016-07-01

The main aim of this study was the investigation of the influence of several ion pair reagents towards both the retention and the mass spectrometry sensitivity of phosphorothioate oligonucleotides. A cholesterol stationary phase was applied for the first time in the analysis of this group of compounds. The mobile phase composition was modified by changing the concentration and the type of amines and acetates or 1,1,1,3,3,3-hexafluoroisopropanol. It has been shown that the increase of amines concentration results in the retention factor increase for each oligonucleotide, on each adsorbent. The only exception was the mobile phase composed of triethylamine and 1,1,1,3,3,3-hexafluoroisopropanol. This is a consequence of interactions taking place between a cholesterol molecule and an alcohol. This effect was convenient when the mass spectrometry detection was applied, since it allowed an increase in the sensitivity. Moreover, optimization of the mobile phase composition and its impact on the efficiency of ionization process and on the sensitivity in mass spectrometry were also presented. The optimization of this new method, based on cholesterol stationary phase coupled with mass spectrometry detection, was finally applied for the determination of phosphorothioate oligonucleotides impurity in a real sample. Copyright © 2016 Elsevier B.V. All rights reserved.

Global dynamics of the Escherichia coli proteome and phosphoproteome during growth in minimal medium.

PubMed

Soares, Nelson C; Spät, Philipp; Krug, Karsten; Macek, Boris

2013-06-07

Recent phosphoproteomics studies have generated relatively large data sets of bacterial proteins phosphorylated on serine, threonine, and tyrosine, implicating this type of phosphorylation in the regulation of vital processes of a bacterial cell; however, most phosphoproteomics studies in bacteria were so far qualitative. Here we applied stable isotope labeling by amino acids in cell culture (SILAC) to perform a quantitative analysis of proteome and phosphoproteome dynamics of Escherichia coli during five distinct phases of growth in the minimal medium. Combining two triple-SILAC experiments, we detected a total of 2118 proteins and quantified relative dynamics of 1984 proteins in all measured phases of growth, including 570 proteins associated with cell wall and membrane. In the phosphoproteomic experiment, we detected 150 Ser/Thr/Tyr phosphorylation events, of which 108 were localized to a specific amino acid residue and 76 were quantified in all phases of growth. Clustering analysis of SILAC ratios revealed distinct sets of coregulated proteins for each analyzed phase of growth and overrepresentation of membrane proteins in transition between exponential and stationary phases. The proteomics data indicated that proteins related to stress response typically associated with the stationary phase, including RpoS-dependent proteins, had increasing levels already during earlier phases of growth. Application of SILAC enabled us to measure median occupancies of phosphorylation sites, which were generally low (<12%). Interestingly, the phosphoproteome analysis showed a global increase of protein phosphorylation levels in the late stationary phase, pointing to a likely role of this modification in later phases of growth.

Improved separation with the intermittently pressed tubing of multilayer coil in type-I counter-current chromatography.

PubMed

Yang, Yi; Yang, Jiao; Fang, Chen; Wang, Jihui; Gu, Dongyu; Tian, Jing; Ito, Yoichiro

2018-05-25

The intermittently pressed tubing was introduced in type-I counter-current chromatographic system as the separation column to improve the separation performance in the present study. The separations were performed with two different solvent systems composed of 1-butanol-acetic acid-water (4:1:5, v/v) (BAW) and hexane-ethyl acetate-methanol-0.1 M HCl (1:1:1:1, v/v) (HEMW) using dipeptides and DNP-amino acids as test samples, respectively. The chromatographic performance was evaluated in terms of retention of the stationary phase (Sf), theoretical plate (N) and peak resolution (Rs). In general, the type-I planetary motion with the multilayer coil of non-modified standard tubing can yield the best separation at a low revolution speed of 200 rpm with lower flow rate. The present results with intermittently pressed tubing indicated that the performance was also optimal at the revolution speed of 200 rpm where the lower flow rate was more beneficial to retention of stationary phase and resolution. In the moderately hydrophobic two-phase solvent system composed of hexane-ethyl acetate-metanol-0.1 M hydrochloric acid (1:1:1:1, v/v), DNP-amino acids were separated with Rs at 1.67 and 1.47, respectively, with 12.66% of stationary phase retention at a flow rate of 0.25 ml/min. In the polar solvent system composed of 1-butanol-acetic acid-water (4:1:5, v/v), dipeptide samples were resolved with Rs at 2.18 and 18.75% of stationary phase retention at a flow rate of 0.25 ml/min. These results indicate that the present system substantially improves the separation efficiency of type-I counter-current chromatographic system. Published by Elsevier B.V.

Preparation and retention mechanism study of graphene and graphene oxide bonded silica microspheres as stationary phases for high performance liquid chromatography.

PubMed

Zhang, Xiaoqiong; Chen, Sha; Han, Qiang; Ding, Mingyu

2013-09-13

Graphene oxide (GO) bonded stationary phase for high performance liquid chromatography (HPLC) was fabricated by coating GO sheets onto aminosilica microspheres via covalent coupling. Graphene (G) functionalized HPLC stationary phase was then prepared through hydrazine reduction of GO bonded silica (GO@SiO2) composite, which was the first example of using graphene as stationary-phase component for HPLC. Effective separations of the tested neutral and polar compounds on both GO@SiO2 and graphene bonded silica (G@SiO2) columns were achieved under the optimal experimental conditions. Compared with commercial C18 column, the different chromatographic performances of GO and graphene bonded columns were ascribed to their unique retention mechanisms. The polyaromatic scaffold of GO and graphene gives π-π stacking property and hydrophobic effect, and other retention mechanisms, such as π-π electron-donor-acceptor (EDA) interaction for the separation of nitroaromatic compounds and hydrogen bonding for hydroxyl and amino compounds, may also be taken into consideration. Experimental results indicated that the mixed-mode retention mechanism can facilitate the separation of analytes with similar hydrophobicity, which is a unique property compared with C18 column. Additionally, G@SiO2 showed higher affinity to aromatic analytes in contrast with GO@SiO2 and its retention mechanism was not consistent with the typical reversed phase behavior. The separation of aromatic compounds on G@SiO2 column relies primarily on the π-π stacking interaction and then the hydrophobicity, while the two interactions have equal shares on GO@SiO2 column. Copyright © 2013 Elsevier B.V. All rights reserved.

Sample displacement chromatography as a method for purification of proteins and peptides from complex mixtures

PubMed Central

Gajdosik, Martina Srajer; Clifton, James; Josic, Djuro

2012-01-01

Sample displacement chromatography (SDC) in reversed-phase and ion-exchange modes was introduced approximately twenty years ago. This method takes advantage of relative binding affinities of components in a sample mixture. During loading, there is a competition among different sample components for the sorption on the surface of the stationary phase. SDC was first used for the preparative purification of proteins. Later, it was demonstrated that this kind of chromatography can also be performed in ion-exchange, affinity and hydrophobic-interaction mode. It has also been shown that SDC can be performed on monoliths and membrane-based supports in both analytical and preparative scale. Recently, SDC in ion-exchange and hydrophobic interaction mode was also employed successfully for the removal of trace proteins from monoclonal antibody preparations and for the enrichment of low abundance proteins from human plasma. In this review, the principals of SDC are introduced, and the potential for separation of proteins and peptides in micro-analytical, analytical and preparative scale is discussed. PMID:22520159

Stationary phase method and delay times for relativistic and non-relativistic tunneling particles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bernardini, A.E.

2009-06-15

The stationary phase method is frequently adopted for calculating tunneling phase times of analytically-continuous Gaussian or infinite-bandwidth step pulses which collide with a potential barrier. This report deals with the basic concepts on deducing transit times for quantum scattering: the stationary phase method and its relation with delay times for relativistic and non-relativistic tunneling particles. After reexamining the above-barrier diffusion problem, we notice that the applicability of this method is constrained by several subtleties in deriving the phase time that describes the localization of scattered wave packets. Using a recently developed procedure - multiple wave packet decomposition - for somemore » specifical colliding configurations, we demonstrate that the analytical difficulties arising when the stationary phase method is applied for obtaining phase (traversal) times are all overcome. In this case, we also investigate the general relation between phase times and dwell times for quantum tunneling/scattering. Considering a symmetrical collision of two identical wave packets with an one-dimensional barrier, we demonstrate that these two distinct transit time definitions are explicitly connected. The traversal times are obtained for a symmetrized (two identical bosons) and an antisymmetrized (two identical fermions) quantum colliding configuration. Multiple wave packet decomposition shows us that the phase time (group delay) describes the exact position of the scattered particles and, in addition to the exact relation with the dwell time, leads to correct conceptual understanding of both transit time definitions. At last, we extend the non-relativistic formalism to the solutions for the tunneling zone of a one-dimensional electrostatic potential in the relativistic (Dirac to Klein-Gordon) wave equation where the incoming wave packet exhibits the possibility of being almost totally transmitted through the potential barrier. The conditions for the occurrence of accelerated and, eventually, superluminal tunneling transmission probabilities are all quantified and the problematic superluminal interpretation based on the non-relativistic tunneling dynamics is revisited. Lessons concerning the dynamics of relativistic tunneling and the mathematical structure of its solutions suggest revealing insights into mathematically analogous condensed-matter experiments using electrostatic barriers in single- and bi-layer graphene, for which the accelerated tunneling effect deserves a more careful investigation.« less

Behavior of bubbles in glassmelts. II - Dissolution of a stationary bubble containing a diffusing and a nondiffusing gas

NASA Technical Reports Server (NTRS)

Weinberg, M. C.; Onorato, P. I. K.; Uhlmann, D. R.

1980-01-01

The effect of a foreign nondiffusing gas on the rate of shrinkage of an oxygen bubble in a soda-lime-silica melt was studied. The rate of change of bubble radius with time was computed using the quasi-stationary approximation. The effects of melt undersaturation and initial fraction of foreign gas in the bubble are considered and compared with those calculated using previously derived expressions.

The frequency hopping pattern design for random hopping frequency signal based on stationary phase principle

NASA Astrophysics Data System (ADS)

Liao, Zhikun; Lu, Dawei; Hu, Jiemin; Zhang, Jun

2018-04-01

For the random hopping frequency signal, the modulated frequencies are randomly distributed over given bandwidth. The randomness of modulated frequency not only improves the electronic counter countermeasure capability for radar systems, but also determines its performance of range compression. In this paper, the range ambiguity function of RHF signal is firstly derived. Then, a design method of frequency hopping pattern based on stationary phase principle to improve the peak to side-lobe ratio is proposed. Finally, the simulated experiments show a good effectiveness of the presented design method.

How High Pressure Unifies Solvation Processes in Liquid Chromatography.

PubMed

Bocian, Szymon; Škrinjar, Tea; Bolanca, Tomislav; Buszewski, Bogusław

2017-11-01

A series of core-shell-based stationary phases of varying surface chemistry were subjected to solvent adsorption investigation under ultra-HPLC conditions. Acetonitrile and water excess isotherms were measured using a minor disturbance method. It was observed that adsorption of organic solvent is unified under high pressure. Preferential solvation due to specific interactions between the stationary phases and solvent molecules was limited. The obtained results showed that the solvation process is almost independent of surface chemistry, in contrast to HPLC conditions in which specific interactions differentiate solvation processes.

In vitro observations on the suitability of new rifamycins for the intermittent chemotherapy of tuberculosis.

PubMed

Dickinson, J M; Mitchison, D A

1987-09-01

The bactericidal activity of six new rifamycin derivatives--rifabutin (RBU), FCE 22250 (F22), rifapentine (RPE), CGP 29861 (C29), CGP 7040 (C70) and CGP 27557 (C27) and rifampicin (RMP)--have been measured against log phase and, as a better test of sterilising activity, against stationary phase cultures of Mycobacterium tuberculosis, H37Rv. The order of activity of 1.0 and 0.2 mg/l rifamycin against log phase cultures was RMP greater than RPE & C27 greater than RBU & C29 greater than C70. The order of activity of 1.0 and 0.4 mg/l, adjusted for stability of the rifamycin, against stationary phase cultures was F22 & RMP greater than RBU greater than RPE greater than C27 & C29 greater than C70. Viable counts were done during and after pulsed exposures of 6, 24 or 96 h to C29 and RMP. The curves were similar though C29 was less bactericidal and the lag period before recovery was 1-2 days longer. F22, having high bactericidal activity against stationary organisms and a long half-life, was considered likely to be the most effective sterilising drug.

Influence of simulated microgravity on the longevity of insect-cell culture

NASA Technical Reports Server (NTRS)

Cowger, N. L.; O'Connor, K. C.; Bivins, J. E.

1997-01-01

Simulated microgravity within the NASA High Aspect Rotating-Wall Vessel (HARV) provides a quiescent environment to culture fragile insect cells. In this vessel, the duration of stationary and death phase for cultures of Spodoptera frugiperda cells was greatly extended over that achieved in shaker-flask controls. For both HARV and control cultures, S. frugiperda cells grew to concentrations in excess of 1 x 10(7) viable cells ml-1 with viabilities greater than 90%. In the HARV, stationary phase was maintained 9-15 days in contrast to 4-5 days in the shaker flask. Furthermore, the rate of cell death was reduced in the HARV by a factor of 20-90 relative to the control culture and was characterized with a death rate constant of 0.01-0.02 day-1. Beginning in the stationary phase and continuing in the death phase, there was a significant decrease in population size in the HARV versus an increase in the shaker flask. This phenomenon could represent cell adaptation to simulated microgravity and/or a change in the ratio of apoptotic to necrotic cells. Differences observed in this research between the HARV and its control were attributed to a reduction in hydrodynamic forces in the microgravity vessel.

Anthracenyl polar embedded stationary phases with enhanced aromatic selectivity. Part II: A density functional theory study.

PubMed

Mignot, Mélanie; Schammé, Benjamin; Tognetti, Vincent; Joubert, Laurent; Cardinael, Pascal; Peulon-Agasse, Valérie

2017-10-13

New polar embedded aromatic stationary phases (mono- and trifunctional versions) that contain an amide-embedded group coupled with a tricyclic aromatic moiety were developed for chromatographic applications and described in the first paper of this series. These phases offered better separation performance for PAHs than for alkylbenzene homologues, and an enhanced ability to differentiate aromatic planarity to aromatic tridimensional conformation, especially for the trifunctional version and when using methanol instead of acetonitrile. In this second paper, a density functional theory study of the retention process is reported. In particular, it was shown that the selection of the suitable computational protocol allowed for describing rigorously the interactions that could take place, the solvent effects, and the structural changes for the monofunctional and the trifunctional versions. For the first time, the experimental data coupled with these DFT results provided a better understanding of the interaction mechanisms and highlighted the importance of the multimodal character of the designed stationary phases: alkyl spacers for interactions with hydrophobic solutes, amide embedded groups for dipole-dipole and hydrogen-bond interactions, and aromatic terminal groups for π-π interactions. Copyright © 2017 Elsevier B.V. All rights reserved.

A phase angle based diagnostic scheme to planetary gear faults diagnostics under non-stationary operational conditions

NASA Astrophysics Data System (ADS)

Feng, Ke; Wang, Kesheng; Ni, Qing; Zuo, Ming J.; Wei, Dongdong

2017-11-01

Planetary gearbox is a critical component for rotating machinery. It is widely used in wind turbines, aerospace and transmission systems in heavy industry. Thus, it is important to monitor planetary gearboxes, especially for fault diagnostics, during its operational conditions. However, in practice, operational conditions of planetary gearbox are often characterized by variations of rotational speeds and loads, which may bring difficulties for fault diagnosis through the measured vibrations. In this paper, phase angle data extracted from measured planetary gearbox vibrations is used for fault detection under non-stationary operational conditions. Together with sample entropy, fault diagnosis on planetary gearbox is implemented. The proposed scheme is explained and demonstrated in both simulation and experimental studies. The scheme proves to be effective and features advantages on fault diagnosis of planetary gearboxes under non-stationary operational conditions.

Space shuttle: Longitudinal aerodynamic characteristics of low aspect ratio wing configurations in ground effect for a moving and stationary ground surface

NASA Technical Reports Server (NTRS)

Romere, P. O.; Chambliss, E. B.

1972-01-01

A 0.05-scale model of the NASA-MSC Orbiter 040A Configuration was tested. Test duration was approximately 80 hours during which the model was tested in and out of ground effect with a stationary and moving ground belt. Model height from ground plane surface was varied from one and one-half wing span to landing touchdown while angle of attack varied from -4 to 20 degrees. Eleven effectiveness and alternate configuration geometries were tested to insure complete analysis of low aspect ratio wing aircraft in the presence of ground effect. Test Mach number was approximately 0.067 with a corresponding dynamic pressure value of 6.5 psf.

Stationary Cycling and Children with Cerebral Palsy: Case Reports for Two Participants

ERIC Educational Resources Information Center

Siebert, Kara L.; DeMuth, Sharon K.; Knutson, Loretta M.; Fowler, Eileen G.

2010-01-01

These case reports describe a stationary cycling intervention and outcomes for two child participants (P1 and P2) with spastic diplegic cerebral palsy. Each child completed a 12-week, 30-session cycling intervention consisting of strengthening and cardiorespiratory fitness phases. P1 exhibited higher training intensities, particularly during the…

77 FR 24843 - Approval and Promulgation of Air Quality Implementation Plans; Virginia; Removal of...

Federal Register 2010, 2011, 2012, 2013, 2014

2012-04-26

... requirements for large stationary internal combustion engines under the NO X SIP Call. Transco Station 175 has...), large stationary internal combustion engines, and large cement kilns. The NO X SIP Call was challenged... internal combustion engines and large cement kilns. EPA approved Virginia's Phase I NO X SIP Call...

Bernoulli-Langevin Wind Speed Model for Simulation of Storm Events

NASA Astrophysics Data System (ADS)

Fürstenau, Norbert; Mittendorf, Monika

2016-12-01

We present a simple nonlinear dynamics Langevin model for predicting the instationary wind speed profile during storm events typically accompanying extreme low-pressure situations. It is based on a second-degree Bernoulli equation with δ-correlated Gaussian noise and may complement stationary stochastic wind models. Transition between increasing and decreasing wind speed and (quasi) stationary normal wind and storm states are induced by the sign change of the controlling time-dependent rate parameter k(t). This approach corresponds to the simplified nonlinear laser dynamics for the incoherent to coherent transition of light emission that can be understood by a phase transition analogy within equilibrium thermodynamics [H. Haken, Synergetics, 3rd ed., Springer, Berlin, Heidelberg, New York 1983/2004.]. Evidence for the nonlinear dynamics two-state approach is generated by fitting of two historical wind speed profiles (low-pressure situations "Xaver" and "Christian", 2013) taken from Meteorological Terminal Air Report weather data, with a logistic approximation (i.e. constant rate coefficients k) to the solution of our dynamical model using a sum of sigmoid functions. The analytical solution of our dynamical two-state Bernoulli equation as obtained with a sinusoidal rate ansatz k(t) of period T (=storm duration) exhibits reasonable agreement with the logistic fit to the empirical data. Noise parameter estimates of speed fluctuations are derived from empirical fit residuals and by means of a stationary solution of the corresponding Fokker-Planck equation. Numerical simulations with the Bernoulli-Langevin equation demonstrate the potential for stochastic wind speed profile modeling and predictive filtering under extreme storm events that is suggested for applications in anticipative air traffic management.

Cellulose tris-(3,5-dimethylphenylcarbamate)-based chiral stationary phase for the enantioseparation of drugs in supercritical fluid chromatography: comparison with HPLC.

PubMed

Kalíková, Květa; Martínková, Monika; Schmid, Martin G; Tesařová, Eva

2018-03-01

A cellulose tris-(3,5-dimethylphenylcarbamate)-based chiral stationary phase was studied as a tool for the enantioselective separation of 21 selected analytes with different pharmaceutical and physicochemical properties. The enantioseparations were performed using supercritical fluid chromatography. The effect of the mobile phase composition was studied. Four different additives (diethylamine, triethylamine, isopropylamine, and trifluoroacetic acid) and isopropylamine combined with trifluoroacetic acid were tested and their influence on enantioseparation was compared. The influence of two different mobile phase co-solvents (methanol and propan-2-ol) combined with all the additives was also evaluated. The best mobile phase compositions for the separation of the majority of enantiomers were CO 2 /methanol/isopropylamine 80:20:0.1 v/v/v or CO 2 /propan-2-ol/isopropylamine/trifluoroacetic acid 80:20:0.05:0.05 v/v/v/v. The best results were obtained from the group of basic β-blockers. A high-performance liquid chromatography separation system composed of the same stationary phase and mobile phase of similar properties prepared as a mixture of hexane/propan-2-ol/additive 80:20:0.1 v/v/v was considered for comparison. Supercritical fluid chromatography was found to yield better results, i.e. better enantioresolution for shorter analysis times than high-performance liquid chromatography. However, examples of enantiomers better resolved under the optimized conditions in high-performance liquid chromatography were also found. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Characterization of Ascentis RP-Amide column: Lipophilicity measurement and linear solvation energy relationships.

PubMed

Benhaim, Deborah; Grushka, Eli

2010-01-01

This study investigates lipophilicity determination by chromatographic measurements using the polar embedded Ascentis RP-Amide stationary phase. As a new generation of amide-functionalized silica stationary phase, the Ascentis RP-Amide column is evaluated as a possible substitution to the n-octanol/water partitioning system for lipophilicity measurements. For this evaluation, extrapolated retention factors, log k'w, of a set of diverse compounds were determined using different methanol contents in the mobile phase. The use of n-octanol enriched mobile phase enhances the relationship between the slope (S) of the extrapolation lines and the extrapolated log k'w (the intercept of the extrapolation),as well as the correlation between log P values and the extrapolated log k'w (1:1 correlation, r2 = 0.966).In addition, the use of isocratic retention factors, at 40% methanol in the mobile phase, provides a rapid tool for lipophilicity determination. The intermolecular interactions that contribute to the retention process in the Ascentis RP-Amide phase are characterized using the solvation parameter model of Abraham.The LSER system constants for the column are very similar to the LSER constants of the n-octanol/water extraction system. Tanaka radar plots are used for quick visual comparison of the system constants of the Ascentis RP-Amide column and the n-octanol/water extraction system. The results all indicate that the Ascentis RP-Amide stationary phase can provide reliable lipophilic data. Copyright 2009 Elsevier B.V. All rights reserved.

High-performance liquid chromatography study of the enantiomer separation of chrysanthemic acid and its analogous compounds on a terguride-based stationary phase.

PubMed

Dondi, M; Flieger, M; Olsovska, J; Polcaro, C M; Sinibaldi, M

1999-10-29

The direct enantioseparation of chrysanthemic acid [2,2-dimethyl-3-(2-methylpropenyl)-cyclopropanecarboxylic acid] and its halogen-substituted analogues was systematically studied by HPLC using a terguride-based chiral stationary phase in combination with a UV diode array and chiroptical detectors. Isomers with (1R) configuration always eluted before those with (IS) configuration. The elution sequence of cis- and trans-isomers was strongly affected by mobile phase pH, whereas the enantioselectivity remained the same. Conditions for the separation of all the enantiomers were also examined. This method was used for monitor the hydrolytic degradation products of Cyfluthrin (Baythroid) in soil under laboratory conditions.

Poly(butylene terephthalate) based novel achiral stationary phase investigated under supercritical fluid chromatography conditions.

PubMed

Nagai, Kanji; Shibata, Tohru; Shinkura, Satoshi; Ohnishi, Atsushi

2018-05-11

Poly(butylene terephthalate) based novel stationary phase (SP), composed of planar aromatic phenyl group together with ester group monomer units, was designed for supercritical fluid chromatography (SFC) use. As expected from its structure, this phase shows planarity recognition of isomeric aromatics and closely similar compounds. Interestingly, for most analytes, the retention behavior of this SP is significantly distinct from that of the 2-ethylpyridine based SPs which is among the most well-known SFC dedicated phases. Although the poly(butylene terephthalate) is coated on silica gel, the performance of the column did not change by using extended range modifiers such as THF, dichloromethane or ethyl acetate and column robustness was confirmed by cycle durability testing. Copyright © 2018 The Authors. Published by Elsevier B.V. All rights reserved.

An approximate stationary solution for multi-allele neutral diffusion with low mutation rates.

PubMed

Burden, Conrad J; Tang, Yurong

2016-12-01

We address the problem of determining the stationary distribution of the multi-allelic, neutral-evolution Wright-Fisher model in the diffusion limit. A full solution to this problem for an arbitrary K×K mutation rate matrix involves solving for the stationary solution of a forward Kolmogorov equation over a (K-1)-dimensional simplex, and remains intractable. In most practical situations mutations rates are slow on the scale of the diffusion limit and the solution is heavily concentrated on the corners and edges of the simplex. In this paper we present a practical approximate solution for slow mutation rates in the form of a set of line densities along the edges of the simplex. The method of solution relies on parameterising the general non-reversible rate matrix as the sum of a reversible part and a set of (K-1)(K-2)/2 independent terms corresponding to fluxes of probability along closed paths around faces of the simplex. The solution is potentially a first step in estimating non-reversible evolutionary rate matrices from observed allele frequency spectra. Copyright © 2016 Elsevier Inc. All rights reserved.

Bacteriophage T4 Infection of Stationary Phase E. coli: Life after Log from a Phage Perspective

PubMed Central

Bryan, Daniel; El-Shibiny, Ayman; Hobbs, Zack; Porter, Jillian; Kutter, Elizabeth M.

2016-01-01

Virtually all studies of phage infections investigate bacteria growing exponentially in rich media. In nature, however, phages largely encounter non-growing cells. Bacteria entering stationary phase often activate well-studied stress defense mechanisms that drastically alter the cell, facilitating its long-term survival. An understanding of phage-host interactions in such conditions is of major importance from both an ecological and therapeutic standpoint. Here, we show that bacteriophage T4 can efficiently bind to, infect and kill E. coli in stationary phase, both in the presence and absence of a functional stationary-phase sigma factor, and explore the response of T4-infected stationary phase cells to the addition of fresh nutrients 5 or 24 h after that infection. An unexpected new mode of response has been identified. “Hibernation” mode is a persistent but reversible dormant state in which the infected cells make at least some phage enzymes, but halt phage development until appropriate nutrients become available before producing phage particles. Our evidence indicates that the block in hibernation mode occurs after the middle-mode stage of phage development; host DNA breakdown and the incorporation of the released nucleotides into phage DNA indicate that the enzymes of the nucleotide synthesizing complex, under middle-mode control, have been made and assembled into a functional state. Once fresh glucose and amino acids become available, the standard lytic infection process rapidly resumes and concentrations of up to 1011 progeny phage (an average of about 40 phage per initially present cell) are produced. All evidence is consistent with the hibernation-mode control point lying between middle mode and late mode T4 gene expression. We have also observed a “scavenger” response, where the infecting phage takes advantage of whatever few nutrients are available to produce small quantities of progeny within 2 to 5 h after infection. The scavenger response seems able to produce no more than an average of one phage per originally available cell, and few if any further progeny are produced by cells in this mode even if fresh nutrients are made available later. PMID:27660625

Evaluation of the phase ratio for three C18 high performance liquid chromatographic columns.

PubMed

Caiali, Edvin; David, Victor; Aboul-Enein, Hassan Y; Moldoveanu, Serban C

2016-02-26

For a chromatographic column, phase ratio Φ is defined as the ratio between the volume of the stationary phase Vst and the void volume of the column V0, and it is an important parameter characterizing the HPLC process. Although apparently simple, the evaluation of Φ presents difficulties because there is no sharp boundary between the mobile phase and the stationary phase. In addition, the boundary depends not only on the nature of the stationary phase, but also on the composition of the mobile phase. In spite of its importance, phase ratio is seldom reported for commercially available HPLC columns and the data typically provided by the vendors about the columns do not provide key information that would allow the calculation of Φ based on Vst and V0 values. A different procedure for the evaluation of Φ is based on the following formula: log k'j=a log Kow,j+log Φ, where k'j is the retention factor for a compound j that must be a hydrocarbon, Kow,j is the octanol/water partition coefficient, and a is a proportionality constant. Present study describes the experimental evaluation of Φ based on the measurement of k'j for the compounds in the homologous series between benzene and butylbenzene for three C18 columns: Gemini C18, Luna C18 both with 5 μm particles, and a Chromolith Performance RP-18. The evaluation was performed for two mobile phase systems at different proportions of methanol/water and acetonitrile/water. The octanol/water partition coefficients were obtained from the literature. The results obtained in the study provide further support for the new procedure for the evaluation of phase ratio. Copyright © 2016 Elsevier B.V. All rights reserved.

Surface charge fine tuning of reversed-phase/weak anion-exchange type mixed-mode stationary phases for milder elution conditions.

PubMed

Zimmermann, Aleksandra; Horak, Jeannie; Sánchez-Muñoz, Orlando L; Lämmerhofer, Michael

2015-08-28

A series of new mixed-mode reversed-phase/weak anion-exchange (RP/WAX) phases have been synthesized by immobilization of N-undecenyl-3-α-aminotropane onto thiol-modified silica gel by thiol-ene click chemistry and subsequent introduction of acidic thiol-endcapping functionalities of different type and surface densities. Click chemistry allowed to adjust a controlled surface concentration of the RP/WAX ligand in such a way that a sufficient quantity of residual thiols remained unmodified which have been capped by thiol click with either 3-butenoic acid or allylsulfonic acid as co-ligands. In another embodiment, performic acid oxidation of N-undecenyl-3-α-aminotropane-derivatized thiol-modified silica gave a RP/WAX phase with high density of sulfonic acid end-capping groups. ζ-Potential determinations confirmed the fine-tuned pI of these mixed-mode stationary phases which was shifted from 9.5 to 8.2, 7.8, and 6.5 with 3-butenoic acid and allylsulfonic acid end-capping as well as performic acid oxidation. For acidic solutes, the co-ionic endcapping leads to strongly reduced retention times and clearly allowed elution of these analytes under lower ionic strength thus milder elution conditions. In spite of the acidic endcapping, the new mixed-mode phases maintained their hydrophobic and anion-exchange selectivity as well as their multimodal nature featuring RP and HILIC elution domains at acetonitrile percentages below and above 50%, respectively. Column classification by principal component analysis of an extended retention map in comparison to a set of polar commercial and in-house synthesized stationary phases confirmed complementarity of the new mixed-mode phases with respect to HILIC, polar RP, amino and commercial mixed-mode phases. Copyright © 2015 Elsevier B.V. All rights reserved.

SlyD-dependent nickel delivery limits maturation of [NiFe]-hydrogenases in late-stationary phase Escherichia coli cells.

PubMed

Pinske, Constanze; Sargent, Frank; Sawers, R Gary

2015-04-01

Fermentatively growing Escherichia coli cells have three active [NiFe]-hydrogenases (Hyd), two of which, Hyd-1 and Hyd-2, contribute to H2 oxidation while Hyd-3 couples formate oxidation to H2 evolution. Biosynthesis of all Hyd involves the insertion of a Fe(CN)2CO group and a subsequent insertion of nickel ions through the HypA/HybF, HypB and SlyD proteins. With high nickel concentrations the presence of none of these proteins is required, but under normal growth conditions and during late stationary growth SlyD is important for hydrogenase activities. The slyD mutation reduced H2 production during exponential phase growth by about 50%. Assaying stationary phase grown cells for the coupling of Hyd activity to the respiratory chain or formate-dependent H2 evolution showed that SlyD is essential for both H2 evolution and H2 oxidation. Although introduction of plasmid-coded slyD resulted in an overall decrease of Hyd-2 polypeptides in slyD and hypA slyD mutants, processing and dye-reducing activity of the Hyd-2 enzyme was nevertheless restored. Similarly, introduction of the slyD plasmid restored only some H2 evolution in the slyD mutant while Hyd-3 polypeptides and dye-reducing activity were fully restored. Taken together, these results indicate an essential role for SlyD in the generation of the fully cofactor-equipped hydrogenase large subunits in the stationary phase where the level of each Hyd enzyme is finely tuned by SlyD for optimal enzyme activity.

An efficient implementation of 3D high-resolution imaging for large-scale seismic data with GPU/CPU heterogeneous parallel computing

NASA Astrophysics Data System (ADS)

Xu, Jincheng; Liu, Wei; Wang, Jin; Liu, Linong; Zhang, Jianfeng

2018-02-01

De-absorption pre-stack time migration (QPSTM) compensates for the absorption and dispersion of seismic waves by introducing an effective Q parameter, thereby making it an effective tool for 3D, high-resolution imaging of seismic data. Although the optimal aperture obtained via stationary-phase migration reduces the computational cost of 3D QPSTM and yields 3D stationary-phase QPSTM, the associated computational efficiency is still the main problem in the processing of 3D, high-resolution images for real large-scale seismic data. In the current paper, we proposed a division method for large-scale, 3D seismic data to optimize the performance of stationary-phase QPSTM on clusters of graphics processing units (GPU). Then, we designed an imaging point parallel strategy to achieve an optimal parallel computing performance. Afterward, we adopted an asynchronous double buffering scheme for multi-stream to perform the GPU/CPU parallel computing. Moreover, several key optimization strategies of computation and storage based on the compute unified device architecture (CUDA) were adopted to accelerate the 3D stationary-phase QPSTM algorithm. Compared with the initial GPU code, the implementation of the key optimization steps, including thread optimization, shared memory optimization, register optimization and special function units (SFU), greatly improved the efficiency. A numerical example employing real large-scale, 3D seismic data showed that our scheme is nearly 80 times faster than the CPU-QPSTM algorithm. Our GPU/CPU heterogeneous parallel computing framework significant reduces the computational cost and facilitates 3D high-resolution imaging for large-scale seismic data.

The suitability of DEAE-Cl active groups on customized poly(GMA-co-EDMA) continuous stationary phase for fast enzyme-free isolation of plasmid DNA.

PubMed

Danquah, Michael K; Forde, Gareth M

2007-06-15

The creation of a commercially viable and a large-scale purification process for plasmid DNA (pDNA) production requires a whole-systems continuous or semi-continuous purification strategy employing optimised stationary adsorption phase(s) without the use of expensive and toxic chemicals, avian/bovine-derived enzymes and several built-in unit processes, thus affecting overall plasmid recovery, processing time and economics. Continuous stationary phases are known to offer fast separation due to their large pore diameter making large molecule pDNA easily accessible with limited mass transfer resistance even at high flow rates. A monolithic stationary sorbent was synthesised via free radical liquid porogenic polymerisation of ethylene glycol dimethacrylate (EDMA) and glycidyl methacrylate (GMA) with surface and pore characteristics tailored specifically for plasmid binding, retention and elution. The polymer was functionalised with an amine active group for anion-exchange purification of pDNA from cleared lysate obtained from E. coli DH5alpha-pUC19 pellets in RNase/protease-free process. Characterization of the resin showed a unique porous material with 70% of the pores sizes above 300 nm. The final product isolated from anion-exchange purification in only 5 min was pure and homogenous supercoiled pDNA with no gDNA, RNA and protein contamination as confirmed with DNA electrophoresis, restriction analysis and SDS page. The resin showed a maximum binding capacity of 15.2 mg/mL and this capacity persisted after several applications of the resin. This technique is cGMP compatible and commercially viable for rapid isolation of pDNA.

Scattering of Internal Tides by Irregular Bathymetry of Large Extent

NASA Astrophysics Data System (ADS)

Mei, C.

2014-12-01

We present an analytic theory of scattering of tide-generated internal gravity waves in a continuously stratified ocean with a randomly rough seabed. Based on the linearized approximation, the idealized case of constant mean sea depth and Brunt-Vaisala frequency is considered. The depth fluctuation is assumed to be a stationary random function of space characterized by small amplitude and correlation length comparable to the typical wavelength. For both one- and two-dimensional topography the effects of scattering on wave phase over long distances are derived explicitly by the method of multiple scales. For one-dimensional topography, numerical results are compared with Buhler-& Holmes-Cerfon(2011) computed by the method of characteristics. For two-dimensional topography, new results are presented for both statistically isotropic and anisotropic cases. In thi talk we shall apply the perturbation technique of multiple scales to treat analytically the random scattering of internal tides by gently sloped bathymetric irregularities.The basic assumptions are: incompressible fluid, infinitestimal wave amplitudes, constant Brunt-Vaisala frequency, and constant mean depth. In addition, the depth disorder is assumed to be a stationary random function of space with zero mean and small root-mean-square amplitude. The correlation length can be comparable in order of magnitude as the dominant wavelength. Both one- and two-dimensional disorder will be considered. Physical effects of random scattering on the mean wave phase i.e., spatial attenuation and wavenumber shift will be calculated and discussed for one mode of incident wave. For two dimensional topographies, statistically isotropic and anisotropic examples will be presented.

[Systematic evaluation of retention behavior of carbohydrates in hydrophilic interaction liquid chromatography].

PubMed

Fu, Qing; Wang, Jun; Liang, Tu; Xu, Xiaoyong; Jin, Yu

2013-11-01

A systematic evaluation of retention behavior of carbohydrates in hydrophilic interaction liquid chromatography (HILIC) was performed. The influences of mobile phase, stationary phase and buffer salt on the retention of carbohydrates were investigated. According to the results, the retention time of carbohydrates decreased as the proportion of acetonitrile in mobile phase decreased. Increased time of carbohydrates was observed as the concentration of buffer salt in mobile phase increased. The retention behavior of carbohydrates was also affected by organic solvent and HILIC stationary phase. Furthermore, an appropriate retention equation was used in HILIC mode. The retention equation lnk = a + blnC(B) + cC(B) could quantitatively describe the retention factors of carbohydrates of plant origin with good accuracy: the relative error of the predicted time to actual time was less than 0.3%. The evaluation results could provide guidance for carbohydrates to optimize the experimental conditions in HILIC method development especially for carbohydrate separation

Incorporation of ionic liquid into porous polymer monoliths to enhance the separation of small molecules in reversed-phase high-performance liquid chromatography.

PubMed

Wang, Jiafei; Bai, Ligai; Wei, Zhen; Qin, Junxiao; Ma, Yamin; Liu, Haiyan

2015-06-01

An ionic liquid was incorporated into the porous polymer monoliths to afford stationary phases with enhanced chromatographic performance for small molecules in reversed-phase high-performance liquid chromatography. The effect of the ionic liquid in the polymerization mixture on the performance of the monoliths was studied in detail. While monoliths without ionic liquid exhibited poor resolution and low efficiency, the addition of ionic liquid to the polymerization mixture provides highly increased resolution and high efficiency. The chromatographic performances of the monoliths were demonstrated by the separations of various small molecules including aromatic hydrocarbons, isomers, and homologues using a binary polar mobile phase. The present column efficiency reached 27 000 plates/m, which showed that the ionic liquid monoliths are alternative stationary phases in the separation of small molecules by high-performance liquid chromatography. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Prethermal Phases of Matter Protected by Time-Translation Symmetry

NASA Astrophysics Data System (ADS)

Else, Dominic V.; Bauer, Bela; Nayak, Chetan

2017-01-01

In a periodically driven (Floquet) system, there is the possibility for new phases of matter, not present in stationary systems, protected by discrete time-translation symmetry. This includes topological phases protected in part by time-translation symmetry, as well as phases distinguished by the spontaneous breaking of this symmetry, dubbed "Floquet time crystals." We show that such phases of matter can exist in the prethermal regime of periodically driven systems, which exists generically for sufficiently large drive frequency, thereby eliminating the need for integrability or strong quenched disorder, which limited previous constructions. We prove a theorem that states that such a prethermal regime persists until times that are nearly exponentially long in the ratio of certain couplings to the drive frequency. By similar techniques, we can also construct stationary systems that spontaneously break continuous time-translation symmetry. Furthermore, we argue that for driven systems coupled to a cold bath, the prethermal regime could potentially persist to infinite time.

Lack of synchronization between iron uptake and cell growth leads to iron overload in Saccharomyces cerevisiae during post-exponential growth modes

PubMed Central

Park, Jinkyu; McCormick, Sean P.; Chakrabarti, Mrinmoy; Lindahl, Paul A.

2014-01-01

Fermenting cells growing exponentially on rich (YPAD) medium transitioned to a slow-growing state as glucose levels declined and their metabolism shifted to respiration. During exponential growth, Fe import and cell growth rates were matched, affording an approximately invariant cellular Fe concentration. During the transitionary period, the high-affinity Fe import rate declined slower than the cell growth rate declined, causing Fe to accumulate, initially as FeIII oxyhydroxide nanoparticles but eventually as mitochondrial and vacuolar Fe. Once in slow-growth mode, Fe import and cell growth rates were again matched, and the cellular Fe concentration was again approximately invariant. Fermenting cells grown on minimal medium (MM) grew more slowly during exponential phase and transitioned to a true stationary state as glucose levels declined. The Fe concentration of MM cells that just entered stationary state was similar to that of YPAD cells, but MM cells continued to accumulate Fe in stationary state. Fe initially accumulated as nanoparticles and high-spin FeII species, but vacuolar FeIII also eventually accumulated. Surprisingly, Fe-packed 5-day-old MM cells suffered no more ROS damage than younger cells, suggesting that Fe concentration alone does not accurately predict the extent of ROS damage. The mode and rate of growth at the time of harvesting dramatically affected cellular Fe content. A mathematical model of Fe metabolism in a growing cell was developed. The model included Fe import via a regulated high-affinity pathway and an unregulated low-affinity pathway. Fe import from the cytosol into vacuoles and mitochondria, and nanoparticle formation were also included. The model captured essential trafficking behavior, demonstrating that cells regulate Fe import in accordance with their overall growth rate and that they misregulate Fe import when nanoparticles accumulate. The lack of regulation of Fe in yeast is perhaps unique compared to the tight regulation of other cellular metabolites. This phenomenon likely derives from the unique chemistry associated with Fe nanoparticle formation. PMID:24344915

Epidemic Dynamics in Open Quantum Spin Systems

NASA Astrophysics Data System (ADS)

Pérez-Espigares, Carlos; Marcuzzi, Matteo; Gutiérrez, Ricardo; Lesanovsky, Igor

2017-10-01

We explore the nonequilibrium evolution and stationary states of an open many-body system that displays epidemic spreading dynamics in a classical and a quantum regime. Our study is motivated by recent experiments conducted in strongly interacting gases of highly excited Rydberg atoms where the facilitated excitation of Rydberg states competes with radiative decay. These systems approximately implement open quantum versions of models for population dynamics or disease spreading where species can be in a healthy, infected or immune state. We show that in a two-dimensional lattice, depending on the dominance of either classical or quantum effects, the system may display a different kind of nonequilibrium phase transition. We moreover discuss the observability of our findings in laser driven Rydberg gases with particular focus on the role of long-range interactions.

Convective fluid flows in a horizontal channel with evaporation: analytical and experimental investigations

NASA Astrophysics Data System (ADS)

Lyulin, Y. V.; Rezanova, E. V.

2017-11-01

Heat- and mass transfer processes in a two-layer system of the liquid and gas are studied with respect to evaporation at interface. The stationary convective flows of two immiscible viscous incompressible fluids filling an infinite channel and being under action of the transverse gravitation field are studied analytically. Mathematical modeling of the flows is carried out with the help of the Navier-Stokes equations in Boussinesq approximation. The Dufour and Soret effects are taken into consideration in the gas-vapor phase. In the two-dimensional case the exact solutions of special type are constructed under condition of a given specific gas flow rate. Comparison of the analytical results with results of the physical experiments with the “liquid-gas” system like “ethanol-air” are presented.

Ocean acoustic interferometry.

PubMed

Brooks, Laura A; Gerstoft, Peter

2007-06-01

Ocean acoustic interferometry refers to an approach whereby signals recorded from a line of sources are used to infer the Green's function between two receivers. An approximation of the time domain Green's function is obtained by summing, over all source positions (stacking), the cross-correlations between the receivers. Within this paper a stationary phase argument is used to describe the relationship between the stacked cross-correlations from a line of vertical sources, located in the same vertical plane as two receivers, and the Green's function between the receivers. Theory and simulations demonstrate the approach and are in agreement with those of a modal based approach presented by others. Results indicate that the stacked cross-correlations can be directly related to the shaded Green's function, so long as the modal continuum of any sediment layers is negligible.

Wave Field Synthesis of moving sources with arbitrary trajectory and velocity profile.

PubMed

Firtha, Gergely; Fiala, Péter

2017-08-01

The sound field synthesis of moving sound sources is of great importance when dynamic virtual sound scenes are to be reconstructed. Previous solutions considered only virtual sources moving uniformly along a straight trajectory, synthesized employing a linear loudspeaker array. This article presents the synthesis of point sources following an arbitrary trajectory. Under high-frequency assumptions 2.5D Wave Field Synthesis driving functions are derived for arbitrary shaped secondary source contours by adapting the stationary phase approximation to the dynamic description of sources in motion. It is explained how a referencing function should be chosen in order to optimize the amplitude of synthesis on an arbitrary receiver curve. Finally, a finite difference implementation scheme is considered, making the presented approach suitable for real-time applications.

Investigating Marine Dissolved Organic Matter Fluorescence Transformations with Organic Geochemical Proxies in a Growth and Degradation Experiment using Amino Acids, Amino Sugars, and Phenols

NASA Astrophysics Data System (ADS)

Shields, M. R.; Bianchi, T. S.; Osburn, C. L.; Kinsey, J. D.; Ziervogel, K.; Schnetzer, A.

2017-12-01

The origin and mechanisms driving the formation of fluorescent dissolved organic matter (FDOM) in the open ocean remain unclear. Although recent studies have attempted to deconvolve the chemical composition and source of marine FDOM, these studies have been qualitative in nature. Here, we investigate these transformations using a more quantitative biomarker approach in a controlled growth and degradation experiment. In this experiment, a natural assemblage of phytoplankton was collected off the coast of North Carolina and incubated within roller bottles containing 0.2 µm-filtered North Atlantic surface water amended with f/2 nutrients. Samples were collected at the beginning (day 0), during exponential growth (day 13), stationary (day 20), and degradation (day 62) phases of the phytoplankton incubation. Amino acids, amino sugars, and phenolic compounds of the dissolved (DOM) were measured in conjunction with enzyme assays and bacterial counts to track shifts in OM quality as FDOM formed and was then transformed throughout the experiment. The results from the chemical analyses showed that the OM composition changed significantly from the initial and exponential phases to the stationary and degradation phases of the experiment. The percentage of aromatic amino acids to the total amino acid pool increased significantly during the exponential phase of phytoplankton growth, but then decreased significantly during the stationary and degradation phases. This increase was positively correlated to the fractional contribution of the protein-like peak in fluorescence to the total FDOM fluorescence. An increase in the concentration of amino acid degradation products during the stationary and degradation phases suggests that compositional changes in OM were driven by microbial transformation. This was further supported by a concurrent increase in total enzyme activity and increase in "humic-like" components of the FDOM. These findings link the properties and formation of FDOM to the overall quality and diagenetic state of marine OM and to the marine carbon and nitrogen cycles.

The Development of Novel Nanomaterials for Separation Science

NASA Astrophysics Data System (ADS)

Zewe, Joseph William

Separation efficiency is inversely proportional to the diameter of the particles of the stationary phase. Accordingly, a major aim of current separations research is focused on the reduction of both the diameter and particle-to-particle size variation of sorbent materials utilized as stationary phases. Herein, novel methods for the fabrication and application of various nanoscale stationary phases are described. Electrospinning is a simple and cost-effective method of generating nanofibers; here both polymeric and carbon electrospun nanofibers are applied as sorbent materials. Carbon nanofibers are of particular interest; graphite and glassy carbon are widely utilized in separation science due to their chemical and mechanical stability and unique selectivity. Electrospun carbon nanofibers have proven to be ideal for use as an extractive phase for solid phase microextraction (SPME) and have been successfully coupled to both gas and liquid chromatography. The high surface area nanofibrous mat provides extraction efficiencies for both polar and nonpolar compounds that range from 2-8 times greater than those attainable using currently available commercial SPME fibers. The electrospun nanofibrous SPME phases proved to be very stable when immersed in a range of solvents, demonstrating increased stability relative to conventional liquid SPME coatings. The chemical and mechanical stability of the electrospun carbon nanofiber SPME phases expands the range of compounds that are applicable to SPME while extending the lifetime of the SPME fibers. Molecularly imprinted (MI) electrospun polymeric and carbon nanofibers were also generated using the template molecule dibutyl butyl phosphonate (DBBP), a surrogate for chemical warfare agents. Nicotine was also used as a template molecule. The MI-nanofibers imprinted with DBBP were applied as an adsorbent for SPME. The MI-SPME fibers preferentially adsorbed the DBBP template molecule relative to the non-imprinted SPME fibers, demonstrating that imprinted surfaces containing analyte-specific recognition sites can be produced. MI-nicotine electrospun nanofibers were also studied as a solid phase extraction (SPE) adsorbent for the extraction of nicotine from water. The MI-nanofibers showed a greater extraction efficiency for nicotine relative to their non-imprinted counterparts. Electrospun nanofibers have proven to be effective stationary phases in ultra-thin layer chromatography (UTLC), giving more efficient separations in shorter analysis times than traditional particle-based stationary phases. This technology was further enhanced by aligning the nanofibrous mats in a single direction. Aligned electrospun UTLC (AE-UTLC) devices showed improved performance relative to non-aligned electrospun UTLC phases, demonstrating higher separation efficiency and reduced times of analysis. All currently utilized carbon sorbents, including the carbon nanofibers described in this work, possess at least two different surface sites for interaction with solutes, namely basal-plane and edge-plane sites. It is predicted that a more homogenous carbon surface, consisting entirely of either all-basal or all-edge plane sites, would produce a separation with a significant improvement in chromatographic efficiency. Progress toward homogenous carbon phases and their application and sorption behavior are also discussed.

pi-Selective stationary phases: (II) Adsorption behavior of substituted aromatic compounds on n-alkyl-phenyl stationary phases

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gritti, Fabrice; Guiochon, Georges A; Mayfield, Kirsty

2010-01-01

The frontal analysis method was used to measure the adsorption isotherms of phenol, 4-chlorophenol, p-cresol, 4-methoxyphenol and caffeine on a series of columns packed with home-made alkyl-phenyl bonded silica particles. These ligands consist of a phenyl ring tethered to the silica support via a carbon chain of length ranging from 0 to 4 atoms. The adsorption isotherm models that fit best to the data account for solute-solute interactions that are likely caused by p-p interactions occurring between aromatic compounds and the phenyl group of the ligand. These interactions are the dominant factor responsible for the separation of low molecular weightmore » aromatic compounds on these phenyl-type stationary phases. The saturation capacities depend on whether the spacer of the ligands have an even or an odd number of carbon atoms, with the even alkyl chain lengths having a greater saturation capacity than the odd alkyl chain lengths. The trends in the adsorption equilibrium constant are also significantly different for the even and the odd chain length ligands.« less

Low intensity infrared laser induces filamentation in Escherichia coli cells

NASA Astrophysics Data System (ADS)

Fonseca, A. S.; Presta, G. A.; Geller, M.; Paoli, F.

2011-10-01

Low intensity continuous wave and pulsed emission modes laser is used in treating many diseases and the resulting biostimulative effect on tissues has been described, yet the photobiological basis is not well understood. The aim of this wok was to evaluate, using bacterial filamentation assay, effects of laser on Escherichia coli cultures in exponential and stationary growth phase. E. coli cultures, proficient and deficient on DNA repair, in exponential and stationary growth phase, were exposed to low intensity infrared laser, aliquots were spread onto microscopic slides, stained by Gram method, visualized by optical microscopy, photographed and percentage of bacterial filamentation were determined. Low intensity infrared laser with therapeutic fluencies and different emission modes can induce bacterial filamentation in cultures of E. coli wild type, fpg/ mutM, endonuclease III and exonuclease III mutants in exponential and stationary growth phase. This study showed induction of bacterial, filamentation in E. coli cultures expose to low intensity infrared laser and attention to laser therapy protocols, which should take into account fluencies, wavelengths, tissue conditions, and genetic characteristics of cells before beginning treatment.

The incorporation of calix[6]arene and cyclodextrin derivatives into sol-gels for the preparation of stationary phases for gas chromatography.

PubMed

Delahousse, Guillaume; Peulon-Agasse, Valérie; Debray, Jean-Christophe; Vaccaro, Marie; Cravotto, Giancarlo; Jabin, Ivan; Cardinael, Pascal

2013-11-29

New polyethylene-glycol-based sol-gels containing cyclodextrin or calix[6]arene derivatives have been synthesized. An original method for sol-gel preparation and capillary column coating, which consumes smaller quantities of selectors and allows for control of their amounts in the stationary phase, is reported herein. The new stationary phases exhibited excellent column efficiencies over a large range of temperatures and thermal stability up to 280°C. The cyclodextrin derivative generally showed the best separation factors for aromatic positional isomers. The calix[6]arene derivative exhibited the best selectivity for the polychlorobiphenyl congeners and some polycyclic aromatic hydrocarbon isomers. The relationship between the structure and the chromatographic properties of the selectors is discussed. The tert-butyl groups on the upper rim of the calix[6]arene were found to possibly play an important role in the recognition of solutes. The incorporation of the cyclodextrin derivative into the sol-gel matrix did not affect its enantioselective recognition capabilities. Copyright © 2013 Elsevier B.V. All rights reserved.

Fabrication of powdery polymer aerogel as the stationary phase for high-resolution gas chromatographic separation.

PubMed

Zheng, Juan; Lu, Cuiming; Huang, Junlong; Chen, Luyi; Ni, Chuyi; Xie, Xintong; Zhu, Fang; Wu, Dingcai; Ouyang, Gangfeng

2018-08-15

Novel powdery polymer aerogel (PPA) prepared via the (micro)emulsion polymerization and the following hyper crosslinking reaction was fabricated as stationary phase of capillary column for the first time. Due to its powdery morphology, unique 3D nano-network structure, high surface area and good thermostability, the PPA-coated capillary column demonstrated high-resolution chromatographic separation towards nonpolar and weakly polar organic compounds, including benzene series, n-alkanes, ketone mixtures and trichlorobenzenes. Moreover, the reproducibility, quantitative analysis ability and thermostability of PPA-coated capillary column were also evaluated. The relative standard deviations for three replicate determinations of selected analytes were 0.02-0.11%, 0.12-0.26% and 1.2-3.6% for run-to-run, day-to-day and column-to-column analyses, respectively. The PPA demonstrated good thermostability, and the PPA-coated capillary column was proved to be heat-resistant (270 °C). The results of this study show PPA is an excellent candidate to be employed as stationary phase for gas chromatography capillary. Copyright © 2018 Elsevier B.V. All rights reserved.

Graphene-ZIF8 composite material as stationary phase for high-resolution gas chromatographic separations of aliphatic and aromatic isomers.

PubMed

Yang, Xiaohong; Li, Changxia; Qi, Meiling; Qu, Liangti

2016-08-19

This work presents the separation performance of graphene-ZIF8 (G-Z) composite material as stationary phase for capillary gas chromatography (GC). The G-Z stationary phase achieved high column efficiency of 5000 plates/m determined by n-dodecane (k=1.22) at 120°C and showed weakly polar nature. Importantly, it exhibited high selectivity and resolving capability for branched alkane isomers and aromatic positional isomers, showing clear advantages over the reported neat graphene and ZIF8. In addition, it attained high resolution for geometric cis-/trans-isomers. The G-Z column exhibited good column thermal stability up to 300°C and column repeatability with RSD values of retention times in the range of 0.01-0.19% for intra-day, 0.05-0.88% for inter-day and 0.66-5.6% for between-column, respectively, Moreover, the G-Z column was employed for the determination of minor impurity isomers in real reagent samples, which demonstrates its promising potential in GC applications. Copyright © 2016 Elsevier B.V. All rights reserved.

π-Extended triptycene-based material for capillary gas chromatographic separations.

PubMed

Yang, Yinhui; Wang, Qinsi; Qi, Meiling; Huang, Xuebin

2017-10-02

Triptycene-based materials feature favorable physicochemical properties and unique molecular recognition ability that offer good potential as stationary phases for capillary gas chromatography (GC). Herein, we report the investigation of utilizing a π-extended triptycene material (denoted as TQPP) for GC separations. As a result, the TQPP capillary column exhibited high column efficiency of 4030 plates m -1 and high-resolution performance for a wide range of analytes, especially structural and positional isomers. Interestingly, the TQPP stationary phase showed unique shape selectivity for alkanes isomers and preferential retention for analytes with halogen atoms and H-bonding nature mainly through their halogen-bonding and H-bonding interactions. In addition, the TQPP column had good repeatability and reproducibility with the RSD values of 0.02-0.34% for run-to-run, 0.09-0.80% for day-to-day and 1.4-5.2% for column-to-column, respectively, and favorable thermal stability up to 280 °C. This work demonstrates the promising future of triptycene-based materials as a new class of stationary phases for GC separations. Copyright © 2017 Elsevier B.V. All rights reserved.

On Maximal Hard-Core Thinnings of Stationary Particle Processes

NASA Astrophysics Data System (ADS)

Hirsch, Christian; Last, Günter

2018-02-01

The present paper studies existence and distributional uniqueness of subclasses of stationary hard-core particle systems arising as thinnings of stationary particle processes. These subclasses are defined by natural maximality criteria. We investigate two specific criteria, one related to the intensity of the hard-core particle process, the other one being a local optimality criterion on the level of realizations. In fact, the criteria are equivalent under suitable moment conditions. We show that stationary hard-core thinnings satisfying such criteria exist and are frequently distributionally unique. More precisely, distributional uniqueness holds in subcritical and barely supercritical regimes of continuum percolation. Additionally, based on the analysis of a specific example, we argue that fluctuations in grain sizes can play an important role for establishing distributional uniqueness at high intensities. Finally, we provide a family of algorithmically constructible approximations whose volume fractions are arbitrarily close to the maximum.

Adsorption behavior of the (+/-)-Tröger's base enantiomers in the phase system of a silica-based packing coated with amylose tri(3,5-dimethyl carbamate) and 2-propanol and molecular modeling interpretation.

PubMed

Mihlbachler, Kathleen; De Jesús, Marco A; Kaczmarski, Krzysztof; Sepaniak, Michael J; Seidel-Morgenstern, Andreas; Guiochon, Georges

2006-04-28

The binary adsorption isotherms of the enantiomers of Tröger's base in the phase system made of Chiral Technologies ChiralPak AD [a silica-based packing coated with amylose tri(3,5-dimethyl carbamate)] as the chiral stationary phase (CSP) and 2-propanol as the mobile phase were measured by the perturbation method. The more retained enantiomer exhibits a S-shaped adsorption isotherm with a clear inflection point, the concentration of the less retained enantiomer having practically no competitive influence on this isotherm: In the entire range of concentrations studied, dq2/dC1 approximately 0. By contrast, the less retained enantiomer has a Langmuir adsorption isotherm when pure. At constant mobile phase concentrations, however, its equilibrium concentration in the adsorbed phase increases with increasing concentration of the more retained enantiomer and dq1/dC2 > 0. This cooperative adsorption behavior, opposed to the classical competitive behavior, is exceedingly rare but was clearly demonstrated in this case. Two adsorption isotherm equations that account for these physical observations were derived. They are based on the formation of an adsorbed multi-layer, as suggested by the isotherm data. The excellent agreement between the experimental overloaded elution profiles of binary mixtures and the profiles calculated with the equilibrium-dispersive model validates this binary isotherm model. The adsorption energies calculated by molecular mechanics (MM) and by molecular dynamics (MD) indicate that the chiral recognition arising from the different interactions between the functional groups of the CSP and the molecules of the Tröger's base enantiomers are mainly driven by their Van der Waals interactions. The MD data suggest that the interactions of the (-)-Tröger's base with the CSP are more favored by 8+/-(5) kJ/mol than those of (+)-Tröger's base. This difference seems to be a contributing factor to the increased retention of the - enantiomer on this chromatographic system. The modeling of the data also indicates that both enantiomers can form high stoichiometry complexes while binding onto the stationary phase, in agreement with the results of the equilibrium isotherm studies.

Supramolecular separation mechanism of pentafluorophenyl column using ibuprofen and omeprazole as markers: LC-MS and simulation study.

PubMed

Hussain, Afzal; AlAjmi, Mohamed F; Ali, Imran

2018-06-01

The pentafluorophenyl (PFP) column is emerging as a new advancement in separation science to analyze a wide range of analytes and, thus, its separation mechanism at supramolecular level is significant. We developed a mechanism for the separation of ibuprofen and omeprazole using different combinations (ranging from 50:50 to 60:40) of water-acetonitrile containing 0.1% formic acid as the mobile phase. The column used was Waters Acquity UPLC HSS PFP (75 × 2.1 mm, 1.8 μm). The reverse order of elution was observed in different combinations of the mobile phases. The docking study indicated hydrogen bonding between ibuprofen and PFP stationary phase (binding energy was -11.30 kJ/mol). Separation at PFP stationary phase is controlled by hydrogen bonding along with π-π interactions. This stationary phase may be used to analyze both aromatic and aliphatic analytes. The developed mechanism will be useful to separate various analytes by considering the possible interactions, leading to saving of energy, time and money. In addition, this work will be highly useful in preparative chromatography where separation is the major problem at a large scale. Moreover, the developed LC-MS-QTOF method may be used to analyze ibuprofen and omeprazole in an unknown sample owing to the low value of detection limits. Copyright © 2018 John Wiley & Sons, Ltd.

Synthesis of monodisperse silica microspheres and modification with diazoresin for mixed-mode ultra high performance liquid chromatography separations.

PubMed

Cong, Hailin; Yu, Bing; Tian, Chao; Zhang, Shuai; Yuan, Hua

2017-11-01

Monodisperse silica particles with average diameters of 1.9-2.9 μm were synthesized by a modified Stöber method, in which tetraethyl orthosilicate was continuously supplied to the reaction mixture containing KCl electrolyte, water, ethanol, and ammonia. The obtained silica particles were modified by self-assembly with positively charged photosensitive diazoresin on the surface. After treatment with ultraviolet light, the ionic bonding between silica and diazoresin was converted into covalent bonding through a unique photochemistry reaction of diazoresin. Depending on the chemical structure of diazoresin and mobile phase composition, the diazoresin-modified silica stationary phase showed different separation mechanisms, including reversed phase and hydrophilic interactions. Therefore, a variety of baseline separation of benzene analogues and organic acids was achieved by using the diazoresin-modified silica particles as packing materials in ultra high performance liquid chromatography. According to the π-π interactional difference between carbon rings of fullerenes and benzene rings of diazoresin, C 60 and C 70 were also well separated by ultra-high performance liquid chromatography. Because it has a small size, the ∼2.5 μm monodisperse diazoresin-modified silica stationary phase shows ultra-high efficiency compared with the commercial C 18 -silica high-performance liquid chromatography stationary phase with average diameters of ∼5 μm. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Application of a Short Intracellular pH Method to Flow Cytometry for Determining Saccharomyces cerevisiae Vitality ▿

PubMed Central

Weigert, Claudia; Steffler, Fabian; Kurz, Tomas; Shellhammer, Thomas H.; Methner, Frank-Jürgen

2009-01-01

The measurement of yeast's intracellular pH (ICP) is a proven method for determining yeast vitality. Vitality describes the condition or health of viable cells as opposed to viability, which defines living versus dead cells. In contrast to fluorescence photometric measurements, which show only average ICP values of a population, flow cytometry allows the presentation of an ICP distribution. By examining six repeated propagations with three separate growth phases (lag, exponential, and stationary), the ICP method previously established for photometry was transferred successfully to flow cytometry by using the pH-dependent fluorescent probe 5,6-carboxyfluorescein. The correlation between the two methods was good (r2 = 0.898, n = 18). With both methods it is possible to track the course of growth phases. Although photometry did not yield significant differences between exponentially and stationary phases (P = 0.433), ICP via flow cytometry did (P = 0.012). Yeast in an exponential phase has a unimodal ICP distribution, reflective of a homogeneous population; however, yeast in a stationary phase displays a broader ICP distribution, and subpopulations could be defined by using the flow cytometry method. In conclusion, flow cytometry yielded specific evidence of the heterogeneity in vitality of a yeast population as measured via ICP. In contrast to photometry, flow cytometry increases information about the yeast population's vitality via a short measurement, which is suitable for routine analysis. PMID:19581482

Oxygen Consumption Rates of Bacteria under Nutrient-Limited Conditions

PubMed Central

Riedel, Timothy E.; Nealson, Kenneth H.; Finkel, Steven E.

2013-01-01

Many environments on Earth experience nutrient limitation and as a result have nongrowing or very slowly growing bacterial populations. To better understand bacterial respiration under environmentally relevant conditions, the effect of nutrient limitation on respiration rates of heterotrophic bacteria was measured. The oxygen consumption and population density of batch cultures of Escherichia coli K-12, Shewanella oneidensis MR-1, and Marinobacter aquaeolei VT8 were tracked for up to 200 days. The oxygen consumption per CFU (QO2) declined by more than 2 orders of magnitude for all three strains as they transitioned from nutrient-abundant log-phase growth to the nutrient-limited early stationary phase. The large reduction in QO2 from growth to stationary phase suggests that nutrient availability is an important factor in considering environmental respiration rates. Following the death phase, during the long-term stationary phase (LTSP), QO2 values of the surviving population increased with time and more cells were respiring than formed colonies. Within the respiring population, a subpopulation of highly respiring cells increased in abundance with time. Apparently, as cells enter LTSP, there is a viable but not culturable population whose bulk community and per cell respiration rates are dynamic. This result has a bearing on how minimal energy requirements are met, especially in nutrient-limited environments. The minimal QO2 rates support the extension of Kleiber's law to the mass of a bacterium (100-fg range). PMID:23770901

Growth phase-dependent control of R27 conjugation is mediated by the interplay between the plasmid-encoded regulatory circuit TrhR/TrhY-HtdA and the cAMP regulon.

PubMed

Gibert, Marta; Paytubi, Sonia; Beltrán, Sergi; Juárez, Antonio; Balsalobre, Carlos; Madrid, Cristina

2016-12-01

Plasmids of the incompatibility group HI1 (IncHI1) have been isolated from several Gram-negative pathogens and are associated with the spread of multidrug resistance. Their conjugation is tightly regulated and it is inhibited at temperatures higher than 30°C, indicating that conjugation occurs outside warm-blooded hosts. Using R27, the prototype of IncHI1 plasmids, we report that plasmid transfer efficiency in E. coli strongly depends on the physiological state of the donor cells. Conjugation frequency is high when cells are actively growing, dropping sharply when cells enter the stationary phase of growth. Accordingly, our transcriptomic assays show significant downregulation of numerous R27 genes during the stationary phase, including several tra (transfer) genes. Growth phase-dependent regulation of tra genes transcription is independent of H-NS, a silencer of horizontal gene transfer, and ppGpp and RpoS, regulators of the stationary phase, but highly dependent on the plasmid-encoded regulatory circuit TrhR/TrhY-HtdA. The metabolic sensor cAMP, whose synthesis is chromosomally encoded, is also involved in the growth phase regulation of R27 conjugation by modulating htdA expression. Our data suggest that the involvement of regulators encoded by both chromosome and plasmid are required for efficient physiological control of IncHI1 plasmid conjugation. © 2016 Society for Applied Microbiology and John Wiley & Sons Ltd.

The three-dimensional model for helical columns on type-J synchronous counter-current chromatography.

PubMed

Guan, Y H; van den Heuvel, Remco

2011-08-05

Unlike the existing 2-D pseudo-ring model for helical columns undergoing synchronous type-J planetary motion of counter-current chromatograph (CCC), the 3-D "helix" model developed in this work shows that there is a second normal force (i.e. the binormal force) applied virtually in the axial direction of the helical column. This force alternates in the two opposite directions and intensifies phase mixing with increasing the helix angle. On the contrary, the 2-D spiral column operated on the same CCC device lacks this third-dimensional mixing force. The (principal) normal force quantified by this "helix" model has been the same as that by the pseudo-ring model. With β>0.25, this normal centrifugal force has been one-directional and fluctuates cyclically. Different to the spiral column, this "helix" model shows that the centrifugal force (i.e. the hydrostatic force) does not contribute to stationary phase retention in the helical column. Between the popular helical columns and the emerging spiral columns for type-J synchronous CCC, this work has thus illustrated that the former is associated with better phase mixing yet poor retention for the stationary phase whereas the latter has potential for better retention for the stationary phase yet poor phase mixing. The methodology developed in this work may be regarded as a new platform for designing optimised CCC columns for analytical and engineering applications. Copyright © 2011 Elsevier B.V. All rights reserved.

Differential high pressure survival in stationary-phase Escherichia coli MG1655

NASA Astrophysics Data System (ADS)

Griffin, Patrick L.; Kish, Adrienne; Steele, Andrew; Hemley, Russell J.

2011-06-01

Hydrostatic pressure exerts a profound influence on nearly all facets of cellular structure and function with exposures to sufficiently high pressure leading to microbial inactivation. We report the first observation of a persistent, pressure-resistant subpopulation within stationary-phase samples of Escherichia coli MG1655, a mesophilic bacterium adapted to surface pressure. This high pressure-resistant subpopulation exhibits pressure survival ranging from 0.6 to 2.0 orders of magnitude greater survival than high pressure treatments at pressures of 225-400 MPa. We also examine some aspects of pressure treatment protocol that may influence the measurements of high pressure survival.

Retention Indices for Frequently Reported Compounds of Plant Essential Oils

NASA Astrophysics Data System (ADS)

Babushok, V. I.; Linstrom, P. J.; Zenkevich, I. G.

2011-12-01

Gas chromatographic retention indices were evaluated for 505 frequently reported plant essential oil components using a large retention index database. Retention data are presented for three types of commonly used stationary phases: dimethyl silicone (nonpolar), dimethyl silicone with 5% phenyl groups (slightly polar), and polyethylene glycol (polar) stationary phases. The evaluations are based on the treatment of multiple measurements with the number of data records ranging from about 5 to 800 per compound. Data analysis was limited to temperature programmed conditions. The data reported include the average and median values of retention index with standard deviations and confidence intervals.

Hierarchy of Supercurrents in Multicomponent Atomic Josephson Vortices

NASA Astrophysics Data System (ADS)

Kaurov, Vitaliy

2009-03-01

We show that a quasi-1D long atomic Josephson junction [1,2] containing a mixture of BECs can sustain multi-component Josephson vortices (mJV). A new exact soliton solution is given to describe a stationary mJV in the general N-component case. Depending on system parameters (scattering lengths, tunneling strengths, and chemical potentials) Josephson supercurrents of different components form a hierarchy according to their intensity and proximity to phase slip. By tuning the parameters it is possible to turn off or on particular currents using the JV -- dark soliton interconversion effect [1,2]. Inside the mJV different components may circulate either in the same or opposite directions resulting in bulk super-counter-flow in the latter case. The weak tunneling limit can be described by a modified Sine-Gordon model. An approximate solution for mJV propagating along the junction is found for the two-component case. The degeneracy of stationary mJV with respect to co-flow or counter-flow configurations is lifted by the uniform motion of mJV. Which configuration is energetically preferable depends on the interspecies scattering length. [1] V. M. Kaurov and A. B. Kuklov, Phys. Rev. A 71, 011601(R) (2005). [2] V. M. Kaurov and A. B. Kuklov, Phys. Rev. A 73, 013627 (2006).

Influence of the noise sources motion on the estimated Green's functions from ambient noise cross-correlations.

PubMed

Sabra, Karim G

2010-06-01

It has been demonstrated theoretically and experimentally that an estimate of the Green's function between two receivers can be obtained by cross-correlating acoustic (or elastic) ambient noise recorded at these two receivers. Coherent wavefronts emerge from the noise cross-correlation time function due to the accumulated contributions over time from noise sources whose propagation path pass through both receivers. Previous theoretical studies of the performance of this passive imaging technique have assumed that no relative motion between noise sources and receivers occurs. In this article, the influence of noise sources motion (e.g., aircraft or ship) on this passive imaging technique was investigated theoretically in free space, using a stationary phase approximation, for stationary receivers. The theoretical results were extended to more complex environments, in the high-frequency regime, using first-order expansions of the Green's function. Although sources motion typically degrades the performance of wideband coherent processing schemes, such as time-delay beamforming, it was found that the Green's function estimated from ambient noise cross-correlations are not expected to be significantly affected by the Doppler effect, even for supersonic sources. Numerical Monte-Carlo simulations were conducted to confirm these theoretical predictions for both cases of subsonic and supersonic moving sources.

Stationary swarming motion of active Brownian particles in parabolic external potential

NASA Astrophysics Data System (ADS)

Zhu, Wei Qiu; Deng, Mao Lin

2005-08-01

We investigate the stationary swarming motion of active Brownian particles in parabolic external potential and coupled to its mass center. Using Monte Carlo simulation we first show that the mass center approaches to rest after a sufficient long period of time. Thus, all the particles of a swarm have identical stationary motion relative to the mass center. Then the stationary probability density obtained by using the stochastic averaging method for quasi integrable Hamiltonian systems in our previous paper for the motion in 4-dimensional phase space of single active Brownian particle with Rayleigh friction model in parabolic potential is used to describe the relative stationary motion of each particle of the swarm and to obtain more probability densities including that for the total energy of the swarm. The analytical results are confirmed by comparing with those from simulation and also shown to be consistent with the existing deterministic exact steady-state solution.

Role and regulation of sigma S in general resistance conferred by low-shear simulated microgravity in Escherichia coli.

PubMed

Lynch, S V; Brodie, E L; Matin, A

2004-12-01

Life on Earth evolved in the presence of gravity, and thus it is of interest from the perspective of space exploration to determine if diminished gravity affects biological processes. Cultivation of Escherichia coli under low-shear simulated microgravity (SMG) conditions resulted in enhanced stress resistance in both exponential- and stationary-phase cells, making the latter superresistant. Given that microgravity of space and SMG also compromise human immune response, this phenomenon constitutes a potential threat to astronauts. As low-shear environments are encountered by pathogens on Earth as well, SMG-conferred resistance is also relevant to controlling infectious disease on this planet. The SMG effect resembles the general stress response on Earth, which makes bacteria resistant to multiple stresses; this response is sigma s dependent, irrespective of the growth phase. However, SMG-induced increased resistance was dependent on sigma s only in stationary phase, being independent of this sigma factor in exponential phase. sigma s concentration was some 30% lower in exponential-phase SMG cells than in normal gravity cells but was twofold higher in stationary-phase SMG cells. While SMG affected sigma s synthesis at all levels of control, the main reasons for the differential effect of this gravity condition on sigma s levels were that it rendered the sigma protein less stable in exponential phase and increased rpoS mRNA translational efficiency. Since sigma s regulatory processes are influenced by mRNA and protein-folding patterns, the data suggest that SMG may affect these configurations.

An improved model of homogeneous nucleation for high supersaturation conditions: aluminum vapor.

PubMed

Savel'ev, A M; Starik, A M

2016-12-21

A novel model of stationary nucleation, treating the thermodynamic functions of small clusters, has been built. The model is validated against the experimental data on the nucleation rate of water vapor obtained in a broad range of supersaturation values (S = 10-120), and, at high supersaturation values, it reproduces the experimental data much better than the traditional classical nucleation model. A comprehensive analysis of the nucleation of aluminum vapor with the usage of developed stationary and non-stationary nucleation models has been performed. It has been shown that, at some value of supersaturation, there exists a double potential nucleation barrier. It has been revealed that the existence of this barrier notably delayed the establishment of a stationary distribution of subcritical clusters. It has also been demonstrated that the non-stationary model of the present work and the model of liquid-droplet approximation predict different values of nucleation delay time, τ s . In doing so, the liquid-droplet model can underestimate notably (by more than an order of magnitude) the value of τ s .

Determination of the temperature field of shell structures

NASA Astrophysics Data System (ADS)

Rodionov, N. G.

1986-10-01

A stationary heat conduction problem is formulated for the case of shell structures, such as those found in gas-turbine and jet engines. A two-dimensional elliptic differential equation of stationary heat conduction is obtained which allows, in an approximate manner, for temperature changes along a third variable, i.e., the shell thickness. The two-dimensional problem is reduced to a series of one-dimensional problems which are then solved using efficient difference schemes. The approach proposed here is illustrated by a specific example.

Systematic investigations of peak deformations due to co-solvent adsorption in preparative supercritical fluid chromatography.

PubMed

Glenne, Emelie; Leek, Hanna; Klarqvist, Magnus; Samuelsson, Jörgen; Fornstedt, Torgny

2017-05-05

Strangely shaped overloaded bands were recently reported using a standard supercritical fluid chromatographic system comprising a diol column as the stationary phase and carbon dioxide with methanol as the mobile phase. Some of these overloaded elution profiles appeared strongly deformed and even had "anti-Langmuirian" shapes although their solute compounds had "Langmuirian" adsorption. To obtain a more complete understanding of the generality of these effects, the investigation was expanded to cover also other common co-solvents, such as ethanol, 2-propanol, and acetonitrile, as well as various stationary phase materials, such as silica, and 2-ethylpyridine. From this expanded study it could be confirmed that the effects of deformed overloaded solute band shapes, due to co-solvent adsorption, is general phenomena in supercritical fluid chromatographic. It could also be concluded that these effects as well as previously observed "solvent effects" or "plug effects" are entirely due to competition between the solute and solvent molecules for the adsorption sites on the stationary phase surface. Finally, guidelines were given for how to evaluate the risk of deformations occurring for a given solvent-column combination, based simply on testing retention times of solutes and co-solvent. Copyright © 2017 Elsevier B.V. All rights reserved.

Validation of Reference Genes for Real-Time Quantitative PCR (qPCR) Analysis of Avibacterium paragallinarum.

PubMed

Wen, Shuxiang; Chen, Xiaoling; Xu, Fuzhou; Sun, Huiling

2016-01-01

Real-time quantitative reverse transcription PCR (qRT-PCR) offers a robust method for measurement of gene expression levels. Selection of reliable reference gene(s) for gene expression study is conducive to reduce variations derived from different amounts of RNA and cDNA, the efficiency of the reverse transcriptase or polymerase enzymes. Until now reference genes identified for other members of the family Pasteurellaceae have not been validated for Avibacterium paragallinarum. The aim of this study was to validate nine reference genes of serovars A, B, and C strains of A. paragallinarum in different growth phase by qRT-PCR. Three of the most widely used statistical algorithms, geNorm, NormFinder and ΔCT method were used to evaluate the expression stability of reference genes. Data analyzed by overall rankings showed that in exponential and stationary phase of serovar A, the most stable reference genes were gyrA and atpD respectively; in exponential and stationary phase of serovar B, the most stable reference genes were atpD and recN respectively; in exponential and stationary phase of serovar C, the most stable reference genes were rpoB and recN respectively. This study provides recommendations for stable endogenous control genes for use in further studies involving measurement of gene expression levels.

Ion chromatographic determination of hydroxide ion on monolithic reversed-phase silica gel columns coated with nonionic and cationic surfactants.

PubMed

Xu, Qun; Mori, Masanobu; Tanaka, Kazuhiko; Ikedo, Mikaru; Hu, Wenzhi; Haddad, Paul R

2004-07-02

The determination of hydroxide by ion chromatography (IC) is demonstrated using a monolithic octadecylsilyl (ODS)-silica gel column coated first with a nonionic surfactant (polyoxyethylene (POE)) and then with a cationic surfactant (cetyltrimethylammonium bromide (CTAB)). This stationary phase, when used in conjunction with a 10 mmol/l sodium sulfate eluent at pH 8.2, was found to be suitable for the rapid and efficient separation of hydroxide from some other anions, based on a conventional ion-exchange mechanism. The peak directions and detection responses for these ions were in agreement with their known limiting equivalent ionic conductance values. Under these conditions, a linear calibration plot was obtained for hydroxide ion over the range 16 micromol/l to 15 mmol/l, and the detection limit determined at a signal-to-noise ratio of 3 was 6.4 micromol/l. The double-coated stationary phase described above was shown to be superior to a single coating of cetyltrimethylammonium bromide alone, in terms of separation efficiency and stability of the stationary phase. A range of samples comprising solutions of some strong and weak bases was analyzed by the proposed method and the results obtained were in good agreement with those obtained by conventional potentiometric pH measurement.

Stationary phase gene expression of Mycobacterium tuberculosis following a progressive nutrient depletion: a model for persistent organisms?,

PubMed Central

Hampshire, Tobias; Soneji, Shamit; Bacon, Joanna; James, Brian W.; Hinds, Jason; Laing, Ken; Stabler, Richard A; Marsh, Philip D.; Butcher, Philip D

2011-01-01

Summary The majority of individuals infected with TB develop a latent infection, in which organisms survive within the body while evading the host immune system. Such persistent bacilli are capable of surviving several months of combinatorial antibiotic treatment. Evidence suggests that stationary phase bacteria adapt to increase their tolerance to environmental stresses. We have developed a unique in vitro model of dormancy based on the characterization of a single, large volume fermenter culture of M. tuberculosis, as it adapts to stationary phase. Cells are maintained in controlled and defined aerobic conditions (50% dissolved oxygen tension), using probes that measure dissolved oxygen tension, temperature, and pH. Microarray analysis has been used in conjunction with viability and nutrient depletion assays to dissect differential gene expression. Following exponential phase growth the gradual depletion of glucose/glycerol resulted in a small population of survivors that were characterized for periods in excess of 100 days. Bacilli adapting to nutrient depletion displayed characteristics associated with persistence in vivo, including entry into a non-replicative state and the up-regulation of genes involved in β-oxidation of fatty acids and virulence. A reduced population of non-replicating bacilli went on to adapt sufficiently to re-initiate cellular division. PMID:15207492

Supercritical Fluid Chromatography of Drugs: Parallel Factor Analysis for Column Testing in a Wide Range of Operational Conditions

PubMed Central

Al-Degs, Yahya; Andri, Bertyl; Thiébaut, Didier; Vial, Jérôme

2017-01-01

Retention mechanisms involved in supercritical fluid chromatography (SFC) are influenced by interdependent parameters (temperature, pressure, chemistry of the mobile phase, and nature of the stationary phase), a complexity which makes the selection of a proper stationary phase for a given separation a challenging step. For the first time in SFC studies, Parallel Factor Analysis (PARAFAC) was employed to evaluate the chromatographic behavior of eight different stationary phases in a wide range of chromatographic conditions (temperature, pressure, and gradient elution composition). Design of Experiment was used to optimize experiments involving 14 pharmaceutical compounds present in biological and/or environmental samples and with dissimilar physicochemical properties. The results showed the superiority of PARAFAC for the analysis of the three-way (column × drug × condition) data array over unfolding the multiway array to matrices and performing several classical principal component analyses. Thanks to the PARAFAC components, similarity in columns' function, chromatographic trend of drugs, and correlation between separation conditions could be simply depicted: columns were grouped according to their H-bonding forces, while gradient composition was dominating for condition classification. Also, the number of drugs could be efficiently reduced for columns classification as some of them exhibited a similar behavior, as shown by hierarchical clustering based on PARAFAC components. PMID:28695040

Properties of water as a novel stationary phase in capillary gas chromatography.

PubMed

Gallant, Jonathan A; Thurbide, Kevin B

2014-09-12

A novel method of separation that uses water as a stationary phase in capillary gas chromatography (GC) is presented. Through applying a water phase to the interior walls of a stainless steel capillary, good separations were obtained for a large variety of analytes in this format. It was found that carrier gas humidification and backpressure were key factors in promoting stable operation over time at various temperatures. For example, with these measures in place, the retention time of an acetone test analyte was found to reduce by only 44s after 100min of operation at a column temperature of 100°C. In terms of efficiency, under optimum conditions the method produced about 20,000 plates for an acetone test analyte on a 250μm i.d.×30m column. Overall, retention on the stationary phase generally increased with analyte water solubility and polarity, but was relatively little correlated with analyte volatility. Conversely, non-polar analytes were essentially unretained in the system. These features were applied to the direct analysis of different polar analytes in both aqueous and organic samples. Results suggest that this approach could provide an interesting alternative tool in capillary GC separations. Copyright © 2014 Elsevier B.V. All rights reserved.

Accounting for inherent variability of growth in microbial risk assessment.

PubMed

Marks, H M; Coleman, M E

2005-04-15

Risk assessments of pathogens need to account for the growth of small number of cells under varying conditions. In order to determine the possible risks that occur when there are small numbers of cells, stochastic models of growth are needed that would capture the distribution of the number of cells over replicate trials of the same scenario or environmental conditions. This paper provides a simple stochastic growth model, accounting only for inherent cell-growth variability, assuming constant growth kinetic parameters, for an initial, small, numbers of cells assumed to be transforming from a stationary to an exponential phase. Two, basic, microbial sets of assumptions are considered: serial, where it is assume that cells transform through a lag phase before entering the exponential phase of growth; and parallel, where it is assumed that lag and exponential phases develop in parallel. The model is based on, first determining the distribution of the time when growth commences, and then modelling the conditional distribution of the number of cells. For the latter distribution, it is found that a Weibull distribution provides a simple approximation to the conditional distribution of the relative growth, so that the model developed in this paper can be easily implemented in risk assessments using commercial software packages.

Capillary trap column with strong cation-exchange monolith for automated shotgun proteome analysis.

PubMed

Wang, Fangjun; Dong, Jing; Jiang, Xiaogang; Ye, Mingliang; Zou, Hanfa

2007-09-01

A 150 microm internal diameter capillary monolithic column with a strong cation-exchange stationary phase was prepared by direct in situ polymerization of ethylene glycol methacrylate phosphate and bisacrylamide in a trinary porogenic solvent consisting dimethylsulfoxide, dodecanol, and N,N'-dimethylformamide. This phosphate monolithic column exhibits higher dynamic binding capacity, faster kinetic adsorption of peptides, and more than 10 times higher permeability than the column packed with commercially available strong cation-exchange particles. It was applied as a trap column in a nanoflow liquid chromatography-tandem mass spectrometry system for automated sample injection and online multidimensional separation. It was observed that the sample could be loaded at a flow rate as high as 40 microL/min with a back pressure of approximately 1300 psi and without compromising the separation efficiency. Because of its good orthogonality to the reversed phase separation mechanism, the phosphate monolithic trap column was coupled with a reversed-phase column for online multidimensional separation of 19 microg of the tryptic digest of yeast proteins. A total of 1522 distinct proteins were identified from 5608 unique peptides (total of 54,780 peptides) at the false positive rate only 0.46%.

Separation and characterization of polycyclic aromatic hydrocarbons and alkylphenols in coal derived solvents

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hurtubise, R.J.; Allen, T.W.; Hussain, A.

1981-03-29

Dry-column chromatography with an aluminum oxide stationary phase and a n-hexane-ether (19:1) mobile phase was used to separate polycyclic aromatic hydrocarbons (PAH) by ring size. Prior to the dry-column chromatography step, the coal derived solvents were added to an acid treated silica gel column and eluted with chloroform. This step removed pyridine-type nitrogen heterocycles. After separation of the individual ring fractions, the fractions were further separated by either thin layer chromatography (TLC) or high performance liquid chromatography (HPLC). If TLC was used, then after separation fluorescence profiles of each PAH ring fraction distributed on 30%-acetylated cellulose chromatoplates were obtained withmore » a spectrodensitometer. Measurement of fluorescence peak heights gave an approximate measure of the amount of the 3-, 4-, 5-, and 6- ring PAH. For HPLC separation, the 3- and 4- ring PAH fractions obtained from the dry-column chromatography step were separated with a ..mu..-Bondapak C/sub 18/ column and methanol:water (65:35) mobile phase. The HPLC separated PAH were characterized by chromatographic correlation factors and corrected fluorescence excitation spectra. Alkylphenols were identified in coal recycle solvent sample following separation by HPLC.« less

Evaluation of colour temperatures in the cultivation of Dunaliella salina and Nannochloropsis oculata in the production of lipids and carbohydrates.

PubMed

Pavón-Suriano, Salim Gabriel; Ortega-Clemente, Luis Alfredo; Curiel-Ramírez, Sergio; Jiménez-García, María Isabel; Pérez-Legaspi, Ignacio Alejandro; Robledo-Narváez, Paula Natalia

2017-07-25

The production of biofuels from microalgae is a promising and sustainable alternative. Its production is determined by the content of lipids and carbohydrates, which is different for each microalgae species and is affected by environmental factors, being lighting one of the principal determining their biochemical composition. The colour temperature (electromagnetic radiation and light spectrum) is a determining factor for the production of lipids and carbohydrates in microalgae. The aim of this assay was to evaluate the effect of three colour temperatures (6500, 10,000 and 20,000 °K) on the biomass (cel mL -1 ), biomass production and productivity (g L -1 and g L -1  day -1 ), lipid and carbohydrate content (%), lipid and carbohydrate production and productivity (mg L -1 and mg L -1  day -1 ), composition and content of fatty acids (%) in two microalgae species: Dunaliella salina and Nannochloropsis oculata. The highest cell density was observed for N. oculata in stationary phase in the control (83.93 × 106 cel mL -1 ). However, higher lipid content was obtained in D. salina in stationary phase at 10,000 °K (80%), while N. oculata showed 67% at 6500 °K. The highest carbohydrate content was 25% in stationary phase for D. salina at 20,000 °K. Regarding the production of lipids, D. salina reached a maximum of 523 mg L -1 in exponential phase at 6500 and 10,000 °K. The highest carbohydrate production was 38 mg L -1 for D. salina in exponential phase at 20,000 °K. In both microalgae, 15 different fatty acids were identified; the most abundant was palmitic acid with 35.8% for N. oculata in stationary phase at 10,000 °K, while D. salina showed 67% of polyunsaturated fatty acids in exponential phase at 6500 °K. In conclusion, the ideal colour temperature for microalgae culture to obtain biofuels should be based on the biomolecule of interest, being necessary to individually evaluate for each species.

Mixed Stationary Liquid Phases for Gas-Liquid Chromatography.

ERIC Educational Resources Information Center

Koury, Albert M.; Parcher, Jon F.

1979-01-01

Describes a laboratory technique for use in an undergraduate instrumental analysis course that, using the interpretation of window diagrams, prepares a mixed liquid phase column for gas-liquid chromatography. A detailed procedure is provided. (BT)

Microarray and functional analysis of growth-phase dependent gene regulation in Bordetella bronchiseptica

USDA-ARS?s Scientific Manuscript database

Growth-phase dependent gene regulation has recently been demonstrated to occur in B. pertussis, with many transcripts, including known virulence factors, significantly decreasing during the transition from logarithmic to stationary-phase growth. Given that B. pertussis is thought to have derived fro...

Theory for Transitions Between Exponential and Stationary Phases: Universal Laws for Lag Time

NASA Astrophysics Data System (ADS)

Himeoka, Yusuke; Kaneko, Kunihiko

2017-04-01

The quantitative characterization of bacterial growth has attracted substantial attention since Monod's pioneering study. Theoretical and experimental works have uncovered several laws for describing the exponential growth phase, in which the number of cells grows exponentially. However, microorganism growth also exhibits lag, stationary, and death phases under starvation conditions, in which cell growth is highly suppressed, for which quantitative laws or theories are markedly underdeveloped. In fact, the models commonly adopted for the exponential phase that consist of autocatalytic chemical components, including ribosomes, can only show exponential growth or decay in a population; thus, phases that halt growth are not realized. Here, we propose a simple, coarse-grained cell model that includes an extra class of macromolecular components in addition to the autocatalytic active components that facilitate cellular growth. These extra components form a complex with the active components to inhibit the catalytic process. Depending on the nutrient condition, the model exhibits typical transitions among the lag, exponential, stationary, and death phases. Furthermore, the lag time needed for growth recovery after starvation follows the square root of the starvation time and is inversely related to the maximal growth rate. This is in agreement with experimental observations, in which the length of time of cell starvation is memorized in the slow accumulation of molecules. Moreover, the lag time distributed among cells is skewed with a long time tail. If the starvation time is longer, an exponential tail appears, which is also consistent with experimental data. Our theory further predicts a strong dependence of lag time on the speed of substrate depletion, which can be tested experimentally. The present model and theoretical analysis provide universal growth laws beyond the exponential phase, offering insight into how cells halt growth without entering the death phase.

Evaluation of innovative stationary phase ligand chemistries and analytical conditions for the analysis of basic drugs by supercritical fluid chromatography.

PubMed

Desfontaine, Vincent; Veuthey, Jean-Luc; Guillarme, Davy

2016-03-18

Similar to reversed phase liquid chromatography, basic compounds can be highly challenging to analyze by supercritical fluid chromatography (SFC), as they tend to exhibit poor peak shape, especially those with high pKa values. In this study, three new stationary phase ligand chemistries available in sub -2 μm particle sizes, namely 2-picolylamine (2-PIC), 1-aminoanthracene (1-AA) and diethylamine (DEA), were tested in SFC conditions for the analysis of basic drugs. Due to the basic properties of these ligands, it is expected that the repulsive forces may improve peak shape of basic substances, similarly to the widely used 2-ethypyridine (2-EP) phase. However, among the 38 tested basic drugs, less of 10% displayed Gaussian peaks (asymmetry between 0.8 and 1.4) using pure CO2/methanol on these phases. The addition of 10mM ammonium formate as mobile phase additive, drastically improved peak shapes and increased this proportion to 67% on 2-PIC. Introducing the additive in the injection solvent rather than in the organic modifier, gave acceptable results for 2-PIC only, with 31% of Gaussian peaks with an average asymmetry of 1.89 for the 38 selected basic drugs. These columns were also compared to hybrid silica (BEH), DIOL and 2-EP stationary phases, commonly employed in SFC. These phases commonly exhibit alternative retention and selectivity. In the end, the two most interesting ligands used as complementary columns were 2-PIC and BEH, as they provided suitable peak shapes for the basic drugs and almost orthogonal selectivities. Copyright © 2016 Elsevier B.V. All rights reserved.

A motion algorithm to extract physical and motion parameters of mobile targets from cone-beam computed tomographic images.

PubMed

Alsbou, Nesreen; Ahmad, Salahuddin; Ali, Imad

2016-05-17

A motion algorithm has been developed to extract length, CT number level and motion amplitude of a mobile target from cone-beam CT (CBCT) images. The algorithm uses three measurable parameters: Apparent length and blurred CT number distribution of a mobile target obtained from CBCT images to determine length, CT-number value of the stationary target, and motion amplitude. The predictions of this algorithm are tested with mobile targets having different well-known sizes that are made from tissue-equivalent gel which is inserted into a thorax phantom. The phantom moves sinusoidally in one-direction to simulate respiratory motion using eight amplitudes ranging 0-20 mm. Using this motion algorithm, three unknown parameters are extracted that include: Length of the target, CT number level, speed or motion amplitude for the mobile targets from CBCT images. The motion algorithm solves for the three unknown parameters using measured length, CT number level and gradient for a well-defined mobile target obtained from CBCT images. The motion model agrees with the measured lengths which are dependent on the target length and motion amplitude. The gradient of the CT number distribution of the mobile target is dependent on the stationary CT number level, the target length and motion amplitude. Motion frequency and phase do not affect the elongation and CT number distribution of the mobile target and could not be determined. A motion algorithm has been developed to extract three parameters that include length, CT number level and motion amplitude or speed of mobile targets directly from reconstructed CBCT images without prior knowledge of the stationary target parameters. This algorithm provides alternative to 4D-CBCT without requirement of motion tracking and sorting of the images into different breathing phases. The motion model developed here works well for tumors that have simple shapes, high contrast relative to surrounding tissues and move nearly in regular motion pattern that can be approximated with a simple sinusoidal function. This algorithm has potential applications in diagnostic CT imaging and radiotherapy in terms of motion management.

Proteomic Analysis of Stationary Phase in the Marine Bacterium "Candidatus Pelagibacter ubique"

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sowell, S. M.; Norbeck, A. D.; Lipton, M. S.

2008-05-09

The α-proteobacterium ‘Candidatus Pelagibacter ubique’ str. HTCC1062, and most other members of the SAR11 clade, lack genes for assimilatory sulfate reduction, making them dependent on organosulfur compounds that occur naturally in seawater. To investigate how these cells adapt to sulfur limitation, batch cultures were grown in defined media containing either limiting or non-limiting amounts of dimethylsulfoniopropionate (DMSP) as the sole sulfur source. Protein and mRNA expression were measured during exponential growth, immediately prior to stationary phase, and in late stationary phase. Two distinct responses were observed: one as DMSP became exhausted, and another as cells acclimated to a sulfur-limited environment.more » The first response was characterized by increased transcription and translation of all Ca. P. ubique genes downstream of previously confirmed S-adenosyl methionine (SAM) riboswitches: bhmT, mmuM, and metY. Proteins encoded by these genes were up to 33 times more abundant as DMSP became limiting. Their predicted function is to shunt all available sulfur to methionine. The secondary response, observed during sulfur-depleted stationary phase, was a 6-10 fold increase in transcription of the heme c shuttle ccmC and two small genes of unknown function (SAR11_1163 and SAR11_1164). This bacterium's strategy for coping with sulfur stress appears to be intracellular redistribution to support methionine biosynthesis, rather than increasing organosulfur import. Many of the genes and SAM riboswitches involved in this response are located in a hypervariable genome region (HVR). One of these HVR genes, ordL, is located downstream of a conserved motif that evidence suggests is a novel riboswitch.« less

Validation of stationary phases in (111)In-pentetreotide planar chromatography.

PubMed

Moreno-Ortega, E; Mena-Bares, L M; Maza-Muret, F R; Hidalgo-Ramos, F J; Vallejo-Casas, J A

2013-01-01

Since Pall-German stopped manufacturing ITLC-SG, it has become necessary to validate alternative stationary phases. To validate different stationary phases versus ITLC-SG Pall-Gelman in the determination of the radiochemical purity (RCP) of (111)In-pentetreotide ((111)In-Octreoscan) by planar chromatography. We conducted a case-control study, which included 66 (111)In-pentetreotide preparations. We determined the RCP by planar chromatography, using a freshly prepared solution of 0,1M sodium citrate (pH 5) and the following stationary phases: ITLC-SG (Pall-Gelman) (reference method), iTLC-SG (Varian), HPTLC silica gel 60 (Merck), Whatman 1, Whatman 3MM and Whatman 17. For each of the methods, we calculated: PRQ, relative front values (RF) of the radiopharmaceutical and free (111)In, chromatographic development time, resolution between peaks. We compared the results obtained with the reference method. The statistical analysis was performed using the SPSS program. The p value was calculated for the study of statistical significance. The highest resolution is obtained with HPTLC silica gel 60 (Merck). However, the chromatographic development time is too long (mean=33.62minutes). Greater resolution is obtained with iTLC-SG (Varian) than with the reference method, with lower chromatographic development time (mean=3.61minutes). Very low resolutions are obtained with Whatman paper, essentially with Whatman 1 and 3MM. Therefore, we do not recommend their use. Although iTLC-SG (Varian) and HPTLC silica gel 60 (Merck) are suitable alternatives to ITLC-SG (Pall-Gelman) in determining the RCP of (111)In-pentetreotide, iTLC-SG (Varian) is the method of choice due to its lower chromatographic development time. Copyright © 2012 Elsevier España, S.L. and SEMNIM. All rights reserved.

Solvation molar enthalpies and heat capacities of n-alkanes and n-alkylbenzenes on stationary phases of wide-ranging polarity.

PubMed

Lebrón-Aguilar, Rosa; Quintanilla-López, Jesús Eduardo; Santiuste, José María

2010-12-03

A comparison of the most usual gas chromatographic methods for the calculation of partial molar enthalpies of solvation (Δ(sol)H(o)) has been carried out. Those methods based on the fitting of lnV(g) or ln(k/T) vs. 1/T and ln(k/T) vs. (1/T and the temperature arrangement, T(a)) are the most adequate ones for obtaining Δ(sol)H(o) values. However, the latter is the only reliable option for Δ(sol)H(o) estimation when commercial WCOT capillary columns are used, since in this case the estimation of some variables involved in the V(g) determination is less accurate or even impossible. Consequently, in this paper, Δ(sol)H(o) obtained from ln(k/T) vs. (1/T+T(a)) fitting at 373.15 and 298.15K for n-alkanes and n-alkylbenzenes on 12 commercial capillary columns coated with stationary phases covering the 203-3608 McReynolds polarity range are reported. Moreover, molar heat capacities of solvation at constant pressure (Δ(sol)C(p)(o)) have also been calculated using this method. A clear influence on Δ(sol)H(o) of the type and content of the substitution group in the stationary phase was observed. In addition, a linear relationship of Δ(sol)C(p)(o) with the van der Waals volume of the n-alkanes and the temperature gradient of density of the stationary phase was found. The effect of the size of the hydrocarbon on both thermodynamic variables was also investigated. Copyright © 2010 Elsevier B.V. All rights reserved.

Prolonged Stationary-Phase Incubation Selects for lrp Mutations in Escherichia coli K-12

PubMed Central

Zinser, Erik R.; Kolter, Roberto

2000-01-01

Evolution by natural selection occurs in cultures of Escherichia coli maintained under carbon starvation stress. Mutants of increased fitness express a growth advantage in stationary phase (GASP) phenotype, enabling them to grow and displace the parent as the majority population. The first GASP mutation was identified as a loss-of-function allele of rpoS, encoding the stationary-phase global regulator, ςS (M. M. Zambrano, D. A. Siegele, M. A. Almirón, A. Tormo, and R. Kolter, Science 259:1757–1760, 1993). We now report that a second global regulator, Lrp, can also play a role in stationary-phase competition. We found that a mutant that took over an aged culture of an rpoS strain had acquired a GASP mutation in lrp. This GASP allele, lrp-1141, encodes a mutant protein lacking the critical glycine in the turn of the helix-turn-helix DNA-binding domain. The lrp-1141 allele behaves as a null mutation when in single copy and is dominant negative when overexpressed. Hence, the mutant protein appears to retain stability and the ability to dimerize but lacks DNA-binding activity. We also demonstrated that a lrp null allele generated by a transposon insertion has a fitness gain identical to that of the lrp-1141 allele, verifying that cells lacking Lrp activity have a competitive advantage during prolonged starvation. Finally, we tested by genetic analysis the hypothesis that the lrp-1141 GASP mutation confers a fitness gain by enhancing amino acid catabolism during carbon starvation. We found that while amino acid catabolism may play a role, it is not necessary for the lrp GASP phenotype, and hence the lrp GASP phenotype is due to more global physiological changes. PMID:10894750

A 3-D open-framework material with intrinsic chiral topology used as a stationary phase in gas chromatography.

PubMed

Xie, Sheng-Ming; Zhang, Xin-Huan; Zhang, Ze-Jun; Zhang, Mei; Jia, Jia; Yuan, Li-Ming

2013-04-01

Compared with liquid chromatography and capillary electrophoresis, the diversity of gas chromatography chiral stationary phases is rather limited. Here, we report the fabrication of Co(D-Cam)1/2(bdc)1/2(tmdpy) (D-Cam = D-camphoric acid; bdc = 1,4-benzenedicarboxylate; tmdpy = 4,4'-trimethylenedipyridine)-coated open tubular columns for high-resolution gas chromatographic separation of compounds. The Co(D-Cam)1/2(bdc)1/2(tmdpy) compound possesses a 3-D framework containing enantiopure building blocks embedded in intrinsically chiral topological nets. In this study, two fused-silica open tubular columns with different inner diameters and lengths, including column A (30 m × 530 μm i.d.) and column B (2 m × 75 μm i.d.), were prepared by a dynamic coating method using Co-(D-Cam)1/2(bdc)1/2(tmdpy) as the stationary phase. The chromatographic properties of the two columns were investigated using n-dodecane as the test compound at 120 °C. The number of theoretical plates (plates/m) of the two metal-organic framework columns was 1,450 and 3,100, respectively. The separation properties were evaluated using racemates, isomers, alkanes, alcohols, and Grob's test mixture. The limit of detection and limit of quantification were found to be 0.125 and 0.417 ng for citronellal enantiomers, respectively. Repeatability (n = 6) showed lower than 0.25 % relative standard deviation (RSD) for retention times and lower than 2.2 % RSD for corrected peak areas. The experimental results showed that the stationary phase has excellent selectivity and also possesses good recognition ability toward these organic compounds, especially chiral compounds.

Icm/Dot-Independent Entry of Legionella pneumophila into Amoeba and Macrophage Hosts

PubMed Central

Bandyopadhyay, Purnima; Xiao, Huifang; Coleman, Hope A.; Price-Whelan, Alexa; Steinman, Howard M.

2004-01-01

Legionella pneumophila, the causative agent of Legionnaires' disease, expresses a type IVB secretion apparatus that translocates bacterial proteins into amoeba and macrophage hosts. When stationary-phase cultures are used to infect hosts, the type IVB apparatus encoded by the icm/dot genes is required for entry, delay of phagosome-lysosome fusion, and intracellular multiplication within host cells. Null mutants with mutations in icm/dot genes are defective in these phenotypes. Here a new model is described in which hosts are infected with stationary-phase cultures that have been incubated overnight in pH 6.5 buffer. This model is called Ers treatment because it enhances the resistance to acid, hydrogen peroxide, and antibiotic stress beyond that of stationary-phase cultures. Following Ers treatment entry into amoeba and macrophage hosts does not require dotA, which is essential for Legionella virulence phenotypes when hosts are infected with stationary-phase cultures, dotB, icmF, icmV, or icmX. Defective host entry is also suppressed for null mutants with mutations in the KatA and KatB catalase-peroxidase enzymes, which are required for proper intracellular growth in amoeba and macrophage hosts. Ers treatment-induced suppression of defective entry is not associated with increased bacterial adhesion to host cells or with morphological changes in the bacterial envelope but is dependent on protein expression during Ers treatment. By using proteomic analysis, Ers treatment was shown to induce a protein predicted to contain eight tetratricopeptide repeats, a motif previously implicated in enhanced entry of L. pneumophila. Characterization of Ers treatment-dependent changes in expression is proposed as an avenue for identifying icm/dot-independent factors that function in the entry of Legionella into amoeba and macrophage hosts. PMID:15271914

Preparative separation of the polar part from the rhizomes of Anemarrhena asphodeloides using a hydrophilic C18 stationary phase.

PubMed

Cai, Jianfeng; Xin, Huaxia; Cheng, Lingping; Fu, YanHui; Jiang, Dasen; Feng, Jiatao; Fu, Qing; Jin, Yu; Liang, Xinmiao

2017-09-15

The goal of this study was to develop a method that utilized a hydrophilic C18 stationary phase in the preparative high performance liquid chromatography to isolate the polar part from the rhizomes of Anemarrhena asphodeloides. The results showed that an initial mobile phase of pure water for the separation could greatly increase the retention and solubility of the polar compounds at the preparative scale. Introducing polar groups on the surface of the hydrophilic C18 column together with the use of optimized mobile phase compositions improved the column separation selectivity for polar compounds. Eleven previously undescribed compounds in Anemarrhena asphodeloides were obtained, indicating that the method developed in this study would facilitate the purification and separation of the polar part of traditional Chinese medicines. Copyright © 2017 Elsevier B.V. All rights reserved.

21 CFR 862.2270 - Thin-layer chromatography system for clinical use.

Code of Federal Regulations, 2011 CFR

2011-04-01

... a mixture. The mixture of compounds is absorbed onto a stationary phase or thin layer of inert material (e.g., cellulose, alumina, etc.) and eluted off by a moving solvent (moving phase) until equilibrium occurs between the two phases. (b) Classification. Class I (general controls). The device is...

Aggregation Dynamics Using Phase Wave Signals and Branching Patterns

NASA Astrophysics Data System (ADS)

Sakaguchi, Hidetsugu; Kusagaki, Takuma

2016-09-01

The aggregation dynamics of slime mold is studied using coupled equations of phase ϕ and cell concentration n. Phase waves work as tactic signals for aggregation. Branching structures appear during the aggregation. A stationary branching pattern appears like a river network, if cells are uniformly supplied into the system.

Towards multimodal HPLC separations on humic acid-bonded aminopropyl silica: RPLC and HILIC behavior.

PubMed

Gezici, Orhan; Kara, Hüseyin

2011-09-15

The stationary phase characteristics of the material obtained through immobilization of humic acid (HA) to aminopropyl silica (APS) via amide-bond formation were investigated. The material was characterized in terms of elemental analysis, FTIR, thermogravimetric analyses, pH point of zero charge measurements, potentiometric titrations, and contact angle measurements. Amount of HA bonded to APS was determined from the elemental analysis results, and found as 170 mgHA/gAPS. Stability of the material was studied in aqueous media at different pH values, and amount of HA released at pH=8 did not exceed 2% of the total immobilized HA. Stationary phase characteristics of the well-characterized material were investigated in an HPLC system by using some low-molecular weight polar compounds (i.e. some nucleosides and nucleobases) as test solutes. Effect of some experimental variables such as column conditioning, composition of mobile phase, and temperature on the chromatographic behavior of the studied compounds was studied. Role of ammonium solutions at different pH values on retentive properties of the species was also studied. Retention factors (k') versus volume percentage of organic modifier exhibited a U-curve, which was evaluated as an indication for RPLC/HILIC mixed-mode behavior of the stationary phase. Orthogonality between RPLC and HILIC modes was analyzed through geometric approach, and found as 48.5%. Base-line separation for the studied groups of compounds was achieved under each studied mode, and some differentiations were observed in elution order of the compounds depending on the HPLC mode applied. Chromatograms recorded under RPLC and HILIC modes were compared with those recorded on APS under similar conditions, and thus the influence/importance of HA immobilization process was evaluated in detail. In light of the obtained results, immobilized HA is represented as a useful stationary phase for HPLC separations. Copyright © 2011 Elsevier B.V. All rights reserved.

Development of Electrospun Nanomaterials and their Applications in Separation Science

NASA Astrophysics Data System (ADS)

Newsome, Toni Elwell

In separations, efficiency is inversely related to the diameter of the sorbent particles of the stationary phase. Thus, materials research in separation science has primarily been directed towards reducing the diameter of the sorbent particle used in the stationary phase. In this dissertation, innovative methods designed for the fabrication and application of electrospun sorbent nanomaterials for separation science are described. Electrospinning is a facile, cost-effective technique that relies on repulsive electrostatic forces to produce nanofibers from a viscoelastic solution. Here, electrospinning is used to generate polymer, carbon, and silica-based nanofibers which are employed as sorbent nanomaterials in extractions and separations. Electrospun carbon nanofibers have proven to be ideal extractive phases for solid-phase microextraction (SPME) when coupled to gas chromatography (GC) for headspace sampling of volatile analytes. Herein, these carbon nanofibers were employed in the direct extraction of nonvolatile analytes and coupled to liquid chromatography (LC) for the first time. The high surface area of the coatings led to enhanced extraction efficiencies; they offered a 3-33 fold increase in efficiency relative to a commercial SPME phase. Carbon nanofibers proved to be stable when immersed in liquids common to LC demonstrating the enhanced stability of these coatings in SPME coupled to LC relative to conventional SPME fibers. The enhanced chemical and mechanical stability of the carbon SPME coatings considerably expanded the range of compounds applicable to SPME and extended the lifetimes of the fibers. Electrospun nanofibers have also proven to be ideal stationary phases in ultra-thin layer chromatography (UTLC). Nanofibers provide faster separations and enhanced separation efficiencies compared to commercial particle-based stationary phases in a relatively short distance. Here, the electrospun-UTLC technology was extended for the first time to nanofibers composed of silica, the most commonly used surface for TLC. An electrospinning method was optimized to produce silica-based nanofibers with the smallest diameter possible (300-380 nm) while maintaining homogenous nanofiber morphology. Highly efficient separations were performed in 15 mm with observed plate heights as low as 8.6 mum. Silica-based nanofibers proved to be chemically stable with a wide variety of TLC reagents demonstrating the enhanced compatibility of these phases with common TLC methods relative to polymer and carbon nanofiber UTLC plates. The extension of electrospun UTLC to silica-based nanofibers vastly expanded the range of analytes and TLC methods which can be used with this technology. The main disadvantage of conventional TLC development methods is that the mobile phase velocity decreases with increasing separation distance. Here, the chromatographic performance of electrospun polymer stationary phases was further improved by using a forced-flow mobile phase in planar electrochromatography (PEC) in which mobile phase velocity does not diminish with increasing distance. Separations were performed on polymer nanofiber UTLC plates in 1-2 min. Compared to UTLC, PEC offered unique selectivity, decreased analysis times (> 4 times faster), and enhanced efficiency (2-3 times lower plate height). In addition, two-dimensional (2D) separations of a complex analyte mixture using UTLC followed by PEC required only 11 min and exhibited a significant increase in separation number (70-77).

A comparison of visual and kinesthetic-tactual displays for compensatory tracking

NASA Technical Reports Server (NTRS)

Jagacinski, R. J.; Flach, J. M.; Gilson, R. D.

1983-01-01

Recent research on manual tracking with a kinesthetic-tactual (KT) display suggests that under certain conditions it can be an effective alternative or supplement to visual displays. In order to understand better how KT tracking compares with visual tracking, both a critical tracking and stationary single-axis tracking tasks were conducted with and without velocity quickening. In the critical tracking task, the visual displays were superior, however, the quickened KT display was approximately equal to the unquickened visual display. In stationary tracking tasks, subjects adopted lag equalization with the quickened KT and visual displays, and mean-squared error scores were approximately equal. With the unquickened displays, subjects adopted lag-lead equalization, and the visual displays were superior. This superiority was partly due to the servomotor lag in the implementation of the KT display and partly due to modality differences.

A comparison of tracking with visual and kinesthetic-tactual displays

NASA Technical Reports Server (NTRS)

Jagacinski, R. J.; Flach, J. M.; Gilson, R. D.

1981-01-01

Recent research on manual tracking with a kinesthetic-tactual (KT) display suggests that under appropriate conditions it may be an effective means of providing visual workload relief. In order to better understand how KT tracking differs from visual tracking, both a critical tracking task and stationary single-axis tracking tasks were conducted with and without velocity quickening. On the critical tracking task, the visual displays were superior; however, the KT quickened display was approximately equal to the visual unquickened display. Mean squared error scores in the stationary tracking tasks for the visual and KT displays were approximately equal in the quickened conditions, and the describing functions were very similar. In the unquickened conditions, the visual display was superior. Subjects using the unquickened KT display exhibited a low frequency lead-lag that may be related to sensory adaptation.

A study of stationarity in time series by using wavelet transform

NASA Astrophysics Data System (ADS)

Dghais, Amel Abdoullah Ahmed; Ismail, Mohd Tahir

2014-07-01

In this work the core objective is to apply discrete wavelet transform (DWT) functions namely Haar, Daubechies, Symmlet, Coiflet and discrete approximation of the meyer wavelets in non-stationary financial time series data from US stock market (DJIA30). The data consists of 2048 daily data of closing index starting from December 17, 2004 until October 23, 2012. From the unit root test the results show that the data is non stationary in the level. In order to study the stationarity of a time series, the autocorrelation function (ACF) is used. Results indicate that, Haar function is the lowest function to obtain noisy series as compared to Daubechies, Symmlet, Coiflet and discrete approximation of the meyer wavelets. In addition, the original data after decomposition by DWT is less noisy series than decomposition by DWT for return time series.

Fast assessment of planar chromatographic layers quality using pulse thermovision method.

PubMed

Suszyński, Zbigniew; Świta, Robert; Loś, Joanna; Zarzycka, Magdalena B; Kaleniecka, Aleksandra; Zarzycki, Paweł K

2014-12-19

The main goal of this paper is to demonstrate capability of pulse thermovision (thermal-wave) methodology for sensitive detection of photothermal non-uniformities within light scattering and semi-transparent planar stationary phases. Successful visualization of stationary phases defects required signal processing protocols based on wavelet filtration, correlation analysis and k-means 3D segmentation. Such post-processing data handling approach allows extremely sensitive detection of thickness and structural changes within commercially available planar chromatographic layers. Particularly, a number of TLC and HPTLC stationary phases including silica, cellulose, aluminum oxide, polyamide and octadecylsilane coated with adsorbent layer ranging from 100 to 250μm were investigated. Presented detection protocol can be used as an efficient tool for fast screening the overall heterogeneity of any layered materials. Moreover, described procedure is very fast (few seconds including acquisition and data processing) and may be applied for fabrication processes online controlling. In spite of planar chromatographic plates this protocol can be used for assessment of different planar separation tools like paper based analytical devices or micro total analysis systems, consisted of organic and non-organic layers. Copyright © 2014 Elsevier B.V. All rights reserved.

Determination of volatile compounds in cider apple juices using a covalently bonded ionic liquid coating as the stationary phase in gas chromatography.

PubMed

Pello-Palma, Jairo; González-Álvarez, Jaime; Gutiérrez-Álvarez, María Dolores; Dapena de la Fuente, Enrique; Mangas-Alonso, Juan José; Méndez-Sánchez, Daniel; Gotor-Fernández, Vicente; Arias-Abrodo, Pilar

2017-04-01

A chromatographic method for the separation of volatile compounds in Asturian cider apple juices has been developed. For this separation purpose, a monocationic imidazolium-based ionic liquid bearing a reactive terminal iodine atom was synthesized by a quaternization-anion exchange chemical sequence. Next, the gas chromatography (GC) stationary phase was prepared by covalently linking the imidazolium monolith to the reactive silanol groups of the inner capillary wall at 70 °C. This coated GC column exhibited good thermal stability (290 °C), as well as good efficiency (2000 plates/m) in the separation of volatile compounds from Asturian apple cider juices, and was characterized using the Abraham solvation parameter model. The intra-day and inter-day precision of the chromatographic method was evaluated, obtaining relative standard deviations from 3.7 to 12.9% and from 7.4 to 18.0%, respectively. Furthermore, recoveries from 82.5 to 122% were achieved. Graphical Abstract Covalent bonding of an ionic liquid to inner column wall led to a great improvement of the separation efficiencies of stationary phases in gas chromatography.

Preparation, characterization, and performance evaluation of UiO-66 analogues as stationary phase in HPLC for the separation of substituted benzenes and polycyclic aromatic hydrocarbons

PubMed Central

Yan, Zengguang; Li, Jianrong; Xie, Yabo; Bai, Liping; Jiang, Lin; Li, Fasheng

2017-01-01

UiO-66 analogues are good candidates as stationary phase in HPLC because of their chemical/thermal stability, large surface area, and two cage structures. Here, two UiO-66 analogues, UiO-66-NH2 and UiO-67, were synthesized and used as stationary phase in HPLC to evaluate their performance in the separation of substituted benzenes (SBs) and polycyclic aromatic hydrocarbons (PAHs). The results showed that SBs could be well separated on UiO-66-NH2 column but not on UiO-67 column. Nonetheless, PAHs could be well separated on UiO-67 column. The separation mechanisms of SBs and PAHs on UiO-66 analogues may be involved in the pore size and functional group in the frameworks of UiO-66 analogues. Introduction of the–NH2 into UiO-66 significantly reduced its adsorption capacity for SB congeners, which resulted in less separation of SBs on UiO-66-NH2. As for the separation of PAHs on UiO-67 column, the π-π stacking effect was supposed to play a vital role. PMID:28582453

Poly-proline-based chiral stationary phases: a molecular dynamics study of triproline, tetraproline, pentaproline and hexaproline interfaces.

PubMed

Ashtari, M; Cann, N M

2012-11-23

Poly-proline chains and derivatives have been recently examined as the basis for new chiral stationary phases in high performance liquid chromatography. The selectivity of poly-proline has been measured for peptides with up to ten proline units. In this article, we employ molecular dynamics simulations to examine the interfacial structure and solvation of surface-bound poly-proline chiral selectors. Specifically, we study the interfacial structure of trimethylacetyl-terminated poly-proline chains with three-to-six prolines. The surface includes silanol groups and end-caps, to better capture the characteristics of the stationary phase, and the solvent is either a polar water/methanol or a relatively apolar n-hexane/2-propanol mixture. We begin with a comprehensive ab initio study of the conformers, their energies, and an assessment of conformer flexibility. Force fields have been developed for each poly-proline selector. Molecular dynamics simulations are employed to study the preferred backbone conformations and solvent hydrogen bonding for different poly-proline/solvent interfaces. For triproline, the effect of two different terminal groups, trimethylacetyl and t-butyl carbamate are compared. Copyright © 2012 Elsevier B.V. All rights reserved.

Simultaneous determination of carotenoids, tocopherols, and gamma-oryzanol in crude rice bran oil by liquid chromatography coupled to diode array and mass spectrometric detection employing silica C30 stationary phases.

PubMed

Stöggl, Wolfgang; Huck, Christain; Wongyai, Surapote; Scherz, Heimo; Bonn, Günther

2005-09-01

Crude rice bran oil contains tocopherols (vitamin E), carotenoids (vitamin A), and phytosterols, which possess antioxidant activities and show promising effects as preventive and therapeutic agents. The aim of this work was to establish methods and to compare C18 and C30 silica stationary phases in order to separate and detect tocopherols, carotenoids, and gamma-oryzanol in one single run. Comparing RP-LC on silica C18 and C30, higher resolution between all target compounds was obtained using the C30 stationary phase. Methanol was used as eluent and the elution strength was increased by the addition of tert-butyl methyl ether for highly hydrophobic analytes such as gamma-oryzanol. Detection was accomplished by diode array detection from 200 to 500 nm. Absorbance maxima were found at 295 nm for tocopherols, 324 nm for gammaoryzanol, and 450 nm for carotenoids. Furthermore, compounds were characterized and identified on the basis of their UV-spectra. Both RP systems were coupled to MS (LC-MS) by using an atmospheric pressure chemical ionization interface.

Preparation, characterization, and performance evaluation of UiO-66 analogues as stationary phase in HPLC for the separation of substituted benzenes and polycyclic aromatic hydrocarbons.

PubMed

Zhao, Weiwei; Zhang, Chaoyan; Yan, Zengguang; Zhou, Youya; Li, Jianrong; Xie, Yabo; Bai, Liping; Jiang, Lin; Li, Fasheng

2017-01-01

UiO-66 analogues are good candidates as stationary phase in HPLC because of their chemical/thermal stability, large surface area, and two cage structures. Here, two UiO-66 analogues, UiO-66-NH2 and UiO-67, were synthesized and used as stationary phase in HPLC to evaluate their performance in the separation of substituted benzenes (SBs) and polycyclic aromatic hydrocarbons (PAHs). The results showed that SBs could be well separated on UiO-66-NH2 column but not on UiO-67 column. Nonetheless, PAHs could be well separated on UiO-67 column. The separation mechanisms of SBs and PAHs on UiO-66 analogues may be involved in the pore size and functional group in the frameworks of UiO-66 analogues. Introduction of the-NH2 into UiO-66 significantly reduced its adsorption capacity for SB congeners, which resulted in less separation of SBs on UiO-66-NH2. As for the separation of PAHs on UiO-67 column, the π-π stacking effect was supposed to play a vital role.

Chiral stationary phase optimized selectivity liquid chromatography: A strategy for the separation of chiral isomers.

PubMed

Hegade, Ravindra Suryakant; De Beer, Maarten; Lynen, Frederic

2017-09-15

Chiral Stationary-Phase Optimized Selectivity Liquid Chromatography (SOSLC) is proposed as a tool to optimally separate mixtures of enantiomers on a set of commercially available coupled chiral columns. This approach allows for the prediction of the separation profiles on any possible combination of the chiral stationary phases based on a limited number of preliminary analyses, followed by automated selection of the optimal column combination. Both the isocratic and gradient SOSLC approach were implemented for prediction of the retention times for a mixture of 4 chiral pairs on all possible combinations of the 5 commercial chiral columns. Predictions in isocratic and gradient mode were performed with a commercially available and with an in-house developed Microsoft visual basic algorithm, respectively. Optimal predictions in the isocratic mode required the coupling of 4 columns whereby relative deviations between the predicted and experimental retention times ranged between 2 and 7%. Gradient predictions led to the coupling of 3 chiral columns allowing baseline separation of all solutes, whereby differences between predictions and experiments ranged between 0 and 12%. The methodology is a novel tool allowing optimizing the separation of mixtures of optical isomers. Copyright © 2017 Elsevier B.V. All rights reserved.

Battle of the Bacteria: Characterizing the Evolutionary Advantage of Stationary Phase Growth †

PubMed Central

Kram, Karin E.; Yim, Kristina M.; Coleman, Aaron B.; Sato, Brian K.

2016-01-01

Providing students with authentic research opportunities has been shown to enhance learning and increase retention in STEM majors. Accordingly, we have developed a novel microbiology lab module, which focuses on the molecular mechanisms of evolution in E. coli, by examining the growth advantage in stationary phase (GASP) phenotype. The GASP phenotype is demonstrated by growing cells into long-term stationary phase (LTSP) and then competing them against un-aged cells in a fresh culture. This module includes learning goals related to strengthening practical laboratory skills and improving student understanding of evolution. In addition, the students generate novel data regarding the effects of different environmental stresses on GASP and the relationship between evolution, genotypic change, mutation frequency, and cell stress. Pairs of students are provided with the experimental background, select a specific aspect of the growth medium to modify, and generate a hypothesis regarding how this alteration will impact the GASP phenotype. From this module, we have demonstrated that students are able to achieve the established learning goals and have produced data that has furthered our understanding of the GASP phenotype. Journal of Microbiology & Biology Education PMID:27158307

Function of the Pyruvate Oxidase-Lactate Oxidase Cascade in Interspecies Competition between Streptococcus oligofermentans and Streptococcus mutans

PubMed Central

Liu, Lei

2012-01-01

Complex interspecies interactions occur constantly between oral commensals and the opportunistic pathogen Streptococcus mutans in dental plaque. Previously, we showed that oral commensal Streptococcus oligofermentans possesses multiple enzymes for H2O2 production, especially lactate oxidase (Lox), allowing it to out-compete S. mutans. In this study, through extensive biochemical and genetic studies, we identified a pyruvate oxidase (pox) gene in S. oligofermentans. A pox deletion mutant completely lost Pox activity, while ectopically expressed pox restored activity. Pox was determined to produce most of the H2O2 in the earlier growth phase and log phase, while Lox mainly contributed to H2O2 production in stationary phase. Both pox and lox were expressed throughout the growth phase, while expression of the lox gene increased by about 2.5-fold when cells entered stationary phase. Since lactate accumulation occurred to a large degree in stationary phase, the differential Pox- and Lox-generated H2O2 can be attributed to differential gene expression and substrate availability. Interestingly, inactivation of pox causes a dramatic reduction in H2O2 production from lactate, suggesting a synergistic action of the two oxidases in converting lactate into H2O2. In an in vitro two-species biofilm experiment, the pox mutant of S. oligofermentans failed to inhibit S. mutans even though lox was active. In summary, S. oligofermentans develops a Pox-Lox synergy strategy to maximize its H2O2 formation so as to win the interspecies competition. PMID:22287002

Trace identities and their semiclassical implications

NASA Astrophysics Data System (ADS)

Smilansky, Uzy

2000-03-01

The compatibility of the semiclassical quantization of area-preserving maps with some exact identities which follow from the unitarity of the quantum evolution operator is discussed. The quantum identities involve relations between traces of powers of the evolution operator. For classically integrable maps, the semiclassical approximation is shown to be compatible with the trace identities. This is done by the identification of stationary phase manifolds which give the main contributions to the result. The compatibility of the semiclassical quantization with the trace identities demonstrates the crucial importance of non-diagonal contributions. The same technique is not applicable for chaotic maps, and the compatibility of the semiclassical theory in this case remains unsettled. However, the trace identities are applied to maps which appear naturally in the theory of quantum graphs, revealing some features of the periodic orbit theory for these paradigms of quantum chaos.

Comparative study of the requantization of the time-dependent mean field for the dynamics of nuclear pairing

NASA Astrophysics Data System (ADS)

Ni, Fang; Nakatsukasa, Takashi

2018-04-01

To describe quantal collective phenomena, it is useful to requantize the time-dependent mean-field dynamics. We study the time-dependent Hartree-Fock-Bogoliubov (TDHFB) theory for the two-level pairing Hamiltonian, and compare results of different quantization methods. The one constructing microscopic wave functions, using the TDHFB trajectories fulfilling the Einstein-Brillouin-Keller quantization condition, turns out to be the most accurate. The method is based on the stationary-phase approximation to the path integral. We also examine the performance of the collective model which assumes that the pairing gap parameter is the collective coordinate. The applicability of the collective model is limited for the nuclear pairing with a small number of single-particle levels, because the pairing gap parameter represents only a half of the pairing collective space.

Modeling of convection phenomena in Bridgman-Stockbarger crystal growth

NASA Technical Reports Server (NTRS)

Carlson, F. M.; Eraslan, A. H.; Sheu, J. Z.

1985-01-01

Thermal convection phenomena in a vertically oriented Bridgman-Stockbarger apparatus were modeled by computer simulations for different gravity conditions, ranging from earth conditions to extremely low gravity, approximate space conditions. The modeling results were obtained by the application of a state-of-the art, transient, multi-dimensional, completely densimetrically coupled, discrete-element computational model which was specifically developed for the simulation of flow, temperature, and species concentration conditions in two-phase (solid-liquid) systems. The computational model was applied to the simulation of the flow and the thermal conditions associated with the convection phenomena in a modified Germanium-Silicon charge enclosed in a stationary fused-silica ampoule. The results clearly indicated that the gravitational field strength influences the characteristics of the coherent vortical flow patterns, interface shape and position, maximum melt velocity, and interfacial normal temperature gradient.

Addendum to "Colored-noise-induced discontinuous transitions in symbiotic ecosystems".

PubMed

Sauga, Ako; Mankin, Romi

2005-06-01

A symbiotic ecosystem with Gompertz self-regulation and with adaptive competition between populations is studied by means of a N-species Lotka-Volterra stochastic model. The influence of fluctuating environment on the carrying capacity of a population is modeled as a dichotomous noise. The study is a follow up of previous investigations of symbiotic ecosystems subjected to the generalized Verhulst self-regulation [Phys. Rev. E 69, 061106 (2004); 65, 051108 (2002)]. In the framework of mean-field approximation the behavior of the solutions of the self-consistency equation for a stationary system is examined analytically in the full phase space of system parameters. Depending on the mutual interplay of symbiosis and competition of species, variation of noise parameters (amplitude, correlation time) can induce doubly unidirectional discontinuous transitions as well as single unidirectional discontinuous transitions of the mean population size.

Addendum to ``Colored-noise-induced discontinuous transitions in symbiotic ecosystems''

NASA Astrophysics Data System (ADS)

Sauga, Ako; Mankin, Romi

2005-06-01

A symbiotic ecosystem with Gompertz self-regulation and with adaptive competition between populations is studied by means of a N -species Lotka-Volterra stochastic model. The influence of fluctuating environment on the carrying capacity of a population is modeled as a dichotomous noise. The study is a follow up of previous investigations of symbiotic ecosystems subjected to the generalized Verhulst self-regulation [Phys. Rev. E 69, 061106 (2004); 65, 051108 (2002)]. In the framework of mean-field approximation the behavior of the solutions of the self-consistency equation for a stationary system is examined analytically in the full phase space of system parameters. Depending on the mutual interplay of symbiosis and competition of species, variation of noise parameters (amplitude, correlation time) can induce doubly unidirectional discontinuous transitions as well as single unidirectional discontinuous transitions of the mean population size.

On the asymptotic evolution of finite energy Airy wave functions.

PubMed

Chamorro-Posada, P; Sánchez-Curto, J; Aceves, A B; McDonald, G S

2015-06-15

In general, there is an inverse relation between the degree of localization of a wave function of a certain class and its transform representation dictated by the scaling property of the Fourier transform. We report that in the case of finite energy Airy wave packets a simultaneous increase in their localization in the direct and transform domains can be obtained as the apodization parameter is varied. One consequence of this is that the far-field diffraction rate of a finite energy Airy beam decreases as the beam localization at the launch plane increases. We analyze the asymptotic properties of finite energy Airy wave functions using the stationary phase method. We obtain one dominant contribution to the long-term evolution that admits a Gaussian-like approximation, which displays the expected reduction of its broadening rate as the input localization is increased.

Synthesis and chromatographic characterization of dextran-coated zirconia high-performance liquid chromatographic stationary phases.

PubMed

Dunlap, C J; Carr, P W

1996-10-11

Porous zirconia particles made by the oil emulsion (OE) method and the polymerization-induced colloid aggregation (PICA) method have been coated with a small, carboxymethylated (approximately 5%) dextran polymer and crosslinked in place. The parameters of the coating process (dextran concentration, adsorption time and crosslinker concentration) have all been examined and an optimum value for each determined. The coated and uncoated materials were characterized by nitrogen sorptometry and size-exclusion chromatography (SEC) using solutes (polystyrenes and dextrans) of well-defined molecular masses. Nitrogen sorptometry results show that the PICA material has a much lower pore volume and smaller pore diameter than do the OE materials. Despite this, the elution volumes of the SEC probes change very little upon polymer coating the PICA material while the OE material shows a very large change upon coating.

Structural Crashworthiness and Failure

DTIC Science & Technology

1993-04-16

body motion occurs. This rigid -plastic idealization for dynamically loaded structures is based upon the fact that the plastic deformation of a...in general, for any tensor variable x, i represents the convective derivative. It should be noted that the rigid body rotation is included in the...clamped, impulsively loaded, rigid - plastic beam.’ (a) First phase of motion with stationary transverse plastic hinges at A and E and stationary plastic

The PEDALS Stationary Cycling Intervention and Health-Related Quality of Life in Children with Cerebral Palsy: A Randomized Controlled Trial

ERIC Educational Resources Information Center

DeMuth, Sharon K.; Knutson, Loretta M.; Fowler, Eileen G.

2012-01-01

Aim: The aim of this study was to assess health-related quality of life (HRQOL) following a stationary cycling intervention in children with cerebral palsy (CP). Method: This was a phase I multisite randomized controlled trial with single blinding. HRQOL was evaluated using the Pediatric Quality of Life Inventory SF15 (PedsQL; children) and…

HPLC SEPARATION OF CHIRAL ORGANOPHOSPHORUS PESTICIDES ON POLYSACCHARIDE CHIRAL STATIONARY PHASES

EPA Science Inventory

High-performance liquid chromatographic separation of the individual enantiomers of 12 organophosphorus pesticides (OPs) were obtained on polysaccharide chiral HPLC columns using an alkane-alcohol mobile phase. The OP pesticides were crotoxyphos, dialifor, dyfonate, fenamiphos, ...

Effects of growth phase on the membrane lipid composition of the thaumarchaeon Nitrosopumilus maritimus and their implications for archaeal lipid distributions in the marine environment

NASA Astrophysics Data System (ADS)

Elling, Felix J.; Könneke, Martin; Lipp, Julius S.; Becker, Kevin W.; Gagen, Emma J.; Hinrichs, Kai-Uwe

2014-09-01

The characteristic glycerol dibiphytanyl glycerol tetraether membrane lipids (GDGTs) of marine ammonia-oxidizing archaea (AOA) are widely used as biomarkers for studying their occurrence and distribution in marine environments and for reconstructing past sea surface temperatures using the TEX86 index. Despite an increasing use of GDGT biomarkers in microbial ecology and paleoceanography, the physiological and environmental factors influencing lipid composition in AOA, in particular the cyclization of GDGTs, remain unconstrained. We investigated the effect of metabolic state on the composition of intact polar and core lipids and the resulting TEX86 paleothermometer in pure cultures of the marine AOA Nitrosopumilus maritimus as a function of growth phase. The cellular lipid content ranged from 0.9 to 1.9 fg cell-1 and increased during growth but was lower in the stationary phases, indicating changes in average cell size in response to metabolic status. The relative abundances of monoglycosidic GDGTs increased from 27% in early growth phase to 60% in late stationary phase, while monohydroxylated GDGTs increased only slightly. The proportions of characteristic hexose-phosphohexose GDGTs were up to 7-fold higher during growth than in stationary phase, suggesting that they are valuable biomarkers for the metabolically active fraction of AOA assemblages in the environment. Methoxy archaeol was identified as novel, genuine archaeal lipid of yet unknown function; it is one of the most abundant single compounds in the lipidome of N. maritimus. TEX86 values of individual intact GDGTs and total GDGTs differed substantially, were generally lower during early and late growth phases than in stationary phase, and did not reflect growth temperature. Consequently, our results strongly suggest that biosynthesis is at least partially responsible for the systematic offsets in TEX86 values between different intact polar GDGT classes observed previously in environmental samples. Nevertheless, differences in degradation rates of intact polar GDGTs may influence the TEX86 index because the intact polar lipid precursors differ for individual core GDGTs and moreover their relative abundances change with growth stage, which may result in distinct release rates of core GDGTs from their polar precursors. Overall, our findings stress the need to accurately describe the factors influencing GDGT cyclization in thaumarchaea and thus paleotemperature reconstructions.

Ralstonia eutropha H16 Flagellation Changes According to Nutrient Supply and State of Poly(3-Hydroxybutyrate) Accumulation▿

PubMed Central

Raberg, Matthias; Reinecke, Frank; Reichelt, Rudolf; Malkus, Ursula; König, Simone; Pötter, Markus; Fricke, Wolfgang Florian; Pohlmann, Anne; Voigt, Birgit; Hecker, Michael; Friedrich, Bärbel; Bowien, Botho; Steinbüchel, Alexander

2008-01-01

Two-dimensional polyacrylamide gel electrophoresis (2D PAGE), in combination with matrix-assisted laser desorption ionization-time of flight analysis, and the recently revealed genome sequence of Ralstonia eutropha H16 were employed to detect and identify proteins that are differentially expressed during different phases of poly(3-hydroxybutyric acid) (PHB) metabolism. For this, a modified protein extraction protocol applicable to PHB-harboring cells was developed to enable 2D PAGE-based proteome analysis of such cells. Subsequently, samples from (i) the exponential growth phase, (ii) the stationary growth phase permissive for PHB biosynthesis, and (iii) a phase permissive for PHB mobilization were analyzed. Among several proteins exhibiting quantitative changes during the time course of a cultivation experiment, flagellin, which is the main protein of bacterial flagella, was identified. Initial investigations that report on changes of flagellation for R. eutropha were done, but 2D PAGE and electron microscopic examinations of cells revealed clear evidence that R. eutropha exhibited further significant changes in flagellation depending on the life cycle, nutritional supply, and, in particular, PHB metabolism. The results of our study suggest that R. eutropha is strongly flagellated in the exponential growth phase and loses a certain number of flagella in transition to the stationary phase. In the stationary phase under conditions permissive for PHB biosynthesis, flagellation of cells admittedly stagnated. However, under conditions permissive for intracellular PHB mobilization after a nitrogen source was added to cells that are carbon deprived but with full PHB accumulation, flagella are lost. This might be due to a degradation of flagella; at least, the cells stopped flagellin synthesis while normal degradation continued. In contrast, under nutrient limitation or the loss of phasins, cells retained their flagella. PMID:18502919

Determination of pterins in urine by HPLC with UV and fluorescent detection using different types of chromatographic stationary phases (HILIC, RP C8, RP C18).

PubMed

Kośliński, Piotr; Jarzemski, Piotr; Markuszewski, Michał J; Kaliszan, Roman

2014-03-01

Pterins are a class of potential cancer biomarkers. New methods involving hydrophilic interaction liquid chromatography (HILIC) and reversed phase (RP) high-performance liquid chromatography have been developed for analysis of eight pterin compounds: 6,7-dimethylpterin, pterin, 6-OH-methylpterin, biopterin, isoxanthopterin, neopterin, xanthopterin, and pterin-6-carboxylic acid. The effect of mobile phase composition, buffer type, pH and concentration on retention using HILIC, C8 and C18 RP stationary phases were examined. Separation of pterins on RP and HILIC stationary phase was performed and optimized. Eight pterins were successfully separated on HILIC Luna diol-bonded phases, Aquasil C18 RP column and LiChrospher C8 RP column. Determination and separation of the pterins from urine samples were performed on HILIC Luna and LiChrospher C8 RP columns which were chosen as the most appropriate ones. Finally, LiChrospher C8 RP column with fluorescence detection was selected for further validation of the method. The optimum chromatographic condition was mobile phase methanol (A)/phosphoric buffer pH 7, 10mM (B), isocratic elution 0-15min 5% A flow=0.5ml/min 15-17min. 5% A, flow=0.5-1ml/min the linearity (R(2)>0.997) and retention time repeatability (RSD%<1) were at satisfactory level. The precision of peak areas expressed as RSD in % was between 0.55 and 14. Pterins detection limits varied from 0.041ng/ml to 2.9ng/ml. Finally, HPLC method was used for the analysis of pterins in urine samples with two different oxidation procedures. Concentration levels of pterin compounds in bladder cancer patients and healthy subjects were compared. Copyright © 2013 Elsevier B.V. All rights reserved.

A proteomic approach to cold acclimation of Staphylococcus aureus CECT 976 grown at room and human body temperatures.

PubMed

Sánchez, B; Cabo, M L; Margolles, A; Herrera, J J R

2010-11-15

Staphylococcus aureus is an important pathogenic microorganism that has been associated with serious infection problems in different fields, from food to clinic. In the present study, we have taken into account that the main reservoirs of this microorganism are the human body and some parts of food processing plants, which have normal temperatures of around 37 and 25°C, respectively. It can be expected that S. aureus must acclimate its metabolism to colder temperatures before growing in food matrices. Since temperature abuse for foods occurs at approximately 12°C, it is expected that S. aureus must acclimate its metabolism to colder temperatures before growing in food. For this reason, we have performed a proteomic comparison between exponential- and stationary-phase cultures of S. aureus CECT 976 acclimated to 12°C after growing at 25°C or 37°C. The analysis led to the identification of two different protein patterns associated with cold acclimation, denominated pattern A and pattern B. The first was characteristic of cultures at stationary phase of growth, grown at 25°C and acclimated to 12°C. The second appeared in the rest of experimental cases. Pattern A was distinguished by the presence of glycolytic proteins, whereas pattern B was differentiated by the presence of general stress and regulatory proteins. Pattern A was related through physiological experiments with a cross-resistance to acid pH, whereas pattern B conferred resistance to nisin. This prompted us to conclude that both molecular strategies could be valid, in vivo, for the process of acclimation of S. aureus to cold temperatures. Copyright © 2010 Elsevier B.V. All rights reserved.

Particle Interactions Mediated by Dynamical Networks: Assessment of Macroscopic Descriptions

NASA Astrophysics Data System (ADS)

Barré, J.; Carrillo, J. A.; Degond, P.; Peurichard, D.; Zatorska, E.

2018-02-01

We provide a numerical study of the macroscopic model of Barré et al. (Multiscale Model Simul, 2017, to appear) derived from an agent-based model for a system of particles interacting through a dynamical network of links. Assuming that the network remodeling process is very fast, the macroscopic model takes the form of a single aggregation-diffusion equation for the density of particles. The theoretical study of the macroscopic model gives precise criteria for the phase transitions of the steady states, and in the one-dimensional case, we show numerically that the stationary solutions of the microscopic model undergo the same phase transitions and bifurcation types as the macroscopic model. In the two-dimensional case, we show that the numerical simulations of the macroscopic model are in excellent agreement with the predicted theoretical values. This study provides a partial validation of the formal derivation of the macroscopic model from a microscopic formulation and shows that the former is a consistent approximation of an underlying particle dynamics, making it a powerful tool for the modeling of dynamical networks at a large scale.

A novel partitioning method for block-structured adaptive meshes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fu, Lin, E-mail: lin.fu@tum.de; Litvinov, Sergej, E-mail: sergej.litvinov@aer.mw.tum.de; Hu, Xiangyu Y., E-mail: xiangyu.hu@tum.de

We propose a novel partitioning method for block-structured adaptive meshes utilizing the meshless Lagrangian particle concept. With the observation that an optimum partitioning has high analogy to the relaxation of a multi-phase fluid to steady state, physically motivated model equations are developed to characterize the background mesh topology and are solved by multi-phase smoothed-particle hydrodynamics. In contrast to well established partitioning approaches, all optimization objectives are implicitly incorporated and achieved during the particle relaxation to stationary state. Distinct partitioning sub-domains are represented by colored particles and separated by a sharp interface with a surface tension model. In order to obtainmore » the particle relaxation, special viscous and skin friction models, coupled with a tailored time integration algorithm are proposed. Numerical experiments show that the present method has several important properties: generation of approximately equal-sized partitions without dependence on the mesh-element type, optimized interface communication between distinct partitioning sub-domains, continuous domain decomposition which is physically localized and implicitly incremental. Therefore it is particularly suitable for load-balancing of high-performance CFD simulations.« less

Self-immobilization and/or thermal treatment for preparing silica-poly(methyloctylsiloxane) stationary phases.

PubMed

Bottoli, Carla B G; Vigna, Camila R M; Fischer, Gerd; Albert, Klaus; Collins, Kenneth E; Collins, Carol H

2004-03-19

Batches of poly(methyloctylsiloxane) (PMOS)-loaded silica were prepared by the deposition of PMOS, into the pores of HPLC silica. Portions of PMOS-loaded silica were allowed to remain at ambient temperature, without further treatment for 2, 9, 20, 31, 51, 105 and 184 days after preparation to undergo self-immobilization (irreversible adsorption of a layer of polymer on silica at ambient temperature in the absence of initiators). Other portions were subjected to a thermal treatment (100 degrees C for 4h) after 1, 2, 5, 7, 9, 15, 20, 25, 70, 111 and 184 days. Self-immobilized and thermally treated samples were characterized by % C, 29Si cross-polarization magic angle spinning (CP/MAS) NMR spectroscopy and reversed-phase column performance. The results show that thermal immobilization accelerates the distribution and rearrangement of the polymer on the silica surface. However, from the time that a monolayer has been formed by self-immobilization (approximately 100 days for PMOS on Kromasil silica), the thermal treatment does not alter this configuration and, thus, does not change the resulting chromatographic parameters.

A novel partitioning method for block-structured adaptive meshes

NASA Astrophysics Data System (ADS)

Fu, Lin; Litvinov, Sergej; Hu, Xiangyu Y.; Adams, Nikolaus A.

2017-07-01

We propose a novel partitioning method for block-structured adaptive meshes utilizing the meshless Lagrangian particle concept. With the observation that an optimum partitioning has high analogy to the relaxation of a multi-phase fluid to steady state, physically motivated model equations are developed to characterize the background mesh topology and are solved by multi-phase smoothed-particle hydrodynamics. In contrast to well established partitioning approaches, all optimization objectives are implicitly incorporated and achieved during the particle relaxation to stationary state. Distinct partitioning sub-domains are represented by colored particles and separated by a sharp interface with a surface tension model. In order to obtain the particle relaxation, special viscous and skin friction models, coupled with a tailored time integration algorithm are proposed. Numerical experiments show that the present method has several important properties: generation of approximately equal-sized partitions without dependence on the mesh-element type, optimized interface communication between distinct partitioning sub-domains, continuous domain decomposition which is physically localized and implicitly incremental. Therefore it is particularly suitable for load-balancing of high-performance CFD simulations.

Particle Interactions Mediated by Dynamical Networks: Assessment of Macroscopic Descriptions.

PubMed

Barré, J; Carrillo, J A; Degond, P; Peurichard, D; Zatorska, E

2018-01-01

We provide a numerical study of the macroscopic model of Barré et al. (Multiscale Model Simul, 2017, to appear) derived from an agent-based model for a system of particles interacting through a dynamical network of links. Assuming that the network remodeling process is very fast, the macroscopic model takes the form of a single aggregation-diffusion equation for the density of particles. The theoretical study of the macroscopic model gives precise criteria for the phase transitions of the steady states, and in the one-dimensional case, we show numerically that the stationary solutions of the microscopic model undergo the same phase transitions and bifurcation types as the macroscopic model. In the two-dimensional case, we show that the numerical simulations of the macroscopic model are in excellent agreement with the predicted theoretical values. This study provides a partial validation of the formal derivation of the macroscopic model from a microscopic formulation and shows that the former is a consistent approximation of an underlying particle dynamics, making it a powerful tool for the modeling of dynamical networks at a large scale.

The alternative sigma factor, sigmaS, affects polyhydroxyalkanoate metabolism in Pseudomonas putida.

PubMed

Raiger-Iustman, Laura J; Ruiz, Jimena A

2008-07-01

To determine whether the stationary sigma factor, sigma(S), influences polyhydroxyalkanoate metabolism in Pseudomonas putida KT2440, an rpoS-negative mutant was constructed to evaluate polyhydroxyalkanoate accumulation and expression of a translational fusion to the promoter region of the genes that code for polyhydroxyalkanoate synthase 1 (phaC1) and polyhydroxyalkanoate depolymerase (phaZ). By comparison with the wild-type, the rpoS mutant showed a higher polyhydroxyalkanoate degradation rate and increased expression of the translational fusion during the stationary growth phase. These results suggest that sigma(S) might control the genes involved in polyhydroxyalkanoate metabolism, possibly in an indirect manner. In addition, survival and oxidative stress assays performed under polyhydroxyalkanoate- and nonpolyhydroxyalkanoate- accumulating conditions demonstrated that the accumulated polyhydroxyalkanoate increased the survival and stress tolerance of the rpoS mutant. According to this, polyhydroxyalkanoate accumulation would help cells to overcome the adverse conditions encountered during the stationary phase in the strain that lacks RpoS.

Phase diagrams for the spatial public goods game with pool punishment

NASA Astrophysics Data System (ADS)

Szolnoki, Attila; Szabó, György; Perc, Matjaž

2011-03-01

The efficiency of institutionalized punishment is studied by evaluating the stationary states in the spatial public goods game comprising unconditional defectors, cooperators, and cooperating pool punishers as the three competing strategies. Fines and costs of pool punishment are considered as the two main parameters determining the stationary distributions of strategies on the square lattice. Each player collects a payoff from five five-person public goods games, and the evolution of strategies is subsequently governed by imitation based on pairwise comparisons at a low level of noise. The impact of pool punishment on the evolution of cooperation in structured populations is significantly different from that reported previously for peer punishment. Representative phase diagrams reveal remarkably rich behavior, depending also on the value of the synergy factor that characterizes the efficiency of investments payed into the common pool. Besides traditional single- and two-strategy stationary states, a rock-paper-scissors type of cyclic dominance can emerge in strikingly different ways.

Preparation of hydrophilic polymer-grafted polystyrene beads for hydrophilic interaction chromatography via surface-initiated atom transfer radical polymerization.

PubMed

Dai, Xiaojun; He, Yuan; Wei, Yinmao; Gong, Bolin

2011-11-01

A one-step procedure based on surface-initiated atom transfer radical polymerization (SI-ATRP) to hydrophilize monodisperse poly(chloromethylstyrene-co-divinylbenzene) beads has been presented in this work, using 2-hydroxyl-3-[4-(hydroxymethyl)-1H-1,2,3-triazol-1-yl]propyl 2-methylacrylate (HTMA) as a monomer. The chain length of the grafted poly(HTMA) was controlled via varying the ratio of HTMA to initiator on the surface of the beads. When using the grafted beads as a stationary phase in hydrophilic interaction chromatography (HILIC), good resolution for nucleobases/nucleosides was obtained with acetonitrile aqueous solution as an eluent; while for phenolic acids and glycosides, they could be eluted and separated in the presence of TFA. The retention time of the solutes increased with the amount of the grafted HTMA. The retention mechanisms of solutes were investigated by the effects of mobile phase composition and buffer pH on the retention of solutes. The results illustrated that the retention behaviors of the tested solutes were dominated by hydrogen bonding interaction and electrostatic interaction. From the chemical structure of the ligands, the modified beads could not only be used as a stationary phase in HILIC, but also act as a useful building block to develop new stationary phases for other chromatographic modes such as affinity media. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Investigation on the preparation and chromatographic behavior of a new para-tert-butylcalix[4]arene-1,2-crown-4 stationary phase for high performance liquid chromatography.

PubMed

Hu, Kai; Zhao, Wenjie; Wen, Fuyong; Liu, Junwei; Zhao, Xiaolan; Xu, Zhanhui; Niu, Bailin; Ye, Baoxian; Wu, Yangjie; Zhang, Shusheng

2011-07-15

In the present work, a new para-tert-butylcalix[4]arene-1,2-crown-4 bonded silica stationary phase (CBS4-4) was synthesized, structurally characterized, and employed to separate polycyclic aromatic hydrocarbons (PAHs), phenols, aromatic amines, benzoic acid and its derivatives. The chromatographic behaviors of the prepared stationary phase were investigated and compared with ODS. The effects of methanol concentrations on the retention index show that CBS4-4 exhibits high selectivity for the above analytes. The separation mechanisms based on the different interactions between calixarene and the analytes were discussed. With the assistance of quantum chemistry calculation, the interaction Gibbs free energy change ΔG(solv) (in the mobile phase) of p, m and o-phenylenediamine positional isomers and para-tert-butylcalix[4]arene-1,2-crown-4 were obtained. The ΔG(solv) values were consistent with the retention behavior of p, m and o-phenylenediamine on the CBS4-4. According to the chromatographic data, it can be concluded that the selectivity of CBS4-4 for analytes is mainly ascribed to hydrophobic interaction, accompanied by other effects such as hydrogen bonding interaction, π-π and inclusion interaction. The CBS4-4 column has been successfully employed for the analysis of benzoic acid in Sprite drink. Copyright © 2011 Elsevier B.V. All rights reserved.

Antibacterial Activity of a Novel Peptide-Modified Lysin Against Acinetobacter baumannii and Pseudomonas aeruginosa

PubMed Central

Yang, Hang; Wang, Mengyue; Yu, Junping; Wei, Hongping

2015-01-01

The global emergence of multidrug-resistant (MDR) bacteria is a growing threat to public health worldwide. Natural bacteriophage lysins are promising alternatives in the treatment of infections caused by Gram-positive pathogens, but not Gram-negative ones, like Acinetobacter baumannii and Pseudomonas aeruginosa, due to the barriers posed by their outer membranes. Recently, modifying a natural lysin with an antimicrobial peptide was found able to break the barriers, and to kill Gram-negative pathogens. Herein, a new peptide-modified lysin (PlyA) was constructed by fusing the cecropin A peptide residues 1–8 (KWKLFKKI) with the OBPgp279 lysin and its antibacterial activity was studied. PlyA showed good and broad antibacterial activities against logarithmic phase A. baumannii and P. aeruginosa, but much reduced activities against the cells in stationary phase. Addition of outer membrane permeabilizers (EDTA and citric acid) could enhance the antibacterial activity of PlyA against stationary phase cells. Finally, no antibacterial activity of PlyA could be observed in some bio-matrices, such as culture media, milk, and sera. In conclusion, we reported here a novel peptide-modified lysin with significant antibacterial activity against both logarithmic (without OMPs) and stationary phase (with OMPs) A. baumannii and P. aeruginosa cells in buffer, but further optimization is needed to achieve broad activity in diverse bio-matrices. PMID:26733995

Metallomesogenic stationary phase for open-tubular capillary electrochromatography.

PubMed

Chen, Jian-Lian

2006-02-01

A synthetic coppermesogenic polymer is prepared and then covalently bonded to the siloxane-based deactivated column as the stationary phases of open-tubular CEC with essentially high phase ratio. The EOF generated from the modified phase is surveyed through conventional aqueous buffers and hydroorganic mobile phases. Zeta potentials, which are computed from the EOF data and the ratio of dielectric constant to viscosity, are plotted as a function of pH, ionic molarity, and compositional range. These plots responsible for the electroosmotic characteristic of the bonded phases are found to be like those of bare fused-silica or deactivated columns through decreasing or increasing the ACN content in the mobile phase, respectively. This two-phase characteristic is basically derived from the polymeric configuration with carboxylato ligands attached onto the polysiloxane backbone. Phthalates and amino acids are suitable probes to examine the two phenomena, more-polar and less-polar mediums, respectively, and to judge whether the chromatographic retention is the major source of separation mechanism. With the mixing modes of Lewis acid-base interaction, dispersive force, and shape discrimination, the chromatographic partition adequately accomplishes the uneasily resolved separations by only CZE mode, although the electrophoretic migration is truly somewhat involved.

SEPARATION OF SOME RARE EARTHS BY REVERSED-PHASE PARTITION CHROMATOGRAPHY. Report No. 129/V; Rozdzielenie Niektorych Ziem Rzadkich za Pomoca Chromatografii Podzialowej z Odwroconymi Fazami

DOE Office of Scientific and Technical Information (OSTI.GOV)

Siekierski, S.; Fidelis, I.

1960-01-01

The reversed phase partition chromatography was applied to the separation of small amounts of some rare earths. As a stationary phase TBP was used. and the elution was carried out with concentrated HNO/sub 3/. (auth)

Column temperature programming in enantioseparation of dihydropyrimidinone compounds using derivatized cellulose and amylose chiral stationary phases.

PubMed

Wang, Fang; Yeung, David; Han, Jun; Semin, David; McElvain, James S; Cheetham, Janet

2008-03-01

We report the application of column temperature programs as a tool to examine unusual temperature-induced behaviors of polysaccharide chiral stationary phases (CSPs). Using dihydropyrimidinone (DHP) compounds as probes we observed the heating (10-50 degrees C) and cooling (50-10 degrees C) van't Hoff plots of retention factors and/or selectivities of DHP compounds were not superimposable on AD, IA, and AS-H columns solvated with ethanol (EtOH)/n-hexane (n-Hex) mobile phases. The plots were not superimposable on AD, IB, and AS-H columns solvated with 2-propanol (2-PrOH)/n-Hex mobile phases. The thermally induced path-dependant behaviors were caused by slow equilibration as evidenced by the disappearance of the hysteresis in the second heating to cooling cycle and in a cooling to heating cycle. From the step-temperature program (10-50-10 degrees C), only EtOH solvated AD and AS-H phases showed the change of retention factors and/or selectivities with time while only 2-PrOH solvated AS-H phase showed similar behaviors.

Survey of Manual Methods of Measurements of Asbestos, Beryllium, Lead, Cadmium, Selenium, and Mercury in Stationary Source Emissions. Environmental Monitoring Series.

ERIC Educational Resources Information Center

Coulson, Dale M.; And Others

The purpose of this study is to evaluate existing manual methods for analyzing asbestos, beryllium, lead, cadmium, selenium, and mercury, and from this evaluation to provide the best and most practical set of analytical methods for measuring emissions of these elements from stationary sources. The work in this study was divided into two phases.…

Ultrasound beam transmission using a discretely orthogonal Gaussian aperture basis

NASA Astrophysics Data System (ADS)

Roberts, R. A.

2018-04-01

Work is reported on development of a computational model for ultrasound beam transmission at an arbitrary geometry transmission interface for generally anisotropic materials. The work addresses problems encountered when the fundamental assumptions of ray theory do not hold, thereby introducing errors into ray-theory-based transmission models. Specifically, problems occur when the asymptotic integral analysis underlying ray theory encounters multiple stationary phase points in close proximity, due to focusing caused by concavity on either the entry surface or a material slowness surface. The approach presented here projects integrands over both the transducer aperture and the entry surface beam footprint onto a Gaussian-derived basis set, thereby distributing the integral over a summation of second-order phase integrals which are amenable to single stationary phase point analysis. Significantly, convergence is assured provided a sufficiently fine distribution of basis functions is used.

Effect of Secondary Equilibria on the Adsorption of Ibuprofen Enantiomers on a Chiral Stationary Phase with a Grafted Antibiotic Eremomycin

NASA Astrophysics Data System (ADS)

Reshetova, E. N.; Asnin, L. D.; Kachmarsky, K.

2018-02-01

The chromatographic separation of ibuprofen enantiomers on a Nautilus-E chiral stationary phase with a grafted eremomycin antibiotic at high column loading is accompanied by distortion of the shape of chromatographic peaks. A model is proposed to explain this phenomenon. A number of factors are considered in the model: the ionization of ibuprofen in the mobile phase, the pH change in the mass transfer zone caused by ionization, and competitive adsorption involving buffer components. Simulations performed using this model within the theory of nonequilibrium chromatography allow the shape of chromatograms for large amounts of S- and R-ibuprofen samples to be predicted. The adsorption mechanism is found to be mainly ion-exchange. The contribution from the molecular adsorption of ibuprofen to the total retention is shown to be several percent.

Ingestion of Brachionus plicatilis under different microalgae conditions

NASA Astrophysics Data System (ADS)

Zhou, Wenli; Tang, Xuexi; Qiao, Xiuting; Wang, You; Wang, Renjun; Feng, Lei

2009-09-01

The effects of four microalgae, Chlorella vulgaris, Platymonas helgolandicavar, Isochrysis galbana, and Nitzschia closterium on the grazing and filtering rates of the marine rotifer, Brachionus plicatilis, were evaluated under laboratory conditions. The grazing rates in separate cultures of the four microalga were as follows: C. vulgaris > P. helgolandicavar > I. galbana > N. closterium. However, the filtering rates occurred in the following order: P. helgolandicavar > N. closterium > C. vulgaris > I. galbana. A mixed diets experiment revealed that P. helgolandicavar was the preferred diet of B. plicatilis. In addition, the grazing rate of B. plicatilis increased gradually as the density of the microalgae increased, until concentrations of 2.5×106 cells mL-1 for C. vulgaris and 1.5×106 cells mL-1 for I. galbana were obtained. Furthermore, the filtering rate increased slightly when the density of the microalgae was low, after which it declined as the microalgal density increased. The grazing rates of B. plicatilis were as follows during the different growth phases: stationary phase > exponential phase > lag phase > decline phase. Additionally, the filtering rates during the growth phases were: exponential phase > lag phase > stationary phase > decline phase. The results of this study provide foundational information that can be used to explore the optimal culture conditions for rotifers and to promote the development of aquaculture.

Effect of temperature gradient on liquid-liquid phase separation in a polyolefin blend.

PubMed

Jiang, Hua; Dou, Nannan; Fan, Guoqiang; Yang, Zhaohui; Zhang, Xiaohua

2013-09-28

We have investigated experimentally the structure formation processes during phase separation via spinodal decomposition above and below the spinodal line in a binary polymer blend system exposed to in-plane stationary thermal gradients using phase contrast optical microscopy and temperature gradient hot stage. Below the spinodal line there is a coupling of concentration fluctuations and thermal gradient imposed by the temperature gradient hot stage. Also under the thermal gradient annealing phase-separated domains grow faster compared with the system under homogeneous temperature annealing on a zero-gradient or a conventional hot stage. We suggest that the in-plane thermal gradient accelerates phase separation through the enhancement in concentration fluctuations in the early and intermediate stages of spinodal decomposition. In a thermal gradient field, the strength of concentration fluctuation close to the critical point (above the spinodal line) is strong enough to induce phase separation even in one-phase regime of the phase diagram. In the presence of a temperature gradient the equilibrium phase diagrams are no longer valid, and the systems with an upper critical solution temperature can be quenched into phase separation by applying the stationary temperature gradient. The in-plane temperature gradient drives enhanced concentration fluctuations in a binary polymer blend system above and below the spinodal line.

HIGH PERFORMANCE LIQUID CHROMATOGRAPHIC SEPARATION OF THE ENANTIOMERS OF ORGANOPHOSPHORUS PESTICIDES ON POLYSACCHARIDE CHIRAL STATIONARY PHASES

EPA Science Inventory

High-performance liquid chromatographic separation of the individual enantiomers of 12 organophosphorus pesticides (OPs) was obtained on polysaccharide enantioselective HPLC columns using alkane-alcohol mobile phase. The OP pesticides were crotoxyphos, dialifor, fonofos, fenamiph...

Weakly nonparallel and curvature effects on stationary crossflow instability: Comparison of results from multiple-scales analysis and parabolized stability equations

NASA Technical Reports Server (NTRS)

Singer, Bart A.; Choudhari, Meelan; Li, Fei

1995-01-01

A multiple-scales approach is used to approximate the effects of nonparallelism and streamwise surface curvature on the growth of stationary crossflow vortices in incompressible, three-dimesional boundary layers. The results agree with results predicted by solving the parabolized stability equations in regions where the nonparallelism is sufficiently weak. As the nonparallelism increases, the agreement between the two approaches worsens. An attempt has been made to quantify the nonparallelism on flow stability in terms of a nondimensional number that describes the rate of change of the mean flow relative to the disturbance wavelength. We find that the above nondimensional number provides useful information about the adequacy of the multiple-scales approximation for different disturbances for a given flow geometry, but the number does not collapse data for different flow geometries onto a single curve.

Approximate dynamic programming for optimal stationary control with control-dependent noise.

PubMed

Jiang, Yu; Jiang, Zhong-Ping

2011-12-01

This brief studies the stochastic optimal control problem via reinforcement learning and approximate/adaptive dynamic programming (ADP). A policy iteration algorithm is derived in the presence of both additive and multiplicative noise using Itô calculus. The expectation of the approximated cost matrix is guaranteed to converge to the solution of some algebraic Riccati equation that gives rise to the optimal cost value. Moreover, the covariance of the approximated cost matrix can be reduced by increasing the length of time interval between two consecutive iterations. Finally, a numerical example is given to illustrate the efficiency of the proposed ADP methodology.

Application of the zeta potential for stationary phase characterization in ion chromatography.

PubMed

Buszewski, Bogusław; Jaćkowska, Magdalena; Bocian, Szymon; Dziubakiewicz, Ewelina

2013-01-01

Two series of homemade stationary bonded phases for ion chromatography were investigated according to their zeta potential. One set of dendrimer anion exchanger was synthesized on the polymer support whereas the second material was prepared on the silica gel. The zeta potential data in water environment as well as buffered water solution were obtained. The influence of the length of anion-exchanger chains, the type of the support of the modified surface, and charge distribution on these data was investigated. Additionally, the zeta potential was correlated with retention factor of inorganic ions to describe their influence on the retention mechanism in ion chromatography. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Electrochromatography on acrylate-based monolith in cyclic olefin copolymer microchip: an attractive technology.

PubMed

Ladner, Y; Cretier, G; Faure, K

2015-01-01

Electrochromatography (EC) on a porous monolithic stationary phase prepared within the channels of a microsystem is an attractive alternative for on-chip separation. It combines the separation mechanisms of electrophoresis and liquid chromatography. Moreover, the porous polymer monolithic materials have become popular as stationary phase due to the ease and rapidity of fabrication via free radical photopolymerization. Here, we describe a hexyl acrylate (HA)-based porous monolith which is simultaneously in situ synthesized and anchored to the inner walls of the channel of a cyclic olefin copolymer (COC) device in only 2 min. The baseline separation of a mixture of neurotransmitters including six amino acids and two catecholamines is realized.

Electrokinetic pump

DOEpatents

Patel, Kamlesh D.

2007-11-20

A method for altering the surface properties of a particle bed. In application, the method pertains particularly to an electrokinetic pump configuration where nanoparticles are bonded to the surface of the stationary phase to alter the surface properties of the stationary phase including the surface area and/or the zeta potential and thus improve the efficiency and operating range of these pumps. By functionalizing the nanoparticles to change the zeta potential the electrokinetic pump is rendered capable of operating with working fluids having pH values that can range from 2-10 generally and acidic working fluids in particular. For applications in which the pump is intended to handle highly acidic solutions latex nanoparticles that are quaternary amine functionalized can be used.

Bistability in the chemical master equation for dual phosphorylation cycles.

PubMed

Bazzani, Armando; Castellani, Gastone C; Giampieri, Enrico; Remondini, Daniel; Cooper, Leon N

2012-06-21

Dual phospho/dephosphorylation cycles, as well as covalent enzymatic-catalyzed modifications of substrates are widely diffused within cellular systems and are crucial for the control of complex responses such as learning, memory, and cellular fate determination. Despite the large body of deterministic studies and the increasing work aimed at elucidating the effect of noise in such systems, some aspects remain unclear. Here we study the stationary distribution provided by the two-dimensional chemical master equation for a well-known model of a two step phospho/dephosphorylation cycle using the quasi-steady state approximation of enzymatic kinetics. Our aim is to analyze the role of fluctuations and the molecules distribution properties in the transition to a bistable regime. When detailed balance conditions are satisfied it is possible to compute equilibrium distributions in a closed and explicit form. When detailed balance is not satisfied, the stationary non-equilibrium state is strongly influenced by the chemical fluxes. In the last case, we show how the external field derived from the generation and recombination transition rates, can be decomposed by the Helmholtz theorem, into a conservative and a rotational (irreversible) part. Moreover, this decomposition allows to compute the stationary distribution via a perturbative approach. For a finite number of molecules there exists diffusion dynamics in a macroscopic region of the state space where a relevant transition rate between the two critical points is observed. Further, the stationary distribution function can be approximated by the solution of a Fokker-Planck equation. We illustrate the theoretical results using several numerical simulations.

Bidentate urea-based chiral selectors for enantioselective high performance liquid chromatography: synthesis and evaluation of "Crab-like" stationary phases.

PubMed

Kotoni, Dorina; Villani, Claudio; Bell, David S; Capitani, Donatella; Campiglia, Pietro; Gasparrini, Francesco

2013-07-05

A rational approach for the design and preparation of two new "Crab-like" totally synthetic, brush-type chiral stationary phases is presented. Enantiopure diamines, namely 1,2-diaminocyclohexane and 1,2-diphenyl-1,2-ethylene-diamine were treated with 3-(triethoxysilyl)propyl isocyanate, to yield reactive ureido selectors that were eventually attached to unmodified silica particles through a stable, bidentate tether, through a facile two-step one-pot procedure. A full chemical characterization of the new materials has been obtained through solid-state NMR (both (29)Si and (13)C CPMAS) spectroscopy. Columns packed with the two Crab-like chiral stationary phases allow for different mechanisms of separation: normal phase liquid chromatography, reversed phase liquid chromatography and polar organic mode and show a high stability at basic pH values. In particular, the Crab-like column containing the 1,2-diphenyl-1,2-ethylene-diamine selector proved a promising candidate for the resolution of a wide range of racemates (including benzodiazepines, N-derivatized amino acids, and free carboxylic acids) both in normal phase and polar organic mode. An Hmin of 9.57 at a μsf of 0.80mm/s (corresponding to 0.8mL/min) was obtained through van Deemter analysis, based on toluene, for the Crab-like column with the 1,2-diphenyl-1,2-ethylene-diamine selector (250mm×4.6mm I.D.), with a calculated reduced height equivalent to a theoretical plate (h) of only 1.91. Finally, comparative studies were performed with a polymeric commercially available P-CAP-DP column in order to evaluate enantioselectivity and resolution of the Crab-like columns. Copyright © 2013 Elsevier B.V. All rights reserved.

Simulation study on characteristics of long-range interaction in randomly asymmetric exclusion process

NASA Astrophysics Data System (ADS)

Zhao, Shi-Bo; Liu, Ming-Zhe; Yang, Lan-Ying

2015-04-01

In this paper we investigate the dynamics of an asymmetric exclusion process on a one-dimensional lattice with long-range hopping and random update via Monte Carlo simulations theoretically. Particles in the model will firstly try to hop over successive unoccupied sites with a probability q, which is different from previous exclusion process models. The probability q may represent the random access of particles. Numerical simulations for stationary particle currents, density profiles, and phase diagrams are obtained. There are three possible stationary phases: the low density (LD) phase, high density (HD) phase, and maximal current (MC) in the system, respectively. Interestingly, bulk density in the LD phase tends to zero, while the MC phase is governed by α, β, and q. The HD phase is nearly the same as the normal TASEP, determined by exit rate β. Theoretical analysis is in good agreement with simulation results. The proposed model may provide a better understanding of random interaction dynamics in complex systems. Project supported by the National Natural Science Foundation of China (Grant Nos. 41274109 and 11104022), the Fund for Sichuan Youth Science and Technology Innovation Research Team (Grant No. 2011JTD0013), and the Creative Team Program of Chengdu University of Technology.

Effect of growth phase on the fatty acid compositions of four species of marine diatoms

NASA Astrophysics Data System (ADS)

Liang, Ying; Mai, Kangsen

2005-04-01

The fatty acid compositions of four species of marine diatoms ( Chaetoceros gracilis MACC/B13, Cylindrotheca fusiformis MACC/B211, Phaeodactylum tricornutum MACC/B221 and Nitzschia closterium MACC/B222), cultivated at 22°C±1°C with the salinity of 28 in f/2 medium and harvested in the exponential growth phase, the early stationary phase and the late stationary phase, were determined. The results showed that growth phase has significant effect on most fatty acid contents in the four species of marine diatoms. The proportions of 16:0 and 16:1n-7 fatty acids increased while those of 16:3n-4 and eicosapentaenoic acid (EPA) decreased with increasing culture age in all species studied. The subtotal of saturated fatty acids (SFA) increased with the increasing culture age in all species with the exception of B13. The subtotal of monounsaturated fatty acids (MUFA) increased while that of polyunsaturated fatty acids (PUFA) decreased with culture age in the four species of marine diatoms. MUFA reached their lowest value in the exponential growth phase, whereas PUFA reached their highest value in the same phase.

Exploring Liquid Sequential Injection Chromatography to Teach Fundamentals of Separation Methods: A Very Fast Analytical Chemistry Experiment

ERIC Educational Resources Information Center

Penteado, Jose C.; Masini, Jorge Cesar

2011-01-01

Influence of the solvent strength determined by the addition of a mobile-phase organic modifier and pH on chromatographic separation of sorbic acid and vanillin has been investigated by the relatively new technique, liquid sequential injection chromatography (SIC). This technique uses reversed-phase monolithic stationary phase to execute fast…

Peak distortion effects in analytical ion chromatography.

PubMed

Wahab, M Farooq; Anderson, Jordan K; Abdelrady, Mohamed; Lucy, Charles A

2014-01-07

The elution profile of chromatographic peaks provides fundamental understanding of the processes that occur in the mobile phase and the stationary phase. Major advances have been made in the column chemistry and suppressor technology in ion chromatography (IC) to handle a variety of sample matrices and ions. However, if the samples contain high concentrations of matrix ions, the overloaded peak elution profile is distorted. Consequently, the trace peaks shift their positions in the chromatogram in a manner that depends on the peak shape of the overloading analyte. In this work, the peak shapes in IC are examined from a fundamental perspective. Three commercial IC columns AS16, AS18, and AS23 were studied with borate, hydroxide and carbonate as suppressible eluents. Monovalent ions (chloride, bromide, and nitrate) are used as model analytes under analytical (0.1 mM) to overload conditions (10-500 mM). Both peak fronting and tailing are observed. On the basis of competitive Langmuir isotherms, if the eluent anion is more strongly retained than the analyte ion on an ion exchanger, the analyte peak is fronting. If the eluent is more weakly retained on the stationary phase, the analyte peak always tails under overload conditions regardless of the stationary phase capacity. If the charge of the analyte and eluent anions are different (e.g., Br(-) vs CO3(2-)), the analyte peak shapes depend on the eluent concentration in a more complex pattern. It was shown that there are interesting similarities with peak distortions due to strongly retained mobile phase components in other modes of liquid chromatography.

Bayesian inference based on stationary Fokker-Planck sampling.

PubMed

Berrones, Arturo

2010-06-01

A novel formalism for bayesian learning in the context of complex inference models is proposed. The method is based on the use of the stationary Fokker-Planck (SFP) approach to sample from the posterior density. Stationary Fokker-Planck sampling generalizes the Gibbs sampler algorithm for arbitrary and unknown conditional densities. By the SFP procedure, approximate analytical expressions for the conditionals and marginals of the posterior can be constructed. At each stage of SFP, the approximate conditionals are used to define a Gibbs sampling process, which is convergent to the full joint posterior. By the analytical marginals efficient learning methods in the context of artificial neural networks are outlined. Offline and incremental bayesian inference and maximum likelihood estimation from the posterior are performed in classification and regression examples. A comparison of SFP with other Monte Carlo strategies in the general problem of sampling from arbitrary densities is also presented. It is shown that SFP is able to jump large low-probability regions without the need of a careful tuning of any step-size parameter. In fact, the SFP method requires only a small set of meaningful parameters that can be selected following clear, problem-independent guidelines. The computation cost of SFP, measured in terms of loss function evaluations, grows linearly with the given model's dimension.

Modulational Instability and Quantum Discrete Breather States of Cold Bosonic Atoms in a Zig-Zag Optical Lattice

NASA Astrophysics Data System (ADS)

Chang, Xia; Xie, Jiayu; Wu, Tianle; Tang, Bing

2018-07-01

A theoretical study on modulational instability and quantum discrete breather states in a system of cold bosonic atoms in zig-zag optical lattices is presented in this work. The time-dependent Hartree approximation is employed to deal with the multiple body problem. By means of a linear stability analysis, we analytically study the modulational instability, and estimate existence conditions of the bright stationary localized solutions for different values of the second-neighbor hopping constant. On the other hand, we get analytical bright stationary localized solutions, and analyze the influence of the second-neighbor hopping on their existence conditions. The predictions of the modulational instability analysis are shown to be reliable. Using these stationary localized single-boson wave functions, the quantum breather states corresponding to the system with different types of nonlinearities are constructed.

Stationary multifaceted asymmetric radiation from the edge and improved confinement mode in a superconducting tokamak.

PubMed

Gao, X; Xie, J K; Wan, Y X; Ushigusa, K; Wan, B N; Zhang, S Y; Li, J; Kuang, G L

2002-01-01

Stationary multifaceted asymmetric radiation from the edge (MARFE) is studied by gas-puffing feedback control according to an empirical MARFE critical density ( approximately 1.8 x 10(13) cm(-3)) in the HT-7 Ohmic discharges (where the plasma current I(p) is about 170 kA, loop voltage V(loop)=2-3 V, toroidal field B(T)=1.9 T, and Z(eff)=3-4). It is observed that an improved confinement mode characterized by D(alpha) line emissions drops and the line-averaged density increase is triggered in the stationary MARFE discharges. The mode is not a symmetric "detachment" state, because the quasi-steady-state poloidally asymmetric radiation (e.g., C III line emissions) still exists. This phenomenon has not been predicted by the current MARFE theory.

An LO Phase Link Using a Commercial Geo-Stationary Satellite

NASA Technical Reports Server (NTRS)

Bardin, Joseph C.; Weinreb, Sander; Bagri, Durgadas S.

2005-01-01

This viewgraph presentation reviews an experiment to determine feasibility of achieving 1 ps level time transfer using a satellite link and make use of inexpensive Ku band transmit/receive equipment. It reviews the advantages of Two Way Satellite Time Transfer using a commercial Geo-Stationary Satellite: (1) Commercial satellites are available (2) Significant cost reduction when compared to Hydrogen Masers and (3) Large footprint- entire US (including Hawaii) with just one satellite.

Fingerprinting of traditional Chinese medicines on the C18-Diol mixed-mode column in online or offline two-dimensional liquid chromatography on the single column modes.

PubMed

Wang, Qing; Tong, Ling; Yao, Lin; Zhang, Peng; Xu, Li

2016-06-05

In the present study, a mixed-mode stationary phase, C18-Diol, was applied for fingerprint analysis of traditional Chinese medicines. Hydrophobic, hydrogen bonding and electrostatic interactions were demonstrated to contribute the retention separately or jointly, which endowed the C18-Diol stationary phase with distinct selectivity compared to the bare C18 one. The separation of total alkaloids extracted from Fritillaria hupehensis was compared on the C18-Diol and conventional C18 column with the greater resolving power and better symmetry responses on the former one. Besides, a novel two-dimensional liquid chromatography on the single column (2D-LC-1C) was realized on C18-Diol with the offline mode for the alcohol extract of Fritillaria hupehensis and online mode for Ligusticum chuanxiong Hort. The early co-eluted extracted components with great polarity on the first dimension were reinjected on the same column and well separated on the second dimension. The results exhibited that the two complementary RPLC and HILIC modes on C18-Diol stationary phase enhanced the separation capacity and revealed more abundant chemical information of the sample, which was a powerful tool in analyzing complex herbal medicines. Copyright © 2016 Elsevier B.V. All rights reserved.

Deep liquid-chromatographic purification of uranium extract from technetium

DOE Office of Scientific and Technical Information (OSTI.GOV)

Volk, V.; Dvoeglazov, K; Podrezova, L.

The recycling of uranium in the nuclear fuel cycle requires the removal of a number of radioactive and stable impurities like {sup 99}Tc from spent fuels. In order to improve the grade of uranium extract purification from technetium the method of liquid chromatography and the apparatus for its performance have been developed. Process of technetium extraction and concentrating in aqueous solution containing reducing agent has been studied on simulated solutions (U-Tc-HNO{sub 3}-30% TBP-isoparM). The dynamic tests of the method have been carried out on the laboratory unit. Solution of diformyl-hydrazine in nitric acid was used as a stationary phase. Silicamore » gel with specific surface of 186 m{sup 2}/g was used as a carrier of the stationary phase. It is shown that the volume of purified extract increases as the solution temperature increases, concentration of reducing agent increases and extract flow rate decreases. It is established that the technetium content in uranium by this method could achieve a value below 0.3 ppm. Some variants of overload and composition of the stationary phase containing the extracted technetium have been offered and tested. It is defined that the method provides reduction of processing medium-active wastes by more than 10 times during finish refining process. (authors)« less

A stationary-phase protein of Escherichia coli that affects the mode of association between the trp repressor protein and operator-bearing DNA.

PubMed

Yang, W; Ni, L; Somerville, R L

1993-06-15

Highly purified preparations of trp repressor (TrpR) protein derived from Escherichia coli strains that were engineered to overexpress this material were found to contain another protein, of 21 kDa. The second protein, designated WrbA [for tryptophan (W) repressor-binding protein] remained associated with its namesake through several sequential protein fractionation steps. The N-terminal amino acid sequence of the WrbA protein guided the design of two degenerate oligonucleotides that were used as probes in the cloning of the wrbA gene (198 codons). The WrbA protein, in purified form, was found by several criteria to enhance the formation and/or stability of noncovalent complexes between TrpR holorepressor and its primary operator targets. The formation of an operator-holorepressor-WrbA ternary complex was demonstrated by gel mobility-shift analysis. The WrbA protein alone does not interact with the trp operator. During the stationary phase, cells deficient in the WrbA protein were less efficient than wild type in their ability to repress the trp promoter. It is proposed that the WrbA protein functions as an accessory element in blocking TrpR-specific transcriptional processes that might be physiologically disadvantageous in the stationary phase of the bacterial life cycle.

Non-stationary and relaxation phenomena in cavity-assisted quantum memories

NASA Astrophysics Data System (ADS)

Veselkova, N. G.; Sokolov, I. V.

2017-12-01

We investigate the non-stationary and relaxation phenomena in cavity-assisted quantum memories for light. As a storage medium we consider an ensemble of cold atoms with standard Lambda-scheme of working levels. Some theoretical aspects of the problem were treated previously by many authors, and recent experiments stimulate more deep insight into the ultimate ability and limitations of the device. Since quantum memories can be used not only for the storage of quantum information, but also for a substantial manipulation of ensembles of quantum states, the speed of such manipulation and hence the ability to write and retrieve the signals of relatively short duration becomes important. In our research we do not apply the so-called bad cavity limit, and consider the memory operation of the signals whose duration is not much larger than the cavity field lifetime, accounting also for the finite lifetime of atomic coherence. In our paper we present an effective approach that makes it possible to find the non-stationary amplitude and phase behavior of strong classical control field, that matches the desirable time profile of both the envelope and the phase of the retrieved quantized signal. The phase properties of the retrieved quantized signals are of importance for the detection and manipulation of squeezing, entanglement, etc by means of optical mixing and homodyning.

Mutations Enhancing Amino Acid Catabolism Confer a Growth Advantage in Stationary Phase

PubMed Central

Zinser, Erik R.; Kolter, Roberto

1999-01-01

Starved cultures of Escherichia coli undergo successive rounds of population takeovers by mutants of increasing fitness. These mutants express the growth advantage in stationary phase (GASP) phenotype. Previous work identified the rpoS819 allele as a GASP mutation allowing cells to take over stationary-phase cultures after growth in rich media (M. M. Zambrano, D. A. Siegele, M. A. Almirón, A. Tormo, and R. Kolter, Science 259:1757–1760, 1993). Here we have identified three new GASP loci from an aged rpoS819 strain: sgaA, sgaB, and sgaC. Each locus is capable of conferring GASP on the rpoS819 parent, and they can provide successively higher fitnesses for the bacteria in the starved cultures. All four GASP mutations isolated thus far allow for faster growth on both individual and mixtures of amino acids. Each mutation confers a growth advantage on a different subset of amino acids, and these mutations act in concert to increase the overall catabolic capacity of the cell. We present a model whereby this enhanced ability to catabolize amino acids is responsible for the fitness gain during carbon starvation, as it may allow GASP mutants to outcompete the parental cells when growing on the amino acids released by dying cells. PMID:10482523

Characterization of Dynamical Phase Transitions in Quantum Jump Trajectories Beyond the Properties of the Stationary State

NASA Astrophysics Data System (ADS)

Lesanovsky, Igor; van Horssen, Merlijn; Guţă, Mădălin; Garrahan, Juan P.

2013-04-01

We describe how to characterize dynamical phase transitions in open quantum systems from a purely dynamical perspective, namely, through the statistical behavior of quantum jump trajectories. This approach goes beyond considering only properties of the steady state. While in small quantum systems dynamical transitions can only occur trivially at limiting values of the controlling parameters, in many-body systems they arise as collective phenomena and within this perspective they are reminiscent of thermodynamic phase transitions. We illustrate this in open models of increasing complexity: a three-level system, the micromaser, and a dissipative version of the quantum Ising model. In these examples dynamical transitions are accompanied by clear changes in static behavior. This is however not always the case, and, in general, dynamical phases need to be uncovered by observables which are strictly dynamical, e.g., dynamical counting fields. We demonstrate this via the example of a class of models of dissipative quantum glasses, whose dynamics can vary widely despite having identical (and trivial) stationary states.

Figure-ground organization in different phases of the perceptual alternation phenomenon.

PubMed

Tuccio, M T

1995-12-01

Two experiments on figure-ground organization were designed to examine whether the regions of an ambiguous stimulus perceived as "figure" vary as a function of regional area and experience with the stimulus. In Exp. 1 the perceived duration of each interpretation was recorded during continuous viewing for 10 subjects who had been trained until both percepts appeared with statistical regularity (stationary phase). In Exp. 2 the first interpretation reported by 172 naive observers after a few seconds of pattern exposure was recorded. The well-known tendency to interpret smaller regions as figure was noted in Exp. 2 whereas the results of Exp. 1 suggested equal probability of the percepts. Over-all results suggest that alternation is learned during the transient or "early" phase of perception, with some stimulus features and cultural factors influencing the figure-ground organization. During the stationary or late phase of perception the subject is well practiced and the alternating of interpretations becomes largely automatic.

High-performance liquid chromatographic enantioseparation of unusual isoxazoline-fused 2-aminocyclopentanecarboxylic acids on macrocyclic glycopeptide-based chiral stationary phases.

PubMed

Sipos, László; Ilisz, István; Nonn, Melinda; Fülöp, Ferenc; Pataj, Zoltán; Armstrong, Daniel W; Péter, Antal

2012-04-06

The enantiomers of four unusual isoxazoline-fused 2-aminocyclopentanecarboxylic acids were directly separated on chiral stationary phases containing macrocyclic glycopeptide antibiotics teicoplanin (Astec Chirobiotic T and T2), teicoplanin aglycone (Chirobiotic TAG), vancomycin (Chirobiotic V) and vancomycin aglycone (Chirobiotic VAG) as chiral selectors. The effects of the mobile phase composition, the structure of the analytes and temperature on the separations were investigated. Experiments were performed at constant mobile phase compositions in the temperature range 5-45 °C to study the effects of temperature, and thermodynamic parameters were calculated from plots of lnk or lnα versus 1/T. Some mechanistic aspects of the chiral recognition process are discussed with respect to the structures of the analytes. It was found that the enantiomeric separations were in most cases enthalpy-driven. The sequence of elution of the enantiomers was determined in all cases. Copyright © 2011 Elsevier B.V. All rights reserved.

Solvation enthalpies and heat capacities of n-alkanes in four polymer phases by capillary gas chromatography.

PubMed

Görgenyi, Miklós; Héberger, Károly

2005-04-01

Molar solvation enthalpy (deltasol H(o)298) and molar heat capacity changes (deltasol C(o)p) were determined by gas chromatography for the C6-C12 n-alkanes on four preferred stationary phases (100% polydimethyl siloxane, 50% diphenyl-50% dimethyl polysiloxane, 50% trifluoropropyl methylsiloxane, and polyethylene glycol) in commercial FSOT. Statistical evaluation indicated the temperature independence of deltasol C(o)p in the range 303-393 K. Deltasol H(o)298 depends linearly on the number of carbon atoms in the n-alkanes, but no linearity could be established for deltasol C(o)p of higher homologues on polar columns, which may be due to a more ordered state on the liquid phase. The homologues for which a linear temperature dependence exists demonstrated that deltasol C(o)p is related linearly to the van der Waals volume and the temperature derivative of the density of the stationary phase. The results are consistent with a simple physical explanation at the molecular level.

HPLC of fluoroquinolone antibacterials using chiral stationary phase based on enantiomeric (3,3'-diphenyl-1,1'-binaphthyl)-20-crown-6.

PubMed

Choi, Hee Jung; Cho, Hwan Sun; Han, Sang Cheol; Hyun, Myung Ho

2009-02-01

A residual silanol group-protecting chiral stationary phase (CSP) based on optically active (3,3'-diphenyl-1,1'-binaphthyl)-20-crown-6 was successfully applied to the resolution of fluoroquinolone compounds including gemifloxacin mesylate. The chiral recognition ability of the residual silanol group-protecting CSP was generally greater than that of the residual silanol group-containing CSP. From these results, it was concluded that the simple protection of the residual silanol groups of the latter CSP with lipophilic n-octyl groups can improve its chiral recognition ability for the resolution of racemic fluoroquinolone compounds. The chromatographic resolution behaviors were investigated as a function of the content and type of organic and acidic modifiers and the ammonium acetate concentration in aqueous mobile phase and the column temperature. Especially, the addition of ammonium acetate to the mobile phase was found to be a quite effective means of reducing the enantiomer retentions without sacrificing the chiral recognition efficiency of the CSP.

Characterization of dynamical phase transitions in quantum jump trajectories beyond the properties of the stationary state.

PubMed

Lesanovsky, Igor; van Horssen, Merlijn; Guţă, Mădălin; Garrahan, Juan P

2013-04-12

We describe how to characterize dynamical phase transitions in open quantum systems from a purely dynamical perspective, namely, through the statistical behavior of quantum jump trajectories. This approach goes beyond considering only properties of the steady state. While in small quantum systems dynamical transitions can only occur trivially at limiting values of the controlling parameters, in many-body systems they arise as collective phenomena and within this perspective they are reminiscent of thermodynamic phase transitions. We illustrate this in open models of increasing complexity: a three-level system, the micromaser, and a dissipative version of the quantum Ising model. In these examples dynamical transitions are accompanied by clear changes in static behavior. This is however not always the case, and, in general, dynamical phases need to be uncovered by observables which are strictly dynamical, e.g., dynamical counting fields. We demonstrate this via the example of a class of models of dissipative quantum glasses, whose dynamics can vary widely despite having identical (and trivial) stationary states.

Standardization of HPTLC method for the estimation of oxytocin in edibles.

PubMed

Rani, Roopa; Medhe, Sharad; Raj, Kumar Rohit; Srivastava, Manmohan

2013-12-01

Adulteration in food stuff has been regarded as a major social evil and is a mind-boggling problem in society. In this study, a rapid, reliable and cost effective High Performance thin layer Chromatography (HPTLC) has been established for the estimation of oxytocin (adulterant) in vegetables, fruits and milk samples. Oxytocin is one of the most frequently used adulterant added in vegetables and fruits for increasing the growth rate and also to enhance milk production from lactating animals. The standardization of the method was based on simulation parameters of mobile phase, stationary phase and saturation time. The mobile phase used was MeOH: Ammonia (pH 6.8), optimized stationary phase was silica gel and saturation time of 5 min. The method was validated by testing its linearity, accuracy, precision, repeatability and limits of detection and quantification. Thus, the proposed method is simple, rapid and specific and was successfully employed for quality and quantity monitoring of oxytocin content in edible products.

Near-field limitations of Fresnel-regime coherent diffraction imaging

DOE PAGES

Pound, Benjamin A.; Barber, John L.; Nguyen, Kimberly; ...

2017-08-04

Coherent diffraction imaging (CDI) is a rapidly developing form of imaging that offers the potential of wavelength-limited resolution without image-forming lenses. In CDI, the intensity of the diffraction pattern is measured directly by the detector, and various iterative phase retrieval algorithms are used to “invert” the diffraction pattern and reconstruct a high-resolution image of the sample. But, there are certain requirements in CDI that must be met to reconstruct the object. Although most experiments are conducted in the “far-field”—or Fraunhofer—regime where the requirements are not as stringent, some experiments must be conducted in the “near field” where Fresnel diffraction mustmore » be considered. According to the derivation of Fresnel diffraction, successful reconstructions can only be obtained when the small-angle number, a derived quantity, is much less than one. We show, however, that it is not actually necessary to fulfill the small-angle condition. The Fresnel kernel well approximates the exact kernel in regions where the phase oscillates slowly, and in regions of fast oscillations, indicated by large A n , the error between kernels should be negligible due to stationary-phase arguments. Finally we verify, by experiment, this conclusion with a helium neon laser setup and show that it should hold at x-ray wavelengths as well.« less

Near-field limitations of Fresnel-regime coherent diffraction imaging

NASA Astrophysics Data System (ADS)

Pound, Benjamin A.; Barber, John L.; Nguyen, Kimberly; Tyson, Matthew C.; Sandberg, Richard L.

2017-08-01

Coherent diffraction imaging (CDI) is a rapidly developing form of imaging that offers the potential of wavelength-limited resolution without image-forming lenses. In CDI, the intensity of the diffraction pattern is measured directly by the detector, and various iterative phase retrieval algorithms are used to "invert" the diffraction pattern and reconstruct a high-resolution image of the sample. However, there are certain requirements in CDI that must be met to reconstruct the object. Although most experiments are conducted in the "far-field"—or Fraunhofer—regime where the requirements are not as stringent, some experiments must be conducted in the "near field" where Fresnel diffraction must be considered. According to the derivation of Fresnel diffraction, successful reconstructions can only be obtained when the small-angle number, a derived quantity, is much less than one. We show, however, that it is not actually necessary to fulfill the small-angle condition. The Fresnel kernel well approximates the exact kernel in regions where the phase oscillates slowly, and in regions of fast oscillations, indicated by large A n , the error between kernels should be negligible due to stationary-phase arguments. We experimentally verify this conclusion with a helium neon laser setup and show that it should hold at x-ray wavelengths as well.

Impact of environmental colored noise in single-species population dynamics

NASA Astrophysics Data System (ADS)

Spanio, Tommaso; Hidalgo, Jorge; Muñoz, Miguel A.

2017-10-01

Variability on external conditions has important consequences for the dynamics and the organization of biological systems. In many cases, the characteristic timescale of environmental changes as well as their correlations play a fundamental role in the way living systems adapt and respond to it. A proper mathematical approach to understand population dynamics, thus, requires approaches more refined than, e.g., simple white-noise approximations. To shed further light onto this problem, in this paper we propose a unifying framework based on different analytical and numerical tools available to deal with "colored" environmental noise. In particular, we employ a "unified colored noise approximation" to map the original problem into an effective one with white noise, and then we apply a standard path integral approach to gain analytical understanding. For the sake of specificity, we present our approach using as a guideline a variation of the contact process—which can also be seen as a birth-death process of the Malthus-Verhulst class—where the propagation or birth rate varies stochastically in time. Our approach allows us to tackle in a systematic manner some of the relevant questions concerning population dynamics under environmental variability, such as determining the stationary population density, establishing the conditions under which a population may become extinct, and estimating extinction times. We focus on the emerging phase diagram and its possible phase transitions, underlying how these are affected by the presence of environmental noise time-correlations.

Determination of catechins and caffeine in camillia sinensis raw materials, extracts, and dietary supplements by HPLC-uv: single-laboratory validation.

PubMed

Roman, Mark C

2013-01-01

A rapid method has been developed to quantify seven catechins and caffeine in green tea (Camillia sinensis) raw material and powdered extract, and dietary supplements containing green tea extract. The method utilizes RP HPLC with a phenyl-based stationary phase and gradient elution. Detection is by UV absorbance. The total run time, including column re-equilibration, is 13 min. Single-laboratory validation (SLV) has been performed on the method to determine the repeatability, accuracy, selectivity, LOD, LOQ, ruggedness, and linearity for (+)-catechin, (-)-epicatechin, (-)-epicatechin gallate, (-)-epigallocatechin, (-)-gallocatechin gallate, (-)-epigallocatechin gallate, and (+)-gallocatechin, as well as caffeine. Repeatability precision and recovery results met AOAC guidelines for SLV studies for all catechins and caffeine down to a level of approximately 20 mg/g. Finished products containing high concentrations of minerals require the use of EDTA to prevent decomposition of the catechins.

Nonequilibrium dynamics of a pure dry friction model subjected to colored noise

NASA Astrophysics Data System (ADS)

Geffert, Paul M.; Just, Wolfram

2017-06-01

We investigate the impact of noise on a two-dimensional simple paradigmatic piecewise-smooth dynamical system. For that purpose, we consider the motion of a particle subjected to dry friction and colored noise. The finite correlation time of the noise provides an additional dimension in phase space, causes a nontrivial probability current, and establishes a proper nonequilibrium regime. Furthermore, the setup allows for the study of stick-slip phenomena, which show up as a singular component in the stationary probability density. Analytic insight can be provided by application of the unified colored noise approximation, developed by Jung and Hänggi [Phys. Rev. A 35, 4464(R) (1987), 10.1103/PhysRevA.35.4464]. The analysis of probability currents and of power spectral densities underpins the observed stick-slip transition, which is related with a critical value of the noise correlation time.

Vortex and Rings

NASA Image and Video Library

2014-07-07

NASA Cassini spacecraft captures three magnificent sights at once: Saturn north polar vortex and hexagon along with its expansive rings. The hexagon, which is wider than two Earths, owes its appearance to the jet stream that forms its perimeter. The jet stream forms a six-lobed, stationary wave which wraps around the north polar regions at a latitude of roughly 77 degrees North. This view looks toward the sunlit side of the rings from about 37 degrees above the ringplane. The image was taken with the Cassini spacecraft wide-angle camera on April 2, 2014 using a spectral filter which preferentially admits wavelengths of near-infrared light centered at 752 nanometers. The view was obtained at a distance of approximately 1.4 million miles (2.2 million kilometers) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 43 degrees. Image scale is 81 miles (131 kilometers) per pixel. http://photojournal.jpl.nasa.gov/catalog/PIA18274

Keyhole and weld shapes for plasma arc welding under normal and zero gravity

NASA Technical Reports Server (NTRS)

Keanini, R. G.; Rubinsky, B.

1990-01-01

A first order study of the interfacial (keyhole) shape between a penetrating argon plasma arc jet and a stationary liquid metal weld pool is presented. The interface is determined using the Young-Laplace equation by assuming that the plasma jet behaves as a one-dimensional ideal gas flow and by neglecting flow within the weld pool. The solution for the keyhole shape allows an approximate determination of the liquid-solid metal phase boundary location based on the assumption that the liquid melt is a stagnant thermal boundary layer. Parametric studies examine the effect of plasma mass flow rate, initial plasma enthalpy, liquid metal surface tension, and jet shear on weldment shape under both normal and zero gravity. Among the more important findings of this study is that keyhole and weld geometries are minimally affected by gravity, suggesting that data gathered under gravity can be used in planning in-space welding.

Nonlinear Dynamic Behavior of Impact Damage in a Composite Skin-Stiffener Structure

NASA Technical Reports Server (NTRS)

Ooijevaar, T. H.; Rogge, M. D.; Loendersloot, R.; Warnet, L.; Akkerman, R.; deBoer, A.

2013-01-01

One of the key issues in composite structures for aircraft applications is the early identification of damage. Often, service induced damage does not involve visible plastic deformation, but internal matrix related damage, like delaminations. A wide range of technologies, comprising global vibration and local wave propagation methods can be employed for health monitoring purposes. Traditional low frequency modal analysis based methods are linear methods. The effectiveness of these methods is often limited since they rely on a stationary and linear approximation of the system. The nonlinear interaction between a low frequency wave field and a local impact induced skin-stiffener failure is experimentally demonstrated in this paper. The different mechanisms that are responsible for the nonlinearities (opening, closing and contact) of the distorted harmonic waveforms are separated with the help of phase portraits. A basic analytical model is employed to support the observations.

Nonequilibrium dynamics of a pure dry friction model subjected to colored noise.

PubMed

Geffert, Paul M; Just, Wolfram

2017-06-01

We investigate the impact of noise on a two-dimensional simple paradigmatic piecewise-smooth dynamical system. For that purpose, we consider the motion of a particle subjected to dry friction and colored noise. The finite correlation time of the noise provides an additional dimension in phase space, causes a nontrivial probability current, and establishes a proper nonequilibrium regime. Furthermore, the setup allows for the study of stick-slip phenomena, which show up as a singular component in the stationary probability density. Analytic insight can be provided by application of the unified colored noise approximation, developed by Jung and Hänggi [Phys. Rev. A 35, 4464(R) (1987)0556-279110.1103/PhysRevA.35.4464]. The analysis of probability currents and of power spectral densities underpins the observed stick-slip transition, which is related with a critical value of the noise correlation time.

Selective Essential Oils from Spice or Culinary Herbs Have High Activity against Stationary Phase and Biofilm Borrelia burgdorferi

PubMed Central

Feng, Jie; Zhang, Shuo; Shi, Wanliang; Zubcevik, Nevena; Miklossy, Judith; Zhang, Ying

2017-01-01

Although the majority of patients with acute Lyme disease can be cured with the standard 2–4 week antibiotic treatment, about 10–20% of patients continue suffering from chronic symptoms described as posttreatment Lyme disease syndrome. While the cause for this is debated, one possibility is that persister bacteria are not killed by the current Lyme antibiotics and remain active in the system. It has been reported that essential oils have antimicrobial activities and some have been used by patients with persisting Lyme disease symptoms. However, the activity of essential oils against the causative agent Borrelia burgdorferi (B. burgdorferi) has not been well studied. Here, we evaluated the activity of 34 essential oils against B. burgdorferi stationary phase culture as a model for persister bacteria. We found that not all essential oils had activity against the B. burgdorferi stationary phase culture, with top five essential oils (oregano, cinnamon bark, clove bud, citronella, and wintergreen) at a low concentration of 0.25% showing high anti-persister activity that is more active than the known persister drug daptomycin. Interestingly, some highly active essential oils were found to have excellent anti-biofilm ability as shown by their ability to dissolve the aggregated biofilm-like structures. The top three hits, oregano, cinnamon bark, and clove bud completely eradicated all viable cells without any regrowth in subculture in fresh medium, whereas but not citronella and wintergreen did not have this effect. Carvacrol was found to be the most active ingredient of oregano oil showing excellent activity against B. burgdorferi stationary phase cells, while other ingredients of oregano oil p-cymene and α-terpinene had no apparent activity. Future studies are needed to characterize and optimize the active essential oils in drug combination studies in vitro and in vivo and to address their safety and pharmacokinetic properties before they can be considered as a novel treatment of persistent Lyme disease. PMID:29075628

Acid stress management by Cronobacter sakazakii.

PubMed

Alvarez-Ordóñez, Avelino; Cummins, Conor; Deasy, Thérèse; Clifford, Tanya; Begley, Máire; Hill, Colin

2014-05-16

Cronobacter sakazakii is a foodborne pathogenic microorganism associated with sporadic cases of neonatal meningitis, necrotising enterocolitis, septicaemia, bloody diarrhoea and brain abscesses acquired through the consumption of contaminated powdered infant formula (PIF). This study aimed to investigate the growth of C. sakazakii DPC6529, a particularly stress tolerant clinical isolate, in acidified laboratory media and PIF. The possibility of a stationary-phase acid tolerance response (ATR) was also investigated. C. sakazakii DPC6529 grew in LB broth acidified to pH4.2 with hydrochloric acid (HCl) and was capable of relatively fast growth in PIF acidified to pH5.0 with HCl, representing the stomach pH reported for newborns and infants. Moreover, bacterial growth in LB broth supplemented with 1% (w/v) glucose gave rise to a stationary-phase ATR which resulted in enhanced survival against a subsequent acid challenge at pH3.0. A transposon mutagenesis approach was used to shed light on some of the molecular mechanisms involved in the response C. sakazakii DPC6529 to normally lethal acid exposures. The data suggests that repairing damage in proteins and nucleic acids, posttranscriptional modification of tRNA molecules and maintenance of the integrity of the cellular envelope are key processes in the defence against acid stress. Clones carrying transposon insertions in genes encoding the envelope stress response regulators CpxR and OmpR were identified as acid-sensitive mutants. Further analyses of the ompR defective mutant and its complemented counterpart evidenced that OmpR is a key player in the response of C. sakazakii to acid stress, although it was not essential to mount an active stationary-phase ATR, at least under the tested conditions. The ability of C. sakazakii DPC6529 to grow in acid environments and to develop an adaptive stationary-phase ATR may allow for its survival or even proliferation within the infant gastrointestinal tract after consumption of contaminated milk formulae. Copyright © 2014 Elsevier B.V. All rights reserved.

Selective Essential Oils from Spice or Culinary Herbs Have High Activity against Stationary Phase and Biofilm Borrelia burgdorferi.

PubMed

Feng, Jie; Zhang, Shuo; Shi, Wanliang; Zubcevik, Nevena; Miklossy, Judith; Zhang, Ying

2017-01-01

Although the majority of patients with acute Lyme disease can be cured with the standard 2-4 week antibiotic treatment, about 10-20% of patients continue suffering from chronic symptoms described as posttreatment Lyme disease syndrome. While the cause for this is debated, one possibility is that persister bacteria are not killed by the current Lyme antibiotics and remain active in the system. It has been reported that essential oils have antimicrobial activities and some have been used by patients with persisting Lyme disease symptoms. However, the activity of essential oils against the causative agent Borrelia burgdorferi ( B. burgdorferi ) has not been well studied. Here, we evaluated the activity of 34 essential oils against B. burgdorferi stationary phase culture as a model for persister bacteria. We found that not all essential oils had activity against the B. burgdorferi stationary phase culture, with top five essential oils (oregano, cinnamon bark, clove bud, citronella, and wintergreen) at a low concentration of 0.25% showing high anti-persister activity that is more active than the known persister drug daptomycin. Interestingly, some highly active essential oils were found to have excellent anti-biofilm ability as shown by their ability to dissolve the aggregated biofilm-like structures. The top three hits, oregano, cinnamon bark, and clove bud completely eradicated all viable cells without any regrowth in subculture in fresh medium, whereas but not citronella and wintergreen did not have this effect. Carvacrol was found to be the most active ingredient of oregano oil showing excellent activity against B. burgdorferi stationary phase cells, while other ingredients of oregano oil p-cymene and α-terpinene had no apparent activity. Future studies are needed to characterize and optimize the active essential oils in drug combination studies in vitro and in vivo and to address their safety and pharmacokinetic properties before they can be considered as a novel treatment of persistent Lyme disease.

Quantitative Effects of 2,4-Dichlorophenoxyacetic Acid on Growth of Suspension-cultured Acer pseudoplatanus Cells

PubMed Central

Leguay, Jean-Jacques; Guern, Jean

1977-01-01

The utilization of 2,4-dichlorophenoxyacetic acid (2,4-D) molecules by Acer pseudoplatanus cells is governed mainly by a glucosylation process. Evidence that 2,4-D glucoside molecules are biologically inactive is presented. 2,3,5-Triiodobenzoic acid (TIBA), by inhibiting 2,4-D glucosylation, has a sparing effect on 2,4-D molecules; thus TIBA treatments increase growth yield (expressed as the ratio of the maximum number of cells produced to the initial concentration of 2,4-D in the culture medium). Significant amounts of intact 2,4-D molecules remain outside and inside the cells when cell division stops at the onset of the stationary phase. This result and the previous demonstration that, at the onset of the stationary phase, 2,4-D is the specific limiting factor of cell division (Leguay JJ, J Guern 1975 Plant Physiol 56: 356-359) suggest that a threshold concentration of auxin is needed for cell division to proceed. The distribution of 2,4-D molecules between the cells and the culture medium is dependent on the population density at the stationary phase. The extracellular 2,4-D concentration at that time is a linear function of the population density whereas intracellular amounts of 2,4-D and 2,4-D metabolites are constant. By using a modified 2-14C,-5,5-dimethyloxazolidine-2,4-dione technique, it has been shown that the intracellular pH is markedly lowered as the population density at the plateau is increased. This intracellular pH modification is likely to be responsible for a large modification of the ratio between intracellular and extracellular auxin concentrations. The intracellular auxin concentration reaches a constant value (about 3 × 10−7m), independent of population density when cell division stops at the onset of the stationary phase suggesting that it represents the threshold value of the control for cell division. PMID:16660072

On-Chip Microfluidic Components for In Situ Analysis, Separation, and Detection of Amino Acids

NASA Technical Reports Server (NTRS)

Zheng, Yun; Getty, Stephanie; Dworkin, Jason; Balvin, Manuel; Kotecki, Carl

2013-01-01

The Astrobiology Analytical Laboratory at GSFC has identified amino acids in meteorites and returned cometary samples by using liquid chromatography-electrospray ionization time-of-flight mass spectrometry (LCMS). These organic species are key markers for life, having the property of chirality that can be used to distinguish biological from non-biological amino acids. One of the critical components in the benchtop instrument is liquid chromatography (LC) analytical column. The commercial LC analytical column is an over- 250-mm-long and 4.6-mm-diameter stainless steel tube filled with functionized microbeads as stationary phase to separate the molecular species based on their chemistry. Miniaturization of this technique for spaceflight is compelling for future payloads for landed missions targeting astrobiology objectives. A commercial liquid chromatography analytical column consists of an inert cylindrical tube filled with a stationary phase, i.e., microbeads, that has been functionalized with a targeted chemistry. When analyte is sent through the column by a pressurized carrier fluid (typically a methanol/ water mixture), compounds are separated in time due to differences in chemical interactions with the stationary phase. Different species of analyte molecules will interact more strongly with the column chemistry, and will therefore take longer to traverse the column. In this way, the column will separate molecular species based on their chemistry. A lab-on-chip liquid analysis tool was developed. The microfluidic analytical column is capable of chromatographically separating biologically relevant classes of molecules based on their chemistry. For this analytical column, fabrication, low leak rate, and stationary phase incorporation of a serpentine microchannel were demonstrated that mimic the dimensions of a commercial LC column within a 5 10 1 mm chip. The microchannel in the chip has a 75- micrometer-diameter oval-shaped cross section. The serpentine microchannel has four different lengths: 40, 60, 80, and 100 mm. Functionized microbeads were filled inside the microchannel to separate molecular species based on their chemistry.