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The paramagnetic fraction surviving at the impurity-induced antiferromagnetic phase transition in the spin-Peierls magnet CuGeO3 is found to increase with an external magnetic field. This effect is explained by the competition of the Zeeman interaction and of the exchange interaction of local antiferromagnetic clusters formed on the spin-gap background near impurities.
The separation of several isomer pairs of widely varied structure was studied as a function of changes in temperature, gradient time, mobile phase pH, column type ("monomeric" vs. "polymeric" C18-silica) and organic solvent (methanol vs. acetonitrile). General conclusions are drawn which may prove useful in future attempts at the separation of these and other achiral isomers.
An electrospray ionization (ESI) compatible separation of phospholipids (PL), phosphatidylglycerol (PG), phosphatidylethanolamine (PE), and phosphatidylcholine (PC), was performed on a C18 column by reversed phase High Performance Liquid Chromatography (HPLC) with minimal ESI suppression. The mobile phase, used isocratically, consisted of methanol and water. ESI was used to efficiently transfer the ions present in solution to the gas phase for mass spectrometric (MS) detection. Formation of negative ions was reinforced by incorporating piperidine post column. Limits of detection (LOD) and limits of quantitation (LOQ) were experimentally determined to be 20 and 60 fmol/microl, respectively, when acquiring data in the selected ion monitoring (SIM) mode monitoring three ions with a single quadrupole MS. When acquiring data from m/z 110-900 in the scanning mode, the LOD and LOQ were experimentally determined to be 1 pmol/microl and 3 pmol/microl. When acquiring product ion spectra for m/z 747, the LOD and LOQ were experimentally determined to be 446 attomol/microl and 1.3 fmol/microl, respectively.
The human proteome project will demand faster, easier, and more reliable methods to isolate and purify protein targets. Membrane proteins are the most valuable group of proteins since they are the target for 70-80% of all drugs. Perbio Science has developed a protocol for the quick, easy, and reproducible isolation of integral membrane proteins from eukaryotic cells. This procedure utilizes a proprietary formulation to facilitate cell membrane disruption in a mild, nondenaturing environment and efficiently solubilizes membrane proteins. The technique utilizes a two-phase partitioning system that enables the class separation of hydrophobic and hydrophilic proteins. A variety of protein markers were used to investigate the partitioning efficiency of the membrane protein extraction reagents (Mem-PER) (Mem-PER is a registered trademark of Pierce Biotechnology, Inc) system. These included membrane proteins with one or more transmembrane spanning domains as well as peripheral and cytosolic proteins. Based on densitometry analyses of our Western blots, we obtained excellent solubilization of membrane proteins with less than 10% contamination of the hydrophobic fraction with hydrophilic proteins. Compared to other methodologies for membrane protein solubilization that use time-consuming protocols or expensive and cumbersome instrumentation, the Mem-PER reagents system for eukaryotic membrane protein extraction offers an easy, efficient, and reproducible method to isolate membrane proteins from mammalian and yeast cells.
The effect of CO2 on the phase behavior of the reaction system and equilibrium conversion for esterification of acetic acid and ethanol in ionic liquid (1-butyl-3-methylimidazolium hydrogen sulfate, [bmim][HSO4]) was studied at 60.0 degrees C up to 15 MPa. It was demonstrated that there was only one phase in the reaction system in the absence of CO2. The reaction system underwent two-phase-->three-phase-->two-phase transitions with increasing pressure. The pressure of CO2 or the phase behavior of the system affected the equilibrium conversion of the reaction markedly. As the pressure was less than 3.5 MPa, there were two phases in the system, and the equilibrium conversion increased as pressure was increased. In the pressure range of 3.5-9.5 MPa, there existed three phases, and the equilibrium conversion increased more rapidly with increasing pressure. As the pressure was higher than 9.5 MPa, the reaction system entered another two-phase region and the equilibrium conversion was nearly independent of pressure. The total equilibrium conversion was 64% without CO2 and could be as high as 80% as pressure was higher than 9.0 MPa. The apparent equilibrium constants (K(x)) in different phases were also determined, showing that the K(x) in the middle phase or top phase was much greater than that in the bottom phase.
We consider the demixing of a binary fluid mixture, under gravity, which is steadily driven into a two-phase region by slowly ramping the temperature. We assume, as a first approximation, that the system remains spatially isothermal, and we examine the interplay of two competing nonlinearities. One of these arises because the supersaturation is greatest far from the meniscus, creating inversions of the density which can lead to fluid motion; although isothermal, this is somewhat like the Bénard problem (a single-phase fluid heated from below). The other is the intrinsic diffusive instability which results either in nucleation or in spinodal decomposition at large supersaturations. Experimental results on a simple binary mixture show interesting oscillations in heat capacity and optical properties, for a wide range of ramp parameters. We argue that these oscillations arise under conditions where both nonlinearities are important.
Spectrophotometric determination of iron by using eriochrome cyanine R as extractant and color-developing agent in organic solvents was studied. The complex was extracted by PEG phase from the water solutions of pH4.5-6.5 (NaAc-HAc). The maximum absorption of the complex is at 560 nm and the molar absorptivity is 5.36 x 10(4) L x mol(-1) x cm(-1). Beers law was obeyed in the range of 0-40 microg Fe. Iron and eriochrome cyanine R formed a stable complex with a molar ratio of 1:2. The proposed method has been applied to the determination of copper in aluminium alloys with satisfactory results.
Lattice Monte Carlo simulations are used to study the effect of nonionic surfactant concentration and CO2 density on the micellization and phase equilibria of supercritical CO2/surfactant systems. The interaction parameter for carbon dioxide is obtained by matching the critical temperature of the model fluid with the experimental critical temperature. Various properties such as the critical micelle concentration and the size, shape, and structure ofmicelles are calculated, and the phase diagram in the surfactant concentration-CO2 density space is constructed. On increasing the CO2 density, we find an increase in the critical micelle concentration and a decrease in the micellar size; this is consistent with existing experimental results. The variation of the micellar shape and structure with CO2 density shows that the micelles are spherical and that the extension of the micellar core increases with increasing micellar size, while the extension of the micellar corona increases with increasing CO2 density. The predicted phase diagram is in qualitative agreement with experimental phase diagrams for nonionic surfactants in carbon dioxide.
We have measured and theoretically analyzed the diffuse scattering in the binary alloy system Au-Ni, which has been proposed as a testing ground for theories of alloy phase stability. We found strong evidence that in the alloys Au3Ni and Au3Ni2, fluctuations of both ordering- and clustering-type are competing with each other. Our results resolve a long-standing controversy on the balance of relaxation and mixing energies in this alloy system and explain recent findings of ordering in thin Au-Ni films.
We use molecular dynamics to simulate experiments where a symmetric binary fluid mixture (AB), confined between walls that preferentially attract one component (A), is quenched from the one-phase region into the miscibility gap. Surface enrichment occurs during the early stages, yielding a B-rich mixture in the film center with well-defined A-rich droplets. The droplet size grows with time as l(t) proportional t(2/3) after a transient regime. The present atomistic model is also compared to mesoscopic coarse-grained models for this problem.
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We use a lattice Boltzmann scheme within which the noise can be turned on and off to investigate the effect of stochastic terms on the phase ordering of a two-dimensional binary fluid. Sufficiently strong noise slows the growth in the hydrodynamic regime, changing the growth exponent alpha=2/3 to alpha=1/2.
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Doped manganite perovskites AMnO(3) exhibit a rich variety of electronic properties, resulting from the interplay of charge (Mn(3+)/Mn(4+)), spin (Mn magnetic moment) and orbital (Mn(3+) Jahn-Teller distortion) degrees of freedom. Magnetisation measurements and ESR spectra have been used to study a series of eight AMnO(3) perovskites, in which the A cation sites are occupied by a distribution of 70% trivalent lanthanide and 30% divalent Ca, Sr or Ba ions. These all have a mean A cation radius of 1.20 Angstrom but different values of the cation size variance sigma(2). A change from orbital disorder to order (cooperative Jahn-Teller distortions) was previously found in the insulating regime at sigma(2) = approximately 0.005 Angstrom(2). This work has shown that co-existence of the orbitally ordered and disordered phases is found in sigma(2)= 0.0016-0.0040 Angstrom(2) samples, with a difference of 40 K between their Curie temperatures. This is ascribed to competition between orbital ordering and microstructural lattice strains. At larger sigma(2) > 0.005 Angstrom(2), the orbital ordering strains are dominant and only this phase is observed. This intermediate temperature phase segregation is one of many strain-driven separation phenomena in manganites.
Ordinary differential equations are used to model a peculiar motor behaviour in the anomuran decapod crustacean Emerita analoga. Little is known about the neural circuitry that permits E. analoga to control the phase relationships between movements of the fourth legs and pair of uropods as it digs into sand, so mathematical models might aid in identifying features of the neural structures involved. The geometric arrangement of segmental ganglia controlling the movements of each limb provides an intuitive framework for modelling. Specifically, due to the rhythmic nature of movement, the network controlling the fourth legs and uropods is viewed as three coupled identical oscillators, one dedicated to the control of each fourth leg and one for the pair of uropods, which always move in bilateral synchrony. Systems of Morris-Lecar equations describe the voltage and ion channel dynamics of neurons. Each central pattern generator for a limb is first modelled as a single neuron and then, more realistically as a multi-neuron oscillator. This process results in high-dimensional systems of equations that are difficult to analyse. In either case, reduction to phase equations by averaging yields a two-dimensional system of equations where variables describe only each oscillator's phase along its limit cycle. The behaviour observed in the reduced equations approximates that of the original system. Results suggest that the phase response function in the two dimensional system, together with minimal input from asymmetric bilateral coupling parameters, is sufficient to account for the observed behaviour.
Using a combination of Monte Carlo techniques, we locate the liquid-vapor critical point of adhesive hard spheres. We find that the critical point lies deep inside the gel region of the phase diagram. The (reduced) critical temperature and density are tau(c)=0.1133+/-0.0005 and rho(c)=0.508+/-0.01. We compare these results with the available theoretical predictions. Using a finite-size scaling analysis, we verify that the critical behavior of the adhesive hard sphere model is consistent with that of the 3D Ising universality class, the default for systems with short-range attractive forces.
We report the coexistence of lamellar charge-ordered (CO) and charge-disordered (CD) domains, and their dynamical behavior, in La0.23Ca0.77MnO3. Using high-resolution transmission electron microscopy (TEM), we show that below T(CD) approximately 170 K a CD-monoclinic phase forms within the established CO-orthorhombic matrix. The CD phase has a sheetlike morphology, perpendicular to the q vector of the CO superlattice (a axis of the Pnma structure). For temperatures between 64 and 130 K, both the TEM and resistivity experiments show a dynamic competition between the two phases: at constant T, the CD phase slowly advances over the CO one. This slow dynamics appears to be linked to the magnetic transitions occurring in this compound, suggesting important magnetoelastic effects.
Many samples contain compounds with various numbers of two or more regular structural groups. Such "multidimensional" samples (according to the Giddings' notation) are best separated in orthogonal chromatographic systems with different selectivities for the individual repeat structural groups, described by separation factors. Correlations between the repeat group selectivities characterize the degree of orthogonality and suitability of chromatographic systems for two-dimensional (2D) separations of two-dimensional samples. The range of the structural units in that can be resolved in a given time can be predicted on the basis of a model describing the repeat group selectivity in the first- and second-dimension systems. Two-dimensional liquid chromatographic system combining reversed-phase (RP) mode in the first dimension and normal-phase (NP) mode in the second dimension were studied with respect to the possibilities of in-line fraction transfer between the two modes. Hydrophilic interaction liquid chromatography (HILIC) with an aminopropyl silica column (APS) is more resistant than classical non-aqueous NP systems against adsorbent desactivation with aqueous solvents transferred in the fractions from the first, RP dimension to the second dimension. Hence, HILIC is useful as a second-dimension separation system for comprehensive RP-NP LCxLC. A comprehensive 2D RP-NP HPLC method was developed for comprehensive 2D separation of ethylene oxide-propylene oxide (EO-PO) (co)oligomers. The first-dimension RP system employed a 120 min gradient of acetonitrile in water on a C18 microbore column at the flow-rate of 10 microL/min. In the second dimension, isocratic HILIC NP with ethanol-dichloromethane-water mobile phase on an aminopropyl silica column at 0.5 mL/min was used. Ten microliter fractions were transferred from the RP to the HILIC NP system at 1 min switching valve cycle frequency.