CiteULike: Tag phase

A Full-Bridge Resonant Inverter With Modified Phase-Shift Modulation for High-Frequency AC Power Distribution Systems

Z Ye — 2007-11-10T18:47:27-00:00

Industrial Electronics, IEEE Transactions on, Vol. 54, No. 5. (2007), pp. 2831-2845.

<para> The design of a resonant inverter for high-frequency ac (HFAC) power distribution systems is complicated by the following three factors: 1) A number of electronic loads located in different locations are connected to the resonant inverter, the impedance, and the power factor of the equivalent load of which varies over a wider range than a system with a certain load; 2) the resonant inverter is subject to an input-line voltage varying over a wide range; and 3) the characteristics of the resonant inverter depend on the load impedance. It is mandatory to operate the inverter with zero-voltage switching under various load conditions of different power factors and over wide input variations. It is further desirable that multiple resonant inverters can be paralleled with simple current-sharing control (CSC). A phase-shift-modulation (PSM)-controlled full-bridge series-parallel resonant inverter is proposed for the HFAC power distribution architectures. A new PSM method is proposed with which the phase angle of the inverter output voltage is independent of the modulation signal of the phase-shift modulator. Such a feature allows multiple resonant inverters to operate in parallel with a magnitude CSC. The resonant inverter is analyzed with a general nonresistive load model, and the design curves are developed. A prototype resonant inverter system is designed and implemented with an operation frequency of 1 MHz, a rated output power of 150 W, and a sinusoidal output voltage of 1-MHz 28-V rms. The proposed resonant inverter has the advantages of high efficiency over wide input/output line variations, high waveform quality of the output voltage, and phase-angle independence of the voltage-feedback/feed-forward control and CSC. </para>

Phase equilibria of mixtures of mutually immiscible ionic liquids

Alberto Arce — 2007-11-30T15:05:47-00:00

Fluid Phase Equilibria, Vol. 261, No. 1-2. (1 December 2007), pp. 427-433.

In the last decade, the scientific community has witnessed a burgeoning research in ionic liquids. Numerous and diverse applications for them have been pointed out in the literature, with some processes based on ionic liquid technology already working in real plants. Among the possible fields of application, that of solvent extraction involving ionic liquids as solvents holds an important position. The opportunities of ionic liquids as alternative solvents for these kind of processes could be improved by the recent discovery of mutually immiscible ionic liquids. The use of ionic liquids presenting mutual immiscibility can generate stable multi-layer solvent systems, which, combined with the typical advantages offered by ionic liquids (good solvation properties, task-specific tuned structures, etc.), can mean a powerful medium for multi-component separations. To get a deeper knowledge of the behaviour of mutually immiscible ionic liquids, the phase equilibria of binary and ternary mixtures of ionic liquids were investigated. Specifically, hydrophobic ionic liquids with the common anion bis(trifluoromethyl)sulfonylamide were selected. Pairs of ionic liquids with largely different cations were chosen, looking for the existence of mutual immiscibility between them. It was found that ionic liquids with a tetraalkylphosphonium cation are largely immiscible at ambient temperature with some other ionic liquids including 1,3-dialkylimidazolium or 1-alkylpyridinium cations. The miscibility of such pairs of ionic liquids was temperature dependent, following an upper critical solution temperature (UCST) behaviour. It was also found that small changes in the structure of an ionic liquid can drastically affect the mutual solubility with another ionic liquid. The liquid-liquid equlibrium (LLE) data of these systems were acceptably correlated by means of the classical non-random two-liquid (NRTL) equation.

Phase-field models for free-boundary problems

Thierry Biben — 2005-07-09T16:58:54-00:00

European Journal of Physics, Vol. 26, No. 5. (September 2005), pp. S47-S55.

Using phase information for symmetry detection

Zhitao Xiao — 2005-11-09T13:28:45-00:00

Pattern Recognition Letters, Vol. 26, No. 13. (1 October 2005), pp. 1985-1994.

Symmetry exists widely in the real world and plays a remarkable role in perception problems. The existing symmetry detection algorithms are mainly based on luminance or gradient information. Upon analyzing the relationship between symmetry and phase, based on phase congruency, we propose a phase-based symmetry detection (PSD) algorithm. PSD is calculated based on log Gabor wavelet. The symmetric points of objects are obtained by inspecting the phase information. The feasibility analysis, phase-based symmetry detection definition, and rationality demonstrations established the theoretic foundation for this algorithm. The experiments show that this algorithm can be applied directly to original images without segmentation--it is invariant to rotation, luminance and contrast--and it can detect several types of symmetries at the same time and it is compared with several other methods.

Measuring phase synchrony in brain signals.

JP Lachaux — 2005-12-17T15:51:41-00:00

Hum Brain Mapp, Vol. 8, No. 4. (1999), pp. 194-208.

This article presents, for the first time, a practical method for the direct quantification of frequency-specific synchronization (i.e., transient phase-locking) between two neuroelectric signals. The motivation for its development is to be able to examine the role of neural synchronies as a putative mechanism for long-range neural integration during cognitive tasks. The method, called phase-locking statistics (PLS), measures the significance of the phase covariance between two signals with a reasonable time-resolution (<100 ms). Unlike the more traditional method of spectral coherence, PLS separates the phase and amplitude components and can be directly interpreted in the framework of neural integration. To validate synchrony values against background fluctuations, PLS uses surrogate data and thus makes no a priori assumptions on the nature of the experimental data. We also apply PLS to investigate intracortical recordings from an epileptic patient performing a visual discrimination task. We find large-scale synchronies in the gamma band (45 Hz), e.g., between hippocampus and frontal gyrus, and local synchronies, within a limbic region, a few cm apart. We argue that whereas long-scale effects do reflect cognitive processing, short-scale synchronies are likely to be due to volume conduction. We discuss ways to separate such conduction effects from true signal synchrony.

Phase correlation among rhythms present at different frequencies: spectral methods, application to microelectrode recordings from visual cortex and functional implications.

T Schanze — 2005-12-17T15:31:08-00:00

Int J Psychophysiol, Vol. 26, No. 1-3. (June 1997), pp. 171-189.

In classical EEG analysis rhythms with different frequencies occurring at separable regions and states of the brain are analysed. Rhythms in different frequency bands have often been assumed to be independent and their occurrence was interpreted as a sign of different functional operations. Independence has scarcely been proved because of conceptual and computational difficulties. It is, on the other hand, probable that different rhythmic brain processes are coupled because of the broad recurrent connectivity among brain structures. We, therefore, set out to find interactions among rhythmic signals at different frequencies. We were particularly interested in interactions between lower frequency bands and gamma-activities (30-90 Hz), because the latter have been analysed in our laboratory in great detail and had properties suggesting their involvement in perceptual feature linking. Fast oscillations occurred synchronized in a stimulus-specific way in the visual cortex of cat and monkey. Their presence was often accompanied by lower frequency components at considerable power. Such multiple spectral peaks are known from many cortical and subcortical structures. Despite their well known occurrence, coupling among different frequencies has not been established, apart from harmonic components. For the present investigation we extended existing analytical tools to detect non-linear correlations among signal pairs at any frequency (including incommensurate ones). These methods were applied to multiple microelectrode recordings from visual cortical areas 17 and 18 of anesthetized cats and V1 of awake monkeys. In particular, we assessed non-linear correlations by means of higher order spectral analysis of multi-unit spike activities (MUA) and local slow wave field potentials (LFP, 1-120 Hz) recorded with microelectrodes. Non-linear correlations among signal components at different frequencies were investigated in the following steps. First, the frequency content of short (approximately 250 ms) sliding window signal epochs was analyzed for simultaneously occurring rhythms of significant power at different frequencies. This was done by a newly developed method derived from the trispectrum using separate averaging of the products of short-epoch power spectra for any possible combination of frequency pairs. Second, non-linear (quadratic) phase coupling between different frequencies was assessed by the methods of bispectrum and bicoherence. We found phase correlations at different frequencies in the visual cortex of the cat and monkey. These couplings were significant in about 60% of the investigated MUA and LFP recordings, including several cases of coupling among incommensurate (i.e. non-harmonic) frequencies. Significant phase correlations were present: (1) within the gamma-frequency range; (2) between gamma- and low frequency ranges (1-30 Hz, including alpha- and beta-rhythms); and (3) within the low frequency range. Phase correlations depended, in most cases, on specific visual stimulation. We discuss the possible functional significance of phase correlations among high and low frequencies by including proposals from previous work about potential roles of single-frequency rhythms of the EEG. Our suggestions include: (1) visual feature linking across different temporal and spatial scales provided by coherent oscillations at high and low frequencies; (2) linking of visual cortical representations (high frequencies) to subcortical centers (low frequencies) like the thalamus and hippocampus; and (3) temporal segmentation of the sustained stream of incoming visual information into separate frames at different temporal resolutions in order to prevent perceptual smearing due to shifting retinal images. These proposals are, at present, merely speculative. However, they can, in principle, be proved by microelectrode recordings from trained behaving animals.

Statistical method for detection of phase-locking episodes in neural oscillations.

JM Hurtado — 2005-12-17T15:00:08-00:00

J Neurophysiol, Vol. 91, No. 4. (April 2004), pp. 1883-1898.

In many networks of oscillatory neurons, synaptic interactions can promote the entrainment of units into phase-coupled groups. The detection of synchrony in experimental data, especially if the data consist of single-trial runs, can be problematic when, for example, phase entrainment is of short duration, buried in noise, or masked by amplitude fluctuations that are uncorrelated among the oscillating units. In the present study, we tackle the problem of detecting neural interactions from pairs of oscillatory signals in a narrow frequency band. To avoid the interference of amplitude fluctuations in the detection of synchrony, we extract a phase variable from the data and utilize statistical indices to measure phase locking. We use three different phase-locking indices based on coherence, entropy, and mutual information between the phase variables. Phase-locking indices are calculated over time using sliding analysis windows. By varying the duration of the analysis windows, we were able to inspect the data at different levels of temporal resolution and statistical reliability. The statistical significance of high index values was evaluated using four different surrogate data methods. We determined phase-locking indices using alternative methods for generating surrogate data and found that results are sensitive to the particular method selected. Surrogate methods that preserve the temporal structure of the individual phase time series decrease substantially the number of false positives when tested on a pair of independent signals.

Wang-Landau sampling with self-adaptive range

Andreas Troster — 2005-08-10T23:38:59-00:00

Physical Review E (Statistical, Nonlinear, and Soft Matter Physics), Vol. 71, No. 6. (2005)

We report a self-adapting version of the Wang-Landau algorithm that is ideally suited for application to systems with a complicated structure of the density of states. Applications include determination of two-dimensional densities of states and high-precision numerical integration of sharply peaked functions on multidimensional integration domains.

Control of phase synchronization of neuronal activity in the rat hippocampus

Jun Lian — 2005-11-25T16:22:12-00:00

Journal of Neural Engineering, Vol. 1, No. 1. (2004), pp. 46-54.

Analysis of the synchronization mechanisms of neural activity is crucial to the understanding of the generation, propagation and control of epileptiform activity. Recently, phase synchronization (PS) analysis was applied to quantify the partial synchrony that exists in complex chaotic or noisy systems. In a previous study, we have shown that neural activity between two remotely located sites can be synchronized through a complete cut of the tissue by endogenous non-synaptic signals. Therefore, it should be possible to apply signals to control PS. In this study, we test the hypothesis that stimulation amplitudes below excitation level (sub-threshold) can be used to control phase synchronization of two neural signals and we investigate the underlying mechanisms. PS of neuronal activity is first analysed in two coupled Rössler neuron models. Both synchronization and desynchronization could be generated with sub-threshold sinusoidal stimulation. Phase synchronization was then studied in in vitro brain slices. Neuronal activity between two sites was modulated by the application of small sinusoidal electric fields. PS between two remote sites could be achieved by the application of two identical waveforms while phase desynchronization of two close sites was generated by the application of a stimulus at a single site. These results show that sub-threshold stimuli are able to phase synchronize or desynchronize two networks and suggest that small signals could play an important role in normal neural activity and epilepsy.

Phase synchronization in temperature and precipitation records

Diego Rybski — 2005-11-13T18:26:26-00:00

Physica A: Statistical Mechanics and its Applications, Vol. 320 (15 March 2003), pp. 601-610.

We study phase synchronization between atmospheric variables such as daily mean temperature and daily precipitation records. We find significant phase synchronization between records of Oxford and Vienna as well as between the records of precipitation and temperature in each city. To find the time delay in the synchronization between the records we study the time lag phase synchronization when the records are shifted by a variable time interval of days. We also compare the results of the method with the classical cross-correlation method and find that in certain cases the phase synchronization yields more significant results.

Towards a proper estimation of phase synchronization from time series.

M Chavez — 2006-03-17T11:32:37-00:00

J Neurosci Methods (27 January 2006)

In experimental synchronization studies a continuous phase variable is commonly estimated from a scalar time series by means of its representation on the complex plane. The aim is to obtain a pair of functions A(t), phi(t) defining its instantaneous amplitude and phase, respectively. However, any arbitrary pair of functions cannot be considered as the amplitude and the phase of the real observable. Here, we point out some criteria that the pair A(t), phi(t) must observe to unambiguously define the instantaneous amplitude and phase of the observed signal. In this work, we illustrate how the complex representation may fail if the signal possesses a multi-component or a broadband spectra. We also point out a practical procedure to test whether a signal, not displaying a single oscillation at a unique frequency, has a narrow-band behavior. Implications for the study of phase interdependencies are illustrated and discussed. Phase dynamics estimated from electric brain activities recorded from an epileptic patient are also discussed.

Collective synchronization in spatially extended systems of coupled oscillators with random frequencies.

H Hong — 2005-12-17T18:03:22-00:00

Phys Rev E Stat Nonlin Soft Matter Phys, Vol. 72, No. 3 Pt 2. (September 2005)

We study collective behavior of locally coupled limit-cycle oscillators with random intrinsic frequencies, spatially extended over d -dimensional hypercubic lattices. Phase synchronization as well as frequency entrainment are explored analytically in the linear (strong-coupling) regime and numerically in the nonlinear (weak-coupling) regime. Our analysis shows that the oscillator phases are always desynchronized up to d=4 , which implies the lower critical dimension dP(l) =4 for phase synchronization. On the other hand, the oscillators behave collectively in frequency (phase velocity) even in three dimensions (d=3) , indicating that the lower critical dimension for frequency entrainment is dF(l)=2 . Nonlinear effects due to the periodic nature of limit-cycle oscillators are found to become significant in the weak-coupling regime: So-called runaway oscillators destroy the synchronized (ordered) phase and there emerges a fully random (disordered) phase. Critical behavior near the synchronization transition into the fully random phase is unveiled via numerical investigation. Collective behavior of globally coupled oscillators is also examined and compared with that of locally coupled oscillators.

Controlling the elongation phase of transcription with P-TEFb.

BM Peterlin — 2007-03-13T21:40:55-00:00

Mol Cell, Vol. 23, No. 3. (4 August 2006), pp. 297-305.

The positive transcription elongation factor b (P-TEFb) is a cyclin-dependent kinase that controls the elongation phase of transcription by RNA polymerase II (RNAPII). This process is made possible by the reversal of effects of negative elongation factors that include NELF and DSIF. In complex organisms, elongation control is critical for the regulated expression of most genes. In those organisms, the function of P-TEFb is influenced negatively by HEXIM proteins and 7SK snRNA and positively by a variety of recruiting factors. Phylogenetic analyses of the components of the human elongation control machinery indicate that the number of mechanisms utilized to regulate P-TEFb function increased as organisms developed more complex developmental patterns.

F-Box Proteins Are Receptors that Recruit Phosphorylated Substrates to the SCF Ubiquitin-Ligase Complex

Dorota Skowyra — 2008-05-14T19:55:19-00:00

Cell, Vol. 91, No. 2. (17 October 1997), pp. 209-219.

We have reconstituted the ubiquitination pathway for the Cdk inhibitor Sic1 using recombinant proteins. Skp1, Cdc53, and the F-box protein Cdc4 form a complex, SCFCdc4, which functions as a Sic1 ubiquitin-ligase (E3) in combination with the ubiquitin conjugating enzyme (E2) Cdc34 and E1. Cdc4 assembled with Skp1 functions as the receptor that selectively binds phosphorylated Sic1. Grr1, an F-box protein involved in Cln destruction, forms complexes with Skp1 and Cdc53 and binds phosphorylated Cln1 and Cln2, but not Sic1. Because the constituents of the SCF complex are members of protein families, SCFCdc4 is likely to serve as the prototype for a large class of E3s formed by combinatorial interactions of related family members. SCF complexes couple protein kinase signaling pathways to the control of protein abundance.

A Complex of Cdc4p, Skp1p, and Cdc53p/Cullin Catalyzes Ubiquitination of the Phosphorylated CDK Inhibitor Sic1p

Renny Feldman — 2008-05-14T19:53:05-00:00

Cell, Vol. 91, No. 2. (17 October 1997), pp. 221-230.

In S. cerevisiae, the G1/S transition requires Cdc4p, Cdc34p, Cdc53p, Skp1p, and the Cln/Cdc28p cyclin-dependent kinase (Cdk). These proteins are thought to promote the proteolytic inactivation of the S-phase Cdk inhibitor Sic1p. We show here that Cdc4p, Cdc53p, and Skp1p assemble into a ubiquitin ligase complex named SCFCdc4p. When mixed together, SCFCdc4p subunits, E1 enzyme, the E2 enzyme Cdc34p, and ubiquitin are sufficient to reconstitute ubiquitination of Cdk-phosphorylated Sic1p. Phosphorylated Sic1p substrate is specifically targeted for ubiquitination by binding to a Cdc4p/Skp1p subcomplex. Taken together, these data illuminate the molecular basis for the G1/S transition in budding yeast and suggest a general mechanism for phosphorylation-targeted ubiquitination in eukaryotes.

A Study of the Passive Gait of a Compass-Like Biped Robot: Symmetry and Chaos

Ambarish Goswami — 2007-07-17T17:46:46-00:00

The International Journal of Robotics Research, Vol. 17, No. 12. (1 December 1998), pp. 1282-1301.

The focus of this work is a systematic study of the passive gait of a compass-like, planar, biped robot on inclined slopes. The robot is kinematically equivalent to a double pendulum, possessing two kneeless legs with point masses and a third point mass at the "hip" joint. Three parameters, namely, the ground-slope angle and the normalized mass and length of the robot describe its gait. We show that in response to a continuous change in any one of its parame ters, the symmetric and steady stable gait of the unpowered robot gradually evolves through a regime of bifurcations characterized by progressively complicated asymmetric gaits, eventually arriving at an apparently chaotic gait where no two steps are identical. The robot can maintain this gait indefinitely. A necessary (but not sufficient) condition for the stability of such gaits is the contraction of the "phase-fluid" volume. For this frictionless robot, the volume contraction, which we compute, is caused by the dissipative effects of the ground-impact model. In the chaotic regime, the fractal dimension of the robot's strange attractor We present a novel graphical technique based on the first return map that compactly captures the entire evolution of the gait, from symmetry to chaos. Additional passive dissipative elements in the robot joint result in a significant improvement in the stability and the versatility of the gait, and provide a rich repertoire for simple control laws. 10.1177/027836499801701202

Consistent non-cartesian off-axis MRI quality: Calibrating and removing multiple sources of demodulation phase errors

Youngkyoo Jung — 2006-12-04T15:16:00-00:00

Magnetic Resonance in Medicine, Vol. 9999, No. 9999. (2006), NA.

The consistency of off-axis MRI with non-Cartesian sequences across a large number of scanners is highly variable. Improper timing alignment of the gradient fields, data acquisition system, and real-time frequency demodulation reference signal, which are necessary for off-axis imaging, is an important source of this variability. In addition, eddy currents and anisotropic gradient delays cause deviations in k-space trajectories that in turn make the demodulation reference signals inaccurate. A method is presented to quickly measure the timing error in the frequency demodulation reference signal and separate it from anisotropic gradient delays. k-Space deviations, as measured with a previous gradient calibration technique, are shown to be a second source of demodulation phase errors that degrade image quality. Using the timing delay and k-space deviations, a retrospective phase correction is applied to each k-space sample before the data are regridded during reconstruction. The timing delays of four MR scanners were measured to be 4.2-7.5 ?s below the manufacturer's suggested delay. Significant degradation in 3D radial (3D projection reconstruction (PR)) knee and breast images are retrospectively corrected while a partial prospective correction is applied for spiral imaging. The method allows for more consistent performance of non-Cartesian sequences across multiple scanners without operator intervention. Magn Reson Med, 2007. © 2006 Wiley-Liss, Inc.

Phase contrast X-ray imaging combining free space propagation and Bragg diffraction

Paola Coan — 2004-12-11T12:57:39-00:00

Phase singularities and termination of spiral wave reentry.

J Eason — 2006-02-24T06:45:02-00:00

J Cardiovasc Electrophysiol, Vol. 13, No. 7. (July 2002), pp. 672-679.

INTRODUCTION: Recent defibrillation studies show that electric fields interact with reentrant activity in myocardial tissue through virtual electrode polarization (VEP). This study focuses on determining how VEP relates to the creation and survival of postshock phase singularities in cardiac tissue and demonstrating that interactions between VEP and preshock tissue state engender the probabilistic nature of defibrillation. METHODS AND RESULTS: We constructed a two-dimensional tissue model representing a ventricular cross-section with fiber architecture and surrounding bath. We initiated spiral wave reentry and subjected the tissue to a monophasic shock. We estimated the shock success probability for a given strength by testing 16 coupling intervals throughout a single rotation of the wavefront. Over a range of shock strengths, our model exhibits dose-response behavior similar to experimental defibrillation efficacy curves. At the 50% effective strength (ED50), successful termination of reentry depends upon the interaction between preshock excitable gap and postshock phase singularities. We also found that increasing the stimulus strength toward ED50 increases the number of postshock singularities, whereas further strength increases above ED50 decrease the number of singularities. CONCLUSION: Our results show for the first time that a computational model can account for the probabilistic nature of defibrillation as VEP interacts with the dynamics of an ongoing reentrant wavefront. Further, we demonstrate that success of a shock depends on the annihilation of the phase singularities that arise after any strong stimulus. Our findings imply that VEP completely overrides the preshock tissue state in shocks that are highly likely to defibrillate (ED95).

Microwave potentials and optimal control for robust quantum gates on an atom chip

Philipp Treutlein — 2006-06-12T12:08:02-00:00

(9 Jun 2006)

We propose a two-qubit collisional phase gate that can be implemented with available atom chip technology, and present a detailed theoretical analysis of its performance. The gate is based on earlier phase gate schemes, but uses a qubit state pair with an experimentally demonstrated, very long coherence lifetime. Microwave near-fields play a key role in our implementation as a means to realize the state-dependent potentials required for conditional dynamics. Quantum control algorithms are used to optimize gate performance. We employ circuit configurations that can be built with current fabrication processes, and extensively discuss the impact of technical noise and imperfections that characterize an actual atom chip. We find an overall infidelity compatible with requirements for fault-tolerant quantum computation.

Analyzing oriented textures through phase portraits

AR Rao — 2006-12-11T13:46:29-00:00

Pattern Recognition, 1990. Proceedings., 10th International Conference on, Vol. i (1990), pp. 336-340 vol.1.

An attempt is made to develop a solution for signal-to-symbol transformation in the domain of flowlike or oriented texture. The geometric theory of differential equations is used to derive a symbol set based on the visual appearance of phase portraits. This theory provides a technique for describing textures both qualitatively and quantitatively. An attractive feature of this symbol set is that it is domain independent and makes no assumptions about the kind of texture that may be present. The computational framework for starting with a given oriented texture is provided, and its symbolic representation is derived. This is based on computing the orientation field for the texture and then using a nonlinear least-squares technique over successive windows to determine the changing spatial behavior of the texture. Results of the application of this technique to real texture images are presented

Phase of the atomic polarization in high-order harmonic generation

Maciej Lewenstein — 2008-06-30T08:22:28-00:00

Physical Review A, Vol. 52, No. 6. (1 December 1995), 4747.

Compressive phase retrieval

Matthew Moravec — 2008-07-15T22:29:59-00:00

Wavelets XII, Vol. 6701, No. 1. (2007)

Invited Article: A unified evaluation of iterative projection algorithms for phase retrieval

S Marchesini — 2008-07-15T22:27:35-00:00

Review of Scientific Instruments, Vol. 78, No. 1. (2007)

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Event-related phase reorganization may explain evoked neural dynamics.

Wolfgang Klimesch — 2007-05-30T04:40:14-00:00

Neurosci Biobehav Rev (13 April 2007)

The traditional view holds that event-related potentials (ERPs) reflect fixed latency, fixed polarity evoked responses that appear superimposed on the 'background EEG'. The validity of the evoked model has been questioned by studies arguing that ERPs are generated at least in part by a reset of ongoing oscillations. But a proof of phase reset that is distinct from the 'artificial' influence of evoked components on EEG phase-has been proven difficult for a variety of methodological reasons. We argue that a theoretical analysis of the assumptions and empirical evaluation of predictions of the evoked and oscillatory ERP model offer a promising way to shed new light on mechanisms generating ERPs that goes well beyond attempts to prove phase reset. Research on EEG oscillations documents that oscillations are task relevant and show a common operating principle, which is the control of the timing of neural activity. Both findings suggest that phase reorganization of task relevant oscillations is a theoretical necessity. We further argue and show evidence that (i) task relevant oscillations exhibit a typical interactive and task relevant relationship between pre- and poststimulus power in the theta and alpha frequency range in a way that small prestimulus power is related to large poststimulus power and vice versa, (ii) ERP (interpeak) latencies and (iii) ERP amplitudes reflect frequency characteristics of alpha and theta oscillations. We emphasize that central assumptions of the evoked model cannot be substantiated and conclude that the ERPR model offers a new way for an integrative interpretation of ongoing and event-related EEG phenomena.

Control and measurement of ultrashort pulse shapes (in amplitude and phase) with femtosecond accuracy

JCM Diels — 2007-08-24T01:51:38-00:00

Appl. Opt., Vol. 24 (May 1985), pp. 1270-1282.

Accurate correlation techniques are used to analyze the performance characteristics of a tunable, femtosecond pulse dye laser which is passively mode locked and uses either one or two intracavity prisms to control frequency and its modulation. The main advantages of the interferometric second-order autocorrelations used are the provision of phase information and a high sensitivity to pulse shape. A numerical method is used to analyze the more complex pulse shapes and chirps generated by the laser. Comparisons of autocorrelations and cross correlations calculated for the dispersed pulses with actual measurements demonstrate the accuracy of the fitting procedure used.

Coherent Magnetization Rotation and Phase Control by Ultrashort Optical Pulses in CrO_2 Thin Films

Qiang Zhang — 2007-11-06T01:12:26-00:00

Physical Review Letters, Vol. 89, No. 17. (4 October 2002), 177402.

We have applied photoexcitation by ultrashort laser pulses to single crystal thin CrO 2 films to trigger coherent transient magnetization rotation on a subnanosecond time scale; in macroscale single domains. Moreover; by applying the photoexcitation by pairs of temporally separated pump pulses; the transient precession of the magnetization can be phase controlled; depending on the time separation between the pulses. The mechanism behind the photoexcitation originates from the modulation of the magnetocrystalline anisotropy by nonthermal hot electron spins.

Phase interrogation of localized surface plasmon resonance biosensors based on electro-optic modulation

Tzyy Wang — 2007-10-02T15:06:50-00:00

Applied Physics Letters, Vol. 91, No. 11. (2007)

A resolution-tunable localized surface plasmon resonance (LSPR) biosensor employing electro-optically modulated phase interrogation is presented. This biosensor modulates the analyte-dependent LSPR phase characteristic through electro-optic effect by varying the wave vector of lightwave for exciting surface plasmon. The induced LSPR phase change is measured by the collinear heterodyne technique and its relation with the applied voltage is utilized to determine the analyte concentration. Experimental results show that the regression slope of the phase-voltage relation decreases with the analyte concentration and the detection sensitivity can be increased by widening the waveguide width and using thinner gold film beneath gold nanoparticles. Detection resolution of this LSPR biosensor can be enhanced by increasing the applied voltage to enlarge the induced phase change. The presented LSPR biosensor employing phase interrogation has the features of resolution tunability, fast modulation speed, high modulation stability, and noise reduction. ©2007 American Institute of Physics

Effects of different dietary ideal protein levels on male and female broiler performance during different phases of life: single phase effects, carryover effects, and interactions between phases.

PJ Wijtten — 2006-10-13T18:44:03-00:00

Poult Sci, Vol. 83, No. 12. (December 2004), pp. 2005-2015.

Several experiments in which the dietary ideal protein (IP) levels were increased indicate that with current IP recommendations the maximum performance of broilers will not be achieved. However, available data of this IP-increment approach is scarce and, for the starter phase, entirely lacking. The objective of the present study, therefore, was to generate data regarding the effects in the starter phase and to test the impact of adequate vs. high IP levels in preceding phases on the response to IP increment in the phase under study. To evaluate this, an IP dose response in the starter phase and factorial arrangements combining adequate or high IP levels in starter and grower diets with low, adequate, or high IP levels in finisher diets were carried out with male and female broilers. Enhanced dietary IP levels in the starter diet increased BW gain in the starter phase and in the consecutive grower phase. Moreover, it was shown that a delay in BW gain due to suboptimal IP levels in the starter diet could only be partly compensated for in later phases of life. These results demonstrate the need for a reevaluation of IP levels used in practical starter diets. Feed conversion efficiency and BW gain responses to increased IP levels in the grower and finisher diets were less pronounced when high compared with adequate IP levels were fed in the preceding phase. This difference in response could not be detected statistically but was consistent between experiments and phases. Therefore, this phenomenon should not simply be neglected.

Fluctuations, dissipation, and nonuniversal superfluid jumps in two-dimensional superconductors

RW Crane — 2007-04-17T15:30:07-00:00

Physical Review B (Condensed Matter and Materials Physics), Vol. 75, No. 9. (2007)

We report a comprehensive study of the complex ac conductivity of thin effectively two-dimensional amorphous superconducting InOx films at zero applied field. Below a temperature scale Tc0 where the superconducting order parameter amplitude becomes well defined, there is a temperature where both the generalized superfluid stiffness acquires a frequency dependence and the dc magnetoresistance becomes linear in field. We associate this with a transition of the Kosterlitz-Thouless-Berezinskii (KTB) type. At our measurement frequencies the superfluid stiffness at TKTB is found to be larger than the universal value. Although this may be understood with a vortex dielectric constant of v1.9 within the usual KTB theory, this is a relatively large value and indicates that such a system may be out of the domain of applicability of the low-fugacity (low-vortex-density) KTB treatment. This opens up the possibility that at least some of the discrepancy from a nonuniversal magnitude is intrinsic. Our finite-frequency measurements allow us access to a number of other phenomena concerning the charge dynamics in superconducting thin films, including an enhanced conductivity near the amplitude fluctuation temperature Tc0 and a finite dissipation at low temperature which appears to be a universal aspect of highly disordered superconducting films.

Computing quantum phase transitions

Thomas Vojta — 2007-09-10T08:25:29-00:00

(6 Sep 2007)

This article first gives a concise introduction to quantum phase transitions, emphasizing similarities with and differences to classical thermal transitions. After pointing out the computational challenges posed by quantum phase transitions, a number of successful computational approaches is discussed. The focus is on classical and quantum Monte Carlo methods, with the former being based on the quantum-to classical mapping while the latter directly attack the quantum problem. These methods are illustrated by several examples of quantum phase transitions in clean and disordered systems.

Phase tracking and prediction

T Sherwood — 2006-06-09T18:50:36-00:00

Computer Architecture, 2003. Proceedings. 30th Annual International Symposium on (2003), pp. 336-347.

Automatically characterizing large scale program behavior

T Sherwood — 2007-01-11T23:05:38-00:00

(2002)

Understanding program behavior is at the foundation of computer architecture and program optimization. Many programs have wildly different behavior on even the very largest of scales (over the complete execution of the program). This realization has ramifications for many architectural and compiler techniques, from thread scheduling to feedback directed optimizations, to the way programs are simulated. However, in order to take advantage of time-varying behavior, we must first develop the...

Basic block distribution analysis to find periodic behavior and simulation points in applications

T Sherwood — 2007-01-11T23:02:36-00:00

Parallel Architectures and Compilation Techniques, 2001. Proceedings. 2001 International Conference on (2001), pp. 3-14.

Modern architecture research relies heavily on detailed pipeline simulation. Simulating the full execution of an industry standard benchmark can take weeks to months to complete. To overcome this problem researchers choose a very small portion of a program's execution to evaluate their results, rather than simulating the entire program. In this paper we propose Basic Block Distribution Analysis as an automated approach for finding these small portions of the program to simulate that are representative of the entire program's execution. This approach is based upon using profiles of a program's code structure (basic blocks) to uniquely identify different phases of execution in the program. We show that the periodicity of the basic block frequency profile reflects the periodicity of detailed simulation across several different architectural metrics (e.g., IPC, branch miss rate, cache miss rate, value misprediction, address misprediction, and reorder buffer occupancy). Since basic block frequencies can be collected using very fast profiling tools, our approach provides a practical technique for finding the periodicity and simulation points in applications

Extracting the phase of high-order harmonic emission from a molecule using transient alignment in mixed samples

Nicholas Wagner — 2008-01-02T18:59:26-00:00

Physical Review A (Atomic, Molecular, and Optical Physics), Vol. 76, No. 6. (2007)

We report measurements of both the phase and intensity of high-order harmonic emission from aligned CO2 molecules, using a mixture of a molecular and an atomic gas. The molecules are transiently aligned using an ultrashort pulse, and a subsequent stronger pulse is used to generate high-order harmonics from a mixed Kr/CO2 sample. The high-order harmonic emission from the molecules interferes with the reference emission from the atoms. By monitoring the change in harmonic emission as a function of gas mixture and molecular alignment, we can retrieve the orientational dipole that has general features consistent with a two-center emission model.

Fast and accurate coarsening simulation with an unconditionally stable time step

Benjamin Vollmayr-Lee — 2007-09-12T18:43:18-00:00

Physical Review E, Vol. 68, No. 6. (23 December 2003), 066703.

We present Cahn-Hilliard and Allen-Cahn numerical integration algorithms that are unconditionally stable and so provide significantly faster accuracy-controlled simulation. Our stability analysis is based on Eyre’s theorem and unconditional von Neumann stability analysis; both of which we present. Numerical tests confirm the accuracy of the von Neumann approach; which is straightforward and should be widely applicable in phase-field modeling. For the Cahn-Hilliard case; we show that accuracy can be controlled with an unbounded time step Δ t that grows with time t as Δ t ∼ t α . We develop a classification scheme for the step exponent α and demonstrate that a class of simple linear algorithms gives α=1/3. For this class the speedup relative to a fixed time step grows with N ; the linear size of the system; as N /ln N . With conservative choices for the parameters controlling accuracy and finite-size effects we find that an 8192 2 lattice can be integrated 300 times faster than with the Euler method.

Overview of the HUPO Plasma Proteome Project: results from the pilot phase with 35 collaborating laboratories and multiple analytical groups, generating a core dataset of 3020 proteins and a publicly-available database.

GS Omenn — 2005-09-20T18:00:59-00:00

Proteomics, Vol. 5, No. 13. (August 2005), pp. 3226-3245.

HUPO initiated the Plasma Proteome Project (PPP) in 2002. Its pilot phase has (1) evaluated advantages and limitations of many depletion, fractionation, and MS technology platforms; (2) compared PPP reference specimens of human serum and EDTA, heparin, and citrate-anti-coagulated plasma; and (3) created a publicly-available knowledge base (www.bioinformatics.med.umich.edu/hupo/ppp; www.ebi.ac.uk/pride). Thirty-five participating laboratories in 13 countries submitted datasets. Working groups addressed (a) specimen stability and protein concentrations; (b) protein identifications from 18 MS/MS datasets; (c) independent analyses from raw MS-MS spectra; (d) search engine performance, subproteome analyses, and biological insights; (e) antibody arrays; and (f) direct MS/SELDI analyses. MS-MS datasets had 15 710 different International Protein Index (IPI) protein IDs; our integration algorithm applied to multiple matches of peptide sequences yielded 9504 IPI proteins identified with one or more peptides and 3020 proteins identified with two or more peptides (the Core Dataset). These proteins have been characterized with Gene Ontology, InterPro, Novartis Atlas, OMIM, and immunoassay-based concentration determinations. The database permits examination of many other subsets, such as 1274 proteins identified with three or more peptides. Reverse protein to DNA matching identified proteins for 118 previously unidentified ORFs.We recommend use of plasma instead of serum, with EDTA (or citrate) for anticoagulation. To improve resolution, sensitivity and reproducibility of peptide identifications and protein matches, we recommend combinations of depletion, fractionation, and MS/MS technologies, with explicit criteria for evaluation of spectra, use of search algorithms, and integration of homologous protein matches.This Special Issue of PROTEOMICS presents papers integral to the collaborative analysis plus many reports of supplementary work on various aspects of the PPP workplan. These PPP results on complexity, dynamic range, incomplete sampling, false-positive matches, and integration of diverse datasets for plasma and serum proteins lay a foundation for development and validation of circulating protein biomarkers in health and disease.

Modeling of time-interleaved ADCs with nonlinear hybrid filter banks

Christian Vogel — 2008-07-14T20:19:12-00:00

AEU - International Journal of Electronics and Communications, Vol. 59, No. 5. (15 July 2005), pp. 288-296.

In this paper, we model time-interleaved analog-to-digital converters (TIADCs) with nonlinear hybrid filter banks (NHFBs), which greatly unifies and simplifies the analysis of TIADCs. The input/output relation of such a nonlinear hybrid filter bank can be used to describe combined offset, gain, aperture delay, input behavior, and nonlinearity mismatches and is therefore an extendable starting point for profound analyses of TIADC behaviors. We show the connection of offset and gain mismatches to nonlinearity mismatches and reveal the two error sources of timing mismatches.

An autocorrelation model of bat sonar

Wiegrebe — 2008-05-26T18:06:53-00:00

Biological Cybernetics, Vol. 98, No. 6. (June 2008), pp. 587-595.

Effect of potassium perfluorooctanesulfonate, perfluorooctanoate and octanesulfonate on the phase transition of dipalmitoylphosphatidylcholine (DPPC) bilayers

W Xie — 2008-01-27T03:11:50-00:00

Biochimica et Biophysica Acta (BBA) - Biomembranes, Vol. 1768, No. 5. (May 2007), pp. 1299-1308.

Perfluorooctanesulfonic acid (PFOS) is a persistent environmental pollutant that may cause adverse effects by inhibiting pulmonary surfactant. To gain further insights in this potential mechanism of toxicity, we investigated the interaction of PFOS potassium salt with dipalmitoylphosphatidylcholine (DPPC) - the major component of pulmonary surfactant - using steady-state fluorescence anisotropy spectroscopy and DSC (differential scanning calorimetry). In addition, we investigated the interactions of two structurally related compounds, perfluorooctanoic acid (PFOA) and octanesulfonic acid (OS) potassium salt, with DPPC. In the fluorescence experiments a linear depression of the main phase transition temperature of DPPC (Tm) and an increased peak width was observed with increasing concentration of all three compounds, both using 1,6-diphenyl-1,3,5-hexatriene (DPH) and 1-(4-trimethylammoniumphenyl)-6-phenyl-1,3,5-hexatriene p-toluenesulfonate (TMA-DPH) as fluorescent probes. PFOS caused an effect on Tm and peak width at much lower concentrations because of its increased tendency to partition onto DPPC bilayers, i.e., the partition coefficients decrease in the K(PFOS) > K(PFOA) >> K(OS). Similar to the fluorescence anisotropy measurements, all three compounds caused a linear depression in the onset of the main phase transition temperature and a significant peak broadening in the DSC experiments, with PFOS having the most pronounced effect of the peak width. The effect of PFOS and other fluorinated surfactants on DPPC in both mono- and bilayers may be one mechanism by which these compounds cause adverse biological effects.

Phase Fluctuations on the Micron-Submicron Scale in GUVs Composed of a Binary Lipid Mixture

Anna Celli — 2007-12-20T01:31:46-00:00

Biophys. J., Vol. 94, No. 1. (1 January 2008), pp. 104-116.

We used a combination of imaging and fluctuation techniques to investigate the temporal evolution of gel phase domains at the onset of phase separation, as well as the correlation between domain topology and local lipid ordering in GUVs composed of a binary mixture of DPPC/DLPC 1:1. The data acquired at temperatures immediately above the transition temperature of the two lipids suggest fluctuations in the lipid organization with a lifetime <0.1 s and a characteristic length of 1.2 microm. As the temperature is decreased below the transition temperature of one of the lipids, coupling between the two leaflets of the bilayer is observed to begin within the first five minutes after the onset of phase separation. However, domains confined to only one leaflet can be found during the first 4550 min after the onset of phase separation. Our analysis using a two-state model (liquid and gel) indicates that for the first 4550 min from the onset of phase separation the two lipid phases do not strongly influence the phase behavior of each other on the micron-length scale. At longer times, behavior that deviates from the two-state model is observed and appears to be correlated to domain morphology. 10.1529/biophysj.107.105353

Lateral Diffusion in Lipid Membranes through Collective Flows

E Falck — 2008-01-18T21:39:06-00:00

J. Am. Chem. Soc., Vol. 130, No. 1. (9 January 2008), pp. 44-45.

Abstract: There is no comprehensive model for the dynamics of cellular membranes. Even mechanisms of basic dynamic processes, such as lateral diffusion of lipids, are poorly understood. Our atomic-scale molecular dynamics simulations support a novel, concerted mechanism for lipid diffusion. We find that a lipid and its nearest neighbors move in unison, forming loosely defined clusters. What is more, the motions of lipids are correlated over tens of nanometers: the lateral displacements of lipids in a given monolayer produce striking two-dimensional flow patterns. These flow patterns should have wide implications, affecting, for example, the formation of membrane domains, protein functionality, and action of lipases and drugs on membranes.

Structural Determinants for Partitioning of Lipids and Proteins Between Coexisting Fluid Phases in Giant Plasma Membrane Vesicles

Prabuddha Sengupta — 2007-09-13T17:47:37-00:00

Biochimica et Biophysica Acta (BBA) - Biomembranes, Vol. In Press, Accepted Manuscript

Wetting, Mixing, and Phase Transitions in Langmuir-Gibbs Films

E Sloutskin — 2007-10-17T23:55:25-00:00

Physical Review Letters, Vol. 99, No. 13. (2007)

Millimolar bulk concentrations of the surfactant cetyltrimethylammonium bromide (CTAB) induce spreading of alkanes, H(CH2)nH (denoted Cn) 12n21, on the water surface, which is not otherwise wet by these alkanes. The novel Langmuir-Gibbs film (LGF) formed is a liquidlike monolayer comprising both alkanes and CTAB tails. Upon cooling, an ordering transition occurs, yielding a hexagonally packed, quasi-2D crystal. For 11n17 this surface-frozen LGF is a crystalline monolayer. For 18n21 the LGF is a bilayer with a crystalline, pure-alkane, upper monolayer, and a liquidlike lower monolayer. The phase diagram and film structure were determined by x-ray, ellipsometry, and surface tension measurements. A thermodynamic theory accounts quantitatively for the observations.

Conformational and hydrational properties during the L[beta]- to L[alpha]- and L[alpha]- to HII-phase transition in phosphatidylethanolamine

Michael Rappolt — 2008-03-24T17:55:10-00:00

Chemistry and Physics of Lipids, Vol. In Press, Uncorrected Proof

Differential scanning calorimetry (DSC) measurements have been carried out simultaneously with small- and wide-angle X-ray scattering recordings on liposomal dispersions of stearoyl-oleoyl-phosphatidylethanolamine (PE) in a temperature range from 20 to 80 [degree sign]C. The main transition temperature, Tm, was determined at 30.9 [degree sign]C with an enthalpy of 28.5 kJ/mol and the lamellar-to-inverse hexagonal phase transition temperature, Thex, at 61.6 [degree sign]C with an enthalpy of 3.8 kJ/mol. Additionally highly resolved small angle X-ray diffraction experiments performed at equilibrium conditions allowed a reliable decomposition of the lattice spacings into hydrophobic and hydrophilic structure elements as well as the determination of the lipid interface area of the lamellar gel-phase (L[beta]), the fluid lamellar phase (L[alpha]) and of the inverse hexagonal phase (HII). The rearrangement of the lipid matrix and the coincident change of free water per lipid is illustrated for both transitions. Last, possible transition mechanisms are discussed on a molecular level.

Consequences of Ions and pH on the Supramolecular Organization of Sphingomyelin and Sphingomyelin/Cholesterol Bilayers

Caroline Chemin — 2008-03-24T17:51:23-00:00

Chemistry and Physics of Lipids, Vol. In Press, Accepted Manuscript

Why are lipid rafts not observed in vivo?

Arun Yethiraj — 2007-08-07T05:18:25-00:00

Biophys J (27 July 2007)

The existence of lipid rafts in live cells remains a topic of lively debate. While large, micron-sized rafts are readily observed in artificial membranes, attempts to observe analogous domains in live cells place an upper limit of ~5 nm on their size. We suggest that integral membrane proteins attached to the cytoskeleton act as obstacles that limit the size of lipid domains. Computer simulations of a binary lipid mixture show that the presence of protein obstacles at only 5-10% by area dramatically reduces the tendency of the lipids to phase separate. These calculations emphasize the importance of spatial heterogeneity in cell membranes, which limits the transferability of conclusions drawn from artificial membranes to live cells.

Effect of Cholesterol and Ergosterol on the Compressibility and Volume Fluctuations of Phospholipid-Sterol Bilayers in the Critical Point Region - A Molecular Acoustic and Calorimetric Study

Roland Krivanek — 2008-01-24T02:31:17-00:00

Biophys. J. (16 January 2008), biophysj.107.122549.

Although sterol-phospholipid interactions have been in the focus of interest for many years now, a complete thermodynamic profile of these systems is still missing. To contribute to a better understanding of the thermodynamic functions of these systems, we determined isothermal compressibility coefficient data for dipalmitoylphosphocholine (DPPC) and DPPC containing cholesterol and ergosterol vesicles by means of molecular acoustics (ultrasound velocimetry, densimetry) and differential scanning and pressure perturbation calorimetric techniques. A particular focus was on the influence of the differential structural properties of the two sterols on the thermodynamic properties of lipid bilayers, and on the nature of the critical point region of phospholipid-sterols systems by determining thermodynamic fluctuation parameters. Contrary to significant changes in conformational and dynamical properties of the DPPC-sterol membranes, no marked differences were found in the various thermodynamic properties studied, including the adiabatic (betaSlipid) and isothermal (betaTlipid) compressibility as well as the volume fluctuations. Differences in betaTlipid and betaSlipid become dramatic in the gel-fluid transition region only, due to a significant degree of slow relaxational processes in the micros time range in the transition region. Our data show no evidence for the existence of a typical critical point phenomenon in the concentration and temperature range where a critical point in the DPPC-sterol phase diagram is expected to appear. Hence, on a macroscopic level, it seems more appropriate to describe the sterol-phospholipid binary mixtures in the liquid-ordered/liquid-disordered coexistence region as a phase region consisting essentially of small nanodomains, only. Such small-domain dimensions with a series of particular properties, such as increased line energy, spontaneous curvature and limited lifetime, seem to be also typical of raft-like domains in cell membranes. 10.1529/biophysj.107.122549

Interfacial Behavior of Cholesterol, Ergosterol, and Lanosterol in Mixtures with DPPC and DMPC

Karen Sabatini — 2008-06-02T23:26:16-00:00

Biophys. J. (30 May 2008), biophysj.108.132076.

Binary mixtures of cholesterol, ergosterol, and lanosterol with phosphatidylcholines differing in the length of the saturated acyl chains, viz. 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1-palmitoyl-2-myristoyl-sn-glycero-3-phosphocholine (DMPC), were analyzed using a Langmuir balance for recording force-area (pi-A) and surface potential-area (psi-A) isotherms. A progressive disappearance of the liquid expanded - liquid condensed transition was observed in mixed monolayers with DPPC following the increase in the content of all three sterols. For fluid DMPC matrix no modulation of the monolayer phase behavior due to the sterols was evident with the exception of lanosterol, for which between mole fractions of X = 0.3 and X = 0.75 a pronounced discontinuity was discernible in the compression isotherms. Condensing and expanding effects in force-area (pi-[A]) isotherms due to varying Xsterols and differences in the monolayer physical state were assessed from the values for the interfacial compression moduli. Surface potential measurements support the notion that cholesterol and ergosterol, but not lanosterol, reduce the penetration of water into the lipid monolayers. Examination of the excess free energy of mixing revealed an enhanced stability of binary monolayers containing cholesterol compared to those with ergosterol or lanosterol, the differences being emphasized in the range of surface pressure values found in natural membranes. 10.1529/biophysj.108.132076

Coupled composition-deformation phase-field method for multicomponent lipid membranes.

CM Funkhouser — 2008-03-09T01:04:09-00:00

Phys Rev E Stat Nonlin Soft Matter Phys, Vol. 76, No. 1 Pt 1. (July 2007)

We present a method for modeling phase transitions and morphological evolution of binary lipid membranes with approximately planar geometries. The local composition and the shape of the membrane are coupled through composition-dependent spontaneous curvature in a Helfrich free energy. The evolution of the composition field is described by a Cahn-Hilliard-type equation, while shape changes are described by relaxation dynamics. Our method explicitly treats the full nonlinear form of the geometrical scalars, tensors, and differential operators associated with the curved shape of the membrane. The model is applied to examine morphological evolution and stability of lipid membranes initialized in a variety of compositional and geometric configurations. Specifically, we investigate the dynamics of systems which have a lamellar structure as their lowest energy state. We find that evolution is very sensitive to initial conditions; only membranes with sufficiently large lamellar-type compositional perturbations or ripple-type shape perturbations in their initial configuration can deterministically evolve into a lamellar equilibrium morphology. We also observe that rigid topographical surface patterns have a strong effect on the phase separation and compositional evolution in these systems.