Narrow Phase Research Articles

Chaos thresholds in finite Fermi systems

The development of Quantum Chaos in finite interacting Fermi systems is considered. At sufficiently high excitation energy the direct two-particle interaction may mix into an eigen-state the exponentially large number of simple Slater-determinant states. Nevertheless, the transition from Poisson to Wigner-Dyson statistics of energy levels is governed by the effective high order interaction between states very distant in the Fock space. The concrete form of the transition depends on the way one chooses to work out the problem of factorial divergency of the number of Feynman diagrams. In the proposed scheme the change of statistics has a form of narrow phase transition and may happen even below the direct interaction threshold.

Reactive diffusion and phase equilibria in the V–C, Nb–C, Ta–C and Ta–N systems

The reactive formation of vanadium, niobium and tantalum carbides as well as tantalum nitrides was investigated by means of diffusion couples. For the preparation of the carbides the compact metals were reacted with graphite powder and the formation of the phases MeC 1− x and Me 2C could be observed. The slow growth rate of the Me 4C 3 phases made it necessary to provide restricted diffusion geometry (wedge-type or plane-sheet samples) or, preferentially, diffusion couples of the type Me 2C/graphite. The phases ζ-V 4C 3− x , ζ-Nb 4C 3− x and ζ-Ta 4C 3− x could be observed as distinct diffusion bands below 1900, 1575 and 2170°C, respectively. The compositions of the phase boundaries as a function of temperature were measured by EPMA. The composition of ζ-V 4C 3− x is 37.9 at.%C (with a narrow homogeneity range of <0.5 at.%C), that of ζ-Nb 4C 3− x is 40.1–40.7 at.%C and that of ζ-Ta 4C 3− x is 38.2–39.0 at.%C (standard deviations ca. ±0.2 at.%C). For the β-Me 2C phases the carbon content was found to be greater than the values given in recent assessments, whereas the homogeneity regions measured for the δ-MeC 1− x phases are consistent with established data. In the Ta–N system the ε-TaN and the δ-TaN 1− x phases usually form very narrow phase bands. Here again wedge-type diffusion samples were applied in order to enlarge the thickness of the phase bands. δ-TaN 1− x undergoes a eutectoid decomposition at 1821±19°C into ε-TaN and β-Ta 2N. The formation of ε-TaN occurs at 1888±15°C at 25 bar N 2, its homogeneity range at 1873°C is smaller than 0.4 at.%N. Re-investigated portions of the phase diagrams of all four systems are given.

Dynamic phase boundary topography by latent heat effects

When radial flow passes through a mantle phase boundary, the interplay of advection and diffusion of latent heat creates “dynamic” topography of this boundary, which means a deflection that is related to the sense and magnitude of radial velocity even though the flow does not advect temperature differences towards the phase boundary. A one-dimensional stationary model is used to quantify the effect, which does not dependent on the sign of the Clapeyron slope. Significant deflection requires slow radial flow and a narrow phase loop. These conditions are most probably met for the phase transition from spinel to perovskite and magnesiowüstite at 660-km depth. Up to 4 km of topography (peak-to-peak) are created, with a mass anomaly that is equivalent to 440 m of dynamic topography at the Earth's surface. Other phase transitions of the olivine component also contribute to a degree that is less certain. The time scale of adjustment of phase boundary topography is studied in a two-dimensional model, where a deep mass anomaly in an isentropic mantle drives flow through the 660-km phase boundary. The adjustment time depends on the inverse square of the vertical velocity and is on the order of 10 Ma in the Earth, which is shorter than the convective time scale for a high-viscosity lower mantle. Dynamic phase boundary topography created by this mechanism can replace a significant part of the surface topography required in dynamic geoid models and can help to reduce the misfit between predicted dynamic surface topography and the upper limit that observations pose on its amplitude.

Collective and non-collective excitations in antiferroelectric and ferrielectric liquid crystals studied by dielectric relaxation spectroscopy and electro-optic measurements

The dynamics of different molecular modes in four antiferroelectric liquid crystal substances have been studied by a combination of spectroscopic methods.The fastest motion is the reorientation around the molecular long axis, here found in the low GHz range by time domain spectroscopy. The reorientation around the short axis has a characteristic frequency of about 10kHz and is detected by frequency domain spectroscopy in the homeotropic configuration. As for the collective excitations, the Goldstone and soft modes, characteristic of the ferroelectric phase, have counterparts in the antiferroelectric phase which appear very different. There are two characteristic peaks in the spectrum, one at high frequency, about 100kHz, the other at low frequency, about 10 kHz. The latter has often been mistaken for short axis reorientation and both have been attributed to soft modes. By combining different experimental techniques and different geometries it can be shown that neither is a soft mode, but both are collective modes of different character: the high frequency mode corresponds to fluctuations where molecules in neighbouring layers are moving in opposite phase, the low frequency mode to phase fluctuations in the helicoidal superstructure. In materials exhibiting a C* phase in addition to the C*a or C* gamma phases, an additional strong peak appears in at least one lower-lying phase adjacent to the C* phase. We show that this peak, which we call a hereditary peak, has nothing to do with the antiferroelectric or ferrielectric order, but is just the Goldstone peak from a coexisting C* phase. In the same way, a Goldstone mode peak from the C* gamma phase may appear in the underlying C* a phase. In a general way, narrow phases like C* gamma, being bounded by first order transitions on both sides (C* a -C* gamma -C*) are likely to show non-characteristic (hereditary) peaks from both adjacent phases.

Liquid‐crystalline ordering in solutions of polyelectrolytes

AbstractThe isotropic‐nematic phase transition in solutions of stiff‐chain polyelectrolytes is considered on the basis of the Onsager approach for the limiting cases of charged rods and persistent macrolecules. We plotted a full family of phase diagrams for orientational transitions in solutions of polyelectrolytes with any charge density as a function of the low‐molecular‐weight salt concentration. It is shown that charging of macromolecules can lead not only to the renormalization of the chain diameter (discussed by Onsager) or to the twisting effect (predicted by Odijk et al.), but in some cases also to a variety of other regimes, including transitions with very narrow phase separation regions, or with a second orientational transition to a highly oriented nematic phase upon the increase of polymer concentration.

Linewidth narrowing and optical phase control of mode-locked semiconductor ring laser employing optical injection locking

The linewidth of the individual modes of an actively mode-locked extended-ring-cavity semiconductor laser is reduced from a free running linewidth of over 200-20 kHz by the injection of a narrow linewidth continuous-wave (CW) light. The optical phase of the injection-locked pulses can be controlled by adjusting the free-running optical frequency of the semiconductor ring laser. The variation in the optical phase of the output pulses versus the change of the free-running optical frequency is evaluated to be 0.57/spl pi/ radians within the locking range of about 96 MHz by observing temporal shape of the beat signal formed between output pulses and CW injection light.

Phase angle predicts survival in hemodialysis patients

Objective: To determine the relation between phase angle by bioelectrical impedance analysis (BIA) and survival in hemodialysis patients. Design: Cohort analytic study. Setting: One hundred one free-standing outpatient dialysis units. Patients: Three thousand nine adult patients on thrice weekly hemodialysis. Patients with amputations above the transmetatarsal site were excluded from participation. Main Outcome Measure: Vital status, with follow-up to at least 1 year. Results: Mean phase angle was 4.8 &#x0026;#x0026;#x0026;#x0026;#x0026;#x0026;#x0026;#x0026;#x0026;#x0026;#x0026;#x00B1; 1.8 degrees. Patients with narrow (low) phase angle experienced an increased relative risk (RR) of death (<3 degrees; RR 4.3; 95% confidence interval [Cl], 2.9–6.2; and 3 to 4 degrees); RR 2.2; 95% Cl, 1.6–3.2; compared with the ≥6 degrees reference). There were no significant differences in risk among patients with phase angle 4 to 5 degrees (RR 1.2; 95% Cl, 0.8–1.8), 5 to 6 degress (RR 1.1; 95% Cl, 0.7–1.7), and ≥6 degrees, suggesting a nonlinear relation between phase angle and survival. The RRs for phase angle <4 degrees remained statistically significant after adjusting for age, gender, race, serum albumin and creatinine concentrations, and dialysis intensity (<3 degrees, RR 2.2; 95% Cl, 1.6–3.1, and 3 to 4 degrees, RR 1.3; 95% Cl, 1.0–1.7, compared with all patients ≥4 degrees). Conclusions: In patients on hemodialysis, BIA-derived phase angle <4 degrees was associated with an increased RR of death, even after adjustment for case mix and several nutritional indicators. Further research is required to determine whether BIA can be used to monitor health status over time, or to gauge response to nutrition support or other clinical interventions in patients with end-stage renal disease.

Phase behavior and permeability properties of phospholipid bilayers containing a short-chain phospholipid permeability enhancer

The thermodynamic phase behavior and trans-bilayer permeability properties of multilamellar phospholipid vesicles containing a short-chain DC 10PC phospholipid permeability enhancer have been studied by means of differential scanning calorimetry and fluorescence spectroscopy. The calorimetric scans of DC 14PC lipid bilayer vesicles incorporated with high concentrations of DC 10PC demonstrate a distinct influence on the lipid bilayer thermodynamics manifested as a pronounced freezing-point depression and a narrow phase coexistence region. Increasing amounts of DC 10PC lead to a progressive lowering of the melting enthalpy, implying a mixing behavior of the DC 10PC in the bilayer matrix similar to that of a substitutional impurity. The phase behavior of the DC 10PC–DC 14PC mixture is supported by fluorescence polarization measurements which, furthermore, in the low-temperature gel phase reveal a non-monotonic concentration-dependent influence on the structural bilayer properties; small concentrations of DC 10PC induce a disordering of the acyl chains, whereas higher concentrations lead to an ordering. Irreversible fluorescence quench measurements demonstrate a substantial increase in the trans-bilayer permeability over broad temperature and composition ranges. At temperatures corresponding to the peak positions of the heat capacity, a maximum in the trans-bilayer permeability is observed. The influence of DC 10PC on the lipid bilayer thermodynamics and the associated permeability properties is discussed in terms of microscopic effects on the lateral lipid organization and heterogeneity of the bilayer.

AMADEUS Project and Microscopic Simulation of Boiling Two-Phase Flow by the Lattice-Boltzmann Method

A two-dimensional lattice-Boltzmann model with a hexagonal lattice is developed to simulate a boiling two-phase flow microscopically. Liquid-gas phase transition and bubble dynamics, including bubble formation, growth and deformation, are modeled by using an interparticle potential based on the van der Waals equation of state. Thermohydrodynamics is incorporated into the model by adding extra velocities to define temperature. The lattice-Boltzmann model is solved by a finite difference scheme so that numerical stability can be ensured at large discontinuity across the liquid-gas phase boundary and the narrow phase interface thickness can be attained. It is shown from numerical simulations that the model has the ability to reproduce phase transition, bubble dynamics and thermohydrodynamics while assuring numerical instability and narrow phase interface.

An experimental and theoretical study of the suppression of interferometric noise and distortion in AM optical links by phase dither

The effects of phase dither on the magnitude and spectral distribution of interferometric fiber optic noise and intermodulation products is considered. A theory is presented as well as experimental data which show major reduction of AM noise brought about by intentional narrow band and wide band phase dither of the laser output.

Compensation of tool axis misalignment in active magnetic bearing spindle system

The tool axis misalignment, which causes machining inaccuracies in an active magnetic bearing (AMB)-spindle system, can be compensated by tracking control of the rotor-spindle. The pseudo-derivative feedback (PDF) control scheme alone does not correct the tool axis misalignment since the integral action results in the narrow bandwidth and large phase lag in the controlled system. To improve the tracking performance, the feedback and feedforward controllers are combined with the existing proportional-derivative controller, which stabilizes the inherently unstable AMB-spindle system dynamics. The theoretical and experimental results show that proposed control scheme efficiently compensates the tool axis misalignment compared with the conventional PDF control scheme.

A Gibbs ensemble Monte Carlo study of phase coexistence in model C60

Extensive Gibbs ensemble Monte Carlo (GEMC) simulations of a rigid molecule model of C60, characterized by a deeply attractive short-ranged interaction potential, are performed with the aim to establish the effect of the system size on the existence and location of the liquid–vapor binodal line and of its critical point. The results obtained with N=300, 600, and 1500 particles indicate that the position and the overall shape of the binodal is only minorly influenced by finite size effects. The estimated critical temperature and density at the different N fall in the ranges 1920–1940 K, and 0.4–0.45 nm−3, respectively. The results are discussed by making reference to previous studies of finite size effects in GEMC simulations. The GEMC predictions are also compared with previous computer simulation and theoretical calculations for the same model fluid. The agreement is on the whole satisfactory for both the liquid–vapor coexistence line and the critical point parameters. On the basis of previously determined freezing lines of C60, and of the actual binodal line, different estimates of the location of the triple point are also made. Triple point temperatures are found, in any case, definitely lower (by at least 150 K) than the critical temperatures, thus confirming the existence of a relatively narrow liquid phase region in the phase diagram, as predicted in previous molecular dynamics and theoretical works. The existence of such a liquid phase for the adopted model potential is discussed and assessed in the more general framework of liquid–vapor coexistence conditions in fluids interacting through short-ranged forces. The possibility to get the liquid phase of “real life” C60, hitherto not observed experimentally, is also discussed in connection with recent high temperature experimental results on fullerite samples.

Synthesis and Characterization of Bis(3-chloro-4-dodecyloxyphenyl) Malondialdehyde Complexes of Cu(II) and Ni(II)

Bis (3-chloro-4-dodecyloxyphenyl) malondialdehyde copper(II), as well as its nickel(II) homologue have been synthesised. The copper(II) complex shows a narrow (15 °C) nematic phase below its clearing temperature. The nickel(II) complex is polymeric in nature.

Activation phase ensures kinematic efficacy in flight-steering muscles of Drosophila melanogaster

During tethered flight in Drosophila melanogaster, spike activity of the second basalar flight-control muscle (M.b2) is correlated with an increase in both the ipsilateral wing beat amplitude and the ipsilateral flight force. The frequency of muscle spikes within a burst is about 100 Hz, or 1 spike for every two wing beat cycles. When M.b2 is active, its spikes tend to occur within a comparatively narrow phase band of the wing beat cycle. To understand the functional role of this phase-lock of firing in the control of flight forces, we stimulated M.b2 in selected phases of the wing beat cycle and recorded the effect on the ipsilateral wing beat amplitude. Varying the phase timing of the stimulus had a significant effect on the wing beat amplitude. A maximum increase of wing beat amplitude was obtained by stimulating M.b2 at the beginning of the upstroke or about 1 ms prior to the narrow phase band in which the muscle spikes typically occur during flight. Assuming a delay of 1 ms between the stimulation of the motor nerve and muscle activation, these results indicate that M.b2 is activated at an instant of the stroke cycle that produces the greatest effect on wing beat amplitude.

The diboride compounds of molybdenum: MoB 2− x and Mo 2B 5− y

The phase relations of the molybdenum diboride compounds MoB 2− x and Mo 2B 5− y and the structure of Mo 2B 5− y have been re-examined with samples prepared between 1400 and 1800°C. Two types of six-membered boron ring, nearly planar and puckered, occur within the Mo 2B 5− y structure. The sites at the centers of the puckered rings may be unoccupied (K′ layers) or occupied by boron atoms (K layers). Neutron diffraction refinements show that these sites are completely unoccupied (K′ layers) in Mo 2B 5− y samples of several batch compositions. This result, combined with the insensitivity of the unit cell dimensions of Mo 2B 5− y to batch composition, shows that this phase has a narrow single phase region, with y close to unity, between 1400 and 1800°C. MoB 2− x also has a narrow single-phase region centered at about 61 at.% boron over this temperature range.

Microwave inverse C-caronerenkov accelerator.

Analysis and experimental tests have been carried out on a dielectrically lined waveguide, which appears to be a suitable structure for accelerating electrons. From the dispersion relation for the ${\mathrm{TM}}_{01}$ mode, inner and outer radii of a copper-clad alumina pipe (\ensuremath{\varepsilon}=9.40) have been determined such that the phase and group velocities are 0.9732c and 0.1096c, respectively. Analysis and particle simulation studies for the injection of 6-MeV microbunches from a 2.856-GHz rf gun, and subsequent acceleration by the ${\mathrm{TM}}_{01}$ fields, predict that an acceleration gradient of 6.3 Mv/m can be achieved with a traveling-wave power of 15 MW applied to the structure. Synchronous injection into a narrow phase window is shown to allow trapping of all injected particles. The rf fields of the accelerating structure are shown to provide radial focusing, so that longitudinal and transverse emittance growth during acceleration is small and that no external magnetic fields are required for focusing. The acceleration mechanism is the inverse of that in which electrons radiate as they traverse a waveguide at speeds exceeding the phase velocity of the microwaves (\ifmmode \check{C}\else \v{C}\fi{}erenkov radiation) and is thus referred to as a microwave inverse \ifmmode \check{C}\else \v{C}\fi{}erenkov accelerator. For 0.16-nC, 5-psec microbunches, the normalized emittance of the accelerated beam is predicted to be less than 5\ensuremath{\pi} mm mrad. Experiments on sample alumina tubes have been conducted that verify the theoretical dispersion relation for the ${\mathrm{TM}}_{01}$ mode over a two-to-one range in frequency. No excitation of axisymmetric or nonaxisymmetric competing waveguide modes was observed. High power tests showed that tangential electric fields at the inner surface of an uncoated sample of alumina pipe could be sustained up to 8.4 MV/m without breakdown. These considerations suggest that a microwave inverse \ifmmode \check{C}\else \v{C}\fi{}erenkov test accelerator can be built to examine these predictions using an available rf power source, a 6-MeV rf gun, and an associated beam line. \textcopyright{} 1996 The American Physical Society.

Optomotor Control of Course and Altitude in Drosophila Melanogaster is Correlated With Distinct Activities of at Least Three Pairs of Flight Steering Muscles

Flight control in the fruitfly Drosophila melanogaster is achieved by minute sets of muscles on either side of the thorax. Control responses of wings and muscles were elicited during fixed flight by moving a striped pattern in front of the eyes. For example, pattern motion from the lower right to the upper left signals to the test fly a rotatory course deviation to the right and simultaneously a translatory altitude displacement downwards. The counteracting response to the displacement of the retinal image is an increase in thrust and lift on the right, accomplished mainly by increasing the wingbeat amplitude (WBA) on that side. A comparison of such responses with the simultaneously recorded action potentials in the prominent basalar muscles M.b1 and M.b2 and axillary muscles M.I1 and M.III1 on either side suggests that three of these muscles act on the WBA more or less independently and contribute to the optomotor control of course and altitude. During flight, M.b1 is almost continuously active with a frequency equal to or slightly below 1 spike per wingbeat cycle. The spikes occur within a narrow phase interval of this cycle, normally at the beginning of the transition from upstroke to downstroke. However, the visual stimulus described above causes a substantial phase lead in M.b1 on the right; the spikes occur shortly before the end of the upstroke. Such phase shifts are accompanied by comparatively smooth 'tonic' responses of the WBA. The activities of M.b2 and M.I1 are normally very low. However, the stimulus described above activates M.b2 on the right in a phase interval approximately two-thirds into the upstroke and M.I1 on the left in a phase interval at the beginning of the downstroke. The spikes tend to occur in bursts. These bursts are correlated with WBA-increasing 'hitches' (rapid changes in amplitude) on the right and WBA-decreasing hitches on the left. As fast 'phasic' responses, the burst-induced hitches are likely to account for the course-controlling 'body saccades' observed during free flight. For unknown reasons, M.I1 is activated by pattern motion but cannot conceivably assist the other muscles in altitude control. Unlike its homologues in larger flies (Musca domestica, Calliphora erythrocephala), M.III1 does not participate in optomotor flight control. Its activation seems to support the termination of flight and wing retraction at rest. The essential properties of the three pairs of muscles M.b1, M.b2 and M.I1 resemble those found in larger flies; the muscles are controlled by motion detectors with muscle-specific 'preferred directions' in the hexagonal array of retinal elements. Optomotor control of the three pairs of muscles in Drosophila melanogaster could explain most, but not all, of the WBA responses recorded so far.

Two-dimensional thermo-kinetic model for the olivine-spinel phase transition in subducting slabs

We have investigated the effects of the latent-heat release on the kinetics of the olivine-spinel phase transition to clarify the role of the thermo-kinetic coupling process for the structure of the metastable olivine-wedge in subducting slabs. We have laid out the mathematical formulation of a two-dimensional time-dimensional time-dependent model consisting of the kinetic equations, which are cast as a system of four nonlinear ordinary differential equations (ODE) at each spatial grid point and the time-dependent partial differential equation (PDE) for the temperature, which is coupled to the kinetics by virtue of latent-heat release. This set of ODE-PDE system has been solved by the differential-algebraic method. The structure of the kinetic phase boundary is strongly determined by thermo-kinetic coupling effects during the phase transition. For slow, warm slabs a very narrow phase boundary is obtained near the typical depth for equilibrium phase transformations. From laboratory data we obtain a small latent-heat release (< 10 kJ mol −1), which results in a small heating up of the slab (around 50°). Hence thermo-kinetic coupling effects will not significantly influence the structure of the phase boundary in this regime. For fast, cold slabs narrow regions with metastable olivine may be pushed down to a depth of about 600 km while the thermo-kinetic coupling due to the latent-heat release drastically reduces the depth and the width of the region where olivine and spinel coexist in the cold slab interior. Below the metastable wedge the latent-heat results in a significant and localized heating of the cold slab interior (around 150°), because in this regime the heat release is three times higher. The depth of the metastable wedge in the subducting slab is found to be very sensitive to certain thermodynamic parameters such as the activation energy for growth and the internal slab heating caused by the phase transformation. We propose that deep or intermediate earthquakes occur due to a thermal runaway-effect caused by shear instabilities while these effects are enhanced by the latent-heat release associated with the olivine-spinel transformation. The correlation between fast subducting velocity and the concentration of deep-focus earthquakes at around 600 km depth, as shown for the Tonga-Kermadec trench, can be predicted by this 2-D thermo-kinetic model.

Effect of the Bi2201 coexistence on the Bi2212 solidification in the LPE film

The solidification of the Bi2212 phase has been investigated by using the LPE method. The dependence of the relative content of the Bi2212 phase in the as-grown film on the growth temperature has made it clear that the Bi2212 phase can be obtained only from a temperature near 980°C. It has suggested that the narrow solid phase of the Bi2212 phase adjoins to the liquid phase of the Bi2201 phase.

Hydrogen-induced structural changes of Fe2Ce alloys

The amorphization kinetics of the Fe2Ce Laves phase were studied, utilizing X-ray diffraction (XRD), differential scanning calorimetry (DSC) and thermal H desorption measurements. Additionally, the local H diffusion process in this ferromagnetic compound was investigated by means of magnetic susceptibility and magnetic after-effect (MAE) measurements. Fe2Ce can easily be amorphized (pH2 = 5 × 103to1 × 105Pa, T < 400K); irreversible hydrogen-induced amorphization takes place in a narrow phase boundary which migrates from the surface into the sample. Furthermore, cyclic H-charging of amorphous Fe2Ce below its crystallization temperature reveals a severe degradation in H-storage capacity from 53 at.% to 18 at.% after only three cycles. This degradation is attributed to a hydrogen-induced phase separation into crystalline CeH2 and α-Fe which is enhanced by the high mobility of Fe atoms.