Three-dimensional large-eddy simulations of the early phase of contrail-to-cirrus transition: effects of atmospheric turbulence and radiative transfer

DOE PAGES

Paoli, Roberto; Thouron, Odile; Cariolle, Daniel; ...

2017-12-08

Here, this article presents the results from numerical experiments of the early phase of contrail-cirrus formation using a limited set of fully three-dimensional, high-resolution large-eddy-simulations. The focus is laid on the interplay between atmospheric turbulence and the radiative transfer (and to a limited extent the ambient ice relative humidity), and how this interaction affects the contrail evolution and the characteristics of the resulting contrail-cirrus one hour after emission. Turbulence is sustained via a large-scale stochastic forcing that creates a non-uniform shear in addition to pure turbulent fluctuations. This effect manifests in the formation of vertically sheared structures of ice crystals.more » When radiative transfer is activated, ice tends to redistribute more uniformly along the vertical direction forming spotty vertical structures. For the conditions analyzed in this study, atmospheric turbulence, inclusive of non-uniform turbulent shear and turbulent fluctuations, affects primarily the contrail width whereas the microphysical properties such ice water path and ice mass are controlled by radiative transfer and relative humidity.« less

Three-dimensional large-eddy simulations of the early phase of contrail-to-cirrus transition: effects of atmospheric turbulence and radiative transfer

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

Paoli, Roberto; Thouron, Odile; Cariolle, Daniel

Here, this article presents the results from numerical experiments of the early phase of contrail-cirrus formation using a limited set of fully three-dimensional, high-resolution large-eddy-simulations. The focus is laid on the interplay between atmospheric turbulence and the radiative transfer (and to a limited extent the ambient ice relative humidity), and how this interaction affects the contrail evolution and the characteristics of the resulting contrail-cirrus one hour after emission. Turbulence is sustained via a large-scale stochastic forcing that creates a non-uniform shear in addition to pure turbulent fluctuations. This effect manifests in the formation of vertically sheared structures of ice crystals.more » When radiative transfer is activated, ice tends to redistribute more uniformly along the vertical direction forming spotty vertical structures. For the conditions analyzed in this study, atmospheric turbulence, inclusive of non-uniform turbulent shear and turbulent fluctuations, affects primarily the contrail width whereas the microphysical properties such ice water path and ice mass are controlled by radiative transfer and relative humidity.« less

Persistent fluctuations in synchronization rate in globally coupled oscillators with periodic external forcing

NASA Astrophysics Data System (ADS)

Atsumi, Yu; Nakao, Hiroya

2012-05-01

A system of phase oscillators with repulsive global coupling and periodic external forcing undergoing asynchronous rotation is considered. The synchronization rate of the system can exhibit persistent fluctuations depending on parameters and initial phase distributions, and the amplitude of the fluctuations scales with the system size for uniformly random initial phase distributions. Using the Watanabe-Strogatz transformation that reduces the original system to low-dimensional macroscopic equations, we show that the fluctuations are collective dynamics of the system corresponding to low-dimensional trajectories of the reduced equations. It is argued that the amplitude of the fluctuations is determined by the inhomogeneity of the initial phase distribution, resulting in system-size scaling for the random case.

Effects of Fluctuations on Inhomogeneous Chiral Transitions

NASA Astrophysics Data System (ADS)

Lee, Tong-Gyu; Yoshiike, Ryo; Tatsumi, Toshitaka

We discuss the features of the order-parameter fluctuations in the normal phase near the phase boundary and their effects on the phase transition from the normal to the inhomogeneous phase with spatially modulated order parameter. Focusing on the chiral symmetry breaking, i.e., inhomogeneous chiral transition, we consider the fluctuation of the chiral pair consisting of quark-antiquark or quark-hole pair within the two-flavor Nambu-Jona-Lasinio model in the chiral limit. We clarify the roles of quantum and thermal fluctuations and also argue that anomalies for thermodynamic quantities in the inhomogeneous chiral transition should lead to phenomenological implications.

Phase Fluctuation Enhanced Adaptive Processor

DTIC Science & Technology

2000-02-04

Serial Number Filing Date Inventor 09/498.348 4 February 2000 Ronald A. Wagstaff Jackson A. Mobbs NOTICE The above identified patent...phase angle, as describedin Phase Variations in a Fluctuation Based Processor, Ronald A. Wagstaff and Jacob George, SPIE Vol. 2751, April 1996, pages...16 17 18 19 20 21 22 Docket No.: N.C. 79,518 PATENT APPT TPATT™ Inventor’s Name: Wagstaff , et al APPLICATION 1 have medium phase fluctuations

Detection of stably bright squeezed light with the quantum noise reduction of 12.6  dB by mutually compensating the phase fluctuations.

PubMed

Yang, Wenhai; Shi, Shaoping; Wang, Yajun; Ma, Weiguang; Zheng, Yaohui; Peng, Kunchi

2017-11-01

We present a mutual compensation scheme of three phase fluctuations, originating from the residual amplitude modulation (RAM) in the phase modulation process, in the bright squeezed light generation system. The influence of the RAM on each locking loop is harmonized by using one electro-optic modulator (EOM), and the direction of the phase fluctuation is manipulated by positioning the photodetector (PD) that extracts the error signal before or after the optical parametric amplifier (OPA). Therefore a bright squeezed light with non-classical noise reduction of π is obtained. By fitting the squeezing and antisqueezing measurement results, we confirm that the total phase fluctuation of the system is around 3.1 mrad. The fluctuation of the noise suppression is 0.2 dB for 3 h.

The Compressed Baryonic Matter experiment at FAIR

NASA Astrophysics Data System (ADS)

Höhne, Claudia

2018-02-01

The CBM experiment will investigate highly compressed baryonic matter created in A+A collisions at the new FAIR research center. With a beam energy range up to 11 AGeV for the heaviest nuclei at the SIS 100 accelerator, CBM will investigate the QCD phase diagram in the intermediate range, i.e. at moderate temperatures but high net-baryon densities. This intermediate range of the QCD phase diagram is of particular interest, because a first order phase transition ending in a critical point and possibly new highdensity phases of strongly interacting matter are expected. In this range of the QCD phase diagram only exploratory measurements have been performed so far. CBM, as a next generation, high-luminosity experiment, will substantially improve our knowledge of matter created in this region of the QCD phase diagram and characterize its properties by measuring rare probes such as multi-strange hyperons, dileptons or charm, but also with event-by-event fluctuations of conserved quantities, and collective flow of identified particles. The experimental preparations with special focus on hadronic observables and strangeness is presented in terms of detector development, feasibility studies and fast track reconstruction. Preparations are progressing well such that CBM will be ready with FAIR start. As quite some detectors are ready before, they will be used as upgrades or extensions of already running experiments allowing for a rich physics program prior to FAIR start.

Nonequilibrium life-cycles in Ocean Heat Content

NASA Astrophysics Data System (ADS)

Weiss, Jeffrey B.; Fox-Kemper, Baylor; Mandal, Dibyendu; Zia, Royce K. P.

2014-03-01

Natural climate variability can be considered as fluctuations in a nonequilibrium steady state. A fundamental property of nonequilibrium steady states is the phase space current which provides a preferred direction for fluctuations, and is manifested as preferred life-cycles for climate fluctuations. We propose a new quantity, the phase space angular momentum, to quantify the phase space rotation. In analogy with traditional angular momentum, which quantifies the rotation of mass in physical space, the phase space angular momentum quantifies the rotation of probability in phase space. It has the additional advantage that it is straightforward to calculate from a time series. We investigate the phase space angular momentum for fluctuations in ocean heat content in both observations and ocean general circulation models. We gratefully acknowledge financial support from the National Science Foundation (USA) under grant OCE 1245944.

A method to calibrate phase fluctuation in polarization-sensitive swept-source optical coherence tomography

NASA Astrophysics Data System (ADS)

Lu, Zenghai; Kasaragod, Deepa K.; Matcher, Stephen J.

2011-06-01

A phase fluctuation calibration method is presented for polarization-sensitive swept-source optical coherence tomography (PS-SS-OCT) using continuous polarization modulation. The method consists of the generation of a continuous triggered tone-burst waveform rather than an asynchronous waveform by use of a function generator and the removal of the global phases of the measured Jones matrices by use of matrix normalization. This could remove the use of auxiliary optical components for the phase fluctuation compensation in the system, which reduces the system complexity. Phase fluctuation calibration is necessary to obtain the reference Jones matrix by averaging the measured Jones matrices at sample surfaces. Measurements on an equine tendon sample were made by the PS-SS-OCT system to validate the proposed method.

Direct comparison of Viking 2.3-GHz signal phase fluctuation and columnar electron density between 2 and 160 solar radii

NASA Technical Reports Server (NTRS)

Berman, A. L.; Wackley, J. A.; Hietzke, W. H.

1982-01-01

The relationship between solar wind induced signal phase fluctuation and solar wind columnar electron density has been the subject of intensive analysis during the last two decades. In this article, a sizeable volume of 2.3-GHz signal phase fluctuation and columnar electron density measurements separately and concurrently inferred from Viking spacecraft signals are compared as a function of solar geometry. These data demonstrate that signal phase fluctuation and columnar electron density are proportional over a very wide span of solar elongation angle. A radially dependent electron density model which provides a good fit to the columnar electron density measurements and, when appropriately scaled, to the signal phase fluctuation measurements, is given. This model is also in good agreement with K-coronameter observations at 2 solar radii (2r0), with pulsar time delay measurements at 10r0, and with spacecraft in situ electron density measurements at 1 AU.

Entorhinal stellate cells show preferred spike phase-locking to theta inputs that is enhanced by correlations in synaptic activity

PubMed Central

Fernandez, Fernando R.; Malerba, Paola; Bressloff, Paul C.; White, John A.

2013-01-01

In active networks, excitatory and inhibitory synaptic inputs generate membrane voltage fluctuations that drive spike activity in a probabilistic manner. Despite this, some cells in vivo show a strong propensity to precisely lock to the local field potential and maintain a specific spike-phase relationship relative to other cells. In recordings from rat medial entorhinal cortical stellate cells, we measured spike phase-locking in response to sinusoidal “test” inputs in the presence of different forms of background membrane voltage fluctuations, generated via dynamic clamp. We find that stellate cells show strong and robust spike phase-locking to theta (4–12 Hz) inputs. This response occurs under a wide variety of background membrane voltage fluctuation conditions that include a substantial increase in overall membrane conductance. Furthermore, the IH current present in stellate cells is critical to the enhanced spike phase-locking response at theta. Finally, we show that correlations between inhibitory and excitatory conductance fluctuations, which can arise through feed-back and feed-forward inhibition, can substantially enhance the spike phase-locking response. The enhancement in locking is a result of a selective reduction in the size of low frequency membrane voltage fluctuations due to cancelation of inhibitory and excitatory current fluctuations with correlations. Hence, our results demonstrate that stellate cells have a strong preference for spike phase-locking to theta band inputs and that the absolute magnitude of locking to theta can be modulated by the properties of background membrane voltage fluctuations. PMID:23554484

Fluctuation driven electroweak phase transition

NASA Technical Reports Server (NTRS)

Gleiser, Marcelo; Kolb, Edward W.

1991-01-01

We examine the dynamics of the electroweak phase transition in the early Universe. For Higgs masses in the range 46 less than or = M sub H less than or = 150 GeV and top quark masses less than 200 GeV, regions of symmetric and asymmetric vacuum coexist to below the critical temperature, with thermal equilibrium between the two phases maintained by fluctuations of both phases. We propose that the transition to the asymmetric vacuum is completed by percolation of these subcritical fluctuations. Our results are relevant to scenarios of baryogenesis that invoke a weakly first-order phase transition at the electroweak scale.

Fluctuation-driven electroweak phase transition. [in early universe

NASA Technical Reports Server (NTRS)

Gleiser, Marcelo; Kolb, Edward W.

1992-01-01

We examine the dynamics of the electroweak phase transition in the early Universe. For Higgs masses in the range 46 less than or = M sub H less than or = 150 GeV and top quark masses less than 200 GeV, regions of symmetric and asymmetric vacuum coexist to below the critical temperature, with thermal equilibrium between the two phases maintained by fluctuations of both phases. We propose that the transition to the asymmetric vacuum is completed by percolation of these subcritical fluctuations. Our results are relevant to scenarios of baryogenesis that invoke a weakly first-order phase transition at the electroweak scale.

Preliminary analysis of amplitude and phase fluctuations in the JAPE multiple tone data to distances of 500 meters

NASA Technical Reports Server (NTRS)

Rogers, James; Sokolov, Radomir; Hicks, Daniel; Cartwright, Lloyd

1993-01-01

The JAPE short range data provide a good opportunity for studying phase and amplitude fluctuations of acoustic signals in the atmosphere over distances of several hundred meters. Several factors contribute to the usefulness of these data: extensive meteorological measurements were made, controlled sources were used, the data were recorded with a high dynamic range digital system that preserved phase information and a significant number of measurement points were obtained allowing both longitudinal and transverse studies. Further, Michigan Tech, in cooperation with the U.S. Army TARDEC, has developed phase tracking algorithms for studying vehicle acoustic signals. These techniques provide an excellent tool for analyzing the amplitude and phase fluctuations of the JAPE data. The results of studies such as those reported here have application at several levels: the mechanisms of signal amplitude and phase fluctuations in propagating acoustic signals are not well understood nor are the mathematical models highly developed, acoustic arrays depend strongly on signal coherence and signal amplitude stability in order to perform to their design specifications and active noise control implementation in regions considerably removed from the primary and secondary sources depends upon signal amplitude and phase stability. Work reported here is preliminary in nature but it does indicate the utility of the phase tracking and amplitude detection algorithms. The results obtained indicate that the phase fluctuations of the JAPE continuous multiple tone data (simultaneous transmission of 80, 200 and 500 Hz) are in general agreement with existing theories but the amplitude fluctuations are seen to be less well behaved and show less consistency.

Traffic jams induced by fluctuation of a leading car.

PubMed

Nagatani, T

2000-04-01

We present a phase diagram of the different kinds of congested traffic triggered by fluctuation of a leading car in an open system without sources and sinks. Traffic states and density waves are investigated numerically by varying the amplitude of fluctuation using a car following model. The phase transitions among the free traffic, oscillatory congested traffic, and homogeneous congested traffic occur by fluctuation of a leading car. With increasing the amplitude of fluctuation, the transition between the free traffic and oscillatory traffic occurs at lower density and the transition between the homogeneous congested traffic and the oscillatory traffic occurs at higher density. The oscillatory congested traffic corresponds to the coexisting phase. Also, the moving localized clusters appear just above the transition lines.

Dynamic light scattering microscopy

NASA Astrophysics Data System (ADS)

Dzakpasu, Rhonda

An optical microscope technique, dynamic light scattering microscopy (DLSM) that images dynamically scattered light fluctuation decay rates is introduced. Using physical optics we show theoretically that within the optical resolution of the microscope, relative motions between scattering centers are sufficient to produce significant phase variations resulting in interference intensity fluctuations in the image plane. The time scale for these intensity fluctuations is predicted. The spatial coherence distance defining the average distance between constructive and destructive interference in the image plane is calculated and compared with the pixel size. We experimentally tested DLSM on polystyrene latex nanospheres and living macrophage cells. In order to record these rapid fluctuations, on a slow progressive scan CCD camera, we used a thin laser line of illumination on the sample such that only a single column of pixels in the CCD camera is illuminated. This allowed the use of the rate of the column-by-column readout transfer process as the acquisition rate of the camera. This manipulation increased the data acquisition rate by at least an order of magnitude in comparison to conventional CCD cameras rates defined by frames/s. Analysis of the observed fluctuations provides information regarding the rates of motion of the scattering centers. These rates, acquired from each position on the sample are used to create a spatial map of the fluctuation decay rates. Our experiments show that with this technique, we are able to achieve a good signal-to-noise ratio and can monitor fast intensity fluctuations, on the order of milliseconds. DLSM appears to provide dynamic information about fast motions within cells at a sub-optical resolution scale and provides a new kind of spatial contrast.

Constraints on Fluctuations in Sparsely Characterized Biological Systems.

PubMed

Hilfinger, Andreas; Norman, Thomas M; Vinnicombe, Glenn; Paulsson, Johan

2016-02-05

Biochemical processes are inherently stochastic, creating molecular fluctuations in otherwise identical cells. Such "noise" is widespread but has proven difficult to analyze because most systems are sparsely characterized at the single cell level and because nonlinear stochastic models are analytically intractable. Here, we exactly relate average abundances, lifetimes, step sizes, and covariances for any pair of components in complex stochastic reaction systems even when the dynamics of other components are left unspecified. Using basic mathematical inequalities, we then establish bounds for whole classes of systems. These bounds highlight fundamental trade-offs that show how efficient assembly processes must invariably exhibit large fluctuations in subunit levels and how eliminating fluctuations in one cellular component requires creating heterogeneity in another.

Constraints on Fluctuations in Sparsely Characterized Biological Systems

NASA Astrophysics Data System (ADS)

Hilfinger, Andreas; Norman, Thomas M.; Vinnicombe, Glenn; Paulsson, Johan

2016-02-01

Biochemical processes are inherently stochastic, creating molecular fluctuations in otherwise identical cells. Such "noise" is widespread but has proven difficult to analyze because most systems are sparsely characterized at the single cell level and because nonlinear stochastic models are analytically intractable. Here, we exactly relate average abundances, lifetimes, step sizes, and covariances for any pair of components in complex stochastic reaction systems even when the dynamics of other components are left unspecified. Using basic mathematical inequalities, we then establish bounds for whole classes of systems. These bounds highlight fundamental trade-offs that show how efficient assembly processes must invariably exhibit large fluctuations in subunit levels and how eliminating fluctuations in one cellular component requires creating heterogeneity in another.

Effect of Water-Table Fluctuations on Source Depletion and Dissolved-Plume Behavior of a Multi-Component Light Nonaqueous-Phase Liquid

NASA Astrophysics Data System (ADS)

Dobson, R.; Schroth, M. H.; Zeyer, J.

2006-12-01

Light nonaqueous-phase liquids (LNAPLs) such as gasoline and diesel are among the most common soil and groundwater contaminants. Dissolution and subsequent advective transport of LNAPL components can negatively impact downgradient water supplies, while biodegradation is commonly thought to be an important sink for this class of contaminants. Water-table fluctuations, either naturally occurring or intentionally induced, may affect LNAPL component transport and biodegradation in aquifers. We present a laboratory investigation of the effect of water-table fluctuations on the dissolution and biodegradation of a multi-component LNAPL in a pair of similar model aquifers, one of which was subjected to a water-table fluctuation. Water-table fluctuation resulted in LNAPL and air entrapment below the water table, an increase in the vertical extent of LNAPL contamination and an increase in the volume of water passing through the contaminated zone. Effluent concentrations of dissolved LNAPL components were higher and those of dissolved nitrate were lower in the aquifer model where a fluctuation had been induced. Thus, water table fluctuation led to enhanced LNAPL dissolution as well as enhanced biodegradation activity. The increase in biodegradation observed after fluctuation was of lesser magnitude than the increase in LNAPL dissolution, such that water-table fluctuations might be expected to result in increased exposure of downgradient receptors to dissolved LNAPL components. Conversely, the potential for free-phase LNAPL migration was reduced following a water-table fluctuation, as LNAPL entrapment by the rising water table reduced the amount of free phase LNAPL. Lateral migration of LNAPL following emplacement was observed in the model aquifer where no fluctuation occurred, but not in the model aquifer where a water-table fluctuation was induced.

Fluctuations of radio occultation signals in sounding the Earth's atmosphere

NASA Astrophysics Data System (ADS)

Kan, Valery; Gorbunov, Michael E.; Sofieva, Viktoria F.

2018-02-01

We discuss the relationships that link the observed fluctuation spectra of the amplitude and phase of signals used for the radio occultation sounding of the Earth's atmosphere, with the spectra of atmospheric inhomogeneities. Our analysis employs the approximation of the phase screen and of weak fluctuations. We make our estimates for the following characteristic inhomogeneity types: (1) the isotropic Kolmogorov turbulence and (2) the anisotropic saturated internal gravity waves. We obtain the expressions for the variances of the amplitude and phase fluctuations of radio occultation signals as well as their estimates for the typical parameters of inhomogeneity models. From the GPS/MET observations, we evaluate the spectra of the amplitude and phase fluctuations in the altitude interval from 4 to 25 km in the middle and polar latitudes. As indicated by theoretical and experimental estimates, the main contribution into the radio signal fluctuations comes from the internal gravity waves. The influence of the Kolmogorov turbulence is negligible. We derive simple relationships that link the parameters of internal gravity waves and the statistical characteristics of the radio signal fluctuations. These results may serve as the basis for the global monitoring of the wave activity in the stratosphere and upper troposphere.

Structural instability and phase co-existence driven non-Gaussian resistance fluctuations in metal nanowires at low temperatures.

PubMed

Bid, Aveek; Raychaudhuri, A K

2016-11-11

We report a detailed experimental study of the resistance fluctuations measured at low temperatures in high quality metal nanowires ranging in diameter from 15-200 nm. The wires exhibit co-existing face-centered-cubic and 4H hcp phases of varying degrees as determined from the x-ray diffraction data. We observe the appearance of a large non-Gaussian noise for nanowires of diameter smaller than 50 nm over a certain temperature range around ≈30 K. The diameter range ∼30 nm, where the noise has maxima coincides with the maximum volume fraction of the co-existing 4H hcp phase thus establishing a strong link between the fluctuation and the phase co-existence. The resistance fluctuation in the same temperature range also shows a deviation of [Formula: see text] behavior at low frequency with appearance of single frequency Lorentzian type contribution in the spectral power density. The fluctuations are thermally activated with an activation energy [Formula: see text] meV, which is of same order as the activation energy of creation of stacking fault in FCC metals that leads to the co-existing crystallographic phases. Combining the results of crystallographic studies of the nanowires and analysis of the resistance fluctuations we could establish the correlation between the appearance of the large resistance noise and the onset of phase co-existence in these nanowires.

Propagation of coherently combined truncated laser beam arrays with beam distortions in non-Kolmogorov turbulence.

PubMed

Tao, Rumao; Si, Lei; Ma, Yanxing; Zhou, Pu; Liu, Zejin

2012-08-10

The propagation properties of coherently combined truncated laser beam arrays with beam distortions through non-Kolmogorov turbulence are studied in detail both analytically and numerically. The analytical expressions for the average intensity and the beam width of coherently combined truncated laser beam arrays with beam distortions propagating through turbulence are derived based on the combination of statistical optics methods and the extended Huygens-Fresnel principle. The effect of beam distortions, such as amplitude modulation and phase fluctuation, is studied by numerical examples. The numerical results reveal that phase fluctuations have significant influence on the spreading of coherently combined truncated laser beam arrays in non-Kolmogorov turbulence, and the effects of the phase fluctuations can be negligible as long as the phase fluctuations are controlled under a certain level, i.e., a>0.05 for the situation considered in the paper. Furthermore, large phase fluctuations can convert the beam distribution rapidly to a Gaussian form, vary the spreading, weaken the optimum truncation effects, and suppress the dependence of spreading on the parameters of the non-Kolmogorov turbulence.

Successive Phase Transitions and Magnetic Fluctuation in a Double-Perovskite NdBaMn2O6 Single Crystal

NASA Astrophysics Data System (ADS)

Yamada, S.; Sagayama, H.; Sugimoto, K.; Arima, T.

2018-03-01

We have succeeded in growing large high-quality single crystals of double-perovskite NdBaMn2O6 with c-axis aligned. Curie-Weiss paramagnetism and metallic conduction are observed above 290 K (TMI ). The magnetic susceptibility suddenly drops at TMI accompanied by a metal-insulator transition. Pervious studies using polycrystalline samples proposed that this material undergoes a ferromagnetic phase transition near 300K, and that the magnetic anomaly at TMI should be ascribed to layered antiferromagnetic phase transition. However, single-crystalline samples do not show any anomaly that indicates the ferromagnetic phase transition above TMI . We assign the onset of magnetic anisotropy at 235 K as antiferromagnetic transition temperature TN . Though the magnetization just above TMI shows the ferromagnetic-like magnetic-field dependence, the magnetization does not saturate under 70kOe at 300K. The magnetization behavior implies ferromagnetic fluctuation in the paramagnetic phase. The ferromagnetic fluctuation are also observed just below TMI . Because a metamagnetic transition is observed at a higher magnetic field, the ferromagnetic fluctuation competes with antiferromagnetic fluctuation in this temperature range.

Deterministic entanglement generation from driving through quantum phase transitions.

PubMed

Luo, Xin-Yu; Zou, Yi-Quan; Wu, Ling-Na; Liu, Qi; Han, Ming-Fei; Tey, Meng Khoon; You, Li

2017-02-10

Many-body entanglement is often created through the system evolution, aided by nonlinear interactions between the constituting particles. These very dynamics, however, can also lead to fluctuations and degradation of the entanglement if the interactions cannot be controlled. Here, we demonstrate near-deterministic generation of an entangled twin-Fock condensate of ~11,000 atoms by driving a arubidium-87 Bose-Einstein condensate undergoing spin mixing through two consecutive quantum phase transitions (QPTs). We directly observe number squeezing of 10.7 ± 0.6 decibels and normalized collective spin length of 0.99 ± 0.01. Together, these observations allow us to infer an entanglement-enhanced phase sensitivity of ~6 decibels beyond the standard quantum limit and an entanglement breadth of ~910 atoms. Our work highlights the power of generating large-scale useful entanglement by taking advantage of the different entanglement landscapes separated by QPTs. Copyright © 2017, American Association for the Advancement of Science.

Field data and numerical simulation of btex concentration trends under water table fluctuations: Example of a jet fuel-contaminated site in Brazil

NASA Astrophysics Data System (ADS)

Teramoto, Elias Hideo; Chang, Hung Kiang

2017-03-01

Mass transfer of light non-aqueous phase liquids (LNAPLs) trapped in porous media is a complex phenomenon. Water table fluctuations have been identified as responsible for generating significant variations in the concentration of dissolved hydrocarbons. Based on field evidence, this work presents a conceptual model and a numerical solution for mass transfer from entrapped LNAPL to groundwater controlled by both LNAPL saturation and seasonal water table fluctuations within the LNAPL smear zone. The numerical approach is capable of reproducing aqueous BTEX concentration trends under three different scenarios - water table fluctuating within smear zone, above the smear zone and partially within smear zone, resulting in in-phase, out-of-phase and alternating in-phase and out-of-phase BTEX concentration trend with respect to water table oscillation, respectively. The results demonstrate the model's applicability under observed field conditions and its ability to predict source zone depletion.

Fluctuation spectroscopy: From Rayleigh-Jeans waves to Abrikosov vortex clusters

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

Varlamov, A. A.; Galda, A.; Glatz, A.

Superconducting (SC) fluctuations, discovered in the late 1960s, have constituted an important research area in superconductivity as they are manifest in a variety of phenomena. Indeed, the underlying physics of SC fluctuations makes it possible to elucidate the fundamental properties of the superconducting state. The interest in SC fluctuation phenomena was further enhanced with the discovery of cuprate high-temperature superconductors (HTSs). In these materials, superconducting fluctuations appear over a wide range of temperatures due to the superconductors extremely short coherence lengths and low effective dimensionality of the electron systems. These strong fluctuations lead to anomalous properties of the normal statemore » in some HTS materials. Within the framework of the phenomenological Ginzburg-Landau theory, and more extensively in the diagrammatic microscopic approach based on BCS theory, SC fluctuations as well as other quantum contributions (weak localization, etc.) enabled a new way to investigate and characterize disordered electron systems, granular metals, Josephson structures, artificial superlattices, and others. The characteristic feature of SC fluctuations is its strong dependence on temperature and magnetic field in the vicinity of the superconducting phase transition. This dependence allows the separation of fluctuation effects from other contributions and provides information about the microscopic parameters of a material, in particular, the critical temperature and the zero-temperature critical magnetic field. As such, SC fluctuations are very sensitive to the relaxation processes that break phase coherence and can be used as a versatile characterization instrument for SCs: Fluctuation spectroscopy has emerged as a powerful tool for studying the properties of superconducting systems on a quantitative level. Here the physics of SC fluctuations is reviewed, commencing from a qualitative description of thermodynamic fluctuations close to the critical temperature and quantum fluctuations at zero temperature in the vicinity of the second critical field. The analysis of the latter allows us to present fluctuation formation as a fragmentation of the Abrikosov lattice. Finally, this review highlights a series of experimental findings followed by microscopic description and numerical analysis of the effects of fluctuations on numerous properties of superconductors in the entire phase diagram and beyond the superconducting phase.« less

Fluctuation spectroscopy: From Rayleigh-Jeans waves to Abrikosov vortex clusters

DOE PAGES

Varlamov, A. A.; Galda, A.; Glatz, A.

2018-03-27

Superconducting (SC) fluctuations, discovered in the late 1960s, have constituted an important research area in superconductivity as they are manifest in a variety of phenomena. Indeed, the underlying physics of SC fluctuations makes it possible to elucidate the fundamental properties of the superconducting state. The interest in SC fluctuation phenomena was further enhanced with the discovery of cuprate high-temperature superconductors (HTSs). In these materials, superconducting fluctuations appear over a wide range of temperatures due to the superconductors extremely short coherence lengths and low effective dimensionality of the electron systems. These strong fluctuations lead to anomalous properties of the normal statemore » in some HTS materials. Within the framework of the phenomenological Ginzburg-Landau theory, and more extensively in the diagrammatic microscopic approach based on BCS theory, SC fluctuations as well as other quantum contributions (weak localization, etc.) enabled a new way to investigate and characterize disordered electron systems, granular metals, Josephson structures, artificial superlattices, and others. The characteristic feature of SC fluctuations is its strong dependence on temperature and magnetic field in the vicinity of the superconducting phase transition. This dependence allows the separation of fluctuation effects from other contributions and provides information about the microscopic parameters of a material, in particular, the critical temperature and the zero-temperature critical magnetic field. As such, SC fluctuations are very sensitive to the relaxation processes that break phase coherence and can be used as a versatile characterization instrument for SCs: Fluctuation spectroscopy has emerged as a powerful tool for studying the properties of superconducting systems on a quantitative level. Here the physics of SC fluctuations is reviewed, commencing from a qualitative description of thermodynamic fluctuations close to the critical temperature and quantum fluctuations at zero temperature in the vicinity of the second critical field. The analysis of the latter allows us to present fluctuation formation as a fragmentation of the Abrikosov lattice. Finally, this review highlights a series of experimental findings followed by microscopic description and numerical analysis of the effects of fluctuations on numerous properties of superconductors in the entire phase diagram and beyond the superconducting phase.« less

Fluctuation spectroscopy: From Rayleigh-Jeans waves to Abrikosov vortex clusters

NASA Astrophysics Data System (ADS)

Varlamov, A. A.; Galda, A.; Glatz, A.

2018-01-01

Superconducting (SC) fluctuations, discovered in the late 1960s, have constituted an important research area in superconductivity as they are manifest in a variety of phenomena. Indeed, the underlying physics of SC fluctuations makes it possible to elucidate the fundamental properties of the superconducting state. The interest in SC fluctuation phenomena was further enhanced with the discovery of cuprate high-temperature superconductors (HTSs). In these materials, superconducting fluctuations appear over a wide range of temperatures due to the superconductors extremely short coherence lengths and low effective dimensionality of the electron systems. These strong fluctuations lead to anomalous properties of the normal state in some HTS materials. Within the framework of the phenomenological Ginzburg-Landau theory, and more extensively in the diagrammatic microscopic approach based on BCS theory, SC fluctuations as well as other quantum contributions (weak localization, etc.) enabled a new way to investigate and characterize disordered electron systems, granular metals, Josephson structures, artificial superlattices, and others. The characteristic feature of SC fluctuations is its strong dependence on temperature and magnetic field in the vicinity of the superconducting phase transition. This dependence allows the separation of fluctuation effects from other contributions and provides information about the microscopic parameters of a material, in particular, the critical temperature and the zero-temperature critical magnetic field. As such, SC fluctuations are very sensitive to the relaxation processes that break phase coherence and can be used as a versatile characterization instrument for SCs: Fluctuation spectroscopy has emerged as a powerful tool for studying the properties of superconducting systems on a quantitative level. Here the physics of SC fluctuations is reviewed, commencing from a qualitative description of thermodynamic fluctuations close to the critical temperature and quantum fluctuations at zero temperature in the vicinity of the second critical field. The analysis of the latter allows us to present fluctuation formation as a fragmentation of the Abrikosov lattice. This review highlights a series of experimental findings followed by microscopic description and numerical analysis of the effects of fluctuations on numerous properties of superconductors in the entire phase diagram and beyond the superconducting phase.

Effects of laser phase fluctuations on squeezing in intracavity second-harmonic generation

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

Kennedy, T. A. B.; Anderson, T. B.; Walls, D. F.

1989-08-01

Excellent squeezing in intracavity second-harmonic generation has been predicted to occur on cavity resonance in the output intensity fluctuations. Cavity detunings cause laser phase noise to couple in and reduce the squeezing observable. Here we consider the effects of laser phase fluctuations on the output-squeezing spectrum. Laser phase noise is modeled as an Ornstein-Uhlenbeck (colored-noise) Gaussian stochastic process and its effects are compared with the white-noise limit. This indicates that the white-noise model may qualitatively overestimate the deleterious effects of laser fluctuations on sideband squeezing. We compare our results with the recently reported experiment of Pereira /ital et/ /ital al/.more » (Phys. Rev. A 38, 4931 (1988)) and present an analysis of the empty cavity for comparison.« less

Pairing versus phase coherence of doped holes in distinct quantum spin backgrounds

NASA Astrophysics Data System (ADS)

Zhu, Zheng; Sheng, D. N.; Weng, Zheng-Yu

2018-03-01

We examine the pairing structure of holes injected into two distinct spin backgrounds: a short-range antiferromagnetic phase versus a symmetry protected topological phase. Based on density matrix renormalization group (DMRG) simulation, we find that although there is a strong binding between two holes in both phases, phase fluctuations can significantly influence the pair-pair correlation depending on the spin-spin correlation in the background. Here the phase fluctuation is identified as an intrinsic string operator nonlocally controlled by the spins. We show that while the pairing amplitude is generally large, the coherent Cooper pairing can be substantially weakened by the phase fluctuation in the symmetry-protected topological phase, in contrast to the short-range antiferromagnetic phase. It provides an example of a non-BCS mechanism for pairing, in which the paring phase coherence is determined by the underlying spin state self-consistently, bearing an interesting resemblance to the pseudogap physics in the cuprate.

Electronic structure and quantum spin fluctuations at the magnetic phase transition in MnSi

NASA Astrophysics Data System (ADS)

Povzner, A. A.; Volkov, A. G.; Nogovitsyna, T. A.

2018-05-01

The effect of spin fluctuations on the heat capacity and homogeneous magnetic susceptibility of the chiral magnetic MnSi in the vicinity of magnetic transition has been investigated by using the free energy functional of the coupled electron and spin subsystems and taking into account the Dzyaloshinsky-Moriya interaction. For helical ferromagnetic ordering, we found that zero-point fluctuations of the spin density are large and comparable with fluctuations of the non-uniform magnetization. The amplitude of zero-point spin fluctuations shows a sharp decrease in the region of the magnetic phase transition. It is shown that sharp decrease of the amplitude of the quantum spin fluctuations results in the lambda-like maxima of the heat capacity and the homogeneous magnetic susceptibility. Above the temperature of the lambda anomaly, the spin correlation radius becomes less than the period of the helical structure and chiral fluctuations of the local magnetization appear. It is shown that formation of a "shoulder" on the temperature dependence of the heat capacity is due to disappearance of the local magnetization. Our finding allows to explain the experimentally observed features of the magnetic phase transition of MnSi as a result of the crossover of quantum and thermodynamic phase transitions.

Nematic fluctuations balancing the zoo of phases in half-filled quantum Hall systems

NASA Astrophysics Data System (ADS)

Mesaros, Andrej; Lawler, Michael J.; Kim, Eun-Ah

2017-03-01

Half-filled Landau levels form a zoo of strongly correlated phases. These include non-Fermi-liquids (NFLs), fractional quantum Hall (FQH) states, nematic phases, and FQH nematic phases. This diversity begs the following question: what keeps the balance between the seemingly unrelated phases? The answer is elusive because the Halperin-Lee-Read description that offers a natural departure point is inherently strongly coupled. However, the observed nematic phases suggest that nematic fluctuations play an important role. To study this possibility, we apply a recently formulated controlled double-expansion approach in large-N composite fermion flavors and small ɛ nonanalytic bosonic action to the case with both gauge and nematic boson fluctuations. In the vicinity of a nematic quantum critical line, we find that depending on the amount of screening of the gauge- and nematic-mediated interactions controlled by ɛ 's, the renormalization-group flow points to all four mentioned correlated phases. When pairing preempts the nematic phase, NFL behavior is possible at temperatures above the pairing transition. We conclude by discussing measurements at low tilt angles, which could reveal the stabilization of the FQH phase by nematic fluctuations.

Oscillator Noise Analysis

NASA Astrophysics Data System (ADS)

Demir, Alper

2005-08-01

Oscillators are key components of many kinds of systems, particularly electronic and opto-electronic systems. Undesired perturbations, i.e. noise, that exist in practical systems adversely affect the spectral and timing properties of the signals generated by oscillators resulting in phase noise and timing jitter. These are key performance limiting factors, being major contributors to bit-error-rate (BER) of RF and optical communication systems, and creating synchronization problems in clocked and sampled-data electronic systems. In noise analysis for oscillators, the key is figuring out how the various disturbances and noise sources in the oscillator end up as phase fluctuations. In doing so, one first computes transfer functions from the noise sources to the oscillator phase, or the sensitivity of the oscillator phase to these noise sources. In this paper, we first provide a discussion explaining the origins and the proper definition of this transfer or sensitivity function, followed by a critical review of the various numerical techniques for its computation that have been proposed by various authors over the past fifteen years.

Transitional Flow in an Arteriovenous Fistula: Effect of Wall Distensibility

NASA Astrophysics Data System (ADS)

McGah, Patrick; Leotta, Daniel; Beach, Kirk; Aliseda, Alberto

2012-11-01

Arteriovenous fistulae are created surgically to provide adequate access for dialysis in patients with end-stage renal disease. Transitional flow and the subsequent pressure and shear stress fluctuations are thought to be causative in the fistula failure. Since 50% of fistulae require surgical intervention before year one, understanding the altered hemodynamic stresses is an important step toward improving clinical outcomes. We perform numerical simulations of a patient-specific model of a functioning fistula reconstructed from 3D ultrasound scans. Rigid wall simulations and fluid-structure interaction simulations using an in-house finite element solver for the wall deformations were performed and compared. In both the rigid and distensible wall cases, transitional flow is computed in fistula as evidenced by aperiodic high frequency velocity and pressure fluctuations. The spectrum of the fluctuations is much more narrow-banded in the distensible case, however, suggesting a partial stabilizing effect by the vessel elasticity. As a result, the distensible wall simulations predict shear stresses that are systematically 10-30% lower than the rigid cases. We propose a possible mechanism for stabilization involving the phase lag in the fluid work needed to deform the vessel wall. Support from an NIDDK R21 - DK08-1823.

Fluctuation solution theory of pure fluids

NASA Astrophysics Data System (ADS)

Ploetz, Elizabeth A.; Pallewela, Gayani N.; Smith, Paul E.

2017-03-01

Fluctuation Solution Theory (FST) provides an alternative view of fluid thermodynamics in terms of pair fluctuations in the particle number and excess energy observed for an equivalent open system. Here we extend the FST approach to provide a series of triplet and quadruplet particle and excess energy fluctuations that can also be used to help understand the behavior of fluids. The fluctuations for the gas, liquid, and supercritical regions of three fluids (H2O, CO2, and SF6) are then determined from accurate equations of state. Many of the fluctuating quantities change sign on moving from the gas to liquid phase and, therefore, we argue that the fluctuations can be used to characterize gas and liquid behavior. Further analysis provides an approach to isolate contributions to the excess energy fluctuations arising from just the intermolecular interactions and also indicates that the triplet and quadruplet particle fluctuations are related to the pair particle fluctuations by a simple power law for large regions of the phase diagram away from the critical point.

PHYSICAL EFFECTS OCCURRING DURING GENERATION AND AMPLIFICATION OF LASER RADIATION: Spatial phase fluctuations of the fundamental laser mode caused by spontaneous emission

NASA Astrophysics Data System (ADS)

Belinskiĭ, A. V.; Chirkin, Anatolii S.

1989-02-01

A calculation is reported of the degree of spatial coherence of the fundamental radiation mode subject to phase fluctuations in space. It is shown that the degree of spatial coherence (within the beam width) is perturbed only slightly by these fluctuations, compared with subthreshold excitation of higher transverse modes.

Effect of temperature gradient on liquid-liquid phase separation in a polyolefin blend.

PubMed

Jiang, Hua; Dou, Nannan; Fan, Guoqiang; Yang, Zhaohui; Zhang, Xiaohua

2013-09-28

We have investigated experimentally the structure formation processes during phase separation via spinodal decomposition above and below the spinodal line in a binary polymer blend system exposed to in-plane stationary thermal gradients using phase contrast optical microscopy and temperature gradient hot stage. Below the spinodal line there is a coupling of concentration fluctuations and thermal gradient imposed by the temperature gradient hot stage. Also under the thermal gradient annealing phase-separated domains grow faster compared with the system under homogeneous temperature annealing on a zero-gradient or a conventional hot stage. We suggest that the in-plane thermal gradient accelerates phase separation through the enhancement in concentration fluctuations in the early and intermediate stages of spinodal decomposition. In a thermal gradient field, the strength of concentration fluctuation close to the critical point (above the spinodal line) is strong enough to induce phase separation even in one-phase regime of the phase diagram. In the presence of a temperature gradient the equilibrium phase diagrams are no longer valid, and the systems with an upper critical solution temperature can be quenched into phase separation by applying the stationary temperature gradient. The in-plane temperature gradient drives enhanced concentration fluctuations in a binary polymer blend system above and below the spinodal line.

Vibration signal correction of unbalanced rotor due to angular speed fluctuation

NASA Astrophysics Data System (ADS)

Cao, Hongrui; He, Dong; Xi, Songtao; Chen, Xuefeng

2018-07-01

The rotating speed of a rotor is hardly constant in practice due to angular speed fluctuation, which affects the balancing accuracy of the rotor. In this paper, the effect of angular speed fluctuation on vibration responses of the unbalanced rotor is analyzed quantitatively. Then, a vibration signal correction method based on zoom synchrosqueezing transform (ZST) and tacholess order tracking is proposed. The instantaneous angular speed (IAS) of the rotor is extracted by the ZST firstly and then used to calculate the instantaneous phase. The vibration signal is further resampled in angular domain to reduce the effect of angular speed fluctuation. The signal obtained in angular domain is transformed into order domain using discrete Fourier transform (DFT) to estimate the amplitude and phase of the vibration signal. Simulated and experimental results show that the proposed method can successfully correct the amplitude and phase of the vibration signal due to angular speed fluctuation.

Field data and numerical simulation of btex concentration trends under water table fluctuations: Example of a jet fuel-contaminated site in Brazil.

PubMed

Teramoto, Elias Hideo; Chang, Hung Kiang

2017-03-01

Mass transfer of light non-aqueous phase liquids (LNAPLs) trapped in porous media is a complex phenomenon. Water table fluctuations have been identified as responsible for generating significant variations in the concentration of dissolved hydrocarbons. Based on field evidence, this work presents a conceptual model and a numerical solution for mass transfer from entrapped LNAPL to groundwater controlled by both LNAPL saturation and seasonal water table fluctuations within the LNAPL smear zone. The numerical approach is capable of reproducing aqueous BTEX concentration trends under three different scenarios - water table fluctuating within smear zone, above the smear zone and partially within smear zone, resulting in in-phase, out-of-phase and alternating in-phase and out-of-phase BTEX concentration trend with respect to water table oscillation, respectively. The results demonstrate the model's applicability under observed field conditions and its ability to predict source zone depletion. Copyright © 2017 Elsevier B.V. All rights reserved.

A Local Quantum Phase Transition in YFe 2Al 10

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

Gannon, W J.; Zaliznyak, Igor A.; Wu, L. S.

Here, a phase transition occurs when correlated regions of a new phase grow to span the system and the fluctuations within the correlated regions become long-lived. Here we present neutron scattering measurements showing that this conventional picture must be replaced by a new paradigm in YFe 2Al 10, a compound that forms naturally very close to a T = 0 quantum phase transition. Fully quantum mechanical fluctuations of localized moments are found to diverge at low energies and temperatures, however the fluctuating moments are entirely without spatial correlations. Zero temperature order in YFe 2Al 10 is achieved by a newmore » and entirely local type of quantum phase transition that may originate with the creation of the moments themselves.« less

A Local Quantum Phase Transition in YFe 2Al 10

DOE PAGES

Gannon, W J.; Zaliznyak, Igor A.; Wu, L. S.; ...

2018-06-29

Here, a phase transition occurs when correlated regions of a new phase grow to span the system and the fluctuations within the correlated regions become long-lived. Here we present neutron scattering measurements showing that this conventional picture must be replaced by a new paradigm in YFe 2Al 10, a compound that forms naturally very close to a T = 0 quantum phase transition. Fully quantum mechanical fluctuations of localized moments are found to diverge at low energies and temperatures, however the fluctuating moments are entirely without spatial correlations. Zero temperature order in YFe 2Al 10 is achieved by a newmore » and entirely local type of quantum phase transition that may originate with the creation of the moments themselves.« less

Electrostatic swelling of bicontinuous cubic lipid phases.

PubMed

Tyler, Arwen I I; Barriga, Hanna M G; Parsons, Edward S; McCarthy, Nicola L C; Ces, Oscar; Law, Robert V; Seddon, John M; Brooks, Nicholas J

2015-04-28

Lipid bicontinuous cubic phases have attracted enormous interest as bio-compatible scaffolds for use in a wide range of applications including membrane protein crystallisation, drug delivery and biosensing. One of the major bottlenecks that has hindered exploitation of these structures is an inability to create targeted highly swollen bicontinuous cubic structures with large and tunable pore sizes. In contrast, cubic structures found in vivo have periodicities approaching the micron scale. We have been able to engineer and control highly swollen bicontinuous cubic phases of spacegroup Im3m containing only lipids by (a) increasing the bilayer stiffness by adding cholesterol and (b) inducing electrostatic repulsion across the water channels by addition of anionic lipids to monoolein. By controlling the composition of the ternary mixtures we have been able to achieve lattice parameters up to 470 Å, which is 5 times that observed in pure monoolein and nearly twice the size of any lipidic cubic phase reported previously. These lattice parameters significantly exceed the predicted maximum swelling for bicontinuous cubic lipid structures, which suggest that thermal fluctuations should destroy such phases for lattice parameters larger than 300 Å.

Effects of ammonium sulfate and sodium chloride concentration on PEG/protein liquid-liquid phase separation.

PubMed

Dumetz, André C; Lewus, Rachael A; Lenhoff, Abraham M; Kaler, Eric W

2008-09-16

When added to protein solutions, poly(ethylene glycol) (PEG) creates an effective attraction between protein molecules due to depletion forces. This effect has been widely used to crystallize proteins, and PEG is among the most successful crystallization agents in current use. However, PEG is almost always used in combination with a salt at either low or relatively high concentrations. Here the effects of sodium chloride and ammonium sulfate concentration on PEG 8000/ovalbumin liquid-liquid (L-L) phase separation are investigated. At low salt the L-L phase separation occurs at decreasing protein concentration with increasing salt concentration, presumably due to repulsive electrostatic interactions between proteins. At high salt concentration, the behavior depends on the nature of the salt. Sodium chloride has little effect on the L-L phase separation, but ammonium sulfate decreases the protein concentration at which the L-L phase separation occurs. This trend is attributed to the effects of critical fluctuations on depletion forces. The implications of these results for designing solution conditions optimal for protein crystallization are discussed.

Multi-point measurement using two-channel reflectometer with antenna switching for study of high-frequency fluctuations in GAMMA 10

NASA Astrophysics Data System (ADS)

Ikezoe, R.; Ichimura, M.; Okada, T.; Itagaki, J.; Hirata, M.; Sumida, S.; Jang, S.; Izumi, K.; Tanaka, A.; Yoshikawa, M.; Kohagura, J.; Sakamoto, M.; Nakashima, Y.

2017-03-01

A two-channel microwave reflectometer system with fast microwave antenna switching capability was developed and applied to the GAMMA 10 tandem mirror device to study high-frequency small-amplitude fluctuations in a hot mirror plasma. The fast switching of the antennas is controlled using PIN diode switches, which offers the significant advantage of reducing the number of high-cost microwave components and digitizers with high bandwidths and large memory that are required to measure the spatiotemporal behavior of the high-frequency fluctuations. The use of two channels rather than one adds the important function of a simultaneous two-point measurement in either the radial direction or the direction of the antenna array to measure the phase profile of the fluctuations along with the normal amplitude profile. The density fluctuations measured using this system clearly showed the high-frequency coherent fluctuations that are associated with Alfvén-ion-cyclotron (AIC) waves in GAMMA 10. A correlation analysis applied to simultaneously measured density fluctuations showed that the phase component that was included in a reflected microwave provided both high coherence and a clear phase difference for the AIC waves, while the amplitude component showed neither significant coherence nor clear phase difference. The axial phase differences of the AIC waves measured inside the hot plasma confirmed the formation of a standing wave structure. The axial variation of the radial profiles was evaluated and a clear difference was found among the AIC waves for the first time, which would be a key to clarify the unknown boundary conditions of the AIC waves.

Three superconducting phases with different categories of pairing in hole- and electron-doped LaFeAs1 -xPxO

NASA Astrophysics Data System (ADS)

Miyasaka, S.; Uekubo, M.; Tsuji, H.; Nakajima, M.; Tajima, S.; Shiota, T.; Mukuda, H.; Sagayama, H.; Nakao, H.; Kumai, R.; Murakami, Y.

2017-06-01

The phase diagram of the LaFeAs1 -xPxO system has been extensively studied through hole and electron doping as well as As/P substitution. It has been revealed that there are three different superconducting phases with different Fermi surface (FS) topologies and thus with possibly different pairing glues. One of them is well understood as spin fluctuation-mediated superconductivity within a FS nesting scenario. Another one with the FSs in a bad nesting condition must be explained in a different context such as orbital or spin fluctuation in a strongly correlated electronic system. In both phases, T -linear resistivity was commonly observed when the superconducting transition temperature Tc becomes the highest value, indicating that the strength of bosonic fluctuation determines Tc. In the last superconducting phase, the nesting condition of FSs and the related bosonic fluctuation are moderate. Variety of phase diagram characterizes the multiple orbital nature of the iron-based superconductors which are just near the boundary between weak and strong correlation regimes.

Quantum Phase Transition in Few-Layer NbSe2 Probed through Quantized Conductance Fluctuations

NASA Astrophysics Data System (ADS)

Kundu, Hemanta Kumar; Ray, Sujay; Dolui, Kapildeb; Bagwe, Vivas; Choudhury, Palash Roy; Krupanidhi, S. B.; Das, Tanmoy; Raychaudhuri, Pratap; Bid, Aveek

2017-12-01

We present the first observation of dynamically modulated quantum phase transition between two distinct charge density wave (CDW) phases in two-dimensional 2 H -NbSe2 . There is recent spectroscopic evidence for the presence of these two quantum phases, but its evidence in bulk measurements remained elusive. We studied suspended, ultrathin 2 H -NbSe2 devices fabricated on piezoelectric substrates—with tunable flakes thickness, disorder level, and strain. We find a surprising evolution of the conductance fluctuation spectra across the CDW temperature: the conductance fluctuates between two precise values, separated by a quantum of conductance. These quantized fluctuations disappear for disordered and on-substrate devices. With the help of mean-field calculations, these observations can be explained as to arise from dynamical phase transition between the two CDW states. To affirm this idea, we vary the lateral strain across the device via piezoelectric medium and map out the phase diagram near the quantum critical point. The results resolve a long-standing mystery of the anomalously large spectroscopic gap in NbSe2 .

Improving Estimates Of Phase Parameters When Amplitude Fluctuates

NASA Technical Reports Server (NTRS)

Vilnrotter, V. A.; Brown, D. H.; Hurd, W. J.

1989-01-01

Adaptive inverse filter applied to incoming signal and noise. Time-varying inverse-filtering technique developed to improve digital estimate of phase of received carrier signal. Intended for use where received signal fluctuates in amplitude as well as in phase and signal tracked by digital phase-locked loop that keeps its phase error much smaller than 1 radian. Useful in navigation systems, reception of time- and frequency-standard signals, and possibly spread-spectrum communication systems.

Ordered phase and non-equilibrium fluctuation in stock market

NASA Astrophysics Data System (ADS)

Maskawa, Jun-ichi

2002-08-01

We analyze the statistics of daily price change of stock market in the framework of a statistical physics model for the collective fluctuation of stock portfolio. In this model the time series of price changes are coded into the sequences of up and down spins, and the Hamiltonian of the system is expressed by spin-spin interactions as in spin glass models of disordered magnetic systems. Through the analysis of Dow-Jones industrial portfolio consisting of 30 stock issues by this model, we find a non-equilibrium fluctuation mode on the point slightly below the boundary between ordered and disordered phases. The remaining 29 modes are still in disordered phase and well described by Gibbs distribution. The variance of the fluctuation is outlined by the theoretical curve and peculiarly large in the non-equilibrium mode compared with those in the other modes remaining in ordinary phase.

Chaotic Dynamical Ferromagnetic Phase Induced by Nonequilibrium Quantum Fluctuations

NASA Astrophysics Data System (ADS)

Lerose, Alessio; Marino, Jamir; Žunkovič, Bojan; Gambassi, Andrea; Silva, Alessandro

2018-03-01

We investigate the robustness of a dynamical phase transition against quantum fluctuations by studying the impact of a ferromagnetic nearest-neighbor spin interaction in one spatial dimension on the nonequilibrium dynamical phase diagram of the fully connected quantum Ising model. In particular, we focus on the transient dynamics after a quantum quench and study the prethermal state via a combination of analytic time-dependent spin wave theory and numerical methods based on matrix product states. We find that, upon increasing the strength of the quantum fluctuations, the dynamical critical point fans out into a chaotic dynamical phase within which the asymptotic ordering is characterized by strong sensitivity to the parameters and initial conditions. We argue that such a phenomenon is general, as it arises from the impact of quantum fluctuations on the mean-field out of equilibrium dynamics of any system which exhibits a broken discrete symmetry.

Microscopic Phase-Space Exploration Modeling of ^{258}Fm Spontaneous Fission.

PubMed

Tanimura, Yusuke; Lacroix, Denis; Ayik, Sakir

2017-04-14

We show that the total kinetic energy (TKE) of nuclei after the spontaneous fission of ^{258}Fm can be well reproduced using simple assumptions on the quantum collective phase space explored by the nucleus after passing the fission barrier. Assuming energy conservation and phase-space exploration according to the stochastic mean-field approach, a set of initial densities is generated. Each density is then evolved in time using the nuclear time-dependent density-functional theory with pairing. This approach goes beyond the mean-field theory by allowing spontaneous symmetry breaking as well as a wider dynamical phase-space exploration leading to larger fluctuations in collective space. The total kinetic energy and mass distributions are calculated. New information on the fission process: fluctuations in scission time, strong correlation between TKE and collective deformation, as well as prescission particle emission, are obtained. We conclude that fluctuations of the TKE and mass are triggered by quantum fluctuations.

Chaotic Dynamical Ferromagnetic Phase Induced by Nonequilibrium Quantum Fluctuations.

PubMed

Lerose, Alessio; Marino, Jamir; Žunkovič, Bojan; Gambassi, Andrea; Silva, Alessandro

2018-03-30

We investigate the robustness of a dynamical phase transition against quantum fluctuations by studying the impact of a ferromagnetic nearest-neighbor spin interaction in one spatial dimension on the nonequilibrium dynamical phase diagram of the fully connected quantum Ising model. In particular, we focus on the transient dynamics after a quantum quench and study the prethermal state via a combination of analytic time-dependent spin wave theory and numerical methods based on matrix product states. We find that, upon increasing the strength of the quantum fluctuations, the dynamical critical point fans out into a chaotic dynamical phase within which the asymptotic ordering is characterized by strong sensitivity to the parameters and initial conditions. We argue that such a phenomenon is general, as it arises from the impact of quantum fluctuations on the mean-field out of equilibrium dynamics of any system which exhibits a broken discrete symmetry.

Phase diagram of the frustrated J 1 ‑ J 2 transverse field Ising model on the square lattice

NASA Astrophysics Data System (ADS)

Sadrzadeh, M.; Langari, A.

2018-03-01

We study the zero-temperature phase diagram of transverse field Ising model on the J 1 ‑ J 2 square lattice. In zero magnetic field, the model has a classical Néel phase for J 2/J 1 < 0.5 and an antiferromagnetic collinear phase for J 2/J 1 > 0.5. We incorporate harmonic fluctuations by using linear spin wave theory (LSWT) with single spin flip excitations above a magnetic order background and obtain the phase diagram of the model in this approximation. We find that harmonic quantum fluctuations of LSWT fail to lift the large degeneracy at J 2/J 1 = 0.5 and exhibit some inconsistent regions on the phase diagram. However, we show that anharmonic fluctuations of cluster operator approach (COA) resolve the inconsistency of the LSWT, which reveals a string-valence bond solid ordered phase for the highly frustrated region.

Velocity Measurement by Scattering from Index of Refraction Fluctuations Induced in Turbulent Flows

NASA Technical Reports Server (NTRS)

Lading, Lars; Saffman, Mark; Edwards, Robert

1996-01-01

Induced phase screen scattering is defined as scatter light from a weak index of refraction fluctuations induced by turbulence. The basic assumptions and requirements for induced phase screen scattering, including scale requirements, are presented.

Marshall N. Rosenbluth Outstanding Doctoral Thesis Award Talk: Simultaneous Measurement of Electron Temperature and Density Fluctuations in the Core of DIII-D Plasmas

NASA Astrophysics Data System (ADS)

White, A. E.

2009-11-01

Multi-field fluctuation measurements provide opportunities for rigorous comparison between experiment and nonlinear gyrokinetic turbulence simulations. A unique set of diagnostics on DIII-D allows for simultaneous study of local, long-wavelength (0 < kθρs< 0.5) electron temperature and density fluctuations in the core plasma (0.4 < ρ< 0.8). Previous experiments in L-mode indicate that normalized electron temperature fluctuation levels (40 < f < 400,kHz) increase with radius from ˜0.4% at ρ= 0.5 to ˜2% at ρ=0.8, similar to simultaneously measured density fluctuations. Electron cyclotron heating (ECH) is used to increase Te, which increases electron temperature fluctuation levels and electron heat transport in the experiments. In contrast, long wavelength density fluctuation levels change very little. The different responses are consistent with increased TEM drive relative to ITG-mode drive. A new capability at DIII-D is the measurement of phase angle between electron temperature and density fluctuations using coupled correlation electron cyclotron emission radiometer and reflectometer diagnostics. Linear and nonlinear GYRO runs have been used to design validation experiments that focus on measurements of the phase angle. GYRO shows that if Te and ∇Te increase 50% in a beam-heated L-mode plasma (ρ=0.5), then the phase angle between electron temperature and density fluctuations decreases 30%-50% and electron temperature fluctuation levels increase a factor of two more than density fluctuations. Comparisons between these predictions and experimental results will be presented.

2D image of local density and magnetic fluctuations from line-integrated interferometry-polarimetry measurements.

PubMed

Lin, L; Ding, W X; Brower, D L

2014-11-01

Combined polarimetry-interferometry capability permits simultaneous measurement of line-integrated density and Faraday effect with fast time response (∼1 μs) and high sensitivity. Faraday effect fluctuations with phase shift of order 0.05° associated with global tearing modes are resolved with an uncertainty ∼0.01°. For physics investigations, local density fluctuations are obtained by inverting the line-integrated interferometry data. The local magnetic and current density fluctuations are then reconstructed using a parameterized fit of the polarimetry data. Reconstructed 2D images of density and magnetic field fluctuations in a poloidal cross section exhibit significantly different spatial structure. Combined with their relative phase, the magnetic-fluctuation-induced particle transport flux and its spatial distribution are resolved.

2D image of local density and magnetic fluctuations from line-integrated interferometry-polarimetry measurements

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

Lin, L., E-mail: lianglin@ucla.edu; Ding, W. X.; Brower, D. L.

2014-11-15

Combined polarimetry-interferometry capability permits simultaneous measurement of line-integrated density and Faraday effect with fast time response (∼1 μs) and high sensitivity. Faraday effect fluctuations with phase shift of order 0.05° associated with global tearing modes are resolved with an uncertainty ∼0.01°. For physics investigations, local density fluctuations are obtained by inverting the line-integrated interferometry data. The local magnetic and current density fluctuations are then reconstructed using a parameterized fit of the polarimetry data. Reconstructed 2D images of density and magnetic field fluctuations in a poloidal cross section exhibit significantly different spatial structure. Combined with their relative phase, the magnetic-fluctuation-induced particlemore » transport flux and its spatial distribution are resolved.« less

Plasma turbulence and coherent structures in the polar cap observed by the ICI-2 sounding rocket

NASA Astrophysics Data System (ADS)

Spicher, A.; Miloch, W. J.; Clausen, L. B. N.; Moen, J. I.

2015-12-01

The electron density data from the ICI-2 sounding rocket experiment in the high-latitude F region ionosphere are analyzed using the higher-order spectra and higher-order statistics. Two regions of enhanced fluctuations are chosen for detailed analysis: the trailing edge of a polar cap patch and an electron density enhancement associated with particle precipitation. While these two regions exhibit similar power spectra, our analysis reveals that their internal structures are significantly different. The structures on the edge of the polar cap patch are likely due to nonlinear wave interactions since this region is characterized by intermittency and significant coherent mode coupling. The plasma enhancement subjected to precipitation, however, exhibits stronger random characteristics with uncorrelated phases of density fluctuations. These results suggest that particle precipitation plays a fundamental role in ionospheric plasma structuring creating turbulent-like structures. We discuss the physical mechanisms that cause plasma structuring as well as the possible processes for the low-frequency part of the spectrum in terms of plasma instabilities.

Transport with Reversed Er in Gamma -10, LAPD and the Sao Paulo Tokamak

NASA Astrophysics Data System (ADS)

Fu, Sean; Morrison, P. J.; Horton, W.; Caldas, Ibere

2009-11-01

The understanding of how and when the reversed radial electric field produces an internal transport barrier is still poorly understood. There are two linked aspects to the problem: (i) the change in the plasma instabilities and thus the fluctuation spectrum from changes away from or towards the generalized Rayleigh condition for destabilizing the drift wave/ Rossby wave instabilities and (2) for a fixed fluctuation spectrum the role of the Er reversal in creating a layer where the resonant surfaces do not overlap so the condition for the onset of diffusion from overlapping resonances in phase space is not satisfied. We look at a model that is representative of the externally controlled Er shear in the G-10 Tsukuba tandem mirror and in the wall biasing experiments in the LAPD and the Sao Paulo Tokamak to ask when the effects are dominant and how they may compete with each other to determine the conditions for the transport suppression that is reported in numerous plasma experiments.

Performance improvement of coherent free-space optical communication with quadrature phase-shift keying modulation using digital phase estimation.

PubMed

Li, Xueliang; Geng, Tianwen; Ma, Shuang; Li, Yatian; Gao, Shijie; Wu, Zhiyong

2017-06-01

The performance of coherent free-space optical (CFSO) communication with phase modulation is limited by both phase fluctuations and intensity scintillations induced by atmospheric turbulence. To improve the system performance, one effective way is to use digital phase estimation. In this paper, a CFSO communication system with quadrature phase-shift keying modulation is studied. With consideration of the effects of log-normal amplitude fluctuations and Gauss phase fluctuations, a two-stage Mth power carrier phase estimation (CPE) scheme is proposed. The simulation results show that the phase noise can be suppressed greatly by this scheme, and the system symbol error rate performance with the two-stage Mth power CPE can be three orders lower than that of the single-stage Mth power CPE. Therefore, the two-stage CPE we proposed can contribute to the performance improvements of the CFSO communication system and has determinate guidance sense to its actual application.

Performance of synchronous optical receivers using atmospheric compensation techniques.

PubMed

Belmonte, Aniceto; Khan, Joseph

2008-09-01

We model the impact of atmospheric turbulence-induced phase and amplitude fluctuations on free-space optical links using synchronous detection. We derive exact expressions for the probability density function of the signal-to-noise ratio in the presence of turbulence. We consider the effects of log-normal amplitude fluctuations and Gaussian phase fluctuations, in addition to local oscillator shot noise, for both passive receivers and those employing active modal compensation of wave-front phase distortion. We compute error probabilities for M-ary phase-shift keying, and evaluate the impact of various parameters, including the ratio of receiver aperture diameter to the wave-front coherence diameter, and the number of modes compensated.

A comparison of atmospheric effects on differential phase for a two-element antenna array and nearby site test interferometer

NASA Astrophysics Data System (ADS)

Morabito, David D.; D'Addario, Larry; Finley, Susan

2016-02-01

Phased arrays of reflector antennas can be used to obtain effective area and gain that are much larger than is practical with a single antenna. This technique is routinely used by NASA for receiving weak signals from deep space. Phase alignment of the signals can be disrupted by turbulence in the troposphere, which causes fluctuations in the differences of signal delays among the antennas. At the Deep Space Network stations, site test interferometers (STIs) are being used for long-term monitoring of these delay fluctuations using signals from geostationary satellites. In this paper, we compare the STI measurements with the phase variations seen by a nearby two-element array of 34 m diameter antennas tracking 8.4 GHz and 32 GHz signals from the Cassini spacecraft in orbit around Saturn. It is shown that the statistics of the STI delay fluctuations, after appropriate scaling for differences in antenna separation and elevation angle and conversion to phase at the spacecraft frequencies, provide reliable estimates of the phase fluctuations seen by the large antennas on the deep space signal. Techniques for adaptive compensation of the phase fluctuations are available when receiving a sufficiently strong signal, but compensation is often impractical or impossible when using the array for transmitting. These results help to validate the use of long-term STI data for assessing the feasibility of large transmitting arrays at various sites.

Notes on phase transitions and the role of spin fluctuations

NASA Astrophysics Data System (ADS)

Stishov, S. M.

2016-09-01

The physical properties of two chiral systems with localized and delocalized magnetic moments, {\\text{Cu}}2{\\text{OSeO}}3 and MnSi, are reviewed. It is concluded that the longitudinal fluctuations of magnetic moments have no strong effect on the qualitative picture of phase transitions and the magnetic phase diagrams of chiral systems.

Exploration of dielectric relaxations of a room temperature anti-ferroelectric liquid crystal mixture

NASA Astrophysics Data System (ADS)

Dwivedi, Aanchal; Verma, Rohit; Dhar, R.; Dabrowski, R.

2018-05-01

Dielectric characterization of a technologically important room temperature anti-ferroelectric liquid crystal (AFLC) mixture has been carried out as a function of temperature and frequency. The mixture has a phase sequence of I-SmA*-SmC*-SmCA* -SmIA* -Cr. Electrical study for the planar anchoring of the molecules demonstrates seven relaxation mechanisms in various mesophases of the mixture. Dielectric spectrum of paraelectric SmA* phase exhibits a relaxation mechanism due to the tilt fluctuation of the molecules. In ferroelectric SmC* phase, Goldstone mode has been observed due to the fluctuation in azimuthal angle. In antiferroelectric SmCA*and hexatic SmIA* phases two relaxation mechanisms are observed due to bond orientation order & anti-phase fluctuation and rotation around the short axes respectively.

Phase fluctuations in a strongly disordered s-wave NbN superconductor close to the metal-insulator transition.

PubMed

Mondal, Mintu; Kamlapure, Anand; Chand, Madhavi; Saraswat, Garima; Kumar, Sanjeev; Jesudasan, John; Benfatto, L; Tripathi, Vikram; Raychaudhuri, Pratap

2011-01-28

We explore the role of phase fluctuations in a three-dimensional s-wave superconductor, NbN, as we approach the critical disorder for destruction of the superconducting state. Close to critical disorder, we observe a finite gap in the electronic spectrum which persists at temperatures well above T(c). The superfluid density is strongly suppressed at low temperatures and evolves towards a linear-T variation at higher temperatures. These observations provide strong evidence that phase fluctuations play a central role in the formation of a pseudogap state in a disordered s-wave superconductor.

A phase contrast imaging–interferometer system for detection of multiscale electron density fluctuations on DIII-D

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

Davis, E. M.; Rost, J. C.; Porkolab, M.

2016-11-15

Heterodyne interferometry and phase contrast imaging (PCI) are robust, mature techniques for measuring low-k and high-k electron density fluctuations, respectively. This work describes the first-ever implementation of a combined PCI–interferometer. The combined system uses a single 10.6 μm probe beam, two interference schemes, and two detectors to measure electron density fluctuations at large spatiotemporal bandwidth (10 kHz

Optimal Operation of a Josephson Parametric Amplifier for Vacuum Squeezing

NASA Astrophysics Data System (ADS)

Malnou, M.; Palken, D. A.; Vale, Leila R.; Hilton, Gene C.; Lehnert, K. W.

2018-04-01

A Josephson parametric amplifier (JPA) can create squeezed states of microwave light, lowering the noise associated with certain quantum measurements. We experimentally study how the JPA's pump influences the phase-sensitive amplification and deamplification of a coherent tone's amplitude when that amplitude is commensurate with vacuum fluctuations. We predict and demonstrate that, by operating the JPA with a single current pump whose power is greater than the value that maximizes gain, the amplifier distortion is reduced and, consequently, squeezing is improved. Optimizing the singly pumped JPA's operation in this fashion, we directly observe 3.87 ±0.03 dB of vacuum squeezing over a bandwidth of 30 MHz.

Giant phonon anomaly associated with superconducting fluctuations in the pseudogap phase of cuprates

DOE PAGES

Liu, Ye-Hua; Konik, Robert M.; Rice, T. M.; ...

2016-01-20

The pseudogap in underdoped cuprates leads to significant changes in the electronic structure, and was later found to be accompanied by anomalous fluctuations of superconductivity and certain lattice phonons. Here we propose that the Fermi surface breakup due to the pseudogap, leads to a breakup of the pairing order into two weakly coupled sub-band amplitudes, and a concomitant low energy Leggett mode due to phase fluctuations between them. This increases the temperature range of superconducting fluctuations containing an overdamped Leggett mode. In this range inter-sub-band phonons show strong damping due to resonant scattering into an intermediate state with a pairmore » of overdamped Leggett modes. In the ordered state, the Leggett mode develops a finite energy, changing the anomalous phonon damping into an anomaly in the dispersion. Finally, this proposal explains the intrinsic connection between the anomalous pseudogap phase, enhanced superconducting fluctuations and giant anomalies in the phonon spectra.« less

"Fluctuoscopy" of Superconductors

NASA Astrophysics Data System (ADS)

Varlamov, A. A.

Study of fluctuation phenomena in superconductors (SCs) is the subject of great fundamental and practical importance. Understanding of their physics allowed to clear up the fundamental properties of SC state. Being predicted in 1968, one of the fluctuation effects, namely paraconductivity, was experimentally observed almost simultaneously. Since this time, fluctuations became a noticeable part of research in the field of superconductivity, and a variety of fluctuation effects have been discovered. The new wave of interest to fluctuations (FL) in superconductors was generated by the discovery of cuprate oxide superconductors (high-temperature superconductors, HTS), where, due to extremely short coherence length and low effective dimensionality of the electron system, superconductive fluctuations manifest themselves in a wide range of temperatures. Moreover, anomalous properties of the normal state of HTS were attributed by many theorists to strong FL in these systems. Being studied in the framework of the phenomenological Ginzburg-Landau theory and, more extensively, in diagrammatic microscopic approach, SC FLs side by side with other quantum corrections (weak localization, etc.) became a new tool for investigation and characterization of such new systems as HTS, disordered electron systems, granular metals, Josephson structures, artificial super-lattices, etc. The characteristic feature of SC FL is their strong dependence on temperature and magnetic fields in the vicinity of phase transition. This allows one to definitely separate the fluctuation effects from other contributions and to use them as the source of information about the microscopic parameters of a material. By their origin, SC FLs are very sensitive to relaxation processes, which break phase coherence. This allows using them for versatile characterization of SC. Today, one can speak about the " fluctuoscopy" of superconductive systems. In review, we present the qualitative picture both of thermodynamic fluctuations close to critical temperature T c0and quantum fluctuations at zero temperature and in vicinity of the second critical field H c2(0). Then in the frameworks of the Ginzburg-Landau theory, we discuss the characteristic crossovers in fluctuation properties of superconductive nanoparticles and layered superconductors. We present the general expression for fluctuation magneto-conductivity valid through all phase diagram of superconductor and apply it to study of the quantum phase transition close to H c2(0). Fluctuation analysis of this transition allows us to present the scenario of fluctuation defragmentation of the Abrikosov lattice.

Femtosecond-level timing fluctuation suppression in atmospheric frequency transfer with passive phase conjunction correction.

PubMed

Sun, Fuyu; Hou, Dong; Zhang, Danian; Tian, Jie; Hu, Jianguo; Huang, Xianhe; Chen, Shijun

2017-09-04

We demonstrate femtosecond-level timing fluctuation suppression in indoor atmospheric comb-based frequency transfer with a passive phase conjunction correction technique. Timing fluctuations and Allan deviations are both measured to characterize the excess frequency instability incurred during the frequency transfer process. By transferring a 2 GHz microwave over a 52-m long free-space link in 5000 s, the total root-mean-square (RMS) timing fluctuation was measured to be about 280 fs with a fractional frequency instability on the order of 3 × 10 -13 at 1 s and 6 × 10 -17 at 1000 s. This atmospheric comb-based frequency transfer with passive phase conjunction correction can be used to build an atomic clock-based free-space frequency transmission link because its instability is less than that of a commercial Cs or H-master clock.

An upgraded interferometer-polarimeter system for broadband fluctuation measurements

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

Parke, E., E-mail: eparke@ucla.edu; Ding, W. X.; Brower, D. L.

2016-11-15

Measuring high-frequency fluctuations (above tearing mode frequencies) is important for diagnosing instabilities and transport phenomena. The Madison Symmetric Torus interferometer-polarimeter system has been upgraded to utilize improved planar-diode mixer technology. The new mixers reduce phase noise and allow more sensitive measurements of fluctuations at high frequency. Typical polarimeter rms phase noise values of 0.05°–0.07° are obtained with 400 kHz bandwidth. The low phase noise enables the resolution of fluctuations up to 250 kHz for polarimetry and 600 kHz for interferometry. The importance of probe beam alignment for polarimetry is also verified; previously reported tolerances of ≤0.1 mm displacement for equilibriummore » and tearing mode measurements minimize contamination due to spatial misalignment to within acceptable levels for chords near the magnetic axis.« less

[Influence of microbiological quality of lactic acid cheese on water phase in conditions of hermetic packing].

PubMed

Steinka, Izabela

2005-01-01

Aim of research was to assess the influence of lactic acid cheese micro-flora on water phase fluctuation between surface of products and the packaging. Results of research showed that changes of water content could be expressed with the help of polynomial cubic equation. From linear correlation equations describing level of micro-flora in lactic acid cheese and water content it resulted micro-organisms had a significant influence on the water phase fluctuation. Values of determined coefficients of determination suggested that yeast, enterococci and staphylococci had a significant influence on water fluctuation between product and the packaging.

Observations of tropospheric phase scintillations at 5 GHz on vertical paths

NASA Technical Reports Server (NTRS)

Armstrong, J. W.; Sramek, R. A.

1982-01-01

The article presents observations of turbulence-induced tropospheric phase fluctuations measured at 5 GHz on the near-vertical paths relevant to many astronomical and geophysical measurements. The data are summarized as phase power spectra, structure functions, and Allan variances. Comparisons to other microwave observations indicate relatively good agreement in both the level and shape of the power spectrum of these tropospheric phase fluctuations. Implications for precision Doppler tracking of spacecraft and geodesy/radio interferometry are discussed.

Dissipation-driven phase transitions in superconducting wires

NASA Astrophysics Data System (ADS)

Lobos, Alejandro; Iucci, Aníbal; Müller, Markus; Giamarchi, Thierry

2010-03-01

Narrow superconducting wires with diameter dξ0 (where ξ0 is the bulk superconducting coherence length) are quasi-1D systems in which fluctuations of the order parameter strongly affect low-temperature properties. Indeed, fluctuations cause the magnitude of the order parameter to temporarily vanish at some point along the wire, allowing its phase to slip by 2π, and to produce finite resistivity for all temperatures below Tc. In this work, we show that a weak coupling to a diffusive metallic film reinforces superconductivity in the wire through a quench of phase fluctuations. We analyze the effective phase-only action of the system by a perturbative renormalization-group and a self-consistent variational approach to obtain the critical points and phases at T=0. We predict a quantum phase transition towards a superconducting phase with long-range order as a function of the wire stiffness and coupling to the metal. Finally we discuss implications for the DC resistivity of the wire.

A description of phases with induced hybridisation at finite temperatures

NASA Astrophysics Data System (ADS)

Golosov, D. I.

2018-05-01

In an extended Falicov-Kimball model, an excitonic insulator phase can be stabilised at zero temperature. With increasing temperature, the excitonic order parameter (interaction-induced hybridisation on-site, characterised by the absolute value and phase) eventually becomes disordered, which involves fluctuations of both its phase and (at higher T) its absolute value. In order to build an adequate mean field description, it is important to clarify the nature of degrees of freedom associated with the phase and absolute value of the induced hybridisation, and the corresponding phase space volume. We show that a possible description is provided by the SU(4) parametrisation on-site. In principle, this allows to describe both the lower-temperature regime where phase fluctuations destroy the long-range order, and the higher temperature crossover corresponding to a decrease of absolute value of the hybridisation relative to the fluctuations level. This picture is also expected to be relevant in other contexts, including the Kondo lattice model.

Amplitude and phase fluctuations of Van der Pol oscillator under external random forcing

NASA Astrophysics Data System (ADS)

Singh, Aman K.; Yadava, R. D. S.

2018-05-01

The paper presents an analytical study of noise in Van der Pol oscillator output subjected to an external force noise assumed to be characterized by delta function (white noise). The external fluctuations are assumed to be small in comparison to the average response of the noise free system. The autocorrelation function and power spectrum are calculated under the condition of weak nonlinearity. The latter ensures limit cycle oscillations. The total spectral power density is dominated by the contributions from the phase fluctuations. The amplitude fluctuations are at least two orders of magnitude smaller. The analysis is shown to be useful to interpretation microcantilever based biosensing data.

Bedload fluctuations in a steep macro-rough channel

NASA Astrophysics Data System (ADS)

Ghilardi, Tamara; Franca, Mário J.; Schleiss, Anton J.

2014-05-01

It is known that bedload fluctuates over time in steep rivers with wide grain size distributions, even when conditions of constant sediment feed and water discharge are met. Bedload fluctuations are periodic and related to fluctuations in the flow velocity and channel bed morphology. In cascade morphologies, the presence of large relatively immobile boulders has a strong impact on flow conditions and sediment transport; their influence on bedload fluctuations is considered in this research. Sediment transport fluctuations were investigated in a set of 38 laboratory experiments carried out on a steep tilting flume, under several conditions of constant sediment and water discharge, for three different slopes (S=6.7%, 9.9%, and 13%). The impact of the diameter and spatial density of randomly placed boulders was studied for several flow conditions. Along with the sediment transport and bulk mean flow velocity, the boulder protrusion, boulder surface, and number of hydraulic jumps, which are indicators of the channel morphology, were measured regularly during the experiments. Periodic bedload pulses are clearly visible in the data collected during the experiments, along with well correlated fluctuations in the flow velocity and bed morphology parameters. Well-behaved cyclic oscillations in the auto-correlation and cross-correlation functions confirm the periodicity of the observed fluctuations and show that the durations of these cycles are similar, although not necessarily in phase. A detailed analysis of data time series and image acquired during the tests show a link between bedload pulses and different bed states, boulder protrusion, and surface grain size distributions. A feedback system exists among channel morphology, flow kinematics and sediment transport. A phase analysis for the observed variables, based on the identification of bedload cycles in the instantaneous signal, is performed. The link between the phases of bedload and each of the morphological parameters show a hysteretic path. The relation between the phase-averaged bedload and the phase-averaged flow velocity show a considerable lesser degree of hysteresis. Comparing the phase averaged bedload of the experiments, it is observed that the shape of bedload cycles is the same for all tested hydraulic conditions. The cycles present a long duration low sediment transport event and a shorter peak transport event. This indicates that long periods of sediment aggradations alternate with short erosion periods, even under constant hydraulic conditions. The bedload pulses may be characterized by their amplitude and period as a function of various boulder spatial densities and diameters. We show that for higher stream power, the fluctuations decrease, both in cycle duration and in amplitude. The presence of boulders increases the stream power needed to transport a given amount of sediment, thus decreasing fluctuations. KEY WORDS: Bedload fluctuations; Morphological changes; Sediment transport; Boulders; Steep channel.

Sub-picosecond timing fluctuation suppression in laser-based atmospheric transfer of microwave signal using electronic phase compensation

NASA Astrophysics Data System (ADS)

Chen, Shijun; Sun, Fuyu; Bai, Qingsong; Chen, Dawei; Chen, Qiang; Hou, Dong

2017-10-01

We demonstrated a timing fluctuation suppression in outdoor laser-based atmospheric radio-frequency transfer over a 110 m one-way free-space link using an electronic phase compensation technique. Timing fluctuations and Allan Deviation are both measured to characterize the instability of transferred frequency incurred during the transfer process. With transferring a 1 GHz microwave signal over a timing fluctuation suppressed transmission link, the total root-mean-square (rms) timing fluctuation was measured to be 920 femtoseconds in 5000 s, with fractional frequency instability on the order of 1 × 10-12 at 1 s, and order of 2 × 10-16 at 1000 s. This atmospheric frequency transfer scheme with the timing fluctuation suppression technique can be used to fast build an atomic clock-based frequency free-space transmission link since its stability is superior to a commercial Cs and Rb clock.

Influence of longitudinal spin fluctuations on the phase transition features in chiral magnets

NASA Astrophysics Data System (ADS)

Belemuk, A. M.; Stishov, S. M.

2018-04-01

Using the classical Monte Carlo calculations, we investigate the effects of longitudinal spin fluctuations on the helimagnetic transition in a Heisenberg magnet with the Dzyaloshinskii-Moriya interaction. We use variable spin amplitudes in the framework of the spin-lattice Hamiltonian. It is this kind of fluctuations that naturally occur in an itinerant system. We show that the basic features of the helical phase transition are not changed much by the longitudinal spin fluctuations though the transition temperature Tc and the fluctuation hump seen in specific heat at T >Tc is significantly affected. We report thermodynamic and structural effects of these fluctuations. By increasing the system size in the Monte Carlo modeling, we are able to reproduce the ring shape scattering intensity above the helimagnetic transition temperature Tc, which transforms into the spiral spots seen below Tc in the neutron scattering experiments.

Anomalous propagation of Omega VLF waves near the geomagnetic equator

NASA Astrophysics Data System (ADS)

Ohtani, A.; Kikuchi, T.; Nozaki, K.; Kurihara, N.; Kuratani, Y.; Ohse, M.

1983-09-01

Omega HAIKU, REUNION, and LIBERIA signals were received and anomalous propagation characteristics were obtained near the geomagnetic equator. Short-period fluctuations were found in the phase of the HAIKU 10.2 kHz signal in November 1979 and in the phase and amplitude of the HAIKU 13.6 kHz signal in November 1981. These cyclic fluctuations are in close correlation with the phase cycle slippings, which occur most frequently when the receiver is located at 6 S geomagnetic latitude. On the basis of anisotropic waveguide mode theory indicating much less attenuation in WE propagation than in EW propagation at the geomagnetic equator, it is concluded that the short-period fluctuations in the phase and amplitude are due to interference between the short-path and the long-path signals.

Temperature-fluctuation-sensitive accumulative effect of the phase measurement errors in low-coherence interferometry in characterizing arrayed waveguide gratings.

PubMed

Zhao, Changyun; Wei, Bing; Yang, Longzhi; Wang, Gencheng; Wang, Yuehai; Jiang, Xiaoqing; Li, Yubo; Yang, Jianyi

2015-09-20

We investigate the accumulative effect of the phase measurement errors in characterizing optical multipath components by low-coherence interferometry. The accumulative effect is caused by the fluctuation of the environment temperature, which leads to the variation of the refractive index of the device under test. The resulting phase measurement errors accumulate with the increasing of the phase difference between the two interferometer arms. Our experiments were carried out to demonstrate that the accumulative effect is still obvious even though the thermo-optical coefficient of the device under test is quite small. Shortening the measurement time to reduce the fluctuation of the environment temperature can effectively restrain the accumulative effect. The experiments show that when the scanning speed increases to 4.8 mm/s, the slope of the phase measurement errors decreases to 5.52×10(-8), which means the accumulative effect can be ignored.

Studying Suspended Sediment Mechanism with Two-Phase PIV

NASA Astrophysics Data System (ADS)

Matinpour, H.; Atkinson, J. F.; Bennett, S. J.; Guala, M.

2017-12-01

Suspended sediment transport affects soil erosion, agriculture and water resources quality. Turbulent diffusion is the most primary force to maintain sediments in suspension. Although extensive previous literature have been studying the interactions between turbulent motion and suspended sediment, mechanism of sediments in suspension is still poorly understood. In this study, we investigate suspension of sediments as two distinct phases: one phase of sediments and another phase of fluid with turbulent motions. We designed and deployed a state-of-the-art two-phase PIV measurement technique to discriminate these two phases and acquire velocities of each phase separately and simultaneously. The technique that we have developed is employing a computer-vision based method, which enables us to discriminate sediment particles from fluid tracer particles based on two thresholds, dissimilar particle sizes and different particle intensities. Results indicate that fluid turbulence decreases in the presence of suspended sediments. Obtaining only sediment phase consecutive images enable us to compute fluctuation sediment concentration. This result enlightens understanding of complex interaction between the fluctuation velocities and the fluctuation of associated mass and compares turbulent viscosity with turbulent eddy diffusivity experimentally.

Reentrant Phase Coherence in Superconducting Nanowire Composites.

PubMed

Ansermet, Diane; Petrović, Alexander P; He, Shikun; Chernyshov, Dmitri; Hoesch, Moritz; Salloum, Diala; Gougeon, Patrick; Potel, Michel; Boeri, Lilia; Andersen, Ole Krogh; Panagopoulos, Christos

2016-01-26

The short coherence lengths characteristic of low-dimensional superconductors are associated with usefully high critical fields or temperatures. Unfortunately, such materials are often sensitive to disorder and suffer from phase fluctuations in the superconducting order parameter which diverge with temperature T, magnetic field H, or current I. We propose an approach to overcome synthesis and fluctuation problems: building superconductors from inhomogeneous composites of nanofilaments. Macroscopic crystals of quasi-one-dimensional Na2-δMo6Se6 featuring Na vacancy disorder (δ ≈ 0.2) are shown to behave as percolative networks of superconducting nanowires. Long-range order is established via transverse coupling between individual one-dimensional filaments, yet phase coherence remains unstable to fluctuations and localization in the zero (T,H,I) limit. However, a region of reentrant phase coherence develops upon raising (T,H,I). We attribute this phenomenon to an enhancement of the transverse coupling due to electron delocalization. Our observations of reentrant phase coherence coincide with a peak in the Josephson energy EJ at nonzero (T,H,I), which we estimate using a simple analytical model for a disordered anisotropic superconductor. Na2-δMo6Se6 is therefore a blueprint for a future generation of nanofilamentary superconductors with inbuilt resilience to phase fluctuations at elevated (T,H,I).

Experimental limits on the fidelity of adiabatic geometric phase gates in a single solid-state spin qubit

DOE PAGES

Zhang, Kai; Nusran, N. M.; Slezak, B. R.; ...

2016-05-17

While it is often thought that the geometric phase is less sensitive to fluctuations in the control fields, a very general feature of adiabatic Hamiltonians is the unavoidable dynamic phase that accompanies the geometric phase. The effect of control field noise during adiabatic geometric quantum gate operations has not been probed experimentally, especially in the canonical spin qubit system that is of interest for quantum information. We present measurement of the Berry phase and carry out adiabatic geometric phase gate in a single solid-state spin qubit associated with the nitrogen-vacancy center in diamond. We manipulate the spin qubit geometrically bymore » careful application of microwave radiation that creates an effective rotating magnetic field, and observe the resulting Berry phase signal via spin echo interferometry. Our results show that control field noise at frequencies higher than the spin echo clock frequency causes decay of the quantum phase, and degrades the fidelity of the geometric phase gate to the classical threshold after a few (~10) operations. This occurs in spite of the geometric nature of the state preparation, due to unavoidable dynamic contributions. In conclusion, we have carried out systematic analysis and numerical simulations to study the effects of the control field noise and imperfect driving waveforms on the quantum phase gate.« less

Experimental limits on the fidelity of adiabatic geometric phase gates in a single solid-state spin qubit

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

Zhang, Kai; Nusran, N. M.; Slezak, B. R.

While it is often thought that the geometric phase is less sensitive to fluctuations in the control fields, a very general feature of adiabatic Hamiltonians is the unavoidable dynamic phase that accompanies the geometric phase. The effect of control field noise during adiabatic geometric quantum gate operations has not been probed experimentally, especially in the canonical spin qubit system that is of interest for quantum information. We present measurement of the Berry phase and carry out adiabatic geometric phase gate in a single solid-state spin qubit associated with the nitrogen-vacancy center in diamond. We manipulate the spin qubit geometrically bymore » careful application of microwave radiation that creates an effective rotating magnetic field, and observe the resulting Berry phase signal via spin echo interferometry. Our results show that control field noise at frequencies higher than the spin echo clock frequency causes decay of the quantum phase, and degrades the fidelity of the geometric phase gate to the classical threshold after a few (~10) operations. This occurs in spite of the geometric nature of the state preparation, due to unavoidable dynamic contributions. In conclusion, we have carried out systematic analysis and numerical simulations to study the effects of the control field noise and imperfect driving waveforms on the quantum phase gate.« less

Path Length Fluctuations Derived from Site Testing Interferometer Data

NASA Technical Reports Server (NTRS)

Acosta, Roberto J.; Nessel, James A.; Morse, Jacquelynne R.

2010-01-01

To evaluate possible sites for NASA's proposed Ka-band antenna array, the NASA Glenn Research Center has constructed atmospheric phase monitors (APM) which directly measure the tropospheric phase stability. These instruments observe an unmodulated 20.2 GHz beacon signal broadcast from a geostationary satellite (Anik F2) and measure the phase difference between the signals received by the two antennas. Two APM's have been deployed, one at the NASA Deep Space Network (DSN) Tracking Complex in Goldstone, California, and the other at the NASA White Sands Complex, in Las Cruces, New Mexico. Two station-years of atmospheric phase fluctuation data have been collected at Goldstone since operations commenced in May 2007 and 0.5 station-years of data have been collected at White Sands since operations began February 2009. With identical instruments operating simultaneously, we can directly compare the phase stability at the two sites. Phase stability is analyzed statistically in terms of the root-mean-square (rms) of the tropospheric path length fluctuations over 10 min blocks. Correlation between surface wind speed and relative humidity with interferometer phase are discussed. For 2 years, the path length fluctuations at the DSN site in Goldstone, California, have been better than 757 micrometer (with reference to a 300 m baseline and to Zenith) for 90 percent of the time. For the 6 months of data collected at White Sands, New Mexico, the path length fluctuations have been better than 830 micrometers (with reference to a 300 m baseline and to Zenith) for 90 percent of the time. This type of data analysis, as well as many other site quality characteristics (e.g., rain attenuation, infrastructure, etc.), will be used to determine the suitability of both sites for NASA s future communication services at Ka-band using an array of antennas.

Statistical assessment of optical phase fluctuations through turbulent mixing layers

NASA Astrophysics Data System (ADS)

Gardner, Patrick J.; Roggemann, Michael C.; Welsh, Byron M.; Bowersox, Rodney D.

1995-09-01

A lateral shearing interferometer is used to measure the slope of perturbed wavefronts after propagating through turbulent shear flows. This provides a two-dimensional flow visualization technique which is nonintrusive. The slope measurements are used to reconstruct the phase of the turbulence-corrupted wave front. Experiments were performed on a plane shear mixing layer of helium and nitrogen gas at fixed velocities, for five locations in the flow development. The two gases, having a density ratio of approximately seven, provide an effective means of simulating compressible shear layers. Statistical autocorrelation functions and structure functions are computed on the reconstructed phase maps. The autocorrelation function results indicate that the turbulence-induced phase fluctuations are not wide-sense stationary. The structure functions exhibit statistical homogeneity, indicating the phase fluctuation are stationary in first increments. However, the turbulence-corrupted phase is not isotropic. A five-thirds power law is shown to fit one-dimensional, orthogonal slices of the structure function, with scaling coefficients related to the location in the flow.

Real-time observation of fluctuations at the driven-dissipative Dicke phase transition

PubMed Central

Brennecke, Ferdinand; Mottl, Rafael; Baumann, Kristian; Landig, Renate; Donner, Tobias; Esslinger, Tilman

2013-01-01

We experimentally study the influence of dissipation on the driven Dicke quantum phase transition, realized by coupling external degrees of freedom of a Bose–Einstein condensate to the light field of a high-finesse optical cavity. The cavity provides a natural dissipation channel, which gives rise to vacuum-induced fluctuations and allows us to observe density fluctuations of the gas in real-time. We monitor the divergence of these fluctuations over two orders of magnitude while approaching the phase transition, and observe a behavior that deviates significantly from that expected for a closed system. A correlation analysis of the fluctuations reveals the diverging time scale of the atomic dynamics and allows us to extract a damping rate for the external degree of freedom of the atoms. We find good agreement with our theoretical model including dissipation via both the cavity field and the atomic field. Using a dissipation channel to nondestructively gain information about a quantum many-body system provides a unique path to study the physics of driven-dissipative systems. PMID:23818599

Synchrony in broadband fluctuation and the 2008 financial crisis.

PubMed

Lin, Der Chyan

2013-01-01

We propose phase-like characteristics in scale-free broadband processes and consider fluctuation synchrony based on the temporal signature of significant amplitude fluctuation. Using wavelet transform, successful captures of similar fluctuation pattern between such broadband processes are demonstrated. The application to the financial data leading to the 2008 financial crisis reveals the transition towards a qualitatively different dynamical regime with many equity price in fluctuation synchrony. Further analysis suggests an underlying scale free "price fluctuation network" with large clustering coefficient.

ARO-URI Center for Opto-Electronic Systems Research. Addendum

DTIC Science & Technology

1992-12-01

5, 2015-2020 (1988). 36. "Cancellation of laser phase fluctuations in Stokes and anti-Stokes generation ," Z . W. Li, C. Radzewicz, and M. G. Raymer, J...G. Raymer, Opt. Lett. 13, 491-493 (1988). (34) "Cancellation of laser phase fluctuations in Stokes and anti-Stokes generation ," Z . W. Li, C

A hybrid strain and thermal energy harvester based on an infra-red sensitive Er3+ modified poly(vinylidene fluoride) ferroelectret structure.

PubMed

Ghosh, Sujoy Kumar; Xie, Mengying; Bowen, Christopher Rhys; Davies, Philip R; Morgan, David J; Mandal, Dipankar

2017-12-01

In this paper, a novel infra-red (IR) sensitive Er 3+ modified poly(vinylidene fluoride) (PVDF) (Er-PVDF) film is developed for converting both mechanical and thermal energies into useful electrical power. The addition of Er 3+ to PVDF is shown to improve piezoelectric properties due to the formation of a self-polarized ferroelectric β-phase and the creation of an electret-like porous structure. In addition, we demonstrate that Er 3+ acts to enhance heat transfer into the Er-PVDF film due to its excellent infrared absorbance, which, leads to rapid and large temperature fluctuations and improved pyroelectric energy transformation. We demonstrate the potential of this novel material for mechanical energy harvesting by creating a durable ferroelectret energy harvester/nanogenerator (FTNG). The high thermal stability of the β-phase enables the FTNG to harvest large temperature fluctuations (ΔT ~ 24 K). Moreover, the superior mechanosensitivity, S M  ~ 3.4 VPa -1 of the FTNG enables the design of a wearable self-powered health-care monitoring system by human-machine integration. The combination of rare-earth ion, Er 3+ with the ferroelectricity of PVDF provides a new and robust approach for delivering smart materials and structures for self-powered wireless technologies, sensors and Internet of Things (IoT) devices.

Optical phase nanoscopy in red blood cells using low-coherence spectroscopy.

PubMed

Shock, Itay; Barbul, Alexander; Girshovitz, Pinhas; Nevo, Uri; Korenstein, Rafi; Shaked, Natan T

2012-10-01

We propose a low-coherence spectral-domain phase microscopy (SDPM) system for accurate quantitative phase measurements in red blood cells (RBCs) for the prognosis and monitoring of disease conditions that affect the visco-elastic properties of RBCs. Using the system, we performed time-recordings of cell membrane fluctuations, and compared the nano-scale fluctuation dynamics of healthy and glutaraldehyde-treated RBCs. Glutaraldehyde-treated RBCs possess lower amplitudes of fluctuations, reflecting an increased membrane stiffness. To demonstrate the ability of our system to measure fluctuations of lower amplitudes than those measured by the commonly used holographic phase microscopy techniques, we also constructed wide-field digital interferometry (WFDI) system and compared the performances of both systems. Due to its common-path geometry, the optical-path-delay stability of SDPM was found to be less than 0.3 nm in liquid environment, at least three times better than WFDI under the same conditions. In addition, due to the compactness of SDPM and its inexpensive and robust design, the system possesses a high potential for clinical applications.

Development of TEC fluctuations in northern and southern hemispheres on the base of GPS observations

NASA Astrophysics Data System (ADS)

Shagimuratov, Irk; Krankowski, Andrzej; Sieradzki, Rafal; Ephishov, I. I.

GPS technique is widely used to study the global structure and dynamics of the ionosphere. In this paper GPS observations carried out at Arctic and Antarctic stations belonging to the IGS network were used to study TEC fluctuations in the high-latitude ionosphere during the ionospheric storms. Dual-frequency GPS phase measurements along individual satellite passes served as raw data. It was shown that ionospheric irregularities of a different scale were devel-oped in the auroral and polar ionosphere. It is a common phenomenon caused phase fluctuations of GPS signals. In November 2009, West Department of IZMIRAN in Kaliningrad (Russia) and University of Warmia and Mazury in Olsztyn (Poland) established computer server for automatic monitoring of these irregularities. The rate of TEC index (ROTI) expressed in TECU/min was used as a measure of TEC fluctuations. During its operation TEC variations related to ionospheric structures of a spatial scale more than 200-300 km were detected. Large-scale ionospheric structures cause an increase in horizontal gradients and difficulties with the carrier phase ambiguity resolution in GPS positioning. In turn, the phase fluctuations can cause cycle-slip effects. At the polar stations, ionospheric structures with TEC enhanced by a factor of 3-5 relative to the background were detected, whereas TEC increased to 5-8 TECU in about 10-15 min. These structures were observed during a storm, as well as during a moderate geomagnetic activity. It can be probably attributed to the polar cap patches. In this study are presented the extended and more detailed analyses of TEC fluctuations in both the northern and southern hemispheres and compare the winter and summer events (November and July 2004 storms). A special attention is given to the features related to TEC fluctuations occur-rence in both hemispheres for conjugated GPS stations. The temporal development of both storms was rather similar. During storms the intensity of irregularities essentially increases and its location expands to equator. Maximal activity of TEC fluctuations took place when IMF Bz component was negative. Storm-time development of TEC fluctuations caused by ionospheric irregularities was controlled by UT. At polar stations TEC fluctuations were more expressed at southern (winter) hemisphere. Over auroral stations the difference of TEC fluctuations oc-currence was less expressed. During storm the strong TEC fluctuations can be registered at subauroral ionosphere (on latitudes lower than 55 CGL). The seasonal effect in this area also took place. Differences and similarities of these storms occurrence of TEC fluctuations with dependence on season are discussed.

Implementation of adiabatic geometric gates with superconducting phase qubits.

PubMed

Peng, Z H; Chu, H F; Wang, Z D; Zheng, D N

2009-01-28

We present an adiabatic geometric quantum computation strategy based on the non-degenerate energy eigenstates in (but not limited to) superconducting phase qubit systems. The fidelity of the designed quantum gate was evaluated in the presence of simulated thermal fluctuations in a superconducting phase qubits circuit and was found to be quite robust against random errors. In addition, it was elucidated that the Berry phase in the designed adiabatic evolution may be detected directly via the quantum state tomography developed for superconducting qubits. We also analyze the effects of control parameter fluctuations on the experimental detection of the Berry phase.

Ultra-wideband microwave photonic phase shifter with configurable amplitude response.

PubMed

Pagani, M; Marpaung, D; Eggleton, B J

2014-10-15

We introduce a new principle that enables separate control of the amplitude and phase of an optical carrier, simply by controlling the power of two stimulated Brillouin scattering (SBS) pumps. This technique is used to implement a microwave photonic phase shifter with record performance, which solves the bandwidth limitation of previous gain-transparent SBS-based phase shifters, while achieving unprecedented minimum power fluctuations, as a function of phase shift. We demonstrate 360° continuously tunable phase shift, with less than 0.25 dB output power fluctuations, over a frequency band from 1.5 to 31 GHz, limited only by the measurement equipment.

Detection limit for rate fluctuations in inhomogeneous Poisson processes

NASA Astrophysics Data System (ADS)

Shintani, Toshiaki; Shinomoto, Shigeru

2012-04-01

Estimations of an underlying rate from data points are inevitably disturbed by the irregular occurrence of events. Proper estimation methods are designed to avoid overfitting by discounting the irregular occurrence of data, and to determine a constant rate from irregular data derived from a constant probability distribution. However, it can occur that rapid or small fluctuations in the underlying density are undetectable when the data are sparse. For an estimation method, the maximum degree of undetectable rate fluctuations is uniquely determined as a phase transition, when considering an infinitely long series of events drawn from a fluctuating density. In this study, we analytically examine an optimized histogram and a Bayesian rate estimator with respect to their detectability of rate fluctuation, and determine whether their detectable-undetectable phase transition points are given by an identical formula defining a degree of fluctuation in an underlying rate. In addition, we numerically examine the variational Bayes hidden Markov model in its detectability of rate fluctuation, and determine whether the numerically obtained transition point is comparable to those of the other two methods. Such consistency among these three principled methods suggests the presence of a theoretical limit for detecting rate fluctuations.

Detection limit for rate fluctuations in inhomogeneous Poisson processes.

PubMed

Shintani, Toshiaki; Shinomoto, Shigeru

2012-04-01

Estimations of an underlying rate from data points are inevitably disturbed by the irregular occurrence of events. Proper estimation methods are designed to avoid overfitting by discounting the irregular occurrence of data, and to determine a constant rate from irregular data derived from a constant probability distribution. However, it can occur that rapid or small fluctuations in the underlying density are undetectable when the data are sparse. For an estimation method, the maximum degree of undetectable rate fluctuations is uniquely determined as a phase transition, when considering an infinitely long series of events drawn from a fluctuating density. In this study, we analytically examine an optimized histogram and a Bayesian rate estimator with respect to their detectability of rate fluctuation, and determine whether their detectable-undetectable phase transition points are given by an identical formula defining a degree of fluctuation in an underlying rate. In addition, we numerically examine the variational Bayes hidden Markov model in its detectability of rate fluctuation, and determine whether the numerically obtained transition point is comparable to those of the other two methods. Such consistency among these three principled methods suggests the presence of a theoretical limit for detecting rate fluctuations.

Preliminary measurements of the edge magnetic field pitch from 2-D Doppler backscattering in MAST and NSTX-U (invited)

NASA Astrophysics Data System (ADS)

Vann, R. G. L.; Brunner, K. J.; Ellis, R.; Taylor, G.; Thomas, D. A.

2016-11-01

The Synthetic Aperture Microwave Imaging (SAMI) system is a novel diagnostic consisting of an array of 8 independently phased antennas. At any one time, SAMI operates at one of the 16 frequencies in the range 10-34.5 GHz. The imaging beam is steered in software post-shot to create a picture of the entire emission surface. In SAMI's active probing mode of operation, the plasma edge is illuminated with a monochromatic source and SAMI reconstructs an image of the Doppler back-scattered (DBS) signal. By assuming that density fluctuations are extended along magnetic field lines, and knowing that the strongest back-scattered signals are directed perpendicular to the density fluctuations, SAMI's 2-D DBS imaging capability can be used to measure the pitch of the edge magnetic field. In this paper, we present preliminary pitch angle measurements obtained by SAMI on the Mega Amp Spherical Tokamak (MAST) at Culham Centre for Fusion Energy and on the National Spherical Torus Experiment Upgrade at Princeton Plasma Physics Laboratory. The results demonstrate encouraging agreement between SAMI and other independent measurements.

Preliminary measurements of the edge magnetic field pitch from 2-D Doppler backscattering in MAST and NSTX-U (invited).

PubMed

Vann, R G L; Brunner, K J; Ellis, R; Taylor, G; Thomas, D A

2016-11-01

The Synthetic Aperture Microwave Imaging (SAMI) system is a novel diagnostic consisting of an array of 8 independently phased antennas. At any one time, SAMI operates at one of the 16 frequencies in the range 10-34.5 GHz. The imaging beam is steered in software post-shot to create a picture of the entire emission surface. In SAMI's active probing mode of operation, the plasma edge is illuminated with a monochromatic source and SAMI reconstructs an image of the Doppler back-scattered (DBS) signal. By assuming that density fluctuations are extended along magnetic field lines, and knowing that the strongest back-scattered signals are directed perpendicular to the density fluctuations, SAMI's 2-D DBS imaging capability can be used to measure the pitch of the edge magnetic field. In this paper, we present preliminary pitch angle measurements obtained by SAMI on the Mega Amp Spherical Tokamak (MAST) at Culham Centre for Fusion Energy and on the National Spherical Torus Experiment Upgrade at Princeton Plasma Physics Laboratory. The results demonstrate encouraging agreement between SAMI and other independent measurements.

Observation of subsecond variations in auroral region total electron content using 100 Hz sampling of GPS observables

NASA Astrophysics Data System (ADS)

McCaffrey, A. M.; Jayachandran, P. T.

2017-06-01

First ever auroral region total electron content (TEC) measurements at 100 Hz using a Septentrio PolaRxS Pro receiver are analyzed to discover ionospheric signatures which would otherwise be unobtainable with the frequently used lower sampling rates. Two types of variations are observed: small-magnitude (amplitude) variations, which are present consistently throughout the data set, and larger-magnitude (amplitude) variations, which are less frequent. Small-amplitude TEC fluctuations are accounted for by the receiver phase jitter. However, estimated secondary ionospheric effects in the calculation of TEC and the receiver phase jitter were unable to account for the larger-amplitude TEC fluctuations. These variations are also accompanied by fluctuations in the magnetic field, which seems to indicate that these fluctuations are real and of geophysical significance. This paper presents a technique and the capability of high-rate TEC measurements in the study of auroral dynamics. Further detailed study is needed to identify the cause of these subsecond TEC fluctuations and associated magnetic field fluctuations.

Quasi-critical fluctuations: a novel state of matter?

PubMed

Bertel, Erminald

2013-05-01

Quasi-critical fluctuations occur close to critical points or close to continuous phase transitions. In three-dimensional systems, precision tuning is required to access the fluctuation regime. Lowering the dimensionality enhances the parameter space for quasi-critical fluctuations considerably. This enables one to make use of novel properties emerging in fluctuating systems, such as giant susceptibilities, Casimir forces or novel quasi-particle interactions. Examples are discussed ranging from simple metal-adsorbate systems to unconventional superconductivity in iron-based superconductors.

THE PHASE COHERENCE OF INTERSTELLAR DENSITY FLUCTUATIONS

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

Burkhart, Blakesley; Lazarian, A.

2016-08-10

Studies of MHD turbulence often investigate the Fourier power spectrum to provide information on the nature of the turbulence cascade. However, the Fourier power spectrum only contains the Fourier amplitudes and rejects all information regarding the Fourier phases. Here, we investigate the utility of two statistical diagnostics for recovering information on Fourier phases in ISM column density maps: the averaged amplitudes of the bispectrum and the phase coherence index (PCI), a new phase technique for the ISM. We create three-dimensional density and two-dimensional column density maps using a set of simulations of isothermal ideal MHD turbulence with a wide rangemore » of sonic and Alfvénic Mach numbers. We find that the bispectrum averaged along different angles with respect to either the k {sub 1} or k {sub 2} axis is primarily sensitive to the sonic Mach number while averaging the bispectral amplitudes over different annuli is sensitive to both the sonic and Alfvénic Mach numbers. The PCI of density suggests that the most correlated phases occur in supersonic sub-Alfvénic turbulence and near the shock scale. This suggests that nonlinear interactions with correlated phases are strongest in shock-dominated regions, in agreement with findings from the solar wind. Our results suggest that the phase information contained in the bispectrum and PCI can be used to find the turbulence parameters in column density maps.« less

Spatial fluctuations in transient creep deformation

NASA Astrophysics Data System (ADS)

Laurson, Lasse; Rosti, Jari; Koivisto, Juha; Miksic, Amandine; Alava, Mikko J.

2011-07-01

We study the spatial fluctuations of transient creep deformation of materials as a function of time, both by digital image correlation (DIC) measurements of paper samples and by numerical simulations of a crystal plasticity or discrete dislocation dynamics model. This model has a jamming or yielding phase transition, around which power law or Andrade creep is found. During primary creep, the relative strength of the strain rate fluctuations increases with time in both cases—the spatially averaged creep rate obeys the Andrade law epsilont ~ t - 0.7, while the time dependence of the spatial fluctuations of the local creep rates is given by Δepsilont ~ t - 0.5. A similar scaling for the fluctuations is found in the logarithmic creep regime that is typically observed for lower applied stresses. We review briefly some classical theories of Andrade creep from the point of view of such spatial fluctuations. We consider these phenomenological, time-dependent creep laws in terms of a description based on a non-equilibrium phase transition separating evolving and frozen states of the system when the externally applied load is varied. Such an interpretation is discussed further by the data collapse of the local deformations in the spirit of absorbing state/depinning phase transitions, as well as deformation-deformation correlations and the width of the cumulative strain distributions. The results are also compared with the order parameter fluctuations observed close to the depinning transition of the 2d linear interface model or the quenched Edwards-Wilkinson equation.

Mesoscopic fluctuations of the population of a qubit in a strong alternating field

NASA Astrophysics Data System (ADS)

Denisenko, M. V.; Satanin, A. M.

2016-12-01

Fluctuations of the population of a Josephson qubit in an alternating field, which is a superposition of electromagnetic pulses with large amplitudes, are studied. It is shown that the relative phase of pulses is responsible for the rate of Landau-Zener transitions and, correspondingly, for the frequency of transitions between adiabatic states. The durations of pulses incident on the qubit are controlled with an accuracy of the field period, which results in strong mesoscopic fluctuations of the population of the qubit. Similar to the magnetic field in mesoscopic physics, the relative phase of pulses can destroy the interference pattern of the population of the qubit. The influence of the duration of the pulse and noise on the revealed fluctuation effects is studied.

Magnetic-field induced quantum critical points of valence transition in Ce- and Yb-based heavy fermions

NASA Astrophysics Data System (ADS)

Watanabe, Shinji; Tsuruta, Atsushi; Miyake, Kazumasa; Flouquet, Jacques

2009-03-01

Valence instability and its critical fluctuations have attracted much attention recently in the heavy-electron systems. Valence fluctuations are essentially charge fluctuations, and it is highly non-trivial how the quantum critical point (QCP) as well as the critical end point is controlled by the magnetic field. To clarify this fundamental issue, we have studied the mechanism of how the critical points of the first-order valence transitions are controlled by the magnetic field [1]. We show that the critical temperature is suppressed to be the QCP by the magnetic field and unexpectedly the QCP exhibits nonmonotonic field dependence in the ground-state phase diagram, giving rise to emergence of metamagnetism even in the intermediate valence-crossover regime. The driving force of the field-induced QCP is clarified to be a cooperative phenomenon of Zeeman effect and Kondo effect, which creates a distinct energy scale from the Kondo temperature. This mechanism explains a peculiar magnetic response in CeIrIn5 and metamagnetic transition in YbXCu4 for X=In as well as a sharp contrast between X=Ag and Cd. We present the novel phenomena under the magnetic field to discuss significance of the proximity of the critical points of the first-order valence transition. [1] S. Watanabe et al. PRL100, (2008) 236401.

Phase separation in artificial vesicles driven by light and curvature

NASA Astrophysics Data System (ADS)

Rinaldin, Melissa; Pomp, Wim; Schmidt, Thomas; Giomi, Luca; Kraft, Daniela; Physics of Life Processes Team; Soft; Bio Mechanics Collaboration; Self-Assembly in Soft Matter Systems Collaboration

The role of phase-demixing in living cells, leading to the lipid-raft hypothesis, has been extensively studied. Lipid domains of higher lipid chain order are proposed to regulate protein spatial organization. Giant Unilamellar Vesicles provide an artificial model to study phase separation. So far temperature was used to initiate the process. Here we introduce a new methodology based on the induction of phase separation by light. To this aim, the composition of the lipid membrane is varied by photo-oxidation of lipids. The control of the process gained by using light allowed us to observe vesicle shape fluctuations during phase-demixing. The presence of fluctuations near the critical mixing point resembles features of a critical process. We quantitatively analyze these fluctuations using a 2d elastic model, from which we can estimate the material parameters such as bending rigidity and surface tension, demonstrating the non-equilibrium critical behaviour. Finally, I will describe recent attempts toward tuning the membrane composition by controlling the vesicle curvature.

On the valence fluctuation in the early actinide metals

DOE PAGES

Soderlind, P.; Landa, A.; Tobin, J. G.; ...

2015-12-15

In this study, recent X-ray measurements suggest a degree of valence fluctuation in plutonium and uranium intermetallics. We are applying a novel scheme, in conjunction with density functional theory, to predict 5f configuration fractions of states with valence fluctuations for the early actinide metals. For this purpose we perform constrained integer f-occupation calculations for the α phases of uranium, neptunium, and plutonium metals. For plutonium we also investigate the δ phase. The model predicts uranium and neptunium to be dominated by the f 3 and f 4 configurations, respectively, with only minor contributions from other configurations. For plutonium (both αmore » and δ phase) the scenario is dramatically different. Here, the calculations predict a relatively even distribution between three valence configurations. The δ phase has a greater configuration fraction of f 6 compared to that of the α phase. The theory is consistent with the interpretations of modern X-ray experiments and we present resonant X-ray emission spectroscopy results for α-uranium.« less

Pacing the phasing of leg and arm movements in breaststroke swimming to minimize intra-cyclic velocity fluctuations

PubMed Central

Roerdink, Melvyn; Huibers, Alja V.; Evers, Lotte L. W.; Beek, Peter J.

2017-01-01

In swimming propelling efficiency is partly determined by intra-cyclic velocity fluctuations. The higher these fluctuations are at a given average swimming velocity, the less efficient is the propulsion. This study explored whether the leg-arm coordination (i.e. phase relation ϕ) within the breaststroke cycle can be influenced with acoustic pacing, and whether the so induced changes are accompanied by changes in intra-cyclic velocity fluctuations. Twenty-six participants were asked to couple their propulsive leg and arm movements to a double-tone metronome beat and to keep their average swimming velocity constant over trials. The metronome imposed five different phase relations ϕi (90, 135, 180, 225 and 270°) of leg-arm coordination. Swimmers adjusted their technique under the influence of the metronome, but failed to comply to the velocity requirement for ϕ = 90 and 135°. For imposed ϕ = 180, 225 and 270°, the intra-cyclic velocity fluctuations increased with increasing ϕ, while average swimming velocity did not differ. This suggests that acoustic pacing may be used to adjust ϕ and thereby performance of breaststroke swimming given the dependence of propelling efficiency on ϕ. PMID:29023496

Pacing the phasing of leg and arm movements in breaststroke swimming to minimize intra-cyclic velocity fluctuations.

PubMed

van Houwelingen, Josje; Roerdink, Melvyn; Huibers, Alja V; Evers, Lotte L W; Beek, Peter J

2017-01-01

In swimming propelling efficiency is partly determined by intra-cyclic velocity fluctuations. The higher these fluctuations are at a given average swimming velocity, the less efficient is the propulsion. This study explored whether the leg-arm coordination (i.e. phase relation ϕ) within the breaststroke cycle can be influenced with acoustic pacing, and whether the so induced changes are accompanied by changes in intra-cyclic velocity fluctuations. Twenty-six participants were asked to couple their propulsive leg and arm movements to a double-tone metronome beat and to keep their average swimming velocity constant over trials. The metronome imposed five different phase relations ϕi (90, 135, 180, 225 and 270°) of leg-arm coordination. Swimmers adjusted their technique under the influence of the metronome, but failed to comply to the velocity requirement for ϕ = 90 and 135°. For imposed ϕ = 180, 225 and 270°, the intra-cyclic velocity fluctuations increased with increasing ϕ, while average swimming velocity did not differ. This suggests that acoustic pacing may be used to adjust ϕ and thereby performance of breaststroke swimming given the dependence of propelling efficiency on ϕ.

Active control on high-order coherence and statistic characterization on random phase fluctuation of two classical point sources.

PubMed

Hong, Peilong; Li, Liming; Liu, Jianji; Zhang, Guoquan

2016-03-29

Young's double-slit or two-beam interference is of fundamental importance to understand various interference effects, in which the stationary phase difference between two beams plays the key role in the first-order coherence. Different from the case of first-order coherence, in the high-order optical coherence the statistic behavior of the optical phase will play the key role. In this article, by employing a fundamental interfering configuration with two classical point sources, we showed that the high- order optical coherence between two classical point sources can be actively designed by controlling the statistic behavior of the relative phase difference between two point sources. Synchronous position Nth-order subwavelength interference with an effective wavelength of λ/M was demonstrated, in which λ is the wavelength of point sources and M is an integer not larger than N. Interestingly, we found that the synchronous position Nth-order interference fringe fingerprints the statistic trace of random phase fluctuation of two classical point sources, therefore, it provides an effective way to characterize the statistic properties of phase fluctuation for incoherent light sources.

A study of geomagnetic storms

NASA Technical Reports Server (NTRS)

Patel, V. L.

1975-01-01

Twenty-one geomagnetic storm events during 1966 and 1970 were studied by using simultaneous interplanetary magnetic field and plasma parameters. Explorer 33 and 35 field and plasma data were analyzed on large-scale (hourly) and small-scale (3 min.) during the time interval coincident with initial phase of the geomagnetic storms. The solar-ecliptic Bz component turns southward at the end of the initial phase, thus triggering the main phase decrease in Dst geomagnetic field. When the Bz is already negative, its value becomes further negative. The By component also shows large fluctuations along with Bz. When there are no clear changes in the Bz component, the By shows abrupt changes at the main phase onet. On the small-scale behavior of the magnetic field and electric field (E=-VxB) studied in details for the three events, it is found that the field fluctuations in By, Bz and Ey and Ez are present in the initial phase. These fluctuations become larger just before the main phase of the storm begins. In the largescale behavior field remains quiet because the small scale variations are averaged out.

Metal-insulator transition and magnetic fluctuations in polycrystalline Ru1 -xRhxP investigated by 31P NMR

NASA Astrophysics Data System (ADS)

Li, Shang; Kobayashi, Yoshiaki; Itoh, Masayuki; Hirai, Daigorou; Takagi, Hidenori

2017-04-01

31P NMR measurements have been made on polycrystalline samples to study a metal-insulator (MI) transition and magnetic fluctuations in Ru1 -xRhxP which has metallic (M), pseudogap (PG), insulating (I), and superconducting (SC) phases. We find that RuP undergoes a crossover from the high-temperature (high-T ) M phase to the PG phase with the pseudo spin-gap behavior probed by the nuclear spin-lattice relaxation rate at TPG=330 K . The first-order MI transition is observed to take place from the PG phase to the low-T nonmagnetic I phase with the spin-gap energy of 1250 K at TMI=270 K . In the PG phase of Ru1 -xRhxP with 0 ≤x <0.45 , an analysis based on the modified Korringa relation, which is applicable to an itinerant paramagnet with weak electron correlation, shows that antiferromagnetic (AFM) fluctuations described in the random-phase approximation are enhanced in the low-T and low-x region. Around the PG-M phase boundary at xc˜0.45 , there is the SC phase whose normal state has negligible electron-electron interaction. We discuss the MI transition, the crossover from the M phase to the PG phase, and the magnetic properties of each phase based on the band structure.

Quantum correlations in microwave frequency combs

NASA Astrophysics Data System (ADS)

Weissl, Thomas; Jolin, Shan W.; Haviland, David B.; Department of Applied Physics Team

Non-linear superconducting resonators are used as parametric amplifiers in circuit quantum electrodynamics experiments. When a strong pump is applied to a non-linear microwave oscillator, it correlates vacuum fluctuations at signal and idler frequencies symmetrically located around the pump, resulting in two-mode squeezed vacuum. When the non-linear oscillator is pumped with a frequency comb, complex multipartite entangled states can be created as demonstrated with experiments in the optical domain. Such cluster states are considered to be a universal resource for one-way quantum computing. With our microwave measurement setup it is possible to pump and measure response at as many as 42 frequencies in parallel, with independent control over all pump amplitudes and phases. We show results of two-mode squeezing for of pairs of tones in a microwave frequency comb. The squeezing is created by four-wave mixing of a pump tone applied to a non-linear coplanar-waveguide resonator. We acknowledge financial support from the Knut and Alice Wallenberg foundation.

Algorithm for Screening Phasor Measurement Unit Data for Power System Events and Categories and Common Characteristics for Events Seen in Phasor Measurement Unit Relative Phase-Angle Differences and Frequency Signals

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

Allen, A.; Santoso, S.; Muljadi, E.

2013-08-01

A network of multiple phasor measurement units (PMU) was created, set up, and maintained at the University of Texas at Austin to obtain actual power system measurements for power system analysis. Power system analysis in this report covers a variety of time ranges, such as short- term analysis for power system disturbances and their effects on power system behavior and long- term power system behavior using modal analysis. The first objective of this report is to screen the PMU data for events. The second objective of the report is to identify and describe common characteristics extracted from power system eventsmore » as measured by PMUs. The numerical characteristics for each category and how these characteristics are used to create selection rules for the algorithm are also described. Trends in PMU data related to different levels and fluctuations in wind power output are also examined.« less

Current Fluctuations in Stochastic Lattice Gases

NASA Astrophysics Data System (ADS)

Bertini, L.; de Sole, A.; Gabrielli, D.; Jona-Lasinio, G.; Landim, C.

2005-01-01

We study current fluctuations in lattice gases in the macroscopic limit extending the dynamic approach for density fluctuations developed in previous articles. More precisely, we establish a large deviation theory for the space-time fluctuations of the empirical current which include the previous results. We then estimate the probability of a fluctuation of the average current over a large time interval. It turns out that recent results by Bodineau and Derrida [Phys. Rev. Lett.922004180601] in certain cases underestimate this probability due to the occurrence of dynamical phase transitions.

Viking S-band Doppler RMS phase fluctuations used to calibrate the mean 1976 equatorial corona

NASA Technical Reports Server (NTRS)

Berman, A. L.; Wackley, J. A.

1977-01-01

Viking S-band Doppler RMS phase fluctuations (noise) and comparisons of Viking Doppler noise to Viking differenced S-X range measurements are used to construct a mean equatorial electron density model for 1976. Using Pioneer Doppler noise results (at high heliographic latitudes, also from 1976), an equivalent nonequatorial electron density model is approximated.

Fluctuations and the QCD Phase Diagram

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

Koch, Volker; Bzdak, Adam

2016-07-01

Here, we will discuss how the study of various fluctuation observables may be used to explore the phase diagram of the strong interaction. Furthermore, we will briefly summarize the present study of experimental and theoretical research in this area. We will then discuss various corrections and issues which need to be understood and applied for a meaningful comparison of experimental measurements with theoretical predictions.

Drift of Phase Fluctuations in the ABC Model

NASA Astrophysics Data System (ADS)

Bertini, Lorenzo; Buttà, Paolo

2013-07-01

In a recent work, Bodineau and Derrida analyzed the phase fluctuations in the ABC model. In particular, they computed the asymptotic variance and, on the basis of numerical simulations, they conjectured the presence of a drift, which they guessed to be an antisymmetric function of the three densities. By assuming the validity of the fluctuating hydrodynamic approximation, we prove the presence of such a drift, providing an analytical expression for it. This expression is then shown to be an antisymmetric function of the three densities. The antisymmetry of the drift can also be inferred from a symmetry property of the underlying microscopic dynamics.

Nanosecond X-ray Photon Correlation Spectroscopy on Magnetic Skyrmions

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

Seaberg, M. H.; Holladay, B.; Lee, J. C. T.

We report an X-ray photon correlation spectroscopy method that exploits the recent development of the two-pulse mode at the Linac Coherent Light Source. By using coherent resonant X-ray magnetic scattering, we studied spontaneous fluctuations on nanosecond timescales in thin films of multilayered Fe/Gd that exhibit ordered stripe and skyrmion lattice phases. The correlation time of the fluctuations was found to differ between the skyrmion phase and near the stripe-skyrmion boundary. As a result, this technique will enable a significant new area of research on the study of equilibrium fluctuations in condensed matter.

Nonadiabatic fluctuation in the measured geometric phase

NASA Astrophysics Data System (ADS)

Ai, Qing; Huo, Wenyi; Long, Gui Lu; Sun, C. P.

2009-08-01

We study how the nonadiabatic effect causes the observable fluctuation in the “geometric phase” for a two-level system, which is defined as the experimentally measurable quantity in the adiabatic limit. From the Rabi exact solution to this model, we give a reasonable explanation to the experimental discovery of phase fluctuation in the superconducting circuit system [P. J. Leek, J. M. Fink, A. Blais, R. Bianchetti, M. Göppl, J. M. Gambetta, D. I. Schuster, L. Frunzio, R. J. Schoelkopf, and A. Wallraf, Science 318, 1889 (2007)], which seemed to be regarded as the conventional experimental error.

Nanosecond X-ray Photon Correlation Spectroscopy on Magnetic Skyrmions

DOE PAGES

Seaberg, M. H.; Holladay, B.; Lee, J. C. T.; ...

2017-08-09

We report an X-ray photon correlation spectroscopy method that exploits the recent development of the two-pulse mode at the Linac Coherent Light Source. By using coherent resonant X-ray magnetic scattering, we studied spontaneous fluctuations on nanosecond timescales in thin films of multilayered Fe/Gd that exhibit ordered stripe and skyrmion lattice phases. The correlation time of the fluctuations was found to differ between the skyrmion phase and near the stripe-skyrmion boundary. As a result, this technique will enable a significant new area of research on the study of equilibrium fluctuations in condensed matter.

Fluctuation-exchange study of antiferromagnetism in disordered electron-doped cuprate superconductors.

PubMed

Yan, Xin-Zhong; Ting, C S

2006-08-11

On the basis of the Hubbard model, we extend the fluctuation-exchange (FLEX) approach to investigating the properties of the antiferromagnetic (AF) phase in electron-doped cuprate superconductors. Furthermore, by incorporating the effect of scatterings due to the disordered dopant atoms into the FLEX formalism, our numerical results show that the antiferromagnetic transition temperature, the onset temperature of pseudogap due to spin fluctuations, the spectral density of the single particle near the Fermi surface, and the staggered magnetization in the AF phase as a function of electron doping can consistently account for the experimental measurements.

Characterizing the correlations between local phase fractions of gas-liquid two-phase flow with wire-mesh sensor.

PubMed

Tan, C; Liu, W L; Dong, F

2016-06-28

Understanding of flow patterns and their transitions is significant to uncover the flow mechanics of two-phase flow. The local phase distribution and its fluctuations contain rich information regarding the flow structures. A wire-mesh sensor (WMS) was used to study the local phase fluctuations of horizontal gas-liquid two-phase flow, which was verified through comparing the reconstructed three-dimensional flow structure with photographs taken during the experiments. Each crossing point of the WMS is treated as a node, so the measurement on each node is the phase fraction in this local area. An undirected and unweighted flow pattern network was established based on connections that are formed by cross-correlating the time series of each node under different flow patterns. The structure of the flow pattern network reveals the relationship of the phase fluctuations at each node during flow pattern transition, which is then quantified by introducing the topological index of the complex network. The proposed analysis method using the WMS not only provides three-dimensional visualizations of the gas-liquid two-phase flow, but is also a thorough analysis for the structure of flow patterns and the characteristics of flow pattern transition. This article is part of the themed issue 'Supersensing through industrial process tomography'. © 2016 The Author(s).

Characterizing the correlations between local phase fractions of gas–liquid two-phase flow with wire-mesh sensor

PubMed Central

Liu, W. L.; Dong, F.

2016-01-01

Understanding of flow patterns and their transitions is significant to uncover the flow mechanics of two-phase flow. The local phase distribution and its fluctuations contain rich information regarding the flow structures. A wire-mesh sensor (WMS) was used to study the local phase fluctuations of horizontal gas–liquid two-phase flow, which was verified through comparing the reconstructed three-dimensional flow structure with photographs taken during the experiments. Each crossing point of the WMS is treated as a node, so the measurement on each node is the phase fraction in this local area. An undirected and unweighted flow pattern network was established based on connections that are formed by cross-correlating the time series of each node under different flow patterns. The structure of the flow pattern network reveals the relationship of the phase fluctuations at each node during flow pattern transition, which is then quantified by introducing the topological index of the complex network. The proposed analysis method using the WMS not only provides three-dimensional visualizations of the gas–liquid two-phase flow, but is also a thorough analysis for the structure of flow patterns and the characteristics of flow pattern transition. This article is part of the themed issue ‘Supersensing through industrial process tomography’. PMID:27185959

Simultaneous Global Positioning System observations of equatorial scintillations and total electron content fluctuations

NASA Astrophysics Data System (ADS)

Beach, Theodore L.; Kintner, Paul M.

1999-10-01

One aspect of the Global Positioning System (GPS) is the potential to conduct geophysical research, and worldwide networks of GPS receivers have been established to exploit this potential. Several research groups have begun using this global GPS data to study ionospheric total electron content (TEC) variations, also referred to as GPS phase fluctuations, as surrogates for ionospheric scintillations. This paper investigates the relationship between GPS amplitude scintillations and TEC variations for the same line of sight using observations from Ancón, Peru. These observations were taken under equatorial spread F conditions for three nights in April 1997. As expected, only when the spectrum of TEC fluctuations includes significant power at the Fresnel scale do scintillations appear. We also find that when the TEC fluctuation spectrum includes the Fresnel scale, the S4 scintillation index is roughly proportional to measures of TEC fluctuation for the weak scintillations observed. The proportionality constant varies from night to night, however, casting doubt on the ability to predict GPS S4 successfully from TEC fluctuation data alone. We also present a simple theoretical phase screen model and show that if a relationship between TEC fluctuation measures and S4 exists, that relationship depends on the power spectrum of phase variations at the screen. Unfortunately, the available TEC data, at 30 s per sample (with some aliasing apparently permitted), offer limited spectral information. A preliminary comparison of 1 s/sample data with the same data decimated to a 30 s/sample interval suggests, however, that the level of successful S4 prediction, based on TEC fluctuation measures alone, is comparable at either sample rate.

Fluctuations of conserved charges in relativistic heavy ion collisions: An introduction

NASA Astrophysics Data System (ADS)

Asakawa, Masayuki; Kitazawa, Masakiyo

2016-09-01

Bulk fluctuations of conserved charges measured by event-by-event analysis in relativistic heavy ion collisions are observables which are believed to carry significant amount of information on the hot medium created by the collisions. Active studies have been done recently experimentally, theoretically, and on the lattice. In particular, non-Gaussianity of the fluctuations has acquired much attention recently. In this review, we give a pedagogical introduction to these issues, and survey recent developments in this field of research. Starting from the definition of cumulants, basic concepts in fluctuation physics, such as thermal fluctuations in statistical mechanics and time evolution of fluctuations in diffusive systems, are described. Phenomena which are expected to occur in finite temperature and/or density QCD matter and their measurement by event-by-event analyses are also elucidated.

Emergence of Quantum Phase-Slip Behaviour in Superconducting NbN Nanowires: DC Electrical Transport and Fabrication Technologies.

PubMed

Constantino, Nicolas G N; Anwar, Muhammad Shahbaz; Kennedy, Oscar W; Dang, Manyu; Warburton, Paul A; Fenton, Jonathan C

2018-06-16

Superconducting nanowires undergoing quantum phase-slips have potential for impact in electronic devices, with a high-accuracy quantum current standard among a possible toolbox of novel components. A key element of developing such technologies is to understand the requirements for, and control the production of, superconducting nanowires that undergo coherent quantum phase-slips. We present three fabrication technologies, based on using electron-beam lithography or neon focussed ion-beam lithography, for defining narrow superconducting nanowires, and have used these to create nanowires in niobium nitride with widths in the range of 20⁻250 nm. We present characterisation of the nanowires using DC electrical transport at temperatures down to 300 mK. We demonstrate that a range of different behaviours may be obtained in different nanowires, including bulk-like superconducting properties with critical-current features, the observation of phase-slip centres and the observation of zero conductance below a critical voltage, characteristic of coherent quantum phase-slips. We observe critical voltages up to 5 mV, an order of magnitude larger than other reports to date. The different prominence of quantum phase-slip effects in the various nanowires may be understood as arising from the differing importance of quantum fluctuations. Control of the nanowire properties will pave the way for routine fabrication of coherent quantum phase-slip nanowire devices for technology applications.

Dynamics of the Ili delta with consideration of fluctuations of the level of Lake Balkhash

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

Abdrasilov, S.A.; Tulebaeva, K.A.

1995-02-01

This article examines the dynamics of the Ili delta region of Russia, with consideration of the fluctuations of the level of Lake Balkhash. Level fluctuations over a period of approximately 700 years are reviewed, and numerical data is presented. It is shown that the dynamics of the delta region affect both the amplitude and duration of the cycle of fluctuations of the lake level. In particular, the phase of the delta cycle that started cuts off the peak of the maximum ordinate of the level at the end of the tranasgressive period reduces still more the minimum elevations of themore » lake level at the end of the regressive period. It also accelerates the time of occurence of individual phases of the intrasecular cycle.« less

Mesoscopic fluctuations of the population of a qubit in a strong alternating field

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

Denisenko, M. V., E-mail: mar.denisenko@gmail.com; Satanin, A. M.

Fluctuations of the population of a Josephson qubit in an alternating field, which is a superposition of electromagnetic pulses with large amplitudes, are studied. It is shown that the relative phase of pulses is responsible for the rate of Landau–Zener transitions and, correspondingly, for the frequency of transitions between adiabatic states. The durations of pulses incident on the qubit are controlled with an accuracy of the field period, which results in strong mesoscopic fluctuations of the population of the qubit. Similar to the magnetic field in mesoscopic physics, the relative phase of pulses can destroy the interference pattern of themore » population of the qubit. The influence of the duration of the pulse and noise on the revealed fluctuation effects is studied.« less

Tunneling probe of fluctuating superconductivity in disordered thin films

NASA Astrophysics Data System (ADS)

Dentelski, David; Frydman, Aviad; Shimshoni, Efrat; Dalla Torre, Emanuele G.

2018-03-01

Disordered thin films close to the superconductor-insulator phase transition (SIT) hold the key to understanding quantum phase transition in strongly correlated materials. The SIT is governed by superconducting quantum fluctuations, which can be revealed, for example, by tunneling measurements. These experiments detect a spectral gap, accompanied by suppressed coherence peaks, on both sides of the transition. Here we describe the insulating side in terms of a fluctuating superconducting field with finite-range correlations. We perform a controlled diagrammatic resummation and derive analytic expressions for the tunneling differential conductance. We find that short-range superconducting fluctuations suppress the coherence peaks even in the presence of long-range correlations. Our approach offers a quantitative description of existing measurements on disordered thin films and accounts for tunneling spectra with suppressed coherence peaks.

Dynamical properties of nematic liquid crystals subjected to shear flow and magnetic fields: tumbling instability and nonequilibrium fluctuations.

PubMed

Fatriansyah, Jaka Fajar; Orihara, Hiroshi

2013-07-01

We investigate the dynamical properties of monodomain nematic liquid crystals under shear flow and magnetic fields on the basis of the Ericksen-Leslie theory. Stable and unstable states appear depending on the magnetic field and the shear rate. The trajectory of the unstable state shows tumbling motion. The phase diagram of these states is plotted as a function of the three components of the magnetic field at a constant shear rate. The phase diagram changes depending on the viscous properties of different types of nematic liquid crystals. In this nonequilibrium steady state, we calculate the correlation function of director fluctuations and the response function, and discuss the nonequilibrium fluctuations and the modified fluctuation-dissipation relation in connection with nonconservative forces due to shear flow.

Simultaneous Ka-Band Site Characterization: Goldstone, CA, White Sands, NM, and Guam, USA

NASA Technical Reports Server (NTRS)

Acosta, Roberto; Morse, Jacquelynne; Zemba, Michael; Nessel, James; Morabito, David; Caroglanian, Armen

2011-01-01

To statistically characterize atmospheric effects on Ka-band links at NASA operational sites, NASA has constructed site test interferometers (STI s) which directly measure the tropospheric phase stability and rain attenuation. These instruments observe an unmodulated beacon signal broadcast from a geostationary satellite (e.g., Anik F2) and measure the phase difference between the signals received by the two antennas and its signal attenuation. Three STI s have been deployed so far: the first one at the NASA Deep Space Network Tracking Complex in Goldstone, California (May 2007); the second at the NASA White Sands Complex, in Las Cruses, New Mexico (February 2009); and the third at the NASA Tracking and Data Relay Satellite (TDRS) Remote Ground Terminal (GRGT) complex in Guam (May 2010). Two station-years of simultaneous atmospheric phase fluctuation data have been collected at Goldstone and White Sands, while one year of data has been collected in Guam. With identical instruments operating simultaneously, we can directly compare the phase stability and rain attenuation at the three sites. Phase stability is analyzed statistically in terms of the root-mean-square (rms) of the tropospheric induced time delay fluctuations over 10 minute blocks. For two years, the time delay fluctuations at the DSN site in Goldstone, CA, have been better than 2.5 picoseconds (ps) for 90% of the time (with reference to zenith), meanwhile at the White Sands, New Mexico site, the time delay fluctuations have been better than 2.2 ps with reference to zenith) for 90% of time. For Guam, the time delay fluctuations have been better than 12 ps (reference to zenith) at 90% of the time, the higher fluctuations are as expected from a high humidity tropical rain zone. This type of data analysis, as well as many other site quality characteristics (e.g., rain attenuation, infrastructure, etc.) will be used to determine the suitability of all the sites for NASA s future communication services at Ka-band.

Nonlinear dynamics of mushy layers induced by external stochastic fluctuations.

PubMed

Alexandrov, Dmitri V; Bashkirtseva, Irina A; Ryashko, Lev B

2018-02-28

The time-dependent process of directional crystallization in the presence of a mushy layer is considered with allowance for arbitrary fluctuations in the atmospheric temperature and friction velocity. A nonlinear set of mushy layer equations and boundary conditions is solved analytically when the heat and mass fluxes at the boundary between the mushy layer and liquid phase are induced by turbulent motion in the liquid and, as a result, have the corresponding convective form. Namely, the 'solid phase-mushy layer' and 'mushy layer-liquid phase' phase transition boundaries as well as the solid fraction, temperature and concentration (salinity) distributions are found. If the atmospheric temperature and friction velocity are constant, the analytical solution takes a parametric form. In the more common case when they represent arbitrary functions of time, the analytical solution is given by means of the standard Cauchy problem. The deterministic and stochastic behaviour of the phase transition process is analysed on the basis of the obtained analytical solutions. In the case of stochastic fluctuations in the atmospheric temperature and friction velocity, the phase transition interfaces (mushy layer boundaries) move faster than in the deterministic case. A cumulative effect of these noise contributions is revealed as well. In other words, when the atmospheric temperature and friction velocity fluctuate simultaneously due to the influence of different external processes and phenomena, the phase transition boundaries move even faster. This article is part of the theme issue 'From atomistic interfaces to dendritic patterns'.This article is part of the theme issue 'From atomistic interfaces to dendritic patterns'. © 2018 The Author(s).

The temporal power spectrum of atmospheric fluctuations due to water vapor

NASA Astrophysics Data System (ADS)

Lay, O. P.

1997-05-01

Irregular variations in the refractivity of the atmosphere cause fluctuations in the phase measured by interferometers, limiting the spatial resolution that can be obtained. For frequencies up to the far infrared, water vapor is the dominant cause of the variations. The temporal power spectrum of the phase fluctuations is needed to assess correction schemes such as phase referencing using a nearby calibrator and water vapor radiometry. A model is developed for the temporal power spectrum of phase fluctuations measured by an interferometer through a layer of Kolmogorov turbulence of arbitrary thickness. It is found that both the orientation of the baseline with respect to the wind direction and the elevation of the observations can have a large effect on the temporal power spectrum. Plots of the spectral density distribution, where the area under the curve is proportional to phase power, show that substantial contributions from length scales as long as 100 times the interferometer baseline are possible. The model is generally consistent with data from the 12-GHz phase monitor at the Owens Valley Radio Observatory, and allows the data to be extrapolated to an arbitrary baseline, observing frequency and elevation. There is some evidence that there can be more than one component of turbulence present at a given time for the Owens Valley. The validity of the frozen turbulence assumption and the geometrical optics approximation is discussed and found to be reasonable under most conditions. The models and data presented here form the basis of an analysis of phase calibration and water vapor radiometry \\cite[(Lay 1997)]{lay96}.

Electromagnetic fluctuations generated in the boundary layer of laboratory-created ionospheric depletions

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

Liu, Yu; Lei, Jiuhou, E-mail: leijh@ustc.edu.cn; Collaborative Innovation Center of Astronautical Science and Technology, Harbin 150001

Ionospheric depletions, produced by release of attachment chemicals into the ionosphere, were widely investigated and taken as a potential technique for the artificial modification of space weather. In this work, we reported the experimental evidence of spontaneously generated electromagnetic fluctuations in the boundary layer of laboratory-created ionospheric depletions. These depletions were produced by releasing attachment chemicals into the ambient plasmas. Electron density gradients and sheared flows arose in the boundary layer between the ambient and the negative ions plasmas. These generated electromagnetic fluctuations with fundamental frequency f{sub 0} = 70 kHz lie in the lower hybrid frequency range, and the mode propagates withmore » angles smaller than 90° (0.3π–0.4π) relative to the magnetic field. Our results revealed that these observed structures were most likely due to electromagnetic components of the electron-ion hybrid instability. This research demonstrates that electromagnetic fluctuations also can be excited during active release experiments, which should be considered as an essential ingredient in the boundary layer processes of ionospheric depletions.« less

Two Stochastic Phases of Tick-wise Price Fluctuation and the Price Prediction Generator

NASA Astrophysics Data System (ADS)

Tanaka-Yamawaki, Mieko; Tokuoka, Seiji

2007-07-01

We report in this paper the existence of two different stochastic phases in the tick-wise price fluctuations. Based on this observation, we improve our old method of developing the evolutional strategy to predict the direction of the tick-wise price movements. We obtain a stable predictive power even in the region where the old method had a difficulty.

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

Xia, Zhenwei; Yang, Weihong, E-mail: whyang@ustc.edu.cn

By using analytical method, the exact solutions of the incompressible dissipative Hall magnetohydrodynamics (MHD) equations are derived. It is found that a phase difference may occur between the velocity and magnetic field fluctuations when the kinetic and magnetic Reynolds numbers are both very large. Since velocity and magnetic field fluctuations are both circular polarized, the phase difference makes them no longer parallel or anti-parallel like that in the incompressible ideal Hall MHD.

Phase separation and large deviations of lattice active matter

NASA Astrophysics Data System (ADS)

Whitelam, Stephen; Klymko, Katherine; Mandal, Dibyendu

2018-04-01

Off-lattice active Brownian particles form clusters and undergo phase separation even in the absence of attractions or velocity-alignment mechanisms. Arguments that explain this phenomenon appeal only to the ability of particles to move persistently in a direction that fluctuates, but existing lattice models of hard particles that account for this behavior do not exhibit phase separation. Here we present a lattice model of active matter that exhibits motility-induced phase separation in the absence of velocity alignment. Using direct and rare-event sampling of dynamical trajectories, we show that clustering and phase separation are accompanied by pronounced fluctuations of static and dynamic order parameters. This model provides a complement to off-lattice models for the study of motility-induced phase separation.

Non-equilibrium time evolution of higher order cumulants of conserved charges and event-by-event analysis

NASA Astrophysics Data System (ADS)

Kitazawa, Masakiyo; Asakawa, Masayuki; Ono, Hirosato

2014-01-01

We investigate the time evolution of higher order cumulants of conserved charges in a volume with the diffusion master equation. Applying the result to the diffusion of non-Gaussian fluctuations in the hadronic stage of relativistic heavy ion collisions, we show that the fourth-order cumulant of net-electric charge at LHC energy is suppressed compared with the recently observed second-order cumulant at ALICE, if the higher order cumulants at hadronization are suppressed compared with their values in the hadron phase in equilibrium. The significance of the experimental information on the rapidity window dependence of various cumulants in investigating the history of the dynamical evolution of the hot medium created in relativistic heavy ion collisions is emphasized.

Forces and mechanical energy fluctuations during diagonal stride roller skiing; running on wheels?

PubMed

Kehler, Alyse L; Hajkova, Eliska; Holmberg, Hans-Christer; Kram, Rodger

2014-11-01

Mechanical energy can be conserved during terrestrial locomotion in two ways: the inverted pendulum mechanism for walking and the spring-mass mechanism for running. Here, we investigated whether diagonal stride cross-country roller skiing (DIA) utilizes similar mechanisms. Based on previous studies, we hypothesized that running and DIA would share similar phase relationships and magnitudes of kinetic energy (KE), and gravitational potential energy (GPE) fluctuations, indicating elastic energy storage and return, as if roller skiing is like 'running on wheels'. Experienced skiers (N=9) walked and ran at 1.25 and 3 m s(-1), respectively, and roller skied with DIA at both speeds on a level dual-belt treadmill that recorded perpendicular and parallel forces. We calculated the KE and GPE of the center of mass from the force recordings. As expected, the KE and GPE fluctuated with an out-of-phase pattern during walking and an in-phase pattern during running. Unlike walking, during DIA, the KE and GPE fluctuations were in phase, as they are in running. However, during the glide phase, KE was dissipated as frictional heat and could not be stored elastically in the tendons, as in running. Elastic energy storage and return epitomize running and thus we reject our hypothesis. Diagonal stride cross-country skiing is a biomechanically unique movement that only superficially resembles walking or running. © 2014. Published by The Company of Biologists Ltd.

The effect of neutrally buoyant finite-size particles on channel flows in the laminar-turbulent transition regime

NASA Astrophysics Data System (ADS)

Loisel, Vincent; Abbas, Micheline; Masbernat, Olivier; Climent, Eric

2013-12-01

The presence of finite-size particles in a channel flow close to the laminar-turbulent transition is simulated with the Force Coupling Method which allows two-way coupling with the flow dynamics. Spherical particles with channel height-to-particle diameter ratio of 16 are initially randomly seeded in a fluctuating flow above the critical Reynolds number corresponding to single phase flow relaminarization. When steady-state is reached, the particle volume fraction is homogeneously distributed in the channel cross-section (ϕ ≅ 5%) except in the near-wall region where it is larger due to inertia-driven migration. Turbulence statistics (intensity of velocity fluctuations, small-scale vortical structures, wall shear stress) calculated in the fully coupled two-phase flow simulations are compared to single-phase flow data in the transition regime. It is observed that particles increase the transverse r.m.s. flow velocity fluctuations and they break down the flow coherent structures into smaller, more numerous and sustained eddies, preventing the flow to relaminarize at the single-phase critical Reynolds number. When the Reynolds number is further decreased and the suspension flow becomes laminar, the wall friction coefficient recovers the evolution of the laminar single-phase law provided that the suspension viscosity is used in the Reynolds number definition. The residual velocity fluctuations in the suspension correspond to a regime of particulate shear-induced agitation.

Quasi-One-Dimensional Ultracold Fermi Gases

NASA Astrophysics Data System (ADS)

Revelle, Melissa C.

Ultracold atoms have become an essential tool in studying condensed matter phenomena. The advantage of atomic physics experiments is that they provide an easily tunable system. This experiment uses the lowest two ground state hyperfine levels of fermionic lithium. Having two different states creates a pseudo-spin- 1/2 system and allows us to emulate electronic systems, such as superconductors and crystal lattices. In our experiment, we can control the ratio between these two states resulting in either a spin-balanced or a spin-imbalanced gas. Imposing an imbalance is analogous to applying a magnetic field to a superconductor which causes the electrons in the material to align to the field (thus breaking the electron pairs which cause superconductivity). This motivates us to understand the phases created when a spin-imbalance is created and the effect of changing the atomic interactions. In a 3D system, we find where superfluidity is suppressed throughout the BEC to BCS crossover. Using phase separation as a guide, we probe the dimensional crossover between 1D and 3D. The phase separation in 1D is inverted from that in 3D, which provides a unique characteristic to distinguish between the dimensions. By varying the tunneling between tubes and the atomic interactions in a 2D optical lattice, we control whether the system is 1D, 3D, or in between. Using the properties of a 3D gas as a guide, we directly observe when the gas has crossed over from being dominated by 1D-like behavior to 3D. In this way, we have found a universal value for the dimensional crossover. The 1D-3D crossover paves the way to search for the exotic FFLO (Fulde-Ferrell-Larkin-Ovchinnikov) superconductor. While most superconductors do not coexist with magnetism, the FFLO phase requires large magnetic fields to support its pairing mechanism. Additionally, this phase is more likely to be found in lower dimensional systems. However, at low dimensions, the effect of temperature fluctuations on the phase is destabilizing, but these temperature effects are reduced with higher dimensionality. Thus, the quasi-1D regime is the optimal region of parameter space to find this phase. The search for direct evidence of FFLO continues in this regime.

Causal Diffusion and the Survival of Charge Fluctuations

NASA Astrophysics Data System (ADS)

Abdel-Aziz, Mohamed; Gavin, Sean

2004-10-01

Diffusion may obliterate fluctuation signals of the QCD phase transition in nuclear collisions at SPS and RHIC energies. We propose a hyperbolic diffusion equation to study the dissipation of net charge fluctuations [1]. This equation is needed in a relativistic context, because the classic parabolic diffusion equation violates causality. We find that causality substantially limits the extent to which diffusion can dissipate these fluctuations. [1] M. Abdel-Aziz and S. Gavin, nucl-th/0404058

Turbulent fluctuations during pellet injection into a dipole confined plasma torus

NASA Astrophysics Data System (ADS)

Garnier, D. T.; Mauel, M. E.; Roberts, T. M.; Kesner, J.; Woskov, P. P.

2017-01-01

We report measurements of the turbulent evolution of the plasma density profile following the fast injection of lithium pellets into the Levitated Dipole Experiment (LDX) [Boxer et al., Nat. Phys. 6, 207 (2010)]. As the pellet passes through the plasma, it provides a significant internal particle source and allows investigation of density profile evolution, turbulent relaxation, and turbulent fluctuations. The total electron number within the dipole plasma torus increases by more than a factor of three, and the central density increases by more than a factor of five. During these large changes in density, the shape of the density profile is nearly "stationary" such that the gradient of the particle number within tubes of equal magnetic flux vanishes. In comparison to the usual case, when the particle source is neutral gas at the plasma edge, the internal source from the pellet causes the toroidal phase velocity of the fluctuations to reverse and changes the average particle flux at the plasma edge. An edge particle source creates an inward turbulent pinch, but an internal particle source increases the outward turbulent particle flux. Statistical properties of the turbulence are measured by multiple microwave interferometers and by an array of probes at the edge. The spatial structures of the largest amplitude modes have long radial and toroidal wavelengths. Estimates of the local and toroidally averaged turbulent particle flux show intermittency and a non-Gaussian probability distribution function. The measured fluctuations, both before and during pellet injection, have frequency and wavenumber dispersion consistent with theoretical expectations for interchange and entropy modes excited within a dipole plasma torus having warm electrons and cool ions.

Turbulent fluctuations during pellet injection into a dipole confined plasma torus

DOE PAGES

Garnier, D. T.; Mauel, M. E.; Roberts, T. M.; ...

2017-01-01

Here, we report measurements of the turbulent evolution of the plasma density profile following the fast injection of lithium pellets into the Levitated Dipole Experiment (LDX) [Boxer et al., Nat. Phys. 6, 207 (2010)]. As the pellet passes through the plasma, it provides a significant internal particle source and allows investigation of density profile evolution, turbulent relaxation, and turbulent fluctuations. The total electron number within the dipole plasma torus increases by more than a factor of three, and the central density increases by more than a factor of five. During these large changes in density, the shape of the densitymore » profile is nearly “stationary” such that the gradient of the particle number within tubes of equal magnetic flux vanishes. In comparison to the usual case, when the particle source is neutral gas at the plasma edge, the internal source from the pellet causes the toroidal phase velocity of the fluctuations to reverse and changes the average particle flux at the plasma edge. An edge particle source creates an inward turbulent pinch, but an internal particle source increases the outward turbulent particle flux. Statistical properties of the turbulence are measured by multiple microwave interferometers and by an array of probes at the edge. The spatial structures of the largest amplitude modes have long radial and toroidal wavelengths. Estimates of the local and toroidally averaged turbulent particle flux show intermittency and a non-Gaussian probability distribution function. The measured fluctuations, both before and during pellet injection, have frequency and wave number dispersion consistent with theoretical expectations for interchange and entropy modes excited within a dipole plasma torus having warm electrons and cool ions.« less

Day-to-day variations in the amplitude of the soil temperature cycle and impact on adult eclosion timing of the onion fly.

PubMed

Tanaka, Kazuhiro; Watari, Yasuhiko

2017-06-01

The onion fly Delia antiqua advances its eclosion timing with decreasing temperature amplitude to compensate for a depth-dependent phase delay of the zeitgeber. To elucidate whether or not naturally occurring day-to-day variations in the amplitude of soil temperature cycle disturb this compensatory response, we monitored daily variations in the temperature amplitude in natural soils and evaluated the impact on adult eclosion timing. Our results indicated that both median and variance of the soil temperature amplitude become smaller as depth increases. Insertion of a larger temperature fluctuation into the thermoperiod with smaller temperature amplitude induced a stronger phase delay, while insertion of a smaller temperature fluctuation into the thermoperiod with larger temperature amplitude had a weaker phase-advancing effect. It is therefore expected that larger diurnal temperature fluctuations disturb the compensatory response, particularly if they occur at deeper locations, while smaller temperature fluctuations do so only at shallower locations. Under natural conditions, however, the probability of occurrence of smaller or larger temperature fluctuations in shallower or deeper soils, respectively, is relatively small. Thus, naturally occurring day-to-day variations in the temperature amplitude rarely disturb the compensatory response, thereby having a subtle or negligible impact on adult eclosion timing.

Fluctuations and QCD phase structure

NASA Astrophysics Data System (ADS)

Kitazawa, Masakiyo

2014-11-01

Fluctuation observables are invaluable tools in relativistic heavy ion collisions to investigate primordial thermodynamics of fireballs. Active experimental measurements have been performed at RHIC and LHC. In particular, interesting experimental results were recently reported on the electric charge fluctuation at ALICE and on the higher order cumulants at STAR, which show nontrivial behaviors reflecting non-hadronic and/or non-thermal physics. We argue that more detailed understanding on these observables are needed to use them effectively in the analysis of QCD phase structure. We suggest that the measurement of various cumulants of conserved charges including baryon number and their rapidity window dependence will provide important information needed for making progress in this subject.

Identifying a correlated spin fluctuation in an entangled spin chain subject to a quantum phase transition.

PubMed

Shimizu, Kaoru; Tokura, Yasuhiro

2015-12-01

This paper presents a theoretical framework for analyzing the quantum fluctuation properties of a quantum spin chain subject to a quantum phase transition. We can quantify the fluctuation properties by examining the correlation between the fluctuations of two neighboring spins subject to the quantum uncertainty. To do this, we first compute the reduced density matrix ρ of the spin pair from the ground state |Ψ⟩ of a spin chain, and then identify the quantum correlation part ρ(q) embedded in ρ. If the spin chain is translationally symmetric and characterized by a nearest-neighbor two-body spin interaction, we can determine uniquely the form of ρ(q) as W|Φ〉〈Φ| with the weight W ≤1, and quantify the fluctuation properties using the two-spin entangled state |Φ〉. We demonstrate the framework for a transverse-field quantum Ising spin chain and indicate its validity for more general spin chain models.

Magnetic fluctuations driven insulator-to-metal transition in Ca(Ir1−xRux)O3

PubMed Central

Gunasekera, J.; Harriger, L.; Dahal, A.; Heitmann, T.; Vignale, G.; Singh, D. K.

2015-01-01

Magnetic fluctuations in transition metal oxides are a subject of intensive research because of the key role they are expected to play in the transition from the Mott insulator to the unconventional metallic phase of these materials, and also as drivers of superconductivity. Despite much effort, a clear link between magnetic fluctuations and the insulator-to-metal transition has not yet been established. Here we report the discovery of a compelling link between magnetic fluctuations and the insulator-to-metal transition in Ca(Ir1−xRux)O3 perovskites as a function of the substitution coefficient x. We show that when the material turns from insulator to metal, at a critical value of x ~ 0.3, magnetic fluctuations tend to change their character from antiferromagnetic, a Mott insulator phase, to ferromagnetic, an itinerant electron state with Hund’s orbital coupling. These results are expected to have wide-ranging implications for our understanding of the unconventional properties of strongly correlated electrons systems. PMID:26647965

Magnetic fluctuations driven insulator-to-metal transition in Ca(Ir(1-x)Rux)O3.

PubMed

Gunasekera, J; Harriger, L; Dahal, A; Heitmann, T; Vignale, G; Singh, D K

2015-12-09

Magnetic fluctuations in transition metal oxides are a subject of intensive research because of the key role they are expected to play in the transition from the Mott insulator to the unconventional metallic phase of these materials, and also as drivers of superconductivity. Despite much effort, a clear link between magnetic fluctuations and the insulator-to-metal transition has not yet been established. Here we report the discovery of a compelling link between magnetic fluctuations and the insulator-to-metal transition in Ca(Ir1-xRux)O3 perovskites as a function of the substitution coefficient x. We show that when the material turns from insulator to metal, at a critical value of x ~ 0.3, magnetic fluctuations tend to change their character from antiferromagnetic, a Mott insulator phase, to ferromagnetic, an itinerant electron state with Hund's orbital coupling. These results are expected to have wide-ranging implications for our understanding of the unconventional properties of strongly correlated electrons systems.

Phase Averaged Measurements of the Coherent Structure of a Mach Number 0.6 Jet. M.S. Thesis

NASA Technical Reports Server (NTRS)

Emami, S.

1983-01-01

The existence of a large scale structure in a Mach number 0.6, axisymmetric jet of cold air was proven. In order to further characterize the coherent structure, phase averaged measurements of the axial mass velocity, radial velocity, and the product of the two were made. These measurements yield information about the percent of the total fluctuations contained in the coherent structure. These measured values were compared to the total fluctuation levels for each quantity and the result expressed as a percent of the total fluctuation level contained in the organized structure at a given frequency. These measurements were performed for five frequencies (St=0.16, 0.32, 0.474, 0.95, and 1.26). All of the phase averaged measurements required that the jet be artificially excited.

Loop corrections to primordial fluctuations from inflationary phase transitions

NASA Astrophysics Data System (ADS)

Wu, Yi-Peng; Yokoyama, Jun'ichi

2018-05-01

We investigate loop corrections to the primordial fluctuations in the single-field inflationary paradigm from spectator fields that experience a smooth transition of their vacuum expectation values. We show that when the phase transition involves a classical evolution effectively driven by a negative mass term from the potential, important corrections to the curvature perturbation can be generated by field perturbations that are frozen outside the horizon by the time of the phase transition, yet the correction to tensor perturbation is naturally suppressed by the spatial derivative couplings between spectator fields and graviton. At one-loop level, the dominant channel for the production of primordial fluctuations comes from a pair-scattering of free spectator fields that decay into the curvature perturbations, and this decay process is only sensitive to field masses comparable to the Hubble scale of inflation.

Multiplicity fluctuation analysis of target residues in nucleus-emulsion collisions at a few hundred MeV/nucleon

NASA Astrophysics Data System (ADS)

Zhang, Dong-Hai; Chen, Yan-Ling; Wang, Guo-Rong; Li, Wang-Dong; Wang, Qing; Yao, Ji-Jie; Zhou, Jian-Guo; Zheng, Su-Hua; Xu, Li-Ling; Miao, Hui-Feng; Wang, Peng

2014-07-01

Multiplicity fluctuation of the target evaporated fragments emitted in 290 MeV/u 12C-AgBr, 400 MeV/u 12C-AgBr, 400 MeV/u 20Ne-AgBr and 500 MeV/u 56Fe-AgBr interactions is investigated using the scaled factorial moment method in two-dimensional normal phase space and cumulative variable space, respectively. It is found that in normal phase space the scaled factorial moment (ln) increases linearly with the increase of the divided number of phase space (lnM)for lower q-value and increases linearly with the increase of lnM, and then becomes saturated or decreased for a higher q-value. In cumulative variable space ln decreases linearly with increase of lnM. This indicates that no evidence of non-statistical multiplicity fluctuation is observed in our data sets. So, any fluctuation indicated in the results of normal variable space analysis is totally caused by the non-uniformity of the single-particle density distribution.

Sound quality characteristics of refrigerator noise in real living environments with relation to psychoacoustical and autocorrelation function parameters.

PubMed

Sato, Shin-ichi; You, Jin; Jeon, Jin Yong

2007-07-01

Psychoacoustical and autocorrelation function (ACF) parameters were employed to describe the temporal fluctuations of refrigerator noise during starting, transition into/from the stationary phase and termination of operation. The temporal fluctuations of refrigerator noise include a click at start-up, followed by a rapid increase in volume, a change of pitch, and termination of the operation. Subjective evaluations of the noise of 24 different refrigerators were conducted in a real living environment. The relationship between objective measures and perceived noisiness was examined by multiple regression analysis. Sound quality indices were developed based on psychoacoustical and ACF parameters. The psychoacoustical parameters found to be important for evaluating noisiness in the stationary phase were loudness and roughness. The relationship between noisiness and ACF parameters shows that sound energy and its fluctuations are important for evaluating noisiness. Also, refrigerator sounds that had a fluctuation of pitch were rated as more annoying. The tolerance level for the starting phase of refrigerator noise was found to be 33 dBA, which is the level where 65% of the participants in the subjective tests were satisfied.

Critical phenomena at the complex tensor ordering phase transition

NASA Astrophysics Data System (ADS)

Boettcher, Igor; Herbut, Igor F.

2018-02-01

We investigate the critical properties of the phase transition towards complex tensor order that has been proposed to occur in spin-orbit-coupled superconductors. For this purpose, we formulate the bosonic field theory for fluctuations of the complex irreducible second-rank tensor order parameter close to the transition. We then determine the scale dependence of the couplings of the theory by means of the perturbative renormalization group (RG). For the isotropic system, we generically detect a fluctuation-induced first-order phase transition. The initial values for the running couplings are determined by the underlying microscopic model for the tensorial order. As an example, we study three-dimensional Luttinger semimetals with electrons at a quadratic band-touching point. Whereas the strong-coupling transition of the model receives substantial fluctuation corrections, the weak-coupling transition at low temperatures is rendered only weakly first order due to the presence of a fixed point in the vicinity of the RG trajectory. If the number of fluctuating complex components of the order parameter is reduced by cubic anisotropy, the theory maps onto the field theory for frustrated magnetism.

Structural phase transition at high temperatures in solid molecular hydrogen and deuterium

NASA Astrophysics Data System (ADS)

Cui, T.; Takada, Y.; Cui, Q.; Ma, Y.; Zou, G.

2001-07-01

We study the effect of temperature up to 1000 K on the structure of dense molecular para-hydrogen (p-H2) and ortho-deuterium (o-D2), using the path-integral Monte Carlo method. We find a structural phase transition from orientationally disordered hexagonal close packed (hcp) to an orthorhombic structure of Cmca symmetry before melting. The transition is basically induced by thermal fluctuations, but quantum fluctuations of protons (deuterons) are important in determining the transition temperature through effectively hardening the intermolecular interaction. We estimate the phase line between hcp and Cmca phases as well as the melting line of the Cmca solid.

Acoustic Fluctuations: Guidelines for R and D Based on the Acoustic Fluctuation Workshop 22-23 February 1978

DTIC Science & Technology

1978-11-28

Noise was sponsored by CNO (OP-95) and supported by Chief of Naval Research (CNR) and held at Woods Hole Oceano - graphic Institute (WHOI) in October...SURFACE ARRAY 1 Sol ’ ARRAY 2 S~BOTTOM (C) Calculate standard deviation of phase-difference fluctuations as a function of integration time, Calculate

Nematic and chiral superconductivity induced by odd-parity fluctuations

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

Wu, Fengcheng; Martin, Ivar

Recent experiments indicate that superconductivity in Bi 2Se 3 intercalated with Cu, Nb, or Sr is nematic with rotational symmetry breaking. Motivated by this observation, we present a model study of nematic and chiral superconductivity induced by odd-parity fluctuations. Additionally, we show that odd-parity fluctuations in the two-component E u representation of D 3d crystal point group can generate attractive interaction in both the even-parity s-wave and odd-parity E-u pairing channels, but repulsive interaction in other odd-parity pairing channels. Coulomb repulsion can suppress s-wave pairing relative to E u pairing, and thus the latter can have a higher critical temperature.more » E u pairing has two distinct phases: a nematic phase and a chiral phase, both of which can be realized in our model. Finally, when s-wave and E u pairings have similar instability temperature, we find an intermediate phase in which both types of pairing coexist.« less

Nematic and chiral superconductivity induced by odd-parity fluctuations

DOE PAGES

Wu, Fengcheng; Martin, Ivar

2017-10-09

Recent experiments indicate that superconductivity in Bi 2Se 3 intercalated with Cu, Nb, or Sr is nematic with rotational symmetry breaking. Motivated by this observation, we present a model study of nematic and chiral superconductivity induced by odd-parity fluctuations. Additionally, we show that odd-parity fluctuations in the two-component E u representation of D 3d crystal point group can generate attractive interaction in both the even-parity s-wave and odd-parity E-u pairing channels, but repulsive interaction in other odd-parity pairing channels. Coulomb repulsion can suppress s-wave pairing relative to E u pairing, and thus the latter can have a higher critical temperature.more » E u pairing has two distinct phases: a nematic phase and a chiral phase, both of which can be realized in our model. Finally, when s-wave and E u pairings have similar instability temperature, we find an intermediate phase in which both types of pairing coexist.« less

The topology of large-scale structure. I - Topology and the random phase hypothesis. [galactic formation models

NASA Technical Reports Server (NTRS)

Weinberg, David H.; Gott, J. Richard, III; Melott, Adrian L.

1987-01-01

Many models for the formation of galaxies and large-scale structure assume a spectrum of random phase (Gaussian), small-amplitude density fluctuations as initial conditions. In such scenarios, the topology of the galaxy distribution on large scales relates directly to the topology of the initial density fluctuations. Here a quantitative measure of topology - the genus of contours in a smoothed density distribution - is described and applied to numerical simulations of galaxy clustering, to a variety of three-dimensional toy models, and to a volume-limited sample of the CfA redshift survey. For random phase distributions the genus of density contours exhibits a universal dependence on threshold density. The clustering simulations show that a smoothing length of 2-3 times the mass correlation length is sufficient to recover the topology of the initial fluctuations from the evolved galaxy distribution. Cold dark matter and white noise models retain a random phase topology at shorter smoothing lengths, but massive neutrino models develop a cellular topology.

Frequency offset locking of AlGaAs semiconductor lasers

NASA Astrophysics Data System (ADS)

Kuboki, Katsuhiko; Ohtsu, Motoichi

1987-04-01

Frequency offset locking is proposed as a technique for tracking and sweeping of a semiconductor laser frequency to improve temporal coherence in semiconductor lasers. Experiments were carried out in which a frequency stabilized laser (of residual frequency fluctuation value of 140 Hz at the integration time between 100 ms and 100 s) was used as a master laser, using a digital phase comparator of a large dynamic range (2 pi x 10 to the 11th rad) in the feedback loop to reduce the phase fluctuations of the beat signal between the master laser and the slave laser. As a result, residual frequency fluctuations of the beat signal were as low as 11 Hz at the integration time of 100 s (i.e., the residual frequency fluctuations of the slave laser were almost equal to those of the master laser).

Large-Scale Chaos and Fluctuations in Active Nematics

NASA Astrophysics Data System (ADS)

Ngo, Sandrine; Peshkov, Anton; Aranson, Igor S.; Bertin, Eric; Ginelli, Francesco; Chaté, Hugues

2014-07-01

We show that dry active nematics, e.g., collections of shaken elongated granular particles, exhibit large-scale spatiotemporal chaos made of interacting dense, ordered, bandlike structures in a parameter region including the linear onset of nematic order. These results are obtained from the study of both the well-known (deterministic) hydrodynamic equations describing these systems and of the self-propelled particle model they were derived from. We prove, in particular, that the chaos stems from the generic instability of the band solution of the hydrodynamic equations. Revisiting the status of the strong fluctuations and long-range correlations in the particle model, we show that the giant number fluctuations observed in the chaotic phase are a trivial consequence of density segregation. However anomalous, curvature-driven number fluctuations are present in the homogeneous quasiordered nematic phase and characterized by a nontrivial scaling exponent.

Influences of climate on aflatoxin producing fungi and aflatoxin contamination.

PubMed

Cotty, Peter J; Jaime-Garcia, Ramon

2007-10-20

Aflatoxins are potent mycotoxins that cause developmental and immune system suppression, cancer, and death. As a result of regulations intended to reduce human exposure, crop contamination with aflatoxins causes significant economic loss for producers, marketers, and processors of diverse susceptible crops. Aflatoxin contamination occurs when specific fungi in the genus Aspergillus infect crops. Many industries frequently affected by aflatoxin contamination know from experience and anecdote that fluctuations in climate impact the extent of contamination. Climate influences contamination, in part, by direct effects on the causative fungi. As climate shifts, so do the complex communities of aflatoxin-producing fungi. This includes changes in the quantity of aflatoxin-producers in the environment and alterations to fungal community structure. Fluctuations in climate also influence predisposition of hosts to contamination by altering crop development and by affecting insects that create wounds on which aflatoxin-producers proliferate. Aflatoxin contamination is prevalent both in warm humid climates and in irrigated hot deserts. In temperate regions, contamination may be severe during drought. The contamination process is frequently broken down into two phases with the first phase occurring on the developing crop and the second phase affecting the crop after maturation. Rain and temperature influence the phases differently with dry, hot conditions favoring the first and warm, wet conditions favoring the second. Contamination varies with climate both temporally and spatially. Geostatistics and multiple regression analyses have shed light on influences of weather on contamination. Geostatistical analyses have been used to identify recurrent contamination patterns and to match these with environmental variables. In the process environmental conditions with the greatest impact on contamination are identified. Likewise, multiple regression analyses allow ranking of environmental variables based on relative influence on contamination. Understanding the impact of climate may allow development of improved management procedures, better allocation of monitoring efforts, and adjustment of agronomic practices in anticipation of global climate change.

Frequency Response of a Protein to Local Conformational Perturbations

PubMed Central

Eren, Dilek; Alakent, Burak

2013-01-01

Signals created by local perturbations are known to propagate long distances through proteins via backbone connectivity and nonbonded interactions. In the current study, signal propagation from the flexible ligand binding loop to the rest of Protein Tyrosine Phosphatase 1B (PTP1B) was investigated using frequency response techniques. Using restrained Targeted Molecular Dynamics (TMD) potential on WPD and R loops, PTP1B was driven between its crystal structure conformations at different frequencies. Propagation of the local perturbation signal was manifested via peaks at the fundamental frequency and upper harmonics of 1/f distributed spectral density of atomic variables, such as Cα atoms, dihedral angles, or polar interaction distances. Frequency of perturbation was adjusted high enough (simulation length >∼10×period of a perturbation cycle) not to be clouded by random diffusional fluctuations, and low enough (<∼0.8 ns−1) not to attenuate the propagating signal and enhance the contribution of the side-chains to the dissipation of the signals. Employing Discrete Fourier Transform (DFT) to TMD simulation trajectories of 16 cycles of conformational transitions at periods of 1.2 to 5 ns yielded Cα displacements consistent with those obtained from crystal structures. Identification of the perturbed atomic variables by statistical t-tests on log-log scale spectral densities revealed the extent of signal propagation in PTP1B, while phase angles of the filtered trajectories at the fundamental frequency were used to cluster collectively fluctuating elements. Hydrophobic interactions were found to have a higher contribution to signal transduction between side-chains compared to the role of polar interactions. Most of in-phase fluctuating residues on the signaling pathway were found to have high identity among PTP domains, and located over a wide region of PTP1B including the allosteric site. Due to its simplicity and efficiency, the suggested technique may find wide applications in identification of signaling pathways of different proteins. PMID:24086121

An experimental study of the velocity-forced flame response of a lean-premixed multi-nozzle can combustor for gas turbines

NASA Astrophysics Data System (ADS)

Szedlmayer, Michael Thomas

The velocity forced flame response of a multi-nozzle, lean-premixed, swirl-stabilized, turbulent combustor was investigated at atmospheric pressure. The purpose of this study was to analyze the mechanisms that allowed velocity fluctuations to cause fluctuations in the rate of heat release in a gas turbine combustor experiencing combustion instability. Controlled velocity fluctuations were introduced to the combustor by a rotating siren device which periodically allowed the air-natural gas mixture to flow. The velocity fluctuation entering the combustor was measured using the two-microphone method. The resulting heat release rate fluctuation was measured using CH* chemiluminescence. The global response of the flame was quantified using the flame transfer function with the velocity fluctuation as the input and the heat release rate fluctuation as the output. Velocity fluctuation amplitude was initially maintained at 5% of the inlet velocity in order to remain in the linear response regime. Flame transfer function measurements were acquired at a wide range of operating conditions and forcing frequencies. The selected range corresponds to the conditions and instability frequencies typical of real gas turbine combustors. Multi-nozzle flame transfer functions were found to bear a qualitative similarity to the single-nozzle flame transfer functions in the literature. The flame transfer function gain exhibited alternating minima and maxima while the phase decreased linearly with increasing forcing frequency. Several normalization techniques were applied to all flame transfer function data in an attempt to collapse the data into a single curve. The best collapse was found to occur using a Strouhal number which was the ratio of the characteristic flame length to the wavelength of the forced disturbance. Critical values of Strouhal number are used to predict the shedding of vortical structures in shear layers. Because of the collapse observed when the flame transfer functions are plotted versus Strouhal number, vortical structures are thought to have a strong influence on the response of this multi-nozzle configuration. The structure of heat release rate fluctuations throughout the flame is analyzed using CH* chemiluminescence acquired with a high speed camera. Flames with a similar level of flame transfer function gain are found to exhibit similarity in the spatial distribution of their heat release rate fluctuations, regardless of the operating condition. Flames with high gain are found to have high amplitude fluctuations near the downstream end of the flame, with weak fluctuations near the flame base. The phase of the downstream fluctuations changes minimally across the downstream region, indicating that they occur inphase. Flames with low gain exhibit stronger fluctuations near the flame base, but weak fluctuations in the downstream region. The phase of the fluctuations near the flame base changes continuously along the flame axis, indicating that parts of the flame will fluctuate out-of-phase. Accordingly, from a global perspective, destructive interference between heat release rate fluctuations in different parts of the flame can be expected. The behavior observed in the flame is ascribed to the interaction of acoustic velocity fluctuations, vortical disturbances and swirl fluctuations. The response of the multi-nozzle flame to high amplitude velocity fluctuations was tested for a single operating condition. Based on the global flame response, most frequencies responded linearly over the tested range of amplitudes. Nonlinear effects were found to occur at three frequencies. The behaviors observed at these frequencies matched those observed in the literature and included flame response saturation and mode triggering. For conditions which responded linearly at all amplitudes, the structure of heat release rate fluctuations was found to remain nearly constant. For conditions with nonlinear behavior, the structure of the fluctuations was a function of the forcing amplitude, particularly in the downstream region. The behavior of the multi-nozzle flame was compared directly to that of a single-nozzle flame of the same nozzle design. The multi-nozzle characteristic flame length was found to be on average 10% longer than for the single-nozzle flame. The flame transfer functions from the two cases were found to exhibit qualitative similarity, where the frequencies at which the extrema occur are similar. The actual value of gain for the same operating condition and frequency does, however, vary by more than a factor of two in some cases. The phase value can also vary by as much as pi radians. These differences indicate that single-nozzle flame transfer functions should not be used directly to predict the instability driving force of real gas turbine combustors.

Statistical anisotropy in free turbulence for mixing layers at high Reynolds numbers

NASA Astrophysics Data System (ADS)

Gardner, Patrick J.; Roggemann, Michael C.; Welsh, Byron M.; Bowersox, Rodney D.; Luke, Theodore E.

1996-08-01

A lateral shearing interferometer was used to measure the slope of perturbed wave fronts after propagating through free turbulent mixing layers. Shearing interferometers provide a two-dimensional flow visualization that is nonintrusive. Slope measurements were used to reconstruct the phase of the turbulence-corrupted wave front. The random phase fluctuations induced by the mixing layer were captured in a large ensemble of wave-front measurements. Experiments were performed on an unbounded, plane shear mixing layer of helium and nitrogen gas at fixed velocities and high Reynolds numbers for six locations in the flow development. Statistical autocorrelation functions and structure functions were computed on the reconstructed phase maps. The autocorrelation function results indicated that the turbulence-induced phase fluctuations were not wide-sense stationary. The structure functions exhibited statistical homogeneity, indicating that the phase fluctuations were stationary in first increments. However, the turbulence-corrupted phase was not isotropic. A five-thirds power law is shown to fit orthogonal slices of the structure function, analogous to the Kolmogorov model for isotropic turbulence. Strehl ratios were computed from the phase structure functions and compared with classical estimates that assume isotropy. The isotropic models are shown to overestimate the optical degradation by nearly 3 orders of magnitude compared with the structure function calculations.

Electron Temperature Fluctuation Measurements and Transport Model Validation at Alcator C-Mod

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

White, Anne

The tokamak is a type of toroidal device used to confine a fusion plasma using large magnetic fields. Tokamaks and stellarators the leading devices for confining plasmas for fusion, and the capability to predict performance in these magnetically confined plasmas is essential for developing a sustainable fusion energy source. The magnetic configuration of tokamaks and stellarators does not exist in Nature, yet, the fundamental processes governing transport in fusion plasmas are universal – turbulence and instabilities, driven by inhomogeneity and asymmetry in the plasma, conspire to transport heat and particles across magnetic field lines and can play critical roles inmore » impurity confinement and generation of intrinsic rotation. Turbulence exists in all plasmas, and in neutral fluids as well. The study of turbulence is essential to developing a fundamental understanding of the nature of the fourth state of matter, plasmas. Experimental studies of turbulence in tokamaks date back to early scattering observations from the late 1970s. Since that time, great advances in turbulence diagnostics have been made, all of which have significantly enhanced our knowledge and understanding of turbulence in tokamaks. Through comparisons with advanced gyrokinetic theory and turbulent-transport models a great deal of evidence exists to implicate turbulent-driven transport as an important mechanism determining transport in all channels: heat, particle and momentum However, prediction and control of turbulent-driven transport remains elusive. Key to development of predictive transport models for magnetically confined fusion plasmas is validation of the nonlinear gyrokinetic transport model, which describes transport due to turbulence. Validation of gyrokinetic codes must include detailed and quantitative comparisons with measured turbulence characteristics, in addition to comparisons with inferred transport levels and equilibrium profiles. For this reason, advanced plasma diagnostics for studying core turbulence are needed in order to assess the accuracy of gyrokinetic models for turbulent-driven particle, heat and momentum transport. New core turbulence diagnostics at the world-class tokamaks Alcator C-Mod at MIT and ASDEX Upgrade at the Max Planck Institute for Plasma Physics have been designed, developed, and operated over the course of this project. These new instruments are capable of measuring electron temperature fluctuations and the phase angle between density and temperature fluctuations locally and quantitatively. These new data sets from Alcator C-Mod and ASDEX Upgrade are being used to fill key gaps in our understanding of turbulent transport in tokamaks. In particular, this project has results in new results on the topics of the Transport Shortfall, the role of ETG turbulence in tokamak plasmas, profile stiffness, the LOC/SOC transition, and intrinsic rotation reversals. These data are used in a rigorous process of “Transport model validation”, and this group is a world-leader on using turbulence models to design new hardware and new experiments at tokamaks. A correlation electron cyclotron emission (CECE) diagnostic is an instrument used to measure micro-scale fluctuations (mm-scale, compared to the machine size of meters) of electron temperature in magnetically confined fusion plasmas, such as those in tokamaks and stellarators. These micro-scale fluctuations are associated with drift-wave type turbulence, which leads to enhanced cooling and mixing of particles in fusion plasmas and limits achieving the required temperatures and densities for self-sustained fusion reactions. A CECE system can also be coupled with a reflectometer system that measured micro-scale density fluctuations, and from these simultaneous measurements, one can extract the phase between the density (n) and temperature (T) fluctuations, creating an nT phase diagnostic. Measurements of the fluctuations and the phase angle between them are extremely useful for testing and validating predictive models for the transport of heat and particles in fusion plasmas due to turbulence. Once validated, the models are used to predict performance in ITER and other burning plasmas, such as the MIT ARC design. Most recently, data from the newly developed, so-called “CECE diagnostic” [Cima 1995, White 2008] and “nT phase angle measurements” [Haese 1999, White 2010] ]will be combined with data from density fluctuation diagnostics at ASDEX Upgrade to support a long-term program of physics research in turbulence and transport that will allow for more stringent testing and validation of gyrokinetic turbulent-transport codes. This work directly impacts the development of predictive transport models in the U.S. FES program, such as TGLF, developed by General Atomics, which are used to predict performance in ITER and other burning plasma devices as part of advancing the development of fusion energy sciences.« less

Preliminary measurements of the edge magnetic field pitch from 2-D Doppler backscattering in MAST and NSTX-U (invited)

DOE PAGES

Vann, R. G. L.; Brunner, K. J.; Ellis, R.; ...

2016-09-13

The Synthetic Aperture Microwave Imaging (SAMI) system is a novel diagnostic consisting of an array of 8 independently phased antennas. At any one time, SAMI operates at one of the 16 frequencies in the range 10-34.5 GHz. The imaging beam is steered in software post-shot to create a picture of the entire emission surface. In SAMI’s active probing mode of operation, the plasma edge is illuminated with a monochromatic source and SAMI reconstructs an image of the Doppler back-scattered (DBS) signal. By assuming that density fluctuations are extended along magnetic field lines, and knowing that the strongest back-scattered signals aremore » directed perpendicular to the density fluctuations, SAMI’s 2-D DBS imaging capability can be used to measure the pitch of the edge magnetic field. In this paper, we present preliminary pitch angle measurements obtained by SAMI on the Mega Amp Spherical Tokamak (MAST) at Culham Centre for Fusion Energy and on the National Spherical Torus Experiment Upgrade at Princeton Plasma Physics Laboratory. Lastly, the results demonstrate encouraging agreement between SAMI and other independent measurements.« less

Evidence for pressure-tuned quantum structural fluctuations in KCuF3

NASA Astrophysics Data System (ADS)

Yuan, S.; Kim, M.; Seeley, J.; Lal, S.; Abbamonte, P.; Cooper, S. L.

2012-02-01

Frustrated magnetic systems are currently of great interest because of the possibility that these materials exhibit novel ground states such as orbital and spin liquids. We provide evidence in the orbital-ordering material KCuF3 for pressure-tuned quantum melting of a static structural phase to a phase that dynamically fluctuates even near T ˜ 0K.[1] Pressure-dependent Raman scattering measurements show that applied pressure above P* ˜ 7kbar reverses a low temperature structural distortion in KCuF3, resulting in the development of a φ ˜ 0 fluctuational (quasielastic) response near T ˜ 0K. This pressure-induced fluctuational response is temperature independent and exhibits a characteristic fluctuation rate that is much larger than the temperature, γ >> KBT, consistent with quantum fluctuations of the CuF6 octahedra. We show that a previous developed model of pseudospin-phonon coupling qualitatively describes both the temperature- and pressure-dependent evolution of the Raman spectra of KCuF3. Work supported by the U.S. Department of Energy under Award No. DE-FG02-07ER46453 and by the National Science Foundation under Grant NSF DMR 08-56321. [4pt] [1] S. Yuan et al., arXiv:1107.1433 (2011).

Suppression of superconductivity in disordered interacting wires.

PubMed

Pesin, D A; Andreev, A V

2006-09-15

We study superconductivity suppression due to thermal fluctuations in disordered wires using the replica nonlinear sigma-model (NLsigmaM). We show that in addition to the thermal phase slips there is another type of fluctuations that result in a finite resistivity. These fluctuations are described by saddle points in NLsigmaM and cannot be treated within the Ginzburg-Landau approach. The contribution of such fluctuations to the wire resistivity is evaluated with exponential accuracy. The magnetoresistance associated with this contribution is negative.

Phase Transition in Protocols Minimizing Work Fluctuations

NASA Astrophysics Data System (ADS)

Solon, Alexandre P.; Horowitz, Jordan M.

2018-05-01

For two canonical examples of driven mesoscopic systems—a harmonically trapped Brownian particle and a quantum dot—we numerically determine the finite-time protocols that optimize the compromise between the standard deviation and the mean of the dissipated work. In the case of the oscillator, we observe a collection of protocols that smoothly trade off between average work and its fluctuations. However, for the quantum dot, we find that as we shift the weight of our optimization objective from average work to work standard deviation, there is an analog of a first-order phase transition in protocol space: two distinct protocols exchange global optimality with mixed protocols akin to phase coexistence. As a result, the two types of protocols possess qualitatively different properties and remain distinct even in the infinite duration limit: optimal-work-fluctuation protocols never coalesce with the minimal-work protocols, which therefore never become quasistatic.

Impact of excitation waveform on the frequency stability of electrostatically-actuated micro-electromechanical oscillators

NASA Astrophysics Data System (ADS)

Juillard, J.; Brenes, A.

2018-05-01

In this paper, the frequency stability of high-Q electrostatically-actuated MEMS oscillators with cubic restoring forces, and its relation with the amplitude, the phase and the shape of the excitation waveform, is studied. The influence on close-to-the carrier frequency noise of additive processes (such as thermomechanical noise) or parametric processes (bias voltage fluctuations, feedback phase fluctuations, feedback level fluctuations) is taken into account. It is shown that the optimal operating conditions of electrostatically-actuated MEMS oscillators are highly waveform-dependent, a factor that is largely overlooked in the existing literature. This simulation-based study covers the cases of harmonic and pulsed excitation of a parallel-plate capacitive MEMS resonator.

Quantum and superconducting fluctuations effects in disordered Nb 1- xTa x thin films above Tc

NASA Astrophysics Data System (ADS)

Giannouri, M.; Papastaikoudis, C.

1999-05-01

Disordered Nb 1- xTa x thin films are prepared with e-gun coevaporation. The influence of the β-phase of tantalum in the critical temperature Tc is observed as a function of the substrate temperature. The measurements of transverse magnetoresistance at various isothermals are interpreted in terms of weak-localization and superconducting fluctuations. From the fitting procedure, the phase breaking rate τφ-1 and the Larkin parameter βL are estimated as a function of temperature. Conclusions about the dominant inelastic scattering mechanisms at various temperature regions as well as for the dominant mechanism of superconducting fluctuations near the transition temperature are extracted.

Quantum phase slip phenomenon in ultra-narrow superconducting nanorings

NASA Astrophysics Data System (ADS)

Arutyunov, Konstantin Yu.; Hongisto, Terhi T.; Lehtinen, Janne S.; Leino, Leena I.; Vasiliev, Alexander L.

2012-02-01

The smaller the system, typically - the higher is the impact of fluctuations. In narrow superconducting wires sufficiently close to the critical temperature Tc thermal fluctuations are responsible for the experimentally observable finite resistance. Quite recently it became possible to fabricate sub-10 nm superconducting structures, where the finite resistivity was reported within the whole range of experimentally obtainable temperatures. The observation has been associated with quantum fluctuations capable to quench zero resistivity in superconducting nanowires even at temperatures T-->0. Here we demonstrate that in tiny superconducting nanorings the same phenomenon is responsible for suppression of another basic attribute of superconductivity - persistent currents - dramatically affecting their magnitude, the period and the shape of the current-phase relation. The effect is of fundamental importance demonstrating the impact of quantum fluctuations on the ground state of a macroscopically coherent system, and should be taken into consideration in various nanoelectronic applications.

Irregularities in Early Seismic Rupture Propagation for Large Events in a Crustal Earthquake Model

NASA Astrophysics Data System (ADS)

Lapusta, N.; Rice, J. R.; Rice, J. R.

2001-12-01

We study early seismic propagation of model earthquakes in a 2-D model of a vertical strike-slip fault with depth-variable rate and state friction properties. Our model earthquakes are obtained in fully dynamic simulations of sequences of instabilities on a fault subjected to realistically slow tectonic loading (Lapusta et al., JGR, 2000). This work is motivated by results of Ellsworth and Beroza (Science, 1995), who observe that for many earthquakes, far-field velocity seismograms during initial stages of dynamic rupture propagation have irregular fluctuations which constitute a "seismic nucleation phase". In our simulations, we find that such irregularities in velocity seismograms can be caused by two factors: (1) rupture propagation over regions of stress concentrations and (2) partial arrest of rupture in neighboring creeping regions. As rupture approaches a region of stress concentration, it sees increasing background stress and its moment acceleration (to which velocity seismographs in the far field are proportional) increases. After the peak in stress concentration, the rupture sees decreasing background stress and moment acceleration decreases. Hence a fluctuation in moment acceleration is created. If rupture starts sufficiently far from a creeping region, then partial arrest of rupture in the creeping region causes a decrease in moment acceleration. As the other parts of rupture continue to develop, moment acceleration then starts to grow again, and a fluctuation again results. Other factors may cause the irregularities in moment acceleration, e.g., phenomena such as branching and/or intermittent rupture propagation (Poliakov et al., submitted to JGR, 2001) which we have not studied here. Regions of stress concentration are created in our model by arrest of previous smaller events as well as by interactions with creeping regions. One such region is deep in the fault zone, and is caused by the temperature-induced transition from seismogenic to creeping behavior at depth. Small events appear in our model at that transition as we decrease the characteristic slip distance for evolution of frictional strength (but not if that distance is unrealistically large). Such clustering of small events at transitions from seismogenic to creeping behavior seems to occur on real faults as well, as we show in examples. To compute moment acceleration that can be compared with data, we translate the results of our 2-D fault model to a 3-D model with essentially radial symmetry on the fault plane. We will discuss limitations of that interpretation; in particular, it may overestimate the effect of partial arrest of rupture in creeping regions. Our present work cannot resolve whether there are any differences in the early phases of seismic moment release, i.e. in the seismic nucleation phase, that would make the beginning of larger events look different from smaller ones that are about to arrest. We have shown that the aseismic nucleation phase and the earliest phases of dynamic breakout are virtually identical for small and large events in our simulations. If early moment release is mostly affected by stress heterogeneities left by previous small events and by creep processes, as our present study suggests, then any such differences would have to be related to as yet unidentified properties of the pre-stress field that might determine the ultimate event size. See http://esag.harvard.edu/lapusta/Lapusta_Rice_Jun01.pdf, Lapusta and Rice, submitted to JGR, 2001.

Evidence for a Cosmological Phase Transition on the TeVScale

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

Lindesay, James V.; Noyes, H.Pierre; /SLAC

Examining the reverse evolution of the universe from the present, long before reaching Planck density dynamics one expects major modifications from the de-coherent thermal equations of state, suggesting a prior phase that has macroscopic coherence properties. The assumption that the phase transition occurs during the radiation dominated epoch, and that zero-point motions drive the fluctuations associated with this transition, specifies a class of cosmological models in which the cosmic microwave background fluctuation amplitude at last scattering is approximately 10{sup -5}. Quantum measurability constraints (e.g. uncertainly relations) define cosmological scales whose expansion rates can be at most luminal.

X-ray light curves of active galactic nuclei are phase incoherent

NASA Technical Reports Server (NTRS)

Krolik, Julian; Done, Chris; Madejski, Grzegorz

1993-01-01

We compute the Fourier phase spectra for the light curves of five low-luminosity active galactic nuclei observed by EXOSAT. There is no statistically significant phase coherence in any of them. This statement is equivalent, subject to a technical caveat, to a demonstration that their fluctuation statistics are Gaussian. Models in which the X-ray output is controlled wholly by a unitary process undergoing a nonlinear limit cycle are therefore ruled out, while models with either a large number of randomly excited independent oscillation modes or nonlinearly interacting spatially dependent oscillations are favored. We also demonstrate how the degree of phase coherence in light curve fluctuations influences the application of causality bounds on internal length scales.

Approximating Matsubara dynamics using the planetary model: Tests on liquid water and ice

NASA Astrophysics Data System (ADS)

Willatt, Michael J.; Ceriotti, Michele; Althorpe, Stuart C.

2018-03-01

Matsubara dynamics is the quantum-Boltzmann-conserving classical dynamics which remains when real-time coherences are taken out of the exact quantum Liouvillian [T. J. H. Hele et al., J. Chem. Phys. 142, 134103 (2015)]; because of a phase-term, it cannot be used as a practical method without further approximation. Recently, Smith et al. [J. Chem. Phys. 142, 244112 (2015)] developed a "planetary" model dynamics which conserves the Feynman-Kleinert (FK) approximation to the quantum-Boltzmann distribution. Here, we show that for moderately anharmonic potentials, the planetary dynamics gives a good approximation to Matsubara trajectories on the FK potential surface by decoupling the centroid trajectory from the locally harmonic Matsubara fluctuations, which reduce to a single phase-less fluctuation particle (the "planet"). We also show that the FK effective frequency can be approximated by a direct integral over these fluctuations, obviating the need to solve iterative equations. This modification, together with use of thermostatted ring-polymer molecular dynamics, allows us to test the planetary model on water (gas-phase, liquid, and ice) using the q-TIP4P/F potential surface. The "planetary" fluctuations give a poor approximation to the rotational/librational bands in the infrared spectrum, but a good approximation to the bend and stretch bands, where the fluctuation lineshape is found to be motionally narrowed by the vibrations of the centroid.

Dynamical Vertex Approximation for the Hubbard Model

NASA Astrophysics Data System (ADS)

Toschi, Alessandro

A full understanding of correlated electron systems in the physically relevant situations of three and two dimensions represents a challenge for the contemporary condensed matter theory. However, in the last years considerable progress has been achieved by means of increasingly more powerful quantum many-body algorithms, applied to the basic model for correlated electrons, the Hubbard Hamiltonian. Here, I will review the physics emerging from studies performed with the dynamical vertex approximation, which includes diagrammatic corrections to the local description of the dynamical mean field theory (DMFT). In particular, I will first discuss the phase diagram in three dimensions with a special focus on the commensurate and incommensurate magnetic phases, their (quantum) critical properties, and the impact of fluctuations on electronic lifetimes and spectral functions. In two dimensions, the effects of non-local fluctuations beyond DMFT grow enormously, determining the appearance of a low-temperature insulating behavior for all values of the interaction in the unfrustrated model: Here the prototypical features of the Mott-Hubbard metal-insulator transition, as well as the existence of magnetically ordered phases, are completely overwhelmed by antiferromagnetic fluctuations of exponentially large extension, in accordance with the Mermin-Wagner theorem. Eventually, by a fluctuation diagnostics analysis of cluster DMFT self-energies, the same magnetic fluctuations are identified as responsible for the pseudogap regime in the holed-doped frustrated case, with important implications for the theoretical modeling of the cuprate physics.

Approximating Matsubara dynamics using the planetary model: Tests on liquid water and ice.

PubMed

Willatt, Michael J; Ceriotti, Michele; Althorpe, Stuart C

2018-03-14

Matsubara dynamics is the quantum-Boltzmann-conserving classical dynamics which remains when real-time coherences are taken out of the exact quantum Liouvillian [T. J. H. Hele et al., J. Chem. Phys. 142, 134103 (2015)]; because of a phase-term, it cannot be used as a practical method without further approximation. Recently, Smith et al. [J. Chem. Phys. 142, 244112 (2015)] developed a "planetary" model dynamics which conserves the Feynman-Kleinert (FK) approximation to the quantum-Boltzmann distribution. Here, we show that for moderately anharmonic potentials, the planetary dynamics gives a good approximation to Matsubara trajectories on the FK potential surface by decoupling the centroid trajectory from the locally harmonic Matsubara fluctuations, which reduce to a single phase-less fluctuation particle (the "planet"). We also show that the FK effective frequency can be approximated by a direct integral over these fluctuations, obviating the need to solve iterative equations. This modification, together with use of thermostatted ring-polymer molecular dynamics, allows us to test the planetary model on water (gas-phase, liquid, and ice) using the q-TIP4P/F potential surface. The "planetary" fluctuations give a poor approximation to the rotational/librational bands in the infrared spectrum, but a good approximation to the bend and stretch bands, where the fluctuation lineshape is found to be motionally narrowed by the vibrations of the centroid.

Temporal and spatial evolution characteristics of gas-liquid two-phase flow pattern based on image texture spectrum descriptor

NASA Astrophysics Data System (ADS)

Zhou, Xi-Guo; Jin, Ning-De; Wang, Zhen-Ya; Zhang, Wen-Yin

2009-11-01

The dynamic image information of typical gas-liquid two-phase flow patterns in vertical upward pipe is captured by a highspeed dynamic camera. The texture spectrum descriptor is used to describe the texture characteristics of the processed images whose content is represented in the form of texture spectrum histogram, and four time-varying characteristic parameter indexes which represent image texture structure of different flow patterns are extracted. The study results show that the amplitude fluctuation of texture characteristic parameter indexes of bubble flow is lowest and shows very random complex dynamic behavior; the amplitude fluctuation of slug flow is higher and shows intermittent motion behavior between gas slug and liquid slug, and the amplitude fluctuation of churn flow is the highest and shows better periodicity; the amplitude fluctuation of bubble-slug flow is from low to high and oscillating frequence is higher than that of slug flow, and includes the features of both slug flow and bubble flow; the slug-churn flow loses the periodicity of slug flow and churn flow, and the amplitude fluctuation is high. The results indicate that the image texture characteristic parameter indexes of different flow pattern can reflect the flow characteristics of gas-liquid two-phase flow, which provides a new approach to understand the temporal and spatial evolution of flow pattern dynamics.

Entanglement, number fluctuations and optimized interferometric phase measurement

NASA Astrophysics Data System (ADS)

He, Q. Y.; Vaughan, T. G.; Drummond, P. D.; Reid, M. D.

2012-09-01

We derive a phase-entanglement criterion for two bosonic modes that is immune to number fluctuations, using the generalized Moore-Penrose inverse to normalize the phase-quadrature operator. We also obtain a phase-squeezing criterion that is immune to number fluctuations using similar techniques. These are used to obtain an operational definition of relative phase-measurement sensitivity via the analysis of phase measurement in interferometry. We show that these criteria are proportional to the enhanced phase-measurement sensitivity. The phase-entanglement criterion is the hallmark of a new type of quantum-squeezing, namely planar quantum-squeezing. This has the property that it squeezes simultaneously two orthogonal spin directions, which is possible owing to the fact that the SU(2) group that describes spin symmetry has a three-dimensional parameter space of higher dimension than the group for photonic quadratures. A practical advantage of planar quantum-squeezing is that, unlike conventional spin-squeezing, it allows noise reduction over all phase angles simultaneously. The application of this type of squeezing is to the quantum measurement of an unknown phase. We show that a completely unknown phase requires two orthogonal measurements and that with planar quantum-squeezing it is possible to reduce the measurement uncertainty independently of the unknown phase value. This is a different type of squeezing compared to the usual spin-squeezing interferometric criterion, which is applicable only when the measured phase is already known to a good approximation or can be measured iteratively. As an example, we calculate the phase entanglement of the ground state of a two-well, coupled Bose-Einstein condensate, similarly to recent experiments. This system demonstrates planar squeezing in both the attractive and the repulsive interaction regime.

Digital multi-channel stabilization of four-mode phase-sensitive parametric multicasting.

PubMed

Liu, Lan; Tong, Zhi; Wiberg, Andreas O J; Kuo, Bill P P; Myslivets, Evgeny; Alic, Nikola; Radic, Stojan

2014-07-28

Stable four-mode phase-sensitive (4MPS) process was investigated as a means to enhance two-pump driven parametric multicasting conversion efficiency (CE) and signal to noise ratio (SNR). Instability of multi-beam, phase sensitive (PS) device that inherently behaves as an interferometer, with output subject to ambient induced fluctuations, was addressed theoretically and experimentally. A new stabilization technique that controls phases of three input waves of the 4MPS multicaster and maximizes CE was developed and described. Stabilization relies on digital phase-locked loop (DPLL) specifically was developed to control pump phases to guarantee stable 4MPS operation that is independent of environmental fluctuations. The technique also controls a single (signal) input phase to optimize the PS-induced improvement of the CE and SNR. The new, continuous-operation DPLL has allowed for fully stabilized PS parametric broadband multicasting, demonstrating CE improvement over 20 signal copies in excess of 10 dB.

Local Orthorhombicity in the Magnetic C 4 Phase of the Hole-Doped Iron-Arsenide Superconductor Sr 1 - x Na x Fe 2 As 2

DOE PAGES

Frandsen, Benjamin A.; Taddei, Keith M.; Yi, Ming; ...

2017-10-30

We report on temperature-dependent pair distribution function measurements of Sr 1-xNa xFe 2As 2, an iron-based superconductor system that contains a magnetic phase with reentrant tetragonal symmetry, known as the magnetic C 4 phase. Quantitative refinements indicate that the instantaneous local structure in the C 4 phase comprises fluctuating orthorhombic regions with a length scale of similar to 2 nm, despite the tetragonal symmetry of the average static structure. Additionally, local orthorhombic fluctuations exist on a similar length scale at temperatures well into the paramagnetic tetragonal phase. Furthermore, these results highlight the exceptionally large nematic susceptibility of iron-based superconductors andmore » have significant implications for the magnetic C 4 phase and the neighboring C 2 and superconducting phases.« less

Local Orthorhombicity in the Magnetic C 4 Phase of the Hole-Doped Iron-Arsenide Superconductor Sr 1 - x Na x Fe 2 As 2

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

Frandsen, Benjamin A.; Taddei, Keith M.; Yi, Ming

We report on temperature-dependent pair distribution function measurements of Sr 1-xNa xFe 2As 2, an iron-based superconductor system that contains a magnetic phase with reentrant tetragonal symmetry, known as the magnetic C 4 phase. Quantitative refinements indicate that the instantaneous local structure in the C 4 phase comprises fluctuating orthorhombic regions with a length scale of similar to 2 nm, despite the tetragonal symmetry of the average static structure. Additionally, local orthorhombic fluctuations exist on a similar length scale at temperatures well into the paramagnetic tetragonal phase. Furthermore, these results highlight the exceptionally large nematic susceptibility of iron-based superconductors andmore » have significant implications for the magnetic C 4 phase and the neighboring C 2 and superconducting phases.« less

Dual Phase-space Cascades in 3D Hybrid-Vlasov–Maxwell Turbulence

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

Cerri, S. S.; Kunz, M. W.; Califano, F.

To explain energy dissipation via turbulence in collisionless, magnetized plasmas, the existence of a dual real- and velocity-space cascade of ion-entropy fluctuations below the ion gyroradius has been proposed. Such a dual cascade, predicted by the gyrokinetic theory, has previously been observed in gyrokinetic simulations of two-dimensional, electrostatic turbulence. For the first time we show evidence for a dual phase-space cascade of ion-entropy fluctuations in a three-dimensional simulation of hybrid-kinetic, electromagnetic turbulence. Some of the scalings observed in the energy spectra are consistent with a generalized theory for the cascade that accounts for the spectral anisotropy of critically balanced, intermittent,more » sub-ion-Larmor-scale fluctuations. Also, the observed velocity-space cascade is anisotropic with respect to the magnetic-field direction, with linear phase mixing along magnetic-field lines proceeding mainly at spatial scales above the ion gyroradius and nonlinear phase mixing across magnetic-field lines proceeding at perpendicular scales below the ion gyroradius. Such phase-space anisotropy could be sought in heliospheric and magnetospheric data of solar-wind turbulence and has far-reaching implications for the dissipation of turbulence in weakly collisional astrophysical plasmas.« less

Dual Phase-space Cascades in 3D Hybrid-Vlasov–Maxwell Turbulence

DOE PAGES

Cerri, S. S.; Kunz, M. W.; Califano, F.

2018-03-23

To explain energy dissipation via turbulence in collisionless, magnetized plasmas, the existence of a dual real- and velocity-space cascade of ion-entropy fluctuations below the ion gyroradius has been proposed. Such a dual cascade, predicted by the gyrokinetic theory, has previously been observed in gyrokinetic simulations of two-dimensional, electrostatic turbulence. For the first time we show evidence for a dual phase-space cascade of ion-entropy fluctuations in a three-dimensional simulation of hybrid-kinetic, electromagnetic turbulence. Some of the scalings observed in the energy spectra are consistent with a generalized theory for the cascade that accounts for the spectral anisotropy of critically balanced, intermittent,more » sub-ion-Larmor-scale fluctuations. Also, the observed velocity-space cascade is anisotropic with respect to the magnetic-field direction, with linear phase mixing along magnetic-field lines proceeding mainly at spatial scales above the ion gyroradius and nonlinear phase mixing across magnetic-field lines proceeding at perpendicular scales below the ion gyroradius. Such phase-space anisotropy could be sought in heliospheric and magnetospheric data of solar-wind turbulence and has far-reaching implications for the dissipation of turbulence in weakly collisional astrophysical plasmas.« less

Relation between heart beat fluctuations and cyclic alternating pattern during sleep in insomnia patients.

PubMed

de Leon-Lomeli, R; Murguia, J S; Chouvarda, I; Mendez, M O; Gonzalez-Galvan, E; Alba, A; Milioli, G; Grassi, A; Terzano, M G; Parrino, L

2014-01-01

Insomnia is a condition that affects the nervous and muscular system. Thirty percent of the population between 18 and 60 years suffers from insomnia. The effects of this disorder involve problems such as poor school or job performance and traffic accidents. In addition, patients with insomnia present changes in the cardiac function during sleep. Furthermore, the structure of electroencephalographic A-phases, which builds up the Cyclic Alternating Pattern during sleep, is related to the insomnia events. Therefore, the relationship between these brain activations (A-phases) and the autonomic nervous system would be of interest, revealing the interplay of central and autonomic activity during insomnia. With this goal, a study of the relationship between A-phases and heart rate fluctuations is presented. Polysomnography recording of five healthy subjects, five sleep misperception patients and five patients with psychophysiological insomnia were used in the study. Detrended Fluctuation Analysis (DFA) was used in order to evaluate the heart rate dynamics and this was correlated with the number of A-phases. The results suggest that pathological patients present changes in the dynamics of the heart rate. This is reflected in the modification of A-phases dynamics, which seems to modify of heart rate dynamics.

Dual Phase-space Cascades in 3D Hybrid-Vlasov–Maxwell Turbulence

NASA Astrophysics Data System (ADS)

Cerri, S. S.; Kunz, M. W.; Califano, F.

2018-03-01

To explain energy dissipation via turbulence in collisionless, magnetized plasmas, the existence of a dual real- and velocity-space cascade of ion-entropy fluctuations below the ion gyroradius has been proposed. Such a dual cascade, predicted by the gyrokinetic theory, has previously been observed in gyrokinetic simulations of two-dimensional, electrostatic turbulence. For the first time, we show evidence for a dual phase-space cascade of ion-entropy fluctuations in a three-dimensional simulation of hybrid-kinetic, electromagnetic turbulence. Some of the scalings observed in the energy spectra are consistent with a generalized theory for the cascade that accounts for the spectral anisotropy of critically balanced, intermittent, sub-ion-Larmor-scale fluctuations. The observed velocity-space cascade is also anisotropic with respect to the magnetic-field direction, with linear phase mixing along magnetic-field lines proceeding mainly at spatial scales above the ion gyroradius and nonlinear phase mixing across magnetic-field lines proceeding at perpendicular scales below the ion gyroradius. Such phase-space anisotropy could be sought in heliospheric and magnetospheric data of solar-wind turbulence and has far-reaching implications for the dissipation of turbulence in weakly collisional astrophysical plasmas.

Fluctuations of pulsed laser radiation in the case of thermal self-defocusing under conditions of atmospheric turbulence

NASA Astrophysics Data System (ADS)

Vorob'ev, V. V.; Krasil'Nikova, T. G.; Tikhonova, N. S.

1989-09-01

The spectra and structure functions of log-amplitude and phase fluctuations of laser radiation under thermal blooming are calculated on the basis of a smooth perturbation method. The spectrum dynamics is investigated in a wide range of spatial frequencies. The applicability of geometrical-optics and diffraction asymptotics to the calculation of the fluctuations is studied.

Probing and characterizing the growth of a crystal of ultracold bosons and light

NASA Astrophysics Data System (ADS)

Ostermann, S.; Piazza, F.; Ritsch, H.

2017-12-01

The non-linear coupled particle light dynamics of an ultracold gas in the field of two independent counter-propagating laser beams can lead to the dynamical formation of a self-ordered lattice structure as presented in (2016) Phys. Rev. X 6 021026. Here we present new numerical studies on experimentally observable signatures to monitor the growth and properties of such a crystal in real time. While, at least theoretically, optimal non-destructive observation of the growth dynamics and the hallmarks of the crystalline phase can be performed by analyzing scattered light, monitoring the evolution of the particle’s momentum distribution via time-of-flight probing is an experimentally more accessible choice. In this work we show that both approaches allow us to unambiguously distinguish the crystal from independent collective scattering as it occurs in matter wave super-radiance. As a clear crystallization signature, we identify spatial locking between the two emerging standing laser waves, together creating the crystal potential. For sufficiently large systems, the system allows reversible adiabatic ramping into the crystalline phase as an alternative to a quench across the phase transition and growth from fluctuations.

Self-catalyzed growth of S layers via an amorphous-to-crystalline transition limited by folding kinetics.

PubMed

Chung, Sungwook; Shin, Seong-Ho; Bertozzi, Carolyn R; De Yoreo, James J

2010-09-21

The importance of nonclassical, multistage crystallization pathways is increasingly evident from theoretical studies on colloidal systems and experimental investigations of proteins and biomineral phases. Although theoretical predictions suggest that proteins follow these pathways as a result of fluctuations that create unstable dense-liquid states, microscopic studies indicate these states are long-lived. Using in situ atomic force microscopy to follow 2D assembly of S-layer proteins on supported lipid bilayers, we have obtained a molecular-scale picture of multistage protein crystallization that reveals the importance of conformational transformations in directing the pathway of assembly. We find that monomers with an extended conformation first form a mobile adsorbed phase, from which they condense into amorphous clusters. These clusters undergo a phase transition through S-layer folding into crystalline clusters composed of compact tetramers. Growth then proceeds by formation of new tetramers exclusively at cluster edges, implying tetramer formation is autocatalytic. Analysis of the growth kinetics leads to a quantitative model in which tetramer creation is rate limiting. However, the estimated barrier is much smaller than expected for folding of isolated S-layer proteins, suggesting an energetic rationale for this multistage pathway.

Fluctuation effects in blends of A + B homopolymers with AB diblock copolymer

NASA Astrophysics Data System (ADS)

Spencer, Russell K. W.; Matsen, Mark W.

2018-05-01

Field-theoretic simulations (FTSs) are performed on ternary blends of A- and B-type homopolymers of polymerization Nh and symmetric AB diblock copolymers of polymerization Nc. Unlike previous studies, our FTSs are conducted in three-dimensional space, with the help of two new semi-grand canonical ensembles. Motivated by the first experiment to discover bicontinuous microemulsion (BμE) in the polyethylene-polyethylene propylene system, we consider molecules of high molecular weight with size ratios of α ≡ Nh/Nc = 0.1, 0.2, and 0.4. Our focus is on the A + B coexistence between the two homopolymer-rich phases in the low-copolymer region of the phase diagram. The Scott line, at which the A + B phases mix to form a disordered melt with increasing temperature (or decreasing χ), is accurately determined using finite-size scaling techniques. We also examine how the copolymer affects the interface between the A + B phases, reducing the interfacial tension toward zero. Although comparisons with self-consistent field theory (SCFT) illustrate that fluctuation effects are relatively small, fluctuations do nevertheless produce the observed BμE that is absent in the SCFT phase diagram. Furthermore, we find evidence of three-phase A + B + BμE coexistence, which may have been missed in the original as well as subsequent experiments.

Measuring Magnetic Oscillations in the Solar Photosphere: Coordinated Observations with MDI, ASP and MWO

NASA Astrophysics Data System (ADS)

Norton, A. A.; Ulrich, R. K.

2000-03-01

A comprehensive observing effort was undertaken to simultaneously obtain full Stokes profiles as well as longitudinal magnetogram maps of a positive plage region on 8 December, 1998 with the Michelson Doppler Imager, the Advanced Stokes Polarimeter and Mt. Wilson Observatory magnetograph. We compare 1.2'' spatially-averaged signals of velocities as well as filter magnetograph longitudinal flux signals with Stokes determined fluctuations in filling factor, field inclination, magnetic flux and field strength. The velocity signals are in excellent agreement. Michelson Doppler Imager magnetic flux correlates best with fluctuations in the Advanced Stokes Polarimeter filling factor, not inclination angle or field strength. A correlated flux and filling factor change in the absence of a field strength fluctuation can be understood in terms of internally unperturbed flux tubes being buffeted by external pressure fluctuations. The 12.5'' square aperture spatially averaged Mt. Wilson magnetograph signals are compared with Michelson Doppler Imager signals from the corresponding observing area. Velocity signals are in superb agreement. Magnetic signals exhibit similar oscillatory behavior. Lack of Advanced Stokes Polarimeter data for this time excludes interpretation of magnetic fluctuations as due to filling factor or field inclination angle. Mt. Wilson Observatory simultaneous sampling of the nickel and sodium spectral line profiles with several wing pairs allowed inter-comparison of signals from different heights of formation. Slight phase shifts and large propagation speeds for the velocity signals are indicative of modified standing waves. Phase speeds associated with magnetic signals are characteristic of photospheric Alfvén speeds for plage fields. The phase speed increase with height agrees with the altitude dependence of the Alfvén speed. The observed fluctuations and phases are interpreted as a superposition of signatures from the horizontal component of the driving mechanism sweeping the field lines in/out of the resolution area and the magnetic response of the flux tube to this buffeting.

Phase fluctuation spectra: New radio science information to become available in the DSN tracking system Mark III-77

NASA Technical Reports Server (NTRS)

Berman, A. L.

1977-01-01

An algorithm was developed for the continuous and automatic computation of Doppler noise concurrently at four sample rate intervals, evenly spanning three orders of magnitude. Average temporal Doppler phase fluctuation spectra will be routinely available in the DSN tracking system Mark III-77 and require little additional processing. The basic (noise) data will be extracted from the archival tracking data file (ATDF) of the tracking data management system.

Partial information, market efficiency, and anomalous continuous phase transition

NASA Astrophysics Data System (ADS)

Yang, Guang; Zheng, Wenzhi; Huang, Jiping

2014-04-01

It is a common belief in economics and social science that if there is more information available for agents to gather in a human system, the system can become more efficient. The belief can be easily understood according to the well-known efficient market hypothesis. In this work, we attempt to challenge this belief by investigating a complex adaptive system, which is modeled by a market-directed resource-allocation game with a directed random network. We conduct a series of controlled human experiments in the laboratory to show the reliability of the model design. As a result, we find that even under a small information concentration, the system can still almost reach the optimal (balanced) state. Furthermore, the ensemble average of the system’s fluctuation level goes through a continuous phase transition. This behavior means that in the second phase if too much information is shared among agents, the system’s stability will be harmed instead, which differs from the belief mentioned above. Also, at the transition point, the ensemble fluctuations of the fluctuation level remain at a low value. This phenomenon is in contrast to the textbook knowledge about continuous phase transitions in traditional physical systems, namely, fluctuations will rise abnormally around a transition point since the correlation length becomes infinite. Thus, this work is of potential value to a variety of fields, such as physics, economics, complexity science, and artificial intelligence.

Possible mechanism to enhance spin-fluctuation-mediated superconductivity in two-dimensional organic conductor

NASA Astrophysics Data System (ADS)

Nonoyama, Yoshito; Maekawa, Yukiko; Kobayashi, Akito; Suzumura, Yoshikazu; Yamada, Jun-ichi

2008-10-01

Mechanisms of superconductivity in quasi-two-dimensional organic conductors have been investigated using an extended Hubbard model by using the transfer energies between BDA-TTP molecules for β-(BDA-TTP)2I3 based on the X-ray experiment data and the extended Hückel calculation. We obtain several mean-field solutions with charge orderings which may represent short-range orderings or low-energy fluctuations in the low-dimensional electronic system. In the pressure-temperature phase diagram, a charge ordered metal state almost degenerates with a normal metal state between an insulating phase with charge ordering and the normal metal phase. Using the random phase approximation (RPA) and the linearized gap equation, the transition temperature of the superconducting state is estimated for the charge-ordered metal state and the normal metal state. It is found that transition temperature of the superconductivity induced by spin fluctuations in the charge-ordered metal state is much higher than that of the normal metal state and that the superconductivity in the charge-ordered metal state is the gapless d-wave. This suggests that the short range charge ordering may also contribute to an enhancement of spin-fluctuation-mediated superconductivity. The difference in the superconducting states between β-(BDA-TTP)2I3 and β-(BDA-TTP)2SbF6 are briefly discussed.

Direct evidence for cycloidal modulations in the thermal-fluctuation-stabilized spin spiral and skyrmion states of GaV4S8

NASA Astrophysics Data System (ADS)

White, J. S.; Butykai, Á.; Cubitt, R.; Honecker, D.; Dewhurst, C. D.; Kiss, L. F.; Tsurkan, V.; Bordács, S.

2018-01-01

We report small-angle neutron scattering studies of the lacunar spinel GaV4S8 , which reveal the long-wavelength magnetic phases to be cycloidally modulated. Upon cooling, these modulated phases, including a recently proposed Néel-type skyrmion phase, transform into a simple ferromagnetic state. These results indicate the modulated phases in GaV4S8 gain their stability from thermal fluctuations, while at lower temperatures the ferromagnetic state emerges in accord with the strong easy-axis magnetic anisotropy. Crucially, our study provides microscopic evidence that the skyrmions in GaV4S8 indeed display a Néel-type helicity. More generally, our approach can be applied to evidence the helicity of any bulk skyrmion phase.

Advanced Receiver tracking of Voyager 2 near solar conjunction

NASA Technical Reports Server (NTRS)

Brown, D. H.; Hurd, W. J.; Vilnrotter, V. A.; Wiggins, J. D.

1988-01-01

The Advanced Receiver (ARX) was used to track the Voyager 2 spacecraft at low Sun-Earth-Probe (SEP) angles near solar conjunction in December of 1987. The received carrier signal exhibited strong fluctuations in both phase and amplitude. The ARX used spectral estimation and mathematical modeling of the phase and receiver noise processes to set an optimum carrier tracking bandwidth. This minimized the mean square phase error in tracking carrier phase and thus minimized the loss in the telemetry signal-to-noise ratio due to the carrier loop. Recovered symbol SNRs and errors in decoded engineering data for the ARX are compared with those for the current Block 3 telemetry stream. Optimum bandwidths are plotted against SEP angle. Measurements of the power spectral density of the solar phase and amplitude fluctuations are also given.

On the origin of shape fluctuations of the cell nucleus.

PubMed

Chu, Fang-Yi; Haley, Shannon C; Zidovska, Alexandra

2017-09-26

The nuclear envelope (NE) presents a physical boundary between the cytoplasm and the nucleoplasm, sandwiched in between two highly active systems inside the cell: cytoskeleton and chromatin. NE defines the shape and size of the cell nucleus, which increases during the cell cycle, accommodating for chromosome decondensation followed by genome duplication. In this work, we study nuclear shape fluctuations at short time scales of seconds in human cells. Using spinning disk confocal microscopy, we observe fast fluctuations of the NE, visualized by fluorescently labeled lamin A, and of the chromatin globule surface (CGS) underneath the NE, visualized by fluorescently labeled histone H2B. Our findings reveal that fluctuation amplitudes of both CGS and NE monotonously decrease during the cell cycle, serving as a reliable cell cycle stage indicator. Remarkably, we find that, while CGS and NE typically fluctuate in phase, they do exhibit localized regions of out-of-phase motion, which lead to separation of NE and CGS. To explore the mechanism behind these shape fluctuations, we use biochemical perturbations. We find the shape fluctuations of CGS and NE to be both thermally and actively driven, the latter caused by forces from chromatin and cytoskeleton. Such undulations might affect gene regulation as well as contribute to the anomalously high rates of nuclear transport by, e.g., stirring of molecules next to NE, or increasing flux of molecules through the nuclear pores.

Don’t Rock the Boat: How Antiphase Crew Coordination Affects Rowing

PubMed Central

de Brouwer, Anouk J.; de Poel, Harjo J.; Hofmijster, Mathijs J.

2013-01-01

It is generally accepted that crew rowing requires perfect synchronization between the movements of the rowers. However, a long-standing and somewhat counterintuitive idea is that out-of-phase crew rowing might have benefits over in-phase (i.e., synchronous) rowing. In synchronous rowing, 5 to 6% of the power produced by the rower(s) is lost to velocity fluctuations of the shell within each rowing cycle. Theoretically, a possible way for crews to increase average boat velocity is to reduce these fluctuations by rowing in antiphase coordination, a strategy in which rowers perfectly alternate their movements. On the other hand, the framework of coordination dynamics explicates that antiphase coordination is less stable than in-phase coordination, which may impede performance gains. Therefore, we compared antiphase to in-phase crew rowing performance in an ergometer experiment. Nine pairs of rowers performed a two-minute maximum effort in-phase and antiphase trial at 36 strokes min−1 on two coupled free-floating ergometers that allowed for power losses to velocity fluctuations. Rower and ergometer kinetics and kinematics were measured during the trials. All nine pairs easily acquired antiphase rowing during the warm-up, while one pair’s coordination briefly switched to in-phase during the maximum effort trial. Although antiphase interpersonal coordination was indeed less accurate and more variable, power production was not negatively affected. Importantly, in antiphase rowing the decreased power loss to velocity fluctuations resulted in more useful power being transferred to the ergometer flywheels. These results imply that antiphase rowing may indeed improve performance, even without any experience with antiphase technique. Furthermore, it demonstrates that although perfectly synchronous coordination may be the most stable, it is not necessarily equated with the most efficient or optimal performance. PMID:23383024

Don't rock the boat: how antiphase crew coordination affects rowing.

PubMed

de Brouwer, Anouk J; de Poel, Harjo J; Hofmijster, Mathijs J

2013-01-01

It is generally accepted that crew rowing requires perfect synchronization between the movements of the rowers. However, a long-standing and somewhat counterintuitive idea is that out-of-phase crew rowing might have benefits over in-phase (i.e., synchronous) rowing. In synchronous rowing, 5 to 6% of the power produced by the rower(s) is lost to velocity fluctuations of the shell within each rowing cycle. Theoretically, a possible way for crews to increase average boat velocity is to reduce these fluctuations by rowing in antiphase coordination, a strategy in which rowers perfectly alternate their movements. On the other hand, the framework of coordination dynamics explicates that antiphase coordination is less stable than in-phase coordination, which may impede performance gains. Therefore, we compared antiphase to in-phase crew rowing performance in an ergometer experiment. Nine pairs of rowers performed a two-minute maximum effort in-phase and antiphase trial at 36 strokes min(-1) on two coupled free-floating ergometers that allowed for power losses to velocity fluctuations. Rower and ergometer kinetics and kinematics were measured during the trials. All nine pairs easily acquired antiphase rowing during the warm-up, while one pair's coordination briefly switched to in-phase during the maximum effort trial. Although antiphase interpersonal coordination was indeed less accurate and more variable, power production was not negatively affected. Importantly, in antiphase rowing the decreased power loss to velocity fluctuations resulted in more useful power being transferred to the ergometer flywheels. These results imply that antiphase rowing may indeed improve performance, even without any experience with antiphase technique. Furthermore, it demonstrates that although perfectly synchronous coordination may be the most stable, it is not necessarily equated with the most efficient or optimal performance.

Edge localized mode characteristics during edge localized mode mitigation by supersonic molecular beam injection in Korea Superconducting Tokamak Advanced Research

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

Lee, H. Y.; Hong, J. H.; Jang, J. H.

It has been reported that supersonic molecular beam injection (SMBI) is an effective means of edge localized mode (ELM) mitigation. This paper newly reports the changes in the ELM, plasma profiles, and fluctuation characteristics during ELM mitigation by SMBI in Korea Superconducting Tokamak Advanced Research. During the mitigated ELM phase, the ELM frequency increased by a factor of 2–3 and the ELM size, which was estimated from the D{sub α} amplitude, the fractional changes in the plasma-stored energy and the line-averaged electron density, and divertor heat flux during an ELM burst, decreased by a factor of 0.34–0.43. Reductions in themore » electron and ion temperatures rather than in the electron density were observed during the mitigated ELM phase. In the natural ELM phase, frequency chirping of the plasma fluctuations was observed before the ELM bursts; however, the ELM bursts occurred without changes in the plasma fluctuation frequency in the mitigated ELM phase.« less

Physics-based analysis and control of human snoring

NASA Astrophysics Data System (ADS)

Sanchez, Yaselly; Wang, Junshi; Han, Pan; Xi, Jinxiang; Dong, Haibo

2017-11-01

In order to advance the understanding of biological fluid dynamics and its effects on the acoustics of human snoring, the study pursued a physics-based computational approach. From human magnetic resonance image (MRI) scans, the researchers were able to develop both anatomically and dynamically accurate airway-uvula models. With airways defined as rigid, and the uvula defined as flexible, computational models were created with various pharynx thickness and geometries. In order to determine vortex shedding with prescribed uvula movement, the uvula fluctuation was categorized by its specific parameters: magnitude, frequency, and phase lag. Uvula vibration modes were based on one oscillation, or one harmonic frequency, and pressure probes were located in seven different positions throughout the airway-uvula model. By taking fast Fourier transforms (FFT) from the pressure probe data, it was seen that four harmonics were created throughout the simulation within one oscillation of uvula movement. Of the four harmonics, there were two pressure probes which maintained high amplitudes and led the researcher to believe that different vortices formed with different snoring frequencies. This work is supported by the NSF Grant CBET-1605434.

Active DNA gels

NASA Astrophysics Data System (ADS)

Saleh, Omar A.; Fygenson, Deborah K.; Bertrand, Olivier J. N.; Park, Chang Young

2013-02-01

Research into the mechanics and fluctuations of living cells has revealed the key role played by the cytoskeleton, a gel of stiff filaments driven out of equilibrium by force-generating motor proteins. Inspired by the extraordinary mechanical functions that the cytoskeleton imparts to the cell, we sought to create an artificial gel with similar characteristics. We identified DNA, and DNA-based motor proteins, as functional counterparts to the constituents of the cytoskeleton. We used DNA selfassembly to create a gel, and characterized its fluctuations and mechanics both before and after activation by the motor. We found that certain aspects of the DNA gel quantitatively match those of cytoskeletal networks, indicating the universal features of motor-driven, non-equilibrium networks.

Hadronic Correlations and Fluctuations

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

Koch, Volker

2008-10-09

We will provide a review of some of the physics which can be addressed by studying fluctuations and correlations in heavy ion collisions. We will discuss Lattice QCD results on fluctuations and correlations and will put them into context with observables which have been measured in heavy-ion collisions. Special attention will be given to the QCD critical point and the first order co-existence region, and we will discuss how the measurement of fluctuations and correlations can help in an experimental search for non-trivial structures in the QCD phase diagram.

Fluctuations and symmetry energy in nuclear fragmentation dynamics.

PubMed

Colonna, M

2013-01-25

Within a dynamical description of nuclear fragmentation, based on the liquid-gas phase transition scenario, we explore the relation between neutron-proton density fluctuations and nuclear symmetry energy. We show that, along the fragmentation path, isovector fluctuations follow the evolution of the local density and approach an equilibrium value connected to the local symmetry energy. Higher-density regions are characterized by smaller average asymmetry and narrower isotopic distributions. This dynamical analysis points out that fragment final state isospin fluctuations can probe the symmetry energy of the density domains from which fragments originate.

Oscillating plasma bubble and its associated nonlinear studies in presence of low magnetic field

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

Megalingam, Mariammal; Sarma, Bornali; Mitra, Vramori

Oscillating plasma bubbles have been created around a cylindrical mesh grid of 75% optical transparency in a DC plasma system with a low magnetic field. Plasma bubbles are created by developing ion density gradient around a cylindrical grid of 20 cm in diameter and 25 cm in height, inserted into the plasma. Relaxation and contraction of the plasma bubbles in the presence of external conditions, such as magnetic field and pressure, have been studied. A Langmuir probe has been used to detect the plasma floating potential fluctuations at different imposed experimental conditions. Nonlinear behavior of the system has been characterized by adoptingmore » nonlinear techniques such as Fast Fourier Transform, Phase Space Plot, and Recurrence Plot. It shows that the system creates highly nonlinear phenomena associated with the plasma bubble under the imposed experimental conditions. A theoretical and numerical model has also been developed to satisfy the observed experimental analysis. Moreover, observations are extended further to study the growth of instability associated with the plasma bubbles. The intention of the present work is to correlate the findings about plasma bubbles and their related instability with the one existing in the equatorial F-region of the ionosphere.« less

Nuclear magnetic resonance studies of pseudospin fluctuations in URu 2 Si 2

DOE PAGES

Shirer, K. R.; Haraldsen, J. T.; Dioguardi, A. P.; ...

2013-09-26

Here, we report 29Si nuclear magnetic resonance measurements in single crystals and aligned powders of URu 2Si 2 in the hidden order and paramagnetic phases. The spin-lattice relaxation data reveal evidence of pseudospin fluctuations of U moments in the paramagnetic phase. We find evidence for partial suppression of the density of states below 30 K and analyze the data in terms of a two-component spin-fermion model. We propose that this behavior is a realization of a pseudogap between the hidden-order transition T HO and 30 K. This behavior is then compared to other materials that demonstrate precursor fluctuations in amore » pseudogap regime above a ground state with long-range order.« less

Flicker in a twisted nematic spatial light modulator

NASA Astrophysics Data System (ADS)

Calderón-Hermosillo, Yuliana; García-Márquez, Jorge; Espinosa-Luna, Rafael; Ochoa, Noé Alcalá; López, Víctor; Aguilar, Alberto; Noé-Arias, Enrique; Alayli, Yasser

2013-06-01

Liquid Crystal on Silicon (LCoS) Spatial Light Modulators (SLM) are widely used for their capability to control beams howbeit fluctuations in phase and amplitude. It is then necessary to understand the negative effects of these fluctuations, also known as flicker, and the means to mitigate them. The flicker is observed either as high frequency variations of polarization, attenuation or high phase fluctuations on the wave front modulated by the LCoS device. Here, we compare the flicker behavior in a twisted nematic (TN) LCoS-SLM for different polarization schemes and temperatures. The quantitative evaluation shows that flicker is effectively reduced only by chilling the LCoS panel to temperatures just below 0 °C but, the LCoS modulation capability is also affected.

Detecting temperature fluctuations at equilibrium.

PubMed

Dixit, Purushottam D

2015-05-21

The Gibbs and the Boltzmann definition of temperature agree only in the macroscopic limit. The ambiguity in identifying the equilibrium temperature of a finite-sized 'small' system exchanging energy with a bath is usually understood as a limitation of conventional statistical mechanics. We interpret this ambiguity as resulting from a stochastically fluctuating temperature coupled with the phase space variables giving rise to a broad temperature distribution. With this ansatz, we develop the equilibrium statistics and dynamics of small systems. Numerical evidence using an analytically tractable model shows that the effects of temperature fluctuations can be detected in the equilibrium and dynamical properties of the phase space of the small system. Our theory generalizes statistical mechanics to small systems relevant in biophysics and nanotechnology.

Density fluctuations in aqueous solution of ionic liquid with lower critical solution temperature: Mixture of tetrabutylphosphonium trifluoroacetate and water

NASA Astrophysics Data System (ADS)

Nitta, Ayako; Morita, Takeshi; Saita, Shohei; Kohno, Yuki; Ohno, Hiroyuki; Nishikawa, Keiko

2015-05-01

Aqueous solutions of tetrabutylphosphonium trifluoroacetate ([P4444]CF3COO) exhibit a LCST-type phase transition with the critical point near 0.025 in mole fraction of [P4444]CF3COO at T = 302 K. The phase behavior of [P4444]CF3COO-water mixtures was investigated by evaluating their density fluctuations, which provide quantitative descriptions of the mixing states of the solutions. The concentration dependence of the density fluctuations was investigated at 293 and 301 K for the mixtures without distinguishing the components and for the individual components ([P4444]CF3COO and water). A drastic change in the mixing state was observed for the solution when the critical point was approached.

Collapse of superconductivity in cuprates via ultrafast quenching of phase coherence

DOE PAGES

Boschini, F.; da Silva Neto, E. H.; Razzoli, E.; ...

2018-04-02

The possibility of driving phase transitions in low-density condensates through the loss of phase coherence alone has far-reaching implications for the study of quantum phases of matter. This has inspired the development of tools to control and explore the collective properties of condensate phases via phase fluctuations. Electrically gated oxide interfaces, ultracold Fermi atoms and cuprate superconductors, which are characterized by an intrinsically small phase stiffness, are paradigmatic examples where these tools are having a dramatic impact. In this study, we use light pulses shorter than the internal thermalization time to drive and probe the phase fragility of the Bimore » 2Sr 2CaCu 2O 8+δ cuprate superconductor, completely melting the superconducting condensate without affecting the pairing strength. The resulting ultrafast dynamics of phase fluctuations and charge excitations are captured and disentangled by time-resolved photoemission spectroscopy. This work demonstrates the dominant role of phase coherence in the superconductor-to-normal state phase transition and offers a benchmark for non-equilibrium spectroscopic investigations of the cuprate phase diagram.« less

Collapse of superconductivity in cuprates via ultrafast quenching of phase coherence

NASA Astrophysics Data System (ADS)

Boschini, F.; da Silva Neto, E. H.; Razzoli, E.; Zonno, M.; Peli, S.; Day, R. P.; Michiardi, M.; Schneider, M.; Zwartsenberg, B.; Nigge, P.; Zhong, R. D.; Schneeloch, J.; Gu, G. D.; Zhdanovich, S.; Mills, A. K.; Levy, G.; Jones, D. J.; Giannetti, C.; Damascelli, A.

2018-05-01

The possibility of driving phase transitions in low-density condensates through the loss of phase coherence alone has far-reaching implications for the study of quantum phases of matter. This has inspired the development of tools to control and explore the collective properties of condensate phases via phase fluctuations. Electrically gated oxide interfaces1,2, ultracold Fermi atoms3,4 and cuprate superconductors5,6, which are characterized by an intrinsically small phase stiffness, are paradigmatic examples where these tools are having a dramatic impact. Here we use light pulses shorter than the internal thermalization time to drive and probe the phase fragility of the Bi2Sr2CaCu2O8+δ cuprate superconductor, completely melting the superconducting condensate without affecting the pairing strength. The resulting ultrafast dynamics of phase fluctuations and charge excitations are captured and disentangled by time-resolved photoemission spectroscopy. This work demonstrates the dominant role of phase coherence in the superconductor-to-normal state phase transition and offers a benchmark for non-equilibrium spectroscopic investigations of the cuprate phase diagram.

Collapse of superconductivity in cuprates via ultrafast quenching of phase coherence

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

Boschini, F.; da Silva Neto, E. H.; Razzoli, E.

The possibility of driving phase transitions in low-density condensates through the loss of phase coherence alone has far-reaching implications for the study of quantum phases of matter. This has inspired the development of tools to control and explore the collective properties of condensate phases via phase fluctuations. Electrically gated oxide interfaces, ultracold Fermi atoms and cuprate superconductors, which are characterized by an intrinsically small phase stiffness, are paradigmatic examples where these tools are having a dramatic impact. In this study, we use light pulses shorter than the internal thermalization time to drive and probe the phase fragility of the Bimore » 2Sr 2CaCu 2O 8+δ cuprate superconductor, completely melting the superconducting condensate without affecting the pairing strength. The resulting ultrafast dynamics of phase fluctuations and charge excitations are captured and disentangled by time-resolved photoemission spectroscopy. This work demonstrates the dominant role of phase coherence in the superconductor-to-normal state phase transition and offers a benchmark for non-equilibrium spectroscopic investigations of the cuprate phase diagram.« less

In-plane "superresolution" MRI with phaseless sub-pixel encoding.

PubMed

Hennel, Franciszek; Tian, Rui; Engel, Maria; Pruessmann, Klaas P

2018-04-15

Acquisition of high-resolution imaging data using multiple excitations without the sensitivity to fluctuations of the transverse magnetization phase, which is a major problem of multi-shot MRI. The concept of superresolution MRI based on microscopic tagging is analyzed using an analogy with the optical method of structured illumination. Sinusoidal tagging is shown to provide subpixel resolution by mixing of neighboring spatial frequency (k-space) bands. It represents a phaseless modulation added on top of the standard Fourier encoding, which allows the phase fluctuations to be discarded at an intermediate reconstruction step. Improvements are proposed to correct for tag distortions due to magnetic field inhomogeneity and to avoid the propagation of Gibbs ringing from intermediate low-resolution images to the final image. The method was applied to diffusion-weighted EPI. Artifact-free superresolution images can be obtained despite a finite duration of the tagging sequence and related pattern distortions by a field map based phase correction of band-wise reconstructed images. The ringing effect present in the intermediate images can be suppressed by partial overlapping of the mixed k-space bands in combination with an adapted filter. High-resolution diffusion-weighted images of the human head were obtained with a three-shot EPI sequence despite motion-related phase fluctuations between the shots. Due to its phaseless character, tagging-based sub-pixel encoding is an alternative to k-space segmenting in the presence of unknown phase fluctuations, in particular those due to motion under strong diffusion gradients. Proposed improvements render the method practicable in realistic conditions. © 2018 International Society for Magnetic Resonance in Medicine.

Confocal reflectance quantitative phase microscope system for cellular membranes dynamics study (Conference Presentation)

NASA Astrophysics Data System (ADS)

Singh, Vijay Raj; Yaqoob, Zahid; So, Peter T. C.

2017-02-01

Quantitative phase microscopy (QPM) techniques developed so far primarily belongs to high speed transmitted light based systems that has enough sensitivity to resolve membrane fluctuations and dynamics, but has no depth resolution. Therefore, most biomechanics studies using QPM today is confined to simple cells, such as RBCs, without internal organelles. An important instrument that will greatly extend the biomedical applications of QPM is to develop next generation microscope with 3D capability and sufficient temporal resolution to study biomechanics of complex eukaryotic cells including the mechanics of their internal compartments. For eukaryotic cells, the depth sectioning capability is critical and should be sufficient to distinguish nucleic membrane fluctuations from plasma membrane fluctuations. Further, this microscope must provide high temporal resolution since typical eukaryotes membranes are substantially stiffer than RBCs. A confocal reflectance quantitative phase microscope is presented based on multi-pinhole scanning, with the capabilities of higher temporal resolution and sensitivity for nucleic and plasma membranes of eukaryotic cells. System hardware is developed based on an array of confocal pinhole generated by using the `ON' state of subset of micro-mirrors of digital micro-mirror device (DMD, from Texas Instruments) and high-speed raster scanning provides 14ms imaging speed in wide-field mode. A common path interferometer is integrated at the imaging arm for detection of specimens' quantitative phase information. Theoretical investigation of quantitative phase reconstructed from system is investigated and application of system is presented for dimensional fluctuations measurements of both cellular plasma and nucleic membranes of embryonic stem cells.

QCD phase diagram using PNJL model with eight-quark interactions

NASA Astrophysics Data System (ADS)

Deb, Paramita; Bhattacharyya, Abhijit; Ghosh, Sanjay K.; Ray, Rajarshi; Lahiri, Anirban

2011-07-01

We present the phase diagram and the fluctuations of different conserved charges like quark number, charge and strangeness at vanishing chemical potential for the 2+1 flavor Polyakov Loop extended Nambu-Jona-Lasinio model with eight-quark interaction terms using three-momentum cutoff regularisation. The main effect of the higher order interaction term is to shift the critical end point to the lower value of the chemical potential and higher value of the temperature. The fluctuations show good qualitative agreement with the lattice data.

Long-wavelength instabilities in a system of interacting active particles

NASA Astrophysics Data System (ADS)

Fazli, Zahra; Najafi, Ali

2018-02-01

Based on a microscopic model, we develop a continuum description for a suspension of microscopic self-propelled particles. With this continuum description we study the role of long-range interactions in destabilizing macroscopic ordered phases that are developed by short-range interactions. Long-wavelength fluctuations can destabilize both isotropic and symmetry-broken polar phases in a suspension of dipolar particles. The instabilities in a suspension of pullers (pushers) arise from splay (bend) fluctuations. Such instabilities are not seen in a suspension of quadrupolar particles.

News and views in discontinuous phase transitions

NASA Astrophysics Data System (ADS)

Nagler, Jan

2014-03-01

Recent progress in the theory of discontinuous percolation allow us to better understand the the sudden emergence of large-scale connectedness both in networked systems and on the lattice. We analytically study mechanisms for the amplification of critical fluctuations at the phase transition point, non-self-averaging and power law fluctuations. A single event analysis allow to establish criteria for discontinuous percolation transitions, even on the high-dimensional lattice. Some applications such as salad bowl percolation, and inverse fragmentation are discussed.

Curvature perturbation and waterfall dynamics in hybrid inflation

NASA Astrophysics Data System (ADS)

Akbar Abolhasani, Ali; Firouzjahi, Hassan; Sasaki, Misao

2011-10-01

We investigate the parameter spaces of hybrid inflation model with special attention paid to the dynamics of waterfall field and curvature perturbations induced from its quantum fluctuations. Depending on the inflaton field value at the time of phase transition and the sharpness of the phase transition inflation can have multiple extended stages. We find that for models with mild phase transition the induced curvature perturbation from the waterfall field is too large to satisfy the COBE normalization. We investigate the model parameter space where the curvature perturbations from the waterfall quantum fluctuations vary between the results of standard hybrid inflation and the results obtained here.

Ultralow-jitter and -amplitude-noise semiconductor-based actively mode-locked laser.

PubMed

Quinlan, Franklyn; Gee, Sangyoun; Ozharar, Sarper; Delfyett, Peter J

2006-10-01

We report a semiconductor-based, low-noise, 10.24 GHz actively mode-locked laser with 4.65 fs of relative timing jitter and a 0.0365% amplitude fluctuation (1 Hz to 100 MHz) of the optical pulse train. The keys to obtaining this result were the laser's high optical power and the low phase noise of the rf source used to mode lock the laser. The low phase noise of the rf source not only improves the absolute and relative timing jitter of the laser, but also prevents coupling of the rf source phase noise to the pulse amplitude fluctuations by the mode-locked laser.

ColDICE: A parallel Vlasov–Poisson solver using moving adaptive simplicial tessellation

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

Sousbie, Thierry, E-mail: tsousbie@gmail.com; Department of Physics, The University of Tokyo, Tokyo 113-0033; Research Center for the Early Universe, School of Science, The University of Tokyo, Tokyo 113-0033

2016-09-15

Resolving numerically Vlasov–Poisson equations for initially cold systems can be reduced to following the evolution of a three-dimensional sheet evolving in six-dimensional phase-space. We describe a public parallel numerical algorithm consisting in representing the phase-space sheet with a conforming, self-adaptive simplicial tessellation of which the vertices follow the Lagrangian equations of motion. The algorithm is implemented both in six- and four-dimensional phase-space. Refinement of the tessellation mesh is performed using the bisection method and a local representation of the phase-space sheet at second order relying on additional tracers created when needed at runtime. In order to preserve in the bestmore » way the Hamiltonian nature of the system, refinement is anisotropic and constrained by measurements of local Poincaré invariants. Resolution of Poisson equation is performed using the fast Fourier method on a regular rectangular grid, similarly to particle in cells codes. To compute the density projected onto this grid, the intersection of the tessellation and the grid is calculated using the method of Franklin and Kankanhalli [65–67] generalised to linear order. As preliminary tests of the code, we study in four dimensional phase-space the evolution of an initially small patch in a chaotic potential and the cosmological collapse of a fluctuation composed of two sinusoidal waves. We also perform a “warm” dark matter simulation in six-dimensional phase-space that we use to check the parallel scaling of the code.« less

Properties of density and magnetic fluctuations occurring in density striations in the new LAPD

NASA Astrophysics Data System (ADS)

Maggs, J. E.; Morales, G. J.

2001-10-01

Previous studies of density striations (long, narrow magnetic-field-aligned density depletions) in the LAPD plasma device at UCLA revealed an eigenmode structure to fluctuations driven by the pressure gradient in the striation wall (Maggs and Morales, Phys. Plasmas, 4, 1997). The nature of these fluctuations depended on the plasma beta external to the striation, with shear Alfvén wave turbulence developing at betas less than the mass ratio and drift-Alfvén waves at betas above the mass ratio. These fluctuations were found to have a direct connection to turbulence observed at the plasma edge. The new LAPD is 18 meters in length with a background field up to twice previously attainable values. We report on the properties of fluctuations associated with density striations in the new device over a wider range of beta, and compare them to previous results. The behavior of fluctuations in density striations created in flared-field and magnetic-mirror geometries will also be presented. Research sponsored by ONR and NSF

Measuring dynamic membrane fluctuations in cell membrane using quantitative phase imaging (Conference Presentation)

NASA Astrophysics Data System (ADS)

Lee, SangYun; Kim, Kyoohyun; Park, YongKeun

2017-02-01

There is a strong correlation between the dynamic membrane fluctuations and the biomechanical properties of living cells. The dynamic membrane fluctuation consists of submicron displacements, and can be altered by changing the cells' pathophysiological conditions. These results have significant relevance to the understanding of RBC biophysics and pathology, as follows. RBCs must withstand large mechanical deformations during repeated passages through the microvasculature and the fenestrated walls of the splenic sinusoids. This essential ability is diminished with senescence, resulting in physiological destruction of the aging RBCs. Pathological destruction of the red cells, however, occurs in cells affected by a host of diseases such as spherocytosis, malaria, and Sickle cell disease, as RBCs depart from their normal discoid shape and lose their deformability. Therefore, quantifying the RBC deformability insight into a variety of problems regarding the interplay of cell structure, dynamics, and function. Furthermore, the ability to monitor mechanical properties of RBCs is of vital interest in monitoring disease progression or response to treatment as molecular and pharmaceutical approaches for treatment of chronic diseases. Here, we present the measurements of dynamic membrane fluctuations in live cells using quantitative phase imaging techniques. Measuring both the 3-D refractive index maps and the dynamic phase images of live cells are simultaneously measured, from which dynamic membrane fluctuation and deformability of cells are precisely calculated. We also present its applications to various diseases ranging from sickle cell diseases, babesiosis, and to diabetes.

High-density QCD phase transitions inside neutron stars: Glitches and gravitational waves

NASA Astrophysics Data System (ADS)

Srivastava, A. M.; Bagchi, P.; Das, A.; Layek, B.

2017-10-01

We discuss physics of exotic high baryon density QCD phases which are believed to exist in the core of a neutron star. This can provide a laboratory for exploring exotic physics such as axion emission, KK graviton production etc. Much of the physics of these high-density phases is model-dependent and not very well understood, especially the densities expected to occur inside neutron stars. We follow a different approach and use primarily universal aspects of the physics of different high-density phases and associated phase transitions. We study effects of density fluctuations during transitions with and without topological defect production and study the effect on pulsar timings due to changing moment of inertia of the star. We also discuss gravitational wave production due to rapidly changing quadrupole moment of the star due to these fluctuations.

Three-beam coherent combination experiments based on segmented mirrors and measure of phase characteristics of beams passing through Yb-doped fiber amplifier

NASA Astrophysics Data System (ADS)

Yang, Ping; Yang, Ruo fu; Shen, Feng; Ao, Mingwu; Jiang, Wenhan

2009-05-01

Coherent combination is one of the most promising ways to realize high power laser output. A three- laser-beam coherent combination system based on adaptive optics (AO) technique has been set up in our laboratory. In this system, three 1064nm laser beams are placed side-by-side and compressed by two reflective mirrors. An active segmented deformable mirror (DM) is used to compensate the optical path difference (OPD) among three laser beams. The beams are overlapped onto a 2900Hz CCD camera to form an interference pattern while the peak intensity of the interference pattern is taken as the cost function to optimize by a stochastic parallel gradient descent (SPGD) algorithm. SPGD algorithm is realized on a RT-Linux dual-core industrial computer. A series of experiments have been accomplished and experimental results show that both static distorted aberrations in the beams and active distorted aberrations (which are brought in by a hot iron and the frequency is about 5Hz) can be compensated successfully when the gain coefficients and the perturbation amplitude of SPGD are chosed appropriately, thereby three beams can be well combined. For controlling the phase of fiber lasers, the phase characteristics of beams passing through Yb-doped dual-clad fiber amplifier are measured by means of investigating the interference pattern under different output power through experiments. The frequency of phase fluctuation is evaluated through analyzing the fluctuation of power within a 90um aperture of far-field focal spot. Experimental results show that the phase fluctuation frequencies of laser beam transmitted through fiber amplifier are mainly in the range of 100~1500Hz. As a result, to control the phase fluctuation of beams passing through fiber amplifier, the bandwidth of any potential phase control scheme must be greater than 1.5 kilohertz.

Unique Pressure Dependence of the Order-Disorder Transition Temperature of a Series of PEP-PDMS Diblock Copolymers

NASA Astrophysics Data System (ADS)

Mortensen, K.; Almdal, K.; Schwahn, D.; Frielinghaus, H.

1997-03-01

Studies of the phase behavior of polymer systems has proven that the sensitivity to fluctuations is much more distinct than originally anticipated based on theoretical arguments. In blends of homo-polymers, studies have revealed that fluctuations give rise to significant re-normalized critical behavior. It has been argued that the free volume causes an entropic contribution to the Flory-Huggins interaction parameter, \\chi, and is thereby responsible for the re-normalized behavior. In block copolymers fluctuations have even more pronounced effects, as it changes the second order critical point at f=0.5 to first order and additional complex phases are stabilized. Measurements of the structure factor S(q) of PEP-PDMS diblock copolymers have revealed unique character in the phase-diagram with re-entrant ordered structure. Moreover, an unexpected singularity in the conformational compressibility, as identified from the peak-position, q, is observed. In contrary to binary polymer blends, pressure does not affect the Ginzburg number.

Cosmological density fluctuations produced by vacuum strings

NASA Astrophysics Data System (ADS)

Vilenkin, A.

1981-04-01

Consideration is given to the possible role of vacuum domain strings produced in the grand unification phase transition in the early universe in the generation of the density fluctuations giving rise to galaxies. The cosmological evolution of the strings formed in the grand unification phase transition is analyzed, with attention given to possible mechanisms for the damping out of oscillations produced by tension in convoluted strings and closed loops. The cosmological density fluctuations introduced by infinite strings and closed loops smaller than the horizon are then shown to be capable of giving rise to mass condensations on a scale of approximately 10 to the 9th solar masses at the time of the decoupling of radiation from matter, around which the galaxies condense. Differences between the present theory and that suggested by Zel'dovich (1980) are pointed out, and it is noted that string formation at the grand unification phase transition is possible only if the manifold of the degenerate vacua of the gauge theory is not simply connected.

Cu nuclear magnetic resonance study of charge and spin stripe order in La 1.875 Ba 0.125 CuO 4

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

Pelc, D.; Grafe, H. -J.; Gu, G. D.

In this paper, we present a Cu nuclear magnetic/quadrupole resonance study of the charge stripe ordered phase of LBCO, with detection of previously unobserved (“wiped-out”) signal. We show that spin-spin and spin-lattice relaxation rates are strongly enhanced in the charge ordered phase, explaining the apparent signal decrease in earlier investigations. The enhancement is caused by magnetic, rather than charge fluctuations, conclusively confirming the long-suspected assumption that spin fluctuations are responsible for the wipeout effect. Observation of the full Cu signal enables insight into the spin and charge dynamics of the stripe-ordered phase, and measurements in external magnetic fields provide informationmore » on the nature and suppression of spin fluctuations associated with charge order. Lastly, we find glassy spin dynamics, in agreement with previous work, and incommensurate static charge order with charge modulation amplitude similar to other cuprate compounds, suggesting that the amplitude of charge stripes is universal in the cuprates.« less

Cu nuclear magnetic resonance study of charge and spin stripe order in La 1.875 Ba 0.125 CuO 4

DOE PAGES

Pelc, D.; Grafe, H. -J.; Gu, G. D.; ...

2017-02-15

In this paper, we present a Cu nuclear magnetic/quadrupole resonance study of the charge stripe ordered phase of LBCO, with detection of previously unobserved (“wiped-out”) signal. We show that spin-spin and spin-lattice relaxation rates are strongly enhanced in the charge ordered phase, explaining the apparent signal decrease in earlier investigations. The enhancement is caused by magnetic, rather than charge fluctuations, conclusively confirming the long-suspected assumption that spin fluctuations are responsible for the wipeout effect. Observation of the full Cu signal enables insight into the spin and charge dynamics of the stripe-ordered phase, and measurements in external magnetic fields provide informationmore » on the nature and suppression of spin fluctuations associated with charge order. Lastly, we find glassy spin dynamics, in agreement with previous work, and incommensurate static charge order with charge modulation amplitude similar to other cuprate compounds, suggesting that the amplitude of charge stripes is universal in the cuprates.« less

Entanglement contour perspective for "strong area-law violation" in a disordered long-range hopping model

NASA Astrophysics Data System (ADS)

Roy, Nilanjan; Sharma, Auditya

2018-03-01

We numerically investigate the link between the delocalization-localization transition and entanglement in a disordered long-range hopping model of spinless fermions by studying various static and dynamical quantities. This includes the inverse participation ratio, level statistics, entanglement entropy, and number fluctuations in the subsystem along with quench and wave-packet dynamics. Finite systems show delocalized, quasilocalized, and localized phases. The delocalized phase shows strong area-law violation, whereas the (quasi)localized phase adheres to (for large subsystems) the strict area law. The idea of "entanglement contour" nicely explains the violation of area law and its relationship with "fluctuation contour" reveals a signature at the transition point. The relationship between entanglement entropy and number fluctuations in the subsystem also carries signatures for the transition in the model. Results from the Aubry-Andre-Harper model are compared in this context. The propagation of charge and entanglement are contrasted by studying quench and wave-packet dynamics at the single-particle and many-particle levels.

High redshift signatures in the 21 cm forest due to cosmic string wakes

NASA Astrophysics Data System (ADS)

Tashiro, Hiroyuki; Sekiguchi, Toyokazu; Silk, Joseph

2014-01-01

Cosmic strings induce minihalo formation in the early universe. The resultant minihalos cluster in string wakes and create a ``21 cm forest'' against the cosmic microwave background (CMB) spectrum. Such a 21 cm forest can contribute to angular fluctuations of redshifted 21 cm signals integrated along the line of sight. We calculate the root-mean-square amplitude of the 21 cm fluctuations due to strings and show that these fluctuations can dominate signals from minihalos due to primordial density fluctuations at high redshift (zgtrsim10), even if the string tension is below the current upper bound, Gμ < 1.5 × 10-7. Our results also predict that the Square Kilometre Array (SKA) can potentially detect the 21 cm fluctuations due to strings with Gμ ≈ 7.5 × 10-8 for the single frequency band case and 4.0 × 10-8 for the multi-frequency band case.

Fluctuations and correlations of conserved charges in QCD at finite temperature with effective models

NASA Astrophysics Data System (ADS)

Fu, Wei-Jie; Liu, Yu-Xin; Wu, Yue-Liang

2010-01-01

We study fluctuations of conserved charges including baryon number, electric charge, and strangeness as well as the correlations among these conserved charges in the 2+1 flavor Polyakov-Nambu-Jona-Lasinio model at finite temperature. The calculated results are compared with those obtained from recent lattice calculations performed with an improved staggered fermion action at two values of the lattice cutoff with almost physical up and down quark masses and a physical value for the strange quark mass. We find that our calculated results are well consistent with those obtained in lattice calculations except for some quantitative differences for fluctuations related with strange quarks. Our calculations indicate that there is a pronounced cusp in the ratio of the quartic to quadratic fluctuations of baryon number, i.e. χ4B/χ2B, at the critical temperature during the phase transition, which confirms that χ4B/χ2B is a useful probe of the deconfinement and chiral phase transition.

Critical point in the phase diagram of primordial quark-gluon matter from black hole physics

NASA Astrophysics Data System (ADS)

Critelli, Renato; Noronha, Jorge; Noronha-Hostler, Jacquelyn; Portillo, Israel; Ratti, Claudia; Rougemont, Romulo

2017-11-01

Strongly interacting matter undergoes a crossover phase transition at high temperatures T ˜1012 K and zero net-baryon density. A fundamental question in the theory of strong interactions, QCD, is whether a hot and dense system of quarks and gluons displays critical phenomena when doped with more quarks than antiquarks, where net-baryon number fluctuations diverge. Recent lattice QCD work indicates that such a critical point can only occur in the baryon dense regime of the theory, which defies a description from first principles calculations. Here we use the holographic gauge/gravity correspondence to map the fluctuations of baryon charge in the dense quark-gluon liquid onto a numerically tractable gravitational problem involving the charge fluctuations of holographic black holes. This approach quantitatively reproduces ab initio results for the lowest order moments of the baryon fluctuations and makes predictions for the higher-order baryon susceptibilities and also for the location of the critical point, which is found to be within the reach of heavy-ion collision experiments.

Propagations of fluctuations and flow separation on an unsteadily loaded airfoil

NASA Astrophysics Data System (ADS)

Tenney, Andrew; Lewalle, Jacques

2014-11-01

We analyze pressure data from 18 taps located along the surface of a DU-96-W180 airfoil in bothand steady flow conditions. The conditions were set to mimic the flow conditions experienced by a wind turbine blade under unsteady loading to test and to quantify the effects of several flow control schemes. Here we are interested in the propagation of fluctuations along the pressure and suction sides, particularly in relation to the fluctuating separation point. An unsteady phase of the incoming fluctuations is defined using Morlet wavelets, and phase-conditioned cross-correlations are calculated. Using wavelet-based pattern recognition, individual events in the pressure data are identified with several different algorithms utilizing both the original time series pressure signals and their corresponding scalograms. The data analyzed in this study was collected by G. Wang in the Skytop anechoic chamber at Syracuse University in the spring of 2013; the work of Zhe Bai on this data is also acknowledged.

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

Garnier, D. T.; Mauel, M. E.; Roberts, T. M.

Here, we report measurements of the turbulent evolution of the plasma density profile following the fast injection of lithium pellets into the Levitated Dipole Experiment (LDX) [Boxer et al., Nat. Phys. 6, 207 (2010)]. As the pellet passes through the plasma, it provides a significant internal particle source and allows investigation of density profile evolution, turbulent relaxation, and turbulent fluctuations. The total electron number within the dipole plasma torus increases by more than a factor of three, and the central density increases by more than a factor of five. During these large changes in density, the shape of the densitymore » profile is nearly “stationary” such that the gradient of the particle number within tubes of equal magnetic flux vanishes. In comparison to the usual case, when the particle source is neutral gas at the plasma edge, the internal source from the pellet causes the toroidal phase velocity of the fluctuations to reverse and changes the average particle flux at the plasma edge. An edge particle source creates an inward turbulent pinch, but an internal particle source increases the outward turbulent particle flux. Statistical properties of the turbulence are measured by multiple microwave interferometers and by an array of probes at the edge. The spatial structures of the largest amplitude modes have long radial and toroidal wavelengths. Estimates of the local and toroidally averaged turbulent particle flux show intermittency and a non-Gaussian probability distribution function. The measured fluctuations, both before and during pellet injection, have frequency and wave number dispersion consistent with theoretical expectations for interchange and entropy modes excited within a dipole plasma torus having warm electrons and cool ions.« less

Magnification of signatures of a topological phase transition by quantum zero point motion

NASA Astrophysics Data System (ADS)

Lopes, Pedro L. e. S.; Ghaemi, Pouyan

2015-08-01

We show that the zero point motion of a vortex in superconducting doped topological insulators leads to significant changes in the electronic spectrum at the topological phase transition in this system. This topological phase transition is tuned by the doping level, and the corresponding effects are manifest in the density of states at energies which are on the order of the vortex fluctuation frequency. Although the electronic energy gap in the spectrum generated by a stationary vortex is but a small fraction of the bulk superconducting gap, the vortex fluctuation frequency may be much larger. As a result, this quantum zero point motion can induce a discontinuous change in the spectral features of the system at the topological vortex phase transition to energies which are well within the resolution of scanning tunneling microscopy. This discontinuous change is exclusive to superconducting systems in which we have a topological phase transition. Moreover, the phenomena studied in this paper present effects of Magnus forces on the vortex spectrum which are not present in the ordinary s -wave superconductors. Finally, we demonstrate explicitly that the vortex in this system is equivalent to a Kitaev chain. This allows for the mapping of the vortex fluctuating scenario in three dimensions into similar one-dimensional situations in which one may search for other novel signatures of topological phase transitions.

Scale-invariant fluctuations from Galilean genesis

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

Wang, Yi; Brandenberger, Robert, E-mail: wangyi@physics.mcgill.ca, E-mail: rhb@physics.mcgill.ca

2012-10-01

We study the spectrum of cosmological fluctuations in scenarios such as Galilean Genesis \\cite(Nicolis) in which a spectator scalar field acquires a scale-invariant spectrum of perturbations during an early phase which asymptotes in the far past to Minkowski space-time. In the case of minimal coupling to gravity and standard scalar field Lagrangian, the induced curvature fluctuations depend quadratically on the spectator field and are hence non-scale-invariant and highly non-Gaussian. We show that if higher dimensional operators (the same operators that lead to the η-problem for inflation) are considered, a linear coupling between background and spectator field fluctuations is induced whichmore » leads to scale-invariant and Gaussian curvature fluctuations.« less

Critical fluctuations of the proton density in A+A collisions at 158A GeV

DOE PAGES

Anticic, T.; Baatar, B.; Bartke, J.; ...

2015-12-12

Here, we look for fluctuations expected for the QCD critical point using an intermittency analysis in the transverse momentum phase space of protons produced around midrapidity in the 12.5 % most central C+C, Si+Si and Pb+Pb collisions at the maximum SPS energy of 158A GeV. We find evidence of power-law fluctuations for the Si+Si data. The fitted power-law exponent Φ 2=0.96 +0.38 –0.25 (stat.) ± 0.16 (syst.) is consistent with the value expected for critical fluctuations. Power-law fluctuations had previously also been observed in low-mass π +π – pairs in the same Si+Si collisions.

Relation between quantum fluctuations and the performance enhancement of quantum annealing in a nonstoquastic Hamiltonian

NASA Astrophysics Data System (ADS)

Susa, Yuki; Jadebeck, Johann F.; Nishimori, Hidetoshi

2017-04-01

We study the relation between quantum fluctuations and the significant enhancement of the performance of quantum annealing in a mean-field Hamiltonian. First-order quantum phase transitions were shown to be reduced to second order by antiferromagnetic transverse interactions in a mean-field-type many-body-interacting Ising spin system in a transverse field, which means an exponential speedup of quantum annealing by adiabatic quantum computation. We investigate if and how quantum effects manifest themselves around these first- and second-order phase transitions to understand if the antiferromagnetic transverse interactions appended to the conventional transverse-field Ising model induce notable quantum effects. By measuring the proximity of the semiclassical spin-coherent state to the true ground state as well as the magnitude of the concurrence representing entanglement, we conclude that significant quantum fluctuations exist around second-order transitions, whereas quantum effects are much less prominent at first-order transitions. Although the location of the transition point can be predicted by the classical picture, system properties near the transition need quantum-mechanical descriptions for a second-order transition but not necessarily for first order. It is also found that quantum fluctuations are large within the ferromagnetic phase after a second-order transition from the paramagnetic phase. These results suggest that the antiferromagnetic transverse interactions induce marked quantum effects, and this fact would be related to closely to the significant enhancement of the performance of quantum annealing.

On the performance of joint iterative detection and decoding in coherent optical channels with laser frequency fluctuations

NASA Astrophysics Data System (ADS)

Castrillón, Mario A.; Morero, Damián A.; Agazzi, Oscar E.; Hueda, Mario R.

2015-08-01

The joint iterative detection and decoding (JIDD) technique has been proposed by Barbieri et al. (2007) with the objective of compensating the time-varying phase noise and constant frequency offset experienced in satellite communication systems. The application of JIDD to optical coherent receivers in the presence of laser frequency fluctuations has not been reported in prior literature. Laser frequency fluctuations are caused by mechanical vibrations, power supply noise, and other mechanisms. They significantly degrade the performance of the carrier phase estimator in high-speed intradyne coherent optical receivers. This work investigates the performance of the JIDD algorithm in multi-gigabit optical coherent receivers. We present simulation results of bit error rate (BER) for non-differential polarization division multiplexing (PDM)-16QAM modulation in a 200 Gb/s coherent optical system that includes an LDPC code with 20% overhead and net coding gain of 11.3 dB at BER = 10-15. Our study shows that JIDD with a pilot rate ⩽ 5 % compensates for both laser phase noise and laser frequency fluctuation. Furthermore, since JIDD is used with non-differential modulation formats, we find that gains in excess of 1 dB can be achieved over existing solutions based on an explicit carrier phase estimator with differential modulation. The impact of the fiber nonlinearities in dense wavelength division multiplexing (DWDM) systems is also investigated. Our results demonstrate that JIDD is an excellent candidate for application in next generation high-speed optical coherent receivers.

Beam Energy Scan of Specific Heat Through Temperature Fluctuations in Heavy Ion Collisions

NASA Astrophysics Data System (ADS)

Basu, Sumit; Nandi, Basanta K.; Chatterjee, Sandeep; Chatterjee, Rupa; Nayak, Tapan

2016-01-01

Temperature fluctuations may have two distinct origins, first, quantum fluctuations that are initial state fluctuations, and second, thermodynamical fluctuations. We discuss a method of extracting the thermodynamic temperature from the mean transverse momentum of pions, by using controllable parameters such as centrality of the system, and range of the transverse momenta. Event-by-event fluctuations in global temperature over a large phase space provide the specific heat of the system. We present Beam Energy Scan of specific heat from data, AMPT and HRG model prediction. Experimental results from NA49, STAR, PHENIX, PHOBOS and ALICE are combined to obtain the specific heat as a function of beam energy. These results are compared to calculations from AMPT event generator, HRG model and lattice calculations, respectively.

Inverse correlation between quasiparticle mass and T c in a cuprate high-T c superconductor.

PubMed

Putzke, Carsten; Malone, Liam; Badoux, Sven; Vignolle, Baptiste; Vignolles, David; Tabis, Wojciech; Walmsley, Philip; Bird, Matthew; Hussey, Nigel E; Proust, Cyril; Carrington, Antony

2016-03-01

Close to a zero-temperature transition between ordered and disordered electronic phases, quantum fluctuations can lead to a strong enhancement of electron mass and to the emergence of competing phases such as superconductivity. A correlation between the existence of such a quantum phase transition and superconductivity is quite well established in some heavy fermion and iron-based superconductors, and there have been suggestions that high-temperature superconductivity in copper-oxide materials (cuprates) may also be driven by the same mechanism. Close to optimal doping, where the superconducting transition temperature T c is maximal in cuprates, two different phases are known to compete with superconductivity: a poorly understood pseudogap phase and a charge-ordered phase. Recent experiments have shown a strong increase in quasiparticle mass m* in the cuprate YBa2Cu3O7-δ as optimal doping is approached, suggesting that quantum fluctuations of the charge-ordered phase may be responsible for the high-T c superconductivity. We have tested the robustness of this correlation between m* and T c by performing quantum oscillation studies on the stoichiometric compound YBa2Cu4O8 under hydrostatic pressure. In contrast to the results for YBa2Cu3O7-δ, we find that in YBa2Cu4O8, the mass decreases as T c increases under pressure. This inverse correlation between m* and T c suggests that quantum fluctuations of the charge order enhance m* but do not enhance T c.

Inverse correlation between quasiparticle mass and Tc in a cuprate high-Tc superconductor

PubMed Central

Putzke, Carsten; Malone, Liam; Badoux, Sven; Vignolle, Baptiste; Vignolles, David; Tabis, Wojciech; Walmsley, Philip; Bird, Matthew; Hussey, Nigel E.; Proust, Cyril; Carrington, Antony

2016-01-01

Close to a zero-temperature transition between ordered and disordered electronic phases, quantum fluctuations can lead to a strong enhancement of electron mass and to the emergence of competing phases such as superconductivity. A correlation between the existence of such a quantum phase transition and superconductivity is quite well established in some heavy fermion and iron-based superconductors, and there have been suggestions that high-temperature superconductivity in copper-oxide materials (cuprates) may also be driven by the same mechanism. Close to optimal doping, where the superconducting transition temperature Tc is maximal in cuprates, two different phases are known to compete with superconductivity: a poorly understood pseudogap phase and a charge-ordered phase. Recent experiments have shown a strong increase in quasiparticle mass m* in the cuprate YBa2Cu3O7-δ as optimal doping is approached, suggesting that quantum fluctuations of the charge-ordered phase may be responsible for the high-Tc superconductivity. We have tested the robustness of this correlation between m* and Tc by performing quantum oscillation studies on the stoichiometric compound YBa2Cu4O8 under hydrostatic pressure. In contrast to the results for YBa2Cu3O7-δ, we find that in YBa2Cu4O8, the mass decreases as Tc increases under pressure. This inverse correlation between m* and Tc suggests that quantum fluctuations of the charge order enhance m* but do not enhance Tc. PMID:27034989

On the relationship between atmospheric circulation and the fluctuations in the sea ice extents of the Bering and Okhotsk Seas

NASA Technical Reports Server (NTRS)

Cavalieri, D. J.; Parkinson, C. L.

1987-01-01

The influence of the hemispheric atmospheric circulation on the sea ice covers of the Bering Sea and the Sea of Okhotsk is examined using data obtained with the Nimbus 5 electrically scanning microwave radiometer for the four winters of the 1973-1976 period. The 3-day averaged sea ice extent data were used to establish periods for which there is an out-of-phase relationship between fluctuations of the two ice covers. A comparison of the sea-level atmospheric pressure field with the seasonal, interannual, and short-term sea ice fluctuations reveal an association between changes in the phase and the amplitude of the long waves in the atmosphere and advance and retreat of Arctic ice covers.

Impact of resonance decays on critical point signals in net-proton fluctuations

DOE PAGES

Bluhm, Marcus; Nahrgang, Marlene; Bass, Steffen A.; ...

2017-04-03

The non-monotonic beam energy dependence of the higher cumulants of net-proton fluctuations is a widely studied signature of the conjectured presence of a critical point in the QCD phase diagram. In this work we study the effect of resonance decays on critical fluctuations. We show that resonance effects reduce the signatures of critical fluctuations, but that for reasonable parameter choices critical effects in the net-proton cumulants survive. The relative role of resonance decays has a weak dependence on the order of the cumulants studied with a slightly stronger suppression of critical effects for higher-order cumulants.

Anisotropic phase diagram and spin fluctuations of the hyperkagome magnet Gd3Ga5O12 as revealed by sound velocity measurements

NASA Astrophysics Data System (ADS)

Rousseau, Alexandre; Parent, Jean-Michel; Quilliam, Jeffrey A.

2017-08-01

Sound velocity and attenuation measurements on the frustrated garnet material Gd3Ga5O12 (GGG) are presented as a function of field and temperature, with two different magnetic field orientations: [100 ] and [110 ] . We demonstrate that the phase diagram is highly anisotropic, with two distinct field-induced ordered phases for H ||[110 ] and only one for H ||[100 ] . Extensive lattice softening is found to occur at low fields, which can be associated with spin fluctuations. However, deep within the spin liquid phase a low-temperature stiffening of the lattice and reduced attenuation provide evidence for a spin gap which may be related to short-range antiferromagnetic correlations over minimal ten-spin loops.

Nonequilibrium phase transitions, fluctuations and correlations in an active contractile polar fluid.

PubMed

Gowrishankar, Kripa; Rao, Madan

2016-02-21

We study the patterning, fluctuations and correlations of an active polar fluid consisting of contractile polar filaments on a two-dimensional substrate, using a hydrodynamic description. The steady states generically consist of arrays of inward pointing asters and show a continuous transition from a moving lamellar phase, a moving aster street, to a stationary aster lattice with no net polar order. We next study the effect of spatio-temporal athermal noise, parametrized by an active temperature TA, on the stability of the ordered phases. In contrast to its equilibrium counterpart, we find that the active crystal shows true long range order at low TA. On increasing TA, the asters dynamically remodel, concomitantly we find novel phase transitions characterized by bond-orientational and polar order upon "heating".

Perspective: The Asakura Oosawa model: a colloid prototype for bulk and interfacial phase behavior.

PubMed

Binder, Kurt; Virnau, Peter; Statt, Antonia

2014-10-14

In many colloidal suspensions, the micrometer-sized particles behave like hard spheres, but when non-adsorbing polymers are added to the solution a depletion attraction (of entropic origin) is created. Since 60 years the Asakura-Oosawa model, which simply describes the polymers as ideal soft spheres, is an archetypical description for the statistical thermodynamics of such systems, accounting for many features of real colloid-polymer mixtures very well. While the fugacity of the polymers (which controls their concentration in the solution) plays a role like inverse temperature, the size ratio of polymer versus colloid radii acts as a control parameter to modify the phase diagram: when this ratio is large enough, a vapor-liquid like phase separation occurs at low enough colloid packing fractions, up to a triple point where a liquid-solid two-phase coexistence region takes over. For smaller size ratios, the critical point of the phase separation and the triple point merge, resulting in a single two-phase coexistence region between fluid and crystalline phases (of "inverted swan neck"-topology, with possibly a hidden metastable phase separation). Furthermore, liquid-crystalline ordering may be found if colloidal particles of non-spherical shape (e.g., rod like) are considered. Also interactions of the particles with solid surfaces should be tunable (e.g., walls coated by polymer brushes), and interfacial phenomena are particularly interesting experimentally, since fluctuations can be studied in the microscope on all length scales, down to the particle level. Due to its simplicity this model has become a workhorse for both analytical theory and computer simulation. Recently, generalizations addressing dynamic phenomena (phase separation, crystal nucleation, etc.) have become the focus of studies.

Perspective: The Asakura Oosawa model: A colloid prototype for bulk and interfacial phase behavior

NASA Astrophysics Data System (ADS)

Binder, Kurt; Virnau, Peter; Statt, Antonia

2014-10-01

In many colloidal suspensions, the micrometer-sized particles behave like hard spheres, but when non-adsorbing polymers are added to the solution a depletion attraction (of entropic origin) is created. Since 60 years the Asakura-Oosawa model, which simply describes the polymers as ideal soft spheres, is an archetypical description for the statistical thermodynamics of such systems, accounting for many features of real colloid-polymer mixtures very well. While the fugacity of the polymers (which controls their concentration in the solution) plays a role like inverse temperature, the size ratio of polymer versus colloid radii acts as a control parameter to modify the phase diagram: when this ratio is large enough, a vapor-liquid like phase separation occurs at low enough colloid packing fractions, up to a triple point where a liquid-solid two-phase coexistence region takes over. For smaller size ratios, the critical point of the phase separation and the triple point merge, resulting in a single two-phase coexistence region between fluid and crystalline phases (of "inverted swan neck"-topology, with possibly a hidden metastable phase separation). Furthermore, liquid-crystalline ordering may be found if colloidal particles of non-spherical shape (e.g., rod like) are considered. Also interactions of the particles with solid surfaces should be tunable (e.g., walls coated by polymer brushes), and interfacial phenomena are particularly interesting experimentally, since fluctuations can be studied in the microscope on all length scales, down to the particle level. Due to its simplicity this model has become a workhorse for both analytical theory and computer simulation. Recently, generalizations addressing dynamic phenomena (phase separation, crystal nucleation, etc.) have become the focus of studies.

Anomalous metallic state with strong charge fluctuations in BaxTi8O16 +δ revealed by hard x-ray photoemission spectroscopy

NASA Astrophysics Data System (ADS)

Dash, S.; Kajita, T.; Okawa, M.; Saitoh, T.; Ikenaga, E.; Saini, N. L.; Katsufuji, T.; Mizokawa, T.

2018-04-01

We have studied a charge-orbital driven metal-insulator transition (MIT) in hollandite-type BaxTi8O16 +δ by means of hard x-ray photoemission spectroscopy (HAXPES). The Ti 2 p HAXPES indicates strong Ti3 +/Ti4 + charge fluctuation in the metallic phase above the MIT temperature. The metallic phase is characterized by a power-law spectral function near the Fermi level which would be a signature of bad metal with non-Drude polaronic behavior. The power-law spectral shape is associated with the large Seebeck coefficient of the metallic phase in BaxTi8O16 +δ .

Method to calibrate phase fluctuation in polarization-sensitive swept-source optical coherence tomography

NASA Astrophysics Data System (ADS)

Lu, Zenghai; Kasaragod, Deepa K.; Matcher, Stephen J.

2011-07-01

We present a phase fluctuation calibration method for polarization-sensitive swept-source optical coherence tomography (PS-SS-OCT) using continuous polarization modulation. The method uses a low-voltage broadband polarization modulator driven by a synchronized sinusoidal burst waveform rather than an asynchronous waveform, together with the removal of the global phases of the measured Jones matrices by the use of matrix normalization. This makes it possible to average the measured Jones matrices to remove the artifact due to the speckle noise of the signal in the sample without introducing auxiliary optical components into the sample arm. This method was validated on measurements of an equine tendon sample by the PS-SS-OCT system.

Dynamic phases, pinning, and pattern formation for driven dislocation assemblies

DOE PAGES

Zhou, Caizhi; Reichhardt, Charles; Olson Reichhardt, Cynthia J.; ...

2015-01-23

We examine driven dislocation assemblies and show that they can exhibit a set of dynamical phases remarkably similar to those of driven systems with quenched disorder such as vortices in superconductors, magnetic domain walls, and charge density wave materials. These phases include pinned-jammed, fluctuating, and dynamically ordered states, and each produces distinct dislocation patterns as well as specific features in the noise fluctuations and transport properties. Lastly, our work suggests that many of the results established for systems with quenched disorder undergoing plastic depinning transitions can be applied to dislocation systems, providing a new approach for understanding pattern formation andmore » dynamics in these systems.« less

Hotspots of Community Change: Temporal Dynamics Are Spatially Variable in Understory Plant Composition of a California Oak Woodland

PubMed Central

Spotswood, Erica N.; Bartolome, James W.; Allen-Diaz, Barbara

2015-01-01

Community response to external drivers such climate and disturbance can lead to fluctuations in community composition, or to directional change. Temporal dynamics can be influenced by a combination of drivers operating at multiple spatial scales, including external landscape scale drivers, local abiotic conditions, and local species pools. We hypothesized that spatial variation in these factors can create heterogeneity in temporal dynamics within landscapes. We used understory plant species composition from an 11 year dataset from a California oak woodland to compare plots where disturbance was experimentally manipulated with the removal of livestock grazing and a prescribed burn. We quantified three properties of temporal variation: compositional change (reflecting the appearance and disappearance of species), temporal fluctuation, and directional change. Directional change was related most strongly to disturbance type, and was highest at plots where grazing was removed during the study. Temporal fluctuations, compositional change, and directional change were all related to intrinsic abiotic factors, suggesting that some locations are more responsive to external drivers than others. Temporal fluctuations and compositional change were linked to local functional composition, indicating that environmental filters can create subsets of the local species pool that do not respond in the same way to external drivers. Temporal dynamics are often assumed to be relatively static at the landscape scale, provided disturbance and climate are continuous. This study shows that local and landscape scale factors jointly influence temporal dynamics creating hotspots that are particularly responsive to climate and disturbance. Thus, adequate predictions of response to disturbance or to changing climate will only be achieved by considering how factors at multiple spatial scales influence community resilience and recovery. PMID:26222069

Hotspots of Community Change: Temporal Dynamics Are Spatially Variable in Understory Plant Composition of a California Oak Woodland.

PubMed

Spotswood, Erica N; Bartolome, James W; Allen-Diaz, Barbara

2015-01-01

Community response to external drivers such climate and disturbance can lead to fluctuations in community composition, or to directional change. Temporal dynamics can be influenced by a combination of drivers operating at multiple spatial scales, including external landscape scale drivers, local abiotic conditions, and local species pools. We hypothesized that spatial variation in these factors can create heterogeneity in temporal dynamics within landscapes. We used understory plant species composition from an 11 year dataset from a California oak woodland to compare plots where disturbance was experimentally manipulated with the removal of livestock grazing and a prescribed burn. We quantified three properties of temporal variation: compositional change (reflecting the appearance and disappearance of species), temporal fluctuation, and directional change. Directional change was related most strongly to disturbance type, and was highest at plots where grazing was removed during the study. Temporal fluctuations, compositional change, and directional change were all related to intrinsic abiotic factors, suggesting that some locations are more responsive to external drivers than others. Temporal fluctuations and compositional change were linked to local functional composition, indicating that environmental filters can create subsets of the local species pool that do not respond in the same way to external drivers. Temporal dynamics are often assumed to be relatively static at the landscape scale, provided disturbance and climate are continuous. This study shows that local and landscape scale factors jointly influence temporal dynamics creating hotspots that are particularly responsive to climate and disturbance. Thus, adequate predictions of response to disturbance or to changing climate will only be achieved by considering how factors at multiple spatial scales influence community resilience and recovery.

Searching for Supersolidity in Ultracold Atomic Bose Condensates with Rashba Spin-Orbit Coupling

NASA Astrophysics Data System (ADS)

Liao, Renyuan

2018-04-01

We developed a functional integral formulation for the stripe phase of spinor Bose-Einstein condensates with Rashba spin-orbit coupling. The excitation spectrum is found to exhibit double gapless band structures, identified to be two Goldstone modes resulting from spontaneously broken internal gauge symmetry and translational invariance symmetry. The sound velocities display anisotropic behavior with the lower branch vanishing in the direction perpendicular to the stripe in the x -y plane. At the transition point between the plane-wave phase and the stripe phase, physical quantities such as fluctuation correction to the ground-state energy and quantum depletion of the condensates exhibit discontinuity, characteristic of the first-order phase transition. Despite strong quantum fluctuations induced by Rashba spin-orbit coupling, we show that the supersolid phase is stable against quantum depletion. Finally, we extend our formulation to finite temperatures to account for interactions between excitations.

Statistical fluctuations as the origin of nontopological solitons

NASA Technical Reports Server (NTRS)

Griest, Kim; Kolb, Edward W.; Masarotti, Alessandro

1989-01-01

Nontopological solitons can be formed during a phase transition in the early universe as long as some net charge can be trapped in regions of false vacuum. It has been previously suggested that a particle-antiparticle asymmetry would provide a source for such trapped charge. It is pointed out that, for the model and parameters considered, statistical fluctuations provide a much larger concentration of charge, and are therefore, the dominant source of charge fluctuations in solitogenesis.

Edge resonant fluctuations and particle transport in a reversed-field pinch

NASA Astrophysics Data System (ADS)

Möller, A.

1998-12-01

Electrostatic fluctuations are measured in the Extrap T2 reversed-field pinch [J. R. Drake et al., in Plasma Physics and Controlled Nuclear Fusion Research 1996 (International Atomic Energy Agency, Vienna, 1997), Vol. 2, pp. 193-199] using a Langmuir probe array. The electrostatic fluctuation, driven particle transport ΓnΦ is derived and found to constitute a large fraction of the total particle transport. The spectral density of all measured quantities exhibits a peak in the frequency range 100-250 kHz, which originates from fluctuations that are resonant close to the edge [n=-(40-80)]. This peak contains only about 10-20% of the total fluctuation power, but is shown to dominate ΓnΦ. The main reason for this is the high toroidal mode number as compared with internally resonant magnetohydrodynamic fluctuations. The edge resonant fluctuations also features a higher coherence (γ=0.5) and close to 90° phase shift between density and potential fluctuations.

Noise thermometry with two weakly coupled Bose-Einstein condensates.

PubMed

Gati, Rudolf; Hemmerling, Börge; Fölling, Jonas; Albiez, Michael; Oberthaler, Markus K

2006-04-07

Here we report on the experimental investigation of thermally induced fluctuations of the relative phase between two Bose-Einstein condensates which are coupled via tunneling. The experimental control over the coupling strength and the temperature of the thermal background allows for the quantitative analysis of the phase fluctuations. Furthermore, we demonstrate the application of these measurements for thermometry in a regime where standard methods fail. With this we confirm that the heat capacity of an ideal Bose gas deviates from that of a classical gas as predicted by the third law of thermodynamics.

Effect of particle velocity fluctuations on the inertia coupling in two-phase flow

NASA Technical Reports Server (NTRS)

Drew, Donald A.

1989-01-01

Consistent forms for the interfacial force, the interfacial pressure, the Reynolds stresses and the particle stress have been derived for the inviscid, irrotational incompressible flow of fluid in a dilute suspension of spheres. The particles are assumed to have a velocity distribution, giving rise to an effective pressure and stress in the particle phase. The velocity fluctuations also contribute in the fluid Reynolds stress and in the (elastic) stress field inside the spheres. The relation of these constitutive equations to the force on an individual sphere is discussed.

Reduction of magnetic field fluctuations in powered magnets for NMR using inductive measurements and sampled-data feedback control.

PubMed

Li, Mingzhou; Schiano, Jeffrey L; Samra, Jenna E; Shetty, Kiran K; Brey, William W

2011-10-01

Resistive and hybrid (resistive/superconducting) magnets provide substantially higher magnetic fields than those available in low-temperature superconducting magnets, but their relatively low spatial homogeneity and temporal field fluctuations are unacceptable for high resolution NMR. While several techniques for reducing temporal fluctuations have demonstrated varying degrees of success, this paper restricts attention to methods that utilize inductive measurements and feedback control to actively cancel the temporal fluctuations. In comparison to earlier studies using analog proportional control, this paper shows that shaping the controller frequency response results in significantly higher reductions in temporal fluctuations. Measurements of temporal fluctuation spectra and the frequency response of the instrumentation that cancels the temporal fluctuations guide the controller design. In particular, we describe a sampled-data phase-lead-lag controller that utilizes the internal model principle to selectively attenuate magnetic field fluctuations caused by the power supply ripple. We present a quantitative comparison of the attenuation in temporal fluctuations afforded by the new design and a proportional control design. Metrics for comparison include measurements of the temporal fluctuations using Faraday induction and observations of the effect that the fluctuations have on nuclear resonance measurements. Copyright © 2011. Published by Elsevier Inc.

Bose–Einstein condensation versus Dicke–Hepp–Lieb transition in an optical cavity

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

Piazza, Francesco, E-mail: francesco.piazza@ph.tum.de; Strack, Philipp; Zwerger, Wilhelm

We provide an exact solution for the interplay between Bose–Einstein condensation and the Dicke–Hepp–Lieb self-organization transition of an ideal Bose gas trapped inside a single-mode optical cavity and subject to a transverse laser drive. Based on an effective action approach, we determine the full phase diagram at arbitrary temperature, which features a bi-critical point where the transitions cross. We calculate the dynamically generated band structure of the atoms and the associated suppression of the critical temperature for Bose–Einstein condensation in the phase with a spontaneous periodic density modulation. Moreover, we determine the evolution of the polariton spectrum due to themore » coupling of the cavity photons and the atomic field near the self-organization transition, which is quite different above or below the Bose–Einstein condensation temperature. At low temperatures, the critical value of the Dicke–Hepp–Lieb transition decreases with temperature and thus thermal fluctuations can enhance the tendency to a periodic arrangement of the atoms. -- Highlights: •Atoms inside a driven cavity can undergo two transitions: self-organization and BEC. •The phase diagram has four phases which coexist at a bi-critical point. •Atom–cavity coupling creates a dynamical lattice for the atoms. •Finite temperature can enhance the tendency towards self-organization. •We calculate the detailed spectrum of the polaritonic excitations.« less

Study of solar photospheric MHD oscillations: Observations with MDI, ASP and MWO

NASA Astrophysics Data System (ADS)

Norton, Aimee Ann

Magnetodydrodynamical waves are expected to be an important energy transport mechanism in the solar atmosphere. This thesis uses data from a spectro-polarimeter and longitudinal magnetographs to study characteristics of magneto-hydrodynamical oscillations at photospheric heights. Significant oscillatory magnetic power is observed with the Michelson Doppler Imager in three frequency regimes: 0.5--1.0, 3.0--3.5 and 5.5--6.0 mHz corresponding to timescales of magnetic evolution, p-modes and the three minute resonant sunspot oscillation. Spatial distribution of magnetogram oscillatory power exhibits the same general features in numerous datasets. Low frequency magnetogram power is found in rings with filamentary structure surrounding sunspots. Five minute power peaks in extended regions of plage. Three minute oscillations are observed in sunspot umbra. Phase angles between velocity and magnetic fluctuations are found to be approximately -90°, a signature of magnetoacoustic waves, in disk-center active region data. Phase dependence upon observation angle is established through sunspot values decreasing from -100° at disk-center towards -31° at the limb, confirming greater Alfen wave visibility at the limb. Consistent propagation direction or field-aligned velocities explain an unexpected phase jump from negative to positive values for divergent sunspot fields observed away from disk-center. Simultaneously obtained Stokes profiles and longitudinal magnetogram maps of a positive plage region provide time series which could be compared. The velocity signals are in excellent agreement. Magnetic flux correlates best with fluctuations in filling factor, not inclination angle or field strength, implying the responsible physical mechanism is internally unperturbed flux tubes being buffeted by external pressure fluctuations. Sampling signals from different heights of formation provides slight phase shifts and large propagation speeds for velocity, indicative of modified standing waves. Phase speeds associated with magnetic signals are characteristic of photospheric Alfven speeds for plage fields. The phase speed increase with height agrees with the altitude dependence of the Alfven speed. Observed fluctuations, phase angles and phase lags are interpreted as a superposition of signatures from the horizontal component of the driving mechanism sweeping the field lines in/out of the resolution area and the magnetic response of the flux tube to this buffeting.

Power fluctuation reduction methodology for the grid-connected renewable power systems

NASA Astrophysics Data System (ADS)

Aula, Fadhil T.; Lee, Samuel C.

2013-04-01

This paper presents a new methodology for eliminating the influence of the power fluctuations of the renewable power systems. The renewable energy, which is to be considered an uncertain and uncontrollable resource, can only provide irregular electrical power to the power grid. This irregularity creates fluctuations of the generated power from the renewable power systems. These fluctuations cause instability to the power system and influence the operation of conventional power plants. Overall, the power system is vulnerable to collapse if necessary actions are not taken to reduce the impact of these fluctuations. This methodology aims at reducing these fluctuations and makes the generated power capability for covering the power consumption. This requires a prediction tool for estimating the generated power in advance to provide the range and the time of occurrence of the fluctuations. Since most of the renewable energies are weather based, as a result a weather forecast technique will be used for predicting the generated power. The reduction of the fluctuation also requires stabilizing facilities to maintain the output power at a desired level. In this study, a wind farm and a photovoltaic array as renewable power systems and a pumped-storage and batteries as stabilizing facilities are used, since they are best suitable for compensating the fluctuations of these types of power suppliers. As an illustrative example, a model of wind and photovoltaic power systems with battery energy and pumped hydro storage facilities for power fluctuation reduction is included, and its power fluctuation reduction is verified through simulation.

Large-scale fluctuations in the diffusive decomposition of solid solutions

NASA Astrophysics Data System (ADS)

Karpov, V. G.; Grimsditch, M.

1995-04-01

The concept of an instability in the classic Ostwald ripening theory with respect to compositional fluctuations is suggested. We show that small statistical fluctuations in the precipitate phase lead to gigantic Coulomb-like fluctuations in the solute concentration which in turn affect the ripening. As a result large-scale fluctuations in both the precipitate and solute concentrations appear. These fluctuations are characterized by amplitudes of the order of the average values of the corresponding quantities and by a space scale L~(na)-1/2 which is considerably greater than both the average nuclear radius and internuclear distance. The Lifshitz-Slyozov theory of ripening is shown to remain locally applicable, over length scales much less than L. The implications of these findings for elastic light scattering in solid solutions that have undergone Ostwald ripening are considered.

Inelastic Light Scattering Measurements of a Pressure-Induced Quantum Liquid in KCuF3

NASA Astrophysics Data System (ADS)

Yuan, S.; Kim, M.; Seeley, J. T.; Lee, J. C. T.; Lal, S.; Abbamonte, P.; Cooper, S. L.

2012-11-01

Pressure-dependent, low-temperature inelastic light (Raman) scattering measurements of KCuF3 show that applied pressure above P*˜7kbar suppresses a previously observed structural phase transition temperature to zero temperature in KCuF3, resulting in the development of a fluctuational (quasielastic) response near T˜0K. This pressure-induced fluctuational response—which we associate with slow fluctuations of the CuF6 octahedral orientation—is temperature independent and exhibits a characteristic fluctuation rate that is much larger than the temperature, consistent with quantum fluctuations of the CuF6 octahedra. A model of pseudospin-phonon coupling provides a qualitative description of both the temperature- and pressure-dependent evolution of the Raman spectra of KCuF3.

Waves of actin and microtubule polymerization drive microtubule-based transport and neurite growth before single axon formation

PubMed Central

Winans, Amy M; Collins, Sean R; Meyer, Tobias

2016-01-01

Many developing neurons transition through a multi-polar state with many competing neurites before assuming a unipolar state with one axon and multiple dendrites. Hallmarks of the multi-polar state are large fluctuations in microtubule-based transport into and outgrowth of different neurites, although what drives these fluctuations remains elusive. We show that actin waves, which stochastically migrate from the cell body towards neurite tips, direct microtubule-based transport during the multi-polar state. Our data argue for a mechanical control system whereby actin waves transiently widen the neurite shaft to allow increased microtubule polymerization to direct Kinesin-based transport and create bursts of neurite extension. Actin waves also require microtubule polymerization, arguing that positive feedback links these two components. We propose that actin waves create large stochastic fluctuations in microtubule-based transport and neurite outgrowth, promoting competition between neurites as they explore the environment until sufficient external cues can direct one to become the axon. DOI: http://dx.doi.org/10.7554/eLife.12387.001 PMID:26836307

Effect of the collective motions of molecules inside a condensed phase on fluctuations in the density of small bodies

NASA Astrophysics Data System (ADS)

Tovbin, Yu. K.

2017-11-01

An approach to calculating the effects of fluctuations in density that considers the collective motions of molecules in small condensed phases (e.g., droplets, microcrystals, adsorption at microcrystal faces) is proposed. Statistical sums of the vibrational, rotational, and translational motions of molecules are of a collective character expressed in the dependences of these statistical sums on the local configurations of neighboring molecules. This changes their individual contributions to the free energy and modifies fluctuations in density in the inner homogeneous regions of small bodies. Interactions between nearest neighbors are considered in a quasi-chemical approximation that reflects the effects of short-range direct correlations. Expressions for isotherms relating the densities of mixture components to the chemical potentials in a thermostat are obtained, along with equations for pair distribution functions.

Long-wavelength fluctuations and the glass transition in two dimensions and three dimensions

PubMed Central

Vivek, Skanda; Kelleher, Colm P.; Chaikin, Paul M.

2017-01-01

Phase transitions significantly differ between 2D and 3D systems, but the influence of dimensionality on the glass transition is unresolved. We use microscopy to study colloidal systems as they approach their glass transitions at high concentrations and find differences between two dimensions and three dimensions. We find that, in two dimensions, particles can undergo large displacements without changing their position relative to their neighbors, in contrast with three dimensions. This is related to Mermin–Wagner long-wavelength fluctuations that influence phase transitions in two dimensions. However, when measuring particle motion only relative to their neighbors, two dimensions and three dimensions have similar behavior as the glass transition is approached, showing that the long-wavelength fluctuations do not cause a fundamental distinction between 2D and 3D glass transitions. PMID:28137847

Long-wavelength fluctuations and the glass transition in two dimensions and three dimensions.

PubMed

Vivek, Skanda; Kelleher, Colm P; Chaikin, Paul M; Weeks, Eric R

2017-02-21

Phase transitions significantly differ between 2D and 3D systems, but the influence of dimensionality on the glass transition is unresolved. We use microscopy to study colloidal systems as they approach their glass transitions at high concentrations and find differences between two dimensions and three dimensions. We find that, in two dimensions, particles can undergo large displacements without changing their position relative to their neighbors, in contrast with three dimensions. This is related to Mermin-Wagner long-wavelength fluctuations that influence phase transitions in two dimensions. However, when measuring particle motion only relative to their neighbors, two dimensions and three dimensions have similar behavior as the glass transition is approached, showing that the long-wavelength fluctuations do not cause a fundamental distinction between 2D and 3D glass transitions.

Exact Critical Exponents for the Antiferromagnetic Quantum Critical Metal in Two Dimensions

NASA Astrophysics Data System (ADS)

Schlief, Andres; Lunts, Peter; Lee, Sung-Sik

2017-04-01

Unconventional metallic states which do not support well-defined single-particle excitations can arise near quantum phase transitions as strong quantum fluctuations of incipient order parameters prevent electrons from forming coherent quasiparticles. Although antiferromagnetic phase transitions occur commonly in correlated metals, understanding the nature of the strange metal realized at the critical point in layered systems has been hampered by a lack of reliable theoretical methods that take into account strong quantum fluctuations. We present a nonperturbative solution to the low-energy theory for the antiferromagnetic quantum critical metal in two spatial dimensions. Being a strongly coupled theory, it can still be solved reliably in the low-energy limit as quantum fluctuations are organized by a new control parameter that emerges dynamically. We predict the exact critical exponents that govern the universal scaling of physical observables at low temperatures.

Nonequilibrium optical control of dynamical states in superconducting nanowire circuits.

PubMed

Madan, Ivan; Buh, Jože; Baranov, Vladimir V; Kabanov, Viktor V; Mrzel, Aleš; Mihailovic, Dragan

2018-03-01

Optical control of states exhibiting macroscopic phase coherence in condensed matter systems opens intriguing possibilities for materials and device engineering, including optically controlled qubits and photoinduced superconductivity. Metastable states, which in bulk materials are often associated with the formation of topological defects, are of more practical interest. Scaling to nanosize leads to reduced dimensionality, fundamentally changing the system's properties. In one-dimensional superconducting nanowires, vortices that are present in three-dimensional systems are replaced by fluctuating topological defects of the phase. These drastically change the dynamical behavior of the superconductor and introduce dynamical periodic long-range ordered states when the current is driven through the wire. We report the control and manipulation of transitions between different dynamically stable states in superconducting δ 3 -MoN nanowire circuits by ultrashort laser pulses. Not only can the transitions between different dynamically stable states be precisely controlled by light, but we also discovered new photoinduced hidden states that cannot be reached under near-equilibrium conditions, created while laser photoexcited quasi-particles are outside the equilibrium condition. The observed switching behavior can be understood in terms of dynamical stabilization of various spatiotemporal periodic trajectories of the order parameter in the superconductor nanowire, providing means for the optical control of the superconducting phase with subpicosecond control of timing.

Digital micromirror device-based common-path quantitative phase imaging.

PubMed

Zheng, Cheng; Zhou, Renjie; Kuang, Cuifang; Zhao, Guangyuan; Yaqoob, Zahid; So, Peter T C

2017-04-01

We propose a novel common-path quantitative phase imaging (QPI) method based on a digital micromirror device (DMD). The DMD is placed in a plane conjugate to the objective back-aperture plane for the purpose of generating two plane waves that illuminate the sample. A pinhole is used in the detection arm to filter one of the beams after sample to create a reference beam. Additionally, a transmission-type liquid crystal device, placed at the objective back-aperture plane, eliminates the specular reflection noise arising from all the "off" state DMD micromirrors, which is common in all DMD-based illuminations. We have demonstrated high sensitivity QPI, which has a measured spatial and temporal noise of 4.92 nm and 2.16 nm, respectively. Experiments with calibrated polystyrene beads illustrate the desired phase measurement accuracy. In addition, we have measured the dynamic height maps of red blood cell membrane fluctuations, showing the efficacy of the proposed system for live cell imaging. Most importantly, the DMD grants the system convenience in varying the interference fringe period on the camera to easily satisfy the pixel sampling conditions. This feature also alleviates the pinhole alignment complexity. We envision that the proposed DMD-based common-path QPI system will allow for system miniaturization and automation for a broader adaption.

Digital micromirror device-based common-path quantitative phase imaging

PubMed Central

Zheng, Cheng; Zhou, Renjie; Kuang, Cuifang; Zhao, Guangyuan; Yaqoob, Zahid; So, Peter T. C.

2017-01-01

We propose a novel common-path quantitative phase imaging (QPI) method based on a digital micromirror device (DMD). The DMD is placed in a plane conjugate to the objective back-aperture plane for the purpose of generating two plane waves that illuminate the sample. A pinhole is used in the detection arm to filter one of the beams after sample to create a reference beam. Additionally, a transmission-type liquid crystal device, placed at the objective back-aperture plane, eliminates the specular reflection noise arising from all the “off” state DMD micromirrors, which is common in all DMD-based illuminations. We have demonstrated high sensitivity QPI, which has a measured spatial and temporal noise of 4.92 nm and 2.16 nm, respectively. Experiments with calibrated polystyrene beads illustrate the desired phase measurement accuracy. In addition, we have measured the dynamic height maps of red blood cell membrane fluctuations, showing the efficacy of the proposed system for live cell imaging. Most importantly, the DMD grants the system convenience in varying the interference fringe period on the camera to easily satisfy the pixel sampling conditions. This feature also alleviates the pinhole alignment complexity. We envision that the proposed DMD-based common-path QPI system will allow for system miniaturization and automation for a broader adaption. PMID:28362789

Nonequilibrium optical control of dynamical states in superconducting nanowire circuits

PubMed Central

Madan, Ivan; Baranov, Vladimir V.

2018-01-01

Optical control of states exhibiting macroscopic phase coherence in condensed matter systems opens intriguing possibilities for materials and device engineering, including optically controlled qubits and photoinduced superconductivity. Metastable states, which in bulk materials are often associated with the formation of topological defects, are of more practical interest. Scaling to nanosize leads to reduced dimensionality, fundamentally changing the system’s properties. In one-dimensional superconducting nanowires, vortices that are present in three-dimensional systems are replaced by fluctuating topological defects of the phase. These drastically change the dynamical behavior of the superconductor and introduce dynamical periodic long-range ordered states when the current is driven through the wire. We report the control and manipulation of transitions between different dynamically stable states in superconducting δ3-MoN nanowire circuits by ultrashort laser pulses. Not only can the transitions between different dynamically stable states be precisely controlled by light, but we also discovered new photoinduced hidden states that cannot be reached under near-equilibrium conditions, created while laser photoexcited quasi-particles are outside the equilibrium condition. The observed switching behavior can be understood in terms of dynamical stabilization of various spatiotemporal periodic trajectories of the order parameter in the superconductor nanowire, providing means for the optical control of the superconducting phase with subpicosecond control of timing. PMID:29670935

Spectral quantum fluctuations in a stimulated Raman generator: a description in terms of temporally coherent modes.

PubMed

Walmsley, I A

1992-03-15

The probability density of the single-shot mean Stokes frequency from a linear Raman generator is calculated. It is shown that the fluctuations in the Stokes pulse energy spectrum that arise from the quantum initiation of the Stokes light are reduced in the transient regime of amplification. Also, it appears that saturation of the Raman gain does not reduce the phase fluctuations of the Stokes light below those present in the unsaturated gain (linear) regime.

Nernst effect from fluctuating pairs in the pseudogap phase of the cuprates.

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

Levchenko, A.; Norman, M. R.; Varlamov, A. A.

2011-01-31

The observation of a large Nernst signal in cuprates above the superconducting transition temperature has attracted much attention. A potential explanation is that it originates from superconducting fluctuations. Although the Nernst signal is indeed consistent with Gaussian fluctuations for overdoped cuprates, Gaussian theory fails to describe the temperature dependence seen for underdoped cuprates. Here, we consider the vertex correction to Gaussian theory resulting from the pseudogap. This yields a Nernst signal in good agreement with the data.

Application of cross recurrence plot for identification of temperature fluctuations synchronization in parallel minichannels

NASA Astrophysics Data System (ADS)

Grzybowski, H.; Mosdorf, R.

2016-09-01

The temperature fluctuations occurring in flow boiling in parallel minichannels with diameter of 1 mm have been experimentally investigated and analysed. The wall temperature was recorded at each minichannel outlet by thermocouple with 0.08 mm diameter probe. The time series where recorded during dynamic two-phase flow instabilities which are accompanied by chaotic temperature fluctuations. Time series were denoised using wavelet decomposition and were analysed using cross recurrence plots (CRP) which enables the study of two time series synchronization.

Cable delay compensator for microwave signal distribution over optical fibers

NASA Astrophysics Data System (ADS)

Primas, Lori E.

1990-12-01

The basic principles of microwave fiber-optic systems are outlined with emphasis on fiber-optic cable delay compensators (CDC). Degradation of frequency and phase stability is considered, and it is pointed out that the long-term stability of a fiber-optic link is degraded by group delay variations due to temperature fluctuations in the optical fiber and low-frequency noise characteristics of the laser. A CDC employing a voltage-controlled oscillator to correct for phase variations in the optical fiber is presented, and the static as well as dynamic closed-loop analyses of the fiber-optic CDC are discussed. A constructed narrow-band fiber-optic CDC is shown to reduce phase variations caused by temperature fluctuations by a factor of 400. A wide-band CDC utilizing a temperature-controlled coil of fiber to compensate for phase delay is also proposed.

Low-noise phase of a two-dimensional active nematic system

NASA Astrophysics Data System (ADS)

Shankar, Suraj; Ramaswamy, Sriram; Marchetti, M. Cristina

2018-01-01

We consider a collection of self-driven apolar particles on a substrate that organize into an active nematic phase at sufficiently high density or low noise. Using the dynamical renormalization group, we systematically study the two-dimensional fluctuating ordered phase in a coarse-grained hydrodynamic description involving both the nematic director and the conserved density field. In the presence of noise, we show that the system always displays only quasi-long-ranged orientational order beyond a crossover scale. A careful analysis of the nonlinearities permitted by symmetry reveals that activity is dangerously irrelevant over the linearized description, allowing giant number fluctuations to persist although now with strong finite-size effects and a nonuniversal scaling exponent. Nonlinear effects from the active currents lead to power-law correlations in the density field, thereby preventing macroscopic phase separation in the thermodynamic limit.

Orientational fluctuations and phase transitions in 8CB confined by cylindrical pores of the PET film

NASA Astrophysics Data System (ADS)

Maksimochkin, G. I.; Shmeliova, D. V.; Pasechnik, S. V.; Dubtsov, A. V.; Semina, O. A.; Kralj, S.

2016-08-01

Results of optical investigations of the isotropic-nematic and nematic-smectic A phase transitions in porous polyethyleneterephthalate (PET) films filled with octyl-cyanobihenyl (8CB) liquid crystal (LC) are reported. Samples of porous films of thickness 23 µm with normally oriented cylindrical pores of a radius R ranging from 10 nm to 1000 nm were prepared using the track-etched membrane technology. The dynamic light scattering method was used to probe the nematic orientational fluctuations of confined LC samples. The corresponding relaxation time τ was measured as a function of R and temperature T at slow enough cooling rates (0.3-0.6 K/h) to locate the phase transition temperatures. Changes in τ(T) dependencies relatively sensitivity fingerprint the LC phase transformations. Experimental results are analysed using the Landau-de Gennes-Ginzburg phenomenological approach.

Topological phase in a two-dimensional metallic heavy-fermion system

NASA Astrophysics Data System (ADS)

Yoshida, Tsuneya; Peters, Robert; Fujimoto, Satoshi; Kawakami, Norio

2013-04-01

We report on a topological insulating state in a heavy-fermion system away from half filling, which is hidden within a ferromagnetic metallic phase. In this phase, the cooperation of the RKKY interaction and the Kondo effect, together with the spin-orbit coupling, induces a spin-selective gap, bringing about topologically nontrivial properties. This topological phase is robust against a change in the chemical potential in a much wider range than the gap size. We analyze these remarkable properties by using dynamical mean field theory and the numerical renormalization group. Its topological properties support a gapless chiral edge mode, which exhibits a non-Tomonaga-Luttinger liquid behavior due to the coupling with bulk ferromagnetic spin fluctuations. We also propose that the effects of the spin fluctuations on the edge mode can be detected via the NMR relaxation time measurement.

Light nuclei production as a probe of the QCD phase diagram

NASA Astrophysics Data System (ADS)

Sun, Kai-Jia; Chen, Lie-Wen; Ko, Che Ming; Pu, Jie; Xu, Zhangbu

2018-06-01

It is generally believed that the quark-hadron transition at small values of baryon chemical potentials μB is a crossover but changes to a first-order phase transition with an associated critical endpoint (CEP) as μB increases. Such a μB-dependent quark-hadron transition is expected to result in a double-peak structure in the collision energy dependence of the baryon density fluctuation in heavy-ion collisions with one at lower energy due to the spinodal instability during the first-order phase transition and another at higher energy due to the critical fluctuations in the vicinity of the CEP. By analyzing the data on the p, d and 3H yields in central heavy-ion collisions within the coalescence model for light nuclei production, we find that the relative neutron density fluctuation Δρn = 〈(δρn) 2 〉 /〈ρn 〉 2 at kinetic freeze-out indeed displays a clear peak at √{sNN } = 8.8GeV and a possible strong re-enhancement at √{sNN } = 4.86GeV. Our findings thus provide a strong support for the existence of a first-order phase transition at large μB and its critical endpoint at a smaller μB in the temperature versus baryon chemical potential plane of the QCD phase diagram.

Random Telegraph Signal-Like Fluctuation Created by Fowler-Nordheim Stress in Gate Induced Drain Leakage Current of the Saddle Type Dynamic Random Access Memory Cell Transistor

NASA Astrophysics Data System (ADS)

Kim, Heesang; Oh, Byoungchan; Kim, Kyungdo; Cha, Seon-Yong; Jeong, Jae-Goan; Hong, Sung-Joo; Lee, Jong-Ho; Park, Byung-Gook; Shin, Hyungcheol

2010-09-01

We generated traps inside gate oxide in gate-drain overlap region of recess channel type dynamic random access memory (DRAM) cell transistor through Fowler-Nordheim (FN) stress, and observed gate induced drain leakage (GIDL) current both in time domain and in frequency domain. It was found that the trap inside gate oxide could generate random telegraph signal (RTS)-like fluctuation in GIDL current. The characteristics of that fluctuation were similar to those of RTS-like fluctuation in GIDL current observed in the non-stressed device. This result shows the possibility that the trap causing variable retention time (VRT) in DRAM data retention time can be located inside gate oxide like channel RTS of metal-oxide-semiconductor field-effect transistors (MOSFETs).

High-pressure electronic phase diagrams in FeSe1-xSx superconductors

NASA Astrophysics Data System (ADS)

Matsuura, Kohei; Arai, Yuki; Hosoi, Suguru; Ishida, Kousuke; Mizukami, Yuta; Watashige, Tatsuya; Kasahara, Shigeru; Matsuda, Yuji; Maejima, Naoyuki; Machida, Akihiko; Watanuki, Tetsu; Fukuda, Tatsuo; Uwatoko, Yoshiya; Shibauchi, Takasada

The spin fluctuations are believed to be related to the mechanism of the unconventional superconductors. On the other hand, many recent studies suggest that the nematic order that spontaneously breaks rotational symmetry of the system exists in the Fe-based superconductors and its quantum fluctuations may play an essential role for the superconductivity. However, this remains unclear because the nematic order usually coexists with the magnetic order. To solve this issue, FeSe exhibiting a nonmagnetic nematic order is a key system. Under pressure, this order is suppressed and concurrently magnetic order appears, which competes with high-Tc superconducting phase. In isovalent substitution system FeSe1-xSx, we found a nonmagnetic nematic quantum critical point. Here we report our recent high-pressure studies in high-quality single-crystalline FeSe1-xSx up to 8 GPa. We find a systematic change of the pressure phase diagram in FeSe by the S-substitution. Our results imply that the respective role of nematic and magnetic fluctuations can be elucidated from the precise control of pressure and substitution in this system.

Calculation of a fluctuating entropic force by phase space sampling.

PubMed

Waters, James T; Kim, Harold D

2015-07-01

A polymer chain pinned in space exerts a fluctuating force on the pin point in thermal equilibrium. The average of such fluctuating force is well understood from statistical mechanics as an entropic force, but little is known about the underlying force distribution. Here, we introduce two phase space sampling methods that can produce the equilibrium distribution of instantaneous forces exerted by a terminally pinned polymer. In these methods, both the positions and momenta of mass points representing a freely jointed chain are perturbed in accordance with the spatial constraints and the Boltzmann distribution of total energy. The constraint force for each conformation and momentum is calculated using Lagrangian dynamics. Using terminally pinned chains in space and on a surface, we show that the force distribution is highly asymmetric with both tensile and compressive forces. Most importantly, the mean of the distribution, which is equal to the entropic force, is not the most probable force even for long chains. Our work provides insights into the mechanistic origin of entropic forces, and an efficient computational tool for unbiased sampling of the phase space of a constrained system.

Coherent generation of symmetry-forbidden phonons by light-induced electron-phonon interactions in magnetite

NASA Astrophysics Data System (ADS)

Borroni, S.; Baldini, E.; Katukuri, V. M.; Mann, A.; Parlinski, K.; Legut, D.; Arrell, C.; van Mourik, F.; Teyssier, J.; Kozlowski, A.; Piekarz, P.; Yazyev, O. V.; Oleś, A. M.; Lorenzana, J.; Carbone, F.

2017-09-01

Symmetry breaking across phase transitions often causes changes in selection rules and emergence of optical modes which can be detected via spectroscopic techniques or generated coherently in pump-probe experiments. In second-order or weakly first-order transitions, fluctuations of the ordering field are present above the ordering temperature, giving rise to intriguing precursor phenomena, such as critical opalescence. Here, we demonstrate that in magnetite (Fe3O4 ) light excitation couples to the critical fluctuations of the charge order and coherently generates structural modes of the ordered phase above the critical temperature of the Verwey transition. Our findings are obtained by detecting coherent oscillations of the optical constants through ultrafast broadband spectroscopy and analyzing their dependence on temperature. To unveil the coupling between the structural modes and the electronic excitations, at the origin of the Verwey transition, we combine our results from pump-probe experiments with spontaneous Raman scattering data and theoretical calculations of both the phonon dispersion curves and the optical constants. Our methodology represents an effective tool to study the real-time dynamics of critical fluctuations across phase transitions.

A Model of Relation between Fluctuation of Double Differential Total Ionospheric Electron Content and Angular Distance of the Two Satellites Observed by Same-beam VLBI

NASA Astrophysics Data System (ADS)

Xiao, Yao; Qing-hui, Liu

2018-01-01

Time delay and phase fluctuation are produced when the signals of a spacecraft are transmitted through the ionosphere of the earth, which give rise to a great influence on the measurement precision of VLBI (Very Long Baseline Interferometry). Using the 1-year same-beam VLBI data of 2 satellites (Rstar and Vstar) in the Japanese lunar exploration project SELENE, we obtained a model of the relation between the fluctuation of double differential total electron content in the ionosphere and the angular distance of the two satellites. For the 6 baselines, the root mean square r of fluctuation (in units of TECU) and the angular distance of the two satellites θ (in units of ∘) has a relation of r = 0.773θ + 0.562, and for the 4 VLBI stations, the relation is r = 0.554θ + 0.399 from the baselines inversion. The results can serve as a reference for the derivation of differential phase delay and for the occultation observation and study of planetary ionospheres.

Alfven resonance mode conversion in the Phaedrus-T current drive experiments: Modelling and density fluctuations measurements

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

Vukovic, M.; Harper, M.; Breun, R.

1995-12-31

Current drive experiments on the Phaedrus-T tokamak performed with a low field side two-strap fast wave antenna at frequencies below {omega}{sub cH} show loop volt drops of up to 30% with strap phasing (0, {pi}/2). RF induced density fluctuations in the plasma core have also been observed with a microwave reflectometer. It is believed that they are caused by kinetic Alfven waves generated by mode conversion of fast waves at the Alfven resonance. Correlation of the observed density fluctuations with the magnitude of the {Delta}V{sub loop} suggest that the {Delta}V{sub loop} is attributable to current drive/heating due to mode convertedmore » kinetic Alfven waves. The toroidal cold plasma wave code LION is used to model the Alfven resonance mode conversion surfaces in the experiments while the cylindrical hot plasma kinetic wave code ISMENE is used to model the behavior of kinetic Alfven waves at the Alfven resonance location. Initial results obtained from limited density, magnetic field, antenna phase, and impurity scans show good agreement between the RF induced density fluctuations and the predicted behavior of the kinetic Alfven waves. Detailed comparisons between the density fluctuations and the code predictions are presented.« less

Wavenumber-frequency Spectra of Pressure Fluctuations Measured via Fast Response Pressure Sensitive Paint

NASA Technical Reports Server (NTRS)

Panda, J.; Roozeboom, N. H.; Ross, J. C.

2016-01-01

The recent advancement in fast-response Pressure-Sensitive Paint (PSP) allows time-resolved measurements of unsteady pressure fluctuations from a dense grid of spatial points on a wind tunnel model. This capability allows for direct calculations of the wavenumber-frequency (k-?) spectrum of pressure fluctuations. Such data, useful for the vibro-acoustics analysis of aerospace vehicles, are difficult to obtain otherwise. For the present work, time histories of pressure fluctuations on a flat plate subjected to vortex shedding from a rectangular bluff-body were measured using PSP. The light intensity levels in the photographic images were then converted to instantaneous pressure histories by applying calibration constants, which were calculated from a few dynamic pressure sensors placed at selective points on the plate. Fourier transform of the time-histories from a large number of spatial points provided k-? spectra for pressure fluctuations. The data provides first glimpse into the possibility of creating detailed forcing functions for vibro-acoustics analysis of aerospace vehicles, albeit for a limited frequency range.

Probing the stochastic, motor-driven properties of the cytoplasm using force spectrum microscopy

PubMed Central

Guo, Ming; Ehrlicher, Allen J.; Jensen, Mikkel H.; Renz, Malte; Moore, Jeffrey R.; Goldman, Robert D.; Lippincott-Schwartz, Jennifer; Mackintosh, Frederick C.; Weitz, David A.

2014-01-01

SUMMARY Molecular motors in cells typically produce highly directed motion; however, the aggregate, incoherent effect of all active processes also creates randomly fluctuating forces, which drive diffusive-like, non-thermal motion. Here we introduce force-spectrum-microscopy (FSM) to directly quantify random forces within the cytoplasm of cells and thereby probe stochastic motor activity. This technique combines measurements of the random motion of probe particles with independent micromechanical measurements of the cytoplasm to quantify the spectrum of force fluctuations. Using FSM, we show that force fluctuations substantially enhance intracellular movement of small and large components. The fluctuations are three times larger in malignant cells than in their benign counterparts. We further demonstrate that vimentin acts globally to anchor organelles against randomly fluctuating forces in the cytoplasm, with no effect on their magnitude. Thus, FSM has broad applications for understanding the cytoplasm and its intracellular processes in relation to cell physiology in healthy and diseased states. PMID:25126787

Higher Moments of Net-Particle Multiplicity Distributions

NASA Astrophysics Data System (ADS)

Thäder, Jochen

2016-12-01

Studying fluctuations of conserved quantities, such as baryon number, strangeness, and charge, provides insights into the properties of matter created in high-energy nuclear collisions. Lattice QCD calculations suggest that higher moments of these quantities are sensitive to the phase structure of the hot and dense nuclear matter created in such collisions. In this paper, we present first experimental results of volume and temperature independent cumulant ratios of net-charge and net-proton distributions in Au+Au collisions at √{sNN} = 14.5 GeV completing the first RHIC Beam Energy Scan (BES-I) program for √{sNN} = 7.7 to 200GeV, together with the first measurement of fully corrected net-kaon results, measured with the STAR detector at RHIC at mid-rapidity and a transverse momentum up to pT = 2GeV/c. The pseudorapidity dependence of the √{sNN} = 14.5 GeV net-charge cumulant ratios is discussed. The estimated uncertainties on the ratio c4 /c2, the most statistics-hungry of the present observables, at √{sNN} = 7.7 GeV in the upcoming RHIC BES-II program will also be presented.

Magnetic Fluctuations in the Martian Ionosphere

NASA Technical Reports Server (NTRS)

Espley, Jared

2010-01-01

The Martian ionosphere is influenced by both the solar wind and the regional magnetic fields present in the Martian crust. Both influences ought to cause time variable changes in the magnetic fields present in the ionosphere. I report observations of these magnetic field fluctuations in the Martian ionosphere. I use data from the Mars Global Surveyor magnetometer instrument. By using data from the aerobraking low altitude passes (approx. 200 km) I find that there are numerous fluctuations both near and far from the strong crustal sources. Using data from the 400 km altitude mapping phase (which is near the topside of the primary ionosphere), I look at the comparative strength of the fluctuations relative to the solar wind and temporal variations. I discuss which wave modes and instabilities could be contributing to these fluctuations. I also discuss the implications of these fluctuations for understanding energy transfer in the Martian system and the effects on atmospheric escape.

Pressure Fluctuation Characteristics of Narrow Gauge Train Running Through Tunnel

NASA Astrophysics Data System (ADS)

Suzuki, Masahiro; Sakuma, Yutaka

Pressure fluctuations on the sides of narrow (1067 mm) gauge trains running in tunnels are measured for the first time to investigate the aerodynamic force acting on the trains. The present measurements are compared with earlier measurements obtained with the Shinkansen trains. The results are as follows: (1) The aerodynamic force, which stems from pressure fluctuations on the sides of cars, puts the energy into the vibration of the car body running through a tunnel. (2) While the pressure fluctuations appear only on one of the two sides of the trains running in double-track tunnels, the fluctuations in opposite phase on both sides in single-track tunnels. (3) The on-track test data of the narrow gauge trains show the same tendency as those of the Shinkansen trains, although it is suggested that the pressure fluctuations develop faster along the narrow gauge trains than the Shinkansen trains.

Event-by-event fluctuations of the mean transverse momentum in 40, 80, and 158 A GeV/c PbAu collisions

NASA Astrophysics Data System (ADS)

Adamová, D.; Agakichiev, G.; Appelshäuser, H.; Belaga, V.; Braun-Munzinger, P.; Campagnolo, R.; Castillo, A.; Cherlin, A.; Damjanović, S.; Dietel, T.; Dietrich, L.; Drees, A.; Esumi, S.; Filimonov, K.; Fomenko, K.; Fraenkel, Z.; Garabatos, C.; Glässel, P.; Hering, G.; Holeczek, J.; Kushpil, V.; Lenkeit, B.; Ludolphs, W.; Maas, A.; MaríN, A.; Milošević, J.; Milov, A.; Miśkowiec, D.; Musa, L.; Panebrattsev, Yu.; Petchenova, O.; Petráček, V.; Pfeiffer, A.; Rak, J.; Ravinovich, I.; Rehak, P.; Richter, M.; Sako, H.; Schmitz, W.; Schukraft, J.; Sedykh, S.; Seipp, W.; Sharma, A.; Shimansky, S.; SlíVová, J.; Specht, H. J.; Stachel, J.; Šumbera, M.; Tilsner, H.; Tserruya, I.; Wessels, J. P.; Wienold, T.; Windelband, B.; Wurm, J. P.; Xie, W.; Yurevich, S.; Yurevich, V.; Ceres Collaboration

2003-11-01

Measurements of event-by-event fluctuations of the mean transverse momentum in PbAu collisions at 40, 80, and 158 A GeV/c are presented. A significant excess of mean pT fluctuations at mid-rapidity is observed over the expectation from statistically independent particle emission. The results are somewhat smaller than recent measurements at RHIC. A possible non-monotonic behavior of the mean pT fluctuations as function of collision energy, which may have indicated that the system has passed the critical point of the QCD phase diagram in the range of μB under investigation, has not been observed. The centrality dependence of mean pT fluctuations in PbAu is consistent with an extrapolation from pp collisions assuming that the non-statistical fluctuations scale with multiplicity. The results are compared to calculations by the RQMD and URQMD event generators.

Effect of fluctuations on the NMR relaxation beyond the Abrikosov vortex state

DOE PAGES

Glatz, A.; Galda, A.; Varlamov, A. A.

2015-08-25

Here, the effect of fluctuations on the nuclear magnetic resonance (NMR) relaxation rate W = T –1 1 is studied in a complete phase diagram of a two-dimensional superconductor above the upper critical field line H c2(T). In the region of relatively high temperatures and low magnetic fields, the relaxation rate W is determined by two competing effects. The first one is its decrease in the result of suppression of the quasiparticle density of states (DOS) due to formation of fluctuation Cooper pairs (FCPs). The second one is a specific, purely quantum relaxation process of the Maki-Thompson (MT) type, whichmore » for low field leads to an increase of the relaxation rate. The latter describes particular fluctuation processes involving self-pairing of a single electron on self-intersecting trajectories of a size up to phase-breaking length ℓ Φ which becomes possible due to an electron spin-flip scattering event at a nucleus. As a result, different scenarios with either growth or decrease of the NMR relaxation rate are possible upon approaching the normal-metal–type-II superconductor transition. The character of fluctuations changes along the line H c2(T) from the thermal long-wavelength type in weak magnetic fields to the clusters of rotating FCPs in fields comparable to Hc2(0). We find that below the well-defined temperature T* 0 ≈ 0.6T c0, the MT process becomes ineffective even in the absence of intrinsic pair breaking. The small scale of the FCP rotations ξ xy in such high fields impedes formation of long (≲ℓ Φ) self-intersecting trajectories, causing the corresponding relaxation mechanism to lose its efficiency. This reduces the effect of superconducting fluctuations in the domain of high fields and low temperatures to just the suppression of quasiparticle DOS, analogous to the Abrikosov vortex phase below the H c2(T) line.« less

Experimental triplet and quadruplet fluctuation densities and spatial distribution function integrals for pure liquids.

PubMed

Ploetz, Elizabeth A; Karunaweera, Sadish; Smith, Paul E

2015-01-28

Fluctuation solution theory has provided an alternative view of many liquid mixture properties in terms of particle number fluctuations. The particle number fluctuations can also be related to integrals of the corresponding two body distribution functions between molecular pairs in order to provide a more physical picture of solution behavior and molecule affinities. Here, we extend this type of approach to provide expressions for higher order triplet and quadruplet fluctuations, and thereby integrals over the corresponding distribution functions, all of which can be obtained from available experimental thermodynamic data. The fluctuations and integrals are then determined using the International Association for the Properties of Water and Steam Formulation 1995 (IAPWS-95) equation of state for the liquid phase of pure water. The results indicate small, but significant, deviations from a Gaussian distribution for the molecules in this system. The pressure and temperature dependence of the fluctuations and integrals, as well as the limiting behavior as one approaches both the triple point and the critical point, are also examined.

Experimental triplet and quadruplet fluctuation densities and spatial distribution function integrals for pure liquids

NASA Astrophysics Data System (ADS)

Ploetz, Elizabeth A.; Karunaweera, Sadish; Smith, Paul E.

2015-01-01

Fluctuation solution theory has provided an alternative view of many liquid mixture properties in terms of particle number fluctuations. The particle number fluctuations can also be related to integrals of the corresponding two body distribution functions between molecular pairs in order to provide a more physical picture of solution behavior and molecule affinities. Here, we extend this type of approach to provide expressions for higher order triplet and quadruplet fluctuations, and thereby integrals over the corresponding distribution functions, all of which can be obtained from available experimental thermodynamic data. The fluctuations and integrals are then determined using the International Association for the Properties of Water and Steam Formulation 1995 (IAPWS-95) equation of state for the liquid phase of pure water. The results indicate small, but significant, deviations from a Gaussian distribution for the molecules in this system. The pressure and temperature dependence of the fluctuations and integrals, as well as the limiting behavior as one approaches both the triple point and the critical point, are also examined.

Axial distribution of plasma fluctuations, plasma parameters, deposition rate and grain size during copper deposition

NASA Astrophysics Data System (ADS)

Gopikishan, S.; Banerjee, I.; Pathak, Anand; Mahapatra, S. K.

2017-08-01

Floating potential fluctuations, plasma parameters and deposition rate have been investigated as a function of axial distance during deposition of copper in direct current (DC) magnetron sputtering system. Fluctuations were analyzed using phase space, power spectra and amplitude bifurcation plots. It has been observed that the fluctuations are modified from chaotic to ordered state with increase in the axial distance from cathode. Plasma parameters such as electron density (ne), electron temperature (Te) and deposition rate (Dr) were measured and correlated with plasma fluctuations. It was found that more the deposition rate, greater the grain size, higher the electron density, higher the electron temperature and more chaotic the oscillations near the cathode. This observation could be helpful to the thin film technology industry to optimize the required film.

Transport behaviors of locally fractional coupled Brownian motors with fluctuating interactions

NASA Astrophysics Data System (ADS)

Wang, Huiqi; Ni, Feixiang; Lin, Lifeng; Lv, Wangyong; Zhu, Hongqiang

2018-09-01

In some complex viscoelastic mediums, it is ubiquitous that absorbing and desorbing surrounding Brownian particles randomly occur in coupled systems. The conventional method is to model a variable-mass system driven by both multiplicative and additive noises. In this paper, an improved mathematical model is created based on generalized Langevin equations (GLE) to characterize the random interaction with locally fluctuating number of coupled particles in the elastically coupled factional Brownian motors (FBM). By the numerical simulations, the effect of fluctuating interactions on collective transport behaviors is investigated, and some abnormal phenomena, such as cooperative behaviors, stochastic resonance (SR) and anomalous transport, are observed in the regime of sub-diffusion.

Thermodynamic fluctuation in doped BiSrCaCuO superconductors with 110K phase

NASA Astrophysics Data System (ADS)

Han, S. H.; Andersson, M.

1994-02-01

The resistivity has been carefully measured for four sintered samples of Pb and Pb/Sb doped BiSrCaCuO superconductors with the 110 K phase from zero resistance temperature up to 300 K. The thermodynamical fluctuation have been fitted on the form Δσ∝ε x ( ε=( {T- T c)/ }/{T c}) in the regions -4 < ln ε < -2. By choosing T c in different ways, it is shown that consistent results only could be obtained when T c is defined according to the Lawrence-Doniach theory.

Tunnelling magnetoresistance and 1/f noise in phase-separated manganites

NASA Astrophysics Data System (ADS)

Sboychakov, A. O.; Rakhmanov, A. L.; Kugel, K. I.; Kagan, M. Yu; Brodsky, I. V.

2003-03-01

The magnetoresistance and the noise power of non-metallic phase-separated manganites are studied. The material is modelled by a system of small ferromagnetic metallic droplets (magnetic polarons or ferrons) in an insulating matrix. The concentration of metallic phase is assumed to be far from the percolation threshold. The electron tunnelling between ferrons causes the charge transfer in such a system. The magnetoresistance is determined both by the increase in the volume of the metallic phase and by the change in the electron hopping probability. In the framework of such a model, the low-field magnetoresistance is proportional to H2 and decreases with temperature as T-n, where n can vary from 1 to 5, depending on the parameters of the system. In the high-field limit, the tunnelling magnetoresistance grows exponentially. Different mechanisms of the voltage fluctuations in the system are analysed. The noise spectrum generated by the fluctuations of the number of droplets with extra electrons has a 1/f form over a wide frequency range. In the case of strong magnetic anisotropy, the 1/f noise can also arise due to fluctuations of the magnetic moments of ferrons. The 1/f noise power depends only slightly on the magnetic field in the low field range whereas it can increase as H6 in the high-field limit.

On the Phase Transition of N-Isopropylcarbazole.

DTIC Science & Technology

1986-05-01

vacinity of the phase transition (ca. T 137 + 40 K). We propose a semiquantitative interpretation of the phase transition in NIPC based on this assumption...the order parameter fluctuations in the vacinity of TO . V. Conclusions. The elastic properties of NIPC in the temperature range 90 K - 295 K have

Unsteady hydraulic simulation of the cavitating part load vortex rope in Francis turbines

NASA Astrophysics Data System (ADS)

Brammer, J.; Segoufin, C.; Duparchy, F.; Lowys, P. Y.; Favrel, A.; Avellan, F.

2017-04-01

For Francis turbines at part load operation a helical vortex rope is formed due to the swirling nature of the flow exiting the runner. This vortex creates pressure fluctuations which can lead to power swings, and the unsteady loading can lead to fatigue damage of the runner. In the case that the vortex rope cavitates there is the additional risk that hydro-acoustic resonance can occur. It is therefore important to be able to accurately simulate this phenomenon to address these issues. In this paper an unsteady, multi-phase CFD model was used to simulate two part-load operating points, for two different cavitation conditions. The simulation results were validated with test-rig data, and showed very good agreement. These results also served as an input for FEA calculations and fatigue analysis, which are presented in a separate study.

Conserved charge fluctuations at vanishing and non-vanishing chemical potential

NASA Astrophysics Data System (ADS)

Karsch, Frithjof

2017-11-01

Up to 6th order cumulants of fluctuations of net baryon-number, net electric charge and net strangeness as well as correlations among these conserved charge fluctuations are now being calculated in lattice QCD. These cumulants provide a wealth of information on the properties of strong-interaction matter in the transition region from the low temperature hadronic phase to the quark-gluon plasma phase. They can be used to quantify deviations from hadron resonance gas (HRG) model calculations which frequently are used to determine thermal conditions realized in heavy ion collision experiments. Already some second order cumulants like the correlations between net baryon-number and net strangeness or net electric charge differ significantly at temperatures above 155 MeV in QCD and HRG model calculations. We show that these differences increase at non-zero baryon chemical potential constraining the applicability range of HRG model calculations to even smaller values of the temperature.

A phase contrast imaging-interferometer system for detection of multiscale electron density fluctuations on DIII-D

NASA Astrophysics Data System (ADS)

Davis, E. M.; Rost, J. C.; Porkolab, M.; Marinoni, A.; Van Zeeland, M. A.

2016-11-01

Heterodyne interferometry and phase contrast imaging (PCI) are robust, mature techniques for measuring low-k and high-k electron density fluctuations, respectively. This work describes the first-ever implementation of a combined PCI-interferometer. The combined system uses a single 10.6 μm probe beam, two interference schemes, and two detectors to measure electron density fluctuations at large spatiotemporal bandwidth (10 kHz

Unified Phase Diagram for Iron-Based Superconductors.

PubMed

Gu, Yanhong; Liu, Zhaoyu; Xie, Tao; Zhang, Wenliang; Gong, Dongliang; Hu, Ding; Ma, Xiaoyan; Li, Chunhong; Zhao, Lingxiao; Lin, Lifang; Xu, Zhuang; Tan, Guotai; Chen, Genfu; Meng, Zi Yang; Yang, Yi-Feng; Luo, Huiqian; Li, Shiliang

2017-10-13

High-temperature superconductivity is closely adjacent to a long-range antiferromagnet, which is called a parent compound. In cuprates, all parent compounds are alike and carrier doping leads to superconductivity, so a unified phase diagram can be drawn. However, the properties of parent compounds for iron-based superconductors show significant diversity and both carrier and isovalent dopings can cause superconductivity, which casts doubt on the idea that there exists a unified phase diagram for them. Here we show that the ordered moments in a variety of iron pnictides are inversely proportional to the effective Curie constants of their nematic susceptibility. This unexpected scaling behavior suggests that the magnetic ground states of iron pnictides can be achieved by tuning the strength of nematic fluctuations. Therefore, a unified phase diagram can be established where superconductivity emerges from a hypothetical parent compound with a large ordered moment but weak nematic fluctuations, which suggests that iron-based superconductors are strongly correlated electron systems.

Dissipation-Induced Anomalous Multicritical Phenomena

NASA Astrophysics Data System (ADS)

Soriente, M.; Donner, T.; Chitra, R.; Zilberberg, O.

2018-05-01

We explore the influence of dissipation on a paradigmatic driven-dissipative model where a collection of two level atoms interact with both quadratures of a quantum cavity mode. The closed system exhibits multiple phase transitions involving discrete and continuous symmetries breaking and all phases culminate in a multicritical point. In the open system, we show that infinitesimal dissipation erases the phase with broken continuous symmetry and radically alters the model's phase diagram. The multicritical point now becomes brittle and splits into two tricritical points where first- and second-order symmetry-breaking transitions meet. A quantum fluctuations analysis shows that, surprisingly, the tricritical points exhibit anomalous finite fluctuations, as opposed to standard tricritical points arising in He 3 -He 4 mixtures. Our work has direct implications for a variety of fields, including cold atoms and ions in optical cavities, circuit-quantum electrodynamics as well as optomechanical systems.

Equilibrium evolution in oscillating-field current-drive experiments

NASA Astrophysics Data System (ADS)

McCollam, K. J.; Anderson, J. K.; Blair, A. P.; Craig, D.; Den Hartog, D. J.; Ebrahimi, F.; O'Connell, R.; Reusch, J. A.; Sarff, J. S.; Stephens, H. D.; Stone, D. R.; Brower, D. L.; Deng, B. H.; Ding, W. X.

2010-08-01

Oscillating-field current drive (OFCD) is a proposed method of steady-state toroidal plasma sustainment in which ac poloidal and toroidal loop voltages are applied to produce a dc plasma current. OFCD is added to standard, inductively sustained reversed-field pinch plasmas in the Madison Symmetric Torus [R. N. Dexter et al., Fusion Technol. 19, 131 (1991)]. Equilibrium profiles and fluctuations during a single cycle are measured and analyzed for different relative phases between the two OFCD voltages and for OFCD off. For OFCD phases leading to the most added plasma current, the measured energy confinement is slightly better than that for OFCD off. By contrast, the phase of the maximum OFCD helicity-injection rate also has the maximum decay rate, which is ascribed to transport losses during discrete magnetic-fluctuation events induced by OFCD. Resistive-magnetohydrodynamic simulations of the experiments reproduce the observed phase dependence of the added current.

“Ripples” on a relativistically expanding fluid

DOE PAGES

Shi, Shuzhe; Liao, Jinfeng; Zhuang, Pengfei

2014-12-29

Recent studies have shown that fluctuations of various types play important roles in the evolution of the fireball created in relativistic heavy ion collisions and bear many phenomenological consequences for experimental observables. In addition, the bulk dynamics of the fireball is well described by relativistic hydrodynamic expansion and the fluctuations on top of such expanding background can be studied within the linearized hydrodynamic framework. In this paper we present complete and analytic sound wave solutions on top of both Bjorken flow and Hubble flow backgrounds.

Initial Eccentricity in Deformed 197Au+197Au and 238U+238U Collisions at RHIC

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

Filip, Peter; Lednicky, Richard; Masui, Hiroshi

2010-07-07

Initial eccentricity and eccentricity fluctuations of the interaction volume created in relativistic collisions of deformed {sup 197}Au and {sup 238}U nuclei are studied using optical and Monte-Carlo (MC) Glauber simulations. It is found that the non-sphericity noticeably influences the average eccentricity in central collisions and eccentricity fluctuations are enhanced due to deformation. Quantitative results are obtained for Au+Au and U+U collisions at energy {radical}s{sub NN} = 200 GeV.

Dynamically fluctuating electric dipole moments in fullerene-based magnets.

PubMed

Kambe, Takashi; Oshima, Kokichi

2014-09-19

We report here the direct evidence of the existence of a permanent electric dipole moment in both crystal phases of a fullerene-based magnet--the ferromagnetic α-phase and the antiferromagnetic α'-phase of tetra-kis-(dimethylamino)-ethylene-C60 (TDAE-C60)--as determined by dielectric measurements. We propose that the permanent electric dipole originates from the pairing of a TDAE molecule with surrounding C60 molecules. The two polymorphs exhibit clear differences in their dielectric responses at room temperature and during the freezing process with dynamically fluctuating electric dipole moments, although no difference in their room-temperature structures has been previously observed. This result implies that two polymorphs have different local environment around the molecules. In particular, the ferromagnetism of the α-phase is founded on the homogeneous molecule displacement and orientational ordering. The formation of the different phases with respect to the different rotational states in the Jahn-Teller distorted C60s is also discussed.

Dynamically fluctuating electric dipole moments in fullerene-based magnets

PubMed Central

Kambe, Takashi; Oshima, Kokichi

2014-01-01

We report here the direct evidence of the existence of a permanent electric dipole moment in both crystal phases of a fullerene-based magnet—the ferromagnetic α-phase and the antiferromagnetic α′-phase of tetra-kis-(dimethylamino)-ethylene-C60 (TDAE-C60)—as determined by dielectric measurements. We propose that the permanent electric dipole originates from the pairing of a TDAE molecule with surrounding C60 molecules. The two polymorphs exhibit clear differences in their dielectric responses at room temperature and during the freezing process with dynamically fluctuating electric dipole moments, although no difference in their room-temperature structures has been previously observed. This result implies that two polymorphs have different local environment around the molecules. In particular, the ferromagnetism of the α-phase is founded on the homogeneous molecule displacement and orientational ordering. The formation of the different phases with respect to the different rotational states in the Jahn–Teller distorted C60s is also discussed. PMID:25236361

Combined multi-plane phase retrieval and super-resolution optical fluctuation imaging for 4D cell microscopy

NASA Astrophysics Data System (ADS)

Descloux, A.; Grußmayer, K. S.; Bostan, E.; Lukes, T.; Bouwens, A.; Sharipov, A.; Geissbuehler, S.; Mahul-Mellier, A.-L.; Lashuel, H. A.; Leutenegger, M.; Lasser, T.

2018-03-01

Super-resolution fluorescence microscopy provides unprecedented insight into cellular and subcellular structures. However, going `beyond the diffraction barrier' comes at a price, since most far-field super-resolution imaging techniques trade temporal for spatial super-resolution. We propose the combination of a novel label-free white light quantitative phase imaging with fluorescence to provide high-speed imaging and spatial super-resolution. The non-iterative phase retrieval relies on the acquisition of single images at each z-location and thus enables straightforward 3D phase imaging using a classical microscope. We realized multi-plane imaging using a customized prism for the simultaneous acquisition of eight planes. This allowed us to not only image live cells in 3D at up to 200 Hz, but also to integrate fluorescence super-resolution optical fluctuation imaging within the same optical instrument. The 4D microscope platform unifies the sensitivity and high temporal resolution of phase imaging with the specificity and high spatial resolution of fluorescence microscopy.

Impact of Disorder on the Superconducting Phase Diagram in BaFe2(As1-xPx)2

NASA Astrophysics Data System (ADS)

Mizukami, Yuta; Konczykowski, Marcin; Matsuura, Kohei; Watashige, Tatsuya; Kasahara, Shigeru; Matsuda, Yuji; Shibauchi, Takasada

2017-08-01

In many classes of unconventional superconductors, the question of whether the superconductivity is enhanced by the quantum-critical fluctuations on the verge of an ordered phase remains elusive. One of the most direct ways of addressing this issue is to investigate how the superconducting dome traces a shift of the ordered phase. Here, we study how the phase diagram of the iron-based superconductor BaFe2(As1-xPx)2 changes with disorder via electron irradiation, which keeps the carrier concentrations intact. With increasing disorder, we find that the magneto-structural transition is suppressed, indicating that the critical concentration is shifted to the lower side. Although the superconducting transition temperature Tc is depressed at high concentrations (x ≳ 0.28), it shows an initial increase at lower x. This implies that the superconducting dome tracks the shift of the antiferromagnetic phase, supporting the view of the crucial role played by quantum-critical fluctuations in enhancing superconductivity in this iron-based high-Tc family.

Obtaining phase velocity of turbulent boundary layer pressure fluctuations at high subsonic Mach number from wind tunnel data affected by strong background noise

NASA Astrophysics Data System (ADS)

Haxter, Stefan; Brouwer, Jens; Sesterhenn, Jörn; Spehr, Carsten

2017-08-01

Boundary layer measurements at high subsonic Mach number are evaluated in order to obtain the dominant phase velocities of boundary layer pressure fluctuations. The measurements were performed in a transonic wind tunnel which had a very strong background noise. The phase velocity was taken from phase inclination and from the convective peak in one- and two-dimensional wavenumber spectra. An approach was introduced to remove the acoustic noise from the data by applying a method based on CLEAN-SC on the two-dimensional spectra, thereby increasing the frequency range where information about the boundary layer was retrievable. A comparison with prediction models showed some discrepancies in the low-frequency range. Therefore, pressure data from a DNS calculation was used to substantiate the results of the analysis in this frequency range. Using the measured data, the DNS results and a review of the models used for comparison it was found that the phase velocity decreases at low frequencies.

Conductance fluctuations in high mobility monolayer graphene: Nonergodicity, lack of determinism and chaotic behavior

PubMed Central

da Cunha, C. R.; Mineharu, M.; Matsunaga, M.; Matsumoto, N.; Chuang, C.; Ochiai, Y.; Kim, G.-H.; Watanabe, K.; Taniguchi, T.; Ferry, D. K.; Aoki, N.

2016-01-01

We have fabricated a high mobility device, composed of a monolayer graphene flake sandwiched between two sheets of hexagonal boron nitride. Conductance fluctuations as functions of a back gate voltage and magnetic field were obtained to check for ergodicity. Non-linear dynamics concepts were used to study the nature of these fluctuations. The distribution of eigenvalues was estimated from the conductance fluctuations with Gaussian kernels and it indicates that the carrier motion is chaotic at low temperatures. We argue that a two-phase dynamical fluid model best describes the transport in this system and can be used to explain the violation of the so-called ergodic hypothesis found in graphene. PMID:27609184

Conductance fluctuations in high mobility monolayer graphene: Nonergodicity, lack of determinism and chaotic behavior.

PubMed

da Cunha, C R; Mineharu, M; Matsunaga, M; Matsumoto, N; Chuang, C; Ochiai, Y; Kim, G-H; Watanabe, K; Taniguchi, T; Ferry, D K; Aoki, N

2016-09-09

We have fabricated a high mobility device, composed of a monolayer graphene flake sandwiched between two sheets of hexagonal boron nitride. Conductance fluctuations as functions of a back gate voltage and magnetic field were obtained to check for ergodicity. Non-linear dynamics concepts were used to study the nature of these fluctuations. The distribution of eigenvalues was estimated from the conductance fluctuations with Gaussian kernels and it indicates that the carrier motion is chaotic at low temperatures. We argue that a two-phase dynamical fluid model best describes the transport in this system and can be used to explain the violation of the so-called ergodic hypothesis found in graphene.

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

Bluhm, Marcus; Nahrgang, Marlene; Bass, Steffen A.

The non-monotonic beam energy dependence of the higher cumulants of net-proton fluctuations is a widely studied signature of the conjectured presence of a critical point in the QCD phase diagram. In this work we study the effect of resonance decays on critical fluctuations. We show that resonance effects reduce the signatures of critical fluctuations, but that for reasonable parameter choices critical effects in the net-proton cumulants survive. The relative role of resonance decays has a weak dependence on the order of the cumulants studied with a slightly stronger suppression of critical effects for higher-order cumulants.

Sampling rare fluctuations of discrete-time Markov chains

NASA Astrophysics Data System (ADS)

Whitelam, Stephen

2018-03-01

We describe a simple method that can be used to sample the rare fluctuations of discrete-time Markov chains. We focus on the case of Markov chains with well-defined steady-state measures, and derive expressions for the large-deviation rate functions (and upper bounds on such functions) for dynamical quantities extensive in the length of the Markov chain. We illustrate the method using a series of simple examples, and use it to study the fluctuations of a lattice-based model of active matter that can undergo motility-induced phase separation.

Sampling rare fluctuations of discrete-time Markov chains.

PubMed

Whitelam, Stephen

2018-03-01

We describe a simple method that can be used to sample the rare fluctuations of discrete-time Markov chains. We focus on the case of Markov chains with well-defined steady-state measures, and derive expressions for the large-deviation rate functions (and upper bounds on such functions) for dynamical quantities extensive in the length of the Markov chain. We illustrate the method using a series of simple examples, and use it to study the fluctuations of a lattice-based model of active matter that can undergo motility-induced phase separation.

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

Basu, Sumit, E-mail: sumit.basu@cern.ch; Chatterjee, Rupa; Nayak, Tapan K.

Heavy-ion collisions at ultra-relativistic energies are often referred to as little bangs. We propose for the first time to map the heavy-ion collisions at ultra-relativistic energies, similar to the maps of the cosmic microwave background radiation, using fluctuations of energy density and temperature in small phase space bins. We study the evolution of fluctuations at each stage of the collision using an event-by-event hydrodynamic framework. We demonstrate the feasibility of making fluctuation maps from experimental data and its usefulness in extracting considerable information regarding the early stages of the collision and its evolution.

Towards non-invasive 3D hepatotoxicity assays with optical coherence phase microscopy

NASA Astrophysics Data System (ADS)

Nelson, Leonard J.; Koulovasilopoulos, Andreas; Treskes, Philipp; Hayes, Peter C.; Plevris, John N.; Bagnaninchi, Pierre O.

2015-03-01

Three-dimensional tissue-engineered models are increasingly recognised as more physiologically-relevant than standard 2D cell culture for pre-clinical drug toxicity testing. However, many types of conventional toxicity assays are incompatible with dense 3D tissues. This study investigated the use of optical coherence phase microscopy (OCPM) as a novel approach to assess cell death in 3D tissue culture. For 3D micro-spheroid formation Human hepatic C3A cells were encapsulated in hyaluronic acid gels and cultured in 100μl MEME/10%FBS in 96-well plates. After spheroid formation the 3D liver constructs were exposed to acetaminophen on culture day 8. Acetaminophen hepatotoxicity in 3D cultures was evaluated using standard biochemical assays. An inverted OCPM in common path configuration was developed with a Callisto OCT engine (Thorlabs), centred at 930nm and a custom scanning head. Intensity data were used to perform in-depth microstructural imaging. In addition, phase fluctuations were measured by collecting several successive B scans at the same location, and statistics on the first time derivative of the phase, i.e. time fluctuations, were analysed over the acquisition time interval to retrieve overall cell viability. OCPM intensity (cell cluster size) and phase fluctuation statistics were directly compared with biochemical assays. In this study, we investigated optical coherence phase tomography to assess cell death in a 3d liver model after exposure to a prototypical hepatotoxin, acetaminophen. We showed that OCPM has the potential to assess noninvasively and label-free drug toxicity in 3D tissue models.

Physiologic noise regression, motion regression, and TOAST dynamic field correction in complex-valued fMRI time series.

PubMed

Hahn, Andrew D; Rowe, Daniel B

2012-02-01

As more evidence is presented suggesting that the phase, as well as the magnitude, of functional MRI (fMRI) time series may contain important information and that there are theoretical drawbacks to modeling functional response in the magnitude alone, removing noise in the phase is becoming more important. Previous studies have shown that retrospective correction of noise from physiologic sources can remove significant phase variance and that dynamic main magnetic field correction and regression of estimated motion parameters also remove significant phase fluctuations. In this work, we investigate the performance of physiologic noise regression in a framework along with correction for dynamic main field fluctuations and motion regression. Our findings suggest that including physiologic regressors provides some benefit in terms of reduction in phase noise power, but it is small compared to the benefit of dynamic field corrections and use of estimated motion parameters as nuisance regressors. Additionally, we show that the use of all three techniques reduces phase variance substantially, removes undesirable spatial phase correlations and improves detection of the functional response in magnitude and phase. Copyright © 2011 Elsevier Inc. All rights reserved.

Calibration of phase contrast imaging on HL-2A Tokamak

NASA Astrophysics Data System (ADS)

Yu, Y.; Gong, S. B.; Xu, M.; Xiao, C. J.; Jiang, W.; Zhong, W. L.; Shi, Z. B.; Wang, H. J.; Wu, Y. F.; Yuan, B. D.; Lan, T.; Ye, M. Y.; Duan, X. R.; HL-2A Team

2017-10-01

Phase contrast imaging (PCI) has recently been developed on HL-2A tokamak. In this article we present the calibration of this diagnostic. This system is to diagnose chord integral density fluctuations by measuring the phase shift of a CO2 laser beam with a wavelength of 10.6 μm when the laser beam passes through plasma. Sound waves are used to calibrate PCI diagnostic. The signal series in different PCI channels show a pronounced modulation of incident laser beam by the sound wave. Frequency-wavenumber spectrum is achieved. Calibrations by sound waves with different frequencies exhibit a maximal wavenumber response of 12 cm-1. The conversion relationship between the chord integral plasma density fluctuation and the signal intensity is 2.3 × 1013 m-2/mV, indicating a high sensitivity.

Dissipative structure in the photo-induced phase under steady light irradiation in the spin crossover complex.

PubMed

Nishihara, Taishi; Bousseksou, Azzdine; Tanaka, Koichiro

2013-12-16

We report the spatial and temporal dynamics of the photo-induced phase in the iron (II) spin crossover complex Fe(ptz)(6)(BF(4))(2) studied by image measurement under steady light irradiation and transient absorption measurement. The dynamic factors are derived from the spatial and temporal fluctuation of the image in the steady state under light irradiation between 65 and 100 K. The dynamic factors clearly indicate that the fluctuation has a resonant frequency that strongly depends on the temperature, and is proportional to the relaxation rate of the photo-induced phase. This oscillation of the speckle pattern under steady light irradiation is ascribed to the nonlinear interaction between the spin state and the lattice volume at the surface.

Theory of the vortex matter transformations in high-Tc superconductor YBCO.

PubMed

Li, Dingping; Rosenstein, Baruch

2003-04-25

Flux line lattice in type II superconductors undergoes a transition into a "disordered" phase such as vortex liquid or vortex glass, due to thermal fluctuations and random quenched disorder. We quantitatively describe the competition between the thermal fluctuations and the disorder using the Ginzburg-Landau approach. The following T-H phase diagram of YBCO emerges. There are just two distinct thermodynamical phases, the homogeneous and the crystalline one, separated by a single first order transition line. The line, however, makes a wiggle near the experimentally claimed critical point at 12 T. The "critical point" is reinterpreted as a (noncritical) Kauzmann point in which the latent heat vanishes and the line is parallel to the T axis. The magnetization, the entropy, and the specific heat discontinuities at melting compare well with experiments.

Local Polar Fluctuations in Lead Halide Perovskite Crystals

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

Yaffe, Omer; Guo, Yinsheng; Tan, Liang Z.

2017-03-01

Hybrid lead-halide perovskites have emerged as an excellent class of photovoltaic materials. Recent reports suggest that the organic molecular cation is responsible for local polar fluctuations that inhibit carrier recombination. We combine low-frequency Raman scattering with first-principles molecular dynamics (MD) to study the fundamental nature of these local polar fluctuations. Our observations of a strong central peak in the cubic phase of both hybrid (CH3NH3PbBr3) and all-inorganic (CsPbBr3) leadhalide perovskites show that anharmonic, local polar fluctuations are intrinsic to the general lead-halide perovskite structure, and not unique to the dipolar organic cation. MD simulations indicate that head-tohead Cs motion coupledmore » to Br face expansion, occurring on a few hundred femtosecond time scale, drives the local polar fluctuations in CsPbBr3.« less

Fluctuating pressures in flow fields of jets

NASA Technical Reports Server (NTRS)

Schroeder, J. C.; Haviland, J. K.

1976-01-01

The powered lift configurations under present development for STOL aircraft are the externally blown flap (EBF), involving direct jet impingement on the aircraft flaps, and the upper surface blown (USB), where the jet flow is attached on the upper surface of the wing and directed downwards. Towards the goal of developing scaling laws to predict unsteady loads imposed on the structural components of these STOL aircraft from small model tests, the near field fluctuating pressure behavior for the simplified cases of a round free cold jet and the same jet impinging on a flat plate was investigated. Examples are given of coherences, phase lags (giving convection velocities), and overall fluctuating pressure levels measured. The fluctuating pressure levels measured on the flat plate are compared to surface fluctuating pressure levels measured on full-scale powered-lift configuration models.

Quantum vortex melting and phase diagram in the layered organic superconductor κ -(BEDT-TTF)2Cu(NCS ) 2

NASA Astrophysics Data System (ADS)

Uji, S.; Fujii, Y.; Sugiura, S.; Terashima, T.; Isono, T.; Yamada, J.

2018-01-01

Resistance and magnetic torque measurements have been performed to investigate vortex phases for a layered organic superconductor κ -(BEDT-TTF) 2Cu (NCS) 2 [BEDT-TTF = bis(ethylenedithio)tetrathiafulvalene], which is modeled as stacks of Josephson junctions. At 25 mK, the out-of-plane resistivity increases at 0.6 T, has a step feature up to 4 T, and then increases again, whereas the in-plane resistivity monotonically increases above 4 T. The results show that both pancake vortices (PVs) and Josephson vortices (JVs) are in solid phases for μ0H <0.6 T, but only JVs are in a liquid phase for 0.6 <μ0H <4 T. For μ0H >4 T, both PVs and JVs are in liquid phases. These melting transitions are predominantly induced by quantum fluctuations (not by thermal fluctuations). In the magnetic torque curves, the irreversibility transition is clearly observed, roughly corresponding to the melting transition of the PVs but no anomaly is found at the JV melting transition. The detailed vortex phase diagram is determined in a wide temperature region.

Averaging of phase noise in PSK signals by an opto-electrical feed-forward circuit

NASA Astrophysics Data System (ADS)

Inoue, K.; Ohta, M.

2013-10-01

This paper proposes an opto-electrical feed-forward circuit that reduces phase noise in binary PSK signals by averaging the noise. Random and independent phase noise is averaged over several bit slots by externally modulating a phase-fluctuating PSK signal with feed-forward signal obtained from signal processing of the outputs of delay interferometers. The simulation results demonstrate a reduction in the phase noise.

Macromolecular Crowding Induces Spatial Correlations That Control Gene Expression Bursting Patterns.

PubMed

Norred, S Elizabeth; Caveney, Patrick M; Chauhan, Gaurav; Collier, Lauren K; Collier, C Patrick; Abel, Steven M; Simpson, Michael L

2018-05-18

Recent superresolution microscopy studies in E. coli demonstrate that the cytoplasm has highly variable local concentrations where macromolecular crowding plays a central role in establishing membrane-less compartmentalization. This spatial inhomogeneity significantly influences molecular transport and association processes central to gene expression. Yet, little is known about how macromolecular crowding influences gene expression bursting-the episodic process where mRNA and proteins are produced in bursts. Here, we simultaneously measured mRNA and protein reporters in cell-free systems, showing that macromolecular crowding decoupled the well-known relationship between fluctuations in the protein population (noise) and mRNA population statistics. Crowded environments led to a 10-fold increase in protein noise even though there were only modest changes in the mRNA population and fluctuations. Instead, cell-like macromolecular crowding created an inhomogeneous spatial distribution of mRNA ("spatial noise") that led to large variability in the protein production burst size. As a result, the mRNA spatial noise created large temporal fluctuations in the protein population. These results highlight the interplay between macromolecular crowding, spatial inhomogeneities, and the resulting dynamics of gene expression, and provide insights into using these organizational principles in both cell-based and cell-free synthetic biology.

Determining the mean hydraulic gradient of ground water affected by tidal fluctuations

USGS Publications Warehouse

Serfes, Michael E.

1991-01-01

Tidal fluctuations in surface-water bodies produce progressive pressure waves in adjacent aquifers. As these pressure waves propagate inland, ground-water levels and hydraulic gradients continuously fluctuate, creating a situation where a single set of water-level measurements cannot be used to accurately characterize ground-water flow. For example, a time series of water levels measured in a confined aquifer in Atlantic City, New Jersey, showed that the hydraulic gradient ranged from .01 to .001 with a 22-degree change in direction during a tidal day of approximately 25 hours. At any point where ground water tidally fluctuates, the magnitude and direction of the hydraulic gradient fluctuates about the mean or regional hydraulic gradient. The net effect of these fluctuations on ground-water flow can be determined using the mean hydraulic gradient, which can be calculated by comparing mean ground- and surface-water elevations. Filtering methods traditionally used to determine daily mean sea level can be similarly applied to ground water to determine mean levels. Method (1) uses 71 consecutive hourly water-level observations to accurately determine the mean level. Method (2) approximates the mean level using only 25 consecutive hourly observations; however, there is a small error associated with this method.

Quantum phase transition with dissipative frustration

NASA Astrophysics Data System (ADS)

Maile, D.; Andergassen, S.; Belzig, W.; Rastelli, G.

2018-04-01

We study the quantum phase transition of the one-dimensional phase model in the presence of dissipative frustration, provided by an interaction of the system with the environment through two noncommuting operators. Such a model can be realized in Josephson junction chains with shunt resistances and resistances between the chain and the ground. Using a self-consistent harmonic approximation, we determine the phase diagram at zero temperature which exhibits a quantum phase transition between an ordered phase, corresponding to the superconducting state, and a disordered phase, corresponding to the insulating state with localized superconducting charge. Interestingly, we find that the critical line separating the two phases has a nonmonotonic behavior as a function of the dissipative coupling strength. This result is a consequence of the frustration between (i) one dissipative coupling that quenches the quantum phase fluctuations favoring the ordered phase and (ii) one that quenches the quantum momentum (charge) fluctuations leading to a vanishing phase coherence. Moreover, within the self-consistent harmonic approximation, we analyze the dissipation induced crossover between a first and second order phase transition, showing that quantum frustration increases the range in which the phase transition is second order. The nonmonotonic behavior is reflected also in the purity of the system that quantifies the degree of correlation between the system and the environment, and in the logarithmic negativity as an entanglement measure that encodes the internal quantum correlations in the chain.

The occurrence of individual slow waves in sleep is predicted by heart rate

PubMed Central

Mensen, Armand; Zhang, Zhongxing; Qi, Ming; Khatami, Ramin

2016-01-01

The integration of near-infrared spectroscopy and electroencephalography measures presents an ideal method to study the haemodynamics of sleep. While the cortical dynamics and neuro-modulating influences affecting the transition from wakefulness to sleep is well researched, the assumption has been that individual slow waves, the hallmark of deep sleep, are spontaneously occurring cortical events. By creating event-related potentials from the NIRS recording, time-locked to the onset of thousands of individual slow waves, we show the onset of slow waves is phase-locked to an ongoing oscillation in the NIRS recording. This oscillation stems from the moment to moment fluctuations of light absorption caused by arterial pulsations driven by the heart beat. The same oscillating signal can be detected if the electrocardiogram is time-locked to the onset of the slow wave. The ongoing NIRS oscillation suggests that individual slow wave initiation is dependent on that signal, and not the other way round. However, the precise causal links remain speculative. We propose several potential mechanisms: that the heart-beat or arterial pulsation acts as a stimulus which evokes a down-state; local fluctuations in energy supply may lead to a network effect of hyperpolarization; that the arterial pulsations lead to corresponding changes in the cerebral-spinal-fluid which evokes the slow wave; or that a third neural generator, regulating heart rate and slow waves may be involved. PMID:27445083

Topology and the universe

NASA Astrophysics Data System (ADS)

Gott, J. Richard, III

1998-09-01

Topology may play an important role in cosmology in several different ways. First, Einstein's field equations tell us about the local geometry of the universe but not about its topology. Therefore, the universe may be multiply connected. Inflation predicts that the fluctuations that made clusters and groups of galaxies arose from random quantum fluctuations in the early universe. These should be Gaussian random phase. This can be tested by quantitatively measuring the topology of large-scale structure in the universe using the genus statistic. If the original fluctuations were Gaussian random phase then the structure we see today should have a spongelike topology. A number of studies by our group and others have shown that this is indeed the case. Future tests using the Sloan Digital Sky Survey should be possible. Microwave background fluctuations should also exhibit a characteristic symmetric pattern of hot and cold spots. The COBE data are consistent with this pattern and the MAP and PLANCK satellites should provide a definitive test. If the original inflationary state was metastable then it should decay by making an infinite number of open inflationary bubble universes. This model makes a specific prediction for the power spectrum of fluctuations in the microwave background which can be checked by the MAP and PLANCK satellites. Finally, Gott and Li have proposed how a multiply connected cosmology with an early epoch of closed timelike curves might allow the universe to be its own mother.

Computational and theoretical studies of globular proteins

NASA Astrophysics Data System (ADS)

Pagan, Daniel L.

Protein crystallization is often achieved in experiment through a trial and error approach. To date, there exists a dearth of theoretical understanding of the initial conditions necessary to promote crystallization. While a better understanding of crystallization will help to create good crystals suitable for structure analysis, it will also allow us to prevent the onset of certain diseases. The core of this thesis is to model and, ultimately, understand the phase behavior of protein particles in solution. Toward this goal, we calculate the fluid-fluid coexistence curve in the vicinity of the metastable critical point of the modified Lennard-Jones potential, where it has been shown that nucleation is increased by many orders of magnitude. We use finite-size scaling techniques and grand canonical Monte Carlo simulation methods. This has allowed us to pinpoint the critical point and subcritical region with high accuracy in spite of the critical fluctuations that hinder sampling using other Monte Carlo techniques. We also attempt to model the phase behavior of the gamma-crystallins, mutations of which have been linked to genetic cataracts. The complete phase behavior of the square well potential at the ranges of attraction lambda = 1.15 and lambda = 1.25 is calculated and compared with that of the gammaII-crystallin. The role of solvent is also important in the crystallization process and affects the phase behavior of proteins in solution. We study a model that accounts for the contribution of the solvent free-energy to the free-energy of globular proteins. This model allows us to model phase behavior that includes solvent.

Reduction of phase noise in nanowire spin orbit torque oscillators

PubMed Central

Yang, Liu; Verba, Roman; Tiberkevich, Vasil; Schneider, Tobias; Smith, Andrew; Duan, Zheng; Youngblood, Brian; Lenz, Kilian; Lindner, Jürgen; Slavin, Andrei N.; Krivorotov, Ilya N.

2015-01-01

Spin torque oscillators (STOs) are compact, tunable sources of microwave radiation that serve as a test bed for studies of nonlinear magnetization dynamics at the nanometer length scale. The spin torque in an STO can be created by spin-orbit interaction, but low spectral purity of the microwave signals generated by spin orbit torque oscillators hinders practical applications of these magnetic nanodevices. Here we demonstrate a method for decreasing the phase noise of spin orbit torque oscillators based on Pt/Ni80Fe20 nanowires. We experimentally demonstrate that tapering of the nanowire, which serves as the STO active region, significantly decreases the spectral linewidth of the generated signal. We explain the observed linewidth narrowing in the framework of the Ginzburg-Landau auto-oscillator model. The model reveals that spatial non-uniformity of the spin current density in the tapered nanowire geometry hinders the excitation of higher order spin-wave modes, thus stabilizing the single-mode generation regime. This non-uniformity also generates a restoring force acting on the excited self-oscillatory mode, which reduces thermal fluctuations of the mode spatial position along the wire. Both these effects improve the STO spectral purity. PMID:26592432

Symmetry Breaking in the Correlated Electronic and Lattice Degrees of Freedom in the CuxTiSe2 T-x Phase Diagram

NASA Astrophysics Data System (ADS)

Lioi, David B.

In this thesis I investigate the relationship between the charge density wave (CDW) phase and superconductivity in the T-x phase diagram of Cu xTiSe2. I find that the incommensurate (IC)-CDW is related to the superconducting phase due to the fact that the former effectively isolates the CDW subsystem degrees of freedom. This increases the symmetry of the electronic populations within the IC-CDW band structure and leave them susceptible to internal instabilities, which in turn give rise to the superconducting phase. Because the correlated properties of these solid-state phases of matter are highly dependent on the crystalline quality of our samples, I also detail the growth of pristine single crystals and utilize several characterization techniques to aid in this purpose. In this portion of the thesis the single crystals are deliberately injected with heat and monitored to deduce the formation of defects through selenium migration. I also confirm the existence of chiral symmetry breaking in the bulk commensurate (C)-CDW phase in TiSe2 brought about by the cooperation of phonon and exciton degrees of freedom, and also observe chiral character in fluctuations above TCDW. These thermal fluctuations were observed up to 80 K above TCDW via optical signatures of the folded Se-4p band and Raman signatures of the soft L1- phonon mode. The suppression of the excitonic degree of freedom with Cu intercalation brings about a quantum phase transition into the IC-CDW at x=0.04. Large quantum fluctuations of the folded Se-4p electronic band were observed at the quantum phase transition where measurements of the phonon system show the onset of incommensuration in the CDW super-lattice. Optical measurements demonstrate a large decoupling of the electron-phonon degrees of freedom within the electronic band structure of the IC-CDW subsystem.

Characteristics and causal factors of hysteresis in the hydrodynamics of a large floodplain system: Poyang Lake (China)

NASA Astrophysics Data System (ADS)

Zhang, X. L.; Zhang, Q.; Werner, A. D.; Tan, Z. Q.

2017-10-01

A previous modeling study of the lake-floodplain system of Poyang Lake (China) revealed complex hysteretic relationships between stage, storage volume and surface area. However, only hypothetical causal factors were presented, and the reasons for the occurrence of both clockwise and counterclockwise hysteretic functions were unclear. The current study aims to address this by exploring further Poyang Lake's hysteretic behavior, including consideration of stage-flow relationships. Remotely sensed imagery is used to validate the water surface areas produced by hydrodynamic modeling. Stage-area relationships obtained using the two methods are in strong agreement. The new results reveal a three-phase hydrological regime in stage-flow relationships, which assists in developing improved physical interpretation of hysteretic stage-area relationships for the lake-floodplain system. For stage-area relationships, clockwise hysteresis is the result of classic floodplain hysteretic processes (e.g., restricted drainage of the floodplain during recession), whereas counterclockwise hysteresis derives from the river hysteresis effect (i.e., caused by backwater effects). The river hysteresis effect is enhanced by the time lag between the peaks of catchment inflow and Yangtze discharge (i.e., the so-called Yangtze River blocking effect). The time lag also leads to clockwise hysteresis in the relationship between Yangtze River discharge and lake stage. Thus, factors leading to hysteresis in other rivers, lakes and floodplains act in combination within Poyang Lake to create spatial variability in hydrological hysteresis. These effects dominate at different times, in different parts of the lake, and during different phases of the lake's water level fluctuations, creating the unique hysteretic hydrological behavior of Poyang Lake.

Small-scale heterogeneity spectra in the Earth mantle resolved by PKP-ab,-bc and -df waves

NASA Astrophysics Data System (ADS)

Zheng, Y.

2016-12-01

Plate tectonics creates heterogeneities at mid ocean ridges and subducts the heterogeneities back to the mantle at subduction zones. Heterogeneities manifest themselves by different densities and seismic wave speeds. The length scales and spatial distribution of the heterogeneities measure the mixing mechanism of the plate tectonics. This information can be mathematically captured as the heterogeneity spatial Fourier spectrum. Since most heterogeneities created are on the order of 10s of km, global seismic tomography is not able to resolve them directly. Here, we use seismic P-waves that transmit through the outer core (phases: PKP-ab and PKP-bc) and through the inner core (PKP-df) to probe the lower-mantle heterogeneities. The differential traveltimes (PKP-ab versus PKP-df; PKP-bc versus PKP-df) are sensitive to lower mantle structures. We have collected more than 10,000 PKP phases recorded by Japan Hi-Net short-period seismic network. We found that the lower mantle was filled with seismic heterogeneities from scale 20km to 200km. The heterogeneity spectrum is similar to an exponential distribution but is more enriched in small-scale heterogeneities at the high-wavenumber end. The spectrum is "red" meaning large scales have more power and heterogeneities show a multiscale nature: small-scale heterogeneities are embedded in large-scale heterogeneities. These small-scale heterogeneities cannot be due to thermal origin and they must be compositional. If all these heterogeneities were located in the D" layer, statistically, it would have a root-mean-square P-wave velocity fluctuation of 1% (i.e., -3% to 3%).

Elliptic Flow, Initial Eccentricity and Elliptic Flow Fluctuations in Heavy Ion Collisions at RHIC

NASA Astrophysics Data System (ADS)

Nouicer, Rachid; Alver, B.; Back, B. B.; Baker, M. D.; Ballintijn, M.; Barton, D. S.; Betts, R. R.; Bickley, A. A.; Bindel, R.; Busza, W.; Carroll, A.; Chai, Z.; Decowski, M. P.; García, E.; Gburek, T.; George, N.; Gulbrandsen, K.; Halliwell, C.; Hamblen, J.; Hauer, M.; Henderson, C.; Hofman, D. J.; Hollis, R. S.; Holzman, B.; Iordanova, A.; Kane, J. L.; Khan, N.; Kulinich, P.; Kuo, C. M.; Li, W.; Lin, W. T.; Loizides, C.; Manly, S.; Mignerey, A. C.; Nouicer, R.; Olszewski, A.; Pak, R.; Reed, C.; Roland, C.; Roland, G.; Sagerer, J.; Seals, H.; Sedykh, I.; Smith, C. E.; Stankiewicz, M. A.; Steinberg, P.; Stephans, G. S. F.; Sukhanov, A.; Tonjes, M. B.; Trzupek, A.; Vale, C.; van Nieuwenhuizen, G. J.; Vaurynovich, S. S.; Verdier, R.; Veres, G. I.; Walters, P.; Wenger, E.; Wolfs, F. L. H.; Wosiek, B.; Woźniak, K.; Wysłouch, B.

2008-12-01

We present measurements of elliptic flow and event-by-event fluctuations established by the PHOBOS experiment. Elliptic flow scaled by participant eccentricity is found to be similar for both systems when collisions with the same number of participants or the same particle area density are compared. The agreement of elliptic flow between Au+Au and Cu+Cu collisions provides evidence that the matter is created in the initial stage of relativistic heavy ion collisions with transverse granularity similar to that of the participant nucleons. The event-by-event fluctuation results reveal that the initial collision geometry is translated into the final state azimuthal particle distribution, leading to an event-by-event proportionality between the observed elliptic flow and initial eccentricity.

International Heliophysical Year SCINDA Workshop/Abstract

DTIC Science & Technology

2006-10-01

aid in the specification and prediction of satellite communication degradation due to ionospheric scintillation in the equatorial region...Ionospheric disturbances can cause rapid phase and amplitude fluctuations of satellite signals observed at or near the earth’s surface; these fluctuations are...time, satellite -linked, magnetometer network (http://www.intermagnet.org/). A review paper that describes space research activities in Ethiopia and

Critical Fluctuations in Cortical Models Near Instability

PubMed Central

Aburn, Matthew J.; Holmes, C. A.; Roberts, James A.; Boonstra, Tjeerd W.; Breakspear, Michael

2012-01-01

Computational studies often proceed from the premise that cortical dynamics operate in a linearly stable domain, where fluctuations dissipate quickly and show only short memory. Studies of human electroencephalography (EEG), however, have shown significant autocorrelation at time lags on the scale of minutes, indicating the need to consider regimes where non-linearities influence the dynamics. Statistical properties such as increased autocorrelation length, increased variance, power law scaling, and bistable switching have been suggested as generic indicators of the approach to bifurcation in non-linear dynamical systems. We study temporal fluctuations in a widely-employed computational model (the Jansen–Rit model) of cortical activity, examining the statistical signatures that accompany bifurcations. Approaching supercritical Hopf bifurcations through tuning of the background excitatory input, we find a dramatic increase in the autocorrelation length that depends sensitively on the direction in phase space of the input fluctuations and hence on which neuronal subpopulation is stochastically perturbed. Similar dependence on the input direction is found in the distribution of fluctuation size and duration, which show power law scaling that extends over four orders of magnitude at the Hopf bifurcation. We conjecture that the alignment in phase space between the input noise vector and the center manifold of the Hopf bifurcation is directly linked to these changes. These results are consistent with the possibility of statistical indicators of linear instability being detectable in real EEG time series. However, even in a simple cortical model, we find that these indicators may not necessarily be visible even when bifurcations are present because their expression can depend sensitively on the neuronal pathway of incoming fluctuations. PMID:22952464

Superconductivity and non-Fermi liquid behavior near a nematic quantum critical point.

PubMed

Lederer, Samuel; Schattner, Yoni; Berg, Erez; Kivelson, Steven A

2017-05-09

Using determinantal quantum Monte Carlo, we compute the properties of a lattice model with spin [Formula: see text] itinerant electrons tuned through a quantum phase transition to an Ising nematic phase. The nematic fluctuations induce superconductivity with a broad dome in the superconducting [Formula: see text] enclosing the nematic quantum critical point. For temperatures above [Formula: see text], we see strikingly non-Fermi liquid behavior, including a "nodal-antinodal dichotomy" reminiscent of that seen in several transition metal oxides. In addition, the critical fluctuations have a strong effect on the low-frequency optical conductivity, resulting in behavior consistent with "bad metal" phenomenology.

Collective backscattering of gyrotron radiation by small-scale plasma density fluctuations in large helical device

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

Kharchev, Nikolay; Batanov, German; Petrov, Alexandr

2008-10-15

A version of the collective backscattering diagnostic using gyrotron radiation for small-scale turbulence is described. The diagnostic is used to measure small-scale (k{sub s}{approx_equal}34 cm{sup -1}) plasma density fluctuations in large helical device experiments on the electron cyclotron heating of plasma with the use of 200 kW 82.7 GHz heating gyrotron. A good signal to noise ratio during plasma production phase was obtained, while contamination of stray light increased during plasma build-up phase. The effect of the stray radiation was investigated. The available quasioptical system of the heating system was utilized for this purpose.

Hetero-phase fluctuations in the pre-melting region in ionic crystals

NASA Astrophysics Data System (ADS)

Matsunaga, S.; Tamaki, S.

2008-06-01

The theory of the pre-melting phenomena in ionic crystals on the basis of the concept of the hetero phase fluctuation has been applied to KCl and AgCl crystal. The large scale molecular dynamics simulations (MD) in KCl and AgCl crystals are also performed to examine the ionic configuration in premelting region in the vicinity of their melting points. The size of the liquid like clusters are estimated by the theory and MD. The structural features of liquid like clusters are discussed by MD results using the Lindemann instability condition. The ionic conductivities in the pre-melting region are also discussed on the same theoretical basis.

Two-dimensional mapping of polarizations of rhombohedral nanostructures in the orthorhombic phase of KNbO3 by the combined use of scanning transmission electron microscopy and convergent-beam electron diffraction

NASA Astrophysics Data System (ADS)

Tsuda, Kenji; Tanaka, Michiyoshi

2015-08-01

Rhombohedral nanostructures previously found in the orthorhombic phase of KNbO3, by convergent-beam electron diffraction [Tsuda et al., Appl. Phys. Lett. 102, 051913 (2013)], have been investigated by the combined use of scanning transmission electron microscopy and convergent-beam electron diffraction. Two-dimensional distributions of the rhombohedral nanostructures, or nanometer-scale spatial fluctuations of polarization clusters, have been successfully visualized. The correlation length of the observed spatial fluctuations of local polarizations is related to the cpc/apc ratio and the transition entropy.

Fluctuations in the quark-meson model for QCD with isospin chemical potential

NASA Astrophysics Data System (ADS)

Kamikado, Kazuhiko; Strodthoff, Nils; von Smekal, Lorenz; Wambach, Jochen

2013-01-01

We study the two-flavor quark-meson (QM) model with the functional renormalization group (FRG) to describe the effects of collective mesonic fluctuations on the phase diagram of QCD at finite baryon and isospin chemical potentials, μB and μI. With only isospin chemical potential there is a precise equivalence between the competing dynamics of chiral versus pion condensation and that of collective mesonic and baryonic fluctuations in the quark-meson-diquark model for two-color QCD at finite baryon chemical potential. Here, finite μB = 3 μ introduces an additional dimension to the phase diagram as compared to two-color QCD, however. At zero temperature, the (μI, μ) plane of this phase diagram is strongly constrained by the "Silver Blaze problem." In particular, the onset of pion condensation must occur at μI =mπ / 2, independent of μ as long as μ +μI stays below the constituent quark mass of the QM model or the liquid-gas transition line of nuclear matter in QCD. In order to maintain this relation beyond mean field it is crucial to compute the pion mass from its timelike correlator with the FRG in a consistent way.

Quantum work in the Bohmian framework

NASA Astrophysics Data System (ADS)

Sampaio, R.; Suomela, S.; Ala-Nissila, T.; Anders, J.; Philbin, T. G.

2018-01-01

At nonzero temperature classical systems exhibit statistical fluctuations of thermodynamic quantities arising from the variation of the system's initial conditions and its interaction with the environment. The fluctuating work, for example, is characterized by the ensemble of system trajectories in phase space and, by including the probabilities for various trajectories to occur, a work distribution can be constructed. However, without phase-space trajectories, the task of constructing a work probability distribution in the quantum regime has proven elusive. Here we use quantum trajectories in phase space and define fluctuating work as power integrated along the trajectories, in complete analogy to classical statistical physics. The resulting work probability distribution is valid for any quantum evolution, including cases with coherences in the energy basis. We demonstrate the quantum work probability distribution and its properties with an exactly solvable example of a driven quantum harmonic oscillator. An important feature of the work distribution is its dependence on the initial statistical mixture of pure states, which is reflected in higher moments of the work. The proposed approach introduces a fundamentally different perspective on quantum thermodynamics, allowing full thermodynamic characterization of the dynamics of quantum systems, including the measurement process.

A method of investigating the phase response characteristic of the ionospheric scattering communications channel

NASA Technical Reports Server (NTRS)

Yakovets, A. F.

1972-01-01

A method is proposed for measuring the phase difference fluctuations between vibrations at different frequencies that result from scattering properties of the medium. The measurement equipment is described, along with an ideal communication channel.

Density and magnetic fluctuations in type III-ELM pedestal evolution in JET: experimental and numerical characterization

NASA Astrophysics Data System (ADS)

De Masi, G.; Predebon, I.; Spagnolo, S.; Meneses, L.; Delabie, E.; Lupelli, I.; Hillesheim, J. C.; Maggi, C.; Contributors, JET

2018-04-01

Density and magnetic fluctuation measurements in low-β type-III ELM discharges are obtained in the Joint European Torus (JET). They are observed during the inter-ELM pedestal evolution, after the LH transition phase, at about 60-70 kHz. Density fluctuations are measured with a correlation reflectometer system installed on the low-field side and they are localized at the pedestal top. Magnetic fluctuations with a spatial scale k_yρ_i˜ 0.1 are measured through a high resolution coil array. The main features and the relations with local plasma parameters are presented. The nature of these fluctuations is discussed along with linear gyrokinetic simulations. Ion temperature gradient (ITG) modes are the dominant instabilities in the frequency range of interest. In terms of radial localization, typical oscillation frequency and qualitative relation with the possible linear drive, ITG modes are consistent with the experimental density fluctuations measurements. Micro-tearing modes (MTMs), found unstable with a lower growth rate, appear a possible explanation for magnetic fluctuations in terms of typical wavenumbers and direction of propagation.

Influence of the platform jitter on intensity fluctuation for laser launch system

NASA Astrophysics Data System (ADS)

Zhang, Pengfei; Qiao, Chunhong; Huang, Tong; Zhang, Jinghui; Fan, Chengyu

2017-10-01

The jitter of the transmitting system can cause the light intensity fluctuation at the target position of the laser transmission, which affects the performance of the laser communication, imaging and the adaptive optical system. In this paper, the platform jitter is modeled by Gaussian random fluctuation phase and the analytic expression of the system jitter effect on the fluctuation of light intensity is obtained under the vacuum condition based on extended Huygens-Fresnel principle. The numerical simulation is compared with the theoretical expression and the consistency is obtained. At the same time, the influence of the jitter of the launch system on the intensity fluctuation of the target system under different turbulence conditions is analyzed by numerical simulation. The result show that normalized intensity fluctuation variance induced by platform jitter seems to be unrestricted. The jitter of the transmitting system has a more important influence on the fluctuation of the target position caused by the atmospheric turbulence, as the jitter increase. This result provides a reference for the application of the actual laser transmission system.

A decision directed detector for the phase incoherent Gaussian channel

NASA Technical Reports Server (NTRS)

Kazakos, D.

1975-01-01

A vector digital signalling scheme is proposed for simultaneous adaptive data transmission and phase estimation. The use of maximum likelihood estimation methods predicts a better performance than the phase-locked loop. The phase estimate is shown to converge to the true value, so that the adaptive nature of the detector effectively achieves phase acquisition and improvement in performance. No separate synchronization interval is required and phase fluctuations can be tracked simultaneously with the transmission of information.

Heat fluctuations of Brownian oscillators in nonstationary processes: Fluctuation theorem and condensation transition

NASA Astrophysics Data System (ADS)

Crisanti, A.; Sarracino, A.; Zannetti, M.

2017-05-01

We study analytically the probability distribution of the heat released by an ensemble of harmonic oscillators to the thermal bath, in the nonequilibrium relaxation process following a temperature quench. We focus on the asymmetry properties of the heat distribution in the nonstationary dynamics, in order to study the forms taken by the fluctuation theorem as the number of degrees of freedom is varied. After analyzing in great detail the cases of one and two oscillators, we consider the limit of a large number of oscillators, where the behavior of fluctuations is enriched by a condensation transition with a nontrivial phase diagram, characterized by reentrant behavior. Numerical simulations confirm our analytical findings. We also discuss and highlight how concepts borrowed from the study of fluctuations in equilibrium under symmetry-breaking conditions [Gaspard, J. Stat. Mech. (2012) P08021, 10.1088/1742-5468/2012/08/P08021] turn out to be quite useful in understanding the deviations from the standard fluctuation theorem.

Mechanism of Superconductivity in Quasi-Two-Dimensional Organic Conductor β-(BDA-TTP) Salts

NASA Astrophysics Data System (ADS)

Nonoyama, Yoshito; Maekawa, Yukiko; Kobayashi, Akito; Suzumura, Yoshikazu; Ito, Hiroshi

2008-09-01

We investigate theoretically the superconductivity of two-dimensional organic conductors, β-(BDA-TTP)2SbF6 and β-(BDA-TTP)2AsF6, to understand the role of the spin and charge fluctuations. The transition temperature is estimated by applying random phase approximation to an extended Hubbard model wherein realistic transfer energies are estimated by extended Hückel calculation. We find a gapless superconducting state with a dxy-like symmetry, which is consistent with the experimental results obtained by specific heat and scanning tunneling microscope. In the present model with an effectively half-filled triangular lattice, spin fluctuation competes with charge fluctuation as a mechanism of pairing interaction since both fluctuations have the same characteristic momentum q=(π,0) for V being smaller than U. This is in contrast to a model with a quarter-filled square lattice, wherein both fluctuations contribute cooperatively to pairing interaction due to fluctuations having different characteristic momenta. The resultant difference in the superconductivity of these two materials is also discussed.

Conversion of Phase Information into a Spike-Count Code by Bursting Neurons

PubMed Central

Samengo, Inés; Montemurro, Marcelo A.

2010-01-01

Single neurons in the cerebral cortex are immersed in a fluctuating electric field, the local field potential (LFP), which mainly originates from synchronous synaptic input into the local neural neighborhood. As shown by recent studies in visual and auditory cortices, the angular phase of the LFP at the time of spike generation adds significant extra information about the external world, beyond the one contained in the firing rate alone. However, no biologically plausible mechanism has yet been suggested that allows downstream neurons to infer the phase of the LFP at the soma of their pre-synaptic afferents. Therefore, so far there is no evidence that the nervous system can process phase information. Here we study a model of a bursting pyramidal neuron, driven by a time-dependent stimulus. We show that the number of spikes per burst varies systematically with the phase of the fluctuating input at the time of burst onset. The mapping between input phase and number of spikes per burst is a robust response feature for a broad range of stimulus statistics. Our results suggest that cortical bursting neurons could play a crucial role in translating LFP phase information into an easily decodable spike count code. PMID:20300632

Modeling the lag period and exponential growth of Listeria monocytogenes under conditions of fluctuating temperature and water activity values.

PubMed

Muñoz-Cuevas, Marina; Fernández, Pablo S; George, Susan; Pin, Carmen

2010-05-01

The dynamic model for the growth of a bacterial population described by Baranyi and Roberts (J. Baranyi and T. A. Roberts, Int. J. Food Microbiol. 23:277-294, 1994) was applied to model the lag period and exponential growth of Listeria monocytogenes under conditions of fluctuating temperature and water activity (a(w)) values. To model the duration of the lag phase, the dependence of the parameter h(0), which quantifies the amount of work done during the lag period, on the previous and current environmental conditions was determined experimentally. This parameter depended not only on the magnitude of the change between the previous and current environmental conditions but also on the current growth conditions. In an exponentially growing population, any change in the environment requiring a certain amount of work to adapt to the new conditions initiated a lag period that lasted until that work was finished. Observations for several scenarios in which exponential growth was halted by a sudden change in the temperature and/or a(w) were in good agreement with predictions. When a population already in a lag period was subjected to environmental fluctuations, the system was reset with a new lag phase. The work to be done during the new lag phase was estimated to be the workload due to the environmental change plus the unfinished workload from the uncompleted previous lag phase.

Comparative study of helimagnets MnSi and Cu2OSeO3 at high pressures

NASA Astrophysics Data System (ADS)

Stishov, Sergei; Sidorov, Vladimir; Petrova, Alla; Berdonosov, Peter; Dolgikh, Valery

2014-03-01

The heat capacity of helical magnets Cu2OSeO3 and MnSi has been investigated at high pressures by the ac-calorimetric technique. Despite the differing nature of their magnetic moments, Cu2OSeO3 and MnSi demonstrate a surprising similarity in behavior of their magnetic and thermodynamic properties at the phase transition. Two characteristic features of the heat capacity at the phase transitions of both substances (peak and shoulder) behave also in a similar way at high pressures if analyzed as a function of temperature. This probably implies that the longitudinal spin fluctuations typical of weak itinerant magnets like MnSi contribute little to the phase transition. The shoulders of the heat capacity curves shrink with decreasing temperature suggesting that they arise from classical fluctuations. In case of MnSi the sharp peak and shoulder at the heat capacity disappear simultaneously probably signifying the existence of a tricritical point and confirming the fluctuation nature of the first order phase transition in MnSi as well as in Cu2OSeO3. This work was supported by the Russian Foundation for Basic Research (grant 12-02-00376-a, 12-03-92604), Program of the Physics Department of RAS on Strongly Correlated Electron Systems and Program of the Presidium of RAS on Strongly Compressed Matter.

Eccentricity fluctuation effects on elliptic flow in relativistic heavy ion collisions

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

Hirano, Tetsufumi; Nara, Yasushi

2009-06-15

We study effects of eccentricity fluctuations on the elliptic flow coefficient v{sub 2} at midrapidity in both Au+Au and Cu+Cu collisions at {radical}(s{sub NN})=200 GeV by using a hybrid model that combines ideal hydrodynamics for space-time evolution of the quark gluon plasma phase and a hadronic transport model for the hadronic matter. For initial conditions in hydrodynamic simulations, both the Glauber model and the color glass condensate model are employed to demonstrate the effect of initial eccentricity fluctuations originating from the nucleon position inside a colliding nucleus. The effect of eccentricity fluctuations is modest in semicentral Au+Au collisions, but significantlymore » enhances v{sub 2} in Cu+Cu collisions.« less

2D microwave imaging reflectometer electronics.

PubMed

Spear, A G; Domier, C W; Hu, X; Muscatello, C M; Ren, X; Tobias, B J; Luhmann, N C

2014-11-01

A 2D microwave imaging reflectometer system has been developed to visualize electron density fluctuations on the DIII-D tokamak. Simultaneously illuminated at four probe frequencies, large aperture optics image reflections from four density-dependent cutoff surfaces in the plasma over an extended region of the DIII-D plasma. Localized density fluctuations in the vicinity of the plasma cutoff surfaces modulate the plasma reflections, yielding a 2D image of electron density fluctuations. Details are presented of the receiver down conversion electronics that generate the in-phase (I) and quadrature (Q) reflectometer signals from which 2D density fluctuation data are obtained. Also presented are details on the control system and backplane used to manage the electronics as well as an introduction to the computer based control program.

Laboratory simulation of atmospheric turbulence induced optical wavefront distortion

NASA Astrophysics Data System (ADS)

Taylor, Travis Shane

1999-11-01

Many creative approaches have been taken in the past for simulating the effect that atmospheric turbulence has on optical beams. Most of the experimental architectures have been complicated and consisted of many optical elements as well as moving components. These techniques have shown a modicum of success; however, they are not completely controllable or predictable. A benchtop technique for experimentally producing one important effect that atmospheric turbulence has on optical beams (phase distortion) is presented here. The system is completely controllable and predictable while accurately representing the statistical nature of the problem. Previous experimentation in optical processing through turbulent media has demonstrated that optical wavefront distortions can be produced via spatial light modulating (SLM) devices, and most turbulence models and experimental results indicate that turbulence can be represented as a phase fluctuation. The amplitude distributions in the resulting far field are primarily due to propagation of the phase. Operating a liquid crystal television (LCTV) in the ``phase- mostly'' mode, a phase fluctuation type model for turbulence is utilized in the present investigation, and a real-time experiment for demonstrating the effects was constructed. For an optical system to simulate optical wavefront distortions due to atmospheric turbulence, the following are required: (1)An optical element that modulates the phasefront of an optical beam (2)A model and a technique for generating spatially correlated turbulence simulating distributions (3)Hardware and software for displaying and manipulating the information addressing the optical phase modulation device The LCTV is ideal for this application. When operated in the ``phase-mostly'' mode some LCTVs can modulate the phasefront of an optical beam by as much as 2π and an algorithm for generating spatially correlated phase screens can be constructed via mathematical modeling software such as Mathcad[2]. The phase screens can then be manipulated and displayed on the LCTV using a computer with an appropriate framegrabber and software. The present system consists of an Epson liquid crystal television (which was optimized to modulate up to 2π of phase), a Macintosh IIci with a framegrabber card, a QuickTime movie consisting of multiple video frames of two dimensional arrays of spatially correlated grayscale images, and two polarizers. The movie is displayed on the television via the framegrabber, and the polarizers are used to operate the television in a mode that mostly modulates the spatial phase distribution of the optical wavefront. The frames of the movie are created using an accepted turbulence model for spatially correlated variations in index of refraction, and each subsequent frame of the movie is calculated following an accepted model for temporally varying turbulence. The model used for generating spatial functions or ``phase screens'' which simulate turbulence is the well known Kolmogorov model. These ``phase screens'' are then used, employing a Taylor's frozen flow model, to simulate temporally varying turbulence. A single ``phase screen'' is given a random velocity vector between 0 and.55 meters per second to simulate temporally varying turbulence. The system is used to distort optical beams as if the beams had propagated through a long pathlength of wavefront distorting medium, such as the atmosphere.

Low-frequency random telegraphic noise and 1/f noise in the rare-earth manganite Pr0.63Ca0.37MnO3 near the charge-ordering transition

NASA Astrophysics Data System (ADS)

Bid, Aveek; Guha, Ayan; Raychaudhuri, A. K.

2003-05-01

We have studied low-frequency resistance fluctuations (noise) in a single crystal of the rare-earth perovskite manganite Pr0.63Ca0.37MnO3, which shows a charge-ordering transition at a temperature TCO≈245 K. The measurements were made across the charge-ordering transition covering the temperature range 200 K

The effects of the cathode array on emitted hard x-ray from a small plasma focus device

NASA Astrophysics Data System (ADS)

Piriaei, D.; Mahabadi, T. D.; Javadi, S.; Ghoranneviss, M.

2017-08-01

In this study, the effects of the cathode array variations on emitted hard x-rays from a small Mather type plasma focus device (450 J) were investigated. The gradual elimination of the cathode rods inside the cathode array of the device lowered the quality and quantity of the emitted hard x-rays at different pressure values of argon gas. We theorized that the variations of the cathode array were able to change some discharge parameters that could vary the number of the energetic runaway electrons generated during the pinch phase which were responsible for the created features of the emitted hard x-rays. On the other hand, we hypothesized that the removal of the cathode rods could influence the current sheath dynamics during all the phases of a shot including its average axial velocity which was demonstrated by using two axial magnetic probes. We also theorized that cathode rod omission from the cathode array could also increase the initial inductance and the impedance of the system, and the impurities inside the plasma during the pinch phase which could lead to the growth of the instabilities. Moreover, by using the wavelet technique and studying the Mirnov signals, it was shown that the decrease of the cathode rod number increased the plasma magnetic field fluctuations or instabilities (MHD activities) that adversely affected the pinch quality, and reduced the emitted hard x-rays.

Order parameter fluctuations at a buried quantum critical point

PubMed Central

Feng, Yejun; Wang, Jiyang; Jaramillo, R.; van Wezel, Jasper; Haravifard, S.; Srajer, G.; Liu, Y.; Xu, Z.-A.; Littlewood, P. B.; Rosenbaum, T. F.

2012-01-01

Quantum criticality is a central concept in condensed matter physics, but the direct observation of quantum critical fluctuations has remained elusive. Here we present an X-ray diffraction study of the charge density wave (CDW) in 2H-NbSe2 at high pressure and low temperature, where we observe a broad regime of order parameter fluctuations that are controlled by proximity to a quantum critical point. X-rays can track the CDW despite the fact that the quantum critical regime is shrouded inside a superconducting phase; and in contrast to transport probes, allow direct measurement of the critical fluctuations of the charge order. Concurrent measurements of the crystal lattice point to a critical transition that is continuous in nature. Our results confirm the long-standing expectations of enhanced quantum fluctuations in low-dimensional systems, and may help to constrain theories of the quantum critical Fermi surface. PMID:22529348

Local polar fluctuations in lead halide perovskite crystals

DOE PAGES

Yaffe, Omer; Guo, Yinsheng; Tan, Liang Z.; ...

2017-03-28

Hybrid lead-halide perovskites have emerged as an excellent class of photovoltaic materials. Recent reports suggest that the organic molecular cation is responsible for local polar fluctuations that inhibit carrier recombination. We combine low-frequency Raman scattering with first-principles molecular dynamics (MD) to study the fundamental nature of these local polar fluctuations. Our observations of a strong central peak in the cubic phase of both hybrid (CH 3NH 3PbBr 3) and all-inorganic (CsPbBr 3) lead-halide perovskites show that anharmonic, local polar fluctuations are intrinsic to the general lead-halide perovskite structure, and not unique to the dipolar organic cation. Furthermore, MD simulations indicatemore » that head-to-head Cs motion coupled to Br face expansion, occurring on a few hundred femtosecond time scale, drives the local polar fluctuations in CsPbBr 3.« less

RESPONSES OF SALIX GOODDINGII AND TAMARIX RAMOSISSIMA TO FLOODING

EPA Science Inventory

Impoundments create artificial shorelines that differ from natural lake shorelines in patterns of water-level fluctuations, flow, sediment transport, and shoreline vegetation dynamics. Shoreline plant communities in the American Southwest often become dominated by mature, senesce...

Scaling analysis of heart beat fluctuations data and its relationship with cyclic alternating pattern data during sleep

NASA Astrophysics Data System (ADS)

de León-Lomelí, R.; Murguía, J. S.; Chouvarda, I.; Méndez, M. O.; González-Galván, E.; Alba, A.

2016-01-01

During sleep there exists a nonlinear dynamic phenomenon, which is called cyclic alternating pattern. This phenomenon is generated in the brain and is composed of a series of events of short duration known as A-phases. It has been shown that A-phases can be found in other physiological systems such as the cardiovascular. However, there is no evidence that shows the temporal influence of the A-phases with the cardiovascular system. For this purpose, we consider the scaling method known as detrended fluctuation analysis (DFA). The analysis was carried out in well sleepers and insomnia people, and the numerical results show an increment in the scaling parameter for the insomnia subjects compared with the normal ones. In addition, the results of the heart dynamics suggests a persistent behavior toward the 1/f-noise.

Nonuniform fluids in the grand canonical ensemble

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

Percus, J.K.

1982-01-01

Nonuniform simple classical fluids are considered quite generally. The grand canonical ensemble is particularly suitable, conceptually, in the leading approximation of local thermodynamics, which figuratively divides the system into approximately uniform spatial subsystems. The procedure is reviewed by which this approach is systematically corrected for slowly varying density profiles, and a model is suggested that carries the correction into the domain of local fluctuations. The latter is assessed for substrate bounded fluids, as well as for two-phase interfaces. The peculiarities of the grand ensemble in a two-phase region stem from the inherent very large number fluctuations. A primitive model showsmore » how these are quenched in the canonical ensemble. This is taken advantage of by applying the Kac-Siegert representation of the van der Waals decomposition with petit canonical corrections, to the two-phase regime.« less

Theory of hydrodynamic transport in fluctuating electronic charge density wave states

NASA Astrophysics Data System (ADS)

Delacrétaz, Luca V.; Goutéraux, Blaise; Hartnoll, Sean A.; Karlsson, Anna

2017-11-01

We describe the collective hydrodynamic motion of an incommensurate charge density wave state in a clean electronic system. Our description simultaneously incorporates the effects of both pinning due to weak disorder and also phase relaxation due to proliferating dislocations. We show that the interplay between these two phenomena has important consequences for charge and momentum transport. For instance, it can lead to metal-insulator transitions. We furthermore identify signatures of fluctuating density waves in frequency and spatially resolved conductivities. Phase disordering is well known to lead to a large viscosity. We derive a precise formula for the phase relaxation rate in terms of the viscosity in the dislocation cores. We thereby determine the viscosity of the superconducting state of BSCCO from the observed melting dynamics of Abrikosov lattices and show that the result is consistent with dissipation into Bogoliubov quasiparticles.

Perdurance of multiply connected de Sitter space

NASA Astrophysics Data System (ADS)

González-Díaz, Pedro F.

1999-06-01

This paper deals with a study of the effects that spherically symmetric first-order metric perturbations and vacuum quantum fluctuations have on the stability of the multiply connected de Sitter spacetime recently proposed by Gott and Li. It is the main conclusion of this study that although such a spacetime is stable to the classical metric perturbations for any size of the nonchronal region, it is only stable against the quantum fluctuations of vacuum if the size of the multiply connected region is of the order of the Planck scale. Therefore, boundary conditions for the state of the universe based on the notion that the universe created itself in a regime where closed timelike curves were active and stable still appear to be physically and philosophically well supported as are those boundary conditions relying on the notion that the universe was created out of nothing.

On creating macroscopically identical granular systems with different numbers of particles

NASA Astrophysics Data System (ADS)

van der Meer, Devaraj; Rivas, Nicolas

2015-11-01

One of the fundamental differences between granular and molecular hydrodynamics is the enormous difference in the total number of constituents. The small number of particles implies that the role of fluctuations in granular dynamics is of paramount importance. To obtain more insight in these fluctuations, we investigate to what extent it is possible to create identical granular hydrodynamic states with different number of particles. A definition is given of macroscopically equivalent systems, and the dependency of the conservation equations on the particle size is studied. We show that, in certain cases, and by appropriately scaling the microscopic variables, we are able to compare systems with significantly different number of particles that present the same macroscopic phenomenology. We apply these scalings in simulations of a vertically vibrated system, namely the density inverted granular Leidenfrost state and its transition to a buoyancy-driven convective state.

Controlling dispersion forces between small particles with artificially created random light fields

PubMed Central

Brügger, Georges; Froufe-Pérez, Luis S.; Scheffold, Frank; José Sáenz, Juan

2015-01-01

Appropriate combinations of laser beams can be used to trap and manipulate small particles with optical tweezers as well as to induce significant optical binding forces between particles. These interaction forces are usually strongly anisotropic depending on the interference landscape of the external fields. This is in contrast with the familiar isotropic, translationally invariant, van der Waals and, in general, Casimir–Lifshitz interactions between neutral bodies arising from random electromagnetic waves generated by equilibrium quantum and thermal fluctuations. Here we show, both theoretically and experimentally, that dispersion forces between small colloidal particles can also be induced and controlled using artificially created fluctuating light fields. Using optical tweezers as a gauge, we present experimental evidence for the predicted isotropic attractive interactions between dielectric microspheres induced by laser-generated, random light fields. These light-induced interactions open a path towards the control of translationally invariant interactions with tuneable strength and range in colloidal systems. PMID:26096622

Derivation of dynamo current drive in a closed-current volume and stable current sustainment in the HIT-SI experiment

DOE PAGES

Hossack, A. C.; Sutherland, D. A.; Jarboe, T. R.

2017-02-01

A derivation is given showing that the current inside a closed-current volume can be sustained against resistive dissipation by appropriately phased magnetic perturbations. Imposed-dynamo current drive (IDCD) theory is used to predict the toroidal current evolution in the HIT-SI experiment as a function of magnetic fluctuations at the edge. Analysis of magnetic fields from a HIT-SI discharge shows that the injector-imposed fluctuations are sufficient to sustain the measured toroidal current without instabilities whereas the small, plasma-generated magnetic fluctuations are not sufficiently large to sustain the current.

Derivation of dynamo current drive in a closed-current volume and stable current sustainment in the HIT-SI experiment

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

Hossack, A. C.; Sutherland, D. A.; Jarboe, T. R.

A derivation is given showing that the current inside a closed-current volume can be sustained against resistive dissipation by appropriately phased magnetic perturbations. Imposed-dynamo current drive (IDCD) theory is used to predict the toroidal current evolution in the HIT-SI experiment as a function of magnetic fluctuations at the edge. Analysis of magnetic fields from a HIT-SI discharge shows that the injector-imposed fluctuations are sufficient to sustain the measured toroidal current without instabilities whereas the small, plasma-generated magnetic fluctuations are not sufficiently large to sustain the current.

Direct imaging of nanobubble Ostwald ripening using graphene liquid cell TEM

NASA Astrophysics Data System (ADS)

Xu, Cong; Chen, Qian; Granick, Steve

We directly image the growth, morphology evolution and interaction dynamics of gas nanobubbles in a thin liquid, which are relevant to many materials and electrochemical processes. Using the recently emergent liquid phase transmission electron microscopy (TEM), we resolve the dynamics of nanobubbles in situ at nm resolution in real time. We find that nanobubbles grow through an Ostwald ripening-like process, where adjacent bubbles stochastically fluctuate to disappear or enlarge. Capability of feature tracking enables us to characterize the motions and shape fluctuations of nanobubbles, providing insights into the gas-liquid interfacial fluctuations explored at the nanoscale.

Parkinson's disease-associated melanin steal.

PubMed

Hinz, Marty; Stein, Alvin; Cole, Ted

2014-01-01

Urinary dopamine fluctuations in the competitive inhibition state were first documented in 2009. At that time, it was noted that progressively higher daily dosing values of L-tyrosine decreased the magnitude of these fluctuations. While extensive statistical analysis has been performed by the authors since 2004, it was not until 2012 that a plausible explanation was formulated. In the process, correlations with L-tyrosine administration and the on/off effect of Parkinson's disease were defined. This paper documents the current knowledge with regard to the management of retrograde phase 1 dopamine fluctuations and investigates the hypothesis that they are caused by a melanin steal phenomenon.

High-sensitivity density fluctuation detector

NASA Technical Reports Server (NTRS)

Azzazy, M.; Modarress, D.; Hoeft, T.

1987-01-01

A high-sensitivity differential interferometer has been developed to detect small density fluctuations over an optical path length of the order of the boundary layer thickness near transition. Two experimental configurations have been used to evaluate the performance of the interferometer: an open shear-layer configuration and a wind-tunnel turbulent spot configuration. In each experiment small temperature fluctuations were introduced as the signal source. Simultaneous cold-wire measurements have been compared with the interferometer data. The comparison shows that the interferometer is sensitive to very weak phase variations of the order of 0.001 of the laser wavelength.

Impact of physiological hormonal fluctuations on 18F-fluorodeoxyglucose uptake in breast cancer.

PubMed

Miyake, Kanae K; Nakamoto, Yuji; Saji, Shigehira; Sugie, Tomoharu; Kurihara, Kensuke; Kanao, Shotaro; Ikeda, Debra M; Toi, Masakazu; Togashi, Kaori

2018-06-01

Premenopausal physiologic steroid levels change cyclically, in contrast to steady state low levels seen in postmenopausal patients. The purpose of this study was to evaluate whether 18 F-fluorodeoxyglucose ( 18 F-FDG) uptake in breast cancer is influenced by physiological hormonal fluctuations. A total of 160 primary invasive breast cancers from 155 females (54 premenopausal, 101 postmenopausal) who underwent 18 F-FDG positron emission tomography/computed tomography before therapy were retrospectively analyzed. The maximal standardized uptake values (SUVmax) of tumors were compared with menstrual phases and menopausal status according to the following subgroups: 'luminal A-like,' 'luminal B-like,' and 'non-luminal.' Additionally, the effect of estradiol (E2) on 18 F-FDG uptake in breast cancer cells was evaluated in vitro. Among premenopausal patients, SUVmax during the periovulatory-luteal phase was significantly higher than that during the follicular phase in luminal A-like tumors (n = 25, p = 0.004), while it did not differ between the follicular phase and the periovulatory-luteal phase in luminal B-like (n = 24) and non-luminal tumors (n = 7). Multiple regression analysis showed menstrual phase, tumor size, and Ki-67 index are independent predictors for SUVmax in premenopausal luminal A-like tumors. There were no significant differences in SUVmax between pre- and postmenopausal patients in any of the subgroups. In in vitro studies, uptake in estrogen receptor-positive cells was significantly augmented when E2 concentration was increased from 0.01 to ≥ 1 nM. Our data suggest that 18 F-FDG uptake may be impacted by physiological hormonal fluctuations during menstrual cycle in luminal A-like cancers, and that E2 could be partly responsible for these events.

Rowing Crew Coordination Dynamics at Increasing Stroke Rates

PubMed Central

2015-01-01

In rowing, perfect synchronisation is important for optimal performance of a crew. Remarkably, a recent study on ergometers demonstrated that antiphase crew coordination might be mechanically more efficient by reducing the power lost to within-cycle velocity fluctuations of the boat. However, coupled oscillator dynamics predict the stability of the coordination to decrease with increasing stroke rate, which in case of antiphase may eventually yield breakdowns to in-phase. Therefore, this study examined the effects of increasing stroke rate on in- and antiphase crew coordination in rowing dyads. Eleven experienced dyads rowed on two mechanically coupled ergometers on slides, which allowed the ergometer system to move back and forth as one ‘boat’. The dyads performed a ramp trial in both in- and antiphase pattern, in which stroke rates gradually increased from 30 strokes per minute (spm) to as fast as possible in steps of 2 spm. Kinematics of rowers, handles and ergometers were captured. Two dyads showed a breakdown of antiphase into in-phase coordination at the first stroke rate of the ramp trial. The other nine dyads reached between 34–42 spm in antiphase but achieved higher rates in in-phase. As expected, the coordinative accuracy in antiphase was worse than in in-phase crew coordination, while, somewhat surprisingly, the coordinative variability did not differ between the patterns. Whereas crew coordination did not substantially deteriorate with increasing stroke rate, stroke rate did affect the velocity fluctuations of the ergometers: fluctuations were clearly larger in the in-phase pattern than in the antiphase pattern, and this difference significantly increased with stroke rate. Together, these results suggest that although antiphase rowing is less stable (i.e., less resistant to perturbation), potential on-water benefits of antiphase over in-phase rowing may actually increase with stroke rate. PMID:26185987

Determination of Pressure Fluctuations in Rotor Bundle of Centrifugal Compressor at Critical Conditions of Operation

NASA Astrophysics Data System (ADS)

Levashov, V. A.; Lyubchenko, K. Yu

2017-08-01

This article describes the physical processes that occur in the stage flow part of the compressor while it is operating and can create conditions for the occurrence of forced vibrations, which in turn can lead to the destruction of the impellers. Critical conditions of compressor operation are determined. To understand that critical condition of operation is cause of the destruction of the impellers, transient CFD analysis was carried for test stage of compressor. The obtained pressure fluctuation amplitudes allow to evaluate the critical conditions of compressor operation.

Stochastic simulation of nucleation in binary alloys

NASA Astrophysics Data System (ADS)

L’vov, P. E.; Svetukhin, V. V.

2018-06-01

In this study, we simulate nucleation in binary alloys with respect to thermal fluctuations of the alloy composition. The simulation is based on the Cahn–Hilliard–Cook equation. We have considered the influence of some fluctuation parameters (wave vector cutoff and noise amplitude) on the kinetics of nucleation and growth of minority phase precipitates. The obtained results are validated by the example of iron–chromium alloys.

Advanced Optical Fiber Communications Systems

DTIC Science & Technology

1994-08-31

phase locking . The PZT port has a tuning coefficient of 3.4 MHz/V. The time constants of the optical phase - locked loop ( OPLL ) filter’s pole and zero are... with the PSK receiver optical phase -I-ocked loop ( OPLL ). As we increased nz in our experiments, the larger signal fluctuations made it increasingly... lasers , since a phase - locked loop is 114 I not required for the DPSK receiver (unlike

Time-dependent behavior in a transport-barrier model for the quasi-single helcity state

NASA Astrophysics Data System (ADS)

Terry, P. W.; Whelan, G. G.

2014-09-01

Time-dependent behavior that follows from a recent theory of the quasi-single-helicity (QSH) state of the reversed field pinch is considered. The theory (Kim and Terry 2012 Phys. Plasmas 19 122304) treats QSH as a core fluctuation structure tied to a tearing mode of the same helicity, and shows that strong magnetic and velocity shears in the structure suppress the nonlinear interaction with other fluctuations. By summing the multiple helicity fluctuation energies over wavenumber, we reduce the theory to a predator-prey model. The suppression of the nonlinear interaction is governed by the single helicity energy, which, for fixed radial structure, controls the magnetic and velocity shearing rates. It is also controlled by plasma current which, in the theory, sets the shearing threshold for suppression. The model shows a limit cycle oscillation in which the system toggles between QSH and multiple helicity states, with the single helicity phase becoming increasingly long-lived relative to the multiple helicity phase as plasma current increases.

Magnetic field induced anisotropy of 139La spin-lattice relaxation rates in stripe ordered La 1.875Ba 0.125CuO 4

DOE PAGES

S. -H. Baek; Gu, G. D.; Utz, Y.; ...

2015-10-26

We report 139La nuclear magnetic resonance studies performed on a La 1.875Ba 0.125CuO 4 single crystal. The data show that the structural phase transitions (high-temperature tetragonal → low-temperature orthorhombic → low-temperature tetragonal phase) are of the displacive type in this material. The 139La spin-lattice relaxation rate T –1 1 sharply upturns at the charge-ordering temperature T CO = 54 K, indicating that charge order triggers the slowing down of spin fluctuations. Detailed temperature and field dependencies of the T –1 1 below the spin-ordering temperature T SO=40 K reveal the development of enhanced spin fluctuations in the spin-ordered state formore » H ∥ [001], which are completely suppressed for large fields along the CuO 2 planes. Lastly, our results shed light on the unusual spin fluctuations in the charge and spin stripe ordered lanthanum cuprates.« less

A combined phase contrast imaging-interferometer system for the detection of multiscale density fluctuations on DIII-D

NASA Astrophysics Data System (ADS)

Davis, E. M.; Rost, J. C.; Porkolab, M.; Marinoni, A.; van Zeeland, M. A.

2016-10-01

A heterodyne interferometer channel has been added to the DIII-D phase contrast imaging (PCI) system. Both measurements share a single 10.6 μm probe beam. Whereas the PCI excels at detecting medium- to high- k fluctuations (1.5 cm-1 <= k <= 20 cm-1), the interferometer extends the system sensitivity to low- k fluctuations (k <= 5 cm-1), allowing simultaneous measurement of electron- and ion-scale instabilities with sub-microsecond resolution. Further, correlating measurements from the interferometer channel with those from DIII-D's pre-existing, toroidally separated interferometer (Δ∅ = 45°) allows identification of low- n modes. This new capability has been corroborated against magnetic measurements and may allow novel investigations of core - localized MHD that is otherwise inaccessible via external magnetic measurements, with potential applications to fast particle transport and disruptions. Work supported by USDOE under DE-FG02-94ER54235, DE-FC02-04ER54698, and DE-FC02-99ER54512.

Negative magnetoresistance of ultra-narrow superconducting nanowires in the resistive state

NASA Astrophysics Data System (ADS)

Arutyunov, K. Yu.

2008-02-01

We present a phenomenological model that qualitatively explains negative magnetoresistance in quasi-one-dimensional superconducting channels in the resistive state. The model is based on the assumption that fluctuations of the order parameter (phase slips) are responsible for the finite effective resistance of a narrow superconducting wire sufficiently close to the critical temperature. Each fluctuation is accompanied by an instantaneous formation of a quasi-normal region, of the order of the non-equilibrium quasiparticle relaxation length, ‘pinned’ to the core of the phase slip. The effective time-averaged voltage measured in experiments is a sum of two terms. The first is the conventional contribution associated with the rate of the fluctuations via the Josephson relation. The second term is the Ohmic contribution of this quasi-normal region. Depending on the material properties of the wire, there might be a range of magnetic fields where the first term is not significantly affected, while the second term is effectively suppressed, contributing to the experimentally observed negative magnetoresistance.

Molecular Dynamics Study on Nucleation Behavior and Lamellar Mergence of Polyethylene Globule Crystallization

NASA Astrophysics Data System (ADS)

Yang, Xiaozhen; Wang, Simiao

2012-02-01

The site order parameter (SOP) has been adopted to analyze various order structure formation and distribution during the crystallization of a multi-chain polyethylene globule simulated by molecular dynamics. We found that the nucleation relies on crystallinity fluctuation with increase of amplitude, and the baby nucleus in the fluctuation suddenly appears with different shape and increasing size. In the growth stage, a number of lamellar mergence was observed and their selective behaviors were suggested to be related to the orientation difference between the merging lamellae. We obtained that SOP distribution of all atoms in the system during crystallization appears with two peaks: one for the amorphous phase and the other for the crystalline phase. Mesomorphic structures with medium orders locate between the two peaks as an order promotion pathway. Obtained data show that the medium order structure fluctuates at the growth front and does not always be available; the medium order structure existing at the front is not always good for developing. It is possibly caused by chain entanglement.

Scaling functions for the Inverse Compressibility near the QCD critical point

NASA Astrophysics Data System (ADS)

Lacey, Roy

2017-09-01

The QCD phase diagram can be mapped out by studying fluctuations and their response to changes in the temperature and baryon chemical potential. Theoretical studies indicate that the cumulant ratios Cn /Cm used to characterize the fluctuation of conserved charges, provide a valuable probe of deconfinement and chiral dynamics, as well as for identifying the position of the critical endpoint (CEP) in the QCD phase diagram. The ratio C1 /C2 , which is linked to the inverse compressibility, vanishes at the CEP due to the divergence of the net quark number fluctuations at the critical point belonging to the Z(2) universality class. Therefore, it's associated scaling function can give insight on the location of the critical end point, as well as the critical exponents required to assign its static universality class. Scaling functions for the ratio C1 /C2 , obtained from net-proton multiplicity distributions for a broad range of collision centralities in Au+Au (√{sNN} = 7.7 - 200 GeV) collisions will be presented and discussed.

Colossal thermomagnetic response in chiral d-wave superconductor URu2Si2

NASA Astrophysics Data System (ADS)

Matsuda, Yuji

The heavy-fermion compound URu2Si2 exhibits unconventional superconductivity at Tc = 1.45 K deep inside the so-called hidden order phase. An intriguing aspect is that this system has been suggested to be a candidate of a chiral d-wave superconductor, and possible Weyl-type topological superconducting states have been discussed recently. Here we report on the observation of a highly unusual Nernst signal due to the superconducting fluctuations above Tc. The Nernst coefficient is anomalously enhanced (by a factor of ~106) as compared with the theoretically expected value of the Gaussian fluctuations. This colossal Nernst effect intimately reflects the highly unusual superconducting state of URu2Si2. The results invoke possible chiral or Berry-phase fluctuations associated with the broken time-reversal symmetry of the superconducting order parameter. In collaboration with T. Yamashita, Y. Shimoyama, H. Sumiyoshi (Kyoto), S. Fujimoto (Osaka), T. Shibauchi (Tokyo), Y. Haga (JAEA), T. D. Matsuda (TMU) , Y. Onuki (Ryukyus), A. Levchenko (Wisconsin-Madison).

Magnetic field induced anisotropy of 139La spin-lattice relaxation rates in stripe ordered La 1.875Ba 0.125CuO 4

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

S. -H. Baek; Gu, G. D.; Utz, Y.

We report 139La nuclear magnetic resonance studies performed on a La 1.875Ba 0.125CuO 4 single crystal. The data show that the structural phase transitions (high-temperature tetragonal → low-temperature orthorhombic → low-temperature tetragonal phase) are of the displacive type in this material. The 139La spin-lattice relaxation rate T –1 1 sharply upturns at the charge-ordering temperature T CO = 54 K, indicating that charge order triggers the slowing down of spin fluctuations. Detailed temperature and field dependencies of the T –1 1 below the spin-ordering temperature T SO=40 K reveal the development of enhanced spin fluctuations in the spin-ordered state formore » H ∥ [001], which are completely suppressed for large fields along the CuO 2 planes. Lastly, our results shed light on the unusual spin fluctuations in the charge and spin stripe ordered lanthanum cuprates.« less

Pseudogap Regime of a Two-dimensional Uniform Fermi Gas

NASA Astrophysics Data System (ADS)

Matsumoto, Morio; Hanai, Ryo; Inotani, Daisuke; Ohashi, Yoji

2018-01-01

We investigate pseudogap phenomena in a two-dimensional Fermi gas. Including pairing fluctuations within a self-consistent T-matrix approximation, we determine the pseudogap temperature T* below which a dip appears in the density of states ρ(ω) around the Fermi level. Evaluating T*, we identify the pseudogap region in the phase diagram of this system. We find that, while the observed Berezinskii-Kosterlitz-Thouless (BKT) transition temperature TBKTexp in a 6Li Fermi gas is in the pseudogap regime, the detailed pseudogap structure in ρ(ω) at TBKTexp still differs from a fully-gapped one, indicating the importance of amplitude fluctuations in the Cooper channel there. Since the observed TBKTexp in the weak-coupling regime cannot be explained by the recent BKT theory which only includes phase fluctuations, our results may provide a hint about how to improve this BKT theory. Although ρ(ω) has not been measured in this system, we show that the assessment of our results is still possible by using the observable Tan's contact.

Magnetic ground state of FeSe

PubMed Central

Wang, Qisi; Shen, Yao; Pan, Bingying; Zhang, Xiaowen; Ikeuchi, K.; Iida, K.; Christianson, A. D.; Walker, H. C.; Adroja, D. T.; Abdel-Hafiez, M.; Chen, Xiaojia; Chareev, D. A.; Vasiliev, A. N.; Zhao, Jun

2016-01-01

Elucidating the nature of the magnetism of a high-temperature superconductor is crucial for establishing its pairing mechanism. The parent compounds of the cuprate and iron-pnictide superconductors exhibit Néel and stripe magnetic order, respectively. However, FeSe, the structurally simplest iron-based superconductor, shows nematic order (Ts=90 K), but not magnetic order in the parent phase, and its magnetic ground state is intensely debated. Here we report inelastic neutron-scattering experiments that reveal both stripe and Néel spin fluctuations over a wide energy range at 110 K. On entering the nematic phase, a substantial amount of spectral weight is transferred from the Néel to the stripe spin fluctuations. Moreover, the total fluctuating magnetic moment of FeSe is ∼60% larger than that in the iron pnictide BaFe2As2. Our results suggest that FeSe is a novel S=1 nematic quantum-disordered paramagnet interpolating between the Néel and stripe magnetic instabilities. PMID:27431986

Magnetic ground state of FeSe.

PubMed

Wang, Qisi; Shen, Yao; Pan, Bingying; Zhang, Xiaowen; Ikeuchi, K; Iida, K; Christianson, A D; Walker, H C; Adroja, D T; Abdel-Hafiez, M; Chen, Xiaojia; Chareev, D A; Vasiliev, A N; Zhao, Jun

2016-07-19

Elucidating the nature of the magnetism of a high-temperature superconductor is crucial for establishing its pairing mechanism. The parent compounds of the cuprate and iron-pnictide superconductors exhibit Néel and stripe magnetic order, respectively. However, FeSe, the structurally simplest iron-based superconductor, shows nematic order (Ts=90 K), but not magnetic order in the parent phase, and its magnetic ground state is intensely debated. Here we report inelastic neutron-scattering experiments that reveal both stripe and Néel spin fluctuations over a wide energy range at 110 K. On entering the nematic phase, a substantial amount of spectral weight is transferred from the Néel to the stripe spin fluctuations. Moreover, the total fluctuating magnetic moment of FeSe is ∼60% larger than that in the iron pnictide BaFe2As2. Our results suggest that FeSe is a novel S=1 nematic quantum-disordered paramagnet interpolating between the Néel and stripe magnetic instabilities.

Spin-fluctuation-induced non-Fermi-liquid behavior with suppressed superconductivity in LiFe 1-xCo xAs

DOE PAGES

Y. M. Dai; Miao, H.; Xing, L. Y.; ...

2015-09-15

A series of LiFe 1–xCo xAs compounds with different Co concentrations by transport, optical spectroscopy, angle-resolved photoemission spectroscopy, and nuclear magnetic resonance. We observe a Fermi-liquid to non-Fermi-liquid to Fermi-liquid (FL-NFL-FL) crossover alongside a monotonic suppression of the superconductivity with increasing Co content. In parallel to the FL-NFL-FL crossover, we find that both the low-energy spin fluctuations and Fermi surface nesting are enhanced and then diminished, strongly suggesting that the NFL behavior in LiFe 1–xCo xAs is induced by low-energy spin fluctuations that are very likely tuned by Fermi surface nesting. Our study reveals a unique phase diagram of LiFemore » 1–xCo xAs where the region of NFL is moved to the boundary of the superconducting phase, implying that they are probably governed by different mechanisms.« less

Modeling of Quasi-Four-Phase Flow in Continuous Casting Mold Using Hybrid Eulerian and Lagrangian Approach

NASA Astrophysics Data System (ADS)

Liu, Zhongqiu; Sun, Zhenbang; Li, Baokuan

2017-04-01

Lagrangian tracking model combined with Eulerian multi-phase model is employed to predict the time-dependent argon-steel-slag-air quasi-four-phase flow inside a slab continuous casting mold. The Eulerian approach is used for the description of three phases (molten steel, liquid slag, and air at the top of liquid slag layer). The dispersed argon bubble injected from the SEN is treated in the Lagrangian way. The complex interfacial momentum transfers between various phases are considered. Validation is supported by the measurement data of cold model experiments and industrial practice. Close agreements were achieved for the gas volume fraction, liquid flow pattern, level fluctuation, and exposed slag eye phenomena. Many known phenomena and new predictions were successfully reproduced using this model. The vortex slag entrapment phenomenon at the slag-steel interface was obtained using this model, some small slag drops are sucked deep into the liquid pool of molten steel. Varying gas flow rates have a large effect on the steel flow pattern in the upper recirculation zone. Three typical flow patterns inside the mold with different argon gas flow rates have been obtained: double roll, three roll, and single roll. Effects of argon gas flow rate, casting speed, and slag layer thickness on the exposed slag eye and level fluctuation at the slag-steel interface were studied. A dimensionless value of H ave/ h was proposed to describe the time-averaged level fluctuation of slag-steel interface. The exposed slag eye near the SEN would be formed when the value of H ave/ h is larger than 0.4.

Analytical evaluation of the combined influence of polarization mode dispersion and group velocity dispersion on the bit error rate performance of optical homodyne quadrature phase-shift keying systems

NASA Astrophysics Data System (ADS)

Taher, Kazi Abu; Majumder, Satya Prasad

2017-12-01

A theoretical approach is presented to evaluate the bit error rate (BER) performance of an optical fiber transmission system with quadrature phase-shift keying (QPSK) modulation under the combined influence of polarization mode dispersion (PMD) and group velocity dispersion (GVD) in a single-mode fiber (SMF). The analysis is carried out without and with polarization division multiplexed (PDM) transmission considering a coherent homodyne receiver. The probability density function (pdf) of the random phase fluctuations due to PMD and GVD at the output of the receiver is determined analytically, considering the pdf of differential group delay (DGD) to be Maxwellian distribution and that of GVD to be Gaussian approximation. The exact pdf of the phase fluctuation due to PMD and GVD is also evaluated from its moments using a Monte Carlo simulation technique. Average BER is evaluated by averaging the conditional BER over the pdf of the random phase fluctuation. The BER performance results are evaluated for different system parameters. It is found that PDM-QPSK coherent homodyne system suffers more power penalty than the homodyne QPSK system without PDM. A PDM-QPSK system suffers a penalty of 4.3 dB whereas power penalty of QPSK system is 3.0 dB at a BER of 10-9 for DGD of 0.8 Tb and GVD of 1700 ps/nm. Analytical results are compared with the experimental results reported earlier and found to have good conformity.

On the thermodynamics of phase transitions in metal hydrides

NASA Astrophysics Data System (ADS)

di Vita, Andrea

2012-02-01

Metal hydrides are solutions of hydrogen in a metal, where phase transitions may occur depending on temperature, pressure etc. We apply Le Chatelier's principle of thermodynamics to a particular phase transition in TiH x , which can approximately be described as a second-order phase transition. We show that the fluctuations of the order parameter correspond to fluctuations both of the density of H+ ions and of the distance between adjacent H+ ions. Moreover, as the system approaches the transition and the correlation radius increases, we show -with the help of statistical mechanics-that the statistical weight of modes involving a large number of H+ ions (`collective modes') increases sharply, in spite of the fact that the Boltzmann factor of each collective mode is exponentially small. As a result, the interaction of the H+ ions with collective modes makes a tiny suprathermal fraction of the H+ population appear. Our results hold for similar transitions in metal deuterides, too. A violation of an -insofar undisputed-upper bound on hydrogen loading follows.

Exact extreme-value statistics at mixed-order transitions.

PubMed

Bar, Amir; Majumdar, Satya N; Schehr, Grégory; Mukamel, David

2016-05-01

We study extreme-value statistics for spatially extended models exhibiting mixed-order phase transitions (MOT). These are phase transitions that exhibit features common to both first-order (discontinuity of the order parameter) and second-order (diverging correlation length) transitions. We consider here the truncated inverse distance squared Ising model, which is a prototypical model exhibiting MOT, and study analytically the extreme-value statistics of the domain lengths The lengths of the domains are identically distributed random variables except for the global constraint that their sum equals the total system size L. In addition, the number of such domains is also a fluctuating variable, and not fixed. In the paramagnetic phase, we show that the distribution of the largest domain length l_{max} converges, in the large L limit, to a Gumbel distribution. However, at the critical point (for a certain range of parameters) and in the ferromagnetic phase, we show that the fluctuations of l_{max} are governed by novel distributions, which we compute exactly. Our main analytical results are verified by numerical simulations.

Modeling the Atmospheric Phase Effects of a Digital Antenna Array Communications System

NASA Technical Reports Server (NTRS)

Tkacenko, A.

2006-01-01

In an antenna array system such as that used in the Deep Space Network (DSN) for satellite communication, it is often necessary to account for the effects due to the atmosphere. Typically, the atmosphere induces amplitude and phase fluctuations on the transmitted downlink signal that invalidate the assumed stationarity of the signal model. The degree to which these perturbations affect the stationarity of the model depends both on parameters of the atmosphere, including wind speed and turbulence strength, and on parameters of the communication system, such as the sampling rate used. In this article, we focus on modeling the atmospheric phase fluctuations in a digital antenna array communications system. Based on a continuous-time statistical model for the atmospheric phase effects, we show how to obtain a related discrete-time model based on sampling the continuous-time process. The effects of the nonstationarity of the resulting signal model are investigated using the sample matrix inversion (SMI) algorithm for minimum mean-squared error (MMSE) equalization of the received signal

Lipid bilayers: thermodynamics, structure, fluctuations, and interactions.

PubMed

Tristram-Nagle, Stephanie; Nagle, John F

2004-01-01

This article, adapted from our acceptance speech of the Avanti Award in Lipids at the 47th Biophysical Society meeting in San Antonio, 2003, summarizes over 30 years of research in the area of lipid bilayers. Beginning with a theoretical model of the phase transition (J.F.N.), we have proceeded experimentally using dilatometry and density centrifugation to study volume, differential scanning calorimetry to study heat capacity, and X-ray scattering techniques to study structure of lipid bilayers as a function of temperature. Electron density profiles of the gel and ripple phases have been obtained as well as profiles from several fluid phase lipids, which lead to many structural results that compliment molecular dynamics simulations from other groups. Using the theory of liquid crystallography plus oriented lipid samples, we are the first group to obtain both material parameters (KC and B) associated with the fluctuations in fluid phase lipids. This allows us to use fully hydrated lipid samples, as in vivo, to obtain the structure.

Regular and Random Components in Aiming-Point Trajectory During Rifle Aiming and Shooting

PubMed Central

Goodman, Simon; Haufler, Amy; Shim, Jae Kun; Hatfield, Bradley

2009-01-01

The authors examined the kinematic qualities of the aiming trajectory as related to expertise. In all, 2 phases of the trajectory were discriminated. The first phase was regular approximation to the target accompanied by substantial fluctuations obeying the Weber–Fechner law. During the first phase, shooters did not initiate the triggering despite any random closeness of the aiming point (AP) to the target. In the second phase, beginning at 0.6–0.8 s before the trigger pull, shooters applied a different control strategy: They waited until the following random fluctuation brought the AP closer to the target and then initiated triggering. This strategy is tenable when sensitivity of perception is greater than precision of the motor action, and could be considered a case of stochastic resonance. The strategies that novices and experts used distinguished only in the values of parameters. The authors present an analytical model explaining the main properties of shooting. PMID:19508963

Evaluation of a locally homogeneous model of spray evaporation

NASA Technical Reports Server (NTRS)

Shearer, A. J.; Faeth, G. M.; Tamura, H.

1978-01-01

Measurements were conducted on an evaporating spray in a stagnant environment. The spray was formed using an air-atomizing injector to yield a Sauter mean diameter of the order of 30 microns. The region where evaporation occurred extended approximately 1 m from the injector for the test conditions. Profiles of mean velocity, temperature, composition, and drop size distribution, as well as velocity fluctuations and Reynolds stress, were measured. The results are compared with a locally homogeneous two-phase flow model which implies no velocity difference and thermodynamic equilibrium between the phases. The flow was represented by a k-epsilon-g turbulence model employing a clipped Gaussian probability density function for mixture fraction fluctuations. The model provides a good representation of earlier single-phase jet measurements, but generally overestimates the rate of development of the spray. Using the model predictions to represent conditions along the centerline of the spray, drop life-history calculations were conducted which indicate that these discrepancies are due to slip and loss of thermodynamic equilibrium between the phases.

Quantum order by disorder in frustrated diamond lattice antiferromagnets.

PubMed

Bernier, Jean-Sébastien; Lawler, Michael J; Kim, Yong Baek

2008-07-25

We present a quantum theory of frustrated diamond lattice antiferromagnets. Considering quantum fluctuations as the predominant mechanism relieving spin frustration, we find a rich phase diagram comprising of six phases with coplanar spiral ordering in addition to the Néel phase. By computing the specific heat of these ordered phases, we obtain a remarkable agreement between (k, k, 0) spiral ordering and the experimental specific heat data for the diamond lattice spinel compounds MnSc2S4, Co3O4, and CoRh2O4, i.e., specific heat data is a strong evidence for (k, k, 0) spiral ordering in all of these materials. This prediction can be tested in future neutron scattering experiments on Co3O4 and CoRh2O4, and is consistent with existing neutron scattering data on MnSc2S4. Based on this agreement, we infer a monotonically increasing relationship between frustration and the strength of quantum fluctuations.

Lipid bilayers: thermodynamics, structure, fluctuations, and interactions

PubMed Central

Tristram-Nagle, Stephanie; Nagle, John F.

2009-01-01

This article, adapted from our acceptance speech of the Avanti Award in Lipids at the 47th Biophysical Society meeting in San Antonio, 2003, summarizes over 30 years of research in the area of lipid bilayers. Beginning with a theoretical model of the phase transition (J.F.N.), we have proceeded experimentally using dilatometry and density centrifugation to study volume, differential scanning calorimetry to study heat capacity, and X-ray scattering techniques to study structure of lipid bilayers as a function of temperature. Electron density profiles of the gel and ripple phases have been obtained as well as profiles from several fluid phase lipids, which lead to many structural results that compliment molecular dynamics simulations from other groups. Using the theory of liquid crystallography plus oriented lipid samples, we are the first group to obtain both material parameters (KC and B) associated with the fluctuations in fluid phase lipids. This allows us to use fully hydrated lipid samples, as in vivo, to obtain the structure. PMID:14706737

Real-time observation of fluctuations in a driven-dissipative quantum many-body system undergoing a phase transition

NASA Astrophysics Data System (ADS)

Donner, Tobias

2015-03-01

A Bose-Einstein condensate whose motional degrees of freedom are coupled to a high-finesse optical cavity via a transverse pump beam constitutes a dissipative quantum many-body system with long range interactions. These interactions can induce a structural phase transition from a flat to a density-modulated state. The transverse pump field simultaneously represents a probe of the atomic density via cavity- enhanced Bragg scattering. By spectrally analyzing the light field leaking out of the cavity, we measure non-destructively the dynamic structure factor of the fluctuating atomic density while the system undergoes the phase transition. An observed asymmetry in the dynamic structure factor is attributed to the coupling to dissipative baths. Critical exponents for both sides of the phase transition can be extracted from the data. We further discuss our progress in adding strong short-range interactions to this system, in order to explore Bose-Hubbard physics with cavity-mediated long-range interactions and self-organization in lower dimensions.

Intermittent strong transport of the quasi-adiabatic plasma state.

PubMed

Kim, Chang-Bae; An, Chan-Yong; Min, Byunghoon

2018-06-05

The dynamics of the fluctuating electrostatic potential and the plasma density couched in the resistive-drift model at nearly adiabatic state are simulated. The linear modes are unstable if the phase difference between the potential and the density are positive. Exponential growth of the random small perturbations slows down due to the nonlinear E × B flows that work in two ways. They regulate the strength of the fluctuations by transferring the energy from the energy-producing scale to neighboring scales and reduce the cross phase at the same time. During quasi-steady relaxation sporadic appearance of very strong turbulent particle flux is observed that is characterized by the flat energy spectrum and the broad secondary peak in the mesoscale of the order of the gyro-radius. Such boost of the transport is found to be caused by presence of relatively large cross phase as the E × B flows are not effective in cancelling out the cross phase.

A theoretical prediction of the acoustic pressure generated by turbulence-flame front interactions

NASA Technical Reports Server (NTRS)

Huff, R. G.

1984-01-01

The equations of momentum annd continuity are combined and linearized yielding the one dimensional nonhomogeneous acoustic wave equation. Three terms in the non-homogeneous equation act as acoustic sources and are taken to be forcing functions acting on the homogeneous wave equation. The three source terms are: fluctuating entropy, turbulence gradients, and turbulence-flame interactions. Each source term is discussed. The turbulence-flame interaction source is used as the basis for computing the source acoustic pressure from the Fourier transformed wave equation. Pressure fluctuations created in turbopump gas generators and turbines may act as a forcing function for turbine and propellant tube vibrations in Earth to orbit space propulsion systems and could reduce their life expectancy. A preliminary assessment of the acoustic pressure fluctuations in such systems is presented.

A theoretical prediction of the acoustic pressure generated by turbulence-flame front interactions

NASA Technical Reports Server (NTRS)

Huff, R. G.

1984-01-01

The equations of momentum and continuity are combined and linearized yielding the one dimensional nonhomogeneous acoustic wave equation. Three terms in the non-homogeneous equation act as acoustic sources and are taken to be forcing functions acting on the homogeneous wave equation. The three source terms are: fluctuating entropy, turbulence gradients, and turbulence-flame interactions. Each source term is discussed. The turbulence-flame interaction source is used as the basis for computing the source acoustic pressure from the Fourier transformed wave equation. Pressure fluctuations created in turbopump gas generators and turbines may act as a forcing function for turbine and propellant tube vibrations in earth to orbit space propulsion systems and could reduce their life expectancy. A preliminary assessment of the acoustic pressure fluctuations in such systems is presented.

Kinetic Alfvén Wave Generation by Large-scale Phase Mixing

NASA Astrophysics Data System (ADS)

Vásconez, C. L.; Pucci, F.; Valentini, F.; Servidio, S.; Matthaeus, W. H.; Malara, F.

2015-12-01

One view of the solar wind turbulence is that the observed highly anisotropic fluctuations at spatial scales near the proton inertial length dp may be considered as kinetic Alfvén waves (KAWs). In the present paper, we show how phase mixing of large-scale parallel-propagating Alfvén waves is an efficient mechanism for the production of KAWs at wavelengths close to dp and at a large propagation angle with respect to the magnetic field. Magnetohydrodynamic (MHD), Hall magnetohydrodynamic (HMHD), and hybrid Vlasov–Maxwell (HVM) simulations modeling the propagation of Alfvén waves in inhomogeneous plasmas are performed. In the linear regime, the role of dispersive effects is singled out by comparing MHD and HMHD results. Fluctuations produced by phase mixing are identified as KAWs through a comparison of polarization of magnetic fluctuations and wave-group velocity with analytical linear predictions. In the nonlinear regime, a comparison of HMHD and HVM simulations allows us to point out the role of kinetic effects in shaping the proton-distribution function. We observe the generation of temperature anisotropy with respect to the local magnetic field and the production of field-aligned beams. The regions where the proton-distribution function highly departs from thermal equilibrium are located inside the shear layers, where the KAWs are excited, this suggesting that the distortions of the proton distribution are driven by a resonant interaction of protons with KAW fluctuations. Our results are relevant in configurations where magnetic-field inhomogeneities are present, as, for example, in the solar corona, where the presence of Alfvén waves has been ascertained.

Direct evidence of atomic-scale structural fluctuations in catalyst nanoparticles.

PubMed

Lin, Pin Ann; Gomez-Ballesteros, Jose L; Burgos, Juan C; Balbuena, Perla B; Natarajan, Bharath; Sharma, Renu

2017-05-01

Rational catalyst design requires an atomic scale mechanistic understanding of the chemical pathways involved in the catalytic process. A heterogeneous catalyst typically works by adsorbing reactants onto its surface, where the energies for specific bonds to dissociate and/or combine with other species (to form desired intermediate or final products) are lower. Here, using the catalytic growth of single-walled carbon nanotubes (SWCNTs) as a prototype reaction, we show that the chemical pathway may in-fact involve the entire catalyst particle, and can proceed via the fluctuations in the formation and decomposition of metastable phases in the particle interior. We record in situ and at atomic resolution, the dynamic phase transformations occurring in a Cobalt catalyst nanoparticle during SWCNT growth, using a state-of-the-art environmental transmission electron microscope (ETEM). The fluctuations in catalyst carbon content are quantified by the automated, atomic-scale structural analysis of the time-resolved ETEM images and correlated with the SWCNT growth rate. We find the fluctuations in the carbon concentration in the catalyst nanoparticle and the fluctuations in nanotube growth rates to be of complementary character. These findings are successfully explained by reactive molecular dynamics (RMD) simulations that track the spatial and temporal evolution of the distribution of carbon atoms within and on the surface of the catalyst particle. We anticipate that our approach combining real-time, atomic-resolution image analysis and molecular dynamics simulations will facilitate catalyst design, improving reaction efficiencies and selectivity towards the growth of desired structure.

Thermonuclear runaways in nova outbursts. 2: Effect of strong, instantaneous, local fluctuations

NASA Technical Reports Server (NTRS)

Shankar, Anurag; Arnett, David

1994-01-01

In an attempt to understand the manner in which nova outbursts are initiated on the surface of a white dwarf, we investigate the effects fluctuations have on the evolution of a thermonuclear runaway. Fluctuations in temperature density, or the composition of material in the burning shell may arise due to the chaotic flow field generated by convection when it occurs, or by the accretion process itself. With the aid of two-dimensional reactive flow calculations, we consider cases where a strong fluctutation in temperature arises during the early, quiescent accretion phase or during the later, more dynamic, explosion phase. In all cases we find that an instantaneous, local temperature fluctuation causes the affected material to become Rayleigh-Taylor unstable. The rapid rise and subsequent expansion of matter immediately cools the hot blob, which prevents the lateral propagation of burning. This suggests that local temperature fluctuations do not play a significant role in directly initiating the runaway, especially during the early stages. However, they may provide an efficient mechanism of mixing core material into the envelope (thereby pre-enriching the fuel for subsequent episodes of explosive hydrogen burning) and of mixing substantial amounts of the radioactive nucleus N-13 into the surface layers, making novae potential gamma-ray sources. This suggests that it is the global not the local, evolution of the core-envelope interface to high temperatures which dominates the development of the runaway. We also present a possible new scenario for the initiation of nova outbursts based on our results.

Quantum metrology of phase for accelerated two-level atom coupled with electromagnetic field with and without boundary

NASA Astrophysics Data System (ADS)

Yang, Ying; Liu, Xiaobao; Wang, Jieci; Jing, Jiliang

2018-03-01

We study how to improve the precision of the quantum estimation of phase for an uniformly accelerated atom in fluctuating electromagnetic field by reflecting boundaries. We find that the precision decreases with increases of the acceleration without the boundary. With the presence of a reflecting boundary, the precision depends on the atomic polarization, position and acceleration, which can be effectively enhanced compared to the case without boundary if we choose the appropriate conditions. In particular, with the presence of two parallel reflecting boundaries, we obtain the optimal precision for atomic parallel polarization and the special distance between two boundaries, as if the atom were shielded from the fluctuation.

Plastic fluctuations in empty crystals formed by cubic wireframe particles

NASA Astrophysics Data System (ADS)

McBride, John M.; Avendaño, Carlos

2018-05-01

We present a computer simulation study of the phase behavior of colloidal hard cubic frames, i.e., particles with nonconvex cubic wireframe geometry interacting purely by excluded volume. Despite the propensity of cubic wireframe particles to form cubic phases akin to their convex counterparts, these particles exhibit unusual plastic fluctuations in which a random and dynamic fraction of particles rotate around their lattice positions in the crystal lattice while the remainder of the particles remains fully ordered. We argue that this unexpected effect stems from the nonconvex geometry of the particles in which the faces of a particle can be penetrated by the vertices of the nearest neighbors even at high number densities.

Barometric fluctuations in wells tapping deep unconfined aquifers

USGS Publications Warehouse

Weeks, Edwin P.

1979-01-01

Water levels in wells screened only below the water table in unconfined aquifers fluctuate in response to atmospheric pressure changes. These fluctuations occur because the materials composing the unsaturated zone resist air movement and have capacity to store air with a change in pressure. Consequently, the translation of any pressure change at land surface is slowed as it moves through the unsaturated zone to the water table, but it reaches the water surface in the well instantaneously. Thus a pressure imbalance is created that results in a water level fluctuation. Barometric effects on water levels in unconfined aquifers can be computed by solution of the differential equation governing the flow of gas in the unsaturated zone subject to the appropriate boundary conditions. Solutions to this equation for two sets of boundary conditions were applied to compute water level response in a well tapping the Ogallala Formation near Lubbock, Texas from simultaneous microbarograph records. One set of computations, based on the step function unit response solution and convolution, resulted in a very good match between computed and measured water levels. A second set of computations, based on analysis of the amplitude ratios of simultaneous cyclic microbarograph and water level fluctuations, gave inconsistent results in terms of the unsaturated zone pneumatic properties but provided useful insights on the nature of unconfined-aquifer water level fluctuations.

Phase-relationships between scales in the perturbed turbulent boundary layer

NASA Astrophysics Data System (ADS)

Jacobi, I.; McKeon, B. J.

2017-12-01

The phase-relationship between large-scale motions and small-scale fluctuations in a non-equilibrium turbulent boundary layer was investigated. A zero-pressure-gradient flat plate turbulent boundary layer was perturbed by a short array of two-dimensional roughness elements, both statically, and under dynamic actuation. Within the compound, dynamic perturbation, the forcing generated a synthetic very-large-scale motion (VLSM) within the flow. The flow was decomposed by phase-locking the flow measurements to the roughness forcing, and the phase-relationship between the synthetic VLSM and remaining fluctuating scales was explored by correlation techniques. The general relationship between large- and small-scale motions in the perturbed flow, without phase-locking, was also examined. The synthetic large scale cohered with smaller scales in the flow via a phase-relationship that is similar to that of natural large scales in an unperturbed flow, but with a much stronger organizing effect. Cospectral techniques were employed to describe the physical implications of the perturbation on the relative orientation of large- and small-scale structures in the flow. The correlation and cospectral techniques provide tools for designing more efficient control strategies that can indirectly control small-scale motions via the large scales.

Thermodynamics of higher dimensional black holes with higher order thermal fluctuations

NASA Astrophysics Data System (ADS)

Pourhassan, B.; Kokabi, K.; Rangyan, S.

2017-12-01

In this paper, we consider higher order corrections of the entropy, which coming from thermal fluctuations, and find their effect on the thermodynamics of higher dimensional charged black holes. Leading order thermal fluctuation is logarithmic term in the entropy while higher order correction is proportional to the inverse of original entropy. We calculate some thermodynamics quantities and obtain the effect of logarithmic and higher order corrections of entropy on them. Validity of the first law of thermodynamics investigated and Van der Waals equation of state of dual picture studied. We find that five-dimensional black hole behaves as Van der Waals, but higher dimensional case have not such behavior. We find that thermal fluctuations are important in stability of black hole hence affect unstable/stable black hole phase transition.

Quantum Order-by-Disorder in Strongly Correlated Metals

NASA Astrophysics Data System (ADS)

Green, Andrew G.; Conduit, Gareth; Krüger, Frank

2018-03-01

Entropic forces in classical many-body systems, e.g., colloidal suspensions, can lead to the formation of new phases. Quantum fluctuations can have similar effects: spin fluctuations drive the superfluidity of helium-3, and a similar mechanism operating in metals can give rise to superconductivity. It is conventional to discuss the latter in terms of the forces induced by the quantum fluctuations. However, focusing directly upon the free energy provides a useful alternative perspective in the classical case and can also be applied to study quantum fluctuations. Villain first developed this approach for insulating magnets and coined the term order-by-disorder to describe the observed effect. We discuss the application of this idea to metallic systems, recent progress made in doing so, and the broader prospects for the future.

Analysis of Magnetic Resonance Image Signal Fluctuations Acquired During MR-Guided Radiotherapy.

PubMed

Breto, Adrian L; Padgett, Kyle R; Ford, John C; Kwon, Deukwoo; Chang, Channing; Fuss, Martin; Stoyanova, Radka; Mellon, Eric A

2018-03-28

Magnetic resonance-guided radiotherapy (MRgRT) is a new and evolving treatment modality that allows unprecedented visualization of the tumor and surrounding anatomy. MRgRT includes daily 3D magnetic resonance imaging (MRI) for setup and rapidly repeated near real-time MRI scans during treatment for target tracking. One of the more exciting potential benefits of MRgRT is the ability to analyze serial MRIs to monitor treatment response or predict outcomes. A typical radiation treatment (RT) over the span of 10-15 minutes on the MRIdian system (ViewRay, Cleveland, OH) yields thousands of "cine" images, each acquired in 250 ms. This unique data allows for a glimpse in image intensity changes during RT delivery. In this report, we analyze cine images from a single fraction RT of a glioblastoma patient on the ViewRay platform in order to characterize the dynamic signal changes occurring during RT therapy. The individual frames in the cines were saved into DICOM format and read into an MIM image analysis platform (MIM Software, Cleveland, OH) as a time series. The three possible states of the three Cobalt-60 radiation sources-OFF, READY, and ON-were also recorded. An in-house Java plugin for MIM was created in order to perform principal component analysis (PCA) on each of the datasets. The analysis resulted in first PC, related to monotonous signal increase over the course of the treatment fraction. We found several distortion patterns in the data that we postulate result from the perturbation of the magnetic field due to the moving metal parts in the platform while treatment was being administered. The largest variations were detected when all Cobalt-60 sources were OFF. During this phase of the treatment, the gantry and multi-leaf collimators (MLCs) are moving. Conversely, when all Cobalt-60 sources were in the ON position, the image signal fluctuations were minimal, relating to very little mechanical motion. At this phase, the gantry, the MLCs, and sources are fixed in their positions. These findings were confirmed in a study with the daily quality assurance (QA) phantom. While the identified variations were not related to physiological processes, our findings confirm the sensitivity of the developed approach to identify very small fluctuations. Relating these variations to the physical changes that occur during treatment shows the methodical ability of the technique to uncover their underlying sources.

Quantum Field Energy Sensor based on the Casimir Effect

NASA Astrophysics Data System (ADS)

Ludwig, Thorsten

The Casimir effect converts vacuum fluctuations into a measurable force. Some new energy technologies aim to utilize these vacuum fluctuations in commonly used forms of energy like electricity or mechanical motion. In order to study these energy technologies it is helpful to have sensors for the energy density of vacuum fluctuations. In today's scientific instrumentation and scanning microscope technologies there are several common methods to measure sub-nano Newton forces. While the commercial atomic force microscopes (AFM) mostly work with silicon cantilevers, there are a large number of reports on the use of quartz tuning forks to get high-resolution force measurements or to create new force sensors. Both methods have certain advantages and disadvantages over the other. In this report the two methods are described and compared towards their usability for Casimir force measurements. Furthermore a design for a quantum field energy sensor based on the Casimir force measurement will be described. In addition some general considerations on extracting energy from vacuum fluctuations will be given.

Experimental investigations of turbulent temperature fluctuations and phase angles in ASDEX Upgrade

NASA Astrophysics Data System (ADS)

Freethy, Simon

2017-10-01

A complete experimental understanding of the turbulent fluctuations in tokamak plasmas is essential for providing confidence in the extrapolation of heat transport models to future experimental devices and reactors. Guided by ``predict first'' nonlinear gyrokinetic simulations with the GENE code, two new turbulence diagnostics were designed and have been installed on ASDEX Upgrade (AUG) to probe the fundamentals of ion-scale turbulent electron heat transport. The first, a 30-channel correlation ECE (CECE) radiometer, measures radial profiles (0.5

LDV survey of cavitation and resonance effect on the precessing vortex rope dynamics in the draft tube of Francis turbines

NASA Astrophysics Data System (ADS)

Favrel, A.; Müller, A.; Landry, C.; Yamamoto, K.; Avellan, F.

2016-11-01

The large-scale penetration of the electrical grid by intermittent renewable energy sources requires a continuous operating range extension of hydropower plants. This causes the formation of unfavourable flow patterns in the draft tube of turbines and pump-turbines. At partial load operation, a precessing cavitation vortex rope is formed at the Francis turbine runner outlet, acting as an excitation source for the hydraulic system. In case of resonance, the resulting high-amplitude pressure pulsations can put at risk the stability of the machine and of the electrical grid to which it is connected. It is therefore crucial to understand and accurately simulate the underlying physical mechanisms in such conditions. However, the exact impact of cavitation and hydro-acoustic resonance on the flow velocity fluctuations in the draft tube remains to be established. The flow discharge pulsations expected to occur in the draft tube in resonance conditions have for instance never been verified experimentally. In this study, two-component Laser Doppler Velocimetry is used to investigate the axial and tangential velocity fluctuations at the runner outlet of a reduced scale physical model of a Francis turbine. The investigation is performed for a discharge equal to 64 % of the nominal value and three different pressure levels in the draft tube, including resonance and cavitation-free conditions. Based on the convective pressure fluctuations induced by the vortex precession, the periodical velocity fluctuations over one typical precession period are recovered by phase averaging. The impact of cavitation and hydro-acoustic resonance on both axial and tangential velocity fluctuations in terms of amplitude and phase shift is highlighted for the first time. It is shown that the occurrence of resonance does not have significant effects on the draft tube velocity fields, suggesting that the synchronous axial velocity fluctuations are surprisingly negligible compared to the velocity fluctuations induced by the vortex precession.

Macromolecular Crowding Induces Spatial Correlations That Control Gene Expression Bursting Patterns

DOE PAGES

Norred, Sarah Elizabeth; Caveney, Patrick M.; Chauhan, Gaurav; ...

2018-04-24

Recent superresolution microscopy studies in E. coli demonstrate that the cytoplasm has highly variable local concentrations where macromolecular crowding plays a central role in establishing membrane-less compartmentalization. This spatial inhomogeneity significantly influences molecular transport and association processes central to gene expression. Yet, little is known about how macromolecular crowding influences gene expression bursting—the episodic process where mRNA and proteins are produced in bursts. Here, we simultaneously measured mRNA and protein reporters in cell-free systems, showing that macromolecular crowding decoupled the well-known relationship between fluctuations in the protein population (noise) and mRNA population statistics. Crowded environments led to a 10-fold increasemore » in protein noise even though there were only modest changes in the mRNA population and fluctuations. Instead, cell-like macromolecular crowding created an inhomogeneous spatial distribution of mRNA (“spatial noise”) that led to large variability in the protein production burst size. As a result, the mRNA spatial noise created large temporal fluctuations in the protein population. Furthermore, these results highlight the interplay between macromolecular crowding, spatial inhomogeneities, and the resulting dynamics of gene expression, and provide insights into using these organizational principles in both cell-based and cell-free synthetic biology.« less

Macromolecular Crowding Induces Spatial Correlations That Control Gene Expression Bursting Patterns

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

Norred, Sarah Elizabeth; Caveney, Patrick M.; Chauhan, Gaurav

Recent superresolution microscopy studies in E. coli demonstrate that the cytoplasm has highly variable local concentrations where macromolecular crowding plays a central role in establishing membrane-less compartmentalization. This spatial inhomogeneity significantly influences molecular transport and association processes central to gene expression. Yet, little is known about how macromolecular crowding influences gene expression bursting—the episodic process where mRNA and proteins are produced in bursts. Here, we simultaneously measured mRNA and protein reporters in cell-free systems, showing that macromolecular crowding decoupled the well-known relationship between fluctuations in the protein population (noise) and mRNA population statistics. Crowded environments led to a 10-fold increasemore » in protein noise even though there were only modest changes in the mRNA population and fluctuations. Instead, cell-like macromolecular crowding created an inhomogeneous spatial distribution of mRNA (“spatial noise”) that led to large variability in the protein production burst size. As a result, the mRNA spatial noise created large temporal fluctuations in the protein population. Furthermore, these results highlight the interplay between macromolecular crowding, spatial inhomogeneities, and the resulting dynamics of gene expression, and provide insights into using these organizational principles in both cell-based and cell-free synthetic biology.« less

Plasma fluctuations in a Kaufman thruster. [root mean square magnitude, spectra and cross correlation

NASA Technical Reports Server (NTRS)

Serafini, J. S.; Terdan, F. F.

1973-01-01

Measurements of the RMS magnitude, spectra and cross-correlations for the fluctuations in the beam, discharge and neutralizer keeper currents are presented for a 30-cm diameter dished grid ion thrustor for a range of magnetic baffle currents and up to 2.0 amperes beam current. The ratio of RMS to mean ion beam current varied from 0.04 to 0.23. The spectra of the amplitudes of the beam and discharge current fluctuations were taken up to 9 MHz and show that the predominant amplitudes occur at frequencies of 10 kHz or below. The fall-off with increasing frequency is rapid. Frequencies above 100 kHz the spectral levels are 45 kb or more below the maximum peak amplitudes. The cross-correlations revealed the ion beam fluctuations to have large radial and axial scales which implied that the beam fluctuates as a whole or 'in-phase.' The cross-correlations of the beam and neutralizer keeper current fluctuations indicated the neutralizer contributions to the beam fluctuations to be small, but not negligible. The mode of operation of the thrustor (values of beam and magnetic baffle currents) was significant in determining the RMS magnitude and spectral shape of the beam fluctuations. The major oscillations were not found to be directly dependent on the power conditioner inverter frequencies.

Active Brownian particles with velocity-alignment and active fluctuations

NASA Astrophysics Data System (ADS)

Großmann, R.; Schimansky-Geier, L.; Romanczuk, P.

2012-07-01

We consider a model of active Brownian particles (ABPs) with velocity alignment in two spatial dimensions with passive and active fluctuations. Here, active fluctuations refers to purely non-equilibrium stochastic forces correlated with the heading of an individual active particle. In the simplest case studied here, they are assumed to be independent stochastic forces parallel (speed noise) and perpendicular (angular noise) to the velocity of the particle. On the other hand, passive fluctuations are defined by a noise vector independent of the direction of motion of a particle, and may account, for example, for thermal fluctuations. We derive a macroscopic description of the ABP gas with velocity-alignment interaction. Here, we start from the individual-based description in terms of stochastic differential equations (Langevin equations) and derive equations of motion for the coarse-grained kinetic variables (density, velocity and temperature) via a moment expansion of the corresponding probability density function. We focus here on the different impact of active and passive fluctuations on onset of collective motion and show how active fluctuations in the active Brownian dynamics can change the phase-transition behaviour of the system. In particular, we show that active angular fluctuations lead to an earlier breakdown of collective motion and to the emergence of a new bistable regime in the mean-field case.

An Experimental Study of the Effect of Streamwise Vortices on Unsteady Turbulent Boundary-Layer Separation

DTIC Science & Technology

1988-12-09

Measurement of Second Order Statistics .... .............. .54 5.4 Measurement of Triple Products ...... ................. .58 5.6 Uncertainty Analysis...deterministic fluctuations, u/ 2 , were 25 times larger than the mean fluctuations, u𔃼, there were no significant variations in the mean statistical ...input signals, the three velocity components are cal- culated, Awn in ,i-;dual phase ensembles are collected for the appropriate statistical 3

Locked modes in two reversed-field pinch devices of different size and shell system

NASA Astrophysics Data System (ADS)

Malmberg, J.-A.; Brunsell, P. R.; Yagi, Y.; Koguchi, H.

2000-10-01

The behavior of locked modes in two reversed-field pinch devices, the Toroidal Pinch Experiment (TPE-RX) [Y. Yagi et al., Plasma Phys. Control. Fusion 41, 2552 (1999)] and Extrap T2 [J. R. Drake et al., in Plasma Physics and Controlled Nuclear Fusion Research 1996, Montreal (International Atomic Energy Agency, Vienna, 1996), Vol. 2, p. 193] is analyzed and compared. The main characteristics of the locked mode are qualitatively similar. The toroidal distribution of the mode locking shows that field errors play a role in both devices. The probability of phase locking is found to increase with increasing magnetic fluctuation levels in both machines. Furthermore, the probability of phase locking increases with plasma current in TPE-RX despite the fact that the magnetic fluctuation levels decrease. A comparison with computations using a theoretical model estimating the critical mode amplitude for locking [R. Fitzpatrick et al., Phys. Plasmas 6, 3878 (1999)] shows a good correlation with experimental results in TPE-RX. In Extrap T2, the magnetic fluctuations scale weakly with both plasma current and electron densities. This is also reflected in the weak scaling of the magnetic fluctuation levels with the Lundquist number (˜S-0.06). In TPE-RX, the corresponding scaling is ˜S-0.18.

Water-level fluctuations influence sediment porewater ...

EPA Pesticide Factsheets

Reservoirs typically have elevated fish mercury (Hg) levels compared to natural lakes and rivers. A unique feature of reservoirs is water-level management which can result in sediment exposure to the air. The objective of this study is to identify how reservoir water-level fluctuations impact Hg cycling, particularly the formation of the more toxic and bioaccumulative methylmercury (MeHg). Total-Hg (THg), MeHg, stable isotope methylation rates and several ancillary parameters were measured in reservoir sediments (including some in porewater and overlying water) that are seasonally and permanently inundated. The results showed that sediment and porewater MeHg concentrations were over 3-times higher in areas experiencing water-level fluctuations compared to permanently inundated sediments. Analysis of the data suggest that the enhanced breakdown of organic matter in sediments experiencing water-level fluctuations has a two-fold effect on stimulating Hg methylation: 1) it increases the partitioning of inorganic Hg from the solid phase into the porewater phase (lower log Kd values) where it is more bioavailable for methylation; and 2) it increases dissolved organic carbon (DOC) in the porewater which can stimulate the microbial community that can methylate Hg. Sulfate concentrations and cycling were enhanced in the seasonally inundated sediments and may have also contributed to increased MeHg production. Overall, our results suggest that reservoir management a

Tradeoffs in Chemical and Thermal Variations in the Post-perovskite Phase Transition: Mixed Phase Regions in the Deep Lower Mantle?

NASA Astrophysics Data System (ADS)

Giles, G. F.; Spera, F. J.; Yuen, D. A.

2005-12-01

The recent discovery of a phase-transition in Mg-rich perovskite (Pv) to a post-perovskite (pPv) phase at lower mantle depths and its relationship to D", lower mantle heterogeneity and iron content prompted an investigation of the relative importance of lower mantle (LM) compositional and temperature fluctuations in creating topographic undulations on mixed phase regions. Above the transition, Mg-rich Pv makes up ~70 percent by mass of the LM. Using results from experimental phase equilibria, first-principles computations and thermodynamic relations for Fe2+-Mg mixing in silicates, a preliminary thermodynamic model for the perovskite to post-perovskite phase transition in the divariant system MgSiO3-FeSiO3 is developed. Complexities associated with components Fe2O3 and Al2O3 and other phases (Ca-Pv, magnesiowustite) are neglected. The model predicts phase transition pressures are sensitive to the FeSiO3 content of perovskite (~-1.5 GPa per one mole percent FeSiO3). This leads to considerable topography along the top boundary of the mixed phase region. The Clapeyron slope for the Pv to pPv transition at XFeSiO3=0.1 is +11 MPa/K about 20% higher than for pure Mg-Pv. Increasing bulk concentration of iron elevates the mixed (two-phase) layer above the core-mantle boundary (CMB); increasing temperature acts to push the mixed layer deeper into the LM into the D" thermal boundary layer resting upon the (CMB). For various LM geotherms and CMB temperatures, a single mixed layer of thickness ~300 km lies within the bottom 40% of the lower mantle. For low iron contents (XFeSiO3 ~5 mole percent or less), two perched layers are found. This is the divariant analog to the univariant double-crosser. The hotter the mantle, the deeper the mixed phase layer; the more iron-rich the LM, the higher the mixed phase layer. In a hotter Hadean Earth with interior temperatures everywhere 200-500 K warmer pPv is not stable unless the LM bulk composition is Fe-enriched compared to the present upper mantle.

Phase Contrast Imaging on the HL-2A Tokamak

NASA Astrophysics Data System (ADS)

Yu, Yi; Gong, Shaobo; Xu, Min; Jiang, Wei; Zhong, Wulv; Shi, Zhongbin; Wang, Huajie; Wu, Yifan; Yuan, Boda; Lan, Tao; Ye, Minyou; Duan, Xuru; HL-2A Team

2016-10-01

In this article we present the design of a phase contrast imaging (PCI) system on the HL-2A tokamak. This diagnostic is developed to infer line integrated plasma density fluctuations by measuring the phase shift of an expanded CO2 laser beam passing through magnetically confined high temperature plasmas. This system is designed to diagnose plasma density fluctuations with the maximum wavenumber of 66 cm-1. The designed wavenumber resolution is 2.09cm-1, and the time resolution is higher than 0.2 μs. The broad kρs ranging from 0.34 to 13.37 makes it suitable for turbulence measurement. An upgraded PCI system is also discussed, which is designed for the HL-2M tokamak. Supported by the National Magnetic Confinement Fusion Energy Research Project (Grant No. 2015GB120002), the National Natural Science Foundation of China (Grant No. 11375053, 11105144, 10905057, 11535013).

Study of the correlation properties of the surface structure of nc-Si/a-Si:H films with different fractions of the crystalline phase

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

Alpatov, A. V., E-mail: pgnv@mail.ru; Vikhrov, S. P.; Kazanskii, A. G.

The correlation properties of the structure of nc-Si/a-Si:H films with different volume fractions of the crystalline phase are studied using 2D detrended fluctuation analysis. Study of the surface relief of experimental samples showed that with increasing in volume fraction of the crystalline phase in the nc-Si/a-Si:H films, the size and number of nanoclusters on their surface grow. The size of Si nanocrystals in the a-Si:H matrix (6–8 nm) indicates the formation of coarse nanoclusters due to the self-organization of Si nanocrystals in groups under laser radiation. According to 2D detrended fluctuation analysis data, the number of correlation vectors (harmonic components)more » in the nc-Si/a-Si:H film structure increased with an increase in the nanocrystal fraction in the films.« less

Counting of fermions and spins in strongly correlated systems in and out of thermal equilibrium

NASA Astrophysics Data System (ADS)

Braungardt, Sibylle; Rodríguez, Mirta; Sen(de), Aditi; Sen, Ujjwal; Glauber, Roy J.; Lewenstein, Maciej

2011-01-01

Atom counting theory can be used to study the role of thermal noise in quantum phase transitions and to monitor the dynamics of a quantum system. We illustrate this for a strongly correlated fermionic system, which is equivalent to an anisotropic quantum XY chain in a transverse field and can be realized with cold fermionic atoms in an optical lattice. We analyze the counting statistics across the phase diagram in the presence of thermal fluctuations and during its thermalization when the system is coupled to a heat bath. At zero temperature, the quantum phase transition is reflected in the cumulants of the counting distribution. We find that the signatures of the crossover remain visible at low temperature and are obscured with increasing thermal fluctuations. We find that the same quantities may be used to scan the dynamics during the thermalization of the system.

On the Induction of the First-Order Phase Magnetic Transitions by Acoustic Vibrations in MnSi

NASA Astrophysics Data System (ADS)

Pikin, S. A.

2017-12-01

The main result of the paper contains the conclusion that the magnetic phase transition in MnSi always remains first order at any temperature and magnetic field. In these aims, a model of coupling of an order parameter with other degrees of freedom is used. The coupling of magnetic order parameters with long-wave acoustic phonons, in the presence of the nonsingular parts of the bulk and shear moduli, a first-order transition occurs, participle near the transition the heat capacity and the compressibility remain finite, if the heat capacity becomes infinite in the system disregarding the acoustic phonons. The role of the Frenkel heterophase fluctuations is discussed. The impurity effect shows that, for some phases, the heat capacity of the system remains continuous and finite at the transition point. It is supposed that the transition is progressively smoothed by these fluctuations at the application of the magnetic field.

On the induction of the first-order phase magnetic transitions by acoustic vibrations in MnSi

NASA Astrophysics Data System (ADS)

Pikin, S. A.

2017-12-01

The main result of the paper contains the conclusion that the magnetic phase transition in MnSi always remains first order at any temperature and magnetic field. In these aims, a model of coupling of an order parameter with other degrees of freedom is used. The coupling of magnetic order parameters with longwave acoustic phonons, in the presence of the nonsingular parts of the bulk and shear moduli, a first-order transition occurs, participle near the transition the heat capacity and the compressibility remain finite, if in the system without allowance of the acoustic phonons the heat capacity becomes infinite. The role of the Frenkel heterophase fluctuations is discussed. The impurity effect shows that, for some phases, the heat capacity of the system remains continuous and finite at the transition point. It is supposed that the transition is progressively smoothed by these fluctuations at the application of the magnetic field.

Spin-current probe for phase transition in an insulator

DOE PAGES

Qiu, Zhiyong; Li, Jia; Hou, Dazhi; ...

2016-08-30

Spin fluctuation and transition have always been one of the central topics of magnetism and condensed matter science. Experimentally, the spin fluctuation is found transcribed onto scattering intensity in the neutron-scattering process, which is represented by dynamical magnetic susceptibility and maximized at phase transitions. Importantly, a neutron carries spin without electric charge, and therefore it can bring spin into a sample without being disturbed by electric energy. However, large facilities such as a nuclear reactor are necessary. Here we present that spin pumping, frequently used in nanoscale spintronic devices, provides a desktop microprobe for spin transition; spin current is amore » flux of spin without an electric charge and its transport reflects spin excitation. Additionally, we demonstrate detection of antiferromagnetic transition in ultra-thin CoO films via frequency-dependent spin-current transmission measurements, which provides a versatile probe for phase transition in an electric manner in minute devices.« less

Thermal fluctuations of dilaton black holes in gravity's rainbow

NASA Astrophysics Data System (ADS)

Dehghani, M.

2018-06-01

In this work, thermodynamics and phase transition of some new dilaton black hole solutions have been explored in the presence of the rainbow functions. By introducing an energy dependent space time, the dilaton potential has been obtained as the linear combination of two Liouville-type potentials and three new classes of black hole solutions have been constructed. The conserved and thermodynamic quantities of the new dilaton black holes have been calculated in the energy dependent space times. It has been shown that, even if some of the thermodynamic quantities are affected by the rainbow functions, the thermodynamical first law still remains valid. Also, the impacts of rainbow functions on the stability or phase transition of the new black hole solutions have been investigated. Finally, the quantum gravitational effects on the thermodynamics and phase transition of the solutions have been studied through consideration of the thermal fluctuations.

Extinction phase transitions in a model of ecological and evolutionary dynamics

NASA Astrophysics Data System (ADS)

Barghathi, Hatem; Tackkett, Skye; Vojta, Thomas

2017-07-01

We study the non-equilibrium phase transition between survival and extinction of spatially extended biological populations using an agent-based model. We especially focus on the effects of global temporal fluctuations of the environmental conditions, i.e., temporal disorder. Using large-scale Monte-Carlo simulations of up to 3 × 107 organisms and 105 generations, we find the extinction transition in time-independent environments to be in the well-known directed percolation universality class. In contrast, temporal disorder leads to a highly unusual extinction transition characterized by logarithmically slow population decay and enormous fluctuations even for large populations. The simulations provide strong evidence for this transition to be of exotic infinite-noise type, as recently predicted by a renormalization group theory. The transition is accompanied by temporal Griffiths phases featuring a power-law dependence of the life time on the population size.

Distinct nature of orbital-selective Mott phases dominated by low-energy local spin fluctuations

NASA Astrophysics Data System (ADS)

Song, Ze-Yi; Jiang, Xiu-Cai; Lin, Hai-Qing; Zhang, Yu-Zhong

2017-12-01

Quantum orbital-selective Mott (OSM) transitions are investigated within dynamical mean-field theory based on a two-orbital Hubbard model with different bandwidth at half filling. We find two distinct OSM phases both showing coexistence of itinerant electrons and localized spins, dependent on whether the Hund's coupling is full or of Ising type. The critical values and the nature of the OSM transitions are efficiently determined by entanglement entropy. We reveal that vanishing of the Kondo energy scale evidenced by absence of local spin fluctuations at low frequency in local dynamical spin susceptibility is responsible for the appearance of non-Fermi-liquid OSM phase in Ising Hund's coupling case. We argue that this scenario can also be applied to account for emergent quantum non-Fermi liquid in the one-band Hubbard model when short-range antiferromagnetic order is considered.

Transient electronic anisotropy in overdoped NaF e1 -xC oxAs superconductors

NASA Astrophysics Data System (ADS)

Liu, Shenghua; Zhang, Chunfeng; Deng, Qiang; Wen, Hai-hu; Li, Jian-xin; Chia, Elbert E. M.; Wang, Xiaoyong; Xiao, Min

2018-01-01

By combining polarized pump-probe spectroscopic and Laue x-ray diffraction measurements, we have observed nonequivalent transient optical responses with the probe beam polarized along the x and y axes in overdoped NaF e1 -xC oxAs superconductors. Such transient anisotropic behavior has been uncovered in the tetragonal phase with the doping level and temperature range far from the borders of static nematic phases. The measured transient anisotropy can be well explained as a result of nematic fluctuation driven by an orbital order with energy splitting of the dx z- and dy z-dominant bands. In addition, the doping level dependence and the pressure effect of the crossover temperature show significant differences between the transient nematic fluctuation and static nematic phase, implying spin and orbital orders may play different roles in static and transient nematic behaviors.

Absolute calibration of Phase Contrast Imaging on HL-2A tokamak

NASA Astrophysics Data System (ADS)

Yu, Yi; Gong, Shaobo; Xu, Min; Wu, Yifan; Yuan, Boda; Ye, Minyou; Duan, Xuru; HL-2A Team Team

2017-10-01

Phase contrast imaging (PCI) has recently been developed on HL-2A tokamak. In this article we present the calibration of this diagnostic. This system is to diagnose chord integral density fluctuations by measuring the phase shift of a CO2 laser beam with a wavelength of 10.6 μm when the laser beam passes through plasma. Sound waves are used to calibrate PCI diagnostic. The signal series in different PCI channels show a pronounced modulation of incident laser beam by the sound wave. Frequency-wavenumber spectrum is achieved. Calibrations by sound waves with different frequencies exhibit a maximal wavenumber response of 12 cm-1. The conversion relationship between the chord integral plasma density fluctuation and the signal intensity is 2.3-1013 m-2/mV, indicating a high sensitivity. Supported by the National Magnetic Confinement Fusion Energy Research Project (Grant No.2015GB120002, 2013GB107001).

Looking for the Phase Transition—Recent NA61/SHINE Results

NASA Astrophysics Data System (ADS)

Turko, Ludwik

2018-03-01

The fixed-target NA61/SHINE experiment (SPS CERN) looks for the critical point of strongly interacting matter and the properties of the onset of deconfinement. It is a two dimensional scan of measurements of particle spectra and fluctuations in proton-proton, proton-nucleus and nucleus-nucleus interactions as a function of collision energy and system size, corresponding to a two dimensional phase diagram (temperature T - baryonic chemical potential $\\mu_B$). New NA61/SHINE results are presented here, such as transverse momentum and multiplicity fluctuations in Ar+Sc collisions compared to NA61/SHINE p+p and Be+Be data, as well as to earlier NA49 A+A results. Recently, a preliminary signature for the new size dependent effect - rapid changes in system size dependence was observed in NA61-SHINE data, labeled as percolation threshold or onset of fireball. This would be closely related to the vicinity of the hadronic phase transition region.

Raman spectroscopy of KxCo2-ySe2 single crystals near the ferromagnet-paramagnet transition

DOE PAGES

Opacic, M.; Lazarevic, N.; Radonjic, M. M.; ...

2016-10-05

Polarized Raman scattering spectra of the K xCo 2-ySe 2 (x = :::; y = :::) single crystals reveal the presence of two phonon modes, assigned as of the A1g and B1g symmetry. Absence of additional modes excludes the possibility of vacancy ordering, unlike in K xCo 2-ySe 2 . The ferromagnetic (FM) phase transition at Tc 74 K leaves a clear fingerprint on the temperature dependence of the Raman mode energy and linewidth. For T > Tc the temperature dependence looks conventional, driven by the thermal expansion and anharmonicity. The Raman modes are rather broad due to the electron-phononmore » coupling increased by the disorder and spin fluctuation e ects. In the FM phase the phonon frequency of both modes increases, while an opposite trend is seen in their linewidth: the A1g mode narrows in the FM phase, whereas the B 1g mode broadens. We argue that the large asymmetry and anomalous frequency shift of the B 1g mode is due to the coupling of spin fluctuations and vibration. Our density functional theory (DFT) calculations for the phonon frequencies agree rather well with the Raman measurements, with some discrepancy being expected since the DFT calculations neglect the spin fluctuations.« less

The phenomenology of squeezing and its status in non-inflationary theories

NASA Astrophysics Data System (ADS)

Gubitosi, Giulia; Magueijo, João

2017-11-01

In this paper we skim the true phenomenological requirements behind the concept of inflationary squeezing. We argue that all that is required is that at horizon re-entry the fluctuations form standing waves with the correct temporal phase (specifically, sine waves). We quantify this requirement and relate it to the initial conditions fed into the radiation dominated epoch by whatever phase of the Universe produced the fluctuations. The only relevant quantity turns out to be the degree of suppression of the momentum, p, of the fluctuations, y, which we measure by σ~ ω2 |y|2/|p|2. Even though σ equals the squeezing parameter, s, in the case of inflation and bimetric varying speed of light scenarios, this is not true in general, specifically in some bouncing Universe models. It is also not necessary to produce a large σ at the end of the primordial phase: it is enough that σ be not too small. This is the case with scenarios based on modified dispersion relations (MDR) emulating the dispersion relations of Horava-Lifshitz theory, which produce σ~ 1, enough to comply with the observational requirements. Scenarios based on MDR leading to a slightly red spectrum are also examined, and shown to satisfy the observational constraints.

Phase stability in fMRI time series: effect of noise regression, off-resonance correction and spatial filtering techniques.

PubMed

Hagberg, Gisela E; Bianciardi, Marta; Brainovich, Valentina; Cassara, Antonino Mario; Maraviglia, Bruno

2012-02-15

Although the majority of fMRI studies exploit magnitude changes only, there is an increasing interest regarding the potential additive information conveyed by the phase signal. This integrated part of the complex number furnished by the MR scanners can also be used for exploring direct detection of neuronal activity and for thermography. Few studies have explicitly addressed the issue of the available signal stability in the context of phase time-series, and therefore we explored the spatial pattern of frequency specific phase fluctuations, and evaluated the effect of physiological noise components (heart beat and respiration) on the phase signal. Three categories of retrospective noise reduction techniques were explored and the temporal signal stability was evaluated in terms of a physiologic noise model, for seven fMRI measurement protocols in eight healthy subjects at 3T, for segmented CSF, gray and white matter voxels. We confirmed that for most processing methods, an efficient use of the phase information is hampered by the fact that noise from physiological and instrumental sources contributes significantly more to the phase than to the magnitude instability. Noise regression based on the phase evolution of the central k-space point, RETROICOR, or an orthonormalized combination of these were able to reduce their impact, but without bringing phase stability down to levels expected from the magnitude signal. Similar results were obtained after targeted removal of scan-to-scan variations in the bulk magnetic field by the dynamic off-resonance in k-space (DORK) method and by the temporal off-resonance alignment of single-echo time series technique (TOAST). We found that spatial high-pass filtering was necessary, and in vivo a Gaussian filter width of 20mm was sufficient to suppress physiological noise and bring the phase fluctuations to magnitude levels. Stronger filters brought the fluctuations down to levels dictated by thermal noise contributions, and for 62.5mm(3) voxels the phase stability was as low as 5 mrad (0.27°). In conditions of low SNR(o) and high temporal sampling rate (short TR); we achieved an upper bound for the phase instabilities at 0.0017 ppm, which is close to the dHb contribution to the GM/WM phase contrast. Copyright © 2011 Elsevier Inc. All rights reserved.

A new imaging technique on strength and phase of pulsatile tissue-motion in brightness-mode ultrasonogram

NASA Astrophysics Data System (ADS)

Fukuzawa, Masayuki; Yamada, Masayoshi; Nakamori, Nobuyuki; Kitsunezuka, Yoshiki

2007-03-01

A new imaging technique has been developed for observing both strength and phase of pulsatile tissue-motion in a movie of brightness-mode ultrasonogram. The pulsatile tissue-motion is determined by evaluating the heartbeat-frequency component in Fourier transform of a series of pixel value as a function of time at each pixel in a movie of ultrasonogram (640x480pixels/frame, 8bit/pixel, 33ms/frame) taken by a conventional ultrasonograph apparatus (ATL HDI5000). In order to visualize both the strength and the phase of the pulsatile tissue-motion, we propose a pulsatile-phase image that is obtained by superimposition of color gradation proportional to the motion phase on the original ultrasonogram only at which the motion strength exceeds a proper threshold. The pulsatile-phase image obtained from a cranial ultrasonogram of normal neonate clearly reveals that the motion region gives good agreement with the anatomical shape and position of the middle cerebral artery and the corpus callosum. The motion phase is fluctuated with the shape of arteries revealing local obstruction of blood flow. The pulsatile-phase images in the neonates with asphyxia at birth reveal decreases of the motion region and increases of the phase fluctuation due to the weakness and local disturbance of blood flow, which is useful for pediatric diagnosis.

Challenges of Working in a Multicultural Environment.

ERIC Educational Resources Information Center

Howland, Joan S.

2001-01-01

Addresses challenges faced when working in a multicultural library setting and discusses the need for library administration to create supportive environments. Highlights include fluctuating power dynamics; merging diverse opinions and approaches; overcoming perceived lack of empathy; tokenism; accountability; and transforming challenges into…

Using a short-pulse diffraction-limited laser beam to probe filamentation of a random phase plate smoothed beam.

PubMed

Kline, J L; Montgomery, D S; Flippo, K A; Johnson, R P; Rose, H A; Shimada, T; Williams, E A

2008-10-01

A short pulse (few picoseconds) laser probe provides high temporal resolution measurements to elucidate details of fast dynamic phenomena not observable with typical longer laser pulse probes and gated diagnostics. Such a short pulse laser probe (SPLP) has been used to measure filamentation of a random phase plate (RPP) smoothed laser beam in a gas-jet plasma. The plasma index of refraction due to driven density and temperature fluctuations by the RPP beam perturbs the phase front of a SPLP propagating at a 90 degree angle with respect to the RPP interaction beam. The density and temperature fluctuations are quasistatic on the time scale of the SPLP (approximately 2 ps). The transmitted near-field intensity distribution from the SPLP provides a measure of the phase front perturbation. At low plasma densities, the transmitted intensity pattern is asymmetric with striations across the entire probe beam in the direction of the RPP smoothed beam. As the plasma density increases, the striations break up into smaller sizes along the direction of the RPP beam propagation. The breakup of the intensity pattern is consistent with self-focusing of the RPP smoothed interaction beam. Simulations of the experiment using the wave propagation code, PF3D, are in qualitative agreement demonstrating that the asymmetric striations can be attributed to the RPP driven density fluctuations. Quantification of the beam breakup measured by the transmitted SPLP could lead to a new method for measuring self-focusing of lasers in underdense plasmas.

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

Yazdani, Ahmad, E-mail: Yazdania@modares.ac.ir; Shadrokh, Zohreh; Department of Physics, University of Shahrood, P.O. Box 316-36155, Shahrood

Highlights: • Opto-crystalline character of the composition of Cu{sub 2}S and S{sub 2}Sn was considered. • The formation Cu{sub 2}SnS{sub 3} is strongly related to phase separation at interface. • The entanglement of phases is strongly due to the chemical bond competition. • The suggested fluctuation region is approved by PL spectra. • Reconstruction and cluster formation is evident by formation of flat-spiral flowers. - Abstract: Optical character of crystal structure of the composition of two different semiconducting metallic sulfides, Cu{sub 2}S and S{sub 2}Sn, in pure phase formation of the ternary chalcogenide Cu{sub 2}SnS{sub 3} was considered. Because ofmore » the difficulties related to the phase separation at the definite Eutectic temperature for the composite formation, which is evident in optical absorption fluctuations, solvothermal synthesis in the intermediate temperature range 180–220 °C seems convenient where tetragonal crystal structure is investigated by XRD. Absorption fluctuations below E = E{sub g} were more pronounced for the lower limit case (180 °C) reflected in a sharp peak located at 1.48 eV on S1 as seen in UV-PL measurement. The characteristic behavior of the interface, resulting in the reconstruction and cluster formation due to the offset of bond rupturing displacement of atomic positions, is in favor of aggregation instead of agglomeration, which is evident by formation of small flat-spiral flowers in SEM images.« less

Spectral estimation of received phase in the presence of amplitude scintillation

NASA Technical Reports Server (NTRS)

Vilnrotter, V. A.; Brown, D. H.; Hurd, W. J.

1988-01-01

A technique is demonstrated for obtaining the spectral parameters of the received carrier phase in the presence of carrier amplitude scintillation, by means of a digital phased locked loop. Since the random amplitude fluctuations generate time-varying loop characteristics, straightforward processing of the phase detector output does not provide accurate results. The method developed here performs a time-varying inverse filtering operation on the corrupted observables, thus recovering the original phase process and enabling accurate estimation of its underlying parameters.

Nuclear quantum fluctuations in ice I(h).

PubMed

Moreira, Pedro Augusto Franco Pinheiro; de Koning, Maurice

2015-10-14

We discuss the role of nuclear quantum fluctuations in ice Ih, focusing on the hydrogen-bond (HB) structure and the molecular dipole-moment distribution. For this purpose we carry out DFT-based first-principles molecular dynamics and path-integral molecular dynamics simulations at T = 100 K. We analyze the HB structure in terms of a set of parameters previously employed to characterize molecular structures in the liquid phase and compute the molecular dipole moments using the maximally-localized Wannier functions. The results show that the protons experience very large digressions driven by quantum fluctuations, accompanied by major rearrangements in the electronic density. As a result of these protonic quantum fluctuations the molecular dipole-moment distribution is substantially broadened as well as shifted to a larger mean value when compared to the results obtained when such fluctuations are neglected. In terms of dielectric constants, the reconciliation between the greater mean dipole moment and experimental indications that the dielectric constant of H2O ice is lower than that of D2O ice would indicate that the topology of the HB network is sensitive to protonic quantum fluctuations.

Label-free imaging of intracellular motility by low-coherent quantitative phase microscope in reflection geometry

NASA Astrophysics Data System (ADS)

Yamauchi, Toyohiko; Iwai, Hidenao; Yamashita, Yutaka

2011-11-01

We demonstrate tomographic imaging of intracellular activity of living cells by a low-coherent quantitative phase microscope. The intracellular organelles, such as the nucleus, nucleolus, and mitochondria, are moving around inside living cells, driven by the cellular physiological activity. In order to visualize the intracellular motility in a label-free manner we have developed a reflection-type quantitative phase microscope which employs the phase shifting interferometric technique with a low-coherent light source. The phase shifting interferometry enables us to quantitatively measure the intensity and phase of the optical field, and the low-coherence interferometry makes it possible to selectively probe a specific sectioning plane in the cell volume. The results quantitatively revealed the depth-resolved fluctuations of intracellular surfaces so that the plasma membrane and the membranes of intracellular organelles were independently measured. The transversal and the vertical spatial resolutions were 0.56 μm and 0.93 μm, respectively, and the mechanical sensitivity of the phase measurement was 1.2 nanometers. The mean-squared displacement was applied as a statistical tool to analyze the temporal fluctuation of the intracellular organelles. To the best of our knowledge, our system visualized depth-resolved intracellular organelles motion for the first time in sub-micrometer resolution without contrast agents.

Improved fixation quality provided by a Bessel beacon in an adaptive optics system.

PubMed

Lambert, Andrew J; Daly, Elizabeth M; Dainty, Christopher J

2013-07-01

We investigate whether a structured probe beam that creates the beacon for use in a retinal imaging adaptive optics system can provide useful side effects. In particular we investigate whether a Bessel beam that is seen by the subject as a set of concentric rings has a dampening effect on fixation variations of the subject under observation. This calming effect would allow longer periods of observation, particularly for patients with abnormal fixation. An experimental adaptive optics system developed for retinal imaging is used to monitor the fluctuations in aberrations for artificial and human subjects. The probe beam is alternated between a traditional beacon and one provided by a Bessel beam created by SLM. Time-frequency analysis is used to indicate the differences in power and time variation during fixation depending on whether the Bessel beam or the traditional beacon is employed. Comparison is made with the response for an artificial eye to discount systemic variations. Significant evidence is accrued to indicate the reduced fluctuations in fixation when the Bessel beam is employed to create the beacon. © 2013 The Authors Ophthalmic & Physiological Optics © 2013 The College of Optometrists.

Coexistence of Velocity Renormalization and Ferrimagnetic Fluctuation in the Organic Dirac Electron System α-(BEDT-TTF)2I3

NASA Astrophysics Data System (ADS)

Matsuno, Genki; Kobayashi, Akito

2018-05-01

We evaluate the uniform spin susceptibility in an extended Hubbard model describing α-(BEDT-TTF)2I3. Employing the Fock-type self-energy with the long-range Coulomb interaction and the random phase approximation with the on-site Coulomb interaction, it is clarified that the characteristic energy scales at which ferrimagnetic fluctuation and velocity renormalization emerge are different. This is why these phenomena coexist while the ferrimagnetic fluctuation is disturbed by the velocity renormalization. In addition, it is found that screening effect to the self-energy is irrelevant in the presence of a strong on-site Coulomb interaction U.

Discovery of Short-Timescale Oscillations in the Transition Region by CLASP

NASA Technical Reports Server (NTRS)

Kubo, M.; Katsukawa, Y.; Kano, R.; Winebarger, A.; Kobayashi, K.; Ishikawa, R.; Narukage, N.; Bando, T.; Suematsu, Y.; Giono, G.;

Derivation of dynamo current drive in a closed-current volume and stable current sustainment in the HIT-SI experiment

NASA Astrophysics Data System (ADS)

Hossack, A. C.; Sutherland, D. A.; Jarboe, T. R.

2017-02-01

A derivation is given showing that the current inside a closed-current volume can be sustained against resistive dissipation by appropriately phased magnetic perturbations. Imposed-dynamo current drive theory is used to predict the toroidal current evolution in the helicity injected torus with steady inductive helicity injection (HIT-SI) experiment as a function of magnetic fluctuations at the edge. Analysis of magnetic fields from a HIT-SI discharge shows that the injector-imposed fluctuations are sufficient to sustain the measured toroidal current without instabilities whereas the small, plasma-generated magnetic fluctuations are not sufficiently large to sustain the current.

A New Interferometer for Monitoring Atmospheric Phase Fluctuations

NASA Technical Reports Server (NTRS)

Lay, Oliver

2000-01-01

Water vapor in the Earth's troposphere introduces an extra electrical path in the propagation of radio signals through the atmosphere. The distribution of water vapor is irregular and distorts the wavefronts of incoming radio waves, limiting the angular resolution that can be achieved with ground-based telescopes. The level of fluctuations depends both on the location of the site ,and on the prevailing atmospheric conditions. The ability to measure the fluctuations is therefore important when choosing a site for a new instrument, and for scheduling observations of existing telescopes. Existing phase monitors are radio interferometers that monitor monochromatic beacon tones from geostationary communications satellites at a frequency of about 12 GHz. They have a classical heterodyne design based on two satellite receiving antennas; each has a front-end for amplifying and down-converting the incoming signals using a local oscillator that is phase-locked to a common reference frequency. In addition to multiple phase-locked loops these instruments require expensive phase-stable cabling to reduce the effects of thermal drift. The new system uses two consumer 18" digital satellite TV dishes to monitor satellite TV broadcast signals over a bandwidth of 500 MHz (12.2 to 12.7 GHz). The novel design eliminates the need for phase-locked loops and thermally stable components, and uses a pair of Gilbert Cell multipliers to perform the broadband correlation. A phase monitor has been been built and deployed at the site of the Berkeley-Illinois-Maryland Association Millimeter Array in Northern California, and has been operating successfully since June 1998, measuring the difference in electrical path length for parallel lines of sight to the satellite separated by a baseline of 100 m. With a hardware cost of approximately $4000, it is much cheaper than previous instruments, and the low power requirements and high reliability make the system suitable for site testing in remote locations.

Applying time-frequency analysis to assess cerebral autoregulation during hypercapnia.

PubMed

Placek, Michał M; Wachel, Paweł; Iskander, D Robert; Smielewski, Peter; Uryga, Agnieszka; Mielczarek, Arkadiusz; Szczepański, Tomasz A; Kasprowicz, Magdalena

2017-01-01

Classic methods for assessing cerebral autoregulation involve a transfer function analysis performed using the Fourier transform to quantify relationship between fluctuations in arterial blood pressure (ABP) and cerebral blood flow velocity (CBFV). This approach usually assumes the signals and the system to be stationary. Such an presumption is restrictive and may lead to unreliable results. The aim of this study is to present an alternative method that accounts for intrinsic non-stationarity of cerebral autoregulation and the signals used for its assessment. Continuous recording of CBFV, ABP, ECG, and end-tidal CO2 were performed in 50 young volunteers during normocapnia and hypercapnia. Hypercapnia served as a surrogate of the cerebral autoregulation impairment. Fluctuations in ABP, CBFV, and phase shift between them were tested for stationarity using sphericity based test. The Zhao-Atlas-Marks distribution was utilized to estimate the time-frequency coherence (TFCoh) and phase shift (TFPS) between ABP and CBFV in three frequency ranges: 0.02-0.07 Hz (VLF), 0.07-0.20 Hz (LF), and 0.20-0.35 Hz (HF). TFPS was estimated in regions locally validated by statistically justified value of TFCoh. The comparison of TFPS with spectral phase shift determined using transfer function approach was performed. The hypothesis of stationarity for ABP and CBFV fluctuations and the phase shift was rejected. Reduced TFPS was associated with hypercapnia in the VLF and the LF but not in the HF. Spectral phase shift was also decreased during hypercapnia in the VLF and the LF but increased in the HF. Time-frequency method led to lower dispersion of phase estimates than the spectral method, mainly during normocapnia in the VLF and the LF. The time-frequency method performed no worse than the classic one and yet may offer benefits from lower dispersion of phase shift as well as a more in-depth insight into the dynamic nature of cerebral autoregulation.

Airflow elicits a spider's jump towards airborne prey. I. Airflow around a flying blowfly

PubMed Central

Klopsch, Christian; Kuhlmann, Hendrik C.; Barth, Friedrich G.

2012-01-01

The hunting spider Cupiennius salei uses airflow generated by flying insects for the guidance of its prey-capture jump. We investigated the velocity field of the airflow generated by a freely flying blowfly close to the flow sensors on the spider's legs. It shows three characteristic phases (I–III). (I) When approaching, the blowfly induces an airflow signal near the spider with only little fluctuation (0.013 ± 0.006 m s−1) and a strength that increases nearly exponentially with time (maximum: 0.164 ± 0.051 m s−1 s.d.). The spider detects this flow while the fly is still 38.4 ± 5.6 mm away. The fluctuation of the airflow above the sensors increases linearly up to 0.037 m s−1 with the fly's altitude. Differences in the time of arrival and intensity of the fly signal at different legs probably inform the spider about the direction to the prey. (II) Phase II abruptly follows phase I with a much higher degree of fluctuation (fluctuation amplitudes: 0.114 ± 0.050 m s−1). It starts when the fly is directly above the sensor and corresponds to the time-dependent flow in the wake below and behind the fly. Its onset indicates to the spider that its prey is now within reach and triggers its jump. The spider derives information on the fly's position from the airflow characteristics, enabling it to properly time its jump. The horizontal velocity of the approaching fly is reflected by the time of arrival differences (ranging from 0.038 to 0.108 s) of the flow at different legs and the exponential velocity growth rate (16–79 s−1) during phase I. (III) The air flow velocity decays again after the fly has passed the spider. PMID:22572032

Multidetector Scattering as a Probe of Local Structure in Disordered Phases

NASA Astrophysics Data System (ADS)

Clark, Noel A.; Ackerson, Bruce J.; Hurd, Alan J.

1983-05-01

The local translational structure of a two-dimensional colloidal liquid is observed by use of cross correlation of the intensity fluctuations of light scattered by the liquid through two different wave vectors. The utility of multidetector scattering in probing multipoint correlations in disordered phases is thereby demonstrated unambiguously.

Speed control for synchronous motors

NASA Technical Reports Server (NTRS)

Packard, H.; Schott, J.

1981-01-01

Feedback circuit controls fluctuations in speed of synchronous ac motor. Voltage proportional to phase angle is developed by phase detector, rectified, amplified, compared to threshold, and reapplied positively or negatively to motor excitation circuit. Speed control reduces wow and flutter of audio turntables and tape recorders, and enhances hunting in gyroscope motors.

Cascading of Fluctuations in Interdependent Energy Infrastructures. Gas-Grid Coupling

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

Chertkov, Michael; Lebedev, Vladimir; Backhaus, Scott N.

2014-09-05

The revolution of hydraulic fracturing has dramatically increased the supply and lowered the cost of natural gas in the United States driving an expansion of natural gas-fired generation capacity in many electrical grids. Unrelated to the natural gas expansion, lower capital costs and renewable portfolio standards are driving an expansion of intermittent renewable generation capacity such as wind and photovoltaic generation. These two changes may potentially combine to create new threats to the reliability of these interdependent energy infrastructures. Natural gas-fired generators are often used to balance the fluctuating output of wind generation. However, the time-varying output of these generatorsmore » results in time-varying natural gas burn rates that impact the pressure in interstate transmission pipelines. Fluctuating pressure impacts the reliability of natural gas deliveries to those same generators and the safety of pipeline operations. We adopt a partial differential equation model of natural gas pipelines and use this model to explore the effect of intermittent wind generation on the fluctuations of pressure in natural gas pipelines. The mean square pressure fluctuations are found to grow linearly in time with points of maximum deviation occurring at the locations of flow reversals.« less

Low Mach number fluctuating hydrodynamics for electrolytes

NASA Astrophysics Data System (ADS)

Péraud, Jean-Philippe; Nonaka, Andy; Chaudhri, Anuj; Bell, John B.; Donev, Aleksandar; Garcia, Alejandro L.

2016-11-01

We formulate and study computationally the low Mach number fluctuating hydrodynamic equations for electrolyte solutions. We are interested in studying transport in mixtures of charged species at the mesoscale, down to scales below the Debye length, where thermal fluctuations have a significant impact on the dynamics. Continuing our previous work on fluctuating hydrodynamics of multicomponent mixtures of incompressible isothermal miscible liquids [A. Donev et al., Phys. Fluids 27, 037103 (2015), 10.1063/1.4913571], we now include the effect of charged species using a quasielectrostatic approximation. Localized charges create an electric field, which in turn provides additional forcing in the mass and momentum equations. Our low Mach number formulation eliminates sound waves from the fully compressible formulation and leads to a more computationally efficient quasi-incompressible formulation. We demonstrate our ability to model saltwater (NaCl) solutions in both equilibrium and nonequilibrium settings. We show that our algorithm is second order in the deterministic setting and for length scales much greater than the Debye length gives results consistent with an electroneutral approximation. In the stochastic setting, our model captures the predicted dynamics of equilibrium and nonequilibrium fluctuations. We also identify and model an instability that appears when diffusive mixing occurs in the presence of an applied electric field.

Carbon Incorporation and Anion Dynamics as Synergistic Drivers for Ultrafast Diffusion in Superionic LiCB 11H 12 and NaCB 11H 12

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

Dimitrievska, Mirjana; Shea, Patrick; Kweon, Kyoung E.

The disordered phases ofLiCB 11H 12 and NaCB 11H 12 possess superb superionic conductivities that make them suitable as solid electrolytes. In these materials, cation diffusion correlates with high orientational mobilities of the CB 11H 12 - anions; however, the precise relationship has yet to be demonstrated. In this work, ab initio molecular dynamics and quasielastic neutron scattering are combined to probe anion reorientations and their mechanistic connection to cation mobility over a range of timescales and temperatures. It is found that anions do not rotate freely, but rather transition rapidly between orientations defined by the cation sublattice symmetry. Themore » symmetry-breaking carbon atom in CB 11H 12 - also plays a critical role by perturbing the energy landscape along the instantaneous orientation of the anion dipole, which couples fluctuations in the cation probability density directly to the anion motion. Anion reorientation rates exceed 3 x 10 10 s -1, suggesting the underlying energy landscape fluctuates dynamically on diffusion-relevant timescales. Furthermore, carbon is found to modify the orientational preferences of the anions and aid rotational mobility, creating additional symmetry incompatibilities that inhibit ordering. The results suggest that synergy between the anion reorientational dynamics and the carbon-modified cation-anion interaction accounts for the higher ionic conductivity in CB 11H 12 - salts compared with B 12H 12 2-.« less

Carbon Incorporation and Anion Dynamics as Synergistic Drivers for Ultrafast Diffusion in Superionic LiCB 11H 12 and NaCB 11H 12

DOE PAGES

Dimitrievska, Mirjana; Shea, Patrick; Kweon, Kyoung E.; ...

2018-02-20

The disordered phases ofLiCB 11H 12 and NaCB 11H 12 possess superb superionic conductivities that make them suitable as solid electrolytes. In these materials, cation diffusion correlates with high orientational mobilities of the CB 11H 12 - anions; however, the precise relationship has yet to be demonstrated. In this work, ab initio molecular dynamics and quasielastic neutron scattering are combined to probe anion reorientations and their mechanistic connection to cation mobility over a range of timescales and temperatures. It is found that anions do not rotate freely, but rather transition rapidly between orientations defined by the cation sublattice symmetry. Themore » symmetry-breaking carbon atom in CB 11H 12 - also plays a critical role by perturbing the energy landscape along the instantaneous orientation of the anion dipole, which couples fluctuations in the cation probability density directly to the anion motion. Anion reorientation rates exceed 3 x 10 10 s -1, suggesting the underlying energy landscape fluctuates dynamically on diffusion-relevant timescales. Furthermore, carbon is found to modify the orientational preferences of the anions and aid rotational mobility, creating additional symmetry incompatibilities that inhibit ordering. The results suggest that synergy between the anion reorientational dynamics and the carbon-modified cation-anion interaction accounts for the higher ionic conductivity in CB 11H 12 - salts compared with B 12H 12 2-.« less

Energy dependence of Kπ, pπ and Kp fluctuations in Au+Au collisions from √s NN=7.7 to 200 GeV

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

Adamczyk, L.

A search for the quantum chromodynamics (QCD) critical point was performed by the STAR experiment at the Relativistic Heavy Ion Collider, using dynamical fluctuations of unlike particle pairs. Heavy ion collisions were studied over a large range of collision energies with homogeneous acceptance and excellent particle identification, covering a significant range in the QCD phase diagram where a critical point may be located. Dynamical Kπ, pπ, and Kp fluctuations as measured by the STAR experiment in central 0–5% Au+Au collisions from center-of-mass collision energies √s NN=7.7 to 200 GeV are presented. The observable νdyn was used to quantify the magnitudemore » of the dynamical fluctuations in event-by-event measurements of the Kπ, pπ, and Kp pairs. The energy dependences of these fluctuations from central 0–5% Au+Au collisions all demonstrate a smooth evolution with collision energy.« less

The Fluctuation-Dissipation Theorem of Colloidal Particle's energy on 2D Periodic Substrates: A Monte Carlo Study of thermal noise-like fluctuation and diffusion like Brownian motion

NASA Astrophysics Data System (ADS)

Najafi, Amin

2014-05-01

Using the Monte Carlo simulations, we have calculated mean-square fluctuations in statistical mechanics, such as those for colloids energy configuration are set on square 2D periodic substrates interacting via a long range screened Coulomb potential on any specific and fixed substrate. Random fluctuations with small deviations from the state of thermodynamic equilibrium arise from the granular structure of them and appear as thermal diffusion with Gaussian distribution structure as well. The variations are showing linear form of the Fluctuation-Dissipation Theorem on the energy of particles constitutive a canonical ensemble with continuous diffusion process of colloidal particle systems. The noise-like variation of the energy per particle and the order parameter versus the Brownian displacement of sum of large number of random steps of particles at low temperatures phase are presenting a markovian process on colloidal particles configuration, too.

Climate teleconnections, weather extremes, and vector-borne disease outbreaks

USDA-ARS?s Scientific Manuscript database

Fluctuations in climate lead to extremes in temperature, rainfall, flooding, and droughts. These climate extremes create ideal ecological conditions that promote mosquito-borne disease transmission that impact global human and animal health. One well known driver of such global scale climate fluctua...

Initial eccentricity in deformed {sup 197}Au+{sup 197}Au and {sup 238}U+{sup 238}U collisions at {radical}(s{sub NN})=200 GeV at the BNL Relativistic Heavy Ion Collider

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

Filip, Peter; Lednicky, Richard; Masui, Hiroshi

2009-11-15

Initial eccentricity and eccentricity fluctuations of the interaction volume created in relativistic collisions of deformed {sup 197}Au and {sup 238}U nuclei are studied using optical and Monte Carlo (MC) Glauber simulations. It is found that the nonsphericity noticeably influences the average eccentricity in central collisions, and eccentricity fluctuations are enhanced from deformation. Quantitative results are obtained for Au+Au and U+U collisions at energy {radical}(s{sub NN})=200 GeV.

Diffusion of non-Gaussianity in heavy ion collisions

NASA Astrophysics Data System (ADS)

Kitazawa, Masakiyo; Asakawa, Masayuki; Ono, Hirosato

2014-05-01

We investigate the time evolution of higher order cumulants of bulk fluctuations of conserved charges in the hadronic stage in relativistic heavy ion collisions. The dynamical evolution of non-Gaussian fluctuations is modeled by the diffusion master equation. Using this model we predict that the fourth-order cumulant of net-electric charge is suppressed compared with the recently observed second-order one at ALICE for a reasonable parameter range. Significance of the measurements of various cumulants as functions of rapidity window to probe dynamical history of the hot medium created by heavy ion collisions is emphasized.

Fluctuations in a model ferromagnetic film driven by a slowly oscillating field with a constant bias

NASA Astrophysics Data System (ADS)

Buendía, Gloria M.; Rikvold, Per Arne

2017-10-01

We present a numerical and theoretical study that supports and explains recent experimental results on anomalous magnetization fluctuations of a uniaxial ferromagnetic film in its low-temperature phase, which is forced by an oscillating field above the critical period of the associated dynamic phase transition (DPT) [P. Riego, P. Vavassori, and A. Berger, Phys. Rev. Lett. 118, 117202 (2017), 10.1103/PhysRevLett.118.117202]. For this purpose, we perform kinetic Monte Carlo simulations of a two-dimensional Ising model with nearest-neighbor ferromagnetic interactions in the presence of a sinusoidally oscillating field, to which is added a constant bias field. We study a large range of system sizes and supercritical periods and analyze the data using a droplet-theoretical description of magnetization switching. We find that the period-averaged magnetization, which plays the role of the order parameter for the DPT, presents large fluctuations that give rise to well-defined peaks in its scaled variance and its susceptibility with respect to the bias field. The peaks are symmetric with respect to zero bias and located at values of the bias field that increase toward the field amplitude as an inverse logarithm of the field oscillation period. Our results indicate that this effect is independent of the system size for large systems, ruling out critical behavior associated with a phase transition. Rather, it is a stochastic-resonance phenomenon that has no counterpart in the corresponding thermodynamic phase transition, providing a reminder that the equivalence of the DPT to an equilibrium phase transition is limited to the critical region near the critical period and zero bias.

Mechanical Energy and Propulsion in Ergometer Double Poling by Cross-country Skiers.

PubMed

Danielsen, Jørgen; Sandbakk, Øyvind; Holmberg, Hans-Christer; Ettema, Gertjan

2015-12-01

This study aims to investigate fluctuations in total mechanical energy of the body (Ebody) in relation to external ergometer work (Werg) during the poling and recovery phases of simulated double-poling cross-country skiing. Nine male cross-country skiers (mean ± SD age, 24 ± 5 yr; mean ± SD body mass, 81.7 ± 6.5 kg) performed 4-min submaximal tests at low-intensity, moderate-intensity, and high-intensity levels and a 3-min all-out test on a ski ergometer. Motion capture analysis and load cell recordings were used to measure body kinematics and dynamics. From these, Werg, Ebody (sum of the translational, rotational, and gravitational potential energies of all segments), and their time differentials (power P) were calculated. Ptot--the rate of energy absorption or generation by muscles-tendons--was defined as the sum of Pbody and Perg. Ebody showed large fluctuations over the movement cycle, decreasing during poling and increasing during the recovery phase. The fluctuation in Pbody was almost perfectly out of phase with Perg. Some muscle-tendon energy absorption was observed at the onset of poling. For the rest of poling and throughout the recovery phase, muscles-tendons generated energy to do Werg and to increase Ebody. Approximately 50% of cycle Ptot occurred during recovery for all intensity levels. In double poling, the extensive contribution of the lower extremities and trunk to whole-body muscle-tendon work during recovery facilitates a "direct" transfer of Ebody to Werg during the poling phase. This observation reveals that double poling involves a unique movement pattern different from most other forms of legged terrestrial locomotion, which are characterized primarily by inverted pendulum or spring-mass types of movement.

Mesoscale variations in acoustic signals induced by atmospheric gravity waves.

PubMed

Chunchuzov, Igor; Kulichkov, Sergey; Perepelkin, Vitaly; Ziemann, Astrid; Arnold, Klaus; Kniffka, Anke

2009-02-01

The results of acoustic tomographic monitoring of the coherent structures in the lower atmosphere and the effects of these structures on acoustic signal parameters are analyzed in the present study. From the measurements of acoustic travel time fluctuations (periods 1 min-1 h) with distant receivers, the temporal fluctuations of the effective sound speed and wind speed are retrieved along different ray paths connecting an acoustic pulse source and several receivers. By using a coherence analysis of the fluctuations near spatially distanced ray turning points, the internal wave-associated fluctuations are filtered and their spatial characteristics (coherences, horizontal phase velocities, and spatial scales) are estimated. The capability of acoustic tomography in estimating wind shear near ground is shown. A possible mechanism describing the temporal modulation of the near-ground wind field by ducted internal waves in the troposphere is proposed.

Magnetic disorder in superconductors: Enhancement by mesoscopic fluctuations

NASA Astrophysics Data System (ADS)

Burmistrov, I. S.; Skvortsov, M. A.

2018-01-01

We study the density of states (DOS) and the transition temperature Tc in a dirty superconducting film with rare classical magnetic impurities of an arbitrary strength described by the Poissonian statistics. We take into account that the potential disorder is a source of mesoscopic fluctuations of the local DOS, and, consequently, of the effective strength of magnetic impurities. We find that these mesoscopic fluctuations result in a nonzero DOS for all energies in the region of the phase diagram where without this effect the DOS is zero within the standard mean-field theory. This mechanism can be more efficient in filling the mean-field superconducting gap than rare fluctuations of the potential disorder (instantons). Depending on the magnetic impurity strength, the suppression of Tc by spin-flip scattering can be faster or slower than in the standard mean-field theory.

Statistical and temporal irradiance fluctuations modeling for a ground-to-geostationary satellite optical link.

PubMed

Camboulives, A-R; Velluet, M-T; Poulenard, S; Saint-Antonin, L; Michau, V

2018-02-01

An optical communication link performance between the ground and a geostationary satellite can be impaired by scintillation, beam wandering, and beam spreading due to its propagation through atmospheric turbulence. These effects on the link performance can be mitigated by tracking and error correction codes coupled with interleaving. Precise numerical tools capable of describing the irradiance fluctuations statistically and of creating an irradiance time series are needed to characterize the benefits of these techniques and optimize them. The wave optics propagation methods have proven their capability of modeling the effects of atmospheric turbulence on a beam, but these are known to be computationally intensive. We present an analytical-numerical model which provides good results on the probability density functions of irradiance fluctuations as well as a time series with an important saving of time and computational resources.

A low-cost, tunable laser lock without laser frequency modulation

NASA Astrophysics Data System (ADS)

Shea, Margaret E.; Baker, Paul M.; Gauthier, Daniel J.

2015-05-01

Many experiments in optical physics require laser frequency stabilization. This can be achieved by locking to an atomic reference using saturated absorption spectroscopy. Often, the laser frequency is modulated and phase sensitive detection used. This method, while well-proven and robust, relies on expensive components, can introduce an undesirable frequency modulation into the laser, and is not easily frequency tuned. Here, we report a simple locking scheme similar to those implemented previously. We modulate the atomic resonances in a saturated absorption setup with an AC magnetic field created by a single solenoid. The same coil applies a DC field that allows tuning of the lock point. We use an auto-balanced detector to make our scheme more robust against laser power fluctuations and stray magnetic fields. The coil, its driver, and the detector are home-built with simple, cheap components. Our technique is low-cost, simple to setup, tunable, introduces no laser frequency modulation, and only requires one laser. We gratefully acknowledge the financial support of the NSF through Grant # PHY-1206040.

Quantum many-body dynamics of dark solitons in optical lattices

NASA Astrophysics Data System (ADS)

Mishmash, R. V.; Danshita, I.; Clark, Charles W.; Carr, L. D.

2009-11-01

We present a fully quantum many-body treatment of dark solitons formed by ultracold bosonic atoms in one-dimensional optical lattices. Using time-evolving block decimation to simulate the single-band Bose-Hubbard Hamiltonian, we consider the quantum dynamics of density and phase engineered dark solitons as well as the quantum evolution of mean-field dark solitons injected into the quantum model. The former approach directly models how one may create quantum entangled dark solitons in experiment. While we have already presented results regarding the latter approach elsewhere [R. V. Mishmash and L. D. Carr, Phys. Rev. Lett. 103, 140403 (2009)], we expand upon those results in this work. In both cases, quantum fluctuations cause the dark soliton to fill in and may induce an inelasticity in soliton-soliton collisions. Comparisons are made to the Bogoliubov theory which predicts depletion into an anomalous mode that fills in the soliton. Our many-body treatment allows us to go beyond the Bogoliubov approximation and calculate explicitly the dynamics of the system’s natural orbitals.

Global characteristics of zonal flows due to the effect of finite bandwidth in drift wave turbulence

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

Uzawa, K.; Li Jiquan; Kishimoto, Y.

2009-04-15

The spectral effect of the zonal flow (ZF) on its generation is investigated based on the Charney-Hasegawa-Mima turbulence model. It is found that the effect of finite ZF bandwidth qualitatively changes the characteristics of ZF instability. A spatially localized (namely, global) nonlinear ZF state with an enhanced, unique growth rate for all spectral components is created under a given turbulent fluctuation. It is identified that such state originates from the successive cross couplings among Fourier components of the ZF and turbulence spectra through the sideband modulation. Furthermore, it is observed that the growth rate of the global ZF is determinedmore » not only by the spectral distribution and amplitudes of turbulent pumps as usual, but also statistically by the turbulence structure, namely, their probabilistic initial phase factors. A ten-wave coupling model of the ZF modulation instability involving the essential effect of the ZF spectrum is developed to clarify the basic features of the global nonlinear ZF state.« less

Neural correlates of mathematical problem solving.

PubMed

Lin, Chun-Ling; Jung, Melody; Wu, Ying Choon; She, Hsiao-Ching; Jung, Tzyy-Ping

2015-03-01

This study explores electroencephalography (EEG) brain dynamics associated with mathematical problem solving. EEG and solution latencies (SLs) were recorded as 11 neurologically healthy volunteers worked on intellectually challenging math puzzles that involved combining four single-digit numbers through basic arithmetic operators (addition, subtraction, division, multiplication) to create an arithmetic expression equaling 24. Estimates of EEG spectral power were computed in three frequency bands - θ (4-7 Hz), α (8-13 Hz) and β (14-30 Hz) - over a widely distributed montage of scalp electrode sites. The magnitude of power estimates was found to change in a linear fashion with SLs - that is, relative to a base of power spectrum, theta power increased with longer SLs, while alpha and beta power tended to decrease. Further, the topographic distribution of spectral fluctuations was characterized by more pronounced asymmetries along the left-right and anterior-posterior axes for solutions that involved a longer search phase. These findings reveal for the first time the topography and dynamics of EEG spectral activities important for sustained solution search during arithmetical problem solving.

A Refinement of the McMillen (1988) Recursive Digital Filter for the Analysis of Atmospheric Turbulence

NASA Astrophysics Data System (ADS)

Falocchi, Marco; Giovannini, Lorenzo; Franceschi, Massimiliano de; Zardi, Dino

2018-05-01

We present a refinement of the recursive digital filter proposed by McMillen (Boundary-Layer Meteorol 43:231-245, 1988), for separating surface-layer turbulence from low-frequency fluctuations affecting the mean flow, especially over complex terrain. In fact, a straightforward application of the filter causes both an amplitude attenuation and a forward phase shift in the filtered signal. As a consequence turbulence fluctuations, evaluated as the difference between the original series and the filtered one, as well as higher-order moments calculated from them, may be affected by serious inaccuracies. The new algorithm (i) produces a rigorous zero-phase filter, (ii) restores the amplitude of the low-frequency signal, and (iii) corrects all filter-induced signal distortions.