Tilt anisoplanatism in extended turbulence propagation
NASA Astrophysics Data System (ADS)
Magee, Eric P.; Whiteley, Matthew R.; Das, Shashikala T.; Welsh, Byron M.
2003-04-01
The use of high-energy laser (HEL) weapon systems in tactical air-to-ground target engagements offers great promise for revolutionizing the USAF's war-fighting capabilities. Laser directed-energy systems will enable ultra-precision strike with minimal collateral damage and significant stand-off range for the aerial platform. The tactical directed energy application differs in many crucial ways from the conventional approach used in missile defense. Tactical missions occur at much lower altitudes and involve look-down to low-contrast ground targets instead of a high-contrast boosting missile. At these lower altitudes, the strength of atmospheric turbulence is greatly enhanced. Although the target slant ranges are much shorter, tactical missions may still involve moderate values of the Rytov number (0.1-0.5), and small isoplanatic angles compared to the diffraction angle. With increased density of air in the propagation path, and the potential for slow-moving or stationary ground targets, HEL-induced thermal blooming will certainly be a concern. In order to minimize the errors induced by tracking through thermal blooming, offset aimpoint tracking can be used. However, this will result in significant tilt anisoplanatism, thus degrading beam stabilization on target. In this paper we investigate the effects of extended turbulence on tracking (or tilt) anisoplanatism using theory and wave optics simulations. The simulations show good agreement with geometric optics predictions at angles larger than about 5 micro-radians (asymptotic regime) while at smaller angles the agreement is poor. We present a theoretical basis for this observation.
Extended inertial range phenomenology of magnetohydrodynamic turbulence
NASA Technical Reports Server (NTRS)
Matthaeus, William H.; Zhou, YE
1989-01-01
A phenomenological treatment of the inertial range of isotropic statistically steady magnetohydrodynamic turbulence is presented, extending the theory of Kraichnan (1965). The role of Alfven wave propagation is treated on equal footing with nonlinear convection, leading to a simple generalization of the relations between the times characteristic of wave propagation, convection, energy transfer, and decay of triple correlations. The theory leads to a closed-form steady inertial range spectral law that reduces to the Kraichnan and Kolmogorov laws in appropriate limits. The Kraichnan constant is found to be related in a simple way to the Kolmogorov constant; for typical values of the latter constant, the former has values in the range 1.22-1.87. Estimates of the time scale associated with spectral transfer of energy also emerge from the new approach, generalizing previously presented 'golden rules' for relating the spectral transfer time scale to the Alfven and eddy-turnover time scales.
EXTENDED SCALING LAWS IN NUMERICAL SIMULATIONS OF MAGNETOHYDRODYNAMIC TURBULENCE
Mason, Joanne; Cattaneo, Fausto; Perez, Jean Carlos; Boldyrev, Stanislav E-mail: cattaneo@flash.uchicago.edu E-mail: boldyrev@wisc.edu
2011-07-10
Magnetized turbulence is ubiquitous in astrophysical systems, where it notoriously spans a broad range of spatial scales. Phenomenological theories of MHD turbulence describe the self-similar dynamics of turbulent fluctuations in the inertial range of scales. Numerical simulations serve to guide and test these theories. However, the computational power that is currently available restricts the simulations to Reynolds numbers that are significantly smaller than those in astrophysical settings. In order to increase computational efficiency and, therefore, probe a larger range of scales, one often takes into account the fundamental anisotropy of field-guided MHD turbulence, with gradients being much slower in the field-parallel direction. The simulations are then optimized by employing the reduced MHD equations and relaxing the field-parallel numerical resolution. In this work we explore a different possibility. We propose that there exist certain quantities that are remarkably stable with respect to the Reynolds number. As an illustration, we study the alignment angle between the magnetic and velocity fluctuations in MHD turbulence, measured as the ratio of two specially constructed structure functions. We find that the scaling of this ratio can be extended surprisingly well into the regime of relatively low Reynolds number. However, the extended scaling easily becomes spoiled when the dissipation range in the simulations is underresolved. Thus, taking the numerical optimization methods too far can lead to spurious numerical effects and erroneous representation of the physics of MHD turbulence, which in turn can affect our ability to identify correctly the physical mechanisms that are operating in astrophysical systems.
Computation of turbulent flows using an extended k-epsilon turbulence closure model
NASA Technical Reports Server (NTRS)
Chen, Y.-S.; Kim, S.-W.
1987-01-01
An extended kappa-epsilon turbulence model is proposed and tested with successful results. An improved transport equation for the rate of dissipation of the turbulent kinetic energy, epsilon, is proposed. The proposed model gives more effective response to the energy production rate than does the standard kappa-epsilon turbulence model. An extra time scale of the production range is included in the dissipation rate equation. This enables the present model to perform equally well for several turbulent flows with different characteristics, e.g., plane and axisymmetric jets, turbulent boundary layer flow, turbulent flow over a backward-facing step, and a confined turbulent swirling flow. A second-order accurate finite difference boundary layer code and a nearly second-order accurate finite difference elliptic flow solver are used for the present numerical computations.
Extending velocity channel analysis for studying turbulence anisotropies
NASA Astrophysics Data System (ADS)
Kandel, D.; Lazarian, A.; Pogosyan, D.
2016-09-01
We extend the velocity channel analysis (VCA), introduced by Lazarian & Pogosyan, of the intensity fluctuations in the velocity slices of position-position-velocity (PPV) spectroscopic data from Doppler broadened lines to study statistical anisotropy of the underlying velocity and density that arises in a turbulent medium from the presence of magnetic field. In particular, we study analytically how the anisotropy of the intensity correlation in the channel maps changes with the thickness of velocity channels. In agreement with the earlier VCA studies, we find that the anisotropy in the thick channels reflects the anisotropy of the density field, while the relative contribution of density and velocity fluctuations to the thin velocity channels depends on the density spectral slope. We show that the anisotropies arising from Alfvén, slow and fast magnetohydrodynamical modes are different; in particular, the anisotropy in PPV created by fast modes is opposite to that created by Alfvén and slow modes, and this can be used to separate their contributions. We successfully compare our results with the recent numerical study of the PPV anisotropies measured with synthetic observations. We also extend our study to the medium with self-absorption as well as to the case of absorption lines. In addition, we demonstrate how the studies of anisotropy can be performed using interferometers.
NASA Astrophysics Data System (ADS)
Tekriwal, P.
1994-05-01
Standard and extended kappa-epsilon turbulence closure models have been employed for three-dimensional heat transfer calculations for radially outward flow in rectangular and square cooling passages rotating in orthogonal mode. The objective of this modeling effort is to validate the numerical model in an attempt to fill the gap between model predictions and the experimental data for heat transfer in rotating systems. While the trend of heat transfer predictions by the standard kappa-epsilon turbulence model is satisfactory, the differences between the data and the predictions are approximately 30 percent or so in the case of high rotation number flow. The extended kappa-epsilon turbulence model takes an approach where an extra 'source' term based on a second time scale of the turbulent kinetic energy production rate is added to the equation for the dissipation rate of turbulent kinetic energy. This yields a more effective calculation of turbulent kinetic energy as compared to the standard kappa-epsilon turbulence model in the case of high rotation number and high density ratio flow. As a result, comparison with the experimental data available in the literature shows that an improvement of up to a significant 15 percent (with respect to data) in the heat transfer coefficient predictions is achieved over the standard kappa-epsilon model in the case of high rotation number flow. Comparisons between the results of the standard kappa-epsilon model and the extended formulation are made at different rotation numbers, different Reynolds numbers, and varying temperature ratio. The results of the extended kappa-epsilon turbulence model are either as good or better than those of the standard kappa-epsilon model in all these cases of parametric study. Thus, the extended kappa-epsilon turbulence model proves to be more general and reduces the discrepancy between the model predictions and the experimental data for heat transfer in rotating systems.
PREFACE: Complex Dynamics in Spatially Extended Systems
NASA Astrophysics Data System (ADS)
Mosekilde, Erik; Bohr, Tomas; Rasmussen, Jens Juul; Leth Christiansen, Peter
1996-01-01
Self-organization, or the spontaneous emergence of patterns and structures under far-from-equilibrium conditions, turbulence, and related nonlinear dynamic phenomena in spatially extended systems have developed into one of the most exciting topics of modern science. Phenomena of this type arise in a wide variety of different fields, ranging from the development of chemical and biological patterns in reaction-diffusion systems over vortex formation in connection with chemical, optical, hydrodynamic or magnetohydrodynamic turbulence to technical applications in connection with liquid crystal displays or pulse compression in optical communication systems. Lasers often show interesting patterns produced by self-focusing and other nonlinear phenomena, diffusion limited aggregation is known to generate fractal-like structures, and amazing struc- tures also arise in bacterial growth processes or when a droplet of an oil suspension of finely divided magnetic particles is subject to a magnetic field perpendicular to the surface of the cell in which it is contained. In September 1995 the Niels Bohr Institute in Copenhagen was the venue of an International Conference on Complex Dynamics in Spatially Extended Systems. Organizers of the conference were the three Danish centers for nonlinear dynamics: The Center for Chaos and Turbulence Studies (CATS), located at the Niels Bohr Institute; the Center for Modeling, Nonlinear Dynamics and Irreversible Thermodynamics (MIDIT), located at the Technical University of Denmark, and the Center for Nonlinear Dynamics in Continuum Systems, located at the Risø National Laboratories. In the spirit of the successful NATO Advanced Research Workshops on Spatiotemporal Patterns in Nonequilibrium Systems of which the last was held in Santa Fe, New Mexico in 1993, the conference aimed at stimulating new ideas and providing a forum for the exchange of knowledge between leading practitioners of the field. With its 50 invited speakers and more than
Computer correction of turbulent distortions of image of extended objects on near-Earth paths
Averin, A P; Morozov, Yu B; Pryanichkov, V S; Tyapin, V V
2011-05-31
An algorithm of computer-based correction of images of extended objects distorted by turbulent atmosphere is developed. The method of computer correction is used to correct a distorted image of an extended object on a horizontal 2300-m-long observation path. The angular size of the corrected-image region was 15'. (image processing)
Intermittency and extended self-similarity in the solar wind turbulence
NASA Technical Reports Server (NTRS)
Bruno, R.; Carbone, V.
1995-01-01
Using the satellite measurements of the velocity field in the interplanetary plasma. we present some analysis which show the presence of a self-similar intermittent state in the solar wind turbulence. We used the so called Extended Self-Similarity hypothesis, which is well visible in the solar wind turbulence, showing convincing evidences for the presence of universal anomalous scaling laws. Through the Extended Self-Similarity we are able to calculate the scaling exponents of the velocity structure functions with very small uncertainties, and we show that these scaling exponents are in very good agreement with the multifractal models describing intermittency in magnetohydrodynamic flows.
Clear air turbulence - An airborne alert system
NASA Technical Reports Server (NTRS)
Stearns, L. P.; Caracena, F.; Kuhn, P. M.; Kurkowski, R. L.
1981-01-01
An infrared radiometer system has been developed that can alert a pilot of an aircraft 2 to 9 minutes in advance of an encounter with clear air turbulence. The time between the warning and the clear air turbulence event varies with the flight altitude of the aircraft. In turbulence-free areas, the incidence of false alarms is found to be less than one in 3.4 hours of flight time compared to less than one per 10 hours of flight time in areas with turbulence.
Extended mission life support systems
NASA Technical Reports Server (NTRS)
Quattrone, P. D.
1985-01-01
Extended manned space missions which include interplanetary missions require regenerative life support systems. Manned mission life support considerations are placed in perspective and previous manned space life support system technology, activities and accomplishments in current supporting research and technology (SR&T) programs are reviewed. The life support subsystem/system technologies required for an enhanced duration orbiter (EDO) and a space operations center (SOC), regenerative life support functions and technology required for manned interplanetary flight vehicles, and future development requirements are outlined. The Space Shuttle Orbiters (space transportation system) is space cabin atmosphere is maintained at Earth ambient pressure of 14.7 psia (20% O2 and 80% N2). The early Shuttle flights will be seven-day flights, and the life support system flight hardware will still utilize expendables.
Calibration of a universal indicated turbulence system
NASA Technical Reports Server (NTRS)
Chapin, W. G.
1977-01-01
Theoretical and experimental work on a Universal Indicated Turbulence Meter is described. A mathematical transfer function from turbulence input to output indication was developed. A random ergodic process and a Gaussian turbulence distribution were assumed. A calibration technique based on this transfer function was developed. The computer contains a variable gain amplifier to make the system output independent of average velocity. The range over which this independence holds was determined. An optimum dynamic response was obtained for the tubulation between the system pitot tube and pressure transducer by making dynamic response measurements for orifices of various lengths and diameters at the source end.
Extended attention span training system
NASA Technical Reports Server (NTRS)
Pope, Alan T.; Bogart, Edward H.
1991-01-01
Attention Deficit Disorder (ADD) is a behavioral disorder characterized by the inability to sustain attention long enough to perform activities such as schoolwork or organized play. Treatments for this disorder include medication and brainwave biofeedback training. Brainwave biofeedback training systems feed back information to the trainee showing him how well he is producing the brainwave pattern that indicates attention. The Extended Attention Span Training (EAST) system takes the concept a step further by making a video game more difficult as the player's brainwaves indicate that attention is waning. The trainee can succeed at the game only by maintaining an adequate level of attention. The EAST system is a modification of a biocybernetic system that is currently being used to assess the extent to which automated flight management systems maintain pilot engagement. This biocybernetic system is a product of a program aimed at developing methods to evaluate automated flight deck designs for compatibility with human capabilities. The EAST technology can make a contribution in the fields of medical neuropsychology and neurology, where the emphasis is on cautious, conservative treatment of youngsters with attention disorders.
NASA Astrophysics Data System (ADS)
Schlickeiser, R.
2011-05-01
A new transport theory of cosmic rays in magnetized space plasmas with axisymmetric incompressible magnetic turbulence is developed extending the quasilinear approximation to the particle orbit. Arbitrary gyrophase deviations from the unperturbed spiral orbits in the uniform magnetic field are allowed. For quasi-stationary and spatially homogeneous magnetic turbulence, we derive the small Larmor radius approximation gyrophase-averaged cosmic ray Fokker-Planck coefficients. The generalized Fokker-Planck coefficients correctly reduce to their known quasilinear values in the corresponding limit. New forms of the quasilinear Fokker-Planck coefficients in axisymmetric turbulence are derived which no longer involve infinite sums of products of Bessel functions, which facilitate their numerical computation for specified turbulence field correlation tensors. The Fokker-Planck coefficients for arbitrary phase orbits of the cosmic ray particles provide strict upper limits for the perpendicular and pitch-angle Fokker-Planck coefficients, which in turn yield strict upper and lower limits for the perpendicular and parallel spatial diffusion coefficients, respectively, describing the spatial diffusion of the isotropic part of the cosmic ray phase space density. For the associated mean free paths, we find for this general case that the product of the minimum parallel mean free path with the sum of the maximum perpendicular mean free paths equals R 2 L , where RL denotes the cosmic ray gyroradius.
Dynamic Stochastic Superresolution of sparsely observed turbulent systems
Branicki, M.; Majda, A.J.
2013-05-15
Real-time capture of the relevant features of the unresolved turbulent dynamics of complex natural systems from sparse noisy observations and imperfect models is a notoriously difficult problem. The resulting lack of observational resolution and statistical accuracy in estimating the important turbulent processes, which intermittently send significant energy to the large-scale fluctuations, hinders efficient parameterization and real-time prediction using discretized PDE models. This issue is particularly subtle and important when dealing with turbulent geophysical systems with an vast range of interacting spatio-temporal scales and rough energy spectra near the mesh scale of numerical models. Here, we introduce and study a suite of general Dynamic Stochastic Superresolution (DSS) algorithms and show that, by appropriately filtering sparse regular observations with the help of cheap stochastic exactly solvable models, one can derive stochastically ‘superresolved’ velocity fields and gain insight into the important characteristics of the unresolved dynamics, including the detection of the so-called black swans. The DSS algorithms operate in Fourier domain and exploit the fact that the coarse observation network aliases high-wavenumber information into the resolved waveband. It is shown that these cheap algorithms are robust and have significant skill on a test bed of turbulent solutions from realistic nonlinear turbulent spatially extended systems in the presence of a significant model error. In particular, the DSS algorithms are capable of successfully capturing time-localized extreme events in the unresolved modes, and they provide good and robust skill for recovery of the unresolved processes in terms of pattern correlation. Moreover, we show that DSS improves the skill for recovering the primary modes associated with the sparse observation mesh which is equally important in applications. The skill of the various DSS algorithms depends on the energy spectrum
Extended high-angular-frequency analysis of turbulence effects on short-exposure imaging
NASA Astrophysics Data System (ADS)
Tofsted, David H.
2014-04-01
An improved analysis of optical turbulence effects on short-exposure passive (SE) imaging is described, resulting in a new analytic expression for the SE modulation transfer function (MTF). This analysis expands on a 2011 study that examined characteristics of a tilt-phase component discovered in the standard theory of SE turbulence effects characterization. The analysis introduces an improved integration technique and a reformulated phase structure function, facilitating computation of a 38,007 element database of MTF results at low- to high-angular frequencies covering a wide range of diffraction and turbulence conditions. Analysis of this database is described, yielding a new analytic SE MTF, accurate to a root-mean-square error of 0.000218 versus the database. Comparisons show that the new expression is well correlated to an alternative computationally intensive method, and it is a factor 29 to 64 improvement over prior analytic expressions. Limits of applicability of the approach for incoherent imaging are also discussed. The low-computational cost of the new method is suitable for systems performance modeling of turbulence impacts, including path-varying turbulence scenarios.
NASA Astrophysics Data System (ADS)
Frisch, Uriel
1996-01-01
Written five centuries after the first studies of Leonardo da Vinci and half a century after A.N. Kolmogorov's first attempt to predict the properties of flow, this textbook presents a modern account of turbulence, one of the greatest challenges in physics. "Fully developed turbulence" is ubiquitous in both cosmic and natural environments, in engineering applications and in everyday life. Elementary presentations of dynamical systems ideas, probabilistic methods (including the theory of large deviations) and fractal geometry make this a self-contained textbook. This is the first book on turbulence to use modern ideas from chaos and symmetry breaking. The book will appeal to first-year graduate students in mathematics, physics, astrophysics, geosciences and engineering, as well as professional scientists and engineers.
Laser Doppler systems in atmospheric turbulence
NASA Technical Reports Server (NTRS)
Murty, S. S. R.
1976-01-01
The loss of heterodyne signal power for the Marshall Space Flight Center laser Doppler system due to the random changes in the atmospheric index of refraction is investigated. The current status in the physics of low energy laser propagation through turbulent atmosphere is presented. The analysis and approximate evaluation of the loss of the heterodyne signal power due to the atmospheric absorption, scattering, and turbulence are estimated for the conditions of the January 1973 flight tests. Theoretical and experimental signal to noise values are compared. Maximum and minimum values of the atmospheric attenuation over a two way path of 20 km range are calculated as a function of altitude using models of atmosphere, aerosol concentration, and turbulence.
Brenkosh, J.P.
1993-12-23
The X Window System was originally developed in 1984 at Massachusetts Institute of Technology. It provides client-server computing functionality and also facilitates the establishment of a distributed computing environment. Since its inception the X Window System has undergone many enhancements. Despite these enhancements there will always be a functionality desired in the standard released version of X that is not supported or commercially or academically available. The developers of the X Window System have designed it in such a way that it is possible to add functionality that is not included in the standard release. This is called an extension. Extensions are one method used to develop a customized version of the X Window System to support a specialized application. This report presents the mechanics of adding an extension and examines a particular extension that was developed at Sandia National Laboratories to support data compression in X Windows which was one aspect of the Desktop Video and Collaborative Engineering Laboratory Directed Research and Development (LDRD).
Laser system of extended range
NASA Technical Reports Server (NTRS)
Lehr, C. G.
1972-01-01
A pulsed laser system was developed for range measurements from the earth to retroreflecting satellites at distances up to that of the moon. The system has a transportable transmitter unit that can be moved from one location to another. This unit consists of a 0.2 m coude refractor and a high radiance, neodymium-glass, frequency doubled laser that operates in a single transverse mode. It can be used for lunar or distant satellite ranging at any observatory that has a telescope with an aperture diameter of about 1.5 m for the detection of the laser return pulses. This telescope is utilized in the same manner customarily employed for the observation of celestial objects. A special photometric package and the associated electronics are provided for laser ranging.
NASA Technical Reports Server (NTRS)
Cranmer, Steven R.; Wagner, William (Technical Monitor)
2003-01-01
The PI (Cranmer) and Co-I (A. van Ballegooijen) made significant progress toward the goal of building a "unified model" of the dominant physical processes responsible for the acceleration of the solar wind. The approach outlined in the original proposal comprised two complementary pieces: (1) to further investigate individual physical processes under realistic coronal and solar wind conditions, and (2) to extract the dominant physical effects from simulations and apply them to a one-dimensional and time-independent model of plasma heating and acceleration. The accomplishments in the report period are thus divided into these two categories: 1a. Focused Study of Kinetic MHD Turbulence. We have developed a model of magnetohydrodynamic (MHD) turbulence in the extended solar corona that contains the effects of collisionless dissipation and anisotropic particle heating. A turbulent cascade is one possible way of generating small-scale fluctuations (easy to dissipate/heat) from a pre-existing population of low-frequency Alfven waves (difficult to dissipate/heat). We modeled the cascade as a combination of advection and diffusion in wavenumber space. The dominant spectral transfer occurs in the direction perpendicular to the background magnetic field. As expected from earlier models, this leads to a highly anisotropic fluctuation spectrum with a rapidly decaying tail in the parallel wavenumber direction. The wave power that decays to high enough frequencies to become ion cyclotron resonant depends on the relative strengths of advection and diffusion in the cascade. For the most realistic values of these parameters, though, there is insufficient power to heat protons and heavy ions. The dominant oblique waves undergo Landau damping, which implies strong parallel electron heating. We thus investigated the nonlinear evolution of the electron velocity distributions (VDFs) into parallel beams and discrete phase-space holes (similar to those seen in the terrestrial magnetosphere
Direct simulation of turbulent supersonic boundary layers by an extended temporal approach
NASA Astrophysics Data System (ADS)
Maeder, Thierry; Adams, Nikolaus A.; Kleiser, Leonhard
2001-02-01
The present paper addresses the direct numerical simulation of turbulent zero-pressure-gradient boundary layers on a flat plate at Mach numbers 3, 4.5 and 6 with momentum-thickness Reynolds numbers of about 3000. Simulations are performed with an extended temporal direct numerical simulation (ETDNS) method. Assuming that the slow streamwise variation of the mean boundary layer is governed by parabolized Navier Stokes equations, the equations solved locally in time with a temporal DNS are modified by a distributed forcing term so that the parabolized Navier Stokes equations are recovered for the spatial average. The correct mean flow is obtained without a priori knowledge, the streamwise mean-flow evolution being approximated from its upstream history. ETDNS reduces the computational effort by up to two orders of magnitude compared to a fully spatial simulation.
Proton Heating in the Extended Solar Corona Resulting From Kinetic Alfven Turbulence
NASA Astrophysics Data System (ADS)
Cranmer, S. R.; van Ballegooijen, A. A.
2002-12-01
Spectroscopic observations of the solar corona have made it clear that the ``coronal heating problem'' comprises not only the local deposition of heat immediately above the transition region, but also extended heat deposition throughout the (collisionless) acceleration region of the solar wind. The dissipation of magnetohydrodynamic (MHD) waves and/or turbulence has been considered as a likely heating mechanism in the solar wind for several decades. However, it is still not well understood how MHD fluctuations are generated, how they evolve in frequency and wavenumber, or how their damping leads to the observed proton, electron, and ion properties of the fast wind. We present a model of MHD turbulence that specifically addresses the issue of kinetic dissipation and particle heating in the collisionless extended corona. The nonlinear cascade is modeled as a combination of advection and diffusion in wavenumber space, with the dominant cascade occurring in the direction perpendicular to the background magnetic field. This leads to a highly anisotropic fluctuation spectrum (as expected, based on many earlier simulations and scaling models) with a rapidly decreasing power-law tail in the parallel wavenumber direction. In the low-plasma-beta corona, the dominant oblique fluctuations (with dispersion properties of kinetic Alfven waves) are dissipated by electron Landau damping, with only a tiny fraction of the energy going to high-frequency ion cyclotron waves. This implies strong parallel electron heating and weak proton and ion heating, which is not what is observed. We discuss the probable nonlinear evolution of the electron velocity distributions into parallel beams and discrete phase-space holes (similar to those seen in the terrestrial magnetosphere) which can possibly heat protons via stochastic interactions.
CARS system for turbulent flame measurements
NASA Technical Reports Server (NTRS)
Antcliff, R. R.; Jarrett, O., Jr.; Rogers, R. C.
1984-01-01
Simultaneous nitrogen number density and rotational-vibrational temperatures were measured in a turbulent diffusion flame with a Coherent Anti-Stokes Raman Scattering (CARS) instrument. The fuel jet was diluted with nitrogen (20 percent by volume) to allow temperature measurements across the entire jet mixing region. These measurements were compared with fluid dynamics computations. The CARS system incorporated a neodymium YAG laser, an intensified silicon photodiode array detector, and unique dynamic range enhancement methods. Theoretical calculations were based on a parabolic Navier-Stokes computer code. The comparison of these techniques will aid their development in the study of complex flowfields.
NASA Technical Reports Server (NTRS)
Cranmer, Steven R.; Wagner, William (Technical Monitor)
2004-01-01
The PI (Cranmer) and Co-I (A. van Ballegooijen) made substantial progress toward the goal of producing a unified model of the basic physical processes responsible for solar wind acceleration. The approach outlined in the original proposal comprised two complementary pieces: (1) to further investigate individual physical processes under realistic coronal and solar wind conditions, and (2) to extract the dominant physical effects from simulations and apply them to a 1D model of plasma heating and acceleration. The accomplishments in Year 2 are divided into these two categories: 1a. Focused Study of Kinetic Magnetohydrodynamic (MHD) Turbulence. lb. Focused Study of Non - WKB Alfven Wave Rejection. and 2. The Unified Model Code. We have continued the development of the computational model of a time-study open flux tube in the extended corona. The proton-electron Monte Carlo model is being tested, and collisionless wave-particle interactions are being included. In order to better understand how to easily incorporate various kinds of wave-particle processes into the code, the PI performed a detailed study of the so-called "Ito Calculus", i.e., the mathematical theory of how to update the positions of particles in a probabilistic manner when their motions are governed by diffusion in velocity space.
NASA Technical Reports Server (NTRS)
Wagner, William (Technical Monitor); Cranmer, Steven R.
2005-01-01
The paper discusses the following: 1. No-cost Extension. The no-cost extension is required to complete the work on the unified model codes (both hydrodynamic and kinetic Monte Carlo) as described in the initial proposal and previous annual reports. 2. Scientific Accomplishments during the Report Period. We completed a comprehensive model of Alfvtn wave reflection that spans the full distance from the photosphere to the distant heliosphere. 3. Comparison of Accomplishments with Proposed Goals. The proposal contained two specific objectives for Year 3: (1) to complete the unified model code, and (2) to apply it to various kinds of coronal holes (and polar plumes within coronal holes). Although the anticipated route toward these two final goals has changed (see accomplishments 2a and 2b above), they remain the major milestones for the extended period of performance. Accomplishments la and IC were necessary prerequisites for the derivation of "physically relevant transport and mode-coupling terms" for the unified model codes (as stated in the proposal Year 3 goals). We have fulfilled the proposed "core work" to study 4 general types of physical processes; in previous years we studied turbulence, mode coupling (Le., non-WKB reflection), and kinetic wave damping, and accomplishment lb provides the fourth topic: nonlinear steepening.
Extended Huygens-Fresnel principle and optical waves propagation in turbulence: discussion.
Charnotskii, Mikhail
2015-07-01
Extended Huygens-Fresnel principle (EHF) currently is the most common technique used in theoretical studies of the optical propagation in turbulence. A recent review paper [J. Opt. Soc. Am. A31, 2038 (2014)JOAOD60740-323210.1364/JOSAA.31.002038] cites several dozens of papers that are exclusively based on the EHF principle. We revisit the foundations of the EHF, and show that it is burdened by very restrictive assumptions that make it valid only under weak scintillation conditions. We compare the EHF to the less-restrictive Markov approximation and show that both theories deliver identical results for the second moment of the field, rendering the EHF essentially worthless. For the fourth moment of the field, the EHF principle is accurate under weak scintillation conditions, but is known to provide erroneous results for strong scintillation conditions. In addition, since the EHF does not obey the energy conservation principle, its results cannot be accurate for scintillations of partially coherent beam waves. PMID:26367166
In-Service Evaluation of the Turbulence Auto-PIREP System and Enhanced Turbulence Radar Technologies
NASA Technical Reports Server (NTRS)
Prince, Jason B.; Buck, Bill K.; Robinson, Paul A.; Ryan, Tim
2007-01-01
From August 2003 to December 2006, In-Service Evaluations (ISE) of the Turbulence Auto-PIREP System (TAPS) and Enhanced Turbulence (E-Turb) Radar, technologies developed in NASA's Turbulence Prediction and Warning System (TPAWS) element of its Aviation Safety and Security Program (AvSSP), were conducted. NASA and AeroTech Research established an industry team comprising AeroTech, Delta Air Lines, Rockwell Collins, and ARINC to conduct the ISEs. The technologies were installed on Delta aircraft and their effectiveness was evaluated in day-to-day operations. This report documents the establishment and conduct of the ISEs and presents results and feedback from various users.
Market Assessment of Forward-Looking Turbulence Sensing Systems
NASA Technical Reports Server (NTRS)
Kauffmann, Paul
2003-01-01
This viewgraph presentation provides a cost benefit analysis of three next-generation forward-looking turbulence sensing systems: X band turbulence radar system for convective turbulence, LIDAR based turbulence systems to sense clear air turbulence and a combined hybrid system. Parameters for the cost benefit analysis were established using a business model which considered injury rates, cost of injuries, indirect costs, market penetration rate estimates and product success characteristics. Topics covered include: study approach, business case equations, data acquisition, benchmark analysis. Data interpretation from the cost benefit analysis is presented. The researchers conclude that the market potential for these products is based primarily on injury cost reduction and that X band radar systems have the greatest chance for commercial success.
Synchronization in networks of spatially extended systems
Filatova, Anastasiya E.; Hramov, Alexander E.; Koronovskii, Alexey A.; Boccaletti, Stefano
2008-06-15
Synchronization processes in networks of spatially extended dynamical systems are analytically and numerically studied. We focus on the relevant case of networks whose elements (or nodes) are spatially extended dynamical systems, with the nodes being connected with each other by scalar signals. The stability of the synchronous spatio-temporal state for a generic network is analytically assessed by means of an extension of the master stability function approach. We find an excellent agreement between the theoretical predictions and the data obtained by means of numerical calculations. The efficiency and reliability of this method is illustrated numerically with networks of beam-plasma chaotic systems (Pierce diodes). We discuss also how the revealed regularities are expected to take place in other relevant physical and biological circumstances.
How turbulence regulates biodiversity in systems with cyclic competition
NASA Astrophysics Data System (ADS)
Grošelj, Daniel; Jenko, Frank; Frey, Erwin
2015-03-01
Cyclic, nonhierarchical interactions among biological species represent a general mechanism by which ecosystems are able to maintain high levels of biodiversity. However, species coexistence is often possible only in spatially extended systems with a limited range of dispersal, whereas in well-mixed environments models for cyclic competition often lead to a loss of biodiversity. Here we consider the dispersal of biological species in a fluid environment, where mixing is achieved by a combination of advection and diffusion. In particular, we perform a detailed numerical analysis of a model composed of turbulent advection, diffusive transport, and cyclic interactions among biological species in two spatial dimensions and discuss the circumstances under which biodiversity is maintained when external environmental conditions, such as resource supply, are uniform in space. Cyclic interactions are represented by a model with three competitors, resembling the children's game of rock-paper-scissors, whereas the flow field is obtained from a direct numerical simulation of two-dimensional turbulence with hyperviscosity. It is shown that the space-averaged dynamics undergoes bifurcations as the relative strengths of advection and diffusion compared to biological interactions are varied.
Flight Tests of the Turbulence Prediction and Warning System (TPAWS)
NASA Technical Reports Server (NTRS)
Hamilton, David W.; Proctor, Fred H.; Ahmad, Nashat N.
2012-01-01
Flight tests of the National Aeronautics and Space Administration's Turbulence Prediction And Warning System (TPAWS) were conducted in the Fall of 2000 and Spring of 2002. TPAWS is a radar-based airborne turbulence detection system. During twelve flights, NASA's B-757 tallied 53 encounters with convectively induced turbulence. Analysis of data collected during 49 encounters in the Spring of 2002 showed that the TPAWS Airborne Turbulence Detection System (ATDS) successfully detected 80% of the events at least 30 seconds prior to the encounter, achieving FAA recommended performance criteria. Details of the flights, the prevailing weather conditions, and each of the turbulence events are presented in this report. Sensor and environmental characterizations are also provided.
Turbulent plane Couette flow subject to strong system rotation
NASA Astrophysics Data System (ADS)
Bech, Knut H.; Andersson, Helge I.
1997-09-01
System rotation is known to substantially affect the mean flow pattern as well as the turbulence structure in rotating channel flows. In a numerical study of plane Couette flow rotating slowly about an axis aligned with the mean vorticity, Bech & Andersson (1996a) found that the turbulence level was damped in the presence of anticyclonic system rotation, in spite of the occurrence of longitudinal counter-rotating roll cells. Moreover, the turbulence anisotropy was practically unaffected by the weak rotation, for which the rotation number Ro, defined as the ratio of twice the imposed angular vorticity [Omega] to the shear rate of the corresponding laminar flow, was ±0.01. The aim of the present paper is to explore the effects of stronger anticyclonic system rotation on directly simulated turbulent plane Couette flow. Turbulence statistics like energy, enstrophy and Taylor lengthscales, both componental and directional, were computed from the statistically steady flow fields and supplemented by structural information obtained by conditional sampling.
Statistical energy conservation principle for inhomogeneous turbulent dynamical systems.
Majda, Andrew J
2015-07-21
Understanding the complexity of anisotropic turbulent processes over a wide range of spatiotemporal scales in engineering shear turbulence as well as climate atmosphere ocean science is a grand challenge of contemporary science with important societal impact. In such inhomogeneous turbulent dynamical systems there is a large dimensional phase space with a large dimension of unstable directions where a large-scale ensemble mean and the turbulent fluctuations exchange energy and strongly influence each other. These complex features strongly impact practical prediction and uncertainty quantification. A systematic energy conservation principle is developed here in a Theorem that precisely accounts for the statistical energy exchange between the mean flow and the related turbulent fluctuations. This statistical energy is a sum of the energy in the mean and the trace of the covariance of the fluctuating turbulence. This result applies to general inhomogeneous turbulent dynamical systems including the above applications. The Theorem involves an assessment of statistical symmetries for the nonlinear interactions and a self-contained treatment is presented below. Corollary 1 and Corollary 2 illustrate the power of the method with general closed differential equalities for the statistical energy in time either exactly or with upper and lower bounds, provided that the negative symmetric dissipation matrix is diagonal in a suitable basis. Implications of the energy principle for low-order closure modeling and automatic estimates for the single point variance are discussed below. PMID:26150510
Statistical energy conservation principle for inhomogeneous turbulent dynamical systems
Majda, Andrew J.
2015-01-01
Understanding the complexity of anisotropic turbulent processes over a wide range of spatiotemporal scales in engineering shear turbulence as well as climate atmosphere ocean science is a grand challenge of contemporary science with important societal impact. In such inhomogeneous turbulent dynamical systems there is a large dimensional phase space with a large dimension of unstable directions where a large-scale ensemble mean and the turbulent fluctuations exchange energy and strongly influence each other. These complex features strongly impact practical prediction and uncertainty quantification. A systematic energy conservation principle is developed here in a Theorem that precisely accounts for the statistical energy exchange between the mean flow and the related turbulent fluctuations. This statistical energy is a sum of the energy in the mean and the trace of the covariance of the fluctuating turbulence. This result applies to general inhomogeneous turbulent dynamical systems including the above applications. The Theorem involves an assessment of statistical symmetries for the nonlinear interactions and a self-contained treatment is presented below. Corollary 1 and Corollary 2 illustrate the power of the method with general closed differential equalities for the statistical energy in time either exactly or with upper and lower bounds, provided that the negative symmetric dissipation matrix is diagonal in a suitable basis. Implications of the energy principle for low-order closure modeling and automatic estimates for the single point variance are discussed below. PMID:26150510
Progress in Development of an Airborne Turbulence Detection System
NASA Technical Reports Server (NTRS)
Hamilton, David W.; Proctor, Fred H.
2006-01-01
Aircraft encounters with turbulence are the leading cause of in-flight injuries (Tyrvanas 2003) and have occasionally resulted in passenger and crew fatalities. Most of these injuries are caused by sudden and unexpected encounters with severe turbulence in and around convective activity (Kaplan et al 2005). To alleviate this problem, the Turbulence Prediction and Warning Systems (TPAWS) element of NASA s Aviation Safety program has investigated technologies to detect and warn of hazardous in-flight turbulence. This effort has required the numerical modeling of atmospheric convection: 1) for characterizing convectively induced turbulence (CIT) environments, 2) for defining turbulence hazard metrics, and 3) as a means of providing realistic three-dimensional data sets that can be used to test and evaluate turbulence detection sensors. The data sets are being made available to industry and the FAA for certification of future airborne turbulence-detection systems (ATDS) with warning capability. Early in the TPAWS project, a radar-based ATDS was installed and flight tested on NASA s research aircraft, a B-757. This ATDS utilized new algorithms and hazard metrics that were developed for use with existing airborne predictive windshear radars, thus avoiding the installation of new hardware. This system was designed to detect and warn of hazardous CIT even in regions with weak radar reflectivity (i.e. 5-15 dBz). Results from an initial flight test of the ATDS were discussed in Hamilton and Proctor (2002a; 2002b). In companion papers (Proctor et al 2002a; 2002b), a numerical simulation of the most significant encounter from that flight test was presented. Since the presentation of these papers a second flight test has been conducted providing additional cases for examination. In this paper, we will present results from NASA s flight test and a numerical model simulation of a turbulence environment encountered on 30 April 2002. Progress leading towards FAA certification of
Extended LES-PaSR model for simulation of turbulent combustion
NASA Astrophysics Data System (ADS)
Sabelnikov, V.; Fureby, C.
2013-03-01
In this work, a novel model for Large Eddy Simulations (LES) of high Reynolds moderate Damköhler number turbulent flames is proposed. The development is motivated by the need for more accurate and versatile LES combustion models for engineering applications such as jet engines. The model is based on the finite rate chemistry approach in which the filtered species equations of a reduced reaction mechanism are solved prior to closure modeling. The modeling of the filtered reaction rate provides the challenge: as most of the chemical activity, and thus also most of the exothermicity occurs on the subgrid scales, this model needs to be based on the properties of fine-scale turbulence and mixing and Arrhenius chemistry. The model developed here makes use of the similarities with the mathematical treatment of multiphase flows together with the knowledge of fine-scale turbulence and chemistry obtained by Direct Numerical Simulation (DNS) and experiments. In the model developed, equations are proposed for the fine-structure composition and volume fraction that are solved together with the LES equations for the resolved scales. If subgrid convection can be neglected, the proposed model simplifies to the Partially Stirred Reactor (PaSR) model. To validate the proposed LES model, comparisons with experimental data and other LES results are made, using other turbulence chemistry interaction models, for a lean premixed bluff-body stabilized flame.
Thermodynamics. II - The extended thermodynamic system
NASA Technical Reports Server (NTRS)
Zeleznik, F. J.
1981-01-01
The algebraic theory of thermodynamics developed in a previous paper is extended to include the algebraic structure that arises from the introduction of a physical body into the theory. The extension is based on very general definitions of both the thermodynamic states of a body and subsystems of that body. The algebraic analysis, which includes bodies in nonuniform states, shows that the set of all thermodynamic states of a body has the same algebraic structure as the set of thermodynamic states and that composite systems are induced by the algebraic structure of thermodynamic states. The analysis also justifies a variational treatment of thermodynamic bodies in uniform as well as nonuniform states. The variational calculation includes all conventional methods of calculation as special cases and helps to illuminate the origin and interpretation of the electrochemical potential.
System and Method for Finite Element Simulation of Helicopter Turbulence
NASA Technical Reports Server (NTRS)
McFarland, R. E. (Inventor); Dulsenberg, Ken (Inventor)
1999-01-01
The present invention provides a turbulence model that has been developed for blade-element helicopter simulation. This model uses an innovative temporal and geometrical distribution algorithm that preserves the statistical characteristics of the turbulence spectra over the rotor disc, while providing velocity components in real time to each of five blade-element stations along each of four blades. for a total of twenty blade-element stations. The simulator system includes a software implementation of flight dynamics that adheres to the guidelines for turbulence set forth in military specifications. One of the features of the present simulator system is that it applies simulated turbulence to the rotor blades of the helicopter, rather than to its center of gravity. The simulator system accurately models the rotor penetration into a gust field. It includes time correlation between the front and rear of the main rotor, as well as between the side forces felt at the center of gravity and at the tail rotor. It also includes features for added realism, such as patchy turbulence and vertical gusts in to which the rotor disc penetrates. These features are realized by a unique real time implementation of the turbulence filters. The new simulator system uses two arrays one on either side of the main rotor to record the turbulence field and to produce time-correlation from the front to the rear of the rotor disc. The use of Gaussian Interpolation between the two arrays maintains the statistical properties of the turbulence across the rotor disc. The present simulator system and method may be used in future and existing real-time helicopter simulations with minimal increase in computational workload.
AMBIPOLAR DIFFUSION HEATING IN TURBULENT SYSTEMS
Li, Pak Shing; Myers, Andrew; McKee, Christopher F. E-mail: atmyers@berkeley.edu
2012-11-20
The temperature of the gas in molecular clouds is a key determinant of the characteristic mass of star formation. Ambipolar diffusion (AD) is considered one of the most important heating mechanisms in weakly ionized molecular clouds. In this work, we study the AD heating rate using two-fluid turbulence simulations and compare it with the overall heating rate due to turbulent dissipation. We find that for observed molecular clouds, which typically have Alfven Mach numbers of {approx}1 and AD Reynolds numbers of {approx}20, about 70% of the total turbulent dissipation is in the form of AD heating. AD has an important effect on the length scale where energy is dissipated: when AD heating is strong, most of the energy in the cascade is removed by ion-neutral drift, with a comparatively small amount of energy making it down to small scales. We derive a relation for the AD heating rate that describes the results of our simulations to within a factor of two. Turbulent dissipation, including AD heating, is generally less important than cosmic-ray heating in molecular clouds, although there is substantial scatter in both.
Atmospheric turbulence and sensor system effects on biometric algorithm performance
NASA Astrophysics Data System (ADS)
Espinola, Richard L.; Leonard, Kevin R.; Byrd, Kenneth A.; Potvin, Guy
2015-05-01
Biometric technologies composed of electro-optical/infrared (EO/IR) sensor systems and advanced matching algorithms are being used in various force protection/security and tactical surveillance applications. To date, most of these sensor systems have been widely used in controlled conditions with varying success (e.g., short range, uniform illumination, cooperative subjects). However the limiting conditions of such systems have yet to be fully studied for long range applications and degraded imaging environments. Biometric technologies used for long range applications will invariably suffer from the effects of atmospheric turbulence degradation. Atmospheric turbulence causes blur, distortion and intensity fluctuations that can severely degrade image quality of electro-optic and thermal imaging systems and, for the case of biometrics technology, translate to poor matching algorithm performance. In this paper, we evaluate the effects of atmospheric turbulence and sensor resolution on biometric matching algorithm performance. We use a subset of the Facial Recognition Technology (FERET) database and a commercial algorithm to analyze facial recognition performance on turbulence degraded facial images. The goal of this work is to understand the feasibility of long-range facial recognition in degraded imaging conditions, and the utility of camera parameter trade studies to enable the design of the next generation biometrics sensor systems.
Extended Solar System Structures Observed by WISE
NASA Astrophysics Data System (ADS)
Sykes, Mark V.; Masci, Frank; Cutri, Roc; Walker, Russell; Mainzer, Amy; Bauer, James; Stevenson, Rachel; Tricarico, Pasquale
2014-11-01
Extended structures associated with recent asteroid collisions and comets were detected by the Infrared Astronomical Satellite, which conducted the first survey of the thermal emission of the sky in 1983. Twenty-seven years later, the Wide-field Infrared Survey Explorer (WISE), conducted a more sensitive survey of the sky at wavelengths spanning the shorter IRAS bandpasses and detected many of these same structures. Initial identifications include asteroid dust bands associated with collisions giving rise to the Karin and Beagle clusters within the Koronis and Themis asteroid families, respectively. An additional pair of bands is associated with the collision giving rise to the Veritas asteroid family. Comet trails associated with short-period comets have also been observed. Type 2 trails, detected by IRAS and possibly associated with asteroid collisions within the past few thousand years, have yet to be identified. Because WISE is significantly more sensitive than IRAS in the mid-infrared, it has detected some trails extending much further over their orbits and will greatly expand the catalog of trails detected in addition to those observed by IRAS and Spitzer (the latter by targeted observations). WISE and the yet more sensitive NEOCAM survey telescope will provide important insights into the recent collisional history of the asteroid belt and the nature and evolution of comets.
NASA Astrophysics Data System (ADS)
Yang, X. I. A.; Meneveau, C.; Marusic, I.; Biferale, L.
2016-08-01
In wall-bounded turbulence, the moment generating functions (MGFs) of the streamwise velocity fluctuations
Response of wind shear warning systems to turbulence with implication of nuisance alerts
NASA Technical Reports Server (NTRS)
Bowles, Roland L.
1988-01-01
The objective was to predict the inherent turbulence response characteristics of candidate wind shear warning system concepts and to assess the potential for nuisance alerts. Information on the detection system and associated signal processing, physical and mathematical models, wind shear factor root mean square turbulence response and the standard deviation of the wind shear factor due to turbulence is given in vugraph form.
Low current extended duration spark ignition system
Waters, Stephen Howard; Chan, Anthony Kok-Fai
2005-08-30
A system for firing a spark plug is disclosed. The system includes a timing controller configured to send a first timing signal and a second timing signal. The system also includes an ignition transformer having a primary winding and a secondary winding and a spark-plug that is operably associated with the secondary winding. A first switching element is disposed between the timing controller and the primary winding of the ignition transformer. The first switching element controls a supply of power to the primary winding based on the first timing signal. Also, a second switching element is disposed between the timing controller and the primary winding of the ignition transformer. The second switching element controls the supply of power to the primary winding based on the second timing signal. A method for firing a spark plug is also disclosed.
Extended length microchannels for high density high throughput electrophoresis systems
Davidson, James C.; Balch, Joseph W.
2000-01-01
High throughput electrophoresis systems which provide extended well-to-read distances on smaller substrates, thus compacting the overall systems. The electrophoresis systems utilize a high density array of microchannels for electrophoresis analysis with extended read lengths. The microchannel geometry can be used individually or in conjunction to increase the effective length of a separation channel while minimally impacting the packing density of channels. One embodiment uses sinusoidal microchannels, while another embodiment uses plural microchannels interconnected by a via. The extended channel systems can be applied to virtually any type of channel confined chromatography.
Modeling mesoscopic phenomena in extended dynamical systems
Bishop, A.; Lomdahl, P.; Jensen, N.G.; Cai, D.S.; Mertenz, F.; Konno, Hidetoshi; Salkola, M.
1997-08-01
This is the final report of a three-year, Laboratory-Directed Research and Development project at the Los Alamos National Laboratory (LANL). We have obtained classes of nonlinear solutions on curved geometries that demonstrate a novel interplay between topology and geometric frustration relevant for nanoscale systems. We have analyzed the nature and stability of localized oscillatory nonlinear excitations (multi-phonon bound states) on discrete nonlinear chains, including demonstrations of successful perturbation theories, existence of quasiperiodic excitations, response to external statistical time-dependent fields and point impurities, robustness in the presence of quantum fluctuations, and effects of boundary conditions. We have demonstrated multi-timescale effects for nonlinear Schroedinger descriptions and shown the success of memory function approaches for going beyond these approximations. In addition we have developed a generalized rate-equation framework that allows analysis of the important creation/annihilation processes in driven nonlinear, nonequilibiium systems.
CEBAF NEW DIGITAL LLRF SYSTEM EXTENDED FUNCTIONALITY
T. Allison; K. Davis; H. Dong; C. Hovater; L. King; J. Musson; T. Plawski
2007-06-18
The new digital LLRF system for the CEBAF 12GeV accelerator will perform a variety of tasks, beyond field control [1]. In this paper we present the superconducting cavity resonance control system designed to minimize RF power during gradient ramp and to minimize RF power during steady state operation. Based on the calculated detuning angle, which represents the difference between reference and cavity resonance frequency, the cavity length will be adjusted with a mechanical tuner. The tuner has two mechanical driving devices, a stepper motor and a piezo-tuner, to yield a combination of coarse and fine control. Although LLRF piezo processing speed can achieve 10 kHz bandwidth, only 10 Hz speed is needed for 12 GeV upgrade. There will be a number of additional functions within the LLRF system; heater controls to maintain cryomodule's heat load balance, ceramic window temperature monitoring, waveguide vacuum interlocks, ARC detector interlock and quench detection. The additional functions will be divided between the digital board, incorporating an Altera FPGA and an embedded EPICS IOC. This paper will also address hardware evolution and test results performed with different SC cavities.
Solar system plasma Turbulence: Observations, inteRmittency and Multifractals
NASA Astrophysics Data System (ADS)
Echim, Marius M.
2016-04-01
The FP7 project STORM is funded by the European Commission to "add value to existing data bases through a more comprehensive interpretation". STORM targets plasma and magnetic field databases collected in the solar wind (Ulysses and also some planetary missions), planetary magnetospheres (Venus Express, Cluster, a few orbits from Cassini), cometary magnetosheaths (e.g. Haley from Giotto observations). The project applies the same package of analysis methods on geomagnetic field observations from ground and on derived indices (e.g. AE, AL, AU, SYM-H). The analysis strategy adopted in STORM is built on the principle of increasing complexity, from lower (like, e.g., the Power Spectral Density - PSD) to higher order analyses (the Probability Distribution Functions - PDFs, Structure Functions - SFs, Fractals and Multifractals - MFs). Therefore STORM targets not only the spectral behavior of turbulent fluctuations but also their topology and scale behavior inferred from advanced mathematical algorithms and geometrical-like analogs. STORM started in January 2013 and ended in December 2015. We will report on a selection of scientific and technical achievements and will highlight: (1) the radial evolution of solar wind turbulence and intermittency based on Ulysses data with some contributions from Venus Express and Cluster; (2) comparative study of fast and slow wind turbulence and intermittency at solar minimum; (3) comparative study of the planetary response (Venus and Earth magnetosheaths) to turbulent solar wind; (4) the critical behavior of geomagnetic fluctuations and indices; (5) an integrated library for non-linear analysis of time series that includes all the approaches adopted in STORM to investigate solar system plasma turbulence. STORM delivers an unprecedented volume of analysed data for turbulence. The project made indeed a systematic survey, orbit by orbit, of data available from ESA repositories and Principal Investigators and provides results ordered as a
Extended professional development for systemic curriculum reform
NASA Astrophysics Data System (ADS)
Kubitskey, Mary Elizabeth
Education standards call for adopting inquiry science instruction. Successful adoption requires professional development (PD) to support teachers, increasing the need for research on PD. This dissertation examines the question: What is the influence of high quality, curriculum aligned, long-term group workshops and related practice on teacher learning? I focus on the following subquestions: (1) What is the influence of high quality, curriculum aligned, long-term, group workshops on teacher knowledge and beliefs? (2) What is the impact of the workshops on teacher practice? (3) What is the influence of practice on student response? (4) What is the impact of practice and student response on teacher knowledge and beliefs? I focus on an instance of PD nested within a long-term systemic change initiative, tracing eleven science teachers' learning from workshops and associated enactments. The data included pre and post-unit interviews (n=22), two post-workshop interviews (n=17), workshop observations (n=2), classroom observations (n=24) and student work (n=351). I used mixed-methods analysis. Quantitative analysis measured teacher learning by comparing pre and post-unit interview ratings. Qualitative components included two case study approaches: logic model technique and cross-case synthesis, examining teacher learning within and across teachers. The findings suggested a teacher-learning model incorporating PD, teacher knowledge, beliefs, practice and student response. PD impacts teachers' knowledge by providing teachers with new knowledge, adapting previous knowledge, or convincing them to value existing knowledge they chose not to use. The workshops can influence beliefs, providing teachers with confidence and motivation to adopt the practice. Beliefs can mediate how knowledge manifested itself in practice that, in turn, impacts students' response. Student response influences the teachers' beliefs, either reinforcing or motivating change. This teacher-learning model
Neuroanatomy of the Extended Circadian Rhythm System
Morin, Lawrence P
2012-01-01
The suprachiasmatic nucleus (SCN), site of the primary clock in the circadian rhythm system, has three major afferent connections. The most important consists of a retinohypothalamic projection through which photic information, received by classical rod/cone photoreceptors and intrinsically photoreceptive retinal ganglion cells, gains access to the clock. This information influences phase and period of circadian rhythms. The two other robust afferent projections are the median raphe serotonergic pathway and the geniculohypothalamic (GHT), NPY-containing pathway from the thalamic intergeniculate leaflet (IGL). Beyond this simple framework, the number of anatomical routes that could theoretically be involved in rhythm regulation is enormous, with the SCN projecting to 15 regions and being directly innervated by about 35. If multisynaptic afferents to the SCN are included, the number expands to approximately brain 85 areas providing input to the SCN. The IGL, a known contributor to circadian rhythm regulation, has a still greater level of complexity. This nucleus connects abundantly throughout the brain (to approximately 100 regions) by pathways that are largely bilateral and reciprocal. Few of these sites have been evaluated for their contributions to circadian rhythm regulation, although most have a theoretical possibility of doing so via the GHT. The anatomy of IGL connections suggests that one of its functions may be regulation of eye movements during sleep. Together, neural circuits of the SCN and IGL are complex and interconnected. As yet, few have been tested with respect to their involvement in rhythm regulation. PMID:22766204
Shock-induced turbulent flow in baffle systems
Kuhl, A.L.; Reichenbach, H.
1993-07-01
Experiments are described on shock propagation through 2-D aligned and staggered baffle systems. Flow visualization was provided by shadow and schlieren photography, recorded by the Cranz-Schardin camera. Also single-frame, infinite-fringe, color interferograms were used. Intuition suggests that this is a rather simple 2-D shock diffraction problem. However, flow visualization reveals that the flow rapidly evolved into a complex 3-D turbulent mixing problem. Mushroom-shaped mixing regions blocked the flow into the next baffle orifice. Thus energy was transferred from the directed kinetic energy (induced by the shock) to rotational energy of turbulent mixing, and then dissipated by molecular effects. These processes dramatically dissipate the strength of the shock wave. The experiments provide an excellent test case that could be used to assess the accuracy of computer code calculations of such problems.
The role of extended conical intersection seams in photochromic systems
NASA Astrophysics Data System (ADS)
Boggio-Pasqua, Martial; Bearpark, Michael J.; Robb, Michael A.
2015-01-01
We describe the role of conical intersections in the mechanism of photochromic molecular systems. In particular, the extended nature of the crossing seam associated with a conical intersection is highlighted and its significance on dihydroazulenes and diarylethenes photochromism is explained.
Mooring system of ocean turbulence observation based on submerged buoy
NASA Astrophysics Data System (ADS)
Song, Da-lei; Sun, Jing-jing; Xue, Bing; Jiang, Qian-li; Wu, Bing-wei
2013-06-01
A comparison experiment has been taken in the Kiaochow Bay between a newly designed mooring turbulence observation instrument (MTOI) and microstructure profiler MSS60 made by Sea & Sun. The whole observing system is based on a submerged buoy, in which the turbulence observation instrument is embedded, with a streamline-shape floating body, which is made of buoyancy material of glass microsphere. For the movement of seawater and the cable shaking strongly anytime influence the behaviors of the floating body, the accelerate sensors are used for the vibration measurement in the instrument together with the shear probe sensor. Both the vibration data and the shear data are acquired by the instrument at the same time. During data processing, the vibration signals can be removed and leave the shear data which we really need. In order to prove the reliability of the new turbulence instrument MTOI, a comparison experiment was designed. The measuring conditions are the same both in time and space. By this way, the two groups of data are comparable. In this paper, the conclusion gives a good similarity of 0.93 for the two groups of shear data in dissipation rate. The processing of the data acquired by MTOI is based on the cross-spectrum analysis, and the dissipation rate of it matches the Nasmyth spectrum well.
Calibration of NASA Turbulent Air Motion Measurement System
NASA Technical Reports Server (NTRS)
Barrick, John D. W.; Ritter, John A.; Watson, Catherine E.; Wynkoop, Mark W.; Quinn, John K.; Norfolk, Daniel R.
1996-01-01
A turbulent air motion measurement system (TAMMS) was integrated onboard the Lockheed 188 Electra airplane (designated NASA 429) based at the Wallops Flight Facility in support of the NASA role in global tropospheric research. The system provides air motion and turbulence measurements from an airborne platform which is capable of sampling tropospheric and planetary boundary-layer conditions. TAMMS consists of a gust probe with free-rotating vanes mounted on a 3.7-m epoxy-graphite composite nose boom, a high-resolution inertial navigation system (INS), and data acquisition system. A variation of the tower flyby method augmented with radar tracking was implemented for the calibration of static pressure position error and air temperature probe. Additional flight calibration maneuvers were performed remote from the tower in homogeneous atmospheric conditions. System hardware and instrumentation are described and the calibration procedures discussed. Calibration and flight results are presented to illustrate the overall ability of the system to determine the three-component ambient wind fields during straight and level flight conditions.
NASA Astrophysics Data System (ADS)
Ouyang, Bing; Hou, Weilin; Gong, Cuiling; Caimi, Frank M.; Dalgleish, Fraser R.; Vuorenkoski, Anni K.
2016-05-01
The Compressive Line Sensing (CLS) active imaging system has been demonstrated to be effective in scattering mediums, such as turbid coastal water through simulations and test tank experiments. Since turbulence is encountered in many atmospheric and underwater surveillance applications, a new CLS imaging prototype was developed to investigate the effectiveness of the CLS concept in a turbulence environment. Compared with earlier optical bench top prototype, the new system is significantly more robust and compact. A series of experiments were conducted at the Naval Research Lab's optical turbulence test facility with the imaging path subjected to various turbulence intensities. In addition to validating the system design, we obtained some unexpected exciting results - in the strong turbulence environment, the time-averaged measurements using the new CLS imaging prototype improved both SNR and resolution of the reconstructed images. We will discuss the implications of the new findings, the challenges of acquiring data through strong turbulence environment, and future enhancements.
Ensemble Kalman filters for dynamical systems with unresolved turbulence
Grooms, Ian; Lee, Yoonsang; Majda, Andrew J.
2014-09-15
Ensemble Kalman filters are developed for turbulent dynamical systems where the forecast model does not resolve all the active scales of motion. Coarse-resolution models are intended to predict the large-scale part of the true dynamics, but observations invariably include contributions from both the resolved large scales and the unresolved small scales. The error due to the contribution of unresolved scales to the observations, called ‘representation’ or ‘representativeness’ error, is often included as part of the observation error, in addition to the raw measurement error, when estimating the large-scale part of the system. It is here shown how stochastic superparameterization (a multiscale method for subgridscale parameterization) can be used to provide estimates of the statistics of the unresolved scales. In addition, a new framework is developed wherein small-scale statistics can be used to estimate both the resolved and unresolved components of the solution. The one-dimensional test problem from dispersive wave turbulence used here is computationally tractable yet is particularly difficult for filtering because of the non-Gaussian extreme event statistics and substantial small scale turbulence: a shallow energy spectrum proportional to k{sup −5/6} (where k is the wavenumber) results in two-thirds of the climatological variance being carried by the unresolved small scales. Because the unresolved scales contain so much energy, filters that ignore the representation error fail utterly to provide meaningful estimates of the system state. Inclusion of a time-independent climatological estimate of the representation error in a standard framework leads to inaccurate estimates of the large-scale part of the signal; accurate estimates of the large scales are only achieved by using stochastic superparameterization to provide evolving, large-scale dependent predictions of the small-scale statistics. Again, because the unresolved scales contain so much energy
Modeling atmospheric turbulence effects on ground-based telescope systems
Flatte, S.M.; Bradford, L.W.; Max, C.E.
1994-12-31
Bester et al. report measurements of atmospheric fluctuations made with the Infrared Spatial Interferometer, which indicated behavior not in accord with the standard Kolmogorov model with only a single constant wind velocity. The numerical simulations use relatively complex models of the atmosphere to investigate both Kolmogorov and non-Kolmogorov models. The authors find that the measurements of Bester et al. for light passing through the upper atmosphere are within the limits of behavior for Kolmogorov models, but often only if the outer scale of turbulent fluctuations is between 15 to 100 meters. The possibility that the measured behavior might be non-Kolmogorov is not excluded. They also examine measurements made along short paths in the surface boundary layer, where some measurements of Bester et al. showed variations in the atmospheric fluctuations with seeing conditions which appeared to be non-Kolmogorov. These variations can perhaps be explained by standard models, but require that seeing improve with increasing wind speed in the surface layer. They discuss some other measurements which lend some support to that idea. However, they cannot exclude non-Kolmogorov behavior. They find that meteorological data is needed concurrent with astronomical observations, to help constrain the models. The size of the outer scale, the wind velocity profile and the turbulence spectrum are important to the ultimate capabilities of interferometers and other systems with adaptive optics.
Market Assessment of Forward-Looking Turbulence Sensing Systems
NASA Technical Reports Server (NTRS)
Kauffmann, Paul; Sousa-Poza, Andres
2001-01-01
In recognition of the importance of turbulence mitigation as a tool to improve aviation safety, NASA's Aviation Safety Program developed a Turbulence Detection and Mitigation Sub-element. The objective of this effort is to develop highly reliable turbulence detection technologies for commercial transport aircraft to sense dangerous turbulence with sufficient time warning so that defensive measures can be implemented and prevent passenger and crew injuries. Current research involves three forward sensing products to improve the cockpit awareness of possible turbulence hazards. X-band radar enhancements will improve the capabilities of current weather radar to detect turbulence associated with convective activity. LIDAR (Light Detection and Ranging) is a laser-based technology that is capable of detecting turbulence in clear air. Finally, a possible Radar-LIDAR hybrid sensor is envisioned to detect the full range of convective and clear air turbulence. To support decisions relating to the development of these three forward-looking turbulence sensor technologies, the objective of this study was defined as examination of cost and implementation metrics. Tasks performed included the identification of cost factors and certification issues, the development and application of an implementation model, and the development of cost budget/targets for installing the turbulence sensor and associated software devices into the commercial transport fleet.
[Extending the palliative approach across the French health system].
Mino, Jean-Christophe
2015-11-01
The care provision for people at the end of life requires a palliative care approach to be extended across the whole healthcare system. Access to palliative care for everyone requires training for professionals, support for specialised structures and teams as well as clear political will. PMID:26567066
Juarez, Juan C; Brown, David M; Young, David W
2014-05-19
Current Strehl ratio models for actively compensated free-space optical communications terminals do not accurately predict system performance under strong turbulence conditions as they are based on weak turbulence theory. For evaluation of compensated systems, we present an approach for simulating the Strehl ratio with both low-order (tip/tilt) and higher-order (adaptive optics) correction. Our simulation results are then compared to the published models and their range of turbulence validity is assessed. Finally, we propose a new Strehl ratio model and antenna gain equation that are valid for general turbulence conditions independent of the degree of compensation. PMID:24921373
Extended phase space description of human-controlled systems dynamics
NASA Astrophysics Data System (ADS)
Zgonnikov, Arkady; Lubashevsky, Ihor
2014-03-01
Humans are often incapable of precisely identifying and implementing the desired control strategy in controlling unstable dynamical systems. That is, the operator of a dynamical system treats the current control effort as acceptable even if it deviates slightly from the desired value, and starts correcting the actions only when the deviation has become evident. We argue that the standard Newtonian approach does not allow such behavior to be modeled. Instead, the physical phase space of a controlled system should be extended with an independent phase variable characterizing the motivated actions of the operator. The proposed approach is illustrated via a simple non-Newtonian model capturing the operators' fuzzy perception of their own actions. The properties of the model are investigated analytically and numerically; the results confirm that the extended phase space may aid in capturing the intricate dynamical properties of human-controlled systems.
Approaching complexity by stochastic methods: From biological systems to turbulence
NASA Astrophysics Data System (ADS)
Friedrich, Rudolf; Peinke, Joachim; Sahimi, Muhammad; Reza Rahimi Tabar, M.
2011-09-01
This review addresses a central question in the field of complex systems: given a fluctuating (in time or space), sequentially measured set of experimental data, how should one analyze the data, assess their underlying trends, and discover the characteristics of the fluctuations that generate the experimental traces? In recent years, significant progress has been made in addressing this question for a class of stochastic processes that can be modeled by Langevin equations, including additive as well as multiplicative fluctuations or noise. Important results have emerged from the analysis of temporal data for such diverse fields as neuroscience, cardiology, finance, economy, surface science, turbulence, seismic time series and epileptic brain dynamics, to name but a few. Furthermore, it has been recognized that a similar approach can be applied to the data that depend on a length scale, such as velocity increments in fully developed turbulent flow, or height increments that characterize rough surfaces. A basic ingredient of the approach to the analysis of fluctuating data is the presence of a Markovian property, which can be detected in real systems above a certain time or length scale. This scale is referred to as the Markov-Einstein (ME) scale, and has turned out to be a useful characteristic of complex systems. We provide a review of the operational methods that have been developed for analyzing stochastic data in time and scale. We address in detail the following issues: (i) reconstruction of stochastic evolution equations from data in terms of the Langevin equations or the corresponding Fokker-Planck equations and (ii) intermittency, cascades, and multiscale correlation functions.
Extending the infoway benefits evaluation framework for health information systems.
Lau, Francis
2009-01-01
A proposal is made that extends the current Canada Health Infoway Benefits Evaluation (BE) Framework for Health Information Systems (HIS) being deployed in Canada. The current BE framework takes a micro view of HIS quality, use and impact at the local level whereas the extended framework takes into account the broader socio-organizational and contextual aspects known as the meso and macro views of HIS deployment. The meso view addresses the people, organization, network and implementation dimensions. The macro view focuses on the contextual dimensions of technology standard, funding/incentive, legislation/policy and professional practice. Validation of this extended BE framework is being planned through a comparative review of recent HIS evaluation literature, a Delphi-consensus process with HIS experts and users, and multiple validation studies with recent HIS implementation projects in British Columbia. PMID:19380969
Cheng, Mingjian; Zhang, Yixin; Gao, Jie; Wang, Fei; Zhao, Fengsheng
2014-06-20
We model the average channel capacity of optical wireless communication systems for cases of weak to strong turbulence channels, using the exponentiation Weibull distribution model. The joint effects of the beam wander and spread, pointing errors, atmospheric attenuation, and the spectral index of non-Kolmogorov turbulence on system performance are included. Our results show that the average capacity decreases steeply as the propagation length L changes from 0 to 200 m and decreases slowly down or tends to a stable value as the propagation length L is greater than 200 m. In the weak turbulence region, by increasing the detection aperture, we can improve the average channel capacity and the atmospheric visibility as an important issue affecting the average channel capacity. In the strong turbulence region, the increase of the radius of the detection aperture cannot reduce the effects of the atmospheric turbulence on the average channel capacity, and the effect of atmospheric visibility on the channel information capacity can be ignored. The effect of the spectral power exponent on the average channel capacity in the strong turbulence region is higher than weak turbulence region. Irrespective of the details determining the turbulent channel, we can say that pointing errors have a significant effect on the average channel capacity of optical wireless communication systems in turbulence channels. PMID:24979434
Estimating Power System Dynamic States Using Extended Kalman Filter
Huang, Zhenyu; Schneider, Kevin P.; Nieplocha, Jaroslaw; Zhou, Ning
2014-10-31
Abstract—The state estimation tools which are currently deployed in power system control rooms are based on a steady state assumption. As a result, the suite of operational tools that rely on state estimation results as inputs do not have dynamic information available and their accuracy is compromised. This paper investigates the application of Extended Kalman Filtering techniques for estimating dynamic states in the state estimation process. The new formulated “dynamic state estimation” includes true system dynamics reflected in differential equations, not like previously proposed “dynamic state estimation” which only considers the time-variant snapshots based on steady state modeling. This new dynamic state estimation using Extended Kalman Filter has been successfully tested on a multi-machine system. Sensitivity studies with respect to noise levels, sampling rates, model errors, and parameter errors are presented as well to illustrate the robust performance of the developed dynamic state estimation process.
Wind Shear/Turbulence Inputs to Flight Simulation and Systems Certification
NASA Technical Reports Server (NTRS)
Bowles, Roland L. (Editor); Frost, Walter (Editor)
1987-01-01
The purpose of the workshop was to provide a forum for industry, universities, and government to assess current status and likely future requirements for application of flight simulators to aviation safety concerns and system certification issues associated with wind shear and atmospheric turbulence. Research findings presented included characterization of wind shear and turbulence hazards based on modeling efforts and quantitative results obtained from field measurement programs. Future research thrusts needed to maximally exploit flight simulators for aviation safety application involving wind shear and turbulence were identified. The conference contained sessions on: Existing wind shear data and simulator implementation initiatives; Invited papers regarding wind shear and turbulence simulation requirements; and Committee working session reports.
Turbulence Measurements by the DC-8 Meteorological Measurement System
NASA Technical Reports Server (NTRS)
Chan, K. R.; Dean-Day, J.; Bowen, S. W.; Bui, T. P.; Chan, K. Roland (Technical Monitor)
1997-01-01
The instrumentation of a new MMS on the DC-8 aircraft is briefly described. Methods to compute and evaluate the turbulent dissipation rate epsilon, based on theory and MMS data, are discussed. Examples of turbulence measurements during encounters of a wake vortex, wave clouds, persistent contrails, mountain are gravity waves are illustrated.
Extended Duration Orbiter (EDO) Improved Waste Collection System (IWCS)
NASA Technical Reports Server (NTRS)
1992-01-01
This high angle overall view shows the top side components of the Extended Duration Orbiter (EDO) Waste Collection System (WCS) scheduled to fly aboard NASA's Endeavour, Orbiter Vehicle (OV) 105, for the STS-54 mission. Detailed Test Objective 662, Extended duration orbiter WCS evaluation, will verify the design of the new EDO WCS under microgravity conditions for a prolonged period. OV-105 has been modified with additional structures in the waste management compartment (WMC) and additional avionics to support/restrain the EDO WCS. Among the advantages the new IWCS is hoped to have over the currect WCS are greater dependability, better hygiene, virtually unlimited capacity, and more efficient preparation between shuttle missions. Unlike the previous WCS, the improved version will not have to be removed from the spacecraft to be readied for the next flight. The WCS was documented in JSC's Crew Systems Laboratory Bldg 7.
Extended Duration Orbiter (EDO) Improved Waste Collection System (IWCS)
NASA Technical Reports Server (NTRS)
1992-01-01
This overall front view shows the Extended Duration Orbiter (EDO) Waste Collection System (WCS) scheduled to fly aboard NASA's Endeavour, Orbiter Vehicle (OV) 105, for the STS-54 mission. Detailed Test Objective 662, Extended duration orbiter WCS evaluation, will verify the design of the new EDO WCS under microgravity conditions for a prolonged period. OV-105 has been modified with additional structures in the waste management compartment (WMC) and additional avionics to support/restrain the EDO WCS. Among the advantages the new IWCS is hoped to have over the currect WCS are greater dependability, better hygiene, virtually unlimited capacity, and more efficient preparation between shuttle missions. Unlike the previous WCS, the improved version will not have to be removed from the spacecraft to be readied for the next flight. The WCS was documented in JSC's Crew Systems Laboratory Bldg 7.
Extended Darknet: Multi-Dimensional Internet Threat Monitoring System
NASA Astrophysics Data System (ADS)
Shimoda, Akihiro; Mori, Tatsuya; Goto, Shigeki
Internet threats caused by botnets/worms are one of the most important security issues to be addressed. Darknet, also called a dark IP address space, is one of the best solutions for monitoring anomalous packets sent by malicious software. However, since darknet is deployed only on an inactive IP address space, it is an inefficient way for monitoring a working network that has a considerable number of active IP addresses. The present paper addresses this problem. We propose a scalable, light-weight malicious packet monitoring system based on a multi-dimensional IP/port analysis. Our system significantly extends the monitoring scope of darknet. In order to extend the capacity of darknet, our approach leverages the active IP address space without affecting legitimate traffic. Multi-dimensional monitoring enables the monitoring of TCP ports with firewalls enabled on each of the IP addresses. We focus on delays of TCP syn/ack responses in the traffic. We locate syn/ack delayed packets and forward them to sensors or honeypots for further analysis. We also propose a policy-based flow classification and forwarding mechanism and develop a prototype of a monitoring system that implements our proposed architecture. We deploy our system on a campus network and perform several experiments for the evaluation of our system. We verify that our system can cover 89% of the IP addresses while darknet-based monitoring only covers 46%. On our campus network, our system monitors twice as many IP addresses as darknet.
Extended space expectation values in quantum dynamical system evolutions
Demiralp, Metin
2014-10-06
The time variant power series expansion for the expectation value of a given quantum dynamical operator is well-known and well-investigated issue in quantum dynamics. However, depending on the operator and Hamiltonian singularities this expansion either may not exist or may not converge for all time instances except the beginning of the evolution. This work focuses on this issue and seeks certain cures for the negativities. We work in the extended space obtained by adding all images of the initial wave function under the system Hamiltonian’s positive integer powers. This requires the introduction of certain appropriately defined weight operators. The resulting better convergence in the temporal power series urges us to call the new defined entities “extended space expectation values” even though they are constructed over certain weight operators and are somehow pseudo expectation values.
The performance of heterodyne detection system for partially coherent beams in turbulent atmosphere
NASA Astrophysics Data System (ADS)
Chengqiang, Li; Tingfeng, Wang; Heyong, Zhang; Jingjiang, Xie; Lisheng, Liu; Shuai, Zhao; Jin, Guo
2015-12-01
The performance of heterodyne system is discussed for partially coherent beams in turbulent atmosphere by introducing turbulence spectrum of refractive-index fluctuations. Several analytic formulae for the heterodyne detection system using the partially coherent Gaussian Schell-model beam are presented. Based on Tatarskii spectrum model, some numerical results are given for the variation in the heterodyne efficiency with the misalignment angle, detector diameter, turbulence conditions, and parameters of the overlapping beams. According to the numerical results, we find that the turbulent atmosphere degrades the heterodyne efficiency significantly, and the variation in heterodyne efficiency is even slower against the misalignment angle in turbulence. For the deterministic received signal and the detector, the performance of the heterodyne detection can be adjusted by controlling the local oscillator signal parameters.
Gaussianity versus intermittency in solar system plasma turbulence
NASA Astrophysics Data System (ADS)
Echim, M.
2014-12-01
Statistical properties of plasma and magnetic field fluctuations exhibit features linked with the dynamics of the targeted system and sometimes with the physical processes that are at the origin of these fluctuations. Intermittency is sometimes discussed in terms of non-Gaussianity of the Probability Distribution Functions (PDFs) of fluctuations for ranges of spatio/temporal scales. Some examples of self-similarity have been however shown for PDFs whose wings are not Gaussian. In this study we discuss intermittency in terms of non-Gaussianity as well as scale dependence of the higher order moments of PDFs, in particular the flatness. We use magnetic field and plasma data from several space missions, in the solar wind (Ulysses, Cluster, and Venus Express), and in the planetary magnetosheaths (Cluster and Venus Express). We analyze Ulysses data that satisfy a consolidated set of selection criteria able to identify "pure" fast and slow wind. We investigate Venus Express data close to the orbital apogee, in the solar wind, at 0.72 AU, and in the Venus magnetosheath. We study Cluster data in the solar wind (for time intervals not affected by planetary ions effects), and the magnetosheath. We organize our results in three solar wind data bases (one for the solar maximum, 1999-2001, two for the solar minimum, 1997-1998 and respectively, 2007-2008), and two planetary databases (one for the solar maximum, 2000-2001, that includes PDFs obtained in the terrestrial magnetosphere, and one for the solar minimum, 2007-2008, that includes PDFs obtained in the terrestrial and Venus magnetospheres and magnetosheaths). In addition to investigating the statistical properties of fluctuations for the minimum and maximum of the solar cycle we also analyze the similarities and differences between fast and slow wind. We emphasize the importance of our data survey and analysis in the context of understanding the solar wind turbulence and complexity, and the exploitation of data bases and as
Extended Kepler-Coulomb quantum superintegrable systems in three dimensions
NASA Astrophysics Data System (ADS)
Kalnins, E. G.; Kress, J. M.; Miller, W., Jr.
2013-03-01
The quantum Kepler-Coulomb system in three dimensions is well known to be second order superintegrable, with a symmetry algebra that closes polynomially under commutators. This polynomial closure is also typical for second order superintegrable systems in 2D and for second order systems in 3D with nondegenerate (four-parameter) potentials. However, the degenerate three-parameter potential for the 3D Kepler-Coulomb system (also second order superintegrable) is an exception, as its symmetry algebra does not close polynomially. The 3D four-parameter potential for the extended Kepler-Coulomb system is not even second order superintegrable, but Verrier and Evans (2008 J. Math. Phys. 49 022902) showed it was fourth order superintegrable, and Tanoudis and Daskaloyannis (2011 arXiv:11020397v1) showed that, if a second fourth order symmetry is added to the generators, the symmetry algebra closes polynomially. Here, based on the Tremblay, Turbiner and Winternitz construction, we consider an infinite class of quantum extended Kepler-Coulomb three- and four-parameter systems indexed by a pair of rational numbers (k1, k2) and reducing to the usual systems when k1 = k2 = 1. We show these systems to be superintegrable of arbitrarily high order and determine the structure of their symmetry algebras. We demonstrate that the symmetry algebras close algebraically; only for systems admitting extra discrete symmetries is polynomial closure achieved. Underlying the structure theory is the existence of raising and lowering operators, not themselves symmetry operators or even defined independent of basis, that can be employed to construct the symmetry operators and their structure relations.
Flight Tests of the DELICAT Airborne LIDAR System for Remote Clear Air Turbulence Detection
NASA Astrophysics Data System (ADS)
Vrancken, Patrick; Wirth, Martin; Ehret, Gerhard; Witschas, Benjamin; Veerman, Henk; Tump, Robert; Barny, Hervé; Rondeau, Philippe; Dolfi-Bouteyre, Agnès; Lombard, Laurent
2016-06-01
An important aeronautics application of lidar is the airborne remote detection of Clear Air Turbulence which cannot be performed with onboard radar. We report on a DLR-developed lidar system for the remote detection of such turbulent areas in the flight path of an aircraft. The lidar, consisting of a high-power UV laser transmitter and a direct detection system, was installed on a Dutch research aircraft. Flight tests executed in 2013 demonstrated the performance of the lidar system to detect local subtle variations in the molecular backscatter coefficient indicating the turbulence some 10 to 15 km ahead.
Algorithm for Simulating Atmospheric Turbulence and Aeroelastic Effects on Simulator Motion Systems
NASA Technical Reports Server (NTRS)
Ercole, Anthony V.; Cardullo, Frank M.; Kelly, Lon C.; Houck, Jacob A.
2012-01-01
Atmospheric turbulence produces high frequency accelerations in aircraft, typically greater than the response to pilot input. Motion system equipped flight simulators must present cues representative of the aircraft response to turbulence in order to maintain the integrity of the simulation. Currently, turbulence motion cueing produced by flight simulator motion systems has been less than satisfactory because the turbulence profiles have been attenuated by the motion cueing algorithms. This report presents a new turbulence motion cueing algorithm, referred to as the augmented turbulence channel. Like the previous turbulence algorithms, the output of the channel only augments the vertical degree of freedom of motion. This algorithm employs a parallel aircraft model and an optional high bandwidth cueing filter. Simulation of aeroelastic effects is also an area where frequency content must be preserved by the cueing algorithm. The current aeroelastic implementation uses a similar secondary channel that supplements the primary motion cue. Two studies were conducted using the NASA Langley Visual Motion Simulator and Cockpit Motion Facility to evaluate the effect of the turbulence channel and aeroelastic model on pilot control input. Results indicate that the pilot is better correlated with the aircraft response, when the augmented channel is in place.
Extending TOPS: Ontology-driven Anomaly Detection and Analysis System
NASA Astrophysics Data System (ADS)
Votava, P.; Nemani, R. R.; Michaelis, A.
2010-12-01
Terrestrial Observation and Prediction System (TOPS) is a flexible modeling software system that integrates ecosystem models with frequent satellite and surface weather observations to produce ecosystem nowcasts (assessments of current conditions) and forecasts useful in natural resources management, public health and disaster management. We have been extending the Terrestrial Observation and Prediction System (TOPS) to include a capability for automated anomaly detection and analysis of both on-line (streaming) and off-line data. In order to best capture the knowledge about data hierarchies, Earth science models and implied dependencies between anomalies and occurrences of observable events such as urbanization, deforestation, or fires, we have developed an ontology to serve as a knowledge base. We can query the knowledge base and answer questions about dataset compatibilities, similarities and dependencies so that we can, for example, automatically analyze similar datasets in order to verify a given anomaly occurrence in multiple data sources. We are further extending the system to go beyond anomaly detection towards reasoning about possible causes of anomalies that are also encoded in the knowledge base as either learned or implied knowledge. This enables us to scale up the analysis by eliminating a large number of anomalies early on during the processing by either failure to verify them from other sources, or matching them directly with other observable events without having to perform an extensive and time-consuming exploration and analysis. The knowledge is captured using OWL ontology language, where connections are defined in a schema that is later extended by including specific instances of datasets and models. The information is stored using Sesame server and is accessible through both Java API and web services using SeRQL and SPARQL query languages. Inference is provided using OWLIM component integrated with Sesame.
NASA Astrophysics Data System (ADS)
Meneguz, Elena; Turp, Debi; Wells, Helen
2015-04-01
It is well known that encounters with moderate or severe turbulence can lead to passenger injuries and incur high costs for airlines from compensation and litigation. As one of two World Area Forecast Centres (WAFCs), the Met Office has responsibility for forecasting en-route weather hazards worldwide for aviation above a height of 10,000 ft. Observations from commercial aircraft provide a basis for gaining a better understanding of turbulence and for improving turbulence forecasts through verification. However there is currently a lack of information regarding the possible cause of the observed turbulence, or whether the turbulence occurred within cloud. Such information would be invaluable for the development of forecasting techniques for particular types of turbulence and for forecast verification. Of all the possible sources of turbulence, convective activity is believed to be a major cause of turbulence. Its relative importance over the Europe and North Atlantic area has not been yet quantified in a systematic way: in this study, a new approach is developed to automate identification of turbulent encounters in the proximity of convective clouds. Observations of convection are provided from two independent sources: a surface based lightning network and satellite imagery. Lightning observations are taken from the Met Office Arrival Time Detections network (ATDnet). ATDnet has been designed to identify cloud-to-ground flashes over Europe but also detects (a smaller fraction of) strikes over the North Atlantic. Meteosat Second Generation (MSG) satellite products are used to identify convective clouds by applying a brightness temperature filtering technique. The morphological features of cold cloud tops are also investigated. The system is run for all in situ turbulence reports received from airlines for a total of 12 months during summer 2013 and 2014 for the domain of interest. Results of this preliminary short term climatological study show significant intra
NASA Technical Reports Server (NTRS)
Gage, K. S.; Jasperson, W. H.
1977-01-01
An analysis is presented of the tropospheric turbulence data obtained by the Metrac positioning system, a radio location system which employs the Doppler principle to track inexpensive expendable balloon-borne transmitters. A Minneapolis field test of the Metrac system provided one-second samples of transmitter frequency from balloons tracked by four ground stations for more than an hour. The derivation of diffusion coefficients from the turbulence data was conducted by two methods, yielding highly consistent results.
Database of extended radiation maps and its access system
NASA Astrophysics Data System (ADS)
Verkhodanov, O. V.; Naiden, Ya. V.; Chernenkov, V. N.; Verkhodanova, N. V.
2014-01-01
We describe the architecture of the developed computing web server http://cmb.sao.ru allowing to synthesize the maps of extended radiation on the full sphere from the spherical harmonics in the GLESP pixelization grid, smooth them with the power beam pattern with various angular resolutions in the multipole space, and identify regions of the sky with given coordinates. We describe the server access and administration systems as well as the technique constructing the sky region maps, organized in Python in the Django web-application development framework.
Extended performance solar electric propulsion thrust system design
NASA Technical Reports Server (NTRS)
Cake, J. E.; Hawthorne, E. I.; Poeschel, R. L.
1978-01-01
A thrust system design has been established for an extended performance technology, 6.4 kW, 4800 sec specific impulse ion thruster. The configuration is comprised of ten thrusters configured with a power management and control subsystem in a modular thrust system design. The system design approach is an adaptation of that previously established for the baseline technology 2.7 kW, 3000 sec specific impulse ion thruster. The power management and control subsystem design includes a combination of individual electronics for each thruster and a set of electronics with redundancy that are common to all thrusters. The thermal dissipation from all electronics is removed with a common heat pipe/radiator assembly.
Particle deposition due to turbulent diffusion in the upper respiratory system
NASA Technical Reports Server (NTRS)
Hamill, P.
1979-01-01
Aerosol deposition in the upper respiratory system (trachea to segmental bronchi) is considered and the importance of turbulent diffusion as a deposition mechanism is evaluated. It is demonstrated that for large particles (diameter greater than about 5 microns), turbulent diffusion is the dominant deposition mechanism in the trachea. Conditions under which turbulent diffusion may be important in successive generations of the pulmonary system are determined. The probability of particle deposition is compared with probabilities of deposition, as determined by the equations generally used in regional deposition models. The analysis is theoretical; no new experimental data is presented.
Performance characteristics of a scanning laser imaging system through atmospheric turbulence
NASA Astrophysics Data System (ADS)
Nairat, Mazen; Voelz, David
2012-10-01
The transverse angular (spatial) imaging performance of a laser imaging system through atmospheric turbulence is characterized and described in a practical sense. The system is assumed to scan a far-field scene with a collimated Gaussian beam truncated by a circular aperture and a single channel receiver records the returns. The system point spread function is defined as the average beam profile at the scene and the half-angle beam spread is used to characterize the point spread function. A system modulation transfer function is defined that includes the effects of beam diffraction and turbulence. Spatial sampling of the scene is also considered. A normalized resolution metric (Strehl ratio) is applied to investigate the effects of sampling, beam size, turbulence, and beam truncation. The analysis indicates that resolution will be reduced by more than 90% in homogenous turbulence when the beam waist size is on the order of the atmospheric coherence length. Consistency with conventional imaging performance is discussed.
The report gives results of an analysis of flue gas desulfurization by a turbulent contact absorber (TCA) employing lime slurry, including the development of performance equations for the scrubber-hold tank recycle system. Performance characteristics investigated include pressure...
Transient dynamics and nonlinear stability of spatially extended systems.
Handel, Andreas; Grigoriev, Roman O
2006-09-01
As studies of various systems have shown, the sole focus on the eigenvalues in a linear stability analysis can be misleading, especially when the dynamics of disturbances is characterized by strong transient growth. The aim of this paper is to extend the generalized stability analysis, in the context of spatially extended systems, by examining the role of the nonlinear terms in the destabilization process. The critical noise level leading to destabilization is often found to scale as a power of the magnitude of transient amplification. In what follows we show that the power law exponent sensitively depends on the type of nonlinear terms and their potential for generating self-sustaining noise amplification cycles (bootstrapping). We find, however, that the exponents are not universal and also depend on the more subtle details of the transient dynamics. We also show that the basin of attraction of a spatially uniform state is bounded by the stable manifold(s) of nearby saddle(s) which play a major role in the transition. PMID:17025738
Limits of localized control in extended nonlinear systems
NASA Astrophysics Data System (ADS)
Handel, Andreas
We investigate the limits of localized linear control in spatially extended, nonlinear systems. Spatially extended, nonlinear systems can be found in virtually every field of engineering and science. An important category of such systems are fluid flows. Fluid flows play an important role in many commercial applications, for instance in the chemical, pharmaceutical and food-processing industries. Other important fluid flows include air- or water flows around cars, planes or ships. In all these systems, it is highly desirable to control the flow of the respective fluid. For instance control of the air flow around an airplane or car leads to better fuel-economy and reduced noise production. Usually, it is impossible to apply control everywhere. Consider an airplane: It would not be feasibly to cover the whole body of the plane with control units. Instead, one can place the control units at localized regions, such as points along the edge of the wings, spaced as far apart from each other as possible. These considerations lead to an important question: For a given system, what is the minimum number of localized controllers that still ensures successful control? Too few controllers will not achieve control, while using too many leads to unnecessary expenses and wastes resources. To answer this question, we study localized control in a class of model equations. These model equations are good representations of many real fluid flows. Using these equations, we show how one can design localized control that renders the system stable. We study the properties of the control and derive several expressions that allow us to determine the limits of successful control. We show how the number of controllers that are needed for successful control depends on the size and type of the system, as well as the way control is implemented. We find that especially the nonlinearities and the amount of noise present in the system play a crucial role. This analysis allows us to determine under
Modelling atmospheric turbulence effects on ground-based telescope systems
Bradford, L.W.; Flatte, S.M.; Max, C.E.
1993-09-30
Questions still exist concerning the appropriate model for turbulence- induced phase fluctuations seen in ground-based telescopes. Bester et al. used a particular observable (slope of the Allan variance) with an infrared interferometer in an attempt to distinguish models. The authors have calculated that observable for Kolmogorov and {open_quotes}random walk{close_quotes} models with a variety of outer scales and altitude-dependent turbulence and wind velocity. The authors have found that clear distinction between models requires good data on the vertical distribution of wind and turbulence. Furthermore, measurements at time separations of order 60 s are necessary to distinguish the {open_quotes}random walk{close_quotes} model from the Kolmogorov model.
An active control system for the turbulent boundary layer
NASA Astrophysics Data System (ADS)
Lew, James
This thesis presents the development process and the experimental results of a system constructed to apply real-time control to the structures of the turbulent boundary layer region in order to reduce surface shear stress. The system is composed of three main components: an array of MEMS surface shear stress, tauw sensors; a MEMS flap actuator; and a control logic which integrates the hardware components together into a closed system. The objective of this system is to reduce the stress contained in streak-like regions of high tauw. The sensor array, used to image the tauw distribution, is an extension of the thermal based tauw sensor developed by Jiang. Numerous studies have been performed using this device, the results of which have validated its performance. For this study, a new temperature compensation methodology, based on the surface temperature of the sensor chip, was employed in order to account for possible temperature variations at the wall surface. The actuator, a pneumatically driven flap, is developed as part of the present research. The device is, in essence, a 3 mm x 1 mm cantilever beam that sits on top of an inflatable diaphragm and is capable of actuation frequencies of over 200 Hz and amplitudes of over .11 mm. When it is oscillated in the open loop mode, the effect over one cycle of motion is an average reduction by as much as 2.5% in tauw in the region immediately downstream. A neural network is employed to identify the streak-like regions of interest. Results have shown that this network is successful in identifying the streak-like regions of interest. The control logic employs this network in a predictive, feed-forward scheme to determine the appropriate actuator response. Offline studies have shown that under optimal conditions, the signature of the streak-like regions can be eliminated. Online results conform well to the offline predictions. While unable to achieve the optimal conditions, online experiments show that the system is capable
Extending TOPS: Knowledge Management System for Anomaly Detection and Analysis
NASA Astrophysics Data System (ADS)
Votava, P.; Nemani, R. R.; Michaelis, A.
2009-12-01
Terrestrial Observation and Prediction System (TOPS) is a flexible modeling software system that integrates ecosystem models with frequent satellite and surface weather observations to produce ecosystem nowcasts (assessments of current conditions) and forecasts useful in natural resources management, public health and disaster management. We have been extending the Terrestrial Observation and Prediction System (TOPS) to include capability for automated anomaly detection and analysis of both on-line (streaming) and off-line data. While there are large numbers of anomaly detection algorithms for multivariate datasets, we are extending this capability beyond the anomaly detection itself and towards an automated analysis that would discover the possible causes of the anomalies. There are often indirect connections between datasets that manifest themselves during occurrence of external events and rather than searching exhaustively throughout all the datasets, our goal is to capture this knowledge and provide it to the system during automated analysis. This results in more efficient processing. Since we don’t need to process all the datasets using the original anomaly detection algorithms, which is often compute intensive; we achieve data reduction as we don’t need to store all the datasets in order to search for possible connections but we can download selected data on-demand based on our analysis. For example, an anomaly observed in vegetation Net Primary Production (NPP) can relate to an anomaly in vegetation Leaf Area Index (LAI), which is a fairly direct connection, as LAI is one of the inputs for NPP, however the change in LAI could be caused by a fire event, which is not directly connected with NPP. Because we are able to capture this knowledge we can analyze fire datasets and if there is a match with the NPP anomaly, we can infer that a fire is a likely cause. The knowledge is captured using OWL ontology language, where connections are defined in a schema
Linear versus nonlinear response of a forced wave turbulence system.
Cadot, Olivier; Touzé, Cyril; Boudaoud, Arezki
2010-10-01
A vibrating plate is set into a chaotic state of wave turbulence by a forcing having periodic and random components. Both components are weighted in order to explore continuously intermediate forcing from the periodic to the random one, but keeping constant its rms value. The transverse velocity of the plate is measured at the application point of the force. It is found that whatever the detail of the forcing is, the velocity spectra exhibit a universal cascade for frequencies larger than the forcing frequency range. In contrast, the velocity spectra strongly depend on the nature of the forcing within the range of forcing frequencies. The coherence function is used to extract the contribution of the velocity fluctuations that display a linear relationship with the forcing. The nonlinear contribution to the velocity fluctuations is found to be almost constant, about 55% of the total velocity fluctuations whatever the nature of the forcing from random to periodic. On the other hand, the nonlinear contribution to the fluctuations of the injected power depends on the nature of the forcing; it is significantly larger for the periodic forcing (60%) and decreases continuously as the randomness is increased, reaching a value of 40% for the pure random forcing. For all the cases of intermediate forcing from random to periodic, a simple model of the velocity response recovers in a fairly good agreement the probability density function of the injected power. The consequence of the existence of a linear-response component is discussed in the context of the fluctuation-dissipation theorem validation in experiments of out-of-equilibrium systems. PMID:21230369
He, Ping; Basu, Sukanta
2016-05-01
In Wyngaard et al., 1971, a simple model was proposed to estimate Cn2 in the atmospheric surface layer, which only requires routine meteorological information (wind speed and temperature) as input from two heights. This Cn2 model is known to have satisfactory performance in unstable conditions; however, in stable conditions, the model only covers a relatively short range of atmospheric stabilities which significantly limits its applicability during nighttime. To mitigate this limitation, in this study we construct a new Cn2 model utilizing an extensive turbulence dataset generated by a high-fidelity numerical modeling approach (known as direct numerical simulation). The most distinguishing feature of this new Cn2 model is that it covers a wide range of atmospheric stabilities including the strongly stratified (very stable) conditions. To validate this model, approximately four weeks of Cn2 data collected at the Mauna Loa Observatory, Hawaii are used for comparison, and reasonably good agreement is found between the observed and estimated values. PMID:27137570
Stochastic thermodynamics of reactive systems: An extended local equilibrium approach
NASA Astrophysics Data System (ADS)
De Decker, Yannick; Derivaux, Jean-François; Nicolis, Grégoire
2016-04-01
The recently developed extended local equilibrium approach to stochastic thermodynamics is applied to reactive systems. The properties of the fluctuating entropy and entropy production are analyzed for general linear and for prototypical nonlinear kinetic processes. It is shown that nonlinear kinetics typically induces deviations of the mean entropy production from its value in the deterministic (mean-field) limit. The probability distributions around the mean are derived and shown to qualitatively differ in thermodynamic equilibrium, under nonequilibrium conditions and in the vicinity of criticalities associated to the onset of multistability. In each case large deviation-type properties are shown to hold. The results are compared with those of alternative approaches developed in the literature.
Extended depth of field system for long distance iris acquisition
NASA Astrophysics Data System (ADS)
Chen, Yuan-Lin; Hsieh, Sheng-Hsun; Hung, Kuo-En; Yang, Shi-Wen; Li, Yung-Hui; Tien, Chung-Hao
2012-10-01
Using biometric signatures for identity recognition has been practiced for centuries. Recently, iris recognition system attracts much attention due to its high accuracy and high stability. The texture feature of iris provides a signature that is unique for each subject. Currently most commercial iris recognition systems acquire images in less than 50 cm, which is a serious constraint that needs to be broken if we want to use it for airport access or entrance that requires high turn-over rate . In order to capture the iris patterns from a distance, in this study, we developed a telephoto imaging system with image processing techniques. By using the cubic phase mask positioned front of the camera, the point spread function was kept constant over a wide range of defocus. With adequate decoding filter, the blurred image was restored, where the working distance between the subject and the camera can be achieved over 3m associated with 500mm focal length and aperture F/6.3. The simulation and experimental results validated the proposed scheme, where the depth of focus of iris camera was triply extended over the traditional optics, while keeping sufficient recognition accuracy.
Modeling the pharmacokinetics of extended release pharmaceutical systems
NASA Astrophysics Data System (ADS)
di Muria, Michela; Lamberti, Gaetano; Titomanlio, Giuseppe
2009-03-01
The pharmacokinetic (PK) models predict the hematic concentration of drugs after the administration. In compartment modeling, the body is described by a set of interconnected “vessels” or “compartments”; the modeling consisting of transient mass balances. Usually the orally administered drugs were considered as immediately available: this cannot describe the administration of extended-release systems. In this work we added to the traditional compartment models the ability to account for a delay in administration, relating this delay to in vitro data. Firstly, the method was validated, applying the model to the dosage of nicotine by chewing-gum; the model was tuned by in vitro/in vivo data of drugs (divalproex-sodium and diltiazem) with medium-rate release kinetics, then it was applied in describing in vivo evolutions due to the assumption of fast- and slow-release systems. The model reveals itself predictive, the same of a Level A in vitro/in vivo correlation, but being physically based, it is preferable to a purely statistical method.
Recent insights into instability and transition to turbulence in open-flow systems
NASA Technical Reports Server (NTRS)
Morkovin, Mark V.
1988-01-01
Roads to turbulence in open-flow shear layers are interpreted as sequences of often competing instabilities. These correspond to primary and higher order restructurings of vorticity distributions which culminate in convected spatial disorder (with some spatial coherence on the scale of the shear layer) traditionally called turbulence. Attempts are made to interpret these phenomena in terms of concepts of convective and global instabilities on one hand, and of chaos and strange attractors on the other. The first is fruitful, and together with a review of mechanisms of receptivity provides a unifying approach to understanding and estimating transition to turbulence. In contrast, current evidence indicates that concepts of chaos are unlikely to help in predicting transition in open-flow systems. Furthermore, a distinction should apparently be made between temporal chaos and the convected spatial disorder of turbulence past Reynolds numbers where boundary layers and separated shear layers are formed.
Turbulent Motion in Ethyl Acetate-Water System
NASA Astrophysics Data System (ADS)
Ahmad, Jamil
2000-09-01
An overhead projector demonstration is described in which 4 mL of ethyl acetate is added to 10 mL of water contained in a 10-cm diameter Petri dish. Within a minute or so of the addition, image of a turbulent motion appears on the screen, at first at a few centers that eventually organize themselves in a line. The image of the line of turbulence is quite striking and resembles a moving front of dancing flames. The phenomenon arises because as ethyl acetate evaporates from the region where it has spread in the form of a monolayer, fresh material gets transferred to take its place. Because of the viscosity effects, this transfer of the surface film causes movement in the bulk of the material as well, making the process visible.
Sapsis, Themistoklis P; Majda, Andrew J
2013-08-20
A framework for low-order predictive statistical modeling and uncertainty quantification in turbulent dynamical systems is developed here. These reduced-order, modified quasilinear Gaussian (ROMQG) algorithms apply to turbulent dynamical systems in which there is significant linear instability or linear nonnormal dynamics in the unperturbed system and energy-conserving nonlinear interactions that transfer energy from the unstable modes to the stable modes where dissipation occurs, resulting in a statistical steady state; such turbulent dynamical systems are ubiquitous in geophysical and engineering turbulence. The ROMQG method involves constructing a low-order, nonlinear, dynamical system for the mean and covariance statistics in the reduced subspace that has the unperturbed statistics as a stable fixed point and optimally incorporates the indirect effect of non-Gaussian third-order statistics for the unperturbed system in a systematic calibration stage. This calibration procedure is achieved through information involving only the mean and covariance statistics for the unperturbed equilibrium. The performance of the ROMQG algorithm is assessed on two stringent test cases: the 40-mode Lorenz 96 model mimicking midlatitude atmospheric turbulence and two-layer baroclinic models for high-latitude ocean turbulence with over 125,000 degrees of freedom. In the Lorenz 96 model, the ROMQG algorithm with just a single mode captures the transient response to random or deterministic forcing. For the baroclinic ocean turbulence models, the inexpensive ROMQG algorithm with 252 modes, less than 0.2% of the total, captures the nonlinear response of the energy, the heat flux, and even the one-dimensional energy and heat flux spectra. PMID:23918398
Competition between shock and turbulent heating in coronal loop system
NASA Astrophysics Data System (ADS)
Matsumoto, Takuma
2016-08-01
2.5-dimensional magnetohydrodynamic (MHD) simulations are performed with high spatial resolution in order to distinguish between competing models of the coronal heating problem. A single coronal loop powered by Alfvén waves excited in the photosphere is the target of the present study. The coronal structure is reproduced in our simulations as a natural consequence of the transportation and dissipation of Alfvén waves. Further, the coronal structure is maintained as the spatial resolution is changed from 25 to 3 km, although the temperature at the loop top increases with the spatial resolution. The heating mechanisms change gradually across the magnetic canopy at a height of 4 Mm. Below the magnetic canopy, both the shock and the MHD turbulence are dominant heating processes. Above the magnetic canopy, the shock heating rate reduces to less than 10 % of the total heating rate while the MHD turbulence provides significant energy to balance the radiative cooling and thermal conduction loss or gain. The importance of compressibility shown in the present study would significantly impact on the prospects of successful MHD turbulence theory in the solar chromosphere.
DARPA super resolution vision system (SRVS) robust turbulence data collection and analysis
NASA Astrophysics Data System (ADS)
Espinola, Richard L.; Leonard, Kevin R.; Thompson, Roger; Tofsted, David; D'Arcy, Sean
2014-05-01
Atmospheric turbulence degrades the range performance of military imaging systems, specifically those intended for long range, ground-to-ground target identification. The recent Defense Advanced Research Projects Agency (DARPA) Super Resolution Vision System (SRVS) program developed novel post-processing system components to mitigate turbulence effects on visible and infrared sensor systems. As part of the program, the US Army RDECOM CERDEC NVESD and the US Army Research Laboratory Computational & Information Sciences Directorate (CISD) collaborated on a field collection and atmospheric characterization of a two-handed weapon identification dataset through a diurnal cycle for a variety of ranges and sensor systems. The robust dataset is useful in developing new models and simulations of turbulence, as well for providing as a standard baseline for comparison of sensor systems in the presence of turbulence degradation and mitigation. In this paper, we describe the field collection and atmospheric characterization and present the robust dataset to the defense, sensing, and security community. In addition, we present an expanded model validation of turbulence degradation using the field collected video sequences.
The Turbulent Fragmentation Origin of Low-Mass Binary Star Systems
NASA Astrophysics Data System (ADS)
Offner, Stella; Kratter, K. M.; Matzner, C. D.; Krumholz, M. R.; Klein, R. I.
2011-01-01
Using self-gravitating, radiation-hydrodynamic simulations, we compare turbulent fragmentation and disk fragmentation as avenues for forming low-mass binary systems. We employ two dimensionless parameters to characterize the infall rate onto protostellar systems, describe disks' susceptability to fragmentation, and place limits on protostellar system multiplicity. While protostellar disks are predominatly stable in the presence of radiative feedback, purely hydrodynamic systems exhibit fundamentally different parameters and are strongly susceptible to disk fragmentation. Consequently, we find that turbulent fragmentation, occuring on thousand AU scales, is the more common mode of fragmentation and is likely responsible for producing most low-mass binary systems. Although fragmentation in young embedded protostellar disks cannot be directly imaged, turbulent fragmentation on these scales is potentially observable.
Spontaneous Charge Carrier Localization in Extended One-Dimensional Systems
NASA Astrophysics Data System (ADS)
Vlček, Vojtěch; Eisenberg, Helen R.; Steinle-Neumann, Gerd; Neuhauser, Daniel; Rabani, Eran; Baer, Roi
2016-05-01
Charge carrier localization in extended atomic systems has been described previously as being driven by disorder, point defects, or distortions of the ionic lattice. Here we show for the first time by means of first-principles computations that charge carriers can spontaneously localize due to a purely electronic effect in otherwise perfectly ordered structures. Optimally tuned range-separated density functional theory and many-body perturbation calculations within the G W approximation reveal that in trans-polyacetylene and polythiophene the hole density localizes on a length scale of several nanometers. This is due to exchange-induced translational symmetry breaking of the charge density. Ionization potentials, optical absorption peaks, excitonic binding energies, and the optimally tuned range parameter itself all become independent of polymer length as it exceeds the critical localization length. Moreover, we find that lattice disorder and the formation of a polaron result from the charge localization in contrast to the traditional view that lattice distortions precede charge localization. Our results can explain experimental findings that polarons in conjugated polymers form instantaneously after exposure to ultrafast light pulses.
Extending human proprioception to cyber-physical systems
NASA Astrophysics Data System (ADS)
Keller, Kevin; Robinson, Ethan; Dickstein, Leah; Hahn, Heidi A.; Cattaneo, Alessandro; Mascareñas, David
2016-04-01
Despite advances in computational cognition, there are many cyber-physical systems where human supervision and control is desirable. One pertinent example is the control of a robot arm, which can be found in both humanoid and commercial ground robots. Current control mechanisms require the user to look at several screens of varying perspective on the robot, then give commands through a joystick-like mechanism. This control paradigm fails to provide the human operator with an intuitive state feedback, resulting in awkward and slow behavior and underutilization of the robot's physical capabilities. To overcome this bottleneck, we introduce a new human-machine interface that extends the operator's proprioception by exploiting sensory substitution. Humans have a proprioceptive sense that provides us information on how our bodies are configured in space without having to directly observe our appendages. We constructed a wearable device with vibrating actuators on the forearm, where frequency of vibration corresponds to the spatial configuration of a robotic arm. The goal of this interface is to provide a means to communicate proprioceptive information to the teleoperator. Ultimately we will measure the change in performance (time taken to complete the task) achieved by the use of this interface.
Ohira, Yutaka
2013-04-10
We consider particle acceleration by large-scale incompressible turbulence with a length scale larger than the particle mean free path. We derive an ensemble-averaged transport equation of energetic charged particles from an extended transport equation that contains the shear acceleration. The ensemble-averaged transport equation describes particle acceleration by incompressible turbulence (turbulent shear acceleration). We find that for Kolmogorov turbulence, the turbulent shear acceleration becomes important on small scales. Moreover, using Monte Carlo simulations, we confirm that the ensemble-averaged transport equation describes the turbulent shear acceleration.
Imaging through atmospheric turbulence for laser based C-RAM systems: an analytical approach
NASA Astrophysics Data System (ADS)
Buske, Ivo; Riede, Wolfgang; Zoz, Jürgen
2013-10-01
High Energy Laser weapons (HEL) have unique attributes which distinguish them from limitations of kinetic energy weapons. HEL weapons engagement process typical starts with identifying the target and selecting the aim point on the target through a high magnification telescope. One scenario for such a HEL system is the countermeasure against rockets, artillery or mortar (RAM) objects to protect ships, camps or other infrastructure from terrorist attacks. For target identification and especially to resolve the aim point it is significant to ensure high resolution imaging of RAM objects. During the whole ballistic flight phase the knowledge about the expectable imaging quality is important to estimate and evaluate the countermeasure system performance. Hereby image quality is mainly influenced by unavoidable atmospheric turbulence. Analytical calculations have been taken to analyze and evaluate image quality parameters during an approaching RAM object. In general, Kolmogorov turbulence theory was implemented to determine atmospheric coherence length and isoplanatic angle. The image acquisition is distinguishing between long and short exposure times to characterize tip/tilt image shift and the impact of high order turbulence fluctuations. Two different observer positions are considered to show the influence of the selected sensor site. Furthermore two different turbulence strengths are investigated to point out the effect of climate or weather condition. It is well known that atmospheric turbulence degenerates image sharpness and creates blurred images. Investigations are done to estimate the effectiveness of simple tip/tilt systems or low order adaptive optics for laser based C-RAM systems.
Vorontsov, Mikhail; Riker, Jim; Carhart, Gary; Gudimetla, V S Rao; Beresnev, Leonid; Weyrauch, Thomas; Roberts, Lewis C
2009-01-01
Compensation of extended (deep) turbulence effects is one of the most challenging problems in adaptive optics (AO). In the AO approach described, the deep turbulence wave propagation regime was achieved by imaging stars at low elevation angles when image quality improvement with conventional AO was poor. These experiments were conducted at the U.S. Air Force Maui Optical and Supercomputing Site (AMOS) by using the 3.63 m telescope located on Haleakala, Maui. To enhance compensation performance we used a cascaded AO system composed of a conventional AO system based on a Shack-Hartmann wavefront sensor and a deformable mirror with 941 actuators, and an AO system based on stochastic parallel gradient descent optimization with four deformable mirrors (75 control channels). This first-time field demonstration of a cascaded AO system achieved considerably improved performance of wavefront phase aberration compensation. Image quality was improved in a repeatable way in the presence of stressing atmospheric conditions obtained by using stars at elevation angles as low as 15 degrees. PMID:19107154
Transmission analysis of CPolM-based OFDM FSO system in atmospheric turbulence
NASA Astrophysics Data System (ADS)
Su, Yuwei; Bai, Fan; Sato, Takuro
2016-06-01
In this paper, we propose to implement a consecutive polarization modulation (CPolM) scheme to transmit orthogonal frequency division multiplexing (OFDM) signal over the turbulent free-space optical (FSO) links. We analyze the fluctuation of polarization states of an optical wave while propagating through the turbulence channel of which the refractive-index property is described by Kolmogorov spectrum. The transmission performance in terms of signal-to-noise-ratio (SNR), symbol-error-ratio (SER) and outage probability of the proposed system are evaluated. The proposed system provides a more efficient way to compensate scintillation effects in a comparison with the intensity modulation (IM) based OFDM FSO system under a varying degrees of turbulence strength regimes.
A feasibility study for measuring stratospheric turbulence using metrac positioning system
NASA Technical Reports Server (NTRS)
Gage, K. S.; Jasperson, W. H.
1975-01-01
The feasibility of obtaining measurements of Lagrangian turbulence at stratospheric altitudes is demonstrated by using the METRAC System to track constant-level balloons. The basis for current estimates of diffusion coefficients are reviewed and it is pointed out that insufficient data is available upon which to base reliable estimates of vertical diffusion coefficients. It is concluded that diffusion coefficients could be directly obtained from Lagrangian turbulence measurements. The METRAC balloon tracking system is shown to possess the necessary precision in order to resolve the response of constant-level balloons to turbulence at stratospheric altitudes. A small sample of data recorded from a tropospheric tetroon flight tracked by the METRAC System is analyzed to obtain estimates of small-scale three-dimensional diffusion coefficients. It is recommended that this technique be employed to establish a climatology of diffusion coefficients and to ascertain the variation of these coefficients with altitude, season, and latitude.
Kinetic theory and turbulent discontinuities. [shock tube flow
NASA Technical Reports Server (NTRS)
Johnson, J. A., III; I, L.; Li, Y.; Ramaian, R.; Santigo, J. P.
1981-01-01
Shock tube discontinuities were used to test and extend a kinetic theory of turbulence. In shock wave and contact surface fluctuations, coherent phenomena were found which provide new support for the microscopic nonempirical approach to turbulent systems, especially those with boundary layer-like instabilities.
Intermittency of solar system plasma turbulence near Venus and Earth
NASA Astrophysics Data System (ADS)
Teodorescu, Eliza; Echim, Marius; Chang, Tom
2016-04-01
We analyze magnetic field data from Venus Express (VEX) and CLUSTER to investigate the turbulent properties of the solar wind and the Earth's and Venus' magnetosheaths. A systematic study of the PDFs (Probability Distribution Functions) of the measured magnetic fluctuations and their fourth order moments (kurtosis) reveals numerous intermittent time series. The presence of intermittency is marked by non-Gaussian PDFs with heavy wings and a scale dependent kurtosis. Higher order analyses on the scale dependence of several moment orders of the PDFs, the structure functions, along with the scaling of the kurtosis allow for a selection of scales that pertain to different scaling regimes, governed by different physics. On such sub-ranges of scales we investigate the fractal structure of fluctuations through the Rank Ordered Multifractal Analysis - ROMA (Chang and Wu, 2008). ROMA is applied to a selection of intermittent magnetic field time series in the solar wind and planetary magnetosheaths and helps to quantify the turbulence properties through the estimation of a spectrum of local Hurst exponents. Research supported by the European Community's Seventh Framework Programme (FP7/2007-2013) under grant agreement no 313038/STORM, and a grant of the Romanian Ministry of National Education, CNCS - UEFISCDI, project number PN-II-ID-PCE-2012-4-0418.
Turbine airfoil with an internal cooling system having vortex forming turbulators
Lee, Ching-Pang
2014-12-30
A turbine airfoil usable in a turbine engine and having at least one cooling system is disclosed. At least a portion of the cooling system may include one or more cooling channels having a plurality of turbulators protruding from an inner surface and positioned generally nonorthogonal and nonparallel to a longitudinal axis of the airfoil cooling channel. The configuration of turbulators may create a higher internal convective cooling potential for the blade cooling passage, thereby generating a high rate of internal convective heat transfer and attendant improvement in overall cooling performance. This translates into a reduction in cooling fluid demand and better turbine performance.
Fichtl, G.H.
1983-09-01
When designing a wind energy converison system (WECS), it may be necessary to take into account the distribution of wind across the disc of rotation. The specific engineering applications include structural strength, fatigue, and control. This wind distribution consists of two parts, namely that associated with the mean wind profile and that associated with the turbulence velocity fluctuation field. The work reported herein is aimed at the latter, namely the distribution of turbulence velocity fluctuations across the WECS disk of rotation. A theory is developed for the two-time covariance matrix for turbulence velocity vector components for wind energy conversion system (WECS) design. The theory is developed for homogeneous and iotropic turbulance with the assumption that Taylor's hypothesis is valid. The Eulerian turbulence velocity vector field is expanded about the hub of the WECS. Formulae are developed for the turbulence velocity vector component covariance matrix following the WECS blade elements. It is shown that upon specification of the turbulence energy spectrum function and the WECS rotation rate, the two-point, two-time covariance matrix of the turbulent flow relative to the WECS bladed elements is determined. This covariance matrix is represented as the sum of nonstationary and stationary contributions. Generalized power spectral methods are used to obtain two-point, double frequency power spectral density functions for the turbulent flow following the blade elements. The Dryden turbulence model is used to demonstrate the theory. A discussion of linear system response analysis is provided to show how the double frequency turbulence spectra might be used to calculate response spectra of a WECS to turbulent flow. Finally the spectrum of the component of turbulence normal to the WECS disc of rotation, following the blade elements, is compared with experimental results.
Zhang, Jiankun; Ding, Shengli; Zhai, Huili; Dang, Anhong
2014-12-29
In wireless optical communications (WOC), polarization multiplexing systems and coherent polarization systems have excellent performance and wide applications, while its state of polarization affected by atmospheric turbulence is not clearly understood. This paper focuses on the polarization fluctuations caused by atmospheric turbulence in a WOC link. Firstly, the relationship between the polarization fluctuations and the index of refraction structure parameter is introduced and the distribution of received polarization angle is obtained through theoretical derivations. Then, turbulent conditions are adjusted and measured elaborately in a wide range of scintillation indexes (SI). As a result, the root-mean-square (RMS) variation and probability distribution function (PDF) of polarization angle conforms closely to that of theoretical model. PMID:25607210
Experimental manipulation of wall turbulence: A systems approacha)
NASA Astrophysics Data System (ADS)
McKeon, B. J.; Sharma, A. S.; Jacobi, I.
2013-03-01
We review recent progress, based on the approach introduced by McKeon and Sharma [J. Fluid Mech. 658, 336-382 (2010), 10.1017/S002211201000176X], in understanding and controlling wall turbulence. The origins of this analysis partly lie in nonlinear robust control theory, but a differentiating feature is the connection with, and prediction of, state-of-the-art understanding of velocity statistics and coherent structures observed in real, high Reynolds number flows. A key component of this line of work is an experimental demonstration of the excitation of velocity response modes predicted by the theory using non-ideal, but practical, actuation at the wall. Limitations of the approach and promising directions for future development are outlined.
Laser imaging system for determination of three-dimensional scalar gradients in turbulent flames.
Karpetis, Adonios N; Settersten, Thomas B; Schefer, Robert W; Barlow, Robert S
2004-02-15
An imaging system for the measurement of three-dimensional (3D) scalar gradients in turbulent hydrocarbon flames is described. Combined line imaging of Raman scattering, Rayleigh scattering, and CO laser-induced fluorescence (LIF) allows for simultaneous single-shot line measurements of major species, temperature, mixture fraction, and a one-dimensional surrogate of scalar dissipation rate in hydrocarbon flames, while simultaneous use of two crossed, planar LIF measurements of OH allows for determination of instantaneous flame orientation. In this manner the full 3D scalar dissipation can be estimated in some regions of a turbulent flame on a single-shot basis. PMID:14971751
Solar system plasma turbulence and intermittency at the maximum and minimum of the solar cycle
NASA Astrophysics Data System (ADS)
Echim, Marius M.
2015-04-01
discuss how the exploitation of data bases produced by the FP7 project STORM contribute to developing a (virtual) laboratory for studying solar system plasma turbulence and intermittency. Research supported by the European FP7 Programme (grant agreement 313038/STORM), and a national grant CNCS -UEFISCDI, project number PN-II-ID-PCE-2012-4-0418.
On self-organizing during transition from a laminar to a turbulent flow for nonextensive systems
NASA Astrophysics Data System (ADS)
Zaripov, R. G.
2016-06-01
The evolution of parametric q-entropy and q-information divergence to the equilibrium state during spontaneous transitions and transitions from a laminar to a turbulent flow is considered as applied to nonextensive self-organizing systems. The S- and I-theorems on the variations of measures with constant mean energies are proved.
System for measuring Reynolds in a turbulently flowing fluid. [signal processing
NASA Technical Reports Server (NTRS)
Cheng, D. Y. (Inventor)
1976-01-01
A system for measuring momentum flux in a turbulently flowing fluid includes: a sensing apparatus for dynamically sensing the mainstream and the cross velocity components of the fluid, a transducer operative to provide two electrical output signals representative of the velocity components in the mainstream and in the cross direction, and signal processors to derive the Reynolds stress wave and the Reynolds stress.
Highly turbulent counterflow flames: A laboratory scale benchmark for practical systems
Coppola, Gianfilippo; Coriton, Bruno; Gomez, Alessandro
2009-09-15
We propose a highly turbulent counterflow flame as a very useful benchmark of complexity intermediate between laminar flames and practical systems. By operating in a turbulent Reynolds number regime of relevance to practical systems such as gas turbines and internal combustion engines, it retains the interaction of turbulence and chemistry of such environments, but offers several advantages including: (a) the achievement of high Reynolds numbers without pilot flames, which is particularly advantageous from a modeling standpoint; (b) control of the transition from stable flames to local extinction/reignition conditions; (c) compactness of the domain by comparison with jet flames, with obvious advantages from both a diagnostic and, especially, a computational viewpoint; and (d) the reduction or, altogether, elimination of soot formation, thanks to the high strain rates and low residence times of such a system, and the establishment of conditions of large stoichiometric mixture fraction, as required for robust flame stabilization. We demonstrate the phenomenology of such highly strained turbulent flames under conditions spanning unpremixed, partially premixed and premixed regimes. The system lends itself to the validation of DNS and other computational models. It is also well-suited for the examination of practical fuel blends - a need that is becoming more and more pressing in view of the anticipated diversification of the future fossil fuel supply. (author)
STORM: a new FP7 project devoted to solar system plasma turbulence, intermittency and multifractals
NASA Astrophysics Data System (ADS)
Echim, Marius M.
2013-04-01
In this project we investigate space plasma turbulence from in-situ data gathered over more than 15 years by spacecraft launched by the European Space Agency (ESA). By using large sets of data instead of focusing on particular events, we advance the understanding on the energy transfer, intermittent turbulence and multifractals in space plasmas. Moreover, since the data cover different phases of the solar cycle, we investigate how the features of space plasma turbulence vary with the solar activity and discriminate between effects specific to solar maximum and minimum. We use electromagnetic field and plasma data provided by three core ESA spacecraft: Ulysses, Venus Express and Cluster, as well as other solar system missions (e.g. Giotto, Cassini, Rosetta, Mars Global Surveyor). We also study the fluctuations of ground based geomagnetic time-series as a measure of the global magnetospheric state whose statistical properties may reveal trends linked to the turbulence properties observed in-situ at higher altitudes. A powerful package of nonlinear analysis methods are applied to all data sets: (i) Power Spectral Densities (PSD) and Probability Distribution Functions (PDF), (ii) higher-order methods of analysis for intermittent data, like the partition function multifractal analysis, the Rank Ordered Multifractal analysis; (iii) the wave telescope, (iv) the multi-spacecraft methods adapted to investigate anisotropic turbulence, (v) discriminating statistics for nonlinearity and nonstationarity. The expertise of the Consortium members is complementary and therefore the synergy within them provides a large spectrum of techniques and models, never applied in a coherent approach over the same datasets. STORM is expected to make advancements in understanding and modeling space plasma turbulence in the solar system and to add value to existing data bases collected from decades by space missions of the major national and international space agencies, in particular by the
Extending quantum control of time-independent systems to time-dependent systems
Wang Zhenyu; Liu Renbao
2011-06-15
We establish that if a scheme can control a time-independent system arbitrarily coupled to a generic finite bath over a short period of time T with control precision O(T{sup N+1}), it can also realize the control with the same order of precision on smoothly time-dependent systems. This result extends the validity of various universal dynamical control schemes to arbitrary analytically time-dependent systems.
Applicability of Mixing Length Theory to a Turbulent Vortex System
NASA Technical Reports Server (NTRS)
Ragsdale, Robert G.
1961-01-01
The ability of mixing length theory to correlate vortex data is evaluated. Expressions are derived for eddy diffusivity by applying the techniques of von Karman and Prandtl which have been established for pipe flow. Total and static pressures were measured from the outer radius to the exhaust-nozzle radius of a vortex generator for a range of mass flows. These data are combined with Navier-Stokes solutions for this region of a compressible vortex to determine turbulent Reynolds numbers. The Reynolds number is related to Prandtl and Karman functions for various assumed boundary conditions, and the experimental data are used to determine the usefulness of these expressions. The following conclusions were reached: (1) Mixing length functions developed by applying von Karman's similarity hypothesis to vortex motion correlate the data better than do Prandtl functions obtained with the assumption that mixing length is proportional to radius. (2) Some of the expressions developed do not adequately represent the experimental data. (3) The data are correlated with acceptable scatter by evaluating the fluid radial inertia at the outer boundary and the shear stress at the inner boundary. The universal constant K was found to be 0.04 to 0.08, rather than the value of 0.4 which is accepted for rectilinear flow. (4) The data are best correlated by a modified Karman expression which includes an effect of radial inertia, as well as shear stress, on eddy diffusivity.
Modeling Compressed Turbulence
Israel, Daniel M.
2012-07-13
From ICE to ICF, the effect of mean compression or expansion is important for predicting the state of the turbulence. When developing combustion models, we would like to know the mix state of the reacting species. This involves density and concentration fluctuations. To date, research has focused on the effect of compression on the turbulent kinetic energy. The current work provides constraints to help development and calibration for models of species mixing effects in compressed turbulence. The Cambon, et al., re-scaling has been extended to buoyancy driven turbulence, including the fluctuating density, concentration, and temperature equations. The new scalings give us helpful constraints for developing and validating RANS turbulence models.
NASA Astrophysics Data System (ADS)
Bernotas, Marius P.; Nelson, Charles
2016-05-01
The Weibull and Exponentiated Weibull probability density functions have been examined for the free space regime using heuristically derived shape and scale parameters. This paper extends current literature to the underwater channel and explores use of experimentally derived parameters. Data gathered in a short range underwater channel emulator was analyzed using a nonlinear curve fitting methodology to optimize the scale and shape parameters of the PDFs. This method provides insight into the scaled effects of underwater optical turbulence on a long range link, and may yield a general set of equations for determining the PDF for an underwater optical link.
Tensoral: A system for post-processing turbulence simulation data
NASA Technical Reports Server (NTRS)
Dresselhaus, Eliot
1993-01-01
Many computer simulations in engineering and science -- and especially in computational fluid dynamics (CFD) -- produce huge quantities of numerical data. These data are often so large as to make even relatively simple post-processing of this data unwieldy. The data, once computed and quality-assured, is most likely analyzed by only a few people. As a result, much useful numerical data is under-utilized. Since future state-of-the-art simulations will produce even larger datasets, will use more complex flow geometries, and will be performed on more complex supercomputers, data management issues will become increasingly cumbersome. My goal is to provide software which will automate the present and future task of managing and post-processing large turbulence datasets. My research has focused on the development of these software tools -- specifically, through the development of a very high-level language called 'Tensoral'. The ultimate goal of Tensoral is to convert high-level mathematical expressions (tensor algebra, calculus, and statistics) into efficient low-level programs which numerically calculate these expressions given simulation datasets. This approach to the database and post-processing problem has several advantages. Using Tensoral the numerical and data management details of a simulation are shielded from the concerns of the end user. This shielding is carried out without sacrificing post-processor efficiency and robustness. Another advantage of Tensoral is that its very high-level nature lends itself to portability across a wide variety of computing (and supercomputing) platforms. This is especially important considering the rapidity of changes in supercomputing hardware.
Turbulent anomalous transport and anisotropic electron heating in a return current system
Lee, Kuang Wu; Buechner, Joerg
2011-02-15
Anisotropic electron heating due to self-generated electromagnetic turbulences is observed in collisionless return current plasmas. The corresponding energy conversion, electron heating, and associated anomalous momentum transport are investigated by means of a two-dimensional electromagnetic particle-in-cell simulation code. The return current model consists of two counterstreaming electron beams with different temperatures and a stationary ion background. First, a general multifluid dispersion analyzer is presented in a clear matrix form that allows to study electron streaming instabilities. The numerical simulation confirms the predicted electrostatic electron-electron acoustic instability. Generating electromagnetic waves, the system evolves into a nonlinear stage. As a result, the electron drifts are slowed down due to turbulence-induced anomalous momentum exchange. Localized electric and magnetic field fluctuations play major roles in the energy conversion. Perpendicular electron heating follows the growth of magnetic field perturbations and the slowing of the electron drifts. Parallel and perpendicular electron heating occurs at different time scales. It is shown that the longer lasting perpendicular electron heating is caused by preheated parallel electron flows. The deflection of the preheated parallel electron flows in the localized turbulences, which is essentially a two-dimensional effect, leads to perpendicular electron heating even after the saturation of parallel electron heating. We conclude that the self-generated magnetic turbulence dominates the anomalous transport process in the late stage of return current system evolution.
The Formation of Low-mass Binary Star Systems Via Turbulent Fragmentation
NASA Astrophysics Data System (ADS)
Offner, Stella S. R.; Kratter, Kaitlin M.; Matzner, Christopher D.; Krumholz, Mark R.; Klein, Richard I.
2010-12-01
We characterize the infall rate onto protostellar systems forming in self-gravitating radiation-hydrodynamics simulations. Using two dimensionless parameters to determine the disks' susceptibility to gravitational fragmentation, we infer limits on protostellar system multiplicity and the mechanism of binary formation. We show that these parameters give robust predictions even in the case of marginally resolved protostellar disks. We find that protostellar systems with radiation feedback predominately form binaries via turbulent fragmentation, not disk instability, and predict that turbulent fragmentation is the dominant channel for binary formation for low-mass stars. We clearly demonstrate that systems forming in simulations including radiative feedback have fundamentally different parameters than those in purely hydrodynamics simulations.
The Tremblay-Turbiner-Winternitz system as extended Hamiltonian
NASA Astrophysics Data System (ADS)
Chanu, Claudia Maria; Degiovanni, Luca; Rastelli, Giovanni
2014-12-01
We generalize the idea of "extension of Hamiltonian systems"—developed in a series of previous articles—which allows the explicit construction of Hamiltonian systems with additional non-trivial polynomial first integrals of arbitrarily high degree, as well as the determination of new superintegrable systems from old ones. The present generalization, that we call "modified extension of Hamiltonian systems," produces the third independent first integral for the (complete) Tremblay-Turbiner-Winternitz system, as well as for the caged anisotropic oscillator in dimension two.
Wake Turbulence Mitigation for Departures (WTMD) Prototype System - Software Design Document
NASA Technical Reports Server (NTRS)
Sturdy, James L.
2008-01-01
This document describes the software design of a prototype Wake Turbulence Mitigation for Departures (WTMD) system that was evaluated in shadow mode operation at the Saint Louis (KSTL) and Houston (KIAH) airports. This document describes the software that provides the system framework, communications, user displays, and hosts the Wind Forecasting Algorithm (WFA) software developed by the M.I.T. Lincoln Laboratory (MIT-LL). The WFA algorithms and software are described in a separate document produced by MIT-LL.
Renormalized perturbation theory - Vlasov-Poisson system, weak turbulence limit, and gyrokinetics
NASA Astrophysics Data System (ADS)
Zhang, Y. Z.; Mahadjan, S. M.
1988-10-01
The self-consistency of the renormalized perturbation theory of Zhang and Mahajan (1985) is demonstrated by applying it to the Vlasov-Poisson system and showing that the theory has the correct weak turbulence limit. Energy conservation is proved to arbitrary high order for the electrostatic drift waves. The theory is applied to derive renormalized equations for a low-beta gyrokinetic system. Comparison of this theory with other current theories is presented.
Vorontsov, Mikhail; Filimonov, Grigory; Ovchinnikov, Vladimir; Polnau, Ernst; Lachinova, Svetlana; Weyrauch, Thomas; Mangano, Joseph
2016-05-20
The performance of two prominent laser beam projection system types is analyzed through wave-optics numerical simulations for various atmospheric turbulence conditions, propagation distances, and adaptive optics (AO) mitigation techniques. Comparisons are made between different configurations of both a conventional beam director (BD) using a monolithic-optics-based Cassegrain telescope and a fiber-array BD that uses an array of densely packed fiber collimators. The BD systems considered have equal input power and aperture diameters. The projected laser beam power inside the Airy size disk at the target plane is used as the performance metric. For the fiber-array system, both incoherent and coherent beam combining regimes are considered. We also present preliminary results of side-by-side atmospheric beam projection experiments over a 7-km propagation path using both the AO-enhanced beam projection system with a Cassegrain telescope and the coherent fiber-array BD composed of 21 densely packed fiber collimators. Both wave-optics numerical simulation and experimental results demonstrate that, for similar system architectures and turbulence conditions, coherent fiber-array systems are more efficient in mitigation of atmospheric turbulence effects and generation of a hit spot of the smallest possible size on a remotely located target. PMID:27411147
Extending Fuzzy System Concepts for Control of a Vitrification Melter
Whitehouse, J.C.; Sorgel, W.; Garrison, A.; Schalkoff, R.J.
1995-08-16
Fuzzy systems provide a mathematical framework to capture uncertainty. The complete description of real, complex systems or situations often requires far more detail and information than could ever be obtained (or understood). Fuzzy approaches are an alternative technology for both system control and information processing and management. In this paper, we present the design of a fuzzy control system for a melter used in the vitrification of hazardous waste. Design issues, especially those related to melter shutdown and obtaining smooth control surfaces, are addressed. Several extensions to commonly-applied fuzzy techniques, notably adaptive defuzzification and modified rule structures are developed.
NASA Astrophysics Data System (ADS)
Rickenstorff, Carolina; Rodrigo, Jóse A.; Alieva, Tatiana
2016-04-01
Different applications such as astronomy, remote optical sensing and free space optical communications, among others, require both numerical and laboratory experimental simulations of beam propagation through turbulent atmosphere prior to an outdoor test. While rotating phase plates or hot chambers can be applied to such studies, they do not allow changing the atmospheric conditions and the propagation distance in situ. In contrast, the spatial light modulators (SLMs) are a flexible alternative for experimental turbulence simulation. In this work we consider an experimental setup comprising two SLMs for studying laser beam propagation in weak atmospheric turbulence. The changes of atmospheric conditions and propagation distances are properly achieved by the adjustment of the phase screens and the focal distances of digital lenses implemented in both SLMs. The proposed system can be completely automatized and all its elements are in fixed positions avoiding mechanical misalignment. Its design, propagation distance and atmospheric condition adjustment are provided. The setup performance is verified by numerical simulation of Gaussian beam propagation in the weak turbulence regime. The obtained parameters: scintillation index, beam wander and spreading are compared to their theoretical counterparts for different propagation distances and atmospheric conditions.
Modelling the pressure-strain correlation of turbulence - An invariant dynamical systems approach
NASA Technical Reports Server (NTRS)
Speziale, Charles G.; Sarkar, Sutanu; Gatski, Thomas B.
1991-01-01
The modeling of the pressure-strain correlation of turbulence is examined from a basic theoretical standpoint with a view toward developing improved second-order closure models. Invariance considerations along with elementary dynamical systems theory are used in the analysis of the standard hierarchy of closure models. In these commonly used models, the pressure-strain correlation is assumed to be a linear function of the mean velocity gradients with coefficients that depend algebraically on the anisotropy tensor. It is proven that for plane homogeneous turbulent flows the equilibrium structure of this hierarchy of models is encapsulated by a relatively simple model which is only quadratically nonlinear in the anisotropy tensor. This new quadratic model - the SSG model - is shown to outperform the Launder, Reece, and Rodi model (as well as more recent models that have a considerably more complex nonlinear structure) in a variety of homogeneous turbulent flows. Some deficiencies still remain for the description of rotating turbulent shear flows that are intrinsic to this general hierarchy of models and, hence, cannot be overcome by the mere introduction of more complex nonlinearities. It is thus argued that the recent trend of adding substantially more complex nonlinear terms containing the anisotropy tensor may be of questionable value in the modeling of the pressure-strain correlation. Possible alternative approaches are discussed briefly.
Modeling the pressure-strain correlation of turbulence: An invariant dynamical systems approach
NASA Technical Reports Server (NTRS)
Speziale, Charles G.; Sarkar, Sutanu; Gatski, Thomas B.
1990-01-01
The modeling of the pressure-strain correlation of turbulence is examined from a basic theoretical standpoint with a view toward developing improved second-order closure models. Invariance considerations along with elementary dynamical systems theory are used in the analysis of the standard hierarchy of closure models. In these commonly used models, the pressure-strain correlation is assumed to be a linear function of the mean velocity gradients with coefficients that depend algebraically on the anisotropy tensor. It is proven that for plane homogeneous turbulent flows the equilibrium structure of this hierarchy of models is encapsulated by a relatively simple model which is only quadratically nonlinear in the anisotropy tensor. This new quadratic model - the SSG model - is shown to outperform the Launder, Reece, and Rodi model (as well as more recent models that have a considerably more complex nonlinear structure) in a variety of homogeneous turbulent flows. Some deficiencies still remain for the description of rotating turbulent shear flows that are intrinsic to this general hierarchy of models and, hence, cannot be overcome by the mere introduction of more complex nonlinearities. It is thus argued that the recent trend of adding substantially more complex nonlinear terms containing the anisotropy tensor may be of questionable value in the modeling of the pressure-strain correlation. Possible alternative approaches are discussed briefly.
SERT 2 1979 extended flight thruster system performance
NASA Technical Reports Server (NTRS)
Kerslake, W. R.; Ignaczak, L. R.
1979-01-01
Steady state tests of the thruster 2 system on the SERT 2 spacecraft are presented. A direct thrust measurement was obtained for the ion thruster during operations to increase the spacecraft spin rate to maintain spacecraft attitude stability. The continued restart tests of thruster 1 and a report on the general status of all spacecraft systems including the main solar array are presented.
Percolation-based precursors of transitions in extended systems.
Rodríguez-Méndez, Víctor; Eguíluz M, Víctor M; Hernández-García, Emilio; Ramasco, José J
2016-01-01
Abrupt transitions are ubiquitous in the dynamics of complex systems. Finding precursors, i.e. early indicators of their arrival, is fundamental in many areas of science ranging from electrical engineering to climate. However, obtaining warnings of an approaching transition well in advance remains an elusive task. Here we show that a functional network, constructed from spatial correlations of the system's time series, experiences a percolation transition way before the actual system reaches a bifurcation point due to the collective phenomena leading to the global change. Concepts from percolation theory are then used to introduce early warning precursors that anticipate the system's tipping point. We illustrate the generality and versatility of our percolation-based framework with model systems experiencing different types of bifurcations and with Sea Surface Temperature time series associated to El Niño phenomenon. PMID:27412567
Blended particle methods with adaptive subspaces for filtering turbulent dynamical systems
NASA Astrophysics Data System (ADS)
Qi, Di; Majda, Andrew J.
2015-04-01
It is a major challenge throughout science and engineering to improve uncertain model predictions by utilizing noisy data sets from nature. Hybrid methods combining the advantages of traditional particle filters and the Kalman filter offer a promising direction for filtering or data assimilation in high dimensional turbulent dynamical systems. In this paper, blended particle filtering methods that exploit the physical structure of turbulent dynamical systems are developed. Non-Gaussian features of the dynamical system are captured adaptively in an evolving-in-time low dimensional subspace through particle methods, while at the same time statistics in the remaining portion of the phase space are amended by conditional Gaussian mixtures interacting with the particles. The importance of both using the adaptively evolving subspace and introducing conditional Gaussian statistics in the orthogonal part is illustrated here by simple examples. For practical implementation of the algorithms, finding the most probable distributions that characterize the statistics in the phase space as well as effective resampling strategies is discussed to handle realizability and stability issues. To test the performance of the blended algorithms, the forty dimensional Lorenz 96 system is utilized with a five dimensional subspace to run particles. The filters are tested extensively in various turbulent regimes with distinct statistics and with changing observation time frequency and both dense and sparse spatial observations. In real applications perfect dynamical models are always inaccessible considering the complexities in both modeling and computation of high dimensional turbulent system. The effects of model errors from imperfect modeling of the systems are also checked for these methods. The blended methods show uniformly high skill in both capturing non-Gaussian statistics and achieving accurate filtering results in various dynamical regimes with and without model errors.
Extended Evaluations of the Commercial Spectrometer Systems for Safeguards Applications
Duc T. Vo
1999-08-01
Safeguards applications require the best of the spectrometer system with excellent resolution, stability, and throughput. Instruments must perform well in all situations and environments. Data communication to the computer should be convenient, fast, and reliable. The software should have all the necessary tools and be easy to use. Portable systems should be small in size, lightweight, and have a long battery life. Nine commercially available spectrometer systems are tested with five different germanium detectors. Considering the performance of the Digital Signal Processors (DSP), digital-based spectroscope y may become the way of future gamma-ray spectroscopy.
Infrared Laser System for Extended Area Monitoring of Air Pollution
NASA Technical Reports Server (NTRS)
Snowman, L. R.; Gillmeister, R. J.
1971-01-01
An atmospheric pollution monitoring system using a spectrally scanning laser has been developed by the General Electric Company. This paper will report on an evaluation of a breadboard model, and will discuss applications of the concept to various ambient air monitoring situations. The system is adaptable to other tunable lasers. Operating in the middle infrared region, the system uses retroreflectors to measure average concentrations over long paths at low, safe power levels. The concept shows promise of meeting operational needs in ambient air monitoring and providing new data for atmospheric research.
Nonlinear Dynamics of Extended Hydrologic Systems over long time scales
NASA Astrophysics Data System (ADS)
Lall, Upmanu
2014-05-01
We often view our knowledge of hydrology and hence of nature as intransient, at least over the time scales over which we study processes we wish to predict and understand. Over the last few decades, this assumption has come under question, largely because of the vocal expression of a changing climate, but also the recurrent demonstration of significant land use change, both of which significantly affect the boundary conditions for terrestrial hydrology that is our forte. Most recently, the concepts of hydromorphology and social hydrology have entered the discussion, and the notion that climate and hydrology influence human action, which in turn shapes hydrology, is being recognized. Finally, as a field, we seem to be coming to the conclusion that the hydrologic system is an open system, whose boundaries evolve in time, and that the hydrologic system, at many scales, has a profound effect on the systems that drive it -- whether they be the ecological and climatic systems, or the social system. What a mess! Complexity! Unpredictability! At a certain level of abstraction, one can consider the evolution of these coupled systems with nonlinear feedbacks and ask what types of questions are relevant in terms of such a coupled evolution? What are their implications at the planetary scale? What are their implications for a subsistence farmer in an arid landscape who may under external influence achieve a new transient hydro-ecological equilibrium? What are the implications for the economy and power of nations? In this talk, I will try to raise some of these questions and also provide some examples with very simple dynamical systems that suggest ways of thinking about some practical issues of feedback across climate, hydrology and human behavior.
NASA Technical Reports Server (NTRS)
1971-01-01
A preliminary plan and procedure are presented for conducting an extended manned test program for a regenerative life support system. Emphasis will be placed on elements associated with long-term system operation and long-term uninterrupted crew confinement.
Extending NASA's SPICE ancillary information system to meet future mission needs
NASA Technical Reports Server (NTRS)
Acton, C.; Bachman, N.; Elson, L.; Semenov, B.; Turner, F.; Wright, E.
2002-01-01
This paper summarizes the architecture, capabilities, characteristics and uses of the current SPICE ancillary information system, and then outlines plans and ideas for how this system can be extended to meet future space mission requirements.
Small-scale universality in fluid turbulence
Schumacher, Jörg; Scheel, Janet D.; Krasnov, Dmitry; Donzis, Diego A.; Yakhot, Victor; Sreenivasan, Katepalli R.
2014-01-01
Turbulent flows in nature and technology possess a range of scales. The largest scales carry the memory of the physical system in which a flow is embedded. One challenge is to unravel the universal statistical properties that all turbulent flows share despite their different large-scale driving mechanisms or their particular flow geometries. In the present work, we study three turbulent flows of systematically increasing complexity. These are homogeneous and isotropic turbulence in a periodic box, turbulent shear flow between two parallel walls, and thermal convection in a closed cylindrical container. They are computed by highly resolved direct numerical simulations of the governing dynamical equations. We use these simulation data to establish two fundamental results: (i) at Reynolds numbers Re ∼ 102 the fluctuations of the velocity derivatives pass through a transition from nearly Gaussian (or slightly sub-Gaussian) to intermittent behavior that is characteristic of fully developed high Reynolds number turbulence, and (ii) beyond the transition point, the statistics of the rate of energy dissipation in all three flows obey the same Reynolds number power laws derived for homogeneous turbulence. These results allow us to claim universality of small scales even at low Reynolds numbers. Our results shed new light on the notion of when the turbulence is fully developed at the small scales without relying on the existence of an extended inertial range. PMID:25024175
Percolation-based precursors of transitions in extended systems
Rodríguez-Méndez, Víctor; Eguíluz M, Víctor M.; Hernández-García, Emilio; Ramasco, José J.
2016-01-01
Abrupt transitions are ubiquitous in the dynamics of complex systems. Finding precursors, i.e. early indicators of their arrival, is fundamental in many areas of science ranging from electrical engineering to climate. However, obtaining warnings of an approaching transition well in advance remains an elusive task. Here we show that a functional network, constructed from spatial correlations of the system’s time series, experiences a percolation transition way before the actual system reaches a bifurcation point due to the collective phenomena leading to the global change. Concepts from percolation theory are then used to introduce early warning precursors that anticipate the system’s tipping point. We illustrate the generality and versatility of our percolation-based framework with model systems experiencing different types of bifurcations and with Sea Surface Temperature time series associated to El Niño phenomenon. PMID:27412567
Percolation-based precursors of transitions in extended systems
NASA Astrophysics Data System (ADS)
Rodríguez-Méndez, Víctor; Eguíluz M, Víctor M.; Hernández-García, Emilio; Ramasco, José J.
2016-07-01
Abrupt transitions are ubiquitous in the dynamics of complex systems. Finding precursors, i.e. early indicators of their arrival, is fundamental in many areas of science ranging from electrical engineering to climate. However, obtaining warnings of an approaching transition well in advance remains an elusive task. Here we show that a functional network, constructed from spatial correlations of the system’s time series, experiences a percolation transition way before the actual system reaches a bifurcation point due to the collective phenomena leading to the global change. Concepts from percolation theory are then used to introduce early warning precursors that anticipate the system’s tipping point. We illustrate the generality and versatility of our percolation-based framework with model systems experiencing different types of bifurcations and with Sea Surface Temperature time series associated to El Niño phenomenon.
NASA Astrophysics Data System (ADS)
Kiasaleh, Kamran
2002-04-01
The performance of a free-space optical (FSO) communication system is investigated when communication is established via a short-range, turbulent optical channel. The system under investigation utilizes on-off-keying (OOK) modulation combined with direct-detection to establish a duplex communication link. It is further assumed that the optical beam obeys a Gaussian profile. The received signal is detected using a p-i-n diode which is followed by a trans-impedance amplifier (TIA), limiting amplifier, and a clock/data recovery subsystem. Furthermore, it is assumed that optical front-end provides a relatively large aperture so that the impact of turbulence is somewhat mitigated and that the channel/system parameters result in a weak turbulent condition. The performance of the proposed system for a bit error rate of 10-9 in the absence of forward error correction (FEC) is assessed in terms of probability of fade (PF), average number of fades per second (FPS), mean fade duration (MFD), mean-guard-to-mean-burst (MGMB) ratio, and mean time between fades (MTBF).
Development and implementation of a robust angle of arrival turbulence measurement system
NASA Astrophysics Data System (ADS)
Manning, Sean; Clare, Bradley A.; Grant, Kenneth J.; Mudge, Kerry A.
2015-11-01
Free space optical communications (FSOC) systems are a promising complement to existing wireless communications technologies. FSOC systems have many significant advantages over traditional radio frequency links, including high bandwidth, no spectrum licensing requirements, low-power consumption, small payloads, low probability of intercept, and greater immunity from interference or jamming. However, atmospheric turbulence (scintillation) imparts significant phase noise onto the laser beam, resulting in intensity fluctuations at the receiver. In order to develop scintillation mitigation strategies, it is necessary to monitor scintillation in parallel to the communications channel. We report on the development and implementation of a robust angle of arrival (AoA) turbulence measurement instrument that is suitable for this task. Several key data acquisition and processing techniques were designed to enhance the reliability and robustness of the scintillation measurement.
Multi-level segment analysis: definition and application in turbulent systems
NASA Astrophysics Data System (ADS)
Wang, L. P.; Huang, Y. X.
2015-06-01
For many complex systems the interaction of different scales is among the most interesting and challenging features. It seems not very successful to extract the physical properties in different scale regimes by the existing approaches, such as the structure-function and Fourier spectrum method. Fundamentally, these methods have their respective limitations, for instance scale mixing, i.e. the so-called infrared and ultraviolet effects. To make improvements in this regard, a new method, multi-level segment analysis (MSA) based on the local extrema statistics, has been developed. Benchmark (fractional Brownian motion) verifications and the important case tests (Lagrangian and two-dimensional turbulence) show that MSA can successfully reveal different scaling regimes which have remained quite controversial in turbulence research. In general the MSA method proposed here can be applied to different dynamic systems in which the concepts of multiscale and multifractality are relevant.
Active laser radar systems with stochastic electromagnetic beams in turbulent atmosphere.
Cai, Yangjian; Korotkova, Olga; Eyyuboğlu, Halil T; Baykal, Yahya
2008-09-29
Propagation of stochastic electromagnetic beams through paraxial ABCD optical systems operating through turbulent atmosphere is investigated with the help of the ABCD matrices and the generalized Huygens-Fresnel integral. In particular, the analytic formula is derived for the cross-spectral density matrix of an electromagnetic Gaussian Schell-model (EGSM) beam. We applied our analysis for the ABCD system with a single lens located on the propagation path, representing, in a particular case, the unfolded double-pass propagation scenario of active laser radar. Through a number of numerical examples we investigated the effect of local turbulence strength and lens' parameters on spectral, coherence and polarization properties of the EGSM beam. PMID:18825220
NASA Technical Reports Server (NTRS)
Frost, W.; Harper, W. L.
1975-01-01
Flow over surface obstructions can produce significantly large wind shears such that adverse flying conditions can occur for aeronautical systems (helicopters, STOL vehicles, etc.). Atmospheric flow fields resulting from a semi-elliptical surface obstruction in an otherwise horizontally homogeneous statistically stationary flow are modelled with the boundary-layer/Boussinesq-approximation of the governing equation of fluid mechanics. The turbulence kinetic energy equation is used to determine the dissipative effects of turbulent shear on the mean flow. Iso-lines of turbulence kinetic energy and turbulence intensity are plotted in the plane of the flow and highlight regions of high turbulence intensity in the stagnation zone and sharp gradients in intensity along the transition from adverse to favourable pressure gradient. Discussion of the effects of the disturbed wind field in CTOL and STOL aircraft flight path and obstruction clearance standards is given. The results indicate that closer inspection of these presently recommended standards as influenced by wind over irregular terrains is required.
System for measuring three fluctuating velocity components in a turbulently flowing fluid
NASA Technical Reports Server (NTRS)
Cheng, D. Y. (Inventor)
1977-01-01
A system is described for measuring fluid velocity in a turbulently flowing fluid including a sensing apparatus for dynamically sensing the mainstream and two orthogonal cross velocity components of the fluid. A transducer operative is included to provide three electrical output signals representative of the velocity components in the mainstream, and in the cross directions. Signal processors can be utilized to derive the Reynolds stress wave and the Reynolds stress.
Modular open RF architecture: extending VICTORY to RF systems
NASA Astrophysics Data System (ADS)
Melber, Adam; Dirner, Jason; Johnson, Michael
2015-05-01
Radio frequency products spanning multiple functions have become increasingly critical to the warfighter. Military use of the electromagnetic spectrum now includes communications, electronic warfare (EW), intelligence, and mission command systems. Due to the urgent needs of counterinsurgency operations, various quick reaction capabilities (QRCs) have been fielded to enhance warfighter capability. Although these QRCs were highly successfully in their respective missions, they were designed independently resulting in significant challenges when integrated on a common platform. This paper discusses how the Modular Open RF Architecture (MORA) addresses these challenges by defining an open architecture for multifunction missions that decomposes monolithic radio systems into high-level components with welldefined functions and interfaces. The functional decomposition maximizes hardware sharing while minimizing added complexity and cost due to modularization. MORA achieves significant size, weight and power (SWaP) savings by allowing hardware such as power amplifiers and antennas to be shared across systems. By separating signal conditioning from the processing that implements the actual radio application, MORA exposes previously inaccessible architecture points, providing system integrators with the flexibility to insert third-party capabilities to address technical challenges and emerging requirements. MORA leverages the Vehicular Integration for Command, Control, Communication, Computers, Intelligence, Surveillance, and Reconnaissance (C4ISR)/EW Interoperability (VICTORY) framework. This paper concludes by discussing how MORA, VICTORY and other standards such as OpenVPX are being leveraged by the U.S. Army Research, Development, and Engineering Command (RDECOM) Communications Electronics Research, Development, and Engineering Center (CERDEC) to define a converged architecture enabling rapid technology insertion, interoperability and reduced SWaP.
NASA Technical Reports Server (NTRS)
Tchen, C. M.
1986-01-01
Theoretical and numerical works in atmospheric turbulence have used the Navier-Stokes fluid equations exclusively for describing large-scale motions. Controversy over the existence of an average temperature gradient for the very large eddies in the atmosphere suggested that a new theoretical basis for describing large-scale turbulence was necessary. A new soliton formalism as a fluid analogue that generalizes the Schrodinger equation and the Zakharov equations has been developed. This formalism, processing all the nonlinearities including those from modulation provided by the density fluctuations and from convection due to the emission of finite sound waves by velocity fluctuations, treats large-scale turbulence as coalescing and colliding solitons. The new soliton system describes large-scale instabilities more explicitly than the Navier-Stokes system because it has a nonlinearity of the gradient type, while the Navier-Stokes has a nonlinearity of the non-gradient type. The forced Schrodinger equation for strong fluctuations describes the micro-hydrodynamical state of soliton turbulence and is valid for large-scale turbulence in fluids and plasmas where internal waves can interact with velocity fluctuations.
Extended atmospheres of comets and outer planet-satellite systems
NASA Technical Reports Server (NTRS)
Smyth, William H.; Marconi, Max L.
1992-01-01
For the hydrogen coma of comet P/Halley, both a Lyman-alpha image and extensive Lyman-alpha scan data obtained by the Pioneer Venus Orbiter Ultraviolet spectrometer as well as H-alpha ground-based spectral observations obtained by the University of Wisconsin Space Physics Group were successfully interpreted and analyzed with our Monte Carlo particle trajectory model. The excellent fit of the model and the Halley data and the water production rate determined near perihelion (9 Feb. 1986) from 13 Dec. 1985 to 13 Jan. 1986 and from 1 Feb. to 7 Mar. 1986 are discussed. Studies for the circumplanetary distribution of atomic hydrogen in the Saturn and Neptune systems were undertaken for escape of H atoms from Titan and Triton, respectively. The discovery of a new mechanism which can dramatically change the normal cylindrically symmetric distribution of hydrogen about the planet is discussed. The implications for the Titan-Saturn and Triton-Neptune are summarized.
Linear optical coherence tomography system with extended measurement range.
Koch, Peter; Hellemanns, Volker; Hüttmann, Gereon
2006-10-01
Optical coherence tomography (OCT) sensors traditionally use scanning optical delay lines with moving parts and a single detector. OCT systems with a linear detector array (linear OCT or L-OCT) are simple and robust, but a detector with approximately 10,000 pixels is needed for an imaging depth of 2mm, which is necessary for most biomedical applications. We present a new optical setup for L-OCT with an increased measurement range. An additional grating performs a reduction of the spatial frequencies of the fringe pattern on the detector without loss in the signal-to-noise ratio, so the signal can be sampled with a minimal number of pixels. The theory for this approach is addressed and the first measurements are presented. PMID:16969410
Nonimaging active system determination of target shape through turbulent medium
NASA Astrophysics Data System (ADS)
Chandler, Susan M.; Lukesh, Gordon W.
2001-01-01
Image reconstruction techniques for atmospheric applications often work best with an initial estimate of the object support. This paper examines the ability of a non-imaging laser pointing system to obtain an estimate of target size and shape based on the statistics of the return signal. Fundamental limits on system pointing, such as the tracking errors, corrupt a simple raster scan that would provide gross object shape form the convolution of the far-field pattern with the target. Using techniques developed previously for the estimation of pointing performance, it is possible to distinguish between simple shapes such as bars, circles and T's based on the statistics of the received time signal. Simulated space objects, such as those illuminated during field experiments, may also be distinguished.
Effects of turbulence on the geodynamic laser ranging system
NASA Technical Reports Server (NTRS)
Churnside, James H.
1993-01-01
The Geodynamic Laser Ranging System (GLRS) is one of several instruments being developed by the National Aeronautics and Space Administration (NASA) for implementation as part of the Earth Observing System in the mid-1990s (Cohen et al., 1987; Bruno et al., 1988). It consists of a laser transmitter and receiver in space and an array of retroreflectors on the ground. The transmitter produces short (100 ps) pulses of light at two harmonics (0.532 and 0.355 microns) of the Nd:YAG laser. These propagate to a retroreflector on the ground and return. The receiver collects the reflected light and measures the round-trip transit time. Ranging from several angles accurately determines the position of the retroreflector, and changes in position caused by geophysical processes can be monitored.
Turbulent traveling-wave convection in a two-layer system
NASA Astrophysics Data System (ADS)
Stamp, Andrew P.; Griffiths, Ross W.
1997-04-01
When layers of salt and sugar solution are separated by a "diffusive" interface, interfacial waves are spontaneously generated by the turbulent convection once the system evolves to a critical value of the density-anomaly ratio Rρ≡βΔS/αΔT (Stamp et al., to appear in J. Fluid Mech). The waves modulate the interfacial fluxes by modifying the interface thickness and thereby organize the otherwise random convective motions into coherent large-scale circulations. In narrow rectangular channels a wide range of conditions give rise to a single wave which propagates back-and-forth, resulting in quasi-periodic reversals of tank-scale circulations. Here it is shown that in annular and equant rectangular cavities this same coupling phenomenon produces turbulent convection cells of a traveling-wave nature, coupled to large-amplitude solitary waves on the interface.
The Turbulent Origin of Outflow and Spin Misalignment in Multiple Star Systems
NASA Astrophysics Data System (ADS)
Offner, Stella S. R.; Dunham, Michael M.; Lee, Katherine I.; Arce, Héctor G.; Fielding, Drummond B.
2016-08-01
The protostellar outflows of wide-separation forming binaries frequently appear misaligned. We use magneto-hydrodynamic simulations to investigate the alignment of protostellar spin and molecular outflows for forming binary pairs. We show that the protostellar pairs, which form from turbulent fragmentation within a single parent core, have randomly oriented angular momentum. Although the pairs migrate to closer separations, their spins remain partially misaligned. We produce 12CO(2-1) synthetic observations of the simulations and characterize the outflow orientation in the emission maps. The CO-identified outflows exhibit a similar random distribution and are also statistically consistent with the observed distribution of molecular outflows. We conclude that the observed misalignment provides a clear signature of binary formation via turbulent fragmentation. The persistence of misaligned outflows and stellar spins following dynamical evolution may provide a signature of binary origins for more evolved multiple star systems.
NASA Astrophysics Data System (ADS)
Giannuzzi, M.
2014-07-01
In electronic systems the presence of bluff bodies, sharp corners and bends are the cause of flow separation and large recirculation bubbles. Since the recirculation vortices develop they encapsulate the heat from an electronic component becoming one of the major contributors of malfunction. Going in depth in this, some numerical simulations of conjugate heat transfer for a heat wall-mounted cube have been performed using the commercial CFD code scSTREAM V11 by Software Cradle Co, Ltd. It is well known that the reliability of CFD analysis depends heavily on the turbulent model employed together with the wall functions implemented. The three low- Reynolds k - epsilon turbulent models developed by Abe-Nagano-Kondoh have been validated against experimental data consisting mainly of velocity profiles and surface temperature distributions provided in literature. The performed validation shows a satisfactory agreement between the measured and simulated data. The turbulent model chosen is then used for the CFD simulation of a complex electronic system.
Extending Hydrologic Information Systems to accommodate Arctic marine observations data
NASA Astrophysics Data System (ADS)
Hersh, Eric S.; Maidment, David R.
2014-04-01
The Chukchi Sea Offshore Monitoring in Drilling Area - Chemical and Benthos (COMIDA CAB) project characterizes the biota and chemistry of the continental shelf ecosystem of a region of the Chukchi Sea to form a baseline survey of environmental conditions before drilling for oil commences. This paper describes the COMIDA CAB project data and processing methods, which provide a novel approach to data tracking and archiving from marine sampling cruises. This approach features an adaptation of the Consortium of Universities for the Advancement of Hydrologic Science. Observations Data Model for application with physical, chemical, and biological oceanographic data - a new extension of the CUAHSI Hydrologic Information System - thus bringing hydroinformatics into the oceanographic realm. Environmental sampling has been carried out by five separate scientific teams who characterize particular classes of physical, chemical and biological variables, and who each have their own methods of processing samples in their laboratories following the two sampling cruises made to the Chukchi Sea in the summers of 2009 and 2010. The results of their observations and analyses are stored in data files, mostly in Excel format, whose structure is defined differently by each scientific team. In all, the 2009 and 2010 COMIDA CAB field efforts yielded a database of 510,405 data values. Of these, 474,129 were derived from continuous in-situ data sonde profiles and 36,276 were derived from non-sonde extracted samples of the sediment, epibenthos, and water column. These data values represent 301 variables measured at 65 sites and originated from 26 different source files. The biological observations represented 519 distinct taxa. The data from these files are transformed and synthesized into a comprehensive project database in which a set of standardized descriptors of each observed data value are specified and each data value is linked to the data file from which it was created to establish a
NASA Technical Reports Server (NTRS)
Perras, G. H.; Dasey, T. J.
2000-01-01
Potential adaptive wake vortex spacing systems may need to rely on wake vortex decay rather than wake vortex transport in reducing wake separations. A wake vortex takeoff-spacing system in particular will need to rely on wake decay. Ambient turbulence is the primary influence on wake decay away from the ground. This study evaluated 18 months of ambient turbulence measurements at Dallas/Ft. Worth (DFW) Airport. The measurements show minor variation in the turbulence levels at various times of the year or times of the day for time periods when a departure system could be used. Arrival system operation was also examined, and a slightly lower overall turbulence level was found as compared to departure system benefit periods. The Sarpkaya model, a validated model of wake vortex behavior, was applied to various turbulence levels and compared to the DFW turbulence statistics. The results show that wake vortices from heavy aircraft on takeoff should dissipate within one minute for the majority of the time and will rarely last two minutes. These results will need to be verified by wake vortex measurements on departure.
The Turbulent Life of Phytoplankton
NASA Technical Reports Server (NTRS)
Ghosal, S.; Rogers, M.; Wray, A.
2000-01-01
Phytoplankton is a generic name for photosynthesizing microscopic organisms that inhabit the upper sunlit layer (euphotic zone) of almost all oceans and bodies of freshwater. They are agents for "primary production," the incorporation of carbon from the environment into living organisms, a process that, sustains the aquatic food web. It is estimated that phytoplankton contribute about half of the global primary production, the other half being due to terrestrial plants. By sustaining the aquatic food web and controlling the biogeochemical cycles through primary production, phytoplankton exert a dominant influence on life on earth. Turbulence influences this process in three very important ways. First, essential mineral nutrients are transported from the deeper layers to the euphotic zone through turbulence. Second, turbulence helps to suspend phytoplankton in the euphotic zone since in still water, the phytoplankton, especially the larger species, tend to settle out of the sunlit layers. Third, turbulence transports phytoplankton from the surface to the dark sterile waters, and this is an important mechanism of loss. Thus, stable phytoplankton populations are maintained through a delicate dynamic balance between the processes of turbulence, reproduction, and sinking. The first quantitative model for this was introduced by Riley, Stommel and Bumpus in 1949. This is an attempt to extend their efforts through a combination of analysis and computer simulation in order to better understand the principal qualitative aspects of the physical/biological coupling of this natural system.
Forecasting of Optical Turbulence in Support of Realtime Optical Imaging and Communication Systems
NASA Astrophysics Data System (ADS)
Alliss, R.; Felton, B.
2012-09-01
Optical turbulence (OT) acts to distort light in the atmosphere, degrading imagery from large astronomical and imaging telescopes and possibly reducing data quality of free space optical communication (FSOC) links. Some of the degradation due to optical turbulence can be corrected by adaptive optics. However, the severity of optical turbulence, and thus the amount of correction required, is largely dependent upon the turbulence at the location of interest. In addition, clouds, precipitation, and inhomogeneities in atmospheric temperature and moisture all have the potential to disrupt imaging and communications through the atmosphere. However, there are strategies that can be employed to mitigate the atmospheric impacts. These strategies require an accurate characterization of the atmosphere through which the communications links travel. To date these strategies have been to climatological characterize OT and its properties. Recently efforts have been developed to employ a realtime forecasting system which provides planners useful information for maintaining links and link budgets. The strength of OT is characterized by the refractive index structure function Cn2, which in turn is used to calculate atmospheric seeing parameters. Atmospheric measurements provided by local instrumentation are valuable for link characterization, but provide an incomplete picture of the atmosphere. While attempts have been made to characterize Cn2 using empirical models, Cn2 can be calculated more directly from Numerical Weather Prediction (NWP) simulations using pressure, temperature, thermal stability, vertical wind shear, turbulent Prandtl number, and turbulence kinetic energy (TKE). During realtime FSOC demonstrations, in situ measurements are supplemented with NWP simulations, which provide near realtime characterizations and forecasts of the Cn2, the Fried Coherence Length (ro), and time-varying, three-dimensional characterizations of the atmosphere. The three dimensional Weather
Extended performance solar electric propulsion thrust system study. Volume 2: Baseline thrust system
NASA Technical Reports Server (NTRS)
Poeschel, R. L.; Hawthorne, E. I.
1977-01-01
Several thrust system design concepts were evaluated and compared using the specifications of the most advanced 30- cm engineering model thruster as the technology base. Emphasis was placed on relatively high-power missions (60 to 100 kW) such as a Halley's comet rendezvous. The extensions in thruster performance required for the Halley's comet mission were defined and alternative thrust system concepts were designed in sufficient detail for comparing mass, efficiency, reliability, structure, and thermal characteristics. Confirmation testing and analysis of thruster and power-processing components were performed, and the feasibility of satisfying extended performance requirements was verified. A baseline design was selected from the alternatives considered, and the design analysis and documentation were refined. The baseline thrust system design features modular construction, conventional power processing, and a concentractor solar array concept and is designed to interface with the space shuttle.
NASA Astrophysics Data System (ADS)
Kawaguchi, Y.; Li, F. C.; Yu, B.; Wei, J. J.
It is well known that a small amount of chemicals such as water-soluble polymers or surfactants dramatically suppresses turbulence when they are added to liquid flow at large Reynolds number. In the last two decades, the application of surfactants to heat transportation systems such as district heating and cooling systems has attracted much interest among researchers. It has been revealed that 70% of the pumping power used to drive hot water in primary pipelines or district heating systems was saved by adding only a few hundred ppm of surfactant into the circulating water. The technological achievement requires a new design strategy for pipeline networks and heat exchangers to handle the drag reducing liquid flow. In the case of a Newtonian fluid such as water or air, the knowledge for designing fluid systems has been accumulated and the accuracy of numerical prediction is sufficient. On the other hand, the design system for surfactant solutions is not mature because drag-reducing flow phenomena are much more complicated than for Newtonian flow, for example, the friction factor for a surfactant solution depends not only on Reynolds number but also pipe diameter. In order to provide a design strategy for heat transportation systems using surfactant additives, we are now carrying out both experimental and numerical studies for surfactant solutions. In this lecture, experimental and numerical studies on the turbulence structure in drag reducing flow will be introduced. The result of an application study relating to the air conditioning system will be also shown.
Chaotic transport in Hamiltonian systems perturbed by a weak turbulent wave field
Abdullaev, S. S.
2011-08-15
Chaotic transport in a Hamiltonian system perturbed by a weak turbulent wave field is studied. It is assumed that a turbulent wave field has a wide spectrum containing up to thousands of modes whose phases are fluctuating in time with a finite correlation time. To integrate the Hamiltonian equations a fast symplectic mapping is derived. It has a large time-step equal to one full turn in angle variable. It is found that the chaotic transport across tori caused by the interactions of small-scale resonances have a fractal-like structure with the reduced or zero values of diffusion coefficients near low-order rational tori thereby forming transport barriers there. The density of rational tori is numerically calculated and its properties are investigated. It is shown that the transport barriers are formed in the gaps of the density of rational tori near the low-order rational tori. The dependencies of the depth and width of transport barriers on the wave field spectrum and the correlation time of fluctuating turbulent field (or the Kubo number) are studied. These numerical findings may have importance in understanding the mechanisms of transport barrier formation in fusion plasmas.
Multiple Current Sheet Systems in the Outer Heliosphere: Energy Release and Turbulence
NASA Astrophysics Data System (ADS)
Burgess, D.; Gingell, P. W.; Matteini, L.
2016-05-01
In the outer heliosphere, beyond the solar wind termination shock, it is expected that the warped heliospheric current sheet forms a region of closely packed, multiple, thin current sheets. Such a system may be subject to the ion-kinetic tearing instability, and hence may generate magnetic islands and hot populations of ions associated with magnetic reconnection. Reconnection processes in this environment have important implications for local particle transport, and for particle acceleration at reconnection sites and in turbulence. We study this complex environment by means of three-dimensional hybrid simulations over long timescales, in order to capture the evolution from linear growth of the tearing instability to a fully developed turbulent state at late times. The final state develops from the highly ordered initial state via both forward and inverse cascades. Component and spectral anisotropy in the magnetic fluctuations is present when a guide field is included. The inclusion of a population of newborn interstellar pickup protons does not strongly affect these results. Finally, we conclude that reconnection between multiple current sheets can act as an important source of turbulence in the outer heliosphere, with implications for energetic particle acceleration and propagation.
Manned orbital systems concepts study. Book 2: Requirements for extended-duration missions
NASA Technical Reports Server (NTRS)
1975-01-01
In order to provide essential data needed in long-range program planning, the Manned Orbital Systems Concepts (MOSC) study attempted to define, evaluate, and compare concepts for manned orbital systems that provide extended experiment mission capabilities in space, flexibility of operation, and growth potential. Specific areas discussed include roles and requirements for man in future space missions, requirements for extended capability, mission/payload concepts, and preliminary design and operational requirements.
Analysis on Chopper's output mode of the extended blackbody radiation calibration system
NASA Astrophysics Data System (ADS)
Yu, Xun; Wei, Yu-han; Hu, Tie-li; Shang, Xiao-yan; Wu, Ji-an
2009-05-01
In the extended blackbody radiant system, Chopper plays a very important role.Herein the chopper's working principle is analyzed in the system of black body radical calibration, and the chopper's closed-loop control motor is simulated. With SimPowerSystems toolbox of MATLAB, the model of DC motor driving systems is built and its startup, steady state and speed regulation performance are simulated. Experiment result shows that the output is steady, accurate, reliable and could drive the chopper evenly which can satisfy technological requirement of the extended black body radiation calibration system.
Distinguishing ichthyogenic turbulence from geophysical turbulence
NASA Astrophysics Data System (ADS)
Pujiana, Kandaga; Moum, James N.; Smyth, William D.; Warner, Sally J.
2015-05-01
Measurements of currents and turbulence beneath a geostationary ship in the equatorial Indian Ocean during a period of weak surface forcing revealed unexpectedly strong turbulence beneath the surface mixed layer. Coincident with the turbulence was a marked reduction of the current speeds registered by shipboard Doppler current profilers, and an increase in their variability. At a mooring 1 km away, measurements of turbulence and currents showed no such anomalies. Correlation with the shipboard echo sounder measurements indicate that these nighttime anomalies were associated with fish aggregations beneath the ship. The fish created turbulence by swimming against the strong zonal current in order to remain beneath the ship, and their presence affected the Doppler speed measurements. The principal characteristics of the resultant ichthyogenic turbulence are (i) low wave number roll-off of shear spectra in the inertial subrange relative to geophysical turbulence, (ii) Thorpe overturning scales that are small compared with the Ozmidov scale, and (iii) low mixing efficiency. These factors extend previous findings by Gregg and Horne (2009) to a very different biophysical regime and support the general conclusion that the biological contribution to mixing the ocean via turbulence is negligible.
A simplified free-space adaptive optics system against atmospheric turbulence
NASA Astrophysics Data System (ADS)
Sharma, Sanjay
2012-03-01
Optical free-space communications have the distinct advantages over conventional radio frequency and microwave systems in terms of information capacity and increased security. However, optical carrier frequencies drastically suffer due to atmospheric turbulence. This effect is a random process and time-varying process; therefore, it is very difficult to overcome the effect. Adaptive optics is the technology used to mitigate chaotic optical wave-front distortions in real time by measuring the wave-front distortion with the help of a sensor and then adapting the wave-front corrector to lessen the phase distortions and ultimately to recover a closely approximated signal to its original counterpart. But these systems are too expensive and large. This study employs the various aspects of Adaptive Optics system, such as wave-front corrector, wave-front sensors and analytical analysis of open and closed-loop systems using loop equations, in order to make free-space optics communication links more vulnerable against atmospheric turbulence and wave-front phase distributions. The purpose of this study is to investigate a wave-front sensorless adaptive optics system, which would provide reduced complexity, size and cost.
A discrete analog of the extended Bass algorithm for stabilizing constant linear systems
NASA Technical Reports Server (NTRS)
Armstrong, E. S.; Rublein, G. T.
1976-01-01
Two methods for stabilizing constant linear systems, namely, the extended Bass algorithm for continuous systems and a discrete system analog, are discussed. For the continuous algorithm, a new result on the degree of stability of the closed-loop eigenvalues is presented, and for both methods, typical results and asymptotic trends in the data are illustrated through an example computation.
Talbot, L.; Cheng, R.K.
1993-12-01
Turbulent combustion is the dominant process in heat and power generating systems. Its most significant aspect is to enhance the burning rate and volumetric power density. Turbulent mixing, however, also influences the chemical rates and has a direct effect on the formation of pollutants, flame ignition and extinction. Therefore, research and development of modern combustion systems for power generation, waste incineration and material synthesis must rely on a fundamental understanding of the physical effect of turbulence on combustion to develop theoretical models that can be used as design tools. The overall objective of this program is to investigate, primarily experimentally, the interaction and coupling between turbulence and combustion. These processes are complex and are characterized by scalar and velocity fluctuations with time and length scales spanning several orders of magnitude. They are also influenced by the so-called {open_quotes}field{close_quotes} effects associated with the characteristics of the flow and burner geometries. The authors` approach is to gain a fundamental understanding by investigating idealized laboratory flames. Laboratory flames are amenable to detailed interrogation by laser diagnostics and their flow geometries are chosen to simplify numerical modeling and simulations and to facilitate comparison between experiments and theory.
The extended depth of field microscope imaging system with the phase pupil mask
NASA Astrophysics Data System (ADS)
Lyu, Qinghua; Zhai, Zhongsheng; Sharp, Martin; French, Paul
2015-11-01
A `0/π' phase pupil mask was developed to extend the depth of field of a circularly symmetric optical microscope imaging system. The modulation transfer function curves, the normalized point spread function figures and the spot diagrams of the imaging system with the optimal mask were analyzed and simulated. The results show that the large depth of field imaging system with the `0/π' phase pupil mask has a high resolution in a long frequency band and can obtain clear images without any post-processing. The experimental results also demonstrate that the depth of field of the imaging system is extended successfully.
An atmospheric turbulence generator for dynamic tests with LINC-NIRVANA's adaptive optics system
NASA Astrophysics Data System (ADS)
Meschke, D.; Bizenberger, P.; Gaessler, W.; Zhang, X.; Mohr, L.; Baumeister, H.; Diolaiti, E.
2010-07-01
LINC-NIRVANA[1] (LN) is an instrument for the Large Binocular Telescope[2] (LBT). Its purpose is to combine the light coming from the two primary mirrors in a Fizeau-type interferometer. In order to compensate turbulence-induced dynamic aberrations, the layer oriented adaptive optics system of LN[3] consists of two major subsystems for each side: the Ground-Layer-Wavefront sensor (GLWS) and the Mid- and High-Layer Wavefront sensor (MHLWS). The MHLWS is currently set up in a laboratory at the Max-Planck-Institute for Astronomy in Heidelberg. To test the multi-conjugate AO with multiple simulated stars in the laboratory and to develop the necessary control software, a dedicated light source is needed. For this reason, we designed an optical system, operating in visible as well as in infrared light, which imitates the telescope's optical train (f-ratio, pupil position and size, field curvature). By inserting rotating surface etched glass phase screens, artificial aberrations corresponding to the atmospheric turbulence are introduced. In addition, different turbulence altitudes can be simulated depending on the position of these screens along the optical axis. In this way, it is possible to comprehensively test the complete system, including electronics and software, in the laboratory before integration into the final LINC-NIRVANA setup. Combined with an atmospheric piston simulator, also this effect can be taken into account. Since we are building two identical sets, it is possible to feed the complete instrument with light for the interferometric combination during the assembly phase in the integration laboratory.
Introduction to quantum turbulence.
Barenghi, Carlo F; Skrbek, Ladislav; Sreenivasan, Katepalli R
2014-03-25
The term quantum turbulence denotes the turbulent motion of quantum fluids, systems such as superfluid helium and atomic Bose-Einstein condensates, which are characterized by quantized vorticity, superfluidity, and, at finite temperatures, two-fluid behavior. This article introduces their basic properties, describes types and regimes of turbulence that have been observed, and highlights similarities and differences between quantum turbulence and classical turbulence in ordinary fluids. Our aim is also to link together the articles of this special issue and to provide a perspective of the future development of a subject that contains aspects of fluid mechanics, atomic physics, condensed matter, and low-temperature physics. PMID:24704870
Introduction to quantum turbulence
Barenghi, Carlo F.; Skrbek, Ladislav; Sreenivasan, Katepalli R.
2014-01-01
The term quantum turbulence denotes the turbulent motion of quantum fluids, systems such as superfluid helium and atomic Bose–Einstein condensates, which are characterized by quantized vorticity, superfluidity, and, at finite temperatures, two-fluid behavior. This article introduces their basic properties, describes types and regimes of turbulence that have been observed, and highlights similarities and differences between quantum turbulence and classical turbulence in ordinary fluids. Our aim is also to link together the articles of this special issue and to provide a perspective of the future development of a subject that contains aspects of fluid mechanics, atomic physics, condensed matter, and low-temperature physics. PMID:24704870
Eighmy, T. Taylor; Bishop, P. L.
1985-01-01
This research documents an effect of reactor turbulence on the ability of gram-negative wastewater biofilm bacteria to actively transport l-aspartate via a binding-protein-mediated transport system. Biofilms which were not preadapted to turbulence and which possessed two separate and distinct aspartate transport systems (systems 1 and 2) were subjected to a turbulent flow condition in a hydrodynamically defined closed-loop reactor system. A shear stress treatment of 3.1 N · m−2 for 10 min at a turbulent Reynolds number (Re = 11,297) inactivated the low-affinity, high-capacity binding-protein-mediated transport system (system 2) and resolved the high-affinity, low-capacity membrane-bound proton symport system (system 1). The Kt and Vmax values for the resolved system were statistically similar to Kt and Vmax values for system 1 when system 2 was inactivated either by osmotic shock or arsenate, two treatments which are known to inactivate binding-protein-mediated transport systems. We hypothesize that shear stress disrupts system 2 by deforming the outer membranes of the firmly adhered gram-negative bacteria. PMID:16346830
Robust extended dissipative control for sampled-data Markov jump systems
NASA Astrophysics Data System (ADS)
Shen, Hao; Park, Ju H.; Zhang, Lixian; Wu, Zheng-Guang
2014-08-01
This paper investigates the problem of the sampled-data extended dissipative control for uncertain Markov jump systems. The systems considered are transformed into Markov jump systems with polytopic uncertainties and sawtooth delays by using an input delay approach. The focus is on the design of a mode-independent sampled-data controller such that the resulting closed-loop system is mean-square exponentially stable with a given decay rate and extended dissipative. A novel exponential stability criterion and an extended dissipativty condition are established by proposing a new integral inequality. The reduced conservatism of the criteria is demonstrated by two numerical examples. Furthermore, a sufficient condition for the existence of a desired mode-independent sampled-data controller is obtained by solving a convex optimisation problem. Finally, a resistance, inductance and capacitance (RLC) series circuit is employed to illustrate the effectiveness of the proposed approach.
ERIC Educational Resources Information Center
Ferran, C.; Bosch, S.; Carnicer, A.
2012-01-01
A practical activity designed to introduce wavefront coding techniques as a method to extend the depth of field in optical systems is presented. The activity is suitable for advanced undergraduate students since it combines different topics in optical engineering such as optical system design, aberration theory, Fourier optics, and digital image…
Stirring turbulence with turbulence
NASA Astrophysics Data System (ADS)
Cekli, Hakki Ergun; Joosten, René; van de Water, Willem
2015-12-01
We stir wind-tunnel turbulence with an active grid that consists of rods with attached vanes. The time-varying angle of these rods is controlled by random numbers. We study the response of turbulence on the statistical properties of these random numbers. The random numbers are generated by the Gledzer-Ohkitani-Yamada shell model, which is a simple dynamical model of turbulence that produces a velocity field displaying inertial-range scaling behavior. The range of scales can be adjusted by selection of shells. We find that the largest energy input and the smallest anisotropy are reached when the time scale of the random numbers matches that of the largest eddies of the wind-tunnel turbulence. A large mismatch of these times creates a highly intermittent random flow with interesting but quite anomalous statistics.
Robust energy transfer mechanism via precession resonance in nonlinear turbulent wave systems
NASA Astrophysics Data System (ADS)
Lucas, Dan; Bustamante, Miguel; Quinn, Brenda
2014-11-01
The precise mechanisms by which energy is most efficiently transferred in a turbulent system remain an important open question for the fluid mechanics community. In this talk we present a newly discovered resonance which is found to drive transfers across the spectrum of Fourier modes in a nonlinear wave system. Quadratic nonlinearity results in modes interacting in triads and, by considering the ``truly dynamical degrees of freedom'' (amplitudes and triad phases) and the precessional frequencies of the triads, we show transfers are maximal when the precession resonates with the nonlinear temporal frequencies. This can lead to a collective state of synchronised triads with intense cascades at intermediate nonlinearity; we find greatest transfer between the traditional weak and strong turbulence regimes and discover that this new mechanism is dominant here. We present the effect in a hierarchy of models including a full DNS of the Charney-Hasegawa-Mima equation and confirm analytical predictions. Supported by Science Foundation Ireland (SFI) under Grant Number 12/IP/1491.
Design of a collective scattering system for electron gyroscale turbulence study in KSTAR
NASA Astrophysics Data System (ADS)
Lee, Woochang; Park, Hyeon; Lee, Dongjae; Leem, Juneeok; Nam, Yongun
2015-11-01
The design characteristics of a multi-channel collective (or coherent) scattering system for electron scale turbulence study in KSTAR, which is planned to be installed in 2016, are investigated. A few critical issues are discussed in depth such as effect of the Faraday rotation of the electric field polarization of probing and scattered, the probing wave frequency which is related to the optics for measurement of electron gyro scale turbulence, the wave polarization to minimize absorption of the probing power by electron cyclotron resonant layers, and the probing power. A proper and feasible optics with 300 GHz probing wave, which is based on these issues, provides a simultaneous measurement of electron density fluctuations at four discrete poloidal wave numbers up to 21 cm-1. The upper limit corresponds to the normalized wave number k⊥ρe of 0.2 in KSTAR plasmas. To detect scattered wave power and extract phase information, a quadrature detection system consisting of four-channel antenna/detector array and electronics will be employed. Work supported by NRF Korea under grant numbers NRF-2015M1A7A1A02002627 and NRF-2014M1A7A1A03029865.
NASA Astrophysics Data System (ADS)
Zhu, Lin; Luo, Xudong; Ma, Hongru
2016-03-01
We analytically extend the scope of transformation optics (TO) to metamaterial-modified wireless power transfer (WPT) systems and demonstrate that the extended TO can help design the highly efficient WPT. The methodology is based on rigorous scattering theory, enabling an equivalent model under certain circumstances to be established, that can significantly simplify investigating metamaterial-enhanced WPT. More important, from the analytical study on the equivalent model, we prove that TO is still applicable, even when the conditions of complementary media are not satisfied. Our findings are verified numerically using our methodology as well as COMSOL simulations. Moreover, a further study also indicates the extended TO explanation as well as the analysis of the equivalent model could help improve the transfer efficiency of WPT significantly. The demonstrations are not restricted to any specific frequency, and the conclusions could be extended to a broad range of wavelengths, including applications to active cloaks and other related devices.
Influence of atmospheric turbulence on OAM-based FSO system with use of realistic link model
NASA Astrophysics Data System (ADS)
Li, Ming; Yu, Zhongyuan; Cvijetic, Milorad
2016-04-01
We study the influence of atmospheric turbulence on OAM-based free-space optical (FSO) communication by using the Pump turbulence spectrum model which accurately characterizes the realistic FSO link. A comprehensive comparison is made between the Pump and Kolmogorov spectrum models with respect to the turbulence impact. The calculated results show that obtained turbulence-induced crosstalk is lower, which means that a higher channel capacity is projected when the realistic Pump spectrum is used instead of the Kolmogorov spectrum. We believe that our results prove that performance of practical OAM-based FSO is better than one predicted by using the original Kolmogorov turbulence model.
The onset of vortex turbulence
Huber, G. . Center for Polymer Studies Lawrence Berkeley Lab., CA )
1992-12-01
It is the goal of this thesis to investigate some of the unusual and spectacular properties near the transition to turbulence in a two-dimensional field of limit-cycle oscillators. Of particular interest are the dynamics of topological defects (vortices) associated with the onset of turbulence. The complex Ginzburg-Landau equation describes an extended reaction-diffusion system close to the bifurcation of a steady state into a stable, periodic orbit. In the jargon of nonlinear dynamics, it is the amplitude equation corresponding to a Hopf bifurcation. Because of the generality of the assumptions under which it is derived, the complex Ginzburg-Landau equation describes systems in contexts other than chemical reactions with diffusion. Examples include Rayleigh-Benard convection and the phase fields of multimode lasers. The reaction-diffusion model is however, a sufficiently general model to frame our discussion.
NASA Astrophysics Data System (ADS)
Hasan, Omar M.; Taha, Mohamed; Abu Sharkh, Osama
2016-06-01
In this paper, we investigate outage capacity, outage probability, and outage rate performance of multiple-input multiple-output (MIMO) free-space optical system operating over strong turbulence channels. The MIMO optical system employs intensity modulation direct detection with on-off signaling, and equal gain combining technique at the receiver. We derived novel closed-form expressions for three system metrics, namely, outage capacity, outage probability, and outage rate. Expressions derived here are based on the generalized Gamma-Gamma channel model, which is based on scintillation theory that assumes that the irradiance of the received optical wave is modeled as the product of small-scale and large-scale turbulence eddies. The results are evaluated for different values of received signal-to-noise ratios, strong turbulence conditions, and several values of transmit/receive diversity.
NASA Astrophysics Data System (ADS)
Wang, Xudong; Syrmos, Vassilis L.
2004-07-01
In this paper, an adaptive reconfigurable control system based on extended Kalman filter approach and eigenstructure assignments is proposed. System identification is carried out using an extended Kalman filter (EKF) approach. An eigenstructure assignment (EA) technique is applied for reconfigurable feedback control law design to recover the system dynamic performance. The reconfigurable feedforward controllers are designed to achieve the steady-state tracking using input weighting approach. The proposed scheme can identify not only actuator and sensor variations, but also changes in the system structures using the extended Kalman filtering method. The overall design is robust with respect to uncertainties in the state-space matrices of the reconfigured system. To illustrate the effectiveness of the proposed reconfigurable control system design technique, an aircraft longitudinal vertical takeoff and landing (VTOL) control system is used to demonstrate the reconfiguration procedure.
Edge of chaos and genesis of turbulence.
Chian, Abraham C-L; Muñoz, Pablo R; Rempel, Erico L
2013-11-01
The edge of chaos is analyzed in a spatially extended system, modeled by the regularized long-wave equation, prior to the transition to permanent spatiotemporal chaos. In the presence of coexisting attractors, a chaotic saddle is born at the basin boundary due to a smooth-fractal metamorphosis. As a control parameter is varied, the chaotic transient evolves to well-developed transient turbulence via a cascade of fractal-fractal metamorphoses. The edge state responsible for the edge of chaos and the genesis of turbulence is an unstable traveling wave in the laboratory frame, corresponding to a saddle point lying at the basin boundary in the Fourier space. PMID:24329334
Siemieniuch, C E; Sinclair, M A
2014-01-01
Socio-technical issues for Systems of Systems (SoS) differ in several ways from those for systems, mainly because the individual systems that are components of the SoS are usually owned by different organisations, each responsible for the optimisation and operation of its own system. Consequently, management of the SoS is about negotiation and management of the interfaces. Because of issues of Intellectual Property Rights (IPRs), commercial confidence, and the like, there is seldom sufficient, timely information in circulation about the SoS. Surprises are endemic to SoS, and resilience is a fundamental requirement. This paper outlines the different characteristics of SoS compared to ordinary systems, discusses many of the socio-technical issues involved, and then outlines a generic approach to these issues, treating the SoS as a 'wicked problem'. Endemic to this is the need for governance, which is discussed briefly. This is followed by a description of the evident gaps in knowledge about the functioning of SoS, and a listing of tool classes, the development of which would enable progress to be made more effectively. Finally, the paper discusses how the SoS approach might be the best way to entrain ICT to address global drivers, thus pointing to the importance of the SoS approach. PMID:24011651
Local heterogeneities in cardiac systems suppress turbulence by generating multi-armed rotors
NASA Astrophysics Data System (ADS)
Zhang, Zhihui; Steinbock, Oliver
2016-05-01
Ventricular fibrillation is an extremely dangerous cardiac arrhythmia that is linked to rotating waves of electric activity and chaotically moving vortex lines. These filaments can pin to insulating, cylindrical heterogeneities which swiftly become the new rotation backbone of the local wave field. For thin cylinders, the stabilized rotation is sufficiently fast to repel the free segments of the turbulent filament tangle and annihilate them at the system boundaries. The resulting global wave pattern is periodic and highly ordered. Our cardiac simulations show that also thicker cylinders can establish analogous forms of tachycardia. This process occurs through the spontaneous formation of pinned multi-armed vortices. The observed number of wave arms N depends on the cylinder radius and is associated to stability windows that for N = 2, 3 partially overlap. For N = 1, 2, we find a small gap in which the turbulence is removed but the pinned rotor shows complex temporal dynamics. The relevance of our findings to human cardiology are discussed in the context of vortex pinning to more complex-shaped anatomical features and remodeled myocardium.
NASA Astrophysics Data System (ADS)
Bian, Shiyao; Ceccio, Steven L.; Driscoll, James F.
2004-11-01
Simultaneous measurements of velocity and concentration fields are of great importance to understand the mechanism of turbulent mixing. We are developing a combined cinematographic particle image velocimetry (CPIV) and cinematographic planar laser-induced fluorescence (CPLIF) system that is capable of recording velocity fields and concentration profiles at 2 kHz with a spatial resolution of 0.5 mm. Two registered cameras will be used to the CPIV and a third for the CPLIF. We are validating the system through the examination of a well-characterized flow: the round turbulent jet. A series of measurements are performed in the self-similar far field of an axisymmetric turbulent water jet. Mean and fluctuating velocity and concentration quantities are obtained by simultaneous CPLIF and CPIV measurements. The precision of single and duel camera CPIV is investigated. [Sponsored by National Science Foundation Grant: CTM 0203140
Angle extended linear MEMS scanning system for 3D laser vision sensor
NASA Astrophysics Data System (ADS)
Pang, Yajun; Zhang, Yinxin; Yang, Huaidong; Zhu, Pan; Gai, Ye; Zhao, Jian; Huang, Zhanhua
2016-09-01
Scanning system is often considered as the most important part for 3D laser vision sensor. In this paper, we propose a method for the optical system design of angle extended linear MEMS scanning system, which has features of huge scanning degree, small beam divergence angle and small spot size for 3D laser vision sensor. The principle of design and theoretical formulas are derived strictly. With the help of software ZEMAX, a linear scanning optical system based on MEMS has been designed. Results show that the designed system can extend scanning angle from ±8° to ±26.5° with a divergence angle small than 3.5 mr, and the spot size is reduced for 4.545 times.
Tactical missile turbulence problems
NASA Technical Reports Server (NTRS)
Dickson, Richard E.
1987-01-01
Of particular interest is atmospheric turbulence in the atmospheric boundary layer, since this affects both the launch and terminal phase of flight, and the total flight for direct fire systems. Brief discussions are presented on rocket artillery boost wind problems, mean wind correction, turbulent boost wind correction, the Dynamically Aimed Free Flight Rocket (DAFFR) wind filter, the DAFFR test, and rocket wake turbulence problems. It is concluded that many of the turbulence problems of rockets and missiles are common to those of aircraft, such as structural loading and control system design. However, these problems have not been solved at this time.
Extended Attention Span Training System: Video Game Neurotherapy for Attention Deficit Disorder.
ERIC Educational Resources Information Center
Pope, Alan T.; Bogart, Edward H.
1996-01-01
Describes the Extended Attention Span Training (EAST) system for modifying attention deficits, which takes the concept of biofeedback one step further by making a video game more difficult as the player's brain waves indicate that attention is waning. Notes contributions of this technology to neuropsychology and neurology, where the emphasis is on…
Federal Register 2010, 2011, 2012, 2013, 2014
2010-08-16
... Subcommittee of the Trade Policy Staff Committee; Office of the U.S. Trade Representative. BILLING CODE 3190-W0... TRADE REPRESENTATIVE Generalized System of Preferences (GSP): Notice Extending Deadline for Submission of Petitions for the 2010 Annual GSP Product Review AGENCY: Office of the United States...
Kang, Yu; Zhai, Di-Hua; Liu, Guo-Ping; Zhao, Yun-Bo
2016-05-01
An extended asynchronous switching model is investigated for a class of switched stochastic nonlinear retarded systems in the presence of both detection delay and false alarm, where the extended asynchronous switching is described by two independent and exponentially distributed stochastic processes, and further simplified as Markovian. Based on the Razumikhin-type theorem incorporated with average dwell-time approach, the sufficient criteria for global asymptotic stability in probability and stochastic input-to-state stability are given, whose importance and effectiveness are finally verified by numerical examples. PMID:26068932
Data-driven prediction and prevention of extreme events in a spatially extended excitable system
NASA Astrophysics Data System (ADS)
Bialonski, Stephan; Ansmann, Gerrit; Kantz, Holger
2015-10-01
Extreme events occur in many spatially extended dynamical systems, often devastatingly affecting human life, which makes their reliable prediction and efficient prevention highly desirable. We study the prediction and prevention of extreme events in a spatially extended system, a system of coupled FitzHugh-Nagumo units, in which extreme events occur in a spatially and temporally irregular way. Mimicking typical constraints faced in field studies, we assume not to know the governing equations of motion and to be able to observe only a subset of all phase-space variables for a limited period of time. Based on reconstructing the local dynamics from data and despite being challenged by the rareness of events, we are able to predict extreme events remarkably well. With small, rare, and spatiotemporally localized perturbations which are guided by our predictions, we are able to completely suppress extreme events in this system.
Definition study for an extended manned test of a regenerative life support system
NASA Technical Reports Server (NTRS)
1971-01-01
A program was defined which consists of extended ground-based manned tests of regenerative life support systems. The tests are to evaluate prototypes of advanced life support systems under operational, integrated conditions, thus providing data for the design of efficient environmental control and life support systems for use in long-duration space missions. The requirements are defined for test operations to provide a simulation of an orbiting space laboratory. The features of Phase A and B programs are described. These tests use proven backup equipment to ensure successful evaluation of the advanced subsystems. A pre-tests all-systems checkout period is provided to minimize equipment problems during extended testing and to familiarize all crew and operating staff members with test equipment and procedures.
NASA Astrophysics Data System (ADS)
Papp, John Laszlo
2000-10-01
The successful application of CFD and turbulence modeling methods to an aerospike nozzle system first involves the successful simulation of its key flow components. This report addresses the task using the Chien low-Re k-epsilon and the Yakhot et al. high-Re RNG k-epsilon turbulence models. An improved implicit axis of symmetry boundary condition is also developed to increase stability and lower artificial dissipation. Grid adaptation through the SAGE post-processing package is used throughout the study. The RNG model, after low-Re modifications, and the Chien low-Re k-epsilon model are applied to the supersonic axisymmetric base flow problem. Both models predict a peak recirculation velocity almost twice as large as experiment. The RNG model predicts a flatter base pressure and lower recirculation velocity more consistent with experimental data using less grid points than a comparable Chien model solution. The turbulent quantities predicted by both models are typical of other numerical results and generally under predict peak values obtained in experiment suggesting that too little turbulent eddy viscosity is produced. After several test cases, the full 3-D aerospike nozzle is simulated using both the Chien and modified RNG low-Re models. The Chien model outperforms the RNG model in all circumstances. The surface pressure predicted by the Chien model along the nozzle center-plane is very near experiment while mid-plane results are not as close but useful for design purposes. The lack of a thick boundary layer along the nozzle surface in RNG simulations is the cause of poor surface pressure comparisons. Although initial base flow comparisons between the model predictions and experiment are poor, the profiles are relatively flat. To accelerate the progress to a steady-state solution, a process involving the artificial lowering of the base pressure and subsequent iteration to a new steady state is undertaken. After several of these steps, the resulting steady
Open-loop correction of horizontal turbulence: system design and result.
Mu, Quanquan; Cao, Zhaoliang; Li, Dayu; Hu, Lifa; Xuan, Li
2008-08-10
Adaptive optics systems often work in a closed-loop configuration due to the hysteretic and nonlinearity properties of conventional deformable mirrors. Because of the high-precision wavefront generation and nonhysteretic properties of liquid-crystal devices, the open-loop control becomes possible. Open-loop control is a requirement for advanced adaptive optics concepts. We designed an open-loop adaptive optics system with a liquid-crystal-on-silicon wavefront corrector. This system is simple, fast, and can save much more light compared to conventional liquid-crystal-based closed-loop systems. The detailed principle, construction, and operation are discussed. The 500 m horizontal turbulence correction experiment was done using a 250 mm telescope in the laboratory. The whole system can reach a 60 Hz correction frequency. Evaluation of the correction precision was done at closed-loop configuration, which is 0.2 lambda (lambda=0.633 microm) in peak to valley. The dynamic image under open-loop correction got the same resolution compared to closed-loop correction. The whole system reached 0.68 arc sec resolution capability at open-loop correction, which is slightly larger than the system's diffraction-limited resolution of 0.65 arc sec. PMID:18690274
A POD-based analysis of turbulence in the reduced nonlinear dynamics system
NASA Astrophysics Data System (ADS)
Nikolaidis, M.-A.; Farrell, B. F.; Ioannou, P. J.; Gayme, D. F.; Lozano-Durán, A.; Jiménez, J.
2016-04-01
The structure of turbulence in a reduced model of turbulence (RNL) is analyzed by means of a Proper Orthogonal Decomposition (POD modes). POD analysis was carried out on two different components of the flow, the roll/streak and the perturbation structure. The POD structure in both RNL and direct numerical simulations (DNS) is similar and this correspondence suggests that the dynamics retained in RNL are the essential dynamical ingredients underlying the self-sustaining mechanism of the turbulent state.
NASA Technical Reports Server (NTRS)
Katzberg, S. J.
1972-01-01
A primary limitation of many solid-state photodetectors used in electro-optical systems such as the facsimile camera is their slow response in converting light intensities into electrical signals. An optical feedback technique is presented which can extend the frequency response of systems that use these detectors by orders of magnitude without significantly degrading their signal-to-noise performance. This technique is analyzed to predict improvement, implemented, and evaluated to verify analytical results.
NASA Astrophysics Data System (ADS)
Lynch, Gillian C.; Pettitt, B. Montgomery
1997-11-01
The extended system Hamiltonian for carrying out grand canonical ensemble molecular dynamics simulations is reformulated. This new Hamiltonian includes a generalized treatment of the reference state partition function of the total chemical potential that reproduces the ideal gas behavior and various previous partitionings of ideal and excess terms. Initial calculations are performed on a system of Lennard-Jones particles near the triple point and on liquid water at room temperature.
A Huygens principle for diffusion and anomalous diffusion in spatially extended systems
Gottwald, Georg A.; Melbourne, Ian
2013-01-01
We present a universal view on diffusive behavior in chaotic spatially extended systems for anisotropic and isotropic media. For anisotropic systems, strong chaos leads to diffusive behavior (Brownian motion with drift) and weak chaos leads to superdiffusive behavior (Lévy processes with drift). For isotropic systems, the drift term vanishes and strong chaos again leads to Brownian motion. We establish the existence of a nonlinear Huygens principle for weakly chaotic systems in isotropic media whereby the dynamics behaves diffusively in even space dimension and exhibits superdiffusive behavior in odd space dimensions. PMID:23653481
Controlling chaos in spatially extended beam-plasma system by the continuous delayed feedback
Hramov, Alexander E.; Koronovskii, Alexey A.; Rempen, Irene S.
2006-03-15
In this paper we discuss the control of complex spatio-temporal dynamics in a spatially extended nonlinear system (fluid model of Pierce diode) based on the concepts of controlling chaos in the systems with few degrees of freedom. A presented method is connected with stabilization of unstable homogeneous equilibrium state and the unstable spatio-temporal periodical states analogous to unstable periodic orbits of chaotic dynamics of the systems with few degrees of freedom. We show that this method is effective and allows to achieve desired regular dynamics chosen from a number of possible in the considered system.
NASA Technical Reports Server (NTRS)
Devasirvatham, D. M. J.; Hodge, D. B.
1981-01-01
A model of the microwave and millimeter wave link in the presence of atmospheric turbulence is presented with emphasis on satellite communications systems. The analysis is based on standard methods of statistical theory. The results are directly usable by the design engineer.
NASA Technical Reports Server (NTRS)
Manning, Robert M.
2005-01-01
Solutions are derived for the generalized mutual coherence function (MCF), i.e., the second order moment, of a random wave field propagating through a random medium within the context of the extended parabolic equation. Here, "generalized" connotes the consideration of both the transverse as well as the longitudinal second order moments (with respect to the direction of propagation). Such solutions will afford a comparison between the results of the parabolic equation within the pararaxial approximation and those of the wide-angle extended theory. To this end, a statistical operator method is developed which gives a general equation for an arbitrary spatial statistical moment of the wave field. The generality of the operator method allows one to obtain an expression for the second order field moment in the direction longitudinal to the direction of propagation. Analytical solutions to these equations are derived for the Kolmogorov and Tatarskii spectra of atmospheric permittivity fluctuations within the Markov approximation.
Spatial and spectral evolution of turbulence
Guercan, O. D.; Diamond, P. H.; Hahm, T. S.
2007-05-15
Spreading of turbulence as a result of nonlinear mode couplings and the associated spectral energy transfer is studied. A derivation of a simple two-field model is presented using the weak turbulence limit of the two-scale direct interaction approximation. This approach enables the approximate overall effect of nonlinear interactions to be written in the form of Fick's law and leads to a coupled reaction-diffusion system for turbulence intensity. For this purpose, various classes of triad interactions are examined, and the effects that do not lead to spreading are neglected. It is seen that, within this framework, large scale, radially extended eddies are the most effective structures in promoting spreading of turbulence. Thus, spectral evolution that tends toward such eddies facilitates spatial spreading. Self-consistent evolution of the background profile is also considered, and it is concluded that the profile is essentially slaved to the turbulence in this phase of rapid evolution, as opposed to the case of avalanches, where it is the turbulence intensity that would be slaved to the evolving profile. The characteristic quantity describing the evolving background profile is found to be the mean ''potential vorticity'' (PV). It is shown that the two-field model with self-consistent mean PV evolution can be reduced to a single Fisher-like turbulence intensity transport equation. In addition to the usual nonlinear diffusion term, this equation also contains a 'pinch' of turbulence intensity. It is also noted that internal energy spreads faster than kinetic energy because of the respective spectral tendencies of these two quantities.
A knowledge based application of the extended aircraft interrogation and display system
NASA Technical Reports Server (NTRS)
Glover, Richard D.; Larson, Richard R.
1991-01-01
A family of multiple-processor ground support test equipment was used to test digital flight-control systems on high-performance research aircraft. A unit recently built for the F-18 high alpha research vehicle project is the latest model in a series called the extended aircraft interrogation and display system. The primary feature emphasized monitors the aircraft MIL-STD-1553B data buses and provides real-time engineering units displays of flight-control parameters. A customized software package was developed to provide real-time data interpretation based on rules embodied in a highly structured knowledge database. The configuration of this extended aircraft interrogation and display system is briefly described, and the evolution of the rule based package and its application to failure modes and effects testing on the F-18 high alpha research vehicle is discussed.
ERIC Educational Resources Information Center
Starratt, Robert J.
2004-01-01
In this article, the author discusses how superintendents function in an environment of nearly continuous turbulence challenged by concerns and pressures that compete for their attention and resolution. The turbulence is inescapable. Today it constitutes the natural--but not the exceptional--environment of school board politics, local…
Structure Theory for Extended Kepler-Coulomb 3D Classical Superintegrable Systems
NASA Astrophysics Data System (ADS)
Kalnins, Ernie G.; Miller, Willard, Jr.
2012-06-01
The classical Kepler-Coulomb system in 3 dimensions is well known to be 2nd order superintegrable, with a symmetry algebra that closes polynomially under Poisson brackets. This polynomial closure is typical for 2nd order superintegrable systems in 2D and for 2nd order systems in 3D with nondegenerate (4-parameter) potentials. However the degenerate 3-parameter potential for the 3D extended Kepler-Coulomb system (also 2nd order superintegrable) is an exception, as its quadratic symmetry algebra doesn't close polynomially. The 3D 4-parameter potential for the extended Kepler-Coulomb system is not even 2nd order superintegrable. However, Verrier and Evans (2008) showed it was 4th order superintegrable, and Tanoudis and Daskaloyannis (2011) showed that in the quantum case, if a second 4th order symmetry is added to the generators, the double commutators in the symmetry algebra close polynomially. Here, based on the Tremblay, Turbiner and Winternitz construction, we consider a! n infinite class of classical extended Kepler-Coulomb 3- and 4-parameter systems indexed by a pair of rational numbers (k1,k2) and reducing to the usual systems when k1=k2=1. We show these systems to be superintegrable of arbitrarily high order and work out explicitly the structure of the symmetry algebras determined by the 5 basis generators we have constructed. We demonstrate that the symmetry algebras close rationally; only for systems admitting extra discrete symmetries is polynomial closure achieved. Underlying the structure theory is the existence of raising and lowering constants of the motion, not themselves polynomials in the momenta, that can be employed to construct the polynomial symmetries and their structure relations.
A nonequilibrium statistical field theory of swarms and other spatially extended complex systems
Millonas, M.M. Santa Fe Inst., NM )
1993-01-01
A class of models with applications to swarm behavior as well as many other types of spatially extended complex biological and physical systems is studied. Internal fluctuations can play an active role in the organization of the phase structure of such systems. Consequently, it is not possible to fully understand the behavior of these systems without explicitly incorporating the fluctuations. In particular, for the class of models studied here the effect of internal fluctuations due to finite size is a renormalized decrease in the temperature near the point of spontaneous symmetry breaking. We briefly outline how these models can be applied to the behavior of an ant swarm.
A nonequilibrium statistical field theory of swarms and other spatially extended complex systems
Millonas, M.M. |
1993-07-01
A class of models with applications to swarm behavior as well as many other types of spatially extended complex biological and physical systems is studied. Internal fluctuations can play an active role in the organization of the phase structure of such systems. Consequently, it is not possible to fully understand the behavior of these systems without explicitly incorporating the fluctuations. In particular, for the class of models studied here the effect of internal fluctuations due to finite size is a renormalized decrease in the temperature near the point of spontaneous symmetry breaking. We briefly outline how these models can be applied to the behavior of an ant swarm.
Spreading and wandering of Gaussian–Schell model laser beams in an anisotropic turbulent ocean
NASA Astrophysics Data System (ADS)
Wu, Yuqian; Zhang, Yixin; Zhu, Yun; Hu, Zhengda
2016-09-01
The effect of anisotropic turbulence on the spreading and wandering of Gaussian–Schell model (GSM) laser beams propagating in an ocean is studied. The long-term spreading of a GSM beam propagating through the paraxial channel of a turbulent ocean is also developed. Expressions of random wander for such laser beams are derived in an anisotropic turbulent ocean based on the extended Huygens–Fresnel principle. We investigate the influence of parameters in a turbulent ocean on the beam wander and spreading. Our results indicate that beam spreading and random beam wandering are smaller without considering the anisotropy of turbulence in the oceanic channel. Salinity fluctuation has a greater contribution to both the beam spreading and beam wander than that of temperature fluctuations in a turbulent ocean. Our results could be helpful for designing a free-space optical wireless communication system in an oceanic environment.
Interacting Thin Film Systems Probed by Electron Induced Extended Fine Structure
NASA Astrophysics Data System (ADS)
Idzerda, Yves Ulrich
In order to obtain information on the structure and dynamics of various systems including interacting thin films, it is necessary to be able to measure local structure information with surface sensitivity. Three techniques of Electron Induced Extended Fine Structure (EIEFS), the electron analog of Extended X-ray Absorption Fine Structure (EXAFS), are described, compared, and applied to thin film systems. Surface Extended Electron Loss Fine Structure (SEELFS), Extended Appearence Potential Fine Structure (EAPFS) and Auger-Monitored Extended Fine Structure (AMEFS), are all local structure probes with varying degrees of surface sensitivity, and all yield similar information. Our results show that each technique can be measured by commercially available electron optics, SEELFS and AMEFS by either a cylindrical mirror analyzer (CMA) or by low energy electron diffraction (LEED) optics and EAPFS by the LEED optics. We have addressed questions concerning proper phase shifts for the analysis, short data ranges, required use of undifferentiated data, and experimental difficulties. Investigations of carbon, oxygen, sodium, potassium, cesium, and sulfur on Cu(111) and titanium on silicon demonstrate that SEELFS is applicable to single monolayer coverages of very low Z adsorbates and thin films. Many of the theoretical difficulties surrounding the analysis of SEELFS can be circumvented by the use of standards and the ratio technique analysis developed for EXAFS. We also find in our studies of silicon, titanium, and aluminum oxide that systems with plasmon losses in the region of interest cannot be analyzed, but systems with other characteristic losses which are very sharp or very broad can be. Examination of EAPFS shows that it is more surface sensitive and is applicable to single monolayer coverages (of a broader range of elements than SEELFS) and thin films. Unfortunately, EAPFS is not applicable to single crystal systems with low electron binding energies where diffraction
NASA Astrophysics Data System (ADS)
Vanag, Vladimir K.
1999-05-01
Spatially extended dynamical systems are ubiquitous and include such things as insect and animal populations; complex chemical, technological, and geochemical processes; humanity itself, and much more. It is clearly desirable to have a certain universal tool with which the highly complex behaviour of nonlinear dynamical systems can be analyzed and modelled. For this purpose, cellular automata seem to be good candidates. In the present review, emphasis is placed on the possibilities that various types of probabilistic cellular automata (PCA), such as DSMC (direct simulation Monte Carlo) and LGCA (lattice-gas cellular automata), offer. The methods are primarily designed for modelling spatially extended dynamical systems with inner fluctuations accounted for. For the Willamowskii-Roessler and Oregonator models, PCA applications to the following problems are illustrated: the effect of fluctuations on the dynamics of nonlinear systems; Turing structure formation; the effect of hydrodynamic modes on the behaviour of nonlinear chemical systems (stirring effects); bifurcation changes in the dynamical regimes of complex systems with restricted geometry or low spatial dimension; and the description of chemical systems in microemulsions.
NASA Astrophysics Data System (ADS)
Aggarwal, Priyanka; Syed, Zainab; El-Sheimy, Naser
2009-05-01
Navigation includes the integration of methodologies and systems for estimating time-varying position, velocity and attitude of moving objects. Navigation incorporating the integrated inertial navigation system (INS) and global positioning system (GPS) generally requires extensive evaluations of nonlinear equations involving double integration. Currently, integrated navigation systems are commonly implemented using the extended Kalman filter (EKF). The EKF assumes a linearized process, measurement models and Gaussian noise distributions. These assumptions are unrealistic for highly nonlinear systems like land vehicle navigation and may cause filter divergence. A particle filter (PF) is developed to enhance integrated INS/GPS system performance as it can easily deal with nonlinearity and non-Gaussian noises. In this paper, a hybrid extended particle filter (HEPF) is developed as an alternative to the well-known EKF to achieve better navigation data accuracy for low-cost microelectromechanical system sensors. The results show that the HEPF performs better than the EKF during GPS outages, especially when simulated outages are located in periods with high vehicle dynamics.
An Extended Membrane System with Active Membranes to Solve Automatic Fuzzy Clustering Problems.
Peng, Hong; Wang, Jun; Shi, Peng; Pérez-Jiménez, Mario J; Riscos-Núñez, Agustín
2016-05-01
This paper focuses on automatic fuzzy clustering problem and proposes a novel automatic fuzzy clustering method that employs an extended membrane system with active membranes that has been designed as its computing framework. The extended membrane system has a dynamic membrane structure; since membranes can evolve, it is particularly suitable for processing the automatic fuzzy clustering problem. A modification of a differential evolution (DE) mechanism was developed as evolution rules for objects according to membrane structure and object communication mechanisms. Under the control of both the object's evolution-communication mechanism and the membrane evolution mechanism, the extended membrane system can effectively determine the most appropriate number of clusters as well as the corresponding optimal cluster centers. The proposed method was evaluated over 13 benchmark problems and was compared with four state-of-the-art automatic clustering methods, two recently developed clustering methods and six classification techniques. The comparison results demonstrate the superiority of the proposed method in terms of effectiveness and robustness. PMID:26790484
Contributions to the simulation of turbulence
NASA Technical Reports Server (NTRS)
Dutton, J. A.; Kerman, B. R.; Petersen, E. L.
1976-01-01
The simulation modeling of turbulence in the boundary layer in consolidated in terms of boundary layer similarity principles and empirical results. The modeling is extended for some aspects of the nonlinear and non-Gaussian structure of the turbulence. Properties of the discrete gust form structure of the modeled turbulence are identified.
Workshop on Computational Turbulence Modeling
Not Available
1993-01-01
This document contains presentations given at Workshop on Computational Turbulence Modeling held 15-16 Sep. 1993. The purpose of the meeting was to discuss the current status and future development of turbulence modeling in computational fluid dynamics for aerospace propulsion systems. Papers cover the following topics: turbulence modeling activities at the Center for Modeling of Turbulence and Transition (CMOTT); heat transfer and turbomachinery flow physics; aerothermochemistry and computational methods for space systems; computational fluid dynamics and the k-epsilon turbulence model; propulsion systems; and inlet, duct, and nozzle flow. Separate abstracts have been prepared for articles from this report.
Workshop on Computational Turbulence Modeling
NASA Technical Reports Server (NTRS)
1993-01-01
This document contains presentations given at Workshop on Computational Turbulence Modeling held 15-16 Sep. 1993. The purpose of the meeting was to discuss the current status and future development of turbulence modeling in computational fluid dynamics for aerospace propulsion systems. Papers cover the following topics: turbulence modeling activities at the Center for Modeling of Turbulence and Transition (CMOTT); heat transfer and turbomachinery flow physics; aerothermochemistry and computational methods for space systems; computational fluid dynamics and the k-epsilon turbulence model; propulsion systems; and inlet, duct, and nozzle flow.
Extended Logic Intelligent Processing System for a Sensor Fusion Processor Hardware
NASA Technical Reports Server (NTRS)
Stoica, Adrian; Thomas, Tyson; Li, Wei-Te; Daud, Taher; Fabunmi, James
2000-01-01
The paper presents the hardware implementation and initial tests from a low-power, highspeed reconfigurable sensor fusion processor. The Extended Logic Intelligent Processing System (ELIPS) is described, which combines rule-based systems, fuzzy logic, and neural networks to achieve parallel fusion of sensor signals in compact low power VLSI. The development of the ELIPS concept is being done to demonstrate the interceptor functionality which particularly underlines the high speed and low power requirements. The hardware programmability allows the processor to reconfigure into different machines, taking the most efficient hardware implementation during each phase of information processing. Processing speeds of microseconds have been demonstrated using our test hardware.
Advanced Extended Plate and Beam Wall System in a Cold-Climate House
Mallay, Dave; Wiehagen, Joseph; Kochkin, Vladimir
2016-01-01
This report presents the design and evaluation of an innovative wall system. This highly insulated (high-R) light-frame wall system for use above grade in residential buildings is referred to as Extended Plate & Beam (EP&B). The EP&B design is the first of its kind to be featured in a new construction test house (NCTH) for the DOE Building America program. The EP&B wall design integrates standard building methods and common building products to construct a high-R wall that minimizes transition risks and costs to builders.
NASA Astrophysics Data System (ADS)
Lee, Joon Sang
The compressible filtered Navier-Stokes equations were solved using a second order accurate finite volume method with low Mach number preconditioning. A dynamic subgrid-scale stress model accounted for the subgrid-scale turbulence. The study focused on the effects of buoyancy and rotation on the structure of turbulence and transport processes including heat transfer. Several different physical arrangements were studied as outlined below. The effects of buoyancy were first studied in a vertical channel using large eddy simulation (LES). The walls were maintained at constant temperatures, one heated and the other cooled. Results showed that aiding and opposing buoyancy forces emerge near the heated and cooled walls, respectively. In the aiding flow, the turbulent intensities and heat transfer were suppressed at large values of Grashof number. In the opposing flow, however, turbulence was enhanced with increased velocity fluctuations. Another buoyancy study considered turbulent flow in a vertically oriented annulus. Isoflux wall boundary conditions with low and high heating were imposed on the inner wall while the outer wall was adiabatic. The results showed that the strong heating and buoyancy force caused distortions of the flow structure resulting in reduction of turbulent intensities, shear stress, and turbulent heat flux, particularly near the heated wall. Flow in an annular pipe with and without an outer wall rotation about its axis was first investigated at moderate Reynolds numbers. When the outer pipe wall was rotated, a significant reduction of turbulent kinetic energy was realized near the rotating wall. Secondly, a large eddy simulation has been performed to investigate the effect of swirl on the heat and momentum transfer in an annular pipe flow with a rotating inner wall. The simulations indicated that the Nusselt number and the wall friction coefficient increased with increasing rotation speed of the wall. It was also observed that the axial velocity
The Turbulent Origin of Spin-Orbit Misalignment in Planetary Systems
Fielding, Drummond B.; McKee, Christopher F.; Socrates, Aristostle; Cunningham, Andrew J.; Klein, Richard I.
2015-05-13
The turbulent environment from which stars form may lead to misalignment between the stellar spin and the remnant protoplanetary disk. By using hydrodynamic and magnetohydrodynamic simulations, we demonstrate that a wide range of stellar obliquities may be produced as a by-product of forming a star within a turbulent environment. We present a simple semi-analytic model that reveals this connection between the turbulent motions and the orientation of a star and its disk. Our results are consistent with the observed obliquity distribution of hot Jupiters. Migration of misaligned hot Jupiters may, therefore, be due to tidal dissipation in the disk, rather than tidal dissipation of the star-planet interaction.
Calibrating Multi-machine Power System Parameters with the Extended Kalman Filter
Kalsi, Karanjit; Sun, Yannan; Huang, Zhenyu; Du, Pengwei; Diao, Ruisheng; Anderson, Kevin K.; Li, Yulan; Lee, Barry
2012-07-24
Large-scale renewable resources and novel smart-grid technologies continue to increase the complexity of power systems. As power systems continue to become more complex, accurate modeling for planning and operation becomes a necessity. Inaccurate system models would result in an unreliable assessment of system security conditions and could cause large-scale blackouts. This motivates the need for model parameter calibration, since some or all of the model parameters could be unknown or inaccurate. In this paper, the extended Kalman filter is used to calibrate the parameters of a multi-machine power system. The calibration performance is tested under varying fault locations, parameter errors and measurement noise giving an insight into how many generators and which generators could be difficult to calibrate.
The variational two-electron reduced-density-matrix method for extended systems
NASA Astrophysics Data System (ADS)
Rubin, Nicholas C.
In this thesis we develop the variational two-electron reduced-density-matrix method for extended systems. Extended systems are represented in two ways: i) lattice models describing the dominant valence electronic structure with periodic boundaries to account for their extended nature and ii) a crystalline-orbital basis built from atomic orbitals using the generalization of molecular orbital theory to polymers. The first part of this thesis (Ch. 3--4) examines the performance of the variational 2-RDM method on lattice systems with tunable electron correlation. The first of these systems is the classic Hubbard model with linear and ladder lattice topologies. Because electron correlation functions, such as charge- and spin-ordering, are linear functions of the 2-RDM, the difference in electronic structure between one- and quasi-one-dimensional systems is accurately characterized. The second model contains only two-body interactions and is unique among typical spin models in that it does not have a mean-field reference wave function. The ground state wave functions from all Hamiltonians in the model have the same 1-electron reduced density matrix; consequently, one-electron theories are largely inapplicable. The superconducting eta-pairing ground states make the model a unique tool for demonstrating the necessary N-representability in highly correlated environments. The second part of this thesis (Ch. 5--6) develops a formalism for modeling materials by solving the full Schrodinger equation. Crystalline-orbital Hartree-Fock provides a set of orbitals and integral tensors for the variational 2-RDM method. We demonstrate that time-reversal symmetry, which is implicitly included in position space electronic structure calculations, must be explicitly included as an N-representability constraint on the 2-RDM when using a momentum space basis. The necessity of these equality constraints is demonstrated by the accurate recovery of the binding energy of two polymers and the
Optimization of wavefront-coded infinity-corrected microscope systems with extended depth of field
Zhao, Tingyu; Mauger, Thomas; Li, Guoqiang
2013-01-01
The depth of field of an infinity-corrected microscope system is greatly extended by simply applying a specially designed phase mask between the objective and the tube lens. In comparison with the method of modifying the structure of objective, it is more cost effective and provides improved flexibility for assembling the system. Instead of using an ideal optical system for simulation which was the focus of the previous research, a practical wavefront-coded infinity-corrected microscope system is designed in this paper by considering the various aberrations. Two new optimization methods, based on the commercial optical design software, are proposed to design a wavefront-coded microscope using a non-symmetric phase mask and a symmetric phase mask, respectively. We use polynomial phase mask and rational phase mask as examples of the non-symmetric and symmetric phase masks respectively. Simulation results show that both optimization methods work well for a 32 × infinity-corrected microscope system with 0.6 numerical aperture. The depth of field is extended to about 13 times of the traditional one. PMID:24010008
NASA Astrophysics Data System (ADS)
Strelnikov, B.; Lubken, F.-J.; Rapp, M.; Krein, G.; Henkel, H.; Heckl, H.-J.
2015-09-01
Leibniz Institute of Atmospheric Physics (TAP) at the Rostock University in Kuhlungsborn, Germany together with the company von Hoerner and Sulger GmbH (vH&S) in Schwetzingen, Germany develop a new instrumental setup for 3-dimensional in-situ turbulence and temperature measurements in the mesosphere and lower thermosphere (MLT) region. The setup consists of a mother payload carrying a new generation CONE instrument and three identical daughter payloads that will be ejected from the main payload at a predefined altitude. When ejected, all the payloads measure densities of neutral air and one of the plasma species, either electrons or ions. Each payload has its own telemetry and positioning system and sends all the data directly down to the ground. The new measurements will thereby yield four simultaneously measured profiles of neutral and plasma densities, neutral air temperature, and turbulence energy dissipation rate, separated by up to some hundreds of meters. Important for turbulence studies, these measurements will infer spectra information that cover a wide range of spatial scale characteristics for MLT turbulence in both horizontal and vertical directions.
Extended quantification of the generalized recurrence plot
NASA Astrophysics Data System (ADS)
Riedl, Maik; Marwan, Norbert; Kurths, Jürgen
2016-04-01
The generalized recurrence plot is a modern tool for quantification of complex spatial patterns. Its application spans the analysis of trabecular bone structures, Turing structures, turbulent spatial plankton patterns, and fractals. But, it is also successfully applied to the description of spatio-temporal dynamics and the detection of regime shifts, such as in the complex Ginzburg-Landau- equation. The recurrence plot based determinism is a central measure in this framework quantifying the level of regularities in temporal and spatial structures. We extend this measure for the generalized recurrence plot considering additional operations of symmetry than the simple translation. It is tested not only on two-dimensional regular patterns and noise but also on complex spatial patterns reconstructing the parameter space of the complex Ginzburg-Landau-equation. The extended version of the determinism resulted in values which are consistent to the original recurrence plot approach. Furthermore, the proposed method allows a split of the determinism into parts which based on laminar and non-laminar regions of the two-dimensional pattern of the complex Ginzburg-Landau-equation. A comparison of these parts with a standard method of image classification, the co-occurrence matrix approach, shows differences especially in the description of patterns associated with turbulence. In that case, it seems that the extended version of the determinism allows a distinction of phase turbulence and defect turbulence by means of their spatial patterns. This ability of the proposed method promise new insights in other systems with turbulent dynamics coming from climatology, biology, ecology, and social sciences, for example.
Amato, Alberto; Fortini, Stefania; Watteaux, Romain; Diano, Marcello; Espa, Stefania; Esposito, Serena; Ferrante, Maria I; Peters, Francesc; Iudicone, Daniele; Ribera d'Alcalà, Maurizio
2016-03-01
In recent years, there has been a renewed interest in the impact of turbulence on aquatic organisms. In response to this interest, a novel instrument has been constructed, TURBOGEN, that generates turbulence in water volumes up to 13 l. TURBOGEN is fully computer controlled, thus, allowing for a high level of reproducibility and for variations of the intensity and characteristics of turbulence during the experiment. The calibration tests, carried out by particle image velocimetry, showed TURBOGEN to be successful in generating isotropic turbulence at the typical relatively low levels of the marine environment. TURBOGEN and its sizing have been devised with the long-term scope of analyzing in detail the molecular responses of plankton to different mixing regimes, which is of great importance in both environmental and biotechnological processes. PMID:27036831
NASA Astrophysics Data System (ADS)
Amato, Alberto; Fortini, Stefania; Watteaux, Romain; Diano, Marcello; Espa, Stefania; Esposito, Serena; Ferrante, Maria I.; Peters, Francesc; Iudicone, Daniele; Ribera d'Alcalà, Maurizio
2016-03-01
In recent years, there has been a renewed interest in the impact of turbulence on aquatic organisms. In response to this interest, a novel instrument has been constructed, TURBOGEN, that generates turbulence in water volumes up to 13 l. TURBOGEN is fully computer controlled, thus, allowing for a high level of reproducibility and for variations of the intensity and characteristics of turbulence during the experiment. The calibration tests, carried out by particle image velocimetry, showed TURBOGEN to be successful in generating isotropic turbulence at the typical relatively low levels of the marine environment. TURBOGEN and its sizing have been devised with the long-term scope of analyzing in detail the molecular responses of plankton to different mixing regimes, which is of great importance in both environmental and biotechnological processes.
MHD Turbulence and Magnetic Dynamos
NASA Technical Reports Server (NTRS)
Shebalin, John V
2014-01-01
Incompressible magnetohydrodynamic (MHD) turbulence and magnetic dynamos, which occur in magnetofluids with large fluid and magnetic Reynolds numbers, will be discussed. When Reynolds numbers are large and energy decays slowly, the distribution of energy with respect to length scale becomes quasi-stationary and MHD turbulence can be described statistically. In the limit of infinite Reynolds numbers, viscosity and resistivity become zero and if these values are used in the MHD equations ab initio, a model system called ideal MHD turbulence results. This model system is typically confined in simple geometries with some form of homogeneous boundary conditions, allowing for velocity and magnetic field to be represented by orthogonal function expansions. One advantage to this is that the coefficients of the expansions form a set of nonlinearly interacting variables whose behavior can be described by equilibrium statistical mechanics, i.e., by a canonical ensemble theory based on the global invariants (energy, cross helicity and magnetic helicity) of ideal MHD turbulence. Another advantage is that truncated expansions provide a finite dynamical system whose time evolution can be numerically simulated to test the predictions of the associated statistical mechanics. If ensemble predictions are the same as time averages, then the system is said to be ergodic; if not, the system is nonergodic. Although it had been implicitly assumed in the early days of ideal MHD statistical theory development that these finite dynamical systems were ergodic, numerical simulations provided sufficient evidence that they were, in fact, nonergodic. Specifically, while canonical ensemble theory predicted that expansion coefficients would be (i) zero-mean random variables with (ii) energy that decreased with length scale, it was found that although (ii) was correct, (i) was not and the expected ergodicity was broken. The exact cause of this broken ergodicity was explained, after much
Statistical Mechanics of Turbulent Dynamos
NASA Technical Reports Server (NTRS)
Shebalin, John V.
2014-01-01
Incompressible magnetohydrodynamic (MHD) turbulence and magnetic dynamos, which occur in magnetofluids with large fluid and magnetic Reynolds numbers, will be discussed. When Reynolds numbers are large and energy decays slowly, the distribution of energy with respect to length scale becomes quasi-stationary and MHD turbulence can be described statistically. In the limit of infinite Reynolds numbers, viscosity and resistivity become zero and if these values are used in the MHD equations ab initio, a model system called ideal MHD turbulence results. This model system is typically confined in simple geometries with some form of homogeneous boundary conditions, allowing for velocity and magnetic field to be represented by orthogonal function expansions. One advantage to this is that the coefficients of the expansions form a set of nonlinearly interacting variables whose behavior can be described by equilibrium statistical mechanics, i.e., by a canonical ensemble theory based on the global invariants (energy, cross helicity and magnetic helicity) of ideal MHD turbulence. Another advantage is that truncated expansions provide a finite dynamical system whose time evolution can be numerically simulated to test the predictions of the associated statistical mechanics. If ensemble predictions are the same as time averages, then the system is said to be ergodic; if not, the system is nonergodic. Although it had been implicitly assumed in the early days of ideal MHD statistical theory development that these finite dynamical systems were ergodic, numerical simulations provided sufficient evidence that they were, in fact, nonergodic. Specifically, while canonical ensemble theory predicted that expansion coefficients would be (i) zero-mean random variables with (ii) energy that decreased with length scale, it was found that although (ii) was correct, (i) was not and the expected ergodicity was broken. The exact cause of this broken ergodicity was explained, after much
Probe systems for measuring static pressure and turbulence intensity in fluid streams
NASA Technical Reports Server (NTRS)
Rossow, Vernon J. (Inventor)
1993-01-01
A method and an apparatus for measuring time-averaged static or ambient pressure and turbulence intensity in a turbulent stream are discussed. The procedure involves placing a plurality of probes in the stream. Each probe responds in a different manner to characteristics of the fluid stream, preferably as a result of having varying cross sections. The responses from the probes are used to eliminate unwanted components in the measured quantities for accurate determination of selected characteristics.
Extended performance solar electric propulsion thrust system study. Volume 1: Executive summary
NASA Technical Reports Server (NTRS)
Poeschel, R. L.; Hawthorne, E. I.
1977-01-01
Several thrust system design concepts were evaluated and compared using the specifications of the most advanced 30 cm engineering model thruster as the technology base. The extensions in thruster performance required for the Halley's comet mission were defined and alternative thrust system concepts were designed. Confirmation testing and analysis of thruster and power-processing components were performed, and the feasibility of satisfying extended performance requirements was verified. A baseline design was selected from the alternatives considered, and the design analysis and documentation were refined. A program development plan was formulated that outlines the work structure considered necessary for developing, qualifying, and fabricating the flight hardware for the baseline thrust system within the time frame of a project to rendezvous with Halley's comet. An assessment was made of the costs and risks associated with a baseline thrust system as provided to the mission project under this plan. Critical procurements and interfaces were identified and defined. Results are presented.
Magnetohydrodynamic Turbulence
NASA Astrophysics Data System (ADS)
Montgomery, David C.
2004-01-01
Magnetohydrodynamic (MHD) turbulence theory is modeled on neutral fluid (Navier-Stokes) turbulence theory, but with some important differences. There have been essentially no repeatable laboratory MHD experiments wherein the boundary conditions could be controlled or varied and a full set of diagnostics implemented. The equations of MHD are convincingly derivable only in the limit of small ratio of collision mean-free-paths to macroscopic length scales, an inequality that often goes the other way for magnetofluids of interest. Finally, accurate information on the MHD transport coefficients-and thus, the Reynolds-like numbers that order magnetofluid behavior-is largely lacking; indeed, the algebraic expressions used for such ingredients as the viscous stress tensor are often little more than wishful borrowing from fluid mechanics. The one accurate thing that has been done extensively and well is to solve the (strongly nonlinear) MHD equations numerically, usually in the presence of rectangular periodic boundary conditions, and then hope for the best when drawing inferences from the computations for those astrophysical and geophysical MHD systems for which some indisputably turbulent detailed data are available, such as the solar wind or solar prominences. This has led to what is perhaps the first field of physics for which computer simulations are regarded as more central to validating conclusions than is any kind of measurement. Things have evolved in this way due to a mixture of the inevitable and the bureaucratic, but that is the way it is, and those of us who want to work on the subject have to live with it. It is the only game in town, and theories that have promised more-often on the basis of some alleged ``instability''-have turned out to be illusory.
Numerical simulation of turbulence in the presence of shear
NASA Technical Reports Server (NTRS)
Shaanan, S.; Ferziger, J. H.; Reynolds, W. C.
1975-01-01
The numerical calculations are presented of the large eddy structure of turbulent flows, by use of the averaged Navier-Stokes equations, where averages are taken over spatial regions small compared to the size of the computational grid. The subgrid components of motion are modeled by a local eddy-viscosity model. A new finite-difference scheme is proposed to represent the nonlinear average advective term which has fourth-order accuracy. This scheme exhibits several advantages over existing schemes with regard to the following: (1) the scheme is compact as it extends only one point away in each direction from the point to which it is applied; (2) it gives better resolution for high wave-number waves in the solution of Poisson equation, and (3) it reduces programming complexity and computation time. Examples worked out in detail are the decay of isotropic turbulence, homogeneous turbulent shear flow, and homogeneous turbulent shear flow with system rotation.
Fuel cell powered small unmanned aerial systems (UASs) for extended endurance flights
NASA Astrophysics Data System (ADS)
Chu, Deryn; Jiang, R.; Dunbar, Z.; Grew, Kyle; McClure, J.
2015-05-01
Small unmanned aerial systems (UASs) have been used for military applications and have additional potential for commercial applications [1-4]. For the military, these systems provide valuable intelligence, surveillance, reconnaissance and target acquisition (ISRTA) capabilities for units at the infantry, battalion, and company levels. The small UASs are light-weight, manportable, can be hand-launched, and are capable of carrying payloads. Currently, most small UASs are powered by lithium-ion or lithium polymer batteries; however, the flight endurance is usually limited less than two hours and requires frequent battery replacement. Long endurance small UAS flights have been demonstrated through the implementation of a fuel cell system. For instance, a propane fueled solid oxide fuel cell (SOFC) stack has been used to power a small UAS and shown to extend mission flight time. The research and development efforts presented here not only apply to small UASs, but also provide merit to the viability of extending mission operations for other unmanned systems applications.
Kalay, Berfin; Demiralp, Metin
2014-10-06
The expectation value definitions over an extended space from the considered Hilbert space of the system under consideration is given in another paper of the second author in this symposium. There, in that paper, the conceptuality rather than specification is emphasized on. This work uses that conceptuality to investigate the time evolutions of the position related operators' expectation values not in its standard meaning but rather in a new version of the definition over not the original Hilbert space but in the space obtained by extensions via introducing the images of the given initial wave packet under the positive integer powers of the system Hamiltonian. These images may not be residing in the same space of the initial wave packet when certain singularities appear in the structure of the system Hamiltonian. This may break down the existence of the integrals in the definitions of the expectation values. The cure is the use of basis functions in the abovementioned extended space and the sandwiching of the target operator whose expectation value is under questioning by an appropriately chosen operator guaranteeing the existence of the relevant integrals. Work specifically focuses on the hydrogen-like quantum systems whose Hamiltonians contain a polar singularity at the origin.
Kwon, Gayeung; Lee, Jiyun; Lim, Young-Hee
2016-01-01
Dairy Propionibacterium freudenreichii is a candidate non-lactic acid probiotic. However, little information is available on the effect of P. freudenreichii on lifespan extension in humans. The aim of this study was to evaluate the effects of P. freudenreichii on lifespan extension and to elucidate the mechanism of P. freudenreichii-dependent lifespan extension in Caenorhabditis elegans. The results showed that P. freudenreichii significantly (p < 0.05) extended the lifespan of C. elegans compared with Escherichia coli OP50, a standard food for the worm. Analysis of age-related biomarkers showed that P. freudenreichii retards ageing. Moreover, P. freudenreichii increased resistance against a human pathogen, Salmonella typhimurium, through the activation of skn-1, which is involved in pathogen resistance in C. elegans. Furthermore, P. freudenreichii-fed daf-16, jnk-1, skn-1 or daf-7 loss-of-function mutants showed an extended mean lifespan compared with E. coli OP50-fed worms. However, the increase in lifespan was not observed in pmk-1, sek-1, mek-1, dbl-1, daf-12 or daf-2 mutants, which suggests potential roles for these genes in P. freudenreichii-induced longevity in C. elegans. In conclusion, P. freudenreichii extends the lifespan of C. elegans via the p38 MAPK pathway involved in stress response and the TGF-β pathways associated with anti-inflammation processes in the immune system. PMID:27531646
Kwon, Gayeung; Lee, Jiyun; Lim, Young-Hee
2016-01-01
Dairy Propionibacterium freudenreichii is a candidate non-lactic acid probiotic. However, little information is available on the effect of P. freudenreichii on lifespan extension in humans. The aim of this study was to evaluate the effects of P. freudenreichii on lifespan extension and to elucidate the mechanism of P. freudenreichii-dependent lifespan extension in Caenorhabditis elegans. The results showed that P. freudenreichii significantly (p < 0.05) extended the lifespan of C. elegans compared with Escherichia coli OP50, a standard food for the worm. Analysis of age-related biomarkers showed that P. freudenreichii retards ageing. Moreover, P. freudenreichii increased resistance against a human pathogen, Salmonella typhimurium, through the activation of skn-1, which is involved in pathogen resistance in C. elegans. Furthermore, P. freudenreichii-fed daf-16, jnk-1, skn-1 or daf-7 loss-of-function mutants showed an extended mean lifespan compared with E. coli OP50-fed worms. However, the increase in lifespan was not observed in pmk-1, sek-1, mek-1, dbl-1, daf-12 or daf-2 mutants, which suggests potential roles for these genes in P. freudenreichii-induced longevity in C. elegans. In conclusion, P. freudenreichii extends the lifespan of C. elegans via the p38 MAPK pathway involved in stress response and the TGF-β pathways associated with anti-inflammation processes in the immune system. PMID:27531646
Extended Lyα emission around quasars with eclipsing damped Lyα systems
NASA Astrophysics Data System (ADS)
Fathivavsari, H.; Petitjean, P.; Noterdaeme, P.; Pâris, I.; Finley, H.; López, S.; Srianand, R.
2016-09-01
We present spectroscopic observations of six high redshift (zem > 2) quasars, which have been selected for their Lyman α (Lyα) emission region being only partially covered by a strong proximate (zabs ˜ zem) coronagraphic damped Lyα system (DLA). We detected spatially extended Lyα emission envelopes surrounding these six quasars, with projected spatial extent in the range 26 ≤ dLyα ≤ 51 kpc. No correlation is found between the quasar ionizing luminosity and the Lyα luminosity of their extended envelopes. This could be related to the limited covering factor of the extended gas and/or due to the AGN being obscured in other directions than towards the observer. Indeed, we find a strong correlation between the luminosity of the envelope and its spatial extent, which suggests that the envelopes are probably ionized by the AGN. The metallicity of the coronagraphic DLAs is low and varies in the range -1.75 < [Si/H] < -0.63. Highly ionized gas is observed to be associated with most of these DLAs, probably indicating ionization by the central AGN. One of these DLAs has the highest Al III/Si II ratio ever reported for any intervening and/or proximate DLA. Most of these DLAs are redshifted with respect to the quasar, implying that they might represent infalling gas probably accreted on to the quasar host galaxies through filaments.
An Integrated Nonlinear Analysis library - (INA) for solar system plasma turbulence
NASA Astrophysics Data System (ADS)
Munteanu, Costel; Kovacs, Peter; Echim, Marius; Koppan, Andras
2014-05-01
We present an integrated software library dedicated to the analysis of time series recorded in space and adapted to investigate turbulence, intermittency and multifractals. The library is written in MATLAB and provides a graphical user interface (GUI) customized for the analysis of space physics data available online like: Coordinated Data Analysis Web (CDAWeb), Automated Multi Dataset Analysis system (AMDA), Planetary Science Archive (PSA), World Data Center Kyoto (WDC), Ulysses Final Archive (UFA) and Cluster Active Archive (CAA). Three main modules are already implemented in INA : the Power Spectral Density (PSD) Analysis, the Wavelet and Intemittency Analysis and the Probability Density Functions (PDF) analysis.The layered structure of the software allows the user to easily switch between different modules/methods while retaining the same time interval for the analysis. The wavelet analysis module includes algorithms to compute and analyse the PSD, the Scalogram, the Local Intermittency Measure (LIM) or the Flatness parameter. The PDF analysis module includes algorithms for computing the PDFs for a range of scales and parameters fully customizable by the user; it also computes the Flatness parameter and enables fast comparison with standard PDF profiles like, for instance, the Gaussian PDF. The library has been already tested on Cluster and Venus Express data and we will show relevant examples. Research supported by the European Community's Seventh Framework Programme (FP7/2007-2013) under grant agreement no 313038/STORM, and a grant of the Romanian Ministry of National Education, CNCS UEFISCDI, project number PN-II-ID PCE-2012-4-0418.
Samanta, Devranjan; Dubief, Yves; Holzner, Markus; Schäfer, Christof; Morozov, Alexander N; Wagner, Christian; Hof, Björn
2013-06-25
Turbulence is ubiquitous in nature, yet even for the case of ordinary Newtonian fluids like water, our understanding of this phenomenon is limited. Many liquids of practical importance are more complicated (e.g., blood, polymer melts, paints), however; they exhibit elastic as well as viscous characteristics, and the relation between stress and strain is nonlinear. We demonstrate here for a model system of such complex fluids that at high shear rates, turbulence is not simply modified as previously believed but is suppressed and replaced by a different type of disordered motion, elasto-inertial turbulence. Elasto-inertial turbulence is found to occur at much lower Reynolds numbers than Newtonian turbulence, and the dynamical properties differ significantly. The friction scaling observed coincides with the so-called "maximum drag reduction" asymptote, which is exhibited by a wide range of viscoelastic fluids. PMID:23757498
Verification of Gamma Knife extend system based fractionated treatment planning using EBT2 film
Natanasabapathi, Gopishankar; Bisht, Raj Kishor
2013-12-15
Purpose: This paper presents EBT2 film verification of fractionated treatment planning with the Gamma Knife (GK) extend system, a relocatable frame system for multiple-fraction or serial multiple-session radiosurgery.Methods: A human head shaped phantom simulated the verification process for fractionated Gamma Knife treatment. Phantom preparation for Extend Frame based treatment planning involved creating a dental impression, fitting the phantom to the frame system, and acquiring a stereotactic computed tomography (CT) scan. A CT scan (Siemens, Emotion 6) of the phantom was obtained with following parameters: Tube voltage—110 kV, tube current—280 mA, pixel size—0.5 × 0.5 and 1 mm slice thickness. A treatment plan with two 8 mm collimator shots and three sectors blocking in each shot was made. Dose prescription of 4 Gy at 100% was delivered for the first fraction out of the two fractions planned. Gafchromic EBT2 film (ISP Wayne, NJ) was used as 2D verification dosimeter in this process. Films were cut and placed inside the film insert of the phantom for treatment dose delivery. Meanwhile a set of films from the same batch were exposed from 0 to 12 Gy doses for calibration purposes. An EPSON (Expression 10000 XL) scanner was used for scanning the exposed films in transparency mode. Scanned films were analyzed with inhouse written MATLAB codes.Results: Gamma index analysis of film measurement in comparison with TPS calculated dose resulted in high pass rates >90% for tolerance criteria of 1%/1 mm. The isodose overlay and linear dose profiles of film measured and computed dose distribution on sagittal and coronal plane were in close agreement.Conclusions: Through this study, the authors propose treatment verification QA method for Extend frame based fractionated Gamma Knife radiosurgery using EBT2 film.
NASA Astrophysics Data System (ADS)
Khallaf, Haitham S.; Garrido-Balsells, José M.; Shalaby, Hossam M. H.; Sampei, Seiichi
2015-12-01
The performance of multiple-input multiple-output free space optical (MIMO-FSO) communication systems, that adopt multipulse pulse position modulation (MPPM) techniques, is analyzed. Both exact and approximate symbol-error rates (SERs) are derived for both cases of uncorrelated and correlated channels. The effects of background noise, receiver shot-noise, and atmospheric turbulence are taken into consideration in our analysis. The random fluctuations of the received optical irradiance, produced by the atmospheric turbulence, is modeled by the widely used gamma-gamma statistical distribution. Uncorrelated MIMO channels are modeled by the α-μ distribution. A closed-form expression for the probability density function of the optical received irradiance is derived for the case of correlated MIMO channels. Using our analytical expressions, the degradation of the system performance with the increment of the correlation coefficients between MIMO channels is corroborated.
NASA Astrophysics Data System (ADS)
Laizet, Sylvain; Lamballais, Eric; Vassilicos, J. Christos
2015-11-01
Incompact3d is a high-order flow solver dedicated to Direct and Large Eddy Simulations (DNS/LES) using High Performance Computing (HPC) systems which isdevoted to turbulent flows at the interface between academic research and upstream industrial R&D. It is originating from the University of Poitiers (France) and was developed there as well as, more recently, in the Turbulence, Mixing and Flow Control Group at Imperial College London (UK). This high-order flow solver can reconcile accuracy, efficiency, versatility and scalability using a simple Cartesian mesh and up to one million computational cores. The three key ingredients of this successful cocktail to tackle turbulence on HPC systemswill be given in this talkfollowed by various applications such as fractal-generated turbulence, gravity currents in an open basin, impinging jets on a heated plate and a micro-jet device to control a turbulent jet.
Extending the mirror neuron system model, I. Audible actions and invisible grasps.
Bonaiuto, James; Rosta, Edina; Arbib, Michael
2007-01-01
The paper introduces mirror neuron system II (MNS2), a new version of the MNS model (Oztop and Arbib in Biol Cybern 87 (2):116-140, 2002) of action recognition learning by mirror neurons of the macaque brain. The new model uses a recurrent architecture that is biologically more plausible than that of the original model. Moreover, MNS2 extends the capacity of the model to address data on audio-visual mirror neurons and on the response of mirror neurons when the target object was recently visible but is currently hidden. PMID:17028884
Majda, Andrew J; Grote, Marcus J
2007-01-23
Many contemporary problems in science involve making predictions based on partial observation of extremely complicated spatially extended systems with many degrees of freedom and physical instabilities on both large and small scales. Various new ensemble filtering strategies have been developed recently for these applications, and new mathematical issues arise. Here, explicit off-line test criteria for stable accurate discrete filtering are developed for use in the above context and mimic the classical stability analysis for finite difference schemes. First, constant coefficient partial differential equations, which are randomly forced and damped to mimic mesh scale energy spectra in the above problems are developed as off-line filtering test problems. Then mathematical analysis is used to show that under natural suitable hypothesis the time filtering algorithms for general finite difference discrete approximations to an sxs partial differential equation system with suitable observations decompose into much simpler independent s-dimensional filtering problems for each spatial wave number separately; in other test problems, such block diagonal models rigorously provide upper and lower bounds on the filtering algorithm. In this fashion, elementary off-line filtering criteria can be developed for complex spatially extended systems. The theory is illustrated for time filters by using both unstable and implicit difference scheme approximations to the stochastically forced heat equation where the combined effects of filter stability and model error are analyzed through the simpler off-line criteria. PMID:17227864
Lou, Der-Chyuan; Lee, Tian-Fu; Lin, Tsung-Hung
2015-05-01
Authenticated key agreements for telecare medicine information systems provide patients, doctors, nurses and health visitors with accessing medical information systems and getting remote services efficiently and conveniently through an open network. In order to have higher security, many authenticated key agreement schemes appended biometric keys to realize identification except for using passwords and smartcards. Due to too many transmissions and computational costs, these authenticated key agreement schemes are inefficient in communication and computation. This investigation develops two secure and efficient authenticated key agreement schemes for telecare medicine information systems by using biometric key and extended chaotic maps. One scheme is synchronization-based, while the other nonce-based. Compared to related approaches, the proposed schemes not only retain the same security properties with previous schemes, but also provide users with privacy protection and have fewer transmissions and lower computational cost. PMID:25795325
NASA Technical Reports Server (NTRS)
Poeschel, R. L.; Hawthorne, E. I.; Weisman, Y. C.; Frisman, M.; Benson, G. C.; Mcgrath, R. J.; Martinelli, R. M.; Linsenbardt, T. L.; Beattie, J. R.
1977-01-01
Several thrust system design concepts were evaluated and compared using the specifications of the most advanced 30 cm engineering model thruster as the technology base. Emphasis was placed on relatively high power missions (60 to 100 kW) such as a Halley's comet rendezvous. The extensions in thruster performance required for the Halley's comet mission were defined and alternative thrust system concepts were designed in sufficient detail for comparing mass, efficiency, reliability, structure, and thermal characteristics. Confirmation testing and analysis of thruster and power processing components were performed, and the feasibility of satisfying extended performance requirements was verified. A baseline design was selected from the alternatives considered, and the design analysis and documentation were refined. The baseline thrust system design features modular construction, conventional power processing, and a concentrator solar array concept and is designed to interface with the Space Shuttle.
NASA Astrophysics Data System (ADS)
Gonczarek, Ryszard; Krzyzosiak, Mateusz; Gonczarek, Adam; Jacak, Lucjan
2015-06-01
In this paper, we discuss the mathematical structure of the s-wave superconducting gap and other quantitative characteristics of superconducting systems. In particular, we evaluate and discuss integrals inherent in fundamental equations describing superconducting systems. The results presented here extend the approach formulated by Abrikosov and Maki, which was restricted to the first-order expansion. A few infinite families of integrals are derived and allow us to express the fundamental equations by means of analytic formulas. They can be then exploited in order to find some quantitative characteristics of superconducting systems by the method of successive approximations. We show that the results can be applied to some modern formalisms in order to study high-Tc superconductors and other superconducting materials of the new generation.
Moment Equations in a Lotka--Volterra Extended System with Time Correlated Noise
NASA Astrophysics Data System (ADS)
Valenti, D.; Schimansky-Geier, L.; Sailer, X.; Spagnolo, B.; Iacomi, M.
2007-05-01
A spatially extended Lotka--Volterra system of two competing species in the presence of two correlated noise sources is analyzed: (i) an external multiplicative time correlated noise, which mimics the interaction between the system and the environment; (ii) a dichotomous stochastic process, whose jump rate is a periodic function, which represents the interaction parameter between the species. The moment equations for the species densities are derived in Gaussian approximation, using a mean field approach. Within this formalism we study the effect of the external time correlated noise on the ecosystem dynamics. We find that the time behavior of the 1st order moments are independent on the multiplicative noise source. However, the behavior of the 2nd order moments is strongly affected both by the intensity and the correlation time of the multiplicative noise. Finally we compare our results with those obtained studying the system dynamics by a coupled map lattice model.
Effect of laminar and turbulent fluid flow on mass transfer in some electrochemical systems
NASA Astrophysics Data System (ADS)
Chen, Qian
2000-10-01
The influence of fluid flow on electrode-shape change that results from electrodeposition in the presence of a model leveling agent is simulated and discussed. The treatment is more rigorous than past studies in that flow and concentration fields are recalculated as the electrode shape changes. It is shown that uncertainties due to approximate treatments of fluid flow may be as significant as existing discrepancies between experiment and theory. The mass transfer characteristics of a turbulent slot jet impinging normally on a target wall are examined using numerical simulations. Fluid flow is modeled using the k-turbulence model of Wilcox [1]. The computations are validated against existing experimental fluid flow, heat transfer and mass transfer data. The range of Reynolds numbers examined is from 450 to 20,000 with Prandtl or Schmidt numbers from 1 to 2,400. The distance of the target plate from the slot jet varies between 2 to 8 times the slot jet width. The study reveals computational aspects that are unique to the solution of flow and mass transfer problems with the combination of high Schmidt numbers and turbulent flows. A low order "coherent structure" near-wall flow model first proposed by Chapman and Kuhn [2] is used to obtain the near-wall fluid flow field. This flow field is then used to compute high Schmidt number mass transfer for a turbulent boundary layer flow. It is shown that useful insight can be obtained into high Schmidt number mass transfer for a turbulent fluid flow using this model. The boundary conditions for this near-wall field for more complicated flow or geometries may be obtained either from experimental turbulent velocity and frequency data or from a k-o type of turbulence model.
Transport of magnetic turbulence in supernova remnants
NASA Astrophysics Data System (ADS)
Brose, R.; Telezhinsky, I.; Pohl, M.
2016-08-01
Context. Supernova remnants are known as sources of Galactic cosmic rays for their nonthermal emission of radio waves, X-rays, and gamma rays. However, the observed soft broken power-law spectra are hard to reproduce within standard acceleration theory based on the assumption of Bohm diffusion and steady-state calculations. Aims: We point out that a time-dependent treatment of the acceleration process together with a self-consistent treatment of the scattering turbulence amplification is necessary. Methods: We numerically solve the coupled system of transport equations for cosmic rays and isotropic Alfvénic turbulence. The equations are coupled through the growth rate of turbulence determined by the cosmic-ray gradient and the spatial diffusion coefficient of cosmic rays determined by the energy density of the turbulence. The system is solved on a comoving expanding grid extending upstream for dozens of shock radii, allowing for the self-consistent study of cosmic-ray diffusion in the vicinity of their acceleration site. The transport equation for cosmic rays is solved in a test-particle approach. Results: We demonstrate that the system is typically not in a steady state. In fact, even after several thousand years of evolution, no equilibrium situation is reached. The resulting time-dependent particle spectra strongly differ from those derived assuming a steady state and Bohm diffusion. Our results indicate that proper accounting for the evolution of the scattering turbulence and hence the particle diffusion coefficient is crucial for the formation of the observed soft spectra. In any case, the need to continuously develop magnetic turbulence upstream of the shock introduces nonlinearity in addition to that imposed by cosmic-ray feedback.
Matching of an extended high-current Z-discharge to a pulsed power system
NASA Astrophysics Data System (ADS)
Burtsev, V. A.; Kalinin, N. V.
2013-08-01
Conditions for matching an extended high-current Z-discharge to a pulsed power system are numerically investigated. The power system consists of a pulsed voltage generator and a long transmission line. Experiments are aimed at generating a highly ionized dense plasma as an active medium for an extreme ultraviolet laser on hydrogen-like ions of nitrogen (λ = 13.4 nm). Emphasis is on the distribution of the energy transmitted from a storage ring to a load among its components and on the reduction of the energy that remains in the electrical circuit by the end of the pump pulse and will inevitably dissipate in the discharge tube. The solution of this problem will make it possible to diminish the load on the walls of the discharge chamber and extend its service life. It is shown that energy deposition into the load is effective when the timeaveraged sum of the ohmic and dynamic components of the discharge resistance is roughly equal to the wave impedance of the transmission line. In this case, the wave reflected from the load carries away a minimal energy, which allows for optimization of the energy deposited into the load. The input and output energy balances for different matching conditions are calculated with an eye to designing an efficient short-wavelength extreme ultraviolet laser with a long service life of the discharge tube.
Automatic system to control the operation of an extended cavity diode laser
NASA Astrophysics Data System (ADS)
Allard, F.; Maksimovic, I.; Abgrall, M.; Laurent, Ph.
2004-01-01
This article describes an automatic system that permanently keeps an extended cavity diode laser (ECDL) frequency locked to a cesium line (852 nm). The ECDL has a new architecture based on an intracavity étalon. The laser power is 30 mW and the linewidth is narrower than 50 kHz. Two acousto-optic modulators finely change the laser frequency and optical power. The electronic control is composed of a computer, microcontrollers, digital analog converters, and direct digital synthesizers. The computer searches the ECDL parameters to tune it to the Cs line and closes the servoloop. It permanently checks the servoloop and relocks the laser if necessary. Both acousto-optic modulators are driven in real time by microcontrollers. They are programed in order to control the laser power and frequency with a predefined time sequence. This system, especially developed for an atomic fountain, can be easily adapted to a wide range of applications.
NASA Technical Reports Server (NTRS)
Boykin, William H., Jr.
1993-01-01
Adaptive optics are used in telescopes for both viewing objects with minimum distortion and for transmitting laser beams with minimum beam divergence and dance. In order to test concepts on a smaller scale, NASA MSFC is in the process of setting up an adaptive optics test facility with precision (fraction of wavelengths) measurement equipment. The initial system under test is the adaptive optical telescope called PAMELA (Phased Array Mirror Extendible Large Aperture). Goals of this test are: assessment of test hardware specifications for PAMELA application and the determination of the sensitivities of instruments for measuring PAMELA (and other adaptive optical telescopes) imperfections; evaluation of the PAMELA system integration effort and test progress and recommended actions to enhance these activities; and development of concepts and prototypes of experimental apparatuses for PAMELA.
Extending dispersive waves theory to use in semi-open systems
NASA Astrophysics Data System (ADS)
Chumakova, Lyubov; Rosales, Ruben; Rzeznik, Andrew; Tabak, Esteban
2015-11-01
In the classical linear dispersive wave theory the sinusoidal waves e i (kx - ωt) carry energy with the group speed cg = dω / dk . This concept is limited to the case where both the frequency ω (k) and the wavenumber k are real. On the other hand, semi-open dispersive systems allow more than just sinusoidal solutions: they can have exponentially blowing up and/or decaying solutions as well. In this talk I will address the questions of what is direction and the speed of the energy propagation for these exponential waves, extend the classical concept of group velocity, and use this theory to construct radiation boundary conditions for semi-open dispersive systems. This approach will be demonstrated on an example of dry hydrostatic troposphere which experiences effective damping due to gravity waves propagating into the stratosphere. RSE, Scottish government.
NASA Astrophysics Data System (ADS)
Gemmrich, J.; Farmer, D.
2003-04-01
Breaking surface waves are believed to provide a major pathway for the energy input from the atmosphere to the ocean and are a source of enhanced turbulent kinetic energy levels in the near-surface layer. Increased turbulence levels relate to enhanced air-sea exchange processes. The ocean surface is a complex system with a wide range of relevant scales. We use direct measurement of the small-scale velocity field as a first step to evaluate near-surface turbulence. At wind speed up to 14 m/s, velocity profiles were obtained with pulse-to-pulse coherent acoustic Doppler profilers. Based on wavenumber spectra calculated with the empirical mode decomposition, dissipation of turbulent kinetic energy at ~1m beneath the free surface and 1 Hz sampling rate is estimated. In addition, bubble size distributions were obtained from acoustic resonator measurements and whitecap occurrence was monitored with video cameras. High turbulence levels with dissipation rates more than four orders larger than the background dissipation are linked to wave breaking. The decay and depth-dependence of the wave-induced turbulence are examined and implications for turbulence models are discussed. In individual breaking waves, the onset of enhanced dissipation occurs up to a quarter wave period prior to the air entrainment. Magnitude and occurrence of the pre-breaking turbulence are consistent with wave-turbulence interaction in a rotational wave field. The detailed structure of the turbulence and bubble field associated with breaking waves will be presented. Implications for air-sea exchange processes will be discussed.
How to Extend the Capabilities of Space Systems for Long Duration Space Exploration Systems
NASA Technical Reports Server (NTRS)
Marzwell, Neville I.; Waterman, Robert D.; KrishnaKumar, Kalmanje; Waterman, Susan J.
2005-01-01
For sustainable Exploration Missions the need exists to assemble systems-of-systems in space, on the Moon or on other planetary surfaces. To fulfill this need new and innovative system architecture is needed that can be satisfied with the present lift capability of existing rocket technology without the added cost of developing a new heavy lift vehicle. To enable ultra-long life missions with minimum redundancy and lighter mass the need exists to develop system soft,i,are and hardware reconfigurability, which enables increasing functionality and multiple use of launched assets while at the same time overcoming any components failures. Also the need exists to develop the ability to dynamically demate and reassemble individual system elements during a mission in order to work around failed hardware or changed mission requirements. Therefore to meet the goals of Space Exploration Missions in hiteroperability and Reconfigurability, many challenges must be addressed to transform the traditional static avionics architecture into architecture with dynamic capabilities. The objective of this paper is to introduce concepts associated with reconfigurable computer systems; review the various needs and challenges associated with reconfigurable avionics space systems; provide an operational example that illustrates the needs applicable to either the Crew Exploration Vehicle or a collection of "Habot like" mobile surface elements; summarize the approaches that address key challenges to acceptance of a Flexible, Intelligent, Modular and Affordable reconfigurable avionics space system.
How to Extend the Capabilities of Space Systems for Long Duration Space Exploration Systems
NASA Technical Reports Server (NTRS)
Marzwell, Neville I.; Waterman, Robert D.; KrishnaKumar, Kalmanje; Waterman, Susan J.
2005-01-01
For sustainable Exploration Missions the need exists to assemble systems-of-systems in space, on the Moon or on other planetary surfaces. To fulfill this need new and innovative system architectures must be developed to be modularized and launched with the present lift capability of existing rocket technology. To enable long duration missions with minimal redundancy and mass, system software and hardware must be reconfigurable. This will enable increased functionality and multiple use of launched assets while providing the capability to quickly overcome components failures. Additional required capability includes the ability to dynamically demate and reassemble individual system elements during a mission in order to recover from failed hardware or to adapt to changes in mission requirements. To meet the Space Exploration goals of Interoperability and Reconfigurability, many challenges must be addressed to transform the traditional static avionics architectures into architectures with dynamic capabilities. The objective of this paper is to introduce concepts associated with reconfigurable computer systems; to review the various needs and challenges associated with reconfigurable avionics space systems; to provide an operational example that illustrates the application to both the Crew Exploration Vehicle and a collection of 'Habot-like' mobile surface elements; to summarize the approaches that address key challenges to the acceptance of a Flexible, Intelligent, Modular, Affordable and Reconfigurable avionics space system.
One-dimensional wave turbulence
NASA Astrophysics Data System (ADS)
Zakharov, Vladimir; Dias, Frédéric; Pushkarev, Andrei
2004-08-01
The problem of turbulence is one of the central problems in theoretical physics. While the theory of fully developed turbulence has been widely studied, the theory of wave turbulence has been less studied, partly because it developed later. Wave turbulence takes place in physical systems of nonlinear dispersive waves. In most applications nonlinearity is small and dispersive wave interactions are weak. The weak turbulence theory is a method for a statistical description of weakly nonlinear interacting waves with random phases. It is not surprising that the theory of weak wave turbulence began to develop in connection with some problems of plasma physics as well as of wind waves. The present review is restricted to one-dimensional wave turbulence, essentially because finer computational grids can be used in numerical computations. Most of the review is devoted to wave turbulence in various wave equations, and in particular in a simple one-dimensional model of wave turbulence introduced by Majda, McLaughlin and Tabak in 1997. All the considered equations are model equations, but consequences on physical systems such as ocean waves are discussed as well. The main conclusion is that the range in which the theory of pure weak turbulence is valid is narrow. In general, wave turbulence is not completely weak. Together with the weak turbulence component, it can include coherent structures, such as solitons, quasisolitons, collapses or broad collapses. As a result, weak and strong turbulence coexist. In situations where coherent structures cannot develop, weak turbulence dominates. Even though this is primarily a review paper, new results are presented as well, especially on self-organized criticality and on quasisolitonic turbulence.
Extending and expanding the Darwinian synthesis: the role of complex systems dynamics.
Weber, Bruce H
2011-03-01
Darwinism is defined here as an evolving research tradition based upon the concepts of natural selection acting upon heritable variation articulated via background assumptions about systems dynamics. Darwin's theory of evolution was developed within a context of the background assumptions of Newtonian systems dynamics. The Modern Evolutionary Synthesis, or neo-Darwinism, successfully joined Darwinian selection and Mendelian genetics by developing population genetics informed by background assumptions of Boltzmannian systems dynamics. Currently the Darwinian Research Tradition is changing as it incorporates new information and ideas from molecular biology, paleontology, developmental biology, and systems ecology. This putative expanded and extended synthesis is most perspicuously deployed using background assumptions from complex systems dynamics. Such attempts seek to not only broaden the range of phenomena encompassed by the Darwinian Research Tradition, such as neutral molecular evolution, punctuated equilibrium, as well as developmental biology, and systems ecology more generally, but to also address issues of the emergence of evolutionary novelties as well as of life itself. PMID:21300318
The Turbulent Origin of Spin-Orbit Misalignment in Planetary Systems
Fielding, Drummond B.; McKee, Christopher F.; Socrates, Aristostle; Cunningham, Andrew J.; Klein, Richard I.
2015-05-13
The turbulent environment from which stars form may lead to misalignment between the stellar spin and the remnant protoplanetary disk. By using hydrodynamic and magnetohydrodynamic simulations, we demonstrate that a wide range of stellar obliquities may be produced as a by-product of forming a star within a turbulent environment. We present a simple semi-analytic model that reveals this connection between the turbulent motions and the orientation of a star and its disk. Our results are consistent with the observed obliquity distribution of hot Jupiters. Migration of misaligned hot Jupiters may, therefore, be due to tidal dissipation in the disk, rathermore » than tidal dissipation of the star-planet interaction.« less
Raupach, Marc; Tonner, Ralf
2015-05-21
The development and first applications of a new periodic energy decomposition analysis (pEDA) scheme for extended systems based on the Kohn-Sham approach to density functional theory are described. The pEDA decomposes the bonding energy between two fragments (e.g., the adsorption energy of a molecule on a surface) into several well-defined terms: preparation, electrostatic, Pauli repulsion, and orbital relaxation energies. This is complemented by consideration of dispersion interactions via a pairwise scheme. One major extension toward a previous implementation [Philipsen and Baerends, J. Phys. Chem. B 110, 12470 (2006)] lies in the separate discussion of electrostatic and Pauli and the addition of a dispersion term. The pEDA presented here for an implementation based on atomic orbitals can handle restricted and unrestricted fragments for 0D to 3D systems considering periodic boundary conditions with and without the determination of fragment occupations. For the latter case, reciprocal space sampling is enabled. The new method gives comparable results to established schemes for molecular systems and shows good convergence with respect to the basis set (TZ2P), the integration accuracy, and k-space sampling. Four typical bonding scenarios for surface-adsorbate complexes were chosen to highlight the performance of the method representing insulating (CO on MgO(001)), metallic (H{sub 2} on M(001), M = Pd, Cu), and semiconducting (CO and C{sub 2}H{sub 2} on Si(001)) substrates. These examples cover diverse substrates as well as bonding scenarios ranging from weakly interacting to covalent (shared electron and donor acceptor) bonding. The results presented lend confidence that the pEDA will be a powerful tool for the analysis of surface-adsorbate bonding in the future, enabling the transfer of concepts like ionic and covalent bonding, donor-acceptor interaction, steric repulsion, and others to extended systems.
Sushil; Pankaj
1992-12-31
This paper develops an integrated systems approach towards quality and cost in production systems. A spinning unit producing medium count ranges of yarn, has been taken as a case for study. The first part deals with developing a suitable methodology for the purpose by modifying the existing physical system theory modelling framework. The second part deals with the aspect of simulation for studying the impact of various processes and the quality of the output. Finally, the response of cost of output to the quality of output has been studied using the modified cost equation and carrying out the sensitivity analysis. 24 refs.
NASA Astrophysics Data System (ADS)
Vollmer, David Russell
The role of jet streaks and their associated upper-level structures (fronts, troughs, thermal fields, etc.) in enhancing orographically-induced aviation turbulence near and above the tropopause is investigated. The primary hypothesis for this research suggests that there is an optimal configuration for the positioning of upper-level circulations leading to vertically confluent flow and differential thermal advection, forming an intense inversion. Such a configuration may be associated with vertically-intersecting ageostrophic jet circulations or trough-induced differential vertical motions leading to cold air undercutting a warm layer aloft, and compression of the warm layer in the presence of jet-induced shear. This structure is then perturbed by mountain waves, leading to a downscale cascade of kinetic energy, eventually leading to potential aviation turbulence. Two cases of clear-air turbulence (CAT) are examined using mesoscale numerical simulations. The first case involved a DC-8 attempting to cross the Colorado Front Range when it encountered extreme CAT resulting in loss of part of one wing and an engine. In this case the superposition of two distinct jet features was hypothesized to have established an unusually strong tropopause which allowed strong buoyancy-driven motions to enhance the horizontal shear and turbulent eddies, eventually leading to the turbulent downburst hypothesized to have played a role in damaging the aircraft. The second study used data from the Terrain-Induced Rotor Experiment (T-REX) and examined a turbulent wave-breaking event recorded by a research aircraft in the lower stratosphere. A different jet regime was found in this case, with a strong upstream trough and decreasing cyclonic curvature with height above the tropopause and a strong lower stratospheric inversion. The vertical variation of static stability in the lower stratosphere was found to create a favorable environment for amplification and breaking of the mountain wave
NASA Technical Reports Server (NTRS)
Frehlich, Rod; Kavaya, Michael J.
2000-01-01
The explanation for the difference between simulation and the zero-order theory for heterodyne lidar returns in a turbulent atmosphere proposed by Belmonte and Rye is incorrect. The theoretical expansion is not developed under a square- law-structure function approximation (random wedge atmosphere). Agreement between the simulations and the zero-order term of the theoretical expansion is produced for the limit of statistically independent paths (bi-static operation with large transmitter-receiver separation) when the simulations correctly include the large-scale gradients of the turbulent atmosphere.
Energy transfer by inertial waves during the buildup of turbulence in a rotating system.
Kolvin, Itamar; Cohen, Kobi; Vardi, Yuval; Sharon, Eran
2009-01-01
We study the transition from fluid at rest to turbulence in a rotating tank. The energy is transported by inertial wave packets through the fluid volume. These high amplitude waves propagate at velocities consistent with those calculated from linearized theory [H. P. Greenspan, (Cambridge University Press, Cambridge, England, 1968)]. A "front" in the temporal evolution of the energy power spectrum indicates a time scale for energy transport at the linear wave speed. Nonlinear energy transfer between modes is governed by a different, longer, time scale. The observed mechanisms can lead to significant differences between rotating and two-dimensional turbulent flows. PMID:19257200
Deco, Gustavo; Martí, Daniel
2007-03-01
The analysis of transitions in stochastic neurodynamical systems is essential to understand the computational principles that underlie those perceptual and cognitive processes involving multistable phenomena, like decision making and bistable perception. To investigate the role of noise in a multistable neurodynamical system described by coupled differential equations, one usually considers numerical simulations, which are time consuming because of the need for sufficiently many trials to capture the statistics of the influence of the fluctuations on that system. An alternative analytical approach involves the derivation of deterministic differential equations for the moments of the distribution of the activity of the neuronal populations. However, the application of the method of moments is restricted by the assumption that the distribution of the state variables of the system takes on a unimodal Gaussian shape. We extend in this paper the classical moments method to the case of bimodal distribution of the state variables, such that a reduced system of deterministic coupled differential equations can be derived for the desired regime of multistability. PMID:17500732
NASA Astrophysics Data System (ADS)
Deco, Gustavo; Martí, Daniel
2007-03-01
The analysis of transitions in stochastic neurodynamical systems is essential to understand the computational principles that underlie those perceptual and cognitive processes involving multistable phenomena, like decision making and bistable perception. To investigate the role of noise in a multistable neurodynamical system described by coupled differential equations, one usually considers numerical simulations, which are time consuming because of the need for sufficiently many trials to capture the statistics of the influence of the fluctuations on that system. An alternative analytical approach involves the derivation of deterministic differential equations for the moments of the distribution of the activity of the neuronal populations. However, the application of the method of moments is restricted by the assumption that the distribution of the state variables of the system takes on a unimodal Gaussian shape. We extend in this paper the classical moments method to the case of bimodal distribution of the state variables, such that a reduced system of deterministic coupled differential equations can be derived for the desired regime of multistability.
An extended grammar system for learning and recognizing complex visual events.
Zhang, Zhang; Tan, Tieniu; Huang, Kaiqi
2011-02-01
For a grammar-based approach to the recognition of visual events, there are two major limitations that prevent it from real application. One is that the event rules are predefined by domain experts, which means huge manual cost. The other is that the commonly used grammar can only handle sequential relations between subevents, which is inadequate to recognize more complex events involving parallel subevents. To solve these problems, we propose an extended grammar approach to modeling and recognizing complex visual events. First, motion trajectories as original features are transformed into a set of basic motion patterns of a single moving object, namely, primitives (terminals) in the grammar system. Then, a Minimum Description Length (MDL) based rule induction algorithm is performed to discover the hidden temporal structures in primitive stream, where Stochastic Context-Free Grammar (SCFG) is extended by Allen's temporal logic to model the complex temporal relations between subevents. Finally, a Multithread Parsing (MTP) algorithm is adopted to recognize interesting complex events in a given primitive stream, where a Viterbi-like error recovery strategy is also proposed to handle large-scale errors, e.g., insertion and deletion errors. Extensive experiments, including gymnastic exercises, traffic light events, and multi-agent interactions, have been executed to validate the effectiveness of the proposed approach. PMID:21193807
NASA Astrophysics Data System (ADS)
Chen, James C.
1997-05-01
The primary focus of laser based oncologic PDT has been on the treatment of skin and hollow organ tumors. Extending PDT to other primary internal lesions and metastasis requires a different approach. Light Sciences has developed a series of semiconductor-based devices which will be completely implanted in the patient using established, minimally invasive surgical techniques. These devices are energized noninvasively utilizing inductive coupling. The light delivery system will allow the clinician to modulate the intensity, spatial distribution, and duration of light delivery in order to maximize the benefits derived from each PDT drug dose. Light Sciences' technology minimizes patient risk and discomfort, is cost competitive, and expands the treatment options available to the clinician. Avoidance of lengthy operations, bone marrow suppression, and an emphasis on organ preservation allow this next generation of PDT light delivery devices to be effectively integrated with other forms of cancer treatment, if desired. We have termed our technique 'Multi-treatment Extended Duration PDT'. In what follows, we shall describe Light Sciences' technology and development of minimally invasive oncologic PDT.
NASA Astrophysics Data System (ADS)
Berakdar, Jamal
2003-09-01
Knowledge of the excitation characteristics of matter is decisive for the descriptions of a variety of dynamical processes, which are of significant technological interest. E.g. transport properties and the optical response are controlled by the excitation spectrum. This self-contained work is a coherent presentation of the quantum theory of correlated few-particle excitations in electronic systems. It begins with a compact resume of the quantum mechanics of single particle excitations. Particular emphasis is put on Green function methods, which offer a natural tool to unravel the relations between the physics of small and large electronic systems. The book contains explicit expressions for the Coulomb Green function of two charge particles and a generalization to three-body systems. Techniques for the many-body Green function of finite systems are introduced and some explicit calculations of the Green functions are given. Concrete examples are provided and the theories are contrasted with experimental data, when available. A complimentary volume presents an up-to-date selection of applications of the developed concepts and a comparison with available experiments is made
NASA Astrophysics Data System (ADS)
Berakdar, Jamal
2006-02-01
Knowledge of the excitation characteristics of matter is decisive for the descriptions of a variety of dynamical processes, which are of significant technological interest. E.g. transport properties and the optical response are controlled by the excitation spectrum. This self-contained work is a coherent presentation of the quantum theory of correlated few-particle excitations in electronic systems. It begins with a compact resume of the quantum mechanics of single particle excitations. Particular emphasis is put on Green function methods, which offer a natural tool to unravel the relations between the physics of small and large electronic systems. The book contains explicit expressions for the Coulomb Green function of two charge particles and a generalization to three-body systems. Techniques for the many-body Green function of finite systems are introduced and some explicit calculations of the Green functions are given. Concrete examples are provided and the theories are contrasted with experimental data, when available. A complimentary volume presents an up-to-date selection of applications of the developed concepts and a comparison with available experiments is made
NASA Astrophysics Data System (ADS)
Tap, F. A.; Hilbert, R.; Thévenin, D.; Veynante, D.
2004-03-01
Auto-ignition of turbulent non-premixed systems is encountered in practical devices such as diesel internal combustion engines. It remains a challenge for modellers, as it exhibits specific features such as unsteadiness, flame propagation and combustion far from stoichiometric conditions. In this paper, a two-dimensional DNS database of an igniting H2/O2/N2 mixing layer, including detailed chemistry and transport, is extensively post-processed in order to gain physical insight into the flame structure and dynamics during auto-ignition. The results are used as a framework for the development of a generalized flame surface density modelling approach by integrating the equations over all possible mixture fraction values. The mean reaction rate is split into two contributions: a generalized flame surface density and a mean reaction rate per unit generalized flame surface density. The unsteadiness of the ignition phenomenon is accounted for via a generalized progress variable. Closures for the generalized surface average of the reaction rate and for the generalized progress variable are proposed, and the modelling approach is tested a priori versus the DNS data. The use of a laminar database for the chemistry coupled to the mean turbulent field via the generalized progress variable shows very promising results, capturing the correct ignition delay and the premixed peak in the turbulent mean heat release rate evolution. This allows confidence in future inclusion and validation of this approach in a RANS-CFD code.
Extended Plate and Beam Wall System: Concept Investigation and Initial Evaluation
Wiehagen, J.; Kochkin, V.
2015-08-01
A new and innovative High-R wall design, referred to as the Extended Plate & Beam (EP&B), is under development. The EP&B system uniquely integrates foam sheathing insulation with wall framing such that wood structural panels are installed exterior of the foam sheathing, enabling the use of standard practices for installation of drainage plane, windows and doors, claddings, cavity insulation, and the standard exterior foam sheathing installation approach prone to damage of the foam during transportation of prefabricated wall panels. As part of the ongoing work, the EP&B wall system concept has undergone structural verification testing and has been positively vetted by a group of industry stakeholders. Having passed these initial milestone markers, the advanced wall system design has been analyzed to assess cost implications relative to other advanced wall systems, undergone design assessment to develop construction details, and has been evaluated to develop representative prescriptive requirements for the building code. This report summarizes the assessment steps conducted to-date and provides details of the concept development.
Extended Kalman filtering for joint mitigation of phase and amplitude noise in coherent QAM systems.
Pakala, Lalitha; Schmauss, Bernhard
2016-03-21
We numerically investigate our proposed carrier phase and amplitude noise estimation (CPANE) algorithm using extend Kalman filter (EKF) for joint mitigation of linear and non-linear phase noise as well as amplitude noise on 4, 16 and 64 polarization multiplexed (PM) quadrature amplitude modulation (QAM) 224 Gb/s systems. The results are compared to decision directed (DD) carrier phase estimation (CPE), DD phase locked loop (PLL) and universal CPE (U-CPE) algorithms. Besides eliminating the necessity of phase unwrapping function, EKF-CPANE shows improved performance for both back-to-back (BTB) and transmission scenarios compared to the aforementioned algorithms. We further propose a weighted innovation approach (WIA) of the EKF-CPANE which gives an improvement of 0.3 dB in the Q-factor, compared to the original algorithm. PMID:27136830
An extended optimal velocity difference model in a cooperative driving system
NASA Astrophysics Data System (ADS)
Cao, Jinliang; Shi, Zhongke; Zhou, Jie
2015-10-01
An extended optimal velocity (OV) difference model is proposed in a cooperative driving system by considering multiple OV differences. The stability condition of the proposed model is obtained by applying the linear stability theory. The results show that the increase in number of cars that precede and their OV differences lead to the more stable traffic flow. The Burgers, Korteweg-de Vries (KdV) and modified Korteweg-de Vries (mKdV) equations are derived to describe the density waves in the stable, metastable and unstable regions, respectively. To verify these theoretical results, the numerical simulation is carried out. The theoretical and numerical results show that the stabilization of traffic flow is enhanced by considering multiple OV differences. The traffic jams can be suppressed by taking more information of cars ahead.
Extended flight evaluation of a near-term pitch active control system
NASA Technical Reports Server (NTRS)
Guinn, Wiley A.; Willey, Craig S.; Chong, Michael G.
1983-01-01
Fuel savings can be achieved by moving the center of gravity of an aircraft aft which reduces the static stability margin and consequently the trim drag. However, flying qualities of an aircraft with relaxed static stability can be significantly degraded. The flying qualities can be restored by using a pitch active control system (PACS). This report documents the work accomplished during a follow-on program (see NASA CR-165951 for initial program report) to perform extended flight tests of a near-term PACS. The program included flying qualities analyses, piloted flight simulation tests, aircraft preparation and flight tests to demonstrate that the near-term PACS provided good flying qualities within the linear static stability envelope to a negative 3% static stability margin.
NASA Technical Reports Server (NTRS)
Glover, Richard D.
1987-01-01
A pipelined, multiprocessor, general-purpose ground support equipment for digital flight systems has been developed and placed in service at the NASA Ames Research Center's Dryden Flight Research Facility. The design is an outgrowth of the earlier aircraft interrogation and display system (AIDS) used in support of several research projects to provide engineering-units display of internal control system parameters during development and qualification testing activities. The new system, incorporating multiple 16-bit processors, is called extended AIDS (XAIDS) and is now supporting the X-29A forward-swept-wing aircraft project. This report describes the design and mechanization of XAIDS and shows the steps whereby a typical user may take advantage of its high throughput and flexible features.
Measurement of Turbulent Water Vapor Fluxes from Lightweight Unmanned Aircraft Systems
NASA Astrophysics Data System (ADS)
Thomas, R. M.; Ramanathan, V.; Nguyen, H.; Lehmann*, K.
2010-12-01
Scientists at the Center for Clouds, Chemistry and Climate (C4) at the Scripps Institution of Oceanography have successfully used Unmanned Aircraft Systems (UASs) for measurements of radiation fluxes, aerosol concentrations and cloud microphysical properties. Building on this success, a payload to measure water vapor fluxes using the eddy covariance (EC) technique has been recently developed and tested. To our knowledge this is the first UAS turbulent flux system to incorporate high-frequency water vapor measurements. The driving aim of the water vapor flux system’s development is to investigate ‘atmospheric rivers’ in the north-western Pacific Ocean, these can lead to sporadic yet extreme rainfall and flooding events upon landfall in California. Such a flux system may also be used to investigate other weather events (e.g. the formation of hurricanes) and offers a powerful aerosol-cloud-radiative forcing investigative tool when combined with the existing aerosol/radiation and cloud microphysics UAS payloads. The atmospheric vertical wind component (w) is derived by this system at up to 100Hz using data from a GPS/Inertial Measurement Unit (GPS/IMU) combined with a fast-response gust probe mounted on the UAV. Measurements of w are then combined with equally high frequency water vapor data (collected using a Campbell Scientific Krypton Hygrometer) to calculate latent heat fluxes (λE). Two test flights were conducted at the NASA Dryden test facility on 27th May 2010, located in the Mojave Desert. Horizontal flight legs were recorded at four altitudes between 1000-2500 masl within the convective boundary layer. Preliminary data analysis indicates averaged spectral data follow the theoretical -5/3 slope , and extrapolation of the flux profile to the surface resulted in λE of 1.6 W m-2; in good agreement with 1.0 W m-2 λE measured by NOAA from a surface tower using standard flux techniques. The system performance during the Dryden test, as well as subsequent
Horton, W.; Hu, G.
1998-07-01
The origin of plasma turbulence from currents and spatial gradients in plasmas is described and shown to lead to the dominant transport mechanism in many plasma regimes. A wide variety of turbulent transport mechanism exists in plasmas. In this survey the authors summarize some of the universally observed plasma transport rates.
NASA Astrophysics Data System (ADS)
Ochoa, Maicol A.; Bruch, Anton; Nitzan, Abraham
2016-07-01
We study the energy distribution in the extended resonant level model at equilibrium. Previous investigations [Phys. Rev. B 89, 161306 (2014), 10.1103/PhysRevB.89.161306; Phys. Rev. B 93, 115318 (2016), 10.1103/PhysRevB.93.115318] have found, for a resonant electronic level interacting with a thermal free-electron wide-band bath, that the expectation value for the energy of the interacting subsystem can be correctly calculated by considering a symmetric splitting of the interaction Hamiltonian between the subsystem and the bath. However, the general implications of this approach were questioned [Phys. Rev. B 92, 235440 (2015), 10.1103/PhysRevB.92.235440]. Here, we show that, already at equilibrium, such splitting fails to describe the energy fluctuations, as measured here by the second and third central moments (namely, width and skewness) of the energy distribution. Furthermore, we find that when the wide-band approximation does not hold, no splitting of the system-bath interaction can describe the system thermodynamics. We conclude that in general no proper division subsystem of the Hamiltonian of the composite system can account for the energy distribution of the subsystem. This also implies that the thermodynamic effects due to local changes in the subsystem cannot in general be described by such splitting.
Xiao, Suzhi; Tao, Wei; Zhao, Hui
2016-01-01
In order to acquire an accurate three-dimensional (3D) measurement, the traditional fringe projection technique applies complex and laborious procedures to compensate for the errors that exist in the vision system. However, the error sources in the vision system are very complex, such as lens distortion, lens defocus, and fringe pattern nonsinusoidality. Some errors cannot even be explained or rendered with clear expressions and are difficult to compensate directly as a result. In this paper, an approach is proposed that avoids the complex and laborious compensation procedure for error sources but still promises accurate 3D measurement. It is realized by the mathematical model extension technique. The parameters of the extended mathematical model for the ’phase to 3D coordinates transformation’ are derived using the least-squares parameter estimation algorithm. In addition, a phase-coding method based on a frequency analysis is proposed for the absolute phase map retrieval to spatially isolated objects. The results demonstrate the validity and the accuracy of the proposed flexible fringe projection vision system on spatially continuous and discontinuous objects for 3D measurement. PMID:27136553
Two-Phase Thermal Switching System for a Small, Extended Duration Lunar Science Platform
NASA Technical Reports Server (NTRS)
Bugby, D.; Farmer, J.; OConnor, B.; Wirzburger, M.; Abel, E.; Stouffer, C.
2010-01-01
Issue: extended duration lunar science platforms, using solar/battery or radioisotope power, require thermal switching systems that: a) Provide efficient cooling during the 15-earth-day 390 K lunar day; b) Consume minimal power during the 15-earth-day 100 K lunar night. Objective: carry out an analytical study of thermal switching systems that can meet the thermal requirements of: a) International Lunar Network (ILN) anchor node mission - primary focus; b) Other missions such as polar crater landers. ILN Anchor Nodes: network of geophysical science platforms to better understand the interior structure/composition of the moon: a) Rationale: no data since Apollo seismic stations ceased operation in 1977; b) Anchor Nodes: small, low-power, long-life (6-yr) landers with seismographic and a few other science instruments (see next chart); c) WEB: warm electronics box houses ILN anchor node electronics/batteries. Technology Need: thermal switching system that will keep the WEB cool during the lunar day and warm during the lunar night.
Re-Engineering the Mission Operations System (MOS) for the Prime and Extended Mission
NASA Technical Reports Server (NTRS)
Hunt, Joseph C., Jr.; Cheng, Leo Y.
2012-01-01
One of the most challenging tasks in a space science mission is designing the Mission Operations System (MOS). Whereas the focus of the project is getting the spacecraft built and tested for launch, the mission operations engineers must build a system to carry out the science objectives. The completed MOS design is then formally assessed in the many reviews. Once a mission has completed the reviews, the Mission Operation System (MOS) design has been validated to the Functional Requirements and is ready for operations. The design was built based on heritage processes, new technology, and lessons learned from past experience. Furthermore, our operational concepts must be properly mapped to the mission design and science objectives. However, during the course of implementing the science objective in the operations phase after launch, the MOS experiences an evolutional change to adapt for actual performance characteristics. This drives the re-engineering of the MOS, because the MOS includes the flight and ground segments. Using the Spitzer mission as an example we demonstrate how the MOS design evolved for both the prime and extended mission to enhance the overall efficiency for science return. In our re-engineering process, we ensured that no requirements were violated or mission objectives compromised. In most cases, optimized performance across the MOS, including gains in science return as well as savings in the budget profile was achieved. Finally, we suggest a need to better categorize the Operations Phase (Phase E) in the NASA Life-Cycle Phases of Formulation and Implementation
NASA Astrophysics Data System (ADS)
Munoz-Arriola, F.; Thomas, G.; Wood, A.; Wagner-Gomez, A.; Lobato-Sanchez, R.; Lettenmaier, D. P.
2007-12-01
Hydrologic forecasting in areas constrained by the availability of hydrometeorological records is a notable challenge in water resource management. Techniques from the University of Washington West-wide Seasonal Hydrologic Forecast system www.hydro.washington.edu/forecast/westwide) for generating daily nowcasts in areas with sparse and time-varying station coverage have been extended from the western U.S. into Mexico. The primary forecasting approaches consist of ensembles based on the NWS ensemble streamflow prediction method (ESP; essentially resampling of climatology) and on NCEP Coupled Forecast System (CFS) outputs. These in turn are used to force the Variable Infiltration Capacity (VIC) macroscale hydrology model to produce streamflow ensembles. The initial hydrologic state utilized in the seasonal forecasting is generated by VIC using daily real-time hydrologic nowcasts, produced using forcings derived via an 'index-station percentile' approach from meteorological station data accessed in real time from Servicio Meteorológico Nacional (SMN). One-year lead time streamflow forecasts at monthly time step are produced at a set of major river locations in Mexico. As a case study, the streamflow forecasts, along with forecasts of reservoir evaporation, are used as input to the Simulation-Optimization (SIMOP) model of the Rio Yaqui system, one of the major agricultural production centers of Mexico. This is the first step in an eventual planned water management implementation over all of Mexico.
Costa-Quintana, J. Lopez-Aguilar, F.
2012-08-15
We analyze the conditions of the electromagnetic potentials for systems with electric and magnetic charges and the Lagrangian theory with these potentials. The constructed Lagrangian function is valid for obtaining the field equations and the extended Lorentz force for dyonic charges for both relativistic particles in vacuum and non-relativistic entities in solids. In a second part, with the one-body Hamiltonian of independent particles in external fields, we explore some dual properties of the dyonic system under external fields. We analyze the possible diamagnetic (and 'diaelectric') response of magnetic monopoles under a weak and constant electromagnetic field and the theory of Landau levels in the case of magnetic charges under strong electromagnetic constant fields. - Highlights: Black-Right-Pointing-Pointer We study the Lagrangian formalism for magnetic charges. Black-Right-Pointing-Pointer We analyze the electromagnetic potentials for dyons. Black-Right-Pointing-Pointer We study two dual properties of solid systems with magnetic charges. Black-Right-Pointing-Pointer A quantum study of solids with monopoles under electromagnetic constant fields.
Effect of a commercial housing system on egg quality during extended storage.
Jones, D R; Karcher, D M; Abdo, Z
2014-05-01
Egg producers in the United States are utilizing a variety of commercial egg production systems to provide consumer choice and meet legislative requirements. Consumer egg grades in the United States were developed for conventional cage production, and it is unclear what effect alternative production systems might have on egg quality during retail and consumer home storage. The current study was undertaken to determine what changes in egg quality characteristics occur during extended cold storage for commercially produced conventional cage, enriched colony cage, and cage-free aviary eggs. During 12 wk of cold storage, egg weight, albumen height, Haugh unit, static compression shell strength, vitelline membrane strength and deformation, yolk index, shell dynamic stiffness, and whole egg total solids were monitored. Overall, aviary and enriched eggs were significantly (P < 0.05) heavier than conventional cage. Albumen height and Haugh unit (P < 0.05) were significantly greater for conventional cage than enriched eggs. Static compression shell strength was greatest (P < 0.05) for enriched eggs compared with aviary. No overall housing system effects for yolk measurements, shell dynamic stiffness, or whole egg total solids were observed. Albumen height, Haugh unit, and yolk quality measurements were all greatest at 0 and lowest at 12 wk of storage (P < 0.05). The rate of quality change among the housing systems for each measured attribute at 4, 6, and 12 wk was determined. Other than differences in the change of egg weight at 4 wk, no significant differences in the rate of quality decline were found among the housing systems. The results of the current study indicate that current US egg quality standards should effectively define quality for commercially produced conventional cage, enriched colony cage, and cage-free aviary eggs. PMID:24795324
Extended Burnup Credit for BWR Spent Nuclear Fuel in Storage and Transportation Systems
Ade, Brian J; Bowman, Stephen M; Gauld, Ian C; Ilas, Germina; Martinez, J. S.
2015-01-01
[Full Text] Oak Ridge National Laboratory and the United States Nuclear Regulatory Commission have initiated a multiyear project to investigate the application of burnup credit (BUC) for boiling-water reactor (BWR) fuel in storage and transportation casks. This project includes two phases. The first phase investigates the applicability of peak reactivity methods currently used for spent fuel pools to spent fuel storage and transportation casks and the validation of reactivity (k_{eff}) calculations and depleted fuel compositions. The second phase focuses on extending BUC beyond peak reactivity. This paper documents work performed to date, investigating some aspects of extended BUC, and it also describes the plan to complete the evaluations. The technical basis for application of peak reactivity methods to BWR fuel in storage and transportation systems is presented in a companion paper. Two reactor operating parameters are being evaluated to establish an adequate basis for extended BWR BUC, including investigation of the axial void profile effect and the effect of control blade utilization during operation. A detailed analysis of core simulator data for one cycle of an operating BWR plant was performed to determine the range of void profiles and the variability of the profile experienced during irradiation. While a single cycle does not provide complete data, the data obtained are sufficient to use to determine the primary effects and identify conservative modeling approaches. Using data resulting from a single cycle, the axial void profile is studied by first determining the temporal fidelity necessary in depletion modeling, and then using multiple void profiles to examine the effect of the void profile on cask reactivity. The results of these studies are being used to develop recommendations for conservatively modeling the void profile effects for BWR depletion calculations. The second operational parameter studied is control blade exposure. Control blades
NASA Technical Reports Server (NTRS)
1975-01-01
Mission planning, systems analysis, and design concepts for the Space Shuttle/Spacelab system for extended manned operations are described. Topics discussed are: (1) payloads, (2) spacecraft docking, (3) structural design criteria, (4) life support systems, (5) power supplies, and (6) the role of man in long duration orbital operations. Also discussed are the assembling of large structures in space. Engineering drawings are included.
Pulsating Instability of Turbulent Thermonuclear Flames in Type Ia Supernovae
NASA Astrophysics Data System (ADS)
Poludnenko, Alexei Y.
2014-01-01
Presently, one of the main explosion scenarios of type Ia supernovae (SNIa), aimed at explaining both "normal" and subluminous events, is the thermonuclear incineration of a white-dwarf in a single-degenerate system. The underlying engine of such explosions is the turbulent thermonuclear flame. Modern, large-scale, multidimensional simulations of SNIa cannot resolve the internal flame structure, and instead must include a subgrid-scale prescription for the turbulent-flame properties. As a result, development of robust, parameter-free, large-scale models of SNIa crucially relies on the detailed understanding of the turbulent flame properties during each stage of the flame evolution. Due to the complexity of the flame dynamics, such understanding must be validated by the first-principles direct numerical simulations (DNS). In our previous work, we showed that sufficiently fast turbulent flames are inherently susceptible to the development of detonations, which may provide the mechanism for the deflagration-to-detonation transition (DDT) in the delayed-detonation model of SNIa. Here we extend this study by performing detailed analysis of the turbulent flame properties at turbulent intensities below the critical threshold for DDT. We carried out a suite of 3D DNS of turbulent flames for a broad range of turbulent intensities and system sizes using a simplified, single-step, Arrhenius-type reaction kinetics. Our results show that at the later stages of the explosion, as the turbulence intensity increases prior to the possible onset of DDT, the flame front will become violently unstable. We find that the burning rate exhibits periodic pulsations with the energy release rate varying by almost an order of magnitude. Furthermore, such flame pulsations can produce pressure waves and shocks as the flame speed approaches the critical Chapman-Jouguet deflagration speed. Finally, in contrast with the current theoretical understanding, such fast turbulent flames can propagate at
NASA Technical Reports Server (NTRS)
Avery, D. E.
1978-01-01
An experimental heat-transfer investigation was conducted on two staggered arrays of metallic tiles in laminar and turbulent boundary layers. This investigation was conducted for two purposes. The impingement heating distribution where flow in a longitudinal gap intersects a transverse gap and impinges on a downstream blocking tile was defined. The influence of tile and gap geometries was analyzed to develop empirical relationships for impingement heating in laminar and turbulent boundary layers. Tests were conducted in a high temperature structures tunnel at a nominal Mach number of 7, a nominal total temperature of 1800 K, and free-stream unit Reynolds numbers from 1.0 x 10 million to 4.8 x 10 million per meter. The test results were used to assess the impingement heating effects produced by parameters that include gap width, longitudinal gap length, slope of the tile forward-facing wall, boundary-layer displacement thickness, Reynolds number, and local surface pressure.
Nonlinear reduced order models for fluids systems using extended dynamic mode decomposition
NASA Astrophysics Data System (ADS)
Dawson, Scott; Rowley, Clarence
2015-11-01
The development of techniques that can extract simple, accurate, and computationally tractable models from fluids data is of importance for enhanced prediction, control, and fundamental understanding of such systems. Modeling approaches can take the form of identifying modes upon which to project the governing equations (e.g., Galerkin projection onto a set of POD modes), or in determining (or calibrating) the temporal dynamics from data, such as in dynamic mode decomposition (DMD), or various modifications to Galerkin projection. Here, we demonstrate that choosing appropriate observables (such as linear and quadratic monomials of POD coefficients) can allow for nonlinear behavior to be accurately captured using the recently proposed extended DMD algorithm. For cylinder wake data spanning the transient and vortex shedding limit cycle regimes, the identified nonlinear models show significant improvement in accuracy and robustness over standard DMD and Galerkin projection. Compared to traditional DMD, this approach should also allow for a better global approximation of the Koopman operator for the dynamical system. We make connections with other related model identification algorithms, and additionally investigate the performance of the method upon spatially sparse and noisy data. This work was supported by the Air Force Office of Scientific Research, under award No. FA9550-12-1-0075.
Effects of Turbulence on Cosmic Ray Propagation in Protostars and Young Star/Disk Systems
NASA Astrophysics Data System (ADS)
Fatuzzo, Marco; Adams, Fred C.
2014-05-01
The magnetic fields associated with young stellar objects are expected to have an hour-glass geometry, i.e., the magnetic field lines are pinched as they thread the equatorial plane surrounding the forming star but merge smoothly onto a background field at large distances. With this field configuration, incoming cosmic rays experience both a funneling effect that acts to enhance the flux impinging on the circumstellar disk and a magnetic mirroring effect that acts to reduce that flux. To leading order, these effects nearly cancel out for simple underlying magnetic field structures. However, the environments surrounding young stellar objects are expected to be highly turbulent. This paper shows how the presence of magnetic field fluctuations affects the process of magnetic mirroring, and thereby changes the flux of cosmic rays striking circumstellar disks. Turbulence has two principle effects: (1) the (single) location of the magnetic mirror point found in the absence of turbulence is replaced with a wide distribution of values. (2) The median of the mirror point distribution moves outward for sufficiently large fluctuation amplitudes (roughly when δB/B 0 > 0.2 at the location of the turbulence-free mirror point); the distribution becomes significantly non-Gaussian in this regime as well. These results may have significant consequences for the ionization fraction of the disk, which in turn dictates the efficiency with which disk material can accrete onto the central object. A similar reduction in cosmic ray flux can occur during the earlier protostellar stages; the decrease in ionization can help alleviate the magnetic braking problem that inhibits disk formation.
Effects of turbulence on cosmic ray propagation in protostars and young star/disk systems
Fatuzzo, Marco; Adams, Fred C. E-mail: fca@umich.edu
2014-05-20
The magnetic fields associated with young stellar objects are expected to have an hour-glass geometry, i.e., the magnetic field lines are pinched as they thread the equatorial plane surrounding the forming star but merge smoothly onto a background field at large distances. With this field configuration, incoming cosmic rays experience both a funneling effect that acts to enhance the flux impinging on the circumstellar disk and a magnetic mirroring effect that acts to reduce that flux. To leading order, these effects nearly cancel out for simple underlying magnetic field structures. However, the environments surrounding young stellar objects are expected to be highly turbulent. This paper shows how the presence of magnetic field fluctuations affects the process of magnetic mirroring, and thereby changes the flux of cosmic rays striking circumstellar disks. Turbulence has two principle effects: (1) the (single) location of the magnetic mirror point found in the absence of turbulence is replaced with a wide distribution of values. (2) The median of the mirror point distribution moves outward for sufficiently large fluctuation amplitudes (roughly when δB/B {sub 0} > 0.2 at the location of the turbulence-free mirror point); the distribution becomes significantly non-Gaussian in this regime as well. These results may have significant consequences for the ionization fraction of the disk, which in turn dictates the efficiency with which disk material can accrete onto the central object. A similar reduction in cosmic ray flux can occur during the earlier protostellar stages; the decrease in ionization can help alleviate the magnetic braking problem that inhibits disk formation.
Relevance of convective turbulent dust emission (CTDE) in the Earth system
NASA Astrophysics Data System (ADS)
Klose, Martina; Shao, Yaping; Butler, Harry; Leys, John
2015-04-01
Convective turbulence generates localized and intermittent surface shear stress and can effectively entrain dust into the atmosphere. This mechanism is referred to as "Convective Turbulent Dust Emission" (CTDE) and is considered as the most important form of direct aerodynamic dust entrainment. CTDE occurs predominantly at weak mean wind conditions, when the buoyancy production of atmospheric turbulence is most pronounced. CTDE is a stochastic process and does not need to involve the saltation of sand-sized grains. An improved parameterization for CTDE is presented, which represents both aerodynamic lifting and inter-particle cohesive forces as probability distributions. The dust emission scheme therefore accounts for the stochastic nature of CTDE. The scheme was evaluated against field data recorded in the Horqin Sandy Land area in China and during the Japan-Australia Dust Experiment (JADE) in Australia. Coupled to the regional model WRF/Chem, the calibrated dust emission scheme was used to assess the long-term regional contribution of CTDE to the overall dust budget for Australia. We show that a persistent background dust concentration can be generated by CTDE. The modeled dust concentrations were compared to PM10 measurements monitored by the DustWatch Australia network. An estimate on the relevance of CTDE compared to saltation bombardment at the local and regional scales is given and implications for climate are highlighted.
Development and testing of a user-friendly Matlab interface for the JHU turbulence database system
NASA Astrophysics Data System (ADS)
Graham, Jason; Frederix, Edo; Meneveau, Charles
2011-11-01
One of the challenges that faces researchers today is the ability to store large scale data sets in a way that promotes easy access to the data and sharing among the research community. A public turbulence database cluster has been constructed in which 27 terabytes of a direct numerical simulation of isotropic turbulence is stored (Li et al., 2008, JoT). The public database provides researchers the ability to retrieve subsets of the spatiotemporal data remotely from a client machine anywhere over the internet. In addition to C and Fortran client interfaces, we now present a new Matlab interface based on Matlab's intrinsic SOAP functions. The Matlab interface provides the benefit of a high-level programming language with a plethora of intrinsic functions and toolboxes. In this talk, we will discuss several aspects of the Matlab interface including its development, optimization, usage, and application to the isotropic turbulence data. We will demonstrate several examples (visualizations, statistical analysis, etc) which illustrate the tool. Supported by NSF (CDI-II, CMMI-0941530) and Eindhoven University of Technology's Masters internship program.
NEXUS/NASCAD- NASA ENGINEERING EXTENDIBLE UNIFIED SOFTWARE SYSTEM WITH NASA COMPUTER AIDED DESIGN
NASA Technical Reports Server (NTRS)
Purves, L. R.
1994-01-01
NEXUS, the NASA Engineering Extendible Unified Software system, is a research set of computer programs designed to support the full sequence of activities encountered in NASA engineering projects. This sequence spans preliminary design, design analysis, detailed design, manufacturing, assembly, and testing. NEXUS primarily addresses the process of prototype engineering, the task of getting a single or small number of copies of a product to work. Prototype engineering is a critical element of large scale industrial production. The time and cost needed to introduce a new product are heavily dependent on two factors: 1) how efficiently required product prototypes can be developed, and 2) how efficiently required production facilities, also a prototype engineering development, can be completed. NEXUS extendibility and unification are achieved by organizing the system as an arbitrarily large set of computer programs accessed in a common manner through a standard user interface. The NEXUS interface is a multipurpose interactive graphics interface called NASCAD (NASA Computer Aided Design). NASCAD can be used to build and display two and three-dimensional geometries, to annotate models with dimension lines, text strings, etc., and to store and retrieve design related information such as names, masses, and power requirements of components used in the design. From the user's standpoint, NASCAD allows the construction, viewing, modification, and other processing of data structures that represent the design. Four basic types of data structures are supported by NASCAD: 1) three-dimensional geometric models of the object being designed, 2) alphanumeric arrays to hold data ranging from numeric scalars to multidimensional arrays of numbers or characters, 3) tabular data sets that provide a relational data base capability, and 4) procedure definitions to combine groups of system commands or other user procedures to create more powerful functions. NASCAD has extensive abilities to
NASA Astrophysics Data System (ADS)
Liu, Xiaojun; Hong, Ling; Jiang, Jun
2016-08-01
Global bifurcations include sudden changes in chaotic sets due to crises. There are three types of crises defined by Grebogi et al. [Physica D 7, 181 (1983)]: boundary crisis, interior crisis, and metamorphosis. In this paper, by means of the extended generalized cell mapping (EGCM), boundary and interior crises of a fractional-order Duffing system are studied as one of the system parameters or the fractional derivative order is varied. It is found that a crisis can be generally defined as a collision between a chaotic basic set and a basic set, either periodic or chaotic, to cause a sudden discontinuous change in chaotic sets. Here chaotic sets involve three different kinds: a chaotic attractor, a chaotic saddle on a fractal basin boundary, and a chaotic saddle in the interior of a basin and disjoint from the attractor. A boundary crisis results from the collision of a periodic (or chaotic) attractor with a chaotic (or regular) saddle in the fractal (or smooth) boundary. In such a case, the attractor, together with its basin of attraction, is suddenly destroyed as the control parameter passes through a critical value, leaving behind a chaotic saddle in the place of the original attractor and saddle after the crisis. An interior crisis happens when an unstable chaotic set in the basin of attraction collides with a periodic attractor, which causes the appearance of a new chaotic attractor, while the original attractor and the unstable chaotic set are converted to the part of the chaotic attractor after the crisis. These results further demonstrate that the EGCM is a powerful tool to reveal the mechanism of crises in fractional-order systems.
Two-Phase Thermal Switching System for a Small, Extended Duration Lunar Surface Science Platform
NASA Technical Reports Server (NTRS)
Bugby, David C.; Farmer, Jeffery T.; OConnor, Brian F.; Wirzburger, Melissa J.; Abel, Elisabeth D.; Stouffer, Chuck J.
2010-01-01
This paper describes a novel thermal control system for the Warm Electronics Box (WEB) on board a small lunar surface lander intended to support science activities anywhere on the lunar surface for an extended duration of up to 6 years. Virtually all lander electronics, which collectively dissipate about 60 W in the reference mission, are contained within the WEB. These devices must be maintained below 323 K (with a goal of 303 K) during the nearly 15-earth-day lunar day, when surface temperatures can reach 390K, and above 263 K during the nearly 15-earth-day lunar night, when surface temperatures can reach 100K. Because of the large temperature swing from lunar day-to-night, a novel thermal switching system was required that would be able to provide high conductance from WEB to radiator(s) during the hot lunar day and low (or negligible) conductance during the cold lunar night. The concept that was developed consists of ammonia variable conductance heat pipes (VCHPs) to collect heat from WEB components and a polymer wick propylene loop heat pipe (LHP) to transport the collected heat to the radiator(s). The VCHPs autonomously maximize transport when the WEB is warm and autonomously shut down when the WEB gets cold. The LHP autonomously shuts down when the VCHPs shut down. When the environment transitions from lunar night to day, the VCHPs and LHP autonomously turn back on. Out of 26 analyzed systems, this novel arrangement was able to best achieve the combined goals of zero control power, autonomous operation, long life, low complexity, low T, and landed tilt tolerance.
Liu, Xiaojun; Hong, Ling; Jiang, Jun
2016-08-01
Global bifurcations include sudden changes in chaotic sets due to crises. There are three types of crises defined by Grebogi et al. [Physica D 7, 181 (1983)]: boundary crisis, interior crisis, and metamorphosis. In this paper, by means of the extended generalized cell mapping (EGCM), boundary and interior crises of a fractional-order Duffing system are studied as one of the system parameters or the fractional derivative order is varied. It is found that a crisis can be generally defined as a collision between a chaotic basic set and a basic set, either periodic or chaotic, to cause a sudden discontinuous change in chaotic sets. Here chaotic sets involve three different kinds: a chaotic attractor, a chaotic saddle on a fractal basin boundary, and a chaotic saddle in the interior of a basin and disjoint from the attractor. A boundary crisis results from the collision of a periodic (or chaotic) attractor with a chaotic (or regular) saddle in the fractal (or smooth) boundary. In such a case, the attractor, together with its basin of attraction, is suddenly destroyed as the control parameter passes through a critical value, leaving behind a chaotic saddle in the place of the original attractor and saddle after the crisis. An interior crisis happens when an unstable chaotic set in the basin of attraction collides with a periodic attractor, which causes the appearance of a new chaotic attractor, while the original attractor and the unstable chaotic set are converted to the part of the chaotic attractor after the crisis. These results further demonstrate that the EGCM is a powerful tool to reveal the mechanism of crises in fractional-order systems. PMID:27586621
Predicting two-dimensional turbulence
NASA Astrophysics Data System (ADS)
Cerbus, R. T.; Goldburg, W. I.
2015-04-01
Prediction is a fundamental objective of science. It is more difficult for chaotic and complex systems like turbulence. Here we use information theory to quantify spatial prediction using experimental data from a turbulent soap film. At high Reynolds number, Re, where a cascade exists, turbulence becomes easier to predict as the inertial range broadens. The development of a cascade at low Re is also detected.
NASA Astrophysics Data System (ADS)
Nistazakis, H. E.; Ninos, M. P.; Tsigopoulos, A. D.; Zervos, D. A.; Tombras, G. S.
2016-08-01
The free-space optical communication systems attract significant research and commercial interest the last few years, due to their high performance and reliability characteristics along with their, relatively, low installation and operational cost. Moreover, due to the fact that these systems are using the atmosphere as propagation path, their performance is varying according to its characteristics. Here, we present the performance analysis of a serially relayed radio-on-free-space-optical (RoFSO) communication system which employs the orthogonal frequency division multiplexing technique, with a quadrature amplitude modulation scheme, over atmospheric turbulence channels modelled by either the Gamma-Gamma or the Gamma distribution model. For this RoFSO communication link, we derive closed-form mathematical expressions for the estimation of its average bit error rate and outage probability, taking into account the relays' number, the atmospheric turbulence and the pointing errors effect. Furthermore, for realistic parameter values, numerical results are presented using the derived mathematical expressions, which are verified through the corresponding numerical simulations.
Transport of quantum excitations coupled to spatially extended nonlinear many-body systems
NASA Astrophysics Data System (ADS)
Iubini, Stefano; Boada, Octavi; Omar, Yasser; Piazza, Francesco
2015-11-01
The role of noise in the transport properties of quantum excitations is a topic of great importance in many fields, from organic semiconductors for technological applications to light-harvesting complexes in photosynthesis. In this paper we study a semi-classical model where a tight-binding Hamiltonian is fully coupled to an underlying spatially extended nonlinear chain of atoms. We show that the transport properties of a quantum excitation are subtly modulated by (i) the specific type (local versus non-local) of exciton-phonon coupling and by (ii) nonlinear effects of the underlying lattice. We report a non-monotonic dependence of the exciton diffusion coefficient on temperature, in agreement with earlier predictions, as a direct consequence of the lattice-induced fluctuations in the hopping rates due to long-wavelength vibrational modes. A standard measure of transport efficiency confirms that both nonlinearity in the underlying lattice and off-diagonal exciton-phonon coupling promote transport efficiency at high temperatures, preventing the Zeno-like quench observed in other models lacking an explicit noise-providing dynamical system.
Extending Climate Analytics-As to the Earth System Grid Federation
NASA Astrophysics Data System (ADS)
Tamkin, G.; Schnase, J. L.; Duffy, D.; McInerney, M.; Nadeau, D.; Li, J.; Strong, S.; Thompson, J. H.
2015-12-01
We are building three extensions to prior-funded work on climate analytics-as-a-service that will benefit the Earth System Grid Federation (ESGF) as it addresses the Big Data challenges of future climate research: (1) We are creating a cloud-based, high-performance Virtual Real-Time Analytics Testbed supporting a select set of climate variables from six major reanalysis data sets. This near real-time capability will enable advanced technologies like the Cloudera Impala-based Structured Query Language (SQL) query capabilities and Hadoop-based MapReduce analytics over native NetCDF files while providing a platform for community experimentation with emerging analytic technologies. (2) We are building a full-featured Reanalysis Ensemble Service comprising monthly means data from six reanalysis data sets. The service will provide a basic set of commonly used operations over the reanalysis collections. The operations will be made accessible through NASA's climate data analytics Web services and our client-side Climate Data Services (CDS) API. (3) We are establishing an Open Geospatial Consortium (OGC) WPS-compliant Web service interface to our climate data analytics service that will enable greater interoperability with next-generation ESGF capabilities. The CDS API will be extended to accommodate the new WPS Web service endpoints as well as ESGF's Web service endpoints. These activities address some of the most important technical challenges for server-side analytics and support the research community's requirements for improved interoperability and improved access to reanalysis data.
NASA Astrophysics Data System (ADS)
Hunt, Joshua M.
The necessity for evaluating the accuracy and characteristics of new Large-Eddy Simulation (LES) turbulence models in modern fluid mechanics research has inspired the development of a Three-Dimensional Particle Tracking Velocimetry (3DPTV) system capable of producing 3-Dimension 3-Component (3D3C) velocity vector fields. The system is based on the triangulation method of particle location and utilizes an optical system comprised of three 4008 x 2672 charge-coupled devices (CCDs), three 120mm lenses, and a water-filled prism. The tracer particles used in the system were <5microm TiO2 and were illuminated using a 532 nm Nd:YAG dual pulsed laser. The system was configured to study a backward-facing step flow in a 6" x 12" water tunnel due to this flow's consistency in separation and unsteady, turbulent characteristics. The experimental flow had a freestream velocity of 22 cm/s, a Reynolds number based on the step height of 6274, and a Taylor-microscale Reynolds number of approximately 130. Data from this flow was used in a priori testing of various LES models including the Smagorinsky, Similarity, Mixed, Dynamic, Coherent Structures, and Stretched Vortex Models. The system is preferable to Direct Numerical Simulation (DNS) for such testing in that it is capable of acquiring data at a resolution adequate for a priori testing without the computational restrictions for high Reynolds numbers. In the present configuration, the system is capable of achieving a Taylor-microscale Reynolds number of 214, but with an increase to the CCD resolution of the system, a Taylor-microscale Reynolds number of nearly 400 would be attainable.
ERIC Educational Resources Information Center
Hanratty, Thomas J.
1980-01-01
This paper gives an account of research on the structure of turbulence close to a solid boundary. Included is a method to study the flow close to the wall of a pipe without interferring with it. (Author/JN)
NASA Astrophysics Data System (ADS)
Nazarenko, Sergey
2015-07-01
Wave turbulence is the statistical mechanics of random waves with a broadband spectrum interacting via non-linearity. To understand its difference from non-random well-tuned coherent waves, one could compare the sound of thunder to a piece of classical music. Wave turbulence is surprisingly common and important in a great variety of physical settings, starting with the most familiar ocean waves to waves at quantum scales or to much longer waves in astrophysics. We will provide a basic overview of the wave turbulence ideas, approaches and main results emphasising the physics of the phenomena and using qualitative descriptions avoiding, whenever possible, involved mathematical derivations. In particular, dimensional analysis will be used for obtaining the key scaling solutions in wave turbulence - Kolmogorov-Zakharov (KZ) spectra.
Gentili, Pier Luigi; Rightler, Amanda L; Heron, B Mark; Gabbutt, Christopher D
2016-01-25
Photochromic fuzzy logic systems have been designed that extend human visual perception into the UV region. The systems are founded on a detailed knowledge of the activation wavelengths and quantum yields of a series of thermally reversible photochromic compounds. By appropriate matching of the photochromic behaviour unique colour signatures are generated in response differing UV activation frequencies. PMID:26658700
Wake Turbulence Mitigation for Arrivals (WTMA)
NASA Technical Reports Server (NTRS)
Williams, Daniel M.; Lohr, Gary W.; Trujillo, Anna C.
2008-01-01
The preliminary Wake Turbulence Mitigation for Arrivals (WTMA) concept of operations is described in this paper. The WTMA concept provides further detail to work initiated by the Wake Vortex Avoidance System Concept Evaluation Team and is an evolution of the Wake Turbulence Mitigation for Departure concept. Anticipated benefits about reducing wake turbulence separation standards in crosswind conditions, and candidate WTMA system considerations are discussed.
Neural Summation in the Hawkmoth Visual System Extends the Limits of Vision in Dim Light.
Stöckl, Anna Lisa; O'Carroll, David Charles; Warrant, Eric James
2016-03-21
Most of the world's animals are active in dim light and depend on good vision for the tasks of daily life. Many have evolved visual adaptations that permit a performance superior to that of manmade imaging devices [1]. In insects, a major model visual system, nocturnal species show impressive visual abilities ranging from flight control [2, 3], to color discrimination [4, 5], to navigation using visual landmarks [6-8] or dim celestial compass cues [9, 10]. In addition to optical adaptations that improve their sensitivity in dim light [11], neural summation of light in space and time-which enhances the coarser and slower features of the scene at the expense of noisier finer and faster features-has been suggested to improve sensitivity in theoretical [12-14], anatomical [15-17], and behavioral [18-20] studies. How these summation strategies function neurally is, however, presently unknown. Here, we quantified spatial and temporal summation in the motion vision pathway of a nocturnal hawkmoth. We show that spatial and temporal summation combine supralinearly to substantially increase contrast sensitivity and visual information rate over four decades of light intensity, enabling hawkmoths to see at light levels 100 times dimmer than without summation. Our results reveal how visual motion is calculated neurally in dim light and how spatial and temporal summation improve sensitivity while simultaneously maximizing spatial and temporal resolution, thus extending models of insect motion vision derived predominantly from diurnal flies. Moreover, the summation strategies we have revealed may benefit manmade vision systems optimized for variable light levels [21]. PMID:26948877
NASA Technical Reports Server (NTRS)
Perry, B., III
1981-01-01
Comparisons are presented analytically predicted and experimental turbulence responses of a wind tunnel model of a DC-10 derivative wing equipped with an active control system. The active control system was designed for the purpose of flutter suppression, but it had additional benefit of alleviating gust loads (wing bending moment) by about 25%. Comparisions of various wing responses are presented for variations in active control system parameters and tunnel speed. The analytical turbulence responses were obtained using DYLOFLEX, a computer program for dynamic loads analyses of flexible airplanes with active controls. In general, the analytical predictions agreed reasonably well with the experimental data.
Containerless Ripple Turbulence
NASA Technical Reports Server (NTRS)
Putterman, Seth; Wright, William; Duval, Walter; Panzarella, Charles
2002-01-01
interaction. Furthermore, the steady state distribution of energy again follows a Kolmogorov scaling law; in this case the ripple energy is distributed according to 1/k (sup 7/4). Again, in parallel with vortex turbulence ripple turbulence exhibits intermittency. The problem of ripple turbulence presents an experimental opportunity to generate data in a controlled, benchmarked system. In particular the surface of a sphere is an ideal environment to study ripple turbulence. Waves run around the sphere and interact with each other, and the effect of walls is eliminated. In microgravity this state can be realized for over 2 decades of frequency. Wave turbulence is a physically relevant problem in its own right. It has been studied on the surface of liquid hydrogen and its application to Alfven waves in space is a source of debate. Of course, application of wave turbulence perspectives to ocean waves has been a major success. The experiment which we plan to run in microgravity is conceptually straightforward. Ripples are excited on the surface of a spherical drop of fluid and then their amplitude is recorded with appropriate photography. A key challenge is posed by the need to stably position a 10cm diameter sphere of water in microgravity. Two methods are being developed. Orbitec is using controlled puffs of air from at least 6 independent directions to provided the positioning force. This approach has actually succeeded to position and stabilize a 4cm sphere during a KC 135 segment. Guigne International is using the radiation pressure of high frequency sound. These transducers have been organized into a device in the shape of a dodecahedron. This apparatus 'SPACE DRUMS' has already been approved for use for combustion synthesis experiments on the International Space Station. A key opportunity presented by the ripple turbulence data is its use in driving the development of codes to simulate its properties.
Containerless Ripple Turbulence
NASA Astrophysics Data System (ADS)
Putterman, Seth; Wright, William; Duval, Walter; Panzarella, Charles
2002-11-01
interaction. Furthermore, the steady state distribution of energy again follows a Kolmogorov scaling law; in this case the ripple energy is distributed according to 1/k 7/4. Again, in parallel with vortex turbulence ripple turbulence exhibits intermittency. The problem of ripple turbulence presents an experimental opportunity to generate data in a controlled, benchmarked system. In particular the surface of a sphere is an ideal environment to study ripple turbulence. Waves run around the sphere and interact with each other, and the effect of walls is eliminated. In microgravity this state can be realized for over 2 decades of frequency. Wave turbulence is a physically relevant problem in its own right. It has been studied on the surface of liquid hydrogen and its application to Alfven waves in space is a source of debate. Of course, application of wave turbulence perspectives to ocean waves has been a major success. The experiment which we plan to run in microgravity is conceptually straightforward. Ripples are excited on the surface of a spherical drop of fluid and then their amplitude is recorded with appropriate photography. A key challenge is posed by the need to stably position a 10cm diameter sphere of water in microgravity. Two methods are being developed. Orbitec is using controlled puffs of air from at least 6 independent directions to provided the positioning force. This approach has actually succeeded to position and stabilize a 4cm sphere during a KC 135 segment. Guigne International is using the radiation pressure of high frequency sound. These transducers have been organized into a device in the shape of a dodecahedron. This apparatus 'SPACE DRUMS' has already been approved for use for combustion synthesis experiments on the International Space Station. A key opportunity presented by the ripple turbulence data is its use in driving the development of codes to simulate its properties.
NASA Astrophysics Data System (ADS)
Tugend, Julie; Manatschal, Gianreto; Kusznir, Nicolas J.; Masini, Emmanuel; Thinon, Isabelle
2013-04-01
Research conducted at present-day passive continental margins shows more varied crustal architectures than previously assumed. New seismic data together with drill-holes have revealed the occurrence of extremely thinned continental crust in the distal part of the margin as well as exhumed serpentinised sub-continental mantle oceanwards. In addition the understanding of the formation of hyper-extended rift systems has also greatly benefited from the study of onshore analogs preserved in mountain belts. The Bay of Biscay and Western Pyrenees correspond to a Lower Cretaceous rift system leading to the development of hyper-extended domains and ultimately oceanic crust in the Bay of Biscay. This domain represents one of the best natural laboratories to study the formation processes and evolution of hyper-extended domains. During late Cretaceous compression, these rifted domains were inverted resulting in the present-day Pyrenean mountain belt. In this contribution, we present a new paleogeographic map of the Bay of Biscay-Pyrenean rift system. We integrate results from previous works and new work using different mapping methods to distinguish distinctive crustal domains related to hyper-extended systems both offshore and onshore. We combine seismic interpretations with gravity anomaly inversion and residual depth anomaly analysis to distinguish the different crustal domains across the offshore margin. Onshore, we use an innovative approach based on observations from present-day rifted margin architecture associated with classical field work to map the former hyper-extended domains. Another outcome of this work is the creation of a crustal thickness map using gravity inversion linking offshore and onshore domains from the Bay of Biscay to that of the Western-Pyrenees. This multidisciplinary approach enables us to investigate the spatial and temporal evolution of the Bay of Biscay rift system with the aim of better understanding the formation of hyper-extended domains
Maul, Timothy M.; Hamilton, Douglas W.; Nieponice, Alejandro; Soletti, Lorenzo
2007-01-01
Mechanical forces have been shown to be important stimuli for the determination and maintenance of cellular phenotype and function. Many cells are constantly exposed in vivo to cyclic pressure, shear stress, and/or strain. Therefore, the ability to study the effects of these stimuli in vitro is important for understanding how they contribute to both normal and pathologic states. While there exist commercial as well as custom-built devices for the extended application of cyclic strain and shear stress, very few cyclic pressure systems have been reported to apply stimulation longer than 48 h. However, pertinent responses of cells to mechanical stimulation may occur later than this. To address this limitation, we have designed a new cyclic hydrostatic pressure system based upon the following design variables: minimal size, stability of pressure and humidity, maximal accessibility, and versatility. Computational fluid dynamics (CFD) was utilized to predict the pressure and potential shear stress within the chamber during the first half of a 1.0 Hz duty cycle. To biologically validate our system, we tested the response of bone marrow progenitor cells (BMPCs) from Sprague Dawley rats to a cyclic pressure stimulation of 120/80 mm Hg, 1.0 Hz for 7 days. Cellular morphology was measured using Scion Image, and cellular proliferation was measured by counting nuclei in ten fields of view. CFD results showed a constant pressure across the length of the chamber and no shear stress developed at the base of the chamber where the cells are cultured. BMPCs from Sprague Dawley rats demonstrated a significant change in morphology versus controls by reducing their size and adopting a more rounded morphology. Furthermore, these cells increased their proliferation under cyclic hydrostatic pressure. We have demonstrated that our system imparts a single mechanical stimulus of cyclic hydrostatic pressure and is capable of at least 7 days of continuous operation without affecting cellular
Turbulence in Natural Environments
NASA Astrophysics Data System (ADS)
Banerjee, Tirtha
Problems in the area of land/biosphere-atmosphere interaction, hydrology, climate modeling etc. can be systematically organized as a study of turbulent flow in presence of boundary conditions in an increasing order of complexity. The present work is an attempt to study a few subsets of this general problem of turbulence in natural environments- in the context of neutral and thermally stratified atmospheric surface layer, the presence of a heterogeneous vegetation canopy and the interaction between air flow and a static water body in presence of flexible protruding vegetation. The main issue addressed in the context of turbulence in the atmospheric surface layer is whether it is possible to describe the macro-states of turbulence such as mean velocity and turbulent velocity variance in terms of the micro-states of the turbulent flow, i.e., a distribution of turbulent kinetic energy across a multitude of scales. This has been achieved by a `spectral budget approach' which is extended for thermal stratification scenarios as well, in the process unifying the seemingly different and unrelated theories of turbulence such as Kolmogorov's hypothesis, Heisenberg's eddy viscosity, Monin Obukhov Similarity Theory (MOST) etc. under a common framework. In the case of a more complex scenario such as presence of a vegetation canopy with edges and gaps, the question that is addressed is in what detail the turbulence is needed to be resolved in order to capture the bulk flow features such as recirculation patterns. This issue is addressed by a simple numerical framework and it has been found out that an explicit prescription of turbulence is not necessary in presence of heterogeneities such as edges and gaps where the interplay between advection, pressure gradients and drag forces are sufficient to capture the first order dynamics. This result can be very important for eddy-covariance flux calibration strategies in non-ideal environments and the developed numerical model can be
Coshcous turbulence and its thermalization
Zhu, Jian-zhou; Taylor, Mark
2008-01-01
Dissipation rate {mu}[cosh(k/k{sub c}) - 1] in Fourier space, which reduces to the Newtonian viscosity dissipation rate {nu}k{sup 2} for small k/k{sub c}, can be scaled to make a hydrodynamic system either actually or potentially converge to its Galerkin truncation. The former case acquires convergence to the truncation at a finite wavenumber k{sub G}; the latter realizes as the wavenumber grows to infinity. Intermittency reduction and vitiation of extended self-similarity (ESS) in the partially thermalized regime of turbulence are confirmed and clarified. Onsager's pictures of intermittent versus nonintermittent flows are visualized from thermalized numerical fields, showing cleanly spotty versus mistily uniform properties, the latter of which destroys self-organization and so the ESS property.
NASA Technical Reports Server (NTRS)
Cebeci, T.; Carr, L. W.
1981-01-01
A procedure which solves the governing boundary layer equations within Keller's box method was developed for calculating unsteady laminar flows with flow reversal. This method is extended to turbulent boundary layers with flow reversal. Test cases are used to investigate the proposition that unsteady turbulent boundary layers also remain free of singularities. Turbulent flow calculations are performed. The governing equations for both models are solved. As in laminar flows, the unsteady turbulent boundary layers are free from singularities, but there is a clear indication of rapid thickening of the boundary layer with increasing flow reversal. Predictions of both turbulence models are the same for all practical purposes.
Compressible Alfvenic Turbulence in One Dimension
NASA Astrophysics Data System (ADS)
Fleischer, J.; Diamond, P. H.
1997-11-01
Burgers' equation for 1-D compressible fluid dynamics is extended to a two-equation system which includes the effects of magnetic pressure. For the special case of equal fluid viscosity and magnetic diffusivity, the system reduces to two decoupled Burgers' equations in the characteristic (Elsasser) variables \\upsilon ± \\upsilon _A. Energy transfer, with and without external forcing, is examined for arbitrary molecular diffusivities. For forced turbulence, renormalized perturbation theory is used to calculate the effective transport coefficients. It is found that energy equi-dissipation, not equipartition, is fundamental to the turbulent state. In other words, the system dynamically self-adjusts to propagate disturbances along its characteristics. However, shock formation due to wave steepening is inhibited by the presence of small-scale forcing. Alternate large-scale structures, propagating ballistically, lead to asymmetry in the characteristic velocity pdf. These non-Gaussian tails, a hallmark of intermittency, are examined through the pdf generating functional. It is argued that the probability path integral may be approximated by the instanton contribution. Corresponding distribution functions for velocity and magnetic field fluctuations are given. Finally, implications for the spectra of turbulence and self-organization phenomena in MHD are discussed.
NEXUS/NASCAD- NASA ENGINEERING EXTENDIBLE UNIFIED SOFTWARE SYSTEM WITH NASA COMPUTER AIDED DESIGN
NASA Technical Reports Server (NTRS)
Purves, L. R.
1994-01-01
NEXUS, the NASA Engineering Extendible Unified Software system, is a research set of computer programs designed to support the full sequence of activities encountered in NASA engineering projects. This sequence spans preliminary design, design analysis, detailed design, manufacturing, assembly, and testing. NEXUS primarily addresses the process of prototype engineering, the task of getting a single or small number of copies of a product to work. Prototype engineering is a critical element of large scale industrial production. The time and cost needed to introduce a new product are heavily dependent on two factors: 1) how efficiently required product prototypes can be developed, and 2) how efficiently required production facilities, also a prototype engineering development, can be completed. NEXUS extendibility and unification are achieved by organizing the system as an arbitrarily large set of computer programs accessed in a common manner through a standard user interface. The NEXUS interface is a multipurpose interactive graphics interface called NASCAD (NASA Computer Aided Design). NASCAD can be used to build and display two and three-dimensional geometries, to annotate models with dimension lines, text strings, etc., and to store and retrieve design related information such as names, masses, and power requirements of components used in the design. From the user's standpoint, NASCAD allows the construction, viewing, modification, and other processing of data structures that represent the design. Four basic types of data structures are supported by NASCAD: 1) three-dimensional geometric models of the object being designed, 2) alphanumeric arrays to hold data ranging from numeric scalars to multidimensional arrays of numbers or characters, 3) tabular data sets that provide a relational data base capability, and 4) procedure definitions to combine groups of system commands or other user procedures to create more powerful functions. NASCAD has extensive abilities to
The impact of the declining extended family support system on the education of orphans in Lesotho
Tanga, Pius T
2013-01-01
This paper examines the impact of the weakening of the extended family on the education of double orphans in Lesotho through in-depth interviews with participants from 3 of the 10 districts in Lesotho. The findings reveal that in Lesotho the extended family has not yet disintegrated as the literature suggests. However, it shows signs of rupturing, as many orphans reported that they are being taken into extended family households, the incentive for these households being, presumably, the financial and other material assistance that they receive from the government and non-governmental organisations (NGOs) which supplements household income and material wellbeing. The findings show that financial and other assistance given by the government and NGOs have resulted in conflict between the orphans and caregivers. This has also prompted many extended families to shift responsibilities to the government and NGOs. Most of the extended households provided the orphans with poor living conditions, such as unhygienic houses, poor nutrition, and little or no provision of school materials, which has had a negative impact on the education of the orphans. The combined effects of economic crisis and HIV and AIDS have resulted in extended families not being able to care for the needs of the orphans adequately, whilst continuing to accept them into their households. It is recommended that although extended families are still accepting orphans, the government should strengthen and recognise the important role played by families and the communities in caring for these vulnerable children. The government should also introduce social grants for orphans and other vulnerable children and review the current meagre public assistance (R100) it provides for orphans and vulnerable children in Lesotho. Other stakeholders should concentrate on strengthening the capacity of families and communities through programmes and projects which could be more sustainable than the current handouts given by
NASA Astrophysics Data System (ADS)
Djordjevic, Goran T.; Petkovic, Milica I.
2016-04-01
This paper presents the exact average bit error rate (BER) analysis of the free-space optical system employing subcarrier intensity modulation (SIM) with Gray-coded quadrature amplitude modulation (QAM). The intensity fluctuations of the received optical signal are caused by the path loss, atmospheric turbulence and pointing errors. The exact closed-form analytical expressions for the average BER are derived assuming the SIM-QAM with arbitrary constellation size in the presence of the Gamma-Gamma scintillation. The simple approximate average BER expressions are also provided, considering only the dominant term in the finite summations of obtained expressions. Derived expressions are reduced to the special case when optical signal transmission is affected only by the atmospheric turbulence. Numerical results are presented in order to illustrate usefulness of the derived expressions and also to give insights into the effects of different modulation, channel and receiver parameters on the average BER performance. The results show that the misalignment between the transmitter laser and receiver detector has the strong effect on the average BER value, especially in the range of the high values of the average electrical signal-to-noise ratio.
Jeong Ik Lee; Hejzlar, Pavel; Kazimi, Mujid S.; Saha, Pradip
2006-07-01
Increased reliance on passive emergency cooling using natural circulation of gas at elevated pressure is one of the major goals for the Gas-cooled Fast Reactor (GFR). Since GFR cores have high power density and low thermal inertia, the decay heat removal (DHR) in depressurization accidents is a key challenge. Furthermore, due to its high surface heat flux and low velocities under natural circulation in any post-LOCA scenario, three effects impair the capability of turbulent gas flow to remove heat from the GFR core, namely: (1) Acceleration effect (2) Buoyancy effect (3) Properties variation. This paper reviews previous work on heat transfer mechanisms and flow characteristics of the Deteriorated Turbulent Heat Transfer (DTHT) regime. It is shown that the GFR's DHR system has a potential for operating in the DTHT regime by performing a simple analysis. A description of the MIT/INL experimental facility designed and built to investigate the DTHT regime is provided together with the first test results. The first runs were performed in the forced convection regime to verify facility operation against well-established forced convection correlations. The results of the three runs at Reynolds numbers 6700, 8000 and 12800 showed good agreement with the Gnielinsky correlation [4], which is considered the best available heat transfer correlation in the forced convection regime and is valid for a large range of Reynolds and Prandtl numbers. However, even in the forced convection regime, the effect of heat transfer properties variation of the fluid was found to be still significant. (authors)
Miles, A R; Edwards, M J; Greenough, J A
2004-11-08
Perturbations on an interface driven by a strong blast wave grow in time due to a combination of Rayleigh-Taylor, Richtmyer-Meshkov, and decompression effects. In this paper, results from three-dimensional numerical simulations of such a system under drive conditions to be attainable on the National Ignition Facility [E. M. Campbell, Laser Part. Beams, 9(2), 209 (1991)] are presented. Using the multi-physics, adaptive mesh refinement, higher order Godunov Eulerian hydrocode, Raptor [L. H. Howell and J.A. Greenough, J. Comp. Phys. 184, 53 (2003)], the late nonlinear instability evolution, including transition to turbulence, is considered for various multimode perturbation spectra. The 3D post-transition state differs from the 2D result, but the process of transition proceeds similarly in both 2D and 3D. The turbulent mixing transition results in a reduction in the growth rate of the mixing layer relative to its pre-transition value and, in the case of the bubble front, relative to the 2D result. The post-transition spike front velocity is approximately the same in 2D and 3D. Implications for hydrodynamic mixing in core-collapse supernova are discussed.
Active turbulence in active nematics
NASA Astrophysics Data System (ADS)
Thampi, S. P.; Yeomans, J. M.
2016-07-01
Dense, active systems show active turbulence, a state characterised by flow fields that are chaotic, with continually changing velocity jets and swirls. Here we review our current understanding of active turbulence. The development is primarily based on the theory and simulations of active liquid crystals, but with accompanying summaries of related literature.
NASA Astrophysics Data System (ADS)
Lee, W.; Park, H. K.; Lee, D. J.; Nam, Y. U.; Leem, J.; Kim, T. K.
2016-04-01
The design characteristics of a multi-channel collective (or coherent) scattering system for small scale turbulence study in Korea Superconducting Tokamak Advanced Research (KSTAR), which is planned to be installed in 2017, are given in this paper. A few critical issues are discussed in depth such as the Faraday and Cotton-Mouton effects on the beam polarization, radial spatial resolution, probe beam frequency, polarization, and power. A proper and feasible optics with the 300 GHz probe beam, which was designed based on these issues, provides a simultaneous measurement of electron density fluctuations at four discrete poloidal wavenumbers up to 24 cm-1. The upper limit corresponds to the normalized wavenumber kθρe of ˜0.15 in nominal KSTAR plasmas. To detect the scattered beam power and extract phase information, a quadrature detection system consisting of four-channel antenna/detector array and electronics will be employed.
NASA Astrophysics Data System (ADS)
Zhang, Chunxia; Zhang, Hong; Ouyang, Qi; Hu, Bambi; Gunaratne, Gemunu H.
2003-09-01
The transition from spiral waves to defect-mediated turbulence was studied in a spatial open reactor using Belousov-Zhabotinsky reaction. The experimental results show a new mechanism of the transition from spirals to spatiotemporal chaos, in which the gradient effects in the three-dimensional system are essential. The transition scenario consists of two stages: first, the effects of gradients in the third dimension cause a splitting of the spiral tip and a deletion of certain wave segments, generating new wave sources; second, the waves sent by the new wave sources undergo a backfire instability, and the back waves are laterally unstable. As a result, defects are automatically generated and fill all over the system. The result of numerical simulation using the FitzHugh-Nagumo model essentially agrees with the experimental observation.
Lee, W; Park, H K; Lee, D J; Nam, Y U; Leem, J; Kim, T K
2016-04-01
The design characteristics of a multi-channel collective (or coherent) scattering system for small scale turbulence study in Korea Superconducting Tokamak Advanced Research (KSTAR), which is planned to be installed in 2017, are given in this paper. A few critical issues are discussed in depth such as the Faraday and Cotton-Mouton effects on the beam polarization, radial spatial resolution, probe beam frequency, polarization, and power. A proper and feasible optics with the 300 GHz probe beam, which was designed based on these issues, provides a simultaneous measurement of electron density fluctuations at four discrete poloidal wavenumbers up to 24 cm(-1). The upper limit corresponds to the normalized wavenumber kθρe of ∼0.15 in nominal KSTAR plasmas. To detect the scattered beam power and extract phase information, a quadrature detection system consisting of four-channel antenna/detector array and electronics will be employed. PMID:27131668
NASA Technical Reports Server (NTRS)
Poehler, H. A.
1978-01-01
Results of a test of the use of a Lightning Detection and Ranging (LDAR) remote display in the Patrick AFB RAPCON facility are presented. Agreement between LDAR and radar precipitation echoes of the RAPCON radar was observed, as well as agreement between LDAR and pilot's visual observations of lightning flashes. A more precise comparison between LDAR and KSC based radars is achieved by the superposition of LDAR precipitation echoes. Airborne measurements of updrafts and turbulence by an armored T-28 aircraft flying through the thunderclouds are correlated with LDAR along the flight path. Calibration and measurements of the accuracy of the LDAR System are discussed, and the extended range of the system is illustrated.
Energy transfer in compressible turbulence
NASA Technical Reports Server (NTRS)
Bataille, Francoise; Zhou, YE; Bertoglio, Jean-Pierre
1995-01-01
This letter investigates the compressible energy transfer process. We extend a methodology developed originally for incompressible turbulence and use databases from numerical simulations of a weak compressible turbulence based on Eddy-Damped-Quasi-Normal-Markovian (EDQNM) closure. In order to analyze the compressible mode directly, the well known Helmholtz decomposition is used. While the compressible component has very little influence on the solenoidal part, we found that almost all of the compressible turbulence energy is received from its solenoidal counterpart. We focus on the most fundamental building block of the energy transfer process, the triadic interactions. This analysis leads us to conclude that, at low turbulent Mach number, the compressible energy transfer process is dominated by a local radiative transfer (absorption) in both inertial and energy containing ranges.
Review and assessment of turbulence models for hypersonic flows
NASA Astrophysics Data System (ADS)
Roy, Christopher J.; Blottner, Frederick G.
2006-10-01
Accurate aerodynamic prediction is critical for the design and optimization of hypersonic vehicles. Turbulence modeling remains a major source of uncertainty in the computational prediction of aerodynamic forces and heating for these systems. The first goal of this article is to update the previous comprehensive review of hypersonic shock/turbulent boundary-layer interaction experiments published in 1991 by Settles and Dodson (Hypersonic shock/boundary-layer interaction database. NASA CR 177577, 1991). In their review, Settles and Dodson developed a methodology for assessing experiments appropriate for turbulence model validation and critically surveyed the existing hypersonic experiments. We limit the scope of our current effort by considering only two-dimensional (2D)/axisymmetric flows in the hypersonic flow regime where calorically perfect gas models are appropriate. We extend the prior database of recommended hypersonic experiments (on four 2D and two 3D shock-interaction geometries) by adding three new geometries. The first two geometries, the flat plate/cylinder and the sharp cone, are canonical, zero-pressure gradient flows which are amenable to theory-based correlations, and these correlations are discussed in detail. The third geometry added is the 2D shock impinging on a turbulent flat plate boundary layer. The current 2D hypersonic database for shock-interaction flows thus consists of nine experiments on five different geometries. The second goal of this study is to review and assess the validation usage of various turbulence models on the existing experimental database. Here we limit the scope to one- and two-equation turbulence models where integration to the wall is used (i.e., we omit studies involving wall functions). A methodology for validating turbulence models is given, followed by an extensive evaluation of the turbulence models on the current hypersonic experimental database. A total of 18 one- and two-equation turbulence models are reviewed
Conceptual dynamical models for turbulence.
Majda, Andrew J; Lee, Yoonsang
2014-05-01
Understanding the complexity of anisotropic turbulent processes in engineering and environmental fluid flows is a formidable challenge with practical significance because energy often flows intermittently from the smaller scales to impact the largest scales in these flows. Conceptual dynamical models for anisotropic turbulence are introduced and developed here which, despite their simplicity, capture key features of vastly more complicated turbulent systems. These conceptual models involve a large-scale mean flow and turbulent fluctuations on a variety of spatial scales with energy-conserving wave-mean-flow interactions as well as stochastic forcing of the fluctuations. Numerical experiments with a six-dimensional conceptual dynamical model confirm that these models capture key statistical features of vastly more complex anisotropic turbulent systems in a qualitative fashion. These features include chaotic statistical behavior of the mean flow with a sub-Gaussian probability distribution function (pdf) for its fluctuations whereas the turbulent fluctuations have decreasing energy and correlation times at smaller scales, with nearly Gaussian pdfs for the large-scale fluctuations and fat-tailed non-Gaussian pdfs for the smaller-scale fluctuations. This last feature is a manifestation of intermittency of the small-scale fluctuations where turbulent modes with small variance have relatively frequent extreme events which directly impact the mean flow. The dynamical models introduced here potentially provide a useful test bed for algorithms for prediction, uncertainty quantification, and data assimilation for anisotropic turbulent systems. PMID:24753605
Conceptual dynamical models for turbulence
Majda, Andrew J.; Lee, Yoonsang
2014-01-01
Understanding the complexity of anisotropic turbulent processes in engineering and environmental fluid flows is a formidable challenge with practical significance because energy often flows intermittently from the smaller scales to impact the largest scales in these flows. Conceptual dynamical models for anisotropic turbulence are introduced and developed here which, despite their simplicity, capture key features of vastly more complicated turbulent systems. These conceptual models involve a large-scale mean flow and turbulent fluctuations on a variety of spatial scales with energy-conserving wave–mean-flow interactions as well as stochastic forcing of the fluctuations. Numerical experiments with a six-dimensional conceptual dynamical model confirm that these models capture key statistical features of vastly more complex anisotropic turbulent systems in a qualitative fashion. These features include chaotic statistical behavior of the mean flow with a sub-Gaussian probability distribution function (pdf) for its fluctuations whereas the turbulent fluctuations have decreasing energy and correlation times at smaller scales, with nearly Gaussian pdfs for the large-scale fluctuations and fat-tailed non-Gaussian pdfs for the smaller-scale fluctuations. This last feature is a manifestation of intermittency of the small-scale fluctuations where turbulent modes with small variance have relatively frequent extreme events which directly impact the mean flow. The dynamical models introduced here potentially provide a useful test bed for algorithms for prediction, uncertainty quantification, and data assimilation for anisotropic turbulent systems. PMID:24753605
Suret, Pierre; Picozzi, Antonio; Randoux, Stéphane
2011-08-29
We study theoretically, numerically and experimentally the nonlinear propagation of partially incoherent optical waves in single mode optical fibers. We revisit the traditional treatment of the wave turbulence theory to provide a statistical kinetic description of the integrable scalar NLS equation. In spite of the formal reversibility and of the integrability of the NLS equation, the weakly nonlinear dynamics reveals the existence of an irreversible evolution toward a statistically stationary state. The evolution of the power spectrum of the field is characterized by the rapid growth of spectral tails that exhibit damped oscillations, until the whole spectrum ultimately reaches a steady state. The kinetic approach allows us to derive an analytical expression of the damped oscillations, which is found in agreement with the numerical simulations of both the NLS and kinetic equations. We report the experimental observation of this peculiar relaxation process of the integrable NLS equation. PMID:21935152
ERIC Educational Resources Information Center
Lancioni, G. E.; O'Reilly, M. F.; Singh, N. N.; Sigafoos, J.; Oliva, D.; Montironi, G.; Savino, M.; Bosco, A.
2005-01-01
Background: Microswitches can be vital tools to help individuals with extensive multiple disabilities acquire control of environmental stimulation. This study was aimed at extending the evaluation of a computer system used as a microswitch for word utterances with three participants with multiple disabilities. Method: Sets of 7 or 12 word…
Crenshaw, C C; Martin, L M; Mains, C R; Wright, R D; Dart, M G; Perkins, R M; Purdy, P H; Ericsson, S A
2000-07-01
Because the aoudad has been hunted to near extinction, cryopreservation of their semen would be useful for DNA conservation and for the possible re-establishment of captive bred animals to their former ranges. This study was conducted to investigate the effectiveness of cryopreserving aoudad spermatozoa. Semen samples from four post-pubertal animals were collected using electro-ejaculation. Microscopic analysis was performed to assess the percentages of progressively and non-progressively motile spermatozoa as well as intact acrosomes in samples prior to freezing and post-thaw. Extended samples (0.2 mL) were frozen using 2 different extenders and packaging systems and stored in LN2 Post-thaw data were arcsine-transformed and analyzed using ANOVA, 2 x 2 factorial. Samples that were processed using the ram/straw method had a significantly higher percentage (P < 0.05) of spermatozoa with intact acrosomes than did any other system. In addition, samples that were processed with the buck/pellet system had significantly greater percentages (P < 0.05) of progressive and non-progressively motile spermatozoa than the samples processed using either extender and packaged in straws. This study illustrates that some aoudad spermatozoa may be cryopreserved using the extender/processing systems developed for the domestic buck and ram. PMID:10990348
Alert Confidence Fusion in Intrusion Detection Systems with Extended Dempster- Shafer Theory
Yu, Dong; Frincke, Deborah A.
2005-03-01
Extend Dempster-Shafer Theory of Evidence to include differential weightings of alerts drawn from multiple sources. The intent is to support automated (and manual) response to threat by producing more realistic confidence ratings for IDS alerts than is currently available.
ERIC Educational Resources Information Center
Smull, Ned W.; And Others
The basic purposes of the Profile Examination for Physician Extenders (PEPE) project included: (1) development of a computerized test item bank from which Profile Examinations could be generated, (2) review and analysis of curricula for the allied health groups, and (3) assessment of the reliability and validity of the Profile Examinations. The…
Adams, Allan; Chesler, Paul M; Liu, Hong
2014-04-18
We construct turbulent black holes in asymptotically AdS4 spacetime by numerically solving Einstein's equations. Using the AdS/CFT correspondence we find that both the dual holographic fluid and bulk geometry display signatures of an inverse cascade with the bulk geometry being well approximated by the fluid-gravity gradient expansion. We argue that statistically steady-state black holes dual to d dimensional turbulent flows have horizons whose area growth has a fractal-like structure with fractal dimension D=d+4/3. PMID:24785028
Turbulence in Compressible Flows
NASA Technical Reports Server (NTRS)
1997-01-01
Lecture notes for the AGARD Fluid Dynamics Panel (FDP) Special Course on 'Turbulence in Compressible Flows' have been assembled in this report. The following topics were covered: Compressible Turbulent Boundary Layers, Compressible Turbulent Free Shear Layers, Turbulent Combustion, DNS/LES and RANS Simulations of Compressible Turbulent Flows, and Case Studies of Applications of Turbulence Models in Aerospace.
Wave Turbulence on Water Surface
NASA Astrophysics Data System (ADS)
Nazarenko, Sergey; Lukaschuk, Sergei
2016-03-01
We overview the wave turbulence approach by example of one physical system: gravity waves on the surface of an infinitely deep fluid. In the theoretical part of our review, we derive the nonlinear Hamiltonian equations governing the water-wave system and describe the premises of the weak wave turbulence theory. We outline derivation of the wave-kinetic equation and the equation for the probability density function, and most important solutions to these equations, including the Kolmogorov-Zakharov spectra corresponding to a direct and an inverse turbulent cascades, as well as solutions for non-Gaussian wave fields corresponding to intermittency. We also discuss strong wave turbulence as well as coherent structures and their interaction with random waves. We describe numerical and laboratory experiments, and field observations of gravity wave turbulence, and compare their results with theoretical predictions.
Forced Turbulence in Relativistic Conformal Fluids
NASA Astrophysics Data System (ADS)
Westernacher-Schneider, John Ryan; Green, Stephen; Lehner, Luis; Canon, Kipp; Oz, Yaron
2015-04-01
Given the renewed interest arising both from AdS/CFT and astrophysics, we revisit the phenomenon of relativistic turbulence. We build on some recent work which extends known non-relativistic results in turbulence to the case of relativistic (and thus compressible) fluids. In particular, we derive the scaling behaviour of two-point correlation functions in 2+1 dimensions--holographically dual to 3+1 dimensional gravity. Turbulence in 2+1 dimensions also approximates several astrophysical situations, such as thin accretion disks around black holes. We perform numerical simulations of forced steady-state turbulence to verify our derived correlation functions.
Optimized non-integer order phase mask to extend the depth of field of an imaging system
NASA Astrophysics Data System (ADS)
Liu, Jiang; Miao, Erlong; Sui, Yongxin; Yang, Huaijiang
2016-09-01
Wavefront coding is an effective optical technique used to extend the depth of field for an incoherent imaging system. Through introducing an optimized phase mask to the pupil plane, the modulated optical transfer function is defocus-invariant. In this paper, we proposed a new form phase mask using non-integer order and signum function to extend the depth of field. The performance of the phase mask is evaluated by comparing defocused modulation transfer function invariant and Fisher information with other phase masks. Defocused imaging simulation is also carried out. The results demonstrate the advantages of non-integer order phase mask and its effectiveness on the depth of field extension.
Evidence of critical balance in kinetic Alfven wave turbulence simulations
TenBarge, J. M.; Howes, G. G.
2012-05-15
A numerical simulation of kinetic plasma turbulence is performed to assess the applicability of critical balance to kinetic, dissipation scale turbulence. The analysis is performed in the frequency domain to obviate complications inherent in performing a local analysis of turbulence. A theoretical model of dissipation scale critical balance is constructed and compared to simulation results, and excellent agreement is found. This result constitutes the first evidence of critical balance in a kinetic turbulence simulation and provides evidence of an anisotropic turbulence cascade extending into the dissipation range. We also perform an Eulerian frequency analysis of the simulation data and compare it to the results of a previous study of magnetohydrodynamic turbulence simulations.
Abarzhi, S I; Sreenivasan, K R
2010-04-13
Turbulence is a supermixer. Turbulent mixing has immense consequences for physical phenomena spanning astrophysical to atomistic scales under both high- and low-energy-density conditions. It influences thermonuclear fusion in inertial and magnetic confinement systems; governs dynamics of supernovae, accretion disks and explosions; dominates stellar convection, planetary interiors and mantle-lithosphere tectonics; affects premixed and non-premixed combustion; controls standard turbulent flows (wall-bounded and free-subsonic, supersonic as well as hypersonic); as well as atmospheric and oceanic phenomena (which themselves have important effects on climate). In most of these circumstances, the mixing phenomena are driven by non-equilibrium dynamics. While each article in this collection dwells on a specific problem, the purpose here is to seek a few unified themes amongst diverse phenomena. PMID:20211872
NASA Astrophysics Data System (ADS)
Pimshtein, V. G.
2016-07-01
The shadow visualization method is applied to study the process of loss of stability of the mixing layer of a subsonic axially symmetric turbulent jet under longitudinal internal action of saw-tooth sound waves of finite amplitude. Such action leads to the formation of a system of ring vortices in the mixing layer at the frequency of its intrinsic instability. The interaction of the vortices can be accompanied by sound emission. A similar phenomenon is also observed in turbulent jets for small supercritical pressure fluctuations on a nozzle.
NASA Astrophysics Data System (ADS)
Kolesnichenko, A. V.
2010-08-01
This paper considers the modern approach to the thermodynamic modeling of developed turbulent flows of a compressible fluid based on the systematic application of the formalism of extended irreversible thermodynamics (EIT) that goes beyond the local equilibrium hypothesis, which is an inseparable attribute of classical nonequilibrium thermodynamics (CNT). In addition to the classical thermodynamic variables, EIT introduces new state parameters—dissipative flows and the means to obtain the respective evolutionary equations consistent with the second law of thermodynamics. The paper presents a detailed discussion of a number of physical and mathematical postulates and assumptions used to build a thermodynamic model of turbulence. A turbulized liquid is treated as an indiscrete continuum consisting of two thermodynamic sub-systems: an averaged motion subsystem and a turbulent chaos subsystem, where turbulent chaos is understood as a conglomerate of small-scale vortex bodies. Under the above formalism, this representation enables the construction of new models of continual mechanics to derive cause-and-effect differential equations for turbulent heat and impulse transfer, which describe, together with the averaged conservations laws, turbulent flows with transverse shear. Unlike gradient (noncausal) relationships for turbulent flows, these differential equations can be used to investigate both hereditary phenomena, i.e., phenomena with history or memory, and nonlocal and nonlinear effects. Thus, within EIT, the second-order turbulence models underlying the so-called invariant modeling of developed turbulence get a thermodynamic explanation. Since shear turbulent flows are widespread in nature, one can expect the given modification of the earlier developed thermodynamic approach to developed turbulence modeling (see Kolesnichenko, 1980; 1998; 2002-2004; Kolesnichenko and Marov, 1985; Kolesnichenko and Marov, 2009) to be used in research on a broad class of dissipative
Dang, Ngoc T; Pham, Anh T
2012-11-19
Previous studies show that, compared to on-off keying (OOK) signaling, pulse-position modulation (PPM) is favorable in FSO/CDMA systems thanks to its energy efficiency and simple detection. Nevertheless, when the system bit rate increases and the transmission distance is far, the FSO/CDMA systems using PPM signaling critically suffer from the impact of pulse broadening caused by dispersion, especially when the modulation level is high. In this paper, we therefore propose to use multi-wavelength PPM (MWPPM) signaling to overcome the limitation of PPM. To further improve the system performance, avalanche photodiode (APD) is also used. The performance of the proposed system is theoretically analyzed using a realistic model of Gaussian pulse propagation. To model the impact of intensity fluctuation caused by the atmospheric turbulence, the log-normal channel is used. We find that, by using MWPPM, the effects of both intensity fluctuation and pulse broadening are mitigated, the BER is therefore significantly improved. Additionally, we quantitatively show that the system performance is further improved by using APD, especially when the average APD gain is chosen properly. PMID:23187533
Auldist, M J; Grainger, C; Houlihan, A V; Mayes, J J; Williams, R P W
2010-04-01
Extending the lactation length of dairy cows beyond the traditional 10 mo toward lactations of up to 22 mo has attracted interest in the pasture-based seasonal dairying systems of Australia and New Zealand as a way of alleviating the need for cows to conceive during peak lactation, such as is required to maintain seasonally concentrated calving systems. Lactation lengths longer than 10 mo instead provide cows with more time to cycle and conceive after parturition and may therefore be more suitable systems for high-producing Holstein-Friesian cows. Before recommending such systems there is a need to evaluate the effects of long lactations on the suitability of milk for manufacture of high-quality dairy products. In the current experiment, the composition of milk from cows entering the second half of a 22-mo lactation was examined in detail and compared with that from cows undergoing a traditional 10-mo lactation. On 2 occasions, coagulation properties were measured using low amplitude strain oscillation rheometry, and Cheddar cheese was made in 250-L pilot-scale vats. Results showed that milk from extended lactations had higher concentrations of fat and protein than cows undergoing 10-mo lactations under similar management conditions and at the same time of year. The ratio of casein to true protein was not affected by lactation length and neither were the proportions of individual caseins. The increase in milk solids during extended lactations translated into a more rapid rate of coagulation and ultimately a firmer curd on one of the two occasions. Milk from extended lactations yielded more cheese per 100 kg of milk, and there were few differences in the composition or organoleptic properties of the cheese. These data are the first to show that pasture-based dairy industries could embrace the use of extended lactations without compromising the core business of producing high-quality dairy products. PMID:20338417
NASA Technical Reports Server (NTRS)
Bardina, Jorge E.
1995-01-01
The objective of this work is to develop, verify, and incorporate the baseline two-equation turbulence models which account for the effects of compressibility into the three-dimensional Reynolds averaged Navier-Stokes (RANS) code and to provide documented descriptions of the models and their numerical procedures so that they can be implemented into 3-D CFD codes for engineering applications.
Effects of spin-orbit coupling on magnetic properties of discrete and extended magnetic systems.
Dai, Dadi; Xiang, Hongjun; Whangbo, Myung-Hwan
2008-10-01
In accounting for the magnetic properties of discrete and extended compounds with unpaired spins, it is crucial to know the nature of their ground and low-lying excited states. In this review we surveyed quantum mechanical descriptions on how these states are affected by spin-orbit coupling and attempted to provide a conceptual framework with which to think about spin-orbit coupling and its applications. PMID:18484639
A second-order closure prediction of premixed turbulent combustion in jets
NASA Astrophysics Data System (ADS)
Davé, N.; Kollmann, W.
1987-02-01
In this paper, a numerical prediction is reported involving second-order closure of a turbulent flow of a vertically burning, lean mixture of premixed combustible gases discharging from a pipe and developing into a turbulent combusting roundjet. Classical closures are used where available. Expressions for the chemical reaction rate term and other unclosed terms related to variable density flow in the Favre-averaged turbulent transport equations are based on the Bray-Moss-Libby aerothermochemistry for premixed turbulent combustion, extended to variable enthalpy systems. Mixing of hot burned and cool ambient gases and the attendant buoyancy effects are found to be significant physical phenomena in the behavior of such lean premixed combusting jets. Results of the simulation are compared with experimental data of Yoshida [Proceedings of the Eighteenth International Symposium on Combustion (The Combustion Institute, Pittsburgh, 1981), p. 931] with which reasonable numerical agreement is obtained. Reasons for discrepancies and possible lines for future research are discussed.
Simulations of turbulent mixing and reacting flows and their applications to turbulence modeling
NASA Technical Reports Server (NTRS)
Ferziger, J. H.; Cantwell, B. J.
1986-01-01
The method of full simulation is applied to reacting turbulent flows. Full simulation has proven of great value as a complement to experiments for the study of nonreacting turbulent flows. It provides insight into the physics of turbulent flows and their modeling. It is natural to try to extend these methods to the simulation of reacting turbulent flows. Because this is one of the first attempts at this type of simulation, a subsidiary goal of this work is to demonstrate the feasibility of using simulation to study turbulent reacting flows. In addition, it is shown that such simulations can be used to provide physical insight into the nature of turbulent combustion and to provide data that will help to construct models that can be used in engineering simulations of turbulent reacting flows.
Bartsch, L.A.; Richardson, W.B.; Sandheinrich, M.B.
2003-01-01
We conducted a factorial experiment, in outdoor mesocosms, on the effects of zebra mussels and water column mixing (i.e., turbulence) on the diet, growth, and survival of larval fathead minnows (Pimephales promelas). Significant (P < 0.05) larval mortality occurred by the end of the experiment with the highest mortality (90%) occurring in the presence of both turbulence and zebra mussels, whereas mortality was 37% in treatment with turbulence and 17% and 18% in the zebra mussels treatment, and the control, respectively. The size of individual fish was significantly different among treatments at the end of the experiment and was inversely related to survival. Levels of trophic resources (i.e., phyto and zooplankton) varied among treatments and were treatment specific. Turbulent mixing facilitated removal of phytoplankton by zebra mussels by making the entire water column of the tanks available to these benthic filter feeders. Early in the experiment (Day = 0 to 14) the physical process of turbulent mixing likely caused a reduction in standing stocks of zooplankton. The interactive effect of turbulence and mussels reduced copepod and rotifer stocks, through physical processes and through filtration by zebra mussels, relative to the turbulence treatment. The reductions in the number of total zooplankton in the turbulent mixing mesocosms and the further reduction of rotifer and copepod in the turbulence and mussels treatment coincided with a period of increased reliance of larval fathead minnows on these prey. Estimates of consumption from bioenergetics modeling and measured prey standing stocks indicated caloric resources of suitable prey in turbulence treatments during the early weeks of the experiment were insufficient to prevent starvation. Early mortality in the turbulence and mussels treatment likely released surviving fish from intense intraspecific competition and resulted in higher individual growth rates. A combination of high abundance of zebra mussels in an
Bartsch, L.A.; Richardson, W.B.; Sandheinrich, M.B.
2003-01-01
We conducted a factorial experiment, in outdoor mesocosms, on the effects of zebra mussels and water column mixing (i.e., turbulence) on the diet, growth, and survival of larval fathead minnows (Pimephales promelas). Significant (P < 0.05) larval mortality occurred by the end of the experiment with the highest mortality (90%) occurring in the presence of both turbulence and zebra mussels, whereas mortality was 37% in treatment with turbulence and 17% and 18% in the zebra mussels treatment, and the control, respectively. The size of individual fish was significantly different among treatments at the end of the experiment and was inversely related to survival. Levels of trophic resources (i.e., phyto and zooplankton) varied among treatments and were treatment specific. Turbulent mixing facilitated removal of phytoplankton by zebra mussels by making the entire water column of the tanks available to these benthic filter feeders. Early in the experiment (Day = 0 to 14) the physical process of turbulent mixing likely caused a reduction in standing stocks of zooplankton. The interactive effect of turbulence and mussels reduced copepod and rotifer stocks, through physical processes and through filtration by zebra mussels, relative to the turbulence treatment. The reductions in the number of total zooplankton in the turbulent mixing mesocosms and the further reduction of rotifer and copepod in the turbulence and mussels treatment coincided with a period of increased reliance of larval fathead minnows on these prey. Estimates of consumption from bioenergetics modeling and measured prey standing stocks indicated caloric resources of suitable prey in turbulence treatments during the early weeks of the experiment were insufficient to prevent starvation. Early mortality in the turbulence and mussels treatment likely released surviving fish from intense intraspecific competition and resulted in higher individual growth rates. A combination of high abundance of zebra mussels in an
Passive adaptive imaging through turbulence
NASA Astrophysics Data System (ADS)
Tofsted, David
2016-05-01
Standard methods for improved imaging system performance under degrading optical turbulence conditions typically involve active adaptive techniques or post-capture image processing. Here, passive adaptive methods are considered where active sources are disallowed, a priori. Theoretical analyses of short-exposure turbulence impacts indicate that varying aperture sizes experience different degrees of turbulence impacts. Smaller apertures often outperform larger aperture systems as turbulence strength increases. This suggests a controllable aperture system is advantageous. In addition, sub-aperture sampling of a set of training images permits the system to sense tilts in different sub-aperture regions through image acquisition and image cross-correlation calculations. A four sub-aperture pattern supports corrections involving five realizable operating modes (beyond tip and tilt) for removing aberrations over an annular pattern. Progress to date will be discussed regarding development and field trials of a prototype system.
Evans, J.L.; Frank, W.M.; Young, G.S.
1996-04-01
Successful simulations of the global circulation and climate require accurate representation of the properties of shallow and deep convective clouds, stable-layer clouds, and the interactions between various cloud types, the boundary layer, and the radiative fluxes. Each of these phenomena play an important role in the global energy balance, and each must be parameterized in a global climate model. These processes are highly interactive. One major problem limiting the accuracy of parameterizations of clouds and other processes in general circulation models (GCMs) is that most of the parameterization packages are not linked with a common physical basis. Further, these schemes have not, in general, been rigorously verified against observations adequate to the task of resolving subgrid-scale effects. To address these problems, we are designing a new Integrated Cumulus Ensemble and Turbulence (ICET) parameterization scheme, installing it in a climate model (CCM2), and evaluating the performance of the new scheme using data from Atmospheric Radiation Measurement (ARM) Program Cloud and Radiation Testbed (CART) sites.
Simulation of HF waves reflected from a turbulent ionosphere for spread spectrum systems
Wagen, J.F.O.
1988-01-01
The communication channel established with HF waves reflected by the ionosphere is investigated. The background ionosphere is modeled by a horizontally stratified medium. This model is superimposed with random irregularities. The resulting channel is characterized by a random transfer function. Each frequency component of this transfer function is determined from the received wave, field, knowing the transmitted wave field. The computation of the random fluctuations of the received wave field is performed by using the phase screen-diffraction layer method. This scheme simulates the propagation of an HF wave in the turbulent ionosphere. Based on the forward-scatter approximation, the scheme computes sequentially the effects of phase fluctuations due to the irregularities and the effects of diffraction due to phase mixing. Stepping along the ray path, phase fluctuations are imbedded into a number of phase screens. Diffraction effects are then computed between phase screens using FFT techniques. Special attention is given to the reflection region where the classical WKB approximations are invalid. The computed statistics of the received signal include probability distribution, power spectrum, correlation function and scintillation index.
Workshop on Computational Turbulence Modeling
NASA Technical Reports Server (NTRS)
Shabbir, A. (Compiler); Shih, T.-H. (Compiler); Povinelli, L. A. (Compiler)
1994-01-01
The purpose of this meeting was to discuss the current status and future development of turbulence modeling in computational fluid dynamics for aerospace propulsion systems. Various turbulence models have been developed and applied to different turbulent flows over the past several decades and it is becoming more and more urgent to assess their performance in various complex situations. In order to help users in selecting and implementing appropriate models in their engineering calculations, it is important to identify the capabilities as well as the deficiencies of these models. This also benefits turbulence modelers by permitting them to further improve upon the existing models. This workshop was designed for exchanging ideas and enhancing collaboration between different groups in the Lewis community who are using turbulence models in propulsion related CFD. In this respect this workshop will help the Lewis goal of excelling in propulsion related research. This meeting had seven sessions for presentations and one panel discussion over a period of two days. Each presentation session was assigned to one or two branches (or groups) to present their turbulence related research work. Each group was asked to address at least the following points: current status of turbulence model applications and developments in the research; progress and existing problems; and requests about turbulence modeling. The panel discussion session was designed for organizing committee members to answer management and technical questions from the audience and to make concluding remarks.
Laser beam scintillation beyond the turbulent atmosphere A numerical computation
NASA Technical Reports Server (NTRS)
Bufton, J. L.; Taylor, L. S.
1976-01-01
The extended Huygens-Fresnel formulation for propagation through turbulence is used to examine scintillation of a finite laser beam. The method is demonstrated analytically for propagation beyond a weak Gaussian phase screen. A numerical integration technique is used to extend the results to a more realistic turbulence model. Results are compared with existing Gaussian beam propagation theory.
NASA Astrophysics Data System (ADS)
Leakeas, Charles L.; Capehart, Shay R.; Bartell, Richard J.; Cusumano, Salvatore J.; Whiteley, Matthew R.
2011-06-01
Laser weapon systems comprised of tiled subapertures are rapidly emerging in importance in the directed energy community. Performance models of these laser weapon systems have been developed from numerical simulations of a high fidelity wave-optics code called WaveTrain which is developed by MZA Associates. System characteristics such as mutual coherence, differential jitter, and beam quality rms wavefront error are defined for a focused beam on the target. Engagement scenarios are defined for various platform and target altitudes, speeds, headings, and slant ranges along with the natural wind speed and heading. Inputs to the performance model include platform and target height and velocities, Fried coherence length, Rytov number, isoplanatic angle, thermal blooming distortion number, Greenwood and Tyler frequencies, and atmospheric transmission. The performance model fit is based on power-in-the-bucket (PIB) values against the PIB from the simulation results for the vacuum diffraction-limited spot size as the bucket. The goal is to develop robust performance models for aperture phase error, turbulence, and thermal blooming effects in tiled subaperture systems.
Laboratory detection of extended-spectrum beta-lactamase by an automated system.
Gagliotti, Carlo; Sarti, Mario; Benini, Franca; Cipolloni, Antonio Paolo; Testa, Giovanna; Venturelli, Claudia; Moro, Maria Luisa
2008-10-01
This study aims to evaluate the positive predictive value (PPV) and the negative predictive value (NPV) of Vitek2 in detecting extended-spectrum beta-lactamase (ESBL) phenotypes when compared to a manual confirmatory test as gold standard. A sample of Escherichia coli, Klebsiella spp and Proteus mirabilis isolates were collected by 5 laboratories in the Emilia-Romagna Region (Italy). Vitek2 appears to be an accurate tool to detect ESBL phenotypes of E. coli isolates; some concern remains about its performance with the other bacterial species, especially P. mirabilis. PMID:19123314
General Purpose Kernel Integration Shielding Code System-Point and Extended Gamma-Ray Sources.
1981-06-11
PELSHIE3 calculates dose rates from gamma-emitting sources with different source geometries and shielding configurations. Eight source geometries are provided and are called by means of geometry index numbers. Gamma-emission characteristics for 134 isotopes, attenuation coefficients for 57 elements or shielding materials and Berger build-up parameters for 17 shielding materials can be obtained from a direct access data library by specifying only the appropriate library numbers. A different option allows these data to be read frommore » cards. For extended sources, constant source strengths as well as exponential and Bessel function source strength distributions are allowed in most cases.« less
Evidence of big bang turbulence
NASA Astrophysics Data System (ADS)
Gibson, Carl H.
2002-11-01
Chaotic, eddy-like motions dominated by inertial-vortex forces begin at Planck scales in a hot big-bang-turbulence (BBT) cosmological model where this version of the quantum-gravitational-dynamics epoch produces not only the first space-time-energy of the universe but the first high Reynolds number turbulence and turbulent mixing with Kolmogorov and Batchelor-Obukhov-Corrsin velocity and temperature gradient spectra. Strong-force-freeze-out and inflation produced the first fossil-temperature-turbulence by stretching the fluctuations beyond the horizon scale ct of causal connection for light speed c and time t. Recent Cosmic Background Imager spectra of the cosmic microwave background (CMB) temperature anisotropies at high wavenumbers support the prediction that fossil BBT fluctuation patterns imprinted by nucleosynthesis on light element densities and the associated Sachs-Wolfe temperature fluctuations should not decay by thermal diffusion as expected if the CMB anisotropies were acoustic as commonly assumed. Extended Self Similarity coefficients of the CMB anisotropies exactly match those of high Reynolds number turbulence (Bershadskii and Sreenivasan 2002), supporting the conclusion that fossil big-bang-turbulence seeded nucleosynthesis of light elements and the first hydro-gravitational structure formation.
NASA Astrophysics Data System (ADS)
Fusiek, G.; Niewczas, Pawel; McDonald, James R.
2005-03-01
We present details of the design and laboratory evaluation of the fiber Bragg grating (FBG) interrogation system developed specifically for condition monitoring of electrical submersible pumps (ESPs). The system, based on the microelectromechanical systems (MEMS) Fabry-Pérot tunable filter, is capable of interrogating several FBG sensors placed around an ESP unit and configured to measure static and dynamic parameters, e.g., temperature, vibration signature and/or instantaneous voltage, and current. Sensor interrogation over the extended step-out length distance of 24 km is demonstrated in the laboratory in a simple experiment of multipoint dynamic strain monitoring in a vibrated cantilever beam.
NASA Technical Reports Server (NTRS)
Lewandowski, Edward J.; Schreiber, Jeffre G.; Wilson, Scott D.; oriti, Salvatore M.; Cornell, Peggy; Schifer, Nicholas
2008-01-01
100 We class Stirling convertors began extended operation testing at NASA Glenn Research Center (GRC) in 2003 with a pair of Technology Demonstration Convertors (TDCs) operating in air. Currently, the number of convertors on extended operation test has grown to 12, including both TDCs and Advanced Stirling Convertors (ASCs) operating both in air and in thermal vacuum. Additional convertors and an electrically heated radioisotope generator will be put on test in the near future. This testing has provided data to support life and reliability estimates and the quality improvements and design changes that have been made to the convertor. The convertors operated 24/7 at the nominal amplitude and power levels. Performance data were recorded on an hourly basis. Techniques to monitor the convertors for change in internal operation included gas analysis, vibration measurements and acoustic emission measurements. This data provided a baseline for future comparison. This paper summarizes the results of over 145,000 hours of TDC testing and 40,000 hours of ASC testing and discusses trends in the data. Data shows the importance of improved materials, hermetic sealing, and quality processes in maintaining convertor performance over long life.
NASA Technical Reports Server (NTRS)
Lewandowski, Edward J.; Schreiber, Jeffrey G.; Wilson, Scott D.; Oriti, Salvatore M.; Cornell, Peggy; Schifer, Nicholas
2009-01-01
100 We class Stirling convertors began extended operation testing at NASA Glenn Research Center (GRC) in 2003 with a pair of Technology Demonstration Convertors (TDCs) operating in air. Currently, the number of convertors on extended operation test has grown to 12, including both TDCs and Advanced Stirling Convertors (ASCs) operating both in air and in thermal vacuum. Additional convertors and an electrically heated radioisotope generator will be put on test in the near future. This testing has provided data to support life and reliability estimates and the quality improvements and design changes that have been made to the convertor. The convertors operated 24/7 at the nominal amplitude and power levels. Performance data were recorded on an hourly basis. Techniques to monitor the convertors for change in internal operation included gas analysis, vibration measurements, and acoustic emission measurements. This data provided a baseline for future comparison. This paper summarizes the results of over 145,000 hr of TDC testing and 40,000 hr of ASC testing and discusses trends in the data. Data shows the importance of improved materials, hermetic sealing, and quality processes in maintaining convertor performance over long life.
New class of turbulence in active fluids.
Bratanov, Vasil; Jenko, Frank; Frey, Erwin
2015-12-01
Turbulence is a fundamental and ubiquitous phenomenon in nature, occurring from astrophysical to biophysical scales. At the same time, it is widely recognized as one of the key unsolved problems in modern physics, representing a paradigmatic example of nonlinear dynamics far from thermodynamic equilibrium. Whereas in the past, most theoretical work in this area has been devoted to Navier-Stokes flows, there is now a growing awareness of the need to extend the research focus to systems with more general patterns of energy injection and dissipation. These include various types of complex fluids and plasmas, as well as active systems consisting of self-propelled particles, like dense bacterial suspensions. Recently, a continuum model has been proposed for such "living fluids" that is based on the Navier-Stokes equations, but extends them to include some of the most general terms admitted by the symmetry of the problem [Wensink HH, et al. (2012) Proc Natl Acad Sci USA 109:14308-14313]. This introduces a cubic nonlinearity, related to the Toner-Tu theory of flocking, which can interact with the quadratic Navier-Stokes nonlinearity. We show that as a result of the subtle interaction between these two terms, the energy spectra at large spatial scales exhibit power laws that are not universal, but depend on both finite-size effects and physical parameters. Our combined numerical and analytical analysis reveals the origin of this effect and even provides a way to understand it quantitatively. Turbulence in active fluids, characterized by this kind of nonlinear self-organization, defines a new class of turbulent flows. PMID:26598708
New class of turbulence in active fluids
Bratanov, Vasil; Frey, Erwin
2015-01-01
Turbulence is a fundamental and ubiquitous phenomenon in nature, occurring from astrophysical to biophysical scales. At the same time, it is widely recognized as one of the key unsolved problems in modern physics, representing a paradigmatic example of nonlinear dynamics far from thermodynamic equilibrium. Whereas in the past, most theoretical work in this area has been devoted to Navier–Stokes flows, there is now a growing awareness of the need to extend the research focus to systems with more general patterns of energy injection and dissipation. These include various types of complex fluids and plasmas, as well as active systems consisting of self-propelled particles, like dense bacterial suspensions. Recently, a continuum model has been proposed for such “living fluids” that is based on the Navier–Stokes equations, but extends them to include some of the most general terms admitted by the symmetry of the problem [Wensink HH, et al. (2012) Proc Natl Acad Sci USA 109:14308–14313]. This introduces a cubic nonlinearity, related to the Toner–Tu theory of flocking, which can interact with the quadratic Navier–Stokes nonlinearity. We show that as a result of the subtle interaction between these two terms, the energy spectra at large spatial scales exhibit power laws that are not universal, but depend on both finite-size effects and physical parameters. Our combined numerical and analytical analysis reveals the origin of this effect and even provides a way to understand it quantitatively. Turbulence in active fluids, characterized by this kind of nonlinear self-organization, defines a new class of turbulent flows. PMID:26598708
NASA Technical Reports Server (NTRS)
Rubesin, Morris W.
1987-01-01
Recent developments at several levels of statistical turbulence modeling applicable to aerodynamics are briefly surveyed. Emphasis is on examples of model improvements for transonic, two-dimensional flows. Experience with the development of these improved models is cited to suggest methods of accelerating the modeling process necessary to keep abreast of the rapid movement of computational fluid dynamics into the computation of complex three-dimensional flows.
Development of solid amine CO2 control systems for extended duration missions
NASA Technical Reports Server (NTRS)
Dresser, K. J.; Cusick, R. J.
1984-01-01
This paper briefly discusses the development history of solid amine CO2 control systems, describes two distinct CO2 control system concepts, and presents the performance characteristics for both system concepts. The first concept (developed under NASA Contract NAS9-13624) incorporates a solid amine canister, an automatic microprocessor controller, and an accumulator to collect CO2 and to provide regulated CO2 delivery to an oxygen recovery system. This system is currently operating in the Crew Systems Division's Advanced Life Support Development Laboratory (ALSDL). The second system concept (being developed under NASA Contract NAS9-16978) employs multiple solid amine canisters, an advanced automatic controller and system status display, the ability to regulate CO2 delivery for oxygen recovery, and energy saving features that allow system operation at lower power levels than the first concept.
Davies, Jim; Michaelian, Kourken
2016-08-01
This article argues for a task-based approach to identifying and individuating cognitive systems. The agent-based extended cognition approach faces a problem of cognitive bloat and has difficulty accommodating both sub-individual cognitive systems ("scaling down") and some supra-individual cognitive systems ("scaling up"). The standard distributed cognition approach can accommodate a wider variety of supra-individual systems but likewise has difficulties with sub-individual systems and faces the problem of cognitive bloat. We develop a task-based variant of distributed cognition designed to scale up and down smoothly while providing a principled means of avoiding cognitive bloat. The advantages of the task-based approach are illustrated by means of two parallel case studies: re-representation in the human visual system and in a biomedical engineering laboratory. PMID:27033708
NASA Astrophysics Data System (ADS)
Kühnen, Jakob; Hof, Björn
2015-11-01
We show that a simple modification of the velocity profile in a pipe can lead to a complete collapse of turbulence and the flow fully relaminarises. The annihilation of turbulence is achieved by a steady manipulation of the streamwise velocity component alone, greatly reducing control efforts. Several different control techniques are presented: one with a local modification of the flow profile by means of a stationary obstacle, one employing a nozzle injecting fluid through a small gap at the pipe wall and one with a moving wall, where a part of the pipe is shifted in the streamwise direction. All control techniques act on the flow such that the streamwise velocity profile becomes more flat and turbulence gradually grows faint and disappears. In a smooth straight pipe the flow remains laminar downstream of the control. Hence a reduction in skin friction by a factor of 8 and more can be accomplished. Stereoscopic PIV-measurements and movies of the development of the flow during relaminarisation are presented.
On the prediction of turbulent secondary flows
NASA Technical Reports Server (NTRS)
Speziale, C. G.; So, R. M. C.; Younis, B. A.
1992-01-01
The prediction of turbulent secondary flows, with Reynolds stress models, in circular pipes and non-circular ducts is reviewed. Turbulence-driven secondary flows in straight non-circular ducts are considered along with turbulent secondary flows in pipes and ducts that arise from curvature or a system rotation. The physical mechanisms that generate these different kinds of secondary flows are outlined and the level of turbulence closure required to properly compute each type is discussed in detail. Illustrative computations of a variety of different secondary flows obtained from two-equation turbulence models and second-order closures are provided to amplify these points.
NASA Astrophysics Data System (ADS)
Gibson, C. H.; Bondur, V. G.; Keeler, R. N.; Leung, P. T.
2011-11-01
Sea surface brightness spectral anomalies from a Honolulu municipal outfall have been detected from space satellites in 200 km2 areas extending 20 km from the wastewater diffuser (Bondur 2005, Keeler et al. 2005, Gibson et al. 2005). Dropsonde and towed body microstructure measurements show outfall enhanced viscous and temperature dissipation rates above the turbulence trapping layer. Fossil turbulence waves and secondary (zombie, zebra) turbulence waves break as they propagate near-vertically and then break again near the surface to produce wind ripple smoothing in narrow frequency band (zebra) patterns from soliton-like sources of secondary turbulence energy acting on fossils advected from the outfall. The 30-250 m solitons reflect a nonlinear cascade from tidal and current kinetic energy to boundary layer turbulence events, to fossil turbulence waves, to internal soliton and tidal waves. Secondary (zombie) turbulence acts on outfall fossil patches to amplify, channel in chimneys, and vertically beam ambient internal wave energy just as energized metastable molecules around stars amplify and beam quantum frequencies in astrophysical masers. Kilowatts of buoyancy power from the treatment plant produces fossil turbulence patches trapped below the thermocline. Beamed zombie turbulence maser action (BZTMA) in mixing chimneys amplifies these kilowatts into the megawatts of surface turbulence dissipation required to affect brightness on wide sea surface areas by maser action vertical beaming of fossil-wave-power extracted from gigawatts dissipated by intermittent bottom turbulence events on topography from the tides and currents.
Toward a systems-oriented approach to the role of the extended amygdala in adaptive responding.
Waraczynski, Meg
2016-09-01
Research into the structure and function of the basal forebrain macrostructure called the extended amygdala (EA) has recently seen considerable growth. This paper reviews that work, with the objectives of identifying underlying themes and developing a common goal towards which investigators of EA function might work. The paper begins with a brief review of the structure and the ontological and phylogenetic origins of the EA. It continues with a review of research into the role of the EA in both aversive and appetitive states, noting that these two seemingly disparate avenues of research converge on the concept of reinforcement - either negative or positive - of adaptive responding. These reviews lead to a proposal as to where the EA may fit in the organization of the basal forebrain, and an invitation to investigators to place their findings in a unifying conceptual framework of the EA as a collection of neural ensembles that mediate adaptive responding. PMID:27216212
Extending the life and recycle capability of earth storable propellant systems.
NASA Technical Reports Server (NTRS)
Schweickert, T. F.
1972-01-01
Rocket propulsion systems for reusable vehicles will be required to operate reliably for a large number of missions with a minimum of maintenance and a fast turnaround. For the space shuttle reaction control system to meet these requirements, current and prior related system failures were examined for their impact on reuse and, where warranted, component design and/or system configuration changes were defined for improving system service life. It was found necessary to change the pressurization component arrangement used on many single-use applications in order to eliminate a prevalent check valve failure mode and to incorporate redundant expulsion capability in propellant tank designs to achieve the necessary system reliability. Material flaws in pressurant and propellant tanks were noted to have a significant effect on tank cycle life. Finally, maintenance considerations dictated a modularized systems approach, allowing the system to be removed from the vehicle for service and repair at a remote site.
Ofuchi, César Yutaka; Coutinho, Fabio Rizental; Neves, Flávio; de Arruda, Lucia Valéria Ramos; Morales, Rigoberto Eleazar Melgarejo
2016-01-01
In this paper the extended autocorrelation velocity estimator is evaluated and compared using a nondestructive ultrasonic device. For this purpose, three velocity estimators are evaluated and compared. The autocorrelation method (ACM) is the most used and well established in current ultrasonic velocity profiler technology, however, the technique suffers with phase aliasing (also known as the Nyquist limit) at higher velocities. The cross-correlation method (CCM) is also well known and does not suffer with phase aliasing as it relies on time shift measurements between emissions. The problem of this method is the large computational burden due to several required mathematical operations. Recently, an extended autocorrelation method (EAM) which combines both ACM and CCM was developed. The technique is not well known within the fluid engineering community, but it can measure velocities beyond the Nyquist limit without the ACM phase aliasing issues and with a lower computational cost than CCM. In this work, all three velocity estimation methods are used to measure a uniform flow of the liquid inside a controlled rotating cylinder. The root-mean-square deviation variation coefficient (CVRMSD) of the velocity estimate and the reference cylinder velocity was used to evaluate the three different methods. Results show that EAM correctly measures velocities below the Nyquist limit with less than 2% CVRMSD. Velocities beyond the Nyquist limit are only measured well by EAM and CCM, with the advantage of the former of being computationally 15 times faster. Furthermore, the maximum value of measurable velocity is also investigated considering the number of times the velocity surpasses the Nyquist limit. The combination of number of pulses and number of samples, which highly affects the results, are also studied in this work. Velocities up to six times the Nyquist limit could be measurable with CCM and EAM using a set of parameters as suggested in this work. The results validate
Future Air Force aircraft propulsion control systems: The extended summary paper
NASA Technical Reports Server (NTRS)
Skira, C. A.
1980-01-01
Hydromechanical control technology simply cannot compete against the performance benefits offered by electronics. Future military aircraft propulsion control systems will be full authority, digital electronic, microprocessor base systems. Anticipating the day when microprocessor technology will permit the integration and management of aircraft flight control, fire control and propulsion control systems, the Air Force Aero Propulsion Laboratory is developing control logic algorithms for a real time, adaptive control and diagnostic information system.
Akhmediev, N; Soto-Crespo, J M; Devine, N
2016-08-01
Turbulence in integrable systems exhibits a noticeable scientific advantage: it can be expressed in terms of the nonlinear modes of these systems. Whether the majority of the excitations in the system are breathers or solitons defines the properties of the turbulent state. In the two extreme cases we can call such states "breather turbulence" or "soliton turbulence." The number of rogue waves, the probability density functions of the chaotic wave fields, and their physical spectra are all specific for each of these two situations. Understanding these extreme cases also helps in studies of mixed turbulent states when the wave field contains both solitons and breathers, thus revealing intermediate characteristics. PMID:27627303
NASA Astrophysics Data System (ADS)
Masini, Emmanuel; Manatschal, Gianreto; Tugend, Julie; Mohn, Geoffroy; Robin, Cécile; Geoffroy, Laurent; Unternehr, Patrick
2013-04-01
The discovery of hyper-extended domains in deep water rifted margins challenged the classical view of the evolution of rift systems leading to continental breakup. In these hyper-extended domains, rift basins occur over less than 10km thick extended continental crust or exhumed subcontinental mantle. Neither their imaged stratigraphic architecture and drilled facies nor the subsidence history can be explained by classical McKenzie-type rift models. Studies performed on off- and on-shore examples demonstrate the importance of tectonic exhumation by detachment faulting. However, despite their apparent widespread occurrence in present-day rifted margins, the overall tectono-sedimentary evolution of these systems remains poorly understood. In this study we review and compare key multi-scale observations from 3 different hyper-extended rift systems. 1) The first example, in the Western Pyrenees, corresponds to a complete sediment-rich Cretaceous hyper-extended rift system that can be investigated. 2) The second example in the Swiss Alps, gives the access to supra-detachment sedimentary evolution in a sediment-starved context. 3) The last example exposed in Baja California Sur, shows supra-detachment sedimentary evolution in sediment-rich and shallow water environment. Based on these studies in three different settings, we conclude that the basins forming in the lower and upper plate position respective to detachment fault polarity develop as two different types of basins. Lower plate basins develop over top-basement detachment systems and discontinuous pieces of pre-rift strata (extensional allochthons). In this setting, the sequential development of low-angle detachment systems implies the creation of new real estate crust (new seafloor surfaces) and a complex syn-rift stratigraphic architecture. Through this domain, the deposition of syn- and post-tectonic sediments above exhumation surfaces are diachronous along stretching direction illustrating relative migration of
NASA Astrophysics Data System (ADS)
Long, Zi-Xuan; Zhang, Yi
2014-11-01
This paper focuses on the Noether symmetries and the conserved quantities for both holonomic and nonholonomic systems based on a new non-conservative dynamical model introduced by El-Nabulsi. First, the El-Nabulsi dynamical model which is based on a fractional integral extended by periodic laws is introduced, and El-Nabulsi—Hamilton's canonical equations for non-conservative Hamilton system with holonomic or nonholonomic constraints are established. Second, the definitions and criteria of El-Nabulsi—Noether symmetrical transformations and quasi-symmetrical transformations are presented in terms of the invariance of El-Nabulsi—Hamilton action under the infinitesimal transformations of the group. Finally, Noether's theorems for the non-conservative Hamilton system under the El-Nabulsi dynamical system are established, which reveal the relationship between the Noether symmetry and the conserved quantity of the system.
NASA Technical Reports Server (NTRS)
Bass, J; Agostini, L
1955-01-01
The theory of turbulence reached its full growth at the end of the 19th century as a result of the work by Boussinesq and Reynolds. It then underwent a long period of stagnation which ended under the impulse given to it by the development of wind tunnels caused by the needs of aviation. Numerous researchers, attempted to put Reynolds' elementary statistical theory into a more precise form. During the war, some isolated scientists - von Weizsacker and Heisenberg in Germany, Kolmogoroff in Russia, Onsager in the U.S.A. - started a program of research. By a system of assumptions which make it possible to approach the structure of turbulence in well-defined limiting conditions quantitatively, they obtained a certain number of laws on the correlations and the spectrum. Since the late reports have improved the mathematical language of turbulence, it was deemed advisable to start with a detailed account of the mathematical methods applicable to turbulence, inspired at first by the work of the French school, above all for the basic principles, then the work of the foreigners, above all for the theory of the spectrum.
Cygankiewicz, Iwona
2013-01-01
Heart rate turbulence (HRT) is a baroreflex-mediated biphasic reaction of heart rate in response to premature ventricular beats. Heart rate turbulence is quantified by: turbulence onset (TO) reflecting the initial acceleration of heart rate following premature beat and turbulence slope (TS) describing subsequent deceleration of heart rate. Abnormal HRT identifies patients with autonomic dysfunction or impaired baroreflex sensitivity due to variety of disorders, but also may reflect changes in autonomic nervous system induced by different therapeutic modalities such as drugs, revascularization, or cardiac resynchronization therapy. More importantly, impaired HRT has been shown to identify patients at high risk of all-cause mortality and sudden death, particularly in postinfarction and congestive heart failure patients. It should be emphasized that abnormal HRT has a well-established role in stratification of postinfarction and heart failure patients with relatively preserved left ventricular ejection fraction. The ongoing clinical trials will document whether HRT can be used to guide implantation of cardioverter-defibrillators in this subset of patients, not covered yet by ICD guidelines. This review focuses on the current state-of-the-art knowledge regarding clinical significance of HRT in detection of autonomic dysfunction and regarding the prognostic significance of this parameter in predicting all-cause mortality and sudden death. PMID:24215748
An extended steepness model for leg-size determination based on Dachsous/Fat trans-dimer system
Yoshida, Hiroshi; Bando, Tetsuya; Mito, Taro; Ohuchi, Hideyo; Noji, Sumihare
2014-01-01
What determines organ size has been a long-standing biological question. Lawrence et al. (2008) proposed the steepness hypothesis suggesting that the protocadherin Dachsous/Fat (Ds/Ft) system may provide some measure of dimension to the cells in relation to the gradient. In this paper we extended the model as a means of interpreting experimental results in cricket leg regeneration. We assumed that (1) Ds/Ft trans-heterodimers or trans-homodimers are redistributed during cell division, and (2) growth would cease when a differential of the dimer across each cell decreases to a certain threshold. We applied our model to simulate the results obtained by leg regeneration experiments in a cricket model. The results were qualitatively consistent with the experimental data obtained for cricket legs by RNA interference methodology. Using our extended steepness model, we provided a molecular-based explanation for leg size determination even in intercalary regeneration and for organ size determination. PMID:24613915
An extended steepness model for leg-size determination based on Dachsous/Fat trans-dimer system.
Yoshida, Hiroshi; Bando, Tetsuya; Mito, Taro; Ohuchi, Hideyo; Noji, Sumihare
2014-01-01
What determines organ size has been a long-standing biological question. Lawrence et al. (2008) proposed the steepness hypothesis suggesting that the protocadherin Dachsous/Fat (Ds/Ft) system may provide some measure of dimension to the cells in relation to the gradient. In this paper we extended the model as a means of interpreting experimental results in cricket leg regeneration. We assumed that (1) Ds/Ft trans-heterodimers or trans-homodimers are redistributed during cell division, and (2) growth would cease when a differential of the dimer across each cell decreases to a certain threshold. We applied our model to simulate the results obtained by leg regeneration experiments in a cricket model. The results were qualitatively consistent with the experimental data obtained for cricket legs by RNA interference methodology. Using our extended steepness model, we provided a molecular-based explanation for leg size determination even in intercalary regeneration and for organ size determination. PMID:24613915
NASA Astrophysics Data System (ADS)
Shin, D.; Hwang, T.; Band, L. E.
2007-12-01
HydroMet is a project of RENCI (Renaissance Computing Institute) to develop a new hydrologic modeling and forecasting system. It aims to provide accurate predictions for geophysical hazards including flash floods, droughts, and fire hazard at a fine spatial resolution. For this purpose, the system needs to integrate multi- disciplinary models including weather forecasting models (WRF, Weather Research and Forecasting and LDAS, Land Data Assimilation Systems), and a distributed watershed model (RHESSys, Regional Hydro-Ecologic Simulation System). As a core component to simulate full cycles of water, carbon, and nutrients in watersheds, RHESSys is required to be re-engineered to have a highly usable and extendable architecture. To build the architecture, we restructure RHESSys as a dynamically loadable package for Python, a scripting language for rapid prototyping of new algorithms and seamless integration of external programs. The entire internal structure of RHESSys is exposed to external programming environment, which enables users and external programs to closely inspect the model's states and flexibly control its behavior. The output file format is also redesigned as platform-independent and fully-annotated binary files with intuitive data access interface. Furthermore, packages for the direct access to GIS database and uncertainty estimation on parallel computing resources are newly developed. These reconstruction efforts extend the functional capability of RHESSys as a versatile model able to assimilate and produce massive spatiotemporal data, which is a critical feature required for building the operational nowcasting and forecasting system.
Manned orbital systems concept study. Book 4: Programmatics for extended-duration missions
NASA Technical Reports Server (NTRS)
1975-01-01
The cost estimates, schedule data, and funding distributions generated in the Manned Orbital Systems Concepts (MOSC) study are presented. The overall objectives were to examine the requirements for, and to describe, a cost-effective concept for an orbital facility capable of supporting manned operations in earth orbit beyond the 7-to-30-day mission duration provided by the Shuttle/Spacelab system. The cost, schedule, and other programmatic data were developed to provide information useful for their long-range planning activities. The major portion of the data documented and discussed consists of project- and system-level schedule and funding information and also project-, system-, and subsystem-level cost summaries.
NASA Astrophysics Data System (ADS)
Quintana-Seguí, Pere; Míguez-Macho, Gonzalo; Llasat, María del Carmen
2015-04-01
Within the FP7 eartH2Observe project we are studying the ability of different LSMs to simulate the processes of drought on the Iberian Peninsula. In order to perform our simulations we need a good atmospheric forcing dataset that covers the whole area of study at the right resolution (5 km in hour case). Currently, in Spain, there are some high resolution datasets, but none of them have all the variables necessary to run a LSM. Thus, we decided to extend the SAFRAN meteorological analysis system to the whole Iberian Peninsula and the Balearic Islands. SAFRAN uses optimal interpolation to analyze the variables of interest using all available observed data (from AEMET's network) and a first guess (ERA-Interim). SAFRAN, which was developed by Météo France to force its LSMs (CROCUS for snow, ISBA and SURFEX for hydrological studies), was recently extended to the Ebro basin in a pilot study that covered only three years. In eartH2Observe we are extending it to cover the 1995-2007 period. This period is not long enough to study climate variability, but it already useful to a range of studies that need a decade long dataset. In the future, we plan to extend SAFRAN to a period that covers several decades. We present the SAFRAN analysis system, its main features and its performance in the study area. In addition, we also present a first comparison with alternative databases in the context of the eartH2Observe Spanish Case Study. In the future, we expect SAFRAN to be useful, not only to large scale hydrology projects, but also to a large range of projects simulating land surface processes for other purposes. SAFRAN will also be useful as reference dataset for downscaling climate simulations. Thus, we also discuss these applications.
Mollusc-Microbe Mutualisms Extend the Potential for Life in Hypersaline Systems
NASA Astrophysics Data System (ADS)
Hickman, Carole S.
2003-11-01
Metazoans in extreme environments have evolved mutualisms with microbes that extend the physical and chemical capabilities of both partners. Some of the best examples are bivalve molluscs in evaporite and hypersaline settings. Mollusc tissue is developmentally and evolutionarily amenable to housing vast numbers of symbiotic microbes. Documented benefits to the host are nutritional. Multiple postulated benefits to the microbes are related to optimizing metabolic performance at interfaces, where heterogeneity and steep gradients that cannot be negotiated by microbes can be spanned by larger metazoan hosts. A small cockle, Fragum erugatum, and its photosymbiotic microbes provide a remarkable example of a mutualistic partnership in the hypersaline reaches of Shark Bay, Western Australia. Lucinid bivalves and their endosymbiotic chemolithotrophic bacteria provide examples in which hosts span oxic/anoxic interfaces on behalf of their symbionts at sites of seafloor venting. Multiple lines of evidence underscore the antiquity of mutualisms and suggest that they may have played a significant role in life's first experiments above the prokaryotic grade of complexity. The study of metazoan-microbe mutualisms and their signatures in extreme environments in the geologic record will provide a significant augmentation to microbial models in paleobiology and astrobiology. There are strong potential links between mutualisms and the early history of life on Earth, the persistence of life in extreme environments at times of global crisis and mass extinction, and the possibilities for life elsewhere in the universe.
ECCD performance analysis of future KSTAR ECH systems for extended applications
NASA Astrophysics Data System (ADS)
Sahu, B. B.; Bae, Y. S.; Jeong, J. H.; Joung, M.; Kwak, J. G.; Han, W. S.; Rhee, I.
2014-10-01
The ability of the KSTAR 170 GHz electron cyclotron (EC) wave launcher to drive a localized current is analyzed by means of the TORAY-GA ray-tracing code looking at extended physics application of the EC current drive (CD) in the KSTAR. Computation reveals that the EC-driven CD performance ( J CD), as compared to the plasma's boot-strap current ( J BS), i.e., the ratio J CD/ J BS, for the normalized minor radius, ρ > 0.5, is not good for the current design of the 1-MW 170-GHz launcher. Calculations at a lower frequency of 105 GHz have shown improved values for the J CD. Depending upon the launcher port's availability, computations are carried out to find the pivot position for future proposed launchers by optimizing the figures of merit at respective locations. These computations show that Z = +30 cm gives the maximum figure of merit. Computations also show a possible synergy between the two launchers, one pivoted at Z = +30 cm and the other at Z = -25.2 cm. The main aim of this study is to provide guidance for the design of both launchers in order to optimize their performance according to the physics application.
Martínez-Fonseca, Nadhynee; Castañeda, Luis Ángel; Uranga, Agustín; Luviano-Juárez, Alberto; Chairez, Isaac
2016-05-01
This study addressed the problem of robust control of a biped robot based on disturbance estimation. Active disturbance rejection control was the paradigm used for controlling the biped robot by direct active estimation. A robust controller was developed to implement disturbance cancelation based on a linear extended state observer of high gain class. A robust high-gain scheme was proposed for developing a state estimator of the biped robot despite poor knowledge of the plant and the presence of uncertainties. The estimated states provided by the state estimator were used to implement a feedback controller that was effective in actively rejecting the perturbations as well as forcing the trajectory tracking error to within a small vicinity of the origin. The theoretical convergence of the tracking error was proven using the Lyapunov theory. The controller was implemented by numerical simulations that showed the convergence of the tracking error. A comparison with a high-order sliding-mode-observer-based controller confirmed the superior performance of the controller using the robust observer introduced in this study. Finally, the proposed controller was implemented on an actual biped robot using an embedded hardware-in-the-loop strategy. PMID:26928517
Nonthermal plasma system for extending shelf life of raw broiler breast fillets
Technology Transfer Automated Retrieval System (TEKTRAN)
A nonthermal dielectric barrier discharge (DBD) plasma system was developed and enhanced to treat broiler breast fillets (BBF) in order to improve the microbial quality of the meat. The system consisted of a high-voltage source and two parallel, round-aluminum electrodes separated by three semi-rig...
Extend Instruction outside the Classroom: Take Advantage of Your Learning Management System
ERIC Educational Resources Information Center
Jensen, Lauren A.
2010-01-01
Numerous institutions of higher education have implemented a learning management system (LMS) or are considering doing so. This web-based software package provides self-service and quick (often personalized) access to content in a dynamic environment. Learning management systems support administrative, reporting, and documentation activities. LMSs…
Adaptive decision systems with extended learning for deployment in partially exposed environments
NASA Astrophysics Data System (ADS)
Dasarathy, Belur V.
1995-05-01
The design and development of decision systems capable of adaptively learning in the operational environment is presented. Innovative adaptive learning concepts and methodologies are offered that are designed for enhancing the performance of decision systems, such as automatic target recognition systems, wherein robustness of performance is a significant issue. The fundamental concept underlying this design is that of learning in partially exposed environments, wherein, at the start, the system is not necessarily aware of all the pattern classes that may be encountered in the future phase of operations. The decision system is based on a variant to the widely popular nearest-neighbor concept. Several stages of sophistication of the system design are presented. The potential problem of increase in computational loads is addressed in detail by exploring the benefits of employing the recently proposed concept of minimal consistent set. The effectiveness of the system design is experimentally illustrated using two data sets, the now classical IRIS data and some real-world TV image data.
Bochenkov, Vladimir; Suetin, Nikolay; Shankar, Sadasivan
2014-09-07
A new method, the Extended Temperature-Accelerated Dynamics (XTAD), is introduced for modeling long-timescale evolution of large rare-event systems. The method is based on the Temperature-Accelerated Dynamics approach [M. Sørensen and A. Voter, J. Chem. Phys. 112, 9599 (2000)], but uses full-scale parallel molecular dynamics simulations to probe a potential energy surface of an entire system, combined with the adaptive on-the-fly system decomposition for analyzing the energetics of rare events. The method removes limitations on a feasible system size and enables to handle simultaneous diffusion events, including both large-scale concerted and local transitions. Due to the intrinsically parallel algorithm, XTAD not only allows studies of various diffusion mechanisms in solid state physics, but also opens the avenue for atomistic simulations of a range of technologically relevant processes in material science, such as thin film growth on nano- and microstructured surfaces.
Analysis of non-Kolmogorov weak turbulence effects on infrared imaging by atmospheric turbulence MTF
NASA Astrophysics Data System (ADS)
Xue, Bindang; Cao, Lei; Cui, Linyan; Bai, Xiangzhi; Cao, Xiaoguang; Zhou, Fugen
2013-07-01
The atmospheric turbulence modulation transfer functions (MTF) can be used to describe the degrading effects of atmospheric turbulence on an optical imaging system. In this study, new expressions of long exposure atmospheric turbulence MTF are derived with the generalized atmospheric spectral model for optical waves propagating through non-Kolmogorov weak turbulence with horizontal path. They consider the finite turbulence inner and outer scales, and have a general spectral power law value in the range of 3 to 4 instead of the standard power law value of 11/3. Numerical calculations are conducted to analyze the influence of non-Kolmogorov weak turbulence on the infrared imaging in term of atmospheric turbulence MTF, and results show that the non-Kolmogorov weak turbulence produces less effect on the far infrared imaging.
NASA Technical Reports Server (NTRS)
Shapiro, Bruce E.; Levchenko, Andre; Meyerowitz, Elliot M.; Wold, Barbara J.; Mjolsness, Eric D.
2003-01-01
Cellerator describes single and multi-cellular signal transduction networks (STN) with a compact, optionally palette-driven, arrow-based notation to represent biochemical reactions and transcriptional activation. Multi-compartment systems are represented as graphs with STNs embedded in each node. Interactions include mass-action, enzymatic, allosteric and connectionist models. Reactions are translated into differential equations and can be solved numerically to generate predictive time courses or output as systems of equations that can be read by other programs. Cellerator simulations are fully extensible and portable to any operating system that supports Mathematica, and can be indefinitely nested within larger data structures to produce highly scaleable models.
Analysis of a stability valve system for extending the dynamic range of a supersonic inlet
NASA Technical Reports Server (NTRS)
Webb, J. A., Jr.; Dustin, M. O.
1975-01-01
A stability valve system designed for a full-scale, flight, supersonic, mixed-compression inlet was modeled dynamically by using analog computer techniques. The system uses poppet valves mounted in the inlet cowl to bypass airflow and augments the inlet shock position control system by preventing unstarts caused by high-frequency perturbations. The model was used as a design aid to investigate the effects of varying both the physical configurations of the valve and the flight and wind tunnel conditions. Results of the analysis indicate that the stability valve will provide a bandpass operation of 1 hertz to 17 hertz.
Linear stability analysis of swirling turbulent flows with turbulence models
NASA Astrophysics Data System (ADS)
Gupta, Vikrant; Juniper, Matthew
2013-11-01
In this paper, we consider the growth of large scale coherent structures in turbulent flows by performing linear stability analysis around a mean flow. Turbulent flows are characterized by fine-scale stochastic perturbations. The momentum transfer caused by these perturbations affects the development of larger structures. Therefore, in a linear stability analysis, it is important to include the perturbations' influence. One way to do this is to include a turbulence model in the stability analysis. This is done in the literature by using eddy viscosity models (EVMs), which are first order turbulence models. We extend this approach by using second order turbulence models, in this case explicit algebraic Reynolds stress models (EARSMs). EARSMs are more versatile than EVMs, in that they can be applied to a wider range of flows, and could also be more accurate. We verify our EARSM-based analysis by applying it to a channel flow and then comparing the results with those from an EVM-based analysis. We then apply the EARSM-based stability analysis to swirling pipe flows and Taylor-Couette flows, which demonstrates the main benefit of EARSM-based analysis. This project is supported by EPSRC and Rolls-Royce through a Dorothy Hodgkin Research Fellowship.
2016-01-01
This report presents the design and evaluation of a innovative wall system. This highly insulated (high-R) light-frame wall system for use above grade in residential buildings is referred to as Extended Plate & Beam (EP&B). The EP&B design is the first of its kind to be featured in a new construction test house (NCTH) for the DOE Building America program. The EP&B wall design integrates standard building methods and common building products to construct a high-R wall that minimizes transition risks and costs to builders. The EP&B design combines optimized framing with integrated rigid foam sheathing to increase the wall system's R-value and reduce thermal bridging. The foam sheathing is installed between the wall studs and structural wood sheathing. The exterior wood sheathing is attached directly to a framing extension formed by extended top and bottom plates. The exterior wood sheathing can dry to the exterior and provides bracing, a clear drainage plane and flashing surface for window and door openings, and a nailing surface for siding attachment. With support of the DOE Building America program, Home Innovation Research Labs partnered with Lancaster County Career and Technology Center (LCCTC) to build a NCTH in Lancaster, PA to demonstrate the EP&B wall design in a cold climate (IECC climate zone 5A). The results of the study confirmed the benefits of the systems and the viability of its integration into the house construction process.
Extended-capacity high-speed-disk recording system for TREAT hodoscope
Rhodes, E.A.; Travis, D.; DeVolpi, A.; Burrows, D.; Ray, D.; Stanford, G.
1983-01-01
New requirements for time resolution, test duration, field of view, and recording redundancy in dynamic digital radiographic imaging of fuel motion in TREAT and TREAT-Upgrade (TU) in-pile experiments have been formulated. This has necessitated the design and fabrication of a new hodoscope high-speed data acquisition system. Recently an array of proportional counters was installed to operate in tandem with the Hornyak-button array. The full implementation of this new array, together with the increased field-of-view needed for future TU 37-pin experiments, required a separate recording system operting in parallel with that for the Hornyak buttons. The new recording system was required to have substantially higher capacity than the earlier recording system in use, in order to record sufficient data channels and samples with adequately small collection intervals, for some new types of experiments.
Thomas, John
2012-05-01
Systems Theoretic Process Analysis (STPA) is a powerful new hazard analysis method designed to go beyond traditional safety techniques - such as Fault Tree Analysis (FTA) - that overlook important causes of accidents like flawed requirements, dysfunctional component interactions, and software errors. While proving to be very effective on real systems, no formal structure has been defined for STPA and its application has been ad-hoc with no rigorous procedures or model-based design tools. This report defines a formal mathematical structure underlying STPA and describes a procedure for systematically performing an STPA analysis based on that structure. A method for using the results of the hazard analysis to generate formal safety-critical, model-based system and software requirements is also presented. Techniques to automate both the analysis and the requirements generation are introduced, as well as a method to detect conflicts between the safety and other functional model-based requirements during early development of the system.
Thermal Control System for a Small, Extended Duration Lunar Surface Science Platform
NASA Technical Reports Server (NTRS)
Bugby, D.; Farmer, J.; OConnor, B.; Wirzburger, M.; Abel, E.; Stouffer, C.
2010-01-01
The presentation slides include: Introduction: lunar mission definition, Problem: requirements/methodology, Concept: thermal switching options, Analysis: system evaluation, Plans: dual-radiator LHP (loop heat pipe) test bed, and Conclusions: from this study.
Portable inference engine: An extended CLIPS for real-time production systems
NASA Technical Reports Server (NTRS)
Le, Thach; Homeier, Peter
1988-01-01
The present C-Language Integrated Production System (CLIPS) architecture has not been optimized to deal with the constraints of real-time production systems. Matching in CLIPS is based on the Rete Net algorithm, whose assumption of working memory stability might fail to be satisfied in a system subject to real-time dataflow. Further, the CLIPS forward-chaining control mechanism with a predefined conflict resultion strategy may not effectively focus the system's attention on situation-dependent current priorties, or appropriately address different kinds of knowledge which might appear in a given application. Portable Inference Engine (PIE) is a production system architecture based on CLIPS which attempts to create a more general tool while addressing the problems of real-time expert systems. Features of the PIE design include a modular knowledge base, a modified Rete Net algorithm, a bi-directional control strategy, and multiple user-defined conflict resolution strategies. Problems associated with real-time applications are analyzed and an explanation is given for how the PIE architecture addresses these problems.
Damage-Mitigating Control of Space Propulsion Systems for High Performance and Extended Life
NASA Technical Reports Server (NTRS)
Ray, Asok; Wu, Min-Kuang
1994-01-01
A major goal in the control of complex mechanical system such as spacecraft rocket engine's advanced aircraft, and power plants is to achieve high performance with increased reliability, component durability, and maintainability. The current practice of decision and control systems synthesis focuses on improving performance and diagnostic capabilities under constraints that often do not adequately represent the materials degradation. In view of the high performance requirements of the system and availability of improved materials, the lack of appropriate knowledge about the properties of these materials will lead to either less than achievable performance due to overly conservative design, or over-straining of the structure leading to unexpected failures and drastic reduction of the service life. The key idea in this report is that a significant improvement in service life could be achieved by a small reduction in the system dynamic performance. The major task is to characterize the damage generation process, and then utilize this information in a mathematical form to synthesize a control law that would meet the system requirements and simultaneously satisfy the constraints that are imposed by the material and structural properties of the critical components. The concept of damage mitigation is introduced for control of mechanical systems to achieve high performance with a prolonged life span. A model of fatigue damage dynamics is formulated in the continuous-time setting, instead of a cycle-based representation, for direct application to control systems synthesis. An optimal control policy is then formulated via nonlinear programming under specified constraints of the damage rate and accumulated damage. The results of simulation experiments for the transient upthrust of a bipropellant rocket engine are presented to demonstrate efficacy of the damage-mitigating control concept.
Explosive turbulent magnetic reconnection.
Higashimori, K; Yokoi, N; Hoshino, M
2013-06-21
We report simulation results for turbulent magnetic reconnection obtained using a newly developed Reynolds-averaged magnetohydrodynamics model. We find that the initial Harris current sheet develops in three ways, depending on the strength of turbulence: laminar reconnection, turbulent reconnection, and turbulent diffusion. The turbulent reconnection explosively converts the magnetic field energy into both kinetic and thermal energy of plasmas, and generates open fast reconnection jets. This fast turbulent reconnection is achieved by the localization of turbulent diffusion. Additionally, localized structure forms through the interaction of the mean field and turbulence. PMID:23829741
NASA Astrophysics Data System (ADS)
Nistazakis, H. E.; Stassinakis, A. N.; Sheikh Muhammad, S.; Tombras, G. S.
2014-12-01
The optical wireless and in particular the radio-on-free-space-optical (RoFSO) communication systems are gaining popularity due to their high date rates, license free spectrum and adequate reliability at installation and operational costs which are much lower than comparable technologies. One significant disadvantage of these systems concerns the randomly time varying characteristics of the propagation path mainly caused by the atmospheric turbulence. In this work, we study the BER performance of a multi-hop RoFSO system which is using an orthogonal frequency division multiplexing (OFDM) scheme, with either quadrature amplitude modulation (QAM) or phase shift keying format (PSK), over atmospheric turbulence channels modeled with the gamma gamma or the negative exponential distribution. The individual RoFSO parts of the whole optical link are connected to each other by using regenerators relay nodes. The dominant impairments which are the most significant and have been taken into account are the atmospheric turbulence, the path losses, the nonlinear responsivity of the laser diode and the inter-modulation distortion effect. For this setup, we derive closed form mathematical expressions for the estimation of the BER performance for each individual OFDM RoFSO link and for the whole relayed optical communication system, as well. Finally, the corresponding numerical results, for common link's parameters, are presented.
Turbulent transport in the solar nebula
NASA Technical Reports Server (NTRS)
Thompson, Kevin W.
1989-01-01
It is likely that turbulence played a major role in the evolution of the solar nebula, which is the flattened disk of dust and gas out of which our solar system formed. Relevant turbulent processes include the transport of angular momentum, mass, and heat, which were critically important to the formation of the solar system. This research will break ground in the modeling of compressible turbulence and its effects on the evolution of the solar nebula. The computational techniques which were developed should be of interest to researchers studying other astrophysical disk systems (e.g., active galactic nuclei), as well as turbulence modelers outside the astrophysics community.
Field Effects of Buoyancy on Lean Premixed Turbulent Flames
NASA Technical Reports Server (NTRS)
Cheng, R. K.; Johnson, M. R.; Greenberg, P. S.; Wernet, M. P.
2003-01-01
The study of field effects of buoyancy on premixed turbulent flames is directed towards the advancement of turbulent combustion theory and the development of cleaner combustion technologies. Turbulent combustion is considered the most important unsolved problem in combustion science and laboratory studies of turbulence flame processes are vital to theoretical development. Although buoyancy is dominant in laboratory flames, most combustion models are not yet capable to consider buoyancy effects. This inconsistency has impeded the validation of theories and numerical simulations with experiments. Conversely, the understanding of buoyancy effects is far too limited to help develop buoyant flame models. Our research is also relevant to combustion technology because lean premixed combustion is a proven method to reduce the formation of oxides of nitrogen (NOx). In industrial lean premixed combustion systems, their operating conditions make them susceptible to buoyancy thus affecting heat distribution, emissions, stability, flashback and blowoff. But little knowledge is available to guide combustion engineers as to how to avoid or overcome these problems. Our hypothesis is that through its influence on the mean pressure field, buoyancy has direct and indirect effects on local flame/turbulence interactions. Although buoyancy acts on the hot products in the farfield the effect is also felt in the nearfield region upstream of the flame. These changes also influence the generation and dissipation of turbulent kinetic energy inside the flame brush and throughout the flowfield. Moreover, the plume of an open flame is unstable and the periodic fluctuations make additional contributions to flame front dynamics in the farfield. Therefore, processes such as flame wrinkling, flow acceleration due to heat release and flame- generated vorticity are all affected. Other global flame properties (e.g. flame stabilization limits and flame speed) may all be coupled to buoyancy. This
Turbulent equipartitions in two dimensional drift convection
Isichenko, M.B.; Yankov, V.V.
1995-07-25
Unlike the thermodynamic equipartition of energy in conservative systems, turbulent equipartitions (TEP) describe strongly non-equilibrium systems such as turbulent plasmas. In turbulent systems, energy is no longer a good invariant, but one can utilize the conservation of other quantities, such as adiabatic invariants, frozen-in magnetic flux, entropy, or combination thereof, in order to derive new, turbulent quasi-equilibria. These TEP equilibria assume various forms, but in general they sustain spatially inhomogeneous distributions of the usual thermodynamic quantities such as density or temperature. This mechanism explains the effects of particle and energy pinch in tokamaks. The analysis of the relaxed states caused by turbulent mixing is based on the existence of Lagrangian invariants (quantities constant along fluid-particle or other orbits). A turbulent equipartition corresponds to the spatially uniform distribution of relevant Lagrangian invariants. The existence of such turbulent equilibria is demonstrated in the simple model of two dimensional electrostatically turbulent plasma in an inhomogeneous magnetic field. The turbulence is prescribed, and the turbulent transport is assumed to be much stronger than the classical collisional transport. The simplicity of the model makes it possible to derive the equations describing the relaxation to the TEP state in several limits.
NASA Technical Reports Server (NTRS)
1987-01-01
The objectives consisted of three major tasks. The first was to establish the definition of Space Station and Orbital Maneuvering Vehicle (OMV) user requirements and interfaces and to evaluate system requirements of a water tanker to be used at the station. The second task is to conduct trade studies of system requirements, hardware/software, and operations to evaluate the effect of automatic operation at the station or remote from the station in consonance with the OMV. The last task is to evaluate automatic refueling concepts and to evaluate the impact to Orbital Spacecraft Consumable Resupply System (OSCRS) concept/design to use expendable launch vehicles (ELV) to place the tank into orbit. Progress in each area is discussed.
NASA Technical Reports Server (NTRS)
Bayard, David S. (Inventor)
1996-01-01
Periodic gain adjustment in plants of irreducible order, n, or for equalization of communications channels is effected in such a way that the plant (system) appears to be minimum phase by choosing a horizon time N greater then n of liftings in periodic input and output windows Pu and Py, respectively, where N is an integer chosen to define the extent (length) of each of the windows Pu and Py, and n is the order of an irreducible input/output plant. The plant may be an electrical, mechanical or chemical system, in which case output tracking (OT) is carried out for feedback control or a communication channel, in which case input tracking (IT) is carried out. Conditions for OT are distinct from IT in terms of zero annihilation, namely for OT and of IT, where the OT conditions are intended for gain adjustments in the control system, and IT conditions are intended for equalization for communication channels.
Extending PowerPack for Profiling and Analysis of High Performance Accelerator-Based Systems
Li, Bo; Chang, Hung-Ching; Song, Shuaiwen; Su, Chun-Yi; Meyer, Timmy; Mooring, John; Cameron, Kirk
2014-12-01
Accelerators offer a substantial increase in efficiency for high-performance systems offering speedups for computational applications that leverage hardware support for highly-parallel codes. However, the power use of some accelerators exceeds 200 watts at idle which means use at exascale comes at a significant increase in power at a time when we face a power ceiling of about 20 megawatts. Despite the growing domination of accelerator-based systems in the Top500 and Green500 lists of fastest and most efficient supercomputers, there are few detailed studies comparing the power and energy use of common accelerators. In this work, we conduct detailed experimental studies of the power usage and distribution of Xeon-Phi-based systems in comparison to the NVIDIA Tesla and at SandyBridge.
Pressure atomizer having multiple orifices and turbulent generation feature
VanBrocklin, Paul G.; Geiger, Gail E.; Moran, Donald James; Fournier, Stephane
2002-01-01
A pressure atomizer includes a silicon plate having a top surface and a bottom surface. A portion of the top surface defines a turbulent chamber. The turbulent chamber is peripherally bounded by the top surface of the plate. The turbulent chamber is recessed a predetermined depth relative to the top surface. The silicon plate further defines at least one flow orifice. Each flow orifice extends from the bottom surface of the silicon plate to intersect with and open into the turbulent chamber. Each flow orifice is in fluid communication with the turbulent chamber.
3D Extended Logging for Geothermal Resources: Field Trials with the Geo-Bilt System
Mallan, R; Wilt, M; Kirkendall, B; Kasameyer, P
2002-05-29
Geo-BILT (Geothermal Borehole Induction Logging Tool) is an extended induction logging tool designed for 3D resistivity imaging around a single borehole. The tool was developed for deployment in high temperature geothermal wells under a joint program funded by the California Energy Commission, Electromagnetic Instruments (EMI) and the U.S. Department of Energy. EM1 was responsible for tool design and manufacture, and numerical modeling efforts were being addressed at Lawrence Livermore Laboratory (LLNL) and other contractors. The field deployment was done by EM1 and LLNL. The tool operates at frequencies from 2 to 42 kHz, and its design features a series of three-component magnetic sensors offset at 2 and 5 meters from a three-component magnetic source. The combined package makes it possible to do 3D resistivity imaging, deep into the formation, from a single well. The manufacture and testing of the tool was completed in spring of 2001, and the initial deployment of Geo-BILT occurred in May 2001 at the Lost Hills oil field in southern California at leases operated by Chevron USA. This site was chosen for the initial field test because of the favorable geological conditions and the availability of a number of wells suitable for tool deployment. The second deployment occurred in April 2002 at the Dixie Valley geothermal field, operated by Caithness Power LLC, in central Nevada. This constituted the first test in a high temperature environment. The Chevron site features a fiberglass-cased observation well in the vicinity of a water injector. The injected water, which is used for pressure maintenance and for secondary sweep of the heavy oil formation, has a much lower resistivity than the oil bearing formation. This, in addition to the non-uniform flow of this water, creates a 3D resistivity structure, which is analogous to conditions produced from flowing fractures adjacent to geothermal boreholes. Therefore, it is an excellent site for testing the 3D capability of
Damage-mitigating control of space propulsion systems for high performance and extended life
NASA Technical Reports Server (NTRS)
Ray, Asok; Wu, Min-Kuang; Dai, Xiaowen; Carpino, Marc; Lorenzo, Carl F.
1993-01-01
Calculations are presented showing that a substantial improvement in service life of a reusable rocket engine can be achieved by an insignificant reduction in the system dynamic performance. The paper introduces the concept of damage mitigation and formulates a continuous-time model of fatigue damage dynamics. For control of complex mechanical systems, damage prediction and damage mitigation are carried out based on the available sensory and operational information such that the plant can be inexpensively maintained and safely and efficiently steered under diverse operating conditions. The results of simulation experiments are presented for transient operations of a reusable rocket engine.
New extended {pi}-electron donors. Tetrathiafulvalene systems with heterocyclic spacer groups
Hansen, T.K.; Jensen, F.; Becher, J.
1992-06-17
Nine new heterocyclic {pi}-electron donors 10a-c, 11a-c, and 12a-c based upon the well-known TTF (tetrathiafulvalene) system, but incorporating a pyrrole, thiophene, or furan ring between the 1,3-thiole rings, have been synthesized. The compounds show two single-electron reversible oxidation waves in cyclic voltammetry. Some TCNQ complexes and conductivity measurements are reported, indicating the new compounds to be good candidates for {open_quotes}organic metals{close_quotes}. The influence of the central conjugated system on redox properties is discussed using MNDO-PM3 calculations. 17 refs., 5 figs., 1 tab.
Extending the POSIX I/O interface: a parallel file system perspective.
Vilayannur, M.; Lang, S.; Ross, R.; Klundt, R.; Ward, L.; Mathematics and Computer Science; VMWare, Inc.; SNL
2008-12-11
The POSIX interface does not lend itself well to enabling good performance for high-end applications. Extensions are needed in the POSIX I/O interface so that high-concurrency HPC applications running on top of parallel file systems perform well. This paper presents the rationale, design, and evaluation of a reference implementation of a subset of the POSIX I/O interfaces on a widely used parallel file system (PVFS) on clusters. Experimental results on a set of micro-benchmarks confirm that the extensions to the POSIX interface greatly improve scalability and performance.
ULF turbulence in the Neptunian polar cusp
NASA Astrophysics Data System (ADS)
Farrell, W. M.; Lepping, R. P.; Smith, C. W.
1993-03-01
Results of a spectral analysis of the ULF wave turbulence in the Neptunian polar cusp are presented. The activity is characterized as broadbanded, extending up to a maximum frequency of about 0.5 Hz, and having maximum wave amplitudes as large as 6 percent of the dc magnetic field. Activity in the cusp region was particularly intense at its frontside and backside, associated with the magnetopause and cusp/magnetosphere boundaries, respectively. The turbulence, particularly that above f(ci), is tentatively identified as whistler mode. It is argued that such whistler mode turbulence should resonate with electrons having energies in the tens of kiloelectron volts. Observations indicate a very strong correlation of the ULF turbulence with the energetic electrons between 22 and 35 keV measured by Voyager's low-energy charged particle experiment. A vigorous interaction between the two is inferred. ULF wave turbulence in the cusp may represent a significant but not complete power source for the magnetosphere.
Elastic turbulence in curvilinear flows of polymer solutions
NASA Astrophysics Data System (ADS)
Groisman, Alexander; Steinberg, Victor
2004-03-01
Following our first report (A Groisman and V Steinberg 2000 Nature 405 53), we present an extended account of experimental observations of elasticity-induced turbulence in three different systems: a swirling flow between two plates, a Couette-Taylor (CT) flow between two cylinders, and a flow in a curvilinear channel (Dean flow). All three set-ups had a high ratio of the width of the region available for flow to the radius of curvature of the streamlines. The experiments were carried out with dilute solutions of high-molecular-weight polyacrylamide in concentrated sugar syrups. High polymer relaxation time and solution viscosity ensured prevalence of non-linear elastic effects over inertial non-linearity, and development of purely elastic instabilities at low Reynolds number (Re) in all three flows. Above the elastic instability threshold, flows in all three systems exhibit features of developed turbulence. They include: (i) randomly fluctuating fluid motion excited in a broad range of spatial and temporal scales and (ii) significant increase in the rates of momentum and mass transfer (compared with those expected for a steady flow with a smooth velocity profile). Phenomenology, driving mechanisms and parameter dependence of the elastic turbulence are compared with those of the conventional high-Re hydrodynamic turbulence in Newtonian fluids. Some similarities as well as multiple principal differences were found. In two out of three systems (swirling flow between two plates and flow in the curvilinear channel), power spectra of velocity fluctuations decayed rather quickly, following power laws with exponents of about -3.5. It suggests that, being random in time, the flow is rather smooth in space, in the sense that the main contribution to deformation and mixing (and, possibly, elastic energy) is coming from flow at the largest scale of the system. This situation, random in time and smooth in space, is analogous to flows at small scales (below the Kolmogorov
Extended cubic B-spline method for solving a linear system of second-order boundary value problems.
Heilat, Ahmed Salem; Hamid, Nur Nadiah Abd; Ismail, Ahmad Izani Md
2016-01-01
A method based on extended cubic B-spline is proposed to solve a linear system of second-order boundary value problems. In this method, two free parameters, [Formula: see text] and [Formula: see text], play an important role in producing accurate results. Optimization of these parameters are carried out and the truncation error is calculated. This method is tested on three examples. The examples suggest that this method produces comparable or more accurate results than cubic B-spline and some other methods. PMID:27547688
Aleksovski, Aleksandar; Luštrik, Matevž; Šibanc, Rok; Dreu, Rok
2015-07-30
Mini-tablets are gaining great attention as systems capable of being formulated into multiple unit systems providing a specific drug release pattern. Within the presented research a combined, multiple-unit system, based on different coated matrix mini-tablets, has been developed in order to achieve 24-h specific sigmoid extended release of the model drug paliperidone. The mini-tablets were based on different amounts of polyvinyl acetate/polyvinyl pyrolidone mixture as the matrix former, providing extended release, and two different types of pH-dependent, acrylic polymer coatings, providing delay in release onset, and thus achieving the required specific sigmoid release pattern imposed by the original drug on the market. The selected formulation proved to be consistent with pharmacopoeial requirements. It was also in vitro similar (f2) to the original drug and the theoretical linear release profile, as well as robust and reproducible regarding in vitro release in different fasted gastro-intestinal conditions. This is proof of concept that 24-h, specific, and almost linear release profile of drugs with high solubility can be achieved by employing technology of coated matrix mini-tablets. PMID:25845632
Intra-articular bioactivity of a p38 MAPK inhibitor and development of an extended-release system.
Pradal, Julie; Zuluaga, Maria-Fernanda; Maudens, Pierre; Waldburger, Jean-Marc; Seemayer, Christian Alexander; Doelker, Eric; Gabay, Cem; Jordan, Olivier; Allémann, Eric
2015-06-01
In the treatment of arthritic diseases, oral or systemic administration of anti-inflammatory substances, such as p38 MAPK inhibitors, is hampered by numerous side effects. To overcome them, formulations of rapid and extended drug delivery systems were studied in intra-articular administration. For the first time, VX-745, a highly selective p38 MAPK inhibitor, demonstrated in vivo bioactivity, similar to dexamethasone activity, following intra-articular administration in an antigen-induced arthritic (AIA) mouse model. The in vitro bioactivity of VX-745 was also shown on synoviocytes, reducing the IL-6 concentration. Process and formulation parameters (i.e., polymer concentration, aqueous/organic phase ratio, emulsification speed and process, and evaporation pressure) and particle characterisation (i.e., drug loading, size of particle, and surface aspect) were extensively examined to produce optimised formulations. Indeed, a burst release provides a rapid saturation of intracellular p38 MAPK to relieve patients from pain and inflammation. Then, drug diffusion would be sufficient to maintain an effective dose over 2-3 months. This study confirms the effectiveness of encapsulated p38 MAPK inhibitors in extended drug delivery systems and seems to be a promising strategy for intra-articular treatment. PMID:25836052
NASA Astrophysics Data System (ADS)
Graf, Urs; Buehler, Christof; Betz, Michael; Zuber, Herbert; Anliker, M.
1994-08-01
A new versatile system for the measurement of time-resolved fluorescence emission spectra of biomolecules is presented. Frequency doubling and tripling of a Ti:Sapphire laser allows excitation over a wide wavelength range. The influence of increasing the spectral resolution on the time resolution has been investigated. System performance can be optimized for best resolution in the spectral or time domain, respectively. System performance can be optimized for best resolution in the spectral or time domain, respectively. The currently achieved temporal resolution is 6 psec, and the best spectral resolution is 3 nm. Long fluorescence decays can be resolved with optimal time resolution by way of taking into account the flyback of the streak camera. With the system described, the core complex ((alpha) (beta) )3APCLC8.9 of the phycobilisome from the photosynthetic cyanobacteria Mastigocladus laminosus has been analyzed. Lifetime analysis clearly demonstrated the influence of the linker polypeptide on the phycobiliprotein complex and the identity of native and reconstituted complex.
NASA Astrophysics Data System (ADS)
Tannenbaum, Emmanuel; Shakhnovich, Eugene I.
2005-12-01
Quasispecies theory has emerged as an important tool for modeling the evolutionary dynamics of biological systems. We review recent advances in the field, with an emphasis on the quasispecies dynamics of semiconservatively replicating genomes. Applications to cancer and adult stem cell growth are discussed. Additional topics, such as genetic repair and many-gene genomes, are covered as well.
A quantum-mechanics molecular-mechanics scheme for extended systems
NASA Astrophysics Data System (ADS)
Hunt, Diego; Sanchez, Veronica M.; Scherlis, Damián A.
2016-08-01
We introduce and discuss a hybrid quantum-mechanics molecular-mechanics (QM-MM) approach for Car–Parrinello DFT simulations with pseudopotentials and planewaves basis, designed for the treatment of periodic systems. In this implementation the MM atoms are considered as additional QM ions having fractional charges of either sign, which provides conceptual and computational simplicity by exploiting the machinery already existing in planewave codes to deal with electrostatics in periodic boundary conditions. With this strategy, both the QM and MM regions are contained in the same supercell, which determines the periodicity for the whole system. Thus, while this method is not meant to compete with non-periodic QM-MM schemes able to handle extremely large but finite MM regions, it is shown that for periodic systems of a few hundred atoms, our approach provides substantial savings in computational times by treating classically a fraction of the particles. The performance and accuracy of the method is assessed through the study of energetic, structural, and dynamical aspects of the water dimer and of the aqueous bulk phase. Finally, the QM-MM scheme is applied to the computation of the vibrational spectra of water layers adsorbed at the TiO2 anatase (1 0 1) solid–liquid interface. This investigation suggests that the inclusion of a second monolayer of H2O molecules is sufficient to induce on the first adsorbed layer, a vibrational dynamics similar to that taking place in the presence of an aqueous environment. The present QM-MM scheme appears as a very interesting tool to efficiently perform molecular dynamics simulations of complex condensed matter systems, from solutions to nanoconfined fluids to different kind of interfaces.
A quantum-mechanics molecular-mechanics scheme for extended systems.
Hunt, Diego; Sanchez, Veronica M; Scherlis, Damián A
2016-08-24
We introduce and discuss a hybrid quantum-mechanics molecular-mechanics (QM-MM) approach for Car-Parrinello DFT simulations with pseudopotentials and planewaves basis, designed for the treatment of periodic systems. In this implementation the MM atoms are considered as additional QM ions having fractional charges of either sign, which provides conceptual and computational simplicity by exploiting the machinery already existing in planewave codes to deal with electrostatics in periodic boundary conditions. With this strategy, both the QM and MM regions are contained in the same supercell, which determines the periodicity for the whole system. Thus, while this method is not meant to compete with non-periodic QM-MM schemes able to handle extremely large but finite MM regions, it is shown that for periodic systems of a few hundred atoms, our approach provides substantial savings in computational times by treating classically a fraction of the particles. The performance and accuracy of the method is assessed through the study of energetic, structural, and dynamical aspects of the water dimer and of the aqueous bulk phase. Finally, the QM-MM scheme is applied to the computation of the vibrational spectra of water layers adsorbed at the TiO2 anatase (1 0 1) solid-liquid interface. This investigation suggests that the inclusion of a second monolayer of H2O molecules is sufficient to induce on the first adsorbed layer, a vibrational dynamics similar to that taking place in the presence of an aqueous environment. The present QM-MM scheme appears as a very interesting tool to efficiently perform molecular dynamics simulations of complex condensed matter systems, from solutions to nanoconfined fluids to different kind of interfaces. PMID:27352028
NASA Technical Reports Server (NTRS)
Bayard, David S. (Inventor)
1994-01-01
Periodic gain adjustment in plants of irreducible order, n, or for equalization of communications channels is effected in such a way that the plant (system) appears to be minimum phase by choosing a horizon time N is greater than n of liftings in periodic input and output windows rho sub u and rho sub y, respectively, where N is an integer chosen to define the extent (length) of each of the windows rho sub u and rho sub y, and n is the order of an irreducible input/output plant. The plant may be an electrical, mechanical, or chemical system, in which case output tracking (OT) is carried out for feedback control or a communication channel, in which case input tracking (IT) is performed. Conditions for OT are distinct from IT in terms of zero annihilation, namely H(sub s)H(sub s)(sup +) = I for OT and H(sub s)H(sub s)(sup +) = I of IT, where the OT conditions are intended for gain adjustments in the control system, and IT conditions are intended for equalization for communication channels.
Impact of resonant magnetic perturbations on nonlinearly driven modes in drift-wave turbulence
Leconte, M.; Diamond, P. H.
2012-05-15
In this work, we study the effects of resonant magnetic perturbations (RMPs) on turbulence, flows, and confinement in the framework of resistive drift wave turbulence. We extend the Hasegawa-Wakatani model to include RMP fields. The effect of the RMPs is to induce a linear coupling between the zonal electric field and the zonal density gradient, which drives the system to a state of electron radial force balance for large ({delta}B{sub r}/B{sub 0}). Both the vorticity flux (Reynolds stress) and particle flux are modulated. We derive an extended predator prey model which couples zonal potential and density dynamics to the evolution of turbulence intensity. This model has both turbulence drive and RMP amplitude as control parameters and predicts a novel type of transport bifurcation in the presence of RMPs. We find states that are similar to the ZF-dominated state of the standard predator-prey model, but for which the power threshold is now a function of the RMP strength. For small RMP amplitude, the energy of zonal flows decreases and the turbulence energy increases with ({delta}B{sub r}/B{sub 0}), corresponding to a damping of zonal flows.
Multi-level segment analysis: definition and applications in turbulence
NASA Astrophysics Data System (ADS)
Wang, Lipo
2015-11-01
The interaction of different scales is among the most interesting and challenging features in turbulence research. Existing approaches used for scaling analysis such as structure-function and Fourier spectrum method have their respective limitations, for instance scale mixing, i.e. the so-called infrared and ultraviolet effects. For a given function, by specifying different window sizes, the local extremal point set will be different. Such window size dependent feature indicates multi-scale statistics. A new method, multi-level segment analysis (MSA) based on the local extrema statistics, has been developed. The part of the function between two adjacent extremal points is defined as a segment, which is characterized by the functional difference and scale difference. The structure function can be differently derived from these characteristic parameters. Data test results show that MSA can successfully reveal different scaling regimes in turbulence systems such as Lagrangian and two-dimensional turbulence, which have been remaining controversial in turbulence research. In principle MSA can generally be extended for various analyses.
Turbulent energy generated by accelerations and shocks
Mikaelian, K.O.
1986-10-08
The turbulent energy generated at the interface between two fluids undergoing a constant acceleration or a shock is calculated. Assuming linear density profiles in the mixed region we find E/sub turbulent//E/sub directed/ = 2.3A/sup 2/% (constant acceleration) and 9.3A/sup 2/% (shock), where A is the Atwood number. Diffusion models predict somewhat less turbulent energy and a density profile with a tail extending into the lower density fluid. Eddy sizes are approximately 27% (constant acceleration) and 17% (shock) of the mixing depth into the heavier fluid. 6 refs., 3 figs.
Honoré, Paul; Granjeaud, Samuel; Tagett, Rebecca; Deraco, Stéphane; Beaudoing, Emmanuel; Rougemont, Jacques; Debono, Stéphane; Hingamp, Pascal
2006-01-01
Background High throughput gene expression profiling (GEP) is becoming a routine technique in life science laboratories. With experimental designs that repeatedly span thousands of genes and hundreds of samples, relying on a dedicated database infrastructure is no longer an option. GEP technology is a fast moving target, with new approaches constantly broadening the field diversity. This technology heterogeneity, compounded by the informatics complexity of GEP databases, means that software developments have so far focused on mainstream techniques, leaving less typical yet established techniques such as Nylon microarrays at best partially supported. Results MAF (MicroArray Facility) is the laboratory database system we have developed for managing the design, production and hybridization of spotted microarrays. Although it can support the widely used glass microarrays and oligo-chips, MAF was designed with the specific idiosyncrasies of Nylon based microarrays in mind. Notably single channel radioactive probes, microarray stripping and reuse, vector control hybridizations and spike-in controls are all natively supported by the software suite. MicroArray Facility is MIAME supportive and dynamically provides feedback on missing annotations to help users estimate effective MIAME compliance. Genomic data such as clone identifiers and gene symbols are also directly annotated by MAF software using standard public resources. The MAGE-ML data format is implemented for full data export. Journalized database operations (audit tracking), data anonymization, material traceability and user/project level confidentiality policies are also managed by MAF. Conclusion MicroArray Facility is a complete data management system for microarray producers and end-users. Particular care has been devoted to adequately model Nylon based microarrays. The MAF system, developed and implemented in both private and academic environments, has proved a robust solution for shared facilities and
An extended real-time flood impact forecasting system for the Chapare watershed in Bolivia
NASA Astrophysics Data System (ADS)
Rossi, Lauro; Gabellani, Simone; Masoero, Alessandro; Dolia, Daniele; Rudari, Roberto
2016-04-01
All over the world a lot of cities are located in flood-prone areas and million of people are exposed to inundation risk. To cope with that the social safety demands efficient civil protection structures able to reduce flood risk by issuing warnings. This task requires civil protection organisms to adopt systems able to support their activities in predicting floods and rainfall impacts. For this reason flood early warning systems, based on rainfall observations and predictions, has become very useful because they are able to provide in advance a quantitative evaluation of possible effects in term of discharge and peak flow. Traditionally those forecasting systems use hydrologic models coupled with meteorological models to forecast discharge in relevant river sections and are called hydro-meteorological chains. In order to have a better representation of the flood dynamics, these hydro-meteorological chains can be expanded to include bi-dimensional hydraulic models where the level exposure is high or flow singularities (e.g. junctions, deltas, etc.) require more accurate investigation. That information allows the generation of real-time inundation scenarios that can be used by civil protection and authorities to estimate impact on population and take counter-measures. The new real-time flood impact forecasting chain consists of a suite of hydrometeorological tools that combines meteorological models, a disaggregation tool and a fully distributed hydrological model and a bidimensional hydraulic model that produces inundation scenarios in the most exposed river segments of the flood plain and a scenario tool that allows the assessment of assets involved. The complete modelling chain has been implemented in the Chapare watershed in Bolivia and it is managed by the Dewetra platform, which since 2013 is used by the Civil Defense and National Meteorological service as the main national Early Warning supporting tool.
Lilly, M.P.; Wootters, A.H.; Hallock, R.B.
1996-11-01
Capacitive studies of hysteretic capillary condensation of superfluid {sup 4}He in Nuclepore have shown that the initial draining of the pores occurs over a small range of the chemical potential with avalanches present as groups of pores drain. In the work reported here, the avalanches in this system are shown to be nonlocal events which involve pores distributed at low density across the entire sample. The nonlocal avalanche behavior is shown to be enabled by the presence of a superfluid film connection among the pores. {copyright} {ital 1996 The American Physical Society.}
NASA Astrophysics Data System (ADS)
Bi, Siwei; Liu, Chengbu; Hu, Haiquan; Zhang, Changqiao
2001-12-01
The magnetic coupling interaction for Cu(II) binuclear systems with bridging groups C2O4 2- , C2O2( NH) 2 2- ( cis), C2O2( NH) 2 2- ( trans) and C2S2( NH) 2 2- ( trans) was studied by the broken symmetry (BS) approach within the framework of the density functional theory (DFT). The influence of different coordination atoms and geometry on magnetic coupling interaction was theoretically analyzed. Both of the calculated and experimental results were compared. The variation trends of coupling interaction calculated are in agreement with experimental ones.
Model predictive torque control with an extended prediction horizon for electrical drive systems
NASA Astrophysics Data System (ADS)
Wang, Fengxiang; Zhang, Zhenbin; Kennel, Ralph; Rodríguez, José
2015-07-01
This paper presents a model predictive torque control method for electrical drive systems. A two-step prediction horizon is achieved by considering the reduction of the torque ripples. The electromagnetic torque and the stator flux error between predicted values and the references, and an over-current protection are considered in the cost function design. The best voltage vector is selected by minimising the value of the cost function, which aims to achieve a low torque ripple in two intervals. The study is carried out experimentally. The results show that the proposed method achieves good performance in both steady and transient states.
DONAR - A computer processing system to extend ultrasonic pulse-echo testing.
NASA Technical Reports Server (NTRS)
Lees, S.; Gerhard, F. B.; Barber, F. E.; Cheney, S. P.
1973-01-01
A dedicated general purpose digital computer has been built on the principle of a sampled-data system to run an ultrasonic subsystem under programmed control. A most significant application is the ability to extract a signal from an interfering background. As illustrated in the paper, a 1 mm diameter transducer was used to measure the diameter of a 2.5 mm OD plastics tube with 0.4 mm wall thickness. Echoes from all four surfaces were displayed and the measurements indicated an uncertainty of less than 0.1 mm.
Kawano, Yoshihiro; Higgins, Christopher; Yamamoto, Yasuhito; Nyhus, Julie; Bernard, Amy; Dong, Hong-Wei; Karten, Harvey J; Schilling, Tobias
2013-01-01
We present a new method for whole slide darkfield imaging. Whole Slide Imaging (WSI), also sometimes called virtual slide or virtual microscopy technology, produces images that simultaneously provide high resolution and a wide field of observation that can encompass the entire section, extending far beyond any single field of view. For example, a brain slice can be imaged so that both overall morphology and individual neuronal detail can be seen. We extended the capabilities of traditional whole slide systems and developed a prototype system for darkfield internal reflection illumination (DIRI). Our darkfield system uses an ultra-thin light-emitting diode (LED) light source to illuminate slide specimens from the edge of the slide. We used a new type of side illumination, a variation on the internal reflection method, to illuminate the specimen and create a darkfield image. This system has four main advantages over traditional darkfield: (1) no oil condenser is required for high resolution imaging (2) there is less scatter from dust and dirt on the slide specimen (3) there is less halo, providing a more natural darkfield contrast image, and (4) the motorized system produces darkfield, brightfield and fluorescence images. The WSI method sometimes allows us to image using fewer stains. For instance, diaminobenzidine (DAB) and fluorescent staining are helpful tools for observing protein localization and volume in tissues. However, these methods usually require counter-staining in order to visualize tissue structure, limiting the accuracy of localization of labeled cells within the complex multiple regions of typical neurohistological preparations. Darkfield imaging works on the basis of light scattering from refractive index mismatches in the sample. It is a label-free method of producing contrast in a sample. We propose that adapting darkfield imaging to WSI is very useful, particularly when researchers require additional structural information without the use of
Melas, Christos D; Zampetakis, Leonidas A; Dimopoulou, Anastasia; Moustakis, Vassilis
2011-08-01
Recent empirical research has utilized the Technology Acceptance Model (TAM) to advance the understanding of doctors' and nurses' technology acceptance in the workplace. However, the majority of the reported studies are either qualitative in nature or use small convenience samples of medical staff. Additionally, in very few studies moderators are either used or assessed despite their importance in TAM based research. The present study focuses on the application of TAM in order to explain the intention to use clinical information systems, in a random sample of 604 medical staff (534 physicians) working in 14 hospitals in Greece. We introduce physicians' specialty as a moderator in TAM and test medical staff's information and communication technology (ICT) knowledge and ICT feature demands, as external variables. The results show that TAM predicts a substantial proportion of the intention to use clinical information systems. Findings make a contribution to the literature by replicating, explaining and advancing the TAM, whereas theory is benefited by the addition of external variables and medical specialty as a moderator. Recommendations for further research are discussed. PMID:21292029
Exciton Localization in Extended π-Electron Systems: Comparison of Linear and Cyclic Structures.
Thiessen, Alexander; Würsch, Dominik; Jester, Stefan-S; Aggarwal, A Vikas; Idelson, Alissa; Bange, Sebastian; Vogelsang, Jan; Höger, Sigurd; Lupton, John M
2015-07-30
We employ five π-conjugated model materials of different molecular shape-oligomers and cyclic structures-to investigate the extent of exciton self-trapping and torsional motion of the molecular framework following optical excitation. Our studies combine steady state and transient fluorescence spectroscopy in the ensemble with measurements of polarization anisotropy on single molecules, supported by Monte Carlo simulations. The dimer exhibits a significant spectral red shift within ∼100 ps after photoexcitation which is attributed to torsional relaxation. This relaxation mechanism is inhibited in the structurally rigid macrocyclic analogue. However, both systems show a high degree of exciton localization but with very different consequences: while, in the macrocycle, the exciton localizes randomly on different parts of the ring, scrambling polarization memory, in the dimer, localization leads to a deterministic exciton position with luminescence characteristics of a dipole. Monte Carlo simulations allow us to quantify the structural difference between the emitting and absorbing units of the π-conjugated system in terms of disorder parameters. PMID:26035080
Extending Birthday Paradox Theory to Estimate the Number of Tags in RFID Systems
Shakiba, Masoud; Singh, Mandeep Jit; Sundararajan, Elankovan; Zavvari, Azam; Islam, Mohammad Tariqul
2014-01-01
The main objective of Radio Frequency Identification systems is to provide fast identification for tagged objects. However, there is always a chance of collision, when tags transmit their data to the reader simultaneously. Collision is a time-consuming event that reduces the performance of RFID systems. Consequently, several anti-collision algorithms have been proposed in the literature. Dynamic Framed Slotted ALOHA (DFSA) is one of the most popular of these algorithms. DFSA dynamically modifies the frame size based on the number of tags. Since the real number of tags is unknown, it needs to be estimated. Therefore, an accurate tag estimation method has an important role in increasing the efficiency and overall performance of the tag identification process. In this paper, we propose a novel estimation technique for DFSA anti-collision algorithms that applies birthday paradox theory to estimate the number of tags accurately. The analytical discussion and simulation results prove that the proposed method increases the accuracy of tag estimation and, consequently, outperforms previous schemes. PMID:24752285
Extending birthday paradox theory to estimate the number of tags in RFID systems.
Shakiba, Masoud; Singh, Mandeep Jit; Sundararajan, Elankovan; Zavvari, Azam; Islam, Mohammad Tariqul
2014-01-01
The main objective of Radio Frequency Identification systems is to provide fast identification for tagged objects. However, there is always a chance of collision, when tags transmit their data to the reader simultaneously. Collision is a time-consuming event that reduces the performance of RFID systems. Consequently, several anti-collision algorithms have been proposed in the literature. Dynamic Framed Slotted ALOHA (DFSA) is one of the most popular of these algorithms. DFSA dynamically modifies the frame size based on the number of tags. Since the real number of tags is unknown, it needs to be estimated. Therefore, an accurate tag estimation method has an important role in increasing the efficiency and overall performance of the tag identification process. In this paper, we propose a novel estimation technique for DFSA anti-collision algorithms that applies birthday paradox theory to estimate the number of tags accurately. The analytical discussion and simulation results prove that the proposed method increases the accuracy of tag estimation and, consequently, outperforms previous schemes. PMID:24752285
Assessment of dispersion-corrected density functional approaches for extended systems
NASA Astrophysics Data System (ADS)
Al-Saidi, Wissam; Voora, Vamsee; Jordan, Ken
2011-03-01
Standard density functional (DFT) methods are known to fail in describing the long range van der Waals interactions, and currently, there is a great interest in incorporating dispersion corrections in density functionals. Recently, Tkatchenko and Scheffler introduced a new scheme where dispersion corrections are included by a summation of damped interatomic C6 / R6 terms. However, contrary to the DFT-D2 approach of Grimme, the C6 coefficients depend on the electron density through a Hirshfeld atom-in-a-molecule decomposition scheme. We have implemented the vdW-TS approach in VASP and applied it to the study of a series of prototype dispersion-dominated systems including layered materials, noble-gas solids and molecular crystals. Full optimization of all degrees of freedom is possible in our implementation because dispersion corrections are computed for the forces acting on the atoms, and also the stresses on the unitcell. Our results show that the vdW-TS method yield good structure, bulk moduli, and cohesive energies of weakly bonded systems in much better agreement with experiment than those obtained with standard DFT approaches.
NASA Astrophysics Data System (ADS)
Jiang, Shixiao W.; Lu, Haihao; Zhou, Douglas; Cai, David
2016-08-01
Characterizing dispersive wave turbulence in the long time dynamics is central to understanding of many natural phenomena, e.g., in atmosphere ocean dynamics, nonlinear optics, and plasma physics. Using the β-Fermi–Pasta–Ulam nonlinear system as a prototypical example, we show that in thermal equilibrium and non-equilibrium steady state the turbulent state even in the strongly nonlinear regime possesses an effective linear stochastic structure in renormalized normal variables. In this framework, we can well characterize the spatiotemporal dynamics, which are dominated by long-wavelength renormalized waves. We further demonstrate that the energy flux is nearly saturated by the long-wavelength renormalized waves in non-equilibrium steady state. The scenario of such effective linear stochastic dynamics can be extended to study turbulent states in other nonlinear wave systems.
Berbert, Juliana Militão; Martinez, Alexandre Souto
2010-06-01
Consider N sites randomly and uniformly distributed in a d-dimensional hypercube. A walker explores this disordered medium going to the nearest site, which has not been visited in the last μ (memory) steps. The walker trajectory is composed of a transient part and a periodic part (cycle). For one-dimensional systems, travelers can or cannot explore all available space, giving rise to a crossover between localized and extended regimes at the critical memory μ1=log2 N. The deterministic rule can be softened to consider more realistic situations with the inclusion of a stochastic parameter T (temperature). In this case, the walker movement is driven by a probability density function parameterized by T and a cost function. The cost function increases as the distance between two sites and favors hops to closer sites. As the temperature increases, the walker can escape from cycles that are reminiscent of the deterministic nature and extend the exploration. Here, we report an analytical model and numerical studies of the influence of the temperature and the critical memory in the exploration of one-dimensional disordered systems. PMID:20866398
Turbulent Fluxes of Suspended Sediment from Coupled Acoustic Doppler Current Profilers
NASA Astrophysics Data System (ADS)
Hoitink, T.; Sassi, M.; Vermeulen, B.
2014-12-01
Turbulent diffusion is a cornerstone in geophysical fluid mechanics, controlling the exchange of momentum, heat and mass in surface flows occurring in the atmosphere, in rivers and in the ocean. In fluvial and coastal systems, modeling turbulent diffusion of momentum and suspended sediment requires knowledge about turbulent diffusivities, which is generally derived from parameterizations based on laboratory experiments. Field determinations of momentum and sediment diffusivities are cumbersome, requiring an instrumental array to simultaneously sample turbulence and mean flow quantities in time and in space. Recently, a new technique to analyze geophysical surface flow turbulence was introduced, appropriate for large scale systems, based on coupling of acoustic Doppler current profilers (ADCPs). Here, we extend this approach to obtain collocated profiles of both the Reynolds stress tensor and eddy covariance fluxes, to derive vertical profiles of turbulent momentum and sediment diffusivity in a tidal river. Shear and normal stresses are obtained by combining the variances in radial velocities measured by the ADCP beams. The covariances between radial velocities and calibrated acoustic backscatter allow to determine the three Cartesian components of the turbulent flux of suspended sediment. The main advantage of this new approach is that flow velocity and sediment concentration measurements are exactly collocated, and that it allows to profile over longer ranges, in comparison to existing techniques. Results show that vertical profiles of the inverse turbulent Prandtl-Schmidt number is coherent with corresponding profiles of the sediment diffusivity, rather than with profiles of the eddy viscosity. This implies modelling suspended sediment dynamics requires knowledge about the sediment diffusivity, as the Prandtl-Schmidt number cannot be estimated from the eddy viscosity alone.
NASA Astrophysics Data System (ADS)
Cui, Linyan; Xue, Bindang; Zhou, Fugen
2014-07-01
Infrared optical wave's propagation in marine environment is particularly challenging, not only for scattering and absorption due to high humidity, but also for a different behavior of atmospheric turbulence with respect to terrestrial propagation. In this paper, the marine atmospheric turbulence modulation transfer functions (MTF), which describes the degrading effects of marine atmospheric turbulence on an optical imaging system, is investigated in detail both analytically and numerically. New analytic expressions of the MTF are derived for plane and spherical waves under marine atmospheric turbulence, and they consider physically the influences of finite turbulence inner and outer scales. The final results indicate that, the marine atmospheric turbulence brings more degrading effects on the imaging system than the terrestrial atmospheric turbulence.
Moist turbulent Rayleigh-Bénard convection with Neumann and Dirichlet boundary conditions
NASA Astrophysics Data System (ADS)
Weidauer, Thomas; Schumacher, Jörg
2012-07-01
Turbulent Rayleigh-Bénard convection with phase changes in an extended layer between two parallel impermeable planes is studied by means of three-dimensional direct numerical simulations for Rayleigh numbers between 104 and 1.5 × 107 and for Prandtl number Pr = 0.7. Two different sets of boundary conditions of temperature and total water content are compared: imposed constant amplitudes which translate into Dirichlet boundary conditions for the scalar field fluctuations about the quiescent diffusive equilibrium and constant imposed flux boundary conditions that result in Neumann boundary conditions. Moist turbulent convection is in the conditionally unstable regime throughout this study for which unsaturated air parcels are stably and saturated air parcels unstably stratified. A direct comparison of both sets of boundary conditions with the same parameters requires to start the turbulence simulations out of differently saturated equilibrium states. Similar to dry Rayleigh-Bénard convection the differences in the turbulent velocity fluctuations, the cloud cover, and the convective buoyancy flux decrease across the layer with increasing Rayleigh number. At the highest Rayleigh numbers the system is found in a two-layer regime, a dry cloudless and stably stratified layer with low turbulence level below a fully saturated and cloudy turbulent one which equals a classical Rayleigh-Bénard convection layer. Both are separated by a strong inversion that gets increasingly narrower for growing Rayleigh number.
Sensitivity analysis of complex coupled systems extended to second and higher order derivatives
NASA Technical Reports Server (NTRS)
Sobieszczanski-Sobieski, Jaroslaw
1989-01-01
In design of engineering systems, the what if questions often arise such as: what will be the change of the aircraft payload, if the wing aspect ratio is incremented by 10 percent. Answers to such questions are commonly sought by incrementing the pertinent variable, and reevaluating the major disciplinary analyses involved. These analyses are contributed by engineering disciplines that are, usually, coupled, as are the aerodynamics, structures, and performance in the context of the question above. The what if questions can be answered precisely by computation of the derivatives. A method for calculation of the first derivatives has been developed previously. An algorithm is presented for calculation of the second and higher order derivatives.
Survey of materials for hydrazine propulsion systems in multicycle extended life applications
NASA Technical Reports Server (NTRS)
Coulbert, C. D.; Yankura, G.
1972-01-01
An assessment is presented of materials compatibility data for hydrazine monopropellant propulsion systems applicable to the Space Shuttle vehicle missions. Materials were evaluated for application over a 10-yr/100-mission operational lifetime with minimum refurbishment. A general materials compatibility rating for a broad range of materials and several propellants based primarily on static liquid propellant immersion testing and an in-depth evaluation of hydrazine decomposition as a function of purity, temperature, material, surface conditions, etc., are presented. The most promising polymeric material candidates for propellant diaphragms and seals appear to have little effect on increasing hydrazine decomposition rates, but the materials themselves do undergo changes in physical properties which can affect their 10-yr performance in multicycle applications. The available data on these physical properties of elastomeric materials as affected by exposure to hydrazine or related environments are presented.
Statistical turbulence theory and turbulence phenomenology
NASA Technical Reports Server (NTRS)
Herring, J. R.
1973-01-01
The application of deductive turbulence theory for validity determination of turbulence phenomenology at the level of second-order, single-point moments is considered. Particular emphasis is placed on the phenomenological formula relating the dissipation to the turbulence energy and the Rotta-type formula for the return to isotropy. Methods which deal directly with most or all the scales of motion explicitly are reviewed briefly. The statistical theory of turbulence is presented as an expansion about randomness. Two concepts are involved: (1) a modeling of the turbulence as nearly multipoint Gaussian, and (2) a simultaneous introduction of a generalized eddy viscosity operator.
Bauer, Roger E.; Figley, Reed R.; Innes, A. G.
2013-11-11
A history of the evolution and the design development of Extended Reach Sluicer System (ERSS) is presented. Several challenges are described that had to be overcome to create a machine that went beyond the capabilities of prior generation sluicers to mobilize waste in Single Shell Tanks for pumping into Double Shell Tank receiver tanks. Off-the-shelf technology and traditional hydraulic fluid power systems were combined with the custom-engineered components to create the additional functionality of the ERSS, while still enabling it to fit within very tight entry envelope into the SST. Problems and challenges inevitably were encountered and overcome in ways that enhance the state of the art of fluid power applications in such constrained environments. Future enhancements to the ERSS design are explored for retrieval of tanks with different dimensions and internal obstacles.
Simulation of atmospheric turbulence layers with phase screens by JAVA
NASA Astrophysics Data System (ADS)
Zhang, Xiaofang; Chen, Wenqin; Yu, Xin; Yan, Jixiang
2008-03-01
In multiconjugate Adaptive Optics (MCAO), the phase screens are used to simulate atmospheric turbulence layers to study the optimal turbulence delamination and the determination of layer boundary position. In this paper, the method of power spectrum inversion and sub-harmonic compensation were used to simulate atmospheric turbulence layers and results can be shown by grey map. The simulation results showed that, with the increase of turbulence layers, the RMS of adaptive system decreased, but the amplitude diminished. So the atmospheric turbulence can be split into 2-3 layers and be modeled by phase screens. Otherwise, a small simulation atmospheric turbulence delamination system was realized by JAVA.
Haihua Zhao; Ling Zou; Hongbin Zhang; David Andrs; Richard Martineau
2014-04-01
The reactor core isolation cooling (RCIC) system in a boiling water reactor (BWR) provides makeup water to the reactor vessel for core cooling when the main steam lines are isolated and the normal supply of water to the reactor vessel is lost. It was one of the very few safety systems still available during the Fukushima Daiichi accidents after the tsunamis hit the plants and the system successfully delayed the core meltdown for a few days for unit 2 & 3. Therefore, detailed models for RCIC system components are indispensable to understand extended station black-out accidents (SBO) for BWRs. As part of the effort to develop the new generation reactor system safety analysis code RELAP-7, major components to simulate the RCIC system have been developed. This paper describes the models for those components such as turbine, pump, and wet well. Selected individual component test simulations and a simplified SBO simulation up to but before core damage is presented. The successful implementation of the simplified RCIC and wet well models paves the way to further improve the models for safety analysis by including more detailed physical processes in the near future.
Abdel-Rehim, A M; Stathopoulos, Andreas; Orginos, Kostas
2014-08-01
The technique that was used to build the EigCG algorithm for sparse symmetric linear systems is extended to the nonsymmetric case using the BiCG algorithm. We show that, similarly to the symmetric case, we can build an algorithm that is capable of computing a few smallest magnitude eigenvalues and their corresponding left and right eigenvectors of a nonsymmetric matrix using only a small window of the BiCG residuals while simultaneously solving a linear system with that matrix. For a system with multiple right-hand sides, we give an algorithm that computes incrementally more eigenvalues while solving the first few systems and then uses the computed eigenvectors to deflate BiCGStab for the remaining systems. Our experiments on various test problems, including Lattice QCD, show the remarkable ability of EigBiCG to compute spectral approximations with accuracy comparable to that of the unrestarted, nonsymmetric Lanczos. Furthermore, our incremental EigBiCG followed by appropriately restarted and deflated BiCGStab provides a competitive method for systems with multiple right-hand sides.
Collective Behaviors in Spatially Extended Systems with Local Interactions and Synchronous Updating
NASA Astrophysics Data System (ADS)
ChatÉ, H.; Manneville, P.
1992-01-01
Assessing the extent to which dynamical systems with many degrees of freedom can be described within a thermodynamics formalism is a problem that currently attracts much attention. In this context, synchronously updated regular lattices of identical, chaotic elements with local interactions are promising models for which statistical mechanics may be hoped to provide some insights. This article presents a large class of cellular automata rules and coupled map lattices of the above type in space dimensions d = 2 to 6.Such simple models can be approached by a mean-field approximation which usually reduces the dynamics to that of a map governing the evolution of some extensive density. While this approximation is exact in the d = infty limit, where macroscopic variables must display the time-dependent behavior of the mean-field map, basic intuition from equilibrium statistical mechanics rules out any such behavior in a low-dimensional systems, since it would involve the collective motion of locally disordered elements.The models studied are chosen to be as close as possible to mean-field conditions, i.e., rather high space dimension, large connectivity, and equal-weight coupling between sites. While the mean-field evolution is never observed, a new type of non-trivial collective behavior is found, at odds with the predictions of equilibrium statistical mechanics. Both in the cellular automata models and in the coupled map lattices, macroscopic variables frequently display a non-transient, time-dependent, low-dimensional dynamics emerging out of local disorder. Striking examples are period 3 cycles in two-state cellular automata and a Hopf bifurcation for a d = 5 lattice of coupled logistic maps. An extensive account of the phenomenology is given, including a catalog of behaviors, classification tables for the celular automata rules, and bifurcation diagrams for the coupled map lattices.The observed underlying dynamics is accompanied by an intrinsic quasi-Gaussian noise
Dissipation range turbulent cascades in plasmas
Terry, P. W.; Almagri, A. F.; Forest, C. B.; Nornberg, M. D.; Rahbarnia, K.; Sarff, J. S.; Fiksel, G.; Hatch, D. R.; Jenko, F.; Prager, S. C.; Ren, Y.
2012-05-15
Dissipation range cascades in plasma turbulence are described and spectra are formulated from the scaled attenuation in wavenumber space of the spectral energy transfer rate. This yields spectra characterized by the product of a power law and exponential fall-off, applicable to all scales. Spectral indices of the power law and exponential fall-off depend on the scaling of the dissipation, the strength of the nonlinearity, and nonlocal effects when dissipation rates of multiple fluctuation fields are different. The theory is used to derive spectra for MHD turbulence with magnetic Prandtl number greater than unity, extending previous work. The theory is also applied to generic plasma turbulence by considering the spectrum from damping with arbitrary wavenumber scaling. The latter is relevant to ion temperature gradient turbulence modeled by gyrokinetics. The spectrum in this case has an exponential component that becomes weaker at small scale, giving a power law asymptotically. Results from the theory are compared to three very different types of turbulence. These include the magnetic plasma turbulence of the Madison Symmetric Torus, the MHD turbulence of liquid metal in the Madison Dynamo Experiment, and gyrokinetic simulation of ion temperature gradient turbulence.
Effect of Curvature on Carbon Chemical Shielding in Extended Carbon Systems.
Casabianca, Leah B
2016-09-01
The effect of curvature on the chemical shielding of carbons in curved polycyclic aromatic hydrocarbons has been systematically studied by examining structures analogous to the circumcoronene molecule with different degrees of curvature. We attempt to eliminate effects from Knight shifts in carbon nanotubes, differing ring currents from five-membered rings, and edge effects in finite nanotube models in order to separate out the change in shielding that is due to curvature alone. Using curved structures derived from geometry-optimized structures of carbon nanotubes, we calculate the carbon chemical shielding tensor for carbons in the central aromatic ring as well as the Nucleus Independent Chemical Shift (NICS) on the convex and concave side of each structure. All three tensor components become less shielded with increasing curvature of the system, with the σ33 component radial to the curve experiencing the greatest change. The NICS values are influenced by both the decrease in aromaticity as the structure is curved as well as geometric effects that bring the outside rings closer to the central aromatic ring. PMID:27564451
NASA Astrophysics Data System (ADS)
Clough, Matthew; Dixon, Steve; Fleming, Matthew; Stone, Mark
2016-02-01
Guided waves are now commonly used in industrial NDT for locating corrosion in pipelines in the form of wall thinning. Shear Horizontal waves generated by EMATs are used in a screening arrangement in this work to locate and size corrosion in terms of axial extent and circumferential positioning. This is facilitated by propagating SH waves circumferentially around the pipeline whilst moving a scanning rig axially, keeping transducer separation constant. This arrangement is preferential in that it can operate through thin(up to 1mm) coatings and does not require full access to the pipe's circumference and is useful for detecting corrosion in difficult to access regions, such as below pipe supports and in subsea applications. The performance of the system in terms of screening capability and the possibilities of extension into more quantitative measures are assessed. The behaviour of different wave modes as they interact with defects is investigated via experimental measurements on artificially induced corrosion patches and measurements on samples with in service corrosion. Measurement of the axial extent of corrosion patches, circumferential positioning and a range of possible remaining thickness is assessed. Finite element modelling of SH mode interaction with defects is used to understand what happens to different wave modes when they interact with defects in terms of reflection, diffraction and mode conversion.
Baczewski, Andrew David; Shulenburger, Luke; Desjarlais, Michael Paul; Magyar, Rudolph J.
2014-02-01
In recent years, DFT-MD has been shown to be a useful computational tool for exploring the properties of WDM. These calculations achieve excellent agreement with shock compression experiments, which probe the thermodynamic parameters of the Hugoniot state. New X-ray Thomson Scattering diagnostics promise to deliver independent measurements of electronic density and temperature, as well as structural information in shocked systems. However, they require the development of new levels of theory for computing the associated observables within a DFT framework. The experimentally observable x-ray scattering cross section is related to the electronic density-density response function, which is obtainable using TDDFT - a formally exact extension of conventional DFT that describes electron dynamics and excited states. In order to develop a capability for modeling XRTS data and, more generally, to establish a predictive capability for rst principles simulations of matter in extreme conditions, real-time TDDFT with Ehrenfest dynamics has been implemented in an existing PAW code for DFT-MD calculations. The purpose of this report is to record implementation details and benchmarks as the project advances from software development to delivering novel scienti c results. Results range from tests that establish the accuracy, e ciency, and scalability of our implementation, to calculations that are veri ed against accepted results in the literature. Aside from the primary XRTS goal, we identify other more general areas where this new capability will be useful, including stopping power calculations and electron-ion equilibration.
High-speed extended-term time-domain simulation for online cascading analysis of power system
NASA Astrophysics Data System (ADS)
Fu, Chuan
A high-speed extended-term (HSET) time domain simulator (TDS), intended to become a part of an energy management system (EMS), has been newly developed for use in online extended-term dynamic cascading analysis of power systems. HSET-TDS includes the following attributes for providing situational awareness of high-consequence events: (i) online analysis, including n-1 and n-k events, (ii) ability to simulate both fast and slow dynamics for 1-3 hours in advance, (iii) inclusion of rigorous protection-system modeling, (iv) intelligence for corrective action ID, storage, and fast retrieval, and (v) high-speed execution. Very fast on-line computational capability is the most desired attribute of this simulator. Based on the process of solving algebraic differential equations describing the dynamics of power system, HSET-TDS seeks to develop computational efficiency at each of the following hierarchical levels, (i) hardware, (ii) strategies, (iii) integration methods, (iv) nonlinear solvers, and (v) linear solver libraries. This thesis first describes the Hammer-Hollingsworth 4 (HH4) implicit integration method. Like the trapezoidal rule, HH4 is symmetrically A-Stable but it possesses greater high-order precision (h4 ) than the trapezoidal rule. Such precision enables larger integration steps and therefore improves simulation efficiency for variable step size implementations. This thesis provides the underlying theory on which we advocate use of HH4 over other numerical integration methods for power system time-domain simulation. Second, motivated by the need to perform high speed extended-term time domain simulation (HSET-TDS) for on-line purposes, this thesis presents principles for designing numerical solvers of differential algebraic systems associated with power system time-domain simulation, including DAE construction strategies (Direct Solution Method), integration methods(HH4), nonlinear solvers(Very Dishonest Newton), and linear solvers(SuperLU). We have
Space Resource Utilization and Extending Human Presence Across the Solar System
NASA Technical Reports Server (NTRS)
Curreri, Peter A.
2005-01-01
investment enables commercial and private viability beyond Earth orbit. For example, analysis has shown the lunar oxygen production for propellant becomes commercially viable after the exploration program completes the R&D, and power from lunar derived photovoltaics could, according to past NASA sponsored studies, pay for themselves while supplying most of Earth's electrical energy after about 17 years. Besides the Moon and Mars the resources of the near Earth asteroids enable the building of large space structures and science payloads. Analysis has shown that one of the thousands of these objects (some as easily accessible in space as the Moon and Mars), 2 km dia, the size of a typical open pit mine, would cost the total global financial product of Earth for 30,000 years if we were to launch it from Earth. Beyond Mars, the belt asteroids have been calculated to contain enough materials for habitat and life to support 10 quadrillion people. Thus, the development and use of space resources enables the extension of human life through the solar system allowing humanity to move from a planetary to a solar system society.
Instabilities in wormlike micelle systems. From shear-banding to elastic turbulence.
Fardin, M-A; Lerouge, S
2012-09-01
Shear-banding is ubiquitous in complex fluids. It is related to the organization of the flow into macroscopic bands bearing different viscosities and local shear rates and stacked along the velocity gradient direction. This flow-induced transition towards a heterogeneous flow state has been reported in a variety of systems, including wormlike micellar solutions, telechelic polymers, emulsions, clay suspensions, colloidal gels, star polymers, granular materials, or foams. In the past twenty years, shear-banding flows have been probed by various techniques, such as rheometry, velocimetry and flow birefringence. In wormlike micelle solutions, many of the data collected exhibit unexplained spatio-temporal fluctuations. Different candidates have been identified, the main ones being wall slip, interfacial instability between bands or bulk instability of one of the bands. In this review, we present experimental evidence for a purely elastic instability of the high shear rate band as the main origin for fluctuating shear-banding flows. PMID:23001785
Kolosz, Ben Grant-Muller, Susan
2015-01-15
The paper reports research involving three cost–benefit analyses performed on different ITS schemes (Active Traffic Management, Intelligent Speed Adaptation and the Automated Highway System) on one of the UK's busiest highways — the M42. The environmental scope of the assets involved is widened to take into account the possibility of new technology linked by ICT and located within multiple spatial regions. The areas focused on in the study were data centre energy emissions, the embedded emissions of the road-side infrastructure, vehicle tailpipe emissions, additional hardware required by the vehicles (if applicable) and safety, and all aspects of sustainability. Dual discounting is applied which aims to provide a separate discount rate for environmental elements. For ATM, despite the energy costs of the data centre, the initial implementation costs and mitigation costs of its embedded emissions, a high cost–benefit ratio of 5.89 is achieved, although the scheme becomes less effective later on its lifecycle due to rising costs of energy. ISA and AHS generate a negative result, mainly due to the cost of getting the vehicle on the road. In order to negate these costs, the pricing of the vehicle should be scaled depending upon the technology that is outfitted. Retrofitting on vehicles without the technology should be paid for by the driver. ATM will offset greenhouse gas emissions by 99 kt of CO{sub 2} equivalency over a 25 year lifespan. This reduction has taken into account the expected improvement in vehicle technology. AHS is anticipated to save 280 kt of CO{sub 2} equivalency over 15 years of operational usage. However, this offset is largely dependent on assumptions such as the level of market penetration. - Highlights: • Three cost–benefit analyses are applied to inter-urban intelligent transport. • For ATM, a high cost–benefit ratio of 5.89 is achieved. • ATM offsets greenhouse gas emissions by 99 kt of CO{sub 2} equivalency over 25 years.
Scale-invariant cascades in turbulence and evolution
NASA Astrophysics Data System (ADS)
Guttenberg, Nicholas Ryan
In this dissertation, I present work addressing three systems which are traditionally considered to be unrelated: turbulence, evolution, and social organization. The commonality between these systems is that in each case, microscopic interaction rules give rise to an emergent behavior that in some way makes contact with the macroscopic scale of the problem. The open-ended evolution of complexity in evolving systems is analogous to the scale-free structure established in turbulent flows through local transportation of energy. In both cases, an invariance is required for the cascading behavior to occur, and in both cases the scale-free structure is built up from some initial scale from which the behavior is fed. In turbulence, I examine the case of two-dimensional turbulence in order to support the hypothesis that the friction factor and velocity profile of turbulent pipe flows depend on the turbulent energy spectrum in a way unpredicted by the classic Prandtl theory. By simulating two-dimensional flows in controlled geometries, either an inverse energy cascade or forward enstrophy cascade can be produced. The friction factor scaling of the flow changes depending on which cascade is present, in a way consistent with momentum transfer theory and roughness-induced criticality. In the problem of evolution, I show that open-ended growth of complexity can be obtained by ensuring that the evolutionary dynamics are invariant with respect to changes in complexity. Finite system size, finite point mutation rate, and fixed points in the fitness landscape can all interrupt this cascade behavior, producing an analogue to the integral scale of turbulence. This complexity cascade can exist both for competing and for symbiotic sets of organisms. Extending this picture to the qualitatively-different levels of organization of real lifeforms (viruses, unicellular, biofilms, multicellular) requires an understanding of how the processes of evolution themselves evolve. I show that a
Variable density turbulence tunnel facility
NASA Astrophysics Data System (ADS)
Bodenschatz, E.; Bewley, G. P.; Nobach, H.; Sinhuber, M.; Xu, H.
2014-09-01
The Variable Density Turbulence Tunnel at the Max Planck Institute for Dynamics and Self-Organization in Göttingen, Germany, produces very high turbulence levels at moderate flow velocities, low power consumption, and adjustable kinematic viscosity between 10-4 m2/s and 10-7 m2/s. The Reynolds number can be varied by changing the pressure or flow rate of the gas or by using different non-flammable gases including air. The highest kinematic viscosities, and hence lowest Reynolds numbers, are reached with air or nitrogen at 0.1 bar. To reach the highest Reynolds numbers the tunnel is pressurized to 15 bars with the dense gas sulfur hexafluoride (SF6). Turbulence is generated at the upstream ends of two measurement sections with grids, and the evolution of this turbulence is observed as it moves down the length of the sections. We describe the instrumentation presently in operation, which consists of the tunnel itself, classical grid turbulence generators, and state-of-the-art nano-fabricated hot-wire anemometers provided by Princeton University [M. Vallikivi, M. Hultmark, S. C. C. Bailey, and A. J. Smits, Exp. Fluids 51, 1521 (2011)]. We report measurements of the characteristic scales of the flow and of turbulent spectra up to Taylor Reynolds number Rλ ≈ 1600, higher than any other grid-turbulence experiment. We also describe instrumentation under development, which includes an active grid and a Lagrangian particle tracking system that moves down the length of the tunnel with the mean flow. In this configuration, the properties of the turbulence are adjustable and its structure is resolvable up to Rλ ≈ 8000.
Enhanced Turbulent Mixing on Highways
NASA Astrophysics Data System (ADS)
Gordon, M.; Staebler, R. M.; Liggio, J.; Makar, P.; Brook, J.; Wentzell, J. J.; Lu, G.; Lee, P.
2010-12-01
Traffic emissions have a substantial effect on air quality and turbulence affects how these emissions mix with the surrounding air. In July and August of 2010, measurements of turbulent fluxes and turbulent kinetic energy were made on highways in the Toronto area (Ontario, Canada) as part of the ALMITEE (Advancing Local-scale Modeling through Inclusion of Transportation Emission Experiments) subproject FEVER (Fast Evolution of Vehicle Emissions from Roadways). The aim of this project was to study and parameterize the turbulent mixing of traffic emissions on highways as a function of traffic density, speed, and vehicle type. The mobile station CRUISER (Canadian Regional and Urban Investigation System for Environmental Research) was equipped with two sonic anemometers, an air flow probe (AIMMS-20), inertial motion sensing, GPS, video recording equipment, and various particle and gas measurement instrumentation. This allowed in-situ turbulence measurements while driving on the highway with traffic. These measurements differ from previous studies in that turbulence can be measured in realistic conditions, while traffic densities, vehicle types, and vehicle to measurement distances can be extracted from video recording by automated video processing software. Although the turbulent motion of air is often measured from aircraft and ship-based instrumentation, the analysis and interpretation of sonic anemometer measurements from a highway-speed vehicle, moving over uneven and often bumpy terrain presents a very different challenge. Various analytical approaches to process these measurements will be compared and the development of the video processing software to determine vehicle size and following distance will be discussed. Results will be presented which demonstrate a strong dependence of turbulent energy on vehicle type, speed, and following distance.
MHD Turbulence through the Heliosphere
NASA Astrophysics Data System (ADS)
Veltri, P.
Velocity and magnetic field fluctuations in a wide range of space and time scales have been directly detected in the interplanetary medium In the solar corona the presence of MHD turbulence is naturally generated by the mechanical and magnetic energy input from the photosphere and it could be related to coronal heating as well as to energy release events like micro and nanoflares A certain amount of fluctuations from the solar corona arrives in the solar wind mainly as Alfvénic turbulence i e strongly correlated velocity and magnetic field fluctuations with a very low level of compressible density magnetic field intensity temperature fluctuations The whole system formed by the solar corona and the solar wind represents a sort of wind tunnel extremely useful to study the MHD turbulence properties The presence of magnetic turbulence in the heliosphere is identified as the source of charged particle collisionless diffusion which according the values of parameters like the energy level on magnetic fluctuations or the turbulence correlation length can display both a normal gaussian random walk and an anomalous subdiffusive or super diffusive behavior The former case is obtained in a situation of global stochasticity high level of fluctuation energy while the latter in a situation of weak chaos low level of fluctuation energy The talk will discuss turbulence generation at photospheric level its propagation and its interaction with heliospheric structures and its effects on anomalous transport processes of charged
Lu, Yanrong; Li, Lixiang; Peng, Haipeng; Xie, Dong; Yang, Yixian
2015-06-01
The Telecare Medicine Information Systems (TMISs) provide an efficient communicating platform supporting the patients access health-care delivery services via internet or mobile networks. Authentication becomes an essential need when a remote patient logins into the telecare server. Recently, many extended chaotic maps based authentication schemes using smart cards for TMISs have been proposed. Li et al. proposed a secure smart cards based authentication scheme for TMISs using extended chaotic maps based on Lee's and Jiang et al.'s scheme. In this study, we show that Li et al.'s scheme has still some weaknesses such as violation the session key security, vulnerability to user impersonation attack and lack of local verification. To conquer these flaws, we propose a chaotic maps and smart cards based password authentication scheme by applying biometrics technique and hash function operations. Through the informal and formal security analyses, we demonstrate that our scheme is resilient possible known attacks including the attacks found in Li et al.'s scheme. As compared with the previous authentication schemes, the proposed scheme is more secure and efficient and hence more practical for telemedical environments. PMID:25900328
Moon, Jongho; Choi, Younsung; Kim, Jiye; Won, Dongho
2016-03-01
Recently, numerous extended chaotic map-based password authentication schemes that employ smart card technology were proposed for Telecare Medical Information Systems (TMISs). In 2015, Lu et al. used Li et al.'s scheme as a basis to propose a password authentication scheme for TMISs that is based on biometrics and smart card technology and employs extended chaotic maps. Lu et al. demonstrated that Li et al.'s scheme comprises some weaknesses such as those regarding a violation of the session-key security, a vulnerability to the user impersonation attack, and a lack of local verification. In this paper, however, we show that Lu et al.'s scheme is still insecure with respect to issues such as a violation of the session-key security, and that it is vulnerable to both the outsider attack and the impersonation attack. To overcome these drawbacks, we retain the useful properties of Lu et al.'s scheme to propose a new password authentication scheme that is based on smart card technology and requires the use of chaotic maps. Then, we show that our proposed scheme is more secure and efficient and supports security properties. PMID:26743628
Evers, H; Mayer, A; Engelmann, U; Schröter, A; Baur, U; Wolsiffer, K; Meinzer, H P
1998-01-01
This paper describes ongoing research concerning interactive volume visualization coupled with tools for volumetric analysis. To establish an easy to use application, the 3D-visualization has been embedded in a state of the art teleradiology system, where additional functionality is often desired beyond basic image transfer and management. Major clinical requirements for deriving spatial measures are covered by the tools, in order to realize extended diagnosis support and therapy planning. Introducing the general plug-in mechanism this work exemplarily describes the useful extension of an approved application. Interactive visualization was achieved by a hybrid approach taking advantage of both the precise volume visualization based on the Heidelberg Raytracing Model and the graphics acceleration of modern workstations. Several tools for volumetric analysis extend the 3D-viewing. They offer 3D-pointing devices to select locations in the data volume, measure anatomical structures or control segmentation processes. A haptic interface provides a realistic perception while navigating within the 3D-reconstruction. The work is closely related to research work in the field of heart, liver and head surgery. In cooperation with our medical partners the development of tools as presented proceed the integration of image analysis into clinical routine. PMID:10384617
Evers, H; Mayer, A; Engelmann, U; Schröter, A; Baur, U; Demiris, A M; Giess, C; Wolsiffer, K; Meinzer, H P
1999-01-01
This paper describes ongoing research concerning interactive volume visualization coupled with tools for volumetric analysis. To establish an easy to use application, the three-dimensional-visualization has been embedded in a state of the art teleradiology system, where additional functionality is often desired beyond basic image transfer and management. Major clinical requirements for deriving spatial measures are covered by the tools, in order to realize extended diagnosis support and therapy planning. Introducing a general plug-in mechanism, this work exemplarily describes the useful extension of an approved application. Interactive visualization was achieved by a hybrid approach taking advantage of both the precise volume visualization based on the Heidelberg ray-tracing model and the graphics acceleration capabilities of modern workstations. Several tools for volumetric analysis extend the three-dimensional-viewing. They are controlled by adequate input devices to select locations in the data volume, measure anatomical structures or initiate a segmentation process. Moreover, a haptic interface can be connected to provide a more realistic feedback while navigating within the three-dimensional-reconstruction. The work is closely related to research in the field of heart, liver and head surgery. In cooperation with our medical partners the development of tools as presented facilitates the integration of image analysis into the clinical routine. PMID:10193894
NASA Astrophysics Data System (ADS)
Hecker, Peter; Doehler, Hans-Ullrich; Korn, Bernd; Ludwig, T.
2001-08-01
DLR has set up a number of projects to increase flight safety and economics of aviation. Within these activities one field of interest is the development and validation of systems for pilot assistance in order to increase the situation awareness of the aircrew. All flight phases ('gate-to-gate') are taken into account, but as far as approaches, landing and taxiing are the most critical tasks in the field of civil aviation, special emphasis is given to these operations. As presented in previous contributions within SPIE's Enhanced and Synthetic Vision Conferences, DLR's Institute of Flight Guidance has developed an Enhanced Vision System (EVS) as a tool assisting especially approach and landing by improving the aircrew's situational awareness. The combination of forward looking imaging sensors (such as EADS's HiVision millimeter wave radar), terrain data stored in on-board databases plus information transmitted from ground or other aircraft via data link is used to help pilots handling these phases of flight especially under adverse weather conditions. A second pilot assistance module being developed at DLR is the Taxi And Ramp Management And Control - Airborne System (TARMAC-AS), which is part of an Advanced Surface Management Guidance and Control System (ASMGCS). By means of on-board terrain data bases and navigation data a map display is generated, which helps the pilot performing taxi operations. In addition to the pure map function taxi instructions and other traffic can be displayed as the aircraft is connected to TARMAC-planning and TARMAC-communication, navigation and surveillance modules on ground via data-link. Recent experiments with airline pilots have shown, that the capabilities of taxi assistance can be extended significantly by integrating EVS- and TARMAC-AS-functionalities. Especially an extended obstacle detection and warning coming from the Enhanced Vision System increases the safety of ground operations. The presented paper gives an overview
NASA Astrophysics Data System (ADS)
Comte-Bellot, Genevieve; Mathieu, Jean
1987-06-01
The fundamental physics of turbulence, measurement techniques for turbulent flows, and engineering applications of turbulence theory are discussed in reviews and reports of recent theoretical and experimental investigations. Topics addressed include instability and transition, chaotic behavior in nonlinear systems and turbulent fields, direct and large-eddy simulation of turbulence, Fourier-mode coupling and the spectral analysis of turbulence, and two-dimensional velocity fields in geophysical and astrophysical turbulence. Consideration is given to coherent structures, conditional averaging, and pattern recognition; hot-wire anemometry, vorticity meters, electrochemical methods, and image analysis; and the effects of artificially produced external disturbances on turbulence.
NASA Astrophysics Data System (ADS)
Di Girolamo, Paolo; Summa, Donato; Stelitano, Dario; Cacciani, Marco; Scoccione, Andrea; Behrendt, Andreas; Wulfmeyer, Volker
2016-06-01
Measurements carried out by the Raman lidar system BASIL are reported to demonstrate the capability of this instrument to characterize turbulent processes within the Convective Boundary Layer (CBL). In order to resolve the vertical profiles of turbulent variables, high resolution water vapour and temperature measurements, with a temporal resolution of 10 sec and a vertical resolution of 90 and 210 m, respectively, are considered. Measurements of higher-order moments of the turbulent fluctuations of water vapour mixing ratio and temperature are obtained based on the application of spectral and auto-covariance analyses to the water vapour mixing ratio and temperature time series. The algorithms are applied to a case study (IOP 5, 20 April 2013) from the HD(CP)2 Observational Prototype Experiment (HOPE), held in Central Germany in the spring 2013. The noise errors are demonstrated to be small enough to allow the derivation of up to fourth-order moments for both water vapour mixing ratio and temperature fluctuations with sufficient accuracy.
Bogenschutz, Peter; Moeng, Chin-Hoh
2015-10-13
The PI’s at the National Center for Atmospheric Research (NCAR), Chin-Hoh Moeng and Peter Bogenschutz, have primarily focused their time on the implementation of the Simplified-Higher Order Turbulence Closure (SHOC; Bogenschutz and Krueger 2013) to the Multi-scale Modeling Framework (MMF) global model and testing of SHOC on deep convective cloud regimes.
Scattering of sonic booms by anisotropic turbulence in the atmosphere
Kelly; Raspet; Bass
2000-06-01
An earlier paper [J. Acoust. Soc. Am. 98, 3412-3417 (1995)] reported on the comparison of rise times and overpressures of sonic booms calculated with a scattering center model of turbulence to measurements of sonic boom propagation through a well-characterized turbulent layer under moderately turbulent conditions. This detailed simulation used spherically symmetric scatterers to calculate the percentage of occurrence histograms of received overpressures and rise times. In this paper the calculation is extended to include distorted ellipsoidal turbules as scatterers and more accurately incorporates the meteorological data into a determination of the number of scatterers per unit volume. The scattering center calculation overpredicts the shifts in rise times for weak turbulence, and still underpredicts the shift under more turbulent conditions. This indicates that a single-scatter center-based model cannot completely describe sonic boom propagation through atmospheric turbulence. PMID:10875351
RELATIVISTIC ACCRETION MEDIATED BY TURBULENT COMPTONIZATION
Socrates, Aristotle E-mail: socrates@astro.princeton.ed
2010-08-10
Black hole and neutron star accretion flows display unusually high levels of hard coronal emission in comparison to all other optically thick, gravitationally bound, turbulent astrophysical systems. Since these flows sit in deep relativistic gravitational potentials, their random bulk motions approach the speed of light, therefore allowing turbulent Comptonization to be an important effect. We show that the inevitable production of hard X-ray photons results from turbulent Comptonization in the limit where the turbulence is trans-sonic and the accretion power approaches the Eddington limit. In this regime, the turbulent Compton y-parameter approaches unity and the turbulent Compton temperature is a significant fraction of the electron rest mass energy, in agreement with the observed phenomena.
Wiegand, Irith; Geiss, Heinrich K; Mack, Dietrich; Stürenburg, Enno; Seifert, Harald
2007-04-01
Three commercially available microbiology identification and susceptibility testing systems were compared with regard to their ability to detect extended-spectrum beta-lactamase (ESBL) production in Enterobacteriaceae, i.e., the Phoenix Automated Microbiology System (BD Diagnostic Systems, Sparks, MD), the VITEK 2 System (bioMérieux, Marcy l'Etoile, France), and the MicroScan WalkAway-96 System (Dade Behring, Inc., West Sacramento, CA), using routine testing panels. One hundred fifty putative ESBL producers were distributed blindly to three participating laboratories. Conventional phenotypic confirmatory tests such as the disk approximation method, the CLSI double-disk synergy test, and the Etest ESBL were also evaluated. Biochemical and molecular characterization of beta-lactamases performed at an independent laboratory was used as the reference method. One hundred forty-seven isolates of Escherichia coli, Klebsiella pneumoniae, Klebsiella oxytoca, Enterobacter cloacae, Enterobacter aerogenes, Citrobacter freundii, Serratia marcescens, Proteus mirabilis, Proteus vulgaris, and Morganella morganii were investigated. Of these isolates, 85 were identified as ESBL producers by the reference method. The remaining isolates were identified as non-ESBL producers; they were either hyperproducers of their chromosomal AmpC, Koxy, or SHV enzymes or lacked any detectable beta-lactamase activity. The system with the highest sensitivity for the detection of ESBLs was the Phoenix (99%), followed by the VITEK 2 (86%) and the MicroScan (84%); however, specificity was more variable, ranging from 52% (Phoenix) to 78% (VITEK 2). The performance of the semiautomated systems differed widely with the species investigated. The sensitivities of the conventional test methods ranged from 93 to 94%. The double-disk synergy test showed the highest specificity and positive predictive value among all test methods, i.e., 97% and 98%, respectively. PMID:17287329
Wave turbulence in one-dimensional models
NASA Astrophysics Data System (ADS)
Zakharov, V. E.; Guyenne, P.; Pushkarev, A. N.; Dias, F.
2001-05-01
A two-parameter nonlinear dispersive wave equation proposed by Majda, McLaughlin and Tabak is studied analytically and numerically as a model for the study of wave turbulence in one-dimensional systems. Our ultimate goal is to test the validity of weak turbulence theory. Although weak turbulence theory is independent on the sign of the nonlinearity of the model, the numerical results show a strong dependence on the sign of the nonlinearity. A possible explanation for this discrepancy is the strong influence of coherent structures - wave collapses and quasisolitons - in wave turbulence.
New Atmospheric Turbulence Model for Shuttle Applications
NASA Technical Reports Server (NTRS)
Justus, C. G.; Campbell, C. W.; Doubleday, M. K.; Johnson, D. L.
1990-01-01
An updated NASA atmospheric turbulence model, from 0 to 200 km altitude, which was developed to be more realistic and less conservative when applied to space shuttle reentry engineering simulation studies involving control system fuel expenditures is presented. The prior model used extreme turbulence (3 sigma) for all altitudes, whereas in reality severe turbulence is patchy within quiescent atmospheric zones. The updated turublence model presented is designed to be more realistic. The prior turbulence statistics (sigma and L) were updated and were modeled accordingly.
Mountain Wave-Induced Turbulence - "Lower Turbulent Zones" Revisited
NASA Astrophysics Data System (ADS)
Strauss, Lukas; Grubišić, Vanda; Serafin, Stefano; Mühlgassner, Rita
2014-05-01
In their seminal 1974 paper on "Lower Turbulent Zones Associated with Mountain Lee Waves" P. F. Lester and W. A. Fingerhut attempted to characterize regions of low-level turbulence in the lee of mountain ranges that are commonly associated with large-amplitude mountain waves aloft. For their study, they made extensive use of airborne measurements with small research aircraft that penetrated into the "lower turbulent zone" (LTZ). The Lester and Fingerhut study complemented previous work on wave-induced LTZs by J. P. Kuettner and others in the 1950s who were among the first to employ sailplanes as scientific measurement platforms. Given the limitations of scientific instrumentation on research aircraft in the 1970s (e.g., no GPS) and, in particular, on sailplanes in the 1950s, credit has to be given to these authors for their remarkably detailed account and classification of LTZs. Ever since then, scientists have been trying to refine the conceptual model of the LTZ and shed more light on the origin of turbulence therein. The Terrain-Induced Rotor Experiment (T-REX, Sierra Nevada, California, 2006) is the most recent, major effort organized to investigate the characteristics of LTZs by studying the coupled mountain-wave, rotor, and boundary-layer system. During T-REX, comprehensive ground-based and airborne, in situ and remote sensing measurements were collected during 15 Intensive Observation Periods (IOPs). In this study, we make use of the extensive T-REX datasets to revisit the LTZ concept. During T-REX IOPs, the University of Wyoming King Air (UWKA) research aircraft flew straight-and-level legs aligned with the mean wind direction to document the variation of flow and turbulence over and downwind of the Sierra Nevada. In order to characterize the structure and intensity of turbulence within the LTZ, turbulent kinetic energy (TKE) and eddy-dissipation rate (EDR) were computed from UWKA research flights. In contrast to the rough average values of TKE and EDR
NASA Astrophysics Data System (ADS)
Bates, Jefferson; Laricchia, Savio; Ruzsinszky, Adrienn
The Random Phase Approximation (RPA) is quickly becoming a standard method beyond semi-local Density Functional Theory that naturally incorporates weak interactions and eliminates self-interaction error. RPA is not perfect, however, and suffers from self-correlation error as well as an incorrect description of short-ranged correlation typically leading to underbinding. To improve upon RPA we introduce a short-ranged, exchange-like kernel that is one-electron self-correlation free for one and two electron systems in the high-density limit. By tuning the one free parameter in our model to recover an exact limit of the homogeneous electron gas correlation energy we obtain a non-local, energy-optimized kernel that reduces the errors of RPA for both homogeneous and inhomogeneous solids. To reduce the computational cost of the standard kernel-corrected RPA, we also implement RPA renormalized perturbation theory for extended systems, and demonstrate its capability to describe the dominant correlation effects with a low-order expansion in both metallic and non-metallic systems. Furthermore we stress that for norm-conserving implementations the accuracy of RPA and beyond RPA structural properties compared to experiment is inherently limited by the choice of pseudopotential. Current affiliation: King's College London.
NASA Astrophysics Data System (ADS)
Ishizuka, Ryosuke; Yoshida, Norio
2013-08-01
An extended molecular Ornstein-Zernike (XMOZ) integral equation is formulated to calculate the spatial distribution of solvent around a solute of arbitrary shape and solid surfaces. The conventional MOZ theory employs spherical harmonic expansion technique to treat the molecular orientation of components of solution. Although the MOZ formalism is fully exact analytically, the truncation of the spherical harmonic expansion requires at a finite order for numerical calculation and causes the significant error for complex molecules. The XMOZ integral equation is the natural extension of the conventional MOZ theory to a rectangular coordinate system, which is free from the truncation of spherical harmonic expansion with respect to solute orientation. In order to show its applicability, we applied the XMOZ theory to several systems using the hypernetted-chain (HNC) and Kovalenko-Hirata approximations. The quality of results obtained within our theory is discussed by comparison with values from the conventional MOZ theory, molecular dynamics simulation, and three-dimensional reference interaction site model theory. The spatial distributions of water around the complex of non-charged sphere and dumbbell were calculated. Using this system, the approximation level of the XMOZ and other methods are discussed. To assess our theory, we also computed the excess chemical potentials for three realistic molecules (water, methane, and alanine dipeptide). We obtained the qualitatively reasonable results by using the XMOZ/HNC theory. The XMOZ theory covers a wide variety of applications in solution chemistry as a useful tool to calculate solvation thermodynamics.
Ishizuka, Ryosuke; Yoshida, Norio
2013-08-28
An extended molecular Ornstein-Zernike (XMOZ) integral equation is formulated to calculate the spatial distribution of solvent around a solute of arbitrary shape and solid surfaces. The conventional MOZ theory employs spherical harmonic expansion technique to treat the molecular orientation of components of solution. Although the MOZ formalism is fully exact analytically, the truncation of the spherical harmonic expansion requires at a finite order for numerical calculation and causes the significant error for complex molecules. The XMOZ integral equation is the natural extension of the conventional MOZ theory to a rectangular coordinate system, which is free from the truncation of spherical harmonic expansion with respect to solute orientation. In order to show its applicability, we applied the XMOZ theory to several systems using the hypernetted-chain (HNC) and Kovalenko-Hirata approximations. The quality of results obtained within our theory is discussed by comparison with values from the conventional MOZ theory, molecular dynamics simulation, and three-dimensional reference interaction site model theory. The spatial distributions of water around the complex of non-charged sphere and dumbbell were calculated. Using this system, the approximation level of the XMOZ and other methods are discussed. To assess our theory, we also computed the excess chemical potentials for three realistic molecules (water, methane, and alanine dipeptide). We obtained the qualitatively reasonable results by using the XMOZ/HNC theory. The XMOZ theory covers a wide variety of applications in solution chemistry as a useful tool to calculate solvation thermodynamics. PMID:24006986
Chaos, patterns, coherent structures, and turbulence: Reflections on nonlinear science
NASA Astrophysics Data System (ADS)
Ecke, Robert E.
2015-09-01
The paradigms of nonlinear science were succinctly articulated over 25 years ago as deterministic chaos, pattern formation, coherent structures, and adaptation/evolution/learning. For chaos, the main unifying concept was universal routes to chaos in general nonlinear dynamical systems, built upon a framework of bifurcation theory. Pattern formation focused on spatially extended nonlinear systems, taking advantage of symmetry properties to develop highly quantitative amplitude equations of the Ginzburg-Landau type to describe early nonlinear phenomena in the vicinity of critical points. Solitons, mathematically precise localized nonlinear wave states, were generalized to a larger and less precise class of coherent structures such as, for example, concentrated regions of vorticity from laboratory wake flows to the Jovian Great Red Spot. The combination of these three ideas was hoped to provide the tools and concepts for the understanding and characterization of the strongly nonlinear problem of fluid turbulence. Although this early promise has been largely unfulfilled, steady progress has been made using the approaches of nonlinear science. I provide a series of examples of bifurcations and chaos, of one-dimensional and two-dimensional pattern formation, and of turbulence to illustrate both the progress and limitations of the nonlinear science approach. As experimental and computational methods continue to improve, the promise of nonlinear science to elucidate fluid turbulence continues to advance in a steady manner, indicative of the grand challenge nature of strongly nonlinear multi-scale dynamical systems.
Chaos, patterns, coherent structures, and turbulence: Reflections on nonlinear science.
Ecke, Robert E
2015-09-01
The paradigms of nonlinear science were succinctly articulated over 25 years ago as deterministic chaos, pattern formation, coherent structures, and adaptation/evolution/learning. For chaos, the main unifying concept was universal routes to chaos in general nonlinear dynamical systems, built upon a framework of bifurcation theory. Pattern formation focused on spatially extended nonlinear systems, taking advantage of symmetry properties to develop highly quantitative amplitude equations of the Ginzburg-Landau type to describe early nonlinear phenomena in the vicinity of critical points. Solitons, mathematically precise localized nonlinear wave states, were generalized to a larger and less precise class of coherent structures such as, for example, concentrated regions of vorticity from laboratory wake flows to the Jovian Great Red Spot. The combination of these three ideas was hoped to provide the tools and concepts for the understanding and characterization of the strongly nonlinear problem of fluid turbulence. Although this early promise has been largely unfulfilled, steady progress has been made using the approaches of nonlinear science. I provide a series of examples of bifurcations and chaos, of one-dimensional and two-dimensional pattern formation, and of turbulence to illustrate both the progress and limitations of the nonlinear science approach. As experimental and computational methods continue to improve, the promise of nonlinear science to elucidate fluid turbulence continues to advance in a steady manner, indicative of the grand challenge nature of strongly nonlinear multi-scale dynamical systems. PMID:26428558
NASA Astrophysics Data System (ADS)
Rivet, Sylvain; Marques, Manuel J.; Bradu, Adrian; Podoleanu, Adrian
2016-06-01
This article presents a theoretical study on an optical module (OM) that can be inserted between an object under investigation and a Fourier-domain optical coherence tomography system, transforming the latter into a polarisation-sensitive optical coherence tomography optical coherence tomography (OCT) system. The module consists of two electro-optic modulators, a Faraday rotator, a linear polariser and a quarter-wave plate. A detailed description on how the module can be used to extract both the net retardance and the fast axis orientation of a linear birefringent sample is presented. This is achieved by taking two sequential measurements for different values of retardance produced by the electro-optic modulator. The module keeps measurements free from undesired polarimetric effects due to birefringence in the single-mode optical fibre and diattenuation in fibre-based couplers within OCT systems. Simulations have been carried out in order to evaluate the effects of chromatic behaviour of the components within the OM.
Zonal flows and turbulence in fluids and plasmas
NASA Astrophysics Data System (ADS)
Parker, Jeffrey Bok-Cheung
In geophysical and plasma contexts, zonal flows are well known to arise out of turbulence. We elucidate the transition from statistically homogeneous turbulence without zonal flows to statistically inhomogeneous turbulence with steady zonal flows. Starting from the Hasegawa--Mima equation, we employ both the quasilinear approximation and a statistical average, which retains a great deal of the qualitative behavior of the full system. Within the resulting framework known as CE2, we extend recent understanding of the symmetry-breaking 'zonostrophic instability'. Zonostrophic instability can be understood in a very general way as the instability of some turbulent background spectrum to a zonally symmetric coherent mode. As a special case, the background spectrum can consist of only a single mode. We find that in this case the dispersion relation of zonostrophic instability from the CE2 formalism reduces exactly to that of the 4-mode truncation of generalized modulational instability. We then show that zonal flows constitute pattern formation amid a turbulent bath. Zonostrophic instability is an example of a Type I s instability of pattern-forming systems. The broken symmetry is statistical homogeneity. Near the bifurcation point, the slow dynamics of CE2 are governed by a well-known amplitude equation, the real Ginzburg-Landau equation. The important features of this amplitude equation, and therefore of the CE2 system, are multiple. First, the zonal flow wavelength is not unique. In an idealized, infinite system, there is a continuous band of zonal flow wavelengths that allow a nonlinear equilibrium. Second, of these wavelengths, only those within a smaller subband are stable. Unstable wavelengths must evolve to reach a stable wavelength; this process manifests as merging jets. These behaviors are shown numerically to hold in the CE2 system, and we calculate a stability diagram. The stability diagram is in agreement with direct numerical simulations of the quasilinear
Geophysical and astrophysical turbulence
NASA Astrophysics Data System (ADS)
Moffatt, H. K.
Spiral structures in two-dimensional turbulence are studied and a theory (Moffatt, 1985, 1986) which regards fully three-dimensional turbulence as an agglomeration of 'random vortex sheets and coherent helical structures' is reviewed. Consideration is given to the process by which current-sheet discontinuities may appear during magnetic relaxation. Within the framework of dynamo theory, the determination of the generation coefficient and the turbulent diffusivity in mean-field electrodynamics for turbulence with helicity in the limit of a large magnetic Reynolds number is discussed. Certain features of 'chromospheric turbulence' (i.e., turbulence in the solar atmosphere outside the photosphere) are also examined.
Borges, Boniek C D; Souza-Junior, Eduardo Jose; Brandt, William C; Loguercio, Alessandro D; Montes, Marcos A J R; Puppin-Rontani, Regina M; Sinhoreti, Mario Alexandre Coelho
2012-01-01
This study evaluated the effect of five methods of solvent volatilization on the degree of conversion (DC) of nine one-bottle adhesive systems using Fourier transform infrared/attenuated total reflectance (FTIR/ATR) analysis. Nine adhesives were tested: Adper Single Bond 2 (SB), Adper Easy One (EO), One Up Bond F Plus (OUP), One Coat Bond SL (OC), XP Bond (XP), Ambar (AM), Natural Bond (NB), GO, and Stae. The adhesive systems were applied to a zinc-selenide pellet and 1) cured without solvent volatilization, 2) left undisturbed for 10 seconds before curing, 3) left undisturbed for 60 seconds before curing, 4) air-dried with an air stream for 10 seconds before curing, and 5) air-dried with an air stream for 60 seconds before curing. FTIR/ATR spectra were obtained, and the DC was calculated by comparing the aliphatic bonds/reference peaks before and after light activation for 10 seconds (FlashLite 1401). The DC means of each material were analyzed by one-way analysis of variance and post hoc Tukey test (p<0.05). The DC of GO and Stae adhesive systems was not affected by the five evaporation conditions. Air-drying for 60 seconds before curing yielded the highest DC for SB, EO, and OC. Extended solvent volatilization time (60 seconds) either with or without air-drying before curing provided the highest DC for AM, NB, XP, and OUP. Thus, the monomer conversion of adhesive systems was material dependent. In general, the 60-second passive or active air-drying modes to volatilize solvents before curing enhanced the degree of conversion for the one-bottle simplified adhesive systems. PMID:22313268