Postural stability of preoperative acoustic neuroma patients assessed by sway magnetometry: are they unsteady?

PubMed

Collins, Melanie M; Johnson, Ian J M; Clifford, Elaine; Birchall, John P; O'Donoghue, Gerald M

2003-04-01

The objective was to evaluate the preoperative postural stability of acoustic neuroma patients using sway magnetometry. Prospective two-center study. Fifty-one patients (mean age, 53 years) diagnosed with unilateral acoustic neuroma on magnetic resonance imaging at two tertiary referral centers were studied. Preoperatively, each patient had sway patterns (with eyes open and with eyes closed, and standing on foam) recorded for 120 seconds by sway magnetometry. Path length for 30 seconds was calculated. The Romberg coefficient (path length with eyes open divided by path length with eyes closed) was calculated. Forty-four percent of patients had abnormal path lengths with eyes open, and 49% with eyes closed. The Romberg coefficients were significantly lower than normal (P <.001; 95% CI, 0.19-0.87). Mean Romberg coefficient was 0.59 (normal value = 0.73), and all patients had a coefficient of less than 1. Half of preoperative acoustic neuroma patients are unsteady, exhibiting abnormal sway patterns based on path length measurements. The increase in sway path length demonstrable in normal subjects with eyes closed was significantly exaggerated in patients with acoustic neuroma.

Robotic path-finding in inverse treatment planning for stereotactic radiosurgery with continuous dose delivery

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

Vandewouw, Marlee M., E-mail: marleev@mie.utoronto

Purpose: Continuous dose delivery in radiation therapy treatments has been shown to decrease total treatment time while improving the dose conformity and distribution homogeneity over the conventional step-and-shoot approach. The authors develop an inverse treatment planning method for Gamma Knife® Perfexion™ that continuously delivers dose along a path in the target. Methods: The authors’ method is comprised of two steps: find a path within the target, then solve a mixed integer optimization model to find the optimal collimator configurations and durations along the selected path. Robotic path-finding techniques, specifically, simultaneous localization and mapping (SLAM) using an extended Kalman filter, aremore » used to obtain a path that travels sufficiently close to selected isocentre locations. SLAM is novelly extended to explore a 3D, discrete environment, which is the target discretized into voxels. Further novel extensions are incorporated into the steering mechanism to account for target geometry. Results: The SLAM method was tested on seven clinical cases and compared to clinical, Hamiltonian path continuous delivery, and inverse step-and-shoot treatment plans. The SLAM approach improved dose metrics compared to the clinical plans and Hamiltonian path continuous delivery plans. Beam-on times improved over clinical plans, and had mixed performance compared to Hamiltonian path continuous plans. The SLAM method is also shown to be robust to path selection inaccuracies, isocentre selection, and dose distribution. Conclusions: The SLAM method for continuous delivery provides decreased total treatment time and increased treatment quality compared to both clinical and inverse step-and-shoot plans, and outperforms existing path methods in treatment quality. It also accounts for uncertainty in treatment planning by accommodating inaccuracies.« less

Combined Monte Carlo and path-integral method for simulated library of time-resolved reflectance curves from layered tissue models

NASA Astrophysics Data System (ADS)

Wilson, Robert H.; Vishwanath, Karthik; Mycek, Mary-Ann

2009-02-01

Monte Carlo (MC) simulations are considered the "gold standard" for mathematical description of photon transport in tissue, but they can require large computation times. Therefore, it is important to develop simple and efficient methods for accelerating MC simulations, especially when a large "library" of related simulations is needed. A semi-analytical method involving MC simulations and a path-integral (PI) based scaling technique generated time-resolved reflectance curves from layered tissue models. First, a zero-absorption MC simulation was run for a tissue model with fixed scattering properties in each layer. Then, a closed-form expression for the average classical path of a photon in tissue was used to determine the percentage of time that the photon spent in each layer, to create a weighted Beer-Lambert factor to scale the time-resolved reflectance of the simulated zero-absorption tissue model. This method is a unique alternative to other scaling techniques in that it does not require the path length or number of collisions of each photon to be stored during the initial simulation. Effects of various layer thicknesses and absorption and scattering coefficients on the accuracy of the method will be discussed.

Kuiper Belt Objects Along the Pluto-Express Path

NASA Technical Reports Server (NTRS)

Jewitt, David (Principal Investigator)

1997-01-01

The science objective of this work is to identify objects in the Kuiper Belt which will, in the 5 years following Pluto encounter, be close to the flight path of NASA's Pluto Express. Our hope is that we will find a Kuiper Belt object or objects close enough that a spacecraft flyby will be possible. If we find a suitable object, the science yield of Pluto Express will be substantially enhanced. The density of objects in the Kuiper Belt is such that we are reasonably likely to find an object close enough to the flight path that on-board gas thrusters can effect a close encounter.

Construct User Guide

DTIC Science & Technology

2012-11-01

interactions in construct: An empirical validation using calibrated grounding. In 2007 BRIMS Conference Proceedings, Norfolk, VA. Simon, H. A...by the path name. Users should ensure that if they have opened any output files (e.g., in Excel to view the files), they should either close the file...stringvars to delimit string variables. Common Gotchas If Construct is unable to open an input file, it will exit and close. There are times when an

path integral approach to closed form pricing formulas in the Heston framework.

NASA Astrophysics Data System (ADS)

Lemmens, Damiaan; Wouters, Michiel; Tempere, Jacques; Foulon, Sven

2008-03-01

We present a path integral approach for finding closed form formulas for option prices in the framework of the Heston model. The first model for determining option prices was the Black-Scholes model, which assumed that the logreturn followed a Wiener process with a given drift and constant volatility. To provide a realistic description of the market, the Black-Scholes results must be extended to include stochastic volatility. This is achieved by the Heston model, which assumes that the volatility follows a mean reverting square root process. Current applications of the Heston model are hampered by the unavailability of fast numerical methods, due to a lack of closed-form formulae. Therefore the search for closed form solutions is an essential step before the qualitatively better stochastic volatility models will be used in practice. To attain this goal we outline a simplified path integral approach yielding straightforward results for vanilla Heston options with correlation. Extensions to barrier options and other path-dependent option are discussed, and the new derivation is compared to existing results obtained from alternative path-integral approaches (Dragulescu, Kleinert).

Practical method and device for enhancing pulse contrast ratio for lasers and electron accelerators

DOEpatents

Zhang, Shukui; Wilson, Guy

2014-09-23

An apparatus and method for enhancing pulse contrast ratios for drive lasers and electron accelerators. The invention comprises a mechanical dual-shutter system wherein the shutters are placed sequentially in series in a laser beam path. Each shutter of the dual shutter system has an individually operated trigger for opening and closing the shutter. As the triggers are operated individually, the delay between opening and closing first shutter and opening and closing the second shutter is variable providing for variable differential time windows and enhancement of pulse contrast ratio.

Swimming path statistics of an active Brownian particle with time-dependent self-propulsion

NASA Astrophysics Data System (ADS)

Babel, S.; ten Hagen, B.; Löwen, H.

2014-02-01

Typically, in the description of active Brownian particles, a constant effective propulsion force is assumed, which is then subjected to fluctuations in orientation and translation, leading to a persistent random walk with an enlarged long-time diffusion coefficient. Here, we generalize previous results for the swimming path statistics to a time-dependent, and thus in many situations more realistic, propulsion which is a prescribed input. We analytically calculate both the noise-free and the noise-averaged trajectories for time-periodic propulsion under the action of an additional torque. In the deterministic case, such an oscillatory microswimmer moves on closed paths that can be much more complicated than the commonly observed straight lines and circles. When exposed to random fluctuations, the mean trajectories turn out to be self-similar curves which bear the characteristics of their noise-free counterparts. Furthermore, we consider a propulsion force which scales in time t as ∝tα (with α = 0,1,2, …) and analyze the resulting superdiffusive behavior. Our predictions are verifiable for diffusiophoretic artificial microswimmers with prescribed propulsion protocols.

Arrival Time Tracking of Partially Resolved Acoustic Rays with Application to Ocean Acoustic Tomography

DTIC Science & Technology

1991-03-01

ocean acoustic tomography. A straightforward method of arrival time estimation, based on locating the maximum value of an interpolated arrival, was...used with limited success for analysis of data from the December 1988 Monterey Bay Tomography Experiment. Close examination of the data revealed multiple...estimation of arrival times along an ocean acoustic ray path is an important component of ocean acoustic tomography. A straightforward method of arrival time

Resolving multiple propagation paths in time of flight range cameras using direct and global separation methods

NASA Astrophysics Data System (ADS)

Whyte, Refael; Streeter, Lee; Cree, Michael J.; Dorrington, Adrian A.

2015-11-01

Time of flight (ToF) range cameras illuminate the scene with an amplitude-modulated continuous wave light source and measure the returning modulation envelopes: phase and amplitude. The phase change of the modulation envelope encodes the distance travelled. This technology suffers from measurement errors caused by multiple propagation paths from the light source to the receiving pixel. The multiple paths can be represented as the summation of a direct return, which is the return from the shortest path length, and a global return, which includes all other returns. We develop the use of a sinusoidal pattern from which a closed form solution for the direct and global returns can be computed in nine frames with the constraint that the global return is a spatially lower frequency than the illuminated pattern. In a demonstration on a scene constructed to have strong multipath interference, we find the direct return is not significantly different from the ground truth in 33/136 pixels tested; where for the full-field measurement, it is significantly different for every pixel tested. The variance in the estimated direct phase and amplitude increases by a factor of eight compared with the standard time of flight range camera technique.

An Integrated Architecture for On-Board Aircraft Engine Performance Trend Monitoring and Gas Path Fault Diagnostics

NASA Technical Reports Server (NTRS)

Simon, Donald L.

2010-01-01

Aircraft engine performance trend monitoring and gas path fault diagnostics are closely related technologies that assist operators in managing the health of their gas turbine engine assets. Trend monitoring is the process of monitoring the gradual performance change that an aircraft engine will naturally incur over time due to turbomachinery deterioration, while gas path diagnostics is the process of detecting and isolating the occurrence of any faults impacting engine flow-path performance. Today, performance trend monitoring and gas path fault diagnostic functions are performed by a combination of on-board and off-board strategies. On-board engine control computers contain logic that monitors for anomalous engine operation in real-time. Off-board ground stations are used to conduct fleet-wide engine trend monitoring and fault diagnostics based on data collected from each engine each flight. Continuing advances in avionics are enabling the migration of portions of the ground-based functionality on-board, giving rise to more sophisticated on-board engine health management capabilities. This paper reviews the conventional engine performance trend monitoring and gas path fault diagnostic architecture commonly applied today, and presents a proposed enhanced on-board architecture for future applications. The enhanced architecture gains real-time access to an expanded quantity of engine parameters, and provides advanced on-board model-based estimation capabilities. The benefits of the enhanced architecture include the real-time continuous monitoring of engine health, the early diagnosis of fault conditions, and the estimation of unmeasured engine performance parameters. A future vision to advance the enhanced architecture is also presented and discussed

Kinematics, controls, and path planning results for a redundant manipulator

NASA Technical Reports Server (NTRS)

Gretz, Bruce; Tilley, Scott W.

1989-01-01

The inverse kinematics solution, a modal position control algorithm, and path planning results for a 7 degree of freedom manipulator are presented. The redundant arm consists of two links with shoulder and elbow joints and a spherical wrist. The inverse kinematics problem for tip position is solved and the redundant joint is identified. It is also shown that a locus of tip positions exists in which there are kinematic limitations on self-motion. A computationally simple modal position control algorithm has been developed which guarantees a nearly constant closed-loop dynamic response throughout the workspace. If all closed-loop poles are assigned to the same location, the algorithm can be implemented with very little computation. To further reduce the required computation, the modal gains are updated only at discrete time intervals. Criteria are developed for the frequency of these updates. For commanding manipulator movements, a 5th-order spline which minimizes jerk provides a smooth tip-space path. Schemes for deriving a corresponding joint-space trajectory are discussed. Modifying the trajectory to avoid joint torque saturation when a tip payload is added is also considered. Simulation results are presented.

Vehicle path-planning in three dimensions using optics analogs for optimizing visibility and energy cost

NASA Technical Reports Server (NTRS)

Rowe, Neil C.; Lewis, David H.

1989-01-01

Path planning is an important issue for space robotics. Finding safe and energy-efficient paths in the presence of obstacles and other constraints can be complex although important. High-level (large-scale) path planning for robotic vehicles was investigated in three-dimensional space with obstacles, accounting for: (1) energy costs proportional to path length; (2) turn costs where paths change trajectory abruptly; and (3) safety costs for the danger associated with traversing a particular path due to visibility or invisibility from a fixed set of observers. Paths optimal with respect to these cost factors are found. Autonomous or semi-autonomous vehicles were considered operating either in a space environment around satellites and space platforms, or aircraft, spacecraft, or smart missiles operating just above lunar and planetary surfaces. One class of applications concerns minimizing detection, as for example determining the best way to make complex modifications to a satellite without being observed by hostile sensors; another example is verifying there are no paths (holes) through a space defense system. Another class of applications concerns maximizing detection, as finding a good trajectory between mountain ranges of a planet while staying reasonably close to the surface, or finding paths for a flight between two locations that maximize the average number of triangulation points available at any time along the path.

Turbulence effects in a horizontal propagation path close to ground: implications for optics detection

NASA Astrophysics Data System (ADS)

Sjöqvist, Lars; Allard, Lars; Gustafsson, Ove; Henriksson, Markus; Pettersson, Magnus

2011-11-01

Atmospheric turbulence effects close to ground may affect the performance of laser based systems severely. The variations in the refractive index along the propagation path cause effects such as beam wander, intensity fluctuations (scintillations) and beam broadening. Typical geometries of interest for optics detection include nearly horizontal propagation paths close to the ground and up to kilometre distance to the target. The scintillations and beam wander affect the performance in terms of detection probability and false alarm rate. Of interest is to study the influence of turbulence in optics detection applications. In a field trial atmospheric turbulence effects along a 1 kilometre horizontal propagation path were studied using a diode laser with a rectangular beam profile operating at 0.8 micrometer wavelength. Single-path beam characteristics were registered and analysed using photodetectors arranged in horizontal and vertical directions. The turbulence strength along the path was determined using a scintillometer and single-point ultrasonic anemometers. Strong scintillation effects were observed as a function of the turbulence strength and amplitude characteristics were fitted to model distributions. In addition to the single-path analysis double-path measurements were carried out on different targets. Experimental results are compared with existing theoretical turbulence laser beam propagation models. The results show that influence from scintillations needs to be considered when predicting performance in optics detection applications.

Design of a feedback-feedforward steering controller for accurate path tracking and stability at the limits of handling

NASA Astrophysics Data System (ADS)

Kapania, Nitin R.; Gerdes, J. Christian

2015-12-01

This paper presents a feedback-feedforward steering controller that simultaneously maintains vehicle stability at the limits of handling while minimising lateral path tracking deviation. The design begins by considering the performance of a baseline controller with a lookahead feedback scheme and a feedforward algorithm based on a nonlinear vehicle handling diagram. While this initial design exhibits desirable stability properties at the limits of handling, the steady-state path deviation increases significantly at highway speeds. Results from both linear and nonlinear analyses indicate that lateral path tracking deviations are minimised when vehicle sideslip is held tangent to the desired path at all times. Analytical results show that directly incorporating this sideslip tangency condition into the steering feedback dramatically improves lateral path tracking, but at the expense of poor closed-loop stability margins. However, incorporating the desired sideslip behaviour into the feedforward loop creates a robust steering controller capable of accurate path tracking and oversteer correction at the physical limits of tyre friction. Experimental data collected from an Audi TTS test vehicle driving at the handling limits on a full length race circuit demonstrates the improved performance of the final controller design.

Dynamical characterization of inactivation path in voltage-gated Na+ ion channel by non-equilibrium response spectroscopy

PubMed Central

Pal, Krishnendu; Gangopadhyay, Gautam

2016-01-01

ABSTRACT Inactivation path of voltage gated sodium channel has been studied here under various voltage protocols as it is the main governing factor for the periodic occurrence and shape of the action potential. These voltage protocols actually serve as non-equilibrium response spectroscopic tools to study the ion channel in non-equilibrium environment. In contrast to a lot of effort in finding the crystal structure based molecular mechanism of closed-state(CSI) and open-state inactivation(OSI); here our approach is to understand the dynamical characterization of inactivation. The kinetic flux as well as energetic contribution of the closed and open- state inactivation path is compared here for voltage protocols, namely constant, pulsed and oscillating. The non-equilibrium thermodynamic quantities used in response to these voltage protocols serve as improved characterization tools for theoretical understanding which not only agrees with the previously known kinetic measurements but also predict the energetically optimum processes to sustain the auto-regulatory mechanism of action potential and the consequent inactivation steps needed. The time dependent voltage pattern governs the population of the conformational states which when couple with characteristic rate parameters, the CSI and OSI selectivity arise dynamically to control the inactivation path. Using constant, pulsed and continuous oscillating voltage protocols we have shown that during depolarization the OSI path is more favored path of inactivation however, in the hyper-polarized situation the CSI is favored. It is also shown that the re-factorisation of inactivated sodium channel to resting state occurs via CSI path. Here we have shown how the subtle energetic and entropic cost due to the change in the depolarization magnitude determines the optimum path of inactivation. It is shown that an efficient CSI and OSI dynamical profile in principle can characterize the open-state drug blocking phenomena. PMID:27367642

Bulimic symptoms and the social withdrawal syndrome.

PubMed

Rotenberg, Ken J; Bharathi, Carla; Davies, Helen; Finch, Tom

2013-08-01

One hundred and thirty-seven undergraduates (81 females; mean age = 21 years-10 months) completed the Bulimic SEDS subscale and standardized measures of trust beliefs in close others (mother, father, and friend), disclosure to them, and loneliness. Structural Equation Modelling yielded: (1) a negative path between Bulimic Symptoms and trust beliefs, (2) a positive path between trust beliefs and disclosure, (3) a negative path between trust beliefs and loneliness, and (4) a negative path between disclosure and loneliness. As expected, trust beliefs statistically mediated the relations between Bulimic Symptoms and both disclosure and loneliness and disclosure statistically mediated the relation between trust beliefs and loneliness. The findings supported the conclusion that individuals with bulimia nervosa are prone to the social withdrawal syndrome comprising a coherent and integrated pattern of low trust beliefs in close others, low disclosure to close others, and high loneliness. Copyright © 2013 Elsevier Ltd. All rights reserved.

The Rupture Characteristic of 1999 Izmit Sequence Using IRIS Data

NASA Astrophysics Data System (ADS)

Konca, A. O.; Helmberger, D. V.; Ji, C.; Tan, Y.

2003-12-01

The standard source studies use teleseismic data (30° to 90° ) to analyze earthquakes. Therefore, only a limited portion of the focal sphere is involved in source determinations. Furthermore, the locations and origin times of events remain incompatible with local determinations. Here, we attempt to resolve such issues by using IRIS data at all distances, leading to more accurate and detailed rupture properties and accurate relative locations. The 1999 Izmit earthquake sequence is chosen to test our method. The challenge of using data outside the conventional teleseismic distance range is that the arrival times and waveforms are affected more by the Earth structure. We overcome this difficulty by calibrating the path effects for the mainshock using the simpler aftershocks. Therefore, it is crucial to determine the source parameters of the aftershock. We constructed a Green's function library from a regionalized 1-D model and performed a grid search to establish the depth and fault parameters based on waveform matching for the Pnl waves between the synthetics and data, allowing the synthetics in each station to shift separately to account for the path effect. Our results show that the earthquake depth was around 7 km, rather than 19 km from local observatory (Kandilli) and 15 km from the Harvard's CMT solution. The best focal mechanism has a strike of 263° , a dip of 65° , and a rake of 180° , which is very close to the Harvard's CMT solution. The waveform fits of this aftershock is then used as a criterion to select useful source-station paths. A path with a cross-correlation value above 90% between data and synthetics is defined as a "good path" and can be used for studying the Izmit and Duzce earthquakes. We find that the stations in Central Europe and some of the Greek Islands are "good paths", while the stations in Northeast Africa and Italy cannot be used. The time shifts that give the best cross-correlation values are used to calibrate the picks of the Izmit and Duzce events. We realize that this is a very objective way to pick arrival times. However, our preliminary inversions using teleseismic data for Duzce and Izmit events show that handpicked P and S arrival times of the same station from two very close events are not always well correlated. Obviously, how we pick the arrival time governs the rupture pattern and rupture velocity. Therefore, our methodology brings a more objective approach to pick the travel times. To the end, we will invert for the source history of the Duzce and Izmit earthquakes with the regional data and compare with the inversion result using teleseismic data. Moreover, predictions of the teleseismic data, using the solution from the inversion using regional phases will be presented.

Developmental dysplasia of the hip: A computational biomechanical model of the path of least energy for closed reduction.

PubMed

Zwawi, Mohammed A; Moslehy, Faissal A; Rose, Christopher; Huayamave, Victor; Kassab, Alain J; Divo, Eduardo; Jones, Brendan J; Price, Charles T

2017-08-01

This study utilized a computational biomechanical model and applied the least energy path principle to investigate two pathways for closed reduction of high grade infantile hip dislocation. The principle of least energy when applied to moving the femoral head from an initial to a final position considers all possible paths that connect them and identifies the path of least resistance. Clinical reports of severe hip dysplasia have concluded that reduction of the femoral head into the acetabulum may occur by a direct pathway over the posterior rim of the acetabulum when using the Pavlik harness, or by an indirect pathway with reduction through the acetabular notch when using the modified Hoffman-Daimler method. This computational study also compared the energy requirements for both pathways. The anatomical and muscular aspects of the model were derived using a combination of MRI and OpenSim data. Results of this study indicate that the path of least energy closely approximates the indirect pathway of the modified Hoffman-Daimler method. The direct pathway over the posterior rim of the acetabulum required more energy for reduction. This biomechanical analysis confirms the clinical observations of the two pathways for closed reduction of severe hip dysplasia. The path of least energy closely approximated the modified Hoffman-Daimler method. Further study of the modified Hoffman-Daimler method for reduction of severe hip dysplasia may be warranted based on this computational biomechanical analysis. © 2016 The Authors. Journal of Orthopaedic Research Published by Wiley Periodicals, Inc. on behalf of Orthopaedic Research Society. J Orthop Res 35:1799-1805, 2017. © 2016 The Authors. Journal of Orthopaedic Research Published by Wiley Periodicals, Inc. on behalf of Orthopaedic Research Society.

Lower Limb Interjoint Postural Coordination One Year after First-Time Lateral Ankle Sprain.

PubMed

Doherty, Cailbhe; Bleakley, Chris; Hertel, Jay; Caulfield, Brian; Ryan, John; Sweeney, Kevin; Patterson, Matthew R; Delahunt, Eamonn

2015-11-01

Longitudinal analyses of participants with a history of lateral ankle sprain are lacking. This investigation combined measures of lower limb interjoint coordination and stabilometry to evaluate static unipedal stance with the eyes open (condition 1) and closed (condition 2) in a group of participants with chronic ankle instability (CAI) compared to lateral ankle sprain "copers" (both recruited 12 months after sustaining an acute first-time lateral ankle sprain) and a group of noninjured controls. Twenty-eight participants with CAI, 42 lateral ankle sprain "copers," and 20 noninjured controls completed three 20-s single-limb stance trials in conditions 1 and 2. An adjusted coefficient of multiple determination statistic was used to compare stance limb three-dimensional kinematic data for similarity to establish patterns of interjoint coordination. The fractal dimension of the stance limb center of pressure path was also calculated. Between-group analyses revealed that participants with CAI displayed notable increases in ankle-hip linked coordination compared with both lateral ankle sprain "copers" (-0.52 (1.05) vs 0.28 (0.9), P = 0.007) and controls (-0.52 (1.05) vs 0.63 (0.64), P = 0.006) in condition 1 and compared with controls only (0.62 (1.92) vs 0.1 (1.0) P = 0.002) in condition 2. Participants with CAI also exhibited a decrease in the fractal dimension of the center-of-pressure path during condition 2 compared with both controls and lateral ankle sprain "copers." Participants with CAI present with a hip-dominant strategy of eyes-open and eyes-closed static unipedal stance. This coincided with reduced complexity of the stance limb center of pressure path in the eyes-closed condition.

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

Wang, Yujie; Gong, Sha; Wang, Zhen

The thermodynamic and kinetic parameters of an RNA base pair were obtained through a long-time molecular dynamics simulation of the opening-closing switch process of the base pair near its melting temperature. The thermodynamic parameters were in good agreement with the nearest-neighbor model. The opening rates showed strong temperature dependence, however, the closing rates showed only weak temperature dependence. The transition path time was weakly temperature dependent and was insensitive to the energy barrier. The diffusion constant exhibited super-Arrhenius behavior. The free energy barrier of breaking a single base stack results from the enthalpy increase, ΔH, caused by the disruption ofmore » hydrogen bonding and base-stacking interactions. The free energy barrier of base pair closing comes from the unfavorable entropy loss, ΔS, caused by the restriction of torsional angles. These results suggest that a one-dimensional free energy surface is sufficient to accurately describe the dynamics of base pair opening and closing, and the dynamics are Brownian.« less

On the spatial relationship between lightning discharges and propagation paths of perturbed subionospheric VLF/LF signals

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

Wai-Yeung Yip; Inan, U.S.; Orville, R.E.

1991-01-01

A study has been made of the spatial relationship between propagation paths of subionospheric VLF/LF signals exhibiting sudden amplitude perturbations (Trimpi events) and time correlated cloud-to-ground lightning flashes. On each of the 4 days examined the storm centers were located close to the signal path from the NAU transmitter (28.5-kHz) in Puerto Rico to Stanford (SU) and were at large distances from the propagation path of the 48.5-kHz transmitter signal from Nebraska to SU. Nevertheless, no Trimpi events were observed on the former path, while many were seen on the latter. Furthermore, the detected Trimpi perturbations of the 48.5-kHz signalmore » received at Stanford were found to be associated with the lightning activity in the distant storm centers. Since the NAU-SU path lies entirely at L < 2 and the 48.5-SU path is located mostly at 2< L <3, the L dependent magnetospheric conditions which determine the level of lightning-induced electron precipitation are different along the two paths. Thus, the authors postulate that the observed difference in Trimpi occurence on the two paths was due to the different magnetospheric conditions. Hence the occurence of Trimpi events over the geographical region corresponding to L <3 may be more dominantly controlled by magnetospheric conditions than the source lightning distribution.« less

Open-path, closed-path and reconstructed aerosol extinction at a rural site.

PubMed

Gordon, Timothy D; Prenni, Anthony J; Renfro, James R; McClure, Ethan; Hicks, Bill; Onasch, Timothy B; Freedman, Andrew; McMeeking, Gavin R; Chen, Ping

2018-04-09

The Handix Scientific Open-Path Cavity Ringdown Spectrometer (OPCRDS) was deployed during summer 2016 in Great Smoky Mountains National Park (GRSM). Extinction coefficients from the relatively new OPCRDS and from a more well-established extinction instrument agreed to within 7%. Aerosol hygroscopic growth (f(RH)) was calculated from the ratio of ambient extinction measured by the OPCRDS to dry extinction measured by a closed-path extinction monitor (Aerodyne's Cavity Attenuated Phase Shift Particulate Matter Extinction Monitor, CAPS PMex). Derived hygroscopicity (RH < 95%) from this campaign agreed with data from 1995 at the same site and time of year, which is noteworthy given the decreasing trend for organics and sulfate in the eastern U.S. However, maximum f(RH) values in 1995 were less than half as large as those recorded in 2016-possibly due to nephelometer truncation losses in 1995. Two hygroscopicity parameterizations were investigated using high time resolution OPCRDS+CAPS PMex data, and the K ext model was more accurate than the γ model. Data from the two ambient optical instruments, the OPCRDS and the open-path nephelometer, generally agreed; however, significant discrepancies between ambient scattering and extinction were observed, apparently driven by a combination of hygroscopic growth effects, which tend to increase nephelometer truncation losses and decrease sensitivity to the wavelength difference between the two instruments as a function of particle size. There was not a statistically significant difference in the mean reconstructed extinction values obtained from the original and the revised IMPROVE (Interagency Monitoring of Protected Visual Environments) equations. On average IMPROVE reconstructed extinction was ~25% lower than extinction measured by the OPCRDS, which suggests that the IMPROVE equations and 24-hr aerosol data are moderately successful in estimating current haze levels at GRSM. However, this conclusion is limited by the coarse temporal resolution and the low dynamic range of the IMPROVE reconstructed extinction.

An Optimization Principle for Deriving Nonequilibrium Statistical Models of Hamiltonian Dynamics

NASA Astrophysics Data System (ADS)

Turkington, Bruce

2013-08-01

A general method for deriving closed reduced models of Hamiltonian dynamical systems is developed using techniques from optimization and statistical estimation. Given a vector of resolved variables, selected to describe the macroscopic state of the system, a family of quasi-equilibrium probability densities on phase space corresponding to the resolved variables is employed as a statistical model, and the evolution of the mean resolved vector is estimated by optimizing over paths of these densities. Specifically, a cost function is constructed to quantify the lack-of-fit to the microscopic dynamics of any feasible path of densities from the statistical model; it is an ensemble-averaged, weighted, squared-norm of the residual that results from submitting the path of densities to the Liouville equation. The path that minimizes the time integral of the cost function determines the best-fit evolution of the mean resolved vector. The closed reduced equations satisfied by the optimal path are derived by Hamilton-Jacobi theory. When expressed in terms of the macroscopic variables, these equations have the generic structure of governing equations for nonequilibrium thermodynamics. In particular, the value function for the optimization principle coincides with the dissipation potential that defines the relation between thermodynamic forces and fluxes. The adjustable closure parameters in the best-fit reduced equations depend explicitly on the arbitrary weights that enter into the lack-of-fit cost function. Two particular model reductions are outlined to illustrate the general method. In each example the set of weights in the optimization principle contracts into a single effective closure parameter.

Multi-chord fiber-coupled interferometer with a long coherence length laser

NASA Astrophysics Data System (ADS)

Merritt, Elizabeth C.; Lynn, Alan G.; Gilmore, Mark A.; Hsu, Scott C.

2012-03-01

This paper describes a 561 nm laser heterodyne interferometer that provides time-resolved measurements of line-integrated plasma electron density within the range of 1015-1018 cm-2. Such plasmas are produced by railguns on the plasma liner experiment, which aims to produce μs-, cm-, and Mbar-scale plasmas through the merging of 30 plasma jets in a spherically convergent geometry. A long coherence length, 320 mW laser allows for a strong, sub-fringe phase-shift signal without the need for closely matched probe and reference path lengths. Thus, only one reference path is required for all eight probe paths, and an individual probe chord can be altered without altering the reference or other probe path lengths. Fiber-optic decoupling of the probe chord optics on the vacuum chamber from the rest of the system allows the probe paths to be easily altered to focus on different spatial regions of the plasma. We demonstrate that sub-fringe resolution capability allows the interferometer to operate down to line-integrated densities of the order of 5 × 1015 cm-2.

Stochastic Evolutionary Algorithms for Planning Robot Paths

NASA Technical Reports Server (NTRS)

Fink, Wolfgang; Aghazarian, Hrand; Huntsberger, Terrance; Terrile, Richard

2006-01-01

A computer program implements stochastic evolutionary algorithms for planning and optimizing collision-free paths for robots and their jointed limbs. Stochastic evolutionary algorithms can be made to produce acceptably close approximations to exact, optimal solutions for path-planning problems while often demanding much less computation than do exhaustive-search and deterministic inverse-kinematics algorithms that have been used previously for this purpose. Hence, the present software is better suited for application aboard robots having limited computing capabilities (see figure). The stochastic aspect lies in the use of simulated annealing to (1) prevent trapping of an optimization algorithm in local minima of an energy-like error measure by which the fitness of a trial solution is evaluated while (2) ensuring that the entire multidimensional configuration and parameter space of the path-planning problem is sampled efficiently with respect to both robot joint angles and computation time. Simulated annealing is an established technique for avoiding local minima in multidimensional optimization problems, but has not, until now, been applied to planning collision-free robot paths by use of low-power computers.

Direct Position Determination of Unknown Signals in the Presence of Multipath Propagation

PubMed Central

Yu, Hongyi

2018-01-01

A novel geolocation architecture, termed “Multiple Transponders and Multiple Receivers for Multiple Emitters Positioning System (MTRE)” is proposed in this paper. Existing Direct Position Determination (DPD) methods take advantage of a rather simple channel assumption (line of sight channels with complex path attenuations) and a simplified MUltiple SIgnal Classification (MUSIC) algorithm cost function to avoid the high dimension searching. We point out that the simplified assumption and cost function reduce the positioning accuracy because of the singularity of the array manifold in a multi-path environment. We present a DPD model for unknown signals in the presence of Multi-path Propagation (MP-DPD) in this paper. MP-DPD adds non-negative real path attenuation constraints to avoid the mistake caused by the singularity of the array manifold. The Multi-path Propagation MUSIC (MP-MUSIC) method and the Active Set Algorithm (ASA) are designed to reduce the dimension of searching. A Multi-path Propagation Maximum Likelihood (MP-ML) method is proposed in addition to overcome the limitation of MP-MUSIC in the sense of a time-sensitive application. An iterative algorithm and an approach of initial value setting are given to make the MP-ML time consumption acceptable. Numerical results validate the performances improvement of MP-MUSIC and MP-ML. A closed form of the Cramér–Rao Lower Bound (CRLB) is derived as a benchmark to evaluate the performances of MP-MUSIC and MP-ML. PMID:29562601

Direct Position Determination of Unknown Signals in the Presence of Multipath Propagation.

PubMed

Du, Jianping; Wang, Ding; Yu, Wanting; Yu, Hongyi

2018-03-17

A novel geolocation architecture, termed "Multiple Transponders and Multiple Receivers for Multiple Emitters Positioning System (MTRE)" is proposed in this paper. Existing Direct Position Determination (DPD) methods take advantage of a rather simple channel assumption (line of sight channels with complex path attenuations) and a simplified MUltiple SIgnal Classification (MUSIC) algorithm cost function to avoid the high dimension searching. We point out that the simplified assumption and cost function reduce the positioning accuracy because of the singularity of the array manifold in a multi-path environment. We present a DPD model for unknown signals in the presence of Multi-path Propagation (MP-DPD) in this paper. MP-DPD adds non-negative real path attenuation constraints to avoid the mistake caused by the singularity of the array manifold. The Multi-path Propagation MUSIC (MP-MUSIC) method and the Active Set Algorithm (ASA) are designed to reduce the dimension of searching. A Multi-path Propagation Maximum Likelihood (MP-ML) method is proposed in addition to overcome the limitation of MP-MUSIC in the sense of a time-sensitive application. An iterative algorithm and an approach of initial value setting are given to make the MP-ML time consumption acceptable. Numerical results validate the performances improvement of MP-MUSIC and MP-ML. A closed form of the Cramér-Rao Lower Bound (CRLB) is derived as a benchmark to evaluate the performances of MP-MUSIC and MP-ML.

Paving the Way to the Future? Education and Young Europeans' Paths to Work and Independence

ERIC Educational Resources Information Center

Lundahl, Lisbeth

2011-01-01

This article discusses young people's transitions from school to work at a time when educational systems have become more closely connected to the economy than ever before. The serious situation of high unemployment, unstable employment conditions and poverty among young people and young adults in Europe is highlighted. Using Sweden as an…

Dissolution Dynamic Nuclear Polarization capability study with fluid path

NASA Astrophysics Data System (ADS)

Malinowski, Ronja M.; Lipsø, Kasper W.; Lerche, Mathilde H.; Ardenkjær-Larsen, Jan H.

2016-11-01

Signal enhancement by hyperpolarization is a way of overcoming the low sensitivity in magnetic resonance; MRI in particular. One of the most well-known methods, dissolution Dynamic Nuclear Polarization, has been used clinically in cancer patients. One way of ensuring a low bioburden of the hyperpolarized product is by use of a closed fluid path that constitutes a barrier to contamination. The fluid path can be filled with the pharmaceuticals, i.e. imaging agent and solvents, in a clean room, and then stored or immediately used at the polarizer. In this study, we present a method of filling the fluid path that allows it to be reused. The filling method has been investigated in terms of reproducibility at two extrema, high dose for patient use and low dose for rodent studies, using [1-13C]pyruvate as example. We demonstrate that the filling method allows high reproducibility of six quality control parameters with standard deviations 3-10 times smaller than the acceptance criteria intervals in clinical studies.

An experimental study of transmission, reflection and scattering of sound in a free-jet flight simulation facility and comparison with theory

NASA Technical Reports Server (NTRS)

Ahuja, K. K.; Tester, B. J.; Tanna, H. K.; Searle, N.

1977-01-01

Acoustic time delays across a free-jet shear layer are measured and compared with predictions based on (1) ray paths refracted abruptly across a cylindrical vortex sheet and (2) ray paths traced through a more realistic diverging flow model. The close agreement between measurement and theory confirms that Snell's law provides an accurate prediction of wavefront refraction or angle changes across a diverging shear layer. Microphones are placed on calculated ray paths to determine the coherent transmission and internal reflection characteristics of the shear layer and also the scattering of sound by the shear-layer turbulence. The transmission data essentially verify the proposed, theoretical calibration factor which forms part of a computational procedure that is being developed to convert model jet data from a free-jet facility to inflight conditions.

Non-linear control of a hydraulic piezo-valve using a generalised Prandtl-Ishlinskii hysteresis model

NASA Astrophysics Data System (ADS)

Stefanski, Frederik; Minorowicz, Bartosz; Persson, Johan; Plummer, Andrew; Bowen, Chris

2017-01-01

The potential to actuate proportional flow control valves using piezoelectric ceramics or other smart materials has been investigated for a number of years. Although performance advantages compared to electromagnetic actuation have been demonstrated, a major obstacle has proven to be ferroelectric hysteresis, which is typically 20% for a piezoelectric actuator. In this paper, a detailed study of valve control methods incorporating hysteresis compensation is made for the first time. Experimental results are obtained from a novel spool valve actuated by a multi-layer piezoelectric ring bender. A generalised Prandtl-Ishlinskii model, fitted to experimental training data from the prototype valve, is used to model hysteresis empirically. This form of model is analytically invertible and is used to compensate for hysteresis in the prototype valve both open loop, and in several configurations of closed loop real time control system. The closed loop control configurations use PID (Proportional Integral Derivative) control with either the inverse hysteresis model in the forward path or in a command feedforward path. Performance is compared to both open and closed loop control without hysteresis compensation via step and frequency response results. Results show a significant improvement in accuracy and dynamic performance using hysteresis compensation in open loop, but where valve position feedback is available for closed loop control the improvements are smaller, and so conventional PID control may well be sufficient. It is concluded that the ability to combine state-of-the-art multi-layer piezoelectric bending actuators with either sophisticated hysteresis compensation or closed loop control provides a route for the creation of a new generation of high performance piezoelectric valves.

Direct multiple path magnetospheric propagation - A fundamental property of nonducted VLF waves

NASA Technical Reports Server (NTRS)

Sonwalkar, V. S.; Bell, T. F.; Helliwell, R. A.; Inan, U. S.

1984-01-01

An elongation of 20-200 ms, attributed to closely spaced multiple propagation paths between the satellite and the ground, is noted in well defined pulses observed by the ISEE 1 satellite in nonducted whistler mode signals from the Siple Station VLF transmitter. Electric field measurements show a 2 to 10 dB amplitude variation in the observed amplitude fading pattern which is also consistent with direct multiple path propagation. The results obtained for two cases, one outside and one inside the plasmapause, establish that the direct signals transmitted from the ground arrive almost simultaneously at any point in the magnetosphere along two or more closely spaced direct ray paths. It is also shown that multiple paths can be explained by assuming field-aligned irregularities, and the implications of these results for nonducted wave-particle interaction in the magnetosphere are discussed. For reasonable parameters of nonducted, multiple path propagation, a cyclotron-resonant electron will experience a wave Doppler broadening of a few tens to a few hundreds of Hz.

Data-driven Modeling of the Solar Corona by a New Three-dimensional Path-conservative Osher-Solomon MHD Model

NASA Astrophysics Data System (ADS)

Feng, Xueshang; Li, Caixia; Xiang, Changqing; Zhang, Man; Li, HuiChao; Wei, Fengsi

2017-11-01

A second-order path-conservative scheme with a Godunov-type finite-volume method has been implemented to advance the equations of single-fluid solar wind plasma magnetohydrodynamics (MHD) in time. This code operates on the six-component composite grid system in three-dimensional spherical coordinates with hexahedral cells of quadrilateral frustum type. The generalized Osher-Solomon Riemann solver is employed based on a numerical integration of the path-dependent dissipation matrix. For simplicity, the straight line segment path is used, and the path integral is evaluated in a fully numerical way by a high-order numerical Gauss-Legendre quadrature. Besides its very close similarity to Godunov type, the resulting scheme retains the attractive features of the original solver: it is nonlinear, free of entropy-fix, differentiable, and complete, in that each characteristic field results in a different numerical viscosity, due to the full use of the MHD eigenstructure. By using a minmod limiter for spatial oscillation control, the path-conservative scheme is realized for the generalized Lagrange multiplier and the extended generalized Lagrange multiplier formulation of solar wind MHD systems. This new model that is second order in space and time is written in the FORTRAN language with Message Passing Interface parallelization and validated in modeling the time-dependent large-scale structure of the solar corona, driven continuously by Global Oscillation Network Group data. To demonstrate the suitability of our code for the simulation of solar wind, we present selected results from 2009 October 9 to 2009 December 29 show its capability of producing a structured solar corona in agreement with solar coronal observations.

Eddy covariance measurements with a new fast-response, enclosed-path analyzer: Spectral characteristics and cross-system comparisons

Treesearch

K. Novick; J. Walker; W.S. Chan; A. Schmidt; C. Sobek; J.M. Vose

2013-01-01

A new class of enclosed path gas analyzers suitable for eddy covariance applications combines the advantages of traditional closed-path systems (small density corrections, good performance in poor weather) and open-path systems (good spectral response, low power requirements), and permits estimates of instantaneous gas mixing ratio. Here, the extent to which these...

HARPA: A versatile three-dimensional Hamiltonian ray-tracing program for acoustic waves in the atmosphere above irregular terrain

NASA Astrophysics Data System (ADS)

Jones, R. M.; Riley, J. P.; Georges, T. M.

1986-08-01

The modular FORTRAN 77 computer program traces the three-dimensional paths of acoustic rays through continuous model atmospheres by numerically integrating Hamilton's equations (a differential expression of Fermat's principle). The user specifies an atmospheric model by writing closed-form formulas for its three-dimensional wind and temperature (or sound speed) distribution, and by defining the height of the reflecting terrain vs. geographic latitude and longitude. Some general-purpose models are provided, or users can readily design their own. In addition to computing the geometry of each raypath, HARPA can calculate pulse travel time, phase time, Doppler shift (if the medium varies in time), absorption, and geometrical path length. The program prints a step-by-step account of a ray's progress. The 410-page documentation describes the ray-tracing equations and the structure of the program, and provides complete instructions, illustrated by a sample case.

Path integral approach to closed-form option pricing formulas with applications to stochastic volatility and interest rate models

NASA Astrophysics Data System (ADS)

Lemmens, D.; Wouters, M.; Tempere, J.; Foulon, S.

2008-07-01

We present a path integral method to derive closed-form solutions for option prices in a stochastic volatility model. The method is explained in detail for the pricing of a plain vanilla option. The flexibility of our approach is demonstrated by extending the realm of closed-form option price formulas to the case where both the volatility and interest rates are stochastic. This flexibility is promising for the treatment of exotic options. Our analytical formulas are tested with numerical Monte Carlo simulations.

The mean free path of hydrogen ionizing photons during the epoch of reionization

NASA Astrophysics Data System (ADS)

Rahmati, Alireza; Schaye, Joop

2018-05-01

We use the Aurora radiation-hydrodynamical simulations to study the mean free path (MFP) for hydrogen ionizing photons during the epoch of reionization. We directly measure the MFP by averaging the distance 1 Ry photons travel before reaching an optical depth of unity along random lines-of-sight. During reionization the free paths tend to end in neutral gas with densities near the cosmic mean, while after reionization the end points tend to be overdense but highly ionized. Despite the increasing importance of discrete, over-dense systems, the cumulative contribution of systems with NHI ≲ 1016.5 cm-2 suffices to drive the MFP at z ≈ 6, while at earlier times higher column densities are more important. After reionization the typical size of HI systems is close to the local Jeans length, but during reionization it is much larger. The mean free path for photons originating close to galaxies, {MFP_{gal}}, is much smaller than the cosmic MFP. After reionization this enhancement can remain significant up to starting distances of ˜1 comoving Mpc. During reionization, however, {MFP_{gal}} for distances ˜102 - 103 comoving kpc typically exceeds the cosmic MFP. These findings have important consequences for models that interpret the intergalactic MFP as the distance escaped ionizing photons can travel from galaxies before being absorbed and may cause them to under-estimate the required escape fraction from galaxies, and/or the required emissivity of ionizing photons after reionization.

Thioarsenides: A case for long-range Lewis acid-base-directed van der Waals interactions

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

Gibbs, Gerald V.; Wallace, Adam F.; Downs, R. T.

2011-04-01

Electron density distributions, bond paths, Laplacian and local energy density properties have been calculated for a number of As4Sn (n = 3,4,5) thioarsenide molecular crystals. On the basis of the distributions, the intramolecular As-S and As-As interactions classify as shared bonded interactions and the intermolecular As-S, As-As and S-S interactions classify as closed-shell van der Waals bonded interactions. The bulk of the intermolecular As-S bond paths link regions of locally concentrated electron density (Lewis base regions) with aligned regions of locally depleted electron density (Lewis acid regions) on adjacent molecules. The paths are comparable with intermolecular paths reported for severalmore » other molecular crystals that link aligned Lewis base and acid regions in a key-lock fashion, interactions that classified as long range Lewis acid-base directed van der Waals interactions. As the bulk of the intermolecular As-S bond paths (~70%) link Lewis acid-base regions on adjacent molecules, it appears that molecules adopt an arrangement that maximizes the number of As-S Lewis acid-base intermolecular bonded interactions. The maximization of the number of Lewis acid-base interactions appears to be connected with the close-packed array adopted by molecules: distorted cubic close-packed arrays are adopted for alacránite, pararealgar, uzonite, realgar and β-AsS and the distorted hexagonal close-packed arrays adopted by α- and β-dimorphite. A growth mechanism is proposed for thioarsenide molecular crystals from aqueous species that maximizes the number of long range Lewis acid-base vdW As-S bonded interactions with the resulting directed bond paths structuralizing the molecules as a molecular crystal.« less

Impact of different eddy covariance sensors and set-up on the annual balance of CO2 and fluxes of CH4 and latent heat in the Arctic

NASA Astrophysics Data System (ADS)

Goodrich, J. P.; Zona, D.; Gioli, B.; Murphy, P.; Burba, G. G.; Oechel, W. C.

2015-12-01

Expanding eddy covariance measurements of CO2 and CH4 fluxes in the Arctic is critical for refining the global C budget. Continuous measurements are particularly challenging because of the remote locations, low power availability, and extreme weather conditions. The necessity for tailoring instrumentation at different sites further complicates the interpretation of results and may add uncertainty to estimates of annual CO2 budgets. We investigated the influence of different sensor combinations on FCO2, latent heat (LE), and FCH4, and assessed the differences in annual FCO2 estimated with different instrumentation at the same sites. Using data from four sites across the North Slope of Alaska, we resolved FCO2 and FCH4 to within 5% using different combinations of open- and closed-path gas analyzers and within 10% using heated and non-heated anemometers. A continuously heated anemometer increased data coverage relative to non-heated anemometers while resulting in comparable annual FCO2, despite over-estimating sensible heat fluxes by 15%. We also implemented an intermittent heating strategy whereby activation only when ice or snow blockage of the transducers was detected. This resulted in comparable data coverage (~ 60%) to the continuously heated anemometer, while avoiding potential over-estimation of sensible heat and gas fluxes. We found good agreement in FCO2 and FCH4 from two closed-path and one open-path gas analyzer, despite the need for large spectral corrections of closed-path fluxes and density and temperature corrections to open-path sensors. However, data coverage was generally greater when using closed-path, especially during cold seasons (36-40% vs 10-14% for the open path), when fluxes from Arctic regions are particularly uncertain and potentially critical to annual C budgets. Measurement of Arctic LE remains a challenge due to strong attenuation along sample tubes, even when heated, that could not be accounted for with spectral corrections.

Slant Path Low Visibility Atmospheric Conditions.

DTIC Science & Technology

1980-09-01

situation. a) An optical propagation slant test path , of a length over which infrared transmissometer measurements can be made that are in a magnitude...transmission measure - ments which are close to 100% and therefore do not accurately relate to absolute transmissivity. A path which is too long will result in...is available for measurement of backscatter cross section along the chosen transmissometer path . 3. Rough Cross Cut of the Works unde Contract in

Control of Space-Based Electron Beam Free Form Fabrication

NASA Technical Reports Server (NTRS)

Seifzer. W. J.; Taminger, K. M.

2007-01-01

Engineering a closed-loop control system for an electron beam welder for space-based additive manufacturing is challenging. For earth and space based applications, components must work in a vacuum and optical components become occluded with metal vapor deposition. For extraterrestrial applications added components increase launch weight, increase complexity, and increase space flight certification efforts. Here we present a software tool that closely couples path planning and E-beam parameter controls into the build process to increase flexibility. In an environment where data collection hinders real-time control, another approach is considered that will still yield a high quality build.

Germany's ECEC Workforce: A Difficult Path to Professionalisation

ERIC Educational Resources Information Center

Rauschenbach, Thomas; Riedel, Birgit

2016-01-01

In a European comparison, the childcare profession in Germany has taken a distinct path of development which is closely interwoven with the history of early childhood education and care (ECEC) in general. Institutional choices critical to this path are the assignment of childcare as part of social welfare, the pursuit of a maternalist tradition in…

Hydraulic analysis of harmonic pumping tests in frequency and time domains for identifying the conduits networks in a karstic aquifer

NASA Astrophysics Data System (ADS)

Fischer, P.; Jardani, A.; Cardiff, M.; Lecoq, N.; Jourde, H.

2018-04-01

In a karstic field, the flow paths are very complex as they globally follow the conduit network. The responses generated from an investigation in this type of aquifer can be spatially highly variable. Therefore, the aim of the investigation in this case is to define a degree of connectivity between points of the field, in order to understand these flow paths. Harmonic pumping tests represent a possible investigation method for characterizing the subsurface flow of groundwater. They have several advantages compared to a constant-rate pumping (more signal possibilities, ease of extracting the signal in the responses and possibility of closed loop investigation). We show in this work that interpreting the responses from a harmonic pumping test is very useful for delineating a degree of connectivity between measurement points. We have firstly studied the amplitude and phase offset of responses from a harmonic pumping test in a theoretical synthetic modeling case in order to define a qualitative interpretation method in the time and frequency domains. Three different type of responses have been separated: a conduit connectivity response, a matrix connectivity, and a dual connectivity (response of a point in the matrix, but close to a conduit). We have then applied this method to measured responses at a field research site. Our interpretation method permits a quick and easy reconstruction of the main flow paths, and the whole set of field responses appear to give a similar range of responses to those seen in the theoretical synthetic case.

Dissolution Dynamic Nuclear Polarization capability study with fluid path.

PubMed

Malinowski, Ronja M; Lipsø, Kasper W; Lerche, Mathilde H; Ardenkjær-Larsen, Jan H

2016-11-01

Signal enhancement by hyperpolarization is a way of overcoming the low sensitivity in magnetic resonance; MRI in particular. One of the most well-known methods, dissolution Dynamic Nuclear Polarization, has been used clinically in cancer patients. One way of ensuring a low bioburden of the hyperpolarized product is by use of a closed fluid path that constitutes a barrier to contamination. The fluid path can be filled with the pharmaceuticals, i.e. imaging agent and solvents, in a clean room, and then stored or immediately used at the polarizer. In this study, we present a method of filling the fluid path that allows it to be reused. The filling method has been investigated in terms of reproducibility at two extrema, high dose for patient use and low dose for rodent studies, using [1-13C]pyruvate as example. We demonstrate that the filling method allows high reproducibility of six quality control parameters with standard deviations 3-10 times smaller than the acceptance criteria intervals in clinical studies. Copyright © 2016 Elsevier Inc. All rights reserved.

Use of a New Low-Power Laser-Based Instrumentation to Measure Methane Emissions from Remote Permafrost Regions

NASA Astrophysics Data System (ADS)

Burba, George; Sturtevant, Cove; Peltola, Olli; Schreiber, Peter; Zulueta, Rommel; Haapanala, Sami; Mammarella, Ivan; Rinne, Janne; Vesala, Timo; McDermitt, Dayle; Oechel, Walt

2013-04-01

The permafrost regions store significant amount of organic materials under anaerobic conditions, leading to large methane production and accumulation in the upper layers of bedrock, soil and ice. These regions are currently undergoing dramatic change in response to warming trends, and may become a significant potential source of global methane release under a warming climate over following decades and centuries. Present measurements of methane fluxes in permafrost regions have mostly been made with static chamber techniques, and very few were done with the eddy covariance approach using closed-path analyzers. Although chambers and closed-path analyzers have advantages, both techniques have significant limitations, especially for remote or portable research in cold regions. Static chamber measurements are discrete in time and space, and particularly difficult to use over polygonal tundra with highly non-uniform micro-topography and active water layer. They also may not capture the dynamics of methane fluxes on varying time scales (hourly to annual). In addition, placement of the chamber may disturb the surface integrity causing a significant over-estimation of the measured flux. Closed-path gas analyzers for measuring methane eddy fluxes employ advanced technologies such as TDLS (Tunable Diode Laser Spectroscopy), ICOS (Integrated Cavity Output Spectroscopy), WS-CRDS (wavelength scanned cavity ring-down spectroscopy), but require high flow rates at significantly reduced optical cell pressures to provide adequate response time and sharpen absorption features. Such methods, when used with the eddy covariance technique, require a vacuum pump and a total of 400-1500 Watts of grid power for the pump, climate control, and analyzer systems. The weight of such systems often exceeds 100-200 lbs, restricting practical applicability for remote or portable field studies. As a result, spatial coverage of eddy covariance methane flux measurements in cold regions remains limited. Remote permafrost wetlands of Arctic tundra, northern boreal peatlands of Canada and Siberia, and other highly methanogenic ecosystems have few eddy covariance methane measurement stations. Those existing are often located near grid power sources and roads rather than in the middle of the methane-producing ecosystem, while those that are placed appropriately may require extraordinary efforts to build and maintain them, with large investments into man-power and infrastructure. Alternatively, open-path instrumentation allows methane flux measurements at normal pressure without a need for a pump. As a result, the measurements can be done with very low-power (e.g., 7-10 Watts) light (5 .2 kg) instruments permitting solar- and wind- powered remote deployments in hard-to-reach sites from permanent, portable or mobile stations, and cost-effective additions of a methane measurement to the present array of CO2 and H2O measurements. The low-power operation and light weight of open-path eddy covariance station is important for number of ecosystems (rice fields, landfills, wetlands, cattle yards, etc.), but it is especially important for permafrost and other cold regions where grid power and access roads are generally not available, and logistics of running the experiment is particularly expensive. Emerging research using low-power laser-based instrumentation to measure CH4 emissions are presented from several permafrost ecosystems with contrasting setups, weather, and moisture conditions. Principles of open-path instrument operation, station characteristics and requirements are also discussed, as well as concurrent measurements of CO2 and H2O emissions using open-path and enclosed instrumentation.

Regional measurements of infrasound signals from ARIANE-5 engine tests in Southern Germany

NASA Astrophysics Data System (ADS)

Koch, K.

2012-04-01

A well-controlled source of repetitive infrasound emissions was previously identified and has been related to development and acceptance tests of the European Space Agencies ARIANE-5 main engine. The propulsion testing facility of the German Aerospace Agency (DLR) near Heilbronn, Southern Germany, is a distance of about 320 km away from the International Monitoring System (IMS) station IS26 in east-southeasterly direction. In the past, signals associated with these propulsion tests could normally be detected at IS26 during winter months, but not during summer months, reflecting the changes in atmospheric conditions between winter and summer. Over the last year, DLR has prepared to conduct a series of seven propulsion tests which started in November 2011; with interim times between tests of 3-4 weeks it will last until late March or early April 2012. With mobile infrasound recording equipment available at BGR we planned to record the infrasonic wavefield along the path to IS26 at regular distances starting as close as 20 km from the source. Our aim is to study sound propagation from direct paths mainly involving the tropospheric layer through the "zone of silence" to distances close to IS26, where paths through stratospheric layers are followed. Preliminary results show that during the relevant winter season direct path propagation can be observed to some 40 km from the propulsion test source, even at seismographic stations where the acoustic wave couples into the ground. The tests are also observed at IS26, and waveform duration and f-k-analysis confirm the signals to be associated with the GT-type propulsion tests.

Funnel for localizing biological cell placement and arrangement

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

Soscia, David; Benett, William J.; Mukerjee, Erik V.

2018-03-06

The present disclosure relates to a funnel apparatus for channeling cells onto a plurality of distinct, closely spaced regions of a seeding surface. The funnel apparatus has a body portion having an upper surface and a lower surface. The body portion forms a plurality of flow paths, at least one of which is shaped to have a decreasing cross-sectional area from the upper surface to the lower surface. The flow paths are formed at the lower surface to enable cells deposited into the flow paths at the upper surface of the funnel apparatus to be channeled into a plurality ofmore » distinct, closely spaced regions on the seeding surface positioned adjacent the lower surface.« less

An anomalous CO2 uptake measured over asphalt surface by open-path eddy-covariance system

NASA Astrophysics Data System (ADS)

Bogoev, Ivan; Santos, Eduardo

2017-04-01

Measurements of net ecosystem exchange of CO2 in desert environments made by Wohlfahrt et al. (2008) and Ma (2014) indicate strong CO2 sink. The results of these studies have been challenged by Schlesinger (2016) because the rates of the CO2 uptake are incongruent with the increase of biomass in the vegetation and accumulation of organic and inorganic carbon in the soil. Consequently, the accuracy of the open-path eddy-covariance systems in arid and semi-arid ecosystems has been questioned. A new technology merging the sensing paths of the gas analyzer and the sonic anemometer has recently been developed. This integrated open-path system allows a direct measurement of CO2 mixing ratio in the open air and has the potential to improve the quality of the temperature related density and spectroscopic corrections by synchronously measuring the sensible heat flux in the optical path of the gas analyzer. We evaluate the performance and the accuracy of this new sensor over a large parking lot with an asphalt surface where the water vapor and CO2 fluxes are expected to be low and the interfering sensible heat fluxes are above 200 Wm-2. For independent CO2 flux reference measurements, we use a co-located closed-path analyzer with a short intake tube and a standalone sonic anemometer. We compare energy and carbon dioxide fluxes between the open- and the closed-path systems. During periods with sensible heat flux above 100 W m-2, the open-path system reports an apparent CO2 uptake of 0.02 mg m-2 s-1, while the closed-path system consistently measures a more acceptable upward flux of 0.015 mg m-2 s-1. We attribute this systematic bias to inadequate fast-response temperature compensation of absorption-line broadening effects. We demonstrate that this bias can be eliminated by using the humidity-corrected fast-response sonic temperature to compensate for the abovementioned spectroscopic effects in the open-path analyzer.

Methane Emissions from Permafrost Regions using Low-Power Eddy Covariance Stations

NASA Astrophysics Data System (ADS)

Burba, G.; Sturtevant, C.; Schreiber, P.; Peltola, O.; Zulueta, R.; Mammarella, I.; Haapanala, S.; Rinne, J.; Vesala, T.; McDermitt, D.; Oechel, W.

2012-04-01

Methane is an important greenhouse gas with a warming potential 23 times that of carbon dioxide over a 100-year cycle. The permafrost regions of the world store significant amounts of organic materials under anaerobic conditions, leading to large methane production and accumulation in the upper layers of bedrock, soil and ice. These regions are currently undergoing dramatic change in response to warming trends, and may become a significant potential source of global methane release under a warming climate over the coming decades and centuries. Presently, most measurements of methane fluxes in permafrost regions have been made with static chamber techniques, and very few were done with the eddy covariance approach using closed-path analyzers. Although chambers and closed-path analyzers have advantages, both techniques have significant limitations, especially for permafrost research. Static chamber measurements are discrete in time and space, and particularly difficult to use over polygonal tundra with highly non-uniform micro-topography and active water layer. They also may not capture the dynamics of methane fluxes on varying time scales (hours to annual estimates). In addition, placement of the chamber may disturb the surface integrity causing a significant over-estimation of the measured flux. Closed-path gas analyzers for measuring methane eddy fluxes employ advanced technologies such as TDLS (Tunable Diode Laser Spectroscopy), ICOS (Integrated Cavity Output Spectroscopy), WS-CRDS (wavelength scanned cavity ring-down spectroscopy), but require high flow rates at significantly reduced optical cell pressures to provide adequate response time and sharpen absorption features. Such methods, when used with the eddy covariance technique, require a vacuum pump and a total of 400-1500 Watts of grid power for the pump and analyzer system. The weight of such systems often exceeds 100-200 lbs, restricting practical applicability for remote or portable field studies. As a result, spatial coverage of eddy covariance methane flux measurements remains limited. Remote permafrost wetlands of Arctic tundra, northern boreal peatlands of Canada and Siberia, and other highly methanogenic ecosystems have few eddy covariance methane measurement stations. Those existing are often located near grid power sources and roads rather than in the middle of the methane-producing ecosystem, while those that are placed appropriately may require extraordinary efforts to build and maintain them, with large investments into man-power and infrastructure. Alternatively, open-path approach allows methane flux measurements at ambient pressure without the need for a pump. As a result, the measurements can be done with very low-power (e.g. 5-10 Watts), light (5 .2 kg) instruments permitting solar- and wind- powered remote deployments in hard-to-reach sites from permanent, portable or mobile stations, and cost-effective additions of a methane measurement to the present array of CO2 and H2O measurements. The low-power operation and light weight of open-path eddy covariance stations is important for a number of ecosystems (rice fields, landfills, wetlands, cattle yards), but it is especially important for permafrost regions where grid power and access roads are generally not available, and the logistics of running the experiments are particularly expensive. Emerging research on methane flux measurements using low-power stations equipped with LI-7700 open-path methane analyzer (LI-COR Biosciences) are presented from several permafrost ecosystems with contrasting setups, and weather conditions. Principles of operation, station characteristics and requirements are also discussed.

Effects of Uncertainty in TRMM Precipitation Radar Path Integrated Attenuation on Interannual Variations of Tropical Oceanic Rainfall

NASA Technical Reports Server (NTRS)

Robertson, Franklin R.; Fitzjarrald, Dan E.; Kummerow, Christian D.; Arnold, James E. (Technical Monitor)

2002-01-01

Considerable uncertainty surrounds the issue of whether precipitation over the tropical oceans (30 deg N/S) systematically changes with interannual sea-surface temperature (SST) anomalies that accompany El Nino (warm) and La Nina (cold) events. Time series of rainfall estimates from the Tropical Rainfall Measuring Mission (TRMM Precipitation Radar (PR) over the tropical oceans show marked differences with estimates from two TRMM Microwave Imager (TMI) passive microwave algorithms. We show that path-integrated attenuation derived from the effects of precipitation on the radar return from the ocean surface exhibits interannual variability that agrees closely with the TMI time series. Further analysis of the frequency distribution of PR (2A25 product) rain rates suggests that the algorithm incorporates the attenuation measurement in a very conservative fashion so as to optimize the instantaneous rain rates. Such an optimization appears to come at the expense of monitoring interannual climate variability.

NASA Exploration Forum: Human Path to Mars

NASA Image and Video Library

2014-04-29

Robert Lightfoot, NASA Associate Adminstrator, delivers closing remarks at an Exploration Forum showcasing NASA's human exploration path to Mars in the James E. Webb Auditorium at NASA Headquarters on Tuesday, April 29, 2014. Photo Credit: (NASA/Joel Kowsky)

A method for measuring aircraft height and velocity using dual television cameras

NASA Technical Reports Server (NTRS)

Young, W. R.

1977-01-01

A unique electronic optical technique, consisting of two closed circuit television cameras and timing electronics, was devised to measure an aircraft's horizontal velocity and height above ground without the need for airborne cooperative devices. The system is intended to be used where the aircraft has a predictable flight path and a height of less than 660 meters (2,000 feet) at or near the end of an air terminal runway, but is suitable for greater aircraft altitudes whenever the aircraft remains visible. Two television cameras, pointed at zenith, are placed in line with the expected path of travel of the aircraft. Velocity is determined by measuring the time it takes the aircraft to travel the measured distance between cameras. Height is determined by correlating this speed with the time required to cross the field of view of either camera. Preliminary tests with a breadboard version of the system and a small model aircraft indicate the technique is feasible.

Kinematics of the human mandible for different head postures.

PubMed

Visscher, C M; Huddleston Slater, J J; Lobbezoo, F; Naeije, M

2000-04-01

The influence of head posture on movement paths of the incisal point (IP) and of the mandibular condyles during free open-close movements was studied. Ten persons, without craniomandibular or cervical spine disorders, participated in the study. Open close mandibular movements were recorded with the head in five postures, viz., natural head posture, forward head posture, military posture, and lateroflexion to the right and to the left side, using the Oral Kinesiologic Analysis System (OKAS-3D). This study showed that in a military head posture, the opening movement path of the incisal point is shifted anteriorly relative to the path in a natural head posture. In a forward head posture, the movement path is shifted posteriorly whereas during lateroflexion, it deviates to the side the head has moved to. Moreover, the intra-articular distance in the temporomandibular joint during closing is smaller with the head in military posture and greater in forward head posture, as compared to the natural head posture. During lateroflexion, the intra-articular distance on the ipsilateral side is smaller. The influence of head posture upon the kinematics of the mandible is probably a manifestation of differences in mandibular loading in the different head postures.

An empirical relationship for path diversity gain. [earth-space microwave propagation attenuation

NASA Technical Reports Server (NTRS)

Hodge, D. B.

1976-01-01

Existing 15.3 and 16 GHz path diversity gain data for earth-space propagation paths are used to generate an empirical relationship for diversity gain as a function of terminal separation distance and single terminal fade depth. The agreement between the resulting closed form expression and the data is within 0.75 dB in all cases.

A Novel Low-Power, High-Performance, Zero-Maintenance Closed-Path Trace Gas Eddy Covariance System with No Water Vapor Dilution or Spectroscopic Corrections

NASA Astrophysics Data System (ADS)

Sargent, S.; Somers, J. M.

2015-12-01

Trace-gas eddy covariance flux measurement can be made with open-path or closed-path analyzers. Traditional closed-path trace-gas analyzers use multipass absorption cells that behave as mixing volumes, requiring high sample flow rates to achieve useful frequency response. The high sample flow rate and the need to keep the multipass cell extremely clean dictates the use of a fine-pore filter that may clog quickly. A large-capacity filter cannot be used because it would degrade the EC system frequency response. The high flow rate also requires a powerful vacuum pump, which will typically consume on the order of 1000 W. The analyzer must measure water vapor for spectroscopic and dilution corrections. Open-path analyzers are available for methane, but not for nitrous oxide. The currently available methane analyzers have low power consumption, but are very large. Their large size degrades frequency response and disturbs the air flow near the sonic anemometer. They require significant maintenance to keep the exposed multipass optical surfaces clean. Water vapor measurements for dilution and spectroscopic corrections require a separate water vapor analyzer. A new closed-path eddy covariance system for measuring nitrous oxide or methane fluxes provides an elegant solution. The analyzer (TGA200A, Campbell Scientific, Inc.) uses a thermoelectrically-cooled interband cascade laser. Its small sample-cell volume and unique sample-cell configuration (200 ml, 1.5 m single pass) provide excellent frequency response with a low-power scroll pump (240 W). A new single-tube Nafion® dryer removes most of the water vapor, and attenuates fluctuations in the residual water vapor. Finally, a vortex intake assembly eliminates the need for an intake filter without adding volume that would degrade system frequency response. Laboratory testing shows the system attenuates the water vapor dilution term by more than 99% and achieves a half-power band width of 3.5 Hz.

Transformation of BCC and B2 High Temperature Phases to HCP and Orthorhombic Structures in the Ti-Al-Nb System. Part II: Experimental TEM Study of Microstructures

PubMed Central

Bendersky, L. A.; Boettinger, W. J.

1993-01-01

Possible transformation paths that involve no long range diffusion and their corresponding microstructural details were predicted by Bendersky, Roytburd, and Boettinger [J. Res. Natl. Inst. Stand. Technol. 98, 561 (1993)] for Ti-Al-Nb alloys cooled from the high temperature BCC/B2 phase field into close-packed orthorhombic or hexagonal phase fields. These predictions were based on structural and symmetry relations between the known phases. In the present paper experimental TEM results show that two of the predicted transformation paths are indeed followed for different alloy compositions. For Ti-25Al-12.5Nb (at%), the path includes the formation of intermediate hexagonal phases, A3 and DO19, and subsequent formation of a metastable domain structure of the low-temperature O phase. For alloys close to Ti-25Al-25Nb (at%), the path involves an intermediate B19 structure and subsequent formation of a translational domain structure of the O phase. The path selection depends on whether B2 order forms in the high temperature cubic phase prior to transformation to the close-packed structure. The paper also analyzes the formation of a two-phase modulated microstructure during long term annealing at 700 °C. The structure forms by congruent ordering of the DO19 phase to the O phase, and then reprecipitation of the DO19 phase, possibly by a spinodal mechanism. The thermodynamics underlying the path selection and the two-phase formation are also discussed. PMID:28053488

Construct User Guide

DTIC Science & Technology

2012-11-01

validation using calibrated grounding. In 2007 BRIMS Conference Proceedings, Norfolk, VA. Simon, H. A. (1957). Administrative Behavior: A study of...Construct will write the output to the directory specified by the path name. Users should ensure that if they have opened any output files (e.g., in Excel... open an input file, it will exit and close. There are times when an error message is not present to the user in this situation! Users should ensure

Direct synthesis of BiCuChO-type oxychalcogenides by mechanical alloying

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

Pele, Vincent; Barreteau, Celine; CNRS, Orsay F-91405

2013-07-15

We report on the direct synthesis of BiCuChO based materials by mechanical alloying (Ch=Se, Te). We show that contrary to the synthesis paths used in the previous reports dealing with this family of materials, which use costly annealings in closed silica tubes under controlled atmosphere, this new synthesis route enables the synthesis of pure phase materials at room temperature under air, with reasonable milling time. This synthesis procedure is easily scalable for large scale applications. - Highlights: • Phase pure BiCuSeO doped and undoped prepared by mechanical alloying. • Synthesis performed under air at room temperature. • Electrical properties similarmore » to that of samples synthesized by a classical path.« less

Tendency towards maximum complexity in a nonequilibrium isolated system

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

Calbet, Xavier; Lopez-Ruiz, Ricardo

2001-06-01

The time evolution equations of a simplified isolated ideal gas, the {open_quotes}tetrahedral{close_quotes} gas, are derived. The dynamical behavior of the Lopez-Ruiz{endash}Mancini{endash}Calbet complexity [R. Lopez-Ruiz, H. L. Mancini, and X. Calbet, Phys. Lett. A >209, 321 (1995)] is studied in this system. In general, it is shown that the complexity remains within the bounds of minimum and maximum complexity. We find that there are certain restrictions when the isolated {open_quotes}tetrahedral{close_quotes} gas evolves towards equilibrium. In addition to the well-known increase in entropy, the quantity called disequilibrium decreases monotonically with time. Furthermore, the trajectories of the system in phase space approach themore » maximum complexity path as it evolves toward equilibrium.« less

There was movement that was stationary, for the four-velocity had passed around

NASA Astrophysics Data System (ADS)

Roukema, Boudewijn F.

2010-05-01

Is the Doppler interpretation of galaxy redshifts in a Friedmann-Lemaître-Robertson-Walker (FLRW) model valid in the context of the approach to comoving spatial sections pioneered by de Sitter, Friedmann, Lemaître and Robertson, i.e. according to which the three-manifold of comoving space is characterized by both its curvature and topology? Holonomy transformations for flat, spherical and hyperbolic FLRW spatial sections are proposed. By quotienting a simply connected FLRW spatial section by an appropriate group of holonomy transformations, the Doppler interpretation in a non-expanding Minkowski space-time, obtained via four-velocity parallel transport along a photon path, is found to imply that an inertial observer is receding from herself at a speed greater than zero, implying contradictory world lines. The contradiction in the multiply connected case occurs for arbitrary redshifts in the flat and spherical cases, and for certain large redshifts in the hyperbolic case. The link between the Doppler interpretation of redshifts and cosmic topology can be understood physically as the link between parallel transport along a photon path and the fact that the comoving spatial geodesic corresponding to a photon's path can be a closed loop in an FLRW model of any curvature. Closed comoving spatial loops are fundamental to cosmic topology. With apologies to Andrew Barton `Banjo' Paterson. E-mail: boud@astro.uni.torun.pl

X-33 LH2 Tank Failure Investigation Findings

NASA Technical Reports Server (NTRS)

Niedermeyer, M.

2001-01-01

The X-33 liquid hydrogen tank failure investigation found the following: (1) The inner skin microcracked and hydrogen infiltrated into it; (2) The cracks grew larger under pressure; (3) When pressure was removed, the cracks closed slightly; (4) When the tank was drained and warmed, the cracks closed and blocked the leak path; (5) Foreign object debris (FOD) and debond areas provided an opportunity for a leak path; and (6) There is still hydrogen in the other three lobes today.

APPARATUS FOR ARC WELDING

DOEpatents

Lingafelter, J.W.

1960-04-01

An apparatus is described in which a welding arc created between an annular electrode and a workpiece moves under the influence of an electromagnetic field about the electrode in a closed or annular path. This mode of welding is specially suited to the enclosing of nuclear-fuel slugs in a protective casing. For example, a uranium slug is placed in an aluminum can, and an aluminum closure is welded to the open end of the can along a closed or annular path conforming to the periphery of the end closure.

Stray magnetic-field response of linear birefringent optical current sensors

NASA Astrophysics Data System (ADS)

MacDougall, Trevor W.; Hutchinson, Ted F.

1995-07-01

It is well known that the line integral, describing Faraday rotation in an optical medium, reduces to zero at low frequencies for a closed path that does not encircle a current source. If the closed optical path possesses linear birefringence in addition to Faraday rotation, the cumulative effects on the state of polarization result in a response to externally located current-carrying conductors. This effect can induce a measurable error of the order of 0.3% during certain steady-state operating conditions.

Statistical estimation of ultrasonic propagation path parameters for aberration correction.

PubMed

Waag, Robert C; Astheimer, Jeffrey P

2005-05-01

Parameters in a linear filter model for ultrasonic propagation are found using statistical estimation. The model uses an inhomogeneous-medium Green's function that is decomposed into a homogeneous-transmission term and a path-dependent aberration term. Power and cross-power spectra of random-medium scattering are estimated over the frequency band of the transmit-receive system by using closely situated scattering volumes. The frequency-domain magnitude of the aberration is obtained from a normalization of the power spectrum. The corresponding phase is reconstructed from cross-power spectra of subaperture signals at adjacent receive positions by a recursion. The subapertures constrain the receive sensitivity pattern to eliminate measurement system phase contributions. The recursion uses a Laplacian-based algorithm to obtain phase from phase differences. Pulse-echo waveforms were acquired from a point reflector and a tissue-like scattering phantom through a tissue-mimicking aberration path from neighboring volumes having essentially the same aberration path. Propagation path aberration parameters calculated from the measurements of random scattering through the aberration phantom agree with corresponding parameters calculated for the same aberrator and array position by using echoes from the point reflector. The results indicate the approach describes, in addition to time shifts, waveform amplitude and shape changes produced by propagation through distributed aberration under realistic conditions.

Continuous-time quantum search on balanced trees

NASA Astrophysics Data System (ADS)

Philipp, Pascal; Tarrataca, Luís; Boettcher, Stefan

2016-03-01

We examine the effect of network heterogeneity on the performance of quantum search algorithms. To this end, we study quantum search on a tree for the oracle Hamiltonian formulation employed by continuous-time quantum walks. We use analytical and numerical arguments to show that the exponent of the asymptotic running time ˜Nβ changes uniformly from β =0.5 to β =1 as the searched-for site is moved from the root of the tree towards the leaves. These results imply that the time complexity of the quantum search algorithm on a balanced tree is closely correlated with certain path-based centrality measures of the searched-for site.

Postural control strategies during single limb stance following acute lateral ankle sprain.

PubMed

Doherty, Cailbhe; Bleakley, Chris; Hertel, Jay; Caulfield, Brian; Ryan, John; Delahunt, Eamonn

2014-06-01

Single-limb stance is maintained via the integration of visual, vestibular and somatosensory afferents. Musculoskeletal injury challenges the somatosensory system to reweight distorted sensory afferents. This investigation supplements kinetic analysis of eyes-open and eyes-closed single-limb stance tasks with a kinematic profile of lower limb postural orientation in an acute lateral ankle sprain group to assess the adaptive capacity of the sensorimotor system to injury. Sixty-six participants with first-time acute lateral ankle sprain completed a 20-second eyes-open single-limb stance task on their injured and non-injured limbs (task 1). Twenty-three of these participants successfully completed the same 20-second single-limb stance task with their eyes closed (task 2). A non-injured control group of 19 participants completed task 1, with 16 completing task 2. 3-dimensional kinematics of the hip, knee and ankle joints, as well as associated fractal dimension of the center-of-pressure path were determined for each limb during these tasks. Between trial analyses revealed significant differences in stance limb kinematics and fractal dimension of the center-of-pressure path for task 2 only. The control group bilaterally assumed a position of greater hip flexion compared to injured participants on their side-matched "involved"(7.41 [6.1°] vs 1.44 [4.8]°; η(2)=.34) and "uninvolved" (9.59 [8.5°] vs 2.16 [5.6°]; η(2)=.31) limbs, with a greater fractal dimension of the center-of-pressure path (involved limb=1.39 [0.16°] vs 1.25 [0.14°]; uninvolved limb=1.37 [0.21°] vs 1.23 [0.14°]). Bilateral impairment in postural control strategies present following a first time acute lateral ankle sprain. Copyright © 2014 Elsevier Ltd. All rights reserved.

CORRECTING FOR INTERPLANETARY SCATTERING IN VELOCITY DISPERSION ANALYSIS OF SOLAR ENERGETIC PARTICLES

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

Laitinen, T.; Dalla, S.; Huttunen-Heikinmaa, K.

2015-06-10

To understand the origin of Solar Energetic Particles (SEPs), we must study their injection time relative to other solar eruption manifestations. Traditionally the injection time is determined using the Velocity Dispersion Analysis (VDA) where a linear fit of the observed event onset times at 1 AU to the inverse velocities of SEPs is used to derive the injection time and path length of the first-arriving particles. VDA does not, however, take into account that the particles that produce a statistically observable onset at 1 AU have scattered in the interplanetary space. We use Monte Carlo test particle simulations of energeticmore » protons to study the effect of particle scattering on the observable SEP event onset above pre-event background, and consequently on VDA results. We find that the VDA results are sensitive to the properties of the pre-event and event particle spectra as well as SEP injection and scattering parameters. In particular, a VDA-obtained path length that is close to the nominal Parker spiral length does not imply that the VDA injection time is correct. We study the delay to the observed onset caused by scattering of the particles and derive a simple estimate for the delay time by using the rate of intensity increase at the SEP onset as a parameter. We apply the correction to a magnetically well-connected SEP event of 2000 June 10, and show it to improve both the path length and injection time estimates, while also increasing the error limits to better reflect the inherent uncertainties of VDA.« less

Spatially-global integration of closed, fragmented contours by finding the shortest-path in a log-polar representation

PubMed Central

Kwon, TaeKyu; Agrawal, Kunal; Li, Yunfeng; Pizlo, Zygmunt

2015-01-01

Finding the occluding contours of objects in real 2D retinal images of natural 3D scenes is done by determining, which contour fragments are relevant, and the order in which they should be connected. We developed a model that finds the closed contour represented in the image by solving a shortest path problem that uses a log-polar representation of the image; the kind of representation known to exist in area V1 of the primate cortex. The shortest path in a log-polar representation favors the smooth, convex and closed contours in the retinal image that have the smallest number of gaps. This approach is practical because finding a globally-optimal solution to a shortest path problem is computationally easy. Our model was tested in four psychophysical experiments. In the first two experiments, the subject was presented with a fragmented convex or concave polygon target among a large number of unrelated pieces of contour (distracters). The density of these pieces of contour was uniform all over the screen to minimize spatially-local cues. The orientation of each target contour fragment was randomly perturbed by varying the levels of jitter. Subjects drew a closed contour that represented the target’s contour on a screen. The subjects’ performance was nearly perfect when the jitter-level was low. Their performance deteriorated as jitter-levels were increased. The performance of our model was very similar to our subjects’. In two subsequent experiments, the subject was asked to discriminate a briefly-presented egg-shaped object while maintaining fixation at several different positions relative to the closed contour of the shape. The subject’s discrimination performance was affected by the fixation position in much the same way as the model’s. PMID:26241462

Coherent nonlinear optical studies of elementary processes in biological complexes: diagrammatic techniques based on the wave function versus the density matrix

PubMed Central

Biggs, Jason D.; Voll, Judith A.; Mukamel, Shaul

2012-01-01

Two types of diagrammatic approaches for the design and simulation of nonlinear optical experiments (closed-time path loops based on the wave function and double-sided Feynman diagrams for the density matrix) are presented and compared. We give guidelines for the assignment of relevant pathways and provide rules for the interpretation of existing nonlinear experiments in carotenoids. PMID:22753822

X-33 LH2 Tank Failure Investigation Findings

NASA Technical Reports Server (NTRS)

Niedermeyer, Melinda; Munafo, Paul (Technical Monitor)

2002-01-01

This viewgraph presentation gives an overview of the X-33 LH2 tank failure investigation findings. The conclusions of the investigation include the following: (1) the inner skin microcracked and hydrogen infiltrated; (2) the cracks grew larger under pressure; (3) when pressure was removed, the cracks closed slightly; (4) when the tank was drained and warmed, the cracks closed and blocked the leak path; (5) FOD and debond areas provided an opportunity for a leak path; and (6) there is still hydrogen in the the other three lobes today.

Fabrication of photonic amorphous diamonds for terahertz-wave applications

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

Komiyama, Yuichiro; Abe, Hiroyuki; Kamimura, Yasushi

2016-05-09

A recently proposed photonic bandgap material, named “photonic amorphous diamond” (PAD), was fabricated in a terahertz regime, and its terahertz-wave propagation properties were investigated. The PAD structure was fabricated from acrylic resin mixed with alumina powder, using laser lithographic, micro-additive manufacturing technique. After fabrication, the resulting structure was dewaxed and sintered. The formation of a photonic bandgap at around 0.45 THz was demonstrated by terahertz time-domain spectroscopy. Reflecting the disordered nature of the random network structure, diffusive terahertz-wave propagation was observed in the passbands; the scattering mean-free path decreased as the frequency approached the band edge. The mean-free paths evaluated atmore » the band edges were close to the Ioffe-Regel threshold value for wave localization.« less

Real-time control of hind limb functional electrical stimulation using feedback from dorsal root ganglia recordings

NASA Astrophysics Data System (ADS)

Bruns, Tim M.; Wagenaar, Joost B.; Bauman, Matthew J.; Gaunt, Robert A.; Weber, Douglas J.

2013-04-01

Objective. Functional electrical stimulation (FES) approaches often utilize an open-loop controller to drive state transitions. The addition of sensory feedback may allow for closed-loop control that can respond effectively to perturbations and muscle fatigue. Approach. We evaluated the use of natural sensory nerve signals obtained with penetrating microelectrode arrays in lumbar dorsal root ganglia (DRG) as real-time feedback for closed-loop control of FES-generated hind limb stepping in anesthetized cats. Main results. Leg position feedback was obtained in near real-time at 50 ms intervals by decoding the firing rates of more than 120 DRG neurons recorded simultaneously. Over 5 m of effective linear distance was traversed during closed-loop stepping trials in each of two cats. The controller compensated effectively for perturbations in the stepping path when DRG sensory feedback was provided. The presence of stimulation artifacts and the quality of DRG unit sorting did not significantly affect the accuracy of leg position feedback obtained from the linear decoding model as long as at least 20 DRG units were included in the model. Significance. This work demonstrates the feasibility and utility of closed-loop FES control based on natural neural sensors. Further work is needed to improve the controller and electrode technologies and to evaluate long-term viability.

Real-time control of hind limb functional electrical stimulation using feedback from dorsal root ganglia recordings

PubMed Central

Bruns, Tim M; Wagenaar, Joost B; Bauman, Matthew J; Gaunt, Robert A; Weber, Douglas J

2013-01-01

Objective Functional electrical stimulation (FES) approaches often utilize an open-loop controller to drive state transitions. The addition of sensory feedback may allow for closed-loop control that can respond effectively to perturbations and muscle fatigue. Approach We evaluated the use of natural sensory nerve signals obtained with penetrating microelectrode arrays in lumbar dorsal root ganglia (DRG) as real-time feedback for closed-loop control of FES-generated hind limb stepping in anesthetized cats. Main results Leg position feedback was obtained in near real-time at 50 ms intervals by decoding the firing rates of more than 120 DRG neurons recorded simultaneously. Over 5 m of effective linear distance was traversed during closed-loop stepping trials in each of two cats. The controller compensated effectively for perturbations in the stepping path when DRG sensory feedback was provided. The presence of stimulation artifacts and the quality of DRG unit sorting did not significantly affect the accuracy of leg position feedback obtained from the linear decoding model as long as at least 20 DRG units were included in the model. Significance This work demonstrates the feasibility and utility of closed-loop FES control based on natural neural sensors. Further work is needed to improve the controller and electrode technologies and to evaluate long-term viability. PMID:23503062

Computer hardware and software for robotic control

NASA Technical Reports Server (NTRS)

Davis, Virgil Leon

1987-01-01

The KSC has implemented an integrated system that coordinates state-of-the-art robotic subsystems. It is a sensor based real-time robotic control system performing operations beyond the capability of an off-the-shelf robot. The integrated system provides real-time closed loop adaptive path control of position and orientation of all six axes of a large robot; enables the implementation of a highly configurable, expandable testbed for sensor system development; and makes several smart distributed control subsystems (robot arm controller, process controller, graphics display, and vision tracking) appear as intelligent peripherals to a supervisory computer coordinating the overall systems.

Autonomous Collision-Free Navigation of Microvehicles in Complex and Dynamically Changing Environments.

PubMed

Li, Tianlong; Chang, Xiaocong; Wu, Zhiguang; Li, Jinxing; Shao, Guangbin; Deng, Xinghong; Qiu, Jianbin; Guo, Bin; Zhang, Guangyu; He, Qiang; Li, Longqiu; Wang, Joseph

2017-09-26

Self-propelled micro- and nanoscale robots represent a rapidly emerging and fascinating robotics research area. However, designing autonomous and adaptive control systems for operating micro/nanorobotics in complex and dynamically changing environments, which is a highly demanding feature, is still an unmet challenge. Here we describe a smart microvehicle for precise autonomous navigation in complicated environments and traffic scenarios. The fully autonomous navigation system of the smart microvehicle is composed of a microscope-coupled CCD camera, an artificial intelligence planner, and a magnetic field generator. The microscope-coupled CCD camera provides real-time localization of the chemically powered Janus microsphere vehicle and environmental detection for path planning to generate optimal collision-free routes, while the moving direction of the microrobot toward a reference position is determined by the external electromagnetic torque. Real-time object detection offers adaptive path planning in response to dynamically changing environments. We demonstrate that the autonomous navigation system can guide the vehicle movement in complex patterns, in the presence of dynamically changing obstacles, and in complex biological environments. Such a navigation system for micro/nanoscale vehicles, relying on vision-based close-loop control and path planning, is highly promising for their autonomous operation in complex dynamic settings and unpredictable scenarios expected in a variety of realistic nanoscale scenarios.

Millimeter-wave studies

NASA Technical Reports Server (NTRS)

Allen, Kenneth C.

1988-01-01

Progress on millimeter-wave propagation experiments in Hawaii is reported. A short path for measuring attenuation in rain at 9.6, 28.8, 57.6, and 96.1 GHz is in operation. A slant path from Hilo to the top of Mauna Kea is scheduled. On this path, scattering from rain and clouds that may cause interference for satellites closely spaced in geosynchronous orbit will be measured at the same frequencies at 28.8 and 96.1 GHz. In addition the full transmission matrix will be measured at the same frequencies on the slant path. The technique and equipment used to measure the transmission matrix are described.

Differences between the chewing and non-chewing sides of the mandibular first molars and condyles in the closing phase during chewing in normal subjects.

PubMed

Tomonari, Hiroshi; Kwon, Sangho; Kuninori, Takaharu; Miyawaki, Shouichi

2017-09-01

This study aimed to assess differences between the closing paths of the chewing and non-chewing sides of mandibular first molars and condyles during natural mastication, using standardized model food in healthy subjects. Thirty-two healthy young adults (age: 19-25 years; 22 men, 10 women) with normal occlusion and function chewed on standardized gummy jelly. Using an optoelectric jaw-tracking system with six degrees of freedom, we recorded the path of the mandibular first molars and condyles on both sides for 10 strokes during unilateral chewing. Variables were compared between the chewing side and the non-chewing side of first molars and condyles on frontal, sagittal, and horizontal views during the early-, middle- and late-closing phases. On superior/inferior displacements, the chewing side first molar and condyle were positioned superior to those on the non-chewing side during the early- and middle-closing phases. Conversely, the first molar and condyle on the non-chewing side were positioned significantly superior to those on the chewing side during the late-closing phase. On anterior/posterior displacements, the chewing side mandibular first molar and condyle were positioned significantly posterior to those on the non-chewing side throughout all closing phases. Our results showed the differences between the mandibular first molars and condyles on both sides with respect to masticatory path during natural chewing of a model food. These differences can be useful for informing initial diagnostic tests for impaired masticatory function in the clinical environment. Copyright © 2017 Elsevier Ltd. All rights reserved.

Shape Sensing Techniques for Continuum Robots in Minimally Invasive Surgery: A Survey.

PubMed

Shi, Chaoyang; Luo, Xiongbiao; Qi, Peng; Li, Tianliang; Song, Shuang; Najdovski, Zoran; Fukuda, Toshio; Ren, Hongliang

2017-08-01

Continuum robots provide inherent structural compliance with high dexterity to access the surgical target sites along tortuous anatomical paths under constrained environments and enable to perform complex and delicate operations through small incisions in minimally invasive surgery. These advantages enable their broad applications with minimal trauma and make challenging clinical procedures possible with miniaturized instrumentation and high curvilinear access capabilities. However, their inherent deformable designs make it difficult to realize 3-D intraoperative real-time shape sensing to accurately model their shape. Solutions to this limitation can lead themselves to further develop closely associated techniques of closed-loop control, path planning, human-robot interaction, and surgical manipulation safety concerns in minimally invasive surgery. Although extensive model-based research that relies on kinematics and mechanics has been performed, accurate shape sensing of continuum robots remains challenging, particularly in cases of unknown and dynamic payloads. This survey investigates the recent advances in alternative emerging techniques for 3-D shape sensing in this field and focuses on the following categories: fiber-optic-sensor-based, electromagnetic-tracking-based, and intraoperative imaging modality-based shape-reconstruction methods. The limitations of existing technologies and prospects of new technologies are also discussed.

How to use the Sun-Earth Lagrange points for fundamental physics and navigation

NASA Astrophysics Data System (ADS)

Tartaglia, A.; Lorenzini, E. C.; Lucchesi, D.; Pucacco, G.; Ruggiero, M. L.; Valko, P.

2018-01-01

We illustrate the proposal, nicknamed LAGRANGE, to use spacecraft, located at the Sun-Earth Lagrange points, as a physical reference frame. Performing time of flight measurements of electromagnetic signals traveling on closed paths between the points, we show that it would be possible: (a) to refine gravitational time delay knowledge due both to the Sun and the Earth; (b) to detect the gravito-magnetic frame dragging of the Sun, so deducing information about the interior of the star; (c) to check the possible existence of a galactic gravitomagnetic field, which would imply a revision of the properties of a dark matter halo; (d) to set up a relativistic positioning and navigation system at the scale of the inner solar system. The paper presents estimated values for the relevant quantities and discusses the feasibility of the project analyzing the behavior of the space devices close to the Lagrange points.

Field and laboratory studies of moving and temporally variable noise sources (aircraft); perception of location, movement, and direction.

PubMed

Gunn, W J; Shigehisa, T; Shepherd, W T

1979-10-01

The conditions were examined under which more valid and reliable estimates could be made of the effects of aircraft noise on people. In Exper. 1, 12 Ss in 2 different houses directly under the flight path of a major airport (JFK) indicated 1 of 12 possible flight paths (4 directly overhead and 8 to one side) for each of 3 jet aircraft flyovers: 3% of cases in House A and 56% in House B (which had open windows) were correctly identified. Despite judgment inaccuracy, Ss were more than moderately certain of the correctness of their judgments. In Exper. II. Ss either inside or outside of 2 houses in Wallops Station, Virginia, indicated on diagrams the direction of flyovers. Each of 4 aircraft (Boeing 737, C-54, UE-1 helicopter, Queenaire) made 8 flyovers directly over the houses and 8 to one side. Windows were either open or closed. All flyovers and conditions were counterbalanced. All sound sources under all conditions were usually judged to be overhead and moving, but for Ss indoors with windows closed the to-the-side flyovers were judged to be off to the side in 24% of cases. Outdoor Ss reported correct direction in 75% of cases while indoor Ss were correct in only 25% (windows open) or 18% (windows closed). Judgments "to the side" were significantly better (p = less than .02) with windows open vs closed, while with windows closed judgments were significantly better (p = less than .05) for flyovers overhead vs to the side. In Exper. III, Ss localized in azimuth and in the vertical plane recorded noises (10 1-oct noise bands of CF = 28.12 c/s - 14.4kc/s, spoken voice, and jet aircraft takeoffs and landings), presented through 1, 2, or 4 floor-level loudspeakers at each corner of a simulated living room (4.2 x 5.4m)built inside an IAC soundproof room. Aircraft noises presented by 4 loudspeakers were localized as "directly" overhead 80% of the time and "generally overhead" about 90% of the time; other sounds were so localized about 50% and 75% of the time respectively. Through only 2 loudspeakers, aircraft noises were localized 25-36 degrees above horizontal. Implications are that acoustic realism can be achieved in simulated aircraft overflights and that future laboratory noise-effects research should incorporate the required conditions.

Gas Path On-line Fault Diagnostics Using a Nonlinear Integrated Model for Gas Turbine Engines

NASA Astrophysics Data System (ADS)

Lu, Feng; Huang, Jin-quan; Ji, Chun-sheng; Zhang, Dong-dong; Jiao, Hua-bin

2014-08-01

Gas turbine engine gas path fault diagnosis is closely related technology that assists operators in managing the engine units. However, the performance gradual degradation is inevitable due to the usage, and it result in the model mismatch and then misdiagnosis by the popular model-based approach. In this paper, an on-line integrated architecture based on nonlinear model is developed for gas turbine engine anomaly detection and fault diagnosis over the course of the engine's life. These two engine models have different performance parameter update rate. One is the nonlinear real-time adaptive performance model with the spherical square-root unscented Kalman filter (SSR-UKF) producing performance estimates, and the other is a nonlinear baseline model for the measurement estimates. The fault detection and diagnosis logic is designed to discriminate sensor fault and component fault. This integration architecture is not only aware of long-term engine health degradation but also effective to detect gas path performance anomaly shifts while the engine continues to degrade. Compared to the existing architecture, the proposed approach has its benefit investigated in the experiment and analysis.

Three-dimensional automated nanoparticle tracking using Mie scattering in an optical microscope.

PubMed

Gineste, J-M; Macko, P; Patterson, E A; Whelan, M P

2011-08-01

The forward scattering of light in a conventional inverted optical microscope by nanoparticles ranging in diameter from 10 to 50nm has been used to automatically and quantitatively identify and track their location in three-dimensions with a temporal resolution of 200ms. The standard deviation of the location of nominally stationary 50-nm-diameter nanoparticles was found to be about 50nm along the light path and about 5nm in the plane perpendicular to the light path. The method is based on oscillating the microscope objective along the light path using a piezo actuator and acquiring images with the condenser aperture closed to a minimum to enhance the effects of diffraction. Data processing in the time and spatial domains allowed the location of particles to be obtained automatically so that the technique has potential applications both in the processing of nanoparticles and in their use in a variety of fields including nanobiotechnology, pharmaceuticals and food processing where a simple optical microscope maybe preferred for a variety of reasons. © 2011 The Authors Journal of Microscopy © 2011 Royal Microscopical Society.

Closed-loop adaptive optic comparison between a Shack-Hartmann and a distorted grating wavefront sensor

NASA Astrophysics Data System (ADS)

Harrison, Paul; Erry, Gavin R. G.; Otten, Leonard J.; Cuevas, Desirae M.; Weaver, Lawrence D.

2004-11-01

Earlier research reported a comparison of the wavefronts recorded simultaneously by a Shack-Hartmann and a Distorted Grating Wavefront Sensor (DGWFS). In this paper we present the results of a continuation of this earlier work where we have now closed an adaptive optics loop under simulated propagation conditions using the Advanced Concept Laboratory (ACL) at Lincoln Laboratory. For these measurements only one wavefront sensor controlled the deformable mirror at a time. To make direct comparisons between the sensors we took advantage of the ACL's ability to exactly replicate a time varying propagation simulation. Time varying and static comparisons of the two sensors controlling the ACL adaptive system under conditions that ranged from a benign path, D/r0 = 2, to a propagation condition with significant scintillation, D/r0 =9, will be shown using the corrected far field spot as a measure of performance. The paper includes a description of the DGWFS used for these tests and describes the procedure used to align and calibrate the sensor.

Closed-loop adaptive optic comparison between a Shack-Hartmann and a distorted-grating wavefront sensor

NASA Astrophysics Data System (ADS)

Harrison, Paul; Erry, Gavin R. G.; Otten, Leonard J., III; Cuevas, D. M.; Weaver, Lawrence D.

2004-02-01

Earlier research reported a comparison of the wavefronts recorded simultaneously by a Shack-Hartmann and a Distorted Grating Wavefront Sensor (DGWFS). In this paper we present the results of a continuation of this earlier work where we have now closed an adaptive optics loop under simulated propagation conditions using the Advanced Concept Laboratory (ACL) at Lincoln Laboratory. For these measurements only one wavefront sensor controlled the deformable mirror at a time. To make direct comparisons between the sensors we took advantage of the ACL"s ability to exactly replicate a time varying propagation simulation. Time varying and static comparisons of the two sensors controlling the ACL adaptive system under conditions that ranged from a benign path, D/r0 = 2, to a propagation condition with significant scintillation, D/r0 =9, will be shown using the corrected far field spot as a measure of performance. The paper includes a description of the DGWFS used for these tests and describes the procedure used to align and calibrate the sensor.

Spreading paths in partially observed social networks

NASA Astrophysics Data System (ADS)

Onnela, Jukka-Pekka; Christakis, Nicholas A.

2012-03-01

Understanding how and how far information, behaviors, or pathogens spread in social networks is an important problem, having implications for both predicting the size of epidemics, as well as for planning effective interventions. There are, however, two main challenges for inferring spreading paths in real-world networks. One is the practical difficulty of observing a dynamic process on a network, and the other is the typical constraint of only partially observing a network. Using static, structurally realistic social networks as platforms for simulations, we juxtapose three distinct paths: (1) the stochastic path taken by a simulated spreading process from source to target; (2) the topologically shortest path in the fully observed network, and hence the single most likely stochastic path, between the two nodes; and (3) the topologically shortest path in a partially observed network. In a sampled network, how closely does the partially observed shortest path (3) emulate the unobserved spreading path (1)? Although partial observation inflates the length of the shortest path, the stochastic nature of the spreading process also frequently derails the dynamic path from the shortest path. We find that the partially observed shortest path does not necessarily give an inflated estimate of the length of the process path; in fact, partial observation may, counterintuitively, make the path seem shorter than it actually is.

Spreading paths in partially observed social networks.

PubMed

Onnela, Jukka-Pekka; Christakis, Nicholas A

2012-03-01

Understanding how and how far information, behaviors, or pathogens spread in social networks is an important problem, having implications for both predicting the size of epidemics, as well as for planning effective interventions. There are, however, two main challenges for inferring spreading paths in real-world networks. One is the practical difficulty of observing a dynamic process on a network, and the other is the typical constraint of only partially observing a network. Using static, structurally realistic social networks as platforms for simulations, we juxtapose three distinct paths: (1) the stochastic path taken by a simulated spreading process from source to target; (2) the topologically shortest path in the fully observed network, and hence the single most likely stochastic path, between the two nodes; and (3) the topologically shortest path in a partially observed network. In a sampled network, how closely does the partially observed shortest path (3) emulate the unobserved spreading path (1)? Although partial observation inflates the length of the shortest path, the stochastic nature of the spreading process also frequently derails the dynamic path from the shortest path. We find that the partially observed shortest path does not necessarily give an inflated estimate of the length of the process path; in fact, partial observation may, counterintuitively, make the path seem shorter than it actually is.

Converging Towards the Optimal Path to Extinction

DTIC Science & Technology

2011-01-01

the reproductive rate R0 should be greater than but very close to 1. However, most real diseases have R0 larger than 1.5, which translates into a...can analytically find an expression for the action along the optimal path. The expression for the action is a function of k and the reproductive number...the optimal path for a range of values of the reproductive number R0. In contrast to the prior two examples, here the action must be computed

Closed Paths of Light Trapped in a Closed Fermat Curve

ERIC Educational Resources Information Center

Dana-Picard, Thierry; Naiman, Aaron

2002-01-01

Geometric constructions have previously been shown that can be interpreted as rays of light trapped either in polygons or in conics, by successive reflections. The same question, trapping light in closed Fermat curves, is addressed here. Numerical methods are used to study the behaviour of the reflection points of a triangle when the degree of the…

Monitoring spacecraft atmosphere contaminants by laser absorption spectroscopy

NASA Technical Reports Server (NTRS)

Steinfeld, J. I.

1976-01-01

Laser-based spectrophotometric methods which have been proposed for the detection of trace concentrations of gaseous contaminants include Raman backscattering (LIDAR) and passive radiometry (LOPAIR). Remote sensing techniques using laser spectrometry are presented and in particular a simple long-path laser absorption method (LOLA), which is capable of resolving complex mixtures of closely related trace contaminants at ppm levels is discussed. A number of species were selected for study which are representative of those most likely to accumulate in closed environments, such as submarines or long-duration manned space flights. Computer programs were developed which will permit a real-time analysis of the monitored atmosphere. Estimates of the dynamic range of this monitoring technique for various system configurations, and comparison with other methods of analysis, are given.

A Non-Abelian Geometric Phase for Spin Systems

NASA Astrophysics Data System (ADS)

H M, Bharath; Boguslawski, Matthew; Barrios, Maryrose; Chapman, Michael

Berry's geometric phase has been used to characterize topological phase transitions. Recent works have addressed the question of whether generalizations of Berry's phase to mixed states can be used to characterize topological phase transitions. Berry's phase is essentially the geometric information stored in the overall phase of a quantum system. Here, we show that geometric information is also stored in the higher order spin moments of a quantum spin system. In particular, we show that when the spin vector of a quantum spin system with a spin 1 or higher is transported along a closed path inside the Bloch ball, the tensor of second moments picks up a geometric phase in the form of an SO(3) operator. Geometrically interpreting this phase is tantamount to defining a steradian angle for closed paths inside the Bloch ball. Typically the steradian angle is defined by projecting the path onto the surface of the Bloch ball. However, paths that pass through the center cannot be projected onto the surface. We show that the steradian angles of all paths, including those that pass through the center can be defined by projecting them onto a real projective plane, instead of a sphere. This steradian angle is equal to the geometric phase picked up by a spin system.

Two carbon fluxes to reserve starch in potato (Solanum tuberosum L.) tuber cells are closely interconnected but differently modulated by temperature

PubMed Central

Fettke, Joerg; Leifels, Lydia; Brust, Henrike; Herbst, Karoline; Steup, Martin

2012-01-01

Parenchyma cells from tubers of Solanum tuberosum L. convert several externally supplied sugars to starch but the rates vary largely. Conversion of glucose 1-phosphate to starch is exceptionally efficient. In this communication, tuber slices were incubated with either of four solutions containing equimolar [U-14C]glucose 1-phosphate, [U-14C]sucrose, [U-14C]glucose 1-phosphate plus unlabelled equimolar sucrose or [U-14C]sucrose plus unlabelled equimolar glucose 1-phosphate. 14C-incorporation into starch was monitored. In slices from freshly harvested tubers each unlabelled compound strongly enhanced 14C incorporation into starch indicating closely interacting paths of starch biosynthesis. However, enhancement disappeared when the tubers were stored. The two paths (and, consequently, the mutual enhancement effect) differ in temperature dependence. At lower temperatures, the glucose 1-phosphate-dependent path is functional, reaching maximal activity at approximately 20 °C but the flux of the sucrose-dependent route strongly increases above 20 °C. Results are confirmed by in vitro experiments using [U-14C]glucose 1-phosphate or adenosine-[U-14C]glucose and by quantitative zymograms of starch synthase or phosphorylase activity. In mutants almost completely lacking the plastidial phosphorylase isozyme(s), the glucose 1-phosphate-dependent path is largely impeded. Irrespective of the size of the granules, glucose 1-phosphate-dependent incorporation per granule surface area is essentially equal. Furthermore, within the granules no preference of distinct glucosyl acceptor sites was detectable. Thus, the path is integrated into the entire granule biosynthesis. In vitro 14C-incorporation into starch granules mediated by the recombinant plastidial phosphorylase isozyme clearly differed from the in situ results. Taken together, the data clearly demonstrate that two closely but flexibly interacting general paths of starch biosynthesis are functional in potato tuber cells. PMID:22378944

Two carbon fluxes to reserve starch in potato (Solanum tuberosum L.) tuber cells are closely interconnected but differently modulated by temperature.

PubMed

Fettke, Joerg; Leifels, Lydia; Brust, Henrike; Herbst, Karoline; Steup, Martin

2012-05-01

Parenchyma cells from tubers of Solanum tuberosum L. convert several externally supplied sugars to starch but the rates vary largely. Conversion of glucose 1-phosphate to starch is exceptionally efficient. In this communication, tuber slices were incubated with either of four solutions containing equimolar [U-¹⁴C]glucose 1-phosphate, [U-¹⁴C]sucrose, [U-¹⁴C]glucose 1-phosphate plus unlabelled equimolar sucrose or [U-¹⁴C]sucrose plus unlabelled equimolar glucose 1-phosphate. C¹⁴-incorporation into starch was monitored. In slices from freshly harvested tubers each unlabelled compound strongly enhanced ¹⁴C incorporation into starch indicating closely interacting paths of starch biosynthesis. However, enhancement disappeared when the tubers were stored. The two paths (and, consequently, the mutual enhancement effect) differ in temperature dependence. At lower temperatures, the glucose 1-phosphate-dependent path is functional, reaching maximal activity at approximately 20 °C but the flux of the sucrose-dependent route strongly increases above 20 °C. Results are confirmed by in vitro experiments using [U-¹⁴C]glucose 1-phosphate or adenosine-[U-¹⁴C]glucose and by quantitative zymograms of starch synthase or phosphorylase activity. In mutants almost completely lacking the plastidial phosphorylase isozyme(s), the glucose 1-phosphate-dependent path is largely impeded. Irrespective of the size of the granules, glucose 1-phosphate-dependent incorporation per granule surface area is essentially equal. Furthermore, within the granules no preference of distinct glucosyl acceptor sites was detectable. Thus, the path is integrated into the entire granule biosynthesis. In vitro C¹⁴C-incorporation into starch granules mediated by the recombinant plastidial phosphorylase isozyme clearly differed from the in situ results. Taken together, the data clearly demonstrate that two closely but flexibly interacting general paths of starch biosynthesis are functional in potato tuber cells.

Assist-as-needed path control for the PASCAL rehabilitation robot.

PubMed

Keller, Urs; Rauter, Georg; Riener, Robert

2013-06-01

Adults and children with neurological disorders often require rehabilitation therapy to improve their arm motor functions. Complementary to conventional therapy, robotic therapy can be applied. Such robots should support arm movements while assisting only as much as needed to ensure an active participation of the patient. Different control strategies are known to provide arm support to the patient. The path controller is a strategy that helps the patient's arm to stay close to a given path while allowing for temporal and spatial freedom. In this paper, an assist-as-needed path controller is presented that is implemented in the end-effector-based robot PASCAL, which was designed for children with cerebral palsy. The new control approach is a combination of an existing path controller with additional speed restrictions to support, when the arm speed is too slow, and to resist, when the speed is too fast. Furthermore, a target position gain scheduling is introduced in order to reach a target position with a predefined precision as well as an adaptable direction-dependent supportive flux that supports along the path. These path control features were preliminarily tested with a healthy adult volunteer in different conditions. The presented controller covers the range from a completely passive user, who needs full support to an actively performed movement that needs no assistance. In close future, the controller is planned to be used to enable reaching in children as well as in adults and help to increase the intensity of the rehabilitation therapy by assisting the hand movement and by provoking an active participation.

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

Miley, G.H.

Remarks made in the author{close_quote}s acceptance lecture for the 1995 Edward Teller Medal are presented and expanded. Topics covered include research on nuclear-pumped lasers, the first direct e-beam-pumped laser, direct energy conversion and advanced fuel fusion, plus recent work on inertial electrostatic confinement. {open_quote}{open_quote}Patience{close_quote}{close_quote} and {open_quote}{open_quote}optimism{close_quote}{close_quote} are viewed as essential elements needed by scientists following the {open_quote}{open_quote}zig-zag{close_quote}{close_quote} path to fusion energy production. {copyright} {ital 1996 American Institute of Physics.}

Time optimal paths for high speed maneuvering

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

Reister, D.B.; Lenhart, S.M.

1993-01-01

Recent theoretical results have completely solved the problem of determining the minimum length path for a vehicle with a minimum turning radius moving from an initial configuration to a final configuration. Time optimal paths for a constant speed vehicle are a subset of the minimum length paths. This paper uses the Pontryagin maximum principle to find time optimal paths for a constant speed vehicle. The time optimal paths consist of sequences of axes of circles and straight lines. The maximum principle introduces concepts (dual variables, bang-bang solutions, singular solutions, and transversality conditions) that provide important insight into the nature ofmore » the time optimal paths. We explore the properties of the optimal paths and present some experimental results for a mobile robot following an optimal path.« less

Single-bunch synchrotron shutter

DOEpatents

Norris, James R.; Tang, Jau-Huei; Chen, Lin; Thurnauer, Marion

1993-01-01

An apparatus for selecting a single synchrotron pulse from the millions of pulses provided per second from a synchrotron source includes a rotating spindle located in the path of the synchrotron pulses. The spindle has multiple faces of a highly reflective surface, and having a frequency of rotation f. A shutter is spaced from the spindle by a radius r, and has an open position and a closed position. The pulses from the synchrotron are reflected off the spindle to the shutter such that the speed s of the pulses at the shutter is governed by: s=4.times..pi..times.r.times.f. such that a single pulse is selected for transmission through an open position of the shutter.

Time-periodic solutions of the Benjamin-Ono equation

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

Ambrose , D.M.; Wilkening, Jon

2008-04-01

We present a spectrally accurate numerical method for finding non-trivial time-periodic solutions of non-linear partial differential equations. The method is based on minimizing a functional (of the initial condition and the period) that is positive unless the solution is periodic, in which case it is zero. We solve an adjoint PDE to compute the gradient of this functional with respect to the initial condition. We include additional terms in the functional to specify the free parameters, which, in the case of the Benjamin-Ono equation, are the mean, a spatial phase, a temporal phase and the real part of one ofmore » the Fourier modes at t = 0. We use our method to study global paths of non-trivial time-periodic solutions connecting stationary and traveling waves of the Benjamin-Ono equation. As a starting guess for each path, we compute periodic solutions of the linearized problem by solving an infinite dimensional eigenvalue problem in closed form. We then use our numerical method to continue these solutions beyond the realm of linear theory until another traveling wave is reached (or until the solution blows up). By experimentation with data fitting, we identify the analytical form of the solutions on the path connecting the one-hump stationary solution to the two-hump traveling wave. We then derive exact formulas for these solutions by explicitly solving the system of ODE's governing the evolution of solitons using the ansatz suggested by the numerical simulations.« less

Temporal dynamics in dominant runoff sources and flow paths in the Andean Páramo

NASA Astrophysics Data System (ADS)

Correa, Alicia; Windhorst, David; Tetzlaff, Doerthe; Crespo, Patricio; Célleri, Rolando; Feyen, Jan; Breuer, Lutz

2017-07-01

The relative importance of catchment's water provenance and flow paths varies in space and time, complicating the conceptualization of the rainfall-runoff responses. We assessed the temporal dynamics in source areas, flow paths, and age by End Member Mixing Analysis (EMMA), hydrograph separation, and Inverse Transit Time Proxies (ITTPs) estimation within a headwater catchment in the Ecuadorian Andes. Twenty-two solutes, stable isotopes, pH, and electrical conductivity from a stream and 12 potential sources were analyzed. Four end-members were required to satisfactorily represent the hydrological system, i.e., rainfall, spring water, and water from the bottom layers of Histosols and Andosols. Water from Histosols in and near the riparian zone was the highest source contributor to runoff throughout the year (39% for the drier season, 45% for the wetter season), highlighting the importance of the water that is stored in the riparian zone. Spring water contributions to streamflow tripled during the drier season, as evidenced by geochemical signatures that are consistent with deeper flow paths rather than shallow interflow through Andosols. Rainfall exhibited low seasonal variation in this contribution. Hydrograph separation revealed that 94% and 84% is preevent water in the drier and wetter seasons, respectively. From low-flow to high-flow conditions, all the sources increased their contribution except spring water. The relative age of stream water decreased during wetter periods, when the contributing area of the riparian zone expands. The multimethod and multitracer approach enabled to closely study the interchanging importance of flow processes and water source dynamics from an interannual perspective.

The relationship between hippocampal volume and static postural sway: results from the GAIT study.

PubMed

Beauchet, Olivier; Barden, John; Liu-Ambrose, Teresa; Chester, Victoria L; Szturm, Tony; Allali, Gilles

2016-02-01

The role of the hippocampus in postural control, in particular in maintaining upright stance, has not been fully examined in normal aging. This study aims to examine the association of postural sway with hippocampal volume while maintaining upright stance in healthy older individuals. Seventy healthy individuals (mean age 69.7 ± 3.4 years; 41.4 % women) were recruited in this study based on cross-sectional design. Hippocampal volume (quantified from a three-dimensional T1-weighted MRI using semi-automated software), three center of pressure (COP) motion parameters (sway area, path length of anterior-posterior (AP) and medial-lateral (ML) displacement) while maintaining upright stance (eyes open and closed), and the relative difference between open and closed eye conditions were used as outcome measures. Age, sex, body mass index, lower limb proprioception, distance vision, 15-item geriatric depression scale score, total cranial volume, and white matter abnormalities were used as covariates. The sway area decreased from open to closed eye condition but this variation was non-significant (P = 0.244), whereas path length of AP and ML displacement increased significantly (P < 0.003). Increase in sway area from open to closed eyes was associated with greater hippocampal volume (β -18.21; P = 0.044), and a trend for an association of increase in path length of AP displacement (P = 0.075 for open eyes and P = 0.071 for closed eyes) with greater hippocampal volume was reported. The hippocampus is involved in upright postural control in normal aging, such that an increase in sway area of COP motion from open to closed eyes is associated with greater hippocampal volume in healthy older adults.

Spatial and temporal allocation of ship exhaust emissions in Australian coastal waters using AIS data: Analysis and treatment of data gaps

NASA Astrophysics Data System (ADS)

Goldsworthy, Brett

2017-08-01

Ship exhaust emissions need to be allocated accurately in both space and time in order to examine many of the associated impacts, including on air quality and health. Data on ship activity from the Automatic Identification System (AIS) allow ship exhaust emissions to be calculated with fine spatial and temporal resolution. However, there are spatial gaps in the coverage afforded by the coastal network of ground stations that are used to collect the AIS data. This paper focuses on the problem of allocating emissions to the coastal gap regions. Allocating emissions to these regions involves generating interpolated ship tracks that both span the gaps and avoid coming too close to land. In most cases, a simple shortest path or straight line interpolation produces tracks that do not overlap or come too close to land. Where the simple method does not produce acceptable results, vessel tracks are steered around land on shortest available paths using a combination of visibility graphs and Dijkstra's algorithm. A geographical cluster analysis is first used to identify the boundary regions of the data gaps. The properties of the data gaps are summarised in terms of the length, duration and speed of the spanning tracks. The interpolation methods are used to improve the spatial distribution of emissions. It is also shown that emissions in the gap regions can contribute substantially to the total ship exhaust emissions in close proximity to highly populated areas.

Tri-state logic circuit

NASA Technical Reports Server (NTRS)

Pryor, Richard Lee (Inventor)

1977-01-01

A line driver including a pair of complementary transistors having their conduction paths serially connected between an operating and a reference potential and their bases connected through a first switch to a signal input terminal. A second switch is connected between the common base connection and the common connection of the conduction paths. With the second switch open and the first closed, an output voltage, responsive to the input signal, corresponding to first or second binary values is obtained. When the second switch is closed and the first opened, the transistor pair is turned off, disconnecting the line driver from its load, thereby providing tri-state logic operation.

Electrical crosstalk-coupling measurement and analysis for digital closed loop fibre optic gyro

NASA Astrophysics Data System (ADS)

Jin, Jing; Tian, Hai-Ting; Pan, Xiong; Song, Ning-Fang

2010-03-01

The phase modulation and the closed-loop controller can generate electrical crosstalk-coupling in digital closed-loop fibre optic gyro. Four electrical cross-coupling paths are verified by the open-loop testing approach. It is found the variation of ramp amplitude will lead to the alternation of gyro bias. The amplitude and the phase parameters of the electrical crosstalk signal are measured by lock-in amplifier, and the variation of gyro bias is confirmed to be caused by the alternation of phase according to the amplitude of the ramp. A digital closed-loop fibre optic gyro electrical crosstalk-coupling model is built by approximating the electrical cross-coupling paths as a proportion and integration segment. The results of simulation and experiment show that the modulation signal electrical crosstalk-coupling can cause the dead zone of the gyro when a small angular velocity is inputted, and it could also lead to a periodic vibration of the bias error of the gyro when a large angular velocity is inputted.

Rankine cycle load limiting through use of a recuperator bypass

DOEpatents

Ernst, Timothy C.

2011-08-16

A system for converting heat from an engine into work includes a boiler coupled to a heat source for transferring heat to a working fluid, a turbine that transforms the heat into work, a condenser that transforms the working fluid into liquid, a recuperator with one flow path that routes working fluid from the turbine to the condenser, and another flow path that routes liquid working fluid from the condenser to the boiler, the recuperator being configured to transfer heat to the liquid working fluid, and a bypass valve in parallel with the second flow path. The bypass valve is movable between a closed position, permitting flow through the second flow path and an opened position, under high engine load conditions, bypassing the second flow path.

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

Russell, J.S.

Several factors in the development of the East Wilmington oil field by THUMS Long Beach Co. are described. These include: critical path scheduling, complex stratigraphy, reservoir engineering, drilling program, production methods, pressure maintenance, crude oil processing, automation, transportation facilities, service lines, and electrical facilities. The complexity and closely scheduled operational events interwoven in the THUMS project demands a method for the carefully planned sequence of jobs to be done, beginning with island construction up through routine production and to the LACT system. These demanding requirements necessitated the use of a critical path scheduling program. It was decided to use themore » program evaluation technique. This technique is used to assign responsibilities for individual assignments to time assignments, and to keep the overall program on schedule. The stratigraphy of East Wilmington complicates all engineering functions associated with recovery methods and reservoir evaluation. At least 5 major faults are anticipated.« less

A novel method for trajectory planning of cooperative mobile manipulators.

PubMed

Bolandi, Hossein; Ehyaei, Amir Farhad

2011-01-01

We have designed a two-stage scheme to consider the trajectory planning problem of two mobile manipulators for cooperative transportation of a rigid body in the presence of static obstacles. In the first stage, with regard to the static obstacles, we develop a method that searches the workspace for the shortest possible path between the start and goal configurations, by constructing a graph on a portion of the configuration space that satisfies the collision and closure constraints. The final stage is to calculate a sequence of time-optimal trajectories to go between the consecutive points of the path, with regard to the nonholonomic constraints and the maximum allowed joint accelerations. This approach allows geometric constraints such as joint limits and closed-chain constraints, along with differential constraints such as nonholonomic velocity constraints and acceleration limits, to be incorporated into the planning scheme. The simulation results illustrate the effectiveness of the proposed method.

A Novel Method for Trajectory Planning of Cooperative Mobile Manipulators

PubMed Central

Bolandi, Hossein; Ehyaei, Amir Farhad

2011-01-01

We have designed a two-stage scheme to consider the trajectory planning problem of two mobile manipulators for cooperative transportation of a rigid body in the presence of static obstacles. In the first stage, with regard to the static obstacles, we develop a method that searches the workspace for the shortest possible path between the start and goal configurations, by constructing a graph on a portion of the configuration space that satisfies the collision and closure constraints. The final stage is to calculate a sequence of time-optimal trajectories to go between the consecutive points of the path, with regard to the nonholonomic constraints and the maximum allowed joint accelerations. This approach allows geometric constraints such as joint limits and closed-chain constraints, along with differential constraints such as nonholonomic velocity constraints and acceleration limits, to be incorporated into the planning scheme. The simulation results illustrate the effectiveness of the proposed method. PMID:22606656

Mechanisms of postural control in alcoholic men and women: biomechanical analysis of musculoskeletal coordination during quiet standing.

PubMed

Sullivan, Edith V; Rose, Jessica; Pfefferbaum, Adolf

2010-03-01

Excessive sway during quiet standing is a common sequela of chronic alcoholism even with prolonged sobriety. Whether alcoholic men and women who have remained abstinent from alcohol for weeks to months differ from each other in the degree of residual postural instability and biomechanical control mechanisms has not been directly tested. We used a force platform to characterize center-of-pressure biomechanical features of postural sway, with and without stabilizing conditions from touch, vision, and stance, in 34 alcoholic men, 15 alcoholic women, 22 control men, and 29 control women. Groups were matched in age (49.4 years), general intelligence, socioeconomic status, and handedness. Each alcoholic group was sober for an average of 75 days. Analysis of postural sway when using all 3 stabilizing conditions versus none revealed diagnosis and sex differences in ability to balance. Alcoholics had significantly longer sway paths, especially in the anterior-posterior direction, than controls when maintaining erect posture without balance aids. With stabilizing conditions the sway paths of all groups shortened significantly, especially those of alcoholic men, who demonstrated a 3.1-fold improvement in sway path difference between the easiest and most challenging conditions; the remaining 3 groups, each showed a approximately 2.4-fold improvement. Application of a mechanical model to partition sway paths into open-loop and closed-loop postural control systems revealed that the sway paths of the alcoholic men but not alcoholic women were characterized by greater short-term (open-loop) diffusion coefficients without aids, often associated with muscle stiffening response. With stabilizing factors, all 4 groups showed similar long-term (closed loop) postural control. Correlations between cognitive abilities and closed-loop sway indices were more robust in alcoholic men than alcoholic women. Reduction in sway and closed-loop activity during quiet standing with stabilizing factors shows some differential expression in men and women with histories of alcohol dependence. Nonetheless, enduring deficits in postural instability of both alcoholic men and alcoholic women suggest persisting liability for falling.

On the relation between phase path, group path and attenuation in a cold absorbing plasma

NASA Technical Reports Server (NTRS)

Bennett, J. A.; Dyson, P. L.

1978-01-01

Consideration is given to a cold absorbing plasma in which the collision frequency is zero. Expressions are developed which relate the attenuation and the group and phase refractive indices. It is found that because the expressions for the group and phase refractive indices and the imaginary part of the refractive index are closely related in form, the attenuation is related to the difference between the group and phase paths. Numerical calculations have derived approximations which significantly increase the range of known approximations of this type.

A New Control Paradigm for Stochastic Differential Equations

NASA Astrophysics Data System (ADS)

Schmid, Matthias J. A.

This study presents a novel comprehensive approach to the control of dynamic systems under uncertainty governed by stochastic differential equations (SDEs). Large Deviations (LD) techniques are employed to arrive at a control law for a large class of nonlinear systems minimizing sample path deviations. Thereby, a paradigm shift is suggested from point-in-time to sample path statistics on function spaces. A suitable formal control framework which leverages embedded Freidlin-Wentzell theory is proposed and described in detail. This includes the precise definition of the control objective and comprises an accurate discussion of the adaptation of the Freidlin-Wentzell theorem to the particular situation. The new control design is enabled by the transformation of an ill-posed control objective into a well-conditioned sequential optimization problem. A direct numerical solution process is presented using quadratic programming, but the emphasis is on the development of a closed-form expression reflecting the asymptotic deviation probability of a particular nominal path. This is identified as the key factor in the success of the new paradigm. An approach employing the second variation and the differential curvature of the effective action is suggested for small deviation channels leading to the Jacobi field of the rate function and the subsequently introduced Jacobi field performance measure. This closed-form solution is utilized in combination with the supplied parametrization of the objective space. For the first time, this allows for an LD based control design applicable to a large class of nonlinear systems. Thus, Minimum Large Deviations (MLD) control is effectively established in a comprehensive structured framework. The construction of the new paradigm is completed by an optimality proof for the Jacobi field performance measure, an interpretive discussion, and a suggestion for efficient implementation. The potential of the new approach is exhibited by its extension to scalar systems subject to state-dependent noise and to systems of higher order. The suggested control paradigm is further advanced when a sequential application of MLD control is considered. This technique yields a nominal path corresponding to the minimum total deviation probability on the entire time domain. It is demonstrated that this sequential optimization concept can be unified in a single objective function which is revealed to be the Jacobi field performance index on the entire domain subject to an endpoint deviation. The emerging closed-form term replaces the previously required nested optimization and, thus, results in a highly efficient application-ready control design. This effectively substantiates Minimum Path Deviation (MPD) control. The proposed control paradigm allows the specific problem of stochastic cost control to be addressed as a special case. This new technique is employed within this study for the stochastic cost problem giving rise to Cost Constrained MPD (CCMPD) as well as to Minimum Quadratic Cost Deviation (MQCD) control. An exemplary treatment of a generic scalar nonlinear system subject to quadratic costs is performed for MQCD control to demonstrate the elementary expandability of the new control paradigm. This work concludes with a numerical evaluation of both MPD and CCMPD control for three exemplary benchmark problems. Numerical issues associated with the simulation of SDEs are briefly discussed and illustrated. The numerical examples furnish proof of the successful design. This study is complemented by a thorough review of statistical control methods, stochastic processes, Large Deviations techniques and the Freidlin-Wentzell theory, providing a comprehensive, self-contained account. The presentation of the mathematical tools and concepts is of a unique character, specifically addressing an engineering audience.

Use of (N-1)-D expansions for N-D phase unwrapping in MRI

NASA Astrophysics Data System (ADS)

Bones, Philip J.; King, Laura J.; Millane, Rick P.

2017-09-01

In MRI the presence of metal implants causes severe artifacts in images and interferes with the usual techniques used to separate fat signals from other tissues. In the Dixon method, three images are acquired at different echo times to enable the variation in the magnetic field to be estimated. However, the estimate is represented as the phase of a complex quantity and therefore suffers from wrapping. High field gradients near the metal mean that the phase estimate is undersampled and therefore challenging to unwrap. We have developed POP, phase estimation by onion peeling, an algorithm which unwraps the phase along 1-D paths for a 2-D image obtained with the Dixon method. The unwrapping is initially performed along a closed path enclosing the implant and well separated from it. The recovered phase is expanded using a smooth periodic basis along the path. Then, path-by-path, the estimate is applied to the next path and then the expansion coefficients are estimated to best fit the wrapped measurements. We have successfully tested POP on MRI images of specially constructed phantoms and on a group of patients with hip implants. In principle, POP can be extended to 3-D imaging. In that case, POP would entail representing phase with a suitably smooth basis over a series of surfaces enclosing the implant (the "onion skins"), again beginning the phase estimation well away from the implant. An approach for this is proposed. Results are presented for fat and water separation for 2-D images of phantoms and actual patients. The practicality of the method and its employment in clinical MRI are discussed.

Flight path control strategies and preliminary deltaV requirements for the 2007 Mars Phoenix (PHX) mission

NASA Technical Reports Server (NTRS)

Raofi, Behzad

2005-01-01

This paper describes the methods used to estimate the statistical deltaV requirements for the propulsive maneuvers that will deliver the spacecraft to its target landing site while satisfying planetary protection requirements. the paper presents flight path control analysis results for three different trajectories, open, middle, and close of launch period for the mission.

The Development of Close Relationships in Japan and the United States: Paths of Symbiotic Harmony and Generative Tension.

ERIC Educational Resources Information Center

Rothbaum, Fred; Pott, Martha; Azuma, Hiroshi; Miyake, Kazuo; Weisz, John

2000-01-01

Compares paths of development in Japan (symbiotic harmony) and the United States (generative tension) of parent-child and adult mate relationships, challenging assumptions that certain processes are central in all relationships or that U.S. relationships are less valued or weaker than Japan's. Suggests need to investigate processes underlying, and…

Moderating Effects of Prevention-Focus on the Paths from Two Insecure Attachment Dimensions to Depression.

PubMed

Lee, Dong-Gwi; Park, Jae Joon; Bae, Byeong Hoon; Lim, Hyun-Woo

2018-04-03

The present study investigated the moderating effects of prevention-focus on the paths from the dimensions of insecure attachment (attachment avoidance and attachment anxiety) to depression. Two hundred twenty eight Korean college students completed the Experience in Close Relationship - Revised Scale; the Regulatory Focus Strategies Scale; and the Center for Epidemiologic Studies Depression Scale. Results revealed a significant moderating effect for prevention-focus on the path from attachment avoidance to depression, but not on the path from attachment anxiety to depression. They further suggest that different interventions are needed for different combinations of persons' insecure attachment dimensions and levels of prevention-focus. Counseling implications and suggestions for future research are discussed.

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

Reister, D.B.; Lenhart, S.M.

Recent theoretical results have completely solved the problem of determining the minimum length path for a vehicle with a minimum turning radius moving from an initial configuration to a final configuration. Time optimal paths for a constant speed vehicle are a subset of the minimum length paths. This paper uses the Pontryagin maximum principle to find time optimal paths for a constant speed vehicle. The time optimal paths consist of sequences of axes of circles and straight lines. The maximum principle introduces concepts (dual variables, bang-bang solutions, singular solutions, and transversality conditions) that provide important insight into the nature ofmore » the time optimal paths. We explore the properties of the optimal paths and present some experimental results for a mobile robot following an optimal path.« less

Predictors of satisfaction in geographically close and long-distance relationships.

PubMed

Lee, Ji-yeon; Pistole, M Carole

2012-04-01

In this study, the authors examined geographically close (GCRs) and long-distance (LDRs) romantic relationship satisfaction as explained by insecure attachment, self-disclosure, gossip, and idealization. After college student participants (N = 536) completed a Web survey, structural equation modeling (SEM) multigroup analysis revealed that the GCR and LDR models were nonequivalent, as expected. Self-disclosure mediated the insecure attachment-idealization path differently in GCRs and in LDRs. Self-disclosure was positively associated with idealization in GCRs and negatively associated with idealization in LDRs, with the insecure attachment-idealization and the insecure attachment-satisfaction paths negative for both GCRs and LDRs. Furthermore, the insecure attachment-idealization path was stronger than the mediated path, especially for LDRs; the insecure attachment-satisfaction path was stronger than the mediation model for GCRs and LDRs. In other words, the GCR and LDR models differed despite some similarities. For both, with higher insecure (i.e., anxious and avoidant) attachment, the person discloses less to the partner, idealizes the partner less, and is less satisfied with the relationship. Also, people who idealize are more satisfied. In contrast, in LDRs only, with higher insecure attachment, the people tend to gossip more. With higher insecure attachment and with higher self-disclosure, people idealize more in GCRs but idealize less in LDRs. Overall, attachment insecurity explained more idealization and satisfaction in LDRs than in GCRs. Implications are discussed.

Twist-induced guidance in coreless photonic crystal fiber: A helical channel for light.

PubMed

Beravat, Ramin; Wong, Gordon K L; Frosz, Michael H; Xi, Xiao Ming; Russell, Philip St J

2016-11-01

A century ago, Einstein proposed that gravitational forces were the result of the curvature of space-time and predicted that light rays would deflect when passing a massive celestial object. We report that twisting the periodically structured "space" within a coreless photonic crystal fiber creates a helical channel where guided modes can form despite the absence of any discernible core structure. Using a Hamiltonian optics analysis, we show that the light rays follow closed spiral or oscillatory paths within the helical channel, in close analogy with the geodesics of motion in a two-dimensional gravitational field. The mode diameter shrinks, and its refractive index rises, as the twist rate increases. The birefringence, orbital angular momentum, and dispersion of these unusual modes are explored.

Geomagnetic acceleration and rapid hydromagnetic wave dynamics in advanced numerical simulations of the geodynamo

NASA Astrophysics Data System (ADS)

Aubert, Julien

2018-04-01

Geomagnetic secular acceleration, the second temporal derivative of Earth's magnetic field, is a unique window on the dynamics taking place in Earth's core. In this study, the behaviours of the secular acceleration and underlying core dynamics are examined in new numerical simulations of the geodynamo that are dynamically closer to Earth's core conditions than earlier models. These new models reside on a theoretical path in parameter space connecting the region where most classical models are found to the natural conditions. The typical time scale for geomagnetic acceleration is found to be invariant along this path, at a value close to 10 years that matches Earth's core estimates. Despite this invariance, the spatio-temporal properties of secular acceleration show significant variability along the path, with an asymptotic regime of rapid rotation reached after 30% of this path (corresponding to a model Ekman number E = 3 - 7). In this regime, the energy of secular acceleration is entirely found at periods longer than that of planetary rotation, and the underlying flow acceleration patterns acquire a two-dimensional columnar structure representative of the rapid rotation limit. The spatial pattern of the secular acceleration at the core-mantle boundary shows significant localisation of energy within an equatorial belt. Rapid hydromagnetic wave dynamics is absent at the start of the path because of insufficient time scale separation with convective processes, weak forcing and excessive damping but can be clearly exhibited in the asymptotic regime. This study reports on ubiquitous axisymmetric geostrophic torsional waves of weak amplitude relatively to convective transport, and also stronger, laterally limited, quasi-geostrophic Alfvén waves propagating in the cylindrical radial direction from the tip of convective plumes towards the core-mantle boundary. In a system similar to Earth's core where the typical Alfvén velocity is significantly larger than the typical convective velocity, quasi-geostrophic Alfvén waves are shown to be an important carrier of flow acceleration to the core surface that links with the generation of strong, short-lived and intermittent equatorial pulses in the secular acceleration energy. The secular acceleration time scale is shown to be insensitive to magnetic signatures from torsional waves because of their weak amplitude, and from quasi-geostrophic Alfvén waves because of their intermittent character, and is therefore only indicative of convective transport phenomena that remain invariant along the parameter space path.

Balance and gait performance after maximal and submaximal endurance exercise in seniors: is there a higher fall-risk?

PubMed

Donath, Lars; Zahner, Lukas; Roth, Ralf; Fricker, Livia; Cordes, Mareike; Hanssen, Henner; Schmidt-Trucksäss, Arno; Faude, Oliver

2013-03-01

Impaired balance and gait performance increase fall-risk in seniors. Acute effects of different exercise bouts on gait and balance were not yet addressed. Therefore, 19 healthy seniors (10 women, 9 men, age: 64.6 ± 3.2 years) were examined on 3 days. After exhaustive treadmill testing, participants randomly completed a 2-km treadmill walking test (76 ± 8 % VO(2max)) and a resting control condition. Standing balance performance (SBALP) was assessed by single limb-eyes opened (SLEO) and double limb-eyes closed (DLEC) stance. Gait parameters were collected at comfortable walking velocity. A condition × time interaction of center of pressure path length (COP(path)) was observed for both balance tasks (p < 0.001). Small (Cohen's d = 0.42, p = 0.05) and large (d = 1.04, p < 0.001) COP(path) increases were found after 2-km and maximal exercise during DLEC. Regarding SLEO, slightly increased COP(path) occurred after 2-km walking (d = 0.29, p = 0.65) and large increases after exhaustive exercise (d = 1.24, p < 0.001). No significant differences were found for gait parameters. Alterations of SBALP after exhaustive exercise might lead to higher fall-risk in seniors. Balance changes upon 2-km testing might be of minor relevance. Gait is not affected during single task walking at given velocities.

US tornadoes. Part 1: 70-year statistics

NASA Technical Reports Server (NTRS)

Fujita, T. T.

1987-01-01

If tornadoes were counted as the Gross National Product, no other country on the surface of the earth could come even close to the United States. During the recent 70 year period, the United States produced 31,054 tornadoes which left behind a cumulative path of 132,005 miles (212,396 km) which would circle the world 5.3 times along the equator. In completing the book, staff members of the Satellite and Mesometeorlogy Research Project (1961 to the present) played an important role in collecting, evaluating, and archiving the historical tornado data.

The Path of Carbon in Photosynthesis VIII. The Role of Malic Acid

DOE R&D Accomplishments Database

Bassham, James A.; Benson, Andrew A.; Calvin, Melvin

1950-01-25

Malonate has been found to inhibit the formation of malic acid during short periods of photosynthesis with radioactive carbon dioxide. This result, together with studies which show the photosynthetic cycle to be operating normally at the same time, indicates that malic acid is not an intermediate in photosynthesis but is probably closely related to some intermediate of the cycle. Absence of labeled succinic and fumaric acids in these experiments, in addition to the failure of malonate to inhibit photosynthesis, precludes the participation of these acids as intermediates in photosynthesis.

Transition path time distributions for Lévy flights

NASA Astrophysics Data System (ADS)

Janakiraman, Deepika

2018-07-01

This paper presents a study of transition path time distributions for Lévy noise-induced barrier crossing. Transition paths are short segments of the reactive trajectories and span the barrier region of the potential without spilling into the reactant/product wells. The time taken to traverse this segment is referred to as the transition path time. Since the transition path is devoid of excursions in the minimum, the corresponding time will give the exclusive barrier crossing time, unlike . This work explores the distribution of transition path times for superdiffusive barrier crossing, analytically. This is made possible by approximating the barrier by an inverted parabola. Using this approximation, the distributions are evaluated in both over- and under-damped limits of friction. The short-time behaviour of the distributions, provide analytical evidence for single-step transition events—a feature in Lévy-barrier crossing as observed in prior simulation studies. The average transition path time is calculated as a function of the Lévy index (α), and the optimal value of α leading to minimum average transition path time is discussed, in both the limits of friction. Langevin dynamics simulations corroborating with the analytical results are also presented.

Postural stability changes during large vertical diplopia induced by prism wear in normal subjects.

PubMed

Matsuo, Toshihiko; Yamasaki, Hanako; Yasuhara, Hirotaka; Hasebe, Kayoko

2013-01-01

To test the effect of double vision on postural stability, we measured postural stability by electric stabilometry before prism-wearing and immediately, 15, 30, and 60min after continuous prism-wearing with 6 prism diopters in total (a 3-prism-diopter prism placed with the base up in front of one eye and with the base down in front of the other eye) in 20 normal adult individuals with their eyes open or closed. Changes in stabilometric parameters in the time course of 60min were analyzed statistically by repeated-measure analysis of variance. When subjectsｾ eyes were closed, the total linear length (cm) and the unit-time length (cm/sec) of the sway path were significantly shortened during the 60-minute prism-wearing (p＜0.05). No significant change was noted in any stabilometric parameters obtained with the eyes open during the time course. In conclusion, postural stability did not change with the eyes open in the condition of large vertical diplopia, induced by prism-wearing for 60min, while the stability became better when measured with the eyes closed. A postural control mechanism other than that derived from visual input might be reinforced under abnormal visual input such as non-fusionable diplopia.

Analytic solution of the Spencer-Lewis angular-spatial moments equations

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

Filippone, W.L.

A closed-form solution for the angular-spatial moments of the Spencer-Lewis equation is presented that is valid for infinite homogeneous media. From the moments, the electron density distribution as a function of position and path length (energy) is reconstructed for several sample problems involving plane isotropic sources of electrons in aluminium. The results are in excellent agreement with those determined numerically using the streaming ray method. The primary use of the closed form solution will most likely be to generate accurate electron transport benchmark solutions. In principle, the electron density as a function of space, path length, and direction can bemore » determined for planar sources of arbitrary angular distribution.« less

Metastable phases of silver and gold in hexagonal structure

NASA Astrophysics Data System (ADS)

Jona, F.; Marcus, P. M.

2004-07-01

Metastable phases of silver and gold in hexagonal close-packed structures are investigated by means of first-principles total-energy calculations. Two different methods are employed to find the equilibrium states: determination of the minima along the hexagonal epitaxial Bain path, and direct determination of minima of the total energy by a new minimum-path procedure. Both metals have two equilibrium states at different values of the hexagonal axial ratio c/a. For both metals, the elastic constants show that the high-c/a states are stable, hence, since the ground states are face-centred cubic, these states represent hexagonal close-packed metastable phases. The elastic constants of the low-c/a states show that they are unstable.

The deep fovea, sideways vision and spiral flight paths in raptors.

PubMed

Tucker, V A

2000-12-01

Raptors - falcons, hawks and eagles in this study - have two regions of the retina in each eye that are specialized for acute vision: the deep fovea and the shallow fovea. The line of sight of the deep fovea points forwards and approximately 45 degrees to the right or left of the head axis, while that of the shallow fovea also points forwards but approximately 15 degrees to the right or left of the head axis. The anatomy of the foveae suggests that the deep fovea has the higher acuity. Several species of raptors in this study repeatedly moved their heads among three positions while looking at an object: straight, with the head axis pointing towards the object; or sideways to the right or left, with the head axis pointing approximately 40 degrees to the side of the object. Since raptors do not rotate their eyes noticeably in the sockets, these movements presumably cause the image of the object to fall on the shallow and deep foveae. The movements occurred approximately every 2 s on average in hawks and falcons, and approximately every 5 s in bald eagles. The proportion of time that the raptors spent looking straight or sideways at an object depended on how far away the object was. At a distances closer than 8 m, they spent more time looking at the object straight, but as the distance increased to 21 m, they spent more time looking at it sideways. At distances of 40 m or more, raptors looked sideways at the object 80 % or more of the time. This dependence of head position on distance suggests that raptors use their more acute sideways vision to look at distant objects and sacrifice acuity for stereoscopic binocular vision to look at close objects. Having their most acute vision towards the side causes a conflict in raptors such as falcons, which dive at prey from great distances at high speeds: at a speed of 70 m s(-)(1), turning their head sideways to view the prey straight ahead with high visual acuity may increase aerodynamic drag by a factor of 2 or more and slow the raptor down. Raptors could resolve this conflict by diving along a logarithmic spiral path with their head straight and one eye looking sideways at the prey, rather than following the straight path to the prey with their head turned sideways. Although the spiral path is longer than the straight path, a mathematical model for an 'ideal falcon' shows that the falcon could reach the prey more quickly along the spiral path because the speed advantage of a straight head more than compensates for the longer path.

Autonomous underwater vehicle adaptive path planning for target classification

NASA Astrophysics Data System (ADS)

Edwards, Joseph R.; Schmidt, Henrik

2002-11-01

Autonomous underwater vehicles (AUVs) are being rapidly developed to carry sensors into the sea in ways that have previously not been possible. The full use of the vehicles, however, is still not near realization due to lack of the true vehicle autonomy that is promised in the label (AUV). AUVs today primarily attempt to follow as closely as possible a preplanned trajectory. The key to increasing the autonomy of the AUV is to provide the vehicle with a means to make decisions based on its sensor receptions. The current work examines the use of active sonar returns from mine-like objects (MLOs) as a basis for sensor-based adaptive path planning, where the path planning objective is to discriminate between real mines and rocks. Once a target is detected in the mine hunting phase, the mine classification phase is initialized with a derivative cost function to emphasize signal differences and enhance classification capability. The AUV moves adaptively to minimize the cost function. The algorithm is verified using at-sea data derived from the joint MIT/SACLANTCEN GOATS experiments and advanced acoustic simulation using SEALAB. The mission oriented operating system (MOOS) real-time simulator is then used to test the onboard implementation of the algorithm.

Robust Flight Path Determination for Mars Precision Landing Using Genetic Algorithms

NASA Technical Reports Server (NTRS)

Bayard, David S.; Kohen, Hamid

1997-01-01

This paper documents the application of genetic algorithms (GAs) to the problem of robust flight path determination for Mars precision landing. The robust flight path problem is defined here as the determination of the flight path which delivers a low-lift open-loop controlled vehicle to its desired final landing location while minimizing the effect of perturbations due to uncertainty in the atmospheric model and entry conditions. The genetic algorithm was capable of finding solutions which reduced the landing error from 111 km RMS radial (open-loop optimal) to 43 km RMS radial (optimized with respect to perturbations) using 200 hours of computation on an Ultra-SPARC workstation. Further reduction in the landing error is possible by going to closed-loop control which can utilize the GA optimized paths as nominal trajectories for linearization.

Path Forward to Space Solar Power using the O'Neill - Glaser Model Modified for Climate Change Demand and Considering the Increasing Risk of Human Self-Extinction if Confined to Earth

NASA Technical Reports Server (NTRS)

Curreri, Peter A.; Nall, Mark

2013-01-01

The cost of energy is humanity's economic exchange rate with the universe. Space solar power is the first great step that our technological species has to utilize the energy of its star. The classic Peter Glaser Solar Power Satellite, SPS, and later designs collect a large area of solar energy in space and beam it back to Earth for use in the electric grid, but even with optimistic launch costs and technology innovation a clear economic path is not evident using Earth launch of SPS. O Neill in 1969 solved the transportation costs problem by a model that uses lunar and asteroid materials to build SPS and locates the labor force permanently in space (O Neill free space habitats). This solution closes the economics and predicts large profits after 17-35 years. However the costs of time have up to now prevented this solution. We discuss a strategy to move forward in SPS with the motivations to stop global warming and prevent human selfextinction. There are near term steps that can be taken that place us on this path forward. First, we must reevaluate the technologies for the classic model and update the parameters to current technology. As technological capability continues to increase exponentially, we need to understand when the monetary potential energy hills are small as the technology gets larger. But the chance for self-extinction, if humanity remains in a single vulnerable habitat, also increased exponentially with time. The path forward is to identify investment points while assessing the risks of non-action.

Limb muscle sound speed estimation by ultrasound computed tomography excluding receivers in bone shadow

NASA Astrophysics Data System (ADS)

Qu, Xiaolei; Azuma, Takashi; Lin, Hongxiang; Takeuchi, Hideki; Itani, Kazunori; Tamano, Satoshi; Takagi, Shu; Sakuma, Ichiro

2017-03-01

Sarcopenia is the degenerative loss of skeletal muscle ability associated with aging. One reason is the increasing of adipose ratio of muscle, which can be estimated by the speed of sound (SOS), since SOSs of muscle and adipose are different (about 7%). For SOS imaging, the conventional bent-ray method iteratively finds ray paths and corrects SOS along them by travel-time. However, the iteration is difficult to converge for soft tissue with bone inside, because of large speed variation. In this study, the bent-ray method is modified to produce SOS images for limb muscle with bone inside. The modified method includes three steps. First, travel-time is picked up by a proposed Akaike Information Criterion (AIC) with energy term (AICE) method. The energy term is employed for detecting and abandoning the transmissive wave through bone (low energy wave). It results in failed reconstruction for bone, but makes iteration convergence and gives correct SOS for skeletal muscle. Second, ray paths are traced using Fermat's principle. Finally, simultaneous algebraic reconstruction technique (SART) is employed to correct SOS along ray paths, but excluding paths with low energy wave which may pass through bone. The simulation evaluation was implemented by k-wave toolbox using a model of upper arm. As the result, SOS of muscle was 1572.0+/-7.3 m/s, closing to 1567.0 m/s in the model. For vivo evaluation, a ring transducer prototype was employed to scan the cross sections of lower arm and leg of a healthy volunteer. And the skeletal muscle SOSs were 1564.0+/-14.8 m/s and 1564.1±18.0 m/s, respectively.

Multiscale simulations of patchy particle systems combining Molecular Dynamics, Path Sampling and Green's Function Reaction Dynamics

NASA Astrophysics Data System (ADS)

Bolhuis, Peter

Important reaction-diffusion processes, such as biochemical networks in living cells, or self-assembling soft matter, span many orders in length and time scales. In these systems, the reactants' spatial dynamics at mesoscopic length and time scales of microns and seconds is coupled to the reactions between the molecules at microscopic length and time scales of nanometers and milliseconds. This wide range of length and time scales makes these systems notoriously difficult to simulate. While mean-field rate equations cannot describe such processes, the mesoscopic Green's Function Reaction Dynamics (GFRD) method enables efficient simulation at the particle level provided the microscopic dynamics can be integrated out. Yet, many processes exhibit non-trivial microscopic dynamics that can qualitatively change the macroscopic behavior, calling for an atomistic, microscopic description. The recently developed multiscale Molecular Dynamics Green's Function Reaction Dynamics (MD-GFRD) approach combines GFRD for simulating the system at the mesocopic scale where particles are far apart, with microscopic Molecular (or Brownian) Dynamics, for simulating the system at the microscopic scale where reactants are in close proximity. The association and dissociation of particles are treated with rare event path sampling techniques. I will illustrate the efficiency of this method for patchy particle systems. Replacing the microscopic regime with a Markov State Model avoids the microscopic regime completely. The MSM is then pre-computed using advanced path-sampling techniques such as multistate transition interface sampling. I illustrate this approach on patchy particle systems that show multiple modes of binding. MD-GFRD is generic, and can be used to efficiently simulate reaction-diffusion systems at the particle level, including the orientational dynamics, opening up the possibility for large-scale simulations of e.g. protein signaling networks.

Role of post-field raw data processing: a multi-site and full factorial uncertainty analysis

NASA Astrophysics Data System (ADS)

Sabbatini, Simone; Fratini, Gerardo; Arriga, Nicola; Papale, Dario

2013-04-01

Uncertainties in the Eddy Covariance flux measurements are a fundamental issue not yet completely solved. The complexity of the method, involving many, not standardized processing steps is one among the source of such uncertainty. The goal of our work is to quantify uncertainties deriving from post-field raw data processing, needed to calculate fluxes from collected turbulence measurements. The methodology we propose is a full-factorial design, performed using as factors a number of selected processing steps. We applied this approach to 15 European flux stations representative of different ecosystems (forests, croplands and grasslands), climates (Mediterranean, Nordic, arid and humid) and instrumental setups (e.g. open vs. closed path systems). Then we processed one year of raw data from each of the selected stations so as to cover all possible combinations of the available options (levels) relative to all the critical processing steps, i.e: angle of attack correction; coordinate rotation; trend removal; time lag compensation; low- and high- frequency spectral correction; correction for air density fluctuations; and length of the flux averaging interval. The software we used is EddyPro™. At last we calculated the cumulative NEE (response) for each process, and performed an analysis of variance of the factorial design. In addition to the global uncertainty, from this statistical approach we obtain information about the factors that most contribute to the uncertainties, and also the most relevant two-level interactions between factors. Here we present partial results from the first sites analysed. For the beech forest of Sorø, Denmark (Gill R2 anemometer and closed path GA, tube length = 50 m) the factor that most contributes to the variance in 2007 (40.4 %) is the trend removal, with an uncertainty of 7.5%. It is followed by the angle of attack (16.1 % of the total variability, uncertainty 3.5 %) and the interaction between trend removal and time lag compensation (11.42 % of variance explained). The overall uncertainty is about 8.7 % (cumulative NEE = -440.22 ± 38.36 g C m-2 year-1). The Oak forest of Roccarespampani, Italy (Metek anemometer and closed path GA, tube length = 22 m) was a sink in 2006. The coordinate rotation has the main influence on the variance (46.14 %, against an uncertainty of 4 %), then comes the average interval with 17.34 % (unc. 2 %), and their interaction (9.70 % of variance explained). The total uncertainty is 4.8 % (NEE = -515.19 ± 24.7 g C m-2 year-1). The mixed forest of Norunda, Sweden, in the year 2008 is a source of CO2 (Metek anemometer and closed path GA, tube length = 8 m). For this site we found a strong influence of the coordinate rotation (74.02 %, with an uncertainty of 32.5 %), while the trend removal explains the 17.41 % of the variance (unc. 15 %), against a total uncertainty of about 26.8 % (155.04 ± 41.50 g C m-2 year-1).

Transition path time distributions

NASA Astrophysics Data System (ADS)

Laleman, M.; Carlon, E.; Orland, H.

2017-12-01

Biomolecular folding, at least in simple systems, can be described as a two state transition in a free energy landscape with two deep wells separated by a high barrier. Transition paths are the short part of the trajectories that cross the barrier. Average transition path times and, recently, their full probability distribution have been measured for several biomolecular systems, e.g., in the folding of nucleic acids or proteins. Motivated by these experiments, we have calculated the full transition path time distribution for a single stochastic particle crossing a parabolic barrier, including inertial terms which were neglected in previous studies. These terms influence the short time scale dynamics of a stochastic system and can be of experimental relevance in view of the short duration of transition paths. We derive the full transition path time distribution as well as the average transition path times and discuss the similarities and differences with the high friction limit.

Flight-Path Characteristics for Decelerating From Supercircular Speed

NASA Technical Reports Server (NTRS)

Luidens, Roger W.

1961-01-01

Characteristics of the following six flight paths for decelerating from a supercircular speed are developed in closed form: constant angle of attack, constant net acceleration, constant altitude" constant free-stream Reynolds number, and "modulated roll." The vehicles were required to remain in or near the atmosphere, and to stay within the aerodynamic capabilities of a vehicle with a maximum lift-drag ratio of 1.0 and within a maximum net acceleration G of 10 g's. The local Reynolds number for all the flight paths for a vehicle with a gross weight of 10,000 pounds and a 600 swept wing was found to be about 0.7 x 10(exp 6). With the assumption of a laminar boundary layer, the heating of the vehicle is studied as a function of type of flight path, initial G load, and initial velocity. The following heating parameters were considered: the distribution of the heating rate over the vehicle, the distribution of the heat per square foot over the vehicle, and the total heat input to the vehicle. The constant G load path at limiting G was found to give the lowest total heat input for a given initial velocity. For a vehicle with a maximum lift-drag ratio of 1.0 and a flight path with a maximum G of 10 g's, entry velocities of twice circular appear thermo- dynamically feasible, and entries at velocities of 2.8 times circular are aerodynamically possible. The predominant heating (about 85 percent) occurs at the leading edge of the vehicle. The total ablated weight for a 10,000-pound-gross-weight vehicle decelerating from an initial velocity of twice circular velocity is estimated to be 5 percent of gross weight. Modifying the constant G load flight path by a constant-angle-of-attack segment through a flight- to circular-velocity ratio of 1.0 gives essentially a "point landing" capability but also results in an increased total heat input to the vehicle.

Real-Time Hazard Detection and Avoidance Demonstration for a Planetary Lander

NASA Technical Reports Server (NTRS)

Epp, Chirold D.; Robertson, Edward A.; Carson, John M., III

2014-01-01

The Autonomous Landing Hazard Avoidance Technology (ALHAT) Project is chartered to develop and mature to a Technology Readiness Level (TRL) of six an autonomous system combining guidance, navigation and control with terrain sensing and recognition functions for crewed, cargo, and robotic planetary landing vehicles. In addition to precision landing close to a pre-mission defined landing location, the ALHAT System must be capable of autonomously identifying and avoiding surface hazards in real-time to enable a safe landing under any lighting conditions. This paper provides an overview of the recent results of the ALHAT closed loop hazard detection and avoidance flight demonstrations on the Morpheus Vertical Testbed (VTB) at the Kennedy Space Center, including results and lessons learned. This effort is also described in the context of a technology path in support of future crewed and robotic planetary exploration missions based upon the core sensing functions of the ALHAT system: Terrain Relative Navigation (TRN), Hazard Detection and Avoidance (HDA), and Hazard Relative Navigation (HRN).

Learning from Schools That Close Opportunity Gaps

ERIC Educational Resources Information Center

LaCour, Sarah E.; York, Adam; Welner, Kevin; Valladares, Michelle Renée; Kelley, Linda Molner

2017-01-01

The Schools of Opportunity Project recognizes public high schools that employ research-based practices to close opportunity gaps. The commended schools illustrate how school quality can and should be measured by far more than just test scores. In doing so, they offer exemplars and a path forward for the nation's schools. The selection criteria for…

Parameter optimization on the convergence surface of path simulations

NASA Astrophysics Data System (ADS)

Chandrasekaran, Srinivas Niranj

Computational treatments of protein conformational changes tend to focus on the trajectories themselves, despite the fact that it is the transition state structures that contain information about the barriers that impose multi-state behavior. PATH is an algorithm that computes a transition pathway between two protein crystal structures, along with the transition state structure, by minimizing the Onsager-Machlup action functional. It is rapid but depends on several unknown input parameters whose range of different values can potentially generate different transition-state structures. Transition-state structures arising from different input parameters cannot be uniquely compared with those generated by other methods. I outline modifications that I have made to the PATH algorithm that estimates these input parameters in a manner that circumvents these difficulties, and describe two complementary tests that validate the transition-state structures found by the PATH algorithm. First, I show that although the PATH algorithm and two other approaches to computing transition pathways produce different low-energy structures connecting the initial and final ground-states with the transition state, all three methods agree closely on the configurations of their transition states. Second, I show that the PATH transition states are close to the saddle points of free-energy surfaces connecting initial and final states generated by replica-exchange Discrete Molecular Dynamics simulations. I show that aromatic side-chain rearrangements create similar potential energy barriers in the transition-state structures identified by PATH for a signaling protein, a contractile protein, and an enzyme. Finally, I observed, but cannot account for, the fact that trajectories obtained for all-atom and Calpha-only simulations identify transition state structures in which the Calpha atoms are in essentially the same positions. The consistency between transition-state structures derived by different algorithms for unrelated protein systems argues that although functionally important protein conformational change trajectories are to a degree stochastic, they nonetheless pass through a well-defined transition state whose detailed structural properties can rapidly be identified using PATH. In the end, I outline the strategies that could enhance the efficiency and applicability of PATH.

Two betweenness centrality measures based on Randomized Shortest Paths

PubMed Central

Kivimäki, Ilkka; Lebichot, Bertrand; Saramäki, Jari; Saerens, Marco

2016-01-01

This paper introduces two new closely related betweenness centrality measures based on the Randomized Shortest Paths (RSP) framework, which fill a gap between traditional network centrality measures based on shortest paths and more recent methods considering random walks or current flows. The framework defines Boltzmann probability distributions over paths of the network which focus on the shortest paths, but also take into account longer paths depending on an inverse temperature parameter. RSP’s have previously proven to be useful in defining distance measures on networks. In this work we study their utility in quantifying the importance of the nodes of a network. The proposed RSP betweenness centralities combine, in an optimal way, the ideas of using the shortest and purely random paths for analysing the roles of network nodes, avoiding issues involving these two paradigms. We present the derivations of these measures and how they can be computed in an efficient way. In addition, we show with real world examples the potential of the RSP betweenness centralities in identifying interesting nodes of a network that more traditional methods might fail to notice. PMID:26838176

A two-component rain model for the prediction of attenuation and diversity improvement

NASA Technical Reports Server (NTRS)

Crane, R. K.

1982-01-01

A new model was developed to predict attenuation statistics for a single Earth-satellite or terrestrial propagation path. The model was extended to provide predictions of the joint occurrences of specified or higher attenuation values on two closely spaced Earth-satellite paths. The joint statistics provide the information required to obtain diversity gain or diversity advantage estimates. The new model is meteorologically based. It was tested against available Earth-satellite beacon observations and terrestrial path measurements. The model employs the rain climate region descriptions of the Global rain model. The rms deviation between the predicted and observed attenuation values for the terrestrial path data was 35 percent, a result consistent with the expectations of the Global model when the rain rate distribution for the path is not used in the calculation. Within the United States the rms deviation between measurement and prediction was 36 percent but worldwide it was 79 percent.

Identifying decohering paths in closed quantum systems

NASA Technical Reports Server (NTRS)

Albrecht, Andreas

1990-01-01

A specific proposal is discussed for how to identify decohering paths in a wavefunction of the universe. The emphasis is on determining the correlations among subsystems and then considering how these correlations evolve. The proposal is similar to earlier ideas of Schroedinger and of Zeh, but in other ways it is closer to the decoherence functional of Griffiths, Omnes, and Gell-Mann and Hartle. There are interesting differences with each of these which are discussed. Once a given coarse-graining is chosen, the candidate paths are fixed in this scheme, and a single well defined number measures the degree of decoherence for each path. The normal probability sum rules are exactly obeyed (instantaneously) by these paths regardless of the level of decoherence. Also briefly discussed is how one might quantify some other aspects of classicality. The important role that concrete calculations play in testing this and other proposals is stressed.

Efficient computation paths for the systematic analysis of sensitivities

NASA Astrophysics Data System (ADS)

Greppi, Paolo; Arato, Elisabetta

2013-01-01

A systematic sensitivity analysis requires computing the model on all points of a multi-dimensional grid covering the domain of interest, defined by the ranges of variability of the inputs. The issues to efficiently perform such analyses on algebraic models are handling solution failures within and close to the feasible region and minimizing the total iteration count. Scanning the domain in the obvious order is sub-optimal in terms of total iterations and is likely to cause many solution failures. The problem of choosing a better order can be translated geometrically into finding Hamiltonian paths on certain grid graphs. This work proposes two paths, one based on a mixed-radix Gray code and the other, a quasi-spiral path, produced by a novel heuristic algorithm. Some simple, easy-to-visualize examples are presented, followed by performance results for the quasi-spiral algorithm and the practical application of the different paths in a process simulation tool.

Guidance of a Solar Sail Spacecraft to the Sun - L(2) Point.

NASA Astrophysics Data System (ADS)

Hur, Sun Hae

The guidance of a solar sail spacecraft along a minimum-time path from an Earth orbit to a region near the Sun-Earth L_2 libration point is investigated. Possible missions to this point include a spacecraft "listening" for possible extra-terrestrial electromagnetic signals and a science payload to study the geomagnetic tail. A key advantage of the solar sail is that it requires no fuel. The control variables are the sail angles relative to the Sun-Earth line. The thrust is very small, on the order of 1 mm/s^2, and its magnitude and direction are highly coupled. Despite this limited controllability, the "free" thrust can be used for a wide variety of terminal conditions including halo orbits. If the Moon's mass is lumped with the Earth, there are quasi-equilibrium points near L_2. However, they are unstable so that some form of station keeping is required, and the sail can provide this without any fuel usage. In the two-dimensional case, regulating about a nominal orbit is shown to require less control and result in smaller amplitude error response than regulating about a quasi-equilibrium point. In the three-dimensional halo orbit case, station keeping using periodically varying gains is demonstrated. To compute the minimum-time path, the trajectory is divided into two segments: the spiral segment and the transition segment. The spiral segment is computed using a control law that maximizes the rate of energy increase at each time. The transition segment is computed as the solution of the time-optimal control problem from the endpoint of the spiral to the terminal point. It is shown that the path resulting from this approximate strategy is very close to the exact optimal path. For the guidance problem, the approximate strategy in the spiral segment already gives a nonlinear full-state feedback law. However, for large perturbations, follower guidance using an auxiliary propulsion is used for part of the spiral. In the transition segment, neighboring extremal feedback guidance using the solar sail, with feedforward control only near the terminal point, is used to correct perturbations in the initial conditions.

Voltage scheduling for low power/energy

NASA Astrophysics Data System (ADS)

Manzak, Ali

2001-07-01

Power considerations have become an increasingly dominant factor in the design of both portable and desk-top systems. An effective way to reduce power consumption is to lower the supply voltage since voltage is quadratically related to power. This dissertation considers the problem of lowering the supply voltage at (i) the system level and at (ii) the behavioral level. At the system level, the voltage of the variable voltage processor is dynamically changed with the work load. Processors with limited sized buffers as well as those with very large buffers are considered. Given the task arrival times, deadline times, execution times, periods and switching activities, task scheduling algorithms that minimize energy or peak power are developed for the processors equipped with very large buffers. A relation between the operating voltages of the tasks for minimum energy/power is determined using the Lagrange multiplier method, and an iterative algorithm that utilizes this relation is developed. Experimental results show that the voltage assignment obtained by the proposed algorithm is very close (0.1% error) to that of the optimal energy assignment and the optimal peak power (1% error) assignment. Next, on-line and off-fine minimum energy task scheduling algorithms are developed for processors with limited sized buffers. These algorithms have polynomial time complexity and present optimal (off-line) and close-to-optimal (on-line) solutions. A procedure to calculate the minimum buffer size given information about the size of the task (maximum, minimum), execution time (best case, worst case) and deadlines is also presented. At the behavioral level, resources operating at multiple voltages are used to minimize power while maintaining the throughput. Such a scheme has the advantage of allowing modules on the critical paths to be assigned to the highest voltage levels (thus meeting the required timing constraints) while allowing modules on non-critical paths to be assigned to lower voltage levels (thus reducing the power consumption). A polynomial time resource and latency constrained scheduling algorithm is developed to distribute the available slack among the nodes such that power consumption is minimum. The algorithm is iterative and utilizes the slack based on the Lagrange multiplier method.

Valve for gas centrifuges

DOEpatents

Hahs, Charles A.; Burbage, Charles H.

1984-01-01

The invention is a pneumatically operated valve assembly for simultaneously (1) closing gas-transfer lines connected to a gas centrifuge or the like and (2) establishing a recycle path between two of the lines so closed. The valve assembly is especially designed to be compact, fast-acting, reliable, and comparatively inexpensive. It provides large reductions in capital costs for gas-centrifuge cascades.

Oscillations of a Simple Pendulum with Extremely Large Amplitudes

ERIC Educational Resources Information Center

Butikov, Eugene I.

2012-01-01

Large oscillations of a simple rigid pendulum with amplitudes close to 180[degrees] are treated on the basis of a physically justified approach in which the cycle of oscillation is divided into several stages. The major part of the almost closed circular path of the pendulum is approximated by the limiting motion, while the motion in the vicinity…

Valve for gas centrifuges

DOEpatents

Hahs, C.A.; Rurbage, C.H.

1982-03-17

The invention is pneumatically operated valve assembly for simulatenously (1) closing gas-transfer lines connected to a gas centrifuge or the like and (2) establishing a recycle path between two on the lines so closed. The value assembly is especially designed to be compact, fast-acting, reliable, and comparatively inexpensive. It provides large reductions in capital costs for gas-centrifuge cascades.

Field evaluation of open and closed-path CO2 flux systems over asphalt surface

NASA Astrophysics Data System (ADS)

Bogoev, I.; Santos, E.

2016-12-01

Eddy covariance (EC) is a widely used method for quantifying surface fluxes of heat, water vapor and carbon dioxide between ecosystems and the atmosphere. A typical EC system consists of an ultrasonic anemometer measuring the 3D wind vector and a fast-response infrared gas analyzer for sensing the water vapor and CO2 density in the air. When using an open-path analyzer that detects the constituent's density in situ a correction for concurrent air temperature and humidity fluctuations must be applied, Webb et al. (1980). In environments with small magnitudes of CO2 flux (<5µmol m-2 s-1) and in the presence of high sensible heat flux, like wintertime over boreal forest, open-path flux measurements have been challenging since the magnitude of the density corrections are as large as the uncorrected CO2 flux itself. A new technology merging the sensing paths of the gas analyzer and the sonic anemometer has been recently developed. This new integrated instrument allows a direct measurement of CO2 mixing ratio in the open air and has the potential to improve the quality of the temperature related density corrections by synchronously measuring the sensible heat flux in the optical path of the gas analyzer. We evaluate the performance and the accuracy of this new sensor over a large parking lot with an asphalt surface where the CO2 fluxes are considered low and the interfering sensible heat fluxes are above 200 Wm-2. A co-located closed-path EC system is used as a reference measurement to examine any systematic biases and apparent CO2 uptake observed with open-path sensors under high sensible heat flux regimes. Half-hour mean and variance of CO2 and water vapor concentrations are evaluated. The relative spectral responses, covariances and corrected turbulent fluxes using a common sonic anemometer are analyzed. The influence of sensor separation and frequency response attenuation on the density corrections is discussed.

Path Flow Estimation Using Time Varying Coefficient State Space Model

NASA Astrophysics Data System (ADS)

Jou, Yow-Jen; Lan, Chien-Lun

2009-08-01

The dynamic path flow information is very crucial in the field of transportation operation and management, i.e., dynamic traffic assignment, scheduling plan, and signal timing. Time-dependent path information, which is important in many aspects, is nearly impossible to be obtained. Consequently, researchers have been seeking estimation methods for deriving valuable path flow information from less expensive traffic data, primarily link traffic counts of surveillance systems. This investigation considers a path flow estimation problem involving the time varying coefficient state space model, Gibbs sampler, and Kalman filter. Numerical examples with part of a real network of the Taipei Mass Rapid Transit with real O-D matrices is demonstrated to address the accuracy of proposed model. Results of this study show that this time-varying coefficient state space model is very effective in the estimation of path flow compared to time-invariant model.

Euclidean commute time distance embedding and its application to spectral anomaly detection

NASA Astrophysics Data System (ADS)

Albano, James A.; Messinger, David W.

2012-06-01

Spectral image analysis problems often begin by performing a preprocessing step composed of applying a transformation that generates an alternative representation of the spectral data. In this paper, a transformation based on a Markov-chain model of a random walk on a graph is introduced. More precisely, we quantify the random walk using a quantity known as the average commute time distance and find a nonlinear transformation that embeds the nodes of a graph in a Euclidean space where the separation between them is equal to the square root of this quantity. This has been referred to as the Commute Time Distance (CTD) transformation and it has the important characteristic of increasing when the number of paths between two nodes decreases and/or the lengths of those paths increase. Remarkably, a closed form solution exists for computing the average commute time distance that avoids running an iterative process and is found by simply performing an eigendecomposition on the graph Laplacian matrix. Contained in this paper is a discussion of the particular graph constructed on the spectral data for which the commute time distance is then calculated from, an introduction of some important properties of the graph Laplacian matrix, and a subspace projection that approximately preserves the maximal variance of the square root commute time distance. Finally, RX anomaly detection and Topological Anomaly Detection (TAD) algorithms will be applied to the CTD subspace followed by a discussion of their results.

NASA's Flexible Path for the Human Exploration

NASA Technical Reports Server (NTRS)

Soeder, James F.

2016-01-01

The idea of human exploration of Mars has been a topic in science fiction for close to a century. For the past 50 years it has been a major thrust in NASAs space mission planning. Currently, NASA is pursuing a flexible development path with the final goal to have humans on Mars. To reach Mars, new hardware will have to be developed and many technology hurdles will have to be overcome. This presentation discusses Mars and its Moons; the flexible path currently being followed; the hardware under development to support exploration; and the technical and organizational challenges that must be overcome to realize the age old dream of humans traveling to Mars.

Effective pathway of charge transfer in DNA duplex

NASA Astrophysics Data System (ADS)

Kim, Seongjin; Yi, Juyeon; Hwang, Sun-Yong

2009-03-01

We examine the most efficient route for charge propagation in DNA duplex. We find a direct path along one strand and a detour using the complementary strand compete with each other. Charge tends to take the path along the strand whose energy levels are close to its energy, and yet there exists a crossover length Nc so that for a transfer over a distance shorter than Nc the direct path is always advantageous. We obtain the analytic results for the behavior together with various decay types such as a constant decay, an exponential decay, and a crossover between them, whose validity is confirmed by the numerical calculation.

Particle paths and phase plane for time-dependent similarity solutions of the one-dimensional Vlasov-Maxwell equations

NASA Technical Reports Server (NTRS)

Roberts, Dana Aaron; Abraham-Shrauner, Barbara

1987-01-01

The phase trajectories of particles in a plasma described by the one-dimensional Vlasov-Maxwell equations are determined qualitatively, analyzing exact general similarity solutions for the cases of temporally damped and growing (sinusoidal or localized) electric fields. The results of numerical integration in both untransformed and Lie-group point-transformed coordinates are presented in extensive graphs and characterized in detail. The implications of the present analysis for the stability of BGK equilibria are explored, and the existence of nonlinear solutions arbitrarily close to and significantly different from the BGK solutions is demonstrated.

The minimal scenario of leptogenesis

NASA Astrophysics Data System (ADS)

Blanchet, Steve; Di Bari, Pasquale

2012-12-01

We review the main features and results of thermal leptogenesis within the type I seesaw mechanism, the minimal extension of the Standard Model explaining neutrino masses and mixing. After presenting the simplest approach, the vanilla scenario, we discuss various important developments of recent years, such as the inclusion of lepton and heavy neutrino flavour effects, a description beyond a hierarchical heavy neutrino mass spectrum and an improved kinetic description within the density matrix and the closed-time-path formalisms. We also discuss how leptogenesis can ultimately represent an important phenomenological tool to test the seesaw mechanism and the underlying model of new physics.

Extensive electron transport and energization via multiple, localized dipolarizing flux bundles

NASA Astrophysics Data System (ADS)

Gabrielse, Christine; Angelopoulos, Vassilis; Harris, Camilla; Artemyev, Anton; Kepko, Larry; Runov, Andrei

2017-05-01

Using an analytical model of multiple dipolarizing flux bundles (DFBs) embedded in earthward traveling bursty bulk flows, we demonstrate how equatorially mirroring electrons can travel long distances and gain hundreds of keV from betatron acceleration. The model parameters are constrained by four Time History of Events and Macroscale Interactions during Substorms satellite observations, putting limits on the DFBs' speed, location, and magnetic and electric field magnitudes. We find that the sharp, localized peaks in magnetic field have such strong spatial gradients that energetic electrons ∇B drift in closed paths around the peaks as those peaks travel earthward. This is understood in terms of the third adiabatic invariant, which remains constant when the field changes on timescales longer than the electron's drift timescale: An energetic electron encircles a sharp peak in magnetic field in a closed path subtending an area of approximately constant flux. As the flux bundle magnetic field increases the electron's drift path area shrinks and the electron is prevented from escaping to the ambient plasma sheet, while it continues to gain energy via betatron acceleration. When the flux bundles arrive at and merge with the inner magnetosphere, where the background field is strong, the electrons suddenly gain access to previously closed drift paths around the Earth. DFBs are therefore instrumental in transporting and energizing energetic electrons over long distances along the magnetotail, bringing them to the inner magnetosphere and energizing them by hundreds of keV.